JPH11277606A - Polystyrene-based resin foamed sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polystyrene-based resin foamed sheet, the curved surface printability to a molded container of which is favorable. SOLUTION: This foamed sheet is treated through heating only its surface layer by bringing the surface of a polystyrene-based resin foamed sheet 1 in contact with a roller 2, which is heated up to a temperature higher than the softening temperature of a resin by 20 deg.C or higher and cooled by bringing the heated surface of the foamed sheet with a mirror-finished metal roll 4, which is cooled to the softening temperature of resin or lower. Since the foaming agent left on the surface layer can be volatilized without deteriorating the surface smoothness of the foamed sheet through this surface treatment, the secondary foaming of the surface layer can be prevented from developing at molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed polystyrene resin sheet capable of forming a container or the like having excellent surface smoothness. Lamination, so-called extrusion lamination to laminate hot-melted resin, or so-called sand lamination to laminate a film with hot-melted resin as an adhesive is performed on one or both sides,
The present invention relates to a polystyrene-based resin foamed laminated sheet that can form a container or the like having excellent printability.

[0002]

2. Description of the Related Art Resin foam sheets are used in various fields such as food trays and bowls for ready-to-cook foods. Among them, polystyrene resin foam sheets having excellent moldability and economical efficiency are used. Used in large quantities. For such a polystyrene resin foam sheet, an extrusion foam molding method, which has features such as a simple molding process and a stable quality, has been widely used.

In a method for producing a foamed polystyrene resin sheet using an extrusion foam molding method, a resin composition melt-kneaded together with a foaming agent and a nucleating agent is discharged from a circular die orifice into the atmosphere to form a tubular foamed resin. Obtain the composition. At that time, it is manufactured by developing the surface while cooling it with air, contacting the inner surface with a cooling drum to cool, and then cutting open one end of the tube.

When the obtained polystyrene resin foam sheet is used for instant cooked food bowls or the like, the strength, glossiness, luxury feeling, etc., of the foamed sheet alone are insufficient. Or, so-called extrusion lamination in which hot-melted resin is laminated on both sides, sand lamination in which a film and a foamed sheet are laminated using the hot-melted resin as an adhesive, and heat lamination in which the film is directly thermocompression-bonded to the foamed sheet. It is used as a foam laminated sheet for molding rice bowls and the like.

The foamed polystyrene resin sheet is formed into a container such as a bowl by molding, and thereafter, the outer surface of the container is subjected to a curved surface printing such as a design or a character as needed for the purpose of imparting a design property or the like. At this time, if the surface smoothness of the outer surface of the container is inferior, printing omission or fading occurs, causing a problem that the appearance is lacking and the product image is impaired.

Usually, the polystyrene resin foam sheet is formed by softening by heating and embossing with a convex mold and a concave mold. However, a foaming agent added and used at the time of manufacture remains in the polystyrene resin foam sheet, and further foams when heated. This phenomenon is called secondary foaming.

[0007] The foamed polystyrene resin sheet undergoes secondary foaming due to the vaporization of the residual foaming agent used during the production due to the heat generated during the above-mentioned forming process. At this time, the surface of the polystyrene resin foam sheet before the forming process is cooled by air at the time of manufacturing, and the inner surface particularly has high smoothness because it is further contacted with the metal drum and cooled. However, secondary foaming is caused by heating during the molding process, and bubbles forming the polystyrene-based resin foam sheet expand, causing irregularities on the surface. For that,
The surface smoothness of the molded container becomes poor, and the suitability for printing on a curved surface becomes poor.

[0008]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned drawbacks. As a result, prior to molding, only the surface layer of the polystyrene resin foam sheet was softened to form a surface layer portion. While volatilizing the remaining foaming agent, the mirror surface metal roll is pressed against the softened surface and cooled to maintain or improve the smoothness of the surface, whereby the design is remarkably improved and a high quality product is obtained. They have found that they can do so and arrived at the present invention.

