JP2008246947A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film having no unconfirmable fine stain let alone no visibly confirmable residual matter relating to the stain to the body to be bonded after removing the protective film, excellent in secondary processing such as printing, and excellent in blocking resistance with no blocking when unwinding again after winding around in a role shape. <P>SOLUTION: The surface protective film is characterized by comprising a coextruding laminated film laminating a base material layer containing a crystalline propylene based polymer (A1) as a main component, and an adhesive layer containing a mixed resin consisting of 5 to 50 mass% of an amorphous α-olefin based polymer (B1), 50 to 95 mass% of a linear low-density polyethylene (B2) with a density of 0.880 to 0.938 g/cm<SP>3</SP>or 5 to 50 mass% of an amorphous α-olefin based polymer (B1), 40 to 90 mass% of a linear low-density polyethylene (B2) with a density of 0.880 to 0.938 g/cm<SP>3</SP>, and 5 to 50 mass% of an ethylene-α-olefin copolymer rubber (B3) as a main component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is applied to the surface of various resin plates, glass plates, metal plates, etc. used in building materials, electrical / electronic fields, etc. for the purpose of protection, storage, transportation and post-processing. The present invention relates to a surface protective film that protects a kimono from scratches and contamination. In particular, when heated or thermoformed with a surface protective film attached to the adherend, there is no lifting or peeling from the adherend, and to the adherend surface after film peeling. The present invention relates to a surface protective film with very little contamination such as adhesive residue.

  The basic required performance for the surface protective film includes excellent adherence workability that can be uniformly applied to the above-mentioned various adherends without involving wrinkles or air, storage of the adherend, transportation, etc. Adhesive strength that does not float or peel between the surfaces of the adherend, environmental changes during storage of the adherend, and changes in the adhesive strength over time due to post-processing are less likely to be easily peeled off and the surface of the adherend after peeling It does not contaminate.

  As a conventional surface protection film, a film made of polyvinyl chloride resin, polyethylene resin, polypropylene resin, etc. is used as a base material, and one surface thereof is coated with an adhesive such as urethane, acrylic or rubber. Are known. However, these surface protective films sometimes have poor adhesion between the base film and the pressure-sensitive adhesive, or when peeled from the adherend due to the low cohesive strength of the pressure-sensitive adhesive itself. There is a problem that a part of the film remains on the surface of the adherend. In addition, the surface protection film produced by applying a pressure-sensitive adhesive to the film requires a minimum of two steps, ie, a film production process and a pressure-sensitive adhesive coating process, which increases the production cost. There is a problem that a large amount of solvent needs to be removed in the pressure-sensitive adhesive coating process, which increases the environmental load.

As a method for improving the above problems, a self-adhesive surface protective film is proposed in which a base film layer and an adhesive layer are simultaneously extruded and laminated by a coextrusion lamination method. As such a surface protective film, for example, a low-density polyethylene (LDPE) is used as a base layer, a release layer made of a silicone resin on one side, and an ethylene-vinyl acetate copolymer (EVA) on the other side. ) And an adhesive layer made of a mixed resin of tackifiers made of an aliphatic hydrocarbon resin, and a co-extruded laminated film having a three-layer structure (for example, see Patent Document 1), a resin mainly composed of polypropylene. A co-extruded laminated film having a three-layer structure comprising a base layer, a resin mainly composed of polyethylene as a surface layer, and a resin mainly composed of an α-olefin copolymer having 2 to 12 carbon atoms as an adhesive layer ( For example, refer to Patent Document 2.), an adhesive layer made of a styrene-based elastomer, a tackifier, and a styrene-compatible resin is provided on one side of a base material layer made of a polyolefin-based thermoplastic resin. Coextruded multilayer film (e.g., see Patent Document 3.), Melting point 115 to 125 ° C., a density of ethylene -α- olefin copolymer is 0.915~0.932g / cm ³ and the adhesive layer, the adhesive Coextruded laminated film with a base layer composed of polyethylene and / or ethylene-α-olefin copolymer containing 30% by weight or more of polyethylene having a lower melting point than the ethylene-α-olefin copolymer used in the layer ( For example, see Patent Document 4), a co-extruded laminated film (for example, having an adhesive layer composed of an amorphous olefin copolymer, a crystalline olefin polymer, and a styrene elastomer as a base layer made of a thermoplastic resin) Patent Documents 5 and 6).

However, depending on the application, after the protective film is peeled off, secondary processing such as printing may be performed on the surface of the resin plate or the like as the adherend. In the surface protective film made of the above-mentioned co-extruded laminated film, a very small amount of residue due to adhesive residue or the like is generated on the surface of the adherend after the film is peeled off. It was. Moreover, when a styrene-based elastomer is blended in the adhesive layer, there is a problem that it is difficult to unwind the adhesive layer and the base material layer when they are rewound and then rewound again.
JP 2000-177059 A Japanese Patent Laid-Open No. 11-21519 JP-A-8-253744 JP-A-8-323944 JP 2006-188646 A JP 2006-257247 A

  The problem of the present invention relates to contamination on the surface of the adherend after the protective film is peeled, as well as residues that can be visually confirmed, there are no traces of contamination that cannot be confirmed, and suitability for secondary processing such as printing is good, and The object of the present invention is to provide a surface protective film which has no blocking and excellent blocking resistance when it is rewound again after being wound into a roll.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a base layer composed mainly of a crystalline propylene polymer, an amorphous α-olefin polymer, and a linear low-density polyethylene. And / or use of a coextruded laminated film in which an adhesive layer composed mainly of a mixed resin of ethylene-α-olefin copolymer rubber is used, the contamination of the adherend surface is extremely low, and the suitability for secondary processing is improved. The improvement was found and the present invention was completed.

