JP2010036448A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film causing remarkably small contamination due to residual paste or the like on the surface of an adherend after the surface protective film is peeled off and excellently keeping secondary workability of the adherend. <P>SOLUTION: The surface protective film has an adhesive layer (I) and a substrate layer (II) and the adhesive layer (I) is mainly made up of a block copolymer (Ia) having a crystalline olefin block and a linear low density polyethylene (Ib) having 0.880-0.938 g/cm<SP>3</SP>density. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is a surface protective film used for the purpose of protecting the surface of various resin plates, glass plates, metal plates, etc., and in particular, contamination such as adhesive residue on the adherend surface after film peeling is extremely high. The present invention relates to a surface protective film characterized in that the secondary workability of the adherend can be kept small.

  Surface protective films are used for the purpose of protecting the surface of adherends from scratches and contamination by sticking to the surface of various resin plates, glass plates, metal plates, etc. used in the building materials and electrical / electronic fields. Is. Many inventions have been reported so far in order to satisfy various performance requirements for the surface protective film. One of the required performances for the surface protective film is minimization of contamination due to adhesive residue on the adherend surface after film peeling. When secondary processing such as printing is performed on the adherend after film peeling, even fine contamination that cannot be visually confirmed affects the workability, so a very high level of glue is required. Reduction of the remaining is required. Other required performances are that there is no so-called blocking phenomenon that the contact surfaces of the film cannot be easily peeled off when the film is rolled up and then used, and the film is stuck on the adherend. When heat treatment or the like is performed in a worn state, there is no lifting or peeling from the adherend, and there is no increase in adhesion strength over time after film attachment, so-called no adhesion enhancement. It is done. In order to combine these, various technical measures such as selecting an appropriate resin combination in consideration of the affinity between the adhesive layer and the base material layer as well as appropriately adjusting the adhesive performance of the adhesive layer Ingenuity is required.

  As an example of a conventional surface protection film, as an example of suppressing the enhancement of adhesion of the surface protection film, a base material layer made of a thermoplastic resin, an amorphous olefin copolymer, a crystalline olefin polymer, and a crystallinity Coextruded laminated film having a pressure-sensitive adhesive layer made of a block copolymer having an olefin block (for example, see Patent Document 1), and improving heat processability in a state where a surface protective film is adhered to an adherend. As an example, a coextruded laminated film having a base layer composed mainly of a crystalline propylene polymer and an adhesive layer made of an amorphous α-olefin copolymer and a crystalline propylene polymer ( For example, refer to Patent Document 2.), heat processability in a state where the surface protection film is adhered to the adherend, and a block when the film is wound up and used after being rolled up. As an example of the suppression of curing, a surface layer mainly composed of a polypropylene resin composed of a propylene homopolymer and a propylene-ethylene copolymer elastomer, and a base material layer mainly composed of a crystalline propylene polymer; And a coextruded laminated film having an adhesive layer composed of an amorphous α-olefin copolymer and a crystalline propylene polymer (for example, see Patent Document 3).

  However, in these techniques, there are certainly effects such as suppression of enhancement of adhesion of the film, heat processability when the film is adhered to the adherend, suppression of blocking after winding the film, and the like. However, in any of the techniques, the minimization of contamination due to adhesive residue on the surface of the adherend after film peeling is insufficient, and there is a problem in the secondary processability of the adherend after film peeling.

JP 2006-257247 A Japanese Patent Laid-Open No. 2007-130872 JP 2008-68564 A

  Accordingly, the problem to be solved by the present invention is that the surface protection film is capable of maintaining good secondary workability of the adherend with very little contamination such as adhesive residue on the adherend surface after peeling the surface protective film. Is to provide a film.

As a result of intensive studies to solve the above problems, the present inventors have found that the surface protective film is a block copolymer having a crystalline olefin block and a density of 0.880 to 0.938 g / cm ^3. When having a pressure-sensitive adhesive layer mainly composed of chain-shaped low-density polyethylene, the surface protective film that can keep the secondary workability of the adherend satisfactorily with very little contamination to the adherend surface after film peeling. As a result, the present invention has been completed.

That is, the present invention is a surface protective film having an adhesive layer (I) and a base material layer (II), wherein the adhesive layer (I) comprises a block copolymer (Ia) having a crystalline olefin block. The present invention provides a novel surface protective film comprising a linear low density polyethylene (Ib) having a density of 0.880 to 0.938 g / cm ³ as a main component.

