JPH0860112A - Surface-protective film - Google Patents

Abstract

PURPOSE: To provide a surface-protective film which is suitable for a metal plate to be bent such as a stainless steel plate of thicker than 1mm thickness. CONSTITUTION: This surface-protective film is produced by forming an adhesive layer on one face of the substrate of a polyolefin resin which is prepared by orienting, at 70-150 deg.C at a draw ratio of 1.2-5, a polyolefin resin film containing more than 50wt.% of an ethylene-α-olefin copolymer having 30-55% crystallinity, 0.894-0.918g/m<3> density and less than 3g/10min. melt flow rate, or on a substrate film of a polyolefin containing more than 50wt.% of ethylene-α-olefin copolymer having less than 120kg/cm<2> tensile yield strength in both film-forming and the traverse direction or no yield point, and higher than 300kg/cm<2> tensile strength at break and 0.7-1.3 ratio of tensile strength at break in the film-forming direction/in the traverse direction (lengthwise/widthwise) and more than 70% elongation recovery.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a surface protective film. More specifically, it is mainly used to temporarily adhere to the surface of a metal plate that is bent by bending, such as a stainless steel plate having a thickness of 1 mm or more, and to protect the surface so that dust is not attached or scratched. Surface protection film.

[0002]

2. Description of the Related Art Conventionally, as a surface protective film for a metal plate which is subjected to various kinds of processing, one having a plasticized vinyl chloride resin as a base material has been widely used. Further, as a material suitable for drawing, a surface protective film using a linear low density polyethylene (LLDPE) made of an ethylene-α-olefin copolymer as a base material is disclosed in JP-A-53-21239 and Japanese Patent Publication No. No. 14265, etc., the force applied to the surface protective film at the time of processing is different. Even if the cold work followability and stress relaxation property at the time of drawing are good, when bender bending is performed. As a surface protection film for a metal plate which is broken and bender-bent, it cannot be used.

In addition, a collection of papers by Hitachi Chemical (10
(Month issue, Nakao et al.) Proposed that a surface protective film for a metal plate to be bent is preferably a substrate having a large tensile fracture strength when the substrate is made of a polyolefin resin. Has been done. However, in the case of a base material made of a polyolefin-based resin having a large tensile fracture strength, there is no problem in light bending, but in strong bending, the processed metal plate cannot follow and breaks. In the case of a base material made of a polyolefin resin, it is sufficient if there is one having a high tensile fracture strength and no yield point, but in general, one having a large tensile fracture strength has a yield point. Then, further, the vertical and horizontal balance of film strength is lost due to flow orientation during film formation,
Cutting occurs in the weak direction. Moreover, this tendency becomes greater as the tensile strength at break becomes higher, and as a result, the breakage during bending is not improved.

Further, since the surface protective film based on the plasticized vinyl chloride resin is superior in stress relaxation property to the conventional surface protective film based on the above-mentioned polyolefin resin, it can be bent. It is hard to break and is widely used, but it has a problem of waste treatment such as generating harmful hydrogen chloride when incinerated. In addition, the surface protection film based on plasticized vinyl chloride resin has a thickness of 2
It is not able to cope with breakage during bending of stainless steel sheets of mm or more.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention As a result of intensive investigations by the present inventors, a surface protective film using a polyolefin resin as a base material capable of preventing breakage occurring during bending is found to have good stress relaxation properties. The strength characteristics required for drawing such as low strength during stretching and stretching are not necessary so much, and since a film with a high elongation recovery rate or a high tear resistance is difficult to cut, it is generally used as a protected object. It has been said that it cannot be used because the punching property and cutting property in the pasted state will be low, but the protective film is cut together with the protected object, so the protected object is thick like a stainless steel plate of 1 mm or more. In the case of a metal plate, its yield strength is much smaller than that of the surface protection film, and the rubber-like properties of the above surface protection film almost affect the function of the surface protection film. To obtain knowledge of such that there is no example, it is to have completed the present invention.

