JP7553430B2 - Expandable resin particles, pre-expanded particles, and foamed molded article - Google Patents

Description

The present invention relates to expandable resin particles and pre-expanded particles, as well as foamed molded articles, which have a low content of volatile organic compounds and can suppress the amount of volatile organic compounds emitted.

Expandable polystyrene resin particles are well known as expandable resin particles. Expandable polystyrene resin particles are widely used because they can be easily used to produce molded articles by in-mold foaming and are inexpensive.

Although expandable polystyrene resin particles are lightweight and have excellent heat insulating properties, the problem is that they emit a large amount of volatile organic compounds (hereinafter sometimes referred to as "VOCs," an acronym for Volatile Organic Compounds) per unit time. In particular, with expandable polystyrene resin particles, it is difficult for the VOC components styrene and ethylbenzene to meet the strict emission standards set by the automotive and building materials industries, making it necessary to take measures such as drying the foamed molded body for several days, which is one of the reasons for the increased costs.

In order to solve the above problems, Patent Documents 1 and 2 disclose that expandable polystyrene resin particles having a low amount of residual styrene in the resin particles can be provided by improving the manufacturing method, such as by increasing the amount of initiator added and/or adding a flame retardant later.

Furthermore, Patent Document 3 discloses heat-resistant styrene-based resin particles of a styrene/acrylonitrile/alpha-methylstyrene system produced using the initiator described in Patent Document 1 or an initiator similar to said initiator.

Patent Publication 2017-052894 Patent Publication 2010-195936 Patent Publication 2016-164213

In terms of reducing VOC emissions, the above-mentioned conventional technology was an improvement over typical expandable resin particles at the technological level at the time the conventional technology was developed. However, there is high interest in reducing VOC emissions in the market, and the above-mentioned conventional technology left room for further improvement in terms of VOC (particularly styrene and ethylbenzene) emissions.

One embodiment of the present invention has been developed in consideration of the above problems, and its object is to provide novel expandable resin particles having a low VOC content and low emission rate, and novel foamed molded products having a low VOC emission rate and low emission rate.

The present inventors have completed the present invention as a result of intensive research. That is, expandable resin particles according to one embodiment of the present invention are expandable resin particles containing a base resin containing styrene units and acrylonitrile units as constituent units, and a blowing agent, and the expandable resin particles are expanded to have an infrared absorption spectrum of a surface of the expanded particles having an absorbance ratio D2230/D1600 of 0.80 or more at wavelengths of 2230 cm ⁻¹ and 1600 cm ⁻¹ .

In addition, a method for producing expandable resin particles according to one embodiment of the present invention is a method for producing expandable resin particles, which includes a copolymerization step of copolymerizing monomers including a styrene monomer and an acrylonitrile monomer, and a blowing agent impregnation step of impregnating the resulting copolymer with a blowing agent, the copolymerization step including a first polymerization step and a second polymerization step successively having different polymerization temperatures, the first polymerization step using a polymerization initiator including a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or more and 94°C or less, the polymerization initiator (X) including benzoyl peroxide, and the TH/TQ ratio of the expandable resin particles being less than 1.20.

One embodiment of the present invention can provide expandable resin particles and pre-expanded particles (expanded particles), as well as foamed molded articles, that have a low content of volatile organic compounds (VOCs) and can suppress the amount of volatile organic compounds (VOCs) emitted.

1 is a graph showing an example of a GPC measurement chart of expandable resin particles.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. In addition, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention.

Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, "A to B" indicating a numerical range means "A or more (including A and greater than A) and B or less (including B and smaller than B)."

<Expandable Resin Particles>
The expandable resin particles according to one embodiment of the present invention are characterized in that the expandable resin particles contain a base resin containing styrene units and acrylonitrile units as constituent units, and a blowing agent, and that the surface of the expanded particles obtained by expanding the expandable resin particles has an absorbance ratio D2230/D1600 of 0.80 or more at wavelengths of 2230 cm ^-1 and 1600 cm ^-1 in an infrared absorption spectrum. The infrared absorption spectrum according to one embodiment of the present invention can be obtained by ATR-FTIR analysis.

In this specification, "infrared absorption spectrum of the surface of expanded beads" refers to "infrared absorption spectrum obtained by Fourier transform infrared spectroscopy using the total reflectance measurement method on the surface of expanded beads." In this specification, "Fourier transform infrared spectroscopy using the total reflectance measurement method" is sometimes referred to as "ATR-FTIR analysis."

In one embodiment of the present invention, the expanded particles used in measuring the infrared absorption spectrum are obtained by processing the expandable resin particles according to one embodiment of the present invention in the following order of (1) to (3): (1) The expandable resin particles are placed into a pressurized foaming machine; (2) Next, steam is blown into the foaming machine at an inlet steam pressure of 0.09 MPa to 0.10 MPa, and the pressure inside the foaming machine is adjusted to a range of 0.01 MPa to 0.02 MPa, thereby setting the temperature inside the foaming machine to 100°C to 104°C, thereby expanding the expanded particles to a magnification of 40 times; (3) Next, the obtained expanded particles are cured at 25°C for 12 to 24 hours, to obtain the expanded particles used in measuring the infrared absorption spectrum.

The expandable resin particles according to one embodiment of the present invention have the above-mentioned configuration, and thus have the advantage of being able to provide a foamed molded article with low VOC emission. This allows the VOC emission standards required in the automotive and building materials fields to be met. In other words, the expandable resin particles according to one embodiment of the present invention have the advantage of being able to provide a foamed molded article with high productivity.

Here, the expandable resin particles according to one embodiment of the present invention can be used to produce expanded beads by a known method, and then the expanded beads can be used to perform expansion molding by a known method to provide a foamed molded article.

In this specification, the "expandable resin particles according to one embodiment of the present invention" may be referred to simply as "the present expandable resin particles." In other words, the term "the present expandable resin particles" intends one embodiment of the expandable resin particles of the present invention.

In a broad sense, VOC means "organic compounds that are gaseous when discharged into the atmosphere from an exhaust outlet or dispersed," as defined in the Air Pollution Control Law of Japan. Compounds that should be regulated as VOCs are designated in each technical field. For example, the Ministry of Health, Labor and Welfare of Japan has established indoor concentration guideline values for the following substances: formaldehyde, acetaldehyde, toluene, ethylbenzene, xylene, styrene, nonanal, tetradecane, di-n-butyl phthalate, di-2-ethylhexyl phthalate, p-dichlorobenzene, chlorpyrifos, diazinon, and fenobucarb. The Japan Automobile Manufacturers Association has also set concentration restrictions for the following substances in automobile cabins: formaldehyde, acetaldehyde, toluene, ethylbenzene, xylene, styrene, tetradecane, di-n-butyl phthalate, and di-2-ethylhexyl phthalate.

In this specification, VOC refers to "compounds that may be contained in expandable resin particles or foamed molded articles, which (a) are in the form of gas when emitted into the atmosphere or dispersed, and (b) are organic compounds for which the Ministry of Health, Labor and Welfare of Japan has established indoor concentration guideline values." Specifically, VOC refers to styrene and ethylbenzene.

The base resin contained in the expandable resin particles contains styrene units and acrylonitrile units as structural units. In this specification, a "styrene unit" is a structural unit derived from a styrene monomer, and an "acrylonitrile unit" is a structural unit derived from an "acrylonitrile monomer."

In the base resin contained in the expandable resin particles, it is preferable that (a) the content of styrene units is 55 parts by weight or more and 80 parts by weight or less, the content of acrylonitrile units is 20 parts by weight or more and 45 parts by weight or less, and (b) the total content of styrene units and acrylonitrile units is 100 parts by weight.

The content of styrene units is preferably 55 parts by weight or more and 80 parts by weight or less, more preferably 60 parts by weight or more and 80 parts by weight or less, and more preferably 65 parts by weight or more and 75 parts by weight or less. When the content of styrene units is (a) 55 parts by weight or more, the expandable resin particles have excellent moldability, and when it is (b) 80 parts by weight or less, the expandable resin particles can provide a foamed molded article having excellent heat resistance.

The content of acrylonitrile units is preferably 20 parts by weight or more and 45 parts by weight or less, more preferably 20 parts by weight or more and 40 parts by weight or less, more preferably 25 parts by weight or more and 35 parts by weight or less. When the content of acrylonitrile units is 20 parts by weight or more, the expandable resin particles can provide a foamed molded article that (a) has excellent gas barrier properties, so that the amount of styrene released as a VOC is small, and (b) has excellent heat resistance. When the content of acrylonitrile units is 45 parts by weight or less, the expandable resin particles have excellent moldability and the polymerization stability is increased during the production of the expandable resin particles.

