JP2022162776A - Oil-resistant styrene resin sheet, package - Google Patents

Abstract

The present invention provides a styrene-based resin sheet that has both anti-fogging properties and heat-resistant oil resistance, and that hardly generates gel foreign matter when remnants from the manufacturing process are reused as raw materials. A styrene-based resin sheet having a coating layer on at least one surface, the coating layer comprising a sulfo group-containing polymer (A) and an antifogging agent (B). When the total solid content of the molecule (A) and the antifogging agent (B) is 100% by mass, the sulfo group-containing polymer (A) is 50% by mass or more and 95% by mass or less, and the antifogging agent (B ) is 5% by mass or more and 50% by mass. [Selection figure] None

Description

The present invention relates to an oil-resistant styrenic resin sheet and a package using the sheet.

Polystyrene biaxially oriented sheets are widely used for packaging containers because of their transparent and glossy appearance, moldability, and mechanical strength. When used for a fitting lid, a technique of providing an anti-fogging coating layer on the sheet surface facing the contents is widely used.
In addition, in order to reduce the production cost and suppress the consumption of petroleum resources, trimming loss and other offcuts generated in the production process of polystyrene biaxially oriented sheets are pulverized and used as new polystyrene resin pellets (virgin pellets). It is necessary to mix them and reuse (return) them as raw materials for polystyrene-based biaxially oriented sheets. In that case, it is a requirement for improving production efficiency and economic efficiency that there is no step of removing the anti-fogging coating layer or the like provided on the polystyrene biaxially oriented sheet.

In recent years, due to the development of the food processing and distribution industries and changes in food culture, there has been a growing market demand for microwave oven heating of refrigerated and frozen foods containing oil, such as boxed lunches, gratin, pasta, and fried foods, together with their packaging. It is also required to impart heat oil resistance to polystyrene biaxially oriented sheets. In particular, among various oils, resistance under heating to medium-chain fatty acid triglycerides (MCT), which is contained in many foods and tends to corrode polystyrene-based biaxially oriented sheets, is required.

Regarding the imparting of oil resistance to a polystyrene-based resin sheet, for example, the following documents can be cited.
In Patent Document 1, it has excellent oil resistance while maintaining the transparency and gloss that are the characteristics of polystyrene resins, exhibits excellent oil resistance even in water / oil coexistence, and has excellent oil resistance even after molding. As a polystyrene resin film capable of maintaining properties, the minimum film-forming temperature (MFT) is 0 to {(Vsp)-10}°C (Vsp is the Vicat softening point of the polystyrene resin film). A technique for forming the membrane is disclosed. The thermoplastic emulsion resins include polyethylene emulsion, acrylic acid ester emulsion, polyester emulsion, vinylidene chloride latex, ionomer dispersion, ethylene-vinyl acetate copolymer emulsion, ethylene-methacrylic acid copolymer emulsion, styrene- Acrylate copolymer emulsions, styrene-acrylic acid emulsions, acrylate-urethane core-shell structured particles are exemplified in the examples.

In Patent Document 2, as a polystyrene resin sheet that has both heat resistance and oil resistance without impairing moldability and sheet strength and is suitable as a packaging container for food heated in a microwave oven, a polystyrene resin sheet having a polymerization degree of 1500 is formed on one side of the sheet. As described above, a coating film of polyvinyl alcohol having a saponification degree of 85 mol% or more is formed, and the polystyrene resin contains 5 to 20% by mass of either methacrylic acid or maleic anhydride, and has a weight average molecular weight of 15 to 40. It discloses the technology of being ten thousand.

In Patent Document 3, as a styrene resin sheet with improved heat and oil resistance without impairing antifogging properties, a hydrophilic acrylic sheet containing a sugar-derived fatty acid ester (b) is provided on at least one side of a styrene resin sheet (A). Having a coating layer formed using the coating agent (B), in particular, the total mass of the sugar-derived fatty acid ester (b) and the acrylic resin (solid content) of the acrylic hydrophilic coating agent (B) On the other hand, a technique is disclosed in which the fatty acid ester (b) is preferably contained in the range of 20 to 60% by mass.

JP 2007-277428 A JP 2015-113443 A JP 2016-98253 A

However, in the technique of Patent Document 1, the technical knowledge is limited to medium-chain fatty acid triglycerides (MCT) up to 70° C., and further heat resistance to oil is a problem. Further, when the coating films of these thermoplastic resin emulsions were studied, it was found that the antifogging properties were insufficient, and that the oil resistance of the coating films obtained by adding an antifogging agent to these emulsions was lowered.

In addition, when the technique of Patent Document 2 was examined by forming a coating film of polyvinyl alcohol with a degree of saponification of 85 mol% or more, the higher the degree of saponification, the more insufficient the anti-fogging property, and the obtained polystyrene It was found that when the resin sheet was reused (returned), many gels occurred, and it was not possible to combine anti-fogging properties, return properties, and oil resistance.

In addition, when an acrylic hydrophilic coating agent was examined for the technique of Patent Document 3, it was found that the coating amount of ²⁰⁰ mg/m ² was insufficient in oil resistance. However, the amount of coating is large, and in-line coating of styrene resin sheets hinders productivity.

In view of the above circumstances, an object of the present invention is to provide a styrene-based resin sheet that has both anti-fogging properties and heat-resistant oil resistance, and that does not easily generate gel foreign matter when remnants from the manufacturing process are reused as raw materials. is.

The present inventors have made intensive studies on the above problems and completed the following inventions.
[1] A styrene-based resin sheet having a coating layer on at least one surface, wherein the coating layer contains a sulfo group-containing polymer (A) and an antifogging agent (B), and the sulfo group-containing polymer When the total solid content of (A) and the antifogging agent (B) is 100% by mass, the sulfo group-containing polymer (A) is 50% by mass or more and 95% by mass or less, and the antifogging agent (B) is is 5% by mass or more and 50% by mass.

