Sheet

Abstract

This invention provides a sheet comprising hollow resin particles with higher compressive strength than conventional sheets, and excellent thermal insulation and heat resistance. The hollow resin particles are hollow resin microparticles having one or more hollow sections, with a number-average particle size of 0.1–9.0 μm, a porosity of 70–99%, and containing less than 5% by mass of volatile organic compounds.

Description

[0001] This application is a divisional application of the invention patent application with application number 201980020581.6, the original application being filed on March 25, 2019, and the invention being entitled "Hollow Resin Particles and Sheets". Technical Field

[0002] The present invention relates to hollow resin particles with higher compressive strength than before, and excellent thermal insulation and heat resistance, as well as sheets comprising the same. Background Technology

[0003] Hollow resin particles, compared to resin particles that do not actually have pores inside, can scatter light well and reduce light transmittance. Therefore, they are widely used as organic pigments and masking agents with excellent optical properties such as opacity and whiteness, and are used in water-based coatings, paper coating compositions and other applications.

[0004] However, in applications such as water-based coatings and paper coating compositions, it is desirable to increase the porosity of the incorporated hollow resin particles in order to improve the lightweight, heat insulation, and opacity of the coatings and paper coating compositions. However, in existing manufacturing methods, it is difficult to control the particle size and produce hollow resin particles with high porosity and excellent heat resistance.

[0005] For example, Patent Document 1 discloses a method for manufacturing thermally expandable microspheres, which are composed of a shell containing a thermoplastic resin and a foaming agent encapsulated therein. This document describes a method for stably manufacturing thermally expandable microspheres with a specified average particle size in good yield without deteriorating their expansion properties.

[0006] Furthermore, Patent Document 2 discloses the following: In manufacturing hollow resin particles, (1) a dispersed phase is prepared, which includes vinyl monomers without nitrile groups, a phase separation promoter, a volatile solvent, a polymerization initiator, and a reaction catalyst; (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 supplied to the polymerization reaction under pressure; (5) the mixture after the polymerization reaction is depressurized at a temperature above the boiling point of the volatile solvent, thereby obtaining an aqueous dispersion; (6) the resulting aqueous dispersion is filtered and dried, thereby obtaining hollow resin particles. This document describes that the resin constituting the shell of the hollow resin particles contains vinyl monomers without nitrile groups, therefore the nitrile groups will not detach even at high temperatures, and the strength of the shell is unlikely to decrease.

[0007] Patent document 3 discloses a method for manufacturing hollow polymer particles as follows: after polymerizing a dispersion of hydrophilic monomers, crosslinking monomers and other monomers that coexist with oily substances, the oily substances in the particles are removed in a liquid or gas, thereby preparing hollow polymer particles.

[0008] Patent document 4 discloses a method for manufacturing hollow resin particles by removing the organic solvent encapsulated within the particles in an aqueous medium to induce hollowing, thereby suppressing collapse.

[0009] Patent document 5 discloses hollow polymer microparticles containing a high proportion of crosslinking monomers.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent No. 6152237;

[0013] Patent Document 2: Japanese Patent Application Publication No. 2008-231241;

[0014] Patent Document 3: Japanese Patent Application Publication No. 61-87734;

[0015] Patent document 4: Japanese Patent No. 5727962;

[0016] Patent document 5: Japanese Patent No. 4448930.

[0017] The problem the invention aims to solve

[0018] Patent Document 1 describes a preferred composition containing nitrile monomers as an essential component, considering expansion performance. However, resin particles containing nitrile monomers typically have poor heat resistance. Furthermore, the technology in Patent Document 1 has the following problem: the foaming and thermal expansion reaction generated by the foaming agent causes the microspheres to expand, making it difficult to precisely control the particle size of the microspheres.

[0019] Furthermore, Patent Document 2 describes a method of forming hollow resin particles by depressurizing the resin at a temperature above the boiling point of the volatile solvent, causing the resin to expand due to the pressure of the encapsulated volatile solvent during evaporation. However, since the particles are expanded by simultaneously heating and depressurizing, there is a problem that the resulting hollow resin particles become uneven in size.

[0020] In the technology of Patent Document 3, when increasing the amount of oily substance to produce hollow particles with thin shells, there are problems such as low shell strength, particle breakage when removing oily substance, and inability to obtain particles with high porosity.

[0021] Hollow particles containing water, manufactured using the method described in Patent Document 4, require a process to remove the internal water when used as heat insulation agents or similar applications. During this process, there is a problem of particle collapse and reduced porosity.

[0022] In the case of hollow polymer microparticles as described in Patent Document 5, there is a problem that even with high-temperature conditions and long-term processing, it is difficult to remove the hydrocarbon solvent inside the particles.

[0023] In addition to the high porosity and excellent heat resistance mentioned above, hollow resin particles are also required to maintain high compressive strength in the hollow portion of the particles. Furthermore, although depending on the application, hollow resin particles also need to utilize the excellent thermal insulation properties of the hollow portion, which makes it difficult to conduct heat. Summary of the Invention

[0024] The problem to be solved by the present invention is to provide a hollow resin particle with higher compressive strength than existing materials, and excellent thermal insulation and heat resistance, as well as a sheet containing the same.

[0025] Solution for solving the problem

[0026] To improve compressive strength, the inventors focused on the optimal particle size of hollow resin particles. Furthermore, they carefully studied the physical properties required to obtain hollow resin particles with superior thermal insulation and heat resistance compared to existing materials. As a result, the inventors discovered that hollow resin particles with specific number-average particle size, porosity, and volatile organic compound content exhibit high compressive strength, as well as excellent thermal insulation and heat resistance.

[0027] That is, the hollow resin particles of the present invention are characterized in that they are hollow resin particles having one or more hollow parts, having a number average particle size of 0.1 to 9.0 μm, a porosity of 70 to 99%, and containing volatile organic compounds of 5% by mass or less.

[0028] In this invention, the repeating units constituting the above-mentioned resin may include crosslinking monomer units.

[0029] In this invention, when the repeating unit constituting the above-mentioned resin is 100 parts by mass, the content ratio of the above-mentioned crosslinking monomer unit can be 25 to 59 parts by mass.

[0030] In this invention, the repeating units constituting the above-mentioned resin may include hydrophilic monomer units.

[0031] In this invention, the repeating unit constituting the above-mentioned resin includes a crosslinking monomer unit, which may include at least one selected from divinylbenzene monomer unit and ethylene glycol dimethacrylate monomer unit.

[0032] In this invention, the hydrophilic monomer unit may include at least one selected from carboxyl-containing monomer units and hydroxyl-containing monomer units.

[0033] In this invention, the repeating units constituting the above-mentioned resin may include monovinyl monomer units.

[0034] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow resin particles of the present invention can be 1.1 to 2.5.

[0035] The hollow resin particles of the present invention have a shell, the thickness of which can be 0.01 to 1.0 μm.

[0036] The hollow resin particles of the present invention can be hollow resin particles for thermal recording materials having the above-mentioned characteristics.

[0037] The hollow resin particles of the present invention can be hollow resin particles for fillers having the above-mentioned characteristics.

[0038] The hollow resin particles of the present invention can be hollow resin particles for coatings having the above-mentioned characteristics.

[0039] The sheet of the present invention is characterized in that it comprises the above-mentioned hollow resin particles.

[0040] The sheet material of the present invention can be a thermal recording sheet containing the above-mentioned hollow resin particles.

[0041] Invention Effects

[0042] As described above, according to the present invention, hollow resin particles have high compressive strength and excellent thermal insulation and heat resistance because they have specific number-average particle size, porosity and volatile organic compound content. Attached Figure Description

[0043] Figure 1 This is a schematic diagram illustrating one embodiment of the manufacturing method of the present invention.

[0044] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in the suspension preparation process.

[0045] Figure 3A This is an SEM image of the hollow resin particles from Example 1.

[0046] Figure 3B This is a SEM image of a cross-section of the hollow resin particles from Example 1.

[0047] Figure 4 This is a schematic diagram showing a dispersion used in existing emulsion polymerization.

[0048] Figure 5 This diagram illustrates the test sheet used in the experiment to evaluate the thickness change of sheet material under high temperature conditions. Detailed Implementation

[0049] In this invention, "hollow" means that at least one of the following states, selected from liquid, gas, and a mixture of liquid and gas, can be confirmed by conventional observation methods: "Liquid portion" refers to a continuous portion filled with liquid. "Gas portion" refers to a continuous portion filled with gas. "Mixed portion of liquid and gas" refers to a continuous portion filled with both liquid and gas.

[0050] In this invention, "hollow portion" refers to the hollow part inside the particle. Whether a particle has a hollow portion can be confirmed, for example, by observing a cross-section of the particle under test using SEM, or by directly observing the particle under test using transmission electron microscopy (TEM).

[0051] The shell of the resin in the granules may not have a connecting hole, and the "hollow part" of the present invention can be isolated from the outside of the granules through the shell of the granules.

[0052] The resin shell in the granules may also have one or more connecting holes, and the "hollow part" in this invention may also be connected to the outside of the granules through the connecting holes.

[0053] In this invention, "hollow resin particle precursor" means a particle whose hollow portion is filled with water or a mixture of water and gas, or an aqueous medium or a mixture of an aqueous medium and gas. In this invention, "precursor composition" means a composition comprising the hollow resin particle precursor.

[0054] In this invention, "hollow resin particles" means resin particles whose hollow parts are filled with gas.

[0055] 1. Hollow resin particles

[0056] The hollow resin particles of the present invention are characterized in that they are hollow resin particles having one or more hollow parts, having a number average particle size of 0.1 to 9.0 μm, a porosity of 70 to 99%, and containing less than 5% by mass of volatile organic compounds.

