JPS6044121B2 - Manufacturing method of high elastic modulus film for packaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is obtained by heat-treating a low-density ethylene, a polymer, or a copolymer film of ethylene and α-olefins mainly composed of ethylene and having an unstretched heat resistance temperature of 107 to 118°C. It relates to high modulus films and aims to provide a method for producing films that are strong and suitable for packaging.

Conventionally, low-density polyethylene film with a heat resistance temperature of 107 to 118°C has been widely used in general packaging without stretching, but compared to high-density polyethylene or polypropylene film, it has a lower Young's modulus or tensile strength. The reality is that there is a shortage.

Of course, this problem can be solved by using high-density polyethylene or polypropylene film, but on the other hand, high-density polyethylene film has poor transparency, and polypropylene film has poor productivity in the film forming process.
Furthermore, it has been pointed out that both of them have poor adhesiveness, so that they can hardly be used for food packaging applications such as cling films. Furthermore, polyethylene films to which additives such as low polymerization degree polyolefins, adhesives, and antifogging agents are added have problems in heat resistance, and the addition of additives itself has problems. The present inventors have developed a low-grade material that has good productivity, low cost, does not contain harmful ingredients, has excellent transparency, and can maintain tackiness, but has a slightly insufficient Young's modulus or tensile strength. As a result of intensive research aimed at establishing a technological method for manufacturing packaging films that use high-density polyethylene (unstretched) and maintain a sufficient Young's modulus, we have developed a heat-resistant film formed by extrusion at a resin temperature of 260°C or higher. The present inventors have discovered that a high modulus film with a significantly improved Young's modulus can be produced by heat-treating a low-density polyethylene film at a temperature of 107 to 118°C under appropriate conditions without stretching, and has completed the present invention.

In addition, the heat-resistant temperature referred to in the present invention refers to all of the heat resistance temperatures when the temperature is increased at a rate of 3°C/min, and the film starts to melt and reaches a width of 1.5cm.
This is the temperature at which a piece of Tn film can no longer withstand a tensile load of 5 g.

Low-density polyethylene, which is the raw material resin for the high-elastic film of the present invention, has a density of 0.925 to 0.939, which is among the higher density polyethylenes (density 0.91 to 0.939). The heat-resistant temperature of the film is 107 to 118.
℃ range is used.

In general, films formed by extruding so-called low-density polyethylene at high temperatures of 260°C or higher have excellent transparency and adhesiveness due to the rapid cooling effect during film formation, making them suitable for applications such as food packaging. It is known.

However, the Young's modulus of these low-density polyethylene films is 1000 to 3000k9/Cl in an unstretched state.
600 for high-density polyethylene film.
It is considerably lower than 0 to 11000 kg/c#f, and its tensile strength is also inferior. Furthermore, it has conventionally been considered difficult to significantly improve these physical properties without substantially reducing transparency by changing film forming conditions other than stretching, such as changing extrusion temperature. However, among the low-density polyethylenes that have characteristics such as high transparency and adhesiveness, after extrusion forming a low-density polyethylene film having the above-mentioned specific heat-resistant temperature range at a resin temperature of 260°C or higher, (heat-resistant temperature -70) It has been found that when heat treatment is carried out within the range of (allowable temperature limit -10) degrees Celsius, Young's modulus is significantly improved, and strength such as tensile strength is also increased accordingly. In contrast, extrusion film formation is performed at a resin temperature of 250°C or less. Even if the film was heat treated, the Young's modulus of the film could not be significantly improved as in Comparative Example 3 in Table 1. Young's modulus can be improved by heat treatment for low-density polyethylene films with a heat resistance temperature of 106°C or lower, that is, a density of 0.924 or lower as mentioned above. It is not noticeable even when the film is formed at a resin temperature of 260°C or higher as in Comparative Example 1 in Table 1, and the optimum range is expressed by the heat resistance temperature of 107 to 118°C for the raw material resin in addition to the film forming temperature. It is clear from the comparative examples and examples that the following exists. The low-density polyethylene film for packaging of the present invention generally refers to one that is transparent and has a thickness of 100μ or less, with a thickness of 10 to 25μ for wrap or stretch film for food packaging, and 25 to 50μ for general packaging. is desirable.

