JP2753004B2 - Binder for paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a polymer latex for use as a binder in paper coating paints, and more particularly, it has excellent ink pick resistance and blister resistance in offset printing. Provide useful materials for producing coated paper.

<Conventional technology> Coated paper is used to improve the printability of paper and to improve optical characteristics such as gloss, and to apply kaolin clay, calcium carbonate, satin white, talc, titanium oxide, etc. It is coated with a paint containing a pigment, a polymer latex as a binder thereof, and a water-retaining polymer such as starch, polyvinyl alcohol, and carboxymethyl cellulose as a water retention agent or an auxiliary binder. Here, as a polymer latex as a binder, a styrene-butadiene-based polymer latex emulsion-polymerized with styrene and butadiene as main monomer components, a so-called SB latex, has been generally used.

By the way, production of coated paper has increased remarkably with the recent increase in demand for color printed magazines, pamphlets, and advertisements. On the other hand, coated paper printing is mainly performed by offset printing, but the demand for the high-speed printing is increasing due to the growing demand, and the required level of the quality is also becoming more sophisticated. For this reason, among the quality of coated paper, particularly, improvement in ink pick resistance, so-called pick strength and blister resistance is strongly demanded.
Such quality is used as a binder for pigments
Various considerations have been made so far because of the strong dependence on the design of SB latex. Among them, the gel fraction of the latex, that is, a polymer film formed by coagulating and depositing polymer particles by adding isopropyl alcohol or the like to the film formed by drying the latex or to the latex, separating and drying the polymer particles of benzene and toluene Since it has been confirmed that the proportion of a portion insoluble in a solvent such as tetrahydrofuran or the like is a controlling factor of pick strength and blister resistance, various studies have been made from this aspect. That is, JP-B-59-3598, JP-B-60-17879 and JP-A-58-4894 show excellent performance by adjusting the latex to a specific range of polymer composition and gel fraction. It has been proposed to do so. In addition,
JP-A-62-117897 discloses that a latex having a low gel fraction and a latex having a high gel fraction having a specific polymer composition are mixed at a ratio in a specific range to thereby provide excellent pick strength and blister resistance. It is said that it can be.

By the way, the pick strength of the coated paper is highest in the SB latex when its gel fraction is in the range of 75 to 95% by weight, whereas the blister resistance is better as the gel fraction is lower. It is generally confirmed. Therefore, it is very difficult to simultaneously increase both the pick strength and the blister resistance to a high level, and in the past, it has been necessary to adjust the gel fraction of the latex in an appropriate range and compromise until now. Was.

<Problems to be Solved by the Invention> With such a conventional technology, latex as a binder capable of producing high-quality coated paper cannot be adapted to recent high-speed printing. At present, it is strongly required to appear. In view of such a situation, the present inventors provide a binder that can further increase the pick strength and the blister resistance of the current coated paper for offset printing.

<Means for Solving the Problem> The present invention relates to a method for synthesizing 25 to 50% by weight of butadiene, 1 to 8% by weight of an ethylenically unsaturated carboxylic acid and 42 to 74% by weight of other monomers copolymerizable therewith. A latex (A) having a polymer particle diameter of 600 to 1500 A ゜ and a gel fraction of a film formed from the latex of 40 to 95% by weight, butadiene 20 to 45% by weight A polymer latex synthesized from 1 to 8% by weight of an ethylenically unsaturated carboxylic acid and 47 to 79% by weight of another monomer copolymerizable therewith, having a polymer particle diameter of 1300 to 3500 A And a latex (A), wherein the gel fraction of the coating formed from the latex is 0 to 50% by weight.
The ratio of the particle size of the latex (B) to the particle size of the latex (B) is 0.8 or less, and the mixing ratio of the latex (A) is in the range of 5 to 65% by weight in terms of polymer dry weight. The present invention relates to a binder for paper coating.

 Hereinafter, the present invention will be described in detail.

The polymer of the latex (A) is a monomer composed of 25 to 50% by weight of butadiene, 1 to 8% by weight of an ethylenically unsaturated carboxylic acid, and 42 to 74% by weight of another monomer copolymerizable therewith. Obtained by subjecting the body to emulsion polymerization. And
The polymer particle diameter is 600 to 1500 A〜 and the gel fraction of the film formed from the latex is 40 to 95% by weight.

