JP2007185781A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film capable of being suppressed in blocking even if pressure-sensitive adhesive strength is planned high while holding good productivity and film forming properties due to a coextrusion multilayer lamination method, capable of keeping a pressure-sensitive adhesive surface clean until use, having sufficient pressure-sensitive adhesive strength with respect to an adherend and capable of smoothly peeling a peeling layer at the time of use. <P>SOLUTION: The surface protective film is constituted by laminating the peeling layer (A) comprising a polyamide resin, a pressure-sensitive adhesive layer (B) comprising an amorphous α-olefinic polymer and a propylene polymer and a base material layer (C) comprising a thermoplastic resin in an order of (A)/(B)/(C) by the coextrusion multilayer lamination method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is affixed to the surface of various resin plates, glass plates, and steel plates including building materials, electrical / electronic fields, etc., and the adherend is damaged, contaminated, etc. during storage, transportation and post-processing. The present invention relates to a surface protective film that protects against damage. In particular, the present invention relates to a surface protective film that can prevent blocking of the film even if the adhesive strength is designed strongly, keeps the adhesive surface clean until it is used, and does not contaminate the adherend.

  The basic required performance for the surface protection film is that it has excellent adhesion workability that can be uniformly applied to the above-mentioned various adherends, and that the adherends are floated and peeled off during storage, transportation, etc. It has moderate adhesive strength that does not occur, there are few environmental changes during storage of the adherend and changes in adhesive strength over time due to post-processing, it can be easily peeled off, and it will not contaminate the surface of the adherend after peeling. Etc. However, in recent years, with regard to optical-related members such as light guide plates used in flat panel displays (FPD), the need for cleanliness of the surface protective film has increased due to the need for visual inspection with the surface protective film attached. It is coming. In addition, in order to increase the functionality of optical-related members, irregularities may be formed on the surface, and a stronger adhesive force is required.

  As a conventional surface protection film, a pressure sensitive adhesive in which an urethane, acrylic or rubber resin is dissolved in an organic solvent is applied to one side of a film substrate made of polyvinyl chloride resin, polyethylene resin, polypropylene resin or the like. A surface protective film in which an adhesive layer is formed after drying is known. However, since this surface protective film requires at least two steps of a film base material production process and an adhesive coating process, a complicated production process is required, resulting in a problem that the production cost is increased. In addition, there is also a problem that the environmental load becomes high because it is necessary to remove a large amount of the organic solvent when drying after applying the adhesive.

  Therefore, a self-adhesive surface protective film in which a base film layer and an adhesive layer are simultaneously extruded and laminated by a coextrusion multilayer lamination method has been proposed (see, for example, Patent Document 1). This self-adhesive surface protective film can be manufactured in one step, can reduce the manufacturing cost, and has an effect that the environmental load is low because no organic solvent is used. However, the self-adhesive surface protective film exposes the adhesive surface to the air during film formation or slitting, so adhesion of dust in the air to the adhesive surface, or the adhesive surface comes into contact with a machine guide roll, etc. As a result, there is a problem that dust, dust, and other foreign matters adhere to the adhesive surface and the adhesive surface is contaminated. Therefore, in order to produce a surface protective film for applications that require cleanliness of the adhesive surface, there has been a problem that the entire production line of the film needs to be made into a clean room. Further, when the adhesive strength is designed strongly, there is a problem that after the film is wound up in a roll shape, blocking progresses before use, and an excessive rewinding force is required to deteriorate workability.

  As a method of suppressing the above blocking, after extruding the base material layer and the adhesive layer simultaneously by co-extrusion multilayer lamination method, cooling and solidifying, by applying a release agent on the surface of the base material layer by a roll coater or spray, A surface protective sheet that suppresses blocking has been proposed (see, for example, Patent Document 2). However, when a release agent is applied with a roll coater or the like, in addition to a normal multilayer film forming apparatus, a coating apparatus, a drying apparatus, etc. are required. When a solvent was used, the problem of environmental burden remained.