[2] The oil-resistant styrene resin sheet according to [1], wherein the sulfo group-containing polymer (A) has a sulfo group content of 0.1 mol % or more and 40 mol % or less.

[3] The sulfo group-containing polymer (A) is one or more selected from the group consisting of polyvinyl alcohol, polyester, poly(meth)acrylic ester, and poly(meth)acrylic acid (salt) [1] or [ 2].

[4] The oil-resistant styrene resin sheet according to any one of [1] to [3], wherein the coating layer has a thickness of 30 to 300 nm.

[5] The oil-resistant styrenic resin sheet according to any one of [1] to [4], wherein the antifogging agent (B) is sucrose fatty acid ester and/or polyglycerol fatty acid ester.

[6] The oil-resistant styrene resin sheet according to any one of [1] to [5], which is a biaxially oriented sheet.

[7] A package using the oil-resistant styrene resin sheet according to any one of [1] to [6].

According to the present invention, a styrene-based resin sheet having both antifogging properties and resistance to heat and oil can be obtained. It can be suitably used for heating in a microwave oven.
In addition, since it is difficult to generate gel contaminants when scraps from the manufacturing process of the styrene resin sheet are reused as raw materials, the coating layer is formed without the step of removing the anti-fogging and oil-resistant coating layers. The styrene-based resin sheet can be reused (returned) as it is, improving production efficiency and economic efficiency.

An embodiment of the present invention will be described. In addition, the scope of the present invention is not limited to the embodiments described below.
<Oil-resistant styrene resin sheet>
The oil-resistant styrene-based resin sheet of the present invention (hereinafter sometimes referred to as "the sheet of the present invention") uses a styrene-based resin sheet as a base sheet and has an oil-resistant function on at least one side of the base sheet. It has a coating layer.
Unless otherwise specified, the notation "△ to △△" means "more than △ and less than △△", preferably "more than △ and less than △".

(Styrene resin sheet (base material sheet))
Examples of the styrene-based resin used for the base sheet constituting the sheet of the present invention include polymers using styrene-based monomers and copolymers of styrene-based monomers and other monomers copolymerizable therewith.
Styrenic monomers include alkyl-substituted styrenes such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene, α-methyl Examples include styrene, α-alkyl-substituted styrenes such as α-methyl-4-methylstyrene, and halogenated styrenes such as 2-chlorostyrene and 4-chlorostyrene. These styrene-based monomers may be used alone, or two or more of them may be copolymerized and used. From the viewpoint of improving heat resistance, a copolymer of styrene and α-methylstyrene is preferred.

Other monomers copolymerizable with styrene monomers include, for example, (meth)acrylic acid, (meth)acrylic acid ester, maleic anhydride, vinyl acetate, acrylonitrile, butadiene, isoprene, 2-methyl-1,3 -Conjugated diene hydrocarbons such as butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, ethylene, propylene, 1-butene, 1-hexene, 4-methyl- Examples include α-olefins such as 1-pentene and 1-octene. From the viewpoint of improving heat resistance, it is preferable to use α-methylstyrene, (meth)acrylic acid, (meth)acrylic acid ester, maleic anhydride, acrylonitrile, α-methylstyrene, (meth)acrylic acid, (meth) It is more preferable to use an acrylic acid ester, and it is particularly preferable to use (meth)acrylic acid.

Although the weight average molecular weight of the styrene resin is not particularly limited, it is preferably 150,000 or more and 2,000,000 or less, more preferably 150,000 or more and 1,800,000 or less. Within such a range, good extrusion moldability is obtained from melt viscosity characteristics. Further, when it is 150,000 or more, the mechanical strength of the sheet becomes sufficient, and when it is 2,000,000 or less, the elastic modulus of the sheet becomes suitable and the low-temperature moldability is improved.
The melt flow rate (MFR) of the styrene resin is preferably 1.5 g/10 minutes or more and 5.0 g/10 minutes or less, more preferably 2.0 g/10 minutes or more and 4.0 g/10 minutes or less.
From the viewpoint of heat resistance and moldability, the styrene resin preferably has a glass transition temperature of 80° C. or higher and 140° C. or lower, and the upper limit is more preferably 130° C. or lower. The glass transition temperature is obtained from the value when the temperature is reheated at 10° C./min by differential scanning calorimetry based on JIS K7121:2012.

- Impact-resistant polystyrene-based resin The base sheet constituting the sheet of the present invention can contain an impact-resistant polystyrene-based resin. The inclusion of the impact-resistant polystyrene resin improves the blocking resistance and impact resistance of the base sheet. The content of the impact-resistant polystyrene resin is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.5% by mass or more and 4.0% by mass or less, when the base sheet is 100.0% by mass. is more preferred.
As the impact-resistant polystyrene-based resin, any polystyrene-based resin containing a component such as rubber may be used, and a styrene homopolymer containing a rubber component can be preferably used. Examples of rubber components include polybutadiene, styrene-butadiene copolymers, polyisoprene, and butadiene-isoprene copolymers. The rubber component may be dispersed in polystyrene as a matrix resin in the form of particles independently, or may be dispersed in the form of particles by graft polymerization to polystyrene. good.

