JP2018083908A - Styrenic oriented sheet and package, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a styrenic oriented sheet that has excellent moldability, rigidity, and transparency, and prevents scratches and dents from occurring during the production of the sheet, its molding into a container, or their conveyance, and a package obtained therefrom and a method for producing the same.SOLUTION: A styrenic oriented sheet contains an aromatic vinyl copolymer that contains, as monomer units: an aromatic vinyl compound of 50-98 mass%; and at least one of a vinyl cyanide or a derivative thereof, a (meth) acrylic acid or a derivative thereof, an unsaturated dicarboxylic anhydride or a derivative thereof, of 2-50 mass%. The styrenic oriented sheet has a Rockwell hardness of 70-110 by M scale based on JISZ 2245. The sheet can be molded to obtain a package.SELECTED DRAWING: None

Description

  The present invention relates to a styrene-based stretched sheet and a packaging container, and a method for producing them.

  Conventionally, a packaging container made of a synthetic resin sheet has been used as a container used when selling foods, processed foods, and the like in stores such as supermarkets, convenience stores, department stores, and lunch boxes.

  Among them, styrene-based stretched sheets are widely used in the food packaging container field because of their excellent transparency and high rigidity.

  In general, the styrene-based stretched sheet includes a production method in which a resin composition mainly composed of polystyrene is extruded into a sheet shape and fed out with a metal roll, and the uniaxially or biaxially stretched sheet is wound into a scroll shape. In addition, as a method for forming the styrene-based stretched sheet into a packaging container, die forming mainly by hot plate forming, vacuum forming or the like is used. Further, it is common that a plurality of obtained packaging containers are stacked, packed in a resin bag, and further provided to a supermarket or the like in a state of being laid in a cardboard box.

  These styrene-based stretched sheets are in contact with a metal roll during production, or have a concern that the surface may be damaged due to contact between the sheets when unwinding in order to wind up in the form of a roll, and the appearance and transparency may be impaired. . In addition, the packaging container obtained by molding the styrene-based stretched sheet is brought into contact with the mold during molding, or when the packaging container is transported in a stacked state, the surface of the packaging container is brought into contact with the packaging container. There was a concern of scratching the surface and impairing the appearance and transparency. In addition, when there are impurities between styrene-based stretched sheets or between packaging containers, between styrene-based stretched sheets and metal rolls, or between packaging containers and molds, these surfaces are scratched and the appearance and transparency There was a concern that damages.

  Up to now, measures against scratches on styrene-based stretched sheets and packaging containers have largely depended on quality inspections within the manufacturing process, measures on packaging methods and transportation methods, and for styrene-based stretched sheets for food packaging containers, the sheet itself There were few requests for scratch resistance. However, due to the recent diversification of food demand, high quality requirements for these packaging containers, increased export of sheets and containers to foreign countries due to liberalization of trade and increase in overseas demand, and the above-mentioned quality control know-how As the number of sheet forming opportunities at manufacturers increases, it is necessary to consider the high scratch resistance of sheets and containers themselves.

In past reports, methods for imparting lubricity to a polystyrene-based stretched sheet (Patent Documents 1 and 2) are known. However, these methods can reduce the damage caused by the reduction of frictional force when the sheets and containers are in contact with each other, but fundamental measures cannot be taken, and metal rolls, molds, Damage due to contact or damage due to deformation when a load is applied to the packaging container cannot be avoided, and it was insufficient as a method for imparting scratch resistance.

JP-A-50-74649 JP-A-53-115781

  The present invention has been made in view of these present circumstances, and an object thereof is to provide a styrene-based stretched sheet that is excellent in scratch resistance and deformation resistance in addition to moldability, rigidity, and transparency, and a manufacturing method. Furthermore, it aims at providing the packaging container using this styrene-type stretched sheet, and its manufacturing method. An object of the present invention is to provide a styrene-based stretched sheet that prevents scratches and dents that may occur during sheet production and molding into a container and during transportation thereof, a packaging container obtained therefrom, and a method for producing them.

The present invention provides the following styrene-based stretched sheet and packaging container, and methods for producing them.
(1) 50 to 98% by mass of an aromatic vinyl compound, 2 to 50% by mass of any one or more of vinyl cyanide or a derivative thereof, (meth) acrylic acid or a derivative thereof, an unsaturated dicarboxylic acid anhydride or a derivative thereof A styrene-based stretched sheet having a Rockwell hardness of 70 to 110 on the M scale based on JISZ 2245 comprising an aromatic vinyl-based copolymer containing 1%.
(2) The styrene-based stretched sheet according to (1), wherein the vinyl cyanide is acrylonitrile.
(3) The styrene-based stretched sheet according to (1) or (2), wherein the (meth) acrylic acid is methacrylic acid and the derivative of methyl (meth) acrylate is methyl methacrylate.
(4) The styrene-based stretched sheet according to any one of (1) to (3), wherein the unsaturated dicarboxylic acid is maleic anhydride.
(5) The value (R value) obtained by dividing the difference between the maximum value and the minimum value of the thickness of the styrene-based stretched sheet by the average value of the thickness is less than 20%. The styrene-type stretched sheet as described.
(6) The styrene-based stretched sheet according to any one of (1) to (5), which has a layer containing silicone on at least one surface.
(7) The styrene-based stretched sheet according to (6), wherein the silicone content per unit area of the layer containing silicone is 2 to 50 mg / square meter.
(8) The styrene-based stretched sheet according to any one of (1) to (5), which has a layer containing 150 mg / square meter or less of a fatty acid ester on at least one surface.
(9) The styrene-based stretched sheet according to any one of (1) to (8), wherein the gel fraction in the styrene-based stretched sheet is 0.05 to 1.5% by mass.
(10) The styrene-based stretched sheet according to any one of (1) to (9), wherein a dynamic friction coefficient in an R contact based on ASTM D 1894 is 0.3 to 1.5.
(11) The styrene-based stretched sheet according to any one of (1) to (10), wherein the tensile elastic modulus is 2700 to 3700 MPa.
(12) The styrene-based stretched sheet according to any one of (1) to (11), wherein HAZE is less than 3%.
(13) The method for producing a styrene-based stretched sheet according to any one of (1) to (12) obtained through a biaxial stretching process.
(14) A packaging container formed using the styrene-based stretched sheet according to any one of (1) to (12).
(15) A method for producing a packaging container, comprising a step of thermoforming the styrene-based stretched sheet according to any one of (1) to (12).

