JP4859630B2 - Battery separator containing ethylene-vinyl alcohol copolymer fiber - Google Patents

Description

The present invention relates to a battery separator including a nonwoven fabric produced using a split type composite fiber containing a novel ethylene-vinyl alcohol copolymer and a specific thermoplastic resin , and more specifically, an alkaline solution as an electrolyte. about the separators of the secondary battery to be used.

Fibers made from ethylene-vinyl alcohol copolymer (hereinafter abbreviated as EVOH) have hydroxyl groups in EVOH, so they have superior hydrophilicity and moisture absorption and desorption properties that are not found in conventional synthetic fibers. The single fibers and the composite fibers with other thermoplastic resins have been widely used as materials for sports clothing and the like.
Various other uses have been studied, and among them, studies are being made to apply nonwoven fabrics made of such EVOH fibers and composite fibers to separators for alkaline secondary batteries.

Such a separator separates an anode active material and a cathode active material of a battery, and a nonwoven fabric made of polyamide fiber or polyolefin fiber is widely used in an alkaline secondary battery.
However, the polyamide fiber is easily oxidized and has a drawback that it is oxidized and deteriorated by oxygen gas generated during charging. In addition, since polyolefin fibers are inferior in hydrophilicity, hydrophilic treatment such as introduction of sulfonic acid groups is required, leading to cost increase, and the hydrophilicity does not last for a long time. There was a problem that it was easy to deteriorate.

  Thus, in order to solve these problems, a battery separator using a fiber containing EVOH and a nonwoven fabric thereof has been studied. EVOH can be expected to have an effect on the liquid absorbency and retention of the electrolytic solution due to its hydrophilicity. For example, a separator fiber made of EVOH having a specific saponification degree and an ethylene content (see, for example, Patent Document 1) and the like. A separator fiber made of a mixture of EVOH having a specific ethylene content and polyamide (see, for example, Patent Document 2) has been proposed.

However, in recent years, there has been an increasing demand for smaller size and higher output for alkaline secondary batteries, and as a result, separators are required to have more advanced characteristics with respect to liquid absorption / retention properties and oxidation resistance of electrolytes. became. Then, when this inventor examined in detail about the fiber for battery separators described in these patent documents, it turned out that the characteristic is still inadequate with respect to the present high demand.
JP 2002-227031 A JP 2002-242024 A

An object of this invention is to provide the battery separator suitable as a separator for alkaline secondary batteries , including the nonwoven fabric containing EVOH fiber excellent in the liquid absorption property / retention property and oxidation resistance of electrolyte solution.

（ここで、Ｒ¹は水素原子または有機基を表わし、Ｘはエーテル結合を除く結合鎖を表わし、ｎは０または１を表し、Ｒ²〜Ｒ⁴はそれぞれ水素原子または有機基を表わす） As a result of intensive studies in view of the above circumstances, the present inventors have found that the object of the present invention can be achieved by EVOH in which a functional group having a 1,2-glycol structure is introduced into the side chain, thereby completing the present invention. did.
That is, the gist of the present invention is a battery separator including a non-woven fabric produced using a split type composite fiber containing EVOH having the following structural unit (1) and a thermoplastic resin, wherein the thermoplastic resin is: , polyester polymers, polyamide polymers, a one or more resins selected from a polyolefin-based polymer, a composite ratio of the thermoplastic resin and EVOH is 10 / 90-90 / 10 der Rukoto It has characteristics.

(Wherein R ¹ represents a hydrogen atom or an organic group, X represents a bond chain excluding an ether bond, n represents 0 or 1, and R ^{2 to} R ⁴ each represents a hydrogen atom or an organic group)

  In the present invention, since EVOH has such a structural unit, the hydrophilicity and moisture retention superior to those of conventional EVOH can be obtained, and such a structural unit is stable even under oxidizing conditions. For example, when used as a material for a battery separator, it is presumed that excellent electrolyte absorbability and retention can be obtained stably.

The battery separator of the present invention, the nonwoven fabric used has excellent absorbent, retention and oxidation resistance of the electrolytic solution, it is preferable as a alkaline secondary battery separators.

Hereinafter, the present invention will be specifically described.
In addition, description of the component requirement described below is an example (representative example) of the embodiment of this invention, and is not specified by these content.

The EVOH fiber of the present invention is an EVOH fiber containing EVOH (A) containing the following structural unit (1), R ¹ represents a hydrogen atom or an organic group, X represents a bond chain excluding an ether bond, n represents 0 or 1, and R ^{2 to} R ⁴ each represents a hydrogen atom or an organic group.

The composition of EVOH (A) in the present invention is not particularly limited.
The content of the structural unit (1) in the EVOH (A) is usually 0.1 to 30 mol%, preferably 0.2 to 20 mol%, particularly preferably 0.3 to 10 mol%, particularly preferably. 1 to 5 mol%. If the content is too small, the effects of the present invention are not sufficiently exhibited. Conversely, if the content is too large, the oxidation resistance tends to decrease.
Moreover, when adjusting this content, it is also possible to adjust by blending at least two kinds of EVOH (A) having different contents, and at least one of them contains no structural unit (1). It does not matter.
With regard to EVOH in which the 1,2-glycol bond amount is adjusted in this way, the 1,2-glycol bond amount can be calculated by weight average, and the ethylene content can also be calculated by weight average. However, precisely, the ethylene content and the 1,2-glycol bond amount can be calculated from the measurement result of ¹ H-NMR.

