JP3494805B2 - Grafted polyolefin-based nonwoven fabric - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin-based non-woven fabric obtained by graft-polymerizing a hydrophilic vinyl monomer, its use and its production method.

[0002]

2. Description of the Related Art Nonwoven fabrics can be manufactured directly from fibers without undergoing a spinning process or a twisting process, and therefore the manufacturing process is simpler than that of woven or knitted fabrics. Nonwoven fabrics having such advantages are currently widely used as sanitary materials such as paper diapers and clothing materials. And, as the fibers which become the material of the non-woven fabric, a single fiber such as polypropylene fiber, a homopolymer composite fiber such as a copolymer polyester-polyethylene terephthalate composite fiber and a copolymer polypropylene-polypropylene composite fiber, or a polyethylene-polypropylene composite fiber. And heterogeneous polymer composite fibers such as polyethylene-polyethylene terephthalate composite fibers have been developed.

By the way, conventionally, a battery such as nickel is used.
Nonwoven fabrics made of synthetic fibers are used as separators in cadmium batteries, but these nonwoven fabrics are required to have appropriate mechanical strength, good gas permeability, electrolyte retention capacity, electrolyte durability and oxidation resistance. To be done.

Nonwoven fabrics made of polyamide fiber, which are generally used as battery separators at present, have hydrophilicity and excellent electrolyte retaining ability, but have poor electrolyte durability and oxidation resistance. During repeated charging and discharging, decomposition occurs from the amide bond site, and the decomposed product dissolves in the electrolytic solution, causing self-discharge.

On the other hand, a polyolefin non-woven fabric made of polyolefin fibers such as polypropylene and polyethylene is excellent in electrolytic solution durability and oxidation resistance,
Since it is hydrophobic in itself, it has a poor electrolyte retaining ability.
For this reason, it has been attempted to give hydrophilicity to the polyolefin-based nonwoven fabric by subjecting it to a surfactant treatment, but the surfactant is eluted by a large number of charging / discharging times, and the self-discharge characteristics deteriorate at the same time. There is a drawback that the hydrophilicity is lowered and the electrolyte holding ability is lowered.

Therefore, it is conceivable to introduce a hydrophilic functional group into the surface of the polyolefin fiber by a chemical reaction so as to maintain permanent hydrophilicity. An example of a battery separator that is made hydrophilic by such means is a battery separator described in Japanese Patent Publication No. 1-36231. The battery separator described in this publication uses a nonwoven fabric composed of a sheath-core type composite fiber having a polypropylene resin as a core component and a polyethylene resin as a sheath component, and generates radical active centers by an electron beam irradiation method (pre-irradiation method). The hydrophilicity is imparted by graft-polymerizing a hydrophilic monomer.

However, in the method for manufacturing a battery separator described in this publication, radicals are generated even inside the fiber due to strong electron beam irradiation, graft polymerization occurs even inside the fiber, and the flexibility of the nonwoven fabric decreases, The strength is also reduced. Further, when it is used as a battery separator, it has a drawback that its swelling due to water absorption lowers its porosity and gas permeability. If the electron beam irradiation amount is limited in order to improve these points, other problems such as non-uniform grafting and elimination of hydrophilic functional groups occur.

[0008] Further, as a battery separator described in Japanese Unexamined Patent Publication No. 7-6745, there is a battery separator having improved deterioration of gas permeability caused by swelling of the battery separator due to water absorption. The battery separator according to the present disclosure, after adjusting the amount of the grafting monomer attached, is subjected to graft polymerization by electron beam irradiation to change the degree of graft polymerization in the vicinity of the joint between the adjacent fibers of the woven or non-woven fabric. The degree of graft polymerization is higher than that of the portion.
That is, it is intended to increase the degree of graft polymerization in the fiber-bonded portion of the woven or non-woven fabric, limit the swelling to only the vicinity of the fiber-bonded portion, and suppress the decrease in the porosity of other portions. However, in the method for manufacturing a battery separator described in the present publication, strength reduction due to electron beam irradiation is unavoidable, and when the irradiation dose is limited (10 Mrad or less), the problem of non-uniform grafting has been solved. Absent. Further, in the method described in this publication, since the graft polymer is mainly present in the joint portion of the fibers, the effect of improving hydrophilicity is not sufficient.

In a non-woven fabric composed of a sheath-core type composite fiber having a polypropylene resin as a core component and a polyethylene resin as a sheath component, a relatively soft polyethylene resin is used as a sheath component, so that the nonwoven fabric strength (row breaking length) is Difficult to improve. Therefore, when this is used as a battery separator, there are cases in which pinholes are generated when the nonwoven fabric is wound, and the positive and negative electrodes come into contact with each other to cause a short circuit.

As described above, a hydrophilic non-woven fabric made of a polyolefin fiber, which has excellent hydrophilicity and does not cause a decrease in strength and a decrease in gas permeability due to swelling due to water absorption, has been known so far. Has not been done.

A sheath-core type composite fiber containing polypropylene resin as a core component and a sheath component is currently being developed. However, those which have been developed so far do not have sufficient graft polymerization reactivity and thus have a battery separator. No material having excellent hydrophilicity required for the above was obtained.

[0012]

Under the above circumstances, an object of the present invention is to use a non-woven fabric composed of a polyolefin fiber having a high graft-polymerizing property, which has excellent hydrophilicity, strength reduction, and swelling due to water absorption. It is an object of the present invention to provide a grafted polyolefin-based non-woven fabric that does not cause a decrease in gas permeability, its use as a battery separator, and its manufacturing method.

[0013]

[Means for Solving the Problems] In order to achieve the above object,
As a result of intensive studies conducted by the present inventors, (i) a nonwoven fabric composed of a polyolefin-based fiber was subjected to a treatment for uniformly attaching a hydrophobic radical initiator to the fiber surface, and then a hydrophilic vinyl monomer was graft-polymerized. However, not only the joint between the fibers that make up the nonwoven fabric due to the graft polymerization reaction,
It is possible to obtain a grafted nonwoven fabric that occurs uniformly on the entire fiber surface and the graft polymer is present on the entire fiber surface, and (ii) the hydrophilic nonwoven fabric thus obtained has reduced strength and gas permeability. It has been found that it has physicochemical properties capable of achieving the above-mentioned object without deterioration of

The present invention has been completed based on these findings, and the present invention is a graft copolymer of a nonwoven fabric composed of polyolefin fibers and a hydrophilic vinyl monomer formed on the fibers constituting the nonwoven fabric. A grafted polyolefin-based non-woven fabric containing a
The constituent polyolefin fiber constitutes (a) the sheath component
At least a part of the polymer having 2 or 4 to 8 carbon atoms
Random Copolymerization Using Aliphatic Unsaturated Hydrocarbon as Copolymerization Component
Polypropylene, the polymer that constitutes the core component is polypropylene
Pyrene-sheath core composite fiber or (b) sheath component is straight
Chain-like low density polyethylene (L-LDPE), core-formed
A sheath-core type heat-fusible composite fiber whose content is polypropylene.
The graft polymer is a grafted polyolefin-based nonwoven fabric characterized by being present on the entire surface of the fiber without being localized at the joints of the fibers constituting the nonwoven fabric (hereinafter referred to as the grafted nonwoven fabric of the present invention. ) Is the first gist, and the battery separator comprising the grafted nonwoven fabric of the present invention is the second gist.

Further, according to the present invention, a polyolefin-based nonwoven fabric is treated with a dispersion of at least one kind of hydrophobic radical initiator in an organic solvent, and then the organic solvent is dried and removed to uniformly disperse the hydrophobic radical initiator on the fiber surface. A third aspect of the present invention is a method for producing a grafted polyolefin-based non-woven fabric, which is characterized in that the graft polymerization reaction is carried out by immersing and fixing it on, and then dipping it in an aqueous solution of a hydrophilic vinyl monomer to carry out a graft polymerization reaction.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The grafted nonwoven fabric of the present invention is characterized in that the graft polymer is present on the entire surface of the fiber without being localized at the joint portion of the polyolefin fibers constituting the nonwoven fabric.

In the grafted nonwoven fabric of the present invention, the polyolefin fibers constituting the nonwoven fabric include a single fiber composed of a single polymer (including a homopolymer and a copolymer), and a homopolymer or a heteropolymer (a homopolymer and a copolymer). (Including) is included. Here, the single fiber is a fiber obtained by spinning one kind of polymer, and the composite fiber is a fiber obtained by compounding a plurality of kinds of polymers with a spinneret and simultaneously spinning.

