JPS6346200B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new paper coating latex. More specifically, the present invention comprises (A) conjugated diolefin (a) 10-20% by weight, aromatic vinyl monomer (b) 40-89% by weight, unsaturated carboxylic acid ester (c) 5-30% by weight. , and an unsaturated carboxylic acid (d) having a copolymer composition of 1 to 5% by weight, (B) the glass transition temperature of the copolymer is 30 to 60°C, and (C) the average of the copolymer particles The particle size is in the range of 0.15 to 0.30μ, and (D) 80% by weight or more of the copolymer particles have a particle size of 0.15
Copolymer latex (a) in the range of ~0.30μ, (A) conjugated diolefin (a) 25 to 50% by weight, aromatic vinyl monomer (b) or this and unsaturated carboxylic acid ester (c) and a copolymer latex (b) having a copolymer composition of 49 to 65% by weight and 1 to 5% by weight of an unsaturated carboxylic acid (d), the above copolymer latex (a) and a copolymer latex. The ratio of (b) to (a)/(b) is 5 to 60/95 in terms of dry weight.
The present invention relates to a latex for paper coating, which has a particularly good luster-producing property, and is characterized by having a hardness of 40%. Generally, the surface of paper is coated with a paper coating composition comprising a pigment and a binder to improve printability and optical properties. The optical properties include, among others, the gloss of coated paper (referring to paper coated with a paper coating composition, hereinafter the same). The gloss of coated paper appeals to the visual sense, and may also be the most important optical property. Therefore, various attempts have been made to obtain coated paper with high gloss. The gloss of coated paper appears after drying during the finishing process, the so-called calendering process. The friction generated by this operation provides smoothness to the surface of the coated paper and also orients the pigment particles, and the higher the degree of orientation, the higher the gloss. Therefore, the simplest method is to reduce the amount of binder, but on the other hand, there is a limit to this because printability, such as adhesive strength, dry adhesive strength of the coated surface, and water-resistant adhesive strength, decreases. be. In addition, as pigments, mainly inorganic pigments, especially clays, are used. Attempts have been made to increase the gloss by making this clay a delaminate type, but the range of gloss increased by this method is not sufficiently large. One notable example of this endeavor is: This is an attempt to improve gloss by substituting some or all of the inorganic pigments with organic pigments, and a method using polystyrene polymer latex is known from Japanese Patent Publication No. 6524/1983. This uses a thermoplastic polymer to make it easier to calender, and by using this pigment, compared to the case of using only conventional inorganic pigments,
It is possible to obtain white paper with a fairly high gloss. However, compared to other pigments, it has the disadvantage of poor adhesion to paper and requires an increased amount of binder, so it has not been used satisfactorily. The present inventors developed a paper coating as a binder for the purpose of obtaining a coated paper with high gloss and good adhesive strength on the coated surface using conventional finishing methods and without using any special pigments. We have conducted extensive research on latex for use and have now completed the present invention. That is, the present inventors synthesized a latex binder for paper coating consisting of two types of copolymer components having different proportions of monomers such as conjugated diolefins and other properties, either continuously or individually, and then mixed them. It was found that by preparing a binder and using it as a binder, good gloss development by calendering and good adhesive strength could be obtained, and the present invention was achieved. Surprisingly, if the latex binder for paper coating of the present invention is used, ink receptivity and printing gloss are extremely good even without the use of special organic pigments. It has been found that good results are also achieved with respect to blister resistance, which is often a problem in offset printing. The present invention relates to the copolymer latex (a) described in detail below.
and a copolymer latex (b), characterized in that the ratio of (a) to (b) is 5 to 60/95 to 40 on a dry weight basis. In copolymer latex (a), the amount of conjugated diolefin has a great effect on gloss and adhesive strength.
