Surface protective film

Abstract

To provide a surface protective film that can be laser processed irrespective of the surface condition of an adherend, such as a stainless steel plate or an aluminum plate.SOLUTION: A surface protective film includes a substrate layer and an adhesive layer stacked on at least one of the surfaces of the substrate layer, wherein the substrate layer includes at least one layer of a laser light absorbing layer, and the adhesive layer is mainly composed of an acrylic resin, contains no curing agent, has an adhesive force with respect to a SUS plate 304 in the range of 2.0 to 10.0 N / 25 mm, has a storage elastic modulus at 23°C in the range of 0.05 to 0.40 MPa, and has a loss tangent (tanα) in the range of 0.30 to 0.70 at 80°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protection film. [Background technology]

[0002] A protective film for laser processing is known, which has a base film having a white laser absorbing layer and an adhesive layer disposed on at least one surface of the base film, wherein the laser absorbing layer contains titanium oxide as a laser absorbent and magnesium and zinc organic acids as dispersants (see Patent Document 1). Examples of adhesives that form the adhesive layer include synthetic rubber-based adhesives, natural rubber-based adhesives, and acrylic adhesives.

[0003] A known adhesive film has an acrylic adhesive layer formed by polymerizing a monomer mixture containing 2-ethylhexyl acrylate, vinyl acetate, and acrylic acid in a mass ratio of 100 / 80 / 5 in toluene using benzoyl peroxide (polymerization initiator) to obtain an acrylic polymer having a weight-average molecular weight of 60 × 10 4 , adding 2 parts of an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name "Tetrad C") to 100 parts of this acrylic polymer, and mixing the resulting acrylic adhesive composition P1, which is then coated and dried to a thickness of 4 μm after drying (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-6379 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-18964 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the films described in Patent Documents 1 and 2 are described as having excellent laser cuttability when attached to an adherend and subjected to laser processing, the evaluation was based on an adherend being a 1 mm stainless steel plate, and there was a problem in that peeling and peeling of the film occurred when laser processing a thicker stainless steel plate. In such cases, the output of the laser and assist gas were reduced, and the processing speed was slowed down to address the problem. To provide a surface protection film for laser processing which does not peel off or turn over without reducing the output of a laser or adjusting the processing speed, even when an adherend is thick. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by providing a surface protection film consisting of a base layer and an adhesive layer, in which the adhesive layer is mainly composed of an acrylic resin, does not contain a curing agent, and has adhesive strength, storage modulus, and loss tangent within specific ranges, thereby completing the present invention.

[0007] That is, the present invention relates to a surface protection film having a base layer and an adhesive layer laminated on at least one surface of the base layer, wherein the base layer includes at least one laser light absorbing layer, the adhesive layer contains an acrylic resin as a main component and does not contain a curing agent, and the adhesive strength to SUS plate 304 is in the range of 2.0 to 10.0 N / 25 mm, the storage modulus at 23°C is in the range of 0.05 to 0.40 MPa, and the loss tangent (tan α) at ​​80°C is in the range of 0.30 to 0.70. Furthermore, at least one laser ray-absorbing layer used in the surface protective film of the present invention is preferably a resin layer containing a laser ray-absorbing agent. Furthermore, the resin of the resin layer used in the surface protection film of the present invention is preferably a polyolefin resin. Furthermore, the base layer used in the surface protective film of the present invention may include at least the laser light absorbing layer having a laser light absorbent containing titanium oxide, and the laser light absorbing layer having a laser light absorbent containing carbon black. Furthermore, the thickness of the adhesive layer of the surface protection film of the present invention is preferably 6 μm to 15 μm. Furthermore, the surface protective film of the present invention is preferably a surface protective film that is temporarily attached to protect the surface of a metal plate that is to be processed by laser light. [Effects of the Invention]

[0008] By using the surface protection film of the present invention, it is possible to laser process an adherend to which the surface protection film of the present invention is attached without generating burrs on the cut surface, even if the adherend is thick, without adjusting the laser output or processing speed. DETAILED DESCRIPTION OF THE INVENTION

[0009] The surface protection film of the present invention is a surface protection film having a base layer and an adhesive layer laminated on at least one surface of the base layer, and the base layer includes at least one laser light-absorbing layer.

