JP2019011434A - Copolymer latex cof inkjet coated paper and copolymer latex-containing composition - Google Patents

Abstract

To provide a copolymer latex for an inkjet coated paper which is excellent in water-based ink absorbability to a coating layer and a surface strength of the coating layer and is excellent in stability of a coating composition.SOLUTION: The copolymer latex for inkjet coated paper is provided that includes 5-30 wt.% of a structural unit derived from aliphatic conjugated diene monomer, 0.1-10 wt.% of a structural unit derived from an ethylene unsaturated carboxylic acid monomer and 60-94.9 wt.% of other structural units, wherein a contact angle I of a latex film I (LxFI) prepared in the following method with respect to ion-exchanged water is 40° or less, a contact angle II of a latex film II (LxFII) prepared in the following method with respect to the ion-exchanged water is 60° or more, and a difference between the contact angles of the LxFI and that of LFII with respect to the ion-exchanged water is 30° or more. (Preparation method of LxFI) A copolymer latex is applied onto a PET film, and is dried at 200°C for 1 minute. (Preparation method of LxFII) The copolymer latex is dried at 120°C for 1 minute.SELECTED DRAWING: None

Description

  The present invention relates to a copolymer latex for inkjet coated paper and a composition containing the copolymer latex. Specifically, it is a copolymer latex used as a binder in inkjet coated paper for water-based inks, and contains a copolymer latex excellent in water-based ink absorbability of inkjet-coated paper and the copolymer latex. The present invention relates to a coating composition for inkjet coated paper.

In recent years, coated paper has been used in 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, on-demand printing is becoming the mainstream for sending personal information such as direct mail and product catalogs in the mail order business. Specifically, on-demand printing such as electrophotography and inkjet printing is being used. Yes.
A general offset printing paper coating composition comprises 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 base paper, and other additives. A water-based coating composition is used, and as the binder, a synthetic emulsion binder represented by styrene-butadiene copolymer latex or a natural binder represented by starch or casein is used.
On the other hand, a coating composition used for an inkjet system (hereinafter referred to as a coating composition for inkjet coated paper) is a pigment dispersion in which a porous pigment such as silica having excellent water absorbability is dispersed in water, Consists of a binder for fixing the pigment to the base paper, a cationic fixing agent for fixing the water-based ink on the paper surface, and other additives. The binder is polyvinyl alcohol with excellent protective colloid properties and hydrophilicity. Is generally used. And in the coating composition for offset printing paper, the use of styrene-butadiene copolymer latex, which is a general synthetic emulsion binder, tends to be limited due to poor absorbability of water-based ink.

  On the other hand, the polyvinyl alcohol used in the coating composition for inkjet coated paper tends to be inferior in surface strength of the coating layer as compared with the synthetic emulsion binder.

Inkjet printing is a method in which very small droplets of ink are ejected to adhere and fix to inkjet paper to form characters and images. The water-based ink absorbs into the coating layer that forms the surface of the coated paper. Retention properties and fixing properties affect character bleeding and image sharpness. Furthermore, it is known that the absorbability of water-based ink also affects the printing workability because it affects the drying of the ink on the surface after printing. Therefore, there is a demand for ink-jet coated paper that does not blur characters, provides a clear image, and has good printing workability. In order to improve the above-mentioned points, for example, in Japanese Patent Application Laid-Open No. 2001-219646 (Patent Document 1), the ink absorption capacity in the ink receiving layer of the inkjet recording medium and the contact angle of the ink receiving layer with respect to the ink can be defined. Have been described. Further, WO2003 / 008198 (Patent Document 2) describes that the contact angle with respect to pure water on the surface of an ink jet recording sheet is defined as 90 ° or more and the contact angle with respect to ink is defined as 30 ° or less. However, the balance between ink jet printing suitability and the surface strength of the coating layer is still insufficient.

JP 2001-219646 A

WO2003 / 008198

  The present invention relates to a synthetic emulsion binder that is limited in use due to poor water-based ink absorbability in ink-jet coated paper. Even if it is used in a coating composition for ink-jet coated paper, the water-based ink absorbability to the coating layer It is another object of the present invention to provide a copolymer latex and a copolymer latex-containing composition that are excellent in the surface strength of the coating layer and are excellent in the stability of the coating composition.