  As another method for suppressing blocking, a surface protective film formed by coextrusion molding a surface protective film having a three-layer structure in which an adhesive layer is provided on one side of a base material layer and a release layer is provided on the other side. Has been proposed (see, for example, Patent Document 3). In this surface protective film, blocking of the fatty acid amide contained in the release layer is suppressed to some extent by bleeding out to the release layer surface. However, since the fatty acid amide bleed out on the surface of the release layer contaminates the adhesive surface of the adhesive layer, there is a problem of contaminating the surface of the adherend when the surface protective film is attached to the adherend. It was. In addition, there is a problem that the adhesive strength is reduced due to the fatty acid amide contaminating the adhesive surface.

Therefore, as a method for preventing contamination of the adhesive surface, a method has been proposed in which a surface protective film in which an adhesive layer is disposed between a base material layer and a release layer is coextruded with a multilayer coextrusion circular die (for example, , See Patent Document 4). In this surface protective film, since the adhesive surface of the adhesive layer is protected by the release layer, blocking of the adhesive layer and contamination of the adhesive surface due to dust can be prevented. However, in production by multilayer coextrusion using a T-die that can produce a wider film instead of a multilayer coextrusion circular die, due to the difference in fluidity at the time of melting of the resin used for the adhesive layer and the release layer, There was a problem that film formation defects such as poor film appearance and uneven thickness of each layer occurred. In addition, since a hydrogenated random copolymer composed of styrene and diene hydrocarbon, a mixture thereof, or an ethylene-vinyl acetate copolymer mixture is used as the adhesive layer, there is a problem that the adhesive strength of the surface protective film is insufficient. There was also a problem that the release layer could not be smoothly peeled off when used.
JP 2002-265704 A JP2003-041216 JP 2002-285116 A JP 2005-111769 A

  The object of the present invention is to maintain the good productivity and film formability by the co-extrusion multilayer lamination method, and to suppress blocking even if the adhesive strength is designed high, and clean the adhesive surface of the surface protective film until it is used. Furthermore, it is to provide a surface protective film having sufficient peel strength to the adherend and having a peelability capable of smoothly peeling the release layer during use.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have found that a release layer made of a polyamide resin, an adhesive layer made of an amorphous α-olefin polymer and a propylene polymer, and a thermoplastic resin The surface protective film obtained by laminating the base layer made of the above by the coextrusion laminating method can prevent blocking even if the adhesive strength is designed to be high, and clean the adhesive surface until the surface protective film is used. Furthermore, the present inventors have found that the adhesive layer has sufficient adhesive force to the adherend and can release the release layer smoothly during use, and the present invention has been completed.

  That is, the present invention includes a release layer (A) made of a polyamide resin, an adhesive layer (B) made of an amorphous α-olefin polymer and a propylene polymer, and a base material layer made of a thermoplastic resin ( And (C) are coextrusion laminated in the order of (A) / (B) / (C).

  Since the surface protective film of the present invention has a releasability that can prevent blocking and can smoothly peel the release layer, the workability when using the surface protective film is improved. In the surface protective film of the present invention, a release layer is laminated by a coextrusion method during film formation on the adhesive surface to be adhered to the adherend, so that the adhesive surface is in the air until it is used. Since it is isolated from the film, it is excellent in cleanliness of the adhesive surface of the film, and can be suitably used in applications where optically related members such as light guide plates that require cleanliness are used as adherends. Since it has a practical adhesive force even to an adherend having a surface, it can be applied to an optical-related member having irregularities on its surface in order to achieve high functionality.

  The present invention is described in detail below. The surface protective film of the present invention comprises a release layer (A) made of a polyamide resin, an adhesive layer (B) made of an amorphous α-olefin polymer and a propylene polymer, and a substrate made of a thermoplastic resin. The layer (C) is coextruded and laminated in the order of (A) / (B) / (C).

  Examples of the polyamide resin used for the release layer (A) include polyamide 6, polyamide 12, polyamide 66, polyamide 610, polyamide 11, polyamide 46, polyamide 412, polyamide MXD-6, and the like as polyamide resins. Examples thereof include copolymer polyamides obtained by copolymerizing these polyamides. These polyamide resins may be used alone or in combination of two or more. By using these polyamide-based resins for the release layer (A), a surface protective film excellent in easy peelability from the adhesive layer (B) can be obtained. In particular, among polyamide-based resins, polyamide 6 and 6-66 copolymer polyamide obtained by copolymerizing polyamide 6 and polyamide 66 are preferable because they are excellent in easy peelability.

