JP2007332329A - Surface protection film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protection film which is capable of protecting surely the exterior surface of the lens part of a prism sheet in which a plurality of practically trianglar prisms are fixed on one surface of a sheet, and which hardly causes damage to the lens part even when applied with a load owing to laminating or the like. <P>SOLUTION: The surface protection film to be stuck on the exterior surface of the undermentioned lens part of the prism sheet which, has a sheet and the plurality of lens parts each of which has a prism form comprising practically a triangle pole, and in which the plurality of lens parts are fixed on the one surface of the sheet at each side surface of the each triangle pole facing each ridge line thereof such that the each ridge line extending to the longitudinal direction of the triangle pole runs approximately parallel with one another, is characterized in that the above film has a polyolefin substrate laminated with a pressure-sensitive adhesive layer comprising a rubber-based resin component as a main component and in that the prism lens shall have a biting depth into the pressure-sensitive adhesive layer of less than 100% of the thickness of the pressure-sensitive adhesive layer in the case when the surface protection film is stuck to the above prism lens and thereafter is pressed for three days with a force of 0.123 N/cm<SP>2</SP>under 60°C atmosphere. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface protective film for protecting an outer surface of a prism type lens portion of a prism sheet used in an optical device, and more specifically, an adhesive made of a rubber-based resin component on one surface of a substrate. The present invention relates to a surface protective film in which layers are laminated, and prevents dust from adhering to or scratching the lens part.

  In order to protect the surface of various adherends, a surface protective film in which an adhesive layer is laminated on one surface of a sheet-like substrate is widely used. On the other hand, prism sheets in which a plurality of substantially prismatic prisms are fixed to one surface of a sheet are used in various optical devices. In this type of prism sheet, it is necessary to protect the outer surface of the lens portion before use. Therefore, the said surface protection film was used also for such a use.

  By the way, in the surface protective film for protecting the surface of the prism sheet, when the increase in adhesive force with time is large, it is difficult to smoothly peel the protective film from the surface of the lens portion of the prism sheet. Therefore, an acrylic pressure-sensitive adhesive having a large increase in adhesive strength over time has not been used, and a natural rubber pressure-sensitive adhesive has been mainly used.

  However, when natural rubber adhesive is used, there is a problem that weather resistance is not sufficient.

  On the other hand, the prism sheets with the surface protective film attached are generally stacked and stored in units of several tens of sheets until they are incorporated into a product. In this case, the apex of the lens portion of the prism sheet disposed below may be destroyed due to the load of the prism sheet disposed above, and the optical quality may deteriorate. This is because the ridge line of the lens of the prism sheet bites into the adhesive layer of the surface protective film due to the load, the ridge line of the lens portion collides with the base material of the surface protective film, and the load distribution / relaxation effect by the adhesive layer is no longer present. This may be due to exceeding the limit. In order to solve this problem, it is considered that the thickness of the pressure-sensitive adhesive layer may be sufficiently increased. However, increasing the thickness of the pressure-sensitive adhesive layer is not only disadvantageous because it rebounds from the manufacturing cost, but also increases the depth of penetration of the lens portion into the pressure-sensitive adhesive layer, which may increase the adhesive strength over time.

In order to solve such a problem, the following Patent Document 1 discloses a surface protective film in which an adhesive layer having a thickness of 10 μm or more mainly composed of a styrene-based elastomer is used instead of natural rubber, It is described that a sufficient protection function and adhesion characteristics for the adherend can be satisfied at the same time. However, when the present inventors examined, even if the adhesion layer using the styrene-type elastomer of patent document 1 was used for the surface protection of a prism sheet, depending on selection of the material used for an adhesion layer, it is a prism over time. It was found that the surface bites into the adhesive layer and the peel force increases.
JP 2000-80336 A

  An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and a prism sheet in which a plurality of substantially triangular prisms are fixed on one surface of the sheet without increasing the thickness of the adhesive layer. It is an object of the present invention to provide a surface protective film that can reliably protect the outer surface of the lens part and that is less likely to damage the lens part even when a load is applied due to lamination or the like.

