JP7100464B2 - Styrene-based resin composition, styrene-based resin mixture, foamed sheet, and molded product - Google Patents

Description

The present invention relates to a styrene-based resin composition, a styrene-based resin mixture, a foamed sheet, and a molded product.

In addition to its excellent moldability, styrene-based resins have many advantages such as excellent resistance to water and excellent electrical characteristics, and are molded by various molding methods, such as electrical product materials, miscellaneous goods, food containers, and packaging materials. It is used in large quantities as. Among them, foamed sheet containers for foods have been widely used for various food containers, mainly instant noodle containers, as containers having heat insulating properties, strong strength, light weight, and low cost. However, when a food containing hot oil is put in a container, the styrene monomer, dimer, and trimer, which are low molecular weight components, tend to be easily transferred to oil and the like, and the content of these low molecular weight components is high. Less material is required. Further, the styrene monomer is required to be reduced from the viewpoint of the odor of the resin, and the styrene dimer and the trimer are the edges of the die when the resin is extruded into a sheet or a strand by an extruder. It may precipitate on the sheet and adhere to the sheet or sland after long-term residence, which may cause a poor appearance, and therefore, reduction is required.

Styrene-based resins are generally produced by a solution polymerization method or a bulk polymerization method, and the apparatus is a polymerization apparatus for polymerizing styrene monomers, and a devolatilization apparatus for removing unreacted styrene monomers and polymerization solvents. Consists of. In order to further reduce the amount of styrene monomer in the resin, it is necessary to set the volatilization device to a high temperature and a high vacuum. However, if the temperature is too high, styrene monomers are generated by the thermal decomposition of the resin, so there is an appropriate temperature range. Further, the styrene dimer and the trimer are mainly produced by the thermal polymerization reaction in the polymerization process and the thermal decomposition of the resin when recovering the unreacted styrene monomer or the polymerization solvent at a high temperature. The generation in is dominant. To reduce these, it is effective to suppress the thermal polymerization reaction by low-temperature polymerization using a polymerization initiator. Even if a resin manufacturing device produces a styrene monomer and a resin with few low molecular weight components such as styrene dimer and trimer, the subsequent production of colored pelletize, solid sheet, foam sheet, etc. by an extruder, Further, since a low molecular weight component is generated by thermal decomposition of the resin during the subsequent secondary molding process, there is a demand for a material that produces a small amount of the low molecular weight component even during extrusion or secondary molding process. Further, if the decrease in molecular weight is large during the resin molding process, the mechanical strength is decreased, and further, in the production of the foamed sheet, the diameter of the foamed cell, the distribution of the cell diameter, the ratio of closed cells, etc. are significantly changed, and the appearance of the sheet is improved. In some cases, problems may occur due to the influence of the above, and materials with less decrease in molecular weight are also required.

In Patent Documents 1 and 2, a phenolic thermal deterioration inhibitor is added before the step of degassing the unreacted styrene monomer and the polymerization solvent at the time of resin production, whereby the styrene monomer and the styrene dimer by thermal decomposition are added. It is disclosed that the formation of a body and a trimer is suppressed, but no effect on the molecular weight of the resin is disclosed.
Patent Document 3 discloses that by adding a phenolic antioxidant to a resin, the styrene monomer newly generated is effectively suppressed even if a thermal history is applied by an extruder or the like. There is room for improvement in suppressing the decrease in molecular weight.
Patent Document 4 discloses that by adding an antioxidant of a phenol-based, phosphorus-based, or a combination thereof to a resin, an increase in styrene dimers and trimers during molding is suppressed. However, there is room for improvement in suppressing the decrease in the molecular weight of the resin.
In Patent Document 5, a volatile substance derived from thermal deterioration, a styrene dimer, and a trimer obtained by adding a thioether-based compound containing at least one thioether bond in the molecule to an aromatic vinyl compound-based resin composition. However, the odor of the thioether-based compound is not disclosed at all, although the resin composition with less odor is disclosed.

Japanese Unexamined Patent Publication No. 5-170825 Japanese Unexamined Patent Publication No. 7-149817 Japanese Unexamined Patent Publication No. 7-292188 Japanese Unexamined Patent Publication No. 2000-15857 Japanese Unexamined Patent Publication No. 2007-326964

The subject of the present invention is a styrene-based resin composition having a low content of styrene monomer and styrene dimer and trimer, excellent thermal stability and mechanical strength, and low odor, and a decrease in molecular weight during extrusion. It is an object of the present invention to provide a styrene-based resin mixture, a foamed sheet, and a molded product having a small amount of water.

In view of the current situation, the present inventors have made diligent studies, and as a result, a phenol / thioether-based antioxidant and a phenol-based thermal deterioration inhibitor are used as essential components, and a specific ratio is used to obtain a styrene monomer. It was also found that a styrene-based resin composition having an extremely low content of styrene dimer and trimer, suitable for applications such as food packaging materials, excellent in thermal stability and mechanical strength, and having a low odor can be obtained. , Which led to the present invention.

