JP2024007832A - Method for producing foamable styrenic resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing foamable styrenic resin particles which can provide a styrenic foam molding that is excellent in dimensional stability at 95°C, and can provide styrenic foam particles that are made spherical.

SOLUTION: A method for producing foamable styrenic resin particles includes: a styrenic resin particle preparation step using a styrene-(meth)acrylic acid copolymer, in which shear stress in die passage is 30-90 kPa, and L1/D1 of resin particles is 1.30 to 2.90; and a foaming agent impregnation step.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing expandable styrenic resin particles.

Styrenic foam moldings, which are lightweight and easy to assemble, are sometimes used as heat insulators for hot water storage tanks, roof heat insulators, piping heat insulators, and the like. These applications require dimensional stability when used for long periods of time in high-temperature environments, so styrenic foam molded products with increased heat resistance through copolymerization or the like are used.

For example, in Patent Document 1, regarding expandable polystyrene resin particles made of a polystyrene resin composition containing a carbon-based radiation heat transfer inhibitor and a blowing agent, the aspect ratio of the expandable polystyrene resin particles is 0.95 or less, and discloses expandable polystyrene resin particles that have a sphericity of 0.970 or more and can provide a polystyrene resin foam molded product that has both a high expansion ratio and high heat insulation properties.

JP2020-33481A

However, in the conventional technology as described above, there is room for further improvement from the viewpoints of heat resistance and sphericity.

One embodiment of the present invention has been made in view of the above-mentioned problems, and its purpose is to provide a styrenic foamed particle that can provide a styrenic foamed molded product having excellent dimensional stability at 95°C, which has a spherical shape. An object of the present invention is to provide a new method for producing expandable styrenic resin particles that can provide expanded styrenic particles.

The present inventor has completed the present invention as a result of intensive studies to solve the above problems. That is, one embodiment of the present invention includes the following configuration.
[1] The styrenic resin particle preparation step includes a styrenic resin particle preparation step and a blowing agent impregnation step, and the styrenic resin particle preparation step includes a styrenic resin composition containing a styrene resin including a styrene/(meth)acrylic acid copolymer. a melt-kneading step of melt-kneading the product in an extruder; an extrusion step of extruding the melt-kneaded product obtained in the melt-kneading step from a discharge hole of a die provided at the tip of the extruder in the extrusion direction; a step of pulling and cutting the melt-kneaded material extruded from the discharge hole in the extrusion step to obtain styrene resin particles, and the blowing agent impregnation step includes adding the styrenic resin particles to the styrenic resin particles in an aqueous suspension. and a step of impregnating a hydrocarbon foaming agent, and in the extrusion step, the shear stress of the melt-kneaded material when passing through the die is 30 kPa to 90 kPa, and the shear stress in the tensile direction of the styrene resin particles is A method for producing expandable styrenic resin particles, wherein the ratio (L1/D1) of length (L1) to cross-sectional length (D1) is 1.30 to 2.90.
[2] The foaming property according to [1], wherein the styrenic resin composition contains graphite, and the content of the graphite is 1 part by weight to 10 parts by weight with respect to 100 parts by weight of the styrene resin. A method for producing styrenic resin particles.
[3] The styrenic resin composition contains a flame retardant, and the content of the flame retardant is 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the styrene resin. ] or the method for producing expandable styrenic resin particles according to [2].
[4] The method for producing expandable styrenic resin particles according to [3], wherein the flame retardant contains a bromine-containing organic compound having a 2,3-dibromo-2-alkylpropyl group.
[5] The hydrocarbon blowing agent according to any one of [1] to [4], wherein the hydrocarbon blowing agent contains any one selected from the group consisting of normal pentane, isopentane, neopentane, and cyclopentane. A method for producing expandable styrenic resin particles.
[6] The ratio (L2/D2) of the length of the major axis (L2) to the length (D2) of the minor axis in the expandable styrenic resin particles is 1.00 to 1.20, [1 ] to [5]. The method for producing expandable styrenic resin particles according to any one of [5].
[7] The method for producing expandable styrenic resin particles according to [2], wherein the graphite has a volume average particle diameter of 1 μm to 5 μm.
[8] The method for producing expandable styrenic resin particles according to any one of [1] to [7], wherein the styrenic resin particles have a weight average molecular weight Mw of 150,000 to 300,000.

According to one aspect of the present invention, the expandable styrenic resin is a styrenic foamed particle capable of providing a styrenic foamed molded article having excellent dimensional stability at 95° C., which is capable of providing spherical styrenic expanded particles. A method of manufacturing particles can be provided.

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 each configuration described below, and various changes can be made within the scope of the claims. Further, embodiments or examples obtained by appropriately combining 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. Note that all academic literature and patent literature described in this specification are incorporated as references in this specification. Furthermore, unless otherwise specified in this specification, the numerical range "A to B" is intended to be "above A (including A and greater than A) and less than or equal to B (including B and less than B)."

[1. Technical idea of one embodiment of the present invention]
The present inventors have independently found that in conventional methods for producing expandable styrenic resin particles, the resulting expandable styrenic resin particles tend to be flat (hardly spherical). When the expandable styrenic resin particles are flat, the expanded styrenic particles obtained by foaming the expandable styrenic resin particles may also be flat. Flat styrene-based foamed particles are difficult to fill into a complex-shaped mold, and the resulting styrene-based foamed molded product has a poor appearance. That is, a styrenic foam molded article obtained from flat styrene foam particles has poor moldability.

Furthermore, as described above, styrene foam molded articles are sometimes required to have dimensional stability at high temperatures (for example, 95° C.).

Therefore, the present inventors have developed expandable styrenic resin particles that can provide a styrenic foam molded article with excellent dimensional stability at 95° C. and that can provide spherical styrenic expanded particles. We conducted extensive research with the aim of providing a new manufacturing method. As a result, in the production of expandable styrenic resin particles, the present inventors have found that (a) the shear stress when the melt-kneaded product of the styrenic resin composition passes through the die is within a specific range, and (b) ) Surprisingly, by setting the ratio (L1/D1) of the length in the tensile direction (L1) to the cross-sectional length (D1) of the styrenic resin particles before impregnation with the blowing agent within a specific range. , have independently discovered that the above-mentioned problems can be achieved, and have completed the present invention.

[2. Method for manufacturing expandable styrenic resin particles]
A method for producing expandable styrenic resin particles according to an embodiment of the present invention includes a styrenic resin particle preparation step and a blowing agent impregnation step, and the styrenic resin particle preparation step includes styrene/(meth) A melt-kneading step of melt-kneading a styrene-based resin composition containing a styrene-based resin containing an acrylic acid copolymer in an extruder, and a melt-kneaded product obtained in the melt-kneading step at the tip of the extruder in the extrusion direction. and a step of pulling and cutting the melt-kneaded material extruded from the discharge hole in the extrusion step to obtain styrene-based resin particles. The impregnation step includes a step of impregnating the styrenic resin particles with a hydrocarbon blowing agent in an aqueous suspension, and in the extrusion step, the shear stress of the melt-kneaded material when passing through the die is , 30 kPa to 90 kPa, and the ratio (L1/D1) of the length (L1) in the tensile direction of the styrene resin particles to the cross-sectional length (D1) is 1.30 to 2.90.

In this specification, "styrenic resin composition" may be referred to as "composition", "styrenic resin particles" may be referred to as "resin particles", and "expandable styrenic resin particles" may be referred to as "composition". "expandable resin particles", "styrenic foam particles" may be referred to as "expanded particles", and "styrenic foam molded articles" may be referred to as "foamed molded articles". Moreover, in this specification, "the manufacturing method of expandable styrenic resin particles according to one embodiment of the present invention" may be referred to as "the present manufacturing method".

Since this manufacturing method has the above-mentioned configuration, the present manufacturing method is capable of providing styrenic foamed particles having excellent dimensional stability at 95° C., and is capable of providing spherical styrenic foamed particles. Styrenic resin particles can be provided. The expandable styrenic resin particles obtained by this production method are also an embodiment of the present invention. In this specification, "expandable styrenic resin particles according to an embodiment of the present invention" may be referred to as "expandable resin particles."

In this specification, a repeating unit derived from the X monomer may be referred to as an "X unit". A repeating unit can also be said to be a constituent unit.

In this specification, "dimensional stability at 95° C." can also be referred to as "heat resistance." The method for evaluating dimensional stability at 95°C will be explained in detail in Examples below.

In this specification, "spheroidal styrenic foamed particles" means that the ratio (L3/D3) of the length of the long axis (L3) to the length of the short axis (D3) of the foamed particles is 1.00. ~1.20 is intended. In other words, the present manufacturing method can provide expandable styrenic resin particles that can provide expanded styrenic particles with L3/D3 of 1.00 to 1.20.