[0057] As mentioned above, the required characteristics of hollow resin particles include high compressive strength, as well as excellent thermal insulation and heat resistance. To achieve these characteristics, the three physical properties of hollow resin particles—number-average particle size, porosity, and volatile organic compound (VOC) content—must each be within specific numerical ranges. The following is a summary of the relationship between these three physical properties (number-average particle size, porosity, and VOC content) and the three characteristics (compressive strength, thermal insulation, and heat resistance).

[0058] The number-average particle size of hollow resin particles is a parameter related to their compressive strength and heat resistance. When the number-average particle size of hollow resin particles is sufficiently small, particles with larger number-average particle sizes are less prone to breakage, thus exhibiting high compressive strength. A sufficiently small number-average particle size also results in a small surface area, making the particles less susceptible to external environmental influences, thus contributing to excellent heat resistance.

[0059] Next, the porosity of hollow resin particles is a parameter related to their thermal insulation properties. The hollow portion of hollow resin particles is generally less susceptible to heat transfer than if resin were assumed to be present in that portion. Therefore, a higher porosity indicates a higher proportion of hollow space, resulting in superior thermal insulation properties for hollow resin particles.

[0060] Next, the amount of volatile organic compounds (VOCs) contained in the hollow resin particles is a parameter related to their thermal insulation and heat resistance. In this invention, "volatile organic compounds contained in the hollow resin particles" refers to organic compounds with a boiling point below 400°C among the organic compounds contained in the hollow resin particles. Typical examples of VOCs include hydrocarbon solvents used in the preparation method described later, unreacted monomers, etc., but are not limited to these typical examples. When the amount of VOCs in the hollow resin particles is sufficiently low, the risk of the VOCs becoming a heat medium inside the hollow resin particles is small, and the risk of heat transferred to a part of the particles dissipating to the entire particles is small, thus the risk of reduced thermal insulation is small. Furthermore, when the amount of VOCs in the hollow resin particles is sufficiently low, even if the hollow resin particles are exposed to high temperatures, the risk of expansion of the hollow resin particles due to the volatilization of VOCs is small, thus the risk of reduced heat resistance is small.

[0061] Thus, the three physical properties of hollow resin particles (number-average particle size, porosity, and volatile organic compound content) will affect the above three characteristics (compressive strength, thermal insulation, and heat resistance), respectively.

[0062] The following sections will explain the three physical properties (number-average particle size, porosity, and volatile organic compound content) in detail.

[0063] The number-average particle size of the hollow resin particles is typically 0.1–9.0 μm, preferably 0.2–8.0 μm, more preferably 0.4–6.0 μm, even more preferably 0.6–5.0 μm, and particularly preferably 0.8–4.0 μm.

[0064] When the number average particle size of hollow resin particles is 0.1 μm or larger, heat is difficult to conduct to the entire hollow resin particle, thus the hollow resin particles exhibit excellent thermal insulation properties. Furthermore, when the number average particle size of hollow resin particles is 9.0 μm or smaller, the hollow resin particles become less prone to breakage, resulting in high compressive strength. Moreover, when the number average particle size of hollow resin particles is 9.0 μm or smaller, the surface area of ​​the hollow resin particles is sufficiently small, making them less susceptible to external environmental influences, resulting in excellent heat resistance.

[0065] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow resin particles can be 1.1 to 2.5, 1.1 to 2.3, or 1.1 to 2.0. With a particle size distribution of 2.5 or less, particles with small deviations in compressive strength and heat resistance between particles can be obtained. Furthermore, with a particle size distribution of 2.5 or less, products with uniform thickness can be manufactured when producing products such as sheets, as described later.

[0066] The volume-average particle size (Dv) and number-average particle size (Dn) of hollow resin particles can be determined using, for example, a laser diffraction particle size distribution measuring device. The number-average and volume-average particle sizes are calculated, and these values ​​are used as the number-average particle size (Dn) and volume-average particle size (Dv) for that particle. Particle size distribution is the value of volume-average particle size divided by number-average particle size.

[0067] The porosity of hollow resin particles is typically 70% or more, preferably 72% or more, more preferably 74% or more, even more preferably 78% or more, even more preferably 80% or more, and particularly preferably 82% or more. When the porosity of the hollow resin particles is 70% or more, the proportion of hollow space is high, thus the hollow resin particles exhibit excellent thermal insulation properties. From the viewpoint of maintaining the strength of the hollow resin particles, the porosity can be 99% or less, or 95% or less.

[0068] The porosity of hollow resin particles can be calculated by subtracting the following value from 100: This value is obtained by dividing the apparent density D1 of the hollow resin particles by the actual density D0, and then multiplying by 100.

[0069] The method for determining the apparent density D1 of hollow resin particles is as follows. First, in a volume of 100 cm³... 3 Fill the volumetric flask with approximately 30cm 3 The hollow resin particles were precisely weighed, and the mass of the filled hollow resin particles was accurately measured. Next, isopropanol was precisely added to the volumetric flask filled with the hollow resin particles up to the mark, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm³) of the hollow resin particles was calculated according to the following formula (I).3 ).

[0070] Formula (I)

[0071] Apparent density D1 = [mass of hollow resin particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0072] Apparent density D1 is equivalent to the overall density of the hollow resin particles when the hollow portion is considered as part of the hollow resin particles.

[0073] The method for determining the true density D0 of hollow resin particles is as follows. After pre-crushing the hollow resin particles, they are measured in a 100cm³ container. 3 Approximately 10 g of hollow resin granule fragments were filled into a volumetric flask, and the mass of the filled fragments was accurately weighed. Then, isopropanol was added to the volumetric flask in the same manner as the apparent density determination described above, and the mass of the isopropanol was accurately weighed. The true density D0 (g / cm³) of the hollow resin granules was calculated according to the following formula (II). 3 ).

[0074] Equation (II)

[0075] True density D0 = [mass of hollow resin particle fragments] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0076] The true density D0 corresponds to the specific gravity of the shell portion only in the hollow resin particle. It is clear from the above measurement method that the hollow portion is not considered part of the hollow resin particle when calculating the true density D0.

[0077] The porosity of hollow resin particles can also be described as the proportion of the hollow portion in the total weight of hollow resin particles.

[0078] The hollow resin particles of the present invention contain volatile organic compounds in an amount that is typically 5% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, further preferably 2% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass.

[0079] When the amount of volatile organic compounds (VOCs) in hollow resin particles is less than 5% by mass, the risk of VOCs becoming a heat medium inside the hollow resin particles is low, and the risk of heat transferred to a portion of the particles dissipating to the entire particle is low, thus the risk of reduced thermal insulation is low. Furthermore, when the amount of VOCs in hollow resin particles is less than 5% by mass, even assuming the hollow resin particles are exposed to high temperatures, the risk of expansion due to the volatilization of VOCs is low, thus the risk of reduced heat resistance and odor generation is low.

[0080] The method for determining the amount of volatile organic compounds (VOCs) in hollow resin particles is as follows: Approximately 100 mg of hollow resin particles, accurately weighed, is added to a 30 mL screw-top glass bottle. Then, approximately 10 g of tetrahydrofuran (THF), accurately weighed, is added. The mixture in the glass bottle is stirred with a stirrer for 1 hour to extract the VOCs contained in the hollow resin particles. Stirring is stopped, and the resin components of the hollow resin particles insoluble in THF are allowed to precipitate. A filter (Advantec MFS, Inc., trade name: Membrane Filters 25JP020AN) is installed in a syringe, and the precipitate is filtered to obtain a sample solution. This sample solution is injected into a gas chromatograph (GC) for analysis. The amount of VOCs (mass%) per unit mass of hollow resin particles is determined based on the peak area of ​​the GC and a pre-prepared calibration curve. Detailed analytical conditions are as follows.

[0081] (Analysis conditions)

[0082] Device: GC-2010 (manufactured by Shimadzu Corporation)

[0083] Column: DB-5 (Made by Agilent Technologies)

[0084] df = 0.25μm 0.25mm ID × 30m

[0085] Detector: FID

[0086] Carrier gas: nitrogen (linear velocity: 28.8 cm / s)

[0087] Inlet temperature: 200℃

[0088] Detector temperature: 250℃

[0089] Oven temperature: Increase from 40℃ to 230℃ at a rate of 10℃ / minute, and hold at 230℃ for 2 minutes.

[0090] Sample size: 2 μL

[0091] The compressive strength of hollow resin particles can be determined by methods such as the following.

[0092] The 10% compressive strength of the particles was determined using a micro compression testing machine (e.g., MCTM-500, manufactured by Shimadzu Corporation) under the following test conditions.

[0093] (Experimental conditions)

[0094] • Type of pressure head: FLAT50

[0095] • Objective lens magnification: 50

[0096] • Load speed: 0.8924 mN / s

[0097] While it also depends on the intended use of the hollow resin particles, if, for example, the compressive strength of the hollow resin particles is 5.0 MPa or higher, then the hollow resin particles can be evaluated as having high compressive strength.

[0098] The heat resistance and insulation properties of hollow resin particles can be evaluated using the particles themselves or using sheets made from them. Evaluations of the heat resistance and insulation properties of hollow resin particles used in sheets will be described later.

[0099] If the above three physical properties (number-average particle size, porosity, and volatile organic compound content) meet the above conditions, then there are no particular limitations on the type of resin contained in the hollow resin particles or the type of repeating units constituting the resin. The following describes the resin contained in the hollow resin particles and its repeating units.