Furthermore, the ethylene content of EVOH (A) in the present invention is usually 0.1 to 60 mol%, preferably 10 to 60 mol%, particularly preferably 20 to 50 mol%. If the content is too small, the strength of the fiber tends to be reduced. Conversely, if the content is too high, the liquid absorbency and liquid retention of the electrolyte solution tend to be reduced.
The content of the vinyl alcohol structural unit is usually 40 to 90 mol%, preferably 50 to 80 mol%, particularly preferably 60 to 70 mol%. When the content is too small, the hydrophilicity tends to decrease, and when the content is too large, the heat melting stability may decrease.
The balance is a structural unit derived from vinyl acetate.

  The saponification degree of EVOH (A) is usually 90 mol% or more, preferably 95 mol% or more, particularly preferably 99 mol% or more. If the degree of saponification is too low, the oxidation resistance tends to decrease.

In the case where _n of the connecting unit (X) _n of the structural unit (1) is 1, any connecting chain other than an ether bond can be applied, and is not particularly limited, but non-aromatic such as alkylene, alkenylene, alkynylene, etc. In addition to hydrocarbon chains, aromatic hydrocarbon chains such as phenylene and naphthylene (these hydrocarbon chains may be substituted with halogen such as fluorine, chlorine and bromine), -CO-, -COCO-,- _{CO (CH 2) m CO -} , - CO (C 6 H 4) CO -, - S -, - CS -, - SO -, - SO 2 -, - NR -, - CONR -, - NRCO -, - CSNR -, - NRCS -, - NRNR -, - HPO 4 -, - Si (OR) 2 -, - OSi (OR) 2 -, - OSi (OR) 2 O -, - Ti (OR) 2 -, - _{OTi (OR) 2 -, -} OTi (OR) 2 O -, - Al (OR) , -OAl (OR)-, -OAl (OR) O-, and the like (R is each independently an optional substituent, preferably a hydrogen atom or an alkyl group, and m is a natural number). Among these, non-aromatic hydrocarbon chains are preferable from the viewpoint of heat melting stability, and alkylene is particularly preferable. As such alkylene, those having a small number of carbon atoms are preferable and those having 6 or less carbon atoms are suitably used from the viewpoint that the liquid retaining property of the electrolytic solution is good.
The ether bond is not preferable in that it is easily decomposed during melt spinning, and the heat melting stability of EVOH is lowered.

When R ¹ and R ^{2 to} R ⁴ of the structural unit (1) are organic groups, the organic group is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and an n-butyl group. And an alkyl group having 1 to 4 carbon atoms such as an isobutyl group and a tert-butyl group, and optionally has a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group. Also good.

そして、本発明の共重合体の最も好ましい組成は、上記構造単位（１ａ）が１〜５モル％、エチレン含有量が２０〜５０モル％、ビニルアルコール構造単位の含有量は６０〜７０モル％、および残部が酢酸ビニル由来のビニルアセトキシ構造単位であるものである。 In the most preferred structure of EVOH (A) in the present invention, R ¹ and R ^{2 to} R ⁴ in the structural unit (1) are all hydrogen atoms, and _n of the bond chain (X) n is 0, that is, a single bond. Is. That is, those containing a structural unit represented by the following structural formula (1a) are preferable.

The most preferred composition of the copolymer of the present invention is that the structural unit (1a) is 1 to 5 mol%, the ethylene content is 20 to 50 mol%, and the vinyl alcohol structural unit content is 60 to 70 mol%. , And the balance is vinylacetoxy structural units derived from vinyl acetate.

  The method for producing EVOH (A) used in the present invention is not particularly limited, but taking EVOH (A) containing structural unit (1a) as the most preferred structure as an example, [1] 3,4- Diol-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-ol-1-butene, 4-acyloxy-3-ol-1-butene, 3,4-diacyloxy-2-methyl- Using 1-butene or the like, copolymerizing these with a vinyl ester monomer and ethylene to obtain a copolymer, and then saponifying the copolymer, or [2] using vinyl ethylene carbonate or the like as a comonomer A method in which a vinyl ester monomer and ethylene are copolymerized to obtain a copolymer, which is then saponified and decarboxylated, or [3] Komono 2,2-dialkyl-4-vinyl-1,3-dioxolane and the like are used as a copolymer, and a vinyl ester monomer and ethylene are copolymerized to obtain a copolymer, followed by saponification and deacetalization, etc. Is mentioned.

Among them, a method of saponifying a copolymer obtained by copolymerizing 3,4-diacyloxy-1-butene, a vinyl ester monomer and ethylene is preferable in terms of excellent copolymerization reactivity. It is preferable to use 3,4-diacetoxy-1-butene as -diasiloxy-1-butene. A mixture of these monomers may also be used.
Further, 3,4-diacetoxy-1-butane, 1,4-diacetoxy-1-butene, 1,4-diacetoxy-1-butane and the like may be contained as a small amount of impurities.

（ここで、Ｒはアルキル基であり、好ましくはメチル基である。）

（ここで、Ｒはアルキル基であり、好ましくはメチル基である。）

（ここで、Ｒはアルキル基であり、好ましくはメチル基である。） Hereinafter, the copolymerization method using 3,4-diacetoxy-1-butene as a comonomer will be described, but the present invention is not limited thereto.
The 3,4-diol-1-butene is represented by the following formula (2), and the 3,4-diacyloxy-1-butene is represented by the following formula (3), 3-acyloxy-4-ol-1-butene. Represents the following formula (4), and 4-acyloxy-3-ol-1-butene is represented by the following formula (5).

(Here, R is an alkyl group, preferably a methyl group.)

(Here, R is an alkyl group, preferably a methyl group.)

(Here, R is an alkyl group, preferably a methyl group.)

  The compound represented by the above formula (2) is available from Eastman Chemical Co., and the compound represented by the above formula (3) is commercially available from Eastman Chemical Co. for industrial production and from Across Co. at the reagent level. can do. Further, 3,4-diacetoxy-1-butene obtained as a by-product during the production process of 1,4-butanediol can also be used.

  Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, Although vinyl versatate etc. are mentioned, vinyl acetate is preferably used especially from an economical viewpoint.

  There are no particular restrictions on the copolymerization of 3,4-diacyloxy-1-butene, etc. with vinyl ester monomers and ethylene monomers, such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization. Although known methods can be employed, solution polymerization is usually performed.

The method for charging the monomer component at the time of copolymerization is not particularly limited, and any method such as batch charging, split charging, continuous charging, etc. may be employed.
The copolymerization ratio of 3,4-diasiloxy-1-butene and the like is not particularly limited, but the copolymerization ratio may be determined in accordance with the amount of the structural unit (1) introduced.
Further, the ethylene content in the copolymer can be controlled by the ethylene pressure during the polymerization, and it cannot be generally determined by the intended ethylene content, but is usually in the range of 25 to 80 kg / cm ² . Selected from.

Examples of the solvent used in such copolymerization usually include saturated alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propanol, and butanol, and ketones such as acetone and methyl ethyl ketone. Preferably used.
The amount of the solvent used may be appropriately selected in consideration of the chain transfer constant of the solvent in accordance with the degree of polymerization of the target copolymer. For example, when the solvent is methanol, S (solvent) / M ( Monomer) = 0.01 to 10 (weight ratio), preferably 0.05 to 7 (weight ratio).

  In the copolymerization, a polymerization catalyst is used. Examples of the polymerization catalyst include known radical polymerization catalysts such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauryl peroxide, and t-butylperoxyneodeca Noate, t-butylperoxypivalate, α, α′bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3, -tetramethylbutylperoxyneodeca Peroxyesters such as noate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-hexylperoxypivalate, di-n-propylperoxydi Carbonate, di-iso-propyl peroxydicarbonate], di-sec- Til peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, dimethoxybutyl peroxydicarbonate, di Peroxydicarbonates such as (3-methyl-3-methoxybutylperoxy) dicarbonate, diacyl peroxides such as 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide, lauroyl peroxide, etc. A low temperature active radical polymerization catalyst etc. are mentioned.

The amount of the polymerization catalyst used varies depending on the type of catalyst and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate. For example, when azobisisobutyronitrile or acetyl peroxide is used, 10 to 2000 ppm is preferable with respect to the vinyl ester monomer, and 50 to 1000 ppm is particularly preferable.
Moreover, although the reaction temperature of a copolymerization reaction changes with the solvent and pressure to be used, it is preferable to select normally from the range of about 40 degreeC-a boiling point.

  In the present invention, EVOH (A) obtained by allowing a hydroxylactone compound or hydroxycarboxylic acid to coexist with the above catalyst is preferable in terms of improving the color tone of the EVOH (A), and the hydroxylactone compound is preferably a molecule. It is not particularly limited as long as it is a compound having a lactone ring and a hydroxyl group, and examples thereof include L-ascorbic acid, erythorbic acid, glucono delta lactone, etc., preferably L-ascorbic acid and erythorbic acid are used. Examples of the hydroxycarboxylic acid include glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid, and the like, and citric acid is preferably used.

  The amount of the hydroxylactone compound or hydroxycarboxylic acid used is not particularly limited, but is usually 0.0001 to 0.1 parts by weight, preferably 0.0005 to 0.05 parts by weight based on 100 parts by weight of vinyl acetate. Parts by weight, particularly preferably 0.001 to 0.03 parts by weight. If the amount used is too small, these addition effects may not be obtained. As a result of inhibiting the polymerization of vinyl, it is not preferable.

  There is no particular limitation on charging such a compound into the polymerization system, but it is usually charged into a polymerization reaction system by diluting with a solvent such as an aliphatic ester containing lower aliphatic alcohol or vinyl acetate, water, or a mixed solvent thereof. .

  Further, in the present invention, a copolymer substantially comprising ethylene and vinyl acetate containing the structural unit of the general formula (1) shown above is produced. A small amount of a copolymerizable ethylenically unsaturated monomer may be copolymerized within a range that does not inhibit the above.

  The obtained copolymer is then saponified. In such saponification, an alkali catalyst or an acid catalyst is used in a state where the copolymer obtained above is dissolved in alcohol or hydrous alcohol. Done. Examples of the alcohol include saturated alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propanol, and tert-butanol, and methanol is particularly preferably used. The concentration of the copolymer in the alcohol is appropriately selected depending on the viscosity of the system, but is usually selected from the range of 10 to 60% by weight.

Catalysts used for saponification include alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, lithium methylate, etc., sulfuric acid, Examples include acid catalysts such as hydrochloric acid, nitric acid, metasulfonic acid, zeolite, and cation exchange resin.
The amount of the saponification catalyst used is appropriately selected depending on the saponification method, the target degree of saponification, and the like. Usually, when an alkali catalyst is used, a vinyl ester monomer and 3,4-diacyloxy-1- 0.001-0.1 equivalent with respect to the total amount of monomers, such as butene, Preferably 0.005-0.05 equivalent is suitable.

With regard to such a saponification method, batch saponification, continuous saponification on a belt, and continuous saponification of a tower type are possible depending on the target saponification degree, etc., and the amount of alkali catalyst during saponification can be reduced and saponification reaction is high. For reasons such as efficiency and ease of progress, tower saponification under constant pressure is preferably used. The pressure during saponification cannot be generally specified depending on the target ethylene content, but is selected from the range of ^{2 to} 7 kg / cm ² , and the temperature at this time is 80 to 150 ° C., preferably from 100 to 130 ° C. Selected.