[0010] The resin constituting the substrate layer is preferably suitable for application to an adherend as a surface protection film, has a certain degree of flexibility and stiffness for easy peeling, and is relatively easily melted and burned away by the laser light energy during laser processing. Specific examples of such resins include polyolefin resins and polyester resins, with polyolefin resins being particularly preferred.

[0011] The polyolefin resin is not particularly limited as long as it is a homopolymer or copolymer of an olefin monomer such as ethylene, propylene, or butadiene, or a copolymer of the olefin monomer and an alkene derivative such as vinyl acetate. More specifically, examples include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, low-crystalline or amorphous ethylene-α-olefin copolymers, polypropylene, propylene-ethylene copolymers (random copolymers and / or block copolymers), propylene-α-olefin copolymers, ethylene-ethyl (meth)acrylate copolymers, ethylene-methyl (meth)acrylate copolymers, ethylene-n-butyl (meth)acrylate copolymers, and ethylene-vinyl acetate copolymers. These may be used alone or in combination of two or more.

[0012] The substrate layer includes at least one laser-light-absorbing layer. The laser-light-absorbing layer is a layer in which a laser-absorbing agent is contained in the resin constituting the substrate layer, and specific examples of the laser-absorbing agent include titanium oxide. In this specification, a laser-light-absorbing layer containing titanium oxide as a laser-light-absorbing agent may be referred to as a white laser-light-absorbing layer.

[0013] The amount of titanium oxide as the laser absorber is preferably in the range of 0.1 to 10% by mass, more preferably 2 to 6% by mass. If the amount of titanium oxide is 0.1% by mass or more, the laser absorbency is good, and if the amount of titanium oxide is 10% by mass or less, the laser reflectance is low and energy loss is small, resulting in good laser cutting processability.

[0014] The laser absorbent may contain a component other than titanium oxide, and specific examples of such a component include oxides and carbides of calcium and aluminum.

[0015] The white laser absorbing layer preferably contains a dispersant. Laser absorbing layers using titanium oxide as the laser absorbent have sometimes exhibited poor laser cuttability due to high reflectance and low transmittance, but by incorporating a specific dispersant into the laser absorbing layer, the reflectance decreases and the transmittance increases, even when the amount of laser absorbent incorporated is the same, thereby improving the laser cuttability. The laser absorbent and the dispersant are usually incorporated into the resin that constitutes the base layer, and the white laser absorbing layer is formed from such a resin composition.

[0016] Specific examples of the dispersing agent include organic magnesium acid, organic zinc acid, etc. Specific examples of the organic acid include monosaturated fatty acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, persulfuric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid; oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and benzoic acid. Examples of unsaturated fatty acids include saturated fatty acids such as di-saturated fatty acids such as zelaic acid and sebacic acid, mono-unsaturated fatty acids such as myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid and nervonic acid, di-unsaturated fatty acids such as linoleic acid, eicosadienoic acid and docosadienoic acid, and tri-unsaturated fatty acids such as linoleic acid, pinolenic acid, eleostearic acid, mead acid and eicosatrienoic acid. Among these, saturated fatty acids are preferred, saturated fatty acids having 6 to 20 carbon atoms are more preferred, and stearic acid is even more preferred.

[0017] The amount of the dispersant blended is preferably in the range of 0.01 to 1 mass %, more preferably 0.05 to 0.5 mass %, relative to the total mass of the laser absorbing layer. If the amount of the dispersant is 0.01 mass % or more, good laser absorbency is achieved, and if the amount of the dispersant is 1 mass % or less, good laser cutting processability is achieved.