The expandable resin particles according to one embodiment of the present invention are characterized in that the absorbance D2230 at 2230 cm ^-1 and the absorbance D1600 at 1600 cm- ¹ are determined in an infrared absorption spectrum obtained by ATR-FTIR analysis of the surface of the expanded particles obtained by expanding the expandable resin particles, and the absorbance ratio D2230/D1600 is 0.8 or more. The absorbance ratio D2230/D1600 is preferably in the range of 1.2 to 2.5. By having the absorbance ratio D2230/D1600 be 0.8 or more, the VOC components emitted from the foamed molded article can be significantly suppressed.

In this specification, "ATR-FTIR analysis" refers to "Fourier transform infrared spectroscopy using attenuated total reflection measurement."

The base resin contained in the expandable resin particles may further contain alpha-methylstyrene units as a constituent unit. By adding alpha-methylstyrene, the glass transition temperature of the base resin increases, so that the expandable resin particles can provide a foamed molded article having sufficient heat resistance.

In this specification, an "alpha-methylstyrene unit" is a structural unit derived from alpha-methylstyrene monomer.

The content of alpha-methylstyrene units is preferably 3 parts by weight or more and 15 parts by weight or less, more preferably 4 parts by weight or more and 10 parts by weight or less, and even more preferably 4 parts by weight or more and 7 parts by weight or less, when the total content of styrene units, acrylonitrile units, and alpha-methylstyrene units in the base resin is 100 parts by weight. Alpha-methylstyrene has a methyl group at the alpha position, which causes large steric hindrance and therefore has the characteristic of poor reactivity. In addition, when alpha-methylstyrene is contained in the base resin, the alpha-methylstyrene moiety in the base resin is easily decomposed. Therefore, when the content of alpha-methylstyrene units is 3 parts by weight or more, the polymerization rate does not become too fast during the production of expandable resin particles, making it easier to control the polymerization. Furthermore, when the content of alpha-methylstyrene units is 15 parts by weight or less, (a) the resulting base resin is less likely to decompose, and the expandable resin particles can provide a foamed molded article with excellent flame retardancy, (b) the reactivity during the polymerization reaction is not deteriorated, and the weight average molecular weight of the resulting base resin does not become too low, and (c) the expandable resin particles have a low styrene content as a VOC.

In the base resin contained in the expandable resin particles, it is preferable that (a) (a-1) the content of styrene units is 55 parts by weight or more and 80 parts by weight or less, the content of acrylonitrile units is 20 parts by weight or more and 45 parts by weight or less, the content of alpha-methylstyrene units is 0 parts by weight or more and 15 parts by weight or less, and (a-2) the total content of styrene units, acrylonitrile units and alpha-methylstyrene units is 100 parts by weight, and (b) (b-1) the content of styrene units is 60 parts by weight or more and 80 parts by weight or less, the content of acrylonitrile units is 20 parts by weight or more and 40 parts by weight or less, and the content of alpha-methylstyrene units is 0 parts by weight or more and 15 parts by weight or less. It is preferred that the content of styrene units is 0 parts by weight or more and 15 parts by weight or less, and that the total content of (b-2) styrene units, acrylonitrile units and alpha-methylstyrene units is 100 parts by weight, and more preferably that (c)(c-1) the content of styrene units is 60 parts by weight or more and 75 parts by weight or less, the content of acrylonitrile units is 21 parts by weight or more and 27 parts by weight or less, the content of alpha-methylstyrene units is 3 parts by weight or more and 15 parts by weight or less, and that the total content of (c-2) styrene units, acrylonitrile units and alpha-methylstyrene units is 100 parts by weight.

The foaming agents contained in the expandable resin particles include, but are not limited to, volatile foaming agents such as (a) aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane cyclohexane, and (b) fluorohydrocarbons with zero ozone depletion potential such as difluoroethane and tetrafluoroethane. The above-mentioned foaming agents may be used alone or in combination of two or more.

The content of the blowing agent in the expandable resin particles is preferably 2 parts by weight or more and 7 parts by weight or less, more preferably 3 parts by weight or more and 6 parts by weight or less, and even more preferably 4 parts by weight or more and 5 parts by weight or less, per 100 parts by weight of the expandable resin particles. According to the above configuration, (a) it is possible to produce expanded beads having an expansion ratio of 40 times or more using the expandable resin particles, and (b) the expandable resin particles can provide a foamed molded article having excellent heat resistance and flame retardancy.

In addition to the base resin and the blowing agent, the expandable resin particles may optionally contain other additives. Examples of the other additives include plasticizers, cell regulators, flame retardants, flame retardant assistants, heat radiation inhibitors, pigments, dyes, and antistatic agents.

Examples of the plasticizer include high-boiling plasticizers having a boiling point of 200°C or higher. Examples of such plasticizers include fatty acid glycerides such as (a) stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, and stearic acid monoglyceride, (b) vegetable oils such as coconut oil, palm oil, and palm kernel oil, (c) aliphatic esters such as dioctyl adipate and dibutyl sebacate, and (d) organic hydrocarbons such as liquid paraffin and cyclohexane. When the expandable resin particles contain a large amount of the substances listed as plasticizers, the heat resistance of the foamed molded product that the expandable resin particles can provide tends to deteriorate. Therefore, the content of the plasticizer in the expandable resin particles can be appropriately set so that the foamed molded product that the expandable resin particles can provide has the desired heat resistance.

The expandable resin particles may contain a bubble regulator to adjust the bubble diameter in the foamed molded product that the expandable resin particles can provide. Examples of the bubble regulator include (a) aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide, and (b) polyethylene wax. The content of the bubble regulator in the expandable resin particles is preferably less than 0.1 parts by weight per 100 parts by weight of the expandable resin particles. According to the above configuration, in the foamed molded product that the expandable resin particles can provide, deterioration of heat resistance and increase in VOC emission due to fine bubbles do not occur.

The expandable resin particles may contain a flame retardant so that the foamed molded article that can be provided by the expandable resin particles is flame retardant. The flame retardant is preferably a bromine-based flame retardant. Examples of the bromine-based flame retardant include 2,2-bis[4'-(2'',3''-dibromo-2''-methylpropyloxy)-,3',5'-dibromophenyl]-propane, hexabromocyclododecane, tetrabromocyclooctane, brominated polystyrene, and brominated butadiene-styrene block copolymer. Since the foamed molded article that can be provided by the expandable resin particles is easily flame retardant, the expandable resin particles preferably contain 2,2-bis[4'-(2'',3''-dibromo-2''-methylpropyloxy)-,3',5'-dibromophenyl]-propane as a flame retardant. In addition, 2,2-bis[4'-(2'',3''-dibromo-2''-methylpropyloxy)-3',5'-dibromophenyl]-propane is also called tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether.

The content of the flame retardant in the expandable resin particles is preferably 1.5 parts by weight or more and 3.0 parts by weight or less, and more preferably 1.8 parts by weight or more and 2.5 parts by weight or less, per 100 parts by weight of the expandable resin particles. When the content of the flame retardant in the expandable resin particles is (a) 1.5 parts by weight or more, per 100 parts by weight of the expandable resin particles, the foamed molded product that can be provided by the expandable resin particles can have sufficient flame retardant performance, and when (b) 3.0 parts by weight or less, the expandable resin particles have a low VOC content and excellent moldability.

When the expandable resin particles contain a flame retardant, it is preferable that the expandable resin particles further contain a flame retardant assistant. A radical generator such as a peroxide can be used as the flame retardant assistant. Examples of such radical generators include dicumyl peroxide, t-butyl peroxybenzoate, 2,3-dimethyl-2,3-diphenylbutane, and 3,4-dialkyl-3,4-diphenylhexane. Since it has little effect on the polymerization reaction and can provide a foamed molded product with good flame retardant performance, it is more preferable that the expandable resin particles contain a peroxide having a 10-hour half-life temperature of 130°C or more and 150°C or less as a flame retardant assistant, and it is particularly preferable that the expandable resin particles contain dicumyl peroxide.

The content of the flame retardant auxiliary in the expandable resin particles is preferably 0.3 parts by weight or more and 1.5 parts by weight or less per 100 parts by weight of the expandable resin particles. When the content of the flame retardant in the expandable resin particles is (a) 0.3 parts by weight or more per 100 parts by weight of the expandable resin particles, the foamed molded product that can be provided by the expandable resin particles has sufficient flame retardant performance, and when (b) 1.5 parts by weight or less, the foamed molded product that can be provided by the expandable resin particles has sufficient heat resistance.

