JP6628101B2 - Laminated film - Google Patents

Description

  The present invention relates to a laminated film having a pressure-sensitive adhesive layer containing a styrene-based elastomer as a main component on at least one surface of a substrate layer. The laminated film of the present invention can be suitably used as a protective film, and in particular, can protect and store various adherends within an appropriate adhesive force range without depending on the shape and composition of the back surface of the optical prism sheet. Related to a laminated film.

  Products made of various materials such as synthetic resin, metal, and glass are often handled with a material that protects the surface attached thereto in order to prevent scratches and stains generated during the processing step, the transportation step, and storage. A typical material for protecting the surface is a protective film, which is generally formed by forming an adhesive layer on a support substrate, and applying the adhesive layer surface to an adherend and covering the support substrate. To protect the surface.

  2. Description of the Related Art In recent years, liquid crystal displays and touch panel devices have become widespread, and are composed of members such as a large number of optical sheets made of synthetic resin. In such an optical sheet, since it is necessary to reduce defects such as optical distortion as much as possible, a protective film is frequently used to prevent scratches and stains that may cause the defects.

  The characteristics required for the protective film include that it does not easily peel off from the adherend when it is subjected to environmental changes such as temperature and humidity or a small stress, and that the adherent adheres to the adherend when peeled from the adherend. That no agent component remains.

  Among the above optical sheets, in the case of a member having irregularities on the surface, such as a diffusion plate or a prism sheet, immediately after bonding the protective film, the adhesive layer does not sufficiently follow the irregularities, and a desired adhesive force is not obtained. It may not be obtained and may peel off. To solve such problems, a method of softening the adhesive layer and a method of increasing the adhesive strength by using a tackifier are known (for example, Patent Documents 1 to 3).

  However, when the uneven portion of the adherend is soft, it is difficult to obtain a sufficient contact area by simply adjusting the softness of the adhesive layer as in Patent Documents 1 and 2, and the adhesive strength may be insufficient. there were. Even if the adhesive layer is extremely soft and a sufficient contact area is obtained, the contact area tends to increase over time, and as a result, peeling becomes difficult due to an excessive increase in adhesive strength, and the peeling after peeling becomes difficult. In some cases, glue residue may be left on the body.

  Patent Literature 3 discloses a method of controlling the adhesive strength by adjusting the amount of a tackifier in an adhesive layer. By adding a large amount of tackifier, even if the contact area is small immediately after lamination, sufficient tackiness can be exhibited, but the tackifier becomes sticky during storage over time or under high temperature and high pressure. In some cases, bleed-out to the surface of the layer contaminates the adherend, or adhesion may increase, making it difficult to peel off the adherend.

  Patent Document 4 proposes a surface protection film for protecting a lens portion (prism surface) of an optical prism sheet. However, since this proposal focuses only on the storage elastic modulus of the adhesive layer, it is possible to stably obtain an appropriate adhesive force on any adherend when the shape and surface characteristics of the adherend are different. In particular, there has been a problem that the adhesive strength is excessive to the mat surface for an optical sheet having various surface morphologies, and the adhesive fluctuates with time.

  Patent Documents 5 and 6 also propose a surface protection film for protecting a lens portion (prism surface) of an optical prism sheet. In this proposal, the properties are controlled by controlling the block structure of the block copolymer, and further attention is paid to the loss tangent tan δ peak temperature range of the adhesive layer and the value of the shear storage modulus at 70 ° C. The optical prism sheet has various back shapes and characteristics, and it is difficult to widely apply the protective film to various adherends only at the characteristic at a specific temperature.

JP 2005-298630 A JP 2012-77244 A JP 2012-111793 A JP-A-2006-335000 International Publication No. 2010/029773 JP 2011-16354 A

  An object of the present invention is to solve the above problems. That is, when the laminated film of the present invention is used as a protective film, the surface of the optical sheet, in particular, the back surface of the prism sheet, regardless of its shape, composition, in a range of suitable adhesive force to various adherends. An object of the present invention is to provide a laminated film capable of protection and storage.

