JPH0517596A - Biaxially drawn styrenic resin sheet - Google Patents

Abstract

PURPOSE:To obtain a biaxially drawn styrenic resin sheet having excellent toughness, impact resistance and transparency and resistant to cracking in the case of trimming a formed article of the sheet. CONSTITUTION:(A) A styrene-butadiene block copolymer preferably having a styrene:butadiene ratio of 25:75 to 75:25 and a weight-average molecular weight of 100,000-230,000 is compounded with (B) a graft-type high-impact styrene resin preferably having a rubber content of 5.0-10.0 and (C) a styrene resin in such a manner as to get a drawn sheet having an average rubber particle diameter of 0.08-0.25mum (especially 0.15-0.20mum) and also having a product of the particle diameter (mum) and the rubber concentration (wt.%) of 0.009-0.028 (especially 0.015-0.023). The composition is formed in the form of a sheet and biaxially drawn while adjusting the product of (the birefringence of the drawn sheet) and (the thickness mm of the sheet) to 1.00X10<-5>-2.25X10<-4> (especially 5.00X10<-5>-1.5X10<-4>).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched sheet, and more particularly to a styrene resin biaxially stretched sheet having excellent transparency, strength and molding processability.

[0002]

2. Description of the Related Art Conventionally, biaxially stretched styrenic resin sheets have been widely used as various food containers because of their excellent transparency, gloss and visible light transmission without the use of additives that are harmful to food hygiene. However, especially in recent years, the demand for high transparency and high strength is increasing. As a molding machine used to mold biaxially stretched styrene resin biaxial sheets into various food containers, vacuum molding machines and pressure molding machines are often used. There is a problem that the product will break. In order to solve the problem of cracking of a molded product, as disclosed in Japanese Patent Publication No. 57-201335, a synthetic rubber having an average rubber particle diameter is added to a styrene resin and biaxially stretched. A rubber-reinforced styrenic resin biaxially stretched sheet, which is superior in toughness and impact resistance to the biaxially stretched styrene resin sheet, has been proposed. However, when the strength of the sheet is increased by such a method, there is a drawback that the synthetic rubber particles reduce the transparency.

[0003]

The present invention has been made in view of the above-mentioned drawbacks of the conventional biaxially stretched styrenic resin biaxially stretched sheet, and has excellent toughness and impact resistance and is suitable for trimming a molded product. It is an object of the present invention to provide a styrene-based resin biaxially stretched sheet that is less likely to crack in a molded product and has excellent transparency.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has made the average rubber particle diameter in a biaxially stretched styrene resin sheet a specific range, and further By setting the product of the particle diameter and the rubber concentration in a specific range, and by setting the product of the birefringence of the styrene resin biaxially stretched sheet and the thickness of the sheet in a specific range,
The inventors have found that the above problems can be solved, and have completed the present invention based on this finding.

That is, the present invention provides a resin comprising (a) a styrene-butadiene block copolymer, (b) a rubber-reinforced styrene resin comprising a graft type high-impact styrene resin, and (c) a styrene resin. A biaxially stretched sheet made of a composition, wherein the average rubber particle diameter in the biaxially stretched sheet is 0.08 to 0.25 μm, and the F value represented by the formula 1 is 0.009 to 0.028. And the range of Equation 2
The present invention provides a transparent styrenic resin biaxially stretched sheet having a K value of 1.00 × 10 ^{−5 to} 2.25 × 10 ⁻⁴ . Formula 1 F = [C] × [D] Formula 2 K = [Δn] × [t] (where [C] is the rubber concentration in the biaxially stretched sheet in the unit of% by weight, and [D] is μm. A unit is the average rubber particle diameter in the biaxially oriented sheet, [Δn] is the birefringence of the biaxially oriented sheet, and [t] is the thickness of the biaxially oriented sheet in mm.)

