Method for producing resin particles

Abstract

To provide a method for producing resin particles, enabling production of resin particles that are flattened by suspension polymerization and have low moisture content.SOLUTION: A method for producing resin particles, comprises an adjustment step of adjusting the L / D of the resulting resin particles to fall within a specific range, wherein the adjustment step includes a polymerization initiation stage of initiating suspension polymerization of a monomer in an aqueous suspension containing water, the monomer, and a specific amount of tricalcium phosphate having a specific average particle size.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing resin particles. [Background technology]

[0002] BACKGROUND ART Conventionally, a technique for producing an extruded foam (board) of a styrene-based resin is known in which styrene-based resin particles are charged into an extruder and a blowing agent is injected under pressure while the resin is melted.

[0003] Resin particles used in the production of extruded foams are sometimes required to be non-spherical (for example, flat) and have a low moisture content.

[0004] Patent Document 1 discloses non-spherical polymer particles obtained by suspension polymerization, in which the ratio (L / D) of the major axis (L) to the minor axis (D) of a projected two-dimensional image obtained by irradiating the particles with light from directions perpendicular to the major axis direction is 1.3 or more, and the average particle diameter is 300 μm or more. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-207999 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques have room for further improvement in terms of the moisture content of the resin particles.

[0007] An object of one aspect of the present invention is to provide a novel method for producing resin particles, which is capable of producing flattened resin particles having a low moisture content by suspension polymerization. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, one embodiment of the present invention includes the following features.

[0009] [1] A method for producing resin particles, and adjusting the L / D ratio of the resulting resin particles so that L / D is equal to or greater than -0.02 x (weight average molecular weight (10,000)) + 1.25 and 0.55 ≦ L / D ≦ 0.85, the preparation step includes a polymerization initiation step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, and 0.01 part by weight to 0.30 parts by weight of tricalcium phosphate having an average particle size of 10 μm to 30 μm; The L / D is a value obtained by the following formula: L / D=L / ((Dl+Ds) / 2), In the formula, L is the particle diameter at a point corresponding to 30% by weight of the cumulative weight on a cumulative distribution curve of the ellipse minor axis of the resin particles based on weight, Dl is a particle diameter at a point corresponding to 40% by weight of a cumulative weight on a weight-based cumulative distribution curve of the ellipse major axis of the resin particles, Ds is a particle diameter at a point corresponding to 60% by weight of a cumulative weight on a weight-based cumulative distribution curve of the ellipse major axis of the resin particles, The weight-based cumulative distribution curve of the ellipse's minor axis and the weight-based cumulative distribution curve of the ellipse's major axis are each measured using a particle size measuring device with the resin particles as a sample.

[0010] [2] The method for producing resin particles according to [1], wherein the aqueous suspension in the polymerization initiation step further contains an anionic surfactant.

[0011] [3] The method for producing resin particles according to [1] or [2] further comprises a heat treatment step of treating the aqueous suspension at a temperature higher than that at the start of polymerization when the polymerization conversion rate is 80% by weight or more.

[0012] [4] The method for producing resin particles according to any one of [1] to [3], wherein the adjusting step further includes an adding step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate to the aqueous suspension per 100 parts by weight of the monomer.

[0013] [5] The method for producing resin particles according to any one of [1] to [4], wherein the addition step includes a step of adding tricalcium phosphate when the polymerization conversion rate is 40% by weight to 60% by weight.

[0014] [6] The method for producing resin particles according to any one of [1] to [5], wherein the adding step includes a step of adding tricalcium phosphate having an average particle size of 1 μm to 30 μm.

[0015] [7] The method for producing resin particles according to any one of [1] to [6], wherein the heat treatment step includes treating the aqueous suspension at 110° C. or higher.

[0016] [8] The method for producing resin particles according to any one of [1] to [7], wherein the aqueous suspension in the polymerization initiation step further contains a low-temperature decomposition initiator.

[0017] [9] The method for producing resin particles described in any one of [1] to [8], wherein the amount of the low-temperature decomposition initiator used in the aqueous suspension in the polymerization initiation step is 0.05 to 0.30 parts by weight per 100 parts by weight of the monomer.

[0018]

[10] The method for producing resin particles according to any one of [1] to [9], wherein the amount of water used is 60 parts by weight to 100 parts by weight per 100 parts by weight of the monomer.

[0019]

[11] The method for producing resin particles according to any one of [1] to

[10] , wherein the weight average molecular weight of the resin particles is 150,000 to 500,000.

[0020]

[12] The method for producing resin particles according to any one of [1] to

[11] , wherein the moisture content of the resin particles is 0.30% by weight or less.

[0021]

[13] The method for producing resin particles according to any one of [1] to

[12] , wherein the monomer contains styrene.

[0022]

[14] The method for producing resin particles according to any one of [1] to

[13] , wherein the resin particles have an average particle size of 0.90 mm or more.

[0023]

[15] The method for producing resin particles according to any one of [1] to

[14] , wherein the amount of residual monomer in the resin particles is 500 ppm or less. [Effects of the Invention]

[0024] According to one aspect of the present invention, there is provided a novel method for producing resin particles, which can produce flattened resin particles having a low moisture content using a suspension polymerization method. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a view of a resin particle according to an embodiment of the present invention as viewed from one direction. [Figure 2] 2 is a cross-sectional view of the resin particle of FIG. 1 taken along the line AA'. FIG. [Figure 3] This is a graph showing the relationship between L / D and weight average molecular weight of resin particles according to one embodiment of the present invention, and shows the ranges of L / D≧−0.02×(weight average molecular weight (10,000))+1.25 and 0.55≦L / D≦0.85. DETAILED DESCRIPTION OF THE INVENTION

[0026] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0027] 1. Technical Concept of One Embodiment of the Present Invention As described above, there are cases where resin particles are required to be non-spherical (for example, flat) and have a low moisture content.

[0028] A technique for producing non-spherical (for example, flat) resin particles is known from Patent Document 1. However, Patent Document 1 does not disclose or suggest the moisture content of the resin particles, and no consideration has been given to this.

[0029] Therefore, the present inventors have conducted extensive research with the aim of providing a method for producing resin particles that can produce flattened resin particles with a low moisture content.

[0030] As a result of extensive research, the present inventors independently discovered the following novel findings, which led to the completion of the present invention: (i) the discovery that resin particles having an L / D ratio within a specific range and satisfying a specific relationship between L / D and weight average molecular weight surprisingly become flattened resin particles with a low moisture content, and (ii) the discovery that by initiating polymerization of monomers in an aqueous suspension containing a specific amount of tricalcium phosphate having a specific average particle size, the resulting resin particles have an L / D ratio within a specific range and satisfy a specific relationship between L / D and weight average molecular weight.

