JPS59114029A - Longitudinally uniaxially stretched sheet or film with excellent mechanical strength - Google Patents

Abstract

PURPOSE:To enhance the tear strengths in the machine direction (MD) and in the transverse direction (TD) of sheet or film without impairing mechanical performances and the like by a method wherein the sheet or film is longitudinally uniaxially stretched under specified conditions so as to have the Elmendorf tear strengths in MD and in TD of 60kg/cm and above after stretched. CONSTITUTION:Ethylene-alpha-olefin copolymer, which substantially has no long branched chain and the density of which is 0.91-0.94, is made in a form of sheet or film and then formed in an uniaxially stretched sheet or film by stretching 2 or more times longitudinally uniaxially without exceeding 5% in neck-in rate. The Elmendorf tear strengths of the resultant molded product must be 60kg/cm and above in MD and TD. Said ethylene-alpha-olefin copolymer having substantially no long branched chain can be obtained by copolymizing ethylene and alpha-olefin under moderate pressure with transition-metal catalyst. Furthermore, longitudinal uniaxial stretching can be preformed by applying roll stretching, rolling or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a longitudinally-axially stretched sheet or film (hereinafter referred to as film). More specifically, the present invention relates to a longitudinally-axially stretched film having excellent tear strength in the longitudinal and transverse directions.

Conventionally, low-density polyethylene (hereinafter referred to as high-pressure low-density polyethylene) manufactured using a high-pressure method has excellent hygiene and moisture resistance, and is also excellent in gloss and transparency, so it is often used in packaging. Widely used as materials. Furthermore, in order to improve the mechanical, optical, thermal properties, etc. of high-pressure low-density polyethylene films, stretching is carried out along the longitudinal axis, thereby increasing added value.

- High-density polyethylene produced by a low-pressure method (hereinafter referred to as low-pressure high-density polyethylene) also has excellent hygiene and moisture resistance, and is widely used mainly as packaging materials. Furthermore, low-pressure high-density polyethylene films are also stretched in the longitudinal direction for the purpose of improving mechanical and optical properties, thereby increasing added value.

However, the -axis stretched film is not satisfactory because there is a difference in mechanical properties between the stretching direction and the rolling body direction. Specific properties imparted by vertically stretching a polyethylene film include improved tensile strength in the longitudinal direction, improved shrinkage properties in the longitudinal direction, improved optical properties, and improved impact strength. . However, polyethylene-axially stretched films have the disadvantage of being extremely easy to tear in one direction, and this appears as defects such as torn bags, corner tears, cracks, etc. when used in various ways such as packaging films, and improvements are desired.

The present invention focuses on the optical properties of polyethylene-axially stretched film.
The present invention was achieved as a result of extensive research aimed at obtaining a uniaxially stretched film that is resistant to tearing in both the machine direction (MD) and the transverse direction (TD) without impairing its mechanical and thermal properties.

That is, the present invention has a density of 0, which has substantially no long chain branching.
．． A stretched sheet or film obtained by forming an ethylene-α olefin copolymer of 91 to 0.94 into a sheet or film, and then stretching it in the longitudinal-axial direction at a neck-in rate of 25% or more and at least twice as much, and 1. Long chain branches used in the present invention relating to a longitudinally-axially stretched sheet or film with excellent tear strength, characterized in that the stretched product has an Elmendorf tear strength of 60 Kg/m or more in both the longitudinal and transverse directions. Ethylene-α substantially free of
Olefin copolymer is a resin obtained by copolymerizing ethylene and α-olefin under medium-low pressure using a transition metal catalyst, and has a density similar to that of high-pressure polyethylene, or a resin similar to that obtained by high-pressure polyethylene. O is a resin having a density comparable to that of high-pressure polyethylene obtained by copolymerizing ethylene and α-olefin using a transition metal catalyst under high pressure and high temperature.Also, the longitudinal-axial stretching method used in the present invention For this purpose, either an inter-roll stretching method in which stretching is performed while applying a tensile force between rolls, or a rolling method in which stretching is performed by applying a reduction blade between rolls may be used, but depending on the application, the rolling method may be used depending on the thermal properties. It shows good results in terms of optical properties and optical properties.

In addition, when carrying out longitudinal-axial stretching, it is necessary to keep the neck-in rate calculated by the following formula below 25%; if it exceeds 25%, the thickness unevenness in the lateral direction of the stretched film will become extremely bad, and the This is not suitable because of the problem that the tear strength is significantly reduced.

