JPS6362538B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a styrenic resin film/sheet that has excellent antifogging properties and removability, and has a beautiful appearance. Films and sheets made of styrene resins are molded into various containers and widely used for food packaging because they have excellent moldability, water resistance, transparency, gloss, and beautiful appearance. However, the manufacturing of containers using this film sheet is carried out by forming containers on the film sheet, stacking a large number of sheets, and punching them out all at once, so the containers tend to come into close contact with each other during the punching process. When peeling off a large number of stacked containers one by one to store the contents, there are disadvantages in that it is difficult to peel off, reducing work efficiency, and the containers are easy to tear if peeled off forcibly. In addition, due to the highly hydrophobic surface of styrene resin films and sheets, when containers contain water, such as cooked rice, fish, boiled beans, pickles, sweets, etc., and are sealed, the contents may The water vapor generated from the water remains as minute water droplets on the inside of the container,
The excellent transparent wall of the container had a drawback in that it appeared so-called cloudy, making it impossible to see through the contents from the outside. In addition, in order to prevent the container wall from becoming cloudy, conventional methods have been taken to coat the surface of the film/sheet with, for example, a high HLB surfactant or sucrose fatty acid ester as an antifogging agent. The highly hydrophilic antifogging agent remains on the surface of the film/sheet and functions for a short period of time, but if the film/sheet surface continues to get wet with water for a long time, it dissolves in the wetness and gradually washes away. It was difficult to expect antifogging properties from this for a long period of time. In addition, the antifogging agent film formed on the surface of styrene resin films and sheets, which are generally used by drawing and forming into food pack containers or cup-shaped containers, is easily divided during stretching during drawing and forming. I was concerned that the anti-fog function could not be fully achieved. In order to solve the problems of such styrene resin films and sheets, and to provide them with excellent antifogging properties and removability, Japanese Patent Application Laid-Open No. 53-115781 was first proposed.
The invention of No. 1 was disclosed. As described in the 9th line from the bottom of the upper right column on page 453 of the patent specification, this invention first applies a mixture of an antifogging agent and silicone oil, which has been difficult to apply uniformly to a film sheet. This is made possible by corona discharge treatment on the surface. However, this invention is based on styrene resin film.
The above-mentioned problems in the sheet's anti-fogging properties and removability were solved by
The aim was to find a solution by creating a strong bond between the antifogging agent and release agent coating and the film/sheet surface, and although we succeeded in somewhat strengthening the adhesion between the two, There is no mention of the core points, such as the dissolution of the antifogging agent in the coating film due to surface wetting and the resulting loss of function over time, and the separation of the coating film during drawing forming that involves heating. Nor does it have any suggestion of a solution. The present invention uses an antifogging agent and a release agent as a mixed agent to firmly and uniformly adhere to the surface of a styrene resin film/sheet at the same time, thereby achieving excellent antifogging properties without impairing the original beautiful appearance of the film/sheet. The purpose is to impart releasability. A second object of the present invention is to provide an antifogging agent film that can maintain its function for a long time without being washed away even when the surface gets wet with water. is formed on the surface of a film or sheet. A third object of the present invention is that even when a styrene resin film/sheet is formed into a deep-drawn container,
The purpose of this method is to form a film of an antifogging agent and release agent on the surface of a film or sheet that will not be cut. That is, the present invention provides sucrose fatty acid ester (A) whose main fatty acid component is lauric acid, and non-sucrose fatty acid ester (A) whose degree of polymerization is 800 or less on the surface of a styrene resin film sheet running along the surface of a rotating roller. Modified polyvinyl alcohol (B) and average particle size