  The peel strength (peel rate 300 mm / min, peel angle 180 °) between the release layer (A) and the adhesive layer (B) is preferably 5.0 N / 25 mm or less, more preferably 2.0 N / 25 mm or less. preferable. When the peel strength is 5.0 N / 25 mm or less, the release layer can be easily peeled off, and can be peeled smoothly thereafter, resulting in excellent adhesion workability.

  The resin used for the adhesive layer (B) is an amorphous α-olefin polymer and a propylene resin.

  The amorphous α-olefin polymer used for the adhesive layer (B) is a polymer containing a monomer unit based on an α-olefin having 3 to 20 carbon atoms, and is a differential scanning calorimeter (DSC). ) In the measurement range of −100 to 200 ° C., neither a melting peak having a heat of fusion of 1 J / g or more nor a crystallization peak having a heat of crystallization of 1 J / g or more is observed.

  The α-olefin having 3 to 20 carbon atoms may be linear or branched, for example, propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1 , Nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nanodecene-1, eicosene-1, etc. Linear α-olefin; branched such as 3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1, 2-ethyl-1-hexene, 2,2,4-trimethylpentene-1, etc. Α-olefins and the like. The amorphous α-olefin polymer is preferably a polymer containing two or more of these α-olefins, and is a monomer unit based on a monomer unit based on propylene and an α-olefin having 4 to 20 carbon atoms. A polymer containing one or more body units is more preferable. The amorphous α-olefin polymer may contain a monomer other than the α-olefin. Examples of such monomers include ethylene, polyene compounds, cyclic olefins, vinyl aromatic compounds, and the like. Among the amorphous α-olefin polymers, an amorphous propylene-butene-1 copolymer and an amorphous propylene-ethylene-butene-1 copolymer are preferable. These amorphous α-olefin polymers may be used alone or in combination of two or more.

  The monomer unit based on propylene in the amorphous propylene-butene-1 copolymer is 70% by mass when the total monomer units of the amorphous propylene-butene-1 copolymer is 100% by mass. The above is preferable, More preferably, it is 80 mass% or more, More preferably, it is 90 mass% or more. When the monomer unit based on propylene is within this range, the heat resistance is improved.

  The monomer unit based on propylene in the amorphous propylene-ethylene-butene-1 copolymer is 100% by mass based on the total monomer units of the amorphous propylene-ethylene-butene-1 copolymer. , 50% by mass or more, preferably 60% by mass or more. When the monomer unit based on propylene is within this range, the heat resistance is improved. The monomer unit based on ethylene in the amorphous propylene-ethylene-butene-1 copolymer is preferably 10% by mass or more, more preferably 20% by mass or more. If the monomer unit based on ethylene is in this range, the adhesive layer becomes relatively soft, and even if the adherend surface has irregularities, it adheres in a form that follows the irregularities. Power is obtained.

  The intrinsic viscosity [η] of the amorphous α-olefin polymer is preferably from 0.1 to 10.0 dl / g, more preferably from 0.7 to 7.0 dl / g. Furthermore, the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is preferably more than 1 and 4 or less, more preferably 2 to 3. . When the intrinsic viscosity and molecular weight distribution of the amorphous α-olefin polymer are in this range, the heat resistance, transparency, and adhesiveness are improved, and the adherend with the surface protective film attached is stored for a long time. Even when exposed to a high temperature environment, the low molecular weight component in the amorphous α-olefin polymer (B1) does not migrate to the adherend surface and contaminate the adherend. In addition, since the amorphous α-olefin polymer is an olefin polymer, the time-lapse due to the alteration of the resin such as deacetic acid as in the case where the ethylene-vinyl acetate copolymer is used for the adhesive layer. There is no significant increase in adhesive strength, and stable adhesive strength can be maintained over a long period of time.

  Examples of the method for producing the amorphous α-olefin polymer include a method of polymerizing with a metallocene catalyst using a gas phase polymerization method, a solution polymerization method, a slurry polymerization method, a bulk polymerization method, and the like. As a more preferable manufacturing method, the manufacturing method disclosed in JP-A-2002-348417 is exemplified.

