JP2015042725A - Copolymer latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolymer latex that can realize a sufficient adhesive strength as well as that can realize the lowering of viscosity and yet that is excellent in freezing stability.SOLUTION: The copolymer latex is a copolymer composed of respective monomer of aliphatic conjugated diene, ethylenic unsaturated carboxylic acid, and vinyl cyanide, and the polymerization is carried out in such a way in which 40 mass% or less of the ethylenic unsaturated carboxylic acid monomer is contained at the polymerization starting time point, and the addition of the remainder of the monomer is started after 5% of the time duration from the reaching time point when the polymer conversion percentage has reached 1.0%, to the finishing time point when the inputting of the total amount of the monomer component has finished, has passed, and 92 mass% or more of the monomer is input before 80% of the time duration from said reaching time point to said finishing time point has passed, and the copolymer latex has a heat of fusion ΔH (mJ/mg) at -20°C to 0°C satisfying the equation (1). [ΔH×(100/100-C)]/ΔH≤0.8 -- (1) [Cis a solid concentration of the copolymer latex (mass%), and ΔHis a heat of fusion of distilled water (mJ/mg)]

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).

Japanese Patent No. 4125078 Japanese Patent Laid-Open No. 05-301907

  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.

  However, the response to higher performance tends to increase the viscosity of the copolymer latex, and generally there is a trade-off relationship between higher performance and lower viscosity of the copolymer latex. When attempting to improve the adhesive strength of the copolymer latex, there is a concern that workability will decrease with increasing viscosity.

  On the other hand, when handling latex in a cold region, it was necessary to take measures such as keeping all the pipes warm so as not to freeze the latex. When the latex freezes, it often does not return to its original state even when thawed, and there has been a demand for a latex having good stability even when exposed to some low temperature conditions.

  An object of the present invention is to provide a copolymer latex that can exhibit sufficient adhesive strength, can achieve low viscosity, and is excellent in freeze stability.

The present invention is a copolymer latex obtained by emulsion polymerization, wherein the copolymer is 15 to 60% by mass of an aliphatic conjugated diene monomer and 5 to 35% by mass of an ethylenically unsaturated carboxylic acid monomer. , Vinyl cyanide monomer 0.5 to 30% by mass, and monomers 0 to 79.5% by mass copolymerizable therewith, and emulsion polymerization is carried out by polymerization. When the reaction system at the start of the introduction of the initiator contains more than 0% by mass and 40% by mass or less of the total amount of the ethylenically unsaturated carboxylic acid monomer, and when the polymer conversion rate of the reaction system reaches 1.0% From the time of 5% of the time until the end when the entire amount of monomer components has been charged, the remaining amount of the ethylenically unsaturated carboxylic acid monomer is started, and from the time of arrival to the time of completion. Up to 80% of the time until the ethylenic unsaturation Performed by charging 92% by mass or more of the total amount of rubonic acid monomer, and obtained by differential scanning calorimetry when the copolymer latex cooled to -25 ° C was heated at a rate of temperature increase of 1 ° C / min. A copolymer latex in which the heat of fusion ΔH (mJ / mg) from −20 ° C. to 0 ° C. calculated from the DSC curve obtained satisfies the following formula (1) is provided.
[ΔH × (100 / 100−C _S )] / ΔH _W ≦ 0.8 (1)
[In formula (1), C _S indicates the solid content concentration (mass%) of the copolymer latex measurement sample, and ΔH _W is the heat of fusion (mJ / mg) when distilled water is measured under the same conditions. Indicates. ]

  The copolymer latex of the present invention can exhibit a sufficient adhesive strength, can realize a low viscosity, and can be a latex having excellent freezing stability. In addition, the present inventors consider the reason why the copolymer latex of the present invention is excellent in freezing stability as follows. The left side of the formula (1) indicates the ratio of the heat of fusion of water detected from −20 ° C. to 0 ° C. with respect to the total heat of fusion of water contained in the copolymer latex. When this value is 0.8 or less on the right side of the formula (1), it is considered that the amount of water not detected from -20 ° C. to 0 ° C. is present in the latex by 20% by mass or more. The peaks detected from −20 ° C. to 0 ° C. are bound water and free water, and the water not detected is presumed to be antifreeze water. Such antifreeze water can be sufficiently present in the latex by the above specific emulsion polymerization, and as a result, it has become possible to improve freezing stability while achieving both adhesive strength and low viscosity. Conceivable.