The present invention is as follows.
[1] 5 to 30% by weight of structural units derived from an aliphatic conjugated diene monomer, 0.1 to 10% by weight of structural units derived from an ethylenically unsaturated carboxylic acid monomer, and other structural units 60 A latex of a copolymer latex for inkjet coated paper containing ˜94.9% by weight, wherein the latex film I prepared by the following method has a contact angle I with respect to ion exchange water of 40 ° or less, and is prepared by the following method. Ink-jet coated paper characterized in that the contact angle II of film II with respect to ion-exchanged water is 60 ° or more and the difference in contact angle between latex film I and latex film II with respect to ion-exchanged water is 30 ° or more Copolymer latex.
(How to make Latex Film I)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 200 ° C. for 1 minute, and then taken out.
(How to make Latex Film II)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 120 ° C. for 1 minute, and then taken out.
[2] The copolymer latex for inkjet coated paper according to the above [1], wherein the minimum film-forming temperature (MFT) of the copolymer latex is 50 ° C. or higher.
[3] The copolymer latex for inkjet coated paper according to any one of [1] to [2] above, wherein the gel content is 80% by weight or more.
[4] The copolymer latex for inkjet coated paper as described in any one of [1] to [3] above, wherein the average particle size is 120 nm or more.
[5] The inkjet coating as described in any one of [1] to [4] above, wherein the content of the anionic emulsifier contained in the copolymer latex (solid content) is 0.1% by weight or more. Copolymer latex for paper.

  By using the copolymer latex for ink-jet coated paper of the present invention, since the water-based ink absorbability is excellent, letters are not blurred, a clear image is obtained, and an ink-jet coated paper excellent in surface strength is obtained. Furthermore, the coating composition using the copolymer latex for inkjet coated paper of the present invention can be obtained with a small amount of aggregate.

  The copolymer latex of the present invention contains a structural unit derived from an aliphatic conjugated diene monomer, a structural unit derived from an ethylenically unsaturated carboxylic acid monomer, and other structural units.

  The structural unit derived from an aliphatic conjugated diene monomer is a structural unit formed by polymerizing an aliphatic conjugated diene monomer. Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted Examples thereof include linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like, and these can be used alone or in combination. In particular, the use of 1,3-butadiene is preferred.

  The structural unit derived from an ethylenically unsaturated carboxylic acid monomer is a structural unit formed by polymerizing an ethylenically unsaturated carboxylic acid monomer. Examples of the ethylenically unsaturated carboxylic acid monomer include monobasic acids or dibasic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Or 2 or more types can be used.

  Other monomers corresponding to the structural unit include alkenyl aromatic monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, and unsaturated monomers containing hydroxyalkyl groups. And unsaturated carboxylic acid amide monomers.

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

  Examples of the vinyl cyanide monomer include monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile. These can be used alone or in combination of two or more. In the present embodiment, the use of acrylonitrile or methacrylonitrile is particularly preferable from the viewpoints of easy industrial production and availability and cost.

  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 , Monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. These can be used alone or in combination of two or more. In the present embodiment, the use of methyl methacrylate is particularly preferred 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, 2-hydroxyethyl methyl fumarate and the like. These can be used alone or in combination of two or more.

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

  In addition to the above monomers, any of the monomers used in ordinary emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, can be used.

  The structural single unit constituting the copolymer latex of the present invention comprises 5 to 30% by weight of a structural unit derived from an aliphatic conjugated diene monomer, and a structural unit derived from an ethylenically unsaturated carboxylic acid monomer. 1 to 10% by weight and other structural units 60 to 94.9% by weight.

  The structural unit derived from the aliphatic conjugated diene monomer must be contained in an amount of 5 to 30% by weight. If it is less than 5% by weight, the surface strength of the coating layer tends to be inferior, and if it exceeds 30% by weight, the film-forming property of the copolymer latex is improved. As a result, the water-based ink absorbability to the coating layer tends to be inferior. is there. Preferably it is 7 to 27% by weight.

