JP2005194429A - Method for producing copolymer latex - Google Patents

Abstract

An object of the present invention is to provide a copolymer latex excellent in physical properties of coated paper such as pick strength, and also excellent in operability in the production process of the coated paper, and a composition for paper coating.
A first step (A) for emulsion polymerization of a monomer having a specific composition and a second step (B) for removing unreacted monomers by blowing water vapor, the second step (B) A specific chain transfer agent is added at a specific polymerization temperature before starting.
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Description

  The present invention relates to a method for producing a copolymer latex used in a pigment binder for coated paper, a carpet backing sizing agent, an adhesive, a pressure-sensitive adhesive, a fiber binder, a paint, and the like. Among these, a copolymer latex that is particularly suitable for paper coating and has a high balance of adhesive strength, blister resistance and coating operability in coated paper for offset printing, its production method and The present invention relates to a paper coating composition using a combined latex.

Conjugated diene copolymer latexes have been used in a wide range of applications such as pigment binders in paper coating, carpet backing agents, various adhesives and tackifiers, fiber binders and paints. The copolymer latex used for these uses is required to have excellent adhesion to water and water resistance with respect to the substrate and the pigment to be blended.
Paper coating is intended to increase the smoothness of the surface of the paper that has been made, and to improve gloss and printability. For example, kaolin clay, calcium carbonate, satin white, talc, titanium oxide and other inorganic pigments and plastic pigments are used as the base paper. A diene copolymer latex is generally used as a binder for these pigments. It is known that the properties of copolymer latex used as a pigment binder have a great influence not only on the surface strength of paper but also on the printability of coated paper.

  In recent years, with 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 pick strength) Improvement of adhesive strength such as pick strength (wet pick strength) when fountain solution is applied has been required more than before. In addition, since the drying conditions of the ink have become stricter with this, the resistance to the so-called blistering that causes blistering on the surface of the coated paper due to the vapor pressure when the water remaining inside the coated paper evaporates. The demand for (blister resistance) is also increasing.

  Improvement in pick strength and improvement in wet pick strength and blister resistance are generally contradictory properties, and there is a relationship that when one improves, the other decreases. Known methods for improving the blister resistance include lowering the toluene insoluble content of the copolymer latex, increasing the particle size, and increasing the glass transition temperature to improve the air permeability of the coating layer. However, in this case, it is known that not only the pick strength is lowered but also the printing gloss is lowered, and coating operability problems such as occurrence of a backing roll stain during the production of coated paper are also caused. Therefore, it is required to balance these physical properties to a high degree.

  On the other hand, in the production of coated paper, which is printing paper, the coating speed has been increased in order to improve production capacity and productivity. In coating liquids mainly composed of pigments, copolymer latex, and water-soluble polymers such as starch and casein, high solid differentiation is required in order to cope with the decrease in drying capacity accompanying higher speed coating. Yes. In order to improve the decrease in fluidity due to high solidification of the coating liquid, the amount of calcium carbonate is increased, and the amount of water-soluble binder with high viscosity such as starch is reduced. Investigations from the binder side, such as increasing latex, are being conducted. However, there is a problem that the gloss of the coated paper decreases when the blending ratio of calcium carbonate is increased, and when the blending amount of the copolymer latex is increased, the stickiness of the coated paper surface increases, and a backing roll or calendar roll It becomes easy to generate operational problems such as dirt.

  Due to the problems relating to the quality of coated paper and the production of coated paper as described above, various improvements have been made to copolymer latex. For example, the proportion of the insoluble portion of the copolymer latex film with respect to solvents such as benzene, toluene and tetrahydrofuran, the so-called gel fraction, has been confirmed to be the controlling factor for pick strength and blister resistance. Various studies have been made on the surface. Specifically, it has been proposed to exhibit excellent performance by adjusting the composition and gel fraction of the copolymer in the latex to a specific range (see, for example, Patent Documents 1 to 3).

The latex gel fraction varies depending on various polymerization factors such as the monomer composition and polymerization temperature, and a method for adjusting this to a desired level is generally simple and easy to add a chain transfer agent. As chain transfer agents, carbon tetrachloride, alkyl mercaptans represented by t- or n-dodecyl mercaptan, sulfides and the like have been used. However, in general, the pick strength of the coated paper is the highest in the range of 75 to 95% by weight of the gel fraction in the SB latex, whereas the blister resistance is better as the gel fraction is lower. It is recognized that it is difficult to simultaneously improve both pick strength and blister resistance to a high level. In addition, when the gel fraction is set low for the purpose of improving the blister resistance, the sticking resistance deteriorates, and therefore a problem of backing roll contamination also occurs.
It has also been proposed to use terpinolene, α-methylstyrene dimer or the like as a specific chain transfer agent. However, none of them is sufficiently satisfactory (for example, see Patent Documents 4 to 5).

