JPH06143517A - Surface protective film and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the generation of creases at the time when a surface protective film is stuck onto an adherend by co-extruding and forming a specific high-density polyethylene resin and a self-adhesive resin by a T die using a feed block. CONSTITUTION:A high-density polyethylene resin having density of 0.950 or more and a melt index of 5-10 and a self-adhesive resin are co-extruded and formed by a T die employing a feed block. Accordingly, a surface protective film, in which the self-adhesive resin is laminated on a base material film consisting of the high-density polyethylene resin having density of 0.950 or greater and the melt index of 5-10, is obtained. An ethylene-vinyl acetate copolymer having vinyl acetate content of 5-30%, a styrene-isoprene-styrene block copolymer, etc., are quoted as the proper example of said self-adhesive resin. No crease is generated when the acquired surface protective film is stuck on an adherend, and the film does not float from the adherend after sticking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to protect a surface of an adherend such as a synthetic resin plate, a decorative plywood, or a metal plate, which is temporarily adhered to the surface of the adherend so that dust is not attached or scratched. The present invention relates to a surface protective film used and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as such a surface protective film, for example, in JP-A-54-160482, low density polyethylene (density 0.916 g /
cc, melt index 7 g / 10 mm) and an adhesive layer made of an ethylene-vinyl acetate copolymer are coextrusion-molded by an inflation method to describe a surface protecting laminated film.

Generally, coextrusion molding using a T die is also performed. As the adhesive resin, in addition to the above ethylene-vinyl acetate copolymer, various resins such as polyisobutylene and styrene-isoprene-styrene block copolymer are used.

[0004]

When a polyethylene resin having a low density is used, wrinkles are generated at the time of sticking when the sticking tension is large as when applied to a metal surface.
The film shrinks after being applied, so that it is lifted from the adherend. It is considered that the above problems can be solved by using a surface protective film having a tensile elastic modulus of 3000 kg / cm ² or more. Therefore, it is conceivable to use a polyethylene resin having a large thickness and a high 1% modulus, or to mix a polyethylene resin with a polypropylene resin.

To increase the 1% modulus by increasing the thickness of the low-density polyethylene resin film, a considerable thickness is required, the cost becomes high, and the conformability to an adherend becomes poor. It is difficult to meet the demand. In addition, mixing a polypropylene resin with a polyethylene resin requires changing the screw shape of the extruder due to the difference in molding characteristics of the two resins, which causes problems in kneading property, productivity, and the like.

As a co-extrusion molding method, there is a problem that a fish eye is generated when a low density polyethylene (LDPE) having a low melt index is extruded at a high temperature by a T-die or an inflation method in order to improve the productivity. . Also, if you use the inflation method,
The surface of the formed film is rough, and when it is attached to the adherend, the film surface is scraped due to the friction between the application roll and the film, and white powder of polyethylene resin is generated, which adheres to the roll surface and protects the surface. It adheres to the film surface and causes various problems. Therefore, it is preferable to use the T-die to avoid such a point.

In the T-die method, for example, as shown in FIG.
A feed block 3 that joins a plurality of resin streams A, B, and C is provided immediately before the resin is introduced into the die 2, and each resin is joined in the feed block and then sent to the T die 2 to co-extrude the laminated film 1. There are a single-manifold method for molding, a multi-manifold method in which a plurality of manifolds are provided in a T-die, and resin flows are joined at a die lip portion. According to the multi-manifold method, this mold has the advantage that the thickness ratio of each layer in the entire width direction can be adjusted even if there is a difference in viscosity between the base film resin and the adhesive resin, but changes in resin raw material, width size, etc. Since it takes a lot of time and effort to adjust each time, it is not suitable for small lot and multi-size production.

According to the single manifold method using the feed block 3, the temperature of the base film resin and the adhesive resin can be separately adjusted up to the feed block 3, but the temperatures thereafter become equal, and the respective resins become the same. The viscosity changes. In addition, since the viscosity characteristics of the base film resin and the adhesive resin are different when a resin having a low melt index is used, the thickness accuracy of each layer in the width direction fluctuates greatly, especially in the vicinity of the end in the width direction compared to the base film. However, there is a tendency that a single layer is formed only of an adhesive resin having a high melt index. However, when the base film resin has a large melt index, such a single layer does not form, and the thickness ratio of each resin in the width direction can be easily and uniformly adjusted by adjusting the vanes and pins. .

The present invention solves the above-mentioned problems of the prior art, is capable of producing small lots and a wide variety of products, has good productivity, and a method for producing a surface protective film in which the thickness ratio of each layer to be laminated is constant, and It is an object of the present invention to provide a surface protection film which does not cause wrinkles when attached to an adherend and does not rise from the adherend after being attached.

[0010]

A method for producing a surface protective film according to the present invention is a T-die using a feed block of a high density polyethylene resin having a density of 0.950 or more and a melt index of 5 to 10 and an adhesive resin. It is characterized in that it is coextruded.

