JPWO2017169451A1 - Surface protection film - Google Patents

Abstract

A surface protective film comprising an adhesive layer, an intermediate layer and a back layer, the back layer comprising a polyolefin resin composition containing 0.3 wt% to 10 wt% of a fluorine-based mold release agent, and constituting the intermediate layer The resin is mainly composed of low-density polyethylene, and the haze after heating at 160 ° C. for 1 minute or longer and after slow cooling is 10% or less, and the haze after heating at 200 ° C. for 1 minute or longer and after slow cooling is 5% or less. A surface protective film characterized by Provided is a surface protective film that is easy to heat-mold even when bonded to an adherend and that is excellent in transparency and gloss even after heat-molding of the adherend.

Description

  The present invention relates to a surface protective film, and more particularly to a surface protective film excellent in transparency even after heat molding is performed in a state of being bonded to a resin plate.

  Resin plates and metal plates (hereinafter sometimes referred to as adherends) are generally transported and transported with a surface protective film bonded to prevent scratches on the surface. In addition, the surface protective film is required to have an adhesive property that matches the adherend. In addition, the resin plate is often exposed to secondary processing such as printing and heat molding while the surface protective film is bonded, and suitability for heat molding is required.

  Applications of resin plates such as polycarbonate and polymethyl methacrylate with such heat molding are diverse, including nameplates, bathtubs, helmets, and exteriors of carrier bags. As a manufacturing process of these products, with the surface protective film pasted on one side of the resin plate, the surface opposite to the resin plate is subjected to processing such as printing or coating, and then laminated with another base resin sheet, and the surface protective film In many cases, the surface to which the material is bonded is integrally heat-molded at a temperature of 100 ° C. to 200 ° C. with the product front surface. The final products of these resin plates are often lined up in stores with the surface protective film bonded, and the beauty of the front surface with the surface protective film affects the appeal to customers. Therefore, the surface protective film may be required to have high transparency after heat molding in addition to followability to heat molding.

  However, the surface protective film using a general olefin resin for the back layer as shown in Patent Documents 1 and 2 has a high haze after heat molding and is far from the required high transparency. Also, as shown in Patent Documents 3 and 4, those using low density polyethylene for the back layer are suitable for heat molding because the film has a low tensile elastic modulus and stretches well when the film is pulled. The haze of the subsequent surface protective film is as high as 4 to 8%. However, since the center line average roughness (Ra) of the surface roughness of the back surface layer is about 0.05 μm, the back surface layer and the adhesive layer of the surface protection film are difficult to slip, and air is trapped when the surface protection film is wound on the product roll. In some cases, the surface protective film is deformed and wrinkles occur when it is bonded to the resin plate.

JP 2015-189909 A JP 2007-106857 A JP-A-8-323944 JP-A-5-229082

  The object of the present invention is to eliminate the above-mentioned problems in the prior art, maintain high transparency with low haze after heat molding, and air inside the roll when the surface protective film is wound into a roll. An object of the present invention is to provide a surface protective film capable of suppressing stagnation and preventing deformation of the film.