[0100] The repeating units of the resin that make up the hollow resin particles may include monovinyl monomer units.

[0101] In this invention, a monovinyl monomer means a compound having one polymerizable vinyl functional group, as well as compounds other than the hydrophilic monomers described later. By polymerizing the monovinyl monomer, a resin comprising monovinyl monomer units is generated. Furthermore, in this invention, unless otherwise specified, "monovinyl monomer" does not include "crosslinking monomers" described later.

[0102] In this invention, examples of monovinyl monomers include acrylic monovinyl monomers such as (meth)acrylate; aromatic vinyl monomers such as styrene, vinyltoluene, and α-methylstyrene; and monoolefin monomers such as ethylene, propylene, and butene.

[0103] In this invention, (meth)acrylate means a general term encompassing acrylates and methacrylates. Examples of (meth)acrylates 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. (Methacryl)acrylates can be used alone or in combination of two or more.

[0104] Of the above-mentioned (meth)acrylates, it is preferred to use at least one selected from butyl acrylate and methyl methacrylate.

[0105] In this way, by using a monomer that is more resistant to high-temperature conditions, such as (meth)acrylate, the heat resistance of the obtained hollow resin particles can be improved compared with the case of using monomers having, for example, nitrile groups.

[0106] The repeating units of the resin that make up hollow resin particles may include hydrophilic monomer units.

[0107] In this invention, a hydrophilic monomer means a compound that is soluble in water, and more specifically, a compound with a solubility of 1 (g / 100g-H2O) or higher in water. From the viewpoint of minimizing aggregates in the resulting hollow resin particles, the use of hydrophilic monomers in the polymerization of the aforementioned resin is particularly preferred.

[0108] The hollow resin particles may contain, for example, carboxyl-containing monomer units, hydroxyl-containing monomer units, amide-containing monomer units, or polyoxyethylene monomer units as hydrophilic monomer units. From the perspective of obtaining particles with high heat resistance, it is preferable that the resin contains carboxyl-containing monomer units. Furthermore, from the perspective of the effect obtained by using hydrophilic monomer units, that is, the effect of using hydrophilic monomers in the polymerization of the above-mentioned resin, resulting in hollow resin particles with particularly low aggregate content, it is preferable that the resin contains hydroxyl-containing monomer units.

[0109] Examples of carboxyl-containing monomers include (meth)acrylic acid monomers, maleic acid monomers, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, etc. In this invention, (meth)acrylic acid refers to the general term encompassing acrylic acid and methacrylic acid.

[0110] When using carboxyl-containing monomers and the above-mentioned (meth)acrylates in combination, the preferred mass ratio is carboxyl-containing monomer: (meth)acrylate = 100:0 to 10:90, a more preferred mass ratio is carboxyl-containing monomer: (meth)acrylate = 100:0 to 20:80, a further preferred mass ratio is carboxyl-containing monomer: (meth)acrylate = 100:0 to 30:70, and a particularly preferred mass ratio is carboxyl-containing monomer: (meth)acrylate = 100:0 to 35:65.

[0111] When using (meth)acrylic acid as a carboxyl-containing monomer, the preferred mass ratio is the same as described above. That is, when using (meth)acrylic acid and the above-described (meth)acrylate in combination, the preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 100:0 to 10:90, a more preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 100:0 to 20:80, a further preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 100:0 to 30:70, and a particularly preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 100:0 to 35:65.

[0112] Examples of hydroxyl-containing monomers include 2-hydroxyethyl acrylate monomer, 2-hydroxyethyl methacrylate monomer, 2-hydroxypropyl acrylate monomer, 2-hydroxypropyl methacrylate monomer, and 4-hydroxybutyl acrylate monomer.

[0113] Examples of amide-containing monomers include acrylamide monomers and dimethylacrylamide monomers.

[0114] Examples of monomers containing polyoxyethylene esters include methoxy polyethylene glycol acrylate monomers and methoxy polyethylene glycol methacrylate monomers.

[0115] The repeating units of the resin that make up hollow resin particles may include crosslinked monomer units.

[0116] In this invention, a crosslinking monomer means a compound having two or more polymerizable functional groups. By using a crosslinking monomer, the mechanical properties of the resulting copolymer shell can be improved. Furthermore, because it has multiple polymerizable functional groups, the aforementioned monovinyl monomers and hydrophilic monomers can be linked together, which in particular improves the heat resistance of the resulting hollow resin particles.

[0117] As a crosslinking monomer, there are no particular limitations as long as it has two or more polymerizable functional groups. Examples of crosslinking monomers include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, diallyl phthalate, and their derivatives; ester compounds such as allyl (meth)acrylate, ethylene (meth)acrylate, and diethylene (meth)acrylate, which form ester bonds with compounds having two or more hydroxyl or carboxyl groups and compounds having two or more carbon-carbon double bonds; and other divinyl compounds such as N,N-divinylaniline and divinyl ether. Among these, divinylbenzene and ethylene (meth)acrylate are preferred.

[0118] In addition, as monomers, besides monovinyl monomers, hydrophilic monomers, and crosslinking monomers, other monomers capable of polymerization may also be included.

[0119] When the repeating unit constituting the resin is 100 parts by mass, the content of the crosslinking monomer unit can be 25 to 59 parts by mass, preferably 30 to 57 parts by mass, and more preferably 35 to 55 parts by mass. If the content of the crosslinking monomer unit is 25 to 59 parts by mass, the resulting hollow resin particles have no risk of sinking, thus maintaining a high porosity of the hollow resin particles and minimizing the risk of residual volatile organic compounds in the hollow resin particles.

[0120] The aforementioned proportion of crosslinking monomer units can be calculated based on, for example, the amount of crosslinking monomer fed during polymerization and the amount of crosslinking monomer remaining at the end of polymerization, to determine the proportion supplied to the polymerization reaction.

[0121] In addition to the resins mentioned above, the resins constituting the hollow resin particles can also be polyurethane resins or epoxy resins. Among these resins, polyurethane resins can be used to constituting the hollow resin particles from the perspective of excellent thermal insulation properties, while epoxy resins can be used from the perspective of expecting high compressive strength.

[0122] The shape of the hollow resin particles is not particularly limited as long as a hollow portion is formed inside; examples include spherical, ellipsoidal, and irregular shapes. Among these shapes, spherical is preferred because it is easy to manufacture.

[0123] The particles have one or more hollow parts inside. If the hollow parts can be ensured, the particles can also be porous. 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 particles preferably have five or fewer hollow parts, more preferably three or fewer hollow parts, even more preferably two or fewer hollow parts, and particularly preferably only one hollow part.

[0124] The average roundness of the hollow resin particles can be 0.950–0.995, 0.970–0.995, or 0.980–0.995.

[0125] In this invention, roundness is defined as the value of dividing the circumference of a circle having a projected area equal to that of the particle image by the circumference of the particle's projected image. Furthermore, the average roundness in this invention serves as a convenient method for quantitatively representing the shape of hollow resin particles, and is an indicator of the degree of unevenness or roughness of the hollow resin particles. When the hollow resin particles are perfectly spherical, the average roundness is represented as 1; the more complex the surface shape of the hollow resin particles, the smaller the value.

[0126] When the hollow resin particles of the present invention have a shell, the shell thickness can be 0.01 to 1.0 μm, 0.02 to 0.95 μm, or 0.05 to 0.90 μm.

[0127] When the shell thickness is 0.01 μm or more, hollow resin particles can maintain higher compressive strength to preserve their shape as much as possible. When the shell thickness is 1.0 μm or less, a larger volume of hollow space can be ensured inside the hollow resin particles.

[0128] The method for determining the shell thickness of hollow resin particles is as follows. First, 20 hollow resin particles were selected as the subjects, and their cross-sections were observed using a scanning electron microscope (SEM). Next, based on the SEM images of the particle cross-sections, the shell thickness of each of the 20 hollow resin particles was measured. The average value of this thickness was taken as the shell thickness of the hollow resin particles.

[0129] An example of the shape of hollow resin particles is a bag formed by a thin film and inflated by gas, the cross-section of which is described later. Figure 1 Hollow resin particles 100. In this example, the outermost layer of the hollow resin particles is formed by a thin membrane, which is filled with gas.

[0130] The shape of hollow resin particles can be confirmed by, for example, SEM and TEM. Furthermore, the internal shape of the hollow resin particles can be confirmed by SEM and TEM after the particles are cut into circular slices using known methods.

[0131] Applications of hollow resin particles include, for example, base coating materials for thermal paper. Typically, base coating materials require thermal insulation, cushioning, and heat resistance suitable for thermal paper applications. The hollow resin particles of this invention address these requirements through their high porosity, shatter-resistant hollow shape, specific number-average particle size, and high heat resistance.

[0132] Furthermore, hollow resin particles are useful as plastic pigments with excellent properties such as gloss and opacity. In addition, hollow resin particles obtained by encapsulating useful components such as fragrances, pharmaceuticals, pesticides, and ink ingredients inside through impregnation, depressurization, or pressurization impregnation processes can be used for various applications depending on the components contained within.

[0133] Specific applications of hollow resin particles include, for example, thermal recording materials, fillers, scattering agents, coatings, and insulating materials, but are not limited to these examples.

[0134] 2. Manufacturing method of hollow resin particles

[0135] The method for manufacturing hollow resin particles is not particularly limited as long as it can produce hollow resin particles that meet the above-mentioned conditions of number-average particle size, porosity, and volatile organic compound content. Hereinafter, one embodiment of the method for manufacturing hollow resin particles will be described, but the method for manufacturing hollow resin particles of the present invention is not necessarily limited to the embodiment described below.

