hollow particles

Abstract

This invention provides hollow particles with a reduced coefficient of thermal expansion. The hollow particles have a shell containing resin and a hollow portion surrounded by the shell, a porosity of 50% or more, and a volume average particle size of 1.0 μm or more. The shell contains a polymer as the resin, and the polymer contains 70 to 100 parts by mass of crosslinking monomer units in 100 parts by mass of all monomer units. The hollow particles have a coefficient of thermal expansion of 10 × 10⁻⁶ at 80 to 200°C. ‑5 In the impregnation test of hollow particles, 0.1 mg of hollow particles were added to 4 mL of acetone at 25°C, and the mixture was shaken at 100 rpm for 10 minutes and then allowed to stand for 48 hours. The amount of hollow particles precipitated in acetone was less than 10% by mass.

Description

Technical Field

[0001] This invention relates to hollow particles. Background Technology

[0002] Hollow granules (hollow resin granules) are granules with cavities inside. Compared to solid granules that are essentially filled with resin, hollow granules 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 in water-based coatings and paper coating compositions. In recent years, they have also been further used as lightweighting agents and heat-resistant agents in resins and coatings used in various fields such as automobiles, electrical appliances, electronics, and construction.

[0003] In electronic materials applications, such as in electronic circuit boards, hollow particles are sometimes incorporated into the insulating resin layer to suppress crosstalk and increase transmission loss. Crosstalk and transmission loss in electronic circuit boards can be suppressed by reducing the relative permittivity and dielectric loss tangent of the insulating resin layer. Since the interior of hollow particles is void, attempts have been made to reduce the dielectric constant and dielectric loss tangent of the insulating resin layer by adding hollow particles.

[0004] Furthermore, insulating resin layers used in electronic materials require good adhesion and dimensional stability when fabricated as laminates or bonded materials. In electronic materials, insulating resin layers are sometimes laminated onto metal substrates such as copper-clad laminates. To improve the adhesion and dimensional stability of the insulating resin layer to the metal substrate, it is effective to make the coefficient of thermal expansion (CTE) of the insulating resin layer close to that of the metal substrate. To reduce the CTE of the insulating resin layer, it has traditionally been incorporated with inorganic fillers such as silica.

[0005] However, when the proportion of inorganic fillers in the insulating resin layer is increased, physical properties such as increased susceptibility to cracking will decrease. In addition, there is the problem that the relative permittivity and dielectric loss tangent cannot be sufficiently reduced.

[0006] On the other hand, hollow particles typically have a lower CTE compared to insulating resins. Therefore, by including hollow particles in the insulating resin layer, it is expected that not only can the dielectric constant and dielectric loss tangent be reduced, but the CTE can also be lowered.

[0007] Patent documents 1 and 2 describe techniques for adding hollow particles to resin compositions used in electronic materials to achieve low dielectric constant and low dielectric loss tangent.

[0008] Patent Document 1 discloses a hollow particle obtained by suspending a solution of a mixture of divinylbenzene, an initiator, and hexadecane in an aqueous solution containing polyvinyl alcohol and then performing suspension polymerization. Furthermore, Patent Document 1 shows a reduced coefficient of thermal expansion in copper-clad laminates using a resin composition containing hollow particles.

[0009] Patent Document 2 discloses hollow particles obtained by interfacial polymerization. This interfacial polymerization is carried out by adding an oil component, consisting of a mixture of an epoxy backbone and an organic solvent, to an aqueous solution containing a curing agent and a water-soluble emulsifier, and then emulsifying it. Furthermore, Patent Document 2 demonstrates that when the ratio of the average linear expansion coefficient α2 at a temperature 10–50°C higher than the glass transition temperature to the average linear expansion coefficient α1 at a temperature 10–50°C lower than the glass transition temperature is 3 or less, wrinkling and warping near the glass transition temperature can be suppressed.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: International Publication No. 2004 / 067638;

[0013] Patent Document 2: Japanese Patent Application Publication No. 2007-48615. Summary of the Invention

[0014] The problem the invention aims to solve

[0015] However, in hollow particles used in applications such as electronic materials, there is a need to further reduce the coefficient of thermal expansion.

[0016] The purpose of this invention is to provide a hollow particle with a reduced coefficient of thermal expansion.

[0017] Solution for solving the problem

[0018] The inventors focused on the permeability of the shell of hollow particles to polar solvents and discovered that hollow particles with shells that are not easily permeated by acetone, produced by adjusting the composition and formation method of the shell, have a low coefficient of thermal expansion.

[0019] This invention provides hollow particles having a shell containing resin and a hollow portion surrounded by the shell, having a porosity of 50% or more, a volume average particle size of 1.0 μm or more, and wherein, in 100 parts by mass of all monomer units, the shell contains a polymer comprising 70 to 100 parts by mass of crosslinkable monomer units as the resin, and having a coefficient of thermal expansion of 10.0 × 10⁻⁶ at 80 to 200°C. -5At temperatures below ℃, in the impregnation test of hollow particles, the amount of hollow particles precipitated in acetone is less than 10% by mass. The impregnation test is conducted by adding 0.1 mg of hollow particles to 4 mL of acetone at 25℃, shaking at 100 rpm for 10 minutes, and then letting it stand for 48 hours.

[0020] In the hollow particles of this invention, the coefficient of thermal expansion at 25–80°C can be 6.0 × 10⁻⁶. -5 / ℃ below.

[0021] In the hollow particles of the present invention, the relative permittivity at a frequency of 1 GHz can be 1.6 or less.

[0022] In the hollow particles of the present invention, the dielectric loss tangent at a frequency of 1 GHz can be less than 0.010.

[0023] In the hollow particles of the present invention, the polymer contained in the shell contains a bifunctional crosslinking monomer unit derived from a bifunctional crosslinking monomer as the crosslinking monomer unit, and the content of the bifunctional crosslinking monomer unit in all monomer units of 100 parts by mass of the polymer can be 70 to 100 parts by mass.

[0024] In the hollow particles of the present invention, the polymer contained in the shell comprises a trifunctional or higher crosslinking monomer unit derived from a trifunctional or higher crosslinking monomer as the crosslinking monomer unit, and the content of the trifunctional or higher crosslinking monomer unit in 100 parts by mass of all monomer units of the polymer may be 5 to 50 parts by mass.

[0025] In the hollow particles of the present invention, the polymer contained in the shell further comprises hydrophilic non-crosslinked monomer units derived from a hydrophilic non-crosslinked monomer having a solubility of 0.3 g / L or more in distilled water at 20°C.

[0026] In 100 parts by mass of all monomer units of the above polymer, the content of the hydrophilic non-crosslinked monomer unit can be 2 to 15 parts by mass, and the content of the crosslinked monomer unit can be 70 to 98 parts by mass.

[0027] In the hollow particles of the present invention, the aforementioned crosslinking monomer unit may comprise a crosslinking monomer unit derived from a (meth)acryloyl-based crosslinking monomer having (meth)acryloyl as a polymerizable functional group.

[0028] Invention Effects

[0029] As described above, the present invention provides a hollow particle with a reduced coefficient of thermal expansion. Attached Figure Description

[0030] Figure 1 A figure illustrating an example of a method for manufacturing hollow particles according to the present invention.

[0031] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in the suspension process. Detailed Implementation

[0032] Furthermore, in this invention, the "~" in the numerical range refers to the lower limit and upper limit values, including the values ​​recorded before and after them.

[0033] Furthermore, in this invention, (meth)acrylate represents acrylate and methacrylate, (meth)acrylic acid represents acrylic acid and methacrylic acid, and (meth)acryloyl group represents acryloyl group and methacryloyl group.

[0034] Furthermore, in this invention, a polymerizable monomer refers to a compound having a functional group capable of addition polymerization (sometimes simply referred to as a polymerizable functional group in this invention). In this invention, compounds having an olefinic unsaturated bond as a functional group capable of addition polymerization are generally used as polymerizable monomers.

[0035] As polymerizable monomers, there exist non-crosslinked monomers and crosslinked monomers. Non-crosslinked monomers are polymerizable monomers with only one polymerizable functional group, while crosslinked monomers are polymerizable monomers with two or more polymerizable functional groups that form crosslinked bonds in the resin through a polymerization reaction.

[0036] Furthermore, in this invention, polymerizable monomers with a solubility of 0.3 g / L or more in distilled water at 20°C are called hydrophilic monomers, and polymerizable monomers with a solubility of less than 0.3 g / L in distilled water at 20°C are called non-hydrophilic monomers.

[0037] 1. Hollow particles

[0038] The hollow particles of the present invention are characterized by having a shell containing resin and a hollow portion surrounded by the shell comprising 50% or more, having a volume average particle size of 1.0 μm or more, having the shell containing 70 to 100 parts by mass of a polymer as the resin comprising crosslinkable monomer units in 100 parts by mass of all monomer units, and having a coefficient of thermal expansion of 10.0 × 10⁻⁶ at 80 to 200°C. -5 At temperatures below ℃, in the impregnation test of hollow particles, the amount of hollow particles precipitated in acetone is less than 10% by mass. The impregnation test is conducted by adding 0.1 mg of hollow particles to 4 mL of acetone at 25℃, shaking at 100 rpm for 10 minutes, and then letting it stand for 48 hours.

[0039] The hollow particles of the present invention are particles having a shell (outer shell) containing resin and a hollow portion surrounded by the shell.

[0040] In this invention, the hollow portion is a hollow space that is clearly distinguishable from the shell of the hollow particles formed of resin material. The shell of the hollow particles may have a porous structure, in which case the hollow portion has a size that can be clearly distinguished from a plurality of tiny spaces uniformly dispersed within the porous structure.

[0041] The hollow portion of hollow particles can be confirmed by, for example, SEM observation of particle profiles or TEM observation of the particles directly.

[0042] From the viewpoint of achieving low dielectric constant and low dielectric loss tangent, the hollow particles of the present invention preferably have a hollow portion filled with air or nitrogen or in a depressurized state close to vacuum.

[0043] Hollow particles have a hollow interior, thus enabling various compositions and molded articles incorporating hollow particles to acquire properties such as lightweight, heat resistance, and low dielectric constant. The hollow particles of the present invention have a reduced coefficient of thermal expansion (CTE), therefore, in various compositions and molded articles incorporating the hollow particles of the present invention, the CTE can also be reduced.

[0044] The hollow particles of the present invention contain 70 to 100 parts by mass of crosslinked monomer units per 100 parts by mass of all monomer units in the shell. Therefore, it can be inferred that the proportion of crosslinked monomer units in the shell is large, and the covalent bond network is densely distributed throughout the shell. Furthermore, since less than 10% of the hollow particles precipitated in acetone during the aforementioned impregnation test, it can be inferred that the shell has a dense structure that is not easily impregnated by acetone, and the crosslinked structure in the shell of the hollow particles of the present invention is even denser. It is speculated that the low CTE of the hollow particles of the present invention is due to a porosity of over 50%, a sufficiently large proportion of hollow portions in the particles, i.e., a sufficiently small proportion of shells in the particles. Consequently, the shell has a dense structure, resulting in excellent heat resistance and resistance to dimensional changes caused by heat.

[0045] Furthermore, the hollow particles of the present invention are particles with reduced relative permittivity and dielectric loss tangent. Since the hollow particles of the present invention have a porosity of 50% or more, the proportion of hollow portions within the particles is sufficiently large, resulting in a dense shell structure. Therefore, it can be inferred that molecular motion is significantly restricted, making dielectric relaxation less likely, thus exhibiting excellent dielectric properties. In addition, the shells of the hollow particles of the present invention have excellent strength, making them less prone to deformation or breakage, suppressing the increase in relative permittivity caused by deformation or breakage of the hollow particles, and thus maintaining a low permittivity.

[0046] The hollow particles of the present invention are particles with a reduced coefficient of thermal expansion (CTE).

[0047] The hollow particles of this invention have a coefficient of thermal expansion of 10.0 × 10⁻⁶ at 80–200 °C. -5 Below / ℃, according to the preferred embodiment, it can be 9.9×10 -5 Below / ℃, it can further reach 9.8×10 -5 / ℃ or below. The lower limit of the coefficient of thermal expansion of the hollow particles of this invention at 80–200℃ is not particularly limited, but is typically 5.0 × 10⁻⁶. -5 / ℃ or above.

[0048] Furthermore, the coefficient of thermal expansion in the hollow particles of this invention can be 6.0 × 10⁻⁶ at 25–80°C. -5 Below / ℃, according to a more preferred embodiment, it can be 5.9 × 10 -5 Below / ℃, it can further reach 5.8×10 -5 / ℃ or below. The lower limit of the coefficient of thermal expansion of the hollow particles of this invention at 25–80℃ is not particularly limited, but is typically 1.0 × 10⁻⁶. -5 / ℃ or above.

[0049] Furthermore, in this invention, the coefficient of thermal expansion α of the hollow particles is... p The coefficient of thermal expansion α of the molded plate formed by the resin composition of the matrix resin and hollow particles can be determined. c The coefficient of thermal expansion α of the matrix resin monomer r The volume ratio SG of the matrix resin in the above-mentioned molded plate r And the volume ratio W of the hollow particles in the above-mentioned molded plate. p It can be obtained by the following formula (E).

[0050]

[0051] In addition, the coefficient of thermal expansion was measured within the specified temperature range in accordance with JIS K7197:2012.

[0052] As the matrix resin mentioned above, additives such as epoxy resin and curing catalysts can be used to cure the resin.

[0053] Furthermore, the hollow particles of the present invention are particles in which the relative permittivity and dielectric loss tangent are reduced.

[0054] In the hollow particles of the present invention, the relative permittivity at a frequency of 1 GHz can be 1.6 or less, and according to a more preferred embodiment, the relative permittivity at a frequency of 1 GHz can be 1.5 or less. The lower limit of the aforementioned relative permittivity of the hollow particles of the present invention is not particularly limited, and is generally 1.0 or more.

