JPS6234928A - Production of drawn polyethylene film - Google Patents

Abstract

PURPOSE:To obtain a film having excellent transparency, moistureproofness and surface gloss, etc., by coating a polyethylene film with an electron radiation curable coating agent, irradiating with electron radiation in a manner to decrease the crosslinking degree toward the inner part in the direction of thickness, and drawing the film under heating. CONSTITUTION:One or both surfaces of a sheet composed of a polyethylene resin is coated with an electron radiation curable coating agent which may contain an additive and the sheet is irradiated with electron radiation from both sides in a manner to decrease the crosslinking degree toward the inner part in the direction of thickness. The crosslinked sheet is drawn under heating to obtain the objective drawn film. The electron radiation curable coating agent is the one containing a monomer and/or oligomer having one ethylenic unsaturated double bond as >=30wt% of the binder.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to a method for producing a stretched polyethylene film, and more specifically, after applying an electron beam curing paint to an unstretched polyethylene film, The present invention relates to a method for producing a polyethylene film that has improved surface performance upon irradiation and heat stretching, and has excellent moisture resistance and transparency.

(Prior Art) Conventionally, films made from high-density polyethylene have poor transparency, moisture resistance, and surface gloss, and have rarely been used in applications requiring display effects.

The present inventors have already proposed a method for producing a polyethylene film with excellent transparency and moisture resistance using a special crosslinking and heating stretching method (Japanese Patent Application Laid-Open No. 174322/1983), but in order to improve the surface performance of the film. Second, applying electron beam curing paint to the stretched film.

Application of liquid additive solutions to large area films was required.

(Problems to be Solved by the Invention) Ordinarily, electron beam curing paints cannot be stretched after curing, and it is necessary to apply the paint to a stretched large area film and then irradiate it with electron beams. The area occupied by the irradiation equipment, the cost required for the equipment, the time required for paint curing,
There were problems both economically in terms of line speed and in terms of workability.

Furthermore, it has been difficult to obtain a uniform thin coating film because it requires coating over a large area.

Furthermore, when obtaining a polyethylene film with good transparency and moisture resistance by electron beam crosslinking and stretching, it is necessary to perform electron beam irradiation many times, which causes problems such as deterioration of the resin itself.

[Structure of the Invention] (Means for Solving the Problems) The present inventors have developed a transparent thin film structure that has higher moisture resistance without coating a large area film or irradiating it with electron beams. As a result of various studies in order to obtain a polyethylene film with surface performance improved by a cured coating, the present invention was completed by applying a stretchable electron beam cured coating to an unstretched film. .

In other words, in the present invention, an electron beam curing paint containing or not containing additives is applied to one or both sides of a sheet made of polyethylene resin, and the degree of crosslinking is reduced in the direction of the thickness of the sheet. This method of producing a stretched polyethylene film is characterized in that the film is irradiated with an electron beam from both sides, and then heated and stretched.

According to the present invention, an unstretched polyethylene sheet coated with an electron beam curing paint is irradiated with an electron beam, and then the film is stretched, so that coating and electron beam irradiation can be done over a small area, increasing the line speed for coating and curing. In addition, the area occupied by the equipment for coating and curing and the equipment cost are reduced, which is extremely advantageous in terms of economy and workability compared to the case where coating and electron beam irradiation are performed after stretching. Furthermore, during electron beam irradiation, the electron beam that has passed through the coating film acts on the polyethylene sheet. By performing this electron beam irradiation from both sides of the sheet and controlling its degree, a crosslinked layer/uncrosslinked layer/crosslinked layer is formed in the thickness direction of the original fabric, thereby obtaining a film with good moisture resistance and transparency. Stretchable electron beam cured coatings yield oriented polyethylene films with improved surface performance.

The polyethylene resin in the present invention includes polyethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or ethylene and propylene having an ethylene content of 50% by weight or more, 1-butene, ■- Pentene, 1-hexene, 4
-Methyl-1-pentene.