  The structural unit derived from the ethylenically unsaturated carboxylic acid monomer needs to be contained in an amount of 0.1 to 10% by weight. If it is less than 0.1% by weight, the hydrophilicity tends to be inferior, and if it exceeds 10% by weight, the mixing stability with the cationic fixing agent tends to be inferior when mixed as a coating composition. Preferably it is 0.2 to 6 weight%.

  The other structural unit needs to be contained in an amount of 60 to 94.9% by weight. If it is less than 60% by weight, it tends to be inferior in water-based ink absorbability and the mixing stability with a cationic fixing agent when mixed as a coating composition, and if it exceeds 94.9% by weight, the surface strength of the coating layer is inferior. There is a tendency. Preferably it is 67-92.8 weight%.

  The copolymer latex of the present invention can be obtained, for example, by an emulsion polymerization method.

When performing emulsion polymerization, in addition to the above monomers, an emulsifier (surfactant), a polymerization initiator, and a chain transfer agent, a reducing agent, and the like can be blended as necessary.

Examples of emulsifiers (surfactants) include higher alcohol sulfates, alkylbenzene sulfonates, alkyl diphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, and nonionic emulsifier sulfates. Nonionic emulsifiers such as a water-soluble emulsifier, an alkyl ester type of polyethylene glycol, an alkylphenyl ether type, and an alkyl ether type can be used alone or in combination of two or more. Especially, it is preferable to contain an anionic emulsifier 0.1weight% or more with respect to copolymer latex (solid content), and it is more preferable to contain 0.3weight% or more. When the content is 0.1% by weight or more, water-based ink absorbability tends to be improved. The upper limit is preferably 3.0% by weight or less, and more preferably 1.0% by weight or less. If it exceeds 3.0% by weight, the copolymer latex tends to foam and the surface strength of the coating layer tends to be poor.

  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 And 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. It is particularly 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 a combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  Examples of chain transfer agents include 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 tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; 2,6-di-t-butyl-4-methylphenol, and styrenated phenols Phenolic compounds; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; α- Vinyl ethers such as benzyloxystyrene, α-benzyloxyacrylonitrile, and α-benzyloxyacrylamide; triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate, terpinolene, And chain transfer agents such as 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 combinations of other additives.

  Examples of the reducing agent include reducing sugars such as dextrose and saccharose; amines such as dimethylaniline and triethanolamine; carboxylic acids such as L-ascorbic acid, erythorbic acid, tartaric acid, and citric acid and salts thereof; Examples thereof include salts, bisulfites, pyrosulfites, nithionates, nithionates, thiosulfates, formaldehyde sulfonates, and benzaldehyde sulfonates. In particular, it is preferable to select from L-ascorbic acid and erythorbic acid. The blending amount of the reducing agent can be appropriately adjusted in consideration of a combination of other additives.

  In addition, the emulsion polymerization described above includes saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane, etc. Hydrocarbon compounds such as saturated hydrocarbons, aromatic hydrocarbons such as benzene, toluene and xylene can be used. In particular, cyclohexene and toluene, which have a moderately low boiling point and can be easily recovered and reused by steam distillation after the completion of polymerization, are suitable from the viewpoint of environmental problems, although they are different from the object of the present invention.

Furthermore, known additives such as oxygen scavengers, chelating agents, and dispersants may be used as necessary, and these types and amounts are not particularly limited, and appropriate amounts can be used as appropriate. Furthermore, known additives such as antifoaming agents, anti-aging agents, antiseptics, antibacterial agents, flame retardants, and UV absorbers may be used. I can do it.
Further, the copolymer latex of the present invention can be appropriately blended with other latexes depending on the purpose of use.

  The temperature during emulsion polymerization is preferably set in the range of 30 to 100 ° C., more preferably in the range of 40 to 85 ° C., from the viewpoint of safety in the tank and productivity in consideration of safety.

  Examples of the method for adding the monomer component and other components during the emulsion polymerization include a batch addition method, a divided addition method, a continuous addition method, and a power feed method. Among them, 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.

  About the reaction time of emulsion polymerization, it is preferable to set it as 1 to 15 hours from a viewpoint of productivity, for example, and it is more preferable to set it as 2 to 10 hours.