The high elastic modulus film of the present invention can be obtained by heat-treating these films.The specific conditions for the heat treatment are: Depending on the form, it may be left for 1 second to 15 days. In particular, the present invention is advantageous in the case of wrap film rolls or packages of wrap films. The object of the invention is achieved even better than in the case of heat treatment.

For example, in the form of a 20rr roll of wrap film packaged in a cardboard box, 2 to 15
for 3 to 10 days, preferably in an atmosphere of 50 to 60°C.
You can leave it for a few days. In the case of a single-layer film, a heat treatment of 1 to 50 seconds, preferably 2 to ■ seconds in an atmosphere (open) heated to 80 to 95 DEG C. using an infrared heater or the like is sufficient.

Of course, in any case, if the film is heat treated at a high temperature of (heat resistance temperature -40)° C. or higher for a long time, the film will deteriorate and its tensile strength will decrease. The high elastic modulus film of the present invention will be described below based on Examples.

[Examples 1 to 2 and Comparative Examples 1 to 2] The film was formed by normal T-die extrusion at a resin temperature of 260°C, and had a thickness of 12 to 13μ, and a heat resistant temperature of 103°C, 107°C, and 11°C.
Four types of polyethylene films for food packaging at 8°C and 123°C were rolled to 20rr1 and stored in a household wrap film carton.

Next, these force tons are divided into 504 by type of film.
1 (1) A packed cardboard box is placed in an atmosphere of 50°C.
After standing for 0 days, the physical properties of the film were measured. From Table 1, in Examples 1 and 2 regarding films with heat resistance temperatures of 107°C and 118°C, the average temperature was 3500 to 3600 k.
A wrap film that had only a Young's modulus of 9/d now maintains a high Young's modulus of an average of 4,700 to 4,900 kg/C7lf through heat treatment, and the adhesive strength and transparency necessary for a wrap film have hardly decreased. It turns out there isn't. On the other hand, when the heat resistance temperature is 103℃ and 123℃, as shown in Comparative Examples 1 and 2, the Young's modulus hardly improves, and in Comparative Example 2, the density of the resin is high, so the film Adhesion and clarity are low regardless of heat treatment. [Comparative Examples 3 to 4] One roll of 500TI of a 15μ thick film formed by ordinary T-die extrusion at a resin temperature of 220'C using the same low density polyethylene as in Example 1 (Comparative Example 3) ), and a roll-up film (Comparative Example 4) in which a 15μ film, which was normally inflation-formed at a resin temperature of 220°C using the same low-density polyethylene as in Example 2, was rolled into a tube with a width of 60cm at 500rT1. The film was left in an atmosphere at 50'C for 10 days, and the physical properties of the film were measured.

As a result, the elastic modulus of both films was only slightly improved, and since both films were formed at low resin temperatures, the adhesive strength and transparency of the films were low regardless of the heat treatment. [Example 3] A 50cm wide 250rT1 roll of a low density polyethylene film with a thickness of 30μ and a heat resistance temperature of 110°C, which was formed by ordinary T-die extrusion at a resin temperature of 280°C, was rolled as it was at 60°. After being left in an atmosphere of C for 5 days, the physical properties of the film were measured.

The results are shown in Table 1, where the film, which initially exhibited only a low elastic modulus, came to maintain a high elastic modulus of 4500k9/C7i or higher with almost no decrease in transparency after heat treatment. [Example 4] Using the same low-density polyethylene as in Example 3, a 50μ thick, 60cm wide packaging film was formed by T-die extrusion at the same resin temperature, and heated to 85°C from one end using an infrared heater. During the open state, the core was continuously fed for 5 seconds to rewind onto another core.

As can be seen from the table, the obtained film had a weight of 5212 kg/Cl. with almost no decrease in transparency after being heat-treated for a short time. It can be seen that this large ring rate was maintained. In addition, in Table 1, the Young's modulus in the film physical properties section is 15 × 10
h rectangular sample with spans 5h and 50m: m/
Transparency (%) = 100
- (Haze % according to JIS K67l4).

Claims (1)

[Claims] 1. Heat resistant temperature (
When the temperature is raised at a rate of 3°C/min, the temperature at which the film starts to melt and a piece of film with a width of 1.5 cm cannot withstand a tensile load of 5 g) is 107 to 113°C. The temperature range is (heat resistant temperature -70)
1. A method for producing a high elastic modulus film for packaging, characterized by heat treatment at a temperature of ℃ to (heat-resistant temperature -10) ℃.