KR20170052528A - Biaxially stretched sheet and container for packaging - Google Patents

Abstract

The present invention relates to a biaxially oriented sheet obtained by biaxially stretching an acrylonitrile-styrene copolymer, wherein the content of acrylonitrile units in the copolymer is 10 to 40% by mass, the weight average molecular weight of the copolymer is 100,000 To 250,000, a polydispersity of 2.0 to 2.5, a surface multiplication factor of biaxial orientation of biaxially oriented sheet is 4 to 10 times, a maximum orientation relaxation stress in MD direction and TD direction is 0.2 to 0.6 MPa, (Ab |) of the difference between the maximum orientation relaxation stress (a) and the maximum orientation relaxation stress (b) in the TD direction is 0.3 MPa or less and the sulfur content in the biaxially oriented sheet is 0 ppm or more and less than 100 ppm, Is 200 to 2000 ppm.

Description

[0001] Description [0002] BIAXIALLY STRETCHED SHEET AND CONTAINER FOR PACKAGING [0003]

The present invention relates to a biaxially oriented sheet and a packaging container.

The biaxially oriented polystyrene resin sheet has excellent transparency and high rigidity, and is thermoformed and widely used in the field of food packaging containers. However, the resin of polystyrene has a lower oil resistance than the olefin resin, and the oil resistance is lowered by biaxial stretching. For example, when oil is attached to the polystyrene resin biaxially oriented sheet and the state is maintained for a long time, the sheet surface is whitened. Particularly, in the case of a food container having a joining portion connecting the lid portion and the main body portion, which is referred to as a hinge, stress is applied to the joining portion, so that the joining portion tends to be cracked due to oil adhesion.

In addition, in the case of the lunch box lid container, since the whitening and perforation are caused by heating in the microwave oven while the source used in the filling material is attached, the OPP film is inserted between the food material and the lid so that the source material does not come into contact with the lid .

However, the problem of polystyrene-based stretched sheet has been raised by an increase in labor cost and an increase in waste after use by manually setting the film.

For this reason, the use of a sheet made of polypropylene or polyethylene terephthalate, which is a highly oil resistant resin, has been studied. However, as compared with the polystyrene-based sheet, the polypropylene sheet has poor transparency and poor visibility of the contents. In addition, since it is low rigidity, there is a problem in that the shelf can not be stacked at the store, and the cover is deformed after the heating of the range and the cover is peeled off. Further, since the polyethylene terephthalate sheet has a low heat resistance and a low rigidity of the resin, there is a problem that significant deformation is seen when it is used at 60 DEG C or more. In these respects, the polystyrene-based sheet can be a sheet suitable for food packaging containers having transparency, rigidity and heat resistance, but in particular, improvement in oil resistance has been required.

Therefore, studies on imparting oil resistance to a biaxially oriented polystyrene resin sheet by resin modification have been conducted. For example, Patent Document 1 discloses a styrene-based biaxial oriented sheet composed mainly of a copolymer of styrenic copolymer with styrene containing 4 to 20% by weight of any one of acrylic acid, methacrylic acid and maleic anhydride. Shows a practical heat resistance of 100 deg. C or higher and a whitening phenomenon does not occur even if the oil contacts the food oil at that temperature.

In Patent Documents 2, 3 and 4, a multilayer co-extrusion using a resin having a low Vicat softening point is performed on the surface layer, and a biaxial stretching is carried out at a drawing temperature suitable for the center layer. A method of improving the oil resistance is shown.

In Patent Documents 5 and 6, a film containing an oil-resistant resin such as polypropylene, acrylic resin, or amorphous polyethylene terephthalate resin is laminated on the food contact surface of the polystyrene biaxially oriented sheet, so that the oil does not come into direct contact with the polystyrene sheet A method of improving oil resistance is shown.

Patent Document 7 also shows improvement in oil resistance by an acrylonitrile homopolymer which is a resin having higher oil resistance than polystyrene and a sheet obtained from a copolymer containing 90% by mass or more of an acrylonitrile component.

Japanese Patent Application Laid-Open No. 62-25031 Japanese Patent Application Laid-Open No. 2005-35208 Japanese Patent Application Laid-Open No. 2005-349591 Japanese Patent Application Laid-Open No. 2007-277428 Japanese Patent No. 4217591 Japanese Patent No. 4812072 Japanese Patent Application Laid-Open No. 59-106922

However, in the technique disclosed in Patent Document 1, by copolymerizing acrylic acid, methacrylic acid, and maleic anhydride monomer, a crosslinking reaction by an acid dehydration reaction tends to occur at the time of melt kneading, and a gel is generated to cause defective appearance of the sheet. In addition, each monomer improves heat resistance, but has a drawback that the resin becomes brittle. Therefore, in order to be practically used as a food container, it is necessary to design a high alignment relaxation stress. For this reason, the highly oriented stretched sheet has a large shrinkage against oil and heat, thereby increasing whiteness. Also, the higher the concentration is, the more difficult it becomes to form the container.

