Fiber-reinforced molded article and method for manufacturing fiber-reinforced molded article

Abstract

Provided is a lightweight fiber-reinforced molded article. The fiber-reinforced molded article contains a matrix resin, a reinforcing fiber, and a hollow particle, the hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, the shell containing, as the resin, a polymer containing 80 mass% or more of a crosslinkable monomer unit in 100 mass% of the total monomer units, and in an impregnation test of the hollow particle, the hollow particle precipitated in acetone is less than 5 mass%, the impregnation test being a test in which 0.1 mg of the hollow particle is added to 4 mL of acetone in an environment at 25°C, and after being shaken at a shaking speed of 100 rpm for 10 minutes, left to stand for 48 hours.

Description

Technical Field

[0001] This invention relates to a fiber-reinforced molded article containing a matrix resin, reinforcing fibers and hollow particles, and a method for manufacturing the fiber-reinforced molded article. Background Technology

[0002] Fiber-reinforced plastics (FRPs), which enhance strength by incorporating reinforcing fibers into resins, are widely used in various fields such as automobiles, aircraft, ships, construction, electrical engineering, and electronics due to their lightweight nature and excellent mechanical properties such as strength and elastic modulus.

[0003] Fiber-reinforced plastics can be obtained, for example, by impregnating a matrix resin with reinforcing fibers. However, in order to further reduce the weight of fiber-reinforced plastics, lightweight materials such as foaming agents or inorganic hollow spheres are often incorporated. In this case, the resin composition impregnated with the reinforcing fibers becomes highly viscous, and problems arise such as difficulty in impregnating the matrix resin and difficulty in uniformly dispersing the lightweight materials.

[0004] On the other hand, Patent Document 1 discloses a fiber-reinforced plastic, which is polymerized by polymerizing a reactive monomer containing 20% ​​by weight or more of a crosslinking monomer. This fiber-reinforced plastic contains hollow microparticles having at least one outer wall layer with a thickness of 20 nm or more, a hollowness of 20-95% by volume, and an average particle size of 0.1-100 μm. In the embodiments of Patent Document 1, a reactive monomer containing 30-75% by weight of a crosslinking monomer is used in the synthesis of the hollow microparticles.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent document 1: Japanese Patent Application Publication No. 2009-242477. Summary of the Invention

[0008] The problem the invention aims to solve

[0009] Patent document 1 describes that the aforementioned specific hollow microparticles are not infiltrated by the raw material monomers and organic solvents of the matrix resin, and that high strength and low specific gravity can be achieved when the fiber-reinforced plastic contains the aforementioned specific hollow microparticles.

[0010] However, since the hollow microparticles described in Patent Document 1 do not have sufficient resistance to polar solvents, when the resin composition impregnated with the reinforcing fiber contains the hollow microparticles described in Patent Document 1 and a polar solvent as a diluent, the hollow microparticles become easily deformed or broken due to the polar solvent penetrating into them, making it impossible to maintain the pores inside the particles and achieve sufficient lightweighting.

[0011] The purpose of this invention is to provide a lightweight fiber-reinforced molded body and a method for manufacturing the fiber-reinforced molded body.

[0012] Solution for solving the problem

[0013] The inventors focused on the permeability of the shell of hollow particles to polar solvents and discovered that by adjusting the composition and formation method of the shell, hollow particles with shells that are not easily permeable to acetone can be made. These particles are less prone to breakage in resin compositions containing solvents and during molding of the resin compositions. They can be preferably used as lightweight materials for fiber-reinforced molded articles.

[0014] This invention provides a fiber-reinforced molded article comprising a matrix resin, reinforcing fibers, and hollow particles.

[0015] The aforementioned hollow particles have a shell containing resin and a hollow portion surrounded by the shell.

[0016] The aforementioned shell contains a polymer comprising at least 80 parts by mass of crosslinkable monomer units in all monomer units per 100 parts by mass as the aforementioned resin.

[0017] In the impregnation test of hollow particles, the hollow particles precipitated in acetone were less than 5% by mass. The above impregnation test of hollow particles was carried out by adding 0.1 mg of hollow particles to 4 mL of acetone at 25°C, shaking for 10 minutes at a shaking speed of 100 rpm, and then letting it stand for 48 hours.

[0018] In the fiber-reinforced molded body of the present invention, the polymer contained in the shell of the hollow particles further comprises hydrophilic non-crosslinked monomer units derived from hydrophilic non-crosslinked monomers having a solubility of 0.3 g / L or more in distilled water at 20°C. In 100 parts by mass of all monomer units of the polymer, the content of the hydrophilic non-crosslinked monomer units is 2 to 20 parts by mass, and the content of the crosslinked monomer units is preferably 80 to 98 parts by mass.

[0019] In the fiber-reinforced molded article of the present invention, the polymer contained in the shell of the hollow particle includes a trifunctional or higher crosslinking monomer unit 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 is preferably 5 to 50 parts by mass.

[0020] This invention provides a method for manufacturing a fiber-reinforced molded article, wherein the fiber-reinforced molded article comprises a matrix resin, reinforcing fibers, and hollow particles.

[0021] The method for manufacturing the aforementioned fiber-reinforced molded article includes: a step of manufacturing hollow particles; a step of preparing a resin composition containing the hollow particles obtained in the above step, a matrix resin, and a solvent; and a step of impregnating the above resin composition with reinforcing fibers.

[0022] In the above-mentioned process of manufacturing hollow particles, hollow particles are manufactured using the following method:

[0023] The method for manufacturing the hollow particles includes: a step of preparing a mixture comprising a first polymerizable monomer, a hydrocarbon solvent, 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.

[0024] The above mixture contains a crosslinking monomer as the first polymerizable monomer, and the content of the crosslinking monomer in 100 parts by mass of the first polymerizable monomer is 80 parts by mass or more.

[0025] In the process of supplying the above 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 with a solubility of 0.3 g / L or more in distilled water at 20°C is added and further supplied to the polymerization reaction.

[0026] In the method for manufacturing the fiber-reinforced molded body of the present invention, in the step of supplying the suspension to the polymerization reaction in the step of manufacturing hollow particles, the amount of the second polymerizable monomer added is preferably 3 to 15 parts by mass relative to 100 parts by mass of the first polymerizable monomer.

[0027] In the method for manufacturing the fiber-reinforced molded body of the present invention, in the step of preparing the mixture in the step of manufacturing hollow particles, the first polymerizable monomer includes a trifunctional or higher crosslinking monomer as the crosslinking monomer, and the content of the trifunctional or higher crosslinking monomer in 100 parts by mass of the first polymerizable monomer is preferably 5 to 50 parts by mass.

[0028] In the method for manufacturing the fiber-reinforced molded body of the present invention, in the step of preparing the above-mentioned mixture in the step of manufacturing hollow particles, the above-mentioned dispersing stabilizer is preferably an inorganic dispersing stabilizer.

[0029] In the method for manufacturing the fiber-reinforced molded article of the present invention, the inorganic dispersion stabilizer is more preferably a water-insoluble metal salt.

[0030] Invention Effects

[0031] According to the present invention as described above, a lightweight fiber-reinforced molded body and a method for manufacturing the fiber-reinforced molded body can be provided. Attached Figure Description

[0032] Figure 1 A figure illustrating an example of a method for manufacturing hollow particles used in the fiber-reinforced molded article of the present invention.

[0033] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in the suspension process. Detailed Implementation

[0034] In addition, 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.

[0035] Furthermore, in this invention, (meth)acrylate refers to acrylate and methacrylate, (meth)acrylic acid refers to acrylic acid and methacrylic acid, and (meth)acryloyl refers to acryloyl and methacryloyl.

[0036] 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.

[0037] As polymerizable monomers, there are 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 crosslinks in the resin through polymerization.

[0038] Furthermore, in this invention, polymerizable monomers with a solubility of 0.3 g / L or more in distilled water at 20°C are referred to as hydrophilic monomers, and polymerizable monomers with a solubility of less than 0.3 g / L in distilled water at 20°C are referred to as non-hydrophilic monomers.

[0039] Furthermore, in this invention, curing refers to curing with or without a chemical reaction.

[0040] I. Fiber-reinforced molded parts

[0041] The fiber-reinforced molded article of the present invention is characterized by containing a matrix resin, reinforcing fibers, and hollow particles.

[0042] The aforementioned hollow particles have a shell containing resin and a hollow portion surrounded by the shell.

[0043] The aforementioned shell contains a polymer comprising at least 80 parts by mass of crosslinkable monomer units in all monomer units per 100 parts by mass as the aforementioned resin.

[0044] In the impregnation test of hollow particles, the hollow particles precipitated in acetone were less than 5% by mass. The above impregnation test of hollow particles was carried out by adding 0.1 mg of hollow particles to 4 mL of acetone at 25°C, shaking for 10 minutes at a shaking speed of 100 rpm, and then letting it stand for 48 hours.

[0045] The fiber-reinforced molded article of the present invention can be obtained by impregnating reinforcing fibers with a resin composition containing a matrix resin, hollow particles, and a solvent and molding it, for example, as described in the manufacturing method of the present invention below. The fiber-reinforced molded article of the present invention can be an intermediate product such as a prepreg in which the resin composition is in a semi-cured state, or a finished product obtained by curing the resin composition.

[0046] In fiber-reinforced molded articles obtained by impregnating existing resin compositions containing hollow particles with reinforcing fibers, the hollow particles sometimes become easily broken because the solvent and resin in the resin composition (varnish) penetrate into the interior of the hollow particles. The hollow particles cannot maintain the porosity inside the particles, and the resulting molded articles are not sufficiently lightweight.

[0047] In contrast, the fiber-reinforced molded body of the present invention is less prone to cracking in the varnish and during the process of impregnating the reinforcing fiber with the varnish and drying and curing it, and the porosity inside the particles is maintained even in the molded body. Therefore, compared with the existing fiber-reinforced molded bodies containing hollow particles, the fiber-reinforced molded body of the present invention achieves further lightweighting.

[0048] The hollow particles, matrix resin, and reinforcing fibers contained in the fiber-reinforced molded article of the present invention will be described below.

[0049] I-1. Hollow Particles

[0050] The fiber-reinforced molded articles of the present invention contain hollow particles that have a shell (outer shell) containing resin and a hollow portion surrounded by the shell.

[0051] In this invention, the hollow portion is a void-like space that is clearly distinguishable from the shell of a hollow particle formed of resin material. The shell of the hollow particle may have a porous structure, in which case the hollow portion has a size that is clearly distinguishable from the many tiny spaces uniformly dispersed within the porous structure.

[0052] The hollow portion of hollow particles can be confirmed by, for example, by SEM observation of particle profiles or by TEM observation of the particles directly.

[0053] From the perspective of lightweighting, the hollow particles of the present invention preferably have hollow portions filled with air or nitrogen or in a depressurized state close to a vacuum.

[0054] The hollow particles used in the fiber-reinforced molded body of the present invention contain a high proportion of cross-linked monomer units in the shell, with more than 80 parts by mass of cross-linked monomer units per 100 parts by mass of all monomer units. This suggests a dense covalent network within the shell. Furthermore, since less than 5% of the hollow particles precipitate in acetone during the aforementioned impregnation test, the shell is presumably dense, making it difficult for acetone to penetrate, and the cross-linked structure within the shell becomes even denser. It can be considered that, compared to existing hollow particles with shells containing a large number of cross-linked monomer units, the hollow particles used in the fiber-reinforced molded body of the present invention have a more dense structure, as described above, improving solvent resistance and strength. Therefore, solvents do not easily penetrate the interior of the particles, resulting in excellent strength. Even when added to a varnish and further impregnated with the reinforcing fibers, followed by drying and curing, they are less prone to cracking, maintaining the porosity within the particles in the fiber-reinforced molded body.

[0055] Hereinafter, the hollow particles used in the fiber-reinforced molded articles of the present invention will sometimes be referred to as the hollow particles of the present invention or simply as hollow particles.

[0056] The porosity of the hollow particles of the present invention is preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. By making the porosity above the above-mentioned lower limit value, the hollow particles provide excellent effects such as lightweighting. 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 of the strength of the hollow particles and making the hollow particles less prone to breakage, it is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less.

[0057] 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.

[0058] The method for determining the apparent density D1 of hollow particles is as follows. First, in a volume of 100 cm³... 3 Fill the volumetric flask with approximately 30cm 3 The hollow granules were precisely weighed. Next, isopropanol was precisely added to the volumetric flask filled with the hollow granules up to the mark, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was precisely weighed, and the apparent density D1 (g / cm³) of the hollow granules was calculated according to the following formula (I). 3 ).

