JP5613316B1 - Copolymer latex - Google Patents

Abstract

The present invention provides a copolymer latex capable of exhibiting sufficient adhesive strength both during drying and when wet and having good operability during preparation of coated paper. A copolymer latex obtained by emulsion polymerization, wherein (a) an aliphatic conjugated diene monomer is 15 to 60% by mass, and (b) an ethylenically unsaturated carboxylic acid monomer is 6.5 to 6.5%. 35% by mass, (c) 1 to 30% by mass of vinyl cyanide monomer, and (d) 0 to 77.5% by mass of monomer copolymerizable therewith. A desiccator equipped with a moisture content of a 0.3-0.5 mm thick, 4 cm square film prepared using a polymer and dried for 2 days at 23 ° C. and 50% RH, and a silica gel for drying. The difference in water content when dried for 2 days in the medium is 3.0% by mass or less, and pure water is used as a dispersion medium to adjust the solid content concentration to 50.0% by mass, pH 6.5, and liquid temperature of 25 ° C. Copolymer latex having a viscosity at time of 1000 mPa · s or less. [Selection figure] None

Description

  The present invention relates to a copolymer latex.

  Conventionally, copolymer latex has been used in various applications such as coated paper and battery electrode materials. Copolymer latex has excellent operability in each application, is easy to use, and has been improved to give a high balance of physical properties to the final product. Longed for.

  For example, coated paper is used for a large number of printed materials because of its high printing effect. Even in periodicals such as quarterly and monthly papers, the use of coated paper on all pages has increased considerably. In particular, most direct mails and product catalogs in the mail order business use coated paper for all pages.

  Generally, a composition for paper coating is composed of a pigment dispersion in which a white pigment such as clay or calcium carbonate is dispersed in water, a binder for adhering and fixing the pigments to each other, and the pigment and the base paper, and other additives. It is a water-based paint. As the binder, a synthetic emulsion binder represented by styrene-butadiene copolymer latex, or a natural binder represented by starch or casein is used. Among them, styrene-butadiene copolymer latex obtained by emulsion polymerization has a high degree of freedom in quality design, and is widely used as the most suitable binder for paper coating compositions. It is known that it affects the performance of the composition for coating, the operability at the time of creating coated paper, or the quality of the final coated paper product, such as surface strength and printing gloss (for example, Patent Documents 1 and 2 below) reference).

JP 2009-91669 A JP 2008-248446 A

  Recently, cost reduction has been achieved for paints such as paper coating compositions, and the proportion of copolymer from expensive kaolin to inexpensive calcium carbonate has increased, and copolymer latex has a large proportion of paint cost. There is a movement to reduce the amount of blending. Therefore, there is a demand for a copolymer latex that can exhibit sufficient adhesive strength even with a small amount.

  Further, since dampening water is used for coated paper products during offset printing, a copolymer latex capable of exhibiting sufficient adhesive strength not only when dried but also when wet is desired. Furthermore, the copolymer latex is also required to have good operability when preparing coated paper.

  Further, the copolymer latex is also used as a material for battery electrodes, and it is desired to have excellent coverage with an electrode active material at the time of electrode preparation.

  An object of the present invention is to provide a copolymer latex that can exhibit sufficient adhesive strength both during drying and when wet, and has good operability during coating paper preparation and coating on an electrode active material. There is to do.

  The present invention is a copolymer latex obtained by emulsion polymerization, wherein the copolymer comprises (a) 15 to 60% by mass of an aliphatic conjugated diene monomer, and (b) an ethylenically unsaturated carboxylic acid monomer. A monomer consisting of 6.5 to 35% by mass of a monomer, (c) 1 to 30% by mass of a vinyl cyanide monomer, and (d) 0 to 77.5% by mass of a monomer copolymerizable therewith. It is composed of a monomer component, and is a latex film having a thickness of 0.3 to 0.5 mm and a side of 4 cm square prepared using the above copolymer latex, and is 2 in an atmosphere of 23 ° C. and 50% RH. The difference between the moisture content when humidity was adjusted for days and the moisture content when dried for 2 days in a desiccator provided with a silica gel for drying was 3.0% by mass or less. As a dispersion medium, solid content concentration 50.0 mass%, pH 6.5, liquid temperature 25 Viscosity when adjusted to at most 1000 mPa · s, to provide a copolymer latex.

  The copolymer latex of the present invention can exhibit sufficient adhesive strength both during drying and when wet, and also has good operability during coating paper preparation and coating on an electrode active material. The reason why the above effect is obtained is as follows. That is, by using 6.5% by mass or more of the ethylenically unsaturated carboxylic acid monomer, the adhesive strength at the time of drying is excellent, but the copolymer latex after drying becomes easy to absorb moisture, so that it becomes wet. In some cases, the adhesive strength at the time and the operability at the time of preparing the coated paper may be poor. Since the copolymer latex suppresses the moisture absorption of the latex film after drying to a certain level or less, it has excellent adhesive strength when wet and operability when creating coated paper. Here, the operability at the time of preparing the coated paper can be evaluated by the stickiness resistance of the copolymer latex and the redispersibility of the paper coating composition. Moreover, the cycle characteristic of the battery at the time of repeating charging / discharging can be improved because the covering property to the electrode active material of copolymer latex is favorable.

  In the copolymer latex of the present invention, the (b) ethylenically unsaturated carboxylic acid monomer preferably contains 50% by mass or more of the ethylenically unsaturated monocarboxylic acid monomer. Thereby, the effect which suppresses the ease of water | moisture content absorption of the latex film after drying is acquired.

  In the copolymer latex of the present invention, the emulsion polymerization is carried out without introducing the total amount of the (c) vinyl cyanide monomer by the time when the polymer conversion rate of the reaction system reaches 1.0%, At least 60% by mass of the total amount of the (c) vinyl cyanide monomer is charged by 60% of the time from the time when the monomer component is reached until the time when the monomer component is completely charged. Are preferred. By introducing the vinyl cyanide monomer (c) so as to satisfy the above conditions, the copolymer latex obtained can exhibit sufficient adhesive strength and can realize low viscosity, and coated paper The operability at the time of creation is also good.

