WO2018092554A1 - Method for producing thermally expandable microspheres - Google Patents

Abstract

The purpose of the present invention is to provide a method for producing thermally expandable microspheres, whereby it becomes possible to reduce the use amount of a silica sol compared with those in the conventional methods. A method for producing thermally expandable microspheres, in which an aqueous dispersion medium is prepared by mixing (a) an aqueous silica sol having a pH value of 9 to 11 and an SiO₂ concentration of 15 to 40% by weight, (b) a dispersion stabilization aid, (c) an acid, (d) water and (e) a polymerization aid together. In the step of preparing the aqueous dispersion medium, when the time point at which the preparation of the aqueous dispersion medium starts is defined as T0, the time point at which the preparation of the aqueous dispersion medium is completed is defined as T100, the SiO₂ concentration in an intermediate of the aqueous dispersion medium which is produced at an arbitrary time point T that satisfies the formula: T0 < T < T100 is defined as A_T% by weight, and the SiO₂ concentration in the aqueous dispersion medium at T100 is defined as A_T100% by weight, the pH value of the intermediate at A_T that satisfies the formula: 0 < A_T < 15 is kept in a range from 0.8 to 7 and the A_T100 value is adjusted to 0.5 to 8.

Description

Method for producing thermally expandable microspheres

The present invention relates to a method for producing thermally expandable microspheres. More specifically, a method for producing thermally expandable microspheres using silica sol as a raw material for an aqueous dispersion medium, and capable of reducing the amount of silica sol used compared to conventional methods. Regarding the method.

Thermally expansible microspheres having a structure in which a thermoplastic resin is used as an outer shell and a foaming agent is enclosed therein are used in a wide range of fields, such as weight reduction of resins and paints, and application of wallpaper and ink designs. As the polymerizable component of the thermoplastic resin material, vinylidene chloride, (meth) acrylonitrile-based monomers, (meth) acrylic acid ester-based monomers and the like are usually used. Moreover, hydrocarbons, such as isobutane and isopentane, are mainly used as a foaming agent (refer patent document 1).

In general, a method for producing thermally expandable microspheres includes a step of preparing an aqueous dispersion medium by mixing water, a dispersion stabilizer, a dispersion stabilization auxiliary agent, and the like, and a polymerizable component, a foaming agent and a polymerization agent in the aqueous dispersion medium. And dispersing an oily mixture containing an initiator to polymerize the polymerizable component. When silica sol is used as a dispersion stabilizer, silica particles derived from silica sol are mixed in wastewater in the process of producing thermally expandable microspheres, particularly in the process of solid-liquid separation. Therefore, it is desired to reduce the amount of silica sol used as much as possible. Also, from the viewpoint of manufacturing cost, it is desirable to reduce the amount of silica sol used as much as possible.

By the way, there are two types of aqueous silica sols in which amorphous silica particles are dispersed in an aqueous medium: alkaline silica sols and acidic silica sols. Of these, alkaline silica sol is usually used in the method for producing thermally expandable microspheres. By using alkaline silica sol, thermally expandable microspheres can be produced efficiently.
However, in the method for producing thermally expandable microspheres using alkaline silica sol, the aqueous dispersion medium is not subjected to suspension polymerization while maintaining an alkaline state. That is, an aqueous dispersion medium prepared by mixing alkaline silica sol with water and other necessary components is usually added with an acid such as sulfuric acid or hydrochloric acid at the final stage of the process, and the pH is changed from the alkaline side to the acidic side ( After being adjusted to about 2-4, it is subjected to suspension polymerization.

In general, it is known that aqueous silica sol has the property that when the pH of the liquid is greatly changed, the dispersion state is broken and the silica particles are aggregated or settled. In this production method, it can be said that the amorphous silica particles stably dispersed in the aqueous medium are used in a state of being destabilized (aggregated state).
Thus, in the method for producing thermally expandable microspheres using alkaline silica sol, it is considered that the produced aggregated silica particles function as a true dispersion stabilizer. However, there is no example that reports in detail about the conditions under which aggregated silica particles can be produced to exhibit a better function as a dispersion stabilizer and consequently reduce the amount of silica sol used. . Patent Document 2 describes a process for producing thermally expandable microspheres that use silica sol as a dispersion stabilizer and reduce the turbidity of washing wastewater by setting the amount of alkali components contained in the silica sol within a predetermined range. . However, this production method merely reduces the whitening of the washing waste water by firmly attaching the silica particles to the surface of the thermally expandable microspheres, and discloses a method for reducing the amount of silica sol used. It is not a thing.

US Pat. No. 3,615,972 Japanese Unexamined Patent Publication No. 2013-212433

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing thermally expandable microspheres capable of reducing the amount of silica sol used as compared with the conventional method.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved if an aqueous dispersion medium is prepared so as to satisfy specific conditions after using specific raw materials, The present invention has been reached.
That is, the present invention relates to a method for producing thermally expandable microspheres comprising a step of dispersing an oily mixture containing a polymerizable component, a foaming agent and a polymerization initiator in an aqueous dispersion medium and polymerizing the polymerizable component. The aqueous dispersion medium has an aqueous silica sol (a) having a pH of 9 to 11 and an SiO ₂ concentration of 15 to 40% by weight, a dispersion stabilizing aid (b), an acid (c), water (d ) And a polymerization aid (e), and in the step of preparing the aqueous dispersion medium, the preparation start time of the aqueous dispersion medium is T0, the preparation end time is T100, and T0 <T <T100 is satisfied. When the SiO ₂ concentration of the intermediate of the aqueous dispersion medium produced at an arbitrary time T is _AT wt%, and the SiO ₂ concentration of the aqueous dispersion medium at T 100 is _{AT 100} wt%, A satisfying 0 <A _T <15 in the _T, said in The pH of the body is maintained in the range of 0.8 to ₇ and _{A T100} 0.5 to 8, and method for producing heat-expandable microspheres.

2 to 100 parts by weight of the aqueous silica sol (a), 0.01 to 5 parts by weight of the dispersion stabilizing aid (b), and the polymerization aid (e) with respect to 100 parts by weight of the water (d). It is preferable to use 0.0001 to 0.1 parts by weight.
It is preferable to use 150 to 1000 parts by weight of the aqueous dispersion medium with respect to 100 parts by weight of the oily mixture.
The aqueous dispersion medium is preferably prepared by further mixing an inorganic salt (f). In this case, the aqueous dispersion medium contains an inorganic salt aqueous solution obtained by dissolving a part or all of the inorganic salt (f) in a part or all of the water (d), and the aqueous silica sol (a). It is preferable to prepare by mixing.

The method for producing thermally expandable microspheres according to the present invention reduces the amount of silica sol used compared to the conventional method, and therefore has a small environmental load in the production wastewater treatment.

Is a diagram illustrating an example of a SiO ₂ concentration changes in intermediates of the aqueous dispersion medium. (When the SiO ₂ concentration _AT increases) Is a diagram illustrating an example of a SiO ₂ concentration changes in intermediates of the aqueous dispersion medium. (When the SiO ₂ concentration _AT decreases) It is the schematic which shows an example of a thermally expansible microsphere. It is the schematic which shows an example of a hollow particle.

[Method for producing thermally expandable microspheres]
In the method for producing thermally expandable microspheres of the present invention, an oily mixture containing a polymerizable component, a foaming agent and a polymerization initiator is dispersed in an aqueous dispersion medium, and the polymerizable component is polymerized (hereinafter referred to as “the polymerizable component”). A suspension polymerization step). Hereinafter, the present invention will be described in detail.

The suspension polymerization step includes a step of preparing an aqueous dispersion medium.
The aqueous dispersion medium is a medium for dispersing the oily mixture, and has an aqueous silica sol (a) having a pH of 9 to 11 and an SiO ₂ concentration of 15 to 40% by weight, a dispersion stabilizing aid (b), an acid ( It is prepared by mixing c), water (d), and polymerization aid (e). First, details of each component will be described.

(A): Aqueous silica sol The aqueous silica sol used in the present invention is a colloidal dispersion of silica particles in which amorphous silica particles are dispersed in an aqueous medium, having a pH of 9 to 11, and a SiO ₂ concentration. Is 15 to 40% by weight.
In the method for producing thermally expandable microspheres, silica particles derived from an aqueous silica sol stabilize the dispersion state of oil droplets dispersed in an aqueous dispersion medium, and serve as a dispersion stabilizer that keeps the dispersion system stable during polymerization. It is a component that plays a role. While examining the subject of the present invention to reduce the amount of silica sol used, the inventors have prepared an aqueous dispersion medium using an aqueous silica sol having the specific pH and SiO ₂ concentration. It was found that the amount of aqueous silica sol used can be reduced by keeping the pH of the system acidic in the range where the SiO ₂ concentration is low. The pH of the aqueous silica sol used in the present invention is preferably 9.0 to 10.5, more preferably 9.5 to 10.5, and the SiO ₂ concentration is preferably 18 to 38% by weight, more preferably 20 to 35% by weight.