The above problem can be solved by the following preferred embodiments.
(1) A laminated film having a pressure-sensitive adhesive layer containing a styrene-based elastomer as a main component on at least one surface of a base material layer, wherein the styrene-based elastomer has a shear storage modulus G ′ at 1 Hz and 30 to 60 ° C. A laminated film having a loss modulus G ″ satisfying the following formulas (1) and (2).
0.5 × 10 ⁶ ≦ G ′ (Pa) ≦ 2.0 × 10 ⁶ (1)
0.08 × 10 ⁶ ≦ G ″ (Pa) ≦ 0.18 × 10 ⁶ (2)
(2) The laminated film according to (1), wherein the change width Δtanδ of the loss tangent tanδ at 1 Hz and 30 to 60 ° C of the styrene-based elastomer is 0.05 or less.
(3) The laminated film according to claim 1 or 2, wherein the styrene-based elastomer has a shear storage modulus G ′ at 1 Hz and 30 to 60 ° C. that satisfies the following expression (3).
0.6 × 10 ⁶ ≦ G ′ (Pa) ≦ 1.3 × 10 ⁶ (3)
(4) The laminated film according to any one of (1) to (3), wherein the base layer contains a polyolefin resin.
(5) The laminated film according to any one of (1) to (4), wherein the pressure-sensitive adhesive layer contains a fatty acid amide compound in an amount of 0.01 to 10% by mass.
(6) The laminated film according to any one of (1) to (5), which is used for protecting the back surface of the prism sheet.
(7) The laminated film according to (6), wherein the back surface of the prism sheet is made of an ester resin or an acrylic resin.
(8) The laminated film according to (6) or (7), wherein the average surface roughness Ra of the back surface of the prism sheet is 0.01 to 1 μm.

  When the laminated film of the present invention is used as a protective film, a laminated film capable of protecting and storing various adherends within an appropriate adhesive force range regardless of the shape and composition of the back surface of the optical prism sheet is provided. can do.

  The laminated film of the present invention is preferably a laminated film having an adhesive layer containing a styrene-based elastomer as a main component on at least one surface of a substrate layer. Examples of the styrene elastomer include styrene / conjugated diene copolymers such as styrene / butadiene copolymer (SBR), styrene / isoprene / styrene copolymer (SIS), and styrene / butadiene / styrene copolymer (SBS). These hydrogenated products (for example, hydrogenated styrene / butadiene copolymer (HSBR) and styrene / ethylene / butylene / styrene copolymer (SEBS)), and styrene / isobutylene-based copolymer (for example, styrene / isobutylene / styrene) Triblock copolymer (SIBS), styrene / isobutylene diblock copolymer (SIB) or a mixture thereof). Among them, hydrogenated styrene / butadiene copolymer (HSBR), styrene / ethylene / butylene / styrene copolymer (SEBS), and styrene / isobutylene copolymer can be preferably used. In the present invention, the term "main component" means that the component accounts for 50% by mass or more of the adhesive layer, and more preferably a component that accounts for 70% by mass or more of the adhesive layer. Further, a plurality of the styrene-based elastomers may be used as a mixture, and it is sufficient that the total of the mixture accounts for 50% by mass or more of the adhesive layer.

  The styrene-based elastomer used in the present invention preferably has a weight average molecular weight of 50,000 to 400,000. More preferably, it is 50,000 to 200,000. It is preferable that the weight average molecular weight is within the above-mentioned range from the viewpoint of achieving both cohesive strength required for the adhesive layer and processability into a film.

  The styrene-based elastomer used in the present invention is preferably a block copolymer of a hard segment composed of a styrene component and a soft segment composed of an olefin component. It is preferably 50% by mass, more preferably 10 to 50% by mass, further preferably 15 to 50% by mass, and particularly preferably 20 to 45% by mass. Further, not only the hard segment but also the soft segment may be copolymerized with a styrene monomer at a ratio of 0.1 to 20% by mass. By including a styrene component in the soft segment, the initial adhesive strength and the adhesion promoting behavior may be controlled in some cases.

The styrene-based elastomer in the adhesive layer of the laminated film of the present invention can control the surface protection of the optical prism sheet, the adhesion to the back surface of the optical prism sheet having various compositions and structures, and the peeling in a preferable adhesive force range. In view of this, the shear storage modulus G ′ (hereinafter may be simply referred to as “G ′”) and the shear loss modulus G ″ (hereinafter simply referred to as “G”) at 30 to 60 ° C. measured at 1 Hz. ) May satisfy formulas (1) and (2), respectively.
0.5 × 10 ⁶ ≦ G ′ (Pa) ≦ 2.0 × 10 ⁶ (1)
0.08 × 10 ⁶ ≦ G ″ (Pa) ≦ 0.18 × 10 ⁶ (2).

