JPH0820757A - Surface-protective film - Google Patents

Abstract

PURPOSE:To prepare a surface-protective film made by using a polyolefinic resin film as the base material and desirably used for a material subjected to bending. CONSTITUTION:This film is prepared by forming a pressure-sensitive adhesive layer on either surface of a base material made of a polyolefinic resin. The polyolefinic resin film has lengthwise and crosswise mechanical properties including a tensile breaking strength of 3kg/10mm width or above, a tensile yield strength of 0.4kg/10mm width or above and an elongation recovery of 70% or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a metal plate such as a stainless steel plate, an aluminum plate, a colored steel plate or a colored aluminum plate, which is processed, transported or stored, and has dust or scratches on its surface. The present invention relates to a surface protection film used to prevent the formation of marks, and particularly to a surface protection film suitable for bending.

[0002]

2. Description of the Related Art Conventionally, as a surface protection film suitable for bending a metal plate, since it is bent by a piece that is temporarily adhered to the surface of an adherend, the quality characteristics originally required for the surface protection film. It is required to have bending workability in addition to the temporary adhesion property and the removability. Therefore, as the base material, a soft vinyl chloride resin film which is rich in elasticity, such as a soft vinyl chloride resin film formed by extrusion molding or a film obtained by coating a solvent solution of vinyl chloride on a substrate and drying it, and then peeling it off. Resin films are widely used.

[0003]

However, a film made of a soft vinyl chloride resin produces a toxic gas at the time of incineration after disposal after use, which is a problem in terms of hygiene and pollution. On the other hand, the use of a polyolefin resin film as a base material of the surface protection film has been studied (see JP-A-53-21239 and JP-B-1-14265). However, the polyolefin-based resin film disclosed herein is intended to provide a film suitable for drawability, and is not a technology pursuing a film suitable for bendability.

Although bending is the most frequently used processing method in the processing of metal sheets, the literature on bending workability is the Hitachi Chemical Technical Papers (Sho 57.10, Nakao). In other), it is disclosed only to the extent that a high-strength substrate is preferable,
At present, it is not found anywhere else.

In view of the above situation, the inventors of the present invention have conducted research to find a surface protective film having a polyolefin resin film as a base material, which is particularly suitable for bending work. As for the required mechanical properties, unlike those required for drawing, stress relaxation and cold workability do not matter so much, and those with high tensile fracture strength and high elongation recovery rate Found what is required.

Conventionally, in a surface protective film, a film having a high elongation recovery rate or a film having a large tear resistance is generally excellent in cutting resistance, so that the surface protection film is subjected to various machining processes including drawing. Although it was evaluated that it was not suitable for a film, the research by the present inventors revealed that tensile fracture strength and elongation recovery rate are the most important mechanical properties as far as bending is concerned. That is, even if the same machining is performed, the mechanical mechanism of bending is different from that of drawing, so that the mechanical characteristics of drawing cannot be adopted as they are.

That is, an object of the present invention is to provide a surface protective film having a polyolefin resin film as a base material, which is particularly suitable for use in a bending process.

[0008]

The surface protective film of the present invention, in the state of the surface protective film having the pressure-sensitive adhesive layer formed, Tensile breaking strength in both vertical and horizontal directions is 3kg / 10mm
Being wider than the width ,. Tensile yield strength 0.4kg / 1
0 mm width or more ,. It must satisfy all the conditions that the elongation recovery rate is 70% or more. However, the tensile fracture strength and tensile yield strength are JIS
It is measured according to K-7127, and the elongation recovery rate is 10 mm in width and 100 m between marked lines (grasping interval).
m, pulling 100 mm at a pulling speed of 200 mm / min, released immediately thereafter, and shown by the recovery rate after 5 minutes.
If there is no yield point in the tensile test, the flat portion up to about 100% elongation is taken as the tensile yield strength.

Since a stainless steel plate having a thickness of about 2 mm is generally used as a metal plate to be bent by a bender, the present inventors actually use this adherend to actually provide a surface protective film. The experiment was repeated with the adhesive attached. As a result, first, regarding the tensile fracture strength, it was 3 kg / 10 m.
It was found that a material having a value of m width or more can sufficiently withstand the stress during bending. If less than this, breakage occurred during bending.

In order to prevent breakage during bending, the tensile fracture strength should be within the above range and 70%.
It must satisfy the above elongation recovery rate.

That is, when bending is performed by using a bender, plastic deformation does not occur when pressure is applied to the shoulder portion of the die, and the shape is quickly recovered when the pressure portion moves. It turned out that it was necessary to choose, and imposed such a condition. When the elongation recovery rate is 70% or more, it is possible to prevent breakage of the film when it is stretched perpendicularly to the bending ridgeline during the bending process.