Specific examples of the single fiber include, for example, high density polyethylene (HDPE) fiber, low density polyethylene (LDPE) fiber, linear low density polyethylene (LLD).
Examples thereof include PE) fibers and polypropylene (PP) fibers. In addition, high density polyethylene (HDPE) fiber,
Porous fibers having fine pores formed by mixing high-density polyethylene and paraffin wax under melting, melt spinning, and stretching and heat treatment to remove the paraffin wax (JP-A-4-18112). )
Is also included.

Specific examples of the same type of polymer composite fiber include:
For example, copolymer polyester-polyethylene terephthalate-based composite fiber, copolymer polypropylene-polypropylene-based composite fiber and the like can be mentioned.

Specific examples of the different polymer composite fibers include:
Examples thereof include polyethylene-polypropylene-based composite fibers and polyethylene-polyethylene terephthalate-based composite fibers.

From the viewpoint of chemical resistance, it is difficult to use a copolyester and / or polyethylene terephthalate fiber type.

The conjugate fiber can be in various forms, for example, sheath-core type (concentric type, eccentric type) conjugate fiber, side-by-side type conjugate fiber, etc., and any form can be used for the production of nonwoven fabric. However, a sheath-core type composite fiber is particularly preferable. At least a part of the surface of the composite fiber is preferably arranged such that the sheath component covers the core component continuously in the length direction. Specifically, in the sheath-core cross-sectional area ratio,
A ratio of sheath component / core component of about 3/7 to 7/3 is preferred.

The polymer constituting the sheath component in the sheath-core type composite fiber has a lower softening point or melting point than the polymer constituting the core component, and is melt-spun with the polymer constituting the core component. The type is not particularly limited as long as it can form the conjugate fiber.
A preferred combination of the sheath component of the sheath-core type composite fiber and the polymer of the core component is, for example, polypropylene (P
P) in which the sheath component is a known homopolymer or copolymer. Specific examples of the sheath component include, for example, high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (L-LDPE), and copolymers containing ethylene as a main component (for example, ethylene-vinyl acetate). Copolymers, etc.), polypropylene-based copolymers (eg, ethylene-propylene random copolymers, ethylene-propylene-butene-1 random copolymers, etc.) and the like, and further, a mixture of these homopolymers and copolymers. It may be. However, among these sheath components, ethylene-vinyl acetate copolymer (EVA) is not preferable from the viewpoint of chemical resistance when it is intended for a battery separator.

In the present invention, the polymer constituting the sheath component is preferably a low crystalline polymer or a polymer having a slow crystallization rate. Here, the "low crystalline polymer" means
When formed into fibers by a conventional method, it means a polymer having a crystallinity of less than 80%, for example. Such a polymer is originally difficult to crystallize because it has some cause of inhibiting crystallization, and a slow crystallization rate. There are two types of polymers that do not rise to their native crystallinity.

Since the grafting reaction is a solid-liquid reaction, the fact that the reaction solution containing the hydrophilic vinyl monomer permeates into the surface of the non-woven fabric faster is a factor that enhances the reactivity. Therefore, the low crystallinity itself does not directly participate in the grafting reaction, but it is considered that the lower the crystallinity, that is, the larger the number of amorphous parts, the higher the graft reactivity.

As a preferable specific example of the low crystalline polymer, a polymer at least partially containing a random copolymer polypropylene having a C 2 or C 4 to C 8 aliphatic unsaturated hydrocarbon as a copolymer component is preferable.

Random copolymerized polypropylene having a C 2 or C 4-8 aliphatic unsaturated hydrocarbon as a copolymerization component is particularly excellent in graft polymerizability of hydrophilic vinyl monomers. The reason is that in order to graft-polymerize a hydrophilic vinyl monomer onto a polyolefin resin, it is necessary to first extract hydrogen from the polyolefin to generate radicals. Here, as for the ease of abstracting hydrogen, hydrogen bonded to the secondary carbon is easier to extract than hydrogen bonded to the primary carbon, and hydrogen bonded to the tertiary carbon is easier. Easy to pull out. In addition, the one having a larger number of carbon atoms in the side chain bonded to the tertiary carbon (that is, the ethyl group is more preferred than the methyl group, and the propyl group is more preferred than the ethyl group) is bonded to the tertiary carbon Hydrogen is easily extracted. Therefore, it contains more tertiary carbon and has 2 carbon atoms.
3 with a large side chain above (ie above the ethyl group)
The polyolefin resin containing a large amount of graded carbon has a structure in which the hydrophilic vinyl monomer is easily graft-polymerized. That is, in order to facilitate the graft polymerization reaction, it is important to distribute a large amount of tertiary carbon (reactive sites) on the surface of the nonwoven fabric fiber.

Further, in the above preferable sheath component, the total number of polymers constituting the sheath component has 2 or 4 carbon atoms.
The content of aliphatic unsaturated hydrocarbon of ~ 8 is 3.0 to 7.0.
It is preferably in the weight%. Below 3.0% by weight,
Since the absolute number of the tertiary carbon is too small, it may be difficult to obtain the intended effect. If it exceeds 7.0% by weight, the intended effect is easily obtained, but the spinnability is lost during fiberization. There are some cases where it is not desirable.

When the polyolefin fiber constituting the grafted nonwoven fabric of the present invention has a form of a sheath-core type composite fiber, the first aspect of a preferable combination of the sheath component and the core component is the weight constituting the sheath component. At least a part of the coalescence is a random copolymer polypropylene having a C 2 or C 4-8 aliphatic unsaturated hydrocarbon as a copolymer component, and the core component is polypropylene (PP).

Random copolymer polypropylene in which at least a part of the polymer constituting the sheath component is butene-1 (having 2 carbon atoms or 4 to 8 carbon atoms in an unsaturated aliphatic hydrocarbon) as a copolymerization component. Is preferred.

Butene in the total amount of the polymer constituting the sheath component
The content of 1 is preferably 3.0 to 7.0% by weight. The reason is as described above.

Specific examples of the random copolymerized polypropylene containing particularly preferred butene-1 as a copolymerization component include butene-1 / propylene copolymer and ethylene / butene-1 / propylene copolymer.

The grafted polyolefin-based nonwoven fabric of the present invention comprising the polyolefin-based fibers having the first embodiment of the preferred combination of the sheath component and the core component described above uniformly coats the surface of the fibers constituting the nonwoven fabric with the graft polymer. It has been done.

In the case where the polyolefin fiber constituting the grafted nonwoven fabric of the present invention has a form of a sheath-core type composite fiber, the second embodiment of a preferable combination of the sheath component and the core component is that the sheath component is linear. It is low density polyethylene (L-LDPE) and its core component is polypropylene (P
P) which is a sheath-core type heat-fusible composite fiber.

Here, linear low-density polyethylene (L-
LDPE) is obtained by copolymerizing ethylene and an α-olefin having 4 to 8 carbon atoms in the presence of an ionic polymerization catalyst, and is an ethyl group, a propyl group, a butyl group or a hexyl group in a linear polymer. It has a structure in which side chains such as 2-methylpropyl group are formed, and can be selected from commercially available products generally called linear low-density polyethylene.

L-LDPE is a kind of polymer which intentionally imparts irregularity to the molecular structure to inhibit crystallization, resulting in low crystallinity. Therefore, it is one of the low crystalline polymers and has a property that the graft polymerization reaction easily proceeds.

The grafted polyolefin-based non-woven fabric of the present invention comprising the polyolefin-based fiber having the second embodiment of the preferred combination of the sheath component and the core component, the surface of the fiber constituting the non-woven fabric is uniformly coated with the graft polymer. It has been done.

Further, in the second embodiment, as is clear from the electron micrographs of the grafted nonwoven fabric of the present invention shown in FIGS. 1 to 6, when the grafting ratio becomes high, the granular graft polymer lumps form a polyolefin fiber surface. It is distributed at a constant ratio on the graft polymer film.

Here, with reference to electron micrographs (FIGS. 1 to 6) of the grafted nonwoven fabric, the graft ratio and the distribution state of the graft polymer of the grafted nonwoven fabric comprising the composite fiber of the second embodiment of the present invention will be described. explain.