[0031] 2. Method for producing resin particles A method for producing resin particles according to one embodiment of the present invention is a method for producing resin particles, comprising: an adjusting step of adjusting L / D of the resin particles to be obtained so that L / D≧−0.02×(weight average molecular weight (10,000))+1.25 and 0.55≦L / D≦0.85; the adjusting step comprises a polymerization initiation step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of a monomer, and 0.01 part by weight to 0.30 parts by weight of tricalcium phosphate having an average particle size of 10 μm to 30 μm; and the L / D is a value obtained by the following formula: L / D=L / ((Dl+Ds) / 2), In the above formula, L is the particle size at a point corresponding to 30% by weight of the cumulative weight on the weight-based cumulative distribution curve of the ellipse minor axis of the resin particle, Dl is the particle size at a point corresponding to 40% by weight of the cumulative weight on the weight-based cumulative distribution curve of the ellipse major axis of the resin particle, and Ds is the particle size at a point corresponding to 60% by weight of the cumulative distribution curve of the ellipse major axis of the resin particle, and the weight-based cumulative distribution curve of the ellipse minor axis and the weight-based cumulative distribution curve of the ellipse major axis are each measured using a particle size measuring device with the resin particle as a sample.

[0032] In this specification, "a method for producing resin particles according to one embodiment of the present invention" may be referred to as "the present production method."

[0033] The present manufacturing method has the above-mentioned configuration, and therefore has the advantage of being able to manufacture flattened resin particles with a low moisture content.

[0034] The resin particles obtained by the present production method also represent one embodiment of the present invention. In this specification, "resin particles according to one embodiment of the present invention" may be referred to as "the present resin particles."

[0035] The resin particles of the present invention can be suitably used as a raw material for extruded foams, and also as a raw material for expandable resin particles.

[0036] In this specification, a repeating unit derived from an X monomer may be referred to as an “X unit.” A repeating unit may also be referred to as a structural unit.

[0037] In this specification, the term "amount used" is synonymous with the term "amount added."

[0038] In this specification, "resin particles with a low moisture content" means, for example, that the moisture content is 0.75% by weight or less in 100% by weight of resin particles. The method for measuring the moisture content of resin particles will be described in detail in the Examples below.

[0039] In this specification, the term "polymerization conversion rate" refers to the ratio (% by weight) of the amount of monomer converted into a polymer relative to the amount of monomer used in polymerization (100% by weight). The method for measuring the polymerization conversion rate will be described in detail in the Examples below.

[0040] In this specification, the term "minor axis of an ellipse" refers to one of the particle sizes of resin particles obtained by measurement using an image analysis particle distribution measuring device (e.g., Millitrac JPA, manufactured by Nikkiso Co., Ltd.), and refers to the value of the minor axis of each resin particle obtained by capturing an image of the shadow (projection) of a group of resin particles falling with a camera, and analyzing the captured image.

[0041] In this specification, the term "major axis of an ellipse" refers to one of the particle sizes of resin particles obtained by measurement using an image analysis particle distribution measuring device, and refers to the value of the major axis of each resin particle obtained by capturing an image of the shadow (projection) of a group of falling resin particles with a camera, and analyzing the captured image.

[0042] (2-1. Adjustment process) This production method includes an adjusting step. The adjusting step is a step of adjusting the L / D of the resulting resin particles so that L / D≧−0.02×(weight average molecular weight (10,000))+1.25 and 0.55≦L / D≦0.85. In this specification, the formula "L / D≧−0.02×(weight average molecular weight (10,000))+1.25" is sometimes referred to as the "relationship between L / D and weight average molecular weight." The relationship between L / D and weight average molecular weight includes two variables: L / D and weight average molecular weight. The adjusting step can also be said to be a step of adjusting L / D and / or weight average molecular weight so that the resulting resin particles have an L / D within a specific range (specifically, 0.55 to 0.85) and satisfy the relationship between L / D and weight average molecular weight.

[0043] In L / D≧−0.02×(weight average molecular weight (10,000))+1.25, the “+1.25” can be changed. For example, the “+1.25” may be “+1.28,” “+1.32,” “+1.39,” or “+1.44.” This configuration allows for the stable production of flattened resin particles with a low moisture content.

[0044] In L / D≧−0.02×(weight average molecular weight (10,000))+1.25, the “−0.02” can be changed. For example, the “−0.02” may be “−0.019,” “−0.018,” “−0.0155,” or “−0.014.” With this configuration, flattened resin particles with a low moisture content can be stably produced.

[0045] In the case of L / D≧−0.02×(weight average molecular weight (10,000))+1.25, (i) only “−0.02” may be changed, (ii) only “+1.25” may be changed, or (iii) both “−0.02” and “+1.25” may be changed.

[0046] (2-1-1. Polymerization initiation step) In this production method, the preparation step includes a polymerization initiation step. The polymerization initiation step is a step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, and 0.01 to 0.30 parts by weight of tricalcium phosphate having an average particle size of 10 μm to 30 μm. By including the polymerization initiation step in the preparation step, the obtained resin particles have an L / D ratio within a specific range and can satisfy the relationship between L / D and weight average molecular weight through adjustment of the L / D ratio and weight average molecular weight. As a result, there is an advantage in that flattened resin particles with a low moisture content can be obtained.

[0047] (water) In this production method, water is used. The water used in this production method is not particularly limited, but examples include tap water, industrial water, RO water (water purified by reverse osmosis membrane method), distilled water, and deionized water (water purified by ion exchange resin).

[0048] The amount of water used in this production method is preferably 60 to 100 parts by weight, more preferably 70 to 100 parts by weight, even more preferably 80 to 100 parts by weight, and particularly preferably 90 to 100 parts by weight, per 100 parts by weight of the monomer. When the amount of water used is 100 parts by weight or less per 100 parts by weight of the monomer, it has the advantage of being possible to reduce production costs and environmental load. When the amount of water used is 60 parts by weight or more per 100 parts by weight of the monomer, it has the advantage of being possible to obtain expanded resin particles with a sharp particle size distribution.

[0049] (monomer) In this production method, a monomer is used. The monomer used in this production method is not particularly limited, but preferably includes styrene and an alkyl (meth)acrylate, and more preferably includes styrene. In this production method, in addition to a monomer including styrene and / or an alkyl (meth)acrylate, a monomer including a monomer other than styrene and / or an alkyl (meth)acrylate that is copolymerizable with styrene and / or an alkyl (meth)acrylate (hereinafter also referred to as "other monomer") may also be used.

[0050] The amount of styrene used in this production method is preferably 70 parts by weight or more, more preferably 80 parts by weight or more, more preferably 85 parts by weight or more, more preferably 90 parts by weight or more, even more preferably 92 parts by weight or more, and particularly preferably 95 parts by weight or more, per 100 parts by weight of the monomer. The monomer may contain 100 parts by weight of styrene per 100 parts by weight of the monomer. In other words, the monomer may be composed only of styrene.

[0051] The alkyl(meth)acrylate is not particularly limited, but examples thereof include methyl(meth)acrylate, ethyl(meth)acrylate, isopropyl(meth)acrylate, n-propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, hexyl(meth)acrylate, and ethylhexyl(meth)acrylate.

