JPH09183818A - Styrenic copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a styrenic copolymer not generating surface defects such as microgels on the surface of a molded product, having a moderate viscosity on melting, and good in molding characteristics. SOLUTION: This styrenic copolymer is obtained by copolymerizing ethylstyrene with one or more kinds of monomers capable of being copolymerized with the ethylstyrene. Therein, the styrenic copolymer has the following characteristics: (A) ethylstyrene monomer units: 2-80wt.%; (B) one or more kinds of the monomers capable of being copolymerized with the ethylstyrene: 98-20wt.%; (C) the weight-average mol.wt. of the styrenic copolymer: 100,000-2,000,000 and (D) mol.wt. distribution (Mw /Mn ): 2.0-8.0.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a styrene-based copolymer suitable for injection molding, foam molding, blow molding and sheet molding.

[0002]

2. Description of the Related Art Styrenic resins are a molding material which has both good moldability and transparency, and since it can be impact-modified by being modified with rubber, it can be widely used in the fields of weak electricity, machine parts, sundries and the like. However, when a large styrene resin molded product is to be obtained by injection molding, foam molding, blow molding, or sheet molding, the moldability is poor because the strain (viscosity) when the resin melts is insufficient, and the resulting molded product In addition, uneven thickness (thickness unevenness) and uneven foaming occurred, and there was a drawback that it could not be used in fields where the original characteristics of the resin were utilized.

Therefore, in order to impart a strain (viscosity) when the resin is melted, a resin is designed with an average molecular weight higher than before. However, in the resin production in this case, it is not preferable to raise the polymerization temperature, so that not only problems under low-temperature polymerization, that is, increase in load on production equipment due to increase in resin viscosity and deterioration of productivity, but also special When such a polyfunctional initiator is used, there are drawbacks such as an increase in manufacturing cost. The resulting high molecular weight styrene-based resin was inferior in fluidity and moldability as compared with general styrene-based resins. When using such a high molecular weight resin,
In order to secure the fluidity, a means of mixing a low molecular weight resin component or blending an additive such as wax has been adopted. However, even in this case, as a result, it works in the direction of inhibiting the strain (toughness) at the time of melting the resin, and it is the current situation that it does not reach a satisfactory level.

On the other hand, JP-A-2-170806, JP-A-2-173130, and JP-A-6-166795.
In the publication, polyfunctional vinyl such as divinylbenzene is added to 30
A technique has been proposed in which the average molecular weight of a resin is increased by adding it to a polymerization system of up to 1000 ppm to polymerize it and to develop a strain (viscosity) when the resin is melted. However, the above-mentioned polyfunctional vinyl is originally used as a cross-linking agent, and when the polyfunctional vinyl is added in a large amount and the polymerization conversion rate becomes high, the resin in the polymerization reactor is apt to undergo a cross-linking reaction and gels. There is concern about equipment problems.
Therefore, when the resin is produced by this method, it is inevitable to control the addition amount of the polyfunctional vinyl very strictly. Further, the resin produced by using the polyfunctional vinyl tends to contain microgel, which causes a surface defect of the molded product and is insufficient in quality.

By the way, JP-A-6-100637 and JP-A-6-345923 disclose that ethylstyrene can be used as a specific example of the styrene-based monomer. However, unlike other vinyl aromatic alkyl-substituted derivatives, ethylstyrene (ethylvinylbenzene) monomer has not been industrially produced and is not commercially available as a research reagent. Was not used as a monomer component for polymerization of the styrene-based copolymer for use in the molding material of the present invention, and its properties in a molten state were not known.

From the above, it has been desired to develop a molding material containing no microgel or the like and having a good molding property by a technique which does not cause a trouble in the operation of resin production.

[0007]

[Problems to be Solved by the Invention]

It is an object of the present invention to provide a styrene-based copolymer having good molding characteristics, in which surface defects such as microgels do not occur on the surface of the molded product, and a strain (tackiness) at the time of melting is imparted. .

[0009]

In order to solve the above-mentioned problems, the inventors of the present invention polymerized an ethylstyrene (ethylvinylbenzene) monomer which has not been industrially used in the production of styrene-based copolymers. It was found that the above problem can be solved by using it as a monomer component, and the present invention has been solved.

