JP4333357B2 - Hollow polymer particles, aqueous dispersions thereof, and methods for producing them - Google Patents

Description

  The present invention relates to hollow polymer particles, aqueous dispersions thereof, and methods for producing them. More specifically, the present invention relates to a hollow polymer particle having a high porosity, an aqueous dispersion thereof, and a method for producing them efficiently with a small amount of aggregates during production.

  Conventionally, hollow polymer particles scatter light better and lower light transmission than polymer particles in which the polymer is densely and uniformly packed in the particles. As an organic pigment having excellent optical properties such as whiteness, it is widely used in applications such as water-based paints and paper coating compositions.

  In such applications, it is desirable to increase the porosity of the hollow polymer particles to be blended in order to improve the effects of reducing the weight of paints, coated papers, etc., heat insulation by the hollow polymer particles, and opacification. It is rare. However, it has been difficult to efficiently and stably produce hollow polymer particles having a high porosity with the conventionally known methods for producing hollow polymer particles (for example, Patent Documents 1 to 5). .

As a means for solving the above problem, Patent Document 6 discloses a core polymer obtained by copolymerizing a monomer mixture containing an acidic group-containing monomer, and a monomer mixture containing a small amount of an acidic group-containing monomer. And an outer layer polymer obtained by copolymerizing a monomer mixture containing a very small amount of an acidic group-containing monomer and an aromatic vinyl monomer. A method for producing hollow polymer particles is disclosed in which an aqueous dispersion of polymer particles having at least a three-layer structure is treated with a nonvolatile base. According to this method, it is possible to efficiently obtain hollow polymer particles with a small amount of aggregates during production and a relatively high porosity. However, the void ratio of the hollow polymer particles obtained by this method is about 40%, and if an attempt is made to obtain hollow polymer particles having a higher void ratio, the amount of aggregates generated during the production of the hollow polymer particles increases. There was a problem.
JP-A-6-2448012 JP-A-61-185505 JP-A-1-48805 JP-A-1-201313 JP-A-4-224803 Japanese Patent Laid-Open No. 10-182761

  The main object of the present invention is to provide a hollow polymer particle having a high porosity, an aqueous dispersion thereof, and a method capable of producing them efficiently with a small amount of aggregates during production.

  As a result of diligent research in view of the above circumstances, the present inventor obtained an intermediate layer when polymerizing polymer particles having at least a three-layer structure each consisting of a core polymer, an intermediate layer polymer and an outer layer polymer, each having a specific composition. By using a specific amount of chain transfer agent during the formation of the polymer and adding a base to the obtained aqueous dispersion containing the polymer particles, the pH of the aqueous dispersion is adjusted to 7 or more. Based on this finding, the present inventors have found that the problem can be solved.

