JPWO2011046066A1 - Lithium secondary battery substrate and lithium secondary battery separator - Google Patents

Abstract

A base material for a lithium secondary battery comprising a non-woven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and a lithium secondary battery separator using the base material for lithium secondary batteries The synthetic resin constituting the resin short fibers is at least one selected from polyester resins, acrylic resins, and polyolefin resins, or the content of fibrillated lyocell fibers is 5 to 80% by mass of the nonwoven fabric. Preferably there is.

Description

  The present invention relates to a lithium secondary battery substrate and a lithium secondary battery separator that can be suitably used for lithium secondary batteries such as lithium ion secondary batteries and lithium ion polymer secondary batteries.

  With the recent spread of portable electronic devices and higher performance, secondary batteries having high energy density are desired. As this type of battery, a lithium secondary battery using an organic electrolyte (non-aqueous electrolyte) has attracted attention. This lithium secondary battery has a high energy density because an average voltage of about 3.7 V, which is about three times that of an alkaline secondary battery, which is a conventional secondary battery, can be obtained. Since an aqueous electrolyte solution cannot be used, a non-aqueous electrolyte solution having sufficient oxidation-reduction resistance is used. Since non-aqueous electrolytes are flammable, there is a risk of ignition and the like, and careful attention is paid to safety in their use. There are several possible cases of exposure to fire and other hazards, but overcharging is particularly dangerous.

  In order to prevent overcharging, current non-aqueous secondary batteries are charged at a constant voltage and a constant current, and the battery is equipped with a precise IC (protection circuit). The cost required for this protection circuit is large, and it is a factor that increases the cost of non-aqueous secondary batteries.

  When overcharging is prevented by the protection circuit, it is naturally assumed that the protection circuit does not operate well, and it is difficult to say that it is intrinsically safe. The current non-aqueous secondary battery has a safety circuit / PTC element equipped and a separator with a thermal fuse function for the purpose of destroying the battery safely when overcharged. Has been made. However, even if equipped with the above-mentioned means, depending on the overcharge conditions, the safety during overcharge is not guaranteed, and in fact, non-aqueous secondary battery ignition accidents Is still happening.

  As a separator for a lithium secondary battery, a film-like porous film made of polyolefin such as polyethylene is often used, and when the temperature inside the battery is around 130 ° C., it melts and closes the micropores. There is a thermal fuse function (shutdown function) that prevents the movement of lithium ions and cuts off the current, but if the temperature rises further due to some situation, the polyolefin itself may melt and short-circuit, suggesting the possibility of thermal runaway Has been. Therefore, there is a need for a heat-resistant separator that does not melt and shrink even at temperatures close to 200 ° C.

  For example, an attempt has been proposed in which a nonwoven fabric composed of glass fibers is laminated on a film-like porous film made of polyolefin and bonded with a resin such as polyvinylidene fluoride to form a composite (see, for example, Patent Document 1). . However, in the case of the composite separator of Patent Document 1, since the porous film and the glass nonwoven fabric are laminated after being manufactured separately, the thickness is inevitably increased, and as a result, the field that can be used is limited, There was a problem that battery characteristics such as internal resistance were inferior.

  On the other hand, a heat-resistant separator using a nonwoven fabric instead of a porous film made of polyolefin has been proposed. For example, there are non-woven fabrics composed of polyester fibers, and non-woven fabrics in which aramid fibers, which are heat-resistant fibers, are blended with polyester fibers, but they are impractical because they have larger pore diameters and internal short circuits compared to porous films. (For example, refer to Patent Documents 2 to 4).

  Attempts have also been made to impart shutdown characteristics to separators using nonwoven fabric. For example, a separator in which polyethylene fine powder is attached to a polypropylene nonwoven fabric or the like has been proposed (see, for example, Patent Document 5). However, polypropylene has a melting point of around 165 ° C., and if the shutdown characteristic is not manifested, the nonwoven fabric melts and shrinks, resulting in further thermal runaway. In addition, the fiber diameter and pore diameter of the nonwoven fabric, the particle diameter of the polyethylene fine particles to be attached, etc. are not described in detail, there are problems such as liquid retention and internal resistance, and sufficient battery characteristics can be expressed. It can not be said.

  In addition, by using a nonwoven fabric mainly composed of ultrafine fibers composed of a low melting point resin component and a high melting point resin component as a separator, when the temperature inside the battery rises, the low melting point resin component melts and pores between the fibers are formed. It has been proposed that a shut-down characteristic is expressed by blocking (see, for example, Patent Document 6). In such a separator, in order to express the strength of the nonwoven fabric, it is necessary to melt the low melting point resin component and bond the fibers sufficiently, but the difference between the heating temperature and the shutdown temperature required for strength development is small, It is very difficult to control the pore diameter and the number of pores between fibers while maintaining the strength. In addition, when the shutdown characteristic is not sufficiently developed, the nonwoven fabric itself may melt and shrink and may cause a short circuit.

  In addition, a separator made of a nonwoven fabric obtained by mixing a heat-resistant fiber and a heat-meltable resin material and wet-making is proposed (for example, see Patent Document 7). However, like the separator of Patent Document 6, it is difficult to balance the heating temperature necessary for developing the strength of the nonwoven fabric made of heat-resistant fibers and the melting temperature of the heat-meltable resin material, and the shutdown characteristics are reduced. In order to fully develop, it is necessary to contain a large amount of the heat-meltable resin material, but it cannot be said that the heat-meltable resin material is sufficiently bonded to the heat-resistant fiber, and the heat-meltable resin material is not removed. There was a problem that the uniformity of the fiber sheet was insufficient.

  On the other hand, a non-woven fabric, a woven fabric or the like is not used as a separator as it is, but is used as a base material, and various materials are combined with the base material to provide heat resistance and a shutdown function. . For example, a separator that has been combined with a porous film on a base material, and a separator that has been composited by impregnating and surface coating filler particles, resin, gel electrolyte, solid electrolyte, etc. on the base material have been reported. (For example, refer to Patent Documents 8 to 10). However, in these patent documents, a detailed study is made on composite materials (hereinafter referred to as “composites”) such as filler particles, resins, and porous films, but they are used as substrates. No consideration has been given to the nonwoven fabric. The base material that has been used so far has large pores, so that the surface smoothness when composited by bonding, surface coating, impregnation, etc. is poor, and the composite is easy to peel off or fall off was there. In addition, since the composite material is filled in the base material and the pores inside the base material are closed, the electrolyte solution retainability is deteriorated and the internal resistance of the separator is increased.

JP 2003-323878 A JP 2003-123728 A JP 2007-317675 A (Pamphlet of International Publication No. 2001/67536, US Patent Application Publication No. 2003/0003363) JP 2006-19191 A JP-A-60-52 JP 2004-115980 A JP 2004-214066 A JP 2005-293891 A JP 2005-536857 A (Pamphlet of International Publication No. 2004/021476, US Patent Application Publication No. 2006/0024569) JP 2007-157723 A (International Publication No. 2006/062153, US Patent Application Publication No. 2007/0264577)

  An object of the present invention is to provide a lithium secondary battery substrate that is used to form a composite for a lithium secondary battery by combining with a composite such as a porous film, filler particles, a resin, a gel electrolyte, and a solid electrolyte. , A base material for a lithium secondary battery that has a small variation in the surface when composited and can reduce peeling and dropping of the composite, and a separator for a lithium secondary battery using the base material for the lithium secondary battery Is to provide.

This invention which solves the said subject consists of the following base materials (1)-(22) for lithium secondary batteries, and the separator (23) for lithium secondary batteries.
(1) A base material for a lithium secondary battery comprising a nonwoven fabric containing, as essential components, synthetic resin short fibers and fibrillated lyocell fibers,
(2) The base material for a lithium secondary battery according to the above (1), wherein the content of the fibrillated lyocell fiber is 5 to 80% by mass of the nonwoven fabric.
(3) The above-mentioned (1) or (2) wherein the modified freeness defined below of the fibrillated lyocell fiber is 0 to 250 ml and the length weighted average fiber length is 0.20 to 2.00 mm. 2) A base material for a lithium secondary battery as described above,
Modified freeness: Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.
(4) In the fiber length distribution histogram of the fibrillated lyocell fiber, the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 10% or more. A base material for a lithium secondary battery according to the above (1) or (2),
(5) In the fiber length distribution histogram of the fibrillated lyocell fiber, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5. The base material for a lithium secondary battery according to the above (4),
(6) In the fiber length distribution histogram of the fibrillated lyocell fiber, the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 50% or more. A base material for a lithium secondary battery according to the above (1) or (2),
(7) In the fiber length distribution histogram of the fibrillated lyocell fiber, the base material for a lithium secondary battery according to the above (6) having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak,
(8) The base material for a lithium secondary battery according to the above (1) or (2), wherein the synthetic resin constituting the synthetic resin short fiber is at least one selected from polyester resins, acrylic resins, and polyolefin resins. ,
(9) The above-mentioned (1) or (2), which comprises a nonwoven fabric containing core-sheath-type heat-fusible short fibers composed of a heat-fusion component and a non-heat-fusion component as at least one kind of synthetic resin short fibers Base material for lithium secondary battery,
(10) The base for a lithium secondary battery according to (9), wherein the core of the core-sheath type heat-fusible short fiber is polyethylene terephthalate and the sheath is a polyester copolymer,
(11) The base material for a lithium secondary battery according to (9) or (10), which is heat-treated,
(12) The base material for a lithium secondary battery according to (1) or (2), further comprising a nonwoven fabric containing a paper strength enhancer as an essential component,
(13) The base material for a lithium secondary battery according to (12), wherein the paper strength enhancer is at least one selected from a synthetic polymer, a semi-synthetic polymer, a vegetable gum, and starch,
(14) The base material for a lithium ion battery according to the above (12), wherein the paper strength enhancer is at least one selected from amphoteric or cationic polyacrylamide resins.
(15) The base for a lithium secondary battery according to any one of the above (12) to (14), wherein the paper strength enhancer is contained in an amount of 0.01 to 20 parts by mass with respect to 100 parts of the fibrillated lyocell fiber. Material,
(16) The base material for a lithium secondary battery according to (1) or (2) above, wherein the nonwoven fabric further comprises fibrillated heat-resistant fibers,
(17) The base material for a lithium secondary battery according to (16), wherein the fibrillated heat-resistant fiber is at least one selected from a fibrillated wholly aromatic polyamide fiber and a fibrillated acrylic fiber,
(18) The base material for a lithium secondary battery according to the above (1) or (2), wherein the base material has a minimum pore diameter of 0.10 μm or more and a maximum pore diameter of 20 μm or less,
(19) The base material for a lithium secondary battery according to (18), wherein the ratio dmax / dave between the maximum pore diameter dmax and the average pore diameter dave is 10.0 or less in the base material,
(20) The base material for a lithium secondary battery according to the above (1) or (2), wherein the center line average roughness Ra in the flow direction and the width direction of the base material is 3.0 or less,
(21) The above (1) or (2), wherein the base material for the lithium secondary battery is composed of a multilayer nonwoven fabric, and at least one layer is a layer containing the synthetic resin short fibers and the fibrillated lyocell fibers as essential components. Base material for lithium secondary battery,
(22) A heat-resistant layer (A) containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and a heat-melting layer (B) containing synthetic resin short fibers and polyethylene synthetic pulp as essential components The lithium secondary battery substrate according to (22),
(23) A treatment for impregnating or applying a slurry containing filler particles to a base material for a lithium secondary battery according to any one of (1) to (22) above, or impregnating or applying a slurry containing a resin. The separator for lithium secondary batteries which performs at least 1 process chosen from the process to carry out, the process which laminates and integrates a porous film, the process which impregnates or coats a solid electrolyte or a gel electrolyte.

  The base material for lithium secondary batteries of this invention consists of the nonwoven fabric which contains the synthetic resin short fiber and the fibrillated lyocell fiber as an essential component. The fibrillated lyocell fiber is entangled with the synthetic resin short fiber, so that the surface is highly smooth and excellent in denseness. The lithium secondary battery separator of the present invention obtained by bonding to the lithium secondary battery base material of the present invention, combining with impregnation, surface coating, etc. has reduced surface variation. , The composite is less likely to be peeled off or dropped off. Further, the fibrillated lyocell fiber present on the surface of the base material for the lithium secondary battery is firmly bound to the composite, whereby the composite can be further prevented from being peeled off or dropped off.

FIG. 1 is a graph showing the relationship between Canadian standard freeness of fibrillated lyocell fibers and modified freeness (freeness measured in accordance with JIS P8121 except that the sample concentration is 0.03%). It is.
Fig. 2 shows the modified drainage of fibrillated lyocell fiber (according to JIS P8121 except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as the sieve plate, and the sample concentration is 0.1%) It is an example of the graph showing the modified drainage degree measured in this way.
FIG. 3 shows a modified drainage degree of fibrillated lyocell fibers used in the examples of the present invention (80 mesh wire mesh having a wire diameter of 0.14 mm and openings of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. It is the graph showing the modified drainage degree measured based on JIS P8121 except having made it.
FIG. 4 is a fiber length distribution histogram of fibrillated lyocell fiber [I].
FIG. 5 is a fiber length distribution histogram of fibrillated lyocell fiber [II].
FIG. 6 is a graph of the ratio of fibers having a fiber length every 0.05 mm between 1.0 and 2.0 mm and an approximate straight line in a fiber length distribution histogram of fibrillated lyocell fibers [I] and [II]. FIG.
FIG. 7 is an example of a fiber length distribution histogram of fibrillated lyocell fiber [i] having a maximum frequency peak between 0.00 and 1.00 mm.
FIG. 8 is an example of a fiber length distribution histogram of fibrillated lyocell fiber [ii] having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak.

  Hereinafter, the base material for a lithium secondary battery of the present invention will be described in detail. The base material for a lithium secondary battery of the present invention (hereinafter sometimes referred to as “base material”) is a base material for impregnating or coating a slurry containing filler particles, and a slurry containing a resin. A substrate for impregnating or coating, a substrate for laminating and integrating porous films, a substrate for impregnating or coating a solid electrolyte or a gel electrolyte, and a precursor of a separator for a lithium secondary battery It is a body sheet. The filler may be either inorganic or organic. Inorganic fillers include alumina, gibbsite, boehmite, magnesium oxide, magnesium hydroxide, silica, titanium oxide, barium titanate, zirconium oxide and other inorganic oxides, aluminum nitride and silicon nitride inorganic nitrides, aluminum compounds, zeolites And mica. Examples of the organic filler include polyethylene, polypropylene, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide, polystyrene, polyvinylidene fluoride, ethylene-vinyl monomer copolymer, polyolefin wax, and the like. The porous film is not particularly limited as long as it is a resin capable of forming a film, but is preferably a polyolefin resin such as a polyethylene resin and a polypropylene resin. Polyethylene resins include not only ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, or ultra high density polyethylene alone, but also ethylene propylene copolymers. Or a mixture of a polyethylene-based resin and another polyolefin-based resin. Polypropylene resins include homopropylene (propylene homopolymer), or α-, such as propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1-decene. Examples thereof include random copolymers with olefins and block copolymers.

The lithium secondary battery in the present invention means a lithium ion battery, a lithium ion polymer battery, or the like. Examples of the negative electrode active material of the lithium secondary battery include carbon materials such as graphite and coke, metallic lithium, aluminum, silica, tin, nickel, and an alloy of lithium and lithium, SiO, SnO, Fe Metal oxides such as ₂ O ₃ , WO ₂ , Nb ₂ O ₅ , Li _4/3 Ti _5/3 O ₄ , and nitrides such as Li _0.4 CoN are used. As the positive electrode active material, lithium cobaltate, lithium manganate, lithium nickelate, lithium titanate, lithium nickel manganese oxide, or lithium iron phosphate is used. Further, the lithium iron phosphate may be a composite with one or more metals selected from manganese, chromium, cobalt, copper, nickel, vanadium, molybdenum, titanium, zinc, aluminum, gallium, magnesium, boron, and niobium.

  As an electrolytic solution for a lithium secondary battery, a solution obtained by dissolving a lithium salt in an organic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, dimethoxymethane, or a mixed solvent thereof is used. Examples of the lithium salt include lithium hexafluorophosphate and lithium tetrafluoroborate. As solid electrolyte, what melt | dissolved lithium salt in gel-like polymers, such as polyethyleneglycol, its derivative (s), polymethacrylic acid derivative, polysiloxane, its derivative (s), polyvinylidene fluoride, is used.

  The base material for lithium secondary batteries of this invention consists of the nonwoven fabric which contains the synthetic resin short fiber and the fibrillated lyocell fiber as an essential component.

  “Lyocell” of fibrillated lyocell fiber is a term defined in ISO standards and Japanese JIS standards, and refers to “cellulose fibers obtained by spinning directly in an organic solvent without spinning through cellulose derivatives”. is there.

  Lyocell fibers are beater and dispersion equipment such as beaters, PFI mills, single disc refiners (SDR), double disc refiners (DDR), ball mills and dyno mills used to disperse and pulverize pigments, etc. Can be fibrillated. By adjusting the types of beating / dispersing equipment and processing conditions (fiber concentration, temperature, pressure, number of revolutions, refiner blade shape, gap between refiner plates, number of treatments), the desired optimally fibrillated lyocell Fibers (fiber length, fiber length distribution, modified freeness) can be achieved.

  Like the base material for a lithium secondary battery (3) of the present invention, the modified freeness of the fibrillated lyocell fiber is 0 to 250 ml, and the length weighted average fiber length is 0.20 to 2.00 mm. It is preferable that the pores of the substrate are formed relatively uniformly. As a result, the back-through of the coating liquid containing the composite such as filler particles and resin is suppressed, and the composite is concentrated on the surface of the base material, so that the surface smoothness after coating is excellent, Unnecessary gaps are unlikely to occur between the two. In addition, since the back-through of the coating liquid is suppressed, there is no problem that pores inside the base material are blocked by the composite material filled inside the base material, and a separator with a high electrolyte retention rate is obtained. Can do.