As a result of intensive research and development in order to solve the above problems, the present inventor has found that the object can be achieved by adopting the following configuration of the present invention.
(1) A surface protective film comprising an adhesive layer, an intermediate layer and a back layer, the back layer comprising a polyolefin resin composition containing 0.3 wt% to 10 wt% of a fluorine-based mold release agent, The constituent resin is mainly low-density polyethylene, has a haze of 10% or less after heating at 160 ° C. for 1 minute or longer and gradually cooling, and a haze after heating and cooling at 200 ° C. for 1 minute or longer is 5%. A surface protective film characterized by:
(2) The surface protective film according to (1), wherein the back layer has a centerline surface roughness (Ra) of 0.15 μm or less.
(3) The surface protective film according to (1) or (2) above, wherein inorganic particles having a particle size of 5 μm or more are added to the back layer.
(4) The surface protective film according to any one of (1) to (3), wherein the polyolefin resin of the back layer is a high-pressure low-density polyethylene having a density of 0.90 to 0.93 g / cm ^3. .
(5) The surface protective film according to any one of (1) to (3), wherein the polyolefin resin of the back layer is a polypropylene random copolymer.
(6) Low density polyethylene constituting the intermediate layer is a straight-chain having a density of high-pressure low-density polyethylene or 0.88~0.93g / cm ³ having a density of 0.90~0.93g / cm ³ The surface protective film according to any one of (1) to (5), which is a low-density polyethylene.
(7) The surface protective film according to any one of (1) to (6), wherein the resin constituting the adhesive layer is an ethylene / vinyl acetate copolymer or linear low-density polyethylene.
(8) The surface protective film according to any one of (1) to (7), wherein the fluorine-based mold release agent is a fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group.
(9) The surface protective film according to any one of the above (1) to (8) is bonded to one side of a resin plate made of polycarbonate or polymethyl methacrylate, and a printed layer and acrylonitrile / butadiene / A structure in which a styrene copolymer or polycarbonate is laminated.
(10) A molded body obtained by heat-molding the structure according to (9) above with a surface on which a surface protective film is bonded as a front surface.

The surface protective film of the present invention has the following effects.
(1) The surface protective film of the present invention has low haze after heat molding, and can maintain the appearance of the heat molded product beautifully.
(2) The surface protective film of the present invention can be easily discharged of air entering between the films when the surface protective film is wound up, and the roll is not deformed due to air accumulation and is uniformly bonded to the adherend without wrinkles. can do.

Hereinafter, the present invention will be described in detail together with embodiments.
The surface protective film of the present invention is a laminated film comprising a back layer, an intermediate layer and an adhesive layer. Surface protection film used at the time of heat molding by suppressing the trouble of roll shape at the time of winding by making the surface protection films easy to slide with the back layer and expressing the characteristics of tensile strength under high temperature environment by the intermediate layer In consideration of compatibility with the adherend, the adhesive layer can be designed independently of the intermediate layer and the back layer, focusing on the adhesive properties.

  The surface protective film of the present invention is applied to the surface of a resin plate made of polycarbonate, polymethyl methacrylate resin, etc., and then the resin plate is heat-molded to continue protecting the surface until the final product using the resin plate Therefore, at the time of heat molding, it is necessary not to be broken while following the resin plate, and to maintain a beautiful surface of the final product with the resin plate exposed on the surface.

  The adhesive layer of the surface protective film of the present invention can be co-extruded and laminated with the intermediate layer and the back layer by an inflation method such as ethylene / vinyl acetate copolymer or linear low density polyethylene, or a T-die method. Any resin may be used. However, in consideration of molding in an environment of 100 ° C. to 200 ° C., linear low-density polyethylene that is less prone to sticking by heating is particularly preferably used. Specific examples of linear low density polyethylene include ethylene / butene copolymer, ethylene / pentene copolymer, ethylene / hexene copolymer, ethylene / 4-methyl-1-pentene copolymer, and ethylene / octene copolymer. A polymer etc. can be mentioned. Also, for the purpose of improving adhesive strength, terpene resin groups such as hydrogenated terpene phenol and terpene styrene resin, tackifiers such as rosins such as polymerized rosin and hydrogenated rosin, styrene elastomers and urethane elastomers, etc. May be added, and various additives such as an ultraviolet absorber may be added as long as the adhesiveness is not impaired.

  Next, the intermediate layer in the present invention is required to be resistant to tearing of the surface protective film during heat molding and to have low haze after heat molding. For this reason, the resin constituting the intermediate layer is mainly composed of low-density polyethylene that hardly undergoes crystallization or hardly forms large-size crystals even during slow cooling from a high temperature (100 ° C. to 200 ° C.). is important. Here, “mainly” means that the main raw material is contained in an amount of 50% by weight or more. In the laminated film composed of the back layer, the intermediate layer and the adhesive layer according to the present invention, it was slit for economic reasons. In general, the edge or the like is reused as a recovered raw material in the intermediate layer. In this case, the recovered raw material and the new raw material are blended based on the above guidelines. By making the resin constituting the intermediate layer in the present invention mainly composed of low-density polyethylene, the center line surface roughness (Ra) of the back layer described later can be reduced, and the glossy surface without dullness. A protective film can be obtained.