  Here, that the shear storage modulus G ′ at 30 to 60 ° C. satisfies the expression (1) means that the maximum value and the minimum value of the shear storage modulus G ′ at 30 to 60 ° C. both satisfy the expression (1). It means to satisfy. Further, that the shear loss elastic modulus G ″ at 30 to 60 ° C. satisfies the formula (2) means that the maximum value and the minimum value of the shear loss elastic modulus G ″ at 30 to 60 ° C. both satisfy the formula (2). That means.

If the shear storage modulus G ′ is less than 0.5 × 10 ⁶ Pa, the pressure-sensitive adhesive layer becomes too soft, resulting in remarkable over-adhesion and increased adhesion, and it may be difficult to peel off depending on the adherend. Further, when G ′ exceeds 2.0 × 10 ⁶ Pa, depending on the adherend, the laminated film may float on the surface of the adherend without exhibiting adhesive strength. More preferably, the shear storage modulus G ′ is 0.6 × 10 ^{6 to} 1.6 × 10 ⁶ Pa, and 0.6 × 10 ^{6 to} 1.3 × 10 ⁶ Pa (range of Formula 3). It is more preferable if it is 0.8 × 10 ^{6 to} 1.3 × 10 ⁶ Pa.

If the shear loss elastic modulus G ″ is less than 0.08 × 10 ⁶ Pa, the adhesion increase may be large depending on the adherend, and peeling after storage may be difficult. If it exceeds 18 × 10 ⁶ Pa, the initial adhesive strength may be too high depending on the adherend. The shear loss elastic modulus G ″ is more preferably 0.09 × 10 ^{6 to} 0.16 × 10 ⁶ Pa, and particularly preferably 0.1 × 10 ^{6 to} 0.15 × 10 ⁶ Pa.

  The styrene-based elastomer in the pressure-sensitive adhesive layer of the laminated film of the present invention has a change width Δtanδ of the loss tangent tanδ at 1 Hz and 30 to 60 ° C. of 0. It is preferably at most 05. If Δtan δ exceeds 0.05, the adherence dependency and the change over time in adhesive strength may increase. Δtan δ is more preferably 0.04 or less, and particularly preferably 0.03 or less.

  Here, that the variation width Δtanδ of the loss tangent tanδ at 30 to 60 ° C. is 0.05 or less means that the difference between the maximum value and the minimum value of the loss tangent tanδ at 30 to 60 ° C is 0.05 or less. Say.

  In the present invention, the method for controlling the shear storage modulus G ′, the shear loss modulus G ″ and Δtan δ of the styrene-based elastomer, which is the main component of the adhesive layer, to within the above-mentioned preferred ranges includes the styrene component constituting the styrene-based elastomer. It is possible to control the block length and ratio of the soft segment consisting of the hard segment and the olefin component, and the amount of the styrene component in the soft segment, and furthermore, it is possible to control a plurality of styrene-based elastomers having different viscoelastic properties. It can also be adjusted by mixing.

  In the present invention, the shear storage modulus G ′ and the shear loss modulus G ″ of the styrene elastomer which is the main component of the adhesive layer can be calculated by the methods described in Examples.

  The adhesive layer of the laminated film of the present invention may contain a tackifier, an antiblocking agent, an antioxidant, a softener, and the like, in addition to the styrene-based elastomer.

  Examples of the tackifier used in the adhesive layer in the present invention include aliphatic copolymers, aromatic copolymers, petroleum resins such as aliphatic / aromatic copolymers and alicyclic copolymers, and cumarone-indene. Modified resins such as rosin resins such as phenol resins, terpene resins, terpene phenol resins, and polymerized rosin, phenol resins, xylene resins, and hydrogenated products thereof. These tackifiers may be used in combination of a plurality of types. The tackifier preferably contains 0.01 to 20% by mass in the adhesive layer from the viewpoint of controlling the adhesive properties, and more preferably 0.1 to 10% by mass from the viewpoint of adhesive residue.