The content of styrene in the expandable resin particles is preferably less than 20 ppm, and the content of ethylbenzene is preferably 130 ppm or less. The content of styrene in the expandable resin particles is more preferably 10 ppm or less, and even more preferably 5 ppm or less. Particularly preferably 0 ppm or less. 0 ppm means below the detection limit in gas chromatography. The content of ethylbenzene in the expandable resin particles is more preferably 100 ppm or less, and even more preferably 70 ppm or less. According to the above configuration, the foamed molded product that can be provided by the expandable resin particles can reduce the amount of VOC released into the environment, and as a result, it is possible to suppress adverse effects on the human body. Here, the content of styrene in the expandable resin particles means the content of styrene monomer in the expandable resin particles, and the content of ethylbenzene in the expandable resin particles means the content of ethylbenzene monomer in the expandable resin particles. As a method for measuring the content of styrene and ethylbenzene in the expandable resin particles (i.e., VOC content), for example, a measurement method using gas chromatography can be mentioned. A specific method will be described in the Examples below.

In the present expandable resin particles, the weight average molecular weight of the base resin is preferably 150,000 or more and 220,000 or less, more preferably 170,000 or more and 200,000 or less. When the weight average molecular weight of the base resin is (a) 150,000 or more, the foamed molded product that can be provided by the expandable resin particles has sufficient strength, flame retardancy, and heat resistance, and when it is (b) 220,000 or less, it has sufficient foaming power and the moldability of the expandable resin particles is good. For example, a measurement method using gel permeation chromatography can be used to measure the weight average molecular weight of the base resin.

The expandable resin particles preferably have a weight average molecular weight of 150,000 or more and 220,000 or less, more preferably 170,000 or more and 200,000 or less. When the weight average molecular weight of the expandable resin particles is (a) 150,000 or more, the foamed molded product that can be provided by the expandable resin particles obtained has sufficient strength, flame retardancy, and heat resistance, and when it is (b) 220,000 or less, it has sufficient foaming power and the moldability of the expandable resin particles is good. For example, a measurement method using gel permeation chromatography can be used to measure the weight average molecular weight of the expandable resin particles.

(TH/TQ ratio of expandable resin particles)
The TH/TQ ratio of the present expandable resin particles will be described. The expandable resin particles are subjected to GPC measurement using gel permeation chromatography to obtain a GPC measurement chart. Here, the GPC measurement chart is a relationship chart between molecular weight and differential distribution value, and is obtained as a graph with the horizontal axis representing molecular weight and the vertical axis representing differential distribution value. Here, the horizontal axis is represented in logarithm (Log). An example of a GPC measurement chart of expandable resin particles is shown in FIG. 1.

FIG. 1 is a diagram showing an example of a GPC measurement chart of expandable resin particles. The point where the integral distribution value on the GPC curve of the GPC measurement chart is the highest is the peak top, and as shown in FIG. 1, it is set to point P. Next, a line _L1 is drawn that passes through point P (peak top) and is perpendicular to the horizontal axis of the graph. The intersection point between the line _L1 and the GPC curve is point P, and the intersection point between the line _L1 and the horizontal axis of the graph is point S. For the line segment PS, the point that is 2/3 the length of the line segment PS from point P is set to point T. That is, the length of the line segment ST is twice the length of the line segment PT. Next, a line _L2 is drawn that passes through point T and is parallel to the horizontal axis of the graph. Of the two intersection points between the line _L2 and the GPC curve, the intersection point on the left side (low molecular weight side) of the line L1 is set to point _Q , and the intersection point on the right side (high molecular weight side) of the line _L1 is set to point H. The ratio of the length of the line segment TQ to the length of the line segment TH is set to the TH/TQ ratio. The larger the TH/TQ ratio, the more the expandable resin particles contain high molecular weight components. In the production of expandable resin particles, the composition of the base resin does not change, and the blowing agent does not affect the TH/TQ ratio, so the TH/TQ ratio of the expandable resin particles can also be said to be the TH/TQ ratio of the base resin. In other words, the TH/TQ ratio obtained by analyzing the base resin, which is the raw material of the expandable resin particles, can be regarded as the TH/TQ ratio of the expandable resin particles. The conditions for GPC measurement of the expandable resin particles using gel permeation chromatography will be described in detail in the following examples.

The TH/TQ ratio of the expandable resin particles may be less than 1.20, 1.19 or less, 1.18 or less, 1.17 or less, 1.16 or less, 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, or less than 1.10. The low TH/TQ ratio of the expandable resin particles is a characteristic that appears when a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or more and 94°C or less is used in the copolymerization step (preparation step of the base resin) in the production of the expandable resin particles. In other words, the expandable resin particles produced using a polymerization initiator containing a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or more and 94°C or less may have a TH/TQ ratio within the above-mentioned range. That is, the expandable resin particles produced by the production method described in the section <Production method of expandable resin particles> described later can have a TH/TQ ratio within the above-mentioned range. In addition, when benzoyl peroxide (also known as dibenzoyl peroxide), ditoluyl peroxide, toluylbenzoyl peroxide, or the like is used as the polymerization initiator (X) described later, expandable resin particles having a lower TH/TQ ratio can be obtained compared to when di-t-butylperoxyhexahydroterephthalate is used as the polymerization initiator (X). It can also be said that expandable resin particles containing a base resin containing an acrylonitrile unit as a constituent unit and having a TH/TQ ratio of less than 1.20 tend to have a low VOC content. It can also be said that expandable resin particles containing a base resin containing an acrylonitrile unit as a constituent unit and having a TH/TQ ratio of less than 1.20 tend to provide a molded product with a low VOC emission amount. Further, expandable resin particles having a TH/TQ ratio of less than 1.20 have the advantage that they can be easily expanded, that is, can be easily foamed.

The TH/TQ ratio of the expandable resin particles is preferably 0.90 or more, and more preferably 1.00 or more. Expandable resin particles having a TH/TQ ratio of 0.90 or more have the advantage of being able to provide a foamed molded article with excellent heat resistance.

In the production of expandable resin particles, the composition of the base resin does not change. In addition, in the expanded beads produced using the expandable resin particles, the structure of the expandable resin particles changes, but the composition of the expandable resin particles does not change. In addition, in the expanded beads produced using the expandable resin particles, and the expanded molded body produced using the expanded beads, the structure of the expanded particles changes, but the composition of the expanded particles does not change. Therefore, the type of structural unit and the content of each structural unit, and the weight average molecular weight obtained by analyzing the expandable resin particles, the expanded particles, or the expanded molded body can be regarded as the type of structural unit and the content of each structural unit contained in the base resin, which is the raw material thereof, and the weight average molecular weight of the base resin, respectively. In addition, the TH/TQ ratio obtained by analyzing the expanded particles or the expanded molded body can be regarded as the TH/TQ ratio of the expandable resin particles, which are the raw material thereof.

The weight average molecular weight of the expandable resin particles, expanded particles, or expanded molded article can be obtained by measuring the expandable resin particles, expanded particles, or expanded molded article using gel permeation chromatography. The TH/TQ ratio of the base resin, expanded particles, or expanded molded article can be calculated in the same manner as the TH/TQ ratio of the expandable resin particles, except that the base resin, expanded particles, or expanded molded article is subjected to GPC measurement using gel permeation chromatography to obtain a GPC measurement chart.

<Method of producing expandable resin particles>
A method for producing expandable resin particles according to one embodiment of the present invention includes a copolymerization step of copolymerizing monomers including a styrene monomer and an acrylonitrile monomer, and a blowing agent impregnation step of impregnating the obtained copolymer with a blowing agent, and the copolymerization step includes a first polymerization step and a second polymerization step successively performed at different polymerization temperatures.

In this specification, the "manufacturing method for expandable resin particles according to one embodiment of the present invention" may be referred to simply as "the present manufacturing method." In other words, the term "the present manufacturing method" intends one embodiment of the manufacturing method for expandable resin particles in the present invention. Note that the "copolymer" in the present manufacturing method corresponds to the "base resin" contained in the expandable resin particles described in the <Expandable Resin Particles> section.

