KR20000019067A - Latex composition for printing paper - Google Patents

Abstract

PURPOSE: A latex composition for printing paper is provide which has improved blister resistance and adhesive strength both. CONSTITUTION: A latex composition of printing paper is prepared by emulsion copolymerization of monomer mixture containing aliphatic monomer derived from conjugated diene, unsaturated acid monomer derived from ethylene, and monomer derived from vinyl capable of copolymerizing with the monomers. This composition needs to satisfy the mathematics formula (1) to improve adhesive strength and blister resistance both. Gel content(X) needs to be kept the range between 30 to 60 %, gel swelling(S) is minimum 20, the soluble part molecular weight of tetrahydrofuran(MW) is minimum 80000 and the graft efficiency(Z) is 70 to 90 %.

Description

Latex composition for paper coating

The present invention relates to a latex composition for paper coating, and more particularly, vinyl copolymerizable with aliphatic conjugated diene monomer (a), ethylenically unsaturated acid monomer (b), and (a) and (b) monomers. In the latex composition for paper coating satisfying the conditions represented by the following formula (1), the monomer mixture consisting of the monomer (c) is divided into two stages in a specific content ratio so that the blister resistance and the adhesive strength are balanced. It is about.

Equation 1

In Equation 1 above:

X represents the gel content of the copolymer latex; M _w represents the weight average molecular weight of the tetrahydrofuran soluble component; Z represents the graft rate; S represents the degree of swelling of the gel.

Recently, in the printing industry, with the increase of printing speed and the increase in the use of web offset type printers, the web offset type printing method is different from the sheet offset type printing method. Immediately after the high temperature and high speed drying. At this time, since the paper is blistered due to the rapid evaporation of the moisture remaining on the paper, it is necessary to prevent it. Therefore, blister resistance is required for the web offset type printing paper (hereinafter referred to as "coated paper"). In addition, since the excellent adhesive strength is required along with the blister resistance, the blister resistance and the adhesive strength are in a mutually opposite relationship, so it is very difficult to simultaneously satisfy the two characteristics.

In the related art, various kinds of proposals for satisfying blister resistance and adhesive strength at the same time have been proposed.

For example, Japanese Laid-Open Patent Publication No. 57-10237 discloses a method of controlling gel content by the amount of chain transfer agent added to latex as a binder. However, if the gel content is high, the adhesive strength may be improved to some extent, but the blister resistance is remarkably decreased, and thus it is difficult to obtain good results only by controlling the gel content.

In Japanese Patent Laid-Open No. 7-173798, it is disclosed that the blister resistance and the adhesive strength can be balanced by the relationship between the molecular weight, the gel content, and the particle size, but in this case, the blister resistance and the dry adhesion strength can be improved to some extent. However, it is insufficient to improve the wet adhesion strength required in the offset type printing method.

In addition, Japanese Patent Application Laid-Open No. 6-184993 discloses that a balance between blister resistance and adhesive strength can be achieved by controlling molecular weight, gel content, and swelling degree of the gel, but the degree of improvement is uncertain, and the blister resistance is improved. In order to reduce the gel content, the gel swells and the molecular weight decreases, thereby decreasing the adhesive strength. Conversely, increasing the gel content in order to improve the adhesive strength lowers the blister resistance, thereby improving the blister resistance and the adhesive strength simultaneously. Insufficient

Accordingly, the inventors of the present invention have tried to prepare a latex composition for paper coating which can improve the blister resistance and adhesive strength at the same time, and as a result, an aliphatic conjugated diene monomer, an ethylenically unsaturated acid monomer, and the above monomers In the emulsion polymerization of the monomer mixture composed of copolymerizable vinyl monomers in two stages at an appropriate ratio, the correlation between the gel content, the gel swelling degree, the graft ratio, and the weight average molecular weight of the tetrahydrofuran soluble component satisfies Equation 1 above. By this, the present invention was completed.

Accordingly, an object of the present invention is to provide a latex composition for paper coating which will improve the blister resistance and the adhesive strength in a balanced manner.