From the viewpoint of achieving both impact resistance and stretch moldability, the content of the rubber component in the impact-resistant polystyrene resin is 1.0% by mass when the impact-resistant polystyrene resin is 100.0% by mass. 15.0 mass % or less is preferable, 3.0 mass % or more and 15.0 mass % or less is more preferable, and 5.0 mass % or more and 15.0 mass % or less is still more preferable.
The content of the rubber component is calculated by measuring the diene content by potentiometric titration using iodine monochloride, potassium iodide and sodium thiosulfate standard solutions, and taking the diene content as the content of the rubbery polymer. The measurement method is described, for example, by the Japan Society for Analytical Chemistry, Polymer Analysis Research Council, "New Edition Polymer Analysis Handbook", Kinokuniya Shoten (1995 edition), p. 659(3) rubber content.
The melt flow rate (MFR) of the impact-resistant polystyrene resin is preferably 1.5 g/10 minutes or more and 5.0 g/10 minutes or less, more preferably 2.0 g/10 minutes or more and 4.0 g/10 minutes or less.

-Other components The base sheet constituting the sheet of the present invention may contain other components such as resins other than the above-described resins and additives within a range that does not impair the effects of the present invention.
Other resins include polyolefin resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, and ethylene acetate. Vinyl copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin , polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamideimide resins, polyamide bismaleimide resins, polyarylate resins, polyetherimide resins, Examples include polyetheretherketone-based resins, polyetherketone-based resins, polyethersulfone-based resins, polyketone-based resins, polysulfone-based resins, aramid-based resins, fluorine-based resins, and the like.

Additives include processing aids, melt viscosity improvers, antioxidants, anti-aging agents, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet absorbers, neutralizers, nucleating agents, cross-linking agents, lubricants, materials, anti-blocking agents, mineral oils, slip agents, anti-fogging agents, antimicrobial agents, deodorants, flame retardants, antistatic agents, colorants and pigments.
Anti-blocking agents include inorganic particles and organic particles. Examples of inorganic particles include silica, glass beads, etc., and those whose surfaces have been chemically treated. Examples of organic particles include polystyrene, polymethyl methacrylate, and the like, and those obtained by subjecting them to heat treatment or chemical treatment. Among them, spherical silica containing silicon oxide as a main component is preferred because it is chemically stable, does not denature the resin by catalytic action, and is easy to apply a release agent silicone oil to the sheet surface, which will be described later.
The content of the antiblocking agent in the base sheet is preferably 50-500 ppm. The average particle size is preferably 1-20 μm.

(coating layer)
The sheet of the present invention has a coating layer on at least one surface of the styrene-based resin sheet that is the base sheet, and the coating layer contains a sulfo group-containing polymer (A) and an antifogging agent (B) agent. .
・Sulfo group-containing polymer (A)
The sheet of the present invention contains a sulfo group-containing polymer (A) (hereinafter sometimes referred to as polymer (A)) in the coating layer.
The coating layer on the surface of the styrene resin sheet is preferably formed by applying a water-based coating agent and drying it from the viewpoint of production environment and economy. Preferably. Hydrophilicity means both water solubility and water dispersibility. Good to have. Hydrophilic polymers are also preferable because they have oil repellency and oil resistance.

However, although there have been techniques for forming a coating film of a hydrophilic polymer such as polyvinyl alcohol or acrylic for the purpose of imparting oil resistance to a styrene resin sheet (Patent Documents 1 to 3), these techniques In this case, oil resistance and anti-fogging properties cannot be achieved at the same time, and there is a problem that if the sheet structure on which the coating film is formed is reused (returned), gel contaminants frequently occur. In this regard, the present inventors have made intensive studies and found that hydrophilic polymers having only hydroxyl groups and carboxyl groups cannot have both oil resistance and anti-fogging properties, and that hydrogen bonding and dehydration condensation occur during the manufacturing process of recycled pellets. By using a hydrophilic polymer with a sulfo group (sulfonic acid group), which is more polar than a hydroxyl group or a carboxyl group, the oil contained in foods, etc., even under high temperature conditions. It can provide excellent oil resistance that suppresses the permeation of styrene resin sheets, and even if an anti-fogging agent is added, it achieves both oil resistance and anti-fogging properties without lowering oil resistance, and has good return properties. It was found that a styrene-based resin sheet can be obtained.

The sulfo group-containing polymer (A) only needs to have a sulfo group in the molecule, and can be obtained, for example, by sulfonic acid modification. ) acrylic acid ester, sulfo group-containing poly(meth)acrylic acid (salt), etc., and sulfo group-containing polyvinyl alcohol and sulfo group-containing polyester are preferable in terms of oil resistance.
In addition to the sulfo group, the sulfo group-containing polymer (A) may have a hydrophilic group such as a hydroxyl group, a carboxyl group, an amino group, or a phosphoric acid group. For example, the sulfo group-containing polyvinyl alcohol described below may have a hydroxyl group, and the sulfo group-containing polyester may have a carboxyl group.

The sulfo group content of the sulfo group-containing polymer (A) is preferably 0.1 mol % or more and 40 mol % or less, more preferably 1 mol % or more and 30 mol % or less. When the content is 0.1 mol % or more, the oil resistance is good, and when it is 40 mol % or less, the flexibility and coatability of the polymer (A) are good.
The sulfo group content can be analyzed using ¹ H-NMR (solvent: DMSO-d ₆ ).