[0136] One embodiment of the method for manufacturing hollow resin particles includes the following steps:

[0137] The process of preparing a mixture comprising at least one monomer selected from monovinyl monomers and hydrophilic monomers, a crosslinking monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium (mixture preparation process).

[0138] The process of preparing a suspension containing monomer droplets of a hydrocarbon solvent dispersed in an aqueous medium by suspending the above mixture (suspension preparation process)

[0139] The process (polymerization step) involves polymerizing the above suspension to prepare a precursor composition containing a hollow resin particle precursor encapsulated with a hydrocarbon solvent.

[0140] The process of obtaining hollow resin particle precursors through solid-liquid separation of the above precursor composition (solid-liquid separation process), and

[0141] The process of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the hollow resin particle precursor in a gas (solvent removal process).

[0142] As described above, this embodiment includes (1) a mixture preparation process, (2) a suspension preparation process, (3) a polymerization process, (4) a solid-liquid separation process, and (5) a solvent removal process. The processes in this embodiment are not limited to these five.

[0143] Figure 1 This is a schematic diagram illustrating this embodiment. Figure 1 (1) to (5) in the diagram correspond to the aforementioned processes (1) to (5). The white arrows between the diagrams indicate the sequence of each process. Additionally, Figure 1 The schematic diagrams are for illustrative purposes only, and the method for manufacturing hollow resin particles of the present invention is not limited to this. Figure 1 As shown. Furthermore, the structure, size, and shape of the materials used in the method for manufacturing hollow resin particles of the present invention are not limited to those described above. Figure 1 The structure, size, and shape of various materials in the process.

[0144] Figure 1 (1) is a schematic diagram illustrating one embodiment of the mixture in the mixture preparation process. As shown in the figure, the mixture comprises an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 means, for example, a monovinyl monomer, a hydrocarbon solvent, or other material with low polarity that is difficult to mix with the aqueous solvent 1.

[0145] Figure 1 (2) is a schematic diagram showing one embodiment of the suspension in the suspension preparation process. The suspension includes an aqueous medium 1 and micelles 10 (monomer droplets) dispersed in the aqueous medium 1. The micelles 10 are formed by surrounding an oil-soluble monomer composition 4 (containing an oil-soluble polymerization initiator 5, etc.) with a surfactant 3.

[0146] Figure 1 (3) is a schematic diagram showing one embodiment of the precursor composition after the polymerization process. The precursor composition includes 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 the monovinyl monomer, etc., in the micelles 10, and a hydrocarbon solvent 7 is encapsulated inside the shell 6.

[0147] Figure 1 Figure (4) is a schematic diagram showing one embodiment of the hollow resin particle precursor after the solid-liquid separation process. Figure (4) shows the state in which the aqueous medium 1 has been separated from the state described in (3) above.

[0148] Figure 1 Figure (5) is a schematic diagram showing one embodiment of hollow resin particles after the solvent removal process. Figure (5) shows the state after the hydrocarbon solvent 7 has been removed from the state described in (4). As a result, hollow resin particles 100 having a hollow portion 8 inside the shell 6 are obtained.

[0149] The following sections will describe the five processes mentioned above and other processes in turn.

[0150] (1) Mixture preparation process

[0151] This process is for preparing a mixture comprising (A) at least one monomer selected from monovinyl monomers and hydrophilic monomers, (B) a crosslinking monomer, (C) an oil-soluble polymerization initiator, (D) a hydrocarbon solvent, (E) a suspension stabilizer and an aqueous medium.

[0152] The (A) monovinyl monomer and hydrophilic monomer and (B) crosslinking monomer are as described in "1. Hollow Resin Particles" above. In addition to containing at least one monomer selected from monovinyl monomer and hydrophilic monomer (A) and crosslinking monomer (B) as described in "1. Hollow Resin Particles" above, the mixture may also contain other monomers capable of polymerization.

[0153] (C) Oil-soluble polymerization initiator

[0154] In this embodiment, suspension polymerization using an oil-soluble polymerization initiator is employed instead of emulsion polymerization using a water-soluble polymerization initiator. The advantages of using suspension polymerization are detailed in "(2) Suspension Preparation Process".

[0155] There are no particular restrictions on oil-soluble polymerization initiators as long as they are lipophilic polymerization initiators with a solubility of less than 0.2 g / 100 g H₂O in water. Examples of oil-soluble polymerization initiators include benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide, 2,2'-azobis(2,4-dimethylpentanonitrile), and azobisisobutyronitrile.

[0156] When the total mass of (A) at least one monomer selected from monovinyl monomers and hydrophilic monomers, and (B) crosslinking monomers is 100 parts by mass, the content of (C) oil-soluble polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass. When the above-mentioned content of (C) oil-soluble polymerization initiator is 0.1 parts by mass or more, the polymerization reaction is more likely to proceed fully. On the other hand, when the above-mentioned content of (C) oil-soluble polymerization initiator is 10 parts by mass or less, the risk of oil-soluble polymerization initiator residue after the polymerization reaction is completed is small, and the risk of unpredictable side reactions is also small.

[0157] (D) Hydrocarbon solvents

[0158] The hydrocarbon solvent in this embodiment has the effect of creating a hollow space inside the particles.

[0159] In the suspension preparation process described later, a suspension containing hydrocarbon solvents dispersed in an aqueous medium is obtained. During the suspension preparation process, phase separation occurs in the monomer droplets, resulting in the low-polarity hydrocarbon solvents becoming more likely to aggregate inside the monomer droplets. Ultimately, within the monomer droplets, according to their respective polarities, the hydrocarbon solvents are distributed inside the monomer droplets, while other materials besides the hydrocarbon solvents are distributed around the monomer droplets.

[0160] Furthermore, in the polymerization process described later, a precursor composition containing a hollow resin particle precursor encapsulated with a hydrocarbon solvent can be obtained. That is, by the aggregation of the hydrocarbon solvent inside the particles, a hollow structure containing the hydrocarbon solvent is formed inside the obtained polymer particles (hollow resin particle precursor).

[0161] There are no particular limitations on the types of hydrocarbon solvents. Examples of hydrocarbon solvents include highly volatile solvents such as benzene, toluene, xylene, butane, pentane, hexane, heptane, and cyclohexane.

[0162] The hydrocarbon solvent used in this embodiment preferably has a relative permittivity of 3 or less at 20°C. The relative permittivity is one of the indicators of the polarity of a compound. When the relative permittivity of the hydrocarbon solvent is sufficiently small to be below 3, it is considered that phase separation in the monomer droplets proceeds rapidly, easily forming hollow structures.

[0163] Examples of solvents with a relative permittivity of 3 or less at 20°C are shown below. The values ​​in parentheses are the relative permittivity values.

[0164] Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4).

[0165] Regarding the relative permittivity at 20°C, one can refer to the values ​​recorded in well-known literature (e.g., *Basic Handbook of Chemistry*, edited by the Chemical Society of Japan, revised 4th edition, Maruzen Co., Ltd., published September 30, 2016, pp. II-498 to II-503), and other technical information. As a method for determining the relative permittivity at 20°C, examples include the relative permittivity test performed according to item 23 of JIS C 2101:1999 at a measurement temperature of 20°C.

[0166] The hydrocarbon solvent used in this embodiment can be a hydrocarbon compound with 5 to 7 carbon atoms. Hydrocarbon compounds with 5 to 7 carbon atoms can be easily encapsulated within the hollow resin particle precursor during the polymerization process and easily removed from the hollow resin particle precursor during the solvent removal process. Preferably, the hydrocarbon solvent is a hydrocarbon compound with 6 carbon atoms.

[0167] When the total mass of (A) at least one monomer selected from monovinyl monomers and hydrophilic monomers, and (B) crosslinking monomers is 100 parts by mass, the content of (D) hydrocarbon solvent is preferably 100 to 900 parts by mass, more preferably 150 to 700 parts by mass, and even more preferably 200 to 500 parts by mass. When the content of (D) hydrocarbon solvent is 100 parts by mass or more, the risk of low porosity in the obtained hollow resin particles is low. On the other hand, when the content of (D) hydrocarbon solvent is 900 parts by mass or less, the mechanical properties of the obtained hollow resin particles are mostly excellent, and the risk of not being able to maintain hollowness is low.

[0168] (E) Suspension stabilizer

[0169] Suspension stabilizers are reagents that stabilize the suspension state in the suspension of the suspension polymerization process described later.

[0170] Suspension stabilizers may contain surfactants. Surfactants are materials used in suspension polymerization, as described later, to form micelles encapsulating at least one monomer selected from monovinyl monomers and hydrophilic monomers, crosslinking monomers, oil-soluble polymerization initiators, and hydrocarbon solvents.

[0171] As a surfactant, any of cationic, anionic, or nonionic surfactants can be used, or a combination of these can be used. Among these, anionic and nonionic surfactants are preferred, and anionic surfactants are more preferred.

[0172] Examples of anionic surfactants include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dialkyl sulfosuccinate, and formalin condensate salts of naphthalene sulfonic acid.

[0173] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters.

[0174] Examples of cationic surfactants include dialcyldimethylammonium chloride and stearyltrimethylammonium chloride.

[0175] Suspension stabilizers may contain water-insoluble inorganic compounds, water-soluble polymers, etc.

[0176] When the total mass of (A) at least one monomer selected from monovinyl monomers and hydrophilic monomers, (B) crosslinking monomers, (C) oil-soluble polymerization initiators, and (D) hydrocarbon solvents is 100 parts by mass, the content of (E) suspension stabilizer is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, and even more preferably 0.3 to 1 part by mass. When the above-mentioned content of (E) suspension stabilizer is 0.1 parts by mass or more, micelles are easily formed in aqueous media. On the other hand, when the above-mentioned content of (E) suspension is 3 parts by mass or less, the reduction in productivity due to increased foaming is less likely to occur in the process of removing hydrocarbon solvents.

