Method for producing resin particles

Abstract

To provide a method for producing resin particles that enables stable production of flattened resin particles.SOLUTION: A method for producing resin particles comprises: a polymerization initiation step in which suspension polymerization of a monomer is initiated in an aqueous suspension containing water, the monomer, a specific amount of tricalcium phosphate having a specific average particle diameter, and an anionic surfactant; and a heat treatment step in which the aqueous suspension is treated at a temperature higher than that at the polymerization initiation point, at a specific timing, wherein the L / D of the resin particles is 0.85 or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing resin particles, and particularly to a method for producing flattened resin particles.

Background Art

[0002] Conventionally, a technique for producing an extruded foam (board) of a styrene resin by charging styrene resin particles into an extruder and injecting a foaming agent during melting is known.

[0003] As the resin particles used for producing the extruded foam, resin particles that are non-spherical (for example, flat-shaped) may sometimes be required.

[0004] Patent Document 1 discloses polymer particles obtained by a suspension polymerization method, wherein the ratio (L / D) of the major axis (L) to the minor axis (D) of the projected two-dimensional figure obtained by irradiating light from directions orthogonal to the major axis direction of the particles is 1.3 or more, and the average particle diameter is 300 μm or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the above-described conventional technology still has room for further improvement from the viewpoint of stably producing flattened resin particles.

[0007] One aspect of the present invention aims to provide a novel method for producing resin particles that can stably produce flattened resin particles.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, one embodiment of the present invention includes the following configuration.

[0009] [1] A method for producing resin particles, comprising: In an aqueous suspension containing water, 100 parts by weight of a monomer, 0.01 to 0.30 parts by weight of tricalcium phosphate having an average particle diameter of 10 μm to 30 μm, and an anionic surfactant, a polymerization initiation step of initiating suspension polymerization of the monomer; A heat treatment step of treating the aqueous suspension at a temperature higher than the polymerization start time when the polymerization conversion rate is 80% by weight or more, The resin particles have an L / D of 0.85 or less, 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 where the cumulative weight corresponds to 30% by weight in the cumulative passage distribution curve of the minor axis of the resin particles based on weight, Dl is the particle size at a point where the cumulative weight corresponds to 40% by weight in the cumulative passage distribution curve of the major axis of the resin particles based on weight, Ds is the particle size at a point where the cumulative weight corresponds to 60% by weight in the cumulative passage distribution curve of the major axis of the resin particles based on weight, The cumulative passage distribution curve of the minor axis of the resin particles based on weight and the cumulative passage distribution curve of the major axis of the resin particles based on weight are each measured using a particle size measuring device with the resin particles as a sample. A method for producing resin particles.

[0010] [2] Further, at the time when the polymerization conversion rate is 40 to 60% by weight, an addition step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate to 100 parts by weight of the monomer to the aqueous suspension is included. The method for producing resin particles according to [1].

[0011] [3] The method for producing resin particles according to [1] or [2], wherein the monomer contains styrene.

[0012] [4] The amount of water used is 100 parts by weight or less with respect to 100 parts by weight of the monomer, the method for producing resin particles according to [1] or [2].

[0013] [5] The average particle diameter of the resin particles is 0.90 mm or more, the method for producing resin particles according to [1] or [2].

[0014] [6] The heat treatment step includes a step of treating the aqueous suspension at 110°C or higher, the method for producing resin particles according to [1] or [2].

[0015] [7] The amount of residual monomer in the resin particles is 500 ppm or less, the method for producing resin particles according to [1] or [2].

Advantages of the Invention

[0016] According to one aspect of the present invention, there is an effect that a method for producing resin particles capable of stably producing flattened resin particles can be provided.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims. Also, 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, by combining the technical means disclosed in each embodiment, new technical features can be formed. All academic documents and patent documents described in this specification are incorporated herein by reference. Also, unless otherwise specified in this specification, "A~B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0019] 〔1. Technical idea of one embodiment of the present invention〕 As described above, resin particles may sometimes be required to be non-spherical (for example, flat-shaped). As a technique for producing non-spherical (for example, flat-shaped) resin particles, the technique of Patent Document 1 was known.

[0020] When the inventor replicated the technique of Patent Document 1, the inventor independently found a problem that abnormal dispersion occurs and polymerization may not be able to continue in the technique of Patent Document 1.

[0021] Therefore, the inventor intensively studied for the purpose of providing a method for producing resin particles that can stably produce flattened resin particles.

[0022] As a result of intensive studies, the inventor independently found the following new findings and completed the present invention: By initiating the polymerization of a monomer in an aqueous suspension containing a specific amount of tricalcium phosphate having a specific average particle diameter and an anionic surfactant, surprisingly, flattened resin particles can be stably produced.