[0059] Formula (I)

[0060] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[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, the density is measured in a 100 cm³ container. 3 Approximately 10 g of hollow particle fragments were filled into a volumetric flask, and the mass of the filling fragments was accurately weighed. Then, isopropanol was added to the volumetric flask in the same manner as the apparent density determination described above, and the mass of the isopropanol was accurately weighed. The true density D0 (g / cm³) of the hollow particles was calculated based on the following formula (II). 3 ).

[0063] Equation (II)

[0064] True density D0 = [mass of fragments of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0065] True density D0 corresponds to the specific gravity of the shell portion only in a hollow particle. As can be seen from the above measurement method, the hollow portion is not considered part of the hollow particle when calculating true density D0.

[0066] The porosity (%) of the hollow particles is calculated by the following formula (III) based on the apparent density D1 and true density D0 of the hollow particles.

[0067] Equation (III)

[0068] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0069] The volume average particle size of the hollow particles of the present invention is preferably 1.0 to 80 μm. By making the volume average particle size of the hollow particles above or above the aforementioned lower limit, the agglomeration of the hollow particles is reduced, thus enabling excellent dispersibility. On the other hand, by making the volume average particle size of the hollow particles below or below the aforementioned upper limit, the reduction in the strength of the hollow particles can be suppressed, and since the hollow particles can easily enter the interfibers of the reinforcing fibers, they can be easily and uniformly dispersed in the molded article.

[0070] The lower limit of the volume average particle size of the hollow particles of the present invention is more preferably 3.0 μm or more, further 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 more preferably 30.0 μm or less, further preferably 20.0 μm or less, and even more preferably 10.0 μm or less.

[0071] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow particles can be, for example, 1.05 or more and 2.5 or less. By setting this particle size distribution to 2.5 or less, particles with small deviations in properties such as pressure resistance and heat resistance can be obtained. Furthermore, by setting this particle size distribution to 2.5 or less, products with uniform thickness can be manufactured, for example, when manufacturing sheet-like molded bodies.

[0072] The volume-average particle size (Dv) and number-average particle size (Dn) of hollow particles can be determined by measuring the particle size using, for example, a laser diffraction particle size distribution measuring device. The number-average and volume-average sizes are calculated separately, 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.

[0073] 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 viewpoint of ease of manufacture and the viewpoint of excellent strength and pressure resistance of the hollow particles.

[0074] Hollow particles can have one or more hollow sections. Furthermore, the shell of the hollow particle, and the spacers 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.

[0075] The average roundness of hollow particles can be 0.950 to 0.995.

[0076] An example of the shape of hollow particles is a bag made of a thin membrane and inflated, 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.

[0077] The shape of the particles can be confirmed by, for example, SEM and TEM. In addition, the internal shape of the particles can be confirmed by SEM and TEM after the particles are cut into discs using known methods.

[0078] The hollow particles of the present invention contain a resin in which at least 80 parts by mass of crosslinked monomer units are included in the shell of all 100 parts by mass of the monomer units. The above-mentioned polymer forms the skeleton of the shell of the hollow particles, and by including crosslinked monomer units in the above proportion, the shell of the hollow particles of the present invention becomes a shell with a densely distributed covalent bond network.

[0079] In the aforementioned polymer, from the viewpoint of improving the strength and solvent resistance of hollow particles and enhancing the lightweight effect brought about by hollow particles, the content of crosslinkable monomer units in 100 parts by mass of all monomer units is preferably 85 parts by mass or more, more preferably 90 parts by mass or more. The upper limit of the aforementioned crosslinkable monomer units is not particularly limited and can be 100 parts by mass or less. From the viewpoint of sufficiently containing the hydrophilic non-crosslinkable monomer units described later, it is preferably 98 parts by mass or less, more preferably 97 parts by mass or less.

[0080] Furthermore, in this invention, the crosslinking monomer unit is a monomer unit derived from the crosslinking monomer. When the content of the crosslinking monomer unit in the polymer 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.

[0081] The polymer described above is typically a polymer of a first polymerizable monomer and a second polymerizable monomer obtained through a first polymerization reaction and a second polymerization reaction in the method for manufacturing hollow particles of the present invention, as 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 polymerizable monomer and the second polymerizable monomer described later.

[0082] Furthermore, the specific details of the crosslinked and non-crosslinked monomers used in the synthesis of the aforementioned polymers are described later in the method for manufacturing hollow particles of the present invention.

[0083] The polymer described above comprises at least one crosslinking monomer unit selected from difunctional crosslinking monomers and trifunctional or higher crosslinking monomer units as crosslinking monomer units. From the viewpoint of improving the strength and solvent resistance of hollow particles and enhancing the lightweight properties resulting from hollow particles, it is preferable to include at least a difunctional crosslinking monomer unit. From the viewpoint of further improving the strength of hollow particles, it is more preferable to combine a difunctional crosslinking monomer unit and a trifunctional or higher crosslinking monomer unit.

[0084] In addition, in this invention, a crosslinking monomer unit derived from a difunctional crosslinking monomer is sometimes referred to as a "difunctional crosslinking monomer unit", and a crosslinking monomer unit derived from a trifunctional or higher crosslinking monomer is sometimes referred to as a "trifunctional or higher crosslinking monomer unit".

[0085] When the polymer described above contains difunctional crosslinkable monomer units, the content of difunctional 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 improving the strength and solvent resistance of hollow particles and enhancing the lightweight effect brought about by hollow particles, it is preferably 65 parts by mass or more, more preferably 70 parts by mass or more, and even 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 sufficiently containing 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.

[0086] When the polymer contains trifunctional or higher crosslinkable monomer units, the content of trifunctional or higher crosslinkable monomer units in 100 parts by mass of all monomer units of the polymer is not particularly limited. As a lower limit, from the viewpoint of improving the strength and solvent resistance of hollow particles and improving the lightweight effect brought about by 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 sufficiently containing difunctional or higher 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.

[0087] Furthermore, the crosslinking monomer units contained in the above polymer may include crosslinking monomer units derived from (meth)acryloyl-based crosslinking monomers having (meth)acryloyl groups as polymerizable functional groups. This allows the formation of hollow particles with excellent strength and heat resistance.

[0088] When the polymer contains crosslinking monomer units derived from (meth)acrylic acid-based crosslinking monomers, the content of crosslinking monomer units derived from the (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. The crosslinking monomer units may be composed of (meth)acrylic acid-based crosslinking monomer units.

[0089] 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.

[0090] Furthermore, the polymer preferably includes 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 including both crosslinked and non-crosslinked monomer units in the polymer combination, 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 easily improving the strength and solvent resistance of the hollow particles, thereby easily enhancing the lightweight effects of the hollow particles.

[0091] In the above polymer, the content of non-crosslinked monomer units in 100 parts by mass of all monomer units is 0 to 20 parts by mass. From the viewpoint of improving the strength of hollow particles, the lower limit is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more. The upper limit is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less.

[0092] From the viewpoint of improving the strength and solvent resistance of hollow particles and the lightweighting effect brought about by hollow particles, in the above polymer, the lower limit of the content of hydrophilic non-crosslinked monomer units in 100 parts by mass of all monomer units is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more. The upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less.

[0093] 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.

[0094] In the impregnation test of the hollow particles of the present invention, less than 5% 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 for 10 minutes at 100 rpm, and then allowing it to stand for 48 hours. The proportion of hollow particles precipitated in acetone in the above impregnation test is an indicator of the density of the hollow particle shell. A smaller proportion of hollow particles precipitated in acetone in the above impregnation test is presumably associated with a denser shell.

[0095] To ensure that the hollow particles precipitated in acetone during the above-mentioned impregnation test are less than 5% by mass, hollow particles can be manufactured as follows: for example, as described later in the method for manufacturing hollow particles of the present invention, 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 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, and the crosslinking monomer unit content in the polymer forming the shell is 80% by mass or more.

[0096] Furthermore, in SEM observation, preferably, out of 100 hollow particles, there are 5 or fewer hollow particles with interconnecting holes or shell defects.

[0097] Hollow particles typically include those whose shells lack connecting holes that link the hollow portion to the outside space of the particle, and those whose shells have one or more connecting holes through which the hollow portion communicates with the outside of the particle. While the diameter of the connecting holes generally depends on the size of the hollow particle, it is typically around 10–500 nm. Although connecting holes can sometimes provide beneficial functions to hollow particles, they also contribute to reduced strength and increased susceptibility to breakage, as they are defects in the shell.

[0098] In addition, hollow particles sometimes have crack-like shell defects that are very large compared to the size of the particles. Although it also depends on the size of the hollow particles, cracks with a length of more than 1 μm are considered shell defects because they usually significantly deteriorate the strength of the hollow particles.

[0099] In the aforementioned impregnation test of hollow particles, if less than 5% by mass of hollow particles precipitate in acetone, it can be considered that out of the 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, the percentage of hollow particles precipitating in the aforementioned impregnation test sometimes reaches 5% or more by mass. Therefore, it is considered that if less than 5% by mass of hollow particles precipitate in the aforementioned impregnation test of hollow particles, it indicates that the shell has very few interconnecting pores and shell defects, and that the shell has a dense cross-linked structure.

[0100] The content of hollow particles in the fiber-reinforced molded article of the present invention is not particularly limited. Based on mass, the lower limit is preferably 5% by mass or more, more preferably 10% by mass or more, and the upper limit is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0101] Furthermore, the content of hollow particles in the fiber-reinforced molded article of the present invention, on a volume basis, is preferably 15% or more (lower limit), more preferably 25% or more (more preferably 30% or more (upper limit), and preferably 60% or less (upper limit), more preferably 50% or less (upper limit), and more preferably 40% or less (upper limit).

[0102] By setting the content of hollow particles above the aforementioned lower limit, the lightweighting effect of the fiber-reinforced molded body can be improved; by setting it below the aforementioned upper limit, the reduction in the physical properties of the fiber-reinforced molded body can be suppressed.

[0103] When determining the content of hollow particles in the fiber-reinforced molded body based on mass, firstly, the content (mass%) of the resin component in the fiber-reinforced molded body is calculated using the following formula (1) based on the mass of the fiber-reinforced molded body and the mass of the reinforcing fibers in the fiber-reinforced molded body. Next, the content (mass%) of hollow particles based on mass is calculated using the following formula (2) based on the content (mass%) of the resin component and the content (mass%) of hollow particles in the solid component of the resin composition impregnated by the reinforcing fibers.

[0104] Here, resin composition refers to the total amount of materials other than reinforcing fibers in the materials constituting the fiber-reinforced molded body, typically the total amount of matrix resin and hollow particles in the fiber-reinforced molded body.

[0105] In addition, the fiber-reinforced molded body used to determine the content of hollow particles based on mass can be a fiber-reinforced molded body with solvent removed, and the content of hollow particles contained in the finished product obtained by curing the prepreg can be determined using an intermediate product such as prepreg.

[0106] Equation (1)

[0107] Resin content (mass %) = (mass of fiber-reinforced molded body - mass of reinforcing fiber) ÷ mass of fiber-reinforced molded body × 100

[0108] Equation (2)

[0109] Hollow particle content (mass%) = Resin component content (mass%) x Hollow particle content (mass%) in the solid component of the resin composition impregnated with the reinforcing fiber ÷ 100

[0110] The volumetric content of hollow particles in the fiber-reinforced molded body can be calculated, for example, as follows: the volumes of the hollow particles constituting the fiber-reinforced molded body, the matrix resin and the reinforcing fibers are determined by the following equations (3), (4) and (5), and the determined values ​​are used to calculate the volume of the hollow particles constituting the fiber-reinforced molded body by the following equation (6).

[0111] Equation (3)

[0112] Volume of hollow particles = Hollow particle content (mass%) ÷ Specific gravity of hollow particles (g / cm³) 3 )

[0113] Equation (4)

[0114] Volume of matrix resin = Content of matrix resin (mass%) ÷ Specific gravity of matrix resin after curing (g / cm³) 3 )

[0115] Equation (5)

[0116] Volume of reinforcing fiber = Reinforcing fiber content (mass%) ÷ Specific gravity of reinforcing fiber (g / cm³) 3 )

[0117] Equation (6)

[0118] Hollow particle content (volume %) = Volume of hollow particles ÷ (Volume of hollow particles + Volume of matrix resin + Volume of reinforcing fibers) × 100

[0119] In addition, the "content of hollow particles (mass%)" used in the above formula (3) is a value obtained by formula (2) above.