  On the other hand, examples of the propylene polymer used for the adhesive layer (B) include a propylene homopolymer, a propylene-ethylene copolymer, a polypropylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. Etc. These propylene polymers may be used alone or in combination of two or more. These propylene polymers are preferably crystalline, and have an MFR (measured at 230 ° C. and 21.18 N) of 0.5 to 30.0 g / 10 minutes and a melting point of 120 to 165. Those having a temperature of ° C are preferred, more preferably those having an MFR of 2.0 to 15.0 g / 10 min and a melting point of 130 to 165 ° C. If MFR and melting | fusing point are this range, there will be little change with time of adhesive force, and the film-forming property of a film will improve. Further, by adding a propylene polymer to the pressure-sensitive adhesive layer (B), the pressure-sensitive adhesive force can be adjusted according to the required properties depending on the surface state of the adherend, the material of the adherend, the use, and the like.

  The blending ratio of the amorphous α-olefin polymer and the propylene polymer is preferably amorphous α-olefin polymer: propylene polymer = 30 to 95:70 to 5 on a mass basis. If the blending ratio of the amorphous α-olefin polymer and the propylene polymer is within this range, sufficient adhesive strength can be obtained, and these resin pellets used as raw materials during film production are blocked by adhesive strength. The handling becomes good without doing. Moreover, by adjusting the blending ratio of the amorphous α-olefin polymer and the propylene polymer, it can be made to correspond to the required adhesive strength, and is about 0.1 to 7.0 N / The adhesive strength can be adjusted to about 25 mm.

  Further, in the surface protective film of the present invention, it is preferable to increase the uniformity of the appearance, thickness, etc. of the film in order to ensure sufficient mechanical suitability and adhesiveness uniformity in sticking to an adherend. . In order to improve the uniformity of the appearance, thickness, etc. of the film, the relative viscosity η of the polyamide resin used in the release layer (A) (value measured with a 96% by mass sulfuric acid solvent in accordance with JIS K6810) and , A melt flow rate of a resin composition comprising an amorphous α-olefin polymer and a propylene polymer used for the adhesive layer (B) (hereinafter referred to as “MFR”; measurement temperature 230 in accordance with JIS K7210) It is preferable that the value measured at a temperature of 21 ° C. and a load of 21.18 N be within a specific range. The relative viscosity η of the polyamide-based resin is preferably in the range of 2.5 to 5.0, and more preferably in the range of 3.0 to 4.5. On the other hand, the MFR of the resin composition comprising the amorphous α-olefin polymer and the propylene polymer is preferably in the range of 1.0 to 20.0 g / 10 minutes, and 2.0 to 15.0 g / 10. A range of minutes is more preferred.

  Furthermore, when producing a laminated film by the coextrusion multilayer lamination method, from the viscosity of the polyamide resin used for the release layer and the amorphous α-olefin polymer and propylene polymer used for the adhesive layer It is preferable to balance the viscosity of the resulting resin composition because the film formability of the laminated film is improved. Specifically, the product of the relative viscosity η of the polyamide resin and the MFR value of the resin composition comprising the amorphous α-olefin polymer and the propylene polymer is in the range of 10 to 50. It is preferable that The relative viscosity η of the polyamide resin and the MFR of the resin composition comprising the amorphous α-olefin polymer and the propylene polymer are each in the above ranges, and the product of these two values is If it is within the range, it is possible to further improve the uniformity of the appearance, thickness, etc. of the film, and to obtain a surface protective film that can be sufficiently used in optical-related member applications that require higher accuracy and uniformity. be able to.

  The resin used for the base material layer (C) is not particularly limited as long as it is a thermoplastic resin and can maintain sufficient adhesion with the adhesive layer (B), but is preferably a polyolefin resin. Examples of the polyolefin resin include propylene homopolymers, propylene-ethylene copolymers, propylene polymers such as propylene-ethylene-butene-1 copolymers, low density polyethylene, medium density polyethylene, high density polyethylene, Examples thereof include ethylene polymers such as linear low density polyethylene. These propylene polymers and ethylene polymers may be used alone or in combination of two or more. Among these thermoplastic resins, it is preferable to use a propylene homopolymer because the heat resistance of the surface protective film can be improved.