Examples include copolymers with α-olefins such as 1-octene or vinyl monomers such as vinyl acetate, (meth)acrylic acid, (meth)acrylic acid esters, acrylamide, acrylonitrile, styrene, and vinyl chloride. The polyethylene resin may be used alone or in a mixture of two or more. Among these polyethylene resins, those having a density of 0.935 g/- or more, preferably 0.950 g/cJ or more and a melt flow index (according to JIS K6760 at a temperature of 190°C and a load of 2.1
Crystalline polyethylene or ethylene copolymer having a weight ratio of 0.05 g/10 minutes or more, preferably 0.5 to 20 g/10 minutes (measured at 6 kg, hereinafter referred to as "old") is preferred. In addition,
Known additives such as antioxidants, ultraviolet absorbers, anti-blocking agents, lubricants, neutralizing agents, pigments, and dyes can be added to these polyethylene resins as necessary.

The polyethylene resin used in the production of the film of the present invention is supplied to a commonly used extruder, and is melt-extruded, cooled, and solidified to form a sheet-like or tube-like raw material.

Melt extrusion molding is a method of extruding from a commonly used T-die to form a flat raw fabric.

Either method can be used, such as extruding it from an annular die to make a tube-shaped raw fabric and cutting it open to make a sheet-shaped raw fabric, or cutting both sides of the tubular raw fabric to make two sheet-shaped raw fabrics. Good too. In this case, the thickness of each raw fabric may be such that it can be crosslinked from both sides in the thickness direction of the raw fabric so that the degree of crosslinking decreases in the middle direction, and it depends on the stretching ratio and the thickness of the film after stretching. It is up to you to decide, but usually it is 2.
10-2000 μm.

Preferably, the range is from 400 to 1000 μm from the viewpoint of handling and forming the above-mentioned crosslinks.

These films undergo corona discharge treatment, low temperature plasma treatment, flame treatment, chemical oxidation treatment, mechanical roughening,
The surface may be subjected to surface treatment such as primer coating or ultraviolet irradiation.

As a binder for an electron beam curing paint containing or not containing an additive used in the present invention.

Cationic polymerization type, radical polymerization type, A-6
~Although a mixture of these types can be used,
When using a radical polymerizable type, it is preferable to use one containing 30% by weight or more of a monomer and/or oligomer having one ethylenically unsaturated double bond. A monomer and/or oligomer having one ethylenically unsaturated double bond is present in the binder.
By being present in an amount of 0% by weight or more, the molecules constituting the coating film after electron beam curing become close to a linear structure, exhibiting thermoplasticity,
It is thought that this makes stretching possible.

Usually, the main components of the binder of radical polymerizable electron beam curable paints include monomers and/or oligomers (A) containing two or more ethylenically unsaturated double bonds;
and, if necessary, a monomer and/or oligomer (B) containing one ethylenically unsaturated double bond is used, but a paint containing only component (A) as a binder;
Alternatively, in a paint using a binder consisting of 70 parts by weight or more of component (A) and 30 parts by weight or less of component (B), three-dimensional network bonds based on intermolecular crosslinking due to electron beam irradiation develop, resulting in poor thermoplasticity. There is a tendency for the coating film to break easily when the film is stretched.

As a monomer and/or oligomer (B) containing one ethylenically unsaturated double bond.

(meth)acrylic acid monoesters of various aliphatic alcohols and their substituted products, (meth)acrylic acid monoesters of various aromatic alcohols and their substituted products, (meth)acrylic acid monoesters of various alicyclic alcohols and its substituted products, (meth)acrylamide and its substituted products, styrene and its substituted products, monoallyl compounds, monovinyl compounds such as vinyl acetate, vinyl ether, etc., or a mixture of two or more thereof is used. It can be selected or blended as appropriate, taking into account the type of polyethylene film to be processed, stretching conditions, film performance required after stretching, etc.

