JP2018145365A - Surface protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film less in dents to an adherend by fish eye or contamination derived from the film, excellent in transparency, having moderate adhesive force without peeling during processing, in which the adhesive force is insusceptible to temperature change, and excellent in re-adhesiveness.SOLUTION: There is provided a surface protective film consisting of at least 2 layer composite form of a back surface layer (A) and an adhesive layer (B), where the back surface layer (A) consists of at least a polypropylene resin (a1), the adhesive layer (B) consists of 6 wt.% or more and 40 wt.% or less of a propylene copolymer (b1) obtained by using a metallocene catalyst, 55 wt.% or more and 75 wt.% or less of an olefinic elastomer (b2) mainly containing α-olefin having 3 or more carbon atoms, and 1 wt.% or more and 19 wt.% or less of a styrenic elastomer (b3), and rubber hardness (Durometer type A) of the olefinic elastomer (b2) and the styrenic elastomer (b3) is 50 or more and 91 or less.SELECTED DRAWING: None

Description

  The present invention relates to a surface protective film mainly used for members of optical products. Specifically, it has excellent appearance and transparency, has few scratches / contamination on the adherend, has moderate adhesive strength that does not peel off during processing, has little change in adhesive strength due to temperature, and has excellent re-adhesiveness It relates to the surface protection film.

  For products made of various materials such as synthetic resin, metal, and glass, surface protection films have been conventionally used in order to prevent scratches and dirt generated during processing, transportation, and storage.

  Particularly in recent years, liquid crystal displays and touch panel devices have been widely used, and these are composed of a number of members such as optical sheets and optical films made of synthetic resin. Since such optical product members need to reduce defects such as optical distortion as much as possible, surface protection films are frequently used to prevent scratches and dirt that may cause defects.

  The surface protective film used for such optical product members has little dents and film-derived contamination on the adherend due to fish eyes, is transparent for product inspection, and is used during processing processes such as punching and cutting. It is required to have an appropriate adhesive strength that does not peel off. Furthermore, the adhesive strength is not affected by temperature changes during processing, transportation, storage, etc., and it is required that the adhesive strength is mild enough to be easily peeled off when the surface protection function is finished. . Moreover, a part of surface protection film may be peeled off at the time of product inspection, the surface of the adherend may be confirmed, and then bonded again. In this case, re-adhesion is required.

  On the other hand, the surface protective film is provided in the form of a roll, but it is also important that it can be easily unwound from the roll due to its excellent slipperiness and blocking resistance between the adhesive layer and the back layer, and is attached to the adherend. The workability at the time is also required to be stable.

  As a protective film for optics, in order to reduce fish eyes, the main component is polyethylene produced using a sintered filter made by laminating and sintering a metal fine fiber nonwoven fabric with a filtration accuracy of 50 μm or less. A surface protective film has been proposed (Patent Document 1). However, the suppression of the generation of fish eyes is not sufficient, and the heat resistance and scratch resistance are not satisfactory.

  On the other hand, from the point that gelation due to crosslinking deterioration hardly occurs, use of a polypropylene resin as a constituent material of the surface protective film instead of a polyethylene resin has been studied. For example, an α-olefin (co) polymer mainly composed of an α-olefin having a melting point of less than 50 ° C. or having no melting point observed and having 3 or more carbon atoms, and a metallocene catalyst are used. A surface protective film comprising a propylene (co) polymer obtained in this manner has been proposed (Patent Document 2). In Patent Document 3, an adhesive layer is obtained using a low-crystalline α-olefin (co) polymer mainly composed of an α-olefin having 3 or more carbon atoms obtained using a metallocene catalyst, and a metallocene catalyst. A surface protective film comprising a propylene (co) polymer has been proposed. However, the surface protective films of Patent Documents 2 and 3 in which the adhesive layer is composed of an α-olefin (co) polymer and a propylene (co) polymer have low adhesive strength and are particularly at the end during processing steps such as punching and cutting. There have been problems such as peeling or peeling in a low temperature environment.