  Moreover, the copolymer latex of this invention can improve the cycling characteristics of the battery at the time of repeating charging / discharging by the coating | cover property to an electrode active material being favorable. Furthermore, the composition for battery electrodes which mix | blended the copolymer latex of this invention can form the coating layer which has the outstanding binding force with respect to a collector.

  In the copolymer latex of the present invention, the ethylenically unsaturated carboxylic acid monomer preferably contains more than 30% by mass of a monocarboxylic acid monomer. In this case, the effect of reducing the viscosity in the neutral pH range can be further enhanced as compared with the case where the proportion of the monocarboxylic acid monomer in the ethylenically unsaturated carboxylic acid monomer is 30% by mass or less.

In addition, the emulsion polymerization is performed according to the Fedors method for monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system by the end of the introduction of the entire amount of the ethylenically unsaturated carboxylic acid monomer. Fedors method for monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system after the end of charging all of the ethylenically unsaturated carboxylic acid monomer, with a solubility parameter of SP ₁ It is preferable that the monomer component is added to the reaction system so that the difference between SP ₁ and SP ₂ is 1.50 or less in absolute value when the solubility parameter is SP _2. . In this case, a copolymer latex having further excellent freezing stability can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to express sufficient adhesive strength, the low viscosity can be implement | achieved and the copolymer latex excellent in freezing stability can be provided.

The DSC chart of the copolymer latex obtained in Example 1 is shown. The DSC chart of the copolymer latex obtained in Example 3 is shown. The DSC chart of the copolymer latex obtained in Comparative Example 1 is shown.

The copolymer latex according to this embodiment is a copolymer latex obtained by emulsion polymerization, and the copolymer is 15 to 60% by mass of an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer. It is composed of a monomer component consisting of 5 to 35% by mass of a monomer, 0.5 to 30% by mass of a vinyl cyanide monomer, and 0 to 99.5% by mass of a monomer copolymerizable therewith. In the above emulsion polymerization, the reaction system at the start of charging the polymerization initiator contains 0% by mass to 40% by mass or less of the total amount of the ethylenically unsaturated carboxylic acid monomer, and polymer conversion of the reaction system From the time when the rate reaches 1.0% to the end when the entire amount of the monomer component has been charged, the remainder of the ethylenically unsaturated carboxylic acid monomer is charged. Start and time from the time of arrival to the end of time By the time of 0%, 92% by mass or more of the total amount of the above-mentioned ethylenically unsaturated carboxylic acid monomer was added, and the copolymer latex cooled to −25 ° C. by differential scanning calorimetry was 1 ° C. The heat of fusion ΔH (mJ / mg) from −20 ° C. to 0 ° C. calculated from the DSC curve obtained when heated at a rate of temperature rise / min satisfies the following formula (1).
[ΔH × (100 / 100−C _S )] / ΔH _W ≦ 0.8 (1)

In the formula (1), C _S indicates the solid content concentration (% by mass) of the copolymer latex measurement sample, and ΔH _W indicates the heat of fusion (mJ / mg) when distilled water is measured under the same conditions. Show. The measurement sample of the copolymer latex can be adjusted to pH 7. For adjusting the pH, ammonia, potassium hydroxide, sodium hydroxide, or the like can be used. C _S can be set to 10 to 50 mass% is preferably set to 40 mass%. For adjusting the concentration, distilled water, ion-exchanged water, or purified water can be used. Water for calculating the [Delta] H _W may be used distilled water (manufactured by Wako Pure Chemical Industries).

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

  Examples of the aliphatic conjugated diene monomer (hereinafter sometimes referred to as component (a)) include 1,3-butadiene, 2-methyl-1,3-butadiene, and 2,3-dimethyl-1,3-butadiene. , 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and monomers such as 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.

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

  Examples of the 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.

  As the monomer copolymerizable with the component (a) to the component (c) (hereinafter sometimes referred to as the component (d)), an alkenyl aromatic monomer, an unsaturated carboxylic acid alkyl ester monomer, Monomers such as unsaturated monomers and unsaturated carboxylic acid amide monomers containing a hydroxyalkyl group may be mentioned.