In general, in an aqueous silica sol, when the pH of the liquid fluctuates greatly, the amount of ions in the liquid becomes very large, or the dilution ratio becomes very large, bonding occurs between the silica particles, and the aggregated silica particles are formed. It is known to generate. As a mechanism of the formation of the agglomerated silica particles, silica particles (primary particles) having a size of several nanometers to several tens of nanometers initially form aggregated silica particles (secondary particles) of about several hundred nanometers by bonding. Furthermore, it is known that these agglomerated silica particles (secondary particles) combine to produce agglomerated large particles of about several μm, and the formation of such agglomerated silica particles is observed in the form of cloudiness of the liquid. Is done.

General alkaline silica sol is stable in the alkaline region and can exist stably even in the acidic region (pH 4 or lower), while the alkaline silica sol is unstable in the neutral region, and the aggregation of silica particles (primary particles) It is known to progress. Conventionally, since an aqueous dispersion medium is prepared by acidifying an alkaline silica sol through a neutral region that is temporarily unstable, agglomerated silica particles (secondary particles) are easily agglomerated in silica particles (primary particles). ) Is considered to be large. On the other hand, in the method of the present invention, when the silica particles are aggregated, they do not pass through an unstable neutral region, so the size of the generated aggregated silica particles is small, and this exhibits an excellent function as a dispersion stabilizer. It is estimated that

Examples of the shape of the amorphous silica particles contained in the aqueous silica sol include a spherical shape, a chain shape, a bead shape, and a flat shape. Among these, a spherical shape is preferable.
The particle diameter of the amorphous silica particles is not particularly limited, but is preferably 1.0 to 50 nm, more preferably 2.0 to 40 nm, and still more preferably 3.0 to 30 nm. When the particle diameter is outside this range, the suspension system is insufficiently stable, and the dispersion system may be broken during the polymerization. In addition, the particle diameter of the amorphous silica particle here means the conversion value from the specific surface area measured value (JIS Z8830) by the BET adsorption method.

The specific surface area of the amorphous silica particles is not particularly limited, is preferably 54 ~ 2720m ² / g, more preferably 68 ~ 1360m ² / g, more preferably 91 ~ 910m ² / g. In addition, the specific surface area of an amorphous silica particle here means what is measured by the Sears method. As described in Analytical Chemistry, Vol. 28, No. 12 (December 1956), p. 1981, the Sears method determines the specific surface area by quantifying the amount of silanol groups on the surface of silica particles. It is a method of measuring.

Various grades of aqueous silica sol are commercially available. For example, "Quatron" series manufactured by Fuso Chemical Industry Co., Ltd., "Adelite" series manufactured by ADEKA Co., Ltd., "Silica Doll" series manufactured by Nippon Chemical Industry Co., Ltd. “Snowtex” series manufactured by Nissan Chemical Industries, Ltd., “Ludox” series manufactured by Dupont, and the like. As the aqueous silica sol used in the present invention, those satisfying the above specific pH and SiO ₂ concentration can be appropriately selected from these commercially available products.
The amount of the aqueous silica sol (a) is preferably 2 to 100 parts by weight, more preferably 2 to 80 parts by weight with respect to 100 parts by weight of water (d).

(B): Dispersion stabilizing aid The dispersion stabilizing aid aggregates the aqueous silica sol, and makes the coalesced oil droplets containing a polymerizable monomer coalesced by causing the aggregated silica particles to exist at the water / oil interface. It is a component which suppresses and stabilizes the polymerization process. The dispersion stabilizing aid is not particularly limited, and examples thereof include polymer type dispersion stabilizing aids; interfaces such as cationic surfactants, anionic surfactants, zwitterionic surfactants and nonionic surfactants. Mention may be made of activators. Among these, a polymer type dispersion stabilizing aid is preferable. One dispersion stabilizer may be used alone, or two or more dispersion stabilizers may be used in combination.
Examples of the polymer type dispersion stabilizing auxiliary agent include condensation products of diethanolamine and aliphatic dicarboxylic acid, condensation products of urea and formaldehyde, polyvinylpyrrolidone, polyethylene oxide, gelatin, methylcellulose, polyvinyl alcohol and the like. .

Examples of the cationic surfactant include alkylamine salts such as laurylamine acetate and stearylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride.
Examples of the anionic surfactant include fatty acid salts such as sodium oleate and castor oil potassium; alkyl sulfate salts such as sodium lauryl sulfate and ammonium lauryl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; alkylnaphthalene sulfone. Examples include acid salt; alkane sulfonate; dialkyl sulfosuccinate; alkyl phosphate ester salt; naphthalene sulfonic acid formalin condensate; polyoxyethylene alkyl phenyl ether sulfate ester; polyoxyethylene alkyl sulfate ester salt.
Examples of the zwitterionic surfactant include alkyldimethylaminoacetic acid betaine, alkyldihydroxyethylaminoacetic acid betaine, and lauryldimethylamine oxide.
Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin fatty acid Examples thereof include esters and polyoxyethylene-polyoxypropylene block polymers.
These dispersion stabilizing aids may be diluted with water (d) in advance and used as an active ingredient, for example, in the form of an aqueous solution of about 10 to 50% by weight.
The blending amount of the dispersion stabilizing auxiliary (b) is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight with respect to 100 parts by weight of water (d).

(C); Acid The acid used in the present invention is a component used for the purpose of maintaining the pH of the aqueous dispersion medium acidic, and it is usually sufficient to add a very small amount to the aqueous dispersion medium.
The acid is not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, and organic acids such as formic acid, acetic acid, and oxalic acid. In these, an inorganic acid is preferable and a sulfuric acid is especially preferable. These acids may be used individually by 1 type, and may use 2 or more types together.
These acids may be diluted with water (d) in advance and used as an active ingredient, for example, in the form of an aqueous solution of about 10 to 50% by weight.
The compounding amount of the acid (c) is not particularly limited. In the present invention, as described later, in the step of preparing the aqueous dispersion medium, the acid (c) may be appropriately adjusted so as to maintain the pH within a desired range.

(D); Water Water used in the present invention is a component constituting most of the aqueous dispersion medium. Examples of water include pure water, distilled water, purified water, soft water, ion exchange water, industrial water, well water, tap water, and the like. Among these, soft water and / or ion exchange water are preferable.

(E): Polymerization aid The polymerization aid used in the present invention is a component that suppresses the generation of an emulsion polymer in an aqueous dispersion medium and also prevents the generation of scale (scum). The scale (scum) means a huge polymer lump that adheres to the inner wall of the reactor, the stirring blade, or the like after the polymerization reaction, or floats in the slurry after polymerization.
The polymerization aid is not particularly limited. For example, a polyalkyleneimine having a structure in which an alkyl group substituted with a hydrophilic functional group selected from a carboxylic acid (salt) group and a phosphonic acid (salt) group is bonded to a nitrogen atom. Water-soluble 1,1-substituted compounds having a structure in which a hetero atom and a hydrophilic functional group selected from a hydroxyl group, a carboxylic acid (salt) group and a phosphonic acid (salt) group are bonded to the same carbon atom; Dichromates such as sodium chromate, potassium dichromate and ammonium dichromate; alkali metal nitrites such as sodium nitrite and potassium nitrite; zirconium salts such as zirconium sulfate, zirconium acetate, zirconium chloride and zirconium nitrate; Titanium chloride; metal (III) halide; boric acid; water-soluble ascorbic acids; water-soluble polypheno S; water-soluble vitamin B; water-soluble phosphonic acid (salt) and the like can be mentioned. In addition, water solubility here means the state which melt | dissolves 1g or more per 100g of water. These polymerization aids may be used alone or in combination of two or more.
The blending amount of the polymerization aid (e) is preferably 0.0001 to 1 part by weight, more preferably 0.001 to 0.1 part by weight with respect to 100 parts by weight of water (d).