  On the other hand, many adhesive films in which an adhesion-imparting agent is added to the adhesive layer for the development of adhesive strength have been proposed (Patent Documents 4, 5, 6, etc.). There was a problem that the re-tackiness was low.

JP 9-314642 A JP 2011-37039 A International Publication No. 2011/034045 Japanese Patent Laid-Open No. 03-47886 JP 05-229080 A Japanese Patent Laid-Open No. 08-245934

  An object of the present invention is to solve the above-described problems. That is, there are few dents and film-derived contamination on the adherend due to fish eyes, excellent transparency, and moderate adhesive strength that does not peel off during the processing step, and such adhesive strength is less susceptible to temperature changes, It is also intended to provide a surface protective film excellent in re-adhesiveness.

  As a result of intensive studies in view of the above problems, the present inventors have found that the object can be achieved by adopting the following configuration of the present invention.

  That is, the present invention comprises at least a two-layer composite form of a back layer (A) and an adhesive layer (B), the back layer (A) has a polypropylene resin (a1), and the adhesive layer (B) has a propylene co-polymer. Polymer (b1) 6 wt% to 40 wt%, olefin elastomer (b2) mainly composed of α-olefin having 3 or more carbon atoms, 55 wt% to 75 wt%, and styrene elastomer (b3) 1 wt %, And the rubber hardness (durometer type A) of the olefin elastomer (b2) and the styrene elastomer (b3) are both 50 or more and 91 or less. It is.

  Moreover, this invention is the said surface protection film whose initial adhesive force of the said adhesion layer (B) with respect to a polycarbonate sheet is 0.10 N / 50mm or more and 0.40 N / 50mm or less.

  Moreover, this invention is the said surface protection film whose re-adhesion power of the said adhesion layer (B) with respect to a polycarbonate sheet is 90 to 120% with respect to initial stage adhesive force.

  Moreover, it is the said surface protection film whose adhesive force after the heat storage (50 degreeC x 7 days) of the said adhesion layer (B) with respect to a polycarbonate sheet is 0.09 N / 50mm or more and 1.00N / 50mm or less.

  Furthermore, the above-mentioned surface protection wherein the pressure-sensitive adhesive force after the low-temperature storage (−30 ° C. × 30 minutes) of the pressure-sensitive adhesive layer (B) to the polycarbonate sheet is 0.09 N / 50 mm or more and 0.40 N / 50 mm or less and does not float. It is a film.

  According to the present invention, there are few dents and film-derived contamination on the adherend due to fish eyes, excellent transparency, no peeling during processing steps such as punching and cutting, and such adhesive force is a processing step and a transportation step. Thus, it is possible to provide a surface protective film that is not easily affected by temperature changes during storage and that is excellent in re-adhesiveness.

  The present invention is described in detail below.

  The surface protective film of the present invention has at least two layers of the back layer (A) and the adhesive layer (B) or three layers including the intermediate layer (C). Here, when winding in a roll shape, the back layer (A) is the outermost layer, then the intermediate layer (C), the innermost layer is the adhesive layer (B), the back layer (A) and the adhesive layer ( B) contacts.

  Usually, when the film is formed by melt extrusion, the unstable part at the initial stage of film formation and the uneven part of the film thickness at the end part are removed, but this removed part is recovered in the back layer (A) or the intermediate layer (C). It can be reused as a material, and the raw materials to be used can be reduced, which is economically preferable. In other words, while the back layer (A) or the intermediate layer (C) is mixed with the recovered raw material to make an economical manufacturing method, the adhesive layer (B) uses the specified virgin raw material, and the characteristics of the adhesive layer surface There is merit that can be kept.

  Next, the requirements for the back layer (A) in the present invention are as follows.

  The back layer (A) in the present invention has at least a polypropylene resin (a1), and may be used by adding and mixing the adhesive layer resin and the intermediate layer resin which are the recovered raw materials as described above.

