WO2009087797A1

WO2009087797A1 - Surface protection film

Info

Publication number: WO2009087797A1
Application number: PCT/JP2008/068020
Authority: WO
Inventors: Tatsuhiko Usui; Takashi Moriya; Kazunori Kobashi
Original assignee: Dic Corporation
Priority date: 2008-01-11
Filing date: 2008-10-03
Publication date: 2009-07-16
Also published as: TW200930783A; JP2009166277A; CN101909887A; JP4412408B2; KR20100046267A; TWI364446B

Abstract

The invention relates to a surface protection film which is to be applied to the surfaces of building materials, various resin plates for use in electrical and electronic fields, glass plates, metal plates and so on for the purpose of protecting the adherends from scratching, contamination or the like in storage, transportation, or post-processing. A surface protection film which little stains the surface of an adherend and is excellent in fabricability is provided by using, as the main resin component constituting the pressure-sensitive adhesive layer of the film, a resin blend which comprises an amorphous α-olefin polymer and a linear low-density polyethylene at a specific ratio or which comprises an amorphous α-olefin polymer, a linear low-density polyethylene, and a crystalline ethylene/α-olefin copolymer at a specific ratio.

Description

Surface protection film

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, after the surface protective film is adhered to the adherend, the surface protective film does not float or peel off from the adherend, and has very little contamination such as adhesive residue on the adherend surface after film peeling. About.

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 or the like 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 may be inferior in adhesion between the base film and the pressure-sensitive adhesive, or when peeled from the adherend due to the low cohesive force 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 in which a base film layer and an adhesive layer are simultaneously extruded and laminated by a coextrusion lamination method has been proposed. As such a surface protective film, for example, as a resin composition for an adhesive layer, a mixture containing an amorphous olefin copolymer, a crystalline olefin copolymer, and a thermoplastic elastomer and having specific properties is used. Use (for example, refer to Patent Document 1) or use a mixture of an amorphous olefin copolymer, a crystalline olefin polymer, and a block copolymer having a crystalline olefin block at a specific ratio. (For example, refer to Patent Document 2) provides a multilayer film that is excellent in adhesive strength and peeling stability and has no adhesive residue after peeling.

In addition, the present inventors already have a crystalline propylene-based polymer as a main component as a surface protective film that has both moderate adhesiveness and heat resistance and has little contamination on the surface of the adherend after peeling. Provided is a surface protective film in which a base material layer and an adhesive layer composed mainly of a resin in which an amorphous α-olefin polymer and a crystalline propylene polymer are mixed at a specific ratio are laminated (for example, a patent) Reference 3).

However, when the surface protective film provided in Patent Document 1 or 2 is adhered to an acrylic plate or the like, peeling from the adherend may be difficult due to its high initial adhesive strength. It was. Depending on the application, after the protective film is peeled off, secondary processing such as printing may be performed on the surface of a resin plate or the like as an adherend. In the surface protective film comprising the coextruded laminated film provided in Patent Document 1 or 2, 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 printing is performed in such secondary processing. There was a problem that caused the failure. Furthermore, when a styrene-based elastomer is blended in the adhesive layer, the problem arises that the adhesive layer and the base material layer are in close contact when used again after being rolled up, so-called blocking occurs. There was a case.

Moreover, in the surface protective film provided in Patent Document 3, although there is no contamination to the adherend surface after peeling, the property of the adherend surface may be changed. -There was an adverse effect when performing secondary processing such as printing.

JP 2006-188646 A JP 2006-257247 A Japanese Patent Laid-Open No. 2007-130872

The problem of the present invention is that it has moderate adhesiveness and adhesive stability, has not only a residue that can be visually confirmed on the surface of the adherend after peeling, but also a minute amount of contamination that cannot be confirmed. It is intended to provide a surface protective film having good next processing suitability, and having no blocking when it is rolled out and then used again.

As a result of diligent research to solve the above problems, the present inventors have determined that a specific ratio of an amorphous α-olefin polymer and a linear low density polyethylene as a resin used for the adhesive layer of the surface protective film. Or a resin in which an amorphous α-olefin polymer, a linear low density polyethylene, and a crystalline ethylene-α-olefin copolymer are mixed at a specific ratio as a main component. The inventors found that the surface of the adherend is very little contaminated and the suitability for secondary processing is improved, and the present invention has been completed.

That is, the present invention is a surface protective film in which an adhesive layer (A) and a base material layer (B) are laminated, wherein the adhesive layer (A) is an amorphous α-olefin polymer (A1) 5 A mixed resin of 50 to 95% by mass and a linear low density polyethylene (A2) having a density of 0.880 to 0.938 g / cm ³ , or an amorphous α-olefin polymer. (A1) 5 to 50% by mass, linear low density polyethylene (A2) having a density of 0.880 to 0.938 g / cm ³ and 40 to 90% by mass, and a crystalline ethylene-α-olefin copolymer (A3) Provided is a surface protective film comprising a mixed resin of 5 to 50% by mass as a main component. In addition, in this invention, having a specific resin in each layer as a main component means that in the resin composition used in the layer (all including various additives and other resins used in combination as necessary) This means that the resin or mixed resin specified in the present invention is contained in an amount of 65% by mass or more.

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 rolls up in roll shape, and it extends | stretches out again and uses it, there is no blocking and it is excellent also in blocking resistance.

In addition to the above performance, the surface protective film of the present invention obtained using an ethylene polymer as a base material layer, in particular, cuts the adherend in a state where the surface protective film is adhered to the adherend. In this case, the surface protective film cuts cleanly and exhibits excellent properties that do not cause appearance defects such as stringing and fluffing, and its application fields are wide.

