JP6896573B2 - Styrene-based copolymer and its manufacturing method, molded product - Google Patents

Description

The present invention relates to a styrene-based copolymer suitable for shrink film and sheet applications.

Styrene-based resins are widely used as molding materials and food packaging materials for home appliances, office machine products, miscellaneous goods, housing equipment, etc. because they are excellent in transparency, molding processability, and the like. Among these, it has a large elongation as a packaging material and a label material for food containers, and one of its uses is a film for low temperature shrinkage. As a film for low temperature shrinkage, a film having excellent low temperature processability and mechanical strength is desired, and in order to solve these problems, some resins composed of a styrene monomer and a (meth) acrylic acid alkyl ester are used. Proposed.

As such a method, Patent Document 1 is realized by setting the weight average molecular weight and the Vicat softening temperature of a copolymer of a specific aliphatic unsaturated carboxylic acid alkyl ester and a vinyl aromatic hydrocarbon within a specific range. It states that it can be done. Patent Document 2 describes a copolymer of a vinyl aromatic hydrocarbon and an aliphatic unsaturated carboxylic acid acrylic ester having a specific alkyl group having a carbon number and a large molecular weight, or a specific amount of liquid paraffin added to the copolymer. Low-temperature processability (film stretchability, shrinkage), in which a mixture of a resin, a vinyl aromatic hydrocarbon, a conjugated diene-based block copolymer, or a polystyrene resin is used for the intermediate layer or both outer layers. It is described that a film having excellent solvent resistance during printing with an oil-based ink can be realized.

JP-A-2007-177120 Japanese Unexamined Patent Publication No. 2007-276338

However, it has been found that the copolymer described in Patent Document 1 is not sufficient in terms of low temperature processability, and there is room for further improvement. It was found that the copolymer described in Patent Document 2 is also not sufficient in terms of low temperature processability, and there is room for further improvement.
The present invention has been devised in view of such conventional circumstances, and an object of the present invention is to provide a styrene-based copolymer having an excellent balance between low-temperature processability and mechanical strength, a method for producing the same, and the like. To do.

As a result of diligent research to achieve the above object, the present inventors have made appropriate styrene-based copolymers with a predetermined conjugated divinyl compound, a predetermined monovinyl compound, and an aliphatic unsaturated carboxylic acid alkyl ester. By controlling the molecular weight and molecular weight distribution of the styrene-based copolymer in an appropriate range, it is possible to realize a styrene-based copolymer having excellent molding processability and a small amount of gel-like substances. We have found and completed the present invention.
That is, the present invention is as shown below.
[1]
A styrene-based copolymer of one or more types of monovinyl compounds including at least a styrene-based compound, a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000, and an aliphatic unsaturated carboxylic acid alkyl ester.
The content of the conjugated divinyl compound is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol per mol of the monovinyl compound.
The content of the aliphatic unsaturated carboxylic acid alkyl ester is 5.0 to 30.0% by mass, assuming that the styrene-based copolymer is 100% by mass.
The styrene-based copolymer has a weight average molecular weight (Mw) of 200,000 to 600,000, and a proportion of the molecular weight of 1,000,000 or more is 3.0 to 15.0%.
A styrene-based copolymer characterized by this.
[2]
The styrene-based copolymer according to [1], wherein the conjugated divinyl compound has a number average molecular weight (Mn) of 1000 to 30,000.
[3]
The styrene-based copolymer according to [1] or [2], wherein the conjugated divinyl compound is in the form of a chain.
[4]
The styrene-based copolymer according to any one of [1] to [3], wherein the conjugated vinyl group of the conjugated divinyl compound is located at the terminal.
[5]
The styrene-based copolymer according to any one of [1] to [4], which has a maximum rising ratio of 1.1 to 5.0.
[6]
The styrene-based copolymer according to any one of [1] to [5], wherein the conjugated divinyl compound is a (hydrogenated) polybutadiene di (meth) acrylate.
[7]
The method for producing a styrene-based copolymer according to any one of [1] to [6], which comprises using continuous solution polymerization or continuous bulk polymerization.
[8]
A sheet containing the styrene-based copolymer according to any one of [1] to [6].
[9]
A film comprising the styrene-based copolymer according to any one of [1] to [6].
[10]
A multi-layer heat-shrinkable film containing an intermediate layer and both outer layers sandwiching the intermediate layer.
The resin of the intermediate layer is 10 to 95% by mass of the styrene-based copolymer (a) according to any one of [1] to [9], and a polymer block mainly composed of vinyl aromatic hydrocarbons and a conjugated diene. The resin (b) is composed of a mixture containing 5 to 90% by mass of a resin (b) composed of a polymer block mainly composed of a derivative.
The resins of both outer layers are the styrene-based copolymer (a) 0 to 10% by mass according to any one of [1] to [9], and a polymer block mainly composed of a vinyl aromatic hydrocarbon and a conjugated diene. A multilayer heat-shrinkable film comprising a mixture containing 90 to 100% by mass of a resin (b) composed of a polymer block mainly composed of a derivative.

According to the present invention, it is possible to provide a styrene-based copolymer having an excellent balance between low-temperature processability and mechanical strength, a method for producing the same, and the like.

It is a log-log graph which plotted the Henky strain on the horizontal axis and the extensional viscosity on the vertical axis about the styrene-based copolymers obtained in Examples and Comparative Examples.

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.

(Styrene-based copolymer)
The styrene-based copolymer of the present embodiment contains a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000, one or more monovinyl compounds containing at least a styrene-based compound, and an aliphatic unsaturated carboxylic acid alkyl ester. The content of the conjugated divinyl compound is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol per mol of the monovinyl compound, and the aliphatic unsaturated compound is saturated with the above. The content of the carboxylic acid alkyl ester is 5.0 to 30.0% by mass, where the styrene-based copolymer is 100% by mass, and the styrene-based copolymer has a weight average molecular weight (Mw) of 200,000. It is ~ 600,000, and the ratio of the molecular weight of 1 million or more is 3.0 to 15.0%.

