JP3516640B2 - Styrene resin sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is mainly formed by secondary molding by means such as vacuum forming, pressure air vacuum forming, hot plate pressure air forming, and the like.
The present invention relates to a styrene resin sheet used for lightweight food packaging containers and other various containers. More specifically, the present invention relates to a transparent styrene-based resin sheet having excellent antifogging properties, releasability, and releasability of a sheet and a molded container thereof and having little triboelectricity during molding.

[0002]

2. Description of the Related Art Stretched styrenic resin sheets, typified by biaxially stretched polystyrene resin sheets, are used for various thermoforming methods such as hot plate heating pressure forming, radiation heating vacuum forming, and pressure forming. Molded by the plate heating type pressure molding method, it is widely used as various molded containers such as food packaging applications. These styrene-based resin sheet molded containers, especially food packaging containers, have a surfactant applied to the inside of the molded product as an anti-fog agent (anti-fog agent) for the container, and the mold releasability from the mold of the molding machine and the molded product. In order to give a peeling property to each other,
It is common to apply a silicone oil as a release agent in a mixture with the antifogging agent or on the surface opposite to the antifogging agent,
Various techniques have been developed.

For example, Japanese Patent Publication No. 63-62538.
JP-A-5-287097 describes a method of applying a mixture containing sucrose fatty acid ester and silicone oil (emulsion) as main components to a biaxially oriented polystyrene sheet. Further, Japanese Patent Application Laid-Open No. 9-295384 proposes a styrene resin sheet roll having one surface coated with an antifogging agent and the other surface coated with silicone oil as a release agent. Further, as a method for improving the antifogging property of a polystyrene-based biaxially stretched sheet, a method of using polyglycerin fatty acid ester alone or in mixture is disclosed in JP-A-9-
No. 12751, Japanese Patent Laid-Open No. 11-166061,
JP-A-11-277688, JP-A-11-300
No. 904, etc. Also in these methods, when used as a thermoforming sheet, in order to impart releasability and releasability as well as antifogging property, silicone oil is mixed with an antifogging agent as a releasing agent, or applied. It is described that it is preferable to use a sheet in which is coated on the opposite surface.

As described above, most of the styrene resin sheets are a mixture of an antifogging agent and silicone oil as a releasing agent, or an antifogging agent on one side, in order to impart antifogging property, releasing property and releasability. A silicone oil is applied on the opposite side of the agent as a release agent, which is rolled into a roll and is commercially available. As a silicone oil, dimethylpolysiloxane is used in most sheets because of its safety and economy. A sheet to which silicone oil is not applied causes problems such as deterioration of mold releasability between a mold and a sheet at the time of molding, and deterioration of peelability between molded products when sheet molded products are stacked,
Although it is not practical for molding, it is the current situation.

[0005]

However, styrene coated with a mixture of the above-mentioned antifogging agent (sucrose fatty acid ester, polyglycerin fatty acid ester, a mixture thereof, etc.) and silicone oil (dimethylpolysiloxane). Molded containers obtained from styrene resin sheets or styrene resin sheets coated with antifogging agent on one side and silicone oil on the other side cannot be said to completely meet the level of antifogging requirements on the market. is there. Anti-fog performance required in the market for packaging containers, especially food packaging containers, refers to anti-fog properties against water vapor when high-temperature contents are packaged (high-temperature anti-fog properties), contents such as food containing water. Anti-fogging property against condensation (low-temperature anti-fog property) when packed and stored in a refrigerator, and also against contents that are heated after refrigeration, both against condensation and water vapor, and has anti-fog performance. It must be maintained immediately after packaging until the contents are consumed. The required level is increasing with the improvement of the level of anti-fogging technology in the packaging sheet and film industry as a whole. However, it has been pointed out that the molded product of the styrene-based resin sheet generally has a low-temperature anti-fog property level and its durability are lower than those of other materials such as packaging sheets and films. Insufficient antifogging property of the molded product of styrene resin sheet, the antifogging property deterioration is remarkable especially at low temperature in a molding container having a deep drawing ratio, and sucrose fatty acid ester, polyglycerin fatty acid ester, and these as an antifogging agent. This is a phenomenon observed when any of the above mixtures is used.

In addition, the above-mentioned known sheet generally has a drawback that static electricity is easily generated due to friction between the mold and the sheet during molding of the container. An object of the present invention is to supply a transparent styrene-based stretched sheet that retains mold releasability during molding, has improved practical antifogging properties, and suppresses triboelectric charging during molding, that is, a styrene-based resin sheet. A molding machine with excellent initial anti-fog level at low temperature and improved durability, and excellent initial anti-fog property at high temperature and continuous anti-fog property even in molded containers, especially molded products with large drawing ratio. It is an object of the present invention to provide a styrene-based resin sheet that has good mold releasability from a mold and releasability between molded products and that generates little static electricity during molding.

