JP2009166277A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film relating to stain on a surface of an adherend after peeling the protective film from the adherend, which causes no visibly recognizable residual matter and besides no visibly unconfirmable fine stain, which is excellent in secondary processability such as printing, is cleanly cut when the adherend is cut while the film stuck on the adherend, is free from the appearance defects such as webbing and fuzzing, and is excellent in blocking resistance. <P>SOLUTION: The surface protective film is characterized by comprising a coextruded laminated film obtained by laminating: a base material layer containing an ethylene based polymer (A1) as a main component; and an adhesive layer containing a mixed resin consisting of 5 to 40 mass% of an amorphous α-olefin based polymer (B1) and 60 to 95 mass% of a linear low-density polyethylene (B2) with a density of 0.880 to 0.938 g/cm<SP>3</SP>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 the adherend is cut with the surface protective film attached to the adherend, the surface protective film is cut cleanly and does not cause poor appearance such as stringing or fluffing, and after film peeling The present invention relates to a surface protective film with extremely little contamination such as adhesive residue on the adherend surface.

  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 on the surface of a resin plate or the like as an adherend may be performed. 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 film peeling, and there is a problem that causes printing defects in such secondary processing. It was. Further, there has been a problem that the surface protective film causes poor appearance such as stringing and fluffing during the cutting process with the surface protective film adhered to the adherend. Furthermore, when a styrene-based elastomer is blended in the adhesive layer, there is a problem in 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 off, and there is no residue that can be visually confirmed, there is no trace contamination that cannot be confirmed, and secondary workability such as printing is good. When cutting the adherend with the surface protective film attached to the adherend, the surface protective film cuts cleanly, does not cause poor appearance such as stringing and fluffing, and has good blocking resistance It is to provide a surface protective film.

  As a result of intensive studies to solve the above problems, the present inventors have mixed a base material layer mainly composed of an ethylene polymer, an amorphous α-olefin polymer, and a linear low density polyethylene. When a co-extruded laminated film laminated with a resin-based adhesive layer is used, there is very little contamination on the adherend surface after the surface protective film is peeled off, the printability on the adherend surface is good, and When cutting with the surface protective film attached to the adherend, the present invention was completed by finding that it does not cause poor appearance such as stringing and fluffing and has excellent cutting properties.

That is, the present invention includes a base material layer mainly composed of an ethylene polymer (A1), an amorphous α-olefin polymer (B1) of 5 to 40% by mass, and a density of 0.880 to 0.00. The present invention provides a surface protective film having a co-extruded laminated film in which an adhesive layer mainly composed of 60 to 95% by mass of a linear low-density polyethylene (B2) that is 938 g / cm ³ is laminated.

  The surface protective film of the present invention can be visually observed on the surface of the adherend after peeling, even after being stuck to various resin plates, glass plates, metal plates, etc., and left for a long time or placed in a high temperature environment. There is no adhesive residue that can be confirmed, and there are very few residues that cannot be visually confirmed, which is suitable for applications where secondary processing such as printing is performed after the protective film is peeled off. Further, when the adherend is cut and processed with the surface protective film adhered to the adherend, the surface protective film cuts cleanly and has a cutting property that does not cause poor appearance such as stringing or fluffing. Furthermore, the surface protective film of the present invention has no blocking and excellent blocking resistance when it is rewound again after being rolled up. As described above, the surface protective film of the present invention is useful as a film for protecting the surfaces of various resin plates, glass plates, metal plates and the like.

  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 ethylene polymer (A1) used for the base material layer of the surface protective film of the present invention include low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene. These may be used alone or in combination of two or more. By using these ethylene-based polymers as a base material layer, when cutting the adherend in a state where the surface protective film is adhered to the adherend, the surface protective film is cut cleanly, stringing, Cutting ability that does not cause poor appearance such as fluffing is exhibited. Among these, linear low-density polyethylene, medium-density polyethylene, or a mixed resin of low-density polyethylene and high-density polyethylene is preferable because of good heat resistance.