Binder components other than those listed above include monomers and oligomers (A) 1 containing two or more ethylenically unsaturated double bonds, such as unsaturated polyesters and polyester poly(meth)acrylates.

Epoxy poly(meth)acrylates, polyurethane poly(meth)acrylates, polyol poly(meth)acrylates, polyallyl compounds, and paint resins that are inert to electron beams and do not have ethylenically unsaturated double bonds. 1 For example, selected from the group consisting of various thermoplastic resins such as saturated polyester resins, polyolefin resins, vinyl chloride-vinyl acetate copolymer resins, acrylic resins, polyamide resins, vinyl resins, ethylene-vinyl acetate copolymer resins, and urethane elastomers. One type or two or more types can be used.

Additives that may be added to the electron beam curing paint as necessary include: water and/or organic solvent to adjust the viscosity of the coating solution during painting; 2 dyes and pigments used for coloring; 1 extender pigment; capping agent; , various additives for plastic films 2
For example, it is possible to use one or more desired agents selected from antistatic agents, ultraviolet absorbers, lubricants, antifogging agents, and the like.

The electron beam curing paint used in the present invention can be applied using a spray coater, a roll coater, a curtain flow coater,
It can be applied to one or both sides of the plastic film using conventional known coating machines such as a doctor blade coater.

91 In the present invention, crosslinking of a sheet-like raw fabric made of polyethylene resin coated with a stretchable electron beam-cured paint is carried out from both sides so that the degree of crosslinking decreases toward the inside in the thickness direction of the raw fabric. It is necessary. The degree of crosslinking is
In order to achieve the object of the present invention, the gel fraction at the lowest degree of crosslinking is 0 to less than 5%, and the gel fraction of each crosslinked surface layer on both sides is is preferably 5% or more, particularly in the range of 20 to 70%. In particular, it is preferable that the gel fraction with the lowest degree of crosslinking is 0% and that the composition of crosslinked layer/uncrosslinked N/crosslinked layer is formed in the thickness direction of the original fabric.In this case, the composition ratio of each layer is uncrosslinked layer:both sides It is desirable that each crosslinked layer is in the range of 170.1 to 10.

In particular, it is preferable that the crosslinked layers on both sides have the same degree of crosslinking.

When the above-mentioned crosslinking is not performed such that the degree of crosslinking decreases in the direction of the thickness of the original fabric.

Especially when the gel fraction with the lowest degree of crosslinking exceeds 5%.

Although the stretching process is uniform and the transparency is improved, a film with improved moisture resistance, which is the main objective of the present invention, cannot be obtained. Further, if the degree of crosslinking of the crosslinked surface layers on both sides is less than 20%, the stretching process will not be uniformly performed and the transparency and moisture resistance of the film will not be improved. On the other hand, when the gel fraction exceeds 70%.

The film easily breaks during stretching and cannot be stretched smoothly. Furthermore, when cross-linking is performed uniformly across the entire thickness of the original fabric, stretching is performed uniformly and transparency is improved, but moisture resistance is not improved; If only one side is crosslinked, the film will easily break during stretching, and if all layers are crosslinked so that the degree of crosslinking decreases from one side in the thickness direction of the original film, the moisture resistance of the resulting film will not be sufficiently improved. Both are undesirable.

Note that the above gel fraction indicates the insoluble portion obtained by extracting the sample with boiling p-xylene.

The source of the electron beam in the present invention is a 100 to 2000 Keν (preferably 100 ~
An electron beam with an acceleration energy of 500 KeV is used. The electron beam irradiation is preferably carried out in an atmosphere of an inert gas such as nitrogen in order to avoid polymerization inhibition due to oxygen in the air. If so, prior to electron beam irradiation.

It is preferable to evaporate water and/or organic solvent from the coating film in advance by means such as air drying or heating.

