JPH06211911A - Paper coating copolymer latex and paper coating composition containing the latex - Google Patents

Abstract

PURPOSE:To obtain a paper coating compn excellent in flow under a high shear, moisture retention and mechanical stability which are necessary for high-speed coating and gives coated paper having good surface strength and printing gloss. CONSTITUTION:The objective letex is prepared by the emulsion polymn. of 100 pts.wt. mixture of 15-65wt.% conjugated diolefin, 2-40wt.% unsatd. carboxylic ester, 1-8wt.% unsatd. carboxylic acid, 0.5-5wt.% unsatd. carboxamide and 10-81.5wt.% other copolymerizable monomer by using an emulsifier comprising 0.3-2 pts.wt. at least one anionic surfactant selected from among salts of alkylbenzenesulfonic acids, salts of alkylsulfuric acids, salts of alkldiphenyl ether sulfuric acid and salts of sulfonic acid of naphthalene-formaldehyde condensate, and 0.2-6 pts.wt. at least one anionic surfactant selected from among salts of polyoxyethylene alkyl ether sulfuric acids and salts of polyoxyethylene alkylphenyl ether sulfuric acids.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is suitable for use as a binder in the production of coated paper having excellent various properties required for high-speed coating suitability and having good surface strength and printing gloss. The present invention relates to a copolymer for paper coating and a composition for paper coating containing the same.

[0002]

2. Description of the Related Art In recent years, coated paper has been used for an extremely large number of printed matters because of its high printing effect. Even in periodical publications such as quarterly and monthly papers, the number of cases in which coated paper is used for all items is considerably increasing.
In particular, in direct mails and product catalogs in the mail order business, most of them use coated paper for all items, and the demand for them is ever increasing.

Against the background of such an increase in demand, technical efforts in the production of coated papers are focused on how to produce coated papers of higher quality with high productivity, and the productivity is improved. As a means, high-speed coating technology has been attracting attention.
Among them, the coating machine, especially the speed-up technology of the blade coater is remarkable.

On the other hand, as a composition for paper coating, a mineral pigment is mainly used, and as its binder, a natural binder such as starch and casein, a synthetic binder such as a copolymer latex, and other auxiliary agents are blended. Aqueous dispersion compositions have been widely used.

The various properties suitable for high-speed coating required for the composition for paper coating are, as a matter of course, that the dispersion stability and miscibility of each compound are good and the fluidity is good, and in particular, blade coating. Good water retention to maintain good fluidity even under high shear during work, excellent mechanical stability, capable of withstanding high-speed coating for a long time, circulation from paint supply tank to coater head It is difficult to introduce bubbles therein.

Development of a paper coating composition satisfying such various performances and responding to the high speed performance of the blade coater which has been remarkably advanced as described above has also been advanced. For example, use of a specific pigment dispersant (JP-A-60-20909).
3), use of acetic acid esterified starch subjected to specific viscosity reduction treatment (JP-A-1-162894), use of specific copolymer latex (JP-A-61-266697, JP-B-4-
66960), a combination of a specific copolymer latex and a specific pigment (JP-A-61-266696), and a combination of a copolymer latex having a specific number average particle diameter and a starch having a specific dextrose equivalent (JP-A-61-26696). (Sho 58-60091)
Although such attempts have been made, these attempts have not yet reached the level of sufficiently satisfying all the performances required for the above-mentioned paper coating composition.

For example, as described in JP-A-58-60091, when a copolymer latex having a small average particle size is used in a paper coating composition or a specific starch is used, Although the viscosity of the paper coating composition can be controlled to be low under high shear, there is a problem that the mechanical stability of the paper coating composition is poor and stable coating cannot be performed for a long time. Further, a relatively large amount of an emulsifier is required to produce a copolymer latex having a small average particle size, and therefore a paper coating composition using this copolymer latex has a large amount of foaming and is difficult to form. It causes problems such as deterioration of screen suitability and overflow of the circulating paint supply tank, and in terms of the quality of coated paper, coated paper products are coated with minute coatings that are not covered with the paper coating composition. There have been various problems that the workability is reduced and the water resistance such as the wet pick strength is reduced, and the printability and the commercial value of the product are reduced.