  In the copolymer latex of the present invention, the emulsion polymerization is carried out by adding 0% by mass to 40% by mass of the total amount of the (b) ethylenically unsaturated carboxylic acid monomer in the reaction system at the start of charging the polymerization initiator. From the time point of 5% from the time when the polymer conversion rate of the reaction system reached 1.0% to the time when the entire amount of monomer components was charged, the above (b) ethylene was added. The addition of the remainder of the unsaturated carboxylic acid monomer is started and by 80% of the time from the arrival to the end, the (b) the ethylenically unsaturated carboxylic acid monomer It is preferable to carry out by adding 92% by mass or more of the total amount. By adding (b) an ethylenically unsaturated carboxylic acid monomer so as to satisfy the above conditions, (b) even when a large amount of the ethylenically unsaturated carboxylic acid monomer is added, an increase in latex viscosity is suppressed. In addition, the adhesive strength of the copolymer latex and the operability during preparation of the coated paper can be improved in a balanced manner.

  According to the present invention, it is possible to provide a copolymer latex that can exhibit sufficient adhesive strength both during drying and when wet, and has good operability during coating paper preparation and coating on an electrode active material. can do.

  The copolymer latex according to this embodiment is a copolymer latex obtained by emulsion polymerization, and the copolymer comprises (a) 15 to 60% by mass of an aliphatic conjugated diene monomer, (b). 6.5 to 35% by mass of an ethylenically unsaturated carboxylic acid monomer, (c) 1 to 30% by mass of a vinyl cyanide monomer, and (d) a monomer 0 to 77. copolymerizable with these. 5% by mass of a monomer component composed of a latex film having a thickness of 0.3 to 0.5 mm and a side of 4 cm square prepared using the above copolymer latex, 23 ° C., 50% The difference between the moisture content when humidity is adjusted for 2 days in an RH atmosphere and the moisture content when dried for 2 days in a desiccator provided with drying silica gel is 3.0 mass% or less. The polymer latex is treated with pure water as a dispersion medium and the solid content concentration is 50.0. The amount%, pH 6.5, a viscosity at the time of adjusting the liquid temperature 25 ° C. or less 1000 mPa · s, a copolymer latex.

  First, the monomer component which comprises the said copolymer is demonstrated.

  As the (a) aliphatic conjugated diene monomer (hereinafter sometimes referred to as the component (a)), 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1, Examples include monomers such as 3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side chain conjugated hexadienes. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use 1,3-butadiene from the viewpoint of easy production industrially and availability and cost.

  (B) As the ethylenically unsaturated carboxylic acid monomer (hereinafter also referred to as component (b)), monocarboxylic acid monomers such as acrylic acid, methacrylic acid and crotonic acid, maleic acid, fumaric acid and Examples thereof include dicarboxylic acid monomers such as itaconic acid and anhydrides thereof. These monomers can be used alone or in combination of two or more.

  Examples of (c) vinyl cyanide monomer (hereinafter sometimes referred to as component (c)) include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use acrylonitrile or methacrylonitrile from the viewpoint of easy production industrially and availability and cost.

  (D) Monomers copolymerizable with the above components (a) to (c) (hereinafter sometimes referred to as (d) component) include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers. And monomers such as a monomer, an unsaturated monomer containing a hydroxyalkyl group, and an unsaturated carboxylic acid amide monomer.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyl toluene and divinylbenzene. These can be used alone or in combination of two or more. In this embodiment, it is preferable to use styrene from the viewpoint of easy production industrially and availability and cost.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, Examples include monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use methyl methacrylate from the viewpoint of easy production industrially and availability and cost.

  Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Examples include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. These can be used alone or in combination of two or more.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide and N, N-dimethylacrylamide. These can be used alone or in combination of two or more.

  Furthermore, in addition to the above monomers, monomers used in ordinary emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, and the like can be used.

  (A) Content of a component is 15-60 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 17-56 mass%, and it is 20-52 mass%. Is more preferable. In addition, when using copolymer latex for the composition for paper coating, content of (a) component is 25-60 mass% with respect to the monomer component whole quantity which comprises a copolymer. It is preferably 27 to 56% by mass, more preferably 30 to 52% by mass, and particularly preferably 30 to 55% by mass. By making content of (a) component into the said range, the copolymer latex excellent in the balance of adhesive strength and operativity can be obtained.

  (B) Content of a component is 6.5-35 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 7-30 mass%, 7.5-23 mass % Is more preferable. By making content of (b) component into the said range, the adhesive strength of copolymer latex and the covering property to an electrode active material can fully be improved. By improving the coverage of the electrode active material, the cycle characteristics of the battery when charging and discharging are repeated can be improved.

  In this embodiment, the component (b) preferably contains more than 30% by mass of the ethylenically unsaturated monocarboxylic acid monomer, more preferably contains 50% by mass or more, and contains 65% by mass or more. More preferably. By setting the content of the ethylenically unsaturated monocarboxylic acid monomer in the above range, it is possible to obtain a copolymer latex that has excellent adhesive strength when wet and can be reduced in viscosity.

  (C) Content of a component is 1-30 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 2-28 mass%, and it is 4-25 mass%. Is more preferable. By making content of (c) component into the said range, the copolymer latex excellent in solvent resistance can be obtained.

  (D) Content of component is 0-77.5 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 2-75 mass%, and is 5-70 mass%. More preferably. In addition, when using copolymer latex for the composition for paper coating, content of (d) component is 0-67.5 mass% with respect to the monomer component whole quantity which comprises a copolymer. It is preferable that it is 2-65 mass%, and it is more preferable that it is 5-60 mass%.

  In the present embodiment, for the purpose of controlling the hardness of the copolymer latex, the component (d) contains 1 to 75% by mass of styrene, based on the total amount of monomer components constituting the copolymer. In the case of using the copolymer latex in a paper coating composition, it is preferably contained in an amount of 0 to 65% by mass.

  Next, the emulsion polymerization according to this embodiment will be described.

  In the emulsion polymerization reaction system according to the present embodiment, in addition to the components (a) to (d), an emulsifier (surfactant), a polymerization initiator, and, if necessary, a chain transfer agent, a reducing agent, and the like. Can be blended.

  Examples of the emulsifier include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalene sulfonic acid, Anionic surfactants such as sulfate ester salts of ionic surfactants, and nonionic surfactants such as alkyl ester type, alkyl phenyl ether type, and alkyl ether type of polyethylene glycol. These can be used alone or in combination of two or more. The blending amount of the emulsifier can be appropriately adjusted in consideration of a combination of other additives.

  Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, acetyl peroxide, Examples thereof include oil-soluble polymerization initiators such as diisopropylbenzene hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide. These can be used alone or in combination of two or more. Of these, potassium persulfate, sodium persulfate, cumene hydroperoxide, or t-butyl hydroperoxide is preferably used. The blending amount of the polymerization initiator is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; Allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; α-benzyloxystyrene, α-benzine Vinyl ethers such as ruoxyacrylonitrile and α-benzyloxyacrylamide; linkage of triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, α-methylstyrene dimer A transfer agent is mentioned. These can be used alone or in combination of two or more. The blending amount of the chain transfer agent can be appropriately adjusted in consideration of combinations of other additives.

  Examples of the reducing agent include sulfite, bisulfite, pyrosulfite, nithionate, nithionate, thiosulfate, formaldehyde sulfonate, benzaldehyde sulfonate; L-ascorbic acid, erythorbic acid, tartaric acid. And carboxylic acids such as citric acid and salts thereof; reducing sugars such as dextrose and saccharose; and amines such as dimethylaniline and triethanolamine. These can be used alone or in combination of two or more. Of these, L-ascorbic acid and erythorbic acid are preferred. The blending amount of the reducing agent can be appropriately adjusted in consideration of a combination of other additives.

  In addition, the reaction system according to the present embodiment includes saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane; pentene, hexene, heptene, for the purpose of controlling the molecular weight and cross-linked structure of the copolymer. Unsaturated hydrocarbons such as cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene; hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and xylene can be blended. These can be used alone or in combination of two or more. Of these, cyclohexene and toluene are preferably used.

  Furthermore, in the reaction system according to the present embodiment, an electrolyte, an oxygen scavenger, a chelating agent, a dispersant, an antifoaming agent, an antiaging agent, an antiseptic agent, an antibacterial agent, a flame retardant, an ultraviolet absorber, etc. These additives may be blended. These additives can be used in appropriate amounts in both types and amounts.

  In the present embodiment, a part of the component (a), part of the component (b), part of the component (c), part of the component (d), emulsifier, It is preferable to contain a reducing agent and a chain transfer agent.

  When a part of the component (a) is included in the reaction system at the start of charging the polymerization initiator, it is preferable to include 1 to 25% by mass, and 3 to 20% by mass of the total amount of the component (a). Is more preferable.

  When a part of the component (b) is included in the reaction system at the start of charging the polymerization initiator, it is preferable to include more than 0% by mass and 40% by mass or less of the total amount of the component (b). % Is more preferable. Furthermore, the component (b) is from the time when the polymer conversion rate of the reaction system reaches 1.0% (hereinafter simply referred to as “when reached”) to the time when the entire amount of the monomer component has been charged (hereinafter simply referred to as “only”). From the time point of 5% of the time to “end time”), the addition of the remainder of the (b) ethylenically unsaturated carboxylic acid monomer is started, and the time from the arrival time to the end time, It is preferable to add 92% by mass or more of the total amount of the (b) ethylenically unsaturated carboxylic acid monomer by the time point of 80%. By adding the component (b) so as to satisfy these conditions, sufficient adhesive strength can be expressed both during drying and when wet, and a low viscosity copolymer latex can be obtained. Further, it is preferable to add 95% or more of the total amount of the (b) ethylenically unsaturated carboxylic acid monomer by 70% of the time from the arrival time to the end time, most preferably 60%. % Of the total amount of the (b) ethylenically unsaturated carboxylic acid monomer is preferred.

  The term “arrival time” refers to the time when the polymer conversion rate of the monomer added to the reaction system reaches 1.0%. The time point when the polymer conversion rate reaches 1.0% is calculated from actual measurement 30 minutes after the time point (0 point) when the monomer component, the initiator and water coexist. If the polymer conversion rate measured after 30 minutes does not exceed 1%, it is measured after another 30 minutes, and is measured every 30 minutes until the polymer conversion rate exceeds 1%. When the polymer conversion rate exceeds 1%, the time when the polymer conversion rate reaches 1.0% by connecting the data exceeding 1% and 0 point is defined as “at the time of arrival”.

The polymer conversion rate can be calculated from the following equation by weighing the reaction solution collected from the reaction vessel, drying at 150 ° C. for 1 hour, weighing again, and measuring the solid content C.
Polymer conversion (%) = [Solid content C (g) −Solid content other than monomer contained in reaction solution (g)] / Amount of monomer component added to reaction system (g) × 100
Note that “at the time of arrival” can be set based on data obtained in advance. For example, a reaction system similar to the emulsion polymerization to be performed can be prepared, and the arrival time can be obtained in advance based on the transition of the polymer conversion rate of this reaction system.

  When a part of the component (c) is included in the reaction system at the start of charging the polymerization initiator, it is preferable to include 10 to 90% by mass of the total amount of the component (c), and 15 to 80% by mass. Is more preferable. In addition, the component (c) is not charged with the total amount of the component (c) by the time of arrival, and is 80% of the total amount of the component (c) by 60% of the time from the arrival to the end. % Or more is preferably added.

  By the time of the above, (c) the vinyl cyanide monomer is not charged into the reaction system by the time 60% of the time from the time of arrival to the time of the introduction, without charging the total amount of the (c) vinyl cyanide monomer. By carrying out emulsion polymerization by adding 80% by mass or more of the total amount of the copolymer latex, the resulting copolymer latex can exhibit sufficient adhesive strength both when dry and when wet, and at the time of creating coated paper The operability is also good, and it is possible to easily lower the viscosity. When the total amount of (c) vinyl cyanide monomer is introduced into the reaction system by the time when the above is reached, the solvent resistance when the copolymer latex is made into a film is inferior, and the adhesive strength tends to decrease. Further, when 60% or more of the total amount of the vinyl cyanide monomer is not charged by 60% of the time from the above arrival to the end of the total amount of monomer components, There is a tendency that the latex viscosity reducing effect is remarkably inferior.

  In addition, the amount of the component (c) to be added up to 60% of the time from the time of arrival to the time of completion is the total amount of the component (c) from the viewpoint of improving the adhesive strength and reducing the latex viscosity. The reference is preferably 85% by mass or more, and more preferably 90% by mass or more.

  When a part of the component (d) is contained in the reaction system at the start of charging the polymerization initiator, it is preferable to contain 1 to 45% by mass, and 2 to 30% by mass of the total amount of the component (d). Is more preferable.

  The total amount of the emulsifier and the polymerization initiator is preferably contained in the reaction system at the start of charging the polymerization initiator.