  Examples of the polypropylene resin (a1) in the present invention include homopolypropylene, a random or block copolymer of ethylene and propylene, a terpolymer of ethylene, butene and propylene (so-called terpolymer, ethylene / propylene / butene copolymer). Polymer) and the like, but a polypropylene resin having a melting point of 145 to 165 ° C. is preferable from the viewpoint of heat resistance, slipperiness, film handling, and scratch resistance, and a terpolymer is preferable from the viewpoint of transparency.

  In the back layer (A), additives such as an antistatic agent, a release agent, an antiblocking agent and an antioxidant, and a resin modifier such as a polyolefin resin and an elastomer are added within a range not impairing the physical properties thereof. be able to.

  The center line average roughness (Ra) of the surface of the back layer (A) in the present invention formed by the above configuration is preferably 0.1 μm or more and 0.5 μm or less. By forming such an uneven surface state, it is easy to wind in the form of a roll at the time of film formation, and the unwinding is stable at the time of use, so the workability when sticking to the adherend is stabilized.

  Next, the requirements for the adhesive layer (B) in the present invention are as follows.

  The pressure-sensitive adhesive layer (B) in the present invention preferably has the following. The propylene copolymer (b1) obtained using the metallocene catalyst is 6% by weight or more and 40% by weight or less, preferably 11% by weight or more and 30% by weight or less in the adhesive layer (B). The olefin elastomer (b2) mainly composed of an α-olefin having 3 or more carbon atoms is 55 wt% or more and 75 wt% or less, preferably 60 wt% or more and 70 wt% or less in the adhesive layer (B). The styrene-based elastomer (b3) is 1% by weight or more and 19% by weight or less, preferably 5% by weight or more and 15% by weight or less in the adhesive layer (B).

The propylene copolymer (b1) obtained using the metallocene catalyst is blended for the purpose of controlling the adhesive strength, but if it is less than 6% by weight, the adhesive strength becomes high and it is difficult to peel off from the adherend, and more than 40% by weight. The adhesive strength becomes low and floating occurs during processing. Moreover, the propylene copolymer obtained using the metallocene catalyst referred to in the present invention is polydispersity, which is an index of molecular weight distribution: weight average molecular weight (Mw) / number average molecular weight (Mn) is 1.5 to 3. The low molecular weight / low crystal component in the range of 5 is small and the molecular weight distribution is narrow. The polydispersity is measured according to JIS K7252-2016.
The olefin elastomer (b2) mainly composed of an α-olefin having 3 or more carbon atoms is blended for the purpose of exhibiting adhesive strength and re-adhesiveness, but if it is less than 55% by weight, the initial adhesive strength is low and 75% by weight. If it is more, the stickiness is so bad that film formation becomes difficult. The styrene-based elastomer (b3) is blended for the purpose of increasing the initial adhesive strength. However, if it is less than 5% by weight, sufficient initial adhesive force cannot be obtained, and if it exceeds 15% by weight, the adhesion progress becomes remarkable.

  The propylene copolymer (b1) in the present invention is a crystalline polymer, and is a copolymer of propylene produced using a metallocene catalyst and a carbon number of 2 to 10 (excluding propylene). Examples thereof include propylene / ethylene copolymer, propylene / 1-butene copolymer, propylene / ethylene / 1-butene copolymer, and propylene / ethylene copolymer is preferable.