[0008]

[Means for Solving the Problems] In view of the above-mentioned circumstances, the inventors of the present invention have made diligent studies to solve the problems at present, and as a result, found that a specific copolymer latex was added to a paper coating composition. It was found that the above problems can be solved at the same time by using them, and the present invention has been completed.

That is, the present invention comprises 15 to 65% by weight of the aliphatic conjugated diolefin monomer, 2 to 40% by weight of the ethylenically unsaturated carboxylic acid ester monomer, and 1 of the ethylenically unsaturated carboxylic acid monomer. ~ 8 wt%, 0.5 to 5 wt% ethylenically unsaturated carboxylic acid amide monomer and 100 to 81.5 wt% of a monomer mixture consisting of 10 to 81.5 wt% of another copolymerizable monomer is emulsified. Upon copolymerization, as an emulsifier, alkylbenzene sulfonate, alkyl sulfate,
At least one selected from alkyl diphenyl ether sulfate and sulfonate of naphthalene-formalin condensate
0.3 to 2 parts by weight of at least one anionic surfactant and at least one anionic surfactant selected from polyoxyethylene alkyl ether sulfate and polyoxyethylene alkylphenyl ether sulfate. A copolymer latex having excellent performance required for high-speed coating suitability, which is characterized by using 2 to 6 parts by weight, and a paper coating composition containing the latex and a pigment are provided. is there.

The present invention will be described in more detail below.

Examples of the aliphatic conjugated diolefin monomer used in the copolymer latex of the present invention include 1,
3-butadiene, 2-methyl-1,3 butadiene, 2,
3-dimethyl-1,3 butadiene, 2-chloro-1,3
Butadiene etc. are mentioned, and these can be used 1 type or 2 types or more. The use of 1,3-butadiene is particularly preferable.

The aliphatic conjugated diolefin monomer is 15
Used in the range of up to 65% by weight, the amount used is 1
When it is less than 5% by weight, the dry pick strength, wet pick strength and printing gloss of the obtained coated paper are lowered, and when it exceeds 65% by weight, the wet pick strength and printing gloss are lowered. More preferably, it is 18 to 60% by weight.

The ethylenically unsaturated carboxylic acid ester monomer used in the copolymer latex of the present invention includes
For example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate,
Examples thereof include monomethyl fumarate and monoethyl fumarate, and these can be used alone or in combination of two or more. The use of methyl methacrylate is particularly preferable.

The ethylenically unsaturated carboxylic acid ester monomer is used in the range of 2 to 40% by weight. If the amount used is less than 2% by weight, the mechanical stability of the paper coating composition will be high. And the printing gloss of the obtained coated paper decreases, and when it exceeds 40% by weight, the wet pick strength of the obtained coated paper decreases. More preferably, it is 3 to 35% by weight.

Examples of the ethylenically unsaturated carboxylic acid monomer used in the copolymer latex of the present invention include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid and the like. Two or more types can be used.

The ethylenically unsaturated carboxylic acid monomer is 1
It is used in the range of up to 8% by weight, but if the amount used is less than 1% by weight, there is a problem in the polymerization stability of the copolymer latex, and if it exceeds 8% by weight, the viscosity of the copolymer latex becomes high. It is not preferable because it becomes too much.

Examples of the ethylenically unsaturated carboxylic acid amide monomer used in the copolymer latex of the present invention include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N.
-Dimethyl acrylamide, etc. are mentioned, and these can be used 1 type or 2 types or more. The use of acrylamide is particularly preferable.

The ethylenically unsaturated carboxylic acid amide monomer is used in the range of 0.5 to 5% by weight. If the amount used is less than 0.5% by weight, the composition for paper coating will be used. The mechanical stability is lowered, and if it exceeds 5% by weight, the viscosity of the copolymer latex becomes too high, which is not preferable.