[0023] 〔2. Method for producing resin particles〕 The method for producing resin particles according to an embodiment of the present invention is a method for producing resin particles, including: a polymerization initiation step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, 0.01 to 0.30 parts by weight of tricalcium phosphate having an average particle diameter of 10 to 30 μm, and an anionic surfactant; and a heat treatment step of treating the aqueous suspension at a temperature higher than the polymerization initiation time when the polymerization conversion rate is 80% by weight or more. The resin particles have an L / D of 0.85 or less, 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 diameter at the point where the cumulative weight corresponds to 30% by weight in the cumulative passage distribution curve of the minor axis of the resin particles based on weight, Dl is the particle diameter at the point where the cumulative weight corresponds to 40% by weight in the cumulative passage distribution curve of the major axis of the resin particles based on weight, Ds is the particle diameter at the point where the cumulative weight corresponds to 60% by weight in the cumulative passage distribution curve of the major axis of the resin particles based on weight. The cumulative passage distribution curve of the minor axis based on weight and the cumulative passage distribution curve of the major axis based on weight are each measured using a particle size measuring device with the resin particles as a sample.

[0024] In this specification, the "method for producing resin particles according to an embodiment of the present invention" may be referred to as the "present production method".

[0025] Since the present production method has the above-described configuration, it has the advantage of being able to stably produce flattened resin particles.

[0026] The resin particles obtained by the present production method are also an embodiment of the present invention. In this specification, the "resin particles according to an embodiment of the present invention" may be referred to as the "present resin particles".

[0027] In addition to being suitably used as a raw material for an extrusion foam molded article, the present resin particles can also be suitably used as a raw material for expandable resin particles.

[0028] In this specification, the repeating unit derived from the X monomer may be referred to as the "X unit". The repeating unit can also be said to be a constituent unit.

[0029] In this specification, "usage amount" is synonymous with "addition amount".

[0030] In this specification, "stably producing flattened resin particles" is intended to mean that resin particles with an L / D of 0.85 or less can be produced without causing abnormal dispersion.

[0031] In this specification, "polymerization conversion rate" refers to the ratio (weight %) of the amount of monomer converted from monomer to polymer to the amount of monomer used in the polymerization (100% by weight). The measurement method of the polymerization conversion rate will be described in detail in the following examples.

[0032] In this specification, "minor axis of the ellipse" is one of the particle sizes of the resin particles measured using an image analysis method particle size distribution measuring device (for example, MilliTrack JPA, manufactured by Nikkiso Co., Ltd.), and is intended to be the value of the minor axis of each resin particle obtained by imaging the shadow (projection diagram) of the resin particle group falling with a camera to obtain an imaging image and analyzing the imaging image.

[0033] In this specification, "major axis of the ellipse" is one of the particle sizes of the resin particles measured using an image analysis method particle size distribution measuring device, and is intended to be the value of the major axis of each resin particle obtained by imaging the shadow (projection diagram) of the resin particle group falling with a camera to obtain an imaging image and analyzing the imaging image.

[0034] (2-1. Polymerization Initiation Step) This is a step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, 0.01 to 0.30 parts by weight of tricalcium phosphate having an average particle diameter of 10 to 30 μm, and an anionic surfactant.

[0035] (Water) In this manufacturing method, water is used. The water used in this manufacturing method is not particularly limited, and examples include tap water, industrial water, RO water (water purified by the reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin), and the like.

[0036] The amount of water used in this manufacturing method is 100 parts by weight or less, preferably 60 to 100 parts by weight, more preferably 70 to 100 parts by weight, still more preferably 80 to 100 parts by weight, and particularly preferably 90 to 100 parts by weight, based on 100 parts by weight of the monomer. When the amount of water used is 100 parts by weight or less based on 100 parts by weight of the monomer, it has the advantage of reducing production costs and environmental load. When the amount of water used is 60 parts by weight or more based on 100 parts by weight of the monomer, it has the advantage of obtaining foamed particle resin particles having a sharp particle size distribution.

[0037] (Monomer) In this manufacturing method, a monomer is used. The monomer used in this manufacturing method is not particularly limited, but preferably contains styrene and alkyl (meth)acrylate, and more preferably contains styrene. In this manufacturing method, in addition to the monomer containing styrene and / or alkyl (meth)acrylate, a monomer containing a monomer copolymerizable with styrene and / or alkyl (meth)acrylate (hereinafter, also referred to as "other monomer") other than styrene and / or alkyl (meth)acrylate may be further used.

[0038] The amount of styrene used in this manufacturing method is preferably 70 parts by weight or more, more preferably 80 parts by weight or more, still more preferably 85 parts by weight or more, still more preferably 90 parts by weight or more, further preferably 92 parts by weight or more, and particularly preferably 95 parts by weight or more, in 100 parts by weight of the monomer. The monomer may contain 100 parts by weight of styrene in 100 parts by weight of the monomer. In other words, the monomer may be composed of only styrene.

[0039] The alkyl (meth)acrylate is not particularly limited, and 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.

[0040] In the present production method, the amount of the alkyl (meth)acrylate used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, still more preferably 10 parts by weight or less, further preferably 8 parts by weight or less, and particularly preferably 5 parts by weight or less, based on 100 parts by weight of the monomer. The amount of the alkyl (meth)acrylate used in the monomer may be 0 parts by weight. In other words, in the present production method, it is not necessary to use the alkyl (meth)acrylate. When the amount of the alkyl (meth)acrylate used is 20 parts by weight or less based on 100 parts by weight of the monomer, it has the advantage of preventing or reducing the coalescence of the resulting resin particles.