Accordingly, a first object of the present invention is to improve the surface smoothness of a container or the like processed by thermoforming, and to provide a molded product which has good printability when performing curved surface printing and does not impair the product image. To provide a foamed polystyrene resin sheet for molding. A second object of the present invention is to provide a resin-laminated polystyrene-based resin foam laminated sheet capable of forming a container or the like having good printability and excellent design. Further, a third object of the present invention is to provide a method for producing a resin-laminated polystyrene-based resin foam laminated sheet that can form a container or the like having excellent printability.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polystyrene resin foam sheet on at least one surface of which is provided with a heating roll heated to a resin softening temperature + 20 ° C. or higher so that only the surface layer is softened. Immediately after heating by contact, the surface layer is cooled by contacting a mirror-finished metal roll cooled to a resin softening temperature or lower, and the surface is smoothed while the foaming agent remaining on the surface layer is volatilized. This is achieved by a polystyrene-based resin foam sheet.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The foamed polystyrene resin sheet which can be used in the present invention can be appropriately selected from known ones. Generally, the foamed sheet obtained by a usual extrusion foaming method is used. It is preferably a sheet. Further, the styrene resin is not particularly limited. For example, general-purpose polystyrene resin, high impact polystyrene resin, styrene-acrylonitrile copolymer resin, styrene-methyl methacrylate copolymer resin, styrene-acrylic acid copolymer resin, styrene-
It can be appropriately selected from maleic anhydride copolymer resins and the like and mixtures thereof and used.

[0012] To these polystyrene resins, an inorganic substance such as talc or calcium carbonate as a nucleating agent and additives such as a lubricant, a plasticizer and a stabilizer may be added according to desired physical properties. it can. The foaming agent can be appropriately selected from known ones used for polystyrene resins. As such a foaming agent, for example,
Examples thereof include hydrocarbon compounds such as propane, butane, hexane, and heptane, and halogenated hydrocarbon compounds such as methyl chloride and methylene chloride.

The heating roll temperature, processing speed, nip pressure, etc., when treating the surface of the polystyrene resin foam sheet, depend on the combination of conditions, the properties of the polystyrene resin foam sheet, the composition of the resin (raw material) used, and the like. Set appropriately as it changes. For example, in the case of a foamed sheet using general-purpose polystyrene and having an expansion ratio of about 10 times, the roll temperature is 120 to 220 ° C. and the processing speed is 3 to 2
5 m / min, the linear pressure of the nip is about 2 to 15 kg / cm, and in particular, it is possible to perform short-time processing at a high temperature by setting the roll temperature to 160 to 220 ° C. and the processing speed to 10 to 25 m / min. preferable.

In this case, it is necessary not to apply excessive heat so as to destroy bubbles in the surface layer of the foamed polystyrene resin sheet. Therefore, in the present invention, the temperature of the heating roll is higher than the softening temperature of the resin by 20 ° C. or more,
It is preferable that the temperature be as high as possible within a range in which bubbles in the surface layer are not destroyed by heating. If the heating roll temperature is lower than the resin softening temperature + 20 ° C., the polystyrene resin foam sheet must be brought into contact with the heating roll for a long time, so that not only the surface layer portion but also the inside of the polystyrene resin foam sheet is heated. Next foaming occurs,
It is not preferable because a product having desired characteristics (thickness or the like) cannot be obtained. Here, the surface layer is not strict, but can be considered as a layer from the surface to a depth of about 1/10 of the sheet thickness.

In the present invention, the surface of the foamed polystyrene resin sheet, which is in a softened state immediately after contact with the heating roll, is brought into contact with a mirror-finished metal roll cooled to a temperature lower than the softening temperature of the resin to be cooled. Therefore, it is necessary to install the mirror-finished metal roll with as little space as possible from the heating roll, and to bring the polystyrene-based resin foam sheet into contact with the mirror-finished metal roll in a softened state in which the surface temperature is as high as possible.

The temperature of the mirror metal roll is not higher than the softening temperature of the polystyrene resin used for the polystyrene resin foam sheet, preferably not higher than -30 ° C. If the temperature of the mirror-finished metal roll is higher than the resin softening temperature of −30 ° C., the efficiency of cooling and solidifying the polystyrene resin foam sheet having a softened surface is poor, and the processing speed cannot be increased. Therefore, the polystyrene-based resin foam sheet must be brought into contact with the mirror-finished metal roll for a long time, and the angle of wrapping of the sheet with respect to the roll must be increased, so that the treated polystyrene-based resin foam sheet is likely to be curled.