  As the low density polyethylene, high pressure method low density polyethylene or linear low density polyethylene is preferably used, but both resins have low tensile elastic modulus compared to other materials and excellent elongation of the film during heat molding. Because of its excellent transparency and low haze, it is optimally used for the required characteristics during heat molding.

The high-pressure low-density polyethylene used for the intermediate layer of the surface protective film of the present invention preferably has a density in the range of 0.90 to 0.93 g / cm ³ . If the density of the low density polyethylene is more than 0.93 g / cm ³ , the crystal size increases in the annealing step after heat molding, and the amount of incident light that is scattered / reflected and transmitted is reduced. It will be high. If the density of the high-pressure low-density polyethylene is less than 0.90 g / cm ³ , it will have properties similar to rubber, and the elongation at break will be too high to cut the surface protective film.

The density of the linear low density polyethylene used for the intermediate layer of the surface protective film of the present invention is preferably in the range of 0.88 to 0.93 g / cm ³ . The reason for the upper limit and the lower limit is the same as in the case of using the high pressure method low density polyethylene.

  As described above, when high-pressure low-density polyethylene or linear low-density polyethylene is used for the intermediate layer, the tensile elastic modulus is remarkably lowered and the surface protective film becomes softer than when high-density polyethylene or polypropylene is used. . If the surface protective film is soft, air is difficult to escape when the film is wound up as a product roll after film formation. If the surface protective film is bonded to the adherend while it is deformed, wrinkles and protrusions may enter and the appearance may not be good, and unexpected problems may occur during heat molding. Therefore, the back layer is designed as follows.

  That is, the back layer in the present invention is composed of a polyolefin resin composition containing 0.3 wt% to 10 wt% of a fluorine-based mold release agent. When the addition amount of the fluorine-based mold release agent is less than 0.3% by weight, the slippage between the surface protection films is poor, and when the film is wound up as a product roll after film formation, it is difficult for air to escape and air accumulation occurs. The surface protection film may be deformed. Further, even if 10% by weight or more is added, the effect of slipperiness is peaked, and on the contrary, it may be scattered at the time of film formation or deposited on the die to contaminate the process.

  The polyolefin resin used for the back layer is not particularly limited as long as it can be co-extruded and laminated with an intermediate layer resin or adhesive layer resin and a T-die or inflation die. A copolymer is desirable. When linear low-density polyethylene is used, stickiness appears on the back layer, and when the surface protective film is wound up in a roll shape, the air inside the roll does not escape and air accumulation occurs, causing the film to deform, and the adherend Wrinkles will enter when pasting to the product, detracting from the beauty of the product. In addition, when high-density polyethylene is used, it is not desirable because the surface protection film comes into contact with and rubbing with the guide roll during winding or laminating, and the resin is scraped and white powder appears.

The high-pressure low-density polyethylene used for the back layer in the present invention preferably has a density in the range of 0.90 to 0.93 g / cm ³ . If the density is more than 0.93 g / cm ³ , the crystal size increases in the slow cooling stage after heat forming, and the amount of incident light that is scattered and reflected more and transmitted is reduced, resulting in an increase in haze. . Conversely, if it is less than 0.90 g / cm ^3, it will have properties similar to rubber, and when used for the back layer, the resin will become sticky and sticky, and the surface protection film will be rolled. When the film is wound on, the air inside the roll does not escape and air accumulation occurs and the film is deformed. In addition, the breaking elongation becomes too high and the surface protective film cannot be cut.

  The polypropylene-based random copolymer used for the back layer in the present invention is specifically an ethylene / propylene random copolymer (hereinafter referred to as “EPC”) which is a copolymer of a propylene monomer and an ethylene monomer. And ethylene / propylene / butene random copolymer (hereinafter sometimes abbreviated as “EPBC”) which is a copolymer of propylene monomer, ethylene monomer and butene monomer.

