JP4876387B2 - Biaxially oriented microporous film and method for producing the same - Google Patents

Description

  The present invention relates to a biaxially oriented microporous film and a method for producing the same. More specifically, the present invention has fine pores, low Gurley permeability, i.e., excellent air permeability, good slipperiness, high stress during stretching, and excellent film winding. Furthermore, the present invention relates to a biaxially oriented microporous film excellent in heat resistance (low thermal shrinkage) and useful for separators such as electrolytic capacitors and lithium batteries, separation membranes, air permeable waterproof sheets and filters, and a method for producing the same.

As a conventional white film or porous film technique, there is a method for producing a polypropylene microporous film in which a composition comprising a polypropylene resin and a polymer having a higher melting crystallization temperature than that of the polypropylene resin and a β crystal nucleating agent is uniaxially stretched ( For example, see Patent Document 1). However, in Patent Document 1, a β crystal nucleating agent phthalocyanine or quinacridone has a low β crystal production rate and a polymer having a melt crystallization temperature higher than that of polypropylene resin is added in an amount of 15 parts by weight or more. Since it exceeded 10,000 sec / 100 cc, the air permeability was low, the surface roughness was large, and the mechanical strength was low, there were cases where the polymer dropped off or the film was broken in the film forming process and the secondary processing process. Also, there are biaxially stretched film porous films containing an amide compound-based β crystal nucleating agent and methods for producing the same (see, for example, Patent Documents 2 and 3). In Patent Documents 2 and 3, the air permeability value is low and the air permeability is excellent, but the friction coefficient is high and the slip property is inferior, and the heat resistance (low heat shrinkage), the long winding property and the secondary workability are inferior. It is. There is a method for producing a microporous membrane that is drawn by adding a β crystal nucleating agent and resin particles to a polypropylene resin (for example, Patent Document 4). In Patent Document 4, the β crystal nucleating agent and the resin particles are used in combination for the purpose of preventing the particles from falling with a high porosity, but in order to obtain a high porosity, the resin particles are added in a high amount of 20 to 50 parts by weight. For this reason, in some cases, particle dropping or film tearing occurs in the film forming process and the secondary processing process. In addition, there is a microporous film having a high β crystal fraction that defines an average pore size, nitrogen permeability coefficient, and stretching strength, and a method for producing the same (for example, Patent Document 5). In Patent Document 5, a polypropylene resin having a high β crystal ratio is stretched to a low area ratio at a relatively low temperature to form a microporous film. However, the film is inferior in slipperiness, and is wrinkled and broken during secondary processing. The heat resistance (low thermal shrinkage rate) was inferior.
Japanese Patent Publication No. 7-5780 (Claims 1, 4, 1 to 11 lines, Examples 1 to 4) Japanese Patent No. 3341358 (Claims 1-2, Examples 1-5) JP-A-7-33895 (Claims 1 to 5, Examples 1 to 17) JP-A-9-176352 (Claim 1, Examples 1 to 12) Japanese Patent No. 25009030 (Claims 1 to 8, Examples 1 to 7)

  The present invention has excellent air permeability, is excellent in slipping and wrinkle generation necessary for long roll-up property in a film production (film formation) step, and is excellent in heat resistance (low heat shrinkage). Another object of the present invention is to provide a biaxially oriented microporous film having excellent processability and printing characteristics.

In order to solve the above-described problems, the present invention mainly has the following configuration. That is, the present invention comprises 90 to 99.8% by weight of a polypropylene resin having a β crystal ratio of 50 to 99% and 0.2 to 10% by weight of a resin that is incompatible with the polypropylene resin, and has a Gurley air permeability of 5%. a ~10000sec / 100cc, Ri range der coefficient of static friction μs is 0.2 to 2 when the superposed films sided, 80 ° C. · 1 hour longitudinal thermal shrinkage rate during heating the film (MD direction) The width direction (TD direction) is 3% or less, the maximum surface roughness Rt of at least one side is in the range of 0.5 to 2 μm, the average surface roughness Ra is in the range of 0.05 to 0.3 μm, and the length of the film in the range direction (MD direction) of a 2% elongation when the stress (F2 value) of 5～12MPa, and porosity is biaxially oriented microporous film according to claim 42 to 80% der Rukoto .

In a preferred embodiment, an air gap ratio of 50% to 80%, a film thickness of 5 to 100 [mu] m, beta crystal ratio 50 to 99% of polypropylene resin, beta 0.01 to 2 wt% content of nucleating agent And a resin incompatible with the polypropylene resin is one or more resins having a glass transition point (Tg) of 100 to 160 ° C. or a melting temperature of 200 to 270 ° C., or an ethylene / α-olefin copolymer. It is a biaxially oriented microporous film characterized by being.

  Further, as a production method thereof, after mixing a mixed composition of a polypropylene resin, a β crystal nucleating agent and a resin incompatible with the polypropylene resin at a melting temperature or higher of the incompatible resin, the mixed resin is mixed at 180 ° C. to 240 ° C. A sheet extruded by melt extrusion into a sheet at ℃, kept at a temperature of 80 ℃ to 150 ℃ for 1 second to 60 seconds, and cooled and solidified was stretched 2 to 7 times at a temperature of 80 ℃ to 130 ℃, and then 120 to 145 ℃ This is a method for producing a biaxially oriented microporous film, wherein the film is stretched 3 to 12 times at a temperature and heat-treated at 130 to 160 ° C. for 1 to 10 seconds.

  According to the present invention, as described below, a biaxially oriented microporous film having excellent characteristics for separators such as electrolytic capacitors and lithium batteries, separation membranes, air permeable waterproof sheets, and filters can be provided.

  (1) High porosity, low Gurley air permeability, excellent electrolyte solution retention when used as an electrical element separator, and excellent air permeability and waterproofness.

  (2) Good slipperiness, excellent wrinkle resistance, high stress during stretching, and excellent long winding and secondary slitting properties during film formation.

  (3) It has a low thermal shrinkage rate and excellent thermal dimensional stability, excellent secondary processability when laminated with another substrate as a separation membrane or a gas-permeable moisture-proof sheet, and excellent heat resistance as a separator.

  Hereinafter, the best mode for obtaining the film of the present invention and the case where the film of the present invention is applied to a battery separator or a moisture-proof moisture-proof sheet will be described as examples.

  The intrinsic viscosity [η] of a polypropylene resin having a β crystal ratio of 50 to 99% (hereinafter abbreviated as β crystal PP) used in the biaxially oriented microporous film of the present invention is preferably 1.0 to 3 dl / g. Is preferably from 1.2 to 2.5 dl / g because the biaxial stretchability is good. Further, the isotactic index (II) is preferably 85% or more, and preferably 90% or more, since the mechanical strength and crease resistance are increased. The melt flow rate (MFR) is in the range of 1.0 to 30 g / 10 min (230 ° C., 2.16 kg) in terms of extrudability and openability (improvement of pore uniformity and porosity). preferable.

  The β crystal PP may be copolymerized with a second component other than polypropylene, for example, ethylene, butene, hexene, etc., in a small amount randomly or in a block, and when ethylene is copolymerized in an amount of 1 to 5% by weight, In some cases, uniformity and wrinkle resistance are improved.

  Also, known additives such as antioxidants, heat stabilizers, antistatic agents, slipping agents, antiblocking agents, polyterpene resins, petroleum resins, fillers, and the like are included to such an extent that the production process and film properties are not deteriorated. Also good.

The β crystal ratio of the β crystal PP of the microporous film of the present invention needs to be in the range of 50 to 99%, more preferably 60 to 95%, and still more preferably 70 to 90%. . If the β crystal ratio is less than 50%, it is difficult to obtain uniform holes in the thickness direction of the film, the through-hole property is lowered, and the value of the Gurley air permeability is increased. On the other hand, if the β crystal ratio exceeds 99%, it is difficult to satisfy both the Gurley permeability and the mechanical strength due to the formation improvement, and the film forming stability is inferior.