[0052] The amount of alkyl(meth)acrylate used in this production method is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and particularly preferably 5 parts by weight or less, per 100 parts by weight of the monomer. The amount of alkyl(meth)acrylate used in the monomer may be 0 parts by weight. In other words, no alkyl(meth)acrylate may be used in this production method. When the amount of alkyl(meth)acrylate used is 20 parts by weight or less per 100 parts by weight of the monomer, there is an advantage in that coalescence of the resulting resin particles can be prevented or reduced.

[0053] The other monomer is not particularly limited, but examples thereof include (a) styrene-based monomers other than styrene, such as α-methylstyrene, p-methylstyrene, t-butylstyrene, and chlorostyrene, (b) vinyl cyanide-based monomers, such as acrylonitrile and methacrylonitrile, and (c) polyfunctional monomers, such as divinylbenzene and polyethylene glycol dimethacrylate. For example, an embodiment in which the monomers consist of styrene and acrylonitrile, and an embodiment in which the monomers consist of styrene, acrylonitrile, and α-methylstyrene are also preferred.

[0054] The above-mentioned styrene-based monomers, alkyl (meth)acrylates and other monomers may each be used alone or in combination of two or more.

[0055] (tricalcium phosphate) In this manufacturing method, tricalcium phosphate is used. In this manufacturing method, tricalcium phosphate can have the function of dispersing monomer droplets and resin particles in an aqueous suspension. In other words, tricalcium phosphate can function as a dispersant.

[0056] The tricalcium phosphate in one embodiment of the present invention is preferably hydroxyapatite having the structural formula 3[Ca3(PO4)2·Ca(OH)2] with CAS number 1306-06-05.

[0057] The form of tricalcium phosphate is not particularly limited, but examples thereof include powder and slurry (for example, aqueous slurry).

[0058] The average particle size of the tricalcium phosphate used in the polymerization initiation step is 10 μm to 30 μm. The method for measuring the average particle size of tricalcium phosphate will be described in detail in the Examples below. The average particle size of the tricalcium phosphate is preferably 12 μm to 28 μm, more preferably 14 μm to 26 μm, even more preferably 16 μm to 24 μm, and particularly preferably 18 μm to 22 μm. When the average particle size of tricalcium phosphate is 10 μm to 30 μm, the obtained resin particles tend to be flattened, the average particle size becomes large, and the polymerization reaction is stabilized, which are advantageous.

[0059] The amount of tricalcium phosphate used in the polymerization initiation step is 0.01 to 0.30 parts by weight, preferably 0.05 to 0.28 parts by weight, more preferably 0.10 to 0.26 parts by weight, even more preferably 0.12 to 0.24 parts by weight, still more preferably 0.13 to 0.23 parts by weight, and particularly preferably 0.15 to 0.22 parts by weight, relative to 100 parts by weight of the monomer, from the viewpoints of preventing or reducing adhesion between resin particles and stabilizing the dispersion system.

[0060] (anionic surfactant) The aqueous suspension in the polymerization initiation step preferably further contains an anionic surfactant. In other words, the aqueous suspension in the polymerization initiation step preferably further contains an anionic surfactant in addition to the monomer and tricalcium phosphate. This has the advantage of improving the dispersion stability of the monomer droplets and resin particles in the aqueous suspension during polymerization.

[0061] The anionic surfactant is not particularly limited, but examples thereof include sodium alkyldiphenyl ether sulfonate, sodium α-olefin sulfonate, sodium dodecylbenzene sulfonate, etc. These anionic surfactants may be used alone or in combination of two or more. When two or more anionic surfactants are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0062] The amount of the anionic surfactant used is preferably 0.001 to 0.010 parts by weight, more preferably 0.002 to 0.009 parts by weight, even more preferably 0.003 to 0.008 parts by weight, and particularly preferably 0.004 to 0.008 parts by weight, relative to 100 parts by weight of the monomer, from the viewpoints of dispersion stability of the monomer droplets and resin particles in the aqueous suspension and preventing or reducing adhesion of the resin particles to each other.

[0063] (Polymerization initiator) In this production method, it is preferable to use a polymerization initiator, and it is more preferable to use a polymerization initiator that is soluble in the monomer. In other words, the aqueous suspension in the polymerization initiation step preferably contains a polymerization initiator in addition to the monomer and tricalcium phosphate, and it is more preferable to contain a polymerization initiator that is soluble in the monomer.

[0064] The polymerization initiator is not particularly limited, and radical-generating polymerization initiators generally used in the production of thermoplastic polymers can be used. Examples of such polymerization initiators include benzoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperpivalate, t-butylperoxyisopropyl carbonate, di-t-butylperoxyhexahydroterephthalate, 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxy-2-ethylhexyl monocarbonate, and t-amylperoxy-2-ethylhexyl monocarbonate. All of these polymerization initiators are soluble in the monomer. These polymerization initiators may be used alone or in combination of two or more.

[0065] In this production method, it is preferable to use a combination of a low-temperature decomposition initiator having a 10-hour half-life temperature of 74°C or higher and lower than 90°C and a high-temperature decomposition initiator having a 10-hour half-life temperature of 90°C or higher and lower than 110°C. This configuration has the advantage of reducing the amount of unreacted monomer remaining in the resin particles. A suitable example of the low-temperature decomposition initiator is benzoyl peroxide. A suitable example of the high-temperature decomposition initiator is 1,1-di(t-butylperoxy)cyclohexane.

[0066] The amount of polymerization initiator used in this production method is appropriately determined depending on the target weight-average molecular weight of the resin particles and is not particularly limited. The amount of polymerization initiator used is preferably 0.100 to 1.000 parts by weight, more preferably 0.200 to 0.800 parts by weight, even more preferably 0.300 to 0.600 parts by weight, and particularly preferably 0.350 to 0.500 parts by weight, per 100 parts by weight of the monomer. When the amount of polymerization initiator used is 0.100 parts by weight or more, polymerization proceeds sufficiently, while when it is 1.000 parts by weight or less, there is the advantage that the polymerization reaction is easy to control. Note that when a low-temperature decomposition type initiator and a high-temperature decomposition type initiator are used in combination, the "amount of polymerization initiator used" refers to the total amount of the low-temperature decomposition type initiator and the high-temperature decomposition type initiator.

[0067] The aqueous suspension in the polymerization initiation step preferably further contains a low-temperature decomposition initiator. The amount of the low-temperature decomposition initiator used in the aqueous suspension in the polymerization initiation step is preferably 0.05 to 0.30 parts by weight, more preferably 0.06 to 0.28 parts by weight, even more preferably 0.07 to 0.28 parts by weight, and particularly preferably 0.10 to 0.26 parts by weight, per 100 parts by weight of the monomer. This configuration has the advantage of easily obtaining resin particles having a desired weight-average molecular weight. This configuration also has the advantage that, by adjusting the weight-average molecular weight, the resulting resin particles can easily satisfy the relationship between L / D and the weight-average molecular weight. That is, this configuration has the advantage of easily obtaining resin particles with a low moisture content. In other words, the adjustment step preferably includes a step of using 0.05 to 0.30 parts by weight of the low-temperature decomposition initiator per 100 parts by weight of the monomer in the polymerization initiation step.