[0018] The thickness of the white laser absorbing layer is preferably in the range of 20 to 70 μm, more preferably in the range of 40 to 60 μm. When the thickness of the laser absorbing layer is 20 μm or more, the appearance design is good, and when the thickness of the laser absorbing layer is 70 μm or less, the laser cutting processability is good.

[0019] The reflectance of the single white laser absorbing layer to laser light having a wavelength of 1060 nm is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. If the reflectance of laser light is 40% or less, the laser light transmittance increases, improving energy efficiency during processing and thereby improving laser cuttability. There is no particular lower limit for the reflectance of the single laser absorbing layer to laser light having a wavelength of 1060 nm, but it is preferably 10% or more.

[0020] The transmittance of the single white laser absorbing layer for a laser beam having a wavelength of 1060 nm is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. If the laser beam transmittance is 50% or more, the laser beam can easily pass through the laser absorbing layer, improving energy efficiency during processing and thereby improving laser cuttability. The transmittance of the single laser absorbing layer for a laser beam having a wavelength of 1060 nm can be high, but is usually 80% or less.

[0021] The substrate layer preferably includes a laser absorbing layer that absorbs laser light while preventing it from transmitting through, thereby melting and burning off the surface protection film itself. Specific examples of the laser light absorbing agent contained in such a laser light absorbing layer include carbon black. In this specification, a laser light absorbing layer containing carbon black as a laser light absorbing agent is sometimes referred to as a black laser absorbing layer. Carbon black is blended into the resin that constitutes the substrate layer, and the black laser absorbing layer is formed from such a resin composition.

[0022] The amount of carbon black blended into the black laser absorbing layer is preferably in the range of 0.1 to 10% by mass, more preferably 3 to 8% by mass. If the amount of carbon black is 0.1% by mass or more, the laser light absorption efficiency increases and the laser cuttability becomes good, and if the amount of carbon black is 10% by mass or less, the residue after cutting the adherend becomes less noticeable.

[0023] The laser absorbing agent to be blended in the black laser absorbing layer may contain components other than carbon black, and specific examples thereof include oxides of iron, copper, and chromium, and oxides of alloys of iron, copper, and chromium.

[0024] The thickness of the black laser absorbing layer is preferably 10 to 60 μm, and more preferably 20 to 40 μm.

[0025] Here, the black laser absorbing layer has high adhesion to metal due to the influence of the carbon black contained therein, and in the case of a two-layer substrate layer in which the black laser absorbing layer is disposed opposite the white laser absorbing layer, color removal from the adherend to which the surface protective foil is attached may be poor. Therefore, it is preferable to dispose a protective layer that covers the surface of the black laser absorbing layer, so that the layer structure of the substrate layer is the white laser absorbing layer / the black laser absorbing layer / the protective layer.

[0026] Suitable resins for forming the protective layer include polyethylene, polypropylene, polyethylene-polypropylene blend resins, and polyester resins. Among these, polyethylene-polypropylene blend materials are preferred. When the protective layer is formed from a polyethylene-polypropylene blend material, a primer layer made of a polypropylene-based adhesive resin can be formed between the protective layer and the adhesive layer, making it possible to form the adhesive layer without corona treatment on the surface of the protective layer of the base layer. Furthermore, similar to the white laser absorbing layer, the protective layer preferably contains titanium oxide as a laser absorbent and magnesium and zinc organic acids as dispersants.

[0027] The thickness of the protective layer is preferably in the range of 5 to 30 μm, more preferably in the range of 10 to 20 μm. If the thickness of the protective layer exceeds 30 μm, the energy efficiency decreases due to melting and burning of the protective layer itself, and the laser cutting properties may be poor.

[0028] The substrate layer may contain additives as needed, such as antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents, surface lubricants, leveling agents, plasticizers, low-molecular-weight polymers, corrosion inhibitors, polymerization inhibitors, silane coupling agents, inorganic and organic fillers (e.g., calcium oxide, magnesium oxide, silica, zinc oxide, titanium oxide, etc.), metal powders, colorants, pigments, heat stabilizers, anti-emulsion agents, lubricants, and anti-blocking agents.