[0055] Furthermore, in the hollow particles of the present invention, the dielectric loss tangent at a frequency of 1 GHz can be 0.010 or less, and according to a more preferred embodiment, the dielectric loss tangent at a frequency of 1 GHz can be 0.009 or less. The lower limit of the aforementioned dielectric loss tangent of the hollow particles of the present invention is not particularly limited, and is generally 0.001 or more.

[0056] Furthermore, in this invention, the relative permittivity and dielectric loss tangent of the hollow particles are measured using a perturbation-based measuring device at a measurement frequency of 1 GHz.

[0057] The hollow particles of the present invention have a porosity of 50% or more, preferably 60% or more. By maintaining a porosity of 50% or more, the hollow particles exhibit low CTE, low relative permittivity, and low dielectric loss tangent. Furthermore, they possess excellent lightweight, heat resistance, and thermal insulation properties. The upper limit of the porosity of the hollow particles of the present invention is not particularly limited, but from the viewpoint of suppressing the reduction in strength and preventing breakage, it is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less.

[0058] The porosity of the hollow particles of the present invention is calculated based on the apparent density D1 and true density D0 of the hollow particles.

[0059] The method for determining the apparent density D1 of hollow particles is as follows. First, approximately 30 cm³ of... 3 Hollow particles are filled in a volume of 100 cm³ 3 In a volumetric flask, accurately weigh the mass of the hollow granules used to fill it. Next, precisely 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 hollow granules according to the following formula (I). 3 ).

[0060]

[0061] Apparent density D1 is equivalent to the total density of the hollow particle when the hollow part is considered as part of the hollow particle.

[0062] The method for determining the true density D0 of hollow granules is as follows: After pre-crushing the hollow granules, approximately 10g of the granule fragments are filled into a 100cm³ container. 3 In a volumetric flask, the mass of the filled fragments is accurately weighed. Then, isopropanol is added to the volumetric flask in the same manner as the apparent density determination described above, the mass of the isopropanol is accurately weighed, and the true density D0 (g / cm³) of the hollow particles is calculated according to the following formula (II). 3 ).

[0063]

[0064] True density D0 corresponds to the specific gravity of the shell portion of a hollow particle. As can be clearly seen from the above measurement method, the hollow portion is not considered part of the hollow particle when calculating true density D0.

[0065] The porosity (%) of the hollow particles is calculated using the following formula (III) based on the apparent density D1 and true density D0 of the hollow particles.

[0066]

[0067] The hollow particles of the present invention have a volume average particle size of 1.0 μm or more. By making the volume average particle size of the hollow particles at or above the aforementioned lower limit, the agglomeration of the hollow particles is reduced, thus exhibiting excellent dispersibility. Even when contained in the insulating resin layer of an electronic circuit board, it is less likely to cause wiring defects, so it is preferably used as a material for electronic circuit boards.

[0068] The lower limit of the volume average particle size of the hollow particles of the present invention is preferably 3.0 μm or more, more preferably 5.0 μm or more, and even more preferably 7.0 μm or more. The upper limit of the volume average particle size of the hollow particles of the present invention is not particularly limited, but from the viewpoints of improving the strength of the hollow particles, making the shell thickness more uniform, and facilitating their use as a material for electronic circuit boards, it is preferably 30.0 μm or less, more preferably 20.0 μm or less, and even more preferably 15.0 μm or less.

[0069] In order to make the volume average particle size of the hollow particles within the above-mentioned preferred range, for example, in the mixture preparation process, the above-mentioned preferred dispersing stabilizer is preferably used, and the above-mentioned preferred hydrophobic solvent is even more preferably used.

[0070] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow particles can, for example, be 1.1 or higher and 2.5 or lower. By setting this particle size distribution to 2.5 or lower, particles with small deviations in compressive strength and heat resistance between particles can be obtained. Furthermore, by setting this particle size distribution to 2.5 or lower, for example, when manufacturing sheet-like molded bodies, products with uniform thickness can be manufactured.

[0071] The volume-average particle size (Dv) and number-average particle size (Dn) of hollow particles can be determined by measuring the particle size of the hollow particles using, for example, a laser diffraction particle size distribution measuring device. The number-average and volume-average sizes are then calculated, and the obtained values ​​are used as the number-average particle size (Dn) and volume-average particle size (Dv) of the particle. Particle size distribution is the value of volume-average particle size divided by number-average particle size.

[0072] Regarding the shell thickness of the hollow particles of the present invention, from the viewpoint of improving the strength of the hollow particles, it is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. From the viewpoint of improving porosity, it is preferably 6 μm or less, more preferably 4 μm or less, even more preferably 2 μm or less, and even more preferably 1 μm or less. By making the shell thickness of the hollow particles at or above the above-mentioned lower limit value, the shell strength is improved. On the other hand, the shell of the hollow particles of the present invention has a dense structure that is not easily impregnated with acetone, so even if the shell thickness is thin to below the above-mentioned upper limit value, the hollow particles have excellent strength and are not easily broken.

[0073] Furthermore, the thickness of the shell of the hollow particles can be calculated using the volume average particle size R and porosity of the hollow particles through the following formula (1), and the inner diameter r of the hollow particles can be calculated using the inner diameter r and the volume average particle size R through the following formula (2). In addition, the porosity in the following formula (1) is a value expressed as a proportion.

[0074]

[0075] The difference between the shell thickness calculated in this way and the average thickness of the actual measured shell at 20 is usually within ±10% of their average value. Therefore, the shell thickness calculated as described above can be regarded as the thickness of the shell of the hollow particle.

[0076] The thickness of the shell at each of the hollow particles used to calculate the average thickness at 20 points can be determined, for example, by observing fragments of the shell obtained by cutting the hollow particles using SEM.

[0077] The shape of the hollow particles of the present invention is not particularly limited as long as a hollow portion is formed inside; examples include spherical, ellipsoidal, and irregular shapes. Among these, a spherical shape is preferred from the perspective of ease of manufacture.

[0078] Hollow particles can have one or more hollow sections. Furthermore, the shell of the hollow particle, and the partitions separating adjacent hollow sections when there are two or more hollow sections, can be porous. To maintain a good balance between the high porosity and mechanical strength of the hollow particles, it is preferable that the particle has only one hollow section inside.

[0079] The average roundness of hollow particles can be 0.950 to 0.995.

[0080] An example of the shape of hollow particles is a bag formed by a thin membrane and inflated with air, the cross-section of which is described later. Figure 1 The hollow particle 100 in (5) is shown. In this example, a thin membrane is provided on the outside, and the inside is filled with gas.

[0081] The shape of the particles can be confirmed using methods such as SEM and TEM. Furthermore, the internal shape of the particles can be confirmed using SEM and TEM after the particles are cut into circular slices using known methods.

[0082] The hollow particles of the present invention contain a polymer comprising 70 to 100 parts by mass of crosslinked monomer units as a resin in the shell of all monomer units in 100 parts by mass. The polymer forms the skeleton of the shell of the hollow particles, and the crosslinked monomer units are contained in the above proportion, thereby the hollow particles of the present invention have a shell with a densely distributed covalent bond network.

[0083] In the above polymer, from the viewpoint of reducing the CTE, relative permittivity and dielectric loss tangent of hollow particles, and from the viewpoint of improving the strength of hollow particles, the content of crosslinking monomer units in 100 parts by mass of all monomer units is preferably 75 parts by mass or more, more preferably 85 parts by mass or more. On the other hand, when a hydrophilic non-crosslinking monomer is added as a second polymerizable monomer, from the viewpoint of adding a sufficient amount of the second polymerizable monomer, it is preferably 98 parts by mass or less, more preferably 97 parts by mass or less.

[0084] Furthermore, in this invention, the crosslinking monomer unit is a monomer unit derived from the crosslinking monomer. In the polymer described above, when the content of the crosslinking monomer unit is less than 100 parts by mass, the monomer units other than the crosslinking monomer unit are non-crosslinking monomer units derived from the non-crosslinking monomer.

[0085] The polymer described above is typically a polymer of a first polymeric monomer and a second polymeric monomer obtained through a first polymerization reaction and a second polymerization reaction in the method for manufacturing hollow particles of the present invention, described later. That is, in the hollow particles of the present invention, the crosslinked monomer units and non-crosslinked monomer units contained in the polymer are generally derived from the first polymeric monomer and the second polymeric monomer described later.

[0086] Furthermore, the specific details of the crosslinked and non-crosslinked monomers used to synthesize the above-mentioned polymers are described in the method for manufacturing hollow particles of the present invention, which will be described later.

[0087] The polymer described above comprises at least one crosslinking monomer unit selected from bifunctional crosslinking monomers and trifunctional or higher crosslinking monomer units as crosslinking monomer units. From the viewpoint of reducing CTE and improving the strength of hollow particles, it is preferable to include at least a bifunctional crosslinking monomer unit; from the viewpoint of further improving the strength of hollow particles, it is more preferable to combine a bifunctional crosslinking monomer unit and a trifunctional or higher crosslinking monomer unit.

[0088] In addition, in this invention, crosslinking monomer units derived from bifunctional crosslinking monomers are sometimes referred to as "bifunctional crosslinking monomer units", and crosslinking monomer units derived from trifunctional or higher crosslinking monomers are sometimes referred to as "trifunctional or higher crosslinking monomer units".

[0089] When the polymer contains bifunctional crosslinkable monomer units, the content of bifunctional crosslinkable monomer units in all monomer units of the polymer in 100 parts by mass is not particularly limited. As a lower limit, from the viewpoint of reducing CTE and improving strength of hollow particles, it is preferably 70 parts by mass or more, more preferably 75 parts by mass or more. On the other hand, as an upper limit, it can be 100 parts by mass or less. From the viewpoint of ensuring that it sufficiently contains trifunctional or higher crosslinkable monomer units or hydrophilic non-crosslinkable monomer units described later, it is preferably 98 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less.

[0090] When the polymer described above contains trifunctional or higher crosslinkable monomer units, the content of trifunctional or higher crosslinkable monomer units in all monomer units of the polymer in 100 parts by mass is not particularly limited. As a lower limit, from the viewpoint of reducing CTE and improving strength of hollow particles, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more. On the other hand, as an upper limit, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less. From the viewpoint of ensuring that it fully contains bifunctional crosslinkable monomer units or hydrophilic non-crosslinkable monomer units described later, it is even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

[0091] Furthermore, the crosslinking monomer units included in the above-mentioned polymer may comprise crosslinking monomer units derived from (meth)acryloyl-based crosslinking monomers having (meth)acryloyl groups as polymerizable functional groups. Consequently, the hollow particles of the present invention exhibit excellent strength and heat resistance, thereby improving the adhesion of resin compositions incorporating the hollow particles of the present invention.

[0092] When the polymer contains crosslinking monomer units derived from (meth)acrylic acid-based crosslinking monomers, the content of the crosslinking monomer units derived from (meth)acrylic acid-based crosslinking monomers in 100 parts by mass is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 90 parts by mass or more, and the crosslinking monomer units can be formed from (meth)acrylic acid-based crosslinking monomer units.

[0093] Furthermore, the specific details regarding the (meth)acrylic acid-based crosslinking monomer are as described later in the method for manufacturing the hollow particles of the present invention.

[0094] Furthermore, the polymer preferably further comprises non-crosslinked monomer units, more preferably hydrophilic non-crosslinked monomer units with a solubility of 0.3 g / L or more in distilled water at 20°C, and particularly preferably hydrophilic non-crosslinked monomer units derived from the second polymerizable monomer described later. By combining crosslinked and non-crosslinked monomer units, the mechanical properties of the hollow particle shell are improved. In particular, by including hydrophilic non-crosslinked monomer units as non-crosslinked monomer units, the shell tends to form a dense structure, thus the CTE, relative permittivity, and dielectric loss tangent of the hollow particles are easily reduced. In addition, the strength of the hollow particles is easily improved.

[0095] In the above polymer, the content of non-crosslinked monomer units in 100 parts by mass of all monomer units is 0 to 30 parts by mass, and from the viewpoint of improving the strength of hollow particles, it is preferably 2 to 25 parts by mass, and more preferably 4 to 15 parts by mass.

[0096] In the above polymer, from the viewpoint of improving the strength of hollow particles and reducing the CTE, relative permittivity and dielectric loss tangent of hollow particles, the content of hydrophilic non-crosslinked monomer units in 100 parts by mass of all monomer units is preferably 2 to 15 parts by mass, more preferably 3 to 13 parts by mass, and even more preferably 4 to 10 parts by mass.

[0097] In the hollow particles of the present invention, the content of the aforementioned polymer is preferably 90% by mass or more, more preferably 95% by mass or more, in 100% by mass of the total solid component of the shell. By setting the content of the aforementioned polymer to the aforementioned lower limit or above, the strength of the hollow particles can be improved.

[0098] The shell of the hollow particles of the present invention may further contain a polar component. Examples of polar components include organic acids or their metal salts, and polar resins.

[0099] Furthermore, the specific details regarding the polar components are as described later in the method for manufacturing the hollow particles of the present invention.

[0100] The shell of the hollow particles contains polar components, and their content can be confirmed by, for example, pyrolysis gas chromatography.

[0101] When the shell of the hollow particles of the present invention contains an organic acid or its metal salt as a polar component, the total content of the organic acid or its metal salt in the shell is preferably 0.0001 to 0.1% by mass, more preferably 0.001 to 0.01% by mass.

[0102] On the other hand, when the shell of the hollow particles of the present invention contains a polar resin as a polar component, the content of the polar resin in the shell is preferably 0.1 to 10.0% by mass, more preferably 0.3 to 8.0% by mass.

[0103] The shell contains organic acids or their metal salts, and polar resins, which can inhibit the reduction of shell strength and further inhibit the breakage of hollow particles.