That is, the present invention relates to a styrene-based copolymer obtained by copolymerizing an ethylstyrene monomer with another monomer which is copolymerizable with at least one ethylstyrene. In the copolymer, (A)
It contains 2 to 80 wt% of ethylstyrene monomer units and 98 to 20 wt% of (B) other monomer units copolymerizable with one or more kinds of ethylstyrene. Weight average molecular weight (Mw) is in the range of 100,000 to 2,000,000, and (D) molecular weight distribution (Mw / Mn) is in the range of 2.0 to 8.0. It is about coalescence.

Hereinafter, the present invention will be described in detail. The ethylstyrene (ethylvinylbenzene) monomer referred to in the present invention may be an ortho isomer, a meta isomer, a para isomer, or a mixture thereof. The content of ethylstyrene needs to be in the range of 2 to 80 wt% in the copolymer, preferably 3 to 40 wt%, more preferably 4 to
It is 20 wt%. If the content of ethylstyrene exceeds 80 wt%, not only is the heat resistance deteriorated, but gelation tends to occur, which may lead to surface defects of the molded product, which is not preferable. Is difficult to obtain, and it is difficult for the resin to become a stiff resin when melted.

The ethylstyrene monomer is present as an impurity of divinylbenzene, and is contained in divinylbenzene in a form in which only one ethyl group of diethylbenzene which is a precursor of the dehydrogenation reaction is dehydrogenated. Therefore,
It can be obtained by distilling divinylbenzene.

The monomers copolymerizable with ethylstyrene in the present invention include styrene-based monomers other than ethylstyrene monomer, vinyl cyanide-based monomers such as acrylonitrile, and methyl methacrylate. Methacrylates, acrylates, maleic acid, maleic acid esters, itaconic acid and itaconic acid esters, N-alkylmaleimides, N-phenylmaleimide (PMI)
And other monomers. You may use these monomers individually or in combination of 2 or more types.

More specifically, styrene derivatives other than styrene as styrene-based monomers include side chain alkyl-substituted styrenes such as α-methylstyrene, nuclear alkyl-substituted styrenes such as vinyltoluene, halogenated styrenes such as chlorostyrene, and divinyl. Benzene etc. can be mentioned.
Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile, and α-chloroacrylonitrile. Examples of the methacrylates include methacrylic acid alkyl esters such as ethyl methacrylate, propylene methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, and phenyl methacrylate, in addition to methyl methacrylate.
Examples of acrylates include methyl acrylate, ethyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, dodecyl acrylate, phenyl acrylate, and benzyl acrylate, but there is no particular limitation. In the present invention, when a strain (viscosity) at the time of melting is expressed, a monomer having a strong hydrogen abstraction ability (chain transfer ability) during the polymerization reaction, such as a vinyl cyanide monomer such as acrylonitrile, has a molecular weight distribution. It is effective because it can be widened. Further, copolymerization with a maleimide-based monomer such as N-alkylmaleimide and N-phenylmaleimide (PMI) is effective for improving the glass transition temperature, and cyclohexylmaleimide and N-phenylmaleimide are particularly effective. When the maleimide-based monomer is used, its content is preferably 2 to 30 wt% in the total amount of the monomers.

The content of the other radically polymerizable monomer copolymerizable with ethylstyrene in the present invention must be in the range of 20 to 98 wt% in the styrene copolymer.

The styrene-based copolymer of the present invention is required to have a styrene-equivalent weight average molecular weight (Mw) in the range of 100,000 to 2,000,000, preferably 200,000 to 180.
10,000, more preferably 250,000 to 1.5 million. When the weight average molecular weight (Mw) is less than 100,000, it is not preferable because the strain (toughness) is insufficient at the time of melting, and when it exceeds 2,000,000, the fluidity is remarkably lowered, which is not preferable. Furthermore, the styrene-based copolymer of the present invention needs to have a molecular weight distribution (Mw / Mn) calculated from the styrene-converted average molecular weight in the range of 2.0 to 8.0, preferably Mw / Mn. 2.3 to 4.5 is good. Mw / Mn is 2.
If it is less than 0, it is not preferable because the strain (tackiness) is insufficient during melting, and if it exceeds 8.0, surface defects due to the generation of microgels are likely to occur, which is not preferable.

The styrene-based copolymer of the present invention may be modified according to need by n-octadecyl 3- (3,5-di-tert).
-Butyl-4-hydroxyphenyl) propionate,
Hindered phenol-based compounds such as 2,6-di-tert-butyl-4-methylphenol, phosphorus-based compounds such as trisnonylphenyl phosphite and tris (2,4-di-tert-butylphenyl) phosphite, pentaerythrityl Sulfur-based compounds such as tetrakis (3-laurylthiopropionate), 2- [1- (2-hydroxy-3,5-di-te]
rt-Pentylphenyl) ethyl] -4,6-di-te
Antioxidants such as phenol acrylates such as rt-pentylphenyl acrylate may be added.