[0120] The “content of matrix resin (mass%)” used in the above formula (4) can be calculated by the following formula (7).

[0121] Equation (7)

[0122] The content of the matrix resin (mass %) = the content of resin components (mass %) × the content of the matrix resin in the solid components of the resin composition impregnated by the reinforcing fiber (mass %) ÷ 100

[0123] Here, "the content of resin components (mass%)" is the value obtained by formula (1) above.

[0124] Furthermore, the "specific gravity (g / cm³) of the cured matrix resin" used in formula (4) above 3 ")" can be used to determine the true density of a cured product of a composition from which hollow resin particles have been removed from a resin composition impregnated with reinforcing fibers, using the same method as for hollow particles.

[0125] The “content of reinforcing fiber (mass%)” used in the above formula (5) can be calculated by the following formula (8).

[0126] Equation (8)

[0127] Reinforcing fiber content (mass%) = Mass of reinforcing fiber ÷ Mass of fiber-reinforced molded body × 100

[0128] I-2. Matrix resin

[0129] The matrix resin used in this invention can be any resin commonly used as a matrix resin for fiber-reinforced molded articles. It can be a thermoplastic resin, a thermosetting resin, or a room-temperature curing resin.

[0130] The fiber-reinforced molded article of the present invention can be manufactured by a wet process, for example, impregnating a resin composition comprising a matrix resin, hollow particles, and a solvent into reinforcing fibers and then removing the solvent. When the matrix resin comprises a thermoplastic resin, the fiber-reinforced molded article of the present invention can be manufactured by, for example, by heating a resin composition comprising a matrix resin and hollow particles to reduce its viscosity and impregnating it into reinforcing fibers; or by a hot-melt process, such as molding a resin composition comprising a matrix resin and hollow particles into a sheet, overlapping the sheet from both sides or one side of the reinforcing fibers, and heating and pressurizing to impregnate the reinforcing fibers with the resin composition.

[0131] From the viewpoint of easily leveraging the lightweight effect brought about by the hollow particles used in this invention, the matrix resin is preferably a resin that can be applied to the above-mentioned wet process, for example, preferably containing a thermosetting resin.

[0132] Examples of thermoplastic resins that can be used as matrix resins include: polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimides, polyamide-imides, polyether-imides, polyetherketone-ketones, polyvinyl chloride, polystyrene, poly(meth)acrylate, polycarbonate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, and thermoplastic elastomers. These thermoplastic resins can be used individually or in combination of two or more.

[0133] Examples of thermosetting resins that can be used as matrix resins include: phenolic resins, melamine resins, urea resins, unsaturated polyester resins, epoxy resins, polyurethane resins, silicone resins, alkyd resins, thermosetting polyphenylene ether resins, thermosetting polyimide resins, and benzo[a]benzene resins. These thermosetting resins include aziridine 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, and polyetherimide resins. These thermosetting resins can be used individually or in combination of two or more.

[0134] Examples of room-temperature curing resins that can be used as matrix resins include epoxy resins and polyurethane resins. These room-temperature curing resins can be used alone or in combination of two or more.

[0135] The matrix resin may, as needed, contain additives such as curing agents, curing catalysts, or curing accelerators to facilitate resin curing. The specific contents of these additives for resin curing are described later in the section on the manufacturing method of the fiber-reinforced molded article.

[0136] The content of matrix resin in the fiber-reinforced molded article of the present invention is not particularly limited. From the viewpoint of mechanical properties, the content of matrix resin is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, relative to the total of matrix resin and hollow particles in 100 parts by mass of the fiber-reinforced molded article. From the viewpoint of lightweighting, it is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less.

[0137] In addition, in this invention, the content of the matrix resin also includes the content of additives used to cure the resin, such as curing agents, curing catalysts, or curing accelerators.

[0138] I-3. Reinforcing Fibers

[0139] The reinforcing fiber used in this invention can be any fiber commonly used in fiber-reinforced molded articles, and is not particularly limited to any particular type. Examples of organic or inorganic reinforcing fibers include carbon fiber, glass fiber, aramid fiber, alumina fiber, boron fiber, Tyranno fiber, and SiC fiber. Among these, carbon fiber is preferred from the viewpoint of superior mechanical properties, heat oxidation resistance, and dimensional stability.

[0140] The form of the reinforcing fiber is not particularly limited; it can be used to process reinforcing fibers into fabrics, non-woven fabrics, pads, etc. Furthermore, the reinforcing fiber can be a long fiber or a short fiber.

[0141] The content of reinforcing fibers in the fiber-reinforced molded article of the present invention is not particularly limited, but is preferably 20 to 80% by mass in 100% by mass of the fiber-reinforced molded article of the present invention. When the content of reinforcing fibers is within the above range, a fiber-reinforced molded article with excellent fatigue strength and impact characteristics can be produced.

[0142] In addition, without impairing the effects of the present invention, the fiber-reinforced molded articles of the present invention may, as needed, contain inorganic fillers, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, flame retardants, release agents, antistatic agents, colorants, and other additives, in addition to the hollow particles, matrix resin, and reinforcing fibers described above.

[0143] I-4. Physical properties of fiber-reinforced molded products

[0144] By appropriately selecting the types and amounts of the above-mentioned components, the fiber-reinforced molded articles of the present invention possess physical properties corresponding to their intended uses.

[0145] The tensile modulus of elasticity of the fiber-reinforced molded article of the present invention is not particularly limited. As a lower limit, it is preferably 13 GPa or more, more preferably 14 GPa or more. As an upper limit, it is preferably 20 GPa or less, more preferably 18 GPa or less.

[0146] The tensile strength of the fiber-reinforced molded article of the present invention is not particularly limited, but as a lower limit, it is preferably 350 MPa or more, more preferably 400 MPa or more, and as an upper limit, it is preferably 500 MPa or less, more preferably 450 MPa or less.

[0147] In addition, in this invention, the tensile modulus of elasticity and tensile strength of the fiber-reinforced molded body are determined according to JIS K7165:2008.

[0148] The shape of the fiber-reinforced molded body of the present invention is not particularly limited, and it can be made into various shapes that can be formed, such as sheet, film, plate, tube and other three-dimensional shapes.

[0149] I-5. Applications of Fiber Reinforced Molded Articles

[0150] The applications of the fiber-reinforced molded articles of the present invention are not particularly limited, but they are preferred for use in various fields such as automobiles, bicycles, aviation, aerospace, railway vehicles, ships, construction, electrical, electronic, and sporting goods as various components requiring mechanical properties and lightweighting.

[0151] II. Manufacturing method of fiber-reinforced molded articles

[0152] The method for manufacturing the fiber-reinforced molded article of the present invention is characterized in that the fiber-reinforced molded article contains a matrix resin, reinforcing fibers, and hollow particles.

[0153] The method for manufacturing the aforementioned fiber-reinforced molded article includes: a step of manufacturing hollow particles; a step of preparing a resin composition containing the hollow particles obtained in the above step, a matrix resin, and a solvent; and a step of impregnating the above resin composition with reinforcing fibers.

[0154] In the above-mentioned process of manufacturing hollow particles, hollow particles are manufactured using the following method:

[0155] The method for manufacturing the hollow particles includes: a step of preparing a mixture comprising a first polymerizable monomer, a hydrocarbon solvent, 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.

[0156] The above mixture contains a crosslinking monomer as the first polymerizable monomer, and the content of the crosslinking monomer in 100 parts by mass of the first polymerizable monomer is 80 parts by mass or more.

[0157] In the process of supplying the above 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 with a solubility of 0.3 g / L or more in distilled water at 20°C is added and further supplied to the polymerization reaction.

[0158] The method for manufacturing the fiber-reinforced molded article of the present invention includes a step of manufacturing hollow particles, a step of preparing a resin composition, and a step of impregnating the resin composition with reinforcing fibers, and may also include other steps besides these. Furthermore, the manufacturing method of the present invention can, where technically feasible, perform two or more steps simultaneously as a single step, or change the order of the steps.

[0159] II-1. Process for manufacturing hollow pellets

[0160] The hollow particles used in this invention can be obtained by a method for manufacturing hollow particles, which includes:

[0161] The process of preparing a mixture comprising a first polymerizable monomer containing a crosslinking monomer, a hydrocarbon solvent, a dispersing stabilizer and an aqueous medium;

[0162] The process 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 above-described mixture; and

[0163] The process of supplying the above suspension to the polymerization reaction

[0164] The above mixture contains a crosslinking monomer as the first polymerizable monomer, and the content of the crosslinking monomer in 100 parts by mass of the first polymerizable monomer is 80 parts by mass or more.

[0165] In the process of supplying the above 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 with a solubility of 0.3 g / L or more in distilled water at 20°C is added and further supplied to the polymerization reaction.

[0166] 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 and the first polymerizable monomer is predominantly present on the surface side and the hydrocarbon solvent is predominantly present in the center are dispersed in an aqueous medium. By supplying the suspension to a polymerization reaction, the surface of the droplets is solidified to form hollow particles with hollow parts filled with hydrocarbon solvent.

[0167] 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 with a solubility in distilled water at 20°C of the aforementioned specific value or more, is added and further supplied to the polymerization reaction. This allows the production of hollow particles in which less than 5% by mass precipitate in acetone during the impregnation test of the hollow particles. When using the crosslinking monomer as the polymeric monomer for forming the shell of the hollow particles, unreacted polymeric functional groups easily remain in the shell. The more unreacted polymeric functional groups directly remain, the coarser the crosslinking structure of the shell becomes. Therefore, it is considered that in hollow particles obtained by the existing manufacturing method, due to the residual unreacted polymeric functional groups, the percentage of hollow particles precipitating in acetone during the impregnation test of the hollow particles becomes 5% or more by mass.

[0168] It can be considered that in the above-mentioned method for manufacturing hollow particles, by supplying a suspension containing droplets of a monomer composition containing a first polymerizable monomer comprising a large amount of crosslinking monomers in an aqueous medium to a polymerization reaction, a first polymerization reaction is carried out until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, and then a second polymerizable monomer as a hydrophilic monomer is added to further carry out a second polymerization reaction, thereby improving the overall reaction rate of the polymerizable monomers containing the first polymerizable monomer and the second polymerizable monomer.

[0169] Furthermore, in this invention, the 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 the composition containing such first precursor particles is sometimes referred to as a first precursor composition. Additionally, the 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 gas-filled hollow portions, and are sometimes referred to as second precursor particles, and the composition containing such second precursor particles is sometimes referred to as a second precursor composition.

[0170] 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, the second polymerizable monomer readily enters the shell of the first precursor particles. As a hydrophilic monomer, the second polymerizable monomer has an affinity for both the first polymerizable monomer and the aqueous medium. Therefore, it is believed that when added to the first precursor composition, the second polymerizable monomer enters the shell formed by the first polymerizable monomer, promoting the thermal motion of the shell. It is speculated that during the second polymerization reaction, with the second polymerizable monomer inside the shell formed by the first polymerizable monomer, the polymerization reaction occurs simultaneously with the promoted thermal motion of the shell. Therefore, the reaction rate is high, and the polymerization reaction between the second polymerizable monomer inside the shell and the unreacted but directly residual polymerizable functional groups of the first polymerizable monomer proceeds fully, resulting in a dense cross-linked structure and thus forming a shell that is difficult for acetone to penetrate.

[0171] The method for manufacturing the aforementioned hollow particles includes a step of preparing a mixture, a step of preparing a suspension, and a step of supplying the suspension to a polymerization reaction, and may also include steps other than these steps. Furthermore, provided it is technically feasible, two or more of the aforementioned steps and other additional steps can be performed simultaneously as a single step, or their order can be changed. For example, the preparation and suspension of the mixture can be carried out simultaneously in one process by adding the material for preparing the mixture while simultaneously suspending it.

[0172] As a preferred example of the manufacturing method of the above-mentioned hollow particles, a manufacturing method including the following steps can be cited.

[0173] (1) Mixture preparation process

[0174] The process of preparing a mixture comprising a first polymerizable monomer, a hydrocarbon solvent, a dispersing stabilizer and an aqueous medium;

[0175] (2) Suspension process

[0176] 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.

[0177] (3) Polymerization process

[0178] (3-1) First polymerization process

[0179] A first polymerization reaction is carried out by supplying the above suspension to the polymerization reaction until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, thereby preparing a first precursor composition containing first precursor particles, the first precursor particles having a shell of polymer containing the first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0180] (3-2) Second polymerization process

[0181] A process of preparing a second precursor composition containing second precursor particles 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 and carrying out a second polymerization reaction, 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.

