JPS5898222A - Biaxially stretched sheet of styrene resin - Google Patents

Abstract

PURPOSE:To obtain the sheet that is excellent in transparency, rigidity, slipperiness with stretched film and free from rain drop phenomenon in the time of molding by stretching biaxially the sheet with the skin layer containing a small quantity of inorganic powder at least on one surface of a styrene resin sheet. CONSTITUTION:A skin layer containing 0.1-2wt% of inorganic material with average grain diameters 0.5-20mum to styrene resin is provided at least one side of a styrene sheet to be stretched biaxially. Thus, it is possible to obtain the biaxially stretched styrene resin sheet excellent in transparency, rigidity, slipperiness with stretched film and completely free from rain drop phenomenon in the time of molding.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a styrene resin sheet that is biaxially stretched and has a skin layer containing a small amount of inorganic powder on at least one side, and has excellent transparency and rigidity. In addition, we have developed biaxially stretched sheets of 0 styrene resin (hereinafter referred to as ops sheets), which have good slip properties with stretch films and do not cause any raindrop phenomenon during molding. ) are used as food storage containers due to their excellent safety, transparency, and rigidity. Types of ops sheets include transparent type sheets and tray type sheets to which DEM is added. To mold OPS sheets, a hot plate air pressure forming method is usually used in which the sheet is brought into contact with a hot plate to prevent the sheet from shrinking. However, in this method, the OPS sheet tends to stick to the hot plate surface, causing A defective phenomenon called raindrop occurs. Methods have been proposed for this raindrop, such as setting selective molding conditions or roughening the hot plate surface of the hot plate air pressure forming machine to allow the air present at the contact surface to escape, but even these methods are not completely effective. Not resolved. Currently, transparent Tyzo ops sheet molded products are not completely free from the raindrop phenomenon.

In addition, one of the packaging formats for OF8 food storage containers is various
There is a method of overrunning with a snack film. This method involves filling the container with food, then using soft polychlorinated chloride,
The entire opening of the container is covered with a so-called stretch film made of polyethylene, ethylene vinyl acetate copolymer, polycitadiene, or the like. At this time, the stretch film is pulled downward by sliding the container flange so that the upper covering surface of the stretch film is wrinkle-free and taut. It is a packaging form in which the container is fixed at the bottom of the container by taking advantage of the self-adhesive properties of the stretch film or by using a heat sealer or the like. In this method, if the slipperiness between the stretch film and the flange portion of the container 7 is poor, wrinkles will remain on the upper covering surface of the stretch film, making packaging difficult and at the same time reducing the commercial value of the packaged product. In particular, for high-speed packaging using recent automatic packaging machines, good lubricity with stretch films is an essential element. Transparent Tyzo ops sheets do not have the packaging suitability of this stretch film at all, and are not used for this purpose.

Mano The OPB sheet, which was developed to improve these drawbacks, is coated with synthetic imms such as polybutadiene, polyisoprene, polyisoprene, and ethylene-propyleneim.
There is a sheet in which 6.0% by weight is added and biaxially stretched to create fine irregularities on the surface of the sheet. (% Kosho 5
6 35240/The molded product made from this im-added ops sheet does not completely eliminate the phenomenon of raindrops occurring during molding, but is suitable for packaging with stretch film. However, if the rubber content is added until these performances are satisfied, the transparency and rigidity, which are important characteristics of the ops sheet, will be impaired, and the degree of sanding, which is an index of the transparency of the sheet, will be 13. It will be ~30 inches. Also,
Even the tensile modulus, which is an index expressing rigidity, is 180 Kf/
- degree, and it is difficult to say that the sheet has both the transparency and rigidity inherent to OPB sheets.

The inventors of the present invention have previously proposed a multilayer type sheet to which rubber is added, which improves the drawbacks of the above two types. This multilayer type sheet has the benefit of adding rubber only to the skin layer, which allows for good slipperiness with the stretch film without compromising transparency and rigidity, and prevents the occurrence of raindrop phenomenon during molding. It never occurs. However, depending on the molding conditions when molding this multilayer type sheet, it may become flat due to stretching, and the rubber particles that contributed to improving transparency may return to their original shape, resulting in a slight loss of transparency. There were times when it decreased.