The shear stress in one embodiment of the present invention refers to the shear stress applied to the melt-kneaded material when the melt-kneaded material passes through the discharge hole (small hole) of the die. Shear stress can be measured using the device "capillary rheometer (capillograph)". More specifically, the state of the melt-kneaded material as it passes through the discharge hole of the die is simulated using a capillary rheometer, and the shear rate (sec ^-1 ) (a) and viscosity (Pa・s) of the melt are measured using the capillary rheometer. ) Obtain the relationship with (b). Separately, from the diameter (cm) of each discharge hole of the die and the discharge amount (cm ³ /sec) of each discharge hole of the die, the shear rate (sec) of the molten mixture when passing through the discharge hole of the die is determined. ^-1 ). Next, using the relational expression between the value of shear rate (sec ⁻¹ ) (a) and the value of viscosity (Pa・s) (b) obtained with a capillary rheometer, melt kneading during passage through the discharge hole of the die was performed. Calculate the viscosity of a substance. Next, the shear stress of the melt-kneaded material when passing through the discharge hole of the die is calculated from the product (a×b) of the shear rate and the viscosity. The method for measuring shear stress will be explained in detail in Examples below.

L1/D1 in one embodiment of the present invention is the ratio of the length (L1) in the tensile direction of the styrene resin particle to the cross-sectional length (D1), and is calculated by the following formula.
L1/D1=length in the tensile direction of styrene resin particles (L1)/length of cross section of styrene resin particles (D1).
Here, the tensile direction in the styrene resin particles refers to the direction in which the melt-kneaded material extruded from the die is pulled. The length (L1) of the styrene-based resin particles in the tensile direction is intended to be the longest length among the lengths of the styrene-based resin particles in the tensile direction. Further, the cross section of the styrene resin particles refers to the cross section perpendicular to the tensile direction. The cross-sectional length (D1) of the styrene-based resin particles is intended to be the shortest length among the cross-sectional lengths of the styrene-based resin particles.

This manufacturing method includes a styrenic resin particle preparation step and a blowing agent impregnation step.

(2-1. Styrenic resin particle preparation process)
The styrenic resin particle preparation step can also be said to be a step of molding (processing) a styrene resin composition containing a styrene resin containing a styrene/(meth)acrylic acid copolymer into a particle shape.

(Styrene resin)
The styrenic resin composition contains a styrenic resin. The styrenic resin includes a styrene/(meth)acrylic acid copolymer. In this specification, a styrene/(meth)acrylic acid copolymer refers to at least styrene units derived from a styrene monomer and (meth)acrylic acid derived from a (meth)acrylic acid monomer. A copolymer having a series unit is intended. In other words, the styrene/(meth)acrylic acid copolymer is a copolymer obtained by polymerizing a monomer mixture containing at least a styrene monomer and a (meth)acrylic acid monomer. be.

Styrenic monomers are not particularly limited, but include, for example, styrene (sometimes referred to as styrene monomer), α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. The styrenic unit preferably contains a styrene unit, more preferably a styrene unit, because it is easy to handle in production and the raw materials are inexpensive.

Examples of the (meth)acrylic acid monomer include acrylic acid and methacrylic acid. The (meth)acrylic acid unit preferably contains a methacrylic acid unit, more preferably a methacrylic acid unit, because it is easy to handle in production and the raw materials are inexpensive.

The styrene/(meth)acrylic acid copolymer may contain structural units derived from monomers other than the styrene monomer and the (meth)acrylic acid monomer.

The styrene/(meth)acrylic acid copolymer preferably contains 85% by weight or more of styrene-based units, preferably 87% by weight out of 100% by weight of all structural units contained in the styrene/(meth)acrylic acid copolymer. It is more preferable to contain 90% by weight or more, particularly preferably 90% by weight or more. The upper limit of the styrene units in 100% by weight of all structural units contained in the styrene/(meth)acrylic acid copolymer is not particularly limited, but is preferably 99% by weight or less, for example.

The styrene/(meth)acrylic acid copolymer preferably contains 15% by weight or less of (meth)acrylic acid units based on 100% by weight of all structural units contained in the styrene/(meth)acrylic acid copolymer. , more preferably 13% by weight or less, particularly preferably 10% by weight or less. The lower limit of the (meth)acrylic acid units based on 100% by weight of all structural units contained in the styrene/(meth)acrylic acid copolymer is not particularly limited, but is preferably, for example, 1% by weight or more.

If the amounts of styrene units and (meth)acrylic acid units in the styrene/(meth)acrylic acid copolymer are within the ranges mentioned above, the glass transition point of the styrene/(meth)acrylic acid copolymer is It can be within the range of 105°C to 125°C.

The styrene resin may contain a styrene homopolymer in addition to the styrene/(meth)acrylic acid copolymer. Styrene homopolymer is a resin that is incompatible with styrene/(meth)acrylic acid copolymer, so if it is added in excess, it tends to reduce heat resistance and make the cell chord length of the foam molded product finer. It is in.

The styrenic resin preferably contains 90% by weight or more, more preferably 95% by weight or more, and 99% by weight or more of the styrene/(meth)acrylic acid copolymer based on 100% by weight of the styrene resin. is particularly preferred. The styrenic resin may contain 100% by weight of a styrene/(meth)acrylic acid copolymer based on 100% by weight of the styrene-based resin. In other words, the styrenic resin may be composed only of a styrene/(meth)acrylic acid copolymer.

In the styrene resin, the content of the resin incompatible with the styrene/(meth)acrylic acid copolymer (for example, styrene homopolymer) is preferably as small as possible. The lower the content of the resin that is incompatible with the styrene/(meth)acrylic acid copolymer in the styrene resin, the lower the tendency to obtain flat expanded particles, and the lower the tendency to obtain spherical expanded particles. It has the advantage of increasing In addition, the smaller the content of the resin incompatible with the styrene/(meth)acrylic acid copolymer in the styrene resin, the less the possibility that the cell chord length of the resulting foam molded product will become fine, and the foam molded product It also has the advantage that the tendency of the surface to melt is reduced and the appearance of the foamed molded product is improved.

The content of resin incompatible with the styrene/(meth)acrylic acid copolymer, for example, the content of styrene homopolymer, in 100% by weight of the styrene resin is preferably 10% by weight or less, and 5% by weight. The following is more preferable, 3% by weight or less is even more preferable, and 1% by weight or less is particularly preferable.

The glass transition point of the styrene/(meth)acrylic acid copolymer is preferably 105°C to 125°C, more preferably 107°C to 123°C, even more preferably 108°C to 120°C, particularly preferably 110°C to 115°C. . This configuration has the advantage that the obtained foamed molded product has excellent dimensional stability at 95° C. (that is, excellent dimensional stability as a heat insulating material) and also has excellent moldability. When the glass transition point of the styrene/(meth)acrylic acid copolymer is 105° C. or higher, it has the advantage that sufficient dimensional stability can be obtained when used at high temperatures (for example, in an environment of 95° C. or higher). In addition, when the glass transition point of the styrene/(meth)acrylic acid copolymer is 125°C or lower, the heat resistance does not become too high, so that the foamed particles obtained by foaming the expandable resin particles have a sufficient expansion ratio. It has the advantage that it can be obtained. Note that as the content of (meth)acrylic acid units in the styrene/(meth)acrylic acid copolymer increases, the glass transition point of the styrene/(meth)acrylic acid copolymer increases.

The glass transition point of the styrene resin is preferably 105°C to 125°C, more preferably 107°C to 123°C, even more preferably 108°C to 120°C, particularly preferably 110°C to 115°C. This configuration has the advantage that the obtained foamed molded product has excellent dimensional stability at 95° C. (that is, excellent dimensional stability as a heat insulating material) and also has excellent moldability. When the glass transition point of the styrenic resin is 105° C. or higher, it has the advantage that sufficient dimensional stability can be obtained when used at high temperatures (for example, in an environment of 95° C. or higher). In addition, when the glass transition point of the styrene resin is 125°C or lower, the heat resistance does not become too high, so the foamed particles obtained by foaming the expandable resin particles have the advantage of being able to obtain a sufficient expansion ratio. have Note that as the content of (meth)acrylic acid units in the styrene resin increases, the glass transition point of the styrene resin increases.

The weight average molecular weight Mw of the styrene/(meth)acrylic acid copolymer is not particularly limited, but is preferably from 150,000 to 400,000, more preferably from 180,000 to 300,000. When the weight average molecular weight Mw of the styrene/(meth)acrylic acid copolymer is 400,000 or less, the viscosity of the melt-kneaded product does not become too high, making it possible to easily obtain spherical expandable styrenic resin particles. can. When the weight average molecular weight Mw of the styrene/(meth)acrylic acid copolymer is 150,000 or more, the viscosity of the melt-kneaded product does not become too low, so the melt-kneaded product extruded from the die (sometimes referred to as a strand) ) can be pulled (pulled) stably, and the resulting foamed molded product has the advantage of being excellent in strength.