According to the present invention, a sheet and a plurality of prism-shaped lens portions each substantially consisting of a triangular prism, the ridge lines extending in the length direction of the triangular prism are substantially mutually connected. A surface protective film that is affixed to the outer surface of the lens portion of the prism sheet that is fixed to one surface of the sheet on the side surface facing the ridge line so as to be parallel to the base material made of synthetic resin A pressure-sensitive adhesive layer mainly composed of a rubber-based resin component is laminated. When a surface protective film is attached to the prism lens, it is pressed for 3 days with a force of 0.123 N / cm ^{2 in} an atmosphere of 60 ° C. A surface protective film is provided in which the depth of penetration of the prism lens into the adhesive layer is less than 100% of the thickness of the adhesive layer. Even if a load is applied from the surface protective film side to the prism sheet side, the depth of penetration of the lens part into the adhesive layer is less than 100% of the adhesive layer thickness, so the ridge line located at the apex of the lens part Damage to the part is difficult to occur.

Preferably, a 6 μm thick adhesive layer is formed on a synthetic resin substrate to form a surface protective film, and a cylinder made of an acrylic resin having a diameter of 100 μm is perpendicular to the adhesive layer surface in an atmosphere of 60 ° C. The hardness of the adhesive layer is set so that the depth of biting into the cylindrical adhesive layer is 5 μm or less when pressed with a force of 100 mN for 1 minute. In this case, the biting of the prism sheet into the surface protective film adhesive layer can surely be less than 100%. Such adhesive layer hardness is achieved by setting the shear storage modulus of the adhesive layer at a frequency of 10 Hz to 5 × 10 ⁵ Pa or more at 70 ° C. Moreover, as for the adhesion layer thickness of the surface protection film of this invention, it is desirable to set to 3-10 micrometers.

  In the surface protective film according to the present invention, the rubber-based resin component is preferably (1) a block copolymer of a styrene polymer block (A) and a conjugated diene polymer block (B), (2) A block copolymer of a styrene polymer block (A) and a random copolymer block (B ′) of a styrene monomer and a conjugated diene monomer, or (3) styrene having a hydrogenated product thereof as a main skeleton Based elastomer.

  In the surface protective film according to the present invention, preferably, in the styrene elastomer, the content ratio of the styrene monomer-derived component is in the range of 5 to 20% by weight. In this case, adhesive residue at the time of peeling from the prism sheet can be surely prevented, and further, it can be easily and reliably attached to the lens surface of the prism sheet.

  Details of the present invention will be described below.

(Prism sheet)
The adherend to which the surface protective film of the present invention is applied is a prism sheet. A prism sheet is a side surface in which a plurality of substantially prismatic prism-shaped lenses on one surface of the sheet are parallel to each other with one ridge line extending in the length direction of the prism. And has a fixed structure. Such prism sheets are widely used in optical devices such as liquid crystal displays.

  Examples of the material constituting the prism-shaped lens unit include, but are not limited to, a resin having translucency, such as an acrylic resin or polycarbonate.

  Moreover, although the material which comprises the said sheet | seat generally uses polyester and a polycarbonate widely, what is necessary is just a thing excellent in the optical characteristic, and it does not restrict | limit.

  Examples of the prism sheet manufacturing method include a method of forming a lens part made of electromagnetic radiation curable resin on a sheet, or a sheet and a thermoplastic resin for lens part formation are melt-extruded into a sheet shape, and then the lens shape is embossed. A method of forming is mentioned. In the latter method, the difference between the sheet and the lens portion forming resin does not matter.

