JP2021195549A - Polymer latex - Google Patents

Abstract

To provide a polymer latex that is excellent in coating operability in the coated paper production process and is excellent in dry pick strength and blister resistance of the coated paper especially when used as a binder for a paper coating composition.SOLUTION: Provided is a polymer latex, and in which, characterized, the component in which the molecular weight (in terms of polystyrene) of the polymer latex in tetrahydrofuran dissolution content is more than 200 and 3000 or less is 13.0% or less.SELECTED DRAWING: None

Description

The present invention relates to polymer latex, preferably its use for paper coating.

Polymer latex is widely used as a binder in the fields of paper coating, backsizing of carpets, wood products such as plywood and veneer, battery electrodes, and tire cords. Coated paper is produced by applying a paper coating composition to the surface of a coated base paper and drying it. Coated paper is widely used for printed matter, and research and improvement of paper coating compositions containing pigments and water-based binders as main components are being promoted in order to obtain high-quality coated paper. As the water-based binder, natural binders such as starch and synthetic rubber binders such as styrene-butadiene copolymer latex are widely used. Among them, conjugated diene-based latex and acrylic-based latex have a large degree of freedom in quality design, and are widely used today as the most suitable binder for paper coating compositions, and the performance of the binder is the paper coating composition. It is known to affect the performance, operability at the time of producing coated paper, the surface strength of the final coated paper product, and the quality such as printing gloss.
In recent years, while high-speed coating and high production have been promoted in the paper processing field, various studies have been conducted on the quality design and manufacturing method of synthetic rubber binders, and technological improvements have been introduced.

Aimed at high balance of the above-mentioned physical properties, a conjugated diene-based latex using a method of controlling the molecular weight of the solvent-dissolved portion of the copolymer has been proposed. For example, in Patent Document 1, in polymer latex, the polystyrene-equivalent weight average molecular weight (Mw) of the dissolved tetrahydrafuran of the latex film is 2000 or more and less than 100,000, so that the coating operability of the paper coating composition is improved. It is disclosed that a coated paper having excellent dry pick strength and blister resistance can be obtained. Further, in Patent Document 2, regarding the conjugated diene-based latex, firstly, the composition of the monomer mixture used when producing the polymer is defined in a specific range, and secondly, when the conjugated diene-based latex is produced, it is specified. The product obtained by emulsion polymerization of the monomer mixture in the presence of the above components has excellent coating workability, exhibits high printing gloss, lowers the viscosity of the conjugated diene-based latex, and is a good coated paper. It is disclosed that a binder for a paper coating that can simultaneously satisfy the stickiness resistance of a surface can be provided.
However, these various improvement techniques have not satisfied the high level of quality required for polymer latex for paper coating, and further improvement has been strongly demanded.

Japanese Unexamined Patent Publication No. 2012-140518

Japanese Unexamined Patent Publication No. 2011-225716

INDUSTRIAL APPLICABILITY The present invention is a polymer latex having excellent coating operability in a coated paper manufacturing process and excellent dry pick strength and blister resistance of coated paper, particularly when used as a binder for a composition for paper coating. Is intended to provide.

As a result of diligent studies, the present inventors have found that the above-mentioned problems can be solved by the content of the polymer latex having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of tetrahydrofuran is 13.0% or less. We have found and completed the present invention.

That is, the present invention is composed of the following.
[1] A polymer latex having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of the polymer latex in tetrahydrofuran is 13.0% or less. ..
[2] The polymer latex according to [1] for paper coating.

When the polymer latex of the present invention is used as a binder for coating compositions for various purposes, it is possible to obtain one having excellent coating operability and excellent adhesive strength and surface appearance of the coating layer. In particular, when used as a binder for a paper coating composition, a coated paper having excellent coating operability in the coated paper manufacturing process and excellent dry pick strength and blister resistance of the coated paper can be obtained. ..

The composition of the polymer latex of the present invention is not particularly limited, but for example, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR) and the like. Conjugate diene latex; acrylic latex mainly composed of (meth) acrylic acid ester; natural rubber latex; chloroprene rubber latex; vinyl acetate latex; silicone latex and the like can be used alone or in combination of two or more. Of these, conjugated diene-based latex and acrylic-based latex are preferable. The acrylic latex referred to here is one in which the structural unit derived from the aliphatic conjugated diene-based monomer is less than 10% by weight.