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

The amorphous α-olefin polymer (A1) used for the adhesive layer (A) of the surface protective film of the present invention is a polymer containing monomer units based on α-olefins having 3 to 20 carbon atoms, or A copolymer having a melting peak with a heat of fusion of 1 J / g or more and a crystallization peak with a heat of crystallization of 1 J / g or more in a differential scanning calorimeter (DSC) measurement range of −100 to 200 ° C. None of these polymers are observed, and these may be used alone or in combination of two or more.

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 These α-olefins are included.

The amorphous α-olefin polymer (A1) is preferably a copolymer having two or more monomer units based on these α-olefins. Copolymers having at least one monomer unit based on 4 to 20 α-olefin are industrially available, linear low density polyethylene (A2) described later or crystalline ethylene-α-olefin copolymer. From the viewpoint of compatibility with the polymer (A3), coextrusion moldability and the like, amorphous propylene-butene-1 copolymer and amorphous propylene-ethylene-butene-1 copolymer are most preferable. . The amorphous α-olefin polymer (A1) may have a monomer unit other than the α-olefin. Examples of such monomer units include monomer units based on ethylene, polyene compounds, cyclic olefins, vinyl aromatic compounds, and the like.

The content of monomer units based on propylene in the amorphous propylene-butene-1 copolymer is selected from the viewpoint of improving the heat resistance of the resulting surface protective film. When the total monomer unit of the polymer is 100% by mass, it is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more.

The content of monomer units based on propylene in the amorphous propylene-ethylene-butene-1 copolymer is selected from the viewpoint of improving the heat resistance of the resulting surface protective film. When the total monomer unit of the butene-1 copolymer is 100% by mass, it is preferably 50% by mass or more, and more preferably 60% by mass or more. Similarly, the content of monomer units based on ethylene in the amorphous propylene-ethylene-butene-1 copolymer is the same as the total amount of amorphous propylene-ethylene-butene-1 copolymer. The amount is preferably 10% by mass or more, more preferably 20% by mass or more, based on 100% by mass of the monomer unit. If the content of the monomer unit based on ethylene is within this range, the adhesive layer (B) becomes relatively soft, and even if the adherend surface has irregularities, it adheres in a form that follows the irregularities. Therefore, sufficient adhesive strength can be obtained.

In addition, the intrinsic viscosity [η] of the amorphous α-olefin polymer (A1) 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) to 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 (A1) are within this range, the heat resistance, transparency and adhesiveness are improved, and the adherend to which a surface protective film is attached is provided. Reduces contamination of the adherend due to migration of low molecular weight components in the amorphous α-olefin polymer (A1) to the adherend surface even when stored for a long period of time or exposed to a high temperature environment. be able to. Further, since the amorphous α-olefin polymer (A1) is an olefin polymer, it is possible to remove acetic acid as in the case where an ethylene-vinyl acetate copolymer is used as a resin for the adhesive layer. There is no increase in adhesive strength over time due to resin alteration, and stable adhesive strength can be maintained over a long period of time.

The method for producing the amorphous α-olefin polymer (A1) is not particularly limited, and for example, using a gas phase polymerization method, a solution polymerization method, a slurry polymerization method, a bulk polymerization method, or the like, Examples thereof include a method of polymerizing with a metallocene catalyst. A more preferable production method includes the production method disclosed in JP-A-2002-348417.

The resin used for the adhesive layer (A) in the surface protective film of the present invention is a resin obtained by mixing the amorphous α-olefin polymer (A1) and the linear low density polyethylene (A2), or the amorphous This is a resin in which an α-olefin polymer (A1), a linear low density polyethylene (A2), and a crystalline ethylene-α-olefin copolymer (A3) are mixed. By blending the linear low density polyethylene (A2) and the crystalline ethylene-α-olefin copolymer (A3) into the amorphous α-olefin polymer (A1), the surface state of the adherend is obtained. Adhesive strength can be adjusted according to the required properties depending on the material and application of the adherend, and contamination on the adherend surface after peeling can be reduced regardless of the strength of the adhesive strength.

The linear low density polyethylene (A2) are those having a density in the range of 0.880 ~ 0.938g / cm ^3, the density is more preferably from 0.898 ~ 0.925g / cm ^3. The melt flow rate (MFR, measured at 190 ° C. and 21.18 N according to JIS K7210: 1999) is preferably 0.5 to 30.0 g / 10 min. More preferred is 0 to 15.0 g / 10 min. If the density and MFR of the linear low density polyethylene (A2) are within this range, the compatibility with the above-mentioned amorphous α-olefin polymer (A1) is good, and the film formability of the laminated film is improved. To do.

Examples of the crystalline ethylene-α-olefin copolymer (A3) include an ethylene-propylene copolymer and an ethylene-butene-1 copolymer, and the ethylene-butene-1 copolymer is preferred. It is preferable from the viewpoint of easy industrial availability and easy adjustment of the adhesive strength of the resulting surface protective film. The crystalline ethylene-α-olefin copolymer (A3) has an MFR (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. Those having a .905 g / cm ³ are preferable, and those having an MFR of 2.0 to 15.0 g / 10 min and a density of 0.880 to 0.900 g / cm ³ are more preferable. If the MFR and density of the crystalline ethylene-α-olefin copolymer (A3) are within this range, the compatibility with the amorphous α-olefin polymer (A1) described above is good and the laminated film is formed. Film properties are improved. Further, from the viewpoint of the effect of preventing contamination of the adherend surface, these resins are more preferably a metallocene catalyst system described later with a small amount of low molecular weight components. The crystallinity is a melting peak with a melting heat of 1 J / g or more and a crystallization peak with a crystallization heat of 1 J / g or more in a measurement range of −100 to 200 ° C. with a differential scanning calorimeter (DSC). Is a polymer in which any of the above is observed.