Other copolymerizable monomers used in the copolymer latex of the present invention include, for example, alkenyl aromatic monomers, hydroxyalkyl group-containing unsaturated monomers, and vinyl cyanide monomer. The body etc. are mentioned.

Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene and vinyltoluene. The use of styrene is particularly preferred.

Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl methacrylate, 3
-Chloro-2-hydroxybutyl methacrylate, di-
(Ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, 2-hydroxyethyl fumarate and the like can be mentioned.
It is particularly preferable to use β-hydroxyethyl acrylate.

The vinyl cyanide monomer may, for example, be acrylonitrile, α-chloroacrylonitrile, methacrylonitrile or α-ethylacrylonitrile. It is particularly preferable to use acrylonitrile.

These other copolymerizable monomers may be used either individually or in combination of two or more. Also,
These other copolymerizable monomers are used in the range of 10 to 81.5% by weight, but the amount used is 10% by weight.
If less than 81, the wet pick strength of the coated paper decreases, and 81.
If it exceeds 5% by weight, the dry pick strength, wet pick strength, and print gloss of the obtained coated paper are deteriorated. More preferably, it is 10 to 77.5% by weight.

The number average particle diameter of the copolymer latex of the present invention must be 110 nm or less. 110
When it exceeds nm, the water-holding property of the paper coating composition and the fluidity under high shear are deteriorated.

When the copolymer latex of the present invention is emulsion-copolymerized with 100 parts by weight of the above-mentioned monomer mixture, an alkyl benzene sulfonate, an alkyl sulfate, an alkyl diphenyl ether sulfate, a naphthalene-formalin condensate is used as an emulsifier. At least one anionic surfactant (A) 0.3 to 2 selected from sulfonates
Parts by weight and polyoxyethylene alkyl ether sulfate,
It is necessary to use 0.2 to 6 parts by weight of at least one anionic surfactant (B) selected from polyoxyethylene alkylphenyl ether sulfate.

When the amount of the anionic surfactant (A) is less than 0.3 part by weight, the mechanical stability of the paper coating composition is lowered,
If it exceeds 2 parts by weight, foaming of the composition for paper coating becomes severe and the wet pick strength of the obtained coated paper is lowered.

When the amount of the anionic surfactant (B) is less than 0.2 part by weight, the mechanical stability of the paper coating composition is lowered,
If it exceeds 6 parts by weight, the dry pick strength of the coated paper obtained is lowered.

The copolymer latex of the present invention can be produced by a known emulsion polymerization method except that the surfactant specified as the emulsifying agent is used in the specified amount. That is, a batch addition polymerization method, a division addition polymerization method, a continuous addition polymerization method, a two-step polymerization method, a power feed polymerization method, etc. can be adopted.

In producing the copolymer latex of the present invention, a conventional chain transfer agent, polymerization initiator, electrolyte,
A polymerization accelerator, a chelating agent, etc. can be used.

The chain transfer agent used in the copolymer latex of the present invention includes alkyl mercaptans represented by t-dodecyl mercaptan and the like, as well as xanthogen compounds, thiuram-based compounds and phenol-based compounds such as styrenated phenol. Compounds, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as carbon tetrachloride,
Examples thereof include vinyl ethers such as α-benzyloxystyrene, thioglycolic acid, thiomalic acid, α-methylstyrene dimer, and terpinolene, and one or more of them can be used.

The polymerization initiator used in the copolymer latex of the present invention includes water-soluble polymerization initiators such as potassium persulfate, sodium persulfate and ammonium persulfate, redox type polymerization initiators and oils such as benzoyl peroxide. Soluble polymerization initiators can be used as appropriate.

The amount of the copolymer latex used in the paper coating composition of the present invention is preferably 5 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of all pigments used. If the amount is less than 5 parts by weight, the effect of the present invention becomes small,
If it exceeds 30 parts by weight, it is not preferable in terms of economy.