[0041] The other monomers are not particularly limited, and 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, a mode in which the monomer consists of styrene and acrylonitrile, and a mode in which the monomer consists of styrene, acrylonitrile, and α-methylstyrene are also preferred modes.

[0042] The above-mentioned styrene-based monomer, alkyl (meth)acrylate, and other monomers may each be used alone or in combination of two or more.

[0043] (Tricalcium phosphate) In this manufacturing method, tricalcium phosphate is used. In this manufacturing method, tricalcium phosphate may have a function of dispersing monomer droplets and resin particles in an aqueous suspension. That is, tricalcium phosphate can function as a dispersant.

[0044] The tricalcium phosphate in one embodiment of the present invention is preferably hydroxyapatite having a structural formula of 3[Ca 3 (PO 4 ) 2 ·Ca(OH) 2 with the CAS number 1306-06-05.

[0045] The form of tricalcium phosphate is not particularly limited, and examples thereof include powder, slurry (for example, aqueous slurry), and the like.

[0046] The average particle diameter of the tricalcium phosphate used in the polymerization initiation step is 10 μm to 30 μm. The method for measuring the average particle diameter of tricalcium phosphate will be described in detail in the later examples. The average particle diameter 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 diameter of tricalcium phosphate is 10 μm to 30 μm, the resulting resin particles are likely to be flattened, the average particle diameter becomes larger, and the polymerization reaction is stable.

[0047] The amount of tricalcium phosphate used in the polymerization initiation step is 0.01 part by weight to 0.30 part by weight, preferably 0.05 part by weight to 0.28 part by weight, more preferably 0.10 part by weight to 0.26 part by weight, even more preferably 0.12 part by weight to 0.24 part by weight, still more preferably 0.13 part by weight to 0.23 part by weight, and particularly preferably 0.15 part by weight to 0.22 part by weight, based on 100 parts by weight of the monomer, from the viewpoint of preventing or reducing the adhesion of resin particles to each other.

[0048] (Anionic surfactant) In this manufacturing method, an anionic surfactant is used. In other words, the aqueous suspension 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.

[0049] The anionic surfactant used in this manufacturing method is not particularly limited. For example, sodium alkyl diphenyl ether sulfonate, sodium α-olefin sulfonate, sodium dodecylbenzene sulfonate, etc. can be mentioned. These anionic surfactants may be used alone or in combination of two or more. When using a combination of two or more anionic surfactants, the mixing ratio may be appropriately adjusted according to the purpose.

[0050] 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, still more preferably 0.003 to 0.008 parts by weight, and particularly preferably 0.004 to 0.008 parts by weight, based on 100 parts by weight of the monomer, from the viewpoints of the dispersion stability of the monomer droplets and resin particles in the aqueous suspension and prevention or reduction of adhesion between the resin particles.

[0051] (Polymerization initiator) In this manufacturing 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 preferably further contains a polymerization initiator in addition to the monomer, tricalcium phosphate, and the anionic surfactant, and more preferably contains a polymerization initiator that is soluble in the monomer.

[0052] 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-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 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-butyl peroxy-2-ethylhexyl monocarbonate, t-amyl peroxy-2-ethylhexyl monocarbonate, and the like. All of these polymerization initiators are soluble in the monomer. These polymerization initiators may be used alone or in combination of two or more.

[0053] In this production method, it is preferable to use a combination of a polymerization initiator A having a 10-hour half-life temperature of 74 °C or higher and less than 90 °C and a polymerization initiator B having a 10-hour half-life temperature of 90 °C or higher and less than 110 °C. According to this configuration, there is an advantage that the amount of unreacted monomer remaining in the resin particles can be reduced. Benzoyl peroxide is preferably mentioned as the polymerization initiator A. 1,1-Di(t-butylperoxy)cyclohexane is preferably mentioned as the polymerization initiator B.

[0054] The amount of the polymerization initiator used in this production method is appropriately set according to the molecular weight of the target resin particles and is not particularly limited. The amount of the polymerization initiator used is preferably 0.100 to 1.000 parts by weight, more preferably 0.200 to 0.800 parts by weight, still more preferably 0.300 to 0.600 parts by weight, and particularly preferably 0.350 to 0.500 parts by weight, based on 100 parts by weight of the monomer. When the amount of the polymerization initiator used is 0.100 parts by weight or more, the polymerization proceeds sufficiently, and when it is 1.000 parts by weight or less, there is an advantage that the polymerization reaction is easily controlled. When the polymerization initiator A and the polymerization initiator B are used in combination, the "amount of the polymerization initiator used" means the total amount of the polymerization initiator A and B.

[0055] (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, tricalcium phosphate, and the anionic surfactant. Using a thickener has the advantage that the viscosity of the aqueous suspension can be easily adjusted (optimized).