[0029] The content of the additive is not particularly limited, but is preferably 0.10% by mass or more, more preferably in the range of 0.20 to 0.64% by mass, more preferably in the range of 0.30 to 0.60% by mass, and particularly preferably in the range of 0.34 to 0.55% by mass, based on the entire base layer.

[0030] The thickness of the substrate layer is not particularly limited, but is preferably in the range of 2 to 200 μm, more preferably in the range of 10 to 180 μm, more preferably in the range of 50 to 160 μm, more preferably in the range of 60 to 140 μm, and particularly preferably in the range of 90 to 130 μm.

[0031] The adhesive layer used in the present invention contains a (meth)acrylic resin as a main component and does not contain a curing agent. Here, in this specification, "main component" means preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0032] In addition, in this specification, "(co)polymer" means a homopolymer and / or a copolymer, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylate" means acrylate and / or methacrylate. The weight average molecular weight Mw and number average molecular weight Mn of the polymer are values ​​calculated as standard polystyrene using gel permeation chromatography (GPC).

[0033] The (meth)acrylic resin is a polymer obtained by polymerization of a monomer containing a (meth)acrylic compound, and contains at least a structural unit derived from the (meth)acrylic compound. Therefore, the (meth)acrylic resin may be a (co)polymer consisting only of structural units derived from the (meth)acrylic compound, or may be a copolymer consisting of structural units derived from a compound having a polymerizable unsaturated bond copolymerizable with the (meth)acrylic compound.

[0034] When the (meth)acrylic resin is a copolymer of a structural unit derived from a (meth)acrylic compound and a structural unit derived from a compound having a polymerizable unsaturated bond copolymerizable with the (meth)acrylic compound, the content of the structural unit derived from the (meth)acrylic compound in the acrylic resin is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total mass of the acrylic resin.

[0035] The (meth)acrylic compound constituting the structural unit derived from the (meth)acrylic compound is a polymerizable compound represented by the chemical formula CH2=C(R1)COOR (R1 represents a hydrogen atom or a methyl group, and R represents a hydrocarbon group containing at least one selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group).

[0036] Examples of the (meth)acrylic compound include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-dodecyl (meth)acrylate, n-octadecyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, and benzyl (meth)acrylate. These compounds may be used alone or in combination of two or more.

[0037] The compound having a polymerizable unsaturated bond copolymerizable with the (meth)acrylic compound is not particularly limited as long as it is a polymerizable vinyl-based unsaturated compound, and examples thereof include aromatic vinyl compounds, unsaturated carboxylic acids, unsaturated acid anhydrides, hydroxyl group-containing unsaturated compounds, amino group-containing unsaturated compounds, amide group-containing unsaturated compounds, alkoxyl group-containing unsaturated compounds, cyano group-containing unsaturated compounds, nitrile group-containing unsaturated compounds, maleimide compounds, dialkyl esters of unsaturated dicarboxylic acids, vinyl ester compounds, vinyl ether compounds, etc. These may be used alone or in combination of two or more.

[0038] Examples of the aromatic vinyl compound include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, vinyltoluene, β-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylxylene, vinylnaphthalene, etc. These compounds may be used alone or in combination of two or more.

[0039] Examples of the unsaturated carboxylic acid include (meth)acrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, cinnamic acid, monoalkyl esters of unsaturated dicarboxylic acids (monoalkyl esters of maleic acid, fumaric acid, itaconic acid, citraconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, etc.), etc. These compounds may be used alone or in combination of two or more.

[0040] Examples of the unsaturated acid anhydride include maleic anhydride, itaconic anhydride, citraconic anhydride, etc. These compounds may be used alone or in combination of two or more.