[0104] In the impregnation test of the hollow particles of the present invention, less than 10% by mass of the hollow particles precipitated in acetone were observed. This impregnation test was conducted by adding 0.1 mg of hollow particles to 4 mL of acetone at 25°C, shaking at 100 rpm for 10 minutes, and then allowing it to stand for 48 hours. In the above impregnation test, the proportion of hollow particles precipitated in acetone serves as an indicator of the density of the hollow particle shell. It can be inferred that the smaller the proportion of hollow particles precipitated in acetone in the above impregnation test, the denser the shell of the hollow particles. Furthermore, it can be inferred that the denser the shell of the hollow particles, the lower the CTE, relative permittivity, and dielectric loss tangent of the hollow particles tend to be.

[0105] In the hollow particles of the present invention, in the above-mentioned impregnation test, the proportion of hollow particles precipitated in acetone is less than 10% by mass, more preferably less than 5% by mass.

[0106] In hollow particles with a porosity of 50% or more, in order to make the hollow particles precipitated in acetone in the above-mentioned impregnation test less than 10% by mass, hollow particles can be manufactured, for example, by using the following method and in such a way that the crosslinking monomer unit in the above-mentioned polymer forming the shell contains 70% by mass or more. The above-mentioned method is as described later in the method for manufacturing hollow particles of the present invention, in which, in the step of supplying the suspension to the polymerization reaction, when the polymerization conversion rate of the first polymeric monomer containing a certain amount or more of the crosslinking monomer reaches 93% by mass or more, a second polymeric monomer as a hydrophilic monomer is added and further supplied to the polymerization reaction.

[0107] Furthermore, in SEM observation, preferably, among 100 hollow particles of the present invention, there are 5 or fewer hollow particles with interconnecting holes or shell defects.

[0108] Hollow particles typically exhibit two types of interconnections: those where the shell lacks a connecting hole that links the hollow portion to the outside space of the particle; and those where the shell has one or more connecting holes through which the hollow portion communicates with the outside of the particle. While the diameter of the connecting hole typically ranges from 10 to 500 nm, depending on the size of the hollow particle, it can also contribute to the particle's strength and make it prone to breakage, as the connecting hole is a defect in the shell.

[0109] Furthermore, hollow particles sometimes exhibit crack-like shell defects that are very large relative to their size. Although this also depends on the size of the hollow particles, cracks with a length of 1 μm or more typically significantly degrade the strength of the hollow particles and are therefore considered shell defects.

[0110] In the aforementioned impregnation test of hollow particles, if the percentage of hollow particles precipitating in acetone is less than 10% by mass, it can be considered that out of 100 hollow particles, fewer than 5 have interconnecting pores or shell defects. Furthermore, even when the shell does not have interconnecting pores or shell defects, sometimes the percentage of hollow particles precipitating in the aforementioned impregnation test is more than 10% by mass. Therefore, it can be considered that in the aforementioned impregnation test of hollow particles, a percentage of hollow particles precipitating is less than 10% by mass, indicating that the shell has very few interconnecting pores and shell defects, and that the shell has a dense cross-linked structure.

[0111] 2. Manufacturing method of hollow particles

[0112] The hollow particles of the present invention can be obtained by, for example, the following method of manufacturing hollow particles, which includes: a step of preparing a mixture comprising a hydrocarbon solvent, a first polymerizable monomer containing a crosslinking monomer, a dispersing stabilizer, and an aqueous medium; a step of preparing a suspension in which droplets of a monomer composition comprising the first polymerizable monomer and the hydrocarbon solvent are dispersed in the aqueous medium by suspending the mixture; and a step of supplying the suspension to a polymerization reaction, wherein, in the step of supplying the suspension to the polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C is added and further supplied to the polymerization reaction.

[0113] The manufacturing method of the above-mentioned hollow particles follows the following basic technology: by suspending a mixture containing a first polymerizable monomer, a hydrocarbon solvent, a dispersing stabilizer, and an aqueous medium, a suspension is prepared in which droplets with a distribution structure in which the first polymerizable monomer and the hydrocarbon solvent are phase-separated, the first polymerizable monomer is concentrated on the surface side, and the hydrocarbon solvent is concentrated in the center are dispersed in an aqueous medium. The suspension is then supplied to a polymerization reaction to solidify the surface of the droplets, thereby forming hollow particles with a hollow part filled with hydrocarbon solvent.

[0114] In this basic technology, during the process of supplying the suspension to the polymerization reaction, when the polymerization conversion rate of the first polymeric monomer containing the crosslinking monomer reaches 93% by mass or more, a second polymeric monomer, which is a hydrophilic monomer and has a solubility in distilled water at 20°C of 93% or more, is added and further supplied to the polymerization reaction. This allows the production of hollow particles in which less than 10% by mass precipitate in acetone during the impregnation test of the hollow particles described above. When a crosslinking monomer is used as the polymeric monomer for forming the shell of the hollow particles, unreacted polymeric functional groups tend to remain in the shell. The more unreacted polymeric functional groups remain directly, the coarser the crosslinking structure of the shell becomes. Therefore, it can be considered that in hollow particles obtained by conventional manufacturing methods, due to the presence of unreacted polymeric functional groups, the percentage of hollow particles precipitating in acetone during the impregnation test of the hollow particles described above is 10% by mass or more.

[0115] It can be considered that in the above-mentioned method for manufacturing hollow particles, a suspension containing droplets of a monomer composition having a large amount of a first polymerizable monomer containing a crosslinking monomer is dispersed in an aqueous medium and supplied to a polymerization reaction, and a first polymerization reaction is carried out until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more. Then, a second polymerizable monomer, which is a hydrophilic monomer, is added, and a second polymerization reaction is carried out. This can improve the overall reaction rate of the polymerizable monomer containing the first polymerizable monomer and the second polymerizable monomer.

[0116] Furthermore, in this invention, particles obtained through the first polymerization reaction described above, having a shell of a polymer containing a first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent, are sometimes referred to as first precursor particles, and compositions containing such first precursor particles are sometimes referred to as first precursor compositions. Additionally, particles obtained through the second polymerization reaction described above, having a shell of a polymer containing a first polymerizable monomer and a second polymerizable monomer and a hollow portion filled with a hydrocarbon solvent, are considered intermediates of hollow particles with a gas-filled hollow portion, and are sometimes referred to as second precursor particles, and compositions containing such second precursor particles are sometimes referred to as second precursor compositions.

[0117] In the above-described method for manufacturing hollow particles, the solubility of the second polymerizable monomer in distilled water at 20°C is above the specified value. Therefore, when added to the first precursor composition, it easily enters the shell of the first precursor particles. Since the second polymerizable monomer, being a hydrophilic monomer, has an affinity for both the first polymerizable monomer and the aqueous medium, it can be assumed that when the second polymerizable monomer is added to the first precursor composition, it enters the shell formed by the first polymerizable monomer, promoting the thermal motion of the shell. During the second polymerization reaction, with the second polymerizable monomer inside the shell formed by the first polymerizable monomer, the polymerization reaction proceeds simultaneously with the promotion of the shell's thermal motion. Therefore, it can be inferred that the reaction rate is high, and the polymerization reaction of the polymerizable functional groups of the second polymerizable monomer inside the shell and the first polymerizable monomer remaining in an unreacted state proceeds fully, resulting in a dense cross-linked structure and thus forming a shell that is difficult for acetone to impregnate.

[0118] The aforementioned method for manufacturing hollow particles includes a step of preparing a mixture, a step of preparing a suspension, and a step of supplying the suspension to the polymerization reaction, and may further include steps other than these. Furthermore, provided it is technically feasible, two or more of the aforementioned steps and other additional steps may be performed simultaneously as a single step, or their order may be reversed. For example, the preparation and suspension of the mixture can be performed simultaneously in one process by adding the material for preparing the mixture while simultaneously suspending it.

[0119] As a preferred example of the manufacturing method of the above-mentioned hollow particles, a manufacturing method including the following steps can be cited.

[0120] (1) Mixture preparation process

[0121] The process of preparing a mixture comprising a first polymerizable monomer, a hydrocarbon solvent, a dispersing stabilizer, and an aqueous medium;

[0122] (2) Suspension process

[0123] The process of preparing a suspension in an aqueous medium by suspending the above-mentioned mixture, wherein droplets of a monomer composition comprising a first polymerizable monomer and a hydrocarbon solvent are dispersed in the monomer medium.

[0124] (3) Polymerization process

[0125] (3-1) First polymerization process

[0126] The process of supplying the above suspension to the first polymerization reaction of the polymerization reaction to the polymerization conversion of the first polymerizable monomer to 93% by mass or more, thereby preparing a first precursor composition comprising the first precursor particles having a shell of a polymer comprising the first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0127] (3-2) Second polymerization process

[0128] A process of preparing a second precursor composition comprising second precursor particles by adding a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C to the first precursor composition described above to carry out a second polymerization reaction, wherein the second precursor particles have a shell of a polymer comprising the first polymerizable monomer and the second polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0129] (4) Solid-liquid separation process

[0130] The process of obtaining second precursor particles containing a hydrocarbon solvent in a hollow section by solid-liquid separation of the above-mentioned second precursor composition; and

[0131] (5) Solvent removal process

[0132] The process of removing the hydrocarbon solvent contained in the second precursor particles obtained through the above solid-liquid separation process to obtain hollow particles.

[0133] Figure 1 A schematic diagram illustrating an example of the manufacturing method described above. Figure 1 Steps (1) to (5) in the diagram correspond to the steps (1) to (5) mentioned above. The white arrows between the diagrams indicate the sequence of each step. Additionally, Figure 1 These are merely illustrative diagrams, and the manufacturing methods described are not limited to those shown. Furthermore, the structure, size, and shape of the materials used in the manufacturing methods of this invention are not limited to the structures, sizes, and shapes of the various materials shown in these figures.

[0134] Figure 1 Figure (1) is a cross-sectional schematic diagram showing one embodiment of the mixture in the mixture preparation process. As shown in the figure, the mixture includes an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 refers to a material with low polarity that is not easily mixed with the aqueous medium 1. In this invention, the low-polarity material 2 includes a first polymerizable monomer and a hydrocarbon solvent.

[0135] Figure 1 (2) is a cross-sectional schematic diagram showing one embodiment of the suspension in the suspension process. The suspension includes an aqueous medium 1 and droplets 10 of a monomer composition dispersed in the aqueous medium 1. The droplets 10 of the monomer composition contain a first polymerizable monomer and a hydrocarbon solvent, but the distribution within the droplets is not uniform. The droplets 10 of the monomer composition have the following structure: the hydrocarbon solvent 4a and the material 4b containing the first polymerizable monomer, excluding the hydrocarbon solvent, undergo phase separation, with the hydrocarbon solvent 4a concentrated in the central part and the material 4b, excluding the hydrocarbon solvent, concentrated on the surface side, and a dispersion stabilizer (not shown) adhering to the surface.

[0136] Figure 1 (3) is a cross-sectional schematic diagram showing one embodiment of a composition (second precursor composition) containing hollow particles (second precursor particles) with a hydrocarbon solvent in the hollow portion, obtained by a polymerization process. The composition includes an aqueous medium 1 and hollow particles (second precursor particles) 20 dispersed in the aqueous medium 1, each containing a hydrocarbon solvent 4a in the hollow portion. The shell 6 forming the outer surface of the second precursor particles 20 is formed by the polymerization of a first polymerizable monomer in the droplets 10 of the monomer composition described above, and the polymerization of a second polymerizable monomer subsequently added.

[0137] Figure 1 (4) is a cross-sectional schematic diagram showing one embodiment of hollow particles (second precursor particles) containing hydrocarbon solvent in the hollow section after the solid-liquid separation process. Figure 1 (4) shows the above Figure 1 The state of (3) is the state of water medium 1.

[0138] Figure 1 (5) is a cross-sectional schematic diagram showing one embodiment of hollow particles after the solvent removal process. Figure 1 (5) shows the above Figure 1 The state of (4) is in which the hydrocarbon solvent 4a has been removed. By removing the hydrocarbon solvent from the hollow particles (second precursor particles) containing the hydrocarbon solvent in the hollow part, hollow particles 100 with a gas-filled hollow part 8 inside the shell 6 can be obtained.

[0139] The following sections will describe the five processes mentioned above and the other processes in turn.

[0140] (1) Mixture preparation process

[0141] This process is for preparing a mixture containing a first polymerizable monomer, a hydrocarbon solvent, a dispersant stabilizer, and an aqueous medium.

[0142] The mixture may further contain polar components. Furthermore, the mixture preferably contains an oil-soluble polymerization initiator as a polymerization initiator. In addition, without impairing the effects of the present invention, the mixture may further contain other materials such as suspension stabilizers.

[0143] The materials for the mixture are described in the following order: (A) primary polymerizable monomer, (B) polar component, (C) oil-soluble polymerization initiator, (D) hydrocarbon solvent, (E) dispersant stabilizer, and (F) aqueous medium.

[0144] (A) First polymerizing monomer

[0145] The first polymerizable monomer contains at least a crosslinking monomer, and may further contain a non-crosslinking monomer without impairing the effects of the invention.

[0146] From the viewpoint that the polymerization reaction is easy to stabilize and hollow particles with high heat resistance can be obtained, (meth)acrylic acid-based polymerizable monomers with (meth)acryloyl groups as polymerizable functional groups can be preferred as the first polymerizable monomer.

[0147] On the other hand, from the viewpoint of reducing the relative permittivity and dielectric loss tangent of hollow particles, it is also possible to preferably use hydrocarbon monomers composed of carbon and hydrogen.

[0148] [Crosslinking monomers]

[0149] Crosslinkable monomers have multiple polymerizable functional groups, which enable them to link monomers together and increase the crosslinking density of the shell.

[0150] Examples of crosslinking monomers include: divinylbenzene, divinylbiphenyl, divinylnaphthalene, diallyl phthalate, diallylamine, allyl acrylate, vinyl methacrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, and 2-hydroxy-3-(meth)acryloyloxypropyl methacrylate, which are bifunctional crosslinking monomers with two polymerizable functional groups; and trifunctional or higher crosslinking monomers with three or more polymerizable functional groups, such as trimethylolpropane tri(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and their ethoxylates. These crosslinking monomers can be used alone or in combination of two or more.