[0056] The thickener is not particularly limited, but is preferably a water-soluble polysaccharide. For example, ramzanjam, glyoxal, curdlan, xanthan gum, welan gum, xanthan gum, etc. are preferably mentioned. 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 according to the purpose.

[0057] The amount of the thickener used is preferably from 0.00005 parts by weight to 0.00200 parts by weight, more preferably from 0.00010 parts by weight to 0.00150 parts by weight, still more preferably from 0.00015 parts by weight to 0.00100 parts by weight, particularly preferably from 0.00015 parts by weight to 0.00080 parts by weight, and most preferably from 0.00020 parts by weight to 0.00050 parts by weight, based on 100 parts by weight of the monomer. When the amount of the thickener used is in the range of 0.00005 parts by weight to 0.00200 parts by weight based on 100 parts by weight of the monomer, there is an advantage that the droplets of the monomer during the polymerization reaction can be uniformly coalesced and dispersed.

[0058] (Water-soluble inorganic salt) In this 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, tricalcium phosphate, and the anionic surfactant.

[0059] The water-soluble inorganic salt is not particularly limited, and examples thereof include sodium chloride, potassium chloride, sodium sulfate, sodium bisulfite, potassium bisulfite, potassium persulfate, ammonium bisulfite, and the like. Further, a substance that dissolves in water and / or reacts in the polymerization reaction system to form a sulfite, that is, a precursor substance, can also be used as the water-soluble inorganic salt.

[0060] The amount of the water-soluble inorganic salt used is not particularly limited, and for example, it is preferably 1.0 part by weight or less, more preferably 0.5 part by weight or less, based on 100 parts by weight of the monomer.

[0061] (Other additives) In this production method, if necessary, a flame retardant, a flame retardant aid, a plasticizer, a bubble regulator (sometimes referred to as a nucleating agent), etc. (these may be collectively referred to as "other additives") may be used. In other words, the aqueous suspension may contain the above-mentioned other additives.

[0062] By using a flame retardant, flame retardancy can be imparted to resin particles, an extruded foam, expanded particles, and a foam molded article obtained using the resin particles. In this production method, only a flame retardant may be used, or a combination of a flame retardant and a flame retardant aid may be used.

[0063] The flame retardant is not particularly limited. For example, (a) low molecular compounds such as polyglycerol dibromopropyl ether, tetrabromobisphenol A, tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl ether), 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 novolak resin allyl ether, brominated poly(1,3-cycloalkadiene), and brominated poly(4-vinylphenol allyl ether) can be mentioned. These flame retardants may be used alone or in combination of two or more.

[0064] The flame retardant aid is not particularly limited. For example, thermally decomposable organic substances such as cumene peroxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane can be mentioned. These flame retardant aids may be used alone or in combination of two or more.

[0065] The plasticizer is not particularly limited. For example, (a) fatty acid glycerides such as tristearin, tripalmitin, trilaurin, distearin, and monostearin, (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) cycloaliphatics such as cyclohexane and cyclopentane can be mentioned. These plasticizers may be used alone or in combination of two or more.

[0066] Examples of the bubble regulator include, for example, (a) aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide, (b) polyethylene wax, and (c) acrylic resins (manufactured by Kaneka Corporation: Kane Ace PA-20). These bubble regulators may be used alone or in combination of two or more.

[0067] (Container) The container used in this production method is not particularly limited, but it is preferably a container that can be sealed and has pressure resistance and heat resistance. In this production method, in the aqueous suspension, the 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 is equipped with a stirrer. Examples of the container preferably include an autoclave equipped with a stirrer.

[0068] The temperature of the polymerization initiation step is not particularly limited. The temperature of 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 less than 100°C, more preferably 92°C or higher and less than 100°C, even more preferably 94°C or higher and less than 100°C, and particularly preferably 96°C or higher and less than 100°C. According to this configuration, since the polymerization initiator A can efficiently promote the polymerization reaction, it has the advantage of shortening the polymerization time.

[0069] (Addition step) This production method preferably further includes an addition step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate to 100 parts by weight of the monomer to the aqueous suspension at least once when the polymerization conversion rate is 40 to 60% by weight after the polymerization initiation step. By including the addition step, flattened resin particles can be stably produced. The addition step is also a step of continuing the polymerization of the monomer following the polymerization initiation step to obtain resin particles.

[0070] In the addition step, the amount of tricalcium phosphate used is preferably 0.01 to 0.30 parts by weight, more preferably 0.02 to 0.20 parts by weight, still more preferably 0.04 to 0.15 parts by weight, and particularly preferably 0.05 to 0.10 parts by weight, based on 100 parts by weight of the monomer. When the amount of tricalcium phosphate used is within the above-described range, resin particles can be stably produced. Specifically, when the amount of tricalcium phosphate used is (a) 0.01 parts by weight or more based on 100 parts by weight of the monomer, there is an advantage that the amount of resin particles that are flat and have a large particle diameter is reduced, and when (b) it is 0.30 parts by weight or less, there is an advantage that the amount of resin particles having a small (fine) particle diameter is reduced.

[0071] When the addition step is carried out, 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, still 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 (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, may be 0.40 or less, may be 0.35 or less, or may be 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 is, for example, greater than 0 and may be 0.20 or more.