Thus, according to the present invention, the following inventions 1 to 4 are provided.
1. (1) A core polymer obtained by copolymerizing a monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated monocarboxylic acid and 80 to 40% by weight of another monomer copolymerizable therewith. ,
(2) A monomer mixture (b) comprising 1 to 15% by weight of an ethylenically unsaturated monocarboxylic acid and 99 to 85% by weight of another monomer copolymerizable therewith is converted into a monomer mixture (b) At least one intermediate layer polymer formed by copolymerization in the presence of 0.1 to 1% by weight of a chain transfer agent, substantially surrounding the core polymer, based on the total amount;
(3) By copolymerizing a monomer mixture (c) consisting of 0.2 to 3.5% by weight of ethylenically unsaturated monocarboxylic acid and 99.8 to 96.5% by weight of aromatic vinyl monomer . Formed by having at least a three-layer structure consisting of an outer layer polymer substantially surrounding the intermediate layer polymer formed, and at least a part of acidic groups contained in the core polymer being neutralized It is to have at least one void,
Hollow polymeric particles wherein the core polymer and said outer layer wherein the polymer der Rukoto those formed by copolymerizing without the addition of chain transfer agent.
2. 2. An aqueous dispersion of hollow polymer particles as described in 1 above.
3. (1) A monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated monocarboxylic acid and 80 to 40% by weight of another monomer copolymerizable therewith without adding a chain transfer agent Preparing core polymer particles by copolymerization,
(2) A monomer mixture (b) comprising 1 to 15% by weight of ethylenically unsaturated monocarboxylic acid and 99 to 85% by weight of other monomers copolymerizable therewith in the presence of the core polymer particles. At least one layer substantially surrounding the polymer particles by copolymerizing in the presence of 0.1 to 1% by weight of a chain transfer agent with respect to the total amount of the monomer mixture (b) Forming an intermediate layer polymer of
(3) 0.2 to 3.5% by weight of an ethylenically unsaturated monocarboxylic acid and an aromatic vinyl monomer in the presence of polymer particles in which an intermediate layer polymer surrounding the core polymer particles is formed. By copolymerizing the monomer mixture (c) consisting of 99.8 to 96.5% by weight without adding a chain transfer agent, an outer layer polymer substantially surrounding the intermediate layer polymer is formed. ,
(4) A base is added to the obtained aqueous dispersion containing polymer particles having at least a three-layer structure so that the pH of the dispersion is 7 or more.
The manufacturing method of the hollow polymer particle characterized by including the process of said (1)-(4).
4). 4. A process for producing an aqueous dispersion of hollow polymer particles, comprising the steps (1) to (4) described in 3 above.

  According to the present invention, there are provided hollow polymer particles having a high porosity, an aqueous dispersion thereof, and a method for producing them efficiently with a small amount of aggregates during production.

  The hollow polymer particles of the present invention have at least a three-layer structure consisting of a core polymer, an intermediate layer polymer and an outer layer polymer, and at least a part of acidic groups contained in the core polymer is neutralized. It is characterized by having at least one void formed.

1. Core polymer The core polymer is an acid group-containing monomer of 20 to 60% by weight, preferably 30 to 50% by weight, and another monomer copolymerizable with this 80 to 40% by weight, preferably 70 to 50%. It is obtained by copolymerizing a monomer mixture (a) consisting of% by weight.
If the amount of the acidic group-containing monomer is too small, it becomes difficult for the base to penetrate into the polymer particles in the base treatment step, and it becomes difficult to form voids in the polymer particles. Further, if the amount is excessive, the core polymer is likely to move to the outside of the intermediate layer polymer or the outer layer polymer, the stability during polymerization or the base treatment step is impaired, and the amount of aggregates generated is large. Become.

The acidic group-containing monomer used in the present invention is a monomer having an acidic functional group, and specific examples thereof include ethylenic unsaturated compounds such as acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid. Monocarboxylic acids; ethylenically unsaturated polyvalent carboxylic acids such as itaconic acid, fumaric acid, maleic acid and butenetricarboxylic acid; ethylenically unsaturated polyvalent carboxylic acids such as monoethyl itaconic acid, monobutyl fumarate and monobutyl maleate Esterified products; sulfonic acid group-containing monomers such as styrene sulfonic acid. These acidic group-containing monomers can be used alone or in combination of two or more.
If the acid is excessively hydrophilic, acidic groups are likely to be localized outside the polymer particles, making it difficult to coat the core polymer with the intermediate layer polymer and forming voids in the polymer particles. . Among the acidic group-containing monomers, ethylenically unsaturated monocarboxylic acid is preferable, and methacrylic acid is more preferable.

  Examples of other monomers copolymerizable with the acid group-containing monomer include aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, and halogenated styrene; methyl (meth) acrylate , Ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and other ethylenically unsaturated carboxylic acid esters Monomer; Ethylene unsaturated carboxylic acid amide monomer such as (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide; Conjugated diene monomer such as butadiene and isoprene; Acetic acid Carboxylic acid vinyl ester monomers such as vinyl Vinyl halide monomers such as vinyl chloride; and the like vinylpyridine; halogenated vinylidene monomers such as vinylidene chloride. Among these monomers, ethylenically unsaturated carboxylic acid ester monomers are preferable. These monomers can be used alone or in combination of two or more.