When the mixed resin of the amorphous α-olefin polymer (A1) and the linear low density polyethylene (A2) is used as the main component for the adhesive layer (A), the blending ratio thereof is amorphous α-olefin. The polymer (A1) is 5 to 50% by mass, the linear low density polyethylene (A2) is 50 to 95% by mass, more preferably the component (A1) is 5 to 40% by mass, and the component (A2) is 60 to 95% by mass. %. If the blending ratio of the amorphous α-olefin polymer (A1) 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. Also, by adjusting the blending ratio of component (A1) and component (A2) 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. Easy to do.

In addition, a resin obtained by mixing the amorphous α-olefin polymer (A1), the linear low density polyethylene (A2), and the crystalline ethylene-α-olefin copolymer (A3) into the adhesive layer (A) is used. When used as a main component, the blending ratio is 5 to 50% by mass of an amorphous α-olefin polymer (A1), and a linear low density polyethylene (density 0.880 to 0.938 g / cm ³ ). A2) 40 to 90% by mass, crystalline ethylene-α-olefin copolymer (A3) 5 to 50% by mass, more preferably component (A1) 5 to 30% by mass, and component (A2) 40 to 85% by mass. %, Component (A3) is 10 to 45 mass%. By adjusting the blending ratio of component (A1), component (A2), and component (A3) within the above range, an adhesive of about 0.1 to 7.0 N / 25 mm depending on the required adhesive strength It becomes easy to adjust to the force.

In the present invention, the resin used for the adhesive layer (A) is mainly composed of the above-mentioned mixed resin, but other resins may be used in combination as long as the effects of the present invention are not impaired. Examples of other resins that can be used at this time include propylene homopolymer, propylene-butene-1 copolymer, propylene-butene-1-ethylene terpolymer, butene-1 homopolymer, styrene-butadiene- Styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene- Butadiene copolymer (SB), styrene-isoprene copolymer (SI), styrene-ethylene-butylene copolymer (SEB), styrene-butadiene rubber (SBR), styrene-ethylene-butylene-ethylene copolymer (SEBC) ) And these hydrogenated products.

The method for preparing the mixed resin used in the pressure-sensitive adhesive layer (A) of the present invention is not particularly limited, but the amorphous α-olefin polymer (A1) is difficult to handle at room temperature. In view of the above, in order to more easily apply the coextrusion lamination method, the amorphous α-olefin polymer (A1) is previously melted with the linear low density polyethylene (A2) or other crystalline polymer. It is preferable to knead and form pellets that are easy to handle.

As described above, in the present invention, the main component is a specific resin in each layer means that the resin composition used in the layer (various additives and other resins used in combination as necessary). Including all), it means that the resin or mixed resin specified in the present invention is contained in an amount of 65% by mass or more, and that it is 75% by mass or more from the point that the effect of the present invention is more easily expressed. Particularly preferred is 85% by mass or more.

The resin used for the base material layer (B) of the surface protective film of the present invention is not particularly limited as long as it is a thermoplastic resin and can be coextruded with the adhesive layer (A), but the adhesive layer (A It is preferable that the olefin polymer is a main component from the viewpoint of good affinity with), and it is particularly preferable that the main component is an ethylene polymer (B1) or a crystalline propylene polymer (B2). .

Examples of the ethylene polymer (B1) include low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene. These may be used alone or in combination. Among these, since heat resistance is favorable, it is preferable to use a linear low density polyethylene, a medium density polyethylene, or a mixed resin of low density polyethylene and high density polyethylene as a main component.

When the ethylene-based polymer (B1) is used as the base material layer (B), in addition to the effect of preventing contamination of the adherend surface after peeling, which is the main object of the present invention, the surface of the adherend is When the adherend is cut and processed with the protective film attached, the surface protective film is cut cleanly and also exhibits good cutting properties that do not cause appearance defects such as stringing and fluffing.

Further, as these ethylene polymers (B1), those having an MFR (measured at 190 ° C. and 21.18 N) of 0.5 to 30.0 g / 10 min can be easily extruded. The MFR is preferably 2.0 to 15.0 g / 10 min. Furthermore, if these ethylene-based polymers (B1) have a melting point of 90 to 135 ° C., the film can be exposed to a high temperature environment by drying, thermoforming or the like after being attached to the adherend. Since the shrinkage is small, it is preferable because the floating and peeling from the adherend and the warpage of the adherend can be suppressed. More preferably, the melting point is 105 to 130 ° C.

When heat resistance is required by the surface protective film of the present invention, it is preferable to use a crystalline propylene polymer (B2) as the resin used for the base material layer (B). Examples of the crystalline propylene polymer (B2) include a propylene homopolymer, an ethylene-propylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. . These may be used alone or in combination of two or more. These crystalline polypropylene polymers (B2) have an MFR (measured at 230 ° C. and 21.18 N) of 0.5 to 30.0 g / 10 min and a melting point of 120 to 165 ° C. More preferably, the MFR is 2.0 to 15.0 g / 10 min and the melting point is 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. The crystallinity is a melting peak with a melting heat of 1 J / g or more and a crystallization peak with a crystallization heat of 1 J / g or more in a measurement range of −100 to 200 ° C. with a differential scanning calorimeter (DSC). Refers to a polymer in which one of the following is observed.

Among the crystalline propylene polymers (B2) used for the base material layer (B), a crystalline propylene polymer (also referred to as a metallocene catalyst polypropylene) obtained by using a metallocene catalyst 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 catalysts are disclosed in JP-A-5-155931, JP-A-8-104691, JP-A-8-157515, JP-A-8-231621, and the like. The metallocene catalyst-based polypropylene has high uniformity in molecular weight distribution and composition distribution, and the content of the low molecular weight component is small. Therefore, by using the metallocene catalyst-based polypropylene for the base material layer (B) of the present invention, the low molecular weight component It becomes easy to prevent contamination of the adherend surface due to bleeding. The metallocene catalyst-based polypropylene may be a propylene homopolymer or a copolymer of propylene and other α-olefins. Examples of copolymers of propylene and other α-olefins include ethylene-propylene copolymer. Examples include coalescence.

