Polymer particles and producing method thereof

Abstract

This invention provides polymer particles that can suppress yellowing upon heating. The polymer particles of this invention have a cumulative proportion of particles with a diameter less than 60% of the median diameter in the number-based particle size distribution of 17% or less. This ensures that the number of small-diameter particles is below a specific proportion, thereby reducing yellowing caused by heating the polymer particles. Therefore, it can prevent coloring caused by yellowing of polymer particles in articles containing these particles, making it suitable for manufacturing articles for optical applications.

Description

[Technical Field]

[0001] This invention relates to polymer particles and methods for manufacturing the same. [Previous Technology]

[0002] Polymer particles with a volume average particle size of 1 to 100 μm have been widely used, for example, as matting agents for coatings and printing inks, additives for adhesives, low-shrinkage agents for artificial marble, paper treatment agents, fillers for cosmetics and other external agents, column fillers for chromatography, additives for toners used in electrostatic development, anti-caking agents for films, or light diffusers for optical films such as light diffuser sheets, anti-glare sheets, and light diffuser sheets.

[0003] In particular, when polymer particles are used as light diffusers, they are dispersed in light diffuser sheets. In order to prevent yellowing of the light diffuser sheets, it is necessary to reduce the yellowing degree of the polymer particles themselves at high temperatures. If yellowing occurs during the molding of the light diffuser sheets, the total light transmittance will decrease, and sometimes the desired properties cannot be obtained.

[0004] The aforementioned polymer particles are generally manufactured by polymerizing monomers using common polymerization methods such as suspension polymerization, seed polymerization, and emulsion polymerization. In these polymerization methods, surfactants are typically used to stabilize the polymerization reaction and suppress the generation of coarse particles.

[0005] For example, Patent Document 1 discloses a light diffuser composed of resin microparticles, which are obtained by polymerizing vinyl monomers in a medium containing surfactants. The amount of surfactant remaining in the resin microparticles is 0.05 parts by weight or less relative to 100 parts by weight of the resin microparticles. [Prior Art Documents] [Patent Documents]

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-233055 [Summary of the Invention]

[0007] [Problem to be solved by the invention] However, the above-mentioned light diffuser suppresses yellowing during heating by reducing the amount of interfacial active agent remaining in the resin microparticles to below a fixed amount, but it may not be able to sufficiently suppress yellowing. For example, there is a case where the degree of yellowing increases after heating in an oven at 180°C for 3 hours, indicating that the yellowing suppression of the resin microparticles is not sufficient.

[0008] Furthermore, if the amount of surfactant used in the manufacture of resin microparticles is reduced in order to reduce the amount of surfactant remaining in the resin microparticles, the particles growing during polymerization will aggregate with each other, causing other problems such as difficulty in manufacturing resin microparticles.

[0009] This invention provides polymer particles that reduce yellowing upon heating and a method for manufacturing the same. [Means for solving the problem]

[0010] The polymer particles of the present invention are characterized in that the cumulative number of particles having a diameter of less than 60% of the median diameter in the number-based particle size distribution is less than 17%.

[0011] The method for manufacturing polymer particles of the present invention is characterized in that raw material monomers are polymerized in a dispersed state in an aqueous medium, and a surfactant is supplied in the aqueous medium when the polymerization rate of the raw material monomers is less than 94% and more than 94%, respectively. [Effects of the Invention]

[0012] As described above, the polymer particles of the present invention have a cumulative number ratio of particles with a diameter of less than 60% of the median diameter in the number reference particle size distribution of less than 17%, so that the number of small diameter particles is less than a certain proportion, thereby reducing yellowing caused by heating polymer particles.

[0013] Therefore, it can prevent the products containing polymer particles from developing color due to yellowing of the polymer particles, and is suitable for use in the manufacture of products for optical purposes.

Implementation Method

[0014] In this specification, within the numerical ranges described in stages, the upper or lower limit of a numerical range in one stage can be arbitrarily combined with the upper or lower limit of the numerical ranges in other stages. Within the numerical ranges described in this specification, the upper or lower limit of the numerical range can be replaced by values ​​that can be shown in the embodiments or obviously derived from the embodiments. In this specification, the numerical values ​​represented by "~" indicate a numerical range containing the values ​​before and after "~" as the lower and upper limits.

[0015] [Polymer Particles] The cumulative number of particles whose median diameter is less than 60% of the particle size distribution of the polymer particles of the present invention is less than 17%.

[0016] In a particle size distribution with the horizontal axis representing particle size (particle diameter) and the vertical axis representing the number (%), the cumulative proportion of particles with a diameter of 60% or less of the median diameter (small-diameter particles) is 17% or less, which reduces the content of small-diameter particles. Furthermore, the particle diameter on the horizontal axis of the particle size distribution is the equivalent sphere diameter.

[0017] The polymer particles are contained in and used in synthetic resins. When manufacturing articles containing polymer particles, for example, synthetic resin and polymer particles are supplied in a conventional mixing device such as an extruder and melt-mixed in the mixing device, or the polymer particles are dispersed in the binder resin of a coating and heated and dried as needed.

[0018] In the past, it was known that heating could cause yellowing of polymer particles in the manufacturing process of products containing polymer particles. As mentioned above, surfactants were known to be the cause. The inventors investigated this issue and found that the small-diameter particles contained in the polymer particles were the main cause, rather than the amount of surfactants contained in the polymer particles.