The present invention will be described in detail below. A styrene-butadiene block copolymer is used as the component (a) in the styrene resin composition used in the present invention. The styrene-butadiene block copolymer used here is not particularly limited and various ones may be used. For example, (AB) n
Examples thereof include those having a structure of A, (AB) mX, [(AB) n] mX and the like. Here, A represents a styrene polymer chain, B represents a butadiene polymer chain, and n is 1 to 20.
, M is an integer of 3 to 7, and X is a polyfunctional compound that links m polymer chains. Further, the block copolymers used in the present invention have a so-called clear cut structure in which both styrene and butadiene components are mixed and at least one taper structure is contained, and both styrene and butadiene components are not mixed. Any of these can be used. These styrene-
Among the butadiene-based block copolymers, preferred are those having a structure of (AB) nA or (AB) mX.

Further, the content ratio of styrene and butadiene in the styrene-butadiene block copolymer is not particularly limited, but is usually 15:85 to 85:15.
Range, preferably 20:80 to 80:20
And particularly preferably 25:75 to 75:
The range is 25. The weight-average molecular weight of this styrene-butadiene block copolymer is not particularly limited, but is usually in the range of 50,000 to 300,000,
The range of 70,000 to 250,000 is preferably used, and the range of 100,000 to 230,000 is particularly preferable.
These styrene-butadiene block copolymers are
They may be used alone or in combination of two or more.

(B) used in styrene resin composition
The graft-type high-impact styrene resin as a component is not particularly limited, and various kinds can be used. Examples of the raw material monomer for the graft-type high-impact styrene-based resin include styrene, alkylstyrene (eg, methylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, tertiary butylstyrene, etc. o-, m-, p-). Each isomer), alpha alkyl styrene (eg, alpha methyl styrene, alpha ethyl styrene, etc.), monohalogenated styrene (eg, chloro styrene, bromo styrene, fluoro styrene, etc.) o-, m-, and p-isomers. ), Dihalogenated styrene (for example, dichlorostyrene, dibromostyrene, difluorostyrene, chlorobromostyrene and other nuclear substitution isomers), trihalogenated styrene (for example, trichlorostyrene, tribromostyrene, trifluorostyrene, dichlorobromine). Styrene, dibromochlorostyrene, difluorochlorostyrene, etc.), tetrahalogenated styrene (eg, tetrachlorostyrene, tetrabromostyrene, tetrafluorostyrene, dichlorodibromostyrene, etc.), pentahalogen Styrene (for example, pentachlorostyrene, pentabromostyrene, trichlorodibromostyrene, trifluorodichlorostyrene, and other nuclear-substituted isomers), alpha- and beta-halogen-substituted styrenes (for example, alphachlorostyrene, alphabromostyrene, beta-chlorostyrene, and beta-) Bromostyrene, etc.) and the like. These monomers may be used alone or in combination of two or more.

As the rubber of the graft type high impact styrene resin, for example, one or more kinds of conjugated 1,3-dienes (for example, butadiene, isoprene, 2-
Chloro-1,3 butadiene, 1-chloro-1,3 butadiene, piperylene, etc.). The rubber content of the raw material of the graft type high impact styrene resin can be selected in an arbitrary range,
Usually, those in the range of 3.0 to 15.0 are used, and those in the range of 5.0 to 10.0 are preferably used. The method for producing the graft-type high-impact styrene-based resin of the present invention is not particularly limited, and for example, a method in which a diene rubber is dissolved in a styrene-based monomer and polymerized, and the amount of the diene rubber is 2 to 10% by weight. Examples thereof include a method in which the graft-type high-impact styrene-based resin and the transparent styrene-based resin contained are mixed arbitrarily.

The styrene resin which is the component (c) of the styrene resin composition used in the present invention is not particularly limited and various ones can be used. For example, styrene and α-methylstyrene. Examples thereof include polymers of monomers composed of one kind or a combination of plural kinds selected from vinyl aromatic compounds, and copolymers of vinyl aromatic compounds and other copolymerizable monomers. Examples of the monomer that can be used for copolymerization with the vinyl aromatic compound include vinyl cyan compounds such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and esters thereof. The molecular weight of the styrene-based resin is not particularly limited, but the one having a weight average molecular weight of 150,000 to 400,000 is usually used.

