JPH10193439A - Manufacture of easily breakable sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate and make safer the cutting off of individual packs by a method wherein an air gap and the nip pressure of a nip roll are made specified values, and a taking over is performed. SOLUTION: In a taking-over process of a styrene based resin expanded sheet of which the free expansion ratio is 1.2-5 times, an air gap (a) is made 2-30cm, and the nip pressure of a nip roll 3 is made 0.2-10kg/cm<2> to perform a taking-off. Also, the thickness of a skin layer which is non-expanded and has no cracks, is made 1-20% of the sheet thickness. Then, the styrene based resin comprises a copolymer of which the major constituent unit is a styrene based vinyl monomer such as styrene, methylstyrene, dimethylstyrene, and it may be other vinyl monomer, e.g. a copolymer with an acrylic acid, methacrylic acid or an ester of these, acrylonitrile, acrylamide, methacrylnitrile, maleic anhydride, etc. For the foaming agent, various kinds of volatile foaming agents or decomposing foaming agents are applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic sheet suitable for forming an integrally connected divided pack which can store foods and the like in small pieces and can be used separately as required. More specifically, the present invention relates to a method for forming an easily breakable styrene-based resin low-foamable sheet which can be easily broken and cut off only by bending, and an applied sheet thereof.

[0002]

2. Description of the Related Art Recently, natto, side dishes, spices, soups, creams, baby foods, etc. can be stored and stored for each meal. It has been heavily used. These are formed by thermoforming a non-foamed or foamed plastic sheet such as polypropylene or polystyrene.The lid and the upper edge of the container are each formed continuously and integrally, or only the lid is a separate sheet material, For example, it has a structure such as using a printed aluminum foil. In these conventional products, in order to easily separate the individual packs, a step of notching or perforating a continuous portion between the packs is inevitable. Moreover, in this case, it is necessary to adjust the depth and width of the notch and the perforation corresponding to the difference in the thickness and rigidity of the sheet, and it becomes more complicated than expected, while the notch and the perforation must be inserted. Incomplete rupture, there is a risk that the fold may be simply bent, or the rupture line may be displaced, causing damage to the adjacent pack, or, at times, the fingertip being cut.

[0003]

SUMMARY OF THE INVENTION It is a main object of the present invention to provide a thermoforming device which does not require notching or perforation and which can be easily and safely broken and separated simply by bending a desired portion. An object of the present invention is to provide a method for forming a styrene-based resin foam sheet for a product. In view of the above problems, the present inventors have conducted intensive studies, and as a result, in the step of taking out a styrene resin foam extruded sheet having a predetermined free expansion ratio, by devising a cooling and pressing method, the desired The inventors have found that a sheet can be obtained, and have reached the present invention.

[0004]

According to the present invention, an air gap is set to 2 to 30 cm and a roll nip pressure is set to 0.2 in a take-up process of a styrene resin foam sheet having a free expansion ratio of 1.2 to 5 times. A method for forming an easily breakable sheet, characterized in that the sheet is taken off at a pressure of 10 to 10 kg / cm ² , is provided.

In the present invention, the free expansion ratio is the expansion ratio obtained when a foamable sheet is extruded and then freely expanded without applying any external force other than take-off, and the bulk density of the foam is obtained. (Also called apparent density)
Hereinafter, it is simply abbreviated as “expansion ratio”. The air gap refers to the distance between the lip and the roll nip of the extruder die.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the expansion ratio at the time of extruding a foam sheet is 1.2 to 5 times, preferably 1.5 to 5 times.
3 times, and when the expansion ratio of the sheet is less than 1.2 times,
Since the number of cracks generated in the sheet is small, the sheet does not easily break. When the expansion ratio exceeds 5 times, the sheet after the nip becomes too flexible and thus does not have rigidity and cannot be broken by bending.