  The anti-blocking agent used for the adhesive layer in the present invention is, when a styrene-based elastomer is formed into chips, the chips are attached to each other to prevent sticking and blocking between the chips, such as calcium stearate and behenic acid. Examples include saturated fatty acid metal salts such as magnesium and fatty acid amide compounds such as ethylene bisstearic acid amide and hexamethylene bisstearic acid amide such as saturated fatty acid aliphatic amide and saturated fatty acid aromatic bisamide. Above all, it is preferable that the fatty acid amide compound is contained in an amount of 0.01 to 10% by mass with respect to the entire adhesive layer as 100% by mass, from the viewpoint of controlling the adhesive force and suppressing the change of the adhesive force with time. The content of the fatty acid amide compound is more preferably 0.1 to 5% by mass, and particularly preferably 0.2 to 3% by mass. In some cases, it is difficult to include an amount exceeding 0.5% by mass simply by attaching these antiblocking agents to a chip surface for the purpose of preventing blocking as usual. It is preferable to melt-knead the antiblocking agent.

  As the antioxidant used in the pressure-sensitive adhesive layer in the present invention, a phenol-based or phosphoric-acid-based antioxidant can be preferably used, and pentaerythrityl-tetrakis [3- ( 3,5-t-butyl-4-hydroxyphenyl) propionate] (trade name: IRGANOX1010 (manufactured by BASF)) and tris (2,4-di-t-butylphenyl) phosphite (trade name: IRGAFOS168 (manufactured by BASF)). Can be used without any problems.

  The laminated film of the present invention has the pressure-sensitive adhesive layer on at least one side of the base material layer. In the present invention, the base material layer preferably contains a polyolefin resin. Although the polyolefin resin contained in the base layer is not particularly limited, high-density polyethylene, medium-density polyethylene, low-density polyethylene, isotactic polypropylene, atactic polypropylene, propylene / ethylene copolymer (random copolymer and / or block Copolymer), propylene / α-olefin copolymer, propylene / ethylene / α-olefin copolymer, ethylene / ethyl (meth) acrylate copolymer, ethylene / methyl (meth) acrylate copolymer, ethylene / n -Butyl (meth) acrylate copolymer, ethylene / vinyl acetate copolymer, polybutene-1, poly-4-methylpentene-1 and the like. Further, a plurality of polyolefin resins may be mixed to form a base material layer. The α-olefin is not particularly limited as long as it can be copolymerized with propylene or ethylene. For example, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, 1-heptene can be mentioned.

  Among the above-mentioned polyolefins, from the viewpoint of high rigidity, isotactic polypropylene, propylene / ethylene copolymer (random copolymer and / or block copolymer), propylene / ethylene / α-olefin copolymer, Propylene-based materials such as propylene / α-olefin copolymers are more preferred.

  Further, the substrate layer may contain an antioxidant, an antiblocking agent, and the like, and may have a release layer on the surface of the substrate layer opposite to the surface having the adhesive layer. The release layer is formed by adding a lubricant such as a fluorine-based resin or inorganic particles as a release agent to the polyolefin resin used for the base material layer, contacting the adhesive layer, winding the film on a film roll, and then rewinding the film. Deployment power can be adjusted.

  In addition, the base layer of the laminated film of the present invention contains a small amount of each component constituting the adhesive layer, such as the styrene-based elastomer used for the adhesive layer, which means that the affinity between the adhesive layer and the substrate layer is low. This is preferable from the viewpoint of improving the adhesiveness and enhancing the adhesive strength between the adhesive layer and the base layer. In addition, as a method of including the adhesive layer component in the base layer, the method of recovering the laminated film, adding the recovered raw material as a raw material and using the method is used from the viewpoint of resin recycling and reduction of production cost. This is the preferred approach.

  The thickness of the pressure-sensitive adhesive layer of the laminated film of the present invention is preferably 1 to 10 μm. More preferably, it is 2 to 8 μm. When the pressure-sensitive adhesive layer is thinner than 1 μm, the pressure-sensitive adhesive strength may be too low to serve the role of surface protection. On the contrary, when the pressure-sensitive adhesive layer is thicker than 10 μm, the pressure-sensitive adhesive strength may be so high that peeling may be difficult.

  The thickness of the substrate layer of the laminated film of the present invention is preferably from 20 to 100 μm, more preferably from 25 to 80 μm. From the viewpoint of achieving both the scratch resistance and the storage efficiency when storing the adherend in a protected state, it is particularly preferably 30 to 60 μm.

  Hereinafter, a preferred method for producing the laminated film of the present invention will be described. However, the method for producing a laminated film of the present invention is not limited to this.