  The reaction system at the start of charging the polymerization initiator is, for example, a pressure-resistant polymerization reaction vessel, pure water, the components (a) to (d) described above, an emulsifier, a polymerization initiator, a chain transfer agent, a reducing agent, and the like. Can be prepared by adding a predetermined amount and stirring with, for example, an inclined blade, a turbine blade, and a Max blend blade.

  In the present embodiment, the reaction temperature is preferably set in the range of 30 to 100 ° C., more preferably set in the range of 40 to 85 ° C., from the viewpoint of safety in the tank and productivity in consideration of safety. preferable. In this case, a polymerization initiator having an initiation temperature in the above reaction temperature range is used.

  The temperature of the reaction system can be raised at, for example, 0.25 to 1.0 ° C./min by external heating.

  As a method of adding the components (a) to (d) to the reaction system after the arrival, for example, a batch addition method, a divided addition method, a continuous addition method, and a power feed method can be employed. From the viewpoint of improving the safety by suppressing the monomer in the reaction system to a certain concentration or less, it is preferable to employ a continuous addition method (hereinafter sometimes referred to as continuous addition). Further, the attachment may be performed a plurality of times.

  Regarding the reaction time of emulsion polymerization, for example, from the viewpoint of productivity, it is preferable that the time from the time of arrival to the end of charging all the components (a) to (d) is 1 to 15 hours. More preferably, it is time. The emulsion polymerization is preferably performed until the polymer conversion rate of the components (a) to (d) is 95% or more, and more preferably 97% or more.

  Moreover, in this embodiment, it is preferable to complete | finish a reaction, confirming that the polymer conversion rate exceeded 95%. The polymer conversion rate can be calculated from the solid content or from the amount of heat obtained by cooling the polymerization tank. In this way, a copolymer latex is obtained.

  From the viewpoint of dispersion stability, the copolymer latex is preferably adjusted to a pH of 5 to 8.5 with ammonia, potassium hydroxide, sodium hydroxide or the like, and adjusted to 5.5 to 7.5. More preferably.

  The copolymer latex is preferably freed of unreacted monomers and other low-boiling compounds by a method such as heating under reduced pressure.

  The copolymer latex of this embodiment is a latex film having a thickness of 0.3 to 0.5 mm and a side of 4 cm square produced using the copolymer latex in an atmosphere of 23 ° C. and 50% RH. The difference between the moisture content when the humidity is adjusted for 2 days and the moisture content when the moisture content is dried for 2 days in a desiccator provided with a silica gel for drying is 3.0% by mass or less. Here, the water absorption rate of the latex film is measured by the following method.

  First, the copolymer latex is adjusted to pH 6.5 with sodium hydroxide or hydrochloric acid, and sodium polyacrylate (weight average molecular weight: 7 million) as a thickener is added thereto at a solid content ratio of 1% by mass or less. The viscosity is adjusted and a coating solution is prepared. Here, since the amount of sodium polyacrylate added does not affect the water absorption rate as long as it does not exceed the above upper limit, a latex film having a coating liquid viscosity of 0.3 to 0.5 mm is produced. What is necessary is just to adjust suitably so that it may become a possible viscosity. As the sodium polyacrylate, for example, IX1177 (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. can be used.

  Next, the obtained coating liquid is thinned with a film applicator and dried. Drying can be performed by leaving it to stand for 40 to 48 hours under the conditions of 20 to 25 ° C. and 45 to 55% RH. In addition, when a continuous film of latex cannot be obtained under the above temperature conditions, the temperature is 17 to 23 ° C. higher than the minimum film forming temperature of latex measured according to the method of JIS K6828-2, and 45 to 55% RH. You may leave it to dry for 40 to 48 hours on condition. Subsequently, a latex film having a thickness of 0.3 mm to 0.5 mm can be obtained by subjecting the dried thin film to a heat treatment at 130 ° C. for 15 minutes.

The obtained latex film is cut into 4 cm squares to make a sample (test piece) for measuring the moisture content. About the obtained sample, the moisture content after humidity control and the moisture content after drying are measured by the following methods (1) and (2), respectively.
(1) Moisture content after conditioning After the sample was conditioned for 48 hours under the conditions of 23 ° C. and 50% RH, the sample mass (A) was accurately weighed to the 0.1 mg unit with an electronic balance. The sample is then dried in an oven set at 150 ° C. for 60 minutes. A sample is taken out, cooled for 10 minutes in a desiccator, and the sample mass (B) after drying is weighed to the nearest 0.1 mg. From the results of weighing, the moisture content is expressed by the following formula:
Moisture content (mass%) = {(A−B) / A} × 100
Ask for.
(2) Moisture content after drying The sample is dried for 48 hours in a desiccator provided with silica gel for drying, and then the sample mass (A) is accurately weighed to the 0.1 mg unit with an electronic balance. The sample is then dried in an oven set at 150 ° C. for 60 minutes. A sample is taken out, cooled for 10 minutes in a desiccator, and the sample mass (B) after drying is weighed to the nearest 0.1 mg. From the results of weighing, the moisture content is expressed by the following formula:
Moisture content (mass%) = {(A−B) / A} × 100
Ask for.

  The difference in moisture content after humidity control and after drying measured by the methods (1) and (2) above is determined, and it is determined whether the difference in moisture content is 3.0% by mass or less. The difference in moisture content is preferably 2.8% by mass or less from the viewpoint of further improving the adhesive strength at the time of drying and wetting, and the operability at the time of creating coated paper. More preferably, it is mass%.

  The viscosity of the copolymer latex is adjusted to a solid content concentration of 50.0% by mass with pure water, and when adjusted to pH 6.5 with a pH adjuster, the viscosity at a liquid temperature of 25 ° C. is 1000 mPa · s or less. It is. When the viscosity is 1000 mPa · s or less, handling properties such as latex transportability by a liquid feed pump are excellent. Moreover, from the viewpoint of obtaining the above effects more sufficiently, the viscosity is preferably 800 mPa · s or less, and more preferably 70 to 700 mPa · s. As the pH adjuster, sodium hydroxide, hydrochloric acid, or the like can be used. The viscosity is measured as a viscosity one minute after the start of rotation at a rotation speed of 60 rpm using a B-type (BL type) viscometer according to the measurement method of JIS K7117-1. In addition, the viscosity of the copolymer latex in the present invention is the viscosity of the copolymer latex after blending them when an additive (dispersant or the like) as described later is blended in the copolymer latex. means.