  In the present invention, a styrene-based stretched sheet having an M-scale Rockwell hardness of 70 to 110, which is made of an aromatic vinyl-based copolymer containing a specific amount of an aromatic vinyl compound, has moldability, rigidity, and transparency. It has been found that it has excellent scratch resistance. Further, due to the improvement in rigidity, the packaging container using the styrene-based stretched sheet of the present invention has good scratch resistance and deformation resistance.

  The styrene-based stretched sheet of the present invention is particularly excellent in rigidity, and can be suitably used for a thin packaging container having a height or depth, such as a food pack.

  In addition, the styrene-based stretched sheet of the present invention is particularly excellent in scratch resistance, enables long-term transportation to a remote place by a large vehicle, aircraft, or ship, and transparent packaging in a field that requires particularly high quality requirements in appearance. It can be suitably used as a container.

  Hereinafter, embodiments of the present invention will be described in detail.

  The styrene-based stretched sheet of the present invention is a styrene-based stretched sheet composed of a polymer or copolymer of an aromatic vinyl compound. Examples of aromatic vinyl compounds include styrene, alkyl styrene (eg, o-, m-, and p-isomers such as methyl styrene, ethyl styrene, isopropyl styrene, butyl styrene, and tertiary butyl styrene), and alpha alkyl styrene. (Eg, alphamethyl styrene, alpha ethyl styrene, etc.), monohalogenated styrene (eg, o-, m-, and p-isomers such as chlorostyrene, bromostyrene, and fluorostyrene), dihalogenated styrene (eg, Nucleosubstituted isomers such as dichlorostyrene, dibromostyrene, difluorostyrene and chlorobromostyrene), trihalogenated styrene (eg, trichlorostyrene, tribromostyrene, trifluorostyrene, dichlorobromostyrene, dibromochloros) Nuclei substituted isomers such as len and difluorochlorostyrene), tetrahalogenated styrene (e.g., each nucleosubstituted isomer such as tetrachlorostyrene, tetrabromostyrene, tetrafluorostyrene and dichlorodibromostyrene), pentahalogenated styrene ( For example, each nucleus-substituted isomer such as pentachlorostyrene, pentabromostyrene, trichlorodibromostyrene, and trifluorodichlorostyrene), alpha and beta halogen substituted styrenes (eg, alphachlorostyrene, alphabromostyrene, beta-chlorostyrene, and beta-bromo) Styrene, etc.) and the like can be mentioned, but styrene and alphamethylstyrene are preferred, and styrene is more preferred. These aromatic vinyl compounds may be used alone or in combination of two or more.

  In the resin composition constituting the styrene-based stretched sheet of the present invention, the content of the aromatic vinyl compound monomer unit is 98 to 50% by mass, preferably 94 to 60% by mass, based on the total amount of the monomer units. Preferably it is 90-64 mass%. By setting the aromatic vinyl compound monomer unit within the range described above, a styrene stretched sheet having excellent moldability, rigidity, and transparency can be obtained.

  The styrene-based stretched sheet of the present invention comprises a resin composition obtained by copolymerizing one or more of vinyl cyanide or a derivative thereof, (meth) acrylic acid or a derivative thereof, an unsaturated dicarboxylic acid anhydride or a derivative thereof. Composed. By containing these monomer units, the hardness described below and scratch resistance can be improved without impairing moldability, rigidity, and transparency.

  The resin composition constituting the styrene-based stretched sheet of the present invention is composed of one or more monomer units of vinyl cyanide or a derivative thereof, (meth) acrylic acid or a derivative thereof, an unsaturated dicarboxylic acid anhydride or a derivative thereof. Content is 2-50 mass% on the basis of the total amount of monomer units, preferably 6-40 mass%, more preferably 10-36 mass%. By making these monomer units in the range of 2 to 50% by mass, a styrene-based stretched sheet having excellent hardness and resulting scratch resistance can be obtained without impairing excellent moldability, rigidity and transparency. I can do it.

  Examples of the vinyl cyanide described above or derivatives thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, 2-methylenemalononitrile and the like, preferably acrylonitrile, methacrylonitrile, and more preferably acrylonitrile. . These vinyl cyanide compounds may be used alone or in combination of two or more.

  Examples of (meth) acrylic acid or derivatives thereof include acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dicyclopentanyl methacrylate, isobornyl methacrylate, and other methacrylate esters, methyl Acrylic acid esters such as acrylate, ethyl acrylate, butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate can be mentioned, but methacrylic acid, methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate are preferred. More preferred are methacrylic acid and methyl methacrylate, and more preferred is methyl methacrylate. These (meth) acrylic acid compounds may be used alone or in combination of two or more.

  Examples of the unsaturated dicarboxylic anhydrides or derivatives thereof described above include maleic anhydride, itaconic anhydride, citraconic anhydride, aconitic anhydride, N-alkylmaleimide (alkyl groups include, for example, methyl, butyl, cyclohexyl), and N-arylmaleimide (as the aryl group, for example, phenyl, chlorophenyl, methylphenyl, methoxyphenyl, tribromophenyl) and the like can be mentioned, preferably maleic anhydride, N-phenylmaleimide, more preferably maleic anhydride. is there. These unsaturated dicarboxylic acid anhydride compounds may be used alone or in combination of two or more.