The present invention emulsifies and co-polymerizes a monomer mixture composed of an aliphatic conjugated diene monomer (a), an ethylenically unsaturated acid monomer (b), and a vinyl monomer (c) copolymerizable with the above-mentioned monomers (a) and (b). In the obtained latex composition,

In the copolymer latex, the gel content (X), the weight average molecular weight (M _w ) of the tetrahydrofuran soluble component, the graft ratio (Z), and the swelling degree (S) of the gel satisfy the following Equation 1, and the weight average molecular weight ( M _w ) is at least 80000, characterized in that the swelling degree (S) of the gel is at least 20.

Equation 1

In Equation 1, X, M _w , Z and S are as defined above.

Referring to the present invention in more detail as follows.

The present invention limits the type and content of the monomers used in the copolymer latex polymerization to a specific range, and also the gel content of the copolymer latex, the swelling degree of the gel, the graft rate of the monomer mixture added to the second step, and the tetrahydrofuran soluble component. It is characterized by a latex composition for paper coating to balance the weight average molecular weight of the fixed range to improve the blister resistance and adhesive strength.

In the latex composition for paper coating according to the present invention, the gel content (X) range is maintained at 30 to 60, which is controlled by the amount of the monomer (a) and the chain transfer agent. If the gel content is less than 30, the adhesive strength is lowered. If the gel content is more than 60, the blister resistance is lowered.

The degree of gel swelling (S) is at least 20, which is controlled by the ratio of the grafting agent and the chain transfer agent and the monomers (a) and (c). If the gel swelling degree of 20 or more can achieve the desired effect of the present invention, when it is lower than 20, the adhesive strength is excellent, but there is a problem that the blister resistance is sharply lowered, which makes it difficult to use. Particularly preferably, the gel swelling degree is maintained in the range of 25 to 50.

The tetrahydrofuran (THF) soluble content weight average molecular weight (Mw) is to be as low as 80000, which is controlled by the chain transfer agent and the ratio of monomers (a) and (c). If the weight-average molecular weight of THF is maintained at 80000 or more, the present invention can achieve the desired effect, but if it is less than 80000, the blister resistance is improved, but there is a problem that the adhesive strength is sharply lowered. In particular, the THF soluble content weight average molecular weight range is preferably 85000 to 125000.

The graft rate (Z) is preferably such that the graft rate (Z) is maintained at about 70 to 90, which is controlled by the amount of the monomer added in step 2 or by the addition of a grafting agent such as allyl methacrylate and a chain transfer agent. do. If the graft ratio is less than 70, the adhesive strength is lowered, while if the graft ratio is greater than 90, there is a problem that the blister resistance is lowered.

Hereinafter, the monomers used in the preparation of the latex composition according to the present invention will be described in detail.

The aliphatic conjugated diene monomer (a) includes 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, and these may be used alone or in combination. Particularly preferred as aliphatic conjugated diene monomer is 1,3-butadiene. The aliphatic conjugated diene monomer is used in an amount of 10 to 60% by weight in total monomers. When the amount of the aliphatic conjugated diene monomer is small, the blister resistance is sufficient, but the adhesive strength is hard to expect. There is a problem of poor performance and water resistance.

The ethylenically unsaturated acid monomer (b) includes monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid and dicarboxylic acids such as maleic acid, humarinic acid and itaconic acid or anhydrides thereof, which may be used alone or in combination. . Said ethylenically unsaturated acid monomer is contained 0.5-10 weight% in the whole monomer, More preferably, 0.5-8 weight%. If the amount of the ethylenically unsaturated acid monomer is used in a small amount, the stability and adhesive strength of the latex are lowered. If the amount of the ethylenically unsaturated acid monomer is too large, the viscosity of the copolymer latex is high, so that it is difficult to handle practically and is difficult to use.

