Resin composition

Abstract

Provided is a resin composition that suppresses any decrease in physical properties when formed into a molded body while containing hollow particles. A resin composition including: a thermoplastic plastomer having an acid value of less than 3.0 mg KOH / g; hollow particles that are provided with a shell including a resin and a hollow portion surrounded by the shell and that contain, as the resin, a polymer including 30-100 parts by mass of crosslinkable monomer units per 100 parts by mass of all monomer units; and an acid-modified polyolefin resin having an acid value of 3.5 mg KOH / g or higher.

Description

[Technical Field]

[0001] The present disclosure relates to a resin composition, and more particularly to a resin composition containing hollow particles. [Background technology]

[0002] Hollow particles (hollow resin particles) are particles that have a cavity inside them, and compared with solid particles whose interiors are substantially filled with resin, hollow particles scatter light well and have low light transmittance. Therefore, they are widely used as organic pigments or hiding agents with excellent optical properties such as opacity and whiteness in applications such as water-based paints and paper coating compositions, and are also used as weight-reducing agents and heat-insulating agents in resins and paints used in various fields such as automobiles, electricity, electronics, and construction.

[0003] The present applicant has disclosed in Patent Document 1 a resin composition containing a thermoplastic plastomer and hollow resin particles. The hollow resin particles contained in the resin composition disclosed in Patent Document 1 have a high porosity and are lightweight. Because the shell is formed from a resin with a high proportion of cross-linkable monomer, the thermoplasticity of the shell is low, and the hollow resin particles have high mechanical strength even at high temperatures and are resistant to crushing. Therefore, the resin composition disclosed in Patent Document 1 shows little change in the porosity of the hollow resin particles during molding processing, and by using this resin composition, it is possible to stably mold lightweight molded articles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 066704 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional resin compositions containing a resin and hollow particles have had the problem that, depending on the type of resin or the conditions for producing the resin composition or the molded article, the physical properties such as tensile strength and flexural strength of the molded article are reduced compared to resin compositions that do not contain hollow particles. In view of the above circumstances, an object of the present disclosure is to provide a resin composition that contains hollow particles but that suppresses deterioration in physical properties when formed into a molded article. [Means for solving the problem]

[0006] The present disclosure provides a thermoplastic plastomer having an acid number of less than 3.0 mg KOH / g; hollow particles comprising a shell containing a resin and a hollow portion surrounded by the shell, the resin containing a polymer containing 30 to 100 parts by mass of crosslinkable monomer units in 100 parts by mass of all monomer units; and an acid-modified polyolefin resin having an acid value of 3.5 mgKOH / g or more.

[0007] In the resin composition of the present disclosure, the content of the acid-modified polyolefin resin is preferably 10 to 150 parts by mass relative to 100 parts by mass of the hollow particles.

[0008] In the resin composition of the present disclosure, the acid-modified polyolefin resin preferably has a weight average molecular weight of 15,000 or more.

[0009] In the resin composition of the present disclosure, the acid-modified polyolefin resin is preferably a carboxylic acid-modified polyolefin resin.

[0010] In the resin composition of the present disclosure, the thermoplastic plastomer is preferably a polyolefin resin. [Effects of the Invention]

[0011] The present disclosure can provide a resin composition that contains hollow particles but that suppresses deterioration in physical properties when formed into a molded article. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a method for producing hollow particles used in the present disclosure. [Figure 2] 1 is a schematic diagram illustrating an embodiment of a suspension in a suspension preparation step. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] In the present disclosure, the use of "to" in a numerical range means that the numerical values ​​before and after it are included as the lower limit and upper limit. In the present disclosure, (meth)acrylate refers to each of acrylate and methacrylate, (meth)acrylic refers to each of acrylic and methacrylic, and (meth)acryloyl refers to each of acryloyl and methacryloyl. The resin composition of the present disclosure and the molded article of the resin composition of the present disclosure will be described below in order.

[0014] 1.Resin composition The resin composition of the present disclosure comprises a thermoplastic plastomer having an acid value of less than 3.0 mg KOH / g; hollow particles comprising a shell containing a resin and a hollow portion surrounded by the shell, the resin containing a polymer containing 30 to 100 parts by mass of crosslinkable monomer units in 100 parts by mass of all monomer units; and an acid-modified polyolefin resin having an acid value of 3.5 mgKOH / g or more.

[0015] Conventional resin compositions containing resin and hollow particles tend to have reduced physical properties such as tensile strength, flexural strength, and flexural modulus when molded into articles compared to resin compositions not containing hollow particles. It is believed that molded articles from conventional resin compositions containing resin and hollow particles have reduced physical properties such as strength against external forces because the strength of the interface between the resin and the hollow particles is relatively low due to low adhesion at the interface between the resin and the hollow particles. In contrast, the resin composition of the present disclosure contains a thermoplastic plastomer as a resin, hollow particles, and an acid-modified polyolefin resin in combination. In the acid-modified polyolefin resin, the polyolefin portion has relatively low polarity, and the acid-modified portion has relatively high polarity. On the other hand, the thermoplastic plastomer usually has lower polarity than the hollow particles. Therefore, the polyolefin portion of the acid-modified polyolefin resin has good affinity with the thermoplastic plastomer, and the acid-modified portion of the acid-modified polyolefin resin has good affinity with the hollow particles. In the resin composition of the present disclosure containing such an acid-modified polyolefin resin, the thermoplastic plastomer, and hollow particles, the acid-modified polyolefin resin is likely to penetrate between the thermoplastic plastomer and the hollow particles, and it is presumed that a molded article of the resin composition of the present disclosure is likely to have a configuration in which the thermoplastic plastomer is present around the hollow particles via the acid-modified polyolefin resin. In the molded body, the adhesion between the hollow particles and the acid-modified polyolefin-based resin, and the adhesion between the thermoplastic plastomer and the acid-modified polyolefin-based resin are good, so that molded bodies of the resin composition of the present disclosure are less likely to have areas with relatively low strength, and as a result, it is presumed that deterioration in physical properties is suppressed. Furthermore, the hollow particles contained in the resin composition of the present disclosure have a shell containing a polymer with a high ratio of crosslinkable monomer units, which results in low thermoplasticity of the shell and high mechanical strength even at high temperatures, making the hollow particles less likely to be crushed and with only a small change in porosity even under the high-temperature, high-pressure environment that occurs during molding of the resin composition of the present disclosure. Therefore, in the resin composition of the present disclosure, crushing of hollow particles during molding processing is suppressed regardless of molding processing conditions such as extrusion molding and injection molding, and by using the resin composition of the present disclosure, it is possible to mold a lightweight molded article. Furthermore, the hollow particles contained in the resin composition of the present disclosure are resistant to crushing even under high temperature and high pressure conditions, and therefore the resin composition of the present disclosure allows for a wide range of selectable molding processing conditions. The thermoplastic plastomer, hollow particles, and acid-modified polyolefin resin contained in the resin composition of the present disclosure will be described below in this order.

[0016] [Thermoplastic plastomer] The resin composition of the present disclosure contains a thermoplastic plastomer as a resin. A plastomer generally refers to a material that exhibits little or no elastic deformation and easily undergoes plastic deformation, whereas an elastomer is the polar opposite of a plastomer, which refers to a material that deforms instantly in response to an external force and quickly recovers its original shape when the external force is removed. In this disclosure, "thermoplastic plastomer" refers to a polymer that has the property of being easily flowable and deformable when heated, and solidifying into the deformed shape when cooled.

[0017] In the present disclosure, the thermoplastic plastomer can typically be a material that can be stretched to 200% of its original dimension at room temperature (20°C) with a small external force in a tensile test, and that does not return to its original dimension less than 130% even after the external force is removed. Specifically, a small external force refers to an external force resulting in a tensile strength of 1 to 100 MPa. More specifically, the thermoplastic plastomer can be a polymer that can be stretched to twice the gauge length of a dumbbell-shaped No. 4 test piece specified in JIS K 6251-1993 without breaking in a tensile set test at 20°C in accordance with JIS K 6262-1997, and that, after being held at twice the gauge length for 60 minutes at the point where it was stretched, has a tensile set of 30% or more 5 minutes after the external tensile force is removed.

[0018] As the thermoplastic plastomer, a wide variety of thermoplastic resins that can be used for conventional molding processes can be used, for example, polyvinyl chloride; polyvinylidene chloride; polyvinyl alcohol; ethylene-based copolymers such as ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-ethyl (meth)acrylate copolymer, and ethylene-butyl (meth)acrylate copolymer; polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (ULDPE), medium-density polyethylene, and high-density polyethylene (HDPE); polypropylene homopolymer (PP homopolymer), random polypropylene (random PP), block polypropylene, etc. Examples of suitable thermoplastic plastomers include polypropylene resins such as propylene (block PP), polybutene resins, polycycloolefins, and polyolefin-based resins such as propylene-α-olefin copolymers; styrene-based copolymers such as styrene-acrylonitrile copolymers and styrene-butadiene-acrylonitrile copolymers; polystyrene; polyterpene; polyacetal; polymethyl (meth)acrylate; cellulose acetate; polycarbonate; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; thermoplastic polyurethane; tetrafluoroethylene resin (PTFE); ionomer resins such as ethylene-based ionomers, urethane-based ionomers, styrene-based ionomers, and fluorine-based ionomers; polyacetal; and polyphenylene sulfide. These thermoplastic plastomers can be used alone or in combination of two or more.