That is, the present invention includes a base material layer mainly composed of a crystalline propylene polymer (A1), an amorphous α-olefin polymer (B1) of 5 to 50% by mass, and a density of 0.880 to 0. .938 g / cm ³ linear low-density polyethylene (B2) 50 to 95% by mass, or amorphous α-olefin polymer (B1) 5 to 50% by mass, density 0.880 to 0.938 g / Cm ³ linear low density polyethylene (B2) 40-90% by mass and ethylene-α-olefin copolymer rubber (B3) 5-50% by mass mixed resin and a pressure-sensitive adhesive layer as a main component A surface protective film comprising the coextruded laminated film is provided.

  The surface protective film of the present invention is visually observed on the surface of the adherend after peeling, even after being stuck to various resin plates, glass plates, metal plates, etc., and then left for a long time or exposed to a high temperature environment. There is no adhesive residue that can be confirmed, and there are very few residues that cannot be visually confirmed. Therefore, the surface protective film of the present invention is useful as a film for protecting the surface of various resin plates, glass plates, metal plates and the like, and is particularly suitable for applications where secondary processing such as printing is performed after the protective film is peeled off. is there. Moreover, when the surface protection film of this invention winds up in roll shape and rewinds again, there is no blocking and it is excellent also in blocking resistance.

  Hereinafter, the present invention will be described in detail. The surface protective film of the present invention is a coextruded laminated film in which a base material layer and an adhesive layer are formed by a coextrusion laminating method.

  Examples of the crystalline propylene polymer (A1) used for the base material layer of the surface protective film of the present invention include propylene homopolymer, propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene- Examples include butene-1 copolymer and metallocene catalyst-based polypropylene. These may be used alone or in combination of two or more. These crystalline polypropylene polymers have a melt flow rate (hereinafter referred to as “MFR”; a value measured at 230 ° C. and 21.18 N in accordance with JIS K7210: 1999) of 0.5 to 30. Those having a melting point of 120 to 165 ° C. at 0.0 g / 10 min are preferred, more preferably those having an MFR of 2.0 to 15.0 g / 10 min and a melting point of 125 to 162 ° C. If the MFR and the melting point are within this range, the film is less shrunk even if it is exposed to a high temperature environment by drying, heat molding or the like after being attached to the adherend, so that it does not float or peel off. The film formability of the laminated film is also improved without causing warpage.

  Among the crystalline propylene polymers (A1) used for the substrate layer, metallocene catalyst polypropylene is preferable. The metallocene catalyst polypropylene is a polypropylene polymerized using a metallocene catalyst instead of the conventional Ziegler-Natta catalyst. Examples of the metallocene catalyst include a metallocene homogeneous mixed catalyst containing a metallocene compound and an aluminoxane, a metallocene supported catalyst in which a metallocene compound is supported on a particulate carrier, and the like. The metallocene supported catalyst is disclosed in JP-A-5-155931, JP-A-8-104691, JP-A-8-157515, JP-A-8-231621, and the like. Metallocene catalyst-based polypropylene has high molecular weight distribution and uniform composition distribution and low content of low molecular weight components. Therefore, by using metallocene catalyst polypropylene for the base material layer, an adherend by bleeding of low molecular weight components is used. Surface contamination can be prevented. The metallocene catalyst-based polypropylene may be a propylene homopolymer or a copolymer of propylene and another α-olefin. As an example of a copolymer of propylene and another α-olefin, a propylene-ethylene copolymer may be used. Coalescence is mentioned.

  Although the said base material layer has the said crystalline propylene polymer (A1) as a main component, when an amorphous alpha olefin polymer (A2) is mix | blended as resin other than this, a softness | flexibility will increase. The followability to the adherend surface at the time of sticking the film is improved, and it can be smoothly peeled off at the time of peeling, which is preferable.

  As the amorphous α-olefin polymer (A2), the same as the amorphous α-olefin polymer (B1) described later can be used. Moreover, when mix | blending an amorphous alpha olefin polymer (A2) with a base material layer, the compounding ratio of a crystalline propylene polymer (A1) and an amorphous alpha olefin polymer (A2) is as follows. (A1) :( A2) = 70 to 95:30 to 5 is preferable on a mass basis, more preferably (A1) :( A2) = 80 to 95:20 to 5. If the blending ratio of the crystalline propylene polymer (A1) and the amorphous α-olefin polymer (A2) is within this range, sufficient flexibility and heat resistance can be obtained.

  Further, in addition to the amorphous α-olefin polymer (A2), the base layer may be blended with an ethylene resin (A3) to adjust flexibility. Examples of the ethylene-based resin include low-density polyethylene (hereinafter referred to as “LDPE”), medium-density polyethylene (hereinafter referred to as “MDPE”), high-density polyethylene (hereinafter referred to as “HDPE”), and straight chain. Low-density polyethylene (hereinafter referred to as “LLDPE”), ethylene-methyl methacrylate copolymer (hereinafter referred to as “EMMA”), and the like, and LLDPE and EMMA are preferred because of their high softening effect. As LLDPE and EMMA, those with MFR (190 ° C., 21.18N) of 0.5 to 30.0 g / 10 min are preferable, and those with MFR of 2.0 to 15.0 g / 10 min are more preferable. is there. In EMMA, the monomer content based on methylmethacrylic acid (hereinafter referred to as “MMA”) is preferably 3 to 30% by mass. More preferably, the MMA-derived monomer content is 8 to 25% by mass. When the contents of the MFR and MMA are within this range, the flexibility of the base material layer and the film formability of the laminated film are improved.

