JPS599347B2 - Method for manufacturing thermoplastic resin multilayer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving multilayer films obtained by polymerically adhering thermoplastic resins in a die by coextrusion.

In recent years, multilayer films have been produced by coextrusion from thermoplastic resins such as polyolefins, polyamides, and ionomer resins, and are used in food packaging bags, etc.
In such a multilayer film, if at least one film layer is made of low-density polyethylene and the layer in contact with it is made of a thermoplastic resin with a higher melting point than that, a large number of fish eyes will occur in this low-density polyethylene layer. Not only does it impair its appearance as a packaging material, but it also reduces its mechanical strength, and during secondary processing such as stretching, tears are likely to occur from the fibers, which inevitably lowers the product value.

Although the cause of such fish eyes has not yet been elucidated, the inventors of the present invention have repeatedly conducted various studies to prevent the occurrence of fish eyes, and have discovered that a specific compound is added to low-density polyethylene in advance when forming a multilayer film. The present invention was created based on the discovery that the occurrence of fish eyes can be significantly reduced by the above-mentioned methods.
In producing a multilayer film by coextrusion, in which the layer in contact with the thermoplastic resin is made of a thermoplastic resin having a higher melting point, low-density polyethylene to be subjected to coextrusion is mixed with a fatty acid having 10 to 25 carbon atoms per molecule and the fatty acid. metal salt (provided that the metal in the salt is from Group 1 or Group 1 of the periodic table and has a period of 2 to 5).

) is added in an amount of 0.02 to 2 parts by weight per 100 parts by weight of low density polyethylene. Fatty acids with 10 to 25 carbon atoms include puric acid, udecylic acid, lauric acid, tridecylic acid, myristic acid, bentadetylic acid, palmitic acid, margaric acid, stearic acid, nondecylic acid, a** lahinic acid, Examples of the metals included in these fatty acid salts include sodium lithium, magnesium, potassium, calcium, strontium, and cadmium.

Additives consisting of one or more compounds selected from the above group are not very effective if the amount is less than 0.02 parts by weight per 100 parts by weight of low-density polyethylene, and if it exceeds 2 parts by weight, smoke may be generated at the exit of the die. and the working environment is harmed. In order to demonstrate the effects of the present invention, the numbers of fisheyes are expressed and compared for some of the Examples and Comparative Examples described later, as follows.

Examples 1 to 3 Using composite annular dies for forming three-layer films of the following sizes, A
．． Diameter 150mm b. Die gap (gap between each molten resin passage in the die) 0
．． 7mmc. The orifice slit (gap at the exit of the multilayer film) has a layer of low-density polyethylene (LDPE) containing stearic acid (St) as an additive in the ratio shown in the first table on both sides of 1.25 mm, and a high-density polyethylene (LDPE) layer in the middle. polyethylene(
A three-layer film with a layer of HDPE) was prepared at a die temperature of 17
When the sample was taken at 0°C, pull-up ratio of 1.5, and take-up speed of 10 m/min, the number of fisheyes (those with a diameter of 0.5 mm or more, the same shall apply hereinafter) was as shown in Table 1.

Comparing these occurrences with the number of occurrences of fisheyes in Comparative Examples 1 to 3 described later, it can be seen that the reduction in fisheyes obtained by the present invention is remarkable. Comparative example 1,
2, 3 The same procedure as in Example 1 was carried out except that the amount of additive added was changed, and the results shown in Table 1 were obtained.

In Comparative Example 3, the number of fisheyes was only 4, but a favorable operating environment could not be obtained as smoke was emitted when the product was removed from the die.

This indicates that increasing the amount added to 2.5 parts by weight is undesirable. Examples 4 to 6 In Example 1, the additive was calcium stearate (Ca
The same procedure was carried out except that St) was added as shown in the first table, and the results shown in the first table were obtained.

Comparing this result with Comparative Examples 4 and 5 described later, the effects obtained by the present invention are remarkable. Comparative Examples 4 and 5 The same procedure as in Example 4 was carried out except that the amount of additive added was changed, and the results shown in Table 1 were obtained.

As in Comparative Example 3, when the amount added was increased to 2.5 parts by weight, smoke was generated and the operating environment was damaged. Example 7
~9 In Example 1, the same weights of stearic acid (St) and calcium stearate (CaSt) were used as additives, and the same procedure was performed except that the additives were added as shown in Table 1. We obtained the following results.

Comparing this result with Comparative Examples 6 and 7 described later, the effects obtained by the present invention are remarkable. Comparative Examples 6 and 7 The same procedure as in Example 7 was carried out except that the amount of additive added was changed, and the results shown in Table 1 were obtained.

As in Comparative Example 3, when the amount added was changed to 2.5 parts by weight, smoke was generated and the operating environment was affected. Example
10 (not shown) Example 1 was repeated except that the additive was changed to lithium stearate, and the number of fish eyes generated was 4/m''.

Example 11 (not shown) The same procedure as in Example 1 was performed except that the additive was changed to cadmium stearate, and the number of fish eyes generated was only 4/day.

Example 12 (not shown) In Example 1, St and CaS were added to LDPE as additives.
Similar results were obtained by carrying out the same procedure except that the same weight of t was mixed, Surlyn A (trade name of ionomer resin manufactured by DuPont) was used for the intermediate layer, and the temperature of the die was 200°C.

Example 13 (not shown) When the same procedure as in Example 12 was carried out except that the intermediate layer was changed to polypropylene (PP) and the die temperature was set to 240°C, the number of fish eyes generated was only 2/day. It was hot.

Example 14 In Example 8, the multilayer film was made of two layers of LDPE/HDPE, and the thickness of each layer was changed to 10μ/60μ.
Comparative example where the same results were obtained by following the instructions in the table.
8 The same procedure as in Example 16 was carried out except that no additives were added, and the results shown in Table 2 were obtained.

Claims (1)

[Claims] 1. In producing a multilayer film by coextrusion, at least one layer of which is made of low density polyethylene, and a layer in contact with this layer is made of a thermoplastic resin having a melting point higher than that of the low density polyethylene, the coextrusion A fatty acid having 10 to 25 carbon atoms in one molecule and a metal salt of the fatty acid (however, the metal in the salt is a group I or II of the periodic table with a period of 2 to 5). A method for producing a thermoplastic resin multilayer film, characterized in that one or more compounds selected from the group consisting of .