  Various compounding agents can be blended in the EVOH (A) of the present invention thus obtained. For example, when an acid such as acetic acid, phosphoric acid or boric acid or a metal salt thereof such as an alkali metal, alkaline earth metal or transition metal is added to EVOH (A), the thermal stability of EVOH (A) can be improved. Therefore, it is preferable.

The amount of acetic acid added to EVOH (A) is usually 0.001 to 1 part by weight, preferably 0.005 to 0.2 part by weight, particularly preferably 0 to 100 parts by weight of EVOH (A). 0.010 to 0.1 part by weight, and if the amount added is too small, the content effect may not be sufficiently obtained. On the other hand, if the amount added is too large, it is difficult to obtain uniform fibers. Tend to be.
Acetic acid salts added to EVOH (A) include alkali metal salts such as sodium acetate and potassium acetate, alkaline earth salts such as magnesium acetate, calcium acetate and barium acetate, and transition metal salts such as zinc acetate and manganese acetate. The amount added is usually 0.0005 to 0.1 parts by weight, preferably 0.001 to 0.05 parts by weight, particularly preferably 0.002 to 100 parts by weight of EVOH (A) in terms of metal. 0.03 part by weight, if the amount added is too small, the content effect may not be sufficiently obtained, and conversely if too much, it tends to be difficult to obtain uniform fibers. is there.

  Examples of boron compounds added to EVOH (A) include boric acid and boric acid metal salts. Such boric acid metal salts include lithium salts such as lithium metaborate, lithium tetraborate, and lithium pentaborate, and metaboric acid. Sodium salts such as sodium, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate, sodium octaborate, potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, Potassium salts such as potassium octaborate, and alkali metal salts thereof, calcium salts such as calcium borate, magnesium orthoborate, magnesium diborate, magnesium metaborate, trimagnesium tetraborate, and magnesium such as pentamagnesium tetraborate Salt, barium orthoborate, barium metaborate, diborate , Barium salts such as barium tetraborate, and alkaline earth metal salts thereof, cobalt salts such as cobalt borate, manganese salts such as manganous borate, manganese metaborate, manganese tetraborate, nickel orthoborate , Nickel salts such as nickel diborate, nickel tetraborate and nickel octaborate, copper salts such as cupric borate, copper metaborate and copper tetraborate, boron such as silver metaborate and silver tetraborate Silver salts, zinc salts such as zinc tetraborate and zinc metaborate, cadmium salts such as cadmium orthoborate and cadmium tetraborate, lead salts such as lead metaborate and lead hexaborate, bismuth such as bismuth borate Ammonium such as ammonium metaborate, ammonium tetraborate, ammonium pentaborate, and ammonium octaborate in addition to salts, double salts such as aluminum and potassium borates Umushio, borax, car night, In'yoaito, isolated island stone, Suian stone, borate minerals such as Zaiberi stone and the like.

  The amount of boron compound added is usually 0.001 to 1 part by weight, preferably 0.002 to 0.2 part by weight, particularly preferably 0.005 to 100 parts by weight of EVOH (A) in terms of boron. If the addition amount is too small, the content effect may not be sufficiently obtained. On the other hand, if the addition amount is too large, it is difficult to obtain uniform fibers, which is not preferable.

  Examples of the phosphorus compound added to EVOH (A) include phosphoric acid and metal phosphates. Examples of the metal phosphate include sodium salts such as sodium dihydrogen phosphate and disodium hydrogen phosphate, and phosphoric acid. Potassium salts such as potassium dihydrogen, dipotassium hydrogen phosphate, and tripotassium phosphate, and alkali metal salts or monovalent salts thereof, calcium monohydrogen phosphate, calcium dihydrogen phosphate, calcium such as tricalcium phosphate Salts, magnesium salts such as magnesium phosphate, magnesium hydrogen phosphate, magnesium dihydrogen phosphate, and divalent salts such as alkaline earth metal salts thereof, zinc hydrogen phosphate, barium hydrogen phosphate, manganese hydrogen phosphate, etc. Preferably phosphoric acid, sodium dihydrogen phosphate, potassium dihydrogen phosphate, calcium dihydrogen phosphate Magnesium dihydrogen phosphate and the like. The amount of the phosphoric acid compound added is usually 0.0005 to 0.1 parts by weight, preferably 0.001 to 0.05 parts by weight, particularly preferably 100 parts by weight of EVOH (A) in terms of phosphate radical. 0.002 to 0.03 part by weight, and if the amount added is too small, the content effect may not be sufficiently obtained. Conversely, if the amount is too large, it tends to be difficult to obtain uniform fibers. .

  The method for adding acids or metal salts thereof to EVOH (A) is not particularly limited. A) A porous precipitate of EVOH (A) having a water content of 20 to 80% by weight is converted into an aqueous solution of acids or metal salts thereof. A method in which the acid or its metal salt is added and then dried, and a) a uniform solution (water / alcohol solution, etc.) of EVOH (A) is mixed with the acid or its metal salt, and then in the coagulation liquid Extruded into strands, then cut the resulting strands into pellets and further dried, c) EVOH (A) and acids and their metal salts are mixed together and then melted in an extruder etc. Method of kneading d) During the production of EVOH (A), the alkali (sodium hydroxide, potassium hydroxide, etc.) used in the saponification step is neutralized with acids such as acetic acid, and the remaining acids such as acetic acid By-product sodium acetate Potassium, the quantity of alkali metal salts such as potassium acetate may be a method like or to adjust the water washing treatment. In order to obtain the effects of the present invention more remarkably, the methods a), b) and d), which are excellent in dispersibility of acids and metal salts thereof, are preferred.