According to this embodiment, it is possible to provide a styrene-based copolymer having an excellent balance between low-temperature processability and mechanical strength.
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 can be easily formed with a moiety derived from a conjugated divinyl compound that is linked to each other, and the interval between the molecular chain portions at that time can be set to a predetermined distance (in the molecular chain of the styrene copolymer). It is presumed that it is easy to make a shape with a branch portion that becomes an "H" shape).
By forming the styrene-based copolymer in this way, the molecular chains of the styrene-based copolymer can be easily entangled with each other effectively (such an effect is also referred to as an "entanglement effect"). Therefore, the low temperature processability of the styrene-based copolymer can be improved.
At the same time, 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 is effectively improved. It is presumed that the styrene-based copolymer can be effectively prevented from gelling while being processed, and the decrease in mechanical strength can be suppressed when the film or sheet is processed.
Therefore, according to the present embodiment, it is possible to provide a styrene-based copolymer having an excellent balance between low-temperature processability and mechanical strength.

<Monovinyl compound>
The styrene-based copolymer of the present embodiment contains at least one or more types of monovinyl compounds (as a monomer forming the styrene-based copolymer) including a styrene-based compound.
The monovinyl compound may be composed of only a styrene-based compound (monomer), or may be composed of a compound having another monovinyl group copolymerizable with the styrene-based compound together 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 in the monovinyl compound is preferably 50 mol% or more, more preferably 70 mol% or more, and further preferably 90 mol% or more of the content of the monovinyl compound.

<Content of monovinyl compound>
The content of the monovinyl compound in the styrene-based copolymer of the present embodiment is preferably 50 to 95% by mass, more preferably 60 to 90% by mass, with the styrene-based copolymer as 100% by mass, from the viewpoint of low-temperature processability. %, More preferably 70 to 85% by mass.

<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 preferably has a chain shape rather than a network shape, and the main chain may or may not have a side chain. This is because the chain shape 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.

Further, the conjugated vinyl group in the conjugated divinyl compound can be positioned arbitrarily in the molecule, but at least two of the two conjugated vinyl groups are located at different ends in the molecule. Is preferable. 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 become conjugated divinyl groups). It is more preferable to have it). The polymerization reactivity can be enhanced by locating the conjugated vinyl group at the terminal.

Further, when the conjugated divinyl compound is chain-like and three or more conjugated vinyl groups are present, it is preferable that two of the three or more conjugated vinyl groups are located at the terminals. More preferably, the remaining one or more conjugated vinyl groups are also terminally located.

When 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 the raw material, and the transparency of the styrene copolymer may occur. Deterioration and the need to clean the reactor may reduce productivity. From these viewpoints, the number of conjugated vinyl groups in the conjugated divinyl compound is preferably 5 or less, more preferably 4 or less, and further preferably 3 or less. From the same viewpoint, it is particularly preferable that the conjugated divinyl compound has two conjugated vinyl groups.

Here, the "terminal" can be the position (atom) at the most end of the molecular chain, but if the conjugated vinyl group is present near the end, it has effective reactivity with the monovinyl compound and gels. In this embodiment, the "terminal" can also be a part (end part) in a certain range including the position (atom) at the most end of the molecular chain in the molecular chain (in other words, the end part). , Conjugated vinyl groups can be located near the end of the molecular chain). The portion in the certain range is not limited, but is preferably in the range of 20% or less of the stretched chain length of the conjugated divinyl compound from the position (atom) at the end of the molecular chain. The range of% or less is more preferable, the range of 10% or less is further preferable, and the range of 5% or less is even more preferable.

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

The number average molecular weight (Mn) of the conjugate divinyl compound of the present embodiment is 850 to 100,000, preferably 1000 to 100,000, more preferably 1000 to 80000, still more preferably 1200 to 80000, still more preferably 1500 to 60000, particularly preferably. Is 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 may decrease.
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 (meth) acrylate (“(hydrogenated)” refers to a hydrogenated or non-hydrogenated compound; the same shall apply hereinafter), polyethylene. Terminal di (meth) acrylate compounds such as glycol-terminated (meth) acrylate, polypropylene glycol-terminated (meth) acrylate, ethoxylated bisphenol A-terminal (meth) acrylate, and ethoxylated bisphenol F-terminal (meth) acrylate, and (hydrogenated). Examples thereof include terminal urethane acrylate compounds such as polybutadiene terminal urethane acrylate, polyethylene glycol terminal urethane acrylate, polypropylene glycol terminal urethane acrylate, ethoxylated bisphenol A terminal urethane acrylate, and ethoxylated bisphenol F terminal urethane acrylate. 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 (meth) acrylate, polystyrene-terminated (meth) acrylate, or polyphenylene ether-terminated divinyl. In addition, "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 styrene-based copolymer of the present embodiment is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol, preferably 5.0 × 10 ^-6 to 1 mol per mol of the monovinyl compound. 3.5 × 10 ^-4 mol, more preferably 1.5 × 10 ^{-5 to} 3.0 × 10 ^-4 mol, even more preferably 2.0 × 10 ^{-5 to} 2.5 × 10 ^-4 mol. is there. When the content is ^{less than 2.0 × 10 -6} mol, sufficient entanglement between the polymers is unlikely to occur, strain curing does not occur, or the degree of strain curing is small, so that the wall thickness of the molded product is non-uniform. In addition, the molded product may be torn during molding, resulting in poor molding processability. On the other hand, when the content exceeds 4.0 × 10 ^-4 mol, a large amount of gel-like substance is generated and the mechanical strength is lowered.
In the present disclosure, the content of the conjugate divinyl compound per mole of the monovinyl compound is a value measured using ^{1 1} H-NMR and ^{13 C-NMR.}

<Alphatic unsaturated carboxylic acid alkyl ester>
The aliphatic unsaturated carboxylic acid alkyl ester in the present embodiment preferably has 4 to 20 carbon atoms, and more preferably 4 to 10 carbon atoms.
Examples of the carboxylic acid moiety include acrylic acid and methacrylic acid, and acrylic acid is preferable.
Examples of the alkyl ester moiety include aliphatic hydrocarbons such as ethyl and butyl, and aliphatic cyclic hydrocarbons such as cyclohexyl, and butyl is preferable.
Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, vinyl acetate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, acrylic acid. Examples thereof include pentadecyl, hexadecyl acrylate, palmitin acrylate, stearyl acrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, palmitin methacrylate and stearyl methacrylate.