  According to the present invention, it is attached to the surface of various resin plates, glass plates, metal plates, etc. used in the building materials and electric / electronic fields, etc., and used for the purpose of protecting these adherend surfaces from scratches and contamination. When the film is rolled up into a roll and then used again after being rolled out, there is no blocking, and the film is stuck to the adherend when heat processing is performed Also has high heat resistance such as no lifting or peeling from the adherend, no adhesion enhancement after film sticking, and very little contamination due to adhesive residue on the adherend surface after film peeling, It is possible to obtain a highly useful surface protective film that can keep the secondary workability of the adherend favorable.

The pressure-sensitive adhesive layer (I) constituting the surface protective film of the present invention comprises a linear low density polyethylene having a density of 0.880 to 0.938 g / cm ³ and a block copolymer (Ia) having a crystalline olefin block. (Ib) as a main component, specifically, the block copolymer (Ia) having the crystalline olefin block and the straight chain with respect to the total amount of the components constituting the adhesive layer (I). The total mass with the chain low density polyethylene (Ib) is 65% by mass or more, and the total mass is 80% by mass or more from the viewpoint of further reducing the adhesive residue on the adherend. Preferably there is.

The block copolymer (Ia) having a crystalline olefin block used in the present application is a copolymer having a block (A) made of crystalline polyolefin and another block (B) having no crystallinity. Preferably, the other block (B) has a block made of a conjugated diene polymer. In addition, as the constitution of the copolymer, the adhesiveness and adhesive residue of the surface protective film obtained when used as a resin for the adhesive layer (I) in combination with the linear low density polyethylene (Ib) described later At least one of the polymer chains represented by (AB) _n1 or ( _AB ) _n2- (A) (where n1 and n2 are integers of 1 or more). It is preferable that the terminal consists of a crystalline olefin block (A).

  Examples of the block copolymer (Ia) having such a crystalline olefin block include those provided in JP-A-3-128957 and JP-A-8-231786. Specifically, a polymer mainly composed of a polybutadiene polymer block having a low 1,2-vinyl bond content (for example, 25% or less) and a conjugated diene compound, which contains 1,2- and 3,4-bonds. A copolymer composed of a polymer block having a high rate (for example, 50% or more) is synthesized, and the polybutadiene portion is made to have a structure similar to polyethylene by hydrogenating the copolymer to form a crystalline polymer block. And the like.

  Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl. -1,3-octadiene, 3-butyl-1,3-octadiene, chloroprene and the like are mentioned, and 1,3-butadiene and isoprene are preferably used from the viewpoint of industrial availability. As a commercially available product that can be preferably used as a block copolymer having such a crystalline olefin block, for example, a block copolymer having a constitution of crystalline olefin-ethylene / butylene copolymer-crystalline olefin (hereinafter referred to as a block copolymer) , Abbreviated as CEBC.) “Dynalon 6200P” manufactured by JSR Corporation.

The pressure-sensitive adhesive layer (I) constituting the surface protective film of the present invention has a linear shape having a density of 0.880 to 0.938 g / cm ³ in combination with the block copolymer (Ia) having a crystalline olefin block. Low density polyethylene (Ib) is one of the main components. When the linear low density polyethylene (Ib) having a density of 0.898 to 0.925 g / cm ³ is used, the balance between the suppression effect of adhesion enhancement and the tackiness of the finally obtained surface protective film is good. This is more preferable. Moreover, the melt flow rate [The value measured at 190 degreeC and 21.18N based on JISK7210: 1999. Hereinafter, it is indicated as “MFR (190 ° C.)”. ] Is preferably in the range of 0.5 to 30.0 g / 10 min since the film formability of the laminated film is improved. Furthermore, what is the range of 2.0-15.0 g / 10min is more preferable.

The pressure-sensitive adhesive layer (I) constituting the surface protective film of the present invention has a block copolymer (Ia) having a crystalline olefin block as its main component and a density of 0.880 to 0.938 g / cm ³ . By using together with linear low density polyethylene (Ib), the contamination to the adherend surface after film peeling can be minimized, and the secondary workability of the adherend surface can be maintained.