That is, the present invention is as follows.
[1]
A styrene-based resin composition containing a styrene-based resin, a phenol-based thermal deterioration inhibitor, and a phenol / thioether-based antioxidant, and 0.01 part of the phenol-based thermal deterioration inhibitor is added to 100 parts by mass of the styrene-based resin. ~ 0.40 parts by mass,
It contains 0.01 to 0.12 parts by mass of the phenol / thioether-based antioxidant.
The content of styrene monomer is less than 150 μg / g,
A styrene-based resin composition, characterized in that the total content of the styrene dimer and the trimer is 2000 μg / g or less.
[2]
The styrene-based resin composition according to [1], wherein the content of the styrene monomer is less than 100 μg / g.
[3]
The weight average molecular weight (Mw) is 180,000 to 450,000, the proportion of components having a molecular weight of 1 million or more is 2 to 12% by mass, and the proportion of components having a molecular weight of 50,000 or less is 5 to 16% by mass. The styrene-based resin composition according to [1] or [2].
[4]
The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.1 to 4.8, and the ratio of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) (Mz / Mw). The styrene-based resin composition according to any one of [1] to [3], wherein) is 1.6 to 4.0.
[5]
The phenolic heat deterioration inhibitor is 2-t-butyl-6- (3'-t-butyl-5'-methyl-2'-hydroxybenzyl) -4-methylphenyl acrylate and / or 2,4-di. The styrene-based according to any one of [1] to [4], which is -t-amyl-6- (3', 5'-di-t-amyl-2'-hydroxy-α-methylbenzyl) phenyl acrylate. Resin composition [6]
The phenol / thioether-based antioxidant is 2,4-bis (octylthiomethyl) -6-methylphenol and / or 2,4-bis (dodecylthiomethyl) -6-methylphenol, [1] to The styrene-based resin composition according to any one of [5].
[7]
It contains a styrene resin, a phenolic thermal deterioration agent, and a phenol / thioether-based antioxidant, and the rate of decrease in the weight average molecular weight (Mw) after extrusion with respect to the weight average molecular weight (Mw) before extrusion at 230 ° C. is 10. % Or less, a styrene-based resin mixture.
[8]
A foamed sheet containing the styrene-based resin composition according to any one of [1] to [6].
[9]
A molded product comprising the foam sheet according to [8].

According to the present invention, a styrene-based resin composition having a low content of styrene monomer and styrene dimer and trimer, excellent thermal stability and mechanical strength, and low odor, reduced in molecular weight during extrusion. It is possible to provide a styrene-based resin mixture having a small amount of water, a foamed sheet, and a molded product.

Hereinafter, embodiments of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present invention is not limited to the present embodiment.

<Styrene-based resin composition>
The styrene-based resin composition of the present embodiment is a styrene-based resin composition containing a styrene-based resin, a phenol-based thermal deterioration inhibitor, and a phenol / thioether-based antioxidant, with respect to 100 parts by mass of the styrene-based resin. The phenol-based thermal deterioration inhibitor is contained in an amount of 0.01 to 0.40 parts by mass, the phenol / thioether-based antioxidant is contained in an amount of 0.01 to 0.12 parts by mass, and the content of the styrene monomer is less than 150 μg / g. The total content of the styrene dimer and the trimer is 2000 μg / g or less.
The styrene-based resin composition of the present embodiment is a resin composition in which the formation of styrene monomers and styrene dimers and trimers is effectively suppressed, the content thereof is low, and the odor is low. Therefore, it is essential that the phenol-based thermal deterioration inhibitor and the phenol / thioether-based antioxidant are contained in a specific amount.
The phenol-based thermal deterioration inhibitor is added to the polymer solution in the final step of manufacturing the styrene-based resin composition to devolatile and recover the unreacted styrene monomer and the polymerization solvent at high temperature and high vacuum. Occasionally, it has the effect of effectively suppressing the formation of styrene monomers and styrene dimers and trimers under high vacuum with less oxygen. Further, even if oxygen is present as in an extruder, it does not reach under high vacuum with less oxygen, but it has an effect of suppressing the generation of oxygen. However, the effect of suppressing the decrease in molecular weight of the styrene resin is low regardless of the amount of oxygen.
When the phenol / thioether antioxidant is added to the resin, it has the effect of suppressing the formation of styrene monomers and styrene dimers and trimers, and further suppressing the decrease in the molecular weight of the styrene resin. On the other hand, odor peculiar to sulfur is generated in the resin due to thermal decomposition or the like.
In the present embodiment, a styrene monomer and a styrene dimer and a trimer are produced by mixing a styrene resin with a phenol-based thermal deterioration inhibitor and a phenol / thioether-based antioxidant in a specific amount. It is possible to extremely effectively suppress the decrease in molecular weight of the styrene-based resin due to thermal decomposition, and to extremely reduce the odor derived from styrene and sulfur.

《Styrene resin》
As the styrene-based monomer constituting the styrene-based resin contained in the styrene-based resin composition of the present embodiment, in addition to styrene, α-methylstyrene, α-methylp-methylstyrene, ο-methylstyrene, m. -Methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, t-butylstyrene, bromostyrene, chlorostyrene, inden and the like can be mentioned. In particular, styrene is preferable. These styrene-based monomers can be used alone or in combination of two or more. Further, another monomer copolymerizable with these styrene-based monomers may be contained in a small amount as long as the effect of the present invention is not impaired, and as another copolymerizable monomer. Examples thereof include acrylic monomers such as acrylic acid, methacrylic acid, butyl acrylate, and methyl methacrylate, and maleic anhydride.

<< Polymerization method of styrene resin >>
Examples of the polymerization method of the styrene-based resin of the present embodiment include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, and a suspension polymerization method.
The shape of the reactor is not particularly limited, but a completely mixed reactor, a laminar reactor, and a circulating reactor can be used in an appropriate combination.