The vinyl monomers (c) capable of copolymerization with the monomers (a) and (b) illustrated above include aromatic vinyl monomers such as styrene, alphamethyl styrene, paramethyl styrene, and vinyl toluene; Acrylic or methacrylic acid esters such as methyl acrylate, methyl methacrylate, butyl acrylate and butyl methacrylate; Vinyl cyanide, such as acrylonitrile and methacrylonitrile. Preferably, styrene is used as the aromatic vinyl monomer, methyl methacrylate and butyl acrylate are used as the acrylic or methacrylic acid ester monomer, and acrylonitrile is used as the cyanoated vinyl monomer. In addition, as a monomer copolymerizable, ethylenic unsaturated carboxylic acid amides, such as acrylamide, methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide, or its N-substituted compound, 2-hydroxyethyl acrylate And unsaturated monomers containing hydroxyl groups such as 2-hydroxyethyl methacrylic acid, glycidyl group-containing unsaturated monomers such as glycidyl methacrylate, vinyl esters such as vinyl acetate, and the like. The copolymerizable monomer as described above is included in the total monomers 30 to 80% by weight, more preferably 50 to 80% by weight. If the amount of the copolymerizable monomer is small, the adhesive strength is excellent but the blister resistance is low, and if too much, the blister resistance is excellent but the adhesive strength is poor.

In the present invention, the mixture of the monomers as described above is added twice in a specific ratio during the emulsion copolymerization. In other words, in the initial stage of the monomer mixture used for the polymerization reaction, and the remaining amount is added when the emulsion co-polymerization of about 80%. The weight ratio of the monomer to be divided into the first step and the second step is to maintain 84.5 ~ 74.5: 15.5 ~ 14.5. If the ratio of the monomer to be added in the first step is too small, the gel content and the graft ratio is lowered, the adhesive strength is lowered, if too much, the gel content is excessive, there is a problem that the blister resistance is lowered. In addition, it is preferable that the composition and the input ratio of the monomers (a) and (c) to be added to the first and second stages are also considered. In particular, the grafting agent to be added to the first stage is more improved in terms of grafting efficiency. Preferably, the monomer (c) is mainly added in the second step and the monomer (a) is mainly added in the first step in view of the grafting efficiency and the THF-soluble content weight average molecular weight improvement.

On the other hand, in the emulsion copolymerization process of the present invention, redox is used as an initiator by combining water-soluble initiators such as potassium persulfate, ammonium persulfate, persulfate such as sodium persulfate, hydrogen peroxide, or reducing agents such as sodium bisulfite and amines. It can also be used as a system initiator. And water-soluble initiators, such as a water-soluble azo initiator, benzoyl peroxide, and azobisisobutyronitrile, can also be used.

In addition, an emulsifier is used to control the particle size of the copolymer latex produced in the emulsion copolymerization or to impart sufficient emulsion stability of the copolymer latex. As emulsifiers, sulfuric acid esters of alkyl alcohols, alkylbenzene sulfonates, and aliphatic sulfonates , Anionic surfactants such as alkyl diphenyl ether sulfonates, nonionic surfactants such as alkyl ester type of polyethylene glycol, alkyl phenyl ether type and alkyl ether type, or cationic surfactants may be used alone or in combination of two or more thereof. .

Examples of the chain transfer agent used in the preparation of the copolymer latex of the present invention include sulfur element-containing compounds such as t-dodecylmerethane, n-dodecylmerethane, n-octylmerethane, mercetoethanol, mercetopropionic acid and esters thereof, Tetraethyl thiuram sulfide and the like can be used singly or in combination of two or more kinds of chain transfer agents used as molecular weight regulators in general emulsion copolymerization reactions such as sulfides, halogenated hydrocarbons such as carbon tetrachloride, and alphamethylstyrene dimer.

In addition, the emulsion copolymerization process according to the present invention is by a conventional method.

In the latex composition for paper coating of the present invention obtained by the emulsion copolymerization process as described above, inorganic pigments such as kaolin cray, calcium carbonate, cetine white, titanium oxide, aluminum hydroxide, barium sulfate, chlorine oxide, polystyrene, styrene Organic pigments such as butadiene rubber (SBR) and phenolic resin can be used alone or in combination of two or more. In addition, additives such as a dispersant, a water repellent, a viscosity modifier, an antifoaming agent, a repairing agent, a dye, a fluorescent dye, a lubricant, a pH adjusting agent, a surfactant, and an anti-corrosive agent, which are commonly applied as necessary, may be used.