Here, the β crystal ratio of the β crystal PP of the present invention refers to a β crystal PP chip or a biaxially oriented white film in accordance with JIS K-7122 using a scanning differential calorimeter (DSC). In a nitrogen atmosphere, the 5 mg sample was heated to 250 ° C. at a rate of 20 ° C./minute, held for 5 minutes, then cooled to 20 ° C. at a cooling rate of 20 ° C./minute, and then again 20 ° C./minute. When the temperature is raised at a rate of 150 ° C. to 157 ° C., the endothermic peak melting heat (ΔHu-1) accompanying melting of the β-crystal derived from polypropylene resin having a peak between 140 ° C. and 157 ° C. From the heat of fusion (ΔHu−2) of the endothermic peak accompanying the melting of the crystal derived from polypropylene resin other than the β crystal, the β crystal ratio (%) = {ΔHu−1 / (ΔHu-1 + ΔHu-2)} × 100 (1)
In addition, when there is an endothermic peak in the above temperature range but it is unclear whether it is due to the melting of β crystal, in addition to the result of DSC, the sample obtained by melting and crystallizing the sample under the following specific conditions is a wide angle. Using the X-ray diffraction method, the presence of a (300) plane diffraction peak observed near 2θ = 16 ° due to the β crystal may be determined as “having β crystal activity”.

Β crystal ratio of the β crystal PP (sometimes hereinafter referred to as K _A) To 50 to 99% is preferably added a β crystal nucleating agent to the polypropylene resin, the addition amount β crystal nucleating agent However, the range of 0.01% by weight to 2% by weight is preferable. If the addition amount is less than 0.01% by weight, it is difficult to make the β crystal ratio 50% or more, and if it is 2% by weight or more, the effect is balanced, and 2% by weight or less is preferable from the viewpoint of economy.

  Examples of the β crystal nucleating agent include, for example, the publicly known document Journal of Applied Polymer Science, Vol. 86, 531-539, 633-638 (2002) 2002 Wiley Periodicals, Inc. “NJ Star NU-100” manufactured by Shin Nippon Rika Co., Ltd. and “Bepol” manufactured by SUNOCO. Among them, an amide compound represented by the general formula represented by the following formula (2) is particularly preferable because of its high β crystal generation effect.

R ₁ —NHCO—R ₂ —CONH—R ₃ (2)
R ₂ in the formula represents a saturated or unsaturated aliphatic, alicyclic or aromatic dicarboxylic acid residue having ₁ to 28 carbon atoms or an amino acid residue, and R ₁ and R ₃ are the same or It is represented by a different cycloalkyl group having 3 to 18 carbon atoms and a cycloalkenyl group having 3 to 12 carbon atoms.

  Specific examples of the amide compound of the general formula (2) include adipic acid dianilide, peric acid dianilide, N, N′-dicyclohexyl terephthalamide, N, N′-dicyclohexyl-1,4-cyclohexanedicarboxamide, N , N′-dicyclohexyl-2,6-naphthalene dicarboxyamide, N, N′-dicyclohexyl-4,4′-biphenyldicarboxamide, N, N′-bis (p-ethylphenyl) hexanediamide, N, And N′-bis (4-cyclohexylphenyl) hexanediamide, p- (N-cyclohexanecarbonylamino) benzoic acid cyclohexylamide, δ- (N-benzoylamino) -N-valeric acid anilide, etc. N, N'-Disic from the effect of β crystal formation and dispersibility in polypropylene resin Rohexyl-2,6-naphthalenedicarboxamide is preferred.

  Next, the present invention needs to be a mixture of 90 to 99.8% by weight of β-crystal PP having a β-crystal ratio of 50 to 99% and 0.2 to 10% by weight of a resin incompatible with polypropylene resin. If the content of the incompatible resin is less than 0.2% by weight, the slipperiness is inferior, the heat shrinkage rate is increased and the heat resistance is deteriorated, which is not preferable, and the pores are crushed in the film forming process and the secondary processing process. In some cases, the Gurley air permeability may increase, which may be undesirable. If it exceeds 10% by weight, the surface roughness becomes too large, and when used as a separator, the adhesion to the electrode plate may be deteriorated, or the laminate strength with other substrates may be reduced, and the film In some cases, excessive voids are generated and film breaks occur frequently, resulting in deterioration of film formation stability. The amount of the incompatible resin mixed with β-crystal PP is more preferably in the range of 0.5 to 8% by weight in terms of quality stability.

  Here, “compatible” means that two or more types of molten mixtures interact with each other, and the melting temperature Tm of the mixture or the peak of the glass transition point Tg is 1 or less. Incompatible means the mixture. Each of which a single peak is observed.

  The incompatible resin is not particularly limited, but polyethylene (high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene, linear low density polyethylene obtained by metallocene catalyst method, ultra low density polyethylene), polymethylpentene -1, olefin polymers such as polybutene and cyclic olefin copolymer, polystyrene, polyamide, polyimide, polyester, polycarbonate, and the like, and two or more of these may be used in combination. In particular, the incompatible resin is preferably at least one resin having a glass transition point (Tg) of 100 to 160 ° C. or a melting temperature of 200 to 270 ° C. The incompatible resin is preferably contained as a pore core. It is difficult to form fine and uniform pores only by adding β-crystal PP alone or incompatible resin alone, and by containing it at the same time, the dispersion diameter of the incompatible resin is reduced, and the pores generated by stretching are further reduced. The film can be uniformly miniaturized, and as a result, the Gurley permeability, slipperiness and heat resistance (low heat shrinkage) of the film can be improved, and further the mechanical strength can be improved. In particular, there is a part that is still unclear as a mechanism for improving the permeability, but the incompatible resin is formed when a very fine void is formed when the crystal form of polypropylene is changed from β crystal to α crystal during stretching. This is thought to be due to peeling at the interface.

  Further, as ethylene / α-olefin copolymers of incompatible resins, (linear) low density polyethylene (LLDPE), very low density polyethylene (VLDPE), ethylene butene rubber (EBR), ethylene propylene rubber (EPR) , Propylene / butene rubber (PBR), ethylene vinyl acetate (EVA), ethylene / ethacrylate (EEA), ethylene / methyl methacrylate (EMMA), ethylene / propylene / diene copolymer (EPDM), isoprene rubber (IR), styrene / When rubber-like polymers such as butadiene rubber (SBR), hydrogenated styrene rubber (H-SBR), styrene / butylene / styrene copolymer (SBS), styrene / ethylene / butylene / styrene copolymer (SEBS) are added. , Effect of improving film formation stability High, it is preferably used since thereby also improving air permeability. Among them, the ethylene / α-olefin copolymer obtained by the metallocene catalyst method is highly effective, and ultra low density polyethylene having a density of 0.86 to 0.90 is particularly preferable, and “engage” (manufactured by DuPont Dow) or “Kernel” (manufactured by Mitsubishi Chemical Co., Ltd.) and the like are exemplified, and the dispersibility in polypropylene resin is good, the effect of improving the film-forming stability is high, and the air permeability is improved accordingly, which is preferable. The amount of the rubbery polymer added is preferably 1 to 5% by weight because the film-forming property is improved without lowering the mechanical strength, particularly the F2 value, and without deteriorating the heat shrinkage rate. If the addition amount is less than 1% by weight, the effect of addition is not observed, and if it exceeds 5% by weight, poor dispersion occurs, gel-like protrusions are formed, the F2 value decreases greatly, and the heat shrinkage rate increases. Since it may be, it is not preferable. As an incompatible resin, by using one or more kinds of resins having a glass transition point (Tg) of 100 to 160 ° C. or a melting temperature of 200 to 270 ° C. and a rubbery polymer, each additive effect is synergistic. Sometimes it can be obtained.

  In order to obtain a biaxially oriented microporous film having through-holes from the front to the back of the film of the present invention, first, crystalline PP, β-crystal nucleating agent and incompatible resin are mixed at a temperature equal to or higher than the melting temperature of the incompatible resin. It is preferable that the β crystal nucleating agent and the incompatible resin are sufficiently finely dispersed by melting and mixing at a temperature of 5 ° C. Melting and mixing at a temperature lower than the melting temperature of the incompatible resin is not preferable because the dispersibility of the incompatible resin is deteriorated, the film is frequently broken, and the coefficient of friction of the film is increased. Next, the mixed resin is melt-extruded at a temperature of 180 ° C. to 240 ° C. When the melt extrusion temperature is less than 180 ° C., extrusion failure occurs. When melt extrusion is performed at a temperature higher than 240 ° C., the dispersion diameter of the incompatible resin is increased, and the effect of lowering the friction coefficient and the heat shrinkage ratio is reduced. Next, the melt-extruded sheet is held for 1 second to 10 seconds on a casting drum maintained at a temperature of 80 ° C. to 150 ° C., preferably 100 ° C. to 130 ° C., and the β crystal ratio is 50% or more. The sheet preferably has a β crystal ratio of 70% or more. If the β crystal ratio of the sheet is less than 50%, the Gurley air permeability of the biaxially stretched film is increased, which is not preferable. Subsequently, the film is made to have a porosity of 20% or more by longitudinally stretching the sheet at a temperature of 80 ° C. to 130 ° C. 2 to 7 times. Is stretched 5 times or more, whereby the porosity becomes 50 to 80%, through-holes are obtained, and a biaxially oriented microporous film having a Gurley air permeability of 5 to 10000 sec / 100 cc is obtained. Furthermore, the heat shrinkage rate at the time of heating at 80 ° C. for 1 hour can be reduced to 3% or less by subsequent heat treatment at 130 ° C. to 160 ° C. for 1 second to 10 seconds.