As the polymerization solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

When the polymerization raw material is polymerized in order to obtain the styrene-based resin of the present embodiment, it is preferable to contain a polymerization initiator and a chain transfer agent in the polymerization raw material.
Examples of the polymerization initiator include organic peroxides such as 2,2-bis (t-butylperoxy) butane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, and 1, Peroxyketals such as 1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, etc. Dialkyl peroxides, acetyl peroxides, diacyl peroxides such as isobutyryl peroxides, peroxydicarbonates such as diisopropylperoxydicarbonates, peroxyesters such as t-butylperoxyacetate, ketone peroxides such as acetylacetone peroxides, t- Examples thereof include hydroperoxides such as butyl hydroperoxide. From the viewpoint of decomposition rate and polymerization rate, 1,1-bis (t-butylperoxy) cyclohexane is particularly preferable.
The polymerization initiator is preferably used in an amount of 0.01 to 0.08% by mass based on the styrene-based monomer.

Examples of the chain transfer agent include α-methylstyrene dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, n-octyl mercaptan and the like.
The chain transfer agent is preferably used in an amount of 0 to 0.5% by mass based on the styrene-based monomer.

Further, in the styrene resin of the present embodiment, a rubber-reinforced aromatic vinyl resin such as HI-PS resin and MBS resin and an aromatic vinyl thermoplastic elastomer such as SBS can be used as a component containing rubber as needed. May be contained in the styrene resin in an amount of 0 to 10% by mass. Further, higher fatty acids such as stearic acid, zinc stearate, calcium stearate, magnesium stearate and salts thereof, lubricants such as ethylenebisstearylamide, plasticizers such as liquid paraffin, and antioxidants are contained in the styrene resin from 0 to 0. It may be contained in an amount of 5% by mass.

In the case of continuous polymerization, a devolatilization step is provided to remove the unreacted monomer and the polymerization solvent after the completion of the polymerization step, but generally a vacuum devolatilization tank with a preheater, a devolatilization extruder, or the like is used. Be done. For example, a vacuum devolatilization tank with a preheater using only one stage, a vacuum devolatilization tank with a preheater connected in two stages in series, or a vacuum devolatilization tank with a preheater and a devolatilization extruder. Examples are those connected in series, but in order to reduce the volatile content as much as possible, a vacuum devolatilization tank with a preheater is connected in two stages in series, or a vacuum devolatilization tank with a preheater and a devolatilization extruder are used. Are preferably connected in series. When two stages of vacuum devolatilization tanks with preheaters are connected in series, the resin temperature in the first stage vacuum devolatilization tank is adjusted to 180 to 250 ° C., and the unreacted monomer and the polymerization solvent at the outlet of the first stage It is preferable that the pressure is adjusted so that the total amount is 3 to 7% by mass (approximately 5 to 10 kPa), and the resin temperature is 200 to 250 ° C. and the pressure is less than 2 kPa in the second-stage vacuum devolatilization tank. Further, after reducing the volatile content in the first-stage vacuum devolatile tank, 0.2 to 1.0% by mass of water is added to the polymer flow rate, mixed with a mixer, and then the second-stage vacuum degassing. A method of evacuating at a pressure of less than 2 kPa in a volatilization tank can also be applied.

<< Phenolic heat deterioration inhibitor >>
Examples of the phenol-based thermal deterioration inhibitor contained in the styrene-based resin composition of the present embodiment include 2-t-butyl-6- (3'-t-butyl-5'-methyl-2'-hydroxybenzyl). -4-Methylphenyl acrylate, 2,4-di-t-amyl-6- (3', 5'-di-t-amyl-2'-hydroxy-α-methylbenzyl) phenyl acrylate, 2-t-butyl -6- (3'-t-butyl-2'-hydroxy-5'-methyl-methylbenzyl) -4-methylphenylacrylate, 2,5-di-t-butyl-6- (3'-5'- Di-t-butyl-2'-hydroxymethylbenzyl) -phenylacrylate and the like can be mentioned, and one type may be used alone or two or more types may be used in combination. From the viewpoint of scattering property, 2,4-di-t-amyl-6- (3', 5'-di-t-amyl-2'-hydroxy-α-methylbenzyl) phenylacrylate is particularly preferable.

In the present embodiment, the content of the phenol-based thermal deterioration inhibitor is 0.01 to 0.40 parts by mass, preferably 0.05 to 0.37 parts by mass, based on 100 parts by mass of the styrene-based resin. It is preferably 0.08 to 0.34 parts by mass, and even more preferably 0.10 to 0.30 parts by mass. If the content is less than 0.01 parts by mass, the effect of suppressing the formation of styrene monomers, styrene dimers, and trimers due to thermal decomposition during extrusion processing and secondary molding processing becomes insufficient, and these are contained. It is not possible to obtain a small amount of sheets, molded products, etc. On the other hand, when it exceeds 0.40 parts by mass, the effect of suppressing the formation of styrene monomer, styrene dimer and trimer corresponding to the content cannot be obtained.

<< Phenol / thioether-based antioxidant >>
The phenol / thioether-based antioxidant contained in the styrene-based resin composition of the present embodiment is, for example, 2,4-bis (octylthiomethyl) -6-methylphenol, 2,4-bis (dodecylthiomethyl)-. 6-Methylphenol and the like can be mentioned, and one type may be used alone or two or more types may be used in combination. From the viewpoint of versatility, 2,4-bis (octylthiomethyl) -6-methylphenol is preferable.