(F): Inorganic salt The aqueous dispersion medium in the present invention may be prepared by further mixing an inorganic salt or the like.
Examples of inorganic salts include sodium chloride, magnesium chloride, calcium chloride, sodium sulfate, magnesium sulfate, ammonium sulfate, and sodium carbonate. These inorganic salts may be used alone or in combination of two or more. When the polymerizable component described later contains a high amount of highly water-soluble monomers, it is preferable to use an inorganic salt in the aqueous dispersion medium in order to suppress elution of these monomers into the aqueous dispersion medium. .
When an inorganic salt is used, the compounding amount of the inorganic salt is preferably 0 to 40 parts by weight, more preferably 1 to 32 parts by weight with respect to 100 parts by weight of water (d).

Next, the process for preparing the aqueous dispersion medium will be described.
In the present invention, in the step of preparing the aqueous dispersion medium, the aqueous dispersion medium intermediate produced at any time T satisfying T0 <T <T100, where T0 is the preparation start time of the aqueous dispersion medium and T100 is the preparation end time. the SiO ₂ concentration _{a T} wt%, when the SiO ₂ concentration of the aqueous dispersion medium in the T100 was _{a T100} wt%, _{0 <in} the _{a T} satisfying a T <15, 0 and the pH of the intermediate The range of 8 to 7 is maintained, and _{AT 100 is set} to 0.5 to 8.
Here, the preparation start time T0 of the aqueous dispersion medium means a point in time when any two or more of (a) to (f) described above are started to be mixed, and an intermediate of the aqueous dispersion medium ( Hereinafter, the term “intermediate” may be used to mean any mixture produced by mixing any two or more of (a) to (f) described above. In the step of preparing the aqueous dispersion medium, the number of intermediates is not necessarily one, and two or more intermediates may be present. Further, the preparation end time T100 of the aqueous dispersion medium means a time point when all components necessary for preparation of the aqueous dispersion medium have been mixed.

The above procedure roughly means that when the aqueous silica sol (a) is diluted mainly with water (d), the pH of the intermediate is kept acidic. By doing in this way, the usage-amount of aqueous silica sol (a) can be reduced.

The SiO ₂ concentration _AT of the intermediate can be obtained by calculation from the initial SiO ₂ concentration of the aqueous silica sol (a) and the amount of each component (a) to (f) required to produce the intermediate. it can.
The SiO ₂ concentration _AT of the intermediate changes in the following two ways depending on the blending order of the aqueous silica sol.
(I) When _AT increases When water is prepared in advance and a dispersion stabilizing aid and an aqueous silica sol are mixed here, _AT increases as the aqueous silica sol is added. A schematic diagram showing the transition of the SiO ₂ concentration _AT in this case is shown in FIG. In FIG. 1, _AT satisfies 0 <A _T <15 in the range of T0 <T <T100. If the pH is maintained in the range of 0.8 to 7 in this range, the effect of the present application is exhibited. Further, SiO ₂ concentration _{A T100} in the preparation end time T100 of the aqueous dispersion medium is prepared as a 0.5-8.
(B) When _AT decreases When an aqueous silica sol is prepared first and then water and a dispersion stabilizing aid are mixed, _AT decreases as water or the like is added. A schematic diagram showing the transition of the SiO ₂ concentration _AT in this case is shown in FIG. In FIG. 2, when the time when the SiO ₂ concentration _AT is 15 wt% is Tx, the time satisfying 0 <A _T <15 is in the range of Tx <T <T100, and in this range the pH is 0.8 to 7 If maintained in the range, the effect of the present application is exhibited. Further, SiO ₂ concentration _{A T100} in the preparation end time T100 the aqueous dispersing medium in this case is prepared so as to 0.5-8.

In order to maintain the pH of the intermediate in the range of 0.8 to 7, the acid (c) described above is used. Usually, in the aqueous silica sol (a), a small amount of Na ₂ O is blended as an alkali component. If the amount of the aqueous silica sol (a) blended in the aqueous dispersion medium is determined, the amount of Na ₂ O contained therein is determined. The amount of acid (c) required to maintain the pH of the intermediate in the range of 0.8-7 can be predicted. Further, if necessary, a method such as appropriately adding the acid (c) while confirming the pH of the intermediate with a pH meter as needed may be used.

Thus, in the present invention, it is naturally desirable to always maintain the pH of the intermediate in the range of 0.8 to 7 in _AT satisfying 0 <A _T <15. In nature, for example, just because there was a moment when the pH of the intermediate exceeded 7 does not mean that the effect of the invention is immediately lost.
The pH of the intermediate may be maintained in the range of 0.8-7, preferably 1-6, more preferably 2-5.
_{AT 100} is usually from 0.5 to 8, preferably from 0.6 to 7, more preferably from 0.7 to 6.5. When _AT100 is less than 0.5, the stability of the suspension system is insufficient, and the dispersion system is broken during the polymerization. When _AT100 is larger than 8, the amount of the aqueous silica sol (a) to be used increases and the effect of the present invention is not exhibited.
The pH of the aqueous dispersion medium at T100 is preferably 2 to 6, more preferably 2 to 4. When the pH is outside the range of 2 to 6, the stability of the suspension system is insufficient, and the dispersion system may be broken during the polymerization.

During the step of preparing the aqueous dispersion medium, it is preferable to keep stirring the intermediate. Stirring may be performed using a normal stirring device, and the method is not particularly limited. For example, a bar-like, plate-like, propeller-like stirrer is rotated in a constant direction at a constant speed via a rotating shaft. And the like.
The required power per unit volume required for preparing the aqueous dispersion medium is not particularly limited, but from the viewpoint of making the aqueous dispersion medium uniform, the required power per unit volume of 0.1 to 10 kW / m ³ is required. It is preferable to stir with power.

Although the process of preparing an aqueous dispersion medium will not be restrict | limited especially if the conditions demonstrated above are satisfy | filled, the following aspects are mentioned specifically.
Aspect 1:
Water (d) is added to a container for preparing an aqueous dispersion medium (hereinafter simply referred to as a container) equipped with a stirrer, and the stirrer of the container is started. Next, the required amount of acid (c) is added to water (d) in the container. Further, a dispersion stabilizing aid (b) is added thereto. Then, the aqueous silica sol (a) is gradually added while maintaining the pH of the intermediate in the container in the range of 0.8-7.

Aspect 2:
In Embodiment 1, an aqueous dispersion medium is prepared in the same manner as in Embodiment 1 except that the order in which the acid (c) and the dispersion stabilizing auxiliary (b) are added is changed.
Aspect 3:
Water (d) is added to the container and the container agitator is activated. Next, the required amount of acid (c) is added to water (d) in the container. Then, the aqueous silica sol (a) is gradually added while maintaining the pH of the intermediate in the container in the range of 0.8-7. Thereafter, the dispersion stabilizing aid (b) is added.
Aspect 4:
Water (d) is added to the container and the container agitator is activated. Next, the dispersion stabilizing aid (b) is added to the water (d) in the container. Then, the aqueous silica sol (a) and the acid (c) are simultaneously added to the intermediate in the container via separate lines. At this time, each feed rate is adjusted so that the pH of the intermediate in the container is maintained in the range of 0.8-7.
Aspect 5:
Water (d) is added to the container and the container agitator is activated. Next, the aqueous silica sol (a) and the acid (c) are simultaneously added to the water (d) in the container via separate lines. At this time, each feed rate is adjusted so that the pH of the intermediate in the container is maintained in the range of 0.8-7. Thereafter, the dispersion stabilizing aid (b) is added.

Aspect 6:
Add the dispersion stabilizing aid (b) to the container. Next, the aqueous silica sol (a) is added and the stirring device of the container is started. Further, acid (c) is added to bring the pH of the intermediate in the container to a range of 0.8-7. Thereafter, water (d) is added.
Aspect 7:
Add the dispersion stabilizing aid (b) to the container. The acid (c) is then added. Furthermore, the aqueous silica sol (a) is added, and the stirring device of the container is started. At this time, the pH of the intermediate in the container is set to a range of 0.8-7. Thereafter, water (d) is added.
Aspect 8:
The aqueous silica sol (a) is added to the container, and the stirring apparatus of the container is started. Then acid (c) is added to bring the pH to the range of 0.8-7. Further, a dispersion stabilizing aid (b) and water (d) are added.
In Embodiments 1 to 8, the polymerization aid (e) may be added at any stage during preparation of the aqueous dispersion medium. In addition, as long as the pH of the intermediate in the container is maintained in the range of 0.8 to 7, there is no limitation on the supply rate of the aqueous silica sol (a) and the acid (c).