[0007]

Means for Solving the Problems As a result of investigations for achieving the above-mentioned object, the present inventors have found that the deterioration of anti-fogging property of a styrene resin sheet is as described in, for example, Japanese Patent Publication No. 63-62538. In the case of a sheet using a mixture of an antifogging agent and silicone oil (dimethylpolysiloxane), sucrose fatty acid ester which is an antifogging agent and silicone oil (dimethylpolysiloxane) having no antifogging effect are mixed. A marked decrease in anti-fog property is observed. Also, for example,
When an antifog agent such as sucrose fatty acid ester or polyglycerin fatty acid ester is applied on one side and silicone oil (dimethylpolysiloxane) is applied on the other side as described in JP-A-9-295384, the roll is used. Although the sheet before being wound into a sheet has an excellent anti-fogging effect, it has a drawback that the anti-fogging property is deteriorated only by winding it on a roll and aging (storing) it for about one day. In the sheet roll, normally, 35% or more of the dimethylpolysiloxane coated on the release surface is transferred to the antifogging surface, which adversely affects the antifogging property (transfer of dimethylpolysiloxane adversely affects the antifogging property. It is very difficult at present to suppress it to a level that does not give).

That is, according to the present invention, a styrene resin sheet having one surface coated with an antifogging agent and the opposite surface coated with a release agent is used. at least one selected from glycerol fatty acid esters is 5 to 30 mg / m ² coating, as a release agent, is characterized in that ether-based multimer is 3 to 30 mg / m ² coating. Another feature is that the ether polymer is selected from polyoxyethylene polyoxypropylene block copolymer and polyethylene glycol. Another feature is that the styrene resin sheet is a biaxially stretched styrene resin sheet.

The present invention will be described in detail below. The present invention is
It was found that the conventionally known anti-fogging property of the styrene-based resin shaft sheet coated with a releasing agent is attributed to the silicone oil coated to give the sheet releasing property and releasability. As a result of various investigations based on the findings, various improvements in the release agent of the styrene resin sheet that do not adversely affect the antifogging property have been achieved. The feature of the present invention resides in that the improvement of the antifogging property of the sheet is achieved mainly by the release agent which forms the coating film on the opposite surface of the antifogging agent. That is, by using an ether-based multimer as a mold release agent, it is possible to maintain the antifogging performance of the sheet and the molded article at a high level, to impart mold releasability and releasability, and further to impart antistatic property. It was done. First, the coating film on the release surface, which is the greatest feature of the sheet of the present invention, will be described. The ether-based polymer forming a coating film on the release surface of the present invention is a condensation reaction product of a polyhydric alcohol such as ethylene glycol, propylene glycol and glycerin, addition of alkylene oxide such as ethylene oxide and propylene oxide. A multimer (a dimer such as a reactant or a copolymer thereof) in which a polyhydric alcohol or an alkylene oxide is used as a monomer unit and two or more monomer units are linked by one or more ether bonds. Body and above).

Preferred ether-based multimers include, for example:
Examples thereof include polyglycerin (diglycerin or more), polyethylene glycol, polypropylene glycol, and polyoxyethylene polyoxypropylene block copolymer. Among these, polyoxyethylene polyoxypropylene block copolymer and polyethylene glycol are particularly preferable. Ether-based multimers selected from polyoxyethylene-polyoxypropylene block copolymers or polyethylene glycols are used to produce sheets with a better appearance (transparency, gloss) than conventional silicone-oil (dimethylpolysiloxane) coated sheets. In many cases, it is particularly preferable.

The polyoxyethylene-polyoxypropylene block copolymer which can be particularly preferably used in the sheet of the present invention is a block copolymer obtained by addition-polymerizing ethylene oxide to a polyoxyethylene chain obtained by addition-polymerizing propylene oxide. Polymer with a molecular weight of 2
A block copolymer of 000 to 20000 is preferable, more preferably 3000 to 18000, and further preferably 4000 to 18000.

The preferred molecular weight is within the range determined by the releasability, releasability of the sheet secondary molded product and the appearance and transparency of the sheet. When the molecular weight is less than 2000, depending on the shape of the sheet secondary molded product, This is an area where sufficient releasability and releasability may not be obtained, and when the molecular weight exceeds 20,000, the dried and solidified coating film may aggregate and whiten, impairing the appearance of the sheet. Further, the block shape of the polyoxyethylene polyoxypropylene block copolymer has a polyoxyethylene polyoxypropylene block copolymer shape of polyoxyethylene from the viewpoint of the performance as a release agent when the coating film is formed on the sheet and the ease of manufacturing the block copolymer. A block copolymer composed of three blocks of ethylene block-polyoxypropylene block-polyoxyethylene block is preferable.

The block copolymer preferably has a polyoxyethylene chain of 50% by weight or more, more preferably 60% by weight or more. Among them, a polyoxyethylene polyoxypropylene block copolymer having a polyoxyethylene content of 60 to 90% by weight has an effect of slightly improving antifogging performance when transferred to an antifogging surface, and has slipperiness and separation of a sheet. This is a particularly preferable ether-based multimer because the moldability can be highly improved. In the case of a block copolymer having a polyoxyethylene chain of less than 50% by weight, when the release agent film is formed by coating with an aqueous solution, the water solubility is decreased, so that the uniformity of the coating film is decreased and sufficient release is achieved. Properties and antistatic properties are difficult to obtain, and the appearance of the sheet tends to deteriorate. Further, a polyethylene glycol having a polyoxyethylene chain of 100% by weight is a polyethylene glycol which can be preferably used in both the block copolymer and the present invention.
Therefore, the preferable upper limit is 100%.