In addition, the emulsion polymerization is preferably completed after confirming that the polymer conversion rate exceeds 97%. In this way, a copolymer latex is obtained. The polymer conversion rate can be calculated from the solid content or from the amount of heat obtained by cooling the polymerization tank.

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

  Moreover, it is preferable that the unreacted monomer and other low boiling point compounds are removed from the obtained copolymer latex by a method such as heating under reduced pressure.

The copolymer latex of the present invention needs to have a contact angle I of 40 ° or less with respect to ion-exchanged water of a latex film I prepared by the following method. When the contact angle I exceeds 40 °, the water-based ink absorbability tends to be inferior. Preferably, it is 30 degrees or less.
(How to make Latex Film I)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 200 ° C. for 1 minute, and then taken out.

Further, the contact angle II of the latex film II prepared by the following method with respect to the ion exchange water must be 60 ° or more, and the difference in contact angle between the latex film I and the latex film II with respect to the ion exchange water needs to be 30 ° or more. . If the difference in contact angle is less than 30 °, the film formability of the latex film is improved, and as a result, the water-based ink absorbability to the coating layer tends to be inferior. Preferably, it is 35 ° or more.
(How to make Latex Film II)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 120 ° C. for 1 minute, and then taken out.

  The contact angle defined in the present invention is adjusted by the composition of the copolymer latex, the average particle size, the gel content, the amount and addition method of the ethylenically unsaturated carboxylic acid monomer, and the type and amount of the emulsifier used. Can do. For example, when the amount of the emulsifier is increased, the contact angles I and II tend to decrease, and when the average particle diameter and gel content of the copolymer latex are decreased, the contact angle II tends to decrease.

  The copolymer latex of the present invention preferably has an average particle size of 120 nm or more. If the average particle size is less than 120 nm, the dispersion stability of the latex tends to be poor. In addition, it affects the film formability of the latex film, and when the average particle size is less than 120 nm, the film formability is improved, so that the water-based ink absorbability tends to be lowered. About an upper limit, it is preferable that it is 400 nm or less, and it is more preferable that it is 300 nm or less. If it exceeds 400 nm, the surface strength of the coating layer tends to be inferior.

  The copolymer latex of the present invention preferably has a gel content of 80% by weight or more. When the gel content is less than 80% by weight, the surface strength and water-based ink absorbability of the coating layer tend to be lowered. The gel content of the copolymer latex is measured, for example, by the method of the example described later.

  The copolymer latex of the present invention preferably has a minimum film-forming temperature (MFT) of 50 ° C. or higher. When the MFT is less than 50 ° C., the surface strength of the coating layer is improved, but the water-based ink absorbability tends to be lowered. About an upper limit, it is preferable that it is 90 degrees C or less. When it exceeds 90 ° C., the surface strength of the coating layer tends to be inferior. The MFT of the copolymer latex is measured according to JIS K6828-2.

The coating composition for inkjet coated paper containing the copolymer latex of the present invention generally uses silica as a pigment, but as other pigments, for example, calcium carbonate, kaolin clay, talc, Inorganic pigments such as barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, and satin white, or organic pigments such as polystyrene latex can be used alone or in combination.
The content of the copolymer latex in the coating composition is preferably 3 to 300 parts by weight (solid content) with respect to 100 parts by weight (solid content) of the pigment. If the content of the copolymer latex is 3 parts by weight or less, the pigment cannot be sufficiently adhered, which is not preferable, and if it exceeds 300 parts by weight, the air permeability and water-based ink absorbability of the coating layer are deteriorated.

Moreover, polyvinyl alcohol, natural binders such as modified starches such as starch, cationized starch, oxidized starch and esterified starch, and water-soluble synthetic binders such as carboxymethyl cellulose may be used as necessary. Furthermore, synthetic latex such as polyvinyl acetate latex and acrylic latex may be used in combination with the copolymer latex of the present invention.
Further, boric acid or the like can be used as a crosslinking agent for polyvinyl alcohol.

  When adjusting the coating composition for inkjet coated paper, a cationic fixing agent can be added. Examples of the cationic fixing agent include cationic polymers such as polyamine, polyethyleneimine, and polyacrylamine, and quaternary. Known fixing agents such as ammonium salts can be used.