  In the back layer of the surface protective film of the present invention, it is necessary to add 0.3 wt% to 10 wt% of a fluorine-based mold release agent to the resin. A fluorine-based mold release agent is used that does not increase the surface roughness of the film and keeps the haze low, and the resin is not easily deteriorated even at a high temperature and is not easily removed from the back layer. Examples of the fluorine-based mold release agent include polyvinylidene fluoride, chlorotrifluoroethylene / ethylene copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, ethylene / tetra Fluoroethylene copolymers, tetrafluoroethylene / perfluoroalkoxyethylene copolymers, terpolymers made of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, and polyfluorohydrocarbon groups and polyoxyethylene groups Mention may be made of fluorine-containing compounds.

  Here, examples of the fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group include a (meth) acrylic acid ester having a C 1-18 perfluoroalkyl group as the monomer (a). It can be obtained by copolymerizing the monomers (b) and (c) described later with (meth) acrylic acid ester having a polyoxyethylene group.

  Among the fluorine-based release agents, the fluorine-containing compound having the polyfluorohydrocarbon group and the polyoxyethylene group is preferable because there is no transfer contamination to the adhesive layer and excellent unwinding characteristics.

  The perfluoroalkyl group of the monomer (a) preferably has 1 to 18 carbon atoms, more preferably 1 to 6 carbon atoms. Such a perfluoroalkyl group may be linear or branched. These may be used alone or in combination of two or more.

  Such a (meth) acrylic acid ester having a perfluoroalkyl group is commercially available from Kyoeisha Chemical Co., Ltd., or can be synthesized by a known method using a commercially available fluorine-containing compound as a raw material.

As the monomer (b) having a polyoxyethylene group, one having a structure in which oxyethylene units (—CH ₂ —CH ₂ —O—) are linked in an amount of 1 to 30 is preferable, and the unit is particularly preferably 1 to 20 Those are more preferred. Incidentally, oxypropylene units in the chain _{(-CH 2 -CH (CH 3)} -O-) may have. Preferable examples include polyethylene glycol monomethacrylate having 8 oxyethylene units. The monomer (b) may be used alone or in combination of two or more.

  Another monomer (c) having a polyoxyethylene group is a di (meth) having a structure in which oxyethylene units are linked in an chain of 1 to 30 and having double bonds at both ends. Examples of acrylates and preferred specific examples include polyethylene glycol dimethacrylate having 8 linkages. Such monomer (c) can also be used alone or in combination of two or more.

  The proportions of the monomers (a), (b) and (c) are as follows: monomer (a) is 1 to 80% by weight, monomer (b) is 1 to 80% by weight, monomer (C) is preferably 1 to 50% by weight.

  Furthermore, it is preferable that inorganic particles are added to the back layer of the surface protective film of the present invention, and silica or zeolite having a particle diameter of 5 μm or more, preferably 6 to 20 μm, more preferably 7 to 15 μm is suitably used.

  The center line surface roughness (Ra) of the back layer of the present invention is preferably 0.15 μm or less. When the center line surface roughness (Ra) of the back layer is higher than 0.15 μm, incident light is irregularly reflected on the surface of the back layer, the surface protection film looks dull, and the beauty of the surface protection film is impaired. There is. Setting the center line surface roughness of the back layer to 0.15 μm or less is mainly made of a polyolefin resin used for the back layer that is difficult to crystallize, such as a high-pressure low-density polyethylene or a polypropylene random copolymer, This can be achieved by making the resin constituting the intermediate layer mainly composed of low-density polyethylene.

  The surface protective film of the present invention has a haze after heating and annealing at 160 ° C. of 1 minute or more and 10% or less, and a haze after heating and annealing at 200 ° C. of 1 minute or more is 5% or less. It is characterized by. When the haze after heating and slow cooling under each condition is higher than 10% and 5%, the transparency is poor and the beauty of the adherend cannot be visually recognized. Here, gradual cooling refers to cooling from room temperature to room temperature by simply immersing it in water, for example, without rapidly cooling, without using a special cooling method, simply by air cooling, spraying, or simply leaving it alone. Represents what to do. In order to set the haze after heating and slow cooling to these ranges, the resin constituting the intermediate layer is mainly composed of low-density polyethylene, and the resin constituting the back layer is subjected to the slow cooling step after thermoforming. This can be achieved by selecting from low density polyethylene or polypropylene random copolymer that does not increase the crystal size, and setting the center line surface roughness (Ra) of the back layer to 0.15 μm or less.

