JP7016059B2 - Surface protective film - Google Patents

Description

The present invention relates to a surface protective film mainly used for members of optical products.

The surface protective film is used to protect an optical product such as an optical film or a sheet. The surface protective film used in such an optical product does not contaminate the adherend, and when it is attached to an adherend such as an optical film, it has a defect in the convex portion derived from the surface protective film such as fish eyes in the surface protective film. Convex parts such as foreign matter derived from the environment and foreign matter are transferred to the adherend due to the stress of bonding and the stress of winding and storing in a roll shape, resulting in dents, deformation and other dents or transfer defects. There is a problem and it is strictly required not to cause these dents or transfer defects.

Further, the surface protective film is also required to have rigidity because it is required to have other appearance such as winding wrinkles, slack, surface unevenness, etc. when it is formed into a roll shape.

These demands have become more and more strict in recent years, and even when a surface protective film is attached to the adherend, then wound into a roll and stored as a rolled body for a long period of time, dents and deformations occur. There is a strong demand for a surface protective film that is less likely to cause dents or transfer defects.

For this reason, in order to eliminate dents (dents or transfer) in the adherend due to defects in the convex parts such as fish eyes, a metallocene-based catalyst was used for the base material layer, and a specific cross-separated extraction ratio was specified. A proposal using a resin (Patent Document 1) or a proposal using a polypropylene-based resin polymerized using a metallocene catalyst (Patent Document 2) has been made, but it is still used to eliminate dents on the adherend due to fine fish eyes or the like. On the other hand, it did not reach a level that was fully satisfactory.

In addition, as a method for improving the ease of unwinding of the surface protective film, it is proposed that the adhesive layer is made of linear low-density polyethylene or ethylene / vinyl acetate copolymer, and the back layer is made of propylene resin and low-density polyethylene ( Patent Document 3) or a proposal (Patent Document 4) in which a base material layer corresponding to the back layer is composed of a fluororesin or a silicone resin and polyolefin has been proposed, but in each case, an adherend made of fine fish eyes or the like has been made. It has not reached a level that is fully satisfactory for eliminating the dents on the surface.

Japanese Unexamined Patent Publication No. 9-111208 Japanese Unexamined Patent Publication No. 2009-143215 Japanese Unexamined Patent Publication No. 2008-03349 Japanese Unexamined Patent Publication No. 2008-81589

From the above, it is required to eliminate dents by fine fish eyes and improve the ease of unwinding, and to achieve both of these characteristics.

INDUSTRIAL APPLICABILITY The present invention is required to have high quality such as not causing dents or deformations in the adherend due to defects such as minute fish eyes and winding wrinkles when the adherend is attached to an optical film or sheet. The adhesive strength does not increase with respect to optical films such as polarizing plates and retardation plates, and the adherend is contaminated, and the adherend is dented or deformed to cause dents or transfer defects. It is an object of the present invention to provide a surface protective film that does not become loose.

The present invention employs the following means in order to solve such a problem. That is, the surface protective film of the present invention has at least a laminated structure of a back layer, an intermediate layer, and an adhesive layer, the back layer is made of a polypropylene resin, and the arithmetic average roughness (Ra) of the back layer is 0.35 μm or more. The ten-point average roughness (Rz) is 3.0 μm or more, the intermediate layer is made of a polypropylene-based resin, the tensile elasticity of the polypropylene-based resin is 1450 MPa or more, and the adhesive layer is 1 to 50% by weight of the polyolefin-based elastomer. It is a surface protective film made of low-density polypropylene of 50 to 99% by weight and having a shore A hardness of 75 or more immediately after the needle is pressed by a polyolefin-based elastomer.

According to the present invention, it is possible to reduce dents or transfer without causing dents by transferring to the adherend due to the stress applied by the stress relaxation property of the adhesive layer, and the surface maintaining a stable appearance due to the rigidity of the intermediate layer. A protective film can be provided with good reproducibility.

The surface protective film of the present invention has a laminated structure of at least three layers, that is, a back surface layer, an intermediate layer, and an adhesive layer.