· Sulfo group-containing polyvinyl alcohol Sulfo group-containing polyvinyl alcohol can be produced by any method, for example, the following methods (a) to (e) can be mentioned, among them, methods (a) and (b) is preferred.
(a) A polymer obtained by polymerizing an olefin sulfonic acid such as ethylenesulfonic acid, allylsulfonic acid, or methallylsulfonic acid or a salt thereof and a vinyl ester such as vinyl acetate in an alcohol or an alcohol/water mixed solvent, and further how to convert.
(b) a copolymer obtained by copolymerizing a sulfoalkyl maleate such as sodium sulfopropyl 2-ethylhexyl maleate, sodium sulfopropyl tridecyl maleate or sodium sulfopropyl eicosyl maleate with a vinyl ester such as vinyl acetate; How to further saponify.
(c) A method of copolymerizing a sulfoalkyl (meth)acrylamide such as N-sulfoisobutylene acrylamide sodium salt and a vinyl ester such as vinyl acetate and saponifying the resulting copolymer. Furthermore, for example, a method of copolymerizing a sulfoalkyl (meth)acrylate such as sodium 2-sulfoethyl acrylate and a vinyl ester such as vinyl acetate and saponifying the obtained copolymer.
(d) A method in which polyvinyl alcohol is treated with bromine, iodine, etc. and then heated in an aqueous solution of acidic sodium sulfite.
(e) A method of heating polyvinyl alcohol in a concentrated aqueous sulfuric acid solution.
(f) A method of acetalizing polyvinyl alcohol with an aldehyde compound containing a sulfonic acid group.

In addition, a well-known method can be used for said copolymerization and saponification.
In addition, the copolymer can be used in combination with copolymerizable monomers such as (meth)acrylamide, (meth)acrylonitrile, styrene, and vinyl chloride.
Also, the sulfo group may be in the form of a free acid, sodium salt, potassium salt, ammonium salt, or the like.

The sulfo group content of the sulfo group-containing polyvinyl alcohol in the present invention is the ratio of the repeating units of the polyvinyl alcohol containing the sulfo group to the total repeating units of the polyvinyl alcohol.
The sulfo group content in the sulfo group-containing polyvinyl alcohol is preferably 0.1 mol % or more and 20 mol % or less, more preferably 1 mol % or more and 10 mol % or less. When the content is 0.1 mol % or more, the oil resistance is good, and when the content is 20 mol % or less, the flexibility of the polymer (A) is good.

The saponification degree of the polyvinyl alcohol portion of the sulfo group-containing polyvinyl alcohol is preferably 75 mol % or more and 98 mol % or less, more preferably 80 mol % or more and 95 mol % or less. At 75 mol % or more, the oil resistance is good, and at 98 mol % or less, the return property is good.
The degree of polymerization of the sulfo group-containing polyvinyl alcohol is preferably 50 or more and 1500 or less, and the upper limit is more preferably 1000 or less, still more preferably 700 or less, and particularly preferably 500 or less. When the degree of polymerization is 50 or more, the mechanical strength of the coating layer is sufficient, and when it is 1500 or less, gel formation during return is suppressed and returnability is improved.

The sulfo group-containing polyvinyl alcohol may contain modified species other than sulfonic acid groups, such as carboxyl groups, oxyalkylene groups, cationic groups, etc., as long as the effects of the present invention are not impaired.
Also, a sulfo group-containing polyvinyl alcohol and a sulfo group-free polyvinyl alcohol can be mixed and used. ratio.

Sulfo-group-containing polyester The sulfo-group-containing polyester is a polyester in which either or both of dicarboxylic acid and diol, which are raw materials of polyester, contain a sulfo group, and the dicarboxylic acid and the diol are polycondensed.

The dicarboxylic acid is not particularly limited, and examples include o-phthalic acid, terephthalic acid, isophthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, octylsuccinic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, fumaric acid, and maleic acid. acid, itaconic acid, decamethylenecarboxylic acid, their anhydrides and lower alkyl esters.

The diol is not particularly limited, and examples include ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, dipropylene glycol and triethylene glycol. , tetraethylene glycol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, neopentyl glycol (2,2-dimethylpropane-1,3-diol), 1,2-hexanediol , 2,5-hexanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol; 2,2 -alicyclic diols such as bis(4-hydroxycyclohexyl)propane, alkylene oxide adducts of 2,2-bis(4-hydroxycyclohexyl)propane, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol are mentioned.

Examples of sulfo group-containing dicarboxylic acids include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfophthalic acid, 5-dialkylsulfoisophthalic acid, 2-dialkylsulfoisophthalic acid, 4-sulfo Examples include dialkyl isophthalate, dialkyl 3-sulfoisophthalate and sodium salts and potassium salts thereof.

Examples of sulfo group-containing diols include 1,3-dihydroxybutanesulfonic acid and 1,4-dihydroxybutanesulfonic acid.

The sulfo group content of the sulfo group-containing polyester in the present invention means that when either the dicarboxylic acid or the diol that is the raw material of the polyester contains a sulfo group, the polyester repeat containing the sulfo group with respect to all the repeating units of the polyester is the ratio of the units, and when both the dicarboxylic acid and the diol contain sulfo groups, the ratio is twice the ratio of the sulfo group-containing polyester repeating units to the total repeating units of the polyester.
The sulfo group content in the sulfo group-containing polyester is preferably 5 to 40 mol %, more preferably 10 to 30 mol %. When the content is 5 mol % or more, the oil resistance and toughness of the coating layer are improved, and when the content is 40 mol % or less, the coatability to the styrene-based resin sheet when forming the coating layer is improved.

The weight average molecular weight of the sulfo group-containing polyester is preferably 1,000 to 100,000, more preferably 3,000 to 50,000 or more, and even more preferably 10,000 to 30,000. When it is 1,000 or more, the oil resistance and film-forming (coating layer formation) properties become good, and when it is 100,000 or less, the coatability to a styrene-based resin sheet when forming the coating layer becomes good. A weight average molecular weight can be analyzed by the GPC method.
The softening temperature of the sulfo group-containing polyester is preferably 80 to 200°C, more preferably 90 to 180°C. A temperature of 80° C. or higher provides good heat resistance, and a temperature of 200° C. or lower provides good return properties. The softening temperature can be measured according to JIS K7206:2016.

