JPH1036794A - Surface protective film and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film excellent in mechanical strength and having a small thickness of a base material, and no elongation or breakage under heating during application of an adhesive and drying during drying, and excellent mechanical strength. Provide a way. SOLUTION: An adhesive is applied to one surface of a base material having a thickness of 15 to 28 μm, which is made of an ethylene polymer and has a tensile strength at a specific temperature in a specific range at 10% elongation in one direction and a direction perpendicular thereto in one direction. A surface protective film, characterized in that a surface protective film is applied. The melting point of the ethylene polymer and 190 ° C
Wherein the melt flow rate is within a specific range. Further, the frost height, the draft ratio is a specific range, by an inflation method, a film of the ethylene-based polymer under specific conditions, characterized by applying an adhesive on one surface of the obtained substrate. A method for producing the above surface protective film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface protection used for the purpose of protecting the surface of resin boards and decorative plywood, for example, in order to prevent minor scratches and dirt during handling and processing during transportation and storage. The present invention relates to a film and a method for producing the film.

[0002]

2. Description of the Related Art Conventionally, the base material of a surface protection film is generally made of a soft vinyl chloride resin or a polyolefin resin, and its thickness is usually 40 to 200 μm, and usually 50 to 120 μm. I have. In recent years, from the viewpoint of waste disposal, studies have been made on dechlorinated vinyl resin of the surface protection film, reduction of the amount of waste, and the like. The surface protection film is subdivided into applications that require high strength such as bending and squeezing, and applications that require low cost such as prevention of dust adhesion during transport and storage, and minor scratches and dirt prevention. Have been. In particular, there is an increasing need for cost reduction and waste reduction. However, if the thickness of the base material is simply reduced with the conversion of the base material to polyolefin, elongation or breakage occurs under heating during application of the adhesive and during drying, and strength and solvent resistance are low. In the case of using the currently used materials and equipment, the actual application of the surface protective film, the peeling operation and the tape formation are extremely difficult, and the productivity is greatly reduced or the processing becomes impossible. There are cases.

As a study on the assumption of processing requiring high strength, for example, in Japanese Patent Application Laid-Open No. 8-27443, a tensile yield strength in one direction and a direction perpendicular thereto is 500 g / 10 mm width or more, and Use a polyolefin-based resin film having a tensile strength of 400 g / 10 mm or less at the time when 10 minutes have passed after the onset of the yield point at the time of measuring the tensile yield strength, and having a tensile breaking strength higher than the tensile yield strength. As a result, a surface protective film having excellent cold workability and stress relaxation properties and suitable for drawing is obtained. In Japanese Patent Application Laid-Open No. 8-20757, the tensile fracture strength in one direction and the direction perpendicular thereto is 3 kg /
10mm width or more and tensile yield strength of 0.4kg / 1
By using a polyolefin-based resin film having a width of 0 mm or more and an elongation recovery of 70% or more, a surface protective film excellent in bending workability is obtained. However, in view of the above problems, much attention has not been paid to resource saving, waste reduction and cost reduction, and no consideration has been given to the thickness of the base material and the like.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a base material having a small thickness, no elongation or breakage under heating during application of an adhesive and drying, and excellent mechanical strength. An object of the present invention is to provide a surface protective film and a method for producing the same.

[0005]

The surface protective film of the present invention has a tensile strength at 10% elongation in one direction of 2% at 120 ° C.
More than 00g / 10mm width, 600g / 10mm at 23 ° C
From an ethylene polymer having a tensile strength of not less than the width (this direction is referred to as a longitudinal direction) and a direction perpendicular thereto (this direction is referred to as a transverse direction) at a 10% elongation of not less than 300 g / 10 mm width at 23 ° C. An adhesive is applied to one surface of a base material having a thickness of 15 to 28 μm.