The phenol / thioether-based antioxidant of the present embodiment is 0.01 to 0.12 parts by mass, preferably 0.02 to 0.10 parts by mass, and more preferably 0.02 to 0.08 parts by mass. Even more preferably, it is 0.03 to 0.05 parts by mass. If the amount added is less than 0.01 parts by mass, the effect of suppressing the formation of styrene monomer, styrene dimer, and trimer by thermal decomposition during extrusion processing and secondary molding processing becomes insufficient, and the sheet with few of these is insufficient. , Molded products, etc. cannot be obtained. On the other hand, when it exceeds 0.12 parts by mass, the effect of suppressing the formation of styrene monomer, styrene dimer and trimer can be obtained, but the odor is inferior due to the sulfur odor.

The total content of the phenol-based thermal deterioration inhibitor and the phenol / thioether-based antioxidant is preferably 0.5 parts by mass or less with respect to 100 parts by mass of the styrene-based resin. If it exceeds 0.5 parts by mass, the effect of suppressing the formation of styrene monomer, styrene dimer and trimer corresponding to the content and the effect of suppressing the reduction of the molecular weight of the styrene-based resin cannot be obtained, and the styrene-based resin cannot be obtained. The heat resistance of the composition tends to decrease.

The method for adding the phenol-based thermal deterioration inhibitor and the phenol / thioether-based antioxidant of the present embodiment is not particularly limited, but is a method of adding the phenol-based resin to the polymerization reactor or the devolatile step at the time of producing the styrene-based resin, or polymerization. Examples thereof include a method of adding and mixing with the styrene-based resin thus obtained.

Hereinafter, the characteristics of the styrene resin composition will be described.

The styrene monomer contained in the styrene-based resin composition of the present embodiment is less than 150 μg / g, preferably less than 120 μg / g, and more preferably less than 100 μg / g. By setting it to less than 150 μg / g, the odor is greatly improved. Further, in terms of the transfer of the styrene monomer from the food packaging container which is a molded product to the oil content of the food or the like, it is preferable that the amount of the styrene monomer is smaller.
In order to reduce the content of the styrene monomer in the styrene-based resin composition to less than 150 μg / g, for example, by setting the concentration of the resin solid content in the polymerization solution to 60 to 90% by mass, the polymer component can be adjusted. There are a method of increasing the amount of styrene monomer and reducing the amount of styrene monomer, and a method of making it easier to remove the styrene monomer by setting the temperature at the time of devolatile at 200 to 260 ° C. and the pressure at 20 kPa or less.
In the present disclosure, the content of the styrene-based monomer can be measured by gas chromatography.

The total content of the styrene dimer and the trimer contained in the styrene-based resin composition of the present embodiment is 2000 μg / g or less, preferably 1800 μg / g or less, and more preferably 1500 μg / g or less. .. If it exceeds 2000 μg / g, the low molecular weight substance deposited on the die during extrusion of the resin composition tends to adhere to the sheet or strand, and a defective phenomenon is likely to occur, which is not preferable. Further, it is desirable that the number of styrene dimers and trimers is smaller in terms of the transfer of styrene dimers and trimers from the food packaging container which is a molded product to the oil content of the food.
Examples of styrene dimers and trimers include 1,3-diphenylpropane, 2,4-diphenyl-1butene, 1,2-diphenylcyclobutane, and 1-phenyltetraline as dimers. Examples of the body include 2,4,6-triphenyl-1-hexene, 1-phenyl-4- (1'-phenylethyl) tetraline and the like.
In order to make the total content of the styrene dimer and trimer in the styrene resin composition 2000 μg / g, for example, in order to reduce the amount produced during the polymerization of the styrene resin, the reaction temperature is set to 80. There are a method of lowering the temperature to about 140 ° C. and a method of adding 100 to 2000 mass ppm of the polymerization initiator to generate many initiator radicals. Further, in order to reduce the amount generated by heat or shearing of the molten resin, there is a method of reducing the pressure at the time of vacuum devolatile of the unreacted monomer or the solvent to 20 kPa or less.
In the present disclosure, the total content of styrene dimer and trimer can be measured by gas chromatography.

The styrene-based resin composition of the present embodiment preferably has a weight average molecular weight (Mw) of 180,000 to 450,000. It is more preferably 210,000 to 430,000, and even more preferably 240,000 to 410,000. If the weight average molecular weight (Mw) is less than 180,000, the mechanical strength is low and it is not practical. On the other hand, if it exceeds 450,000, the fluidity is lowered, it is difficult to extrude the resin composition and the secondary molding process, and the appearance of the obtained molded product is inferior.
In the present disclosure, the weight average molecular weight (Mw) of the styrene resin composition can be measured by gel permeation chromatography (GPC).

In the styrene-based resin composition of the present embodiment, the proportion of components having a molecular weight of 50,000 or less is preferably 5 to 16% by mass, and the proportion of components having a molecular weight of 1,000,000 or more is preferably 2 to 12% by mass. More preferably, the proportion of components having a molecular weight of 50,000 or less is 6 to 14% by mass, the proportion of components having a molecular weight of 1 million or more is 2 to 11% by mass, and even more preferably, the proportion of components having a molecular weight of 50,000 or less is 7 to 13. The ratio of components having a molecular weight of 1 million or more is 2 to 10% by mass. Since the proportion of components having a molecular weight of 50,000 or less is in the range of 5 to 16% by mass and the proportion of components having a molecular weight of 1 million or more is in the range of 2 to 12% by mass, the extrudability of a foamed sheet made of a styrene resin composition is particularly high. Foaming characteristics such as foaming ratio and secondary molding processability are improved, and a molded product having an excellent appearance can be obtained.
In the present disclosure, the proportion of components having a molecular weight of 50,000 or less and the proportion of components having a molecular weight of 1 million or more can be measured by gel permeation chromatography (GPC).

