JPH03258882A - Label made of polyethylene - Google Patents

Abstract

PURPOSE:To obtain the title label capable of being stuck simultaneously with blow molding of bottle, suitable in molds, by providing a crosslinked orientated film of polyethylene having crosslinking degree lowering inside in the thickness direction of film with a printed layer and an adhesive layer. CONSTITUTION:For example, a biaxially orientated polyethylene film 3 which comprises a polyethylene having >=0.935 density and 0.5-20 g/10 minutes melt index (JIS K6,760, measured at 190 deg.C under 2.16kg load) melt index and has crosslinking degree comprising crosslinked layer, uncrosslinked layer/crosslinked layer, in the thickness direction, with a ratio of the uncrosslinked layer: both the crosslinked layer=1:0.1-10 (constituent ratio), >=3 times draw ratio and >=9 times area ratio is provided with a printed layer (e.g. composed of urethane- based ink) 4 on the surface and with an adhesive layer 5 on the back to give the objective label 2. During molding of a bottle 1 by blow molding, the label 2 is stuck to the surface of the bottle 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polyethylene label, and particularly to a label made of polyethylene film that is attached to a container, particularly a polyethylene bottle, and used to indicate the contents thereof.

[Prior Art] Conventionally, labels printed on the surface of paper or synthetic paper have been used as labels attached to containers such as plastic bottles to indicate the contents.

However, labels using such papers have drawbacks such as being opaque and easily peeling off when wet with water. or,
There were also problems such as easy tearing, mold growth, and low rigidity, which required a thickness of 100 μm or more.

When using a plastic label for a plastic bottle, there is no need to remove the label when collecting and recycling the bottle, and the plastic label has the advantage of being resistant to water exposure.

If the bottle is made of polyethylene and the label is also made of polyethylene, the above advantages can be further utilized since they are made of the same material.

On the other hand, when molding bottles, there is a blow molding method. Blow molding is a molding method that creates a hollow interior by blowing air into it.The thermoplastic resin is plasticized using an extruder, the parison is extruded, and before it cools and solidifies, it is placed in a mold and expanded by blowing air inside. This method involves cooling the mold by pressing it against the inner wall of the mold.

During such blow molding, if a label can be set in the mold and affixed to the bottle surface at the same time as the bottle is blow molded, the troublesome label affixing work can be omitted.

However, labels for this purpose (in-mold labels) are attached to curved bottle surfaces, so they need to maintain their shape as a label, that is, they need to be shaped. It is also necessary to have excellent strength and rigidity.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems, has good transparency, is resistant to water and dirt, has rigidity and strength, can be made thin, and has a curved surface. To provide a polyethylene label that is suitable for circular containers such as those that contain polyethylene, does not need to be peeled off during recovery and recycling, and is suitable as an in-mold label that can be attached to a bottle at the same time as blow molding, for example. purpose.

[Means for Solving the Problems] The present invention provides a polyethylene crosslinked stretched film in which the degree of crosslinking is reduced inward in the thickness direction of the film, printed on one side and provided with an adhesive layer on the other side. It is on the manufactured label.

[Function] There are two types of polyethylene: high-pressure polyethylene and medium-low pressure polyethylene. Films obtained from high-pressure polyethylene have relatively good transparency, but films obtained from medium-low-pressure polyethylene have poor transparency. However, it has been difficult to use it in applications that require transparency.

In order to improve this transparency, various stretched polyethylene films in which all layers are uniformly crosslinked by radiation have been proposed, but although the conventional examples improve transparency, they do not have sufficient moisture resistance. Generally, biaxially oriented polypropylene, which has good moisture resistance, has been used in the packaging field. However, polypropylene is not always sufficient for applications that require higher moisture resistance, which increases the film thickness or requires a moisture-proof coating, leading to increased costs. .

The present inventors first crosslinked a sheet or tube-shaped molded product made of polyethylene resin from both sides in the thickness direction of the molded product so that the degree of crosslinking decreased in the middle direction, and then, after heating, We proposed a method for producing a cross-linked stretched polyethylene film (Japanese Patent Application Laid-Open No. 59-1
74322), and this product not only had good transparency but also good moisture resistance. That is,
Even in applications that require high moisture resistance, there is no need to increase the thickness of the film, making it cost-effective, and there is no need for moisture-proofing, which reduces transparency. I no longer have to do it.

Furthermore, this product not only had excellent strength and rigidity, but also had good formability and, when heat set, had little heat shrinkage.

The present invention uses such a polyethylene crosslinked stretched film, and the polyethylene stretched film in which the degree of crosslinking decreases toward the inside in the thickness direction of the film can be used, for example, by applying electronic cotton from both sides of a polyethylene resin raw sheet. By a crosslinking method such as irradiation, a sheet having a specific degree of crosslinking, for example, the image surface layer is crosslinked but the intermediate layer is not crosslinked, is biaxially stretched or rolled;
It can be obtained by then stretching it to make a stretched film, and it has higher transparency than conventional general high-density polyethylene, is resistant to water wetting, and has good formability.
It has little heat shrinkage and is rigid and strong as a label.
Thin labels are possible, and when blow molding polyethylene bottles, there is a
By setting a polyethylene label made of the same material, it can be suitably used as an in-mold label, and since it is made of the same material, there is an advantage that there is no need to remove it when collecting and recycling.

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

The label of the present invention relates to a label 2 that is attached to a plastic (polyethylene) bottle 1 as shown in FIG. 1A for the purpose of indicating the contents thereof.

An example of a cross section of the label 2 is shown in FIG. 1B.