[0182] (4) Solid-liquid separation process

[0183] The process of obtaining second precursor particles containing a hydrocarbon solvent in a hollow section by performing solid-liquid separation on the above-mentioned second precursor composition; and

[0184] (5) Solvent removal process

[0185] 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.

[0186] Figure 1 A schematic diagram illustrating an example of the manufacturing method described above. Figure 1 (1) to (5) in the diagram correspond to the aforementioned steps (1) to (5). 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 depicted in these figures.

[0187] Figure 1 (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. The low-polarity material 2 in this invention includes a first polymerizable monomer and a hydrocarbon solvent.

[0188] 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 include 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 undergoes phase separation from the material 4b containing the first polymerizable monomer, excluding the hydrocarbon solvent; the hydrocarbon solvent 4a is predominantly present in the central part; the material 4b excluding the hydrocarbon solvent is predominantly present on the surface side; and a dispersion stabilizer (not shown) is attached to the surface.

[0189] 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 and 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 droplet 10 of the monomer composition and the subsequent polymerization of a second polymerizable monomer.

[0190] 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.

[0191] 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 hollow part 8 filled with gas inside the shell 6 are obtained.

[0192] The following sections will describe the five processes mentioned above and the other processes in turn.

[0193] (1) Mixture preparation process

[0194] This process is for preparing a mixture containing a first polymerizable monomer, a hydrocarbon solvent, a dispersant stabilizer, and an aqueous medium.

[0195] The mixture preferably contains an oil-soluble polymerization initiator as the polymerization initiator. Furthermore, without impairing the effects of the present invention, the mixture may also contain other materials such as a suspension stabilizer.

[0196] For the materials of the mixture, describe in order: (A) the first polymerizable monomer, (B) the oil-soluble polymerization initiator, (C) the hydrocarbon solvent, (D) the dispersing stabilizer, and (E) the aqueous medium.

[0197] (A) First polymerizing monomer

[0198] The first polymerizable monomer contains at least a crosslinking monomer, and may also contain a non-crosslinking monomer without impairing the effects of the invention.

[0199] 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.

[0200] [Crosslinking monomers]

[0201] Crosslinkable monomers have multiple polymerizable functional groups, which enable them to link monomers together and increase the crosslinking density of the shell.

[0202] 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, tricyclodecanediethanol di(meth)acrylate, and propyl methacrylate-2-hydroxy-3-(meth)acrylate, which are difunctional crosslinking monomers with two polymerizable functional groups; and trifunctional or higher crosslinking monomers, such as trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and their ethoxylates, which have three or more polymerizable functional groups. These crosslinking monomers can be used individually or in combination of two or more.

[0203] 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, propyl acrylate-2-hydroxy-3-methacrylate, diallylamine, etc.

[0204] 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.

[0205] The first polymerizable monomer includes at least one crosslinking monomer selected from difunctional crosslinking monomers and trifunctional or higher crosslinking monomers. From the viewpoint of improving the strength and solvent resistance of the hollow particles, and enhancing the lightweight effect of the hollow particles, a combination including difunctional crosslinking monomers and trifunctional or higher crosslinking monomers is more preferable. While the first polymerizable monomer includes trifunctional or higher crosslinking monomers, it excels in achieving a denser covalent bond network within the shell, but 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 trifunctional or higher crosslinking monomers, by adding a hydrophilic monomer as the 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 crosslinked structure of the shell can be made denser, improving the strength and solvent resistance of the hollow particles, thereby enhancing the lightweight effect of the hollow particles.

[0206] Furthermore, from the viewpoint that the crosslinking monomer included as the first polymerizable monomer is easy to stabilize in the polymerization reaction and can produce hollow particles with excellent strength and heat resistance, a (meth)acryloyl group as the crosslinking monomer is preferred.

[0207] That is, the difunctional crosslinking monomer used as the first polymerizable monomer is preferably a difunctional (meth)acrylate crosslinking monomer such as allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, or pentaerythritol di(meth)acrylate, and more preferably ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate.

[0208] The trifunctional or higher crosslinking monomer used as the first polymerizable monomer is preferably a trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane)tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and these ethoxylated compounds, etc., which are 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.

[0209] 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.

[0210] 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 can be formed from a (meth)acrylic acid-based crosslinking monomer.

[0211] In 100 parts by mass of the first polymerizable monomer, the content of the crosslinking monomer is 80 parts by mass or more, preferably 85 to 100 parts by mass, more preferably 90 to 100 parts by mass, and even more preferably 95 to 100 parts by mass. By ensuring that the content of the crosslinking monomer is at or above the aforementioned lower limit, the polymer contained in the formed shell is likely to be a polymer in which 80 to 100 parts by mass of crosslinking monomer units are contained in all 100 parts by mass of monomer units. Furthermore, since the proportion of crosslinking monomer units in the shell of the hollow particle is sufficiently large, a covalent bond network is densely distributed in the shell, resulting in improved strength and solvent resistance of the hollow particle, thereby enhancing the lightweight effect of the hollow particle.

[0212] When the first polymerizable monomer includes a difunctional crosslinking monomer as a crosslinking monomer, the content of the difunctional crosslinking monomer in 100 parts by mass of the first polymerizable monomer is not particularly limited. As a lower limit, from the viewpoint of improving the strength and solvent resistance of hollow particles and improving the lightweight effect brought about by hollow particles, it is 70 parts by mass or more, more preferably 80 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 fully containing trifunctional or more crosslinking monomer units, it is preferably 95 parts by mass or less, more preferably 90 parts by mass or less.

[0213] 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 improving the strength and solvent resistance of hollow particles and improving the lightweight effect brought about by 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 fully containing a difunctional or higher crosslinking monomer, it is even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

[0214] [Non-crosslinked monomer]

[0215] The first polymerizable monomer may further include non-crosslinked monomers.

[0216] 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 esters of (meth)acrylates with 6 or more carbon atoms, such as 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, and halogenated styrene; 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; halogenated vinyl monomers such as vinyl chloride; vinylidene chloride and other dihalogenated vinyl monomers; non-hydrophilic, non-crosslinking monomers such as vinylpyridine monomers; alkyl esters of (meth)acrylates with 1 to 5 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate; (meth)acrylamides such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide, and their derivatives; (meth)acrylonitrile and its derivatives; and hydrophilic, non-crosslinking monomers containing polar groups.

[0217] 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.

[0218] These non-crosslinked monomers can be used individually or in combination of two or more.

[0219] 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, an alkyl (meth)acrylate having an alkyl group having 1 to 5 carbon atoms is more preferred, and an alkyl (meth)acrylate having an alkyl group having 1 to 4 carbon atoms is even more preferred.

[0220] In the first polymerizable monomer, the polymerizable monomers other than the crosslinking monomers are non-crosslinking monomers. In 100 parts by mass of the first polymerizable monomer, the content of non-crosslinking monomers in the first polymerizable monomer is preferably 0 to 15 parts by mass. From the viewpoint of suppressing the decrease in reactivity of the first polymerizable monomer, improving the strength and solvent resistance of hollow particles, and improving the lightweight effect brought about by hollow particles, the content of non-crosslinking monomers in 100 parts by mass of the first polymerizable monomer is more preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably the first polymerizable monomer does not contain non-crosslinking monomers.

[0221] 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, it is usually 15 to 55% by mass relative to the total mass of 100% by mass of the components in the mixture other than the aqueous medium, and more preferably 25 to 40% by mass.

[0222] 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 solid components other than hydrocarbon solvents in the oil phase material of 100% by mass mixture.

[0223] (B) Oil-soluble polymerization initiator

[0224] In this invention, it is preferable that the mixture 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, allowing suspension polymerization to be performed using oil-soluble polymerization initiators.

[0225] 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-butyl peroxide-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylpentanonitrile), and azobisisobutyronitrile.

[0226] When the total mass of the first polymerizable monomer in the mixture is 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 using an oil-soluble polymerization initiator content of 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 terminated is small, as is the possibility of unexpected side reactions.

[0227] (C) Hydrocarbon solvents

[0228] In this invention, a hydrocarbon solvent is used as a non-polymerizable and water-insoluble organic solvent. The hydrocarbon solvent functions as a spacer material forming 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 within the droplets. Ultimately, within the droplets of the monomer composition, the hydrocarbon solvent is distributed within the droplets according to its polarity, while other materials besides the hydrocarbon solvent are distributed around the droplets.

[0229] Furthermore, in the polymerization process described later, an aqueous dispersion containing hollow particles containing a 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.

[0230] 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 solvents with relatively high volatility such as carbon disulfide and carbon tetrachloride.

[0231] The porosity of hollow particles can be adjusted by changing the amount of hydrocarbon solvent in the mixture. In the suspension process described later, since oil droplets containing crosslinking monomers undergo polymerization in a state containing hydrocarbon solvent, there is a tendency that the higher the content of hydrocarbon solvent, the higher the porosity of the resulting hollow particles.

[0232] Regarding the hydrocarbon solvent, the proportion of saturated hydrocarbon solvent in a total of 100% by mass is preferably 50% by mass or more. This allows for sufficient phase separation within the droplets of the polymerizable monomer, making it easy to obtain hollow particles with only one hollow portion, and suppressing the formation of porous particles. From the perspective of further suppressing the formation of porous particles and facilitating the uniformity of 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.

[0233] Furthermore, hydrocarbon solvents with 4 to 7 carbon atoms are preferred as hydrocarbon solvents. Hydrocarbon compounds with 4 to 7 carbon atoms are easily encapsulated within the first precursor particles during the polymerization process and can be easily removed from the second precursor particles during the solvent removal process. Hydrocarbon solvents with 5 or 6 carbon atoms are particularly preferred.

[0234] Furthermore, although not particularly limited, from the perspective of being easily removed in the solvent removal process described later, hydrocarbon solvents with a boiling point of 130°C or lower are preferred as hydrocarbon solvents, and hydrocarbon solvents with a boiling point of 100°C or lower are more preferred as hydrocarbon solvents. Furthermore, from the perspective of being easily contained within the first precursor particles, hydrocarbon solvents with a boiling point of 50°C or higher are preferred as hydrocarbon solvents, and hydrocarbon solvents with a boiling point of 60°C or higher are more preferred as hydrocarbon solvents.

[0235] 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 is believed that when the relative permittivity of the hydrocarbon solvent is sufficiently low, such as 3 or less, phase separation occurs rapidly in the droplets of the monomer composition, easily forming hollow sections.

[0236] 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.

[0237] Heptane (1.9%), n-hexane (1.9%), cyclohexane (2.0%), benzene (2.3%), toluene (2.4%).

[0238] 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), as well as other technical information. As a method for determining the relative permittivity at 20°C, examples include, for instance, the relative permittivity test based on section 23 of JISC 2101:1999, conducted at 20°C as the measurement temperature.

[0239] In this invention, from the perspectives of easily controlling the particle size of the hollow particles, easily maintaining the strength of the hollow particles and improving porosity, and easily reducing the amount of residual hydrocarbon solvent in the particles, the content of hydrocarbon solvent in the mixture relative to 100 parts by mass of the total mass of the first polymerizable monomer is preferably 50 parts by mass or more and 500 parts by mass or less. More preferably, the content of hydrocarbon solvent in the mixture relative to 100 parts by mass of the total mass of the first polymerizable monomer is 60 parts by mass or more and 400 parts by mass or less, 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.

[0240] (D) Dispersant stabilizer

[0241] 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.

[0242] 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.

[0243] 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.

[0244] 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.

[0245] In this invention, it is particularly preferred to use the water-insoluble inorganic dispersion stabilizer in the form of colloidal particles in an aqueous medium, i.e., in the form of a colloidal dispersion containing the water-insoluble inorganic dispersion stabilizer colloidal particles. This not only narrows the droplet size distribution of the monomer composition, but also allows for easy suppression of the residual amount of inorganic dispersion stabilizer in the resulting hollow particles through washing.

[0246] Colloidal dispersions containing water-insoluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from alkali metal hydroxide and alkaline earth metal hydroxide with a water-soluble polyvalent metal salt (other than alkaline earth metal hydroxide) in an aqueous medium.

[0247] 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.

[0248] 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 is acceptable. 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.

[0249] As a method for reacting at least one of the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium, there is no particular limitation, and a method of mixing an aqueous solution of at least one of the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with an aqueous solution of the water-soluble polyvalent metal salt can be cited.