Each step of the present manufacturing method will be described below, but the description in the section <Expandable Resin Particles> will be used as appropriate for matters other than those detailed below. Furthermore, the present expandable resin particles, i.e., the expandable resin particles described in the section <Expandable Resin Particles>, are preferably manufactured by the present manufacturing method, but may be manufactured by methods other than the present manufacturing method. In other words, the manufacturing method of the present expandable resin particles is not limited to the aspects of the present manufacturing method described below.

Styrene monomer may contain a small amount of ethylbenzene monomer used in the manufacturing process. The styrene monomer used in this manufacturing method preferably has a lower content of ethylbenzene monomer in the styrene monomer, for example, preferably 130 ppm or less, more preferably 100 ppm or less, even more preferably 85 ppm or less, and particularly preferably 70 ppm or less. By using styrene monomer with a low ethylbenzene monomer content, the expandable resin particles obtained by this manufacturing method have the advantage of being able to provide a foamed molded product with even less ethylbenzene emission.

In the copolymerization step of the present production method, the method for copolymerizing the monomers including the styrene monomer and the acrylonitrile monomer is not particularly limited, and a conventionally known polymerization method can be used. The copolymerization step is preferably a suspension polymerization method in which polymerization is performed in an aqueous suspension.

In this specification, the term "aqueous suspension" refers to a liquid (aqueous solution) in which resin particles, expandable resin particles, and/or monomer droplets are dispersed in water or an aqueous solution using a stirrer or the like. In the aqueous suspension, surfactants and monomers may be dissolved, or water-insoluble dispersants, polymerization initiators, crosslinking agents, plasticizers, bubble regulators, flame retardants, and flame retardant assistants may be dispersed together with the monomers. The polymerization initiators, crosslinking agents, chain transfer agents, and polymerization regulators used in the copolymerization process constitute part of the resulting copolymer.

In the copolymerization process, the weight ratio of resin to water in the aqueous suspension is preferably 1.0/0.6 to 1.0/3.0, expressed as the ratio of the weight of the resulting copolymer to the weight of water.

Examples of dispersants that can be used in the copolymerization process include (a) poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin, and (b) water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone. When using poorly water-soluble inorganic salts as dispersants, it is preferable to use an anionic surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzene sulfonate in combination with the poorly water-soluble inorganic salt, as this increases the dispersion stability. These dispersants may be further added to the aqueous suspension at any point in the copolymerization process as necessary.

The amount of dispersant used depends on the type of dispersant. When a poorly water-soluble inorganic salt is used as the dispersant, the amount of dispersant used is preferably 0.1 parts by weight to 1.5 parts by weight per 100 parts by weight of water. When a water-soluble polymer is used as the dispersant, the dispersant is preferably used so that the dispersant is present at 30 ppm to 100 ppm in the aqueous suspension. When an anionic surfactant is used in combination with a poorly water-soluble inorganic salt, the anionic surfactant is preferably used so that the anionic surfactant is present at 30 ppm to 100 ppm in the aqueous suspension.

In the copolymerization step of this production method, a chain transfer agent and a polymerization regulator may further be used. Examples of chain transfer agents include mercaptan compounds such as n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan. Examples of polymerization regulators include α-methylstyrene dimer. α-methylstyrene dimer also contributes to adjusting the weight average molecular weight of the copolymer, so it can also be called a chain transfer agent. The chain transfer agent functions mainly to adjust the weight average molecular weight of the copolymer. The polymerization regulator functions mainly to adjust the polymerization rate.

In the copolymerization step, it is preferable to use α-methylstyrene dimer as a chain transfer agent. According to the above configuration, (a) the polymerization rate and the weight average molecular weight of the copolymer can be easily adjusted, and (b) odors are less likely to be generated from the foamed molded article that can be provided by the expandable resin particles.

The amount of chain transfer agent and polymerization regulator used is preferably 0.6 parts by weight or more, and more preferably 1.4 parts by weight or more, per 100 parts by weight of monomer, in order to facilitate adjustment of (a) the polymerization rate and (b) the weight average molecular weight of the copolymer.

As the polymerization initiator, it is desirable to mainly use polymerization initiator (X) in the first polymerization step and to mainly use polymerization initiator (Y) in the second polymerization step.

The first polymerization step is not particularly limited in terms of the polymerization temperature and polymerization time, etc., as long as the polymerization temperature is different from that of the second polymerization step. The polymerization temperature of the first polymerization step is, for example, 85°C to 95°C, and the polymerization time of the first polymerization step is, for example, 4 hours to 7 hours.

The polymerization temperature in the first polymerization step is preferably 87°C to 93°C, more preferably 88°C to 92°C, and particularly preferably 89°C to 91°C. This configuration has the advantage that (a) expandable resin particles having a D2230/D1600 of 0.80 or more, i.e., expandable resin particles with a low VOC content (emission amount), can be easily obtained. In addition, this configuration allows the amount of decomposition of the polymerization initiator (e.g., polymerization initiator (X)) to be adjusted within an optimal range. This (a) makes it easy to adjust the polymerization rate (reaction rate), thereby improving polymerization stability, and (b) makes it easy to obtain expandable resin particles in an appropriate molecular weight range.

The polymerization time for the first polymerization step is preferably 4.5 to 6.5 hours, and more preferably 5 to 6 hours. This configuration has the advantage of being able to achieve both productivity and polymerization stability.

In the first polymerization step, it is preferable to use a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or higher and 94°C or lower.

In the first polymerization step, it is preferable to (a) use a polymerization initiator (X) having a 10-hour half-life temperature of 74° C. or more and 94° C. or less, and (b) carry out the polymerization reaction at a polymerization temperature of 85° C. or more and 95° C. or less. With the above configuration, the polymerization reaction can be appropriately controlled.

Examples of the polymerization initiator (X) in the first polymerization step include organic peroxides such as benzoyl peroxide, lauroyl peroxide, and di-t-butylperoxyhexahydroterephthalate, and (b) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. Of these polymerization initiators, it is particularly preferable to use benzoyl peroxide as the polymerization initiator (X) because it facilitates the reaction of acrylonitrile, which can impart gas barrier properties.

The above-mentioned polymerization initiator (X) may be used alone or in combination of two or more.

It is more preferable to use only polymerization initiators having a 10-hour half-life temperature of 74°C or more and less than 90°C as the polymerization initiator (X). That is, in the first polymerization step, it is more preferable to use only polymerization initiators having a 10-hour half-life temperature of 74°C or more and less than 90°C as the polymerization initiator (X) (a), and it is even more preferable to use only polymerization initiators having a 10-hour half-life temperature of 74°C or more and less than 90°C as the polymerization initiator (X) (b) (b-1) and to carry out the polymerization reaction at a polymerization temperature of 85°C or more and 95°C or less (b-2). According to the above configuration, the polymerization initiator (X) used in the first polymerization step mainly decomposes in the first polymerization step, so that the polymerization reaction can be more appropriately controlled.

In the first polymerization step, a polymerization initiator (X) is used, and the amount of the polymerization initiator (X) used is preferably 0.08 parts by weight or more and 0.25 parts by weight or less, and more preferably 0.15 parts by weight or less and 0.20 parts by weight or less, relative to 100 parts by weight of the monomer. In the first polymerization step, when the amount of the polymerization initiator (X) used is (a) 0.08 parts by weight or more relative to 100 parts by weight of the monomer, it has the advantage that the polymerization proceeds sufficiently, and when it is (b) 0.25 parts by weight or less, the polymerization reaction does not proceed rapidly, and it is easy to control the polymerization. In addition, if the amount of the weight initiator (X) used is 0.15 parts by weight or less and 0.20 parts by weight or less, the weight average molecular weight of the obtained expandable resin particles is 170,000 or more and less than 200,000, and good quality expandable resin particles are obtained.

In this manufacturing method, the weight average molecular weight of the copolymer can be adjusted by various combinations of polymerization initiators, chain transfer agents, and polymerization conditions for the first polymerization step.

The second polymerization step is carried out consecutively to the first polymerization at any time after the polymerization conversion rate of the monomer reaches 85%.

Here, the polymerization conversion rate of the monomer is calculated as follows:
Polymerization conversion rate (%) of monomer=(amount of monomer supplied to the aqueous suspension−amount of monomer remaining in the aqueous suspension)/amount of monomer supplied to the aqueous suspension×100
The above "amount of monomer supplied to the aqueous suspension - amount of monomer remaining in the aqueous suspension" can be said to be the amount of monomer contained as a structural unit in the copolymer. The "amount of monomer remaining in the aqueous suspension" can be measured, for example, by filtering the aqueous suspension with filter paper or the like and subjecting the residue (which may contain monomer) obtained on the filter paper to gas chromatography.