The present invention is aimed at solving these drawbacks, and involves stretching a styrene resin sheet with a surface layer containing an inorganic substance powder on two wheels to an area magnification of 4 to 16 times. , fine irregularities are formed only on the surface of the sheet to improve slippage with the stretch film, and the inside of the sheet, which does not affect the slippage with the stretch film, does not contain any substances that have an adverse effect on transparency. The present invention aims to provide a biaxially stretched sheet of styrene resin with good transparency.

That is, in the present invention, the sheet has a skin layer on at least one side. It is made by biaxially stretching a styrene resin sheet, and its skin layer contains an inorganic substance with an average particle size of 0.5 to 20 μ in an amount of 0.1 to 2 f% based on the styrene resin. It is characterized by

The present invention will be further explained below. The styrenic resin for base material referred to in the present invention refers to styrene,
Examples include one type or a combination of vinyl aromatic compounds such as α-methylstyrene, or a copolymer of a vinyl aromatic compound and another copolymerizable monomer. Monomers that can be used for copolymerization with vinyl aromatic compounds include vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids and esters such as acrylic acid and methacrylic acid. Furthermore, if necessary, a rubber component may be added to these compounds to an extent that does not remove the transparency of the layer.For the skin layer, a general type of transparent styrene resin is preferable.

Inorganic powders include silica, calcium carbonate,
Aluminum silicate, talc, diatomaceous earth alumina white, titanium oxide, etc. can be used, but the most preferred is porous silica fine powder from the viewpoint of transparency and coloring of the sheet.

The additive concentration is 0.1 to 2.0 of the epidermal layer by weight,
Preferably it is 0.1 to 1.0%. If it is less than 0.1%, it has no effect on stretch film lubricity, and if it is more than 2.0%, transparency is poor. Moreover, the particle size is 0.
It is 5 to 20μ, and if it is smaller than o or sμ, there is no effect on the slipperiness of the stretch film, and if it is 20μ or more, the transparency will be poor, which is not preferable.

It is very difficult to uniformly disperse these inorganic substance powders, and any known method can be used in the present invention, but specific examples include liquid dispersion such as silicone oil or liquid paraffin. Another method is to use one or more lubricants selected from fatty acids, fatty acid amides, fatty acid esters, fatty acid ketones, fatty acid alcohols, esters of fatty acids and polyhydric alcohols, and the like.

Next, in order to manufacture the product of the present invention, first, the styrene resin, inorganic powder, and dispersant used for the skin layer are mixed in a Banbury mixer,
The pellets are kneaded using various mixing machines such as a co-kneader and an extruder, and then the resin for the base material and the skin layer is supplied by two extruders, and then the resin is passed through a two-layer die or a 3N
The base material and the skin layer are extruded and laminated into one piece using an I die or a die that uses a feed block method. The thickness of this sheet before stretching is 1.0 to 4.0 inches, of which the thickness of the skin layer is 1 to 20% of the total thickness, preferably 2 to 10 inches. If it is less than 19b, it will be difficult to form a film during extrusion F) 20
%, maintaining good transparency becomes a national crisis. The sheet extruded by this method is produced using an inflation method or a tenter method with an area magnification of 4 to 16 in the direction of the two wheels.
Stretched twice sequentially or simultaneously biaxially.

The nine sheets produced in this way are formed into trays, and the contents are actually packed and wrapped in an automatic packaging machine to check the slipperiness with the stretch film. The results corresponded very well to the results of the sensitivity test conducted by bending the material and sliding it on the stretch film, so we tested the cleanliness with the stretch film using the sensitivity test. This will be explained in more detail below with reference to Examples.

Examples 1 to 4 As resin for the base material and skin layer, Denki Kagaku Kogyo ■ trade name "
Dencastyrol HRM-2J, porous silica as an inorganic powder Fuji Davison Chemical ■Product name: Thyroid 244, Toshiba silicone as a dispersant ■Product name: Silicone Oil 1000cs+J 0021t, and Kao Soap ■Product name: Kao Wax ICBP J 0.2 weight was mixed in a Henschel mixer so that the siloids were uniformly dispersed, and then pelletized in an extruder.

This is supplied into the extruder from the supply port of the extruder (L/I) = 24) with a diameter of 40 ~, melted and supplied to a multilayer sheet die at 200 ° C. ■Product name “Denka Styrol HRM-2J 65”
% extruder (L/D=25) was supplied to the extruder from the supply port, melted, and supplied to the die.