[0177] (F) Other

[0178] In this embodiment, aqueous solvent means any one of water, hydrophilic solvent, or a mixture of water and hydrophilic solvent.

[0179] In this embodiment, there are no particular limitations on the hydrophilic solvent, as long as it is a hydrophilic solvent that can be thoroughly mixed with water without causing phase separation. Examples of hydrophilic solvents include alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0180] In aqueous media, water is preferred due to its high polarity. When using a mixture of water and a hydrophilic solvent, it is important from the viewpoint of forming monomeric droplets that the overall polarity of the mixture does not become too low. For example, the mixing ratio (mass ratio) of water to hydrophilic solvent can be water:hydrophilic solvent = 99:1 to 50:50, etc.

[0181] The mixture prepared in this process is a composition consisting only of the above-mentioned materials (A) to (E) and an aqueous medium, under appropriate stirring or other conditions. In this mixture, the oil phase containing the above-mentioned materials (A) to (D) is dispersed in the aqueous medium at a particle size of approximately several millimeters. Depending on the type of material, the dispersion state of these materials in the mixture may be observable with the naked eye.

[0182] In this process, a mixture is prepared by mixing an oil phase containing at least one monomer selected from monovinyl monomers and hydrophilic monomers (A), a crosslinking monomer, an oil-soluble polymerization initiator (C), and a hydrocarbon solvent (D), wherein the total mass of at least one monomer selected from monovinyl monomers and hydrophilic monomers and the crosslinking monomer (B) is 100 parts by mass. This mixture contains 25 to 59 parts by mass of an oil phase with the crosslinking monomer content and an aqueous phase containing (E) a suspension stabilizer and an aqueous medium. By mixing the oil and aqueous phases in this way, uniformly composed particles can be formed.

[0183] (2) Suspension preparation process

[0184] This process involves suspending the above mixture to prepare a suspension in which monomer droplets containing hydrocarbon solvents are dispersed in an aqueous medium.

[0185] In the suspension prepared in this process, monomeric droplets containing the aforementioned materials (A) to (D) and having a particle size of approximately 0.1 μm to 9 μm are uniformly dispersed in the aqueous medium. Such monomeric droplets are difficult to observe with the naked eye but can be observed using known observation equipment such as an optical microscope.

[0186] As described above, in this embodiment, suspension polymerization is used instead of emulsion polymerization. Therefore, a comparison with emulsion polymerization will be made below, and the advantages of using suspension polymerization and oil-soluble polymerization initiators will be explained.

[0187] Figure 4 This is a schematic diagram showing the dispersion used in emulsion polymerization. Figure 4 The micelles 60 in the diagram are schematically shown in cross-section.

[0188] exist Figure 4 The diagram shows micelles 60, micelle precursors 60a, monomers 53a dissolved in a solvent, and a water-soluble polymerization initiator 54 dispersed in an aqueous medium 51. The micelles 60 are formed by surrounding the oil-soluble monomer composition 53 with a surfactant 52. The monomer composition 53 contains monomers as raw materials for the polymer, but does not contain a polymerization initiator.

[0189] On the other hand, although the micelle precursor 60a is an aggregate of surfactant 52, it does not contain a sufficient amount of monomer composition 53. The micelle precursor 60a incorporates the monomer 53a dissolved in the solvent into its interior, or collects a portion of the monomer composition 53 from other micelles 60, thereby growing into micelles 60.

[0190] The water-soluble polymerization initiator 54 diffuses in the aqueous medium 51 and penetrates the interior of micelles 60 and micelle precursors 60a, promoting the growth of oil droplets inside them. Therefore, in the emulsion polymerization method, although each micelle 60 is monodispersed in the aqueous medium 51, the particle size of the micelles 60 is predicted to grow to several hundred nm.

[0191] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in this process. Figure 2 The micelles 10 in the diagram are schematically shown in cross-section. Additionally, Figure 2 Since this is just a schematic diagram, the suspension in this embodiment is not necessarily limited to... Figure 2 As shown. Figure 2 A portion of the above corresponds to Figure 1 (2)

[0192] Figure 2 The diagram shows micelles 10 and monomers 4a (including monovinyl monomers and crosslinking monomers, etc.) dispersed in an aqueous medium 1. Micelles 10 are formed by surrounding an oil-soluble monomer composition 4 with a surfactant 3. The monomer composition 4 contains an oil-soluble polymerization initiator 5, as well as monomers (including monovinyl monomers and crosslinking monomers, etc.) and a hydrocarbon solvent (not shown).

[0193] like Figure 2 As shown, in this process, tiny oil droplets containing monomer composition 4 are pre-formed inside the micelles 10. Based on this, polymerization initiation radicals are generated in the tiny oil droplets using an oil-soluble polymerization initiator 5. Therefore, the tiny oil droplets are not allowed to grow excessively, and hollow resin particle precursors with the target particle size can be manufactured.

[0194] In addition, compared with suspension polymerization ( Figure 2 ) and emulsion polymerization ( Figure 4 It can be seen that suspension polymerization ( Figure 2 In this process, the oil-soluble polymerization initiator 5 does not have the opportunity to come into contact with the monomer 4a dispersed in the aqueous medium 1. Therefore, by using an oil-soluble polymerization initiator, it is possible to prevent the formation of excess polymer particles other than the target hollow resin particles.

[0195] A typical example of this process is shown below.

[0196] The mixture containing the above materials (A) to (E) and an aqueous medium is suspended to form monomeric droplets. There are no particular limitations on the method of forming monomeric droplets; it can be carried out using a device capable of strong stirring, such as a (inline type) emulsifying disperser (manufactured by Taihei Kiko Co., Ltd., trade name: Milder) or a high-speed emulsifying disperser (manufactured by PRIMIX CO.,LTD., trade name: TKHOMOMIXER MARK II type).

[0197] As described above, in this process, phase separation occurs in the monomer droplets, thus making it easier for low-polarity hydrocarbon solvents to accumulate inside the monomer droplets. As a result, for the obtained monomer droplets, the hydrocarbon solvent is distributed inside, while materials other than the hydrocarbon solvent are distributed around them.

[0198] The following are examples of variations of this process.

[0199] First, an oil phase containing materials (A) to (D) and an aqueous phase containing material (E) and an aqueous medium are prepared respectively. In the oil phase, it is preferable that the total mass of at least one monomer selected from (A) monovinyl monomer and hydrophilic monomer and (B) crosslinking monomer is 100 parts by mass, and the content of (B) crosslinking monomer is 25 to 59 parts by mass.

[0200] Next, a suspension is prepared by membrane emulsification. Membrane emulsification is a method of extruding a dispersed liquid phase through the pores of a porous membrane into a continuous phase, thereby obtaining a suspension in which tiny droplets of the dispersed phase are dispersed in the continuous phase. Here, the dispersed phase refers to the liquid phase in which the tiny droplets are dispersed, and the continuous phase refers to the liquid phase surrounding the dispersed phase droplets. In this embodiment, as long as the above-mentioned oil phase is used as the dispersed phase and the above-mentioned aqueous phase is used as the continuous phase, either direct membrane emulsification or membrane emulsification accompanied by pre-emulsification can be used.

[0201] In membrane emulsification, a membrane emulsification system (e.g., model MN-20, manufactured by SPG Technology Co., Ltd.) and a membrane with a specific pore size are used. Examples of porous membranes that can be used in membrane emulsification include inorganic porous membranes such as Shirasu porous glass membranes (SPG membranes) and organic porous membranes such as PTFE membranes.

[0202] In membrane emulsification, the pore size of the porous membrane determines the particle size of the resulting microdroplets. Although it also depends on the composition of the dispersed phase, the particle size of the microdroplets affects the number-average particle size of the resulting hollow resin particles; therefore, the selection of the pore size of the porous membrane is important. For example, when using a Shirasu porous glass membrane (SPG membrane), a pore size of 0.1–4.0 μm is preferably selected, more preferably 0.2–3.5 μm, and even more preferably 0.3–3.0 μm.

[0203] Suspensions are prepared by 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.

[0204] Furthermore, the suspension preparation process in this embodiment is not limited to the above-described typical and modified examples.

[0205] (3) Polymerization process

[0206] This step involves polymerizing the aforementioned suspension to prepare a precursor composition comprising a hollow resin particle precursor, wherein the hollow resin particle precursor contains a hydrocarbon solvent. Here, the hollow resin particle precursor refers to particles formed by copolymerization of at least one monomer selected from the aforementioned monovinyl monomer and hydrophilic monomer, and a crosslinking monomer.

[0207] The polymerization method is not particularly limited and can be, for example, batch polymerization, semi-continuous polymerization, or continuous polymerization. The polymerization temperature is preferably 40–80°C, more preferably 50–70°C. Furthermore, the polymerization reaction time is preferably 1–20 hours, more preferably 2–15 hours.

[0208] Because monomer droplets containing hydrocarbon solvents are used, as described above, a hollow structure filled with hydrocarbon solvents is formed inside the hollow resin particle precursor.

[0209] (4) Solid-liquid separation process

[0210] This process involves solid-liquid separation of the above-mentioned precursor composition to obtain hollow resin particle precursors.

[0211] When removing the hydrocarbon solvent encapsulated within the particles from a slurry containing an aqueous medium, the following problem arises: if water of the same volume as the hydrocarbon solvent removed from the particles does not enter the particles, the resulting hollow resin particles will break.