  In addition, the base layer (C) may contain additives such as a lubricant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, an antifogging agent, and a colorant as long as the effects of the present invention are not impaired. It may be added as appropriate to provide functionality. In order to prevent blocking, organic beads such as styrene resin beads, (meth) acrylate resin beads, polyurethane resin beads; silica, hydrophobized silica, spherical silica, soft calcium carbonate, titanium oxide Inorganic fine particles such as talc; antiblocking agents such as silicone resins may be added.

  The surface protective film of the present invention is composed of three layers comprising the release layer (A), the pressure-sensitive adhesive layer (B) and the base material layer (C) as described above, and further on the base material layer (C). A surface layer (D) may be provided. The resin used for the surface layer is not particularly limited as long as it is a thermoplastic resin, but the type of the resin may be appropriately selected according to the required characteristics of the surface protective film. Moreover, you may add various additives and antiblocking agents to a surface layer (D) similarly to a base material layer (C).

  The MFR (C) of the thermoplastic resin used for the base material layer (C) is the MFR (B of the resin composition comprising the amorphous α-olefin polymer and the propylene polymer used for the adhesive layer (B). It is preferable that the value is substantially equivalent to. Specifically, the range of the absolute value of MFR (B) and MFR (C) is preferably 0 to 10, and more preferably 0 to 6. Two kinds of this

  In the surface protective film of the present invention, the thickness of the adhesive layer (A) is preferably 3 to 30 μm, more preferably 5 to 25 μm. When the thickness of the pressure-sensitive adhesive layer (A) is within this range, the pressure-sensitive adhesive properties and the film formability of the laminated film are good. Moreover, 5-50 micrometers is preferable and, as for the thickness of the said peeling layer (B), More preferably, it is 10-40 micrometers. When the thickness of the release layer (B) is within this range, the film-forming property of the laminated film, the release property of the release layer, and the winding workability after peeling are improved. On the other hand, the thickness of the base material layer (C) can be appropriately set according to the properties required for the surface protective film, but is usually preferably 10 to 100 μm. When the thickness of the base material layer (C) is within this range, the design according to the required characteristics is easy, and the film formability of the laminated film is also good. Furthermore, when providing the said surface layer (D) on a base material layer (C), 3-30 micrometers is preferable and, as for the thickness of a surface layer (D), More preferably, it is 5-20 micrometers. When the thickness of the surface layer is within this range, the film formability of the laminated film is good.

  The method for producing the surface protective film of the present invention is not particularly limited as long as it is a coextrusion lamination method. For example, the resin used for each resin layer is melted by using three or more extruders, Examples include a method of laminating in a molten state by a coextrusion method such as an extrusion die method or a feed block method, and then processing into a film using a method such as inflation or a T-die / chill roll method. Among these methods, the T-die chill roll method capable of efficiently producing a film with high thickness accuracy and widening is more preferable.

  As a method of using the surface protective film of the present invention, the pressure-sensitive adhesive layer (B) and the release layer (A) are peeled off at the front end of the surface protective film, and each is separately fed, and the release layer (A) is transferred to a roller or the like. The winding and the pressure-sensitive adhesive layer (B) can be applied to the adherend using a usual method. In addition, when it is difficult to adhere the adherend to the adherend while peeling the adhesive layer (B) and the easily peelable layer (A), pull the peelable layer (B) from the adhesive layer (B) in advance in a separate process. The surface protective film part which peels and peels continuously and consists of an adhesion layer (B) and a base material layer (A) may be wound up, and you may finish in a normal product roll shape previously. In this case, in order to maintain the cleanliness of the adhesive surface of the film, it is preferable that the roll take-up portion is locally a small clean room.

  The present invention will be specifically described below with reference to examples and comparative examples.