  The lens portion of the prism sheet has a prism shape substantially consisting of a triangular prism. More specifically, as shown in FIG. 1, the prism sheet 1 has a structure in which a plurality of triangular prism-shaped lens portions 3 are integrated on one surface of a flat sheet 2. The lens unit 3 has a substantially triangular prism shape. A plurality of lens portions 3 are closely arranged in parallel so that the ridge lines of the triangular prism are parallel to each other. The outer surface of the prism-shaped lens portion 3 is protected by the surface protective film of the present invention. For example, as shown in a cross-sectional view in FIG. 2, the surface protective film 4 is affixed to the portion of the prism sheet 1 where the lens portion 3 is provided. The surface protective film 4 includes a base material 5 and an adhesive layer 6 provided on one surface of the base material 5, and the plurality of lens portions 3 of the prism sheet 1 are provided from the adhesive layer 6 side. Affixed to the side. Therefore, the surface protective film of the present invention is stuck across the ridgeline 3c except for the side surface fixed to the sheet 2 of the prism-shaped lens unit 3. The triangular cross-sectional shape of the lens portion 3 of the triangular prism is a triangle, and this triangle is preferably an isosceles triangle with the side fixed to the sheet as the base, and the apex angle is about 90 ± 10 degrees. Is preferable, and about 90 ± 5 degrees is more preferable.

  In addition, the side surface in the prism shape of a triangular prism shall mean the three side surfaces extended in the length direction of a triangular prism.

  In a plurality of substantially triangular prisms of the prism sheet to which the surface protective film according to the present invention is applied, the distance between adjacent prisms, that is, the prism pitch is preferably about 10 to 1000 μm, more preferably. 10 to 500 μm. Further, the height of the triangular prism is determined by the pitch and apex angle of each triangular prism.

(Configuration of surface protection film)
In the surface protective film of the present invention, an adhesive layer made of a rubber-based resin component is laminated on one surface of a synthetic resin substrate. That is, the surface protective film according to the present invention is an adhesive film having a peelable adhesive layer on one side.

In the present invention, the depth of penetration into the adhesive layer of the prism lens when the surface protective film is applied to the prism lens and then pressed for 3 days with a force of 0.123 N / cm ^{2 in} an atmosphere of 60 ° C. Is set such that the hardness of the adhesive layer is less than 100% of the thickness of the adhesive layer. Therefore, the surface protective film of the present invention is attached to the prism sheet, and, for example, dozens of prism sheets are stacked and stored, and even if the load of the upper prism sheet is applied to the lower prism sheet, Excessive biting of the lens part of the prism sheet is reliably suppressed. Thereby, the lens surface of the prism sheet is hardly damaged.

  Preferably, a 6 μm thick adhesive layer is formed on a synthetic resin substrate to form a surface protective film, and a cylinder made of acrylic resin having a diameter of 100 μm is perpendicular to the adhesive layer surface in an atmosphere at 60 ° C. In addition, the hardness of the adhesive layer is set so that the depth of biting into the cylindrical adhesive layer is 5 μm or less when pressed with a force of 100 mN for 1 minute. In this case, before the surface protective film is actually applied to the prism sheet, the hardness of the pressure-sensitive adhesive layer can be evaluated only by treating the manufactured surface protective film with a cylinder having a diameter of 100 μm for 1 minute under the above conditions. At the same time, when the hardness of the pressure-sensitive adhesive layer is set as described above, the biting of the prism sheet into the surface protective film pressure-sensitive adhesive layer can be surely made less than 100%.

Such adhesive layer hardness is achieved when the shear storage modulus of the adhesive layer at a frequency of 10 Hz is 5 × 10 ⁵ Pa or more at 70 ° C. Moreover, as for the adhesion layer thickness of the surface protection film of this invention, it is desirable to set to 3-10 micrometers.

  In setting the hardness range of the adhesive layer, the thickness of the adhesive layer is set to 3 μm or more and 10 μm or less for the following reason.