The above-mentioned ethylene polymer is 10% in the longitudinal direction.
When the tensile strength at the time of elongation is less than 200 g / 10 mm width at 120 ° C., elongation or breakage occurs under heating during application of the adhesive and at the time of drying, and at less than 600 g / 10 mm width at 23 ° C., the surface protective film. In actual use, the required strength to withstand the tension at the time of peeling or sticking the surface protection film wound in a roll or the tension at the time of peeling from the adherend cannot be obtained. If the tensile strength at 10% elongation in the horizontal direction is less than 300 g / 10 mm width at 23 ° C., the peeling of the surface protection film is not in the vertical direction,
In the case of the horizontal direction, the surface protective film is easily torn.
The tensile strength referred to in the present invention is 100 mm in length and 10 mm in width.
Ethylene polymer film specimen of 200mm speed
This is a value obtained by measuring the tensile strength when the film is stretched 10% in the length direction at a rate of / min. The ethylene polymer used in the present invention is one having the above-mentioned physical properties among ethylene homopolymer, ethylene-propylene copolymer and ethylene-α-olefin copolymer. Low-density polyethylene.

The above ethylene polymer has a melting point of 125 ° C.
The melt flow rate at 190 ° C. (hereinafter referred to as M
FR) is preferably 0.005 to 0.1 g / 10 min. An adhesive is applied and dried on the ethylene-based polymer after film formation, and the adhesive is applied in a state of being dissolved in an organic solvent such as toluene or ethyl acetate. Drying of the organic solvent usually requires a temperature of 100 to 120 ° C. Therefore, if the melting point of the ethylene polymer is less than 125 ° C., the ethylene polymer may be softened by heating during drying of the pressure-sensitive adhesive. The MFR of the ethylene polymer at 190 ° C. is 0.005 g / 10 min.
When it is less than 0.1 g / 10 min or more, it becomes difficult to process, attach and peel under heating during application of the adhesive and drying. The melting point is a value measured using a differential scanning calorimeter (DSC method), and the measuring method is as described below. First, a sample of about 10 mg of an ethylene-based polymer was put into a platinum pan, once melted, and then cooled at 5 ° C./m
Cooled to -50 ° C at a rate of in. Next, 5 ° C / min
And measured with a differential scanning calorimeter (trade name “SSC5200” manufactured by Seiko Instruments Inc.). The above MFR is a value measured in accordance with JIS K7210.

[0008] The substrate in the present invention is obtained by forming the above-mentioned ethylene polymer into a film. When the ethylene polymer film has the above-mentioned physical properties, the thickness of the substrate becomes 15 to 28.
Even if it is as thin as μm, production and use as a surface protective film can be sufficiently performed. When the thickness of the base material is less than 15 μm, the balance between the strength and the flexibility and the handleability are inferior, and the thickness is 28 μm.
If it exceeds, it will not be excellent in terms of cost and reduction of waste. As the film forming method, any conventionally known method can be adopted, and among them, the inflation method described later is preferable. Examples of the pressure-sensitive adhesive used in the present invention include acrylic pressure-sensitive adhesives and rubber-based pressure-sensitive adhesives that are generally used as pressure-sensitive adhesives. As a method for applying the adhesive to the substrate and a method for drying, any conventionally known method can be adopted.
Also, an ethylene-vinyl acetate copolymer-based adhesive or SE
A pressure-sensitive adhesive layer may be formed on the substrate by co-extruding the BS-based pressure-sensitive adhesive with the ethylene-based polymer. In addition,
In order to improve the adhesiveness between the pressure-sensitive adhesive and the substrate, the surface of the substrate coated with the pressure-sensitive adhesive may be subjected to a corona discharge treatment or a primer treatment as necessary.

In the surface protective film of the present invention, various resins and additives may be blended or laminated as needed as long as the physical properties of the surface protective film are not affected. For example, when used for hot press applications, or to laminate a high melting point material on the surface of the surface protection film to prevent fusion by heat, or when used for applications that require transparency, It is possible to arbitrarily reduce the external haze of the surface protective film by laminating a low-haze material in order to improve the transparency. Further, by laminating a material having solvent resistance between the base material and the adhesive of the surface protective film, the problem of the solvent resistance of the base material can be solved.