In addition, in the techniques disclosed in Patent Documents 2 to 6, the cost of materials and processing costs due to the laminate of the film is increased, and the film is an incompatible polymer, making it impossible to recycle to a transparent article. Further, at the time of thermoforming, a resin having a different softening point is molded at the same temperature, so that defective appearance and molding deformation remain.

In the technique disclosed in Patent Document 7, since it is difficult to thermoform because of its high resin strength as compared with polystyrene resin, or it is dissolved in DMSO solvent to prepare a cast film. Subsequently, DMSO solvent is replaced with water in a water tank to prepare a water gel film, And the like, the productivity is low, and the management of the absorption of residual solvent and resin is difficult, and the physical properties of the sheet are liable to fluctuate.

An object of the present invention is to provide a biaxially oriented styrene-based sheet and a packaging container which are excellent in balance of transparency, rigidity, practical strength, heat resistance, whitening resistance under oil-contacting conditions, chemical resistance and resistance to shrinkage by using an acrylonitrile- And the like.

That is, the present invention is as follows.

(1) A biaxially oriented sheet obtained by biaxially stretching an acrylonitrile-styrene copolymer, wherein the content of acrylonitrile units in the copolymer is 10 to 40% by mass and the weight average molecular weight of the copolymer is 100,000 To 250,000, a polydispersity of 2.0 to 2.5, a surface multiplication factor of biaxial orientation of biaxially oriented sheet is 4 to 10 times, a maximum orientation relaxation stress in MD direction and TD direction is 0.2 to 0.6 MPa, (Ab |) of the difference between the maximum orientation relaxation stress (a) and the maximum orientation relaxation stress (b) in the TD direction is 0.3 MPa or less and the sulfur content in the biaxially oriented sheet is 0 ppm or more and less than 100 ppm, Wherein the content of the biaxially oriented sheet is 200 to 2000 ppm.

(2) The biaxially oriented sheet according to (1), wherein the antifogging agent layer is further formed on at least one surface of the biaxially oriented sheet and the water contact angle at the surface of the antifogging agent layer is 5 to 15 °.

(3) A packaging container comprising a main body part, a lid part, and a hinge part for connecting the main body part and the lid part to each other, the biaxially oriented sheet described in (1) or (2) being molded.

(4) A packaging container comprising a biaxially oriented sheet formed by molding a biaxially oriented sheet according to (2), and having a body portion, a lid portion, and a hinge portion connecting the body portion and the lid portion, .

(5) The packaging container according to (3) or (4), wherein the body portion is a main body portion for containing food and the radius of curvature of the hinge portion is 2 to 10 mm when the lid portion is closed.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a biaxially oriented styrene-based sheet and a packaging container excellent in balance of transparency, rigidity, practical strength, heat resistance, whitening resistance under oil-contacting conditions, chemical resistance and resistance to shrinkage by using an acrylonitrile- Is provided.

1 is a perspective view showing an embodiment of a packaging container.
2 is a side view of the packaging container of Fig. 1;

Hereinafter, embodiments of the present invention will be described.

The acrylonitrile-styrene copolymer of the present embodiment contains an acrylonitrile monomer unit (acrylonitrile unit) and a styrene monomer unit (styrene unit), and is obtained, for example, by mass continuous polymerization. The content of the acrylonitrile-based monomer unit in the acrylonitrile-styrene copolymer is 10 to 40 mass%, preferably 18 to 32 mass%, based on the whole monomer units constituting the copolymer. When the content of the acrylonitrile monomer unit is more than 40% by mass, color, appearance, and film formability are deteriorated. When the content of the acrylonitrile monomer unit is less than 10% by mass, the oil resistance, appearance and strength are lowered.

Examples of the acrylonitrile-based monomer unit include acrylonitrile and methacrylonitrile, and acrylonitrile units are preferred. These acrylonitrile monomer units may be used singly or in combination of two or more.

Examples of the styrene-based monomer unit include units such as styrene,? -Methylstyrene, p-methylstyrene,? -Methylstyrene, m-methylstyrene, ethylstyrene and pt-butylstyrene. These styrene-based monomer units may be used singly or in combination of two or more. The content of the styrene-based monomer units in the acrylonitrile-styrene copolymer may be, for example, 60 to 90% by mass based on the whole monomer units constituting the copolymer.