Example 1
6-66 copolymer polyamide (density 1.14 g / cm ³ , melting point 198 ° C., relative viscosity η (96 mass% sulfuric acid solvent): 4.1) is used as the release layer resin, Crystalline α-olefin polymer composition (“Tufselen H3002B” manufactured by Sumitomo Chemical Co., Ltd., amorphous propylene-butene-1 copolymer / propylene homopolymer = 95/5 resin composition, MFR (230 ° C. 21.18N): 3.0 g / 10 min; hereinafter referred to as “amorphous α-olefin polymer composition (1)”), and as a base layer resin, propylene homopolymer, density 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “HOPP”. ) And an extrusion layer 260 (caliber 40 mm), an adhesive layer extruder (caliber 40 mm) and a substrate layer extruder (caliber 50 mm), respectively, and an extrusion temperature of 260 ° C. by co-extrusion. After extruding from the T-die so that the thickness of the release layer is 20 μm, the thickness of the adhesive layer is 10 μm, and the thickness of the base material layer is 50 μm, cooling with a water-cooled metal cooling roll at 40 ° C. The surface protective film was obtained. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 2)
6-66 copolymer polyamide (density 1.14 g / cm ³ , melting point 198 ° C., relative viscosity η (96 mass% sulfuric acid solvent): 4.1) is used as the release layer resin, Crystalline α-olefin polymer composition (“Tufselen H3004” manufactured by Sumitomo Chemical Co., Ltd., amorphous propylene-ethylene-butene-1 copolymer / propylene homopolymer = 95/5 resin composition, MFR ( 230 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “amorphous α-olefin polymer composition (2)”), and a propylene homopolymer as a resin for the base layer , Density 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “HOPP”. ) And an extrusion layer 260 (caliber 40 mm), an adhesive layer extruder (caliber 40 mm) and a substrate layer extruder (caliber 50 mm), respectively, and an extrusion temperature of 260 ° C. by co-extrusion. After extruding from the T-die so that the thickness of the release layer is 20 μm, the thickness of the adhesive layer is 10 μm, and the thickness of the base material layer is 50 μm, cooling with a water-cooled metal cooling roll at 40 ° C. The surface protective film was obtained. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 3)
Polyamide 6 (density 1.14 g / cm ³ , melting point 220 ° C., relative viscosity η (96 mass% sulfuric acid solvent): 3.3) was used as the release layer resin, and the adhesive layer resin was used in Example 1. Amorphous α-olefin polymer composition (1) 50 parts by mass and crystalline propylene-butene-1 copolymer, density 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 20. 0 g / 10 min) 50 mass parts of resin composition (MFR (230 ° C., 21.18 N): 13.0 g / 10 min; hereinafter, “amorphous α-olefin polymer composition (3)” And a propylene homopolymer, density 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “HOPP”. ), And supplied to an extruder for release layer (caliber 40 mm), an extruder for adhesive layer (caliber 40 mm) and an extruder for base layer (caliber 50 mm), respectively, and at an extrusion temperature of 260 ° C. by co-extrusion method. -Extrude from the die so that the thickness of the release layer is 15 μm, the thickness of the adhesive layer is 10 μm, the thickness of the base material layer is 50 μm, and after cooling with a 40 ° C. water-cooled metal cooling roll, A surface protective film was obtained. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Comparative Example 1)
The polyamide 6 used in Example 1 was used as the release layer resin, and the ethylene-vinyl acetate copolymer, density: 0.945 g / cm ³ , MFR (190 ° C., 21.18 N) as the adhesive layer resin: 5.0 g / 10 min, vinyl acetate content: 20% by mass; hereinafter referred to as “EVA”. ), As a resin for the base layer, medium density polyethylene, density: 0.937 g / cm ³ , MFR (190 ° C., 21.18 N); 7.0 g / 10 min; hereinafter referred to as “MDPE”. ), And supplied to an extruder for release layer (caliber 40 mm), an extruder for adhesive layer (caliber 40 mm) and an extruder for base layer (caliber 50 mm), respectively, and at an extrusion temperature of 260 ° C. by co-extrusion method. -Extrude from the die so that the thickness of the release layer is 15 μm, the thickness of the adhesive layer is 15 μm, and the thickness of the base material layer is 45 μm, and after cooling with a 40 ° C. water-cooled metal cooling roll, A surface protective film was obtained. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Comparative Example 2)
As the release layer resin, the 6-66 copolymer polyamide used in Example 1 was used, and as the adhesive layer resin, a styrene-ethylene-propylene-styrene block copolymer ("Septon 2063" manufactured by Kuraray Co., Ltd., MFR ( 230 ° C., 21.18 N): 7.0 g / 10 min; hereinafter referred to as “SEPS”) and a tackifier (“Arcon P-100” manufactured by Arakawa Chemical Industries, Ltd.) were used. As the resin for the base layer, low density polyethylene, density 0.922 g / cm ³ , MFR (190 ° C., 21.18 N) is 4.5 g / 10 min; hereinafter referred to as “LDPE”. ), And supplied to an extruder for release layer (caliber 40 mm), an extruder for adhesive layer (caliber 40 mm) and an extruder for base layer (caliber 50 mm), respectively, and at an extrusion temperature of 260 ° C. by co-extrusion method. -Extrude from the die so that the thickness of the release layer is 20 μm, the thickness of the adhesive layer is 10 μm, and the thickness of the base material layer is 50 μm, and after cooling with a 40 ° C. water-cooled metal cooling roll, A surface protective film was obtained. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Comparative Example 3)
A surface protective film was obtained in the same manner as in Comparative Example 3 except that the release layer was not provided.