[0068] In the present production method, the amount of the high-temperature decomposition initiator used in the aqueous suspension is preferably 0.05 to 0.70 parts by weight, more preferably 0.08 to 0.50 parts by weight, even more preferably 0.10 to 0.40 parts by weight, and particularly preferably 0.15 to 0.30 parts by weight, relative to 100 parts by weight of the monomer. This configuration has the advantage of being able to reduce the amount of unreacted monomer remaining in the resin particles.

[0069] (thickener) In this production method, a thickener may be used. In other words, the aqueous suspension may further contain a thickener in addition to the monomer and tricalcium phosphate. The use of a thickener has the advantage that the viscosity of the aqueous suspension can be easily adjusted (optimized).

[0070] The thickener is not particularly limited, but is preferably a water-soluble polysaccharide, and suitable examples thereof include rhamsan gum, glyoxal, curdlan, xanthan gum, welan gum, and xanthan gum. These thickeners may be used alone or in combination of two or more. When two or more thickeners are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0071] The amount of thickener used is preferably 0.00005 to 0.00200 parts by weight, more preferably 0.00010 to 0.00150 parts by weight, even more preferably 0.00015 to 0.00100 parts by weight, particularly preferably 0.00015 to 0.00080 parts by weight, and most preferably 0.00020 to 0.00050 parts by weight, relative to 100 parts by weight of monomer. If the amount of thickener used is in the range of 0.00005 to 0.00200 parts by weight relative to 100 parts by weight of monomer, there is an advantage that the monomer droplets during the polymerization reaction can be uniformly coalesced and dispersed.

[0072] (Water-soluble inorganic salts) In the present production method, a water-soluble inorganic salt may be used, in other words, the aqueous suspension may further contain a water-soluble inorganic salt in addition to the monomer and tricalcium phosphate.

[0073] The water-soluble inorganic salt is not particularly limited, but examples thereof include sodium chloride, potassium chloride, sodium sulfate, sodium hydrogen sulfite, potassium hydrogen sulfite, potassium persulfate, ammonium hydrogen sulfite, etc. Furthermore, substances that dissolve in water and / or react in the polymerization reaction system to form sulfites, i.e., precursors, can also be used as the water-soluble inorganic salt.

[0074] The amount of the water-soluble inorganic salt used is not particularly limited, and is preferably 1.0 part by weight or less, and more preferably 0.5 part by weight or less, per 100 parts by weight of the monomer, for example.

[0075] (Other additives) In the present production method, flame retardants, flame retardant auxiliaries, plasticizers, cell regulators (sometimes referred to as nucleating agents), etc. (these may be collectively referred to as "other additives") may be used as needed. In other words, the aqueous suspension may contain the above-mentioned other additives.

[0076] The use of a flame retardant can impart flame retardancy to the resin particles, as well as to the extruded foam, expanded beads, and foam-molded articles obtained using the resin particles. In the present production method, the flame retardant alone may be used, or the flame retardant and the flame retardant auxiliary may be used in combination.

[0077] Flame retardants include, but are not limited to, (a) low molecular weight compounds such as polyglycerol dibromopropyl ether, tetrabromobisphenol A, tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl ether), and 2,2-bis[4-(2,3-dibromo-2-methylpropyloxy)-3,5-dibromophenyl]propane, and (b) brominated polymers such as brominated styrene, brominated butadiene-vinyl aromatic copolymer, brominated novolac resin allyl ether, brominated poly(1,3-cycloalkadiene), and brominated poly(4-vinylphenol allyl ether). These flame retardants may be used alone or in combination.

[0078] The flame retardant aid is not particularly limited, but examples thereof include high-temperature decomposition type organic substances such as cumene peroxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, etc. These flame retardant aids may be used alone or in combination of two or more.

[0079] The plasticizer is not particularly limited, but examples thereof include (a) fatty acid glycerides such as stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearate diglyceride, and stearate monoglyceride, (b) vegetable oils such as coconut oil, palm oil, and palm kernel oil, (c) aliphatic esters such as dioctyl adipate and dibutyl sebacate, (d) organic hydrocarbons such as liquid paraffin, and (e) alicyclic plasticizers such as cyclohexane and cyclopentane. These plasticizers may be used alone or in combination of two or more.

[0080] Examples of the cell regulator include (a) aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide, (b) polyethylene wax, and (c) acrylic resins (Kane Ace PA-20 manufactured by Kaneka Corporation), etc. These cell regulators may be used alone or in combination of two or more.

[0081] (container) The container used in this production method is not particularly limited, but is preferably a sealable container that is pressure-resistant and heat-resistant. In this production method, in the aqueous suspension, monomer droplets and resin particles are dispersed in water or an aqueous solution. Therefore, in order to efficiently disperse the monomer droplets and resin particles in the aqueous suspension, it is more preferable that the container be equipped with a stirrer. A suitable example of the container is an autoclave equipped with a stirrer.

[0082] The temperature in the polymerization initiation step is not particularly limited. The temperature in the polymerization initiation step is the temperature of the aqueous suspension, and may also be referred to as the "polymerization initiation temperature." The polymerization initiation temperature is not particularly limited, but is preferably 90°C or higher and lower than 100°C, more preferably 92°C or higher and lower than 100°C, even more preferably 94°C or higher and lower than 100°C, and particularly preferably 96°C or higher and lower than 100°C. This configuration has the advantage that the low-temperature decomposition initiator efficiently promotes the polymerization reaction, thereby shortening the polymerization time.

[0083] (2-1-2. Addition process) In this production method, the preparation step preferably further includes an addition step. The addition step is a step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate per 100 parts by weight of the monomer to the aqueous suspension at least once after the polymerization initiation step. By including the addition step in the preparation step, the polymerization reaction can be stabilized and resin particles having an L / D ratio within a specific range and satisfying the relationship between L / D and weight-average molecular weight can be more easily obtained. As a result, there is an advantage in that flattened resin particles with a low moisture content can be more easily obtained. The addition step is also a step of continuing the polymerization of the monomer following the polymerization initiation step to obtain resin particles.

[0084] The amount of tricalcium phosphate used in the addition step is preferably 0.01 to 0.30 parts by weight, more preferably 0.02 to 0.20 parts by weight, even more preferably 0.04 to 0.15 parts by weight, and particularly preferably 0.05 to 0.10 parts by weight, relative to 100 parts by weight of the monomer. When the amount of tricalcium phosphate used is within the above-mentioned range, resin particles can be stably produced, and resin particles having an L / D ratio within a specific range and satisfying the relationship between L / D and weight-average molecular weight can be more easily obtained. As a result, flattened resin particles with a low moisture content can be more easily obtained. Furthermore, when the amount of tricalcium phosphate used is (a) 0.01 parts by weight or more relative to 100 parts by weight of the monomer, the amount of large-sized resin particles is reduced, and when it is (b) 0.30 parts by weight or less, the amount of small-sized (fine) resin particles is reduced.