[0041] Examples of the hydroxyl group-containing unsaturated compound include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, mono(meth)acrylic acid esters of polyalkylene glycols such as polyethylene glycol and polypropylene glycol, p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene, p-isopropenylphenol, m-isopropenylphenol, o-isopropenylphenol, etc. These compounds may be used alone or in combination of two or more.

[0042] Examples of the amino group-containing unsaturated compound include dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-(di-n-propylamino)ethyl (meth)acrylate, 2-dimethylaminopropyl (meth)acrylate, 2-diethylaminopropyl (meth)acrylate, 2-(di-n-propylamino)propyl (meth)acrylate, 3-dimethylaminopropyl (meth)acrylate, 3-diethylaminopropyl (meth)acrylate, 3-(di-n-propylamino)propyl (meth)acrylate, etc. These compounds may be used alone or in combination of two or more.

[0043] Examples of the amide group-containing unsaturated compound include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-methylol(meth)acrylamide, etc. These compounds may be used alone or in combination of two or more.

[0044] Examples of the alkoxyl group-containing unsaturated compound include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(n-propoxy)ethyl (meth)acrylate, 2-(n-butoxy)ethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 2-(n-propoxy)propyl (meth)acrylate, 2-(n-butoxy)propyl (meth)acrylate, etc. These compounds may be used alone or in combination of two or more.

[0045] Examples of the cyano group-containing unsaturated compound include cyanomethyl (meth)acrylate, 1-cyanoethyl (meth)acrylate, 2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate, 2-cyanopropyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, 4-cyanobutyl (meth)acrylate, 6-cyanohexyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate, 8-cyanooctyl (meth)acrylate, etc. These compounds may be used alone or in combination of two or more.

[0046] Examples of the nitrile group-containing unsaturated compound include (meth)acrylonitrile, ethacrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile, α-chloroacrylonitrile, α-fluoroacrylonitrile, etc. These compounds may be used alone or in combination of two or more.

[0047] Examples of the maleimide compounds include maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-dodecylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(4-methylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-diethylphenyl)maleimide, N-benzylmaleimide, N-1-naphthylmaleimide, etc. These compounds may be used alone or in combination of two or more.

[0048] Examples of the dialkyl ester of the unsaturated dicarboxylic acid include dialkyl esters of maleic acid, fumaric acid, itaconic acid, citraconic acid, etc. These compounds may be used alone or in combination of two or more.

[0049] Examples of the vinyl ester compound include vinyl acetate, vinyl propionate, vinyl pivalate, vinyl butyrate, vinyl benzoate, vinyl formate, vinyl cinnamate, etc. These compounds may be used alone or in combination of two or more.

[0050] Examples of the vinyl ether compound include vinyl methyl ether, vinyl ethyl ether, vinyl-n-butyl ether, vinyl isobutyl ether, vinyl phenyl ether, vinyl cyclohexyl ether, etc. These compounds may be used alone or in combination of two or more.

[0051] When the (meth)acrylic resin is a copolymer, the number of types of constituent units is not particularly limited, and it may be a binary system, a ternary system, or a multi-component system of quaternary or higher. When the (meth)acrylic resin is a copolymer, it is preferably a copolymer consisting of the (meth)acrylic compound and the aromatic vinyl compound or the unsaturated carboxylic acid. When the (meth)acrylic resin is a copolymer, it may be either a block copolymer or a random copolymer, but a block copolymer is preferred. The structure of this block copolymer is not particularly limited, but examples include AB type, ABA type, ABC type, ABCA type, and ABCD type.

[0052] The number average molecular weight Mn of the (meth)acrylic resin is preferably 300,000 or more, more preferably 500,000 or more, particularly preferably 700,000 or more, and particularly preferably 1,000,000 or more. The number average molecular weight Mn of the (meth)acrylic resin is preferably 5,000,000 or less, preferably 4,000,000 or less, particularly preferably 3,000,000 or less.