  In the case where the polyethylene resin (A3) is blended in addition to the amorphous α-olefin polymer (A2) in the base material layer, the crystalline propylene polymer (A1), the amorphous α-olefin polymer ( The blending ratio of A2) and polyethylene resin (A3) is preferably (A1) :( A2) :( A3) = 70 to 95: 4 to 29: 1 to 12, more preferably (A1): (A2) :( A3) = 80 to 95: 4 to 19: 1 to 5. If the blending ratio is within this range, sufficient flexibility and heat resistance can be obtained.

  The amorphous α-olefin polymer (B1) used for the adhesive layer of the surface protective film of the present invention is a polymer containing monomer units based on an α-olefin having 3 to 20 carbon atoms, A polymer in which neither a melting peak with a heat of fusion of 1 J / g or more nor a crystallization peak with a heat of crystallization of 1 J / g or more is observed in a differential scanning calorimeter (DSC) measurement range of −100 to 200 ° C. It is.

  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. In addition, the amorphous α-olefin polymer (B1) is preferably a polymer containing two or more of these α-olefins, and is a monomer unit based on propylene and an α-olefin having 4 to 20 carbon atoms. A polymer containing one or more monomer units based on it is more preferred. The amorphous α-olefin polymer (B1) 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 (B1), an amorphous propylene-butene-1 copolymer and an amorphous propylene-ethylene-butene-1 copolymer are preferable. These 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 (B1) is preferably 0.1 to 10.0 dl / g, more preferably 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 (B1) 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. Further, since the amorphous α-olefin polymer (B1) is an olefin polymer, 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. Thus, there is no increase in adhesive strength over time, and stable adhesive strength can be maintained over a long period of time.

  Examples of the method for producing the amorphous α-olefin polymer (B1) 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, or the like. Can be mentioned. As a more preferable manufacturing method, the manufacturing method disclosed in JP-A-2002-348417 is exemplified.

  In addition to the amorphous α-olefin polymer (B1), linear low density ethylene (B2) and / or ethylene-α-olefin copolymer rubber (B3) is blended in the adhesive layer. . By blending linear low density ethylene (B2) and / or ethylene-α-olefin copolymer rubber (B3), according to the required properties depending on the surface condition of the adherend, the material of the adherend, the application, etc. Thus, the surface of the adherend can be reduced regardless of the strength of the adhesive force.

The linear low density ethylene (B2) used for the adhesive layer of the surface protective film of the present invention has a density of 0.880 to 0.938 g / cm ³ and a density of 0.898 to 0.925 g / cm ^3. More preferred is cm ³ . Further, the MFR (value measured at 190 ° C. and 21.18 N) is preferably 0.5 to 30.0 g / 10 minutes, more preferably 2.0 to 15.0 g / 10 minutes. preferable. When the density and MFR of the linear low density ethylene (B2) are in this range, the compatibility with the amorphous α-olefin polymer is good, and the film formability of the laminated film is improved.

Examples of the ethylene-α-olefin copolymer rubber (B3) include ethylene-propylene copolymer rubber and ethylene-butene-1 copolymer rubber, with ethylene-butene-1 copolymer rubber being preferred. The ethylene-α-olefin copolymer rubber has an MFR (value measured at 190 ° C. and 21.18 N) of 0.5 to 30.0 g / 10 min and a density of 0.870 to 0.905 g / cm. ³ is more preferable, and MFR is 2.0 to 15.0 g / 10 min, and density is 0.880 to 0.900 g / cm ³ . When the MFR and density of the ethylene-butene-1 copolymer rubber (B3) are within this range, the compatibility with the amorphous α-olefin polymer is good, and the film formability of the laminated film is improved. Moreover, it is more preferable that these resin is a metallocene catalyst system with few low molecular weight components from the effect of preventing contamination of the adherend surface.

  When the amorphous α-olefin polymer (B1) and the linear low density polyethylene (B2) are used as the main components for the adhesive layer, the blending ratio is (B1) :( B2) on a mass basis (% by mass). ) = 5-50: 50-95, more preferably 5-40: 60-95. If the blending ratio of the amorphous α-olefin polymer (B1) is less than 5% by mass, sufficient adhesive strength cannot be obtained, and if it exceeds 50% by mass, the adhesive strength is too strong, making it difficult to handle the film. There is a problem. Moreover, by adjusting the blending ratio of the component (B1) and the component (B2) within the above range, the adhesive strength is adjusted to about 0.05 to 5.0 N / 25 mm according to the required adhesive strength. can do.

  Further, when the amorphous α-olefin polymer (B1), the linear low density ethylene (B2) and the ethylene-α-olefin copolymer rubber (B3) are used as the main components for the adhesive layer, the blending ratio thereof Is (B1) :( B2) :( B3) = 5-50: 40-90: 5-50, more preferably 5-30: 40-85: 10-45 on a mass basis (mass%). is there. By adjusting the blending ratio of the component (B1) and the component (B3) within the above range, it can be adjusted to the one depending on the required adhesive strength, and is about 0.1 to 7.0 N / 25 mm. The adhesive strength can be adjusted.

  In the adhesive layer, the blend of the amorphous α-olefin polymer (B1) and the linear low density polyethylene (B2) and / or the ethylene-α-olefin copolymer rubber (B3) is 75% by mass or more. It is preferable that it is 85 mass% or more. When the content of the blend of (B1) and (B2) or (B1), (B2) and (B3) is within this range, the contamination of the adherend surface is extremely reduced, and the secondary of the adherend Processability is improved.

  The surface protective film of the present invention is composed of two layers of a base material layer and an adhesive layer as described above, but a surface layer may be further provided on the base material layer. The resin used for the surface layer is not particularly limited, but is preferably made of a propylene polymer in order to impart high heat resistance. Examples of the propylene polymer include a propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. These are preferably polypropylene based on a metallocene catalyst system in the same manner as the base material layer described above.