The air gap in the present invention needs to be appropriately changed depending on the thickness of the foam sheet, the expansion ratio, the take-up speed, the ambient temperature, the presence / absence of forced air cooling, the degree thereof, etc., but it is generally 2 to 30 cm, preferably 3 to 20 cm. is there. If the air gap is less than 2 cm, the sheet is nipped with insufficient cooling, so that the cells generated inside the sheet are completely crushed and fused, and no crack is generated inside the sheet. On the other hand, if it exceeds 30 cm, the sheet is air-cooled before being nipped, and the cells are completely formed. Therefore, even after the nip, the bubbles do not collapse and do not crack.

The nip pressure of the roll is 0.2 to 10 kg / c.
m ² , preferably 1 to 8 kg / cm ² . When the nip pressure is less than 0.2 kg / cm ² , the cells are not broken and do not crack because of insufficient nip pressure. 10kg /
If it exceeds cm ² , the nip pressure is too high, and the cells are crushed and completely fused, so that no crack occurs.
Alternatively, cracks may be formed on the sheet surface to impair the appearance.

In the sheet of the present invention, the thickness of the non-foamed and crack-free skin layer is in the range of 1 to 20%, preferably 3 to 10% of the sheet thickness. The skin layer is necessary not only for providing a glossy surface to the sheet surface but also for providing a beautiful sheet surface, and also for providing the sheet with rigidity. When the thickness of the skin layer is less than 1%, the sheet does not have the required rigidity, and the sheet has no rigidity. 20%
If it exceeds, the characteristics of the sheet as a solid become stronger,
It is difficult to break.

The raw material styrene resin used in the production method of the present invention is a polymer having a styrene-based vinyl monomer such as styrene, methylstyrene or dimethylstyrene as a main constituent unit, and another vinyl monomer such as acrylic acid. , Methacrylic acid or their esters, acrylonitrile, acrylamide, methacrylonitrile, maleic anhydride, and the like.

[0011] A rubber component may be contained as a blend or copolymer component with the polystyrene resin. Various rubbers are suitable as the rubber component, butadiene rubber, ethylene propylene rubber, styrene butadiene rubber and the like are suitable when used as a blend component, butadiene, isoprene, and the like when used as a copolymer component.
It is appropriate to use a polystyrene resin obtained by copolymerizing a monomer or oligomer such as chloroprene at a predetermined molar ratio.

The polystyrene-based resin composition used in the present invention has additives that do not affect the production of a polystyrene-based foamed sheet having desired properties, such as a coloring agent, a flame retardant, a lubricant, and a spreading agent. , A dispersant, an antistatic agent and the like may be added.

As the foaming agent, various volatile foaming agents and decomposition type foaming agents are applied. Examples of the volatile foaming agent include hydrocarbons having a boiling point of about -40 to 45 ° C, such as propane, butane, and pentane, and boiling points of about -47 to 45, such as trichloromonofluoromethane, dichlorodifluoromethane, and 1,2-dichlorotetrafluoroethane. Suitable are halogenated hydrocarbons at 0 ° C and mixtures thereof. As decomposition type foaming agents,
Organic blowing agents such as azodicarbonamide, dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazine), and combinations of organic acids such as sodium bicarbonate or citric acid or salts thereof with bicarbonates. Appropriate. In some cases, carbon dioxide,
Nitrogen gas, water, etc. can also be applied.

A known extruder can be used in the present invention. The shape of the die may be any of a T shape, a cylindrical shape, and the like.

[0015]

【Example】

Example 1 A sheet was formed by an apparatus shown in FIG. 1 (the die is a T-die). 0.5 parts of sodium bicarbonate and 0.5 parts of citric acid were added to 100 parts by weight of an impact-resistant polystyrene resin (trade name: R81, manufactured by Daicel Chemical Industries, Ltd.). The raw resin is supplied to a rotary screw type extruder and extruded. The temperature gradient of this extruder was 190
℃, then 210 ℃ and die temperature 210 ℃
It was extruded at a screw rotation speed of 0 rpm. Further, the sheet was formed with an air gap of 10 cm and a roll nip pressure of 5 kg / cm ² . The obtained sheet had a smooth skin layer and was easily broken by bending with a finger.
Further, from this sheet, four connected sub-packs were vacuum formed, and the breakability was tested in the same manner, and similar results were obtained.

Example 2 To 100 parts of the impact-resistant polystyrene resin of Example 1, 0.7 part of azodicarbonamide was added. This raw material resin was extruded at the temperature gradient and rotation speed of Example 1. Sheet forming: air gap 20cm, roll nip pressure 8kg / c
Sheet molding was performed at m ² . The obtained sheet had a smooth skin layer and was easily broken by bending with a finger. Further, the breakability of the vacuum molded product was confirmed in the same manner as in Example 1, and similar results were obtained.

Comparative Example 1 To 100 parts by weight of the impact-resistant polystyrene of Example 1, 0.2 parts of sodium bicarbonate and 0.2 parts of citric acid were added. This raw material resin was extruded at the temperature gradient and rotation speed of Example 1. The sheet was formed with an air gap of 10 cm and a roll nip pressure of 5 kg / cm ² . The resulting sheet had a smooth skin layer, but did not break easily when folded with a finger. In addition, as a result of testing the breakability of the vacuum molded product in the same manner as in Example 1,
The result was similar to that of the sheet.

Comparative Example 2 To 100 parts by weight of the impact-resistant polystyrene of Example 1, 2 parts of sodium bicarbonate and 2 parts of citric acid were added. This raw material tree was extruded at the temperature gradient and the rotation speed of Example 1. Sheet forming is air gap 10cm, roll nip pressure 5k
Sheet molding was performed at g / cm ² . The skin layer of the obtained sheet was not smooth and did not easily break by bending with a finger. Further, as in Comparative Example 1, a rupture test was performed on the vacuum-formed product, and the results were similar.

Comparative Examples 3 to 6 To 100 parts by weight of the impact-resistant styrene of Example 1, 0.5 part of sodium bicarbonate and 0.5 part of citric acid were added. This raw material resin was extruded at the temperature gradient and rotation speed of Example 1. The sheet molding was performed under the conditions shown in Table 1 (air gap,
Roll nip pressure). No sheet having both smoothness and easy breakability of the skin layer was obtained in the obtained sheet. In addition, as in Comparative Example 1, a rupture test was performed on the vacuum-formed product, and the results were similar.

The molding conditions and the evaluation results of the molded sheets of the above Examples and Comparative Examples are summarized in Table 1.

[Table 1]

[Evaluation Method] Measurement of Ratio of Skin Layer The cross section of the sheet was observed with an optical microscope or a reflection microscope, and the thickness of the non-foamed portion (skin layer) (A) and the thickness of the foamed layer (B) were determined to be non-foamed. The ratio of the parts (skin layers) was calculated. Breakability 性: easily broken by bending with a finger. ×: Not broken by bending with fingers. Appearance ・ ・ ・: No irregularities are seen on the surface visually, and the surface is glossy. Δ: No irregularities were observed on the surface by visual inspection, and there was no gloss. ×: Unevenness can be visually confirmed on the surface, and there is no gloss.

[0022]

As described above, according to the method for forming a foamable styrenic resin foam sheet of the present invention, a foamable sheet having a non-foamed skin layer having high smoothness can be obtained, and this sheet is continuously integrated. When thermoformed into a package for sub-packaging, the separation of individual packs is much easier and safer than conventional products, so that it is extremely useful as a sub-packaging sheet for foods and the like.

[Brief description of the drawings]

FIG. 1 is a main part process chart of the molding method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder h Hopper 2 Dice 3 Nip roll 4 Winding machine a Air gap n Nip part R Forming material S Finished sheet

Claims (2)

[Claims] In the step of taking a styrene-based resin easily breakable foam sheet having a free expansion ratio of 1.2 to 5 times, an air gap is set to 2 to 30 cm, and a nip pressure of a nip roll is set to 0.2 to 10 kg / cm. ^{2. A} method for forming an easily breakable sheet, wherein the sheet is taken off. 2. The method according to claim 1, wherein the thickness of the non-foamed skin layer in the finished sheet is from 1% to 20% of the sheet thickness.