An aqueous solution of a silicone emulsion (C) having a particle size of less than 1μ mixed in a pure mass ratio of A:B:C=1:0.5 to 2:0.5 to 3 is applied, and then a film is applied to the surface of the film sheet to which the aqueous solution is attached.・This is a method for producing styrene-based resin films and sheets with excellent antifogging and releasability, in which compressed air is blown through the slits of an air knife installed across the sheet. In the present invention, a sucrose fatty acid ester (A) containing at least 50% of lauric acid as a main fatty acid is used as an antifogging agent. Further, as a release agent, a silicone emulsion (C) having an average particle diameter of less than 1 μm is used. In addition to these, unmodified polyvinyl alcohol (B) with a degree of polymerization of 800 or less is used as a binder. These are A:B:C=
It is applied to the surface of the film/sheet as a mixed aqueous solution of 1:0.5 to 2:0.5 to 3. Many surfactants with high HLB are generally known as antifogging agents, but when these are used, not only the antifogging properties are insufficient, but also the appearance of the container is poor. The preferred antifogging agent is sucrose fatty acid ester, but there is a clear difference in superiority between those containing lauric acid as the main fatty acid and other antifogging agents.In particular, sucrose fatty acid ester containing stearic acid as the main fatty acid Almost no anti-fog effect was observed. When using silicone emulsion as a release agent, if the particles are larger than 1μ, the dispersibility of the liquid mixture becomes insufficient, and the appearance of the container as a product deteriorates. In particular, if a film with a thickness exceeding 5μ is used, the film/sheet and the container formed from it will have no commercial value in terms of appearance. However, if we use only the sucrose fatty acid ester (A), which mainly consists of lauric acid, and the silicone emulsion (C) and apply them as a binary mixed aqueous solution to the surface of the film/sheet, the silicone emulsion Due to the presence of sucrose fatty acid ester, the inherent anti-fogging properties of the sucrose fatty acid ester are erased.
The sheet has no effect at all. In order to prevent this, in the present invention, a ternary mixed aqueous solution containing unmodified polyvinyl alcohol (B) as a binder is applied to the surface of the film/sheet. In order for each of these three to function sufficiently, the pure mass ratio of the three is A:B:C=1:0.5~2:
0.5 to 3, and the appropriate amount of adhesion on the film/sheet surface is 0.10 to 0.50 g/m ² in terms of pure mass. If the blending ratio of the silicone emulsion (C) as a release agent is less than the lower limit of the above composition ratio, the release properties will be insufficient, while if it is present in a ratio exceeding the upper limit, it will not be possible to obtain a product with commercial value in terms of appearance. In addition, polyvinyl alcohol as a binder
If the blending ratio of (B) is less than the lower limit of the above composition ratio, the antifogging agent will dissolve while the film/sheet surface is wet with water and will tend to gradually decrease, making it difficult to maintain the antifogging function for a long period of time, and causing the squeezing container to be heated. The coating film is easily analyzed during molding,
On the other hand, if the content exceeds the upper limit, the appearance of the container will deteriorate. Sucrose fatty acid ester (A) has the above composition ratio (B)
The antifogging function is not influenced by the relative fluctuations caused by fluctuations within the range of the composition ratios of (C) and (C). If the amount of the ternary mixed aqueous solution attached to the surface of the film/sheet is less than 0.10 g/m ² in pure mass, the amount of attachment to the surface of the container will become too thin due to the stretching of the film/sheet during drawing. The clouding function is insufficient, and on the other hand, those exceeding 0.50 g/m ² tend to cause whitening during drawing and cannot be used in terms of container appearance. To apply the above-mentioned ternary mixed aqueous solution to the surface of the film/sheet, the roller is positioned on a container containing the above-mentioned aqueous solution so that the lower half of the roller or a part thereof is immersed in the aqueous solution, and then the roller is placed on the film/sheet surface. The roller is placed on a running path of the sheet, and the running film sheet is caused to run along the surface of the roller, and the mixed aqueous solution is adhered to the surface of the roller. Next, the film sheet with the aqueous solution adhered to it is guided to the surface of another roller, and compressed air is blown from the slit of the air knife toward the film sheet on the roller surface to force and spread the aqueous solution, so that the liquid is applied without cuts. Equalize the amount of aqueous solution applied. The air knife slit is 0.3 to 0.7 mm wide, and is installed across the film sheet with a length that exceeds the width of the film sheet, and the compressed air is perpendicular to the film sheet in a water column of 500 to 2500 mm. The film is sprayed uniformly and continuously over the entire width of the film sheet from the direction opposite to the direction of the film sheet. The film sheets are then introduced into a dry air circulation oven, dried, and then wound up one after another. It is important here to blow compressed air using an air knife. This serves to homogenize the aqueous solution applied on the film sheet and to make the aqueous solution sufficiently compatible with the highly hydrophobic surface of the film sheet. Incidentally, attached FIG. 2 is an example of the most effective use of the present invention, and illustrates the case where the above-mentioned aqueous solution coating method shown in the present invention is incorporated into the manufacturing process of a biaxially stretched polystyrene film. . The method of the present invention is a T-die method, an inflation method,
