阅读说明：本技术 中空树脂颗粒和片材 (Hollow resin particles and sheet ) 是由 伊贺隆志 平田刚 矢吹希 于 2019-03-25 设计创作，主要内容包括：本发明提供一种比以往压缩强度高,且隔热性和耐热性优异的中空树脂颗粒,以及包含它的片材。该中空树脂颗粒是具有1个或2个以上中空部的中空树脂微粒,数均粒径为0.1～9.0μm,空隙率为70～99％,含有的挥发性有机化合物量为5质量％以下。(The invention provides a hollow resin particle which has higher compression strength than the prior art and excellent heat insulation performance and heat resistance, and a sheet comprising the hollow resin particle. The hollow resin particles are hollow resin particles having 1 or more hollow portions, the number average particle diameter is 0.1 to 9.0 [ mu ] m, the porosity is 70 to 99%, and the amount of volatile organic compounds contained is 5% by mass or less.)

1. A hollow resin particle characterized by having 1 or 2 or more hollow parts,

The number average particle diameter is 0.1 to 9.0 μm, the void ratio is 70 to 99%, and the amount of the volatile organic compound contained is 5% by mass or less.

2. The hollow resin particle according to claim 1, wherein a repeating unit constituting the resin contains a crosslinkable monomer unit.

3. The hollow resin particle according to claim 2, wherein the content ratio of the crosslinkable monomer unit is 25 to 59 parts by mass when the repeating unit constituting the resin is 100 parts by mass.

4. The hollow resin particle according to any one of claims 1 to 3, wherein a repeating unit constituting the resin contains a hydrophilic monomer unit.

5. The hollow resin particle according to any one of claims 2 to 4, wherein the repeating unit constituting the resin comprises a crosslinkable monomer unit comprising at least 1 selected from a divinylbenzene monomer unit and an ethylene glycol dimethacrylate monomer unit.

6. The hollow resin particle according to claim 4 or 5, wherein the hydrophilic monomer unit contains at least 1 selected from a carboxyl group-containing monomer unit and a hydroxyl group-containing monomer unit.

7. The hollow resin particle according to any one of claims 1 to 6, wherein a repeating unit constituting the resin comprises a monovinyl monomer unit.

8. The hollow resin particle according to any one of claims 1 to 7, wherein the particle size distribution (volume average particle diameter (Dv)/number average particle diameter (Dn)) is 1.1 to 2.5.

9. The hollow resin particle according to any one of claims 1 to 8, wherein the hollow resin particle has a shell having a thickness of 0.01 to 1.0 μm.

10. A hollow resin particle for thermosensitive recording materials, having the features of any one of claims 1 to 9.

11. A hollow resin particle for filler having the features of any one of claims 1 to 9.

12. A hollow resin particle for coating having the features of any one of claims 1 to 9.

13. A sheet comprising the hollow resin particle according to any one of claims 1 to 9.

14. A thermosensitive recording sheet having the features of claim 13.

Technical Field

The present invention relates to hollow resin particles having higher compressive strength than conventional hollow resin particles and excellent heat insulating properties and heat resistance, and a sheet comprising the hollow resin particles.

Background

Hollow resin particles are widely used in applications such as water-based paints and paper coating compositions as organic pigments and masking agents having excellent optical properties such as opacity and whiteness, because they can scatter light more satisfactorily and reduce light transmittance than resin particles having substantially no voids in the interior.

However, in applications such as water-based paints and paper coating compositions, it is desired to increase the porosity of hollow resin particles to be blended in order to improve the effects of weight reduction, heat insulation, opacity, and the like of the paints, paper coating compositions, and the like. However, in the conventionally known production methods, it is difficult to control the particle diameter and produce hollow resin particles having a high porosity and excellent heat resistance.

For example, patent document 1 discloses a method for producing thermally expandable microspheres composed of an outer shell containing a thermoplastic resin and a blowing agent contained therein as essential components. This document describes that thermally expandable microspheres having a predetermined average particle diameter can be produced stably and in good yield without deteriorating the expansion performance.

Further, patent document 2 discloses the following: in producing the hollow resin particles, (1) a dispersed phase containing a vinyl monomer having no nitrile group, a phase separation accelerator, a volatile solvent, a polymerization initiator, and a reaction catalyst is prepared, (2) a continuous phase containing a solvent and a surfactant is prepared, (3) the dispersed phase is added to the continuous phase, and the resulting mixture is stirred, (4) the resulting aqueous dispersion is fed to a polymerization reaction under pressure, (5) the mixture after the polymerization reaction is depressurized at a temperature of not less than the boiling point of the volatile solvent, thereby obtaining an aqueous dispersion, and (6) the resulting aqueous dispersion is filtered and dried, thereby obtaining the hollow resin particles. This document describes that since the resin constituting the shell of the hollow resin particle contains a vinyl monomer having no nitrile group, the nitrile group does not detach even at high temperature, and the strength of the shell is hardly reduced.

Patent document 3 discloses a method for producing hollow polymer particles as follows: after polymerizing a dispersion of a hydrophilic monomer, a crosslinkable monomer and other monomers coexisting with an oily substance, the oily substance in the particles is removed in a liquid or gas, thereby preparing hollow polymer particles.

Patent document 4 discloses a method for producing hollow resin particles in which collapse is suppressed by removing an organic solvent included in fine particles from an aqueous medium and making the particles hollow.

Patent document 5 discloses hollow polymer fine particles having a high content of a crosslinkable monomer.

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 describes that a nitrile monomer is preferably contained as an essential component from the viewpoint of expansion performance. However, resin particles containing a nitrile-based monomer are generally poor in heat resistance. Further, the technique of patent document 1 has the following problems: the foaming and thermal expansion reactions produced by the foaming agent cause the microspheres to expand, and it is therefore difficult to precisely control the particle size of the microspheres.

Patent document 2 describes that the pressure of the volatile solvent contained in the resin is increased by reducing the pressure at a temperature not lower than the boiling point of the volatile solvent, and the pressure is increased when the volatile solvent is volatilized, thereby forming hollow resin particles. However, since the particles are expanded by reducing the pressure while applying heat to the particles, there is a problem that the particle diameters of the obtained hollow resin particles become uneven.

In the technique of patent document 3, when the amount of the oily substance is increased to produce hollow particles having a thin shell thickness, there is a problem that the strength of the shell is low, and the particles are broken when the oily substance is removed, and particles having a high porosity cannot be obtained.

The hollow particles produced by the method described in patent document 4 contain water, and when used for applications such as a heat insulator, a step of removing the water inside is required, and at this stage, the particles collapse, and the porosity is lowered.

In the case of the hollow polymer fine particles described in patent document 5, there is a problem that it is difficult to remove the hydrocarbon solvent inside the particles even if the treatment is performed under high temperature conditions for a long time.

The hollow resin particles are required to have a high compressive strength capable of maintaining the hollow portion of the particles, in addition to the above-mentioned high porosity and excellent heat resistance. Further, the hollow resin particles also need to have excellent heat insulating properties, in which heat is difficult to be conducted through the hollow portion, depending on the use thereof.

The problem to be solved by the present invention is to provide hollow resin particles having higher compressive strength than conventional ones and excellent heat insulating properties and heat resistance, and a sheet comprising the same.

Means for solving the problems

The present inventors have focused on the optimum particle diameter of the hollow resin particles in order to improve the compressive strength. In addition, physical properties required for obtaining hollow resin particles having heat insulation properties and heat resistance superior to those of conventional hollow resin particles have been carefully studied. As a result, the present inventors have found that hollow resin particles having a specific number average particle diameter, porosity, and volatile organic compound amount have high compressive strength, and have excellent heat insulation properties and heat resistance.

