JPS6176532A - Polyethylene film - Google Patents

Abstract

PURPOSE:To obtain a film having excellent transparency, moistureproofness, and ultraviolet-shielding property, by applying a resin layer containing an ultraviolet absorbent to at least one surface of a drawn polyethylene film wherein the degree of crosslinking is decreased along the thickness of the film toward the inside. CONSTITUTION:A sheet or tube of a polyethylene resin is irradiated with electron radiation from both sides of the sheet, etc. in nitrogen gas atmosphere to obtain a sheet wherein the crosslinking degree is decreased along the thickness of the sheet from both surfaces toward inside, the gel fraction of the part having lowest crosslinking degree is 0-5%, especially 0%, the gel fraction of the crosslinked surface layers is >=5%, especially 20-70%, the sheet has a structure of preferably a crosslinked layer/uncrosslinked layer/crosslinked layer, and the ratio of the uncrosslinked layer:each crosslinked layer is 1:0.1-10. The sheet is drawn, and one or both surfaces of the obtained film are coated with an organic solvent solution containing an ultraviolet absorbent (e.g. benzotriazole compound) and a laminating resin (e.g. acrylic resin) and dried to form a resin layer containing 2-60wt% ultraviolet absorbent (based on the resin layer).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a polyethylene film, and more particularly to a polyethylene film having a resin layer containing an ultraviolet absorber.

Conventional technology Polyethylene has traditionally been used for many purposes.
Films made from high-density polyethylene are generally opaque and moisture-proof.

Due to its poor surface gloss, it was rarely used in applications that particularly required display effects. As a method to improve this transparency and moisture resistance, the present inventors first developed a polyethylene film that stretches a sheet or tube-shaped molded product of polyethylene resin whose degree of crosslinking decreases in the thickness direction. Manufacturing method (patent application 1986-47)
No. 108) was proposed.

However, the cross-linked stretched polyethylene film obtained by this method is limited in its transparency.

Although it has excellent moisture resistance and rigidity, there is room for improvement in its UV shielding properties, and it is particularly restricted when packaging foods that are degraded by UV rays, such as foods.

Problems to be Solved by the Invention The object of the present invention is to improve the ultraviolet shielding properties of the polyethylene resin stretched film without impairing its properties such as transparency and moisture resistance.

The gist of the present invention is a polyethylene film having a resin layer containing an ultraviolet absorber on at least one side of a stretched polyethylene resin film in which the degree of crosslinking decreases in the direction of the thickness of the film.

The polyethylene resin in the present invention includes polyethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, or ethylene with an ethylene content of 50% by weight or more, propylene, 1-butene, 1- Pentene, 1-hexene, 4-
Copolymers with α-olefins such as methyl-1-pentene and 1-octene or vinyl monomers such as vinyl acetate, (meth)acrylic acid, (meth)acrylic esters, acrylamide, acrylonitrile, styrene, and vinyl chloride. These polyethylene resins may be used alone or in a mixture of two or more. Among these polyethylene resins, especially the density is 0.9359/-
Melt flow index is preferably 0.950.9/s or more (temperature 190 by J Engineering S K6760)
℃, under a load of 2-16Kf, hereinafter referred to as MI) is 0.05,9/10 minutes or more, preferably 0.5-20I
/10 minutes crystalline polyethylene or ethylene copolymer is preferred. In addition, known additives such as antioxidants, antistatic agents, anti-blocking agents, lubricants, neutralizing agents, pigments, and dyes can be added to these polyethylene resins as necessary.

In the present invention, the polyethylene resin film serving as the base material is an unstretched film or a uniaxially or biaxially stretched film in which the degree of crosslinking decreases in the direction of the thickness of the film.

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 performed by extruding from a commonly used T-die to make a flat fabric, extruding from an annular die to make a tube-shaped fabric, or cutting the tubular fabric open to create a sheet-shaped fabric. Either method may be used, such as a method of cutting the tube-shaped raw fabric on both sides, or cutting both sides of the tube-shaped raw fabric to make two sheet-shaped raw fabrics. In this case, the thickness of each raw film should be such that it can be crosslinked so that the degree of crosslinking decreases in the middle direction from both sides in the thickness direction of the raw film, and the thickness of the film after stretching is determined by the stretching ratio and the thickness of the film after stretching. It depends on the situation, but usually 210-2
000 .mu.m1, preferably in the range of 400 to 1000 .mu.m from the viewpoint of handling and forming the above-mentioned crosslinks.