[0212] As a method to prevent this problem, one could consider, for example, setting the pH of the slurry to above 7, and then removing the hydrocarbon solvent by causing the shell of the particles to swell with alkali. In this case, because the shell of the particles becomes soft, the replacement of the hydrocarbon solvent and water inside the particles occurs rapidly, resulting in water-encapsulated particles.

[0213] The method for solid-liquid separation of the precursor composition is not limited as long as it does not remove the hydrocarbon 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. Known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and settling. Among these, centrifugation or filtration can be used. From the viewpoint of ease of operation, centrifugation can be adopted.

[0214] After the solid-liquid separation process and before the solvent removal process described later, any process such as a pre-drying process can be performed. As a pre-drying process, an example is a process in which the solid components obtained after the solid-liquid separation process are pre-dried by a drying device such as a dryer or a hand dryer.

[0215] (5) Solvent removal process

[0216] This process involves removing the hydrocarbon solvent encapsulated within the hollow resin particle precursor in a gas, thereby obtaining the hollow resin particles.

[0217] In this process, "in the gas" is not limited to the strict sense of "in the gas," meaning an environment where there is absolutely no liquid component on the outside of the hollow resin particle precursor. It implies an environment where only trace amounts of liquid component, insufficient to affect the removal of hydrocarbon solvents, exist on the outside of the hollow resin precursor. "In the gas" can also refer to a state where the hollow resin particle precursor is not present in the slurry, or it can refer to a state where the hollow resin particle precursor is present in the dried powder.

[0218] As shown in Examples 1 to 5 below, the fact that the hollow resin particles maintained their spherical shape after being restored to normal pressure after vacuum drying during the solvent removal process can be considered evidence that the shell itself has relatively high air permeability.

[0219] It is known that nylon, ethylene vinyl alcohol (EVOH), and other polymers typically exhibit increased permeability under high humidity. This is understood to be due to the plasticization of these polymers by water molecules, resulting in increased polymer mobility. However, considering the high degree of crosslinking of the hollow resin particles in this invention, it is presumed that the plasticizing effect caused by the aqueous medium is minimal. Therefore, in this invention, the permeability of the shell of the hollow resin particles is considered to be an inherent property of the polymer constituting the shell.

[0220] There is no particular limitation on the method for removing hydrocarbon solvents from hollow resin particle precursors in a gas, and known methods can be used. Examples of such methods include vacuum drying, heating drying, airflow drying, or a combination of these methods.

[0221] Especially when using the heat drying method, the heating temperature needs to be above the boiling point of the hydrocarbon solvent and below the highest temperature that will not cause the shell structure of the hollow resin particles to collapse. Therefore, although it depends on the composition of the shell in the hollow resin particle precursor and the type of hydrocarbon solvent, the heating temperature can be 50-150°C, 60-130°C, or 70-100°C.

[0222] By performing a drying process in a gas, the hydrocarbon solvent inside the hollow resin particle precursor is replaced by an external gas, resulting in hollow resin particles in which the gas occupies the hollow portion.

[0223] There are no particular limitations on the drying environment; it can be appropriately selected based on the intended use of the hollow resin particles. Suitable drying environments include, for example, air, oxygen, nitrogen, and argon. Alternatively, once the hollow resin particles are filled with gas, vacuum drying can be used to obtain hollow resin particles with a temporarily vacuum interior.

[0224] (6) Other

[0225] As a process other than (1) to (5) above, a process of replacing the gas inside the hollow resin particles with other gases or liquids can be considered. By such replacement, the internal environment of the hollow resin particles can be changed, molecules can be selectively encapsulated inside the hollow resin particles, and the chemical structure inside the hollow resin particles can be modified according to the application.

[0226] 3. Sheets

[0227] The sheet of the present invention is characterized by comprising the above-mentioned hollow resin particles.

[0228] The sheet of the present invention may contain only hollow resin particles, or it may contain hollow resin particles and other materials such as binders. Furthermore, the sheet of the present invention may be a single-layer sheet containing hollow resin particles, or it may be a multilayer sheet formed by stacking a layer containing hollow resin particles with one or more other layers.

[0229] The shape, area, and thickness of the sheet material of the present invention can be freely designed according to its application. The thickness of the sheet material of the present invention can be, for example, 10 μm to 1 mm.

[0230] The method for manufacturing the sheet of the present invention can utilize existing known methods. The sheet of the present invention can be manufactured by, for example, the following methods.

[0231] First, a mixture containing hollow resin particles, a binder such as polyvinyl alcohol (PVA), and a surfactant is applied to a substrate such as a PET substrate. The amount of the mixture applied is adjusted so that the average thickness of the layer containing the hollow resin particles (excluding the average thickness of the substrate) after drying is the desired thickness. The substrate after coating is allowed to dry appropriately, thereby manufacturing a sheet on the substrate. The resulting multilayer sheet can be supplied for various applications described later, or a single-layer sheet obtained by peeling off the substrate can be supplied for these applications as well.

[0232] The following section explains the evaluation of the thermal insulation and heat resistance of sheets using hollow resin particles.

[0233] The thermal insulation properties of sheets using hollow resin particles can be evaluated, for example, by measuring the thermal conductivity of the sheet. The method for measuring the thermal conductivity of the sheet is as follows: Using a rapid thermal conductivity meter (e.g., QTM-500, manufactured by Kyoto Electronics Industry Co., Ltd.) and thin film measurement software (e.g., SOFT-QTM5W, manufactured by Kyoto Electronics Industry Co., Ltd.), the thermal conductivity of the sheet obtained by the transient hot-wire method is measured under the following test conditions.

[0234] (Experimental conditions)

[0235] • Probe: PD-11

[0236] • Baseboard: Foamed polyethylene

[0237] A lower thermal conductivity indicates better insulation performance. While it also depends on the application of the sheet, a sheet with a thermal conductivity of, for example, below 0.060 (W / (m*K)) can be considered to have adequate insulation performance.

[0238] The heat resistance of sheets using hollow resin particles can be evaluated, for example, by the thickness change rate of the sheet under high-temperature conditions. The thickness change rate of the sheet under high-temperature conditions can be determined by the following methods.

[0239] Reference Figure 5The following explanation is provided. First, the sheet material (test sheet 30) is processed into a square with a side length of 5cm. Next, on the plane of the 5cm square test sheet 30, a central point (D0) and eight other points (D1 to D8) are set around this central point. At this time, these nine points are selected as follows: when the nearest points of the other eight points (D1 to D8) are connected by lines, they become squares with a side length of 4cm that are concentric with the central point (D0) of the test sheet and are slightly smaller than the test sheet. Furthermore, when the central point (D0), any one of the four corner points (D1, D2, D3, or D4), and the two points closest to these two points (e.g., D2 and D8) are selected and the nearest points are connected by lines, the four squares with a side length of 2cm are arranged in a grid pattern.

[0240] Next, the thickness of the sheet at each of the nine points was measured using a micrometer (e.g., MDQ-30, manufactured by Mitutoyo Corporation), and the average value was taken as the average thickness T0 (μm) before heating.

[0241] Next, the sheet 30 under test was heated in a dryer at 120°C for 72 hours. After being removed from the dryer and allowed to cool naturally, the thickness was measured at the same nine points as above, and the average value was taken as the average thickness T1 (μm) after heating.

[0242] The thickness change rate of the sheet under high temperature environment is determined based on the following formula (X).

[0243] Formula (X)

[0244] ΔT = 100 × {|T1 - T0| / T0}

[0245] (In the above formula (X), ΔT represents the thickness change rate (%) of the sheet under high temperature environment, T1 represents the average thickness after heating (μm), and T0 represents the average thickness before heating (μm).)

[0246] Sheets with a smaller thickness change rate ΔT under high-temperature conditions are considered to have superior heat resistance. Although it also depends on the application of the sheet, if, for example, the thickness change rate ΔT of the sheet under high-temperature conditions is below 8.0%, then the sheet is not prone to thickness change even under high-temperature conditions and can be considered to have sufficient heat resistance.

[0247] The uses of the sheet material of the present invention are related to the uses of the hollow resin particles described above. Examples of uses for the sheet material of the present invention include thermal recording sheets and insulating sheets, but are not limited to these examples.

[0248] Example

[0249] The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to these examples. Furthermore, unless otherwise specified, parts and percentages are based on mass.

[0250] The test methods performed in this embodiment and comparative example are as follows.

[0251] 1. Manufacturing of hollow resin particles

[0252] [Example 1]

[0253] (1) Mixture preparation process

[0254] First, mix the following materials (a1) to (d1). Use the resulting mixture as the oil phase.

[0255] (a1) 20 parts of methacrylic acid

[0256] (a2) 30 parts of methyl methacrylate

[0257] (b) 50 parts of ethylene glycol dimethacrylate

[0258] (c1) 3 parts of 2,2'-azobis(2,4-dimethylvalerate) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65)

[0259] (d1) 300 parts of cyclohexane

[0260] Next, 4.0 parts of surfactant were added to 800 parts of ion-exchanged water. The resulting mixture was used as the aqueous phase.

[0261] A mixture is prepared by mixing the aqueous phase and the oil phase.

[0262] (2) Suspension preparation process

[0263] The above mixture was stirred at 15,000 rpm using an inline emulsifying disperser (manufactured by Taiheiyo Kiko Co., Ltd., trade name: Milder) to suspend it, thus preparing a suspension of monomer droplets containing cyclohexane dispersed in water.