In the styrene-based resin composition of the present embodiment, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 2.1 to 4.8, and the Z average molecular weight (Mz) is preferable. ) With respect to the weight average molecular weight (Mw) is preferably 1.6 to 4.0. More preferably, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.3 to 4.6, and the ratio of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) ( Mz / Mw) is 1.7 to 3.6, and more preferably the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.5 to 4.4, Z. The ratio (Mz / Mw) of the average molecular weight (Mz) to the weight average molecular weight (Mw) is 1.8 to 3.4. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.1 to 4.8, and the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is. The range of 1.6 to 4.0 improves the extrudability of the foamed sheet made of the styrene resin composition, the foaming characteristics such as the foaming ratio, and the secondary molding processability, and is excellent in appearance. A molded product is obtained.
In the present disclosure, the number average molecular weight (Mn) and the Z average molecular weight (Mz) of the styrene resin composition can be measured by gel permeation chromatography (GPC).

The molecular weight and molecular weight distribution of the styrene-based resin composition of the present embodiment are determined by the types and addition amounts of the polymerization initiator, branching agent, and polymerization solvent when radically polymerizing the styrene-based monomer to obtain a styrene-based tree. It can be controlled by the configuration, reaction temperature, residence time, etc. To control these fine molecular weights and molecular weight distributions, two or more reactors are connected in parallel and / or in series, for example, a resin having a high molecular weight component or a low molecular weight component is prepared in each reactor, and the high molecular weight component and the low molecular weight component are produced. This is possible by finely controlling the amount of the low molecular weight component and further controlling the molecular weight distribution (Mw / Mn).
As the polymerization solvent, ethylbenzene and / or toluene is preferable, and the content of the polymerization solvent in the resin raw material is preferably 2 to 35% by mass. To obtain a high molecular weight component, use a small amount of polymerization solvent, and to obtain a low molecular weight component, use a large amount of polymerization solvent.
In addition to the polymerization solvent, a chain transfer agent such as α-styrene dimer can also be used to generate a low molecular weight component. The styrene conversion rate is preferably 65-75% at the outlet of the final reactor.
The reaction temperature is preferably 110 ° C. or lower to obtain a high molecular weight component, and 120 ° C. to 160 ° C. to obtain a low molecular weight component.
The shape of the reactor is not particularly limited, but a completely mixed reactor, a laminar reactor, and a circulating reactor can be used in an appropriate combination.
Further, in order to efficiently obtain a high molecular weight component, a tetrafunctional polymerization initiator or branching agent is used. On the other hand, by using a thermal polymerization or a monofunctional or bifunctional polymerization initiator, a low molecular weight component can be efficiently obtained.

<Manufacturing method of styrene resin composition>
The styrene-based resin composition of the present embodiment is, for example, a phenol-based thermal deterioration inhibitor and a phenol / thioether-based antioxidant, a polymerization initiator and a chain transfer agent, if necessary, when polymerizing the above-mentioned styrene-based resin. It can be obtained by a method of adding an additive or the like. Further, a styrene resin mixture obtained by polymerizing the above-mentioned styrene-based monomer by the above-mentioned production method, a phenol-based thermal deterioration inhibitor, and a styrene-based resin mixture containing a phenol / thioether-based antioxidant, as required. It is also possible to obtain an additive such as a polymerization initiator and a chain transfer agent by a method of melt-kneading using a known kneader such as a single-screw extruder, a twin-screw extruder, or a Banbury mixer.

The styrene-based resin mixture containing the styrene-based resin, the phenol-based thermal deterioration inhibitor, and the phenol / thioether-based antioxidant is the weight average molecular weight (Mw) after extrusion with respect to the weight average molecular weight (Mw) before extrusion at 230 ° C. The rate of decrease is preferably 10% or less, more preferably 9% or less, still more preferably 7% or less. If the rate of decrease in weight average molecular weight (Mw) exceeds 10%, the decrease in mechanical strength becomes large, which is not preferable.
In the present disclosure, extrusion at 230 ° C. can be specifically carried out under the conditions described in the section [Example] described later. Further, the rate of decrease (%) in the weight average molecular weight (Mw) of the styrene-based resin mixture before and after extrusion can be determined by the procedure described in the section of [Example] described later.

<Foam sheet>
The foamed sheet of the present embodiment is characterized by containing the styrene-based resin composition of the present embodiment.
The foamed sheet of the present embodiment may be multi-layered, for example, by further laminating a film. As the type of film, those used for general polystyrene can be used.

The thickness of the foamed sheet is preferably 0.7 to 3.0 mm, more preferably 1.0 to 3.0 mm, still more preferably 1.0 to 2.5 mm from the viewpoint of moldability and container strength. be. The thickness of the foam sheet can be adjusted according to the equipment structure such as the structure of the die, the processing flow rate of the resin, and the operating conditions such as the take-up speed of the sheet.

The density (ρf) of the foamed sheet can be adjusted by the amount of the foaming agent added, the pressure in the die, and the like, but there is a limit value depending on the characteristics of the resin composition used.
The foam density of the foam sheet can be measured by the method described in the section of [Example] described later based on ISO10350.

The foaming ratio of the foamed sheet is preferably 3 to 20 times, more preferably 4 to 18 times, still more preferably 5 to 15 times. When the foaming ratio is 3 to 20 times, when the foamed sheet is formed into a container, both the strength and the weight reduction of the container can be achieved.
The foaming ratio of the foamed sheet is a value calculated from the following formula using the foam density (ρf) and the density of the styrene resin composition (ρ).
Foaming magnification = ρ / ρf

<Manufacturing method of foam sheet>
The method for producing the foamed sheet of the present embodiment can be carried out by using a commonly known method. For example, without limitation, a method of melt-kneading and extruding the styrene resin composition, the foaming agent, and the foam nucleating agent of the present embodiment with an extruder can be mentioned.
As an apparatus for producing the foamed sheet of the present embodiment, a known extruded foamed sheet manufacturing apparatus is suitable. That is, known melt kneading devices such as a single-screw extruder and a twin-screw extruder can be used alone or in series of two or more, but it is preferable to use two or more extruders in series. Specifically, for example, the foaming agent and the foam nucleating agent are press-fitted into the resin composition heated and melted by the first extruder, mixed, and cooled by the second extruder to raise the resin temperature to 120 to 120. After adjusting to 180 ° C., a method of extruding the foamed sheet into the air from the circular die is preferable.

The foaming agent is not particularly limited, and examples thereof include butane, pentane, chlorofluorocarbon, and water, and butane is preferable. The amount of the foaming agent added is usually 1 to 10% by mass with respect to the resin composition supplied to the extruder.

Examples of the effervescent nucleating agent include inorganic powders such as talc, calcium carbonate, and clay, and can be used alone or as a mixture. Talc is most preferable because it has a large effect of reducing the bubble diameter and is inexpensive. The method of adding the nucleating agent to the extruder is not particularly limited, and the nucleating agent may be added directly to the supply hole of the extruder, or may be added together with the styrene resin. The amount of the nucleating agent added is usually 0.1 to 5% by mass with respect to the resin composition supplied to the extruder. Further, a masterbatch containing a foaming agent, a nucleating agent and the like may be prepared based on the styrene resin composition, and a higher fatty acid metal salt may be previously blended in the masterbatch. Further, a lubricant such as ethylene bisstearyl amide, a spreading agent such as liquid paraffin or silicone oil, other surfactants, an antistatic agent, an antioxidant, a plasticizer, a light resistant agent, a pigment and the like may be contained.

<Molded product>
The molded product of the present embodiment can be produced into various forms by secondary molding from the solid sheet or foamed sheet containing the styrene-based resin composition of the present embodiment. The molded product of the present embodiment can be widely used for food trays, lunch boxes, instant noodle containers, cups and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

<< Measurement and evaluation method >>
The measurement and evaluation methods are described below.

(1) Measurement of Molecular Weight For styrene resin and styrene resin composition, number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of components having a molecular weight of 1 million or more (mass%) The ratio (% by mass) of the components having a molecular weight of 50,000 or less was measured using gel permeation chromatography (GPC) under the following conditions.
Equipment: Tosoh HLC-8220
Sorting column: Tosoh TSK gel Super HZM-H
Guard column: Tosoh TSK guard volume Super HZ-H
Measurement solvent: Tetrahydrofuran Sample concentration: Dissolve 5 mg of the measurement sample in 10 mL of solvent Injection amount: 10 μL
Measurement temperature: 40 ° C
Flow velocity: 0.35 mL / min Detection: UV detector Calibration curve is created by 11 types of TSK standard polystyrene manufactured by Tosoh (F-850, F-450, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000) were used.
The rate of decrease (%) in the weight average molecular weight (Mw) of the styrene resin mixture before and after extrusion at 230 ° C. was used for the styrene resin composition having the weight average molecular weight (Mw) of the styrene resin composition. It was determined as the rate of decrease with respect to the weight average molecular weight (Mw) of the styrene resins (PS-1 to PS-4).

(2) Measurement of content of styrene monomer, dimer, and trimer Content of styrene monomer, dimer, and trimer in styrene resin and styrene resin composition (2) Weight%) was measured under the following conditions and procedures.
-Sample preparation: 2.0 g of a styrene resin or a styrene resin composition was dissolved in 20 mL of methyl ethyl ketone, and then 5 mL of methanol containing a standard substance was added and dissolved. After the styrene-based resin composition was precipitated and allowed to stand, the supernatant liquid was collected and used as a measurement liquid.
-Measurement conditions Equipment: Agilent gas chromatography GC6850
Column: HP-1 30m, film thickness 0.25μm, 0.32mmφ
Column temperature: Hold at 40 ° C for 1 minute → Heat up to 320 ° C at 20 ° C / min → Hold at 320 ° C for 10 minutes Injection port temperature: 250 ° C
Detector temperature: 280 ° C
Carrier gas: Nitrogen The amount of styrene monomer generated during the production (extrusion) of the styrene resin composition is determined from the content of the styrene monomer in the styrene resin composition in the production of the styrene resin composition. The difference was obtained by subtracting the content of the styrene monomer of the styrene resins (PS-1 to PS-4) used in. Further, the total amount of the styrene dimer and the trimer generated during the production (extrusion) of the styrene resin composition is the total content of the styrene dimer and the trimer of the styrene resin composition. The difference was obtained by subtracting the total content of the styrene dimer and the styrene dimer of the styrene resin (PS-1 to PS-4) used for producing the styrene resin composition.

(3) Measurement of Melt Mass Flow Rate (MFR) The melt mass flow rate (g / 10 minutes) of the styrene resin was measured under the condition of a load of 200 ° C. and 49 N in accordance with ISO1133.