[0019] As described above, in the manufacturing process of articles containing polymer particles, the polymer particles are generally heated. If the polymer particles contain small-diameter particles, during the melt mixing of the aforementioned synthetic resin or in the dispersion state of the adhesive resin, the small-diameter particles are prone to agglomeration due to the influence of larger particles (hereinafter referred to as "main particles") other than the small-diameter particles. Furthermore, since the particle size of small-diameter particles is small, the particles as a whole are prone to deterioration due to heating. Therefore, the small-diameter particles as a whole are prone to discoloration and turn yellow due to heating deterioration, and the yellow color is more easily identified through agglomeration.

[0020] On the other hand, the main particle has a larger particle size than the small particle, so even when heated in the same way as the small particle, it is not easy to heat as a whole. Therefore, the thermal degradation of the main particle will be dispersed throughout the particle, and the yellow color caused by the thermal degradation will be dispersed. The yellow color is less likely to be detected than that of the small particle.

[0021] As described above, the above polymer particles reduce yellowing by reducing the number of small-diameter particles, and the overall particle size of the polymer particles is made uniform by reducing the number of small-diameter particles. This can maintain a uniform dispersion in the synthetic resin, thereby preventing aggregation and reducing the increase in thermal conductivity, and reducing yellowing caused by the overall heating deterioration of the polymer particles.

[0022] The particle size distribution based on the number of polymer particles was determined using the following method. When the arithmetic mean particle size of the polymer particle size distribution based on the number of particles is 1 μm or more, it was determined using the following method. The arithmetic mean particle size of the polymer particle size distribution based on the number of particles was determined using a Coulter Multisizer™ 4e (a measuring device manufactured by Beckman Coulter Inc.). The measurement was performed using a calibrated fine aperture according to the Multisizer 3 user manual issued by Beckman Coulter Inc.

[0023] Furthermore, the pore size used for measurement can be appropriately selected based on the size of the polymer particles being measured. Current and Gain can be appropriately set according to the selected pore size. The volume average particle size of the polymer particles and the corresponding pore size are shown in Table 1.

[0024] [Table 1] Fine pore size (μm) Volume average particle size (μm) 50 1μm or larger but less than 10μm 100 10μm or larger but less than 25μm 280 25μm or larger but less than 80μm 400 80μm or larger but less than 150μm

[0025] The sample used for the determination was prepared by dispersing 0.1 g of polymer particles in 10 mL of a 0.1% (w / w) nonionic surfactant aqueous solution using a contact mixer (manufactured by Yamato Scientific Co., Ltd., trade name "TOUCHMIXER MT-31") and an ultrasonic cleaner (manufactured by VELVO-CLEAR Co., Ltd., trade name "ULTRASONIC CLEANER VS-150") to form a dispersion. During the determination, the mixture was stirred slowly until no bubbles were generated in the beaker, and the determination was completed at the point when 100,000 polymer particles were measured. The particle size of the polymer particles is the equivalent sphere diameter. That is, the particle size of the polymer particles is the diameter of a perfect circle with the same volume as the polymer particles. The arithmetic mean particle size of the number-based particle size distribution of the polymer particles is the arithmetic mean of the number-based particle size distribution of 100,000 particles. The median diameter of the number-based particle size distribution of the polymer particles is the diameter D50, which is the 50% of the cumulative frequency (number) of the number-based particle size distribution of 100,000 particles.

[0026] In the number-based particle size distribution of polymer particles, the coefficient of variation (CV value) of the particle size of polymer particles is calculated using the following mathematical formula: Coefficient of variation (CV value) of polymer particle size = 100 × (Standard deviation of particle size in the number-based particle size distribution of polymer particles) / [Arithmetic mean particle size of the number-based particle size distribution of polymer particles]

[0027] When the arithmetic mean particle size of the polymer particle number-based particle size distribution is less than 1 μm, the following method is used for determination. The arithmetic mean particle size of the polymer particle number-based particle size distribution is determined by laser diffraction scattering in a particle size distribution measuring device (Beckman Coulter, Inc., model "LS230"). Specifically, 0.1 g of polymer particles (equivalent to 0.1 g in dispersion) and 20 mL of 2% by mass anionic surfactant solution are added to a test tube. Then, a dispersion is prepared by dispersing the particles for 5 minutes using a test tube mixer (AS ONE, Inc., "TRIO HM-1N Test Tube Mixer") and an ultrasonic cleaner (AS ONE, Inc., "ULTRASONIC CLEANER VS-150"). The resulting dispersion is then irradiated with ultrasound in the particle size distribution measuring device by laser diffraction scattering, and the arithmetic mean (number) particle size of the polymer particles in the dispersion is measured. The optical model used in the measurement is based on the refractive index of the manufactured polymer particles. When the polymer particles are manufactured using one type of monomer, the refractive index of the polymer particles is the refractive index of the homopolymer of that monomer. When the polymer particles are manufactured using multiple types of monomers, the refractive index of the polymer particles is the average of the refractive indices of the homopolymers of each monomer, weighted by the amount of each monomer used. The coefficient of variation (CV) of the polymer particle size is calculated in the same way as when the arithmetic (number) average particle size of the polymer particle size distribution is 1 μm or larger. <Measurement conditions for the laser diffraction particle size distribution measuring device> Medium = Water; Refractive index of the medium = 1.333; Refractive index of the solid = Refractive index of the polymer particles; PIDS relative concentration: 40~55%

[0028] Furthermore, the volume average particle size of the particle size distribution of the polymer particles based on volume is the arithmetic mean obtained by measuring the particle size distribution of the volume based using the same method as the arithmetic (number) average particle size of the particle size distribution based on the number of polymer particles mentioned above.