That is, the hollow resin particles of the present invention are characterized by having 1 or 2 or more hollow portions, a number average particle diameter of 0.1 to 9.0 μm, a porosity of 70 to 99%, and a content of a volatile organic compound of 5% by mass or less.

In the present invention, the repeating unit constituting the resin may include a crosslinkable monomer unit.

In the present invention, the content of the crosslinkable monomer unit may be 25 to 59 parts by mass, based on 100 parts by mass of the repeating unit constituting the resin.

In the present invention, the repeating unit constituting the above resin may contain a hydrophilic monomer unit.

In the present invention, the repeating unit constituting the resin may include a crosslinkable monomer unit, and the crosslinkable monomer unit may include at least 1 selected from a divinylbenzene monomer unit and an ethylene glycol dimethacrylate monomer unit.

In the present invention, the above hydrophilic monomer unit may contain at least 1 selected from the group consisting of a carboxyl group-containing monomer unit and a hydroxyl group-containing monomer unit.

In the present invention, the repeating unit constituting the above resin may contain a monovinyl monomer unit.

The hollow resin particles of the present invention may have a particle size distribution (volume average particle diameter (Dv)/number average particle diameter (Dn)) of 1.1 to 2.5.

The hollow resin particle of the present invention has a shell, and the shell thickness may be 0.01 to 1.0 μm.

The hollow resin particle of the present invention may be a hollow resin particle for a thermosensitive recording material having the above-described characteristics.

The hollow resin particle of the present invention may be a hollow resin particle for filler having the above-described characteristics.

The hollow resin particles of the present invention may be hollow resin particles for paint having the above-described characteristics.

The sheet of the present invention is characterized by containing the hollow resin particles.

The sheet of the present invention may be a thermosensitive recording sheet containing the above hollow resin particles.

Effects of the invention

As described above, according to the present invention, the hollow resin particles have a high compressive strength because they have a specific number average particle diameter, porosity, and volatile organic compound amount, and are capable of exerting excellent heat insulation and heat resistance.

Drawings

Fig. 1 is a schematic view showing one embodiment of the manufacturing method of the present invention.

Fig. 2 is a schematic view showing an embodiment of the suspension in the suspension preparing step.

Fig. 3A is an SEM image of the hollow resin particles of example 1.

Fig. 3B is an SEM image of a cross section of the hollow resin particle of example 1.

Fig. 4 is a schematic view showing a conventional dispersion liquid for emulsion polymerization.

Fig. 5 is a diagram illustrating a test sheet used in a test for evaluating a change in thickness of a sheet in a high-temperature environment.

Detailed Description

Hereinafter, in the present invention, "hollow" means that the presence of at least 1 selected from a liquid portion, a gas portion, and a mixed portion of liquid and gas in the inside of the particle can be confirmed by a general observation method. The term "liquid portion" as used herein means a continuous portion filled with a liquid. The term "gas portion" as used herein means a continuous portion filled with a gas. The "mixing section of liquid and gas" as used herein means a continuous portion filled with liquid and gas.

The "hollow portion" in the present invention means a portion occupied by the hollow inside the particle. Whether or not the particles have a hollow portion can be confirmed by, for example, SEM observation of a cross section of the target particle, or observation of the target particle directly with a Transmission Electron Microscope (TEM).

The shell of the resin in the particle may not have the communicating holes, and the "hollow portion" of the present invention may be isolated from the outside of the particle by the shell of the particle.

The shell of the resin in the particle may have 1 or 2 or more communication holes, and the "hollow portion" in the present invention may be connected to the outside of the particle through the communication holes.

The "hollow resin particle precursor" in the present invention means a particle in which the hollow portion is filled with water or a mixture of water and a gas, or an aqueous medium or a mixture of an aqueous medium and a gas. The "precursor composition" in the present invention means a composition containing a precursor of the hollow resin particles.

The "hollow resin particle" in the present invention means a resin particle in which the hollow portion is filled with a gas.

1. Hollow resin particle

The hollow resin particles of the present invention are characterized by having 1 or 2 or more hollow portions, a number average particle diameter of 0.1 to 9.0 [ mu ] m, a porosity of 70 to 99%, and a content of a volatile organic compound of 5 mass% or less.

As described above, as the characteristics required for the hollow resin particles, there are high compressive strength, and excellent heat insulation and heat resistance. In order to combine these characteristics, 3 physical property parameters of the hollow resin particles, that is, the number average particle diameter, the void ratio and the amount of the volatile organic compound of the hollow resin particles, need to be within specific numerical ranges, respectively. The following describes an outline of the relationship between the 3 physical properties (number average particle diameter, void ratio, and volatile organic compound amount) and the 3 characteristics (compressive strength, heat insulating property, and heat resistance).

The number average particle diameter of the hollow resin particles is a parameter related to the compressive strength and heat resistance thereof. In the case where the number average particle diameter of the hollow resin particles is sufficiently small, the hollow resin particles having a larger number average particle diameter are more difficult to break and thus have high compressive strength. When the number average particle diameter of the hollow resin particles is sufficiently small, the particles are also less susceptible to the external environment because of their small surface area, and as a result, the particles can exhibit excellent heat resistance.

Next, the void ratio of the hollow resin particles is a parameter related to the heat insulating property thereof. The hollow portion of the hollow resin particle is generally more difficult to transfer heat than if the resin is present in this portion. Therefore, the higher the porosity, the higher the proportion of the hollow portion, so the hollow resin particles have excellent heat insulating properties.

Next, the amount of the volatile organic compound contained in the hollow resin particles is a parameter related to the heat insulation property and heat resistance thereof. The "volatile organic compound contained in the hollow resin particles" in the present invention means an organic compound having a boiling point of 400 ℃ or lower among organic compounds contained in the hollow resin particles. Typical examples of the volatile organic compound include a hydrocarbon solvent and an unreacted monomer used in the production method described later, but are not necessarily limited to these typical examples. In the case where the amount of the volatile organic compound in the hollow resin particles is sufficiently small, there is a small risk that the volatile organic compound becomes a heat medium inside the hollow resin particles, and there is a small risk that the heat transmitted to a part of the particles is diffused to the entire particles, and therefore there is a small risk that the heat insulation property is reduced. Further, in the case where the amount of the volatile organic compound in the hollow resin particles is sufficiently small, even if the hollow resin particles are exposed to high temperature, the risk of expansion of the hollow resin particles by volatilization of the volatile organic compound is small, and therefore the risk of reduction in heat resistance is small.

Thus, 3 physical properties (number average particle diameter, void ratio and volatile organic compound amount) of the hollow resin particles affect the 3 properties (compressive strength, heat insulating property and heat resistance) described above.

The above-mentioned 3 physical properties (number average particle diameter, porosity and volatile organic compound amount) are described in detail in the following order.

The number average particle diameter of the hollow resin particles is usually 0.1 to 9.0. mu.m, preferably 0.2 to 8.0. mu.m, more preferably 0.4 to 6.0. mu.m, still more preferably 0.6 to 5.0. mu.m, and particularly preferably 0.8 to 4.0. mu.m.