  In the range not impairing such an effect of the present application, in addition to the block copolymer (Ia) having a crystalline olefin block and the linear low density polyethylene (Ib), other resins are used for the adhesive layer (I) resin. You may use together. The resin that can be used at this time is not particularly limited, but is preferably an olefin polymer that is a polyolefin homopolymer or copolymer from the viewpoint of easy coextrusion molding.

The content of the block copolymer (Ia) having a crystalline olefin block and the linear low density polyethylene (Ib) having a density of 0.880 to 0.938 g / cm ³ in the adhesive layer (I) is as follows: These are preferably (Ia) 10 to 90% by mass and (Ib) 90 to 10% by mass, respectively. By appropriately adjusting the content ratios of the component (Ia) and the component (Ib) within this range, the adhesive strength at the initial stage of adhesion is required to be 0.05 to 10.0 N / 25 mm for a general surface protective film. It becomes easy to adjust to. Furthermore, when it is set to about 0.05 to 5.0 N / 25 mm, the adhesive strength can be easily adjusted by using (Ia) of 10 to 70% by mass and (Ib) of 90 to 30% by mass.

  The resin constituting the base layer (II) used together with the pressure-sensitive adhesive layer (I) constituting the surface protective film of the present invention is a thermoplastic resin and can be coextruded with the pressure-sensitive adhesive layer (I). Although it will not specifically limit if it exists, it is preferable to make an olefin type polymer into a main component from the point that affinity with the adhesion layer (I) which comprises the surface protection film of this invention is favorable.

  Examples of the olefin polymer that can be a main component of the base material layer (II) include an ethylene polymer (IIa) and a crystalline propylene polymer (IIb).

  Examples of the ethylene polymer (IIa) include low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene. These may be used alone or in combination. When these ethylene-based polymers (IIa) are used as the base material layer (II), the surface protective film is cut when the adherend is cut with the surface protective film attached to the adherend. Is cut finely and exhibits good cutting properties that do not cause poor appearance such as stringing and fluffing. Of 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.

  In addition, those ethylene polymers (IIa) having an MFR (190 ° C.) of 0.5 to 30.0 g / 10 min are preferable because extrusion is easy, and more preferably an MFR of 2 0.0-15.0 g / 10 min. Furthermore, if these ethylene-based polymers (IIa) have a melting point of 90 to 135 ° C., even if they are exposed to a high temperature environment by drying, thermoforming or the like after being adhered to the adherend, Since there is little shrinkage | contraction, since it can suppress the float and peeling from a to-be-adhered body, the curvature of an to-be-adhered body, etc., it is preferable, and melting | fusing point is 105-130 degreeC more preferably.

  Examples of the crystalline propylene polymer (IIb) include a propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, and a metallocene catalyst system. Examples include polypropylene. These may be used alone or in combination. When these crystalline propylene-based polymers (IIb) are used as the base material layer (II), the heat resistance of the surface protection film is improved, and the crystalline propylene polymer (IIb) is preferably used for applications such as heat processing after sticking. I can do it. Of these, metallocene catalyst-based polypropylene is preferably used. This is because metallocene-catalyzed polypropylene has a high molecular weight distribution and uniform composition distribution and a low content of low molecular weight components. Therefore, when used as a main component of the base material layer (II), the low molecular weight component bleeds. This is because contamination of the adherend surface is reduced. In addition, in this application, crystallinity means having a peak of 0.5 J / g or more in the range of 95-250 degreeC in DSC (differential scanning calorimetry).

  The metallocene catalyst-based polypropylene can be obtained by polymerization using a metallocene catalyst as an alternative to the conventional Ziegler-Natta catalyst. Examples of the metallocene catalyst include a metallocene homogeneous mixed catalyst containing a metallocene compound and an aluminoxane, and a metallocene supported catalyst in which a metallocene compound is supported on a fine particle carrier. The metallocene supported catalyst is disclosed in JP-A-5-155931, JP-A-8-104691, JP-A-8-157515, JP-A-8-231621, and the like. The metallocene catalyst-based polypropylene used in the present invention may be a propylene homopolymer or a copolymer of propylene and another α-olefin. Examples of copolymers of propylene and other α-olefins include propylene-ethylene copolymers.