When coating the paper using the latex composition of the present invention produced by the above manufacturing process as a binder component, it is usually used in the range of 5 to 30 parts by weight (solid content) based on the pigment (solid content). In addition to the latex composition of the present invention, as a binder component, latexes such as starch, casein, water-soluble polymers such as polyvinyl alcohol, polyvinyl acetate, acrylic ester copolymers, etc. can be used in combination.

Such a present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Examples 1-5 and Comparative Examples 1-4: Preparation of Copolymer Latex

100 parts by weight of water, 1.5 parts by weight of potassium persulfate, 1 part by weight of maleic acid, 0.2 parts by weight of sodium lauryl and 1.5 parts by weight of seed particles of the polystyrene main component in a 5 l autoclave equipped with a stirrer Input. After sufficient stirring and mixing, nitrogen was removed from the reactor using nitrogen. After raising the temperature in the reactor to 65 ℃, the monomer was divided into two stages according to the ratio shown in the following Table 1 was continuously added to the reactor for 16 hours. However, in the case of Comparative Example 4, the monomer mixture was continuously added to the reactor for 16 hours without division of the addition step.

After completion of the monomer addition, when the content of residual monomer is 5000 ppm or less through the aging reaction, the reaction is terminated and the pH is adjusted to 8.0 using sodium hydroxide, and then the unreacted monomer and volatile residual organic matter are removed by steam stripping. And the copolymer latex was prepared by concentrating the solid content concentration to 50%.

Experimental Example 1 Analysis of Copolymer Latex

Physical properties of the copolymer latex prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were measured by the following method.

1) Measurement of gel content (X) and gel swelling degree (S):

Copolymer latex was applied on a polypropylene plate at a thickness of 0.1 to 0.5 mm, left to dry at 25 ° C. for 1 day, and then dried in an 80 ° C. hot air circulation dryer for 1 hour to form a film. Using a precision scale that can measure up to four digits below the decimal point, weigh about 1 g (W1), place it in toluene (100 ml), and soak in the solution for 1 day, then weigh the 300 mesh mesh Pass (W2) and measure the weight (W3) of the residue remaining on the gold mesh. Then, after drying for 1 hour in a 150 ℃ hot air circulation dryer weighed with a gold mesh (W4). Then, the gel content of the copolymer latex and the degree of swelling of the gel were calculated by the following equations (2) and (3).

2) Measurement of the weight average molecular weight (Mw):

Copolymer latex was applied on a polypropylene plate at a thickness of 0.1 to 0.5 mm, left to dry at 25 ° C. for 1 day, and then dried in an 80 ° C. hot air circulation dryer for 1 hour to form a film. Weigh about 1 g using a precision scale that can measure up to four decimal places, place in THF (50 mL), and soak for two days in the solution. Take THF solution from the container and pass it through a 0.45 μm filter. The passed filtrate was measured by weight permeation molecular weight using gel permeation chromatography. The measurement results were converted using the calibration curves of the weight average molecular weights 19000, 50000 and 100000 standard polystyrene samples.

3) Grafting efficiency of copolymer latex:

After the completion of the first step reaction in the preparation of the copolymer latex, a latex sample was taken and applied to the polypropylene plate with a thickness of 0.1 ~ 0.5 ㎜, and left to dry for 1 day at 25 ℃, dried for 1 hour in an 80 ℃ hot air circulation dryer film Formed. Weigh about 1 g using a precision scale that can measure up to four digits (W5), soak in acetone (50 ml) for 2 days, and then use a temperature-controlled centrifuge at 15000 After separating the gel and the sol portion for 100 minutes by rpm, the gel portion was dried well in a vacuum oven and weighed (W6). Then, the gel content (G1) for acetone after the first step emulsion polymerization was calculated by the following equation (4).

The copolymer latex, which had completed the polymerization reaction up to the second stage, was applied on a polypropylene plate at a thickness of 0.1 to 0.5 mm, left to dry at 25 ° C. for 1 day, and then dried in an 80 ° C. hot air circulation dryer for 1 hour to form a film. . Weigh about 1 g using a precision scale that can measure up to four decimal places (W7), deposit for 2 days in acetone (50 ml), and then use a temperature-controlled centrifuge at 15000 rpm. The gel and sol portions were separated for 100 minutes, and the gel portions were dried well in a vacuum oven and weighed (W8). The gel content (G2) for acetone after completion of the second step emulsion polymerization was calculated using Equation 5 below.