  Moreover, for example, crosslinkable monomers such as divinylbenzene, diallyl phthalate, allyl (meth) acrylate, and ethylene glycol di (meth) acrylate can be used as necessary. However, when a large amount of the crosslinkable monomer is used, void formation becomes difficult, so the amount should be limited to a range in which stable void formation can be maintained.

As a polymerization method for forming the core polymer, an emulsion polymerization method is usually employed. However, a polymer obtained by another polymerization method may be an aqueous dispersion containing core polymer particles by a phase inversion method.
As a polymerization method, any method such as a batch method, a semi-continuous method, or a continuous method may be adopted.
The polymerization temperature may be either low or high.
The polymerization pressure and the polymerization time are not particularly limited, and known conditions are adopted.
In addition, as a secondary material for polymerization, known additives such as various additives such as various emulsifiers, polymerization initiators, chelating agents, electrolytes, and surfactants can be used.
The core polymer is preferably formed using a seed. If the seed is used, it becomes easy to control the diameter of the produced polymer particles. The composition of the seed is not particularly limited.
The polymerization conversion rate of the monomer mixture (a) in the polymerization reaction is usually 90% by weight or more, preferably 97% by weight or more, and the composition of the copolymer formed is that of the monomer mixture (a) used. It is almost the same as the composition.

  The volume average particle diameter of the core polymer particles is preferably 100 to 600 nm, more preferably 250 to 400 nm. If the particle size is too small, it tends to be difficult to produce hollow polymer particles having a high porosity and a large particle size. Conversely, if the particle size is too large, the coating of the core polymer with the intermediate layer polymer may be difficult. It tends to be difficult and void formation in the polymer particles tends to be difficult.

  The distribution in the radial direction of the acidic group-containing monomer units in the core polymer particles is not particularly limited. Copolymerization can be carried out while sequentially changing the composition of the monomer mixture and adding it to the polymerization reaction system. By such a polymerization method, the content of the acid group-containing monomer units in the core polymer particles In the case where a radial distribution is generated, the least part of the acidic group-containing monomer unit is 10% by weight or more of the acidic group-containing monomer unit with respect to all the monomer units forming the part, The content is preferably 15% by weight or more. If this ratio is less than 10% by weight, small particles may be generated in the voids of the hollow polymer particles, and the porosity may be lowered.

2. Intermediate Layer Polymer The intermediate layer polymer substantially wraps around the core polymer and is sandwiched between the core polymer and the outer layer polymer. The intermediate layer polymer is copolymerized with 0 to 15% by weight, preferably 1 to 12% by weight, more preferably 3 to 9% by weight of the acid group-containing monomer in the presence of the core polymer particles. The monomer mixture (b) consisting of 100 to 85% by weight of the monomer, preferably 99 to 88% by weight, more preferably 97 to 91% by weight, is added to the total amount of the monomer mixture (b) by 0.00. It is formed on the outer periphery of the core polymer by copolymerization in the presence of 1 to 2% by weight, preferably 0.1 to 1.5% by weight, more preferably 0.2 to 1% by weight of a chain transfer agent. The
The intermediate layer may be formed of a single polymer layer, or may be formed of a plurality of polymer layers. When formed with a plurality of polymer layers, the composition of each polymer layer is not particularly limited as long as each layer satisfies the requirements regarding the above composition.

  When the ratio of the acidic group-containing monomer in the monomer mixture (b) exceeds 15% by weight, it becomes difficult to control the conditions in the base treatment step, and the hollow polymer particles cannot be obtained stably. In order to stably produce hollow polymer particles having a high porosity more efficiently, it is preferable to contain an acidic group-containing monomer in the above range in the monomer mixture (b).