The resin composition constituting the styrene-based stretched sheet of the present invention can be copolymerized with other copolymerizable vinyl monomers as necessary. The content of other vinyl monomer units is not particularly limited, but the aromatic vinyl compound, vinyl cyanide or its derivative, (meth) acrylic acid or its derivative, unsaturated dicarboxylic acid or its derivative It is preferable that the monomer unit content is within a range not deviating from the above range.

In the styrene-based stretched sheet of the present invention, it is essential that the Rockwell hardness on the M scale based on JIS Z 2245 is 70 to 110, preferably 75 to 105, more preferably 80 to 100, still more preferably. 85-95. When the Rockwell hardness is 70 or more, the rigidity and scratch resistance can be improved. Further, when the Rockwell hardness is 110 or less, the intended styrene-based stretched sheet can be obtained without impairing moldability and transparency.

  If necessary, a rubber-modified styrenic resin may be added to the resin composition constituting the styrenic stretched sheet of the present invention. By adding the rubber-modified styrenic resin, it is possible to improve the slipperiness of the styrene-based stretched sheet, but the content of the rubber-modified styrenic resin is the resin composition 100 because of concern that the transparency and rigidity of the sheet are impaired. It is preferable that it is 3 mass parts or less with respect to a mass part, More preferably, it is 2 mass% or less, More preferably, it is 1 mass% or less.

  Examples of the raw material monomer of the rubber-modified styrenic resin include styrene and alkyl styrene (for example, o-, m-, and p- such as methyl styrene, ethyl styrene, isopropyl styrene, butyl styrene, and tertiary butyl styrene). Isomers), alphaalkyl styrene (eg, alphamethyl styrene, alpha ethyl styrene, etc.), monohalogenated styrene (eg, chlorostyrene, bromostyrene, and fluorostyrene, o-, m-, and p-isomers) ), Dihalogenated styrene (for example, nucleosubstituted isomers such as dichlorostyrene, dibromostyrene, difluorostyrene and chlorobromostyrene), trihalogenated styrene (for example, trichlorostyrene, tribromostyrene, trifluorostyrene, dichlorobromos) , Each nucleus-substituted isomer such as dibromochlorostyrene and difluorochlorostyrene), tetrahalogenated styrene (for example, each nucleus-substituted isomer such as tetrachlorostyrene, tetrabromostyrene, tetrafluorostyrene and dichlorodibromostyrene), penta Halogenated styrene (for example, each nucleus-substituted isomer such as pentachlorostyrene, pentabromostyrene, trichlorodibromostyrene, and trifluorodichlorostyrene), alpha- and beta-halogen-substituted styrene (for example, alphachlorostyrene, alphabromostyrene, beta-chloro) Styrene, beta-bromostyrene, etc.) can be mentioned, and styrene is preferred. These monomers may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the rubber-like polymer used as a raw material for the rubber-modified styrene resin include one or more conjugated 1,3-dienes (for example, butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro). -1,3 butadiene, piperylene, etc.), butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, butadiene-styrene-acrylonitrile copolymer, isobutylene-acrylate copolymer, butyl rubber and ethylene-propylene terpolymer (EPDM) and the like are mentioned, but butadiene is preferred. These monomers may be used individually by 1 type, and may be used in combination of 2 or more type.

  As the polybutadiene, any of high-cis polybutadiene, low-cis polybutadiene, and styrene-butadiene copolymer may be used, or a mixture may be used.

  The volume median particle size of the rubber-like dispersed particles of the rubber-modified styrene resin used in the present invention is preferably 0.5 to 5 μm, more preferably 1 to 3 μm. When the volume median particle diameter is less than 0.5 μm, the releasability from the mold when the obtained styrene-based stretched sheet is molded is low. Moreover, when exceeding 5 micrometers, the transparency of the styrene-type stretched sheet obtained falls.

Examples of the method for adjusting the particle diameter include a method for adjusting the stirring speed in the phase transition region of the rubber particles in the polymerization step, a method for adjusting the amount of the chain transfer initiator in the raw material liquid, and the like. The volume-median particle size of the rubber-like dispersed particles is determined by dissolving a rubber-modified styrene resin composition in an electrolytic solution (3% tetra-n-butylammonium / 97% dimethylformamide solution) The volume-median particle diameter of the present invention is defined as 50 volume% particle diameter of a volume-based particle size distribution curve obtained by measurement with sizer II (orifice diameter of aperture tube 30 μm).

  The gel fraction of the rubber-like dispersed particles of the rubber-modified styrene resin used in the present invention is preferably 30 to 60% by mass. Examples of the method for adjusting the gel fraction include a method for adjusting the rubber content in the polymerization step, a method for adjusting the initiator amount, and a method for adjusting by blending with a styrene homopolymer after polymerization. For the gel fraction, a rubber-modified styrene resin having a mass of 1.00 g is precisely weighed (W), 35 ml of methyl ethyl ketone is added and dissolved, and the resulting solution is centrifuged (Hoku2000 H-2000B (rotor: H)). The mixture was centrifuged at 10,000 rpm for 30 minutes to settle the insoluble matter, the supernatant was removed by decantation to obtain the insoluble matter, pre-dried in a safety oven at 90 ° C. for 2 hours, and further in a vacuum dryer After drying under reduced pressure at 120 ° C. for 1 hour and cooling in a desiccator for 20 minutes, the mass (G) of the dried insoluble matter can be measured and determined as follows.

  Gel fraction (amount of rubber-like dispersed particles) (mass%) = (G / W) × 100

  The weight average molecular weight of the soluble component of the resin composition constituting the styrene-based stretched sheet of the present invention is a polystyrene equivalent weight average molecular weight measured by the SEC method. The weight average molecular weight is preferably 100,000 to 250,000, and more preferably 12 to 200,000. If the weight average molecular weight exceeds 250,000, the formability of the sheet is lowered, and if it is 100,000 or less, problems such as uneven thickness are likely to occur during film formation. The number average molecular weight is preferably 50,000 to 100,000, and the Z average molecular weight is preferably 200,000 to 450,000.

