JPS6047105B2 - skin packaging film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in plastic films for skin packaging.

The packaged item is placed on a vacuum-formed package, usually called ``skin packaging,'' which is usually printed with many small holes, covered with a plastic film, and heated to make the film plastic. In the packaging technology, where vacuum suction is applied from below the mount when the mount has become dry, the film is adhered to the object to be packaged and adhered onto the mount. and good thermal adhesion to the mount.

In response to the requirement for good thermal adhesion, polyethylene and ethylene/vinyl acetate copolymer resin with a specific composition (hereinafter referred to as “vinyl acetate copolymer resin”)
A laminate film with corona discharge treatment was proposed (Japanese Patent Publication No. 45-4638).
No. 1), it has been widely used as it has been hailed for its ability to provide sufficient adhesion without the use of a separate adhesive.

There, it is specified that the composition of EVA should be 5 to 30% by weight of vinyl acetate monomer units (hereinafter referred to as "VA"). By the way, as skin packaging has come to be used for packaging many types of goods,
Difficulties in applying this method to articles with acute corners have become noticeable.

This is because the plastic film, which is in a plastic state and is drawn toward the mount by vacuum suction, tends to tear when it hits the corner of the packaged item. The present invention aims to overcome the above-mentioned difficulties and to provide a film with a reduced risk of tearing even in skin packaging of articles with sharp corners. The skin packaging film of the present invention is a laminate film that has a three-layer structure of polyethylene/ionomer/EVA by coextrusion, and the EVA has a VA content of 3 to 25% by weight, and the surface is subjected to corona discharge treatment. This is what happens.

The polyethylene film is preferably a low-density polyethylene film that is often used in laminated films for skin packaging, especially those with a melt index of 0.8 to 5.0 da/10 minutes, and the layer thickness is between the usual two. It is not much different from the layered film, and a range of 50 to 200μ is suitable.

Various ionomers can be used, including those commercially available under the trademark "Surlyn."

This material provides a relatively high melt viscosity to the vacuum-formed thermoplastic film, thereby preventing the film from tearing at the corners of the packaged item.
From this point of view, those having a melt index of 3 or less are particularly useful. The thickness of the layer may be about 10 to 50 μm. As is already known, the higher the ■A content of EVA, the higher the thermal adhesion.Practical adhesive strength can be obtained from ■a few percent of A, but on the other hand, if it is too large, it will not only adhere to the backing paper. Since adhesion to the packaged object may also occur, it is necessary to limit the adhesion force to a certain limit. In the film of the present invention, a VA content of 3 to 25% (by weight) was selected as a range that provides appropriate thermal adhesiveness and melt viscosity. For normal applications, a particularly preferred range is 15-20%.
The appropriate thickness of this layer is 10 to 30 .mu.m, and the appropriate thickness of the entire film is 150 to 200 .mu.m. The three layers of polyethylene/ionomer/EVA are formed all at once by coextrusion.

The method is well known in the art. The obtained laminate film is subjected to a surface treatment by corona discharge, especially on the EVA side which is to be made thermally adhesive.

This technique may also follow what has already been established in the production of skin packaging films. Example The following materials were melted, combined immediately before extrusion, and extruded through a T-die. \Imiran 1
650J1 density 0.94yIcr11 melt index 1.5g/1Cke EVA: 50p. ．． VA content 20% (weight), 1
Yucalon Eva 50Mj consists of layers each having the thickness indicated.

A three-layer cylindrical film was created with the ionomer in the middle, EVA on the outside, and polyethylene on the inside. When the packaged items such as blocks, bolts, gears, grindstones, etc. were placed on a mount with many small holes printed on one side of the paperboard and placed on a packaging machine using the film prepared above, A good package could be made.

Claims (1)

[Claims] 1. A laminate film having a three-layer structure of polyethylene/ionomer/ethylene and vinyl acetate copolymer (EVA) by coextrusion, in which EVA has vinyl acetate monomer units (VA) by weight. A skin packaging film which accounts for 3 to 25% and whose surface is subjected to corona discharge treatment. 2 The polyethylene layer has a density of 0.918 to 0.940 g
/cm^3, melt index 0.8-5.0g/10
a 50-200μ thick layer of low-density polyethylene, an ionomer layer 10-50μ thick, and a layer of EVA with a melt index of 5-13g/10
The skin packaging film according to claim 1, which is a layer of EVA with a thickness of 10 to 50 μm.