Specific examples of the acidic group-containing monomer added as necessary to form the intermediate layer polymer include monomers similar to those exemplified as the acidic group-containing monomer used for forming the core polymer. Can be mentioned.
In addition, specific examples of other monomers copolymerizable with the acidic group-containing monomer include monomers similar to those exemplified as other copolymerizable monomers used for forming the core polymer. Can be mentioned.

  When the amount of the chain transfer agent used when forming the intermediate layer polymer is too small, the void ratio of the resulting hollow polymer particles becomes low. On the other hand, when the amount is excessive, not only the amount of aggregates generated during polymerization is increased, but also the porosity is lowered.

As the chain transfer agent, a known chain transfer agent used in general emulsion polymerization can be used.
Specific examples of such chain transfer agents include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, and t-tetradecyl mercaptan. Xanthogen disulfides such as dimethylxanthogen disulfide, diethylxanthogen disulfide and diisopropylxanthogen disulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetrabutylthiuram disulfide; halogenated carbonization such as carbon tetrachloride and carbon tetrabromide Hydrogens; hydrocarbons such as diphenylethylene, pentaphenylethane, α-methylstyrene dimer; and acrolein, Rain, allyl alcohol, 2-ethylhexyl thioglycolate, terpinolene, alpha-terpinene, .gamma.-terpinene, and the like dipentene. These can be used alone or in combination of two or more. Of these, mercaptans and α-methylstyrene dimer are preferable, mercaptans are more preferable, and t-dodecyl mercaptan is particularly preferable.

The weight ratio of the core polymer to the intermediate layer polymer (core / intermediate layer) is usually 5/95 to 70/30, preferably 30/70 to 60/40, more preferably 40/60 to 55/45. Range.
When the ratio of the intermediate layer polymer is excessive, the base hardly penetrates into the polymer particles in the base treatment step, and void formation in the polymer particles tends to be difficult. On the other hand, if the proportion of the intermediate layer polymer is too small, the core polymer tends to move to the outside of the outer layer polymer during polymerization or in the base treatment step, and void formation tends to be difficult.

  As the polymerization method for forming the intermediate layer polymer, an emulsion polymerization method is usually employed, and any method such as batch, continuous, and semi-continuous methods can be employed. As for the material, known conditions and polymerization auxiliary materials can be used as in the case of the core polymer.

3. Outer layer polymer The outer layer polymer is formed on the outer periphery of polymer particles composed of a core polymer and an intermediate layer polymer, and substantially encloses the core / intermediate layer polymer.
The outer layer polymer constituting the hollow polymer particle of the present invention is an acid group-containing monomer of 0 to 3.5% by weight in the presence of the polymer particle in which the intermediate layer polymer surrounding the core polymer is formed. A monomer mixture (c) comprising preferably 0.2 to 2% by weight and 100 to 96.5% by weight, preferably 99.8 to 98% by weight, of other monomers copolymerizable therewith. It is formed by polymerization.
In addition, from the point which can make a porosity higher, the ratio of the acidic group containing monomer in a monomer mixture (c) is made smaller than the ratio of the acidic group containing monomer in a monomer mixture (b). It is preferable.
Here, if the amount of the acidic group-containing monomer is excessive, the size of voids formed in the polymer particles is reduced, and the shell thickness surrounding the voids is increased, thereby making the hollow polymer particles opaque. As the effect decreases, the amount of aggregates generated during polymerization increases. It is preferable to contain an acidic group-containing monomer in the above-mentioned range in the monomer mixture (c) from the viewpoint that the hollow polymer particles having a high porosity can be stably produced more efficiently.