  As a drying method when various additives are added to EVOH (A) by the above methods a), b) or d), various drying methods can be employed. For example, a substantially pellet-like EVOH (A) composition is subjected to fluid drying performed while being stirred and dispersed mechanically or with hot air, or standing without being subjected to dynamic actions such as stirring and dispersion. Examples of dryers for fluidized drying include cylindrical / grooved agitator dryers, circular tube dryers, rotary dryers, fluidized bed dryers, vibrating fluidized bed dryers, conical rotary dryers, etc. In addition, as a dryer for performing static drying, a batch type box dryer is used as a stationary material type, and a band dryer, a tunnel dryer, a vertical dryer, etc. are used as a material transfer type. However, it is not limited to these. It is also possible to combine fluidized drying and stationary drying.

  Air or an inert gas (nitrogen gas, helium gas, argon gas, etc.) is used as the heating gas used in the drying process, and the temperature of the heating gas is 40 to 150 ° C., which is the productivity and the heat of EVOH. It is preferable in terms of preventing deterioration. Although it depends on the water content of the EVOH (A) composition and its treatment amount, the drying treatment time is usually preferably about 15 minutes to 72 hours in terms of productivity and prevention of thermal deterioration.

  The water content after the drying treatment is usually 0.001 to 5% by weight, preferably 0.01 to 2% by weight, particularly preferably 0.1 to 1% by weight. If the water content is too low, the long-run spinnability tends to be reduced. Conversely, if the water content is too high, foaming may occur during melt spinning.

  Thus, the target EVOH (A) or a composition thereof can be obtained. Such EVOH (A) has some monomer residue (3,4-diol-) within the range not impairing the object of the present invention. 1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-ol-1-butene, 4-acyloxy-3-ol-1-butene, 4,5-diol-1-pentene, 4, 5-diacyloxy-1-pentene, 4,5-diol-3-methyl-1-pentene, 4,5-diol-3-methyl-1-pentene, 5,6-diol-1-hexene, 5,6- Diacyloxy-1-hexene, 4,5-diacyloxy-2-methyl-1-butene, etc.) and saponified monomers (3,4-diol-1-butene, 4,5-diol-1-pentene, 4,5 − All 3-methyl-1-pentene, 4,5-diol-3-methyl-1-pentene, may also contain a 5,6-diol-1-hexene, etc.).

  In addition, EVOH (A) used in the present invention is a blend of EVOH containing the structural unit (1) and other EVOH different from this, and also indicates that the fiber stretchability and fiber strength after stretching are good. Such other EVOHs include those having different structural units, those having different ethylene contents, those having different degrees of saponification, and those having different molecular weights.

  Examples of the EVOH having a structural unit different from the EVOH having the structural unit (1) include, for example, an EVOH composed only of an ethylene structural unit and a vinyl alcohol structural unit, and a modified EVOH having a functional group such as a 2-hydroxyethoxy group in the side chain of the EVOH. Can be mentioned.

  In addition, when different ethylene contents are used, other structural units may be the same or different, but the ethylene content difference is usually 1 mol% or more, preferably 2 mol% or more, particularly preferably. Is 2 to 20 mol%. If the ethylene content difference is too large, the stretchability may be poor. Moreover, the manufacturing method of 2 or more types of different EVOH (blend product) is not particularly limited, for example, a method of mixing each paste of EVA before saponification and then saponifying, alcohol of each EVOH after saponification or water and alcohol And a method of mixing each solution of EVOH in the form of pellets or powder, and then melt-kneading.

  The EVOH (A) thus obtained or the melt flow rate (MFR) (210 ° C., load 2160 g) of the composition is not particularly limited, but is usually 0.1 to 100 g / 10 minutes, preferably 0.5 to 70 g / 10 min, particularly preferably 10-50 g / 10 min. When the melt flow rate is too small, the resin viscosity becomes high during melt spinning, making it difficult to spin uniform fibers, and too large. Tends to reduce the strength of the fiber.

  The EVOH (A) thus obtained or a composition thereof can be processed into a fiber as it is, but in the present invention, various additives are added to the extent that the EVOH (A) does not impair the object of the present invention. It can also be used as a composition blended. Such additives include saturated aliphatic amides (such as stearic acid amide), unsaturated fatty acid amides (such as oleic acid amide), bis fatty acid amides (such as ethylene bisstearic acid amide), fatty acid metal salts (such as calcium stearate) , Magnesium stearate, etc.), lubricants such as low molecular weight polyolefins (for example, low molecular weight polyethylene having a molecular weight of about 500 to 10,000, or low molecular weight polypropylene), inorganic salts (for example, hydrotalcite), plasticizers (for example, ethylene glycol) , Aliphatic polyhydric alcohols such as glycerin and hexanediol), heat stabilizers, light stabilizers, antioxidants, UV absorbers, colorants, antistatic agents, surfactants, antibacterial agents, antiblocking agents, slips Agents, fillers (eg inorganic fillers), other resins (eg poly Olefins, polyamide, etc.) and the like.

The EVOH fiber of the present invention can be obtained by fiberizing the EVOH (A) thus obtained or a composition thereof. The fiberizing method is not particularly limited, and examples thereof include melt spinning, wet spinning, dry spinning, etc. Among them, melt spinning is preferably used because of high spinning speed and easy spinning of split fibers. .
The method for melt spinning is not particularly limited, and melt spinning is performed from a single nozzle or a composite nozzle using a known melt spinning machine. The spinning temperature is a temperature at which EVOH (A) melts and does not change in quality, and EVOH (A) is extruded at a spinning temperature of 200 to 320 ° C. to produce a spinning filament having a predetermined fineness.