Its suitable range is between 10 and 20% by weight. Ten%
If it is less than 20%, it is impossible to obtain sufficient adhesive strength, and if it is more than 20%, the development of gloss will be impaired. The effect becomes especially noticeable when the calendar conditions are relaxed. In this case, even if the proportion of conjugated diolefin in the copolymer latex (b) is increased or decreased accordingly to keep the overall proportion constant, the effect is not recognized at all or is extremely small. Components other than conjugated diolefin include 40 to 89% by weight of aromatic vinyl monomer, 5 to 30% by weight of unsaturated carboxylic acid ester, and 1 to 10% of unsaturated carboxylic acid.
5% by weight is used. If the component proportion of the unsaturated carboxylic acid ester is less than 5% by weight, printing gloss and ink receptivity will be insufficient. On the other hand, if the component proportion of the unsaturated carboxylic acid ester exceeds 30% by weight, the water-resistant adhesive strength will be insufficient. Enough is enough. In addition to the above conditions, copolymer latex (a)
The glass transition temperature is in the range of 30 to 60℃, the average particle size is 0.15 to 0.30μ, and 80% by weight or more of the particles are
Preferably, 90% by weight or more has a narrow particle size distribution in the range of 0.15 to 0.30μ. In this way, the polymer particles constituting the copolymer latex (a) have a specific particle size range with a relatively large value and a sharp particle size distribution, and mainly function as an organic pigment. ing. If the glass transition temperature is 30°C or lower or the average particle size is smaller than 0.15μ, the gloss will not develop well, and if the glass transition temperature is 60°C or higher or the average particle size is larger than 0.30μ, sufficient adhesive strength will not be achieved. I can't get it. Also, 80% by weight of copolymer particles
If the particle size is not within the range of 0.15 to 0.30μ and the particle size distribution is wide, the coated paper tends to have insufficient gloss and adhesive strength. As for the copolymer latex (b), the conjugated diolefin must be present in an amount of 25 to 50% by weight, preferably 30 to 45% by weight; if it is less than 25% by weight, good adhesive strength cannot be obtained; If the amount exceeds % by weight, good gloss cannot be expected and printing suitability such as ink receptivity becomes poor. Other monomers include aromatic vinyl monomer or its unsaturated carboxylic acid ester 49 to 65% by weight, and unsaturated carboxylic acid 1 to 65% by weight.
5% by weight is used. In addition, the above copolymer latex (a) or (b) alone cannot provide sufficient adhesive strength and good gloss at the same time, and the dry weight ratio of (a)/(b) is 5-60/95-40.
It becomes effective only when the ratio of If the copolymer latex (a) is less than 5% by weight, not only will sufficient gloss not be obtained, but the ink receptivity and
Printability such as printing gloss is also poor. If the amount is 60% by weight or more, sufficient adhesive strength, that is, dry adhesive strength and water-resistant adhesive strength of the coated surface, cannot be obtained. Below, the features of the present invention will be explained in more detail. The present invention significantly improves gloss development by combining a latex (B) that primarily functions as a binder with a latex (A) that satisfies the specific requirements (A) to (D). If the properties are good, a latex for paper coating is provided which also satisfies the adhesive strength, which often shows a tendency to decrease. In the present invention, the reason why the luster development is improved by using latex (a) as a component is considered to be due to the following mechanism. That is, the copolymer particles constituting latex (a) have (i) a specific copolymer composition (composition (A)),
Furthermore, the glass transition temperature (30~25℃) is higher than that of ordinary paper coating latex (-50~25℃).