  The thickness of the surface protective film of the present invention is preferably 30 to 90 μm from the viewpoint of handling, and the ratio of the thickness of the back layer, the intermediate layer and the adhesive layer to the thickness of the surface protective film is 5 to 20%: 50 to 80 %: The range of 10 to 45% is preferable from the balance of mechanical properties and adhesive properties, and more preferably 7 to 10%: 65 to 75%: 15 to 25%.

  In addition, the surface protective film of the present invention is an antistatic material for preventing static electricity generated when the surface protective film is peeled, within a range that does not impair transparency, glossiness, surface roughness, and spreadability during heat molding. It is also possible to add an agent, recovery of excess film generated during the formation of the surface protective film, a pigment for coloring the film, an antioxidant for preventing thermal deterioration during heat molding, and the like.

  Hereinafter, although the surface protection film of this invention is demonstrated in detail based on a specific Example, this invention is not limited to these Examples. In addition, it measured and evaluated by the method shown below.

(1) Haze The surface protective film is stored for 3 days or more after creation in a room temperature of 23 ° C. and in a humidity of 50 RH%, and then a polycarbonate plate “Panlite” manufactured by Teijin Limited having a thickness of 0.5 mm and a width of 50 mm. It was pasted at a pasting pressure of 9,100 N / m and a pasting speed of 300 cm / min. Thereafter, it is stored for 15 minutes in each of the hot air dryers that have been kept at 100 ° C., 120 ° C., 140 ° C., and 160 ° C., and for 2 minutes in each of the hot air dryers that are kept at 180 ° C. and 200 ° C. After storing and taking out a sample from a hot air dryer, after storing for 24 hours at 23 degreeC atmosphere, the surface protection film was peeled off and the haze of the surface protection film was measured.

(2) Roughness of the back surface The surface protective film was stored for 3 days or more after preparation in a room temperature of 23 ° C. and a humidity of 50 RH%, and after that, using a surf coder “ET4000A” manufactured by Kosaka Laboratory, centerline average roughness The thickness (Ra) and the ten-point average roughness (Rz) were measured.

(3) Friction coefficient The surface protective film was stored for 3 days or more after preparation in a room temperature of 23 ° C. and a humidity of 50 RH%, and then the back layer surface and the adhesive layer surface of the surface protective film were overlapped to measure the friction coefficient. .

<Example 1>
87% by weight of high-pressure low-density polyethylene having a density of 0.924 g / cm ³ and MFR (Melt Flow Rate) at 190 ° C. of 4.5 g / 10 minutes, and an average particle diameter of 88% by weight of the low-density polyethylene A composition comprising 13% by weight of a master batch of a mixed composition comprising 6% by weight of 11 μm silica and 6% by weight of a fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group is used as the back layer, and the density is 0.924 g. / ^cm 3, MFR under 190 ° C. is a high-pressure low-density polyethylene is 7.5 g / 10 min and an intermediate layer, density 0.922 g / cm ^3, linear ethylene-hexene copolymer having a melting point of 121 ° C. Using a T-die type composite film forming machine with a chain low density polyethylene as the adhesive layer, the back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is 4 A coextruded surface protective film was prepared to have a thickness of 0 μm.