  As for the chain transfer agent addition method, a production method for specifying the continuous sequential addition amount of t-dodecyl mercaptan where the polymerization conversion rate of the monomer is high, and t-dodecyl until the polymerization conversion rate of the monomer reaches a certain level or more. Manufacturing method in which mercaptan is added sequentially, manufacturing method in which specific chain transfer agent α-methylstyrene dimer is combined with other chain transfer agent and added continuously until the polymerization conversion rate of the monomer reaches a certain level or more, single amount Copolymer latex produced by a method in which the addition rate of α-methylstyrene dimer is discontinuously increased during the addition of the body has been studied. However, in all cases, the temperature at the time of addition of the chain transfer agent described in the Examples is high and the blister resistance performance cannot be sufficiently satisfied (for example, see Patent Documents 6 to 9).

  Further, a copolymer latex produced by a method characterized by defining the reaction rate of α-methylstyrene dimer during emulsion polymerization, α-methylstyrene dimer after removing unreacted monomers by blowing water vapor A copolymer latex with a defined residual amount has also been proposed, but since α-methylstyrene dimer is added together with the monomer, the latex produced by these methods has high pick strength and blister resistance. In addition, the improvement in the balance of roll stain resistance was insufficient (see, for example, Patent Documents 10 to 11).

Japanese Patent Publication No.59-3598 Japanese Patent Publication No. 60-17879 JP 58-44894 A U.S. Pat. No. 2,922,781 Japanese Patent Laid-Open No. 3-109451 Japanese Patent No. 2933984 Japanese Patent No. 2615249 Japanese Patent No. 3169638 JP-A-10-36414 Japanese Patent Laid-Open No. 11-80278 Japanese Patent Laid-Open No. 13-11244

  The present invention relates to a diene copolymer having a high balance of pick strength, wet pick strength and blister resistance of coated paper, and excellent performance in roll stain resistance in the coated paper manufacturing process. It is an object of the present invention to provide a latex, a method for producing the latex, and a paper coating composition using the copolymer latex.

The inventors of the present invention have made extensive studies to solve the above problems, and first process (A) for emulsion polymerization of a monomer having a specific composition and second process for removing unreacted monomer by blowing water vapor. (B) and adding the α-methylstyrene dimer at the time of polymerization temperature of 70 ° C. or less before the start of the second step (B), the above object can be achieved. As a result, the inventors have made the present invention.
That is, the first of the present invention is a method for producing a copolymer latex, wherein (a) an aliphatic conjugated diene monomer is 10 to 80% by weight, and (b) an ethylenically unsaturated carboxylic acid monomer. First step (A) for emulsion polymerization of 100 parts by weight of a monomer comprising 0.5 to 10% by weight, (c) another copolymerizable monomer 10 to 89.5% by weight, and blowing water vapor In the second step (B) for removing unreacted monomer at 70 ° C. from the end of addition of 100 parts by weight of the monomer in the first step (A) to the start of the second step (B). A method for producing a copolymer latex, wherein 0.05 to 5 parts by weight of α-methylstyrene dimer is added at the time of the following polymerization temperature.

A second aspect of the invention is a method for producing a copolymer latex, wherein (a) an aliphatic conjugated diene monomer is 10 to 80% by weight, and (b) an ethylenically unsaturated carboxylic acid monomer is 0.5. 1st step (A) for emulsion polymerization of 100 parts by weight of a monomer comprising 10 to 10% by weight, (c) 10 to 99.5% by weight of another copolymerizable monomer, and unreacted by blowing water vapor A second step (B) for removing the monomer, and α-methylstyrene dimer when the polymerization temperature is 70 ° C. or lower and the polymerization conversion rate of the monomer is 75% or higher in the first step (A). Is added in an amount of 0.05 to 5 parts by weight.
A third aspect of the invention is a copolymer latex obtained by the first production method of the invention or the second production method of the invention.
A fourth invention is a paper coating composition characterized by containing 3 to 30 parts by weight of the third copolymer latex of the invention with respect to 100 parts by weight of the pigment.

  The present invention has a high balance between the pick strength, wet pick strength and blister resistance of coated paper, and also has an excellent roll stain resistance effect in the production process of coated paper such as stickiness resistance. .

The present invention will be specifically described below.
The (a) aliphatic conjugated diene monomer in the present invention is an essential component for imparting flexibility to the copolymer and giving adhesive strength and impact absorption, and is 10% by weight based on the weight of the whole monomer. As mentioned above, it is 80 weight% or less from a viewpoint of adhesive force and stickiness resistance, Preferably it is used in the ratio of 25 to 75 weight%. Preferable examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and the like, and these are used alone or in combination of two or more.
The (b) ethylenically unsaturated carboxylic acid monomer in the present invention is an essential component for imparting the necessary dispersion stability to the copolymer latex and enhancing the adhesive force, and based on the weight of all monomers, It is used in a proportion of 0.5% by weight or more and 10% by weight or less, preferably 1 to 5% by weight from the viewpoint of maintaining water resistance. Preferable examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the like, and these are used alone or in combination of two or more.