The polymerization temperature of the second polymerization step is different from that of the first polymerization step, and the polymerization temperature of the second polymerization step is preferably 110 to 120°C. If the polymerization temperature of the second polymerization step is (a) less than 110°C, the VOC content (particularly the styrene content) in the resulting expandable resin particles cannot be reduced, and if it is (b) more than 120°C, the internal pressure of the polymerization machine used in the copolymerization step becomes high, requiring high pressure resistance, and as a result, a heavy-duty polymerization machine is required. The polymerization temperature of the second polymerization step is preferably higher than that of the first polymerization step. According to the above configuration, the VOC content in the resulting expandable resin particles can be reduced.

The polymerization time for the second polymerization step is preferably 3 to 13 hours, more preferably 4 to 11 hours, even more preferably 5 to 9 hours, and particularly preferably 6 to 8 hours. If the polymerization time for the second polymerization step is (a) less than 3 hours, the VOC content (particularly the styrene content) in the resulting expandable resin particles cannot be reduced, and (b) if it exceeds 8 hours, the amount of decomposition of the flame retardant assistant (e.g. dicumyl peroxide) increases, so that the effect of the flame retardant assistant is not fully expressed when the foamed molded article is burned, and as a result, the flame retardancy tends to deteriorate.

The polymerization temperature in the second polymerization step is preferably 111°C to 119°C, more preferably 112°C to 118°C, even more preferably 113°C to 117°C, and particularly preferably 114°C to 116°C. This configuration has the advantage of being able to efficiently reduce VOCs at or below the upper limit of the internal pressure of the polymerization machine used.

The polymerization time for the second polymerization step is preferably 4 to 11 hours, more preferably 5 to 9 hours, and particularly preferably 6 to 8 hours. This configuration has the advantage of being able to reduce VOCs while maintaining qualities such as flame retardancy.

In the second polymerization step, it is preferable to use a polymerization initiator (Y) having a 10-hour half-life temperature of 90°C or more and 100°C or less, and it is more preferable to mainly use a polymerization initiator (Y) having a 10-hour half-life temperature of 90°C or more and 100°C or less.

Examples of the polymerization initiator (Y) include t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-amylperoxyisopropyl monocarbonate, t-amylperoxy-2-ethylhexyl monocarbonate, and 1,1-bis(t-butylperoxy)cyclohexane. These polymerization initiators (Y) may be used alone or in combination of two or more. The polymerization initiator (Y) is preferably used in the second polymerization step.

1,1-bis(t-butylperoxy)cyclohexane cleaves in two stages. The 10-hour half-life temperature when 1,1-bis(t-butylperoxy)cyclohexane before cleavage undergoes the first stage cleavage is 90°C. The 10-hour half-life temperature when the intermediate product generated after the first stage cleavage undergoes the second stage cleavage is about 5°C higher than the 10-hour half-life temperature of the first stage, reaching 95°C or higher. As for 1,1-bis(t-butylperoxy)cyclohexane, the final product generated after the second stage cleavage mainly acts in the second polymerization step. Therefore, in this specification, 1,1-bis(t-butylperoxy)cyclohexane is not considered to be a polymerization initiator (X) but is considered to be a polymerization initiator (Y).

As the polymerization initiator (Y), t-butylperoxy-2-ethylhexyl monocarbonate and t-amylperoxy-2-ethylhexyl monocarbonate are particularly preferred because they promote the reaction between styrene and acrylonitrile remaining in the expandable resin particles or aqueous suspension.

The amount of polymerization initiator (Y) used in the second polymerization step is preferably 0.25 parts by weight or more and 0.90 parts by weight or less, and more preferably 0.28 parts by weight or more and 0.60 parts by weight or less, relative to 100 parts by weight of the monomer. Within this range, the styrene and acrylonitrile remaining in the expandable resin particles or the aqueous suspension tend to react more easily, and the proportion of styrene-acrylonitrile copolymer in the surface layer of the expandable resin particles tends to increase.

The second polymerization step may be carried out in combination with the blowing agent impregnation step, i.e., in the presence of a blowing agent.

The foaming agent impregnation process begins by adding the foaming agent to the aqueous suspension, and the specific treatment temperature (also referred to as the impregnation temperature) and treatment time (also referred to as the impregnation time) are not particularly limited.

There is an inverse relationship between the strength of the bonding force between the polymer chains in the base resin contained in the expandable resin particles and the efficiency of impregnation of the blowing agent into the copolymer in the production of the expandable resin particles. The present production method can provide expandable resin particles containing a base resin having a strong bonding force between the polymer chains. Therefore, from the viewpoint of sufficiently impregnating the copolymer with the blowing agent, the impregnation temperature in the blowing agent impregnation step in the present production method is preferably 110°C to 120°C, more preferably 111°C to 119°C, even more preferably 112°C to 118°C, and particularly preferably 114°C to 116°C. From the viewpoint of sufficiently impregnating the copolymer with the blowing agent, the impregnation time in the blowing agent impregnation step in the present production method is preferably 3 hours to 13 hours, more preferably 4 hours to 11 hours, even more preferably 5 hours to 9 hours, and particularly preferably 6 hours to 8 hours. In addition, when the second polymerization step is also performed as the foaming agent impregnation step, i.e., when the second polymerization step and the foaming agent impregnation step are performed together, the polymerization temperature of the second polymerization step can be said to be the impregnation temperature of the foaming agent impregnation step, and the polymerization time of the second polymerization step can be said to be the impregnation time of the foaming agent impregnation step.

It is preferable that the present manufacturing method further includes a drying step for drying the expandable resin particles. The expandable resin particles are obtained in a state dispersed in an aqueous suspension. Therefore, when the present manufacturing method includes a drying step, the obtained expandable resin particles can be suitably used for manufacturing expanded particles, etc.

In the drying process, the method for drying the expandable resin particles is not particularly limited, and for example, a groove-type or cylindrical agitator dryer, a box-type or band-type aeration dryer, a fluidized bed dryer, etc. can be used.

The drying process in the drying step is preferably carried out at a temperature equal to or lower than the expansion temperature of the expandable resin particles, and from the viewpoint of productivity, it is more preferable to carry out the drying process at a temperature between 30°C and 55°C. The water content of the resulting expandable resin particles can be adjusted by adjusting the temperature at which the drying process is carried out (also referred to as the processing temperature). When the drying process temperature in the drying step is (a) 30°C or higher, the water content does not become too high, so that the expansion particles that can be provided by the expandable resin particles can be prevented from becoming finer, and the amount of VOC emission can be reduced; and when the drying process temperature is (b) 55°C or lower, the water content does not become too low, so that there is no risk of the flame retardancy being deteriorated in the foamed molded article that can be provided by the expandable resin particles.

It is preferable that the polymerization initiator (X) contains at least benzoyl peroxide. That is, a further preferred aspect of the manufacturing method according to one embodiment of the present invention is a method for manufacturing expandable resin particles, which includes a copolymerization step of copolymerizing a monomer (monomer mixture) containing a styrene monomer and an acrylonitrile monomer, and a blowing agent impregnation step of impregnating the obtained copolymer with a blowing agent, the copolymerization step includes a first polymerization step and a second polymerization step successively having different polymerization temperatures, the first polymerization step uses a polymerization initiator containing a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or more and 94°C or less, the polymerization initiator (X) contains benzoyl peroxide, and the TH/TQ ratio of the expandable resin particles is less than 1.20. According to this configuration, it is possible to provide expandable resin particles that can provide a foamed molded product with a low VOC emission amount, in other words, a foamed molded product with high productivity.

The amount of benzoyl peroxide used in the first polymerization step is preferably 0.08 parts by weight or more and 0.25 parts by weight or less, and more preferably 0.15 parts by weight or less and 0.20 parts by weight or less, per 100 parts by weight of monomer. This configuration makes it possible to provide foamed molded products with lower VOC emissions, in other words, expandable resin particles that can provide foamed molded products with higher productivity.

<Foamed Molded Article and Its Manufacturing Method>
The expandable resin particles can be made into expanded particles by a general expansion method. A specific expansion method includes a method in which the following (1) to (3) are carried out in sequence: (1) expandable resin particles are placed in a container equipped with a stirrer, (2) the expandable resin particles are heated with a heat source such as steam, and (3) the expandable resin particles are expanded until a desired expansion ratio is reached, thereby obtaining expanded particles. The expanded particles may also be called pre-expanded particles, and therefore the expansion method for obtaining the pre-expanded particles may also be called a pre-expanding method.