When the crystalline propylene polymer (B2) is used as the substrate layer (B), the same amorphous α-olefin polymer (B3) as that described in detail for the adhesive layer (A) May be used in combination. By using the amorphous α-olefin polymer (B3) in combination, the flexibility of the surface protective film obtained is increased and the followability to the adherend surface when the film is applied is improved. Removes smoothly. The amorphous α-olefin polymer (B3) used at this time may be the same copolymer as the amorphous α-olefin polymer (A1) used for the adhesive layer (A). Different copolymers may be used.

When the amorphous α-olefin polymer (B3) is blended in the base layer (B), the blending ratio of the crystalline propylene polymer (B2) and the amorphous α-olefin polymer (B3) Is preferably in the range of [crystalline propylene polymer (B2)]: [amorphous α-olefin polymer (B3)] = 70 to 95:30 to 5, more preferably The ratio is in the range of 80 to 95:20 to 5. If the blending ratio of the crystalline propylene polymer (B2) and the amorphous α-olefin polymer (B3) is within this range, the surface protection film to be obtained has sufficient flexibility and heat resistance. Can be maintained.

Moreover, you may adjust the softness | flexibility of the surface protection film obtained by using together the said ethylene polymer (B1) and crystalline propylene polymer (B2) as a base material layer (B). Furthermore, the flexibility of the obtained film can be prepared by using an ethylene-methyl methacrylate copolymer (hereinafter referred to as “EMMA”) or the like in combination. The EMMA preferably has an MFR (measured at 190 ° C. and 21.18 N) of 0.5 to 30.0 g / 10 minutes, more preferably an MFR of 2.0 to 15.0 g / 10 minutes. Is. In EMMA, the content of monomer units based on methyl methacrylic acid (hereinafter referred to as “MMA”) is preferably 3 to 30% by mass, and more preferably 8 to 25% by mass. When the contents of the MFR and MMA are within this range, sufficient flexibility is imparted to the resulting surface protective film, and the film formability of the laminated film is improved.

In the base material layer (B), when the amorphous propylene polymer (B2) is blended with the amorphous α-olefin polymer (B3), the ethylene polymer (B1) and / or EMMA, The blending ratio of the crystalline propylene polymer (B2), the amorphous α-olefin polymer (B3), the ethylene polymer (B1) and / or EMMA is [mass based on the crystalline propylene polymer]. (B2)]: [Amorphous α-olefin polymer (B3)]: [Ethylene polymer (B1) and / or EMMA] = 70 to 95: 4 to 29: 1 to 12 More preferably, the ratio is in the range of 80 to 95: 4 to 19: 1 to 5. When the blending ratio is within this range, heat resistance can be maintained while imparting sufficient flexibility to the surface protective film to be obtained.

As described above, the surface protective film of the present invention essentially comprises two layers of the adhesive layer (A) and the base material layer (B). In the base material layer (B), the adhesive layer (A The surface layer (C) may be provided on the surface opposite to the surface on which the layers are stacked. The resin used for the surface layer (C) is not particularly limited, but is preferably composed mainly of an olefin polymer from the viewpoint of good affinity with the base material layer (B). It is more preferable to use the polymer (C1) or the crystalline propylene polymer (C2). In particular, when the main component of the substrate layer (B) is an ethylene polymer (B1), the ethylene polymer (C1) is used, and the main component of the substrate layer (B) is a crystalline propylene polymer ( In the case of B2), it is more preferable that the crystalline propylene polymer (C2) is a main component.

Examples of the ethylene polymer (C1) that can be suitably used as the main component of the surface layer (C) include those similar to the ethylene polymer (B1) used as the main component of the base material layer (B). It is done. Further, by selecting the ethylene polymer (C1) as the main component of the surface layer (C), the final state is the same as when the ethylene polymer (B1) is used as the main component of the base material layer (B). The high cuttability of the surface protective film thus obtained is manifested. The ethylene polymer (B1) used for the base material layer (B) and the ethylene polymer (C1) used for the surface layer (C) may use the same resin, but use different resins. Also good.

Among the ethylene-based polymer (C1) used as the main component of the surface layer (C), when low density polyethylene is used, it is easy to modify the surface of the surface layer (C) into a satin finish. By making the surface of the surface layer (C) satin, blocking can be reduced even when the adhesive force of the adhesive layer (A) is designed to be strong. Moreover, when high-density polyethylene is used in combination with low-density polyethylene, the rigidity of the resulting surface protective film can be increased, and workability such as sticking and peeling is improved.

Further, even when a mixed resin of the ethylene polymer (C1) and the ethylene-propylene copolymer is used as a main component of the surface layer (C), the surface of the surface layer (C) is modified into a satin finish. can do. The ethylene-propylene copolymer may be a resin obtained by copolymerizing ethylene and propylene. For example, the ethylene-propylene copolymer can be obtained by polymerizing ethylene or polymerizing ethylene and propylene in the presence of a propylene homopolymer. Examples thereof include an ethylene-propylene block copolymer. Among these, an ethylene-propylene block copolymer having an ethylene-derived component content of 8 to 20% by mass is preferable because the surface can be easily textured, and the ethylene-derived component content is 10 to 10%. It is more preferable to use 15% by mass of an ethylene-propylene block copolymer. Further, the MFR (value measured at 230 ° C. and 21.18 N) of the ethylene-propylene copolymer is preferably in the range of 4 to 12 g / 10 minutes from the viewpoint of easy extrusion and in the range of 6 to 10 g / 10 minutes It is more preferable that Similarly, the density of the copolymer is preferably in the range of 0.890 to 0.910 g / cm ^{3 from} the viewpoint of easy extrusion, and in the range of 0.895 to 0.905 g / cm ^3. More preferred. Even if the ethylene-propylene copolymer is used alone as the main component of the surface layer (C), the surface of the surface layer (C) can be modified into a satin finish, so that the base material layer (B) It is preferable to select and use it appropriately in view of the affinity with the resin type used in the above.

