JPH0615759B2 - Composition for paper coating - Google Patents

Description

The present invention relates to a paper coating composition, and more particularly to a paper coating composition excellent in printability such as ink receptivity and adhesive strength. is there.

[Conventional technology]

In recent years, it has become more and more important for the quality of coated paper to have excellent printability even under severe printing conditions as printing speed increases. In order to achieve this improvement in printability, it is important that a so-called calendering effect, in which a bulky coating layer having good coverage with the base paper is formed and smoothness is improved by finishing with a super calender or a gloss calender, is large.

As a method for forming such a bulky coating layer, in addition to blending a pigment having a large aspect ratio or increasing the solid content concentration of the paper coating composition, a paper coating composition It is known that a salt or a coagulant is added to destabilize the coating liquid to accelerate the time until immobilization of the coating layer after coating.

In addition, as a method for improving the properties of the latex used as an adhesive in the paper coating composition, as a latex, by the interaction with the pigment in the process of losing water until drying after coating. It is conceivable to use a material that has the effect of accelerating the immobilization of the coating layer,
An amphoteric latex having both anionic and cationic properties is known as one of the latexes expected to have such effects (for example, TAPPI Coatin
g Conference Preprints P. 143-153'81).

Examples of the amphoteric latex used in the paper coating composition include, for example, JP-A-54-3091 and JP-A-58-48.
As disclosed in Japanese Patent Publication No. 940, in producing a carboxy-modified latex, an ethylenically unsaturated amine monomer is used as a cationic monomer, and amphiphilic property is imparted to the latex to improve the performance of coated paper. A method has been proposed.

However, according to the studies of the present inventors, the paper coating composition using the latex produced by this method is certainly recognized as having an improving effect on the properties such as water resistance and inking property, but it has not yet been confirmed. It has not been possible to obtain a coated paper having a sufficiently improved printability. It is considered that this is because in such a latex, the interaction with the pigment is insufficient, and thus a sufficiently bulky coating layer cannot be obtained.

[Problems to be solved by the invention]

The present invention solves the problem that it is difficult to form a sufficiently bulky coating layer in a conventional paper coating composition, and contains a polymer latex having excellent adhesiveness,
It is an object of the present invention to provide a paper coating composition capable of obtaining a coated paper having high printability.

[Means for solving problems]

The problems are as follows: a. Ethylenically unsaturated quaternary ammonium salt monomer
0.1-8 wt% b. 0.5-10% by weight of ethylenically unsaturated carboxylic acid monomer and c. A copolymer latex obtained by emulsion-polymerizing a monomer composition comprising other monomers copolymerizable with these may be contained in a solid content of 1 to 30 parts by weight based on 100 parts by weight of the pigment. A solution is provided by the featured paper coating composition.

Hereinafter, the present invention will be described in detail.

The copolymer latex in the present invention contains, as an essential component, an ethylenically unsaturated quaternary ammonium salt monomer and an ethylenically unsaturated carboxylic acid monomer in a monomer composition for synthesizing the same. By using an ethylenically unsaturated quaternary ammonium salt monomer as a monomer component, a cationic group is introduced into the copolymer, and an ethylenically unsaturated carboxylic acid monomer is used as a monomer. As a result, an anionic group is introduced into the copolymer, and as a result, both cationic and anionic properties are imparted to the copolymer latex. This amphoteric latex has a large interaction (ionic affinity) with a mineral pigment, which will be described in detail later. Therefore, it immediately achieves stabilization (immobilization) of the coating layer immediately after coating and forms a bulky coating layer. can do.

The copolymer latex in the present invention preferably has a glass transition temperature of the copolymer component of + 30 ° C. or lower. When the glass transition temperature exceeds + 30 ° C., the copolymer becomes hard and has a large brittleness, resulting in insufficient adhesion strength and water resistance of the copolymer latex. The glass transition temperature in the present invention is obtained as a result of measuring a sample obtained by drying the copolymer latex with a scanning differential calorimeter.