The conjugated diene-based latex includes an aliphatic conjugated diene-based monomer of 10 to 80% by weight, an ethylene-based unsaturated carboxylic acid monomer of 0.1 to 15% by weight, and other copolymerizable monomers of 5-89. It is preferably made by polymerizing 9.9% by weight.

Examples of the aliphatic conjugated diene-based monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, and substitutions. Examples thereof include linear conjugated pentadiene, substitution and side chain conjugated hexadiene, and one or more of these can be used. In particular, the use of 1,3-butadiene is preferable.

The content of the aliphatic conjugated diene-based monomer is preferably 10 to 80% by weight, more preferably 25 to 60% by weight. By adjusting to the above range, an excellent balance between adhesive strength and operability can be obtained.

As the ethylene-based unsaturated carboxylic acid monomer, one or more monobasic acids or dibasic acids (anhydrous) such as itaconic acid, acrylic acid, methacrylic acid, crotonic acid, maleic acid, and fumaric acid are used. can do.

The content of the ethylene-based unsaturated carboxylic acid monomer is preferably 0.1 to 15% by weight, more preferably 2 to 10% by weight. By adjusting to the above range, a polymer latex having an excellent balance between dispersibility in water and viscosity can be obtained.

Other copolymerizable monomers include alkenyl aromatic monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, and unsaturated monomers containing hydroxyalkyl groups. , Unsaturated carboxylic acid amide-based monomers, monomers containing sulfonic acid groups, and the like.

Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene, divinylbenzene and the like. These can be used alone or in combination of two or more. In particular, the use of styrene is preferable.

Examples of the vinyl cyanide-based monomer include monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile. These can be used alone or in combination of two or more. In particular, the use of acrylonitrile or methacrylonitrile is preferred.

Examples of unsaturated carboxylic acid alkyl ester-based monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaconate. , Monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. These can be used alone or in combination of two or more. In particular, the use of methyl methacrylate is preferred.

Examples of the unsaturated monomer 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 thereof include methacrylate. These can be used alone or in combination of two or more.

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

Examples of the monomer containing a sulfonic acid group include 2-acrylamide-2-methylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, and α-methylstyrenesulfone. Acids, 2-sulfoethyl methacrylate, salts thereof and the like can be mentioned. These can be used alone or in combination of two or more.

In addition to the above-mentioned monomers, any monomer used in emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride and vinylidene chloride can be used. Further, polyvinyl alcohol (PVA); a saponified product of an ethylene-vinyl acetate copolymer, a vinyl alcohol resin typified by poly-α-hydroxyvinyl alcohol; a polymer containing a hydroxyl group such as a cellulose derivative typified by carboxymethyl cellulose. It can also be polymerized in the presence.

The content of the other copolymerizable monomer is preferably 5 to 89.9% by weight, more preferably 30 to 73% by weight.

Examples of the acrylic latex include unsaturated carboxylic acid alkyl ester-based monomers 15 to 99.9% by weight, ethylene-based unsaturated carboxylic acid monomers 0.1 to 70% by weight, and other copolymerizable monomers. It is preferably formed by polymerizing 0 to 84.9% by weight.

As the unsaturated carboxylic acid alkyl ester-based monomer, those described above can be used. In particular, the use of butyl acrylate is preferred.

The content of the unsaturated carboxylic acid alkyl ester-based monomer is preferably 15 to 99.9% by weight, more preferably 20 to 90% by weight.

As the ethylene-based unsaturated carboxylic acid monomer, those described above can be used.

The content of the ethylene-based unsaturated carboxylic acid monomer is preferably 0.1 to 70% by weight, more preferably 10 to 50% by weight.

Other copolymerizable monomers include aliphatic conjugated diene-based monomers, alkenyl aromatic-based monomers, vinyl cyanide-based monomers, unsaturated monomers containing hydroxyalkyl groups, and unsaturated monomers. Examples thereof include saturated carboxylic acid amide-based monomers and monomers containing a sulfonic acid group, and those described above can be used. Further, polyvinyl alcohol (PVA); a saponified product of an ethylene-vinyl acetate copolymer, a vinyl alcohol resin typified by poly-α-hydroxyvinyl alcohol; a polymer containing a hydroxyl group such as a cellulose derivative typified by carboxymethyl cellulose. It can also be polymerized in the presence.

The content of the other copolymerizable monomer is preferably 0 to 84.9% by weight, more preferably 5 to 60% by weight.