The biaxially stretched styrene resin sheet of the present invention comprises the styrene-butadiene block copolymer and
It is composed of the graft type high impact styrene resin and a resin composition containing the styrene resin.
These components have an average rubber particle diameter [D] in the biaxially stretched sheet of 0.08 to 0.25 μm, preferably 0.10.
0.23 μm, particularly preferably 0.15 to 0.20 μm, and the F value represented by the formula 1 is 0.009 to 0.02.
It is necessary to mix 8 or more, preferably 0.012 to 0.024, particularly preferably 0.015 to 0.023.

Here, the rubber means both the styrene-butadiene block copolymer and the rubber contained in the graft type high-impact styrene resin. In addition, the average rubber particle diameter [D] in the biaxially stretched sheet refers to the rubber particle diameter when the flat rubber particles are made spherical by shrinking the biaxially stretched sheet at the stretching temperature. Since the rubber particles of the normally stretched sheet are not spherical but flat due to the orientation, it is difficult to determine the average rubber particle diameter, so in the present invention, the average rubber particle diameter in the sheet after shrinkage is specified. There is. When obtaining the particle diameters of different rubber particles, the average rubber particle diameter is expressed by the following formula.

[0013]

[Equation 1]

Note d _k : individual rubber particle diameter n: number of rubber particles If the average rubber particle diameter is less than 0.08 μm, the impact strength is poor, and if it exceeds 0.25 μm, the transparency of the sheet is poor.
Further, the F value is the product of the rubber concentration [C] in the biaxially stretched sheet in the unit of wt% and the average rubber particle diameter [D] in the biaxially stretched sheet in the unit of μm, and the F value is 0. If it is less than 009, cracks are likely to occur during trimming of the sheet, and the F value is 0.
When it exceeds 028, the transparency decreases. In the present invention, when quantifying the rubber concentration, there are an NMR method, an iodine chloride-potentiometric titration method and the like, but any of them may be used.

The biaxially stretched sheet of the present invention can be obtained by blending the above-mentioned three kinds of resins so as to be within the above F-value range, and the styrene-butadiene block copolymer is preferably 0.05 to 5. 0.50% by weight, particularly preferably 0.0
It is desirable to blend within the range of 8 to 0.30. The order of mixing the above components is not particularly limited, and any kind of mixing species may be used. For example, a method in which the component (a) and the resin (b) are first mixed, and then the resin (c) is mixed, the resin (b) and the resin (c) are mixed,
Then, a method of mixing the component (a), a method of mixing the component (a) and the resin (c), and a method of mixing the resin (b), a component (a), a resin (b) and a resin (c). Examples include a method of simultaneously mixing the components. The mixing is preferably carried out so that it is as uniform as possible. Various mixing methods can be applied, but it is preferable to use a stirring mixer such as a Henschel mixer for mixing.

The mixed resin composition is formed into a sheet by various methods such as an extruder and a press, and further biaxially stretched to obtain a biaxially stretched sheet. The biaxially stretched sheet of the present invention has a K value represented by the above formula 2 of 1.00 × 1.
0 ^{-5 to} 2.25 x 10 ^-4 , preferably 1.00 x 10 ^-5 to
2.0 × 10 ⁻⁴ , particularly preferably 5.00 × 10 ⁻⁵ to 1.
It is necessary that the sheet is obtained by adjusting the range of 5 × 10 ⁻⁴ and biaxially stretching.

The K value is a birefringence index [Δ
n] and the thickness [t] of the biaxially stretched sheet in mm. When the K value is less than 1.00 × 10 ⁻⁵ , the sheet strength is low, and cracks and molding defects are likely to occur at the time of molding. Value is 2.2
If it exceeds 5 × 10 ⁻⁴ , the degree of orientation is large, and the sheet has poor moldability. Biaxial stretching of the styrene-based resin sheet in the present invention may be simultaneous biaxial stretching or sequential biaxial stretching, such as generally known tenter biaxial stretching method, and inflation biaxial stretching method. It can be carried out by various biaxial stretching methods. The effects of the present invention can be obtained regardless of these stretching methods. The styrene-based resin biaxially stretched sheet of the present invention may contain various additives within the range not impairing the object of the present invention.