[0053] In the (meth)acrylic resin, the ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn) is preferably 2.0 or less, more preferably 1.7 or less, 1.5 or less, and particularly preferably 1.4 or less. In the (meth)acrylic resin, the ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn) is preferably 1.01 or more, more preferably 1.02 or more, 1.03 or more, 1.04 or more, and particularly preferably 1.05 or more.

[0054] The curing agent refers to a substance having the function of curing an acrylic resin by crosslinking or the like, and specific examples thereof include isocyanate-based curing agents, epoxy-based curing agents, urea resin-based curing agents, methylol-based curing agents, chelate-based curing agents, aziridine-based curing agents, melamine-based curing agents, polyvalent metal chelate-based curing agents, acid anhydride-based curing agents, polyamine-based curing agents, and carboxyl group-containing polymer-based curing agents.

[0055] In addition to the acrylic resin, the adhesive layer may contain other components such as a plasticizer, a conductive material, a tackifier, an antioxidant, an adhesion adjuster, a filler, a colorant, a flame retardant, a softener, an antioxidant, and a surfactant, as long as the properties of the adhesive layer are not impaired.

[0056] The storage modulus G' and loss tangent (tanδ) of the adhesive layer are determined by viscoelasticity measurement at a frequency of 10 Hz. The loss tangent (tanδ) is the ratio G" / G' of the storage modulus G' to the loss modulus G". The storage modulus G' corresponds to the portion stored as elastic energy when a material deforms, and is an index that represents the degree of hardness. The higher the storage modulus of the adhesive layer, the higher the adhesive holding strength and the more likely peeling due to strain is to be suppressed. The loss modulus G" corresponds to the portion of energy lost that is dissipated due to internal friction, etc. when a material deforms, and represents the degree of viscosity. The higher the loss tangent (tanδ), the stronger the tendency for viscosity, the more liquid-like the deformation behavior, and the smaller the rebound elastic energy.

[0057] The adhesive strength of the adhesive layer to the SUS plate 304 may be in the range of 2.0 to 10.0 N / 25 mm, and more preferably in the range of 2.0 to 5.0 N / 25 mm. The adhesive layer also preferably has a storage modulus (G') at 23°C of 0.05 to 0.40 MPa, and a loss tangent (tan α) at ​​80°C of 0.30 to 0.70. By setting the adhesive strength, storage modulus (G') at 23°C, and loss tangent (tan α) within the above ranges, the surface protection film of the present invention can be removably peeled, sufficient peel strength can be obtained even after adhesion, and curling up of the surface protection film and the generation of burrs during laser processing can be suppressed.

[0058] The thickness of the adhesive layer is not particularly limited as long as it does not interfere with the effects of the present invention, and can be appropriately set depending on the application of the surface protection film of the present invention. The thickness of the adhesive layer is preferably 5 μm or more, more preferably 6 μm, 7 μm, or 8 μm or more, and particularly preferably 9 μm or more. The thickness of the adhesive layer is preferably 20 μm or less, more preferably 19 μm or less, 18 μm or less, 16 μm or less, 15 μm or less, or 13 μm or less, and particularly preferably 12 μm or less, or 11 μm or less. If the thickness of the adhesive layer is less than 5 μm, there is a risk of insufficient adhesion and conformability to the adherend, and if the thickness of the adhesive layer exceeds 20 μm, the adhesive strength is too strong, which may result in poor peeling workability.

[0059] A primer layer can also be formed between the protective layer and the adhesive layer. By forming the primer layer, good adhesion between the protective layer and the adhesive layer can be achieved, eliminating the need for corona treatment of the surface of the base layer facing the protective layer, or making it possible to deal with cases where corona treatment is difficult due to equipment limitations. Examples of resins that form the primer layer include a blend layer of a polypropylene-based adhesive resin and a rubber-based adhesive.

