JPS6174820A - Polyethylene oriented film - Google Patents

Abstract

PURPOSE:To form a polyethylene oriented film which is transparent and superior in moisture resistance, by performing cross-linking from both sides so that a degree of the cross-linking is deteriorated inwardly in the direction of a thickness of a molded article. CONSTITUTION:As for cross-linking of a sheet like or tubular raw fabric made of polyethylene resin, it is performed from both sides so as to deteriorate inwardly a degree of the cross-linking in the direction of a thickness of raw fabric. As for the degree of the cross-linking, it is desirable that a gel content ratio whose degree of the cross-linking is lowest is less than 0-5%, the gel content ratios of cross-linked surface layers each of both the sides are more than 5% and especially within a range of 10-80% in constitution of the cross-linking of the raw fabric. Especially an article wherein the gel content ratio of the lowest degree of the cross-linking is 0% and a cross-linked layer/uncross-linked layer/cross-linked layer is constituted in the direction of the thickness of the raw material is desirable, in this case, it is desirable that a constituting ratio of each layer falls within a range of cross-linked layer:uncross- linked layer:cross-linked layer=1:0.1-10:1, and it is desirable especially that the degrees of cross-linking of the cross-linked layers each of both the sides are identical with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a stretched polyethylene film in which the degree of crosslinking decreases in the direction of the thickness of the film.

BACKGROUND ART Conventionally, various methods for producing crosslinked polyethylene films have been proposed in order to improve the transparency and heat shrinkability of polyethylene films. For example, Japanese Patent Publication No. 57-18895 describes a method in which an ethylene-based resin film such as polyethylene is uniformly crosslinked with an electron beam or radiation, heated to m, and biaxially stretched.

However, although cross-linked stretched polyethylene films obtained by conventional methods have improved transparency and heat shrinkability, they do not have sufficient moisture resistance, and in applications that require moisture resistance, the thickness of the film must be increased. Next, it is necessary to provide a barrier resin layer! It is. The transparency and packaging properties of this thinned film are completely lost, and the manufacturing cost also increases.

Problems to be Solved by the Invention The entire purpose of the present invention is to provide a stretched polyethylene film that is transparent and has excellent moisture resistance.

Poor Means to Solve the Problems The gist of the present invention relates to a stretched polyethylene film in which the degree of crosslinking decreases in the direction of the thickness of the film,
The stretched film is made by crosslinking a sheet or tube-shaped molded product made of polyethylene resin from both sides in the thickness direction of the molded product such that the degree of crosslinking decreases in the middle direction, and then preferably at the melting point of the resin. It can be produced by stretching in at least one direction at the following temperatures.

Next, the polyethylene stretched film of the present invention will be explained.

Root flow index (T-work SK6760, work 0 temperature 1190c% load 2-16 & temperature 11 constant, hereinafter referred to as M-work) is Q, 051/10 minutes or more, preferably 11-2
09/10 crystalline ethylene homopolymer/polyethylene such as linear low density polyethylene, ethylene with an ethylene content of 1% or more, propylene, 1-butene, 1-pentene, 1-hexene, α-olefins such as 4-methyl-1-pentene and 1-octene or vinyl acetate, (meth)acrylic acid, (meth)
Examples include copolymers with vinyl polymers such as acrylic esters, acrylamide, acrylonitrile, styrene, and vinyl chloride.

These polyethylene resins are used alone or in a mixture of two or more. Note that known additives such as antioxidants, ultraviolet absorbers, antiblocking agents, lubricants, neutralizing agents, nucleating agents, pigments, and dyes can be added to these polyethylene resins as necessary.

Of the film of the present invention! ! ! The polyethylene resin in the manufacturing process is supplied to a commonly used extruder, and is melt-extruded, cooled, and solidified to form a sheet or tube-like raw fabric. W3 melt extrusion molding involves extruding from a commonly used T-die to form a flat 7 material, extruding from an annular gouer to form a tube-shaped material, and cutting open a tube-like material to create a sheet-like material. Either method can be used, such as cutting both sides of a tube-shaped raw fabric to make 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, and it depends on the stretching ratio and the thickness of the film after stretching. It depends on F, but usually d2
10S200μm1 preferably 1J400-1000μm
This range is desirable from the viewpoint of handling and forming the above-mentioned crosslinks.

In the present invention, cross-linking of the tube-shaped raw fabric of the sheet-like container made of polyethylene resin requires cross-linking from both sides so that the degree of crosslinking decreases in the thickness direction of the raw fabric. be.