[0019] The thermoplastic plastomer contained in the resin composition of the present disclosure preferably contains a polyolefin resin, in particular, from the viewpoint of good affinity with acid-modified polyolefin resins and improving the mechanical strength when formed into a molded article. Here, the polyolefin resin in the present disclosure includes a polymer of one type of olefin, a copolymer of two or more types of olefin, and a copolymer of one or more types of olefin with one or more types of other monomers. In a polyolefin resin that is a copolymer of one or more types of olefin with one or more types of other monomer, the copolymerization ratio of the olefin is preferably 50 mass% or more. Examples of polyolefin-based resins include the above-mentioned polyethylene-based resins, polypropylene-based resins, polybutene-based resins, polycycloolefins, and propylene-α-olefin copolymers. Among these, polyethylene-based resins, polypropylene-based resins, and propylene-α-olefin copolymers are preferred, and polypropylene-based resins are particularly preferred. Here, for example, polyethylene-based resins may be those copolymerized with a small amount of an olefin other than ethylene or other monomer. The same applies to polypropylene-based resins and polybutene-based resins, which may be those copolymerized with a small amount of an olefin other than propylene or butene or other monomer. A propylene-α-olefin copolymer is a copolymer of propylene and an α-olefin other than propylene, and may also be those copolymerized with a small amount of another monomer. Here, "copolymerized with a small amount" may mean, for example, that the copolymerization ratio is 10% by mass or less, or 5% by mass or less. The olefin used in the synthesis of the polyolefin resin is preferably an alkene having 2 to 30 carbon atoms, more preferably at least one selected from alkenes having 2 to 4 carbon atoms and α-olefins having 5 to 30 carbon atoms, and even more preferably at least one selected from α-olefins having 2 to 10 carbon atoms. Examples of other monomers different from olefins that may be used in the synthesis of polyolefin-based resins include monomers having 4 to 30 carbon atoms and having an unsaturated bond copolymerizable with olefins, and specific examples include vinyl acetate. In the propylene-α-olefin copolymer, the copolymerization ratio of propylene to α-olefin is not particularly limited, but the copolymerization ratio of propylene is preferably 50 to 90 mass%, more preferably 70 to 90 mass%. The α-olefin used in the propylene-α-olefin copolymer is preferably an α-olefin having 2 to 6 carbon atoms, and particularly preferably ethylene or butene.

[0020] The thermoplastic plastomer also has an acid value of less than 3.0 mgKOH / g, preferably less than 2.5 mgKOH / g. Thermoplastic plastomers with acid values ​​less than the upper limit are excellent in that they are less susceptible to humidity due to their low water absorption, have stable chemical properties, have excellent electrical properties, and have extremely small dielectric constants and power factors in the high-frequency range. However, because they have low affinity with hollow particles, when used in conventional resin compositions containing hollow particles, the physical properties of the resin composition when molded into a molded product are likely to deteriorate. On the other hand, in the resin composition of the present disclosure, even when a thermoplastic plastomer with an acid value less than the upper limit is used, deterioration in the physical properties of the molded product can be suppressed. The lower limit of the acid value of the thermoplastic plastomer is not particularly limited, and may be 0 mgKOH / g or more. In the present disclosure, the acid value of a resin is a value obtained by measuring in accordance with JIS K0070, 3.1, neutralization titration method, according to the following steps (i) to (iii). (i) Dissolve 1 g of a measurement sample in 100 g of xylene adjusted to 100°C. (ii) At the same temperature, titration is carried out with 0.1 mol / L potassium hydroxide ethanol solution (trade name: 0.1 mol / L ethanolic potassium hydroxide solution, manufactured by Wako Pure Chemical Industries, Ltd.) using phenolphthalein as an indicator. (iii) Convert the amount of potassium hydroxide required for titration into mg to calculate the acid value (unit: mgKOH / g).

[0021] The thermoplastic plastomer preferably has a solubility parameter (SP value) of 13 (cal / cm 3 ) 1 / 2 Less than 12 (cal / cm 3) 1 / 2 More preferably, 10 (cal / cm 3 ) 1 / 2 or less. Thermoplastic plastomers with an SP value of the above upper limit or less have low water absorption and are therefore less susceptible to humidity environments, and are excellent in electrical properties, with extremely small dielectric constants and power factors in the high-frequency range. However, because they have low affinity with hollow particles, when they are used in conventional resin compositions containing hollow particles, the physical properties of the resin composition when molded into a molded article are likely to deteriorate. On the other hand, in the resin composition of the present disclosure, even when a thermoplastic plastomer with an SP value of the above upper limit or less is used, deterioration in the physical properties of the molded article can be suppressed. The lower limit of the SP value of the thermoplastic plastomer is not particularly limited, but is preferably 6 (cal / cm 3 ) 1 / 2 More preferably, 7 (cal / cm 3 ) 1 / 2 That's all. In addition, 1 (cal / cm 3 ) 1 / 2 is 2.05(J / cm 3 ) 1 / 2 or 2.05 (MPa) 1 / 2 It can be converted as: In this disclosure, the SP value of a resin is a value determined by the method described in "Polymer Handbook Fourth Edition," edited by J. Brandrup et al., published by John Wiley & Sons, Inc., 1999, pp. 675-714. For values ​​not described in the above document, the SP value (δ) is calculated according to the following formula using the statistics (ΣG) of the molar gravitational constants (G), molecular weight (M), and specific gravity (d) based on the molar gravitational constants of various atomic groups proposed by Small. δ=ΣG / V=dΣG / M(δ; SP value, V: specific volume, M: molecular weight, d: specific gravity)

[0022] In the resin composition of the present disclosure, the content of the thermoplastic plastomer is not particularly limited, but is typically 50 to 95% by mass, and preferably 60 to 90% by mass. When the content of the thermoplastic plastomer is equal to or greater than the above lower limit, the resin composition has excellent moldability and the mechanical strength of the resulting molded article can be improved. When the content of the thermoplastic plastomer is equal to or less than the above upper limit, the hollow particles and acid-modified polyolefin resin can be sufficiently contained, thereby suppressing deterioration in physical properties when the resin composition is molded into an article, improving mechanical strength, and also providing an excellent effect of reducing the weight of the molded article.

[0023] [Hollow particles] The hollow particles contained in the resin composition of the present disclosure are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell. In the present disclosure, the hollow portion is a hollow space that is clearly distinguishable from the shell of the hollow particle formed from a resin material. The shell of the hollow particle may have a porous structure, but in that case, the hollow portion has a size that allows it to be clearly distinguished from the numerous minute spaces uniformly dispersed within the porous structure. The hollow particles may have one or more hollow portions. The shell of the hollow particles, and when the hollow particles have two or more hollow portions, the partition walls separating adjacent hollow portions, may be porous. The interior of the particle preferably has only one hollow portion in order to maintain a good balance between the high porosity of the hollow particles and the mechanical strength of the hollow particles. The hollow portion of the hollow particles can be confirmed by, for example, SEM observation of the cross section of the particles or TEM observation of the particles as they are. The hollow portion of the hollow particles is preferably filled with a gas such as air.

[0024] Generally, hollow particles are classified into those in which the shell does not have any interconnecting holes connecting the hollow portion to the external space of the particle, and those in which the shell has one or more interconnecting holes through which the hollow portion is connected to the outside of the particle. Although it depends on the size of the hollow particle, the diameter of the interconnecting holes is usually about 10 to 500 nm. Furthermore, hollow particles may have shell defects in the form of cracks that are extremely large compared to the particle size. Although it depends on the size of the hollow particle, cracks with a length of 1 μm or more generally significantly reduce the strength of the hollow particle and are therefore recognized as shell defects. The hollow particles contained in the resin composition of the present disclosure are preferably such that, in SEM observation, 5 or fewer of 100 hollow particles have interconnected pores or shell defects, since the hollow particles are less likely to be crushed during molding processing of the resin composition.

[0025] The lower limit of the porosity of the hollow particles is preferably 50% or more, more preferably 53% or more, even more preferably 55% or more, even more preferably 58% or more, and particularly preferably 60% or more. When the porosity of the hollow particles is equal to or greater than the above lower limit, the proportion of hollow portions is high, thereby enabling the hollow particles to be made lighter. The upper limit of the porosity of the hollow particles is preferably 90% or less, more preferably 85% or less, and more preferably 80% or less. When the porosity of the hollow particles is equal to or less than the above upper limit, a decrease in the strength of the hollow particles can be suppressed.

[0026] The porosity of the hollow particles is calculated from the apparent density D1 and true density D0 of the hollow particles based on the following formula (0). formula (0) Porosity (%) = 100 - [apparent density D1] / [true density D0] x 100

[0027] The apparent density D1 of the hollow particles is measured as follows. First, a capacity of 100cm 3 30cm into a measuring flask 3The volumetric flask is filled with hollow particles, and the mass of the filled hollow particles is accurately weighed. Next, the volumetric flask filled with the hollow particles is accurately filled up to the marked line with isopropanol, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask is accurately weighed, and the apparent density D1 (g / cm) of the hollow particles is calculated based on the following formula (I): 3 ) is calculated. Formula (I) Apparent density D1 = [Mass of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature]) The apparent density D1 corresponds to the specific gravity of the entire hollow particle when the hollow portion is considered to be a part of the hollow particle.

[0028] The true density D0 of hollow particles is measured as follows: After crushing the hollow particles, 3 Approximately 10 g of crushed pieces of hollow particles are filled into the measuring flask, and the mass of the crushed pieces is accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol is added to the measuring flask, and the mass of the isopropanol is accurately weighed. The true density D0 (g / cm) of the hollow particles is calculated based on the following formula (II): 3 ) is calculated. Formula (II) True density D0 = [mass of crushed hollow particle fragments] / (100-[mass of isopropanol] / [specific gravity of isopropanol at measurement temperature]) The true density D0 corresponds to the specific gravity of only the shell portion of the hollow particle. As is clear from the above measurement method, the hollow portion is not considered to be part of the hollow particle when calculating the true density D0.

[0029] It is preferable that the hollow particles do not exhibit a glass transition temperature (Tg) of 250° C. or less. When the hollow particles do not exhibit a glass transition temperature (Tg) of 250° C. or less, it can be determined that the hollow particles are unlikely to deform or collapse when heated. The glass transition temperature can be measured by differential scanning calorimetry (DSC).

[0030] The volume-based average particle size (volume average particle size) of the hollow particles has a lower limit of preferably 1.0 μm or more, more preferably 3.0 μm or more, even more preferably 4.0 μm or more, and particularly preferably 4.5 μm or more, and an upper limit of preferably 60.0 μm or less, more preferably 55.0 μm or less, and even more preferably 50.0 μm or less. When the volume average particle diameter of the hollow particles is 1.0 μm or more, the desired porosity can be obtained, thereby reducing the weight of the hollow particles. When the volume average particle diameter of the hollow particles is 60.0 μm or less, the hollow particles are less likely to be crushed, thereby exhibiting high compressive strength.

