JP2009114407A - Surface-protecting film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-protecting film formed in a wound body, etc., for example, capable of readily releasing an adhesive layer from the rear of a substrate layer even when the substrate layer is bonded to the rear of the substrate layer and capable of readily rewinding the wound body, by a simple technique to adopt a specific substrate layer structure. <P>SOLUTION: A surface layer which is obtained with the co-extrusion technique with the main component of a polyethylene resin and with the tensile modulus of 400 MPa or more of elasticity and an inner layer made of a polyolefin resin are made a base material layer. Adhesive layers made of an adhesive composition with the main component of a rubber resin component are laminated. The surface-protecting film has the tensile modulus of 550 MPa or more of elasticity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface protective film, and more particularly to a surface protective film used for preventing dust from adhering to the surface of the adherend and damage to the surface of the adherend.

  Conventionally, surface protective films have been used to protect articles and members. The surface protective film is, for example, a variety of adherends such as synthetic resin plates, decorative plywood, painted steel plates, copper plates, stainless steel plates, etc. Used to prevent scratches. This type of surface protective film has a structure in which an adhesive layer is laminated on a base material layer.

  Generally, the surface protective film is industrially manufactured as a wound body obtained by winding a long film in a roll shape, for example. In the surface protective film as such a wound body, when the wound body is unfolded, the outer surface protective film can be easily peeled off from the inner surface protective film, that is, the wound body is unwound. There is a strong demand for being easy.

On the other hand, the method of using polyethylene and random polypropylene for a base material layer is proposed (for example, patent document 1).
In this patent document 1, as the surface layer of the base material layer, polyethylene having a low adhesive strength to the pressure-sensitive adhesive layer is used, and since the film strength is weak only with polyethylene and the base material layer is elongated, by using polypropylene as the inner layer, The elongation of the base material layer is suppressed.

Also, a method of laminating a base material layer made of polyethylene having a polyorganosiloxane as a graft chain and an adhesive layer by a melt coextrusion method (for example, Patent Document 2), a base material layer made of a polyolefin resin and an adhesive After laminating the layers, a method of rubbing the back surface of the base material layer (opposite surface of the base material layer with respect to the pressure-sensitive adhesive layer stacking side) (for example, Patent Document 3), a base material layer containing a polyolefin resin, A method is proposed in which a release layer made of a release agent is formed on the back surface of a base material layer by a coating method after laminating a pressure-sensitive adhesive layer containing a thermoplastic elastomer (for example, Patent Document 4).
JP 2001-302995 A JP-A-2-252777 Japanese Patent Laid-Open No. 2-252782 JP 2003-41216 A

However, as in Patent Document 1, even if polyethylene and random polypropylene are combined, a sufficient effect cannot be obtained, and it has been difficult to make rewinding easier with only a combination of materials.
In addition, adding a step such as forming a release layer after extrusion causes a decrease in the adhesive force with time due to the mutual migration of unreacted components in each layer, and further improvements are required. Yes.

  In view of the current state of the prior art described above, the object of the present invention is to remove the adhesive layer from the back surface of the base material layer even if the adhesive layer adheres to the back surface of the base material layer by a simple method of adopting the type and physical properties of the material. It is an object of the present invention to provide a surface protective film that can easily peel off the pressure-sensitive adhesive layer and can unfold the wound body without difficulty.

  As a result of intensive studies on the above problems and the existing surface protective film, the present inventors have found that the conventional surface protective film is a surface protective film on the inner side of the winding, particularly when stored and transported as a wound body. The pressure-sensitive adhesive layer of the outer surface protective film strongly adheres to the back surface of the base material layer, and when the wound body is developed, the pressure-sensitive adhesive layer of the outer surface protective film becomes the base material of the inner surface protective film. It was found that the base material layer was deformed by not easily peeling from the back surface of the layer, and the pressure-sensitive adhesive layer was forcibly peeled from the back surface of the base material layer, and energy was consumed for this deformation.

  Therefore, in order to prevent deformation of the base material layer, a release agent such as a long-chain fatty acid modified product or silicone is applied to the back surface of the base material layer to make it difficult to stick the adhesive layer to the back surface of the base material layer. Thus, a method for easily developing the wound body has been studied, but in this method, additional steps such as application of a release agent and drying are unavoidable. Moreover, in order to reinforce the anchoring property between the back surface of the base material layer and the release agent, it is necessary to surface-treat the back surface of the base material layer.