The expanded beads obtained by expanding the expandable resin beads according to one embodiment of the present invention are also one embodiment of the present invention. The expanded beads according to one embodiment of the present invention can provide a foamed molded article with a low VOC emission amount, in other words, a foamed molded article with high productivity.

The expanded beads according to one embodiment of the present invention may have the following configuration. That is, the expanded beads according to another embodiment of the present invention are expanded beads obtained by expanding expandable resin beads, the expandable resin beads containing (a) a base resin containing styrene units and acrylonitrile units as constituent units, and (b) a blowing agent, and the absorbance ratio D2230/D1600 at wavelengths of 2230 cm ^-1 and 1600 cm ^-1 in an infrared absorption spectrum of the surface of the expanded beads is 0.80 or more.

The expanded beads according to one embodiment of the present invention may have the following configuration: That is, the expanded beads according to another embodiment of the present invention (a) contain styrene units and acrylonitrile units as structural units, and (b) the absorbance ratio D2230/D1600 at wavelengths of 2230 cm ⁻¹ and 1600 cm ⁻¹ in the infrared absorption spectrum of the surface of the expanded beads is 0.80 or more.

The foamed beads can be molded into a foamed molded article by a general in-mold molding method. A specific in-mold molding method is to fill a mold that can be closed but not sealed with foamed beads, and heat and fuse the foamed beads with water vapor to form a foamed molded article.

A foamed molded article obtained by molding the foamed beads according to one embodiment of the present invention in a mold is also one embodiment of the present invention. The foamed molded article according to one embodiment of the present invention has the advantage of having a low VOC emission amount.

In the foamed molded product according to one embodiment of the present invention, the amount of styrene released is preferably 2 ppm or less, and the amount of ethylbenzene released is preferably less than 15 ppm. Here, the amount of styrene released and the amount of ethylbenzene released are the amounts released into a 20 ml container when 0.025 g of the foamed molded product is left in the container under conditions of 60 ° C. for 2 hours. The amounts of styrene and ethylbenzene released are shown as concentrations (ppm) in the gas in a 20 ml container containing 0.025 g of the foamed molded product. The amount of styrene released in the foamed molded product according to one embodiment of the present invention is preferably 1.5 ppm or less, more preferably 1.0 ppm or less, even more preferably 0.6 ppm or less, and particularly preferably 0.5 ppm or less. The amount of ethylbenzene released in the foamed molded product according to one embodiment of the present invention is preferably less than 13 ppm, more preferably 10 ppm or less, even more preferably 7 ppm or less, and particularly preferably 5 ppm or less.

In this specification, the terms "emission amount" and "dissipation amount" are synonymous and interchangeable.

If the amount of styrene released and the amount of ethylbenzene released in the foamed molded product of one embodiment of the present invention are within the above-mentioned ranges, there is an advantage that there is no risk of adverse effects on the body, such as sick house syndrome, when the foamed molded product is used as an automobile interior material or building insulation material.

In this specification, the "foamed molded product according to one embodiment of the present invention" may be simply referred to as the "foamed molded product." In other words, the term "foamed molded product" refers to one embodiment of the foamed molded product of the present invention.

The oxygen index of the foamed molded product is preferably 26% or more, more preferably 27% or more, even more preferably 28% or more, and particularly preferably 29% or more. The above configuration has the advantage that the foamed molded product can exhibit sufficient flame retardant performance when used as an automobile interior material or a building insulation material.

The present foamed molded article preferably has excellent heat resistance. For example, when the present foamed molded article is used as a heat-insulating material or as a material for parts of an automobile exposed to sunlight, the present foamed molded article preferably has small deformation when used at 90°C or higher. Specifically, when a foamed molded article with an expansion ratio of 40 times is left for 168 hours under conditions of 90°C, the dimensional change rate of the foamed molded article before and after leaving it is preferably 0.4% or less, more preferably 0.35% or less, even more preferably 0.3% or less, and particularly preferably 0.25% or less.

The foamed molded product preferably has an average bubble diameter of 50 μm or more and less than 100 μm, more preferably 60 to 90 μm, in the surface layer. When the average bubble diameter is 50 μm or more, (a) the cell membrane has a sufficient thickness, so that the dimensional change of the foamed molded product with respect to temperature is small, (b) the amount of VOC and total VOC released can be reduced, and (c) the cell membrane has a sufficient thickness, so that the cell membrane does not melt due to pressurized steam during molding in the mold, and therefore the surface property of the foamed molded product is good. When the cell membrane is thin, the foamed molded product may expand in an environment of 90°C or more, and the dimensional stability of the foamed molded product may deteriorate. The expansion of the foamed molded product in a high-temperature environment is sometimes called tertiary expansion. When the average bubble diameter is less than 100 μm, the surface property of the foamed molded product is good.

In this specification, the "average cell diameter of the surface layer" refers to the average chord length of the foamed beads that lie in a straight line on the cut surface of the surface layer of the foamed molded article. The average chord length is a value obtained by measuring in accordance with ASTM-D-2842-97 using a photograph of the cut surface of the foamed molded article projected onto it. The average chord length is determined by randomly selecting 10 foamed beads that lie in a straight line on the cut surface of the surface layer of the foamed molded article in the photograph of the cut surface of the foamed molded article projected onto it, measuring the chord length of each of the selected foamed beads, and averaging the measured values.

An embodiment of the present invention may have the following configuration:

(X1) Expandable resin particles comprising a base resin containing styrene units and acrylonitrile units as constituent units, and a blowing agent, wherein the expandable resin particles are expanded, and the surface of the expanded particles has an absorbance ratio D2230/D1600 of 0.80 or more at wavelengths of 2230 cm ^-1 and 1600 cm ^-1 in an infrared absorption spectrum.

(X2) Expandable resin particles described in (X1), characterized in that the styrene content in the expandable resin particles is less than 20 ppm and the ethylbenzene content is 130 ppm or less.

(X3) Expandable resin particles described in (X1) or (X2), characterized in that the weight average molecular weight is 150,000 or more and 220,000 or less.

(X4) Expandable resin particles described in any one of (X1) to (X3), characterized in that in the base resin, (a) the content of the styrene units is 55 parts by weight or more and 80 parts by weight or less, the content of the acrylonitrile units is 20 parts by weight or more and 45 parts by weight or less, and (b) the total content of the styrene units and the acrylonitrile units is 100 parts by weight.

(X5) Expandable resin particles described in any one of (X1) to (X4), characterized in that the TH/TQ ratio is less than 1.20.

(X6) Expanded particles obtained by expanding expandable resin particles described in any one of (X1) to (X5).

(X7) A foamed molded body obtained by molding the foamed particles described in (X6) in a mold.

(X8) A foamed molded body described in (X7), characterized in that the average bubble diameter of the surface layer is 50 μm or more and less than 100 μm.

(X9) A foamed molded body described in (X7) or (X8), characterized in that the amount of styrene emitted is 2 ppm or less and the amount of ethylbenzene emitted is less than 15 ppm.

(X10) A method for producing expandable resin particles, comprising a copolymerization step of copolymerizing monomers including a styrene monomer and an acrylonitrile monomer, and a blowing agent impregnation step of impregnating the resulting copolymer with a blowing agent, the copolymerization step comprising a first polymerization step and a second polymerization step successively having different polymerization temperatures, the first polymerization step using a polymerization initiator including a polymerization initiator (X) having a 10-hour half-life temperature of 74°C or more and 94°C or less, the polymerization initiator (X) including benzoyl peroxide, and the TH/TQ ratio of the expandable resin particles being less than 1.20.

An embodiment of the present invention may have the following configuration:

(Y1) Expandable resin particles comprising a base resin containing styrene units and acrylonitrile units as constituent units, and a blowing agent, wherein the expandable resin particles are expanded, and the surface of the expanded particles has an absorbance ratio D2230/D1600 of 0.8 or more at wavelengths of 2230 cm ^-1 and 1600 cm ^-1 in an infrared absorption spectrum.

(Y2) Expandable resin particles described in (Y1), characterized in that the styrene content in the expandable resin particles is less than 20 ppm and the ethylbenzene content is 130 ppm or less.

(Y3) Expandable resin particles described in (Y1) or (Y2), characterized in that the weight average molecular weight is 150,000 or more and 220,000 or less.

(Y4) Expanded particles obtained by expanding expandable resin particles described in any one of (Y1) to (Y3).

(Y5) A foamed molded body obtained by molding the foamed particles described in (Y4) in a mold.