[0006]

The present invention according to claim 1 has a crystallinity of 20 to 50% and a density of 0.894 to 0.
918 g / cm ³ , melt flow rate (MFR) 3
A pressure-sensitive adhesive layer is provided on one surface of a base material made of a polyolefin-based resin containing 50% by weight or more of an ethylene-α-olefin copolymer obtained by copolymerizing an α-olefin, the adhesive layer being g / 10 min or less. The gist of the invention is a surface protection film characterized by being The present invention according to claim 2 has a tensile yield strength of 120 kg / cm ² or less in the film forming direction and a direction perpendicular thereto or has no yield point, and a tensile fracture strength of 300 kg / cm ² or more. The ethylene according to claim 1, wherein the ratio of the values of the tensile fracture strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3, and the elongation recovery rate is 70% or more. −
The gist of a surface protective film is that a pressure-sensitive adhesive layer is provided on one surface of a base material made of a polyolefin resin containing 50% by weight or more of an α-olefin copolymer.

The ethylene-α-olefin copolymer used in the present invention according to claims 1 and 2 has a crystallinity of 20.
˜50%, density 0.894-0.918 g / cm ³ ,
It has a melt flow rate (MFR) of 3 g / 10 min or less and is obtained by copolymerizing an α-olefin, or has strength properties in a state of being independently formed into a film in a film forming direction and Tensile yield strength in the vertical direction is 12
0 kg / cm ² or less or has no yield point,
Moreover, the tensile breaking strength is 300 kg / cm ² or more, the ratio of the values of the tensile breaking strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3, and the elongation recovery rate is 70. It indicates a value that is at least%.

When the crystallinity of the ethylene-α-olefin copolymer exceeds 50%, the strength at the initial stage of tensile elongation,
The so-called tensile yield strength increases, but the strength balance is lost because strength anisotropy occurs in the film obtained under the film forming conditions. Further, in this state, the plastic deformation is accompanied and the elasticity is reduced. When a thick metal plate is bent using such a surface protection film, there is no elastic recovery when the film is compressed at the die shoulder, and the film is stretched in the compressed state. Breakage is likely to occur. On the other hand, if the crystallinity is less than 20%, the strength of the film at low elongation decreases, the film tends to stretch in each processing / working process, and adhesion with the protected metal plate such as floating or peeling occurs. Sex matters.

The density of the ethylene-α-olefin copolymer has the same tendency, and the density is 0.918 g.
If it exceeds / cm ³ , the strength at the initial stage of tensile elongation, so-called tensile yield strength, increases, but the anisotropy of strength occurs in the film obtained under the film forming conditions, and the strength balance is lost. Further, in this state, the plastic deformation is accompanied and the elasticity is reduced. When a thick metal plate is bent using such a surface protection film, there is no elastic recovery when the film is compressed at the die shoulder, and the film is stretched in the compressed state. Breakage is likely to occur.
On the other hand, if the density is less than 0.894 g / cm ³ , the strength of the film at low elongation decreases, and the film tends to expand in each processing / working step, and the metal plate to be protected from floating, peeling, etc. Adhesion with is a problem. Further, it is extremely difficult to find suitable working conditions even in the film forming process using such raw materials.

When the MFR of the ethylene-α-olefin copolymer is 3 g / 10 min or more, the pressing pressure for forming the final processing angle during bending is
Since it does not have sufficient strength, the cut resistance decreases.

The surface protective film obtained by the present invention according to claim 1 has a tensile breaking strength of 300 kg / cm ² or more when formed into a film having a thickness of 100 μm by the T-die method, and The material is stretched 100% at a pulling speed of 200 mm / min, then immediately released, the length after 5 minutes is measured, and the value obtained by subtracting the length from twice the length before stretching is stretched. It is necessary that the percentage of the value obtained by dividing by the previous length is the extension recovery rate, and this extension recovery rate is 70% or more. This is because plastic deformation does not occur when pressure is applied to the shoulder part of the die during bender bending, and
This is because by promptly recovering the shape when the pressed portion is released, it is possible to prevent breakage when the film is stretched in the direction perpendicular to the bending ridgeline during the bending process of the protected body.