[0151] In addition, among these crosslinking monomers, examples of hydrophilic crosslinking monomers with a solubility of 0.3 g / L or more in distilled water at 20°C include ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl methacrylate, vinyl methacrylate, 2-hydroxy-3-methacryloyloxypropyl acrylate, diallylamine, etc.

[0152] The crosslinking monomer included as the first polymerizable monomer can be a hydrophilic crosslinking monomer with a solubility of more than 0.3 g / L in distilled water at 20°C, or a non-hydrophilic crosslinking monomer with a solubility of less than 0.3 g / L in distilled water at 20°C, without particular limitation.

[0153] The first polymerizable monomer includes at least one crosslinking monomer selected from bifunctional crosslinking monomers and trifunctional or higher crosslinking monomers. From the viewpoint of reducing the CTE of the hollow particles, it is preferable to include at least a bifunctional crosslinking monomer; from the viewpoint of further improving the strength of the hollow particles, a combination of bifunctional crosslinking monomers and trifunctional or higher crosslinking monomers is more preferable. While it is superior that the first polymerizable monomer includes a trifunctional or higher crosslinking monomer, allowing for a denser distribution of the covalent bond network within the shell, there is a tendency for unreacted polymerizable functional groups to remain after the first polymerization reaction. In the above manufacturing method, even when the first polymerizable monomer includes a trifunctional or higher crosslinking monomer, by adding a hydrophilic monomer as a second polymerizable monomer to carry out a second polymerization reaction, the polymerization reaction of the unreacted polymerizable functional groups remaining after the first polymerization reaction is easily achieved. Therefore, by including trifunctional or higher crosslinking monomers in the first polymerizable monomer, the crosslinking structure of the shell can be made denser, reducing the CTE, relative permittivity and dielectric loss tangent of the hollow particles. In addition, the strength of the hollow particles can be improved.

[0154] Furthermore, from the viewpoint that the crosslinking monomer included as the first polymerizable monomer is easy to stabilize in the polymerization reaction and can obtain hollow particles with excellent strength and heat resistance, and from the viewpoint that the adhesion of the obtained resin composition containing hollow particles is improved, a (meth)acryloyl group as a polymerizable functional group is preferred.

[0155] That is, as a bifunctional crosslinking monomer used for the first polymerizable monomer, allyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, pentaerythritol dimethacrylate and other bifunctional (meth)acrylate crosslinking monomers are preferred, among which ethylene glycol dimethacrylate and pentaerythritol dimethacrylate are more preferred.

[0156] As a trifunctional or higher crosslinking monomer that can be used as the first polymerizable monomer, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and their ethoxylated derivatives are preferred trifunctional or higher (meth)acrylate-based crosslinking monomers. Among them, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol poly(meth)acrylate are more preferred, and trimethylolpropane tri(meth)acrylate and pentaerythritol tetra(meth)acrylate are even more preferred.

[0157] Furthermore, in this invention, the (meth)acrylic acid-based crosslinking monomer is any crosslinking monomer having at least one (meth)acryloyl group as a polymerizable functional group, preferably all polymerizable functional groups being (meth)acryloyl groups.

[0158] When the first polymerizable monomer includes a (meth)acrylic acid-based crosslinking monomer, the content of the (meth)acrylic acid-based crosslinking monomer in 100 parts by mass of the first polymerizable monomer is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 90 parts by mass or more. The crosslinking monomer contained in the first polymerizable monomer may be composed of (meth)acrylic acid-based crosslinking monomers.

[0159] Furthermore, from the viewpoint of easily reducing the relative permittivity and dielectric loss tangent of hollow particles, the crosslinking monomer included as the first polymerizable monomer is preferably a hydrocarbon-based crosslinking monomer such as divinylbenzene, divinylbiphenyl, or divinylnaphthalene, with divinylbenzene being more preferred among these.

[0160] In 100 parts by mass of the first polymerizable monomer, the content of the crosslinking monomer is preferably 75 to 100 parts by mass, more preferably 80 to 100 parts by mass, even more preferably 85 to 100 parts by mass, and even more preferably 90 to 100 parts by mass. By making the content of the crosslinking monomer at or above the above-mentioned lower limit, the polymer contained in the shell formed in 100 parts by mass of all monomer units is likely to be a polymer containing 70 to 100 parts by mass of crosslinking monomer units. Furthermore, since the proportion of crosslinking monomer units in the shell of the hollow particle is sufficiently large, the covalent bond network is densely distributed in the shell, resulting in a reduction in the CTE, relative permittivity, and dielectric loss tangent of the hollow particle, and also an improvement in the strength of the hollow particle.

[0161] When the first polymerizable monomer includes a bifunctional crosslinking monomer as a crosslinking monomer, the content of the bifunctional crosslinking monomer in 100 parts by mass of the first polymerizable monomer is not particularly limited. As a lower limit, from the viewpoint of reducing the CTE, relative permittivity and dielectric loss tangent of the hollow particles, and from the viewpoint of improving the strength of the hollow particles, it is 70 parts by mass or more, more preferably 75 parts by mass or more. On the other hand, as an upper limit, it can be 100 parts by mass or less. From the viewpoint of ensuring that it fully contains trifunctional or more crosslinking monomer units, it is preferably 95 parts by mass or less, more preferably 90 parts by mass or less.

[0162] When the first polymerizable monomer includes a trifunctional or higher crosslinking monomer as a crosslinking monomer, the content of the trifunctional or higher crosslinking monomer in 100 parts by mass of the first polymerizable monomer is not particularly limited. As a lower limit, from the viewpoint of reducing the CTE, relative permittivity and dielectric loss tangent of the hollow particles, and from the viewpoint of improving the strength of the hollow particles, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more. As an upper limit, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less. From the viewpoint of ensuring that it fully contains a bifunctional crosslinking monomer, it is even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

[0163] [Non-crosslinking monomer]

[0164] The first polymerizable monomer may further include non-crosslinked monomers.

[0165] Monovinyl monomers are preferred as non-crosslinking monomers. A monovinyl monomer is a compound having a single polymerizable vinyl functional group. Examples of monovinyl monomers include: alkyl methacrylates such as 2-ethylhexyl methacrylate and lauryl methacrylate, which have alkyl groups with 6 or more carbon atoms; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, and halostyrene; monoolefin monomers such as ethylene, propylene, and butene; diene monomers such as butadiene and isoprene; vinyl carboxylic acid vinyl ester monomers such as vinyl acetate; halovinyl monomers such as vinyl chloride; dihaloethylene monomers such as vinylidene chloride; non-hydrophilic, non-crosslinking monomers such as vinylpyridine monomers; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, which have alkyl groups with 1 to 5 carbon atoms; methacrylamides such as methacrylamide, N-hydroxymethyl methacrylamide, and N-butoxymethyl methacrylamide and their derivatives; methacrylonitrile and its derivatives; and hydrophilic, non-crosslinking monomers such as non-crosslinking monomers containing polar groups.

[0166] As non-crosslinking monomers containing polar groups, examples of preferred non-crosslinking monomers include those containing polar groups selected from carboxyl, hydroxyl, sulfonic acid, amino, polyoxyethylene, and epoxy groups. More specifically, examples include: olefinic unsaturated carboxylic acid monomers such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; hydroxyl monomers such as (meth)acrylic acid-2-hydroxyethyl ester, (meth)acrylic acid-2-hydroxypropyl ester, and (meth)acrylic acid-4-hydroxybutyl ester; sulfonic acid monomers such as styrene sulfonic acid; amino monomers such as (meth)acrylic acid-dimethylaminoethyl ester and (meth)acrylic acid-diethylaminoethyl ester; polyoxyethylene monomers such as methoxy polyethylene glycol (meth)acrylate; and epoxy monomers such as (meth)acrylic acid-glycidyl ether, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether.

[0167] These non-crosslinked monomers can be used individually or in combination of two or more.

[0168] As a non-crosslinking monomer used as the first polymerizable monomer, from the viewpoint of improving the strength of hollow particles, a hydrophilic non-crosslinking monomer is preferred, more preferably an alkyl ester of (meth)acrylate having 1 to 5 carbon atoms, more preferably an alkyl ester of (meth)acrylate having 1 to 4 carbon atoms, and even more preferably methyl methacrylate.

[0169] In the first polymerizable monomer, the polymerizable monomer other than the crosslinking monomer is a non-crosslinking monomer. In 100 parts by mass of the first polymerizable monomer, the content of the non-crosslinking monomer in the first polymerizable monomer is preferably 0 to 25 parts by mass. From the viewpoints of suppressing the decrease in reactivity of the first polymerizable monomer, reducing the CTE, relative permittivity and dielectric loss tangent of the hollow particles, and improving the strength of the hollow particles, the content of the non-crosslinking monomer in the first polymerizable monomer is more preferably 20 parts by mass or less, further preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably the first polymerizable monomer does not contain non-crosslinking monomer.

[0170] The content of the first polymerizable monomer in the mixture is not particularly limited. From the viewpoint of balancing the porosity, particle size and mechanical strength of hollow particles, the content of the first polymerizable monomer is usually 15 to 55% by mass relative to the total mass of the components in the mixture excluding the aqueous medium (100% by mass), more preferably 25 to 40% by mass.

[0171] Furthermore, from the viewpoint of improving the mechanical strength of hollow particles, the content of the first polymerizable monomer is preferably 90% by mass or more, and more preferably 95% by mass or more, relative to the total mass of the solid components other than hydrocarbon solvents in the oil phase material of 100% by mass mixture.

[0172] (B) Polar components

[0173] The mixture can also contain polar components. By including polar components in the mixture, hollow particles that are not easily broken even with high porosity can be obtained.

[0174] As a polar component, organic acids or their metal salts, or polar resins described later, can be used.

[0175] Examples of organic acids include rosin acid and higher fatty acids. Examples of higher fatty acids include, for example, higher fatty acids with 10 to 25 carbon atoms that do not contain a carbon atom in the carboxyl group.

[0176] Examples of metals that can be used as metal salts for organic acids include alkali metals such as Li, Na, and K, and alkaline earth metals such as Mg and Ca, among which alkali metals are preferred, and at least one selected from Li, Na, and K is more preferred.

[0177] When using an organic acid or its metal salt as a polar component, the total content of the organic acid or its metal salt, relative to 100 parts by mass of the first polymerizable monomer and the hydrocarbon solvent, is preferably 0.0001 parts by mass or more and 0.1 parts by mass or less, more preferably 0.001 parts by mass or more and 0.01 parts by mass or less, and even more preferably 0.0015 parts by mass or more and 0.006 parts by mass or less. By setting the above content to the lower limit or above, the thickness of the hollow particle shell can be easily controlled, and the strength of the hollow particle can be improved. On the other hand, by setting the above content to the upper limit or below, the decrease in the content ratio of the polymerizable monomer can be suppressed, thus suppressing the decrease in shell strength and further suppressing the breakage of the hollow particle.

[0178] Polar resins are polymers containing repeating units that include heteroatoms. Examples include acrylic resins, polyester resins, and vinyl resins containing heteroatoms.

[0179] The aforementioned polar resin can be a homopolymer or copolymer of heteroatom-containing monomers, or a copolymer of heteroatom-containing monomers and heteroatom-free monomers. When the aforementioned polar resin is a copolymer of heteroatom-containing monomers and heteroatom-free monomers, from the viewpoint of easily controlling the particle size of the hollow particles, the proportion of heteroatom-containing monomer units in 100% by mass of all repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0180] The number-average molecular weight (Mn) of the aforementioned polar resin is not particularly limited, but is preferably in the range of 3,000 or more and 20,000 or less, more preferably in the range of 4,000 or more and 17,000 or less, and even more preferably in the range of 6,000 or more and 15,000 or less, based on the polystyrene equivalent value determined by gel permeation chromatography (GPC) using tetrahydrofuran. By setting the number-average molecular weight (Mn) of the aforementioned polar resin to the lower limit or above, the solubility of the polar resin is improved, making it easier to control the particle size of the hollow particles; by setting it to the upper limit or below, the reduction in shell strength can be suppressed.

[0181] When using a polar resin as the polar component, the content of the polar resin relative to 100 parts by mass of the first polymerizable monomer is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 0.3 parts by mass or more and 8.0 parts by mass or less, and even more preferably 0.5 parts by mass or more and 8.0 parts by mass or less. By setting the above content to the lower limit or above, the thickness of the hollow particle shell can be easily controlled, thereby improving the strength of the hollow particle. On the other hand, by setting the above content to the upper limit or below, the decrease in the content ratio of the polymerizable monomer can be suppressed, thus suppressing the decrease in shell strength and further suppressing the breakage of the hollow particle.

[0182] (C) Oil-soluble polymerization initiator

[0183] In this invention, the mixture preferably contains an oil-soluble polymerization initiator as the polymerization initiator. As a method for polymerizing droplets of the monomer composition after suspending the mixture, there are emulsion polymerization methods using water-soluble polymerization initiators and suspension polymerization methods using oil-soluble polymerization initiators. Suspension polymerization can be performed using oil-soluble polymerization initiators.

[0184] 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% by mass in water. Examples of oil-soluble polymerization initiators include benzoyl peroxide, lauroyl peroxide, tert-butylperoxy-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylpentanonitrile), and azobisisobutyronitrile.

[0185] When the total mass of the first polymerizable monomer in the mixture is taken as 100 parts by mass, the content of the 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. By keeping the content of the oil-soluble polymerization initiator at 0.1 to 10 parts by mass, the polymerization reaction is fully carried out, and the possibility of oil-soluble polymerization initiator residue after the polymerization reaction is completed is small, as is the possibility of unexpected side reactions.