<Content of aliphatic unsaturated carboxylic acid alkyl ester>
The content of the aliphatic unsaturated carboxylic acid alkyl ester in the styrene-based copolymer of the present embodiment is preferably 5 to 30% by mass, with the styrene-based copolymer as 100% by mass, from the viewpoint of low-temperature processability. It is preferably 10 to 25% by mass, more preferably 12 to 20% by mass.
In the present disclosure, the content of the aliphatic unsaturated carboxylic acid alkyl ester in the styrene copolymer is a value measured using ^{1 1} H-NMR and ^{13 C-NMR.}

<Molecular weight>
The weight average molecular weight (Mw) of the styrene-based copolymer of the present embodiment is 200,000 to 600,000, preferably 250,000 to 550,000, and more preferably 300,000 to 500,000.
By setting the Mw of the styrene-based copolymer to 200,000 to 600,000, 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.
In the styrene-based copolymer of the present embodiment, the above weight average molecular weight (Mw) is determined by the type and amount of the conjugated divinyl compound added, the reaction temperature, the residence time, and the like when the styrene-based monomer is radically polymerized. It can be controlled by the type and amount of the polymerization initiator, the type and amount of the solvent, the type and the amount of the chain transfer agent, and the like. Specifically, the 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 temperature of the polymerization is increased. It can be controlled by a method of lowering the amount of the polymer, a method of reducing the amount of the polymerization solvent used, a method of lengthening the residence time at the time of polymerization, and the like. While the chain has a desired shape, the high molecular weight component side can also be appropriately increased.
The weight average molecular weight (Mw) of the styrene-based copolymer and the ratio of the molecular weight of 1 million or more are the weight ratios of the differential molecular weight distribution measured by gel permeation chromatography (GPC).

<Ratio of high molecular weight components>
In the styrene-based copolymer of the present embodiment, the ratio of the molecular weight of 1 million or more is 3.0 to 15.0%, preferably 5.0 to 14.0%, and 7.0 to 13.0. % Is more preferable. By setting the ratio of the molecular weight of 1,000,000 or more to the range of 3.0 to 15.0%, a styrene-based copolymer having an excellent balance between low-temperature processability and mechanical strength can be obtained.
The molecular weight ratio of the styrene-based copolymer of the present embodiment includes 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. Specifically, the above-mentioned control of the ratio of 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, and the reaction temperature of the polymerization is increased. Can be controlled by a method of reducing the amount of polymerization solvent, a method of reducing the amount of the polymerization solvent used, a method of lengthening the residence time during polymerization, etc., and by doing so, the styrene-based copolymer obtained can be controlled. , The low molecular weight component side can be reduced, and the high molecular weight component side can be increased while making the ratio of the molecular weight of 1 million or more appropriate.

<Melt mass flow rate (MFR)>
The melt mass flow rate (MFR) of the styrene-based copolymer of the present embodiment is preferably 2.0 to 10.0 g / 10 minutes. It is more preferably 3.0 to 8.0 g / 10 minutes, even more preferably 4.0 to 7.0 g / 10 minutes, and particularly preferably 4.5 to 6.5 g / 10 minutes. By setting the melt mass flow rate in the range of 2.0 to 10.0 g / 10 minutes, a styrene-based copolymer having a better balance between molding processability and fluidity can be obtained.
In the present disclosure, the melt mass flow rate is a value measured at 200 ° C. and a load of 49 N in accordance with ISO1133.

<Maximum rise ratio>
The maximum rising ratio of the styrene-based copolymer of the present embodiment is preferably 1.1 to 5.0, more preferably 1.1 to 4.0, and even more preferably 1.2 to 3.0.
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 rising ratio is an index showing the degree of strain hardening at the maximum rising 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 1.1 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 resin is torn during molding. It tends to be difficult. When the maximum rising 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.
In the present disclosure, the maximum rise ratio is a value calculated by the procedure described in the section [Example] described later.

The Vicat softening temperature of the styrene-based copolymer of the present embodiment is preferably 60 to 85 ° C, more preferably 63 to 83 ° C, and even more preferably 65 to 80 ° C. If the temperature is lower than 60 ° C., it becomes difficult to cool the resin during the production of the styrene-based copolymer, which may reduce the productivity, which is not preferable. On the other hand, when the temperature exceeds 85 ° C., the amount of the aliphatic unsaturated carboxylic acid alkyl ester introduced is relatively small, the processability at low temperature is lowered, and the low temperature shrinkage is remarkably lowered, which is not preferable.
The Vicat softening temperature was measured according to ISO 306. The load was 49 N, and the heating rate was 50 ° C./hour.