Further, the copolymer latex in the present invention preferably has a zeta potential of −20 mV or less in an aqueous medium having a pH of 5 or more. If the zeta potential is greater than -20 mV,
Coagulates are easily generated during polymerization of the copolymer latex,
It is not possible to obtain a latex with good dispersion stability, and the paper coating composition using this latex is liable to agglomerate, which is not only inferior in workability during coating, but also in uniform coating. The problem that layers cannot be formed easily occurs.

Here, the zeta potential (mV) is the following formula (1)
The electric potential obtained by the Smolchowski equation (see, for example, "Chemical Chemistry of Dispersion and Emulsion Systems" by Kitahara and Furusawa, co-authored P.86-P.104).

Formula (1) ζ = (4πη / ε) × U = 14.1 × 10 ⁸ × U ζ: Zeta potential η: Viscosity of medium ε: Permittivity of medium U: Mobility Mobility U in equation (1) is , Mobility of latex particles in an aqueous medium (electrolyte aqueous solution). Specifically, electrokinetic phenomenon analyzer "PEN KEM3000" (PEN KEM
(Manufactured by the company) and the following measurement conditions.

Temperature: 25 ° C Aqueous medium: 0.1 M potassium chloride aqueous solution (specific conductivity 1.3 Ω ^-1 m ^-1 ) Copolymer latex concentration: 10 ^-2 wt% Electric field strength: 2.6 x 10 ³ Vm ^-1 current: 2.4 × 10 ^-3 A Zeta potential is a parameter that represents the charge state of the surface of latex particles, and by setting this Zeta potential in the copolymer latex to be within the above specified range. A proper charge state is formed on the surface of the latex particles due to the negative charge. As a result, the electrical repulsion of this negative charge causes the latex particles to be dispersed in a stable state without coagulating with each other.

Next, the monomer composition and the production method for producing the copolymer latex in the present invention will be specifically described.

The monomer composition used to produce the copolymer latex comprises a. Ethylenically unsaturated quaternary ammonium salt monomer
0.1-8 wt% b. Ethylenically unsaturated carboxylic acid monomer 0.5 to 10% by weight c. It is composed of other monomers copolymerizable with these.

The ethylenically unsaturated quaternary ammonium salt (hereinafter,
Also referred to as "monomer a". ), The following (a) ~
Examples thereof include the compounds shown in (c).

(B) Represented by general formula A General formula A(In the formula, R₁Is a hydrogen atom or a methyl group, R_TwoIs charcoal
An alkylene group having a prime number of 2 to 10, orAn alkylene group having a functional group such as R,_Three, R_FourAnd R₅Is an alkyl group having 1 to 12 carbon atoms,
Or a C1-C12 alkyl group having a phenyl group, A isOr -O-, X Is Cl^-, Br^-, I^-, SO_FourH^-, SO
_FourH^2-, CH₃SO_Four ^-, C₂H_FiveSO_Four ^-Or CH₃COO^-Represents ,. ) Ethylenically unsaturated quaternary ammonium represented by the general formula A
The um salts include, for example, the following amino compounds, dimethyl-aminoethyl (meth) acrylate, and dimethy
Luminopropyl (meth) acrylate, dimethylamido
Nohydroxypropyl (meth) acrylate, diethyl
Aminoethyl (meth) acrylate, dibutylaminoe
Ethylenically unsaturated calcium such as chill (meth) acrylate
Aminoalkyl ester of boric acid; dimethylaminoethyl
Le (meth) acrylamide, dimethylaminopropyl
Ethylenically unsaturated carbo such as (meth) acrylamide
Aminoalkylamide of acid; dimethylaminoethylbi
Aminoalkyl vinyl ether such as nyl ether, CH₃Cl, C₆H_FiveCH₂Obtained by reacting with Cl, etc.
You can In addition, the name of the exemplary substance of the amino compound is
“(Meth)” means acrylate compound and methacrime
It is meant to include both relate compounds.