[0031] The particle size distribution of the hollow particles (volume average particle size (Dv) / number average particle size (Dn)) is not particularly limited and may be, for example, 1.00 to 2.50. When the particle size distribution is 2.50 or less, particles with little variation in compressive strength properties and heat resistance among particles can be obtained. Furthermore, when a product such as a molded article described below is produced, a product with a uniform thickness can be produced by having the particle size distribution be 2.50 or less. The volume average particle size (Dv) and number average particle size (Dn) of the hollow particles can be determined by, for example, measuring the particle size of each hollow particle using a laser diffraction particle size distribution analyzer, calculating the number average and volume average, and using the resulting values ​​as the number average particle size (Dn) and volume average particle size (Dv) of the particles. The particle size distribution is calculated by dividing the volume average particle size by the number average particle size.

[0032] The shape of the hollow particles is not particularly limited as long as a hollow portion is formed inside, and examples thereof include spherical, oval spherical, irregular, etc. Among these, spherical is preferred from the viewpoint of ease of production. The hollow particles may have an average circularity of 0.950 to 0.995. In this disclosure, circularity is defined as the perimeter of a circle having the same projected area as the particle image divided by the perimeter of the projected image of the particle. Furthermore, the average circularity in this disclosure is used as a simple method for quantitatively expressing the shape of hollow particles, and is an index showing the degree of irregularity of hollow particles. The average circularity is 1 when the hollow particles are perfectly spherical, and decreases as the surface shape of the hollow particles becomes more complex.

[0033] The shell thickness of the hollow particles according to the present disclosure has a lower limit of preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more, and an upper limit of preferably 6 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. Having a shell thickness equal to or greater than the above-mentioned lower limit improves the strength of the shell. Meanwhile, the hollow particles according to the present disclosure have a dense shell structure that is resistant to acetone penetration, so that even if the shell thickness is thin and equal to or less than the above-mentioned lower limit, the hollow particles have excellent strength and are resistant to crushing. The shell thickness of the hollow particles can be calculated by calculating the inner diameter r of the hollow particles using the volume average particle diameter R and porosity of the hollow particles according to the following formula (1), and then using the inner diameter r and the volume average particle diameter R to calculate the shell thickness of the hollow particles according to the following formula (2). The porosity in the following formula (1) is a numerical value expressed as a percentage. 4 / 3π×(R / 2) 3 ×Porosity=4 / 3π×(r / 2) 3 Formula (1) Shell thickness = (Rr) / 2 Equation (2) The difference between the shell thickness calculated in this manner and the average thickness measured at 20 points on the shell is usually within ±10% of these average values, so the shell thickness calculated as above can be considered to be the shell thickness of the hollow particles. The thickness at each point of the shell of a hollow particle used to calculate the average thickness at 20 points on the shell can be measured, for example, by breaking the hollow particle and observing the shell fragments obtained with an SEM.

[0034] An example of the shape of a hollow particle is a bag made of a thin membrane and inflated with gas, and its cross section is shown in hollow particle 100 in Fig. 1, which will be described later. In this example, a thin membrane is provided on the outside, and the inside is filled with gas. The shape of the hollow particles can be confirmed, for example, by SEM, TEM, etc. Furthermore, the internal shape of the hollow particles can be confirmed by SEM, TEM, etc. after slicing the particles into cross-sections by a known method.

[0035] <Shell composition> The hollow particles contained in the resin composition of the present disclosure have a shell containing a resin, and the resin contains a polymer containing 30 to 100 parts by mass of crosslinkable monomer units per 100 parts by mass of all monomer units. The polymerizable monomers used as raw materials for the polymer include at least a crosslinkable monomer and may further include a non-crosslinkable monomer. Here, the polymerizable monomer is a compound having a functional group capable of addition polymerization (sometimes simply referred to as a polymerizable functional group in the present disclosure). In the present disclosure, a compound having an ethylenically unsaturated bond as a functional group capable of addition polymerization is generally used as the polymerizable monomer. The functional group capable of addition polymerization may be the ethylenically unsaturated bond itself or a group containing an ethylenically unsaturated bond, and specific examples thereof include a vinyl group, a (meth)acrylic group, an ethylene group, and an allyl group. In this disclosure, a non-crosslinkable monomer is a polymerizable monomer having only one polymerizable functional group, and a crosslinkable monomer is a polymerizable monomer having two or more polymerizable functional groups that form crosslinks in the resin by a polymerization reaction.

[0036] (Crosslinkable monomer unit) The crosslinkable monomer from which the crosslinkable monomer unit is derived is not particularly limited as long as it has two or more polymerizable functional groups. Examples of the crosslinkable monomer include difunctional crosslinkable monomers having two polymerizable functional groups, such as divinylbenzene, divinyldiphenyl, divinylnaphthalene, diallyl phthalate, allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, and 2-hydroxy-3-(meth)acrylpropyl (meth)acrylate; and trifunctional or higher crosslinkable monomers having three or more polymerizable functional groups, such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. These crosslinkable monomers can be used either alone or in combination of two or more.

[0037] As the crosslinkable monomer, it is preferable to use a hydrophilic crosslinkable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C. When the shell of the hollow particle contains a hydrophilic crosslinkable monomer unit, it is effective in suppressing deterioration of physical properties when the resin composition of the present disclosure is molded into a molded article. Examples of hydrophilic crosslinkable monomers include ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl methacrylate, vinyl methacrylate, and 2-hydroxy-3-methacrylpropyl acrylate.

[0038] The content of the crosslinkable monomer units in the polymer is 30 to 100 parts by mass, with the lower limit being preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more. The upper limit of the content of the crosslinkable monomer units may be less than 100 parts by mass, or may be 90 parts by mass or less, or may be 80 parts by mass or less. When the content of the crosslinkable monomer units is equal to or greater than the lower limit, the mechanical properties of the shell can be improved, the strength of the hollow particles can be improved, and collapse of the hollow particles and a decrease in porosity during molding of the resin composition can be suppressed. When the content of the crosslinkable monomer units is less than 100 parts by mass, the polymer contains a combination of crosslinkable monomer units and non-crosslinkable monomer units. The crosslinkable monomer has a plurality of polymerizable functional groups and can link the non-crosslinkable monomers to each other. Therefore, when a crosslinkable monomer unit and a non-crosslinkable monomer unit are contained in combination, the strength and heat resistance of the shell can be increased in some cases. The content of each polymerizable monomer unit can be determined by calculating the proportion of each polymerizable monomer used in the polymerization reaction from the amount of each polymerizable monomer charged during polymerization and the remaining amount of each polymerizable monomer at the end of polymerization.

[0039] (Non-crosslinkable monomer) As the non-crosslinkable monomer, for example, a monovinyl monomer can be preferably used. In the present disclosure, a monovinyl monomer is a compound having one polymerizable carbon-carbon double bond. Examples of the monovinyl monomer include (meth)acrylic monovinyl monomers such as (meth)acrylic acid esters and (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; aromatic vinyl monomers such as styrene, vinyl toluene, and α-methylstyrene; and monoolefin monomers such as ethylene, propylene, and butylene. These non-crosslinkable monomers can be used alone or in combination of two or more. Among these, from the viewpoints of reactivity and heat resistance, (meth)acrylic monovinyl monomers are preferred, and at least one selected from butyl acrylate and methyl methacrylate is more preferred.

[0040] As the non-crosslinkable monomer, it is preferable to use a hydrophilic non-crosslinkable monomer having a solubility of 0.3 g / L or more in distilled water at 20° C. When the shell of the hollow particle contains a hydrophilic non-crosslinkable monomer unit, the strength of the hollow particle is improved. Examples of the hydrophilic non-crosslinkable monomer include, among the above-mentioned monovinyl monomers, (meth)acrylic acid alkyl esters having an alkyl group of 1 to 5 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate; and polar group-containing non-crosslinkable monomers, such as (meth)acrylic acid, glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. Further examples of the hydrophilic non-crosslinkable monomer include (meth)acrylamides and derivatives thereof, such as (meth)acrylamide, N-methylol (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; and (meth)acrylic nitrile. Examples of polar group-containing non-crosslinkable monomers include non-crosslinkable monomers containing a polar group selected from a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group. Examples of carboxyl group-containing non-crosslinkable monomers include, in addition to the above-mentioned (meth)acrylic acid, ethylenically unsaturated carboxylic acid monomers such as crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid. Examples of hydroxyl group-containing non-crosslinkable monomers include, in addition to the above-mentioned 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the like. Examples of sulfonic acid group-containing non-crosslinkable monomers include styrenesulfonic acid, and the like. Examples of amino group-containing non-crosslinkable monomers include, for example, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and the like. Examples of the non-crosslinkable monomer containing a polyoxyethylene group include the above-mentioned methoxypolyethylene glycol (meth)acrylate, etc. Examples of the non-crosslinkable monomer containing an epoxy group include the above-mentioned glycidyl (meth)acrylate, as well as allyl glycidyl ether, 4-hydroxybutyl acrylate glycidyl ether, etc. As the hydrophilic non-crosslinkable monomer, from the viewpoint of a high effect of improving the strength of the hollow particles, at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid alkyl esters having an alkyl group of 1 to 5 carbon atoms is preferred, at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid alkyl esters having an alkyl group of 1 to 4 carbon atoms is more preferred, and at least one selected from (meth)acrylic acid and methyl (meth)acrylate is even more preferred.

[0041] The content of non-crosslinkable monomer units in the polymer is 0 to 70 parts by mass based on 100 parts by mass of all monomer units. The total monomer units of the polymer refer to the sum of the crosslinkable and non-crosslinkable monomer units in the polymer. When the polymer contains non-crosslinkable monomer units, the lower limit of the content of the non-crosslinkable monomer units is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, and the upper limit is preferably 65 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 55 parts by mass or less, and particularly preferably 45 parts by mass or less. When the polymer contains non-crosslinkable monomer units and the content of the non-crosslinkable monomer units is equal to or greater than the preferred lower limit, the strength and heat resistance of the shell can be increased, and when the content of the non-crosslinkable monomer units is equal to or less than the preferred upper limit, the crosslinkable monomer units can be contained sufficiently, thereby improving the mechanical properties of the shell and suppressing collapse of the hollow particles.