In the present invention, the sheet-like or tube-like raw fabric made of polyethylene resin must be crosslinked from both sides so that the degree of crosslinking decreases toward the inside in the thickness direction of the raw fabric.

The degree of crosslinking is expressed by the gel fraction, but in order to achieve the purpose of the present invention, the gel fraction at the lowest degree of crosslinking in the crosslinked structure of the above-mentioned raw fabric is 0 to less than 5X, and each crosslinked surface layer on both sides is It is preferable that the gel fraction is 5X or more, especially in the range of 20 to 70. In particular, the gel fraction with the lowest degree of crosslinking is O
It is preferable that X constitutes a crosslinked layer/uncrosslinked layer/crosslinked layer in the thickness direction of the original fabric, in which case the composition ratio of each layer is two uncrosslinked layers, two crosslinked layers on both sides = 1:Q, 1 to 10. It is desirable that the degree of crosslinking of each crosslinked layer on both sides be the same.

If the above-mentioned crosslinking is not performed so that the degree of crosslinking decreases in the direction of the thickness of the original fabric, especially if the gel fraction at the lowest degree of crosslinking exceeds 5X, the stretching process will be performed uniformly. Although the transparency is improved, a film with improved moisture resistance, which is the main objective of the present invention, cannot be obtained. Also,
Regarding the crosslinking degree of each crosslinked surface layer on both sides, if the gel fraction is less than 20X, 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, if the gel fraction exceeds 70X, the film tends to break during stretching, and smooth stretching cannot be achieved. 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.

Examples of methods for performing such crosslinking include a method of irradiating electron beams from both sides 11 of the original fabric, and a method of multilayer coextrusion of polyethylene resin blended with a crosslinking agent.

゛The method of irradiating the baby fins depends on the thickness of the original fabric, type 8 of the resin,
Although it varies depending on the molecular weight and molecular weight distribution, the amount of electron beam irradiation is usually 5 to 50 megarads (Mraa), preferably 15 to 30 megarads. In addition, irradiation can be done simultaneously on both sides of the original fabric sheet or on the inside and outside of the original fabric tube.
Alternatively, it may be performed separately on the front and back, or on the outside and in several times. In this case, it is particularly preferable that the irradiation dose to the original fabric is the same for the outer and outer parts of the fabric. Further, the irradiation may be performed while the original polyethylene resin is extruded and melted or after extrusion and cooling and solidification. Further, the electron beam transmission ability can be adjusted by adjusting the applied voltage depending on the thickness of the original fabric, masking with a trace plate, etc.

Next, to give an example of adjusting the amount of electron beam irradiation, for example, if the thickness of the original fabric to be irradiated is 500 μm,
25 sheets of thin film are stacked closely together and
A test piece with a thickness of 00 μm was irradiated with the same amount of electron beams from both sides in the thickness direction, resulting in a crosslinked test piece with a thickness of 20 μm.
By separating the specimen into 25 films and measuring the degree of crosslinking of each film, it is possible to know the distribution 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.

The above electron beam irradiation is preferably performed in an atmosphere of nitrogen, argon, helium, or other inert gas. Although electron beam irradiation can be performed in the presence of air, the transparency of the resulting film is not sufficiently improved.

In addition, as a method of crosslinking by multilayer coextrusion of polyethylene resin blended with a crosslinking agent, for example, a polyethylene resin blended with a crosslinking agent such as an organic peroxide,
For sheet-like raw fabrics, the outer layers are on both sides in the thickness direction, and for tube-shaped raw fabrics, they are the inner and outer layers in the thickness direction. One example is a method in which a material containing an oxide is supplied to a multilayer coextruder so as to form an intermediate layer in the thickness direction of the original fabric, and then crosslinked and coextruded at a temperature equal to or higher than the melting point of the resin.

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. Biaxial stretching may be carried out simultaneously or sequentially.

The stretching temperature is preferably higher than the softening point of the polyethylene resin, particularly in the range from softening to crystal melting point.

Specifically 70 to 150°C, preferably 70 to 135°C
, particularly preferably 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 cannot be performed. On the other hand, the temperature is 150
If the temperature exceeds .degree. C., the resin will melt excessively, making stable stretching impossible, and the resulting film will not be sufficiently improved in moisture resistance.

In addition, the stretching ratio is 5 in one direction or both vertically and horizontally.
It is desirable to carry out at least twice as much, preferably at least four times as much. When the stretching ratio is less than 5 times, uniform stretching is insufficient and it is difficult to obtain a stretched film with excellent transparency. In addition,
The obtained stretched film has heat shrinkability, so when used as a base film for composite packaging, it is heat set at a temperature below the melting point of the stretched film, for example 110 to 140°C, to reduce the heat shrinkage rate in the transverse direction to 1. .5 or less, preferably 1.
It is preferable to set it to 0x or less.

As the ultraviolet absorber in the present invention, compounds such as benzotriazole type, benzophenone type, salicylic acid ester type, and organic nickel type oxalic acid can be used. Examples of benzotriazole compounds include 2-
(2'-Hydroxy-3', 5'-Ct-7''tylphenyl)-5-chlorobenzotriazole, 2-(
2/-Hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-human α
xyphenylpenztriazole, 2-(2'-hydroxy-5/-, ltylphenyl)benzotriazole,
2- (2'-hydroxy-5'-t-butylphenyl)penztriazole, 2+ (2/-hydroxy-5
'-amylphenyl)penztriazole, 2-(2'
-Hydroxy-4'-octoxyphenyl)benzotriazole, 2-(2'-hydroquine-37,5/-di-t-butylphenyl)benzotriazole, 2-(2
'-Hydroxy-s', s'-diynamylphenyl)
Be/citriazole, 2-(2'-hydroxy-3/,
5'-dimethylphenyl)penztriazole, 2-(
2'-hydroxy-3',5'-dimethylphenyl)-
Examples include 5-chlorobenzotriazole, 2-(2'-hydroxy-3/; 5/-dichlorophenyl)benzotriazole, and the like. Examples of benzophenone compounds include 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-(2-hydroxy-3-methacryloxy)proboxy7benzophenone, 2-hydroquine-4-n-octoxybenzophenone, Examples include 2-hydroxybenzopheno7, 2'-dihydroxy-4-methoxybenzo7dinone, and the like.

Examples of salicylic acid ester compounds include phenyl salicylate, p-t-butylphenol, p-octylphenyl salicylate), 2,4-di-t-butylphenyl-3,5-di-t-butyl-4 -Hydroxybenzoate, resorcinol monobenzoate, etc. Examples of organic nickel compounds include bis(3,5
- nickel salt of (2,2'-thiobis(4-t-
octylferulate)]]n dithylamide, etc. Two or more of these ultraviolet absorbers can be used in combination.

The above-mentioned ultraviolet absorbers are used in 2 to 60 weight x weight categories for the resin layer described below. From the viewpoint of ultraviolet shielding properties and transparency, it is preferable to increase the amount added when the resin layer is thin, and to decrease the amount added when the resin layer is thick. The specific amount of addition is, for example, 20 to 601% by weight for a resin layer thickness CL of 5 to 1 μm, and 2 to 6 weight % for a resin layer H of 5 to 10 μm.

The resin layer containing an ultraviolet absorber in the present invention (hereinafter also referred to as laminated resin) is preferably one that has good adhesiveness to the unstretched or stretched film of the above-mentioned crosslinked polyethylene that serves as the base material, such as acrylic acid, acrylic acid ester,
Acrylic resins such as acrylamide, acrylonitrile, methacrylic acid, methacrylic esters, polymers and copolymers of acrylic acid and its derivatives, dimer acids and polyalkylene polyamines, ethylene diamine,
Polyamide resins obtained by reacting bisphenol A-glycidyl ether, etc., epoxy resins obtained by reacting bisphenol A with epichlorohydrin, polyethylene glycol diglycidyl ether, etc., polyols (polyethers and polyesters), and polyisocyanates. Polyurethane resins obtained by anti-F6 and their prepolymers, vinylidene chloride polymers, vinylidene chloride and vinyl chloride, acrylonitrile,
Acrylic acid, acrylic esters, methacrylic acid, vinylidene chloride resins such as copolymers with methacrylic esters, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, etc. Examples include polymers, polyethylene and ethylene copolymers such as chlorinated polyethylene, diene-based or olefin-based synthetic rubbers, and natural rubbers such as cyclized rubber.

