KR100357654B1 - Composition for coating paper - Google Patents

Abstract

PURPOSE: A composition for coating paper is provided which has the improved adhesive strength, blister prevention and latex stability. CONSTITUTION: A composition for coating paper comprises carboxy modified latex as a binder and metacylic acid single polymer or metacylic acid-containing copolymer oligomer of formula(I) as a chain transfer agent, wherein R is H or CH3; Y is R, H or CH3; X is -C6H6, -CN, -COOR'; R' is R, -C2H5, C4H9; Z is -C6H6, -CN, -COOR"; R" is R, -C2H5, C4H9; and a plus b is 1 to 16; and the chain transfer agent is one or two or more of copolymer oligomer selected from metacylic acid, maleic acid, fumaric acid and itaconic acid.

Description

Paper coating composition

The present invention relates to a composition for paper coating, and more particularly, to prepare a carboxy modified copolymer latex having a controlled gel content by using a new chain transfer agent, and the adhesive strength, blister resistance and latex of the latex as a binder. It relates to a composition for paper coating excellent in stability.

Coated paper is produced and consumed in large quantities by increasing the gloss, whiteness, and smoothness of the paper, and improving the gloss of printed matter and the reproducibility of chain images. Such coated paper is obtained by coating on paper a composition consisting of a pigment and a binder.

As the pigment, white pigments such as clay, calcium carbonate, aluminum hydroxide, titanium dioxide and satin white, and organic pigments made from organic compounds such as polystyrene are used. As a binder, styrene-butadiene-based carboxy-modified copolymers obtained by copolymerizing aliphatic conjugated diene monomers, aromatic vinyl monomers, ethylenically unsaturated carboxylic acid monomers and other copolymerizable monomers, acrylates, and vinyl acetate-based latexes are used as the synthetic binders. Starch, casein and the like are used as secondary binders.

Copolymer latex used as a binder should not only provide adhesion between the pigments, but also provide adhesion between the base paper and the pigment and exhibit excellent printing gloss. In particular, it should be excellent in blister resistance in web-offset printing. Coating with a composition for paper coils using a carboxy-modified styrene-butadiene copolymer latex as a binder is widely used in the paper coating industry because of its excellent adhesive strength, water resistance and printing gloss.

Recently, latex for paper coating has been developed for the development of positive latex that can improve the modling through control of binder migration, development of binder pigment for light weight of coated paper, and latex suitable for high speed coater to improve coating productivity and cost. Is being developed.

On the other hand, in the case of web offset printing, the market is gradually increasing because it is much superior in terms of productivity compared to sheet-off set printing. In the case of the web offset, the drying process of the printing ink requires a high temperature drying process. Therefore, a coating layer capable of easily releasing the water vapor pressure generated by the water content of the printing paper, that is, air permeability should be formed, which requires proper gel content control for latex for web offset printing.

As a method of controlling the gel content of the conventional copolymer latex, it was common to emulsify polymerization in presence of mercaptans, such as dodecyl mercaptan, halogenated hydrocarbons, such as carbon tetrachloride, and alpha methylstyrene dimer, as a chain transfer agent.

However, carbon tetrachloride is limited due to environmental problems, and mercaptans cause odors in the final product, resulting in a decrease in adhesive strength, print gloss, and blister resistance. Therefore, there is a need for the development of a new chain transfer agent capable of controlling the content of the copolymer without causing problems in the environment, the physical properties of the final product and the polymerization rate.

Recently, in accordance with the demand for improved productivity and cost reduction of coatings, it is necessary to develop latex that can maintain its stability even at high speed coating. Latex is stabilized by a protective layer formed on the particle surface, and the protective layer is generally divided into a chemically bonded bond protective layer represented by a carboxylic acid or an adsorption protective layer by physical adsorption of a surfactant (emulsifier) or a water-soluble polymer. . A typical method for providing a bond protective layer is typically formed by copolymerization of a monomer having a carboxylic acid as a functional group.

On the other hand, N. S. Enibolopyan et al. J. Polym. Sci., Chem. Ed. Vol. 19, 879 (1981), published on the molecular weight control of PMMA and PS of cobalt (II) porphyrin compounds. A. F. Barezylc et al. Sci., Chem. Ed., Vol. 22, 3255 (1984) published a study on the control of PMMA molecular weight using cobaloximes.

The present inventors synthesized an oligomer containing carboxylic acid using such a cobalt compound and used it as a new chain transfer agent to prepare a carboxy-modified latex with controlled gel content, and when used as a binder, adhesive strength, white gloss, and blister resistance In addition to obtaining this excellent coated paper, it was found that latex suitable for speeding up the coating was completed to complete the present invention.

