KR100524549B1 - Polystyrenic multi-layer sheet - Google Patents

Abstract

Polystyrene-based multilayer sheets having excellent heat resistance of the present invention, in particular, (A) at least one core layer composed of polystyrene or high impact polystyrene or a mixture of polystyrene and high impact polystyrene; And (B) 2 to 10 parts by weight of a styrene block copolymer based on 100 parts by weight of a resin mixture consisting of 35 to 60% by weight of polystyrene, 15 to 30% by weight of high impact polystyrene, and 25 to 35% by weight of polypropylene. The present invention relates to a polystyrene coextrusion sheet comprising at least one heat-resistant layer, wherein the polystyrene-based multilayer sheet of the present invention is suitable as a food container having a large molding ratio, rigidity and heat resistance.

Description

Polystyrene Co-Extrusion Sheet {POLYSTYRENIC MULTI-LAYER SHEET}

The present invention relates to a polystyrene coextrusion sheet (Sheet) that can be applied to food containers, etc. More specifically, the heat resistance is characterized in that it comprises a heat-resistant layer consisting of a polystyrene-based core layer and polystyrene / polypropylene alloy The present invention relates to an improved polystyrene coextrusion sheet.

In general, polystyrene (PS) sheets are used in various food containers utilizing the excellent rigidity of polystyrene, and in particular, they are also used as food packaging containers having a large molding ratio due to the excellent vacuum molding characteristics of polystyrene.

As the polystyrene sheet used for food packaging, a polystyrene resin or a high impact polystyrene resin or a mixture of a polystyrene resin and a high impact polystyrene resin is used. In addition, when gas barrier properties are required for food storage, ethylene vinyl alcohol (EVOH) may be co-extruded with polystyrene.

However, a container formed of a polystyrene sheet has a problem in that the container is deformed due to lack of heat resistance during heat sterilization during food packaging. The polypropylene resin is a heat resistant sheet material for supplementing the weak heat resistance of such polystyrene resin. Polypropylene sheets are used in microwave ovens and the like requiring heat resistance because they are excellent in heat resistance. However, since polypropylene resin is not excellent in vacuum forming characteristics and stiffness, it cannot be used as a container having a large molding ratio or a container requiring rigidity.

As a solution to this problem, a coextrusion sheet is known in which the core layer is composed of a polystyrene layer, and the polystyrene and polypropylene are composed of a polypropylene layer on one or both surfaces of the surface layer. However, the sheet produced by this method has a slightly increased heat resistance, but there is a problem in that interlayer peeling occurs when vacuum forming is used due to poor interlayer adhesion of the manufactured multilayer sheet. In order to improve the delamination, there is a method of using an ethylene / vinylacetate copolymer as an adhesive layer, but such a manufacturing method is complicated in the manufacturing process, and scrap generated during sheet production and container molding cannot be reused. There is a problem that the manufacturing cost of the rise.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the prior art described above, and to provide a polystyrene coextrusion sheet suitable for a food container, etc., having a large molding ratio and rigidity and excellent heat resistance.

That is, the present invention provides a composition comprising (A) at least one core layer composed of polystyrene or high impact polystyrene or a mixture of polystyrene and high impact polystyrene; And

(B) as long as it is prepared by adding 2 to 10 parts by weight of a styrenic block copolymer based on 100 parts by weight of a resin mixture composed of 35 to 60% by weight of polystyrene, 15 to 30% by weight of high impact polystyrene, and 25 to 35% by weight of polypropylene. It is to provide a polystyrene-based coextrusion sheet comprising a heat-resistant layer or more of the layer.

Hereinafter, (A) polystyrene core layer and (B) polystyrene / polypropylene alloy heat-resistant layer which comprise the polystyrene coextrusion sheet of this invention are demonstrated in detail.

(A) Polystyrene Core Layer

The core layer of the polystyrene coextrusion sheet of the present invention is composed of polystyrene or high impact polystyrene or a mixture of polystyrene and high impact polystyrene according to the required physical properties of the final product, and the layer is composed of at least one layer and has a thickness of 1 It is preferable that it is-5 mm. Polystyrene sheets are used for containers requiring transparency, high impact polystyrene sheets are used for containers requiring impact resistance, and sheets made with a mixture of polystyrene resin and high impact polystyrene resin are used for containers requiring both impact and rigidity. .

