JP2009243004A - Copolymer latex for coating paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide copolymer latexes simultaneously improved in both blister resistance and adhesive strength of coated paper to a high level, having excellent wet stickiness and redispersibility of a composition for coating paper, and having sufficient suppressing effects on stains of backing rolls. <P>SOLUTION: The two kinds of copolymer latexes are obtained by carrying out emulsion polymerization of an aliphatic conjugated diene-based monomer, an ethylenically unsaturated acid monomer, vinyl cyanides, and other copolymerizable monomers, and regulating the latexes to different particle diameters and gel contents within specific ranges. A composition for the coated paper contains the copolymer latexes. When the composition for the coated paper containing the copolymer latexes is used, the coated paper having the excellent blister resistance, adhesive strength, and roll stain preventing performances is obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a paper coating copolymer latex used as a pigment binder in coated paper, and a paper coating composition containing the copolymer latex. More specifically, copolymer latex for paper coating, paper coating, which has both high adhesive strength (dry strength and wet strength) and coating operability, and excellent blister resistance and gloss performance of coated paper. The present invention relates to a coating composition and a coated paper for offset printing.

  Copolymer latex has been used in a wide range of applications such as pigment binders in coated paper, carpet backing agents, various adhesives and tackifiers, fiber binders and paints. Copolymer latex used for these applications is required to have excellent adhesion to substrates and pigments to be blended.

  Coated paper is used to improve the smoothness of the surface of the paper and improve the gloss and printability. The base paper contains inorganic pigments such as kaolin clay, calcium carbonate, satin white, talc, titanium oxide, and plastic pigments. An organic pigment is applied, and a diene copolymer latex is generally used as a binder for these pigments. It is known that the properties of the copolymer latex used as a pigment binder have a great influence on the surface strength of coated paper using this.

  In recent years, with the increasing demand for color-printed magazines, pamphlets, advertisements, etc., the printing speed has been increased, especially resistance to the destruction of the paper surface due to ink tack (so-called dry strength and wetness). (Strength) has been required to be improved. In addition, reducing the cost of products is one of the main issues for paper manufacturers that produce coated paper, and it is required to reduce the proportion of copolymer latex used. Improvement of the adhesive strength (dry strength and wet strength) is desired.

  Also, with the speeding up of the printing process, the use of offset rotary printing presses is remarkable. Compared with sheet-fed offset printing, this printing method requires high-temperature and high-speed drying immediately after printing, so it is necessary to prevent blistering caused by water evaporation in the paper during drying. For coated papers, blister resistance is one of the most important required properties. However, the blister resistance and the adhesive strength have a negative correlation, and it is increasingly important to sufficiently improve the balance between these properties.

  Conventionally, in order to overcome this problem, a method is known in which the gel content of a latex polymer to be produced is adjusted to 50 to 90% by a chain transfer agent used in the production of a copolymer latex (Patent Document 1). ).

  However, it is recognized that the adhesive strength of the coated paper is better as the gel content of the copolymer latex added as a binder is higher, whereas the blister resistance is better as the gel content is lower. Therefore, the technique is not sufficiently satisfactory as a means for simultaneously improving both the adhesive strength and the blister resistance to a high level.

  As a technique for improving blister resistance and adhesive strength, a method of blending copolymer latexes having different particle diameters and gel contents is disclosed (Patent Document 2). However, the above technique is not sufficient to satisfy the printing strength and the blister resistance.

  On the other hand, in the manufacture of coated paper, the coating liquid containing the copolymer latex as the main binder described above is applied to the base paper by the flooded nip roll or jet fountain method, and the excess coating liquid is applied by a blade or the like. It is a common method to scrape off, apply a predetermined amount of the coating liquid, and dry. Coated paper is often printed on both the front and back sides. For this reason, in the production of coated paper, after coating and drying on one side (front side) of the base paper, the other side (back side) is processed in the same way. .

  When weighing with this blade, the coated paper receives a high shear and pressure between the blade and the backing roll, and in particular, the surface of the coating layer on the front surface is transferred to the backing roll during backside coating. If the occurrence of stains becomes significant, it becomes necessary to perform roll cleaning by cutting out of the base paper or frequent polishing, thereby reducing productivity. In order to improve the coating operability, it is necessary to reduce the transfer of the coating composition once applied and dried to the roll, and it is useful to reduce the adhesiveness of the copolymer latex. (Patent Document 3).

  Further, as another idea for countermeasures against dirt on the backing roll, there is a method in which foreign matters once transferred to the backing roll are easily washed and removed with flow clean water. That is, it is also useful to improve the redispersibility of a paper coating composition in water (Patent Document 3).

  In order to solve the above-mentioned problem, a monomer composed of a specific amount of conjugated diene, ethylene monocarboxylic acid, ethylene dicarboxylic acid, and another copolymerizable monomer is divided into two or more specific processes. To obtain a copolymer (Patent Document 3).

  However, the method of Patent Document 3 does not have sufficient stickiness resistance and latex redispersibility.

JP-A-10-330408 JP-A-8-325994 JP 2002-234903 A

  The present invention improves both the blister resistance and adhesive strength of coated paper to a high level at the same time, and also has excellent wet stickiness and redispersibility when used as a paper coating composition, and sufficient backing roll dirt is obtained. It is an object of the present invention to provide a copolymer latex having an excellent suppressing effect.