Polyethylene glycol, which can be particularly preferably used in the sheet of the present invention, is obtained by adding ethylene oxide to ethylene glycol or water, and preferably has a molecular weight of 1,000 to 20,000, more preferably 2,000 to 16,000. More preferably 25
It is 00 to 15000. The preferred molecular weight is within the range determined by the stickiness of the sheet, the releasability of the secondary molded product, the releasability, the appearance of the sheet, and the transparency. When it is less than 1,000, the sheet tends to be sticky and the sheet is sufficiently slipped. If the molecular weight exceeds 20,000, the dried and solidified coating film may aggregate and whiten, impairing the appearance of the sheet. Polyethylene glycol can be expected to have the same effect as the above polyoxyethylene polypropylene block copolymer having 60 to 90% by weight of polyoxyethylene chain.

[0015] These include polyoxyethylene polyoxypropylene block copolymers or polyethylene glycol, Ru suitably usable der as a mixed composition alone or other ethereal multimers. The coating amount of the releasing agent composed of such an ether-based polymer is preferably 3 to 30 mg / m ² on the surface opposite to the surface coated with the antifog agent described below. The preferable coating amount is a region determined from the viewpoint of imparting releasability and releasability of the sheet and the secondary molded product and stickiness. When the coating amount is less than 3 mg / m ² , the sheet and the secondary molding are formed. It is a value at which it is difficult to impart sufficient releasability and releasability of the product, and when it exceeds 30 mg / m ² , stickiness may occur on the sheet and blocking may occur. In addition, the general coating type antistatic agent generally improves the antistatic property as the coating amount increases, but the ether-based polymer release agent used in the present invention has a coating amount of 7 to 7. In most cases, the optimum value of antistatic property is around 15 mg / m ² (slightly different depending on the type of ether-based polymer). Therefore, from the viewpoint of imparting the antistatic property of the sheet, the coating amount of the releasing agent composed of the ether-based polymer is more preferably 3 to 20 mg / m ² , and further preferably 5 to 17 mg / m ² . Good to do.

The quantitative analysis of the coating amount of the ether-based multimer is
The sheet / film is washed, the washing liquid is collected, and the method is carried out by a weight method, a gas chromatography method, a high performance liquid chromatography method or the like, or a calibration curve is prepared using a sheet having a known coating amount as a standard sample, and the FTIR (ATR method is used. ), The sheet surface can be directly analyzed. Since strong infrared absorption by the ester group is observed in the ether-based multimer, quantification by FTIR (ATR method) is particularly preferable because it is simple and accurate.

It is also possible to add a polyether-modified silicone oil in order to enhance the effect of the releasing agent composed of the above-mentioned ether-based polymer. The polyether modified silicone oil is a modified silicone in which a polyether group is introduced into the skeleton of polysiloxane that constitutes the silicone oil. Among these, the preferred polyether-modified silicone is a copolymer in which at least one methyl group or phenyl group of a dimethylpolysiloxane or diphenylpolysiloxane unit is modified with a polyoxyalkylene unit and is represented by the following general formula 1. It is a water-soluble polyether-modified silicone oil.

[0018]

[Chemical 1]

(Wherein R is a methyl group or a phenyl group, R is
¹ is the following formula 2, R ² is a methyl group, a phenyl group or a chemical formula 2
And m is an integer of 0 to 400, n is an integer of 1 to 300, m + n is an integer of 1 to 500, and n / (n + m) is
0.1-1)

[0020]

[Chemical 2]

(R ³ is hydrogen, a C ₁ -C ₄ alkyl group or a phenyl group, a is an integer of 1-6, b is an integer of 1-50, c is an integer of 0-50, and b / c is Ratio is 100/0
50/50)

In the preferred general formulas 1 and 2 of the above polyether silicone oil, n, m, a, b, c
The value of does not cause deterioration of the antifogging property even when the silicone oil is transferred onto the antifogging agent when used in combination with the releasing agent formulation of the present invention, and exerts a synergistic effect as a releasing agent. This is the value specified for

Of the polyether silicone oils represented by the above formulas 1 and 2, more preferably, the viscosity at 25 ° C. is 100 to 5000 sc, and 50 to 85% by weight is a water-soluble polyether modified with a polyether group. It is an ether-modified silicone oil. These polyether-modified silicone oils are based on 100 parts by weight of the ether-based polymer.
By mixing 5 to 80 parts by weight, it becomes possible to impart releasability, sheet slipping property, antistatic property and releasability of a molded article to a high degree without deteriorating the antifogging property of the sheet.