  In the present invention, (c) other copolymerizable monomers are essential. Various properties can be imparted to the copolymer latex by appropriately selecting other monomers capable of copolymerization. Preferred examples of other copolymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and the like. (Meth) acrylic acid alkyl ester monomers such as vinyl cyanide monomer, methyl methacrylate (methyl methacrylate), butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, (Meth) acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl acrylate (hydroxyethyl acrylate) and 2-hydroxyethyl methacrylate, aminoethyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate and the like. (Alkyl) glycidyl acrylate, glycidyl acrylate, glycidyl methacrylate, (meth) acrylic acid glycidyl esters, acrylamide, methacrylamide, N-methylolacrylamide, N-methylacrylamide, N-methylmethacrylamide, glycidylmethacrylamide, Examples include amides such as N, N-butoxymethylacrylamide, pyridines such as 2-vinylpyridine and 4-vinylpyridine, carboxylic acid vinyl esters such as vinyl acetate, and vinyl halides such as vinyl chloride. Are used alone or in combination of two or more.

In the method for producing a copolymer latex of the present invention, it is essential to add 0.05 to 5 parts by weight of α-methylstyrene dimer which is a specific chain transfer agent at a polymerization temperature of 70 ° C. or lower. When the temperature at the time of addition is 70 ° C. or less, cross-linking gelation can be significantly suppressed, and in particular, the blister resistance is sufficiently satisfied. Moreover, it is preferably 65 ° C. or lower, more preferably 60 ° C. or lower.
The addition amount of α-methylstyrene dimer is preferably 0.05 to 5 parts by weight. Blister resistance is good at 0.05 parts by weight or more, and pick strength and stickiness resistance are improved at 5 parts by weight or less. More preferably, it is used in the range of 0.1 to 3 parts by weight, and more preferably in the range of 0.1 to 1 part by weight. α-Methylstyrene dimer includes 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene and 1,1,3-trimethyl-3-phenyl as isomers. Although there is indane, the α-methylstyrene dimer used in the present invention preferably has a ratio of 2,4-diphenyl-4-methyl-1-pentene of 60% by weight or more, particularly preferably 2 , 4-diphenyl-4-methyl-1-pentene is 80% by weight or more.

In the method for producing a copolymer latex of the present invention, it is essential to add α-methylstyrene dimer before starting the second step (B) in which water vapor is blown to remove unreacted monomers. Moreover, it is preferable to add from the end of the addition of 100 parts by weight of the monomer in the first step (A) to the start of the second step (B). Moreover, in order to suppress cross-linking gelation when the monomer in the latter half of the first step (A) is reduced, addition at a time when the polymerization conversion rate of the monomer is 75% or more is preferable.
There is no restriction | limiting in particular about the method of emulsion polymerization for obtaining the copolymer latex of this invention, Well-known methods, such as superposing | polymerizing with a radical initiator in presence of surfactant in an aqueous medium, can be used.

  There is no restriction | limiting in particular also about the emulsifier to use, A conventionally well-known anion, a cation, an amphoteric, and a nonionic surfactant can be used. Examples of preferred surfactants include anions such as aliphatic soaps, rosin acid soaps, alkyl sulfonates, dialkyl allyl sulfonates, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, polyoxyethylene alkyl allyl sulfates, etc. Nonionic surfactants such as a reactive surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, and polyoxyethylene oxypropylene block copolymer are used, and these are used alone or in combination of two or more.

  The radical initiator initiates addition polymerization of the monomer by radical decomposition in the presence of heat or a reducing agent, and either an inorganic initiator or an organic initiator can be used. Preferred examples include peroxodisulfates, peroxides, azobis compounds, and the like. Specifically, potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2 -Azobisbutyronitrile, cumene hydroperoxide, etc. In addition, POLYMER HANDBOOK (3rd edition), J. MoI. Brandrup and E.I. H. Examples include compounds described in Immersutt, published by John Willy & Sons (1989), and these can be used alone or in combination of two or more. In addition, a so-called redox polymerization method in which a reducing agent such as acidic sodium sulfite, ascorbic acid or a salt thereof, erythorbic acid or a salt thereof or Rongalite is used in combination with a polymerization initiator can also be used.

  In the emulsion polymerization for obtaining the copolymer latex of the present invention, a known chain transfer agent usually used in radical polymerization can be used. The chain transfer agent usually added during polymerization includes α-methylstyrene dimer, n-butyl mercaptan, t-butyl mercaptan, n-octyl mercaptan, and n-lauryl, which are one of dimers of nucleus-substituted α-methylstyrene. Mercaptans such as mercaptans, disulfides such as tetramethylthiudium disulfide and tetraethylthuradium disulfide, halogenated derivatives such as carbon tetrachloride and carbon tetrabromide, 2-ethylhexyl thioglycolate, etc. Two or more kinds can be used in combination. Moreover, there is no restriction | limiting in particular also in the addition method of these chain transfer agents other than the addition method of a claim, Well-known addition methods, such as batch addition, batch addition, and continuous addition, are used.