[0042] The content of the polymer contained in the shell of the hollow particles is not particularly limited, but is usually 80% by mass or more, and preferably 90% by mass or more, in order to provide excellent strength to the hollow particles. The shell of the hollow particle may contain a small amount of a resin different from the polymer. Examples of the resin different from the polymer include a polymer having a non-crosslinkable monomer unit content of more than 70% by mass, a urethane resin, a urethane acrylic resin, an epoxy resin, and an epoxy acrylic resin. The content of the resin different from the polymer in the shell of the hollow particle is preferably 20% by mass or less, more preferably 10% by mass or less.

[0043] Furthermore, the shell of the hollow particle may further contain additives in addition to the resin, if necessary. Examples of additives that the shell of the hollow particle may contain include a particle size control agent, which will be described later. The content of the particle size regulator in the shell of the hollow particle is adjusted appropriately depending on the type of the agent, and is not particularly limited, but is preferably 0.0001 to 10% by mass, more preferably 0.001 to 8% by mass.

[0044] <Hollow particle content> In the resin composition of the present disclosure, the content of hollow particles is not particularly limited, but is preferably 5 to 50 mass %, more preferably 5 to 30 mass %, and even more preferably 5 to 15 mass %. When the content of hollow particles is equal to or greater than the above lower limit, the effect of the hollow particles on the weight reduction of the resin composition can be improved. When the content of hollow particles is equal to or less than the above upper limit, the thermoplastic plastomer and acid-modified polyolefin resin can be sufficiently contained in the resin composition, thereby suppressing deterioration in physical properties when formed into a molded article and improving mechanical strength.

[0045] <Method for manufacturing hollow particles> Hereinafter, one embodiment of the method for producing hollow particles will be described, but the method for producing hollow particles of the present disclosure is not necessarily limited to the following embodiment, and is not particularly limited. One embodiment of the method for producing hollow particles comprises: a step of preparing a mixed solution containing a polymerizable monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium (mixed solution preparation step); a step of suspending the mixed liquid to prepare a suspension in which droplets of a monomer composition containing a polymerizable monomer and a hydrocarbon solvent are dispersed in an aqueous medium (suspension preparation step); a step of polymerizing the suspension to prepare a precursor composition containing precursor particles encapsulating a hydrocarbon-based solvent (polymerization step); a step of obtaining precursor particles by performing solid-liquid separation of the precursor composition (solid-liquid separation step); a step of removing the hydrocarbon solvent contained in the precursor particles to obtain hollow particles (solvent removal step); Includes. In the present disclosure, hollow particles whose hollow portions are filled with a hydrocarbon-based solvent are considered to be intermediates of hollow particles whose hollow portions are filled with a gas, and may be referred to as "precursor particles." In the present disclosure, the term "precursor composition" refers to a composition containing precursor particles.

[0046] As described above, this embodiment includes (1) a mixed solution preparation step, (2) a suspension preparation step, (3) a polymerization step, (4) a solid-liquid separation step, and (5) a solvent removal step. The steps of this embodiment are not limited to these five steps, and may include other steps. Furthermore, as far as technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single step, or the order may be reversed. For example, the preparation of the mixed solution and the suspension may be performed simultaneously in a single process, such as by adding the materials for preparing the mixed solution and suspending them at the same time.

[0047] FIG. 1 is a schematic diagram showing an example of the manufacturing method of the present disclosure. (1) to (5) in FIG. 1 correspond to the above-mentioned steps (1) to (5). The white arrows between the figures indicate the order of the steps. Note that FIG. 1 is merely a schematic diagram for explanatory purposes, and the manufacturing method of the present disclosure is not limited to those shown in the figure. Furthermore, the structure, dimensions, and shape of the materials used in each manufacturing method of the present disclosure are not limited to the structure, dimensions, and shape of the various materials in these figures. 1(1) is a cross-sectional view showing one embodiment of a mixed solution in the mixed solution preparation step. As shown in this figure, the mixed solution contains 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 that has low polarity and is difficult to mix with the aqueous medium 1. In the present disclosure, the low-polarity material 2 contains a polymerizable monomer and a hydrocarbon solvent. FIG. 1 (2) is a cross-sectional schematic diagram showing one embodiment of a suspension in a suspension preparation step. The suspension includes an aqueous medium 1 and droplets 10 of a monomer composition dispersed in the aqueous medium 1. The droplets 10 of the monomer composition contain a polymerizable monomer and a hydrocarbon solvent, but the distribution within the droplets is not uniform. The droplets 10 of the monomer composition are phase-separated into a hydrocarbon solvent 4a and a material other than the hydrocarbon solvent, including the polymerizable monomer, 4b, with the hydrocarbon solvent 4a unevenly distributed in the center and the material other than the hydrocarbon solvent 4b unevenly distributed on the surface, and a dispersion stabilizer (not shown) attached to the surface. 1(3) is a cross-sectional schematic diagram showing one embodiment of a composition (precursor composition) containing precursor particles encapsulating a hydrocarbon solvent in their hollow spaces, obtained by a polymerization step. The composition contains an aqueous medium 1 and precursor particles 20 encapsulating a hydrocarbon solvent 4a in their hollow spaces, dispersed in the aqueous medium 1. A shell 6 forming the outer surface of the precursor particles 20 is formed by polymerization of a polymerizable monomer in droplets 10 of the monomer composition. Fig. 1(4) is a cross-sectional schematic diagram showing one embodiment of precursor particles containing a hydrocarbon solvent in the hollow space after the solid-liquid separation step, which shows the state after removing the aqueous medium 1 from the state shown in Fig. 1(3). Fig. 1 (5) is a cross-sectional schematic diagram showing one embodiment of hollow particles after the solvent removal step. Fig. 1 (5) shows the state after removing the hydrocarbon solvent 4a from the state shown in Fig. 1 (4). By removing the hydrocarbon solvent from precursor particles containing the hydrocarbon solvent in the hollow portion, hollow particles 100 having a gas-filled hollow portion 8 inside a shell 6 are obtained. The above five steps and other steps will be explained below in order.

[0048] (1) Mixed liquid preparation process This step is a step of preparing a mixed liquid containing a polymerizable monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium. The mixed liquid preferably further contains a particle size control agent in order to appropriately adjust the particle size of droplets of the monomer composition and the shell thickness of the resulting hollow particles. Among these, the polymerizable monomer is as explained in the section "Shell Composition" of the hollow particles above. Note that the mixed solution may contain other polymerizable compounds in addition to the polymerizable monomer explained in the section "Shell Composition" of the hollow particles above.

[0049] (particle size control agent) The mixed solution preferably contains a particle size control agent for appropriately adjusting the particle size of the droplets of the monomer composition, thereby appropriately adjusting the particle size and shell thickness of the resulting hollow particles, thereby obtaining hollow particles that are resistant to crushing even when they have a high porosity. Examples of particle size control agents include at least one selected from the group consisting of rosin acid, higher fatty acids, and metal salts thereof, or polar resins, as described below. These particle size control agents can appropriately adjust the particle size of droplets of a monomer composition containing a polymerizable monomer and a hydrocarbon solvent in the suspension preparation process described below. In the suspension preparation process, droplets of the monomer composition are formed in an aqueous medium due to the action of a dispersion stabilizer. In the droplets of the monomer composition, phase separation occurs between the hydrocarbon solvent and materials other than the hydrocarbon solvent containing the polymerizable monomer, resulting in the hydrocarbon solvent being concentrated in the center and the materials other than the hydrocarbon solvent being concentrated on the surface. When the mixed liquid contains a particle size control agent, it is estimated that the particle size control agent is concentrated near the surface of the monomer composition droplets, and the dispersion stabilizer is attached to the droplet surface. This distribution structure of materials is formed according to the difference in affinity of each material for the aqueous medium. It is believed that by including a particle size control agent in the mixed liquid, the droplets of the monomer composition in the suspension have the distribution structure of the materials described above, and an interaction occurs between the dispersion stabilizer and the particle size control agent on the droplet surface, which changes the dispersibility of the droplets due to the dispersion stabilizer, making it possible to appropriately adjust the particle size of the droplets of the monomer composition. Among the particle size control agents, at least one selected from the group consisting of rosin acid, higher fatty acids, and metal salts thereof is preferred, and at least one selected from rosin acid and alkali metal salts thereof is more preferred, since the particle size of the droplets can be appropriately adjusted with a small content.

[0050] Rosin acids preferably used as particle size control agents can be obtained from rosins such as gum rosin, tall rosin and wood rosin. Examples of components contained in rosin acids obtained from these rosins include abietic acid, dehydroabietic acid, palustric acid, isopimaric acid, pimaric acid, etc. The component ratios of rosin acids are not constant and vary depending on the type of rosin, the species of pine used as the raw material, the place of origin, etc. The rosin acid and metal salts thereof used in the present disclosure are preferably rosin acids containing 50 mass % or more of abietic acids such as abietic acid, dehydroabietic acid, palustric acid, and hydrogenated products thereof, and alkali metal salts thereof.

[0051] The higher fatty acid used as the particle size control agent is preferably a higher fatty acid having 10 to 25 carbon atoms, excluding the carbon atom in the carboxyl group. Preferred examples of higher fatty acids include lauric acid (CH3(CH2) 10 COOH), tridecanoic acid (CH3(CH2) 11 COOH), myristic acid (CH3(CH2) 12 COOH), pentadecanoic acid (CH3(CH2) 13 COOH), palmitic acid (CH3(CH2) 14 COOH), heptadecanoic acid (CH3(CH2) 15 COOH), stearic acid (CH3(CH2) 16 COOH), arachidic acid (CH3(CH2) 18 COOH), behenic acid (CH3(CH2) 20 COOH), and lignoceric acid (CH3(CH2) 22 COOH) etc.

[0052] Examples of metals used in the metal salts of rosin acid or higher fatty acids include alkali metals such as Li, Na, and K, and alkaline earth metals such as Mg and Ca. Of these, alkali metals are preferred, and at least one selected from Li, Na, and K is more preferred.