The polymerization method for producing the styrene copolymer of the present invention is not particularly limited, and any known method such as solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization may be used. it can.

The degree of strain (viscosity) of the styrene copolymer thus obtained upon melting is such that the die swell ratio [-] (DS) and the melt tension [gf] are 220 ° C in the molten state.
It can be judged by the value of (MT), and i) the shear rate is 10 to 100 sec in the molten state at 220 ° C.
It is desirable that the die swell value (DS) measured in the range of ⁻¹ and ii) the melt tension value (MT) satisfy the following general formula (I). DS × MT ≧ 10 (I) Further, the value of the die swell ratio is preferably 1.2 or more. The (DS) melt tension (MT) is preferably 5 gf or more. If the condition of DS × MT ≧ 10 is not satisfied, strain (tackiness) is insufficient during molding and good molding cannot be performed, which is not preferable.

Here, the die swell means that when the resin is extruded in a molten state from a cylindrical tube having an inner diameter A (mm) at a shear rate, the pressure of the cylindrical resin released from the cylindrical tube is released. This is a phenomenon that the diameter B (mm) of the resin is enlarged, and is an index represented by the die swell ratio DS = B / A. The larger the value of the die swell ratio, the more applicable it is to molding with large deformation. In addition, the melt tension means that the molten resin extruded from the cylindrical tube at a constant shear rate right below by a pulley.
It measures the winding tension when it is guided in the horizontal direction of 0 degree and is wound by a winder, and is measured from a pulley through a load cell. The larger the melt tension, the more applicable it is to molding with large deformation.

The styrene-based copolymer of the present invention can be molded by a known molding method such as injection molding, blow molding, vacuum molding, foam molding, blow molding, and molding of sheets, films and other various shapes. You can get the goods. In particular, it is suitable for molding with large deformation such as foam molding and blow molding by taking advantage of its high strain (viscosity) during melting.

In the foam molding, a method of impregnating pellets with a foaming gas in advance and heating and melting in a molding machine to foam when releasing the pressure, and a method of kneading a foaming agent and then heating and melting in a molding machine There is a method of foaming when releasing the pressure. Since the styrene-based copolymer according to the present invention has a high strain (viscosity) at the time of melting, it is possible to make the size and density of the foam cells uniform, and the strength of the foam and the strain after molding are less likely to occur. The method of can also be used. Further, the foaming gas to be used, the type of the foaming agent and other additives are not limited.

In blow molding, molten resin is extruded from a cylindrical die to form a molding precursor called a parison, which is sandwiched between molds and gas is blown into the parison with the top and bottom closed to form a mold with the pressure. It is known as a pressing method. Here, the superiority or inferiority of blow moldability depends on a phenomenon called drawdown in which the parison hangs from the time the parison is formed until the mold is closed, and when the drawdown is severe, the thickness of the molded product becomes uneven, resulting in a uniform thickness. It does not become a compact body. The styrene-based copolymer according to the present invention is suitable for blow molding because it has a high strain (viscosity) at the time of melting and hardly causes unevenness in the wall thickness of the molded body.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

(1) Ethylstyrene Divinylbenzene (trade name DVB-, manufactured by Nippon Steel Chemical Co., Ltd.)
570) as a basic raw material, and ethyl styrene was obtained by a vacuum precision distillation apparatus having 80 theoretical plates. The degree of vacuum is 7 torr at the top of the tower
Below, a distillation temperature of 70 ° C. and a polymerization inhibitor of 50 at the top of the tower and in the pot
Batch distillation was carried out by adding 00 ppm. The obtained distilled components were analyzed by gas chromatography using a gas chromatograph 14A manufactured by Shimadzu Corporation (column; DB-WAX (0.25φ × 60 m, column temperature 160 ° C., injection temperature 250 ° C., detector; FID). -Ethylstyrene purity 81.2%, P-ethylstyrene purity 16.2
%, Diethylbenzene purity of 2.6% was confirmed to be an ethylstyrene raw material. The divinylbenzene derivative was ND (below the detection limit) at the detection limit of 50 ppm. Further, 80 ppm of tertiary butyl catechol was added as a polymerization inhibitor to the obtained ethylstyrene to stabilize it. (Hereinafter, this ethylstyrene is referred to as ethylstyrene A.)