[0085] When the addition step is performed, the ratio of the amount of tricalcium phosphate used in the addition step to the amount of tricalcium phosphate used in the polymerization initiation step (amount of tricalcium phosphate used in the addition step / amount of tricalcium phosphate used in the polymerization initiation step) is not particularly limited, but is preferably less than 1.00, more preferably 0.80 or less, even more preferably 0.60 or less, and particularly preferably 0.50 or less. The ratio of the amount of tricalcium phosphate used in the addition step to the amount of tricalcium phosphate used in the polymerization initiation step (amount of tricalcium phosphate used in the addition step / amount of tricalcium phosphate used in the polymerization initiation step) may be 0.45 or less, 0.40 or less, 0.35 or less, or even 0.30 or less. The lower limit of the ratio of the amount of tricalcium phosphate used in the addition step (amount of tricalcium phosphate used in the addition step / amount of tricalcium phosphate used in the polymerization initiation step) is not particularly limited, but may be, for example, greater than 0 and 0.20 or greater. When the ratio of the amount of tricalcium phosphate used in the addition step (amount of tricalcium phosphate used in the addition step / amount of tricalcium phosphate used in the polymerization initiation step) is within the above-mentioned range, resin particles can be stably produced, and resin particles having an L / D ratio within a specific range and satisfying the relationship between L / D and weight-average molecular weight can be more easily obtained. As a result, there is an advantage that flattened resin particles with a low moisture content can be more easily obtained.

[0086] The total amount of tricalcium phosphate used in the present production method is not particularly limited, but from the viewpoint of stability during production of resin particles, it is preferably 0.02 to 0.60 parts by weight, more preferably 0.05 to 0.50 parts by weight, even more preferably 0.07 to 0.40 parts by weight, and particularly preferably 0.10 to 0.30 parts by weight, per 100 parts by weight of monomer. The term "total amount of tricalcium phosphate used in the present production method" refers to the total amount of tricalcium phosphate used in the polymerization initiation step and the addition step. When additional tricalcium phosphate is used in other steps, the total amount including those amounts is referred to as "total amount of tricalcium phosphate used in the present production method."

[0087] The addition step preferably includes adding tricalcium phosphate when the polymerization conversion rate is between 40% and 60% by weight. In other words, the addition of tricalcium phosphate in the addition step is preferably carried out at least once when the polymerization conversion rate is between 40% and 60% by weight, preferably between 42% and 58% by weight, and particularly preferably between 45% and 55% by weight. When tricalcium phosphate is added in the addition step when the polymerization conversion rate is within the above-mentioned range, the dispersion of the monomer droplets in the aqueous suspension is stabilized (good), resulting in the production of stably flattened resin particles. While the reason for this is unclear, it is speculated that, although the volume occupied by the monomer is larger than the volume occupied by water at the initial stage of polymerization, the volume occupied by the monomer and the volume occupied by water become approximately equal when the polymerization conversion rate reaches between 40% and 60% by weight. From the perspective of dispersibility, further addition of tricalcium phosphate at this point is preferable. However, one embodiment of the present invention is not limited by this speculation.

[0088] The average particle size of the tricalcium phosphate used in the addition step is not particularly limited, and may be the same as or different from the average particle size of the tricalcium phosphate used in the polymerization initiation step. The average particle size of the tricalcium phosphate used in the addition step is preferably 1 μm to 30 μm, more preferably 10 μm to 30 μm, more preferably 12 μm to 28 μm, more preferably 14 μm to 26 μm, even more preferably 16 μm to 24 μm, and particularly preferably 18 μm to 22 μm. When the average particle size of tricalcium phosphate is 1 μm to 30 μm, the resulting resin particles tend to be flattened, the average particle size increases, and the polymerization reaction is stabilized, which are advantageous.

[0089] (2-1-3. Heat treatment process) The present production method preferably further includes a heat treatment step in which the aqueous suspension is treated at a temperature higher than that at the start of polymerization once the polymerization conversion rate has reached a certain level (e.g., 80% by weight or higher).

[0090] The heat treatment step is preferably carried out when the polymerization conversion rate is 80% by weight or more, and may be carried out when the polymerization conversion rate is 82% by weight or more, or may be carried out when the polymerization conversion rate is 84% ​​by weight or more. The upper limit of the polymerization conversion rate at the time of carrying out the heat treatment step is not particularly limited, but may be, for example, less than 100% by weight, less than 95% by weight, or less than 90% by weight.

[0091] The temperature in the heat treatment step is not particularly limited as long as it is higher than the temperature at the time of polymerization initiation, i.e., it is a temperature higher than the temperature of the aqueous suspension at the time the above-mentioned polymerization initiation step is carried out. The temperature in the heat treatment step is sometimes referred to as the "heat treatment temperature." The heat treatment temperature is preferably 110°C or higher, more preferably 112°C or higher, even more preferably 114°C or higher, and particularly preferably 116°C or higher. A higher heat treatment temperature has the advantage of reducing the amount of residual monomer in the resin particles.

[0092] The duration of the heat treatment step, i.e., the time for treating the aqueous suspension at the heat treatment temperature (sometimes referred to as the "heat treatment time"), is not particularly limited. The heat treatment time is preferably 1 hour or longer, more preferably 2 hours or longer, even more preferably 3 hours or longer, and particularly preferably 3.5 hours or longer. A longer heat treatment time has the advantage of reducing the amount of residual monomer in the resin particles.

[0093] The amount of residual monomer in the resin particles is preferably 500 ppm or less, more preferably 400 ppm or less, and even more preferably 300 ppm or less. Since it is practically difficult to achieve 0 ppm, the lower limit of the amount of residual monomer in the resin particles is 1 ppm or more.

[0094] (2-1-4. Weight average molecular weight adjustment process) In this production method, the adjusting step preferably includes a weight-average molecular weight adjusting step. The weight-average molecular weight adjusting step is a step of adjusting the weight-average molecular weight of the resin particles to 150,000 to 500,000. By including the weight-average molecular weight adjusting step in the adjusting step, resin particles that satisfy the relationship between L / D and weight-average molecular weight can be more easily obtained through adjustment of the weight-average molecular weight. As a result, there is an advantage in that flattened resin particles with a low moisture content can be more easily obtained. The weight-average molecular weight is largely determined by the amount of cleavage of the polymerization initiator (amount of radicals generated) in the polymerization initiation step, and can be adjusted by appropriately adjusting the amount of low-temperature decomposition initiator used and the polymerization temperature. In other words, when 0.05 to 0.30 parts by weight of the low-temperature decomposition initiator is used per 100 parts by weight of the monomer in the polymerization initiation step, the polymerization initiation step can also serve as the weight-average molecular weight adjusting step.