In the present invention, when polystyrene is measured at 200 ° C. and 5 kgf, the melt index is preferably 1 to 50 g / 10 min, more preferably 2 to 10 g / min. When the high impact polystyrene is measured at 200 ° C. and 5 kgf, the melt index is preferably 0.5 to 10 g / 10 minutes, more preferably 1 to 5 g / 10 minutes.

(B) polystyrene / polypropylene alloy heat resistant layer

The heat resistant layer of the polystyrene coextrusion sheet of the present invention is a styrene block copolymer 2 based on 100 parts by weight of a resin mixture composed of 35 to 60% by weight of polystyrene, 15 to 30% by weight of high impact polystyrene, and 25 to 35% by weight of polypropylene. It is composed of polystyrene / polypropylene alloy prepared by adding 10 to 10 parts by weight, and this layer is composed of at least one layer and preferably has a thickness of 0.2 to 2 mm.

As the polystyrene component of the polystyrene / polypropylene alloy layer, conventional polystyrene and high impact polystyrene are used. The polystyrene is preferably 1 to 50 g / min and more preferably 2 to 10 g / 10 min when measured at 200 ° C. and 5 kgf. The high impact polystyrene is preferably 0.5 to 10 g / 10 minutes, more preferably 1 to 5 g / 10 minutes when measured at 200 ° C. and 5 kgf.

It is preferable to use 35 to 60% by weight of polystyrene in the polystyrene / polypropylene alloy layer. If the addition ratio of polystyrene exceeds 60% by weight, the brittleness of the polystyrene / polypropylene alloy is increased, which is likely to cause cracks in the coextrusion sheet. . On the other hand, when the polystyrene is less than 35% by weight, heat resistance is reduced.

High impact polystyrene is preferably used 15 to 30% by weight. If the content of high impact polystyrene is less than 15% by weight, the brittleness of the polystyrene / polypropylene alloy is increased to cause cracks in the coextrusion sheet, and if it exceeds 30% by weight, the heat resistance is reduced.

Among the components of the polystyrene / polypropylene alloy, the polypropylene component may be an isotactic or syndiotactic propylene, a crystalline propylene homopolymer, or a crystalline polyolefin resin made of a random or block copolymer of propylene and an α-olefin monomer. As the -olefin monomer, ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene or 1-hexene is used. The melt index of the polypropylene that can be used is preferably in the range of 0.1 to 20 g / 10 min, more preferably 0.5 to 5 g / 10 min at 230 ° C., 2.16 kgf.

It is preferable to use 25 to 35% by weight of polypropylene in the components of the polystyrene / polypropylene alloy. When the addition ratio of polypropylene is less than 25% by weight, the desired heat resistance improvement is not achieved. Adhesion decreases.

In the present invention, as the styrene block copolymer, an A-B-A type block copolymer is used. Where A and B each represent a polymer block, wherein the central block B consists of a conjugated diene hydrocarbon compound, usually a butadiene copolymer, and hydrogenation converts the double bond of the polybutadiene layer to a saturated hydrocarbon. Terminal block A represents a polymer block of aromatic vinyl hydrocarbons and is preferably polystyrene. Specific examples of such styrene-based thermoplastic elastomers include styrene butadiene styrene block copolymer (SBS), styrene ethylene butylene styrene copolymer (SEBS) with hydrogen added to butadiene, styrene ethylene propylene styrene block copolymer (SEPS), and the like. Among them, styrene ethylene butylene styrene copolymer (SEBS) is most preferred. The molecular weight of the terminal block A is 4,000 to 1000,000, preferably about 5,000 to 15,000, and the central block B has a molecular weight of 20,000 to 450,000, preferably 25,000 to 100,000. Such styrenic thermoplastic elastomers are commercially available and readily available, such as Toughtec JT from Creton G1650, G1651, G1652 or Asahi Chemical Industry from Shell Chemical Company. -56P, L503, H1041 and the like are commercially available.

In the present invention, the content ratio of the styrenic block copolymer constituting the surface layer is preferably 2 to 10 parts by weight based on 100 parts by weight of polystyrene / polypropylene alloy, and if less than 2 parts by weight, compatibility of polystyrene and polypropylene alloy is insufficient. Therefore, peeling occurs between the components in the multilayer sheet alloy layer, and when it exceeds 10 parts by weight, the heat resistance of the alloy is reduced.