In Figure 1B, 3 is a stretched polyethylene film (hereinafter referred to as BOPE film) in which the degree of crosslinking is reduced inward in the thickness direction of the film, and 4 is a printed layer applied to one side (surface) of the POPE film. , 5 is an adhesive layer provided on the other side (back side) of the film.

The BOPE film 3 is made of polyethylene with a density of 0.935 or more and a melt index (according to JIS K 6760, 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 minutes. Therefore, it is preferable that the degree of crosslinking is such that the crosslinked layer/uncrosslinked layer/crosslinked layer is formed in the thickness direction.

Here, the degree of crosslinking can be expressed by the gel fraction,
The gel fraction is determined by extracting the sample with boiling P-xylene,
This shows the insoluble portion.

The crosslinked layer has a gel fraction of 20 to 70 wt%, the uncrosslinked layer has a gel fraction of 0 wt%, the composition ratio of each layer is uncrosslinked layer: both crosslinked layers = 1:0.1 to 10, and the stretching ratio is at least A biaxially stretched film having an area magnification of 3 times or more in one direction and 9 times or more is preferable as the desired label of the present invention.

The thickness of the film 3 is usually about 10 to 1 ooLi.

The film 3 preferably has a haze value of 5% or less.

Regarding the manufacturing method and preferable conditions for the BOPE film 3, please refer to JP-A-59-174322 and JP-A-6.
The matters disclosed in Publication No. 1-74819 can be applied.

Printing on the BOPE film 3 can be performed, for example, by gravure printing, offset printing, flexo printing, silk screen printing, or the like. Before printing, BOP
It is preferable to subject the E film 3 to a corona discharge treatment.

As the printing ink, urethane-based ink is preferable from the viewpoint of heat resistance.

The adhesive constituting the adhesive layer 5 provided on the side opposite to the printed surface of the BOPE film 3 may include various adhesives such as ethylene-vinyl acetate copolymer (EVA) or modified products thereof, acrylic adhesive, urethane adhesive, etc. In particular, an EVA-based adhesive that can be thermally bonded to a blow-molded bottle within a mold during bottle blow-molding is particularly preferred.

Examples of methods for providing the adhesive layer 5 on the BOPE film 3 include applying the adhesive with a roll or the like or extrusion coating. The thickness of the adhesive layer 5 is usually about 3 to 20 μm.

The thickness of the label 2 can be appropriately selected depending on the application, but is usually about 50 to 130 microns.

The label 2 can be simultaneously attached to the bottle surface within the mold during bottle molding by blow molding.

An example of the blow molding will be explained with reference to FIG. 1C.

In blow molding, a softened cylindrical polyethylene parison is extruded from a parison pupil 7 through an extruder 6, then the molds 8 and 9 are closed, and air is injected into the parison from a blowbin (air blowing part) 10. inject,
Expand the parison along the inner shape of the mold 8.9,
After cooling, the molds 8 and 9 are opened and the bottle l is taken out.

When wiping off the air and inflating the parison, the label 2 is set in one of the molds 8 and 9. In the illustration, after the bottle 1 with the label 2 attached is taken out, the label 2 is set in the mold 9, and the process is circulated.

Note that the polyethylene label of the present invention can be used not only in blow molding but also in other molding methods, such as injection molding.

Next, examples (specific examples) of the present invention will be shown.

Example High density polyethylene (density 0.957 g/cm3, Ml
1-Og/10 minutes) and crosslinked with electron beam (gel fraction (%) = crosslinked layer/uncrosslinked layer/crosslinked layer = 5010150, crosslinked composition ratio = crosslinked layer: uncrosslinked layer: crosslinked layer = 1:1.75:1.thickness 750U) at 127℃1
A biaxially stretched film with a thickness of 50μ stretched at a magnification of 3×5 (
BOHD film) was obtained. This film is Haze 2
7%, and moisture permeability was 3.6 g/m2/24 hrs.

Next, the surface of this BOHD film was subjected to corona discharge treatment, and then four-color gravure printing was performed on this treated surface.

5 g/1T12 of EVA-based mixed solvent lacquer was applied to this BOHD film, dried, and then longitudinally io.

It was cut into a shape of mm x width 60 mm to make a label. The obtained label was set in a blow-molding mold, and a bottle with a capacity of 500 mj2 was blow-molded using high-density polyethylene as a raw material, and was attached to the bottle surface to be used as an in-mold label. The resulting bottle label is
The bottle did not lose its shape, the printing was clear, and the bottle itself had a sense of unity, as if it had been printed on a curved surface.

[Effects of the Invention] The label of the present invention has good transparency, is resistant to water wetting and staining, has rigidity and strength, can be made thinner, is economical, and is suitable for containers with curved surfaces, especially blow molding. When used in polyethylene bottles, which are the main type of bottle, there was no need to remove them when collecting and recycling them because they were made of the same material as the bottles, and mold did not grow on them, giving them a clean appearance suitable for sanitary use.

Due to the above characteristics, the label of the present invention can be used as a label for various purposes, and as shown in the above examples, it is suitable as an in-mold label.

[Brief explanation of drawings]

FIG. 1A is a front view showing an example of the mode of use of the present invention;
Figure B is a cross-sectional view showing the embodiment of the label of the present invention, and Figure 1C is
The figure is an explanatory view of a blow molding process using an in-mold label in the present invention. 1... Bottle 2... Label 3... BOPE film 4... Printing layer 5... Adhesive layer 6... Extruder 7... Parison die 8.9... Mold 10.・Blow pin

Claims (1)

[Claims] A polyethylene label made by printing on one side of a polyethylene crosslinked stretched film whose degree of crosslinking decreases inward in the thickness direction of the film, and providing an adhesive layer on the other side.