  When the thickness of the pressure-sensitive adhesive layer is 10 μm or more, the depth of penetration of the prism sheet into the lens portion is increased, the pressure-sensitive adhesive force may be excessively increased with time, and the cost of the surface protective film is increased. On the other hand, when the thickness of the pressure-sensitive adhesive layer is reduced to less than 3 μm, the function of dispersing and relaxing external stress by the pressure-sensitive adhesive layer is not sufficient, and the protective effect by the surface protective film may be reduced.

  In the present invention, the adhesive layer comprises a rubber-based resin component, and the rubber-based resin component is preferably a block copolymer of styrene-based polymer block (A) and conjugated diene-based polymer block (B), styrene. A block copolymer of a polymer block (A), a random copolymer block (B ′) of a styrene monomer and a conjugated diene monomer, or a styrene elastomer having a hydrogenated product thereof as a main skeleton Configured.

  More specifically, the styrene elastomer is the following styrene elastomers (1) to (3).

(1) A styrene elastomer having a main skeleton of a block copolymer of a styrene polymer block (A) and a conjugated diene copolymer block (B). For example, it can be represented by a general formula of _AB , _ABAA , (AB) _n , or (AB) _nX . However, X shows the residue of a coupling agent and n is an integer greater than or equal to 1.

(2) A styrene elastomer having a main skeleton of a block copolymer comprising a styrene polymer block (A) and a random copolymer block (B ′) of a styrene monomer and a conjugated diene monomer. For example, (2-1) (A) and (B ′) one block each bonded: AB ′ block copolymer, (2-2) styrene gradually increased among styrene monomer and conjugated diene monomer Including a tapered block (C): AB′-C block copolymer, (2-3) including a styrenic polymer block (A) instead of the tapered block (C): AB ′ -A block copolymer (2-4) these repeated and the coupled _{ones: (a-B ') n} , (a-B') n X, (a-B'-C) n X, ( A-B'-A) can be represented by a general formula such as nX. However, X shows the residue of a coupling agent and n is an integer greater than or equal to 1.

  (3) A styrenic elastomer comprising a hydrogenated product of the styrenic elastomers of (1) and (2) above.

  In the styrene elastomer (including hydrogenated product), the content ratio of the styrene monomer and the conjugated diene monomer, which are constituent components, is preferably 5:95 to 20:80 by weight. When the styrene content is less than 5% by weight, the cohesive strength of the pressure-sensitive adhesive is reduced, so that adhesive residue may be formed on the adherend during re-peeling. Affixing to the adherend may be difficult.

  In the hydrogenated product of (1) and (2) above, a conjugated diene moiety in the conjugated diene polymer block (B) and the random copolymer block (B ′) of the styrene monomer and conjugated diene monomer. It is preferable that at least 80% of the double bond is saturated by hydrogenation, more preferably 90% or more, still more preferably 95 to 100%. If the ratio of hydrogenation is less than 80%, heat resistance and weather resistance may be deteriorated.

  The weight average molecular weight of the styrene elastomer is preferably 30,000 to 400,000, more preferably 50,000 to 200,000 in terms of polystyrene by GPC method. If the weight average molecular weight is less than 30,000, the cohesive force of the adhesive is reduced, and thus adhesive residue may be generated on the adherend during re-peeling. If it exceeds 400,000, the adhesive force is insufficient and the fluidity is poor. There is a risk.

In the present invention, as described above, the thickness of the pressure-sensitive adhesive layer is preferably 3 μm or more and 10 μm or less, and after the surface protective film is attached to the prism lens, it is 0.123 N / in under an atmosphere of 60 ° C. The hardness of the pressure-sensitive adhesive layer is set so that the depth of penetration of the prism lens into the pressure-sensitive adhesive layer when pressed for 3 days with a force of cm ² is less than 100% of the thickness of the pressure-sensitive adhesive layer. In order to realize such a configuration, the composition of the pressure-sensitive adhesive layer is, for example, SEBS or the like as a styrene-based elastomer, and 3 to 15 parts by weight of a tackifier with respect to 100 parts by weight of a styrene-based elastomer, preferably The composition mix | blended in 5-10 weight part can be used.