Examples of the acid group-containing monomer added as necessary when forming the outer layer polymer include the acid group-containing monomers exemplified as the core polymer-forming monomer.
Specific examples of other monomers copolymerizable with the acid group-containing monomer used in forming the outer layer polymer include those exemplified as other copolymerizable monomers used in forming the core polymer. And the same monomers. As another monomer used here, an aromatic vinyl monomer and an ethylenically unsaturated carboxylic acid ester monomer are preferable, an aromatic vinyl monomer is more preferable, and styrene can be particularly preferably used. When using other monomers other than the aromatic vinyl monomer, it is preferable to use the aromatic vinyl monomer in a proportion of 90% by weight or more of the total amount of the monomer mixture (c).

The chain transfer agent described above can also be used when forming the outer layer polymer for the purpose of promoting base permeation into the polymer particles in the base treatment step, but the amount of aggregates produced during production may increase. Therefore, the copolymerization of the monomer mixture (c) is preferably performed in the absence of a chain transfer agent.
In addition, when a chain transfer agent is used in forming the core polymer, the amount of aggregates tends to increase, so the copolymerization of the monomer mixture (a) is performed in the absence of the chain transfer agent. It is preferable.

The weight ratio of the polymer particles consisting of the core polymer and the intermediate layer polymer to the outer layer polymer ((core polymer + intermediate layer polymer) / outer layer polymer) is usually 5/95 to 50/50, The range is preferably 8/92 to 35/65, more preferably 10/90 to 25/75.
When the ratio of the outer layer polymer is excessive, it is difficult for the base to penetrate into the polymer particles during the base treatment, and the porosity tends to decrease. On the other hand, if the proportion of the outer layer polymer is too small, the core polymer tends to move to the outside of the outer layer polymer during polymerization or in the base treatment step, and void formation tends to be difficult.

  As the polymerization method for forming the outer layer polymer, an emulsion polymerization method is usually employed as in the case of the intermediate layer polymer, and the polymerization method, polymerization conditions, and auxiliary materials for polymerization are also known in the same manner. Things are taken.

4). Base treatment By adding a base to an aqueous dispersion containing polymer particles having at least a three-layer structure consisting of a core polymer, an intermediate layer polymer and an outer layer polymer, the pH of the aqueous dispersion is adjusted to 7 or more, At least one void is formed in the polymer particles (the void is filled with an aqueous liquid that forms an aqueous dispersion).

As the base, a volatile base and / or a nonvolatile base can be used.
Examples of the volatile base include ammonia, ammonium hydroxide, morpholine, trimethylamine, triethylamine and the like.
Nonvolatile bases include, for example, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; And alkali metal (bi) carbonates such as potassium carbonate; (bi) ammonium carbonate salts such as ammonium carbonate and ammonium bicarbonate; and the like.
Among the bases, volatile bases are preferable, and ammonia and ammonium hydroxide can be more preferably used.
The amount of the base used is an amount that neutralizes at least a part of the acidic groups of the core polymer so that the aqueous dispersion containing the polymer particles having the at least three-layer structure has a pH of 7 or more. .

In order to neutralize at least a part of the acid groups of the core polymer by adding the base to the aqueous dispersion, it is necessary to allow time for the base to diffuse into the polymer particles. Thereafter, it is desirable to sufficiently stir over time.
The treatment temperature in the base treatment is preferably equal to or higher than the temperature at which the polymer particles can be sufficiently softened. The treatment time after the base addition is usually about 15 minutes to 90 minutes.
The stability of the aqueous dispersion may decrease due to the addition of a base. To prevent this, an anionic surfactant or a nonionic surfactant may be added alone or in combination before adding a base. Good.

  In the base treatment step, a base may be added in the presence of an organic solvent according to the method disclosed in JP-A-3-26724. The use of an organic solvent softens the polymer particles and promotes base diffusion. Examples of the organic solvent include aromatic hydrocarbons, halogenated hydrocarbons, alcohols, ethers, ketones, saturated carboxylic acid esters, and the like. The organic solvent is usually used in the range of 0.1 to 1000 parts by weight with respect to 100 parts by weight of the polymer particles. The used organic solvent can be removed by evaporation after the base treatment.

