JP6876518B2 - Extruded foam sheet and its molded product - Google Patents

Description

The present invention relates to an extruded foam sheet and a molded product thereof.

Since styrene-based resins are excellent in transparency and moldability, they are widely used as molding materials for home appliances, office machine products, miscellaneous goods, housing equipment, and food packaging materials. In particular, secondary molded products formed by thermal molding from polystyrene resin extruded foam sheets, such as food packaging containers, are for various foods such as trays for meat, fish, prepared foods, cup noodle containers, natto containers, and the like. It is widely used as a simple container for. In such a simple container by thermoforming of a foamed sheet, a high magnification is achieved when the container is foamed in order to reduce the cost. However, if the magnification of the container is increased during foaming, the product strength is lowered, and problems such as the container cracking during wrapping of the container are likely to occur. To solve this problem, by controlling the shape of the foam cell during extrusion foam molding and increasing the thickness of the vacuum forming container (especially the thickness of the fragile part), it is possible to maintain the strength of the container even at high magnification. Has been done. Further, a method of using a styrene resin having a specific number of branches has been proposed as a material for a container.

As such a method, for example, Patent Document 1 describes an extruded foamed sheet containing a vinyl aromatic hydrocarbon polymer composition in which a branched structure is introduced into a molecule using a specific branched polymer to increase the molecular weight. Is described. Further, in Patent Document 2, a polyfunctional vinyl-based aliphatic compound and a component derived from a styrene-based monomer are contained as a base resin, and when the uniaxial extensional viscosity of the base resin is measured under predetermined conditions, time-elongation occurs. We are paying attention to the ratio of the slope of the linear approximation straight line of the non-linear region in the logarithmic plot of the viscosity curve to the slope of the linear approximation straight line of the linear region in the above curve. Specifically, it is described that by setting this ratio in the range of 2.0 to 6.0, weight reduction can be realized without deteriorating the physical characteristics of the container.

Japanese Unexamined Patent Publication No. 2015-083674 Japanese Unexamined Patent Publication No. 2014-189964

However, Patent Documents 1 and 2 are not sufficient for reducing defects in the extruded foamed sheet due to the gel-like substance, and further improvement in moldability is required. Further, since the gel-like substance may act as a defect in the secondary molding of processing the extruded foam sheet into a molded product, a material suitable for further increasing the magnification is required.

The present invention has been devised in view of such conventional circumstances, and an object of the present invention is to provide an extruded foam sheet which is suitable for high magnification and has excellent molding processability. Furthermore, it is also an object of the present invention to provide a molded product having a high foaming ratio obtained from the extruded foamed sheet.

As a result of diligent research to achieve the above object, the present inventors have formed a styrene-based copolymer with a predetermined conjugated divinyl compound and a predetermined monovinyl compound in an appropriate content ratio, and also have a styrene-based copolymer. We have found that by controlling the molecular weight and molecular weight distribution of the copolymer in an appropriate range, it is possible to realize an extruded foam sheet suitable for high magnification and excellent molding processability and a molded product thereof, and completed the present invention. I came to do it.

That is, the present invention is as shown below.
[1]
An extruded foamed sheet having a thickness of 0.5 mm to 5.0 mm and containing a styrene-based copolymer.
The styrene-based copolymer is a copolymer of a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000 and one or more types of monovinyl compounds containing at least styrene, and the content of the conjugated divinyl compound is a said monovinyl compound per mole 2.0 × ¹⁰ -6 ~4.0 × ^{10 -4} mol, weight average molecular weight of the styrene-based copolymer (Mw) of a 200000-500000, molecular weight of 2,000,000 An extruded foam sheet having the above ratio of 0.3% to 6.0%.
[2]
The extruded foam sheet according to item 1, wherein the conjugated divinyl compound has a number average molecular weight (Mn) of 1000 to 30,000.
[3]
The extruded foam sheet according to item 1 or item 2, wherein the conjugated divinyl compound is in the form of a chain.
[4]
The extruded foam sheet according to any one of items 1 to 3, wherein at least one of the conjugated vinyl groups of the conjugated divinyl compound is located at the terminal of the conjugated divinyl compound.
[5]
The extruded foam sheet according to any one of items 1 to 4, wherein the ratio of the Z average molecular weight (Mz) to Mw of the styrene-based copolymer is 1.8 to 5.0.
[6]
The extruded foam sheet according to any one of items 1 to 5, wherein the proportion of the styrene-based copolymer having a molecular weight of 1 million or more is 4.0% to 20.0%.
[7]
The extruded foam sheet according to items 1 to 6, wherein the styrene-based copolymer has a rising start strain of 0.2 to 1.3 and a maximum rising ratio of 1.2 to 4.0.
[8]
The extruded foam sheet according to any one of items 1 to 7, wherein the conjugated divinyl compound is a (hydrogenated) polybutadiene-terminated di (meth) acrylate.
[9]
The secondary molded product of the extruded foam sheet according to any one of items 1 to 8.

The extruded foamed sheet of the present invention exhibits excellent moldability even at a high foaming ratio. Further, by secondary molding the extruded foam sheet of the present invention, it is possible to efficiently obtain a molded product having few defects and a high magnification.

It is a log-log graph which plotted the Henky strain on the horizontal axis and the extensional viscosity on the vertical axis for the styrene-based copolymers obtained in Examples and Comparative Examples. It is a graph which plotted the foaming ratio on the horizontal axis, and the deep drawing formability on the vertical axis about the extruded foam sheet obtained in an Example and a comparative example.

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

<Extruded foam sheet>
The extruded foamed sheet of the present embodiment is an extruded foamed sheet having a thickness of 0.5 mm to 5.0 mm containing a styrene-based copolymer, and the styrene-based copolymer has a number average molecular weight (Mn) of 850 to 100,000. It is a copolymer of the conjugated divinyl compound of the above and one or more kinds of monovinyl compounds containing at least styrene, and the content of the conjugated divinyl compound is 2.0 × ^{10-6 to} 4.0 per mol of the monovinyl compound. × a ^{10 -4} mol, weight average molecular weight of the styrene-based copolymer (Mw) of a 200000-500000, the proportion of molecular weight of 2,000,000 or more is 0.3% to 6.0%.