Butadiene should be in the range of 25-50% by weight based on total monomers. In this range, it is possible to exhibit the highest pick strength, and if it is less than 25% by weight, the polymer becomes too brittle, and if it exceeds 50% by weight, it becomes too soft, and in any case, a high pick strength is provided. It is impossible. The preferred amount of this butadiene is from 30 to
45% by weight.

The ethylenically unsaturated carboxylic acid must be in the range of 1-8% by weight. If the amount is less than 1% by weight, the dispersion stability of the latex cannot be maintained at a high level, and various problems occur at the time of coating preparation and coating. Also, the pick strength is poor. If the content exceeds 8% by weight, the viscosity of the latex or paint becomes too high, and the water resistance is impaired. Examples of the ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid and the like.

Examples of other monomers include styrene, α-methylstyrene, aromatic vinyl compounds such as vinyltoluene,
Alkyl methacrylates such as methyl methacrylate, ethyl methacrylate and butyl methacrylate; alkyl acrylates such as ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile Conjugated dienes such as isoprene, 2-chloro-1,3-butadiene. In addition, various functional monomers other than these can be included in an amount of usually 10% by weight or less as desired. Examples thereof include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, acrylamide, methacrylamide, N-methylol acrylamide, N-
Butoxymethylacrylamide, sodium styrenesulfonate, and the like.

Of the other monomer examples, styrene is the most typical and effective one, followed by methyl methacrylate and acrylonitrile.

The particle size of the polymer latex must be 600 to 1500 A ゜ and the gel fraction of the film formed from the latex must be 40 to 95% by weight. If it is not within this range, a desired big strength cannot be exhibited when combined with the latex (B) described later. Here, the preferred range of the particle size is 700 to 1200 A ゜, and the preferred range of the gel fraction is 60 to 90% by weight.

The polymer of latex (B) is composed of 20 to 45% by weight of butadiene, 1 to 8% by weight of ethylenically unsaturated carboxylic acid, and 47 to 79% by weight of other copolymerizable monomers. Obtained by subjecting the monomer to emulsion polymerization. The polymer particle diameter is 1300 to 3500 A500, and the gel fraction of the film formed from the latex is 0 to 50% by weight. Here, a preferable range of the particle size is 1500 to 2500 A ゜.

In this latex, butadiene must be in the range of 20-45% by weight based on total monomers. In this range, the balance between pick strength and blister resistance can be exhibited to the highest level, and if it is less than 20% by weight, the polymer becomes too brittle and cannot provide high pick strength. If it exceeds, it becomes impossible to increase the blister resistance. The preferred amount of this butadiene is
25 to 35% by weight.

The ethylenically unsaturated carboxylic acid and other monomers are the same as described for the latex (A), and the particle size of this latex is 1300 to 3500 A ゜ and the gel fraction of the film formed from the latex is Must be 0-50% by weight. If it is not in this range, the desired blister resistance cannot be exhibited when combined with the above-mentioned latex (A).

The latex (A) and the latex (B) described above are produced by a conventionally known ordinary emulsion polymerization method. That is, in a dispersion system comprising water, a surfactant, a monomer and a radical polymerization catalyst as a basic component, in a production method in which a monomer is used as an aqueous dispersion of polymer particles, the polymer concentration is generally 40 to It is in the range of 60% by weight. As a surfactant,
Anionic surfactants such as fatty acid soap, rosin acid soap, alkyl sulfonate, dialkylaryl sulfonate, alkyl sulfosuccinate, polyoxyethylene alkyl sulfate, polyoxyethylene alkylaryl sulfate, polyoxyethylene alkyl ether And nonionic surfactants such as polyoxyethylene alkyl aryl ethers, polyoxyethylene sorbitan fatty acid esters, and oxyethylene oxypropylene block copolymers. The surfactant is usually used in the form of an anionic surfactant alone or an anionic / nonionic mixed system.
A range of ２2% by weight is common. The latex particle size can be adjusted by the use ratio of the surfactant. Generally, the higher the use ratio, the smaller the particle size of the produced latex.