  The film of the present invention is particularly suitably used as a battery separator or an air permeable waterproof sheet, and the film characteristics require Gurley air permeability, surface smoothness, and heat resistance (low thermal shrinkage). In the biaxial stretching step, it is important that the thermal deformation of the nuclei of the vacancies is small and the generated vacancies are not crushed. If the glass transition point (Tg) of the incompatible resin is 100 ° C. or higher, or the melting temperature is 200 ° C. or higher, the thermal deformation of the β-crystal PP of the matrix and the incompatible resin differs in the biaxial stretching process, and the β-crystal Peeling between the PP and the incompatible resin occurs to form pores, and the required Gurley permeability, slipperiness, and heat resistance (low heat shrinkage) are obtained. On the other hand, a glass transition point (Tg) of 160 ° C. or a melting temperature exceeding 270 ° C. is not preferable because melt extrudability and sheeting become difficult and productivity decreases. That is, in order to achieve both film formation stability and pore formation, the incompatible resin is uniformly dispersed in the β-crystal PP at a melt extrusion temperature of 200 ° C. to 270 ° C. It is preferable that the incompatible resin is not deformed similarly to the β-crystal PP in the range of the stretching temperature of 100 to 160 ° C.

  Examples of the incompatible resin having a glass transition point (Tg) of 100 to 160 ° C. include cyclic polyolefin, polycarbonate, polymethyl methacrylate, polyphenylene oxide, and liquid crystal resin (LCP). Among these, polycarbonate (hereinafter abbreviated as PC) is considered due to void-forming properties, handleability (undried), production cost (raw material price), dispersibility in PP, hydrolysis resistance, etc. due to interfacial peeling with β-crystal PP. Is preferred).

  The polycarbonate is a polymer produced by reacting an aromatic dihydroxy compound or a small amount thereof with phosgene, and the aromatic dihydroxy compound or a small amount of the polyhydroxy compound is carbonated. It can also be produced by a transesterification reaction with a diester. Furthermore, if necessary, a trifunctional compound and a molecular weight regulator can also be used for the reaction as branching agents. This polycarbonate is a linear or branched thermoplastic aromatic polycarbonate.

  Examples of the aromatic dihydroxy compound include 2,2-bis (4-hydroxyphenyl) propane (hereinafter sometimes abbreviated as bisphenol A), tetramethylbisphenol A, tetrabromobisphenol A, bis (4-hydroxy Phenyl) -p-isopropylbenzene, hydroquinone, resorcinol, 4,4′-dihydroxyphenyl, bis (4-hydroxyphenyl) ether, bis (4-hydroxyphenyl) sulfone, bis (4-hydroxyphenyl) sulfoxide, bis (4 -Hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) ketone, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, etc. Bisphenol A is special Preferred.

  In order to obtain a branched polycarbonate, phloroglucin, 4,6-dimethyl-2,4,6-tri (4-hydroxyphenyl) heptene-2, 4,6-dimethyl-2,4,6-tri (4 -Hydroxyphenyl) heptane, 2,6-dimethyl-2,4,6-tri (4-hydroxyphenyl) heptene-3, 2,6-dimethyl-2,4,6-tri (4-hydroxyphenyl) heptane, Polyhydroxy compounds exemplified by 1,3,5-tri (4-hydroxyphenyl) benzene, 1,1,1-tri (4-hydroxyphenyl) ethane, and 3,3-bis (4-hydroxyaryl) oxy Dihydroxylation of indole [= isatin (bisphenol A)], 5-chloroisatin, 5,7-dichloroisatin, 5-bromoisatin and the like Some of the objects, for example, to replace the 0.1 to 2 mol% polyhydroxy compound.

  Furthermore, monovalent aromatic hydroxy compounds suitable for adjusting the molecular weight include m- and p-methylphenol, m- and p-propylphenol, p-bromophenol, p-tertiary-butylphenol and p-length. Chain alkyl substituted phenols and the like.

  In the polycarbonate used as the incompatible resin of the present invention, it is preferable to use bis (4-hydroxyphenyl) alkane compound, particularly preferably bisphenol A as the main raw material. Moreover, the polycarbonate copolymer obtained by using together 2 or more types of dihydroxy compounds, and the branched polycarbonate obtained by using together a small amount of trivalent phenolic compounds are also preferable. Other resins such as polyethylene terephthalate, polybutylene terephthalate, and polystyrene may be copolymerized.

  The weight average molecular weight (Mw) of the PC is 30000 or less, preferably 20000 or less, and the MFR is 10 or more (300 ° C., 1.2 kg), preferably 20 or more. It is preferable because the bubbles are uniform.

  Moreover, when the melting temperature of the incompatible resin is in the range of 200 to 270 ° C., the incompatible resin is finely dispersed when melt-kneaded with β-crystal PP, and the biaxial stretching temperature of the polypropylene film is 110 to 110. Thermal deformation is suppressed at 150 ° C., the pore shape can be maintained, and heat resistance is further improved, which is preferable. If the melting temperature of the incompatible resin is less than 200 ° C., the amount of pores formed by biaxial stretching may be insufficient. On the other hand, when the melting temperature exceeds 270 ° C., the dispersibility in the polypropylene film is deteriorated and it becomes difficult to obtain uniform pores.

  Examples of the incompatible resin having a melting temperature of 200 to 270 ° C. include polymethylpentene, syndiotactic polystyrene, polyethylene terephthalate, polybutylene terephthalate, and polyamide. Among these, it is particularly preferable to use polymethylpentene (hereinafter abbreviated as PMP) from the viewpoints of handleability, dispersibility in β-crystal PP, fine pore formation, and film surface roughness.

  As the PMP, those having an MFR of 5 to 100 g / 10 min, preferably 10 to 50 g / 10 min at 260 ° C. and 5 kg are preferable because of good dispersibility in a polypropylene film. It is preferable because uniform and fine pores can be formed.

  Moreover, it is preferable that the average dispersion particle diameter of this incompatible resin at this time is the range of 0.2-2 micrometers. If the average dispersed particle size is less than 0.2 μm, the friction coefficient is high and the slipping property is poor, and if it exceeds 2 μm, the pore diameter increases and surface cleaving or film tearing may occur.

  The Gurley permeability of the film of the present invention needs to be in the range of 5 to 10000 sec / 100 cc. When the Gurley air permeability exceeds 10,000 sec / 100 cc, it indicates that the through-hole property is extremely low, and it cannot be used as a battery separator, a gas permeable waterproof sheet, or a filter. Moreover, if the Gurley air permeability is less than 5 sec / 100 cc, it indicates that the through-hole property is extremely high, and film breakage may occur due to the tension in the film forming step and the secondary processing step, which is not preferable. In the present invention, the Gurley air permeability, which is one of the measures of air permeability of the obtained microporous film, is the addition amount of the β crystal nucleating agent added to the polypropylene resin constituting the film, and the production process thereof. Crystallization conditions (metal drum temperature, peripheral speed of the metal drum, thickness of the unstretched sheet to be obtained, etc.) and the stretching conditions (stretching direction (longitudinal or lateral), stretching method) (Longitudinal or lateral uniaxial stretching, longitudinal-horizontal or lateral-longitudinal sequential biaxial stretching, simultaneous biaxial stretching, re-stretching after biaxial stretching, etc.), stretching ratio, stretching speed, stretching temperature, etc.).