The polymer latex of the present invention can be produced by a known emulsion polymerization method using the above-mentioned monomers. When carrying out emulsion polymerization, in addition to the above-mentioned monomer, an emulsifier (surfactant), a polymerization initiator, and if necessary, a chain transfer agent, a reducing agent and the like can be used.

Examples of the emulsifier (surfactant) include sulfate ester salts of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, and sulfate ester salts of nonionic surfactants. Anionic emulsifiers, alkyl ester type of polyethylene glycol, alkyl phenyl ether type, alkyl ether type and other nonionic emulsifiers can be used alone or in combination of two or more. The amount of the emulsifier to be blended is not particularly limited, but is preferably 0.2 to 3.5 parts by weight with respect to 100 parts by weight of the monomer.

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, and acetyl peroxide. , Diisopropylbenzenehydroperoxide, oil-soluble polymerization initiators such as 1,1,3,3-tetramethylbutylhydroperoxide. These can be used alone or in combination of two or more. In particular, it is preferable to select from potassium persulfate, sodium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide. The blending amount of the polymerization initiator is not particularly limited, but is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, other additives and the like.

Chain transfer agents include, for example, alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; dimethylxanthogen disulfide, and diisopropyl. Xanthogen compounds such as xanthogen disulfide; thiuram compounds such as tetramethylthium disulfide, tetraethylthiuram disulfide, and tetramethylthium monosulfide; Allyl compounds such as allyl alcohols; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, and α-benzyloxyacrylamide. Chain transfer agents such as triphenylethane, pentaphenylethane, achlorein, metaacrolein, thioglycolic acid, thioalinic acid, 2-ethylhexylthioglycolate, turpinolene, and α-methylstyrene dimer. 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 the combination of other additives and the like.

Reducing agents include, for example, reducing saccharides such as dextrose and saccharose; amines such as dimethylaniline and triethanolamine; carboxylic acids such as L-ascorbic acid, erythorbic acid, tartrate acid, and citrate and salts thereof; sulfite. Examples thereof include salts, hydrogen sulfites, pyrosulfites, nitionates, nithionates, thiosulfates, formaldehyde sulfonates, benzaldehyde sulfonates and the like. In particular, it is preferable to select from formaldehyde sulfonate. The blending amount of the reducing agent can be appropriately adjusted in consideration of the combination of other additives and the like.

Further, in the emulsified polymerization, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane and cycloheptene, and non-saturated hydrocarbons such as penten, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene are not used. Hydrocarbon compounds such as saturated hydrocarbons, aromatic hydrocarbons such as benzene, toluene and xylene can be used.

Furthermore, known additives such as oxygen supplements, chelating agents, and dispersants may be used as needed, and the types and amounts of these are not particularly limited, and appropriate amounts can be used as appropriate. Furthermore, known additives such as antifoaming agents, antiaging agents, preservatives, antibacterial agents, flame retardants, and ultraviolet absorbers may be used, and the types and amounts of these are not particularly limited, and appropriate amounts are used as appropriate. Can be done.

The temperature during emulsion polymerization is preferably set in the range of 20 to 100 ° C., more preferably 25 to 85 ° C., and even more preferably 30 to 70 ° C. from the viewpoint of the pressure in the tank and productivity in consideration of safety. , 30-60 ° C. is particularly preferable.

Examples of the method of adding the monomer component and other components at the time of emulsion polymerization include a batch addition method, a split addition method, a continuous addition method, and a power feed method. Above all, it is preferable to adopt a continuous addition method (hereinafter, may be referred to as “continuous addition”). Furthermore, the linkage may be performed a plurality of times.

The reaction time of emulsion polymerization is preferably 1 to 15 hours, more preferably 2 to 10 hours, for example, from the viewpoint of productivity.

Further, in the emulsion polymerization, it is preferable to confirm that the polymer conversion rate exceeds 97% and terminate the reaction. In this way, the polymer latex is obtained. The polymer conversion rate can be calculated from the amount of solid content or the amount of heat obtained by cooling the polymerization tank.

From the viewpoint of dispersion stability, the pH of the obtained polymer latex is preferably adjusted to 5 to 9.5 with ammonia, potassium hydroxide, sodium hydroxide or the like, to 5.5 to 8.5. It is more preferable to be adjusted.

Further, it is preferable that the unreacted monomer and other low boiling point compounds are removed from the obtained polymer latex by a method such as steam distillation.