The SEC measurement is performed under the following conditions.
Apparatus: Shodex “SYSTEM-21” manufactured by Showa Denko KK
Column: PLgel MIXED-B
Temperature: 40 ° C
Solvent: Tetrahydrofuran Flow rate: 1.0 ml / min Detection: RI
Concentration: 0.2% by mass
Injection volume: 100 μl
Calibration curve: Standard polystyrene (manufactured by Polymer Laboratories) is used, and the relationship between elution time and elution amount is converted to molecular weight to obtain various average molecular weights.

  The resin composition constituting the styrene-based stretched sheet of the present invention preferably has a melt mass flow rate (MFR) measured at 200 ° C. and a load of 49 N of 1 to 5 g / 10 minutes, more preferably 2 to 4 g / 10 minutes. It is. When the MFR is in the range of 1 to 5 g / 10 minutes, both the fluidity and film-forming property when the resin is melted are improved in the production process of the styrene-based stretched sheet.

  It is preferable that the glass transition point of the resin composition which comprises the styrene-type stretched sheet of this invention is 95-135 degreeC, More preferably, it is 105-125 degreeC. When the glass transition point is in the range of 95 to 135 ° C., the processability of the sheet into the container and the mold reproducibility are both improved in the molding process of the styrene-based stretched sheet.

  The resin composition constituting the styrene-based stretched sheet of the present invention includes an ultraviolet absorber, a light stabilizer, an antioxidant, a lubricant, a plasticizer, a colorant, an antistatic agent, a flame retardant, a mineral oil and the like depending on the application. Additives, reinforcing fibers such as glass fibers, carbon fibers, and aramid fibers, and fillers such as talc, silica, mica, and calcium carbonate may be further contained as long as the performance of the styrene-based stretched sheet is not impaired.

  As a method for producing a styrene-based stretched sheet of the present invention, for example, a resin composition containing an acrylonitrile-styrene copolymer is melt-kneaded with an extruder and extruded from a die (particularly a T-die), and then stretched in a uniaxial direction. Examples thereof include a production method in which the film is stretched sequentially or simultaneously in the biaxial direction and wound into a roll with a winder.

  The styrene-based stretched sheet of the present invention may be a single layer sheet composed of a single layer of resin, or may be a multilayer sheet composed of a plurality of different resin layers. As a method for producing a multi-layer styrene-based stretched sheet, at least two extruders are prepared, and a set of feed blocks and feed block dies connected to these extruders or a multi-manifold die are joined and laminated to perform co-extrusion. The method of doing is mentioned.

  As the extruder, a single screw extruder, a twin screw extruder, a tandem extruder, or the like can be used.

  As the stretching method, uniaxial stretching only in MD (Machine Direction; sheet flow direction) using a roll, sequential biaxial stretching in which MD stretching is followed by TD (Transverse Direction; direction perpendicular to the sheet flow direction), MD and Examples include simultaneous biaxial stretching in which TD stretching is performed at the same time. From the standpoint of isotropic strength of styrene-based stretched sheets and productivity in production in-line, longitudinal stretching using a roll and transverse using a tenter It is preferable to perform stretching.

Although the thickness of a styrene-type stretched sheet is not specifically limited, Usually, 0.01-1 mm, Preferably it is 0.05-0.5 mm, More preferably, it is 0.1-0.4 mm. If the thickness is less than 0.01 mm, the rigidity when molded into a packaging container is lowered. On the other hand, if it exceeds 1 mm, the moldability deteriorates.

Moreover, it is preferable from the surface of the moldability and the rigidity of a packaging container that the difference of the maximum value of the thickness in the styrene-type stretched sheet of this invention and the minimum value is small. The value (R value) obtained by dividing the difference between the maximum value and the minimum value of the thickness by the average thickness value is preferably 20% or less, more preferably 12% or less, and even more preferably 5% or less. If the R value exceeds 20%, a roll-like wound body obtained by winding a styrene-based stretched sheet may cause a hump-like defect. The difference between the maximum value and the minimum value of the thickness can be used in any of the width direction, the length direction, and the constant area of the styrene-based stretched sheet, but the difference between the maximum value and the minimum value and the R value in the present invention. Refers to the thickness in the width direction of the styrene-based stretched sheet.

  The MD and TD stretch ratios of the styrene-based stretched sheet in the present invention are preferably 1.8 to 3.2 times.

  In the present invention, the stretch ratio is a ratio at which the test piece of the styrene-based stretched sheet changes before and after heating, and specifically, a value calculated by the following formula, that is, stretch ratio = Y / Z, unit [times]. Means. In this formula, Y indicates the length [mm] of a straight line drawn on MD and TD on the surface of the styrene-based stretched sheet before heating, and Z indicates the above test piece in an oven at a temperature of 150 ° C. for 60 minutes. The length [mm] of the straight line after placement and contraction is shown.

  Moreover, it is preferable that the thermal contraction stress of MD and TD of a styrene-type stretched sheet is 0.3-1.5 MPa. In addition, the heat shrinkage stress adopts the peak value of the stress obtained by measuring in 150 ° C. silicone oil according to ASTM D-1504.

The tensile elastic modulus of the styrene-based stretched sheet is preferably 2700 to 3700 MPa, more preferably 3000 to 3500 MPa, and still more preferably 3100 to 3400 MPa. If the tensile elastic modulus is less than 2700 MPa, the rigidity of the sheet decreases. On the other hand, if it exceeds 3700 MPa, the moldability is lowered. The tensile modulus is a value measured in accordance with JISK-6251, cut into a No. 2 type test piece shape, and a tensile speed of 500 mm / min.