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 It is preferable that the gel fraction of the crosslinked surface layer is 5% or more, particularly in the range of 10 to 80%. In particular, the gel fraction with the lowest degree of crosslinking is 0%.
In this case, it is preferable to configure crosslinked layer/uncrosslinked layer/crosslinked layer in the thickness direction of the original fabric, in which case the composition ratio of each layer is α1 to 10:1. It is desirable that the degree of crosslinking be within this range, and it is particularly preferable that the degree of crosslinking of each crosslinked layer on both sides be the same.

If the above-mentioned crosslinking is not carried out in such a way that the degree of crosslinking decreases in the direction of the original warp thickness, especially if the gel fraction at the lowest degree of crosslinking exceeds 5 inches, the stretching process will be carried out evenly.
Although the transparency is improved, a film with improved moisture resistance, which is the main objective of the present invention, cannot be obtained. Man,
If the degree of crosslinking of each of the crosslinked layers on both sides is less than the gel fraction of 5, the stretching process will not be uniform and the transparency of the film will not be improved. On the other hand, when the gel fraction exceeds 80%, the film tends to break during stretching and smooth stretching cannot be achieved.711. qFurthermore, if the entire thickness of the original fabric is uniformly crosslinked, the stretching process will be uniformly performed. A
Notes are improved, but moisture proofing does not improve notes, and on the other hand, crosslinking only on one side in the thickness direction of the original fabric causes the film to easily break during l-C stretching, and If the entire layer is crosslinked to L5, where the crosslinking degree V4 decreases, the moisture resistance of the resulting film will not be sufficiently improved, and both are unfavorable.

In addition, the above gel fraction indicates the unnatural portion extracted with p-xylene manufactured by Sample Corporation.

Examples of methods for performing this elaborate 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 entire electron beam varies depending on the thickness of the original fabric, the type of resin, the molecular weight, and the molecular weight distribution, but usually the total amount of electron beam irradiation is 3 to 50 megarads (Mrad), preferably 5 to 50 s. If it costs 30 megaland, it's a lot. Alternatively, the irradiation can be carried out simultaneously on the front and back sides of the original fabric sheet, the inside and outside of the original fabric tube, or the irradiation can be carried out separately on the front and back sides or inside and outside, or even in several batches. In this case, it is particularly preferable that the irradiation dose to the original fabric is the same on the front and back sides of the original fabric, or on the inside and outside. Further, the irradiation can be carried out regardless of whether the original polyethylene resin is in the extrusion melted state or in the state after extrusion cooling and solidification. Furthermore, in order to adjust the transmission ability of the electron beam, it is necessary to adjust the applied voltage depending on the thickness of the original fabric, and to use a shielding material such as a film.
Examples include masking with sheets, boards, etc.

Next, to give an example of adjusting the electron beam irradiation t, for example, when the thickness of the original fabric to be irradiated is 500 μm, 20/A
A test piece with a thickness of 500 μm was obtained by tightly stacking 25 thin films with a thickness of
By separating the sample into 25 films of m and measuring the degree of crosslinking of each film, it is possible to determine the distribution of the degree of crosslinking in the thickness direction of the test piece. From this result, the thickness of the original fabric and the electron beam irradiation Fi
The relationship between tKj and the degree of crosslinking can be known.

In addition, as a method for crosslinking multilayer coextrusion of polyethylene resin by blending a crosslinking agent, for example, a method in which a crosslinking agent such as an organic peroxide is blended with polyethylene resin,
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 method is to supply sea urchin mixed with an organic peroxide to a sea urchin multilayer coextruder to form an intermediate layer in the thickness direction of the original fabric, and crosslink and coextrude at a temperature equal to or higher than the melting point of the resin.

Stretching is carried out by heating the cross-linked raw material and stretching it in the uniaxial and biaxial directions at a predetermined magnification using the usual roll method, tenter method, tubular method, or rolling method, or a combination of these methods. and get the film. Biaxial stretching can be done either simultaneously or sequentially.

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
When the temperature is between 0.degree. On the other hand, if the temperature exceeds the melting point, the resin will melt excessively, making stable stretching impossible, and the resulting film will not be sufficiently improved in moisture resistance.

However, in the stretching ratio, in the tensile stretching, the longitudinal direction (MD
) The machining/machining is desirably carried out at 5 times or more in the transverse direction (TD), preferably 4 to 8 times. If the stretching ratio is less than 3 times, the stretching will be non-uniform and a stretched film excellent in transparency cannot be obtained. Mayu, the stretching ratio when rolling in the MD force direction and tensile stretching in the TD force direction is 1.5 times or more in the MD force direction, preferably 2 to 6 times, and 3 times or more in the TD force direction, preferably 4.
It is desirable to perform the test at a magnification of ~8 times. TD force direction rolling ratio is 1
．． If it is less than 5 times, the effect of improving moisture resistance is insufficient.