  As a result of diligent research to solve these problems, the present inventors firstly made a copolymer because a small amount of washing water called flow clean water was continuously flowed over the roll on the backing roll. Regarding the stickiness of latex, it has been found that the improvement of stickiness through water, that is, the improvement of wet stickiness, is particularly effective. The higher the gel content, the better, but the lower the gel content, the better the blister resistance, which is negatively correlated. By mixing at a ratio, the composition for coated paper containing this improves both the blister resistance and the adhesive strength to a high level at the same time. Woody, found that excellent redispersibility of the paper coating composition can provide a copolymer latex having a sufficient effect of suppressing backing roll contamination, and have completed the present invention.

That is, the present invention is as follows.
[1] The following copolymer latex (A) and copolymer latex (B) are mixed at a solid content weight ratio of (A) / (B) = 25/75 to 5/95. A copolymer latex for paper coating.
Copolymer latex (A): A copolymer latex having an average particle size of 110 to 220 nm, a gel content of 40% or less, and a glass transition region temperature range of 10 to 45 ° C.
Copolymer latex (B): A copolymer latex having an average particle size of 120 nm or less and a gel content of 60% or more.
[2] The copolymer latex (A) is a copolymer latex obtained by emulsion polymerization so that the monomers (a) to (d) below are 100 parts by weight in total. Copolymer latex for paper coating as described in [1] characterized by the above-mentioned.
(A) Aliphatic conjugated diene monomer 20 to 50 parts by weight (b) Ethylene unsaturated acid monomer 0.5 to 10 parts by weight (c) Vinyl cyanides 5 to 30 parts by weight (d) Others Copolymerizable monomer 10-74.5 parts by weight [3] The copolymer latex for paper coating according to [2], wherein the (c) vinyl cyanide is acrylonitrile.
[4] The copolymer latex for paper coating according to [2] or [3], wherein the emulsion polymerization is performed by the following step (I) and step (II).
(I) Polymerization by adding a partial amount of monomer (a), a partial amount of monomer (c), a partial amount of monomer (d) and a total amount of monomer (b). (II) The monomer (a) residual amount, the monomer (c) residual amount, and the monomer (d) residual amount are added in one step or two or more steps and polymerized by continuous addition. Step [5] A paper coating composition comprising the copolymer latex for paper coating according to any one of [1] to [4].
[6] A coated paper for offset printing, wherein the paper coating composition according to [5] is coated on the surface of a base paper.

  According to the present invention, when coated on paper, a copolymer latex for paper coating capable of obtaining an excellent coated paper with good balance in all of blister resistance, adhesive strength and roll dirt prevention performance, A paper coating composition and an offset printing coated paper using the same are provided.

  Hereinafter, the present invention will be described in detail.

  The copolymer latex for paper coating of the present invention comprises a copolymer latex (A) and a copolymer latex (B) (A) / (B) = 25/75 to 5/95 as a solid content weight ratio. It is characterized by being mixed at a ratio.

  The copolymer latex (A) is a copolymer latex having an average particle size of 110 to 220 nm, a gel content of 40% or less, and a glass transition region temperature range of 10 to 45 ° C.

  The monomer constituting the copolymer is not particularly limited as long as the obtained copolymer latex (A) satisfies the above range, but in general, (a) an aliphatic conjugated diene monomer. Monomer, (b) ethylenically unsaturated acid monomer, (c) vinyl cyanides, and (d) other copolymerizable monomers.

  Examples of the (a) aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, and the like. , 3-butadiene is preferably used. The blending ratio of the monomer (a) is preferably 20 to 50 parts by weight, particularly 25 to 40 parts by weight, where the total amount of the monomers (a) to (d) is 100 parts by weight. preferable. If the amount used is less than the above range, sufficient adhesive strength may not be obtained, and if it is too large, water resistance, adhesive strength and roll dirt prevention performance may be deteriorated.

  (B) Examples of the ethylenically unsaturated acid monomer include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, and anhydrides thereof. ) Sulphonic acids such as methyl acrylate, ethyl (meth) acrylate, (meth) acrylic esters such as butyl (meth) acrylate, half esters, styrene sulfonic acid, 2-sulfoethyl acrylate, acrylamide propane sulfonic acid, etc. And group-containing unsaturated monomers and salts thereof. Of these, dicarboxylic acids and anhydrides thereof and (meth) acrylic acid esters such as methyl methacrylate are preferred. The blending ratio of the monomer (b) is preferably 0.5 to 10 parts by weight, preferably 3 to 7 parts by weight, where the total amount of the monomers (a) to (d) is 100 parts by weight. Is particularly preferred. When the amount used is outside the above range, the stability and adhesive strength of the copolymer latex are insufficient, and the viscosity or high shear viscosity of the copolymer latex and the coated paper composition containing the copolymer latex are high. The workability may be inferior.

  Examples of (c) vinyl cyanides include (meth) acrylonitrile and the like, and acrylonitrile is preferred in the present invention.

  The blending ratio of the monomer (c) is preferably 5 to 30 parts by weight, particularly 10 to 20 parts by weight, where the total amount of the monomers (a) to (d) is 100 parts by weight. preferable.