[0053] When at least one particle size control agent selected from the group consisting of rosin acid, higher fatty acid, and metal salts thereof is used as the particle size control agent, the total content of the rosin acid, higher fatty acid, and metal salt thereof is preferably 0.0001 to 0.1 parts by mass, more preferably 0.001 to 0.01 parts by mass, and even more preferably 0.0015 to 0.006 parts by mass, per 100 parts by mass of the polymerizable monomer. When the content is equal to or greater than the lower limit, the particle size and shell thickness of the hollow particles can be easily controlled, thereby improving the strength of the hollow particles. On the other hand, when the content is equal to or less than the upper limit, a decrease in the polymerizable monomer content can be suppressed, thereby suppressing a decrease in shell strength and further suppressing collapse of the hollow particles.

[0054] The polar resin preferably used as a particle size control agent is a polymer containing a repeating unit containing a heteroatom, and specific examples thereof include acrylic resins, polyester resins, and vinyl resins containing a heteroatom. The polar resin may be a homopolymer or copolymer of a heteroatom-containing monomer, or a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer. When the polar resin is a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer, the proportion of heteroatom-containing monomer units in 100% by mass of all repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, in order to easily control the particle size of the hollow particles. Examples of heteroatom-containing monomers used in polar resins include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, acrylic acid, methacrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, and 4-hydroxybutyl acrylate. Examples of suitable monomers include (meth)acrylic monovinyl monomers, which are monomers having a (meth)acryloyl group, such as acrylate glycidyl ether; aromatic vinyl monomers containing heteroatoms, such as halogenated styrenes and styrene sulfonic acids; vinyl carboxylic acid ester monomers, such as vinyl acetate; halogenated vinyl monomers, such as vinyl chloride; halogenated vinylidene monomers, such as vinylidene chloride; vinylpyridine monomers; carboxyl group-containing monomers, such as ethylenically unsaturated carboxylic acid monomers, such as crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; and epoxy group-containing monomers, such as allyl glycidyl ether. These heteroatom-containing monomers can be used alone or in combination of two or more. Examples of heteroatom-free monomers used in polar resins include aromatic vinyl monomers that do not contain heteroatoms, such as styrene, vinyltoluene, α-methylstyrene, and p-methylstyrene; monoolefin monomers, such as ethylene, propylene, and butylene; and diene monomers, such as butadiene and isoprene. These heteroatom-free monomers can be used alone or in combination of two or more.

[0055] Among these, the polar resin is preferably an acrylic resin in which the total mass of (meth)acrylic monovinyl monomer units is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 90 mass% or more, of all repeating units constituting the resin (100 mass%), from the viewpoints of high compatibility with the polymerizable monomer and ease of controlling the particle size of the hollow particles. In particular, it is preferable that the polar resin is an acrylic resin in which all repeating units constituting the resin are (meth)acrylic monovinyl monomer units.

[0056] In particular, the polar resin preferably contains a polar group-containing monomer unit containing a polar group selected from a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group, in order to facilitate control of the particle size of the hollow particles. Examples of polar group-containing monomers used in the polar resin include the same polar group-containing non-crosslinkable monomers that may be contained in the above-mentioned polymerizable monomers. The polar group-containing monomers can be used alone or in combination of two or more. Carboxyl and hydroxyl groups are preferred as polar groups contained in the polar group-containing monomer units contained in the polar resin, in order to facilitate particle size control with a small amount of addition. When the polar resin contains a polar group-containing monomer unit, it is preferable that the polar group be located at the end of the main chain or side chain, or be attached in a pendant manner to the main chain or side chain, since this makes it easier for the polar resin to be positioned on the outer surface of the hollow particle and makes it easier to control the particle size of the hollow particle.

[0057] When the polar resin does not contain the polar group-containing monomer unit, the heteroatom-containing monomer unit contained in the polar resin preferably contains a monomer unit derived from a (meth)acrylic acid alkyl ester, because it has high compatibility with the polymerizable monomer and makes it easy to control the particle size of the hollow particles. In particular, it is preferable that the polar resin contains a monomer unit derived from a (meth)acrylic acid alkyl ester, preferably in which the alkyl group has 3 or less carbon atoms, more preferably in which the alkyl group is a methyl group or an ethyl group, and even more preferably in which the alkyl group is a methyl group, because of its high polarity.

[0058] The acrylic resin serving as the polar resin is preferably a polymer or copolymer of a polymerizable monomer for a polar resin containing 50% by mass or more of methyl methacrylate when the total mass of the polymerizable monomers for a polar resin is taken as 100% by mass, because it has high compatibility with the polymerizable monomer and makes it easy to control the particle size of the hollow particles. In the present disclosure, the polymerizable monomer used in synthesizing the polar resin is referred to as the polymerizable monomer for a polar resin.

[0059] The polar resin can be obtained, for example, by polymerizing a polymerizable monomer for polar resins containing the heteroatom-containing monomer by a polymerization method such as solution polymerization or emulsion polymerization. Furthermore, when the polar resin is a copolymer, the copolymer may be any of a random copolymer, a block copolymer, or a graft copolymer, but is preferably a random copolymer. In addition, the polar resin is preferably pulverized as finely as possible in order to improve solubility.

[0060] The number average molecular weight (Mn) of the polar resin is not particularly limited, but is preferably in the range of 3,000 to 20,000, more preferably 4,000 to 17,000, and even more preferably 6,000 to 15,000, in terms of polystyrene, as measured by gel permeation chromatography (GPC) using tetrahydrofuran. When the number average molecular weight (Mn) of the polar resin is equal to or greater than the lower limit, the solubility of the polar resin is improved and the particle size of the hollow particles can be easily controlled. When the number average molecular weight (Mn) is equal to or less than the upper limit, a decrease in shell strength can be suppressed.

[0061] When a polar resin is used as the particle size control agent, the content of the polar resin is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 8.0 parts by mass, and even more preferably 0.5 to 8.0 parts by mass, relative to 100 parts by mass of the polymerizable monomer. When the content is equal to or greater than the lower limit, the particle size and shell thickness of the hollow particles can be easily controlled, and the strength of the hollow particles can be improved. On the other hand, when the content is equal to or less than the upper limit, a decrease in the polymerizable monomer content can be suppressed, thereby suppressing a decrease in shell strength and further suppressing collapse of the hollow particles.

[0062] (oil-soluble polymerization initiator) In this embodiment, a suspension polymerization method using an oil-soluble polymerization initiator is employed instead of an emulsion polymerization method using a water-soluble polymerization initiator. The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylvaleronitrile), and azobisisobutyronitrile.

[0063] When the total mass of the polymerizable monomers is taken as 100 parts by mass, the content of the oil-soluble polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass. When the content of the oil-soluble polymerization initiator is 0.1 part by mass or more, the polymerization reaction tends to proceed sufficiently. On the other hand, when the content of the oil-soluble polymerization initiator is 10 parts by mass or less, there is little risk of the oil-soluble polymerization initiator remaining after completion of the polymerization reaction, and as a result, there is little risk of unexpected side reactions proceeding.

[0064] (hydrocarbon solvents) The hydrocarbon solvent in this embodiment has the function of forming hollow spaces inside the particles. In the suspension preparation step described below, a suspension is obtained in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium. In the suspension preparation step, phase separation occurs in the monomer droplets, and as a result, the hydrocarbon solvent, which has low polarity, tends to collect inside the monomer droplets. Ultimately, the hydrocarbon solvent is distributed inside the monomer droplets, and other materials other than the hydrocarbon solvent are distributed around the periphery according to their respective polarities. Then, in the polymerization step described below, a precursor composition containing precursor particles encapsulating the hydrocarbon solvent is obtained. That is, the hydrocarbon solvent collects inside the particles, and hollow spaces made of the hydrocarbon solvent are formed inside the resulting polymer particles (precursor particles).

[0065] The type of hydrocarbon solvent is not particularly limited, and examples of hydrocarbon solvents include relatively volatile solvents such as benzene, toluene, xylene, butane, pentane, hexane, heptane, and cyclohexane.

[0066] The hydrocarbon solvent used in this embodiment preferably has a relative dielectric constant of 3 or less at 20°C. The relative dielectric constant is one of the indicators that indicates the polarity of a compound. When the relative dielectric constant of the hydrocarbon solvent is sufficiently small, 3 or less, it is thought that phase separation proceeds quickly in the monomer droplets, and hollow spaces are easily formed. Examples of solvents with a relative dielectric constant of 3 or less at 20°C are as follows. The value in parentheses is the relative dielectric constant. Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4). For the relative permittivity at 20°C, reference can be made to values ​​described in known literature (for example, "Chemical Handbook Basics" edited by the Chemical Society of Japan, 4th revised edition, Maruzen Co., Ltd., published September 30, 1993, pp. II-498 to II-503) and other technical information. Examples of methods for measuring the relative permittivity at 20°C include a relative permittivity test conducted in accordance with JISC 2101:1999, 23, at a measurement temperature of 20°C.

[0067] The hydrocarbon solvent used in this embodiment may be a hydrocarbon compound having 5 to 7 carbon atoms. A hydrocarbon compound having 5 to 7 carbon atoms is easily encapsulated in the precursor particles during the polymerization step and can be easily removed from the precursor particles during the solvent removal step. Of these, the hydrocarbon solvent is preferably a hydrocarbon compound having 6 carbon atoms.

[0068] When the total mass of the polymerizable monomers is taken as 100 parts by mass, the content of the hydrocarbon solvent is preferably 70 to 900 parts by mass, more preferably 150 to 700 parts by mass, and even more preferably 200 to 500 parts by mass. When the content of the hydrocarbon solvent is 70 parts by mass or more, the porosity of the obtained hollow particles increases. On the other hand, when the content of the hydrocarbon solvent is 900 parts by mass or less, the mechanical properties of the obtained hollow particles are often excellent, and there is little risk that the hollow particles will not be able to maintain their hollowness.