[0029] The median diameter of the polymer particle number-based particle size distribution is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, and particularly preferably 1 μm or more. The median diameter of the polymer particle number-based particle size distribution is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less, and particularly preferably 35 μm or less. If the median diameter of the polymer particle number-based particle size distribution is within the above range, the effect of yellowing caused by the heating degradation of small-diameter polymer particles can be effectively reduced, and the heating yellowing of polymer particles can be effectively reduced.

[0030] Among the polymer particles, particles with a diameter of less than 60% of the median diameter in the number-based particle size distribution, that is, the cumulative number ratio of small-diameter particles is less than 17%, preferably less than 16%. As mentioned above, particles with a diameter of less than 60% of the median diameter are prone to agglomeration due to the influence of the main particles. If agglomeration occurs, the thermal conductivity will increase, so small-diameter particles are more prone to yellowing. By making the cumulative number ratio of small-diameter particles less than a certain amount, the polymer particles can reduce yellowing during heating.

[0031] The arithmetic mean particle size Dp of the polymer particles, based on the number of particles, is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1 μm or more, particularly preferably 2 μm or more, and most preferably 3 μm or more. The arithmetic mean particle size Dp of the polymer particles, based on the number of particles, is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less, and particularly preferably 35 μm or less. If the arithmetic mean particle size Dp of the polymer particles, based on the number of particles, is within the above range, the effect of yellowing caused by the heating degradation of small-diameter polymer particles can be effectively reduced, and the heating yellowing of polymer particles can be effectively reduced.

[0032] In the number-based particle size distribution of polymer particles, the CV value of the polymer particle size is preferably below 70%, and more preferably below 69%. If the CV value of the polymer particle size is below 70%, the yellowing effect caused by the heating degradation of small-diameter polymer particles can be effectively reduced, and the heating yellowing of polymer particles can be effectively reduced.

[0033] Even if the polymer particles contain a relatively large amount of surfactant, the yellowing during heating can be reduced because the number of small-diameter particles is kept below a certain proportion. The amount of surfactant adhering to the surface of the polymer particles is preferably 0.2 g or less per 100 g of polymer particles. If the amount of surfactant adhering to the surface of the polymer particles is within the above range, yellowing caused by heating the polymer particles can be reduced.

[0034] The surfactant dose (g / 100g) adhering to the surface of the polymer particles is calculated using the following method. Weigh approximately 0.10g of polymer particles into a centrifuge tube. Add 5mL of methanol extractant using a quantitative pipette, and thoroughly mix the polymer particles and extractant. After ultrasonic extraction for 15 minutes, centrifuge at 3500rpm for 15 minutes, using the resulting supernatant as the test solution. Measure the surfactant concentration in the test solution. Then, using the measured surfactant concentration (g / mL), the mass of polymer particles used as the sample [sample mass (g)], and the volume of extractant (extract volume (mL)), calculate the surfactant dose (g) adhering to the surface of 100g of polymer particles using the following formula. The extract volume is 5mL. Surfactant dose (g / 100g) = 100 × [surfactant concentration in test solution (g / mL) × extract volume (mL)] / sample mass (g)

[0035] There are no particular limitations on the synthetic resins constituting the polymer particles; examples include acrylic resins and styrene resins. Furthermore, synthetic resins may be used alone or in combination of two or more.

[0036] Acrylic resins are preferably polymerized from raw material monomers containing acrylic monomers, or polymerized from raw material monomers containing acrylic monomers and polyfunctional monomers. Acrylic resins are preferably cross-linked via polyfunctional monomers. Acrylic monomers are not particularly limited, and examples include acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tributyl acrylate, dodecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tributyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, etc.

[0037] Examples of polyfunctional monomers include trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, decaethylene glycol di(meth)acrylate, pentadecylethylene glycol di(meth)acrylate, 1,3-dimethylethylene glycol di(meth)acrylate, neopentyl tert-methyl methacrylate, 1,3-dimethyl methacrylate, allyl methacrylate, and other acrylic polyfunctional monomers, as well as aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, or derivatives thereof. Furthermore, (meth)acrylates are acrylates or methacrylates.

[0038] There is no particular limitation on styrene-based resins, and examples include homopolymers or copolymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, and bromostyrene.

[0039] Furthermore, the aforementioned styrene-based resin may be a copolymer of the aforementioned styrene-based monomer as the main component and a vinyl monomer that can copolymerize with the aforementioned styrene-based monomer. Examples of the vinyl monomer include divinylbenzene such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene; multifunctional monomers such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; and (meth)acrylonitrile and (meth)acrylate, etc. Multifunctional monomers are preferred, more preferably ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and divinylbenzene, and especially preferably divinylbenzene and ethylene glycol di(meth)acrylate. Furthermore, the monomer that can copolymerize with styrene may be used alone or in combination.

[0040] The yellowing degree of the polymer particles after heating at 180°C for 3 hours is preferably below 3.0, more preferably below 2.8, and even more preferably below 2.6. If the yellowing degree of the polymer particles after heating at 180°C for 3 hours is below 3.0, then the yellowing caused by heating can be reduced.

[0041] Furthermore, the yellowing degree of the polymer particles after heating at 180°C for 3 hours is determined by the following method. The b* value of the polymer particles (cross-linked polystyrene particles) is measured according to the colorimetric system of the L*a*b* table in JIS Z 8729, thereby determining the yellowing degree.

[0042] Specifically, 3.0g of polymer particles are filled into the measuring container. The b* value of the filled polymer particles is measured using a colorimeter. The b* value of the obtained polymer particles is used as the initial b*.