The electron beam irradiation was performed based on the thickness of the original fabric, cedar, 1 type of fat, 9 molecular weight, 2
Although it varies depending on the molecular weight distribution, the electron beam irradiation dose is usually 5 to 50 Mrad, preferably 15 to 30 Mrad.
It should be d. Further, the irradiation may be performed simultaneously on the front and back sides of the original fabric sheet, or separately on the front and back sides. In this case, it is particularly preferable that the irradiation dose to the original fabric be the same on both sides of the original fabric. Furthermore, the electron beam penetration ability can be adjusted by adjusting the applied voltage depending on the thickness of the original fabric.

Examples include masking with a shielding plate.

Next, an example of a method for adjusting the amount of electron beam irradiation is given. 1. For example, if the thickness of the original fabric to be irradiated is 500 μm, 25 thin films each having a thickness of 220 μm are closely stacked to form a film of approximately 500 μm. A thick test piece was coated with electron beam curing paint on one or both sides, and the same amount of electron beam was irradiated from both sides in the thickness direction to crosslink the test piece. By separating them and measuring the degree of crosslinking of each, it is possible to know the distribution state of the degree of crosslinking in the thickness direction of the test piece. From this result, it is possible to know the relationship between the thickness of the original fabric and the degree of crosslinking depending on the amount of electron beam irradiation.

Stretching is performed by heating the crosslinked original fabric and stretching it uniaxially or biaxially at a predetermined magnification by a conventional roll method, tenter method, tubular method, rolling method, or a combination of these methods to obtain a film. Two-wheel stretching may be done simultaneously or sequentially.

The stretching temperature is above the softening point of polyethylene resin.

Particularly preferred is a range from the softening point to the crystalline melting point. Specifically, the temperature is 70 to 150°C, preferably 70 to 135°C.

Particularly preferred is 100 to 130°C. If the stretching temperature is below the softening point, the resin will not be sufficiently softened and uniform and stable stretching will not be possible. On the other hand, if the temperature exceeds 150° C., the resin will melt excessively, making it impossible to perform stable stretching, and the resulting film will not be sufficiently improved in moisture resistance.

Further, the stretching ratio is desirably 3 times or more, preferably 4 times or more in one direction or in both the vertical and horizontal directions. If the stretching ratio is less than 3 times, uniform stretching is insufficient,
Furthermore, it is difficult to obtain a stretched film with excellent transparency.

In addition, since the obtained stretched film has heat shrinkability, when used as a base film for composite packaging, heat shrinkage is performed at a temperature below the melting point of the stretched film, e.g. is preferably 1.5% or less, preferably 1.0% or less.

(Example) Nine examples of the present invention are shown below. The test method in the examples is as follows.

(1) Haze: ASTM 01003 (2) Moisture permeability: JIS Z 0208B method (measured at a temperature of 40°C and a relative humidity of 90%) (3) Tape peeling test: Adhesive adhesive tape (Cellotape manufactured by Chiban Co., Ltd.) was attached to the film. Example 1 High-density polyethylene (density 0.957 g/aJ,
MIo.

8 g/10 minutes (hereinafter referred to as HDPE) was molded into a sheet-like original fabric with a thickness of 0.6 m using a T-die extrusion sheet molding machine. An electron beam curing paint having the following composition was prepared and applied to one side of the corona discharge treated sheet to a thickness of 30 μm, and then an electron beam cured coating manufactured by Energy Science Co., Ltd. was applied to the coated and non-coated surfaces. Using an accelerator.

Each sample was irradiated with an electron beam of 20 Mrad at an acceleration voltage of 160 and ν in a nitrogen gas atmosphere.

Acrylate oligomer "Kayarad R604J (manufactured by Nippon Kayaku ■) 30 parts diethylene glycol monoacrylate) 70 parts After crosslinking of the polyethylene sheet on both irradiated sides, the degree of crosslinking is 50% gel fraction, and the minimum crosslinking inside the thickness direction is gel The fraction was 0%.Also,
The composition ratio of the thickness of the crosslinked layer and the uncrosslinked layer in the polyethylene sheet was crosslinked layer: uncrosslinked skin: crosslinked layer = 1:2:1.