[0095] The weight-average molecular weight of the resin particles is preferably 150,000 to 500,000. The upper limit of the weight-average molecular weight of the resin particles may be 450,000 or less, 350,000 or less, or 300,000 or less. The lower limit of the weight-average molecular weight of the resin particles may be 180,000 or more, 200,000 or more, or 220,000 or more. If the weight-average molecular weight of the resin particles is 150,000 or more, there is an advantage that the moisture content of the obtained resin particles is low. Furthermore, if the weight-average molecular weight of the resin particles is 500,000 or less, there is an advantage that the amount of resin particles produced that are high in moisture content and spherical is reduced.

[0096] For the explanation of the low-temperature polymerization initiator, the description in the above section (Polymerization initiator) is incorporated herein by reference.

[0097] By carrying out a preparation procedure including at least a polymerization initiation step, resin particles, more specifically, an aqueous suspension containing resin particles, can be obtained. Thereafter, for example, (1) the aqueous suspension containing resin particles is cooled to room temperature (e.g., 25°C), (2) the resin particles are removed from the aqueous suspension, (3) the obtained resin particles are pickled with, for example, hydrochloric acid and washed with water, (4) the washed resin particles are dehydrated using a centrifuge, and (5) the dehydrated resin particles are dried using, for example, an airflow dryer, to obtain dried resin particles.

[0098] (2-3.Characteristics) The L / D of the resin particles is L / D≧−0.02×(weight average molecular weight (10,000))+1.25 and 0.55≦L / D≦0.85. An L / D of 0.85 or less means that the resin particles are flat. Therefore, the resin particles can also be called "flat resin particles" or "flattened resin particles." The upper limit of the L / D of the resin particles is preferably 0.83 or less, more preferably 0.80 or less, even more preferably 0.78 or less, and particularly preferably 0.75 or less. The lower limit of the L / D of the resin particles is preferably 0.57 or more, more preferably 0.60 or more, even more preferably 0.65 or more, and particularly preferably 0.70 or more. The lower limit of the L / D of the resin particles may be 0.80 or more. When resin particles with an L / D within the above range are used as a raw material for extruded foam, they have the advantage of being more easily penetrated into the extruder screw. When resin particles having an L / D ratio within the above range are used as a raw material for expandable resin particles, the expandable resin particles are expanded to form expanded particles, and the expanded molded article obtained by further molding the expanded particles has the advantage of having higher sound absorption properties.

[0099] The moisture content of the resin particles is preferably 0.75% by weight or less, more preferably 0.70% by weight or less, more preferably 0.65% by weight or less, more preferably 0.60% by weight or less, more preferably 0.55% by weight or less, more preferably 0.50% by weight or less, more preferably 0.45% by weight or less, more preferably 0.40% by weight or less, more preferably 0.35% by weight or less, more preferably 0.30% by weight or less, more preferably 0.28% by weight or less, more preferably 0.25% by weight or less, more preferably 0.23% by weight or less, and even more preferably 0.20% by weight or less. When resin particles having a moisture content within the above range are used as a raw material for extruded foam, there is an advantage in that extruded foam can be produced stably.

[0100] Resin particles according to one embodiment of the present invention are shown in FIGS. 1 and 2. FIG. 1 is a view of a resin particle according to one embodiment of the present invention as viewed from one direction. FIG. 2 is a cross-sectional view of the resin particle shown in FIG. 1 taken along the line A-A'. The resin particles shown in FIGS. 1 and 2 have a L / D ratio of 0.55≦L / D≦0.85, i.e., are flattened resin particles. The resin particles shown in FIGS. 1 and 2, i.e., flat resin particles, can be said to have a shape similar to a Go stone, for example. FIG. 1 can also be said to be a view of a resin particle placed on a horizontal table as viewed from the horizontal direction. The "minor axis of an ellipse" can also be said to be the vertical length of the resin particle when placed on a horizontal table. The "major axis of an ellipse" can also be said to be the horizontal length of the resin particle when placed on a horizontal table.

[0101] A graph showing the relationship between L / D, weight-average molecular weight, and moisture content of resin particles according to one embodiment of the present invention is shown in Figure 3. Figure 3 plots resin particles of the examples as circles (○) and resin particles of the comparative examples as triangles (△) on a graph with the vertical axis representing the L / D of the resin particles and the horizontal axis representing the weight-average molecular weight. The graph shows the range of L / D ≧ -0.02 × (weight-average molecular weight (10,000)) + 1.25 and 0.55 ≦ L / D ≦ 0.85. The range is indicated by a shaded area. The moisture content of the resin particles of the examples within the shaded area in Figure 3, i.e., within the shaded area, was 0.3 wt % or less, as shown in the table below.

[0102] The average particle size of the resin particles is preferably 0.90 mm or more, more preferably 0.95 mm or more, even more preferably 1.00 mm or more, and particularly preferably 1.05 mm or more. The method for measuring the average particle size of the resin particles will be described in detail in the Examples below.

[0103] (2-4. Extruded foam) The present resin particles can be used as a raw material for extruded foams. When the present resin particles are used as a raw material for extruded foams, the resin particles can be directly fed to an extruder, and the resin particles are easily bitten into the screw of the extruder, which has the advantage that extruded foams can be stably produced even when a single-screw extruder is used, for example.

[0104] The extruded foam can be produced, for example, by melt-kneading resin particles and a blowing agent. The melt-kneading of the resin particles and the blowing agent can be carried out using a production apparatus equipped with, for example, a conventionally known extruder as a melt-kneading section. The extruder can be, for example, a single-screw extruder or a twin-screw extruder.

[0105] (foaming agent) The blowing agent is not particularly limited. Examples of the blowing agent include (a) aliphatic hydrocarbons such as propane, butane, and pentane; (b) alicyclic hydrocarbons such as cyclobutane and cyclopentane; (c) halogenated hydrocarbons such as methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane; and (d) inorganic substances such as carbon dioxide and water. These blowing agents may be used alone or in combination of two or more. When two or more blowing agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose. Preferred blowing agents for producing extruded foams are butane, pentane, and dichlorotetrafluoroethane.

[0106] (2-5. Expandable resin particles) The present resin particles can be used as a raw material for expandable resin particles. When the present resin particles are used as a raw material for expandable resin particles, expandable resin particles having a flattened shape can be obtained, and by expanding the expandable resin particles, expanded particles (pre-expanded particles) having a flattened shape can be obtained. When the flattened expanded particles are molded (for example, by in-mold foam molding), a foamed molded article with a high porosity can be obtained. A foamed molded article with a high porosity has high sound absorption performance, and therefore has the advantage of being suitable for use as a sound-insulating material. Furthermore, when the present resin particles are used as a raw material for expandable resin particles, there is little variation in the expansion ratio of the pre-expanded particles, which has the advantage that the resulting foamed molded article has a good appearance and high mechanical strength.