  The olefin elastomer (b2) mainly composed of an α-olefin having 3 or more carbon atoms in the present invention is an olefin elastomer having a rubber hardness (durometer type A) of 50 to 91, preferably 67 to 82. When the rubber hardness is less than 50, the followability to the adherend is too high, the initial adhesive strength becomes high and it is difficult to peel off from the adherend, and the adhesive advances during high temperature storage. On the other hand, when the rubber hardness is greater than 91, the followability becomes low, and partial lifting is observed during low-temperature storage. Specific examples of the olefin elastomer include propylene / ethylene copolymer, propylene / ethylene / 1-butene copolymer, 1-butene homopolymer, 1-butene / ethylene copolymer, 1-butene / propylene copolymer. Polymer, 4-methylpentene-1 homopolymer, 4-methylpentene-1 / propylene copolymer, 4-methylpentene-1 / 1-butene copolymer, 4-methylpentene-1 / propylene / 1 -A butene copolymer and a propylene / 1-butene copolymer, preferably a propylene / ethylene copolymer.

  The styrene elastomer (b3) in the present invention is a styrene elastomer having a rubber hardness (durometer type A) of 50 to 91, preferably 67 to 82. When the rubber hardness is less than 50, the followability to the adherend is too high, the initial adhesive strength becomes high and it is difficult to peel off from the adherend, and the adhesive advances during high temperature storage. On the other hand, when the rubber hardness is greater than 91, the followability is lowered, and partial lifting is observed during low temperature storage. Specific styrene elastomers include styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / ethylene / butylene / styrene block copolymer (SEBS), hydrogenated styrene / butadiene random copolymer. Examples thereof include a styrene thermoplastic elastomer of a combined (HSBR).

  Various additives such as a tackifier, an antistatic agent, a crystal nucleating agent, and an antioxidant can be added to the pressure-sensitive adhesive layer (B) as long as the physical properties thereof are not impaired.

  Next, the requirements for providing the intermediate layer (C) in the present invention are as follows.

  The intermediate layer (C) in the present invention is composed of at least a polypropylene resin (c1), and as described above, an adhesive layer resin and a back layer resin, which are recovered raw materials, may be added and mixed.

  Examples include homopolypropylene, random or block copolymers of ethylene and propylene, and terpolymers of ethylene, butene and propylene (so-called terpolymers, ethylene / propylene / butene copolymers). From the viewpoint of properties, those having a melting point of 140 to 165 ° C, preferably 145 to 160 ° C are preferred, and terpolymers are preferred from the viewpoint of transparency.

  In the intermediate layer (C), fillers such as talc, stearamide, calcium stearate, antioxidants, ultraviolet absorbers, pigments, antistatic agents, and crystal nucleating agents are appropriately added within a range that does not impair the physical properties. May be. You may add these individually or in combination of 2 or more types.

  Next, in the surface protective film of the present invention, the initial adhesive strength of the adhesive layer (B) to the polycarbonate sheet is preferably 0.10 N / 50 mm or more and 0.40 N / 50 mm or less. With an adhesive force in this range, it does not peel off during processing and can be easily peeled off.

  Moreover, in the surface protection film of this invention, it is preferable that the re-adhesion power of the adhesion layer (B) with respect to a polycarbonate sheet is 90% or more and 120% or less compared with initial stage adhesive force. With an adhesive force in this range, it can be re-bonded without lifting and can be easily peeled off.

  Moreover, in the surface protection film of this invention, it is preferable that the adhesive force after the heat storage (50 degreeC x 7 days) of the adhesion layer (B) with respect to a polycarbonate sheet is 0.09 N / 50mm or more and 1.00N / 50mm or less. . With an adhesive strength in this range, it can be stored without floating, and there is no contamination due to cohesive failure during peeling.

  Furthermore, in the surface protective film of the present invention, the adhesive strength after low-temperature storage (−30 ° C. × 30 minutes) of the adhesive layer (B) to the polycarbonate sheet is 0.09 N / 50 mm or more and 0.40 N / 50 mm or less. preferable. With an adhesive strength in this range, it can be stored without floating and can be easily peeled off. Hereinafter, the manufacturing method of the surface protection film of this invention is demonstrated.