[0043] Next, the polymer particles were placed in an oven maintained at 180°C and heated for 3 hours. The polymer particles were then removed from the oven and placed at 25°C for 1 hour. The b* value of the polymer particles was then measured using the same procedure as described above, and this b* value was taken as the b* value after heating. The yellowing degree was calculated using the following formula: Yellowing degree = b* value after heating / initial b* value

[0044] [Method for Manufacturing Polymer Particles] Next, the method for manufacturing polymer particles will be described. There are no particular limitations on the method for manufacturing polymer particles. The raw material monomers can be polymerized in the presence of a polymerization initiator as needed, using general methods, thereby manufacturing the polymer particles.

[0045] There are no particular limitations on the polymerization method. Common polymerization methods such as suspension polymerization, seed polymerization, bulk polymerization, and solution polymerization can be used. Suspension polymerization is preferred, and emulsion polymerization is even more preferred. Emulsion polymerization is a polymerization method in which the raw material monomers are dispersed in an aqueous medium and polymerized in the presence of a polymerization initiator and an emulsifier, including suspension polymerization. Furthermore, the aqueous medium can be water, or a mixture of water and an organic solvent [e.g., lower alcohols (alcohols with 5 or fewer carbon atoms)], with water being preferred.

[0046] In the past, when the above dispersion was heated to polymerize the raw material monomers, the total amount of surfactant required for the polymerization of the raw material monomers was supplied to the dispersion before the polymerization started. However, if the total amount of surfactant was supplied to the dispersion before the polymerization started, excessive droplets of raw material monomers would be generated and excessive small-diameter particles would be generated in the early stage of polymerization. Furthermore, in the later stage of the polymerization of raw material monomers, the dispersion state of the raw material monomers became unstable. It was found that the cause was the generation of small-diameter particles.

[0047] This describes the process of manufacturing polymer particles via emulsion polymerization. The method for manufacturing polymer particles according to the present invention is divided into cases where the polymerization rate of the raw material monomers is less than 94% and cases where the polymerization rate of the raw material monomers is 94% or higher. A surfactant is supplied in an aqueous medium, thereby ensuring stable dispersion of the raw material monomers in the aqueous medium throughout all polymerization steps. This allows for stable growth without agglomeration into elongated particles and reduces the formation of small-diameter particles. Furthermore, the polymerization rate (%) of the raw material monomers refers to the percentage of "the raw material monomers used in polymerization" relative to "the total amount of raw material monomers supplied to the dispersion."

[0048] In the method for manufacturing polymer particles, a surfactant is supplied and polymerization of the monomers is carried out in an aqueous medium in which the monomers are dispersed, while the polymerization rate of the monomers is less than 94% (first step). If the polymerization rate of the monomers is less than 94%, the surfactant can be supplied to the aqueous medium either before or after the start of polymerization. Furthermore, the surfactant can be supplied to the aqueous medium in which the monomers are dispersed in multiple portions.

[0049] The surfactant is supplied to the aqueous medium while the polymerization rate of the raw material monomers is less than 94%, but preferably before the polymerization of the raw material monomers begins. Supplying the surfactant to the aqueous medium before the polymerization of the raw material monomers allows the raw material monomers dispersed in the dispersion generated by the aqueous medium to reach a stable state before polymerization, which further reduces the generation of small-diameter particles.

[0050] When supplying the surfactant to the aqueous medium before the polymerization of the raw material monomers begins, the order of supplying the raw material monomers and surfactant to the aqueous medium is not restricted. When dispersing the raw material monomers in the aqueous medium and producing a dispersion, a general mixing device (such as a homogenizer, an ultrasonic processor, a nanovater (registered trademark) microemulsifier, etc.) can be used.

[0051] When supplying a surfactant to a dispersion in which the polymerization rate of the raw material monomer is less than 94%, it is preferable to supply the surfactant when the polymerization rate of the raw material monomer is 0-90%, more preferably when the polymerization rate is 0-85%, and even more preferably when the polymerization rate is 0-80%. Polymerization of the raw material monomer can be carried out after the raw material monomer has reached a stable dispersion state in the aqueous medium, which can reduce the generation of small-diameter particles. Furthermore, a polymerization rate of 0% for the raw material monomer refers to "before the polymerization of the raw material monomer begins."

[0052] Preferably, the surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is less than 94% is supplied at a rate of 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass, before the polymerization of the raw material monomer begins. By supplying the surfactant to the dispersion as described above, the raw material monomer in the dispersion can be stabilized and dispersed before polymerization of the raw material monomer, thereby reducing the generation of small-diameter particles.

[0053] The amount of surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is less than 94% is preferably 0.005 parts by mass or more, more preferably 0.010 parts by mass or more, and even more preferably 0.013 parts by mass or more, relative to 100 parts by mass of the raw material monomer. The amount of surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is less than 94% is preferably 0.15 parts by mass or less, more preferably 0.13 parts by mass or less, and even more preferably 0.10 parts by mass or less, relative to 100 parts by mass of the raw material monomer. If the amount of surfactant is 0.005 parts by mass or more, the raw material monomer can be stably dispersed in an aqueous medium, and the generation of small-diameter particles can be reduced. If the amount of surfactant is 0.15 parts by mass or less, the generation of flat or irregularly shaped particles can be reduced, and it is easier to manufacture perfectly spherical polymer particles.

[0054] The polymerization temperature (temperature of the dispersion) in the first step can be appropriately selected according to the type of raw material monomer or the type of polymerization initiator described later as needed, preferably 25~110℃, more preferably 50~100℃. If the polymerization temperature in the first step is within the above range, the polymerization of the raw material monomer can be carried out after the raw material monomer in the dispersion has reached a stable dispersion state, which can further reduce the generation of small-diameter particles.

