JPS5943056B2 - Polyethylene composition for shrink wrapping - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyethylene composition, and more particularly to a polyethylene composition suitable for producing a shrink wrapping film made by blending high-density polyethylene and low-density polyethylene.

In recent years, demand for heat-shrinkable films has increased significantly in various fields including food packaging.

Various thermoplastic resin films such as polyvinyl chloride, polypropylene, low density polyethylene, and polyvinyl acetate are used as films suitable for such shrink wrapping. In particular, low-density polyethylene film is widely used as a packaging material in place of containers, cardboard, etc. in distribution channels for various products such as foods. Low-density polyethylene film, which has been used for shrink wrapping so far, has poor mechanical strength and is difficult to make thin.When heat-shrinked, the film adheres to the seal bar, resulting in poor finish. However, in order to satisfy a certain level of strength, the thickness of the film is approximately 60 μm.

Furthermore, in order to improve biaxial shrinkability, a biaxial stretching process is added, and further crosslinking and electron beam irradiation are performed.
However, such considerations lead to lower productivity and higher costs, making it less economical. On the other hand, although high-density polyethylene has excellent heat resistance and mechanical strength,
It has poor shrinkability and cannot be used as a shrink film. Here, high density polyethylene has a density of 0.940~
Low density polyethylene refers to one with a density of 0.915 to 0.930. Furthermore, regarding the specifications of the shrink tunnel, low-density polyethylene film has a higher electrical capacity than films made of polypropylene, polyvinyl chloride, etc., and starts shrinking during the cooling process after exiting the tunnel. The work is complicated, as a cooling fan must be installed at the exit of the tunnel in consideration of the shrinkage characteristics of the film. The object of the present invention is to overcome the above-mentioned disadvantages and to provide polyethylene compositions suitable for this purpose.

The present invention uses 60-80% by weight of high-density polyethylene with a melt index of 0.01-0.09 and 40-20% by weight of low-density polyethylene with a melt index of 0.4-0.7.
By blending and using both high-density polyethylene and low-density polyethylene, the excellent properties of both are utilized and the drawbacks are eliminated.

The high-density polyethylene and low-density polyethylene used in the present invention must each satisfy the above-mentioned blending ratio and properties.

High density polyethylene less than 60% by weight, low density polyethylene 40% by weight? If the ratio exceeds 1, the binding force will be lowered due to lack of mechanical strength, and the finish of the heat seal will be poor, which is undesirable.

Here, binding force refers to the effect of preventing the packaged items from collapsing.
This is a particularly required factor for this type of film. On the other hand, high density polyethylene weighs 80? If the amount of low density polyethylene exceeds 20% by weight, defects such as uneven shrinkage will occur. Regarding the melt index of high-density polyethylene, if it is less than 0.01, the film will not have flexibility, and if it exceeds 0.09, it will not be able to be biaxially oriented.

Regarding the melt index of low-density polyethylene, if it is less than 0.4, the transparency of the film will decrease, and if it exceeds 0.7, the compatibility will decrease, so it is not preferable. Synthetic rubber can be added in an amount up to 5 parts by weight per 100 parts by weight of the composition.

Addition of synthetic rubber improves strength and anti-slip properties. The synthetic rubber is not particularly limited, but styrene-butadiene rubber, styrene-isoprene rubber, ethylene-propylene rubber, etc. are preferred. Additionally, additives such as antioxidants, lubricants, and antistatic agents may be added as appropriate depending on the purpose. The polyethylene composition of the present invention can be kneaded using a suitable mixing means such as a Banbury mixer, an extruder roll, etc., and then inflation molded to produce a desired film.

When performing inflation molding, excellent products can be obtained by setting the expansion ratio (expansion bubble diameter/die lip diameter) to 9 or more, preferably 9 to 11. When a shrink wrapping film is produced from the polyethylene composition of the present invention, the film can be made thinner than conventional low-density polyethylene films and has high strength.