As shown in FIG. 1, the graft ratio is 6.
When it is relatively low at 1% by weight, the surface of the fiber is thinly and uniformly coated with the graft polymer, and the surface of the grafted fiber is substantially smooth, but the graft ratio is 1
As the amount increases to 0.1% by weight, 18.3% by weight, and 31.1% by weight, granular graft-polymerized lumps are also formed on the fiber surface, as shown by FIGS.
The graft polymer lump thus formed on the graft polymer coating on the fiber surface is also distributed substantially uniformly at a constant ratio over the entire surface of the fibers of the nonwoven fabric.

The above-mentioned FIGS. 1 to 4 are 300 times magnified photographs of the grafted nonwoven fabric of the present invention, and 3000 times magnified photographs of the grafted nonwoven fabrics having graft ratios of 5.3% by weight and 10.2% by weight, respectively. Is shown in FIGS. 5 and 6. Figure 5
Also from FIG. 6, in the case of the grafted nonwoven fabric of the present invention, when the graft ratio is low, the graft polymer is present as a film on the fiber surface, but when the graft ratio is high, the graft polymer mass is present on the film. Are clearly formed.

That is, the grafted nonwoven fabric comprising the conjugate fiber of the second embodiment of the present invention is (a) an embodiment in which the graft polymer coating is present on the entire fiber surface and (b) a graft polymer coating on the fiber surface. Both of the embodiments which are present and in which the graft polymer mass is uniformly distributed on the coating.

The terms "exist in the whole" and "uniformly exist" are based on macro observation.
The case where the graft polymer coating does not exist in a very limited place includes the case where the graft polymer mass locally exists nonuniformly.

In the grafted nonwoven fabric of the present invention, the size of the particles of the graft polymer mass varies depending on the graft ratio, but the diameter is about 0.1 to 10 μm, and the distribution density on the fiber surface is also the graft ratio. Depending on the graft rate, in the range of about 1 to 40%, about 1 to 200,000 pieces / mm
^{Is 2} .

On the other hand, in the grafted nonwoven fabric obtained by the electron beam irradiation method of the prior art, as shown in FIG. 7, the graft polymer is localized and present only at the joints of the fibers constituting the nonwoven fabric.

The non-woven fabric to be grafted in the grafted non-woven fabric of the present invention is the above-mentioned polyolefin fiber made into a non-woven fabric by a known method. That is, first, a web is produced from the above-mentioned polyolefin resin by a conventional method using a card machine such as a roller card or a flat card which is usually used. The production of a nonwoven fabric from a web may be carried out by appropriately selecting a conventionally known method such as a heat fusion method, a spun bond method, a melt blow method, or a solvent-based flash spinning method according to the intended use of the nonwoven fabric. . Polypropylene (PP) or high density polyethylene (HDP
E) a single fiber such as (melting point: 125 to 135 ° C.) or the above-mentioned sheath-core type composite fiber (for example, the sheath component is ethylene / butene-1 / propylene random copolymer and the core component is polypropylene) is 0. A non-woven fabric can also be obtained by a method of mixing ˜70 wt% and adhering fibers to each other.

In the grafted nonwoven fabric of the present invention, a graft polymer of a hydrophilic vinyl monomer is present on the fibers constituting the nonwoven fabric, and the graft polymer imparts hydrophilicity. The following method can be used to graft-polymerize the hydrophilic vinyl monomer on the polyolefin-based nonwoven fabric obtained as described above. (1) A chemical method in which a non-woven fabric and a hydrophilic vinyl monomer are heated in the presence of a polymerization initiator to perform graft polymerization (2) In a state where the non-woven fabric and the vinyl monomer are contacted, ultraviolet rays or ionizing radiation is irradiated. Simultaneous irradiation method of graft polymerization (3) UV irradiation or ionizing radiation is applied to the nonwoven fabric, and then a pre-irradiation method of contact polymerization with a vinyl monomer to perform graft polymerization, preferably classified into the above (1), of the present invention described later. It is a method for producing a grafted polyolefin-based nonwoven fabric.

Specific examples of the hydrophilic vinyl monomer capable of forming a graft polymer in the grafted nonwoven fabric of the present invention include acrylic acid and its ester derivative, methacrylic acid and its ester derivative, acrylamide and its derivative, styrene and Its induction, N
-Vinylpyrrolidone, acrylonitrile, vinyl sulfonic acid, styrene sulfonic acid, those having a functional group capable of directly reacting with an acid or a base to form a salt such as styrene, or hydrolyzed after graft copolymerization,
Examples thereof include those having a functional group capable of forming a salt by a relatively simple treatment, and other hydrophilic monomers. Of these, acrylic acid and its ester derivative, and methacrylic acid and its ester derivative, which do not have an amide bond, are preferable from the viewpoint of durability when they are intended for battery separators.

The grafted polyolefin-based nonwoven fabric of the present invention is characterized by the distribution state of the graft polymer, and the graft polymer of the hydrophilic vinyl monomer is present in the presence or absence of the lump of the graft polymer. Is present on the entire surface of the fiber without being localized in the vicinity of the joint between the fibers constituting the nonwoven fabric, and the conventional graft copolymer is localized in the vicinity of the joint between fibers. It is clearly distinguished from the grafted non-woven fabric.

In the grafted nonwoven fabric of the present invention, the preferred graft ratio of the hydrophilic vinyl monomer onto the nonwoven fabric surface varies depending on the purpose of use, but is generally about 1 to 4.
It is in the range of 0% by weight. If it is less than 1% by weight, the graft polymer may not be present on the entire surface of the fiber, while 4
If it exceeds 0% by weight, the non-woven fabric becomes stiff, and the handling property deteriorates, and the gas permeability due to swelling due to water absorption decreases. When the grafted nonwoven fabric of the present invention is used as a battery separator, the graft ratio is preferably 1 to 40% by weight, particularly preferably 5 to 30% by weight.

In the grafted non-woven fabric of the present invention, the grafting occurs only on the surface of the fibers constituting the non-woven fabric and does not occur inside the fibers. Therefore, the required flexibility of the nonwoven fabric is not lost, the strength is not lowered, and the gas permeability is not lowered due to the swelling due to water absorption. Further, since the entire surface of the fibers constituting the non-woven fabric is coated with a hydrophilic graft polymer, it has suitable properties as a battery separator, that is, good hydrophilic properties, gas permeability, and a suitable property. Excellent strength, electrolyte retention capacity, electrolyte durability and oxidation resistance.

When the grafted nonwoven fabric of the present invention is used as a battery separator, a spot for evaluating the time required for liquid absorption or the degree of liquid absorption when a specific amount of water or a 30% aqueous potassium hydroxide solution is dropped. In the liquid absorption test, it is preferable to completely absorb the liquid within 10 seconds. The feature that the spot-absorbing property is good is important as a characteristic of the battery separator. In other words, spot absorbency is to evaluate the speed at which the electrolytic solution penetrates into the battery separator, and when the battery is manufactured, the electrolytic solution must penetrate quickly into the separator to produce the battery. Inconvenience that the property deteriorates occurs. Among the grafted nonwoven fabrics of the present invention, those having a graft ratio of about 5 to 30% by weight have a good spot-absorbing property and can be suitably used as a battery separator.

When the grafted nonwoven fabric of the present invention is used as a battery separator, it is immersed in a 30% potassium hydroxide aqueous solution for 10 minutes to absorb the liquid, and then centrifugally dehydrated at 500 rpm or 3000 rpm for 5 minutes. It is preferable that the weight increase rate (electrolyte solution retention rate) is high. Here, the electrolytic solution holding ratio is a value indicating the electrolytic solution holding capacity of the battery separator itself. In the battery separator, the electrolytic solution retention rate is important for the following reasons.

In the initial stage, a sufficient amount of the electrolytic solution in the battery is distributed in the separator, but as the charge and discharge are repeated, the positive electrode (Ni electrode) gradually swells, and as a result, the separator is compressed and the inside of the separator is compressed. The electrolyte solution is exhausted (dried up), the internal resistance of the battery increases, and the battery capacity decreases. As one measure to prevent dry-up, it is important to give the separator itself a sufficient electrolytic solution holding ability.

Among the grafted nonwoven fabrics of the present invention, those having a graft ratio of about 5 to 30% have a centrifugal dehydration retention rate (30%).
(00 rpm, 5 minutes) is as high as 60% or more, which is very effective for the above-mentioned purpose of preventing dry-up and can be suitably used as a battery separator.