When the number average particle diameter of the hollow resin particles is 0.1 μm or more, heat is hardly conducted to the entire hollow resin particles, and therefore the hollow resin particles can exhibit excellent heat insulating properties. Further, in the case where the number average particle diameter of the hollow resin particles is 9.0 μm or less, the hollow resin particles become hard to be broken, and thus have high compressive strength. Further, when the number average particle diameter of the hollow resin particles is 9.0 μm or less, the surface area of the hollow resin particles is sufficiently small, and therefore the hollow resin particles are less susceptible to external environment, and as a result, the hollow resin particles can exhibit excellent heat resistance.

The hollow resin particles may have a particle size distribution (volume average particle diameter (Dv)/number average particle diameter (Dn)) of 1.1 to 2.5, 1.1 to 2.3, or 1.1 to 2.0. When the particle size distribution is 2.5 or less, particles with small variations in compression strength characteristics and heat resistance among particles can be obtained. Further, by setting the particle size distribution to 2.5 or less, for example, when a product such as a sheet described later is manufactured, a product having a uniform thickness can be manufactured.

The volume average particle diameter (Dv) and the number average particle diameter (Dn) of the hollow resin particles can be determined by measuring the particle diameter of the hollow resin particles with, for example, a laser diffraction particle size distribution measuring apparatus, calculating the number average and the volume average of the particle diameters, and determining the obtained values as the number average particle diameter (Dn) and the volume average particle diameter (Dv) of the particles. The particle size distribution is a value obtained by dividing the volume average particle diameter by the number average particle diameter.

The void ratio of the hollow resin particles is usually 70% or more, preferably 72% or more, more preferably 74% or more, still more preferably 78% or more, still more preferably 80% or more, and particularly preferably 82% or more. When the void ratio of the hollow resin particles is 70% or more, the proportion of the hollow portion is high, and therefore the hollow resin particles have excellent heat insulation properties. From the viewpoint of maintaining the strength of the hollow resin particles, the void ratio of the hollow resin particles may be 99% or less, or may be 95% or less.

The void ratio of the hollow resin particles can be calculated by subtracting the following value from 100: the value is the apparent density D of the hollow resin particles₁Divided by the true density D₀And further multiplied by 100.

Apparent density D of hollow resin particles₁The measurement method (2) is as follows. First, at a capacity of 100cm ³About 30cm in the volumetric flask³The mass of the filled hollow resin particles is accurately weighed. Next, in the volumetric flask filled with the hollow resin pellets, isopropyl alcohol was filled up to the scale mark with care taken not to mix in bubbles. The mass of isopropyl alcohol added to the flask was precisely measured, and the amount of the hollow resin particles was calculated from the following formula (I)Apparent density D₁(g/cm³)。

Formula (I)

Apparent density D₁Mass of ═ hollow resin particles]V (100- [ quality of isopropanol)]Specific gravity of isopropyl alcohol at measurement temperature])

Apparent density D₁This corresponds to the specific gravity of the entire hollow resin particle when the hollow portion is regarded as a part of the hollow resin particle.

True density D of hollow resin particles₀The measurement method (2) is as follows. After the hollow resin particles were pulverized in advance, the volume was 100cm³About 10g of pieces of hollow resin pellets were filled in the volumetric flask of (1), and the mass of the filled crushed pieces was accurately weighed. Then, isopropyl alcohol was added to the volumetric flask in the same manner as in the measurement of the apparent density, the mass of isopropyl alcohol was precisely weighed, and the true density D of the hollow resin particles was calculated from the following formula (II)₀(g/cm³)。

Formula (II)

True density D₀Mass of pieces of ═ hollow resin particles ]V (100- [ quality of isopropanol)]Specific gravity of isopropyl alcohol at measurement temperature])

True density D₀Corresponding to the specific gravity of only the shell portion of the hollow resin particles. As is apparent from the above measurement method, in calculating the true density D₀In the case, the hollow portion is not regarded as a part of the hollow resin particle.

The porosity of the hollow resin particles can also be said to be a ratio of the specific gravity of the hollow resin particles to the hollow portion.

The amount of the volatile organic compound contained in the hollow resin particles of the present invention is usually 5% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, still more preferably 1% by mass or less, and particularly preferably less than 1% by mass.

When the amount of the volatile organic compound in the hollow resin particles is 5 mass% or less, there is a small risk that the volatile organic compound becomes a heat medium inside the hollow resin particles, and there is a small risk that heat transferred to a part of the particles spreads to the entire particles, and therefore there is a small risk that the heat insulation property is reduced. Further, in the case where the amount of the volatile organic compound in the hollow resin particles is 5% by mass or less, even if the hollow resin particles are exposed to high temperature, the risk of expansion of the hollow resin particles by volatilization of the volatile organic compound is small, and therefore the heat resistance is reduced and the risk of generation of odor is small.

The amount of the volatile organic compound contained in the hollow resin particles was measured as follows. In a 30mL screw glass bottle, about 100mg of hollow resin particles were added and accurately weighed. About 10g of Tetrahydrofuran (THF) were then added and weighed accurately. The mixture in the glass bottle was stirred by a stirrer for 1 hour, and volatile organic compounds contained in the hollow resin particles were extracted. After stirring was stopped and the resin component of the THF-insoluble hollow resin particles was precipitated, a filter (product name: Membrane Filters 25JP020AN, manufactured by AdvantecmFS, Inc.) was attached to the syringe to filter the precipitate to obtain a sample liquid, and the sample liquid was injected into a Gas Chromatograph (GC) for analysis. The amount of volatile organic compound (mass%) per unit mass of the hollow resin particles was obtained from the peak area of GC and a calibration curve prepared in advance. The detailed analysis conditions are as follows.

(analysis conditions)

The device comprises the following steps: GC-2010 (Shimadzu Kaisha Shimadzu)

Column: DB-5(Agilent Technologies Co., Ltd.)

df＝0.25μm 0.25mm I.D.×30m

A detector: FID

Carrier gas: nitrogen (line speed: 28.8 cm/sec)

Injection port temperature: 200 deg.C

Detector temperature: 250 deg.C

Oven temperature: the temperature was increased from 40 ℃ to 230 ℃ at a rate of 10 ℃ per minute and held at 230 ℃ for 2 minutes.

Sample size: 2 μ L

The compressive strength of the hollow resin particles can be measured by, for example, the following method.

The 10% compressive strength of the pellets was measured under the following test conditions using a micro-compression tester (for example, MCTM-500, manufactured by Shimadzu corporation).

(test conditions)

The kind of indenter: FLAT50

Magnification of objective lens: 50

Load speed: 0.8924 mN/s

Although it depends also on the use of the hollow resin particles, if, for example, the compression strength of the hollow resin particles is 5.0MPa or more, the hollow resin particles can be evaluated as having a high compression strength.

The heat resistance and heat insulating property of the hollow resin particles can be evaluated by using the hollow resin particles themselves, or by using a sheet made of the hollow resin particles. The evaluation of heat resistance and the evaluation of heat insulation of the hollow resin particles using the sheet will be described later.

If the above-mentioned 3 physical property parameters (number average particle diameter, void ratio and volatile organic compound amount) satisfy the above-mentioned conditions, the kind of resin contained in the hollow resin particles and the kind of repeating unit constituting the resin are not particularly limited. The resin contained in the hollow resin particles and the repeating units thereof will be described below.

The repeating unit constituting the resin contained in the hollow resin particle may contain a monovinyl monomer unit.

In the present invention, the monovinyl monomer means a compound having 1 vinyl functional group capable of polymerization, and a compound other than the hydrophilic monomer described later. By polymerization of the monovinyl monomer, a resin comprising monovinyl monomer units is produced. In the present invention, the "monovinyl monomer" does not include the "crosslinkable monomer" described later unless otherwise specified.