The die has multiple manifolds that correspond to separate extruders, and after exiting the manifold, the resins overlap before the lip.The width of the die is 600- and the lip is adjusted to 1.5 mm. As a result, a sheet was obtained in which the skin layer was 2 cm on one side and 41 cm on both sides, and the total sheet thickness was 1.5 mm.

This sheet was cut out to 11]05w x 100cm and stretched 383 times using a biaxial stretching machine (Wakagi Seisakusho■) at a temperature of 160°C.
"The physical properties of this sheet were stretched using the sequential biaxial stretching method, as shown in Table 1. The smoothness with the stretch film was also satisfactory, the transparency and sheet molded product were both good, and the rigidity was not impaired. There was also no occurrence of raindrop phenomenon.

Examples 5 to 7 In the same manner as Examples 1 to 4, inorganic powder Fuji Devinson Chemical ■trade name "Syroid 150° 404 and 6
20'' was used to form a film. As shown in the table, the results met all the performance requirements; however, the finer the particle size of the inorganic substance, the better the transparency.

Examples 8 to 10 Same as Examples 1 to 4, but the thickness of the epidermal layer was 1 to 20%.
The film was formed by changing the As shown in the table, the results satisfied all the performances regardless of the skin layer thickness.

Examples 11-12 Films were formed in the same manner as in Examples 1-4, except that the inorganic substance powder was replaced with calcium legate and fused silica.

As shown in the table, the results were 0 Comparative Examples 1 to 2, which satisfied all the performances as shown in the table.
Thyroid 244 was deposited at a concentration of 0.05% and 2.6 cycles. The results are shown in Table U, with an addition amount of 0.05
%, the transparency, raindrop properties, rigidity, and film formability were good, but the slipperiness with the stretch film was poor. Although the slipperiness and film forming properties were good, the transparency was not satisfactory.

Comparative Examples 3 to 4 Films were formed in the same manner as Examples 1 to 4, with the thickness of the skin layer being 0.8 inch and 2.41 inch. As shown in the table, it was impossible to form a film at 0.8 inch, and at 24 inch, the raindrop properties, rigidity, slipperiness with stretch film, and film formability were satisfied, but the transparency line was not satisfied. It was not worth it.

Comparative Examples 5 to 7 Films were formed in the same manner as Examples 1 to 4, except that polybutadiene was added instead of the inorganic powder under the trade name "Syroid 244." As shown in Table 2, the results showed that all the properties were met at the sheet stage, but when the molded product was made, the transparency decreased and a satisfactory thickness could not be obtained. .

Comparative Examples 8 to 10 Polybutadiene was added to the inorganic powder product name "Syroid 244" in the same manner as in Examples 1 to 4. The slipperiness with the stretch film formed by forming a single-layer sheet was good, but the transparency, rigidity, and raindrop properties were not satisfactory.

Comparative Example 11 The physical properties of a commercially available transparent type OPB were measured. Although the transparency and rigidity were good, the slipperiness with the stretch film was rapid and the raindrop phenomenon occurred frequently.

Comparative Example 12 Commercially available sheet tray type OP with added 24 minutes
The physical properties of s were determined. Although the slipperiness with the stretch film was good and the raindrop phenomenon was reduced, the transparency and rigidity were decreased.The physical properties shown in the table were tested by the following method.

1. Haze (ASTM-D-1003) Nippon Denshoku Kogyo's cloudy needle trade name "NDH-2DJ" was used.

The sharpness was determined by the following formula.

n-10, and the arithmetic mean is shown. Judgment was made by sensitivity test.

O Good Δ Slightly resistant but slippery The tensile modulus was measured and used as an index of rigidity.

4. Raindrop phenomenon 20■ 200X200 with a 0.5■ diameter hole in the pitch
A hot plate was heated to 140 °C, the sample was brought into uniform contact with the hot plate surface, vacuum was drawn through the hole for 1 second, and the sample was removed from the hot plate surface to remove the sample formed on the surface. The number of non-contact parts of the circular hot plate was investigated.

Measurements were performed with n=10, and the arithmetic mean was shown.

Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] A styrenic resin sheet having a skin layer on at least one side of the sheet is biaxially stretched, and the skin layer contains an inorganic substance having an average particle size of 0.5 to 20μ to the styrene resin. A biaxially stretched sheet of styrenic resin containing 1 to 2% by weight.