  When styrene-ethylene-butylene-styrene block copolymer (SEBS) is used as the styrene-based elastomer as the main component of the adhesive layer in the present invention, it is commercially available from Clayton Polymer, JSR Corporation, and Asahi Kasei Chemicals Corporation. Elastomers can be appropriately selected from Clayton G polymer, Dynarone, Tuftec, etc., and mixed and used so as to satisfy viscoelastic properties. Further, for example, with reference to an elastomer polymerization method described in JP-A-2014-148638 or JP-A-2011-57992, SEBS having viscoelastic properties adjusted may be prepared by polymerization.

  88 parts by mass of a styrene-based elastomer as a component of the adhesive layer, 2 parts by mass of ethylene bisstearic acid amide as an antiblocking agent, 5 parts by mass of styrene resin-based FTR6125 manufactured by Mitsui Chemicals, Inc. as a styrene-based tackifier, and terpene phenol A resin-based YS polystar TH130 manufactured by Yashara Chemical Co., Ltd. is mixed at 5 parts by mass and supplied to a melt extruder. In addition, a polypropylene resin is supplied to a melt extruder as a base material layer. Note that a release layer may be provided on the side of the base material layer opposite to the side of the adhesive layer.

  The constituent components of the adhesive layer and the base layer are each extruded from a melt extruder. At this time, it is preferable to control the resin temperature of the adhesive layer to be 190 to 240 ° C. If the resin temperature is lower than 190 ° C., the melt viscosity is too high, so that the resin kneading becomes insufficient and the film characteristics may be uneven. Further, when the resin temperature exceeds 240 ° C., thermal degradation of the elastomer occurs, and adhesive residue may easily be generated at the time of peeling off the adhesive. The resin temperature is preferably from 200 to 230C. Then, the adhesive layer and the base material layer are laminated and integrated inside the T-die, and co-extrusion is performed. Then, it is cooled and solidified by a metal cooling roll, formed into a film shape, and wound up in a roll shape to obtain a laminated film.

  Further, the intermediate product wound into a roll is slit in accordance with the width of the optical sheet to be protected in the next step. At this time, leaving the film at room temperature for 24 to 36 hours before slitting is preferable from the viewpoint of releasing the residual strain in the film and stabilizing the film characteristics.

  The adherend protected by the laminated film of the present invention is preferably the back surface of an optical prism sheet constituting a liquid crystal display or a touch panel device. The optical prism sheet is made of, for example, a biaxially oriented polyester film as a base material, and in order to impart various optical characteristics, a UV curable resin is applied to the surface of the base material, and is UV-cured while being shaped into a prism. A sheet having an optically functional surface. The back surface of the optical prism sheet may be provided with a light diffusion function for the purpose of integrating the functions of the optical sheet.

  The laminated film of the present invention is a protective film particularly suitable for protecting the back surface of the prism sheet particularly among the optical prism sheet surfaces, and the back surface of the surface where the back surface is formed of an ester resin or an acrylic resin. It can be suitably used for protection. Here, that the back surface of the prism sheet is made of an ester resin or an acrylic resin means that the back surface of the prism sheet contains an ester resin or an acrylic resin. The composition of the rear surface can be determined by the FT-IR ATR method.

  For example, in the case of an ester resin, the back surface of the optical prism sheet preferably contains inorganic or organic particles having an average particle diameter of preferably 0.1 to 20 μm, more preferably 1 to 10 μm in the polyester resin, for example, 0.01 to 10 μm. It is obtained by laminating a layer to which 10 to 10% by mass, more preferably 0.1 to 5% by mass is added on the surface opposite to the surface on which the prism is formed by post-processing, and performing melt film formation and biaxial stretching. Further, in the manufacturing process of the biaxially oriented polyester film serving as the base material of the prism sheet, the transparent bead particles are dispersed in an aqueous solution in which the polyester resin is dispersed on the surface opposite to the surface on which the prism is formed, and coating is performed. The functional layer can be formed by a so-called in-line coating method in which the functional layer is stretched and solidified by heat treatment.

  Further, when the back surface of the prism sheet is made of an acrylic resin, for example, as described above, the acrylic resin is applied to the surface opposite to the prism surface with a die coater or the like, and the light diffusion layer is molded while being molded. It can be obtained by forming by UV curing.

  It is preferable that the wetting tension (surface free energy) of the back surface of the prism sheet described above is 25 mN / m or more. When the wetting tension is less than 25 mN / m, it may be difficult to adhere the laminated film of the present invention in close contact. The upper limit is substantially about 60 mN / m. The wet tension of the surface to be adhered can be adjusted by the material of the surface to be adhered, the manufacturing method, and the like.