In the emulsion polymerization, various known polymerization regulators can be used as necessary. These are, for example, pH adjusters, chelating agents, etc. Preferred examples of pH adjusters include sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium hydrogen carbonate, disodium hydrogen phosphate, and the like. Preferable examples include sodium ethylenediaminetetraacetate.
The solid content and particle size of the copolymer latex of the present invention are not particularly limited. Usually, the solid content is 30 to 60% by weight, and the particle size is 0.04 to 0.4 μm, preferably 0.05 to 0.2 μm. It is prepared in the range of It is also possible to use a known seed polymerization method for particle size adjustment, such as an internal seed method in which a copolymer latex is polymerized in the same reaction system after the seed is prepared, an external seed method using a separately prepared seed, etc. A method can be appropriately selected and used.

The polymerization temperature for polymerizing the copolymer latex of the present invention is usually 5 ° C to 100 ° C, preferably 30 ° C to 80 ° C, more preferably 40 ° C to 60 ° C.
Various additives can be added to the copolymer latex of the present invention as necessary, or other latexes can be mixed and used, for example, a dispersant, an antifoaming agent, an anti-aging agent, water resistance. Additives, bactericides, printing suitability agents, etc., alkali-sensitive latexes, plastic pigments and the like can also be mixed and used.

  When the copolymer latex of the present invention is used as a binder for a paper coating composition, it can be carried out in a conventional manner. That is, in water in which a dispersant is dissolved, inorganic pigments such as kaolin clay, calcium carbonate, titanium dioxide, aluminum hydroxide, satin white, and talc, organic pigments known as plastic pigments and binder pigments, starch, casein, and polyvinyl alcohol Add copolymer latex together with various additives such as water-soluble polymers such as carboxymethyl cellulose, thickeners, dyes, antifoaming agents, preservatives, water resistance agents, lubricants, printability improvers, water retention agents, etc. It is an aspect which mixes and makes it a uniform dispersion liquid. The proportion of the pigment and the copolymer latex of the present invention can be appropriately determined depending on the purpose of use of the composition, but is preferably 3 to 30 parts by weight of latex with respect to 100 parts by weight of pigment.

The paper coating solution can be applied to the base paper by a usual method using various blade coaters, roll coaters, air knife coaters, bar coaters and the like. The coating form can be applied to one side of the base paper, or both sides of the front and back sides, and the number of times of coating per side is one so that the coating process is performed twice, in addition to single coating. It can also be used for double coating. In this case, the copolymer latex of the present invention can be used for both the undercoat pigment composition and the overcoat pigment composition.
The composition for paper coating using the copolymer latex of the present invention includes various types of printing paper such as offset sheet-fed printing paper, offset rotary printing paper, gravure printing paper, letterpress printing paper, and paperboard, cardboard paper. It is preferably used for wrapping paper.
Furthermore, the copolymer latex of the present invention can be used for paper coating agents, carpet backing agents, other adhesives, and various paints.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited by these examples.
[Example 1]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 160 parts by weight of ion-exchanged water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, 0.01 parts by weight of ferrous sulfate The internal temperature was raised to 45 ° C. Further, 50 parts by weight of a monomer mixture comprising 20.5 parts by weight of styrene, 22.5 parts by weight of butadiene, 2 parts by weight of acrylonitrile and 5 parts by weight of methyl methacrylate, and t-dodecyl mercaptan (t-DDM) 0. 25 parts by weight was added, and further 1 part by weight of sodium peroxodisulfate and 7 parts by weight of ion-exchanged water were added, and the reaction was carried out for 4.5 hours while maintaining the internal temperature at 45 ° C.

Thereafter, the internal temperature was raised to 60 ° C., 22 parts by weight of styrene, 9 parts by weight of butadiene, 4 parts by weight of acrylonitrile, 9 parts by weight of methyl methacrylate, 3 parts by weight of hydroxyethyl acrylate, 1 part by weight of acrylic acid, 2 parts by weight of itaconic acid, α-methylstyrene dimer (0.1 part by weight), t-dodecyl mercaptan (0.8 part by weight) and ion-exchanged water (30 parts by weight) over 4 hours, sodium bisulfite (0.5 part by weight) and ion-exchanged water (15 parts by weight) Each was added into the reaction vessel at a constant rate over 6 hours.
The inside of the pressure resistant reactor was kept at 60 ° C. for 1 hour to confirm that the polymerization conversion of the monomer was 95% or more, and 0.3 parts by weight of α-methylstyrene dimer (α-MSD) Then, a stripping process was performed in which water vapor was blown to remove unreacted monomers.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide and the solid was concentrated to 50 wt%. The copolymer latex obtained as described above is referred to as copolymer latex L-1.