The crystalline propylene polymer (C2) that can be suitably used as the main component of the surface layer (C) is the same as the crystalline propylene polymer (B2) used as the main component of the substrate layer (B). Can be mentioned. In addition, when the crystalline propylene polymer (C2) is selected as the main component of the surface layer (C), the crystalline propylene polymer (B2) is used as the main component of the base material layer (B). Similarly, high heat resistance of the finally obtained surface protective film is expressed.

In addition, as a main component of the surface layer (C), the crystalline propylene polymer (C2) and the ethylene-propylene copolymer are mixed from the viewpoint of adhesive strength level, required transparency, etc. May be adjusted.

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 within this range, the protective properties and adhesion of the adherend, and workability such as sticking and peeling will be good. The thickness of the adhesive layer (A) is preferably 3 to 30 μm, more preferably 5 to 25 μm. If the thickness of the pressure-sensitive adhesive layer (A) is within this range, the pressure-sensitive adhesive property and the film forming property of the laminated film will be good. Furthermore, when the surface layer (C) is provided on the surface protective film of the present invention, the thickness of the surface layer (C) is preferably 3 to 30 μm, more preferably 5 to 20 μm. When the thickness of the surface layer (C) 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 between a rubber touch roll, a steel belt or the like and the chill roll and cooled.

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 in the longitudinal or transverse direction, more preferably 3 to 30 times. On the other hand, the stretching 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 terms of area ratio.

Also, the longitudinal or lateral stretching process 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. The stretching temperature is preferably 80 ° C. to 160 ° C. in any stretching method in the case of uniaxial stretching, and preferably 90 to 165 ° C. in the case of using tenter stretching in uniaxial stretching. Further, more preferable stretching temperatures are 110 to 155 ° C. and 120 to 160 ° C., 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 60 to 140 ° C., and the temperature of the heat fixing part is preferably 90 to 160 ° C.

The surface protective film of the present invention is further stretched in at least one axial direction and structurally stabilized by heat setting, and further by orientation crystallization of the resin used for the base layer (B) and the surface layer (C). This is preferable because the heat resistance is improved and the change with time of the adhesive force is small. Particularly, when the crystalline propylene polymer is used for the base material layer (B) and / or the surface layer (C), the effect becomes high. .

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 the range not impairing the effects of the present invention. May be added to any layer depending on the purpose. As these additives, it is preferable to use various additives for olefin polymers.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples.

(Synthesis Example 1)
[Synthesis of Amorphous α-Olefin Polymer (Amorphous Propylene-Butene-1 Copolymer)]
In a 100L 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, followed by steps of demonomerization, water washing, and solvent removal. A polymer was obtained. Subsequently, the obtained copolymer was dried under reduced pressure at 80 ° C. for 24 hours. In this amorphous propylene-butene-1 copolymer, the content of propylene monomer units was 94.5% by mass, and the content of butene-1 monomer units was 5.5% by mass. (Each monomer unit was calculated using a nuclear magnetic resonance apparatus JMN-LA300 manufactured by JEOL Ltd.) Further, no melting peak was observed in the DSC (EXSTAR6000 manufactured by Seiko Instruments Inc.) of the copolymer, and the limit was limited. The viscosity [η] was 2.3 dl / g, and the molecular weight distribution (Mw / Mn) was 2.2. (The molecular weight distribution was analyzed by a gel permeation chromatograph manufactured by Tosoh Corporation, HLC-8020.)

(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 × 10 ⁻⁶ cm ³ / min, propylene 4 × 10 ⁻⁶ cm ³ / min and butene-1 1 × 10 ⁻⁶ cm ³ / min are continuously supplied at normal pressure, and the solvent temperature is 30 ° C. It was. After adding 0.75 mmol of triisobutylaluminum (hereinafter referred to as TIBA) to the polymerization vessel, 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 is 61.5% by mass, the content of ethylene monomer units is 21.0% by mass, 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 Pellet Composed of Composition (1) Containing Amorphous α-Olefin Polymer]
The amorphous propylene-butene-1 copolymer obtained in Synthesis Example 1 was added to the crystalline propylene-butene-1 copolymer [density 0.900 g / cm ³ , MFR (measured at 230 ° C., 21.18 N]. Value) 10.0 g / 10 min, maximum melting peak 126 ° C. in DSC], amorphous propylene-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 (Ciba Specialty Chemicals Co., Ltd.). “Irganox 1010”] and 2000 ppm each of the two-screw extruder (IKEMAI PCM3 Was melt-kneaded at 230 ° C. in 30mmφ screws), then to obtain a pellet of granulator (compositions containing amorphous α- olefin polymer by Nakatani Machine CK2) (1).

(Preparation Example 2)
[Preparation of Pellet Composed of Composition (2) Containing Amorphous α-Olefin Polymer]
Amorphous propylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = Amorphous α in the same manner as in Preparation Example 1 except that the blend was made to be 95/5 (mass ratio). -Pellets of the composition (2) containing an olefin polymer were obtained.

(Preparation Example 3)
[Preparation of Pellet Composed of Composition (3) Containing Amorphous α-Olefin Polymer]
In the same manner as in Preparation Example 1, except that the amorphous α-olefin polymer used in Preparation Example 1 is the amorphous propylene-ethylene-butene-1 copolymer obtained in Synthesis Example 2, A pellet of the composition (3) containing an amorphous α-olefin polymer was obtained.