  On the other hand, these ethylene polymers have a melt flow rate (hereinafter referred to as “MFR”; a value measured at 190 ° C. and 21.18 N in accordance with JIS K7210: 1999) of 0.5 to 30.0 g. / 10 minutes is preferable because extrusion is easy, and more preferably, MFR is 2.0 to 15.0 g / 10 minutes. Further, these ethylene polymers preferably have a melting point of 90 to 135 ° C, more preferably a melting point of 105 to 130 ° C. If the melting point is within this range, since the film shrinks less even when placed in a high temperature environment by drying, thermoforming, etc. after being attached to the adherend, the adherend is lifted or peeled off. Can be suppressed.

  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.

  Moreover, linear low density ethylene (B2) is mix | blended with the said adhesion layer other than the said amorphous alpha olefin polymer (B1). By blending linear low density ethylene (B2), it is possible to adjust the adhesive strength according to the required properties depending on the surface condition of the adherend, the material of the adherend, the application, etc. However, contamination of the adherend surface can be reduced.

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 in accordance with JIS K7210: 1999) is preferably 0.5 to 30.0 g / 10 min, and 2.0 to 15.0 g. More preferably, it is / 10 minutes. 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.

  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). ) = 5-40: 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 40% by mass, the adhesive strength is too strong, making it difficult to handle the film. And there is a problem that adhesive residue occurs. 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.

  The blending ratio in the total adhesive layer of the amorphous α-olefin polymer (B1) and the linear low density polyethylene (B2) is preferably 65% by mass or more. With this blending ratio, the contamination of the adherend surface after film peeling is extremely reduced, and the printability on the adherend surface is improved.

  In addition to the amorphous α-olefin polymer (B1) and the linear low density polyethylene (B2), examples of the resin that can be used for the adhesive layer include a crystalline propylene homopolymer and a crystalline propylene-ethylene copolymer. Polymer, crystalline propylene-based polymer such as crystalline propylene-butene-1 copolymer, propylene-butene-1-ethylene terpolymer; ethylene-propylene copolymer rubber, ethylene-butene-1 copolymer Ethylene-α-olefin copolymer rubbers such as united rubber, ethylene-hexene-1 copolymer rubber, ethylene-octene-1 copolymer rubber; butene-1 homopolymer, butene-1-ethylene copolymer, Butene-1-polymers such as butene-1-propylene copolymer; styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene ABA type styrene block copolymers such as styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), and styrene-ethylene-propylene-styrene copolymer (SEPS); Styrene random copolymer such as styrene-butadiene copolymer (SB), styrene-isoprene copolymer (SI), styrene-ethylene-butylene copolymer (SEB), styrene-butadiene rubber (SBR); Examples include an ABC type styrene block copolymer such as ethylene-butylene-ethylene copolymer (SEBC), and hydrogenated products thereof.

  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. For example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, propylene homopolymer, propylene-ethylene copolymer, propylene-butene -1 copolymer, propylene-butene-1-ethylene copolymer, and the like. Among these, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene are more preferable because cutability is improved.

Further, the resin used for the surface layer may be a mixed resin of the resin listed above and a propylene-ethylene block copolymer as a main component, and the surface of the surface layer may be modified into a satin finish. By making the surface of the surface layer a satin finish, blocking can be reduced when the adhesive strength is designed strongly. Here, the propylene-ethylene block copolymer is a resin obtained by block polymerization of propylene and ethylene, and it is not particularly limited as long as the surface of the resin layer becomes satin-like when used for the surface layer. . For example, the propylene-ethylene block copolymer etc. which are obtained by superposing | polymerizing ethylene or superposition | polymerization of ethylene and propylene in presence of a propylene homopolymer are mentioned. Among these, a propylene-ethylene block copolymer having an ethylene-derived component content of 8 to 20% by mass is preferable because the surface is easy to have a satin finish, and the ethylene-derived component content is 10 to 10%. A 15% by mass propylene-ethylene block copolymer is preferred. The melt flow rate (measured in accordance with MFR JIS K7210: 1999 at 230 ° C. and 21.18 N) is preferably 4 to 12 g / 10 minutes in terms of easy extrusion, and 6 to 10 g / 10 minutes. It is more preferable that Preferably the density is 0.890~0.910g / cm ^3, more preferably 0.895~0.905g / cm ^3.