The acrylonitrile-styrene copolymer may contain a vinyl monomer unit which can be copolymerized if necessary. Examples of the vinyl monomer unit include acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dicyclopentyl methacrylate, iso Methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate and the like . The content of the vinyl-based monomer unit may be less than 10 parts by mass based on 100 parts by mass of the total of the styrene-based monomer unit and the acrylonitrile-based monomer unit.

The acrylonitrile-styrene copolymer may contain known reinforcing rubbers such as butadiene rubber, styrene-butadiene rubber, methyl methacrylate-butadiene-styrene rubber, and ethylene-propylene rubber. The content of the reinforcing rubber is preferably less than 10 parts by mass based on 100 parts by mass of the total of the styrene-based monomer unit and the acrylonitrile-based monomer unit. When the content of the rubber component is 10 parts by mass or more, transparency is lowered, which is not preferable.

The acrylonitrile-styrene copolymer is obtained by polymerizing an acrylonitrile-based monomer and a styrene-based monomer. The polymerization method is not particularly limited, but bulk continuous polymerization is preferable for reducing odor.

As the bulk continuous polymerization method, a well-known example can be employed. A solvent such as ethylbenzene, toluene or methyl ethyl ketone is added in an amount of 10 to 40 parts by mass based on the total 100 parts by mass of the styrene monomer and the acrylonitrile monomer, Is preferable.

Butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1- Butyl peroxy isopropyl monocarbonate, di-t-butyl (tert-butylperoxy) -cyclohexane, 2,2- Peroxides, dicumyl peroxide, and ethyl-3,3-di- (t-butylperoxy) butyrate may be added, and also 4-methyl-2,4-diphenylpentene-1, t -Dodecylmercaptan, n-dodecylmercaptan, and the like may be added.

The polymerization temperature is preferably 80 to 170 占 폚, more preferably 100 to 160 占 폚.

The weight-average molecular weight of the acrylonitrile-styrene copolymer in terms of polystyrene measured by the SEC method is preferably 100,000 to 250,000, and more preferably 150,000 to 200,000. If the weight average molecular weight is less than 100,000, the strength of the resin is lowered and the sheet strength and endurance are lowered. When the weight average molecular weight is 250,000 or more, the sheet formability and the container formability are lowered due to the viscosity increase.

The polydispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 2.0 to 2.5, more preferably 2.1 to 2.5. When the polydispersity is less than 2.0, the polymerization method and equipment changes are required, and the productivity of the resin is lowered. If the polydispersity is 2.5 or more, the processability and oil resistance are lowered due to the decrease in the strength due to the increase in the low molecular weight component or the increase in viscosity due to the increase in the high molecular weight component.

The SEC measurement was carried out under the following conditions.

Device: Shodex "SYSTEM-21" manufactured by Showa Denko Co., Ltd.

Column: PLgel MIXED-B

Temperature: 40 ° C

Solvent: tetrahydrofuran

Flow rate: 1.0 ml / min

Detection: RI

Concentration: 0.2 mass%

Injection volume: 100 μl

Calibration curve: The relationship between the elution time and the elution amount was converted into a molecular weight using standard polystyrene (Polymer Laboratories), and various average molecular weights (weight average molecular weight, number average molecular weight, etc.) were determined.

The acrylonitrile-styrene copolymer may be used alone or in combination with an ultraviolet absorber, a light stabilizer and an antioxidant.

Examples of the ultraviolet absorber include 2- (5'-methyl-2'-hydroxyphenyl) benzotriazole, 2- (5'-t-butyl-2'-hydroxyphenyl) benzotriazole, 2- Benzotriazole, 2- (3 ', 5'-di-t-butyl-2'-hydroxyphenyl) benzotriazole, 2 - (3'-t-butyl-5'-methyl-2'-hydroxyphenyl) -5- chlorobenzotriazole, 2- 2- [3 '- (3 ", 4 ", 5 "-di- , 6 "-tetrahydrophthalimidemethyl) -5'-methyl-2'-hydroxyphenyl] benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethyl Butyl-6- (2H-benzotriazol-2-yl) phenol), 2-ethoxy-2'-ethyloxalic acid bisanilide, 2-ethoxy- Anilide oxalide-based ultraviolet absorber such as 2'-ethyloxalic acid bishianylide and 2-ethoxy-4'-isodecylphenyloxalic acid bianilide, 2- 4-n-octoxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy- Dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-2'- Benzophenone type ultraviolet ray absorbing agents such as phenone, salicylic acid type ultraviolet ray absorbing agents such as phenyl salicylate, pt-butylphenyl salicylate and p-octylphenyl salicylate, 2-ethylhexyl-2-cyano- Cyanoacrylate ultraviolet absorbers such as diphenyl acrylate and ethyl-2-cyano-3,3'-diphenylacrylate, rutile-type titanium oxide, anatase-type titanium oxide, alumina, silica, silane coupling agent And a titanium oxide-based ultraviolet stabilizer such as titanium oxide treated with a surface treatment agent such as a titanium-based coupling agent.