(Flame retardants)
In order to impart flame retardancy to the resulting foam molded article, it is preferable to use a flame retardant in this manufacturing method. In other words, the present expandable resin particles preferably contain a flame retardant.

The flame retardant is preferably used in the resin particle preparation step, and the styrenic resin composition to be melt-kneaded preferably contains the flame retardant. According to this configuration, since the resulting resin particles contain a flame retardant, there is an advantage that expandable resin particles containing a flame retardant can be easily obtained.

The flame retardant is not particularly limited, and any known flame retardant conventionally used in styrenic resin foam moldings can be used. Examples of flame retardants include (a) halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane, (b) tetrabromobisphenol A, tetrabromobisphenol F, 2,4, Brominated phenols such as 6-tribromophenol and tris(2,3-dibromopropyl)isocyanurate, (c) tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol S-bis( 2,3-dibromopropyl ether), tetrabromobisphenol F-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A- diglycidyl ether, 2,2-bis[4'(2'',3''-dibromoalkoxy)-3',5'-dibromophenyl]-propane, 2,2-bis[4-(2,3-dibromo- Brominated phenol derivatives such as 2-methylpropoxy)-3,5-dibromophenyl]propane, and (d) brominated styrene/butadiene block copolymers, brominated random styrene/butadiene copolymers and brominated styrene/ Brominated butadiene/vinyl aromatic hydrocarbon copolymers such as butadiene graft copolymers (for example, EMERALD3000 manufactured by Chemtura or the copolymers disclosed in Japanese Patent Publication No. 2009-516019), etc. . In one embodiment of the present invention, among these flame retardants, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), etc. It is preferable to contain a bromine-containing organic compound having a 2,3-dibromo-2-alkylpropyl group. These flame retardants may be used alone or in combination of two or more. Moreover, when using a mixture of two or more types of flame retardants, the mixing ratio may be adjusted as appropriate depending on the purpose.

The amount of flame retardant used (amount added, content) is not particularly limited, but is preferably 0.1 parts by weight to 5.0 parts by weight, and 1.0 parts by weight to 4 parts by weight, based on 100 parts by weight of the styrene resin. 0 parts by weight is more preferable, 2.0 parts by weight to 3.5 parts by weight are even more preferable, and 2.5 parts by weight to 3.0 parts by weight are particularly preferable. This configuration has the advantage that the resulting foamed molded product has a good balance between flame retardancy and dimensional stability at 95°C. Furthermore, when the amount of flame retardant used is 2.0 parts by weight or more with respect to 100 parts by weight of the styrene resin, there is also an advantage that the resulting foamed molded product has better flame retardant performance. In addition, if the amount of flame retardant used is 4.0 parts by weight or less per 100 parts by weight of the styrene resin, the dimensional stability of the resulting foamed molded product at 95°C will not deteriorate, or if it does, it will only decrease slightly. It has the advantage of being

(graphite)
In order to impart heat insulation properties to the resulting foamed molded product, in this manufacturing method, it is preferable to use a carbon-based radiation heat transfer inhibitor, and it is more preferable to use graphite. In other words, the present expandable resin particles preferably contain a carbon-based radiation heat transfer inhibitor, and more preferably contain graphite.

Graphite is preferably used in the resin particle preparation step, and the styrenic resin composition to be melt-kneaded preferably contains a flame retardant. According to this configuration, since the resulting resin particles contain graphite, there is an advantage that expandable resin particles containing graphite can be easily obtained.

Examples of graphite include, but are not limited to, scaly graphite, earthy graphite, spherical graphite, artificial graphite, and the like. In addition, in this specification, the term "scale-like" also includes scale-like, flake-like, or plate-like. In one embodiment of the present invention, the graphite preferably contains a graphite mixture containing flaky graphite as a main component, and more preferably contains flaky graphite, from the viewpoint of a high radiation heat transfer suppressing effect. These graphites may be used alone or in combination of two or more types. Moreover, when using a mixture of two or more types of graphite, the mixing ratio may be adjusted as appropriate depending on the purpose.

The amount of graphite used (added amount, content) is not particularly limited, but is preferably 1.0 to 10.0 parts by weight, and 3.0 to 5.0 parts by weight, based on 100 parts by weight of the styrene resin. It is more preferably 0 parts by weight, and even more preferably 3.5 parts by weight to 4.0 parts by weight. According to this configuration, there is an advantage that the resulting foamed molded product has a good balance between heat insulation, expansion ratio, and heat resistance. Further, when the amount of graphite used is 2.0 parts by weight or more with respect to 100 parts by weight of the styrene resin, there is also the advantage that the resulting foamed molded product has better heat insulation properties. In addition, when the amount of graphite used is 10.0 parts by weight or less with respect to 100 parts by weight of styrene resin, the cells (cell membrane) of the foamed particles are difficult to break during foaming of the foamable resin particles and molding of the foamed particles. This also has the advantage that foam molding having a sufficient expansion ratio and excellent heat resistance can be obtained.

The volume average particle diameter of graphite is preferably 1 μm to 10 μm, more preferably 1 μm to 7 μm, more preferably 1 μm to 5 μm, more preferably 1 μm to 4 μm, and even more preferably 1 μm to 3 μm. This configuration has the advantage that the obtained expanded particles and foamed molded product can be highly foamed, and the foamed molded product has excellent heat insulation properties and moldability. Furthermore, the smaller the volume average particle diameter of graphite, the higher the manufacturing cost. When the volume average particle diameter of graphite is 1 μm or more, the production cost including the cost of pulverization does not become too high, so there is an advantage that the cost of the expandable polystyrene resin particles becomes low. On the other hand, when the volume average particle diameter is 10 μm or less, the cell membrane of the foamed particles becomes difficult to tear during foaming of the expandable resin particles and molding of the foamed particles, so that the resulting foamed particles and foamed molded products can be easily foamed to a high degree. The advantage is that the foam molded product has excellent dimensional stability (heat resistance) at 95°C, and the advantage that the foam molded product has excellent mechanical strength (e.g. compressive strength). have In this specification, the volume average particle size of graphite is the D50 particle size (particle size when the cumulative volume becomes 50%) calculated by the laser diffraction-scattering method based on the Mie theory in accordance with JIS Z8825-1. Point.

(Other additives)
In this manufacturing method, additives other than graphite and flame retardants (other additives) may be used as necessary. In other words, the styrenic resin composition may contain other additives as necessary. Other additives include, but are not particularly limited to, (a) heat stabilizers such as hindered amine compounds, phosphorus compounds, and epoxy compounds, (b) sodium stearate, magnesium stearate, calcium stearate, zinc stearate, Processing aids such as barium stearate and liquid paraffin, (c) hindered amines, phosphorus stabilizers, epoxy compounds, and light resistance such as phenolic antioxidants, nitrogen stabilizers, sulfur stabilizers, benzotriazoles, etc. (d) antistatic agents, (e) colorants such as pigments, (f) silica, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, calcium carbonate, sodium hydrogen carbonate, etc. Inorganic compounds, (g) olefin waxes such as methyl methacrylate copolymers and polyethylene waxes, (h) talc, (i) methylene bis stearyl amide, ethylene bis stearyl amide, hexamethylene bis palmitic acid amide, ethylene bis Foaming of fatty acid bisamides such as oleic acid amide, (j) nucleating agents such as ethylene/vinyl acetate copolymer resins, (k) solvents with a boiling point of 200°C or less at atmospheric pressure such as cyclohexane and ethyl chloride. Auxiliary agents, etc. These other additives may be used alone or in combination of two or more. Furthermore, when two or more types of other additives are mixed and used, the mixing ratio may be adjusted as appropriate depending on the purpose.

(melt kneading process)
In the melt-kneading step, a styrene-based resin composition containing a styrene-based resin containing a styrene/(meth)acrylic acid copolymer is melt-kneaded using an extruder to obtain a melt-kneaded product of the styrene-based resin composition. .

The extruder is not particularly limited, and examples thereof include a single screw extruder, a twin screw extruder, and the like. The two shafts of the twin-screw extruder may be in the same direction or in different directions. A twin-screw extruder is preferred from the viewpoint of dispersibility of additives.

The cylinder temperature (also referred to as extrusion temperature) in the melting section of the extruder is not particularly limited as long as it is a temperature at which the styrene resin melts, but is preferably 200°C to 270°C. When the extrusion temperature is 200° C. or higher, the load on the extruder is not increased, so extrusion can be stably performed, and the dispersibility of additives is improved. On the other hand, when the extrusion temperature is 270° C. or lower, there is an advantage that there is no risk of decomposition of the styrenic resin itself. In addition, when the extrusion temperature is 270°C or lower, there is no risk that the flame retardant itself will decompose, so the desired flame retardance can be obtained, and the flame retardant may not be used in excess in order to impart the desired flame retardance. There is no need to add it.