  These crystalline propylene polymers (IIb) preferably have an MFR (230 ° C.) of 0.5 to 30.0 g / 10 minutes and a melting point of 120 to 165 ° C., more preferably MFR. (230 degreeC) is 2.0-15.0 g / 10min, and melting | fusing point is 125-162 degreeC. If the MFR and the melting point are within this range, the film shrinks little even when exposed to a high temperature environment by drying, heat molding, or the like after being attached to the adherend, so that it floats or peels off from the adherend. This is preferable because warpage of the adherend can be suppressed, and the film forming property of the laminated film is also improved.

  The surface protective film of the present invention may be composed of two layers of the above-mentioned pressure-sensitive adhesive layer (I) and base material layer (II), and a surface layer (III) may be provided in combination therewith. . At this time, the surface layer (III) is placed on the surface opposite to the adhesive layer (I) on the base material layer (II). The resin that is the main component of the surface layer (III) used in the surface protective film of the present invention is a thermoplastic resin, and particularly if coextruding with the adhesive layer (I) and the base material layer (II) is possible. Although not limited, it is preferable that an olefin polymer is a main component from the viewpoint of good affinity with the base material layer (II). In particular, when the main component of the substrate layer (II) is an ethylene polymer (IIa), the ethylene polymer (IIIa) is used, and the main component of the substrate layer (II) is a crystalline propylene polymer ( In the case of IIb), it is more preferable that the crystalline propylene polymer (IIIb) is a main component.

  Examples of the ethylene polymer (IIIa) used as the main component of the surface layer (III) include the same polymers as the ethylene polymer (IIa) used as the main component of the substrate layer (II). Further, by selecting the ethylene polymer (IIIa) as the main component of the surface layer (III), the final result is the same as when the ethylene polymer (IIa) is used as the main component of the base material layer (II). The high cuttability of the surface protective film obtained is exhibited.

  Among the ethylene-based polymers (IIIa) used as the main component of the surface layer (III), when low density polyethylene is used, it is easy to modify the surface of the surface layer (III) into a satin finish. By making the surface of the surface layer (III) satin, blocking can be reduced even when the adhesive force of the adhesive layer (I) is designed strongly. 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 (IIIa) and the propylene-ethylene block copolymer is used as a main component of the surface layer (III), the surface of the surface layer (III) is modified into a satin finish. Can be quality. Here, the propylene-ethylene block copolymer may be a resin obtained by block polymerization of propylene and ethylene. For example, ethylene polymerization or ethylene and propylene polymerization is performed in the presence of a propylene homopolymer. And a propylene-ethylene block copolymer obtained. 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 more preferable. The MFR (230 ° C.) of the mixed resin of the ethylene polymer (IIIa) and the propylene-ethylene block copolymer is preferably in the range of 4 to 12 g / 10 minutes in terms of easy extrusion, and 6 to A range of 10 g / 10 minutes is more preferable. Similarly, the density of the mixed resin is preferable in terms of easier to extruded in the range of 0.890~0.910g / cm ^3, more in the range of 0.895~0.905g / cm ³ preferable.

  Examples of the crystalline propylene polymer (IIIb) used as the main component of the surface layer (III) include the same as the crystalline propylene polymer (IIb) used as the main component of the substrate layer (II). Further, by selecting the crystalline propylene polymer (IIIb) as the main component of the surface layer (III), the crystalline propylene polymer (IIb) is used as the main component of the base material layer (II) Similarly, high heat resistance of the finally obtained surface protective film is expressed.

  When a mixed resin of the crystalline propylene polymer (IIIb) and a propylene-ethylene copolymer elastomer (hereinafter referred to as “EPR”) is used as a main component of the surface layer (III), the surface layer (III ) Can be easily modified into a satin finish. The crystalline propylene polymer used at this time is preferably a highly versatile propylene homopolymer (hereinafter referred to as “HOPP”). On the other hand, as the EPR used at this time, those having a weight average molecular weight in the range of 400,000 to 1,000,000 are preferable in that irregularities are formed on the film surface and the surface can be modified into a satin finish, A range is more preferable. In addition, the EPR content in the mixed resin is preferably in the range of 5 to 35% by mass in that the film surface can be uniformly modified into a satin finish. The MFR (230 ° C.) of the mixed resin of the crystalline propylene polymer (IIIb) and EPR is preferably in the range of 0.5 to 15 g / 10 minutes from the viewpoint of easy extrusion. In addition, the weight average molecular weight of the EPR was obtained by calculating a component extracted from the mixed resin by a cross fractionation method at 40 ° C. using orthodichlorobenzene as a solvent by GPC (gel permeation chromatography). It is. The content of EPR in the mixed resin is obtained from the amount of EPR extracted by cross-fractionation at 40 ° C. using orthodichlorobenzene as a solvent.