In other words, the present invention provides a compound comprising 20 to 60% by weight of an aliphatic diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid and 10 to 90% by weight of other copolymerizable ethylenically unsaturated monomers. It is characterized by containing a copolymer latex and a pigment obtained by emulsion polymerization under the following.

The present invention is described in detail as follows.

Examples of the aliphatic diene monomers used in the present invention include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, halogen substituted butadiene, and the like. These can be used individually or in combination of 2 or more types, respectively. The use range of the aliphatic diene system is 20 to 60% by weight, suitably 25 to 50% by weight in the total monomer mixture.

If the content of the aliphatic diene monomer is less than 20% by weight, the adhesive strength is lowered. If the content of the aliphatic diene monomer is more than 60% by weight, the water resistance is lowered and properties required for offset printing cannot be satisfied.

As the ethylenically unsaturated carboxylic acid monomer used in the present invention, such as ethylenic unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, itaconic acid monoethyl ester, fumaronobutyl ester, maleic acid monobutyl ester, etc. And unsaturated polycarboxylic acid alkaline esters having at least one carboxyl group. These may each be used alone or in combination of two or more. The ethylenically unsaturated carboxylic acid monomers are 0.5-10% by weight, suitably 1-5% by weight of the total monomer mixture. If it is less than 0.5% by weight, the adhesive strength and water resistance are lowered, the stability of the latex is lowered, and if it is more than 10% by weight, the viscosity rises, making handling of the latex difficult.

Other copolymerizable ethylenically unsaturated monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, monochlorostyrene and vinyltoluene; Unsaturated carboxylic acid alkyl esters such as methyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate; Ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Ethylenic unsaturated amides, such as acrylamide, methacrylamide, and N-methol acrylate, such as: hydroxy such as β-hydroxyethyl acrylate, β-hydroxybutyl acrylate, and β-hydroxyethyl methacrylate Oxyethyl acrylates; Glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate and glycidyl methacrylate: other vinyl compounds such as vinyl acetate and vinyl pyridine. These monomers can be used individually or in combination of 2 or more types, respectively.

Ethylenically unsaturated monomers are used in the range of 10-90% by weight, suitably 10-75% by weight of the total monomer mixture. Among the ethylenically unsaturated monomers, anti-aromatic vinyl compounds such as styrene serve to impart proper rigidity and water resistance. Unsaturated carboxylic acid alkyl esters such as methyl methacrylate serve to impart proper hardness and hydrophilicity, and it is preferable to use 5 to 50% by weight, more preferably 5 to 30% by weight.

Ethylenic unsaturated nitrile compounds such as acrylonitrile serve to increase the printing gloss of coated paper with oil resistance, and it is preferable to use 4 to 40% by weight, more preferably 5 to 25% by weight. Hydroxyalkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acid amides and derivatives thereof serve to improve the stability of the copolymerized latex and are preferably used in the range of less than 20% by weight. In this way, in order to satisfy the composition, it is preferable to use these monomers in combination in appropriate ranges, respectively.

Among these ethylenically unsaturated monomers, styrene, methyl methacrylate, butyl acrylate, acrylonitrile, methacrylonitrile, acrylamide, β-hamidoxyethyl acrylate and the like are used as the most suitable monomers.

In the present invention, the monomer mixture may be a single or random copolymer oligomer of methacrylic acid having a structure of the following general formula (I) or one or more random copolymers of methacrylic acid and maleic acid, fumaric acid or itaconic acid. It is characterized in that the emulsion polymerization in the presence.

In the present invention, an organic compound having the structure represented by the general formula (I) is used as a chain transfer agent, and the amount thereof is generally 0.5-5 parts by weight based on 100 parts by weight of the monomer mixture, but 1-3 parts by weight may be used. If it is less than this range, it is difficult to achieve the object of the present invention because the addition effect is insignificant, and if it exceeds this range, the adhesive strength is lowered.

In the present invention, as the chain transfer agent, the organic compound of the general formula (I) and a known chain transfer agent may be used in parallel. Mercaptans such as N-dodecyl mercaptan, t-dodecyl mercaptan, N-stearyl mercaptan and the like: acrolein, methacrolein, aryl alcohol, α-methylstyrene, dimer, 2,5-hydrofuran, 1, 4- cyclohexene etc. are mentioned. These may be used alone or in combination of two or more.

When using another chain transfer agent together, 5 weight part or less, more preferably 3 weight part or less are used combining with said general formula (I) with respect to 100 weight part of monomer mixtures. If it exceeds this range, the problem that the adhesive strength is lowered.