  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 preferable that it is 27-56 mass%, It is more preferable that it is 30-55 mass%, It is more preferable that it is 30-52 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 component is 5-35 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 5.5-33 mass%, It is 6-28 mass%. More preferably. 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. Since the coating property of the copolymer latex on the electrode active material is good, the cycle characteristics of the battery when charging and discharging are repeated can be improved.

  In the present embodiment, the component (b) preferably contains an ethylenically unsaturated monocarboxylic acid monomer in an amount exceeding 30% by mass, more preferably 37% by mass or more, and more preferably 45% by mass or more. More preferably. By setting the content of the ethylenically unsaturated monocarboxylic acid monomer in the above range, a copolymer latex having a higher viscosity reducing effect in the neutral pH range can be obtained.

  (C) Content of a component is 0.5-30 mass% with respect to the monomer component whole quantity which comprises a copolymer, It is preferable that it is 1-28 mass%, It is 3-25 mass%. More preferably. By setting the content of the component (c) in the above range, a copolymer latex having good solvent resistance can be obtained.

  (D) Content of a component is 0-79.5 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 0-69.5 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 polymer, styrene is used as the component (d) in an amount of 1 to 79.5 based on the total amount of monomer components constituting the copolymer. It is preferable to make it contain by mass%, and when using copolymer latex for a paper coating composition, it is preferable to make it contain 1-69.5 mass%.

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

  In the present embodiment, the emulsion polymerization is carried out by adding more than 0% by mass to 40% by mass or less of the total amount of the ethylenically unsaturated carboxylic acid monomer in the reaction system at the start of addition of the polymerization initiator. From the time when the conversion rate reaches 1.0% (hereinafter, sometimes simply referred to as “when it reaches”) to the time when the entire amount of monomer components has been charged (hereinafter referred to simply as “when it ends”). From the time point of 5% of the time until) until the end of the introduction of the remainder of the ethylenically unsaturated carboxylic acid monomer until the time point of 80% of the time from the arrival time to the end time , 92% by mass or more of the total amount of the ethylenically unsaturated carboxylic acid monomer is added.

  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.

  Into the reaction system at the start of charging the polymerization initiator, more than 0% by mass and 40% by mass or less, more preferably 0.1% by mass to 30% by mass of the total amount of the ethylenically unsaturated carboxylic acid monomer, Starting from the time of 5% of the time from the time of arrival to the end of time, the charging of the remainder of the ethylenically unsaturated carboxylic acid monomer is started, and the time from the time of arrival to the time of completion is 80% % By adding 92% by mass or more of the total amount of the ethylenically unsaturated carboxylic acid monomer and performing emulsion polymerization, the viscosity of the resulting copolymer latex can be suppressed, and A copolymer latex satisfying the formula (1) can be obtained.

  In order to further enhance the above effect, the ethylenically unsaturated carboxylic acid monomer is used after 10% of the time from the arrival time to the end time, more preferably after 15%. It is preferable to start charging the remainder of the ethylenically unsaturated carboxylic acid monomer. Further, it is preferable to add 95% by mass or more of the total amount by 70% of the time from the arrival time to the end time. More preferably, it is preferable to add the total amount up to 60% of the time from the arrival time to the end time.

  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 are added to the reaction system according to this embodiment. Can do.

  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; Chain 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 (c) is contained in the reaction system at the start of charging the polymerization initiator, the content of the component (c) is preferably 3 to 55% by mass, and 5 to 50% by mass. Is more preferable.

  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 of the above components and stirring them with, for example, an inclined blade, a turbine blade, a Max blend blade, or the like.

  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.

In the present embodiment, the solubility of monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system by the end of the introduction of the entire amount of the ethylenically unsaturated carboxylic acid monomer by the Fedors method. According to the Fedors method, the parameter is SP ₁ and monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system after the completion of the introduction of the entire amount of the ethylenically unsaturated carboxylic acid monomer the solubility parameter is taken as SP _2, 1.50 or less in the difference absolute value between the SP ₁ and SP _2, more preferably 1.45 or less, more preferably 0.97 or less, still more preferably 0.92 It is preferable to carry out by introducing the monomer component into the reaction system so as to be as follows. In this case, a copolymer latex having further excellent freezing stability can be obtained.