  The method for producing the mixed resin of the crystalline propylene polymer (IIIb) and EPR is not particularly limited, and as a specific example, for example, a propylene homopolymer and an ethylene-propylene copolymer elastomer are separately provided in a Ziegler type. Propylene homopolymer is produced in the first stage by a solution polymerization method, slurry polymerization method, gas phase polymerization method, etc. using a catalyst, and then mixing them with a kneader or a two-stage polymerization method. Thereafter, a method of generating EPR in the presence of the polymer in the second stage is mentioned.

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

  The surface protective film of the present invention preferably has a total film thickness of 20 to 120 μm. When the thickness of all the films is within this range, workability such as sticking and peeling is improved. Moreover, 3-30 micrometers is preferable and, as for the thickness of adhesion layer (I), More preferably, it is 5-25 micrometers. When the thickness of the pressure-sensitive adhesive layer (I) is within this range, in addition to the above-mentioned pressure-sensitive adhesive properties, the film formability of the laminated film becomes good. Furthermore, when providing the said surface layer (III) 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. The base material layer is oriented and crystallized by stretching in at least one axial direction, and the structure is stabilized by heat setting. This is preferable because the heat resistance is improved and the change in adhesive strength with time is reduced.

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

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

Example 1
As a resin for the surface layer, a polypropylene-based mixed resin [a resin composed of propylene homopolymer and EPR, MFR (230 ° C.): 4.0 g / 10 min, EPR content: 11 mass%, EPR weight average molecular weight 550,000 ] was used as the base layer resin, metallocene catalyst system propylene - ethylene random copolymer ^{[density: 0.900g / cm 3, MFR (} 230 ℃, 21.18N): 7.0g / 10 min, ethylene single Content rate of the monomer unit: 3.5 mass%; hereinafter referred to as “metallocene catalyst system COPP”. As a resin for the adhesive layer, “Dynalon 6200P” manufactured by JSR Corporation [density: 0.88 g / cm ³ , MFR (230 ° C.): 2.5 g / 10 min: hereinafter referred to as “CEBC”]. ] 10 parts by mass and linear low density polyethylene [density: 0.902 g / cm ³ , MFR (190 ° C.): 3.0 g / 10 min; hereinafter referred to as “LLDPE (1)”. ] Using 90 parts by mass of the mixture, each was supplied to an extruder for surface layer (caliber 30 mm), an extruder for base layer (caliber 40 mm) and an extruder for adhesive layer (caliber 30 mm), and extruded by coextrusion method. After extruding from a T-die at a temperature of 250 ° C. to a surface layer thickness of 10 μm, a base material layer thickness of 30 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)
A surface protective film of Example 2 was obtained in the same manner as Example 1 except that a mixture of 30 parts by mass of CEBC and 70 parts by mass of LLDPE (1) was used as the adhesive layer resin.

(Example 3)
As a resin for the adhesive layer, 10 parts by mass of CEBC and linear low density polyethylene [density: 0.920 g / cm ³ , MFR (190 ° C.): 3.0 g / 10 min; hereinafter referred to as “LLDPE (2)”. The surface protective film of Example 3 was obtained in the same manner as in Example 1 except that 90 parts by mass of the mixture was used.

Example 4
A surface protective film of Example 4 was obtained in the same manner as in Example 1 except that a mixture of 30 parts by mass of CEBC and 70 parts by mass of LLDPE (2) was used as the adhesive layer resin.

(Example 5)
The surface protective film of Example 5 was the same as Example 4 except that HOPP [density: 0.900 g / cm ³ , MFR (230 ° C.): 8.0 g / 10 min] was used as the base layer resin. Got.

(Example 6)
As a resin for the surface layer, a propylene-based mixed resin [a resin comprising a propylene homopolymer and EPR, MFR (230 ° C.): 4.0 g / 10 min, EPR content: 30 mass%, EPR weight average molecular weight 550,000 The surface protective film of Example 6 was obtained in the same manner as in Example 1 except that a mixture of 50 parts by mass of CEBC and 50 parts by mass of LLDPE (2) was used as the adhesive layer resin.