  When the laminated film of the present invention is used as a protective film, the back surface of the optical prism sheet protected by the laminated film of the present invention is controlled to an appropriate adhesive force having an average surface roughness Ra of 0.01 to 1 μm. It is preferable because it is easy. More preferably, it is 0.05 to 0.8 μm. The ten-point average roughness Rz is preferably smaller than the thickness of the adhesive layer. When Rz is larger than the thickness of the adhesive layer, even if the protrusions dig into the adhesive layer by 100%, the entire adhesive layer cannot contact the adherend, so that it may be difficult to obtain an appropriate adhesive force. .

  Hereinafter, the present invention will be described in detail with reference to examples. The characteristics were measured and evaluated by the following methods.

(1) Viscoelasticity (shear storage modulus, shear loss modulus, loss tangent)
The styrene-based elastomers shown in Examples and Comparative Examples were melt-molded to a thickness of 2 mm, and the temperature range from -50 ° C to 150 ° C was increased by using a rheometer AR2000ex manufactured by TA Instruments at a rate of 3 ° C / min. The shear storage elastic modulus G ′ and the shear loss elastic modulus G ″ were measured at a sampling rate of 20 seconds while dynamically shearing at a frequency of 1 Hz and a strain of 0.01% while raising the temperature. ”, The loss tangent tan δ (= G ″ / G ′) was calculated.

(2) Initial adhesive strength A roll press machine (Yasda Seiki Seisakusho Co., Ltd.) was used for the back surface of the laminated film and the prism sheets of the various adherends shown in Table 1 for 24 hours at a temperature of 23 ° C. and a relative humidity of 50%. (Special pressure roller), at a bonding pressure of 0.35 MPa and a bonding speed of 3 m / min. Then, after storing at a temperature of 23 ° C. and a relative humidity of 50% for 24 hours, the adhesive strength was evaluated.

  The adhesive force was measured at a peeling speed of 300 mm / min and a peeling angle of 180 ° using a tensile tester (Universal testing machine Tensilon manufactured by Orientec). The measurement was performed five times, and the average value was used as the initial adhesive strength.

(3) Adhesive strength over time A roll press machine (manufactured by Yasuda Seiki Seisaku-sho, Ltd.) was used for the rear surface of the prismatic surface of the laminated film and the various adherends shown in Table 1 for 24 hours at a temperature of 23 ° C. and a relative humidity of 50%. Using a special pressure roller, the bonding was performed at a bonding pressure of 0.35 MPa and a bonding speed of 3 m / min. Then, it was stored in a hot-air oven controlled at 50 ° C. for 72 hours, and further stored at a temperature of 23 ° C. and a relative humidity of 50% for 24 hours, and then evaluated for adhesive strength.

  The adhesive force was measured at a peeling speed of 300 mm / min and a peeling angle of 180 ° using a tensile tester (Universal testing machine Tensilon manufactured by Orientec). The measurement was performed three times, and the average value was defined as the adhesive force over time.

(4) Surface Roughness The average surface roughness Ra and the ten-point average roughness Rz of the back surface of the prism sheet were measured using a high-precision fine shape measuring instrument (SURFCORDER ET4000A) manufactured by Kosaka Laboratory Co., Ltd. according to JIS B0601-1994. The measurement was performed 21 times at 2 μm in the lateral direction of the film and at 10 μm intervals in the longitudinal direction (machine direction) of the film, and three-dimensional analysis was performed. The average surface roughness Ra and the ten-point average roughness Rz were obtained and evaluated. The measurement was carried out using a diamond needle having a stylus tip radius of 2.0 μm with a measuring force of 100 μN and a cutoff of 0.8 mm.

(5) Material of adherend Using a Frontier FT-IR manufactured by PerkinElmer Co., Ltd., using a UATR IR unit, a medium crystal as diamond / ZnSe, and a prism sheet by an attenuated total reflection method (ATR method). The spectrum of the back was measured, and the material on the back was confirmed. The measurement was performed with the resolution of the spectrometer being 1 cm ^-1 and the number of times of spectrum integration being four.