  Further, any known technique such as an air knife coater, curtain coater, blade coater, roll coater or bar coater may be used as a method for applying the coating composition to the base paper.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples, unless the summary is exceeded. In the examples, parts and percentages indicating percentages are based on weight unless otherwise specified. In addition, various physical properties in the examples were evaluated by the following methods.

A latex film is prepared in an atmosphere at a measurement temperature of 40 ° C. and a humidity of 85% for the gel content of the copolymer latex . Thereafter, about 1 g of the latex film is weighed to obtain Xg. This is placed in 400 ml of toluene and impregnated for 48 hours. Thereafter, this is filtered through a weighed 300-mesh stainless steel wire net, and then toluene is evaporated to dryness. The mesh weight is subtracted from the weight after drying, and the weight after drying of the sample is weighed to obtain Yg.
Gel content (%) = Y / X × 100

Measurement of average particle diameter of copolymer latex The average particle diameter of the copolymer latex was measured by a dynamic light scattering method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used.

Measurement of contact angle of copolymer latex Copolymer latex was applied on a PET film using # 8 wire-bar (made by RD SPECIALTIES), and each of the following I and II was conducted in a hot air circulating oven. A latex film was prepared by the method, and after standing for 24 hours or more in an environment of 23 ° C. and 50% RH, measurement was performed under the conditions of 23 ° C. and 50% RH. The contact angle was measured using 1100 DAT manufactured by Fibro in accordance with TAPPI T558 & ASTM D-5725. 4 μl of ion-exchanged water was dropped, and the contact angle after 2 seconds was measured.
(How to make Latex Film I)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 200 ° C. for 1 minute, and then taken out.
(How to make Latex Film II)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 120 ° C. for 1 minute, and then taken out.

Evaluation of water-based ink absorptivity to coating layer Printed halftone dots on each coated paper sample using an inkjet printer (Canon, Inc., MX-883), and visually judged the ink spread of the printed pattern And comparatively visually evaluated from the 5th grade (excellent) to the 1st grade (inferior).

Evaluation of surface strength of coated paper Cellophane tape (Cello Tape (registered trademark) CT405AP manufactured by Nichiban Co., Ltd.) is applied to the surface of the coated layer and slowly peeled off. And was relatively visually evaluated from grade 5 (excellent) to grade 1 (poor).

Evaluation of the mixing stability of the coating composition with the cationic fixing agent An index was obtained by measuring the amount of the aggregate of the coating composition for inkjet coated paper.
200 g of the coating composition was sampled and filtered through a 200 mesh stainless steel wire mesh. After drying the agglomerates remaining on the wire mesh, the weight was measured and the ratio to the sample (in terms of solid content) was determined to obtain the agglomerate generation rate. The incidence was evaluated in the following four stages.
: Less than 0.01% (very good)
○: 0.01 to less than 0.05% (good)
Δ: 0.05 to less than 0.1% (slightly inferior)
×: 0.1% or more (inferior)

Synthesis of copolymer latex (A, J) Into a polymerization reactor made of pressure-resistant polymer, 100 parts of polymerization water and 0.9 part of potassium persulfate were charged and stirred sufficiently. The compound was added and polymerization was started at 70 ° C., and the polymerization was terminated when the final polymerization conversion rate exceeded 97%.
Next, the pH of the obtained copolymer latex is adjusted to 8 using sodium hydroxide, unreacted monomers and other low-boiling compounds are removed by distillation under reduced pressure, and copolymer latexes A and J are obtained. Obtained.
Synthesis of copolymer latex (B to I) 95 parts of polymerization water and 1.2 parts of potassium persulfate were charged into a polymerization pressure-resistant polymerization reactor, and after stirring sufficiently, each unit amount in the first stage shown in Table 1 Polymer and other compounds were added to initiate polymerization at 70 ° C. When the polymerization conversion rate exceeds 70%, the respective monomers and other compounds in the second stage are then added and polymerization is carried out at 70 ° C. The polymerization is terminated when the final conversion rate exceeds 97%. did.
Next, the pH of the obtained copolymer latex is adjusted to 8 using sodium hydroxide, unreacted monomers and other low-boiling compounds are removed by distillation under reduced pressure, and copolymer latexes B to I are prepared. Obtained.