This cross-linked sheet was stretched 4 times in the longitudinal direction at a temperature of 130'C.

Biaxially stretched HDP [! Got the film. The haze of this film is 3.9%, and the moisture permeability is 2.4g/rrr/2
4 hours, and the tape peel test was good.

Furthermore, this film was 15c under a load of 65g/-.
After 10 back and forth rubs on a commercially available stretched polypropylene film with a stroke of m, the haze was 4.8% and the transparency was maintained.

Example 2 Electron beam irradiation and stretching were carried out in the same manner as in Example 1 except that the following composition was used for the electron beam curing coating.

Saturated polyester resin [Byron 200/300 =
1: t.

Mixture J 30 parts Diethylene glycol monoacrylate 70 parts Cyroid 150 0.2 parts The haze of the obtained biaxially stretched HDPE film was 4.0%.
The moisture permeability is 2.4 g/nf/24 hrs,
Tape peel test was good. Further, the haze after rubbing was 4.7%.

Comparative Example 1 A biaxially stretched polyethylene film was obtained in the same manner as in Example 1 except that the electron beam curing paint was not used in Example 1. This film had a haze of 4.1% and a moisture permeability of 2.4 g/nf/24 hrs.

The haze after rubbing was 8.5%, and the appearance was not excellent.

Comparative Example 2 In Example I, an electron beam curing paint containing only acrylic oligomer [Resitron 8760J] was used as the electron beam curing paint.
Electron beam irradiation and stretching were carried out in the same manner as in the example except that Polymer (manufactured by Lykolin Polymer Co., Ltd.) was used.

The coating of the obtained film peeled off and did not have a good appearance.

Comparative Example 3 In Example 1, the voltage of the electron beam accelerator was increased to increase the electron beam penetration ability, and the gel fraction of the original fabric sheet was 55%, and the crosslinking in the thickness direction of the original fabric sheet was uniformly performed. The same operation as in Example 1 was performed except that

The moisture permeability of the obtained stretched film is 4.0g/rrr/2
Moisture proofing was not sufficient after 4 hours.

Example 3 Electron beam irradiation was carried out in the same manner as in Example 1 except that the following composition was used for the electron beam curing paint.

Itsubornyl acrylate 100 parts Antistatic agent rKS-1114 (manufactured by Kao Soap ■) 10 parts The haze of the obtained two-wheel stretched HDPE film was 3.9%
The water vapor permeability was 2.4 g/rrr/2 hrs, and the tape peel test was good. Furthermore, the lifespan of the electrostatic voltmeter was 28 seconds, and no adhesion was observed in the "ash test". As described above, it has been found that by adding an antistatic agent to an electron beam-cured paint and performing electron beam irradiation and stretching, a stretched polyethylene film with good antistatic properties, transparency, and moisture resistance can be obtained.

〔Effect of the invention〕

According to the method of the present invention, it is possible to produce a stretched polyethylene film coated with an electron beam curing coating with good transparency and moisture resistance in a small equipment area and with high productivity, and to produce a polyethylene resin film as a base material. crosslinking and curing of the electron beam cured paint are performed simultaneously.

Furthermore, stretching can be performed efficiently. Furthermore, by selecting the formulation of the coating material, it is possible to produce polyethylene films with various added values and good transparency and moisture resistance.

Claims (1)

[Claims] 1. An electron beam curing paint containing or not containing additives is applied to one or both sides of a sheet made of polyethylene resin, and the degree of crosslinking is increased in the middle direction in the thickness direction of the sheet. 1. A method for producing a stretched polyethylene film, which comprises irradiating an electron beam from both sides so as to reduce the concentration of the film, and then heating and stretching the film. 2. 30% by weight or more of the binder of the electron beam curing paint is
The method for producing a stretched polyethylene film according to claim 1, which is an electron beam-curable paint comprising a monomer and/or oligomer having one ethylenically unsaturated double bond.