  (D) The other copolymerizable monomer means a monomer copolymerizable with at least one or two or more of the above-mentioned monomers (a), (b) and (c). Examples thereof include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene. Of these, styrene is preferably used as the aromatic vinyl monomer.

  Furthermore, (d) Other examples of copolymerizable monomers include (meth) acrylamide, N-methylol (meth) acrylamide and other ethylenically unsaturated carboxylic acid amides and N-substituted compounds thereof, (meth) acrylic acid Examples thereof include hydroxyl group-containing unsaturated monomers such as 2-hydroxyethyl, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, and vinyl esters such as vinyl acetate and vinyl propionate.

  The blending ratio of the monomer (d) is preferably 10 to 74.5 parts by weight, and 40 to 60 parts by weight, where the total amount of the monomers (a) to (d) is 100 parts by weight. Is particularly preferred.

  The blending ratio of the monomer (c) and the monomer (d) is 40 to 79.5 parts by weight with the total amount of the monomers (a) to (d) being 100 parts by weight. preferable. If the amount used is outside the above range, sufficient adhesive strength may not be obtained, and glossiness and ink drying properties may be insufficient.

  In the present invention, the method for producing the copolymer latex (A) is not particularly limited, but is preferably by emulsion polymerization. The monomer as a raw material is as described above. In the emulsion polymerization of the copolymer, for example, water, the respective monomers (a), (b), (c), (d), an emulsifier, and a polymerization initiator are added to an autoclave equipped with a stirrer and capable of adjusting the temperature. Can be done.

The addition of the monomer is preferably carried out in two or more steps. For example, it can be performed by the following two steps (I) and (II).
(I) Polymerization by adding a partial amount of monomer (a), a partial amount of monomer (c), a partial amount of monomer (d) and a total amount of monomer (b). (II) The monomer (a) residual amount, the monomer (c) residual amount, and the monomer (d) residual amount are added in one step or two or more steps and polymerized by continuous addition. Process

  In step (I) (first step), a partial amount of monomer (a), a partial amount of monomer (c), a partial amount of monomer (d), and a monomer ( The whole amount of b) is added all at once and a polymerization reaction is performed. In the first step, the monomers (a), (c) and (d) to be added are preferably 10% by weight to 20% by weight, particularly preferably 14% by weight to 16% by weight, based on the total amount added in all steps. %. When using 2 or more types of each monomer, it is good also as an addition rate which changes with each monomer. The reaction temperature is preferably 55 ° C to 65 ° C, particularly preferably 59 ° C to 61 ° C.

In the subsequent step (II) (second step), the remaining monomer (a), monomer (c) and monomer (d) which were not added in the first step are used with a pump or the like. The polymerization reaction is continuously added. The reaction temperature is preferably 5 to 20 ° C., more preferably 5 to 15 ° C. (about 10 ° C.) higher than in step (I). The continuous addition time is preferably 4 to 6 hours, and particularly preferably around 5 hours. If the time for continuous addition is too short, the structure of the latex particles is close to that of the batch addition, which is not preferable.
In the present invention, by making the polymerization reaction into two stages as described above, the core part of the latex particles can be made in the first step, and the monomer can be added little by little to the outside of the core part in the second step. The particles are presumed to have a soft core hard shell structure.

  In step (II), a predetermined amount of each monomer may be continuously added in one step, or may be divided into two or more steps. Moreover, when dividing | segmenting into two or more steps, you may change the addition amount of a monomer (c) by the process of the first half of continuous addition, and the process of the second half. When the step (II) is divided into two steps, the monomer (a) and the monomer (d) are added to the total amount of the first half of the step (I) and the step (II) and the step (II). Can be added so that the addition amount in the second half of the second step is equal), but the addition ratio is [step (I) + first half of step (II)] / [second half of step (II)] = 40/60 It is preferable that

  On the other hand, when the step of continuously adding the monomer (c), that is, when the step (II) is divided into two stages, the preferable addition amount of the monomer (c) is as follows.

  First, (the first half of the first step (collective addition) and the second step (continuous addition)) / second half of the second step (continuous addition) = 100/0 to 50/50 is preferable, and particularly preferably, the first half / second half = 95/5 to 85/15.

Moreover, the addition ratio in the first half of the first step (collective addition step) and the second step (continuous addition) of the monomer (c) is the second step with respect to the addition amount of 10/50 to 20/50 in the first step. The addition amount in the first half is preferably in the range of 30/50 to 40/50. In particular, the first step is 15/50 and the first half of the second step is most preferably 35/50. For example, the addition ratio of the first step and the first half of the second step are 15/50 and 35/50, and (the first half of the first step (collective addition) and the second step (continuous addition)) / second When the latter half of the step (continuous addition) = 95/5, the addition ratio in each step relative to the total amount of the monomer (c) added is calculated by the following equation.
(Formula 1-1) Addition rate x (%) in the first step (collective addition) = 95 × 15/50
(Formula 1-2) Addition rate y (%) in the first half of the second step (continuous addition) = 95 × 35/50
(Formula 1-3) Addition rate z (%) in the latter half of the second step (continuous addition) = 100− (x + y)

  In step (II), the continuous addition of the monomer (c) is divided into at least two steps, whereby the core-shell structure of the copolymer latex (A) is gradually increased from the outside toward the inside (core portion) of the latex particles. It is assumed that a continuous different layer type structure that becomes soft can be obtained. It is assumed that the continuous heterophasic structure makes it easy to absorb external impacts and suppresses a decrease in strength. Therefore, in the present invention, a method of continuously adding the monomer (c) in two stages is more preferable.