60℃: Because it has the structure (B)), it has rubbery properties with film-forming properties and resinous properties as usual latex for paper coating, and as a result, it has moderate thermoplasticity. (ii) Also, since it has a particle size range (0.15 to 0.3μ: configuration (C)) that is larger than the average particle size range (around 0.1μ) of ordinary latex for paper coating,
It has characteristics similar to organic pigments rather than as a binder. Specifically, the copolymer particles of latex (a) having the characteristics described above fill the gaps between the inorganic pigments, which have larger particle sizes, so that the surface of the coating layer becomes in a so-called close-packed structure. . Furthermore, since the copolymer particles of latex (a) have appropriate thermoplasticity, they are heated to 30 to 60 degrees Celsius or higher in the drying process that precedes the calendering process, which causes the inorganic pigments to exist between each other. The copolymer particles will have appropriate flexibility, and as a result, the inorganic pigment will be in a state where it is easy to move, and the orientation of the inorganic pigment during calendering will be significantly improved. As a result, coated paper with excellent glossiness can be obtained. In addition, 80% by weight of the copolymer particles of latex (a)
The particle size is in the range of 0.15 to 0.30μ (configuration
(D)) The sharper the particle size distribution and the higher the uniformity of the copolymer particles, the more remarkable the above effects become. Each element constituting the latex (A) of the present invention, especially its properties (B) to (D), are not selected arbitrarily, but are specific and original so that the above-mentioned effects can be effectively expressed. It was planned. The reasons for limiting the numerical values for each requirement are described below. [Glass transition temperature] If the glass transition temperature of the copolymer is lower than the range of the present invention, its rubbery properties will prevail and there will be no significant difference from ordinary binders, and the copolymer particles of latex (a) will fill the gaps between the inorganic pigments. For example, a film is formed in a drying process before being filled with particles, making it impossible to form a smooth coating surface. As a result, gloss development properties such as white paper gloss and printing gloss are inferior, and furthermore, water resistant adhesive strength and the like are insufficient. Furthermore, if the glass transition temperature is higher than the range of the present invention, the adhesion between the copolymer particles and the inorganic pigment will deteriorate, resulting in poor dry adhesive strength and water-resistant adhesive strength. [Average particle size] If the average particle size of the copolymer particles is smaller than the range of the present invention, the effect of filling the gaps of the inorganic pigment and forming a smooth surface will be small, and therefore the appearance of gloss such as white paper gloss and printing gloss will be reduced. In addition, the ink receptivity is poor. Furthermore, if the average particle diameter of the copolymer particles is larger than the range of the present invention, the stability of the latex will deteriorate, resulting in insufficient adhesive strength such as dry adhesive strength and water-resistant adhesive strength. [Particle Size Distribution] If the particle size distribution of the copolymer particles is outside the range of the present invention and is broad, the gloss development properties such as white paper gloss and printing gloss will be poor. In this way, in the present invention, latex (a)
has an intermediate function between a pigment and a binder, and this function can only be demonstrated when all of requirements (A) to (D) are satisfied.As a result, it has both the contradictory properties of gloss development and adhesive strength. It is something that can be satisfied. Examples of the conjugated diolefin (a) include butadiene, isoprene, chloroprene, etc., and butadiene is particularly preferably used. In addition, as the aromatic monomer (b), styrene, α-methylstyrene,
4-methylstyrene, 2-methylstyrene, 3-
Methylstyrene, 4-methoxystyrene, 2-hydroxylmethylstyrene, 4-ethylstyrene, 4-ethoxystyrene, 3,4-dimethylstyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chloro-3-methylstyrene, 4-tertiary butylstyrene, 2,4-dichlorostyrene,
Examples include 2,6-dichlorostyrene, 1-vinylnaphthalene, divinylbenzene, and styrene is particularly preferably used. Unsaturated carboxylic acid ester
As (c), methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate and the like are used, with methyl methacrylate and methyl acrylate being particularly preferred. Unsaturated carboxylic acids (d) include acrylic acid, itaconic acid, methacrylic acid,
Fumaric acid, crotonic acid, and maleic acid are used, but acrylic acid, itaconic acid, and methacrylic acid are particularly preferred. It is also possible to use a mixture of these monomers. The copolymer latex used in the present invention can be produced by emulsion polymerization. That is, it can be obtained by adding a monomer mixture, a chain transfer agent, a polymerization initiator, an emulsifier, etc. to water and heating the mixture to about 50° C. to 100° C. with stirring to polymerize it. In this case, it is possible to carry out polymerization by continuously or intermittently adding a monomer mixture, etc., and this produces less coagulated material and better results are obtained. The paper coating latex of the present invention is prepared as an aqueous dispersion with conventional inorganic or organic pigments and applied to coated paper. The latex of the present invention may also be used in combination with other binders, such as natural binders such as starch, oxidized starch, soy protein, and casein, or synthetic binders such as polyvinyl alcohol, polyvinyl acetate latex, and acrylic latex. It is possible. Pigments include kaolin clay, talc, barium sulfate, titanium oxide (rutile anatase),
There are inorganic pigments such as calcium carbonate, aluminum hydroxide, zinc oxide, and satin white, and organic pigments such as polystyrene latex, and these may be used alone or in combination. Other auxiliary agents, such as dispersants (sodium pyrophosphate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycols, fatty acid esters, phosphate esters, silicone oils, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.),
Preservatives, water resistance agents (formalin, hexamine, melamine resin, urea resin, glyoxal, etc.), mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention improvers (carboxymethylcellulose, sodium alginate, etc.) ) etc. are added as necessary. A method for applying a paper coating composition using the paper coating latex of the present invention to a paper substrate can be carried out using known techniques.