  In contrast, a pressure-sensitive adhesive composition having a surface layer and an inner layer having a specific component as a base material layer, the base material layer being set to a specific tensile elastic modulus, and a specific rubber-based resin component as a main component By laminating the pressure-sensitive adhesive layer made of the above, it was found that a surface protective film capable of easily developing the wound body can be obtained without performing an additional step such as application of a release agent, and the present invention was completed. It came to.

That is, the surface protective film of the present invention is a surface protective film in which a base material layer and an adhesive layer are formed by coextrusion,
The base material layer is composed of a surface layer and an inner layer, and has a tensile elastic modulus of 550 MPa or more,
The surface layer contains a polyethylene resin and has a tensile modulus of 400 MPa or more,
The inner layer contains a polyolefin resin, and the pressure-sensitive adhesive layer is laminated on one surface thereof.
The pressure-sensitive adhesive layer is made of a pressure-sensitive adhesive composition containing a rubber-based resin component as a main component.
In such a surface protective film, the polyethylene resin of the surface layer is preferably a high density polyethylene resin.
The inner layer is preferably formed of a mixture of a polyolefin resin and a recycled product of the surface protective film.
Furthermore, the rubber-based resin component of the adhesive layer is
(1) a block copolymer of a styrene-based polymer block and an olefin-based or conjugated diene-based polymer block;
(2) A block copolymer of a styrene polymer block and a random copolymer block of a styrene monomer and an olefin monomer or a conjugated diene monomer, and / or (3) These hydrogenated products are used as a main skeleton. A styrene-based elastomer is preferable.

According to the surface protective film of this invention, even if the adhesive layer of a surface protective film adheres to the back surface of a base material layer, the adhesive material layer can be easily peeled from the back surface of a base material layer.
In addition, for example, when the surface protection film is a wound body and the wound body is developed, the deformation of the surface layer of the base material layer, in addition to further deformation of the inner layer, Adhesiveness can be reduced and energy consumed for deformation can be reduced. As a result, the peelability of the wound body can be improved and deployed without difficulty.
Furthermore, by using a rubber-based resin component as a main component, a high-throughput production process by co-extrusion with a base material layer can be adopted, and a strong adhesion design can be achieved. In addition, the surface of the adherend having irregularities can be satisfactorily adhered, and a surface protective film that can be applied over a wide range can be obtained.

The surface protective film of this invention is comprised from the base material layer containing a surface layer and an inner layer, and an adhesive layer.
The surface layer is formed containing a polyethylene resin. The polyethylene resin has poor adhesion to the pressure-sensitive adhesive as compared to other polyolefin resins. Therefore, it is preferable to add as much polyethylene resin as possible to the surface layer, particularly to the back surface of the surface layer (the surface on the side opposite to where the adhesive layer is formed). Thereby, the peelability of the adhered surface protective film is further enhanced, and the wound body can be more easily deployed.

  Examples of the polyethylene resin include ethylene polymers such as low density, high density, and linear low density polyethylene. These polyethylene resins may be used alone or in combination of two or more. Among these, high density polyethylene is preferable. High-density polyethylene has higher crystallinity than other polyethylenes and has low adhesion to pressure-sensitive adhesives. Furthermore, it has a high tensile modulus and is difficult to deform. Therefore, by using high-density polyethylene, the surface protective film adhered to the back surface of the base material layer can be more easily peeled off, and the developing force of the wound body can be further reduced.

The surface layer may contain other polyolefins in addition to the polyethylene resin. The polyolefin is not particularly limited as long as it has a high tensile elastic modulus and can be added to a polyethylene resin to obtain a desired tensile elastic modulus. For example, a propylene polymer such as polypropylene or a propylene component and an ethylene component, such as a block or random polymer; an olefin polymer such as an ethylene-α-olefin copolymer or propylene-α-olefin copolymer; ethylene-vinyl acetate Olefin-based polymer of ethylene component and other monomers such as copolymer, ethylene-methyl methacrylate copolymer; propylene-vinyl alcohol copolymer, propylene-ethyl acrylate copolymer, propylene-methyl methacrylate copolymer, etc. And an olefin polymer of a propylene component and other monomers. These may be used alone or in combination of two or more.
In addition, when there are a plurality of resin components constituting the surface layer, the blending amount is not particularly limited, but it is suitable to blend so as to realize the following tensile elastic modulus.

