JPS60168733A - Polystyrene resin foam sheet - Google Patents

Abstract

PURPOSE:The titled foam sheet rich in flexibility and suitable for the production of fruit trays, etc., prepared by mixing polystyrene with a styrene/butadiene/styrene block copolymer and a higher fatty acid metal salt and expansion-molding the mixture. CONSTITUTION:A resin composition comprising 100pts.wt. polystyrene (number- average MW of 8X10<4>-2.2X10<5>, weight-average MW of 10X10<4>-5X10<5>), 5- 20pts.wt. styrene/butadiene/styrene block copolymer (e.g., Toughprene, a product of Asahi Kasei Co., Ltd.), 0.2-5pts.wt. nucleating agent (e.g., talc or magnesium carbonate) and 0.05-1pt.wt. higher fatty acid metal salt (e.g., zinc stearate) is melted together with a blowing agent (a low-boiling organic compound) by heating in an extruder and expansion-molded through a die to form a sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polystyrene resin foam sheet suitable for forming containers such as fruit trays and fresh fish trays by vacuum forming or pressure forming.

Since the foam sheet of the present invention is highly flexible, it is useful as a cushioning material used as a partition between fruits.

A polystyrene resin foam sheet (so-called styrene paper) is used as a material for molding trays for fresh fish and fruits (Utility Model Application Publication No. 58-92040).

Usually, such styrene vapor is produced by supplying a composition prepared by mixing polystyrene pellets and a nucleating agent such as silica sand, talc, charcoal, etc. in a mixer from a hopper of an extruder, and then extruding the mixture at 230 to 250°C. Shibutane is melted and kneaded, and a pipe is installed in the middle of the extrusion process to extrude the molten mixture.
After adding a blowing agent such as pentane, methylene chloride, dichlorodifluoromethane, etc., the cooling zone of the extruder
It is manufactured by cooling the sheet to 0.degree. C., then extruding it into a tubular foam using a goo, and after cooling, cutting the tubular foam sheet into two sides with a cutter (Japanese Patent Publication No. 15709/1983). In addition, this sheet may be produced using separate extruders for kneading and cooling (Japanese Patent Publication No. 25781/1989).

The polystyrene vapor molded in this way with a wall thickness of 1 to 3 and an apparent density of 0.05 to 0.2 f/crIK is vacuum formed and used as a tray for fresh fish, vegetables, meat, etc. . It is also laminated with another sheet, such as a crosslinked polyethylene foam sheet, and vacuum formed to be used as a tray for fruits such as peaches and pears.

When this polystyrene paper tray is used as a packaging material for meat and seafood, it is usually wrapped in cling film, but since it has poor flexibility (impact resistance), it is necessary to wrap the tray around the tray when wrapping this film. If you apply too much force, it may break.

The present invention attempts to solve such drawbacks of conventional styrene paper by adding a styrene/butadiene/styrene block copolymer and a metal salt of a higher fatty acid to polystyrene to improve its flexibility.

That is, the present invention provides (4) polystyrene ioo parts by weight styrene-butadiene-styrene block copolymer 5 to 20 parts by weight 0 nucleating agent 0.2 to 5 parts by weight 0 metal salts of higher fatty acids 0.05 to 1 part by weight Above (4)
, (8), a sheet obtained by foaming a resin composition containing components (C) and 0 using a foaming agent, and having an apparent density of 0.05 to 0.297 d. The present invention provides a polystyrene resin foam sheet characterized by:

Weight average molecular weight (MY) is 10X 10'-5X
105 polystyrene can be used.

(The styrene-butadiene-styrene block copolymer of the sand component has an average molecular weight of 25,000 to 1.000,
o o oO ones are common, and Cariflex, ', TR1101, TR1102, TR11 from Shell Company in the United States.
84, TRI 107, TRIII, and TR1112, and is sold by Asahi Kasei under the trade name Toughblen.

This styrene-)butadiene-styrene block copolymer is rubbery. JP-A-58-187436 discloses rubber materials such as SBR, NBR, buna rubber, HIPS, and butyl rubber as impact modifiers for polystyrene; Combination is the best.

This styrene-butadiene-styrene block copolymer is blended in a proportion of 5 to 20 parts by weight per 100 parts by weight of component (4). If the amount is less than 5 parts by weight, the effect of improving impact resistance will be low. On the other hand, if it exceeds 20 parts by weight, the bending strength of the resulting sheet will drop significantly, which is not preferable.

Next, the nucleating agent (component 0) is useful for uniformly adjusting the cell diameter of the foam, and is made of talc, magnesium carbonate,
Inorganic nucleating agents such as perlite, calcium silicate, calcium carbonate, silicon oxide, baryta, and vermiculite, and organic acids such as citric acid, tartaric acid, boric acid, and oxalic acid are used.

This nucleating agent is used in a proportion of 0.2 to -2 parts by weight per 100 parts by weight of polystyrene as component (1).

As a metal salt of higher fatty acid with 0 components, carbon number is 12~
22 higher fatty acids, such as capric acid, stearic acid,
Metal salts such as valmitic acid (Ca.