Aspects 1 to 8 are merely examples for explaining the embodiment of the present invention, and various other aspects are possible.
Further, when the components (a) to (e) are mixed, the components do not necessarily have to be mixed all at once, and may be mixed in multiple times at different times. That is, as such an embodiment, for example, in the embodiment 1, the step of adding the dispersion stabilizing auxiliary agent (b) is divided into two (referred to as the first addition step and the second addition step, respectively), and the first addition step is the embodiment 1. It can be performed immediately after adding the acid (c) in the same manner as described above, and the second addition step can be performed after adding the aqueous silica sol (a).

It is preferable that the aqueous dispersion medium is prepared by further mixing the inorganic salt (f) in addition to (a) to (e) because the effect of the present invention is further improved. The inorganic salt (f) may be added at any stage during preparation of the aqueous dispersion medium, but the aqueous dispersion medium dissolves part or all of the inorganic salt (f) in part or all of the water (d). It is preferable to prepare an inorganic salt aqueous solution obtained by mixing the aqueous silica sol (a).

In the technical field of the present invention, it is generally known that there is a relationship between the amount of silica particles used as a dispersion stabilizer and the particle diameter of the resulting thermally expandable microspheres. That is, to obtain thermally expandable microspheres having a large particle size, it is effective to reduce the amount of silica particles to be used, and conversely, to obtain thermally expandable microspheres having a small particle size. It is effective to increase the amount of silica particles. From such a background, the method of the present invention can be applied regardless of the particle size of the target thermally expandable microsphere, but particularly when producing a thermally expandable microsphere having a small particle size. Remarkably effective.

As described above, the present invention exhibits its effect by adopting a specific method in the step of preparing the aqueous dispersion medium. Therefore, there is no restriction | limiting in particular in the oily mixture used for this invention, It is possible to use all sorts of oily mixtures well-known as a manufacturing method of a thermally expansible microsphere. A typical example of an oily mixture is as follows.

The oily mixture contains a polymerizable component, a foaming agent and a polymerization initiator.
The polymerizable component is a component that becomes a thermoplastic resin that forms the outer shell of the thermally expandable microsphere by polymerizing in the presence of a polymerization initiator. The polymerizable component is a component which essentially includes a monomer component and may contain a crosslinking agent.
Here, the monomer component generally means a component called a radical polymerizable monomer having one polymerizable double bond.

The monomer component is not particularly limited. For example, nitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile; acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, maleic acid, itaconic acid, fumaric acid Carboxyl group-containing monomers such as acid, citraconic acid and chloromaleic acid; vinyl halide monomers such as vinyl chloride; vinylidene halide monomers such as vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate Vinyl ester monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate , Phenyl (meth) acrylate, isobornyl (meth) a (Meth) acrylic acid ester monomers such as relate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate; methacrylic, substituted acrylamide, methacrylamide, substituted methacrylamide, etc. ) Acrylamide monomers; Maleimide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide; Styrene monomers such as styrene and α-methylstyrene; Ethylene unsaturated monoolefins such as ethylene, propylene and isobutylene Monomers; vinyl ether monomers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; vinyl ketone monomers such as vinyl methyl ketone; N-vinyl such as N-vinyl carbazole and N-vinyl pyrrolidone Monomer, vinyl naphthalene salt and the like. A monomer component may be used individually by 1 type among these radically polymerizable monomers, and may use 2 or more types together. In addition, (meth) acryl means acryl or methacryl.

Polymerizable components include nitrile monomers, carboxyl group-containing monomers, (meth) acrylate monomers, styrene monomers, vinyl ester monomers, acrylamide monomers, and halogenated monomers. It is preferable to contain at least one monomer component selected from vinylidene monomers.

When the polymerizable component includes a nitrile monomer as a monomer component as an essential component, the resulting thermally expandable microspheres are preferable because of excellent solvent resistance. As the nitrile monomer, acrylonitrile, methacrylonitrile and the like are easily available, and are preferable because of high heat resistance and solvent resistance.
The weight ratio of the nitrile monomer is not particularly limited, but is preferably 20 to 100% by weight of the monomer component, more preferably 50 to 100% by weight, and particularly preferably 80 to 100% by weight. is there. When the nitrile monomer is less than 20% by weight of the monomer component, the effect of improving the solvent resistance may not be obtained.

It is preferable that the polymerizable component contains a carboxyl group-containing monomer as a monomer component as an essential component because the resulting heat-expandable microspheres are excellent in heat resistance. As the carboxyl group-containing monomer, acrylic acid or methacrylic acid is easy to obtain and is preferable because heat resistance is improved.

The weight ratio of the carboxyl group-containing monomer is not particularly limited, but is preferably 10 to 70% by weight, more preferably 25 to 45% by weight, and particularly preferably 30 to 45% by weight with respect to the monomer component. 40% by weight. When the carboxyl group-containing monomer is less than 10% by weight, the heat resistance improvement effect may not be obtained. On the other hand, when the carboxyl group-containing monomer is more than 70% by weight, the gas barrier property may be lowered.

When the polymerizable component contains vinylidene chloride, gas barrier properties are improved. Further, when the polymerizable component contains a (meth) acrylic acid ester monomer and / or a styrene monomer, the thermal expansion characteristics can be easily controlled. When the polymerizable component contains a (meth) acrylamide monomer, the heat resistance is improved.
The weight ratio of at least one selected from vinylidene chloride, (meth) acrylic acid ester monomer, styrene monomer, and (meth) acrylamide monomer is preferably relative to the monomer component. It is less than 80% by weight, more preferably less than 30% by weight.

The polymerizable component may contain a polymerizable monomer (crosslinking agent) having two or more polymerizable double bonds in addition to the monomer component. By polymerizing using a crosslinking agent, the retention of the foaming agent at the time of thermal expansion is improved, and thermal expansion can be effectively performed.

The crosslinking agent is not particularly limited. For example, divinylbenzene, allyl methacrylate, triacryl formal, triallyl isocyanate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) Acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, PEG # 200 di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, polypropylene glycol # 400 di (meth) acrylate, polypropylene glycol # 700 di (meth) acrylate Rate, trimethylolpropane trimethacrylate, EO-modified trimethylolpropane trimethacrylate, glycerin dimethacrylate, dimethylol-tricyclodecane diacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, 2-butyl -2-Ethyl-1,3-propanediol diacrylate, tris (2-acryloyloxyethyl) isocyanurate, triallyl isocyanurate, triallyl cyanurate, triglycidyl isocyanurate, polytetramethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, neopentyl glycol dimethacrylate, nonanediol diacrylate, It can be mentioned trimethylolpropane tri (meth) acrylate, 3-methyl-1,5-pentanediol diacrylate. These crosslinking agents may be used individually by 1 type, and may use 2 or more types together.
The amount of the crosslinking agent is not particularly limited and may be omitted. However, in consideration of the retention of the foaming agent during thermal expansion, the extensibility of the outer shell resin, the heat resistance, etc., the amount of the crosslinking agent is a single amount. The amount is preferably 0.01 to 5 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the body component.

The blowing agent is not particularly limited as long as it is a substance that is vaporized by heating. For example, propane, (iso) butane, (iso) pentane, cyclopentane, (iso) hexane, cyclohexane, methylcyclopentane, (iso ) Heptane, ethylcyclopentane, methylcyclohexane, (iso) octane, ethylcyclohexane, (iso) nonane, (iso) decane, (iso) undecane, (iso) dodecane, (iso) tridecane, (iso) hexadecane, (iso ) Hydrocarbons having 3 to 20 carbon atoms such as eicosane; pseudocumene, petroleum ether, hydrocarbons such as petroleum fractions such as normal paraffin and isoparaffin having an initial boiling point of 150 to 260 ° C. and / or a distillation range of 70 to 360 ° C. ; Methyl chloride, methylene chloride, chloroform, carbon tetrachloride, etc. Hydrocarbon halides having 1 to 12 primes; Fluorine-containing compounds such as hydrofluoroethers; having alkyl groups having 1 to 5 carbon atoms such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane Silanes; azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazide), and the like are compounds that generate a gas upon thermal decomposition by heating. These foaming agents may be used individually by 1 type, and may use 2 or more types together. The blowing agent may be linear, branched or alicyclic, and is preferably aliphatic.

The polymerization initiator is not particularly limited. For example, peroxides such as peroxydicarbonate, peroxyester, and diacyl peroxide; azo compounds such as azonitrile, azoester, azoamide, azoalkyl, and polymeric azo initiator Can be mentioned. These polymerization initiators may be used alone or in combination of two or more. The polymerization initiator is preferably an oil-soluble polymerization initiator that is soluble in the radical polymerizable monomer.