  As the polymerization initiator used for the emulsion copolymerization of the copolymer latex (A) in the present invention, persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate, water-soluble initiators such as hydrogen peroxide, Alternatively, a redox initiator in which these are combined with a reducing agent such as sodium bisulfite or amines is suitable, and an oil-soluble initiator such as a water-soluble azo initiator, benzoyl peroxide, or azobisisobutyronitrile. Etc. can also be used. Moreover, in order to adjust a polymerization state, a polymerization inhibitor can also be used.

  Moreover, an emulsifier can be used in order to give sufficient stability to copolymer latex while adjusting the particle diameter of the copolymer latex (A) to produce | generate at the time of emulsion copolymerization. Examples of emulsifiers used include sulfuric acid esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, anionic surfactants such as alkyl diphenyl ether (di) sulfonates, polyethylene glycol alkyl ester types, alkyls Nonionic surfactants such as phenyl ether type and alkyl ether type, and amphoteric surfactants such as betaine type are used alone or in combination of two or more. The amount of the emulsifier is usually 0.1 to 1.0 parts by weight, particularly 0.2 to 0.8 parts by weight, preferably 0.2 to 0.6 parts by weight based on 100 parts by weight of each monomer. It can be determined in the range of parts by weight. In order to increase the average particle size of the copolymer latex, it is preferable to reduce the amount of the emulsifier, for example, 0.2 to 0.5 parts by weight, preferably 0.2 to 0.4 parts by weight. . On the other hand, in order to reduce the average particle size of the copolymer latex, it is preferable to increase the emulsifier, for example, 0.5 to 1.0 part by weight, preferably 0.6 to 0.8 part by weight. Can do. In addition, the addition time of the emulsifier in the production of the copolymer latex (A) is preferably at the start of the polymerization, and the addition of the emulsifier in the emulsion polymerization in the case where the above-described monomer is added in a divided manner is also a batch addition in the step (I). Is preferred.

  Examples of the chain transfer agent used for the production of the copolymer latex (A) of the present invention include sulfur such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, mercaptoethanol, mercaptopropionic acid and esters thereof. Chain transfer agents generally used for adjusting the molecular weight in emulsion copolymerization reactions such as element-containing compounds, sulfides such as tetraethylthiuram sulfide, alkyl halides such as carbon tetrachloride, terpenoids such as terpinolene, α-methylstyrene dimer, etc. Can be used alone or as a mixture of two or more. The chain transfer agent is preferably added at the start of polymerization in the production of the copolymer latex (A), and the addition of the chain transfer agent in the emulsion polymerization in the case where the above-described monomer is added in a divided manner is carried out by the monomer ( It is preferable to add by adding together with a), (c) and (d). About the addition ratio at the time of carrying out divided addition, process (I) / process (II) = 10-20 / 80-90 is preferable, and 14-16 / 84-86 is more preferable. Furthermore, when performing process (II) by dividing into two or more steps, for example, the addition amount in process (II) is preferably 30-50 / 50-70 in the first half / second half, and more preferably 35-45 / 55-65. . The addition amount of the chain transfer agent can be generally determined in the range of 0.5 to 4.0 parts by weight, preferably 1.0 to 3.0 parts by weight with respect to 100 parts in total of each monomer.

  The average particle diameter of the copolymer latex (A) of the present invention is 110 nm to 220 nm, preferably 130 to 210 nm. The average particle diameter can be adjusted depending on the amount and type of emulsifier. In order to make a particle diameter into said range, what is necessary is just to add 0.2-1.0 part of emulsifiers with respect to a total of 100 parts of each monomer, for example.

  The gel content of the copolymer latex (A) of the present invention is 40% or less, preferably 20% or less. The lower limit is not particularly defined, but is usually 10% or more. The gel content is calculated by the following (Formula 2), and the measurement method will be described later. The gel content can be controlled by a known method such as changing the amount or type of the chain transfer agent. For example, by increasing the chain transfer agent described above, it is possible to make adjustments such as lowering the gel content.

  The temperature range of the glass transition region of the copolymer latex (A) of the present invention is preferably 10 to 45 ° C, particularly preferably 20 to 40 ° C. The temperature range of the glass transition region in the present invention refers to a temperature difference from the glass transition start point to the glass transition end point.

  Our research has shown that the particle structure of the copolymer latex has an effect on the printing strength. To add strength to the copolymer latex itself, the particle structure mitigates external impacts. It has been found that by changing to a structure that can be applied, strength is imparted to the latex itself and a decrease in printing strength can be suppressed. That is, it has been found that a soft core hard shell structure in which the inside of the latex particles is soft and the outside is hard, or a continuous different layer structure in which the latex particles gradually soften from the outside toward the inside (core portion) of the latex particles is suitable. In particular, in the present invention, a particle structure having a continuous heterogeneous structure is preferable because it can absorb impact well and increase strength. And in order to make such a structure, what is necessary is just to make the temperature range of a glass transition area | region into 10-45 degreeC. When the temperature range of the glass transition region is in a range other than 10 to 45 ° C., the blister resistance and adhesive strength of the coated paper composition are low.