The back layer of the surface protective film of the present invention is preferably made of a polypropylene resin. The surface roughness of the back layer is preferably such that the arithmetic average roughness (Ra) defined by JIS B0601: 1982 is 0.35 μm or more and the ten-point average roughness (Rz) is 3.0 μm or more. More preferably, Ra is in the range of 0.5 to 0.65 μm and Rz is in the range of 4.0 to 5.5 μm. If the arithmetic surface roughness (Ra) is less than 0.35 μm or the ten-point average roughness (Rz) is less than 3.0 μm, the slipperiness with the adhesive layer deteriorates and the rolled appearance as a film roll deteriorates. It may be difficult to wind up.

The polypropylene-based resin used for the back layer can be used without limitation as long as it satisfies Ra and Rz, but preferred specific examples thereof include homopolypropylene, random polypropylene, and block polypropylene, more preferably. When block polypropylene is used, the above surface roughness can be easily obtained. Further, in order to obtain the surface roughness, inorganic or organic particles can be added.

The back layer may contain a resin or an additive other than the polypropylene-based resin as long as the effect of the present invention is not impaired.

The intermediate layer of the surface protective film of the present invention is preferably made of a polypropylene resin. The polypropylene-based resin preferably has a tensile elastic modulus of 1450 MPa or more as defined by JIS K7161: 1994 and JIS K7162: 1994. The tensile elastic modulus is preferably 1450 to 2000 MPa, more preferably 1600 to 1950 MPa, still more preferably 1700 to 1900 MPa. When the tensile elastic modulus is less than 1450 MPa, the effect of suppressing transferability by stress absorption becomes small. The polypropylene-based resin can be used without limitation as long as it satisfies the tensile elastic modulus, and a preferred specific example thereof is homopolypropylene.

The intermediate layer may contain a resin or an additive other than the polypropylene-based resin as long as the effect of the present invention is not impaired.

The adhesive layer of the surface protective film of the present invention is preferably composed of 1 to 50% by weight of the polyolefin-based elastomer and 50 to 99% by weight of the low-density polyethylene, and the polyolefin-based elastomer is immediately after the needle pressing specified in JIS K7215: 1986. Shore A hardness of 75 or more is preferable.

The polyolefin-based elastomer constituting the adhesive layer preferably has a shore A hardness of 75 or more immediately after the needle is pressed, and more preferably 80 or more. Further, the shore A hardness after 15 seconds of pressing the needle is preferably 75 or less. Further, the difference between the shore A hardness immediately after the needle push and the shore A hardness 15 seconds after the needle push is preferably 15 or more, and more preferably 20 or more.

The glass transition temperature (Tg) of the polyolefin-based elastomer is preferably in the range of −10 to 70 ° C., preferably in the range of 0 to 50 ° C., and more preferably in the range of 5 to 40 ° C. When the shore A hardness and Tg are in such a range, the stress absorption property is excellent, and the dent suppression effect is excellent in the surface protective film of the present invention.

Preferred specific examples of the polyolefin-based elastomer include an ethylene-based copolymer, a propylene-based copolymer, and a 4-methyl-1-pentene copolymer. A 4-methyl-1-pentene copolymer is preferable.

The density of the low-density polyethylene used for the adhesive layer of the surface protective film of the present invention is preferably 0.890 to 0.940 g / cm ³ , more preferably 0.900 to 0.930 g / cm ³ .

Examples of the low-density polyethylene having such a density include known high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). Of these, LLDPE is more preferable.

Specific examples of LLDPE include ethylene / 1-butene copolymer, ethylene / 1-hexene copolymer, ethylene / 4-methyl-1-pentene copolymer, ethylene / 1-octene copolymer and the like. Can be done.

The pressure-sensitive adhesive layer in the present invention is more preferably 2 to 40% by weight of the polyolefin-based elastomer and 60 to 98% by weight of the low-density polyethylene. If the amount of the polyolefin-based elastomer exceeds 50% by weight, the adhesive strength after being attached to the adherend increases, and so-called adhesive advancement occurs, which may make peeling difficult or leave peeling marks.

The adhesive layer may contain other resins or additives as long as the effects of the present invention are not impaired.