The polystyrene resin foam sheet is pressed against the mirror-finished metal roll by pressing it using a nip with a roll or a belt made of a canvas, metal, or the like. The pressing pressure and contact time of the foamed polystyrene resin sheet to the mirror-finished metal roll are not particularly limited because they differ depending on the combination of conditions, the properties of the foamed sheet, the composition of the resin (raw material) used, and the like. In the present invention, the polystyrene resin foam sheet is cooled by contacting the surface of the polystyrene resin foam sheet at a pressure as high as possible without destroying the bubbles forming the polystyrene resin foam sheet until the surface of the polystyrene resin foam sheet becomes a resin softening temperature or lower.

The diameter of the mirror-finished metal roll is preferably as large as possible in order to prevent curl from remaining in the polystyrene resin foam sheet. There is no particular limitation on the timing of the above-described surface heating / cooling treatment, and the treatment may be performed online immediately after the production of the polystyrene resin foam sheet, offline treatment after curing, or online immediately before lamination.

The foamed polystyrene resin sheet which has been subjected to the surface treatment can be molded as it is to form a packaging container or the like. It is preferable to use lamination on one or both sides by so-called extrusion lamination, so-called sand lamination in which a film is laminated with a hot-melted resin as an adhesive, or thermal lamination in which the film is directly thermocompression-bonded to a foam sheet. .
The polystyrene-based resin foam laminated sheet of the present invention having the resin layers laminated as described above is then molded and processed into a container, and subjected to curved surface printing.

The surface treatment in the present invention is performed for the purpose of improving curved surface printability on a container formed and processed after laminating. However, the surface treatment is not limited to one side and is intended to improve the surface smoothness of the container. It may be applied to both sides. Also,
Even when lamination is not performed, it may be performed for the purpose of improving the surface smoothness of the formed container.

[0021]

When the foamed polystyrene resin sheet of the present invention is used, since the surface of the molded container has a high surface smoothness, good printing without printing omission or blurring can be obtained when performing curved surface printing. I can do it. This effect is particularly remarkable when laminating.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. Embodiment 1 FIG. General-purpose polystyrene resin (JIS K-687
100 parts by weight of the talc were mixed with 0.45 parts by weight of talc and then charged into an extruder having a diameter of 65 mm heated to 200 ° C. to be melt-kneaded.

Next, 3.5 parts by weight of butane as a foaming agent was press-fitted and mixed from an injection port provided in the middle of the extruder, and then passed through an extruder equipped with an oil circulation type cooling mechanism, and then passed through a polystyrene resin. The composition was cooled and discharged from an annular die orifice having a diameter of 150 mm and a lip opening of 0.45 mm attached to the tip of an extruder to obtain a tubular foamed resin. The temperature at the outlet of the annular die at this time was 130 ° C.

Next, the tubular foamed resin was blown up at a take-up speed of 3.9 m / min while blowing the air at 20 ° C. to cool the surface, and the inner surface was further cooled and solidified by a cooling drum having a diameter of 400 mm. After slitting,
A polystyrene foam sheet having a thickness of 2.2 mm and a basis weight of 235 g / m ² was produced.

One week after the production, the inner surface of the polystyrene foam sheet (the surface that was in contact with the metal drum at the time of production) was placed on a hot roll having a diameter of 250 mm and a temperature of 195 ° C. at a speed of 20 mm.
m / min and a linear pressure of 5 kg / cm, and then press it against a mirror-finished metal roll having a diameter of 500 mm and a temperature of 30 ° C. using a canvas belt at a wrap angle of 90 ° while cooling and solidifying to a speed of 20 m / min. Rolled up.

Almost no irregularities were found on the surface of the polystyrene foam sheet after the surface treatment described above. Treated surface of the polystyrene foam sheet, the hot molten high impact polystyrene resin was extrusion laminated in a 1 m ² per 165 g, the thickness at a basis weight 400 g / m ² was prepared 2.4mm polystyrene foam laminated sheet .