<Styrene-based copolymer>
According to this embodiment, it is possible to provide an extruded foam sheet which is suitable for high magnification and has excellent molding processability. Specifically, although not limited to the theory, in the present embodiment, the molecular chains of the obtained styrene-based copolymer are divided into a plurality of molecular chain portions mainly composed of monovinyl compounds and the molecular chain portions thereof. It is easy to form a moiety derived from a conjugated divinyl compound that is interconnected with each other and to set a predetermined distance between the molecular chain portions. That is, it is presumed that a portion having an "H" -shaped branched structure can be easily introduced into the molecular chain of the styrene-based copolymer. In the styrene-based copolymer of the present embodiment, the molecular chains of the styrene-based copolymer are likely to be effectively entangled with each other (such an effect is also referred to as "entanglement effect"), and therefore the styrene-based copolymer is a styrene-based copolymer. The molding processability of the above can be improved. Further, in the present embodiment, the content of the conjugated divinyl compound and the molecular weight and molecular weight distribution of the styrene-based copolymer are within a predetermined range, so that the molding processability of the styrene-based copolymer can be effectively improved. It is possible to effectively prevent the styrene-based copolymer from gelling. Therefore, according to the present embodiment, it is possible to provide an extruded foamed sheet having excellent molding processability even at a high foaming ratio, and due to the small amount of gel-like substance, for example, an extruded foamed sheet containing a styrene-based copolymer. By secondary molding, it is possible to efficiently obtain a molded product having few defects and a high magnification.

(Monovinyl compound)
The styrene-based copolymer contained in the extruded foamed sheet of the present embodiment contains at least one type of monovinyl compound containing at least a styrene-based compound as a monomer forming the styrene-based copolymer. The monovinyl compound may be composed of only a styrene-based compound (monomer), or may be composed of a styrene-based compound and a compound having another monovinyl group copolymerizable with the styrene-based compound. The monovinyl compound is not particularly limited as long as it can be copolymerized with the styrene compound as well as the styrene compound. For example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth). Examples include vinyl compounds such as acrylate and (meth) acrylonitrile, and dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, maleic anhydride, maleimide, and nuclear-substituted maleimide. Examples of the styrene-based compound include styrene, α-methylstyrene, paramethylstyrene, ethylstyrene, propylstyrene, butylstyrene, chlorostyrene, bromostyrene and the like, and styrene is preferable. The content of the styrene compound is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, of the total content of the monovinyl compounds.

(Conjugated divinyl compound)
The conjugated divinyl compound in the present embodiment is a compound having a number average molecular weight (Mn) of 850 to 100,000 and having at least two conjugated vinyl groups in the molecule. Further, the conjugated divinyl compound in the present embodiment is preferably in the form of a chain rather than in the form of a network. The chain may be linear and may have one or more side chains in the main chain. This is because the chain-like conjugated divinyl compound allows the molecular chain to have a more linear shape, which tends to improve the entanglement effect. The side chain preferably has 6 or less carbon atoms, and more preferably 4 or less carbon atoms.
The conjugated vinyl group in the conjugated divinyl compound can be at any position in the molecule, and it is preferable that at least one of the conjugated vinyl groups is located at the end of the conjugated divinyl compound. Of the at least two conjugated vinyl groups, the two conjugated vinyl groups are more preferably located at different ends in the molecule. When the conjugated divinyl compound is in the form of a chain, it is more preferable that the two conjugated vinyl groups are located at different ends of the main chain, that is, both ends of the main chain are conjugated divinyl groups. Since the conjugated vinyl group is located at the terminal, the polymerization reactivity can be enhanced.
When the conjugated divinyl compound is chain-like and three or more conjugated vinyl groups are present, it is preferable that at least two conjugated vinyl groups among the three or more conjugated vinyl groups are located at the terminals, and the remaining one. More preferably, one or more conjugated vinyl groups are also located at the ends.

If the number of conjugated vinyl groups in the conjugated divinyl compound is large, the number of branching points increases, and gelation may easily occur in the process of recovering the reactor and raw materials, resulting in deterioration of the transparency of the styrene copolymer and deterioration of the transparency of the styrene copolymer. Reactor cleaning may be required and productivity may decrease. Therefore, the number of conjugate vinyl groups in the conjugated divinyl compound is preferably 5 or less, more preferably 4 or less, further preferably 3 or less, and particularly preferably 2. ..

When the conjugated vinyl group is present near the terminal, the reactivity with the monovinyl compound can be more effectively enhanced and gelation can be suppressed more effectively. Therefore, in the present embodiment, the “terminal” is referred to as “terminal” in the molecular chain. , A portion (end portion) having a certain range including the position (atom) at the most end of the molecular chain may be used. In other words, the conjugated vinyl group may be located near the terminal, and a certain number of atoms may be present on the terminal side of the conjugated vinyl group. In the present embodiment, the “terminal” is not limited, but is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less of the stretched chain length of the conjugated divinyl compound. 5% or less is even more preferable. Most preferably, the conjugated vinyl group constitutes the position (atom) at the end of the molecule of the conjugated divinyl compound.

In the present embodiment, the conjugated vinyl group includes an olefinic double bond copolymerizable with a monovinyl compound and a structure forming a conjugated system with the olefinic double bond, such as, but not limited to, a carbonyl group and an aryl group. It is a group to have. The conjugated vinyl group is not particularly limited, and examples thereof include an acryloyl group, an aryl group substituted with a vinyl group, and the structure having a conjugated vinyl group in the conjugated divinyl compound is not particularly limited, but for example. , (Meta) acrylate, urethane (meth) acrylate, aromatic vinyl, maleic acid, fumaric acid and the like are also added. The at least two conjugated vinyl groups may be the same or different from each other.

In the present embodiment, the number average molecular weight (Mn) of the conjugated divinyl compound is 850 to 100,000, preferably 1000 to 100,000, more preferably 1000 to 80000, 1000 to 60000, 1000 to 30000, and even more preferably. For example, 1200 to 80000, 1200 to 60000, 1200 to 30000, and even more preferably 1500 to 80000, 1500 to 60000, and particularly preferably 1500 to 30000. When the number average molecular weight (Mn) is less than 850, the distance between the conjugated vinyl groups of the conjugated divinyl compound is short, so that the distance between the polymer chains bonded to the conjugated divinyl compound is short, and a sufficient entanglement effect cannot be obtained. , Inferior in molding processability. When the molecular weight exceeds 100,000, the distance between the conjugated vinyl groups of the conjugated divinyl compound becomes long, and the reactivity of the conjugated vinyl group at the terminal decreases (because the molecular weight of the conjugated divinyl compound is large, the conjugated vinyl group at the terminal reacts. It becomes difficult to do so), and the amount of high-molecular-weight components produced decreases, which is not preferable. The number average molecular weight (Mn) of the conjugated divinyl compound means a polystyrene-equivalent number average molecular weight (Mn) measured by gel permeation chromatography (GPC).

The main chain structure of the conjugated divinyl compound of the present embodiment is not particularly limited, and examples thereof include polyolefins such as polyethylene, polypropylene, and polyisoprene, polystyrene, polybutadiene, hydrogenated polybutadiene, polyphenylene ether, polyester, and polyphenylene sulfide.