The dynamic friction coefficient of the styrene-based stretched sheet is preferably 0.3 to 1.5, more preferably 0.5 to 1.3, and still more preferably 0.6 to 1.0. If the coefficient of dynamic friction is less than 0.3, the slipperiness of the sheet is too high, which tends to cause problems such as winding deviation at the time of winding. On the other hand, if it exceeds 1.5, the slipperiness of the styrene-based stretched sheet is lowered, and the molded body obtained by molding this sheet may have poor stack resistance. There are concerns about blocking and scratching. The dynamic friction coefficient is a value measured with an R contact based on ASTM D 1894.

A smaller amount of unreacted monomers, dimers, trimers and other oligomers in the styrene-based stretched sheet is preferred. The total value of the monomer content and the oligomer content in the styrene-based stretched sheet is essential to be less than 1.0%, and more preferably less than 0.5%.
The total content of the monomer and oligomer can be measured by gas chromatography and can be measured by the following method.
Device name: GC-12A (Shimadzu Corporation)
Column: Glass column φ3 [mm] x 3 [m]
Quantitative method: Internal standard method (cyclopentanol)

The total light transmittance of the styrene-based stretched sheet is preferably 80% or more and HAZE is 3% or less. When HAZE exceeds 3%, the transparency of the molded product is lowered. The total light transmittance and HAZE are measured under the following conditions according to JISK-7361-1.
Sample: One sheet of styrene-based stretched sheet Device: Haze meter NDH5000 (Nippon Denshoku)

The L * value of the styrene-based stretched sheet is preferably 75 or more, the a * value is −4 to +4, and the b * value is 0 to +8. The L * value, a * value, and b * value are the color coordinates of the L * a * b * color space defined by the CIE. These values are measured under the following conditions after the target resin is molded into a 2 mm plate with an injection molding machine.
Sample: A styrene-based stretched sheet laminated and adjusted to a thickness of 4.5 mm Apparatus: Spectral colorimeter CM-2500d (Konica Minolta)
Measurement method: SCI method (including regular reflection light)

The gel content of the styrene-based stretched sheet of the present invention is preferably 0.05 to 1.5% by mass. When the gel content exceeds 1.5% by mass, small spherical defects, which are called “fish eyes” at the time of forming a sheet and are not completely mixed in the resin, are likely to occur. On the other hand, if the gel content is less than 0.05% by mass, surface unevenness due to rubber-modified polystyrene is less likely to occur, and mold releasability and stacking resistance are reduced.
As for the gel content, 1.00 g of a sheet was precisely weighed (W), 35 ml of methyl ethyl ketone was added and dissolved, and the solution was centrifuged at 10,000 rpm for 30 minutes with a centrifuge (Hoku2000 B (rotor: H) manufactured by Kokusan). Centrifugation to settle the insoluble matter, decantation removes the supernatant liquid to obtain the insoluble matter, preliminary drying in a safety oven at 90 ° C for 2 hours, and further vacuum drying at 120 ° C for 1 hour in a vacuum dryer Then, after cooling in a desiccator for 20 minutes, the mass G of the dried insoluble matter can be measured and determined as follows.

Gel content (mass%) = (G / W) × 100

The rubber content (R) of the styrene-based stretched sheet of the present invention is preferably 0.03 to 1.2% by mass. For rubber, dissolve the sheet in chloroform, add a certain amount of iodine monochloride / carbon tetrachloride solution, leave it in the dark for about 1 hour, add potassium iodide solution, and add excess iodine monochloride to 0.1N thiol. Titration with a sodium sulfate / ethanol aqueous solution can be performed from the amount of iodine monochloride added.

The methanol-soluble component of the styrene-based stretched sheet of the present invention is preferably 1% by mass or less. The methanol-soluble component herein refers to a component that is soluble in methanol of a styrene-based stretched sheet. For example, a styrene oligomer (styrene dimer, styrene trimer) that is by-produced in a polymerization step or a devolatilization step of a rubber-modified styrene resin. In addition, various additives such as liquid paraffin and silicone oil, residual styrene monomer, and low molecular weight components such as a polymerization solvent are included. In addition, methanol-soluble matter precisely measures 1.00 g of styrene-type extending | stretching sheets (P), and 40 ml of methyl ethyl ketone is added and melt | dissolved, 400 ml of methanol is added rapidly, methanol insoluble matter (resin component) is deposited, Precipitate. After leaving still for about 10 minutes, it was gradually filtered through a glass filter to separate methanol-soluble components, dried under reduced pressure at 120 ° C. for 2 hours in a vacuum dryer, allowed to cool in a desiccator for 25 minutes, and dried. The mass (N) of the methanol insoluble matter can be measured and determined as follows.

  Methanol-soluble content (mass%) = (P−N) / P × 100

  A layer composed of a release agent and a surfactant can be formed on the surface of the styrene-based stretched sheet of the present invention by using a general-purpose coating method such as a gravure coater.

  Examples of the mold release agent include silicone oil, paraffin wax, and microcrystalline wax. In particular, polydimethylsiloxane is preferably used because it improves lubricity and is excellent in food safety. .

The silicone oil used as the release agent is preferably dispersed in water, and more preferably in the form of an emulsion of silicone oil and water. Examples of the silicone oil include organic polysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane, and dimethylpolysiloxane is particularly preferable in terms of food safety and economy. The viscosity of the silicone oil used in the present invention is preferably 100 to 100000 cst, more preferably 5000 to 30000 cst, based on the slipperiness of the sheet and the releasability from the mold during molding.

The weight per unit area of the release agent is preferably ² to 50 mg / m ² , more preferably 5 to 20 mg / m ² . If it is less than 2 mg / m ² , it is difficult to impart sufficient lubricity to the styrene-based stretched sheet, and the molded body obtained by molding this sheet may have poor stack resistance. On the other hand, if it exceeds 50 mg / m ² , the slipperiness of the sheet is so high that it tends to cause problems such as winding deviation at the time of winding.

Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. Particularly, food safety and economy, other additives and coating agents. From the viewpoint of stability, a nonionic surfactant is preferable, and fatty acid esters such as glycerin fatty acid ester, sucrose fatty acid ester, and sorbitan fatty acid ester are more preferable.

