KR960000561B1 - Heat-shrinkable multi-layer film - Google Patents

Abstract

Multi-layer olefin based heat-shrinkable film comprises : preparing both outside layers by mixing 100 pts. propylene terpolymer comprising 80-98% of propylene, 1-10% ethylene and 1-10% alpha-olefin with 1-10 pts. the resin compsn. comprising 90-99% polyethylene and 1-10% alpha-olefin; preparing inner layer by mixing 100 pts. the copolymer comprising 90-99% polyethylene and 1-10% alpha-olefin with 10-20 pts. polyethylene. The obtd. film has good strength, cold resistance and transparence, then is useful for packing.

Description

Multi-layered Olefin Heat Shrink Film

The present invention relates to a multi-layer olefin-based packaging heat shrink film, particularly to provide an olefin-type heat shrink film having strong physical properties, high cold resistance, transparent and high heat shrink.

1) After primary molding of a film extruded or calendered a variety of synthetic resins such as polyethylene, polypropylene, PVC, and the like, the film is cooled and melted at a high temperature below the thermal potential. Unlike primary molding products, the products that are cold-molded by continuous stretching at the proper ratio physically or biaxially will exhibit civilian heat shrinkage (50-60%) even at low temperatures of 50-120 ℃. Such heat shrink film is effectively used for the packaging of various goods and foods using its heat shrinkability, but such film is a single-layer film usually manufactured with a thickness of 12-70 microns, and has low physical properties such as tensile strength, impact strength, and fracture strength. There was a tendency for the packaged products to be damaged due to easy tearing or lack of thermal bonding strength, resulting in relatively easy heat-sealing areas.

Thus, various multilayer films have been developed to enhance the physical properties to protect the package. That is, US Patent No. 4511609 has been developed in which the first outer layer is formed of a low pressure low density polyethylene layer and the deep layer and the second outer layer are formed of a high pressure low density polyethylene film. However, this strengthens the film's strength but lacks shrinkage, so it has unsuitable physical properties to be used as a heat shrink film.After that, the film is also multilayered to enhance physical properties, high cold resistance, and high transparency. No. 4965109 has been developed. However, the former is obtained by bonding a layer of propylene polypropylene film to the crystalline polypropylene film layer, which is a multilayer film having improved thermal adhesiveness, which is also unsuitable for use as a heat shrink film. It is made by bonding nylon or polyester film to PP film, and it is formed by mixing LLDPE polyisobutylene etc. to improve low temperature impact of PP film layer. It also has inappropriate properties to be used as shrink film. have.

In this multilayer film, as a shrink film, there is a known shrinkage package No. 57-129746. It is formed of a terpolymer of propylene / ethylene / α-olefin terpolymer, that is, random terpolymer or random copolymer of propylene which is a raw material of a known heat-shrinkable film, and has at least one side of the base layer an LLDPE surface layer of ethylene and α-olefin copolymer. It is a composite film. That is, the present invention relates to a film having a structure of LLDPE / PP or LLDPE / PP / LLDPE formed by bonding a LLDPE layer on one surface or both surfaces thereof based on PP, and a heat sealability of a conventional single layer shrink film. The LLDPE layer was formed on the surface to solve the defects in the seal and to improve the tear strength, which is effective in improving the tear strength and improving the heat sealability. It was difficult and had poor printability.

Accordingly, the present invention is to form a film in a multi-layer, the multi-layer film has the same high-quality physical properties, such as the toughness of the conventional shrink film, and provides a shrink film having a high heat resistance and good transparency and good heat shrinkability It is to.

According to the present invention, the shrink film is formed into three layers, and the outer layer, which is the surface layer, is formed by mixing terpolymer of propylene, ethylene and α-olefin, or by mixing a copolymer of ethylene and α-olefin. It improves aptitude, surface strength, especially slipability, and the core is a copolymer of ethylene and α-olefin, that is, LLDPE (Linear Low Density Polyethylen) is usually added in small amount of butene or octene or 10 ~ 20% poly ethylene was formed into a mixed resin composition, which was extruded into a three-ply extrusion die, followed by second heating and stretching by a known method to obtain a soft-shrink film.