  Further, a propylene resin (C1) composed of a propylene homopolymer and a propylene-ethylene copolymer elastomer may be the main component, and the surface layer may be modified into a satin finish. Blocking can be reduced when the surface layer is made into a satin finish and the adhesive strength is designed strongly. The propylene-based resin (C1) is a resin composed of a propylene homopolymer and a propylene-ethylene copolymer elastomer (hereinafter referred to as “EPR”). At this time, the melt flow rate of the propylene-based resin (C1) (measured at 230 ° C. and 21.18 N in accordance with JIS K7210: 1999; hereinafter referred to as “MFR”) is 0.5 to 15 g / 10. A range of minutes is preferred. On the other hand, the weight average molecular weight of the EPR is preferably in the range of 400,000 to 1,000,000, more preferably in the range of 500,000 to 800,000. Moreover, the content of EPR in the propylene resin (C1) is preferably in the range of 5 to 20% by mass, and more preferably in the range of 7 to 15% by mass. The weight average molecular weight of this EPR was calculated by GPC (gel permeation chromatography) using the propylene resin (C1) resin as an orthodichlorobenzene solvent and the components extracted by cross fractionation at 40 ° C. It is what I asked for. The content of EPR is determined from the amount of EPR extracted by the cross-fractionation method at 40 ° C. using polypropylene resin (C1) as a solvent and orthodichlorobenzene.

  The method for producing the propylene-based resin (C1) is not particularly limited. For example, a propylene homopolymer and an ethylene-propylene copolymer elastomer are separately used in a solution polymerization method and a slurry polymerization method using a Ziegler type catalyst. After the production by a gas phase polymerization method or the like, a method of mixing both using a kneader, a propylene homopolymer is produced in the first stage by a two-stage polymerization method, and then the polymer in the second stage. Examples thereof include a method for generating EPR in the presence.

  The Ziegler-type catalyst is a so-called Ziegler-Natta catalyst, and is obtained by supporting a transition metal compound such as a titanium-containing compound or a transition metal compound on a support such as a magnesium compound. The combination with the promoter of an organometallic compound is mentioned.

  The surface layer is mainly composed of the propylene-based resin (C1). However, when an ethylene-based resin (C2) is blended as the other resin, the surface of the surface layer can be made stronger and more satin-like to prevent blocking. Since an effect improves, it is preferable.

Examples of the ethylene resin (C2) include low density polyethylene (hereinafter referred to as “LDPE”), medium density polyethylene (hereinafter referred to as “MDPE”), and high density polyethylene (hereinafter referred to as “HDPE”). These may be used alone or in combination of two or more. Among these, HDPE is preferable because of its high modification effect and high uniformity. As HDPE, it is preferable that a density is 0.940-0.970 g / cm < ³ > and MFR (190 degreeC, 21.18N) is 0.05-20 g / 10min. If the density and MFR of HDPE are in this range, it is difficult for fish eyes to occur in the film, the surface of the surface layer can be made into an appropriate satin finish, and blocking can be prevented.

  Moreover, when mix | blending ethylene-type resin (C2) with the said surface layer, the mixture ratio of the said propylene-type resin (C1) and ethylene-type resin (C2) is (C1) :( C2) = 60 on a mass basis. The range of -97: 40-3 is preferable, and the range of 80-95: 20-5 is more preferable. If the blending ratio is within this range, sufficient heat resistance can be obtained, the surface of the surface layer can be made into an appropriate satin finish, and blocking can be prevented.

  In addition to the propylene resin (C1) and the ethylene resin (C2), a propylene polymer (C3) can also be blended in the surface layer. By blending the propylene-based polymer (C3), the satin state on the surface of the surface layer can be further adjusted to an optimum one. As such a propylene polymer (C3), for example, a propylene homopolymer, a propylene-ethylene copolymer, a propylene-ethylene-butene-1 copolymer and the like may be blended. These may be used alone or in combination of two or more. These propylene polymers (C3) preferably have an MFR (230 ° C., 21.18N) of 0.5 to 30.0 g / 10 minutes and a melting point of 120 to 165 ° C., and MFR (230 ° C., 21.18N) is more preferably 2.0 to 15.0 g / 10 min and a melting point of 135 to 165 ° C. If MFR and melting | fusing point are this range, the heat resistance and the film-forming property of a laminated film will improve.

  The surface protective film of the present invention preferably has a total film thickness of 20 to 120 μm. If the thickness of all the films is in this range, the protective properties of the adherend, the adhesive properties, and the workability such as sticking / peeling will be good. Moreover, 3-30 micrometers is preferable and, as for the thickness of the adhesion layer, More preferably, it is 5-25 micrometers. When the thickness of the adhesive layer is within this range, the adhesive properties and the film formability of the laminated film are good. Furthermore, when providing the said surface layer in the surface protection film of this invention, 3-30 micrometers is preferable and, as for the thickness of a surface layer, More preferably, it is 5-20 micrometers. When the thickness of the surface layer is within this range, the heat resistance and the film formability of the laminated film are 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 two 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. In the case of the T-die / chill roll method, the melt-laminated film may be nipped and cooled between a rubber touch roll, a steel belt or the like and the chill roll.

  Furthermore, the surface protective film of the present invention may be stretched in at least one axial direction. As the stretching method, a known method such as longitudinal or lateral uniaxial stretching, sequential biaxial stretching, simultaneous biaxial stretching, or tubular method biaxial stretching can be employed. Further, the stretching process may be inline or offline. The stretching method for uniaxial stretching may be a proximity roll stretching method or a rolling method. The stretching ratio of uniaxial stretching is preferably 1.1 to 80 times, more preferably 3 to 30 times in the longitudinal or transverse direction. On the other hand, the stretch ratio of biaxial stretching is preferably 1.2 to 70 times in terms of area ratio, more preferably 4 to 6 times in length, 5 to 9 times in width, and 20 to 54 times in area ratio.