The sulfo group-containing polyester may contain modified species other than sulfonic acid groups, such as carboxyl groups, oxyalkylene groups, cationic groups, etc., as long as the effects of the present invention are not impaired.
Further, a sulfo group-containing polyester and a sulfo group-free polyester can be mixed and used, and the sulfo group content in that case is the ratio of the sulfo group-containing polyester repeating unit to the total polyester.

The coating layer of the sheet of the present invention can contain other hydrophilic polymers in addition to the sulfo group-containing polymer (A) within a range that does not impair the effects of the present invention. For example, from the viewpoint of improving mechanical properties, polyvinyl alcohol, cellulose, poly(meth)acrylic acid ester, poly(meth)acrylic acid (salt), etc., and mixtures thereof can be mentioned, and the solid content of the coating layer is 100% by mass. 0 to 30% by mass is preferable, and 3 to 20% by mass is more preferable.

(Anti-fogging agent (B))
The sheet of the present invention contains an antifogging agent (B) in the coating layer.
By containing the anti-fogging agent (B), when the sheet is used for a package for a content containing moisture such as food, the sheet is less likely to be fogged and the content is well visible.
As the antifogging agent (B), known antifogging agents can be used, and for example, polyhydric alcohol-type nonionic surfactants are preferred.

Examples of polyhydric alcohol-type nonionic surfactants include glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, pentaerythritol fatty acid esters, trimethylolpropane fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene glycerin fatty acid esters. , polyoxyethylene sorbitan fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, polyoxyethylene fatty alcohol ether, etc., and two or more of these may be used in combination.
Among them, from the viewpoint of expressing good antifogging properties, 70% by mass or more of the fatty acids constituting the molecule are saturated and/or unsaturated fatty acids with 12 to 18 carbon atoms, and 20% by mass or more of the monoester. Sucrose fatty acid ester, sorbitan fatty acid ester, which is a mixture of mono-, di-, tri-, and poly-esters contained, and 70% by mass or more of the fatty acids constituting the molecule are saturated with 12 to 18 carbon atoms and/or a mixture of mono-, di-, tri-, and poly-esters which are unsaturated fatty acids and have a polycondensation degree of 2 to 20, further 2 to 12, and contain 20% by mass or more of monoesters Polyglycerol fatty acid esters are preferred. Among them, sucrose fatty acid esters and polyglycerol fatty acid esters are preferred from the viewpoint of antifogging properties. These may be used individually by 1 type, and may be used in mixture of 2 or more types. Since the saturated and/or unsaturated fatty acid has 12 or more carbon atoms, it is difficult for the surfactant to permeate the styrene resin sheet, and the occurrence of cracks and cloudiness can be suppressed. It is possible to prevent adverse effects when reusing as a raw material.
Furthermore, from the viewpoint of uniform dispersibility with the polymer (A), the lower limit of the HLB (Hydrophilic-Lipophilic Balance, hydrophilic-lipophilic balance) value is preferably 5 or more. Uniformity is improved, and good oil resistance can be exhibited over the entire coated surface. The upper limit of the HLB value of the polymer (A) is preferably 20 or less, which is the maximum value.

Moreover, other nonionic surfactants, anionic surfactants, cationic surfactants and amphoteric surfactants can be contained together with the polyhydric alcohol type nonionic surfactants. Other nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene fatty acid amides, polyoxyethylene (hardened) castor oil ethers, polyoxyethylene polyoxypropylene block copolymers, and the like. Examples of anionic surfactants include carboxylic acid salts such as fatty acid salts and polyoxyethylene alkyl ether carboxylates, sulfuric acid ester salts such as alkyl sulfate salts and polyoxyethylene alkyl ether sulfate salts, alkylbenzene sulfonates, and Examples include sulfonates such as alkylsulfosuccinates, phosphates such as alkyl phosphates and polyoxyethylene alkyl ether phosphates. Examples of cationic surfactants include alkylammonium salts and alkylpyridinium salts, and examples of amphoteric surfactants include alkylaminobetaine acetates, alkylamidopropylbetaines, alkylsulfobetaines and the like. These can use 1 type(s) or 2 or more types.

・Composition, thickness, etc. of the coating layer The coating layer of the sheet of the present invention has a sulfo group-containing polymer ( A) and the antifogging agent (B) have a mass composition ratio of (50 to 95):(5 to 50), preferably (60 to 92):(8 to 40), and (70 to 92): (8 to 30) is more preferred, and (80 to 92):(8 to 20) is even more preferred.
Regarding the composition ratio of the coating layer, when the sulfo group-containing polymer (A) is large and the antifogging agent (B) is small, the oil resistance and coating appearance are improved. When B) is large, the anti-fogging property and repellency tend to be improved, and within the above range, all of the oil resistance, anti-fogging property, repellency and coating appearance are improved.

The coating layer contains known additives such as antistatic agents, viscosity modifiers, antifoaming agents, ultraviolet absorbers, anti-coloring agents, antibacterial agents, and coloring agents such as pigments and dyes, as long as the effects of the present invention are not impaired. It may contain an agent.

The layer thickness of the coating layer is preferably 30 nm or more and 300 nm or less, and the lower limit thereof is more preferably 50 nm or more, and even more preferably 80 nm or more. The upper limit is more preferably 200 nm or less, still more preferably 150 nm or less, and particularly preferably 100 nm or less. When the thickness is 30 nm or more, the anti-fogging property and oil resistance are good, and when the thickness is 300 nm or less, the production efficiency of coating and drying is good, and blocking and transfer between sheets and whitening of the sheets associated therewith are less likely to occur, which is preferable.
The layer thickness can be measured by washing the coating layer of the resin sheet per unit area, collecting the wash liquid, and measuring by a mass method, a gas chromatography method, a high performance liquid chromatography method, or the like. In addition, the layer thickness can be easily obtained by creating a calibration curve by infrared absorption spectroscopic analysis (total reflection method) using a resin sheet with a known layer thickness as a standard sample, and comparing the measured values of the resin sheet with an unknown layer thickness. be able to.

