JPS6398418A - Foamed and contracted film - Google Patents

Abstract

PURPOSE:To constitute the title film in the manner that printability of a smooth surface turns favorable and a rough surface side can hold heat insulating properties and shock- absorbing properties sufficiently, by specifying the roughness of both sides of a foaming and shrinking film composed of polyolefin series resin and a relation between the roughness of the front surface and that of the rear surface. CONSTITUTION:Only one side of a film is precooled by a device wherein at the time of molding, either a small diameter cooling roll is brought into contact with only the one side of the film in a molten state discharged directly after an extrusion die or a small quantity of cooling water is sprayed only on one surface. Growth of a foamed cell and dissolution of a chemical foaming agent on the one side of the film is controlled with precooling and turned into the state where foaming is controlled. The film where foaming magnification and surface roughness are different from one another at the front surface are rear surface is obtained. As the degree of the precooling of the one side of the film is controlled, it is so constituted that the front surface roughness is A, rear surface roughness B is 10-20mum and they satisfy the expression of (A-B)/A>=0.1. On the foamed and contracted film, the roughness on both sides are different from each other, the one side surface is comparatively smooth and suitable in printability and the roughness, shock-absorbing properties and heat insulation properties of the other side surface turn comparatively coarse, and excellent in heat-insulating property respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foamed shrink film used for shrink labels for glass soft drink containers and the like.

(Prior art and its problems) Shrink labels are made of polyethylene with an expansion ratio of 2 to
It is made of a heat-shrinkable resin film that is about 3 times the size, and one side is printed to display the product name, seller, etc., and is rolled into a cylinder and inserted into a glass container. By heating and shrinking it, it is brought into close contact with a glass container for use.

Since this shrink label is made of a foamed film, it has a mechanical buffering effect and a heat-insulating property, and is particularly suitable as a packaging material for glass containers and the like containing soft drinks such as carbonated drinks.

By the way, in the case of a foamed shrink film used for such a shrink label, in order to obtain sufficient buffering effect and heat-insulating properties, it is necessary to increase the foaming ratio. However, when the expansion ratio is increased, the surface roughness of the film surface increases, resulting in a rough surface, resulting in a significant decrease in print finish, especially sharpness, and a lack of design. On the other hand, if the foaming ratio is reduced in an attempt to improve printability, there arises the disadvantage that the buffering effect and heat-insulating properties cannot be obtained within 4 minutes.

[Problem that the invention seeks to solve]

Therefore, in this invention, in a foam shrink film made of polyolefin resin, the roughness of the front and back surfaces is set to 10 to 10.
The above-mentioned conflicting problems were solved by setting the surface roughness to be 20 μm, and the surface roughness to be A, and the back surface roughness to B.

The surface roughness of the foamed shrink film in this invention is measured by the method specified in JIS-B-0601. Specifically, stylus type (JIS-8-0651),
Average roughness direct reading type (JIS-B-0655), optical cutting type (JIS-8-0653), light wave interference type (JIS-
8-0652), NF rough type (JIS-8'-0
656) etc. can be used.

If the absolute value of the roughness on both sides of the foam shrink film is less than 10 μm, the foaming ratio must be low, resulting in insufficient heat insulation and buffering effects. Furthermore, if the thickness exceeds 20 μm, printability deteriorates on both the front and back surfaces, making it impossible to print clearly.

In addition, if A-B is less than 0.1, the surface roughness will not be sufficiently small, making it unsuitable as a printing surface, and the back surface roughness will not be sufficiently large, resulting in poor cushioning and heat-insulating properties. It will be disadvantageous. Therefore, the average expansion ratio of the foam shrinkage film of the present invention is in the range of about 1.5 to 2.0 times.

Further, the stretching ratio is preferably in the range of 3.5 to 5.0 times.

In this type of foam shrink film, the front and back surfaces have different roughness, one side is relatively smooth and suitable for printing, and the other side is relatively rough and has high cushioning properties and excellent heat and insulation properties. Become.

Next, a method for manufacturing such a foam shrink film will be explained.

First, a polyolefin resin is prepared. As the polyolefin resin, low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, and blend polymers thereof are used.

A chemical blowing agent such as azobisisobutyronitrile, azodicarbonamide, or N,N'-dinitrosopentamethylenetetramine is added to these polyolefin resins at 0.1
Add ~1.5% by weight. In addition, additives such as antioxidants, lubricants, plasticizers, and antistatic agents may be added in required amounts as necessary.

This mixture is homogeneously triblended using a mixer such as a Henschel mixer or a tumbler to obtain a resin composition.

Next, this resin composition is melt-extruded to form a film and foamed by an inflation method using an extruder, a T-die method, or the like. During this forming process, only one side of the film can be formed by contacting only one side of the molten film immediately after the extrusion die with a small-diameter cooling roll, or by spraying a small amount of cooling water only on one side of the film. Pre-cool. This preliminary cooling suppresses the growth of foam cells on one side of the film and the decomposition of the chemical blowing agent, resulting in a state where foaming is suppressed.The film in this state is then cooled with a cooling roll, etc., and then stretched. A foamed shrink film is obtained.

By such a manufacturing method, it is possible to obtain a film in which the front and back surfaces have different expansion ratios and different surface roughnesses, and it is possible to obtain a film in which the degree of preliminary cooling on one side of the film can be adjusted.

〔Example〕

Hereinafter, examples will be shown to clarify the functions and effects.

The foamed shrink films of the present invention were obtained using various polyolefin resins by a method in which a cooling roll was brought into contact with only one side of the molten film immediately after the extruder die. This foamed shrink film has a shrinkage rate of 40 in the machine direction.
% temperature (40% shrinkage temperature), surface roughness, print finish, and heat retention properties were measured. The 40% shrinkage temperature is the heat shrinkage rate in the machine direction at each temperature according to JIS-Z-1709.
The temperature was determined from the graph when the shrinkage rate was 40%. The surface roughness is ■5E-3C manufactured by Kosei Research Institute
It was determined by the universal average roughness method. The print finish was visually observed and evaluated as follows.

◎: Very good ○: Good Δ: Slightly poor ×: Poor Heat retention was determined by wrapping this film around a glass container with a capacity of 300 d, shrinking it, filling it with water, and leaving it in a constant temperature bath at 70°C for 1 hour. It was evaluated by how hot it felt when the film part of the glass container was taken out and held in the hand.

○: Molecular success for more than 1 minute.

△: Can be held in hand for less than 30 seconds.

×: Can be held in hand for less than 10 seconds.

For comparison, a similar study was conducted on a foam shrink film produced using a conventional method without pre-cooling.

The results are also shown in the attached table.

As is clear from the results in the attached table, the foamed shrink film of the present invention has both good printability and heat retention.

〔Effect of the invention〕

As explained above, the foamed shrink film of the present invention is
Since one side of one film is relatively smooth and the other side is relatively rough, the smooth side has good printability, and the rough side has sufficient heat retention and cushioning properties.

Therefore, this foamed shrink film is suitable for, for example, shrink labels for one-way containers and the like.

Claims (1)

[Claims] In a foam shrinkable film made of a polyolefin resin, where the surface roughness of the film is A and the back surface roughness is B, A and B are 10 to 20 μm, and (A-B /A) ≧0.1 (roughness measurement is JIS
- According to B-0601. ) A foam shrink film characterized by: