JPS60230851A - Polyethylene composite film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyethylene composite film, and more particularly to a polyethylene composite film that has excellent moisture resistance, gas barrier properties, and transparency.

Conventionally, high-density polyethylene is a material with high crystallinity, high melting point, and excellent mechanical properties and chemical stability, but the resulting film is generally opaque, moisture-proof, and surface-compatible. Kozueho Jiyu? 100 ノ 社 1r4 ノ 啼 I1ノ ノ It was hardly used for purposes where it was carried away. As a method for improving this transparency, for example, a method is known in which a film of polyethylene or the like is uniformly crosslinked by radiation irradiation, heated, and biaxially stretched (Japanese Patent Publication No. 37-J8893). but,
Although cross-linked stretched polyethylene films obtained by conventional methods have improved transparency and strength, improvements in moisture resistance and gas barrier properties have not been sufficient. In order to further impart moisture resistance and gas barrier properties to this film, it was necessary to provide a barrier resin layer such as vinylidene chloride resin or polyvinyl alcohol on the film surface.

However, in applications that require higher moisture resistance and gas barrier properties, the barrier resin layers that are laminated are inevitably multi-layered and thick, which impairs the transparency and packaging properties of the resulting film, and also reduces the manufacturing process. The disadvantages are that the workability is poor and the cost is high.

The present inventors conducted various studies in order to obtain a polyethylene film with a transparent thin-walled structure and higher moisture and gas barrier properties, and as a result, the cross-linked cross-sectional structure in the film thickness direction was identified. The present invention was completed by combining a highly moisture-proof polyethylene stretched film with a high degree of crystallinity obtained by stretching the original film obtained by stretching the original film, and a barrier resin layer.

That is, the present invention provides at least a layer made of a vinylidene chloride polymer and/or a polyvinyl alcohol polymer on at least one side of a stretched polyethylene resin film in which the degree of crosslinking decreases inward in the thickness direction of the film. It is a polyethylene composite film with one type of layer.

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% or more by weight, 1-butene, 1-butene, and 1-butene. 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, the melt flow index (measured with JIEI K6760 at a temperature of 190°C and a load of 2.16 kg, hereinafter referred to as MI) is 0 when the density is α935f/- or more, preferably 0.950f/51i or more. .051P/10 minutes or more, preferably [15~
201F, /10 min crystalline polyethylene or ethylene copolymer is preferred. In addition, these polyethylene resins may contain antioxidants, ultraviolet absorbers, anti-blocking agents, lubricants, neutralizing agents, antistatic agents, pigments,
Known additives such as dyes can be added.

In the present invention, the polyethylene resin film that serves as the base material of the polyethylene composite film 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.

In the production of the film of the present invention, the polyethylene resin is supplied to a commonly used extruder and subjected to melt extrusion 1. The material is cooled and solidified to form a sheet or tube. Melt extrusion molding is performed by extruding from a commonly used T-die to make a solid fabric, by extruding from an annular die to make a tube-shaped fabric, or by cutting open a tube-shaped fabric to make a sheet-shaped fabric. Either method may be used, such as cutting both sides of a tube-shaped raw fabric to obtain two sheet-shaped raw fabrics. In this case, the thickness of each film should be such that it can be crosslinked from both sides in the thickness direction of the film so that the degree of crosslinking decreases in the middle direction (depending on the stretching ratio and the thickness of the film after stretching). Although it depends on the
The range of 2000μ, preferably 400 to 1000μ is desirable from the viewpoint of handling and formation of 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 5 inches, and each crosslink on both sides is It is preferable that the gel fraction of the surface layer is 5% or more, particularly in the range of 20 to 70%. In particular, it is preferable that the gel fraction at the lowest degree of crosslinking is 0, and that the crosslinked layer/'uncrosslinked layer/crosslinked layer is formed in the thickness direction of the original fabric.In this case, the composition ratio of each layer is the uncrosslinked layer. : Each crosslinked layer on both sides = 1: It is desirable that the range is from 0.1 to 10, and it is particularly preferable that the degree of crosslinking of each crosslinked layer on both sides is the same.

If the above-mentioned crosslinking is not carried out 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 5 inches, the stretching process will be uniform.
(However, although the transparency is improved, a film with improved moisture resistance, which is the main objective of the present invention, cannot be obtained.
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, if the gel diameter exceeds 70 inches, the film is likely to break during stretching and smooth stretching cannot be achieved. Furthermore, when cross-linking is uniformly applied to all layers in the thickness direction of the original fabric, stretching is performed uniformly and transparency is improved in case 1, but moisture resistance is not improved; If only one side of the material is cross-linked, the film will easily break during stretching, and if the entire layer is cross-linked so that the degree of cross-linking decreases from one side in the thickness direction of the material, the resulting film will have poor moisture-proof properties. Although the improvement is sufficient, both are unfavorable.

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 of the original fabric, and a method of multilayer coextrusion of polyethylene resin blended with a crosslinking agent.