  The modified freeness in the present invention means that either the sample concentration or the sieve plate, or both the sample concentration and the sieve plate are changed with respect to the Canadian standard freeness measurement method defined in JIS P8121. Means the freeness measured. So far, the relationship between Canadian standard freeness and modified freeness of natural cellulose fibers such as conifer wood pulp, hardwood wood pulp, hemp pulp and esparto pulp has been reported, but fibrillated lyocell fiber. The relationship between Canadian standard freeness and modified freeness was not clear. In the present invention, the refiner was used to refine the lyocell fiber, and as a result of measuring the Canadian standard freeness and modified freeness for each degree of refinement, the drainage behavior of the lyocell fiber was It has been found that it is different from the drainage behavior of natural cellulose fiber disclosed in Japanese Patent No. 2000-331663.

  FIG. 1 shows the relationship between Canadian standard freeness and modified freeness of fibrillated lyocell fibers. In FIG. 1, the standard freeness means the Canadian standard freeness of JIS P8121. The modified freeness means the freeness measured in accordance with JIS P8121, except that the sample concentration is 0.03%. The horizontal axis in FIG. 1 indicates the length-weighted average fiber length, and the degree of miniaturization progresses toward the right. The Canadian standard freeness is 0.5 ml with a length-weighted average fiber length of 0.72 mm, but the shorter the length-weighted average fiber length is 0.55 mm or less, the greater the freeness. Yes. On the other hand, the modified freeness increases as the degree of refinement progresses. This drainage behavior is the drainage behavior of natural cellulose fibers disclosed in JP 2000-331663 A, that is, the Canadian standard freeness and modified freeness decrease as the degree of refinement progresses. The drainage behavior is quite different.

  The reason why the degree of freezing increases as the degree of refinement progresses is that the length-weighted average fiber length of the fibrillated lyocell fiber becomes shorter as the refinement progresses, especially when the sample concentration is thin, This is because the entanglement between the fibers decreases and the fiber network is hardly formed, so that the fibrillated lyocell fibers themselves pass through the holes in the sieve plate. That is, in the case of lyocell fibers refined, an accurate freeness cannot be measured by the measuring method of JIS P8121. In more detail, as the degree of refinement of natural cellulose fibers increases, a number of thin fibrils are torn from the fiber trunk, so that the fibers tend to entangle with each other through the fibrils, forming a fiber network. On the other hand, lyocell fiber is easily finely divided parallel to the long axis of the fiber by the refinement process, and since the uniformity of the fiber diameter in each fiber after division is high, the shorter the average fiber length, It is considered that the fibers do not easily entangle with each other and it is difficult to form a fiber network.

  Therefore, in the present invention, studies have been conducted to measure the exact freeness of fibrillated lyocell fibers. FIG. 2 shows an example of modified freeness measured by changing both the sample concentration and the sieve plate. That is, the modified freeness measured by using an 80-mesh wire net instead of the sieve plate specified in JIS P8121, and setting the sample concentration to 0.1%. The wire diameter of 80 mesh was 0.14 mm in diameter, and a wire mesh (manufactured by PULP AND PAPER RESEARCH INSTITUTE OF CANADA) having an opening of 0.18 mm was used. As can be seen from FIG. 2, as the degree of refinement progresses, the freeness becomes smaller, and the fibrillated lyocell fiber is prevented from coming off, and the freeness can be measured more accurately. Hereinafter, the modified freeness in the present invention is based on JIS P8121, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as a sieve plate, and the sample concentration is 0.1%. It means the measured modified freeness, and is simply expressed as “modified dryness” unless otherwise specified.

  The fiber length and fiber length distribution histogram of the fibrillated lyocell fiber can be obtained by utilizing the deflection characteristics obtained by applying laser light to the fiber, and can be measured using a commercially available fiber length measuring instrument. In the present invention, JAPAN TAPPI paper pulp test method no. It was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation) according to 52 “Fiber length test method for paper and pulp (automatic optical measurement method)”. The “fiber length”, “average fiber length” and “fiber length distribution” of the fibrillated lyocell fiber are “length-weighted fiber length”, “length-weighted average fiber length” and “ It means “length-weighted fiber length distribution”.

  In the present invention, in order to obtain a fibrillated lyocell fiber having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm, lyocell short fibers are added at an appropriate concentration. Between the refiner, beater, mill, milling device, rotary blade homogenizer that applies shearing force with a high-speed rotary blade, cylindrical inner blade that rotates at high speed, and fixed outer blade Double-cylindrical high-speed homogenizer that generates shearing force, ultrasonic crusher that is refined by impact by ultrasonic waves, high-pressure homogenizer, etc., and conditions such as blade shape, flow rate, processing frequency, processing speed, processing concentration, etc. It may be adjusted and refined. By these refinement treatments, the lyocell fiber is divided parallel to the fiber long axis and the fiber length is shortened. Therefore, the pores of the base material are formed relatively uniformly, preventing the back-through of the coating liquid during coating, and improving the surface smoothness of the coating layer. Further, since the back-through of the coating liquid is suppressed, the filler particles do not block the pores inside the substrate, and a separator having excellent electrolyte solution retention can be obtained.

  In addition, the length-weighted average fiber length can be adjusted in any way within the range of 0 to 250 ml of modified freeness by changing the conditions for refinement. Even so, fibrillated lyocell fibers having different length-weighted average fiber lengths can be produced. FIG. 3 represents the modified freeness of fibrillated lyocell fibers used in Examples 14-36 of the present invention.

  In the present invention, the modified drainage degree of the fibrillated lyocell fiber is more preferably 0 to 200 ml, and further preferably 0 to 160 ml. When the modified freeness exceeds 250 ml, the refinement process is insufficient, the fiber division does not proceed sufficiently, and the ratio of the fiber diameter remaining large increases, so that a large through hole is formed in the base material. , The coating liquid will be broken through during coating. The length weighted average fiber length of the fibrillated lyocell fiber used in the present invention is more preferably 0.30 to 1.80 mm, and further preferably 0.40 to 1.60 mm. When the length-weighted average fiber length is less than 0.20 mm, fibrillated lyocell fibers may fall off from the base material during wet papermaking or after wet papermaking or may be broken during coating due to fluffing. If it is longer than 2.00 mm, the fibers are easily entangled, resulting in unevenness in the formation and unevenness in thickness.

  In the fiber length distribution histogram of the fibrillated lyocell fiber as in the lithium secondary battery substrate (4) of the present invention, it has a maximum frequency peak between 0.00 and 1.00 mm, and is 1.00 mm or more. It is preferable that the ratio of the fibers having a fiber length of 10% or more. Such fibrillated lyocell fibers are well entangled with the synthetic resin short fibers, the surface smoothness of the base material is increased, the denseness is excellent, and the surface variation when combined by surface coating is reduced. , It becomes difficult for the composite to fall off. Moreover, the fibrillated lyocell fiber present on the surface of the base material is firmly bound to the composite, whereby the composite can be further prevented from falling off.

  In the fiber length distribution histogram of the fibrillated lyocell fiber of the base material (4) for a lithium secondary battery of the present invention, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm The base material (5) for a lithium secondary battery having a value of −3.0 or more and −0.5 or less is more preferable because the denseness required for the substrate and the coating property of the substrate are more excellent.

  4 and 5 are fiber length distribution histograms of fibrillated lyocell fibers, which have a maximum frequency peak between 0.00 and 1.00 mm, and the ratio of fibers having a fiber length of 1.00 mm or more. 10% or more. More preferably, the fiber length distribution histogram has a maximum frequency peak between 0.30 and 0.70 mm in terms of the smoothness of the surface when complexed by surface coating such as filler particles or resin. The ratio of the fibers having a fiber length of 1.00 mm or more is 12% or more. In addition, in terms of preventing breakage of the base material when composited, the proportion of fibers having a fiber length of 1.00 mm or more is preferably higher, but about 50% is sufficient.

  In the fiber length distribution histogram of fibrillated lyocell fibers, the slope of the ratio of fibers having a fiber length of 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5 or less. -2.5 or more and -0.8 or less are more preferable, and -2.0 or more and -1.0 or less are still more preferable. It is preferable to use fibrillated lyocell fibers having an inclination in this range because the coating property of the substrate is improved. When the inclination is smaller than −3.0, the base material may be damaged during the composite process, or the composite product may fall off. On the other hand, if the inclination exceeds −0.5, the denseness and the coating property of the substrate may not be improved. As shown in FIGS. 4 and 5, “large inclination” means a state in which the fiber length distribution of the fibrillated lyocell fiber is wide. “Slight inclination” is a state in which the fiber length distribution of fibrillated lyocell fibers is narrow and the fiber lengths are more uniform. The slope of the fibrillated lyocell fiber [I] in FIG. 4 is −2.9, and the slope of the fibrillated lyocell fiber [II] in FIG. 5 is −0.6.

  In addition, "the inclination of the ratio of the fiber having a fiber length of every 0.05 mm between 1.00 and 2.00 mm" is 0. 0 between 1.00 and 2.00 mm as shown in FIG. For the value of the proportion of fibers having a fiber length of every 05 mm, an approximate straight line is calculated by the method of least squares, and the inclination of the obtained approximate straight line is meant.

  In the fiber length distribution histogram of the fibrillated lyocell fiber as in the lithium secondary battery substrate (6) of the present invention, it has a maximum frequency peak between 0.00 and 1.00 mm, and is 1.00 mm or more. It is preferable that the ratio of the fibers having a fiber length of 50% or more. Such fibrillated lyocell fibers are well entangled with the synthetic resin short fibers, the surface smoothness of the base material is increased, the denseness is excellent, and the surface variation when combined by surface coating is reduced. , It becomes difficult for the composite to fall off. Moreover, the fibrillated lyocell fiber present on the surface of the base material is firmly bound to the composite, whereby the composite can be further prevented from falling off.

  In the fiber length distribution histogram of the fibrillated lyocell fiber of the base material for lithium secondary battery (6) of the present invention, a base for lithium secondary battery having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak The material (7) is more preferable because it is more excellent in the denseness required for the base material and the coatability of the base material.

  FIG. 7 is a fiber length distribution histogram of fibrillated lyocell fibers, having a maximum frequency peak between 0.00 and 1.00 mm, and a ratio of fibers having a fiber length of 1.00 mm or more is 50% or more. It is. The fiber length distribution histogram has a maximum frequency peak between 0.30 and 0.70 mm in terms of the smoothness of the surface when composited by surface coating such as filler particles and resin, and is 1.00 mm. More preferably, the proportion of fibers having the above fiber length is 55% or more. A higher proportion of fibers having a fiber length of 1.00 mm or more is desirable, but about 75% is sufficient.

  In the fiber length distribution histogram of the fibrillated lyocell fiber, as shown in FIG. 8, it is more preferable to have a peak between 1.50 and 3.50 mm in addition to the above maximum frequency peak. It is more preferable to have a peak between 3.25 mm, and it is particularly preferable to have a peak between 2.00 to 3.00 mm. By having a peak in this range, it is preferable because both the coatability of the substrate and the prevention of the composite from falling off can be achieved. When the fiber length of the peak is shorter than 1.50 mm, the base material may be damaged during composite formation, or the composite product may fall off. On the other hand, if it exceeds 3.50 mm, the denseness and the coating property of the substrate are not improved, and the composite product may fall off.

  The resins constituting the synthetic resin short fibers include polyolefin resins, polyester resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymer resins, polyamide resins, acrylic resins, polyvinyl chloride resins, and polychlorinated resins. Vinylidene resins, polyvinyl ether resins, polyvinyl ketone resins, polyether resins, polyvinyl alcohol resins, diene resins, polyurethane resins, phenol resins, melamine resins, furan resins, urea resins, aniline resins Examples include resins, unsaturated polyester resins, alkyd resins, fluorine resins, silicone resins, polyamideimide resins, polyphenylene sulfide resins, polyimide resins, and derivatives of these resins. Among these, when a polyester resin, an acrylic resin, or a polyolefin resin is used, a lithium secondary battery substrate having higher surface smoothness and excellent denseness can be obtained. The reason for this is not clear, but it is presumed that the polyester resin, the acrylic resin, the polyolefin resin, and the fibrillated lyocell fiber are intertwined more uniformly than other synthetic resins. Further, with these resins, it is possible to obtain a base material for a lithium secondary battery that is more effective in suppressing damage to the base material and suppressing wrinkles and is excellent in denseness. If a polyester resin, acrylic resin, or polyamide resin is used, the heat resistance of the substrate can be improved.

  Examples of the polyester resin include polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, polyethylene isophthalate resin, and derivatives thereof. Can be mentioned. Among these, when used for a base material for a lithium secondary battery, a polyethylene terephthalate resin having excellent heat resistance and electrolytic solution resistance is preferable.

  Acrylic resin is made of 100% acrylonitrile polymer, and acrylonitrile is copolymerized with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl acetate, etc. And the like.

  Examples of the polyolefin resin include polypropylene, polyethylene, polymethylpentene, ethylene-vinyl alcohol copolymer, olefin copolymer and the like. From the viewpoint of heat resistance, polypropylene, polymethylpentene, ethylene-vinyl alcohol copolymer, olefin copolymer and the like can be mentioned.

  Polyamide resins include aliphatic polyamides such as nylon, poly-p-phenylene terephthalamide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide, and poly-m-phenylene isophthalamide. An aromatic polyamide having, for example, a fatty chain as a part of the main chain can be mentioned.

  The synthetic resin short fiber may be a fiber (single fiber) made of a single resin, or may be a fiber (composite fiber) made of two or more kinds of resins. Moreover, the synthetic resin short fiber contained in the base material for lithium secondary batteries of the present invention may be one kind or a combination of two or more kinds. Examples of the composite fiber include a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, an orange type, and a multiple bimetal type.

  The fineness of the synthetic resin short fiber is preferably 0.004 to 1.3 dtex, more preferably 0.007 to 0.8 dtex, further preferably 0.02 to 0.6 dtex, and particularly preferably 0.04 to 0.3 dtex. . When the fineness of the synthetic resin short fibers exceeds 1.3 dtex, the number of fibers in the thickness direction decreases, so that the required denseness cannot be ensured, the coating liquid is exposed, or the thickness is reduced. It may be difficult. Moreover, the unevenness | corrugation becomes large, the surface at the time of complex | conjugation by surface coating can produce a big variation, and surface smoothness may be impaired. When the fineness of the synthetic resin short fiber is less than 0.004 dtex, stable production of the fiber becomes difficult.

  The fiber length of the synthetic resin short fiber is preferably 0.4 to 10 mm, more preferably 1 to 7 mm, further preferably 1 to 6 mm, and particularly preferably 1 to 5 mm. If the fiber length exceeds 10 mm, formation may be poor. On the other hand, when the fiber length is less than 0.4 mm, the mechanical strength of the base material becomes low, and the base material may be damaged during the composite.

  As the synthetic resin short fiber, a heat-fusible short fiber that functions as a binder may be used. Examples of the heat-fusible short fiber include a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, an orange type, a multi-bimetal type composite fiber, or a single fiber. In particular, it is preferable to contain unstretched polyester-based short fibers and core-sheath type heat-fusible short fibers in which a non-thermal adhesive component is disposed in the core and a thermal adhesive component is disposed in the sheath. Unstretched polyester short fibers are suitable in terms of improving uniformity, and the core-sheath type heat-fusible short fibers are softened, melted or melted by wet heat while maintaining the fiber shape of the core. Since the fibers are thermally bonded to each other, it is suitable for bonding the fibers without impairing the dense structure of the base material. Moreover, you may use the wet heat adhesive fiber which functions as a binder. The wet heat adhesive fiber refers to a fiber that exhibits an adhesive function by flowing or easily deforming from a fiber state at a certain temperature in a wet state. Specifically, it is a thermoplastic fiber that is softened with hot water (for example, about 80 to 120 ° C.) and can be self-adhered or bonded to other fibers. For example, polyvinyl fibers (polyvinyl pyrrolidone, polyvinyl ether, vinyl alcohol). Polymer, polyvinyl acetal, etc.), cellulose fibers (C1-3 alkyl cellulose such as methyl cellulose, hydroxy C1-3 alkyl cellulose such as hydroxymethyl cellulose, carboxy C1-3 alkyl cellulose such as carboxymethyl cellulose or salts thereof), modified Fibers made of vinyl copolymers (copolymers or salts of vinyl monomers such as isobutylene, styrene, ethylene, vinyl ether and unsaturated carboxylic acids such as maleic anhydride or anhydrides thereof) Can be mentioned. When wet heat adhesive fibers are used, it is necessary to control the blending amount and the degree of melting and not to form a film, but to melt only at the intersection between other fibers to act as a binder.

  Like the base material for lithium secondary batteries (9) of the present invention, the core-sheath type short heat-sealable material comprising the heat-seal component and the non-heat-seal component as the base material is at least one kind of synthetic resin short fiber. In the case of a non-woven fabric containing fibers, the core-sheath-type heat-fusible short fibers maintain the fiber shape of the core part, and only the sheath part is softened, melted or wet-heat-dissolved to thermally bond the fibers together, The fibers can be bonded without impairing the dense structure of the base material. By heating or wet heat heating, the sheath portion of the core-sheath type heat-fusible short fiber is softened, melted or melted by wet heat, and the fibers are thermally bonded to each other. Since falling off and fluffing can be prevented, the variation in the surface when combined by surface coating can be reduced.

  There are no particular restrictions on the resin component constituting the core and sheath of the core-sheath type heat-fusible short fiber, and any resin having fiber-forming ability may be used. For example, the core / sheath combination includes polyethylene terephthalate / polyester copolymer, polyethylene terephthalate / polyethylene, polyethylene terephthalate / polypropylene, polyethylene terephthalate / ethylene-propylene copolymer, polyethylene terephthalate / ethylene-vinyl alcohol copolymer. , Polypropylene / polyethylene, high melting point polylactic acid / low melting point polylactic acid, and the like. The melting point, softening point or wet heat melting temperature of the resin component in the core part is preferably 20 ° C. or more higher than the melting point or softening point of the resin component in the sheath part from the viewpoint of easy production of the nonwoven fabric.