  In the base treatment step, a polymerizable monomer may be present instead of the organic solvent. As the polymerizable monomer, a monomer containing no acidic group is usually used. The polymerizable monomer is generally used in an amount of 1 to 20 parts by weight, preferably 2 to 10 parts by weight, based on 100 parts by weight of the polymer particles. The polymerizable monomer may be newly added or added in excess during the formation of the outer layer polymer, and the above base treatment in a state where the polymerization reaction is stopped by adding a polymerization inhibitor or a reducing agent or the like. May be performed. Excess polymerizable monomer can be treated by adding a polymerization initiator or the like after the base treatment for polymerization.

  Even if the formation of the core polymer, the formation of the intermediate layer polymer, the formation of the outer layer polymer and the base treatment are carried out stepwise in the same reactor, the product of the previous step is performed after the previous step is performed. May be transferred to another reactor, and the next step may be performed in the reactor.

The number average particle diameter of the hollow polymer particles of the present invention is usually 0.2 to 3 μm, preferably 0.4 to 2 μm, more preferably 0.8 to 1.5 μm. This particle diameter is a simple average value obtained by measuring the maximum particle diameter of 200 hollow polymer particles using a transmission electron microscope.
The porosity of the hollow polymer particles of the present invention is usually 45 to 60%, preferably 50 to 55%. The porosity is simply determined by measuring the maximum particle diameter and the maximum void diameter of each hollow polymer particle 200 using a transmission electron microscope, and calculating from the numerical values. The average value.

  The hollow polymer particles of the present invention and aqueous dispersions thereof are, for example, organic pigments, light scattering agents or light scattering aids in coatings such as paper, ink, fiber and leather, paints, etc .; thermal printer paper, thermal transfer printers Heat-sensitive layer undercoat for paper and thermal paper; Absorbent filler for inkjet paper, internal filler for papermaking process, high hiding pigment for correction ink and correction ribbon, microcapsule material, toner used in electrophotography Intermediate materials, applications that use the heat insulation properties of air, applications that use weight reduction by air, such as weight reduction by internal addition to resin, cement, concrete, etc. It can be used for applications that utilize the property. Especially, it is suitable for a paper coating composition, and not only can improve the opacity of the coated paper, but also a highly glossy coated paper can be produced.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples. “Parts” and “%” in these examples are based on weight unless otherwise specified.

The physical properties were measured as follows.
(1) Aggregate generation amount (%)
An aqueous dispersion containing hollow polymer particles corresponding to a total solid content of 150 g was filtered through a 325 mesh wire mesh, the residue on the wire mesh was washed with water, and dried at 105 ° C. for 4 hours. The ratio of the dry weight of the residue on the wire net to the total solid content of 150 g was obtained as a percentage.
(2) Number average particle diameter Using a transmission electron microscope, the maximum particle diameter of 200 hollow polymer particles was measured, and they were obtained by simple averaging.
(3) Volume average particle size The volume average particle size of the seed latex and the core polymer is determined based on the volume-based particle size distribution of the polymer particles using a light scattering diffraction particle size measuring device (LS-230: manufactured by Coulter). Based on the average particle diameter calculated by arithmetic averaging (referred to as “volume average particle diameter”).
(4) Porosity (%)
Using a transmission electron microscope, with respect to 200 hollow polymer particles, the maximum particle diameter and the maximum void diameter of each particle are measured, and the void ratio calculated by the following calculation is simply averaged. I got it.

Example 1
In a pressure vessel equipped with a stirrer, 50 parts of methyl methacrylate (MMA), 10 parts of butyl acrylate (BA), 40 parts of methacrylic acid (MAA), surfactant I (sodium polyoxyethylene alkyl ether sulfate: alkyl group) C ₁₂ H ₃₅ , ethylene oxide addition number 18) 0.9 part, sodium tripolyphosphate 0.15 part and ion-exchanged water 80 part are stirred to give an emulsion of monomer mixture (a) for core polymer formation Was prepared.