In the present invention, by using a protective film having a back surface layer, an intermediate layer, and an adhesive layer as described above, the film can be easily rewound when the film is unwound when the film is attached to the adherend, and the adherend can be easily rewound. It is easy to handle and has excellent workability even in the bonding process with. In particular, the adherend is not dented or deformed, or transferred or contaminated due to fish eyes or various wrinkles of the film, which are required for optical films such as polarizing plates and retardation plates. The surface protective film can be provided with good reproducibility.

The surface protective film of the present invention has a laminated structure of at least three layers, that is, a back surface layer, an intermediate layer, and an adhesive layer.

The thickness of the back layer is 0.3 to 30 μm, preferably 0.5 to 20 μm, more preferably 0.7 to 10 μm, and the thickness of the intermediate layer is 5 to 300 μm, preferably 10 to 200 μm, more preferably 15 to. The thickness of the adhesive layer is in the range of 100 μm, preferably 0.5 to 20 μm, preferably 1 to 30 μm, and more preferably 1 to 20 μm.

The thickness of the surface protective film is in the range of 15 to 350 μm, preferably 20 to 250 μm, and more preferably 20 to 150 μm.

Hereinafter, the surface protective film of the present invention will be described based on Examples, but the present invention is not limited to these Examples. It was measured and evaluated by the method shown below.

(1) Melt flow rate Compliant with JIS K7210: 1999 "Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic plastic" using a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd. did. In the case of polypropylene-based resin, the measurement was performed at a temperature of 230 ° C. and a load of 2.16 kgf, and in the case of polyethylene-based resin, the measurement was performed at a temperature of 190 ° C. and a load of 2.16 kgf. The unit is g / 10 minutes.

(2) Surface Roughness Using a fully automatic microshape measuring machine (SURFCORDER ET4000A) manufactured by Kosaka Laboratory Co., Ltd., JIS B0601: 1982 "Geometric characteristic specifications (GPS) of the product-Surface texture: Contour curve method-Terminology, In accordance with "Definition and Surface Texture Parameters", the measurement length is 4 mm in the lateral direction of the film (film width (TD) direction), and the measurement is performed 10 times at a pitch of 10 μm in the longitudinal direction of the film (machine direction) for three-dimensional analysis. , Arithmetic average roughness (Ra) and ten-point average roughness (Rz) were obtained (unit: μm). A diamond needle having a stylus tip radius of 2.0 μm and an apex angle of 60 ° was used, and the measurement was performed with a measuring force of 100 μN and a cutoff of 0.8 mm.

(3) Tensile elastic modulus The tensile elastic modulus was measured in accordance with JIS K7161: 1994 and JIS K7162: 1994 "Plastic-How to determine tensile properties". A polypropylene resin chip is extruded into a sheet from a T-die by a conventional method and cooled on a cooling drum to prepare a sheet having a thickness of about 100 μm, which is punched out in a dumbbell shape in the length direction as a sample for a tensile test. And said. Using a Tensilon type tensile tester, the tensile elastic modulus of the polypropylene resin was measured from the calculated values by the tangential line of the load-elongation curve measured under the conditions of a chuck distance of 100 mm and a tensile speed of 300 mm / min.

(4) Evaluation of dent transferability [Evaluation of dents by bonding to PET film]
Toray polyester film "Lumirror" (registered trademark) U483 (thickness 50 μm) was used as the polyethylene terephthalate (PET) film to be bonded. Using a special crimping roller manufactured by Yasuda Seiki Co., Ltd., the film was bonded at a linear pressure of 9.1 kN / m and a bonding speed of 3000 mm / min, cut into 100 mm x 100 mm, sandwiched between smooth plates, and sandwiched between smooth plates at 60 ° C for 24 hours. After storing in, the film was peeled off, and distortion (distortion) due to dents was observed in a reflection image in which an indoor fluorescent lamp tube was projected on the surface of the PET film.
Judgment criteria: Sensory evaluation LV1 Distortion cannot be confirmed
LV2 distortion can be confirmed slightly LV3 distortion can be clearly confirmed.