The addition of liquid paraffin has the effect of reducing the amount of the aliphatic unsaturated carboxylic acid alkyl ester introduced and improving the solvent resistance when the Vicat softening temperature is kept constant. However, if it is added too much, the plasticizer may be deposited at the die outlet of the extruder during long-term extrusion and molding, and may be mixed in the product, which is not preferable. The amount of liquid paraffin added is preferably 0 to 5 parts by mass, and more preferably 1 to 4 parts by mass with respect to 100 parts by mass of the styrene-based copolymer.
The composition of the styrene-based copolymer that obtains the above-mentioned Vicat softening temperature by the combination of the amount of the liquid paraffin added and the content of the conjugated divinyl compound, the monovinyl compound, and the aliphatic unsaturated carboxylic acid alkyl ester is not aliphatic. The content of the saturated carboxylic acid alkyl ester is preferably 5 to 22% by mass, more preferably 6 to 20% by mass, and the content of the monovinyl compound is 78 to 95% by mass, more preferably 80 to 94% by mass.

<Additives, etc.>
The styrene-based copolymer of the present embodiment may optionally be a resin composition containing an additive or the like. For example, if necessary, a rubber such as HIPS resin or MBS resin may be used as a rubber-containing component. It may contain about 1 to 50% by mass of an aromatic vinyl-based thermoplastic elastomer such as a reinforced aromatic vinyl-based resin or SBS. 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)) is added to the styrene-based copolymer. Ethyl] -4,6-di-t-phenylpentyl acrylate and other processing stabilizers may be included.
In addition, styrene-based copolymers include higher fatty acids such as stearic acid, zinc stearate, calcium stearate, and magnesium stearate, salts thereof, lubricants such as ethylenebisstearylamide, plasticizers such as liquid paraffin, and antioxidants. It may be included. In addition, even if an additive commonly used in the field of styrene-based resin, for example, a nucleating agent, a flame retardant, a coloring agent, etc. is combined and added to the styrene-based copolymer as long as the object of the present embodiment is not impaired. Good. 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.
When the styrene-based polymer is used as pellets, ethylene bisstearylamide, zinc stearate, magnesium stearate or the like may be sprinkled on the pellets as an external lubricant for the pellets.

Antioxidants can generally stabilize peroxide radicals such as hydroperoxy radicals generated during thermoforming or light exposure, or decompose the generated peroxides such as hydroperoxides. 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 to 1 part by mass, more preferably 0.1 to 0.5 part by mass with respect to 100 parts by mass of the styrene-based copolymer.

(Manufacturing method of styrene copolymer)
<(Polymerization process))
Examples of the polymerization method of the styrene-based copolymer of 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, a solvent, a polymerization catalyst, a chain transfer agent, and the like, if necessary, are added and mixed to prepare a raw material solution containing monomers. 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 of the present embodiment, a polymerization solvent, a polymerization initiator such as an organic peroxide, and a chain transfer agent can be used, if necessary, from the viewpoint of controlling the polymerization reaction. .. 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 from the viewpoints of controlling gelation, improving productivity, increasing the molecular weight, etc., usually all the monomers, polymers, solvents, etc. in the polymerization reactor are used. It is preferably 1 to 50% by mass, more preferably 3 to 20% by mass, based on the composition of the mixed solution.

When the polymerization raw material is polymerized in order to obtain the styrene-based copolymer of 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 monovinyl compound. 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 monovinyl compound.

((Devolatile process))
As the volatilization 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.

(Sheet, film)
The sheet and film of the present embodiment contain the styrene-based copolymer of the present embodiment.

The sheet or film of the present embodiment contains the styrene-based copolymer of the present embodiment, and may be a sheet or film produced by using the above-mentioned styrene-based copolymer. The sheet and film may be either non-foamed or foamed.
As a method for producing a sheet or a film, a commonly known method can be used. For non-foamed sheets and non-foamed films, it is possible to use a method of extruding with a single-screw or twin-screw extruder equipped with a T-die or a circular die, and then using a device for taking out the sheet with a uniaxial or biaxial stretching machine. it can. As a method for producing the foamed sheet and the foamed film, a method using an extrusion foam molding machine equipped with a T-die or a circular die can be used.

For non-foamed sheets and non-foamed films, for example, a thickness of about 0.1 to 3.0 mm is preferable from the viewpoint of rigidity and thermoforming cycle.
Further, the sheet and film may be formed only by ordinary low-magnification roll stretching, or may be stretched by a roll about 1.3 to 7 times and then by a tenter about 1.3 to 7 times. Good.

The foamed sheet and the foamed film preferably have a thickness of 0.5 to 5.0 mm, an apparent density of 50 to 300 g / L, and a basis weight of 80 to 300 g / m2. Is preferable.
When forming a foam sheet or a foam film, a substance usually used as a foaming agent and a foam nucleating agent at the time of extrusion foaming can be used. As the foaming agent, butane, pentane, chlorofluorocarbon, carbon dioxide, water and the like can be used, and butane is preferable. Further, talc or the like can be used as the effervescent nucleating agent.
Further, after foam extrusion, the sheet and film may be stretched about 1.3 to 7 times with a roll while being heated, and then stretched about 1.3 to 7 times with a tenter.

The film of the present embodiment may be multi-layered, for example, by further laminating the film. The type of film used may be general polystyrene, polypropylene, polypropylene / polystyrene laminated film, or the like.

(Multilayer heat shrinkable film)
The multilayer heat-shrinkable film of the present embodiment is a multilayer heat-shrinkable film including an intermediate layer and both outer layers sandwiching the intermediate layer.
Here, the resin of the intermediate layer contains 10 to 95% by mass of the styrene-based copolymer (a) of the present embodiment, a polymer block mainly composed of vinyl aromatic hydrocarbons, and a weight mainly composed of a conjugated diene derivative. It is composed of a mixture containing 5 to 90% by mass of the resin (b) composed of a coalesced block.
Further, the resins of both outer layers are the styrene-based copolymer (a) of the present embodiment (0 to 10% by mass), a polymer block mainly composed of vinyl aromatic hydrocarbons, and a polymer mainly composed of a conjugated diene derivative. The resin (b) composed of blocks is composed of a mixture containing 90 to 100% by mass.
Here, the mixture also includes a composition obtained by melt-kneading one or more kinds of resins.