According to a third aspect of the present invention, there is provided the method for producing a surface protective film, wherein the frost height is 5 to 30 times the die diameter, and the draft ratio is 3 to 150. Combine with frost height of 30-8
Blow-up diameter of mold diameter ± 20 to 0% height
%, And thereafter, the film is formed by expanding the blow-up ratio to 2 to 7, and an adhesive is applied to one surface of the obtained base material.

If the frost height of the above-mentioned inflation method is less than 5 times the die diameter, the ethylene polymer is spread in a completely molten state, so that the balance between the strength in the longitudinal direction and the strength in the lateral direction of the obtained base material is not improved. Deteriorate. If it exceeds 30 times,
The ethylene polymer is cooled before being spread,
You cannot get a stable blow. This is not the case if heating is appropriately performed so that the ethylene-based polymer is not cooled. The draft ratio of the inflation method is 3 to 150, preferably 7 to 60.
When the draft ratio is less than 3, the thickness of the obtained base material becomes large, and when it exceeds 150, the balance between the strength in the longitudinal direction and the strength in the horizontal direction of the obtained base material becomes poor.

The above-mentioned ethylene polymer is melt-kneaded by an extruder before the inflation method, and then extruded from a mold. The lip clearance of the mold is not particularly limited, but is generally 2 mm or more, preferably 2.5 to 4 mm. 190 of the ethylene polymer
When the MFR at 0 ° C is less than 0.005 g / 10 min, the load at the time of melt kneading and extrusion by a generally used extruder increases, so that the MFR at 0.005 g / min is 0.005 g / min.
10 min or more is preferable. However, in the above-mentioned inflation method, the film formation of the ethylene-based polymer is stabilized by attaching a cylinder for guiding the film so as not to spread on the upper part of the mold.
It is also possible to form a film almost without being affected by R.

[0013] In the molten state, the ethylene polymer is first pulled up to a height in the range of 30 to 80% of the frost height with a blow-up diameter of ± 20% in the die diameter.
If the withdrawn height is less than 30%, the ethylene-based polymer is spread in a completely molten state, so that the obtained base material has a poor balance of strength in the vertical and horizontal directions. The coalescence does not spread, and the balance with the above-mentioned draft ratio does not match. Further, when the blow-up diameter is raised outside the range of the mold diameter ± 20%, the ethylene polymer is expanded in a completely molten state, and thus the balance between the strength in the longitudinal direction and the strength in the lateral direction of the obtained base material is poor. Become.
Thereafter, the ethylene-based polymer is formed into a film having a blow-up ratio of 2 to 7, preferably 3 to 6, and a base material is obtained. When the blow-up ratio is less than 2, the thickness of the obtained base material becomes large, and when it exceeds 7, the obtained base material may be broken or the like. An adhesive is applied to one surface of the substrate and dried to obtain a surface protective film. As the pressure-sensitive adhesive, those described above are used, and any conventionally known method can be adopted as a method of applying and drying the same.

In the above-mentioned inflation method, at the time of film formation, the thickness of the ethylene-based polymer is reduced at a place away from the exit of the mold, and the blow becomes large after the temperature of the ethylene-based polymer is lowered. Like the film, the molecular orientation becomes strong, and high strength can be obtained with an extremely thin film in both the vertical and horizontal directions. In addition to the inflation method, a substrate having high strength can be obtained in an extremely thin film by sequential biaxial stretching or simultaneous biaxial stretching, but usually requires large-scale equipment for stretching,
The production lot is also very large, so the cost is high. Furthermore, for example, when the stretching ratio is increased as in the case of a biaxially stretched polypropylene film, the elastic modulus becomes large, so that there is a problem that the film is too hard to be stuck or easily torn at the time of peeling. Since the film is heated also in the stretching step in addition to the film, it is necessary to add a heat stabilizer or the like, which affects the adhesive properties.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION 【Example】