The HLB of the nonionic surfactant is not particularly limited, but considering the case where it is used after being dispersed in water, it is preferable that the HLB is high from the viewpoint of coating properties and appearance after coating. In consideration of the case where the silicone oil is used in combination, the HLB is more preferably based on the silicone oil concentration in the emulsion.

Examples of the fatty acid group constituting the fatty acid ester include caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and montanic acid, saturated fatty acids having about 6 to 30 carbon atoms, lindenic acid, Examples include unsaturated fatty acids having about 10 to 24 carbon atoms such as palmitooleic acid, oleic acid, elaidic acid, isooleic acid, erucic acid, linoleic acid, and linolenic acid. From the viewpoint of economy and stability, the number of carbon atoms is 8 ~ 22 saturated fatty acids are preferred.

Examples of the alcohol group constituting the fatty acid ester include ethylene glycol and its polymer, propylene glycol and its polymer, glycerin and its dimer and trimer polymer, sucrose, sorbitan, pentaerythritol and the like. Can do.

The coating amount of the surfactant is not particularly limited, but considering the case of winding in a roll shape, if it exceeds 150 mg / m ² , it tends to be transferred to the other surface, causing a decrease in transparency. Therefore, it is not so preferable.

As a method for forming the release agent and surfactant, an aqueous solution or dispersion adjusted to a predetermined solid content concentration using water as a solvent, and an emulsion were applied by a method such as a spray coater, an air knife coater, or a gravure roll coater. Thereafter, a method of drying the moisture using a hot air dryer, an infrared dryer, or the like to form a coating layer can be used.

The release agents and surfactants listed above may be used alone or in combination of two or more. If necessary, other antistatic agents, antifogging agents, viscosity modifiers, antifoaming agents, wettability improvers, hydrophilic agents, water repellents, coloring inhibitors, antioxidants, antibacterial agents, pigments, An ultraviolet absorber, dye, etc. may be added.

The charge decay of the styrene-based stretched sheet is preferably 1 second or less, more preferably 5 or less, and even more preferably 30 seconds or less. When the electrostatic attenuation exceeds 30 seconds, static electricity is generated due to friction between the sheets, dust and dust, and chips when trimming the sheet adhere to the sheet surface, and the appearance and quality of the sheet are deteriorated.

  The styrene-based stretched sheet according to this embodiment can be used for molded products such as packaging containers by molding. As the molded product, a food packaging container (that is, a packaging container containing food as a content) or a lid for the food packaging container is suitable, and particularly suitable when the food is a food containing fats and oils. Moreover, the food packaging container and the lid of the food packaging container can be used for heating a microwave oven or for refrigeration. When the styrene-based stretched sheet is used as a lid for food packaging containers, the raw materials used in the styrene-based stretched sheet are publicly registered on the Food Additives Official Statement and the Polyolefin Hygiene Council Positive List. It is preferable to use materials that are recognized for hygiene and stability.

  As a method for obtaining a molded product from a styrene-based stretched sheet, it can be molded into a molded product such as a container or tray by a thermoforming method. There is no limitation on the thermoforming method, and conventionally known methods such as a vacuum forming method, a pressure forming method, and a differential pressure forming method combining a vacuum forming method and a pressure forming method are exemplified. Among them, for example, the sheet is heated close to or in close contact with the hot plate by the compressed air pressure from the mold and the vacuum pressure from the hot plate side, and immediately after that, the compressed air pressure from the hot plate side and the mold side is used. A molded product with good mold reproducibility can be obtained by a hot plate heating type air pressure molding method in which a heated and softened sheet is pressed against a mold by the vacuum pressure. The hot plate forming machine to be used is preferably of a type that can set the time during which the sheet is pressed against the hot plate, the time for forming by compressed air, the time lag for switching from sheet pressing to pressure forming, the forming cycle, and the like.

Table 1 shows the aromatic vinyl copolymers used in the present invention.
Abbreviations are as follows.
AS: Styrene-acrylonitrile copolymer (Experimental example 1)
MS: Styrene-methyl methacrylate copolymer (Experimental example 2)
SMM: Styrene-maleic anhydride-methyl methacrylate copolymer (Experimental Example 3)
GPPS: General-purpose polystyrene (Toyostyrene HRM61 manufactured by Toyo Styrene Co., Ltd.)
SBS: Styrene-butadiene-styrene block copolymer (Clearen 850L, manufactured by Denka)
HIPS: Rubber-modified polystyrene (Toyostyrene H850N manufactured by Toyo Styrene Co., Ltd.)

  In addition, the aromatic vinyl-type copolymer (Experimental Examples 1-3) used by this invention was produced with the following method.

{Experimental example 1: Production of styrene-acrylonitrile copolymer (AS)}
A devolatilizing tank in which a first reactor which is a fully mixed stirring tank having a capacity of about 20 L and a second reactor which is a tower-type plug flow reactor with a stirring capacity of about 40 L are connected in series, and a preheater is further attached. Two units were connected in series. As shown in Table 1, 15 parts by mass of ethylbenzene, 0.01 parts by mass of t-butylperoxyisopropyl monocarbonate, 85 parts by mass of t-butyl peroxyisopropyl monocarbonate with respect to 85 parts by mass of a monomer solution containing 24% by mass of acrylonitrile and 76% by mass of styrene A raw material solution was prepared by mixing 0.25 parts by mass of dodecyl mercaptan. This raw material solution was introduced into a first reactor controlled at 125 ° C. at 6.0 kg per hour. The reaction solution was continuously withdrawn from the first reactor, and this reaction solution was introduced into a second reactor adjusted to have a gradient from 125 ° C. to 160 ° C. in the flow direction. Next, after heating to 160 ° C. with a preheater, it was introduced into the first devolatilization tank reduced to 67 kPa, and further heated to 230 ° C. with a preheater and then introduced into the second devolatilization tank reduced to 1.3 kPa. Residual monomer and solvent were removed. This was extruded and cut into strands to obtain pellet-shaped acrylonitrile-styrene copolymer (AS). As a result of analysis using pyrolysis gas chromatography, the mass composition ratio of styrene / acrylonitrile was 76/24.