  Further, when used as a battery separator, as one measure of the through-hole property and the electrolyte permeability, the liquid paraffin permeation time is preferably 0.1 to 60 seconds / 25 μm. Here, the liquid paraffin permeation time is the time when the liquid paraffin has landed on the film surface when liquid paraffin is dripped onto the film surface and permeated in the thickness direction to fill the holes and become transparent. The time until complete transparency is measured, and the average film thickness in the vicinity of the dropping part is used to indicate a value converted per 25 μm thickness. Accordingly, the liquid paraffin permeation time is one of the measures for the permeability of the film, and the lower the liquid paraffin permeation time, the better the permeability, and the higher the liquid paraffin permeation time, the lower the permeability. The liquid paraffin permeation time of the microporous polypropylene film of the present invention is the amount of β crystal nucleating agent added to the polypropylene resin constituting the film, and the crystal when solidifying the molten polymer in the casting process in the production process. Conditions (metal drum temperature, peripheral speed of the metal drum, thickness of the unstretched sheet to be obtained) and stretching conditions in the stretching process (stretching direction (longitudinal or lateral), stretching method (longitudinal or lateral uniaxial stretching, longitudinal-horizontal) Alternatively, it can be controlled by lateral-longitudinal sequential biaxial stretching, simultaneous biaxial stretching, re-stretching after biaxial stretching, etc.), stretching ratio, stretching speed, stretching temperature, and the like. In the case of a highly permeable microporous film, when the liquid paraffin permeation time of the microporous polypropylene film of the present invention is less than the above range, the handling property may be inferior in the film forming step or the subsequent secondary processing step. If the above range is exceeded, the transmission performance may be insufficient and the porosity may be low. The liquid paraffin permeation time is more preferably 1 to 30 seconds / 25 μm, and most preferably 1.5 to 10 seconds / 25 μm.

  Moreover, it is preferable that the thermal contraction rate at the time of heating at 80 ° C. for 1 hour is 3% or less in both the film longitudinal direction (MD direction) and the width direction (TD direction). When the thermal shrinkage rate exceeds 3% in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, when used as a battery separator, the separator shrinks due to heat during charging / discharging of the battery. The cathode may come into contact with the cathode and cause a short circuit. Also, when laminated with other substrates for air-permeable waterproof sheets and filters, the heat shrinks during laminating, closing the holes and increasing the air permeability. This is not preferable because the product may curl.

  In the microporous film of the present invention, the static friction coefficient μs when the film surfaces are superposed is required to be in the range of 0.2 to 2, more preferably in the range of 0.3 to 1.5. . When the static friction coefficient μs is less than 0.2, the film is too slippery and unwinding occurs when the film is wound up in a long length. When μs exceeds 2, wrinkles are formed on the film or processed product, which is not preferable.

  It is preferable that the maximum surface roughness Rt of at least one surface of the film of the present invention is 0.5 to 2 μm and the average surface roughness Ra is 0.1 to 0.3 μm. When the maximum surface roughness Rt and the average surface roughness Ra are within the above ranges, the long winding property during film formation and the process passability during secondary processing are improved. If Rt or Ra exceeds the upper limit, the surface may be scraped when passing through the metal roll, white powder may adhere to the metal roll and the process may be soiled. Sometimes, slipping with the metal roll during passage of the time and the secondary processing step becomes worse, and the film and processed product may be wrinkled.

  As an auxiliary agent for improving the properties of the film of the present invention, it may contain at least one or more of an antistatic agent, an organic lubricant, inorganic particles and organic particles for preventing electrostatic charge and imparting hydrophilicity. The content is preferably 1% by weight or less, more preferably 0.5% by weight or less. If the added amount exceeds 1% by weight, the formation of pores is hindered, and the resin and particles may fall off in the PP film forming process and the secondary processing process, and the process may be soiled.

  The antistatic agent is not particularly limited, and examples thereof include ethylene oxide adducts of betaine derivatives, quaternary amine compounds, alkyldiethanolamine fatty acid esters, glycerin fatty acid esters, stearic acid monoglycerides, stearic acid diglycerides, and mixtures thereof. be able to. Among these, those using an alkyldiethanolamine fatty acid ester and a glycerin fatty acid ester in combination are preferable.

  Lubricant is added to improve fluidity and releasability during thermoforming of thermoplastic resin expressed in JIS terms. It is between the metal surface of the processing machine and the polymer surface, or between polymers. It is added to adjust the frictional force. Examples thereof include stearamide, erucamide, erucamide, stearyl erucamide, amide compounds such as light amide, and the like, or a mixture thereof.

  The total content of the antistatic agent and the lubricant in the film is 0.3 to 2.0 parts by weight, preferably 0.5 to 1.5 parts by weight from the viewpoint of imparting slipperiness.

  When the addition amount of the antistatic agent and the lubricant is larger than the above range, the β crystal ratio is lowered and the gas permeability may be lowered, which is not preferable.

  Examples of inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), antimony oxide, and oxidation. Cerium, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, Kaolin, lithium fluoride, calcium fluoride, and the like can be used.

  Organic particles are particles obtained by crosslinking a polymer compound using a crosslinking agent. For example, crosslinked particles of polymethoxysilane compounds, crosslinked particles of polystyrene compounds, crosslinked particles of acrylic compounds, crosslinked particles of polyurethane compounds, crosslinked particles of polyester compounds, crosslinked particles of fluorine compounds, or a mixture thereof Can be mentioned.

  It is preferable that the inorganic particles and the crosslinked organic particles have a spherical shape and have an average particle size in the range of 0.5 to 4 μm because the aggregation of the particles is small and the slipperiness effect is high. If the average particle size is less than 0.5 μm, the slippery effect is low, and if it exceeds 4 μm, the film surface tends to be damaged when the particles fall off or when the films are rubbed together.

  Further, the stress (hereinafter sometimes abbreviated as F2 value) at 2% in the longitudinal direction (hereinafter sometimes abbreviated as MD direction) of the film of the present invention is preferably in the range of 5 to 12 MPa. . A conventional microporous film has an internal void and thus has a low F2 value in the MD direction, and the film may be stretched due to tension in the film forming process and the secondary processing process, causing vertical wrinkles or breaking. When the F2 value in the MD direction is less than 5 MPa, the film may be stretched by passing through the process or by the winding tension, and vertical wrinkles or film breakage may occur. Further, if the F2 value in the MD direction exceeds 12 MPa, the flexibility is lowered, and creases may occur during secondary processing, which is not preferable.

  The porosity of the film of the present invention is preferably 50 to 80%, and preferably 50 to 70%, since it is easy to achieve both air permeability and F2 value. When the porosity is less than 50%, the value of the Gurley air permeability is large, and the characteristics as a battery separator or a gas permeable waterproof sheet are inferior. Further, when the porosity exceeds 80%, the F2 value becomes 5 MPa or less, and the film is stretched due to the tension in the film forming process and the secondary processing process, and vertical wrinkles may occur or break.

  The film thickness of the present invention is preferably 5 to 100 μm practically. If the film thickness is less than 5 μm, the film may be stretched due to the tension in the film forming step and the secondary processing step, and vertical wrinkles may occur or break. On the other hand, if it exceeds 100 μm, the Gurley air permeability increases, which is not preferable for practical use.

  The film of the present invention may be used alone or in combination with other materials. At this time, it is preferable to perform corona discharge treatment on the film surface in the air or in one or more atmospheres of nitrogen gas and carbon dioxide gas in order to adhere to hydrophilicity, printing ink applicability, or another substrate.

  Examples of the other materials include plain paper, fine paper, medium paper, coated paper, art paper, cast coated paper, resin-impregnated paper, emulsion-impregnated paper, latex-impregnated paper, synthetic resin internal paper, glassine paper, and laminate. Paper such as paper, synthetic paper, cloth or non-woven fabric, or other types of films can be used.

  Next, although an example is demonstrated about the manufacturing method of the biaxially-oriented microporous film of this invention, this invention is not limited only to this example.