It is effective when applied to films and sheets that have been previously subjected to corona discharge treatment, regardless of the manufacturing method such as the calendar method. By having the above structure, the present invention provides styrenic resin films and sheets as well as containers formed from the same with excellent antifogging properties and removability without impairing their original transparency and gloss. It was successfully added in one process. In particular, the antifogging agent and release agent are applied as a film that does not break even when the container is formed by contact with a high-temperature object or during drawing, but spreads as the film or sheet is stretched during drawing. The fact that the anti-fogging agent does not leak out even when the container surface is wet for a long period of time, and the anti-fogging function of the container surface is sufficiently maintained over a long period of time, is a major factor in improving the molding workability and raw material yield of deep-drawn containers and food pack containers. This has made it possible to supply the market with products that are superior in removability and anti-fogging properties compared to conventional products. In conclusion, the present invention can be said to be an invention that has greatly contributed to the field of food distribution. Examples and comparative examples of the present invention will be described below. The polystyrene sheets used in the experiments in Examples 1 to 6 and Comparative Examples 1 to 6 were biaxially stretched sheets with a thickness of 0.21 mm, and the experimental composition was coated with an aqueous solution. It was then dried in an oven. The food pack and the deep-drawn container are both molded from the above polystyrene sheet with the surface to which the aqueous solution is applied inside, and their sizes and shapes are as follows. (1) Food pack container with lid Container part: 200mm length x 130mm width x 30mm depth Lid part: 200mm length x 130mm width x 2mm depth (2) Deep drawn container Cup-shaped container: Opening 80mmφ 50mm depth The evaluation methods and criteria for the evaluation items of antifogging properties, molded article releasability, and appearance in Examples and Comparative Examples are as follows. Anti-fog properties: Hold the sheet or container over a hot water tank at 90°C with the anti-fog treated side facing down and fix it in that position.
The initial antifogging property was observed after 1 minute, and the antifogging retention property was visually observed after 48 hours. Evaluation criteria: ◎...No clouding and no water droplets observed. 〇…There is no cloudiness and large transparent water droplets can be seen. Δ...Less than 20% of the antifogging treated area is cloudy and opaque due to minute water droplets. ×...More than 20% of the antifogging treated area is cloudy and opaque due to minute water droplets. Molded product peelability: Explained with reference to attached Figure 1 A and B. Stack 20 food pack containers ¹ and place them with the opening facing up, and place a 5 kg load on the inside of the top container.
² , and measure the thickness H ₁ [mm] of the overlapping part. Next, load ² is removed, and after 1 minute, the thickness H ₂ [mm] of the overlapped portion is measured again, and the recovery rate R is determined by the following formula. R=H ₂ −H ₁ /H ₁ ×100 (%) Evaluation criteria ◎…250≦R 〇…80≦R＜250 △…30≦R＜80 ×…R＜30 Appearance: Sheet and lid of food pack container The two types were evaluated based on the haze H measured by ASTM-D-1003 and the appearance observed with the naked eye, and if either of them was rated low, it was ranked on the low rated side. Evaluation criteria: For sheets: ◎...H<1.5 or no coating spots are observed. 〇...1.5≦H<2 or very slight paint spots are observed. △...2≦H<3 or coating spots are slightly noticeable. ×...3≦H or painted spots are quite noticeable. Evaluation criteria: Food pack lid ◎...H<1.5 or clear appearance with no whitening observed at all. 〇...1.5≦H<2 or slight mold whitening is observed. △...2≦H<2.5 or molding whitening is slightly noticeable. ×...2.5≦H or molding whitening is noticeable. Further, the product names and manufacturers of the antifogging agents, release agents, and binders used in Examples and Comparative Examples are as follows.