Further, although there is no direct influence on the "breakage" during bending, the tensile yield strength is 0. 0 as a basic mechanical strength required for sticking to an adherend or peeling. 4 kg /
There is a constraint that it must be 10 mm or more. If it is too small, it may be stretched and wrinkled at the time of sticking, stretched at the time of peeling and difficult to be peeled off, or it may be broken in an extreme case.

Next, how to obtain a polyolefin resin film satisfying all of the above mechanical properties will be described. Even a normal polyolefin resin film can be obtained as desired depending on the selection. Although not absent, it is often contained in a stretched or post-crosslinked film having a thickness in the range of 50 to 200 μm.

First, the base resin will be described. As a polyolefin resin capable of satisfying all the above mechanical properties, a wide range of homopolymers such as ethylene and α-olefins having 3 to 8 carbon atoms or Examples thereof include copolymers, and blends of these homopolymers and / or copolymers. Among them, ethylene-propylene copolymers, ethylene containing a certain amount of amorphous components and capable of imparting rubber-like performance. Is an α-olefin having 4 or more carbon atoms, that is, butene-
It is effective to include linear low-density polyethylene obtained by copolymerizing α-olefins such as 1, hexene-1, octene-1, and 4-methylpentene-1, SIS, and SEBS to some extent.

When it is used not only for bending but also for drawing, from the viewpoint of preventing the occurrence of a phenomenon such as floating after processing, ethylene in which propylene is forcibly dispersed or a reactor blend is used. Made from raw materials produced by the method (polymerization of a blend type copolymer resin at the molecular level by performing multi-stage polymerization of two or more steps), or a blend of these specific resins with a polyolefin resin Is preferably used as a raw material. By alloying in the polymerization vessel as in the above reactor blending method, unlike the conventional method of blending after polymerization, ethylene and other components are finely dispersed to exhibit desired performance. Regarding the specific polymerization method and the like of the reactor blending method, for example, Japanese Patent Laid-Open No.
-205439.

The method of molding the film may be a conventionally used molding method such as a calendar method, a casting method, an inflation method or a T-die method, and is not particularly limited. In short, by stretching or crosslinking in the post-processing, the above
It suffices to obtain the one that satisfies the mechanical properties described in (1).

The stretching method may be any method as long as it can be uniformly stretched, and examples thereof include a roll stretching method, a tenter stretching method and a tubular stretching method. The stretching direction is longitudinal (or transverse) uniaxial stretching. Simultaneous (sequential) biaxial stretching, multidirectional stretching and the like. By these stretching processes (pulling and heat treatment), the molecules are oriented in a predetermined direction and a desired mechanical strength is imparted.

The crosslinking method may be any method as long as it satisfies the above-mentioned mechanical properties. For example, a method of heating in the presence of a radical generator to a temperature at which free radicals are generated or higher, ionization And the like. As the radical generator, 2,
5-Dimethyl-2,5-di (t-butylperoxy) hexene-3, α, α'-bis (t-butylperoxy-
Examples thereof include organic peroxides such as m-isopropyl) benzene, di-t-butylperoxide, and t-butylcumylperoxide. Moreover, you may add the compound which has one or more carbon-carbon unsaturated bond as a high molecular-polymerization aid with a radical generator as needed. Due to such cross-linking, the polyolefin polymer has a three-dimensional network structure and is provided with desired mechanical strength.

The pressure-sensitive adhesive used in the surface protective film of the present invention may be either rubber-based or acrylic-based as long as it can fulfill the function of the surface-protective film. As a layer forming means,
Either a coating method or a co-extrusion method may be used.

[0020]

The surface protective film of the present invention has mechanical properties in both longitudinal and lateral directions, such as tensile fracture strength of 3 kg / 10 mm width or more, tensile yield strength of 0.4 kg / 10 mm width or more, and elongation recovery of 70% or more. And the mechanical properties of these are obtained experimentally after actual bending, and thus have desired bendability.

[0021]

EXAMPLES Examples of the present invention will be described in detail below.

Example 1 A linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultozex 2020L) was used to form a film by the T-die method, which was drawn by a tenter drawing method at a drawing temperature of 100 ° C. Uniaxially stretched at a anneal temperature of 120 ° C., an anneal time of 3 minutes, and a stretch ratio of 2 times, and 70 μm.
A film having a thickness of Next, after subjecting one side of the obtained film to a corona discharge treatment, an adhesive solution (manufactured by Soken Chemical Co., Ltd., trade name; AG105) was added to the surface with a solid content of
A sample of the surface protection film was obtained by applying and drying so as to have a thickness of μm.

Example 2 A polyolefin formed of ethylene-propylene copolymer (manufactured by Highmont Co., trade name; KS-051P) was used to form a film by the T-die method, which was uniaxially stretched in the same manner as in Example 1. A pressure-sensitive adhesive layer was formed to obtain a surface protection film sample.