Specific conjugated divinyl compounds include (hydrogenated) polybutadiene-terminated di (meth) acrylate (“(hydrogenated)” refers to a hydrogenated or non-hydrogenated compound; the same shall apply hereinafter). Terminal di (meth) acrylate compounds such as polyethylene glycol-terminated di (meth) acrylate, polypropylene glycol-terminated di (meth) acrylate, ethoxylated bisphenol A-terminal di (meth) acrylate, and ethoxylated bisphenol F-terminal di (meth) acrylate, Examples thereof include (hydrogenated) polybutadiene-terminated urethane acrylates, polyethylene glycol-terminated urethane acrylates, polypropylene glycol-terminated urethane acrylates, ethoxylated bisphenol A-terminal urethane acrylates, and terminal urethane acrylate compounds such as ethoxylated bisphenol F-terminated urethane acrylates. For example, in the case of polypropylene glycol-terminated (meth) acrylate, the number of bonds of propylene glycol in the repeating unit is determined so that the number average molecular weight (Mn) is 850 to 100,000. From the viewpoint of compatibility with the styrene-based copolymer, the conjugated divinyl compound is preferably (hydrous) polybutadiene-terminated di (meth) acrylate, polystyrene-terminated di (meth) acrylate, or polyphenylene ether-terminated divinyl. "Terminal" and "both ends" in the compound name mean that the conjugated vinyl group is located at both ends.

(Content of conjugated divinyl compound)
The content of the conjugated divinyl compound in the present embodiment is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol, preferably 5.0 × 10 ^{-6 to} 3.5 × 10 ^{− per mol of the monovinyl compound. It is 4} mol, more preferably 1.5 × 10 ^{-5 to} 3.0 × 10 ^-4 mol, and even more preferably 2.0 × 10 ^{-5 to} 2.5 × 10 ^-4 mol. If the content is ^{less than 2.0 × 10-6} mol, the molding processability is inferior. On the other hand, when the content exceeds 4.0 × 10 ^-4 mol, a large amount of gel-like substance is generated, which causes defective secondary molding and the like.

(Molecular weight)
The weight average molecular weight (Mw) of the styrene-based copolymer used in the present embodiment is 200,000 to 500,000, preferably 220,000 to 480,000, and more preferably 240,000 to 450,000. By setting the Mw of the styrene-based copolymer to 200,000 to 500,000, it is possible to secure the strength of the styrene-based copolymer, suppress the generation of gel-like substances, and further improve the moldability and fluidity. it can. The ratio of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) of the styrene-based copolymer of the present embodiment is preferably 1.8 to 5.0, more preferably 2.0 to 4.8. More preferably, it is 2.1 to 4.7. By setting the ratio of Mz to Mw of the styrene-based copolymer in the range of 1.8 to 5.0, the strength of the styrene-based copolymer is ensured, the generation of gel-like substances is suppressed, and the molding processability is improved. And fluidity can be improved.

In the styrene-based copolymer used in the present embodiment, the above-mentioned weight average molecular weight (Mw) and the ratio of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) are determined when the styrene-based monomer is radically polymerized. In addition, it can be controlled by the type and addition amount of the conjugated divinyl compound, the reaction temperature, the residence time, the type and addition amount of the polymerization initiator, the type and amount of the solvent, the type and the addition amount of the chain transfer agent, and the like. More specifically, the above-mentioned control of the weight average molecular weight (Mw) and the like is not limited, but for example, in the production method: the amount of the polymerization initiator added at the time of polymerization is increased, and the reaction of the polymerization is carried out. It can be controlled by lowering the temperature; reducing the amount of the polymerization solvent used; and / or increasing the residence time during polymerization, and by doing so, the styrene-based copolymer obtained can be obtained. The coalesced molecular chain can be formed into a desired shape, and the proportion of the high molecular weight component can be appropriately increased.

The weight average molecular weight (Mw), Z average molecular weight (Mz), the ratio of molecular weights of 1 million or more and the ratio of 2 million or more, which will be described later, are the derivatives measured by gel permeation chromatography (GPC). It is the weight ratio of the molecular weight distribution.

(Ratio of high molecular weight components)
The proportion of the styrene-based copolymer used in the present embodiment having a molecular weight of 2 million or more is 0.3 to 6.0%, preferably 0.8 to 5.0%, and 1.4 to 4. More preferably, it is 8%. By setting the ratio of the molecular weight of 2 million or more to the range of 0.3 to 6.0%, the content of the gel-like substance can be very reduced. The ratio of the molecular weight of 1,000,000 or more is preferably 4.0 to 20.0%, more preferably 5.0 to 18.0%, still more preferably 5.0 to 15.0%. By setting the ratio of the molecular weight of 1,000,000 or more to the range of 4.0 to 20.0%, a styrene-based copolymer having excellent molding processability and fluidity can be obtained.
The molecular weight ratio of the styrene-based copolymer used in the present embodiment is the type and addition amount of the conjugated divinyl compound, the reaction temperature, the residence time, the type of the polymerization initiator, and the type of the polymerization initiator when the styrene-based monomer is radically polymerized. It can be controlled by the amount of addition, the type and amount of the solvent, the type and amount of the chain transfer agent, and the like. More specifically, the above-mentioned control of the ratio of the molecular weight of 2 million or more and the molecular weight of 1 million or more is not limited, but for example, in the production method: the amount of the polymerization initiator added at the time of polymerization is increased. It can be controlled by lowering the reaction temperature of the polymerization; reducing the amount of the polymerization solvent used; and / or lengthening the residence time during the polymerization. While reducing the proportion of the low molecular weight component of the styrene-based copolymer, the proportion of the high molecular weight component, that is, the proportion of the molecular weight of 2 million or more and the molecular weight of 1 million or more can be appropriately increased.

(Melt Mass Flow Rate (MFR))
The melt mass flow rate (MFR) of the styrene-based copolymer used in the present embodiment is preferably 0.5 to 8.0. It is more preferably 0.6 to 5.0, even more preferably 0.7 to 4.0, and particularly preferably 0.8 to 3.0. By setting the melt mass flow rate in the range of 0.5 to 8.0, a styrene-based copolymer having a better balance between molding processability and fluidity can be obtained.

(Rising start strain, maximum rising strain, and maximum rising ratio)
The rising start strain of the styrene-based copolymer used in the present embodiment is preferably 0.2 to 1.3, more preferably 0.3 to 1.1, and even more preferably 0.4 to 1. It is 0. In the specification of the present application, the "rising starting strain" is a strain that causes strain hardening and is an index of formability. The smaller the strain at the beginning of the rise, in other words, the faster the rise, the more strain hardening occurs from the time of low stretching, and the better the moldability, so the wall thickness of the secondary molded product may become more uniform, and the secondary molded product may become more uniform. May be thinned.

The maximum rise ratio of the styrene-based copolymer used in the present embodiment is preferably 1.2 to 5.0, more preferably 1.3 to 4.8, and even more preferably 1.4 to 4.6. is there. In the present specification, the "maximum rising ratio" means (extensional viscosity of the non-linear region of the maximum rising strain / the extensional viscosity of the linear region of the maximum rising strain), and the "maximum rising strain" means the maximum extensional viscosity. It means the henky strain when it becomes. The maximum rise ratio is an index showing the degree of strain hardening at the maximum rise strain. The larger the maximum rise ratio, the greater the degree of strain hardening and the better the moldability. When the maximum rise ratio is 1.2 or more, the extensional viscosity becomes high at the time of high strain, that is, when the resin is thinly stretched during the molding process, so that the wall thickness of the molded product becomes uniform and the molded product is torn during molding. It tends to be difficult. When the maximum rise ratio is 5.0 or less, the extensional viscosity at the time of molding does not become too high, which is preferable from the viewpoint of the balance between productivity and moldability.

(Additives, etc.)
The styrene-based copolymer used in the present embodiment contains rubber-containing components such as HI-PS resin and MBS resin as rubber-reinforced aromatic vinyl-based resins and aromatic vinyl-based heat such as SBS, if necessary. A plastic elastomer may be contained in an amount of about 1% to 50%. Further, in order to suppress the thermal decomposition of the polymer in the recovery step of the unreacted monomer, for example, 2- [1- (2-hydroxy-3,5-di-t-phenylpentyl) ethyl] -4,6-di It may contain a processing stabilizer such as -t-phenylpentyl acrylate. 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 may be contained. In addition, additives commonly used in the field of styrene-based resins, such as nucleating agents, flame retardants, and colorants, may be combined and added to the styrene-based copolymer as long as the object of the present embodiment is not impaired. The additive is not particularly limited, and examples thereof include a nucleating agent such as talc, a flame retardant such as hexabromocyclododecane, and a coloring agent such as titanium oxide and carbon black. Further, a styrene resin may be used as pellets, and ethylene bisstearylamide, zinc stearate, magnesium stearate or the like may be sprinkled on the pellets as an external lubricant for the pellets.

Antioxidants are generally capable of stabilizing peroxide radicals such as hydroperoxy radicals generated during thermoforming or light exposure, or decomposing peroxides such as hydroperoxide produced. It is an ingredient that can be produced. The antioxidant is not particularly limited, and examples thereof include a hindered phenolic antioxidant and a peroxide decomposing agent. The hindered phenolic antioxidant can be used as a radical chain inhibitor, and the peroxide decomposition agent can decompose the peroxide produced in the system into more stable alcohols to prevent autoxidation. The hindered phenolic antioxidant is not limited to the following, but is limited to 2,6-di-t-butyl-4-methylphenol, stylenate phenol, and n-octadecyl-3- (3,5-di-). t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-) Methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 4,4' − Butylidenebis (3-methyl-6-t-butylphenol), 4,4'-thiobis (3-methyl-6-t-butylphenol), alkylated bisphenol, tetrakis [methylene-3- (3,5-di-) t-butyl-4-hydroxyphenyl) propionate] methane, and 3,9-bis [2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) -propionyloxy] -1,1 -Dimethylethyl] -2,4,8,10-tetraoxyspiro [5.5] undecane and the like. The peroxide decomposing agent is not limited to the following, but organic phosphorus-based peroxide decomposition such as trisnonylphenylphosphine, triphenylphosphine, and tris (2,4-di-t-butylphenyl) phosphite. Agents, as well as dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, pentaerythrityl tetrakis (3-laurylthiopro) Pionate), ditridecyl-3,3'-thiodipropionate, and organic sulfur peroxide degrading agents such as 2-mercaptobenzimidazole. The amount of the antioxidant added is preferably 0.01 part by mass or more and 1 part by mass or less, and more preferably 0.1 part by mass or more and 0.5 part by mass with respect to 100 parts by mass of the styrene-based copolymer in the extruded foamed sheet. It is less than a part by mass.

The flame retardant is not limited to the following, but from the viewpoint of flame retardancy and compatibility with styrene resins, for example, hexabromocyclododecane, brominated SBS block polymer, and 2,2-bis (4'( Examples thereof include brominated flame retardants such as 2 ", 3" -dibromoalkoxy) -3', 5'-dibromophenyl) -propane, and brominated bisphenol flame retardants.

The brominated bisphenol flame retardant is not limited to the following, but is, for example, tetrabromobisphenol A, tetrabromobisphenol A-bis (2,3-dibromopropyl ether), tetrabromobisphenol A-bis (2,3-dibromo). -2 Methylpropyl ether), Tetrabromobisphenol S, Tetrabromobisphenol S-bis (2,3-dibromoprol ether), Tetrabromobisphenol S-bis (2,3-dibromo-2methylpropyl ether), Tetrabromobisphenol F, tetrabromobisphenol F-bis (2,3-dibromopropyl ether), tetrabromobisphenol F-bis (2,3-dibromo-2 methylpropyl ether) tetrabromobisphenol A-bis (allyl ether), tetrabromobisphenol Examples thereof include A polycarbonate oligomer and an epoxy group adduct of tetrabromobisphenol A oligomer. Among the brominated bisphenol flame retardants, tetrabromobisphenol A bis (2,3-dibromopropyl ether) and tetrabromobisphenol A-bis (2,3-dibromopropyl ether) are polystyrene. It is preferable because it is difficult to decompose during kneading with a system resin, has a high flame retardant effect, and tends to be easily exhibited. When tetrabromobisphenol A-bis (2,3-dibromopropyl ether) and tetrabromobisphenol A-bis (2,3-dibromo-2 methylpropyl ether) are used in combination, flame retardancy and thermal stability are achieved. It is more preferable because it tends to be superior.

As the brominated flame retardant, it is preferable to use a brominated isocyanurate-based flame retardant in combination as a flame retardant aid. The brominated isocyanurate-based flame retardant is not limited to the following, and includes, for example, mono (2,3-dibromopropyl) isocyanurate, di (2,3-dibromopropyl) isocyanurate, and tris (2,3-dibromopropyl). ) Isocyanurate, mono (2,3,4-tribromobutyl) isocyanurate, di (2,3,4-tribromobutyl) isocyanurate, tris (2,3,4-tribromobutyl) isocyanurate, etc. Can be mentioned. Among the brominated isocyanurates, tris (2,3-dibromopropyl) isocyanurate is particularly preferable because it exhibits an extremely high flame retardant effect.

<Manufacturing method of styrene copolymer>
(Polymerization process)
Examples of the polymerization method of the styrene-based copolymer used in the present embodiment include known styrene polymerization methods such as a massive polymerization method, a solution polymerization method, and a suspension polymerization method. These polymerization methods may be a batch polymerization method or a continuous polymerization method, and are preferably continuous polymerization methods from the viewpoint of productivity. As a continuous bulk polymerization method, for example, a monovinyl compound, a conjugated divinyl compound having a conjugated vinyl group, a solvent, a polymerization catalyst, a chain transfer agent, etc., if necessary, are added and mixed, and a raw material solution containing monomers is added. To prepare. The raw material solution is placed in a facility equipped with one or more reactors arranged in series and / or in parallel and a devolatilizer for a volatilization step of removing volatile components such as unreacted monomers. Examples thereof include a method of continuously feeding and gradually advancing the polymerization.

Examples of the reactor include a completely mixed reactor, a laminar reactor, and a loop reactor that extracts a part of the polymerization solution while advancing the polymerization. The order of arrangement of these reactors is not particularly limited.

When polymerizing the styrene-based copolymer used in the present embodiment, a polymerization solvent, a polymerization initiator such as an organic peroxide, and a chain transfer agent should be used as necessary from the viewpoint of controlling the polymerization reaction. Can be done. The polymerization solvent is generally used for adjusting the polymerization rate, molecular weight, etc. in continuous bulk polymerization or continuous solution polymerization. The polymerization solvent is not particularly limited, and examples thereof include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane. The amount of the polymerization solvent used is not particularly limited, but is usually 1 to 50% by mass as the composition in the polymerization reactor from the viewpoints of controlling gelation, improving productivity, increasing the molecular weight, and the like. It is preferably 3 to 20% by mass, and more preferably 3 to 20% by mass.

When the polymerization raw material is polymerized in order to obtain the styrene-based copolymer used in the present embodiment, the polymerization initiator and the chain transfer agent can be contained in the polymerization raw material composition. The polymerization initiator is not particularly limited, but is an organic peroxide, for example, 2,2-bis (t-butylperoxy) butane, 1,1-bis (t-butylperoxy) cyclohexane, and n-butyl-. Peroxyketals such as 4,4-bis (t-butylperoxy) valerate, dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, and dicumyl peroxide, acetyl peroxide, isobutyryl peroxide, etc. Diacyl peroxides, peroxydicarbonates such as diisopropylperoxydicarbonate, peroxyesters such as t-butylperoxyacetate, ketone peroxides such as acetylacetone peroxide, and hydroperoxides such as t-butylhydroperoxide. Can be done. The polymerization initiator is preferably used in an amount of 0.005 to 0.08% by mass based on the styrene-based monomer. The chain transfer agent is not particularly limited, and examples thereof include α-methylstyrene dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan. The chain transfer agent is preferably used in an amount of 0.01 to 0.50% by mass based on the styrene-based monomer.

In the present embodiment, it is preferable to add the phenolic thermal deterioration inhibitor in the polymerization step or the devolatilization step, and after the polymerization step and before the volatilization step. It is more preferable to add a phenolic thermal deterioration inhibitor after the completion of the polymerization step, preferably immediately after the completion of the polymerization step, and before the devolatilization step.

Examples of the phenolic thermal deterioration inhibitor include 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate (trade name: Sumilyzer GM, Sumitomo Chemical). , 2- [1- (2-Hydroxy-3,5-di-t-phenylpentyl) ethyl] -4,6-di-t-phenylpentyl acrylate (trade name: Sumilyzer GS, manufactured by Sumitomo Chemical Co., Ltd.) ) Can be mentioned. The amount added was 0.01 to 0.5% by mass, preferably 0.02 to 0.3% by mass, and more preferably 0.03 to 0.2% by mass with respect to the styrene-based copolymer at the outlet of the final reactor. %.

When the amount of the phenolic thermal deterioration inhibitor added is 0.01% by mass or more, the formation of the monovinyl compound and its dimer or trimer in the volatilization step can be more effectively suppressed. On the other hand, even if the amount of the phenolic thermal deterioration inhibitor added is more than 0.5% by mass, the effect of suppressing the formation of the monovinyl compound and its dimer or trimer may not be sufficiently obtained. is there.

(Devolatile process)
As the devolatilization device, for example, a normal volatilization device such as a flash drum, a twin-screw volatilizer, a thin film evaporator, or an extruder can be used, and generally, a vacuum volatilization tank equipped with a heater or a devolatilizer can be used. A volatile extruder or the like is used. As the arrangement of the devolatilizer, for example, a vacuum devastation tank with a heater is used in only one stage, a vacuum devolatilization tank with a heater is connected in two stages in series, and a vacuum devastation tank with a heater is connected. An example is one in which a volatilization tank and a devolatilization extruder are connected in series. In order to reduce the volatile components as much as possible, it is preferable that a vacuum devastation tank with a heater is connected in two stages in series, or a vacuum devolatilization tank with a heater and a devolatilization extruder are connected in series. ..

The conditions of the devolatilization step are not particularly limited. For example, when the styrene-based copolymer is polymerized by bulk polymerization, the finally unreacted monovinyl compound is preferably 50% by mass in the styrene-based copolymer. Below, the polymerization can proceed until it becomes more preferably 40% by mass or less. By the devolatile treatment, unreacted substances (monovinyl compounds) and / or volatile components such as solvents can be removed.

The temperature of the devolatile treatment is usually about 190 to 280 ° C. The pressure of the devolatilization treatment is preferably 0.1 to 50 kPa, more preferably 0.13 to 13 kPa, still more preferably 0.13 to 7 kPa, and particularly preferably 0.13 to 1.3 kPa. As the volatilization method, for example, it is desirable to volatilize by reducing the pressure under heating, or through an extruder designed to remove volatile components.

<Manufacturing method of extruded foam sheet>
Examples of the method for producing the extruded foam sheet of the present embodiment include a method of melting and kneading the above-mentioned styrene-based copolymer together with other compounds in an extruder and extruding the above-mentioned styrene-based copolymer. The method can be mentioned. First, the styrene-based copolymer is melt-kneaded by an extruder connected to the circular die, and the melt-kneaded product is extruded in a foamed state from an annular opening provided in front of the circular die to form a cylindrical shape. Form foam. Next, the foam is brought into sliding contact with the outer peripheral surface of a cooling mandrel having a diameter larger than the opening of the circular die to be cooled while being stretched in the circumferential direction, and this is continuously cut and developed along the extrusion direction. A commonly known method can be used.

As the foaming agent and foam nucleating agent at the time of extrusion foaming, commonly used substances can be used. The foaming agent is not particularly limited, and examples thereof include butane, pentane, chlorofluorocarbon, and water, and butane is preferable. The effervescent nucleating agent is not particularly limited, but for example, talc or the like can be used. The thickness of the extruded foam sheet of the present embodiment is 0.5 mm to 5.0 mm, and the apparent density is preferably 50 g / L to 300 g / L. The basis weight of the extruded foam sheet of the present embodiment is preferably ^{80g / m 2 ~300g / m 2} . Extruded foam sheet of the present embodiment has a thickness of 0.5 mm to 5.0 mm, an apparent density of 50 g / to 300 g / L, it is preferable that a basis weight of ^{80g / m 2 ~300g / m 2} . The film may be laminated on the extruded foam sheet. As the type of film, those used for general polystyrene may be used.

<Molded product>
The molded product in the present embodiment is a secondary molded product manufactured by using the extruded foam sheet of the present embodiment. By secondary molding the extruded foam sheet of the present embodiment by a conventionally known method such as vacuum forming, vacuum forming, vacuum forming, double-sided vacuum forming, press molding, etc., a tray, a cup, a bowl container, a natto container, etc. It is possible to form a secondary molded product such as. As an example of the secondary molded product of the present embodiment, the extruded foam sheet of the present embodiment described above is used as a molding material, and the width is 5.5 to 21 cm and the width is 6. Examples include food tray containers having a depth of 5 to 36 cm and a depth of 1.1 to 3.4 cm, and food soup / bowl containers having a length of 3.5 to 20 cm, a width of 3.5 to 20 cm, and a depth of 2.0 to 20 cm. .. The temperature condition for vacuum forming is not limited to the following, but is usually preferably 120 to 150 ° C.

Hereinafter, embodiments of the present invention will be specifically described 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 were carried out based on the following methods.

(1) Measurement of molecular weight The number average molecular weight (Mn) of the conjugated divinyl compound, the weight average molecular weight (Mw) of the styrene copolymer, the Z average molecular weight (Mz), the ratio of the molecular weight of 1 million or more, and the molecular weight of 2 million or more. The ratio and the number average molecular weight (Mn) of the conjugated divinyl compound were measured using gel permeation chromatography (GPC). It was measured under the following conditions.
Equipment: Tosoh HLC-8220
Sorting column: Two Tosoh TSK gel Super HZM-H (inner diameter 4.6 mm) are connected in series Guard column: Tosoh TSK gel super HZ-H
Measuring solvent: tetrahydrofuran (THF)
Sample concentration: 5 mg of the measurement sample was dissolved in 10 mL of a solvent and filtered through a 0.45 μm filter.
Injection volume: 10 μl
Measurement temperature: 40 ° C
Flow velocity: 0.35 mL / min Detector: Ultraviolet absorption detector (UV-8020, wavelength 254 nm)
To create a calibration curve, 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) was used. A calibration curve was created using an approximate expression of a linear straight line.

(2) Measurement of Melt Mass Flow Rate (MFR) The melt mass flow rate of the styrene-based copolymer was measured under a load condition of 200 ° C. and 49 N in accordance with ISO1133.

(3) Evaluation of gel-like substance of solid sheet Using a 30 mmφ sheet extruder (manufactured by Soken Co., Ltd.), a styrene-based copolymer was extruded to prepare a sheet (solid sheet) having a thickness of 0.5 mm. Twenty test pieces were cut out from the obtained sheet to a size of 100 mm in length × 100 mm in width, and a gel-like substance having an average of 2 mm or more in minor axis and major axis was visually measured. Judgment was made when the number of test pieces containing the gel-like substance was 0 to 2 as "⊚", 3 to 10 as "○", and 11 or more as "x".

(4) Measurement of rising start strain, maximum rising strain, and maximum rising ratio The rising starting strain, maximum rising strain, and maximum rising ratio of the styrene copolymer were measured based on the following viscoelasticity measurements.
Device name: Viscoelasticity measuring device ARES-G2 (manufactured by TA Instruments)
Measurement system: ARES-EVF option Specimen dimensions: Length 20 mm, Thickness 0.7 mm, Width 10 mm
Elongation strain rate: 0.01 / sec Temperature: 150 ° C
Measurement atmosphere: In a nitrogen stream Preheating time: 2 minutes Preliminary extension strain rate: 0.03 / sec,
Preliminary extension length: 0.295 mm
Relaxation time after pre-stretching: 2 minutes In the viscoelasticity measurement, the test piece was attached to a roller, and after the temperature became stable, the test piece was allowed to stand for the above preheating time and preheated. After the completion of preheating, pre-stretching was performed under the above conditions. After the pre-stretching, the mixture was allowed to stand for 2 minutes to relieve the stress generated by the pre-stretching and measured.

The maximum rising strain refers to the henky strain when the extensional viscosity is maximized in the above viscoelasticity measurement.
In addition, the strain at the start of rising was calculated by the following method. Based on the results obtained by the above viscoelasticity measurement, a semi-logarithm graph was created in which the Henky strain was plotted on the horizontal axis and the extensional viscosity was plotted on the vertical axis, and the Henky strain was linear in the range of 0.2 to 0.5. A power approximation curve was created as the region (for example, the broken line in FIG. 1). When strain hardening occurs, the actual extensional viscosity becomes higher than the extensional viscosity of the approximate straight line extrapolating this linear region. In the same Henky strain, the Henky strain when the difference between the extensional viscosity in the nonlinear region and the extensional viscosity in the linear region was 3% of the extensional viscosity in the nonlinear region was defined as the rising start strain. The maximum rising ratio was calculated by (extensional viscosity of the non-linear region at the maximum rising strain / extensional viscosity of the linear region at the maximum rising strain).

(5) Foam Density The foam density of the extruded foam sheet was measured based on ISO10350. A hydrometer (SGM-220-60 measuring instrument) manufactured by Shimadzu Corporation was used as the measuring device.

(6) Foaming Magnification The foaming ratio was calculated from the following equation using the value of the foam density (ρf) obtained in (5) above and the density of the styrene-based copolymer (ρ).
Foaming magnification = ρ / ρf
(7) Deep-drawing moldability of extruded foamed sheet 0.15 parts by mass of talc (average particle size 1.3 μm) as a foaming nucleating agent and liquefied butane as a foaming agent 4 parts by mass of a styrene-based copolymer. A styrene-based resin composition was obtained by adding parts by mass. The styrene resin composition was extruded and foamed using an extrusion foaming machine equipped with a circular die having a diameter of 150 mm. The temperature of the resin melting zone of the extruder 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 145 ° 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 an extrusion foam sheet having a sheet thickness of 1.4 mm and a width of 1000 mm.
The extruded foam sheet was left at 23 ± 3 ° C. and a relative humidity of 50 ± 5% for 20 days. Then, using a sheet container molding machine manufactured by Soken, the foam sheet was sandwiched between the fixed frames of the sheet molding machine, the average temperature of the heater was set to 200 ° C., the ambient temperature was set to 130 ° C., and the mixture was heated for 15 seconds. Next, vacuum forming was performed by sliding the fixed frame together with a cup-shaped mold (temperature 40 ° C.) having a diameter of 10 cm and a depth of 6 cm, and 100 molded bodies were molded at a time. It was visually confirmed whether or not tearing occurred on the side surface of the molded body, and the number of molded bodies that could be molded without tearing was used as an index of deep drawing formability.

<Production example of conjugated divinyl compound>
Conjugated divinyl compounds 1, 5 and 6 were produced based on the following methods.

(Conjugated divinyl compound 1)
In a 5 L volume reaction vessel equipped with a stirrer, thermometer and reflux condenser, 2742 g of polybutadiene double-ended alcohol (Mn: 1900), 379 g of methyl acrylate, 380 g of n-hexane, 0.8194 g of hydroquinone monomethyl ether, and 0.5533 g of 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl was charged. While passing the obtained mixture through a calcium chloride tube, air was blown into the mixture, and reflux dehydration was performed at 80 to 85 ° C. The water content of this mixture was measured by the Karl Fischer method, and it was confirmed that the water content was 200 ppm or less. Then, as a transesterification catalyst, 1.3685 g of tetra n-butyl titanate was added to the above mixture, and the produced methanol was distilled off from the reaction system under reflux of n-hexane, which is an azeotropic solvent, while stirring. The reaction was carried out at a reaction temperature of 80 to 85 ° C. for 10 hours.

Next, the temperature inside the reaction vessel was adjusted to 75 to 80 ° C., and the mixture was concentrated at a reduced pressure of 70 to 2 kPa until 95% or more of the methyl acrylate and n-hexane used were distilled off to remove excess methyl acrylate. n-Hexane was recovered. To the resulting polybutadiene both ends diacrylate 2070 g, toluene 2000 g, acetone 200 g, ion exchanged water 20g, and hydrotalcite (formula _{Mg 6 Al 2 (OH) 16CO} 3 · 4H 2 O) [manufactured by Kyowa Chemical as an ester exchange catalyst 20 g of Kyoward 500PL, manufactured by Kogyo Co., Ltd., was added and treated at 75 to 80 ° C. for 2 hours. Next, the temperature inside the reaction vessel was adjusted to 75 to 80 ° C., and the mixture was concentrated at a reduced pressure of 90 to 35 kPa to recover 400 g of a mixed distillate of toluene, acetone and water, and the obtained concentrated solution was air-conditioned. The catalyst and the adsorbent were separated by filtration under pressure, and the solvent was further degassed at a temperature of 60 to 80 ° C. and a reduced pressure of 30 to 0.8 kPa to obtain a conjugated divinyl compound 1.

The conversion rate of the polybutadiene biterminal diacrylate of the conjugated divinyl compound 1 was measured by high performance liquid chromatography (HPLC) and found to be 99.3%. The polystyrene-equivalent number average molecular weight (Mn) measured by GPC was 1900.

<Conjugated divinyl compound 5>
The conjugated divinyl compound 5 produced under the same conditions except that the molecular weight of the polybutadiene double-ended alcohol was changed to Mn: 25000 had a conversion rate of 99.5% of the polybutadiene double-ended diacrylate. The polystyrene-equivalent number average molecular weight (Mn) measured by GPC was 26000.

(Conjugated divinyl compound 6)
The conjugated divinyl compound 6 produced under the same conditions except that the molecular weight of the polybutadiene double-ended alcohol was changed to Mn: 57000 had a conversion rate of 99.2% of the polybutadiene double-ended diacrylate. The polystyrene-equivalent number average molecular weight (Mn) measured by GPC was 58,000.

<Production example of styrene copolymer and extruded foam sheet>
(Example 1)
80 parts by mass of styrene monomer, 20 parts by mass of ethylbenzene, 0.035 parts by mass of conjugated divinyl compound 1 (polybutadiene terminal acrylate Mn: 1900) (2.4 × ^10-5 mol with respect to 1 mol of styrene), polymerization initiation 0.030 parts by mass of 2,2-bis (4,4-di-tertiary-butylperoxycyclohexyl) propane [manufactured by Nichiyu Co., Ltd .: Pertetra A] was added as agent 1 to prepare a raw material solution. The prepared raw material solution was continuously supplied at 1.00 L / hour to a completely mixed first reactor having an internal volume of 6 L maintained at a temperature of 105 ° C. Then, the polymerization solution from the first reactor was supplied to the plug-flow type second reactor having an internal volume of 3 L. In the second reactor, the temperatures of the three zones were maintained at 119 ° C., 133 ° C., and 143 ° C., respectively, in the order in which the raw material solutions passed. In the second zone, 0.03 parts by mass of 1,1-di- (tertiary-butylperoxy) cyclohexane [manufactured by NOF CORPORATION: Perhexa C] was added as the polymerization initiator 2. Then, the polymerization solution from the second reactor was supplied to a vacuum degassing tank heated to a temperature of 240 ° C. to remove volatile components such as unreacted monomers and solvents, and after 72 hours of continuous operation, for evaluation. A styrene-based copolymer was obtained.

Table 1 shows the production conditions and analysis results of the styrene-based copolymer. The conjugated divinyl compound 1 was synthesized by the method described in Production Example. The number average molecular weight (Mn) is a polystyrene-equivalent value measured by GPC. The number of moles of the conjugated divinyl compound contained in 1 mole of styrene (monovinyl compound) is a value measured using ^{1 1} H-NMR and ^{13 C-NMR.} As the measuring device, JEOL-ECA500 manufactured by JEOL Ltd. was used. Chloroform-d1 was used as the solvent, and the resonance line of tetramethylsilane was used as an internal standard.

Examples 2 to 14 and Comparative Examples 1 to 6 were carried out in the same manner as in Example 1 except that the conditions were changed as shown in Tables 1 and 2, and the styrene copolymers Mw, Mz / Mw and molecular weight 100 were obtained. The ratio of 10,000 or more, the ratio of molecular weight of 2 million or more, the rising strain, and the maximum rising ratio were controlled as shown in Tables 1 and 2.

The following conjugated divinyl compounds, polymerization initiators, and thermal deterioration inhibitors were used in the table. The conjugated divinyl compounds 2-9, 11 and 12 have a conjugated vinyl group at both ends of the molecule.
Conjugated divinyl compound 2: Polybutadiene diacrylate [Made by Tomoe Kogyo Co., Ltd .: CN307] Mn: 3800
Conjugated divinyl compound 3: Polybutadiene terminal acrylate [Osaka Organic Chemical Industry Co., Ltd .: BAC-45] Mn: 4800
Conjugated divinyl compound 4: Urethane acrylate oligomer [Made by Tomoe Kogyo Co., Ltd .: CN9014NS] Mn: 8000
Conjugated divinyl compound 7: Aromatic urethane acrylate [Made by Tomoe Kogyo Co., Ltd .: CN9782] Mn: 5200
Reaction formation of conjugated divinyl compound 8: (2,2', 3,3', 5,5'-hexamethylbiphenyl-4,4'-diol, 2,6-dimethylphenol polycondensate) and chloromethylstyrene Product [manufactured by Mitsubishi Gas Chemical Co., Ltd .: OPE-2ST] Mn: 1200
Conjugated divinyl compound 9: 1,3-butylenediol dimethacrylate [manufactured by Wako Pure Chemical Industries, Ltd.] Mn: 226
Conjugated divinyl compound 10: NK ester A-GLY-20E [manufactured by Shin-Nakamura Chemical Industry Co., Ltd.] Mn: 1295, the average number of conjugated vinyl in one molecule of the conjugated divinyl compound 10 is 3.
Conjugated divinyl compound 11: Divinylbenzene [manufactured by Wako Pure Chemical Industries, Ltd.] Mn: 130
Conjugated divinyl compound 12: Polyethylene glycol dimethacrylate [manufactured by Sigma-Aldrich] Mn: 750
Polymerization Initiator 2: 1,1-Di- (Turshary-Butyl Peroxy) Cyclohexane [NOF CORPORATION: Perhexa C]
Thermal deterioration inhibitor 1: 2- [1- (2-hydroxy-3,5-di-t-phenylpentyl) ethyl] -4,6-di-t-phenylpentyl acrylate [Sumitomo Chemical Co., Ltd .: Sumilyzer GS] ]
Thermal deterioration inhibitor 2: Octadecyl-3- (3,5-Jeter Chaly Butyl-4-hydroxyphenyl) -propionate [Ciba Specialty Chemicals Co., Ltd .: IRGANOX1076]

The measurement and evaluation results of Examples 2 to 14 and Comparative Examples 1 to 6 are summarized in Tables 1 and 2. As shown in FIG. 1, it can be seen that the styrene-based copolymer of Example 4 exhibited strain curing in the measurement of ARES-EVF.

As is clear from Tables 1 and 2 and FIG. 2, in Comparative Example 1 in which the number of moles of the conjugated divinyl compound contained in 1 mol of the monovinyl compound was ^{as small as 1.7 × 10-6} mol, the viscoelasticity was measured by ARES-EVF. Strain hardening did not occur. Therefore, although the foaming ratio of the extruded foamed sheet of Comparative Example 1 was relatively high, the deep draw moldability was low. In Comparative Example 2 in which the number of moles of the conjugated divinyl compound contained in 1 mol of the monovinyl compound was as large as 4.1 × 10 ^-4 mol, stable data could not be obtained in the measurement of viscoelasticity by ARES-EVF. In addition, a large amount of THF insoluble content could not be measured during the measurement of GPC. Furthermore, the melt mass flow rate (MFR) was small, and there were many gel-like substances on the sheet. For these reasons, it was not possible to prepare an extruded foamed sheet of the styrene-based copolymer of Comparative Example 2. In Comparative Examples 3 and 6 in which the number average molecular weight Mn of the conjugated divinyl compound was as small as 226 and 750, the strain at the beginning of rising was large and the maximum rising ratio was small. Therefore, in Comparative Examples 3 and 6, the deep draw moldability was considerably low. In Comparative Example 4 in which the proportion of the molecular weight of 2 million or more was increased to 6.39%, the strain was large at the beginning of rising, and there were many gel-like substances. For these reasons, it was not possible to prepare an extruded foam sheet for the styrene-based copolymer of Comparative Example 4. In Comparative Example 5 in which the number average molecular weight Mn of the conjugated divinyl compound was as small as 130, the MFR was small and the gel-like substance of the sheet was large. Therefore, the deep draw moldability of the extruded foam sheet of Comparative Example 5 was also considerably low.

On the other hand, it is a styrene-based copolymer of a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000 and one or more kinds of monovinyl compounds including at least a styrene-based compound, and the ratio of the conjugated divinyl compound. There is a 2.0 × ¹⁰ -6 ~4.0 × ^{10 -4} mol per mol the monovinyl compounds, the styrene-based copolymer has a weight average molecular weight (Mw) was 200,000 to 500,000, The ratio of Z average molecular weight (Mz) to Mw is 1.8 to 5.0, the ratio of molecular weight of 1 million or more is 4.0% to 20.0%, and the ratio of molecular weight of 2 million or more is 0. The styrene-based copolymers of Examples 1 to 14, which are 3% to 6.0%, have less sheet-like gel-like substance than the styrene-based copolymers of Comparative Examples 1 to 6, and are further apparent from FIG. As described above, it can be seen that the extruded foam sheets of Examples 1 to 14 have a higher value of deep draw moldability than the extruded foam sheets of Comparative Examples 1 to 6 regardless of the expansion ratio.

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention.

The extruded foam sheet of the present embodiment is easily subjected to molecular orientation when the foam cell is stretched and has strain curability. Therefore, the extruded foam sheet has excellent secondary moldability of a deep-drawn container and has a high foaming ratio. Can be produced at. Therefore, since a secondary molded product, for example, a foam container can be obtained with a small amount of material, it is possible to contribute to cost reduction of the product.

Claims (8)

An extruded foamed sheet having a thickness of 0.5 mm to 5.0 mm and containing a styrene-based copolymer.
The styrene-based copolymer is a copolymer of a chain-linked conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000 and one or more types of monovinyl compounds containing at least a styrene-based compound, and the conjugated divinyl. The content of the compound is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol per mol of the monovinyl compound, and the weight average molecular weight (Mw) of the styrene-based copolymer is 200,000 to 500,000. An extruded foamed sheet having a molecular weight of 2 million or more, which is 0.3% to 6.0%. The extruded foam sheet according to claim 1, wherein the conjugated divinyl compound has a number average molecular weight (Mn) of 1000 to 30,000. The extruded foam sheet according to claim 1 or 2 , wherein at least one of the conjugated vinyl groups of the conjugated divinyl compound is located at the terminal of the conjugated divinyl compound. The extruded foam sheet according to any one of claims 1 to 3 , wherein the ratio of the Z average molecular weight (Mz) to Mw of the styrene-based copolymer is 1.8 to 5.0. The extruded foam sheet according to any one of claims 1 to 4 , wherein the proportion of the styrene-based copolymer having a molecular weight of 1 million or more is 4.0% to 20.0%. The extruded foam according to any one of claims 1 to 5 , wherein the styrene-based copolymer has a rising start strain of 0.2 to 1.3 and a maximum rising ratio of 1.2 to 5.0. Sheet. The extruded foam sheet according to any one of claims 1 to 6 , wherein the conjugated divinyl compound is a (hydrogenated) polybutadiene-terminated di (meth) acrylate. The secondary molded product of the extruded foam sheet according to any one of claims 1 to 7.

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