In the present invention, examples of the monovinyl monomer include acrylic monovinyl monomers such as (meth) acrylate; aromatic vinyl monomers such as styrene, vinyl toluene and α -methylstyrene; and monoolefin monomers such as ethylene, propylene, and butene.

In the present invention, the term (meth) acrylate is intended to include a generic term of acrylate and methacrylate. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, glycidyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate. The (meth) acrylic acid esters may be used singly or in combination of 2 or more.

Among the above (meth) acrylates, at least 1 selected from butyl acrylate and methyl methacrylate is preferably used.

By using a monomer having relatively high temperature resistance such as (meth) acrylate in this way, the heat resistance of the hollow resin particles obtained can be improved as compared with the case of using a monomer having a nitrile group or the like, for example.

The repeating unit constituting the resin included in the hollow resin particle may include a hydrophilic monomer unit.

In the present invention, the hydrophilic monomer means a compound soluble in water, more specifically a compound having a solubility in water of 1 (unit: g/100 g-H)₂O) the above compounds. In particular, it is preferable to use a hydrophilic monomer for polymerization of the resin, because the amount of aggregates of the hollow resin particles obtained is small.

The resin contained in the hollow resin particles may contain, for example, a carboxyl group-containing monomer unit, a hydroxyl group-containing monomer unit, an amide group-containing monomer unit, a polyoxyethylene group-containing monomer unit as the hydrophilic monomer unit. Among them, the resin containing a carboxyl group-containing monomer unit is preferable in that particles having high heat resistance can be obtained. In addition, from the viewpoint of the effect obtained by using a hydrophilic monomer unit, that is, the effect of using a hydrophilic monomer for polymerization of the resin, thereby obtaining particularly less aggregates of the hollow resin particles, it is preferable that the resin contains a hydroxyl group-containing monomer unit.

Examples of the carboxyl group-containing monomer include (meth) acrylic acid monomers, maleic acid monomers, crotonic acid, cinnamic acid, itaconic acid, and fumaric acid. In the present invention, (meth) acrylic acid is a generic term including acrylic acid and methacrylic acid.

In the case of using the carboxyl group-containing monomer and the above (meth) acrylate in combination, the mass ratio of the carboxyl group-containing monomer to the (meth) acrylate is preferably 100: 0 to 10: 90, more preferably 100: 0 to 20: 80, further preferably 100: 0 to 30: 70, and particularly preferably 100: 0 to 35: 65.

In the case of using (meth) acrylic acid as the carboxyl group-containing monomer, the preferable mass ratio is also the same as described above. That is, in the case of using (meth) acrylic acid and the above (meth) acrylate together, the mass ratio of (meth) acrylic acid to (meth) acrylate is preferably 100: 0 to 10: 90, more preferably 100: 0 to 20: 80, still more preferably 100: 0 to 30: 70, and particularly preferably 100: 0 to 35: 65.

Examples of the hydroxyl group-containing monomer include a 2-hydroxyethyl acrylate monomer, a 2-hydroxyethyl methacrylate monomer, a 2-hydroxypropyl acrylate monomer, a 2-hydroxypropyl methacrylate monomer, and a 4-hydroxybutyl acrylate monomer.

Examples of the amide-containing monomer include an acrylamide monomer and a dimethylacrylamide monomer.

Examples of the polyoxyethylene-containing monomer include a methoxypolyethylene glycol acrylate monomer, a methoxypolyethylene glycol methacrylate monomer, and the like.

The repeating unit constituting the resin contained in the hollow resin particle may contain a crosslinkable monomer unit.

In the present invention, the crosslinkable monomer means a compound having 2 or more polymerizable functional groups. By using the crosslinkable monomer, the mechanical properties of the resulting copolymer shell can be improved. Further, since the resin composition has a plurality of polymerizable functional groups, the above-mentioned monovinyl monomer and hydrophilic monomer can be linked to each other, and in particular, the heat resistance of the resulting hollow resin particle can be improved.

The crosslinkable monomer is not particularly limited as long as it has 2 or more polymerizable functional groups. Examples of the crosslinkable monomer include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, diallyl phthalate, and derivatives thereof; ester compounds in which a compound having 2 or more hydroxyl groups or carboxyl groups and a compound having 2 or more carbon-carbon double bonds, such as allyl (meth) acrylate, ethylene glycol di (meth) acrylate, and diethylene glycol di (meth) acrylate, form ester bonds; other divinyl compounds such as N, N-divinylaniline and divinyl ether; among these, divinylbenzene and ethylene glycol di (meth) acrylate are preferable.

In addition, the monomer may contain other polymerizable monomers in addition to the monovinyl monomer, the hydrophilic monomer, and the crosslinkable monomer.

The content of the crosslinkable monomer unit may be 25 to 59 parts by mass, preferably 30 to 57 parts by mass, and more preferably 35 to 55 parts by mass, per 100 parts by mass of the repeating unit constituting the resin. If the content of the crosslinkable monomer unit is 25 to 59 parts by mass, the hollow resin particles obtained are free from the risk of sagging, so that the porosity of the hollow resin particles can be maintained high and the risk of the volatile organic compound remaining in the hollow resin particles is small.

The content ratio of the crosslinkable monomer unit can be determined by calculating the ratio to be supplied to the polymerization reaction from, for example, the amount of the crosslinkable monomer to be fed during the polymerization and the amount of the crosslinkable monomer remaining at the end of the polymerization.

In addition to the above-mentioned resins, for example, the resin constituting the hollow resin particles may be a urethane resin or an epoxy resin. Among these resins, for example, the resin constituting the hollow resin particles may be a polyurethane resin in view of excellent heat insulating properties, or may be an epoxy resin in view of high compressive strength.

The shape of the hollow resin particle is not particularly limited as long as the hollow portion is formed inside, and examples thereof include a spherical shape, an ellipsoidal shape, and an irregular shape. Among these shapes, a spherical shape is preferable because of ease of manufacture.

The inside of the particle has 1 or more than 2 hollow parts. The inside of the particle may be porous if a hollow portion can be secured. In order to maintain a good balance between the high porosity of the hollow resin particles and the compressive strength of the hollow resin particles, the interior of the particles preferably has 5 or less hollow portions, more preferably 3 or less hollow portions, still more preferably 2 or less hollow portions, and particularly preferably only 1 hollow portion.

The hollow resin particles may have an average roundness of 0.950 to 0.995, or 0.970 to 0.995, or 0.980 to 0.995.

In the present invention, the circularity is defined as a value obtained by dividing the circumference of a circle having a projected area equal to the particle image by the circumference of the projected image of the particle. The average circularity in the present invention is a simple method for quantitatively expressing the shape of the hollow resin particles, and is an index for expressing the degree of unevenness of the hollow resin particles. In the case where the hollow resin particles are completely spherical, the average circularity is represented by 1, and the more complicated the surface shape of the hollow resin particles, the smaller the value.

When the hollow resin particles of the present invention have a shell, the shell thickness may be 0.01 to 1.0 μm, 0.02 to 0.95 μm, or 0.05 to 0.90 μm.

In the case where the shell thickness is 0.01 μm or more, the hollow resin particles can maintain a higher compressive strength that maintains their shape as much as possible. In the case where the shell thickness is 1.0 μm or less, a larger volume of hollow portions can be secured inside the hollow resin particles.