  By using polyethylene terephthalate having excellent heat resistance as the core-sheath-type heat-fusible short fiber as in the base material for lithium secondary battery (10) of the present invention, the thermal dimensional stability of the base material is improved. It is preferable because the property can be improved. In addition, it is preferable to use a polyester copolymer for the sheath because the mechanical strength of the base material is improved. The polyester copolymer used for the sheath is a copolymer of polyethylene terephthalate and one or more compounds selected from isophthalic acid, sebacic acid, adipic acid, diethyl glycol, 1,4-butadiol and the like. preferable.

  In the base material for a lithium secondary battery according to the present invention, the content of the heat-fusible short fibers is preferably 5 to 40% by mass, more preferably 8 to 35% by mass with respect to the nonwoven fabric. More preferably, it is 10-30 mass%. If the content is less than 5% by mass, the mechanical strength of the substrate may be reduced, and if it exceeds 40% by mass, the thermal dimensional stability may be reduced.

  In the base material (11) for lithium secondary battery that has been heat-treated, a lithium secondary battery base material having higher mechanical strength can be obtained.

  In the base material for a lithium secondary battery of the present invention, the total content of the fibrillated lyocell fiber and the synthetic resin short fiber is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and 80 to 100% by mass. % Is more preferable. If the total content is less than 50% by mass, the coating liquid may be broken through.

  The base material for a lithium secondary battery of the present invention may contain fibers other than synthetic resin short fibers and fibrillated lyocell fibers. Examples include natural cellulose fibers, pulped and fibrillated natural cellulose fibers, short fibers of regenerated fibers or semi-synthetic fibers, fibrils made of synthetic resins, pulped products, fibrillated products, inorganic fibers, and the like. The modified freeness of the natural cellulose fiber pulped product or fibrillated product is preferably 0 to 400 ml. Examples of the inorganic fiber include glass, alumina, silica, ceramics, and rock wool. When inorganic fiber is contained, the heat-resistant dimensional stability and puncture strength of the substrate may be improved, which is preferable.

  In the base material for a lithium secondary battery of the present invention, the mass ratio of the synthetic resin short fiber and the fibrillated lyocell fiber is preferably 95/5 to 20/80, more preferably 90/10 to 30/70, 70 / 30-40 / 60 is more preferable. The base material for the lithium secondary battery in which the content of the fibrillated lyocell fiber is 5 to 80% by mass of the total content of the synthetic resin short fiber and the fibrillated lyocell fiber is required to be dense and uniform as a base material. The property is better. When the content ratio of the fibrillated lyocell fiber is less than 5% by mass, the denseness and uniformity may not be improved, or the coating liquid may be broken through. Moreover, when the content ratio of the fibrillated lyocell fiber exceeds 80% by mass, the substrate may be damaged when the substrate is handled or combined.

  When the nonwoven fabric further contains a paper strength enhancer as an essential component, as in the lithium secondary battery substrate (12) of the present invention, the fibrillated lyocell fiber and the synthetic resin short fiber are the paper strength enhancer. By being entangled in the presence, surface smoothness is high, density is excellent, and variation in the surface when combined by surface coating is reduced. Moreover, not only does the composite fall off easily, but also prevents the fibers from falling off and fluffing when composited, can provide a uniform surface, can improve the coating suitability, Dirt etc. can also be controlled.

  In the base material (13) for a lithium secondary battery in which the paper strength enhancer is at least one selected from a synthetic polymer, a semi-synthetic polymer, a vegetable gum, and starch, the coating suitability is more excellent. Examples of the synthetic polymer include polyacrylamide resin, polyethyleneimine resin, urea resin, polyethylene oxide (PEO), polyvinyl alcohol (PVA), and the like. Examples of the semi-synthetic polymer include dialdehyde starch, cationic starch, methyl cellulose, carboxymethyl cellulose, and hydroxymethyl cellulose. Examples of vegetable gums include guar gum, locust bean gum, chili pepper gum and the like. Examples of the starch include corn starch, potato starch, wheat starch, tapioca starch and the like.

  Furthermore, in the base material for a lithium secondary battery (14) in which the paper strength enhancer is at least one selected from amphoteric or cationic polyacrylamide resins, the cationic portion of the paper strength enhancer and the fibrillated lyocell fiber The anion part adsorbs and strengthens the bond between fibers. In addition, the amphoteric or cationic polyacrylamide is present between the fibers constituting the nonwoven fabric in a state where the polyacrylamide portion is self-adhered, so that a network having a moderate space is formed without the fibers being aggregated too much. . For this reason, it is possible to further prevent the surface from becoming uneven when it is combined, and to prevent the fine fibers such as the fibrillated lyocell fibers from falling off and the fluffing of the fibers constituting the nonwoven fabric.

  As the amphoteric or cationic polyacrylamide resin, both linear and branched resins can be used. In particular, in the amphoteric polyacrylamide resin having both anionic and cationic functional groups, the cation portion is adsorbed on the fibrillated lyocell fiber, and the anion portion is self-bonded with each other and bonded more firmly. Moreover, since it has both an anion part and a cation part, it is hard to receive the influence of the pH change in a system, and since the coupling | bonding between fibers can be reinforced stably, an amphoteric polyacrylamide type resin is more preferable.

  Further, the polyacrylamide resin preferably has a mass average molecular weight of 10,000 to 6,000,000. When the mass average molecular weight is less than 10,000, the required strength cannot be obtained. When the mass average molecular weight is more than 6 million, the viscosity becomes high, and it may be difficult to produce and apply a nonwoven fabric by a wet method. The mass average molecular weight here refers to the molecular weight measured by gel permeation chromatography.

  The polyacrylamide resin according to the present invention can be produced, for example, as follows. The polyacrylamide resin is obtained, for example, by copolymerizing (a) (meth) acrylamide and (b) a cationic vinyl monomer and / or (c) an anionic vinyl monomer. That is, the cationic polyacrylamide resin can be obtained by copolymerizing (a) (meth) acrylamide and (b) a cationic vinyl monomer. The amphoteric polyacrylamide resin is obtained by copolymerizing (a) (meth) acrylamide, (b) a cationic vinyl monomer, and (c) an anionic vinyl monomer.

  (A) (Meth) acrylamide means acrylamide or methacrylamide. These can be used alone or in combination. Component (a) is preferably used in an amount of 50 to 98.9 mol%, more preferably 50 to 96.5 mol%, based on the total molar sum of the monomers constituting the cationic or amphoteric polyacrylamide resin. When the component (a) is less than 50 mol%, it may be difficult to obtain sufficient coating suitability.

  (B) Examples of cationic vinyl monomers include vinyls having a tertiary amino group such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide and the like. By reaction of monomers or salts of inorganic or organic acids such as hydrochloric acid, sulfuric acid, acetic acid, or the like, or quaternizing agents such as methyl chloride, benzyl chloride, dimethyl sulfate, epichlorohydrin, etc. The vinyl monomer containing the quaternary ammonium salt obtained is mentioned.

  In the amphoteric polyacrylamide resin, it is preferable that the amount of the (b) cationic vinyl monomer used is such that the equivalent ratio of the cationic group / anionic group is 2 or less.

  The means for imparting a cationic group to an amphoteric polyacrylamide resin includes (b) Mannich modification in which formalin and a secondary amine are reacted with anionic acrylamide in addition to the method of copolymerizing a cationic vinyl monomer. A cationic group can also be introduced by a Hofmann reaction in which a hypohalite is reacted. Even when a cationic group is introduced by such modification, the equivalent ratio of the cationic group / anionic group in the amphoteric polyacrylamide resin is preferably 2 or less.

  (C) Examples of the anionic vinyl monomer include α, β-unsaturated monobasic acids such as (meth) acrylic acid, crotonic acid, and (meth) allylcarboxylic acid; maleic acid, fumaric acid, itaconic acid, muconic acid, etc. Α, β-unsaturated dibasic acids of the above; organic sulfonic acids such as vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, (meth) allyl sulfonic acid; or sodium salts of these various organic acids , Alkali metal salts such as potassium salts, ammonium salts and the like. These anionic vinyl monomers can be used alone or in combination of two or more. In particular, the use of a monomer having a (meth) allyl group, particularly (meth) allylsulfonic acid or a salt thereof, as one kind of anionic vinyl monomer is preferable in terms of increasing the molecular weight of the polyacrylamide resin. In addition, it is preferable to use at least one selected from α, β-unsaturated monobasic acid, α, β-unsaturated dibasic acid and salts thereof, and itaconic acid is particularly preferable. Of these, it is preferable to combine (meth) acrylic acid and / or itaconic acid with (meth) allylsulfonic acid or a salt thereof.

  The amount of the (b) cationic vinyl monomer and (c) anionic vinyl monomer used is usually preferably 1 to 40 mol%, preferably 3 to 40 mol, based on the total molar sum of the monomers constituting the amphoteric polyacrylamide resin. % Is more preferable, and 3 to 30 mol% is more preferable.

In addition to the components (a), (b), and (c), the amphoteric or cationic polyacrylamide resin is represented by the general formula (1): CH ₂ = C (R1) -CONR2 (R3) (R1 is A hydrogen atom or a methyl group, R2 is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R3 is a linear or branched alkyl group having 1 to 4 carbon atoms) (Meth) acrylamides and / or polyfunctional monomers can be included as constituent monomers.

  In N-substituted (meth) acrylamides represented by the general formula (1), a methyl group or a methylene group in an N-alkyl group acts as a chain transfer point, and many branched structures are introduced into the polymer. A branched polymer without conversion is obtained. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms in R2 or R3 in the general formula (1) include a methyl group, an ethyl group, an isopropyl group, and a t-butyl group. Specific examples of N-substituted (meth) acrylamides include N, N-dimethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N- Examples include isopropyl (meth) acrylamide, Nt-butyl (meth) acrylamide and the like. Among these, N, N-dimethylacrylamide is preferable in terms of copolymerizability and chain transfer.

  Moreover, a cross-linked structure can be imparted to the amphoteric or cationic polyacrylamide resin by using a polyfunctional monomer. Multifunctional monomers include di (meth) acrylates such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, methylene bis (meth) acrylamide, ethylene bis (meth) Bis (meth) acrylamides such as acrylamide and hexamethylenebis (meth) acrylamide, divinyl esters such as divinyl adipate and divinyl sebacate, allyl methacrylate, diallylamine, diallyldimethylammonium, diallyl phthalate, diallyl chlorendate, divinylbenzene Bifunctional vinyl monomers such as N, N-diallylacrylamide; 1,3,5-triacryloylhexahydro-S-triazine, triallyl isocyanurate Trifunctional vinyl monomers such as triallylamine and triallyl trimellitate; tetramethylolmethane tetraacrylate, tetraallyl pyromellitate, N, N, N ', N'-tetraallyl-1,4-diaminobutane, tetraallylamine salts , Tetrafunctional vinyl monomers such as tetraallyloxyethane; and other examples include N-methylolacrylamide. Among these polyfunctional monomers, 1,3,5-triacryloylhexahydro-S-triazine, triallyl isocyanurate and the like are preferable.

  The amount of N-substituted (meth) acrylamides and / or polyfunctional monomers represented by the general formula (1) is 10 with respect to the total moles of monomers constituting the cationic or amphoteric polyacrylamide resin. It is preferably about mol% or less, more preferably 5 mol% or less. In order to exhibit the function of the N-substituted (meth) acrylamides represented by the general formula (1), it is preferably 0.1 mol% or more, more preferably 0.5 mol% or more. .

  Further, in order to impart hydrophobicity to the amphoteric or cationic polyacrylamide resin, the alkyl ester of the anionic vinyl monomer (alkyl group having 1 to 8 carbon atoms), acrylonitrile, styrenes, vinyl acetate, methyl vinyl ether. Nonionic vinyl monomers such as can also be used. When a nonionic vinyl monomer is used, the amount used is preferably about 30 mol% or less, preferably 20 mol% or less, based on the total molar amount of monomers constituting the cationic or amphoteric polyacrylamide resin. More preferably.

  Polymerization of amphoteric or cationic polyacrylamide resins can be carried out by various methods. For example, it can be obtained by charging the above-mentioned various monomers and water in a predetermined reaction vessel, adding a radical polymerization initiator, and heating with stirring. The reaction temperature is preferably about 50 to 100 ° C., and the reaction time is preferably about 1 to 5 hours. The reaction concentration (monomer concentration) is usually preferably about 10 to 40% by mass, but the polymerization can be performed even at a higher concentration. In addition, the monomer can be charged by various methods such as simultaneous polymerization and continuous dropping polymerization.

  As the radical polymerization initiator, a radical polymerization initiator such as a persulfate such as potassium persulfate or ammonium persulfate or a redox polymerization initiator in the form of a combination of these with a reducing agent such as sodium bisulfite can be used. An azo initiator may be used as the radical polymerization initiator. The amount of the radical polymerization initiator used is preferably 0.05 to 2% by mass, more preferably 0.1 to 0.5% by mass, based on the total mass of the monomers. In addition, Mannich organization, Hoffmann reaction, etc. are performed after manufacturing polyacrylamide or anionic polyacrylamide.

  In the present invention, the content of the paper strength enhancer is 0.01 to 20 in terms of solid content with respect to 100 parts by mass of the fibrillated lyocell fiber in order to provide the coating suitability of the lithium ion battery substrate. It is preferable to set it as a mass part, and it is more preferable to set it as 0.1-5 mass parts. The base material for a lithium secondary battery (15), in which the paper strength enhancer is contained in an amount of 0.01 to 20 parts by mass with respect to 100 parts by mass of the fibrillated lyocell fiber, has the strength and uniformity required for the base material. A surface is obtained, and it becomes a base material for a lithium ion battery in which the occurrence of paper breakage and wrinkles at the time of coating is suppressed and the coating suitability is improved. When the content of the paper strength enhancer is less than 0.01 parts by mass with respect to 100 parts by mass of the fibrillated lyocell fiber, the effect of improving the coating suitability may not be obtained. Moreover, when larger than 20 mass parts, uniformity may be lost by aggregation and coating suitability may fall. In addition, an increase in viscosity may impair manufacturing stability.

  In addition, by adding a paper strength enhancer, unevenness of the surface is suppressed when the coating liquid is exposed or combined, and the coating suitability is improved. Fluffing and the like are less likely to occur, and the effect that the coated surface becomes uniform and the machine is not soiled is obtained. In addition, since the strength of the base material for the lithium secondary battery is improved, the occurrence of paper breaks and wrinkles during coating is reduced, and the handling property during battery assembly is improved.

  In the base material for a lithium secondary battery of the present invention, the paper strength enhancer can be added by a method of adding a nonwoven fabric (internal addition method) or a method of impregnating or coating a nonwoven fabric (external addition method). . Since the paper strength enhancer is uniformly mixed and the network of polymer chains can be stretched uniformly, it is easy to suppress the dropping of fibers and the like, and it is an internal addition method that can improve the uniformity of the entire substrate. Is preferred.

  When the fibrillated heat-resistant fiber is further contained as an essential component as in the lithium secondary battery substrate (16) of the present invention, the substrate has small pores and is formed relatively uniformly. Therefore, the back-through of the coating liquid containing the filler particles is suppressed, and the filler particles are intensively laminated on the surface of the base material. Therefore, the surface smoothness of the coated surface is excellent, and an unnecessary gap is generated between the electrodes. Hateful. Further, since the back-through of the coating liquid is suppressed, the filler particles are not filled inside the base material and do not block the pores inside the base material, so that a separator having a high electrolytic solution retention rate can be obtained. it can. Since it contains fibrillated heat-resistant fibers, it has excellent heat resistance, the lithium secondary battery is internally short-circuited and generates heat, and even if the temperature rises, the separator does not melt or shrink.

  By the way, when charging / discharging is repeated or overcharged, a phenomenon occurs in which metallic lithium is deposited on the negative electrode surface, and this deposit is referred to as “lithium dendrite”. Lithium dendrite grows gradually, penetrates the separator and reaches the positive electrode, which may cause internal short circuit, but the separator and composite base material that have been used conventionally have large pores in the nonwoven fabric, There was also a problem that this internal short circuit was likely to occur. In the base material (16) for lithium secondary batteries of the present invention, the fibrillated heat-resistant fiber is rigid, so that penetration of lithium dendrite can be suppressed.

  The fibrillated heat-resistant fiber, which is an essential component constituting the base material for the lithium secondary battery of the present invention, includes wholly aromatic polyamide, wholly aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, polybenzoe. A fibrillated heat-resistant fiber made of imidazole, poly-p-phenylenebenzobisthiazole, poly-p-phenylenebenzobisoxazole, polytetrafluoroethylene, acrylic resin or the like is used. Of these, para-type wholly aromatic polyamides and acrylic resins are particularly preferred because of their high thermal decomposition temperature, excellent heat resistance, and excellent compatibility with the electrolyte. Acrylic resin is made of 100% acrylonitrile polymer, and acrylonitrile is copolymerized with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl acetate, etc. And the like. As the acrylonitrile-based polymer, the mass% (acrylonitrile ratio) of acrylonitrile with respect to the polymerizable component in the acrylonitrile-based polymer constituting the fiber is preferably 40% by mass or more, and more preferably 50% by mass or more. More preferably, it is 88 mass% or more. If the acrylonitrile ratio is less than 40% by mass, the fibrils of the fibrillated acrylonitrile fiber may become too thick, and it may be difficult to achieve the target degree of fibrillation. The degree of fibrillation is preferably 0 to 500 ml, more preferably 0 to 400 ml, and still more preferably 0 to 300 ml, according to JIS P8121. If it exceeds 500 ml, the fiber diameter distribution becomes wide, and there are cases where it becomes a textured spot or a thick spot, or there is a case where the coating liquid is breached. The length weighted average fiber length of the fibrillated heat resistant fiber is preferably 0.2 to 2.0 mm, more preferably 0.3 to 1.5 mm, and further preferably 0.5 to 1.2 mm. If it is less than 0.2 mm, it may fall off from the substrate or the substrate may become fluffy, and if it is longer than 2.0 mm, it may become lumpy. The fibrillated heat-resistant fiber not only improves the heat resistance of the substrate, but is more rigid than cellulose and other synthetic fibers, and therefore can suppress penetration of the substrate even when lithium dendrite is generated.