<Resin (a)>
The resin (a) used for both outer layers of the multilayer heat-shrinkable film of the present embodiment may be the styrene-based copolymer of the present embodiment described above.

<Resin (b)>
The resin (b) used for the intermediate layer and both outer layers of the multilayer heat-shrinkable film of the present embodiment is obtained by polymerizing a vinyl aromatic hydrocarbon and a conjugated diene in an organic solvent using an organic lithium compound as an initiator. It may be a thing.
Examples of the vinyl aromatic hydrocarbon used in the resin (b) include styrene, α-monomethylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene and the like, but styrene is particularly common. Can be mentioned. These may be used not only as one type but also as a mixture of two or more types.
The conjugated diene used in the resin (b) is a diolefin having a pair of conjugated double bonds, for example, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3. -Dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like, but these may be used in combination of not only one type but also two or more types.
Particularly preferred are 1,3-butadiene and isoprene, and the mass ratio of 1,3-butadiene and isoprene in the block copolymer is 97/3 to 20/80, preferably 90/10 to 25/75. More preferably, it is 85/15 to 30/70. Within this range, a copolymer having less fish eyes can be obtained.

For the resin (b), the following block bonding method can be mentioned.
Assuming that the block segment mainly composed of vinyl aromatic hydrocarbons is S and the block segment mainly composed of conjugated diene is D, one group thereof is (DS) n + 1, (DS) n-D, S. -(DS) n (where n = 1 to 10) is a linear block copolymer having a basic structure, and the production method thereof is an organic lithium-based polymerization initiator in a hydrocarbon-based solvent. This is by means of block copolymerization using. The following groups are [(DS) n] m + 2-X, [(SD) n] m + 2-X, [(SD) n-S] m + 2-X, [(DS). A non-linear block copolymer or the like having a branched basic structure such as n-D] m + 2-X. (However, n = 1-10, m = 1-10), (X represents the residue of the polyfunctional initiator, for example, the initiator is SiCl ₄ , SnCl ₄ , polyfunctional organolithium compound, polyepoxide. , Polyisocyanate, polyaldehyde, polyketone, tetraallyl Sn, etc.).

Among the above, the preferred embodiment is n = 1 to 5, more preferably n = 1 to 3, and even more preferably n = 1 to 2 in the linear block copolymer. Further, in the case of a non-linear block copolymer, m = 1 to 5 and n = 1 to 5, more preferably m = 1 to 3 and n = 1 to 3, and even more preferably m = 1 to 2 and. n = 1-2.
The resin (b) may be any mixture of block copolymers having a structure represented by the above general formula.

These manufacturing methods include, for example, Japanese Patent Publication No. 36-19806, No. 43-14979, No. 48-2423, No. 48-4106, No. 49-36957, No. 51-27701, etc. However, in the present application, the above-mentioned specific range is used.
Further, in at least one portion of the polymer molecular structure of each of the above groups, a random structure or a component composed of both monomers gradually or gradually changes the ratio of the two to form a tapered random shape or block. Copolymers having a similar structure, copolymers containing other types of copolymerizable monomers, and modified polymers shall also be used.

In the resin (b), the number average molecular weight (Mn) of the polymer block mainly composed of vinyl aromatic hydrocarbons is preferably 5000 or more, more preferably 7,000 to 100,000, and further preferably about 1,000 to 80,000. The number average molecular weight (Mn) of the polymer block mainly composed of the conjugated diene derivative is preferably 5000 to 20000, more preferably 70000 to 100000, and further preferably about 1000 to 100,000. Further, the number average molecular weight (Mn) of the entire block copolymer is preferably 20000-500000, more preferably 20000-400000, and even more preferably 30,000-300000. By using the resin (b) having a molecular weight in such a range, a sheet or film having excellent mechanical strength, processability, and low temperature shrinkage can be obtained.
The number average molecular weight (Mn) is a value measured by gel permeation chromatography (hereinafter referred to as GPC) in terms of polystyrene.
The molecular weight of the block mainly composed of vinyl aromatic hydrocarbons of the resin (b) was determined by GPC for the vinyl aromatic hydrocarbon polymer block component obtained by the method of oxidative decomposition with osmium tetroxide and peroxide. Value.
A particularly preferable resin (b) has a melt flow rate (200 ° C., load 49N) of 0.1 to 50 g / 10 minutes, preferably 1 to 20 g / 10 minutes from the viewpoint of molding.

The composition of the resin (b) is such that the content of the conjugated diene derivative is 5 to 40% by mass, preferably 10 to 37% by mass, and more preferably 15 to 32% by mass, based on 100% by mass of the resin (b). The content of vinyl aromatic hydrocarbons is 60 to 95% by mass, preferably 63 to 90% by mass, and more preferably 68 to 85% by mass. When the content of the conjugated diene derivative exceeds 40% by mass and the content of vinyl aromatic hydrocarbon is less than 60% by mass, the mechanical strength is excellent, but the elastic modulus is low, and in an extruder or the like. The gel formation is increased, the surface surface roughness of the film is conspicuously unfavorable, the compatibility with the resin (a) is inferior, and the transparency tends to be lowered. On the other hand, when the content of the conjugated diene derivative is less than 5% by mass and the content of vinyl aromatic hydrocarbons exceeds 95% by mass, the rubber component is reduced and the mechanical strength such as film strength and waist strength is lowered. Is not preferable.

The Vicat softening temperature of the resin (b) is preferably 65 to 93 ° C, more preferably 70 to 90 ° C, and even more preferably 75 to 85 ° C. If the temperature is lower than 65 ° C., the tensile elastic modulus of the film made of the resin (a) becomes too low. On the other hand, if the temperature exceeds 93 ° C., the low temperature shrinkage is inferior, which is not preferable.
The Vicat softening temperature was measured according to ISO 306. The load was 49 N, and the heating rate was 50 ° C./hour.
In particular, the Vicat softening temperature of the resin (b) used for the outer layer is preferably 75 ° C. or higher from the viewpoint of blocking resistance.