To a pressure resistant reactor equipped with a stirrer, 40 parts of ion-exchanged water and 0.28 part of seed latex (methyl methacrylate polymer particles having a volume average particle diameter of 82 nm) were added, and the temperature was raised to 85 ° C.
Next, 1.63 parts of a 3% aqueous solution of potassium persulfate was added, and 7% of the above emulsion was continuously added to the reactor over 3 hours, followed by further reaction for 1 hour.

Thereafter, 250 parts of ion-exchanged water and 18.6 parts of a 3% aqueous solution of potassium persulfate were added, and the remaining emulsion was continuously fed to the reactor over 3 hours while maintaining the reaction temperature at 85 ° C. Added to. After completing the continuous addition of the monomer emulsion, the reaction was continued for another 2 hours. The polymerization conversion rate was 99%.
The polymerization system was cooled to room temperature to obtain an aqueous dispersion containing a core polymer. The volume average particle size of the core polymer was 350 nm.

In a pressure vessel equipped with a stirrer, MMA 7.8 parts, BA 1.6 parts, MAA 0.6 parts, t-dodecyl mercaptan (TDM) 0.03 parts, surfactant I 0.02 parts and ion-exchanged water 16 Part was stirred to prepare an emulsion of the monomer mixture (b).
Separately, 79.44 parts of styrene (ST), 0.56 parts of MAA, 0.4 part of surfactant I and 130 parts of ion-exchanged water were stirred to prepare an emulsion of the monomer mixture (c).

An aqueous dispersion containing 130 parts of ion-exchanged water and 10 parts of the above core polymer was added to a pressure resistant reactor equipped with a stirrer, and the temperature was raised to 85 ° C.
Then, 10 parts of a 4% aqueous potassium persulfate solution was added and the above emulsion of monomer mixture (b) was continuously added to the reactor over 20 minutes. Thereafter, the emulsion of the monomer mixture (c) was continuously added to the reactor over 120 minutes.

Immediately after completing the continuous addition of the emulsion of the monomer mixture (c), 25 parts of 5% aqueous ammonia was added to raise the reaction temperature to 90 ° C. After base treatment for 1 hour, 10 parts of a 4% potassium persulfate aqueous solution was added, and the reaction was continued for another 2 hours. The polymerization conversion rate was 99%.
The polymerization system was cooled to room temperature to obtain an aqueous dispersion containing hollow polymer particles A. The aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

(Examples 2 and 3)
An aqueous dispersion containing hollow polymer particles B and C was obtained in the same manner as in Example 1 except that the polymerization formulation was changed as shown in Table 1. The polymerization conversion rate was 99% in all cases. Aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

(Comparative Example 1)
An aqueous dispersion containing hollow polymer particles D was obtained in the same manner as in Example 1 except that TDM was not used when forming the intermediate layer polymer. The polymerization conversion rate was 99%. The aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

(Comparative Example 2)
An aqueous dispersion containing hollow polymer particles E was obtained in the same manner as in Comparative Example 1 except that TDM was used in the amounts shown in Table 1 when forming the outer layer polymer. The polymerization conversion rate was 99%. The aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

(Comparative Example 3)
Aqueous dispersion containing hollow polymer particles F in the same manner as in Comparative Example 1 except that TDM is used in the amounts shown in Table 1 when the core polymer is formed, and the polymerization prescription shown in Table 1 is changed. A liquid was obtained. The polymerization conversion rate was 99%. The aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

(Comparative Example 4)
An aqueous dispersion containing hollow polymer particles G was obtained in the same manner as in Example 1 except that the amount of TDM shown in Table 1 was used when forming the intermediate layer polymer. The polymerization conversion rate was 99%. The aggregate generation amount, number average particle diameter and porosity were measured, and the results are shown in Table 1.