The polymer latex of the present invention needs to have a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the resolved content of the polymer latex in tetrahydrofuran, and the component is 13.0% or less, and 10.0% or less. Is preferable, and 5.0% or less is more preferable. When the molecular weight (in terms of polystyrene) in the tetrahydrofuran dissolved is more than 200 and the component of 3000 or less exceeds 13.0%, for example, when used in a composition for paper coating, coating operability, dry pick strength and resistance It tends to be inferior in the balance of blister property.

A component having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of the polymer latex in tetrahydrofuran can be obtained by the method described in Examples.

The method for adjusting the component having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of the polymer latex in tetrahydrofuran is not particularly limited, but is not particularly limited. Examples include lowering the rate, using a chain transfer agent, and increasing the concentration of unreacted monomers during the polymerization reaction.

The average particle size of the polymer latex of the present invention is not particularly limited, but is preferably 40 nm or more and 300 nm or less, and the upper limit is more preferably 150 nm or less, and particularly preferably 110 nm or less.

The toluene insoluble content of the polymer latex of the present invention is not particularly limited, but is preferably 70% or more, more preferably 80% or more, and particularly preferably 85% or more.

Since the polymer latex of the present invention functions as a binder, it can be used for various purposes such as paper coating, battery electrodes, tire cords, carpet backing, and wood bonding. Of these, it is preferably used for paper coating and battery electrodes, which are used as binders for coating compositions, and more preferably for paper coating.

When used for paper coating, the polymer latex is blended with a pigment and used as a composition for paper coating.

Pigments to be blended in the composition for paper coating include known pigments such as kaolin clay, calcium carbonate, talc, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, satin white and other inorganic pigments, or polystyrene latex. Organic pigments such as these can be used alone or in admixture. The content of the polymer latex in the paper coating composition is preferably 2 to 20 parts by weight (solid content) with respect to 100 parts by weight (solid content) of the pigment, preferably 4 to 15 parts by weight. More preferred. By adjusting so as to be within the above range, an excellent balance between adhesive strength and blister resistance can be obtained.

Further, if necessary, modified starch such as starch, oxidized starch, esterified starch, natural binder such as soybean protein and casein, or water-soluble synthetic binder such as polyvinyl alcohol and carboxymethyl cellulose may be used.

In addition, when preparing composition for paper coating, other auxiliaries such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), defoamers (polyglycol, fatty acid ester, phosphorus, etc.) Acid esters, silicone oils, etc.), leveling agents (roth oil, dicyandiamide, urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention improvers (carboxymethyl cellulose, sodium alginate, etc.) ) May be added as needed.

As a method for applying the paper coating composition to the coated paper, any known technique such as an air knife coater, a blade coater, a roll coater, a bar coater, or the like may be used. After coating, the surface is dried and finished with a calendar ring or the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. In the examples, the part indicating the ratio and% are based on the weight standard unless otherwise specified. The evaluation of various physical properties in the examples was carried out by the following method.

Example 1
A stirrer is provided, and 140 parts of polymerized water, 3.0 parts of sodium dodecylbenzene sulfonate, 1.2 parts of potassium persulfate, and the first-stage polymerization component in Table 1 are collectively charged into a pressure-resistant polymerization reactor. , The temperature was raised to 30 ° C., and the second-stage polymerization component shown in Table 1 was continuously added for 6 hours to carry out a polymerization reaction. Polymerization was terminated when the polymerization conversion rate exceeded 98%. The pH was then adjusted to 7 using aqueous ammonia and steam distilled to remove unreacted monomers and other low boiling point compounds to give the polymer Latex A.

Example 2
The same operation as in Example 1 was carried out except that the polymerization temperature was set to 40 ° C. to obtain a polymer latex B.

Example 3
A stirrer is provided, and 140 parts of polymerized water, 1.4 parts of sodium dodecylbenzene sulfonate, 1.2 parts of potassium persulfate, and the first-stage polymerization components shown in Table 1 are collectively charged into a pressure-resistant polymerization reactor. , The temperature was raised to 60 ° C., and the second-stage polymerization component shown in Table 1 was continuously added for 6 hours while maintaining the temperature at 60 ° C. After the addition of the second-stage polymerization component was completed, the temperature was raised to 85 ° C., the polymerization was continued, and the polymerization was terminated when the polymerization conversion rate exceeded 98%. Then, using aqueous ammonia, the pH was adjusted to 7, and steam distillation was performed to remove unreacted monomers and other low boiling point compounds to obtain polymer latex C.