Here, a fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group (indicated as fluorine-based (1) in Tables 1 and 2) is a C ₆ F ₁₃ perfluorocarbon monomer as monomer (a). Fluoroalkyl acrylate (CH ₂ ═CHCOOC ₂ H ₄ C ₆ F ₁₃ ) as a 25 wt% monomer (b), polyethylene glycol monoacrylate having 8 oxyethylene repeating units {CH ₂ ═CHCOO (CH ₂ CH ₂ O ) ₈ H} as 50% by weight and monomer (c), polyethylene glycol dimethacrylate having eight oxyethylene repeating units {CH ₂ ═C (CH ₃ ) COO (CH ₂ CH ₂ O) ₈ COC (CH ₃ ) = CH _2} at a rate of 25 wt%, with trifluoroacetic toluene solvent, as a polymerization initiator 2,2'-azobis ( , 4-dimethylvaleronitrile) using lauryl mercaptan as a chain transfer agent and polymerizing at 60 ° C. for 5 hours with stirring in a nitrogen stream, and then precipitated and filtered in methanol, followed by drying under reduced pressure. A thing was used.

<Example 2>
As a back layer, a propylene / ethylene / butene random copolymer (EPBC) having a density of 0.900 g / cm ³ and a melting point of 148 ° C., 87% by weight, 88% by weight of EPBC and 6% by weight of silica having an average particle diameter of 11 μm, Example 1 A surface protective film was prepared in the same manner as in Example 1 except that 13% by weight of a master batch of a mixed composition comprising 6% by weight of a fluorine-containing compound having the same polyfluorohydrocarbon group and polyoxyethylene group was used. .

<Example 3>
The density is linear low density polyethylene 87 wt% which is 0.920 g / cm ³ as an adhesive layer, terpene resin 3 wt% is a tackifier, and high-pressure low density polyethylene having a density of 0.924 g / cm ³ A surface protective film was prepared in the same manner as in Example 1 except that an adhesive layer-forming resin composition consisting of 10% by weight was used and a linear low density polyethylene having a density of 0.930 g / cm ³ was used as the intermediate layer. .

<Example 4>
A surface protective film was prepared in the same manner as in Example 2 except that a linear low density polyethylene having a density of 0.930 g / cm ³ was used as the intermediate layer.

<Example 5>
Silica having 87% by weight of low density polyethylene having a density of 0.900 g / cm ³ , 88% by weight of the low density polyethylene, 6% by weight of a fluorine-containing compound having polyfluorohydrocarbon groups and polyoxyethylene groups, and a particle size of 10 μm a composition comprising the masterbatch 13% by weight consisting of 6 wt% and the back layer, the linear low density polyethylene density is 0.880 g / cm ³ as an intermediate layer, density of 0.922 g / cm ³ A linear low density polyethylene is used as an adhesive layer and a T-die type composite film forming machine is used. The back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness. A co-extruded surface protective film was prepared so as to be 40 μm.

Here, as the fluorine-containing compound (indicated as fluorine-based (2) in Table 1), CH ₂ = CHCOOC ₂ H ₄ C ₈ F ₁₇ is 10 as the perfluoroalkyl acrylate of the monomer (a). _{wt%, CH 2 = CHCOO (CH} 2 CH 2 O) 80 wt% to ₈ H as polyethylene glycol monoacrylate monomer (b), and as a monomer (c), polyethylene glycol dimethacrylate _CH 2 = C Polymerization was carried out in the same manner as in Example 1 except that (CH ₃ ) COO (CH ₂ CH ₂ O) ₈ COC (CH ₃ ) ═CH ₂ was changed to a ratio of 10% by weight to obtain the target fluorine-containing compound.

<Example 6>
87% by weight of high-pressure low-density polyethylene having a density of 0.930 g / cm ³ , 6% by weight of a fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group as in Example 5, and a particle size of 10 μm A composition comprising 13% by weight of a masterbatch containing 7% silica (the base resin is the high-pressure low-density polyethylene) is used as a back layer, and a linear low-density polyethylene having a density of 0.930 g / cm ³ is used as an intermediate layer. And a composition comprising 90% by weight of a linear low density polyethylene having a density of 0.922 g / cm ³ and 10% by weight of a masterbatch of 20% by weight of a terpene tackifier (the base resin is the above linear low density polyethylene). Using a T-die type composite film forming machine with an adhesive layer as the adhesive layer, the back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is So as to be 0μm created a coextruded surface protective film.