[0264] (3) Polymerization process

[0265] The above suspension was stirred for 4 hours in a nitrogen environment at 65°C to carry out a polymerization reaction. Through this polymerization reaction, a precursor composition containing hollow resin particles encapsulated in cyclohexane was prepared.

[0266] (4) Solid-liquid separation process

[0267] The obtained precursor composition was centrifuged using a cooled high-speed centrifuge (manufactured by KOKUSAN Co. Ltd., trade name: H-9R) at a rotor MN1, a rotation speed of 3000 rpm, and a centrifugation time of 20 minutes to dehydrate the solid components. The dehydrated solid components were then dried in a dryer at a temperature of 40°C to obtain a hollow resin particle precursor containing cyclohexane.

[0268] (5) Solvent removal process

[0269] The hollow resin particle precursor was heated in a gas at 80°C for 15 hours using a vacuum dryer to obtain the particles of Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0270] [Example 2-Example 3]

[0271] In the “(1) Mixture Preparation Step” of Example 1, the materials and amounts shown in Table 1 were used, and particles were obtained by the same manufacturing method as in Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0272] [Example 4]

[0273] In the “(1) Mixture Preparation Step” of Example 1, the materials and amounts shown in Table 1 were used, and the aqueous and oil phases were not mixed before being supplied to the next “(2) Suspension Preparation Step”. Furthermore, in the “(2) Suspension Preparation Step” of Example 1, instead of using a straight-line emulsifying disperser, a membrane emulsification system (model: MN-20, manufactured by SPG Technology Co., Ltd.) and a Shirasu porous glass membrane (SPG membrane, diameter 10 mm, length 20 mm, manufactured by SPG Technology Co., Ltd.) with a fine pore size of 3 μm were used to emulsify the oil phase as the dispersed phase and the aqueous phase as the continuous phase, thereby preparing a suspension. Otherwise, the particles of Example 4 were obtained by the same manufacturing method as in Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0274] [Example 5]

[0275] In the “(1) Mixture Preparation Step” of Example 1, the materials and amounts shown in Table 1 were used, and the aqueous and oil phases were not mixed before being supplied to the next “(2) Suspension Preparation Step”. Furthermore, in the “(2) Suspension Preparation Step” of Example 1, instead of using a straight-line emulsifying disperser, a membrane emulsification system (model: MN-20, manufactured by SPG Technology Co., Ltd.) and a Shirasu porous glass membrane (SPG membrane, diameter 10 mm, length 20 mm, manufactured by SPG Technology Co., Ltd.) with a pore size of 0.3 μm were used to emulsify the oil phase as the dispersed phase and the aqueous phase as the continuous phase, thereby preparing a suspension. Otherwise, the particles of Example 5 were obtained by the same manufacturing method as in Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0276] [Comparative Example 1]

[0277] In the “(1) Mixture Preparation Step” of Example 1, the materials and amounts shown in Table 1 were used, and the aqueous and oil phases were not mixed before being supplied to the next “(2) Suspension Preparation Step”. Furthermore, in the “(2) Suspension Preparation Step” of Example 1, instead of using a straight-line emulsifying disperser, a membrane emulsification system (model: MN-20, manufactured by SPG Technology Co., Ltd.) and a Shirasu porous glass membrane (SPG membrane, diameter 10 mm, length 20 mm, manufactured by SPG Technology Co., Ltd.) with a fine pore size of 5 μm were used to emulsify the oil phase as the dispersed phase and the aqueous phase as the continuous phase, thereby preparing a suspension. Otherwise, the particles of Comparative Example 1 were obtained by the same manufacturing method as in Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0278] [Comparative Examples 2-3]

[0279] In the “(1) Mixture Preparation Step” of Example 1, the materials and amounts shown in Table 1 were used, and the particles of Comparative Example 2 and Comparative Example 3 were obtained by the same manufacturing method as in Example 1. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0280] [Comparative Example 4]

[0281] First, mix the following materials (a2), (α1), (α2), (c2), and (d2). Use the resulting mixture as the oil phase.

[0282] (a2) 10 parts of methyl methacrylate

[0283] (α1) 60 parts of acrylonitrile

[0284] (α2) 30 parts of methacrylonitrile

[0285] (c2) 5 parts of azobisisobutyronitrile

[0286] (d2) 30 parts of isopentane

[0287] Next, 200 parts of (y) colloidal silica dispersion (average particle size 5 nm, effective concentration of colloidal silica 20% by mass) were added to 600 parts of ion-exchanged water. The resulting mixture was used as the aqueous phase.

[0288] A mixture is prepared by mixing the aqueous phase and the oil phase.

[0289] The above mixture was stirred for 1 minute at 4000 rpm using a disperser (PRIMIX, trade name: HOMOMIXER) to suspend it. The resulting suspension was stirred at 60°C for 10 hours to carry out the polymerization reaction.

[0290] After the polymerization reaction is completed, the suspension is dried at 40°C using a dryer to obtain the solid components, which are thermally expandable microcapsules.

[0291] One hundred parts of the obtained thermally expandable microcapsules were heated in a gas at 180°C for 3 minutes using a dryer to obtain the hollow resin particles of Comparative Example 4. Based on the observation results of scanning electron microscopy and the porosity value, it was confirmed that these particles were spherical and had only one hollow part.

[0292] 2. Determination and evaluation of particles

[0293] The particles from Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to the following measurements and evaluations. Details are as follows.

[0294] (1) Determination of number-average particle size, volume-average particle size, and particle size distribution.

[0295] The particle size was measured using a laser refractive particle size analyzer (manufactured by Shimadzu Corporation, trade name: SALD-2000), and the number mean and volume mean were calculated. The obtained values ​​were used as the number mean particle size and volume mean particle size. Furthermore, the particle size distribution was calculated by dividing the volume mean particle size by the number mean particle size.

[0296] (2) Particle density determination and porosity calculation

[0297] a. Determination of the apparent density of particles

[0298] First, in a capacity of 100cm 3 Fill the volumetric flask with approximately 30cm 3 Accurately weigh the mass of the granules used for filling. Next, fill the volumetric flask with isopropanol to the mark, taking care not to introduce air bubbles. Accurately weigh the mass of isopropanol added to the volumetric flask, and calculate the apparent density D1 (g / cm³) of the granules according to the following formula (I). 3 ).

[0299] Formula (I)

[0300] Apparent density D1 = [mass of particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0301] b. Determination of the true density of particles

[0302] After pre-crushing the particles, they are placed into a container with a capacity of 100cm³. 3 The volumetric flask is filled with approximately 10g of granular fragments, and the mass of the filled fragments is accurately weighed.

[0303] Then, in the same manner as the apparent density determination described above, isopropanol is added to a volumetric flask, the mass of isopropanol is accurately weighed, and the true density D2 (g / cm³) of the particles is calculated based on the following formula (II). 3 ).

[0304] Equation (II)

[0305] True density D0 = [mass of fragmented particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0306] c. Calculation of porosity

[0307] Divide the apparent density D1 by the true density D0, and then multiply by 100 to get the value. Subtract this value from 100 to get the porosity of the particle.

[0308] (3) Determination and calculation of shell thickness

[0309] Twenty hollow resin particles were selected as the subjects, and their cross-sections were observed using SEM. Then, based on the SEM images of the particle cross-sections, the shell thickness of each of the 20 hollow resin particles was measured. The average of these thicknesses was taken as the shell thickness of the hollow resin particle.

[0310] (4) Amount of volatile organic compounds in hollow resin particles

[0311] The method for determining the amount of volatile organic compounds (VOCs) in hollow resin particles is as follows: Approximately 100 mg of hollow resin particles, accurately weighed, is added to a 30 mL screw-top glass bottle. Then, approximately 10 g of tetrahydrofuran (THF), accurately weighed, is added. The mixture in the glass bottle is stirred for 1 hour to extract the VOCs (hydrocarbon solvents, etc.) contained in the hollow resin particles. Stirring is stopped, and the resin components of the hollow resin particles insoluble in THF are allowed to precipitate. A filter (Advantec MFS, Inc., trade name: Membrane Filters 25JP020AN) is installed in a syringe, and the precipitate is filtered to obtain a sample solution. This sample solution is injected into a gas chromatograph (GC) for analysis. The amount of VOCs per unit mass (mass%) contained in the hollow resin particles is determined based on the peak area of ​​the GC and a pre-prepared calibration curve. Detailed analytical conditions are as follows.

[0312] (Analysis conditions)

[0313] Device: GC-2010 (manufactured by Shimadzu Corporation)

[0314] Column: DB-5 (Made by Agilent Technologies)

[0315] df = 0.25μm 0.25mm ID × 30m

[0316] Detector: FID

[0317] Carrier gas: nitrogen (linear velocity: 28.8 cm / s)

[0318] Inlet temperature: 200℃

[0319] Detector temperature: 250℃

[0320] Oven temperature: Increase from 40℃ to 230℃ at a rate of 10℃ / minute, and hold at 230℃ for 2 minutes.

[0321] Sample size: 2 μL

[0322] (5) Compressive strength of particles

[0323] The 10% compressive strength of the particles was determined using a micro compression tester (MCTM-500, manufactured by Shimadzu Corporation) under the following conditions.

[0324] (Experimental conditions)

[0325] • Type of pressure head: FLAT50

[0326] • Objective lens magnification: 50

[0327] • Load speed: 0.8924 mN / s

[0328] (6) Observation of particle shape

[0329] Figure 3A This is an SEM image of the hollow resin particles from Example 1. Figure 3B This is a SEM image of a cross-section of the hollow resin particles from Example 1.

[0330] The SEM observation conditions are as follows.