[0060] The surface protection film can be produced by a conventionally known multilayer film molding method. Specific examples include a method in which each layer constituting the surface protection film is molded as a separate film or sheet in advance and then the films or sheets constituting each layer are adhered and laminated, and a method in which each layer is formed and laminated in the same process by extrusion. Examples of the former include air-cooled inflation molding, air-cooled two-stage cooling inflation molding, T-die film molding, and water-cooled inflation molding. Examples of the latter include extrusion lamination, dry lamination, sandwich lamination, and co-extrusion.

[0061] The thickness of the surface protection film is not particularly limited, but is preferably in the range of 7 to 220 μm, more preferably in the range of 60 to 180 μm, and more preferably in the range of 70 to 140 μm.

[0062] The surface protection film may have a layer other than the base layer and the adhesive layer. As such a layer, a release agent may be applied to the base layer to form a release layer. This makes it possible to easily unwind the film even when the adhesive layer is wound directly around the release layer.

[0063] The surface protection film is preferably a surface protection film that is temporarily attached to a metal plate to protect the surface of the metal plate to be processed by laser light. The substrate to be attached is not particularly limited, but is preferably a substrate to be subjected to laser processing, and specific examples thereof include metal plates such as iron, stainless steel, aluminum, and copper.

[0064] The laser light used for processing is not particularly limited, but specific examples include a YAG laser (fundamental wavelength 1064 nm), a YVO4 laser (fundamental wavelength 1064 nm), a fiber laser (fundamental wavelength 1090 nm), a semiconductor laser (fundamental wavelength 650 to 905 nm), a carbon dioxide laser (fundamental wavelength 10.6 μm), a helium-neon laser (fundamental wavelength 630 nm), an excimer laser 7 (fundamental wavelength 193 nm), and an argon laser (fundamental wavelength 488 to 514 nm).

[0065] The manner of laser processing is not particularly limited, and specific examples include laser cutting, laser drilling, and laser micro-hole processing. [Example]

[0066] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way. [Example]

[0067] Low density PE (density: 0.92g / m 3 A resin composition for forming a white laser-absorbing layer was obtained by blending 96.7% by mass of low-density PE (density: 0.92 g / m) with 3% by mass of titanium oxide, 0.2% by mass of zinc stearate, and 0.1% by mass of magnesium stearate. 3 A resin composition for forming a black laser absorbing layer was obtained by blending 94% by mass of acrylic resin (white laser absorbing layer, thickness: 40 μm) with 6% by mass of carbon black. Each of the resulting resin compositions was used to form a white laser absorbing layer (thickness: 40 μm) and a black laser absorbing layer (thickness: 30 μm) using an extruder, thereby obtaining a substrate layer. This substrate layer was then subjected to a corona discharge treatment, and a composition for forming an adhesive layer, which was a mixture of acrylic resin (molecular weight Mn 380,000) and toluene, was applied to the composition at a solid coating amount of 10 g / m2 to form a 10 μm-thick adhesive layer, thereby obtaining a surface protection film for laser processing.

[0068] [Comparative Example 1] A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to an acrylic resin (molecular weight Mn 170,000), a curing agent (TDI-based curing agent), and mixing them.

[0069] Comparative Example 2 A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to a rubber-based resin (molecular weight Mn 260,000) and mixing it.

[0070] Comparative Example 3 A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to a rubber-based resin (molecular weight Mn 270,000) and mixing it.

[0071] Comparative Example 4 A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to an acrylic resin (molecular weight Mn 170,000) and mixing it.

[0072] Comparative Example 5 A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to a rubber-based resin (molecular weight Mn 390,000) and mixing it.

[0073] Comparative Example 6 A surface protection film for laser processing was prepared in the same manner as in Example 1, except that the adhesive layer-forming composition was prepared by adding toluene to a rubber-based resin (molecular weight Mn 200,000) and mixing it.