  Examples of the copolymer latex (B) include copolymer latex having an average particle size of 120 nm or less and a gel content of 60% or more.

  The copolymer monomer is not particularly limited as long as it satisfies the above range, but generally, the same monomer as the copolymer latex (A) of the present invention can be used. That is, (a) an aliphatic conjugated diene monomer, (b) an ethylenically unsaturated acid monomer, (c) vinyl cyanides, (d) other copolymerizable monomers as monomers It is preferable to use it. Specific examples of the monomers (a) to (d) are as already described for the copolymer latex (A). Moreover, it is preferable that the addition amount of a monomer (a) is 20-50 weight part, and it is especially preferable that it is 25-40 weight part. The addition amount of the monomer (b) is preferably 0.5 to 10 parts by weight, and particularly preferably 3 to 7 parts by weight. The addition amount of the monomer (c) is preferably 5 to 30 parts by weight, and particularly preferably 10 to 20 parts by weight. The addition amount of the monomer (d) is preferably 10 to 74.5 parts by weight, and particularly preferably 40 to 60 parts by weight. In addition, said addition amount is represented when the sum total of four monomers is 100 weight part.

  The copolymer latex (B) is preferably produced by emulsion polymerization. When the above monomers (a) to (d) are used, they can be added all at once or by divided addition. . In the case of emulsion polymerization by divided addition, it is preferable to proceed the polymerization in two steps (I) and (II) similar to those in the production of the copolymer latex (A). The emulsifier and the polymerization initiator that can be added in the emulsion polymerization are the same as those of the copolymer latex (A). The amount of the emulsifier added is preferably 0.5 to 2.0 parts by weight and more preferably 0.6 to 1.2 parts by weight when the total amount of the monomers is 100 parts by weight. The addition amount of the polymerization initiator is preferably 0.5 to 1.5 parts by weight, and preferably 0.8 to 1.2 parts by weight.

  In the present invention, the average particle size of the copolymer latex (B) is preferably 120 nm or less, particularly preferably 110 nm or less. Although a minimum is not specifically limited, It is preferable that it is 50 nm or more. The average particle diameter can be adjusted by adjusting the amount of the emulsifier added in the same manner as the copolymer latex (A) of the present invention. In order to make a particle diameter into said range, what is necessary is just to add an emulsifier 0.6 parts or more with respect to a total of 100 parts of each monomer, for example.

  In the present invention, the copolymer latex (B) has a gel content of 60% or more, preferably 70% or more. The upper limit is not particularly specified, but is usually 95% or less. The gel content is calculated by the above (Formula 2), and the gel content can be controlled by a known method such as changing the amount or type of the chain transfer agent. For example, by increasing the chain transfer agent described above, it is possible to make adjustments such as lowering the gel content.

  In the present invention, the average particle diameter of the copolymer latex (A) and (B) is within the above range, that is, the average particle diameter DA (nm) of (A) and the average particle diameter DB (nm) of (B). 110 ≦ DA ≦ 220 and DB ≦ 120 are preferably satisfied. If this relationship is not satisfied, problems such as insufficient blister resistance and adhesive strength of the coated paper composition may occur.

  In the present invention, the gel contents GA (%) and GB (%) of the copolymer latexes (A) and (B) preferably satisfy the relationship of GA ≦ 40 and GB ≧ 60. Outside the above range, roll dirt prevention performance may be deteriorated, and problems such as insufficient blister resistance and adhesive strength of the coated paper composition may occur.

  In the present invention, the mixing ratio of the copolymer latex (A) and (B) is preferably in the range of (A) / (B) = 25/75 to 5/95 in terms of the solid content weight ratio, A range of 80 to 10/90 is particularly preferable. Outside the above range, roll dirt prevention performance may be deteriorated, and problems such as insufficient blister resistance and adhesive strength of the coated paper composition may occur.

  The copolymer latex of the present invention can be used as a paper coating latex and can be used as a paper coating composition. In the case of a paper coating composition, other additives can be appropriately added in addition to the paper coating latex of the present invention. For example, as pigments, kaolin, clay, calcium carbonate, satin white, inorganic pigments such as titanium oxide, aluminum hydroxide, barium sulfate, and zinc oxide, and organic pigments such as polystyrene, SBR, and phenol resin can be used alone or in combination of two or more. Can be used. Other dispersants, water resistance agents, viscosity modifiers, antifoaming agents, water retention agents, dyes, fluorescent dyes, lubricants, pH regulators, surfactants, preservatives, other auxiliaries, additives, etc. as required Can be added.

  In addition, as a binder in the paper coating composition of the present invention, if necessary, a water-soluble polymer such as starch, casein or polyvinyl alcohol, or a latex such as polyvinyl acetate or an acrylate copolymer may be used in combination. Can do.

  Although the content rate of the copolymer latex for paper coating in the paper coating composition of this invention is not specifically limited, It is suitably in the range of 5-30 weight part (solid content) normally with respect to a pigment (solid content). Can be determined.

  The paper coating composition of the present invention can be applied to the surface of a base paper and used as a coated paper for offset printing.