  In addition, the longitudinal or lateral stretching step is not necessarily limited to one-stage stretching, and may be multi-stage stretching. In particular, in longitudinal uniaxial stretching such as longitudinal uniaxial roll stretching and longitudinal uniaxial rolling stretching in sequential biaxial stretching, it is preferable to perform multistage stretching in view of thickness, uniformity of physical properties, and the like. Further, in the proximity roll stretching, either the flat method or the cross method may be used, but multistage proximity cross stretching that can reduce width shrinkage is more preferable. In the case of uniaxial stretching, the stretching temperature is preferably 80 ° C to 160 ° C in any stretching method, and in the case of using tenter stretching in uniaxial stretching, 90 to 165 ° C is preferable. Moreover, as more preferable extending | stretching temperature, they are 110-155 degreeC and 120-160 degreeC, respectively. On the other hand, in the case of biaxial stretching, the stretching temperature range similar to that in the case of uniaxial stretching is preferable in any method. Moreover, you may provide a pre-heating part before an extending process, and a heat setting part after an extending process suitably. In this case, the temperature of the preheating part is preferably in the range of 60 to 140 ° C, and the temperature of the heat fixing part is preferably in the range of 90 to 160 ° C.

  The surface protective film of the present invention is oriented by at least uniaxial direction and is subjected to orientation crystallization of the base material layer mainly composed of the crystalline propylene polymer (A1) by heat stabilization. Further, it is preferable because the heat resistance is further improved and the change with time of the adhesive force is reduced.

  In addition, a lubricant, an antiblocking agent, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and the like may be added as appropriate within a range not impairing the effects of the present invention. As these additives, it is preferable to use various additives for olefin-based resins.

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

(Synthesis Example 1)
[Synthesis of Amorphous α-Olefin Polymer (Amorphous Propylene-Butene-1 Copolymer)]
In a 100 L stainless steel polymerization vessel equipped with a stirrer, propylene and butene-1 were continuously copolymerized using hydrogen as a molecular weight regulator to produce amorphous propylene-butene as an amorphous α-olefin polymer. -1 copolymer was obtained. Specifically, hexane as a polymerization solvent is continuously supplied from the lower part of the polymerization vessel at a supply rate of 100 L / hour, propylene at 24.00 kg / hour, and butene-1 at 1.81 kg / hour. From the top of the reaction mixture, the reaction mixture was continuously withdrawn so that the reaction mixture in the polymerization vessel maintained 100 L. Further, from the lower part of the polymerization vessel, dimethylsilyl (tetramethylcyclopentadienyl) (3-t-butyl-5-methyl-2-phenoxy) titanium dichloride is added as a catalyst component at 0.005 g / hour at triphenylmethyl. Tetrakis (pentafluorophenyl) borate was continuously fed at a rate of 0.298 g / hr and triisobutylaluminum was fed at a rate of 2.315 g / hr. The copolymerization reaction was carried out at 45 ° C. by circulating cooling water through a jacket attached to the outside of the polymerization vessel. A small amount of ethanol was added to the reaction mixture continuously extracted from the upper part of the polymerization vessel to stop the polymerization reaction, and after passing through the monomer removal, water washing, and solvent removal steps, the amorphous propylene-butene-1 A polymer was obtained. Subsequently, the obtained copolymer was dried under reduced pressure at 80 ° C. for 24 hours. The content of the propylene monomer unit in the amorphous propylene-butene-1 copolymer was 94.5% by mass, and the content of the butene-1 monomer unit was 5.5% by mass. Moreover, the melting peak in DSC of the copolymer was not observed, the intrinsic viscosity [η] was 2.3 dl / g, and the molecular weight distribution (Mw / Mn) was 2.2.

(Synthesis Example 2)
[Synthesis of Amorphous α-Olefin Polymer (Amorphous Propylene-Ethylene-Butene-1 Copolymer)]
A 2 L separable flask reactor equipped with a stirrer, thermometer, dropping funnel and reflux condenser was decompressed and purged with nitrogen, and then 1 L of dry toluene was introduced as a polymerization solvent. Here, ethylene 2 NL / min, propylene 4 NL / min, and butene-1 1 NL / min were continuously supplied at normal pressure, and the solvent temperature was set to 30 ° C. After adding 0.75 mmol of triisobutylaluminum (hereinafter referred to as TIBA) to the polymerization tank, 0.0015 mmol of dimethylsilyl (tetramethylcyclopentadienyl) (3-t-butyl-5-methyl-2-phenoxy) titanium dichloride was added. Added to the polymerization vessel. 15 seconds later, 0.0075 mmol of triphenylmethyltetrakis (pentafluorophenyl) borate was added to the polymerization tank, and polymerization was carried out for 10 minutes. As a result, an amorphous propylene-butene-1-ethylene copolymer was obtained. In this amorphous propylene-ethylene-butene-1 copolymer, the content of propylene monomer units was 61.5% by mass, the content of ethylene monomer units was 21.0% by mass, butene-1 unit The content of the monomer unit was 17.5% by mass. Moreover, the melting peak in DSC of this copolymer was not observed, the intrinsic viscosity [η] was 1.69 dl / g, and the molecular weight distribution (Mw / Mn) was 2.0.

(Preparation Example 1)
[Preparation of Amorphous α-Olefin Polymer Composition (1)]
To the amorphous propylene-butene-1 copolymer obtained above, a crystalline propylene-butene-1 copolymer (density 0.900 g / cm ³ , MFR (230 ° C., 21.18 N) 10.0 g / 10 minutes, the maximum melting peak in DSC 126 ° C.) is blended so that amorphous propylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 60/40 (mass ratio), Furthermore, an aromatic phosphite antioxidant (Irgafos 168 manufactured by Ciba Specialty Chemicals) and a hindered phenol antioxidant (Irganox 1010 manufactured by Ciba Specialty Chemicals) )) Is blended at 2000 ppm each, melt-kneaded with a twin screw extruder, and then amorphous α-olefins with a granulator. A pellet of the polymer polymer composition (1) was obtained.

