JPH0655864B2 - Polyethylene resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a polyethylene resin composition.

More specifically, the present invention relates to a polyethylene resin composition using low density polyethylene, which is excellent in environmental stress crack resistance, squeezing property and transparency.

[Prior art]

The branched low-density polyethylene has excellent properties in transparency and squeezing property (indicating a measure of container flexibility and elasticity). Therefore, branched low-density polyethylene is used for applications requiring transparency and squeeze, for example, blow-molded products such as frozen dessert containers, tofu containers (egg tofu), and spoid containers, and extrusion-molded products such as straws, bellows, and ducts. It is used. However, branched low-density polyethylene has a low resistance to environmental stress cracking, and in the case of the above-mentioned molded product, an unfavorable situation often occurs in which small cracks are generated due to residual stress in polyethylene added at the time of molding.

Conventionally, various methods have been proposed in order to improve the environmental stress crack resistance of polyethylene, but each method has advantages and disadvantages, and it has not been sufficient for industrial use. For example, (1) a method of adding a rubber-like substance (Journal of Japan Rubber Association, 3
Vol. 5, pp. 111-124 (1962)) (2) Method of adding paraffin wax having specific physical properties (Japanese Patent Publication No. 42-17092) (3) Method of adding polyethylene grease wax having specific physical properties ( JP-A-53-45349) and the like are known.

[Problems to be solved by the invention]

Although the method (1) is expected to improve the environmental stress crack resistance of polyethylene, it causes a decrease in strength, and further has problems in heat resistance and light resistance. Further, the above method (2) is not suitable for industrial use from the viewpoint of cost because the strength of polyethylene is lowered and a large amount of polyethylene is required.
Furthermore, although the method (3) is expected to improve the environmental stress crack resistance of polyethylene, it causes a decrease in strength and is not suitable for industrial use.

[Means for solving problems]

In view of such prior art, the present inventors have improved the environmental stress crack resistance while maintaining the excellent transparency and squeezability of the branched low-density polyethylene, and blow such that it can be industrially sufficiently utilized. As a result of intensive studies to provide a polyethylene resin composition that can be suitably used for various purposes such as molding and extrusion molding, a branched low-density polyethylene having specific physical properties and a linear low-density having specific physical properties are obtained. The inventors have found that the object can be achieved by blending polyethylene in a specific ratio, and have completed the present invention.

That is, the gist of the present invention is that the melt index is 0.2.
~ 2g / 10min branched low density polyethylene 90-70
A polyethylene resin composition for blow molding comprising 10 parts by weight of washed low-density polyethylene having a weight ratio of 0.2 to 4 g / 10 min and a flow ratio of 20 to 70 and a melt ratio of 0.2 to 4 g / 10 min.

To explain the present invention in detail, the branched low-density polyethylene used in the present invention is a high-pressure process polyethylene, that is,
Using a radical generator such as organic peroxide or oxygen, the pressure is 1000 to 3000 kg / cm ² , and the temperature is 150 to 400 ° C.
It is obtained by homopolymerization of ethylene or by copolymerizing ethylene with another copolymerization component under the condition of. Examples of the copolymerization component include α-olefins such as propylene and butene-1, vinyl compounds such as vinyl acetate, methyl acrylate and methyl methacrylate, and the like, and the copolymerization amount of the copolymerization component is 0.5 to 18% by weight, preferably 2-1
It is about 0% by weight.

The branched low density polyethylene has a melt index of 0.2 to 2 g / 10 min, preferably 0.4 g to 2 g / 1.
In the range of 0 minutes, and the density is 0.915 to 0.930
Those in the range of g / cm ³ are used. If the melt index is less than the above range, parison breakage may occur during blow molding, and the surface of the extrudate may be roughened during extrusion molding. Further, if it exceeds the above range, the melt tension of the polyethylene becomes too small, drawdown phenomenon and sag phenomenon of parison occur at the time of blow molding, environmental stress crack resistance and strength of the molded article is reduced. There's a problem.