<Example 7>
Silica having a density of 0.900 g / cm ³ and a melting point of 145 ° C. of 87% by weight of EPBC, a fluorine-containing compound having the same polyfluorohydrocarbon group and polyoxyethylene group as in Example 2, and a particle size of 10 μm a composition comprising the masterbatch 13% by weight, containing 7% and the back layer, the linear low density polyethylene density is 0.880 g / cm ³ as an intermediate layer, density of 0.922 g / cm ³ straight Using a T-die type composite film forming machine with a chain low density polyethylene as the adhesive layer, the back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is 40 μm. A coextruded surface protective film was prepared so that

<Example 8>
87% by weight of a high-pressure low-density polyethylene having a density of 0.930 g / cm ³ , 6% by weight of a fluorine-containing compound having the same polyfluorohydrocarbon group and polyoxyethylene group as in Example 1, and a particle size of 10 μm The intermediate layer of a linear low density polyethylene having a density of 0.880 g / cm ³ with a composition comprising 13% by weight of a master batch containing 7% of silica (the base resin is the high pressure method low density polyethylene). A pressure-sensitive adhesive layer comprising a composition comprising 90% by weight of a linear low density polyethylene having a density of 0.910 g / cm ³ and 10% by weight of a styrene / ethylene / butylene / styrene copolymer (abbreviated as SEBS). Using a T-die type composite film forming machine, the back layer thickness ratio is 8%, the intermediate layer thickness ratio is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is 40 μm. A coextruded surface protective film was prepared.

<Example 9>
94% by weight of high-pressure low-density polyethylene having a density of 0.924 g / cm ³ , 6% by weight of a fluorine-containing compound having the same polyfluorohydrocarbon group and polyoxyethylene group as in Example 1, and a particle size of 11 μm A surface protective film was prepared in the same manner as in Example 1 except that a composition comprising 6% by weight of a master batch containing 6% of silica (the base resin was the above-described high-pressure low-density polyethylene) was used as the back layer.

<Comparative Example 1>
Density is the back layer of high density polyethylene is 0.964 g / cm ^3, density of the high-pressure low-density polyethylene is 0.924 g / cm ³ as an intermediate layer, linear density 0.922 g / cm ³ Low Using a T-die type composite film forming machine with density polyethylene as the adhesive layer, the back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is 40 μm. A coextruded surface protective film was prepared.

<Comparative example 2>
Comparative Example 1 except that the composition of the back layer was a propylene / ethylene block copolymer (abbreviated as B-PP) containing 15% by weight of an ethylene / propylene copolymer as a rubber component having a density of 0.900 g / cm ^3. Similarly, a surface protective film was prepared.

<Comparative Example 3>
Using a T-die type composite film forming machine with a high-density polyethylene having a density of 0.951 g / cm ³ as a back layer and an intermediate layer and an ethylene / vinyl acetate copolymer having a vinyl acetate concentration of 10% by weight as an adhesive layer A co-extruded surface protective film was prepared so that the back layer thickness ratio was 8%, the intermediate layer thickness was 72%, the adhesive layer thickness ratio was 20%, and the total thickness was 40 μm.

<Comparative Example 4>
A high-pressure low-density polyethylene 67 wt% density of 0.919 g / cm ^3, high density polyethylene 17 wt% density of 0.956 g / cm ^3, linear density is at 0.921 g / cm ³ A composition comprising 15.5% by weight of low-density polyethylene and 0.5% by weight of silica having a particle size of 3 μ is used as a back layer and an intermediate layer, and a linear low-density polyethylene having a density of 0.922 g / cm ³ is used as an adhesive layer. Using a T-die type composite film forming machine, coextruded surface protective film so that the back layer thickness ratio is 8%, the intermediate layer thickness is 72%, the adhesive layer thickness ratio is 20%, and the total thickness is 40 μm. Created.