The amount of the polymerization initiator is not particularly limited, but is preferably 0.3 to 8 parts by weight, and more preferably 0.6 to 7 parts by weight with respect to 100 parts by weight of the polymerizable component.
The oily mixture may further contain a chain transfer agent, an organic pigment, a thermosetting resin, and the like.

In the suspension polymerization step, the oily mixture is dispersed in an aqueous dispersion medium so that spherical oil droplets having a predetermined particle diameter (usually about 1 to 100 μm) are prepared.
As a method for dispersing the oily mixture, for example, a method of stirring with a homomixer (for example, manufactured by Primix Co., Ltd.), a homodisper (for example, manufactured by Primix Co., Ltd.) or the like, And the like, a general dispersion method such as a method using a static dispersion apparatus such as a membrane emulsification method, an ultrasonic dispersion method, and a microchannel method.
Further, the ratio of the aqueous dispersion medium and the oily mixture is not particularly limited, but it is preferable to use 150 to 1000 parts by weight of the aqueous dispersion medium with respect to 100 parts by weight of the oily mixture. When the amount of the aqueous dispersion medium is less than 150 parts by weight, the amount of the dispersion medium with respect to the dispersoid is insufficient, so that an O / W emulsion may not be obtained. On the other hand, when the amount of the aqueous dispersion medium exceeds 1000 parts by weight, the amount of products obtained at a time is small and the productivity is poor.

Next, suspension polymerization is started by heating the dispersion in which the oily mixture is dispersed in the aqueous dispersion medium as spherical oil droplets. During the polymerization reaction, it is preferable to stir the dispersion, and the stirring may be performed so gently as to prevent, for example, floating of the monomer and floating or sedimentation of the thermally expandable microspheres after polymerization.
The polymerization temperature is freely set depending on the kind of the polymerization initiator, but is preferably controlled in the range of 30 to 100 ° C, more preferably 40 to 90 ° C, and particularly preferably 50 to 85 ° C. The time for maintaining the reaction temperature is preferably about 0.1 to 20 hours. The initial polymerization pressure is not particularly limited, but the gauge pressure is in the range of 0 to 5.0 MPa, more preferably 0.1 to 3.0 MPa, and particularly preferably 0.2 to 2.0 MPa.

In the slurry containing the heat-expandable microspheres obtained after the suspension polymerization step (hereinafter sometimes referred to as the slurry after polymerization), in addition to the target heat-expandable microspheres, aggregation of the heat-expandable microspheres By-products such as product and polymerization residue may be generated. Since the size of such a by-product is generally larger than the particle size of the thermally expandable microsphere, the by-product does not pass through a certain sieve. Therefore, by evaluating the sieve passage rate of the slurry after polymerization, it can be determined whether or not the thermally expandable microspheres could be stably produced. The sieve passing rate is preferably 80% by weight or more, more preferably 85% by weight or more, and particularly preferably 90% by weight or more. If the sieve passage rate is less than 80% by weight, it cannot be said that thermally expandable microspheres can be produced with good productivity. The definition of the sieve passing rate will be described in the embodiment.

Examples of the method for isolating the thermally expandable microspheres from the slurry after polymerization include isolation methods such as suction filtration, pressure filtration, and centrifugal separation. A liquid cake is obtained.
The dried thermally expandable microspheres can be obtained by further performing drying operations such as shelf drying, reduced pressure drying and airflow drying on the obtained liquid expandable microsphere-containing cake.
In addition, in the process of obtaining dried thermally expandable microspheres from the slurry after polymerization, the thermally expandable microspheres may be washed with water in order to purify the thermally expandable microspheres.

[Thermal expandable microspheres]
Next, the thermally expandable microsphere obtained by the production method of the present invention will be described.
As shown in FIG. 3, the heat-expandable microsphere has a core-shell composed of an outer shell (shell) 11 made of a thermoplastic resin and a foaming agent (core) 12 encapsulated therein and vaporized by heating. It has a structure, and the thermally expandable microsphere exhibits thermal expandability (property that the entire microsphere expands by heating) as the entire microsphere.

The average particle diameter of the heat-expandable microsphere is not particularly limited, but is usually 0.1 to 100 μm, preferably 0.5 to 80 μm, more preferably 1 to 70 μm, and further preferably 2 to 60 μm. Particularly preferred is 2 to 50 μm, particularly preferred is 2 to 40 μm, and most preferred is 2 to 30 μm. When the average particle diameter of the thermally expandable microsphere is less than 0.1 μm, sufficient expandability may not be obtained. Further, when the average particle diameter of the thermally expandable microspheres is more than 100 μm, it may be unsuitable for applications requiring surface smoothness.
The coefficient of variation CV of the particle size distribution of the heat-expandable microspheres is not particularly limited, but is preferably 35% or less, more preferably 30% or less, and particularly preferably 25% or less. The variation coefficient CV is calculated by the following calculation formulas (1) and (2).

(Wherein, s is the standard deviation of the particle size, <x> is an average particle size, x _i is the i-th particle diameter, n is the number of particles.)
The encapsulating rate of the foaming agent is defined as the percentage of the weight of the foaming agent encapsulated in the thermally expandable microspheres relative to the weight of the thermally expandable microspheres. The encapsulating rate of the foaming agent is not particularly limited, and the encapsulating rate is appropriately determined depending on the intended use, but is preferably 1 to 35% by weight, more preferably 2 to 30% by weight, and particularly preferably 3 to 25% by weight. %. If the encapsulation rate is less than 1% by weight, the effect of the foaming agent may not be obtained. On the other hand, when the encapsulation rate exceeds 35% by weight, the thickness of the outer shell of the thermally expandable microspheres becomes thin, which may cause outgassing, resulting in poor heat resistance and high expansion performance.
The thermally expandable microspheres obtained by the method of the present invention have a small amount of silica adhering to the surface and little aggregation during drying.

[Hollow particles]
Hollow particles can be obtained by heating and expanding the thermally expandable microspheres. The hollow particles are lightweight and have excellent material properties when included in a composition or a molded product.
Examples of the method for producing the hollow particles include a dry heat expansion method and a wet heat expansion method. The temperature at which the thermally expandable microspheres are heated and expanded is preferably 60 to 350 ° C.
The average particle size of the hollow particles is not particularly limited because it can be designed freely according to the application, but is preferably 1 to 1000 μm, more preferably 2 to 200 μm. Further, the coefficient of variation CV of the particle size distribution of the hollow particles is not particularly limited, but is preferably 30% or less, and more preferably 25% or less.

The true specific gravity of the hollow particles is not particularly limited, but is preferably 0.005 to 0.5, more preferably 0.01 to 0.3, and particularly preferably 0.01 to 0.2.
As shown in FIG. 4, the hollow particles (1) may be composed of fine particles (4 and 5) attached to the outer surface of the outer shell (2). There is.

The adhesion mentioned here may be a state (4) in which the fine particles (4 and 5) are simply adsorbed on the outer surface of the outer shell (2), and the fine particles sink into the outer shell melted by heating and are fixed. This means that it may be in the state (5). The particle shape of the fine particles may be indefinite or spherical. In the fine particle-adhered hollow particles, workability (handling) during use is improved.
The average particle size of the fine particles is appropriately selected depending on the size of the hollow body used, and is not particularly limited, but is preferably 0.001 to 30 μm, more preferably 0.005 to 25 μm, and particularly preferably 0.01 to 20 μm.

Various particles can be used as the fine particles, and any of inorganic materials and organic materials may be used. Examples of the shape of the fine particles include a spherical shape, a needle shape, and a plate shape.
The average particle size of the fine particles is preferably 1/10 or less of the average particle size of the hollow body. Here, the average particle diameter of the fine particles means the average particle diameter of the primary particles.

The fine particle-adhered hollow particles can be obtained, for example, by heating and expanding fine particle-adhered thermally expandable microspheres. The method for producing the fine particle-attached hollow particles includes a step of mixing thermally expandable microspheres and fine particles (mixing step), and heating the mixture obtained in the mixing step to expand the thermally expandable microspheres. A production method including a step of attaching fine particles to the outer surface of the obtained hollow particles (attachment step) is preferable.