[0186] (D) Hydrocarbon solvents

[0187] In this invention, a hydrocarbon solvent is used as a non-polymerizable organic solvent that is poorly soluble in water. The hydrocarbon solvent functions as a spacer material that forms hollow spaces within the particles. In the suspension process described later, a suspension of droplets containing the hydrocarbon solvent is obtained, dispersed in an aqueous medium. During the suspension process, phase separation occurs within the droplets of the monomer composition, resulting in the low-polarity hydrocarbon solvent easily agglomerating inside the droplets. Ultimately, within the droplets of the monomer composition, the hydrocarbon solvent is distributed inside the droplets according to its polarity, while other materials besides the hydrocarbon solvent are distributed around the droplets.

[0188] Furthermore, in the polymerization process described later, an aqueous dispersion containing hollow particles with an internal hydrocarbon solvent can be obtained. That is, by causing the hydrocarbon solvent to aggregate inside the particles, a hollow portion filled with hydrocarbon solvent is formed inside the obtained precursor particles.

[0189] There are no particular limitations on the types of hydrocarbon solvents. Examples of hydrocarbon solvents include: saturated hydrocarbon solvents such as butane, pentane, n-hexane, cyclohexane, heptane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and highly volatile solvents such as carbon disulfide and carbon tetrachloride.

[0190] The porosity of hollow particles can be adjusted by changing the amount of hydrocarbon solvent in the mixture. In the suspension process described later, oil droplets containing crosslinking monomers undergo polymerization in a state containing hydrocarbon solvent. Therefore, there is a tendency that the higher the content of hydrocarbon solvent, the higher the porosity of the resulting hollow particles.

[0191] Preferably, the proportion of saturated hydrocarbon solvent in a total of 100% by mass is 50% or more. This allows for sufficient phase separation within the droplets of polymerizable monomers, making it easy to obtain hollow particles with only one hollow portion, thus suppressing the formation of porous particles. From the viewpoint of further suppressing the formation of porous particles and from the viewpoint of easily achieving uniformity in the hollow portions of each hollow particle, the proportion of saturated hydrocarbon solvent is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0192] Furthermore, hydrocarbon solvents with 4 to 7 carbon atoms are preferred as hydrocarbon solvents. Hydrocarbon compounds with 4 to 7 carbon atoms are easily contained in the first precursor particles during the polymerization process and can be easily removed from the second precursor particles during the solvent removal process. Among these, hydrocarbon solvents with 5 or 6 carbon atoms are particularly preferred.

[0193] Furthermore, although not particularly limited, from the viewpoint that the hydrocarbon solvent is easily removed in the solvent removal process described later, a hydrocarbon solvent with a boiling point of 130°C or less is preferred, and a hydrocarbon solvent with a boiling point of 100°C or less is more preferred. Furthermore, from the viewpoint that it is easily contained within the precursor particles, a hydrocarbon solvent with a boiling point of 50°C or more is preferred, and a hydrocarbon solvent with a boiling point of 60°C or more is more preferred.

[0194] Furthermore, the hydrocarbon solvent 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. It can be considered that when the relative permittivity of the hydrocarbon solvent is sufficiently small, such as 3 or less, phase separation in the droplets of the monomer composition proceeds rapidly, easily forming hollow structures.

[0195] 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.

[0196] Heptane (1.9%), n-hexane (1.9%), cyclohexane (2.0%), benzene (2.3%), toluene (2.4%).

[0197] Regarding the relative permittivity at 20°C, one can refer to the values ​​recorded in well-known literature (e.g., Chemical Society of Japan, *Basic Handbook of Chemistry*, 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, for instance, the relative permittivity test performed according to section 23 of JIS C 2101:1999, with the measurement temperature set to 20°C.

[0198] In this invention, from the viewpoint of easily controlling the particle size of hollow particles, maintaining the strength of hollow particles while easily increasing porosity, and easily reducing the amount of residual hydrocarbon solvent in the particles, the content of hydrocarbon solvent in the mixture is preferably 50 parts by mass or more and 500 parts by mass or less relative to 100 parts by mass of the total mass of the first polymerizable monomer. More preferably, the content of hydrocarbon solvent in the mixture is 60 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the total mass of the first polymerizable monomer, further preferably 70 parts by mass or more and 300 parts by mass or less, and even more preferably 80 parts by mass or more and 200 parts by mass or less.

[0199] (E) Dispersant stabilizer

[0200] A dispersion stabilizer is a reagent used in a suspension process to disperse droplets of a monomer composition in an aqueous medium. In this invention, from the viewpoints of easily controlling the droplet size in the suspension, narrowing the particle size distribution of the resulting hollow particles, and preventing the shell from becoming too thin and the strength of the hollow particles from decreasing, an inorganic dispersion stabilizer is preferably used as the dispersion stabilizer.

[0201] Examples of inorganic dispersion stabilizers include: sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as alumina and titanium oxide; and inorganic compounds such as metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and iron hydroxide. One or more of these inorganic dispersion stabilizers can be used.

[0202] Among the above-mentioned inorganic dispersing stabilizers, water-insoluble inorganic metal salts such as sulfates, carbonates, phosphates, and metal hydroxides are preferred, metal hydroxides are more preferred, and magnesium hydroxide is particularly preferred.

[0203] Furthermore, in this invention, the water-insoluble inorganic metal salt is preferably an inorganic metal salt with a solubility of 0.5g or less in 100g of water.

[0204] In this invention, it is particularly preferred to use the product in the form of a water-insoluble inorganic dispersion stabilizer dispersed in an aqueous medium as colloidal particles, i.e., in the form of a colloidal dispersion containing water-insoluble inorganic dispersion stabilizer colloidal particles. This not only narrows the droplet size distribution of the monomer composition but also allows for easy and low residual amounts of inorganic dispersion stabilizer in the resulting hollow particles through washing.

[0205] Colloidal dispersions containing inorganic dispersant stabilizer colloidal particles that are poorly soluble in water can be prepared, for example, by reacting at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (other than alkaline earth metal hydroxides) in an aqueous medium.

[0206] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include barium hydroxide and calcium hydroxide.

[0207] As a water-soluble polyvalent metal salt, any polyvalent metal salt exhibiting water solubility other than those belonging to the aforementioned alkaline earth metal hydroxides can be used. Examples include: magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred. Furthermore, water-soluble polyvalent metal salts can be used individually or in combination of two or more.

[0208] There are no particular limitations on the method of reacting at least one of the above-mentioned alkali metal hydroxide and alkaline earth metal hydroxide with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium. For example, a method of mixing an aqueous solution of at least one of the above-mentioned alkali metal hydroxide and alkaline earth metal hydroxide with an aqueous solution of the water-soluble polyvalent metal salt can be cited.

[0209] The content of the dispersant stabilizer is not particularly limited, but is preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8.0 parts by mass, relative to the total mass of 100 parts by mass of the first polymerizable monomer and the hydrocarbon solvent. By setting the content of the dispersant stabilizer at or above the aforementioned lower limit, the droplets of the monomer composition can be sufficiently dispersed in the suspension in a non-agglomerated manner. On the other hand, by setting the content of the dispersant stabilizer at or below the aforementioned upper limit, the viscosity of the suspension can be prevented from increasing during granulation, thus avoiding the undesirable situation of the suspension clogging the granulator.

[0210] Furthermore, relative to 100 parts by weight of the aqueous medium, the content of the dispersant stabilizer is typically 2 parts by weight or more and 15 parts by weight or less, preferably 3 parts by weight or more and 8 parts by weight or less.

[0211] (F) Aquatic media

[0212] In this invention, an aqueous medium refers to a medium selected from water, hydrophilic solvents, and mixtures of water and hydrophilic solvents.

[0213] The hydrophilic solvent used in this invention is not particularly limited as long as it can be thoroughly mixed with water without phase separation. Examples of hydrophilic solvents include: alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0214] In aqueous media, water is preferred from the viewpoint of its high polarity. In the case of using a mixture of water and a hydrophilic solvent, from the viewpoint of forming droplets of monomeric compositions, it is important that the overall polarity of the mixture does not become too low.

[0215] In this case, for example, the mixing ratio (mass ratio) of water and hydrophilic solvent can be water:hydrophilic solvent = 99:1 to 50:50, etc.

[0216] A mixture can be obtained by mixing the above-mentioned materials with other materials as needed and stirring appropriately. In this mixture, the oil phase, containing the above-mentioned (A) first polymerizable monomer, (B) polar component, (C) oil-soluble polymerization initiator, and (D) hydrocarbon solvent, etc., is dispersed in an aqueous phase containing (E) dispersion stabilizer and (F) aqueous medium, etc., with a particle size of about several mm. Depending on the type of materials, the dispersion state of these materials in the mixture can be observed even with the naked eye.

[0217] In the preparation of the mixture, although a mixture can be obtained simply by mixing the aforementioned materials with other materials as needed and stirring appropriately, from the viewpoint of easily achieving uniformity, it is preferable to prepare the mixture by first preparing an oil phase containing a first polymerizable monomer, a polar component, and a hydrocarbon solvent, and an aqueous phase containing a dispersing stabilizer and an aqueous medium, and then mixing them. In this invention, it is preferable to use a colloidal dispersion in which a water-poorly soluble inorganic dispersing stabilizer is dispersed in an aqueous medium in the form of colloidal particles as the aqueous phase.

[0218] By preparing the oil phase and water phase separately in advance and then mixing them, it is possible to manufacture hollow particles with a uniform composition of shell portion.

[0219] (2) Suspension process

[0220] The suspension process is a process of preparing a suspension in which droplets of a monomer composition containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the above mixture.

[0221] There are no particular limitations on the suspension method used to form droplets of monomer compositions. Devices capable of strong stirring, such as (inline) emulsifying dispersers (such as the horizontal inline disperser manufactured by Taihei Kiko Co., Ltd., trade name: Milder, and the horizontal inline disperser manufactured by Eurotec Co., Ltd., trade name: Cavitron; and the vertical inline disperser manufactured by IKA Co., Ltd., trade name: DRS 2000 / 5, etc.) and high-speed emulsifying dispersers (such as the TKHomo Mixer MARK II type manufactured by Pleximix Co., Ltd.), can be used.

[0222] In the suspension prepared during the suspension process, droplets of the monomer composition containing the aforementioned oleophilic material and having a particle size of approximately 1–60 μm are uniformly dispersed in an aqueous medium. These droplets of monomer composition are not easily observed with the naked eye but can be observed using known observation equipment such as an optical microscope.

[0223] During the suspension process, phase separation occurs within the droplets of the monomer composition, causing the low-polarity hydrocarbon solvent to tend to aggregate inside the droplets. As a result, the resulting droplets are characterized by the hydrocarbon solvent distributed inside and the non-hydrocarbon solvent material distributed at their edges.

[0224] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in the suspension process. Figure 2 A cross-section of droplet 10 of the monomer composition is schematically shown. Additionally, Figure 2 This is for illustrative purposes only; the suspension in this invention is not limited to... Figure 2 The suspension shown. Figure 2 Part of the above Figure 1 (2) Corresponds to.

[0225] exist Figure 2 The diagram shows the dispersion of droplets 10 of the monomer composition and the first polymerizable monomer 4c dispersed in the aqueous medium 1. The droplets 10 are formed by surrounding the oil-soluble monomer composition 4 with a dispersion stabilizer 3.

[0226] The monomer composition contains an oil-soluble polymerization initiator 5, a first polymerizable monomer, and a hydrocarbon solvent (none are shown).

[0227] Droplet 10 is a tiny oil droplet containing monomer composition 4, and oil-soluble polymerization initiator 5 generates polymerization initiation free radicals inside the tiny oil droplet. Therefore, precursor particles of the target particle size can be manufactured without causing the tiny oil droplets to overgrow.

[0228] In this suspension polymerization method using an oil-soluble polymerization initiator, there is no opportunity for the polymerization initiator to come into contact with the polymerizable monomer 4c dispersed in the aqueous medium 1. Therefore, by using an oil-soluble polymerization initiator, it is possible to suppress the formation of excess resin particles, such as smaller dense particles other than the target hollow resin particles.

[0229] (3) Polymerization process

[0230] (3-1) First polymerization process

[0231] In the above manufacturing method, the polymerization process is carried out in two stages.

[0232] In the first polymerization step, a first precursor composition is prepared by supplying the suspension to the polymerization reaction and carrying out a first polymerization reaction until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more. This preparation includes first precursor particles having a shell of a polymer containing the first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0233] In the first polymerization reaction, by supplying droplets of the monomer composition to the polymerization reaction in a state containing a hydrocarbon solvent, the polymerization reaction can easily proceed while maintaining its shape. Therefore, in the first polymerization reaction, the size and porosity of the resulting hollow particles can be easily adjusted by regulating the amount of hydrocarbon solvent, the amount of polar component, and the type of dispersant stabilizer. Furthermore, since the first polymerizable monomer and the hydrocarbon solvent are used in combination, the hydrocarbon solvent has low polarity relative to the shell of the first precursor particle, and the hydrocarbon solvent does not readily bind to the shell, thus allowing sufficient phase separation to occur and easily forming only a hollow portion.

[0234] In the first polymerization reaction, there are no particular limitations on the polymerization method, and it can be, for example, batch (intermittent), semi-continuous, or continuous.

[0235] In the first polymerization reaction, the polymerization temperature is preferably 40–80°C, more preferably 50–70°C.

[0236] Furthermore, in the first polymerization reaction, the heating rate at which the temperature is raised to the polymerization temperature is preferably 10°C / h to 60°C / h, and more preferably 15°C / h to 55°C / h.

[0237] Furthermore, the reaction time of the first polymerization reaction is preferably 0.5 to 5 hours, more preferably 1 to 3 hours.

[0238] In the above manufacturing method, the first polymerization reaction is carried out until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more.

[0239] Furthermore, in this invention, the polymerization conversion rate is determined using the following formula (A) based on the mass of the solid component of the first precursor particles obtained through the first polymerization reaction and the mass of the first polymerizable monomer that remains directly in an unreacted state after the first polymerization reaction. In this invention, the solid component refers to all components except the solvent; liquid polymerizable monomers and the like are included in the solid component. Furthermore, the mass of the unreacted first polymerizable monomer can be determined using gas chromatography (GC).