[0107] The expandable resin particles can be obtained, for example, by impregnating resin particles with a blowing agent. The impregnation of the resin particles with the blowing agent can also be carried out during the above-mentioned production method. For example, an impregnation step in which the resin particles are impregnated with the blowing agent may be carried out after the above-mentioned addition step. The expandable resin particles can be obtained through the impregnation step.

[0108] The impregnation step is preferably carried out when the polymerization conversion rate is 85% by weight or higher. This configuration has the advantage that the added blowing agent does not excessively promote softening of the resin particles, stabilizing the dispersibility of the monomer droplets and resin particles in the aqueous suspension and eliminating or reducing agglomeration of the resin particles. The impregnation step is more preferably carried out when the polymerization conversion rate is 90% by weight or higher, even more preferably 92% by weight or higher, and particularly preferably 95% by weight or higher.

[0109] The blowing agent that can be used in the production of expandable resin particles is not particularly limited, and the above-mentioned blowing agents can be used as appropriate. In the production of expandable resin particles, from the viewpoints of volatility and foaming power, it is preferable that the blowing agent contains any one selected from the group consisting of normal pentane, isopentane, neopentane, and cyclopentane. Furthermore, since cells tend to be stabilized during the expansion of resin particles, it is preferable that the blowing agent contains any one selected from the group consisting of pentanes (normal pentane, isopentane, neopentane, cyclopentane, etc.).

[0110] [3.Applications] One embodiment of the present invention can be suitably used in fields where foamed molded articles are used. In the field of extruded foams (e.g., extruded foam boards), the extruded foam can be suitably used, for example, as a building insulation material (core material for tatami mats, panels, walls, etc.). Furthermore, when expandable resin particles, foamed particles, and a foamed molded article are obtained in this order, the resulting foamed molded article has high sound absorption properties and can therefore be suitably used in fields such as sound insulation materials. [Example]

[0111] The present invention will be explained in more detail below with reference to examples and comparative examples, but the technical scope of the present invention is not limited to these examples.

[0112] 〔material〕 The substances used in the examples and comparative examples are shown below. (water) Water: Ion-exchanged water (monomer) ST: Styrene (NS Styrene Monomer Co., Ltd.) (Tricalcium phosphate: CAS number 1306-06-05) ·CaP1:TCP average particle size 20μm (powder, manufactured by Taihei Kagaku Co., Ltd.) CaP2:TCP2 average particle size 16 μm (powder, manufactured by Taihei Chemical Co., Ltd.) CaP3: TCP-10U average particle size 5 μm (slurry 10 wt%, Taihei Chemical Co., Ltd.) CaP4: Instant-S, average particle size 1.5 μm (30% by weight slurry, manufactured by Budenheim) (anionic surfactant) AOS: Sodium alkyldiphenyl ether sulfonate (Kao Corporation) (thickener) KLZ: A mixture of xanthan gum and glyoxal (Kelzan S (CP Kelco)) (Water-soluble inorganic salts) Sodium chloride: manufactured by Nihon Kaisui Co., Ltd. Potassium persulfate (Polymerization initiator) Low-temperature decomposition initiator: Benzoyl peroxide (10-hour half-life temperature 74°C, Niper BW (manufactured by Nippon Oil & Fats Co., Ltd.)) High-temperature decomposition initiator: 1,1-di(t-butylperoxy)cyclohexane (10-hour half-life temperature 91°C, Perhexa C (manufactured by Nippon Oil & Fats Co., Ltd.)) [Measurement method] The measurement methods used in the examples and comparative examples are described below.

[0113] (Measurement of the average particle size of tricalcium phosphate) For each tricalcium phosphate, an aqueous dispersion of tricalcium phosphate with a concentration of 0.1 wt / wt% was used as a sample, and the particle size distribution was measured using a laser diffraction particle size distribution analyzer (Microtrac MT3300EX, manufactured by Microtrac), and a cumulative particle size distribution curve was obtained based on the number. From the obtained cumulative particle size distribution curve, the particle size (μm) at the point corresponding to 50% cumulative number percentage was determined and used as the average particle size.

[0114] (Measurement of polymerization conversion rate) Resin particles were collected from the pressure vessel at three time points: during the suspension polymerization (when tricalcium phosphate was added), at the start of heat treatment, and at the end of heat treatment. The moisture on the surface of the resin particles was wiped off using filter paper. 1.0 g of resin particles was dissolved in 20 ml of dichloromethane, and 0.005 g of an internal standard solution (cyclopentanol) was added to the solution. The solution was then subjected to gas chromatography (GC-14B, Shimadzu Corporation) to measure the polymerization conversion rate under the following conditions. The polymerization conversion rate was calculated from the amount of remaining monomer components.

[0115] Column: PEG-20M 25% Chromosorb W 60 / 80(3.0m×3.0mmI.D.) Column temperature: 110℃ Detector (FID temperature: 170°C).

[0116] (Measurement of the average particle size of resin particles, L, Dl, Ds and L / D) Using 100 g of resin particles as a sample, weight-based cumulative distribution curves for the minor axis and major axis of the ellipse were obtained using an image analysis particle distribution analyzer (Militrack JPA, manufactured by Nikkiso Co., Ltd.). From the obtained cumulative distribution curves, (i) the particle size at the point where the cumulative weight corresponds to 50% by weight on the weight-based cumulative distribution curve for the minor axis of the resin particles was defined as the average particle size (mm), (ii) the particle size at the point where the cumulative weight corresponds to 30% by weight on the weight-based cumulative distribution curve for the minor axis of the resin particles was defined as L (mm), (iii) the particle size at the point where the cumulative weight corresponds to 40% by weight on the weight-based cumulative distribution curve for the major axis of the resin particles was defined as Dl (mm), and (iv) the particle size at the point where the cumulative weight corresponds to 60% by weight on the weight-based cumulative distribution curve for the major axis of the resin particles was defined as Ds (mm).

[0117] Furthermore, L / D was calculated based on the following formula: L / D=L / ((Dl+Ds) / 2).

[0118] (grain weight) Kernel weight was calculated based on the following formula: (Grain weight (mg)) = 4 / 3 x π x (L / 2) x (Dl / 2) x (Ds / 2).

[0119] (Measurement of weight average molecular weight (Mw)) The weight-average molecular weight of the resin particles was measured by the following method. First, the resin particles to be measured were dissolved in tetrahydrofuran, and the resulting solution was used as a sample. The resulting sample was subjected to gel permeation chromatography (GPC) (Tosoh Corporation, HLC-8320GPC) to measure the weight-average molecular weight. The measurement conditions were as follows: Sample solution: 0.02g / THF 20ml Measurement temperature (column temperature): 40°C, Flow rate; 0.35ml / min, Injection volume; 10μl, Column: TSKgel super HZM-H, Mobile phase; THF. Separately, polystyrene with a known weight-average molecular weight was subjected to gel permeation chromatography under the same conditions as the sample to prepare a calibration curve. Using the obtained calibration curve, the weight-average molecular weight of the resin particles was calculated in terms of polystyrene.