[0250] The content of the dispersant stabilizer is not particularly limited, but is preferably 0.5 to 10 parts by mass relative to the total mass of 100 parts by mass of the first polymerizable monomer and the hydrocarbon solvent, more preferably 1.0 to 8.0 parts by mass. By keeping 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 without agglomeration. On the other hand, by keeping 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 in the granulator.

[0251] Furthermore, the content of the dispersant stabilizer is typically 2 parts by mass or more and 15 parts by mass or less relative to 100 parts by mass of the aqueous medium, preferably 3 parts by mass or more and 8 parts by mass or less.

[0252] (E) Aquatic media

[0253] In this invention, an aqueous medium refers to a medium selected from water, hydrophilic solvents, and mixtures of water and hydrophilic solvents.

[0254] The hydrophilic solvent of this invention is not particularly limited as long as it is a substance that 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).

[0255] Based on the polarity of the aqueous medium, water is preferred. When using a mixture of water and a hydrophilic solvent, from the viewpoint of forming droplets of the monomer composition, it is important that the overall polarity of the mixture does not become too low. In this case, for example, the mixing ratio (mass ratio) of water to hydrophilic solvent can be water:hydrophilic solvent = 99:1 to 50:50.

[0256] 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) oil-soluble polymerization initiator, and (C) hydrocarbon solvent, etc., is dispersed in an aqueous phase containing (D) dispersant stabilizer and (E) aqueous medium, etc., with a particle size of about several millimeters. Depending on the type of materials, the dispersion state of these materials in the mixture can be observed even with the naked eye.

[0257] In the preparation process of the mixture, the mixture can be obtained by simply mixing the above-mentioned materials and other materials as needed, and stirring appropriately. From the viewpoint of easily achieving homogeneity, it is preferable to prepare an oil phase containing a first polymerizable monomer and a hydrocarbon solvent, and an aqueous phase containing a dispersing stabilizer and an aqueous medium separately in advance, and then mix them to prepare the mixture. In this invention, it is preferable to use a colloidal dispersion, formed by dispersing a water-poorly soluble inorganic dispersing stabilizer in the form of colloidal particles in an aqueous medium, as the aqueous phase.

[0258] By preparing the oil phase and water phase separately in advance and then mixing them, it is possible to produce hollow particles with a uniform composition of shell portion.

[0259] (2) Suspension process

[0260] 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.

[0261] 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 (horizontal inline dispersers such as those manufactured by Taihei Kiko Co., Ltd., trade name: Milder, and Eurotec Co., Ltd., trade name: Cavitron; vertical inline dispersers such as those manufactured by IKA, trade name: DRS2000 / 5), and high-speed emulsifying dispersers (such as those manufactured by PRIMIX Co., Ltd., trade name: TKHomomixer MARK II), can be used.

[0262] 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 1–80 μm are uniformly dispersed in an aqueous medium. These droplets of monomer composition are difficult to observe with the naked eye but can be observed using known observation equipment such as an optical microscope.

[0263] In the suspension process, due to phase separation occurring within the droplets of the monomer composition, the low-polarity hydrocarbon solvent tends to aggregate inside the droplets. The resulting droplets are characterized by the hydrocarbon solvent distributed inside, with materials other than the hydrocarbon solvent distributed at the outer edge.

[0264] 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) Corresponding.

[0265] Figure 2 The diagram shows the state 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.

[0266] The monomer composition contains an oil-soluble polymerization initiator 5, a first polymerizable monomer, and a hydrocarbon solvent (none of which are shown).

[0267] 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, the tiny oil droplet is not allowed to grow excessively, and precursor particles of the target particle size can be produced.

[0268] 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 small, dense particles other than the target hollow resin particles, as byproducts.

[0269] (3) Polymerization process

[0270] (3-1) First polymerization process

[0271] In the above manufacturing method, the polymerization process is carried out in two stages.

[0272] In the first polymerization step, a first polymerization reaction is carried out by supplying the suspension to the polymerization reaction until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, thereby preparing a first precursor composition containing first precursor particles, wherein the first precursor particles have a shell of polymer containing the first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent.

[0273] In the first polymerization reaction, droplets of the monomer composition are supplied to the polymerization reaction in a state containing a hydrocarbon solvent, thereby facilitating polymerization while maintaining the 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 and the type of dispersant stabilizer. Furthermore, since the first polymerizable monomer and hydrocarbon solvent are used in combination, the hydrocarbon solvent has low polarity relative to the shell of the first precursor particle, making it difficult for the hydrocarbon solvent to fuse with the shell. As a result, sufficient phase separation occurs, and only one hollow portion is easily formed.

[0274] In the first polymerization reaction, there are no particular restrictions on the polymerization method, and it can be, for example, batch (partial), semi-continuous, or continuous.

[0275] In the first polymerization reaction, the polymerization temperature is preferably 40–80°C, and more preferably 50–70°C.

[0276] 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.

[0277] Furthermore, the reaction time of the first polymerization reaction is preferably 0.5 to 5 hours, and more preferably 1 to 3 hours.

[0278] 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.

[0279] Furthermore, the polymerization conversion rate in this invention is calculated using the following formula (A) by 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 after the first polymerization reaction without reacting. In this invention, the solid component refers to all components except the solvent; liquid polymerizable monomers are included in the solid component. Furthermore, the mass of the unreacted first polymerizable monomer can be determined using gas chromatography (GC).

[0280] Polymerization conversion rate (mass%) = 100 - (mass of unreacted first polymerizable monomer / mass of solid component of first precursor particles) × 100 Equation (A)

[0281] (3-2) Second polymerization process

[0282] In the second polymerization step, a second polymerizable monomer with a solubility of 0.3 g / L or more in distilled water at 20°C is added to the first precursor composition obtained in the first polymerization step, and a second polymerization reaction is carried out to prepare a second precursor composition containing second precursor particles. 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.

[0283] In the second polymerization reaction, the polymerization reaction takes place with the second polymerizable monomer inside the shell of the first precursor particle. The entry of the second polymerizable monomer into the shell of the first precursor particle promotes thermal motion. Therefore, it is speculated that in the second polymerization reaction, the polymerizable functional groups of the first polymerizable monomer remaining in an unreacted state inside the shell undergo polymerization with the second polymerizable monomer to form a dense cross-linked structure.

[0284] 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 viewpoint of improving the strength and solvent resistance of the hollow particles and enhancing the lightweight properties 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 monomers that are the same as those that can be used as the first polymerizable monomer. From the viewpoint of improving the strength and solvent resistance of the hollow particles and enhancing the lightweight properties of the hollow particles, at least one of the following is preferred: alkyl (meth)acrylates having 1 to 5 carbon atoms, (meth)acrylonitrile and its derivatives, and non-crosslinked monomers containing polar groups. Alkyl (meth)acrylates having 1 to 5 carbon atoms are more preferred, and alkyl (meth)acrylates having 1 to 4 carbon atoms are even more preferred.

[0285] Alkyl acrylates and acrylates are preferred as the aforementioned (meth)acrylates and (meth)acrylonitrs, respectively. When the polymerizable functional group is acryloyl instead of methacryloyl, the reactivity is excellent, thereby easily improving the lightweight effect brought about by hollow particles. Furthermore, unreacted second polymerizable monomers are less likely to remain. In addition, in this invention, the acrylic crosslinking monomer only needs to be a crosslinking monomer having at least one acryloyl group as a polymerizable functional group and not having a methacryloyl group; preferably, all polymerizable functional groups are acryloyl groups.

[0286] Furthermore, from the viewpoint of improving the lightweight effect brought about by hollow particles, the number of carbon atoms of the alkyl group in the above-mentioned (meth)acrylate is preferably 1 to 4, and from the viewpoint that the unreacted second polymerizable monomer is less likely to remain, it is more preferably 1 to 3, and even more preferably the alkyl group is methyl.

[0287] Of the above-mentioned non-crosslinked monomers containing polar groups, epoxy-containing monomers, hydroxyl-containing monomers, and amino-containing monomers are preferred. Of the epoxy-containing monomers that are the above-mentioned non-crosslinked monomers containing polar groups, glycidyl (meth)acrylate is preferred, and of the hydroxyl-containing monomers, 2-hydroxyethyl methacrylate is preferred.

[0288] 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 also be used. Examples of hydrophilic crosslinking monomers used as the second polymerizable monomer include, for example, monomers that can be used as the first polymerizable monomer. Among these, hydrophilic crosslinking monomers containing hydroxyl or amino groups are preferred. Examples of hydrophilic crosslinking monomers containing hydroxyl groups are propyl acrylate-2-hydroxy-3-methacrylate, and examples of hydrophilic crosslinking monomers containing amino groups are diallylamine, etc.

[0289] Furthermore, from the viewpoint that the second polymerizable monomer can easily promote thermal motion and increase the strength of the hollow particles by entering the shell of the first precursor particles, its solubility 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.

[0290] Furthermore, from the viewpoint that the second polymerizable monomer entering the shell of the first precursor particle easily promotes thermal motion, improves the strength and solvent resistance of the hollow particles, and enhances the lightweight effect brought about by the hollow particles, 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 typically 50 or more.

[0291] The amount of the second polymerizable monomer added is preferably 3 to 15 parts by mass relative to 100 parts by mass of the first polymerizable monomer, more preferably 4 to 10 parts by mass. When the amount of the second polymerizable monomer added is at or above the lower limit mentioned above, the effect of promoting the polymerization reaction by adding the second polymerizable monomer is improved, the cross-linked structure of the shell of the hollow particle becomes denser, thereby improving the strength and solvent resistance of the hollow particle, and thus improving the lightweight effect of the hollow particle. On the other hand, when the amount of the second polymerizable monomer added is below the upper limit mentioned above, the decrease in the content ratio of the first polymerizable monomer relative to the total polymerizable monomer used to form the shell can be suppressed. Since the first polymerizable monomer contains a large amount of cross-linking monomer, by suppressing the decrease in the content ratio of the first polymerizable monomer, hollow particles with excellent strength containing a large amount of cross-linked structure formed by cross-linking monomer can be obtained.

[0292] 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 adopted.

[0293] In the second polymerization reaction, the polymerization temperature is preferably 40–80°C, and more preferably 50–70°C.

[0294] The reaction time for the second polymerization reaction is preferably 1 to 6 hours, and more preferably 2 to 4 hours.

[0295] According to the above manufacturing method, the residual amount of unreacted polymeric 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. If the residual amount of unreacted polymeric monomers after the second polymerization reaction is below the above-mentioned upper limit, it means that the reaction rate of the polymeric monomers is high. When the reaction rate of the polymeric monomers is high, the cross-linked structure in the shell tends to become dense, thereby easily improving the solvent resistance and strength of the hollow particles.

[0296] Furthermore, in this invention, the residual amount of unreacted polymeric monomers after the second polymerization reaction refers to the ratio of the mass of the unreacted residual polymeric monomers to the mass of the solid component of the hollow particles obtained through the second polymerization reaction. Additionally, the mass of the unreacted polymeric monomers can be determined using gas chromatography (GC).

[0297] (4) Solid-liquid separation process

[0298] This process involves solid-liquid separation of a second precursor composition containing hollow particles (second precursor particles) with a hydrocarbon solvent, obtained from the above polymerization process, to obtain a solid component containing the second precursor particles.

[0299] There are no particular limitations 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 centrifugation can also be used from the viewpoint of ease of operation.

[0300] After the solid-liquid separation process and before the solvent removal process described later, any process such as a pre-drying process can be performed. As a pre-drying process, an example is a process in which the solid components obtained after the solid-liquid separation process are pre-dried by a drying device such as a dryer or a hand dryer.

[0301] (5) Solvent removal process

[0302] This process is to remove the hydrocarbon solvent contained in the hollow particles (second precursor particles) obtained through the above solid-liquid separation process.

[0303] By removing the hydrocarbon solvent contained in the second precursor particles from the gas, the hydrocarbon solvent inside the second precursor particles is replaced by air, resulting in hollow particles filled with gas.

[0304] 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 trace amount of liquid component exists outside the second precursor particles, to a degree that does not affect the removal of hydrocarbon solvents. "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 that the second precursor particles remove hydrocarbon solvents in an environment of direct contact with the external gas.

[0305] 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.

[0306] 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, for example, 50–200°C, 70–200°C, or 100–200°C.

[0307] By performing a drying operation in a gas, the hydrocarbon solvent inside the second precursor particle is replaced by an external gas, resulting in hollow particles with gas occupying the hollow part.