The residence time of the styrenic resin composition in the extruder from the time the styrenic resin and various additives are supplied to the extruder until the end of melt-kneading is preferably 9 minutes or less, more preferably 8 minutes or less. , more preferably 7 minutes or less. According to this configuration, since there is no possibility that the flame retardant itself will decompose, the desired flame retardancy can be obtained, and there is no need to add an excessive amount of the flame retardant in order to impart the desired flame retardance.

(Extrusion process)
In the extrusion step, the melt-kneaded material obtained in the melt-kneading step is extruded from the discharge hole of the die. The die is provided at the tip of the extruder in the extrusion direction.

The die only needs to have at least one discharge hole formed therein, and may have a plurality of discharge holes formed therein.

The number of ejection holes formed in the die is appropriately changed depending on the size of the die and is not particularly limited. When the die has two or more discharge holes, from the viewpoint of productivity, the distance between the discharge holes formed in the die is preferably 3 mm to 10 mm. When the distance between the discharge holes is 3 mm or more, there is no possibility that the strands immediately after the discharge holes will coalesce, which has the advantage that there is no possibility that productivity will decrease. When the distance between the ejection holes is 10 mm or less, a relatively large number of ejection holes can be formed in the die, which has the advantage of improving productivity.

The diameter of the discharge hole formed in the die (the diameter of each discharge hole if multiple discharge holes are formed) is not particularly limited, but from the viewpoint of productivity, for example, from 0.05 mm to 2 mm. 0.00 mm is preferable, 0.08 mm to 1.50 mm is more preferable, 0.08 mm to 1.30 mm is more preferable, and even more preferably 0.09 mm to 1.20 mm. When the diameter of the discharge hole is 0.05 mm or more, there is no risk of resin clogging in the discharge hole, and productivity is improved.

The discharge amount of the melt-kneaded material per discharge hole is not particularly limited, but for example, from the viewpoint of making the expanded particles spherical, it is preferably from 0.35 kg/hour to 1.00 kg/hour, and from 0.35 kg/hour to 1.00 kg/hour. More preferably 0.80 kg/hour.

In the extrusion step, the shear stress of the melt-kneaded material when passing through the die is 30 kPa to 90 kPa, preferably 35 kPa to 80 kPa, more preferably 40 kPa to 70 kPa, particularly preferably 45 kPa to 65 kPa. According to this configuration, styrenic resin particles having L1/D1 of 1.30 to 2.50 can be stably obtained, and spheroidized styrenic expanded particles can be easily obtained from the obtained expandable resin particles. be able to. When the shear stress is less than 30 kPa, the fluidity of the molten resin increases, making it difficult to pull the extruded melt-kneaded product (strand), and the length of the cross section of the resin particle in the tensile direction (L1) increases. It becomes difficult to adjust the ratio (L1/D1) to the length (D1). Moreover, when the shear stress is larger than 90 kPa, the melt-kneaded material extruded from the discharge hole expands, resulting in excessively flat resin particles, and the resulting expanded particles also tend to become flat.

In the process of intensive study, the present inventors discovered that the spheroidization of foamed particles ((L3/D3) of foamed particles) involves not only (L1/D1) of resin particles, but also surprisingly the shear stress. We independently obtained the knowledge that it has a strong influence. At first glance, it seems that the spheroidization of expanded particles and the shear stress during the production of resin particles have no or only a weak relationship. Therefore, the knowledge that shear stress strongly influences the spheroidization of expanded particles can be said to be a surprising discovery that could not easily be expected from conventional technical common sense.

As mentioned above, shear stress is a value obtained by multiplying shear rate (a) and viscosity (b) (a×b). When measuring a melt using a capillary rheometer, the shear rate of the melt ( The relationship between a) and viscosity (b) can be obtained. The shear rate (a) is proportional to the volume of resin discharged per capillary hole and inversely proportional to the cube of the radius of the capillary hole. Viscosity (b) decreases as the shear rate increases and decreases as the resin temperature increases. In other words, the shear rate (a) is proportional to the amount of melt-kneaded material discharged per discharge hole formed in the die, and inversely proportional to the cube of the radius of the discharge hole. Viscosity (b) decreases with increasing shear rate and decreases with increasing extrusion temperature. In addition, the resin volume discharge amount per capillary hole is calculated by dividing the volume discharge amount of the extruder used in actual production by the specific gravity of styrene resin 1.0 g/cm ³ divided by the number of holes in the die. obtained by

(Process of obtaining styrene resin particles)
In this step, the melt-kneaded material extruded from the discharge hole is pulled and cut. Thereby, styrenic resin particles can be obtained. In this specification, "the melt-kneaded material extruded from the discharge hole" may be referred to as a "strand." In other words, in this step, the strands are pulled and cut. "Tension" is sometimes referred to as "takeover."

The pulling and cutting of the strand may be performed using separate devices, for example, the strand may be pulled using a pulling machine (pulling machine), and then the strand may be cut using a cutting machine. The strands may be pulled and cut by the same device; for example, a pelletizer with rotating blades or the like may be used to pull and cut the strands.

The pulling direction of the strand is not particularly limited, but is, for example, the same direction as the extrusion direction when extruding the melt-kneaded material from the discharge hole of the die, for example, the horizontal direction. Note that the pulling direction of the strand is the pulling direction L1 of the resin particles, which will be described later.

The tensioning speed of the strand is not particularly limited and may be adjusted as appropriate depending on the discharge amount. The pulling speed of the strand is, for example, preferably 15 m/min to 30 m/min, more preferably 15 m/min to 25 m/min, and even more preferably 18 m/min to 22 m/min. According to this configuration, L1/D1 of the resin particles can be easily adjusted within the range of 1.30 to 2.90. When the pulling speed is 30 m/min or less, L1/D1 can be easily adjusted to 2.90 or less, and the strand tends to be cut stably. On the other hand, when the pulling speed is 15 m/min or more, L1/D1 can be easily adjusted to 1.30 or more, and spherical expanded particles tend to be easily obtained.

The ratio (L1/D1) of the length (L1) in the tensile direction of the resin particles to the cross-sectional length (D1) is 1.30 to 2.90, preferably 1.30 to 2.50, and 1. .25 to 2.00 is more preferable, and 1.20 to 1.50 is even more preferable. According to this configuration, spherical expanded particles can be obtained from the resulting expandable styrene resin particles. When L1/D1 is 1.3 or more, there is no possibility that the resulting expanded particles will have a flat shape (L3/D3 exceeds 1.20). On the other hand, when L1/D1 is 2.90 or less, there is no possibility that the tension of the strand will become unstable, and as a result, L1 of the resin particles becomes substantially uniform. L1/D1 can be adjusted by the pulling speed at which the strand is pulled, the number of blades of the rotary blade of the cutting machine, the rotation speed, etc.

In this step, the melt-kneaded material (strand) extruded from the discharge hole may be cooled and solidified before cutting. In other words, the resin particle preparation step may further include a cooling step of cooling the strands after the extrusion step and before this step. When the resin particle preparation process includes a cooling process, it has the advantage that the strands can be easily pulled and cut.

In the cooling step, the method of cooling the strands is not particularly limited, but examples include a method of passing the strands through a water tank, water channel, or the like that contains water as a cooling medium. The cooling of the strand may be so-called natural cooling, simply by leaving the strand at room temperature.

The temperature (water temperature) in the water tank and water channel is not particularly limited, but from the viewpoint of efficiently cooling and solidifying the melt-kneaded material (strand), it is preferably 10°C to 80°C, more preferably 20°C to 70°C, and 20°C to 80°C. C. to 50.degree. C. is more preferred.

When performing the cooling step, the temperature exhibited by the strand after cooling (hereinafter sometimes referred to as cooling temperature) is not particularly limited. The cooling temperature is preferably 10°C to 80°C, more preferably 20°C to 70°C, even more preferably 20°C to 50°C. According to this configuration, the resin composition in the strand solidifies sufficiently quickly, resulting in good productivity of resin particles.

The particle weight of the styrene resin particles is not particularly limited, but is preferably, for example, 0.3 mg to 1.5 mg, more preferably 0.4 mg to 1.0 mg. The smaller the particle weight of the styrene-based resin particles, the easier it is to obtain a foamed molded article filled with pre-expanded particles in every detail, even in the case of a mold with a complicated shape. The particle weight of the styrene resin particles can be adjusted by adjusting the number of small holes in the die, the small hole diameter, the pulling speed of the pelletizer, the rotation speed of the rotary blade, etc.

(2-2. Foaming agent impregnation step)
This manufacturing method includes a blowing agent impregnation step after the styrenic resin particle preparation step. In the blowing agent impregnation step, expandable styrenic resin particles are obtained by impregnating the styrenic resin particles obtained in the styrenic resin particle preparation step with a hydrocarbon blowing agent in an aqueous suspension. It is a process.