  The manufacturing method of the surface protection film of this invention is not specifically limited. For example, a polypropylene resin (a1) as the back layer resin composition, a propylene copolymer (b1) obtained using a metallocene catalyst as the adhesive layer resin composition, and an olefin mainly composed of an α-olefin having 3 or more carbon atoms A resin composition composed of a series elastomer (b2) and a styrene series elastomer (b3) can be used. And if necessary, the polypropylene resin (c1) that is the intermediate layer resin composition is melt-extruded from individual extruders, laminated and integrated in the die, and co-extruded in two or three layers, The back layer (A), the adhesive layer (B), or the back layer (A), the intermediate layer (C), and the adhesive layer (B) are laminated and integrated in this order. And after shaping | molding, it rolls up in roll shape, or the method of manufacturing a surface protection film, or the said back layer, an intermediate | middle layer, and an adhesion layer are each melt-extruded separately, Then, it laminates and integrates by the lamination method Methods and the like. In the former, a known method such as an inflation method or a T-die method is used, and in the latter, a dry lamination or a melt extrusion method or extrusion lamination method using a T-die can be used, but the thickness accuracy is excellent. In view of control of the surface shape, the melt coextrusion method by the T-die method is preferable from the viewpoint of quality and economy.

  The thickness of the surface protective film of the present invention varies depending on the thickness of the adherend and the required quality level of the adherend, but generally is appropriately selected in the range of 20 to 100 μm from the viewpoint of moldability and ease of use. can do.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples. Various physical properties were measured and evaluated by the following methods. Unless otherwise specified, the following measurements and evaluations were performed in a room at 23 ° C.

(1) Rubber hardness measurement Based on JIS K6253-2012, it measured with the durometer using the resin press sheet of thickness 3mm. Type A was used as the durometer.

(2) Affixing of sample sample Roll press machine (special pressure roller made by Yasuda Seiki Seisakusyo Co., Ltd.) with the sample sample stored and prepared for 24 hours under conditions of temperature 23 ° C and humidity 50% RH Was pasted at a pasting pressure of 9,100 N / m and a pasting speed of 300 cm / min. Thereafter, after storage under each evaluation condition, it was used for measurement or evaluation.

(3) Initial Adhesive Strength A sample sample stored in an atmosphere at 23 ° C. for 3 days or more after production is a polycarbonate sheet having a thickness of 500 μm (hereinafter sometimes referred to as a PC sheet) ) “PC1151) was bonded together under the bonding conditions described in (2), stored in an atmosphere at 23 ° C. for 24 hours, and then used with a peel tester (Kyowa Interface Science Co., Ltd., angle-adhesive type adhesive / film peel analyzer). The adhesive strength was measured at a peeling speed of 2300 mm / min and a peeling angle of 180 °.

(4) Re-adhesiveness The sample sample whose adhesive strength was measured in (3) was pasted again under the pasting conditions described in (2), stored in a 23 ° C atmosphere for 1 hour, and then subjected to the same method as (3) The re-adhesive strength was measured and the ratio to the initial adhesive strength was calculated.

(5) Adhesive strength after heat storage The same bonded sample as in (2) was measured in the same manner as (3) after storing for 7 days in a 50 ° C atmosphere.

(6) Adhesive strength after low-temperature storage The same bonded sample as in (2) was stored in an atmosphere of -30 ° C for 30 minutes, and then the adhesive strength was measured by the same method as in (3). Moreover, the presence or absence of the float was visually evaluated.
○: No floating ×: There is floating.

(7) Contamination A sample sample stored in an atmosphere at 23 ° C. for 3 days or more after production is pasted on an acrylic resin plate having a thickness of 2 mm (“Acrylite (registered trademark)” manufactured by Mitsubishi Rayon Co., Ltd.). Bonding is performed under the bonding conditions, each is stored for 24 hours in an atmosphere of 23 ° C. and 50 ° C., and the surface of the adherend after peeling by hand is visually observed with an LED light in a dark room. The following two stages were evaluated in comparison with the plate.
◯: The surface state does not change from the acrylic resin plate before bonding ×: It is more cloudy than the acrylic resin plate before bonding.