<Characteristics of oil-resistant styrene resin sheet>
The oil-resistant styrenic resin sheet of the present invention has the following features.
(Oil resistance)
The sheet of the present invention has oil resistance, and in particular, has good oil resistance against medium-chain fatty acids (MCT), which are contained in food, etc., which are the contents of the package, and which are easily eroded by styrene-based resins. In addition, the styrene-based resin sheet is less likely to whiten. In addition, since it has good oil resistance even under high temperature conditions, it is possible to heat food while it is packaged.

(Anti-fogging property)
Since the sheet of the present invention has sufficient anti-fogging properties, even if the contents of the package contain moisture such as food, the contents are well visible, and the commercial value of the package and the contents is not impaired.

(transparency)
In the coating layer of the sheet of the present invention, the compatibility between the sulfo group-containing polymer (A) and the antifogging agent (B) is good, and desired oil resistance and antifogging properties can be obtained with a layer thickness of 300 nm or less. The transparency is high, and the transparency of the sheet of the present invention is also improved.

(Return property)
The sheet of the present invention is economical because it is possible to return and reuse the offcuts obtained by trimming the sheet tabs and the like generated in the sheet manufacturing process as part of the raw materials for newly manufactured sheets. It can also contribute to reducing the amount of petroleum-derived raw materials used. In particular, the fact that the styrene resin sheet (base sheet) can be used as a recycled raw material without removing the coating layer formed on the surface thereof is highly valuable in terms of production efficiency and economy.
Reuse (return) of offcuts can be performed by known methods and procedures. The mixture is put into an extruder, melt-extruded, and the strand coming out of the die is rapidly cooled and dried, and then regenerated pellets are produced using a granulator. The set temperature of the extruder is preferably 160 to 260°C, more preferably 180 to 240°C, from the viewpoint of resin melting and heat load to the resin. If the set temperature is lower than 160°C, the motor of the extruder will be overloaded and melt extrusion will be difficult. Moreover, when the set temperature exceeds 260° C., the yellowing of the pellets is accelerated due to thermal deterioration, which is not preferable.
When recycled pellets are used again in the sheet manufacturing process, if the total of new pellets (virgin pellets) used for sheet manufacturing and recycled pellets is 100% by mass, the usage rate of recycled pellets is 5% by mass or more and 50% by mass. % or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less. When the usage rate of the recycled pellets is 50% by mass or less, deterioration of physical properties such as yellowing and reduction in strength of the sheet is unlikely to occur. In addition, since the usage rate of recycled pellets is 5% or more, the efficiency of using scrap materials is high, and costs such as storage and disposal costs for scrap materials, fluff, and recycled pellets can be suppressed.

In general, styrene resin sheets are used in applications that require high transparency and high gloss, so they are required to have a beautiful appearance. lose a lot. In particular, since recycled pellets may gel due to the heat history of the manufacturing process, etc., care must be taken to prevent gel or the like from being mixed into a sheet produced using recycled pellets as a raw material.
For example, in the study of the present invention, when polyvinyl alcohol with a high degree of saponification of the prior art is used for the coating layer, gels frequently occur due to hydrogen bonding and dehydration condensation of polyvinyl alcohol at the time of reuse (return). However, in the case of the sheet of the present invention having a predetermined coating layer, the amount of gel generated during the production of recycled pellets and during the return is small.

(Manufacturing method of the sheet of the present invention)
The sheet of the present invention can be manufactured by known methods. For example, raw materials are melted and kneaded in an extruder, extruded into a sheet from a die, cooled and solidified by cooling rolls, air cooling, or water cooling to produce an unstretched sheet, then stretched in the longitudinal direction and the transverse direction, It can be manufactured by obtaining an axially stretched sheet, applying a water-based coating agent for a coating layer to at least one surface of the stretched sheet, and drying the coating layer to form a coating layer. The surface of the biaxially oriented sheet on which the coating layer is to be formed may be subjected to corona treatment.

As a detailed example of the method for producing an unstretched sheet, after mixing the raw materials that make up the sheet, using an extruder such as a single screw extruder, a counter-rotating twin-screw extruder, or a co-rotating twin screw extruder, the composition Promotes uniform distribution of Raw materials may be mixed in a mixer such as a tumbler mixer, mixing roll, Banbury mixer, ribbon blender, super mixer, etc., and then fed into an extruder, or a strand die may be connected to the tip of another mixer. Alternatively, after pelletizing by a method such as strand cutting or die cutting, the obtained pellets may be fed into an extruder.
Next, the resin composition melted by the extruder is connected to a mouthpiece such as a T-die at the tip of the extruder, molded into a sheet, and then cooled and solidified by cooling rolls. The extrusion temperature is preferably about 180 to 260°C, more preferably 190 to 250°C.

As a detailed example of the stretching method of the unstretched sheet, roll stretching in the sheet flow direction (longitudinal direction, MD), tenter stretching in the direction perpendicular to the sheet flow direction (transverse direction, TD), etc. Biaxial stretching is preferred. Further, after stretching in the longitudinal direction, the film may be stretched in the horizontal direction, or after stretching in the horizontal direction, it may be stretched in the vertical direction. In addition, as long as the film is stretched in the longitudinal direction and the transverse direction, it may be stretched twice or more in the same direction. Furthermore, after stretching in the longitudinal direction, the film may be stretched in the transverse direction and then further stretched in the longitudinal direction. Alternatively, the film may be stretched simultaneously in the machine direction and the transverse direction by a simultaneous biaxial stretching machine. Furthermore, an unstretched sheet may be cut and biaxially stretched by a batch-type stretching machine.