The polymerization catalyst is one that causes addition polymerization of the monomer by radical decomposition in the presence of heat or a reducing substance, and is a water-soluble or oil-soluble persulfate, peroxide, or azobis compound. Potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2-azobisisobutyronitrile, cumene hydroperoxide, etc. Is most preferably used. The use ratio of the polymerization catalyst is usually 0.2 to
1.5% by weight. The polymerization temperature is generally in the range of 60 to 90 ° C., but when it is desired to accelerate the polymerization rate or to carry out polymerization at a low temperature, sodium bisulfite, ascorbic acid or a salt thereof, erythorbic acid or a salt thereof, Rongalit, etc. A so-called redox polymerization method in which the above reducing agent is used in combination with a polymerization catalyst can be used. Further, various polymerization regulators are often added as desired. For example, caustic soda,
PH adjusters such as potassium hydroxide, sodium hydrogen carbonate, sodium carbonate and disodium hydrogen phosphate; and various chelating agents such as sodium ethylenediaminetetraacetate.

In addition, the gel fraction of the latex varies depending on various polymerization factors such as the monomer composition and the polymerization temperature, and the method of adjusting the gel fraction to a desired level generally and conveniently involves the addition of a chain transfer agent. . Examples of the chain transfer agent preferably used in the emulsion polymerization for preparing the polymer latex of the present invention include t-dodecyl mercaptan, n-dodecyl mercaptan, mercaptans such as mercaptoethanol, terpinolene, dipentene, t-terpinene and tetrachloride. And halogenated hydrocarbons such as carbon.

The latex (A) is of a high pick strength-low blister resistance type, and the latex (B) is of a low pick strength-high blister resistance type.

In the present invention, in the blended latex of the latex (A) and the latex (B), the mixing ratio of the latex (A) is 5 to 5 in terms of polymer dry weight.
It must be in the range of 65% by weight, and if it is out of this range, neither the pick strength nor the blister resistance can be exhibited to a high level. That is, if the mixing ratio of the latex (A) is less than 5% by weight, the level of pick strength is low, and if it exceeds 50% by weight, the blister resistance sharply decreases. The mixing ratio of the latex (A) is preferably 15 to 50% by weight.

Further, the ratio of the particle diameter of latex (A) to the particle diameter of latex (B) is set to 0.8 or less, and the ratio of the gel fraction of latex (A) to the gel fraction of latex (B) is set to 1.2 or more. By doing so, the balance between pick strength and blister resistance can be greatly improved. That is, when the ratio of the particle diameter of the latex (A) to the particle diameter of the latex (B) exceeds 0.8, both latexes exhibit average pick strength and blister resistance, but are preferably 0.8 or less, and more preferably 0.8 or less. By making the ratio 0.7 or less, the pick strength can be further improved without impairing the original blister resistance of the latex (B). Similarly, when the ratio between the gel fraction of latex (A) and the gel fraction of latex (B) is less than 1.2, both latexes exhibit average pick strength and blister resistance. By making the ratio 1.2 or more, preferably 1.5 or more, the effects of the present invention can be sufficiently exhibited.

In the case where the latex of the present invention is used as a binder for a paper coating composition, it can be carried out in a usual embodiment. That is, pigments in water in which the dispersant is dissolved,
In this embodiment, a latex is mixed with a water-soluble polymer and various additives to form a uniform dispersion, and the latex (A) and the latex (B) may be mixed in advance or separately added at the time of coating preparation. Good. The paint can be applied to the base paper by a usual method such as a blade coater or a roll coater.

<Examples and Comparative Examples> Next, the present invention will be specifically described based on Examples and Comparative Examples, but it goes without saying that the present invention is not limited only to the following Examples. Parts and% in the text are based on weight.

(1) Preparation of polymer latex In a pressure-resistant reaction vessel equipped with a stirring device and a temperature control jacket, water, surfactant, itaconic acid and monomer shown in the column of <First stage emulsion polymerization> in Table 1 A predetermined amount of the mixture is charged, the internal temperature is raised to 75 ° C., and then the catalyst aqueous solution shown in the same column is added. Then, the first-stage emulsion polymerization is carried out while the polymerization is carried out for the time shown in the same column. Then, the monomer mixture and the aqueous catalyst solution shown in the column of <Second-stage emulsion polymerization> are added at a constant flow rate over the time shown in the same column. Then, the temperature is kept at 75 ° C. for 1 hour and then cooled. The polymer latex thus formed was adjusted to pH 7 with caustic soda, and then unreacted monomers were removed by a steam stripping method, followed by filtration through a 200-mesh filter cloth. In addition, all polymer latexes were adjusted so that the solid content concentration was finally 50%, and subjected to the following tests.