(2) Polymerization of Styrene Copolymer Ethylstyrene monomer (ethylstyrene A), a monomer copolymerizable with ethylstyrene, a solvent, an initiator, a chain transfer agent, etc. are blended in a predetermined ratio. The mixed raw materials were continuously supplied to a full-fill type complete mixing tank reactor (50 liters), and the polymer was continuously extracted from the reactor while maintaining a constant pressure inside the reactor, and a depressurization vent port was provided. The resin was obtained in the form of pellets by a continuous bulk polymerization process in which the solvent, residual monomers and the like were removed in a twin-screw extruder having a.

(3) Method of measuring die swell Using a capillary rheometer (trade name: Capillograph 1C type) manufactured by Toyo Seiki, capillary L [mm] / D [mm] =
10/1, barrel = 9.55mm, measurement temperature = 220 °
The diameter R [mm] of the extruded strand was measured by changing the shear rate in C in the range of ⁰ to 1000 sec ⁻¹ and calculated as die swell DS = R / D. L [mm]: Length of capillary D [mm]: Diameter of capillary

(4) Method of measuring melt tension Using a capillary rheometer (trade name Capirograph 1C type) manufactured by Toyo Seiki Co., Ltd., an extrusion speed of 10 mm /
Capacitance L [mm] / D [mm] = 10/1,
Melt tension was measured by changing the winding speed within a range of 0 to 100 m / sec at a barrel temperature of 9.55 mm and a measurement temperature of 220 ° C.

(5) Method for measuring average molecular weight, method for measuring molecular weight distribution Weight average molecular weight (M) as polystyrene conversion value by gel permeation chromatography analysis manufactured by Tosoh Corporation.
w) and molecular weight distribution (Mw / Mn) were determined.

(6) Analysis of Resin Composition The contents of ethylstyrene monomer units and other monomer units in the styrene copolymer were measured. The measurement was performed by 1H-NMR (EX-400 manufactured by JEOL Ltd.) and a CHNO elemental analyzer manufactured by Perkin Elmer.

[0031]

【Example】

Example 1 Ethylbenzene (EB) was used as a solvent to polymerize ethylstyrene A (E-St) and styrene (St). The mixing ratio of raw materials (total amount: 100) is E-St / St / EB
= 19.0 / 76.0 / 5.0, 300 ppm of t-hexylper-oxyisopropyl monocarbonate, t-dodecyl mercaptan (TD
M) was added at 500 ppm. Then, this raw material solution was reacted at a polymerization temperature of 125 ° C. to a conversion of about 70% by weight to obtain an ethylstyrene-containing styrene-based copolymer. About the obtained styrene-based copolymer, the resin composition,
The average molecular weight, molecular weight distribution, die swell and melt tension were measured. The results are shown in Table 1.

Example 2 Ethylbenzene A (E-St) and styrene (St) were polymerized using ethylbenzene (EB) as a solvent. The mixing ratio of raw materials (total amount: 100) is E-St / St / EB
= 66.5 / 28.5 / 5.0, 300 ppm of t-hexylper-oxyisopropyl monocarbonate, t-dodecyl mercaptan (TD) relative to the total amount of monomer raw materials.
M) was added at 100 ppm. Then, this raw material solution was reacted at a polymerization temperature of 125 ° C. to a conversion of about 50% by weight to obtain an ethylstyrene-containing styrene-based copolymer. About the obtained styrene-based copolymer, the resin composition,
The average molecular weight, molecular weight distribution, die swell and melt tension were measured. The results are shown in Table 1.

Example 3 Using ethylbenzene (EB) and methyl ethyl ketone (MEK) as solvents, ethyl styrene A (E-St),
Polymerization of styrene (St) and acrylonitrile (AN) was performed. The mixing ratio of raw materials (total amount: 100) is E-St /
St / AN / MEK / EB = 8.7 / 49.3 / 26.
0 / 8.0 / 8.0, and t-hexylper-oxyisopropyl monocarbonate was added to 35 with respect to the total amount of monomer raw materials.
0 ppm, t-dodecyl mercaptan (TDM) 20
0 ppm was added. Then, this raw material solution was reacted at a polymerization temperature of 125 ° C. up to a conversion of about 80% by weight to obtain an ethylstyrene-containing styrene-based copolymer. About the obtained styrene-based copolymer, resin composition, average molecular weight,
The molecular weight distribution, die swell and melt tension were measured. The results are shown in Table 1.