Examples of the light stabilizer include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, Dimethyl 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, poly [[6, (1,1,3,3-tetramethylbutyl ) Amino-1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [ Propyloxy] ethyl] -4- (4-methyl-4-piperidyl) imino] [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine.

Examples of the antioxidant include triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,4-bis (n-octylthio) -6- Hydroxy-3,5-di-t-butyl anilino) -1,3,5-triazine, pentaerythrityl tetrakis [3- (3,5- Propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2-thiobis (4- And 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene; antioxidants such as ditridecyl- Thiodipropionate, dilauryl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, Diethoxy-3,3'-thiodipropionate; antioxidants such as trisnonylphenyl phosphite, 4,4'-butylidene-bis (3-methyl- Tridecyl) phosphite, (tridecyl) (Di-t-butylphenyl) pentaerythritol diphosphite, bis (di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, diethyl terephthalate diphosphite, bis (octadecyl) pentaerythritol diphosphite, (2,4-di-t-butylphenyl) 1,4-phenylene-di-phosphonite, tetrakis (2,4- , 4'-biphenylene-di-phosphonite, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene and the like.

The acrylonitrile-styrene copolymer may contain additives such as a lubricant, a plasticizer, a colorant, an antistatic agent, a flame retardant, a mineral oil and the like, reinforcing fibers such as glass fiber, carbon fiber and aramid fiber, talc, silica, The filler may be blended to the extent that the object of the present invention is not impaired.

The biaxially oriented sheet of the present embodiment is formed by biaxially stretching an acrylonitrile-styrene copolymer. Examples of the production method of the biaxially oriented sheet include a production method in which an acrylonitrile-styrene copolymer is melted and kneaded by an extruder and extruded from a die (in particular, a T-die) and subsequently stretched sequentially or simultaneously in biaxial directions to be. The thickness of the biaxially oriented sheet is not particularly limited, but is usually 0.05 mm or more and less than 0.6 mm, preferably 0.1 mm or more and less than 0.5 mm.

When the stretching magnification in MD (Machine Direction) and the stretching magnification in TD (Transverse Direction; direction perpendicular to the sheet flow direction) of the biaxially oriented sheet are denoted by B and B, respectively, 10 times. Also, in such a surface magnification, the MD stretching magnification and the TD stretching magnification are all preferably 1.5 to 3.5 times. When any one of A, B, and A × B is out of the above range, thickness irregularity occurs in the sheet, and the buckling strength of the container obtained by hot plate forming the sheet is undesirable. More preferably, the plane magnification is 4 to 8 times, the MD drawing magnification and the TD drawing magnification are 2.0 to 3.0 times, respectively.

The drawing magnification in the present invention is a rate at which a test piece of a biaxially oriented sheet is changed before and after heating, specifically, a value calculated by the following equation, i.e., a draw ratio = Y / Z (unit [times]) do. In this formula, Y represents the length [mm] of the straight line drawn by MD and TD with respect to the test piece of the biaxially oriented sheet before heating, and Z represents the Vicat softening point temperature of the sheet measured according to JIS K7206 And the length [mm] of the straight line after the test piece is allowed to stand for 60 minutes and shrunk in a high temperature oven.

In the biaxially oriented sheet, a and b are respectively 0.2 to 0.6 MPa when the maximum orientation relaxation stress in the MD direction is a and the maximum orientation relaxation stress in the TD direction is b, and the maximum orientation relaxation stress in the MD direction Ab | of the difference between the maximum orientation relaxation stress in the TD direction is 0.3 MPa or less, preferably a and b are 0.3 MPa to 0.5 MPa and | ab | is 0.15 MPa or less. When a and b are less than 0.2 MPa, the sheet strength is lowered and the yield strength is lowered. If it is more than 0.6 MPa, the shrinkage force is increased, so that whitening at the time of oil adhesion tends to occur and the formability is deteriorated. If | a-b | exceeds 0.3 MPa, the shrinking force in the MD and TD directions is different, which is not preferable because the moldability tends to be poor and deformation of the molded article tends to occur.