In the present invention, normal pulp, filler and the like are blended in the base paper for coating.
In the present invention, the type of pulp blended into the base paper is not particularly limited. For example, hardwood kraft pulp (hereinafter referred to as LBKP), softwood kraft pulp (hereinafter referred to as NBKP), thermomechanical pulp, groundwood pulp, waste paper pulp and the like are used. Further, as fillers to be blended in the base paper, known fillers such as heavy calcium carbonate, light calcium carbonate, kaolin, clay, talc, hydrated silicic acid, white carbon, titanium oxide, synthetic resin filler, etc. can be used. . These fillers may be used alone or in admixture of two or more for the purpose of adjusting papermaking suitability and strength characteristics of the paper stock slurry. The amount of filler used is preferably 3 to 20% by weight based on the pulp weight. Further, if necessary, a sulfuric acid band, a sizing agent, a paper strength enhancer, a yield improver, a color pigment, a dye, an antifoaming agent, and the like may be contained.

  There is no particular limitation on the paper making method of the base paper, and the base paper made by an acid paper making machine, a neutral paper making method, or an alkaline paper making method using a gap former machine, a long net machine including a top wire, or a round netting machine. Of course, medium base paper including mechanical pulp can also be used. Further, if necessary, the base paper can be subjected to a smoothing process such as a super calendar or a soft calendar in advance. Further, a base paper preliminarily coated with starch, polyvinyl alcohol or the like using a size press, a gate roll coater, a bill blade or the like can also be used.

As the base paper, a coated base paper having a basis weight of about 25 to 400 g / m ² used for general coated paper can be used, but a base paper having a basis weight of 30 to 100 g / m ² is preferable. .

In the present invention, for the purpose of improving the surface strength, a surface treatment agent mainly composed of starch may be applied to the coated base paper. As the starch, those usually used as a surface treating agent such as oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch and the like can be used alone or a mixture thereof. The coating amount of starch is preferably 0.2 to 2.5 g / m ² , more preferably 0.3 to 2.0 g / m ² . In addition to starch, a paper strength enhancer for the purpose of water resistance and surface strength improvement and an external sizing agent for the purpose of imparting size can be added to the surface treatment agent. The surface treatment agent can be applied by a coating machine such as a two-roll size press coater, a film transfer type roll coater such as a gate roll coater, a blade metering size press coater, and a rod metalling size press coater. The coating machine is preferably a film transfer type roll coater such as a gate roll coater. When coated with a film transfer type roll coater, the surface treatment agent tends to stay on the paper surface compared to a two-roll size press coater, resulting in a coated paper having a high surface strength with a low coating amount. By lowering, the strength reduction of the folded portion becomes smaller.

  The pigment contained in the coating layer is not particularly limited, and conventionally used for coated paper, kaolin, clay, delaminated clay, heavy calcium carbonate, light calcium carbonate, Select one or more inorganic pigments such as talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin white, and organic pigments such as plastic pigment as required. Can be used.

  In addition, if necessary as a auxiliaries, it is possible to apply ordinary coatings such as dispersants, thickeners, water retention agents, antifoaming agents, colorants, mold release agents, flow modifiers, water resistance agents, preservatives, and printability improvers. Various auxiliaries blended in the coating composition for industrial paper are appropriately used.

As a method for coating the prepared coating composition on the base paper, a two-roll size press coater, a gate roll coater, a blade metalling size press coater, a rod metalling size press coater, a shim sizer, a JF sizer, etc. In addition to film transfer type roll coater, flooded nip / blade coater, jet fountain / blade coater, short dwell time application type coater, rod metering coater using grooved rod, plain rod etc. instead of blade, It can coat with well-known coaters, such as an air knife coater, a curtain coater, or a die coater. The coating amount is preferably 5 to 30 g / m ² , more preferably 15 to 25 g / m ² per side of the base paper. The coating layer can be multi-layered by providing one layer or two or more layers as required. In addition, when making it into a multilayer, each coating liquid does not need to be the same composition, and is not specifically limited. In addition, in order to improve white paper gloss, smoothness, and print gloss, surface treatment such as smoothing the dried coated paper is performed. As the surface treatment method, a known surface treatment apparatus such as a super calender using a cotton roll as an elastic roll, a soft nip calender using a synthetic resin roll as an elastic roll, or brushing can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.

[Production Example 1 to Production Example 4] Production of copolymer latex a-1 to a-4 by two-step reaction In the first step, water and an emulsifier capable of adjusting the temperature, water, and dodecylbenzenesulfone as an emulsifier Sodium sulfate, t-dodecyl mercaptan as a chain transfer agent, potassium persulfate as a polymerization initiator, and monomers are added together at a ratio shown in Table 1, and after carrying out a polymerization reaction at 60 ° C. for 1 hour, As a process, after the temperature was raised to 70 ° C., the remaining monomer was continuously added using a pump at a pump flow rate of 2.9 ml / min until all the monomers were added (5 Time), the polymerization reaction was carried out. Table 1 shows the composition and physical property evaluation results of copolymer latex a-1 to a-4.