[0240]

[0241] (3-2) Second polymerization process

[0242] In the second polymerization step, a second polymerization reaction is carried out by adding a second polymerizable monomer with a solubility of 0.3 g / L or more in distilled water at 20°C to the first precursor composition obtained in the first polymerization step, thereby preparing a second precursor composition containing the following second precursor particles, wherein the second precursor particles have a shell of a polymer containing the first polymerizable monomer and the second polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0243] In the second polymerization reaction, the polymerization reaction takes place with the second polymerizable monomer inside the shell of the first precursor particle. The shell of the first precursor particle promotes thermal motion by absorbing the second polymerizable monomer. Therefore, it can be inferred that in the second polymerization reaction, the polymerizable functional groups of the first polymerizable monomer that remain directly in the shell in an unreacted state undergo polymerization with the second polymerizable monomer to form a dense cross-linked structure.

[0244] As the second polymerizable monomer, there is no particular limitation as long as the polymerizable monomer has a solubility of 0.3 g / L or more in distilled water at 20°C. However, from the viewpoints of reducing the CTE, relative permittivity, and dielectric loss tangent of the hollow particles, and improving the strength of the hollow particles, a non-crosslinked monomer with a solubility of 0.3 g / L or more in distilled water at 20°C, i.e., a hydrophilic non-crosslinked monomer, is preferred. As the hydrophilic non-crosslinked monomer used as the second polymerizable monomer, examples include, for instance, hydrophilic non-crosslinked monomers that can be used as the first polymerizable monomer. From the viewpoints of reducing the CTE, relative permittivity, and dielectric loss tangent of the hollow particles, and improving the strength of the hollow particles, at least one selected from alkyl (meth)acrylates having 1 to 5 carbon atoms, (meth)acrylonitrile and its derivatives, and non-crosslinked monomers containing polar groups is preferred.

[0245] The alkyl group of the above-mentioned (meth)acrylate preferably has 1 to 4 carbon atoms, more preferably 1 to 3. Methyl methacrylate is particularly preferred as the above-mentioned (meth)acrylate.

[0246] As the above-mentioned non-crosslinked monomers containing polar groups, epoxy-containing monomers, hydroxyl-containing monomers, and amino-containing monomers are preferred. Among the epoxy-containing monomers of the above-mentioned non-crosslinked monomers containing polar groups, glycidyl (meth)acrylate is preferred, and among the hydroxyl-containing monomers, 2-hydroxyethyl methacrylate is preferred.

[0247] Furthermore, as the second polymerizable monomer, a hydrophilic crosslinking monomer with a solubility of 0.3 g / L or more in distilled water at 20°C can be used. Examples of hydrophilic crosslinking monomers used as the second polymerizable monomer include, for example, the same hydrophilic crosslinking monomers that can be used as the first polymerizable monomer. Among the hydrophilic crosslinking monomers used as the second polymerizable monomer, those containing hydroxyl or amino groups are preferred. Examples of hydrophilic crosslinking monomers containing hydroxyl groups are, for example, 2-hydroxy-3-methacryloyloxypropyl acrylate, and examples of hydrophilic crosslinking monomers containing amino groups are, for example, diallylamine.

[0248] Furthermore, from the viewpoint that the second polymerizable monomer easily promotes thermal motion and increases the strength of hollow particles by entering the shell of the first precursor particles, the solubility of the second polymerizable monomer in distilled water at 20°C is preferably 2 g / L or more, more preferably 10 g / L or more, and even more preferably 15 g / L or more. Additionally, there is no particular upper limit to the solubility of the second polymerizable monomer in distilled water at 20°C, and it is typically 80 g / L or less.

[0249] Furthermore, from the viewpoint that the second polymerizable monomer entering the shell of the first precursor particle easily promotes thermal motion, reduces the CTE, relative permittivity, and dielectric loss tangent of the hollow particle, and easily improves the strength of the hollow particle, the molecular weight of the second polymerizable monomer is preferably 200 or less, more preferably 100 or less. The lower limit of the molecular weight of the second polymerizable monomer is not particularly limited, but is generally 50 or more.

[0250] The amount of the second polymeric monomer added is preferably 3 to 15 parts by mass, more preferably 4 to 10 parts by mass, relative to 100 parts by mass of the first polymeric monomer. When the amount of the second polymeric monomer added is at or above the lower limit mentioned above, the effect of promoting the polymerization reaction by adding the second polymeric monomer is improved, the cross-linked structure of the shell of the hollow particle becomes denser, thereby reducing the CTE, relative permittivity, and dielectric loss tangent of the hollow particle, and improving the strength of the hollow particle. On the other hand, when the amount of the second polymeric monomer added is below or above the upper limit mentioned above, the decrease in the content ratio of the first polymeric monomer relative to the total polymeric monomer used to form the shell can be suppressed. Since the first polymeric monomer contains more cross-linking monomers, by suppressing the decrease in the content ratio of the first polymeric monomer, hollow particles with excellent strength containing more cross-linked structures formed by cross-linking monomers can be obtained.

[0251] In the second polymerization reaction following the addition of the second polymerizable monomer, the polymerization method is not particularly limited, and the same polymerization method as that used in the first polymerization reaction can be employed.

[0252] In the second polymerization reaction, the polymerization temperature is preferably 40–80°C, more preferably 50–70°C.

[0253] The reaction time for the second polymerization reaction is preferably 1 to 6 hours, more preferably 2 to 4 hours.

[0254] According to the above manufacturing method, the residual amount of unreacted polymerizable monomers after the second polymerization reaction is preferably 750 ppm or less, more preferably 500 ppm or less, and even more preferably 300 ppm or less.

[0255] Furthermore, in this invention, the residual amount of unreacted polymeric monomer after the second polymerization reaction refers to the ratio of the mass of the polymeric monomer remaining directly in an unreacted state to the mass of the solid component of the hollow particles obtained through the second polymerization reaction. Additionally, the mass of the unreacted polymeric monomer can be determined using gas chromatography (GC).

[0256] (4) Solid-liquid separation process

[0257] This process involves solid-liquid separation of the second precursor composition, which contains hollow particles (second precursor particles) containing a hydrocarbon solvent, obtained through the above polymerization process, thereby obtaining a solid component containing the second precursor particles.

[0258] There is no particular limitation on the method for solid-liquid separation of the second precursor composition, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and settling. Among these, centrifugation or filtration can be used, and from the viewpoint of ease of operation, centrifugation can be used.

[0259] 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. Examples of pre-drying processes include pre-drying the solid components obtained after the solid-liquid separation process using a drying device such as a dryer or a hand dryer.

[0260] (5) Solvent removal process

[0261] This process is to remove the hydrocarbon solvent contained in the hollow particles (second precursor particles) obtained through the above solid-liquid separation process.

[0262] By removing the hydrocarbon solvent contained in the second precursor particles from the gas, and replacing the hydrocarbon solvent inside the second precursor particles with air, hollow particles filled with gas can be obtained.

[0263] Strictly speaking, "in the gas" in this process refers to an environment where there is absolutely no liquid component outside the second precursor particles, or an environment where only a very small amount of liquid component exists outside the second precursor particles, to a degree that does not affect the removal of hydrocarbon solvents. In other words, "in the gas" can also refer to a state where the second precursor particles are not present in the slurry, or a state where the second precursor particles are present in the dry powder. That is, in this process, it is important to remove hydrocarbon solvents in an environment where the second precursor particles are in direct contact with the external gas.

[0264] There is no particular limitation on the method for removing the hydrocarbon solvent from the second precursor particles in the gas, and known methods can be used. Examples of such methods include vacuum drying, heating drying, airflow drying, or a combination of these methods.

[0265] Especially when using a heat drying method, the heating temperature needs to be set above the boiling point of the hydrocarbon solvent and below the highest temperature at which the shell structure of the second precursor particles will not be damaged. Therefore, depending on the composition of the shell in the second precursor particles and the type of hydrocarbon solvent, the heating temperature can be set to, for example, 50–200°C, 70–200°C, or 100–200°C.

[0266] By performing a drying operation in a gas, the hydrocarbon solvent inside the second precursor particles is replaced by an external gas, resulting in hollow particles with the gas occupying the hollow part.

[0267] There are no particular limitations on the drying environment; it can be appropriately selected based on the intended use of the hollow particles. Suitable drying environments include, for example, air, oxygen, nitrogen, and argon. Furthermore, once the hollow particles are filled with gas, vacuum drying can be performed to obtain hollow particles with a temporarily vacuum-like interior.

[0268] Alternatively, instead of performing solid-liquid separation on the slurry-like second precursor composition obtained in the polymerization process, the hydrocarbon solvent contained in the second precursor particles is replaced with the aqueous medium of the slurry in the slurry containing the second precursor particles, thereby removing the hydrocarbon solvent.

[0269] In this method, an inactive gas is bubbled into the second precursor composition at a temperature above 35°C below the boiling point of the hydrocarbon solvent, thereby removing the hydrocarbon solvent contained in the second precursor particles.

[0270] Here, when the aforementioned hydrocarbon solvent is a mixed solvent containing multiple hydrocarbon solvents and has multiple boiling points, in the solvent removal process, the boiling point of the hydrocarbon solvent refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, that is, the highest boiling point among multiple boiling points.

[0271] From the viewpoint of reducing the residual amount of hydrocarbon solvent in the hollow particles, the temperature at which the inactive gas is bubbled into the second precursor composition is preferably a temperature at least 30°C below the boiling point of the hydrocarbon solvent, and more preferably a temperature at least 20°C below the boiling point of the hydrocarbon solvent. Furthermore, the temperature during bubbling is generally set to a temperature above the polymerization temperature in the aforementioned polymerization step. While not particularly limited, the temperature during bubbling can be set to 50°C or higher and 100°C or lower.

[0272] There are no particular limitations on the inert gas that can be blown in; examples include nitrogen and argon.

[0273] There are no particular limitations on the conditions for bubbling. The conditions can be adjusted appropriately according to the type and amount of hydrocarbon solvent to remove the hydrocarbon solvent contained in the second precursor particles. For example, inactive gas can be bubbled in at a rate of 1 to 3 L / min for 1 to 10 hours.

[0274] In this method, an aqueous slurry containing an aqueous medium is obtained from the second precursor particles. The hollow particles obtained by solid-liquid separation of the slurry are dried to remove the aqueous medium from the hollow particles, thereby obtaining hollow particles with gas occupying the hollow part.

[0275] The method of obtaining hollow particles with gas-filled hollow sections by solid-liquid separation of a slurry-like second precursor composition and removal of the hydrocarbon solvent from the second precursor particles in a gaseous atmosphere has the advantage that the hollow particles are less likely to break during the hydrocarbon solvent removal process, compared to the method of solid-liquid separation of a slurry containing second precursor particles and an aqueous medium, followed by removal of the aqueous medium from the second precursor particles in a gaseous atmosphere, and removal of the hydrocarbon solvent from the second precursor particles in a gaseous atmosphere.

[0276] Furthermore, when the hydrocarbon solvent contained in the second precursor particles is replaced with water, there is a problem that 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. As a way to prevent this problem, one could consider, for example, removing the hydrocarbon solvent by alkali swelling of the particle shell after the slurry has reached a pH of 7 or higher. In this case, because the particle shell becomes flexible, the replacement of the hydrocarbon solvent with water inside the particles occurs rapidly.

[0277] Alternatively, as a method to remove the hydrophobic organic solvent contained in the precursor particles by solid-liquid separation of the slurry-like precursor composition obtained in the polymerization process after the polymerization process and before the solid-liquid separation process, methods such as evaporating and distilling off the hydrophobic organic solvent contained in the precursor particles from the precursor composition under a specified pressure (high pressure, normal pressure, or reduced pressure); or introducing inactive gases such as nitrogen, argon, or helium, or water vapor into the precursor composition under a specified pressure (high pressure, normal pressure, or reduced pressure) and evaporating and distilling off the solvent.

[0278] (6) Other

[0279] In addition to the processes described in (1) to (5) above, a cleaning process (6-a) and a hollow part replacement process (6-b) below may be added.

[0280] (6-a) Cleaning process

[0281] The cleaning process refers to the process of adding acid or alkali to remove the dispersant stabilizer remaining in the second precursor composition containing the second precursor particles before the aforementioned solid-liquid separation process. When the dispersant stabilizer used is an inorganic dispersant stabilizer soluble in acid, it is preferable to add acid to the second precursor composition containing the second precursor particles for cleaning. On the other hand, when the dispersant stabilizer used is an inorganic compound soluble in alkali, it is preferable to add alkali to the second precursor composition containing the second precursor particles for cleaning.

[0282] Furthermore, when using an acid-soluble inorganic dispersion stabilizer as the dispersion stabilizer, adding an acid to the second precursor composition containing the second precursor particles is preferably done by adjusting the pH to 6.5 or lower, more preferably to 6 or lower. As the added acid, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as formic acid and acetic acid, can be used. From the viewpoint of high removal efficiency of the dispersion stabilizer and low burden on manufacturing equipment, sulfuric acid is particularly preferred.

[0283] (6-b) Re-displacement process of the hollow section

[0284] The hollow particle re-displacement process refers to the process of replacing the gas or liquid inside the hollow particles with other gases or liquids. Through this displacement, the internal environment of the hollow particles can be changed, molecules can be selectively sealed inside the hollow particles, and the internal chemical structure of the hollow particles can be modified according to the intended use.

[0285] 3. Applications of hollow granules

[0286] The hollow particles of the present invention have excellent strength, making them less prone to breakage when mixed with other materials or during molding after mixing. When added to molded articles, they perform excellently as lightweight, heat-insulating, sound-insulating, and shock-absorbing materials. Therefore, they are preferred as additives for molded articles, and particularly preferred as additives for resin-molded articles. The hollow particles of the present invention can be contained as fillers even in molded articles formed using, for example, thermoplastic or thermosetting resins, and in molded articles formed using materials containing thermoplastic or thermosetting resins and further containing organic or inorganic fibers.