When the grafted nonwoven fabric of the present invention is used as a battery separator, a test piece having a width of 50 mm and a length of 200 mm has a gripping interval of 100 mm and a pulling speed of 10 mm.
The breaking strength at 0 mm / min is preferably 10 kg or more. A general method for manufacturing a cylindrical battery requires a step of stacking an electrode plate and a separator in the order of positive electrode / separator / negative electrode and winding them in a spiral shape. A tensile stress is applied to the separator during this winding. Therefore, the separator must have an absolute strength capable of withstanding the tensile stress during winding. If the separator does not have the required breaking strength, if excessive force is applied during winding, the separator may partially break and pinholes may occur, causing the positive and negative electrodes to contact each other and causing the battery to short-circuit. There is a nature. The grafted nonwoven fabric of the present invention has a sufficient tensile breaking strength and can be suitably used as a battery separator.

When the grafted nonwoven fabric of the present invention is used as a battery separator, the ratio of the tensile breaking strength to the tensile breaking strength of the nonwoven fabric before grafting (strength retention rate).
Is 90 to 100%, particularly preferably 99 to 100%. The strength retention rate is a value indicating the degree of strength reduction due to grafting, and the lower this value, the greater the strength reduction due to grafting. As is clear from the results of Examples and Comparative Examples described later (Table 2), the grafted nonwoven fabric of the present invention shows extremely little strength reduction due to grafting as compared with the conventional one. This is because in the grafted non-woven fabric of the present invention, grafting occurs only on the surface of the polyolefin fiber constituting the non-woven fabric, and the interior of the fiber is not grafted.

In the grafted nonwoven fabric of the present invention, the basis weight of the polyolefin nonwoven fabric is preferably 40 to 80 g / m ² . In the battery separator manufacturing industry, the weight per unit area of the non-woven fabric used for the battery separator will be further reduced in the future to increase the liquid retention rate. Therefore, in battery separator applications, gas permeability (air permeability)
It is sufficient to have a basis weight in the above range to ensure that

As described above, the grafted nonwoven fabric of the present invention has excellent properties such as hydrophilicity and strength, and can be suitably used for battery separators and other applications.

Next, the method for producing the grafted polyolefin-based nonwoven fabric of the present invention will be described.

The method for producing the grafted nonwoven fabric of the present invention is as follows:
After treating the polyolefin-based nonwoven fabric with an organic solvent dispersion liquid of at least one hydrophobic radical initiator, the organic solvent is dried and removed so that the hydrophobic radical initiator is evenly attached and fixed on the fiber surface. The graft polymerization reaction is carried out by immersing it in an aqueous solution of a hydrophilic vinyl monomer.

In the method of the present invention, the polyolefin-based nonwoven fabric which is subjected to the grafting treatment is as described in detail in the description of the grafted nonwoven fabric of the present invention.

Various physical properties of the polyolefin-based nonwoven fabric used in the method of the present invention differ depending on the purpose of use of the grafted nonwoven fabric to be obtained and should be appropriately selected, but the basis weight of the nonwoven fabric is usually 40 to 80 g / m ² , Preferably 50 to 7
It is 0 g / m ² . The thickness of the non-woven fabric is usually 0.13 to 0.20 μm, preferably 0.14, though it depends on the basis weight.
Is about 0.16 μm. For the purpose of a battery separator, it is preferable that the thickness of the non-woven fabric is thin in order to increase the battery capacity. Further, if the strength of the nonwoven fabric is low, the strength of the obtained grafted nonwoven fabric is naturally low. Therefore, the tensile strength at break of the nonwoven fabric is usually 10 to 2
The width is 5 kg / 5 cm.

The method of the present invention is characterized in that a specific treatment for graft-polymerizing a hydrophilic vinyl monomer is performed on the fiber surface of the polyolefin-based nonwoven fabric prior to the graft polymerization reaction. This treatment involves contacting the nonwoven fabric with an organic solvent dispersion of a hydrophobic radical initiator for a certain period of time,
It consists of drying and removing the organic solvent. By this treatment, the hydrophobic radical initiator, that is, the radical active center, is uniformly attached and fixed on the fiber surface.

Examples of the hydrophobic radical initiator used in the method of the present invention include benzoyl peroxide (B
PO), dicumyl peroxide, cumene hydroperoxide, peroxides such as peroxides and their derivatives, and peroxide-based medium temperature catalysts; 2,4-dichlorobenzoyl peroxide, o-chlorobenzoyl peroxide Peroxidic low temperature catalysts such as diacyl peroxide compounds such as bis (4-t-butylcyclohexyl) peroxydicarbonate; Other azobisisobutyronitrile (AI
BN) and the like.

Here, the peroxide type low temperature catalyst means 1
It has a 0-hour half-life (a period until the concentration of the organic peroxide is reduced to half the initial value in 10 hours) at a temperature of 40 to 50 ° C.

On the other hand, the peroxide type medium temperature catalyst means a catalyst having a 10-hour half-life temperature of 70 to 80 ° C.
In the method of the present invention, when only a medium-temperature catalyst having a phenyl group is used, the oxidizing effect becomes strong due to the sensitizing effect of the phenyl group, hydrogen is easily desorbed from the polyolefin resin, and the graft ratio becomes high. Spot liquid absorption is also improved.

Further, when a medium temperature catalyst having a phenyl group and a low temperature catalyst, particularly a low temperature catalyst having a phenyl group, are used in combination, the grafting ratio becomes higher than that when the medium temperature catalyst is used alone, and it is relatively high. It is suitable for obtaining a graft ratio. Further, when a mixture of the above-mentioned medium temperature catalyst and low temperature catalyst in a ratio of 1: 9 to 9: 1, particularly 4: 6 to 6: 4 is used as a hydrophobic radical initiator,
The graft ratio is remarkably improved, and the spot-absorbing property is also good, which is particularly suitable when a high graft ratio is desired.

The amount of the hydrophobic radical initiator adhering to the non-woven fabric should be adjusted appropriately depending on the purpose of use of the resulting grafted non-woven fabric. For example, when it is intended for a battery separator, it is 0.02-3. 0.0% by weight, preferably 0.
It is 1 to 2.0% by weight. When the amount of the hydrophobic radical initiator attached to the nonwoven fabric is less than 0.02% by weight, the graft ratio is low and the nonwoven fabric cannot be sufficiently hydrophilic. On the other hand, if it exceeds 3.0% by weight, the graft ratio becomes too high, the flexibility of the nonwoven fabric is impaired, and the strength also decreases, which is not preferable.

The method of contacting the non-woven fabric with the hydrophobic radical initiator is not particularly limited, and the polyolefin fibers constituting the non-woven fabric are uniformly wetted and coated with the organic solvent dispersion liquid of the hydrophobic radical initiator. Just do it. As such a method, for example, a known dip-nip method, spray method, gravure method, rotor dump method or the like can be applied.

The organic solvent in which the hydrophobic radical initiator is dispersed is not particularly limited as long as it can uniformly disperse the hydrophobic radical initiator. Here, the term “dispersion” is a concept including both states of suspension and solution. That is, in the method of the present invention, the hydrophobic radical initiator does not necessarily have to be completely dissolved in the organic solvent, and may be in a uniform suspension state. Examples of the organic solvent used in the method of the present invention include alcohols such as methyl alcohol, ethyl alcohol and cyclohexanol; ketones such as acetone, methyl ethyl ketone and diethyl ketone; aromatic hydrocarbons such as benzene, toluene and xylene; Examples thereof include halogenated aliphatic hydrocarbons such as trichloroethane, trichloroethylene, and tetrachloroethane; halogenated aromatic hydrocarbons such as monochlorobenzene and dichlorobenzene. Aromatic hydrocarbons, halogenated aliphatic hydrocarbons, hydrophobic organic solvents such as halogenated aromatic hydrocarbons, and ketones are preferable, and more preferably the polyolefin resin is swollen to prevent the adhesion of a radical initiator. Examples of strong ones include aromatic hydrocarbons and halogenated aromatic hydrocarbons that can increase the efficiency of graft polymerization.

The amount of the organic solvent used is not particularly limited, and the concentration of the hydrophobic radical initiator is 0.01 to.
The amount is 1.5% by weight, preferably 0.15 to 1.0% by weight.