[0308] There are no particular limitations on the drying environment; air, oxygen, nitrogen, argon, etc., can be considered. Alternatively, by temporarily filling the hollow particles with gas and then drying under reduced pressure, hollow particles with a temporary internal vacuum can also be obtained.

[0309] 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.

[0310] In this method, by blowing an inactive gas into the second precursor composition at a temperature greater than 35°C below the boiling point of the hydrocarbon solvent, the hydrocarbon solvent contained in the second precursor particles can be removed.

[0311] Here, when the aforementioned hydrocarbon solvent is a mixed solvent containing multiple hydrocarbon solvents and has multiple boiling points, the boiling point of the hydrocarbon solvent in the solvent removal process 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.

[0312] 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 bubbling temperature is generally a temperature above the polymerization temperature in the aforementioned polymerization step. While not particularly limited, the bubbling temperature can be 50°C or higher and 100°C or lower.

[0313] There are no particular limitations on the inert gas that can be blown in; examples include nitrogen and argon.

[0314] There are no particular limitations on the bubbling conditions. They can be appropriately adjusted 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.

[0315] 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.

[0316] The method of obtaining hollow particles with gas-filled hollow sections by performing solid-liquid separation on the slurry-like second precursor composition and removing the hydrocarbon solvent from the second precursor particles in a gas is compared with the method of replacing the hydrocarbon solvent contained in the second precursor particles with the aqueous medium of the slurry in a slurry containing the second precursor particles and an aqueous medium, then performing solid-liquid separation and removing the aqueous medium from the second precursor particles in a gas to obtain hollow particles with gas-filled hollow sections. The former method has the advantage of being less likely to cause the hollow particles to break during the process of removing the hydrocarbon solvent, while the latter method has the advantage of reducing the residue of hydrocarbon solvent by using inactive gas for purging.

[0317] Furthermore, when replacing the hydrocarbon solvent contained in the second precursor particles with water, if an equal volume of water equal to the volume of hydrocarbon solvent removed from the particles does not enter the particles, the resulting hollow resin particles may crack. As a way to prevent this, one could consider, for example, removing the hydrocarbon solvent by alkali swelling of the particle shell after ensuring the slurry pH is above 7. In this case, because the particle shell becomes flexible, the replacement of the hydrocarbon solvent with water inside the particles can proceed rapidly.

[0318] Furthermore, as a method to remove the hydrocarbon solvent contained in the second precursor particles by not performing solid-liquid separation on the slurry-like second precursor composition obtained in the polymerization process and before the solid-liquid separation process, for example, the following methods can be used: evaporating and distilling off the hydrocarbon solvent contained in the second precursor particles from the second 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 second precursor composition under a specified pressure (high pressure, normal pressure, or reduced pressure) to evaporate and distill off the hydrocarbon solvent.

[0319] (6) Other

[0320] In addition to the processes described in (1) to (5) above, a cleaning process (6-a) and a re-replacement process of the hollow part (6-b) below may be added.

[0321] (6-a) Cleaning process

[0322] The cleaning process refers to the step of adding acid or alkali to remove residual dispersant stabilizer in the 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.

[0323] Furthermore, when using an acid-soluble inorganic dispersion stabilizer as the dispersion stabilizer, an acid is added to the second precursor composition containing the second precursor particles, and the pH is preferably adjusted to 6.5 or less, more preferably to 6 or less. 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. Sulfuric acid is particularly preferred from the perspective of high removal efficiency of the dispersion stabilizer and low burden on manufacturing equipment.

[0324] (6-b) Re-displacement process of the hollow section

[0325] 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 such displacement, the internal environment of the hollow particles can be changed, molecules can be selectively sealed inside the hollow particles, or the internal chemical structure of the hollow particles can be modified according to the intended use.

[0326] II-2. Procedures for preparing resin compositions

[0327] The method for manufacturing the fiber-reinforced molded article of the present invention includes a step of preparing a resin composition comprising hollow particles, a matrix resin, and a solvent obtained by the above-described step. In this step, the resin composition is prepared, for example, by mixing the hollow particles, the matrix resin, the solvent, and additives added as needed.

[0328] The content of hollow particles in the resin composition is not particularly limited. From the viewpoint of making the fiber-reinforced molded body lighter, it is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more in all solid components of the resin composition. From the viewpoint of suppressing the reduction of the physical properties of the fiber-reinforced molded body, it is preferably 50% by mass or less, and more preferably 30% by mass or less.

[0329] The matrix resin used in this process is in the state before curing of the matrix resin used in the fiber-reinforced molded body of the present invention.

[0330] As the base resin used in this process, a resin containing an epoxy resin is preferably used. Examples of epoxy resins include: bixylenol-type epoxy resin, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, bisphenol AF-type epoxy resin, dicyclopentadiene-type epoxy resin, triphenol-type epoxy resin, naphthol phenolic varnish-type epoxy resin, phenol phenolic varnish-type epoxy resin, tert-butyl-catechol-type epoxy resin, naphthalene-type epoxy resin, naphthol-type epoxy resin, anthracene-type epoxy resin, glycidylamine-type epoxy resin, and glycidyl ester-type epoxy resin. Epoxy resins include cresol-phenolic varnish type, phenol-aryl alkyl type, biphenyl type, linear aliphatic epoxy resin, butadiene-structured epoxy resin, alicyclic epoxy resin, heterocyclic epoxy resin, spirocyclic epoxy resin, cyclohexane type, cyclohexane-diethanol type, naphthyl ether type, trimethylolpropene type, tetraphenylethane type, isocyanurate type, phenol-phthalamide type, and phenolphthalein type. These epoxy resins can be used individually or in combination of two or more.

[0331] The base resin used in this process may contain additives such as curing agents, curing catalysts, or curing accelerators to cure the resin. The additives used in the base resin to cure the resin can be selected from well-known additives, depending on the type of resin, and are not particularly limited. Examples include: amines, acid anhydrides, imidazoles, thiols, phenols, naphthols, and benzo[a]benzene. Azides, cyanates, and carbodiimides, etc.

[0332] Examples of curing agents that can be used in combination with epoxy resins include amine curing agents, amide curing agents, acid anhydride curing agents, phenol curing agents, reactive ester curing agents, carboxyl-containing curing agents, and thiol curing agents.

[0333] In addition, examples of curing catalysts that can be used in combination with epoxy resins include phosphorus compounds, tertiary amine compounds, imidazole compounds, and organometallic salts.

[0334] These additives used to cure resins can be used individually or in combination of two or more.

[0335] In addition, there is no particular limitation on the viscosity of the matrix resin used in this process. As long as the type and amount of solvent are adjusted to make the overall viscosity of the resin composition excellent for the impregnation of the reinforcing fibers, it is acceptable.

[0336] The content of the matrix resin in the resin composition is not particularly limited. From the viewpoint of the impregnation of the resin composition and the mechanical properties of the fiber-reinforced molded article, it is preferably 50% by mass or more, more preferably 70% by mass or more, in all solid components of the resin composition. From the viewpoint of the lightweighting of the fiber-reinforced molded article, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0337] There are no particular limitations on the solvent used in this process; any known solvent suitable for resin compositions can be used, and the appropriate solvent can be selected based on the type and viscosity of the base resin. As the solvent mentioned above, aromatic hydrocarbons such as benzene, toluene, and xylene are preferred. Alkanes, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and other ketones; ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and other ethers. These solvents can be used individually or in combination of two or more.

[0338] From the viewpoint of easily leveraging the lightweight effects of the hollow particles of the present invention, it is preferable that the solvent contains at least one selected from ketones and ethers, and more preferably contains ketones.

[0339] The solvent content in the resin composition is appropriately adjusted in such a way that it becomes viscous enough to be easily impregnated into the reinforcing fibers. There are no particular limitations. From the viewpoint of easily bringing out the lightweight effects brought about by the hollow particles of the present invention, the solvent content in 100% by mass of the total mass of the resin composition is preferably 10 to 50% by mass, more preferably 20 to 40% by mass.

[0340] In addition, the viscosity of the resin composition is only required to be sufficient to impregnate the reinforcing fibers, and there are no particular limitations.

[0341] Without impairing the effects of this disclosure, the resin composition may further contain additives such as ultraviolet absorbers, colorants, defoamers, thickeners, heat stabilizers, leveling agents, lubricants, antistatic agents, and fillers as needed.

[0342] In this process, the mixing of each component can be carried out at a temperature where the solvent does not evaporate, for example, at a temperature above room temperature and below the boiling point of the solvent. Furthermore, when the resin composition contains a thermosetting resin as the matrix resin, the mixing can be carried out at a temperature lower than the curing temperature of the thermosetting resin, without particular limitation, and is usually carried out at a temperature below 240°C.

[0343] When the resin composition contains a thermoplastic resin as the matrix resin, the mixing of the components can be carried out by melt mixing by heating to melt the thermoplastic resin. The temperature during melt mixing is not particularly limited as long as it is sufficient to melt the thermoplastic resin used, but it is preferably below 250°C from the perspective of suppressing the breakage of hollow particles.

[0344] II-3. The process of impregnating the resin composition with the reinforcing fibers.

[0345] The method for manufacturing the fiber-reinforced molded article of the present invention includes a step of impregnating reinforcing fibers with a resin composition obtained through the above-described steps. The reinforcing fibers impregnated with the resin composition obtained in this step are generally referred to as prepreg.

[0346] The reinforcing fibers used in this process are the same as those used in the fiber-reinforced molded articles of the present invention described above.

[0347] As a method for impregnating the resin composition with the reinforcing fiber, methods such as impregnating the resin composition with the reinforcing fiber and then removing the solvent, or the wet process conventionally used for the manufacture of prepregs, can be used, and there is no particular limitation.

[0348] There are no particular limitations on the method for removing the solvent from the resin composition impregnated with the reinforcing fibers; examples include natural drying, heat drying, and combinations thereof. The temperature for heat drying is appropriately selected based on the type of solvent and matrix resin, allowing for direct removal of the solvent while the resin composition is in an uncured or semi-cured state. There are no particular limitations, but it is typically between 40 and 250°C. Furthermore, general drying equipment such as ovens can be used for heat drying. In addition, there are no particular limitations on the drying time, which is typically between 1 minute and 1 hour.

[0349] II-4. Other processes

[0350] The method for manufacturing the fiber-reinforced molded article of the present invention may further include a step of curing the resin composition impregnated in the reinforcing fiber.

[0351] As a process for curing the resin composition impregnated in the reinforcing fibers, examples include heating and pressurizing the reinforcing fibers impregnated with the resin composition using methods such as compression molding, autoclave molding, sheet winding, bag molding, winding tape, internal pressure molding, and sheet wrapping. Furthermore, the resin composition can be cured by stacking multiple sheets of reinforcing fibers impregnated with the resin composition, or by stacking a support. Examples of materials for the support include resins such as polyethylene terephthalate and polyethylene naphthalate, as well as metals such as copper, stainless steel, aluminum, nickel, chromium, gold, and silver.

[0352] There are no particular limitations on the heating and pressurizing conditions for curing the resin composition. They can be appropriately adjusted according to the composition of the resin composition, the content of each component, and the shape of each component. For example, the curing time can be from 5 minutes to 24 hours at a temperature of 23 to 250°C.

[0353] Example

[0354] The present invention will be described in more detail below with examples and comparative examples; however, the present invention is not limited to these examples. Furthermore, unless otherwise specified, parts and percentages are based on mass.

[0355] [Manufacturing Example 1]

[0356] (1) Mixture preparation process

[0357] First, the following materials are mixed to form an oil phase.

[0358] First polymerizable monomer: 80 parts of ethylene glycol dimethacrylate and 20 parts of pentaerythritol tetraacrylate

[0359] 3 parts of 2,2'-azobis(2,4-dimethylvalerate) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65)

[0360] 125 parts of cyclohexane

[0361] Next, in a stirred tank at room temperature, 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 (water-insoluble metal hydroxide colloid) containing 17.1 parts dissolved in 494 parts of ion-exchanged water, while stirring, to prepare a magnesium hydroxide colloid (water-insoluble metal hydroxide colloid) dispersion (4 parts magnesium hydroxide) as the aqueous phase.

[0362] A mixture is prepared by mixing the aqueous and oil phases.

[0363] (2) Suspension process

[0364] The mixture obtained in the above-mentioned mixture preparation process is stirred in a disperser (PRIMIX Co., Ltd., trade name: HOMOMIXER) at 4000 rpm for 1 minute to suspend it, thereby preparing a suspension of droplets of the monomer composition containing cyclohexane dispersed in water.