  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 a manifold 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 a uniaxially stretched film or a biaxially stretched film.

  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 in Synthesis Example 1, 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 126 ° C. in DSC) is blended so that amorphous propylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 60/40 (mass ratio) Furthermore, aromatic phosphite antioxidants (“Irgafos 168” manufactured by Ciba Specialty Chemicals Co., Ltd.) and hindered phenol antioxidants (Irganox manufactured by Ciba Specialty Chemicals Co., Ltd.). ) 1010 "), 2000 ppm each, melt-kneaded with a twin screw extruder, and then amorphous α-ole with a granulator. A pellet of the fin 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 = 95/5 (mass ratio) Pellets of the olefin polymer composition (2) were obtained.

(Preparation Example 3)
[Preparation of Amorphous α-Olefin Polymer Composition (3)]
In place of the amorphous propylene-butene-1 copolymer used in Preparation Example 2, Preparation Example 2 except that the amorphous propylene-ethylene-butene-1 copolymer obtained in Synthesis Example 2 was used. Similarly, a pellet of an amorphous α-olefin polymer composition (3) was obtained.

Example 1
As the resin for the base layer, high-density polyethylene (density: 0.960 g / cm ³ , MFR (190 ° C., 21.18 N): 13 g / 10 min; hereinafter referred to as “HDPE”) 50 parts by mass and low-density polyethylene ( Density: 0.902 g / cm ³ , MFR (190 ° C., 21.18 N): 4 g / 10 min; hereinafter referred to as “LDPE”) 50 parts by mass of the mixed resin was used as the adhesive layer resin prepared above. Amorphous α-olefin polymer composition (1) 30 parts by mass 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 the mixed resin is supplied to an extruder for a base layer (caliber 50 mm) and an extruder for an adhesive layer (caliber 40 mm), respectively, by coextrusion method Extrusion at a temperature of 250 ° C. from a T-die so that the thickness of the base material layer is 56 μm and the thickness of the adhesive layer is 14 μm, cooled with a water-cooled metal cooling roll at 40 ° C. 1 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)
Example 2 is the same as Example 1 except that 50 parts by mass of the amorphous α-olefin polymer composition (1) and 50 parts by mass of LLDPE (1) are used as the adhesive layer resin. A surface protective film was obtained.

(Example 3)
Example 3 is the same as Example 1 except that a mixed resin of 40 parts by mass of the amorphous α-olefin polymer composition (2) and 60 parts by mass of LLDPE (1) was used as the adhesive layer resin. A surface protective film was obtained.

Example 4
Example 4 is the same as Example 1 except that 40 parts by mass of the amorphous α-olefin polymer composition (3) and 60 parts by mass of LLDPE (1) are used as the adhesive layer resin. A surface protective film was obtained.

(Example 5)
As an adhesive layer resin, 40 parts by mass of an amorphous α-olefin polymer composition (2), 40 parts by mass of LLDPE (1), 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”) The surface protective film of Example 5 in the same manner as in Example 1 except that 20 parts by mass of the mixed resin was used. Got.

(Example 6)
As the adhesive layer resin, 15 parts by mass of an amorphous α-olefin polymer composition (2) and linear low-density polyethylene (density: 0.920 g / cm ³ , MFR (190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “LLDPE (2)”) A surface protective film of Example 6 was obtained in the same manner as in Example 1 except that 85 parts by mass of the mixed resin was used.