(Example 7)
A surface protective film of Example 7 was obtained in the same manner as in Example 6 except that a mixture of 70 parts by mass of CEBC and 30 parts by mass of LLDPE (2) was used as the adhesive layer resin.

(Example 8)
The surface protective film of Example 8 in the same manner as in Example 7 except that HOPP [density: 0.900 g / cm ³ , MFR (230 ° C.): 8.0 g / 10 min] was used as the base layer resin. Got.

Example 9
As the resin for the surface layer and the resin for the base layer, low density polyethylene [density: 0.920 g / cm ³ , MFR (190 ° C.): 6 g / 10 min; hereinafter referred to as “LDPE”. ], A mixture of 10 parts by weight of CEBC and 90 parts by weight of LLDPE (1) was used as the adhesive layer resin, the surface layer thickness was 14 μm, the base layer thickness was 42 μm, and the adhesive layer thickness A surface protective film of Example 9 was obtained in the same manner as in Example 1 except that the film was extruded so as to be 14 μm.

(Example 10)
A surface protective film of Example 10 was obtained in the same manner as Example 9 except that a mixture of 30 parts by mass of CEBC and 70 parts by mass of LLDPE (1) was used as the adhesive layer resin.

(Example 11)
A surface protective film of Example 11 was obtained in the same manner as Example 9 except that a mixture of 10 parts by weight of CEBC and 90 parts by weight of LLDPE (2) was used as the adhesive layer resin.

Example 12
A surface protective film of Example 12 was obtained in the same manner as in Example 9 except that a mixture of 30 parts by mass of CEBC and 70 parts by mass of LLDPE (2) was used as the adhesive layer resin.

(Example 13)
As the resin for the surface layer, 50 parts by mass of LDPE and high-density polyethylene [density: 0.960 g / cm 3, MFR (190 ° C.): 5.5 g / 10 min; hereinafter referred to as “HDPE”. ] In the same manner as in Example 9, except that 50 parts by mass of the mixture was used, and 50 parts by mass of CEBC and 50 parts by mass of LLDPE (2) were used as the adhesive layer resin. Got.

(Example 14)
The surface layer resin is not used, and a mixture of 70 parts by mass of CEBC and 30 parts by mass of LLDPE (2) is used as the adhesive layer resin so that the thickness of the base layer is 56 μm and the thickness of the adhesive layer is 14 μm. A surface protective film of Example 14 was obtained in the same manner as Example 9 except that the film was extruded.

(Comparative Example 1)
Example 5 except that a mixture of 57 parts by mass of amorphous propylene-butene-1 copolymer, 3 parts by mass of crystalline propylene-butene-1 copolymer and 40 parts by mass of CEBC was used as the adhesive layer resin. Similarly, the surface protective film of Comparative Example 1 was obtained.

(Comparative Example 2)
As the adhesive layer resin, except that a mixture of 49.4 parts by mass of an amorphous propylene-butene-1 copolymer, 10.6 parts by mass of a crystalline propylene-butene-1 copolymer and 40 parts by mass of CEBC was used, In the same manner as in Example 5, a surface protective film of Comparative Example 2 was obtained.

(Comparative Example 3)
As the adhesive layer resin, a mixture of 50 parts by mass of styrene-ethylene-propylene-styrene block copolymer (“Septon 2063” manufactured by Kuraray Co., Ltd .; hereinafter referred to as “SEPS”) and 50 parts by mass of LLDPE (2) was used. A surface protective film of Comparative Example 3 was obtained in the same manner as Example 5 except for the above.

(Evaluation method of surface protective film obtained in Examples and Comparative Examples)
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 having a thickness of 2 mm (mirror finish, Mitsubishi Rayon) in accordance with the adhesive strength evaluation method of JIS Z0237: 2000. It was attached to "Acrylite" manufactured by the company. 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.

Evaluation of adhesiveness When measuring the above-mentioned adhesive strength, the state of adhesion of the surface protective film adhered to the acrylic plate to the acrylic plate was visually confirmed, and the adhesiveness was evaluated according to the following criteria.
◯: Maintaining uniform adhesion to the acrylic plate surface.
X: Insufficient initial adhesive strength, uniform adhesion cannot be maintained, and partly floated.