(8) Number of fish eyes A film sample of 1 m ² minutes was visually observed, and those having a size that could not be visually identified were observed at a magnification of 300 times using a Keyence digital microscope, and fish eyes with a length of 80 μm or more. Counted about.
○: Less than 50 pieces / m ² ×: 50 pieces / m ² or more.

Example 1
The constituent resin of each layer was prepared as follows.
As the back layer (A) resin composition, ethylene / propylene having a density of 0.900 g / cm ³ , a melting point of 147 ° C., and a melt flow rate (hereinafter also referred to as MFR) of 7.3 g / 10 min at a temperature of 230 ° C. -Butene copolymer (ethylene content 1.1 wt%, butene content 4.2 wt%) (a1) 65 wt%, density 0.900 g / cm ³ , MFR 8.0 g / 10 min at 230 ° C A propylene resin containing a propylene / ethylene block copolymer, so-called 35% by weight of a block polypropylene, was used.

Propylene / ethylene copolymer obtained by using a metallocene catalyst having a density of 0.900 g / cm ³ , a melting point of 115 ° C., and an MFR of 9.0 g / 10 min at 230 ° C. as the adhesive layer (B) resin composition ( b1) Propylene / ethylene copolymer elastomer having a weight of 30% by weight, a density of 0.870 g / cm ³ , a melting point of 160 ° C., an MFR of 6.0 g / 10 min at 230 ° C., and a rubber hardness (durometer type A) of 82 (b2- 1) Styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) of 60% by weight, density 0.890 g / cm ³ , MFR 13.0 g / 10 min at 230 ° C., rubber hardness (durometer type A) 67 ) (B3-1) 10 wt% was used.

  90% by weight of the same ethylene / propylene / butene copolymer (c1) used for the back layer (A) as the intermediate layer (C) resin composition and the same as that used for the adhesive layer (B) 10% by weight of propylene / ethylene copolymer elastomer (b2-1) was used.

  A T-die type composite film forming machine having a die width of 2400 mm having three extruders of φ65 mm (for the back layer (A)), φ90 mm (for the adhesive layer (B)) and φ115 mm (for the intermediate layer (C)) is used. The prepared resin composition is introduced into each extruder, and each extruder is discharged so that the back layer thickness ratio is 10%, the adhesive layer thickness ratio is 17%, and the intermediate layer thickness ratio is 73%. The amount was adjusted, extruded from a composite T die at an extrusion temperature of 230 ° C., rapidly cooled at a cast drum temperature of 30 ° C., wound into a roll, and a three-layer laminated film having a film thickness of 50 μm was obtained.

(Example 2)
The adhesive layer (B) had a density of 0.832 g / cm ³ instead of the propylene / ethylene copolymer elastomer (b2-1) in Example 1, MFR 3.0 g / 10 minutes at 230 ° C., rubber hardness (durometer) Type A) 67 propylene / ethylene copolymer elastomer (b2-2) 60% by weight was used.
In the intermediate layer (C), 10% by weight of the propylene / ethylene copolymer elastomer (b2-2) used in the adhesive layer (B) instead of the propylene / ethylene copolymer elastomer (b2-1) in Example 1 was used. Using.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Example 3)
In the adhesive layer (B), the proportion of the propylene / ethylene copolymer (b1) obtained using the metallocene catalyst in Example 1 was 20% by weight, and the proportion of the propylene / ethylene copolymer elastomer (b2-1) was The content was changed to 70% by weight.
In the intermediate layer (C), the proportion of the ethylene / propylene / butene copolymer (c1) in Example 1 was changed to 88 wt%, and the proportion of the propylene / ethylene copolymer elastomer (b2-1) was changed to 12 wt%. .
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Example 4)
In the adhesive layer (B), the proportion of the propylene / ethylene copolymer (b1) obtained using the metallocene catalyst in Example 1 was 15% by weight, and the proportion of the propylene / ethylene copolymer elastomer (b2-1). The ratio of 70% styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) (b3-1) was changed to 15% by weight.
The intermediate layer (C) was the same as the resin composition of Example 3.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 1)
As the resin composition of the back layer (A), the density was 0.923 g / cm ³ , the melting point was 111 ° C., and the MFR was 5.5 g / 10 minutes under a high pressure method low density polyethylene of 80% by weight, and the density was 0.900 g / cm 3. ^3. Melting point: 143 ° C., 15% by weight of ethylene / propylene random copolymer at MFR of 30 g / 10 min at 230 ° C., and high pressure of MFR of 4.0 g / 10 min at density of 0.915 g / cm ³ at 230 ° C. A resin composition composed of 5% by weight of low density polyethylene was mixed uniformly with a Henschel mixer.