[0055] A surfactant is supplied to a dispersion in which the polymerization rate of the raw material monomer is less than 94%, and the dispersion is heated as needed to carry out the polymerization of the raw material monomer. As the polymerization of the raw material monomer in the dispersion proceeds, the number of growth particles increases and the particle size also increases, which reduces the dispersion stability of the growth particles achieved by the surfactant supplied in the first step.

[0056] Therefore, when the polymerization rate of the raw material monomers reaches 94% or more, a surfactant is supplied to the dispersion and polymerization is carried out (second step). As mentioned above, in the later stage of polymerization when the polymerization rate of the raw material monomers reaches 94% or more, a surfactant is further supplied to the dispersion to ensure the dispersion stability of the growing particles dispersed in the dispersion and to reduce the generation of small-diameter particles.

[0057] The polymerization temperature (temperature of the dispersion) in the second step is preferably 40-60°C higher than the polymerization temperature (temperature of the dispersion) in the first step, more preferably 45-60°C higher, and even more preferably 50-55°C higher. By adjusting the polymerization temperature of the second step to a higher temperature than that of the first step, and by supplying a surfactant to the dispersion, the generation of small-diameter particles can be reduced while the remaining raw material monomers are absorbed into the grown particles, making it easier to produce polymer particles with a lower content of small-diameter particles.

[0058] When supplying a surfactant to a dispersion in which the polymerization rate of the raw material monomers is 94% or higher, it is preferable to supply the surfactant when the polymerization rate of the raw material monomers is 94-100%, more preferably when the polymerization rate is 94-99%, even more preferably when the polymerization rate is 94-98%, and most preferably when the polymerization rate is 94-96%. This allows the raw material monomers in the dispersion to be stabilized before polymerization, further reducing the generation of small-diameter particles.

[0059] Preferably, the surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is 94% or higher is 70% by mass or higher, more preferably 80% by mass or higher, even more preferably 90% by mass or higher, even more preferably 99% by mass or higher, and most preferably 100% by mass. By supplying the surfactant to the dispersion as described above, the growth particles and the raw material monomer in the dispersion can be stabilized and dispersed before the polymerization of the raw material monomer can be carried out, which can further reduce the generation of small-diameter particles.

[0060] The amount of surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is 94% or higher is preferably 0.10 parts by mass or more, more preferably 0.15 parts by mass or more, and even more preferably 0.25 parts by mass or more, relative to 100 parts by mass of the raw material monomer. The amount of surfactant supplied to the dispersion in which the polymerization rate of the raw material monomer is 94% or higher is preferably 0.80 parts by mass or less, more preferably 0.60 parts by mass or less, and even more preferably 0.40 parts by mass or less, relative to 100 parts by mass of the raw material monomer. If the amount of surfactant is 0.10 parts by mass or more, the growth particles and the raw material monomer can be stably dispersed in the dispersion, and the generation of small-diameter particles can be reduced. If the amount of surfactant is 0.80 parts by mass or less, the amount of water used for washing can be reduced, and the environment can be protected.

[0061] The surfactants used in the manufacture of polymer particles may be conventional surfactants such as ester-type, ether-type, and ester-ether-type surfactants. Examples of surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene tridecyl ether, polyoxyethylene alkylphenyl ethers such as polyoxyethylene octylphenyl ether; polyoxyethylene styrene phenyl ether; polyoxyethylene fatty acid esters; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate; polyoxyethylene alkylamines; oxyethyl-oxypropyl block polymers; fatty acid soaps such as sodium oleate and potassium castor oil soap; alkyl sulfate salts such as sodium dodecyl sulfate, sodium lauryl sulfate, and ammonium lauryl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; alkyl naphthalene sulfonates; alkyl sulfonates; dialkyl sulfosuccinates such as sodium di(2-ethylhexyl)sulfosuccinate and sodium dioctyl sulfosuccinate; alkenyl succinates such as sodium alkenyl succinate (mono or di); alkyl phosphates; formalin condensates of naphthalene sulfonate, etc.

[0062] The surfactant is preferably an alkyl sulfate salt such as dodecyl sulfate (e.g., sodium dodecyl sulfate), an alkylbenzene sulfonate such as linear alkylbenzene sulfonate (e.g., sodium dodecylbenzene sulfonate), or a phosphate ester such as polyoxyethylene styrene phenyl ether phosphate.

[0063] Furthermore, in the first step, a polymerization initiator may be added to the aqueous medium in which the raw material monomers are dispersed, as needed. There are no particular limitations on the polymerization initiator; examples include organic peroxides such as benzoyl peroxide, lauryl peroxide, o-chlorobenzoyl peroxide, o-methoxybenzoyl peroxide, 3,5,5-trimethylhexyl peroxide, tert-butyl-2-ethylhexanoate peroxide, and ditert-butyl peroxide; 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), 2,2'-azobis(2,3-dimethylbutyronitrile), 2,2'-... Azo compounds such as 2-methylbutyronitrile (2-azobis(2-methylbutyronitrile)), 2,2'-azobis(2,3,3-trimethylbutyronitrile), 2,2'-azobis(2-isopropylbutyronitrile), 1,1'-azobis(cyclohexane-1-formonitrile), 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile), (2-aminomethoxyazo)isobutyronitrile, 4,4'-azobis(4-cyanopentanoic acid), and dimethyl-2,2'-azobisisobutyrate are preferred. Furthermore, the polymerization initiator is preferably used in the range of 0.1 to 3.0 parts by weight relative to 100 parts by weight of the raw monomer.