Examples of the main pigments used in the present invention include mineral white pigments such as clay, calcined clay, deramie clay heavy calcium carbonate, precipitated calcium carbonate, titanium dioxide, aluminum hydroxide, talc and satin white. These may be used alone or in combination of two or more. If necessary, a plastic pigment,
An organic synthetic white pigment such as a binder pigment or a hollow synthetic pigment may be used in combination.

Other components of the paper coating composition of the present invention include, for example, proteins (gelatin, casein, etc.),
Water-soluble natural polymer compounds such as starches (oxidized starch, esterified starch, etherified starch, enzyme-modified starch, etc.) and cellulose derivatives (carboxymethyl cellulose, hydroxymethyl cellulose, etc.), polyvinyl alcohol, polyacrylates , Polyacrylamide and its derivatives, maleic acid copolymers,
A water-soluble synthetic polymer compound represented by polyvinylpyrrolidone or the like can be used as necessary.

Further, as other auxiliaries, a pH adjusting agent, a stabilizer, a release agent, a lubricant, an antiaging agent, a dispersant, a defoaming agent, an antiseptic agent, and a crosslinking agent, which are commonly used in the field of paper coating. ,
A bluing agent, a fluorescent whitening agent, etc. can be used as needed.

[0036]

EXAMPLES and COMPARATIVE EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples in order to clearly show the excellent effects of the present invention. , But not limited to these examples. In the examples and comparative examples, parts and percentages indicating ratios are based on weight unless otherwise specified. The methods for measuring various physical properties in Examples and Comparative Examples are as follows.

Viscosity of Paper Coating Composition Under Low Shear Using a commercially available BM type viscometer, the B type viscosity of the paper coating composition was measured under the condition of a rotor rotation speed of 60 rpm.

[0038] Using the viscosity commercial Hercules viscometer under high shear of the paper coating composition was measured high shear viscosity of the paper coating composition. Bob F was used for the measurement, and the apparent viscosity at a bob rotation speed of 8000 rpm was determined.

Mechanical Stability of Paper Coating Composition Using a commercially available Maron mechanical stability tester, a paper coating composition (solid content 40% by weight, sample 70 g) was applied with a rotor rotation speed of 1000 rpm. After mechanical shearing was performed under the conditions of a rotor load of 10 kg and a rotation time of 10 minutes, aggregates generated in a 200-mesh wire net were captured. After the captured agglomerates were dried, the ratio of the agglomerates to the original sample solids weight was determined in wt%. According to the obtained value, the mechanical stability of the paper coating composition was evaluated according to the following three grades. Good: Less than 0.01% by weight. Δ: 0.01% by weight or more and less than 0.1% by weight. X: 0.10% by weight or more.

The foaming solid content of the paper coating composition was adjusted to 40%, 300 ml of the defoamed paper coating composition was gently put into a 1000 ml graduated cylinder, and passed through a 200 mesh wire mesh. 800 ml of air was forcibly blown in.
The volume of the foam immediately after blowing air was measured, and the foaming of the paper coating composition was evaluated according to the obtained value according to the following three grades. ○: less than 400. Δ: 400 or more and less than 700. × ... 700 or more.

The paper coating composition was coated with a # 14 wire bar on a coating base paper having a water-holding basis weight of 64 g / m ^{2 and} the paper coating composition was applied immediately after coating. The time until the surface of the composition for use solidifies and the gloss disappears is measured with a stopwatch. The water retention of the paper coating composition was evaluated according to the obtained values according to the following three grades. ○: 15 seconds or more. Δ: 10 seconds or more and less than 15 seconds. X: less than 10 seconds.

Dry Pick Strength The degree of picking when each coated paper sample was simultaneously printed with an RI printing machine was judged with the naked eye and relatively evaluated from the 5th grade (best) to the 1st grade (worst).

Wet Pick Strength A degree of picking when each coated paper sample was simultaneously printed with an ink roll by simultaneously applying dampening water to each coated paper sample with a Molton roll using an RI printer. Was evaluated with the naked eye and relatively evaluated from the 5th grade (best) to the 1st grade (worst).

White paper gloss JIS. It measured according to P-8142. The larger the number, the better the white paper gloss.

