JPH03286831A - Marking polyethylene crosslinked oriented film - Google Patents

Abstract

PURPOSE:To enable an uneven surface to be formed at room temperature with out heating by forming the polyethylene crosslinked oriented film in which crosslinking degree is lowered toward the inside in the thickness-direction. CONSTITUTION:In a polyethylene crosslinked oriented film 1A, the sheet in which both skin layers 11, 12 are crosslinked, but its intermediate layer 10 is crosslinked in low degree, whereby the crosslinking degree of specified struc ture is provided by radiating electron beam from both sides of a polyethylene resin blank sheet, is biaxially oriented as a film. By passing this film (BOPE) 1A at room temperature without heating between a press roll 2 and an embossing roll 3, the crosslinked oriented polyethylene film 1B which is provided with pattern 3 is obtained, and simultaneously pattern 4 may be retained on the film. Recessed parts 100 are formed on the front surface of the film 1B, and projecting parts 101 are formed on its rear surface. The pattern 4 composed of the recessed parts formed on the front surface of the film 1B remains on said film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to stampable crosslinked polyethylene stretched films, and more specifically, the present invention relates to stampable polyethylene crosslinked stretched films, and more specifically, it can form characters, figures, etc. without the need for heating at room temperature.
This invention relates to stampable crosslinked polyethylene stretched films that can form uneven surfaces such as patterns.

[Prior Art] and [Problems to be Solved] In order to manufacture plastic products from plastic raw materials, the thermal properties of plastics are mostly applied. The processing method in this case is generally as follows.

Plastic molding materials - plasticization - shaping - solidification - plastic molded products Therefore, the mainstream of plastic molding is to use this heat. For example, in thermoforming, a plastic sheet or film is heated and softened. The main method is to form sheets or films using vacuum (vacuum forming) or compressed air pressure (air pressure forming).

In addition, in calendering, when crimping a sheet, etc., a crest roll is pressed against the still hot sheet that comes out of the calendar, or a crest is embossed on the cooled and solidified sheet that comes out of the calendar. If you want to do so, heat the crest roll so that it can be embossed, then press the crest roll against the sheet to emboss the crest.

On the other hand, there is a tracing film in which the surface of the plastic film is textured. This film surface is textured (
(1) sandblasting method in which sand is sprayed; (2) etching matting method in which the surface is etched with an alkaline suspension or organic solvent to make it matte; and (3) mattification is achieved by coating the surface with a matting agent. Surface coating method (4) Method of matting during the manufacturing process using an embossing roll, a drum with a plain or matte surface, or an endless belt. Various plastic films can be used for this tracing film, but in the matting method using an embossing roll or the like as described in (4) above, heating is still necessary for matting.

In this way, it is common to use heat and press quite strongly to form unevenness on the surface of the film, and then cool and solidify to maintain the unevenness on the surface of the film.In general, if it is not in a heated state, It is difficult to form irregularities on the surface of films, and once formed, the irregularities on the surface of films disappear, making it difficult to retain them.

The present inventors have been conducting intensive studies on crosslinked stretched polyethylene films.

There are two types of polyethylene: medium- and low-pressure polyethylene and high-pressure polyethylene, but the former is less transparent than the latter, so it has other excellent properties in applications where display effects are required. Despite this, it was rarely used. In order to improve this transparency, a polyethylene film whose entire layer is uniformly crosslinked by radiation and stretched has been proposed (Japanese Patent Publication No. 37-1
8893), although this film improves its transparency, it cannot be said to have sufficient moisture resistance.Therefore, a biaxially oriented polypropylene film (hereinafter referred to as OPP film) is used as a packaging film with good moisture resistance. It was getting worse. However, this OPP film is not necessarily sufficient for applications that require higher moisture resistance, and it is necessary to increase the thickness of the film or
It is necessary to process the P film by coating it with vinylidene chloride, which poses a problem of increased costs.

Therefore, the present inventors have developed a method in which the degree of crosslinking of the film decreases inwardly in the thickness direction, without uniformly crosslinking all the layers. proposed a polyethylene crosslinked stretched film with a low degree of crosslinking or no crosslinking (Japanese Patent Application Laid-open Nos. 59-174322 and 61-7481).
9), this material was found to be excellent in various aspects such as transparency, moisture resistance, strength, and rigidity, and various uses were developed that utilized the various excellent properties of this material, and various patent applications were filed. did.

When I happened to type letters (without using ink) on this film at room temperature, I found that from the conventional film concept, typing would be difficult and the letters would disappear, but the letters did not. I grasped the fact that it did not disappear, but remained.

The present invention was made against this technical background.

[Means for Solving the Problems] Accordingly, the present invention consists of a polyethylene crosslinked stretched film in which the degree of crosslinking decreases inward in the thickness direction of the film, and characters, figures, and patterns are suppressed and formed on the surface of the film at room temperature. It exists in the crosslinked polyethylene crosslinked stretched film with imprintability, which can form an uneven surface at room temperature without the need for heating, and the unevenness can remain without being erased afterwards.

[Example] Next, embodiments of the present invention will be described based on the drawings.