(Examples 1 to 3, Comparative Examples 1 and 2) The ethylene-based polymer shown in Table 1 was formed into a film having a predetermined thickness shown in Table 1 by the inflation method described above to obtain a base material. Example 1
3, Comparative Examples 1 and 2). In Comparative Example 3, a commercially available biaxially oriented polypropylene film shown in Table 1 was used as a base material. Next, one surface was subjected to corona discharge treatment, and a solution obtained by diluting an acrylic pressure-sensitive adhesive with toluene so that the solid content concentration became 20% was applied to the surface of the pressure-sensitive adhesive after drying with a comma coater. Apply so that the thickness becomes 3 μm, 110
It dried at ° C and obtained the surface protection film. Next, the obtained surface protection film was stuck on a stainless steel plate with a laminator at a speed of 5 m / min, left at 40 ° C. for one week, and then at room temperature at a speed of 30 m / min at an angle of 180 °. Peeled off. The frost height of the inflation method, the blow-up diameter at 30% of the frost height, and the blow-up ratio after the ethylene polymer was raised to a height of 30% or more of the frost height are as shown in Table 1. The mold diameter used was 100 mm in diameter, and the lip clearance was 2.4 mm.

The MFR and melting point of the ethylene polymer film and the biaxially oriented polypropylene film used in Examples 1 to 3 and Comparative Examples 1 to 3 at 190 ° C., the thickness after film formation, and 10% in the longitudinal direction. Table 1 shows the tensile strength at 120 ° C. and 23 ° C. during elongation and the tensile strength at 23 ° C. at 10% elongation in the transverse direction. The elongation, wrinkling, and breakage of the surface protective film during application of the adhesive and drying were observed, and the case where none was observed was indicated by ◎. When any one was observed, the type is shown in Table 1. (Workability during application of adhesive and drying) Observe wrinkles and floating of the surface protection film when pasting it to a stainless steel plate. If none were found, mark ◎. Are shown in Table 1. (Paste work) However, in Comparative Examples 1 and 2,
I did not observe. Cuts of the surface protective film and peeling of the adhesive on the stainless steel plate at the time of peeling were observed, and the case where neither was observed is shown in Table 1 as ◎. (Peeling work)
However, in Comparative Examples 1 to 3, no observation was made.

[0017]

[Table 1]

* 1: Nippon Polyolefin Co., Ltd., trade name * 2: Mitsubishi Chemical Co., trade name * 3: Mitsubishi Chemical Co., trade name * 4: Mitsubishi Chemical Co., trade name * 5: Mitsubishi Chemical Co., Ltd. * 6: Pyrene film made by Toyobo Co., Ltd.-OT, trade name

[0019]

The surface protective film of the present invention is also excellent in that the thickness of the substrate is small, there is no elongation or breakage under heating during application of the adhesive and during drying, and there is mechanical strength. It is a thing. The method for producing a surface protective film according to the invention of claim 3 is excellent in that a high mechanical strength can be obtained with an extremely thin film in both the vertical and horizontal directions.

Claims (3)

[Claims] 1. Tensile strength at 10% elongation in one direction is 12
200g / 10mm width or more at 0 ° C, 600g / 23 ° C
A pressure-sensitive adhesive is applied to one surface of a base material having a thickness of 15 to 28 μm, which is made of an ethylene polymer and has a tensile strength of not less than 10 mm and a width of not less than 300 g / 10 mm at 23 ° C. at a stretch of 10% in a direction perpendicular thereto. A surface protective film, characterized in that a surface protective film is applied. 2. An ethylene polymer having a melting point of at least 125 ° C. and a melt flow rate at 190 ° C. of 0.00
The surface protective film according to claim 1, wherein the weight is 5 to 0.1 g / 10 min. 3. The frost height is 5 to 30 times the die diameter,
In addition, by an inflation method with a draft ratio of 3 to 150, the ethylene polymer is cooled to a frost height of 30 to 80.
Blow-up diameter up to a height in the range of ± 20%
3. The surface protection according to claim 1 or 2, wherein the film is formed by raising the film in a range of 2 to 7, and then forming a film by expanding the blow-up ratio to 2 to 7, and applying an adhesive to one surface of the obtained substrate. Film production method.