The draw ratio of the biaxially stretched sheet is preferably 1.1 times or more and 4.0 times or less in both the longitudinal direction and the transverse direction of the sheet, more preferably 1.5 times or more and 3.0 times or less, and 2.0 times or more2. 0.5 times or less is more preferable. When the draw ratio is 1.1 times or more, the molded article formed by molding the sheet has sufficient impact strength, and when it is 4.0 times or less, the shapeability and mold reproducibility when thermoforming the sheet are improved. .
The draw ratio in the present invention is obtained by drawing a straight line on a test piece of a biaxially stretched sheet, heat shrinking the straight line, and calculating the rate of change in the length of the straight line before and after shrinkage. Specifically, it is a value calculated by the formula [stretch ratio = Y / Z], in which Y is a test piece of a biaxially stretched sheet with a ruler and a writing utensil. The length (mm) of the straight line drawn in the direction, Z is the test piece was immersed in a silicone oil bath at a temperature 40 ° C higher than the Vicat softening temperature of the sheet measured in accordance with JIS K7206 for 10 minutes and contracted. is the length (mm) of the straight line after

(Thickness of the sheet of the present invention)
The thickness of the sheet of the present invention is preferably 0.05 mm or more and 0.50 mm or less. Within such a range, handling in the secondary processing step of producing a molded article such as a package becomes easy, and the molded article has sufficient mechanical strength. The lower limit is more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. The upper limit is more preferably 0.40 mm or less, still more preferably 0.30 mm or less.

<Package>
The sheet of the present invention can be molded and used as a package.
The package is used after being molded into a shape suitable for various uses. For example, it is used as a package for housing foods such as fresh foods, side dishes, dried foods, confectionery, and industrial parts, and its shape includes box-bottom containers, cups, plates, trays, containers with lids, lids, and the like. Since the sheet of the present invention has both anti-fogging properties and oil resistance by having a coating layer, it is possible to heat refrigerated and frozen foods containing oil such as lunch boxes, gratin, pasta, and fried foods in a microwave oven together with the packaging container. It is suitably used as a packaging container for use in applications such as In addition, the package is formed so that the coating layer side faces the food.
The sheet of the present invention can be molded by known methods. For example, hot plate contact heating molding method, pressure molding method, vacuum molding method, vacuum pressure molding method, plug assist molding method, and the like. Among them, the hot plate contact heating molding method is preferable from the viewpoint of the uniformity of the thickness of the molded product and the efficiency of molding production. The sheet forming process may be performed continuously using a sheet roll, or may be formed for each shot using a cut plate sheet.

In the case of the hot plate contact heating molding method, the hot plate temperature, which is the lower limit of the hot plate temperature conditions, is preferably the Vicat softening temperature of the sheet + 10 ° C. or higher from the viewpoint of the mold reproducibility of the molded product and the molding cycle efficiency, and +15 ° C. or higher. is more preferable, and +20° C. or higher is even more preferable. The hot plate temperature, which is the upper limit, is preferably the Vicat softening temperature of the sheet +45° C. or less, more preferably +40° C. or less, and even more preferably +35° C. or less, from the viewpoint of occurrence of raindrops on the molded product.
The heating time conditions for the various molding methods described above are preferably 0.5 to 10.0 seconds, more preferably 0.5 to 5.0 seconds. The heating time is the time during which the sheet is brought into contact with the hot plate in vacuum and/or compressed air, and the delay time until the desired vacuum and/or compressed air state is reached in order to spread the sheet to the mold. Say the total.

<Examples 1 to 3, Comparative Examples 1 to 10>
(Preparation of oil-resistant styrene-based resin sheet)
A single layer biaxially oriented polystyrene resin sheet with a thickness of 0.25 mm produced using styrene homopolymer GPPS resin pellets having a weight average molecular weight of 250,000, a melt flow rate of 3.5 g/10 minutes, and a glass transition temperature of 100°C. One surface was subjected to corona treatment, an aqueous coating liquid for a coating layer was applied with a spray coater, and dried with hot air to form a coating layer, thereby obtaining an oil-resistant styrene-based resin sheet.
Table 1 shows the solid content composition of the coating layer.
The layer thickness of the coating layer is calculated using an infrared absorption spectrometer (total reflection method), using the absorption peak intensity near 1720 cm ^-1 , and calculating the ratio of the absorption peak intensity near 1490 cm ^-1 of polystyrene, The layer thickness of each layer was determined by referring to a calibration curve prepared from a sheet having a known layer thickness. The layer thickness of the covering layer was 100 nm.

(coating layer)
Abbreviations, components, and physical properties of the raw materials used in the coating layers of Examples and Comparative Examples are as follows.
PVA1; sulfo group-containing polyvinyl alcohol, sulfo group content 2.6 mol%, degree of saponification 86.5 to 89.0 mol%, degree of polymerization 200
PVA2; polyvinyl alcohol, sulfo group content 0 mol%, degree of saponification 86.5 to 89.0 mol%, degree of polymerization 500
PVA3; polyvinyl alcohol, sulfo group content 0 mol%, degree of saponification 86.5 to 89.0 mol%, degree of polymerization 1,700
PVA4; Polyvinyl alcohol, sulfo group content 0 mol%, degree of saponification about 99 mol%, degree of polymerization 1,100

PEs1; polyester, sulfo group content 14 mol%, acid value less than 5 mgKOH/g, weight average molecular weight 14,000
PEs2; polyester, sulfo group content 10 mol%, acid value less than 5 mgKOH/g, weight average molecular weight 27,000
PEs3; polyester, sulfo group content 0 mol%, acid value 40-55 mgKOH/g, weight average molecular weight 3,000