[0072] The total amount of tricalcium phosphate used in this manufacturing method is not particularly limited. However, from the perspective of the stability during the 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, still more preferably 0.07 to 0.40 parts by weight, and particularly preferably 0.10 to 0.30 parts by weight, based on 100 parts by weight of the monomer. Here, the "total amount of tricalcium phosphate used in this manufacturing method" is intended to be the total amount of the tricalcium phosphate used in the polymerization initiation step and the tricalcium phosphate used in the addition step. In addition, when tricalcium phosphate is further used in other steps, the total amount including their usage amounts is defined as the "total amount of tricalcium phosphate used in this manufacturing method".

[0073] The addition of tricalcium phosphate in the addition step is carried out one or more times within the range where the polymerization conversion rate is 40% to 60% by weight, preferably within the range of 42% to 58% by weight, and particularly preferably within the range of 45% to 55% by weight. When the addition of tricalcium phosphate in the addition step is carried out within the above-mentioned range of the polymerization conversion rate, there is an advantage that the dispersibility of the monomer droplets in the aqueous suspension becomes stable (good), and resin particles with a stably flattened shape can be obtained. Although the reason for this is not clear, in the early stage of polymerization, although the occupied volume of the monomer is larger than the occupied volume of water, the point when the polymerization conversion rate reaches 40% to 60% by weight is the point when the occupied volumes of the monomer and water become almost equal. It is presumed that it is important to further add tricalcium phosphate at this point. It should be noted that one embodiment of the present invention is not limited by such presumption at all.

[0074] The average particle diameter of the tricalcium phosphate used in the addition process is not particularly limited and may be the same as or different from the average particle diameter of the tricalcium phosphate used in the polymerization initiation step. The average particle diameter of the tricalcium phosphate is preferably 10 μm to 30 μm, more preferably 12 μm to 28 μm, still 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 diameter of the tricalcium phosphate is 10 μm to 30 μm, the resulting resin particles tend to be flattened, the average particle diameter becomes larger, and the polymerization reaction is stabilized.

[0075] (2-2. Heat treatment step) This production method includes a heat treatment step. The heat treatment step is a step of treating the aqueous suspension at a temperature higher than the polymerization initiation time point.

[0076] The heat treatment step is 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 is, for example, less than 100% by weight, may be less than 95% by weight, or may be less than 90% by weight.

[0077] The temperature of the heat treatment step only needs to be higher than the polymerization initiation time point, that is, it is not particularly limited as long as it exceeds the temperature of the aqueous suspension at the time when the above-described polymerization initiation step is carried out. The temperature of the heat treatment step is sometimes referred to as the "heat treatment temperature". As the heat treatment temperature, 110°C or higher is preferable, 112°C or higher is more preferable, 114°C or higher is still more preferable, and 116°C or higher is particularly preferable. The higher the heat treatment temperature, the more advantageous it is to reduce the residual monomer in the resin particles.

[0078] The implementation time of the heat treatment step, that is, the time for treating the aqueous suspension at the heat treatment temperature (which may also be referred to as the "heat treatment time") is not particularly limited. As the heat treatment time, 1 hour or more is preferable, 2 hours or more is more preferable, 3 hours or more is further preferable, and 3.5 hours or more is particularly preferable. The longer the heat treatment time, the more advantages there are in reducing the residual monomers in the resin particles.

[0079] The amount of residual monomers in the resin particles is preferably 500 ppm or less, more preferably 400 ppm or less, and further preferably 300 ppm or less. The lower limit of the amount of residual monomers in the resin particles is, in practical terms, difficult to reach 0 ppm, and if it is explicitly stated, it is 1 ppm or more.

[0080] (2-3. Other steps) By carrying out the polymerization initiation step and the heat treatment step described above, and optionally the addition step, resin particles can be obtained in the aqueous suspension.

[0081] Thereafter, for example, (1) the aqueous suspension containing the resin particles is cooled to room temperature (for example, 25°C), (2) the resin particles are taken out from the aqueous suspension, (3) the obtained resin particles are pickled with hydrochloric acid and washed with water, (4) the washed resin particles are dehydrated with a centrifuge, and (5) the dehydrated resin particles are dried with, for example, an air flow dryer, whereby dried resin particles can be obtained.

[0082] (2-3. Characteristics) The L / D of the present resin particles is 0.85 or less. The fact that the L / D of the resin particles is 0.85 or less is intended to mean that the resin particles are flat. Therefore, the present resin particles can also be referred to as "flat resin particles" or "flattened resin particles". The L / D of the present 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 present resin particles is not particularly limited, but for example, it may be greater than 0 and 0.30 or more, or 0.40 or more. When resin particles with an L / D within the above range are used as a raw material for an extruded foam, there is an advantage that the resin particles are more likely to bite into the screw of the extruder. When resin particles with an L / D within the above range are used as a raw material for expandable resin particles, there is an advantage that a foamed molded body formed by further molding the foamed particles obtained by foaming the expandable resin particles has higher sound absorption.