  The following measurements and evaluations were performed on the surface protective films obtained in Examples 1 to 3 and Comparative Examples 1 to 4 described above.

(1) Evaluation of film formability The appearance of the surface protective film was visually observed, and the film formability was evaluated according to the following criteria.
A: A film having a uniform and uniform film appearance.
X: Those in which periodic unevenness, scale-like or stripe-like unevenness occurs.

(2) Evaluation of the uniformity of the thickness of all films Total film thickness at a total of 13 locations at intervals of 5 cm including both ends of the film on the line perpendicular to the extrusion direction of the surface protection film (with a trim cut width of 600 mm) Was measured with a dial gauge, the deviation from the set value of the measured thickness was calculated, and the uniformity of the thickness of all films was evaluated according to the following criteria.
◯: The thickness deviation is ± 10% or less with respect to the set value.
X: Thickness deviation exceeds ± 10% with respect to the set value.

(3) Evaluation of the uniformity of the thickness of the release layer The release layer of the surface protective film (with a width of 600 mm with trimmed off) is peeled off, including both ends of the film on a line perpendicular to the extrusion direction of the release layer. A total of 13 thicknesses were measured with a dial gauge at intervals of 5 cm, the deviation from the set value of the measured thickness was calculated, and the uniformity of the thickness of the release layer was evaluated according to the following criteria.
◯: The thickness deviation is ± 10% or less with respect to the set value.
X: Thickness deviation exceeds ± 10% with respect to the set value.

(4) Evaluation of peelability of release layer The surface protective film was cut into a test piece having a length of 180 mm and a width of 25 mm, and adhesive tape was applied from the front and back sides at the corner of the test piece. The release layer was peeled from the layer by 60 mm in the longitudinal direction. Grab the peeled part of this test piece and the remaining part (adhesive layer and base material layer) of the peeled layer with an air chuck, and use a tensile testing machine (manufactured by A & D Co., Ltd.). The peel strength was measured after peeling in the 180 ° direction at a speed of 300 mm / min. The peel strength was the center value of the amplitude in the measurement chart. From the measured peel strength, the peelability of the release layer was evaluated according to the following criteria.
○: The peel force is 5 N / 25 mm or less.
X: Peeling force exceeds 5 N / 25 mm.

(5) Evaluation of adhesiveness The surface protective film was cut into a test piece having a size of 180 mm in length and 25 mm in width, and an adhesive tape was applied from both the front and back sides at the corners of the test piece. The layer was peeled off. In a temperature-controlled room at 23 ° C. and 50% RH, the acrylic sheet (“Acrylite” manufactured by Mitsubishi Rayon Co., Ltd., mirror-finished product, length 150 mm) is used in a thermostatic chamber at 23 ° C. and 50% RH. X width 50 mm x thickness 2 mm). After the acrylic plate with the film attached was left in a temperature-controlled room for 1 hour, the film was peeled off 20 mm in the longitudinal direction from one end of the acrylic plate. A biaxially stretched polyester film (thickness: 100 μm) previously cut into a size of 150 mm long × 25 mm wide was connected to the end of the peeled film with a tape. Grip the connected biaxially stretched polyester film and the part of the acrylic plate only from which the surface protective film is peeled off by 20 mm with an air chuck, and use a tensile tester (manufactured by A & D Co., Ltd.) to 300 mm. The peel strength was measured after peeling in the 180 ° direction at a speed of / min. From the measured adhesive strength, the adhesiveness was evaluated according to the following criteria.
○: Adhesive strength is 0.5 N / 25 mm or more.
X: Adhesive strength is less than 0.5 N / 25 mm.