The resins used for the intermediate layer and both outer layers include 2- [1- (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 2-t. -Butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate, 2,4-bis [(octylthio) methyl] -o-cresol, 5,7-di- tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one, 3,4-dihydro-2,5,7,8-tetramethyl-2- (4,8,12-trimethyl) At least one stabilizer selected from tridecyl) -2H-benzopyran-6-ol was added in an amount of 0.02 to 3 parts by mass, more preferably 0.02 to 3 parts by mass, based on 100 parts by mass of each resin in the intermediate layer and both outer layers. By adding 0.05 to 2 parts by mass, fish eyes generated when the sheet or film is produced by an extruder can be suppressed.

In addition, n-octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,4-bis [(octylthio) methyl] -o-cresol, tetrakis [methylene-3- (3,3) 5-di-t-butyl-4-hydroxyphenyl) propionate] methane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, etc. At least one of the phenolic stabilizers of the above can be added to 100 parts by mass of each resin of the intermediate layer and both outer layers by 0.02 to 3 parts by mass, respectively, and tris- (nonylphenyl) phosphite, Intermediate at least one of organic phosphate stabilizers such as 2,2-methylenebis (4,6-di-t-butylphenyl) octylphosphite and tris (2,4-di-t-butylphenyl) phosphite. 0.02 to 3 parts by mass can be added to 100 parts by mass of each of the resin of the layer and both outer layers.

Suitable additives for the resins used for the intermediate layer and both outer layers include kumaron-indene resin, terpene resin, softeners such as oil, and plasticizers. Further, as suitable additives, various pigments, antiblocking agents, antistatic agents, lubricants, ultraviolet absorbers and the like can also be added.
Examples of antiblocking agents, antistatic agents, and lubricants include fatty acid amide, ethylene bisstearoamide, sorbitan monostearate, saturated fatty acid esters of fatty acid alcohols, pentaerythritol fatty acid esters, and the like, and UV absorbers. , Pt-butylphenyl salicylate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5- Compounds described in "Practical Handbook of Additives for Plastics and Rubbers" (Chemical Industry Co., Ltd.) such as chlorobenzotriazole, 2,5-bis- [5'-t-butylbenzoxazolyl- (2)] thiophene, etc. Can be used.
These are generally used in the range of preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass with respect to 100 parts by mass of the resin.

By using the styrene-based copolymer of the present embodiment, a multilayer heat-shrinkable film having an excellent balance between low-temperature processability and mechanical strength can be obtained.

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.

"material"
In the examples and comparative examples, the following materials were used.

<Styrene-based copolymer>
<Monovinyl compound>
Styrene: Styrene monomer [manufactured by Asahi Kasei Corporation]

<Conjugated divinyl compound>
Conjugated divinyl compounds 1, 3 and 4 were produced based on the following methods.

<Conjugated divinyl compound 1>
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 4 in a 5 L reaction vessel equipped with a stirrer, thermometer and reflux condenser. 0.5533 g of -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) 16} CO 3 · 4H 2 O) [Kyowa as an ester exchange catalyst 20 g of Kyowa Chemical Industry Co., Ltd., trade name: Kyoward 500PL] was added, and the mixture was 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 2: Polybutadiene terminal acrylate [Osaka Organic Chemical Industry Co., Ltd .: BAC-45] Mn: 4800

<Conjugated divinyl compound 3>
The conjugated divinyl compound 3 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 4>
The conjugated divinyl compound 4 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.

Conjugated divinyl compound 5: Aromatic urethane acrylate [manufactured by Tomoe Engineering Co., Ltd .: CN9782] Mn: 5200
Reaction formation of conjugated divinyl compound 6: (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 7: 1,3-butylenediol dimethacrylate [manufactured by Wako Pure Chemical Industries, Ltd.] Molecular weight: 226
Conjugated divinyl compound 8: NK ester A-GLY-20E [manufactured by Shin-Nakamura Chemical Industry Co., Ltd.] Molecular weight: 1295, the average number of conjugated vinyl in one molecule of conjugated divinyl compound 8 is 3.
Conjugated divinyl compound 9: Divinylbenzene [manufactured by Wako Pure Chemical Industries, Ltd.] Molecular weight: 130
Conjugated divinyl compound 10: Polyethylene glycol dimethacrylate [manufactured by Sigma-Aldrich] Molecular weight: 750

The conjugated divinyl compounds 2 to 7, 9, and 10 had a conjugated vinyl group at both ends of the molecule.

<Alphatic unsaturated carboxylic acid alkyl ester>
Butyl acrylate: manufactured by Wako Pure Chemical Industries, Ltd.]

<Others>
Polymerization Initiator 1: 1,1-Di- (Turshary-Butyl Peroxy) Cyclohexane [NOF CORPORATION: Perhexa C]
Ethylbenzene: manufactured by Wako Pure Chemical Industries, Ltd.

<Example 1>
70.4 parts by mass of styrene, 13.8 parts by mass of ethylbenzene, 15.8 parts by mass of butyl acrylate, 0.079 parts by mass of conjugated divinyl compound 1 (polybutadiene terminal acrylate, Mn: 1900) (6 with respect to 1 mol of styrene) .0 × 10 ^-5 mol), 0.015 parts by mass of the polymerization initiator 1 was added to prepare a raw material solution.
The prepared raw material solution was continuously supplied at 0.77 L / hr to a completely mixed first reactor having an internal volume of 3.6 L maintained at a temperature of 125 ° C. Then, the polymerization solution from the first reactor was supplied to a vacuum degassing tank heated to a temperature of 230 ° 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.