[Examples 2 to 4]
In the same manner as in Example 1, the monomers and chain transfer agents shown in Table 1 were used, and copolymer latexes L-2 to L-4 were obtained at the polymerization temperatures shown in Table 1.

[Comparative Examples 1 and 2]
Except for using the monomers and chain transfer agents shown in Table 1 and performing emulsion polymerization at the polymerization temperatures shown in Table 1 and not adding α-methylstyrene dimer (α-MSD) before the stripping step. Copolymer latexes L-5 and L-6 were obtained in the same manner as in Example 1.

[Comparative Example 3]
After fully replacing the inside of the pressure-resistant reaction vessel equipped with a stirrer and a temperature control jacket with nitrogen gas, put 70 parts by weight of ion exchange water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and 2 parts by weight of itaconic acid. The temperature was raised to 75 ° C. Furthermore, 50 parts by weight of a monomer mixture comprising 8 parts by weight of styrene, 15 parts by weight of butadiene, 10 parts by weight of acrylonitrile and 15 parts by weight of methyl methacrylate, 1.1 parts by weight of t-dodecyl mercaptan (t-DDM) as a chain transfer agent, and 1. 0.5 part by weight of α-methylstyrene dimer (α-MSD) was charged, 0.5 part by weight of sodium peroxodisulfate and 5 parts by weight of ion-exchanged water were added, and the internal temperature was maintained at 75 ° C. The reaction was allowed for 5 hours.

Next, while maintaining the internal temperature at 75 ° C., 6 parts by weight of styrene, 28 parts by weight of butadiene, 10 parts by weight of acrylonitrile, 4 parts by weight of methyl methacrylate, 1 part by weight of hydroxyethyl acrylate, 1 part by weight of acrylic acid, α-methylstyrene 0.5 parts by weight of dimer, 1.4 parts by weight of t-dodecyl mercaptan over 5 hours, 0.5 parts by weight of sodium peroxodisulfate, 0.1 parts by weight of sodium lauryl sulfate, 0.2 parts by weight of sodium hydroxide And 15 parts by weight of ion-exchanged water were added to the reaction vessel at a constant rate over 6 hours.
The inside of the pressure-resistant reaction vessel was kept at 75 ° C. for 1 hour to confirm that the monomer polymerization conversion was 95% or more, and 0.5 parts by weight of α-methylstyrene dimer (α-MSD) Then, a stripping process was performed in which water vapor was blown to remove unreacted monomers.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide, and the solid content was adjusted to 50% by weight. The copolymer latex obtained as described above is referred to as copolymer latex L-7.

[Comparative Example 4]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 160 parts by weight of ion-exchanged water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, 0.01 parts by weight of ferrous sulfate The internal temperature was raised to 50 ° C. Furthermore, 50 parts by weight of a monomer mixture comprising 18 parts by weight of styrene, 24 parts by weight of butadiene and 8 parts by weight of acrylonitrile, 0.5 parts by weight of t-dodecyl mercaptan (t-DDM) as a chain transfer agent, and α-methylstyrene dimer ( α-MSD) was added in an amount of 0.2 parts by weight, and further 1 part by weight of sodium peroxodisulfate and 7 parts by weight of ion-exchanged water were added, followed by reaction for 4 hours while maintaining the internal temperature at 50 ° C.

Thereafter, the internal temperature was raised to 65 ° C., 15.5 parts by weight of styrene, 18 parts by weight of butadiene, 12 parts by weight of acrylonitrile, 2 parts by weight of methyl methacrylate, 2.5 parts by weight of itaconic acid, 0.8% by weight of α-methylstyrene dimer. , 0.9 parts by weight of t-dodecyl mercaptan and 30 parts by weight of ion exchange water over 4 hours, and 0.5 parts by weight of sodium hydrogen sulfite and 15 parts by weight of ion exchange water over 6 hours at a constant rate. Added into the container.
Subsequently, the inside of the pressure resistant reactor was raised to 95 ° C. over 1.5 hours, and it was confirmed that the polymerization conversion rate of the monomer was 95% or more, and α-methylstyrene dimer (α-MSD) 0.2 After adding a weight part, the stripping process which blows in water vapor | steam and removes an unreacted monomer was implemented.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide and the solid was concentrated to 50 wt%. The copolymer latex obtained as described above is referred to as copolymer latex L-8.

[Examples 5 to 8]
A coating liquid for paper coating was prepared using the copolymer latex L-1 to L-4 with the following composition.