(Y6) A foamed molded body described in (Y5), characterized in that the average bubble diameter of the surface layer is 50 μm or more and less than 100 μm.

(Y7) A foamed molded body described in (Y5) or (Y6), characterized in that the amount of styrene emitted is 2 ppm or less and the amount of ethylbenzene emitted is less than 15 ppm.

The following examples and comparative examples are given, but the present invention is not limited to them.

The polymerization initiators, flame retardants, flame retardant assistants and chain transfer agents used in the examples and comparative examples are as follows.
Polymerization initiator (X):
Benzoyl peroxide (Niper BW (manufactured by NOF Corp.)) (10-hour half-life temperature: 74°C); and di-t-butyl peroxyhexahydroterephthalate (Kayaester HTP-65W (manufactured by Kayaku Akzo Co., Ltd.)) (10-hour half-life temperature: 83°C);
Polymerization initiator (Y):
t-Butylperoxy-2-ethylhexyl monocarbonate (Perbutyl E (manufactured by Nippon Oil & Fats Co., Ltd.)) (10-hour half-life temperature: 99°C); and 1,1-bis(t-butylperoxy)cyclohexane (Perhexa C (manufactured by Nippon Oil & Fats Co., Ltd.)) (10-hour half-life temperature: 90°C).
Flame Retardant:
Tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether (Pyroguard SR-130 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)).
Flame retardant synergist:
Dicumyl peroxide (Percumyl D (manufactured by Nippon Oil & Fats Co., Ltd.)).
Chain transfer agent:
α-Methylstyrene dimer (MSD (manufactured by Nippon Oil & Fats Co., Ltd.)).
In the examples and comparative examples, the molecular weight of the expandable resin particles, the contents of styrene and ethylbenzene in the expandable resin particles, and the evaluation of the expandability of the expandable resin particles were measured by the following methods. In addition, "parts" and "%" are based on weight unless otherwise specified, and respectively mean "parts by weight" and "%".

(Weight average molecular weight measurement method)
0.02 g of the expandable resin particles was dissolved in 20 cc of tetrahydrofuran, and the solution was subjected to gel permeation chromatography (GPC) (Tosoh Corporation HLC-8020, column: TSKgel Super HZM-H, column temperature: 40° C., flow rate: 0.35 ml /1 min.) The weight average molecular weight Mw was determined as a polystyrene equivalent value. The results are shown in Tables 1 and 2 as "Mw (weight average molecular weight)."

(Method of Calculating TH/TQ Ratio of Expandable Resin Particles)
0.02 g of the obtained expandable resin particles was dissolved in 20 ml of tetrahydrofuran (THF) to obtain a sample. Thereafter, the obtained sample was subjected to GPC measurement using gel permeation chromatography under the following conditions to obtain a GPC measurement chart.
Measuring device: Tosoh Corporation, high-speed GPC device HLC-8220
Columns used: 2 Super HZM-H and 2 Super H-RC, manufactured by Tosoh Corporation, total of 4 columns Column temperature: 40°C
Mobile phase: THF (tetrahydrofuran)
Flow rate: 0.35ml/min Injection volume: 10μl
Detector: RI.

The TH/TQ ratio was determined for the GPC curve of the obtained GPC measurement chart by the method described above. The results are shown in Tables 1 and 2 as "TH/TQ ratio."

(Method for measuring the content of styrene and ethylbenzene in expanded resin particles)
0.25 g of the expandable resin particles was dissolved in 20 cc of methylene chloride (together with cyclopentanol as an internal standard), and the styrene and ethylbenzene contained in the expandable resin particles were measured using a gas chromatograph GC-2014 manufactured by Shimadzu Corporation (capillary column: Rtx-1 manufactured by GL Sciences, column temperature conditions: heating from 50°C to 80°C (heating rate 3°C/min), then heating from 80°C to 180°C (heating rate 10°C/min), carrier gas: helium). The contents of styrene and ethylbenzene in the expandable resin particles were quantified from the results obtained using the measured calibration curves of styrene and ethylbenzene. The results obtained are shown in Tables 1 and 2 as "residual styrene monomer" and "ethylbenzene".

(Evaluation of expandability of expandable resin particles)
The expandable resin particles were placed in a steamer at 100°C and heated for 5 minutes to obtain expanded particles. 10 g of the resulting expanded particles were placed in a 1000 ^cm3 measuring cylinder, and the volume ( ^cm3 ) of the expanded particles was measured. The bulk ratio ( ^cm3 /g) was calculated using the following formula.

Bulk ratio (cm ³ /g)=volume of expanded beads (cm ³ )/10 g
In addition, when the evaluation result is less than 40 times, the bulk ratio does not reach 40 times or more even if the foam is pre-expanded by the pressurized pre-expanding machine, so this evaluation result is an index of the foamability. The obtained results are shown in Tables 1 and 2 as "Foamability (40 times)".
◯ (Good): 50 times or more △ (Pass): 40 times or more × (Bad): Less than 40 times.

The manufacturing method for expanded beads is as follows:

(Production of expanded beads)
The expandable resin particles were sieved to separate expandable resin particles having a particle diameter of 0.5 to 1.4 mm.

The separated expandable resin particles were pre-expanded to a bulk ratio of 40 times using a pressurized pre-expanding machine (manufactured by Daikai Kogyo, BHP) at an injection steam pressure of 0.09 to 0.10 MPa. The pre-expanded particles were then left at room temperature for one day to obtain expanded particles with a bulk ratio of 40 times.

The amount of blocking of the obtained foamed particles was measured using the following method.

(Method for measuring the amount of blocking during pre-expansion)
Blocking is a mass formed when foam particles are bonded together during the pre-expansion process. If there is a large amount of blocking, poor filling occurs during the molding process, so it is better to have a small amount of blocking. The method for measuring the amount of blocking is as follows.

The entire amount of foamed particles obtained by the foaming operation was passed through a wire mesh with a mesh pitch of 1 cm. The weight of the mass remaining on the wire mesh was measured, and the amount of blocking was calculated by the following formula.
Blocking amount (%) = weight of lump/total weight of foamed particles x 100
The blocking property was evaluated based on the obtained blocking amount according to the following criteria. The obtained results are shown in Tables 1 and 2 as "blocking amount".
◯ (Good): Less than 0.05% △ (Pass): Less than 0.01% 0.05% or more × (Poor): 0.1% or more.

<Measurement of absorbance ratio>
The absorbance ratio of the obtained expandable resin particles was determined by randomly sampling 10 pre-expanded particles (expanded particles) and performing ATR infrared spectroscopic analysis (ATR-FTIR analysis) on the surface of each pre-expanded particle (expansion ratio: 40 times) under the following conditions to obtain an infrared absorption spectrum.
Apparatus: FTIR [Shimadzu Corporation, FTIR-8400S] connected to a single reflection type total reflection (ATR) measurement device [PIKE, MIRacle] ATR prism (high refractive index crystal type): zinc selenide (ZnSe)
Incident angle: 45°
Measurement area: 4000cm ^-1 ~ 600cm ^-1
Detector: DLATGS
Penetration depth: 1.66
Number of reflections: 1 Resolution: 4cm ^-1
Number of times of accumulation: 20 times Other: The infrared absorption spectrum measured without contact with the sample was used as the background, and processing that is not related to the measured spectrum was performed.
In the ATR method, the intensity of the infrared absorption spectrum obtained by measurement varies depending on the degree of adhesion between the sample and the high refractive index crystal. Therefore, the degree of adhesion between the sample and the high refractive index crystal is adjusted so that the absorbance at 1600 cm ⁻¹ is 0.05 to 0.10.

Here, when measuring the surface of the pre-expanded particles, the particle surface was directly attached to the ATR prism for measurement.

From the infrared absorption spectrum thus obtained, the absorbance ratio between the absorbance at 1600 cm ^-1 and the absorbance at 2230 cm ^-1 (D2230/D1600) was calculated. In one embodiment of the present invention, ATR-FTIR measurement is performed on the surfaces of any 10 pre-expanded particles, and the minimum and maximum absorbance ratios are excluded. The arithmetic mean of the remaining 8 absorbance ratios is taken as the absorbance ratio.