In the present invention, on the surface of an unstretched or stretched, preferably biaxially stretched, crosslinked polyethylene resin film serving as a base material,
Methods for forming a laminated resin layer containing an ultraviolet absorber include (-,) coating of a laminated resin solution or dispersion;
(2) Lamination of a resin layer and (3) Application of an electron beam or ultraviolet curable solvent-free laminated resin.

The coating method is as follows: (1) Dissolve the ultraviolet absorber and the laminated resin in an organic solvent, water, etc., apply this solution to one or both sides of the base film using a dipping method, gravure coating method, etc., and then apply hot air, etc. (2) The ultraviolet absorber and laminated resin are dispersed in water or an organic solvent to form an emulsion mold, and this is coated into a base film by reverse roll coating, air knife coating, doctor roll coating, etc. and (3) applying a laminated resin consisting of an ultraviolet absorber, an oligomer, a vinyl monomer, a photopolymerization initiator, etc. to an electronic t! Alternatively, a method of curing by irradiating ultraviolet rays can be mentioned.

The amount of this coating varies depending on the application, but it is usually dry [
It is in the range of 15 to 10 μm. Note that the coating method may be divided into several times and coated in layers.

In addition, lamination methods include melting the ultraviolet absorber and the laminating resin and extrusion laminating it on one or both sides of the base film, or producing an unstretched or stretched film of the laminated resin and applying it to the base film. Examples include a method of laminating on one side or both sides. The thickness of this laminate varies depending on the application, but is usually in the range of L5 to 5μ (after stretching). Incidentally, the coating and lamination of the laminated resin can be carried out as a multilayer of two or more types on one side of the base film, if desired.

Furthermore, in applying and laminating the resin, in order to improve the adhesion with the base film, it is desirable to previously treat the base film surface with corona discharge treatment or the like to increase the wettability index.

Painted film (coated film) by the above method
The laminated film (laminate film) is uniaxially stretched or biaxially stretched when the base polyethylene resin film is an unstretched film. Further, in the case of a uniaxially stretched base film, the film is uniaxially stretched in a direction perpendicular to the uniaxial direction, if necessary. In particular, it is preferable that the crosslinked polyethylene film of the base material be biaxially stretched. In this case, stretching is carried out at a temperature range from the softening point to the melting point of the base film.
It is preferable to carry out the process three times or more in one direction.

Effects of the Invention The polyethylene film of the present invention having the structure described above has excellent ultraviolet shielding properties in addition to the transparency and high moisture resistance of the polyethylene resin stretched film serving as the base material.

The polyethylene film of the present invention has the above-mentioned excellent properties and can be used as a packaging material, particularly for food packaging, and other industrial applications.

Examples Examples of the present invention will be shown below. The test methods used in the examples are as follows.

(1) Haze: ASTM D1003 (2) Moisture permeability:
J Engineering S z0208 B method (temperature 40℃.

Relative humidity 90X) (3) 'g External light transmittance: Measured with a self-recording spectrophotometer.

Example 1 High-density polyethylene (density CL957, 9/i, M engineering α
8,9/10 minutes (hereinafter referred to as HDPK) was molded into a sheet-like original fabric having a thickness of α611tIK using a T-die extrusion sheet molding machine.

Using an electron beam irradiation device (ESI M), this sheet-like material was exposed to 165 kV on each of the front and back sides under a nitrogen gas atmosphere.
A 20 megarad electron beam was irradiated under the condition of 45 mA. In order to know the crosslinking degree of the irradiated surface of this crosslinked sheet and the inside of the sheet in the thickness direction,
Thirty μm-thin films were stacked to form a test method with a thickness of 0.6 m, and the degree of crosslinking of each thin film was examined by irradiating it with an electron beam under the same conditions. The lowest crosslinking inside the thickness direction was at a gel fraction of OX when the gel fraction was 50×1.

Moreover, the composition ratio of the thickness of the crosslinked layer and the uncrosslinked layer was crosslinked layer: uncrosslinked layer: crosslinked layer; 1:2:1.