[0074] (storage modulus and loss tangent) The obtained surface protection film for laser processing was cut into a circle with a diameter of 8 mm to obtain a test piece, and the dynamic viscoelasticity was measured using a viscoelasticity measuring device (TA Instruments, Disco-veryHR-2) to measure the storage modulus (G') and loss tangent (tanδ) at 23°C and 80°C under conditions of an applied frequency of 10 Hz, a normal stress of 0.4 N, and a heating rate of 5°C / min. The results are shown in Table 1.

[0075] (Adhesive strength) A peel test was conducted in accordance with JIS Z 0237-2000, the test method for adhesive tapes and sheets. The resulting surface protection film for laser processing was cut into 25 mm widths and attached to a SUS304 plate polished with #280 abrasive paper. After leaving it at room temperature for 20 minutes, the peeling angle was measured at 180° and a peeling speed of 0.3 m / min. The results are shown in Table 1. In Table 1, adhesive strengths of 2 N or greater but less than 5 N / 25 mm were evaluated as ◯ (good), and adhesive strengths of less than 2 N / 25 mm or greater than 5 N / 25 mm were evaluated as × (poor or not very favorable).

[0076] (Laser cuttability) A laser cutting test was carried out using a processing machine (Amada ENSIS-4020AJ fiber laser) with a laser output of 4 kW. The protective films for laser processing obtained in Example 1 and Comparative Examples 1 to 6 were cut into 25 mm widths, attached to 6 mm thick SUS400 and SUS2B plates, left at room temperature for 3 days, and then laser cut at the processing speed and gas pressure listed below. The results are shown in Table 1. In Table 1, films that showed no peeling were rated as ◯, and films that showed peeling of the surface protective film for laser processing from the cut area were rated as ×.

[0077] Machining speed: outer circumference 7000mm / min 6 holes 6400mm / min 2.5π hole 3100mm / min Gas pressure: 0.65Mpa 6 holes 0.58Mpa 2.5mm diameter hole 0.45Mpa

[0078] (comprehensive evaluation) Based on the results of the storage modulus, loss tangent, adhesive strength, and laser cuttability, the evaluation was made according to the following criteria.

[0079] Good: Adhesion is good, and no peeling or peeling occurred on any of the plates during the laser cutting test. △: Good adhesive strength, but peeling occurred on some boards during the laser cutting test. ×: The adhesive strength was poor or not very good, and defects occurred in at least part of the plate during the laser cutting test.

[0080] [Table 1]

[0081] From the above, it was found that a surface protection film made of an acrylic resin containing no curing agent and including an adhesive layer exhibiting specific adhesive strength, storage modulus, and loss tangent has excellent laser cuttability. [Industrial Applicability]

[0082] The surface protection film of the present invention is useful as a surface protection film for laser processing.

Claims

1. A surface protection film having a base layer and an adhesive layer laminated on at least one surface of the base layer, wherein the base layer includes at least one laser light absorbing layer, and the adhesive layer contains an acrylic resin as a main component and does not contain a curing agent, and the adhesive strength to SUS plate 304 is in the range of 2.0 to 10.0 N / 25 mm, the storage modulus at 23°C is in the range of 0.05 to 0.40 MPa, and the loss tangent (tan α) at ​​80°C is in the range of 0.30 to 0.

70.

2. 2. The surface protective film according to claim 1, wherein the at least one laser ray absorbing layer is a resin layer containing a laser ray absorbing agent.

3. The surface protection film according to claim 2 , wherein the resin of the resin layer is a polyolefin resin.

4. 2. The surface protective film according to claim 1, wherein the base layer comprises at least the laser light absorbing layer having a laser light absorbent containing titanium oxide, and the laser light absorbing layer having a laser light absorbent containing carbon black.

5. 5. The surface protection film according to claim 1, wherein the adhesive layer has a thickness of 6 μm to 15 μm.

6. 2. The surface protective film according to claim 1, which is a surface protective film that is temporarily attached to a metal plate to protect the surface of the metal plate that is to be processed by laser light.

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