In addition, the spinning may be performed as a single fiber, but in order to improve the strength and flexibility of the nonwoven fabric, it is spun as a composite fiber with a thermoplastic resin (B) other than EVOH (A). It is preferable. The composite fiber referred to in the present application means a fiber in which two or more types of resins having different components exist in a single fiber, and may be a monofilament or a multifilament.
Examples of the shape of the composite fiber include a core-sheath type composite fiber, an eccentric sheath-core type composite fiber, a parallel type composite fiber, a split type composite fiber, and a sea-island type composite fiber. For example, any shape such as a circular shape, an elliptical shape, a hollow shape, a triangular shape, a quadrangular shape, a rhombus shape, a star shape, and a flat shape may be used.
In the case of the core-sheath type, the case where the sheath part is the component (A) and the core part is the component (B), and the case where the sheath part is the component (B) and the core part is the component (A) can be adopted. However, the sheath portion is preferably the component (A) and the core portion is the component (B).
In the case of the division type, it is possible to employ either the case where the component (B) is divided into a plurality of segments by the component (A) or the case where the component (A) is divided into a plurality of segments by the component (B). However, the component (A) is preferably divided into a plurality of segments by the component (B). A known shape can be adopted as the divided shape, but it is usually one that is radially divided into even numbers, and preferably one that is radially divided into four to eight.
From the viewpoint liquid retentivity Among these is good, in the present invention are needed use the splittable conjugate fibers.

As the thermoplastic resin to be composited (B), polyethylene terephthalate, polyester polymers such as polybutylene terephthalate, nylon 6, polyamide polymers such as nylon 66, polypropylene, polymethylpentene polyolefin polymer such as such One or more of these homopolymers, copolymers and terpolymers can be selected and used.
EVOH (A) and thermoplastic resin (B) The composite ratio (volume ratio) of the resin other than the EVOH composition is usually 10/90 to 90/10, preferably 25/75 to 75/25, particularly preferably 35 / If the composite ratio of EVOH (A) is too small, the liquid retaining property when used as a battery separator is insufficient, and conversely if too large, the strength of the nonwoven fabric tends to be insufficient.

  Moreover, since the fiber strength improves when the obtained spinning filament is extended | stretched as needed and it processes by extending | stretching temperature 20-90 degreeC and a draw ratio 2 times or more, it is preferable. And if necessary, it is crimped by a crimping device and cut into a predetermined length to obtain the EVOH fiber of the present invention.

  In addition, the fiber diameter of EVOH fiber is not particularly limited, and a preferable fiber diameter is selected depending on the application, but is usually 0.1 to 100 denier, and particularly in a battery separator, the electrolyte solution is retained. In general, it is 0.5 to 50 deniers, particularly preferably 1 to 30 deniers, in order to prevent migration of the electrode active material. The fiber length is also the same, but when the nonwoven fabric is formed by a wet method, it is preferably about 1 to 70 mm.

  The method for producing a nonwoven fabric using the obtained EVOH fiber is not particularly limited, and the form of the nonwoven fabric is a dry web obtained by a card method, an air lay method or the like, a wet web obtained by a wet method, or a melt blow method, A fiber web obtained by a direct method such as a spunbond method, or a mechanical web entanglement treatment using a needle punch method or a spunlace method, a hot roll method, hot air bonding, or a laminate of at least one layer containing two or more layers. A nonwoven fabric is produced by a thermal bonding process such as an ultrasonic bonding method or an ultrasonic bonding method, or a combination thereof.

  Next, the fiber assembly is integrated by a mechanical entanglement process such as a needle punch method or a spunlace method, a thermal roll method, a hot air bonding method, a thermal bonding process such as an ultrasonic bonding method, or a combination thereof. For example, the fiber web may be spunlaced to divide the split composite fiber to form ultrafine fibers having a fineness of 0.5 denier or less and to entangle the fibers.

The basis weight and apparent density of the nonwoven fabric thus obtained are not particularly limited, but usually the basis weight is 10 to 100 g / m ² and the apparent density is 0.01 to 10 g / cm ³ . Particularly in the case of battery separators, those having a basis weight of 30 to 70 g / m ² and an apparent density of 0.1 to 1 g / cm ³ are preferably used. In addition, it is preferable that the unidirectional tensile strength of this nonwoven fabric is 30 N / 5 cm or more, and especially in a battery separator, it is preferable that it is 50 N / 5 cm or more. If the tensile strength is too small, the winding property during battery incorporation is inferior.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the examples.
In the following, “%” and “parts” refer to the weight basis unless otherwise specified.

Production Example 1: EVOH (A1)
A 1 m ³ polymerization can with a cooling coil is charged with 500 kg of vinyl acetate, 100 kg of methanol, 500 ppm of acetyl peroxide (vs. vinyl acetate), 20 ppm of citric acid (vs. vinyl acetate), and 14 kg of 3,4-diacetoxy-1-butene. The system was temporarily replaced with nitrogen gas, then replaced with ethylene, and injected until the ethylene pressure reached 35 kg / cm ^2, and the temperature was raised to 67 ° C. while stirring to initiate polymerization. Thereafter, 4.5 kg of 3,4-diacetoxy-1-butene was added at a rate of 15 g / min, polymerized for 6 hours until the polymerization rate reached 50%, and an ethylene-vinyl acetate copolymer having an ethylene content of 29 mol%. A methanol solution was obtained.

A methanol solution of the obtained ethylene-vinyl acetate copolymer was supplied at a rate of 10 kg / hour from the top of the tower (saponification tower), and at the same time, 0% of the remaining acetic acid groups in the copolymer. A methanol solution containing 0.012 equivalent of sodium hydroxide was fed from the top of the tower. On the other hand, methanol was supplied at 15 kg / hour from the bottom of the tower. The tower temperature was 100 to 110 ° C., and the tower pressure was 3 kg / cm ² G. From 30 minutes after the start of charging, a methanol solution of EVOH (A1) containing the structural unit (1) (EVOH (A1) 30%, methanol 70%) was taken out. The EVOH (A1) had a saponification degree of 99.5 mol%.