[Production Example 5 to Production Example 7] Production of Copolymers a-5 to a-7 by Three-Step Reaction In the first step, water and dodecylbenzenesulfonic acid as an emulsifier in an autoclave equipped with a stirrer and adjustable in temperature Sodium, t-dodecyl mercaptan as a chain transfer agent, potassium persulfate as a polymerization initiator, each monomer are added together at a ratio shown in Table 2, and a polymerization reaction is performed at 60 ° C. for 1 hour, followed by a second step. As shown in Table 2, after the temperature was raised to 70 ° C., the monomer was continuously added at a pump flow rate of 2.9 ml / min at the rate shown in Table 2 until all the monomers had been added. (2 hours), the polymerization reaction was carried out. Thereafter, as a third step, the remaining monomer is continuously added using a pump at a pump flow rate of 2.9 ml / min until polymerization is completed (3 hours). Reaction was performed. Table 2 shows the composition and physical property evaluation results of copolymer latex a-5 to a-7.

[Production Example 8 to Production Example 10] Production of copolymer latex a-8 to a-10 by a two-stage reaction In the first step, water and dodecylbenzenesulfone as an emulsifier were provided in an autoclave equipped with a stirrer and adjustable in temperature. After adding sodium acetate, t-dodecyl mercaptan as a chain transfer agent, and potassium persulfate as a polymerization initiator at a ratio shown in Table 3 and carrying out a polymerization reaction at 60 ° C. for 1 hour, As a process, after the temperature was raised to 70 ° C., the remaining monomer was continuously added using a pump at a pump flow rate of 2.9 ml / min until all the monomers were added (5 Time), the polymerization reaction was carried out. Table 3 shows the composition and physical property evaluation results of copolymer latex a-8 to a-10.

[Production Example 11] Production of copolymer latex a-11 by a three-step reaction In the first step, water, sodium dodecylbenzenesulfonate as an emulsifier, and t as a chain transfer agent were provided in an autoclave equipped with a stirrer and adjustable in temperature. -Dodecyl mercaptan, potassium persulfate as a polymerization initiator, and monomers were added together at the ratios shown in Table 3, and after performing a polymerization reaction at 60 ° C for 1 hour, the temperature was raised to 70 ° C as the second step. Thereafter, the monomer was continuously added at a pump flow rate of 2.9 ml / min using the pump at the rate shown in Table 2 until the addition of all the monomers was completed (2 hours). Went. Thereafter, as a third step, the remaining amount of the monomer (c) is continuously added at a pump flow rate of 2.9 ml / min using a pump, until the addition is completed (3 hours). Went. Table 3 shows the composition and physical property evaluation results of copolymer latex a-11.

[Production Example 12] Production of copolymer latex b-1 by two-stage reaction In the first step, water, sodium dodecylbenzenesulfonate as an emulsifier, t as a chain transfer agent in an autoclave equipped with a stirrer and adjustable in temperature. -Dodecyl mercaptan, potassium persulfate as a polymerization initiator, and monomers were added together at the ratios shown in Table 4 and the polymerization reaction was performed at 60 ° C for 1 hour, and then the temperature was raised to 70 ° C as the second step. Thereafter, the remaining monomer was continuously added at a pump flow rate of 2.9 ml / min using a pump, and the polymerization reaction was carried out until all the monomers had been added (5 hours). . Table 4 shows the composition and physical property evaluation results of copolymer latex b-1.

  In addition, physical property evaluation of each copolymer latex shown in Tables 1-4 was performed as follows.

[1. Particle size]
The average particle size was measured with a light scattering particle size distribution meter (Zeta Sizer 3000HSA (manufactured by MALNERN)).

[2. Gel content]
The copolymer latex is dried at 100 ° C. in a dryer to produce a latex film. Thereafter, 1.0 gram of latex film was accurately weighed, placed in 100 cc of toluene, dissolved for 24 hours, filtered, dried, measured for toluene insoluble matter (gel), and the gel content was calculated based on the formula (2). To do.

[3. Glass-transition temperature]
The copolymer latex was dried at 100 ° C. in a dryer to prepare a latex film, and this film was heated at a rate of temperature increase of 30 ° C./min using a differential scanning calorimeter (DSC-6200 manufactured by Seiko Instruments Inc.). Measured with The glass transition temperature was defined as the glass transition temperature based on the DSC curve peak position obtained by differentiating the DSC curve with temperature.

[4. Glass transition region temperature range]
The temperature difference from the glass transition start point to the glass transition end point is calculated by the following formula from a chart obtained using a differential scanning calorimeter (DSC-6200 manufactured by Seiko Instruments Inc.). (Corresponding to the area of the arrow in FIG. 1)

(Formula 3) Glass transition region temperature range (° C.) = Glass transition end point−glass transition start point FIG. 1 shows the glass transition temperature and glass transition region of copolymer a-5.

[Example 1-8, Comparative Example 1-5]
Copolymers a-1 to a-11 and b-1 produced in Production Examples were blended in the proportions shown in Tables 5 and 6, and performance evaluation of the resulting copolymer latex was performed. The results of performance evaluation are shown in Tables 5 and 6.

  The formulation of the coating solution used for performance evaluation is as follows.

(Formulation of coating liquid)
Kaolin clay 70 parts by weight Heavy calcium carbonate 30 parts by weight Dispersant 0.3 parts by weight NaOH 0.1 part by weight Oxidized starch 3 parts by weight Copolymer latex 12 parts by weight Coating solution concentration 65%

  The physical properties of each copolymer latex shown in Tables 5 and 6 were evaluated as follows.