[0083] The resin particles according to one embodiment of the present invention are shown in FIGS. 1 and 2. FIG. 1 is a view of the resin particles according to one embodiment of the present invention seen from one direction. FIG. 2 is a cross-sectional view of the resin particles of FIG. 1 taken along the line A-A'. The resin particles shown in FIGS. 1 and 2 have an L / D of 0.85 or less, that is, they are flat resin particles. The resin particles shown in FIGS. 1 and 2, that is, the flat resin particles, can be said to have a shape like a go stone, for example. FIG. 1 can also be said to be a view of the resin particles seen from the horizontal direction when the resin particles are placed on a horizontal table. The "minor axis of the ellipse" can also be said to be the vertical length of the resin particles when the resin particles are placed on a horizontal table. The "major axis of the ellipse" can also be said to be the horizontal length of the resin particles when the resin particles are placed on a horizontal table.

[0084] The average particle diameter of the present 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 diameter of the resin particles will be described in detail in the following examples.

[0085] (2-4. Extruded Foam) These resin particles can be used as a raw material for an extruded foam. When these resin particles are used as a raw material for an extruded foam, the resin particles can be directly fed into an extruder, and since the resin particles easily bite into the screw of the extruder, for example, even when a single-screw extruder is used, there is an advantage that an extruded foam can be stably produced.

[0086] An extruded foam can be produced, for example, by melt-kneading resin particles and a foaming agent. In the melt-kneading of resin particles and a foaming agent, as a melt-kneading section, for example, a production apparatus equipped with a conventionally known extruder can be used. As the extruder, for example, a single-screw extruder or a twin-screw extruder can be employed.

[0087] (Foaming agent) The foaming agent is not particularly limited. Examples of the foaming 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 foaming agents may be used alone or in combination of two or more. When two or more foaming agents are used in combination, the mixing ratio may be appropriately adjusted according to the purpose. As the foaming agent in the production of an extruded foam, butane, pentane, and dichlorotetrafluoroethane are preferred.

[0088] (2-5. Foamable resin particles) These resin particles can be used as a raw material for foamable resin particles. When these resin particles are used as a raw material for foamable resin particles, foamable resin particles having a flattened shape can be obtained, and by foaming the foamable resin particles, foam particles (pre-expanded particles) having a flattened shape can be obtained. When foam particles having a flattened shape are molded (for example, in-mold foaming molding), a foam molded body with a high porosity can be obtained. Since a foam molded body with a high porosity has high sound absorption performance, it has an advantage that it can be suitably used as a sound insulation material.

[0089] The expandable resin particles can be obtained, for example, by impregnating resin particles with a foaming agent. The impregnation of the foaming agent into the resin particles can also be carried out during the above-described production method. For example, after the above-described addition step, an impregnation step of impregnating the resin particles with a foaming agent may be carried out. By passing through the impregnation step, expandable resin particles can be obtained.

[0090] The impregnation step is preferably carried out when the polymerization conversion rate is 85% by weight or more. According to this configuration, the foaming agent added does not promote the softening of the resin particles too much, the dispersibility of the monomer droplets and the resin particles in the aqueous suspension is stabilized, and the agglomeration of the resin particles can be eliminated or reduced. The impregnation step is more preferably carried out when the polymerization conversion rate is 90% by weight or more, even more preferably carried out when the polymerization conversion rate is 92% by weight or more, and particularly preferably carried out when the polymerization conversion rate is 95% by weight or more.

[0091] The foaming agent that can be used in the production of the expandable resin particles is not particularly limited, and the above-described foaming agents can be appropriately used. In the production of the expandable resin particles, from the viewpoints of volatility and foaming power, it is preferable to contain any one selected from the group consisting of normal pentane, isopentane, neopentane, and cyclopentane as the foaming agent. Further, since the cells are likely to be stabilized in the foaming of the resin particles, the foaming agent preferably contains any one selected from the group consisting of pentanes (such as normal pentane, isopentane, neopentane, and cyclopentane).

[0092] 〔3. Use〕 One embodiment of the present invention can be suitably used in the fields where the foamed molded article is used. In the field of extrusion foams (for example, extrusion foam boards), it can be suitably used, for example, as a heat insulating material for buildings (core materials for tatami mats, panels, walls, etc.). Further, when obtaining expandable resin particles, foamed particles, and a foamed molded article in this order, the obtained foamed molded article has high sound absorption characteristics and can be suitably used in the fields such as sound insulating materials.

Examples

[0093] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the technical scope of the present invention is not limited by these examples.

