JPS5958044A - Polyethylene film - Google Patents

Abstract

PURPOSE:To provide a polyethylene film having the stiffness of the base resin, capable of keeping the excellent appearance and transparency of the film manufactured at the start of the manufacture, and suitable for fool packaging, by compounding a specific high-pressure polyethylene with an ethylene.alpha-olefin copolymer, and forming the resin to a film. CONSTITUTION:100pts.wt. of a copolymer composed ethylene and an alpha-olefin (<=6wt%) and having a density of 0.930-0.945g/cm<3> and a molecular weight distribution index [(weight-average molecular weight)/(number-average molecular weight)] of <=5 is compounded with 5-50pts.wt., preferably 8-25pts.wt. of a high-pressure polyethylene having a density of >=0.928g/cm<3> and a melt index of 1-10, preferably 1-3 times the melt index of the ethylene.alpha-olefin copolymer. The resin composition is molten, kneaded, and formed to a film. EFFECT:There is no development of continuous longitudinal white stripes nor fish scale clouding from the start of the film manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a film with excellent appearance and transparency, and
This relates to a strong polyethylene film.

The density of ethylene and α-olefin is 0.
．． A film is produced by melt-kneading a copolymer with a molecular weight distribution index of 930 to 0.945 f/all and a molecular weight distribution index Kl/Iw/Mn of 5 or less, and by taking advantage of the above characteristics, it can be used for food packaging, textile packaging, and agricultural products. It is used as a bag, etc.

However, a copolymer made of ethylene and α-olefin with a density of 0.9.30 to 0.945 f/ad and an index of molecular weight distribution Mw/Mn of 5 or less is
When manufacturing films by melt-kneading using the die method, air-cooled, or water-cooled blown film equipment, many continuous white streaks or *i-shaped clouding often occur in the longitudinal direction of the film from the beginning of production. As a result, there is a problem in that it is difficult to stably obtain a film that is strong and has excellent appearance and transparency.

As a means to solve this drawback, there is the use of a screw with a mixing device, the use of a high-precision die with excellent temperature control and thickness unevenness control, or the use of these devices in combination.

However, these solutions suffer from the loss of initial appearance and transparency as the screws, cylinder walls, die channels, etc. become dirty during film production over long periods of time. This device has the disadvantage that the equipment cost is higher than that of a normal film device.

In view of the above circumstances, the inventors of the present invention conducted intensive studies to obtain a film that does not have these drawbacks using ordinary film manufacturing equipment, and as a result, the present inventors applied a specific technology to a copolymer of ethylene and α-olefin. Films made by blending and melt-kneading polyethylene retain the same stiffness as before, and from the start of production, they may develop continuous white streaks in the vertical direction or cloudy clouds. The present inventors have discovered that even if the film is produced for a long period of time, it is possible to maintain the excellent appearance and transparency characteristic of the film at the beginning of production, and the present invention has been developed.

Furthermore, it has been found that the copolymer of ethylene and α-olefin has the added benefit of increasing transparency and increasing the tension of the molten resin, which stabilizes bubbles and improves productivity. That is, the present invention provides [A
]The density of ethylene and α-olefin is 0.930
fx iL 0.945 f/ad.

Formed into a film by melt-kneading a composition whose main components are a copolymer with a molecular weight distribution index IViw/JVtn of 5 or more and CB) high-pressure polyethylene with a density of 0.928 f/ad or more. The present invention relates to a polyethylene film characterized by:

The polyethylene film obtained by the present invention has excellent film appearance and transparency, and has strong film stiffness.
In addition, since it is manufactured at a low cost using ordinary film equipment, it is possible to manufacture high-quality products at low cost in fields such as food packaging, textile packaging, and agricultural products bags, making it valuable for industrial use. is extremely large.

In the present invention, [:A] is a copolymer of ethylene and α-olefin, which has 4 to 6 carbon atoms and 6 weight-m% or less of ethylene.
It is a copolymer with α-olefin of 8, and if the comonomer is 1 to butene, the copolymer is 4 times or less! −Hexene,■
- For octene, etc., it is preferable that the amount is 6M or less.