The true specific gravity of the fine particle-attached hollow particles is not particularly limited, but is preferably 0.01 to 0.5, more preferably 0.03 to 0.4, and particularly preferably 0.05 to 0.35. Most preferably, it is 0.07 to 0.30. When the true specific gravity of the fine particle-adhered hollow particles is less than 0.01, the durability may be insufficient. On the other hand, when the true specific gravity of the fine particle-attached hollow particles is larger than 0.5, the effect of reducing the specific gravity is reduced. Sometimes.
The water content of the hollow particles is not particularly limited, but is preferably 0.5% by weight or less, more preferably 0.4% by weight or less, particularly preferably 0.35% by weight or less, and most preferably 0.3% by weight. It is as follows. The lower limit of the moisture content of the hollow particles is 0% by weight. The moisture of the hollow particles exists like so-called crystal water.

[Composition and molded product]
A composition can be prepared by mixing the thermally expandable microspheres and / or the hollow particles with a base material component.
The base material component is not particularly limited. For example, rubbers; thermosetting resins; waxes; thermoplastic resins; thermoplastic elastomers; bioplastics; modified silicones, urethanes, polysulfides, acrylics, polys Examples include sealing materials such as isobutylene and butyl rubber; and inorganic materials such as cement, mortar, and cordierite.

In addition to thermally expandable microspheres, hollow particles and base material components, the composition includes lightweight fillers such as perlite, fly ash, shirasu balloon, glass balloon, phenol balloon, carbon balloon, alumina bubble, and expanded styrene beads; glass Reinforcing agents such as fibers and aramid fibers; fillers such as silica, talc and calcium carbonate; additives such as pigments such as titanium oxide and magnesium oxide may be further blended. These additives may be used individually by 1 type, and may use 2 or more types together.

Examples of the use of the composition include a molding composition, a coating composition, a clay composition, a fiber composition, an adhesive composition, and a powder composition. More specific uses of the composition include cosmetics, putty, paints, sealants, mortar, paper clay, earthenware, artificial marble, etc. In these uses, thermally expandable microspheres and / or hollow particles Effects such as weight reduction, heat insulation, and shrinkage prevention can be imparted.

Moreover, a molded article can be obtained by molding the composition.
As a molded product, a film, a coating film, a molded product, etc. can be mentioned, for example. A molded product containing an inorganic substance as a base component is further fired to obtain a ceramic filter or the like in which closed cells are formed.

The present invention is described in detail in the following examples and comparative examples, but the present invention is not limited thereto. Unless otherwise specified, “parts” means “parts by weight”.
In the following examples and comparative examples, physical properties were measured in the following manner.

[Measurement of SiO ₂ concentration in silica sol]
10 g of silica sol was measured in a crucible, dried at 130 ° C., heated at 800 ° C., and the SiO ₂ concentration in the silica sol was calculated from the weight ratio of the resulting residue.

[PH]
The pH was measured using a pH meter (product number HM-12P) manufactured by Toa DKK Corporation.

[Average particle diameter of thermally expandable microspheres]
As the measuring apparatus, using a laser diffraction type particle size distribution measuring apparatus (SYMPATEC Co. HEROS & RODOS), the measured heat-expandable microspheres volume mean diameter _{D 50} value was defined as the average particle size by a wet measuring method.

[Slurry state after polymerization]
1) Screening rate Slurry W ₂ (g) after polymerization was prepared, and this slurry was passed through a screening wire mesh (mesh opening 200 μm) made by Kansai Wire Mesh, and the slurry W ₁ (g) that passed through the screen was measured. From W ₁ (g) and W ₂ (g), the sieve passing rate Y (% by weight) of the slurry after polymerization was calculated by the following calculation formula (D).
Y (% by weight) = (W ₁ / W ₂ ) × 100 (D)
From the sieve passing rate Y (% by weight), the sieve passing ability was evaluated according to the following evaluation criteria.
○: Y ≧ 90% by weight
Δ: 80% by weight ≦ Y <90% by weight
X: Y <80% by weight

2) Slurry viscosity The viscosity of the slurry after polymerization was evaluated according to the following evaluation criteria.
○: High fluidity and easy sieving operation.
X: The fluidity was low and the sieving operation was difficult.

[Example 1]
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. Next, 180 g of sodium chloride as an inorganic salt was added and dissolved. To this, 0.30 g of 62% sulfuric acid was added as an acid. The pH of the aqueous dispersion medium intermediate at this stage was 1.0. Next, 2.0 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added as a dispersion stabilizing aid. The pH of the aqueous dispersion medium intermediate at this stage was 1.0. Then, 72 g of silica sol A (average particle diameter 10 nm, specific surface area 270 m ² / g, SiO ₂ concentration 20% by weight, pH 10.2) was gradually added as an aqueous silica sol while confirming the pH. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.0 to 2.5. Finally, 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substituted alkyl group substitution rate: 80%, weight average molecular weight: 50,000) was added as a polymerization aid to prepare an aqueous dispersion medium. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.0-3.0.
Apart from this, monomer components (acrylonitrile 180 g, methacrylonitrile 105 g, methyl methacrylate 15 g), crosslinking agent (trimethylolpropane trimethacrylate 0.80 g), blowing agent (isopentane 50 g), and polymerization initiator A (Lauroyl peroxide 1.5 g) was mixed to prepare an oily mixture.
The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed with a homomixer at 8000 rpm for 2 minutes to prepare a suspension. This suspension was transferred to a pressure reactor having a capacity of 1.5 liters, purged with nitrogen, brought to an initial reaction pressure of 0.2 MPa, and polymerized at a polymerization temperature of 70 ° C. for 15 hours while stirring at 80 rpm. The obtained polymerization product was filtered and dried to obtain thermally expandable microspheres.

[Example 2]
In Example 1, an aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 1 except that the addition order of sulfuric acid and polyvinylpyrrolidone was reversed and the amount of sulfuric acid was changed to 0.24 g. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.0 to 3.8. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 4.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 2.0-4.0.
Example 3
In Example 1, the amount of polyvinyl pyrrolidone (30% by weight aqueous solution) was 4.1 g, and the aqueous dispersion medium and thermal expansibility were the same as in Example 1 except that the order of addition of polyvinyl pyrrolidone and silica sol A was reversed. A microsphere was obtained. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.1 to 2.8. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.1-3.0.
Example 4
In Example 3, an aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 3 except that the amount of silica sol A added was 60 g and the amount of sulfuric acid was 0.27 g. The pH of the aqueous dispersion medium intermediate when adding the aqueous silica sol was in the range of 1.3 to 2.8. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.4, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.4, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 1.3 to 3.0.

Example 5
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. Next, 180 g of sodium chloride as an inorganic salt was added and dissolved, and 4.1 g of polyvinyl pyrrolidone (30% by weight aqueous solution) was added as a dispersion stabilizing aid. Here, 0.30 g of 62% sulfuric acid was added as an acid at a rate of 0.08 g / min using a metering pump. When the pH reached 2.0, 72 g of silica sol A as an aqueous silica sol was started at a rate of 16 g / min using a metering pump. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.0 to 2.7. Finally, 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substituted alkyl group substitution rate: 80%, weight average molecular weight: 50,000) was added as a polymerization aid to prepare an aqueous dispersion medium. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 2.0-3.0. Further, thermally expandable microspheres were obtained in the same manner as in Example 1 except that the aqueous dispersion medium obtained in this example was used.
Example 6
In Example 5, an aqueous dispersion medium and thermally expandable microspheres were prepared in the same manner as in Example 5 except that 4.1 g of polyvinylpyrrolidone (30% by weight aqueous solution) as a dispersion stabilizing aid was mixed after the addition of silica sol A. Obtained. The pH of the aqueous dispersion medium intermediate when adding the aqueous silica sol was in the range of 2.0 to 2.6. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 2.0 to version 3.1.