(Preparation Example 2)
[Preparation of Amorphous α-Olefin Polymer Composition (2)]
Amorphous propylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = amorphous α -The pellet of the olefin polymer composition (2) was obtained.

(Preparation Example 3)
[Preparation of Amorphous α-Olefin Polymer Composition (3)]
To the amorphous propylene-ethylene-butene-1 copolymer obtained above, a crystalline propylene-butene-1 copolymer (density 0.900 g / cm ³ , MFR (230 ° C., 21.18 N)) 10. 0 g / 10 min, maximum melting peak in DSC of 126 ° C.) is amorphous propylene-ethylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 60/40 (mass ratio). In addition, an aromatic phosphite antioxidant ("Irgafos 168" manufactured by Ciba Specialty Chemicals Co., Ltd.) and a hindered phenol antioxidant (Irgafos Chemical Co., Ltd. 2000 ppm of each of Irganox 1010 "), melt-kneaded with a twin screw extruder, and then granulator Give more amorphous α- olefin polymer composition pellets (3).

(Adjustment Example 4)
[Preparation of Amorphous α-Olefin Polymer Composition (4)]
Amorphous propylene-ethylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = Amorphous in the same manner as in Preparation Example 1 except that the blend was made to be 95/5 (mass ratio). Pellets of the hydrophilic α-olefin polymer composition (4) were obtained.

Example 1
As a resin for the surface layer, a propylene resin (a resin composed of a propylene homopolymer and EPR, MFR (230 ° C., 21.18 N): 4.0 g / 10 min, EPR content: 11% by mass, EPR weight average) And a propylene homopolymer (density: 0.900 g / cm ³ , MFR (230 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “HOPP”) And as the resin for the adhesive layer, 30 parts by mass of the amorphous α-olefin polymer composition (1) prepared above and linear low density polyethylene (density: 0.902 g / cm ³ , MFR (190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “LLDPE (1)”) 70 parts by mass of mixture, surface layer extruder (caliber 50 mm), for base material layer Extruder (Mouth 50 mm) and an adhesive layer extruder (40 mm in diameter), and by co-extrusion at an extrusion temperature of 250 ° C., the thickness of the surface layer from the T-die is 12 μm, the thickness of the substrate layer is 38 μm, After extruding to a thickness of 10 μm and cooling with a 40 ° C. water-cooled metal cooling roll, the film was wound on a roll to obtain a surface protective film. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 2)
A surface protective film was obtained in the same manner as in Example 1 except that 50 parts by mass of the amorphous α-olefin polymer composition (1) and 50 parts by mass of LLDPE (1) were used as the adhesive layer resin.

(Example 3)
In the same configuration as in Example 2, it was supplied to an extruder for surface layer (caliber 50 mm), an extruder for substrate layer (caliber 50 mm), and an extruder for adhesive layer (caliber 40 mm), and extrusion temperature by coextrusion method. Extruded at 250 ° C from the T-die so that the surface layer thickness is 40 µm, the base material layer thickness is 120 µm, and the adhesive layer thickness is 40 µm, and after cooling with a 40 ° C water-cooled metal cooling roll, proximity The film was stretched four times in length at 140 ° C. by a roll stretching method, and further heat-set at 145 ° C. to obtain a uniaxially stretched surface protective film. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties. In addition, the thickness of each layer of Example 3 in Table 1 is that after uniaxial stretching.

Example 4
A surface protective film was obtained in the same manner as in Example 1 except that the adhesive layer resin was changed to a mixture of 40 parts by mass of the amorphous α-olefin polymer composition (2) and 60 parts by mass of LLDPE (1). It was.

(Example 5)
HOPP is used as the base layer resin, and 40 parts by mass of the amorphous α-olefin polymer composition (4) and the linear low density polyethylene (density: 0.920 g / cm ³ ) are used as the adhesive layer resin. MFR (190 ° C., 21.18 N): 4.0 g / 10 min; hereinafter referred to as “LLDPE (2)”) A surface protective film was prepared in the same manner as in Example 1 except that 60 parts by mass of the mixture was used. Obtained.

(Example 6)
As a resin for the base layer, a metallocene catalyst-based propylene-ethylene random copolymer (density: 0.900 g / cm ³ , MFR (230 ° C., 21.18 N): 7.0 g / 10 min, ethylene monomer unit Content rate: 3.5% by mass; hereinafter referred to as “metallocene catalyst COPP”), as an adhesive layer resin, 50 parts by mass of amorphous α-olefin polymer composition (3) and LLDPE (2 ) Using 50 parts by mass of the mixture, the mixture was supplied to an extruder for substrate layer (caliber 50 mm) and an extruder for adhesive layer (caliber 40 mm), respectively. After extruding so that the thickness of the layer was 50 μm and the thickness of the adhesive layer being 10 μm and cooling with a water-cooled metal cooling roll at 40 ° C., the film was wound on a roll to obtain a surface protective film. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 7)
A metallocene catalyst COPP is used as the base layer resin, and a mixture of 6.0 parts by mass of the amorphous α-olefin polymer composition (2) and 94 parts by mass of LLDPE (2) is used as the resin for the adhesive layer. A surface protective film was obtained in the same manner as in Example 1 except that it was used.