The time for contacting the nonwoven fabric with the organic solvent dispersion of the hydrophobic radical initiator is usually 0.25 to 2 hours, preferably 0.5 to 1.5 hours. The temperature at this time is
Usually, it may be room temperature (25 ° C), preferably 5 to 35 ° C.

Next, the nonwoven fabric impregnated with the organic radical dispersion of the hydrophobic radical initiator is taken out, and the organic solvent is dried and removed. There is no particular limitation on the method of drying and removing the organic solvent. The temperature for drying the organic solvent is
Usually, room temperature (25 ° C) may be used, preferably room temperature to 35 ° C
Is. The drying time depends on the drying temperature, but is usually 1 to 1.
It is 2 hours, preferably 6 to 12 hours.

By drying and removing the organic solvent as described above, only the hydrophobic radical initiator is uniformly adhered and fixed on the entire surface of the fibers constituting the nonwoven fabric. As a result, radical active centers for the subsequent graft polymerization reaction are uniformly formed on the entire surface of the fibers constituting the nonwoven fabric.

The kind of the hydrophilic vinyl monomer to be graft-polymerized on the nonwoven fabric to which the radical active center is added is as described in detail in the description of the grafted polyolefin-based nonwoven fabric of the present invention.

The preferred concentration of the monomer in the aqueous solution in which the hydrophilic vinyl monomer is dissolved is 1 to 30% by weight, preferably 3 to 20% by weight. When the monomer concentration is less than 1% by weight, the monomer concentration is too low to uniformly coat the surface of the fibers constituting the nonwoven fabric, and when it exceeds 30% by weight, the graft ratio becomes too high, and the obtained grafted nonwoven fabric is obtained. Is unfavorable because the flexibility and strength of the product deteriorate. Also,
In some cases, the polymerization of hydrophilic vinyl monomers progresses selectively to form a homopolymer.

Prior to the graft polymerization reaction, it is preferable to remove the dissolved oxygen in the hydrophilic vinyl monomer aqueous solution. The dissolved oxygen can be removed by a usual method such as ultrasonic degassing. Further, it is preferable to remove air bubbles inside the nonwoven fabric after immersing the nonwoven fabric to which the hydrophobic radical initiator is attached in the monomer aqueous solution. Deaeration can be performed by a usual method such as decompression treatment.

The temperature at which the graft polymerization is carried out varies depending on the graft polymerization method, the monomer concentration to be polymerized, the kind of the hydrophobic radical initiator attached to the nonwoven fabric, etc.
It is usually 50 to 130 ° C, preferably 70 to 100 ° C. If the temperature is less than 50 ° C, the graft polymerization rate is slow, and 13
When it exceeds 0 ° C, the decomposition rate of the radical initiator becomes too fast, and it becomes difficult to obtain a desired graft ratio.

After the completion of the graft polymerization reaction, the grafted nonwoven fabric obtained is washed with a large amount of water to remove unreacted monomers and homopolymers, dehydrated by means such as centrifugal dehydration, and dried. Thus, the intended grafted nonwoven fabric can be obtained.

[0081]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 (1) Production of a sheath-core type composite fiber As a sheath component, an MFR (melt flow rate) value of 27 was obtained.
g / 10 min ethylene-butene-1 propylene random copolymer (Product name: Y794N, Idemitsu Petrochemical Co., Ltd.)
90 parts by weight of butene-1 propylene random copolymer (product name: Tufmer XR300, manufactured by Mitsui Petrochemical Co., Ltd.), and a core component having an MFR value of 27 g / 10 min. Of polypropylene (product name: ZS1337, manufactured by Ube Industries, Ltd.) using a uniaxial extruder and a composite fiber circular nozzle having a hole diameter of 0.4 mm and a spinning temperature of 20.
Spinning was performed at 0 to 240 ° C. at a take-up speed of 500 m / min to obtain a composite fiber (undrawn yarn) having a sheath / core cross-sectional area ratio of 50/50 and a single yarn denier of 3.0 de. .

The obtained undrawn yarn was drawn 3.0 times to obtain a short cut fiber having a fiber length of 5 mm and a single yarn denier of 1.0 de.

(2) Manufacture of Nonwoven Fabric by Wet Method 2.6 g of the short cut fiber obtained in the above (1) was used as a surfactant (UN683 and UN677 each manufactured by Takemoto Yushi Co., Ltd.).
(5% mixed solution) was uniformly dispersed in 10 liters of water, and paper was made on a mesh having dimensions of 250 mm × 200 mm to prepare a wet web. The obtained web was sandwiched between two heating plates, pressed and dried at a temperature of 140 ° C. for 10 minutes, and the sheath portion of the composite fiber was melted to bond the fibers to each other to form a nonwoven fabric.

The obtained non-woven fabric was washed with methanol to remove the surfactant, and in order to adjust the final thickness of the non-woven fabric, the non-woven fabric was thermocompression-bonded again with a heating press machine at 140 ° C. (weight per unit area: 50 g / m ² ) was obtained.

(3) Treatment of Adhering Hydrophobic Radical Initiator to Fiber Surface Constituting Nonwoven Fabric Benzyl peroxide (10-hour half-life temperature: 72 ° C. (medium temperature catalyst), which is a hydrophobic radical initiator, trade name: The nonwoven fabric obtained in (2) above was immersed in an organic solvent solution prepared by dissolving BPO (manufactured by Nacalai Tesque, Inc.) in xylene, which is an organic solvent, at a concentration of 1% by weight for 1 hour at room temperature. The nonwoven fabric was taken out in a state where the inside of the nonwoven fabric was impregnated with the organic solvent solution, dried at 20 ° C. for 10 hours to remove the organic solvent, and the hydrophobic radical initiator was uniformly attached and fixed on the fiber surface.

The amount of the hydrophobic radical initiator attached was determined by measuring the amount of increase in the weight of the nonwoven fabric after the immersion in the organic solution, and was found to be 1% of the weight of the nonwoven fabric before immersion.

(4) Hydrophilization treatment by graft polymerization 800 ml of a 3% acrylic acid aqueous solution was placed in a cylindrical glass container, and the nonwoven fabric to which the hydrophobic radical initiator had been attached in the above (3) was immersed therein for 30 minutes. 90 after degassing under reduced pressure
Heat at 1.5 ° C. for 1.5 hours. After completion of the reaction, the non-woven fabric was washed with hot water and then dried to obtain the desired grafted non-woven fabric.

(5) Performance Evaluation Test of Grafted Nonwoven Fabric Various results of the grafted nonwoven fabric obtained in (4) above are evaluated by the following [Evaluation 1] to [Evaluation 4].
Shown in.

[Evaluation 1] Graft ratio (%): A value showing the ratio of the grafted hydrophilic vinyl monomer, which was calculated by the following formula. Grafting rate (%) = {(extremely dry weight after polymerization-extremely dry weight before polymerization) / extremely dry weight before polymerization} × 100 That is, in the present invention, the grafting rate means the rate of change in weight of the nonwoven fabric before and after polymerization. Means

[Evaluation 2] Spot absorbency: 20 μl of water or a 30% potassium hydroxide aqueous solution was applied to the grafted nonwoven fabric.
The liquid absorbency of the non-woven fabric is evaluated by the time required for the water drop to be completely absorbed in the non-woven fabric, and shows the hydrophilicity (easiness of wetting) by contact with an aqueous solvent. . The liquid absorbency was evaluated according to the following four grades. A: All water droplets are completely absorbed within 10 seconds. ◯: All water drops are completely absorbed within 1 minute. Δ: All water droplets are completely absorbed, but the absorption requires 1 minute or more. X: Some or all of the water droplets are not absorbed.

[Evaluation 3] Electrolysis solution retention rate (%): A value showing the aqueous solution retention capacity of the grafted nonwoven fabric. The grafted non-woven fabric is immersed in a 30% potassium hydroxide aqueous solution for 10 minutes to absorb the liquid, and then the rotation speed is 500 rpm or 3000.
Dewatering is performed for 5 minutes with a centrifugal dehydrator at rpm. Immediately after the operation was completed, the weight of the nonwoven fabric was measured, and the weight increase rate with respect to the weight of the nonwoven fabric during drying was calculated by the following formula. Electrolyte retention rate (%) = {(nonwoven fabric weight during liquid retention (g) -nonwoven fabric weight during drying (g)) / nonwoven fabric weight during drying} x 10
0

[Evaluation 4] Strength of nonwoven fabric (breaking length (m)):
The non-woven fabric is cut into a size of 5 cm × 14 cm and used as a test piece for strength measurement. This test piece was pulled at a speed of 100 mm / min under conditions of a chuck distance of 10 cm and a width of 5 cm, and the strength at which the test piece broke (tensile breaking strength) (g) was measured. From the obtained results and the basis weight of the nonwoven fabric, the breaking length (m)
Was calculated.