[0331] • Scanning electron microscope:

[0332] Manufactured by JEOL Corporation, Model: JSM-7610F Figure 3A )

[0333] Hitachi manufacture, model: S-4700 Figure 3B )

[0334] Accelerating voltage: 2.0kV Figure 3A ), 5.0kV ( Figure 3B )

[0335] Multiplier: 5000x ( Figure 3A , Figure 3B )

[0336] These figures confirm that the particles of Example 1 are hollow inside, and that even though they are hollow inside, they maintain a spherical shape without breaking.

[0337] 3. Sheet manufacturing

[0338] Sheets were manufactured using the hollow resin particles from Examples 1 to 5 and Comparative Examples 1 to 4 described above, by the following method.

[0339] A mixture containing 100 parts by mass of hollow resin particles and 3 parts by mass of polyvinyl alcohol (PVA) was mixed in a 1% aqueous solution of sodium dodecylbenzenesulfonate, bringing the solid content to 10% by mass. The resulting mixture was applied to a PET film substrate (thickness: 50 μm) that had undergone corona treatment using a wire-bar coater. The coating amount was adjusted so that the average thickness of the particle-containing layer after drying (excluding the average thickness of the PET film substrate) was 100 μm. The PET film substrate coated with the mixture was dried at 50°C for 24 hours, thereby producing a multilayer sheet with a layer containing hollow resin particles formed on the PET film substrate. This multilayer sheet was then used in subsequent experiments.

[0340] Hereinafter, the sheets manufactured using the various particles of Examples 1 to 5 and Comparative Examples 1 to 4 will be referred to as the sheets of Examples 1 to 5 and Comparative Examples 1 to 4, respectively.

[0341] 4. Measurement and evaluation of sheet materials

[0342] The following measurements and evaluations were performed on various sheets from Examples 1 to 5 and Comparative Examples 1 to 4. Details are as follows.

[0343] (1) Determination of the thermal conductivity of sheet material

[0344] The thermal conductivity of the sheet obtained by the transient hot-wire method was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Industry Co., Ltd.) and thin film measurement software (SOFT-QTM5W, manufactured by Kyoto Electronics Industry Co., Ltd.) under the following test conditions.

[0345] (Experimental conditions)

[0346] • Probe: PD-11

[0347] • Baseboard: Foamed polyethylene

[0348] (2) Determination of the thickness change rate of sheet material under high temperature environment

[0349] like Figure 5 As shown, firstly, the sheet material (test sheet 30) is processed into a square with a side length of 5cm. Next, on the plane of the 5cm square test sheet 30, a central point (D0) and eight other points (D1 to D8) are set around this central point. At this time, these nine points are selected as follows: when the nearest points of the other eight points (D1 to D8) are connected by lines, they become squares with a side length of 4cm that are concentric with the central point (D0) of the test sheet and are slightly smaller than the test sheet. Furthermore, when the central point (D0), any one of the four corner points (D1, D2, D3, or D4), and the two points closest to these two points (e.g., D2 and D8) are selected and the nearest points are connected by lines, the four squares with a side length of 2cm are arranged in a grid pattern.

[0350] Next, the thickness of the sheet at each of the nine points was measured using a micrometer (model: MDQ-30, manufactured by Mitutoyo Corporation), and the average value was taken as the average thickness T0 (μm) before heating.

[0351] Next, the sheet was heat-treated in a dryer at 120°C for 72 hours. After being removed from the dryer and allowed to cool naturally, the thickness was measured at the same nine points as described above, and the average value was taken as the average thickness T1 (μm) after heating.

[0352] The thickness change rate of the sheet under high temperature environment is determined based on the following formula (X).

[0353] Formula (X)

[0354] ΔT = 100 × {|T1 - T0| / T0}

[0355] (In the above formula (X), ΔT represents the thickness change rate (%) of the sheet under high temperature environment, T1 represents the average thickness after heating (μm), and T0 represents the average thickness before heating (μm).)

[0356] The determination and evaluation results of various particles and sheets in Examples 1 to 5 and Comparative Examples 1 to 4, together with their raw material composition, are shown in Table 1 below.

[0357] [Table 1]

[0358]

[0359] 5. Inspection

[0360] The evaluation results for each particle and each sheet are presented below with reference to Table 1.

[0361] According to Table 1, the number-average particle size of Comparative Example 1 particles was 15 μm, the porosity was 80%, and the amount of volatile organic compounds contained was 2.3% by mass.

[0362] Although the particles of Comparative Example 1 contain a resin with a high proportion of crosslinking monomer units, their compressive strength is as low as 2.2 MPa. As shown in this comparative example, it is difficult to obtain high compressive strength from particles with a number average particle size exceeding 9.0 μm, and therefore they are prone to breakage when processed into materials such as sheets.

[0363] According to Table 1, the number-average particle size of Comparative Example 2 particles was 2.9 μm, the porosity was 63%, and the amount of volatile organic compounds contained was 3.8% by mass.

[0364] The particles in Comparative Example 2 have a thermal conductivity as high as 0.080 (W / (m*K)). As this comparative example shows, particles with a porosity of less than 70% have excessively high thermal conductivity, resulting in poor thermal insulation.

[0365] According to Table 1, the number-average particle size of Comparative Example 3 particles was 1.8 μm, the porosity was 74%, and the amount of volatile organic compounds contained was 20.2% by mass.

[0366] The particles of Comparative Example 3 have a thermal conductivity as high as 0.067 (W / (m*K)) and a thickness change rate ΔT as high as 28% under high temperature conditions. As shown in this comparative example, for particles containing more than 5% by mass of volatile organic compounds, the thermal conductivity is excessively high because the volatile organic compounds such as cyclohexane contained in the particles act as a heat medium, resulting in poor thermal insulation and easy deformation under high temperature conditions, thus resulting in poor heat resistance.

[0367] According to Table 1, the number-average particle size of Comparative Example 4 was 12.0 μm, the porosity was 86%, and the amount of volatile organic compounds contained was 12.0 μm by mass.

[0368] The particles of Comparative Example 4 have a thermal conductivity as high as 0.035 (W / (m*K)) and a thickness change rate ΔT as high as 35% under high temperature conditions. As shown in this comparative example, particles with a number-average particle size exceeding 9.0 μm and containing more than 5% by mass of volatile organic compounds are prone to deformation under high temperature conditions, thus exhibiting poor heat resistance. The content of volatile organic compounds in Comparative Example 4 (12.0% by mass) is lower than that in Comparative Example 3 (20.2% by mass), and since the particles of Comparative Example 4 contain nitrile monomer units, their heat resistance is even worse than that of Comparative Example 3.

[0369] On the other hand, according to Table 1, the hollow resin particles of Examples 1 to 5 have a number-average particle size of 0.9 to 9.0 μm, a porosity of 74 to 90%, and contain 0.8 to 3.0% by mass of volatile organic compounds.

[0370] These hollow resin particles have a compressive strength of over 6.0 MPa, a thermal conductivity of less than 0.059 (W / (m*K)), and a thickness change rate ΔT of less than 7.1% under high temperature conditions.

[0371] Therefore, it has been confirmed that hollow resin particles with one hollow section, a number-average particle size of 0.1–9.0 μm, a porosity of 70–99%, and a volatile organic compound content of less than 5% by mass have high compressive strength and excellent thermal insulation and heat resistance compared with existing particles.

[0372] Explanation of reference numerals in the attached figures

[0373] 1. Aqueous medium 2. Low polarity material

[0374] 3 surfactants and 4 monomer compositions

[0375] 4a Monomer dispersed in an aqueous medium 5 Oil-soluble polymerization initiator

[0376] 6-shell 7-hydrocarbon solvent

[0377] 8 hollow parts 10 micelles

[0378] 20 Hollow resin particle precursor 30 Test sheet

[0379] Measurement sites on the tested sheets D0 and D1 to D8

[0380] 51 Aqueous media 52 Surfactants 53 Monomer compositions

[0381] 53a Monomer dissolved in aqueous medium; 54 Water-soluble polymerization initiator

[0382] 60 micelles, 60a micelle precursor, 100 hollow resin particles

Claims

1. A sheet material, characterized in that, Contains hollow resin particles, The hollow resin particles have one or more hollow sections, a number-average particle size of 0.1–9.0 μm, a porosity of 70–99%, and contain less than 5% by mass of volatile organic compounds. The repeating units of the resin constituting the hollow resin particles include crosslinking monomer units, hydrophilic monomer units, and monovinyl monomer units. When the repeating unit constituting the resin is 100 parts by weight, the content of the crosslinking monomer unit is 25 to 50 parts by weight. The crosslinking monomer unit comprises at least one selected from divinylbenzene monomer units and ethylene glycol dimethacrylate monomer units.

2. The sheet according to claim 1, wherein, The thermal conductivity of the sheet is below 0.060 W / (m*K).

3. The sheet according to claim 1 or 2, wherein, The thickness change rate of the sheet after heat treatment at 120°C for 72 hours is less than 8.0%.

4. The sheet according to claim 1 or 2, wherein, The hollow resin particles have a 10% compressive strength of 5.0 MPa or higher.

5. The sheet according to claim 1 or 2, wherein, The hydrophilic monomer unit comprises at least one selected from carboxyl-containing monomer units and hydroxyl-containing monomer units.

6. The sheet according to claim 1 or 2, wherein, In the hollow resin particles, the particle size distribution, which is the value of volume average particle size divided by number average particle size, is 1.1 to 2.

5.

7. The sheet according to claim 1 or 2, wherein, The hollow resin particles have a shell with a thickness of 0.01 to 1.0 μm.

8. The sheet according to claim 1 or 2, wherein, The sheet is a thermal recording sheet.

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