Example 7
To a container for preparing an aqueous dispersion medium equipped with a stirrer, 4.2 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added as a dispersion stabilizing aid. Here, 72 g of silica sol A was gradually added as an aqueous silica sol, and the stirring device of the container was started. Further, 0.30 g of 62% sulfuric acid was added as an acid. At this stage, the SiO ₂ concentration in the aqueous dispersion medium intermediate was 18.6% by weight, and the pH was 2.8. Separately, 600 g of ion-exchanged water in which 180 g of sodium chloride was dissolved was added to the above vessel while stirring, and polyethyleneimines (substituted alkyl group: —CH ₂ COONa, substitution rate of substituted alkyl group: 80 as a polymerization aid). %, Weight average molecular weight: 50,000) 1.0 g was added to obtain an aqueous dispersion medium. The pH of the aqueous dispersion medium intermediate after the stage where the sodium chloride aqueous solution was added and _AT became less than 15 was 2.8. The obtained aqueous dispersion medium had a SiO ₂ concentration (A _T100 ) of 1.7 and a pH of 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 2.8 to version 3.1.
Apart from this, monomer components (acrylonitrile 180 g, methacrylonitrile 105 g, methyl methacrylate 15 g), crosslinking agent (trimethylolpropane trimethacrylate 1.1 g), blowing agent (isopentane 70 g), and polymerization initiator A (Lauroyl peroxide 1.5 g) was mixed to prepare an oily mixture.
The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed with a homomixer at 8000 rpm for 2 minutes to prepare a suspension. This suspension was transferred to a pressure reactor having a capacity of 1.5 liters, purged with nitrogen, brought to an initial reaction pressure of 0.2 MPa, and polymerized at a polymerization temperature of 70 ° C. for 15 hours while stirring at 80 rpm. The obtained polymerization product was filtered and dried to obtain thermally expandable microspheres.
Example 8
In Example 7, the aqueous dispersion medium and thermal expansion were the same as in Example 7, except that the order of addition of sulfuric acid and silica sol A was reversed and 6.3 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added. Sex microspheres were obtained. The pH of the aqueous dispersion medium intermediate after the stage where the sodium chloride aqueous solution was added and _AT became less than 15 was 2.8. The obtained aqueous dispersion medium had a SiO ₂ concentration (A _T100 ) of 1.7 and a pH of 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 2.8 to version 3.1.
Example 9
In Example 8, except that the order of addition of polyvinylpyrrolidone and silica sol A was reversed, 2.1 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added, and sulfuric acid was 0.42 g. In the same manner, an aqueous dispersion medium and thermally expandable microspheres were obtained. A pH of the aqueous dispersion medium intermediate after the stage in which an aqueous sodium chloride solution was added and _AT was less than 15 was 1.9. The obtained aqueous dispersion medium had a SiO ₂ concentration (A _T100 ) of 1.7 and a pH of 2.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.9-2.1.
Example 10
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. Next, 180 g of sodium chloride as an inorganic salt was added and dissolved, and 2.0 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added as a dispersion stabilizing aid. To this, 0.20 g of 62% sulfuric acid was added as an acid. The pH of the aqueous dispersion medium intermediate at this stage was 2.3. And 72 g of silica sol A was gradually added as aqueous silica sol, confirming pH. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.3 to 6.1. Further, 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substitution rate of substituted alkyl group: 80%, weight average molecular weight: 50,000) was added as a polymerization aid, and finally the pH was adjusted to 3.0. In order to adjust to 62%, 0.10 g of 62% sulfuric acid was added to prepare an aqueous dispersion medium. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, and the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 2.3 to 6.1. Further, thermally expandable microspheres were obtained in the same manner as in Example 1 except that the aqueous dispersion medium obtained in this example was used.

Example 11
In Example 1, instead of silica sol A, silica sol B (average particle size 6 nm, specific surface area 450 m ² / g, SiO ₂ concentration 20 wt%, pH 9.7) was used in the same manner as in Example 1, An aqueous dispersion medium and thermally expandable microspheres were obtained. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.0 to 2.7. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 1.0 to version 3.1.
Example 12
In Example 2, an aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 2 except that 72 g of silica sol B was used instead of silica sol A. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.0 to 2.8. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.2. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.0-3.2.

Example 13
In Example 1, 4.1 g of polyvinyl pyrrolidone (30% by weight aqueous solution) was added, and instead of silica sol A, silica sol C (average particle size 10 nm, specific surface area 270 m ² / g, SiO ₂ concentration 30% by weight, pH 10.2). ) An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 1 except that 48 g was used. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.0 to 2.7. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.9, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.9, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.0-3.0.
Example 14
In Example 2, 4.1 g of polyvinyl pyrrolidone (30% by weight aqueous solution) was added, 48 g of silica sol C was used instead of silica sol A, and sulfuric acid was changed to 0.24 g. Medium and thermally expandable microspheres were obtained. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.2 to 3.9. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 4.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 2.2 to 4.1.

Example 15
In Example 1, 4.1 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added, and instead of silica sol A, silica sol D (average particle size 10 nm, specific surface area 270 m ² / g, SiO ₂ concentration 40% by weight, pH 10.0) ) An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 1 except that 36 g was used. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.0 to 2.7. SiO ₂ concentration of the intermediate in aqueous dispersion medium _{0 <A T ≦ 1.8, SiO} 2 concentration of the obtained aqueous dispersion medium _{(A T100)} is 1.8, pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.0-3.0.
Example 16
In Example 2, 4.1 g of polyvinyl pyrrolidone (30% by weight aqueous solution) was added, 36 g of silica sol D was used instead of silica sol A, and 0.42 g of sulfuric acid was used. Medium and thermally expandable microspheres were obtained. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 0.8 to 1.9. SiO ₂ concentration of the intermediate in aqueous dispersion medium _{0 <A T ≦ 1.8, SiO} 2 concentration of the obtained aqueous dispersion medium _{(A T100)} is 1.8, pH was 2.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 0.8 to 2.1.

[Comparative Example 1]
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. Next, 180 g of sodium chloride as an inorganic salt was added and dissolved. Next, 4.1 g of polyvinylpyrrolidone (30% by weight aqueous solution) was added as a dispersion stabilizing aid. Thereafter, 72 g of silica sol A was gradually added as an aqueous silica sol while confirming the pH. The pH of the aqueous dispersion medium intermediate at this stage was 6.4 to 8.1. To this, 0.30 g of 62% sulfuric acid was added as an acid. At this stage, the pH of the aqueous dispersion medium intermediate changed from 8.1 to 2.7. Finally, 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substituted alkyl group substitution rate: 80%, weight average molecular weight: 50,000) was added as a polymerization aid to prepare an aqueous dispersion medium. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.0 to 8.1.
The following were obtained in the same manner as in Example 1 to obtain thermally expandable microspheres.

[Comparative Example 2]
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 1 except that 120 g of silica sol A, 5.2 g of polyvinylpyrrolidone (30% by weight aqueous solution), and 0.50 g of sulfuric acid were used. The pH of the aqueous dispersion medium intermediate at the stage when the silica sol A was added was 6.4 to 8.1. SiO ₂ concentration of the intermediate in aqueous dispersion medium _{0 <A T ≦ 2.6, SiO} 2 concentration of the obtained aqueous dispersion medium _{(A T100)} is 2.6, pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.0 to 8.1.
[Comparative Example 3]
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 1 except that 135 g of silica sol A, 5.2 g of polyvinylpyrrolidone (30% by weight aqueous solution), and 0.56 g of sulfuric acid were used. The pH of the aqueous dispersion medium intermediate at the stage when the silica sol A was added was 6.4 to 8.1. SiO ₂ concentration of the intermediate in aqueous dispersion medium _{0 <A T ≦ 2.9, SiO} 2 concentration of the obtained aqueous dispersion medium _{(A T100)} is 2.9, pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.0 to 8.1.
[Comparative Example 4]
In Comparative Example 1, an aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 1, except that the order of addition of polyvinylpyrrolidone and silica sol A was reversed. The pH of the aqueous dispersion medium intermediate at the stage when the silica sol A was added was 5.5 to 7.9. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.0 to 7.9.
[Comparative Example 5]
In Comparative Example 4, an aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 4 except that the order of addition of polyvinylpyrrolidone and sulfuric acid was reversed. The pH of the aqueous dispersion medium intermediate at the stage when the silica sol A was added was 5.5 to 7.9. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.0 to 7.9.
Example 17
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 2 except that the components shown in Table 4 were changed. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 1.5 to 3.7. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.0, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.0, and the pH was 4.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 1.5-4.0.
[Comparative Example 6]
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 2, except that the components shown in Table 4 were changed. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 5.2 to 8.3. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.0, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.9, and the pH was 4.0. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 4.0 to 8.3.
Example 18
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 1 except that the components shown in Table 4 were changed. The pH of the aqueous dispersion medium intermediate when adding the aqueous silica sol was in the range of 1.3 to 3.2. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.0, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.4, and the pH was 3.5. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 1.3 to 3.5.
[Comparative Example 7]
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Comparative Example 1, except that the components shown in Table 4 were changed. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 5.5 to 7.9. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.0, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.0, and the pH was 3.5. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.5 to 7.9.