The adhesive layer (B) resin composition has a density of 0.919 g / cm ³ containing a phenolic antioxidant and a phosphorus antioxidant, a melting point of 120 ° C., and a MFR of 2.0 g / 10 min at 190 ° C. 70% by weight of linear low density polyethylene (ethylene 4-methylpentene-1 copolymer), density 0.924 g / cm ³ , melting point 120 ° C., high pressure method low MFR 5.0 g / 10 min at 190 ° C. A density of 0.923 g / cm ³ consisting of 10% by weight polyethylene, 20% by weight terpene hydrocarbon resin and 80% by weight linear low-density polyethylene (ethylene / 1-hexene copolymer), melting point 119 ° C., 190 A 20 wt.% Tackifier masterbatch with a MFR of 2.4 g / 10 min at 0C was used.

As the intermediate layer (C) resin composition, 88 wt% of the same high pressure method low density polyethylene used for the back layer (A) and the same linear low density polyethylene 12 used for the adhesive layer (B) are used. % By weight was used.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 2)
In the adhesive layer (B), the proportion of the propylene / ethylene copolymer (b1) obtained using the metallocene catalyst in Example 1 was 30% by weight, and the proportion of the propylene / ethylene copolymer elastomer (b2-1) was The styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) (b3-1) was not used.
The intermediate layer (C) was the same as the resin composition of Example 3.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 3)
The adhesive layer (B) uses 90% by weight of the propylene / ethylene copolymer (b1) obtained by using the metallocene catalyst in Example 1, and the propylene / ethylene copolymer elastomer (b2-1). There wasn't.
In the intermediate layer (C), the proportion of the ethylene / propylene / butene copolymer (c1) in Example 1 is 85% by weight, and the propylene / ethylene copolymer is used instead of the propylene / ethylene copolymer elastomer (b2-1). (B1) The content was changed to 15% by weight.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 4)
The pressure-sensitive adhesive layer (B) does not use the propylene / ethylene copolymer (b1) obtained using the metallocene catalyst in Example 1, and the proportion of the propylene / ethylene copolymer elastomer (b2-1) is 90 wt. % Changed.
In the intermediate layer (C), the proportion of the ethylene / propylene / butene copolymer (c1) in Example 1 was changed to 85 wt%, and the proportion of the propylene / ethylene copolymer elastomer (b2-1) was changed to 15 wt%. .
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 5)
The adhesive layer (B) had a density of 0.840 g / cm ³ , MFR 10.0 g / 10 min at 230 ° C., rubber hardness (durometer) instead of the propylene / ethylene copolymer elastomer (b2-1) in Example 1. 60% by weight of type A) 92 4-methylpentene-1 / propylene copolymer elastomer (b2-3) was used.
The intermediate layer (C) was a 4-methylpentene-1 / propylene copolymer elastomer (b2-3) used in the adhesive layer (B) instead of the propylene / ethylene copolymer elastomer (b2-1) in Example 1. ) 10% by weight was used.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 6)
The adhesive layer (B) had a density of 0.880 g / cm ³ and MFR of 30.0 g at 230 ° C. instead of the styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) (b3-1) in Example 1. / 10 minutes, 10% by weight of styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) (b3-2) having a rubber hardness (durometer type A) of 49 was used.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