Then, a methanol solution of EVOH (A1) is supplied from the top of the methanol / water solution adjusting tower at 10 kg / hour, methanol vapor at 120 ° C. is supplied at 4 kg / hour, and steam is supplied from the bottom of the tower at a rate of 2.5 kg / hour. At the same time, methanol was distilled from the top of the column at 8 kg / hour, and at the same time, 6 equivalents of methyl acetate with respect to the amount of sodium hydroxide used in the saponification was charged from the middle of the column at 95-110 ° C. To obtain a water / alcohol solution of EVOH (A1) (resin concentration: 35%).
The obtained water / alcohol solution of EVOH (A1) was extruded in a strand form from a nozzle with a pore diameter of 4 mm into a coagulation liquid tank maintained at 5 ° C. composed of 5% methanol and 95% water. The material was cut with a cutter to obtain a porous pellet of EVOH (A1) having a diameter of 3.8 mm and a length of 4 mm and a moisture content of 45%.

［化学式（６）中、（Ｉ）は構造単位（１）由来のユニットであり、（ＩＩ）はエチレン由来のユニットであり、（ＩＩＩ）は酢酸ビニル由来のユニットである。また、ｍ、ｎ、ｌはそれぞれ独立して１以上の整数を示す。］ The content of the structural unit (1) of the obtained EVOH (A1) was determined by ¹ H-NMR (internal standard substance: tetramethylsilane, solvent: d6-DMSO) of the ethylene-vinyl acetate copolymer before saponification. ) To obtain 2.5 mol%. In addition, “AVANCE DPX400” manufactured by Nippon Bruker Co., Ltd. was used for NMR measurement.
Hereinafter, the structure of the ethylene-vinyl acetate copolymer having the structural unit (1) is represented by chemical formula (6).

[In the chemical formula (6), (I) is a unit derived from the structural unit (1), (II) is a unit derived from ethylene, and (III) is a unit derived from vinyl acetate. M, n, and l are each independently an integer of 1 or more. ]

[ ¹ H-NMR] (Chemical formula (6), see FIG. 1)
1.0 to 1.8 ppm: methylene proton (integrated value a in FIG. 1)
1.87 to 2.06 ppm: methyl proton 3.95 to 4.3 ppm: proton on the methylene side of structure (I) + unreacted 3,4-diacetoxy-1-butene proton (integral value b in FIG. 1)
4.6 to 5.1 ppm: methine proton + proton on the methine side of structure (I) (integrated value c in FIG. 1)
5.2 to 5.9 ppm: unreacted 3,4-diacetoxy-1-butene proton (integral value d in FIG. 1)

[Calculation method of structural unit (1) content]
Since there are four protons in 5.2 to 5.9 ppm, the integral value of one proton is d / 4, and the integral value b is an integral value including the protons of the diol and the monomer. The integral value (A) of the proton is A = (b−d / 2) / 2, and the integral value c is an integral value including the protons on the vinyl acetate side and the diol side. Since the integral value (B) is B = 1− (b−d / 2) / 2 and the integral value a is an integral value including ethylene and methylene, the integral value (C) of one proton of ethylene is , C = (a−2 × A−2 × B) / 4 = (a−2) / 4, and the content of the structural unit (1) is 100 × {A / (A + B + C)} = 100 × Calculated from (2 × b−d) / (a + 2).

Moreover, the result of having similarly performed ¹ H-NMR measurement also about EVOH after saponification is shown in FIG. Since the peak corresponding to 1.87 to 2.06 ppm of methyl proton is greatly reduced, the copolymerized 3,4-diacetoxy-1-butene is also saponified into a 1,2-glycol structure. It is clear that

  Next, the obtained EVOH (A1) pellets were washed with 100 parts of water with respect to 100 parts of the pellets, and then mixed with 0.032% boric acid and 0.007% calcium dihydrogen phosphate. The solution was poured into the liquid and stirred at 30 ° C. for 5 hours. Thereafter, in a batch-type ventilated box type dryer, nitrogen gas having a temperature of 70 ° C. and a moisture content of 0.6% was passed through and dried for 12 hours to obtain a moisture content of 30%. Furthermore, using a batch tower type fluidized bed dryer, drying was performed with nitrogen gas having a temperature of 120 ° C. and a water content of 0.5% for 12 hours to obtain a target EVOH (A1) composition pellet.

  The obtained EVOH (A1) composition pellets were 0.015 parts by weight (in terms of boron) and 0.005 parts by weight (phosphorus) of boric acid and calcium dihydrogen phosphate with respect to 100 parts by weight of EVOH (A1). Acid basis conversion). Moreover, MFR of this EVOH (A1) composition was 4.0 g / 10min (210 degreeC2160g).

Production Example 2: EVOH (A2)
In Production Example 1, instead of 3,4-diacetoxy-1-butene, 70 of 3,4-diacetoxy-1-butene, 3-acetoxy-4-ol-1-butene and 1,4-diacetoxy-1-butene EVOH with an ethylene content of 29 mol%, a saponification degree of 99.5 mol%, and a structural unit (1) content of 2.0 mol% is used except that a / 20/10 (weight ratio) mixture is used. A2) was obtained.
Furthermore, the process similar to manufacture example 1 is performed, boric acid content 0.015 weight part (boron conversion) with respect to EVOH (A2) 100 weight part, calcium dihydrogen phosphate content 0.005 weight part ( It was set as the EVOH (A2) composition pellet which is phosphoric acid root conversion.
The MFR of the EVOH (A2) composition was 3.7 g / 10 minutes (210 ° C., 2160 g).