The shell thickness of the hollow resin particles was measured as follows. First, 20 target hollow resin particles were selected, and the cross section of these hollow resin particles was observed with a Scanning Electron Microscope (SEM). Next, the thickness of the shell of each of 20 hollow resin particles was measured from the SEM image of the particle cross section. The average value of the thicknesses was taken as the shell thickness of the hollow resin particles.

An example of the image of the shape of the hollow resin particle is a bag formed of a thin film and inflated by gas, and a cross-sectional view thereof is as shown by a hollow resin particle 100 in fig. 1 described later. In this example, the outermost layer of the hollow resin particles is formed of 1 thin film, and the inside thereof is filled with gas.

The shape of the hollow resin particles can be confirmed by SEM or TEM, for example. The shape of the inside of the hollow resin particle can be confirmed by SEM or TEM after the particle is cut into a wafer by a known method.

As the use of the hollow resin particles, for example, a primer layer material of thermal paper and the like can be considered. In general, a material for the undercoat layer is required to have heat insulation and cushioning properties (cushioning), and in addition, heat resistance suitable for the use of thermal paper. The hollow resin particles of the present invention can meet these requirements by virtue of their high porosity, hollow shape which is difficult to break, specific number average particle diameter, and high heat resistance.

In addition, the hollow resin particles are useful as plastic pigments excellent in, for example, gloss, masking ability, and the like. Hollow resin particles obtained by enclosing useful components such as fragrances, medicines, agricultural chemicals, and ink components inside by means of impregnation treatment, reduced pressure or pressurized impregnation treatment, and the like can be used for various applications depending on the components contained inside.

Specific applications of the hollow resin particles include, for example, those for thermal recording materials, fillers, scattering agents, paints, and insulating materials, but the hollow resin particles are not necessarily limited to these examples.

2. Method for producing hollow resin particles

The method for producing the hollow resin particles is not particularly limited as long as it is a method capable of producing hollow resin particles satisfying the conditions of the number average particle diameter, the porosity and the amount of the volatile organic compound. Hereinafter, one embodiment of the method for producing hollow resin particles will be described, but the method for producing hollow resin particles of the present invention is not necessarily limited to the embodiment described below.

One embodiment of the method for producing hollow resin particles includes the steps of:

a step of preparing a mixed solution containing at least 1 monomer selected from a monovinyl monomer and a hydrophilic monomer, a crosslinkable monomer, an oil-soluble polymerization initiator, a hydrocarbon-based solvent, a suspension stabilizer, and an aqueous medium (mixed solution preparation step),

A step of preparing a suspension in which monomer droplets containing a hydrocarbon-based solvent are dispersed in an aqueous medium by suspending the mixed solution (suspension preparation step),

A step (polymerization step) of preparing a precursor composition containing a hollow resin particle precursor containing a hydrocarbon-based solvent by polymerizing the suspension,

A step of obtaining a precursor of hollow resin particles by solid-liquid separation of the precursor composition (solid-liquid separation step), and

and a step (solvent removal step) of removing the hydrocarbon solvent contained in the hollow resin particle precursor in a gas to obtain hollow resin particles.

As described above, the present embodiment includes (1) a mixed liquid preparation step, (2) a suspension preparation step, (3) a polymerization step, (4) a solid-liquid separation step, and (5) a solvent removal step. The number of steps in the present embodiment is not limited to these 5.

Fig. 1 is a schematic diagram showing the present embodiment. The steps (1) to (5) in fig. 1 correspond to the steps (1) to (5) described above. The white arrows between the drawings indicate the sequence of the respective steps. Fig. 1 is a schematic diagram for explanation, and the method for producing hollow resin particles according to the present invention is not limited to the method shown in fig. 1. Further, the structure, size, and shape of the material used in the method for producing hollow resin particles of the present invention are not limited to those of the various materials in fig. 1.

Fig. 1 (1) is a schematic diagram showing an embodiment of the mixed liquid in the mixed liquid preparation step. As shown in the figure, the mixed liquid includes an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 means a material having low polarity and being difficult to be mixed with the aqueous solvent 1, such as a monovinyl monomer and a hydrocarbon solvent.

Fig. 1 (2) is a schematic view showing one embodiment of the suspension in the suspension preparation step. The suspension includes an aqueous medium 1 and micelles 10 (monomer droplets) dispersed in the aqueous medium 1. The micelle 10 is constituted by surrounding the oil-soluble monomer composition 4 (including the oil-soluble polymerization initiator 5) with the surfactant 3.

Fig. 1 (3) is a schematic diagram showing an embodiment of the precursor composition after the polymerization step. The precursor composition contains an aqueous medium 1 and a hollow resin particle precursor 20 dispersed in the aqueous medium 1. The hollow resin particle precursor 20 is formed by polymerization of a monovinyl monomer or the like in the micelle 10, and the inside of the shell 6 contains the hydrocarbon-based solvent 7.

Fig. 1 (4) is a schematic diagram showing an embodiment of the hollow resin particle precursor after the solid-liquid separation step. Fig. 4 shows a state in which the aqueous medium 1 is separated from the state (3).

Fig. 1 (5) is a schematic diagram showing an embodiment of the hollow resin particles after the solvent removal step. The figure (5) shows a state in which the hydrocarbon-based solvent 7 is removed from the state of the above-mentioned figure (4). As a result, hollow resin particles 100 having the hollow portion 8 in the interior of the shell 6 can be obtained.

The above 5 steps and other steps are described in order below.

(1) Preparation of the Mixed solution

This step is a step of preparing a mixed solution containing (a) at least 1 monomer selected from a monovinyl monomer and a hydrophilic monomer, (B) a crosslinkable monomer, (C) an oil-soluble polymerization initiator, (D) a hydrocarbon-based solvent, (E) a suspension stabilizer, and an aqueous medium.

Among them, (a) a monovinyl monomer and a hydrophilic monomer and (B) a crosslinkable monomer are as described in the above "1. hollow resin particles". The mixed solution may contain other polymerizable monomers in addition to the at least 1 monomer (a) selected from the group consisting of the monovinyl monomers and the hydrophilic monomers described in the above "1. hollow resin particles" and the crosslinkable monomer (B).

(C) Oil-soluble polymerization initiator

In the present embodiment, a suspension polymerization method using an oil-soluble polymerization initiator is adopted, instead of an emulsion polymerization method using a water-soluble polymerization initiator. The advantages of the suspension polymerization method are described in detail in "(2) suspension preparation step".

The oil-soluble polymerization initiator is an oil-soluble polymerization initiator having a solubility in water of 0.2 (unit: g/100 g-H)₂The lipophilic polymerization initiator of O) or less is not particularly limited. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, tert-butyl 2-ethylhexanoate peroxide, 2' -azobis (2, 4-dimethylvaleronitrile), azobisisobutyronitrile, and the like.

The content of the oil-soluble polymerization initiator (C) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and still more preferably 1 to 5 parts by mass, based on 100 parts by mass of the total mass of the at least 1 monomer (A) selected from the group consisting of the monovinyl monomer and the hydrophilic monomer, and the crosslinkable monomer (B). When the content of the oil-soluble polymerization initiator (C) is 0.1 parts by mass or more, the polymerization reaction easily proceeds sufficiently. On the other hand, in the case where the content of the (C) oil-soluble polymerization initiator is 10 parts by mass or less, there is little risk that the oil-soluble polymerization initiator remains after the polymerization reaction is completed, and as a result, there is little risk that an unexpected side reaction proceeds.

(D) Hydrocarbon solvent

The hydrocarbon solvent in the present embodiment has a function of forming a hollow space inside the particle.