(4) Presence or absence of odor 30 g of the styrene resin composition is placed in a glass cylindrical container having a diameter of 50 mm and a height of 100 mm, sealed with a metal cap, heated at 60 ° C. for 3 hours in a constant temperature bath, and then the cap is removed. The presence or absence of odor was judged by the standard.
◎: No odor is felt.
◯: A faint odor is felt.
×: The odor is clearly felt.

(5) Presence or absence of precipitates on the die The styrene resin composition was continuously extruded for 6 hours by a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SS) in [Preparation of styrene resin composition] described later. The presence or absence of precipitates around the die at the outlet of the strand was determined according to the following criteria.
⊚: There is no precipitate.
◯: There is a slight amount of precipitate.
X: There is a precipitate.

(6) Measurement of Impact Strength of Foam Sheet The impact strength (Kgf · cm) of the foam sheet was measured using a film impact tester (A121807502 manufactured by Toyo Seiki Co., Ltd.).

(7) Measurement of foaming ratio of foamed sheet The foaming ratio (times) of the foamed sheet was calculated from the following formula using the foam density (ρf) and the density (ρ) of the styrene resin composition.
Foaming magnification = ρ / ρf
The foam density of the foam sheet was measured based on ISO10350. As a measuring device, a hydrometer (SGM-220-60 measuring device) manufactured by Shimadzu Corporation was used.

"material"
Styrene Monomer: Styrene Polymerization Initiator-1: 1,1-bis (t-butylperoxy) cyclohexane (manufactured by NOF CORPORATION, Perhexa C)
Polymerization Initiator-2: 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane (manufactured by NOF CORPORATION, Pertetra A)
Branching agent: Divinylbenzene Chain transfer agent: α-methylstyrene dimer (manufactured by NOF Corporation)
Polymerization solvent: Ethylbenzene Phenolic thermal deterioration inhibitor A: 2- [1- (2-Hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate (Sumitomo Chemical) SUMILIZER GS, manufactured by Kogyo Co., Ltd.)
Phenolic heat deterioration inhibitor B: 2-t-butyl-6 (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate (Sumitomo Chemical Co., Ltd., SUMILIZER GM)
Phenol / thioether-based antioxidant C: 2,4-bis (octylthiomethyl) -6-methylphenol (manufactured by BASF Japan Ltd., IRGANOX 1520L)
Phenol / thioether-based antioxidant D: 2,4-bis (dodecylthiomethyl) -6-methylphenol (manufactured by BASF Japan Ltd., IRGANOX 1726)
Foaming nucleating agent: talc Foaming agent: liquefied butane

[Manufacturing of styrene-based resins PS-1 to PS-4]
For the polymerization of styrene-based resin, the first reactor and the second reactor are arranged in parallel, the outlets of the respective reactors are merged, then the reactor is connected to the inlet of the third reactor, and the third reactor is followed by the third reactor. 4 The polymerization process was configured by connecting in series to the reactor. The first reactor is a complete mixture type with a capacity of 5.4 liters, and the second, third and fourth reactors are a laminar flow type with a stirrer and each has a capacity of 1.5 liters. A raw material solution was prepared with the composition shown in Table 1, and the prepared raw material solution was continuously and continuously supplied to the first reactor and the second reactor at the flow rates shown in Table 1.
In the second, third, and fourth reactors, a temperature gradient was applied from the inlet portion to the outlet portion along the flow direction at the temperatures shown in Table 1, and the temperature was controlled in three zones. The concentration of the resin solid content in the polymerization solution at the outlets of the first reactor and the fourth reactor was measured. Table 1 shows the measurement results.
Subsequently, the polymerization solution continuously taken out from the outlet of the 4th reactor was introduced into a vacuum devolatilization tank equipped with a preheater composed of two stages in series, and the temperature of the preheater was adjusted to the resin temperature shown in Table 1. Was adjusted to the pressure shown in Table 1 to separate unreacted styrene monomer and ethylbenzene, extruded into strands from a die, cooled, and then cut into pellets.

<< Examples 1 to 7, Comparative Examples 1 to 4 >>
[Preparation of styrene resin composition]
The styrene-based resin compositions of Examples and Comparative Examples were prepared based on the compositions of the styrene-based resin compositions shown in Table 2, and styrene-based resins (types PS-1 to PS-4) and phenol-based thermal deterioration prevention. After preparing a styrene resin mixture by mixing the agents (types A and B) and phenol / thioether-based antioxidants (types C and D), the table is shown using a twin-screw extruder (manufactured by Toshiba Machinery Co., Ltd., TEM26SS). At the resin temperature (230 ° C. or 250 ° C.) described in 2, the resin was extruded into a strand at a discharge rate of 5 kg / hr and a rotation speed of 100 rpm, cooled, and then pelletized. At the time of extrusion, nitrogen flow was performed on the hopper in which the resin was charged.
Table 2 shows the physical properties of the styrene-based resin mixture such as the weight average molecular weight (Mw) and the styrene-based resin composition.

[Preparation of foamed sheet of styrene resin composition]
Using the styrene resin compositions of Examples and Comparative Examples, an extrusion foaming machine equipped with a circular die having a diameter of 150 mm was used, and talc was added as a foaming nucleating agent to 100 parts by mass of the above styrene resin composition. A foamed sheet was produced by extruding and foaming a mixture prepared by adding 5 parts by mass and 4 parts by mass of liquefied butane as a foaming agent. The temperature of the resin melting zone was adjusted to 200 to 230 ° C, the temperature of the rotary cooler was adjusted to 130 to 170 ° C, and the temperature of the die was adjusted to 150 ° C. The foam immediately after extrusion foaming was cooled with a cooling mandrel and cut with a cutter at one point on the circumference to obtain a foamed sheet having a sheet thickness of about 2 mm. Table 2 shows the physical characteristics of the foam sheet.