As shown in FIG. 1, the cross-linked stretched polyethylene film IA according to the present invention is passed between a press roll 2 and a squeezing roll 3 at room temperature without heating, such as by heating the press roll 2. , the stretched cross-linked stretched polyethylene film IB having pattern 4 is obtained.

Polyethylene crosslinked stretched film I used in the present invention, in which the degree of crosslinking decreases inward in the thickness direction of the film
A is the degree of crosslinking of a specific structure, for example, by irradiating an electron beam from both sides of a polyethylene resin raw sheet, for example, both surface layers are crosslinked, but the intermediate layer has a low degree of crosslinking, for example, it is not crosslinked. It can be obtained by two-wheel stretching a sheet having the following properties using a tenter method, or by stretching or rolling the sheet in the machine direction (MD) between rolls, and then stretching it in the transverse direction (TD) to form a film.

FIG. 2 shows a cross-sectional view of an example of the layer structure of the film 1A.

In the figure, 10 is an intermediate layer, a layer with a low degree of crosslinking,
For example, an uncrosslinked layer.

11 and 12 are surface layers, and both surface layers are layers with a high degree of crosslinking due to, for example, irradiation with electron beams from both sides.

Since it has a specific degree of crosslinking and has been stretched, the film (hereinafter referred to as BOPE film) IA can be processed at room temperature without heating, for example by a press roll, as in the above example. 2 and the squeezing roll 3, it is possible to obtain the squeezed cross-linked stretched polyethylene film IB having the pattern 3 as in the above example, and the pattern 4 is allowed to remain in the film. It has the characteristic of being able to

FIG. 3 schematically shows a cross section of an example of the film IB.

A recess 100 is formed on the front surface of the film 18, and a protruding protrusion 101 is formed on the back surface. The pattern 4 consisting of the recesses 100 formed on the surface of the film 18 remains on the film.

For example, the BOPE film IA has a density of 0.93
It is made of polyethylene with a melt index (measured according to JIS K6760, measured at a temperature of 190° C. and a load of 2.16 kg, hereinafter referred to as MI) of 0.5 to 20 g/10 min.

The above-mentioned degree of crosslinking can be expressed as a gel fraction, and the gel fraction is the insoluble portion obtained by extracting a sample with boiling P-xylene.

The crosslinked layer 11.12 has a gel fraction of 20 to 70 wt%, the intermediate layer IO has a gel fraction of 0 to 5 wt%, and the composition ratio of each layer is uncrosslinked layer: both crosslinked layers = 1 + 0.1 to 10. A biaxially stretched film having a stretching ratio of 3 times or more in at least one direction and an area ratio of 7 times or more is preferred. Moreover, a stretched film having a rolling ratio of 1.2 or more may be used.

The thickness of the BOPE film 1A is usually about 10 to 60 microns.

Regarding the manufacturing method and other preferable conditions for the BOPE film LA, the matters disclosed in the above-mentioned Japanese Patent Laid-Open Nos. 59-174322 and 61-74819 are applicable.

The BOPE film IA of the present invention has an inscription property that allows the formation of an uneven surface at room temperature without the need for heating. A label 7 to be attached to a plastic bottle 6 as shown in FIG.
When adding letters, figures, patterns, etc. to decorative films, tracing films, etc., letters, figures, patterns, etc. can be added at room temperature without the need for heating, and by applying light pressure. can be attached, so its practical significance is extremely great.

In addition, the film has superior advantages such as higher transparency, moisture resistance, strength, rigidity, and lower thermal shrinkage after heat setting than conventional high-density polyethylene produced by medium-low pressure method. Its practical significance is also extremely great.

[Effect of the invention] According to the present invention, the practical significance is extremely large.
It is made of polyethylene cross-linked stretched films whose degree of cross-linking decreases inward in the thickness direction, and the unevenness of letters, figures, patterns, etc. formed by pressing on the surface at room temperature can remain without being erased afterwards. It has been possible to provide stampable crosslinked polyethylene stretched stretched films that can form an uneven surface without requiring adhesive bonding underneath.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an example process of the present invention, FIG. 2 is a cross-sectional view of the cross-linked stretched polyethylene films used in the present invention, and FIG. 3 is a cross-sectional view of the cross-linked stretched polyethylene films after unevenness has been formed. FIG. 4 is an explanatory diagram of a tape showing an embodiment of the present invention, and FIG. 5 is an explanatory diagram of a label attached to a bottle showing an embodiment of the present invention. 1 A ◆ I B ・ 2 ・ 3 ・ 4 ・ 5 ・ 6 ・ 7 ・ ・Cross-linked stretched polyethylene film, cross-linked stretched polyethylene film, press roll, crested roll, pattern, tape, bottle, label

Claims (1)

[Claims] It is made of polyethylene cross-linked stretched film or sheet (hereinafter referred to as "films") whose degree of cross-linking decreases inward in the thickness direction, and irregularities such as letters, figures, patterns, etc. formed by pressing on the surface at room temperature cannot be erased afterwards. Cross-linked stretched polyethylene films with imprintability that can form an uneven surface at room temperature without the need for heating.