[Table] Tell

[Table] Tool Example 1, Comparative Example 1 Sucrose fatty acid ester in which 50% or more of the fatty acid is lauric acid and various surfactants with high HLB were used as antifogging agents, and methyl cellulose with a polymerization degree of 800 was used as a binder. Using polyvinyl alcohol and silicone emulsion with an average particle size of 0.5μ as a release agent, they were used alone or in various combinations as an aqueous solution with a pure mass concentration of 4%, and the surface of a biaxially stretched polystyrene sheet with a thickness of 0.21 mm was prepared. was coated using the method of Example 6 Experiment No. 2, and the effects of the differences between each combination on the antifogging properties, releasability, and appearance of the biaxially oriented polystyrene sheet and molded container were investigated, and the evaluation method and evaluation described above were investigated. Evaluation was made according to the criteria. The results are shown in Table 1. The amount of coating was applied at three pure weights of 0.1, 0.3, and 0.5 g/m ² for the present invention, and 0.3 g/m ² for the others. Furthermore, the composition ratio used for the three-way combination of the present invention was also applied to other three-way combinations. The following can be understood from Table 1. (1) From Experiments Nos. 1 to 3, three components of sucrose fatty acid ester, polyvinyl alcohol, and silicone emulsion are essential as coating film components in order to satisfy all of antifogging properties, releasability, and appearance. (2) From Experiment Nos. 1 to 3, the appropriate adhesion amount range is 0.10 to 0.50 g/m ² in terms of pure mass. (3) From Experiment Nos. 1 to 3 and 11 to 17, many surfactants with high HLB are generally known as antifogging agents, but all of them have poor appearance and antifogging properties, especially their long-term retention. In terms of performance, it is far inferior to Experiment Nos. 1 to 3 in which sucrose fatty acid ester, polyvinyl alcohol, and silicone emulsion were used in combination. (4) From Experiment Nos. 1 to 3 and 10, polyvinyl alcohol is superior as a binder, while methyl cellulose is inferior in both antifogging properties and appearance. (5) From Experiment No. 18 and 19, 2 without adding binder.
A combination of antifogging agents and silicone emulsion has almost no antifogging effect.

【table】

【table】

[Table] Example 2, Comparative Example 2 The same composition as Experiment Nos. 1 to 3, which obtained excellent evaluation in Example 1, but with a different composition ratio, was applied to a biaxially stretched polystyrene sheet with a thickness of 0.21 mm. The effects on the antifogging properties, releasability, and appearance of sheets and molded containers were investigated and evaluated. The results are shown in Table 2. The ternary mixed aqueous solution had a pure mass concentration of 4%, and the coating was carried out in the same manner as in Experiment No. 2 of Example 6. The following can be understood from Table 2. (1) The appropriate blending ratio of sucrose fatty acid ester (A), polyvinyl alcohol (B), and silicone emulsion (C) is the pure mass ratio of A:B:C = 1:0.5 to 2.0:
It is 0.5-3. (2) If the blending ratio of polyvinyl alcohol is less than the lower limit of the above-mentioned appropriate range, the antifogging property will be insufficient, and the holding power will be particularly small, and if the blending ratio exceeds the upper limit, the appearance will be poor. (3) If the blending ratio of silicone emulsion is below the lower limit of the appropriate range shown in (1), the releasability will be insufficient;
If the upper limit is exceeded, the appearance is inferior.

【table】

[Table] Example 3, Comparative Example 3 Biaxial stretching to a thickness of 0.21 mm by changing the fatty acid component of the sucrose fatty acid ester in the ternary mixed aqueous solution of Experiment No. 2, which received excellent evaluation in Example 1. It was applied to one side of a polystyrene sheet, and the effects of different fatty acid components on the antifogging properties, releasability, and appearance of biaxially oriented polystyrene sheets and molded containers were investigated and evaluated. The ternary mixed aqueous solution had a pure mass concentration of 4% and was applied to the sheet surface in the manner described in Experiment No. 2 of Example 6. The results are shown in Table 3. Sucrose fatty acid esters containing 50% or more of lauric acid as the main component are good; those containing fatty acids with a larger number of carbon atoms as the main component have poor appearance. Note that the evaluation of Experiment No. 2 is a reproduction of that of Example 1.

[Table] Example 4, Comparative Example 4 The degree of polymerization of polyvinyl alcohol in the ternary mixed aqueous solution of Experiment No. 2, which obtained excellent evaluation in Example 1, was changed, and the degree of polymerization was changed to a sheet of biaxially oriented polystyrene. We also investigated the effects on the antifogging properties, releasability, and appearance of the molded containers. In addition, the ternary mixed aqueous solution has a pure mass concentration of 4%,
Application to the surface of a sheet with a thickness of 0.21 mm was carried out in Example 6.
It is based on the No. 2 coating method. The results are shown in Table 4. Polyvinyl alcohol with a degree of polymerization of 800 or less is good, and if a degree of polymerization of 1000 or more is used, the appearance will be poor. Note that the evaluation of Experiment No. 2 is a reproduction of that of Example 1.