[Comparative Examples 5 to 8]
By the method similar to Examples 5-8, the coating liquid for paper coating was prepared by the following mixing | blending using copolymer latex L-5-L-8.
(Coating liquid formulation)
Kaolin clay 70 parts by weight Heavy calcium carbonate 30 parts by weight Sodium polyacrylate 0.2 parts by weight Sodium hydroxide 0.1 parts by weight Phosphate esterified starch 2.5 parts by weight Copolymer latex 12 parts by weight Water (Coating Add so that the total solid content of the liquid is 64% by weight)

As kaolin clay, Ultra White 90 (manufactured by ENGELHARD), calcium carbonate as Carbital 90 (manufactured by ECC), sodium polyacrylate as Aron T-40 (manufactured by Toagosei Co., Ltd.) and phosphate esterified starch Used MS-4600 (manufactured by Nippon Food Processing Co., Ltd.).
The resulting coating solution was coated on a high-quality coated base paper with a basis weight of 75 g / m ^{2 so} that the coating amount was 12 g / m ^{2 on} one side, and placed in a constant temperature and humidity chamber at 23 ° C. and 65% RH. For 12 hours. This was passed through a super calender device twice on one 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. Table 2 shows the results of evaluating the physical properties of the copolymer latex and the coated paper sample by the following method.

(Pick strength)
Using a RI printing tester (Ming Seisakusho), printing ink (manufactured by Toka Dye Co., Ltd., trade name: SD) is used on a mount (30 cm × 25.5 cm) in which coated paper (1.5 cm × 20 cm) is arranged and pasted at the center. 0.5 ml of Super Deluxe 50 Red B (tack 18) was overprinted on the coated paper with a printing area of 25 cm × 21 cm, and the occurrence of picks appearing on the rubber roll was transferred to another backing paper and visually evaluated. In the evaluation, the score was increased as the number of picks was reduced by the 10-point method.

(Wet pick strength)
Using the same method as the pick strength, printing was performed once on coated paper coated with water with a Molton roll, and the occurrence of picks appearing on the rubber roll was transferred to another mount and visually evaluated. In the evaluation, the score was increased as the number of picks was reduced by the 10-point method.
(Blister resistance)
The coated paper was cut into an appropriate size, and the test piece was immersed in a silicone oil bath adjusted to a predetermined temperature to observe whether or not blisters were generated. The same test was performed while changing the temperature of the oil bath, and the temperature at which blisters were generated was measured for each coated paper. The higher the generation temperature, the better the blister resistance.

(Stickiness resistance)
Copolymer latex is applied to the Mylar film. It was coated with 12 wire bars and dried at 130 ° C. for 30 seconds. This film is overlapped with black lasha paper, passed through a super calendar having a temperature of 80 ° C. and a linear pressure of 19600 N / m, and then the black lasha paper is peeled off. The state of transition of the black lasha paper fiber latex film due to stickiness was visually evaluated. The evaluation was a 10-point evaluation method, and the higher the score, the lower the transition.
As is apparent from Table 2, Examples 5 to 8 have an excellent balance of pick strength, wet pick strength, and blister resistance, and are excellent in stickiness resistance that is an index of operability in the manufacturing process of coated paper. .

On the other hand, Comparative Examples 5 and 6 use copolymer latexes L-5 and L-6 to which α-methylstyrene dimer (α-MSD) is not added before the stripping step. Poor balance between blister resistance and stickiness resistance.
Since Comparative Example 7 uses copolymer latex L-7 having a temperature of 75 ° C. when α-methylstyrene dimer (α-MSD) is added before the stripping step, wet pick strength and resistance Inferior to blister properties.
Since Comparative Example 8 uses copolymer latex L-8 having a temperature of 95 ° C. when α-methylstyrene dimer (α-MSD) is added before the stripping step, wet pick strength and resistance Inferior to blistering and stickiness.

[Example 9]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 120 parts by weight of ion exchange water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and seed particles having an average diameter of 0.02 μm An aqueous dispersion (seed solid content concentration: 10%) 0.5 part by weight, itaconic acid 2 parts by weight, and ferrous sulfate 0.01 part by weight were added, and the internal temperature was raised to 50 ° C. Further, 1 part by weight of sodium peroxodisulfate and 5 parts by weight of ion-exchanged water were charged, and while maintaining the internal temperature at 50 ° C., 37.5 parts by weight of styrene, 34 parts by weight of butadiene, 18 parts by weight of acrylonitrile, methyl methacrylate 4 1 part by weight, 3 parts by weight of hydroxyethyl acrylate and 1.5 parts by weight of methacrylic acid, 1.2 parts by weight of t-dodecyl mercaptan (t-DDM) as a chain transfer agent and α-methylstyrene dimer (α -MSD) Mixing 0.7 parts by weight over 6 hours and reducing agent sodium bisulfite 0.3 parts by weight with ion-exchanged water 15 parts by weight in a reaction vessel at a constant rate, respectively. Added to. The monomer polymerization conversion rate at the end of the addition of the reducing agent was 77%.