(Preparation Example 4)
[Preparation of Pellet Composed of Composition (4) Containing Amorphous α-Olefin Polymer]
Amorphous propylene-ethylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 95/5 (mass ratio) A pellet of the composition (4) containing a hydrophilic α-olefin polymer was obtained.

(Preparation Example 5)
[Preparation of Pellet Composed of Composition (5) Containing Amorphous α-Olefin Polymer]
The amorphous propylene-butene-1 copolymer obtained in Synthesis Example 1 was added to a linear low density polyethylene (density 0.935 g / cm ³ , MFR (measured at 190 ° C. and 21.18 N) 3 0.5 g / 10 min] in the same manner as in Preparation Example 1, except that amorphous propylene-butene-1 copolymer / linear low-density polyethylene = 95/5 (mass ratio). A pellet of the composition (5) containing an amorphous α-olefin polymer was obtained.

Example 1
As the resin for the surface layer, a propylene homopolymer [density: 0.900 g / cm ³ , MFR (value measured at 230 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “HOPP”. ] 80 parts by mass, ethylene-propylene block copolymer [density: 0.900 g / cm ³ , MFR (230 ° C., 21.18N): 8 g / 10 min] As the resin, HOPP is used, and as the adhesive layer resin, 30 parts by mass of the composition (1) containing the amorphous α-olefin polymer prepared above and linear low density polyethylene [density: 0.902 g / Cm ³ , MFR (value measured at 190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “LLDPE (1)”. Using 70 parts by mass of the mixture, the mixture was supplied to a surface layer extruder (caliber 50 mm), a substrate layer extruder (caliber 50 mm) and an adhesive layer extruder (caliber 40 mm), respectively, and extruded by a coextrusion method. After extruding from a T-die at a temperature of 250 ° C. to a surface layer thickness of 12 μm, a base layer thickness of 38 μm, and an adhesive layer 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)
An ethylene-propylene block copolymer is used as the resin for the surface layer, and 50 parts by mass of the composition (1) and LLDPE (1) containing an amorphous α-olefin polymer 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 replaced with.

(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
Surface protection was carried out in the same manner as in Example 2 except that the adhesive layer resin was replaced with a mixture of 40 parts by mass of the composition (2) containing an amorphous α-olefin polymer and 60 parts by mass of LLDPE (1). A film was obtained.

(Example 5)
As an adhesive layer resin, 40 parts by mass of a composition (4) containing an amorphous α-olefin polymer and linear low-density polyethylene [density: 0.920 g / cm ³ , MFR (190 ° C., 21. Value measured at 18N): 4.0 g / 10 min; hereinafter referred to as “LLDPE (2)”. A surface protective film was obtained in the same manner as in Example 2 except that 60 parts by mass of the mixture was used.

(Example 6)
Surface protection was carried out in the same manner as in Example 2 except that a mixture of 20 parts by mass of the composition (5) containing an amorphous α-olefin polymer and 80 parts by mass of LLDPE (2) was used as the adhesive layer resin. A film was obtained.

(Example 7)
HOPP is used as the resin for the surface layer, the same HOPP is used as the resin for the base layer, and a composition (2) containing an amorphous α-olefin polymer as the resin for the adhesive layer and LLDPE (2) Using a mixed resin with 90 masses, each is 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). Same as Example 1 except that the extrusion method was carried out at an extrusion temperature of 250 ° C. and extruded from the T-die so that the surface layer thickness was 14 μm, the base material layer thickness was 42 μm, and the adhesive layer thickness was 14 μm. Thus, a surface protective film was obtained.

(Example 8)
Metallocene catalyst-based ethylene-propylene random copolymer [density: 0.900 g / cm ³ , MFR (value measured at 230 ° C., 21.18 N): 7.0 g / 10 min, ethylene single Content rate of the monomer unit: 3.5 mass%; hereinafter referred to as “metallocene catalyst system COPP”. And a mixture of 50 parts by mass of the composition (3) containing an amorphous α-olefin polymer and 50 parts by mass of LLDPE (2) as the adhesive layer resin. (Diameter 50 mm) and an adhesive layer extruder (40 mm diameter), respectively, by co-extrusion method at an extrusion temperature of 250 ° C., the thickness of the substrate layer from the T-die becomes 50 μm, and the thickness of the adhesive layer becomes 10 μm After being extruded and cooled 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 9
A metallocene catalyst COPP is used as the base layer resin, and 6.0 parts by mass of the amorphous α-olefin polymer (2) and 94 parts by mass of LLDPE (2) are used as the adhesive layer resin. A surface protective film was obtained in the same manner as in Example 2 except that the above mixture was used.

(Example 10)
Metallocene catalyst COPP is used as the base layer resin, and composition containing the amorphous α-olefin polymer as the adhesive layer resin (2) 6.0 parts by mass, LLDPE (2) 84 parts by mass And ethylene-butene-1 copolymer [density: 0.895 g / cm ³ , MFR (measured at 190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “EBR”. A surface protective film was obtained in the same manner as in Example 2 except that 10 parts by mass of the mixture was used.

(Example 11)
A metallocene catalyst COPP is used as the base layer resin, and 30 parts by mass of the composition (2), LLDPE (2) 50 parts by mass and EBR20 containing an amorphous α-olefin polymer as the adhesive layer resin. A surface protective film was obtained in the same manner as in Example 2 except that a mixture of parts by mass was used.

Example 12
The metallocene catalyst COPP is used as the base layer resin, and 20 parts by mass of the composition (2), LLDPE (2) 40 parts by mass and EBR40 containing the amorphous α-olefin polymer as the adhesive layer resin. A surface protective film was obtained in the same manner as in Example 2 except that a mixture of parts by mass was used.