In the suspension preparation step described later, a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium can be obtained. In the suspension preparation step, the monomer droplets are phase-separated, and as a result, the hydrocarbon solvent having a low polarity is likely to be accumulated in the monomer droplets. Finally, in the monomer droplets, the hydrocarbon-based solvent is distributed in the monomer droplets and the materials other than the hydrocarbon-based solvent are distributed around the monomer droplets according to their polarities.

In the polymerization step described later, a precursor composition containing a hollow resin particle precursor containing a hydrocarbon solvent is obtained. That is, the hydrocarbon solvent is aggregated in the particles, and a hollow containing the hydrocarbon solvent is formed in the obtained polymer particles (hollow resin particle precursor).

The kind of the hydrocarbon solvent is not particularly limited. Examples of the hydrocarbon solvent include solvents having a high volatility such as benzene, toluene, xylene, butane, pentane, hexane, heptane, and cyclohexane.

The hydrocarbon solvent used in the present embodiment preferably has a relative dielectric constant of 3 or less at 20 ℃. The relative dielectric constant is one of indexes indicating the polarity of a compound. When the relative dielectric constant of the hydrocarbon solvent is sufficiently small at 3 or less, it is considered that the phase separation of the monomer droplets proceeds rapidly, and the monomer droplets are likely to be hollow.

Examples of the solvent having a relative dielectric constant of 3 or less at 20 ℃ are as follows. The relative dielectric constant is shown in parentheses.

Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4).

As for the relative dielectric constant at 20 ℃, reference can be made to the values described in publicly known documents (for example, the Japanese chemical society, eds. "basic treaty on chemical reviews", revision 4 th edition, pill-type corporation, published 5 years, 9 months, 30 days, pages II-498 to II-503) and other technical information. Examples of the method for measuring the relative dielectric constant at 20 ℃ include, for example, the following methods in accordance with JIS C2101: 1999 item 23, and the measurement temperature is 20 ℃.

The hydrocarbon solvent used in the present embodiment may be a hydrocarbon compound having 5 to 7 carbon atoms. The hydrocarbon compound having 5 to 7 carbon atoms can be easily included in the hollow resin particle precursor in the polymerization step, and can be easily removed from the hollow resin particle precursor in the solvent removal step. Among these, the hydrocarbon solvent is preferably a hydrocarbon compound having 6 carbon atoms.

The content of the hydrocarbon solvent (D) is preferably 100 to 900 parts by mass, more preferably 150 to 700 parts by mass, and still more preferably 200 to 500 parts by mass, when the total mass of the at least 1 monomer selected from the monovinyl monomers and the hydrophilic monomers (A) and the crosslinkable monomer (B) is 100 parts by mass. When the content of the hydrocarbon-based solvent (D) is 100 parts by mass or more, the obtained hollow resin particles have a small risk of having a small porosity. On the other hand, when the content of the hydrocarbon-based solvent (D) is 900 parts by mass or less, the hollow resin particles obtained are often excellent in mechanical properties, and the risk of being unable to maintain the hollowness is small.

(E) Suspension stabilizer

The suspension stabilizer is a reagent for stabilizing a suspension state in a suspension of a suspension polymerization method described later.

The suspension stabilizer may contain a surfactant. The surfactant is a material that forms micelles in a suspension polymerization method described later, the micelles including at least 1 monomer selected from a monovinyl monomer and a hydrophilic monomer, a crosslinkable monomer, an oil-soluble polymerization initiator, and a hydrocarbon solvent.

As the surfactant, any of a cationic surfactant, an anionic surfactant, and a nonionic surfactant can be used, and these may be used in combination. Among these, anionic surfactants and nonionic surfactants are preferable, and anionic surfactants are more preferable.

Examples of the anionic surfactant include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dialkylsulfosuccinate, and formalin condensate salt of naphthalenesulfonic acid.

Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters.

Examples of the cationic surfactant include didecyldimethylammonium chloride and stearyltrimethylammonium chloride.

The suspension stabilizer may contain a sparingly water-soluble inorganic compound, a water-soluble polymer, and the like.

The content of the suspension stabilizer (E) is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, and still more preferably 0.3 to 1 part by mass, based on 100 parts by mass of the total mass of the at least 1 monomer (A) selected from the group consisting of the monovinyl monomer and the hydrophilic monomer, (B) the crosslinkable monomer, (C) the oil-soluble polymerization initiator, and (D) the hydrocarbon solvent. When the content of the suspension stabilizer (E) is 0.1 part by mass or more, micelles are easily formed in the aqueous medium. On the other hand, when the content of (E) suspended is 3 parts by mass or less, a decrease in productivity due to an increase in foaming is less likely to occur in the step of removing the hydrocarbon-based solvent.

(F) Others

In the present embodiment, the aqueous solvent means any of water, a hydrophilic solvent, or a mixture of water and a hydrophilic solvent.

The hydrophilic solvent in the present embodiment is not particularly limited as long as it is a hydrophilic solvent that is sufficiently mixed with water and does not cause phase separation. Examples of the hydrophilic solvent include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO), and the like.

In the aqueous medium, water is preferably used because of its high polarity. In the case of using a mixture of water and a hydrophilic solvent, it is important that the polarity of the entire mixture is not too low from the viewpoint of forming monomer droplets. For example, the mixing ratio (mass ratio) of water to the hydrophilic solvent may be set to 99: 1 to 50: 50.

The mixed solution prepared in this step is a composition obtained by mixing only the above-mentioned materials (a) to (E) with an aqueous medium and stirring the mixture appropriately. In this mixed solution, the oil phase containing the above-mentioned materials (a) to (D) is dispersed in an aqueous medium in a size of about several mm in particle diameter. The dispersion state of these materials in the mixed solution may be observed with the naked eye depending on the kind of the material.

In the present step, when the composition contains (a) at least 1 monomer selected from a monovinyl monomer and a hydrophilic monomer, (B) a crosslinkable monomer, (C) an oil-soluble polymerization initiator, and (D) a hydrocarbon-based solvent, and when the total mass of (a) at least 1 monomer selected from a monovinyl monomer and a hydrophilic monomer, and (B) a crosslinkable monomer is 100 parts by mass, an oil phase in which the content of (B) the crosslinkable monomer is 25 to 59 parts by mass, and an aqueous phase containing (E) a suspension stabilizer and an aqueous medium are mixed, a mixed solution can be prepared. By mixing the oil phase and the aqueous phase in this manner, particles having a uniform composition can be formed.

(2) Suspension preparation step

This step is a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid.

In the suspension prepared in this step, the monomer droplets containing the above-mentioned materials (A) to (D) and having a particle diameter of about 0.1 to 9 μm are uniformly dispersed in the aqueous medium. Such monomer droplets are difficult to observe with the naked eye, and can be observed with a known observation device such as an optical microscope.

As described above, in the present embodiment, the suspension polymerization method is employed instead of the emulsion polymerization method. Therefore, the following is a comparison with the emulsion polymerization method, and an explanation is given of the advantages of using the suspension polymerization method and the oil-soluble polymerization initiator.

Fig. 4 is a schematic diagram showing a dispersion liquid for emulsion polymerization. The micelle 60 in fig. 4 schematically shows a cross section thereof.

Fig. 4 shows a state in which the micelle 60, the micelle precursor 60a, the monomer 53a eluted in the solvent, and the water-soluble polymerization initiator 54 are dispersed in the aqueous medium 51. The micelle 60 is formed by surrounding the oil-soluble monomer composition 53 with the surfactant 52. The monomer composition 53 contains a monomer or the like as a raw material of a polymer, but does not contain a polymerization initiator.