(6) Wetting tension of adherend Using a contact angle meter (CA-D type manufactured by Kyowa Interface Chemical Co., Ltd.), a prism sheet of four kinds of liquids of water, ethylene glycol, formamide, and methylene iodide was prepared. The static contact angle to the back was determined. The components of the contact angle and the surface tension of the measurement liquid obtained for each liquid were substituted into the following equations, and γ ^L , γ ⁺ , and γ ⁻ were calculated to determine the wetting tension (surface free energy) γ. .
_{^{(γ L γ j L) 1/2}} +2 (γ + γ j -) 1/2 +2 (γ j + γ -) 1/2
= (1 + cos θ) [γ _j ^L +2 (γ _j ⁺ γ _j ⁻ ) ^1/2 ] / 2
^{However, γ = γ L +2 (γ} + γ -) 1/2 γ j = γ j L +2 (γ j + γ j -) 1/2
Here, γ, γ ^L , γ ⁺ , and γ ⁻ are the wetting tension (surface free energy), long-range force term, Lewis acid parameter, and Lewis base parameter of the film surface, respectively, γ _j , γ _j ^L , γ _j ⁺ and γ _j ⁻ represent a wetting tension (surface free energy), a long-range force term, a Lewis acid parameter, and a Lewis base parameter of the measurement solution used, respectively. The surface tension of each liquid used here is based on the value of Table 1 proposed by Oss (“Fundamentals of Adhesion”, LH Lee (Ed.), P153, Plenum ess, New York (1991)). Was.

(Styrene-based elastomer A)
A block copolymer of styrene and butadiene was polymerized using cyclohexane as a solvent, n-butyllithium, N, N, N ', N'-tetramethylethylenediamine, and sodium t-pentoxide as a polymerization catalyst. The composition of each block is such that each block of styrene: butadiene: styrene has a mass ratio of 10:80:10, and when the whole butadiene block is 100% by mass, 20% by mass is composed of random styrene monomers. It was controlled to be polymerized.

  Next, the styrene-butadiene block copolymer was subjected to a hydrogenation treatment up to a hydrogenation rate of 98% to obtain a styrene-ethylene-butylene-styrene block copolymer (SEBS) having a weight average molecular weight of 200,000. At this time, the original position of the double bond of butadiene was adjusted so that the mass ratio of ethylene to butylene was 5: 6.

  In addition, about the polymerization conditions of a styrene-type elastomer, superposition | polymerization was performed with reference to the method disclosed in Unexamined-Japanese-Patent No. 2010-255007 and Unexamined-Japanese-Patent No. 2014-148638. In addition, elastomers other than the styrene-based elastomer A were prepared by changing the molecular chain length (degree of polymerization) of each block, the copolymerization ratio of styrene in the middle block, and the like, and used in Examples. Some of the examples were made using commercially available SEBS.

(Example 1)
As the styrene-based elastomer, the styrene block at each end is 12% by mass, the ethylene-butylene block in the intermediate phase is 70% by mass, the styrene component is contained in 100% by mass of the intermediate phase, and the ethylene-butylene ratio is mol%. SEBS (weight average molecular weight: 180,000) at a ratio of 1: 1 was polymerized, and 100 parts by mass of the SEBS was dusted with 1 part by mass of ethylenebisstearylamide as a lubricant to form chips. To 90 parts by mass of the chipped SEBS, 5 parts by mass of FTR6125 manufactured by Mitsui Chemicals, Inc., and 5 parts by mass of Alcon P100 manufactured by Arakawa Chemical Co., Ltd. were dry-blended at a ratio of 5 parts by mass to obtain an adhesive layer resin composition.

  For the base material layer, a commercially available isotactic polypropylene (homopolypropylene) having a melt flow rate (MFR, 230 ° C., 2.16 kg) of 4 g / 10 min was used.

  The above-mentioned pressure-sensitive adhesive layer resin composition and the resin of the base material layer are put into a two-type two-layer T-die film forming machine equipped with two single screw extruders having a compression ratio of 4.5 and L / D = 25, and the pressure-sensitive adhesive layer is formed. Casting is performed so that the side is in contact with a metal cooling roll whose temperature is controlled to 30 ° C., and the film is formed by cooling and solidifying. A laminated film having an adhesive layer thickness of 4 μm, a base material layer thickness of 46 μm, and an overall thickness of 50 μm. Obtained.