The breaking length means the length (m) at which the grafted nonwoven fabric breaks under its own weight, and is calculated from the tenacity (g) measured as described above and the basis weight of the nonwoven fabric by the following formula. To do. Breaking length (m) = Tensile breaking strength of grafted nonwoven (g) /
[Basis weight (g / m ² ) × test piece width (0.05 m)]

Example 2 As a sheath component, ethylene having an MFR value of 27 g / 10 min.
Butene-1 / Propylene Random Copolymer (Product Name: Y
794N, used by Idemitsu Petrochemical Co., Ltd.), as a core component, MFR value is 27 g / 10 min polypropylene: using (product name ZS1337, Ube Industries, Ltd.), in the same manner as in Example 1 To prepare a grafted non-woven fabric, and Example 1
A performance evaluation test was conducted in the same manner as in. The results are shown in Table 1.

Example 3 As a sheath component, ethylene having an MFR value of 20 g / 10 min.
Propylene random copolymer (Product name: Y2035G,
Idemitsu Petrochemical Co., Ltd.) is used as the core component and MFR
Value of 27g / 10min polypropylene (Product name: ZS1
Using 337, manufactured by Ube Industries, Ltd., a grafted nonwoven fabric was prepared in the same manner as in Example 1, and a performance evaluation test was conducted in the same manner as in Example 1. The results are shown in Table 1.

Example 4 As a sheath component, polypropylene having a MFR value of 27 g / 10 min (product name: ZS1337, manufactured by Ube Industries, Ltd.) 90
Parts by weight, butene-1-propylene random copolymer (Product name: Tufmer XR300, manufactured by Mitsui Petrochemical Co., Ltd.) 1
A mixture of 0 parts by weight was used, and the core component was MFR.
Value of 27g / 10min polypropylene (Product name ZS13
No. 37, manufactured by Ube Industries, Ltd., and 20% of the sheath-core type heat-fusible composite fiber constituting the grafted nonwoven fabric of Example 2 was mixed as an adhesive and grafted in the same manner as in Example 1. A nonwoven fabric was prepared and a performance evaluation test was conducted in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 Polypropylene having a MFR value of 27 g / 10 min for both sheath and core components (Product name: ZS1337, Ube Industries Ltd.)
20% of the sheath-core type heat-fusible conjugate fiber constituting the grafted nonwoven fabric of Example 2 was mixed as an adhesive to prepare a grafted nonwoven fabric in the same manner as in Example 1, and Example 1 was used.
A performance evaluation test was conducted in the same manner as in. The results are shown in Table 1.

Comparative Example 2 As the sheath component, high density polyethylene (HDPE) (product name: J310, manufactured by Asahi Kasei Co., Ltd.) having an MFR value of 20 g / 10 min was used, and as the core component, the MFR value was 27 g /
Using 10 minutes of polypropylene (product name: ZS1337, manufactured by Ube Industries, Ltd.), a graft or a non-woven fabric was produced in the same manner as in Example 1, and the performance evaluation test was performed in the same manner as in Example 1. The results are shown in Table 1.

[0100]

[Table 1]

From the results shown in Table 1, the following is clear. The grafted non-woven fabric of Example 1 comprising a sheath-core type heat-fusible composite fiber containing a low crystalline polymer containing 5.3% by weight of butene-1 as a sheath component has a high graft ratio and is extremely graft-polymerized. It can be seen that it has the property of being easy to do. Further, it can be seen that, in all of the spot absorbency, the electrolyte retention rate and the strength of the non-woven fabric, it exhibits extremely excellent performance and is suitable for use as a battery separator.

The grafted nonwoven fabric of Example 2 comprising the sheath-core type heat-fusible composite fiber containing the low crystalline polymer containing 3.1% by weight of butene-1 as the sheath component has a relatively high graft ratio. It can be seen that it has a high property and is easily graft-polymerized.

The grafted non-woven fabric of Example 3 comprising sheath-core type heat-fusible composite fibers containing a random copolymer of polypropylene and polyethylene, which is easier to graft polymerize than polyethylene, as a sheath component is the grafted non-woven fabric of Comparative Example 2. It can be seen that the strength of the non-woven fabric is particularly improved in comparison with.

The grafted non-woven fabric of Example 4 consisting of sheath-core type composite fibers having a mixture of crystalline polypropylene and a butene-1 · propylene random copolymer as a sheath component was a sheath containing only crystalline polypropylene as a sheath component. It can be seen that, in comparison with the grafted nonwoven fabric of Comparative Example 1 made of core-type composite fibers, all of the performances such as graft ratio, spot liquid absorbency, electrolyte retention, and nonwoven fabric strength are greatly improved. It is considered that this is because the graft polymerization reactivity on the fiber surface was improved by using the sheath component in which the butene-1 / propylene random copolymer was mixed. That is, since the graft polymerization is easy, the hydrophilicity of the non-woven fabric is improved, and the liquid absorbing property and the liquid retaining property of the electrolytic solution are improved. Since the sheath-core type composite fiber constituting the grafted nonwoven fabric of Example 4 is not heat-fusible, an adhesive component was added to bond the fibers together. Therefore, Examples 1 to 1
Compared to the grafted non-woven fabric of No. 3, the improvement in the non-woven fabric strength was small.

It can be seen that the grafted nonwoven fabrics of Comparative Examples 1 and 2 in which the sheath component is composed of the sheath-core type composite fiber composed only of the highly crystalline polymer, have a low graft ratio and are difficult to undergo graft polymerization. Moreover, in all or any performance of spot liquid absorption, electrolyte retention, nonwoven fabric strength,
It can be seen that it is inferior to the grafted nonwoven fabrics of Examples 1 to 4.

Example 5 (1) Production of sheath-core type composite fiber As a sheath component, MFR (melt flow rate) value was 12
Linear low-density polyethylene with g / 10 min and ρ = 0.912 g / cc (Product name: CS5005, Sumitomo Chemical Co., Ltd.)
Polypropylene (product name: S130MV, Ube Industries, Ltd.) with a MFR value of 27 g / 10 min as the core component
By using a composite spinning equipment equipped with two single-screw extruders and a circular nozzle for composite fibers having a hole diameter of 0.4 mm, and spinning at a spinning temperature of 200 to 240 ° C. and a take-up speed of 500 m / min. Fiber (undrawn yarn) with a cross-sectional area ratio of the core and core of 50/50 and a denier of single yarn of 3.1 de
Got

The obtained undrawn yarn was drawn 3.1 times to obtain a composite fiber composed of fibers having a fiber length of 5 mm and a single yarn denier of 1.0 de.

(2) Production of Nonwoven Fabric by Wet Method 2.6 g of the fiber obtained in the above (1) was used as a surfactant (UN683 and UN677, each of 0.056 by Takemoto Yushi Co., Ltd.).
% Mixed solution) was uniformly dispersed in 10 liters of water, and paper was made on a mesh having dimensions of 250 mm × 200 mm to prepare a wet web. 2 webs obtained
The nonwoven fabric was sandwiched between heating plates and pressed at a temperature of 110 ° C. for 10 minutes to dry, and at the same time, the sheath portion of the composite fiber was melted to bond the fibers to each other to form a nonwoven fabric.

Further, in order to remove the oil adhering to the obtained non-woven fabric, washing with hot water at 80 ° C. and washing with methanol at room temperature were carried out, and again in order to adjust the final thickness of the non-woven fabric, heating press at 110 ° C. A non-woven fabric (weight per unit area: 51 g / m ² ) was obtained by thermocompression bonding with a machine.