[0069] (Dispersion stabilizer) The dispersion stabilizer is an agent for dispersing droplets of the monomer composition in an aqueous medium in the suspension preparation process. In the present disclosure, it is preferable to use an inorganic dispersion stabilizer as the dispersion stabilizer because it makes it easy to control the particle size of the droplets in the suspension, narrows the particle size distribution of the obtained hollow particles, and prevents the shell from becoming too thin, thereby preventing a decrease in the strength of the hollow particles. Such effects of the inorganic dispersion stabilizer are particularly easily exhibited when the inorganic dispersion stabilizer is used in combination with the above-mentioned particle size control agent. Examples of inorganic dispersion stabilizers include inorganic compounds such as 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 aluminum oxide and titanium oxide, and metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide and ferric hydroxide. These inorganic dispersion stabilizers can be used alone or in combination of two or more. Among the inorganic dispersion stabilizers, the above-mentioned poorly water-soluble inorganic metal salts such as sulfates, carbonates, phosphates and metal hydroxides are preferred, metal hydroxides are more preferred, and magnesium hydroxide is particularly preferred. In the present disclosure, the poorly water-soluble inorganic metal salt is preferably an inorganic metal salt having a solubility of 0.5 g or less in 100 g of water.

[0070] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 10 parts by mass, and more preferably 1.0 to 8.0 parts by mass, per 100 parts by mass of the total mass of the polymerizable monomer and the hydrocarbon solvent. By having the content of the dispersion stabilizer equal to or greater than the above-mentioned lower limit, it is possible to sufficiently disperse the droplets of the monomer composition so that they do not coalesce in the suspension. On the other hand, by having the content of the dispersion stabilizer equal to or less than the above-mentioned upper limit, it is possible to prevent an increase in the viscosity of the suspension during granulation, and to avoid the problem of the suspension being unable to pass through the granulator. The content of the dispersion stabilizer is usually 2 parts by mass or more and 15 parts by mass or less, and more preferably 3 parts by mass or more and 8 parts by mass or less, relative to 100 parts by mass of the aqueous medium.

[0071] (aqueous medium) In this embodiment, the aqueous medium means water, a hydrophilic solvent, or a mixture of water and a hydrophilic solvent. The hydrophilic solvent in this embodiment is not particularly limited as long as it is sufficiently miscible with water and does not cause phase separation. Examples of the hydrophilic solvent include alcohols such as methanol and ethanol, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO). Among aqueous media, water is preferred due to its high polarity. When using a mixture of water and a hydrophilic solvent, it is important that the polarity of the entire mixture is not too low in order to form monomer droplets. For example, the mixing ratio (mass ratio) of water to hydrophilic solvent may be 99:1 to 50:50.

[0072] The mixed solution prepared in this step is a composition obtained by simply mixing the above-mentioned polymerizable monomer, oil-soluble polymerization initiator, hydrocarbon solvent, dispersion stabilizer, and aqueous medium, followed by appropriate stirring. In this mixed solution, the oil phase containing the above-mentioned polymerizable monomer, oil-soluble polymerization initiator, and hydrocarbon solvent is dispersed in the aqueous medium with particle sizes of about several mm. Depending on the type of material, the dispersion state of these materials in the mixed solution can be observed with the naked eye.

[0073] In this step, a mixed solution may be prepared by mixing an oil phase containing a polymerizable monomer, an oil-soluble polymerization initiator, and a hydrocarbon solvent with an aqueous phase containing a dispersion stabilizer and an aqueous medium. By mixing the oil phase and the aqueous phase in this manner, particles having a uniform composition can be formed.

[0074] (2) Suspension preparation process This step is a step of preparing a suspension in which droplets of a monomer composition containing a polymerizable monomer and a hydrocarbon solvent are dispersed in an aqueous medium by suspending the above-mentioned mixed liquid. In the suspension prepared in this step, droplets of the monomer composition containing the above-mentioned polymerizable monomer, oil-soluble polymerization initiator, and hydrocarbon solvent and having a volume average particle size of about 1 to 60 μm are uniformly dispersed in the aqueous medium. Such droplets of the monomer composition are difficult to observe with the naked eye, but can be observed using a known observation device such as an optical microscope.

[0075] Fig. 2 is a schematic diagram showing one embodiment of a suspension in a suspension preparation step. A droplet 10 of the monomer composition in Fig. 2 is intended to show a schematic cross section thereof. Note that Fig. 2 is merely a schematic diagram, and the suspension in the present disclosure is not necessarily limited to that shown in Fig. 2. A part of Fig. 2 corresponds to (2) in Fig. 1 described above. 2 shows droplets 10 of a monomer composition and a polymerizable monomer 4c dispersed in the aqueous medium 1, which are dispersed in the aqueous medium 1. The droplets 10 are formed by surrounding an oil-soluble monomer composition 4 with a dispersion stabilizer 3. The monomer composition contains an oil-soluble polymerization initiator 5, as well as a polymerizable monomer and a hydrocarbon solvent (none of which are shown). The droplets 10 are minute oil droplets containing the monomer composition 4, and the oil-soluble polymerization initiator 5 generates polymerization-initiating radicals inside the minute oil droplets. Therefore, precursor particles of the desired particle size can be produced without causing the minute oil droplets to grow too large. In the suspension polymerization method using such 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 prevent the generation of excess polymer particles such as dense particles having a relatively small particle size in addition to the desired resin particles having hollow portions.

[0076] In the suspension preparation step, the method for forming droplets of the monomer composition is not particularly limited, but examples thereof include a method using an apparatus capable of strong stirring, such as an (in-line type) emulsifying disperser (manufactured by Pacific Machinery Works, trade name: Milder) or a high-speed emulsifying disperser (manufactured by Primix Corporation, trade name: TK Homomixer MARK II type). As described above, in this step, phase separation occurs in the droplets of the monomer composition, and the hydrocarbon solvent with low polarity tends to collect inside the droplets. As a result, the obtained droplets have the hydrocarbon solvent distributed inside and materials other than the hydrocarbon solvent distributed around the periphery.

[0077] Alternatively, in the suspension preparation step, the suspension may be prepared by a membrane emulsification method. When preparing a suspension by the membrane emulsification method, for example, in the mixed liquid preparation step, an oil phase containing a polymerizable monomer, an oil-soluble polymerization initiator, and a hydrocarbon solvent, and an aqueous phase containing a dispersion stabilizer and an aqueous medium are separately prepared, and the suspension is prepared by the membrane emulsification method. The membrane emulsification method is a method in which a dispersed phase liquid is extruded through the pores of a porous membrane into a continuous phase to obtain a suspension in which dispersed phase microdroplets are dispersed in the continuous phase. Here, the dispersed phase refers to the liquid phase dispersed as microdroplets, and the continuous phase refers to the liquid phase surrounding the dispersed phase droplets. In this embodiment, both direct membrane emulsification and membrane emulsification methods involving preliminary emulsification or the like can be used as long as they use the oil phase as the dispersed phase and the aqueous phase as the continuous phase. The membrane emulsification method uses a membrane emulsification system (e.g., Model No. MN-20, manufactured by SPG Techno Co., Ltd.) and a membrane with a specific pore size. Examples of porous membranes that can be used in the membrane emulsification method include inorganic porous membranes such as shirasu porous glass membranes (SPG membranes) and organic porous membranes such as PTFE membranes. In membrane emulsification, the pore size of the porous membrane determines the particle size of the resulting microdroplets. Although it depends on the components in the dispersed phase, the particle size of the microdroplets affects the number-average particle size of the resulting hollow particles, so selection of the pore size of the porous membrane is important. For example, when using a Shirasu porous glass membrane (SPG membrane), the pore size of the membrane is preferably selected to be 0.1 to 5.0 μm. In the suspension preparation process using such a membrane emulsification method, a suspension is prepared by performing membrane emulsification using the membrane emulsification system and the porous membrane, with the oil phase as the dispersed phase and the aqueous phase as the continuous phase. The suspension preparation step in this embodiment is not limited to the above-described method.

[0078] (3) Polymerization process This step is a step of preparing a precursor composition in which precursor particles encapsulating a hydrocarbon solvent are dispersed in an aqueous medium by polymerizing the suspension. The precursor particles are formed by polymerization of a polymerizable monomer contained in droplets of the monomer composition. The polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be used. The polymerization temperature is preferably 40 to 80° C., more preferably 50 to 70° C. The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours. In the polymerization step, the shell portion of the droplets of the monomer composition containing the hydrocarbon-based solvent inside is polymerized, and as described above, a hollow space made of the hydrocarbon-based solvent is formed inside the obtained precursor particles.

[0079] (4) Solid-liquid separation process This step is a step of obtaining precursor particles by subjecting the above-mentioned precursor composition to solid-liquid separation. The method for solid-liquid separation of the precursor composition is not particularly limited as long as it is a method for separating a solid component containing precursor particles from a liquid component containing an aqueous medium, and any known method can be used. Examples of the solid-liquid separation method include centrifugation, filtration, and static separation. Among these, centrifugation or filtration may be used, and centrifugation may be adopted from the viewpoint of ease of operation.

[0080] After the solid-liquid separation step, an optional step such as a pre-drying step may be carried out before the solvent removal step described below is carried out. Examples of the pre-drying step include a step of pre-drying the solid content obtained after the solid-liquid separation step using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0081] (5) Solvent removal process This step is a step for obtaining hollow particles by removing the hydrocarbon solvent contained in the precursor particles. The hydrocarbon solvent contained in the precursor particles may be removed in air or in liquid.

[0082] In this process, "in the air" strictly means an environment in which no liquid exists outside the precursor particles, or an environment in which only a trace amount of liquid exists outside the precursor particles, to the extent that it does not affect the removal of the hydrocarbon solvent. "In the air" can also be described as a state in which the precursor particles do not exist in a slurry, or a state in which the precursor particles exist in a dry powder.

[0083] The method for removing the hydrocarbon solvent from the precursor particles is not particularly limited, and any known method can be used. Examples of methods for removing the hydrocarbon solvent from the precursor particles in air include reduced pressure drying, heat drying, flash drying, and a combination of these methods. In particular, when using a heat drying method, the heating temperature must be equal to or higher than the boiling point of the hydrocarbon solvent and equal to or lower than the maximum temperature at which the shell structure of the hollow particles does not collapse. Therefore, depending on the shell composition of the precursor particles and the type of hydrocarbon solvent, the heating temperature may be, for example, 50 to 250°C, 100 to 240°C, or 150 to 220°C. The heating time may be 1 to 24 hours, preferably 2 to 15 hours, and more preferably 3 to 10 hours. By the drying operation in air, the hydrocarbon solvent inside the precursor particles is replaced by the external gas, resulting in hollow particles whose hollow portions are filled with gas.