Example 19
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. To this, 0.37 g of 62% sulfuric acid was added as an acid. At this stage, the pH of the aqueous dispersion medium intermediate was 2.2. Next, 2.4 g of an adipic acid-diethanolamine condensate (effective concentration 50% by weight) was added as a dispersion stabilizing aid. The pH of the aqueous dispersion medium intermediate at this stage was 2.3. Then, while confirming the pH, 56 g of silica sol A was gradually added as an aqueous silica sol. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.2 to 3.3. Furthermore, 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substitution rate of substituted alkyl group: 80%, weight average molecular weight: 50,000) was added as a polymerization aid, and finally 62% sulfuric acid was added. Then, an aqueous dispersion medium was prepared with a pH of 3.1. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, and the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 2.2 to 3.3.
Apart from this, monomer components (135 g vinylidene chloride, 135 g acrylonitrile, 30 g methyl methacrylate), a crosslinking agent (trimethylolpropane trimethacrylate 0.70 g), a blowing agent (isobutane 63 g), and a polymerization initiator B ( An oily mixture was prepared by mixing 1.5 g of diisopropyl peroxydicarbonate (purity 50%).
The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed with a homomixer at 8000 rpm for 2 minutes to prepare a suspension. This suspension was transferred to a 1.5 liter pressurized reactor and purged with nitrogen, and then the initial reaction pressure was set to 0.2 MPa, and polymerization was carried out at a polymerization temperature of 50 ° C. for 15 hours while stirring at 80 rpm. The obtained polymerization product was filtered and dried to obtain thermally expandable microspheres.

Example 20
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 19 except that the addition order of the condensate of sulfuric acid and adipic acid-diethanolamine was reversed. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.2 to 3.3. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 2.2 to 3.3.
Example 21
An aqueous dispersion medium and thermally expandable microspheres were obtained in the same manner as in Example 19 except that the addition order of the adipic acid-diethanolamine condensate and silica sol A was reversed. The pH of the aqueous dispersion medium intermediate when the aqueous silica sol was added was in the range of 2.2 to 3.5. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared ranged from 2.2 to 3.5.

[Comparative Example 8]
600 g of ion-exchanged water was added to a container for preparing an aqueous dispersion medium equipped with a stirrer, and the stirrer of the container was started. To this, 56 g of silica sol A was gradually added as an aqueous silica sol. The pH of the aqueous dispersion medium intermediate at this stage was 7.0 to 10.2. Next, 2.4 g of an adipic acid-diethanolamine condensate (effective concentration 50% by weight) was added as a dispersion stabilizing aid. At this stage, the pH of the aqueous dispersion medium intermediate changed from 10.2 to 7.2. Further, 0.37 g of 62% sulfuric acid was added as the acid, and 1.0 g of polyethyleneimine (substituted alkyl group: —CH ₂ COONa, substituted alkyl group substitution rate: 80%, weight average molecular weight: 50,000) was added as the polymerization aid. An aqueous dispersion medium was prepared. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 1.7, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 1.7, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.1 to 10.2.
In the same manner as in Example 19, thermally expandable microspheres were obtained.
[Comparative Example 9]
In Comparative Example 8, an aqueous dispersion medium and an aqueous dispersion medium were prepared in the same manner as in Comparative Example 8, except that 90 g of silica sol A, 4.5 g of adipic acid-diethanolamine condensate (effective concentration 50% by weight) and 0.59 g of sulfuric acid were used. Thermally expandable microspheres were obtained. The pH of the aqueous dispersion medium intermediate at the stage when the silica sol A was added was 3.1 to 10.2. The SiO ₂ concentration of the intermediate of the aqueous dispersion medium was 0 <A _T ≦ 2.6, the SiO ₂ concentration (A _T100 ) of the obtained aqueous dispersion medium was 2.6, and the pH was 3.1. 0 in _<A T <satisfy 15 _{A T,} pH of the intermediate during the aqueous dispersion medium prepared was in the range of 3.1 to 10.2.
The blending amounts of various raw materials, the slurry state after polymerization, and the physical properties of the obtained thermally expandable microspheres are shown in Table 1 for Examples 1 to 10, Table 2 for Examples 11 to 16, and Comparative Example 1. Tables 5 to 5 are shown in Table 3, Examples 17 and 18 and Comparative Examples 6 and 7 are shown in Table 4, and Examples 19 to 21 and Comparative Examples 8 and 9 are shown in Table 5.
In Tables 1 to 5, the abbreviations shown in Table 6 are used.
In addition, the case where the inorganic salt (f) is previously dissolved in water (d) is included.
The aqueous dispersion media in Comparative Examples 1 to 9 were prepared by a conventional preparation method.

In Examples 1 to 6 and Examples 10 to 21, since the aqueous silica sol is added to the intermediate of the aqueous dispersion medium, the transition of the SiO ₂ concentration of the aqueous dispersion medium is as shown in FIG. Within this concentration range, the pH of the aqueous dispersion medium intermediate is maintained in the range of 0.8 to 7, so that thermally expandable microspheres having a small particle diameter can be produced with a small amount of aqueous silica sol. It was. The slurry state after polymerization was good. _{AT 100} was in the range of _0.5-8 .
In Examples 7 to 9, since the SiO ₂ concentration of the aqueous silica sol is gradually diluted from a high state, the transition of the SiO ₂ concentration of the aqueous dispersion medium is as shown in FIG. Within this concentration range, the pH of the aqueous dispersion medium intermediate is maintained in the range of 0.8 to 7, so that thermally expandable microspheres having a small particle diameter can be produced with a small amount of aqueous silica sol. It was. The slurry state after polymerization was good. _{AT 100} was in the range of _0.5-8 .
On the other hand, in Comparative Examples 1 to 9, which are conventional methods for preparing an aqueous dispersion medium, since the aqueous silica sol is added to the intermediate of the aqueous dispersion medium, the transition of the SiO ₂ concentration of the aqueous dispersion medium is as shown in FIG. Within this range of concentration, the pH of the intermediate of the aqueous dispersion medium deviated from the range of 0.8 to 7. Therefore, in order to produce thermally expandable microspheres having a small particle size, a large amount compared to the examples. It was necessary to use an aqueous silica sol. In Comparative Examples 1 to 5, 8 and 9, aggregation in the slurry state after polymerization was remarkable, and sieve passing ability was poor. This suggests that the dispersion stability of the oil droplets is lower in the polymerization stage than in the examples.

11 Outer shell made of thermoplastic resin 12 Foaming agent 1 Hollow particle (fine particle-attached hollow particle)
2 Outer shell 3 Hollow part 4 Fine particles (adsorbed state)
5 Fine particles (indented, fixed state)

Claims (5)

1. A method for producing thermally expandable microspheres comprising a step of dispersing an oily mixture containing a polymerizable component, a foaming agent and a polymerization initiator in an aqueous dispersion medium and polymerizing the polymerizable component,
   The aqueous dispersion medium has an aqueous silica sol (a) having a pH of 9 to 11 and an SiO ₂ concentration of 15 to 40% by weight, a dispersion stabilizing aid (b), an acid (c), water (d), and a polymerization Prepared by mixing auxiliary (e),
   In the step of preparing the aqueous dispersion medium, the preparation start time of the aqueous dispersion medium is T0, the preparation end time is T100, and the intermediate SiO ₂ of the aqueous dispersion medium produced at any time T satisfying T0 <T <T100. When the concentration is _AT weight% and the SiO ₂ concentration of the aqueous dispersion medium at T100 is _{AT 100} weight%,
   In _AT satisfying 0 <A _T <15, the pH of the intermediate is maintained in the range of 0.8 to 7, and _{AT 100 is set} to 0.5 to 8.
   A method for producing thermally expandable microspheres.
2. 2 to 100 parts by weight of the aqueous silica sol (a), 0.01 to 5 parts by weight of the dispersion stabilizing aid (b), and the polymerization aid (e) with respect to 100 parts by weight of the water (d). The method for producing thermally expandable microspheres according to claim 1, wherein 0.0001 to 0.1 parts by weight are used.
3. The method for producing thermally expandable microspheres according to claim 1 or 2, wherein 150 to 1000 parts by weight of the aqueous dispersion medium is used with respect to 100 parts by weight of the oily mixture.
4. The method for producing thermally expandable microspheres according to any one of claims 1 to 3, wherein the aqueous dispersion medium is prepared by further mixing an inorganic salt (f).
5. The aqueous dispersion medium is a mixture of an inorganic salt aqueous solution obtained by dissolving a part or all of the inorganic salt (f) in a part or all of the water (d) and the aqueous silica sol (a). The method for producing thermally expandable microspheres according to claim 4, which is prepared by:

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