Example 4
A stirrer is provided, and 140 parts of polymerized water, 3.0 parts of sodium dodecylbenzene sulfonate, 1.2 parts of potassium persulfate, and the first-stage polymerization components shown in Table 1 are collectively charged into a pressure-resistant polymerization reactor. , The temperature was raised to 70 ° C., and the second-stage polymerization component shown in Table 1 was continuously added for 6 hours while maintaining the temperature at 70 ° C. After the addition of the second-stage polymerization component was completed, the temperature was raised to 85 ° C., the polymerization was continued, and the polymerization was terminated when the polymerization conversion rate exceeded 98%. Then, using aqueous ammonia, the pH was adjusted to 7, and steam distillation was performed to remove unreacted monomers and other low boiling point compounds to obtain a polymer latex D.

Comparative Example 1
The same procedure as in Example 3 was carried out except that the reaction temperature was changed from 60 ° C. to 70 ° C. to obtain a polymer latex E.

Percentage of components in which the molecular weight (in terms of polystyrene) of the polymer latex in the dissolved content of tetrahydrofuran is more than 200 and 3000 or less <Sample preparation method>
The polymer latex was dried at room temperature for 24 hours and then vacuum dried at room temperature for 24 hours to prepare a film. The obtained film was cut into about 5 mm squares and then refluxed with water for 16 hours to remove water-dissolved components, and vacuum dried at room temperature for 2 nights. Then, the mixture was refluxed in tetrahydrofuran (without stabilizer) for 16 hours, the obtained tetrahydrofuran solution was filtered, concentrated, dried and dried, and further dried in vacuum at room temperature for 2 nights to obtain a tetrahydrofuran-dissolved component of the polymer latex. ..
After dissolving the obtained polymer latex in 10 ml of tetrahydrofuran (for liquid chromatography) to about 0.03 g, a disposable filter (Specifications: Shimadzu Corporation, liquid chromatograph / non-aqueous 13N pore diameter) It was filtered through 0.45 μm) to prepare a sample for gel permeation chromatography (GPC) measurement.
<GPC conditions>
Measuring device: Agilent Technologies, Inc. LC-1260 infinity
Data processing device: System Instruments Co., Ltd. Micro 7 Plus Data Station
Analytical column: Agilent Technologies, Inc .: PL gel 10 microm Mixed-B (300 mm x 7.5 mm) x 3 Guard columns: Agilent Technologies, Inc. PL gel 10 microm Mixed-B (50 mm x 7. 5 mm)
Column oven: 50 ° C
Carrier liquid: Tetrahydrofuran (for liquid chromatography)
Flow rate: 1 ml / min
Detector: RI
Sample injection volume: 100 μl
<Calculation method>
The time when the sample was injected into the obtained chromatograph was set to 0 minutes, and the points with a detection time of 5 minutes and the points with a detection time of 40 minutes were connected by a line to obtain a baseline. The area of the entire peak was calculated by setting the portion where the detection intensity was higher than this baseline as the entire peak. Next, the area of the component having a molecular weight (polystyrene equivalent) of 200 or less was determined from the whole peak. Similarly, the area of the component having a molecular weight (polystyrene equivalent) of 3000 or less was determined from the whole peak. From each of the obtained areas, a component (%) having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less was determined by the following formula.
(Molecular weight (polystyrene equivalent) 200 or less component area) ÷ (total area of peak) x 100 = (Molecular weight (polystyrene equivalent) 200 or less component (%))
(Molecular weight (polystyrene equivalent) 3000 or less component area) ÷ (total area of peak) x 100 = (Molecular weight (polystyrene equivalent) 3000 or less component (%))
(Molecular weight (polystyrene equivalent) 3000 or less component (%))-(Molecular weight (polystyrene equivalent) 200 or less component (%)) = (Molecular weight (polystyrene equivalent) more than 200 and 3000 or less component (%))