<Comparative Example 5>
87% by weight of linear low-density polyethylene having a density of 0.870 g / cm ³ , 6% by weight of a fluorine-containing compound having the same polyfluorohydrocarbon group and polyoxyethylene group as in Example 1, and a particle size A composition consisting of 13% by weight of a master batch containing 7% of 10 μm silica (the base resin is the above-mentioned linear low density polyethylene) is used as the back layer, the density is 0.900 g / cm ³ , and ethylene / propylene is used as the rubber component. Using a T-die type composite film forming machine with a propylene / ethylene block copolymer containing 20% by weight of a polymer as an intermediate layer and a linear low density polyethylene with a density of 0.922 g / cm ³ as an adhesive layer, A co-extruded surface protective film was prepared so that the ratio was 8%, the intermediate layer thickness was 72%, the adhesive layer thickness ratio was 20%, and the total thickness was 40 μm.

  The evaluation results of Examples 1 to 9 and Comparative Examples 1 to 5 are shown in Tables 1 and 2. In the table, LDPE refers to high-pressure low-density polyethylene, LLDPE refers to linear low-density polyethylene, EVA refers to ethylene / vinyl acetate copolymer, and EPBC refers to propylene / ethylene / butene random copolymer. It refers to a polymer, and B-PP refers to a propylene / ethylene block copolymer.

  The surface protective films obtained in Examples 1 to 9 all had a haze of less than 10% after heating at 160 ° C. and slow cooling, and less than 5% after heating at 200 ° C. and slow cooling. It is 15 μm or less, and there is no concern that the surface protective film after heat molding becomes cloudy and impairs transparency, and the appearance of final products such as helmets and carrier bag exteriors is not impaired. In addition, the coefficient of friction is 1.5 or less for both static friction coefficient and dynamic friction coefficient. When the surface protection film is wound up as a roll, the films are slippery and the air protection is less likely to cause deformation of the surface protection film. It can finish suitably.

  The surface protective films obtained in the comparative examples all have a haze of 10% or more, a center line average roughness of 0.15 μm or more, and insufficient transparency, which impairs the appearance of the final product. In addition, the surface protective film obtained in Comparative Example 4 has both a static friction coefficient and a dynamic friction coefficient exceeding 1.5 and poor transparency, and air trapping occurs when the surface protective film is wound on a roll. The surface protective film is deformed, and all the required characteristics cannot be satisfied.

Claims (10)

  A surface protective film comprising an adhesive layer, an intermediate layer and a back layer, the back layer comprising a polyolefin resin composition containing 0.3 wt% to 10 wt% of a fluorine-based mold release agent, and constituting the intermediate layer Is mainly composed of low density polyethylene, has a haze of 10% or less after heating at 160 ° C. for 1 minute or longer and gradually cooling, and a haze after heating at 200 ° C. for 1 minute or longer and 5% or less. A surface protective film characterized by that.   The surface protection film of Claim 1 whose centerline surface roughness (Ra) of the said back surface layer is 0.15 micrometer or less.   The surface protection film according to claim 1 or 2, wherein inorganic particles having a particle size of 5 µm or more are added to the back layer. The surface protection film according to any one of claims 1 to 3, wherein the polyolefin resin of the back layer is a high-pressure low-density polyethylene having a density of 0.90 to 0.93 g / cm ³ .   The surface protection film in any one of Claims 1-3 whose polyolefin resin of the said back surface layer is a polypropylene-type random copolymer. Low density polyethylene, linear low density having a density of high-pressure low-density polyethylene or 0.88~0.93g / cm ³ having a density of 0.90~0.93g / cm ³ constituting the intermediate layer The surface protection film according to any one of claims 1 to 5, which is polyethylene.   The surface protection film in any one of Claims 1-6 whose resin which comprises the said adhesion layer is an ethylene-vinyl acetate copolymer or a linear low density polyethylene.   The surface protection film according to any one of claims 1 to 7, wherein the fluorine-based release agent is a fluorine-containing compound having a polyfluorohydrocarbon group and a polyoxyethylene group.   The surface protective film according to any one of claims 1 to 8 is bonded to one side of a resin plate made of polycarbonate or polymethyl methacrylate, and a printed layer and an acrylonitrile / butadiene / styrene copolymer or polycarbonate on the opposite side. A structure with stacked layers.   A molded body obtained by heat-molding the structure according to claim 9 with the surface on which the surface protective film is bonded as a front surface.