For example, air knife coater, blade coater,
It is performed using a coating machine such as a roll coater or applicator. After coating, the surface is dried and finished by calendering, etc. By using the paper coating latex of the present invention, coated paper having better gloss and adhesive strength than conventional styrene-butadiene-based or carboxy-modified styrene-butadiene-based latexes can be obtained. In this case, it is particularly characterized by good gloss development even under gentle calendering conditions. That is, by using the paper coating latex of the present invention, it is recognized that the gloss measured at an incident angle of 75° and a reflection angle of 75° is increased by 10 points or more compared to the conventional paper. When the gloss is good, the dry adhesive strength and water-resistant adhesive strength of the coated surface, which often tend to decrease significantly, are also good and have no problems, and the other glossy properties and printability of the coated paper are also good. Particularly in terms of ink receptivity, printing gloss, and blister resistance in rotary offset printing, better results were observed compared to conventional latexes, and the latex for paper coating of the present invention has great advantages in this regard as well. ing. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded. Furthermore, all parts and percentages in the examples are based on weight. In addition, various measurements and preparation of coated paper in Examples were carried out in the following manner. Measurement of average particle size and particle size distribution: Measure the particle size using electron micrographs and calculate the weight average. Tg (glass transition temperature): Measured by differential scanning calorimeter. Preparation of coated paper: The latex for paper coating was blended as a paper coating composition, the solid content concentration was adjusted to 60%, and the mixture was applied to base paper for coating (weighing 100 g/m ² ) with an applicator at a concentration of 19.0±1.
Coat to give g/m ² . Then, it was dried at 120℃ for 10 seconds and calendered twice at 70℃ - 60Kg/cm. The coated paper thus prepared was evaluated as follows. White paper gloss: Measured using a Murakami gloss meter at an incident angle of 75° and a reflection angle of 75°. Dry adhesive strength: Printed 5 times with IPI #6 ink using an RI printability tester type, and judged on a 5-point scale based on the degree of picking, with no picking being 5. Water resistant adhesive strength: Using an RI printability tester type, apply water with IPI #4 ink, print, back out, and judge on a 5-point scale based on the degree of picking, with no picking being rated as 5. Ink receptivity: Toyo Ink #617 using RI printability tester type
Use a 5-point method to judge how well the ink has adhered after applying water and printing. Print gloss: After printing with Toyo Ink #617 using an RI printability tester, measure using a Murakami gloss meter at an incident angle of 75° and a reflection angle of 75°. Blister resistance: Using RI printability tester type, Dainippon Ink
After printing using Wed color OLM ink, 200
After being immersed in an oil bath kept at a constant temperature of ℃, those with no blisters are given a score of 5 and evaluated using a 5-point method. Examples 1 to 5, Comparative Examples 1 to 11 1 Production of latex for paper coating Production of copolymer latex (A) (Copolymer latex (A)) A temperature-adjustable machine equipped with a nitrogen-substituted 100° stirrer Water is added to a pressurized reactor (hereinafter simply referred to as the reactor).