Abbreviations in the table are as follows.
MMA: Methyl methacrylate BA: Butyl acrylate MAA: Methacrylic acid TDM: t-Dodecyl mercaptan ST: Styrene

Table 1 shows the following.
When forming the intermediate layer polymer, the hollow polymer particles D of Comparative Example 1 obtained by polymerization without using TDM have a large amount of aggregates and a low porosity.
When forming the outer layer polymer, the hollow polymer particles E of Comparative Example 2 obtained by polymerization using TDM have a large amount of aggregates and a low porosity.
When the core polymer is formed, the hollow polymer particles F of Comparative Example 3 obtained by polymerization using TDM have a large amount of aggregates and a large decrease in porosity.
When forming the intermediate layer polymer, the hollow polymer particles G of Comparative Example 4 obtained by polymerization using a larger amount of TDM than the range specified in the present invention have a large amount of agglomerates and a porosity. Is also greatly reduced.
In contrast to these comparative examples, the hollow polymer particles A to C of the present invention have a very small amount of aggregates and a large porosity even though the number average particle diameter is large (Example 1). ~ 3).

The hollow polymer particles of the present invention can be suitably used in the fields of water-based paints, paper coating compositions and the like as organic pigments, heat insulating materials, opacifying agents and the like.

Claims (4)

(1) A core polymer obtained by copolymerizing a monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated monocarboxylic acid and 80 to 40% by weight of another monomer copolymerizable therewith. ,
(2) A monomer mixture (b) comprising 1 to 15% by weight of an ethylenically unsaturated monocarboxylic acid and 99 to 85% by weight of another monomer copolymerizable therewith is converted into a monomer mixture (b) At least one intermediate layer polymer formed by copolymerization in the presence of 0.1 to 1% by weight of a chain transfer agent, substantially surrounding the core polymer, based on the total amount;
(3) By copolymerizing a monomer mixture (c) consisting of 0.2 to 3.5% by weight of ethylenically unsaturated monocarboxylic acid and 99.8 to 96.5% by weight of aromatic vinyl monomer . Formed by having at least a three-layer structure consisting of an outer layer polymer substantially surrounding the intermediate layer polymer formed, and at least a part of acidic groups contained in the core polymer being neutralized It is to have at least one void,
Hollow polymeric particles wherein the core polymer and said outer layer wherein the polymer der Rukoto those formed by copolymerizing without the addition of chain transfer agent. An aqueous dispersion of hollow polymer particles according to claim 1. (1) A monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated monocarboxylic acid and 80 to 40% by weight of another monomer copolymerizable therewith without adding a chain transfer agent Preparing core polymer particles by copolymerization,
(2) A monomer mixture (b) comprising 1 to 15% by weight of ethylenically unsaturated monocarboxylic acid and 99 to 85% by weight of other monomers copolymerizable therewith in the presence of the core polymer particles. At least one layer substantially surrounding the polymer particles by copolymerizing in the presence of 0.1 to 1% by weight of a chain transfer agent with respect to the total amount of the monomer mixture (b) Forming an intermediate layer polymer of
(3) 0.2 to 3.5% by weight of an ethylenically unsaturated monocarboxylic acid and an aromatic vinyl monomer in the presence of polymer particles in which an intermediate layer polymer surrounding the core polymer particles is formed. By copolymerizing the monomer mixture (c) consisting of 99.8 to 96.5% by weight without adding a chain transfer agent, an outer layer polymer substantially surrounding the intermediate layer polymer is formed. ,
(4) A base is added to the obtained aqueous dispersion containing polymer particles having at least a three-layer structure so that the pH of the dispersion is 7 or more.
The manufacturing method of the hollow polymer particle characterized by including the process of said (1)-(4). A process for producing an aqueous dispersion of hollow polymer particles, comprising the steps (1) to (4) according to claim 3.