JP3300441B2 - Method for producing flat emulsion particles having concave portions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to coated paper, information recording paper,
The present invention relates to a method for producing flat emulsion particles having concave portions useful as an additive of a coating agent used for paints and the like.

[0002]

2. Description of the Related Art In recent years, various particulate polymers have been studied as additives for coating agents. The most commonly used are uniform, solid polystyrene particles having a particle size of 0.2-0.5μ. For example, JP-A-59-
No. 59741 discloses anionic surfactants and / or
Alternatively, an unsaturated carboxylic acid and a vinyl monomer are copolymerized in the presence of a nonionic surfactant to produce a copolymer emulsion in which 90% or more of the particles are 0.2 to 0.28 µ,
Examples are shown for use in applications such as paper coating or paint.

However, the organic pigments obtained by such a method do not provide sufficient hiding power, whiteness and gloss, and have no practical advantage unless used in large amounts.
In recent years, for the purpose of further improving concealing properties, whiteness and gloss, an organic material having a small hole from a uniform and solid type as described above has been proposed (US Pat. No. 3,152,280).
That is, at least 5% of unsaturated carboxylic acid as a core material
By adding at least one kind of monoethylenically unsaturated sheath monomer that forms a sheath polymer to the copolymerized polymer dispersion, and neutralizing and swelling the emulsion polymerized emulsion with an aqueous volatile base. This is a method for producing an aqueous dispersion that forms microvoids. When an organic pigment is used in a paint or paper coating composition according to the present method, the opacity, whiteness and gloss are improved as compared with a uniform, honey-type organic material, but the pores are impaired by the method of use. Disadvantage. The pores may be damaged due to destruction by freezing, destruction by a certain type of solvent used in coating formulation, or destruction by heating, and can be used only in a limited form in terms of formulation or use.

On the other hand, in the case of flat particles as an organic pigment,
Polyethylene flat particles produced by mechanically heating and compressing a polymer (powder and industry (9) 1986 p3
Although 3) and the like are conventionally known, only particles having a size of 1 μ or more are obtained, and it is difficult to efficiently and accurately produce particles suitable for use. As a method for solving such a problem, a flat emulsion particle having a concave portion and a method for producing the same are disclosed in JP-A-2-14222. Flat emulsion particles having such concave portions exhibit excellent properties such as excellent gloss and hiding power. However, in the coated paper field, there is a drawback that the gloss difference before and after the calender is relatively small. Although there is a method of lowering the polymer Tg in order to improve such a so-called calender effect, blocking tends to occur by lowering the Tg, leaving room for improvement.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention, particularly when used in a paper coating composition, has a concave portion which satisfies physical properties such as gloss, smoothness, strength and the like and has excellent blocking resistance. It is an object of the present invention to provide flat emulsion particles having the following.

[0006]

As a result of intensive studies to solve the above problems, it has been found that flat emulsion particles having a concave portion containing a certain amount of butadiene are excellent especially as organic pigments for paper coating. It has been found that the present invention has been completed. That is, the present invention provides a vinyl monomer (a)
Are used as seed particles, and the polymer obtained by emulsion polymerization of
A vinyl monomer (b) consisting of butadiene in an amount of 50% by weight and 50 to 99% by weight of another monomer is prepared in the presence of a water-insoluble organic solvent having an interfacial tension with water of at least 48 dyne / cm at 20 ° C. Has a concave portion in at least one of the planes obtained by emulsion polymerization, the diameter D of the plane is 0.1
５5.0 μ and the ratio to the particle thickness d (D / d)
Is a method for producing flat emulsion particles having concave portions in the range of 1.5 to 5.0.