[1. Redispersibility]
Using a Meyer bar on a rubber plate, applying a copolymer latex, drying at 80 ° C. for 30 seconds in a dryer, and then lightly rubbing it on water, the ease of falling off the coating layer of the latex film is double circle, ○, △ , X is evaluated in 4 stages. It is an index of the ease of cleaning the coating layer taken on the backing roll surface.

[2. Wet stickiness]
Use a Meyer bar on the OHP sheet, apply a copolymer latex, dry it at 130 ° C in a dryer, and then overlay it with wet black Kent paper and pass it through a 60 ° C calendar roll to take the film onto the black Kent paper. The method of evaluation is evaluated in four stages: double circle, ○, Δ, and ×. It is an index of the adhesion between the coating layer and the backing roll.

[3. Dry strength]
The coating solution was applied with a double-sided blade so that the basis weight was 30 g / m ^2, and was conditioned for 12 hours in a constant temperature and humidity chamber at 23 ° C. and 50% RH. This was passed through a super calender twice on each side under conditions of a roll temperature of 50 ° C. and a linear pressure of 147000 N / m to obtain a sample of coated paper.

  The coated paper is printed using an RI-II type printing machine (Made Seisakusho) and a picking test ink (TV-24) manufactured by Tokyo Ink Co., Ltd., and the degree of picking on the printed surface is visually 1 ( Evaluation is made in 5 stages, from inferior to 5 (excellent). If the evaluation is 3 or more, there is no practical problem.

[4. Wet strength]
Using the RI-I type printing machine (Meiji Seisakusho) and Tokyo Ink Co., Ltd. picking test ink (TV-24), the coated sample was wetted with water. Printing is performed, and the degree of picking of the printed surface is visually evaluated in five stages from 1 (poor) to 5 (excellent). If the evaluation is 3 or more, there is no practical problem.

[5. Blister resistance]
Printing on both sides of the test piece using the RI-II printing machine (Made Seisakusho) and offset printing ink (trade name TK High Unity SOY617 Black MZ) manufactured by Toyo Ink Co., Ltd. Went. The test specimen after printing was conditioned in a temperature-controlled room (20 ° C., 50% RH) for 24 hours, and then heated with hot air from a variable output heating gun for 3 seconds to determine the lowest temperature of the hot air generated by the blister. .

[6. Ink drying property]
The coated paper prepared in step 3 is printed on a test piece using an RI-II type printing machine (Made Seisakusho) and offset printing ink (trade name TK High Unity SOY617 Black MZ) manufactured by Toyo Ink Co., Ltd. After 1 minute, transfer was performed on transfer paper, and the drying property of the ink was measured with a whiteness meter. Here, the lower the value of the ink drying property, the faster the ink drying property.

  The copolymer latex obtained in Examples 1 to 8 has higher blister resistance and adhesive strength than those of Comparative Examples 1 to 5, and further has excellent wet stickiness and redispersibility. I can confirm that.

  In particular, from Examples 5 to 6 and 8, if the temperature range of the glass transition temperature of the copolymer latex (A) is 20 ° C. to 40 ° C., it has higher blister resistance and adhesive strength. I can confirm.

  From Comparative Example 2, when the mixing ratio of the copolymer latex (A) exceeds 30%, the wet stickiness decreases. From Comparative Example 3, when the gel content of the copolymer latex (A) exceeds 40%, the wet strength decreases. From the comparative example 4, when the particle diameter of copolymer latex (A) is too small, blister resistance will fall. From Comparative Example 5, when the particle size of the copolymer latex (A) is too large, the dry strength and the wet strength are lowered.

It is a graph which shows an example of the glass transition temperature and glass transition area | region of copolymer latex (A).

Claims (6)

The following copolymer latex (A) and copolymer latex (B) are mixed at a solid content weight ratio of (A) / (B) = 25/75 to 5/95. Copolymer latex for paper coating.
Copolymer latex (A): A copolymer latex having an average particle size of 110 to 220 nm, a gel content of 40% or less, and a glass transition region temperature range of 10 to 45 ° C.
Copolymer latex (B): A copolymer latex having an average particle size of 120 nm or less and a gel content of 60% or more. The copolymer latex (A) is a copolymer latex obtained by emulsion polymerization so that the monomers consisting of the following (a) to (d) become 100 parts by weight in total. The copolymer latex for paper coating according to claim 1.
(A) Aliphatic conjugated diene monomer 20 to 50 parts by weight (b) Ethylene unsaturated acid monomer 0.5 to 10 parts by weight (c) Vinyl cyanides 5 to 30 parts by weight (d) Others 10-74.5 parts by weight of copolymerizable monomer   The copolymer latex for paper coating according to claim 2, wherein the vinyl cyanide (c) is acrylonitrile. The copolymer latex for paper coating according to claim 2 or 3, wherein the emulsion polymerization is performed by the following step (I) and step (II).
(I) Polymerization by adding a partial amount of monomer (a), a partial amount of monomer (c), a partial amount of monomer (d) and a total amount of monomer (b). (II) The monomer (a) residual amount, the monomer (c) residual amount, and the monomer (d) residual amount are added in one step or two or more steps and polymerized by continuous addition. Process   A composition for paper coating, comprising the copolymer latex for paper coating according to any one of claims 1 to 4.   A coated paper for offset printing, wherein the paper coating composition according to claim 5 is coated on the surface of a base paper.

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