The water-insoluble silicone oil such as dimethylpolysiloxane and diphenylpolysiloxane is
It is not preferable to use them in the sheet of the present invention, because when they are transferred onto the antifogging agent coating film, the antifogging property is lowered. Next, the antifogging agent that constitutes the sheet of the present invention will be described. In the present invention, the antifogging agent is preferably at least one selected from sucrose fatty acid esters or polyglycerin fatty acid esters.

The sucrose fatty acid esters may be used alone or in combination of two or more.
HLB containing a C ₁₀ -C ₂₀ fatty acid component as a main component is 11
More preferably about 18 to 18 sucrose fatty acid esters,
More preferably, the HLB containing sucrose lauric acid monoester as a main component (50% by weight or more) is about 13 to 17. The fatty acid component and HLB constituting the preferred sucrose fatty acid ester are determined by the water solubility and the persistence of antifogging property when the sucrose fatty acid ester is applied as an aqueous solution, and the sucrose fatty acid ester having a fatty acid exceeding C ₂₀ as a main component is used. When a sugar fatty acid ester or a sucrose fatty acid ester having an HLB of less than 11 is used as a main component, the high temperature antifogging property tends to decrease, and the water solubility also decreases, which is a region where application becomes difficult. . Further, a sheet coated with a sucrose fatty acid ester having a fatty acid of less than C _{10 as a} main component or a sucrose fatty acid ester having a HLB of more than 18 as a main component has low-temperature anti-fog properties, Furthermore, the high temperature antifogging property tends to be less durable.

The polyglycerin fatty acid esters may be used alone or in combination of two or more, but the degree of polymerization of the polyglycerin constituting the polyglycerin fatty acid esters is high. HLB containing 6 to 10 and polyglycerin fatty acid esters in which the number of carbon atoms of the fatty acid is C _{10 to} C ₂₀ (50% by weight or more in total) is 11 to 11
About 18 are preferable, and more preferably, hexaglycerin laurate, decaglycerin laurate, hexaglyceryl myristate, decaglycerin myristate, hexaglycerin palmitate, decaglycerin palmitate, decaglycerin stearin. Acid ester,
Decaglycerin oleate (all monoester ratio is 50 mol% or more) alone or as a main component (50
HLB of about 13 to 17% by weight).

Like the sucrose fatty acid esters, the structure of these polyglycerin fatty acid esters, HLB, is the water solubility when the polyglycerin fatty acid esters are applied as an aqueous solution, the durability of the antifogging property, the high temperature antifogging and the low temperature. It is a region determined by the balance with anti-fogging, and the number of carbon atoms of the fatty acid constituting the polyglycerin fatty acid ester exceeds 20, the degree of polymerization of glycerin is less than 6, or the HLB is 11
When the main component is less than polyglycerin fatty acid esters, the antifogging property at high temperature tends to decrease, and the water solubility decreases, so that it is possible to form a uniform antifogging coating film on the sheet. This is a difficult area. In addition, the carbon number of the fatty acid constituting the polyglycerin fatty acid ester is less than 10,
The degree of polymerization of glycerin exceeds 10, or HLB is 1
When the polyglycerin fatty acid ester of more than 8 is contained as a main component, the low temperature anti-fog property and the high temperature anti-fog property tend to be deteriorated in sustainability.

The sucrose fatty acid ester and the polyglycerin fatty acid ester may be used in a mixture at an arbitrary ratio, and in this case, the low-temperature anti-fog property and the high-temperature anti-fog property are more balanced, which is preferable. is there. A particularly preferred combination is HL containing sucrose laurate as a main component.
Sucrose fatty acid esters in which B is 14 to 17 and polyglycerin fatty acid esters in which HLB containing hexaglycerin or decaglycerin lauric acid ester as a main component is 12 to 15 are combined. Is more preferably 10 to 90% by weight, more preferably 15 to
70% by weight, more preferably 20 to 50% by weight of a mixture.

Generally, commercially available sucrose fatty acid esters and polyglycerin fatty acid esters are a mixture of several kinds of constituent fatty acids and a mixture of monoester, diester, triester and the like. As the sucrose fatty acid ester and the polyglycerin fatty acid ester used in the present invention, such a generally commercially available mixture may be used as long as the above-mentioned conditions are satisfied.

These antifogging agents are added to one surface of the sheet in an amount of 5 to 5.
30 mg / m ² is preferable, more preferably 7 to 27 mg / m ² , and further preferably 9 to 23 mg.
/ M ² . The coating amount is a region determined from the viewpoints of imparting low-temperature anti-fogging property and high-temperature anti-fogging property, suppressing stickiness and blocking of the sheet and keeping a good appearance of the sheet, and when the coating amount is 5 mg / m ² , It tends to be difficult to impart sufficient antifogging performance, and when it exceeds 30 mg / m ² , stickiness or blocking of the sheet is likely to occur, and when it exceeds the upper limit, the appearance of the sheet deteriorates due to whitening. This is an area in which can occur. When the sheet of the present invention is used as a non-molding packaging sheet,
Since there is no stretching of the anti-fog agent coating film by secondary molding,
Sufficient effect can be obtained with a small amount of antifogging agent. Therefore, when used as a non-molding packaging sheet, 5 mg / m ²
A coating amount of 20 mg / m ² or less is preferable. 20 mg
The coating amount of / m ² is a value at which the effect of improving the antifogging property reaches almost saturation when used for non-molding.