The method of irradiating the electron beam varies depending on the thickness of the original fabric, the type of resin, the molecular weight, and the molecular weight distribution, but the amount of electron beam irradiation is usually 5 to 50 megarads (Mrad), preferably 15 to 30 megarads. do it. However, irradiation is not yet possible at the same time on both sides of the original fabric sheet or 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 be the same on both the front and back sides of the original fabric, as well as on the outside and outside. However, the irradiation may be carried out while the original polyethylene resin is in an extrusion melted state or in a state after extrusion cooling and assimilation.

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 shielding plate, etc.

Next, to give an example of how to adjust the amount of electron beam irradiation, if the thickness of the original fabric to be irradiated is 500μ, then 25 thin films of 20μ thickness are closely stacked together and the thickness is 550μ.
A test piece with a thickness of 0μ was irradiated with the same amount of electron beams from both sides in the thickness direction to crosslink the test piece.
By separating the film into two sheets 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.

The stretched and crosslinked original fabric is heated and stretched in uniaxial or biaxial directions at a predetermined magnification by a normal roll method, tenter method, tubular method, rolling method, or a combination of these methods to obtain a film. . Biaxial stretching may be simultaneous or sequential.

The stretching temperature is preferably higher than the softening point of the polyethylene resin, particularly in the range from the softening point to the crystal melting point. Specifically 70
-150°C, preferably 70-155°C, especially 100-150°C
130°C is preferred.

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 3 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. If the stretching ratio is less than 3 times, uniform stretching is insufficient and it is difficult to obtain a stretched film with excellent transparency. Power,
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 preferably 0% or less.

Next, the vinylidene chloride-based polymer in the present invention refers to a vinylidene chloride homopolymer and a vinylidene chloride copolymer, and the vinylidene chloride copolymer includes:
Examples include copolymers of vinyl chloride as a main component and comonomers such as vinyl chloride, acrylonitrile, acrylic esters, acrylic acid, methacrylic esters, and methacrylic acid.

Further, examples of the polyvinyl alcohol polymer in the present invention include polyvinyl alcohol, polyvinyl acetal, and ethylene-vinyl alcohol copolymer. The polyvinyl alcohol preferably has a degree of saponification of 70 molar or more. Preferably, the polyvinyl acetal has 25 moles or less of all hydroxyl groups converted into acetal. Still, the ethylene-vinyl alcohol copolymer preferably has an ethylene content of 25 to 50 moles and a saponification degree of 70 moles or more.

Note that the vinylidene chloride polymer or polyvinyl alcohol polymer described above can be used in combination. Further, additives such as antioxidants, antistatic agents, lubricants, antiblocking agents, etc. may be added to the extent that the properties of these polymers are not impaired.

In the present invention, the method of forming a layer of vinylidene chloride polymer and polyvinyl alcohol polymer (hereinafter simply referred to as laminated resin) on the surface of a crosslinked polyethylene resin film serving as a base material includes (1) forming a layer of laminated resin; A method of applying the solution or dispersion to an unstretched or stretched, preferably biaxially stretched, polyethylene resin film (2)
) A method may be mentioned in which a laminated resin layer is laminated on the surface of an unstretched or stretched, preferably biaxially stretched, polyethylene resin film.

The coating method includes dissolving the laminated resin in an organic solvent, water, etc., applying this solution to one or both sides of the preemptive film by dipping or gravure coating, and drying with heat, air, etc. Alternatively, the laminated resin is dispersed in water or an organic solvent to create an emulsion mold, and this is applied to one or both sides of the film using reverse roll coating, air knife coating, doctor roll coating, etc., and then dried. can be given. The thickness of this coating film varies depending on the desired gas barrier properties and moisture proof properties, but is usually in the range of 1 to 10 μm in a dry state.

Note that the coating method may be divided into several times and coated in layers.

In addition, lamination methods include melting the laminated 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 one or both sides of the base film. Examples include a method of pasting. The thickness of this laminate varies depending on the desired gas barrier properties and moisture resistance, but is usually 10 to 50 microns.
m range. Incidentally, the coating and lamination of the laminated resin can be performed in two or more layers on one side of the base film, if desired.

In addition, in the above coating and lamination, in order to improve the adhesion with the base film, the base film surface is treated in advance to increase the wettability index of the film to 36 dyn/m or more.
It is preferable to keep 2.

This treatment method is not particularly limited, but corona discharge treatment is usually used. Furthermore, it is preferable to apply an anchor coating agent, such as an isocyanate-based or titanate-based one, on the treated surface in a dry state at a rate of 02 to 41/m2, and dry and harden it to improve adhesion.

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. If the base film is a -axially stretched film, it 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, the stretching is preferably carried out in one direction by three times or more in a temperature range from the softening point to the melting point of the base film.

The polyethylene composite film of the present invention with the above structure has a transparent polyethylene resin stretched film as a base material,
In addition to high moisture resistance, this product, combined with the gas barrier and moisture resistance properties of vinylidene chloride polymer and polyvinyl alcohol polymer, provides superior moisture and gas barrier properties without compromising transparency compared to conventional products. Therefore, it is suitable as a packaging film.

Examples of the present invention will be shown below. The test method is as follows.