To the polystyrene / polypropylene alloy of the present invention, various additives such as antioxidants, ultraviolet absorbers, antistatic agents, weathering stabilizers, lubricants and pigments may be appropriately selected and added as necessary.

Each of the above components can be kneaded simultaneously after dry blending. Kneading can be performed in the range of 200-280 degreeC normally using a single screw or twin screw extruder.

In the present invention, there is no particular limitation on the method for producing the multilayer sheet, and the multilayer sheet may be formed by a common coextrusion method or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but these are only for the purpose of explanation and should not be construed as limiting the present invention in any sense.

Example 1

As a core layer, a mixture of 70% by weight of polystyrene [GPPS] (Cheil Industries HR-2390) and 30% by weight of high impact polystyrene [HIPS] (Cheil Industries HR-1180) is used, and polystyrene / polypropylene alloy heat-resistant layer is polystyrene. (Cheil Industries HR-2390) 50% by weight, 20% by weight of high impact polystyrene (Cheil Industries HI-1180), 30% by weight of polypropylene [PP] (Samsung Total Chemical HF-11) and ethylene butylene as styrene elastomer A mixture consisting of 5 parts by weight of styrene copolymer [SEBS] (Shell Chemical Company Creton G1652) was used in a twin screw extruder.

Sheet coextrusion is carried out using a conventional sheet extrusion die to produce a sheet by coextrusion so that the thickness of the polystyrene core layer is 1.5 mm, the thickness of the polystyrene / polypropylene alloy heat resistant layer is 0.5 mm, and the total sheet thickness is 2 mm. And the interlayer adhesion force was measured and the results are shown in Table 1 below.

Example 2

A coextrusion sheet was prepared in the same manner as in Example 1 except that 60% by weight of polystyrene, 15% by weight of high impact polystyrene, 25% by weight of polypropylene, and 10 parts by weight of styrene-based elastomer were used as the heat-resistant layer. To evaluate the results are shown in Table 1 together.

Comparative Example 2

Except for using 60% by weight of polystyrene, 40% by weight of polypropylene, and 8 parts by weight of styrene-based elastomer as a heat-resistant layer was carried out in the same manner as in Example 1 to prepare a co-extruded sheet and evaluated the physical properties in Table 1 below Shown together.

Comparative Example 2

Using a core layer consisting of a mixture of 70% by weight of polystyrene and 30% by weight of high impact polystyrene without using a heat-resistant layer, a sheet having a thickness of 2 mm was prepared and the physical properties thereof were shown in Table 1 below.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Polystyrene core layer HIPS composition (%) 30 30 30 30 GPPS Composition (%) 70 70 70 70 Layer thickness (mm) 1.5 1.5 1.5 2 Polystyrene / Polypropylene Alloy Heat Resistant Layer HIPS composition (%) 20 15 - - GPPS Composition (%) 50 60 60 - PP composition (%) 30 25 40 - SEBS composition (phr) 5 10 8 - Layer thickness (mm) 0.5 0.5 0.5 - Interlayer adhesion Good Good Bad - Heat resistance of container 2% One% One% 10%

[Measurement of heat resistance]

Using the prepared sheet as a material, a container having a diameter of 6 cm and a height of 11.5 cm was formed by using a vacuum molding machine, and left for 10 minutes in an oven at 110 ° C., and then the height change of the container was measured to evaluate heat resistance.

As confirmed through the results of Table 1, the polystyrene-based coextrusion sheet of the present invention composed of a polystyrene-based core layer and a polystyrene / polypropylene alloy heat-resistant layer has excellent interlayer adhesion, even when used in vacuum molding. Because it does not generate and has excellent heat resistance, it is suitable as a container having a large molding ratio, rigidity and heat resistance.

Claims (2)

(A) at least one core layer composed of polystyrene or high impact polystyrene or a mixture of polystyrene and high impact polystyrene; And (B) as long as it is prepared by adding 2 to 10 parts by weight of a styrenic block copolymer based on 100 parts by weight of a resin mixture composed of 35 to 60% by weight of polystyrene, 15 to 30% by weight of high impact polystyrene, and 25 to 35% by weight of polypropylene. A polystyrene coextrusion sheet comprising at least a heat resistant layer. The polystyrene coextrusion sheet according to claim 1, wherein the core layer has a thickness of 1 to 5 mm and the surface layer has a thickness of 0.2 to 2 mm.