The pre-expanded particles (expanded particles) used in measuring the absorbance ratio were obtained by treating the expandable resin particles obtained in the examples and comparative examples described below in the following order of (1) to (3): (1) The expandable resin particles were placed into a pressurized expansion machine; (2) Next, steam was blown into the expansion machine at an inlet steam pressure of 0.09 MPa to 0.10 MPa, and the pressure inside the expansion machine was adjusted to a range of 0.01 MPa to 0.02 MPa, thereby setting the temperature inside the expansion machine to 100°C to 104°C, thereby expanding the expandable particles to a magnification of 40 times; (3) Next, the obtained expanded particles were aged at 25°C for 12 to 24 hours to obtain the expanded particles to be used in measuring the infrared absorption spectrum.

The manufacturing method for the foamed molded body is as follows.

(Production of foamed molded products)
The pre-expanded particles with a bulk ratio of 40 times that had been left at room temperature for one day were molded in a molding machine (Daisen, KR-57) at a blowing steam pressure of 0.05 MPa and a heating time of 22 seconds to obtain a flat foamed molded product with a thickness of 20 mm, length of 400 mm, and width of 350 mm.

The obtained foamed molded bodies were evaluated for styrene and ethylbenzene emission, average surface cell diameter, heat resistance, etc. using the following methods.

(Method for measuring the amount of styrene and ethylbenzene emitted from foamed molded products)
A sample piece of 0.025 g was cut out from the foam molded product. The sample piece was placed in a pressure-resistant glass container with a volume of 20 ml and placed in a Shimadzu HS-10 (connected to a GC-2014). The storage conditions of the HS-10 were set to 60°C for 2 hours, and the styrene and ethylbenzene released at that time were collected. Each substance collected was measured using a Shimadzu gas chromatography GC-2014 (capillary column: GL Science Rtx-1, column temperature conditions: heating from 50°C to 70°C (heating rate 3°C/min), followed by heating from 70°C to 180°C (heating rate 10°C/min), carrier gas: helium) in the same manner as in the measurement method for the styrene content in the expandable resin particles. Using the measured calibration curves for styrene and ethylbenzene, the amounts of styrene and ethylbenzene emitted from the foam molded product were quantified from the results obtained. The amounts of styrene and ethylbenzene emitted were shown as concentrations (ppm) in the gas contained in a pressure-resistant glass vessel containing a sample piece.

(Measurement of the average bubble diameter of the surface layer)
The average chord length of each foamed bead of the foam molded article was measured using a photograph of the cut surface of the foam molded article projected in accordance with ASTM-D-2842-97. Specifically, in the photograph of the cut surface of the foam molded article projected, the average chord length was measured from the foamed beads present on a straight line of the cut surface of the surface layer of the foam molded article. In addition, 10 foamed beads present on the surface layer of the foam molded article were arbitrarily selected, and the average of the chord lengths of each of the foamed beads was taken as the final value (average chord length). In this specification, the average chord length thus obtained was taken as the average cell diameter of the surface layer of the foam molded article.

(Heat resistance evaluation)
The heat resistance of the foam molded article was evaluated by (a) calculating the dimensional change rate of the foam molded article at 90° C. and (b) observing the swelling of the surface of the foam molded article, as described below.

A foamed molded body with a molding magnification of 40 times was dried at 60°C for 24 hours. A sample piece with a length of 150 mm, width of 150 mm, and thickness of 20 (t) mm was then cut out from the foamed molded body. The dimensions of the sample piece in the length direction and width direction were measured at three points each to determine the initial dimension (D). The foamed molded body was then left in a dryer at 90°C for 168 hours, and after leaving it, similar measurements were made to determine the dimension (E) after drying at 90°C. The dimensional change rate was calculated using the following formula, and an absolute value of the dimensional change rate of 0.4 or less, that is, a dimensional change rate of -0.4% to 0.4%, was considered to be acceptable.

If the dimensional change rate is a positive value, it indicates that the initial (before drying) dimension (D) is larger than the dimension (E) after drying, i.e., the foamed molded body has shrunk. If the dimensional change rate is a negative value, it indicates that the dimension (E) after drying is larger than the initial dimension (D), i.e., the foamed molded body has expanded.

Dimensional change rate (%) = ((D) - (E)) / (D) x 100
Absolute value of dimensional change rate is 0.4 or less: ◯ (good)
Absolute value of dimensional change rate is more than 0.4 and 0.5 or less: △ (pass)
Absolute value of dimensional change rate exceeds 0.5: × (bad)
(Examples 1 to 10, Comparative Examples 1 to 5)
Into a 6 L autoclave equipped with a stirrer, 110 parts by weight of water, 0.105 parts by weight of tribasic calcium phosphate, 0.0075 parts by weight of sodium α-olein sulfonate, and the amounts of a polymerization initiator, a chain transfer agent, a flame retardant, and a flame retardant assistant shown in Table 1 were charged, and the contents were deoxidized to a gauge pressure of −0.06 MPa using a vacuum pump.

Then, the stirring of the raw materials was started by the stirrer, and the amounts of styrene monomer, alpha-methylstyrene monomer, and acrylonitrile monomer shown in Table 1 were charged into the autoclave, and these raw materials were stirred for another 30 minutes. Then, the first polymerization (first polymerization step) was carried out at the temperature (first polymerization temperature) and time (first polymerization time) shown in Table 1. Then, 5 parts by weight of normal rich butane (normal butane weight parts/isobutane weight parts = 70/30) was charged into the autoclave. Next, the second polymerization (second polymerization step) was carried out at the temperature (second polymerization temperature) and time (second polymerization temperature) shown in Table 1. Then, the temperature inside the autoclave was cooled to 40°C, dehydrated, and further dried to obtain expandable resin particles. The obtained expandable resin particles were subjected to the various measurements and evaluations described above, and the results are shown in Tables 1 and 2.

The obtained expandable resin particles were pre-expanded using the method described above to obtain expanded particles, which were then further molded in a mold using the method described above to obtain an expanded molded product 40 times larger.

The obtained expanded beads and expanded molded articles were subjected to the above-mentioned various measurements and evaluations. The results are shown in Tables 1 and 2.

According to one embodiment of the present invention, it is possible to provide expandable resin particles, pre-expanded particles (expanded particles), and foamed molded articles that have a low VOC content and can suppress the amount of VOC emissions. Therefore, one embodiment of the present invention can be suitably used in the automotive and building material fields.

Claims (10)

Expandable resin particles comprising a base resin containing a styrene unit and an acrylonitrile unit as constituent units, and a blowing agent,
The expandable resin particles are characterized in that the absorbance ratio D2230/D1600 at wavelengths of 2230 cm ^-1 and 1600 cm ^-1 in an infrared absorption spectrum of the surface of the expanded beads obtained by expanding the expandable resin particles is 0.80 or more. The expandable resin particles according to claim 1, characterized in that the styrene content in the expandable resin particles is less than 20 ppm, and the ethylbenzene content is 130 ppm or less. Expandable resin particles according to claim 1 or 2, characterized in that the weight average molecular weight is 150,000 or more and 220,000 or less. The expandable resin particles according to any one of claims 1 to 3, characterized in that in the base resin, (a) the content of the styrene unit is 55 parts by weight or more and 80 parts by weight or less, the content of the acrylonitrile unit is 20 parts by weight or more and 45 parts by weight or less, and (b) the total content of the styrene unit and the acrylonitrile unit is 100 parts by weight. Expandable resin particles according to any one of claims 1 to 4, characterized in that the TH/TQ ratio is less than 1.20. Expanded particles obtained by expanding the expandable resin particles according to any one of claims 1 to 5. A foamed molded article obtained by molding the foamed beads according to claim 6 in a mold. The foam molded article according to claim 7, characterized in that the average bubble diameter of the surface layer is 50 μm or more and less than 100 μm. The foamed molded article according to claim 7 or 8, characterized in that the amount of styrene emitted is 2 ppm or less and the amount of ethylbenzene emitted is less than 15 ppm. A method for producing expandable resin particles, comprising the steps of:
a copolymerization step of copolymerizing monomers including a styrene monomer and an acrylonitrile monomer;
and a blowing agent impregnation step of impregnating the obtained copolymer with a blowing agent,
The copolymerization step includes a first polymerization step and a second polymerization step which are successively performed at different polymerization temperatures,
In the first polymerization step, a polymerization initiator including a polymerization initiator (X) having a 10-hour half-life temperature of 74° C. or more and 94° C. or less is used,
The polymerization initiator (X) contains benzoyl peroxide,
The TH/TQ ratio of the expandable resin particles is less than 1.20;
A method for producing expandable resin particles, characterized in that a polymerization initiator containing a polymerization initiator (Y) having a 10-hour half-life temperature of 90°C or more and 100°C or less is used in the second polymerization step .

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