Furthermore, when carrying out longitudinal-axis stretching, the stretching ratio must be at least 2 times, and if it is less than 2 times, the effect of improving various properties imparted by longitudinal-axis stretching is small and is not suitable.

The present invention will be explained below with reference to Examples.

Example 1.2 An ethylene-α olefin copolymer having a density of 0.921 and an MI of 0.65 was melt-extruded through a circular die, and a film with a thickness of 100 μm was produced by an inflation method.

Next, this extrudate was rolled 2.6 times in the longitudinal direction, 4.
It was stretched 7 times (neck-in rate: 18%). The roll temperature during rolling was 50°C, and water was used as the lubricant. Table 1 shows the results of measuring the tear strength of the longitudinally stretched film.

(5) Example 8 An ethylene-α olefin copolymer having a density of 0.924, MI=1, and 09 was melt-extruded through a circular die to produce a film with a thickness of 40 μm by an inflation method.

Next, this extrudate was subjected to longitudinal treatment using the same method and conditions as in Example 1.2.
The shaft was stretched 4.8 times (neck-in rate: 216%)
. Table 1 shows the tear strength of the stretched film.

Example 4.5 An ethylene-α olefin copolymer having a density of 0.928 and an MI of 0.45 was melt-extruded from a circular die to produce a film with a thickness of 90 μm by an inflation method.

Next, this extrudate was subjected to longitudinal treatment using the same method and conditions as in Example 1.2.
The shaft was stretched 8.0 times and 5.0 times (neck-in rate = 12%). Table 1 shows the tear strength of the stretched film.

Example 6 Density 0.985, M I = 1.8 ethi L/ :/
-(x(6) The olefin copolymer was melt-extruded through a circular die to produce a film with a thickness of 90 μm.

Next, this extrudate was stretched 5.3 times along the longitudinal axis by a rolling method (neck-in rate: 14%).

The roll temperature during rolling was 75°C, and water was used as the lubricant. Table 1 shows the tear strength of the stretched film.

Example 7 The 100 μm thick extruded film produced in Example 1.2 was stretched 2.2 times by a rolling method. The roll temperature during rolling was 60°C, and non-lubricated rolling was performed without using lubricating fluid (neck-in rate 18%). The tear strength of the stretched film is shown in Table 1.

Comparative Example 1, 2.8.4 High-pressure low-density polyethylene with a density of 0.924 and M I = Q, 3 was melt-extruded from an annular die to a thickness of 90 μm.
A film was produced. Next, this extrudate was stretched longitudinally by 2 times, 8 times, 4 times, and 5 times by a rolling method (neck-in rate (7): 12%). The roll temperature during rolling was 50"C! and water was used as the lubricant. Table 1 shows the tear strength of the stretched film.

Comparative Example 5.6.7 Low-pressure high-density polyethylene with a density of 0.965 and M I = 6.0 was melt-extruded from a T-die to produce a sheet with a thickness of 280 μm. Next, this extrudate was stretched longitudinally by 8 times, 4 times, and 5 times by a rolling method (neck-in ratio: 4
%). The roll temperature during rolling was 85°C, and water was used as the lubricant. Table 1 shows the tear strength of the stretched film.

Table 1 Note) 1. The tear strength was measured using JI8P-8116.

2. MD: Stretching direction (longitudinal direction) TD: Counter-stretching direction (horizontal direction) (9) As is clear from the examples and comparative examples shown in Table 1, a film or sheet-like product made of high-pressure low-density polyethylene A film or sheet that has been subjected to longitudinal-axial stretching has extremely low tear strength in the transverse direction, and the higher the stretching ratio to enhance the properties imparted by stretching, the lower the tear strength in the transverse direction. . Furthermore, a film or sheet made of low-pressure high-density polyethylene that is subjected to longitudinal-axis stretching has extremely low tear strength in the longitudinal direction. -10,000, the longitudinally-axially stretched film or sheet made of the ethylene-α olefin copolymer referred to in the present invention has a capacity of 60 b/ca in both the longitudinal and transverse directions.
It has an excellent tear strength of r or more, and the effects of the present invention are obvious.

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Claims (1)

[Claims] After forming an ethylene-α olefin copolymer having a density of 0.91 to 0.94 with substantially no long chain branching into a sheet or film, stretching it in the longitudinal-axial direction at a neck-in rate of 25π or less by a factor of 2 or more. Stretched sheet or film, and the Elmendorf tear strength of the stretched product is M,
A longitudinally-axially stretched sheet or film with excellent tear strength, characterized by having a tear strength of 60 Kg/crR or more in both the D direction and the TD direction.