In the present invention, the initiator used for the emulsion polymerization is not particularly limited. As an inorganic initiator, sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can be used individually or in mixture, for example. As an organic initiator, Organic peroxides, such as t-butyl peroxide and cumene hydroperoxide; Azo compounds, such as azobisisobutyronitrile and azobis-2, 4- dimethyl vareronitrile, etc. are mentioned.

These inorganic initiators and organic initiators can be used individually or in combination of 2 or more types, respectively. Moreover, these polymerization initiators can also be used as a redox-type polymerization initiator in combination with sodium bisulfite. The polymerization initiator is usually used 0.1 to 5 parts by weight based on 100 parts by weight of the monomer mixture, but more preferably 0.5 to 2 parts by weight.

As the emulsifier, any of anionic surfactants, nonionic surfactants and amphoteric surfactants may be used, or two or more thereof may be used in combination. Nonionic surfactants such as anionic surfactants such as sulfuric acid esters of higher alcohols, alkyl benzenesulfonic acid salts and aliphatic sulfonic acids, alkyl esters of polyethylene glycol, and alkylphenyl esters; Amphoteric surfactant which has carboxylate, a sulfuric acid ester salt, a sulfonate, a phosphate, a phosphate ester salt as a negative part, an amine salt, a quaternary ammonium salt, etc. as a cationic part is mentioned. The emulsifier is generally used 0.05 to 2 parts by weight based on 100 parts by weight of the monomer mixture, but more preferably 0.05 to 1 part by weight. If the amount of the emulsifier is used excessively, the water resistance decreases.

In the present invention, a chelating agent, an inorganic salt, and the like may be used in addition to the above, but the type thereof is not particularly limited, and a known one may be used.

In the present invention, the emulsion polymerization method and the conditions thereof are not particularly limited, and various conventional methods may be used. For example, as a method of adding a monomer mixture, the whole amount is added to a reaction container collectively, it is added continuously or at regular intervals during superposition | polymerization, a part of monomer mixture is carried out by batch addition polymerization, and the remaining monomer mixture is collectively added. Any method may be used, such as a polymerization method or a method of polymerization by adding continuously or at regular intervals. The composition of the monomer mixture added continuously or at regular intervals may be the same or vary.

The method of adding a chain transfer agent containing an organic compound having the same structure as the general formula (I) described above is not particularly limited, and may be any of batch addition, split addition, and continuous addition, and any combination thereof may be used. Also good.

The copolymer latex obtained after the completion of the polymerization is usually adjusted to a desired pH by removing residual monomer and, if necessary, with sodium hydroxide, aqueous potassium hydroxide solution, ammonia water and the like. In addition, the solid content can be adjusted through concentration, and preservatives, toughening agents, and dispersants may be added as necessary.

The copolymer gel content in the copolymer latex has a great influence on adhesion strength, blister resistance, and the like. The copolymer latex used in the present invention does not particularly limit the gel content. For example, the sheet offset coating paper may be adjusted within a range suitable for each application, such as a gel content of 50% by weight or more and a web offset coating paper of 70% by weight or less.

The gel content is usually in the range of 20 to 95% by weight, which is insoluble in the organic solvent in the copolymer. The gel content in the copolymer latex is influenced by the monomer composition, polymerization temperature, final conversion rate, polymerization method, etc., but is generally controlled by the use of a chain transfer agent.

Carboxy modified copolymer latex is comprised with 5-40 weight part of solid content normally with respect to 100 weight part of pigments (solid content). Examples of the pigment used in the coating composition of the present invention include inorganic pigments such as clay, calcium carbonate, aluminum hydroxide, titanium dioxide and satin white; And organic pigments known as plastic pigments and binder pigments. These may be used alone or in combination of two or more thereof.

As the binder of the paper coating composition, a water-soluble binder such as starch, casein, polyvinyl alcohol, and synthetic latexes such as polyvinyl acetate and polyacrylate-based latex may be used together with the aforementioned carboxy-modified copolymer latex.

To the composition for paper coating of the present invention, additives such as a dispersant, a thickener, a dye, a coloring pigment, a fluorescent dye, an antifoaming agent, a preservative, a water-resistant agent, a lubricant, a flavourant, and a water-retaining agent may be added as necessary. The paper coated by the composition for paper coating of the present invention is not particularly limited and includes cardboard and the like. In the coating method, for example, it can be coated using various coating equipment such as air knife coater, bar coater, blade coater.

Examples of the present invention are as follows, both parts and percentages of the examples means parts by weight and weight percent.

Example 1

In a flask equipped with a reflux condenser, 400 g of methacrylic acid and 0.56 g of sodium bisulfite initiator were added to 200 ml of ethyl acetate to prepare a solution, followed by the required amount of cobalt catalyst. Bubbling this solution with nitrogen to remove air, reacting at 85 ° C. for about 5 hours and treating with activated carbon to remove the catalyst.