[0094] 〔Materials〕 The substances used in the examples and comparative examples are shown below. (Water) · Water: Ion-exchanged water (Monomer) · ST: Styrene (manufactured by NS Styrene Monomer Co., Ltd.) (Tricalcium Phosphate: CAS No. 1306-06-05) · CaP1: TCP with an average particle size of 20 μm (powder, manufactured by Taihei Chemical Co., Ltd.) · CaP3: TCP2 with an average particle size of 16 μm (powder, manufactured by Taihei Chemical Co., Ltd.) · CaP3: TCP-10U with an average particle size of 5 μm (slurry 10 wt%, manufactured by Taihei Chemical Co., Ltd.) · CaP4: Instant-S with an average particle size of 1.5 μm (slurry 30 wt%, manufactured by Budenheim Co., Ltd.) (Anionic surfactant) · Sodium alkyl diphenyl ether sulfonate (manufactured by Kao Corporation) (Thickener) · KLZ: A mixture of xanthan gum and glyoxal (Kelzan S (manufactured by CP Kelco)) (Water-soluble inorganic salt) · Sodium chloride: manufactured by Nippon Suisan Kaisha, Ltd. · Potassium persulfate (Polymerization initiator) · Polymerization initiator A: Benzoyl peroxide (10-hour half-life temperature 74 °C, Nipper BW (manufactured by NOF Corporation)) · Polymerization initiator B: 1,1-Di(t-butylperoxy)cyclohexane (10-hour half-life temperature 91 °C, Perhexa C (manufactured by NOF Corporation)) 〔Measurement method〕 The measurement methods carried out in the examples and comparative examples will be described below.

[0095] (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 passing distribution curve based on the number was obtained. From the obtained cumulative passing distribution curve, the particle size (μm) at the point corresponding to 50% in terms of the cumulative number percentage was determined and taken as the average particle size.

[0096] (Measurement of the polymerization conversion rate) During the suspension polymerization (when adding tricalcium phosphate), at the start of the heat treatment, and at the end of the heat treatment, resin particles were collected from the pressure-resistant container, and the moisture on the surface of the resin particles was wiped off using filter paper. 1.0 g of the resin particles was dissolved in 20 ml of dichloromethane, and 0.005 g of an internal standard solution (cyclopentanol) was added to the dissolved solution. Subsequently, the dissolved solution was subjected to gas chromatography (GC-14B, manufactured by Shimadzu Corporation), and the polymerization conversion rate was measured under the following conditions. The polymerization conversion rate was calculated from the amount of the remaining monomer component.

[0097] Column: PEG-20M 25% Chromosorb W 60 / 80 (3.0 m × 3.0 mm I.D.) Column temperature: 110 °C Detector (FID temperature: 170 °C).

[0098] (Measurement of the average particle size, L, Dl, Ds, and L / D of the resin particles) Using 100 g of the resin particles as a sample, a cumulative passing distribution curve based on the weight of the minor axis and the major axis of the ellipse was obtained using an image analysis type particle distribution measuring device (Millitrack JPA, manufactured by Nikkiso Co., Ltd.). From the obtained cumulative passing distribution curve, (i) in the cumulative passing distribution curve of the minor axis of the resin particles based on weight, the particle size at the point where the cumulative weight corresponds to 50% by weight was defined as the average particle size (mm); (ii) in the cumulative passing distribution curve of the minor axis of the resin particles based on weight, the particle size at the point where the cumulative weight corresponds to 30% by weight was defined as L (mm); (iii) in the cumulative passing distribution curve of the major axis of the resin particles based on weight, the particle size at the point where the cumulative weight corresponds to 40% by weight was defined as Dl (mm); (iv) in the cumulative passing distribution curve of the major axis of the resin particles based on weight, the particle size at the point where the cumulative weight corresponds to 60% by weight was defined as Ds (mm).

[0099] Furthermore, L / D was calculated based on the following formula: L / D = L / ((Dl + Ds) / 2).

[0100] (Particle weight) The particle weight was calculated based on the following formula: (Particle weight (mg)) = 4 / 3 × π × (L / 2) × (Dl / 2) × (Ds / 2).

[0101] (Residual monomer) From the polymerization conversion rate at the end of the heat treatment, the unreacted amount was defined as the residual monomer. The measurement of the residual monomer was carried out in the same manner as described above (measurement of the polymerization conversion rate).

[0102] [Example 1] (i) Polymerization initiation step 0.19 parts by weight of polymerization initiator A, 0.20 parts by weight of polymerization initiator B, and 100 parts by weight of styrene were mixed to obtain a monomer mixture containing polymerization initiators A and B. 100 parts by weight of water, 0.12 parts by weight of tricalcium phosphate (CaP2: 16 μm), 0.007 parts by weight of 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 were charged into a 6L autoclave equipped with a stirrer (manufactured by Taiatsu Glass Co., Ltd.), and the charged raw materials were stirred with a stirrer. Next, the monomer mixture was charged into the autoclave to prepare an aqueous suspension. Next, the inside of the autoclave was deoxidized by a vacuum pump until the gauge pressure in the autoclave became -0.06 MPa. Next, the aqueous suspension was heated to 94°C, and suspension polymerization of the monomers in the aqueous suspension was started.

[0103] (ii) Addition process At the 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 pressed into the autoclave with nitrogen, and the polymerization of the monomers was further continued.

[0104] (iii) Heat treatment process 4.5 hours after the start of polymerization (polymerization conversion rate 85% by weight), the temperature of the aqueous suspension was raised to 118°C, and the temperature of the aqueous suspension was maintained at 118°C for 4 hours to carry out a heat treatment step.