(6) Evaluation of blocking resistance The surface protective film was wound up to a length of 100 m to form a roll, slit at a width of 100 mm, and stored in a dryer at 40 ° C. for 7 days. Next, the film was taken out from the dryer, left in a thermostatic chamber at 23 ° C. and 50% RH for 1 hour, and then the load when the film was rewound from the roll sample was measured with a push-pull gauge to obtain a blocking force. From the obtained blocking force, blocking resistance was evaluated according to the following criteria.
○: The blocking force is less than 1 N / 100 mm.
X: The blocking force exceeds 1 N / 100 mm.

  Table 1 shows the layer structure of the surface protective films obtained in Examples 1 to 3 and Comparative Examples 1 to 3 (type and ratio of resin used in each layer and thickness of each layer) and the measurement results obtained above. Shown in 1 and 2. In addition, the value in the bracket | parenthesis in the resin composition of the adhesion layer of Examples 1-3 showed the ratio of resin contained in an amorphous alpha-olefin type polymer composition (1)-(3). Is.

  From the results shown in Table 1, the surface protective films of the present invention of Examples 1 to 3 have good film formability, and the appearance, the thickness of the entire film, and the thickness of the release layer are uniform. It turned out that the property is also excellent. Moreover, even if it designed to the high adhesive force of about 4-6N / 25mm, it turned out that favorable handling is possible without blocking and the peelability of a peeling layer is also favorable. Furthermore, since the surface of the adhesive layer (adhesive surface) is covered with a release layer during film formation and is not exposed to the air until use, foreign matter such as dust does not adhere to the adhesive surface and is extremely high It has been found that cleanliness can be maintained and that it can be suitably used in fields where the required characteristics of applications such as optical related members are severe.

  From the results shown in Table 2, it was found that the surface protective films of Comparative Examples 1 to 3 had the following problems.

  Comparative Example 1 is an example of a surface protective film using EVA for the adhesive layer and polyamide 6 for the release layer. In the surface protective film of Comparative Example 1, scale-like unevenness and streak-like unevenness are generated on the entire surface of the film, and there is a problem in film formability, and the uniformity of the thickness of the entire film and the thickness of the release layer is also observed. It turned out to be insufficient. In addition, it was found that the surface of the adhesive layer (adhesive surface) was uneven and the adhesive strength was insufficient.

  The comparative example 2 is an example of the surface protection film which designed the adhesive force highly using SEPS for the adhesion layer. The surface protective film of Comparative Example 2 had good film formability, but the peel strength when peeling the release layer was very high at 10 N / 25 mm, and the release layer when using the surface protective film was used. It was found that there was a problem in workability when peeling.

Comparative Example 3 is an example of a surface protective film having a two-layer structure of a base material layer and an adhesive layer, in which the adhesive force is designed to be high using SEPS for the adhesive layer. The surface protective film of Comparative Example 3 had good film formability, but because it was not provided with a release layer, it had a very high blocking force of 14 N / 100 mm, had a problem with blocking resistance, and had a wide width. It was found that when this film was used, it was difficult to rewind the film.

Claims (4)

A release layer (A) made of a polyamide resin, an adhesive layer (B) made of an amorphous α-olefin polymer and a propylene polymer, and a base material layer (C) made of a thermoplastic resin ( A surface protective film which is coextruded and laminated in the order of A) / (B) / (C). The surface protective film according to claim 1, wherein the amorphous α-olefin polymer is an amorphous propylene-butene-1 copolymer or an amorphous propylene-ethylene-butene-1 copolymer. The propylene polymer is at least one selected from the group consisting of a propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. Item 3. The surface protective film according to Item 1 or 2. The surface protection film according to any one of claims 1 to 3, wherein the polyamide-based resin is 6-66 copolymer polyamide or polyamide 6.