[0084] The drying atmosphere is not particularly limited, and examples thereof include air, oxygen, nitrogen, argon, vacuum, etc. Alternatively, hollow particles with a temporary vacuum inside can be obtained by filling the inside of the hollow particles with a gas and then drying under reduced pressure.

[0085] As an alternative method, the hydrocarbon-based solvent may be removed by replacing the hydrocarbon-based solvent contained in the precursor particles with the aqueous medium of the slurry containing the precursor particles in a slurry containing the precursor particles and the aqueous medium, without subjecting the slurry-like precursor composition obtained in the polymerization step to solid-liquid separation. In this method, the hydrocarbon solvent contained in the precursor particles can be removed by bubbling an inert gas through the precursor composition at a temperature equal to or higher than the boiling point of the hydrocarbon solvent minus 35°C. Here, when the hydrocarbon solvent is a mixed solvent containing multiple types of hydrocarbon solvents and has multiple boiling points, the boiling point of the hydrocarbon solvent in the solvent removal step is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points. The temperature at which the inert gas is bubbled through the precursor composition is preferably at least 30°C below the boiling point of the hydrocarbon solvent, more preferably at least 20°C below that, in order to reduce the amount of hydrocarbon solvent remaining in the hollow particles. The bubbling temperature is usually set to a temperature equal to or higher than the polymerization temperature in the polymerization step. Although not particularly limited, the bubbling temperature may be set to 50°C or higher and 100°C or lower. The inert gas to be bubbled is not particularly limited, but examples thereof include nitrogen and argon. The bubbling conditions are appropriately adjusted depending on the type and amount of hydrocarbon solvent so as to remove the hydrocarbon solvent contained in the precursor particles, and are not particularly limited. For example, an inert gas may be bubbled at a rate of 1 to 3 L / min for 1 to 10 hours. In this method, an aqueous slurry is obtained in which the aqueous medium is encapsulated in the precursor particles. The slurry is subjected to solid-liquid separation to obtain hollow particles, which are then dried to remove the aqueous medium from the hollow particles, thereby obtaining hollow particles whose hollow spaces are filled with gas.

[0086] Comparing a method of obtaining hollow particles having hollow spaces filled with gas by performing solid-liquid separation on a slurry-like precursor composition and then removing the hydrocarbon-based solvent from the precursor particles in an air atmosphere, and a method of obtaining hollow particles having hollow spaces filled with gas by replacing the hydrocarbon-based solvent contained in precursor particles in a slurry containing the precursor particles and an aqueous medium with the aqueous medium of the slurry, performing solid-liquid separation, and removing the aqueous medium from the precursor particles in an air atmosphere, the former method has the advantage that the hollow particles are less likely to be crushed in the step of removing the hydrocarbon-based solvent, and the latter method has the advantage that the amount of residual hydrocarbon-based solvent is reduced by performing bubbling with an inert gas. When replacing the hydrocarbon solvent contained in the precursor particles with water, the resulting hollow particles will collapse unless the same volume of water as the hydrocarbon solvent that has escaped from the particles is introduced into the particles. One way to prevent this is to adjust the pH of the slurry to 7 or higher, swell the particle shells with alkali, and then remove the hydrocarbon solvent. In this case, the particle shells acquire flexibility, allowing the hydrocarbon solvent inside the particles to be replaced with water more quickly.

[0087] (6) Other As steps other than the above steps (1) to (5), for example, the following step (6-a) of cleaning and the following step (6-b) of replacing the hollow portion again may be added. (6-a) Cleaning process The washing step is a step of adding an acid or alkali to wash the precursor composition containing the precursor particles before the solvent removal step in order to remove any dispersion stabilizer remaining in the precursor composition containing the precursor particles. When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in acid, it is preferable to add an acid to the precursor composition containing the precursor particles to wash the precursor composition. On the other hand, when the dispersion stabilizer used is an inorganic compound soluble in alkali, it is preferable to add an alkali to the precursor composition containing the precursor particles to wash the precursor composition. Furthermore, when an acid-soluble inorganic dispersion stabilizer is used as the dispersion stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to adjust the pH to preferably 6.5 or less, more preferably 6 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is particularly preferable because it has a high efficiency in removing the dispersion stabilizer and places a small burden on the production equipment.

[0088] (6-b) Re-replacement process of hollow part The hollow re-substitution process is a process in which the gas or liquid inside the hollow particles is replaced with another gas or liquid. This substitution can change the environment inside the hollow particles, selectively confine molecules inside the hollow particles, or modify the chemical structure inside the hollow particles to suit the application.

[0089] [Acid-modified polyolefin resin] The resin composition of the present disclosure contains an acid-modified polyolefin resin, which is a polyolefin resin into which an acidic group has been introduced. The polyolefin resin used for the acid-modified polyolefin resin may be the same as the polyolefin resin used as the thermoplastic plastomer, but it is preferable to use one having a weight average molecular weight within the preferred range described below. Among them, the polyolefin resin used for the acid-modified polyolefin resin is preferably a polyethylene resin, a polypropylene resin, or a propylene-α-olefin copolymer, and more preferably a polypropylene resin, because of its good affinity with the above-mentioned preferred thermoplastic plastomer.

[0090] Of the acid-modified polyolefin resins used in the resin composition of the present disclosure, carboxylic acid-modified polyolefin resins in which a carboxyl group or a carboxylic anhydride group has been introduced as an acidic group are preferred. The carboxylic acid-modified polyolefin resin can be obtained by adding at least one selected from α,β-unsaturated carboxylic acids and their acid anhydrides to the polyolefin resin during or after polymerization. The α,β-unsaturated carboxylic acid and its acid anhydride may be incorporated into the main chain of the polyolefin resin by an addition reaction, forming a chemical bond between the polyolefin resin and the α,β-unsaturated carboxylic acid and its acid anhydride, or the α,β-unsaturated carboxylic acid and its acid anhydride may be dispersed in the polyolefin resin without forming a chemical bond between the polyolefin resin and the α,β-unsaturated carboxylic acid and its acid anhydride, or the carboxylic acid-modified polyolefin resin may have a combination of these forms. Examples of α,β-unsaturated carboxylic acids and acid anhydrides thereof include (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and acid anhydrides thereof. Among these, maleic anhydride and maleic acid are preferred, and maleic anhydride is more preferred.

[0091] As a method for introducing an acidic group into a polyolefin resin, in addition to the above-mentioned methods, a known method for acid-modifying a resin can also be employed.

[0092] The acid-modified polyolefin resin contained in the resin composition of the present disclosure has a weight-average molecular weight of preferably 10,000 or more, more preferably 15,000 or more, even more preferably 20,000 or more, still more preferably 30,000 or more, and particularly preferably 40,000 or more, and an upper limit of 60,000 or less, more preferably 55,000 or less, and even more preferably 50,000 or less. When the weight-average molecular weight of the acid-modified polyolefin resin is equal to or greater than the above lower limit and equal to or less than the above upper limit, affinity with the thermoplastic plastomer and hollow particles is improved, and deterioration of physical properties when the resin composition is molded into a molded article is easily suppressed. In the present disclosure, the weight average molecular weight of a resin is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0093] The acid-modified polyolefin resin has an acid value of 3.5 mgKOH / g or more, preferably 10 mgKOH / g or more, more preferably 15 mgKOH / g or more, and even more preferably 20 mgKOH / g or more. When the acid value of the acid-modified polyolefin resin is equal to or greater than the above-mentioned lower limit, the affinity with the thermoplastic plastomer and the hollow particles is good, so that the deterioration of physical properties when the resin composition is molded into a molded article can be suppressed. The upper limit of the acid value of the acid-modified polyolefin resin is not particularly limited, but from the viewpoint of affinity with the thermoplastic plastomer, it is preferably 150 mgKOH / g or less, more preferably 100 mgKOH / g or less, even more preferably 80 mgKOH / g or less, even more preferably 60 mgKOH / g or less, even more preferably 50 mgKOH / g or less, and particularly preferably 30 mgKOH / g.

[0094] In the resin composition of the present disclosure, the content of the acid-modified polyolefin resin is not particularly limited, but is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 70 parts by mass per 100 parts by mass of the hollow particles. When the content of the acid-modified polyolefin resin is equal to or greater than the above lower limit, the deterioration of physical properties when formed into a molded article is suppressed, and the effect of improving mechanical strength is excellent. When the content of the acid-modified polyolefin resin is equal to or less than the above upper limit, the thermoplastic plastomer and hollow particles can be sufficiently contained, resulting in a resin composition that is lightweight and has excellent strength.

[0095] [Other additives] In addition to the thermoplastic plastomer, hollow particles, and acid-modified polyolefin resin described above, the resin composition of the present disclosure may further contain additives such as an ultraviolet absorber, a colorant, a heat stabilizer, and a filler, as necessary, within a range that does not impair the effects of the present disclosure. The resin composition of the present disclosure may further contain organic or inorganic fibers such as carbon fibers, glass fibers, aramid fibers, and polyethylene fibers. Examples of uses of the resin composition of the present disclosure include uses similar to those of molded articles described below.

[0096] [Method of producing resin composition] The method for producing the resin composition of the present disclosure is not particularly limited, and may be a method used for producing conventional resin compositions. For example, the resin composition of the present disclosure can be obtained by mixing the above-mentioned thermoplastic plastomer, hollow particles, acid-modified polyolefin resin, and other additives added as needed, followed by melt-kneading. The melt-kneading can be carried out by a known method, and is not particularly limited, but can be carried out using, for example, a melt-kneading machine such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a heating roll, or various kneaders. The temperature during melt-kneading is not particularly limited as long as it is a temperature at which the thermoplastic plastomer used can be melted, but from the viewpoint of suppressing crushing of the hollow particles, it is preferably 250° C. or less. When the resin composition of the present disclosure is made into pellets, for example, after melt-kneading, the resin composition can be molded into pellets by a known molding method such as extrusion molding or injection molding.