Further, the tensile yield strength is similar to the above-mentioned elongation recovery rate, and when the tensile yield strength is large, during bending,
The plastic deformation in the shoulder portion of the die becomes large, and breakage easily occurs.

Further, due to the presence of the α-olefin which is a constituent of the ethylene-α-olefin copolymer, the surface protective film of the present invention according to claims 1 and 2 is less likely to undergo plastic deformation, and therefore, The yield point becomes unclear,
Since the aspect ratio of the film approaches 1 and the strength of the base material is extremely high, the normal surface protection function is to use a base material made of commonly used plasticized vinyl chloride resin, polyethylene or other resin. It has performance equivalent to or better than the surface protection film used, and in particular, has high quality that cannot be achieved by conventional commercial products in terms of scratch resistance and breakage resistance in bending, etc. It is a thing.

Examples of the α-olefin include 1-pentene and 1-hexene. In addition, the above ethylene
As the α-olefin copolymer, VLLDPE or the like can be preferably used as a commercially available product.

Further, the base material used in the present invention according to claims 1 and 2 contains 50% by weight or more of the ethylene-α-olefin copolymer, and the final strength characteristics are as follows.
It is possible to satisfy the tensile fracture strength against breaking during bending, the aspect ratio of the tensile fracture strength, the tensile yield strength, and the elongation recovery rate.

Further, since the base material used in the present invention according to claims 1 and 2 contains 50% by weight or more of the ethylene-α-olefin copolymer, strength characteristics as described above are obtained. In addition to being improved, the substrate is heated to a temperature not lower than the boiling point of the solvent used in the coating step of coating and drying the solvent-based pressure-sensitive adhesive. Orientation changes, tensile fracture strength, etc. decrease, and moreover, usually, since drying is performed under constant tension, the film is stretched in the machine direction, and tensile fracture strength before coating, etc. Although the aspect ratio is increased, this problem does not occur in the present invention.

Further, the base material used in the present invention according to claims 1 and 2 is obtained by blending the ethylene-α-olefin copolymer with a polyolefin resin in the above composition. The resin is not particularly limited as long as it is compatible with the ethylene-α-olefin copolymer, and examples thereof include low density polyethylene, medium density polyethylene, high density polyethylene,
Linear low density polyethylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene- Examples thereof include n-butyl acrylate copolymer and polypropylene (homopolymer, random copolymer, block copolymer). It is also possible to use mixtures of any of the above.

Various thicknesses of the substrate are used depending on the intended use of the surface protective film, and when the thickness of the metal plate to be protected is 1 to 2 mm, it is preferably 50 to 200 μm, more preferably Those having a thickness of 70 to 130 μm are used.

The pressure-sensitive adhesive used in the present invention may be any pressure-sensitive adhesive as long as it can fulfill the function as a surface protective film.
An acrylic adhesive or the like can be used.

In the present invention, the method for laminating the pressure-sensitive adhesive layer on the substrate is not particularly limited, but preferably, the adhesive layer should have a sufficient tensile fracture strength, like the substrate.
Although it is possible to make such a design with an acrylic type, it is possible to produce by coextrusion molding, for example, styrene-isoprene-styrene block copolymer (SI
S), styrene / butadiene / styrene block copolymer (SBS), styrene / ethylene / propylene / styrene block copolymer (SEPS), styrene / ethylene / butylene / styrene block copolymer (SEB)
S), styrene-isoprene block copolymer [(S
I) _n ], ethylene / propylene block copolymer [(EP) _n ], and the like, if a thermoplastic elastomer having a large tensile fracture strength is used, the cut resistance can be further enhanced. In addition, the method by coextrusion molding is a preferable method because the manufacturing apparatus and the manufacturing process are simple, the lamination strength is high, and the manufacturing efficiency is good.