[0365] (3) Polymerization process

[0366] The suspension obtained in the above suspension process was subjected to a first polymerization reaction in a nitrogen environment, with the temperature increased from 40°C to 65°C over 30 minutes (heating rate: 50°C / hour), and stirred at 65°C for 1 hour and 30 minutes to obtain 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 in a nitrogen environment at 65°C for 2 hours and 30 minutes to carry out a second polymerization reaction. Through this second polymerization reaction, a second precursor composition containing second precursor particles containing cyclohexane was obtained.

[0367] (4) Cleaning process and solid-liquid separation process

[0368] 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 ion-exchanged water were added for re-slurrying. The mixture was repeatedly washed several times at room temperature (25°C) (washing, filtration, dehydration), 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.

[0369] (5) Solvent removal process

[0370] The second precursor particles obtained in the above solid-liquid separation process were subjected to a vacuum dryer at 200°C for 6 hours to remove the hydrocarbon solvent contained in the particles, thereby obtaining the hollow particles of Manufacturing Example 1. The obtained hollow particles were confirmed to be spherical and have a hollow portion based on the observation results of a scanning electron microscope and the porosity value.

[0371] [Manufacturing Example 2]

[0372] In Manufacturing Example 1, the amount of cyclohexane added in the above "(1) Mixture Preparation Step" was changed to 160 parts. Otherwise, the hollow particles of Manufacturing Example 2 were manufactured according to the same steps as in Manufacturing Example 1.

[0373] [Manufacturing Examples 3-8]

[0374] In Manufacturing Example 1, the type or amount of the second polymerizable monomer added in the above "(3) polymerization process" is as shown in Table 1. Otherwise, the hollow particles of Manufacturing Examples 3 to 8 are manufactured according to the same steps as in Manufacturing Example 1.

[0375] [Comparative Manufacturing Example 1]

[0376] In Manufacturing Example 1, no second polymerizable monomer was added or a second polymerization reaction was carried out in the above-mentioned "(3) Polymerization process". Otherwise, the hollow particles of Comparative Manufacturing Example 1 were manufactured according to the same steps as Manufacturing Example 1.

[0377] [Comparative Manufacturing Example 2]

[0378] In Manufacturing Example 1, in the above-mentioned "(3) Polymerization Step", the reaction time of the first polymerization reaction was changed from 1 hour and 30 minutes to 30 minutes. When the total polymerization conversion rate of ethylene glycol dimethacrylate and pentaerythritol tetraacrylate, which are the first polymerizable monomers, reached 91.0% by mass, the second polymerizable monomer was added and the second polymerization reaction was carried out. Otherwise, the hollow particles of Comparative Manufacturing Example 2 were manufactured according to the same steps as in Manufacturing Example 1.

[0379] [Comparative Manufacturing Example 3]

[0380] In Manufacturing Example 1, in the above-mentioned "(1) Mixture Preparation Step", the material and amount of the first polymerizable monomer are as shown in Table 1. Otherwise, the hollow particles of Comparative Manufacturing Example 3 are manufactured according to the same steps as Manufacturing Example 1.

[0381] [Comparative Manufacturing Example 4]

[0382] In Manufacturing Example 1, in the above-mentioned "(3) Polymerization step", 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 Manufacturing Example 4 were manufactured according to the same steps as in Manufacturing Example 1.

[0383] [Table 1]

[0384]

[0385] [evaluate]

[0386] 1. Aggregation conversion rate

[0387] In the polymerization process of each manufacturing example and each comparative manufacturing example, 50 g of the first precursor composition generated in the first polymerization reaction was collected and filtered under pressure to obtain the first precursor particles (containing water and hydrocarbon solvents) contained in the first precursor composition, accurately weighed to 1 mg unit. 27 g of ethyl acetate was added to approximately 3 g of the accurately weighed first precursor particles, and the mixture was stirred for 15 minutes. Then, 13 g of methanol was added, and the mixture was stirred for another 10 minutes. The resulting solution was allowed to stand to allow the insoluble components to precipitate, and the supernatant of this solution was collected as the test sample. 2 μL of the test sample was injected into a gas chromatograph, and the amount of polymerizable monomer in the test sample was quantified by gas chromatography (GC) under the following conditions, and this amount was taken as the mass of the unreacted first polymerizable monomer. Furthermore, the first precursor particles obtained by pressure filtration were dried at 200°C for 2 hours to remove water and hydrocarbon solvents, and the mass of the solid component of the first precursor particles was determined. Then, the polymerization conversion rate was calculated using the following formula (A).

[0388] Polymerization conversion rate (mass%) = 100 - (mass of unreacted first polymerizable monomer / mass of solid component of first precursor particles) × 100 Equation (A)

[0389] <Conditions for GC>

[0390] Column: TC-WAX (0.25mm×30m)

[0391] Column temperature: 80℃

[0392] Injection temperature: 200℃

[0393] FID detection side temperature: 200℃

[0394] 2. Residual monomer content

[0395] Accurately weigh 3g of hollow particles to a 1mg unit, add 27g of ethyl acetate, stir for 15 minutes, then add 13g of methanol and stir further for 10 minutes. Allow the resulting solution to stand to precipitate the insoluble components, and collect the supernatant as the test sample. Inject 2μl of the test sample into a gas chromatograph, and quantify the amount of unreacted polymerizable monomers in the test sample by gas chromatography (GC) under the following conditions. Calculate the proportion of unreacted polymerizable monomers contained in the hollow particles as the residual monomer amount.

[0396] <Conditions for GC>

[0397] Column: TC-WAX (0.25mm×30m)

[0398] Column temperature: 80℃

[0399] Injection temperature: 200℃

[0400] FID detection side temperature: 200℃

[0401] The percentage (mass%) of each monomer unit in the polymer contained in the shell of the hollow particles obtained in each manufacturing example and each comparative manufacturing example is shown in Table 2.

[0402] Furthermore, the hollow particles obtained in each manufacturing example and each comparative manufacturing example were subjected to the following measurements and evaluations. The results are shown in Table 2.

[0403] 3. Volume average particle size

[0404] The particle size of hollow particles was measured using a laser diffraction particle size analyzer (manufactured by Shimadzu Corporation, trade name: SALD-2000), and their average volume was calculated as the volume average particle size.

[0405] 4. Density and porosity

[0406] 4-1. Determination of apparent density

[0407] 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 to avoid introducing 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 ).

[0408] Formula (I)

[0409] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0410] 4-2. Determination of True Density

[0411] After pre-crushing the hollow granules, fill a 100cm³ volume with approximately 10g of hollow granule fragments. 3 A volumetric flask, used to precisely weigh the mass of the filling fragments.

[0412] Then, in the same manner as the apparent density determination described above, isopropanol is added to a volumetric flask, the mass of isopropanol is accurately weighed, and the true density D0 (g / cm³) of the hollow particles is calculated according to the following formula (II). 3 ).

[0413] Equation (II)

[0414] True density D0 = [mass of fragments of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0415] 4-3. Calculation of Porosity

[0416] 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).

[0417] Equation (III)

[0418] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0419] 5. Immersion test

[0420] 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. After standing for 48 hours, the proportion of precipitated hollow particles was determined, and the mixture was 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 determined by calculating the ratio of the mass of the precipitated hollow particles to the total mass of the hollow particles impregnated in acetone.

[0421] (Evaluation criteria for immersion test)

[0422] 〇: The hollow particles in the precipitate are less than 5% by mass.

[0423] ×: The precipitated hollow particles account for more than 5% by mass.

[0424] [Table 2]

[0425]

[0426] [Inspection]

[0427] As shown in Table 2 above, the hollow particles obtained in Comparative Manufacturing Examples 1 to 4 precipitated in acetone in the above-mentioned impregnation test accounted for more than 5% by mass of hollow particles.

[0428] In Comparative Manufacturing Example 1, by carrying out the polymerization reaction in one stage, it was deduced that unreacted polymeric functional groups remained in the shell, and the cross-linked structure of the shell was coarse, thus allowing acetone to easily penetrate and obtain hollow particles.

[0429] In Comparative Manufacturing Example 2, the second polymerizable monomer was added before the polymerization conversion of the first polymerizable monomer reached 93% by mass. The timing of adding the second polymerizable monomer was too early, so it is speculated that unreacted polymerizable functional groups remain in the shell, and the cross-linking structure of the shell is rough, so acetone can easily penetrate to obtain hollow particles.

[0430] In Comparative Manufacturing Example 3, the first polymerizable monomer contained a low content of crosslinked monomers and a high content of unreacted and directly residual non-crosslinked monomers. Therefore, it is speculated that the crosslinked structure of the shell is coarse, thus allowing acetone to easily penetrate and obtain hollow particles.

[0431] In Comparative Manufacturing Example 4, styrene with a solubility of 0.2 g / L in distilled water at 20°C was used as the second polymerizable monomer instead of the hydrophilic monomer with a solubility of 0.3 g / L or more in distilled water at 20°C. Therefore, it is speculated that the second polymerizable monomer is not easy to enter the shell, and unreacted polymerizable functional groups remain in the shell. The cross-linking structure of the shell is rough, so acetone can easily penetrate the hollow particles obtained.

[0432] In contrast, the hollow particles obtained in Manufacturing Examples 1-8 contain a polymer in the shell containing at least 80 parts by mass of crosslinked monomer units in all monomer units per 100 parts by mass. In the above-mentioned impregnation test, the hollow particles precipitated in acetone were less than 5% by mass. In Manufacturing Examples 1-8, the first polymerizable monomer contained in the mixture fully contained crosslinked monomers. In the polymerization process, when the polymerization conversion rate of the first polymerizable monomer reached 93% by mass or more, a second polymerizable monomer with a solubility of 0.3 g / L or more in distilled water at 20°C was added and further supplied to the polymerization reaction. Therefore, although a large amount of crosslinked monomer was used, it is presumed that almost no unreacted polymeric functional groups remain in the shell, and the crosslinked structure of the shell becomes dense. Thus, hollow particles that are not easily permeated by acetone can be obtained.

[0433] [Examples 1-10, Comparative Examples 1-4]

[0434] (1) Preparation of resin composition (varnish)

[0435] 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, 65% solids MEK solution), 0.1 parts of 2-ethyl-4-methylimidazolium (manufactured by NACALAI TESQUE, INC., 2E4MZ) as a curing catalyst, and the amounts of methyl ethyl ketone (MEK) shown in Table 3 were added, and the mixture was stirred at room temperature for 30 minutes. After stirring, the hollow particles obtained in Manufacturing Examples 1-8 or Comparative Manufacturing Examples 1-4 were added in the amounts shown in Table 3, and the mixture was stirred for another hour to prepare a resin composition (varnish) with a solids content of approximately 70%.

[0436] (2) Preparation of prepreg

[0437] Carbon fiber (manufactured by Mitsubishi Chemical Corporation, trade name: TR3110MS, thickness: 200μm, unit area mass: 200g / m²) cut into 300mm×200mm pieces. 2 Apply 25-30 ml of the above-mentioned resin composition to the carbon fiber. Suspend the carbon fiber coated with the resin composition, allowing the excess resin composition to fall due to its own weight, and let it air dry naturally (air dry). Dry it in a hot air circulating oven at 140°C for 30 minutes to obtain the prepreg.

[0438] (3) Fabrication of fiber-reinforced molded articles

[0439] A PET film (manufactured by NIPPA Co., Ltd., trade name: SFL, thickness: 50 μm) is placed on an SUS plate. A laminate containing two sheets of the prepreg obtained above is stacked on top of the SUS plate, and then a PET film and an SUS plate are sequentially placed on top of the laminate. The resulting laminate is then fed into a vacuum press. After heating and pressing at 120°C and 0.5 MPa for 20 minutes, the temperature is further increased (4°C / min) to 205°C and held for 1 hour. The laminate is then removed from the vacuum press to produce a plate-shaped molded body.

[0440] [Comparative Example 5]

[0441] 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, 65% solids MEK solution), 0.1 parts of 2-ethyl-4-methylimidazolium (manufactured by NACALAI TESQUE, INC., 2E4MZ) as a curing catalyst, and 20 parts of methyl ethyl ketone (MEK), and stir at room temperature for 30 minutes to prepare a resin composition (varnish).

[0442] Using the obtained varnish, molded articles were prepared following the same steps as in Examples 1-10 and Comparative Examples 1-4.