(Example 7)
As a resin for the surface layer, a mixed resin of 95 parts by mass of LDPE and 5 parts by mass of a propylene-ethylene block copolymer (density: 0.900 g / cm ³ , MFR (230 ° C., 21.18 N): 8 g / 10 min) is used. The mixed resin of 50 parts by mass of HDPE and 50 parts by mass of LDPE was used as the resin for the base layer, and 10 parts by mass of the amorphous α-olefin polymer composition (2) and LLDPE (2) 90 were used as the resin for the adhesive layer. Using the mixed resin of parts by mass, the surface layer extruder (caliber 50 mm), the substrate layer extruder (caliber 50 mm) and the adhesive layer extruder (caliber 40 mm) were respectively supplied and extrusion temperature was obtained by coextrusion method. Example 7 was carried out in the same manner as in Example 1 except that the surface layer was extruded from a T-die at 250 ° C. so that the thickness of the surface layer was 14 μm, the thickness of the base material layer was 42 μm, and the thickness of the adhesive layer was 14 μm. Table A surface protective film was obtained.

(Example 8)
As a resin for the surface layer, 85 parts by mass of 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 propylene -The surface protection film of Example 8 was obtained like Example 7 except having used the mixed resin of 15 mass parts of ethylene block copolymers.

Example 9
Example 7 except that a mixed resin of 95 parts by mass of LLDPE (1) and 5 parts by mass of propylene-ethylene block copolymer was used as the resin for the surface layer, and LLDPE (1) was used as the resin for the base layer. Similarly, the surface protective film of Example 9 was obtained.

(Example 10)
Example 7 except that a mixed resin of 95 parts by mass of LLDPE (2) and 5 parts by mass of propylene-ethylene block copolymer was used as the resin for the surface layer, and LLDPE (2) was used as the resin for the base layer. Similarly, the surface protective film of Example 10 was obtained.

(Example 11)
As a resin for the surface layer, 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)”) 95 The surface protective film of Example 11 is the same as Example 7 except that a mixed resin of 5 parts by mass and 5 parts by mass of propylene-ethylene block copolymer is used, and LLDPE (3) is used as the resin for the base layer. Got.

Example 12
A surface protective film of Example 12 was obtained in the same manner as in Example 6 except that LDPE was used as the resin for the substrate layer.

(Example 13)
Except for using LDPE as the resin for the base layer and using a mixed resin of 10 parts by mass of the amorphous α-olefin polymer composition (2) and 90 parts by mass of LLDPE (2) as the resin for the adhesive layer. In the same manner as in Example 1, the surface protective film of Example 13 was obtained.

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

(Comparative Example 2)
Comparative Example 2 was carried out in the same manner as in Example 1 except that a mixed resin of 30 parts by mass of the amorphous α-olefin polymer composition (1) and 70 parts by mass of LLDPE (3) was used as the adhesive layer resin. A surface protective film was obtained.

(Comparative Example 3)
As the adhesive layer resin, 60 parts by mass of an amorphous α-olefin polymer composition (2) and a styrene-ethylene-propylene-styrene block copolymer (“Septon 2063” manufactured by Kuraray Co., Ltd .; hereinafter, “SEPS”) The surface protective film of Comparative Example 3 was obtained in the same manner as in Example 1 except that 40 parts by mass of the mixed resin was used.

(Comparative Example 4)
Surface protective film of Comparative Example 4 as in Example 1 except that a mixed resin of 50 parts by mass of amorphous α-olefin polymer composition (1) and 50 parts by mass of HOPP was used as the adhesive layer resin. Got.

(Comparative Example 5)
The same procedure as in Example 1 was conducted except that a mixed resin 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. Thus, a surface protective film of Comparative Example 5 was obtained.