Further, on the surface of the base material opposite to the side on which the above-mentioned pressure-sensitive adhesive layer is provided, a release agent such as a silicone-based material or a material mainly composed of a long-chain alkyl group adduct of polyethyleneimine is used. A coating film is provided to further reduce the affinity with the back surface. In addition, it is possible to use a variety of functional additives, such as a base material or a pressure-sensitive adhesive layer, or both, by blending a release agent and other additives to improve the slipperiness of the surface. This is possible without departing from the spirit of the present invention.

As mentioned above, since the surface protective film of the present invention according to claims 1 and 2 contains 50% by weight or more of the ethylene-α-olefin copolymer,
For example, when the plate thickness to be processed is thin or even a slight bending process may be of excessive quality, it can be practically used without any problem.

[0023]

The ethylene used in the present invention according to claim 1
The α-olefin copolymer has a crystallinity of 20 to 50%,
The density is 0.894 to 0.918 g / cm ³ , the melt flow rate (MFR) is 3 g / 10 min or less,
It is obtained by copolymerizing α-olefin, and since the ethylene-α-olefin copolymer is blended in the base material in an amount of 50% by weight or more, the difference in strength between the vertical and horizontal directions of the surface protective film is significantly reduced. , Showing relatively homogeneous performance in each direction,
Due to the presence of α-olefin NO, which is a constituent of the ethylene-α-olefin copolymer, the surface protection film of the present invention according to claims 1 and 2 is less likely to undergo plastic deformation, and thus the yield point is unclear. Since the aspect ratio of the film approaches 1 and the substrate design is extremely high in terms of strength, the usual surface protection function is based on the commonly used plasticized vinyl chloride resin, polyethylene and other resins. It has the same or higher performance as the surface protection film using the material, and especially, with regard to scratch resistance and breakage prevention in high-strength bending, it is a high quality that conventional commercial products cannot reach. Is to have.

The ethylene-α-olefin copolymer used in the present invention according to claim 2 has strength properties in the state of being formed into a film by itself, and the tensile yield strength in the film forming direction and the direction perpendicular thereto. Is 120 kg / cm ² or less, or has no yield point, and has a tensile fracture strength of 300 kg.
/ Cm ² or more, the ratio of the values of the tensile fracture strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3,
Since the elongation recovery rate shows a value of 70% or more, the strength difference between the longitudinal and lateral directions of the surface protection film is greatly alleviated, the performance is relatively uniform in each direction, and the tensile yield strength is 120 kg. / Cm ² or less or does not have a yield point, which promotes the above-mentioned characteristics derived from the structure of the α-olefin.

Further, the tensile breaking strength is 300 kg / cm ² or more, the ratio of the values of the tensile breaking strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3, and elongation recovery Since the modulus of elasticity is 70% or more, it is possible to obtain a thick metal by maintaining the tensile fracture strength required in the bending process of strength and the required elongation and deformation recovery expressed by the deformation recovery rate. As seen in a practical test of bending of a plate, it is possible to impart unbroken performance which cannot be achieved by a conventional surface protection film using a polyolefin resin as a base material.

Further, since the surface protective film of the present invention according to claims 1 and 2 does not use a base material made of a plasticized vinyl chloride resin, the temperature dependence of the base material is small and the influence of the ambient temperature is relatively small. Even in the process of processing metal plates, which are susceptible to problems, it is difficult for problems during processing, especially the breakage of the surface protection film to occur. Further, for the above-mentioned reason, it is not necessary to change the type and blending amount of the raw material of the base material of the surface protective film depending on the season, and it is possible to produce the product very easily from the viewpoint of production control.