  You may mix | blend a dispersing agent with copolymer latex as needed. Examples of the dispersant include polycarboxylates. As the polycarboxylate, polyacrylate is preferable. Examples of sodium polyacrylate include Aron (registered trademark) T-50 (trade name) manufactured by Toagosei Co., Ltd., Aquaric (registered trademark) DL-40S (trade name) manufactured by Nippon Shokubai Co., Ltd. As ammonium acrylate, for example, Aron (registered trademark) A-30SL (trade name) manufactured by Toagosei Co., Ltd. can be used. By blending a dispersant, the latex viscosity can be reduced. However, there is a limit to the reduction of latex viscosity, and even if an excessive amount of a dispersant is added, it is difficult to achieve the effect of lowering the viscosity, and rather, the adhesive strength and the operability during the preparation of coated paper are reduced. May occur. Moreover, if the compounding quantity of a dispersing agent is increased, cost will increase. Therefore, when mix | blending a dispersing agent with copolymer latex, it is preferable that the compounding quantity shall be 0.1-5 mass parts with respect to 100 mass parts of solid content of a copolymer, 0.2-3 More preferably, the content is 5 parts by mass. A dispersing agent can be used individually by 1 type or in combination of 2 or more types.

  Furthermore, the copolymer latex may contain functional additives such as preservatives, anti-aging agents, dispersants, printability improvers, surface sizing agents, lubricants, and surfactants, if necessary. Good. These additives can be used in appropriate amounts in both types and amounts.

  Since the copolymer latex according to the embodiment has a sufficiently low viscosity, the burden on the pump for transferring the copolymer latex can be reduced, and the handling is excellent. In addition, the copolymer latex according to the embodiment can have excellent tack resistance and redispersibility while having high adhesive strength. Therefore, adhesion of latex to a backing roll or the like at the time of creating coated paper can be suppressed, and operability at the time of creating coated paper can be improved. Furthermore, since the copolymer latex according to the embodiment can obtain an excellent adhesive strength both when dry and when wet, the surface strength of the coated paper product (both dry pick strength and wet pick strength). And the binding force of an electrode coating layer can be improved. Since the copolymer latex according to the embodiment is excellent in each of the above-described properties, it is particularly suitable for a paper coating composition for producing a coated paper product and a battery electrode composition for producing an electrode. Useful as a blended binder.

  The copolymer latex according to the embodiment is used for paper coating, fiber bonding such as nonwoven fabric, carpet backing, battery (eg, electrode, separator, heat-resistant protective layer, etc.), paint, adhesive, etc. It is useful as a binder.

  Examples of the composition for paper coating include those containing the copolymer latex according to the embodiment and, if necessary, pigments, other binders, auxiliaries and the like.

  As the pigment, inorganic pigments such as kaolin clay, calcium carbonate, talc, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, and satin white, and organic pigments such as polystyrene latex can be used. These can be used alone or in combination of two or more.

  Other binders include starch, oxidized starch, modified starch such as esterified starch, natural binders such as soybean protein and casein, water-soluble synthetic binders such as polyvinyl alcohol and carboxymethyl cellulose, polyvinyl acetate latex, acrylic latex, etc. Examples include synthetic latex. These can be used alone or in combination of two or more.

  Auxiliaries include dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycol, fatty acid ester, phosphate ester, silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, Urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention agents (sodium alginate, etc.) and the like.

  The content of the copolymer latex in the paper coating composition is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass with respect to 100 parts by mass of the pigment. preferable.

  Examples of the battery electrode composition include those containing the copolymer latex and the active material according to the embodiment, and, if necessary, an auxiliary agent.

As the positive electrode active material is not particularly limited, if the non-aqueous electrolyte secondary battery, for _example, such as _{MnO 2, MoO 3, V 2} O 5, V 6 O 13, Fe 2 O 3, Fe 3 O 4 Transition metal oxides, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , Li _X Co _Y Sn _Z O ₂ -containing complex oxides, LiFePO ₄ and other complex metal oxides, TiS ₂ , TiS ₃ , MoS ₃ and transition metal sulfides such as FeS ₂ and metal fluorides such as CuF ₂ and NiF ₂ . These can be used alone or in combination of two or more.

  The negative electrode active material is not particularly limited, but in the case of a non-aqueous electrolyte secondary battery, for example, carbon fluoride, graphite, carbon fiber, resin-fired carbon, linear graphite hybrid, coke, pyrolysis gas growth carbon , Furfuryl alcohol resin calcined carbon, mesocarbon microbeads, mesophase pitch carbon, graphite whiskers, pseudo-isotropic carbon, calcined natural materials, and pulverized conductive carbonaceous materials such as polyacene organic semiconductors And a conductive polymer such as polyacetylene and poly-p-phenylene, and a single metal such as silicon and tin, or a composite material including a metal oxide or an alloy of the metal. These can be used alone or in combination of two or more.

  Examples of auxiliary agents include water-soluble thickeners, dispersants, stabilizers, and conductive agents. Examples of the water-soluble thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein. Examples of the dispersant include Examples thereof include sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, and sodium polyacrylate. Examples of the stabilizer include nonionic and anionic surfactants. Examples of the conductive agent include acetylene. Examples include black and carbon nanofibers. These can be used alone or in combination of two or more.

  The content of the copolymer latex in the battery electrode composition is preferably 0.1 to 10 parts by mass (solid content) with respect to 100 parts by mass (solid content) of the active material, 0.5 to More preferably, it is 7 parts by mass. When the content of the copolymer latex is 0.1 parts by mass or more, it is preferable from the viewpoint of obtaining a good adhesive force with respect to the active material or the current collector, and when it is 10 parts by mass or less, a secondary battery is assembled. It is preferable from the viewpoint of sometimes preventing the overvoltage from significantly increasing and degrading the battery characteristics.

  The battery electrode composition is applied to a current collector and dried to form an electrode coating layer on the current collector to obtain an electrode sheet. Such an electrode sheet is used as, for example, a positive electrode plate or a negative electrode plate of a non-aqueous electrolyte secondary battery.

  As a method of applying the battery electrode composition to the current collector, for example, a known method such as a reverse roll method, a comma bar method, a gravure method, or an air knife method can be used. A dryer, a warm air dryer, an infrared heater, a far infrared heater, or the like is used.