In addition, the graft efficiency of the copolymer latex was calculated by the following equation (6).

In Equation 6: M2 represents the total amount of the monomer used in the second step.

The relationship between the gel content (X) of the copolymer latex, the swelling degree (S) of the gel, the weight average molecular weight (M _w ) of the THF solubles, and the graft efficiency (Z) measured using the above method is shown in Equation 1 below. The results are shown in Table 1 below.

Equation 1

In Equation 1, X represents the gel content of the copolymer latex, M _w represents the weight average molecular weight of the tetrahydrofuran soluble content, Z represents the graft ratio, S represents the swelling degree of the gel.

division Example Comparative Example One 2 3 4 5 One 2 3 4 Monomer composition weight% 1,3-butadiene 25/0 25/0 20/5 20/0 15/0 25/0 25/5 30/0 25 Acrylic acid 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 0.5 / 0.5 1.0 Itaconic acid 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 2 Styrene 27.5 / 4 27.8 / 4 27.5 / 4 27.5 / 4 27.5 / 4 27.5 / 4 27.5 / 4 28/4 31.8 Methyl methacrylate 25/5 25/5 25/5 25/5 25/5 25/5 25/5 25/5 30 Acrylonitrile 5/0 5/0 5/0 5/0 5/0 5/0 5/0 5/0 5 Allyl methacrylate 0.5 / 0 0.2 / 0 0.5 / 0 0.5 / 0 0.5 / 0 0.5 / 0 0.5 / 0 0/0 0.2 Butyl acrylate 0/5 0/5 0/5 0/10 0/15 0/5 0/0 0/0 5 t-dodecyl mercaptan (parts by weight) ^* 1.0 / 0 1.0 / 0 0.8 / 0.2 1.0 / 0 1.0 / 0 2.0 / 0 1.8 / 0.2 1.0 / 0 1.0 Copolymer Latex Properties 1st step gel content (G1,%) 50 48 35 32 22 20 23 65 - Gel content (X,%) 56 48 50 40 31 28 28 62 51 Gel swelling degree (S) 30 28 25 45 50 50 51 17 20 THF Usable Molecular Weight Average Molecular Weight (× 10000, M _w ) 9.5 9.1 8.5 10.8 12.5 3.1 3.0 10.0 10.0 Graft Rate (Z,%) 82 87 83 72 75 82 78 75 - [X × M _w × Z / S]-[2200 × S] (× 1000000) 12.9 22.9 15.5 6.8 5.7 1.3 1.2 27 - Monomer composition comprising: a first stage copolymer emulsion during dose / second 2-step emulsion polymerization Dose ^* total monomers being calculated on 100 parts by weight.

The copolymer latex of Examples 1-5 which concerns on this invention satisfy | fills the conditions shown by Formula (1), an average molecular weight, and gel swelling degree. On the contrary, Comparative Examples 1 and 2 do not satisfy the condition represented by Equation (1) and the gel content is too low, Comparative Example 3 satisfies the condition represented by Equation 1, but the gel swelling degree is low and the gel content is too high It is shown and the comparative example 4 is an example in which the step polymerization method was not implemented.

Experimental Example 2 Evaluation Test of Paper Coated Paper

11 parts by weight (50% solids) of copolymer latex prepared in Examples 1 to 5 and Comparative Examples 1 to 4, 70 parts by weight of No-1 kaolin crayfish, 30 parts by weight of calcium carbonate, 0.3 part by weight of dispersant, and caustic soda 0.1 Part by weight and 4 parts by weight of starch oxide were mixed and blended so that the content of solid content was 62% by weight to prepare a composition for paper coating. Then, each paper coating composition was coated with 30 g / m 2 of both sides by 15 g / m 2 of single-sided dry weight on a white paper, and immediately dried by hot air at 120 ° C. for 20 seconds to obtain a coated paper.