[0064] The reaction solution containing polymer particles obtained by polymerization as described above is supplied to a general filter, and the polymer particles contained in the dispersion are separated by an aqueous medium. After washing the separated polymer particles with water, they are dried using a general method to almost completely remove water, and then fractionated as needed (preferably by air-jet fractionation) to obtain polymer particles.

[0065] The obtained polymer particles do not require an extreme reduction in surfactant content to reduce yellowing during use. The surfactant can be washed away and removed to a level that will not cause any adverse effects when using the polymer particles. Therefore, not only can the amount of water used for washing the polymer particles separated from the dispersion be reduced, but the washing time of the polymer particles can also be shortened, thereby improving manufacturing efficiency.

[0066] [Uses of Polymer Particles] Polymer particles are suitable for use as optical films such as anti-glare films or light-diffusing films, or as optical components such as light diffusers, and are especially suitable for use as anti-glare components. Polymer particles can also be used as matting agents in coatings, anti-caking agents, and additives to improve the physical properties of resins.

[0067] A polymer particle composition can be prepared by dispersing polymer particles in a dispersion medium. This polymer particle composition is then coated onto a substrate and dried, thereby creating a coating film containing polymer particles on the substrate. Examples of substrates include films and other molded articles. The polymer particle composition can be molded using general techniques to manufacture sheets and other molded articles. The dispersion medium is not particularly limited and can include, for example, synthetic resins and coatings.

[0068] When dispersing polymer particles in a synthetic resin, the synthetic resin needs to be heated and melted, which also applies heat to the polymer particles. Similarly, when molding a polymer particle composition, heat is applied to the polymer particles. Furthermore, when coatings containing polymer particles are applied to and dried on a substrate formed of synthetic resin or the like, heating is sometimes involved, which also applies heat to the polymer particles.

[0069] As described above, the content of small-diameter polymer particles is reduced to a certain level, and coloration can be largely suppressed even when heat is applied during use. Therefore, polymer particles are also suitable for use in optical components where discoloration, such as yellowing, is a problem.

[0070] The synthetic resin can be appropriately selected according to the application, etc. Examples of synthetic resins include (meth)acrylic resins; (meth)acrylic acid-ethyl carbamate resins; ethyl carbamate resins; polyvinyl chloride resins; polyvinylidene chloride resins; melamine resins; styrene resins; alkyd resins; phenolic resins; epoxy resins; polyester resins; polysiloxane resins such as alkyl polysiloxane resins; modified polysiloxane resins such as (meth)acrylic acid-polysiloxane resins, polysiloxane-alkyd resins, polysiloxane-ethyl carbamate resins, and polysiloxane-polyester resins; fluorinated resins such as polyvinylidene fluoride and fluoroolefin vinyl ether polymers. Furthermore, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0071] The amount of polymer particles in the polymer particle composition is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 parts by mass or more, relative to 100 parts by mass of the synthetic resin. The amount of polymer particles in the polymer particle composition is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 100 parts by mass or less, relative to 100 parts by mass of the synthetic resin.

[0072] The material of the substrate for coating the polymer particles is not particularly limited, and examples include polyester polymers such as polyethylene terephthalate (PET) and polyethylene naphthalate, cellulose polymers such as cellulose diacetate and cellulose triacetate (TAC), polycarbonate polymers, (meth)acrylic polymers such as polymethyl methacrylate, as well as synthetic resins, cement, ceramic tiles, metals, and glass. (Example)

[0073] The present invention will be described in more detail below using examples, but the present invention is not limited thereto. The specific values ​​of blending ratio (including ratio), physical property value, parameter, etc. used in the following description can be replaced by the upper limit value (the value defined by "below" or "not reached") or lower limit value (the value defined by "above") of the blending ratio (including ratio), physical property value, parameter, etc., corresponding to those described in the "Implementation Method".

[0074] (Example 1) The raw material monomer composition includes 94 parts by mass of styrene monomer and 6 parts by mass of divinylbenzene, a polyfunctional vinyl monomer; 1 part by mass of 2,2-azobis(2,4-dimethylpentanonitrile) and 0.2 parts by mass of 2,2-azobisisobutyronitrile, a polymerization initiator; 2600 parts by mass of deionized water, an aqueous medium; 3.0 parts by mass of magnesium pyrophosphate (obtained by metathesis generation method), a dispersion stabilizer composed of acid-soluble and water-insoluble inorganic compounds; and 0.03 parts by mass of sodium dodecyl sulfate, a first surfactant. The raw material monomer composition is supplied to a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") and stirred at 6000 rpm for 20 minutes to adjust the droplet diameter to about 6 μm and prepare a dispersion.

[0075] The above dispersion is supplied to a polymerization reactor equipped with a stirrer and a thermometer, and the raw material monomers are polymerized at a constant temperature of 60°C for 4 hours while being stirred by the stirrer (first step).

[0076] Next, at the point when the polymerization rate of the raw material monomers reaches 94%, 0.37 parts by mass of sodium linear alkylbenzene sulfonate, a second surfactant, is supplied to the dispersion, and the mixture is stirred at 100°C for 2.5 hours to carry out the polymerization reaction, thereby obtaining a reaction solution in which cross-linked polystyrene particles, as polymer particles, are dispersed in water.