{Experimental Example 2: Production of styrene-methyl methacrylate copolymer (MS)}
A devolatilizing tank in which a first reactor which is a fully mixed stirring tank having a capacity of about 20 L and a second reactor which is a tower-type plug flow reactor with a stirring capacity of about 40 L are connected in series, and a preheater is further attached. Two units were connected in series. As shown in Table 1, 15 parts by mass of ethylbenzene, 0.01 parts by mass of t-butylperoxyisopropyl monocarbonate with respect to 85 parts by mass of a monomer solution containing 48% by mass of methyl methacrylate and 52% by mass of styrene, 0.25 parts by mass of t-dodecyl mercaptan was mixed to obtain a raw material solution. This raw material solution was introduced into a first reactor controlled at 125 ° C. at 6.0 kg per hour. The reaction solution was continuously withdrawn from the first reactor, and this reaction solution was introduced into a second reactor adjusted to have a gradient from 125 ° C. to 160 ° C. in the flow direction. Next, after heating to 160 ° C. with a preheater, it was introduced into the first devolatilization tank reduced to 67 kPa, and further heated to 230 ° C. with a preheater and then introduced into the second devolatilization tank reduced to 1.3 kPa. Residual monomer and solvent were removed. This was extruded and cut into strands to obtain pellet-shaped styrene-methyl methacrylate copolymer (MS). As a result of analysis using pyrolysis gas chromatography, the mass composition ratio of styrene / methyl methacrylate was 52/48.

{Experimental Example 3 Production of Styrene-Maleic Anhydride-Methyl Methacrylate Copolymer (SMM)}
A devolatilizing tank in which a first reactor which is a fully mixed stirring tank having a capacity of about 20 L and a second reactor which is a tower-type plug flow reactor with a stirring capacity of about 40 L are connected in series, and a preheater is further attached. Two units were connected in series. As shown in Table 1, 15 parts by mass of ethylbenzene and t-butylperoxyisopropyl mono are obtained for 85 parts by mass of a monomer solution containing 18% by mass of maleic anhydride, 18% by mass of methyl methacrylate, and 64% by mass of styrene. Carbonate 0.01 part by mass and t-dodecyl mercaptan 0.25 part by mass were mixed to obtain a raw material solution. This raw material solution was introduced into a first reactor controlled at 125 ° C. at 6.0 kg per hour. The reaction solution was continuously withdrawn from the first reactor, and this reaction solution was introduced into a second reactor adjusted to have a gradient from 125 ° C. to 160 ° C. in the flow direction. Next, after heating to 160 ° C. with a preheater, it was introduced into the first devolatilization tank reduced to 67 kPa, and further heated to 230 ° C. with a preheater and then introduced into the second devolatilization tank reduced to 1.3 kPa. Residual monomer and solvent were removed. This was extruded and cut into strands to obtain pellet-shaped styrene-maleic anhydride-methyl methacrylate copolymer (SMM). As a result of analysis using pyrolysis gas chromatography, the mass composition ratio of styrene / maleic anhydride / methyl methacrylate was 64/18/18.

Table 2 shows the release agent and surfactant used in the present invention.
Abbreviations are as follows.
Silicone: Polydimethylsiloxane SM7025EX (Toray Dow Corning)
DL100: Diglycerin laurate DL100 (RIKEN VITAMINS)
J0021: Decaglycerin laurate J0021 (RIKEN VITAMINS)
C-250: sorbitan caprylate C-250 (RIKEN VITAMINS)
L-250A: Sorbitan laurate L-250A (RIKEN VITAMINS)
B-150: Sorbitan tribenate B-150 (RIKEN VITAMINS)

<Example 1>
Using the tenter type biaxially stretched sheet extruder (T-die width 450 mm, φ65 mm extruder), the aromatic vinyl copolymer AS is extruded at a extrusion temperature of 230 ° C. and a rotation speed of 80 rpm, and a sheet having a thickness of 1.5 mm is extruded. Preheated to 140 ° C, stretched to MD 2.5 times and TD 2.5 times at a strain rate of 0.1 / sec, average thickness 0.250 mm, maximum 0.260 mm, minimum 0.240 mm, R value An 8.0% biaxial styrene stretched sheet was obtained.
Further, polydimethylsiloxane SM7025EX (manufactured by Toray Dow Corning Co., Ltd.) was applied to each side of the sheet using a bar coater, dried with a dryer at 105 ° C., and after drying, styrene having a coating layer with an application amount of 20 mg / m 2. A system stretched sheet was obtained. The results are shown in Table 3.

<Examples 2-3 and Comparative Examples 1-3>
A styrene-based stretched sheet in which the type of the resin composition of Example 1 was changed was obtained. The results are shown in Table 3.

<Examples 4 to 7>
A styrene-based stretched sheet in which the amount of polydimethylsiloxane applied in Example 1 was changed was obtained. The results are shown in Table 4.

<Examples 8 to 12>
A styrene-based stretched sheet in which the thickness accuracy of the styrene-based stretched sheet of Example 1 was changed was obtained. The results are shown in Table 5.

<Examples 13 to 16>
A styrene-based stretched sheet in which the resin composition of Example 1 was made into two different blends was obtained. The results are shown in Table 6.

<Examples 17 to 22>
A styrene-based stretched sheet was obtained by applying and drying a fatty acid ester on each side of the sheet of Example 1 using a bar coater. The results are shown in Table 7.

Lunch boxes (dimensions 241 mm long × 193 mm wide × 28 mm high) were molded from the sheets obtained in Examples and Comparative Examples using a hot plate molding machine HPT-400A (Wakisaka Engineering Co., Ltd.).
The following methods were evaluated for the sheet and the molded container.