  Heat-resistant fiber fibrillation consists of a heat-resistant fiber that is fixed to a refiner, beater, mill, milling device, rotary homogenizer that applies shearing force with a high-speed rotating blade, and circular-shaped inner blade that rotates at high speed. Double-cylindrical high-speed homogenizer that generates shearing force between the blades, ultrasonic crusher that is refined by ultrasonic impact, and a pressure difference of at least 3000 psi is applied to the fiber suspension to pass through a small-diameter orifice. It is obtained by processing using a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fiber by causing a high speed and colliding with this to rapidly decelerate.

  The content of the fibrillated heat-resistant fiber is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and further preferably 15 to 40% by mass. When the content of the fibrillated heat-resistant fiber is less than 5% by mass, the heat resistance and dendrite resistance of the substrate may be insufficient. When the content is more than 60% by mass, the substrate is likely to become fluffy. Occasionally, the fibers may fall off, fouling the rolls and hindering the coatability.

  In the present invention, the nonwoven fabric may have a multilayer structure. The fiber composition of each layer may be the same or different. When the fiber composition of each layer is the same, the basis weight of each layer can be lowered, so that the fiber concentration of the slurry can be lowered, so that the nonwoven fabric is better formed. As a result, the synthetic resin short fibers and fibrillated lyocell The entanglement with the fiber becomes complicated and uniform, and the denseness and uniformity of the base material are improved. Moreover, even when the formation of each layer is non-uniform | heterogenous, it can compensate by laminating | stacking. Further, the paper making speed can be increased, and the operability is improved.

  When the fiber composition of each layer is changed, at least one layer may be a layer containing the synthetic resin short fiber and the fibrillated lyocell fiber as essential components. The function can be separated by changing the fiber composition of each layer. For example, (A) it has a heat-resistant layer containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and a heat melting layer (B) containing synthetic resin short fibers and polyethylene synthetic pulp as essential components. In the case of a base material for a lithium ion secondary battery, in the heat-resistant layer (A), the fibrillated lyocell fiber is entangled with the synthetic resin short fiber, and in the heat melting layer (B), the polyethylene synthetic pulp is the synthetic resin short fiber. Intertwined with the surface, the smoothness of both the front and back surfaces is high, the denseness is excellent, the variation of the surface when combined by surface coating is small, and it has sufficient surface strength, so the composite will fall off It becomes difficult. Furthermore, by laminating the heat-melting layer (B), when the temperature inside the battery becomes around 130 ° C., it melts and closes the micropores, exhibits shutdown characteristics, and further rises in temperature due to some malfunction. Even when the temperature is close to 170 ° C., the separator does not shrink due to the effect of the heat-resistant layer (A). That is, the base material for a lithium ion secondary battery according to the present invention has characteristics that the surface smoothness is higher, the denseness and uniformity are excellent, and the shutdown characteristic can be exhibited while having heat resistance.

  In the heat-resistant layer (A) of the base material for a lithium secondary battery of the present invention, the content mass ratio of the synthetic resin short fibers and the fibrillated lyocell fibers is preferably 95/5 to 20/80, and 90/10 to 30. / 70 is more preferable, and 70/30 to 40/60 is more preferable. When the content ratio of the fibrillated lyocell fiber is less than 5% by mass, sufficient heat resistance may not be obtained or the denseness and uniformity may not be improved. Moreover, when the content ratio of the fibrillated lyocell fiber exceeds 80% by mass, the base material may be damaged during the formation of the composite.

  The polyethylene-based synthetic pulp of the present invention refers to a pulp-like product produced from polyethylene as a raw material. Among them, a solution at a temperature higher than that of the raw material hydrocarbon solvent disclosed in Japanese Patent Publication No. 55-10683 is depressurized. A flash spinning method represented by a method of flash discharge into a region, or a method disclosed in Japanese Patent Publication No. Sho 52-47049, a method of flash discharging a raw emulsion solution into a reduced pressure region at a high temperature and a high pressure. What was obtained by this is preferable. As long as the effect of the present invention is not impaired, the surface of the synthetic pulp may be treated with polyvinyl alcohol. The treatment with polyvinyl alcohol is preferably carried out by adding 0.5 to 3.0% by mass, preferably 1.0 to 2.0% by mass, with respect to the synthetic pulp emulsion solution. You may do it. Polyvinyl alcohol hydrophilizes the polyethylene-based synthetic pulp and prevents the synthetic pulp from flocking during wet papermaking.

  In the heat melting layer (B) of the base material for a lithium secondary battery of the present invention, the content mass ratio of the synthetic resin short fiber and the polyethylene synthetic pulp is preferably 60/40 to 10/90, and 50/50 to 20 / 80 is more preferable, and 40/60 to 20/80 is more preferable. When the content ratio of the polyethylene-based synthetic pulp is less than 40% by mass, sufficient shutdown characteristics may not be exhibited, and the denseness and uniformity may not be improved. The substrate may be damaged.

  The ratio of the heat-resistant layer (A) and the heat-melting layer (B) of the lithium ion battery substrate of the present invention is preferably 20/80 to 80/20, more preferably 30/70 to 70/30, and 40 / 60-60 / 40 is more preferable. When the ratio of the heat-resistant layer (A) is less than 20% by mass, the heat resistance may be inferior. On the other hand, when the ratio of the heat-melted layer (B) is less than 20% by mass, a good shutdown may not occur. .

  In the base material for a lithium secondary battery of the present invention, it is preferable that the minimum pore diameter is 0.10 μm or more and the maximum pore diameter is 20 μm or less. When the fibrillated lyocell fiber is entangled with the synthetic resin short fiber, this pore diameter can be achieved, it is excellent in denseness, and it is possible to suppress the exfoliation / dropping of composites such as filler particles and resin and the generation of pinholes. . In terms of suppressing pinhole generation when compounding by surface coating such as filler particles or resin, the minimum pore diameter is more preferably 0.20 μm or more and the maximum pore diameter is more preferably 15 μm or less. Has a minimum pore diameter of 0.30 μm or more and a maximum pore diameter of 10 μm or less.

  Furthermore, the ratio dmax / dave between the maximum pore diameter dmax (μm) and the average pore diameter dave (μm) is preferably 10 or less. When dmax / dave is 10 or less, the denseness and uniformity are excellent, and more excellent in the prevention of dropping off of composites and pinholes when composited by surface coating such as filler particles or resin. ing. Preferably it is 8.0 or less. As dmax / dave is closer to 1.0, the variation in the pore diameter of the base material is less likely to vary, but a lower limit of dmax / dave is preferably about 2.0.

  The minimum pore diameter, the maximum pore diameter, and the average pore diameter are defined in JIS K 3832, ASTM F316-86, and ASTM E1294-89.

  In order to keep the minimum pore diameter, the maximum pore diameter, and dmax / dave within the preferable numerical ranges, it is preferable to add lyocell fiber having an increased degree of fibrillation. For example, in a double disc refiner (DDR), it is preferable to use one that has been beaten 50 times or more. It is also effective to set the content ratio of the fibrillated lyocell fiber to 5% by mass or more with respect to the total content of the synthetic resin short fiber and the fibrillated lyocell fiber. In order to set dmax / dave to 10.0 or less, the fineness of the synthetic resin short fibers is preferably 0.004 to 1.3 dtex. When the fineness of the synthetic resin short fiber exceeds 1.3 dtex, the maximum pore diameter may increase.

  In the base material for a lithium secondary battery of the present invention, the center line average roughness Ra in the flow direction and the width direction is preferably 3.0 or less, and the variation in the surface when combined is reduced. The value of Ra is more preferably 2.6 or less, and even more preferably 2.3 or less. Most preferably, it is 2.0 or less. In addition, let the same direction as the direction which a fiber web advances at the time of paper making with a paper machine be a flow direction, and let a perpendicular direction to a flow direction be a width direction. The center line average roughness Ra was measured based on the method defined in JIS B 0601-1982.

  In order for Ra to be 3.0 or less, it is preferable that the fineness of the synthetic resin short fiber is 1.3 dtex or less and the fiber length is 7 mm or less.

  In order to keep Ra within the preferable numerical range, it is effective to set the content ratio of the fibrillated lyocell fiber to 5% by mass or more with respect to the total content of the synthetic resin short fiber and the fibrillated lyocell fiber. Moreover, when the fineness of the synthetic resin short fiber exceeds 1.3 dtex, the unevenness becomes large, and the value of the center line average roughness Ra falls outside the preferable numerical range, and the surface when combined by surface coating is large. There may be variations. Furthermore, it is also effective to set the fiber length of the synthetic resin short fibers to 10 mm or less.

  In the base material for a lithium secondary battery of the present invention, the ratio (MDs / CDs) of the tensile strength (MDs) in the flow direction and the tensile strength (CDs) in the width direction is not particularly limited, but is 0.5 to 8. It is preferably within the range of 0, and when (MDs / CDs) is within this range, the generation of wrinkles when combined with surface coating of filler particles, resin, etc., and the accompanying dropout of the composite are suppressed. can do. (MDs / CDs) is more preferably 1.0 to 5.5, and still more preferably 1.0 to 3.0. Most preferably, it is 1.0-2.0.

  In order to set (MDs / CDs) to 0.5 to 8.0, for example, heat-sealable short fibers may be contained. High mechanical strength can be obtained by softening, melting or wet-heat-dissolving the heat-fusible short fibers by heating or wet heat heating, and heat-bonding the fibers to each other. Therefore, the value of (MDs / CDs) is 0. It tends to be 5 to 8.0, and the generation of wrinkles when combined by surface coating can be reduced. Moreover, since the value of (MDs / CDs) may become larger than 8.0 when the fiber length of the synthetic resin short fiber exceeds 7 mm, the fiber length of the synthetic resin short fiber is preferably 7 mm or less. .

  In the present invention, when a paper strength enhancer is used, not only the tensile strength in the flow direction can be improved, but also the tensile strength in the width direction can be greatly improved, and the value of (MDs / CDs) is 0. .5 to 8.0.

  The tensile strength is measured based on the method specified in JIS P 8113, and the ratio of the tensile strength (MDs) in the flow direction to the tensile strength (CDs) in the width direction (MDs / CDs) is based on the measurement result. Calculated.

  In order to keep (MDs / CDs) within a preferable numerical range, the content ratio of the fibrillated lyocell fiber to the total content of the synthetic resin short fiber and the fibrillated lyocell fiber should be 5% by mass or more. It is valid. It is also effective to set the fiber length of the synthetic resin short fibers to 10 mm or less. In addition, by using a paper strength enhancer, not only can the tensile strength in the flow direction be improved, but also the tensile strength in the width direction can be greatly improved, and (MDs / CDs) can easily be kept within the preferred numerical range. Become.

Basis weight of the lithium secondary battery substrate is preferably 3.0~30.0g / ^{m 2,} more preferably ^{6.0~20.0g / m 2, 8.0~12.0g / m} 2 and more preferable. In order to keep the values of minimum pore diameter, maximum pore diameter, dmax / dave, and (MDs / CDs) within a preferable range, it is preferable to increase the basis weight, but if it exceeds 30.0 g / m ² , the substrate It will occupy the majority of the separator alone, and it will be difficult to obtain the effect of the composite, and if it is less than 3.0 g / m ² , it will be difficult to obtain uniformity and the surface after the composite will have a large variation. In some cases, it tends to occur or the maximum pore diameter exceeds the preferred range. The basis weight means a basis weight based on a method defined in JIS P 8124 (paper and paperboard—basis weight measurement method).

4-45 micrometers is preferable, as for the thickness of the base material for lithium secondary batteries of this invention, 6-40 micrometers is more preferable, and 8-30 micrometers is more preferable. If it exceeds 45 μm, the base material alone occupies the majority of the separator, and it becomes difficult to obtain the effect of the composite. If the thickness is less than 4 μm, the strength of the base material becomes too low, and the base material may be damaged when the base material is handled or combined, or the pore diameter may not be within the preferred range. In some cases, pinholes are likely to occur. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured with the outside micrometer at the time of 5N load. Moreover, 0.250-1.000 g / cm < ³ > is preferable and, as for the density of the base material for lithium secondary batteries of this invention, 0.400-0.800 g / cm < ³ > is more preferable. When the density is less than 0.250 g / cm ³ , the coating liquid may be seen through, and when it exceeds 1.000 g / cm ³ , the resistance value of the separator may be increased.

  In the base material for a lithium secondary battery of the present invention, as a method for producing a nonwoven fabric, a method of forming a fiber web and bonding, fusing, and entanglement of fibers in the fiber web can be used. The obtained nonwoven fabric may be used as it is or may be used as a laminate comprising a plurality of sheets. Examples of the method for producing the fiber web include a dry method such as a card method and an air array method, a wet method such as a papermaking method, a spunbond method, and a melt blow method. Among these, the web obtained by a wet method is uniform and dense, and can be suitably used as a base material for a lithium secondary battery.

  In the wet method, the fibers are uniformly dispersed in water to obtain a uniform papermaking slurry, and then passed through processes such as screen (removal of foreign matters, lumps, etc.), and the final fiber concentration is 0.01 to 0.50% by mass. Adjusted to paper. In order to obtain a more uniform nonwoven fabric, chemicals such as a dispersion aid, an antifoaming agent, a hydrophilic agent, and an antistatic agent may be added during the process. In order to obtain a fiber web, a paper machine having at least one of a wire such as a circular net, a long net, and an inclined type can be used for the papermaking slurry. In this papermaking process, by adjusting the papermaking slurry concentration, flow velocity, J / W ratio, inclination angle, draw, etc., the value of (MDs / CDs) can be easily kept within a preferable numerical range. In addition, a fiber web having a uniform flow direction and width direction can be obtained, and Ra can be easily contained within a preferable numerical range.

  Furthermore, as a method for producing a nonwoven fabric from a fiber web, a hydroentanglement method, a needle punch method, a binder adhesion method, or the like can be used. In particular, when the wet method is used with emphasis on uniformity, it is preferable to include a heat-fusible short fiber and bond the heat-fusible short fiber by a binder bonding method. A uniform nonwoven fabric is formed from a uniform web by the binder bonding method. The wet nonwoven fabric thus manufactured may be subjected to heat treatment, calendar treatment, thermal calendar treatment, and the like. By these treatments, effects such as adjustment of thickness, uniformization, and strength improvement are obtained, and the value of Ra is easily kept within a preferable numerical range. Further, the maximum pore diameter and the average pore diameter can be controlled by a process such as a calendar, and as a result, dmax / dave can be easily kept within a preferable numerical range. However, when the heat-fusible short fibers are contained, the temperature at which the heat-fusible short fibers do not form a film (temperature lower by 20 ° C. or more than the melting point of the heat-fusible short fibers), processing time, pressure It is preferable to apply pressure. Further, by adjusting the tension of the calendar, it is possible to control the ratio of the tensile strength and keep (MDs / CDs) within a preferable numerical range.

  When the base material for lithium secondary batteries of this invention contains a core-sheath-type heat-fusible short fiber, it is preferable because the mechanical strength becomes higher by heat treatment. Examples of the heat treatment method include a heat treatment method using a heating device such as a hot air dryer, a heating roll, an infrared (IR) heater, or the like while continuously performing the heat treatment or pressurizing. The heat treatment temperature is equal to or higher than the temperature at which the sheath portion of the core-sheath type heat-fusible short fiber melts or softens, and the core portion of the core-sheath type heat-fusible short fiber and other contained fibers melt, soften, or decompose. It is preferable that the temperature be less than the temperature.

  In the case of a multilayer nonwoven fabric, there is no particular limitation on the method of laminating each layer, but a wet method of combining the layers can be suitably used without peeling between the layers. Wet-making method is a papermaking slurry in which fibers are dispersed in water to form a uniform papermaking slurry. This is a method for obtaining a fibrous web.

  When producing a multilayer structure nonwoven fabric by a wet method, a drying step is required to remove moisture, but when the base material for the lithium secondary battery has a hot melt layer (B), the polyethylene synthetic pulp is Drying is preferably performed at a temperature at which the film is not completely formed (temperature lower by 20 ° C. or more than the melting point) and a treatment time. When over-drying is performed, film formation of the polyethylene-based synthetic pulp is promoted too much, and an optimal void may not be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example. All parts and percentages in the examples are based on mass unless otherwise specified.

<< Examples 1-13, Comparative Examples 1-6 >>
Non-fibrillar lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) was repeatedly treated 50 times using a double disc refiner to produce fibrillated lyocell fiber 1.

  According to the number of parts shown in Table 1, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for paper making is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 130 ° C., and unstretched polyethylene terephthalate (PET) heat-fusible short fibers are bonded to express nonwoven fabric strength. A 50 cm wide nonwoven fabric was produced. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The following evaluation was performed about the base material for lithium secondary batteries obtained in Examples 1-13 and Comparative Examples 1-6, and the result was shown in Table 2.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base material for a lithium secondary battery obtained in the examples is composed of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers, and thus has a dense structure and is composited by surface coating. A good result was obtained that the variation of the surface was small.

  From the comparison of Examples 1-3 and Example 4, when the resin constituting the synthetic resin short fiber is a polyester resin, an acrylic resin, or a polyolefin resin, there is a variation in the surface when combined by surface coating. It was small and high in strength, and no loss of the porous membrane was confirmed.

  From the comparison between Example 1 and Examples 5 to 13, when the content of the fibrillated lyocell fiber is 5 to 80% by mass, the surface variation when combined by surface coating is small, the strength is high, and Also, no loss of the porous film was confirmed. In Example 5 in which the content of fibrillated lyocell fiber was less than 5% by mass, there was a tendency that the surface variation and dropout were slightly increased. On the other hand, in Example 12 in which the content of fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  On the other hand, since the base materials for lithium secondary batteries obtained in Comparative Examples 1 to 6 do not contain fibrillated lyocell fibers, surface variations occur, the strength is low, and the degree of dropping of the porous film is also low. Results larger than those of Examples 1 to 13 were obtained.