[Table] Example 5, Comparative Example 5 The difference in the average particle diameter of the silicone emulsion in the ternary mixed aqueous solution of Experiment No. 2, which received good evaluation in Example 1, was different from that of the biaxially oriented polystyrene sheet and the molded container. Experiments were conducted to examine the effects on antifogging properties, removability, and appearance. The thickness of the sheet was 0.21 mm, the pure mass concentration of the ternary mixed aqueous solution was 4%, and the coating on the sheet surface was carried out by the method described in Experiment No. 2 of Example 6. The results are shown in Table 5. The average particle size of silicone emulsion is
If it is about 1μ or less, it is considered that it can be used with little effect on the appearance. Preferably it is 0.5μ or less. Those with an average particle size of 5μ cannot be used because of their appearance deterioration. Note that the evaluation of Experiment No. 2 is a reproduction of that of Example 1.

[Table] Example 6, Comparative Example 6 The ternary mixed aqueous solution of Example 1 Experiment No. 2 was applied to the surface of a 0.21 mm thick sheet of biaxially oriented polystyrene using various methods, and the differences in application methods were evaluated. We investigated the effects of this on the antifogging properties, releasability, and appearance of sheets and molded containers. The results are shown in Table 6. The coating method of Experiment No. 2 in the table was the method carried out in Examples 1 to 5 and Comparative Examples 1 to 5, in which the sheet was run along the surface of a roller whose lower part was immersed in an aqueous solution. After the aqueous solution is applied to the surface, it is guided to the surface of another roller, and compressed air is blown through the slit of an air knife provided across the sheet to even out the application liquid and separate the application liquid and the sheet. The method involves blending the surface and then introducing the sheet into a dry air circulation oven to dry it. Note that the evaluation of Experiment No. 2 is the same as that of Example 1. From Table 6, it can be seen that the coating methods of the comparative examples all resulted in poor appearance. This is because the coating amount is uneven and the aqueous solution does not mix well with the sheet surface due to the hydrophobicity of the sheet surface, and is repelled, leaving a portion without a coating film on the sheet surface.

[Table] Comparative Example 7 Comparative Example 7 is a comparison with the present invention.
This experiment was conducted to confirm the effectiveness of the method of subjecting biaxially oriented polystyrene to prior corona discharge treatment and then performing antifogging treatment on the biaxially oriented polystyrene according to No. 53-115781. In Experiment No. 42, corona discharge treatment was applied to the surface of a 0.21 mm thick sheet of biaxially oriented polystyrene so that the surface tension measured according to JIS K-6768 was 50 dyn/cm, and sorbitan monooleate was applied to the surface. An aqueous solution containing 3% by weight of ethylene oxide adduct and 0.5% by weight of methylpolysiloxane elastomer was applied onto the sheet surface by roll coating so that the amount of the liquid adhered to the sheet was 6 g/m ² and dried. . In addition, in Experiment No. 43, a binary mixed aqueous solution obtained by removing the polyvinyl alcohol component from the ternary mixed aqueous solution used in the practice of the present invention, that is, polyoxyethylene sorbitan monolayer, was applied to a sheet that had been subjected to a corona discharge treatment in the same manner as in No. 42. Rate 1% by weight and average particle size
An aqueous solution in which 2% by weight of a 0.5μ silicone emulsion was dissolved was applied to the corona discharge treated sheet surface by a roll coating method so that the amount of the liquid adhered to the surface was 0.3g/m ² and dried. The sheets and molded containers coated in this way were investigated for their effects on antifogging properties, releasability, and appearance, and were evaluated in accordance with the evaluation methods and evaluation criteria listed above. The results are shown in Table 7. Table 7 shows that in both Experiment Nos. 42 and 43, the effect of the present invention was not exhibited by the method of applying antifogging agent and silicone to the surface treated with corona discharge, that is, the antifogging property deteriorated over time. It can be seen that the performance also deteriorates when the container is made into a molded container. This is because not only does the adhesive strength of the corona-treated surface decrease over time, but also when the container is thermoformed, the corona-treated surface is heated and stretched, causing a decrease in the surface tension of the treated surface. This is thought to be due to the weakening of the adhesion of the antifogging agent and silicone.

【table】

Claims (1)

[Claims] 1 A sucrose fatty acid ester whose main fatty acid component is lauric acid is applied to the surface of a styrene resin film/sheet running along the surface of a rotating roller.
(A), undenatured polyvinyl alcohol (B) with a degree of polymerization of 800 or less, and silicone emulsion (C) with an average particle size of less than 1μ in a pure mass ratio of A:B:C
= 1:0.5~2:0.5~3 mixed aqueous solution is applied, and then compressed air is blown onto the surface of the film sheet to which the above aqueous solution is attached through the slit of an air knife installed across the film sheet. A method for producing styrenic resin films and sheets that feature excellent anti-fog properties and removability.