Example 3 With respect to 100 parts by weight of the same resin as that used in Example 1, 2,5-dimethyl-2,5 was used as a radical generator.
-Using di (t-butylperoxy) hexene-3 in an amount of 1.0 part by weight and 3.0 parts by weight of divinylbenzene as a polymerization aid, respectively, at a die temperature of 180 ° C by a T-die method. After forming the film, the film was heated to 200 ° C. and crosslinked to obtain a film having a thickness of 70 μm. Then, in the same manner as in Example 1, a pressure-sensitive adhesive layer was formed to obtain a surface protection film sample.

Example 4 A film having a thickness of 70 μm was obtained in the same manner as in Example 3 except that the same resin as that used in Example 2 was used. Then, in the same manner as in Example 1, a pressure-sensitive adhesive layer was formed to obtain a surface protection film sample.

Comparative Example 1 A film having a thickness of 70 μm was obtained in the same manner as in Example 1 except that the film was not stretched, and a pressure-sensitive adhesive layer was formed to obtain a surface protection film sample.

Comparative Example 2 A film having a thickness of 70 μm was obtained in the same manner as in Example 2 except that the stretching process was not performed, and a pressure-sensitive adhesive layer was formed to obtain a surface protection film sample.

Tensile fracture strength, tensile yield strength, and elongation recovery were measured for the samples obtained in the above Examples and Comparative Examples, while each sample was actually attached to an adherend. Bending was performed and the cutting resistance (cutting) was evaluated. Table 1 shows the results.

The test method, evaluation method and evaluation scale are as follows. Tensile breaking strength: Width 10 in the direction perpendicular to the film forming direction
mm sample piece is taken, the distance between the marked lines is 40 mm, and the pulling speed is 20
A tensile test is performed at a speed of 0 mm / min to measure the tensile breaking strength (according to JIS K-7127). Tensile yield strength: During the tensile test, the strength at the yield point was measured (according to JIS K-7127). Elongation recovery rate: Width 10 mm, distance between marked lines 100 mm, pulling 100 mm at a pulling speed of 200 mm / min, released immediately, and measured the distance between marked lines after 5 minutes, elongation recovery rate (%) =
(200 (mm) -5 minutes later, distance between gauge lines (mm)) x 100 / distance between gauge lines before extension (mm). Cut: The film was attached to a stainless steel plate (SUS304HL) with a thickness of 2.0 mm, and a bending machine was used to bend the die to a finish of 90 ° at a processing speed of 8 m / min using a die with a width of 12 mm. Then, the breakage of the film after processing was visually determined. ○ = No cut, △ = Partially cut, × = cut occurred on the entire surface

[0030]

[Table 1]

As is clear from the results shown in Table 1, in each of the examples, excellent values were obtained in all three items of mechanical properties, whereas in each of the comparative examples which were not stretched. Is
The desired tensile fracture strength was not obtained, and in the case of Comparative Example 1, the elongation recovery rate was poor and the cutting was severe, making it unusable.
In Comparative Example 2, the elongation recovery rate was equal to or higher than the predetermined value, so that the occurrence of breakage was small, but it was still not a product.

[0032]

EFFECTS OF THE INVENTION The surface protective film of the present invention has mechanical properties in both longitudinal and transverse directions, such as tensile fracture strength of 3 kg / 10 mm width or more, tensile yield strength of 0.4 kg / 10 mm width or more, and 70% or more. The elongation recovery rate is provided, and these mechanical properties are obtained experimentally by actually performing bending, and thus have desired bendability.

Therefore, it is suitable for use in protecting the surface of an adherend that has undergone a metal plate processing step, and in particular, for subjecting it to bending processing. Moreover, since a polyolefin-based resin film is used as the base material, there is no problem in recycling compared to a soft vinyl chloride-based resin film as the base material, and the temperature dependence is small, so the base material composition depending on the season Change·
Since there is no need for adjustment and the specific gravity is small, the product size can be increased, and the workability on site is also excellent, and the advantages of using a polyolefin resin film can be utilized.

Claims (2)

[Claims] 1. A surface protective film having a pressure-sensitive adhesive layer formed on one surface of a base material made of a polyolefin-based resin film, and having mechanical properties in both longitudinal and lateral directions of 3 kg / 10.
A surface protection film having a tensile breaking strength of mm width or more, a tensile yield strength of 0.4 kg / 10 mm width or more, and an elongation recovery rate of 70% or more. 2. The polyolefin resin film has an ethylene-propylene copolymer or ethylene and 4 carbon atoms.
2. The surface according to claim 1, which is a film made of a copolymer with .alpha.-olefin of .about.8, having a thickness in the range of 50 to 200 .mu.m, and stretched or post-crosslinked. Protective film.