  The battery electrode composition using the copolymer latex according to the present embodiment is suitable for an electrode of a secondary battery such as a non-aqueous electrolyte secondary battery, a nickel metal hydride battery, or a nickel cadmium battery.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Manufacture of copolymer latex>
The materials shown in Tables 1 to 4 were mixed in the amounts (unit: parts by mass) shown in the same table and reacted to synthesize copolymer latex. A specific synthesis procedure is shown below.

In addition, each component and symbol in Tables 1-4 show the following compounds.
(A) component: aliphatic conjugated diene monomer BDE: 1,3-butadiene (b) component: ethylenically unsaturated carboxylic acid monomer IA: itaconic acid FA: fumaric acid AA: acrylic acid MAA: methacrylic acid Component (c): Vinyl cyanide monomer ACN: Acrylonitrile (d) Component: Monomer copolymerizable with components (a) to (c) STY: Styrene MMA: Methyl methacrylate (other components)
tDM: t-dodecyl mercaptan emulsifier: sodium dodecylbenzenesulfonate KPS: potassium persulfate electrolyte: sodium hydrogen carbonate (NaHCO ₃ )
PW: Pure water

Example 1
In a pressure-resistant polymerization reaction vessel, 10 parts by mass of cyclohexene and each monomer component and other compounds in the blending amounts (parts by mass) shown in the first stage of Table 1 are added and stirred sufficiently to obtain a reaction solution. It was.

  Next, the temperature in the polymerization tank was raised, and the time when the polymer conversion rate of the reaction system reached 1.0% was regarded as the arrival time, and after 90 minutes from this arrival time as a reference (0 minute), Each monomer component and other compounds in the blending amount (parts by mass) shown in the second stage are added to the continuous addition time zone shown in the second stage of Table 1 (from 90 minutes to 225 minutes after the arrival time). Was added to the reaction solution. The reaction temperature of the polymerization system was 65 ° C.

  Subsequently, the monomer components and other compounds in the blending amounts (parts by mass) shown in the third row of Table 1 were added to the continuous addition time zone shown in the third row of Table 1 (after 225 minutes based on the arrival time). (Until 495 minutes).

  After the addition of the entire amount of the monomer components was completed, the temperature inside the polymerization tank was raised to 85 ° C. and maintained at 85 ° C. After confirming that the polymer conversion rate exceeded 97% from the amount of heat of cooling the polymerization tank, the polymerization was terminated and a reaction product was obtained.

  After completion of the polymerization reaction, the pH of the reaction product was adjusted to 6.5 using sodium hydroxide. Next, the reaction product was subjected to heating under reduced pressure to remove unreacted monomers and other low-boiling compounds. Further, Aron (registered trademark) T-50 (trade name, sodium polyacrylate, weight average molecular weight: 6000) manufactured by Toagosei Co., Ltd. as a dispersant was added to 2.100 parts by mass of the solid content of the reaction product. 5 parts by mass (in terms of solid content) was added to obtain a copolymer latex A.

(Examples 2 to 11)
Copolymer latexes B to K were prepared in the same manner as in Example 1 except that the blending amounts of each monomer component and other compounds, the addition time zone, and the reaction temperature were changed to the conditions shown in Table 1 or 2. I got each. However, in Example 5, the dispersant (T-50) was not added.

(Comparative Examples 1-3, 7, 8)
Copolymer latex CE-1 to Example 1 except that the amount of each monomer component and other compounds, the addition time zone, and the reaction temperature were changed to the conditions shown in Table 2 or 3. CE-3, CE-7, and CE-8 were obtained. However, in Comparative Example 2, the dispersant (T-50) was not added.

(Comparative Example 4)
Instead of adding 10 parts by mass of cyclohexene to the pressure-resistant polymerization reactor, 0.5 parts by mass of α-methylstyrene dimer was added, and 0.2 parts by mass and α-methylstyrene dimer were added to the second stage and the third stage. In addition to the fact that 0.2 parts by mass were continuously added together with the monomer component, the blending amount of each monomer component and other compounds, the addition time zone, and the reaction temperature were changed to the conditions shown in Table 3. A copolymer latex CE-4 was obtained in the same manner as in Example 1.

(Comparative Example 5)
Table 3 shows the addition of 5 parts by mass of cyclohexene to the pressure-resistant polymerization reactor, the change of the electrolyte to sodium carbonate, the amount of each monomer component and other compounds, the addition time zone, and the reaction temperature. A copolymer latex CE-5 was obtained in the same manner as in Example 1 except that the conditions were changed.

(Comparative Example 6)
Instead of adding 10 parts by mass of cyclohexene to the pressure-resistant polymerization reactor, 0.3 parts by mass of α-methylstyrene dimer was added, and 7 parts by mass of cyclohexene in the second stage and 7 parts by mass in the third stage, respectively. Copolymer latex CE in the same manner as in Example 1 except that the addition was continued, the blending amount of each monomer component and other compounds, the continuous addition time zone, and the reaction temperature were changed to the conditions shown in Table 3. -6 was obtained.

<Input status of component (b) and component (c)>
Table 4 summarizes the charging status of the component (b) and the component (c) during the production of the copolymer latexes of Examples 1 to 11 and Comparative Examples 1 to 8.

<Evaluation of copolymer latex>
The copolymer latex obtained above was measured for water content, latex viscosity, and stickiness resistance according to the following method.

[Moisture content]
Using the copolymer latex, a latex film having a thickness of 0.3 to 0.5 mm was prepared by the following procedure. First, the copolymer latex was adjusted to pH 6.5 with sodium hydroxide or hydrochloric acid, and sodium polyacrylate (trade name: IX-1177, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., weight average molecular weight: 7 million) was used as a thickener. ~ 8 million) was added at a solid content ratio of 1% by mass or less to adjust the viscosity to prepare a coating solution. Here, the amount of sodium polyacrylate added was adjusted as appropriate so that the viscosity of the coating solution was such that a latex film having a thickness of 0.3 to 0.5 mm could be produced within a range not exceeding the upper limit. .

  The obtained coating solution was thinned with a film applicator and allowed to dry for 48 hours under conditions of 23 ° C. and 50% RH. In addition, when a continuous film of latex cannot be obtained under the above drying conditions, it is 48 hours under conditions of a temperature 20 ° C. higher than the minimum film forming temperature of latex measured according to the method of JIS K6828-2 and 50% RH. Allowed to dry. Furthermore, the dried thin film was subjected to heat treatment in an oven set at 130 ° C. for 15 minutes to obtain a latex film having a thickness of 0.3 mm to 0.5 mm. The obtained latex film was cut into 4 cm squares to make a sample for measuring moisture content.

About the obtained sample, the moisture content after humidity control and the moisture content after drying were measured by the method of following (1) and (2), respectively.
(1) Moisture content after conditioning After the sample was conditioned for 48 hours under the conditions of 23 ° C. and 50% RH, the sample mass (A) was accurately weighed to the 0.1 mg unit with an electronic balance. The sample was then dried in an oven set at 150 ° C. for 60 minutes. The sample was taken out, cooled in a desiccator for 10 minutes, and then the dried sample mass (B) was weighed to the nearest 0.1 mg. From the results of weighing, the moisture content is expressed by the following formula:
Moisture content (mass%) = {(A−B) / A} × 100
Determined by
(2) Moisture content after drying The sample was dried for 48 hours in a desiccator provided with silica gel for drying, and then the sample mass (A) was accurately weighed to the 0.1 mg unit with an electronic balance. The sample was then dried in an oven set at 150 ° C. for 60 minutes. The sample was taken out, cooled in a desiccator for 10 minutes, and then the dried sample mass (B) was weighed to the nearest 0.1 mg. From the results of weighing, the moisture content is expressed by the following formula:
Moisture content (mass%) = {(A−B) / A} × 100
Determined by

  The difference in moisture content after humidity control and after drying was measured by the methods (1) and (2), respectively. The results are shown in Table 5.

[Latex viscosity]
The copolymer latex was adjusted to a solid content concentration of 50.0% by mass, pH 6.5, and liquid temperature of 25 ° C. with pure water. The pH of the latex was adjusted with a pH adjuster such as sodium hydroxide or hydrochloric acid as necessary. The viscosity of the copolymer latex after adjustment was measured 1 minute after the start of rotation at a rotation speed of 60 rpm using a B-type (BL type) viscometer according to the measurement method of JIS K7117-1. The results are shown in Table 5.

[Stickiness resistance]
As a measure of the ease with which the latex adheres to a backing roll or the like, a test was conducted on the stickiness resistance (adhesiveness) of the copolymer latex film. Each copolymer latex was applied to a polyester film at a coating amount of 12 g / m ² and dried in an oven at 120 ° C. for 1 minute to form a latex film. Each latex film was cut into a 1 cm wide strip, and all latex film strips were placed side by side on a black mount. Filter paper was placed on top of this and pressure bonded using an RI printer. Thereafter, the state of adhesion of the filter paper fibers on the surface of each latex film after peeling the filter paper was visually observed, and the stickiness resistance of each latex film was comparatively evaluated. The one with less fiber adhesion is rated as A for excellent stickiness resistance, and the one with much fiber adhesion is rated as E for inferior stickiness resistance, with five grades A, B, C, D, and E as shown below. In addition, the superiority or inferiority of the stickiness resistance was relatively evaluated visually. The results are shown in Table 5. The better the sticking resistance, the more difficult the latex adheres to the backing roll and the like, and the better the operability when making coated paper.
(Excellent) A>B>C>D> E (poor)

<Creation and evaluation of coated paper>
Using the copolymer latex obtained above, a paper coating composition was prepared by the following method to prepare a coated paper.

(Preparation of composition for paper coating)
A paper coating composition was prepared according to the formulation shown below. The paper coating composition was adjusted to pH 9.5 with sodium hydroxide, and the solid content concentration was adjusted to 67% by mass by adding a necessary amount of pure water.
(Combination prescription)
Kaolin (Product name: DB Glaze, manufactured by Imerizu Minerals Japan, Inc.) 20 parts by weight Heavy calcium carbonate (Product name: Carbital 90, manufactured by Imeris Minerals Japan Co., Ltd.) 80 parts by weight Modified starch (Japanese food) Kako Co., Ltd., trade name: MS4600) 2 parts by weight copolymer latex 6 parts by weight (solid content)

(Evaluation of redispersibility)
As a measure of the ease with which the latex adheres to a backing roll or the like, the redispersibility of the paper coating composition was tested. Each paper coating composition is lined up on an NBR black rubber plate and applied with a # 6 wire bar, dried in a 60 ° C hot air circulating oven for 3 minutes, washed with running water at 30 ° C for 1 minute, and NBR black The film of the composition remaining on the rubber plate was visually observed. A film with a small amount of remaining film is rated as A for excellent redispersibility, and a film with a large amount of remaining film is evaluated as E for poor redispersibility. A, B, C, D, and E are as follows: At the stage, the superiority or inferiority of the redispersibility was relatively evaluated visually. The results are shown in Table 5. The better the redispersibility, the easier it is to wash the composition for paper coating adhering to the backing roll or the like, and the better the operability when creating coated paper.
(Excellent) A>B>C>D> E (poor)

(Creating coated paper)
After coating and drying the above-mentioned composition for paper coating on a coated base paper (basis weight 55 g / m ² ) using a wire bar so that the coating amount per side is 10 g / m ² , A calender treatment was performed under the conditions of a pressure of 60 kg / cm and a temperature of 50 ° C. to obtain a coated paper. The obtained coated paper was evaluated for dry pick strength and wet pick strength by the following methods. The results are shown in Table 5.

(Evaluation of dry pick strength of coated paper)
Using a RI printer, a black ink for picking test (manufactured by DIC Graphics Co., Ltd.) was simultaneously printed on each coated paper. The obtained printed matter is pressed against coated fine paper to copy the ink, the portion where the ink is not copied (the white portion) is regarded as the picking occurrence point, and the degree of picking at this time is judged with the naked eye, The one with the least amount of picking was classified as grade 5, and was visually evaluated from grade 5 (excellent) to grade 1 (inferior). The higher the numerical value of this evaluation, the higher the dry pick strength and the better the adhesive strength.

(Evaluation of wet pick strength of coated paper)
Using an RI printer, moisturizing rolls are used to simultaneously apply dampening water to each coated paper, and immediately thereafter, ink for picking test (made by DIC Graphics Co., Ltd.) is simultaneously printed on each coated paper using an ink roll. did. The obtained printed matter is pressed against coated fine paper to copy the ink, the portion where the ink is not copied (the white portion) is regarded as the picking occurrence point, and the degree of picking at this time is judged with the naked eye, The one with the least amount of picking was classified as grade 5, and was visually evaluated from grade 5 (excellent) to grade 1 (inferior). The higher the numerical value of this evaluation, the higher the wet pick strength and the better the adhesive strength.