  For example, a crystalline polypropylene resin, a β crystal nucleating agent, a glass transition point (Tg) of 100 to 160 ° C., or a polypropylene resin having a melting temperature of 200 to 270 ° C. A compatible resin is mixed and supplied to a twin-screw extruder, melt-mixed at 190 to 300 ° C. above the melting temperature of the incompatible resin to finely disperse the incompatible resin, and then extruded into a gut shape. It cools by passing through a 50 degreeC water tank, cuts into 3 mm length with a chip cutter, Then, it dries at 80-100 degreeC for 1 hour. Next, the β crystal nucleating agent and the incompatible resin mixed PP are supplied to an extruder heated above the melting temperature of the incompatible resin and melted, and the T die type heated to 180 ° C. to 240 ° C. It introduce | transduces in a nozzle | cap | die and obtains a melt-extrusion sheet | seat. At this time, if the resin temperature exceeds 220 ° C., the Gurley air permeability of the biaxially oriented microporous film obtained by biaxial stretching increases and the air permeability may deteriorate. Next, this melt-extruded sheet is held on a drum maintained at a surface temperature of 80 to 150 ° C. for 1 to 60 seconds to be solidified to produce a cast film. When the cast drum temperature is less than 80 ° C., the Gurley air permeability of the biaxially oriented microporous film obtained by biaxial stretching increases and the air permeability deteriorates. Moreover, when it exceeds 150 degreeC, the adhesion to a cast drum will occur and a surface defect may arise when peeling. Moreover, if the holding time in the said temperature range is less than 1 second, the beta crystal | crystallization of a cast sheet will not fully produce | generate, but the air permeability after extending | stretching does not become high easily. In addition, it is preferable that the holding time in the above temperature range is long, but if it exceeds 60 seconds, the film-forming speed becomes slow and the productivity may be lowered. Next, the cast film is guided to a roll group or oven that is heated and held, the sheet temperature is heated to 80 to 130 ° C., and stretched 2 to 7 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film). It cools with the roll group of deg. At this time, when the sheet temperature is less than 80 ° C., film breakage frequently occurs at the time of biaxial stretching, and when it exceeds 130 ° C., the Gurley air permeability of the biaxially oriented microporous film obtained by biaxial stretching increases and the air permeability is increased. Gets worse. When the longitudinal stretching ratio is less than 2 times, the Gurley air permeability of the biaxially stretched film is large and the air permeability deteriorates. When it exceeds 7 times, the lateral stretchability deteriorates, which is not preferable. Subsequently, both ends of the film stretched in the longitudinal direction are guided to a tenter while being gripped by clips, and stretched 3 to 12 times in a direction (lateral direction) perpendicular to the longitudinal direction in an atmosphere heated to 120 to 145 ° C. When the transverse stretching temperature is less than 120 ° C., film breakage frequently occurs during biaxial stretching, and when it exceeds 145 ° C., the Gurley permeability of the biaxially oriented microporous film obtained by biaxial stretching increases and the air permeability is increased. Getting worse. The area ratio (longitudinal stretch ratio × lateral stretch ratio) is preferably 6 to 84 times, and preferably 15 to 50 times from the viewpoint of film formation stability. When the area magnification is less than 6 times, pore formation of the resulting film becomes insufficient, and conversely when the area magnification exceeds 84 times, there is a tendency that tearing tends to occur during stretching. In order to complete the crystal orientation of the biaxially oriented microporous film thus obtained and to impart flatness and dimensional stability, heat treatment is subsequently performed at 130 to 160 ° C. for 1 to 10 seconds in the tenter. Thereafter, the biaxially oriented microporous film of the present invention can be obtained by gradually cooling it uniformly and then cooling to room temperature and winding. In addition, in the said heat processing process, you may perform a 3-12% relaxation process in a horizontal direction or a vertical direction as needed. When the heat treatment temperature is less than 130 ° C., the heat shrinkage rate when heated at 80 ° C. for 1 hour increases, and when it exceeds 160 ° C., the Gurley permeability of the biaxially oriented microporous film obtained by biaxial stretching is large. This is not preferable because the air permeability deteriorates. Further, if the heat treatment time is less than 1 second, the effect is not seen, and if it exceeds 10 seconds, the productivity is deteriorated, which is not preferable. Biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching, and may be re-stretched in either the longitudinal or lateral direction after biaxial stretching. On the surface of the film of the present invention thus obtained, in the air or nitrogen gas, if necessary, for imparting hydrophilicity with the electrolytic solution of the battery and improving the bonding with a cloth or other base material, Corona discharge treatment is performed in one or more atmospheres of carbon dioxide gas to improve the surface wetting tension and take up.

[Measurement and evaluation method of characteristics]
The characteristic value of this invention is calculated | required with the following evaluation method and evaluation criteria.

(1) Intrinsic viscosity [η]
0.1 g of a sample is completely dissolved in 100 ml of 135 ° C. tetralin, this solution is measured with a viscometer in a constant temperature bath at 135 ° C., and the intrinsic viscosity is obtained from the specific viscosity S according to the following formula. The unit is dl / g.
[Η] = S / 0.1 × (1 + 0.22 × S).

(2) Isotactic index (II) boiling n-heptane extraction residue The isotactic index (II) is determined from the boiling n-heptane extraction residue. The sample is extracted with boiling n-heptane for a certain period of time, and the weight (%) of the portion not extracted is calculated to calculate the isotactic index.

  Specifically, after drying the cylindrical filter paper at 110 ± 5 ° C. for 2 hours and leaving it in a constant temperature and humidity room for 2 hours or more, put 10 g of the sample (powder or flakes) into the cylindrical filter paper, and put a weighing cup and tweezers Use a precision balance (up to 4 digits after the decimal point).

This is set on the top of the extractor containing 80 cc of heptane, and the extractor and the cooler are assembled. This is heated with an oil bath or an electric heater and extracted for 12 hours. Heating is adjusted so that the number of drops from the cooler is 130 drops or more per minute. The cylindrical filter paper containing the extraction residue is taken out, put in a vacuum dryer, and dried at 80 ° C. and a vacuum degree of 100 mmHg or less for 5 hours. After drying, the sample is allowed to stand for 2 hours in constant temperature and humidity, and then precisely weighed and calculated by the following formula.
Isotactic index (II) (%) = (P / Po) × 100
However, Po is the sample weight (g) before extraction, P is the sample weight (g) after extraction.

(3) MFR (melt flow rate)
The crystalline polypropylene resin is measured according to JIS K 7210, Condition M (1995) (230 ° C., 2.16 kg). The ethylene-based resin is measured according to JIS K 7210, condition 4 (1995) (190 ° C., 2.16 kg). The polycarbonate is measured according to JIS K 7210, condition 21 (1995) (300 ° C., 1.2 kg). Polymethylpentene resin is measured according to ASTM D 1238 (260 ° C., 5.0 kg).

(4) β crystal ratio A polypropylene resin, a sheet, and a film are measured according to JIS K-7122 using a scanning differential calorimeter (DSC). Specifically, a 5 mg sample is heated to 250 ° C. at a rate of 20 ° C./min under a nitrogen atmosphere, and then held for 5 minutes, and then cooled to 20 ° C. at a cooling rate of 20 ° C./min. Next, when the temperature was raised again at a rate of 20 ° C./min, the heat of fusion (ΔHu−1) of the endothermic peak accompanying melting of the β crystal derived from the polypropylene resin having a peak between 140 ° C. and 157 ° C. From the heat of fusion (ΔHu−2) of the endothermic peak accompanying the melting of a crystal derived from polypropylene resin other than the β crystal having a peak at 160 ° C. or higher, the following formula is used.

β crystal ratio (%) = {ΔHu−1 / (ΔHu−1 + ΔHu−2)} × 100 (1)
In addition, although a melting peak exists at 140 to 160 ° C. by the above method, if it is unclear whether it is caused by the melting of the β crystal, the presence of a melting peak at 140 to 160 ° C. and wide-angle X-ray diffraction The presence of a diffraction peak due to the β crystal in the diffraction profile obtained by the method may be determined to be a melting peak due to the melting of the β crystal.

The measurement conditions of the wide angle X-ray diffraction method are shown below.
Sample: After aligning the direction of the film of the present invention so that the thickness of the sample after hot press adjustment is about 1 mm, the sample is sandwiched between 0.5 mm thick aluminum plates and hot pressed at 280 ° C. To melt and compress. The obtained sheet was immersed in 100 ° C. boiling water for 5 minutes and crystallized together with the aluminum plate, and then cooled in an atmosphere at 25 ° C., and a sheet obtained by cutting it to a width of 1 mm was subjected to measurement.
-X-ray diffractometer: 4036A2 manufactured by Rigaku Corporation
・ X-ray source: CuKα ray (using Ni filter)
・ Output: 40kV, 20mA
・ Slit system: 2mmφ-1 ° -1 °
-Detector: Scintillation counter-Count recording device: RAD-C type manufactured by Rigaku Denki Co., Ltd.-Measuring method: 2θ / θ scan (step scan, 2θ range 10-55 °, 0.05 ° step, integration time 2 Seconds)
In the obtained diffraction profile, the strongest diffraction peak due to the (300) plane of the β crystal may be observed in the vicinity of 2θ = 16.1 to 16.4 °. The structure of the crystal form (α crystal, β crystal) of polypropylene resin, the obtained wide-angle X-ray diffraction profile, etc. are described in, for example, Edward P. Moore Jr. Written by "Polypropylene Handbook", Industrial Research Committee (1998), p. 135-163; Hiroyuki Tadokoro, “Structure of Polymer”, Kagaku Dojin (1976), p. 393; A. Turner-Jones et al., “Macromolecular Chem.”, 75, p. There are a number of reports including 134-158 and references cited in these documents, which can be referred to.