(B) What is represented by the following general formula B General formula B(In the formula, R₁Is a hydrogen atom or a methyl group, R_TwoIs charcoal
An alkylene group having a prime number of 2 to 10, orAn alkylene group having a functional group such as R,_Three, R_FourIs an alkyl group having 1 to 12 carbon atoms, or
A C1-C12 alkyl group having a nyl group, R₅Is an alkylene group having 1 to 10 carbon atoms,Y Is Cl^-, Br^-, I^-Or represents -CO-
You ) Ethylenically unsaturated quaternary ammonium represented by the general formula B
The um salts include, for example, the following amine compounds, dimethyl-aminoethyl (meth) acrylate, and dimethy
Luminopropyl (meth) acrylate, dimethylamido
Nohydroxypropyl (meth) acrylate, diethyl
Aminoethyl (meth) acrylate, dibutylaminoe
Ethylenically unsaturated calcium such as chill (meth) acrylate
Aminoalkyl ester of boric acid; dimethylaminoethyl
Le (meth) acrylamide, dimethylaminopropyl
Ethylenically unsaturated carbo such as (meth) acrylamide
Aminoalkylamide of acid; dimethylaminoethylbi
Aminoalkyl vinyl ethers such as nyl ether, ClCH₂COOH,Or Cl-CH₂CONH₂Betaine
It can be obtained by

(C) Alkylpyridinium salt having a polymerizable unsaturated bond represented by the following general formula C (In the formula, R represents an alkyl group, R ′ represents a hydrogen atom or a lower alkyl group, and X represents a halogen atom such as chlorine or bromine.) As the monomer a, among the above (a) to (c), Those of (a) and (b) are particularly preferable.

The proportion of the monomer a used is 0.1 to 8% by weight, preferably 0.1 to 6% by weight, based on the whole monomer composition. When the usage rate of the monomer a is less than 0.1% by weight,
The printability such as ink receptivity deteriorates, while the usage rate is 8
If it exceeds 5% by weight, the zeta potential of the latex becomes high and the dispersion stability of the latex becomes poor, and the stability and fluidity of the paper coating composition using this decrease and the operation during coating becomes difficult. Cause

Examples of the ethylenically unsaturated carboxylic acid (hereinafter, referred to as “monomer b”) include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, Furthermore, acid anhydrides or monoalkyl esters of dicarboxylic acids can also be used.

The proportion of the monomer b used is 0.5 to 10% by weight, preferably 0.5 to 8% by weight. If the usage ratio is less than 0.5% by weight, the adhesive strength and mechanical stability of the copolymer latex will be reduced, and if the usage ratio exceeds 10% by weight, the polymerization state will deteriorate.
Further, the water resistance of the copolymer latex is lowered.

Examples of the monomer copolymerizable with the monomer a and the monomer b (hereinafter referred to as “monomer c”) include aliphatic compounds such as butadiene, isoprene, and 2-chloro-1,3-budadiene. Aromatic vinyl compounds such as conjugated diene: styrene, α-methylstyrene, vinyltoluene: methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate Alkyl esters of acrylic acid or methacrylic acid such as: acrylamide, methacrylamide, N-methyl roll acrylamide, and acrylonitrile.

In order to impart appropriate hardness, elasticity and water resistance to the copolymer, these monomers c are added to the entire monomer composition within the range where the glass transition temperature of the copolymer does not exceed + 30 ° C. 82 ~
Used in a proportion of 99.4% by weight.

In order to impart excellent adhesive strength to the copolymer latex and more effectively exhibit the effects of the present invention, the monomer c is an aliphatic conjugated diene monomer 25 to 75% by weight It is preferred to use 7 to 74.4% by weight of other possible monomers.

As the polymerization initiator used for emulsion polymerization of the copolymer latex in the present invention, water-soluble initiators such as sodium persulfate, potassium persulfate and ammonium persulfate, oil-soluble initiators such as benzoyl peroxide or redox-based initiators. Any of the agents can be used.