The biaxially oriented sheet may contain a sulfur compound derived from a chain transfer agent or an antioxidant. The content (sulfur content) of the sulfur component is 0 ppm or more and less than 100 ppm, preferably 10 to 95 ppm, more preferably 30 to 70 ppm to be. When the sulfur content is 100 ppm or more, odor originating from sulfur compounds is generated at the time of thermoforming, thereby lowering the working environment. The sulfur content can be measured by ICP-MS (inductively coupled plasma mass spectrometry).

The content of the volatile substance in the biaxially oriented sheet is preferably 200 to 2000 ppm. Volatile substances are volatile substances specified in the Food Sanitation Act. Specific examples of the volatile substance include styrene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene and acrylonitrile, and the content of volatile substances is the total amount of these volatile components. The content of the volatile substance is adjusted by changing the temperature or the adjustment time of the devolatilization process at the time of polymerization. When the content of the volatile substance is less than 200 ppm, it is not preferable because it is necessary to set the temperature to a high temperature at which decomposition or discoloration of the resin occurs, and it is not preferable to extend the adjustment time. If the content of volatile substances exceeds 2000 ppm, odor is generated during thermoforming as in the case of sulfur, thereby lowering the working environment. The content of volatile substances can be measured by gas chromatography.

The biaxially oriented sheet of acrylonitrile-styrene copolymer may contain, as necessary, additives such as antioxidants, lubricants, release agents, plasticizers, pigments, antioxidants, antioxidants, Dyes, foaming agents, foam nucleating agents, inorganic fillers, antistatic agents, and the like.

The anti-fogging agent is coated on the surface of the sheet in contact with the food, that is, the anti-fogging agent layer is formed on at least one surface of the biaxially oriented sheet.

Examples of the anti-fogging agent include nonionic surfactants such as sorbitan fatty acid ester surfactants such as sucrose fatty acid ester, sorbitan monostearate, sorbitan monopalmitate, sorbitan monobehenate, and sorbitan mono montanate, glycerin monoester Glycerin fatty acid ester surfactants such as glycerin monopalmitate, glycerin monostearate, diglycerin distearate, triglycerin monostearate and tetraglycerin monomontanate, polyethylene glycol monopalmitate, polyethylene glycol monostearate such as polyethylene glycol monostearate , Alkylene oxide adducts of alkylphenols, esters of sorbitan / glycerol condensates with organic acids; Polyoxyethylene alkylamine compounds such as polyoxyethylene (2 mol) stearylamine, polyoxyethylene (2 mol) laurylamine and polyoxyethylene (4 mol) stearylamine, polyoxyethylene (2 mol) (4 mol) stearylamine distearate, polyoxyethylene (4 mol) stearylamine monostearate, polyoxyethylene (4 mol) stearylamine distearate, polyoxyethylene Fatty acid esters of polyoxyethylene alkylamine compounds such as polyoxyethylene (8 mol) stearylamine monostearate, polyoxyethylene (2 mol) stearylamine monobehenate and polyoxyethylene (2 mol) laurylamine stearate, poly And amine surfactants such as fatty acid amides of polyoxyethylene alkylamine compounds such as oxyethylene (2 mol) stearic acid amide. Examples of the antifogging agent include polyvinyl alcohol and a copolymer thereof (e.g., a copolymer of acrylamide and polyvinylpyrrolidone), polyvinylpyrrolidone and a copolymer thereof (e.g., a copolymer of vinyl acetate Starch derivatives, gelatin, gum arabic, casein, xanthan gum, glycogen, chitin, chitosan, agarose, carrageenan, heparin, hyaluronic acid, pectin, and the like), cellulose derivatives (hydroxymethylcellulose, hydroxyethylcellulose and the like) Water-soluble epoxy resin, water-soluble urea resin, water-soluble urea resin, water-soluble melamine resin, water-soluble amino resin, water-soluble polyamide resin, water-soluble acrylic resin, water-soluble polycarboxylic acid salt , A water-soluble polyester resin, a water-soluble polyurethane resin, a water-soluble polyol resin, And water-soluble polymers represented by chemically modified sieves.

The method of coating the antifogging agent on the biaxially oriented sheet is not particularly limited, and a simple method includes a coating method using a roll coater, a knife coater, a gravure roll coater, or the like. Spraying, immersion, etc. may also be employed.

The water contact angle after coating with the antifogging agent, that is, the water contact angle on the surface of the antifogging agent layer of the biaxially oriented sheet is preferably 5 to 15 °. When the water contact angle is less than 5 DEG, there is a problem that the surface is in an adhered state, so that appearance defects at the time of molding and adhesion of the particles are liable to occur. When the water contact angle is 15 ° or more, the lipophilic property is increased and the effect as a protective film is not obtained. The water contact angle can be measured in accordance with JIS R 3257.