This crosslinked sheet was stretched 4 times in the longitudinal direction and 5 times in the transverse direction at a temperature of 150°C to obtain biaxially stretched HDPK with a thickness of 50 pm! Got the film. This film has 10 substantive effects.
When the film was magnified to 0x and the film surface was held with a sharp bottle set, the crosslinked layer on the surface was gently peeled off, but the middle layer of the uncrosslinked layer was fibrillated. The same was true for the opposite side of the film.

The above HDPE biaxially stretched film was subjected to corona discharge treatment to obtain a film with a chipping index of 54 ayl'l/cm.

Acrylic
Vinyl chloride copolymer (manufactured by Toyo Morton Co., Ltd., trade name, AD
S-35) 10 parts by weight and 2-(2'-hydroxy-
3 parts by weight of 31,s/-di-t-butylphenyl)5-chlorotriazole (UV-1) dissolved in 100 parts by weight of toluene was coated with a roll coater and the solvent was removed in a dryer to form a coated film. I got it.

The properties of this film are shown in Table 1.

Example 2 On the corona discharge treated surface of the crosslinked sheet obtained in Example 1,
An acrylic-vinyl chloride copolymer blended in the same manner as in Example 1 and IJV-1 dissolved in 40 parts of toluene were applied using a gravure roll and dried to obtain a crosslinked sheet. This sheet was heated 4 times in the vertical direction and 5 times in the horizontal direction at a temperature of 155℃.
The film was stretched twice and had a thickness of 50 μm. The properties of this film are also listed in Table-1.

Example 3 A cyclized rubber liquid (trade name, manufactured by Shuka Shiki Co., Ltd., oP) was applied to the corona discharge treated surface of the HDPE biaxially stretched film obtained in Example 1.
ff medium) 10 heavy seams and 2,2'-dihydroxy-4-methoxybenzophenone (hereinafter referred to as UV'-2) 3
parts by weight dissolved in 50 parts by weight of toluene was coated and dried to obtain a thin film. The properties of this film are also listed in Table-1.

Example 4 2-Hydroxy-4- was added to 10 parts by weight of an electron beam curable resin (Inu Nippon Ink Shaya trade name, KB-2) on the corona discharge treated surface of the HDPE biaxially stretched film obtained in Example 1. (
A solution containing 5 parts by weight of 2-hydroxy-3-methacryloxy)propoxybenzophenone (hereinafter referred to as LJV-3) was applied, and the coating solution was cured by irradiation with a 5 megarad electron beam to obtain a coated film. Table 1 shows the characteristics of this film.
Also listed.

Comparative Example 1 In Example 1, the characteristics of the HDPE biaxially stretched film alone, which is not coated with a resin containing an ultraviolet absorber, are shown below.
Also listed in 1.

Comparative Example 2 Ultraviolet absorber LIV-12 was added to the HDPE used in Example 1.
Using HDPK mixed with 0% by weight, a sheet-like raw fabric was formed, electron beam crosslinked, and stretched in the same manner as in Example 1, to obtain a film with a thickness of 30 μm. The properties of this film are also listed in Table-1.

Comparative Example 5 The sheet-like original fabric obtained in Example 1 was irradiated with the applied voltage of the electron beam irradiation device increased to increase the electron beam penetration ability, and the gel fraction was 55X, and the sheet thickness direction was irradiated. A crosslinked sheet with a uniform degree of crosslinking was obtained. This crosslinked sheet is 138
Stretched 4 times in the vertical direction and 5 times in the horizontal direction at ℃ to a thickness of 30μ
A biaxially oriented HDPFI film of m was obtained. This film was subjected to the same corona discharge treatment as in ψ111, coating with a resin containing the ultraviolet absorber IJV-1, and drying. The properties of this film are also listed in Table-1.

Example 5 A coated film was obtained in the same manner as in Example 1, except that the crosslinking composition ratio of the biaxially stretched HDPE film was changed as shown in Table 1. The characteristics of this film are -1
Also listed.

Claims (1)

[Claims] On at least one side of a stretched polyethylene resin film in which the degree of crosslinking decreases in the direction of the thickness of the film,
A polyethylene film with a resin layer containing an ultraviolet absorber.