This polystyrene foam laminated sheet was processed into a bowl having a diameter of 145 mm and a depth of 70 mm using a continuous molding machine so that the lamination surface was outside the bowl. The center line average roughness of the outer surface of this bowl was measured to be 0.36 μm. When the curved surface printing was performed, the printing was good without any omission of printing. Table 1 shows the evaluation results. still,
The center line average roughness is a surface roughness meter (manufactured by Kosaka Laboratory Co., Ltd.)
JIS-B using universal surface profiler SE-3C)
0601 was measured.

Comparative Example 1 A polystyrene foam sheet was produced in exactly the same manner as in Example 1. A polystyrene foam laminated sheet having a basis weight of 400 g / m ² and a thickness of 2.4 mm was produced in exactly the same manner as in Example 1 except that the heating / cooling treatment of the present invention was not performed.

Using this polystyrene foam laminated sheet,
In exactly the same manner as in Example 1, the bowl was processed into a bowl having a diameter of 145 mm and a depth of 70 mm so that the laminated surface was outside the bowl. When the center line average roughness of the outer surface of this bowl was measured, it was 0.64 μm.
Missing or faint printing was observed, and the appearance was poor. Table 1 shows the evaluation results.

Comparative Example 2 A polystyrene foam sheet was produced in exactly the same manner as in Example 1. Then, one week after the production, the inner surface of the polystyrene foam sheet (the surface that was in contact with the metal drum at the time of production) was heated to a diameter of 250 mm and a temperature of 19 mm.
A speed of 20 m / min and a linear pressure of 5 kg / cm on a 5 ° C. hot roll
After the contact, the surface was solidified by natural cooling and wound up without contacting the mirror-finished metal roll.

The surface of the polystyrene foam sheet after the surface treatment had irregularities, and the surface smoothness was poor. Then, the basis weight was 40 in the same manner as in Example 1.
A polystyrene foam laminated sheet having a thickness of 0 g / m ² and a thickness of 2.4 mm was prepared. Using this polystyrene foam laminated sheet, in exactly the same manner as in Example 1, the laminated surface was outside the bowl, and the diameter was 145 mm and the depth was 70 mm.
Processed into a bowl. The center line average roughness of the outer surface of this bowl was measured to be 0.72 μm, and when subjected to curved surface printing, missing or blurred printing was observed and the appearance was poor. Table 1 shows the evaluation results.

[0032]

[Table 1] The results in Table 1 demonstrate the effectiveness of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for treating the surface of a polystyrene resin foam sheet in which a nip roll presses a polystyrene resin foam sheet against a mirror-finished metal roll.

FIG. 2 is a schematic diagram of an apparatus for treating the surface of a polystyrene resin foam sheet used in an example, in which a polystyrene resin foam sheet is pressed against a mirror-finished metal roll by a canvas belt.

[Explanation of symbols]

 1. 1. Polystyrene resin foam sheet Heating roll 3. Nip roll 4. Mirror metal roll 5. Canvas belt 6. Rotating roll for canvas belt

Claims (3)

[Claims] 1. Immediately after a heating roll heated to a resin softening temperature + 20 ° C. or more is brought into contact with at least one surface of a foamed polystyrene resin sheet so that only the surface layer is softened, the surface layer is immediately heated. A foamed polystyrene resin sheet characterized in that it is cooled by bringing it into contact with a mirror-finished metal roll cooled to a resin softening temperature or lower to vaporize a foaming agent remaining in the surface layer and smoothen the surface. 2. A foamed polystyrene resin sheet obtained by laminating a resin layer on the smoothed surface of the foamed polystyrene resin sheet according to claim 1, wherein the foaming agent is volatilized. 3. Immediately after heating at least one surface of the polystyrene resin foam sheet by heating it with a heating roll heated to a resin softening temperature + 20 ° C. or higher so that only the surface layer is softened, It is cooled by bringing it into contact with a mirror-finished metal roll cooled to a resin softening temperature or lower, and from the surface layer of one or both surfaces of the polystyrene resin foam sheet, the remaining foaming agent is volatilized and the surface is smoothed. Manufacture of a polystyrene-based resin foam laminated sheet, characterized in that a film is directly thermocompressed on a smoothed surface, a hot-melted resin is laminated, or a film is laminated using the hot-melted resin as an adhesive. Method.