[0097] 2. Molded body The molded article of the resin composition of the present disclosure is lightweight because the hollow particles contained therein are prevented from collapsing. As a molding method for obtaining the molded article of the resin composition of the present disclosure, molding methods performed under heat and pressure conditions, such as injection molding and compression molding, can be suitably used because the hollow particles are resistant to collapsing. Furthermore, known molding methods such as extrusion molding, blow molding, calendar molding, inflation molding, blow molding, stretch molding, and solution casting can be used. The shape of the molded article of the resin composition of the present disclosure may be any shape such as a sheet, a film, a plate, a tube, or any other various three-dimensional shape. Furthermore, when the molded article contains fibers, the fibers in the molded article may be in the form of a nonwoven fabric.

[0098] Examples of uses for molded articles of the resin composition of the present disclosure include light-reflecting materials, heat insulating materials, sound insulating materials, and low-dielectric materials used in various fields such as automobiles, electricity, electronics, construction, aviation, and space, food containers, footwear such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, and tools. [Example]

[0099] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Note that parts and percentages are by mass unless otherwise specified.

[0100] As acid-modified polyolefin resins, PP1 (maleic anhydride-modified polypropylene, manufactured by Sanyo Chemical Industries, Ltd., trade name: Umex 1001) and PP2 (maleic anhydride-modified polypropylene, manufactured by Sanyo Chemical Industries, Ltd., trade name: Umex 1010) were prepared. Furthermore, PP3 (low molecular weight polypropylene, manufactured by Sanyo Chemical Industries, Ltd., trade name: Bizcol 660-P) was prepared as an unmodified polyolefin resin for comparison. Table 1 shows the types of resins used as raw materials, the types of acids used for acid modification, as well as the acid values ​​and weight average molecular weights (Mw) of these acid-modified polyolefin resins and the unmodified polyolefin resins for comparison.

[0101] [Table 1]

[0102] [Production Example 1: Production of hollow particles] (1) Mixed liquid preparation process First, the following materials were mixed to form an oil phase. Ethylene glycol dimethacrylate 100 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) 3 parts Rosin acid 0.0044 parts 187 parts cyclohexane Next, in a stirring tank, an aqueous solution of 5.5 parts of sodium hydroxide (alkali metal hydroxide) in 55 parts of ion-exchanged water was gradually added under stirring to an aqueous solution of 7.8 parts of magnesium chloride (a water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water at room temperature to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion, which was used as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0103] (2) Suspension preparation process The mixture obtained in the mixture preparation step was stirred and suspended for 1 minute using a disperser (manufactured by Primix Corporation, trade name: Homomixer) at a rotation speed of 4,000 rpm, to prepare a suspension in which droplets of the monomer composition encapsulating cyclohexane were dispersed in water.

[0104] (3) Polymerization process The suspension obtained in the suspension preparation step was stirred in a nitrogen atmosphere at a temperature of 65°C for 4 hours to carry out a polymerization reaction. Through this polymerization reaction, a precursor composition containing precursor particles encapsulating cyclohexane was prepared.

[0105] (4) Washing process and solid-liquid separation process The precursor composition obtained in the polymerization step was washed with dilute sulfuric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less. Next, after separating the water by filtration, 200 parts of ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and the mixture was filtered to obtain a solid content. The obtained solid content was dried in a dryer at 40°C to obtain precursor particles containing cyclohexane.

[0106] (5) Solvent removal process The precursor particles obtained in the solid-liquid separation step were heat-treated in a vacuum oven at 200°C for 6 hours to remove the hydrocarbon solvent from the hollows, yielding hollow particles of Production Example 1. The obtained hollow particles had a volume average particle size of 10.6 μm and a porosity of 65%. Furthermore, based on the results of observation with a scanning electron microscope and the porosity value, it was confirmed that the obtained hollow particles were spherical and had hollow portions.

[0107] [Example 1] Polypropylene (manufactured by Mitsubishi Chemical Corporation, product name: MA1B, specific gravity 0.90 g / cm) was used as a thermoplastic plastomer. 3 , acid value 0 mg KOH / g, SP value 8.0 (cal / cm 3 ) 1 / 2 85 parts of the PP1 (50 parts per 100 parts of hollow particles) as an acid-modified polypropylene resin, 10 parts of the hollow particles obtained in Production Example 1, and 5 parts of the PP1 (50 parts per 100 parts of hollow particles) as an acid-modified polypropylene resin were mixed in a blender to obtain a resin composition of Example 1.

[0108] The resulting resin composition was then kneaded under the following kneading conditions using a twin-screw kneader (product name "TEM-35B", manufactured by Toshiba Machine Co., Ltd.), extruded, and pelletized to obtain pellets of the resin composition. <Mixing conditions> Screw diameter 37mm, L / D=32 Screw rotation speed: 250 rpm Resin temperature 190℃ Feed rate 6kg / hour The resulting resin composition pellets were dried by heating at 80° C. for 6 hours, and then molded into a molded article having dimensions of 80 mm×10 mm×thickness 4 mm using an injection molding machine under the following molding conditions. <Molding conditions> Cylinder temperature: 200℃ Mold temperature: 70℃ Injection pressure: 70MPa

[0109] [Examples 2 to 5, Comparative Examples 1 to 3] In Example 1, the resin compositions and molded articles of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the type or amount of thermoplastic plastomer, or the type or amount of acid-modified polyolefin resin, was changed according to Table 2.

[0110] [Reference example 1] A molded article of Reference Example 1 was obtained in the same manner as in Example 1, except that polypropylene (PP) used as the thermoplastic plastomer in Examples 1 to 4 was used instead of the resin composition obtained in Example 1.

[0111] [Reference example 2] A molded article of Reference Example 2 was obtained in the same manner as in Example 1, except that the resin composition obtained in Example 1 was replaced with high-density polyethylene (HDPE) used as the thermoplastic plastomer in Example 5.

[0112] [evaluation] The molded articles obtained in each of the Examples, Comparative Examples, and Reference Examples were measured for the following physical properties. The measurement results are shown in Table 2.

[0113] (1) Tensile strength In accordance with JIS-K7161-2, a multipurpose test piece was used as the test piece, and a tensile test was performed at a test speed of 50 mm / min, a chuck distance of 115 mm, and a test environment of 23°C and 50% RH to measure the tensile strength.

[0114] (2) Bending strength In accordance with JIS K7171, test specimens were cut out from the central parallel section of the multipurpose test specimen, and bending tests were carried out at a test speed of 2 mm / min, a support distance of 64 mm, and in a test environment of 23°C and 50% RH to measure bending strength.

[0115] (3) Flexural modulus A bending test was carried out under the same conditions as in the measurement of the bending strength, and the bending modulus was measured.

[0116] [Table 2]

[0117] In Table 2, PP refers to polypropylene (manufactured by Mitsubishi Chemical Corporation, trade name: MA1B, specific gravity 0.90 g / cm 3 , acid value 0 mg KOH / g, SP value 8.0 (cal / cm 3 ) 1 / 2 ), and HDPE is high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, product name: Novatec HD HJ590N, specific gravity 0.96 g / cm 3 , acid value 0 mg KOH / g, SP value 8.0 (cal / cm 3 ) 1 / 2 )

[0118] The resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 and 2 all contained polypropylene as a thermoplastic plastomer and hollow particles. However, the resin composition of Comparative Example 1, which did not contain an acid-modified polyolefin resin, and the resin composition of Comparative Example 2, which contained unmodified low-molecular-weight polypropylene instead of an acid-modified polyolefin resin, exhibited significantly lower tensile strength, flexural strength, and flexural modulus when molded into articles than the polypropylene molded article shown in Reference Example 1. On the other hand, the resin compositions of Examples 1 to 4, which contained an acid-modified polyolefin resin, exhibited almost no decrease or even slight improvement in tensile strength, flexural strength, and flexural modulus when molded into articles, despite containing hollow particles, and thus suppressed deterioration in physical properties when molded into articles.

[0119] The resin compositions obtained in Example 5 and Comparative Example 3 both contained high-density polyethylene as a thermoplastic plastomer and hollow particles. However, the resin composition of Comparative Example 3, which contained unmodified low-molecular-weight polypropylene instead of the acid-modified polyolefin resin, had significantly lower tensile strength, flexural strength, and flexural modulus when molded into a molded article than the molded article of high-density polyethylene shown in Reference Example 2. On the other hand, the resin composition of Example 5, which contained the acid-modified polyolefin resin, had almost no decrease in tensile strength, flexural strength, and flexural modulus when molded into a molded article, or even slightly improved, compared to the molded article of high-density polyethylene shown in Reference Example 2. Thus, despite containing hollow particles, the deterioration of physical properties when molded into a molded article was suppressed. [Explanation of symbols]

[0120] 1 Aqueous medium 2 Low polarity material 3. Dispersion stabilizer 4. Monomer composition 4a Hydrocarbon solvents 4b Materials other than hydrocarbon solvents 4c Polymerizable monomer dispersed in an aqueous medium 5. Oil-soluble polymerization initiator 6 shells 8 Hollow part 10 Droplets of Monomer Composition 20 precursor particles 100 hollow particles

Claims

1. a thermoplastic plastomer having an acid value of less than 3.0 mg KOH / g; hollow particles comprising a shell containing a resin and a hollow portion surrounded by the shell, the resin containing a polymer containing 30 to 100 parts by mass of crosslinkable monomer units per 100 parts by mass of all monomer units; and an acid-modified polyolefin resin having an acid value of 3.5 mgKOH / g or more, The resin composition, wherein the thermoplastic plastomer is a polyolefin resin.

2. 2. The resin composition according to claim 1, wherein the content of the acid-modified polyolefin resin relative to 100 parts by mass of the hollow particles is 10 to 150 parts by mass.

3. The resin composition according to claim 1 or 2, wherein the acid-modified polyolefin resin has a weight average molecular weight of 15,000 or more.

4. The resin composition according to any one of claims 1 to 3, wherein the acid-modified polyolefin resin is a carboxylic acid-modified polyolefin resin.

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