<< Examples 14 to 36, Comparative Examples 7 to 10 >>
[Physical properties of fibrillated lyocell fiber]
About fibrillated lyocell fiber
(1) Modified freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%. Law Freeness "
(2) Length-weighted average fiber length: “Average fiber length”
Is shown in Table 3. The fibrillated lyocell fibers in each state were prepared by treating unfibrillated lyocell single fibers (fiber diameter: 12 μm, fiber length: 6 mm, manufactured by Coatles Co., Ltd.) using a double disc refiner.

Examples 14-17, 28, Comparative Examples 7-9, Examples 32-36
According to the number of blending parts shown in Table 3, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, both surfaces were brought into contact with a metal roll heated to 210 ° C. and heat-treated, and further, supercalendering was performed to obtain a lithium secondary battery substrate.

Examples 18-27, 29-31, Comparative Example 10
According to the number of blending parts shown in Table 3, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The following evaluation was performed about the base material for lithium secondary batteries obtained in Examples 14-36 and Comparative Examples 7-10, and the result was shown in Table 4.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Base material density]
The basis weight was measured according to JIS P 8124, and the density was determined by dividing by the thickness measured by the above method.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Coating rate]
In the manufacturing process of the separator, the ratio of the coating area to the area of the base material from the start of coating to the base material to the end of coating was defined as the coating rate (%). The greater the area that could not be coated due to cutting or tearing of the substrate, the smaller the coating rate.

[Back-through]
In the manufacturing process of the separator, the strike-through was evaluated according to the following criteria.
○: The coating liquid does not penetrate the substrate at all.
Δ: Slightly penetrated, but there is no problem such that the back surface of the base material sticks to the roll of the coating apparatus.
X: It slipped through and the back surface of the base material stuck to the roll, causing problems such as inability to perform smooth coating.

[Surface smoothness]
About the separator, the thickness of arbitrary 10 places was measured, the standard deviation (micrometer) was computed, and it was set as the parameter | index of surface smoothness. The smaller the standard deviation value, the better the surface smoothness.

[Electrolytic solution retention]
The separator was cut to 100 mm width × 100 mm, immersed in the electrolyte solution for 1 minute, suspended for 1 minute to cut off the excess electrolyte solution, and the mass W1 of the separator was measured. The value obtained by subtracting the mass W0 of the separator before holding the electrolytic solution from W1 and dividing the value W2 by W0 and multiplying by 100 was defined as the electrolytic solution retention rate (%). As the electrolytic solution, a mixed solution in which 1 mol / l of LiPF ₆ was dissolved was used. The mixed solution is ethylene carbonate and diethyl carbonate in a mass ratio of 3: 7.

  The base materials for lithium secondary batteries of Examples 14 to 31 are fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm; Since it consists of a wet nonwoven fabric containing synthetic resin short fibers, the back-through of the coating liquid containing filler particles is suppressed, the surface smoothness of the coated surface is good, and the electrolyte solution retention is high.

  On the other hand, the base materials for lithium secondary batteries of Comparative Examples 7 to 9 are fibrillated lyocell having a modified freeness of 0 to 250 ml and a length weighted average fiber length of 0.20 to 2.00 mm. Since it is composed only of synthetic resin short fibers without containing fibers, the coating liquid containing filler particles is broken through, causing problems in the coating operation, and the surface smoothness of the coated surface is poor. Further, the filler particles were filled in the base material, and the pores inside the base material were closed, so that the electrolyte solution retention rate was poor.

  The base material for a lithium secondary battery of Example 32 contains fibrillated lyocell fiber having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. In addition, since the modified freeness is 33 ml and the weight-weighted average fiber length is 0.17 mm, the fibrillated lyocell fiber tends to fall off. There was slight penetration of the liquid, and the surface smoothness of the coated surface was slightly inferior to Examples 14 to 31. Moreover, since the inside of the base material was filled with filler particles, and the pores inside the base material became clogged, the electrolyte solution retention rate was slightly lower than in Examples 14 to 31.

  The base material for a lithium secondary battery of Example 33 contains fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. In addition, since the modified freeness is 45 ml and the fibrillated lyocell fiber having a length-weighted average fiber length of 2.16 mm is contained, uneven formation occurs, which is compared with Examples 14 to 31. The surface smoothness of the coated surface was poor.

  The base material for a lithium secondary battery of Example 34 does not contain fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. Since the modified lyocell fiber has a modified freeness of 255 ml and a weight-weighted average fiber length of 0.19 mm, it contains 90% by mass of the fibrillated lyocell fiber. Cutting and tearing occurred during the work, and the coating rate was poor as compared with Examples 14 to 31. Further, the coating composition was more coated than Examples 26 and 27 containing 90% by mass of fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. The surface smoothness of the work surface was poor, and the electrolyte retention rate was low.

  The base material for a lithium secondary battery of Example 35 does not contain fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. Since the modified freeness is 257 ml and the weight-weighted average fiber length is 90% by mass of the fibrillated lyocell fiber, the formation unevenness is generated. The surface smoothness of the coated surface is worse than that of Examples 26 and 27 containing 90% by mass of fibrillated lyocell fibers having a weight weighted average fiber length of 0.20 to 2.00 mm at 250 ml. The retention rate was low.

  The base material for a lithium secondary battery of Example 36 does not contain fibrillated lyocell fibers having a modified freeness of 0 to 250 ml and a length-weighted average fiber length of 0.20 to 2.00 mm. In addition, since the modified freeness is 260 ml and 90% by mass of the fibrillated lyocell fiber having a length weighted average fiber length of 2.11 mm is contained, the formation unevenness is further increased than in Examples 34 and 35. The surface smoothness of the coated surface was worse.

  The base material for a lithium secondary battery of Comparative Example 10 is a fibrillated lyocell fiber having no synthetic resin short fiber, a modified freeness of 107 ml, and a length-weighted average fiber length of 1.22 mm. Since the piercing strength was weak and it was torn during coating, the coating rate was poor.

<< Examples 37 to 52, Comparative Examples 11 to 12 >>
[Physical properties of fibrillated lyocell fiber]
About fibrillated lyocell fiber
(1) Maximum frequency peak fiber length in the fiber length distribution histogram: “maximum frequency peak fiber length”,
(2) Ratio of fibers having a fiber length of 1.0 mm or more: “fiber ratio of 1.00 mm or more”,
(3) In the fiber length distribution histogram, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm: “the slope of the ratio”
(4) Length-weighted average fiber length: “Average fiber length”
(5) Modified freeness measured according to JIS P8121, except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%. Law Freeness "
Is shown in Table 5. In addition, the fibrillated lyocell fibers 1A to 1L were prepared by treating fibrillated lyocell single fibers (fiber diameter: 12 μm, fiber length: 6 mm, manufactured by Coatles Co., Ltd.) using a double disc refiner.

Examples 37 to 52, Comparative Example 11
According to the number of parts shown in Table 6, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 130 ° C., unstretched PET-based heat-fusible short fibers are bonded to develop a nonwoven fabric strength, and the width is 50 cm. A non-woven fabric was prepared. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 12
According to the number of parts shown in Table 6, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The base materials for lithium secondary batteries obtained in Examples 37 to 52 and Comparative Examples 11 to 12 were evaluated as follows, and the results are shown in Table 7.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base materials for lithium secondary batteries obtained in Examples 37 to 50 are composed of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers. In the fiber length distribution histogram of the fibrillated lyocell fibers, 0. When the ratio of fibers having a maximum frequency peak between 00 and 1.00 mm and having a fiber length of 1.00 mm or more is 10% or more, it has a dense structure and is combined by surface coating. A good result was obtained that the variation of the surface of the film was small.

  From the comparison of Examples 37, 38, 40, 41, and 46, in the fiber length distribution histogram of the fibrillated lyocell fiber, the ratio of fibers having a fiber length of 0.05 mm between 1.00 and 2.00 mm. When the inclination was −3.0 or more and −0.5 or less, the variation in the surface when combined by surface coating was small, the strength was high, and the removal of the porous film was not confirmed. In Example 41 having an inclination of less than −3.0, there was a tendency for the strength and the dropout of the porous film to slightly decrease. In Example 46 where the inclination was greater than −0.5, the surface variation tended to deteriorate slightly.

  From the comparison of Examples 37 and 47 to 50, when the content of the fibrillated lyocell fiber is 5 to 80% by mass, the surface variation when combined by surface coating is small, the strength is high, and the porosity No membrane loss was observed. In Example 47 in which the content of the fibrillated lyocell fiber was 5% by mass, the surface variation tended to be slightly increased. In Example 50 in which the content of the fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  On the other hand, since the base material for a lithium secondary battery obtained in Comparative Example 11 does not contain fibrillated lyocell fiber, surface unevenness occurs, and the degree of dropout of the porous membrane is also larger than those in Examples 37-50. As a result.

  Since the base material for lithium secondary batteries obtained in Comparative Example 12 did not contain synthetic resin short fibers, the strength was low, and the degree of dropout of the porous membrane was also greater than Examples 37-50. .

  Moreover, in the base material for lithium secondary batteries obtained in Example 51, since the maximum frequency peak in the fiber length distribution histogram deviates from between 0.0 and 1.0 mm, surface variation occurs, and the porous The degree of dropping off of the membrane was also greater than in Examples 37-50.

  Furthermore, the base material for a lithium secondary battery obtained in Example 52 has a low strength because the proportion of fibers having a fiber length of 1.0 mm or more is less than 10%, and the degree of dropping of the porous membrane is also carried out. Results were greater than Examples 37-50.

<< Examples 53 to 67, Comparative Examples 13 to 14 >>
[Physical properties of fibrillated lyocell fiber]
About fibrillated lyocell fiber (1) Ratio of fiber having fiber length of 1.00 mm or more: “fiber ratio of 1.00 mm or more”
(2) Maximum frequency peak fiber length in the fiber length distribution histogram: “maximum frequency peak fiber length”,
(3) Fiber length of peaks other than the maximum frequency peak: “fiber length of second peak”
(4) Freeness measured according to JIS P8121, except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%: Water degree ",
Is shown in Table 8. In addition, the fibrillated lyocell fibers 2A to 2K were prepared by treating fibrillar lyocell single fibers (fiber diameter: 12 μm, fiber length: 6 mm, manufactured by Coatles Co., Ltd.) using a double disc refiner.

Examples 53 to 67, Comparative Example 13
According to the number of parts shown in Table 9, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 130 ° C., unstretched PET-based heat-fusible short fibers are bonded to develop a nonwoven fabric strength, and the width is 50 cm. A non-woven fabric was prepared. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 14
According to the number of parts shown in Table 9, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The base materials for lithium secondary batteries obtained in Examples 53 to 67 and Comparative Examples 13 to 14 were evaluated as follows, and the results are shown in Table 10.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base materials for lithium secondary batteries obtained in Examples 53 to 65 have a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram, and have a fiber length of 1.00 mm or more. Since the ratio of the fibers was 50% or more, a good result was obtained that the structure had a dense structure and the surface variation when combined by surface coating was small.

  From the comparison of Examples 53 and 56 to 61, in the fiber length distribution histogram of the fibrillated lyocell fiber, when having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak, the strength is high, and the porosity is high. No membrane loss was observed. In Example 56, where the fiber length of the peak other than the maximum frequency peak is shorter than 1.50 mm, the strength tends to decrease slightly. Further, in Example 61 in which the fiber length of the peak other than the maximum frequency peak is longer than 3.50 mm, the tendency of the porous film falling off slightly deteriorated was observed.

  From the comparison of Examples 62 to 65, when the content of the fibrillated lyocell fiber was 5 to 80% by mass, the strength was high and the removal of the porous membrane was not confirmed. In Example 62 in which the content of fibrillated lyocell fiber was 5% by mass, the tendency of the porous membrane to drop off was slightly deteriorated. In Example 65 in which the content of the fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  On the other hand, since the base material for lithium secondary batteries obtained in Comparative Example 13 does not contain fibrillated lyocell fibers, the surface variation occurs, and the degree of dropout of the porous membrane is also larger than those in Examples 53 to 65. As a result.

  In the base material for lithium secondary batteries obtained in Comparative Example 14, since the synthetic resin short fibers were not contained, the strength was low, and the degree of dropout of the porous film was also larger than Examples 53-65. .

  Moreover, in the base material for lithium secondary batteries obtained in Example 66, since the maximum frequency peak in the fiber length distribution histogram is out of the range of 0.00 to 1.00 mm, the surface variation occurs, and the porous The degree of dropping of the membrane was also greater than in Examples 53-65.

  Furthermore, the base material for a lithium secondary battery obtained in Example 67 has a low strength because the proportion of fibers having a fiber length of 1.00 mm or more is less than 50%, and the degree of dropping of the porous membrane is also carried out. Results greater than Examples 53-65.

<< Examples 68 to 85, Comparative Examples 15 to 19 >>
Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 60 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC1”.

  Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 75 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC2”.

  Non-fibrillated lyocell fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 110 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC3”.

Examples 68, 70, 72, 73, 76-81, Comparative Example 15
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 120 ° C., and heat-bondable short fibers are bonded by heat or wet heat to develop non-woven fabric strength. A non-woven fabric was prepared. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 69
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 120 ° C., heat-bondable short fibers are thermally bonded to develop a nonwoven fabric strength, and a 50 cm wide nonwoven fabric is produced. Produced. Next, the nonwoven fabric was brought into contact with a heat roll having a diameter of 1.2 m heated to 200 ° C. at a speed of 20 m / min and heat-treated. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 71
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 120 ° C., heat-bondable short fibers are thermally bonded to develop a nonwoven fabric strength, and a 50 cm wide nonwoven fabric is produced. Produced. Next, a heat roll having a diameter of 1.2 m heated to 75 ° C. was subjected to pressure heat treatment at a pressure of 196 N / cm ² and a speed of 10 m / min to obtain a base material for a lithium secondary battery.

Examples 74, 75, 84, 85, Comparative Example 18
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, dried by a cylinder dryer at 140 ° C., heat-bondable short fibers are thermally bonded to develop a nonwoven fabric strength, and a 50 cm wide nonwoven fabric is produced. Produced. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 82, Comparative Examples 16 and 19
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a cylinder dryer at 110 ° C. without thermally bonding the heat-fusible short fibers to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 83, Comparative Example 17
In accordance with the number of parts shown in Table 11, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a cylinder dryer at 110 ° C. without thermally bonding the heat-fusible short fibers to produce a 50 cm wide nonwoven fabric. Next, using a heat roll having a diameter of 1.2 m heated to 230 ° C., pressure heat treatment is performed at a pressure of 196 N / cm ² and a speed of 10 m / min to thermally bond the heat-fusible short fibers, and for lithium secondary batteries A substrate was used.

<Evaluation>
The lithium secondary battery base materials obtained in Examples 68 to 85 and Comparative Examples 15 to 19 were evaluated as follows, and the results are shown in Table 12.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Tensile strength of substrate]
Five or more substrates were cut and arranged in a strip shape having a width of 50 mm and a length of 200 mm. The test piece is sandwiched at 100 mm intervals between sample ends with a sample knob of a desktop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the upper end is cut at a constant speed of 100 mm / min. The maximum load at this time was measured, this was taken as the tensile strength, and evaluated according to the following criteria.
A: 19.6 N / 50 mm or more ○: 11.8 N / 50 mm or more and less than 19.6 N / 50 mm Δ: 9.8 N / 50 mm or more and less than 11.8 N / 50 mm ×: Less than 9.8 N / 50 mm

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (g) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the lowest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 1.0N or more ○: 0.8N or more and less than 1.0N ○ △: 0.5N or more and less than 0.8N △: 0.3N or more and less than 0.5N ×: Less than 0.3N

[Heat shrinkage of substrate]
The substrate was cut into a 100 mm width and a 150 mm length. The test piece was placed on a glass plate, fixed by sandwiching two sides perpendicular to the length direction with a clip, and allowed to stand in a constant temperature dryer set at 150 ° C. for 3 hours. The dimension in the width direction was measured, the ratio of dimensional change due to shrinkage relative to the original dimension was determined, and the heat shrinkage rate (%) was evaluated according to the following criteria.
◎: Thermal shrinkage rate is less than 1.5% ○: 1.5% or more and less than 2.0% △: ○, 2.0% or more and less than 2.5% ×: 2.5% or more

[Abrasion resistance of substrate]
The fiber loss and fluffing of the substrate were examined as wear resistance. The base material was cut to 20 mm width and 50 mm length. Next, the trimmed base material is set in a Gakushin friction fastness tester (trade name: AB-301, manufactured by Tester Sangyo Co., Ltd.), and a test cloth (100% cotton black cloth, Billiken Moss (registered trademark)) ) Was set on the wear jig, and then the wear jig was placed on the base material, and the test was performed by reciprocating 5 times at a speed of 30 reciprocations at a distance of 120 mm with a self weight (1.96 N) applied. . The test was performed once for each sample. After completion of the test, the test location was visually observed and evaluated according to the following criteria.
○: No fiber picked up or fuzzed after being reciprocated five times.
[Delta]: After being reciprocated five times, fibers on the test cloth and fluff are slightly seen, but there is no practical problem.
X: After having been reciprocated five times, fibers are removed from the test cloth and fluffing is found, which is problematic in practice.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base materials for lithium secondary batteries produced in Examples 68 to 81 contain a synthetic resin short fiber and a fibrillated lyocell fiber as essential components, and as at least one kind of the synthetic resin short fiber, a heat fusion component and Because it consists of a non-woven fabric containing core-sheath-type heat-fusible short fibers made of non-heat-sealing components, it forms a dense structure and the fibers are thermally bonded without damaging the structure. Good results were obtained in that the surface variation when composited by surface coating was small. Moreover, the mechanical strength was high, the heat shrinkage was small at 150 ° C., and the thermal dimensional stability was excellent.

  From the comparison of Examples 68, 72 and 74 and the comparison of Examples 70, 73 and 75, the use of polyethylene terephthalate for the core of the core-sheath-type heat-fusible short fiber can improve the thermal dimensional stability of the substrate. There was a tendency to increase. From the comparison between Examples 68 and 72 and the comparison between Examples 70 and 73, when a polyester copolymer is used for the sheath portion of the core-sheath-type heat-fusible short fiber, the mechanical strength of the base material tends to increase. It was observed.