Here, a calculation method of SP ₁ and SP ₂ will be described.
Fedors thinks that both the cohesive energy density and the molar molecular volume depend on the type and number of substituents as a method for calculating the SP value from the molecular structure, and proposes the following formula (2) and constants for various substituents. (See, for example, “A Method for Both the Solidarity Parameters and Molecular Volumes of Liquids”, Robert F. Fedors, POLYMER ENGINERAND. 74 E. ).
δ = [ΣEcoh / ΣV] ^1/2 (2)
Here, ΣEcoh represents the cohesive energy, and ΣV represents the molar molecular volume.
The values of Ecoh and V of typical atoms and atomic groups are shown in POLYMER ENGINEERING AND SCIENCE, FEBRUARY, 1974, Vol. 14, no. 2, p. The values described in 152 table 5 can be used, for example, as shown in the following table.

For example, δ of polystyrene is calculated as [(1180 × 1 + 820 × 1 + 7630) / (16.1 × 1 + (− 1.0) × 1 + 71.4 × 1)] ^1/2 = 10.55.
Further, δ in the copolymer is ΣEcoh in the above formula (2), the sum of the values of ΣEcoh of each monomer component multiplied by the molar ratio of the component, and ΣV in the above formula (2). The total value is calculated by multiplying the value of ΣV of each monomer component by the molar ratio of the component.

Taking Example 1 to be described later as an example of the calculation method of SP ₁ and SP ₂ , first, the ethylenically unsaturated carboxylic acid charged into the reaction system by the end of charging the entire amount of the ethylenically unsaturated carboxylic acid monomer. The monomer components other than the monomer were 18 parts by mass of butadiene, 14 parts by mass of styrene, and 8 parts by mass of acrylonitrile, and were charged into the reaction system after the completion of the total amount of ethylenically unsaturated carboxylic acid monomer. Monomer components other than the ethylenically unsaturated carboxylic acid monomer are 24 parts by mass of butadiene, 19 parts by mass of styrene, and 11 parts by mass of acrylonitrile.
SP ₁ is [{(4420 × 18/54) + (9630 × 14/104) + (8100 × 8/53)} / {(59.2 × 18/54) + (86.5 × 14/104). ) + (39.1 × 8/53)}] ^1/2 = 10.35.
SP ₂ is [{(4420 × 24/54) + (9630 × 19/104) + (8100 × 11/53)} / {(59.2 × 24/54) + (86.5 × 19/104). ) + (39.1 × 11/53)}] ^1/2 = 10.37.
The difference between SP ₁ and SP ₂ is 0.02 in absolute value.

  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.

  According to the method according to the embodiment, a low-viscosity copolymer latex can be obtained with a sufficient solid content concentration. The solid content concentration of the copolymer latex is preferably 35 to 65% by mass, more preferably 40 to 60% by mass, from the viewpoints of cost for transportation and tank capacity at storage.

  Further, the copolymer latex may be concentrated by a method such as an evaporation method so that the solid content concentration is 45 to 69% by mass. The copolymer latex obtained by the method according to the embodiment can have a sufficiently low viscosity even when concentrated.

  The viscosity of the copolymer latex is preferably 50 to 1000 mPa · s, more preferably 70 to 700 mPa · s at 25 ° C. The viscosity is a B-type (BL type) viscometer (VISICOMTER (model BM) manufactured by TOKI SANGYO LTD, model No. 1 rotor in the case of a viscosity of 0 to 100 mPa · s) in accordance with the measuring method of JIS K7117-1. ˜500 mPa · s: No. 2 rotor, 500 to 2000 mPa · s: No. 3 rotor, 2000 mPa · s or more: No. 4 rotor is used, and the rotational speed is 60 rpm) .

