JP2008095116A - Molded article composed of resin sheet excellent in anti-fogging property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molded article composed of a resin sheet which can be used as a lid of a food packaging container to suppress water drops sticking on the inside of the lid and exhibits anti-fogging effect superior to those before. <P>SOLUTION: The molded article composed of the antifogging resin sheet comprises being surface-coated with a mixture of a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polystyrene resin sheet particularly excellent in antifogging performance. More specifically, when used as a lid for food containers, the present invention relates to a molded article made of a biaxially stretched polystyrene-based resin sheet that has particularly few water droplets attached to the inner surface of the lid and exhibits a very excellent anti-fogging effect as compared with the prior art.

Biaxially stretched polystyrene resin sheets are widely used as packaging materials for various foods and the like because they are excellent in transparency, water resistance and moldability. However, because the surface is extremely hydrophobic, moisture that condenses in response to changes in temperature and humidity (water vapor) forms an aggregate of minute water droplets without wetting the resin surface evenly, so-called haze. Often occurs. The occurrence of such fogging makes it difficult to distinguish the stored items in the field of food packaging materials, and thus significantly reduces the commercial value of various containers. This is not only a serious drawback of containers characterized by transparency, but the water that is unevenly agglomerated and adhered also affects the food contained in the container, resulting in poor quality and decay. It will contribute.
Conventionally, in order to prevent such fogging phenomenon, sucrose fatty acid esters have been widely used as highly safe anti-fogging agents [Japanese Patent Laid-Open Nos. 56-166234, 57-80431, 61-36864. Each gazette (patent documents 1 to 3)]. Japanese Patent Application Laid-Open No. 9-12751 (Patent Document 4) proposes an antifogging styrene resin sheet / film using a polyglycerol fatty acid ester.
JP-A-56-166234 JP 57-80431 A Japanese Examined Patent Publication No. 61-36864 JP-A-9-12751

  In recent years, lids for food containers have a tendency to increase the top surface area or deep drawing in order to improve their aesthetics, and biaxially oriented polystyrene resin sheets have better antifogging performance than before. In addition, it is required to have a long-lasting antifogging performance. As for the anti-fogging performance, there are almost no water droplets adhering during low-temperature storage (5 to 8 ° C.), and it is required to make the contents such as sushi and sashimi very refreshing. In addition, when adding warm foods such as freshly cooked white rice, red rice, tempura, fries, etc., the food contains a lot of water, so there are many water droplets adhering to the lid, and it looks more refreshing and has a long-lasting antifogging effect. Some containers are required. However, most of the biaxially stretched polystyrene resin sheet is molded into a container shape by a direct heating type molding machine using a hot plate, so that the antifogging agent coated surface is in contact with the hot plate and roughened by contact. Even if the anti-fogging performance of the molded product did not occur due to peeling off, the adhered water droplets did not flow easily, and the contents were not clearly visible. This situation did not change much even when applied in a large amount in the conventional antifogging agent formulation, and it was difficult to show the contents neatly with little water droplet adhesion.

The present inventors have a particularly excellent anti-fogging performance even in a container molded by a direct heating type molding machine, that is, there is very little adhesion of water droplets during storage at low and high temperatures, and the contents can be displayed particularly neatly. As a result of diligent research on anti-fogging agents and anti-fogging formulations for biaxially oriented polystyrene resin sheets that have sustained their effects, polyhydric alcohol type nonionic surfactants and polyethylene glycol type nonionic surfactants The biaxially stretched polystyrene resin sheet coated with a specific amount of anti-fogging agent blended with an agent is extremely unprecedented in that it has very little water droplet adhesion and the contents look very refreshing and the effect lasts. It has been found that it has anti-fogging performance (clean feeling) and has completed the present invention.
That is, the present invention resides in a molded article comprising an antifogging resin sheet whose surface is coated with a mixture of a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant.

  The molded product made of the biaxially stretched polysterene resin sheet of the present invention has a much better anti-fogging effect than before, has little water droplet adhesion, and the contents can be seen clearly, and the effect will continue so far. Excellent anti-fogging performance (clean feeling). It is particularly suitable as a food packaging container for storing low and high temperature foods.

Hereinafter, the present invention will be described in detail.
The antifogging agent component in the resin sheet of the present invention is a mixture of a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant.
Examples of the polyhydric alcohol type nonionic surfactant include glycerol fatty acid esters, pentaerythritol fatty acid esters, sorbitol and sorbitan fatty acid esters, sucrose fatty acid esters, polyglycerin fatty acid esters, and polyhydric alcohol alkyl ethers. You may mix and use the above. Of these, sucrose fatty acid esters and polyglycerin fatty acid esters are preferred.
The sucrose fatty acid ester is one in which 70% by weight or more of the constituent fatty acid is a saturated and / or unsaturated fatty acid having 12 to 18 carbon atoms, preferably 12 to 16 carbons, and contains 60 mol% or more of a monoester. . The constituent fatty acid may be a mixture of two or more.