Further, as the surfactant that can be used for the polymerization of the copolymer latex, an anionic surfactant, an anion-nonionic surfactant, a nonionic surfactant, an amphoteric surfactant alone or It can be used in combination. Examples of surfactants include anionic surfactants such as higher alcohol sulfates, alkylbenzene sulfonates and aliphatic sulfonates, nonionics such as polyethylene glycol alkyl esters, alkyl ethers and alkyl phenyl ethers. System surfactant, polyoxyethylene alkyl sulfate ester salt,
Anion-nonionic surfactants such as polyoxyethylene alkylallyl sulfate ester salts, carboxylate salts, sulfate ester salts, sulfonate salts and phosphate ester salts as anion moieties, amine salts as cation moieties, and quaternary ammonium salts. Examples thereof include an amphoteric surfactant having a salt. Further, in the polymerization of the copolymer latex of the present invention, it is preferable to add a basic substance to the reaction system to increase the pH of the system in order to prevent the generation of coagulation during the polymerization. However, this is not particularly necessary when the amount of the monomer a used is small. As the basic substance, sodium hydroxide, aqueous ammonia, potassium phosphate, sodium bicarbonate or the like can be used.

In the polymerization of the copolymer latex, in addition to the above-mentioned substances, chain transfer agents, chelating agents and the like known in the emulsion polymerization can be added.

The copolymer latex of the present invention can be produced by ordinary emulsion polymerization, and as the polymerization method, any of batch polymerization, semi-batch polymerization and continuous polymerization may be adopted.

Further, the timing of addition of the monomer a (ethylenically unsaturated quaternary ammonium salt) is not particularly limited, and the monomer a may be mixed with another monomer and polymerized, or After copolymerizing the monomers, the monomer a may be added to the reaction generation system and further polymerized.

In the paper coating composition of the present invention, the copolymer latex obtained as described above can be used alone or in combination with the copolymer latex used in the known paper coating composition. It is composed by using 1 to 30 parts by weight in terms of solid content with respect to 100 parts by weight of mineral pigments such as various clays, aluminum hydroxide, titanium dioxide, satin white and calcium carbonate.

In the paper coating composition of the present invention, other binders such as starch, casein and polyvinyl alcohol can be used in combination.

〔Example〕

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, "part" and "%" in the description of the examples
Means parts by weight and% by weight, respectively.

Examples 1 to 8 and Comparative Examples 1 to 5 (1) Production of Copolymer Latex (Latex A) 45 parts of butadiene styrene 26.5 parts of methyl methacrylate 20 parts of hydroxyethyl methacrylate 5 parts of itaconic acid 2 parts of acrylic acid 1 part of dodecylbenzenesulfate Sodium sulfonate 0.15 parts tert-dodecyl mercaptan 0.3 parts Potassium persulfate 1.5 parts Ethylenediaminetetraacetic acid tetrasodium salt 0.05 parts Water 200 parts The above substances are charged into a stirrable autoclave and polymerized at 50 ° C in a nitrogen gas atmosphere. Let it start. When the polymerization conversion rate of the above monomers reached 80%, a 10% aqueous sodium hydroxide solution was added to adjust the pH of the system to 6.0, and methacrylamide amidopropyltrimethylammonium chloride (dimethylaminopropylmethacrylamide and
When 0.5 part of a quaternary ammonium compound obtained by the reaction with CH ₃ Cl and 4 parts of water were added and the reaction was continued for 4 hours, the polymerization was almost completed. The copolymer latex thus obtained is referred to as "latex A".

The average particle size of the latex particles of latex A was 1250Å. The particle size of the latex particles is the average value of the particle size of 500 particles obtained by observing the latex after treatment with osmic acid with an electron microscope.

(Latex B) Butadiene 45 parts Styrene 25 parts Methyl methacrylate 20 parts Hydroxyethyl methacrylate 5 parts Itaconic acid 3 parts Acrylic acid 1 part Methacrylamideamidopropyltrimethylammonium chloride 1 part Polyoxyethylene alkylphenol ether sodium sulfate 1 part tert-Dodecyl mercaptan 0.3 parts Potassium persulfate 1.5 parts Ethylenediaminetetraacetic acid tetrasodium salt 0.05 part Ammonium hydroxide 1 part Water 210 parts The above substances are charged into a stirrable autoclave and polymerized at 50 ° C for 15 hours in a nitrogen gas atmosphere. The polymerization was stopped when the polymerization conversion rate of the monomer reached 99% or more. The latex thus obtained is referred to as "latex B". The average particle size of the latex particles of this latex B was 1380Å.