Quantitative analysis of the coating amount of the antifogging agent is carried out by washing the sheet / film, collecting the washing liquid, and carrying out by a gravimetric method, a gas chromatography method, a high performance liquid chromatography method, or a sheet having a known coating amount. Is used as a standard sample to prepare a calibration curve, and the sheet surface is directly analyzed by FTIR (ATR method). The HLB value is Griff
in the case of fatty acid ester of polyhydric alcohol of in, HLB = 20 (1-S / A) (where S is the saponification value of the ester, A is the fatty acid value), It is determined by the method described in "Sugar Ester Monogatari (1984)", 56-57, published by Ichikohyo Pharmaceutical Co., Ltd.

As the antifogging agent, water-soluble polymers such as polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, sodium polyphosphate, and polyphosphoric acid K as an antifogging property improver, and hardness modification of the antifogging agent. As the agent, methylcellulose, carbomethoxycellulose or the like is used as the antifogging agent 100 described above.
1 to 40 parts by weight may be added to parts by weight.
Of these, in particular, when polyvinyl alcohol is added, the antifogging durability is further improved, which may be preferable.
The polyvinyl alcohol added is a 4% aqueous solution,
The viscosity at 25 ° C is preferably 3 to 10 mPa · s and the saponification degree is 60 to 80 mol%, more preferably 4 to 8 mPa · s, and the saponification degree is 65 to 75 mol%. The range of the viscosity and saponification degree of polyvinyl alcohol is a preferable range for further improving antifogging durability, and when the saponification degree or the viscosity exceeds the upper limit,
When the amount is less than the lower limit, not only is the anti-fogging sustainability improving effect hardly obtained, but in some cases, the anti-fogging property may be adversely affected.

It is also possible to add the above polyether-modified silicone oil in an amount of 50 parts by weight or less based on 100 parts by weight of the antifogging agent (A). In this case, the releasability, the releasability, the slipperiness of the sheet and the like are further improved, which may be preferable. However, 50% polyether modified silicone oil
When it exceeds the weight part, the antifogging property tends to be deteriorated, which is not preferable. The sheet of the present invention, that is, the sheet characterized in that one surface described above is coated with an antifogging agent, and the opposite surface is coated with an ether-based multimer as a release agent, is excellent in antifogging property, and is a sheet. Further, there are advantages that the secondary molded product of the sheet is excellent in releasability and releasability and less charged during molding. Therefore, for example, when the sheet of the present invention is molded into a fitting deep-drawing lid material, the peelability from the mold at the time of molding is good, the amount of static electricity generated at the time of molding is small, and high temperature anti-fog properties and low temperature protection A molded product having excellent haze can be obtained. On the other hand, the sheet coated with silicone oil (silicone emulsion) as a release agent of the prior art (Comparative Example 1) has a silicone oil transferred to the anti-fog surface when the sheet is wound into a roll, The obtained molded product is remarkably deteriorated in antifogging property, particularly low temperature antifogging property. Further, the sheet (Comparative Example 4) having one surface coated with the antifogging agent and the other surface not coated (Comparative Example 4) has good antifogging property but poor releasability at the time of molding, which makes continuous molding difficult. Further, there is a serious problem in practical use due to strong charging during molding.

Further, when other generally known surfactants are applied to the release surface (for example, Comparative Examples 6 to 8), the release property and slipperiness of the sheet are not sufficiently obtained, which is not practical. is there. As described above, the sheet of the present invention has an antifogging property and a molding time which cannot be achieved by the conventional technique because the surface opposite to the surface coated with the antifogging agent is coated with the ether type polymer as a release agent. The releasability is balanced, and the antistatic property is excellent.

The sheet of the present invention is a sheet in which the above-mentioned components are coated on the anti-fog surface and the release surface, respectively. However, when the sheet is wound into a roll which is a general commercial product, The release agent may be transferred onto the cloudy surface, or the antifogging agent may be transferred onto the release surface. In the case of the sheet of the present invention, this transfer amount is usually less than 30% of the initially formed coating film, and in most cases less than 20% (the release agent formulation of the sheet of the present invention generally has a higher viscosity than silicone oil). Because
It is a sheet coated with a general silicone oil (in most cases, it is presumed that the transfer rate is lower than that of the silicone oil transferred by 35 to 50%), and does not impair the characteristics of the sheet of the present invention. Therefore, a sheet in which a part of these coating films is transferred to the opposite surface does not impair the characteristics of the present invention (in the transferred sheet, the antifogging agent on the antifogging surface and the release agent on the releasing surface are The case where the coating amount is within the range of the present invention) is included in the present invention.