(Example 8)
Metallocene catalyst COPP is used as the base layer resin, and amorphous α-olefin polymer composition (2) 6.0 parts by mass, LLDPE (2) 84 parts by mass and ethylene- Butene-1 copolymer rubber (density: 0.895 g / cm ³ , MFR (190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “EBR”) except for using 10 parts by mass of the mixture Were the same as in Example 1 to obtain a surface protective film.

Example 9
Metallocene catalyst COPP is used as the base layer resin, and 30 parts by mass of the amorphous α-olefin polymer composition (2), 50 parts by mass of LLDPE (2) and 20 parts by mass of EBR are used as the adhesive layer resin. A surface protective film was obtained in the same manner as in Example 1 except that the mixture was used.

(Example 10)
Metallocene catalyst COPP is used as the resin for the base layer, and 20 parts by mass of the amorphous α-olefin polymer composition (2), 40 parts by mass of LLDPE (2) and 40 parts by mass of EBR are used as the resin for the adhesive layer. A surface protective film was obtained in the same manner as in Example 1 except that the mixture was used.

(Comparative Example 1)
As the adhesive layer resin, the same procedure as in Example 1 was conducted, except that a mixture of 3.16 parts by mass of amorphous α-olefin polymer composition (2) LLDPE (2) 96.84 parts by mass was used. A protective film was obtained.

(Comparative Example 2)
As an adhesive layer resin, 30 parts by mass of an amorphous α-olefin polymer composition (1) and linear low-density polyethylene (density: 0.940 g / cm ³ , MFR (190 ° C., 21.18 N): 4.0 g / 10 min; hereinafter referred to as “LLDPE (3)”.) A surface protective film was obtained in the same manner as in Example 1 except that 70 parts by mass of the mixture was used.

(Comparative Example 3)
As an adhesive layer resin, 52 parts by mass of an amorphous α-olefin polymer composition (2), 8 parts by mass of a crystalline propylene-butene-1 copolymer similar to that used in Preparation Example 1, and styrene- A surface protective film was prepared in the same manner as in Example 1 except that 40 parts by mass of an ethylene-propylene-styrene block copolymer (“Septon 2063” manufactured by Kuraray Co., Ltd .; hereinafter referred to as “SEPS”) was used. Obtained.

(Comparative Example 4)
A surface protective film was obtained in the same manner as in Example 1 except that a mixture of 50 parts by mass of the amorphous α-olefin polymer composition (1) and 50 parts by mass of HOPP was used as the adhesive layer resin.

(Comparative Example 5)
The same procedure as in Example 1 was conducted except that a mixture of 50 parts by mass of the amorphous α-olefin polymer composition (1), 30 parts by mass of LLDPE (2) and 20 parts by mass of EBR was used as the adhesive layer resin. A surface protective film was obtained.

(Comparative Example 6)
The same procedure as in Example 1 was conducted except that a mixture of 30 parts by mass of the amorphous α-olefin polymer composition (2), 20 parts by mass of LLDPE (2) and 50 parts by mass of EBR was used as the adhesive layer resin. A surface protective film was obtained.

  The following measurements and evaluations were performed using the surface protective films obtained in Examples 1 to 10 and Comparative Examples 1 to 6.

(1) Measurement of adhesive strength In a thermostatic chamber at 23 ° C. and 50% RH, the surface protective film obtained above was applied to an acrylic plate (mirror finish) in accordance with JIS Z0237: 2000 adhesive strength evaluation method. And “Acrylite” manufactured by Mitsubishi Rayon Co., Ltd.). The acrylic plate with the film attached is left in a constant temperature room at 23 ° C. for 24 hours, and then peeled off in the 180 ° direction at a speed of 300 mm / min using a tensile tester (manufactured by A & D Co., Ltd.). The initial adhesive strength was measured. Moreover, after leaving the acrylic board which stuck the film in a 50 degreeC dryer for one day, adhesive force was measured similarly.

(2) Evaluation of adhesiveness In order to measure the above adhesive strength, the state of adhesion of the surface protective film to the acrylic plate when the surface protective film was adhered to the acrylic plate was visually confirmed, and the following criteria were used. Was used to evaluate the tackiness.
◯: Maintaining uniform adhesion to the acrylic plate surface.
X: Insufficient initial adhesive strength, uniform adhesion cannot be maintained, and partly floated.

(3) Evaluation of adhesive residue In a temperature-controlled room at 23 ° C. and 50% RH, the surface protective film was made into a 15 cm long by 5 cm wide acrylic plate (mirror finish, manufactured by Mitsubishi Rayon Co., Ltd.) in accordance with JIS Z0237: 2000. "Acrylite") was attached to the entire surface. The acrylic plate to which the film was adhered was left in a dryer at 60 ° C. for 3 days and then cooled in a constant temperature room at 23 ° C. for 1 hour. From the cooled test piece, the film was peeled off at a high speed in the direction of 180 °, the state of contamination on the acrylic plate surface was visually confirmed, and the adhesive residue was evaluated according to the following criteria.
○: There is no dirt such as cloudy, white streaks or foreign matter on the acrylic plate surface.
X: The acrylic plate surface has any dirt such as cloudy, white streaks or foreign matters.

(4) Measurement of Wetting Tension on Acrylic Board Surface Wet tension on the acrylic board surface was measured by a method based on JIS K6768: 1999 using the test piece from which the film was peeled off in the evaluation of (3) above.

(5) Evaluation of printability after protective film peeling The value of the wet tension blank obtained by the measurement of (4) above (the surface of the acrylic plate before film attachment was washed with alcohol, and measured by the same method after drying) (Wet tension: 40 mN / m) was evaluated as a substitute evaluation of printability after the protective film was peeled off. The evaluation criteria are as follows.
(Circle): The fall width | variety of a wetting tension is 2 mN / m or less with respect to a blank.
X: The reduction width of the wetting tension with respect to the blank exceeds 2 mN / m.