Further, the surface protective film of the present invention according to claims 1 and 2 is as light as about 40% in terms of specific gravity difference as compared with the surface protective film using a substrate made of a plasticized vinyl chloride resin. Widening and lengthening, which is a limitation of weight, are easy to carry out, and the design of the surface protection film feeding device is also easy. This greatly contributes to the rationalization of work and cost reduction. Further, since the surface protection film of the present invention according to claims 1 and 2 does not use a substrate made of a plasticized vinyl chloride resin, the problem of waste treatment is reduced.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, the tensile fracture strength, the tensile yield strength, the elongation recovery rate, and the bending bending practical test for thick plates were measured and evaluated by the methods described below.

1. Tensile fracture strength, tensile yield strength Measured according to JIS K7127 (Plastic film and sheet tensile test method). For the test piece, the surface protection film was formed in two directions, the film forming direction and the direction perpendicular to it, with a width of 10 mm, and when the tensile strength was 200 mm / min, the distance between the marked lines (grabbing interval) was 40 mm and the tensile strength was 200 mm / min. And the strength at break were measured.

2. Elongation recovery rate As the test piece, the width of the surface protective film in the film forming direction and the direction perpendicular to the surface protective film were respectively set to 10 mm, and the distance between the marked lines (grabbing interval) was 100 mm and the pulling speed was 200 mm /
Tensile force was released at the time of pulling for 100 minutes and elongation of 100 mm, the distance between marked lines was measured after 5 minutes, and the elongation recovery rate was calculated by the following formula.

Elongation recovery rate (%) = [(mark distance before elongation) × 2- (mark distance after 5 minutes)] × 100 /
(Distance between marked lines before extension)

3. Practical bending test (cut) 1.5 mm thick stainless steel plate (SUS304HL)
Attach each surface protection film to the, and use a bender bending machine to use a die with a width of 12 mm, and the descending speed is 8 m / mi.
Bending was performed so that the finish was 90 °, and the presence or absence of breakage of the surface protection film after processing, and the extent of breakage were visually evaluated in three grades of ◯, Δ, and ×. Graceful, ○: No breakage occurred, △: Partial breakage occurred, ×: Breakage occurred on the entire surface.

Example 1 A linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L, density: 0.910 g / cm ³ , MF) was used as a base material layer.
R: 2.0 g / 10 min, crystallinity: 25%) was formed into a film having a thickness of 100 μm by an inflation method, one surface of which was subjected to corona discharge treatment, and an adhesive (manufactured by Soken Kagaku Co., Ltd., trade name) on the treated surface. : AG105) was applied so that the pressure-sensitive adhesive layer after drying had a thickness of 10 μm, and dried to obtain a surface protective film. The performance of the obtained surface protection film is shown in Table 1. However, the linear low-density polyethylene of the copolymer satisfying claim 1 has a density of 0.910 g / cm ^3.
And the content of the ethylene-α-olefin copolymer was 50% by weight or more.

(Example 2) As a base material layer, a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L) (70 parts by weight) and a polyolefin resin consisting of ethylene-propylene (manufactured by Highmont Co., Ltd. Name:
NKS-021P, density: 0.89 g / cm ³ , MF
A surface protective film was obtained in the same manner as in Example 1 except that a mixture of 30 parts by weight of R: 0.8 g / 10 min, crystallinity: 25%) was used. However, the density of the polyethylene of the copolymer satisfying claim 1 is 0.910 g / cm ^3.
And the content of the ethylene-α-olefin copolymer was 50% by weight or more. The performance of the obtained surface protection film is shown in Table 1.

(Example 3) As a base material layer, 70 parts by weight of a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L) and a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., Product Name: Ultzex 352
0 L, density: 0.935 g / cm ³ , MFR: 2.1 g
/ 10 min) A surface protective film was obtained in the same manner as in Example 1 except that a mixture of 30 parts by weight was used. However, the density of the polyethylene of the copolymer satisfying claim 1 was 0.910 g / cm ³ and the content of the ethylene-α-olefin copolymer was 50% by weight or more. The performance of the obtained surface protection film is shown in Table 1.