(5) Glass transition point Tg, melting temperature Tm
When a 5 mg sample is heated at a rate of 20 ° C./min under a nitrogen atmosphere in accordance with JIS K-7122 using a scanning differential calorimeter (DSC), it accompanies the secondary transition. The change in specific heat was determined as the glass transition temperature (Tg). In addition, the Tg of the incompatible resin in the film is that the Tg of the main raw material PP is 0 ° C. or less, and therefore the change in specific heat accompanying the secondary transition exceeding 0 ° C. is defined as the Tg of the incompatible resin. . Further, the temperature was continuously raised, and the main peak temperature of the endothermic peak accompanying the melting of the resin was defined as the melting temperature Tm.

(6) Film thickness Using a dial gauge thickness gauge (JIS B-7509, measuring element 5 mmφ flat type), UPAIGHT DIAL GAUGE (0.001 × 2 mm) manufactured by PEACOCK, No. 25, measuring point 5 mmφ flat type, 125 gf load), 10 points were measured at intervals of 10 cm in the longitudinal direction and width direction of the film, and the average value was obtained (unit: μm).

(7) Gurley air permeability Based on JIS P-8117, it was measured at 23 ° C. and 65% RH (unit: second / 100 ml). The same measurement was performed 5 times for the same sample, and the average value of the obtained Gurley air permeability was taken as the Gurley air permeability of the sample. At this time, the case where the average value of the Gurley air permeability exceeded 10,000 seconds / 100 ml was regarded as substantially having no air permeability, and was set to infinity (∞) seconds / 100 ml.

(8) Average pore diameter of film The surface of the film is magnified 5000 times using a S-2100A type (manufactured by Hitachi, Ltd.) and a plane photograph is taken. All the holes observed in a mesh shape (the portion observed in black) observed in the plane photograph are marked, and the marking portion is subjected to image processing using a high-definition image analysis apparatus PIAS-IV (manufactured by Pierce Co., Ltd.). Thus, the average pore diameter was calculated. In order to determine the average pore diameter of the film, a total of five photometers arbitrarily selected from different measurement fields were used, and the average value was calculated.

(9) Porosity The biaxially oriented film was cut into a square, and the length L (cm), weight W (g), and thickness D (cm) of one side were measured and obtained from the following formula.
Porosity = 100-100 (W / ρ) / (L ² × D)
Ρ in the above formula indicates the film density before stretching. ρ uses a value obtained by the density gradient method of D method of JIS K7112 (1980). At this time, ethanol and water are used as the density gradient liquid.

(10) Dispersed particle size of incompatible resin, particle size of inorganic and organic particles A biaxially oriented microporous film was cut in the short direction using a microtome to form a cross section. The internal plane and the cross section of the film are enlarged and observed 5000 times using a scanning electron microscope (SEM) model S-2100A (manufactured by Hitachi, Ltd.), and a plane photograph and a cross section photograph are taken, respectively. In the internal plan photograph, the major axis length of the incompatible resin observed was measured. Moreover, in the cross-sectional photograph, all the cross sections of the incompatible resin to be observed are marked, and the marking portion is subjected to image processing using a high-definition image analysis apparatus PIAS-IV (manufactured by Pierce Co., Ltd.). The average particle size of the incompatible resin was calculated. However, the average value of the cross-sectional area of the incompatible resin is that the cross-sectional area of each incompatible resin obtained from each of the five photographs is taken by changing the internal plane and the cross-section sampling position and taking a total of five photographs. Calculated on average.

(11) Maximum surface roughness Rt and average surface roughness Ra
According to JIS B0601 (2001), using a stylus type surface roughness meter (manufactured by Kosaka Laboratory Ltd., high-precision thin film level difference measuring instrument, type ET30HK), the maximum surface roughness Rt and average surface of the skin layer surface The roughness Ra was measured. The conditions at this time were a test length of 2 mm, a stylus diameter cone type of 0.5 μm R, a load of 16 mg, and a cutoff of 0.08 mm. At this time, the center line average surface roughness Ra is obtained by extracting a portion having a measurement length L in the direction of the center line from the roughness curve, and setting the center line of the extracted portion as the X axis and the vertical direction as the Y axis. When the length curve is represented by y = f (X), it means a value obtained by the following formula expressed in μm.

(12) Coefficient of static friction μs
Using a slip tester manufactured by Toyo Seiki Co., Ltd., according to JIS K 7125 (1999), the values when the film surfaces were rubbed on both sides were measured, and the initial rise resistance value was determined as the coefficient of static friction μsd. did.

(13) Heat Shrinkage For each of the longitudinal direction and the width direction of the film, 5 pieces of 10 mm width and 300 mm length are cut out and marked at a position of 50 mm from both ends to make a test length of 200 mm (l ₀ ). Next, it was suspended in an oven kept at 80 ° C. with a load of 3 g, taken out after heating for 1 hour, cooled at room temperature, measured for dimensions (l ₁ ), and calculated by the following formula. The average value was used.
Thermal shrinkage S = (l ₀ −l ₁ ) / l ₀ × 100 (%).

(14) Wetting tension (mN / m)
It measured based on the measuring method prescribed | regulated to JISK6768 using the liquid mixture of formamide and ethylene glycol monoethyl ether.

(15) Stress at 2% elongation (F2 value)
The F2 value in the longitudinal direction of the film is a longitudinal length: 15 cm, a width direction: 1 cm, and a sample length of 50 mm. The sample length is 50 mm according to the method defined in JIS K7127 (1999). The sample was stretched and the stress applied to the sample with respect to the elongation of 2% was measured.

(16) Long roll-up property After winding a biaxially oriented film to a width of 5 m and 10,000 m, it was evaluated as follows by looking at the appearance of the product when slit into a 1 m width and 4000 m to produce a product.
Class A: Good end and surface appearance without product roll winding.

  Class B: Winding deviation of 1 to 5 mm is observed at the end of the product roll, and fine wrinkles are observed on the surface.

  Class C: Winding displacement exceeding 5 mm is observed at the end of the product roll, and large wrinkles are observed on the surface.

(17) Secondary workability As an air-permeable waterproof sheet, a 10 μm urethane adhesive (solid content concentration 20%) is applied to a water-repellent cloth, dried at 140 ° C. for 1 minute, and then a biaxially oriented film. When laminating at a temperature of 120 ° C, the thermal shrinkage rate is small and the sliding with the metal roll is good, and the white powder adheres to the metal roll during the process without any void forming agent (void nuclei) or particles falling off. No film wrinkle, air permeability after lamination is less than 30% of the value before lamination, and slipping with metal roll is poor, and pore forming agent (void core) Or particles have fallen off and white powder adheres to the metal roll, resulting in inferior processability, wrinkles in the film, air permeability increased by 50% or more after lamination, or air permeability is too high What can not be used as a waterproof sheet × It was to evaluate.

  The present invention will be described with reference to the following examples, but the present invention is not limited thereto.