85 parts, itaconic acid 2 parts, potassium persulfate 1.4 parts,
1.7 parts of potassium phosphate, 0.06 parts of sodium ethylenediaminetetraacetate, 0.03 parts of sodium alkylbenzenesulfonate, and 1.0 parts of n-dodecylmercaptan were charged, and the mixture was stirred and heated. Meanwhile, 15 parts of butadiene, 70 parts of styrene, and 13 parts of methyl methacrylate were placed in a monomer adjustment tank, and 0.45 parts of sodium alkylbenzenesulfonate was added to water.
An aqueous solution dissolved in 45 parts was placed in an emulsifier aqueous solution tank, and both were sent to an emulsifier using a metering pump to continuously emulsify to prepare an emulsified monomer. When the temperature inside the reactor reached 70°C, the emulsifying monomer was continuously introduced into the reactor while maintaining the temperature at 70°C, and the introduction was completed in 10 hours. 13 hours after the start of the reaction, the polymerization rate was
Reached 99%. A 5% aqueous potassium hydroxide solution was added to the obtained latex to adjust the pH to 6.0, residual monomers were removed by steam distillation, and the mixture was further heated and distilled under reduced pressure to bring the solid content concentration to 50%. In this way, a copolymer latex (A) was obtained. Copolymer latexes (B) to (I) were prepared by using the monomers shown in Table 1 and changing the initial and intermediate addition amounts of the emulsifier sodium alkylbenzenesulfonate to adjust the average particle diameter of the polymer particles and the particles. It was manufactured in the same manner as (A) except that the diameter distribution was changed. 2. Production of copolymer latex (i) (copolymer latex (b)) 85 parts of water, 2.5 parts of itaconic acid, and 0.93 parts of potassium persulfate were placed in a temperature-adjustable reactor equipped with a nitrogen-substituted 100°C stirrer. 1 part, 0.7 part of potassium phosphate, 0.06 part of sodium ethylenediaminetetraacetate, 0.06 part of sodium alkylbenzenesulfonate, and 0.5 part of n-dodecylmercaptan, and the mixture was stirred and heated. Meanwhile, 37 parts of butadiene, 40.5 parts of styrene, and 20 parts of methyl methacrylate were placed in a monomer preparation tank.
Also sodium alkylbenzenesulfonate 0.45
An aqueous solution prepared by dissolving one part in 45 parts of water was charged into an emulsifier aqueous solution tank, and both were sent to an emulsifier using a metering pump and continuously emulsified to prepare an emulsified monomer. When the temperature inside the reaction vessel reached 70°C, the emulsifying monomer was continuously introduced into the reactor while maintaining the temperature at 70°C, and the introduction was completed in 10 hours. The polymerization rate reached 99% 13 hours after the start of the reaction. Add 5% potassium hydroxide aqueous solution to the obtained latex to adjust the pH to 6.0.
Residual monomers were removed by steam distillation, and the mixture was further concentrated under reduced pressure to a solid concentration of 50%. In this way, copolymer latex (i) was obtained. Copolymer latexes (ii) to (iv) were produced in the same manner as (i) except that the monomers shown in Table 1 were used.

[Table] 3 Evaluation of latex for paper coating Copolymer latexes (a) and (b) produced as described above were mixed in the proportions shown in Table 3 to prepare a latex binder for paper coating. With the composition shown in Table 2,
A paper coating composition was prepared, and coated paper was produced using this composition. The evaluation results of the coated paper are shown in Table 3.