The molecular weight distribution index EA, w/Mn, is also effective as an index for the occurrence of heat generation and temperature unevenness in the resin. In the case of copolymers of ethylene and α-olefin, those with Mw/Mn of 5 or less are Although the transparency is excellent, the heat generation of the resin and the temperature unevenness of the resin become large, and the normal T-die method,
When manufacturing films by bath melt kneading using air-cooled or water-cooled blown film equipment, many continuous white streaks or scale cloud-like white turbidity often occur in the longitudinal direction of the film from the beginning of production. It has the disadvantage of

When Q w /'FA-n exceeds 5, the above-mentioned drawbacks are reduced to such an extent that there are no practical problems, but the transparency of the film deteriorates after one night, which is not preferable.

[I3] High-pressure polyethylene is polyethylene produced by so-called high-pressure radical polymerization of ethylene.

A composition consisting of (A, l] and (B), a UV absorber such as 2-hydroxybenzophenone, a stabilizer such as an antioxidant such as distearyl pentaerythritol diphosphite, a lubricant such as zinc stearate, and other Additives may also be added.

[B) The melt index of the high-pressure polyethylene is 1 to 10, preferably 1 to 3 of the melt index of [A] the copolymer of ethylene and α-olefin.
It's double.

Furthermore, [B] the density of the high-pressure polyethylene is determined so that the film of the present invention maintains the same stiffness as the [A] single film of the copolymer of ethylene and α-olefin used in the present invention. , 0.928 t/cgll is not preferable.

Moreover, [A] copolymer of ethylene and α-olefin and CB
, l] The blending ratio with high-pressure polyethylene is determined based on the mechanical properties of the film, stiffness, etc. (A) to.

[B] in an amount of 5 to 50 parts, preferably 8 to 25 parts.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Examples 1 to 5 [A] Density 0.937 t/cnl, Me/l/toindex x, 1f/lo=, Molecular weight distribution index Mw/]
VIn is 4.3 no! Copolymer of tyrene and 1-butene 1
00 parts, [B] 5 parts, 8 parts, 10 parts, 20 parts, and 30 parts of high-pressure polyethylene with a density of 0.930110 J and a melt index of 2.111710 m, respectively, were blended, and a normal air-cooled blown film manufacturing equipment was used. The resin temperature was 200℃, the blow ratio was 2, and the film thickness was 5.
A 0μ film was produced.

The physical properties of this film are shown in Table 1.

Comparative Example 1 [A) Density 0.937? /ai, melt index 1.7'/so=, molecular weight distribution index Mw/Q n is 4.3 copolymer of ethylene and l-butene alone,
A film having a thickness of 50 μm was produced using the same equipment and under the same conditions as in the example.

The physical properties of this film (1μ) are shown in Table 1.

Comparative Example 2 CA) Density 0.937 t/cJ, melt index 1.7-710m, index of molecular elf distribution Mw/M
Copolymer of ethylene and 1-butene with n of 4.3 100
20 parts of [B] high-pressure polyethylene having a density of 0.922 floA, a melt index a, and ot/so += were added to the part, and using the same equipment as in the example,
A film with a film thickness of 50 μm was produced under the same conditions.

The physical properties of this film are as in the first layer.

Comparative Example 3 (A) Density 0.934 j'/crA, melt index 1,4y/1o=n, molecular weight distribution index Mw/Mn
A copolymer of ethylene and 1-butene having a particle diameter of 5.6 was used alone to produce a film having a thickness of 50 μm using the same equipment as in the example and under the same conditions.

The physical properties of this film are as in the first layer.

Margin below

Claims (1)

[Claims] 1. [A] A copolymer of ethylene and α-olefin with a density of 0.930 to 0.945 t/cr/l and a molecular weight distribution index of 5 or less; B)
5 to 50 parts of [B] per 100 parts of a polyethylene film λ (A), which is formed by melt-kneading a composition mainly composed of high-pressure polyethylene having a density of 0.9289704 or more. The polyethylene film according to claim 1, which is obtained by blending