(5) Durometer hardness (Shore A)
A chip of a polyolefin elastomer was molded into a flat plate by a hot press to prepare a sample having a thickness of 6 mm. Based on JIS K7215: 1986 "Plastic Durometer Hardness Test Method", the push needle uses a type A indenter with a columnar tip shape and a conical angle of 35 °, and the pressing load is about 10 N, which is the pressurization standard of the durometer. The measurement was performed by pressing the surface against the sample surface as soon as possible without impact while keeping the surface parallel to the sample surface, and making the pressure reference surface and the sample adhere well. The scales of the durometer were read immediately after the needle was pressed and 15 seconds after the needle was pressed.

(6) Winding appearance Can be wound onto a roll without wrinkles; ○
Wrinkles occur and it is difficult to wind up on the roll; ×.

<Example 1>
As the back layer resin, the density is 0.900 g / cm ³ , the melting point is 160 ° C., the melt flow rate (hereinafter sometimes referred to as MFR) 9.0 g / 10 minutes block polypropylene (J640F manufactured by Hyosung), and the density as the intermediate layer resin. Homopolypropylene (FL4 manufactured by Japan Polypropylene Corporation) with a tensile modulus of 1850 MPa specified by JIS K7161 (1994), MFR 5.0 g / 10 minutes at 0.900 g / cm ³ , melting point 164 ° C, temperature 230 ° C. 100% by weight was used. As an adhesive layer, the density is 0.840 g / cm ³ , MFR 10.0 g / 10 minutes at 230 ° C, the shore A hardness immediately after the needle push is 92, the shore A hardness 15 seconds after the needle push is 70, and the glass transition temperature is 30. Linear low-density polyethylene (ethylene, 1) obtained with a metallocene catalyst having a density of 0.910 g / cm ³ and 25% by weight of an olefin-based elastomer (“Absortmer” (registered trademark) EP1001 manufactured by Mitsui Chemicals Co., Ltd.) at ℃. -Hexene elastomer, KC573) manufactured by Nippon Polyethylene Co., Ltd. (75% by weight) was used. Using a T-die type composite film-forming machine with a base width of 400 mm, which has three extruders of φ25 mm (for the back layer), φ35 mm (for the adhesive layer), and φ45 mm (for the intermediate layer), the resin compositions prepared above are used. The discharge amount of each extruder is adjusted so that the back layer thickness ratio is 8.1%, the adhesive layer thickness ratio is 22.6%, and the intermediate layer thickness ratio is 69.3%. Then, it was extruded from the composite T-die at an extrusion temperature of 220 ° C., rapidly cooled at a cast drum temperature of 30 ° C., and wound into a roll to obtain a three-layer laminated film having a film thickness of 30 μm. (Collecting ○)
The arithmetic average roughness (Ra) of the back surface of the obtained protective film was 0.59 μm, the ten-point average roughness (Rz) was 4.73 μm, and the arithmetic average roughness (Ra) of the adhesive surface was 0.11 μm, ten-point average. The roughness (Rz) was 0.64 μm.

The dent transferability evaluation result by bonding to the PET film was LV1.

<Example 2>
As the adhesive layer, 3 layers having a film thickness of 30 μm were laminated in the same manner as in Example 1 except that 5% by weight of the olefin-based elastomer used in Example 1 and 95% by weight of the linear low-density polyethylene were used. I got a film. (Collecting ○)
The arithmetic average roughness (Ra) of the back surface of the obtained protective film is 0.57 μm, the ten-point average roughness (Rz) is 4.71 μm, and the arithmetic average roughness (Ra) of the adhesive surface is 0.10 μm, ten-point average. The roughness (Rz) was 0.60 μm.

The dent transferability evaluation result by bonding to the PET film was LV1.

<Example 3>
As the adhesive layer, 30% by weight of the olefin-based elastomer used in Example 1 and 70% by weight of the linear low-density polyethylene were used, but the same method as in Example 1 was used to laminate a three-layer film having a film thickness of 30 μm. I got a film. (Collecting ○)

The arithmetic average roughness (Ra) of the back surface of the obtained protective film is 0.60 μm, the ten-point average roughness (Rz) is 4.77 μm, and the arithmetic average roughness (Ra) of the adhesive surface is 0.11 μm, ten-point average. The roughness (Rz) was 0.64 μm.

The dent transferability evaluation result by bonding to the PET film was LV1.