[0018]

EXAMPLES The present invention will now be described in more detail with reference to examples. The physical properties and evaluations of the sheets in Examples and Comparative Examples were performed by the following methods. 1. Rubber particle size A sheet completely heat-shrinked in a gear oven at 130 ° C. for 1 hour was measured using a 15,000 times photograph taken with a transmission electron microscope manufactured by JEOL. 2. Rubber concentration It was measured using 90 MHz H ¹ -NMR manufactured by JEOL Ltd. 3. Birefringence was measured using a polarizing microscope (Perec Conventor) manufactured by Olympus Optical Co., Ltd. 4. Sheet haze Measure the sheet haze according to the ASTM-D-1003 method ◎: Haze is less than 1.0 (%) ○: Haze is 1.0 (%) or more and 1.2 (%) Less than x: The haze was ranked as 1.2 (%) or more. 5. Folding strength of sheet Using a MIT tester manufactured by Toyo Seiki Co., Ltd., the folding strength was measured at a load of 1 kg and a folding angle of 120 ° C. 6. Sheet impact strength Measured with a film impact tester manufactured by Tester Sangyo Co., Ltd.

Example 1 Polystyrene having a weight average molecular weight of 300,000, 0.323% by weight of high-impact polystyrene having a polybutadiene content of 5.5% by weight, and an ABA structure having a butadiene content of 60% by weight. A styrene-butadiene block copolymer having a weight average molecular weight of 200,000 was mixed by a Henschel mixer so that 0.054% by weight was uniformly dispersed, and then pelletized by an extruder. This was fed into the extruder through a feed port of an extruder (L / D = 24) having a diameter of 40 m / m, melted and fed to a sheet die at 200 ° C. to obtain a sheet having a thickness of 0.8 mm. This sheet is 100mm × 10
Cut it out to 0 mm, and use a biaxial stretching machine [Toyo Seiki Co., Ltd.] for Δn
Biaxial stretching was performed so that xt = 0.58 x 10 ^-4 . The average rubber particle diameter (μm) is 0.19 and the rubber concentration is 0.1.
A 050 (wt.%) Sheet was obtained. As shown in Table 1, the physical properties of this sheet were good in both transparency and strength.

Examples 2 to 8 In the same manner as in Example 1, the biaxially stretched sheets of Examples 2 to 8 were produced according to the conditions shown in Table 1. Both were excellent in transparency and strength.

[0021]

[Table 1]

[0022]

[Table 2]

Comparative Examples 1 to 9 Sheets were prepared in the same manner as in Examples 1 to 8 according to the conditions shown in Table 2. Among these sheets, one having both high transparency and sufficient strength could not be obtained.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

EFFECTS OF THE INVENTION The styrenic resin biaxially stretched sheet of the present invention has excellent transparency, excellent toughness and impact resistance, and cracks of the molded product hardly occur when trimming the molded product. It has excellent properties.

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Claims (1)

Claims: 1. A resin composition comprising (a) a styrene-butadiene block copolymer, (b) a graft type high-impact styrene resin, and (c) a styrene resin. An axially stretched sheet, wherein the average rubber particle diameter in the sheet is 0.08 to 0.25 μm, and F represented by Formula 1 is used.
A transparent styrene having a value in the range of 0.009 to 0.028 and a K value represented by Formula 2 in the range of 1.00 × 10 ^{−5 to} 2.25 × 10 ^−4. Resin biaxially stretched sheet. Formula 1 F = [C] × [D] Formula 2 K = [Δn] × [t] (where [C] is the rubber concentration in the biaxially stretched sheet in the unit of% by weight, and [D] is μm. A unit is the average rubber particle diameter in the biaxially oriented sheet, [Δn] is the birefringence of the biaxially oriented sheet, and [t] is the thickness of the biaxially oriented sheet in mm.)