<< Measurement and evaluation method >>
The measurement and evaluation methods are as follows.

(1) Measurement of the number of moles of the conjugated divinyl compound contained in 1 mol of styrene The number of moles of the conjugated divinyl compound contained in 1 mol of styrene in the styrene copolymer is ^{measured using 1} H-NMR and ¹³ C-NMR. did. As a 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.

(2) Measurement of butyl acrylate content The butyl acrylate content in the styrene-based copolymer ^{was measured using 1 1} H-NMR and ¹³ C-NMR. As a 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.

(3) Measurement of molecular weight The number average molecular weight (Mn) of the conjugated divinyl compound, the weight average molecular weight (Mw) of the styrene-based copolymer, the Z average molecular weight (Mz), and the ratio of the molecular weight of 1 million or more are gel permeation chromatography. It was measured under the following conditions using graphics (GPC).
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 guard volume Super HZ-H
Measuring solvent: tetrahydrofuran (THF)
Sample preparation: 5 mg of the measurement sample was dissolved in 10 mL of solvent and filtered through a 0.45 μm filter.
Injection volume: 10 μL
Measurement temperature: 40 ° C
Flow velocity: 0.35 mL / min Detector: Differential refractive index detector (RI-8020)
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.

(4) 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.

(5) Measurement of Vicat softening temperature The measurement was performed in accordance with ISO 306. The load was 49N. The heating rate was 50 ° C./hour.

(6) Measurement of maximum rising strain, rising starting 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 1.0 mm, Width 10 mm
Elongation strain rate: 0.01 / sec Temperature: 130 ° 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 at the measured temperature, 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.
The strain at the start of rising was calculated by the following method. Based on the results obtained by the above viscoelasticity measurement, a bilateral logarithmic 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 0.5 to 0.8. A power approximation curve was created as the region (for example, the linear region extrapolation line in FIG. 1). When strain hardening occurs, the measured extensional viscosity (this extensional viscosity is defined as "non-linear") is higher than the extensional viscosity on the approximate curve extrapolating this linear region (this extensional viscosity is defined as "extensional viscosity of the linear region"). (Defined as the extensional viscosity of the region) becomes higher. In the same Henky strain, the Henky strain when the difference between the extensional viscosity in the non-linear region and the extensional viscosity in the linear region was 3% of the extensional viscosity in the non-linear region was defined as the strain that started to rise.
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).
FIG. 1 shows a log-log graph in which the styrene-based copolymers obtained in Examples and Comparative Examples are plotted with the horizontal axis as the henky strain and the vertical axis as the extensional viscosity.

Here, a multilayer heat-shrinkable film was produced as follows using the styrene-based copolymer obtained in Example 1.

As the resin for the intermediate layer, the styrene-based copolymer of Example 1 was blended in an amount of 75% by mass and the resin (b) was blended in an amount of 25% by mass, and the resin was extruded with a twin-screw extruder to prepare pellets.
As the resin for the outer layer, 100% by mass of the resin (b) was used.
Using these pellets, a three-layer sheet having a thickness of about 300 μm was prepared by coextrusion so that the ratio of the thickness of the outer layer / intermediate layer / outer layer was 10/80/10. Next, this sheet was heated with a batch type tenter (EX6-S1 manufactured by Toyo Seiki Co., Ltd.) at a temperature of Bicut softening temperature of styrene copolymer + 15 ° C., 5 times in the direction orthogonal to the sheet extrusion direction, and 1 in the sheet extrusion direction. A test piece film having a thickness of about 50 μm stretched twice was obtained. When the Vicat softening temperature + 15 ° C. exceeded 110 ° C., 110 ° C. was set as the upper limit of the heating temperature.
The resin (b) for the intermediate layer and both outer layers was synthesized by the method described in JP-A-2007-276338. The obtained resin (b) is a block copolymer of styrene-butadiene-styrene, the butadiene content of which is 22% by mass, the number average molecular weight of the styrene block is 50,000, and the number average molecular weight of the entire copolymer is 130,000. The polymer softened temperature was 82 ° C., and the refractive index was 1.576.

(8) Measurement of tensile elastic modulus and nominal fracture strain The measurement was performed at 25 ° C. using the evaluation test piece obtained as described above in accordance with JIS K7127. The tensile speed was 5 mm / min, the shape of the test piece was type 5, and the tensile test was performed in the direction orthogonal to the main drawing. The retention rate (%) of tensile fracture nominal strain after printing was calculated from the following equation.
Retention rate of tensile fracture nominal strain (%) = E2 / E1 × 100
E1: Tension fracture nominal strain before printing, E2: Tension fracture nominal strain after printing

(9) Measurement of shrinkage rate The untreated film obtained as described above is immersed in hot water at 75 ° C. and 90 ° C. for 10 seconds, and the shrinkage rate (%) at both temperatures in the main stretching direction is calculated by the following formula. did.
Shrinkage rate (%) = (1-L2 / L1) x 100
(L1: Length before immersion, L2: Length after immersion.)
Then, the ratio of the shrinkage rate at 90 ° C. to the shrinkage rate at 75 ° C. was calculated.