The vinyl monomer (a) used for producing the seed particles includes, for example, aromatic vinyl monomers such as styrene, α-methylstyrene and vinyltoluene, methyl acrylate, ethyl acrylate and butyl acrylate. Methacrylates such as methyl methacrylate, ethyl methacrylate and butyl methacrylate; vinyl ester monomers such as vinyl acetate and vinyl propionate; and vinyl cyanone monomers such as (meth) acrylonitrile. Monomers, vinyl halide monomers such as vinyl chloride and vinylidene chloride, diene monomers such as butadiene, divinylbenzene, ethylene glycol di (meth)
Crosslinkable monomers such as acrylate and trimethylolpropane trimethacrylate, and unsaturated carboxylic acids such as acrylic acid, methacrylic acid and itaconic acid, and unsaturated sulfonic acids such as sodium styrenesulfonate for imparting emulsion stability. Functional monomers such as salts, (meth) acrylic esters such as 2-hydroxyethyl (meth) acrylate, and (meth) acrylamides such as (meth) acrylamide and N-methylol (meth) acrylamide. They can be used alone or in combination of two or more, and are not particularly limited. The vinyl monomer (a) is a concept including all the above monomers.

In the production of the seed particles,
As molecular weight regulators, chain transfer agents such as mercaptans such as t-dodecyl mercaptan and halogenated hydrocarbons such as carbon tetrachloride can be used. Although the amount of use is not particularly limited, it is usually used in an amount of about 0.05 to 5.0% by weight based on the monomer. The production of the seed particles is performed by a usual emulsion polymerization method. As the surfactant used, sodium alkylbenzene sulfonate, sodium alkyl sulfate, sodium dialkyl sulfosuccinate, anionic surfactants such as naphthalenesulfonic acid formalin condensate, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, Nonionic surfactants such as ethylene oxide-propylene oxide block copolymers and sorbitan fatty acid esters are used alone or in combination. The amount of the surfactant used is not particularly limited, but is usually 0.1 to 1 based on the monomer.
It is about 0% by weight.

The polymerization initiator may be any of those used in ordinary emulsion polymerization. Examples thereof include peroxides such as potassium persulfate, sodium persulfate and ammonium persulfate, and organic peroxides such as benzoyl peroxide. Kind,
And azo compounds such as azobisisobutyronitrile.
If necessary, it can be used as a redox initiator in combination with a reducing agent. The amount of the polymerization initiator used is not particularly limited, but is usually about 0.1 to 3% by weight based on the monomer.

[0010] To produce a seed particle emulsion,
In the presence of the surfactant and the polymerization initiator, polymerization is carried out by adding the vinyl monomer (a) all at once, dividedly or continuously. At this time, the polymerization was carried out at a polymerization temperature of 20 to 9 under a nitrogen purge.
Performed at 0 ° C. Seed particles produced in this manner 0.5 to
In the presence of 50 parts by weight, 50 to 99.5 parts by weight of a vinyl monomer (b) consisting of 1 to 50% by weight of butadiene and 50 to 99% by weight of another monomer are divided or Add continuously. At this time, the water-insoluble organic solvent may be mixed with the vinyl monomer (b) and added, or may be added alone and initially at once. Also,
The polymerization of the vinyl monomer (a) and the polymerization of the vinyl monomer (b) may be performed continuously or in separate steps, and are not particularly limited.

In this manner, the vinyl monomer (a) and
Flat particles having concave portions made of the vinyl monomer (b) are obtained, and the vinyl monomer (a) and the vinyl monomer (b) are obtained.
Is carried out in a weight ratio of 0.5 / 99.5 to 50/50. In the range other than the above, flat particles having concave portions cannot be obtained.

The vinyl monomer (b) comprises 1 to 50% by weight of butadiene and 50 to 99% by weight of other monomers. Butadiene imparts moderate softness and rubber elasticity to the polymer, i.e., high strength and calender effects and blocking resistance. The content of butadiene is 1 to 50% by weight based on 100 parts by weight of the vinyl monomer (b),
Preferably it is 5 to 30% by weight. If it is less than 1% by weight,
The effect of the addition is low, and the desired particles cannot be obtained. On the other hand, if it exceeds 50% by weight, the Tg of the polymer becomes too low, so that the desired particles cannot be obtained.