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

  The copolymer latex according to the embodiment can exhibit a sufficient adhesive strength and a covering property to the electrode active material, can realize a low viscosity, and can be a latex having excellent freezing stability. Moreover, the composition for battery electrodes which mix | blended the copolymer latex which concerns on embodiment can form the coating layer which has the outstanding binding force with respect to metals, such as a collector. In addition, the present inventors consider the reason why the copolymer latex of this embodiment is excellent in freezing stability as follows. The left side of the formula (1) indicates the ratio of the heat of fusion of water detected from −20 ° C. to 0 ° C. with respect to the total heat of fusion of water contained in the copolymer latex. When this value is 0.8 or less on the right side of the formula (1), it is considered that the amount of water not detected from -20 ° C. to 0 ° C. is present in the latex by 20% by mass or more. The peaks detected from −20 ° C. to 0 ° C. are bound water and free water, and the water not detected is presumed to be antifreeze water. Such antifreeze water can be sufficiently present in the latex by the above specific emulsion polymerization, and as a result, it has become possible to improve freezing stability while achieving both adhesive strength and low viscosity. Conceivable.

  In other words, in the copolymer latex according to the embodiment, the proportion of the antifreeze water obtained by differential scanning calorimetry is preferably 20% by mass or more with respect to the total water content, and is 25% by mass or more. Is more preferable. In this case, the amount of antifreeze water (% by mass) relative to the total amount of water can be determined by the following procedure.

The copolymer latex is adjusted to a solid content C _S (mass%) and pH 7 to prepare a measurement sample. For adjusting the concentration and pH, pure water and sodium hydroxide can be used, respectively. The prepared measurement sample is packed in an aluminum pan and set in a differential scanning calorimeter (DSC6200: manufactured by Seiko Instruments Inc.). After the temperature is set to −25 ° C., the temperature is raised to 30 ° C. at a rate of temperature increase of 1 ° C./min to obtain a DSC curve. The heat of fusion ΔH (mJ / mg) from −20 ° C. to 0 ° C. is calculated from the obtained DSC curve. Similarly, heat of fusion ΔH _W (mJ / mg) for water is calculated. From these values, the ratio (mass%) of the antifreeze water amount to the total water amount is obtained by the following formulas (A), (B), (C), and (D).

Formula (A): Total amount of bound water and free water (mg) = [ΔH (mJ / mg) × mass of measurement sample (mg)] / ΔH _W (mJ / mg)
Formula (B): Total water content in measurement sample (mg) = mass of measurement sample (mg) × (100−C _S ) / 100
Formula (C): Amount of antifreeze water (mg) = Total amount of water in measurement sample (mg) −Total amount of combined water and free water (mg)
Formula (D): Ratio of antifreeze water amount to total water amount (mass%) = antifreeze water amount (mg) × 100 / total water amount in measurement sample (mg)

  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 2 to 4 were mixed in the amounts shown in the same table (unit: part by mass) and reacted to synthesize copolymer latex. A specific synthesis procedure is shown below.

In addition, each component and symbol in Tables 1-3 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 (c) Component: Vinyl cyanide monomer ACN: Acrylonitrile (d) Component: Monomer copolymerizable with components (a) to (c) Body STY: Styrene MMA: Methyl methacrylate AAMID: Acrylamide (other components)
tDM: t-dodecyl mercaptan emulsifier: sodium dodecylbenzenesulfonate electrolyte: sodium hydrogen carbonate (NaHCO ₃ )
KPS: Potassium persulfate STPP: Sodium tripolyphosphate PW: Pure water

Example 1
Into 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 2 were added and stirred sufficiently to obtain a reaction solution. .

  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 reaching time, and after 85 minutes with this reaching time as a reference (0 minutes), 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 2 (from 85 minutes to 220 minutes after the arrival time). Was added to the reaction solution. The reaction temperature of the polymerization system was 65 ° C.

  Subsequently, each monomer component and other compounds in the blending amounts (parts by mass) shown in the third row of Table 2 are added to the continuous time zone shown in the third row of Table 2 (after 220 minutes on the basis of arrival time). (Until 490 minutes later).

  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, in order to remove unreacted monomers and other low-boiling compounds, the reaction product was subjected to heating under reduced pressure 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 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. I got each.

(Comparative Examples 1-4, 6, 7)
Copolymer latex CE-1 to Example 1 in the same manner as in Example 1 except that the amount of each monomer component and other compounds, addition time zone, and reaction temperature were changed to the conditions shown in Table 3 or 4. CE-4, CE-6, and CE-7 were obtained, respectively.