(foaming agent)
In this manufacturing method, a hydrocarbon foaming agent is used as the foaming agent. Examples of hydrocarbon blowing agents include, but are not limited to, (a) aliphatic hydrocarbons such as propane, butane, and pentane, (b) alicyclic hydrocarbons such as cyclobutane and cyclopentane, and (c) methyl. Examples include halogenated hydrocarbons such as chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane. These blowing agents may be used alone or in combination of two or more. Furthermore, when two or more types of blowing agents are mixed and used, the mixing ratio may be adjusted as appropriate depending on the purpose. From the viewpoint of volatility and foaming power, the hydrocarbon foaming agent preferably contains any one selected from the group consisting of normal pentane, isopentane, neopentane, and cyclopentane. In addition, the hydrocarbon blowing agent is selected from the group consisting of pentanes (normal pentane, isopentane, neopentane, cyclopentane, etc.) because the cells are easily stabilized in the foaming of the resulting expandable resin particles. It is preferable to include any one of them.

The amount of blowing agent used is not particularly limited. The blowing agent may also serve to lower the softening temperature of the styrenic resin particles. It is preferably 3.0 parts by weight to 12.0 parts by weight, more preferably 4.0 parts by weight to 11.0 parts by weight, and 5.0 parts by weight based on 100 parts by weight of styrene resin particles. It is more preferably 10.0 parts by weight, and particularly preferably 6.0 parts by weight to 9.0 parts by weight. When the amount of the blowing agent used is 3.0 parts by weight or more per 100 parts by weight of the styrene resin particles, there is no risk that the foaming power during foaming will decrease, and the foamed particles have an expansion ratio that is easy to use as a heat insulating material. It has the advantage of being easily obtainable. On the other hand, if the amount of blowing agent used is 12.0 parts by weight or less with respect to 100 parts by weight of styrene resin particles, there will not be too much of the blowing agent remaining in the foam molded product, so the flame retardancy of the foam molded product will be reduced. It has the advantage that it is difficult to cause deterioration. When the amount of the blowing agent used is 6.0 parts by weight to 9.0 parts by weight with respect to 100 parts by weight of the styrene resin particles, it is particularly possible to obtain expanded particles that have both high foamability and excellent moldability. can.

The specific aspect of the blowing agent impregnation step is not particularly limited, but for example, (a) styrenic resin particles and a dispersant are dispersed in water in a container to prepare an aqueous suspension, and then (b) A blowing agent is supplied into the aqueous suspension, and then (c) the temperature inside the container (temperature of the aqueous suspension) is raised to a predetermined temperature (impregnation temperature), and the blowing agent is added into the styrene resin particles. Preferred examples include a method of impregnating with.

The container used in the blowing agent impregnation step is not particularly limited, but it is preferably a container that can be sealed and has pressure resistance and heat resistance, and is more preferably equipped with a stirrer.

(dispersant)
In the blowing agent impregnation step, it is preferable to use a dispersant. By using a dispersant, it is possible to suppress adhesion of resin particles to each other (sometimes referred to as blocking), and it is possible to stably produce expanded particles. Examples of the dispersant include, but are not particularly limited to, poorly water-soluble inorganic salts such as calcium phosphate, hydroxyapatite, magnesium pyrophosphate, and calcium carbonate. These dispersants may be used alone or in combination of two or more. Moreover, when using a mixture of two or more types of flame retardants, the mixing ratio may be adjusted as appropriate depending on the purpose.

The amount of the dispersant used is not particularly limited, but from the viewpoint of preventing or suppressing mutual adhesion of resin particles, it is preferably 0.1 parts by weight to 3.0 parts by weight, based on 100 parts by weight of styrene resin particles. .2 parts by weight to 2.5 parts by weight are more preferred, 0.3 parts by weight to 2.0 parts by weight are even more preferred, and 0.5 parts by weight to 1.5 parts by weight are particularly preferred.

When using the dispersant in the blowing agent impregnation step, it is preferable to use a dispersion aid together with the dispersant from the viewpoint of improving the effect of suppressing mutual adhesion of resin particles. Examples of the dispersion aid include, but are not limited to, anionic surfactants such as sodium alkanesulfonate, sodium alkylbenzenesulfonate, and sodium α-olefinsulfonate. These dispersion aids may be used alone or in combination of two or more. Furthermore, when two or more types of dispersion aids are mixed and used, the mixing ratio may be adjusted as appropriate depending on the purpose.

The amount of the dispersion aid used is not particularly limited, but from the viewpoint of preventing or suppressing adhesion of resin particles to each other, it is preferably 0.001 part by weight to 0.500 parts by weight based on 100 parts by weight of styrene resin particles. It is more preferably 0.005 part by weight to 0.400 part by weight, even more preferably 0.008 part by weight to 0.300 part by weight, and even more preferably 0.010 part by weight to 0.200 part by weight.

The impregnation temperature is not particularly limited. The impregnation temperature is set at the glass transition point of the styrenic resin (or styrene/(meth)acrylic acid copolymer) from the viewpoint of softening the styrenic resin with the blowing agent and efficiently impregnating the blowing agent into the resin particles. (for example, 105°C to 125°C, or the glass transition point -10°C or higher (more preferably -5°C or higher, still more preferably -3°C or higher) or the glass transition point +10°C or lower (more preferably is preferably +8° or less)). The impregnation temperature is more preferably 107°C to 123°C, even more preferably 110°C to 120°C. If the impregnation temperature is 105°C or higher, the degree of impregnation of the foaming agent into the resin particles will be high, the cell structure of the foamed particles will be uniform or almost uniform, and the surface of the resulting foamed molded product will have a good appearance without hollows. It has the advantage of being On the other hand, when the impregnation temperature is 125° C. or lower, impregnation of the blowing agent is improved and the internal pressure of the polymerization machine does not become too high, so there is an advantage that a polymerization machine specification having heavy equipment pressure resistance is not required. Further, when the impregnation temperature is 125° C. or lower, there is also an advantage that adhesion of resin particles to each other is prevented or suppressed.

The time for maintaining the temperature inside the container at the impregnation temperature (sometimes referred to as the impregnation time) is not particularly limited, but from the viewpoint of sufficiently impregnating the foaming agent inside the resin particles, it is preferably 3 to 10 hours. , more preferably 5 to 8 hours. When the impregnation time is 3 hours or more, there is no possibility that fine cells will exist in the center of the resulting expanded particles when foamed particles are obtained by foaming the expandable resin particles. As a result, there is an advantage that the moldability of the expanded particles is improved. On the other hand, when the impregnation temperature is within 10 hours, there is an advantage that productivity becomes good.

After the resin particles are impregnated with the blowing agent at an appropriate impregnation temperature, impregnation time, and amount of blowing agent used, for example, by cooling the temperature in the container and drying the particles in the aqueous suspension. Expandable styrenic resin particles can be obtained.

In the blowing agent impregnation step, expandable styrenic resin particles having a desired L2/D2 can be obtained efficiently and easily, especially by appropriately adjusting the amount of blowing agent used and the impregnation temperature.

(Expansible styrene resin particles)
The expandable styrenic resin particles according to an embodiment of the present invention have a ratio (L2/D2) of the length of the long axis (L2) to the length of the short axis (D2) of 1.00 to 1.20. It is preferably 1.00 to 1.15, even more preferably 1.00 to 1.10. When L2/D2 is within the above range, spherical foamed particles can be obtained, so that the filling performance of the foamed particles into a mold during production of a foamed molded article is improved. As a result, there is an advantage that even in the case of a mold having a complicated shape, a foamed molded article filled with foamed particles in every detail can be easily obtained. Note that the length (L2) of the long axis of the expandable styrenic resin particles is intended to be the maximum length between any two points of the expandable styrenic resin particles. Further, the length (D2) of the short axis of the expandable styrene resin particles is intended to be the shortest length in the direction perpendicular to the long axis.

(external additive)
Known and commonly used external additives can be applied to the surface of the expandable resin particles. In other words, the present expandable resin particles may contain an external additive on the surface thereof. Examples of external additives include, but are not limited to, (a) fatty acid triglycerides such as lauric acid triglyceride, stearic acid triglyceride, and linoleic acid triglyceride; (b) fatty acid diglycerides such as lauric acid diglyceride, stearic acid diglyceride, and linoleic acid diglyceride. (c) fatty acid monoglycerides such as lauric acid monoglyceride, stearic acid monoglyceride, and linoleic acid monoglyceride; (d) fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, and calcium laurate; (e) silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane; (f) castor wax; and (g) vegetable oils such as castor oil and olive oil. These external additives may be used alone or in combination of two or more. Furthermore, when two or more types of external additives are mixed and used, the mixing ratio may be adjusted as appropriate depending on the purpose.

As a method for coating (applying) the external additive on the surface of the expandable styrenic resin particles, a known method can be employed. A preferred coating method is to dry the obtained expandable styrenic resin particles, then add external additives to the dried expandable styrenic resin particles, and coat them by mixing and stirring. be.