  Examples of the tackifier include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic / aromatic copolymer systems and alicyclic copolymers, and coumarone-indene resins. , Terpene resin, terpene phenol resin, rosin resin such as polymerized rosin, (alkyl) phenol resin, xylene resin or hydrogenated products thereof are generally used for adhesives Things can be used without any particular restrictions. These tackifiers may be used alone or in combination of two or more.

  Of course, a hydrogenated tackifier is preferred in order to improve peelability and weather resistance. In addition, as a tackifier, what is marketed as a blend with an olefin resin can also be used.

  A softening agent may be added to the adhesive layer of the surface protective film according to the present invention. By adding the softening agent, the adhesive force of the pressure-sensitive adhesive layer can be increased. Examples of the softening agent include low molecular weight diene polymers, polyisobutylene, hydrogenated polyisoprene, hydrogenated polybutadiene, and derivatives thereof. Examples of the derivative include those having an OH group or a COOH group at one or both ends, and specifically, hydrogenated polybutadiene diol, hydrogenated polybutadiene monool, hydrogenated polyisoprene diol, hydrogenated polyisoprene. Monool etc. are mentioned. In particular, hydrogenated products of diene polymers such as hydrogenated polybutadiene and hydrogenated polyisoprene, olefinic softeners, and the like are preferable for the purpose of suppressing improvement in adhesion to an adherend. Specifically, “Kuraprene LIR-200” manufactured by Kuraray Co., Ltd. is available. These softeners may be used alone or in combination of two or more.

  The molecular weight of the softening agent is not particularly limited. However, if the molecular weight is too small, the softening agent may move from the adhesive layer to the adherend side, or the peeling force may increase. On the other hand, if the molecular weight of the softening agent becomes too large, the effect of improving the adhesive strength may be reduced. Therefore, the number average molecular weight of the softening agent is preferably about 5,000 to 100,000, more preferably 10,000 to 50,000.

  If the amount of the softener added is too large, adhesive residue tends to occur at high temperatures. Accordingly, the softening agent is preferably 40 parts by weight or less, more preferably 20 parts by weight or less, still more preferably 10 parts by weight or less, with respect to 100 parts by weight of the total of the styrene-based elastomer and the softening agent.

  Moreover, you may add another additive to the adhesion layer of the surface protection film of this invention as needed in the range which does not inhibit achievement of the subject of this invention. Examples of such additives include ultraviolet absorbers, antioxidants, and adhesion progress inhibitors. The ultraviolet absorber is not particularly limited, and examples thereof include commonly used ones such as salicylic acid series, benzophenone series, benzotriazole series, and cyanoacrylate series. The antioxidant is not particularly limited, and examples thereof include those commonly used such as phenolic (monophenolic, bisphenolic, and high-molecular phenolic), sulfur, and phosphorus. Examples of the anti-adhesion agent include fatty acid amides, polyethyleneimine long-chain alkyl grafts, soybean oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 251”), tall oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 6300”, etc.).

  The surface protective film according to the present invention can be obtained by laminating a rubber-based adhesive layer made of the above-mentioned adhesive composition on a synthetic resin substrate.

  The synthetic resin substrate is not particularly limited, and for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer. Polymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene-n-butyl acrylate copolymer, polypropylene homopolymer, random copolymer, block copolymer And olefin resins such as polyethylene terephthalate and polybutylene terephthalate, nylon 6, nylon 6,6, polyamides such as partially aromatic polyamide, polyvinyl chloride, and polyvinylidene chloride. These may be used independently and 2 or more types may be used together. Of these, olefin resins such as polyethylene and polypropylene are preferred.