(Comparative Example 5)
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 weight 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 4. A copolymer latex CE-5 was obtained in the same manner as in Example 1.

<Evaluation of copolymer latex>
About the copolymer latex obtained above, according to the following method, the left side of the above formula (1): [ΔH × (100 / 100−C _S )] / ΔH _W , antifreeze water amount (%), latex viscosity, Evaluation of freezing stability was performed.

(Calculation of [ΔH × (100 / 100−C _S )] / ΔH _W and amount of antifreeze water (%))
The copolymer latex was adjusted to pH 7 and solid content of 40% by mass using pure water and sodium hydroxide to prepare a measurement sample. The prepared measurement sample is packed in an aluminum pan, set in a differential scanning calorimeter (DSC6200: manufactured by Seiko Instruments Inc.), and after the temperature is set to −25 ° C., the temperature is raised to 30 ° C. at a heating rate of 1 ° C./min. A DSC curve was obtained. A heat of fusion ΔH (mJ / mg) from −20 ° C. to 0 ° C. was calculated from the obtained DSC curve. Similarly, heat of fusion ΔH _W (mJ / mg) for water was calculated. Table 7 shows values of [ΔH × (100 / 100−C _S )] / ΔH _W. In addition, DSC curves obtained for the copolymer latexes of Example 1, Example 3 and Comparative Example 1 are shown in FIGS.

From the obtained value, the ratio (mass%) of the amount of antifreeze water to the total amount of water was determined by the following formulas (A), (B), (C) and (D). The results are shown in Table 7, respectively.
Formula (A): Total amount of bound water and free water (mg) = [ΔH (mJ / mg) × mass of measurement sample (mg)] / ΔH _W (mJ / mg)
Formula (B): Total water content in measurement sample (mg) = mass of measurement sample (mg) × (100−C _S ) / 100
Formula (C): Amount of antifreeze water (mg) = Total amount of water in measurement sample (mg) −Total amount of combined water and free water (mg)
Formula (D): Ratio of antifreeze water amount to total water amount (mass%) = antifreeze water amount (mg) × 100 / total water amount in measurement sample (mg)

(Latex viscosity)
Aron (registered trademark) T-50 (trade name, sodium polyacrylate, weight average molecular weight: 6000) manufactured by Toagosei Co., Ltd. as a dispersant was uniformly 2.5 with respect to 100 parts by mass of the solid content of the copolymer latex. After the addition of parts by mass (in terms of solid content), the solid content was adjusted to 50.0% by mass with pure water, pH 6.5, and the liquid temperature was adjusted to 25 ° C. 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. About the obtained viscosity, it determined as follows. The lower the viscosity, the better.
A: 400 mPa · s or less B: More than 400 1000 mPa · s or less C: 1000 mPa · s or less

<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 (made by Imerys Minerals Japan, Inc., trade name: DB Glaze) 20 parts by weight heavy calcium carbonate (made by Imerys Minerals Japan, trade name: Carbital 90) 80 parts by weight modified starch (Japanese food) Kako Co., Ltd., trade name: MS4600) 2 parts by weight of copolymer latex 6 parts by weight (in terms of solid content)

(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. About the obtained coated paper, dry pick strength was evaluated by the following method.

(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).

<Calculation of solubility parameter of monomer component>
Solubility parameter SP ₁ by the Fedors method of monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system by the end of the introduction of the entire amount of the ethylenically unsaturated carboxylic acid monomer, and the ethylene system a solubility parameter SP ₂ by the Fedors method of the monomer component other than the unsaturated carboxylic acid monomer described above is introduced into the reaction system ethylenically unsaturated carboxylic acid monomer later than at the total amount charged completion of the above formula Using (2), calculation was performed as follows. Table 7 shows values of SP ₁ , SP ₂ , and | SP ₁ -SP ₂ |.