  The surface layer preferably has a tensile modulus of 400 MPa or more, more preferably 500 MPa or more. Thereby, it can suppress that a base material layer deform | transforms and can reduce the energy consumed by the deformation | transformation of a base material layer. Moreover, it becomes possible to adjust the tensile elasticity modulus as a surface protection film to a desired value, and even when the surface protection film of this invention is used as a wound body, a wound body can be expand | deployed without difficulty.

  The surface layer may be subjected to a friction treatment on one surface thereof, that is, a surface different from a surface on which an inner layer described later is disposed. The friction treatment can be performed by a known method such as a method described in JP-A-2-252777 or a method based thereon. Specifically, a friction treatment using a rotating object such as a metal roll or a cloth such as gauze is exemplified. Thereby, the crystallinity degree of the resin surface which comprises a base material layer can be raised, and the expansion | deployment force of a wound body can further be reduced.

The inner layer is configured to contain a polyolefin resin. The polyolefin here includes the same ones as described above. In addition, you may contain the polyethylene resin. In particular, it is preferable to use a resin having a higher tensile elastic modulus than the surface layer. As a result, the tensile elastic modulus of the surface protective film itself can be improved, deformation can be further suppressed, and the deployment force can be further reduced.
For the inner layer, a recycled product of the surface protective film may be added to such an extent that physical properties are not affected. The recycled product may be a collected product of a used surface protection film, or an ear end slit product during production of the surface protection film.
In addition, when there are a plurality of resin components constituting the inner layer, the blending amount is not particularly limited, but blended so that a tensile elastic modulus as a base material layer described later can be realized by lamination with the surface layer described above. It is suitable to be done.
In particular, the recycled product of the surface protective film is suitably about 30% or less, more preferably about 20% or less, based on the total weight of the inner layer. This is because if the content of the recycled product is excessively large, components other than the polyolefin resin are contained in a large amount, and the desired tensile elastic modulus may not be ensured. By using recycled products, production costs can be reduced or production efficiency can be increased. Furthermore, the adhesive strength between the pressure-sensitive adhesive layer and the base material can be increased, and mechanical strength such as tear resistance can be improved.

The base material layer is composed of a surface layer and an inner layer, but the inner layer may not have a single layer structure, and may have a structure in which two or more layers are laminated. The film thickness of the surface layer and the inner layer is not particularly limited and can be appropriately adjusted depending on the material used. For example, the total film thickness of the base material layer is suitably about 5 to 180 μm, more preferably about 10 to 130 μm, about 10 to 100 μm, and about 10 to 80 μm.
The base material layer preferably has a tensile elastic modulus, particularly a tensile elastic modulus of 550 MPa or more, and more preferably 600 MPa or more. Thereby, even when the long surface protective film is wound into a roll shape to form a wound body, when the wound body is unfolded, the base material layer is deformed by the adhesive force of the adhesive layer. The energy consumed by the deformation can be reduced, and the wound body can be deployed without difficulty.

  As materials constituting the surface layer and the inner layer, various additives described later may be contained, but it is particularly preferable to use a crystal nucleating agent. Thereby, a tensile elasticity modulus can be improved more and a deformation | transformation of a base material layer can be suppressed more.

An adhesive layer consists of an adhesive composition which has a rubber-type resin component as a main component.
What is used as a base polymer of adhesives, such as a styrene-type elastomer, a urethane-type elastomer, an acryl-type elastomer, an ester-type elastomer, an olefin-type elastomer, can be especially used as a rubber-type resin component without a restriction | limiting. Among these, when a styrene-based elastomer is used, a surface protective film can be easily formed by coextrusion, and a surface protective film having good temporary adhesion to an adherend can be obtained.

  Specifically, AB- such as styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene-butylene / styrene (SEBS), styrene / ethylene / propylene / styrene (SEPS), etc. A type block polymer: AB type block polymer such as styrene / butadiene (SB), styrene / isoprene (SI), styrene / ethylene-butylene (SEB), styrene / ethylene / propylene (SEP); styrene / butadiene rubber ( SBR) and other styrene random copolymers; ABC type styrene / olefin crystal block polymers such as styrene / ethylene / butylene / olefin crystals (SEBC); olefin crystals / ethylene / butylene / olefin crystals (CEBC) ) Etc. The crystalline olefin based block polymers, ethylene -α-olefin, ethylene - propylene -α-olefin, olefin elastomers propylene -α-olefin such as news, etc. These hydrogenated products thereof. These rubber-based resin components may be used alone or in combination of two or more.