Example 4 Ethyl styrene A (E-St), ethyl benzene (EB) and methyl ethyl ketone (MEK) were used as solvents.
Polymerization of styrene (St) and acrylonitrile (AN) was performed. The mixing ratio of raw materials (total amount: 100) is E-St /
St / AN / MEK / EB = 3.3 / 29.5 / 49.
2 / 9.0 / 9.0, and t-hexylper-oxyisopropyl monocarbonate was added to 30 based on the total amount of monomer raw materials.
0 ppm, t-dodecyl mercaptan (TDM) 20
00 ppm was added. Then, this raw material solution was reacted at a polymerization temperature of 125 ° C. until a conversion of about 45% by weight was obtained to obtain an ethylstyrene-containing styrene-based copolymer. The resin composition, average molecular weight, molecular weight distribution, die swell, and melt tension of the obtained styrene-based copolymer were measured. The results are shown in Table 1.

Example 5 Ethylbenzene (EB) and methylethylketone (MEK) were used as solvents, and ethylstyrene (E-St), styrene (St) and N-cyclohexylmaleimide (CH) were used.
MI) was polymerized. Mixing ratio of raw materials (total amount: 10
0) to E-St / St / CHMI / MEK / EB = 1
2.6 / 67.2 / 4.2 / 8.0 / 8.0, t-hexylper-oxyisopropyl monocarbonate 300 ppm and t-dodecyl mercaptan (TDM) relative to the total amount of monomer raw materials. 3000 ppm was added. And
This raw material solution was reacted at a polymerization temperature of 125 ° C. to a conversion of about 70% by weight to obtain an ethylstyrene-containing styrene-based copolymer. The resin composition, average molecular weight, molecular weight distribution, die swell, and melt tension of the obtained styrene-based copolymer were measured. The results are shown in Table 1.

Comparative Example 1 Polymerization was carried out without using ethylstyrene (E-St). Other conditions were the same as in Example 1. The resin composition, average molecular weight, molecular weight distribution, die swell, and melt tension of the obtained styrene-based copolymer were measured.
The results are shown in Table 1.

Comparative Example 2 Polymerization was carried out without using ethylstyrene (E-St). Other conditions were the same as in Example 3. The resin composition, average molecular weight, molecular weight distribution, die swell, and melt tension of the obtained styrene-based copolymer were measured.
The results are shown in Table 1.

Comparative Example 3 Polymerization was carried out without using ethylstyrene (E-St). Other conditions were the same as in Example 5. The obtained resin was measured for average molecular weight, molecular weight distribution, die swell, and melt tension, and the results are shown in Table 1.

[0039]

[Table 1]

Application Example 1 The ethylstyrene-containing styrene copolymer obtained in Example 1 was used for foam molding. Foam width is 60m
The size was m and the thickness was 5 mm, and a foaming extruder was used. As a nucleating agent, Mithron vapor manufactured by Nippon Mistron Co., Ltd. was used, and as a foaming agent, LPG (a mixture of normal butane and isobutane) was used. The expansion ratio of the foam used in the secondary molding evaluation was 10 ± 0.3, and the average cell size was 0.2 mm.
Aligned to ± 0.03. The molded foamed article had an average cell diameter of 130 μm and a closed cell rate of 55%. Further, this foamed molded article had a good appearance in which the foamed particles were well fused to each other and did not shrink.

Here, the closed cell rate can be obtained by the following equation. The higher the closed cell rate, the higher the elasticity (for example, the compression strength or the compression strain restoration rate) and the impact resistance of the molded body, which is preferable. Closed cell ratio (%) = {((ED) / ρ) / ((FD) /
ρ)} × 100 D: Weight of test piece (g) E: True volume of test piece (cm ³ ) F: Apparent volume of test piece (cm ³ ) ρ: Density of resin used in test piece (g / Cm ³ )

Application Example 2 (Comparative Example) The styrene-based copolymer containing no ethylstyrene obtained in Comparative Example 2 was used for foam molding. The method for producing the foam and the method for molding the secondary foam were in accordance with Example 6. The molded foamed article had an average cell diameter of 130 μm and a closed cell rate of 55%. Further, in this foamed molded product, there was uneven fusion of the foamed particles, and due to shrinkage, a small wavy pattern was generated on the surface.