Further, 3 parts by weight of α-methylstyrene dimer (α-MSD) was added at the end of addition of the reducing agent, and the internal temperature was raised from 50 ° C. to 95 ° C. over 1.5 hours, so that the polymerization conversion of the monomer was 95. After confirming that the amount was not less than%, a stripping step was performed in which water vapor was blown to remove unreacted monomers.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide and the solid was concentrated to 50 wt%. The copolymer latex obtained as described above is referred to as copolymer latex L-9.

[Example 10]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 120 parts by weight of ion exchange water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and seed particles having an average diameter of 0.02 μm An aqueous dispersion (seed solid content concentration: 10%) 0.5 part by weight, itaconic acid 2 parts by weight, and ferrous sulfate 0.01 part by weight were added, and the internal temperature was raised to 50 ° C. Furthermore, 1 part by weight of sodium peroxodisulfate and 5 parts by weight of ion-exchanged water were charged, and while maintaining the internal temperature at 50 ° C., 40 parts by weight of styrene, 32 parts by weight of butadiene, 12 parts by weight of acrylonitrile, 12 parts by weight of methyl methacrylate , 1 part by weight of hydroxyethyl acrylate and 1 part by weight of acrylic acid, 1 part by weight of t-dodecyl mercaptan (t-DDM) as chain transfer agent and 0.8 parts of α-methylstyrene dimer (α-MSD) A mixture of parts by weight was added to the reaction vessel at a constant rate over 6 hours, and 0.6 part by weight of sodium hydrogen sulfite as a reducing agent was added together with 15 parts by weight of ion-exchanged water over 8 hours.

The inside of the pressure-resistant reaction vessel was maintained at 50 ° C. for 1 hour, and the polymerization conversion of the monomer was confirmed to be 95% or more. Α-methylstyrene dimer (α-MSD) 0.5 part by weight Then, a stripping process was performed in which water vapor was blown to remove unreacted monomers.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide, and the solid content was adjusted to 50% by weight. The copolymer latex obtained as described above is referred to as copolymer latex L-10.

[Comparative Examples 9 and 10]
Copolymer latex L-11 was prepared in the same manner as in Example 10 except that the monomers and chain transfer agents shown in Table 3 were used, and α-methylstyrene dimer (α-MSD) was not added before the stripping step. And L-12 was obtained.

[Comparative Example 11]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 120 parts by weight of ion exchange water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and seed particles having an average diameter of 0.02 μm An aqueous dispersion (seed solid content concentration: 10%) 0.5 part by weight, itaconic acid 2 parts by weight, and ferrous sulfate 0.01 part by weight were added, and the internal temperature was raised to 50 ° C. Further, 1 part by weight of sodium peroxodisulfate and 5 parts by weight of ion-exchanged water were charged, and while maintaining the internal temperature at 50 ° C., 49 parts by weight of styrene, 30 parts by weight of butadiene, 8 parts by weight of acrylonitrile, 10 parts by weight of methyl methacrylate , 1 part by weight of hydroxyethyl acrylate, 0.8 part by weight of t-dodecyl mercaptan (t-DDM) and 0.5 part by weight of α-methylstyrene dimer (α-MSD) as a chain transfer agent Then, 0.6 parts by weight of sodium hydrogen sulfite as a reducing agent was added to the reaction vessel at a constant rate over 8 hours together with 15 parts by weight of ion-exchanged water.

The inside of the pressure-resistant reaction vessel was kept at 50 ° C. for 1 hour to confirm that the polymerization conversion rate of the monomer was 95% or more, and 0.5 weight of t-dodecyl mercaptan (t-DDM) was continuously added. After the addition, a stripping step for removing unreacted monomers by blowing water vapor was performed.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide, and the solid content was adjusted to 50% by weight. The copolymer latex obtained as described above is designated as copolymer latex L-13.

[Comparative Example 12]
After sufficiently replacing the inside of the pressure resistant reactor equipped with a stirrer and a temperature control jacket with nitrogen gas, 70 parts by weight of ion-exchanged water, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and 0.02 μm average diameter of seed particles An aqueous dispersion (seed solid content concentration: 10%) 0.5 part by weight and itaconic acid 3 parts by weight were added to raise the internal temperature to 75 ° C. While maintaining the internal temperature at 75 ° C., a monomer mixture comprising 35 parts by weight of styrene, 35 parts by weight of butadiene, 5 parts by weight of acrylonitrile, 20 parts by weight of methyl methacrylate and 2 parts by weight of hydroxyethyl acrylate, and t- A mixture of 0.6 parts by weight of dodecyl mercaptan (t-DDM) and 1.2 parts by weight of α-methylstyrene dimer (α-MSD) over 5 hours, 1 part by weight of sodium peroxodisulfate, sodium lauryl sulfate 0.1 part by weight, 0.2 part by weight of sodium hydroxide and 15 parts by weight of ion-exchanged water were respectively added to the reaction vessel at a constant rate over 6 hours.