The amount of external additive used in the present expandable resin particles is not particularly limited, but includes (a) prevention of mutual adhesion of expandable resin particles during production of expanded particles, and (b) surface elongation of the expanded molded product as a final product. (preventing or reducing gaps between particles on the surface of the foam molded product), from 0.01 part by weight to 100 parts by weight of expandable styrenic resin particles before applying external additive It is preferably 2.00 parts by weight, more preferably 0.02 parts by weight to 1.00 parts by weight, and even more preferably 0.02 parts by weight to 0.50 parts by weight.

[3. Styrenic foam particles〕
Styrenic expanded particles formed by foaming the present expandable styrenic resin particles are also an embodiment of the present invention. In other words, the expanded styrenic particles according to an embodiment of the present invention are the expandable styrenic resin particles according to an embodiment of the present invention (for example, in the above [2. Method for producing expandable styrenic resin particles]). It is formed by foaming expandable styrenic resin particles (obtained by the manufacturing method described in 1.). In this specification, "the styrenic foamed particles according to an embodiment of the present invention" may be referred to as "the present foamed particles."

Since the foamed particles have the above-described structure, they have the advantage of being able to provide a foamed molded article with excellent heat resistance and moldability.

Here, when obtaining a foamed molded article from expandable resin particles, the foamed resin particles may be first foamed to obtain expanded particles, and then the foamed particles may be molded to obtain a foamed molded article. Therefore, in the process of obtaining a foam molded article from expandable resin particles, foaming the expandable resin particles is sometimes referred to as "pre-foaming" or "primary foaming", and the resulting expanded particles are referred to as "pre-foaming". "particles" or "primary foam particles".

The present expanded particles can be obtained by foaming (pre-foaming or primary foaming) the expandable styrenic resin particles according to one embodiment of the present invention. The method for foaming the expandable styrenic resin particles is not particularly limited, and for example, a cylindrical foaming device (pre-foaming device) may be used to heat the expandable styrenic resin particles using a heating medium such as water vapor. Ordinary methods such as foaming can be employed. The device used for foaming and the conditions for foaming may be appropriately set depending on the composition of the expandable styrene resin particles, the desired expansion ratio, etc., and are not particularly limited.

The expansion ratio of the present foamed particles is not particularly limited, but may be, for example, 10 times to 90 times, preferably 20 times to 80 times, more preferably 30 times to 70 times, particularly 40 times to 60 times. preferable. Foamed particles having an expansion ratio in the low expansion ratio region and foamed molded products made using the foamed particles can be suitably used as cushioning materials for precision instruments and the like. Foamed particles having an expansion ratio in the high expansion ratio range and a foamed molded article formed by molding the foamed particles can be suitably used as containers for fresh foods and the like. That is, the foamed particles having the expansion ratio within the above-mentioned range can be suitably used for an appropriate use depending on the expansion ratio.

The ratio (L3/D3) of the length of the major axis (L3) to the length of the minor axis (D3) in the expanded particles is preferably 1.00 to 1.20, and preferably 1.00 to 1.20. More preferably, it is 15, and even more preferably 1.00 to 1.10. When L3/D3 of the foamed particles is within the above-mentioned range, filling properties of the foamed particles into a mold will be good in in-mold foam molding. As a result, even if a mold with a complicated shape is used, the foamed particles are filled in even the smallest detail, so there is an advantage that a foamed molded article with excellent moldability can be obtained. Note that the length (L3) of the long axis of the foamed particles is intended to be the maximum length between any two points on the foamed particles. Moreover, the length (D3) of the short axis of the foamed particles is intended to be the shortest length in the direction perpendicular to the long axis.

As long as the expandable resin particles are obtained by the present production method in which the shear stress of the melt-kneaded material when passing through the die is 30 kPa to 90 kPa, and the L1/D1 of the resin particles is 1.30 to 2.90. , L2/D2 can be between 1.00 and 1.20. By foaming such expandable resin particles according to an embodiment of the present invention, expanded particles having L3/D3 within the range of 1.00 to 1.20 can be easily obtained.

The average chord length of the bubbles (sometimes referred to as cells) of the expanded particles is not particularly limited, but is preferably from 50 μm to 200 μm, more preferably from 80 μm to 150 μm. When the average chord length of the foamed particles is 50 μm or more, there is no possibility that the surface of the resulting foamed molded product will melt due to heating during molding, and there is an advantage that moldability is excellent. On the other hand, when the average chord length of the foamed particles is 200 μm or less, there is no tendency for the fusion properties between the foamed particles to deteriorate when molding using the foamed particles, and as a result, a foamed molded product with excellent moldability can be obtained. It has the advantage of being obtained.

[4. Styrenic foam molded product]
A styrenic foam molded product formed by molding the foamed particles of the present invention is also an embodiment of the present invention. In other words, the styrenic foam molded article according to one embodiment of the present invention is the foamed particle according to one embodiment of the present invention (for example, as described in the section [2. Method for manufacturing expandable styrenic resin particles] above). It is formed by molding foamed styrenic particles obtained by foaming expandable styrenic resin particles obtained by the manufacturing method. In this specification, "the styrenic foam molded article according to one embodiment of the present invention" may be referred to as "the present foam molded article".

This foamed molded article has the advantage of excellent dimensional stability at 95° C. and high moldability.

The method for producing a foamed molded product, in other words, the method for molding foamed particles, is not particularly limited. For example, a foamed molded article can be obtained by heating and foaming (secondary foaming) foamed particles by an in-mold foaming method using a mold. More specifically, as an in-mold foam molding method, it is possible to adopt a normal method such as filling a mold with foamed particles and heating the foamed particles by blowing a heating medium such as water vapor into the mold. can. The equipment used for heating and foaming and the conditions for heating and foaming may be appropriately set depending on the desired foaming ratio and the like, and are not particularly limited.

This foamed molded article has excellent dimensional stability at 95°C. For example, a foam molded product obtained by foaming the present expandable resin particles 50 times (pre-foaming) and molding the obtained foamed particles has a dimensional change rate when the foam molded product is heated at 95°C for 168 hours. It has the advantage of being small (eg less than 2%). The smaller the dimensional change rate is, the more preferable it is. The foamed molded article also has the advantage of being excellent in thermal conductivity and lowest oxygen index. For example, the thermal conductivity of the foam molded article can be 0.033 W/mK or less, and the lowest oxygen index can be 26 or more. The foamed molded article preferably has a dimensional change rate of less than 2%, a thermal conductivity of 0.033 W/mK or less, and a minimum oxygen index of 26 or more. This structure has the advantages of being lightweight, easy to assemble, excellent in cost quality, difficult to deform even in a high temperature (for example, 95° C.) environment, and having high heat insulation and flame retardant performance. Such a foamed molded product is particularly suitable as a heat insulating material for a region exposed to a high temperature that has a complex shape, such as a heat insulating material for a hot water storage tank, a heat insulating material for a roof, and a heat insulating material for piping.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the technical scope of the present invention is not limited by these Examples.

〔material〕
The substances used in Examples and Comparative Examples are shown below.

(Styrene resin)
(A1) MA100: Styrene/methacrylic acid copolymer [manufactured by PS Japan Co., Ltd.]
The molar ratio of styrene units/methacrylic acid units is 96/4, weight average molecular weight Mw 270,000, glass transition temperature 110°C
(A2) MR100: Styrene/methacrylic acid copolymer [manufactured by PS Japan Co., Ltd.]
The molar ratio of styrene units/methacrylic acid units is 96/4, weight average molecular weight Mw 220,000, glass transition temperature 110°C
(A3) G9001: Styrene/methacrylic acid copolymer [manufactured by PS Japan Co., Ltd.]
The molar ratio of styrene units/methacrylic acid units is 92/8, weight average molecular weight Mw 190,000, glass transition temperature 120°C
(A4) 680: Styrene homopolymer [manufactured by PS Japan Co., Ltd.]
Weight average molecular weight Mw 250,000, glass transition temperature 100℃
(graphite)
(B1) SGP-40B [manufactured by Marutoyo Casting Materials Co., Ltd., scaly shape, particle size 5 μm]
(B2) MT-2 [manufactured by Marutoyo Casting Materials Co., Ltd., scaly shape: particle size 2 μm]
(Flame retardants)
(C) SR-130: 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., bromine content = 66% by weight]
(foaming agent)
(D1) Pentane: a mixture of normal pentane and isopentane, with a mixing ratio of normal pentane/isopentane = 8/2 (manufactured by Wako Pure Chemical Industries, Ltd.)
(D2) Butane: A mixture of normal butane and isobutane, with a mixing ratio of normal butane/isobutane = 7/3 (manufactured by Iwatani Gas Co., Ltd.).

〔Measuring method〕
The evaluation methods used in Examples and Comparative Examples will be described below.