(3) Hydrophobic Radical Initiator Adhesion Treatment to Fiber Surface Constituting Nonwoven Fabric Benzyl peroxide (10-hour half-life temperature: 72 ° C. (medium temperature catalyst), which is a hydrophobic radical initiator, trade name: The nonwoven fabric obtained in (2) above was immersed in an organic solvent solution prepared by dissolving BPO (manufactured by Nacalai Tesque, Inc.) in acetone, which is an organic solvent, at a concentration of 0.6% by weight for 1 hour at room temperature. The nonwoven fabric was taken out in a state where the inside of the nonwoven fabric was impregnated with the organic solvent solution, dried at room temperature for 12 hours to remove the organic solvent, and the hydrophobic radical initiator was uniformly attached and fixed to the fiber surface.

The amount of the hydrophobic radical initiator attached was 1.3% based on the weight of the non-woven fabric before the dipping, as a result of measuring the weight increase amount of the non-woven fabric after the dipping in the organic solution.

(4) Hydrophilization treatment by graft polymerization Acrylic acid is dissolved in ion-exchanged water to a concentration of 10% by weight, and ultrasonic degassing is performed for 30 minutes to remove dissolved oxygen in the solution. To obtain a monomer solution. Soak the non-woven fabric treated in (3) above in this monomer solution to remove air bubbles inside the non-woven fabric at 70 cm.
The mixture was degassed at room temperature under reduced pressure of Hg for 1 hour. Then 90
The reaction vessel was set in a constant temperature bath maintained at 0 ° C., and a graft polymerization reaction was carried out for 1 hour.

After completion of the reaction, in order to remove unreacted monomers and homopolymer, washing with a large amount of water was performed, and then 8
Washing with hot water at 0 ° C was performed. Further, the wash water was removed by centrifugal dehydration (speed 400 rpm), and then 75 at 55 ° C.
It was dried under reduced pressure of cmHg for 2 hours to obtain an intended grafted nonwoven fabric.

(5) Performance Evaluation Test of Grafted Nonwoven Fabric Table 2 shows the results of evaluation of various properties of the grafted nonwoven fabric obtained in (4) above by the following test methods (a) to (g).

(A) Graft ratio (%): A value showing the ratio of the grafted hydrophilic vinyl monomer, which was calculated by the following formula. Grafting rate (%) = {(extremely dry weight after polymerization-extremely dry weight before polymerization) / extremely dry weight before polymerization} × 100 That is, in the present invention, the grafting rate means the rate of change in weight of the nonwoven fabric before and after polymerization. Means

(B) Spot absorbency: This is to evaluate the absorbency when water and a 30% potassium hydroxide aqueous solution are dripped at 50 locations at a volume of 0.05 cc / drop onto the grafted nonwoven fabric, Hydrophilicity due to contact with aqueous solvent (easy wetting)
Represents The liquid absorbency was evaluated according to the following four grades. A: Complete liquid absorption within 10 seconds. ◯: Completely absorb the liquid within 1 minute. Δ: There is a portion that does not absorb liquid. X: No liquid is absorbed.

(C) Centrifugal dehydration retention rate (%): A value showing the aqueous solution retention capacity of the grafted nonwoven fabric. Immerse the grafted non-woven fabric in 30% potassium hydroxide aqueous solution for 10 minutes to absorb the liquid, and then perform forced dehydration for 5 minutes with a centrifugal dehydrator at 3000 rpm. The rate of change in weight was calculated by the following formula. Centrifugal dehydration retention rate (%) = {(weight of nonwoven fabric after absorbing liquid-weight of nonwoven fabric before absorbing) / weight of nonwoven fabric before absorbing} x 100

(D) Tensile breaking strength (kg): A value showing the strength of the grafted nonwoven fabric against tensile stress. A test piece with a width of 50 mm and a length of 200 mm was cut out from the grafted non-woven fabric, and the strength (kg) at which the test piece broke was measured with a gripping interval of 100 mm and a pulling speed of 100 mm / min.

(E) Strength retention rate (%): A value showing how much the tensile strength of the nonwoven fabric is reduced by the grafting treatment. The breaking strength of the non-woven fabric before grafting
It was determined in the same manner as in (4), and the ratio of the breaking strength of the non-woven fabric after the grafting treatment to the breaking strength of the non-woven fabric before the grafting treatment was calculated by the following formula. Strength retention rate (%) = (breaking strength of non-woven fabric after grafting treatment / breaking strength of non-woven fabric before grafting treatment) × 100

(F) Elongation at break (%): A value showing the flexibility and strength of the grafted nonwoven fabric. A test piece with a width of 50 mm and a length of 200 mm is cut out from the grafted non-woven fabric, the grip interval is 100 mm, the pulling speed is 100 mm / min, and the length (cm) of the test piece when the test piece breaks is measured, and the test starts. The elongation (%) with respect to the length (cm) of the previous test piece was calculated by the following formula. Elongation at break (%) = [Length at break of test piece (cm)
-Length of test piece before start of test (cm)] / Length of test piece before start of test (cm) x 100

(G) Breaking length (m): It means the length (m) at which the grafted nonwoven fabric breaks under its own weight, and the tensile breaking strength (g) of the above (d) and the factor of the unit weight of the nonwoven fabric. Was calculated by the following formula. Breaking length (m) = Tensile breaking strength of grafted nonwoven (g) /
[Basis weight (g / m ² ) × test piece width (0.05 m)]

Example 6 Example 1 was repeated except that a non-woven fabric having a basis weight of 75 g / m ² was used and xylene was used as an organic solvent for dissolving benzoyl peroxide (BPO) which is a hydrophobic radical initiator.
A grafted non-woven fabric was prepared in the same manner as above, and a performance evaluation test was conducted in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3 A non-woven fabric having a basis weight of 65 g / m ² was used, and instead of adhering a hydrophobic radical initiator, an electron beam having a pressure voltage of 200 kV and a beam current of 7.2 mA was irradiated in a nitrogen gas atmosphere at 20 Mrad. Except for the above, a grafted nonwoven fabric was produced in the same manner as in Example 5, and a performance evaluation test was performed in the same manner as in Example 5.
The results are shown in Table 2.

Comparative Example 4 As a battery (battery) separator, a nylon resin non-woven fabric (basis weight: 99 g / m ² ) incorporated in a commercially available nickel-cadmium battery was spot-absorbed in the same manner as in Example 5. And the centrifugal dehydration retention rate were tested. The results are shown in Table 2.

[0125]

[Table 2]

From the results in Table 2, the grafted nonwoven fabrics obtained in Examples 5 and 6 have good hydrophilic properties (spot absorbency, centrifugal dehydration retention rate) and strength and flexibility due to grafting. It can be seen that the deterioration of the battery is small and that it has the characteristics suitable for use as a battery separator.

On the other hand, Comparative Example 3 by the electron beam irradiation method
The grafted non-woven fabric obtained in step 1 is inferior in hydrophilic property, and the strength and flexibility are largely reduced by grafting. Furthermore, it can be seen that the non-woven fabric of Comparative Example 4, which is a non-woven fabric made of nylon resin used in a commercially available battery, has a slightly poor spot-absorbing property, but has a low centrifugal dehydration retention rate.

Example 7 As a hydrophobic radical initiator, bis (4-t-butylcyclohexyl peroxydicarbonate (10 hours half-life temperature: 44 ° C.), which is a percarbonate low temperature catalyst, was used.
Was used, the acrylic acid monomer concentration was set to 3% by weight, and the hydrophilic treatment was performed under the reaction conditions of a temperature of 90 ° C. for 1 hour, and the same procedure as in Example 5 was carried out to obtain a grafted nonwoven fabric.

Example 8 Benzoyl peroxide (BP), which is the same medium temperature catalyst used in Example 5, was used as the hydrophobic radical initiator.
O) and the acrylic acid monomer concentration is 3% by weight,
A grafted nonwoven fabric was obtained in the same manner as in Example 5, except that the hydrophilic treatment was performed under the reaction conditions of a temperature of 90 ° C. for 1 hour.

Example 9 As a hydrophobic radical initiator, benzoyl peroxide (BPO) as a medium temperature catalyst and bis (4-t-butylcyclohexyl peroxydicarbonate as a low temperature catalyst of percarbonate of 6: 5 were used. A grafted nonwoven fabric was obtained in the same manner as in Example 7, except that the proportions were used.

The adhesion ratio (%) of the hydrophobic radical initiator to the nonwoven fabric, the graft ratio (%) and the spot absorbency of the obtained grafted nonwoven fabric in Examples 7 to 9 were examined. The results obtained are shown in Table 3 below.