After printing each coated paper sample under the same conditions with a printing gloss RI printer,
After leaving it for a day and night, the glossiness of the printed surface is determined according to JIS. P-8142
It was measured according to. The larger the value, the better the printing gloss.

Measurement of Average Particle Diameter of Copolymer Latex After dyeing the copolymer latex with osmium tetroxide, a transmission electron microscope photograph was taken to measure the diameter of 1000 particles to obtain the number average particle diameter. It was

Method for producing copolymer latex A pressure-resistant polymerization reactor was charged with 165 parts of polymerization water, 0.2 parts of the surfactant shown in Table 1, sodium carbonate and 0.7 parts of potassium persulfate, and the mixture was sufficiently charged. After stirring, each of the monomers shown in Table 1 was added and polymerization was initiated at 65 ° C. to give a polymerization conversion rate of 98.
The polymerization was terminated when the percentage reached. Next, these copolymer latexes were adjusted to pH 7 with an aqueous ammonia solution, but the copolymer latexes N and P shown in Table 1 were judged to have a handling problem because the viscosity of the latexes became extremely high. In addition, a large amount of aggregate was observed in the copolymer latex O. Unreacted monomers were removed from the copolymer latexes other than N, O and P in Table 1 by steam distillation to obtain copolymer latexes A to M. The number average particle diameter measured for each copolymer latex is shown in Table 1.

Preparation of Paper Coating Compositions Paper coating compositions 1 to 13 were prepared according to the formulation shown below, using the copolymer latex shown in Table 1 as appropriate. The evaluation results are shown in Table 2. * Formulation of the composition for paper coating (solid content 65% by weight) Formulation Number of parts (dry weight part) 1st grade kaolin 40 2nd grade kaolin 30 Heavy calcium carbonate 30 Phosphate esterified starch 3 Copolymer latex 12

Preparation of Coated Paper Using a commercially available hot air coating dryer MLC-100S type, the obtained paper coating compositions 1 to 13 were formed on both sides of the coated base paper having a basis weight of 64 g / m ^2. Coated under the following conditions, coated paper 1-1
Created 3. Coating conditions: Blade coating was performed at a coating speed of 46 m / min. Drying condition: 0.5 seconds after coating, in a drying oven at 150 ° C., a temperature of 190 ° C. and hot air of 36 m / sec.
Dry for seconds.

Each of the coated papers obtained was conditioned at a relative humidity of 65% and a temperature of 20 ° C. for a whole day and night, and then a linear pressure of 70 Kg /
cm, a temperature of 60 ° C., a paper passing speed of 7 m / min, and a four-time paper passing condition, and were subjected to a supercalendering treatment, and subjected to performance tests of each coated paper. The evaluation results are shown in Table 2.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

As described above, by using the specific copolymer latex of the present invention as a binder for paper coating, the above various properties required for high speed coating suitability are excellent and excellent. It is possible to obtain a coated paper having surface strength and printing gloss.

Claims (2)

[Claims] 1. An aliphatic conjugated diolefin-based monomer 15 to
65% by weight, ethylenically unsaturated carboxylic acid ester monomer 2 to 40% by weight, ethylenically unsaturated carboxylic acid monomer 1 to 8% by weight, ethylenically unsaturated carboxylic acid amide monomer 0.5 to 5 Wt% and other monomers copolymerizable 10
In emulsifying and copolymerizing 100 parts by weight of a monomer mixture consisting of 81.5% by weight, an alkyl emulsifier is selected from alkylbenzene sulfonate, alkyl sulfate, alkyl diphenyl ether sulfate, and naphthalene-formalin condensate sulfonate. 0.3 to 2 parts by weight of at least one or more anionic surfactant and at least one or more anionic surfactant selected from polyoxyethylene alkyl ether sulfate and polyoxyethylene alkylphenyl ether sulfate. A copolymer latex for paper coating, comprising 0.2 to 6 parts by weight of the agent and having a number average particle diameter of 110 nm or less. 2. A paper coating composition comprising the copolymer latex according to claim 1 and a pigment.