Furthermore, when heat-sealing a low-density polyethylene film, film residue adhered to the sealing bar and the finish was poor, but the film obtained from the composition of the present invention does not have such defects and has improved heat-sealability. Significant.
The shrinkability of the film also shows well-balanced shrinkage in the vertical and horizontal directions, and the finished product produced by the shrink tunnel is extremely good. In particular, it has a strong binding force compared to conventional low-density polyethylene films. moreover,
Mechanical strength at low temperatures is also significantly improved. Next, examples of the present invention will be shown.〇Examples 1 to 3 High density polyethylene (density 0.955,
melt index 0.05) and low density polyethylene (
(density: 0.921, melt index: 0.6) were dry blended in a tumbler.

This mixture was applied to a die having an annular slit (die lip diameter: 30 mm, lip clearance: 1 mm, die temperature: 180 mm).
0C) into a tubular shape at an expansion ratio of 9.0 to obtain a tubular film with a folded diameter of 425 mm and a thickness of 30 μm. The results of the evaluation of the mechanical strength, anti-slip properties and heat sealability of the film are shown in Table 1, and the results of practical evaluation using a shrink tunnel are shown in Table 2.

Example 4 High-density polyethylene (density 0.955, melt index 0.05) 70 weight? 5 parts by weight of SBR (density 0.95, melt index 9.0) as a synthetic rubber was added to 100 parts by weight of a mixture of 30% by weight of low density polyethylene (density 0.921, melt index 0.6). The mixture obtained by blending was inflation-molded in the same manner as in Example 1 to obtain a tubular film.

Table 1 shows the evaluation results of the mechanical strength, anti-slip properties, and heat sealability of this film, and Table 2 shows the results of practical evaluation using a shrink tunnel. Comparative Example 1 In Example 1, only high-density polyethylene was used, and the die temperature was 200°C.
A tubular film was obtained by inflation molding in the same manner as in Example 1 except that .

Table 1 shows the evaluation results of the mechanical strength, anti-slip properties, and heat sealability of this film, and Table 2 shows the results of practical evaluation using a shrink tunnel.

Comparative Example 2 The low-density polyethylene used in Example 1 was extruded into a tubular shape through a die having a tubular slit (die lip diameter 50 mm, lip clearance 17 x ml, die temperature 180°C), and inflation molding was performed at an expansion ratio of 4.5. A tubular film having a folded diameter of 350 mm and a thickness of 40 μm was obtained.

Table 1 shows the evaluation results of the mechanical strength, anti-slip properties, and heat sealability of this film, and Table 2 shows the results of practical evaluation using a shrink tunnel.

Comparative Examples 3 and 4 In Example 1, the blending amounts of high-density polyethylene and low-density polyethylene were adjusted to the predetermined weight. A tubular film was obtained by inflation molding in the same manner as in Example 1 except that the following was changed.

Table 1 shows the evaluation results of the mechanical strength, anti-slip properties, and heat sealability of this film, and Table 2 shows the results of practical evaluation using a shrink tunnel.

Comparative Example 5 A tubular film was obtained by inflation molding in the same manner as in Example 1 except that the expansion ratio was changed to 6.

The measurement results for the shrinkage rate of this film are shown in Table 1. Comparative Example 6 A tubular film was obtained by inflation molding in the same manner as in Example 1 except that the expansion ratio was changed to 3. .

Table 1 shows the measurement results for the shrinkage rate of this film.

As can be seen from Table 1, the film made of the composition of the present invention is particularly excellent in film impaction and also has excellent heat sealability.

Further, in practical tests, it has a large binding force and has an excellent appearance when packaged, and has high industrial applicability.
*Practical evaluation using a shrink tunnel The integrated packaging of lactic acid bacteria beverage containers (overlap method, 50 containers) was evaluated using a shrink tunnel.

Tunnel conditions are tunnel temperature At 175℃ and tunnel time of 11 seconds. and visually evaluate each item. did.

◎ is extremely good, 〇 is good, △ is poor, × is extremely poor.

Claims (1)

[Claims] 1 60-80% by weight of high-density polyethylene with a melt index of 0.01-0.09 and a melt index of 0.09.
A polyethylene composition for shrink wrapping comprising 40 to 20% by weight of low density polyethylene having a molecular weight of 4 to 0.7.