The method for producing the sheet of the present invention is not particularly limited. For example, a generally known styrene resin sheet, preferably a styrene resin uniaxially or biaxially stretched by a known method such as a tenter method or a bubble method. A sheet, more preferably a biaxially stretched styrenic resin sheet, has one surface provided with a squeeze roll coater, an air knife coater, a knife coater, a spray coater, a gravure roll coater, and a hand coater. After applying and drying by a known method such as the above, an aqueous solution of a release agent is applied and dried on the opposite surface by the same method. The antifogging agent and the release agent may be applied in the reverse order. The drying is not particularly limited, but a hot air dryer is generally used.

From the viewpoint of improving the uniformity of the coating film, it is preferable to apply the antifogging agent or the releasing agent by the above method after the corona treatment of the sheet surface. For example, when applied to a stretched styrene resin sheet, the surface of the sheet is subjected to corona treatment so that the contact angle with water is 80 to 30 °, and then the antifogging agent or polyoxyethylene is applied by the above method or the like. It is often preferable to apply the polyoxypropylene block copolymer because the coating film becomes uniform. The upper limit of the contact angle with water is a value for improving the uniformity of the coating film, and the lower limit of the contact angle is a value for preventing blocking when the sheet is rolled. In particular, it is more preferable that the coated surface of the antifogging agent has a contact angle with water of 50 to 35 ° from the viewpoint of imparting a high antifogging property.
Further, the polyoxyethylene polyoxypropylene block copolymer coated surface prevents blocking of the sheet,
From the viewpoint of forming a uniform coating film, the contact angle with water is more preferably 75 to 50 °.

Further, in consideration of the transfer of the antifogging agent coating film and the release agent coating film after the sheet is wound into a roll, a preferred example of producing the sheet of the present invention is as follows. is there. When considering transfer, compare the viscosities of the antifogging agent and the release agent in the dry state, and set the coating agent on the low viscosity side so that it covers 5 to 30% more than the target coating amount. It is important to apply by the method described above. Further, the coating sheet is sufficiently dried with a hot air dryer (dried under the condition that the energy required for evaporating all the coated moisture is applied), and then 98 to 392 N / m.
The sheet is preferably wound into a sheet roll with a winding tension of a width, preferably 147 to 294 N / m width.
The take-up tension of the sheet and the width of 98 to 392 N / m are in a preferable range so that there is no winding deviation of the roll, excessive transfer is suppressed, and a sheet roll with less transfer unevenness can be obtained.

The styrene resin constituting the sheet of the present invention includes homopolymers of styrene monomers selected from styrene, alkylstyrenes, halogenated styrenes and the like, copolymers thereof, and conjugated diene (butadiene). , Isoprene, etc.), a block of a rubber component such as styrene-conjugated diene copolymer and the styrene-based monomer,
Random and graft copolymers, and block, random and graft copolymers of 50% by weight or more of the styrene-based monomer and other monomers. In addition, plasticizers such as mineral oils, terpenes, and petroleum resins can be added to these styrene resins.
Known additives such as antistatic agents and ultraviolet absorbers may be added.

Of these, preferred resins are homopolymers of styrene (GPPS), styrene-methacrylic acid copolymers, styrene-maleic anhydride copolymers, styrene-
Styrene-alkyl (meth) acrylate copolymers such as butyl (meth) arylate copolymers, ternary or quaternary copolymers composed of styrene-butyl (meth) arylate and / or methyl (meth) arylate-butadiene, and these Blend of styrene and GPPS, styrene-conjugated diene block copolymer (SBBC), SBBC and GPPS
And blends with styrene-alkyl (meth) acrylate copolymers.

The styrene-based resin sheet of the present invention may be a single-layer sheet made of the above-mentioned styrene-based resin or a known multilayer sheet containing one or more layers of the above-mentioned styrene-based resin. These sheets may be unstretched or stretched sheets, but are preferably stretched sheets, and more preferably biaxially stretched sheets. As the multilayer sheet, for example, GPPS (surface layer) / GPPS + SBBC
(Inner layer), heat-resistant styrene copolymers such as styrene-methacrylic acid copolymer (surface layer) / GPPS (inner layer), GP
PS (surface layer) / styrene-alkyl (meth) acrylate copolymers (inner layer), high molecular weight GPPS (surface layer) / medium to low molecular weight GPPS (inner layer), GPPS + SBBC (surface layer) / GPPS (inner layer), GPPS (surface layer) / Plasticization G
2 layers, 3 layers by combination of layers such as PPS (inner layer),
Alternatively, a known sheet having four or more layers can be used.

The sheet of the present invention is mainly used as a molding container obtained by secondary molding by a known thermoforming method. The thermoforming method (thermoforming machine) is not particularly limited, and generally known sheet thermoforming methods, for example, hot plate heating type pressure forming method, vacuum forming method, pressure forming method, vacuum pressure forming method, plug assist forming method. Etc. Of these, the hot plate heating type pressure forming method is the most general method for forming a stretched sheet, and when the present invention is a stretched sheet, it is preferable to perform this method. The molded container of the present invention obtained by such a method has a feature of having a good balance of high anti-fogging property and slipperiness (release property, releasability), like the sheet.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to Examples. The performance evaluation of the sheets and films in Examples and Comparative Examples was performed according to the following criteria (unless otherwise specified, "○" or higher is the passing level of the present invention). (Low temperature antifogging property) Five pieces of sushi (temperature 27 to 30 ° C.) were put in a polystyrene expanded (PSP) fitting container body (120 mm × 170 mm, depth 8 mm), and an opening 120 mm × 170 mm produced from a stretched sheet, Cover with a fitting lid with a depth of 38 mm (inside anti-fog surface) and leave it in a showcase at 5 ° C for 10 minutes (initial anti-fog), and after 24 hours (continuous anti-fog) to attach water drops. The following criteria were evaluated.