In the method of the present invention, the melt index is JIS K
The value is a value measured at 190 ° C. according to 6760, and the density is a value measured according to JIS K 6760.

The linear low-density polyethylene compounded in the branched low-density polyethylene in order to improve the environmental stress crack resistance of the branched low-density polyethylene is a copolymer of ethylene and another α-olefin, and Different from low density polyethylene resin produced by high pressure method. The linear low-density polyethylene is, for example, ethylene and other α-olefins such as butene, hexene, octene, decene, and 4-methylpentene-1 in an amount of about 4 to 17% by weight, preferably 5 to 1%.
It is a copolymer of about 5% by weight and is produced using a Ziegler-type catalyst or Phillips-type catalyst used in the production of medium- and low-pressure method high-density polyethylene. It is a short branched structure of conventional high-density polyethylene with a copolymerization component. The density is appropriately reduced by utilizing this short chain branching to about 0.91 to 0.95 g / cm ³ ,
It is a polyethylene with a structure that is more linear than conventional low-density polyethylene and has more branches than high-density polyethylene.

As the linear low density polyethylene used in the present invention,
The melt index is in the range of 0.2 to 4 g / 10 minutes, preferably 0.4 to 2 g / 10 minutes, and the flow ratio is in the range of 20 to 70, preferably 30 to 65, and its density is Is preferably used in the range of 0.915 to 0.935 g / cm ³ . If the melt index is less than the above range, parison breakage may occur during blow molding, and the surface of the extrudate may be roughened during extrusion molding. On the other hand, when the content exceeds the above range, the melt tension of the polyethylene becomes too small, a drawdown phenomenon and a parison sag phenomenon occur during blow molding, and environmental stress crack resistance and strength of the molded product decrease. There is a problem.

Further, if the flow ratio is less than the above range, a problem of rough skin occurs during extrusion molding and blow molding, and if it exceeds the above range, the effect of improving the environmental stress crack resistance becomes small, which is not preferable.

In the present invention, the flow ratio means a shearing force of 10 ⁶ dyne / cm ² (load 111
31 g) and the extrusion rate (g / 10 min) of 10 ⁵ dynes / cm ² (load 1113 g), It is calculated by.

The blending ratio of the branched low-density polyethylene and the linear low-density polyethylene is such that the branched low-density polyethylene is 90 to 70.
It is used within the range of 10 to 30 parts by weight of linear low-density polyethylene. If the linear low density polyethylene is less than the above range, the effect of improving environmental stress crack resistance is small, and if it is more than the above range, the transparency is lowered, which is not preferable.

The polyethylene resin composition of the present invention is dry blended with the above-mentioned branched low density polyethylene and linear low density polyethylene with a blender or after dry blending,
It can be obtained by melt-mixing at a temperature of 120 to 280 ° C. and pelletizing by a usual melt-kneading method, for example, a Banbury mixer, a continuous mixer, a mixing roll, an extruder or the like.

The polyethylene resin composition thus obtained may optionally contain various known additives commonly used for polyethylene, such as antioxidants, ultraviolet absorbers, antistatic agents, and lubricants.

[Action]

Although the reason why the environmental stress crack resistance of the polyethylene resin composition obtained by blending a branched low-density polyethylene and a linear low-density polyethylene having specific physical properties in the present invention in specific amounts is not clear, Perhaps by mixing a specific amount of linear low-density polyethylene with excellent resistance to environmental stress cracking with branched low-density polyethylene, the linear low-density polyethylene can be retained while maintaining the squeezability and transparency of the branched low-density polyethylene. It is estimated that environmental stress crack resistance is significantly improved by imparting environmental stress crack resistance to high density polyethylene.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Incidentally, the melt index in the examples, density, flow ratio,
Stability (rigidity), environmental stress crack resistance (hereinafter, E
Abbreviated as SCR. ) Physical properties of squeeze property and transparency were measured as follows.

Measurement of melt index Based on JIS K 6760, it was measured at 190 ° C. and expressed in units of g / 10 minutes.

Density measurement Measured according to JIS K 6760, g / cm
Displayed in units of ³ .