Next, the packaging container of the present embodiment will be described. Fig. 1 is a perspective view showing an embodiment of a packaging container, and Fig. 2 is a side view of the packaging container. Fig. 1 and 2, the packaging container 1 includes a main body portion 2 capable of receiving contents, a lid portion 3, and a lid portion 3 connecting the main body portion 2 and the lid portion 3 to each other And a hinge portion (4). The packaging container 1 is formed by molding the above-described biaxially oriented sheet. The lid portion 3 is openable and closable as shown in Figs. 2 (a) and 2 (b). The main body portion 2 and the lid portion 3 are fitted to each other, for example, so that the lid portion 3 is closed (Fig. 2 (b)). When the antifogging agent layer is formed on the biaxially oriented sheet, it is preferable that the surface of the antifogging agent layer is disposed on the inner side of the body portion 2 and the lid portion 3 as the contents contact surface.

The radius of curvature of the hinge portion 4 in the state in which the cover portion 3 is closed (Fig. 2 (b)) (when the hinge portion 4 is viewed in the direction in which the hinge portion 4 extends The radius of curvature of the hinge portion 4 (viewed from the side of (b) of FIG. 2) is preferably 2 to 10 mm. When the radius of curvature of the hinge portion 4 in the closed state of the lid portion 3 is less than 2 mm, the deformation of the hinge portion 4 becomes large, and the sheet tends to be whitened. When the radius of curvature of the hinge portion 4 in the closed state of the lid portion 3 exceeds 10 mm, it is possible to prevent the fitting portion 3 from being closed due to the defective shape or the thinning of the hinge portion 4 Defects occur. Also, it causes cracking in the evaluation of oil resistance by thinning.

The packaging container 1 can be suitably used for food packaging applications, that is, for applications in which foods are contained (the main body 2 houses food). When the packaging container (1) is used for food packaging, the material used for the biaxially oriented sheet is a material that has been publicly recognized as being hygienic and stable, such as being registered in the food additive process sheet or the positive list of the Polyolefin Hygiene Council Is preferably used.

In order to obtain the packaging container 1, for example, a commercially available general hot plate pressure molding machine may be used. The molding machine to be used is preferably a type of molding machine capable of setting the time during which the sheet is pressed against the heat plate, the time for molding by pressing, the time lag for switching from sheet pressing to pressure molding, and the molding cycle. These methods are described, for example, in the Polymer Society Handbook "Plastics Processing Technology Handbook", Japan Daily Newspaper (1995).

Example

An experimental example of the acrylonitrile-styrene copolymer used is shown below.

Experimental Example 1 {Production of acrylonitrile-styrene copolymer (AS-1)} [

A first reactor as a complete mixing type stirring tank of about 20 L in volume and a second reactor as a tower type plug flow type reactor having a stirrer having a volume of about 40 L were connected in series and further connected in series with two pre- . 15 parts by mass of ethylbenzene, 0.01 part by mass of t-butylperoxyisopropyl monocarbonate, and 0.25 parts by mass of t-dodecylmercaptan were added to 85 parts by mass of a monomer solution composed of 10% by mass of acrylonitrile and 90% To prepare a raw material solution. This raw material solution was introduced into a first reactor controlled at 125 캜 at a rate of 6.0 kg per hour. The reaction liquid was continuously withdrawn from the first reactor and the reaction liquid was introduced into a second reactor which was adjusted so as to form a gradient from 125 캜 to 160 캜 toward the direction of flow. Next, the mixture was heated in a preheater to 160 DEG C and then introduced into a first devolatilizing tank reduced in pressure to 67 kPa, further heated in a preheater to 230 DEG C, and then introduced into a second evacuation tank reduced in pressure to 1.3 kPa, . This was extruded and cut into a strand shape to obtain an acrylonitrile-styrene type copolymer (AS-1) in the form of pellets. (AS-1) had a composition of 10% by mass of acrylonitrile units and 90% by mass of styrene units as shown in Table 1, and had a weight average molecular weight of 15,000 and a polydispersity of 2.3.

Experimental Examples 2 to 16 {Production of acrylonitrile-styrene copolymer (AS-2 to 16)

The amounts of various raw materials in Experimental Example 1 were adjusted to obtain the acrylonitrile-styrene resins (AS-2 to 16) shown in Table 1.