(Example 13)
As the resin for the base layer, high density polyethylene [density: 0.960 g / cm ³ , MFR (measured at 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 (value measured at 190 ° C., 21.18 N): 4 g / 10 min; hereinafter referred to as “LDPE”. ) Mixing of 30 parts by mass of the composition (1) containing the amorphous α-olefin polymer prepared above and 70 parts by mass of LLDPE (1) using 50 parts by mass of the mixed resin as the adhesive layer resin The resin is supplied to a substrate layer extruder (caliber 50 mm) and an adhesive layer extruder (caliber 40 mm), respectively, and the thickness of the substrate layer from the T-die at an extrusion temperature of 250 ° C. by coextrusion method. After extruding to 56 μm and the thickness of the adhesive layer to 14 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 14)
The surface was the same as in Example 13 except that 50 parts by mass of the composition (1) containing an amorphous α-olefin polymer and 50 parts by mass of LLDPE (1) were used as the adhesive layer resin. A protective film was obtained.

(Example 15)
The surface was the same as in Example 13 except that 40 mass parts of the composition (2) containing an amorphous α-olefin polymer and 60 mass parts of LLDPE (1) were used as the adhesive layer resin. A protective film was obtained.

(Example 16)
The surface was the same as in Example 13 except that 40 parts by mass of the composition (4) containing an amorphous α-olefin polymer and 60 parts by mass of LLDPE (1) were used as the adhesive layer resin. A protective film was obtained.

(Example 17)
As Example 13 with the exception that 40 parts by mass of the composition (2) containing an amorphous α-olefin polymer, 40 parts by mass of LLDPE (1) and 20 parts by mass of EBR were used as the adhesive layer resin. A surface protective film was obtained in the same manner.

(Example 18)
The surface was the same as in Example 13 except that a mixed resin of 15 parts by mass of composition (2) containing an amorphous α-olefin polymer and 85 parts by mass of LLDPE (2) was used as the adhesive layer resin. A protective film was obtained.

(Example 19)
Adhesive layer resin using a mixed resin of 95 parts by mass of LDPE and 5 parts by mass of ethylene-propylene block copolymer as the resin for the surface layer, and a mixed resin of 50 parts by mass of HDPE and 50 parts by mass of LDPE as the resin for the base layer Using a mixed resin of 10 parts by mass of a composition (2) containing an amorphous α-olefin polymer and 90 parts by mass of LLDPE (2), an extruder for surface layer (caliber 50 mm), base material layer Are fed to an extruder for extrusion (diameter 50 mm) and an adhesive layer extruder (diameter 40 mm), respectively, and the surface layer thickness is 14 μm from the T-die at an extrusion temperature of 250 ° C. by co-extrusion, and the thickness of the substrate layer is A surface protective film was obtained in the same manner as in Example 13 except that extrusion was performed so that the thickness of the adhesive layer was 42 μm and the thickness was 14 μm.

(Example 20)
A surface protective film was obtained in the same manner as in Example 19 except that a mixed resin of 85 parts by mass of HOPP and 15 parts by mass of ethylene-propylene block copolymer was used as the resin for the surface layer.

(Example 21)
Example 19 was used except that a mixed resin of 95 parts by mass of LLDPE (1) and 5 parts by mass of an ethylene-propylene block copolymer was used as the resin for the surface layer, and LLDPE (1) was used as the resin for the base layer. In the same manner, a surface protective film was obtained.

(Example 22)
Example 19 except that a mixed resin of 95 parts by mass of LLDPE (2) and 5 parts by mass of an ethylene-propylene block copolymer was used as the resin for the surface layer, and LLDPE (2) was used as the resin for the base layer. A surface protective film was obtained in the same manner.

(Example 23)
As the resin for the surface layer, linear low density polyethylene [density: 0.940 g / cm ³ , MFR (value measured at 190 ° C., 21.18 N): 4.0 g / 10 min; hereinafter referred to as “LLDPE (3)” That's it. A surface protective film was obtained in the same manner as in Example 19 except that a mixed resin of 95 parts by mass and 5 parts by mass of an ethylene-propylene block copolymer was used, and LLDPE (3) was used as the base layer resin. .

(Example 24)
A surface protective film was obtained in the same manner as in Example 18 except that LDPE was used as the base layer resin.

(Example 25)
As the base layer resin, LDPE is used, and as the adhesive layer resin, 10 parts by mass of a composition (2) containing an amorphous α-olefin polymer and 90 parts by mass of LLDPE (2) are used. A surface protective film was obtained in the same manner as in Example 13 except that.

(Example 26)
Surface protection was carried out in the same manner as in Example 19 except that a mixture of 20 parts by mass of the composition (5) containing an amorphous α-olefin polymer and 80 parts by mass of LLDPE (2) was used as the adhesive layer resin. A film was obtained.

(Comparative Example 1)
Example 2 except that a mixture of the composition (2) 3.16 parts by mass LLDPE (2) 96.84 parts by mass containing the amorphous α-olefin polymer was used as the adhesive layer resin. A surface protective film for comparison was obtained.

(Comparative Example 2)
As in Example 2, except that a mixture of 30 parts by mass of composition (1) containing amorphous α-olefin polymer 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 an adhesive layer resin, 52 parts by mass of a composition (2) containing an amorphous α-olefin polymer and 8 parts by mass of a crystalline propylene-butene-1 copolymer similar to that used in Preparation Example 1 And a styrene-ethylene-propylene-styrene block copolymer (“Septon 2063” manufactured by Kuraray Co., Ltd .; hereinafter referred to as “SEPS”) in the same manner as in Example 2, except that 40 parts by mass of the mixture was used. A surface protective film was obtained.