[0105] The aqueous suspension containing the resin particles was then cooled to room temperature (25°C) and taken out. The obtained 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 using an airflow dryer (manufactured by Hiraiwa Iron Works) to obtain resin particles. The L, Dl, Ds, ellipse minor axis diameter (D50), particle weight, and residual monomer amount of the obtained resin particles were measured using the methods described above. The results are shown in Table 1.

[0106] [Examples 2 to 10, Comparative Examples 2 to 6] The resin particles were obtained by the same operations as in Example 1, except that the type and amount of tricalcium phosphate used in the polymerization initiation step, the type and amount of tricalcium phosphate added in the addition step, the polymerization conversion rate (elapsed time from the start of polymerization) at the time of the addition step, and the polymerization conversion rate at the start of the heat treatment step were changed as described in Table 1 or 2. For the obtained resin particles, the L, Dl, Ds, minor axis particle size (D50), particle weight, and residual monomer amount of the resin particles were measured by the method described above. The results are shown in Table 1 or 2.

[0107] [Comparative Example 1] An attempt was made to obtain resin particles by the same operations as in Example 1, except that the amount of tricalcium phosphate used in the polymerization initiation step was changed as described in Table 2 and the heat treatment step was not carried out. However, since abnormal dispersion occurred at the 3rd hour from the start of polymerization, subsequent operations could not be carried out. That is, resin particles could not be obtained.

[0108] [Comparative Example 7] An attempt was made to obtain resin particles by the same operations as in Example 1, except that an anionic surfactant and a thickener were not added in the polymerization initiation step and 0.0005 parts by weight of potassium persulfate was used instead of sodium chloride as the water-soluble inorganic salt. However, since abnormal dispersion occurred at the 2.7th hour from the start of polymerization, subsequent operations could not be carried out. That is, resin particles could not be obtained.

[0109] [Comparative Example 8] An attempt was made to obtain resin particles by the same operations as in Example 1, except that an anionic surfactant and a thickener were not added in the polymerization initiation step, 0.0005 parts by weight of potassium persulfate was used instead of sodium chloride as the water-soluble inorganic salt, and tricalcium phosphate was changed to calcium carbonate in the addition step. However, since abnormal dispersion occurred at the 2.7th hour from the start of polymerization, subsequent operations could not be carried out. That is, resin particles could not be obtained.

[0110] Further, 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 bit into the screw of the extruder and that an extruded foam could be stably produced using a single-screw extruder.

[0111]

Table 1

[0112]

Table 2

Industrial Applicability

[0113] According to one embodiment of the present invention, it is possible to provide a method for producing resin particles capable of stably producing flattened resin particles. Therefore, one embodiment of the present invention can be suitably used in fields such as packaging materials (trays) for food containers, transport packaging materials such as fish boxes, heat insulating materials (for example, hot water storage tanks, roof heat insulating materials, pipe heat insulating materials, constant temperature storage containers, constant temperature transport containers, etc.), and sound insulating materials.

Claims

1. A method for producing resin particles, comprising: a polymerization initiation step of initiating suspension polymerization of the monomer in an aqueous suspension containing water, 100 parts by weight of the monomer, 0.01 to 0.30 parts by weight of tricalcium phosphate having an average particle diameter of 10 to 30 μm, and an anionic surfactant; a heat treatment step of treating the aqueous suspension at a temperature higher than the polymerization initiation time when the polymerization conversion rate is 80% by weight or more; wherein the resin particles have an L / D of 0.85 or less; wherein 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 the point where the cumulative weight corresponds to 30% by weight in the cumulative passage distribution curve of the minor axis of the elliptical resin particles based on weight; Dl is the particle diameter at the point where the cumulative weight corresponds to 40% by weight in the cumulative passage distribution curve of the major axis of the elliptical resin particles based on weight; Ds is the particle diameter at the point where the cumulative weight corresponds to 60% by weight in the cumulative passage distribution curve of the major axis of the elliptical resin particles based on weight; The cumulative passage distribution curve of the minor axis of the ellipse based on weight and the cumulative passage distribution curve of the major axis of the ellipse based on weight are each measured using a particle size measuring device with the resin particles as a sample, a method for producing resin particles.

2. Furthermore, an addition step of adding 0.01 to 0.30 parts by weight of tricalcium phosphate to 100 parts by weight of the monomer to the aqueous suspension when the polymerization conversion rate is 40 to 60% by weight, the method for producing resin particles according to claim 1.

3. The monomer contains styrene, the method for producing resin particles according to claim 1 or 2.

4. The amount of water used is 100 parts by weight or less with respect to 100 parts by weight of the monomer, the method for producing resin particles according to claim 1 or 2.

5. The average particle diameter of the resin particles is 0.90 mm or more, the method for producing resin particles according to claim 1 or 2.

6. The heat treatment step includes a step of treating the aqueous suspension at 110°C or higher, the method for producing resin particles according to claim 1 or 2.

7. The amount of residual monomer in the resin particles is 500 ppm or less, the method for producing resin particles according to claim 1 or 2.

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