As this rubber-based resin component, it is suitable to use the following styrene-based elastomer (1), (2) or (3).
(1) A styrene elastomer having a main skeleton of a block copolymer of a styrene polymer block (A) and an olefin-based or conjugated diene polymer block polymer block (B). The styrene-based elastomer is not particularly limited as long as the AB block copolymer is a main skeleton. For example, AB, ABA, (AB) _n, or (AB) _n. Examples thereof include a copolymer represented by X or the like. Note that n is an integer of 2 or more, and X is a residue derived from a coupling agent (the same applies hereinafter).

(2) A styrene elastomer having a main copolymer of a block copolymer of a styrene polymer block (A) and a styrene monomer and a random copolymer block (B ′) of an olefin monomer or a conjugated diene monomer. Styrenic monomers and olefinic or conjugated diene monomers here may contain not only monomers but also oligomers (hereinafter the same). Examples of such a styrene-based elastomer include the following (2-1) to (2-4).
(2-1) Block (A) and block (B ′) combined: AB ′ block copolymer,
(2-2) Styrene and olefin-based or conjugated dienes containing taper block (C) in which styrene gradually increases: AB′-C block copolymer (2-3) In place of taper block (C) Including styrene polymer block (A): AB′-A block copolymer (2-4) Repeat of (2-1) to (2-3) and these bonded at an arbitrary ratio _{things: (A-B ') n} , (A-B') n X, (A-B'-C) n X, (A-B'-A) n X or the like.
In addition, n is an integer greater than or equal to 1, and X is a residue by a coupling agent.
(3) A styrene elastomer having the hydrogenated product of (1) or (2) as a main skeleton.

Examples of the olefin used for constituting the olefin polymer block (B) and the random copolymer block (B ′) include ethylene, butylene, isobutylene, and the like, preferably isobutylene. The olefin polymer block (B) is preferably polyisobutylene.
Examples of the conjugated diene used for constituting the conjugated diene copolymer block (B) and the random copolymer block (B ′) include butadiene and isoprene.

  In the styrene elastomer having (2) the styrene elastomer and (3) the hydrogenated product thereof as a main skeleton, all monomers constituting the styrene elastomer are included in the configuration including the random copolymer block (B ′). The total of the styrene monomer-derived component in the block (A) and the styrene monomer-derived component in the random copolymer block (B ′) versus the conjugated diene or olefin monomer-derived component in the composition block (A) is from 5:95 to 5: 95- The range of 60:40 is preferable, and the range of 7:93 to 40:60 is more preferable.

In the styrene elastomer having (2) the styrene elastomer and (3) the hydrogenated product as a main skeleton, the block including the tapered block (C) is a block in the constitution of all monomers constituting the styrene elastomer. The total of the styrene content in (A) and the styrene content in block (C) versus the conjugated diene or olefinic monomer-derived component is preferably in the range of 3:97 to 50:50, more preferably 5: It is 95-40: 60, More preferably, it is the range of 5: 95-25: 75.
If the total content of the components derived from the styrenic monomer of the block (A) and the block (B ′) or the block (C) is too small, the cohesive force of the pressure-sensitive adhesive layer is lowered and the surface protective film is peeled off from the adherend. When doing so, adhesive residue may be generated on the adherend, and if it is too much, the adhesive force of the pressure-sensitive adhesive layer is insufficient, and sticking to the adherend may be difficult.

  When the rubber-based resin component has an unsaturated double bond derived from a conjugated diene, the unsaturated double bond is preferably as small as possible from the viewpoint of improving heat resistance and weather resistance, and hydrogenated as necessary. It is preferable. In this sense, a rubber-based resin component using isobutylene that does not have an unsaturated bond after completion of addition polymerization as a monomer is preferably used.

  Random copolymerization of styrene monomer and conjugated diene monomer in the conjugated diene polymer block in the styrene elastomer of (3) having the hydrogenated product of styrene elastomer of (1) and (2) as the main skeleton. It is preferred that at least 80% of the double bonds of the conjugated diene moiety in the combined block or tapered block are saturated by hydrogenation. A more preferable ratio of hydrogenation is 90% or more, and further preferably 95 to 100%. This is to ensure heat resistance and weather resistance.

  By using such a styrene-based elastomer, deformation of the base material layer can be suppressed when the wound body is deployed, and the deployment force can be further reduced. Furthermore, it is possible to obtain a surface protective film that can be favorably temporarily attached to the adherend surface and can be easily peeled off from the adherend surface.