Other monomers of the vinyl monomer (b) include, for example, aromatic vinyl monomers such as styrene, α-methylstyrene and vinyltoluene, methyl acrylate, ethyl acrylate, butyl acrylate and the like. Acrylates, methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate; vinyl ester monomers such as vinyl acetate and vinyl propionate; and vinyl cyan monomers such as (meth) acrylonitrile Halogenated monomers such as solids, vinyl chloride and vinylidene chloride, and cross-linkable monomers such as divinylbenzene, ethylene glycol di (meth) acrylate, and trimethylolpropane trimethacrylate, and for imparting emulsion stability , Acrylic acid, methacrylic acid, itaconic acid, etc. Unsaturated sulfonates such as boric acids and sodium styrene sulfonate, (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, and (meth) acrylamide, N-methylol (meth) acrylamide and the like One or more functional monomers such as (meth) acrylamides can be used in combination, and are not particularly limited. When a functional monomer is used, it is used in an amount of 20% by weight or less, preferably 10% by weight or less. is there. If it exceeds 20% by weight, secondary particles are likely to be generated. The vinyl monomer (b) is a concept including all of the above monomers, and the combination is free. However, styrene is preferably used in consideration of gloss, whiteness and the like. Further, as in the case of producing the seed particles, the above-mentioned chain transfer agent can be added as a molecular weight regulator. Further, the vinyl monomer (b) can be divided into two kinds of monomer mixtures. In this case, the water-insoluble organic solvent is preferably used in the first half, and butadiene is preferably used in the second half, but is not particularly limited.

The water-insoluble organic solvent (hereinafter simply referred to as an organic solvent) added during the polymerization of the vinyl monomer (b) is 20
It is necessary that the interfacial tension with water at 48 ° C. is 48 dyne / cm or more. From this point, n-pentane, n-hexane, n-heptane, n-octane, i-octane, n-octane
At least one selected from decane and (halogenated) aliphatic hydrocarbons such as 1-chlorodecane. If the interfacial tension between the organic solvent to be added and water is less than 48 dyne / cm, the particles will not be flat particles having concave portions, and spherical particles will be easily generated.

The organic solvent selected as described above has a total amount of 100% of the vinyl monomer (a) and the vinyl monomer (b).
The amount is preferably 1 to 50% by weight, more preferably 5 to 20% by weight, based on parts by weight during the polymerization. When the amount is less than 1% by weight, spherical particles are formed, and when the amount exceeds 50% by weight, the polymerization hardly proceeds. The diameter D of the uneven plane of the particles obtained in this way is 0.1 to 5.0 μ and the ratio (D / d) to the thickness d of the particles is in the range of 1.5 to 5.0. is there. D
And (D / d) are determined by the particle diameter of the seed particles and the weight ratio of the vinyl monomer (a) and the vinyl monomer (b). For example, when the amount of the vinyl monomer (b) is larger than that of the vinyl monomer (a), D and (D / d) increase. If the particle diameter is less than 0.1 μm, sufficient performance cannot be obtained. On the other hand, if it exceeds 5.0μ, the stability decreases,
Manufacturing becomes difficult. In this way, flat emulsion particles having concave portions are produced. The organic solvent remaining in the emulsion is removed together with the water in the process of drying the emulsion, but can be easily removed in the state of the emulsion by steam distillation.

[0016]

EXAMPLES Specific examples of the present invention will be shown below, but the present invention is not limited to these examples. The following parts and percentages indicate parts by weight and percentage by weight, respectively, and the particle diameter was measured by an electron microscope. Example 1 Water was placed in a stainless steel autoclave equipped with a stirrer and a thermometer.
50 parts and 0.1 part of sodium lauryl sulfate are charged, and the temperature is raised to 70 ° C. while purging with nitrogen while stirring. 7 internal temperature
At 0 ° C., 1.0 part of potassium persulfate was added as a polymerization initiator, and after dissolution, 10 parts of styrene and 0.3 part of acrylic acid were added.
Parts and 0.05 part of t-dodecyl mercaptan as a molecular weight modifier are added and reacted for 2 hours. After completion of the reaction, subsequently, 200 parts of water and 1.5 parts of sodium lauryl sulfate were previously added to 50 parts of butadiene, 220 parts of styrene, 40 parts of acrylonitrile, 10 parts of acrylic acid, and 40 parts of n-heptane with stirring to prepare. The mixed emulsion of the vinyl monomer and the organic solvent is continuously added and reacted over 4 hours, and aging is performed for about 3 hours after completion of the addition. As shown in Table 1, the obtained emulsion had a nonvolatile content of about 40%, a diameter D of the uneven surface of 0.5 μm, a particle thickness d of 0.2 μm, and (D / d) of 2.5. The particles were flat particles having concave portions.