(Measurement of glass transition point)
Resin particles of styrene/(meth)acrylic acid copolymer or styrene resin were sealed in an open aluminum pan. Using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science, DSC7000X), the resin particles were heated from 40°C to 150°C at a rate of 10°C/min while nitrogen gas was flowing at 40ml/min. . The inflection point of the endothermic curve (minimum value of the endothermic differential curve) obtained as the measurement result was defined as the glass transition point of the styrene/(meth)acrylic acid copolymer or styrene resin.

(Measurement of shear stress of the melt-kneaded material when passing through the discharge hole of the die)
The shear stress of the melted and kneaded product when passing through the discharge hole of the die was measured using a capillary rheometer (manufactured by Toyo Seiki: Capillograph). Specifically, it was as follows. Using a capillary (φ1.0 mm x L length 5 mm), the temperature of the barrel and piston was set to the cylinder temperature (extrusion temperature) in each example and comparative example, and the temperature of the capillary was set to the temperature of the die tip in each example and comparative example. The resin temperature was set. Thereafter, the styrene/(meth)acrylic acid copolymer was filled into the barrel to prevent air from entering, and after 2 minutes, the piston was lowered to extrude the molten resin from the capillary. The descending speed was changed from 0.5 mm/min to 5 mm/min, and the shear rate (/sec) and viscosity (Pa・s) were measured at each descending speed, and the shear rate (sec ⁻¹ ) (a) was measured. A relational expression between the value and the value of viscosity (Pa·s) (b) was calculated. Separately, from the diameter (cm) of each discharge hole of the die and the discharge amount (cm ³ /sec) of each discharge hole of the die, the shear rate (sec) of the molten mixture when passing through the discharge hole of the die is determined. ^-1 ) was calculated. Subsequently, the viscosity of the melt-kneaded material when passing through the discharge hole of the die was calculated using the above-mentioned relational expression obtained using a capillary rheometer. Next, the shear stress of the melt-kneaded material when passing through the discharge hole of the die was calculated from the product (a×b) of shear rate and viscosity. The shear stress corresponds to the shear stress applied to each discharge hole of the die.
The specific formula for calculating the shear rate (sec ⁻¹ ) was as follows.
Shearing rate (sec ^-1 ) = {4 x discharge amount per die discharge hole (cm ³ /sec)} / {pi (π) x (diameter per die discharge hole (cm)) ) ³ }
(Measurement of particle weight per styrene resin particle)
For each Example and Comparative Example, 10 styrene resin particles were randomly selected from the obtained styrene resin particles, and the weight Wp (mg) of the 10 styrene resin particles was measured. The grain weight per grain was determined from Wp/10 (mg).

(Measurement of the ratio (L1/D1) of the length (L1) of the styrene resin particles in the tensile direction to the cross-sectional length (D1))
For each example and comparative example, five styrene resin particles were randomly selected from the obtained styrene resin particles. For each styrene resin particle, the length in the tensile direction (L1) and the length in the cross-sectional direction (D1) were measured with calipers, and the value of L1/D1 was calculated. Five L1/D1 values were obtained for each example and comparative example (N=5). The arithmetic average value of the five L1/D1 values was taken as the L1/D1 value in each Example and Comparative Example.

(Measurement of the ratio (L2/D2) of the length of the long axis (L2) of the expandable styrenic resin particles to the length (D2) of the short axis)
For each Example and Comparative Example, five expandable styrenic resin particles were randomly selected from the obtained expandable styrene resin particles. For each expandable styrene resin particle, the length of the major axis (L2) and the length of the minor axis (D2) were measured using calipers, and the value of L2/D2 was calculated. Five L2/D2 values were obtained for each example and comparative example (N=5). The arithmetic average value of the five L2/D2 values was taken as the L2/D2 value in each Example and Comparative Example.

(Measurement of expansion ratio of styrene foam particles)
The foamed particles were poured into a 1 L graduated cylinder until it overflowed, and the mixture was scraped off with the opening of the graduated cylinder. The weight (g) of the expanded particles in the graduated cylinder was measured. (Expansion ratio (times)) = 1000 (cc)/weight of expanded particles (g).

(Measurement of the ratio (L3/D3) of the length of the long axis (L3) to the length of the short axis (D3) of styrene foam particles)
For each Example and Comparative Example, five particles were randomly selected from the obtained expanded styrene particles. For each expanded styrene particle, the length of the major axis (L3) and the length of the minor axis (D3) were measured using calipers, and the value of L3/D3 was calculated. Five L3/D3 values were obtained for each example and comparative example (N=5). The arithmetic average value of the five L3/D3 values was taken as the L3/D3 value in each Example and Comparative Example.

(Evaluation of moldability of foam molded product)
The appearance of the foamed molded product was visually judged and evaluated as follows:
Good: There is no shrinkage or melting on the surface of the foamed molded product, and the gap between foam particles on the surface of the foamed molded product is within 0.1 mm, that is, the surface is smooth.
Δ: There is no shrinkage or melting on the surface of the foamed molded product, but the gap between foam particles on the surface of the foamed molded product exceeds 0.1 mm.
×: There is shrinkage and melting on the surface of the foam molded product, and the gap between the foam particles exceeds 0.1 mm.

(95°C dimensional change rate of foam molded product)
Foamed molded product A foamed molded product with a magnification of 50 times was dried at 60° C. for 24 hours. Thereafter, the foamed molded product was cut out to have a length of 150 mm, a width of 150 mm, and a thickness of 20 (t) mm. The dimensions in the length direction and the width direction of the cut out foamed molded article were measured at three locations each, and the average dimension (A) at the six locations was determined. Next, the foamed molded product was left standing in a dryer at 95° C. for 168 hours. Thereafter, the lengthwise and widthwise dimensions of the foamed molded article were measured at three locations each, and the average dimension (B) at the six locations was determined. The dimensional change rate was calculated using the following formula, and evaluated based on the calculated dimensional change rate:
Dimensional change rate (%) = ((A) - (B))/(A) x 100.
◎ (Excellent): Dimensional change rate is less than 1% 〇 (Good): Dimensional change rate is 1% or more and less than 2% × (Poor): Dimensional change rate is 2% or more.

(Thermal conductivity of foam molded product)
A test piece measuring 300 mm in length x 300 mm in width x 25 mm in thickness was cut from the center of the foamed molded product while avoiding the feeder holes of the mold and the mold release pin marks. The test piece had a skin layer (the surface that was in direct contact with the mold) on both sides in the width direction. The cut out test piece was left to stand at 60°C for 48 hours, and further left to stand at 23°C for 24 hours. Thereafter, using a thermal conductivity measuring device (HC-074 manufactured by Hideko Seiki Co., Ltd.), the test piece was measured at an average temperature of 23°C and a temperature difference of 20°C using the heat flow meter method in accordance with JIS A1412-2:1999. The thermal conductivity was measured.

(Flame retardancy of foam molded product)
The foamed molded article was left to stand at 60°C for 48 hours, and then further left to stand at 23°C for 24 hours. Thereafter, the foamed molded product was evaluated in accordance with JIS A9511 (foamed plastic heat insulating material) measurement method A, and a test with an extinguishing time of 3 seconds or less was evaluated as a pass (◯).

[Example 1]
(Styrenic resin particle adjustment process)
Weighed 100 parts by weight of styrene/(meth)acrylic acid copolymer (A1), 4 parts by weight of graphite (B1), and 2 parts by weight of flame retardant (C), and mixed them into 10 parts by weight using a blender (manufactured by Showa Kagaku Kikai Co., Ltd.). The mixture was blended for a minute to obtain a styrenic resin composition. The styrenic resin composition was supplied to a co-directional twin-screw extruder (TEM26 manufactured by Toshiba Machine Co., Ltd.), and melt-kneaded at a cylinder temperature of 230°C (resin temperature when passing through the die: 240°C) and a screw rotation speed of 200 rpm. A melt-kneaded product was obtained (melt-kneading step).
The melt-kneaded product was extruded at a discharge rate of 20 kg/hour through a discharge hole (pore diameter: 1.20 mm) of a die attached to the tip of the extruder (extrusion step). In the extrusion process, the residence time of the styrenic resin composition in the extruder was 7 minutes. Note that the number of discharge holes in the die and the distance between the discharge holes were as shown in Table 1. Subsequently, the strand extruded from the discharge hole was passed through a water bath at 30°C, and the strand was cooled to 30°C and solidified (cooling step). Next, using a pelletizer, the strand was pulled at a pulling speed of 19 m/min and cut at a rotating blade speed of 98 rpm to obtain styrene resin particles. The obtained styrene resin particles had a particle weight of 0.9 mg per particle and a L1/D1 of 2.0.