On the other hand, the micelle precursor 60a is an aggregate of the surfactant 52, but does not contain a sufficient amount of the monomer composition 53 therein. The micelle precursor 60a incorporates the monomer 53a eluted in the solvent, or collects a part of the monomer composition 53 from another micelle 60 or the like, thereby growing into the micelle 60.

The water-soluble polymerization initiator 54 diffuses in the aqueous medium 51, and enters the inside of the micelle 60 and the micelle precursor 60a, thereby promoting the growth of oil droplets in the inside. Therefore, in the emulsion polymerization method, the micelles 60 are monodisperse in the aqueous medium 51, but it is predicted that the particle size of the micelles 60 grows to several hundred nm.

Fig. 2 is a schematic view showing an embodiment of the suspension in this step. The micelle 10 in fig. 2 schematically shows a cross section thereof. Fig. 2 is a schematic view, and the suspension in the present embodiment is not necessarily limited to the one shown in fig. 2. A part of fig. 2 corresponds to (2) of fig. 1 described above.

Fig. 2 shows a state in which the micelles 10 and the monomers 4a (including a monovinyl monomer, a crosslinkable monomer, and the like) dispersed in the aqueous medium are dispersed in the aqueous medium 1. The micelle 10 is formed by surrounding the oil-soluble monomer composition 4 with the surfactant 3. The monomer composition 4 contains an oil-soluble polymerization initiator 5, monomers (including a monovinyl monomer, a crosslinkable monomer, and the like), and a hydrocarbon solvent (both not shown).

As shown in fig. 2, in this step, fine oil droplets containing the monomer composition 4 are formed in advance in the micelles 10, and then polymerization initiating radicals are generated in the fine oil droplets by the oil-soluble polymerization initiator 5. Therefore, the hollow resin particle precursor having a desired particle diameter can be produced without excessively growing the fine oil droplets.

Further, as can be seen from a comparison of the suspension polymerization (fig. 2) and the emulsion polymerization (fig. 4), the oil-soluble polymerization initiator 5 does not have a chance to contact the monomer 4a dispersed in the aqueous medium 1 in the suspension polymerization (fig. 2). Therefore, by using the oil-soluble polymerization initiator, it is possible to prevent the generation of excessive polymer particles other than the target hollow resin particles.

Typical examples of the present process are as follows.

A liquid mixture containing the materials (A) to (E) and an aqueous medium is suspended to form monomer droplets. The method of forming the monomer droplets is not particularly limited, and the formation is carried out using a device capable of strong stirring, such as an in-line type emulsion disperser (product name: miller, manufactured by Atlantic machine Co., Ltd.), a high-speed emulsion disperser (product name: T.K. HOMOMIXER MARK II, manufactured by LTD.).

As described above, in this step, the monomer droplets are phase-separated, and therefore the hydrocarbon-based solvent having a low polarity is likely to be accumulated in the monomer droplets. As a result, the hydrocarbon solvent is distributed in the monomer droplets obtained, and the materials other than the hydrocarbon solvent are distributed around the hydrocarbon solvent.

A modified example of this step is shown below.

First, an oil phase containing the above-mentioned materials (a) to (D) and an aqueous phase containing the material (E) and an aqueous medium are prepared, respectively. In the oil phase, the oil phase is preferably prepared so that the content of the crosslinkable monomer (B) is 25 to 59 parts by mass, when the total mass of the at least 1 monomer selected from the monovinyl monomer (a) and the hydrophilic monomer and the crosslinkable monomer (B) is 100 parts by mass.

Next, a suspension was prepared by a membrane emulsification method. The membrane emulsification method is a method in which a dispersion phase liquid is extruded into a continuous phase through pores of a porous membrane to obtain a suspension in which fine droplets of a dispersion phase are dispersed in the continuous phase. Here, the dispersed phase means a liquid phase dispersed as fine droplets, and the continuous phase means a liquid phase surrounding the dispersed phase droplets. In the present embodiment, any of a direct film emulsification method and a film emulsification method involving pre-emulsification can be employed as long as the film emulsification method uses the oil phase as a dispersed phase and the aqueous phase as a continuous phase.

In the membrane emulsification method, a membrane emulsification system (e.g., model: MN-20, SPG Technology Co., Ltd., etc.) and a membrane having a specific fine pore size are used. Examples of the porous membrane that can be used in the membrane emulsification method include an inorganic porous membrane such as a Shirasu porous glass membrane (SPG membrane) and an organic porous membrane such as a PTFE membrane.

The pore diameter of the porous film in the membrane emulsification method determines the particle diameter of the obtained fine droplets. Although it depends on the components in the dispersed phase, the number average particle diameter of the hollow resin particles obtained is affected by the particle diameter of the fine droplets, and therefore, the selection of the pore diameter of the porous membrane is important. For example, when a Shirasu porous glass membrane (SPG membrane) is used, the pore diameter of the membrane is preferably 0.1 to 4.0. mu.m, more preferably 0.2 to 3.5. mu.m, and still more preferably 0.3 to 3.0. mu.m.

A suspension was prepared by performing membrane emulsification using a membrane emulsification system and a porous membrane with the oil phase as the dispersed phase and the aqueous phase as the continuous phase.

The suspension preparation step in the present embodiment is not limited to the above-described typical example and modification example.

(3) Polymerization Process

This step is a step of preparing a precursor composition containing a hollow resin particle precursor by polymerizing the suspension, wherein the hollow resin particle precursor contains a hydrocarbon solvent. Here, the hollow resin particle precursor means a particle formed by copolymerizing at least 1 monomer selected from the above-mentioned monovinyl monomers and hydrophilic monomers and a crosslinkable monomer.

The polymerization method is not particularly limited, and for example, a batch type (batch type), a semi-continuous type, a continuous type, or the like can be used. The polymerization temperature is preferably 40 to 80 ℃ and more preferably 50 to 70 ℃. The reaction time for the polymerization is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

Since the monomer droplets containing the hydrocarbon solvent therein are used, as described above, a hollow space filled with the hydrocarbon solvent is formed inside the hollow resin particle precursor.

(4) Solid-liquid separation step

This step is a step of obtaining a precursor of hollow resin particles by subjecting the precursor composition to solid-liquid separation.

When removing a hydrocarbon solvent included in particles from a slurry containing an aqueous medium, the following problems occur: if the same volume of water as the hydrocarbon-based solvent removed from the particles does not enter the particles, the resulting hollow resin particles will break.

As a method for preventing this problem, for example, it is conceivable to set the pH of the slurry to 7 or more, then swell the shell of the particles with an alkali, and remove the hydrocarbon solvent. In this case, since the shell of the particle is flexible, the replacement of the hydrocarbon solvent and water in the particle proceeds rapidly, and the water-in-particle can be obtained.

The method for solid-liquid separation of the precursor composition is not limited as long as the method does not remove the hydrocarbon-based solvent contained in the hollow resin particle precursor and separates the solid component containing the hollow resin particle precursor and the liquid component containing the aqueous medium, and a known method can be used. Examples of the method for solid-liquid separation include a centrifugal separation method, a filtration method, a static separation method, and the like, and among them, a centrifugal separation method or a filtration method is possible, and a centrifugal separation method is employed from the viewpoint of ease of operation.

After the solid-liquid separation step and before the solvent removal step described later, an optional step such as a preliminary drying step may be performed. The preliminary drying step includes, for example, a step of preliminarily drying the solid content obtained after the solid-liquid separation step by a drying device such as a dryer or a drying instrument such as a hand dryer.