(Example 4) As a base material layer, 70 parts by weight of linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L) and low-density polyethylene (manufactured by Mitsubishi Petrochemical Co., Ltd., trade name: A surface protective film was obtained in the same manner as in Example 1 except that 30 parts by weight of LK30) was mixed. However, the density of the polyethylene of the copolymer satisfying claim 1 was 0.910 g / cm ³ and the content of the ethylene-α-olefin copolymer was 50% by weight or more. The performance of the obtained surface protection film is shown in Table 1.

(Example 5) As a base material layer, 60 parts by weight of linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L) and linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., Product Name: Ultzex 352
A surface protective film was obtained in the same manner as in Example 1 except that 40 parts by weight of 0 L) was mixed. The density of the polyethylene of the copolymer satisfying claim 1 is 0.91.
It was 0 g / cm ³ , and the content of the ethylene-α-olefin copolymer was 50% by weight or more. The performance of the obtained surface protection film is shown in Table 1. (Example 6) As a base material layer, linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: ULTOZEX 1520)
L, density: 0.910 g / cm ³ , MFR: 2.0 g /
10 min. Crystallinity: 25%) 70 parts by weight and linear low density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 3520L) were used in the same manner as in Example 1 except that a mixture of 30 parts by weight was used. A protective film was obtained.
However, the density of the polyethylene of the copolymer satisfying claim 1 was 0.910 g / cm ³ and the content of the ethylene-α-olefin copolymer was 50% by weight or more.
The performance of the obtained surface protection film is shown in Table 1.

(Comparative Example 1) A surface protective film was obtained in the same manner as in Example 1 except that linear low density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 3520L) was used as the base material layer. . However, the polyethylene has a density of 0.93 g / cm ³ and contains no ethylene-α-olefin copolymer. The performance of the obtained surface protection film is shown in Table 1.

(Comparative Example 2) As a base material layer, 30 parts by weight of linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 1020L) and linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., Product Name: Ultzex 352
A surface protective film was obtained in the same manner as in Example 1 except that a mixture of 70 parts by weight of 0 L) was used. The density of the polyethylene composition was 0.910 g / cm ³ , and the content of the ethylene-α-olefin copolymer was 30% by weight or less. The performance of the obtained surface protection film is shown in Table 1.

(Comparative Example 3) As a base material layer, a linear ultra low density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Toughmer A4085, density: 0.88 g / cm ³ , MFR: 3.
6 g / 10 min. ) 70 parts by weight and linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: ULTOZEX 3
(520 L) A surface protective film was obtained in the same manner as in Example 1 except that a mixture of 30 parts by weight was used. However, the polyethylene has a density of 0.93 g / cm ³ and contains no ethylene-α-olefin copolymer. The performance of the obtained surface protection film is shown in Table 1.

[0041]

[Table 1] The surface protection film of Comparative Example 1 has a high density, a large aspect ratio of the film, and a small tensile breaking strength (horizontal), so that breakage occurs. The surface protection film of Comparative Example 2 has a large aspect ratio of the film because the content of the ethylene-α-olefin copolymer is small, and the tensile fracture strength (horizontal) is small, so that breakage occurs. Since the surface protection film of Comparative Example 3 uses polyethylene having a low density and a low tensile fracture strength, breakage occurs.