Example 1
First, crystalline polypropylene resin (hereinafter abbreviated as crystalline PP) (manufactured by Sumitomo Chemical Co., Ltd., type: WF836DG3, intrinsic viscosity [η]: 2.0 dl / g, MFR: 7 g / 10 min, II: 96%) ) 94.95% by weight and N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (manufactured by Shin Nippon Rika Co., Ltd., “NUJester” NU-100, hereinafter NU-100) 0.05% by weight) and 5% by weight of polymethylpentene resin having a melting temperature of 240 ° C. (Mitsui Chemicals, “TPX” RT-18, MFR: 26, hereinafter abbreviated as PMP) Add and mix, supply to twin screw extruder, melt and mix at 280 ° C, extrude into gut shape, pass through 30 ° C water bath, cool and cut to 3mm length with chip cutter, then at 100 ° C for 2 hours Dried. The β crystal ratio of the β crystal nucleating agent-added PP (hereinafter abbreviated as β crystal PP) was 85%. Next, this β-crystal PP is supplied to an extruder (A) heated to 280 ° C., melted, extruded into a sheet form from a T-die die heated to 200 ° C., and kept at a surface temperature of 120 ° C. The film was solidified on a cast drum to produce a cast film. Next, the cast film was introduced into an oven heated and held at 120 ° C., and after preheating the film temperature, the cast film was stretched 4 times in the longitudinal direction (longitudinal direction, that is, the film traveling direction, hereinafter abbreviated as MD direction), and 30 Cooled with a chill roll. Subsequently, the film stretched in the MD direction is guided to a tenter while gripping both ends with a clip, and stretched 8 times in a direction perpendicular to the MD direction (lateral direction, hereinafter referred to as TD direction) in an atmosphere heated to 135 ° C. (Area magnification: Longitudinal draw ratio × Horizontal draw ratio = 32 times). Subsequently, in order to complete the crystal orientation of the biaxially oriented microporous film and to impart flatness and dimensional stability, a relaxation heat treatment of 5% in the transverse direction at 150 ° C. is performed in the tenter, and after uniform cooling, room temperature Until cooled. Furthermore, in order to impart hydrophilicity to the biaxially oriented microporous film of the present invention and to apply a coating agent and an ink on the surface or to be bonded to another substrate, both surfaces were subjected to corona discharge treatment in air and wound. Table 1 shows the resin composition of this film, and Table 2 shows the film characteristics, winding property and secondary processability. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Example 2)
As the resin composition of the film, crystalline PP (manufactured by Mitsui Chemicals, Inc., intrinsic viscosity [η]: 2 dl / g, MFR: 4 g / 10 min, II: 98.5%) 96.9% by weight, NU- 100 is 0.1% by weight, glass transition point (Tg) 150 ° C. incompatible resin polycarbonate (manufactured by Idemitsu Petrochemical Co., Ltd., type: A1500, molecular weight: 15000, MI: 65 g / min, hereinafter abbreviated as PC) ) Add 3% by weight, feed to twin screw extruder, extrude into guts at 280 ° C, cool through 20 ° C water bath, cut to 3mm length with chip cutter, then at 100 ° C for 2 hours Dried. The β crystal ratio of the β crystal nucleating agent-added PP was 90%. Next, this β crystal PP is supplied to an extruder (A) heated to 260 ° C., melted, and extruded into a sheet form from a T-die die heated to 200 ° C., and the surface temperature is kept at 100 ° C. The film was solidified on a cast drum to produce a cast film. Next, the cast film is guided to an oven heated and held at 120 ° C., and after preheating the film temperature, it is stretched 3.5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film, hereinafter abbreviated as MD direction). After passing through a 120 ° C. roll, it was cooled with a 30 ° C. cooling roll. Subsequently, the film stretched in the MD direction is guided to a tenter while holding both ends of the film with clips, and stretched seven times in a direction perpendicular to the MD direction (lateral direction, hereinafter abbreviated as TD direction) in an atmosphere heated to 145 ° C. (Area magnification: Longitudinal draw ratio x Transverse draw ratio = 24.5 times). Subsequently, in order to complete the crystal orientation of the biaxially oriented microporous film and to impart flatness and dimensional stability, a relaxation heat treatment of 5% in the transverse direction is performed at 160 ° C. in the tenter, and after uniform cooling, room temperature Until cooled. Furthermore, in order to impart hydrophilicity to the biaxially oriented microporous film of the present invention and to apply a coating agent and an ink on the surface or to be bonded to another substrate, both surfaces were subjected to corona discharge treatment in air and wound. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Examples 3 and 4)
In the resin composition of Example 1, biaxial orientation was performed in the same manner as in Example 1 except that the mixing amount of PMP in Example 3 was 0.5 wt% and that in Example 4 was 8 wt%. A microporous film was obtained. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Example 5)
In Example 1, the resin composition was 94.7% by weight of crystalline PP, 0.05% by weight of NU-100, 5% by weight of PMP, and aluminosilicate particles having an average particle size of 2.1 μm (Mizusawa Chemical Co., Ltd.). ) Ltd., type: Silton JC-20, is hereinafter abbreviated as SiO ₂ particles) except for using by adding and mixing 0.25 wt%, in the same manner as in example 1, a biaxially oriented thickness 75μm microporous film Got. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Example 6)
In Example 1, instead of PMP, an incompatible resin syndiotactic polystyrene resin (hereinafter abbreviated as SPS) having a melting temperature of 270 ° C. (“Zarek” S100, manufactured by Idemitsu Petrochemical Co., Ltd.) was used. Furthermore, 0.5% by weight of alkyldiethanolamine fatty acid ester (manufactured by Kao Corporation, electro stripper TS-6B, hereinafter abbreviated as TS6B) as an antistatic agent, and stearic acid monoglyceride (manufactured by Kao Corporation, Excel 84) as a lubricant. (Hereinafter abbreviated as E84) was added and mixed at 0.2% by weight, and a biaxially oriented microporous film was obtained in the same manner as in Example 1 except that it was melt-mixed at 290 ° C. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Example 7)
The resin composition of the film was 91.9% by weight of crystalline PP (manufactured by Sun Allomer Co., Ltd., MFR: 5 g / 10 min) having an ethylene content of 10% by weight, and N, N′-dicyclohexyl- 2,6-naphthalenedicarboxamide (manufactured by Shin Nippon Rika Co., Ltd., “NJESTER” NU-100, hereinafter abbreviated as NU-100) 0.1% by weight and PMP (“TPX” RT-18) 8 The mixture was added to and mixed by weight, supplied to a twin-screw extruder, melted and mixed at 280 ° C., extruded into a gut shape, cooled through a 30 ° C. water bath, cut into a 3 mm length with a chip cutter, and then 100 ° C. And dried for 2 hours. The β crystal ratio of the β crystal nucleating agent-added PP (hereinafter abbreviated as β crystal PP) was 92%. Next, this β-crystal PP is supplied to an extruder (A) heated to 280 ° C., melted, extruded into a sheet form from a T-die die heated to 200 ° C., and kept at a surface temperature of 120 ° C. The film was solidified on a cast drum to produce a cast film. Next, the cast film was introduced into an oven heated and held at 110 ° C., and after preheating the film temperature, it was stretched 5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film, hereinafter abbreviated as MD direction), and 100 Cooled with a roll at 0C. Subsequently, the film stretched in the MD direction is guided to a tenter while holding both ends of the film with clips, and stretched 9 times in a direction perpendicular to the MD direction (lateral direction, hereinafter referred to as TD direction) in an atmosphere heated to 125 ° C. (Area magnification: Longitudinal draw ratio × Horizontal draw ratio = 45 times). Subsequently, in order to complete the crystal orientation of the biaxially oriented microporous film and to impart flatness and dimensional stability, a relaxation heat treatment of 5% in the transverse direction at 150 ° C. is performed in the tenter, and after uniform cooling, room temperature Until cooled. Furthermore, in order to impart hydrophilicity to the biaxially oriented microporous film of the present invention and to apply a coating agent and an ink on the surface or to be bonded to another substrate, both surfaces were subjected to corona discharge treatment in air and wound. Table 1 shows the resin composition of this film, and Table 2 shows the film characteristics, winding property and secondary processability. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Example 8)
In Example 1, a biaxially oriented microporous film was obtained in the same manner as in Example 1 except that the addition amount of the β crystal nucleating agent NU-100 was 0.01% by weight and the casting drum temperature was 110 ° C. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. The film of the present invention has a β crystal ratio of β crystal PP as low as 52%, and the Gurley permeability of the biaxially oriented microporous film is close to the upper limit of the range of the present invention, but can be used without any problem as a gas permeable waterproof sheet. It can be seen that the product roll has good appearance, the appearance of the product roll is good, the heat shrinkage rate is low, and the secondary workability is excellent.

Example 9
As a resin composition, a polypropylene “Bepol” (type: BO22-SP, MFR: 1.8 g / 10 minutes) 90% by weight, a PMP having a melting temperature of 240 ° C. as a non-compatible resin. (“TPX” RT-18) 8 wt% and ethylene / α-olefin copolymer “engage” 8411 (manufactured by DuPont Dow) were mixed and supplied to a twin screw extruder at 280 ° C. The mixture was melt-mixed and extruded into a gut shape, passed through a 30 ° C. water bath, cooled, cut to a length of 3 mm with a chip cutter, and then dried at 100 ° C. for 2 hours. The β crystal ratio of the β crystal nucleating agent-added PP (hereinafter abbreviated as β crystal PP) was 80%. Next, this β-crystal PP composition is supplied to an extruder (A) heated to 280 ° C., melted, extruded into a sheet form from a T-die die heated to 220 ° C., and brought to a surface temperature of 120 ° C. A cast film was prepared by solidifying and solidifying on the retained cast drum. Next, the cast film was introduced into an oven heated and held at 110 ° C., and after preheating the film temperature, it was stretched 5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film, hereinafter abbreviated as MD direction), and 100 Cooled with a roll at 0C. Subsequently, the film stretched in the MD direction is guided to a tenter while holding both ends of the film with clips, and stretched 9 times in a direction perpendicular to the MD direction (lateral direction, hereinafter referred to as TD direction) in an atmosphere heated to 125 ° C. (Area magnification: Longitudinal draw ratio × Horizontal draw ratio = 45 times). Subsequently, in order to complete the crystal orientation of the biaxially oriented microporous film and to impart flatness and dimensional stability, a relaxation heat treatment of 5% in the transverse direction at 150 ° C. is performed in the tenter, and after uniform cooling, room temperature And a microporous polypropylene film having a thickness of 25 μm was obtained. Table 1 shows the resin composition of this film, and Table 2 shows the film characteristics, winding property and secondary processability. It can be seen that the film of the present invention has low Gurley air permeability, excellent air permeability, good slipperiness, good product roll appearance, low heat shrinkage, and excellent secondary workability.