  The thickness of the synthetic resin substrate may be configured to have sufficient strength to protect the lens portion of the prism sheet, and varies depending on the dimensions and surface properties of the prism lens, but is in the range of 20 to 100 μm. If it is designed in.

  The manufacturing method of the surface protection film of this invention is not specifically limited. For example, a method of laminating and integrating the materials used for the synthetic resin base material and the adhesive layer by co-extrusion, and laminating and integrating the adhesive layer on one surface of the synthetic resin base material formed in advance. The method etc. are mentioned.

  As a method of laminating and integrating the synthetic resin base material and the pressure-sensitive adhesive layer by coextrusion, a known method such as an inflation method or a T-die method is used, and a method of laminating the pressure-sensitive adhesive layer on the base material layer For example, a solution coating method for applying a pressure-sensitive adhesive solution, a dry lamination method, an extrusion coating method using a T-die, or the like can be used. Among these, coextrusion by the T-die method is preferable from the viewpoint of quality and economy. In the case of the solution coating method, it is preferable to perform a surface treatment such as primer application on the base material in advance in order to increase the bonding strength between the base material layer and the pressure-sensitive adhesive layer.

In the surface protective film according to the present invention, the depth of penetration of the lens portion into the adhesive layer when pressed against the prism lens with a force of 0.123 N / cm ² under an atmosphere of 60 ° C. for 3 days is the thickness of the adhesive layer. Since the hardness of the pressure-sensitive adhesive layer is set to be 100% or less, even if a large number of prism sheets to which the surface protective film is applied are stacked and stored, damage to the lens top of the prism sheet is unlikely to occur.

  Hereinafter, the present invention will be clarified by giving specific examples and comparative examples of the present invention. In addition, this invention is not limited to a following example.

Example 1
As shown in Table 1 below, 100 parts by weight of a styrene elastomer made of a hydrogenated styrene-butadiene copolymer (manufactured by Kraton Polymer Co., Ltd., product number: Kraton G1657, ethylene / butylene ratio = 2.6) As a tackifier, 5 parts by weight of Alcon P-125 manufactured by Arakawa Chemical Industries, which is an alicyclic petroleum resin, was blended to obtain a pressure-sensitive adhesive composition. The shear storage modulus of the obtained pressure-sensitive adhesive composition was -50 ° C to + 150 ° C at a frequency of 10 Hz and a temperature increase rate of 6 ° C / min using a dynamic viscoelasticity spectrometer (product number: DVA200, manufactured by IT Measurement Control Co., Ltd.). It measured in the range of.

  The results are shown in Table 1 below.

  On the other hand, a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive composition and a base material made of polypropylene were coextruded by a T-die method, and a polypropylene base material having a thickness of 40 μm and a pressure-sensitive adhesive layer having a thickness of 6 μm were laminated and integrated. A surface protective film was produced.

  About this surface protection film, 1) Adhesive layer deformation amount due to biting of the cylinder, 2) Evaluation of biting into the lens part of the prism sheet, and 3) Initial adhesive strength were evaluated as follows. Further, in contrast to the evaluation of biting into the lens part of 2) the prism sheet, 4) evaluation of prism flaws was performed in the following manner. Further, 5) adhesive strength with time and 6) adhesive residue were evaluated as follows.

1) Deformation amount of adhesive layer by biting in a cylinder Cut the obtained surface protective film into 5cm x 5cm size and deformed by load test with micro hardness tester (Fisherscope H-100C; manufactured by Fisher Instruments) The amount was measured. The measurement conditions were a measurement temperature of 60 ° C., a load speed of 1 mN / s, a maximum load of 100 mN, and a holding time of 1 minute. In this case, in the measurement of the deformation amount with a microhardness meter, the deformation amount is measured by pressing a probe made of an acrylic resin having a diameter of 100 μm and a diamond tip from the adhesive layer side of the surface protective film.