(Blowing agent impregnation process)
100 parts by weight of the obtained styrene resin particles, 200 parts by weight of deionized water, 1.0 parts by weight of tricalcium phosphate as a dispersant, 0.03 parts by weight of sodium dodecylbenzenesulfonate as a dispersion aid, and 3 parts by weight of sodium chloride. 0 parts by weight was put into a 6 L autoclave (made of pressure-resistant glass) equipped with a stirring device, and the autoclave was sealed. Next, 7.0 parts by weight of pentane (D1) as a foaming agent was charged into the autoclave. Subsequently, the temperature inside the autoclave was raised to 118°C, and then held at 118°C for 8 hours. Thereafter, the temperature inside the autoclave was cooled to room temperature (25±2° C.), and the foamable resin particles impregnated with the foaming agent were taken out from the autoclave. The obtained expandable resin particles were pickled with hydrochloric acid and then washed with water. Next, the foamable resin particles were dehydrated using a centrifugal separator (manufactured by Matsumoto Kikai), and then dried using a flash dryer (manufactured by Hiraiwa Iron Works) to obtain foamable styrenic resin particles. The obtained expandable styrenic resin particles had L2/D2 of 1.11.

(Manufacture of pre-expanded particles)
100 parts by weight of the obtained expandable styrenic resin particles, 0.2 parts by weight of zinc stearate, and 0.07 parts by weight of castor wax were placed in a pressurized pre-foaming machine equipped with a stirrer (BHP-110 manufactured by Daikai Kogyo Co., Ltd.). The department was introduced. Next, the foamable styrenic resin particles are foamed (primary foaming) by heating the foamable styrene resin particles in the foaming machine using steam as a heating medium and blowing vapor pressure to 0.09 MPa, and the bulk ratio ( Expanded particles with an apparent magnification of 50 times were obtained. The obtained styrene foam particles had a L3/D3 of 1.11.

(Manufacture of foam molded product)
A molding machine (KR-57 manufactured by Daisen Co., Ltd.) equipped with a flat mold having a size of 450 mm in length x 300 mm in width x 250 mm in thickness was used. The mold was filled with foamed particles expanded 50 times by the method described above. In-mold foam molding was performed using steam (steam) as a heating medium to produce a foam molded product. The molding conditions were as follows: blowing steam pressure 0.08 MPa, cracking 1 mm, mold heating for 2 seconds, heating on one side for 6 seconds, heating on the other side for 4 seconds, heating on both sides for 8 seconds, reheating for 5 seconds, water cooling for 5 seconds, Air cooling for 5 seconds and vacuum cooling for 120 seconds. After storing the obtained foamed molded product at 10° C., various evaluations were performed. The density of the foamed molded product was 0.20 kg/m ³ . The evaluation results are shown in Table 1.

[Example 2]
Styrenic resin particles, expandable styrenic resin particles, styrene foam particles, and styrene foam molding were performed by the same operation as in Example 1 except that the temperature setting of the die was changed to 250°C (resin temperature 260°C). A body was prepared and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Example 3]
Styrenic resin particles, expandable styrenic resin particles, and styrene resin particles were produced in the same manner as in Example 1, except that the diameter of the discharge hole of the extruder die was 0.09 cm and the discharge rate was changed to 12 kg/hour. Expanded particles and styrene foam molded articles were produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Examples 4 to 7]
Styrenic resin particles, expandable styrenic resin particles, styrenic foamed particles, and styrene foamed particles were prepared in the same manner as in Example 1, except that the types of styrene resin and graphite used were changed to the formulations shown in Table 1. A molded body was produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Comparative example 1]
The same operations as in Example 1 were carried out, except that the type of styrene resin used was the formulation shown in Table 1, the temperature setting of the die was 210°C (resin temperature 220°C), and the discharge rate was changed to 30kg/hour. Styrenic resin particles, expandable styrenic resin particles, styrene foamed particles, and styrene foam molded articles were produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Comparative example 2]
The same operations as in Example 1 were carried out, except that the type of styrene resin used was the recipe shown in Table 1, the temperature setting of the die was 250 °C (resin temperature 260 °C), and the discharge rate was changed to 10 kg/hour. Styrenic resin particles, expandable styrenic resin particles, styrene foamed particles, and styrene foam molded articles were produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Comparative example 3]
Styrenic resin particles, expandable styrenic resin particles, Styrenic foam particles and styrene foam molded articles were produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Comparative example 4]
Styrenic resin particles, expandable styrenic resin particles, and styrene were prepared in the same manner as in Example 1, except that the type of styrene resin used was the formulation shown in Table 1, and the strand pulling speed by the pelletizer was changed to 30 m/min. The foamed particles and the styrene foam molded article were produced, and the same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Comparative example 5]
Styrenic resin particles, expandable styrene resin particles, and styrene were prepared in the same manner as in Example 1, except that the type of styrene resin used was the formulation shown in Table 1 and the temperature setting of the die was changed to 210°C. foamed particles were produced. In the in-mold molding, a styrene foam molded product was produced by the same operation as in Example 1 except that the blown steam pressure was changed to 0.08 MPa. The same evaluation as in Example 1 was performed. The evaluation results are shown in Table 1.

[Consideration]
From Table 1, the following can be seen:
(1) From Examples 1 to 7, the resin composition contains a copolymer of styrene and (meth)acrylic acid, the shear stress of the melt-kneaded product when passing through the die is within the range of 30 kPa to 90 kPa, and L1 If the expandable styrenic resin particles are obtained by a manufacturing method in which /D1 is within the range of 1.30 to 2.90, a foamed molded product with excellent dimensional stability at 95°C and high moldability can be obtained. You can see what you can get.

(2) In Comparative Examples 1 and 2, the shear stress is outside the range of 30 kPa to 90 kPa. It can be seen that if the expandable styrenic resin particles obtained by such a manufacturing method are used, a foamed molded article with more shrinkage and melting on the surface and poorer appearance than in Example 1 can be obtained.

(3) In Comparative Examples 3 and 4, the ratio of L1/D1 is outside the range of 1.30 to 2.90. It can be seen that if the expandable styrenic resin particles obtained by such a manufacturing method are used, a foamed molded article with more shrinkage and melting on the surface and poorer appearance than in Example 1 can be obtained.

(4) In Comparative Example 5, the styrenic resin does not contain a styrene/(meth)acrylic acid copolymer. If expandable styrenic resin particles obtained by such a manufacturing method are used, the surface of the foamed molded product will shrink and melt more than in Example 1, and the appearance will be poor, and the dimensions at 95°C will decrease. It can be seen that a foamed molded article with a poor rate of change can be obtained.

INDUSTRIAL APPLICABILITY The present invention can be suitably used in the field of heat insulating materials (for example, hot water storage tanks, roof heat insulating materials, piping heat insulating materials, constant temperature storage containers, constant temperature transportation containers, etc.).

Claims (8)

including a styrenic resin particle preparation step and a blowing agent impregnation step,
The styrenic resin particle preparation step includes:
A melt-kneading step of melt-kneading a styrenic resin composition containing a styrene-based resin containing a styrene/(meth)acrylic acid copolymer using an extruder;
an extrusion step of extruding the melt-kneaded material obtained in the melt-kneading step from a discharge hole of a die provided at the tip of the extruder in the extrusion direction;
A step of pulling and cutting the melt-kneaded material extruded from the discharge hole in the extrusion step to obtain styrenic resin particles,
The blowing agent impregnation step includes:
a step of impregnating the styrenic resin particles with a hydrocarbon blowing agent in an aqueous suspension;
In the extrusion step,
The shear stress of the melt-kneaded material when passing through the die is 30 kPa to 90 kPa,
A method for producing expandable styrenic resin particles, wherein the ratio (L1/D1) of the length (L1) in the tensile direction to the cross-sectional length (D1) of the styrenic resin particles is 1.30 to 2.90. . The styrenic resin composition contains graphite,
The method for producing expandable styrenic resin particles according to claim 1, wherein the graphite content is 1 to 10 parts by weight based on 100 parts by weight of the styrenic resin. The styrenic resin composition contains a flame retardant,
The method for producing expandable styrenic resin particles according to claim 1, wherein the content of the flame retardant is 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the styrenic resin. The method for producing expandable styrenic resin particles according to claim 3, wherein the flame retardant contains a bromine-containing organic compound having a 2,3-dibromo-2-alkylpropyl group. The method for producing expandable styrenic resin particles according to claim 1, wherein the hydrocarbon blowing agent includes any one selected from the group consisting of normal pentane, isopentane, neopentane, and cyclopentane. According to claim 1, the ratio (L2/D2) of the length of the long axis (L2) to the length (D2) of the short axis of the expandable styrenic resin particles is 1.00 to 1.20. A method for producing expandable styrenic resin particles. The method for producing expandable styrenic resin particles according to claim 2, wherein the graphite has a volume average particle diameter of 1 μm to 5 μm. The method for producing expandable styrenic resin particles according to any one of claims 1 to 7, wherein the styrenic resin particles have a weight average molecular weight Mw of 150,000 to 300,000.