The surface protective film of the present invention is a surface protective film obtained by laminating an adhesive resin on a base film made of polyethylene resin, wherein the base film has a density of 0.950 or more and a melt index of 5 to 10. The high-density polyethylene resin is

The details of the present invention will be described below. The base film uses a high-density polyethylene resin with a density of 0.950 or more, so that the tensile elastic modulus is 3000 kg / cm.
You can get ² or more. When the melt index (hereinafter referred to as “MI”) of the base film resin is less than 5, the fluidity in the mold is poor and a single-layer film made of only the adhesive resin is apt to be formed especially near the end in the width direction, and the MI is When it is larger than 10, the fluidity is higher than that of the adhesive resin, and the single-layer film made of only the base film resin having no adhesive resin in the vicinity of the edge tends to be formed. Therefore, the MI of the base film resin is in the range of 5-10. Particularly preferred range is 5
8 High density polyethylene may be mixed with linear low density polyethylene, polyethylene wax, etc. as long as the above-mentioned density and MI range are maintained.
Antiaging agents, pigments and the like may be added.

If the thickness of the film is 100 μm or more, the cost and the product price are high, and if it is 20 μm or less, the strength is low and the film is broken.
The range of 0 to 100 μm is preferable. More preferably 30
˜80 μm.

As the adhesive resin used in the surface protective film, ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30%, styrene-isoprene-styrene block copolymer, polyisobutylene and the like have been conventionally used. There is something. The MI of these resins is usually 4 to 10, whereas the MI of the base film resin is 5
By using those of No. 10 to 10, the balance of the flow characteristics of both is maintained, and both are extruded at a constant thickness ratio.

[0015]

【Example】

(Example 1) High density polyethylene (HDPE) having a MI of 5.5 and a density of 0.963 as a base film resin
Send the resin to the feed block in the molten state at 195 ° C,
On the other hand, an ethylene-vinyl acetate copolymer (EVA) having a MI of 6 containing 28% vinyl acetate was sent to a feed block in a molten state at 180 ° C., and the thickness of HDPE extruded was 40 μm and the thickness of EVA was 20 μm. The vane and pin of the feed block were adjusted so that the gap of the resin flow path was adjusted, and the surface protective film was extruded from the T die with a width of 850 mm.

Example 2 A two-layer film was formed in the same manner as in Example 1 except that HDPE having MI of 8.0 and density of 0.961 was used instead of HDPE of Example 1.

Comparative Example 1 A two-layer film was molded in the same manner as in Example 1 except that HDPE having MI of 1.1 and density of 0.955 was used instead of HDPE of Example 1.

Comparative Example 2 A two-layer film was molded in the same manner as in Example 1 except that HDPE having MI of 14.0 and density of 0.965 was used instead of HDPE of Example 1.

Comparative Example 3 A two-layer film was prepared in the same manner as in Example 1 except that low density polyethylene (LDPE) having MI of 2.0 and density of 0.924 was used in place of HDPE of Example 1. Was molded.

With respect to the two-layer films obtained in Examples 1 and 2 and Comparative Examples 1 to 3, the thicknesses of the base film (HDPE) and the adhesive resin (EVA) in the vicinity of the ends in the width direction were measured. Further, the elongation at break and the tensile modulus of elasticity of each two-layer film were measured, and the occurrence of wrinkles and the state of lifting from the adherend when adhered to the adherend were observed. The above results are shown in Table 1.

[0021]

[Table 1]

As is clear from Table 1, in Examples 1 and 2, the thickness of each layer co-extruded was as set in the mold, and there was no wrinkle or lifting from the adherend.
On the other hand, Comparative Example 1 is a single layer having no base material film near the end in the width direction and only the adhesive resin, and Comparative Example 2 has a small elongation at break and thus tears when peeled. In the case of Comparative Example 3, wrinkles were generated and lifted up from the adherend, so that the function as a protective film could not be satisfied.

[0023]

Since the surface protective film manufacturing method of the present invention is constructed as described above, the thickness of the resin extruded from the T-die can be easily adjusted, and it can be produced in small lots and in a wide variety of products. Good sex. Then, it is possible to manufacture a surface protective film in which the thickness of each layer of the film is uniform in the width direction. The surface protective film of the present invention has a substrate film having a density of 0.950 or more and a melt index of 5-10.
Since it is made of high-density polyethylene, there is no generation of polyethylene resin powder due to friction with the fish eye or sticking roll, wrinkles do not occur when sticking to the adherend, and the sticker rises from the adherend after sticking There is nothing to do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a manufacturing method of the present invention.

[Explanation of symbols]

 1: Surface protection film 2: T-die 3: Feed block A, B, C: Resin flow

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Claims (2)

[Claims] 1. A surface protective film produced by co-extruding a high-density polyethylene resin having a density of 0.950 or more and a melt index of 5 to 10 and an adhesive resin with a T die using a feed block. Method. 2. A surface protection film comprising an adhesive resin laminated on a base film made of polyethylene resin, wherein the base film is a high density polyethylene resin having a density of 0.950 or more and a melt index of 5-10. A surface protection film characterized in that