Examples include Na, K, Li, Zn, At). Particularly suitable are zinc stearate, aluminum stearate and calcium stearate.

This metal salt of higher fatty acid improves the processability during extrusion molding of the sheet and also improves the flexibility of the foam sheet. This metal salt of higher fatty acid is used in a proportion of 0.05 to 1 part by weight per 100 parts by weight of polystyrene as the prison component. If the amount is less than 0.05 part by weight, the effect of improving the flexibility of the sheet is small.

If the amount exceeds 1 part by weight, there is a drawback that the film forming stability of the sheet deteriorates.

The resin composition containing components (4), (Bl, (Q and The foaming agent may be press-fitted into the extruder through a pipe as described above, but the polystyrene resin composition is impregnated with the foaming agent in advance, and then this is supplied from the hopper of the extruder. It may also be molded by melt mixing or extrusion foaming.

The tray obtained by thermoforming the foam sheet of the present invention has good impact resistance.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 (4) Polymethylef 100 parts average molecular weight having the following physical properties 2. OX 105 Weight average molecular weight 1. OX 10' (homogeneous styrene-butadiene-styrene block copolymer "Califlex 1102" 10 parts C) Talc 2.5 parts (2) Zinc stearate 0.3 parts The above resin composition was supplied to the first extruder 230 with an extruder
The resin was melted and kneaded under the conditions of 150 Kf/, iG at 150 Kf/c, and then butane at 230°C was poured into the injection port at 160 Kf/c.
The mixture containing butane gas at a ratio of 4% is transferred to the cooling zone of the extruder using a screw inside the extruder, and in this cooling zone, the mixture of butane gas and molten polystyrene is kneaded by the screw to make it uniform. and 15
Cooled to 0°C.

Next, a cylindrical die extrudes an inflation sheet with an upward diameter of 100 m B, and this sheet is internally cooled and expanded in diameter with a mandrel. Next, the inflation sheet is cut at one place at the part separated from the mandrel.
It was collected as a single foam sheet (collection speed 5m/
minutes).

The average wall thickness of the foam sheet was approximately 2.3 m, the sheet width was 790 mm, and the apparent density was 0.09 t/di.

This foam sheet was heated and melted at 170°C using a vacuum forming machine, and then vacuum molded (450 m
Hg) Molding and then trimming until the average wall thickness is 3. Off, length 195cm, width 126mm, depth 22m
15 m trays were obtained.

Grasp both sides of this tray with your hands and instantaneously bend it 90 degrees in the longitudinal direction, and the breakage will be evaluated, and the level of breakage will be digitized into the following four levels, and used as a guideline for brittleness resistance (numerical force; the lower the better). . The result was 0.

0 = Not broken.

1 = Cracks occur only on either the bottom or both sides.

2 = Cracks occur on both sides or either side and the bottom.

3=Cracks occur on both sides and the bottom.

In addition, a three-point bending test was conducted using an autograph manufactured by Takasugi Seisakusho in which the longitudinal center of the tray was pushed up from the bottom surface. The bending strength at this time was 2.0 Kf.

Furthermore, using the autograph described above, the repulsive force of the tray when the tray was deformed by 12.5 m in such a manner that the centers of both measurement parts in the longitudinal direction were sandwiched from both sides was calculated and was found to be o,s Kf. If this repulsive force is large, when packaging using a tray, it becomes easier to resist the tightening force when the wrap film is placed over the tray and the wrap film is stretched. That is, even a thin sheet can be used, resulting in cost reduction.

Furthermore, flexibility was expressed as compressive strain (Shin) when a load of IKg/d was applied to a material with a thickness of 10 fins (sheets were overlapped to form 10 fins). Materials with a large value can be said to be soft. The result was 0.8 mm.

Examples 2 to 4, Comparative Examples 1 to 3 Foam sheets were obtained in the same manner as in Example 1, except that the compositions of the C"l and υ components were changed as shown in Table 1, and vacuum formed. And got the tray.

Table 1 shows the physical properties of the sheet and tray.

Comparative Example 4 Example 1 except that styrene-butadiene random copolymer rubber (SBR) was used instead of component (B) nostyrene e-butadiene-styrene block copolymer (SBS).
A foam sheet was obtained in the same manner as above, and a tray was obtained by vacuum forming.

Table 1 shows the physical properties of the sheet and tray.

Claims (1)

[Claims] 1), (4) Polystyrene 100 parts by weight (9) Styrene-butadiene-styrene block copolymer 5 to 20 parts by weight
Part by weight (0 nucleating agent 0.2 to 5 parts by weight (1)) Metal salt of higher fatty acid 0.05 to 1 part by weight A resin composition containing the above (A), (2), (Q and A polystyrene resin foam sheet obtained by foaming using a foaming agent, characterized in that the sheet has an apparent density of 0.05 to 0.2y/-.2) Higher fatty acid A foam sheet according to claim 1, characterized in that the metal salt is zinc stearate, calcium stearate or aluminum stearate.