(Example 2)
The composition of SEBS used in Example 1 was 10% by mass of styrene blocks at both ends, 80% by mass of ethylene / butylene block, 100% by mass of the intermediate phase, 20% by mass of styrene component, and ethylene / butylene ratio. Was used in the same manner as in Example 1, except that SEBS (weight average molecular weight: 160,000) having a molar ratio of 9:11 was used.

(Example 3)
The adhesive layer resin composition was obtained by dry blending 10 parts by weight of FTR8100 manufactured by Mitsui Chemicals, Inc. and 5 parts by weight of Alcon P100, manufactured by Arakawa Chemical Co., Ltd. in 85 parts by weight of SEBS used in Example 2 and 5 parts by weight of adhesive layer. A laminated film was prepared in the same manner as in Example 2, except that the thickness was 6 μm and the thickness of the base material layer was 44 μm.

(Example 4)
An adhesive layer resin composition was obtained by dry blending 85 parts by mass of Elastomer S1605 manufactured by Asahi Kasei Chemicals Corporation, 5 parts by mass of FTR6125 manufactured by Mitsui Chemicals, Inc., and 10 parts by mass of Alcon P100 manufactured by Arakawa Chemical Co., Ltd.

  A commercially available isotactic polypropylene having a melt flow rate (MFR, 230 ° C., 2.16 kg) of 8 g / 10 min was used for the base material layer.

  The above-mentioned pressure-sensitive adhesive layer resin composition and the resin of the base material layer are put into a two-type two-layer T-die film forming machine equipped with two single screw extruders having a compression ratio of 4.5 and L / D = 25, and the pressure-sensitive adhesive layer is formed. Casting is performed so that the side is in contact with a metal cooling roll whose temperature is controlled to 30 ° C., and is cooled and solidified to form a film. Obtained.

(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 2 except that Tuftec H1052 manufactured by Asahi Kasei Chemicals Corporation was used instead of SEBS used in Example 2.

(Comparative Example 2)
A laminated film was obtained in the same manner as in Comparative Example 1, except that the thickness of the adhesive layer was 5 μm and the thickness of the base material layer was 35 μm, using Dynaron 8300P manufactured by JSR Corporation instead of Tuftec H1052 used in Comparative Example 1.

(Comparative Example 3)
A laminated film having a thickness of 40 μm was obtained in the same manner as in Example 4 except that Dynalon 8903P manufactured by JSR Corporation was used instead of Tuftec L521 in Example 4.

  In the examples of the present invention, a laminated film having a small standard deviation of the initial adhesive strength and a small adherend dependency was obtained. On the other hand, in the comparative example, the adherence dependency on the adherend was large.

  When the laminated film of the present invention is used as a protective film, it can be protected and stored within a range of adhesive strength suitable for various adherends without depending on the shape and composition of the back surface of the optical prism sheet, and is dependent on the adherend. Is low, it can be suitably used as a surface protective film of an optical sheet.

Claims (8)

A laminated film having an adhesive layer containing a styrene-based elastomer as a main component on at least one side of a base material layer, wherein the styrene-based elastomer has a shear storage modulus G ′ and a shear loss modulus at 30 Hz to 30 ° C. G "satisfies the following formulas (1) and (2).
0.5 × 10 ⁶ ≦ G ′ (Pa) ≦ 2.0 × 10 ⁶ (1)
0.08 × 10 ⁶ ≦ G ″ (Pa) ≦ 0.18 × 10 ⁶ (2) 2. The laminated film according to claim 1, wherein a change width Δtanδ of the loss tangent tanδ at 1 Hz and 30 to 60 ° C. of the styrene-based elastomer is 0.05 or less. 3. The laminated film according to claim 1, wherein the styrene-based elastomer has a shear storage modulus G ′ at 1 Hz and 30 to 60 ° C. that satisfies the following expression (3).
0.6 × 10 ⁶ ≦ G ′ (Pa) ≦ 1.3 × 10 ⁶ (3) The laminated film according to any one of claims 1 to 3, wherein the base material layer includes a polyolefin resin. The laminated film according to any one of claims 1 to 4, wherein the adhesive layer contains a fatty acid amide compound in an amount of 0.01 to 10% by mass. The laminated film according to any one of claims 1 to 5, which is used for protecting the back surface of the prism sheet. The laminated film according to claim 6, wherein the back surface of the prism sheet is made of an ester resin or an acrylic resin. The laminated film according to claim 6, wherein the back surface of the prism sheet has an average surface roughness Ra of 0.01 to 1 μm.