(1) Gas detection rate: Compliant with AEITM D1434 (measured using oxygen gas at a temperature of 25°C) (2) Moisture permeability:, TI8 z020B B method (temperature 40°C)
(3) Haze: ASTM D1005 Example 1 High density polyethylene (density α957t/el, M o
, s t / 1 o min, hereinafter referred to as HDPE) is T
A sheet-like original fabric having a thickness of α6 was molded using a die extrusion sheet molding machine.

Using an electron beam irradiation device (manufactured by KSI), this sheet-like original fabric was exposed to 165 kV on each of the front and back sides under a nitrogen gas atmosphere.
A 20 megaland electron beam was irradiated at 45 mA. In order to know the degree of crosslinking on the irradiated surface of this crosslinked sheet and inside the sheet in the thickness direction, 50 thin films of 20 μm thick made of the HDPFi described above were stacked to a thickness of 0.5 μm.
The crosslinking degree of each thin film was investigated by irradiating the electron beam under the same conditions with a test force of 6vah.The crosslinking degree of the thin film on both sides of the irradiated surface was 50% gel fraction, and the lowest crosslinking inside the thickness direction. had a gel fraction of aq6. In addition, the composition ratio of the thickness of the crosslinked layer and the uncrosslinked layer is: crosslinked layer: uncrosslinked layer:
The crosslinked layer ratio was 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 130° C. to obtain a biaxially stretched uDpm film having a thickness of 30 μm. 1- of this film with a stereomicroscope
When the film was magnified twice and the surface of the film was touched with sharp tweezers, the surface crosslinked layer was gently peeled off, but the uncrosslinked middle layer became fibrillated. The same was true for the opposite side of the film.

This film was subjected to a corona discharge treatment to obtain a film with a wettability index of 54 dyn/'cmO.

An isocyanate-based anchor coating agent (Toyo Morton Publishing, EI, 2
20 and (!AT200) mixed and diluted, hereinafter referred to as A
10 agent) was applied uniformly at a coating amount of 0.2 f,/m'' and dried and cured at 80° C. for 1 minute.

A vinylidene chloride resin emulsion [manufactured by Mukasei Co., Ltd., Saran Latex L'-501 (trade name) hereinafter referred to as PVDO] was uniformly applied to the surface of the film treated with A10 agent to a thickness of 3 μm. After drying at 50°C for 1 minute, it was left to stand at 50°C for 24 hours. The properties of the obtained polyethylene composite film are shown in Table-1.

Examples 2 to 4 In Example 1, PVDC! A polyethylene composite film was obtained in the same manner as in Example 1, except that the coating amount and the crosslinking composition ratio of the biaxially stretched HDPR film were as shown in Table 1. The properties of this film are also listed in Table-1.

Example 5 A polyethylene composite film was obtained in the same manner as in Example 1, except that an aqueous solution of polyvinyl alcohol (saponification degree of 88 mol, hereinafter referred to as Pvm) was applied instead of PvDC.

The characteristics of this film are also listed in Table-1.

Comparative Example 1 Biaxial stretching without applying PVDO in Example 1)! D
The characteristics of the PE film alone are also listed in Table-1.

Comparative Example 2 The sheet-like raw material 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 55 cm, and the sheet was irradiated in the thickness direction of the sheet. A crosslinked sheet was obtained in which the degree of crosslinking was uniform. This crosslinked sheet is 138
Stretched 4 times in the vertical direction and 5 times in the horizontal direction at ℃ to a thickness of 50μ
A biaxially oriented HDPK film of m was obtained. This film was subjected to corona discharge treatment, A/C agent treatment, and PVDO coating in the same manner as in Example 1. The characteristics of this film are shown below.
Also listed in 1.

Comparative Example 3 The sheet-like original fabric obtained in Example 1 was irradiated with an electron beam from one side in the thickness direction of the sheet, and the degree of crosslinking on the irradiated side and the non-irradiated side was 50 and 0, respectively. H, the ratio of the crosslinked layer and uncrosslinked layer in the thickness direction of the sheet is 4:
A crosslinked sheet No. 1 was obtained. This crosslinked sheet was heated to 132°C.
Stretched 4 times in the vertical direction and 5 times in the horizontal direction to a thickness of 30 μm.
A biaxially stretched HDPK film was obtained. This film was subjected to corona discharge treatment, A10 agent treatment, and PVDC coating in the same manner as in Example 1. The characteristics of this film are shown below.
Also listed in 1.

Example 6 In Example 1, an ethylene-vinyl alcohol copolymer film with a thickness of 25 μm [EVAL zF- manufactured by Kuraray Co., Ltd. x (product name)] with nip rolls at 60℃, 5 kg/5PG.

A polyethylene composite film was obtained by curing at 40°C for 48 hours. The properties of this film are also listed in Table-1.

Claims (1)

[Claims] A polyethylene composite having at least one layer made of a vinylidene chloride polymer and/or a polyvinylfluorol polymer on at least one side of a stretched polyethylene resin film in which the degree of crosslinking decreases inward in the thickness direction of the film. film.