[0287] Examples of uses for the hollow particles of the present invention include, for instance, as components for reflective materials, heat-insulating materials, sound-insulating materials, and low-dielectric materials used in various fields such as automobiles, electrical engineering, electronics, construction, aerospace, and space; food containers; footwear such as athletic shoes and sandals; appliance parts; bicycle parts; stationery; tools; and filaments for 3D printers. The hollow particles of the present invention are particularly preferred as additives in resin compositions used in the electrical or electronic fields because they have low CTE, low relative permittivity, and low dielectric loss tangent. For example, the hollow particles of the present invention are preferably used as materials for electronic circuit boards. Specifically, by containing the hollow particles of the present invention in the insulating resin layer of the electronic circuit board, the CTE, relative permittivity, and dielectric loss tangent of the insulating resin layer can be reduced. In addition, the hollow particles of the present invention are preferably used as additives in semiconductor materials such as interlayer insulating materials, dry film resists, solder resists, bonding wires, magnetic wires, semiconductor sealing materials, epoxy sealing materials, mold underfills, underfills, die bond pastes, buffer coats, copper-clad laminates, flexible substrates, high-frequency component modules, antenna modules, and automotive radar. Among these, they are particularly preferred as additives in semiconductor materials such as interlayer insulating materials, solder resists, magnetic wires, epoxy sealing materials, underfills, buffer coats, copper-clad laminates, flexible substrates, high-frequency component modules, antenna modules, and automotive radar.

[0288] Furthermore, the hollow particles of this invention have high porosity, are not easily broken, and exhibit excellent heat resistance, thus meeting the requirements for heat insulation and cushioning (shock absorption) of inner coating materials, as well as the heat resistance required for applications in thermal paper. In addition, the hollow particles of this invention are also useful as plastic pigments with excellent gloss and hiding power.

[0289] Furthermore, the hollow particles of the present invention can be filled with useful ingredients such as fragrances, chemicals, pesticides, and ink components through impregnation, depressurization, or pressurization impregnation, and thus can be used for various purposes depending on the contents contained therein.

[0290] 4. Resin composition

[0291] The resin composition of the present invention is characterized by containing the hollow particles and matrix resin described above.

[0292] The resin composition of the present invention is typically obtained by mixing or kneading the hollow particles of the present invention described above, a matrix resin, and additives added as needed, for example, the particles themselves. In the resin composition containing the hollow particles of the present invention, since the hollow particles of the present invention are not easily broken during mixing or kneading and subsequent molding, the effects of lightweighting, low CTE, and low dielectric constant brought about by the hollow particles can be achieved.

[0293] The base resin used in the resin composition of the present invention is not particularly limited, but thermoplastic resin or thermosetting resin is preferred.

[0294] There are no particular limitations on the thermoplastic resins mentioned above; any known thermoplastic resin can be used, such as: polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimide, polyamide-imide, polyether-imide, polyether ketone-ketone, polyvinyl chloride, polystyrene, poly(meth)acrylate, polycarbonate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, thermoplastic elastomers, etc.

[0295] These thermoplastic resins can be used individually or in combination of two or more.

[0296] There are no particular limitations on the aforementioned thermosetting resins; any known thermosetting resin can be used, such as: phenolic resins, melamine resins, urea resins, unsaturated polyester resins, epoxy resins, polyurethane resins, silicone resins, alkyd resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, and benzo[a]benzene resins. Azide resins, urea-formaldehyde resins, allyl resins, aniline resins, maleimide resins, bismaleimide triazine resins, liquid crystal polyester resins, vinyl ester resins, unsaturated polyester resins, cyanate ester resins, polyetherimide resins, etc.

[0297] These thermosetting resins can be used individually or in combination of two or more.

[0298] Furthermore, the aforementioned thermosetting resin is preferably used in conjunction with additives such as curing agents and curing catalysts for curing the resin. As the aforementioned curing agents and curing catalysts, known curing agents and curing catalysts can be used, and can be appropriately selected according to the type of resin. Examples include amines, acid anhydrides, imidazoles, thiols, phenols, naphthols, and benzo[a]benzene. Azides, cyanates, and carbodiimides, etc.

[0299] Furthermore, when the resin composition of the present invention contains a thermosetting resin, it may further contain solvents for dissolving or dispersing the components, as needed.

[0300] When using the resin composition of the present invention as a material for electronic circuit boards, it is preferable to use an insulating resin as the matrix resin.

[0301] As an insulating resin, there are no particular limitations; examples include epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, silicone resins, and benzo[a]benzene resins. Resins include aziridine resins, melamine resins, urea-formaldehyde resins, allyl resins, phenol resins, unsaturated polyester resins, polyurethane resins, and aniline resins. Among these, epoxy resins, thermosetting polyimide resins, modified polyphenylene ether resins, silicone resins, and benzo[a]benzene resins are preferred. Azide resins and melamine resins, etc. These insulating resins can be used alone or in combination of two or more.

[0302] In the total mass percentage (100% by mass) of the resin composition of the present invention, the content of the matrix resin is not particularly limited, but is preferably 50 to 95% by mass. By setting the content of the matrix resin to the lower limit value or above, the moldability of the resin composition when molded into a molded article is excellent, and the resulting molded article has excellent mechanical strength. On the other hand, by setting the content of the matrix resin to the upper limit value or below, since it can fully contain the hollow particles of the present invention, the hollow particles of the present invention can impart properties such as lightweight, low CTE, and low dielectric constant to the resin composition.

[0303] Furthermore, in this invention, when the base resin is a thermosetting resin, the base resin content also includes additives such as curing agents and curing catalysts for curing the resin.

[0304] In the total mass percentage (100% by mass) of the resin composition of the present invention, the content of the hollow particles of the present invention is not particularly limited, but is preferably 5 to 50% by mass. By making the content of hollow particles at or above the aforementioned lower limit, the resin composition can be endowed with properties such as lightweight, low CTE, and low dielectric constant resulting from the hollow particles of the present invention. On the other hand, by making the content of hollow particles at or below the aforementioned upper limit, it can be made to fully contain the matrix resin, thereby improving moldability and mechanical strength.

[0305] In addition to the hollow particles and matrix resin of the present invention, the resin composition of the present invention may further contain additives such as ultraviolet absorbers, colorants, heat stabilizers, fillers, and solvents as needed, without impairing the effects of the present invention.

[0306] Furthermore, the resin composition of the present invention may further comprise organic or inorganic fibers such as carbon fiber, glass fiber, aromatic polyamide fiber, and polyethylene fiber.

[0307] The resin composition of the present invention can be obtained, for example, by mixing the hollow particles of the present invention described above, the matrix resin, and further additives and solvents as needed.

[0308] When the matrix resin in the resin composition of the present invention is a thermoplastic resin, it can also be mixed by melt-blending the hollow particles of the present invention described above and further additives as needed into the molten thermoplastic resin. The resin composition of the present invention obtained as described above can be a liquid resin composition, or it can be a resin molded article formed by molding a liquid resin composition using known methods.

[0309] The resin composition of the present invention can be used as a molded article. Because the molded article of the resin composition of the present invention contains the hollow particles of the present invention, it can effectively utilize the effects of lightweight, low CTE, and low dielectric constant brought about by the hollow particles of the present invention.

[0310] When the resin composition of the present invention contains a thermoplastic resin as a matrix resin and is a liquid resin composition formed by melting the resin, the liquid resin composition can be molded into a desired shape by using known molding methods such as extrusion molding, injection molding, compression molding, and compression molding to obtain a molded body.

[0311] In the case where the resin composition of the present invention is a liquid resin composition formed by containing hollow particles in a liquid matrix resin before the curing reaction, or a liquid resin composition formed by dissolving or dispersing each component in a solvent, a molded article can be obtained by applying the liquid resin composition to a support and drying and curing it as needed.

[0312] Materials that can be used as the aforementioned support include, for example, resins such as polyethylene terephthalate and polyethylene naphthalate; and metals such as copper, aluminum, nickel, chromium, gold, and silver.

[0313] As a method for applying liquid resin compositions, known methods can be used, such as dip coating, roller coating, curtain coating, mold coating, slot coating, gravure coating, etc.

[0314] When the liquid resin composition contains a solvent, it is preferable to dry the resin composition after the above-described coating. The drying temperature is preferably a temperature at which the base resin does not cure, typically 20°C or higher and 200°C or lower, preferably 30°C or higher and 150°C or lower. Furthermore, the drying time is typically 30 seconds or higher and 1 hour or lower, preferably 1 minute or higher and 30 minutes or lower.

[0315] The curing reaction of the resin composition is carried out by a method appropriate to the type of matrix resin, without particular limitation. When the matrix resin is included and cured by heat, the heating temperature for the curing reaction can be appropriately adjusted according to the type of resin, without particular limitation, typically 30°C or higher and 400°C or lower, preferably 70°C or higher and 300°C or lower, more preferably 100°C or higher and 200°C or lower. Furthermore, the curing time is 5 minutes or more and 5 hours or less, preferably 30 minutes or more and 3 hours or less. The heating method is not particularly limited; for example, an electric oven can be used.

[0316] In addition, the matrix resin contained in the liquid resin composition formed by dissolving or dispersing the components in a solvent can be either a thermosetting resin or a thermoplastic resin.

[0317] The shape of the molded article is not particularly limited and can be any shape that can be molded using the resin composition of the present invention, such as sheet, film, plate, tube, and other various three-dimensional shapes. Furthermore, when the molded article contains fibers, the fibers in the molded article can be in the form of nonwoven fabric. Additionally, when the molded article contains fibers, it can also be a molded article of a resin composition containing the hollow particles of the present invention added to a fiber-reinforced plastic containing the aforementioned resin and fibers.

[0318] Applications of the resin composition of the present invention include components such as reflective materials, heat insulation materials, sound insulation materials, and low dielectric materials used in various fields such as automobiles, electrical engineering, electronics, construction, aviation, and aerospace; food containers; footwear such as athletic shoes and sandals; appliance parts; bicycle parts; stationery; and tools. Because of its low CTE, low relative permittivity, and low dielectric loss tangent, the resin composition of the present invention is particularly preferred for use as an insulating resin layer in the electrical or electronic fields.

[0319] Example

[0320] 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.

[0321] [Example 1]

[0322] (1) Mixture preparation process

[0323] First, mix the following materials to form an oil phase.

[0324] First polymerizable monomer: 80 parts of ethylene glycol dimethacrylate and 20 parts of pentaerythritol tetraacrylate

[0325] 2,2'-Azobis(2,4-dimethylvalerate) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) 3 parts

[0326] 0.007 parts of rosin acid

[0327] 120 parts of cyclohexane

[0328] Next, in a stirred tank at room temperature, while stirring, an aqueous solution of sodium hydroxide (alkali metal hydroxide) containing 12.1 parts dissolved in 121 parts of ion-exchanged water was slowly added to an aqueous solution of magnesium hydroxide colloid (a water-insoluble metal hydroxide colloid) containing 17.1 parts dissolved in 494 parts of ion-exchanged water to prepare a magnesium hydroxide colloid (a water-insoluble metal hydroxide colloid) dispersion (4 parts of magnesium hydroxide), thus forming an aqueous phase.

[0329] A mixture is prepared by mixing the aqueous and oil phases.

[0330] (2) Suspension process

[0331] The mixture obtained in the above-mentioned mixture preparation process is suspended by stirring in a disperser (manufactured by Paramicus Corporation, trade name: HOMOMIXER) at 4000 rpm for 1 minute to prepare a suspension of droplets of the monomer composition containing cyclohexane dispersed in water.

[0332] (3) Polymerization process

[0333] The suspension obtained in the above suspension process was heated from 40°C to 65°C over a nitrogen atmosphere for 30 minutes (heating rate: 50°C / hour), and stirred at 65°C for 1 hour and 30 minutes to carry out a first polymerization reaction, yielding a first precursor composition containing first precursor particles. The polymerization conversion rate at the end of the first polymerization reaction was 99.2% by mass. Next, 5 parts of methyl acrylate as a second polymerizable monomer were added to a stirred tank, and the mixture was stirred at 65°C for 2 hours and 30 minutes under a nitrogen atmosphere to carry out a second polymerization reaction. Through this second polymerization reaction, a second precursor composition containing second precursor particles containing cyclohexane was obtained.

[0334] (4) Cleaning process and solid-liquid separation process

[0335] The above-mentioned second precursor composition was washed with dilute sulfuric acid (25°C, 10 minutes) to bring the pH to below 5.5. Next, after separating the water by filtration, 200 parts of fresh ion-exchanged water were added for re-slurrying. The mixture was repeatedly washed with water (washing, filtration, dehydration) at room temperature (25°C), followed by filtration to obtain the solid component. The obtained solid component was dried using a dryer at 40°C to obtain second precursor particles containing cyclohexane.

[0336] (5) Solvent removal process

[0337] The second precursor particles obtained in the above solid-liquid separation process were heated in a vacuum dryer at 200°C for 6 hours to remove the hydrocarbon solvent contained in the particles, thereby obtaining the hollow particles of Example 1. Based on the observation results of a scanning electron microscope and the porosity value, the obtained hollow particles were confirmed to be spherical and have a hollow portion.

[0338] [Examples 2-3 and 8]

[0339] In Example 1, the material of the second polymerizable monomer added in the above "(3) polymerization process" is shown in Table 1. Otherwise, the hollow particles of Examples 2-3 and 8 are manufactured according to the same steps as in Example 1.

[0340] [Example 4]

[0341] In Example 1, in the above "(1) Mixture Preparation Step", the material and amount of the first polymerizable monomer are as shown in Table 1. Otherwise, the hollow particles of Example 4 are manufactured according to the same steps as in Example 1.