2) Evaluation of biting into the lens part of the prism sheet The obtained surface protective film was attached so as to cover the lens surface of the prism sheet to prepare a test piece. As the prism sheet, a lens part was made of acrylic resin, the sheet was made of polyethylene terephthalate having a thickness of 150 μm, and a prismatic lens part having a height of 23 μm and a width of 50 μm was prepared. At the time of sticking, a laminator (Laminator-MRK-650Y; manufactured by MCK Co., Ltd.) is used, the width of the surface protective film is 200 mm, the sticking pressure is 2.0 kg / cm ² (about 19.6 N / cm ² ), the sticking speed is 300 mm / Pasted in minutes. The test piece is cut into a size of 10 cm × 15 cm to form film samples, each film sample is stacked on top of each other, the top and bottom of the five-layer stack are sandwiched between smooth metal plates, and a weight is placed on the upper metal plate. A total load of 1.8 kg (about 17.64 N) was applied, and the plate was left in an oven at 60 ° C. and a humidity of 90% RH for 3 days. Three days later, the test piece was taken out, the cross section was cut, the cross section was observed with a scanning electron microscope (SEM), and the depth of biting into the adhesive layer of the lens portion of the prism sheet was measured.

3) Initial adhesive strength The obtained surface protective film was attached so as to cover the lens surface of the prism sheet in the same manner as in 2) above, and was left in a room at 23 ° C. ± 2 ° C. for 30 minutes. Thereafter, in accordance with JIS Z 0237, 180 degree peel strength at 25 mm width (unit: N) was measured at a peel rate of 300 mm / min and 30 m / min in the direction parallel to the ridge line of the prism, respectively. did.

4) Evaluation of Prism Scratch During the test in 2), the surface protective film taken out from the oven was peeled off from the prism sheet, and the presence or absence of bright spots generated by scratches on the lens surface of the prism sheet was visually observed. In Table 1 below, a sample in which many scratches are observed is marked with ×, Δ when slightly observed, and ○ when not observed at all.

5) Adhesive strength with time After the test piece obtained in the same manner as in 2) above was left in a room at 60 ° C. ± 2 ° C. for 1 week, 180 ° peel strength at 25 mm width was measured according to JIS Z 0237. Measurement was performed at 30 m / min. When the obtained 180-degree peel strength, that is, the adhesive strength with time, is 2 times or less of the initial adhesive strength measured in 1), ◯ is given, and when it exceeds 2 times, X is marked.

6) Adhesive residue Upon the evaluation in 5) above, the presence or absence of adhesive residue on the lens surface of the prism sheet after peeling was visually observed.

  The results are shown in Table 1 below.

(Example 2 and Example 3, and Comparative Examples 1-4)
A surface protective film was prepared and evaluated in the same manner as in Example 1 except that the composition and thickness of the adhesive layer were changed as shown in Table 1 below. Moreover, about the comparative examples 3 and 4, the surface protection film whose adhesion layer thickness is 10 micrometers and 3 micrometers, respectively was also produced, and it used for evaluation of 2) -6). In Table 1, 1321P indicates “Dynalon 1321P” (an elastomer having a styrene polymer block and a hydrogenated random copolymer block of styrene and butadiene) manufactured by JSR. All tackifiers were Alcon P-125.

As is apparent from Table 1, the deformation amount of the adhesive layer when the pressure of 100 mN was applied to a 6 μm thick adhesive at 60 ° C. with a cylinder of 100 μm in diameter and pressed for 1 minute was 5 μm or less. 3, the penetration depth of the lens portion of the prism sheet of the adhesive layer when pressed for 3 days with a force of 0.123 N / cm ² in an atmosphere of 60 ° C. is less than 100% of the thickness of the adhesive layer I understand. In this case, no damage was observed on the prism sheet lens portion after peeling, and no surface contamination was observed.