≪ Example 1 >

An unoriented sheet having a thickness of 1.2 mm was obtained at an extrusion temperature of 230 占 폚 by using a sheet extruder (T die width 500 mm,? 40 mm extruder (manufactured by Tanabe Plastic Kikai Co., Ltd.)) of the acrylonitrile- . This sheet was preheated in a batch type biaxial stretching machine (Toyo Seiki) to 140 占 폚 and stretched at a deformation rate of 0.1 / sec at 2.4 times in the MD direction and at 2.4 times in the TD direction (surface magnification ratio of 5.8 times) Thereby obtaining an axis-stretched sheet. Further, a 1% sucrose lauric acid ester (Rikemal A (manufactured by Daiichi Kogyo Seiyaku K.K.)) was coated in a bar coater at 5 g / m 2 and dried in an oven at 105 ° C for 1 minute. The water contact angle of the coated surface after drying was 10 °. The biaxially oriented sheet had a sulfur content of 50 ppm and a volatile substance content of 1000 ppm.

The obtained sheet was subjected to physical property measurement and evaluation in the following manner. The results are shown in Table 2.

[Draw ratio]

A straight line Y of 100 mm in MD and TD was drawn on the test piece of the biaxially oriented sheet and the test piece was allowed to stand for 60 minutes in an oven at a temperature 30 캜 higher than the Vicat softening point temperature of the sheet measured in accordance with JIS K7206, And the length Z [mm] of the straight line after measurement was measured and calculated by the following equation: stretching magnification = Y / Z, unit [times].

[Maximum orientation relaxation stress (shrinkage resistance)]

A specimen of 20 mm x 200 mm x 0.2 mm was obtained from the biaxially oriented sheet. Both ends of the test piece were fixed and immersed in an oil bath at 130 DEG C, and then the stress value at the time when the load became maximum was calculated. The stress value in the MD direction at that time was regarded as a maximum orientation relaxation stress a and the stress value in the TD direction was regarded as a maximum relaxation stress b to obtain | a-b |.

[Sulfur content]

ICP-MS (inductively coupled plasma mass spectrometer).

[Volatile matter Content]

The biaxially oriented sheet was crushed and about 0.5 g of the biaxially oriented sheet was crushed, dissolved in 50 ml of tetrahydrofuran, added with 1 ml of diethylbenzene standard solution, diluted with tetrahydrofuran, adjusted to 20 ml and analyzed by gas chromatography Respectively.

[Water contact angle]

Contact angle DM-701 (Kyowa Kaimengagaku) was measured in accordance with JIS R 3257 using a distilled water as a test solution, and the contact angle was measured after a drop of 2 μL and 30 seconds after dropping.

[Productivity of resin]

Unreacted monomers in the copolymer were calculated by gas chromatography with respect to each monomer used in the polymerization, and the productivity (polymerization rate) of the actually polymerized monomers was determined based on the following equation to evaluate the productivity of the resin.

Polymerization ratio (%) = polymer mass ÷ (mass of polymer + mass of unreacted monomer) × 100

?: Polymerization rate of 90.0% to 100%

?: Polymerization rate 80.0% or more and less than 90.0%

X: polymerization rate less than 80%

[Sheet formability]

The average thickness and the standard deviation? Of the biaxially oriented sheet were measured by using a micro gauge with respect to the points of intersection of 25 points when the biaxially oriented sheet was made lattice at intervals of 50 mm in the MD direction and the TD direction, For the thickness unevenness, the standard deviation? Was evaluated by the following criteria, and the evaluation of the film formability was made.

?: Less than 0.03 mm

?:? 0.03 mm or more and less than 0.07 mm

X:? Is 0.07 mm or more

[Sheet Strength]

The biaxially oriented sheet was cut into a 1-piece test piece according to JIS K-6251, and the tensile strength was measured at a tensile speed of 500 mm / min using a tensile tester of Shimazu Seisakusho AGS-100D type.

○: exceeding 60 MPa

?: 40 to 60 MPa

×: less than 40 MPa

[Endurance]

The longitudinal bending strength in the sheet extrusion direction (longitudinal direction) and the direction perpendicular thereto (lateral direction) were measured according to ASTM D2176. The average value of longitudinal and lateral directions was obtained and evaluated.

○: 10 times or more

DELTA: 5 times or more and less than 10 times

×: Less than 5 times

[Transparency]

Was measured by a haze meter NDH5000 (manufactured by Nippon Denshoku Co., Ltd.) according to JIS K-7361-1. For the measurement, a 0.21 mm thick biaxially oriented sheet prepared above was used.

○: Less than 1.0%

?: 1.0 to 2.0%

×: exceeding 2.0%

〔color〕

Ten sheets of 0.21 mm thick stretched sheets were stacked, and the b value obtained from the SCI measurement (including regularly reflected light) of the CM-2500d (Konica Minolta) of the spectroscopic colorimetric system was evaluated.