[Rockwell hardness]
Twenty styrene-based stretched sheets were laminated, and a laminated sheet having a total thickness of 4.5 mm was measured for Rockwell hardness according to the M scale based on JIS Z-2245.

[Pencil hardness]
The pencil core hardness (6B to HB to 6H) of the styrene-based stretched sheet was measured by a pencil hardness test based on JIS K-5600-5-4.

[HAZE]
The styrene-based stretched sheet was measured for HAZE according to JIS K-7361-1.

[Tensile modulus]
The styrene-based stretched sheet is compliant with JISK-6251, the styrene-based stretched sheet is cut into the shape of No. 2 type test piece, and using the tensile mode of Autograph AGS-X (manufactured by Shimadzu Corporation), 23 ° C., tensile speed 500 mm / Measured in min.

[Dynamic friction coefficient]
The dynamic friction coefficient of the styrene-based stretched sheet was measured with an R contact based on ASTM D-1894.

[Charging decay]
The time until the voltage was attenuated from the initial stage to the initial half was measured for the styrene-based stretched sheet by a method based on JIS C-61340-28147.

[Windability]
About a roll-shaped winding body when a styrene-based stretched sheet is wound up to a winding core of 25 mm in diameter with a small film winder at a winding speed of 1 m / min, a width of 50 mm, and a winding tension of 10 N, The presence or absence of winding deviation and scratches was observed.

[HAZE after roll storage]
The wound body of the styrene-based stretched sheet is packed with a polyethylene film, placed in a horizontally long state in a constant temperature bath, and then placed in a 60 ° C., 80% RH environment for 24 hours, a 23 ° C., 30% RH environment. It was left to stand for 24 hours. The floor surface of the wound body was peeled off and cut into a predetermined size, and then HAZE was measured by a method according to JISK-7361-1.

[Container characteristics: Formability]
The obtained styrene-based stretched sheet was subjected to a hot plate molding machine HPT-400A (Wakisaka Engineering Co., Ltd.) with a hot plate temperature of 137 ° C., a mold temperature of 95 ° C., a preheating time of 2.0 seconds, and a molding time of 3.0 seconds. Thus, a food pack (lid size 121 mm × width 193 mm × height 10 mm / body size 121 mm × width 193 mm × depth 28 mm connected at the hinge portion) was formed.
Good appearance of the obtained food pack is indicated by ◯.

[Container characteristics: Mold releasability]
After forming a packaging container, there is almost no resistance when peeling from the mold, and scratches, cracks and whitening do not occur ◎, there is some resistance when peeling, but there are no scratches, cracks and whitening ○, the case where scratches occurred was Δ, and the case where cracks or whitening occurred was indicated as ×.

[Container characteristics: Stacking resistance]
A stack of 100 packaging containers was placed on top of each other, a load of 1 kgf was applied for 60 minutes, and then the number of sheets peeled when turning in order from the top was measured. When all 100 sheets are peeled off, 1 is shown when all the sheets are peeled one by one, and when there are two or more pieces peeled off, the maximum number is shown.

[Container characteristics: Compressive strength]
A 121 mm long x 193 mm wide aluminum plate is placed on the top and bottom of the main body of the packaging container (length 121 mm x width 193 mm x depth 28 mm), and the speed is set in the compression mode of Autograph AGS-X (manufactured by Shimadzu Corporation). The maximum load when compressed at 5 mm / min was measured.

[Container characteristics: scratch resistance]
After stacking 50 molded containers and packing them in a polyethylene bag, the container packed in a cardboard box is shaken for 1 hour, then the container is opened and the top surface of the lid is cut off, and in accordance with JISK-7361-1. HAZE was measured by the above method, and 3% or less was accepted.

Claims (15)

Aroma containing 50 to 98% by mass of an aromatic vinyl compound, 2 to 50% by mass of any one or more of vinyl cyanide or a derivative thereof, (meth) acrylic acid or a derivative thereof, an unsaturated dicarboxylic acid anhydride or a derivative thereof A styrene-based stretched sheet having an M-scale Rockwell hardness of 70 to 110 based on JISZ 2245, which is made of an aromatic vinyl copolymer. The styrenic stretched sheet according to claim 1, wherein the vinyl cyanide is acrylonitrile. The styrene-based stretched sheet according to claim 1 or 2, wherein (meth) acrylic acid is methacrylic acid, and a derivative of (meth) acrylic acid is methyl methacrylate. The styrenic stretched sheet according to any one of claims 1 to 3, wherein the unsaturated dicarboxylic acid anhydride is maleic anhydride. The value (R value) obtained by dividing the difference between the maximum value and the minimum value of the thickness of the styrene-based stretched sheet by the average value of the thickness is 20% or less. Sheet.   The styrenic stretched sheet according to any one of claims 1 to 5, which has a layer containing silicone on at least one surface. The styrene-based stretched sheet according to claim 6, wherein the silicone content per unit area of the layer containing silicone is 2 to 50 mg / square meter. The styrenic stretched sheet according to any one of claims 1 to 5, which has a layer containing 150 mg / m2 or less of a fatty acid ester on at least one surface.   The styrene-based stretched sheet according to any one of claims 1 to 8, wherein a gel fraction in the styrene-based stretched sheet is 0.05 to 1.5% by mass. The styrene-based stretched sheet according to any one of claims 1 to 9, wherein a dynamic friction coefficient in an R contact based on ASTM D 1894 is 0.3 to 1.5. The styrene-based stretched sheet according to any one of claims 1 to 10, wherein the tensile elastic modulus is 2700 to 3700 MPa. HAZE is 3% or less, The styrene-type stretched sheet of any one of Claims 1-11. The method for producing a styrene-based stretched sheet according to any one of claims 1 to 12, which is obtained through a biaxial stretching step. The packaging container produced using the styrene-type extending | stretching sheet of any one of Claims 1-12. The manufacturing method of the packaging container which thermoforms the styrene-type stretched sheet of any one of Claims 1-12.