(6) Evaluation of blocking resistance The obtained surface protective film was cut out with the size of A4 (length 297 mm x width 210 mm). At this time, the film was cut out so that the extrusion direction (MD direction) during film formation coincided with the A4 vertical direction. After stacking 10 cut out films, the upper and lower sides were sandwiched between A4 size, 3 mm thick vinyl chloride plates, a weight of 5 kg was placed, and stored in a dryer at 40 ° C. for 14 days, then at 23 ° C. It was stored for 1 hour in a constant temperature room of 50% RH. Next, the film was cut out in a width of 25 mm in the MD direction, and peeled in the direction of 180 ° at a speed of 300 mm / min using a tensile tester (manufactured by A & D Co., Ltd.) to measure the blocking force. From the obtained blocking force, blocking resistance was evaluated according to the following criteria.
A: The blocking force is less than 0.8 N / 25 mm.
X: The blocking force is 0.8 N / 25 mm or more.

  Tables 1 to 3 show the layer structure of the surface protective film produced above and the evaluation results obtained using these surface protective films. The parentheses in the surface layer resin composition in the table indicate the breakdown of each resin component contained in the used polypropylene resin. Moreover, about Example 6, since the surface layer is not provided, it is blank.

  From the results of Examples 1 to 10, the surface protective film of the present invention has an adhesive strength with respect to the acrylic plate of about 0.1 to 2.0 N / 25 mm, and is suitable for the surface protective film from the fine adhesion to the medium adhesion level. It was found to have a wide range of adhesive strength. In addition, it was found that there was no occurrence of floating or peeling after sticking to the acrylic plate, and that the surface protective film had practically good adhesiveness. In particular, when the film is peeled off from the attached acrylic plate, there is no visible contamination such as cloudiness, streaks, or foreign matter, and there is very little reduction in the wetting tension on the acrylic plate surface after peeling off the surface protective film. From this, it was found that after the surface protective film was peeled off, it can be suitably used for applications in which secondary processing such as printing is performed.

  Comparative Example 1 is an example of a surface protective film in which the blending amount of the linear low density polyethylene is about 97% by mass exceeding the prescribed upper limit of 95% by mass. In the surface protective film of Comparative Example 1, the adhesive strength was only about 0.05 N / 25 mm as an initial value, and it was found that the adhesive strength was insufficient due to the occurrence of floating, peeling and the like due to light impact.

Comparative Example 2, the density of the linear low density polyethylene, an example of a surface protective film and 0.940 g / cm ³ greater than the 0.938 g / cm ³ of the upper limit as defined. In the surface protective film of Comparative Example 2, the initial adhesive strength is only about 0.03 N / 25 mm, and the occurrence of peeling and peeling immediately after the film is adhered is observed. It was found that if the density is too high, the adhesive strength becomes insufficient.

  Comparative Example 3 is an example of a surface protective film using a styrene-ethylene-propylene-styrene block copolymer (SEPS) instead of linear low density polyethylene for the adhesive layer. In the surface protective film of Comparative Example 3, generation of adhesive residue was observed, the decrease in the wet tension of the acrylic plate surface after peeling the surface protective film was large, the blocking power was large, and the blocking resistance was inferior. I understood.

  Comparative Example 4 is an example of a surface protective film using a propylene homopolymer instead of a linear low density polyethylene for the adhesive layer. In the surface protective film of Comparative Example 4, generation of adhesive residue was observed, and it was found that the decrease in wet tension on the surface of the acrylic plate after peeling the surface protective film was large.

  Comparative Example 5 is an example of a surface protective film in which the blending amount of the linear low-density polyethylene is 37.5% by mass, which is less than the specified lower limit of 40% by mass. The surface protective film of Comparative Example 5 was found to have a problem that adhesive residue was generated.

  Comparative Example 6 is an example of a surface protective film in which the blending amount of ethylene-α-olefin copolymer rubber (EBR) is about 50.8% by mass exceeding the specified upper limit of 40% by mass. The surface protective film of Comparative Example 6 was found to have a large blocking force and poor blocking resistance.

Claims (6)

A base material layer mainly composed of a crystalline propylene polymer (A1), an amorphous α-olefin polymer (B1) of 5 to 50% by mass, and a density of 0.880 to 0.938 g / cm ³ . A straight low-density polyethylene (B2) 50 to 95% by mass, or an amorphous α-olefin polymer (B1) 5 to 50% by mass, and a density of 0.880 to 0.938 g / cm ³ A coextruded laminated film in which a low-density polyethylene (B2) 40 to 90% by mass and an ethylene-α-olefin copolymer rubber (B3) 5 to 50% by mass of a mixed resin as a main component are laminated. A surface protective film comprising:   The total content ratio of the amorphous α-olefin polymer (B1), the linear low density polyethylene (B2), and the ethylene-α-olefin copolymer rubber (B3) in the adhesive layer is 75% by mass. The surface protective film according to claim 1, which is as described above.   The crystalline propylene polymer (A1) comprises a propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, and a metallocene catalyst polypropylene. The surface protective film according to claim 1, which is at least one selected from the group.   The amorphous α-olefin polymer (B1) is an amorphous propylene-butene-1 copolymer or an amorphous propylene-ethylene-butene-1 copolymer, and an ethylene-α-olefin copolymer. The surface protective film according to claim 1, wherein the rubber is ethylene-butene-1 copolymer rubber.   The surface layer which has as a main component the polypropylene resin (C1) which consists of a propylene homopolymer and a propylene-ethylene copolymer elastomer was provided on the base material layer on the opposite surface of the said adhesion layer. The surface protective film according to 1.   The surface protective film according to claim 1, wherein the surface protective film is stretched in at least one axial direction.