[0342] [Examples 5-6]

[0343] In Example 1, the amount of the second polymerizable monomer added in the above "(3) polymerization step" is shown in Table 1. Otherwise, the hollow particles of Examples 5 and 6 are manufactured according to the same steps as in Example 1.

[0344] [Example 7]

[0345] In Example 1, in the above "(1) Mixture Preparation Step", the materials and amounts of the first polymerizable monomer and the materials and amounts of the hydrocarbon solvent are as shown in Table 1. Otherwise, the hollow particles of Example 7 are manufactured according to the same steps as in Example 1.

[0346] [Comparative Example 1]

[0347] In Example 1, in the above "(3) Polymerization process", no second polymerizable monomer was added and no second polymerization reaction was carried out. Otherwise, the hollow particles of Comparative Example 1 were manufactured according to the same steps as in Example 1.

[0348] [Comparative Example 2]

[0349] In Example 1, in the above-mentioned "(3) polymerization process", 5 parts of styrene (with a solubility of 0.2 g / L in distilled water at 20°C) was added as the second polymerizable monomer to replace 5 parts of methyl acrylate. Otherwise, the hollow particles of Comparative Example 2 were manufactured according to the same steps as in Example 1.

[0350] [Comparative Example 3]

[0351] In Example 1, in the above "(1) Mixture Preparation Step", the amount of hydrocarbon solvent is as shown in Table 1. Otherwise, the hollow particles of Comparative Example 3 are manufactured according to the same steps as in Example 1.

[0352] [Comparative Example 4]

[0353] In Example 1, in the above "(1) Mixture Preparation Step", the material and amount of the first polymerizable monomer are as shown in Table 1. In the above "(3) Polymerization Step", no second polymerizable monomer is added and no second polymerization reaction is carried out. Otherwise, the hollow particles of Comparative Example 4 are manufactured according to the same steps as in Example 1.

[0354] [Comparative Example 5]

[0355] In Example 1, in the above "(1) Mixture Preparation Step", the materials and amounts of the first polymerizable monomer and the hydrocarbon solvent are as shown in Table 1. In the above "(3) Polymerization Step", no second polymerizable monomer is added and no second polymerization reaction is carried out. Otherwise, the hollow particles of Comparative Example 5 are manufactured according to the same steps as in Example 1.

[0356] [Table 1]

[0357]

[0358] [Evaluation]

[0359] 1. Polymerization conversion rate

[0360] In the polymerization processes of each of the examples and comparative examples, 50 g of the first precursor composition produced in the first polymerization reaction was taken, and the first precursor particles (including moisture and hydrocarbon solvents) contained in the first precursor composition were obtained by pressure filtration and accurately weighed to the unit of 1 mg. After adding 27 g of ethyl acetate to about 3 g of accurately weighed first precursor particles and stirring for 15 minutes, 13 g of methanol was added and further stirred for 10 minutes. The resulting solution was allowed to stand to precipitate the insoluble components, and the supernatant of the solution was taken as the measurement sample. 2 μL of the measurement sample was injected into a gas chromatograph, and the amount of polymerizable monomer in the sample was quantitatively determined by gas chromatography (GC) under the following conditions, and it was taken as the mass of the unreacted first polymerizable monomer. In addition, by drying and pressurizing the first precursor particles obtained by filtration at 200 °C for 2 hours to remove moisture and hydrocarbon solvents, the mass of the solid component of the first precursor particles was determined. Then, the polymerization conversion rate was calculated by the following formula (A).

[0361]

[0362] <GC conditions>

[0363] Column: TC-WAX (0.25 mm × 30 m)

[0364] Column temperature: 80 °C

[0365] Injection temperature: 200 °C

[0366] FID detection side temperature: 200 °C

[0367] For the hollow particles obtained in each of the examples and comparative examples, the content ratio (mass %) of each monomer unit in the polymer contained in the shell is shown in Table 2.

[0368] In addition, for the hollow particles obtained in each of the examples and comparative examples, the following measurements and evaluations were carried out. The results are shown in Table 2.

[0369] 2. Volume average particle diameter of hollow particles

[0370] The particle diameter of the hollow particles was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name: SALD-2000), and its average volume was calculated as the volume average particle diameter.

[0371] 3. Density and porosity of hollow particles

[0372] 3-1. Determination of the apparent density of hollow particles

[0373] First, about 30cm 3 Hollow particles are filled in a volume of 100 cm³ 3 In a volumetric flask, accurately weigh the mass of the hollow granules used to fill it. Next, precisely 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 hollow granules according to the following formula (I). 3 ).

[0374]

[0375] 3-2. Determination of the true density of hollow particles

[0376] After pre-crushing the hollow granules, fill a 100cm³ container with approximately 10g of hollow granule fragments. 3 In a volumetric flask, the mass of the filling fragments is precisely weighed.

[0377] Then, in the same manner as the apparent density determination described above, isopropanol is added to the volumetric flask, the mass of isopropanol is accurately weighed, and the true density D0 (g / cm³) of the hollow particles is calculated according to the following formula (II). 3 ).

[0378]

[0379] 3-3. Calculation of Porosity

[0380] The porosity of the hollow particles is calculated based on the apparent density D1 and true density D0 of the hollow particles, according to the following formula (III).

[0381]

[0382] 4. The thickness of the shell of hollow particles

[0383] Using the volume average particle size R and porosity of the hollow particles, the inner diameter r of the hollow particles is calculated by the following formula (1). Using the inner diameter r and the volume average particle size R, the thickness of the shell of the hollow particles is calculated by the following formula (2).

[0384]

[0385] 5. Immersion test

[0386] 0.1 mg of hollow particles were added to 4 mL of acetone at 25°C. The mixture was shaken at 100 rpm for 10 minutes and allowed to stand for 48 hours. The proportion of precipitated hollow particles was determined and evaluated according to the following criteria. Additionally, the hollow particles precipitated in acetone were separated by centrifugation, dried, and their mass was measured. The proportion of precipitated hollow particles was calculated as a percentage of the total mass of hollow particles impregnated in acetone.

[0387] (Evaluation criteria for immersion test)

[0388] ○: The precipitated hollow particles are less than 10% by mass.

[0389] ×: The precipitated hollow particles account for more than 10% by mass.

[0390] 6. Coefficient of thermal expansion

[0391] 6-1. Fabrication of the molding plate for measurement

[0392] Add 50 parts of epoxy resin (manufactured by Daicel Corporation, product number: EHPE3150CE), 24.9 parts of curing agent (manufactured by DIC Corporation, product number: LF6161), 0.1 parts of 2-ethyl-4-methylimidazolium (manufactured by Nacalai Tesque Corporation, 2E4MZ) as a curing catalyst, and 26 parts of methyl ethyl ketone (MEK), and stir for 30 minutes. After stirring, add 16.6 parts of hollow granules and stir further for 1 hour to prepare a varnish. Place 15g of the varnish on copper foil and degas it in a vacuum dryer at 130°C until no more bubbles form. Then cure it in a hot air circulating oven at 110°C for 2 hours. Then, press it at 110°C, starting with heating and pressurizing at 0.5MPa and then increasing the temperature (4°C / min) to 205°C, and hold for 1 hour to prepare a molded plate. Cut the molded plate into 20mm × 40mm × 0.5mm shapes to prepare test samples.

[0393] 6-2. Determination of the thermal expansion coefficient of hollow particles

[0394] According to JIS K 7197:2012, the coefficient of thermal expansion of the molded plate produced was measured in the range of 25 to 250°C using a TMA apparatus (manufactured by Rigaku Corporation, Japan, model: TMA-8311) in a tensile mode.

[0395] For the temperature range of 80–200℃ and the temperature range of 25–80℃, based on the thermal expansion coefficient α of the above-mentioned molding plate... c The coefficient of thermal expansion α of epoxy resin monomers r The volume ratio SG of epoxy resin in the above-mentioned molded plater And the volume ratio W of the hollow particles in the above-mentioned molded plate. p The thermal expansion coefficient α of hollow particles is calculated using the following equation (E). p .

[0396]

[0397] In addition, the value of the coefficient of thermal expansion (CTE) is the value shown in Table 2 multiplied by 10. -5 The value of .

[0398] 7. Determination of relative permittivity and dielectric loss tangent

[0399] The relative permittivity and dielectric loss tangent of hollow particles at a frequency of 1 GHz and room temperature (25 °C) were measured using a perturbation-based measuring apparatus (manufactured by AET Corporation, model: ADMS01Nc).

[0400] [Table 2]

[0401]

[0402] [Inspection]

[0403] As shown in Table 2 above, compared with the examples using the same type of crosslinking monomer, the hollow particles obtained in each comparative example have higher CTE at 80–200°C and CTE at 25–80°C, as well as higher relative permittivity and dielectric loss tangent at a frequency of 1 GHz.

[0404] In the above impregnation test, the hollow particles obtained in Comparative Examples 1, 2, 4 and 5 precipitated more than 10% by mass in acetone. Since the shell density was insufficient, it can be inferred that the CTE, relative permittivity and dielectric loss tangent were not sufficiently reduced.

[0405] In Comparative Examples 1 and 5, since no second polymerizable monomer was added, it can be inferred that the shell density became insufficient.

[0406] In Comparative Example 2, since styrene with a solubility of 0.2 g / L in distilled water at 20°C was used instead of a hydrophilic monomer with a solubility of 0.3 g / L or more in distilled water at 20°C as the second polymerizable monomer, it can be inferred that the shell density became insufficient.

[0407] In Comparative Example 4, since methyl methacrylate was not added to the mixture in one stage as a second polymerizable monomer but together with the first polymerizable monomer to carry out the polymerization reaction in one step, it can be inferred that the shell density became insufficient.

[0408] On the other hand, since the hollow particles obtained in Comparative Example 3 have low porosity and insufficient size of hollow portion, it can be inferred that the CTE, relative permittivity and dielectric loss tangent have not been sufficiently reduced.

[0409] In contrast, the hollow particles obtained in the various embodiments have low CTE at 80–200°C and low CTE at 25–80°C, as well as low relative permittivity and dielectric loss tangent at a frequency of 1 GHz.

[0410] Since the hollow particles obtained in Examples 1 to 8 have a porosity of 50% or more, the proportion of hollow parts in the particles is sufficiently large, that is, the proportion of shells in the particles is sufficiently reduced. In 100 parts by mass of all monomer units, the shell contains a polymer comprising 70 to 100 parts by mass of crosslinked monomer units, and has a dense structure in which less than 10% by mass of hollow particles are precipitated in acetone in the above-mentioned impregnation test. Therefore, it can be inferred that the CTE, relative permittivity and dielectric loss tangent are sufficiently reduced.

[0411] Explanation of reference numerals in the attached figures

[0412] 1: Aquatic medium

[0413] 2: Low polarity materials

[0414] 3: Dispersant stabilizer

[0415] 4: Monomer Composition

[0416] 4a: Hydrocarbon solvents

[0417] 4b: Materials other than hydrocarbon solvents

[0418] 4c: Polymerizable monomers dispersed in aqueous media

[0419] 5: Oil-soluble polymerization initiators

[0420] 6: Shell

[0421] 8: Hollow section

[0422] 10: Droplets

[0423] 20: Hollow particles containing hydrocarbon solvents in the hollow section (second precursor particles)

[0424] 100: Hollow particles whose hollow core is filled with gas

Claims

1. A hollow particle having a shell containing resin and a hollow portion surrounded by said shell, The hollow particles have a porosity of 50% or higher and a volume average particle size of 1.0 μm or higher. The hollow particles are manufactured by adding a second polymerizable monomer, which is a hydrophilic non-crosslinked monomer with a solubility of 0.3 g / L or more in distilled water at 20°C, to the polymerization reaction when the polymerization conversion rate of the first polymerizable monomer containing the crosslinking monomer reaches 93% by mass or more. The shell contains a polymer as the resin, the polymer comprising hydrophilic non-crosslinked monomer units and crosslinked monomer units. In 100 parts by weight of all monomer units of the polymer, the content of the hydrophilic non-crosslinked monomer unit is 2-15 parts by weight, and the content of the crosslinked monomer unit is 70-98 parts by weight. The coefficient of thermal expansion of the hollow particles is 10.0 × 10⁻⁶ at 80–200 °C. -5 / ℃ below, In the impregnation test of hollow particles, less than 10% by mass of hollow particles precipitated in acetone. The hollow particle impregnation test was conducted by adding 0.1 mg of hollow particles to 4 mL of acetone at 25°C, shaking at 100 rpm for 10 minutes, and then letting it stand for 48 hours.

2. The hollow particle according to claim 1, wherein, The coefficient of thermal expansion of the hollow particles is 6.0 × 10⁻⁶ at 25–80°C. -5 / ℃ below.

3. The hollow particles according to claim 1 or 2, wherein, The hollow particles have a relative permittivity of less than 1.6 at a frequency of 1 GHz.

4. The hollow particles according to claim 1 or 2, wherein, The hollow particles have a dielectric loss tangent of less than 0.010 at a frequency of 1 GHz.

5. The hollow particles according to claim 1 or 2, wherein, The polymer contained in the shell comprises bifunctional crosslinking monomer units derived from bifunctional crosslinking monomers as the crosslinking monomer units. In 100 parts by weight of all monomer units of the polymer, the content of the bifunctional crosslinkable monomer unit is 70 to 98 parts by weight.

6. The hollow particles according to claim 1 or 2, wherein, The polymer contained in the shell comprises trifunctional or higher crosslinking monomer units derived from trifunctional or higher crosslinking monomers as the crosslinking monomer units. In 100 parts by weight of all monomer units of the polymer, the content of the trifunctional or higher crosslinkable monomer unit is 5 to 50 parts by weight.

7. The hollow particles according to claim 1 or 2, wherein, The crosslinking monomer unit comprises a crosslinking monomer unit derived from a methacryloyl-based crosslinking monomer having a methacryloyl group as a polymerizable functional group, or a crosslinking monomer unit derived from an acrylic crosslinking monomer having an acryloyl group as a polymerizable functional group.

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