  If polyglycerin fatty acid ester is a saturated and / or unsaturated fatty acid having 12 to 18 carbon atoms, preferably 12 to 16 carbon atoms, 70% by weight or more of the constituent fatty acid, the polycondensation degree and esterification rate of polyglycerin Although not limited, the former is preferably 4 to 20 and more preferably 6 to 12 from the viewpoint of safety as a food additive. In the latter case, the monoester is preferably contained in an amount of 50 mol% or more.

Polyethylene glycol type nonionic surfactants include higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, fat and oil ethylene oxide adducts, polyoxy A propylene polyoxyethylene block copolymer etc. are mentioned. A polyoxypropylene polyoxyethylene block copolymer is particularly preferred in view of the effect of maintaining the antifogging performance. The reason for the improvement in sustainability is not clear, but the affinity between the polyoxyethylene domain (hydrophilic part) of the block polymer and the hydrophilic part of the sucrose fatty acid ester or polyglycerin fatty acid ester or the substrate surface, or the block Water film of sucrose fatty acid ester and polyglycerin fatty acid ester at the time of water film formation due to affinity between polyoxypropylene domain (hydrophobic part) of polymer and sucrose fatty acid ester, polyglycerin fatty acid ester and hydrophobic part of substrate surface It is thought that it has the effect of suppressing large-scale outflow into water and water droplets.
The polyoxypropylene polyoxyethylene block copolymer comprises 10 to 90% by weight of polyoxyethylene chains, preferably 40 to 85% by weight, and 90 to 10% by weight of polyoxypropylene chains, preferably 60 to 15% by weight. The weight average molecular weight is 1900-20000, preferably 2000-16000. When this agent is used for food, it must have a molecular weight of 1900 or more as described in the Voluntary Standard for Food Containers and Packaging Made of Synthetic Resins such as Polyolefins (so-called positive list) issued by the Sanitation Council for Polyolefins. Is used.
The block ratio and composition (A-B block type, A-B-A block type, etc.) of the polyoxyethylene chain and the polyoxypropylene chain are necessary for obtaining the desired antifogging property in the resin sheet of the present invention. If it is a range, there will be no restriction | limiting in particular.

The mixing ratio (solid content ratio) of the polyhydric alcohol type nonionic surfactant and the polyethylene glycol type nonionic surfactant is usually 90 to 40:10 to 60. Here, when the proportion of the polyethylene glycol type nonionic surfactant is less than 10% by weight, not only sufficient antifogging sustainability cannot be obtained, but also the desired good refreshing feeling in low temperature antifogging cannot be obtained. . On the other hand, if it exceeds 60% by weight, it is difficult to obtain sufficient antifogging properties for both low temperature and high temperature antifogging.
In the case of a polyhydric alcohol type nonionic surfactant obtained by mixing a sucrose fatty acid ester and a polyglycerin fatty acid ester, the mixing ratio (solid content ratio) of the sucrose fatty acid ester and the polyglycerin fatty acid ester is 10 to 90: 90- 10 is preferred.
Either of them exhibits anti-fogging performance, but the combined use is preferable for both anti-fogging properties at low and high temperatures, and 30 to 70:70 to 30 is more preferable.

The antifogging agent of the present invention includes various anionic surfactants in addition to the antifogging agent in which a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant are combined. Also good. Examples of the anionic surfactant include fatty acid salts, fatty acid sulfonates, and fatty acid lactic acid ester salts. As fatty acids constituting these fatty acid salts, fatty acid sulfonates, and fatty acid lactic acid ester salts, saturated, unsaturated, linear, and branched ones having 8 to 22 carbon atoms are used. Specifically, caprylic acid , Capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, aragic acid, oleic acid, elaidic acid, ricinoleic acid, 2-butyloctanoic acid, 2-hydroquindecanoic acid and the like. These fatty acids may be a mixture of two or more of any ratio. Examples of the basic substance constituting the salt include alkali metals such as sodium and potassium, alkaline earth metals such as magnesium, alkanolamines such as ethanolamine, and lower alkylamines such as tributylamine. Among these, as the constituent fatty acid, lauric acid, myristic acid, palmitic acid, and oleic acid are preferable, and lauric acid is particularly preferable. Moreover, as a basic substance, an alkali metal is preferable and especially potassium is preferable.
The coating amount after drying of these anionic surfactants is 30% by weight or less, preferably 20%, based on the total of the polyhydric alcohol type nonionic surfactant and the polyethylene glycol type nonionic surfactant. It is as follows.