(Comparative Example 7)
In the adhesive layer (B), the proportion of the propylene / ethylene copolymer (b1) obtained using the metallocene catalyst in Example 1 was 10% by weight, and the proportion of the propylene / ethylene copolymer elastomer (b2-1). The proportion of styrene / ethylene / butylene / styrene block copolymer elastomer (SEBS) (b3-1) was changed to 70% by weight and 20% by weight.
The intermediate layer (C) was the same as the resin composition of Example 3.
Otherwise, a three-layer laminated film having a film thickness of 50 μm was obtained in the same manner as in Example 1.

  Examples 1-4 satisfying the requirements of the present invention all showed good initial adhesive strength and re-adhesiveness, and no major changes were observed in the adhesive strength after heating and low-temperature storage. In addition, good results were obtained in terms of contamination and the number of fish eyes.

  On the other hand, in Comparative Example 1 in which a polyethylene-based resin was used for the back layer, the adhesive layer, and the base material layer, and a tackifier was added to the adhesive layer, the number of fish eyes was large, contamination was poor, and re-adhesion was also low. Further, after the heat storage, adhesion progress was observed.

  In Comparative Example 2 using only the propylene copolymer (b1) and the olefin elastomer (b2-1) obtained by using a metallocene catalyst for the adhesive layer, the initial adhesive force was low, and floating was observed during low-temperature storage. Further, in Comparative Example 3 using only the propylene copolymer (b1) and the styrene-based elastomer (b3-1), no adhesive force was expressed. On the other hand, Comparative Example 4 using only the olefin-based elastomer (b2-1) and the styrene-based elastomer (c3-1) was extremely sticky and could not be formed.

  In Comparative Example 5 using the olefin elastomer (b2-3) having a high rubber hardness, the re-adhesiveness was low, floating was observed after storage at low temperature, and contamination was also poor. On the other hand, in Comparative Example 6 using a styrene elastomer (b3-2) having a low rubber hardness and Comparative Example 7 in which the addition amount of the styrene elastomer (b3-1) was increased, adhesion progress was observed after heating and storage. Contamination due to cohesive failure was observed at ℃ storage.

  It can be preferably used as a surface protective film for preventing various kinds of optical films made of synthetic resins used for thin displays such as liquid crystal displays and optical resin plates from being stained or scratched during processing or transportation.

Claims (5)

  The back layer (A) and the adhesive layer (B) are composed of at least two layers in a composite form, the back layer (A) has a polypropylene resin (a1), and the adhesive layer (B) is a propylene copolymer (b1). Olefin elastomer (b2) mainly composed of 6 to 40% by weight, α-olefin having 3 or more carbon atoms, 55 to 75% by weight, and styrene elastomer (b3) 1 to 19% by weight A surface protection film comprising: the rubber hardness (durometer type A) of the olefin elastomer (b2) and the styrene elastomer (b3) is 50 or more and 91 or less.   The surface protective film according to claim 1, wherein an initial adhesive force of the adhesive layer (B) to the polycarbonate sheet is 0.10 N / 50 mm or more and 0.40 N / 50 mm or less.   The surface protective film according to claim 1 or 2, wherein the re-adhesion force of the adhesive layer (B) to the polycarbonate sheet is 90% or more and 120% or less with respect to the initial adhesive force.   The surface according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive strength (50 ° C x 7 days) of the pressure-sensitive adhesive layer (B) to the polycarbonate sheet is 0.09 N / 50 mm or more and 1.00 N / 50 mm or less. Protective film.   The adhesive strength of the adhesive layer (B) to the polycarbonate sheet after low-temperature storage (-30 ° C x 30 minutes) is 0.09 N / 50 mm or more and 0.40 N / 50 mm or less, and does not float. The surface protection film in any one of.