[0120] (Moisture content measurement) Using 0.05 g of resin particles as a sample, the moisture content was measured using an automatic heating moisture vaporizer (EV-2010 manufactured by Hiranuma Sangyo Co., Ltd.: nitrogen flow rate 100 ml / min, vaporization temperature 150°C).

[0121] (Residual monomer amount) The amount of unreacted monomer was determined as the amount of residual monomer from the polymerization conversion rate at the end of the heat treatment. The amount of residual monomer was measured in the same manner as in the above (measurement of polymerization conversion rate).

[0122] Example 1 (I. Adjustment process) (Ii) Polymerization initiation step A monomer mixture containing both the low-temperature decomposition initiator and the high-temperature decomposition initiator was prepared by mixing 0.19 parts by weight of a low-temperature decomposition initiator, 0.20 parts by weight of a high-temperature decomposition initiator, and 100 parts by weight of styrene. A 6-L autoclave equipped with a stirrer (manufactured by Taiatsu Glass Co., Ltd.) was charged with 100 parts by weight of water, 0.18 parts by weight of tricalcium phosphate (CaP2: 16 μm), 0.007 parts by weight of AOS as an anionic surfactant, 0.47 parts by weight of sodium chloride as a water-soluble inorganic salt, and 0.0002 parts by weight of KLZ as a thickener, and the charged raw materials were stirred with a stirrer. The monomer mixture was then introduced into the autoclave to prepare an aqueous suspension. The autoclave was then deoxidized using a vacuum pump until the gauge pressure inside the autoclave reached -0.06 MPa. The aqueous suspension was then heated to 94°C, and suspension polymerization of the monomers in the aqueous suspension was initiated.

[0123] (I-ii) Addition process At a time point of 1.75 hours from the start of polymerization (polymerization conversion rate: 45% by weight), 0.05 parts by weight of tricalcium phosphate CaP2 was injected into the autoclave with nitrogen, and the polymerization of the monomers was further continued.

[0124] (II) Heat treatment process 4.5 hours after the start of polymerization (polymerization conversion rate 85 wt%), the temperature of the aqueous suspension was raised to 118°C and maintained at 118°C for 4 hours to carry out a heat treatment step.

[0125] The aqueous suspension containing the resin particles was then cooled to room temperature (25°C) and removed. The resulting resin particles were pickled with hydrochloric acid and washed with water, and then dehydrated using a centrifuge (manufactured by Matsumoto Kikai). The resin particles were then dried in an airflow dryer (manufactured by Hiraiwa Iron Works) to obtain resin particles. The L, Dl, Ds, ellipse minor axis diameter (D50), particle weight, weight average molecular weight, moisture content, and residual monomer content of the resulting resin particles were measured using the methods described above. The results are shown in Table 1.

[0126] [Examples 2 to 10, Comparative Examples 1 to 12] Resin particles were obtained in the same manner as in Example 1, except that the amount of water, the type and amount of tricalcium phosphate used in the polymerization initiation step, the amount of thickener, the amount of polymerization initiator, the type and amount of tricalcium phosphate added in the addition step, the polymerization conversion rate during the addition step (time elapsed from the start of polymerization), the polymerization conversion rate at the start of the heat treatment step (time elapsed from the start of polymerization), and the heat treatment temperature were changed as shown in Tables 1 and 2. The L, Dl, Ds, ellipsoid minor axis diameter (D50), particle weight, weight-average molecular weight, moisture content, and residual monomer content of the obtained resin particles were measured using the methods described above. The results are shown in Tables 1 and 2.

[0127] In addition, the resin particles obtained in each example were directly fed into an extruder to attempt to produce an extruded foam. As a result, it was confirmed that the resin was embedded in the extruder screw and that extruded foams could be stably produced in a single-screw extruder.

[0128] [Table 1]

[0129] [Table 2] [Industrial Applicability]

[0130] According to one embodiment of the present invention, there is provided a method for producing resin particles, which can produce resin particles having a low moisture content by suspension polymerization. Therefore, this embodiment of the present invention can be suitably used in fields such as packaging materials (trays) for food containers and the like, packaging materials for transport such as fish crates, heat insulating materials (for example, hot water storage tanks, roof insulating materials, pipe insulating materials, constant temperature storage containers, constant temperature transport containers, etc.), and sound insulating materials.

Claims

1. A method for producing resin particles, comprising: and adjusting the L / D ratio of the resulting resin particles so that L / D is equal to or greater than -0.02 x (weight average molecular weight (10,000)) + 1.25 and 0.55 ≦ L / D ≦ 0.85, the preparation step includes a polymerization initiation step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, and 0.01 part by weight to 0.30 part by weight of tricalcium phosphate having an average particle size of 10 μm to 30 μm; The L / D is a value obtained by the following formula: L / D=L / ((Dl+Ds) / 2), In the above formula, L is the particle diameter at a point corresponding to a cumulative weight of 30% by weight on a cumulative distribution curve of the weight-based ellipse minor axis of the resin particles, Dl is a particle diameter at a point corresponding to 40% by weight of a cumulative weight distribution curve of the ellipse major diameter of the resin particles based on weight, Ds is a particle diameter at a point corresponding to 60% by weight of a cumulative weight distribution curve of the ellipse major diameter of the resin particles based on weight, The weight-based cumulative distribution curve of the ellipse's minor axis and the weight-based cumulative distribution curve of the ellipse's major axis are each measured using a particle size measuring device with the resin particles as a sample.

2. 2. The method for producing resin particles according to claim 1, wherein the adjusting step further includes an adding step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate to the aqueous suspension relative to 100 parts by weight of the monomer.

3. 3. The method for producing resin particles according to claim 2, wherein the adding step includes a step of adding tricalcium phosphate when the polymerization conversion rate is 40% by weight to 60% by weight.

4. 3. The method for producing resin particles according to claim 2, wherein the adding step includes a step of adding tricalcium phosphate having an average particle size of 1 μm to 30 μm.

5. The method for producing resin particles according to claim 1 or 2, wherein the aqueous suspension in the polymerization initiation step further contains a low-temperature decomposition initiator.

6. 3. The method for producing resin particles according to claim 1, wherein the amount of the low-temperature decomposition initiator used in the aqueous suspension in the polymerization initiation step is 0.05 parts by weight to 0.30 parts by weight per 100 parts by weight of the monomer.

7. 3. The method for producing resin particles according to claim 1, wherein the weight average molecular weight of the resin particles is 150,000 to 500,000.

8. The method for producing resin particles according to claim 1 or 2, wherein the moisture content of the resin particles is 0.30% by weight or less.

Images