[0077] Hydrochloric acid is supplied to the above reaction solution to dissolve and disperse the stabilizer (magnesium pyrophosphate). The reaction solution is then supplied to a centrifugal separation dehydration device equipped with a filter cloth in the inner basket. The basket is rotated for 30 minutes with a centrifugal effect of 700G to remove the liquid, thereby obtaining a cake containing cross-linked polystyrene particles.

[0078] Next, while rotating the basket of the dehydration apparatus at a centrifugal effect of 700G, 500 parts by mass of deionized water were supplied to the basket and the cake was washed for 30 minutes. Then, the basket of the dehydration apparatus was rotated at a centrifugal effect of 700G for 60 minutes to obtain a cake containing cross-linked polystyrene particles. The obtained cake was dried to obtain cross-linked polystyrene particles.

[0079] (Example 2) 2.5 parts by mass of metathesis magnesium pyrophosphate (magnesium pyrophosphate obtained by metathesis generation method) and a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") was used to prepare a dispersion. Otherwise, cross-linked polystyrene particles were obtained by the same method as in Example 1.

[0080] (Example 3) 2.5 parts by mass of metathesis magnesium pyrophosphate (magnesium pyrophosphate obtained by metathesis generation method) were prepared by stirring and mixing at 4500 rpm for 15 minutes using a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") to obtain cross-linked polystyrene particles.

[0081] (Example 4) 2.5 parts by mass of metathesis magnesium pyrophosphate (magnesium pyrophosphate obtained by metathesis generation method) were prepared by stirring and mixing at 3500 rpm for 15 minutes using a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") to obtain cross-linked polystyrene particles.

[0082] (Example 5) 2.5 parts by mass of metathesis magnesium pyrophosphate (magnesium pyrophosphate obtained by metathesis generation method), 0.3 parts by mass of sodium linear alkylbenzene sulfonate as the second surfactant, and a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") was set to 3000 rpm and stirred for 12 minutes to prepare a dispersion. Otherwise, cross-linked polystyrene particles were obtained using the same method as in Example 1.

[0083] (Example 6) 2.5 parts by mass of metathesis magnesium pyrophosphate (magnesium pyrophosphate obtained by metathesis generation method) and 0.08 parts by mass of polyoxyethylene styrene phenyl ether phosphate, the first surfactant. Instead of a high-speed emulsifying disperser, a high-pressure dispersion device (manufactured by Nanovater Co., Ltd., trade name "LNP-20 / 300") equipped with a suspension disperser (Nanovater Co., Ltd., trade name "LNP-20 / 300") was used. The raw material monomer composition was added to the high-pressure dispersion device and an impact force was applied under a high pressure of 29.4 MPa to make the droplets of the raw material monomer composition finer. Otherwise, cross-linked polystyrene particles were obtained by the same method as in Example 1.

[0084] (Comparative Example 1) The first surfactant, sodium dodecyl sulfate, was 0.4 parts by mass, and no second surfactant was supplied to the dispersion. Otherwise, cross-linked polystyrene particles were obtained in the same manner as in Example 1.

[0085] (Example 7) The cross-linked polystyrene particles manufactured in Comparative Example 1 were classified using an air classifier (manufactured by Nisshin Engineering Co., Ltd., trade name "Turbo Classifier (registered trademark) TC-15") to obtain cross-linked polystyrene particles.

[0086] (Comparative Example 2) The raw material monomer composition includes 98 parts by mass of styrene monomer and 2 parts by mass of divinylbenzene, a polyfunctional vinyl monomer; 1.5 parts by mass of tert-butyl-2-ethylhexyl peroxide and 0.5 parts by mass of tert-butyl-2-ethylhexyl peroxide carbonate, a polymerization initiator; 2000 parts by mass of deionized water, an aqueous medium; 1.4 parts by mass of magnesium pyrophosphate (obtained by metathesis generation method), a dispersion stabilizer composed of acid-soluble and water-insoluble inorganic compounds; and 0.056 parts by mass of sodium dodecyl sulfate, a first surfactant. The raw material monomer composition is supplied to a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII 2.5") and stirred at 8000 rpm for 15 minutes. The mixture is adjusted to a droplet diameter of about 6 μm to prepare a dispersion.

[0087] The above dispersion is supplied to a polymerization reactor equipped with a stirrer and a thermometer. While stirring with the stirrer, the raw material monomers are polymerized at a constant temperature of 90°C for 8 hours to obtain a reaction solution in which cross-linked polystyrene particles, as polymer particles, are dispersed in water.

[0088] Hydrochloric acid is supplied to the above reaction solution to dissolve and disperse the stabilizer (magnesium pyrophosphate). The reaction solution is then supplied to a centrifugal separation dehydration device equipped with a filter cloth in the inner basket. The basket is rotated for 30 minutes with a centrifugal effect of 700G to remove the liquid, thereby obtaining a cake containing cross-linked polystyrene particles.

[0089] Next, while rotating the basket of the dehydration apparatus at a centrifugal effect of 700G, 500 parts by mass of deionized water were supplied to the basket and the cake was washed for 30 minutes. Then, the basket of the dehydration apparatus was rotated at a centrifugal effect of 700G for 60 minutes to obtain a cake containing cross-linked polystyrene particles. The obtained cake was dried to obtain cross-linked polystyrene particles.