Measurement of flow ratio Using the above melt index measuring device, shear force 1
0 was calculated as the ratio of ⁶ dyne / cm ² (load 11131G) 10 ⁵ extrusion rate of dynes / cm ² (load 1113 g) (g / 10 min).

Measurement of Stiffness (rigidity) was measured according to ASTM D 747,
It is expressed in units of kg / cm ² .

ESCR measurement According to ASTM D 1693-66, 10 samples were immersed in a 50% by weight aqueous solution of alkylaryl polyethylene glycol at 50 ° C., and the time until cracking occurred in 5 of them was visually observed F Displayed in units of ₅₀ hrs.

Squeeze property A container with the same wall thickness is molded under constant conditions. The body of this container is deformed to a yield point or higher with a constant strain amount, and the number of seconds from when the container is opened to when it returns to the original container is measured. In this study, a container with an outer diameter of 80φ was sandwiched between parallel plates and the distance between the plates was 4
It was compressed to 5 mm and then opened, and the number of seconds until returning to the original container was measured. (The wall thickness of the container was set to about 400 μ.) Transparency According to ASTM-D 1003, the haze is measured.

The body of the sample is cut out from the container.

There is a correlation between haze and transparency, with haze increasing and transparency decreasing.

For the judgment, a haze of less than 15 was classified as excellent transparency ◎ 15 to 23 was rated as good ○ 23 and was rated as ordinary △.

Example 1 Branched low-density polyethylene (high-pressure polyethylene, melt index (hereinafter abbreviated as MI)): 1.3 g
/ 10 min, density: 0.918 g / cm ³ ) 70 parts by weight of linear low-density polyethylene (MI: 0.45 g / 10 min, density: 0.919 g / cm ³ , flow ratio: 22, copolymerization component:
30 parts by weight of butene-1, copolymerization amount: 4% by weight) were dry blended, and then melt-kneaded at a temperature of 190 ° C. in a single screw extruder having a cylinder diameter of 40 mmφ to be extruded into pellets.
Physical properties of the obtained polyethylene resin composition were measured by the above test methods. The results are shown in Table 1.

Example 2 The procedure of Example 1 was repeated, except that the physical properties and blending amounts of the branched low-density polyethylene and the linear low-density polyethylene were changed as shown in Table 1. The results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that the physical properties and blending amounts of the branched low-density polyethylene and the linear low-density polyethylene were changed as shown in Table 1. The results are shown in Table 1.

Comparative Examples 2 and 3 Using the branched low-density polyethylene or linear low-density polyethylene used in Example 1, respectively, a physical property test was conducted by the above-mentioned test method. The results are shown in Table 1.

Comparative Examples 4 and 5 Using the branched low-density polyethylene or linear low-density polyethylene used in Comparative Example 1, the physical properties were measured by the above-described test methods. The results are shown in Table 1.

Comparative Example 6 Using the branched low-density polyethylene used in Example 2,
Physical properties were measured by the above test methods. First result
Shown in the table.

[Effects of the Invention] According to the present invention, a branched low-density polyethylene having specific physical properties and a linear low-density polyethylene are blended in a specific amount to maintain the squeeze property and transparency of the branched low-density polyethylene. As it is, a polyethylene resin composition having significantly improved environmental stress crack resistance can be obtained. Therefore, the polyethylene resin composition of the present invention is used for blow molding of frozen dessert containers, tofu containers, spoid containers and the like, which are required to have environmental stress crack resistance, squeeze property and transparency, and extrusion molding of straws, bellows and ducts. It can be preferably used for applications.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 59-215342 (JP, A) JP 59-178221 (JP, A) JP 60-147455 (JP, A) JP 60- 147454 (JP, A) JP-A-61-249 (JP, A)

Claims (1)

[Claims] 1. A melt index of 0.2 to 2 g / 10.
For blow molding consisting of 90 to 70 parts by weight of branched low-density polyethylene and 10 to 30 parts by weight of linear low-density polyethylene having a melt index of 0.2 to 4 g / 10 minutes and a flow ratio of 20 to 70. Polyethylene resin composition.