(Comparative Example 6)
A mixed resin of 80 parts by mass of HOPP and 20 parts by mass of a propylene-ethylene block copolymer is used as the resin for the surface layer, HOPP is used as the resin for the base layer, and an amorphous α-olefin heavy polymer is used as the resin for the adhesive layer. A surface protective film of Comparative Example 6 was obtained in the same manner as in Example 7 except that 10 parts by mass of the combined composition (2) and 90 parts by mass of LLDPE (2) were used.
* The resin density description has been unified to 3 digits after the decimal point.

  Using the surface protective films obtained in Examples 1 to 13 and Comparative Examples 1 to 6, the following measurements and evaluations were performed.

(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, a surface protective film was made into a 15 cm long × 5 cm wide acrylic plate (mirror finish, manufactured by Mitsubishi Rayon Co., Ltd.) according to 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 a test piece from which the film obtained after the evaluation in (3) above was peeled off.

(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.

(7) Evaluation of cutting performance In a thermostatic chamber at 23 ° C. and 50% RH, the surface protective film obtained above was applied to an acrylic plate having a thickness of 2 mm according to JIS Z0237: 2000 (mirror finish). And “Acrylite” manufactured by Mitsubishi Rayon Co., Ltd.). When the acrylic plate to which the film was attached was cut with a high-speed cutter, the cut end face of the film was visually observed, and the cutting ability was evaluated according to the following criteria.
○: No appearance defects such as stringing, fluffing and cracking are observed on the cut end face of the film.
Δ: Some appearance defects such as stringing, fluffing and cracking are slightly seen on the cut end face of the film.
X: Appearance defects such as stringing, fluffing and cracking are observed on the cut end face of the film.

  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. An example in which the surface layer resin composition is blank and the thickness of the surface layer is “−” indicates that no surface layer is provided.

  From the results of Examples 1 to 13, 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. 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. Therefore, after peeling off the surface protective film, it is suitable for applications that are subjected to secondary processing such as printing, and when the adherend is cut and processed with the surface protective film attached to the adherend. It was found that the surface protective film cuts cleanly and has a cutting property that does not cause appearance defects such as stringing and fluffing.

  Comparative Example 1 is an example of a surface protective film in which the blending ratio of the amorphous propylene-butene-1 copolymer of the adhesive layer with the linear low-density polyethylene is about 3% by mass, which is smaller than the lower limit of 5% by mass. is there. 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 used in the adhesive layer, 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 ratio of the amorphous propylene-butene-1 copolymer of the adhesive layer to the linear low density polyethylene is 50% by mass exceeding the upper 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 using a mixed resin of a propylene homopolymer and a propylene-ethylene block copolymer for the surface layer and a propylene homopolymer for the base material layer. It was found that the surface protective film of Comparative Example 6 was inferior in cutting property.

Claims (5)

A base material layer mainly composed of an ethylene polymer (A1), an amorphous α-olefin polymer (B1) of 5 to 40% by mass, and a density of 0.880 to 0.938 g / cm ³ . A surface protective film comprising a coextrusion laminated film in which a linear low density polyethylene (B2) 60 to 95% by mass of a mixed resin as a main component is laminated.   The surface protective film according to claim 1, wherein a total content ratio of the amorphous α-olefin polymer (B1) and the linear low-density polyethylene (B2) in the adhesive layer is 65% by mass or more.   The surface protective film according to claim 1 or 2, wherein the ethylene polymer (A1) is at least one selected from the group consisting of low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene.   The amorphous amorphous α-olefin polymer (B1) is an amorphous propylene-butene-1 copolymer or an amorphous propylene-ethylene-butene-1 copolymer. The surface protective film of description.   Any one of Claims 1-4 which provided the surface layer which has a mixed resin of a low density polyethylene or a propylene homopolymer, and a propylene-ethylene block copolymer as a main component on the base material layer on the opposite surface of the said adhesion layer. A surface protective film according to claim 1.