Application Example 3 The ethylstyrene-containing styrene copolymer obtained in Example 3 was used for blow molding. First, the ethylstyrene-containing styrene-based copolymer 70 obtained in Example 3 was used.
Parts by weight and ABS powder (M5BR manufactured by Ube Saikon)
30 parts by weight of 2) were mixed with 4000 ppm of other antioxidants and 5000 ppm of ethylenebisstearamide by a V-type blender, melt-kneaded by a twin-screw extruder, and then repelletized. The obtained ABS resin has a rubber content of 14 wt%,
Acrylonitrile content 29wt%, 220 ℃, 10Kg
MFR (melt flow rate) measured by 2.4 g /
10 minutes. The ABS resin obtained is used by Placo Ltd.
Blow molding machine DA-50 (extruder 50mm) is used to set parison length at the end of injection to the same value by setting resin temperature to 30-38% at the set temperature of 240 ° C and core stroke of 7.5mm. The drawdown behavior (change of parison length with time) in the free suspension state afterward was confirmed. The elongation of the parison is 10mm 10 seconds after the injection is completed.
Met.

Application Example 4 (Comparative Example) Blow molding was carried out using the styrene-based copolymer containing no ethylstyrene obtained in Comparative Example 2. First, an ABS resin was obtained according to Application Example 3. The obtained ABS resin has a rubber content of 14 wt% and an acrylonitrile content of 29 w.
t%. MFR measured at 220 ° C ・ 10kg
(Melt flow rate) was 2.0 g / 10 minutes.
The obtained ABS resin is blow molding machine D manufactured by Placo Co., Ltd.
Set temperature 24 using A-50 (extruder 50mm)
Resin measurement value is 30 at 0 ° C and core stroke 7.5mm
The parison length at the end of injection was made equal to ˜38%, and the drawdown behavior (change of parison length with time) in the free suspension state after completion of injection was confirmed. The elongation of the parison 10 seconds after the completion of injection was 200 mm.

Application Example 5 Using the styrene-based copolymer containing ethylstyrene obtained in Example 1, a shrink film was prepared and evaluated. First,
80 parts by weight of the styrene-based copolymer containing ethylstyrene obtained in Example 1 and 20 parts by weight of an SBS block copolymer (containing 60% by weight of butadiene) were mixed in a V-blender and then kneaded in a twin-screw extruder to form a sheet. A sheet having a thickness of 100 μm was obtained with a molding machine. Then, with a biaxial stretching device, 120 °
C, the length and width of each under the condition of a drawing speed of 1.5 m / min.
The film was stretched 5 times to obtain a film having a thickness of 11 μm. This film was subjected to a film impact test according to JIS P-8134. As a result, it was 10.2 kg-cm / cm.

Application Example 6 (Comparative Example) Using the styrene-based copolymer containing no ethylstyrene obtained in Comparative Example 1, a shrink film was prepared and evaluated.
The shrink film was prepared in the same manner as in Application Example 5.
The shrink film thus obtained was subjected to an impact test and found to be 5.2 kg-cm / cm.

[0047]

The styrenic copolymer according to the present invention is excellent in melt tension and strain (viscosity) at the time of melting when evaluated by die swell, and can be widely used for parts such as electrical and mechanical fields. Moreover, it is particularly suitable for use in foam molding, blow molding, and shrink film applications due to its excellent molding characteristics.

Claims (3)

[Claims] 1. A styrene-based copolymer obtained by copolymerizing an ethylstyrene monomer and another monomer copolymerizable with one or more kinds of ethylstyrene,
In the styrene-based copolymer, (A) ethyl styrene monomer unit 2 to 80 wt%, (B) one or more ethyl styrene copolymerizable other monomer unit 98 to 20 wt%
Is included, the weight average molecular weight (Mw) of the (C) styrene-based copolymer is in the range of 100,000 to 2,000,000, and (D) the molecular weight distribution (Mw / Mn) is 2.0 to 8 A styrene-based copolymer characterized by being in the range of 0.0. 2. A die swell value [-] (DS) measured at a shear rate of 10 to 100 sec ^-1 and a ii) melt tension value [gf] in a molten state at 220 ° C. (M
The styrene-based copolymer according to claim 1, wherein T) satisfies the following general formula (I). DS × MT ≧ 10 (I) 3. The styrene-based copolymer according to claim 1, wherein the styrene-based copolymer contains 2 to 30 wt% of a maleimide-based monomer unit as a monomer component copolymerizable with the ethylstyrene monomer. Copolymer.