In the present invention, a known release agent such as silicone oil or a lubricant may be added to the antifogging agent in advance, but if the amount added is too large, the target antifogging property (clean feeling) is impaired. Usually, it is added at 1 mg / m ² or less, preferably 0.5 mg / m ² or less.

The resin sheet to be used in the present invention is preferably a biaxially stretched polystyrene sheet, but is not limited to the type of resin sheet, and can be used as a transparent resin sheet in the same application as the biaxially stretched polystyrene resin sheet. It can also be applied to polyester resin sheets, polyvinyl chloride sheets, polypropylene sheets and the like.
The biaxially stretched polystyrene resin sheet is made into a sheet by a known method, and the thickness of the sheet is usually 100 to 700 μm. Usually, the sheet is thermoformed and used as a container. In the present invention, an antifogging agent may be applied immediately to the surface of a sheet obtained by extruding a polystyrene resin and biaxially stretching if necessary, but in advance, corona discharge treatment, high frequency treatment, etc. It is desirable to perform surface treatment and adjust the surface state of the sheet because the antifogging agent is easily coated well. Preferably, the surface tension of the sheet is adjusted to 50 to 60 mN / m by corona discharge treatment. Good.

The antifogging agent is mainly used by being applied to the sheet surface. In this case, the coating amount after drying is in terms of solid content, the lower limit is usually 10 mg / m ² or more, preferably 20 mg / m ² or more, particularly preferably 30 mg / m ² or more, and the upper limit is usually 100 mg / m ² or less. It is preferably applied so that it is 60 mg / m ² or less, particularly preferably 50 mg / m ² or less. When the coating amount after drying of the antifogging agent is less than 10 mg / m ² , a good refreshing feeling cannot be obtained, and when it exceeds 100 mg / m ² , the sheets are blocked due to stickiness and the transparency is lowered. May cause whitening. As a method for applying the antifogging agent, known methods such as spraying, roll coater, gravure coater, knife coater, and dipping method are used, and spraying and roll coater methods are preferable. The solvent used in the antifogging agent solution is most preferably water, but is appropriately selected as long as it is a solvent that dissolves the antifogging agent such as alcohol and does not dissolve the resin sheet, and satisfies the safety depending on the application field. May be used.

  In the present invention, the quantitative analysis of the coating amount of the antifogging agent is carried out by washing the sheet with alcohol or the like and collecting the washings, and by gravimetric method, gas chromatographic method, high performance liquid chromatography method, FT-IR analysis method (ATR method). ) Etc.

  Further, as long as the effects of the present invention are not impaired, an anti-fogging agent is appropriately used together with an anti-blocking agent, an antistatic agent, a viscosity modifier, a defoaming agent, an ultraviolet absorber, an anti-coloring agent, an antibacterial agent, and the like according to conventional methods. be able to.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded. The sucrose fatty acid ester, polyglycerin fatty acid ester, and polyoxypropylene polyoxyethylene block polymer used in Examples and Comparative Examples are as follows.
1. Sucrose fatty acid ester: sucrose laurate 40% solids
2. Polyglycerol fatty acid ester: Hexaglycerol laurate
100% solids
3. Polyoxypropylene polyoxyethylene block polymer:
Molecular weight 3,300 Solid content 100%
The coating amount of the antifogging agent on the sheet was quantitatively confirmed by high performance liquid chromatography after the sheet sample was washed with methanol, the washings were collected and concentrated.

Similarly, the used sheet was a 300 μm thick biaxially stretched polystyrene sheet, and the coated surface side was subjected to a corona treatment of 54 mN / m or more. The sheet was dried in a hot air oven after applying an antifogging agent aqueous solution having an experimental composition.
Moreover, the sushi lid type | mold container used for evaluation made the said biaxially-stretched polystyrene sheet | seat into the inner surface, and shape | molded with the hot-plate heating type pressure-pressure molding machine, and the magnitude | size is as follows.
・ Aperture: 215mm long x 135mm wide x 30mm deep ・ Top surface: 190mm long x 110mm wide

  In addition, the performance evaluation of the sheet | seat in an Example and a comparative example was performed in accordance with the following methods and criteria. (Acceptable level of the present invention is transparency, stickiness is “◯ ′” or more, and other items are “◯” or more.)

<Low temperature initial refreshing feeling>
Cover the container (210 mm long x 130 mm wide x 15 mm deep) with 150 cc of water at 23 ° C and store the sample in a 5 ° C atmosphere. Visual observation and sensory evaluation were performed.
Evaluation criteria A: There is little adhesion of water droplets, and the refreshing feeling is very good.
○: Although water droplets are attached, a refreshing feeling is felt.
Δ: Many water droplets are attached and the refreshing feeling is not so good.
X: Water droplets are very attached and the feeling of refreshing is poor.