(Latex C to H, Comparative Latexes a to e) Using the substances having the compositions shown in Table 1 (Examples) and Tables 2 (Comparative Examples), 6 kinds per example are used in the same manner as in the case of the latex A described above. , 5 kinds of copolymer latices were produced for each comparative example. Let these copolymer latexes be "latex C"-"latex H" and "comparative latex a"-"comparative latex e."

Tables 1 and 2 show the glass transition temperature and zeta potential of each latex obtained by the above-mentioned method.

FIG. 1 is a curve diagram showing the results of an experiment conducted to confirm how the zeta potential of latex changes with the change of pH of the nest medium. In FIG. 1, the horizontal axis is pH, the vertical axis is zeta potential, and the signs attached to the curves match the signs of the latex. As is clear from this result, when the amount of the monomer a used increases (curve b,
It is understood that the zeta potential increases, and that the zeta potential decreases as the pH of the aqueous medium increases.

(2) Preparation of composition for paper coating Each of the copolymer latexes A to H obtained as described above
Using each of the comparative latexes b to e, 8 types of paper coating compositions for the examples and 4 types for the comparative examples were prepared according to the following formulations. In latex a, since the amount of the ethylenically unsaturated quaternary ammonium salt used was excessive, coagulation was significantly generated, and it was difficult to prepare the paper coating composition.

(Compounding) Clay 50 parts Heavy calcium carbonate 50 parts Dispersant 0.5 part Copolymer latex 10 parts Oxidized starch 4 parts Water Amount equivalent to 60% total solids (3) Properties of paper coating composition The following property tests were carried out on each paper coating composition.

Dry Pick "Dry pick" was examined by an RI printing tester. That is, the test piece is fixed to the drum, and after repeatedly printing at a rotation speed of 30 rpm for a certain period of time, the test piece is visually determined. The judgment was 5 points that could be printed completely,
The one that could hardly be printed is set as one point, and the five data obtained from each sample are arithmetically averaged.

Inking property "Inking property" was examined by an RI printing tester. That is,
The test piece fixed to the drum was wetted once with water, and after printing for a certain period of time, printing was performed once, and the ink adhesion was visually determined. Five points obtained with good ink adhesion and one point with poor ink adhesion are arithmetically averaged from five data obtained from each sample.

White paper gloss "White paper gloss" is based on the JIS method.

Printing gloss "Printing gloss" is based on the JIS method.

The above results are shown in Table 3.

As is clear from the results of Table 3, in the examples of the present invention, good results were obtained in all the characteristics, but in the comparative examples, sufficient results were obtained in all the characteristics. There wasn't.

That is, in Comparative Example 2, since the ethylenically unsaturated quaternary ammonium salt was not used as the monomer component of the copolymer latex, the ink receptivity of the coated paper and the printing gloss were poor.

In Comparative Examples 3 and 5, since ethylenically unsaturated carboxylic acid is not used as a monomer component of the copolymer latex, the adhesive strength is particularly poor.

In Comparative Example 4, since the ethylenically unsaturated carboxylic acid was used beyond the range of the present invention, the adhesive strength was particularly poor.

〔The invention's effect〕

The paper coating composition of the present invention is obtained from a specific monomer component, and more preferably uses a copolymer latex having a specific glass transition temperature and a specific zeta potential as a binder. It is possible to form a coated paper for printing which is excellent in printability such as physical properties and adhesive strength.

[Brief description of drawings]

FIG. 1 is a curve diagram showing a relationship between pH of an aqueous medium and zeta potential in latex.

Claims (2)

[Claims] 1. A. Ethylenically unsaturated quaternary ammonium salt monomer 0.1 to 8% by weight b. 0.5-10% by weight of ethylenically unsaturated carboxylic acid monomer and c. A copolymer latex obtained by emulsion-polymerizing a monomer composition comprising other monomers copolymerizable with these may be contained in a solid content of 1 to 30 parts by weight based on 100 parts by weight of the pigment. A characteristic paper coating composition. 2. The composition for paper coating according to claim 1, wherein the copolymer latex has a zeta potential of -20 mV or less in an aqueous medium having a pH of 5 or more.