<Production and evaluation of electrode>
Using the copolymer latex obtained above, a battery electrode composition was prepared by the following method to prepare an electrode.

(Preparation of battery electrode composition)
(1-1) Preparation of positive electrode composition 100 parts by mass of LiCoO ₂ as a positive electrode active material, 5 parts by mass of acetylene black as a conductive agent, and 1 part by mass of a carboxymethyl cellulose aqueous solution as a thickener, As a binder, 2 parts by mass of the copolymer latex of each Example and each Comparative Example was kneaded by adding an appropriate amount of pure water so that the total solid content was 65% by mass, and the composition for the positive electrode A product was prepared.

(1-2) Preparation of composition for negative electrode Natural graphite having an average particle diameter of 20 μm is used as the negative electrode active material, and 1 part by mass of a carboxymethyl cellulose aqueous solution as a thickener is used as a thickener with respect to 100 parts by mass of natural graphite. Then, as a binder, the copolymer latex of each Example and each Comparative Example was kneaded by adding a proper amount of pure water so that the total solid content was 45% by mass with 2 parts by mass in solid content, and the negative electrode A composition was prepared.

(Production of electrodes)
(1-1) Preparation of positive electrode The positive electrode composition obtained as described above was applied to a 20 μm thick aluminum foil serving as a current collector, dried at 130 ° C. for 5 minutes, and then roll-pressed at room temperature. A positive electrode having a coating layer thickness of 100 μm was obtained.

(1-2) Production of Negative Electrode The negative electrode composition obtained as described above was applied to a copper foil having a thickness of 20 μm serving as a current collector, dried at 130 ° C. for 5 minutes, and then roll-pressed at room temperature. A negative electrode having a coating layer thickness of 100 μm was obtained. In addition, when evaluating the coverage of an electrode active material, the thing before the rolling by roll press was used.

(Evaluation of coverage of copolymer latex on active material)
Since the cycle characteristics upon repeated charge / discharge are improved by coating the surface of the active material more with the copolymer latex, in each negative electrode sheet obtained by the above method, copolymerization is performed by the following method. The coverage of the combined latex on the active material was evaluated. That is, each negative electrode sheet (before rolling) obtained above was cut into a 1 cm square and dyed in an osmium tetroxide atmosphere, and then a scanning electron microscope (manufactured by JEOL Ltd., trade name: JSM-6510LA) was used. And observed at 5000 times. In the SEM observation image, the area where the copolymer latex was adhered on the active material was visually confirmed with respect to the area of the active material, and evaluated as follows. Of the 8 SEM observation images, the average image was selected and evaluated. The results are shown in Table 6.
A: Copolymer latex covers 80% or more of the surface of the active material.
B: Copolymer latex covers 60% or more and less than 80% of the surface of the active material.
C: Copolymer latex covers 40% or more and less than 60% of the surface of the active material.
D: Less than 40% of the surface of the active material is coated with the copolymer latex.

(Evaluation of binding strength of electrode coating layer)
Use a knife to cut the surface of each electrode sheet (each positive electrode and each negative electrode) obtained by the above method from the active material layer to the depth reaching the current collector, 6 mm in length and breadth each at 2 mm intervals. Made an incision. An adhesive tape was applied to the surface of the active material layer with the cuts, and the adhesive material was immediately peeled off. The squares from which the active material was dropped were counted and evaluated as follows. The results are shown in Table 6.
A: The grid in which the active material has fallen is less than 5 B: The grid in which the active material has fallen out is 5 or more and less than 12 C: The grid in which the active material has fallen off is 12 or more and less than 18 D: The grid in which the active material has fallen off 18 to 25

As is clear from the results shown in Table 5, the copolymer latexes A to K of Examples 1 to 11 are all compared with the copolymer latexes CE-1 to CE-8 of Comparative Examples 1 to 8. It was confirmed that it had a sufficient balance of sufficient adhesive strength (both dry pick strength and wet pick strength), sufficient tack resistance and sufficient redispersibility. Further, as is apparent from the results shown in Table 6, even in evaluation for battery electrodes, sufficient binding force (both positive and negative electrodes) and good electrode active material coverage are provided in a well-balanced manner. Was confirmed.

Claims (3)

A copolymer latex obtained by emulsion polymerization,
The copolymer is
(A) 15-60 mass% of aliphatic conjugated diene monomer,
(B) 6.5 to 35% by mass of an ethylenically unsaturated carboxylic acid monomer,
(C) 1 to 30% by weight of vinyl cyanide monomer, and
(D) It is composed of monomer components consisting of 0 to 77.5% by mass of monomers copolymerizable with these,
The emulsion polymerization is
Without reaching the total amount of the (c) vinyl cyanide monomer by the time when the polymer conversion rate of the reaction system reached 1.0%,
At least 60% by mass of the total amount of the (c) vinyl cyanide monomer is charged by 60% of the time from the arrival to the end of the completion of the addition of the monomer components. I,
Moisture content when the humidity is adjusted for 2 days in an atmosphere of 23 ° C. and 50% RH of a latex film having a thickness of 0.3 to 0.5 mm and a side of 4 cm square prepared using the copolymer latex The difference from the moisture content when dried for 2 days in a desiccator provided with silica gel for drying is 3.0% by mass or less,
A copolymer latex having a viscosity of 1000 mPa · s or less when the copolymer latex is adjusted to a solid content concentration of 50.0 mass%, pH 6.5, and liquid temperature of 25 ° C. using pure water as a dispersion medium.   The copolymer latex according to claim 1, wherein the (b) ethylenically unsaturated carboxylic acid monomer contains 50 mass% or more of an ethylenically unsaturated monocarboxylic acid monomer. The emulsion polymerization is
The reaction system at the start of charging the polymerization initiator contains (b) more than 0% by mass and 40% by mass or less of the total amount of the ethylenically unsaturated carboxylic acid monomer,
From the time point of 5% from the time when the polymer conversion rate of the reaction system reaches 1.0% to the time when the entire amount of monomer components are charged, the (b) ethylenic unsaturation 92% of the total amount of the (b) ethylenically unsaturated carboxylic acid monomer is reached by the start of addition of the remainder of the carboxylic acid monomer until 80% of the time from the arrival time to the end time. The copolymer latex according to claim 1 or 2 , wherein the copolymer latex is carried out by adding at least mass%.