The particle size and gel fraction of these polymer latexes were measured by the following methods, and the results are shown in Table 1.

<Measurement of particle size> Light scattering particle size analyzer (Model 600 manufactured by C-Nwood Inc.)
The average particle diameter of the polymer latex was measured according to 0).

<Measurement of Gel Fraction> A polymer latex was uniformly coated on a polypropylene film using a No. 26 wire bar, and dried in a dryer at 50 ° C. for 1 hour to form a film.

Next, peel off this latex film and use an analytical balance to
0.5 g is precisely weighed, immersed in a container containing 300 cc of toluene, and stirred with a shaker at room temperature for 6 hours.
Then, the content was filtered through a 325 mesh wire mesh that had been precisely weighed in advance, and the residue remaining on the wire mesh was dried in a 50 ° C.
Let dry for hours. The gel fraction is calculated by the following equation.

(2) Examples and Comparative Examples The polymer latex prepared in (1) was evaluated for its performance as a paper coating binder. The coating composition was prepared by a high-speed stirrer with the amount shown in the second method and the amount of water at which the non-volatile content was 63%. The pH of the paint was adjusted to 9.0 with aqueous ammonia. Table 3 shows the conditions for preparing coated paper using this paint.

The blister resistance and pick strength (dry pick strength and wet pick strength) of the prepared coated paper were evaluated by the following methods.

Blister resistance: 0.3cc printing ink (Webb Zett yellow manufactured by Dai Nippon Ink Co., Ltd.) on both sides of coated paper using RI printing tester (manufactured by Akira Seisakusho)
Print solid. The printed coated paper is cut into an appropriate size, and the test piece is immersed in a silicone oil thermostat adjusted to a predetermined temperature to observe whether blisters are generated. This test is performed by changing the temperature of the thermostatic bath, and the lowest temperature at which blister generation is recognized is determined.
The higher the temperature, the better the blister resistance.

Dry pick strength: Printing ink (manufactured by Toka Pigment Co., Ltd.)
SD Super Deluxe 50 crimson B; tack value 18) Perform 0.4cc overprinting 5 times, backing the picking condition that appeared on the rubber roll on another mount, and observe the situation. The evaluation was performed by a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.

Wet pick strength: Using a RI printing tester, moisten the surface of the coated paper with a water-absorbing roll, and then print 0.4 cc of printing ink (SD Super Deluxe 50 red B, tack value 18) by 0.4 cc one time. The picking state that appears on the rubber roll is backed up by another backing, and the situation is observed. The evaluation was performed by a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.

Table 4 shows test results as examples, and Table 5 shows test results as comparative examples. According to this, it is understood that the coated paper using the latex of the present invention as a binder has a high balance between blister resistance and pick strength.

<Effect of the Invention> The binder for paper coating of the present invention is useful for producing coated paper having excellent ink pick resistance and blister resistance in offset printing.

Claims (1)

(57) [Claims] 1. A polymer latex synthesized from 25 to 50% by weight of butadiene, 1 to 8% by weight of an ethylenically unsaturated carboxylic acid and 42 to 74% by weight of another monomer copolymerizable therewith. A latex (A) having a polymer particle size of 600 to 1500 A ゜ and a gel fraction of a film formed from the latex of 40 to 95% by weight, butadiene 20 to 45% by weight, an ethylenically unsaturated carboxylic acid A polymer latex synthesized from 1 to 8% by weight and 47 to 79% by weight of another monomer copolymerizable therewith, wherein the polymer particle diameter is 1300 to 3500 A ゜ and formed from the latex. A latex (B) blended with a latex (B) having a gel fraction of 0 to 50% by weight, wherein the ratio of the particle diameter of the latex (A) to the particle diameter of the latex (B) is 0.8 or less; The mixing ratio of latex (A) is Paper coating binders, characterized in that in the range of 5 to 65 wt% as a percentage of the combined dry weight.