【table】

【table】

【table】 #
Manufactured by 0691)
From the evaluation results in Table 3, in Examples 1 to 5 of the present invention, white paper gloss, adhesive strength, printability, and blister were all balanced and maintained at a certain level or higher. On the other hand, copolymer latexes (a) in which the proportion of conjugated diolefin did not reach 10% by weight (Comparative Examples 4 and 5) had low adhesive strength. In addition, those having an average particle diameter outside the range of the present invention (Comparative Examples 6 and 7) are inferior in adhesive strength, gloss, and ink receptivity. If the Tg is too low (Comparative Example 8), the white gloss is extremely low. Copolymer latexes (b) in which the proportion of conjugated diolefin was outside the range of the present invention (Comparative Examples 10 and 11) were inferior in adhesive strength, ink receptivity, and blister resistance. In the ratio of copolymer latex (a) and (b),
(A) exceeds the scope of the present invention (Comparative Example 9)
Although the gloss and blister resistance are good, the adhesive strength is extremely low. Comparative Examples 12 to 16 [Manufacture of copolymer latexes (J) to (N)] Five types of comparisons were made in the same manner as in the case of latex (A), except that the monomer composition shown in Table 4 was used. A copolymer latex for use was produced. These are referred to as copolymer latexes (J) to (N). Copolymer latexes (J) and (K) are examples of broad particle size distributions outside the scope of the present invention. Copolymer latexes (L) and (M) are examples in which no unsaturated carboxylic acid ester is used. Copolymer latex (N) is an example in which the amount of unsaturated carboxylic acid ester used is excessive. Table 4 shows the above copolymer latexes (J) to (N).
The properties of are also described. In the copolymer latexes (L) and (M), 3.6% and 4.0% of coagulation were generated, respectively, and the stability was poor. For these copolymer latexes (L) and (M), the coagulated products were filtered through a 120-mesh wire gauze and then used to prepare latexes for paper coating.

[Table] Using the above copolymer latexes (J) to (N), prepare a latex binder for paper coating at the composition ratio shown in Table 5 in the same manner as described in the above section (3. Evaluation of latex for paper coating). Then, a paper coating composition was further adjusted to produce coated paper. The evaluation results of the coated paper are also listed in Table 5.

[Table] From the results in Table 5, the following can be seen. Particle size distribution of copolymer latex (a) is 80% by weight
(Percentage of particles within the particle size range of 0.15 to 0.3μ)
If it is less than , the white paper gloss and print gloss will be poor (Comparative Examples 12 and 13). If no unsaturated carboxylic acid ester is used,
Ink receptivity and printing gloss are poor (Comparative Example 14,
15) On the other hand, if the proportion of unsaturated carboxylic acid ester is greater than the range of the present invention, the water-resistant adhesive strength will be poor.

Claims (1)

[Scope of Claims] 1 (A) Conjugated diolefin (a) 10 to 20% by weight, aromatic vinyl monomer (b) 40 to 89% by weight, unsaturated carboxylic acid ester (c) 5 to 30% by weight, and an unsaturated carboxylic acid (d) having a copolymer composition of 1 to 5% by weight, (B) the glass transition temperature of the copolymer is 30 to 60°C, and (C) an average particle size of the copolymer particles. The diameter is in the range of 0.15 to 0.30μ, and (D) 80% by weight or more of the copolymer particles have a particle diameter of 0.15μ.
Copolymer latex (a) in the range of ~0.30μ, (A) conjugated diolefin (a) 25 to 50% by weight, aromatic vinyl monomer (b) or this and unsaturated carboxylic acid ester (c) A copolymer latex (b) having a copolymer composition of 49 to 65% by weight and 1 to 5% by weight of an unsaturated carboxylic acid (d), the above copolymer latex (a) and a copolymer latex The ratio of (b) to (a)/(b) is 5 to 60/95 in terms of dry weight.
Latex for paper coating, characterized in that it is 40. 2 Copolymer latex (a) (a) is butadiene, (b)
is styrene, (c) is at least one of methyl methacrylate and methyl acrylate, and (d) is at least one of acrylic acid, methacrylic acid, fumaric acid and itaconic acid. Latex for paper coating as described.