(Comparative Example 1)
In Example 1, except that the quinacridone-based nucleating agent (Toyo Soda Co., Ltd. “Rubicron” 400RG, hereinafter abbreviated as 400RG) was 0.1% by weight and the melting temperature was 220 ° C. A biaxially oriented microporous film was obtained in the same manner as in Example 1. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. This film has a low β crystal ratio of PP added with a β crystal nucleating agent of 36%, so that the Gurley air permeability is high and the air permeability is poor, and the melting temperature is lower than the melting temperature of the incompatible resin. Therefore, the dispersibility of the incompatible resin was poor, and the friction coefficient and the heat shrinkage rate were large.

(Comparative Examples 2 and 3)
In Comparative Example 2, the incompatible resin was not added in Example 1, but two components of crystalline PP and β crystal nucleating agent were used. In Comparative Example 3, the amount of PMP added in Example 1 was 15% by weight. A biaxially oriented microporous film was obtained in the same manner as in Example 1 except that. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. The film of Comparative Example 2 has a large coefficient of friction, a large heat shrinkage rate, and voids are crushed in the secondary processing step, or the Gurley permeability after the secondary processing is large. Inferior to sex. The film of Comparative Example 3 has a surface roughness that is excessively large and drops off during the film forming process, fouling the process, causing frequent film tearing during film formation, and being inferior in long winding property and secondary processability. Met.

(Comparative Example 4)
In Example 1, SiO ₂ particles having a crystalline PP of 59.95% by weight, β crystal nucleating agent NU-100 of 0.05% by weight, and an average particle size of 4.9 μm (manufactured by Mizusawa Chemical Co., Ltd., Shilton JC-) A biaxially oriented microporous film was obtained in the same manner as in Example 1 except that 50) was changed to 40% by weight. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. In this film, SiO ₂ particles dropped off in the film forming process and the secondary processing process, and the process was soiled. The F2 value of the film was low and very brittle, and the secondary processability was poor.

(Comparative Example 5)
In Example 1, 10% by weight of polyterpene resin (manufactured by Yashara Chemical Co., Ltd., “Clearon P-125”, hereinafter abbreviated as PT) having good compatibility with crystalline PP and having a Tg of 70 ° C. instead of PMP A biaxially oriented microporous film was obtained in the same manner as in Example 2 except for mixing. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. This film has a large coefficient of friction, a large thermal shrinkage rate, inferior long winding properties and secondary workability, and a large Gurley air permeability.

(Comparative Example 6)
In Example 1, a biaxially oriented microporous film was obtained in the same manner as in Example 1 except that the longitudinal stretching temperature was 110 ° C. and the film was wound without performing heat treatment after transverse stretching. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. This film had a large heat shrinkage ratio, a large dimensional change due to heat during secondary processing, wrinkles in the product, and increased Gurley permeability after processing.

(Comparative Example 7)
In Example 2, the melt extrusion temperature was set to 260 ° C., and the cast film was prepared by solidifying on a cast drum maintained at a surface temperature of 80 ° C. Then, the cast film was placed in an oven heated to 135 ° C. After guiding and preheating the film temperature, the film was stretched 5 times in the MD direction, and then cooled with a 30 ° C. cooling roll. Subsequently, the film stretched in the MD direction is guided to a tenter while holding both ends of the film with clips, and stretched 10 times in the TD direction in an atmosphere heated to 150 ° C. (Area magnification: Longitudinal stretching ratio × Horizontal stretching ratio = 50 times) A biaxially oriented microporous film was obtained in the same manner as in Example 1 except that the film was wound. The resin composition of this film is shown in Table 1, and the film properties, winding properties and secondary processability are shown in Table 2. This film had a Gurley air permeability higher than the measurement limit, and could not be used for separators such as batteries, separation membranes, air permeable waterproof sheets, and filters.

  The biaxially oriented microporous film of the present invention has a low Gurley permeability, excellent air permeability, good slipperiness and high stress during stretching, and thus excellent long-winding properties, and further heat resistance (low heat shrinkage). The secondary processability is excellent, and it can be suitably used for electrolytic capacitors, lithium battery separators, separation membranes, air permeable waterproof sheets, filters, and the like.

FIG. 1 is a diagram schematically showing a peak when an endothermic peak accompanying melting of a polypropylene resin is obtained using a scanning differential calorimeter (DSC). FIG. 2 shows the endothermic peak heat of fusion (ΔHu−1) accompanying melting of β-crystal derived from polypropylene resin having a peak between 145 ° C. and 157 ° C. in FIG. 1, and β-crystal having a peak at 160 ° C. or higher. It is the figure which showed the calorie | heat amount ((DELTA) Hu-2) of the endothermic peak accompanying the melt | dissolution of the crystal | crystallization derived from polypropylene resins other than.

Explanation of symbols

1. Total melting curve of β crystal containing PP and β crystal containing film 2. Heat of fusion ΔHu-1 of β crystal part
3. ・ The heat of fusion of the part other than β crystal ΔHu-2

Claims (8)

It consists of 90 to 99.8% by weight of polypropylene resin with a β-crystal ratio of 50 to 99% and 0.2 to 10% by weight of resin incompatible with polypropylene resin, and the Gurley permeability is 5 to 10000 sec / 100 cc. The static friction coefficient μs when the both surfaces of the film are overlapped is in the range of 0.2 to 2, and the heat shrinkage rate when heated at 80 ° C. for 1 hour is the film longitudinal direction (MD direction) and width direction (TD direction). Both are 3% or less, at least one surface has a maximum surface roughness Rt of 0.5 to 2 μm, an average surface roughness Ra of 0.05 to 0.3 μm, and 2 in the longitudinal direction (MD direction) of the film. A biaxially oriented microporous film having a% elongation stress (F2 value) in the range of 5 to 12 MPa and a porosity of 42 to 80%. The biaxially oriented microporous film according to claim 1, wherein the porosity is 50 to 80%. The biaxially oriented microporous film according to claim 1 or 2, wherein the film thickness is 5 to 100 µm. The biaxially oriented microporous material according to any one of claims 1 to 3, wherein the polypropylene resin having a β crystal ratio of 50 to 99% contains 0.01 to 2% by weight of a β crystal nucleating agent. the film. The resin incompatible with the polypropylene resin is at least one resin having a glass transition point (Tg) of 100 to 160 ° C or a melting temperature of 200 to 270 ° C. A biaxially oriented microporous film according to claim 1. The resin incompatible with the polypropylene resin is an ethylene / α-olefin copolymer, or a mixture of an ethylene / α-olefin copolymer and another incompatible resin. A biaxially oriented microporous film according to claim 1. After melting and mixing a mixed composition of a polypropylene resin, a β crystal nucleating agent and a resin incompatible with the polypropylene resin at a temperature higher than the melting temperature of the incompatible resin, the mixed resin is melted into a sheet at 180 ° C. to 240 ° C. The sheet which has been extruded and held at a temperature of 80 ° C. to 150 ° C. for 1 second to 60 seconds and cooled and solidified is longitudinally stretched 2 to 7 times at a temperature of 80 ° C. to 130 ° C., and then 3 to 12 at a temperature of 120 to 145 ° C. The method for producing a biaxially oriented microporous film according to any one of claims 1 to 6 , wherein the film is horizontally stretched twice and heat-treated at 130 to 160 ° C for 1 to 10 seconds. The polypropylene resin containing the β crystal nucleating agent is 90 to 99.8% by weight, and the resin incompatible with the polypropylene resin is a mixed composition of 0.2 to 10% by weight. The manufacturing method of the biaxially oriented microporous film of description.

Images