Preparation and Evaluation of Coating Composition A coating composition for inkjet coated paper was prepared using copolymer latexes A to J according to the formulation shown below. Polyethyleneimine was used as the cationic fixing agent.
Formulation of coating composition Colloidal silica (average primary particle size 20 nm) 100 parts Cationic fixing agent (solid content) 3 parts Copolymer latex (solid content) 30 parts ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・...
Solid content 9%

Preparation and Evaluation of Coated Paper Apply the above coating composition to a coated base paper (basis weight 55 g / m2) using a wire bar so that the coating amount per side is 15 g / m2 in solid content. The ink-jet coated paper was obtained by drying at 150 ° C. for 3 minutes. The obtained ink-jet coated paper was subjected to each test and evaluated, and the results are shown in Table 1.

Each component in Table 1 is indicated by the following abbreviation.
(Monomer)
BDE: Butadiene STY: Styrene MMA: Methyl methacrylate ACN: Acrylonitrile HEA: Hydroxyethyl acrylate IA: Itaconic acid FA: Fumaric acid AA: Acrylic acid (other compounds)
EML1: Polyoxyethylene lauryl ether (manufactured by Kao Corporation, Emulgen 109P) (nonionic emulsifier)
EML2: Sodium dodecylbenzenesulfonate (Neopelex G-15, manufactured by Kao Corporation) (anionic emulsifier)
CHX: cyclohexene (hydrocarbon compound)
α-MSD: α-methylstyrene dimer (chain transfer agent)
TDM: t-dodecyl mercaptan (chain transfer agent)

  As shown in Table 1, all of the copolymer latexes A to F according to the present invention are excellent in the water-based ink absorbability and surface strength of the obtained ink-jet coated paper, and further excellent in the stability of the coating composition. there were.

In Comparative Example 1, since the structural unit derived from the aliphatic conjugated diene monomer exceeds 30% by weight, the water-based ink absorbability is inferior.
Since Comparative Examples 2 and 3 did not satisfy the contact angle regulations, the water-based ink absorbability was inferior.
In Comparative Example 4, the ethylenically unsaturated carboxylic acid monomer exceeded 10% by weight, and the mixing stability was poor.

As described above, the copolymer latex for ink-jet coated paper of the present invention has excellent mixing stability when used as a coating composition, and further has excellent water-absorbing properties for water-based inks in the coating layer, so that characters are smeared. First, a clear image is obtained, and an ink-jet coated paper having excellent surface strength is obtained. Therefore, it can be suitably used as a binder component of a coating composition for inkjet coated paper.

Claims (5)

5 to 30% by weight of structural units derived from an aliphatic conjugated diene monomer, 0.1 to 10% by weight of structural units derived from an ethylenically unsaturated carboxylic acid monomer, and 60 to 94. A copolymer latex for ink-jet coated paper containing 9% by weight, the contact angle I of the latex film I prepared by the following method with respect to ion-exchanged water is 40 ° or less, and the latex film II prepared by the following method Co-weight for inkjet coated paper, characterized in that the contact angle II with respect to ion exchange water is 60 ° or more and the difference in contact angle between latex film I and latex film II with respect to ion exchange water is 30 ° or more Combined latex.
(How to make Latex Film I)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 200 ° C. for 1 minute, and then taken out.
(How to make Latex Film II)
Copolymer latex (solid content 48%) is applied onto a PET film using # 8 wire-bar, dried in a hot air circulation oven set at 120 ° C. for 1 minute, and then taken out.   The copolymer latex for ink-jet coated paper according to claim 1, wherein the minimum film-forming temperature (MFT) of the copolymer latex is 50 ° C or higher.   Gel content is 80 weight% or more, The copolymer latex for inkjet coated paper as described in any one of Claims 1-2 characterized by the above-mentioned.   The copolymer latex for inkjet coated paper according to any one of claims 1 to 3, wherein the average particle size is 120 nm or more.   Copolymer weight for inkjet coated paper according to any one of claims 1 to 4, wherein the content of an anionic emulsifier contained in the copolymer latex (solid content) is 0.1% by weight or more. Combined latex.