  From the comparison between Examples 68 and 69 and the comparison between Examples 70 and 71, there was a tendency that the mechanical strength was increased by the heat treatment.

  From the comparison of Examples 70, 76, 77, and 78, when the resin constituting the synthetic resin short fiber is a polyester resin, an acrylic resin, or a polyolefin resin, there is a variation in the surface when combined by surface coating. It was small and high in strength, and no falling off of the porous membrane was confirmed.

  The base material for a lithium secondary battery produced in Example 82 and Comparative Example 19 was somewhat inferior in the result of the friction test as compared with Examples 68 to 81 because the fibers were not thermally bonded. It was. For this reason, fibers were dropped or fluffed during surface coating, resulting in increased surface variation. Also, the mechanical strength was low.

  The base materials for lithium secondary batteries of Examples 83 to 85 manufactured using unstretched polyethylene terephthalate short fibers or polyolefin-based split composite fibers as the heat-fusible short fibers were heat-fusible during heat-sealing. Loss of the fiber shape of the short fibers resulted in a decrease in the density of the base material, resulting in a slightly larger variation in the surface when combined by surface coating than in Examples 68 to 81. .

  Since the base materials for lithium secondary batteries prepared in Comparative Examples 15 to 18 do not contain fibrillated lyocell fibers, the thermal dimensional stability is inferior, the surface variation is large, and the degree of dropping of the porous film is also an example. Greater results.

<< Examples 86 to 108, Comparative Examples 20 to 23 >>
Non-fibrillar lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) was repeatedly treated 75 times using a double disc refiner to produce fibrillated lyocell fiber 2.

Example 86
Add a paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin to the pulper to add 2 parts to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 87
A paper strength enhancer of cationic polyacrylamide resin (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 705) is added to the pulper so that it becomes 2 parts per 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 88
After adding and dispersing a cationic starch-based paper strength enhancer (trade name: DD4280, manufactured by Seiko PMC Co., Ltd.) to pulper so as to be 2 parts with respect to 100 parts of fibrillated lyocell fiber, Table 13 shows. According to the number of blending parts, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 89
The composition shown in Table 13 was added to the pulper after adding and dispersing the guar gum paper strength enhancer (trade name: Mayproid 2066, manufactured by Mayhall Chemical Co., Ltd.) to 100 parts of fibrillated lyocell fiber. According to the number of parts, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 90
Alpha pulped potato starch strength enhancer (manufactured by Shikishima Starch Co., Ltd., trade name: Mermaid (registered trademark) M-300) was added to the pulper and dispersed to 100 parts of fibrillated lyocell fiber. Thereafter, the raw materials were mixed together in accordance with the number of blending parts shown in Table 13, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 91
An acrylic ester latex paper strength enhancer (manufactured by Nippon Zeon Co., Ltd., trade name: Nipol (registered trademark) Lx854E) was added to the pulper so as to be 2 parts per 100 parts of fibrillated lyocell fiber and dispersed. Thereafter, the raw materials were mixed together in accordance with the number of blending parts shown in Table 13, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 92
Paper strength enhancer of amphoteric polyacrylamide resin (manufactured by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1810) is added to the pulper so as to be 1.5 parts with respect to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. 0.5 parts relative to 100 parts of lyocell fiber fibrillated with amphoteric polyacrylamide resin paper strength enhancer (trade name: Polystron (registered trademark) 1280) in the pipe before the circular net It added so that it might become. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 93
After adding and dispersing a cation starch (trade name: DD4280 manufactured by Seiko PMC Co., Ltd.) to the pulper so as to be 1.5 parts with respect to 100 parts of the fibrillated lyocell fiber, according to the number of parts shown in Table 13, The raw materials were mixed together and disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. 0.5 parts relative to 100 parts of lyocell fiber fibrillated with amphoteric polyacrylamide resin paper strength enhancer (trade name: Polystron (registered trademark) 1280) in the pipe before the circular net It added so that it might become. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 94
A paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) made of amphoteric polyacrylamide resin is added to the pulper so as to be 0.01 part with respect to 100 parts of lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 95
Paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin is added to the pulper so that it becomes 0.1 part with respect to 100 parts of lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 96
A paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin is added to the pulper so that it becomes 1 part with respect to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 97
A paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin is added to the pulper so that it becomes 5 parts with respect to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 98
A paper strength enhancer of an amphoteric polyacrylamide resin (manufactured by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) is added to the pulper so as to be 10 parts with respect to 100 parts of the fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 99
A paper strength enhancer of an amphoteric polyacrylamide resin (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) is added to the pulper so that it becomes 20 parts with respect to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 100
A paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin is added to the pulper so that it becomes 25 parts with respect to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 101
According to the number of parts shown in Table 13, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. After making this papermaking slurry by a wet method using a circular paper machine, an amphoteric polyacrylamide resin paper strength enhancer (trade name: Polystron (registered trademark) 1250, manufactured by Arakawa Chemical Industries, Ltd.) A diluted solution prepared so as to be 2 parts per 100 parts of fibrillated lyocell fiber was sprayed and dried by a cylinder dryer at 120 ° C. to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Examples 102-104
Add a paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin to the pulper to add 2 parts to 100 parts of fibrillated lyocell fiber. After the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Examples 105-108, Comparative Example 20
According to the number of parts shown in Table 13, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 21
100 parts of fibrillated lyocell fiber 2 was disaggregated in pulper water, and a uniform papermaking slurry (2% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried with a cylinder dryer at 110 ° C. to produce a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 22
A paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of an amphoteric polyacrylamide resin is added to the pulper so as to be 2 parts with respect to 100 parts by mass of the PET fiber. After that, according to the number of blending parts shown in Table 13, the raw materials were mixed together, disaggregated in the pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 23
Add a paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron (registered trademark) 1250) of amphoteric polyacrylamide resin to the pulper to add 2 parts to 100 parts of fibrillated lyocell fiber. After dispersion, 100 parts of fibrillated lyocell fiber 2 was disaggregated in pulper water, and a uniform papermaking slurry (2% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried with a cylinder dryer at 110 ° C. to produce a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The base materials for lithium secondary batteries obtained in Examples 86 to 108 and Comparative Examples 20 to 23 were evaluated as follows, and the results are shown in Table 14.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Tensile strength of substrate]
Five or more substrates were cut and arranged in a strip shape having a width of 50 mm and a length of 200 mm. The test piece is sandwiched at 100 mm intervals between sample ends with a sample knob of a desktop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the upper end is cut at a constant speed of 100 mm / min. The maximum load at this time was measured, this was taken as the tensile strength, and evaluated according to the following criteria.
<Criteria>
A: 19.6 N / 50 mm or more ○: 11.8 N / 50 mm or more and less than 19.6 N / 50 mm Δ: 9.8 N / 50 mm or more and less than 11.8 N / 50 mm x: less than 9.8 N / 50 mm

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

[Abrasion resistance of substrate]
The fiber loss and fluffing of the substrate were examined as wear resistance. The base material was cut to 20 mm width and 50 mm length. Next, the cut base material is set on a Gakushin type friction fastness tester (trade name: AB-301, manufactured by Tester Sangyo Co., Ltd.), and a 100% cotton black cloth (Birikenmos) is set on a wear jig. The test was carried out by placing the wear jig on the base material and reciprocating 5 times at a speed of 30 reciprocations per minute at a distance of 120 mm while applying its own weight (1.96 N). The test was performed once for each sample. After completion of the test, the test location was visually observed and evaluated according to the following criteria.
○: No fiber picked up or fuzzed after being reciprocated five times.
[Delta]: After being reciprocated five times, fibers on the test cloth and fluff are slightly seen, but there is no practical problem.
X: After having been reciprocated five times, fibers are removed from the test cloth and fluffing is found, which is problematic in practice.

  Since the base material for lithium secondary batteries obtained in Examples 86 to 104 is composed of a nonwoven fabric containing synthetic resin short fibers, fibrillated lyocell fibers and paper strength enhancer, it has excellent wear resistance. It is possible to suppress fuzz and fiber dropping due to friction during coating. For this reason, it has become possible to obtain a highly uniform separator that is excellent in surface smoothness and that does not easily cause the porous film to fall off. In addition to improving the coating suitability, the tensile strength was also improved. From Examples 86 to 91, those using synthetic polymers, semi-synthetic polymers, vegetable gums, and starch as paper strength enhancers have coating suitability such as coating smoothness, removal of porous membranes and wear resistance. Although improvement and improvement in tensile strength were observed, more favorable results were obtained when amphoteric or cationic polyacrylamide resins were used.

  From the results of Example 86 and Examples 94 to 100, when the content of the paper strength enhancer is 0.01 to 20 parts by mass with respect to 100 parts by mass of the fibrillated lyocell fiber, fiber aggregation hardly occurs, and the paper strength Since the network between fibers by the enhancer is sufficiently widened, fiber dropping and fluffing are suppressed, and a highly uniform surface can be obtained when combined. Also, the tensile strength was improved. From Example 86 and Examples 95 to 97, when 0.1 to 5 parts by mass of a paper strength enhancer was added to 100 parts of fibrillated lyocell fiber, the tensile strength was further strong and the wear resistance was excellent. A substrate could be obtained.

  From Examples 86 and 101, it is preferable to add a paper strength enhancer by internal addition to the papermaking slurry, or to add a paper strength enhancer by external addition to the nonwoven fabric. Since the agent was uniformly dispersed and uniformly adsorbed on the fibrillated lyocell fiber, the internal addition gave a more preferable result.

  On the other hand, since Comparative Examples 21 and 23 do not contain synthetic resin short fibers, the fibrillated lyocell fibers are partially taken up by the net, and the surface smoothness is low. Was big. Since Comparative Examples 20 and 22 did not contain fibrillated lyocell fiber, the denseness was low and the surface smoothness was low, so the surface variation when combined was large. Further, in Comparative Example 20 which did not contain fibrillated lyocell fiber, the paper strength enhancer could not adsorb with fibrillated lyocell fiber, and no increase in tensile strength was observed as compared with Comparative Example 22. Since Examples 105-108 did not contain a paper strength enhancer, the degree of suppression of fiber dropout and fluffing was slightly inferior, and fiber dropout seemed to occur during compounding. In Examples 105-108, both tensile strength and wear resistance were slightly inferior to Examples 86, 102-104.

<< Examples 109 to 140, Comparative Examples 24 to 36 >>

Examples 109-116, 119-127, 129-140, Comparative Examples 24, 28, 32
According to the number of blending parts shown in Table 15, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, both surfaces were brought into contact with a metal roll heated to 210 ° C., heat-treated, and further subjected to supercalendering to obtain a lithium secondary battery substrate.

Examples 117, 118, 128, Comparative Examples 25, 26, 29, 30, 33-36
According to the number of blending parts shown in Table 15, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 27
According to the number of parts shown in Table 15, the raw material was disaggregated in the water of a pulper, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The papermaking slurry was made by a wet method using a circular paper machine, but the base material could not be prepared because the fibrillated wholly aromatic polyamide fiber had no binding force.

Comparative Example 31
According to the number of parts shown in Table 15, the raw material was disaggregated in the water of a pulper, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The papermaking slurry was made by a wet method using a circular paper machine, but the base material could not be produced because the fibrillated acrylamide fiber had no binding force.

<Evaluation>
The lithium secondary battery base materials obtained in Examples 109 to 140 and Comparative Examples 24 to 36 were evaluated as follows, and the results are shown in Table 16.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Base material density]
The density was measured according to JIS C2111.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Coating properties]
In the manufacturing process of the separator, the coatability was evaluated according to the following criteria.
○: The coating could be carried out without any problems such as breakage of the base material or defects in which the fiber on the surface of the base material was pulled out and the roll became dirty.
Δ: Breakage of the substrate and roll contamination occurred, but the occurrence frequency was low and coating was possible.
X: Breaking of the base material and roll contamination occurred frequently, which hindered coating properties.

[Back-through]
In the manufacturing process of the separator, the strike-through was evaluated according to the following criteria.
○: The coating liquid does not penetrate the substrate at all.
Δ: Slightly penetrated, but there is no problem such that the back surface of the base material sticks to the roll of the coating apparatus.
X: It slipped through and the back surface of the base material stuck to the roll, causing problems such as inability to perform smooth coating.

[Heat-resistant]
The base material was cut into 200 mm width × 200 mm length, and allowed to stand in a constant temperature dryer at 200 ° C. for 3 hours, the shrinkage in the width direction and the length direction was calculated, and the average value was shown.

[Dendrite resistance]
A metal lithium foil was placed on one side of the base material and a positive electrode was placed on the opposite side of the base material and laminated, and an electrolyte was injected to prepare 100 laminate cells. The battery was charged at a constant current of up to 3.6 V at 0.5 mA / cm ² and further overcharged by applying 3.6 V for 24 hours. The case where an abnormal current flowed during this overcharge was regarded as an internal short circuit, the overcharge was stopped, the laminate cell was opened, and the generation state of lithium dendrite was confirmed. The ratio of the cell which lithium dendrite generate | occur | produced by overcharge and penetrated the base material was shown. It means that it is excellent in dendrite resistance, so that this ratio is small. The positive electrode used was a slurry in which an active material lithium cobaltate, a conductive auxiliary agent acetylene black, and a binder polyvinylidene fluoride mixed in a mass ratio of 90: 5: 5 were applied to an aluminum current collector. . As the electrolytic solution, a mixed solution in which 1 mol / l of LiPF ₆ was dissolved was used. The mixed solution is ethylene carbonate and diethyl carbonate in a mass ratio of 3: 7.

[Surface smoothness]
About the separator, the thickness of arbitrary 10 places was measured, the standard deviation (micrometer) was computed, and it was set as the parameter | index of surface smoothness. The smaller the standard deviation value, the better the surface smoothness.

[Electrolytic solution retention]
The separator was cut to 100 mm width × 100 mm, immersed in the electrolyte solution for 1 minute, suspended for 1 minute to cut off the excess electrolyte solution, and the mass W1 of the separator was measured. The value obtained by subtracting the mass W0 of the separator before holding the electrolytic solution from W1 and dividing the value W2 by W0 and multiplying by 100 was defined as the electrolytic solution retention rate (%). As the electrolytic solution, a mixed solution in which 1 mol / l of LiPF ₆ was dissolved was used. The mixed solution is ethylene carbonate and diethyl carbonate in a mass ratio of 3: 7.

  Since the base materials for lithium secondary batteries of Examples 109 to 127 and 130 to 140 are made of wet nonwoven fabric containing fibrillated heat resistant fibers, synthetic resin short fibers, and fibrillated lyocell fibers, heat resistance and dendrite resistance The coating solution containing the filler particles was prevented from seeping through, the surface smoothness of the coated surface was good, and the electrolyte solution retention rate was high. When Examples 113 to 116 and 134 are compared, the base materials for the lithium secondary batteries of Examples 113 and 134 are fibrillated heat-resistant fibers that are fibrillated wholly aromatic polyamide fibers or fibrillated acrylic fibers. The heat resistance was superior to the base materials for lithium secondary batteries of Examples 114 to 116 using the fibrillated heat resistant fiber.

  On the other hand, the base materials for lithium secondary batteries of Comparative Examples 24 and 28 do not contain fibrillated lyocell fibers, and are composed only of fibrillated heat-resistant fibers and synthetic resin short fibers, and thus have good heat resistance and dendrite resistance. However, the surface of the substrate was fuzzy, which hindered coating properties. The smoothness of the coated surface was poor due to the fuzz of the surface.

  Since the base materials for lithium secondary batteries of Comparative Examples 25 and 29 do not contain synthetic resin short fibers and consist only of fibrillated heat-resistant fibers and fibrillated lyocell fibers, heat resistance, electrolyte solution retention, and dendrite resistance Although its properties were good, it was easy to break during coating, which hindered coating properties.

  Although the base materials for lithium secondary batteries of Comparative Examples 26 and 30 do not contain synthetic resin short fibers and fibrillated lyocell fibers, and consist only of fibrillated heat resistant fibers and natural pulp, they have good dendrite resistance, It was easy to break at the time of coating, and it hindered coating properties. Since natural pulp has a large proportion of thick fiber diameters, the substrate surface was uneven, and the surface smoothness of the coated surface was poor.

  Comparative Examples 27 and 31 attempted to produce a base material for a lithium secondary battery using only fibrillated heat-resistant fibers. However, since the fibers have no binding force, it is not possible to produce a base material for a lithium secondary battery. There wasn't.

  Since the base materials for lithium secondary batteries of Comparative Examples 32 and 33 do not contain fibrillated heat-resistant fibers and fibrillated lyocell fibers, and are composed of only synthetic resin short fibers, they have heat resistance and dendrite resistance. It was inferior, and the coating liquid containing the filler particles was broken through, resulting in poor surface smoothness of the coated surface. Further, the filler particles were filled in the base material, and the pores inside the base material were closed, so that the electrolyte solution retention rate was extremely poor.

  Since the base material for a lithium secondary battery of Example 128 does not contain fibrillated heat-resistant fibers and consists only of synthetic resin short fibers and fibrillated lyocell fibers, it is compared with Examples 109 to 127 and 130 to 140. Thus, the heat resistance and dendrite resistance were slightly inferior, and there was a case where the coating was broken at the time of coating, and the coating property was slightly inferior.

  The base material for the lithium secondary battery of Comparative Example 34 does not contain fibrillated heat-resistant fibers and fibrillated lyocell fibers, and is composed only of synthetic resin short fibers and natural pulp, and therefore has poor heat resistance and dendrite resistance. It was. Since natural pulp has a large proportion of thick fiber diameters, the substrate has irregularities, the surface smoothness of the coated surface is poor, and the electrolyte retention rate is poor.

  The base material for a lithium secondary battery of Comparative Example 35 does not contain fibrillated heat-resistant fibers and synthetic resin short fibers, and consists only of fibrillated lyocell fibers, and therefore has poor heat resistance and dendrite resistance. It was easy to break at the time of construction, and it hindered coating properties.