Antifog agent; diglycerin fatty acid ester, HLB8.7

<Evaluation>
The oil-resistant styrene resin sheets obtained in Examples and Comparative Examples were evaluated as follows, and the results are summarized in Tables 1 and 2.
(Oil resistance)
The resulting sheet was cut into 10 cm squares, 0.5 g of medium-chain fatty acid oil (MCT oil manufactured by Nisshin OilliO Group) was applied to the entire surface of the coating layer, and allowed to stand in a constant temperature bath at 80° C. for 5 minutes. Immediately after heating, the appearance was visually observed and evaluated according to the following criteria.
○: No whitening at all △: Slight whitening ×: Clear whitening

(Anti-fogging property)
The resulting sheet was cut into 10 cm squares, covered with a 500 mL plastic cup containing 300 g of water at 80° C. with the coating layer side facing the plastic cup, and allowed to stand for 2 minutes. Characters of font size 10.5 on printed paper placed under the plastic cup were visually identified and evaluated according to the following criteria.
◎ : Characters can be clearly identified even in detail ○ : Characters can be clearly identified without shaking △ : Characters can be identified with slight fluctuation × : Characters fluctuate a lot and are difficult to see ×× : The entire surface is cloudy characters cannot be seen when

(transparency)
It was measured using a haze meter (NDH7000II machine manufactured by Nippon Denshoku Industries Co., Ltd.) and evaluated according to the following criteria.
○: Less than 1.5% haze ×: 1.5% or more haze

(Return property)
200 g of the resulting sheet was cut into 1 cm squares to form fluff, simulating the process of producing fluff from sheet scraps using a crusher in production. This fluff and 200 g of GPPS resin pellets made of a new styrene homopolymer were thoroughly mixed to prepare an extruded raw material having a mixing mass ratio of 50:50 (return rate of 50%). This raw material is melt extruded using a tubular extruder with a diameter of 20 mm under the conditions of a barrel temperature of 200 ° C. and an extruder rotation speed of 40 rpm, and then air is blown into the extruded cylindrical resin to expand it. A 0.01 mm film was taken. The film was observed per 100 cm square (area of 1 m ² ), and the number of gels (unmelted matter) with a diameter of 0.2 mm or more was counted and evaluated according to the following criteria. The number of gels that were evaluated as "◯" is indicated in the table.
○: 35 or less △: More than 35 and less than or equal to 60 ×: More than 60

Example 1 uses a sulfo group-containing polyvinyl alcohol and an antifogging agent in the coating layer, and exhibits good oil resistance, antifogging properties, transparency, and return properties. The number of gels evaluated was as small as 16, which was good. Comparative Example 3 used a sulfo group-containing polyvinyl alcohol and had good return properties, but did not contain an antifogging agent and lacked antifogging properties.

Comparative Examples 1 and 2 used polyvinyl alcohol containing no sulfo group and an antifogging agent, and were insufficient in oil resistance, antifogging property, and return property. Oil resistance was obtained in Comparative Examples 4 to 6 using only polyvinyl alcohol with a high degree of saponification without containing a sulfo group, whereas oil resistance was obtained in Comparative Examples 1 and 2 in which an antifogging agent was added to the same polyvinyl alcohol. decreased, and the anti-fogging property was insufficient. Furthermore, these polyvinyl alcohols had a degree of saponification of 85 mol % or more, a remarkably poor return property, and 200 or more gels.

Examples 2 and 3 used a sulfo group-containing polyester and an antifogging agent, and had good oil resistance, antifogging properties, transparency, and return properties. Comparative Examples 8 and 9 used only the sulfo group-containing polyester, and had insufficient antifogging properties and insufficient return properties.
Comparative Example 7 used a sulfo group-free polyester exhibiting hydrophilicity due to a carboxyl group and an antifogging agent, and had insufficient oil resistance and antifogging properties. Comparative Example 10 used only polyester showing hydrophilicity due to carboxyl groups, and had poor oil resistance and remarkably poor antifogging properties.

According to the present invention, a heat-resistant styrene-based resin sheet having both anti-fogging properties and heat-resistant oil resistance can be obtained. and is suitable for the recent diet, food industry, and distribution industry.
In addition, when the offcuts in the manufacturing process of the heat-resistant styrenic resin sheet of the present invention are reused as a raw material, gel foreign matter is less likely to occur. It can be reused (returned) as it is, and has good productivity and economic efficiency.

Claims (7)

A styrene resin sheet having a coating layer on at least one surface,
The coating layer contains a sulfo group-containing polymer (A) and an antifogging agent (B),
When the total solid content of the sulfo group-containing polymer (A) and the antifogging agent (B) is 100% by mass, the sulfo group-containing polymer (A) is 50% by mass or more and 95% by mass or less, An oil-resistant styrenic resin sheet containing 5% by mass or more and 50% by mass of an antifogging agent (B). 2. The oil-resistant styrenic resin sheet according to claim 1, wherein the sulfo group-containing polymer (A) has a sulfo group content of 0.1 mol % or more and 40 mol % or less. 3. The sulfo group-containing polymer (A) according to claim 1 or 2, which is one or more selected from the group consisting of polyvinyl alcohol, polyester, poly(meth)acrylic ester, and poly(meth)acrylic acid (salt). Oil-resistant styrene resin sheet. The oil-resistant styrene resin sheet according to any one of claims 1 to 3, wherein the coating layer has a thickness of 30 to 300 nm. The oil-resistant styrenic resin sheet according to any one of claims 1 to 4, wherein the antifog agent (B) is sucrose fatty acid ester and/or polyglycerin fatty acid ester. The oil-resistant styrene resin sheet according to any one of claims 1 to 5, which is a biaxially oriented sheet. A package comprising the oil-resistant styrenic resin sheet according to any one of claims 1 to 6.