Examples 2 to 4 In the same manner as in Example 1, the type and amount of the organic solvent,
Polymerization was performed by changing the weight ratio of the vinyl monomer (a) / vinyl monomer (b) and the monomer composition to obtain flat particles having concave portions. The results are shown in Table 1.

Example 5 The same autoclave as in Example 1 was charged with 240 parts of water, and the temperature was raised to 70 ° C. while purging with nitrogen while stirring. The internal temperature was maintained at 70 ° C., and 1.5 parts of potassium persulfate was added as a polymerization initiator. After dissolution, 20 parts of water, 0.1 part of sodium lauryl sulfate, 30 parts of styrene, 5 parts of butyl methacrylate, and 5 parts of acrylic An emulsion of a vinyl monomer prepared by adding 1 part of an acid and 0.5 part of t-dodecyl mercaptan under stirring is continuously added and reacted over 2 hours.
After completion of the reaction, subsequently, 200 parts of water, 1.5 parts of sodium lauryl sulfate and 150 parts of butadiene,
10 parts, acrylonitrile 40 parts, acrylic acid 10 parts,
A mixed emulsion of a vinyl monomer and an organic solvent prepared by adding 45 parts of n-heptane under stirring is continuously added and reacted over 4 hours, and aging is performed for about 3 hours after completion of the addition. . The resulting emulsion, as shown in Table 1,
It was a flat particle having a non-volatile content of about 40%, a flat surface diameter D of 0.7 μ, a particle thickness d of 0.25 μ, and a concave portion with a (D / d) of 2.8.

Example 6 The same autoclave as in Example 1 was charged with 250 parts of water and 0.1 part of sodium lauryl sulfate, and the temperature was raised to 70 ° C. while stirring and replacing with nitrogen. The internal temperature was kept at 70 ° C., and 1.0 part of potassium persulfate was added as a polymerization initiator. After dissolution, 10 parts of styrene, 0.3 part of acrylic acid and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator were added. Add and react for 2 hours. After completion of the reaction, 145 parts of styrene, 10 parts of acrylonitrile, 5 parts of acrylic acid were added to 100 parts of water, 0.8 part of sodium lauryl sulfate in advance.
And a mixed emulsion of a vinyl monomer and an organic solvent, which had been prepared by adding 40 parts of n-heptane while stirring, were added continuously over 2 hours and allowed to react.
Part butadiene 50 parts in 0.7 part sodium lauryl sulfate
Part, styrene 75 parts, acrylonitrile 30 parts, and acrylic acid 5 parts were added under stirring, and the emulsion of the vinyl monomer was continuously added and reacted over 2 hours. Allow time to mature. As shown in Table 1, the obtained emulsion had a nonvolatile content of about 40%, a diameter D of the flat surface of 0.55 μm, a thickness d of the particles of 0.2 μm, and (D /
d) was a flat particle having a concave portion of 2.8.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that butadiene was not used and the whole amount was replaced with styrene. The obtained emulsion was flat particles having a non-volatile content of about 40%, a flat surface diameter D of 0.5 μ, a particle thickness d of 0.25 μ, and (D / d) 2.0. Was.

Comparative Example 2 In Example 5, the polymerization was carried out by increasing the butadiene content of the vinyl monomer (b) to about 70%. The obtained emulsion had a nonvolatile content of about 40% and a diameter D of the uneven plane of 0.1%.
It was a flat particle having a concave portion with a particle diameter of 7 μm, a particle thickness d of 0.3 μm, and a (D / d) of 2.3.