  The weight average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography) of the styrene elastomer is preferably in the range of 30,000 to 400,000, more preferably in the range of 50,000 to 200,000. When the weight average molecular weight is too small, the cohesive force of the pressure-sensitive adhesive layer is lowered, and therefore, an adhesive residue may be generated on the adherend when the surface protective film is peeled off. When the weight average molecular weight is too large, the adhesive strength is insufficient, and troubles such as an increase in solution viscosity and melt viscosity may occur during the preparation of the pressure-sensitive adhesive composition and the production of the surface protective film.

  The pressure-sensitive adhesive composition contains a rubber-based resin component as a main component, but the rubber-based resin component in 100% by weight of the pressure-sensitive adhesive composition is preferably contained in a proportion of 50 to 100% by weight.

  In addition to the rubber-based resin component, the pressure-sensitive adhesive composition includes, for example, a tackifier, a softener, an olefin resin, a silicone polymer, a liquid acrylic copolymer, for the purpose of controlling the adhesive force. Known additives such as coalescence, phosphate ester compounds, anti-aging agents, hindered amine light stabilizers, UV absorbers, fillers (eg, calcium oxide, magnesium oxide, silica, zinc oxide, titanium oxide), pigments, etc. Can be blended appropriately.

  Among additives, the addition of a tackifier is effective for improving the adhesive strength of the pressure-sensitive adhesive layer. Examples of the tackifier include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic / aromatic copolymer systems and alicyclic copolymers, coumarone-indene resins, Terpenic resins, terpene phenolic resins, rosin resins such as polymerized rosin, (alkyl) phenolic resins, xylene resins or hydrogenated products such as those generally used for adhesives are particularly limited It can be used without. These tackifiers may be used alone or in combination of two or more. In addition, you may use the tackifier marketed as a blend with an olefin resin.

  When the pressure-sensitive adhesive composition contains a tackifier, the blending amount is not particularly limited, but the rubber-based resin component can appropriately increase the pressure-sensitive adhesive force while suppressing the occurrence of adhesive residue due to a decrease in cohesive strength. The tackifier is preferably 80 parts by weight or less, more preferably 60 parts by weight or less, and still more preferably 50 parts by weight or less with respect to 100 parts by weight.

  Of the additives, the addition of a softening agent is effective for improving the adhesive strength. Examples of the softening agent include low molecular weight diene polymers, polyisobutylene, hydrogenated polyisoprene, hydrogenated polybutadiene, and derivatives thereof. As said derivative | guide_body, what has OH group and COOH group in the one terminal or both terminal can be illustrated, for example. Specific examples include hydrogenated polybutadiene diol, hydrogenated polybutadiene monool, hydrogenated polyisoprene diol, and hydrogenated polyisoprene monool. Since the adhesive strength of the pressure-sensitive adhesive layer can be appropriately increased, hydrogenated products of diene polymers such as hydrogenated polybutadiene and hydrogenated polyisoprene, olefinic softeners, and the like are preferably used. These softeners may be used alone or in combination of two or more.

The number average molecular weight of the softening agent is not particularly limited, but if the number average molecular weight is too small, substance transfer from the pressure-sensitive adhesive layer to the adherend may occur, which may cause heavy peeling. On the other hand, if the number average molecular weight is too large, the effect of improving the adhesive strength tends to be poor. Therefore, the number average molecular weight of the softening agent is preferably in the range of 5000 to 100,000, and more preferably in the range of 10,000 to 50,000.
When using a softener, the blending amount is not particularly limited, but if the blending amount is too large, an adhesive composition tends to be formed when peeling from the adherend after high temperature or outdoor exposure. In 100% by weight, 40% by weight or less is preferable, 20% by weight is more preferable, and 10% by weight or less is more preferable.

  The thickness of the pressure-sensitive adhesive layer can be appropriately adjusted depending on the use of the surface protective film, and is generally about 4 to 30 μm, for example.

  As the method for producing the surface protective film of the present invention, the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer and the component constituting the base material layer (surface layer and inner layer) are laminated and integrated by melt coextrusion. Is preferred. Among them, the melt coextrusion method by the T-die method is preferable because it can be manufactured easily and at low cost.

  As described above, the surface layer is made of polyethylene resin, has a tensile elastic modulus of 400 MPa or more, and is composed of the surface layer and the inner layer. On one surface of the base material layer having a tensile elastic modulus of 550 MPa or more, a rubber-based resin is provided. By laminating a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive composition containing as a main component, even if the pressure-sensitive adhesive layer is adhered to the back surface of the base material layer, the surface protective film can be easily peeled off from the back surface of the base material layer. can do. This is because the base material layer is hardly deformed at the time of peeling, and energy consumed for the deformation of the base material layer can be reduced. Therefore, the wound body wound in a roll shape can be unreasonably developed.