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, “Acrylite” manufactured by Mitsubishi Rayon Co., Ltd.) in accordance with JIS Z0237: 2000. ). 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 matters on the surface of the acrylic plate.
○-: A very small amount of dirt such as cloudiness, white streaks and foreign matters is observed on the acrylic plate surface.
Δ: Slightly cloudy, white streaks, foreign matter, etc. on the acrylic plate surface.
X: The acrylic plate surface has any dirt such as cloudy, white streaks or foreign matters.

Measurement of the wetting tension on the acrylic plate surface Using the test piece before film sticking (the test piece obtained by washing the surface of the acrylic plate with alcohol and drying) and the test piece after film peeling used in the evaluation of the adhesive residue, The wetting tension on the acrylic plate surface was measured by a method based on JIS K6768: 1999. The wetting tension of the test piece before film attachment was 40 mN / m.

Evaluation of printing suitability after peeling of the surface protective film Using the measured value of the wetting tension on the surface of the acrylic plate, the reduction width of the wetting tension [(wetting tension of the test piece before film sticking: 40 mN / m) − (after peeling the film) Was evaluated as a substitute evaluation of printability after peeling off the protective film. The evaluation criteria are as follows.
A: The decrease width of the wetting tension is 2 mN / m or less.
X: The reduction width of the wetting tension exceeds 2 mN / m.

Evaluation of blocking resistance The obtained surface protective film was cut out in 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.

  The results of the above evaluations are shown in Table 1 for Examples 1-8, Table 2 for Experimental Examples 9-14, and Table 3 for Comparative Examples 1-3.

Regarding adhesion enhancement, the strength of the adhesive strength of the surface protective film obtained in each example is mainly due to the difference in the adhesion layer, and can take various values depending on the composition of the adhesion layer. There is no significant difference between the values of “50 ° C. × 1 day” and there is little increase in adhesion. On the other hand, the surface protective film obtained in each comparative example has a greater adhesion enhancement than the examples.

Regarding the adherend surface contamination after peeling of the surface protective film In the surface protective film obtained in each Example, the adhesive residue on the adherend after peeling of the film could not be visually confirmed. In addition, the decrease in the wet tension of the adherend surface before and after the film was peeled was small, and the contamination of the adherend surface could be minimized to the extent that the printability was not lowered. On the other hand, in the surface protective film obtained in each comparative example, the adhesive residue on the adherend after film peeling can be visually confirmed, and the printability of the adherend surface after film peeling is as in each example. An evaluation result that is lower than the above was obtained.

Claims (9)

A surface protective film having an adhesive layer (I) and a substrate layer (II), wherein the adhesive layer (I) has a block copolymer (Ia) having a crystalline olefin block and a density of 0.880. A surface protective film comprising, as a main component, linear low-density polyethylene (Ib) of ˜0.938 g / cm ³ .   The surface protective film according to claim 1, wherein the block copolymer (Ia) having a crystalline olefin block is a crystalline olefin-ethylene-butylene copolymer-crystalline olefin block copolymer (CEBC). The content of the block copolymer (Ia) having a crystalline olefin block in the adhesive layer (I), the linear low density polyethylene (Ib) having a density of 0.880 to 0.938 g / cm ³ , The surface protective film according to claim 1 or 2, wherein (Ia) is 10 to 90% by mass and (Ib) is 90 to 10% by mass.   The surface protective film according to claim 1, wherein the base material layer (II) contains an olefin polymer as a main component.   The surface protective film according to claim 4, wherein the olefin polymer as a main component of the base material layer (II) is an ethylene polymer (IIa).   The surface protective film according to claim 4, wherein the olefin polymer as a main component of the base material layer (II) is a crystalline propylene polymer (IIb).   The surface layer (III) mainly composed of an olefin polymer is provided on the surface opposite to the surface having the adhesive layer (I) in the base material layer (II). The surface protection film as described in any one of Claims.   The surface protective film according to claim 7, wherein the olefin polymer that is a main component of the surface layer (III) is an ethylene polymer (IIIa).   The surface protective film according to claim 7, wherein the olefin polymer that is a main component of the surface layer (III) is a crystalline propylene polymer (IIIb).