(10) Method for Determining Low Temperature Workability The stretchability of a 250 μm-thick sheet when stretched biaxially with a batch tenter was evaluated. Five films stretched 5 times in the direction orthogonal to the sheet extrusion direction and 3 times in the sheet extrusion direction at a Vicat softening temperature of + 25 ° C. were measured and evaluated according to the following evaluation criteria. When the Vicat softening temperature + 25 ° C. exceeded 110 ° C., 110 ° C. was set as the upper limit of the heating temperature for stretching.
<Evaluation criteria>
⊚: There was no tearing, and the thickness unevenness of the effective portion (excluding the edge portion) of the stretched film could be stretched to <± 10% (range smaller than ± 10%).
◯: There is no tear, the thickness is slightly uneven, and the thickness unevenness is ± 10 ± 30%.
X: There is a tear, or the thickness unevenness is> ± 30% (range larger than ± 30%).
(11) Practical Shrinkage Judgment Method After putting water in a PET bottle for aseptic and capping it, a film having a length of 1.06 times the outer circumference of the PET bottle + a margin of 5 mm is cut out from the obtained untreated film. This was made into an envelope, covered with a bottle, passed through a steam tunnel at 80 ° C. for 10 seconds, attached, and judged according to the following evaluation criteria.
<Evaluation criteria>
◎: Very good finish and appearance.
◯: Good finished appearance.
X: Insufficient shrinkage (poor finished appearance).

<Examples 2 to 7, Comparative Examples 1 to 7>
Examples 2 to 7 and Comparative Examples 1 to 7 were carried out in the same manner as in Example 1 except that the conditions were changed as shown in Table 1, and the Mw of the styrene copolymer, the ratio of the molecular weight of 1 million or more, and The maximum rise ratio and the like were controlled as shown in Table 1.

Table 1 summarizes the measurement and evaluation results of Examples 2 to 7 and Comparative Examples 1 to 7. As shown in FIG. 1, it can be seen that the styrene-based copolymer of Example 3 exhibited strain curing in the measurement of ARES-EVF.

As is clear from Table 1, in Comparative Examples 1 and 4 in which the molecular weight of the conjugated divinyl compound with respect to 1 mol of the monovinyl compound was as small as 226 and 750, the low temperature processability and the practical shrinkage were inferior.
In Comparative Examples 2 and 3 in which the proportions of the components having a molecular weight of 1 million or more were as high as 15.4% and 17.5%, the practical shrinkage was extremely deteriorated.
In Comparative Example 6 in which the proportion of the component having a molecular weight of 1 million or more was as small as 2.8%, strain curing did not occur in the measurement of ARES-EVF, and the low temperature processability and the practical shrinkage were inferior.
In Comparative Examples 5 to 7 to which the conjugated divinyl compound was not added, strain curing did not occur in the measurement of ARES-EVF, and the low temperature processability and the practical shrinkage were inferior.

On the other hand, a styrene-based copolymer of a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000, one or more types of monovinyl compounds containing at least a styrene-based compound, and an aliphatic unsaturated carboxylic acid alkyl ester. The ratio of the conjugated divinyl compound is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol per mol of the monovinyl compound, and the content of the aliphatic unsaturated carboxylic acid alkyl ester is high. The styrene-based copolymer is 5.0 to 30.0% by mass, assuming that the styrene-based copolymer is 100% by mass, and the styrene-based copolymer has a weight average molecular weight (Mw) of 200,000 to 600,000 and a molecular weight of 100. The styrene-based copolymers of Examples 1 to 7, wherein the ratio of 10,000 or more is 3.0 to 15.0%, have appropriate properties and have an excellent balance between low-temperature processability and mechanical strength. You can see that.

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 styrene-based copolymer according to the present invention has excellent low-temperature processability, mechanical strength, and practical shrinkage, for example, for heat-shrinkable films of packaging materials such as food containers and food and beverage containers, or. It can be suitably used for wrapping films, laminate films for foam containers, and the like.

Claims (10)

A styrene-based copolymer of one or more types of monovinyl compounds including at least a styrene-based compound, a conjugated divinyl compound having a number average molecular weight (Mn) of 850 to 100,000, and an aliphatic unsaturated carboxylic acid alkyl ester.
The content of the conjugated divinyl compound is 2.0 × 10 ^{-6 to} 4.0 × 10 ^-4 mol per mol of the monovinyl compound.
The content of the aliphatic unsaturated carboxylic acid alkyl ester is 5.0 to 30.0% by mass, assuming that the styrene-based copolymer is 100% by mass.
The styrene-based copolymer has a weight average molecular weight (Mw) of 200,000 to 600,000, and a proportion of the molecular weight of 1,000,000 or more is 3.0 to 15.0%.
A styrene-based copolymer characterized by this. The styrene-based copolymer according to claim 1, wherein the conjugated divinyl compound has a number average molecular weight (Mn) of 1000 to 30,000. The styrene-based copolymer according to claim 1 or 2, wherein the conjugated divinyl compound is in the form of a chain. The styrene-based copolymer according to any one of claims 1 to 3, wherein the conjugated vinyl group of the conjugated divinyl compound is located at the terminal. The styrene-based copolymer according to any one of claims 1 to 4, wherein the maximum rising ratio is 1.1 to 5.0. The styrene-based copolymer according to any one of claims 1 to 5, wherein the conjugated divinyl compound is a (hydrogenated) polybutadiene di (meth) acrylate. The method for producing a styrene-based copolymer according to any one of claims 1 to 6, wherein continuous solution polymerization or continuous bulk polymerization is used. A sheet comprising the styrene-based copolymer according to any one of claims 1 to 6. A film comprising the styrene-based copolymer according to any one of claims 1 to 6. A multi-layer heat-shrinkable film containing an intermediate layer and both outer layers sandwiching the intermediate layer.
The resin of the intermediate layer contains 10 to 95% by mass of the styrene-based copolymer (a) according to any one of claims 1 to 6, and a polymer block mainly composed of vinyl aromatic hydrocarbons and a conjugated diene. It is composed of a mixture containing 5 to 90% by mass of the resin (b) composed of a polymer block mainly composed of a derivative.
The resins of both outer layers are the styrene-based copolymer (a) 0 to 10% by mass according to any one of claims 1 to 6, and a polymer block mainly composed of a vinyl aromatic hydrocarbon and a conjugated diene. A multilayer heat-shrinkable film comprising a mixture containing 90 to 100% by mass of a resin (b) composed of a polymer block mainly composed of a derivative.

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