  The base material for the lithium secondary battery of Comparative Example 36 does not contain fibrillated heat-resistant fibers and synthetic resin short fibers, and consists of fibrillated lyocell fibers and natural pulp, so that heat resistance and dendrite resistance are inferior. It was easy to break at the time of coating, and the coating property was hindered. Since natural pulp has a large proportion of thick fiber diameters, the substrate was uneven, and the surface smoothness of the coated surface was poor.

  In the base material for the lithium secondary battery of Example 129, the modified freeness of the fibrillated lyocell fiber exceeded 250 ml, so that the beating was insufficient and many thick fibers remained, and the thickness unevenness The surface smoothness of the coated surface was poor.

<< Examples 141-153, Comparative Examples 37-42 >>
Non-fibrillated lyocell fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 110 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC4”.

  Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 60 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC5”.

  Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 75 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC6”.

  Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 50 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC7”.

  Non-fibrillar lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) were repeatedly treated 40 times using a double disc refiner to produce fibrillated lyocell fibers. This is expressed as “FBC8”.

Examples 141-143, 145-147, 149-153, Comparative Examples 37, 39-42
In accordance with the number of parts shown in Table 17, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, and unstretched PET-based heat-fusible short fibers are adhered by a cylinder dryer at 130 ° C. to develop a nonwoven fabric strength, and a nonwoven fabric having a width of 50 cm. Was made. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Examples 144 and 148, Comparative Example 38
In accordance with the number of parts shown in Table 17, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The following evaluation was performed on the base materials for lithium secondary batteries obtained in Examples 141 to 153 and Comparative Examples 37 to 42, and the results are shown in Table 18.

[Measurement of pore diameter of substrate]
About the produced base material, it measured according to JIS K3832, ASTM F316-86, ASTM E1294-89 using the palm porometer CFP-1500A made from PMI, and the minimum pore diameter of each base material and the maximum pore diameter The values of dmax / dave are shown in Table 1.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability 1 of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Applicability 2 of substrate]
About the produced separator, the 1m x 1m sheet | seat was set | placed on the inspection table, light was irradiated from the back surface, generation | occurrence | production of the pinhole was confirmed by seeing passage of light, and the following reference | standard evaluated.
A: The porous membrane layer is homogeneous and no pinholes are generated.
○: There is a portion where the porous membrane layer is thin, but no light transmission is observed when observed with a microscope (100 times).
Δ: There is a portion where the porous membrane layer is thin, and light transmission is observed when observed with a microscope (100 times).
X: Light passes due to the occurrence of pinholes.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base materials for lithium secondary batteries obtained in Examples 141 to 151 are made of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers, and have a minimum pore diameter of 0.10 μm or more and a maximum Since the pore diameter was 20 μm or less, a good result was obtained that the structure had a dense structure and the surface variation when combined by surface coating was small.

  From the comparison of Examples 141 to 147, when the ratio dmax / dave between the maximum pore diameter dmax (μm) and the average pore diameter dave (μm) is 10.0 or less, the occurrence of unevenness in the porous membrane layer is reduced. Good results were obtained that no pinholes were observed. Further, in Example 147 in which the value of dmax / dave was greater than 10.0, there was a tendency for unevenness to occur in the porous membrane layer.

  From the comparison of Examples 141, 144, 145, 147, and 148, when the content of the fibrillated lyocell fiber is 5 to 80% by mass, the surface variation when combined by surface coating is small, and the strength is also high. Also, no loss of the porous membrane was confirmed. In Example 147 in which the content of the fibrillated lyocell fiber is less than 5% by mass, the surface variation tends to increase. In Example 148 in which the content of the fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  From a comparison between Examples 141, 149, and 150 and Example 151, it was found that the resin constituting the synthetic resin short fiber was a polyester resin, an acrylic resin, or a polyolefin resin. The variation was small, the strength was high, and no loss of the porous membrane was confirmed.

  On the other hand, since the base materials for lithium secondary batteries obtained in Comparative Examples 37 and 39 to 42 do not contain fibrillated lyocell fibers, surface irregularity occurs, the strength is low, and the porous film is detached. The degree was also larger than Examples 141-151.

  Further, the base material for lithium secondary battery obtained in Comparative Example 38 does not contain synthetic resin short fibers, and the minimum pore diameter is smaller than 0.10 μm, so that the strength is low and the degree of dropping of the porous film is also low. The results were larger than those of Examples 141-153.

  Furthermore, although the base material for lithium secondary batteries obtained in Example 153 contains synthetic resin short fibers and fibrillated lyocell fibers, the minimum pore diameter is smaller than 0.10 μm. Also, the degree of dropout was larger than that of Examples 141-151.

  The base materials for lithium secondary batteries obtained in Comparative Example 37, Example 152, and Comparative Examples 40-42 have a maximum pore diameter larger than 20 μm, so that the surface variation occurs and the strength is low. The degree of dropout and the degree of pinhole occurrence were also larger than those of Examples 141-151.

«Examples 154-165, Comparative Examples 43-48»

  Non-fibrillar lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) was repeatedly treated 50 times using a double disc refiner to produce fibrillated lyocell fiber 3.

Examples 154-159, 161-165, Comparative Examples 43, 45-48
According to the number of blending parts shown in Table 19, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, and unstretched PET-based heat-fusible short fibers are adhered by a cylinder dryer at 130 ° C. to develop a nonwoven fabric strength, and a nonwoven fabric having a width of 50 cm. Was made. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Comparative Example 44
In accordance with the number of parts shown in Table 19, the raw materials were mixed and disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 130 ° C. cylinder dryer to produce a 50 cm wide nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

Example 160
According to the number of blending parts shown in Table 19, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for paper making is made up using a wet method using a circular paper machine, dried by a cylinder dryer at 120 ° C., the PET core-sheath type heat-fusible short fibers are thermally bonded, and the nonwoven fabric strength is expressed. A nonwoven fabric having a width of 50 cm was produced. Next, the nonwoven fabric was brought into contact with a heat roll having a diameter of 1.2 m heated to 200 ° C. at a speed of 20 m / min and heat-treated. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<Evaluation>
The following evaluation was performed about the obtained base material for lithium secondary batteries in Examples 154 to 165 and Comparative Examples 43 to 48, and the results are shown in Table 20.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Substrate measurement]
About the base material, centerline average roughness Ra of the flow direction and the width direction measured three places of each base material based on the method prescribed | regulated to JISB0601-1982, and shows the average value in Table 22 It was.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base materials for lithium secondary batteries obtained in Examples 154 to 163 are made of nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers, and the center line roughness Ra is 3. Since it was 0 or less, it had a dense structure, and a good result was obtained that the variation in the surface when composited by surface coating was small.

  From the comparison of Examples 154 to 159, when the content of the fibrillated lyocell fiber is 5 to 80% by mass, the surface variation when combined by surface coating is small, the strength is high, and the porous membrane No dropout was confirmed. In Example 159 in which the content of the fibrillated lyocell fiber was less than 5% by mass, the surface variation was increased and the porous membrane was detached. In Example 158 in which the content of the fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  From the comparison of Examples 154 and 161-163, when the resin constituting the synthetic resin short fiber is a polyester resin, an acrylic resin, or a polyolefin resin, the variation in the surface when combined by surface coating is small, The strength was high, and no loss of the porous membrane was confirmed.

  On the other hand, the base material for a lithium secondary battery obtained in Comparative Examples 43 and 45 to 47 does not contain fibrillated lyocell fiber, and the center line average roughness Ra is larger than 3.0, so that the surface has a variation. Was generated, the strength was low, and the degree of dropping of the porous membrane was larger than that of Examples 154 to 163.

  Although the base materials for lithium secondary batteries obtained in Examples 164 and 165 contain synthetic resin short fibers and fibrillated lyocell fibers, the center line average roughness Ra is larger than 3.0. The results showed that the surface variation and the degree of removal of the porous membrane were larger than those of Examples 154 to 163.

  Moreover, since the base material for lithium secondary batteries obtained in Comparative Example 44 does not contain synthetic resin short fibers, the strength is low, and the degree of dropout of the porous membrane is also greater than those in Examples 154 to 163. became.

  Furthermore, although the base material for lithium secondary batteries obtained in Comparative Example 48 has a center line average roughness Ra of 3.0 or less in the flow direction and the width direction, it does not contain fibrillated lyocell fibers, The degree of dropout of the porous membrane was also higher than that of Examples 154 to 165.

<< Examples 166 to 187, Comparative Examples 49 to 53 >>
A fibrillated lyocell fiber 4 was obtained by repeatedly treating a fibrillated lyocell single fiber (fiber diameter: 15 μm, fiber length: 4 mm, manufactured by Coatles Co., Ltd.) 50 times using a double disc refiner.

  3. A fibrous material obtained by flash spinning from polyethylene is dispersed at a concentration of 2% by mass, and the obtained dispersion is charged into a homogenizer (trade name: 15M-8TA, manufactured by Gaulin) at room temperature. A polyethylene standard synthetic pulp having a Canadian standard freeness of 200 ml and a fiber length of 0.7 mm was obtained by passing 30 times under a pressure of 5 MPa. The average fiber diameter was measured by microscopic observation, and the average fiber length was measured according to TAPPI T232hm-85.

Examples 166 to 179, 184, Comparative Examples 49 to 53
For heat-resistant layer (A), according to the number of parts shown in Table 21, the raw materials are mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) is prepared under stirring by an agitator. did. As the hot melt layer (B), the raw materials are mixed together in accordance with the number of blending parts shown in Table 21, disaggregated in the water of the pulper, and a uniform papermaking slurry (1% concentration) is prepared under stirring by an agitator. did. The basis weight of each layer is adjusted to 6.0 g / m ² , the two slurries are combined using a circular two-layer paper machine, and a drying cylinder dryer (surface temperature 130 ° C.) is used. Then, the layers were heated and bonded, and unstretched PET-based heat-fusible short fibers and polyethylene-based synthetic pulp were bonded to develop the strength of the nonwoven fabric, thereby producing a nonwoven fabric having a width of 50 cm. Next, a super calendar process was performed to obtain a base material for a lithium ion secondary battery.

Example 180
According to the number of blending parts shown in Table 22, the raw materials were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. The slurry was made using a circular mesh single layer paper machine, adjusted to a basis weight of 12.0 g / m ² , and then dried using a drying cylinder dryer (surface temperature 130 ° C.). Stretched PET-based heat-fusible short fibers were bonded to develop the strength of the nonwoven fabric, thereby producing a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium ion secondary battery.

Examples 181 to 183, 185 to 187
For layer (I), the raw materials were mixed together according to the number of blending parts shown in Table 22, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. . For layer (II), the raw materials were mixed together according to the number of blends shown in Table 22, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. . Adjusting so that the basis weight of the layer (I) is 6.0 g / m ² and the basis weight of the layer (II) is 6.0 g / m ² , the two slurries are made into a two-layer net-making machine. Using a drying dryer (surface temperature 130 ° C.), the layers are heated and bonded together, and the heat-fusible short fibers are bonded to develop the strength of the nonwoven fabric, and the nonwoven fabric has a width of 50 cm. Was made. Next, a super calendar process was performed to obtain a base material for a lithium ion secondary battery.

<Evaluation>
The lithium ion secondary battery base materials obtained in Examples 166 to 187 and Comparative Examples 49 to 53 were evaluated as follows, and the results are shown in Table 23.

[Basis weight of base material]
Basis weight was measured according to JIS P 8124.

[Base material thickness]
The thickness was measured by a method defined in JIS B 7502, that is, by an outer micrometer at 5N load.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each substrate is passed through this slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried at 120 ° C. in an explosion-proof dryer, A separator having a porous film with a thickness of 3 μm was obtained.

[Applicability of substrate]
About the produced separator, thickness measurement of arbitrary 10 places was implemented, and the following reference | standard evaluated. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.
A: The difference in thickness is 0.8 μm or less.
○: The difference in thickness exceeds 0.8 μm and is 1 μm or less.
(Triangle | delta): The difference of thickness is 2 micrometers or less exceeding 1 micrometer.
X: The thickness difference exceeds 2 μm.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (N) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the smallest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 0.5N or more ○: 0.4N or more and less than 0.5N △: 0.3N or more and less than 0.4N ×: Less than 0.3N

[Existence of dropout]
About the produced separator, it cut and aligned in 50 mm width x 300 mm strip shape, the state of the porous membrane when wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed, and evaluated according to the following criteria.
A: There is no change in the state of the porous membrane.
○: No peeling occurred on the surface portion of the porous membrane.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

[Evaluation of heat resistance]
The produced separator was put into a 170 degreeC thermostat, heat-processed for 40 minutes, the shrinkage rate of each separator was measured, and heat resistance was evaluated. The shrinkage rate was measured as follows. A 50 mm x 50 mm sheet sample is cut out, the CD side of the sample is fixed with a clip and sandwiched between heat-resistant glass plates, stored in a thermostatic bath at 170 ° C for 30 minutes, taken out, and the length of the sheet sample is measured and tested. Compared to the previous length, the value with the percentage of reduction in length as the shrinkage is less than 2%, ◎ 2% or more and less than 5%, ○ 5% or more and less than 8% The heat resistance was evaluated as “Δ”, and “×” as 8% or more. In addition, when the heat resistance of a 20 μm thick polyethylene microporous membrane, which is a conventionally known lithium ion secondary battery separator, was evaluated, the polyethylene microporous membrane melted and contracted, and the shrinkage ratio was 30% or more. Met.

[Evaluation of shutdown (SD) characteristics]
Five sheet samples of 70 mm × 70 mm were cut out from the produced separator, and after measuring the Gurley air permeability with a Oken type air permeability meter, the sheet sample was held in a thermostat at 130 ° C. for 15 minutes. After taking out and allowing to cool, the Gurley permeability was measured with the Oken air permeability meter, and the Gurley permeability value of the separator after the heat treatment was divided by the Gurley permeability value of the separator before the treatment. The shut-off characteristics were evaluated by assigning a value of 20 or more to ◎, a value of 10 to less than 20, ◯, a value of 5 to less than 10, and a value of less than 5 to x.

  The base materials for lithium ion secondary batteries obtained in Examples 166 to 179 are composed of a heat-resistant layer (A) containing synthetic resin short fibers and fibrillated lyocell fibers, synthetic resin short fibers and polyethylene synthetic pulp. Since it is made of a nonwoven fabric having a heat-melting layer (B) to be contained, it has a dense structure and has a good result that the variation of the surface when combined by surface coating is small, and 170 ° C. In addition to being excellent in heat resistance, good results were obtained in which shutdown characteristics at 130 ° C. were exhibited.

  From the comparison between Example 166 and Examples 167 to 170, when the content of the polyethylene-based synthetic pulp that is a component of the hot melt layer (B) is 40 to 90% by mass, The variation was small, the strength was high, the drop-off of the porous film was not confirmed, and not only the heat resistance at 170 ° C. was excellent, but also a shutdown characteristic at 130 ° C. was exhibited. From a comparison between Example 166 and Examples 171 and 172, when the resin constituting the synthetic resin short fiber which is a component of the hot melt layer (B) is a polyester resin or an acrylic resin, the heat resistance at 170 ° C. is extremely high. Excellent results were obtained.

  From the comparison between Examples 166 and 173 and Example 174, when the resin constituting the synthetic resin short fiber, which is a component of the heat-resistant layer (A), is a polyester resin or an acrylic resin, it is combined by surface coating. The surface variation of the film was small, the strength was high, and the removal of the porous film was not confirmed. From the comparison between Example 166 and Examples 175 to 178, when the content of the fibrillated lyocell fiber, which is a component of the heat-resistant layer (A), is 10 to 80% by mass, The variation was small, the strength was high, and no loss of the porous membrane was confirmed. In Example 175 in which the content of the fibrillated lyocell fiber is less than 10% by mass, the surface variation tends to increase. In Example 178 in which the content of fibrillated lyocell fiber exceeded 80% by mass, the strength tended to decrease slightly.

  On the other hand, the base materials for lithium ion secondary batteries obtained in Comparative Examples 49 to 53 do not contain the fibrillated lyocell fiber in the heat-resistant layer (A), so the surface variation occurs and the strength is low. The degree of removal of the porous film was also larger than that of the example. Moreover, since the base material for lithium ion secondary batteries obtained in Examples 180 to 183 and 185 to 187 does not contain polyethylene-based synthetic pulp in the hot melt layer (B), a shutdown characteristic at 130 ° C. is exhibited. The result was not. Since the base material for a lithium ion secondary battery obtained in Example 184 does not contain synthetic resin short fibers in the hot melt layer (B), there is no entanglement between the polyethylene synthetic pulp and the synthetic resin short fibers. As a result, the surface strength was weakened, resulting in poor removal of the porous membrane.

  Moreover, since the base material for lithium ion secondary batteries obtained in Example 185 is a two-layer structure nonwoven fabric of the same composition and does not contain polyethylene-based synthetic pulp in the hot melt layer (B), at 130 ° C. Although the shutdown characteristic was not exhibited, the coating property, the puncture strength, the drop-off, and the heat resistance were the same as those obtained in Example 180, which is a single-layered nonwoven fabric. In addition, in the case of a two-layer structure nonwoven fabric, when making a nonwoven fabric having the same basis weight, the basis weight per net (one layer) can be reduced, so that there is an advantage that the paper making speed can be increased.

  The base material for lithium secondary batteries and the separator for lithium secondary batteries of the present invention can be suitably used for lithium ion secondary batteries such as lithium ion secondary batteries and lithium ion polymer secondary batteries.