○: Less than 3

?: 3 to 5

×: exceed 5

[Formability]

In a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering Co., Ltd.), a food pack with a hot plate temperature of 135 占 폚 and a heating time of 2.0 seconds, a food pack (body length: 130 × 110 × depth: 28 mm, 25 mm, radius of curvature of the hinge portion: 3 mm) was molded and the appearance was evaluated. Also, the fitting state of the molded article when the lid was closed was evaluated.

○: Good

?: Minor whitening, slight rain drop

X: Significant whiteness, remarkable rain drop, defective shape, poor fitting (discrepancy, peeling, distortion) (can not be commercialized)

[Odor during container molding]

The odor of the atmosphere in the vicinity of the hot plate molding machine after 10 pieces of the attached food packs were molded under the condition of the hot plate temperature of 135 DEG C and the heating time of 2.0 seconds in the hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering Co., Ltd.) was evaluated.

○: No specific odor

△: Feeling a little odd smell

×: Feeling the smell of poking a nose

[Oil Resistance (Chemical Resistance)]

A hermetically sealed food pack having a hinge portion was molded in a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering Co., Ltd.), and 10 x 10 mm of gauze made of salad oil (manufactured by Nissin Seisai Co., Ltd.) and mayonnaise (manufactured by Ajinomoto Co., And allowed to stand in an oven at 60 DEG C for 24 hours to observe the surface of the attachment portion.

○: No change

△: There is a little whiteness

X: remarkable white puffy, with punch

[Range resistance]

Attached to the inside of the food pack cover was mayonnaise 2x2 cm, 100 g of water was placed in the container body, and the container was covered. The container was heated in a microwave oven of 1500 W for 30 minutes, and the state of the portion with the mayonnaise was visually evaluated Respectively.

○: No change

DELTA: The container was slightly deformed

X: White papers are present, punched, and the container is significantly deformed (can not be commercialized)

≪ Examples 2 to 29 >

In the same manner as in Example 1, sheets were produced under the conditions of the resin and stretching conditions described in Tables 2 and 3, and evaluation was conducted. The results are shown in Tables 2 and 3.

≪ Comparative Examples 1 to 18 >

In the same manner as in Example 1, a sheet was produced under the conditions of the resin and stretching conditions shown in Tables 4 and 5 and evaluated. The results are shown in Tables 4 and 5.

As shown in the table, the sheets shown in the examples are well-balanced and balanced in performance, but the sheets shown in the comparative examples are sheets having insufficient practical properties such as sheet strength, endurance, oil resistance and the like.

The biaxially oriented sheet of the present invention is excellent in transparency, rigidity, practical strength, heat resistance, whitening resistance under oil-contacting conditions, chemical resistance, and shrinkage resistance, and can be suitably used as a packaging container for packaging foods and the like.

1: Packaging container
2:
3:
4: Hinge section

Claims (5)

A biaxially oriented sheet obtained by biaxially stretching an acrylonitrile-styrene copolymer,
The content of the acrylonitrile unit in the copolymer is 10 to 40% by mass,
The copolymer has a weight average molecular weight of 100,000 to 250,000, a polydispersity of 2.0 to 2.5,
Wherein the biaxially oriented sheet has a biaxial stretching ratio of 4 to 10 times, a maximum orientation relaxation stress in the MD direction and a TD direction of 0.2 to 0.6 MPa, a maximum orientation relaxation stress in the MD direction (a) (Ab |) of the difference in the orientation relaxation stress (b) is 0.3 MPa or less,
Wherein the biaxially oriented sheet has a sulfur content of 0 ppm or more and less than 100 ppm and a content of a volatile substance of 200 to 2,000 ppm. The biaxially oriented sheet according to claim 1, wherein an anti-fogging agent layer is further formed on at least one surface of the biaxially oriented sheet and a water contact angle on the surface of the anti-fog agent layer is 5 to 15 °. A biaxially oriented sheet according to any one of claims 1 to 3,
A packaging container comprising: a body portion; a lid portion; and a hinge portion connecting the body portion and the lid portion to each other. A biaxially stretched sheet obtained by molding the biaxially oriented sheet according to claim 2,
And a hinge portion connecting the main body portion and the lid portion to each other,
Wherein the surface of the antifogging agent layer is a content contact surface. The food according to claim 3 or 4, wherein the main body portion is a main body portion for containing food,
Wherein a radius of curvature of the hinge portion in a state in which the lid portion is closed is 2 to 10 mm.

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