[0042]

The ethylene-α-olefin copolymer used in the present invention according to claim 1 has a crystallinity of 20-5.
0%, the density is 0.894 to 0.918 g / cm ³ , the melt flow rate (MFR) is 3 g / 10 min or less, and the side chain has 3 to 9 carbon atoms, and is formed by copolymerizing α-olefin. Since the ethylene-α-olefin copolymer is blended in the base material in an amount of 50% by weight or more, the strength difference between the length and the width of the surface protection film is significantly reduced, and the performance is relatively uniform in each direction. And the presence of the α-olefin which is a constituent of the ethylene-α-olefin copolymer makes the surface protective film of the present invention according to claims 1 and 2 less likely to undergo plastic deformation, and thus yield point Becomes unclear, and the aspect ratio of the film approaches 1 so that the substrate design is extremely high in strength, so the usual surface protection function is to use commonly used plasticized vinyl chloride resin, polyethylene resin, etc. From It has the same or higher performance as a surface protection film that uses a base material that cannot be achieved by conventional commercial products with regard to scratch resistance and breakage resistance, especially during high-strength bending. It has high quality.

The ethylene-α-olefin copolymer used in the present invention according to claim 2 has strength properties in the state of being formed into a film by itself, and the tensile yield strength in the film forming direction and the direction perpendicular thereto. Is 120 kg / cm ² or less, or has no yield point, and has a tensile fracture strength of 300 kg.
/ Cm ² or more, the ratio of the values of the tensile fracture strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3,
Since the elongation recovery rate shows a value of 70% or more, the strength difference between the longitudinal and lateral directions of the surface protection film is greatly alleviated, the performance is relatively uniform in each direction, and the tensile yield strength is 120 kg. / Cm ² or less or does not have a yield point, which promotes the above-mentioned characteristics derived from the structure of the α-olefin.

Further, the tensile breaking strength is 300 kg / cm ² or more, the ratio of the values of the tensile breaking strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3, and elongation recovery Since the modulus of elasticity is 70% or more, it is possible to obtain a thick metal by maintaining the tensile fracture strength required in the bending process of strength and the required elongation and deformation recovery expressed by the deformation recovery rate. As seen in a practical test of bending of a plate, it is possible to impart unbroken performance which cannot be achieved by a conventional surface protection film using a polyolefin resin as a base material.

Further, since the surface protective film of the present invention according to claims 1 and 2 does not use a base material made of a plasticized vinyl chloride resin, the temperature dependence of the base material is small and the influence of the ambient temperature is relatively small. Even in the process of processing metal plates, which are susceptible to problems, it is difficult for problems during processing, especially the breakage of the surface protection film to occur. Further, for the above-mentioned reason, it is not necessary to change the type and blending amount of the raw material of the base material of the surface protective film depending on the season, and it is possible to produce the product very easily from the viewpoint of production control.

Further, the surface protective film of the present invention according to claims 1 and 2 is about 40% lighter in difference in specific gravity than a surface protective film using a substrate made of a plasticized vinyl chloride resin. It is possible to make the width and length of which are limited by weight, to facilitate the designing of the surface protective film feeding device, and to greatly contribute to the rationalization of work and cost reduction.
Further, since the surface protection film of the present invention according to claims 1 and 2 does not use a substrate made of a plasticized vinyl chloride resin, the problem of waste treatment is reduced.

Claims (2)

[Claims] 1. A crystallinity of 20 to 50% and a density of 0.8.
94 to 0.918 g / cm ³ , melt flow rate (M
FR) is 3 g / 10 min or less, and a pressure-sensitive adhesive layer is provided on one surface of a substrate made of a polyolefin resin containing 50% by weight or more of an ethylene-α-olefin copolymer obtained by copolymerizing an α-olefin. A surface protection film characterized by being provided. 2. The tensile yield strength in the film forming direction and the direction perpendicular thereto is 120 kg / cm ² or less or has no yield point, and the tensile breaking strength is 300 kg /
A cm ² or more, the ratio of the values of the tensile fracture strength in the film forming direction and the direction perpendicular thereto (aspect ratio) is 0.7 to 1.3, and the elongation recovery rate is 70% or more. 1. A surface protective film, wherein a pressure-sensitive adhesive layer is provided on one surface of a substrate made of a polyolefin resin containing 50% by weight or more of the ethylene-α-olefin copolymer described in 1.