Comparative Example 3 Polymerization was carried out in the same manner as in Example 1 except that butadiene was completely replaced with butyl acrylate. The resulting emulsion is
The flat particles had a non-volatile content of about 40%, a flat surface diameter D of 0.5 μ, a particle thickness d of 0.2 μ, and (D / d) 2.5 with concave portions.

Comparative Example 4 In Example 1, polymerization was carried out without using an organic solvent. The obtained emulsion had a non-volatile content of about 42%, and the particles were not flat with concave portions but had an average particle size of 0.4 μm.
Was spherical particles. Table 1 summarizes the above Examples and Comparative Examples.

[0024]

[Table 1]

Application Example: Application as Pigment for Paper Coating Performance evaluation was performed when the emulsions obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were used as a pigment for paper coating. First, 90 parts of kaolin (UW90: manufactured by Engelhardt USA) and Alon T-A as a dispersant were prepared.
40 (manufactured by Toa Gosei Chemical Co., Ltd.) was dispersed in water using a Cowles disperser, and then the starch (MS) was dissolved by heating.
3600: 3 parts by latex (Polylac 755: manufactured by Mitsui Toatsu Chemicals) and 3 parts of Examples 1 to 3
6 and 10 parts of the emulsions obtained in Comparative Examples 1 to 4 were added, and finally, prepared water was added to obtain a coating solution having a solid content of 60%. The above coating liquid is applied to a high quality paper with an applicator so that the dry coating amount is about 15 g / m ² ,
After drying for 2 seconds and leaving it in a constant temperature and humidity room at 20 ° C. and a humidity of 65% for 24 hours, a calender at a temperature of 60 ° C. and a linear pressure of 60 kg / cm was passed twice to obtain a coated paper. The performance of the obtained coated paper was evaluated under the following conditions. (1) Gloss on white paper: Measured according to JIS P-8142. (2) Printing gloss: Printing was performed using an RI printing tester (manufactured by Meisho Seisakusho) and measured according to JISP-8142. (3) Dry pick: RI printing tester (Akira Seisakusho)
And printing was evaluated by observing picking on the surface according to a 10-point scale. (4) Wet topic: For wet coated paper, the same method as that for dry pick was used. (5) Smoothness: Measured with an Oken-type smoothness tester (manufactured by Asahi Seiko). Table 2 shows the results.

[0026]

[Table 2]

[0027]

The flat emulsion particles having concave portions obtained by the present invention satisfy physical properties such as gloss, smoothness, strength and the like, have excellent blocking resistance, and are particularly useful as organic pigments for paper coating applications. It is clear.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-190504 (JP, A) JP-A-61-66710 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 2/22-2/30

Claims (4)

(57) [Claims] A polymer obtained by emulsion polymerization of a vinyl monomer (a) is used as a seed particle, and a vinyl monomer comprising 1 to 50% by weight of butadiene and 50 to 99% by weight of another monomer. The body (b) has an interfacial tension of 48 dyne with water at 20 ° C.
/ Cm or more has a concave part in at least one of the planes obtained by emulsion polymerization in the presence of a water-insoluble organic solvent, the diameter D of the plane is 0.1 to 5.0μ, And a method for producing flat emulsion particles having concave portions having a ratio (D / d) to the thickness d of the particles in the range of 1.5 to 5.0. 2. The process for producing flat emulsion particles having concave portions according to claim 1, wherein the butadiene contained in 100 parts by weight of the vinyl monomer (b) is 5 to 30 parts by weight. 3. The concave part according to claim 1, wherein the amount of the water-insoluble organic solvent is 1 to 50 parts by weight based on 100 parts by weight of the total amount of the vinyl monomer (a) and the vinyl monomer (b). A method for producing flat emulsion particles. 4. A vinyl monomer (a) and a vinyl monomer (b)
The method for producing flat emulsion particles having concave portions according to claim 1, wherein the weight ratio is 0.5 / 99.5 to 50/50.