⊚: The lid of the molding container is not fogged, and the content can be seen without “haze” over an area of 90% or more of the lid of the molding container. ◯: There is no fog on the molding container lid and 76% of the molding container lid
In the area of 90% or more, the contents can be seen without "haze". Δ: There is no fogging on the lid of the molding container, but the content looks “misty” in an area of 25% or more and less than 50% of the lid of the molding container. X: The lid of the molding container is not clouded, but the content looks "misty" in an area larger than 50% of the lid of the molding container. Or, clouding occurs due to a collection of small water droplets.

(High-temperature anti-fog property) 400 ml of 90 ° C. water was put in a container having an opening of 100 mm × 100 mm and a depth of 50 mm in which a plate having 100 characters of 10.5 points in size was printed. After that, 15% of the letters placed on the bottom of the stretched sheet were covered with a molded product having an opening of 100 mm x 100 mm and a depth of 35 mm, which was manufactured by the method described below.
The time until the above cannot be identified is measured at n = 6,
The following criteria were evaluated from the average. ◎: 600 seconds or more ○: 300 seconds or more and less than 600 seconds △: 120 seconds or more and less than 300 seconds ×: less than 120 seconds

(Releasability and antistatic property at the time of molding) A continuous hot plate heating type molding machine (manufactured by Kansai Automatic Co., Ltd.) was set so that the anti-fog surface of the stretched sheet would be on the hot plate side (inside the container), and opened. Part 1
The mold releasability of a molded product when a fitting sushi lid container having a size of 20 mm × 70 mm and a depth of 38 mm was molded was evaluated according to the following criteria (a molding die having no knockout pin was used). ◎: Smoothly released from the mold at the end of molding ○: Slightly caught on the mold at the time of release, but the resulting molded container is free from scratches, whitening, etc. . Δ: The mold is caught at the time of release, and the obtained molded product has scratches, whitening, etc., and the commercial value of the obtained molded product is poor. X: The mold is caught at the time of releasing the mold, and it cannot be molded unless human beings deal with it each time (continuous molding is impossible). Further, the electrification voltage of the sheet immediately after molding was measured with a digital electrostatic potential measuring device manufactured by Kasuga Electric Co., Ltd. (23 ° C., relative humidity 40 to 50%).
Measured by). The amount of static electricity generated at this location is preferably 25 kv or less, more preferably 20 kv or less.

(Sheet slipping property) As a guideline for evaluating the releasability of a sheet and a molded product, the coefficient of dynamic friction between the release agent coated surface of the sheet and the mirror-finished stainless steel plate was measured in accordance with JIS-K-7125. It was evaluated according to the standard. ◎: Dynamic friction coefficient is less than 0.17 ○: Dynamic friction coefficient is 0.17 or more and less than 0.21 △: Dynamic friction coefficient is 0.21 or more and less than 0.25 ×: Dynamic friction coefficient is 0.25 or more

(Stickiness) A sticky feeling when a sheet-treated surface was pressed with a finger and separated was evaluated according to the following criteria. ◎: Does not feel sticky: Moist △: Slightly sticky ×: Sticky

The antifogging agent, release agent and other coating agents used are as follows. Antifogging agent (A-1): Sucrose fatty acid ester of HLB16 (A-2) containing sucrose lauric acid monoester as the main component (about 70% by weight): Decaglycerin lauric acid monoester as the main component (about HLB 14.8 polyglycerin fatty acid ester (A-3): HLB 13.5 polyglycerin fatty acid ester (A-) containing hexaglycerin lauric acid monoester as a main component (about 65 wt%). 4): HLB 13.3 polyglycerin fatty acid ester containing decaglycerin oleic acid monoester as a main component (about 65% by weight)

Release agent (B-1): polyoxyethylene polyoxypropylene block copolymer, average molecular weight 15,000, polyoxyethylene 80 wt% (B-2): polyoxyethylene polyoxypropylene block copolymer, average Molecular weight about 8000, polyoxyethylene 65 wt% (B-3): polyethylene glycol, average molecular weight 33
00 (B-4): dimethylpolysiloxane (used in emulsion), viscosity 10,000 cs

Other coating agent (C-1): polyvinyl alcohol, viscosity of 4% aqueous solution 5 mPa · s (20 ° C.), saponification number 73 mol% (C-2) polyether modified silicone oil, 60% by weight polyether Modified with base, viscosity (25 ℃) 300c
s (C-3): polyoxyethylene nonylphenyl ether, polyoxyethylene 12 mol, HLB14.1 (C-4): polyoxyethylene sorbitan lauric acid ester, polyoxyethylene 20 mol, HLB16.
7 (C-5): polyoxyethylene stearic acid ester, polyoxyethylene 15 mol, HLB 16.5