[0443] [evaluate]

[0444] 6. Specific gravity of fiber-reinforced molded bodies

[0445] The specific gravity of the fiber-reinforced molded body was determined by the water displacement method according to JIS K7112.

[0446] 7. Content of hollow particles and reinforcing fibers in fiber-reinforced molded articles (based on mass standard)

[0447] The prepregs obtained as intermediates in each embodiment and comparative example were cut into 150mm × 150mm pieces and used as prepregs for testing. The mass of the prepregs for testing was measured. Furthermore, the mass per unit area of ​​carbon fiber (200g / m²) was also measured. 2 The mass of carbon fibers in the prepreg used for testing is calculated. For this prepreg used for testing, the content (mass %) of the resin component in the prepreg is calculated by the above formula (1) from the mass of the prepreg and the mass of the reinforcing fibers in the prepreg. The content (mass %) of the hollow particles in the solid component of the resin composition impregnated by the reinforcing fibers is calculated by the above formula (2) from the content (mass %) of the resin component and the content (mass %) of the hollow particles in the solid component of the resin composition impregnated by the reinforcing fibers. In addition, the mass of the prepreg used for testing is used as "mass of the fiber-reinforced molded body" in the above formula (1).

[0448] Furthermore, the content (mass %) of reinforcing fibers is calculated as the ratio of the mass of reinforcing fibers in the prepreg used for the above test to the mass of the prepreg used for the above test.

[0449] Furthermore, the content of hollow particles and the content of reinforcing fibers, based on the mass reference, were calculated from six prepregs cut from the prepregs obtained in each embodiment and each comparative example. The content of hollow particles and the content of reinforcing fibers in the fiber-reinforced molded articles obtained in each embodiment and each comparative example were the average values ​​obtained from the six prepregs used for measurement.

[0450] 8. Volumetric content of hollow particles in fiber-reinforced molded articles

[0451] Using the content (mass%) of hollow particles, matrix resin, and reinforcing fibers in the prepreg used in “7. Content of hollow particles and reinforcing fibers in fiber-reinforced molded body” above, the volume of hollow particles, the volume of matrix resin, and the volume of reinforcing fibers are calculated by formulas (3), (4), and (5) above, and the content of hollow particles (volume%) is calculated by formula (6) above.

[0452] In addition, the resin composition prepared in Comparative Example 5 was heated and pressurized under the same conditions as in Example 1 to obtain a cured product. The true density of the cured product was measured and used as the specific gravity (g / cm³) of the cured matrix resin used in the above formula (4). 3 ).

[0453] 9. Tensile modulus of elasticity and tensile strength

[0454] The fiber-reinforced molded bodies obtained in each embodiment and comparative example were cut into test pieces at right angles to the winding direction of the fabric. These test pieces were then cut into strips of 130 mm × 15 mm with the winding direction of the fabric as the minor axis. Tensile tests were performed on these test pieces under the following conditions according to JIS K 7165:2008 to determine the tensile modulus of elasticity and tensile strength.

[0455] <Conditions for Tensile Testing>

[0456] Testing machine: Shimadzu Corporation, model AG-5kNI

[0457] Load sensor: 5t

[0458] Chuck: Wedge type

[0459] Stretching speed: 1mm / minute

[0460] Chuck spacing: 60mm

[0461] Temperature: 25℃

[0462] Humidity: 50% RH

[0463] In addition, the tensile modulus of elasticity and tensile strength were measured from five test pieces cut from the test sample. The tensile modulus of elasticity and tensile strength of the fiber-reinforced molded articles obtained in each embodiment and each comparative example were the average of the three measured values ​​from the five test pieces, excluding the maximum and minimum values.

[0464] [Table 3]

[0465]

[0466] [Inspection]

[0467] As shown in Table 3 above, the specific gravity of the fiber-reinforced molded bodies of Comparative Examples 1-4 obtained using the varnish containing 20% ​​by mass of hollow particles from Comparative Manufacturing Examples 1-4 was 1.36-1.45 g / cm³. 3 Compared with the fiber-reinforced molded body of Comparative Example 5 (specific gravity: 1.48 g / cm³), which does not contain hollow particles. 3 Compared to the previous method, the specific gravity decreased by only 0.03–0.12 g / cm³. 3 .

[0468] In contrast, compared to Comparative Examples 1-4, although the fiber-reinforced molded body of Example 1 obtained using the varnish containing 10% by mass of hollow particles from Manufacturing Example 1 had a lower content of hollow particles, its specific gravity was 1.30 g / cm³. 3Compared to the fiber-reinforced molded body of Comparative Example 5, which does not contain hollow particles, the specific gravity of the hollow particles in the fiber-reinforced molded body of Example 1 was also reduced by 0.18 g / cm³. 3 .

[0469] The fiber-reinforced molded body of Example 2, obtained using the varnish containing 20% ​​by mass of hollow particles from Manufacturing Example 1, has a specific gravity of 1.18 g / cm³. 3 Compared to the fiber-reinforced molded body of Comparative Example 5, which does not contain hollow particles, the specific gravity of the fiber-reinforced molded body of Example 2 was also reduced by 0.30 g / cm³. 3 .

[0470] The fiber-reinforced molded body of Example 3, obtained using the varnish containing 25% by mass of hollow particles from Manufacturing Example 1, has a specific gravity of 1.11 g / cm³. 3 Compared to the fiber-reinforced molded body of Comparative Example 5, which does not contain hollow particles, the specific gravity of the fiber-reinforced molded body of Example 3 was also reduced by 0.37 g / cm³. 3 .

[0471] The fiber-reinforced molded bodies of Examples 4-10, obtained using the varnish containing 20% ​​by mass of hollow particles from Examples 2-8, had a specific gravity of 1.13-1.20 g / cm³. 3 Compared to the fiber-reinforced molded body of Comparative Example 5, which does not contain hollow particles, the specific gravity of the fiber-reinforced molded bodies of Examples 4-10 was also reduced by 0.28-0.35 g / cm³. 3 .

[0472] As shown in Table 2 above, the hollow particles of Comparative Manufacturing Examples 1-4 precipitated in acetone during the above impregnation test accounted for more than 5% by mass, suggesting that the cross-linking structure of the shell was coarse and therefore prone to breakage. Therefore, in the fiber-reinforced molded articles of Comparative Examples 1-4 containing the hollow particles of Comparative Manufacturing Examples 1-4, it is presumed that the hollow particles broke during the manufacturing process and could not maintain porosity, thus failing to achieve sufficient lightweighting.

[0473] In contrast, the hollow particles of Manufacturing Examples 1-8, as shown in Table 2 above, contain a large number of cross-linked monomer units in their shells. In the aforementioned impregnation test, less than 5% by mass of the hollow particles precipitated in acetone, suggesting that the cross-linked structure of the shell is dense and therefore not easily broken. Therefore, in the fiber-reinforced molded articles of Examples 1-10 containing the hollow particles of Manufacturing Examples 1-8, it is presumed that the hollow particles are not easily broken and maintain porosity during the manufacturing process, thus achieving sufficient lightweighting.

[0474] Furthermore, in comparative examples 1 to 3, the higher the content of hollow particles, the lighter the fiber-reinforced molded body.

[0475] In comparative examples 2 and 4, the higher the porosity of the hollow particles, the lighter the fiber-reinforced molded body.

[0476] In comparative examples 2, 5, and 6, the higher the content of cross-linked monomer units in the shell of the hollow particles, the lighter the fiber-reinforced molded body. This is presumably because increasing the content of cross-linked monomer units in the shell makes the cross-linked structure of the shell denser, thereby improving the solvent resistance and strength of the hollow particles.

[0477] In Comparative Examples 2, 7-10, the specific gravity of the fiber-reinforced molded articles varied depending on the type of second polymerizable monomer used in the production of the hollow particles. When using alkyl acrylates having 1 to 4 carbon atoms as the second polymerizable monomer, there was a tendency for the specific gravity to decrease.

[0478] Furthermore, the fiber-reinforced molded articles obtained in Examples 1 to 10 have tensile modulus of elasticity and tensile strength within the range applicable to fiber-reinforced molded articles.

[0479] Explanation of reference numerals in the attached figures

[0480] 1: Aquatic medium

[0481] 2: Low polarity materials

[0482] 3: Dispersing stabilizer

[0483] 4: Monomer Compositions

[0484] 4a: Hydrocarbon solvents

[0485] 4b: Materials other than hydrocarbon solvents

[0486] 4c: Polymerizable monomers dispersed in aqueous media

[0487] 5: Oil-soluble polymerization initiators

[0488] 6: Shell

[0489] 8: Hollow section

[0490] 10: Droplets

[0491] 20: Hollow particles containing hydrocarbon solvents in the hollow section (second precursor particles)

[0492] 100: Hollow particles whose hollow core is filled with gas

Claims

1. A fiber-reinforced molded article comprising a matrix resin, reinforcing fibers, and hollow particles. The hollow particles are manufactured by adding a second polymerizable monomer, which is a hydrophilic non-crosslinked monomer with a solubility of 2 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 hollow particle has a shell containing resin and a hollow portion surrounded by the shell. The shell contains a polymer as the resin, wherein the polymer comprises at least 80 parts by mass of crosslinking monomer units derived from the crosslinking monomer in 100 parts by mass of all monomer units, the crosslinking monomer units being composed of (meth)acrylic acid-based crosslinking monomer units. In the impregnation test of hollow particles, less than 5% 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 for 10 minutes at a shaking speed of 100 rpm, and then letting it stand for 48 hours.

2. The fiber-reinforced molded article according to claim 1, wherein, Of all 100 parts by weight of the polymer contained in the shell of the hollow particle, the content of the hydrophilic non-crosslinked monomer unit from the hydrophilic non-crosslinked monomer is 2 to 20 parts by weight, and the content of the crosslinked monomer unit is 80 to 98 parts by weight.

3. The fiber-reinforced molded article according to claim 1 or 2, wherein, The hollow particle has a shell containing a polymer that includes trifunctional or higher crosslinking monomer units derived from trifunctional or higher crosslinking monomers as crosslinking monomer units, wherein the content of the trifunctional or higher crosslinking monomer units in 100 parts by mass of all monomer units of the polymer is 5 to 50 parts by mass.

4. A method for manufacturing a fiber-reinforced molded article, wherein the fiber-reinforced molded article comprises a matrix resin, reinforcing fibers, and hollow particles. The method for manufacturing the fiber-reinforced molded article includes: The process of manufacturing hollow pellets; The process of preparing a resin composition containing hollow particles obtained through the aforementioned process, a matrix resin, and a solvent; and the process of impregnating the resin composition with reinforcing fibers. In the process of manufacturing hollow particles, the hollow particles are manufactured by the following method: The method for manufacturing the hollow particles includes a step of preparing a mixture comprising a first polymerizable monomer, a hydrocarbon solvent, a dispersing stabilizer and an aqueous medium. The steps of preparing a suspension of droplets containing the first polymerizable monomer and the hydrocarbon solvent dispersed in the aqueous medium by suspending the mixture; and the steps of supplying the suspension to the polymerization reaction. The mixture contains a crosslinking monomer as the first polymerizable monomer, and the content of the crosslinking monomer in 100 parts by weight of the first polymerizable monomer is 80 parts by weight or more, and the crosslinking monomer is composed of a (meth)acrylic acid-based crosslinking monomer. In the process 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 with a solubility of 2 g / L or more in distilled water at 20°C is added and further supplied to the polymerization reaction.

5. The method for manufacturing the fiber-reinforced molded article according to claim 4, wherein, In the process of manufacturing hollow particles, in the step of supplying the suspension to the polymerization reaction, the amount of the second polymerizable monomer added is 3 to 15 parts by mass relative to 100 parts by mass of the first polymerizable monomer.

6. The method for manufacturing the fiber-reinforced molded article according to claim 4 or 5, wherein, In the process of preparing the mixture in the process of manufacturing hollow particles, the first polymerizable monomer includes a trifunctional or higher crosslinking monomer as the crosslinking monomer, and the content of the trifunctional or higher crosslinking monomer in 100 parts by mass of the first polymerizable monomer is 5 to 50 parts by mass.

7. The method for manufacturing a fiber-reinforced molded article according to claim 4 or 5, wherein, In the process of preparing the mixture in the process of manufacturing hollow particles, the dispersing stabilizer is an inorganic dispersing stabilizer.

8. The method for manufacturing the fiber-reinforced molded article according to claim 7, wherein, The inorganic dispersing stabilizer is a water-insoluble metal salt.

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