<Long-lasting low temperature feeling>
Three hours after the start of the low temperature refresh feeling evaluation, the refresh feeling of the lid-shaped molded product was sensory-evaluated again.
Evaluation criteria A: A very good state of refreshing feeling is maintained.
○: Although water droplets are attached, it is maintained in a state where a refreshing feeling can be felt.
Δ: Refreshing feeling is slightly inferior.
X: A refreshing feeling is bad.

<High-temperature initial refreshing feeling>
Cover the container (210 mm long x 130 mm wide x 15 mm deep) with 150 cc of hot water of 80 ° C and store it in a 23 ° C atmosphere and keep the lid molded product refreshed after 10 minutes. Visual observation and sensory evaluation were performed.
Evaluation criteria A: There is little adhesion of water droplets, and the refreshing feeling is very good.
○: Although water droplets are attached, a refreshing feeling is felt.
Δ: Many water droplets are attached and the refreshing feeling is not so good.
X: Water droplets are very attached and the feeling of refreshing is poor.

<High-temperature refreshing sustainability>
One hour after the start of the high temperature refresh feeling evaluation, the refresh feeling of the lid mold product was sensory-evaluated again.
Evaluation criteria A: A very good state of refreshing feeling is maintained.
○: Although water droplets are attached, it is maintained in a state where a refreshing feeling can be felt.
Δ: Refreshing feeling is slightly inferior.
X: A refreshing feeling is bad.

<Sheet transparency>
The transparency of the sheet was evaluated by both the haze H (%) measured by NDH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.) and the appearance observed with the naked eye. It was set as the evaluation result of sex.
Evaluation criteria A: H <1.5 or no smears are observed.
○: 1.5 ≦ H <2 or very slight smears are observed.
Δ: 2 ≦ H <3 or smear is slightly noticeable.
X: 2 ≦ H or smear is noticeable.

<Stickness of sheet>
The sheet was touched with a fingertip and the stickiness was subjected to sensory evaluation.
Evaluation criteria ○: Little stickiness.
○ ′: Stickiness is somewhat, but at a practically acceptable level.
×: Large stickiness.

<Examples 1 to 7>
The “coating liquid” in the table with respect to 100% by weight of water so that the sucrose fatty acid ester, the polyglycerin fatty acid ester and the polyoxypropylene polyoxyethylene block polymer have the “solid content ratio in the coating liquid” in the table. An aqueous solution in which the composition was dissolved at a ratio of “composition” was prepared. Next, this anti-fogging agent aqueous solution was applied to one side of a corona-treated biaxially stretched polystyrene sheet with a bar coater. The solid content of the antifogging agent after drying is shown in the table as “coating amount after drying”.
The obtained sheet was molded into a sushi container lid with a hot plate heating type air pressure molding machine so that the coated surface was the inner surface, and used as a sample for evaluation. The result evaluated about the said evaluation item was combined with the table | surface, and was shown.

<Comparative Examples 1-4>
As in the examples, sucrose fatty acid ester and / or polyglycerin at a ratio of “coating liquid composition” in the table to 100% by weight of water so that the “solid content ratio in the coating liquid” in the table is obtained. An aqueous solution in which a fatty acid ester or a polyoxypropylene polyoxyethylene block polymer was dissolved was prepared. Subsequent sheet coating and sushi container lid creation and evaluation were performed in the same manner as in Examples 1-7. The results are shown in the table.

Claims (7)

  A molded article comprising an antifogging resin sheet having a surface coated with a mixture of a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant, the polyethylene glycol type nonionic interface A molded article, wherein the activator is a polyoxypropylene polyoxyethylene block copolymer.   The molded article according to claim 1, wherein the polyhydric alcohol type nonionic surfactant is a sucrose fatty acid ester and / or a polyglycerol fatty acid ester.   The molded article according to claim 1 or 2, wherein the solid content ratio (weight ratio) of the mixture of the polyhydric alcohol type nonionic surfactant and the polyethylene glycol type nonionic surfactant is 90 to 40:10 to 60. .   The molded article according to any one of claims 2 to 3, wherein the sucrose fatty acid ester and the polyglycerin fatty acid ester have a solid content ratio (weight ratio) of 10 to 90:90 to 10.   The polyoxyethylene chain constituting the polyoxypropylene polyoxyethylene block copolymer is 10 to 90% by weight, the polyoxypropylene chain is 90 to 10% by weight, and the weight average molecular weight of the block copolymer is 1900 to 20000. Item 5. The molded article according to any one of Items 1 to 4.   The molded article according to any one of claims 1 to 6, wherein the surface is coated with a mixture of a polyhydric alcohol type nonionic surfactant and a polyethylene glycol type nonionic surfactant after the corona discharge treatment.   The molded article according to any one of claims 1 to 7, wherein the resin sheet is a biaxially stretched polystyrene resin sheet.