[0052]

Examples 1 to 7 Commercially available polystyrene biaxially stretched sheet (manufactured by Asahi Kasei Corporation, trade name: OPS sheet # 300)
An aqueous solution prepared by corona-treating one surface (0 thickness 0.3 mm) so that the contact angle with pure water is 40 to 45 degrees and then having the composition of the anti-fog surface coating film shown in Table 1. Was coated with a spray coater (wet coating amount 3 g / m ² ),
After the drying treatment, the opposite surface is subjected to corona treatment so that the contact angle with pure water becomes 55 to 60 degrees, and then an aqueous solution adjusted to have the composition of the release surface coating film shown in Table 1 is spray coater. Was coated (wet coating amount: 3 g / m ² ) and dried, and the sheet was wound into a roll. The wound sheet was aged for 1 week and then the physical properties were evaluated. Table 1 shows the physical property evaluation results of the sheet after aging and the molded product from the sheet. The contact angle of the sheet was confirmed using a solid surface energy analyzer CA-XE manufactured by Kyowa Interface Science Co., Ltd. The coating amount on the sheet was determined by FTIR (ATR method) immediately after the sheet coating, based on the characteristic absorption of the ester of the antifogging agent and the characteristic absorption of the ether of the release agent, based on the calibration curve prepared from the sample with the known coating amount. confirmed.
Further, the transfer of the antifogging agent and the release agent after aging was 0 to 10% of the initial coating amount in all the sheets.

[0053]

[Table 1]

[0054]

Comparative Examples 1 to 5 The same procedure as in Example 1 was carried out except that the coating solution was adjusted so that the composition of the coating film on the anti-fog surface and the coating film on the release surface shown in Table 2 were adjusted. The sheets of Comparative Examples 3 and 4 were coated only on the antifogging surface, and the other surface was untreated. Further, in the silicone oil of the sheets of Comparative Examples 1, 2 and 3, 40 to 45% after completion of aging was transferred to the silicone oil non-coated surface by FT.
It was confirmed by IR (ATR method). Table 2 shows the physical properties of the obtained sheet.

[0055]

[Table 2]

The sheets of Comparative Examples 1, 2 and 3 are sheets in which silicone oil is used as a conventionally known release agent. These sheets had a low antifogging property due to the transfer of silicone oil due to aging or the influence of the silicone oil mixed with the antifogging agent, and the electrostatic charge during molding was large.
Further, the sheet of Comparative Example 4 not coated with silicone oil had good antifogging property, but was inferior in slipperiness of the sheet and releasability at the time of molding and was difficult to be continuously molded. The sheet of Comparative Example 5 is an example in which a large amount of the release agent usable in the present invention is applied, and it is found that the sheet becomes sticky and the stickiness also reduces the slipperiness. On the other hand, it can be seen that the sheets of the examples of the present invention have a good balance of antifogging property, releasability, and sheet slipperiness, and also have a characteristic of being less charged during molding.

[0057]

[Comparative Examples 6 to 9] The same procedure as in Example 5 was repeated except that C-2 to C-5 were used as coating agents for coating the release surface.
Table 2 shows the physical properties of the obtained sheets and molded products. It was confirmed by FTIR (ATR method) that about 40% of the silicone oil of the sheet of Comparative Example 9 was transferred to the silicone oil non-coated surface (anti-fog surface) after aging.
From Comparative Examples 6 to 9, when a surfactant other than the ether-based multimer was applied as the release agent, the release property, slipperiness, and antifogging property of the sheet were insufficient, and the antifogging property was adversely affected. Not give
It can be seen that the coating agent that is effective as a release agent must be carefully selected.

[0058]

EFFECTS OF THE INVENTION A stretched sheet having one surface coated with an antifogging agent and the other side coated with an ether polymer as a release agent, and a secondary molding container comprising the stretched sheet are
It is excellent in both high-temperature and low-temperature anti-fog properties, excellent in releasability and releasability of a sheet and a sheet secondary molded product, and less charged during molding. Therefore, it can be suitably used as various molded containers and packaging container molding sheets, including those for food packaging that requires excellent antifogging properties.

Claims (3)

(57) [Claims] 1. A styrene-based resin sheet having one surface coated with an antifogging agent and the opposite surface coated with a release agent, wherein sucrose fatty acid esters and polyglycerin fatty acid esters are used as antifogging agents. at least one is 5 to 30 mg / m ² coating selected from a styrene-based resin sheet to the opposite surface thereof, as a release agent, characterized in that the ether-based multimer is 3 to 30 mg / m ² coating . 2. The styrene resin sheet according to claim 1, wherein the ether polymer is selected from polyoxyethylene polyoxypropylene block copolymer and polyethylene glycol. 3. The styrene resin sheet according to claim 1, wherein the styrene resin sheet is a biaxially stretched styrene resin sheet.