(Comparative Example 4)
The surface for comparison was obtained in the same manner as in Example 2 except that the adhesive layer resin was a mixture of 50 parts by mass of composition (1) containing amorphous α-olefin polymer and 50 parts by mass of HOPP. A protective film was obtained.

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

(Comparative Example 6)
Example 2 except that a mixture of 30 parts by mass of the composition (2) containing an amorphous α-olefin polymer, 20 parts by mass of LLDPE (2) and 50 parts by mass of EBR was used as the adhesive layer resin. Similarly, a comparative surface protective film was obtained.

(Comparative Example 7)
Example 13 except that a mixed resin of 3.16 parts by mass of composition (2) containing an amorphous α-olefin polymer and 96.84 parts by mass of LLDPE (2) containing an amorphous α-olefin polymer was used as the adhesive layer resin. In the same manner, a comparative surface protective film was obtained.

(Comparative Example 8)
The same procedure as in Example 13 was conducted except that a mixed resin of 30 parts by mass of the composition (1) containing an amorphous α-olefin polymer and 70 parts by mass of LLDPE (3) was used as the adhesive layer resin. A comparative surface protective film was obtained.

(Comparative Example 9)
As an adhesive layer resin, 52 parts by mass of a composition (2) containing an amorphous α-olefin polymer and 8 parts by mass of a crystalline propylene-butene-1 copolymer similar to that used in Preparation Example 1 And the surface protection film for a comparison was obtained like Example 13 except having used the mixed resin of 40 mass parts of SEPS.

(Comparative Example 10)
Comparative surface as in Example 13 except that the resin for the adhesive layer was a mixed resin of 50 parts by mass of composition (1) containing amorphous α-olefin polymer and 50 parts by mass of HOPP. A protective film was obtained.

(Comparative Example 11)
Example 13 except that a mixed resin of 50 parts by mass of the composition (1) containing an amorphous α-olefin polymer, 30 parts by mass of LLDPE (2) and 20 parts by mass of EBR was used as the adhesive layer resin. In the same manner, a comparative surface protective film was obtained.

The following measurements and evaluations were performed using the surface protective films obtained in Examples 1 to 26 and Comparative Examples 1 to 11 described above.

(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 1 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: A thing in which uniform adhesion cannot be maintained and a part of it is lifted.

(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.

(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 6 show the layer structures of the surface protective films produced above and the evaluation results obtained using these surface protective films. In Examples and Comparative Examples in which no surface layer is provided, the column is left blank. The composition containing the amorphous α-olefin polymer used for the adhesive layer is shown separately for each component.

From the results of Examples 1 to 26, the surface protective film of the present invention has an adhesive strength with respect to the acrylic plate of about 0.1 to 2.2 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. 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. Furthermore, by using an ethylene-based polymer for the base material layer, when the adherend is cut with the surface protective film adhered to the adherend, the surface protective film is cut cleanly, and stringing is performed. It was found that a surface protective film having excellent cutting properties that does not cause poor appearance such as fuzzing can be obtained.

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 40% by mass of the specified lower limit. 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 the ethylene-α-olefin copolymer (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 power and poor blocking resistance.

Comparative Example 7 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 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 7, 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 by light impact.

Comparative Example 8, the density of the linear low density polyethylene used in the adhesive layer, an example of the surface protection 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 8, the adhesive strength is only about 0.03 N / 25 mm as an initial value, and the occurrence of floating, peeling, etc. is observed immediately after the film is attached. It was found that if the density is too high, the adhesive strength becomes insufficient.

Comparative Example 9 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 9, generation of adhesive residue was observed, the decrease in 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 10 is an example of a surface protective film using a propylene homopolymer instead of linear low density polyethylene for the adhesive layer. In the surface protective film of this comparative example 10, generation | occurrence | production of adhesive residue was seen and it turned out that the fall of the wet tension of the acrylic board surface after peeling a surface protective film is also large.

Comparative Example 11 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. . It was found that the surface protective film of Comparative Example 11 had a problem that adhesive residue was generated.

The surface protective film of the present invention has a wide range of adhesive strengths ranging from optimum fine adhesion to medium adhesion level, and does not cause floating or peeling after sticking to an acrylic plate. 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, it is suitable for applications in which secondary processing such as printing is performed after the surface protective film is peeled off.

Claims

A surface protective film obtained by laminating an adhesive layer (A) and a base material layer (B), wherein the adhesive layer (A)
Mixing of 5 to 50% by mass of amorphous α-olefin polymer (A1) and 50 to 95% by mass of linear low density polyethylene (A2) having a density of 0.880 to 0.938 g / cm 3 Resin, or
Amorphous α-olefin polymer (A1) 5 to 50% by mass, linear low density polyethylene (A2) 40 to 90% by mass with a density of 0.880 to 0.938 g / cm 3 , crystals Mixed resin with 5 to 50% by mass of a conductive ethylene-α-olefin copolymer (A3),
A surface protective film characterized by comprising as a main component.
The surface protective film according to claim 1, wherein the base material layer (B) is mainly composed of an ethylene polymer (B1) or a crystalline propylene polymer (B2).
The surface protection according to claim 1 or 2, wherein the amorphous α-olefin polymer (A1) is an amorphous propylene-butene-1 copolymer or an amorphous propylene-ethylene-butene-1 copolymer. the film.
The surface protective film according to any one of claims 1 to 3, wherein the ethylene-α-olefin copolymer (A3) is an ethylene-butene-1 copolymer.
The surface layer (C) mainly composed of an olefin polymer is provided on the surface opposite to the surface on which the adhesive layer (A) is laminated in the base material layer (B). The surface protective film as described.
The surface protective film according to any one of claims 1 to 5, which is stretched in at least one axial direction.