The polyethylene stretched film of the present invention, which has a structure that exceeds the effects of the invention, is uniformly cross-linked in all layers, has superior moisture resistance and rigidity compared to stretched polyethylene films, and is also more resistant to transparent processing than uncrosslinked polyethylene films. It is excellent.

The stretched polyethylene film of the present invention has the above-mentioned excellent properties and is suitable as a transparent moisture-proof packaging film.

Examples Examples of the present invention will be shown below. In addition, the test method in the example is as follows.

(1) Haze: ASTM D1005 (2) Moisture permeability f:
, 7I8 Z0208B method (temperature 240°C, relative humidity 9
[Both feet at 0] 3) Tsuyoshi Note: ASTM D882 (4
) Gel fraction: ASTM D2765, A method Example 1 Low density polyethylene (density α92017cm3, M]:
50 f/10 minutes (hereinafter referred to as LDPE) was extruded using a T-die to form a sheet-like raw fabric with an F thickness of Q and 6 m.

Using an electron beam irradiation device (manufactured by ESI), this sheet-like material was exposed to 165 kV on each front and back under a nitrogen gas atmosphere.
A 10 megaland electron beam was irradiated under the condition of -45mA. The irradiated surface of this crosslinked sheet is made of the above-mentioned LDPK so that the degree of crosslinking inside the sheet in the thickness direction is completely reduced.
Fifty sheets of 0 μm thin film were layered to form a test piece with a thickness of 16 mm, and the degree of crosslinking of each thin film was examined by irradiating it with electron beams under the same conditions. The gel fraction is 30%, and the lowest crosslinking inside the thickness direction is when the gel fraction is 0.

Further, the composition ratio of the thickness of the crosslinked layer and the uncrosslinked 44 layers was crosslinked layer: uncrosslinked m: crosslinked layer = 1:t821.

This cross-linked sheet metal temperature is 105℃, 4 times in MD direction, TD
A biaxial i-stretched HNPG film with a thickness of 30 μm was obtained by stretching 5 times in the direction. The properties of this film are shown in Table 1.

This film was magnified 100 times using a 1i'ft stereoscopic microscope, and when used with a sharp bin set on the entire surface of the film, the crosslinked layer on the surface was gently peeled off, but the uncrosslinked middle layer was fibrillated. The same goes for the other side of the film.

Examples 2 to 10 LDP Ko, I, DPIIC (density f1922) of Example 1
S'/cm", MI &' Of/10 minutes), linear low density polyethylene (density α924 f/cm', M work 2.
09710 minutes, hereinafter referred to as I, LDPK 2-hole medium-density polyethylene (density CL954f/α3, M-work t0
2/10 minutes, hereinafter referred to as MDIC), the thickness of the original fabric, the degree of crosslinking in the thickness direction of the original fabric were adjusted, and the stretching was carried out under the conditions shown in Table 1. Each stretched film was obtained in the same manner as in Example 1. The custom orders for each film are listed in Table 1.

Comparative Examples 1 and 2 In Step 7 of Example 1, the applied voltage of the electron beam irradiation device was increased to increase the electron beam penetration ability, the degree of crosslinking in the thickness direction of the raw sheet was made uniform, and the gel fraction was A stretched film was obtained by stretching under the conditions shown in Table 1 using A65-thick and 45-thick A65 film. The properties of this film are also listed in Table-1.

Comparative Example 3.4 In the process 7 of Example 1, crosslinking with electron beam was performed from one side in the thickness direction of the original fabric, and the ratio of the crosslinked layer to the uncrosslinked layer in the thickness direction of the original fabric was 1:19, respectively. The gel fraction of the irradiated side and the non-irradiated side of the original sheet were set to 65 and 0%, respectively, and 45 and 0%, and the stretching was carried out under the conditions shown in Table 1. Get the film. All custom orders for this film are listed in Table-1.

Examples 11 to 13 Using polyethylene with different density, M process, and melting point, the thickness of the original fabric, the degree of crosslinking in the thickness direction of the original fabric were adjusted, and the stretching process was performed under the conditions shown in Table 2. Each stretched film was obtained in the same manner as in Example 1 except for the following steps. The characteristics of each film are shown in Table 2.

Comparative Example 5 Table 2 also shows the properties of the stretched film in which the degree of crosslinking in the thickness direction of the raw sheet in Example 12 was made uniform throughout the thickness.

Claims (1)

[Claims] A stretched polyethylene film in which the degree of crosslinking decreases in the direction of the thickness of the film.