A heat shrink film is manufactured by extruding and cooling a cylindrical tubular product of three layers of outer layer and deep layer by combining a extrusion die for production of three-ply with two or three extruders. According to the general technique, three-layer heat shrinkage is performed by heating the three-layer film again secondly by forcibly stretching and cooling 3-7 times in the width direction and 3-7 times in the longitudinal direction at 160 ° C-220 ° C, the maximum temperature below the potential point. In preparing the film, the synthetic resin composition forming the outer layer is a terpolymer of polypropylene, i.e., a copolymer copolymerized with 80-98% propylene, 1-10% ethylene and 1-10% α-olefin. To 100 parts by weight (weight ratio) of the copolymer or such a copolymer, a copolymer obtained by copolymerizing 90-99% of polyethylene and 1-10% of an α-olefin, that is, 1-10 parts of LLDPE, is formed. The core is formed of a resin having good cold resistance and transparency and high puncture resistance at low temperature. The LLDPE, which is a copolymer of ethylene and α-olefin, has a density of 0.918-0.920 g / cc and a melt index (MI). It is preferable to form with resin which is 0.65-0.85g / 10min. As such a resin, YUCLAIR (trade name) manufactured by Korea Petroleum Corporation and DOWLEX (trade name) manufactured by Dow Chemical Co., Ltd. may be used. As the resin to be used in the deep layer, it is more preferable to mix and use 10-20 parts of conventional polyethylene having a melt index (MI) of 0.25 g / 10 min and a density of 0.92 g / cc with 100 parts of the copolymer described above.

Such a deep portion can be coextruded to be about 15-80% (weight ratio) of the total film thickness, thereby obtaining the soft-shrinkable film of the present invention.

Referring to the method for producing a heat shrink film of the present invention according to a specific embodiment as follows.

EXAMPLE

A three-layer stacking die (diameter of 200-300 mm) is combined with a screw extruder of 120 mm / m and L / D 27-30, which is a known polyolefin extruder, and the temperature of the extruder and the die is about 200 ° C. Then, YUCLAIR (trade name, manufactured by Korea Petroleum Corporation), a resin composition having a melt index of 6 g / 10 min density 0.9 g / cc as a copolymer of 90% propylene, 5% ethylene and 5% α-olefin, was introduced into the main extruder. Extruded into the inner and outer layers of the die, and a copolymer of ethylene and α-olefin, i.e., LLDPE, in a resin composition having a density of 0.92 g / cc and a melt index of 0.69 g / 10 min, is extruded into the middle layer of the die. The 3-ply cylindrical tube is discharged through the die. The discharged cylindrical tube had a thickness of 300-600 microns and a width of about 40 cm. It was first pinched in a water cooling tank at 10 ° C. and cooled, and then placed in a secondary heating hot air tank at 190 ° C., a temperature as high as possible below the thermal potential point. The film was reheated and biaxially stretched five times in the width direction and five times in the width direction to prepare a heat shrink film having a thickness of 15 microns and a width of 200 cm.

Compared with the conventional single layer heat shrink film, the multilayer olefin heat shrink film of the present invention has a remarkable improvement in physical properties, that is, an improvement in tensile strength, impact strength, and breaking strength, and particularly resistant to cold at low temperatures. In addition, the thermal bonding strength is good, so that the thermal bonding portion does not fall. In addition, the heat shrinkable film of the present invention exhibited a shrinkage of 50-60%, which is the same as that of a single layer film, at a low temperature of 50-120 ° C., and can be effectively used as a packaging material with good transparency.

Claims (1)

100 parts of propylene terpolymer (terpolymer) of 80-98% propylene, 1-10% ethylene and 1-10% α-olefin in a multilayer olefin heat shrink film having a deep layer formed inside the outer layer 1-10 parts of a resin composition containing 90-99% of polyethylene and 1-10% of an α-olefin to form an outer layer, 90-99% of polyethylene and 1-10% of an α-olefin. A multi-layer olefin type heat shrink film, characterized in that it is formed of a resin composition which forms a deep layer by mixing 10-20 parts of polyethylene with 100 parts of a copolymer.