Further, during monomer addition, 0.5 hours after the start of monomer addition (0.5 hours before the end of monomer addition), 0.5-α-methylstyrene dimer (α-MSD) 0.5 Part by weight was added.
Stripping in which the inside of the pressure-resistant reaction vessel is raised to 95 ° C. over 1.5 hours, and after confirming that the polymerization conversion rate of the monomer is 95% or more, steam is blown to remove unreacted monomers. The process was carried out.
The pH was adjusted to 8 with a 1: 1 mixture of sodium hydroxide and potassium hydroxide, and the solid content was adjusted to 50% by weight. The copolymer latex obtained as described above is referred to as copolymer latex L-14.

[Examples 11 and 12]
Using the latex latex L-9 and L-10, a coating liquid for paper coating was prepared with the following composition.

[Comparative Examples 13 to 16]
By the same method as in Examples 11 and 12, a coating liquid for paper coating was prepared with the following composition using copolymer latex L-11 to L-14.
(Coating liquid formulation)
Kaolin clay 60 parts by weight Heavy calcium carbonate 40 parts by weight Sodium polyacrylate 0.2 parts by weight Sodium hydroxide 0.1 parts by weight Phosphate esterified starch 2.5 parts by weight Copolymer latex 12 parts by weight Water (Coating Add so that the total solid content of the liquid is 65% by weight)

As kaolin clay, Ultra White 90 (manufactured by ENGELHARD), calcium carbonate as Carbital 90 (manufactured by ECC), sodium polyacrylate as Aron T-40 (manufactured by Toagosei Co., Ltd.) and phosphate esterified starch Used MS-4600 (manufactured by Nippon Food Processing Co., Ltd.).
The resulting coating solution was coated on a high-quality coated base paper with a basis weight of 75 g / m ^{2 so} that the coating amount was 12 g / m ^{2 on} one side, and placed in a constant temperature and humidity chamber at 23 ° C. and 65% RH. For 12 hours. This was passed through a super calender device twice on one 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. Table 4 shows the results of evaluating the physical properties of the copolymer latex and the coated paper sample by the following method.
As is apparent from Table 4, Examples 11 and 12 have an excellent balance of pick strength, wet pick strength, and blister resistance, and are excellent in stickiness resistance that is an index of operability in the manufacturing process of coated paper. .

On the other hand, Comparative Examples 13 and 14 use copolymer latexes L-11 and L-12 to which α-methylstyrene dimer (α-MSD) is not added before the stripping step. Poor balance between blister resistance and stickiness resistance.
Comparative Example 15 is a copolymer latex L-13 in which 0.5 parts by weight of t-dodecyl mercaptan (t-DDM) is added instead of α-methylstyrene dimer (α-MSD) before the stripping step. Since it is used, the balance between wet pick strength, blister resistance, and stickiness resistance is particularly poor.
In Comparative Example 16, copolymer latex L-14 in which 0.5 part by weight of α-methylstyrene dimer (α-MSD) was added during monomer addition, and the internal temperature at the time of addition was 75 ° C. Therefore, the balance of adhesive strength, blister resistance, and stickiness resistance is poor.

The conjugated diene copolymer latex of the present invention is used in a wide range of applications such as pigment binders, carpet backing agents, various adhesives and pressure-sensitive adhesives, fiber binders and paints in paper coating.
It can cope with high-speed printing of color printed magazines, pamphlets, advertisements, etc.

Claims (4)

A method for producing a copolymer latex, comprising (i) 10-80% by weight of an aliphatic conjugated diene monomer, (b) 0.5-10% by weight of an ethylenically unsaturated carboxylic acid monomer, ( C) The first step (A) of emulsion polymerization of 100 parts by weight of a monomer comprising 10 to 89.5% by weight of another copolymerizable monomer, and removing unreacted monomer by blowing water vapor. It has a second step (B), and after the addition of 100 parts by weight of the monomer in the first step (A) until the second step (B) is started, α- A method for producing a copolymer latex, comprising adding 0.05 to 5 parts by weight of methylstyrene dimer. A method for producing a copolymer latex, comprising (i) 10-80% by weight of an aliphatic conjugated diene monomer, (b) 0.5-10% by weight of an ethylenically unsaturated carboxylic acid monomer, ( C) The first step (A) of emulsion polymerization of 100 parts by weight of a monomer comprising 10 to 89.5% by weight of another copolymerizable monomer, and removing unreacted monomer by blowing water vapor. It has a second step (B), and in the first step (A), when the polymerization temperature is 70 ° C. or less and the polymerization conversion rate of the monomer is 75% or more, α-methylstyrene dimer is added in an amount of 0.05 to 5%. The method for producing a copolymer latex according to claim 1, wherein parts by weight are added. A copolymer latex obtained by the production method of claim 1 or 2. A paper coating composition comprising 3 to 30 parts by weight of the copolymer latex of claim 3 with respect to 100 parts by weight of the pigment.