On the other hand, in Comparative Examples 1 and 2 in which the deformation amount of the adhesive layer exceeds 5 μm when a load of 100 mN is applied to a cylinder having a diameter of 100 μm at 60 ° C. to a 6 μm thick adhesive and pressed for 1 minute, The depth of penetration into the adhesive layer of the lens portion of the prism sheet of the adhesive layer when pressed for 3 days with a force of 0.123 N / cm ^{2 in} an atmosphere becomes 100% of the thickness of the adhesive layer, Large scratches were observed on the lens.

On the other hand, in Comparative Example 3, the deformation amount of the adhesive layer due to a load of 100 mN for 1 minute by a cylinder having a diameter of 100 μm at 60 ° C. is 5.3 μm, and the prism with a force of 0.123 N / cm ^{2 in} an atmosphere at 60 ° C. The depth of penetration of the adhesive layer into the lens part when pressed against the sheet for 3 days was less than 100% of the thickness of the adhesive layer, but the thickness of the adhesive layer itself was as thick as 10 μm, so the amount of penetration was not deep. Did not get. For this reason, the adhesive strength with time increased, and adhesive residue was generated during peeling.

In Comparative Example 4, the deformation amount of the adhesive layer due to a 100 mN load for 1 minute with a cylinder having a diameter of 100 μm at 60 ° C. is 5 μm or less, but since the thickness of the adhesive layer is as thin as 3 μm, 0.123 N in an atmosphere at 60 ° C. When the pressure layer was pressed against the prism sheet with a force of / cm ² for 3 days, the depth of penetration of the adhesive layer into the lens portion was 100% of the thickness of the adhesive layer, and the lens portion of the prism sheet after peeling was greatly damaged. .

FIG. 1 is a perspective view of a prism sheet to which the present invention is applied. FIG. 2 is a cross-sectional view of a structure in which a surface protective film according to an embodiment of the present invention is attached to a prism sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Prism sheet 2 ... Sheet 3 ... Lens part 3c ... Ridge line 4 ... Surface protection film 5 ... Base material 6 ... Adhesive layer

Claims (5)

A sheet and a plurality of prism-shaped lens portions each substantially consisting of a triangular prism, and the plurality of lens portions are arranged such that one ridge line extending in the length direction of the triangular prism is substantially parallel to each other. A surface protective film that is affixed to the outer surface of the lens portion of the prism sheet that is fixed to one surface of the sheet on the side surface facing the ridgeline,
An adhesive layer mainly composed of a rubber-based resin component is laminated on a synthetic resin base material.
After the surface protective film is attached to the prism lens, the depth of penetration into the adhesive layer of the prism lens when the surface protective film is pressed with a force of 0.123 N / cm ² for 3 days in an atmosphere of 60 ° C. is 100 of the adhesive layer thickness. Surface protective film that is less than%.   A 6 μm thick adhesive layer is formed on a synthetic resin substrate to form a surface protective film, and a 100 μm diameter cylinder made of acrylic resin having a diameter of 100 μm is perpendicular to the adhesive layer surface in an atmosphere of 60 ° C. The surface protective film according to claim 1, wherein the depth of biting into the cylindrical adhesive layer is 5 μm or less when pressed for 1 minute. The surface protective film according to claim 1, wherein the adhesive layer has a shear storage elastic modulus of 5 × 10 ⁵ Pa or more at 70 ° C. at a frequency of 10 Hz.   The rubber resin component is (1) a block copolymer of a styrene polymer block (A) and a conjugated diene polymer block (B), (2) a styrene polymer block (A) and a styrene monomer. A random copolymer block with a conjugated diene monomer and a block copolymer with a block (B '), or (3) a styrene elastomer having these hydrogenated products as a main skeleton. The surface protective film as described.   The surface protection film according to any one of claims 1 to 4, wherein the styrene-based elastomer has a content ratio of a component derived from a styrene-based monomer in the range of 5 to 20% by weight.

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