[Examples 1 to 7]
The styrene-based resin compositions of Examples 1 to 7 are excellent in thermal stability by adding a predetermined amount of a phenol-based thermal deterioration inhibitor and a phenol / thioether-based antioxidant, and are excellent in thermal stability, styrene monomer, and styrene. The amount of dimer and trimer generated was small, and the content of styrene monomer, styrene dimer and trimer was small. In addition, the odor is good, the weight average molecular weight of the styrene resin mixture does not decrease much, and the impact strength of the foamed sheet is excellent.

[Comparative Example 1]
In Comparative Example 1, the contents of the phenol-based thermal deterioration inhibitor and the phenol / thioether-based antioxidant are low, the thermal stability is inferior, and the amount of styrene monomer, styrene dimer and trimer generated is large. It had a styrene odor and was inferior in odor. In addition, the weight average molecular weight of the styrene resin mixture was significantly reduced, and the impact strength of the foamed sheet was also inferior.

[Comparative Example 2]
In Comparative Example 2, only the phenol-based thermal deterioration inhibitor was added in a predetermined amount, and the phenol / thioether-based antioxidant was not added. The amount of styrene monomer, styrene dimer and trimer generated was small, and the odor was good, but the weight average molecular weight of the styrene-based resin mixture was significantly reduced, and the impact strength of the foamed sheet was inferior.

[Comparative Example 3]
In Comparative Example 3, only the phenol / thioether-based antioxidant was added in a predetermined range or more, and the phenol-based thermal deterioration inhibitor was not added. The amount of styrene monomer, styrene dimer and trimer generated was small, but the sulfur odor was strong and the odor was inferior.

[Comparative Example 4]
In Comparative Example 4, only the phenol / thioether-based antioxidant was added in a predetermined range or more, and the phenol-based thermal deterioration inhibitor was not added. The amount of styrene monomer, styrene dimer and trimer generated was large, and the odor was inferior because of the strong sulfur odor. In addition, due to the high content of styrene dimer and trimer in the resin composition, precipitates were observed on the die.

Since the styrene-based resin composition of the present invention has excellent thermal stability, the content of the styrene monomer, styrene dimer and trimer is small, the molecular weight of the styrene-based resin is not reduced, and the mechanical strength is small. Since it is excellent in and has little odor, it is suitable for the production of extruded sheets and extruded foam sheets, and its secondary molding process, and the obtained molded products can be suitably used for applications such as food packaging materials.

Claims (9)

A styrene-based resin composition containing a styrene-based resin, a phenol-based thermal deterioration inhibitor, and a phenol / thioether-based antioxidant, and 0.08 of the phenol-based thermal deterioration inhibitor with respect to 100 parts by mass of the styrene-based resin. ~ 0.40 parts by mass,
Contains 0.03 to 0.10 parts by mass of the phenol / thioether-based antioxidant.
The content of styrene monomer is less than 150 μg / g,
The ratio (Mz / Mw) of the Z average molecular weight (Mz) of the styrene resin to the weight average molecular weight (Mw) of the styrene resin is 1.6 to 4.0.
A styrene-based resin composition, characterized in that the total content of the styrene dimer and the trimer is 2000 μg / g or less. The styrene-based resin composition according to claim 1, wherein the content of the styrene monomer is less than 100 μg / g. The weight average molecular weight (Mw) is 180,000 to 450,000, the proportion of components having a molecular weight of 1 million or more is 2 to 12% by mass, and the proportion of components having a molecular weight of 50,000 or less is 5 to 16% by mass. The styrene-based resin composition according to claim 1 or 2. The styrene-based resin composition according to any one of claims 1 to 3, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.1 to 4.8. The phenolic heat deterioration inhibitor is 2-t-butyl-6- (3'-t-butyl-5'-methyl-2'-hydroxybenzyl) -4-methylphenyl acrylate and / or 2,4-di. The styrene-based according to any one of claims 1 to 4, which is -t-amyl-6- (3', 5'-di-t-amyl-2'-hydroxy-α-methylbenzyl) phenyl acrylate. Resin composition Claims 1 to 1, wherein the phenol / thioether-based antioxidant is 2,4-bis (octylthiomethyl) -6-methylphenol and / or 2,4-bis (dodecylthiomethyl) -6-methylphenol. 5. The styrene-based resin composition according to any one of 5. A styrene-based resin composition containing a styrene-based resin, a phenol-based thermal deterioration inhibitor, and a phenol / thioether-based antioxidant, with respect to 100 parts by mass of the styrene-based resin.
0.08 to 0.40 parts by mass of the phenolic heat deterioration inhibitor,
It contains 0.03 to 0.12 parts by mass of the phenol / thioether-based antioxidant.
The content of styrene monomer is less than 150 μg / g,
The ratio (Mz / Mw) of the Z average molecular weight (Mz) of the styrene resin to the weight average molecular weight (Mw) of the styrene resin is 1.6 to 4.0.
The total content of the styrene dimer and trimer is 2000 μg / g or less.
2 A styrene-based resin mixture characterized in that the rate of decrease in the weight average molecular weight (Mw) after extrusion with respect to the weight average molecular weight (Mw) before extrusion at 30 ° C. is 10% or less. A foamed sheet comprising the styrene-based resin composition according to any one of claims 1 to 6. A molded product comprising the foamed sheet according to claim 8.