(5) Solvent removal step

This step is a step of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the hollow resin particle precursor in a gas.

The term "in-gas" in the present step is not limited to "in-gas" in a strict sense, that is, an environment in which no liquid component is present outside the hollow resin particle precursor at all, and means an environment in which only a very small amount of liquid component is present outside the hollow resin precursor to such an extent that the removal of the hydrocarbon solvent is not affected. The "in-gas" may be said to be a state in which the hollow resin particle precursor is not present in the slurry, and may also be said to be a state in which the hollow resin particle precursor is present in the dry powder.

As shown in examples 1 to 5 described later, it is considered that the hollow resin particles maintained a spherical shape after returning to normal pressure after vacuum drying in the solvent removal step are evidence that the permeability of the shell itself is relatively high.

It is generally known that nylon, ethylene vinyl alcohol (EVOH), and the like have increased air permeability under high humidity. This is understood to be due to the fact that these polymers are plasticized by water molecules, as a result of which the mobility of the polymers is increased. However, considering that the hollow resin particles of the present invention have a high degree of crosslinking, it is presumed that the effect of plasticization by the action of the aqueous medium is small. Therefore, in the present invention, it is considered that the air permeability of the shell of the hollow resin particle is caused by the inherent property of the polymer constituting the shell.

The method for removing the hydrocarbon solvent in the hollow resin particle precursor in a gas is not particularly limited, and a known method can be used. Examples of the method include a reduced pressure drying method, a heat drying method, a pneumatic drying method, and a combination thereof.

In particular, when the heat drying method is used, it is necessary to set the heating temperature to a temperature not lower than the boiling point of the hydrocarbon solvent and not higher than the maximum temperature at which the shell structure of the hollow resin particles is not collapsed. Therefore, the heating temperature may be 50 to 150 ℃, 60 to 130 ℃, or 70 to 100 ℃ depending on the composition of the shell in the hollow resin particle precursor and the type of the hydrocarbon solvent.

By the drying operation in the gas, the hydrocarbon-based solvent inside the hollow resin particle precursor is replaced with the gas outside, and as a result, the hollow resin particles having the hollow portion occupied with the gas can be obtained.

The drying environment is not particularly limited, and can be appropriately selected according to the use of the hollow resin particles. As the drying atmosphere, for example, air, oxygen, nitrogen, argon, or the like can be considered. After the interior of the hollow resin particles is once filled with the gas, the hollow resin particles can be dried under reduced pressure to obtain hollow resin particles having a temporarily vacuum interior.

(6) Others

As the steps other than the above (1) to (5), for example, a step of replacing the gas inside the hollow resin particles with another gas or liquid is conceivable. By such substitution, the environment inside the hollow resin particle can be changed, and the molecule can be selectively encapsulated inside the hollow resin particle, thereby modifying the chemical structure inside the hollow resin particle according to the application.

3. Sheet material

The sheet of the present invention is characterized by containing the above hollow resin particles.

The sheet of the present invention may contain only the hollow resin particles, or may contain other materials such as the hollow resin particles and the binder. The sheet of the present invention may be a single-layer sheet containing hollow resin particles, or may be a multilayer sheet in which a layer containing hollow resin particles and 1 or 2 or more other layers are laminated.

The shape, area, and thickness of the sheet of the present invention can be freely designed according to the use thereof. The sheet of the present invention may have a thickness of, for example, 10 μm to 1 mm.

The sheet of the present invention can be produced by a conventionally known method. The sheet of the present invention can be produced by, for example, the following method.

First, a mixed liquid containing hollow resin particles, a binder such as polyvinyl alcohol (PVA), and a surfactant is applied to a substrate such as a PET substrate. At this time, the amount of the liquid mixture applied is adjusted so that the average thickness of the layer including the hollow resin particles (average thickness not including the base material) after the liquid mixture is dried becomes a desired thickness. The substrate coated with the mixed solution is appropriately dried, thereby producing a sheet on the substrate. The obtained multilayer sheet may be used for various applications described later, or a single-layer sheet obtained by peeling the sheet from a substrate may be used for various applications described later.

The following describes the evaluation of heat insulation properties and the evaluation of heat resistance of a sheet using hollow resin particles.

The heat insulating property of the sheet using the hollow resin particles can be evaluated by, for example, the thermal conductivity of the sheet. The thermal conductivity of the sheet was measured as follows. The thermal conductivity of the sheet obtained by the transient hot-wire method (transient hot-wire method) was measured under the following test conditions using a rapid thermal conductivity meter (for example, QTM-500, manufactured by kyoto electronics industries, inc.) and film measurement software (for example, SOFT-QTM5W, manufactured by kyoto electronics industries, inc.).

(test conditions)

Probe: PD-11

Reference plate: foamed polyethylene

The lower the thermal conductivity, the more excellent the heat insulating property can be evaluated. Although depending on the use of the sheet, if the sheet has a thermal conductivity of 0.060(W/(m × K)) or less, for example, the sheet can be evaluated as having sufficient thermal insulation.

The heat resistance of a sheet using hollow resin particles can be evaluated by, for example, the thickness change rate of the sheet in a high-temperature environment. The thickness change rate of the sheet in a high-temperature environment can be measured by the following method.

This is explained with reference to fig. 5. First, a sheet (sheet 30 to be measured) was processed into a square shape having a side length of 5 cm. Next, on the plane of the 5cm square measured sheet 30, 1 point (D0) at the center and the other 8 points (D1 to D8) arranged with the 1 point as the center are set, respectively. At this time, the 9 points are selected as follows: when the other 8 points (D1 to D8) are connected to each other by a line, respectively, a square having a side length of 4cm is formed in a similar shape concentric with the center point (D0) of the sheet to be measured and smaller by one turn than the sheet to be measured, and when the center point (D0), any one point of four corners (D1, D2, D3, or D4), and 2 points (e.g., D2 and D8) closest to the two points are selected, and the points closest to each other are connected to each other by a line, 4 squares having a side length of 2cm are arranged in a grid pattern.

Next, the thickness of the sheet at each position of these 9 points was measured using a micrometer (for example, MDQ-30, manufactured by Mitutoyo Corporation, etc.), and the average value thereof was taken as the average thickness T before heating₀(μm)。

Next, the test sheet 30 was subjected to heat treatment in a dryer at 120 ℃ for 72 hours. Then, the sheet was taken out from the dryer and naturally cooled, and the thickness was measured similarly for the 9 points, and the average value thereof was defined as the average thickness T after heating₁(μm)。

The thickness change rate of the sheet in a high-temperature environment was measured based on the following formula (X).

Formula (X)

ΔT＝100×{|T₁-T₀|/T₀}

(in the above formula (X), Δ T represents the thickness change rate (%) of the sheet in a high-temperature environment), and T₁Represents the average thickness (. mu.m) after heating, T₀The average thickness (μm) before heating is shown. )

The smaller the thickness change rate Δ T in a high-temperature environment, the more excellent the heat resistance can be evaluated. Although it depends on the use of the sheet, if the thickness change rate Δ T of the sheet in a high-temperature environment is 8.0% or less, for example, the sheet is not likely to change in thickness even under high-temperature conditions, and can be evaluated as having sufficient heat resistance.

The use of the sheet of the present invention is related to the use of the hollow resin particles described above. Examples of the use of the sheet of the present invention include a thermosensitive recording sheet, an insulating sheet, and the like, but the sheet is not necessarily limited to these examples.