Removal of the solvent and methacrylic acid from the distillation apparatus yields about 250 g (yield 62%) of methacrylic acid oligomer. The GPC molecular weight determined based on polystyrene and methyl methacrylate as a standard was a number average molecular weight Mn = 450, Mw = 810, and a molecular weight distribution Mw / Mn = 1.8.

The polymerization of latex

Was put in a high pressure tank to form an emulsion. 10% of the total content was transferred to a high pressure reactor for 4 hours at 70 ° C, and the remaining emulsion solution was added to the high pressure reactor for 8 hours, and the temperature of the reactor was raised to 75 ° C and left for about 4 hours. At this time, the polymerization rate of all the monomers was 97%. The particle size of the latex was 0.19 μm as measured by the light scattering method. 10 parts of sodium hydroxide solution (10% solution) was added to the obtained latex to adjust the pH to 8, and the solid content of the latex was adjusted to 50% through a distillation apparatus.

The formulation for preparing the coating color is as follows.

(* 1) Ultra White 90 (manufactured by Engelhards)

(2) Ultracoat (made by Engelhards)

(* 3) Hydraka 90 (made by Omiya Korea)

(* 4) Aaron T-40 (Dong-A Synthetic Chemical Co., Ltd.)

(* 5) MS-4600 (Japan Food Processing Products)

The coating composition obtained by the above formulation was weighed and coated on a base paper of 70 g / m ^{2 so that} the coating amount on one side was 15 ± 1 g / m ² , followed by drying for 20 seconds with hot air at 150 ° C. immediately after coating. Thereafter, the mixture was left in a constant temperature and humidity chamber at 20 ° C. and 65% RH for 1 day, and then subjected to two supercalendar treatments at 60 ° C. and tjsdkq 60 Kg / cm. Evaluation results of the physical properties of the coated paper are shown in Table 1 below.

Example 2, 3)

It carried out similarly to Example 1 except having changed the polymerization degree of oligomer into 8 and 17, respectively.

Examples 4 and 5)

The same procedure as in Example 2 was carried out except that the oligomer of Example 2 was used together with t-dodecylmercaptan.

Comparative Examples 1-3)

The result is when t-dodecyl mercaptan is used as a chain transfer agent.

The physical property measuring method and evaluation method of the coated paper obtained by each said Example and comparative example are as follows.

(1) gel amount

The sample latex is adjusted to pH 8.5 and dried. When drying, the film is put in an aluminum plate so that the thickness is 0.2 mm. It is left to stand for 48 hours in a constant temperature and humidity chamber of 20 ℃, 65% RH to prepare a dry film. This film is cut to a size of 2 mm in width and weighed 0.2 g. This is placed in a 100 mesh mesh net and 100 ml of THF is left to stand at room temperature for 24 hours with a solvent. After that, the net mesh is dried in a vacuum dryer and the weight of the insoluble part is weighed, and the weight of the initial copolymer film is obtained to determine the amount of gel.

(2) adhesive strength

The RI printing tester was used to apply the ink having the appropriate tack to the coated paper, and the appearance of the pick was visually determined. 5 points for no pick are scored and 1 point for severe pick is scored.

(3) Blister Resistance

Prepare coated paper coated on both sides on the basis of 15 ± 1g / m ² on one side and adjust the moisture content to about 6%. After the coating paper is removed for several seconds from the silicone oil set to an appropriate temperature, it is visually determined whether blisters are generated and the lowest temperature of blister generation is indicated.

(4) printing gloss

0.4 ml of blue ink was applied to coated paper specimens using an RI printing tester, and then measured at an angle of incidence-reflection angle of 75 ° -75 ° using a gloss meter.

(5) Stability of coating color

A certain amount of the coating solution was filtered using a 120 mesh and then stirred at 70 ° C. for 10 minutes using a Maron mechanical stability tester. Thereafter, the above sample was filtered using a 120 mesh mesh, and the residue content on the mesh was measured to display the stability of the color as in the following example.

◎: Excellent

○: good

△: normal

X: bad

Claims (2)

A composition for paper coating using a carboxy-modified latex as a binder, wherein a methacrylic acid homopolymer having a structure of the following general formula (I) or a copolymer oligomer containing methacrylic acid is used as a chain transfer agent. The method of claim 1, A composition for paper coating using carboxy-modified latex as a binder, wherein one or two or more copolymer oligomers of methacrylic acid, maleic acid, fumaric acid and itaconic acid are used as a chain transfer agent.