For each coated paper, the evaluation test was carried out according to the following method, and the results are shown in Table 2 below.

a) dry adhesive strength:

After the coated paper was subjected to two super calender treatments under conditions of 60 ° C and a linear pressure of 100 kg / cm, the tack No. Several prints were made with 14 inks and the picking of the printed surface was visually observed. The evaluation is a 5-point relative evaluation, and the higher the value, the higher the adhesive strength.

b) wet adhesion strength:

After the coated paper was subjected to two super calender treatments under conditions of 60 ° C. and a linear pressure of 100 kg / cm, the surface of the coated paper was wetted with a Morton roll wetted with water using a RI tester. Several prints were made with 16 ink and the picking of the printing surface was visually observed. The evaluation is a 5-point relative evaluation, and the higher the value, the higher the adhesive strength.

c) ink development:

The same method as the wet adhesion strength test method was performed, but the ink tack No. 10 lower than the inktec used in the wet adhesion strength test was used. At this time, it was printed carefully so that picking did not occur, and the transition state of ink was visually observed. The evaluation is a 5-point relative evaluation, and the higher the value, the higher the adhesive strength.

d) white paper gloss:

It measured at the incident angle of 75 degrees and the reflection angle of 75 degrees using the scanning optical scale.

e) Blister aptitude:

A super-calendered coated paper was placed in a temperature-controlled oil bath to observe the temperature at which blisters were generated.

division Example Comparative Example One 2 3 4 5 One 2 3 4 Coating Properties Dry adhesive strength 5.0 4.5 4.5 4.0 3.5 2.0 2.0 3.5 2.5 Wet Adhesion Strength 4.0 5.0 5.0 4.5 4.0 3.0 3.0 3.5 3.8 Ink growth 4.0 5.0 4.0 4.5 5.0 3.5 3.0 3.0 3.5 White paper gloss (%) 57.8 59.3 58.9 61.0 62.1 57.6 56.9 54.9 55.9 Blister Temperature (℃) 225 230 230 245 250 225 230 160 200

The coated paper produced using the copolymer latex of Examples 1 to 5 according to the present invention was excellent while all the physical properties were balanced. On the contrary, Comparative Examples 1 and 2 were excellent in blister resistance, but the dry adhesive strength and the wet adhesive strength were remarkably decreased, and ink adhesion and white paper gloss were also reduced. In Comparative Example 3, the dry adhesive strength and the wet adhesive strength were somewhat superior to Comparative Examples 1 and 2, but the blister resistance and the white paper gloss were significantly decreased. In Comparative Example 4, the wet adhesive strength was excellent, but the blister resistance and the white paper gloss were decreased.

Based on the above experimental results, the coated paper using the copolymer latex composition for paper coating of the present invention has an effect of achieving the overall physical property balance while significantly improving the adhesive strength, ink build-up and blister resistance.

Claims (2)

In a latex composition obtained by emulsion copolymerizing a monomer mixture composed of an aliphatic conjugated diene monomer (a), an ethylenically unsaturated acid monomer (b), and a monomer (c) copolymerizable with the above-mentioned monomers (a) and (b). , In the copolymer latex, the gel content (X), the weight average molecular weight (M _w ) of the tetrahydrofuran soluble component, the graft ratio (Z), and the swelling degree (S) of the gel satisfy the following Equation 1, and the weight average molecular weight ( M _w ) is at least 80000, the swelling degree (S) of the gel is at least 20, the latex composition for paper coating. Equation 1 In Equation 1 above: X represents the gel content of the copolymer latex; M _w represents the weight average molecular weight of the tetrahydrofuran soluble component; Z represents the graft rate; S represents the degree of swelling of the gel. The copolymer latex according to claim 1, wherein the copolymer latex comprises 10 to 60% by weight of an aliphatic conjugated diene monomer (a), 0.5 to 10% by weight of an ethylenically unsaturated acid monomer (b), and (a) and (b) monomers. Vinyl copolymer (c) capable of copolymerization with a monomer mixture consisting of 30 to 80% by weight of the latex composition for paper coating, characterized in that obtained by emulsion copolymerization in two stages within the range of 84.5 to 74.5: 15.5 to 14.5 weight ratio.