[0090] (Comparative Example 3) The raw material monomer composition includes 100 parts by mass of styrene monomer and 6 parts by mass of divinylbenzene, a polyfunctional vinyl monomer; 0.4 parts by mass of antioxidant (ADK STAB PEP-36: manufactured by ADEKA); 1 part by mass of polymerization initiator 2,2-azobis(2,4-dimethylpentanonitrile) and 0.2 parts by mass of 2,2-azobisisobutyronitrile; 2600 parts by mass of deionized water as an aqueous medium; 3.0 parts by mass of magnesium pyrophosphate (obtained by metathesis generation method), a dispersion stabilizer composed of acid-soluble and water-insoluble inorganic compounds; 0.04 parts by mass of sodium dodecyl sulfate as a first surfactant; and 0.6 parts by mass of sodium thiosulfate. This raw material monomer composition is supplied to a high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., trade name "HOMOMIXER MARKII"). The sample was processed at 4500 rpm for 15 minutes, and the droplet diameter was adjusted to be about 9 μm to prepare a dispersion.

[0091] The above dispersion is supplied to a polymerization reactor equipped with a stirrer and a thermometer, and the raw material monomers are polymerized at a constant temperature of 60°C for 4 hours while being stirred by the stirrer (first step).

[0092] Next, at the point when the polymerization rate of the raw material monomers reaches 80-90%, 0.4 parts by mass of sodium linear alkylbenzene sulfonate, a second surfactant, is supplied to the dispersion, and the mixture is stirred at 100°C for 2.5 hours to carry out the polymerization reaction, thereby obtaining a reaction solution in which cross-linked polystyrene particles, as polymer particles, are dispersed in water.

[0093] Hydrochloric acid is supplied to the above reaction solution to dissolve and disperse the stabilizer (magnesium pyrophosphate). Then the reaction solution is supplied to a centrifugal separation dehydration device equipped with a filter cloth in the inner basket, and the basket is rotated for 30 minutes with a centrifugal effect of 700G to remove the liquid, thereby obtaining a cake containing cross-linked polystyrene particles.

[0094] Next, while rotating the basket of the dehydration apparatus at a centrifugal effect of 700G, 500 parts by mass of deionized water were supplied to the basket and the cake was washed for 30 minutes. Then, the basket of the dehydration apparatus was continuously rotated for 60 minutes to obtain a cake containing cross-linked polystyrene particles. The obtained cake was dried to obtain cross-linked polystyrene particles.

[0095] The median diameter of the cross-linked polystyrene particles obtained were determined, and the cumulative number ratio of particles with a diameter less than 60% of the median diameter of the cross-linked polystyrene particles (small diameter particles) was determined. The results are shown in Table 2 under “Median diameter [μm]” and “Cumulative number ratio of small diameter particles [%)”.

[0096] The arithmetic mean particle size Dp of the number-based particle size distribution, the volume-based particle size distribution, the CV value of the particle size distribution of the number-based particle size distribution, and the interfacial activity dose attached to the surface of the polymer particles were determined using the above-described method. The results are shown in Table 2 for “arithmetic mean particle size [μm]”, “volume-based particle size distribution [μm]”, “CV value [%]” and “interfacial activity dose [g / 100g]”.

[0097] The yellowing degree of the obtained cross-linked polystyrene particles was determined using the following method, and the results are shown in Table 2.

[0098] (Yellowing) Colorimetric determination was performed using the L*a*b* colorimetric system according to JIS Z8729, thereby determining the b* value of the polymer particles (cross-linked polystyrene particles). Specifically, 3.0 g of polymer particles were filled into a testing container (powder trough manufactured by Konica Minolta Sensing, trade name "CR-A50"). The b* value of the filled polymer particles was measured using a colorimeter (manufactured by Konica Minolta Sensing, trade name "CR-300"). The obtained b* value of the polymer particles was taken as the "initial b* value". Furthermore, the larger the b* value is towards the + sign, the greater the yellowing.

[0099] Next, the polymer particles were placed in an oven maintained at 180°C and heated for 3 hours. The polymer particles were then removed from the oven and placed at 25°C for 1 hour. The b* value of the polymer particles was then measured using the same procedure as described above and recorded as the "b* value after heating". Yellowing was calculated using the following formula: Yellowing = b* value after heating / initial b* value

[0100] [Table 2]

[0101] (Cross Reference to Related Applications) This application claims priority to Japanese Patent Application No. 2024-55910, filed March 29, 2024, the entire disclosure of which is incorporated herein by reference. (Industrial Applicability)

[0102] The polymer particles of the present invention can reduce yellowing caused by heating the polymer particles. Therefore, it can prevent the discoloration of articles containing polymer particles due to yellowing of the polymer particles, and is suitable for use in the manufacture of articles for optical applications.

Claims

1. A polymer particle, comprising a synthetic resin, wherein the cumulative number of particles having a diameter of 60% or less of the median diameter in a number-based particle size distribution is 17% or less.

2. The polymer particles as described in claim 1, wherein, The yellowing degree after heating at 180℃ for 3 hours is below 3.

0.

3. The polymer particles as described in claim 1 or 2, wherein, In the number-based particle size distribution, the arithmetic mean particle size is 1~50μm and the CV value of the particle size is less than 70%.

4. The polymer particles as described in claim 1 or 2, wherein, The aforementioned synthetic resins contain acrylic resins or styrene resins.

5. The polymer particles as described in claim 1 or 2, wherein, It also contains surfactants, which include dodecyl sulfate or linear alkylbenzene sulfonate.

6. The polymer particles as described in claim 1 or 2, used in optical components.

7. A method for manufacturing polymer particles, as described in any one of claims 1 to 5, comprising the step of polymerizing raw material monomers in a dispersed state in an aqueous medium, and wherein, in a stage where the polymerization rate of the raw material monomers is less than 94%, a first surfactant is supplied in the aqueous medium, and in a stage where the polymerization rate of the raw material monomers is 94% or more, a second surfactant is supplied in the aqueous medium.