Production Example 3: Unmodified EVOH
Unmodified EVOH (ethylene content 29 mol%, saponification degree 99.5 mol%) not containing the structural unit (1) is treated in the same manner as in Production Example 1, and boric acid is added to 100 parts by weight of EVOH. An unmodified EVOH composition having a content of 0.015 parts by weight (in terms of boron) and a calcium dihydrogen phosphate content of 0.005 parts by weight was obtained.
The MFR of the unmodified EVOH composition was 3.2 g / 10 min (210, 2160 g).

Example 1
Using EVOH (A1) composition pellets obtained in Production Example 1 and polypropylene having a MFR of 11 g / 10 min (JIS K7210) (“Novatech PP SA3A” manufactured by Nippon Polypro Co., Ltd.), a spinning temperature of 260 ° C., a take-up speed of 600 m / Spinning was performed at min, and an unstretched yarn filament having a fineness of 5 deniers having a fiber cross section in which the composite ratio was 50/50 and the two components were radially divided into eight was obtained. This was drawn at a drawing temperature of 100 ° C. and a draw ratio of 3 times to obtain an 8-part composite fiber having a fineness of 1.7 denier.
The obtained composite fiber is cut to a fiber length of 10 mm, dispersed in water, a slurry having a concentration of 0.5% is prepared, and wet papermaking is performed to obtain a base paper having a basis weight of 50 g / m ² . The nonwoven fabric was obtained by entanglement.
The following evaluation was performed about the obtained nonwoven fabric.

[Liquid absorption]
The weight (W ₀ ) of a 5 cm × 5 cm non-woven fabric test piece was measured, immersed in a saturated aqueous solution of potassium hydroxide at 30 ° C. for 15 minutes, then placed on a horizontal plate and left under a load of 5 kg for 30 minutes. Thereafter, the weight (W ₁ ) of the test piece was measured, and the liquid absorption rate was obtained from the following formula (7).
Liquid absorption rate (%) = (W ₁ −W ₀ ) / W ₀ × 100 (7)

[Oxidation resistance]
After thoroughly drying a 5 cm × 5 cm non-woven fabric test piece, the weight (W ₂ ) was measured, immersed in a 30% concentrated sulfuric acid aqueous solution at 60 ° C. for 24 hours, washed well, sufficiently dried, (W ₃ ) was measured, and the weight change rate was determined from the following formula (8). The smaller the weight change rate due to the concentrated sulfuric acid treatment, the higher the oxidation resistance.
Weight change rate (%) = (W ₂ −W ₃ ) / W ₂ × 100 (8)

Example 2
In Example 1, the nonwoven fabric was obtained similarly except having used EVOH composition (A2) instead of EVOH composition (A1), and evaluated similarly.

Comparative Example 1
In Example 1, a non-woven fabric was obtained in the same manner except that an unmodified EVOH composition was used instead of the EVOH composition (A1), and evaluation was performed in the same manner.

上記の結果より、本発明の不織布は、前記構造単位（１）を有していないＥＶＯＨ繊維からなる不織布よりも電解液の吸液率が高いために、電池用セパレータとしたときに電池が充分な起電反応を起こすことができる。同様に、酸処理による重量変化が小さいために、電池が劣化しにくいという特徴を有することが示された。
本願発明の効果は前記構造単位（１）を有するＥＶＯＨ（Ａ）を含むことによるものである。
The evaluation results of Examples and Comparative Examples are summarized in Table 1.
[Table 1]

From the above results, the nonwoven fabric of the present invention has a higher electrolyte absorption rate than the nonwoven fabric composed of EVOH fibers not having the structural unit (1). Can cause an electromotive reaction. Similarly, since the weight change by acid treatment is small, it was shown that it has the characteristic that a battery does not deteriorate easily.
The effect of the present invention is due to the inclusion of EVOH (A) having the structural unit (1).

2 is a ¹ H-NMR chart before saponification of EVOH obtained in Polymerization Example 1. FIG. 2 is a ¹ H-NMR chart of EVOH obtained in Polymerization Example 1.

Claims (7)

A battery separator comprising a non-woven fabric produced using a split composite fiber containing an ethylene-vinyl alcohol copolymer (A) having the following structural unit (1) and a thermoplastic resin (B),
The thermoplastic resin (B) is one or more resins selected from a polyester polymer, a polyamide polymer, and a polyolefin polymer, and an ethylene-vinyl alcohol copolymer (A) and a thermoplastic resin. A battery separator, wherein the composite ratio of (B) is 10/90 to 90/10 .

(Wherein R ¹ represents a hydrogen atom or an organic group, X represents a bond chain excluding an ether bond, n represents 0 or 1, and R ^{2 to} R ⁴ each represents a hydrogen atom or an organic group) The battery separator according to claim ¹ , wherein R ^{1 in the} structural unit (1) is a hydrogen atom, n is 0, and R ^{2 to} R ⁴ are all hydrogen atoms. The battery separator according to claim 1 or 2, wherein the content of the structural unit (1) in the ethylene-vinyl alcohol copolymer (A) is 0.1 to 30 mol%. The ethylene-vinyl alcohol copolymer (A) is obtained by saponifying a copolymer of 3,4-diasiloxy-1-butene, a vinyl ester monomer and ethylene. The battery separator according to any one of 1 to 3. The battery separator according to any one of claims 1 to 4, wherein the ethylene-vinyl alcohol copolymer (A) is a composition containing a boron compound. Battery separator according to any one of claims 1-5, wherein the fiber diameter of 0.1 to 100 denier. Battery separator in accordance with claim 1, wherein the basis weight of the nonwoven fabric is 10 to 100 g / m ^2.

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