[0132]

[Table 3]

As is clear from the results in Table 3, even when the low temperature catalyst alone has a high peroxide adhesion rate, the grafting rate does not increase, and therefore the hydrophilicity is low. The medium temperature catalyst alone has a higher graft ratio than the low temperature catalyst alone, even though the peroxide deposition rate is low. Furthermore, when the low temperature catalyst and the medium temperature catalyst are mixed and used, the adhesion rate of the peroxide is low, but the graft ratio is dramatically higher than that of the low temperature catalyst or the medium temperature catalyst alone. Therefore, it can be seen that the hydrophilicity is also good.

Test Example: Evaluation of uneven dyeing of grafted nonwoven fabric
Test In the same manner as in Example 6, the graft ratio was 28.1% (CAT
1) and 26.5% (referred to as CAT2) of two grafted non-woven fabrics of the present invention. Also, in the same manner as in Comparative Example 3, a grafted non-woven fabric was prepared by an electron beam irradiation method with a graft ratio of 15.6% (referred to as EB1) and 13.6% (referred to as EB2).

These four kinds of grafted nonwoven fabrics were immersed in an aqueous solution of a disperse dye (Sumikaron Red S-GG, Sumitomo Chemical Co., Ltd.) at 90 ° C. for 30 minutes to dye the grafted nonwoven fabric red. This dyed nonwoven fabric (test piece: 50 ×
(100 mm) is measured with a formation measuring machine (Nomura Shoji Co., Ltd., Formention Tester FMT2000; a device for generally measuring the non-uniform weight of non-woven fabric) to measure the light-blocking degree and the light-blocking rate, and evaluate the dyeing non-uniformity of the grafted non-woven fabric. did.

Specifically, the dyed test piece is placed on the sample table of the formation measuring machine, light (intensity I ₀ ) is applied from the bottom of the test piece, and this transmission image is taken by the CCD camera above the test piece. Was decomposed into 256 × 243 pixels, each light intensity (I) was detected, and the light shielding degree (E) was calculated by the following equation. E = (I ₀ −I) / I ₀

Further, each light-shielding degree has all pixels (total number of pixels: 2).
56 × 243 = 62,208), the ratio of the light blocking ratio (%) is taken as a graph showing the relationship between the light blocking ratio and the light blocking ratio.
It was shown to.

Further, the average degree of shading of each grafted nonwoven fabric,
Table 4 shows the standard deviation and the variation rate of the light shielding degree. The variation rate (%) of the degree of shading was calculated by the following formula. Shading degree variation (%) = (standard deviation / average shading degree) x 1
00

[0139]

[Table 4]

From the results shown in FIG. 9 and Table 4, the uneven dyeing (rate of variation of light-shielding degree) of the grafted nonwoven fabric of the present invention is about 1/2 of that of the grafted nonwoven fabric produced by the electron beam irradiation method. It can be seen that they are dyed uniformly. From this, in the grafted nonwoven fabric of the present invention, the entire surface of the fibers constituting the nonwoven fabric is covered with the graft polymer, and the graft polymer is not localized at the joint portion of the fibers constituting the nonwoven fabric. Is clear.

[0141]

Therefore, according to the present invention, the graft polymer is uniformly coated on the entire surface of the fiber without being localized at the joint portion of the fibers constituting the polyolefin-based nonwoven fabric. There is provided a grafted polyolefin-based nonwoven fabric having high strength and excellent hydrophilicity while maintaining its original oxidation resistance and alkali resistance, and a method for producing the same. The grafted polyolefin-based nonwoven fabric of the present invention has excellent hydrophilicity, electrolytic solution holding ability, electrolytic solution durability, oxidation resistance and the like, and can be suitably used as a battery separator.

[Brief description of drawings]

FIG. 1 is a photograph (500 times magnification) showing the shape of fibers of a grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 6.1%.

FIG. 2 is a photograph (500 times magnification) showing the fiber shape of the grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 10.2%.

FIG. 3 is a photograph (500 times magnification) showing the fiber shape of the grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 18.3%.

FIG. 4 is a photograph (500 times magnification) showing the fiber shape of the grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 31.1%.

FIG. 5 is a photograph (3,000 times magnification) showing the fiber shape of the grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 5.3%.

FIG. 6 is a photograph (3,000 times magnification) showing the fiber shape of the grafted polyolefin-based nonwoven fabric of the present invention having a graft ratio of 10.2%.

FIG. 7 is a photograph (500 times magnification) showing the shape of fibers of a grafted polyolefin-based nonwoven fabric having a graft ratio of 33.1% produced by an electron beam irradiation method.

FIG. 8 is a photograph (2,000 times magnification) showing the fiber shape of the same grafted polyolefin-based nonwoven fabric as in FIG. 7.

FIG. 9 is a graph showing the degree of uneven dyeing of the grafted nonwoven fabric of the present invention and the grafted nonwoven fabric produced by the electron beam irradiation method.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI H01M 2/16 H01M 2/16 G (56) Reference JP-A-7-26453 (JP, A) JP-A-4-281014 ( JP, A) JP-A-5-140848 (JP, A) JP-A-5-230747 (JP, A) JP-B 1-336231 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) D04H 1/00-18/00 D06M 10/00-23/18 D01F 1/00-13/04 D21H 11/00-27/42 H01M 2/14-2/18 C08F 255/00-255 / Ten

Claims (9)

(57) [Claims] 1. A grafted polyolefin-based non-woven fabric comprising a non-woven fabric composed of a polyolefin-based fiber and a graft polymer of a hydrophilic vinyl monomer formed on a fiber constituting the non-woven fabric, wherein
Olefin fiber has less polymer that constitutes the sheath component
Both are partially unsaturated hydrocarbons having 2 or 4 to 8 carbon atoms
Random copolymerized polypropylene with element as a copolymerization component
Yes, the polymer forming the core component is polypropylene
A grafted polyolefin-based nonwoven fabric , which is a sheath-core type composite fiber, and in which the graft polymer is present on the entire surface of the fiber without being localized at the joint portion of the fibers constituting the nonwoven fabric. 2. The number of carbon atoms in the total amount of the polymer constituting the sheath component.
The content of the aliphatic unsaturated hydrocarbon of 2 or 4 to 8 is 3.
The grafted polyolefin-based nonwoven fabric according to claim 1 , which is 0 to 7.0% by weight. 3. The grafted polyolefin-based non-woven fabric according to claim 2 , wherein at least a part of the polymer constituting the sheath component is a random copolymer polypropylene containing butene-1 as a copolymer component. Random copolymer of polypropylene containing 4. A butene-1 as a copolymerizable component, butene-1-propylene copolymer or ethylene - to claim 3, characterized in that the butene-1-propylene copolymer The grafted polyolefin-based nonwoven fabric described. 5. A non-woven fabric made of a polyolefin fiber.
And a hydrophilic vinyl chloride formed on the fibers constituting the nonwoven fabric.
Graft polymer containing a graft polymer of a monomer
In the reffin-based non-woven fabric, the polyolefin- based fiber constituting the non-woven fabric has a sheath component of linear low-density polyethylene (L-LDPE) and a core component of polypropylene. composite fiber der is, graft polymer
Is not localized at the joints of the fibers that make up the nonwoven fabric.
A graphitized polyolefin-based nonwoven fabric characterized by being present on the entire surface of the fiber . 6. The grafted polyolefin-based nonwoven fabric according to claim 5 , wherein the granular graft polymer lumps are distributed at a constant ratio on the graft-polymer coating on the surface of the polyolefin-based fiber. 7. The grafted polyolefin-based non-woven fabric according to claim 6 , wherein the granular graft polymer mass is distributed on the surface of the polyolefin-based fiber at a rate of 1 to 200,000 / mm ² . 8. A battery separator comprising the grafted polyolefin-based nonwoven fabric according to any one of claims 1 to 7 . 9. A polyolefin-based nonwoven fabric is treated with an organic solvent dispersion liquid of at least one hydrophobic radical initiator, and then the organic solvent is dried and removed to uniformly attach the hydrophobic radical initiator to the fiber surface. A method for producing a grafted polyolefin-based nonwoven fabric, which comprises fixing and then immersing it in an aqueous solution of a hydrophilic vinyl monomer to carry out a graft polymerization reaction.