Hereinafter, examples of the surface protective sheet of the present invention will be described in detail. In addition, this invention is not limited to a following example.
Resins shown in Table 1 were prepared as materials constituting the surface layer and the inner layer of the base material layer.

In Table 1, MFR was measured according to JIS K 7210.
Furthermore, using a Tensilon tensile tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), in accordance with JIS K 7161, the film is formed under the conditions of a tensile speed of 500 mm / min, a chuck interval of 100 mm, 23 ° C., and a relative humidity of 50% RH. The tensile modulus of the resin was measured.

Example 1
A resin composition containing 35 parts by weight of a low density / high density polyethylene resin and 65 parts by weight of block polypropylene shown in Table 1 is used as a material for the surface layer, 90 parts by weight of block polypropylene, and 10 parts by weight of low density / high density polyethylene. Was prepared as an inner layer material.
Also, a pressure-sensitive adhesive composition containing 100 parts by weight of SEBS (made by Kraton Polymer, model number G1657) as a styrene-based elastomer that is a rubber-based resin component, and 10 parts by weight of Alcon P125 manufactured by Arakawa Chemical Co., Ltd. as a tackifier. Prepared.
The surface layer, the inner layer made of the resin composition, and the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition are coextruded by the T-die method, and 10 μm is formed on the substrate layer made of the surface layer having a thickness of 5 μm and the inner layer having a thickness of 30 μm A surface protective film on which a thick pressure-sensitive adhesive layer was laminated was obtained. This surface protective film was wound around a paper core having an inner diameter of 3 inches to obtain a wound body of the surface protective film.

(Examples 2 to 4 and Comparative Examples 1 to 4)
A wound body of the surface protective film was obtained in the same manner as in Example 1 except that the components of the composition for the surface layer, inner layer and pressure-sensitive adhesive were changed as shown in Table 2. However, regarding Comparative Examples 1 and 2, the inner layer thickness was set to 35 μm.

(Evaluation)
(1) Tensile elastic modulus When producing each surface protective film of an Example and a comparative example, the 35-micrometer-thick base material layer which did not provide the adhesive layer was prepared separately. This base material layer was cut into a size of width 10 cm × length 150 mm.
Using a Tensilon tensile tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), in accordance with JIS K 7161, under the conditions of a tensile speed of 500 mm / min, a chuck interval of 100 mm, 23 ° C. and a relative humidity of 50% RH, Tensile modulus was measured.

(2) Unfolding force The force required when the wound bodies of the surface protective films of Examples and Comparative Examples were rewound at a speed of 20 m / min was measured, and the unfolding force was determined in terms of N / 50 mm width.
(3) Tear strength The tear strength of each surface protective film of Examples and Comparative Examples was measured with an Elmendorf tear tester in accordance with JIS P8116.
These results are shown in Table 2.

Not limited to various articles and members such as optical devices, metal plates, coated steel plates, resin plates, glass plates, etc. For all adherends that require prevention of dirt and scratches during transportation, processing or curing Can be used.

Claims (4)

A surface protective film formed by coextrusion of a base material layer and an adhesive layer,
The base material layer is composed of a surface layer and an inner layer, and has a tensile elastic modulus of 550 MPa or more,
The surface layer contains a polyethylene resin and has a tensile modulus of 400 MPa or more,
The inner layer contains a polyolefin resin, and the pressure-sensitive adhesive layer is laminated on one surface thereof.
The surface-protective film, wherein the pressure-sensitive adhesive layer comprises a pressure-sensitive adhesive composition containing a rubber-based resin component as a main component.   The surface protective film according to claim 1, wherein the polyethylene resin of the surface layer is a high-density polyethylene resin.   The surface protective film according to claim 1 or 2, wherein the inner layer is formed of a mixture of a polyolefin resin and a recycled product of the surface protective film. The rubber-based resin component of the adhesive layer
(1) a block copolymer of a styrene-based polymer block and an olefin-based or conjugated diene-based polymer block;
(2) A block copolymer of a styrene polymer block and a random copolymer block of a styrene monomer and an olefin monomer or a conjugated diene monomer, and / or (3) These hydrogenated products are used as a main skeleton. The surface protective film according to any one of 1 to 3, which is a styrene-based elastomer.