This invention which solves the said subject consists of the following base materials (1)-(22) for lithium secondary batteries, and the separator (23) for lithium secondary batteries.
(1) A base material for a lithium secondary battery comprising a nonwoven fabric containing, as essential components, synthetic resin short fibers and fibrillated lyocell fibers,
(2) The base material for a lithium secondary battery according to the above (1), wherein the content of the fibrillated lyocell fiber is 5 to 80% by mass of the nonwoven fabric.
(3) The above-mentioned (1) or (2) wherein the modified freeness defined below of the fibrillated lyocell fiber is 0 to 250 ml and the length weighted average fiber length is 0.20 to 2.00 mm. 2) A base material for a lithium secondary battery as described above,
Modified freeness: Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.
(4) In the fiber length distribution histogram of the fibrillated lyocell fiber, the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 10% or more. A base material for a lithium secondary battery according to the above (1) or (2),
(5) In the fiber length distribution histogram of the fibrillated lyocell fiber, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5. The base material for a lithium secondary battery according to the above (4),
(6) In the fiber length distribution histogram of the fibrillated lyocell fiber, the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 50% or more. A base material for a lithium secondary battery according to the above (1) or (2),
(7) In the fiber length distribution histogram of the fibrillated lyocell fiber, the base material for a lithium secondary battery according to the above (6) having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak,
(8) The base material for a lithium secondary battery according to the above (1) or (2), wherein the synthetic resin constituting the synthetic resin short fiber is at least one selected from polyester resins, acrylic resins, and polyolefin resins. ,
(9) The above-mentioned (1) or (2), which comprises a nonwoven fabric containing core-sheath-type heat-fusible short fibers composed of a heat-fusion component and a non-heat-fusion component as at least one kind of synthetic resin short fibers Base material for lithium secondary battery,
(10) The base for a lithium secondary battery according to (9), wherein the core of the core-sheath type heat-fusible short fiber is polyethylene terephthalate and the sheath is a polyester copolymer,
(11) The base material for a lithium secondary battery according to (9) or (10), which is heat-treated,
(12) The base material for a lithium secondary battery according to (1) or (2), further comprising a nonwoven fabric containing a paper strength enhancer as an essential component,
(13) The base material for a lithium secondary battery according to (12), wherein the paper strength enhancer is at least one selected from a synthetic polymer, a semi-synthetic polymer, a vegetable gum, and starch,
(14) The lithium secondary battery substrate according to (12) above, wherein the paper strength enhancer is at least one selected from amphoteric or cationic polyacrylamide resins.
(15) The base for a lithium secondary battery according to any one of the above (12) to (14), wherein the paper strength enhancer is contained in an amount of 0.01 to 20 parts by mass with respect to 100 parts of the fibrillated lyocell fiber. Material,
(16) The base material for a lithium secondary battery according to (1) or (2) above, wherein the nonwoven fabric further comprises fibrillated heat-resistant fibers,
(17) The base material for a lithium secondary battery according to (16), wherein the fibrillated heat-resistant fiber is at least one selected from a fibrillated wholly aromatic polyamide fiber and a fibrillated acrylic fiber,
(18) The base material for a lithium secondary battery according to the above (1) or (2), wherein the base material has a minimum pore diameter of 0.10 μm or more and a maximum pore diameter of 20 μm or less,
(19) The base material for a lithium secondary battery according to (18), wherein the ratio dmax / dave between the maximum pore diameter dmax and the average pore diameter dave is 10.0 or less in the base material,
(20) The base material for a lithium secondary battery according to the above (1) or (2), wherein the center line average roughness Ra in the flow direction and the width direction of the base material is 3.0 or less,
(21) The above (1) or (2), wherein the base material for the lithium secondary battery is composed of a multilayer nonwoven fabric, and at least one layer is a layer containing the synthetic resin short fibers and the fibrillated lyocell fibers as essential components. Base material for lithium secondary battery,
(22) A heat-resistant layer (A) containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and a heat-melting layer (B) containing synthetic resin short fibers and polyethylene synthetic pulp as essential components The lithium secondary battery substrate according to (22),
(23) A treatment for impregnating or applying a slurry containing filler particles to a base material for a lithium secondary battery according to any one of (1) to (22) above, or impregnating or applying a slurry containing a resin. The separator for lithium secondary batteries which performs at least 1 process chosen from the process to carry out, the process which laminates and integrates a porous film, the process which impregnates or coats a solid electrolyte or a gel electrolyte.

Fiber length and fiber length distribution histogram of the lyocell fibers to fibrillate may be obtained by using a polarization characteristics obtained by applying laser light to the fiber, it can be measured using a commercially available fiber length measuring device . In the present invention, JAPAN TAPPI paper pulp test method no. It was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation) according to 52 “Fiber length test method for paper and pulp (automatic optical measurement method)”. The “fiber length”, “average fiber length” and “fiber length distribution” of the fibrillated lyocell fiber are “length-weighted fiber length”, “length-weighted average fiber length” and “ It means “length-weighted fiber length distribution”.

By using polyethylene terephthalate having excellent heat resistance as the core-sheath-type heat-fusible short fiber as in the base material for lithium secondary battery (10) of the present invention, the thermal dimensional stability of the base material is improved. It is preferable because the property can be improved. In addition, it is preferable to use a polyester copolymer for the sheath because the mechanical strength of the base material is improved. The polyester copolymer used in the sheath portion, isophthalic acid polyethylene terephthalate, sebacic acid, adipic acid, diethylene glycol, copolymerized with one or more compounds selected from 1,4 porcine down diol Those are preferred.

In the base material (13) for a lithium secondary battery in which the paper strength enhancer is at least one selected from a synthetic polymer, a semi-synthetic polymer, a vegetable gum, and starch, the coating suitability is more excellent. Examples of the synthetic polymer include polyacrylamide resin, polyethyleneimine resin, urea resin, polyethylene oxide (PEO), polyvinyl alcohol (PVA), and the like. Examples of the semi-synthetic polymer include dialdehyde starch, cationic starch, methyl cellulose, carboxymethyl cellulose, and hydroxymethyl cellulose. The vegetable gum, guar gum, locust bean gum, tragacanth gum and the like. Examples of the starch include corn starch, potato starch, wheat starch, tapioca starch and the like.

Furthermore, in the base material for a lithium secondary battery (14) in which the paper strength enhancer is at least one selected from amphoteric or cationic polyacrylamide resins, the cationic portion of the paper strength enhancer and the fibrillated lyocell fiber The anion part adsorbs and strengthens the bond between fibers. In addition, the amphoteric or cationic polyacrylamide is present between the fibers constituting the nonwoven fabric in a state where the polyacrylamide portion is self-adhered, so that a network having a moderate space is formed without the fibers being aggregated too much. . Therefore, it is possible to prevent more non-uniformity of the surface when complexed, also, it is possible to suppress fuzz of fibers composing the disconnection or nonwoven microfibers, such as lyocell fibers fibrillated.

As the amphoteric or cationic polyacrylamide resin, both linear and branched resins can be used. In particular, amphoteric polyacrylamide-based resin having an anionic and both functional groups of the cation, the cation portion is adsorbed on the lyocell fibers to fibrillate the anion is self bonded polyacrylamide each other, more strongly bound. Moreover, since it has both an anion part and a cation part, it is hard to receive the influence of the pH change in a system, and since the coupling | bonding between fibers can be reinforced stably, an amphoteric polyacrylamide type resin is more preferable.

As the radical polymerization initiator, a radical polymerization initiator such as a persulfate such as potassium persulfate or ammonium persulfate or a redox polymerization initiator in the form of a combination of these with a reducing agent such as sodium bisulfite can be used. An azo initiator may be used as the radical polymerization initiator. The amount of the radical polymerization initiator used is preferably 0.05 to 2% by mass, more preferably 0.1 to 0.5% by mass, based on the total mass of the monomers. Mannich modification , Hoffmann reaction, etc. are carried out after producing polyacrylamide or anionic polyacrylamide.

Fibrillated heat-resistant fibers, refiner heat resistant fibers, a beater, a mill, grinders, rotary homogenizer, an outer fixed to the inner blade circle cylindrical rotating at high speed to provide a shearing force by high speed rotary blade Double-cylindrical high-speed homogenizer that generates shearing force between the blades, ultrasonic crusher that is refined by ultrasonic impact, and a pressure difference of at least 3000 psi is applied to the fiber suspension to pass through a small-diameter orifice. It is obtained by processing using a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fiber by causing a high speed and colliding with this to rapidly decelerate.

When the fiber composition of each layer is changed, at least one layer may be a layer containing the synthetic resin short fiber and the fibrillated lyocell fiber as essential components. The function can be separated by changing the fiber composition of each layer. For example, heat-resistant layer containing a lyocell fibers synthetic resin short fiber and fibrillated as essential components and (A), hot-melt layer containing synthetic resin short fiber and a polyethylene-based synthetic pulp as an essential component and (B) In the case of the base material for a lithium ion secondary battery, the fibrillated lyocell fiber is entangled with the synthetic resin short fiber in the heat resistant layer (A), and the polyethylene synthetic pulp is short in the synthetic resin short fiber in the heat melting layer (B). Intertwined with the fiber, the smoothness of both front and back surfaces is high, it is excellent in denseness, the variation of the surface when combined by surface coating is reduced, and it has sufficient surface strength, so the composite can be removed. Less likely to occur. Furthermore, by laminating the heat-melting layer (B), when the temperature inside the battery becomes around 130 ° C., it melts and closes the micropores, exhibits shutdown characteristics, and further rises in temperature due to some malfunction. Even when the temperature is close to 170 ° C., the separator does not shrink due to the effect of the heat-resistant layer (A). That is, the base material for a lithium ion secondary battery according to the present invention has characteristics that the surface smoothness is higher, the denseness and uniformity are excellent, and the shutdown characteristic can be exhibited while having heat resistance.

Furthermore, the ratio dmax / dave between the maximum pore diameter dmax (μm) and the average pore diameter dave (μm) is preferably 10 or less. When dmax / dave is 10 or less, the denseness and uniformity are excellent, and more excellent in the prevention of dropping off of composites and pinholes when composited by surface coating such as filler particles or resin. ing. Preferably it is 8.0 or less. dmax / dave is more desirable because Bas variability in pore size of the substrate is small close to 1.0, the lower limit of dmax / dave, be about 2.0 is sufficient.

Further, the resulting lithium secondary battery substrate in Example 67, the proportion of fibers having a textiles length of more than 1.00mm is less than 50%, the strength is low, even falling off degree of the porous membrane, Results greater than Examples 53-65 were obtained.

[Puncture strength of substrate]
The substrate was cut into a 50 mm width strip. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load ( N ) at this time was measured and used as the puncture strength. The puncture strength was measured at five or more locations for one sample, and the lowest puncture strength among all the measured values was evaluated according to the following criteria.
◎: 1.0N or more ○: 0.8N or more and less than 1.0N ○ △: 0.5N or more and less than 0.8N △: 0.3N or more and less than 0.5N ×: Less than 0.3N

[Heat shrinkage of substrate]
The substrate was cut into a 100 mm width and a 150 mm length. The test piece was placed on a glass plate, fixed by sandwiching two sides perpendicular to the length direction with a clip, and allowed to stand in a constant temperature dryer set at 150 ° C. for 3 hours. The dimension in the width direction was measured, the ratio of dimensional change due to shrinkage relative to the original dimension was determined, and the heat shrinkage rate (%) was evaluated according to the following criteria.
A: Thermal shrinkage is less than 1.5% B: 1.5% or more and less than 2.0% B : 2 . 0% or more and less than 2.5% ×: 2.5% or more

Example 92
Amphoteric polyacrylamide resins paper strength agent to the pulper: adding (manufactured by Arakawa Chemical Industries, Ltd., trade name Polystron (R) 1810) so as to be 1.5 parts based on lyocell fibers 100 parts of fibrillated Then, after the dispersion, the raw materials were mixed together according to the number of blending parts shown in Table 13, disintegrated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. 0.5 parts relative to 100 parts of lyocell fiber fibrillated with amphoteric polyacrylamide resin paper strength enhancer (trade name: Polystron (registered trademark) 1280) in the pipe before the circular net It added so that it might become. This papermaking slurry was made up by a wet method using a circular paper machine and dried by a 120 ° C. cylinder dryer to prepare a nonwoven fabric. Next, a super calendar process was performed to obtain a base material for a lithium secondary battery.

<< Examples 166 to 187, Comparative Examples 49 to 53 >>
Using a double disc refiner, fibrillated non lyocell monofilament (fiber diameter 15 [mu] m, fiber length of 4 mm, manufactured by Kotoruzu Co.) 50 times iterate to the give the lyocell fibers 4 were fibrillated.

Examples 166 to 179, 184, Comparative Examples 49 to 53
For heat-resistant layer (A), according to the number of parts shown in Table 21, the raw materials are mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) is prepared under stirring by an agitator. did. For the hot-melt layer (B), according to the formulations parts shown in Table 21, the raw material are mixed together and allowed to macerated in water pulper under agitation by agitator, a uniform sheet-forming slurry (1% concentration) Prepared. The basis weight of each layer is adjusted to 6.0 g / m ² , the two slurries are combined using a circular two-layer paper machine, and a drying cylinder dryer (surface temperature 130 ° C.) is used. Then, the layers were heated and bonded, and unstretched PET-based heat-fusible short fibers and polyethylene-based synthetic pulp were bonded to develop the strength of the nonwoven fabric, thereby producing a nonwoven fabric having a width of 50 cm. Next, a super calendar process was performed to obtain a base material for a lithium ion secondary battery.

From the comparison between Example 166 and Examples 167 to 170, when the content of the polyethylene-based synthetic pulp that is a component of the hot melt layer (B) is 40 to 90% by mass, The variation was small, the strength was high, the drop-off of the porous membrane was not confirmed , and not only the heat resistance at 170 ° C. was excellent, but also a shutdown characteristic at 130 ° C. was exhibited. From a comparison between Example 166 and Examples 171 and 172, when the resin constituting the synthetic resin short fiber which is a component of the hot melt layer (B) is a polyester resin or an acrylic resin, the heat resistance at 170 ° C. is extremely high. Excellent results were obtained.

Claims (23)

  A base material for a lithium secondary battery comprising a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components.   The base material for a lithium secondary battery according to claim 1, wherein the content of the fibrillated lyocell fiber is 5 to 80% by mass of the nonwoven fabric. 3. The lithium bismuth according to claim 1, wherein the fibrillated lyocell fiber has a modified freeness as defined below of 0 to 250 ml and a length weighted average fiber length of 0.20 to 2.00 mm. Secondary battery substrate.
Modified freeness: Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.   The fiber length distribution histogram of the fibrillated lyocell fiber has a maximum frequency peak between 0.00 and 1.00 mm, and the ratio of fibers having a fiber length of 1.00 mm or more is 10% or more. The base material for lithium secondary batteries of 1 or 2.   In the fiber length distribution histogram of the fibrillated lyocell fiber, the gradient of the ratio of fibers having a fiber length of 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5 or less. The base material for lithium secondary batteries of Claim 4.   The fiber length distribution histogram of the fibrillated lyocell fiber has a maximum frequency peak between 0.00 and 1.00 mm, and a ratio of fibers having a fiber length of 1.00 mm or more is 50% or more. The base material for lithium secondary batteries of 1 or 2.   The base material for lithium secondary batteries according to claim 6, wherein the fiber length distribution histogram of the fibrillated lyocell fiber has a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak.   The base material for a lithium secondary battery according to claim 1 or 2, wherein the synthetic resin constituting the synthetic resin short fiber is at least one selected from a polyester resin, an acrylic resin, and a polyolefin resin.   The base for a lithium secondary battery according to claim 1 or 2, comprising a non-woven fabric containing a core-sheath type heat-fusible short fiber comprising a heat-fusion component and a non-heat-fusion component as at least one kind of synthetic resin short fibers. Wood.   The base material for a lithium secondary battery according to claim 9, wherein the core portion of the core-sheath type heat-fusible short fiber is polyethylene terephthalate, and the sheath portion is a polyester copolymer.   The base material for lithium secondary batteries according to claim 9 or 10, which is heat-treated.   Furthermore, the base material for lithium secondary batteries of Claim 1 or 2 which consists of a nonwoven fabric containing the paper strength enhancer as an essential component.   The base material for a lithium secondary battery according to claim 12, wherein the paper strength enhancer is at least one selected from a synthetic polymer, a semi-synthetic polymer, a vegetable gum, and starch.   The base material for a lithium ion battery according to claim 12, wherein the paper strength enhancer is at least one selected from amphoteric or cationic polyacrylamide resins.   The base material for lithium secondary batteries according to any one of claims 12 to 14, wherein the paper strength enhancer is contained in an amount of 0.01 to 20 parts by mass with respect to 100 parts of the fibrillated lyocell fiber.   Furthermore, the base material for lithium secondary batteries of Claim 1 or 2 in which a nonwoven fabric contains a fibrillated heat-resistant fiber.   The base material for a lithium secondary battery according to claim 16, wherein the fibrillated heat-resistant fiber is at least one selected from a fibrillated wholly aromatic polyamide fiber and a fibrillated acrylic fiber.   The base material for a lithium secondary battery according to claim 1 or 2, wherein the base material has a minimum pore diameter of 0.10 µm or more and a maximum pore diameter of 20 µm or less.   The base material for a lithium secondary battery according to claim 18, wherein a ratio dmax / dave between the maximum pore diameter dmax and the average pore diameter dave is 10.0 or less.   The base material for lithium secondary batteries according to claim 1 or 2, wherein a center line average roughness Ra in a flow direction and a width direction of the base material is 3.0 or less.   3. The lithium secondary battery according to claim 1 or 2, wherein the base material for the lithium secondary battery is made of a multilayered nonwoven fabric, and at least one layer is a layer containing the synthetic resin short fiber and the fibrillated lyocell fiber as essential components. Base material.   A heat-resistant layer (A) containing, as essential components, synthetic resin short fibers and fibrillated lyocell fibers, and a heat-melting layer (B) containing synthetic resin short fibers and polyethylene synthetic pulp as essential components. 21. The base material for a lithium secondary battery according to 21.   A treatment for impregnating or applying a slurry containing filler particles to a substrate for a lithium secondary battery according to any one of claims 1 to 22, a treatment for impregnating or applying a slurry containing a resin, a porous film A separator for a lithium secondary battery, which is subjected to at least one treatment selected from a treatment for laminating and integrating, and a treatment for impregnating or coating a solid electrolyte or a gel electrolyte.

Images