Evaluation of stickiness resistance of polymer latex <br /> As a guideline for the ease with which the polymer latex adheres to a backing roll or the like, a test was conducted on the stickiness resistance (adhesiveness) of the polymer latex film. It is shown that the better the stickiness resistance, the less likely the polymer latex adheres to the backing roll or the like, and the better the operability in the coated paper manufacturing process.
Each polymer latex is applied to a polyester film at a coating amount of 12 g / m2, dried in an oven at 120 ° C. for 1 minute, and then cut into strips having a width of 1 cm. Place all the latex film strips side by side on the black mount. A filter paper is placed on top of the filter paper, and the heat rolls heated to 110 ° C. are passed through and crimped using a heat calendar for laboratory testing. Then, after the filter paper was peeled off, the state of adhesion of the fibers of the filter paper to the surface of each latex film was visually judged, and the stickiness resistance of each latex film was compared. Those with less fiber adhesion were evaluated as having excellent stickiness resistance, and those with more fiber adhesion were inferior in stickiness resistance, and were relatively evaluated from 5th grade (excellent) to 1st grade (inferior).

<Making coated paper>
A composition for paper coating was prepared according to the formulation shown below. The pH of the composition for paper coating was adjusted to 9.5 with sodium hydroxide, and the solid content concentration was adjusted to 67% by weight by adding a required amount of pure water.

(Combined prescription)
Kaolin (manufactured by Shiraishi Calcium Co., Ltd., Kaofine): 30 parts by weight Heavy calcium carbonate (manufactured by Fimatec Co., Ltd., FMT-90): 70 parts by weight of modified starch (manufactured by Nihon Shokuhin Kako Co., Ltd., MS4600): 2 parts by weight polymer latex: 8 parts by weight (solid content conversion value)

A coating composition is applied to a coated base paper (basis weight 65 g / m2) using a wire bar so that the coating amount per side is 10 g / m2, dried, and then a linear pressure of 60 kg / cm. A coated paper was obtained by performing calendar processing under the condition of a temperature of 50 ° C.

Evaluation of Dry Pick Strength of Coated Paper Using an RI printing machine, picking test ink (manufactured by DIC Graphics Co., Ltd.) was printed on each coated paper at the same time. The obtained printed matter was pressed against the coated wood-free paper to copy the ink, and the portion where the ink was not copied (white spot) was regarded as the picking occurrence location. The degree of picking at this time was visually determined and evaluated relatively from 5th grade (excellent) to 1st grade (inferior).

Evaluation of blister resistance of coated paper <br /> For the test piece (4 cm x 5 cm) of each coated paper sample, RI printing machine using offset printing ink (WD Leo X, manufactured by Toyo Ink Co., Ltd.) Both sides were printed with, and the printed test piece was humidity-controlled for 24 hours in a constant temperature and humidity chamber at 23 ° C. × 50% RH. Using a blister tester (manufactured by Osugi Co., Ltd.), the test plate was heated with hot air, and the minimum temperature of the test plate on which the test piece generated blister was determined. The higher the generation temperature, the better the blister resistance.

Each component in Table 1 below is indicated by the following abbreviations.
(Polymer)
BDE: Butadiene STY: Styrene MMA: Methyl Methacrylate ACN: Acrylonitrile AA: Acrylic acid (other compounds)
EML: Sodium dodecylbenzene sulfonate (Kao Corporation, Neoperex G-15) (anionic emulsifier)
KPS: Potassium persulfate (polymerization initiator)
EDTA-4Na: Ethylenediaminetetraacetate SFS: Sodium formaldehyde sulfoxylate NaHCO ₃ : Sodium hydrogen carbonate TMTM: Tetramethylthiumum monosulfide CHX: Cyclohexene (unsaturated hydrocarbon)
TDM: t-dodecyl mercaptan (chain transfer agent)
Molecular weight 200 to 3000: A component (%) having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of the polymer latex in tetrahydrofuran.

As shown in Table 1, by using a polymer latex having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the resolved content of the polymer latex in tetrahydrofuran, coating operability can be improved. It can be seen that the balance between dry pick strength and blister resistance is excellent.

As described above, the polymer latex of the present invention is excellent in coating operability in the coated paper manufacturing process, especially when used as a binder for a paper coating composition, and has dry pick strength and resistance to coated paper. It has excellent blister properties and is extremely useful as a binder for paper coating compositions. Further, the binder of the present invention has a good balance between adhesive resistance, adhesive strength and easiness of deformation when heat is applied, and is therefore useful in other applications requiring these effects. ..

Claims (2)

A polymer latex, wherein the component having a molecular weight (in terms of polystyrene) of more than 200 and 3000 or less in the dissolved content of the polymer latex in tetrahydrofuran is 13.0% or less. The polymer latex according to claim 1, which is used for paper coating.