<Comparative Example 1>
As the intermediate layer, 100% by weight of high-density polyethylene having a density of 0.960 g / cm ³ , a melting point of 134 ° C. and a melt flow rate of 7.0 g / 10 minutes at a temperature of 190 ° C. was used.
A three-layer laminated film having a film thickness of 30 μm was obtained by the same method as in Example 1 except for the above. (Collecting ○)
The arithmetic mean roughness (Ra) of the back surface of the obtained protective film was 0.60 μm, and the ten-point average roughness (Rz) was 4.68 μm.

The rigidity of the intermediate layer was insufficient, and the dent transferability evaluation result by bonding to the PET film was LV3.

<Comparative Example 2>
As the intermediate layer, 100% by weight of low-density polyethylene having a density of 0.924 g / cm ³ , a melting point of 116 ° C. and a melt flow rate of 5.8 g / 10 min at a temperature of 190 ° C. was used.
A three-layer laminated film having a film thickness of 30 μm was obtained by the same method as in Example 1 except for the above. (Collecting ○)
The arithmetic mean roughness (Ra) of the back surface of the obtained protective film was 0.59 μm, and the ten-point average roughness (Rz) was 4.75 μm.

The rigidity of the intermediate layer was insufficient, and the dent transferability evaluation result by bonding to the PET film was LV2.

<Comparative Example 3>
As the back layer, 100% by weight of homopolypropylene having a density of 0.900 g / cm ³ , a melting point of 163 ° C. and a melt flow rate of 7.5 g / 10 min at a temperature of 230 ° C. was used, and the density was 0.960 g / cm. ^3. 100% by weight of high-density polyethylene with a melting point of 134 ° C. and a melt flow rate of 7.0 g / 10 min at a temperature of 190 ° C. was used.

As the adhesive layer, 100% by weight of linear low-density polyethylene (ethylene 1-hexene copolymer) having a density of 0.922 g / cm ³ , a melting point of 122 ° C. and an MFR of 5.0 g / 10 min at 190 ° C. was used.
A three-layer laminated film having a film thickness of 30 μm was obtained by the same method as in Example 1 except for the above. However, the surface roughness of the back layer was small, the film roll was wrinkled, and it could not be wound up well. (Collecting figure ×)
The arithmetic mean roughness (Ra) of the back surface of the obtained protective film was 0.10 μm, and the ten-point average roughness (Rz) was 1.66 μm.

The stress absorption was insufficient, and the dent transferability evaluation result by bonding to the PET film was LV3.

<Comparative Example 4>
Random polypropylene (FW4BT manufactured by Japan Polypropylene Corporation) with a density of 0.900 g / cm ³ as an intermediate layer resin, an MFR of 6.5 g / 10 minutes at a temperature of 230 ° C., and a tensile elastic modulus of 900 MPa specified by JIS K7161 (1994). ) 100% by weight was used.
A three-layer laminated film having a film thickness of 30 μm was obtained by the same method as in Example 1 except for the above. (Collecting ○)
The rigidity of the polypropylene-based resin in the intermediate layer was insufficient, and the dent transferability evaluation result by bonding to the PET film was LV2.

Claims (3)

It is composed of a laminated structure of at least a back layer, an intermediate layer, and an adhesive layer, the back layer is made of a polypropylene resin, the arithmetic average roughness (Ra) of the back layer is 0.35 μm or more, and the ten-point average roughness (Rz) is 3. It is 0.0 μm or more, the intermediate layer is made of a polypropylene resin, the tensile elasticity of the polypropylene resin is 1450 MPa or more, and the adhesive layer is made of 1 to 50% by weight of a polyolefin-based elastomer and 50 to 99% by weight of a low-density polyethylene. , A surface protective film having a shore A hardness of 75 or more immediately after pressing a needle of a polyolefin-based elastomer. The surface protective film according to claim 1, wherein the shore A hardness of the polyolefin-based elastomer immediately after the needle is pressed is 80 or more, and the shore A hardness 15 seconds after the needle is pressed is less than 75. The surface protective film according to claim 1 or 2, wherein the difference between the shore A hardness immediately after the needle is pressed and the shore A hardness 15 seconds after the needle is pressed is 15 or more.