For example, in the case of Example 1, monomer components other than the ethylenically unsaturated carboxylic acid monomer charged into the reaction system by the end of the total amount of the ethylenically unsaturated carboxylic acid monomer were 18 masses of butadiene. Monomer other than the ethylenically unsaturated carboxylic acid monomer, which was added to the reaction system after the end of charging the entire amount of the ethylenically unsaturated carboxylic acid monomer. The components are 24 parts by mass of butadiene, 19 parts by mass of styrene, and 11 parts by mass of acrylonitrile.
SP ₁ is [{(4420 × 18/54) + (9630 × 14/104) + (8100 × 8/53)} / {(59.2 × 18/54) + (86.5 × 14/104). ) + (39.1 × 8/53)}] ^1/2 = 10.35.
SP ₂ is [{(4420 × 24/54) + (9630 × 19/104) + (8100 × 11/53)} / {(59.2 × 24/54) + (86.5 × 19/104). ) + (39.1 × 11/53)}] ^1/2 = 10.37.
The difference between SP ₁ and SP ₂ is 0.02 in absolute value.

<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 7.
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 peel strength of electrode coating layer)
Each negative electrode sheet obtained by the above method was cut into a strip of 7 cm × 2 cm, a cellophane adhesive tape was attached to the coating layer side, and the coating layer and the current collector were peeled off by about 5 mm by hand. The current collector of the peeled part was fixed to a tensile tester, and the stress applied to peeling when the cellophane adhesive tape was pulled in the direction perpendicular to the peeling surface was measured. The tensile rate was 100 mm / min, and the average value (unit (N / m)) of n = 3 is shown in Table 7. A larger numerical value indicates a better binding force at the interface between the current collector of the negative electrode sheet and the coating layer.

  It was confirmed that the copolymer latex obtained in Examples 1 to 10 was excellent in dry pick strength, low viscosity, and excellent in freeze stability. Moreover, the copolymer latex obtained in Examples 1-11 confirmed that the peel strength of the electrode coating layer obtained by apply | coating the composition for battery electrodes, and the coating property to an electrode active material are also favorable. It was done.

Claims (3)

A copolymer latex obtained by emulsion polymerization,
The copolymer is
15 to 60% by mass of an aliphatic conjugated diene monomer,
5-35% by mass of an ethylenically unsaturated carboxylic acid monomer,
It is composed of a monomer component consisting of 0.5 to 30% by mass of a vinyl cyanide monomer and 0 to 99.5% by mass of a monomer copolymerizable therewith,
In the emulsion polymerization, the reaction system at the start of addition of the polymerization initiator contains 0% by mass to 40% by mass or less of the total amount of the ethylenically unsaturated carboxylic acid monomer, and the polymer conversion rate of the reaction system is 1 Addition of the remainder of the ethylenically unsaturated carboxylic acid monomer is started after 5% from the time when it reaches 0.0% to the time when the whole amount of the monomer components is finished. Then, by 80% of the time from the arrival time to the end time, 92% by mass or more of the total amount of the ethylenically unsaturated carboxylic acid monomer is charged,
By differential scanning calorimetry, the heat of fusion ΔH (from −20 ° C. to 0 ° C. calculated from the DSC curve obtained when the copolymer latex cooled to −25 ° C. is heated at a rate of temperature increase of 1 ° C./min. mJ / mg) copolymer latex satisfying the following formula (1).
[ΔH × (100 / 100−C _S )] / ΔH _W ≦ 0.8 (1)
[In formula (1), C _S indicates the solid content concentration (mass%) of the copolymer latex measurement sample, and ΔH _W is the heat of fusion (mJ / mg) when distilled water is measured under the same conditions. Indicates. ]   The copolymer latex according to claim 1, wherein the ethylenically unsaturated carboxylic acid monomer contains more than 30% by mass of a monocarboxylic acid monomer. Solubility parameter by Fedors method of monomer components other than the ethylenically unsaturated carboxylic acid monomer charged into the reaction system by the end of the emulsion polymerization when the whole amount of the ethylenically unsaturated carboxylic acid monomer is charged SP ₁ and the solubility of monomer components other than the ethylenically unsaturated carboxylic acid monomer introduced into the reaction system after the end of the introduction of the entire amount of the ethylenically unsaturated carboxylic acid monomer by the Fedors method The process is carried out by adding the monomer component to the reaction system so that the difference between SP ₁ and SP ₂ is 1.50 or less in absolute value when the parameter is SP _2. The copolymer latex according to 2.

Images