JP2016169263A - Surface protective film, and prism sheet with surface protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film that has a high adhesive force (initial adhesive force) against a self-recovering prism sheet and the like, and can keep the high adhesive force even with the lapse of time; and a prism sheet with a surface protective film containing the surface protective film.SOLUTION: A surface protective film has a base material layer and an adhesive layer. The adhesive layer contains a styrene-based elastomer and a phenolic resin. The styrene-based elastomer is a copolymer having a structure represented by general formulae A, B and C or its hydrogenated product. A is an aromatic alkenyl polymer containing 80 wt.% or more of an aromatic alkenyl compound unit. B is a conjugated diene polymer that contains 50 wt.% or more of a conjugated diene compound unit, and contains 50 mol% or more of a conjugated diene compound-derived vinyl bond. C is an aromatic alkenyl-conjugated diene copolymer that contains 50 wt.% or more and less than 95 wt.% of the aromatic alkenyl compound unit and the conjugated diene compound unit.SELECTED DRAWING: None

Description

The present invention relates to a surface protective film that has a high adhesive force (initial adhesive force) even for a self-recovering prism sheet and the like and can maintain a high adhesive force over time. Moreover, this invention relates to the prism sheet with a surface protection film containing this surface protection film.

Conventionally, a surface having a base material layer and an adhesive layer laminated on one surface thereof in order to protect the surface of a member such as an optical device, a metal plate, a painted metal plate, a resin plate, or a glass plate A protective film (generally called a protective tape or the like) is widely used.

In particular, in recent years, surface protective films have been used to protect the surface of optical members for liquid crystal displays (for example, Patent Document 1). Some optical members have a concavo-convex shape on one or both surfaces, such as a prism sheet, a diffusion film, etc., and in order not to damage this concavo-convex shape, the surface is surfaced before using the optical member. It is protected with a protective film.
When a surface protective film is applied to the surface of such an adherend, a large contact area cannot be obtained, and peeling is likely to occur at the interface between the adherend and the surface protective film. A film is required.

In recent years, a so-called self-healing prism sheet has been proposed as a prism sheet that can be elastically recovered even when the uneven shape of the prism layer (prism surface) is deformed in a very small region during the manufacture of a liquid crystal display. ing.
However, the self-healing prism sheet is deformed in an extremely minute region of the prism layer due to the pressure applied when the surface protective film is applied, and then elastically recovers. There is a problem that it is likely to occur.
In recent years, prism sheets have been produced by a soft mold method using a resin mold for the purpose of cost reduction, and the release agent tends to bleed out on the prism sheet surface produced by the soft mold method. However, there is a problem that the surface protective film is likely to be peeled off over time. Such peeling is presumed to be caused by transfer of the release agent contained in the resin mold to the prism sheet.

International Publication No. 2010/029773 Pamphlet

An object of this invention is to provide the surface protection film which has high adhesive force (initial adhesive force) with respect to a self-recoverable prism sheet etc., and can maintain high adhesive force even if time passes. Moreover, an object of this invention is to provide the prism sheet with a surface protection film containing this surface protection film.

This invention is a surface protection film which has a base material layer and an adhesive layer, Comprising: The said adhesive layer contains a styrene-type elastomer and a phenol resin, The said styrene-type elastomer is general formula A-. It is a surface protective film which is a copolymer having a structure represented by BC or a hydrogenated product thereof.
A: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit at a content of 80% by weight or more B: Containing a conjugated diene compound unit at a content of 50% by weight or more and containing 50 vinyl bonds derived from the conjugated diene compound Conjugated diene polymer C contained at a content of at least mol%: an aromatic alkenyl compound unit and a conjugated diene compound unit, wherein the content of the aromatic alkenyl compound unit is 50 wt% or more and less than 95 wt% Certain aromatic alkenyl-conjugated diene copolymers The present invention is described in detail below.

The present inventor self-recovered by blending a specific styrene-based elastomer and a phenolic resin among tackifiers into the adhesive layer of the surface protective film having the base material layer and the adhesive layer. It has been found that a surface protective film having a high adhesive strength (initial adhesive strength) and capable of maintaining a high adhesive strength over time can be obtained even for prism sheets and the like, and the present invention has been completed.

The surface protective film of this invention has a base material layer and an adhesive layer.
The pressure-sensitive adhesive layer contains a styrene-based elastomer and a phenol resin, and the styrene-based elastomer is a copolymer having a structure represented by a general formula ABC or a hydrogenated product thereof.
A: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit at a content of 80% by weight or more B: Containing a conjugated diene compound unit at a content of 50% by weight or more and containing 50 vinyl bonds derived from the conjugated diene compound Conjugated diene polymer C contained at a content of at least mol%: an aromatic alkenyl compound unit and a conjugated diene compound unit, wherein the content of the aromatic alkenyl compound unit is 50 wt% or more and less than 95 wt% An aromatic alkenyl-conjugated diene copolymer Adhesive strength to a self-recovering prism sheet and the like by blending the above-mentioned styrenic elastomer and the above-mentioned phenol resin among tackifiers into the above-mentioned adhesive layer. A surface protective film having a high (initial adhesive strength) and capable of maintaining a high adhesive strength over time can be obtained.

The aromatic alkenyl polymer represented by A is an aromatic alkenyl polymer containing an aromatic alkenyl compound unit at a content of 80% by weight or more.
The aromatic alkenyl compound unit is a repeating unit derived from an aromatic alkenyl compound, and examples of the aromatic alkenyl compound include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, and p-ethylstyrene. , Divinylbenzene, 1,1-diphenylethylene, vinylnaphthalene, vinylanthracene, N, N-diethyl-p-aminoethylstyrene, vinylpyridine and the like. Of these, styrene is preferable because it is easily available industrially.

By setting the content of the aromatic alkenyl compound unit to 80% by weight or more, an appropriate holding force can be imparted to the pressure-sensitive adhesive layer, and the thermoplasticity of the pressure-sensitive adhesive layer can be improved. The recycling of the surface protection film becomes easier.
The “content” of the repeating unit means a weight ratio in terms of the monomer from which the repeating unit is derived, that is, a ratio (% by weight) of the weight of the monomer from which the repeating unit is derived relative to the weight of all monomers. To do.

The aromatic alkenyl polymer represented by A may contain a repeating unit other than the aromatic alkenyl compound unit.
Examples of the repeating unit other than the aromatic alkenyl compound unit include a repeating unit derived from a conjugated diene compound (for example, 1,3-butadiene, isoprene), a (meth) acrylic acid ester compound, and the like. Of these, 1,3-butadiene and isoprene are preferred because of their high copolymerizability with the aromatic alkenyl compound.

The conjugated diene polymer represented by B contains a conjugated diene compound unit at a content of 50% by weight or more, and a conjugated diene polymer containing a vinyl bond derived from a conjugated diene compound at a content of 50 mol% or more. It is.
The conjugated diene compound unit is a repeating unit derived from a conjugated diene compound. Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3- Pentadiene, 2-methyl-1,3-octadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, chloroprene Etc. These conjugated diene compounds may be used alone or in combination of two or more. Of these, 1,3-butadiene and isoprene are preferred because they have high polymerization reactivity and are easily industrially available.

By making the content rate of the said conjugated diene compound unit 50 weight% or more, the preferable effect that the softness | flexibility for an adhesive composition part improves can be exhibited. The content of the conjugated diene compound unit is preferably 70% by weight or more, and more preferably 80% by weight or more.

The conjugated diene polymer represented by B may contain a repeating unit other than the conjugated diene compound unit.
Examples of the repeating unit other than the conjugated diene compound unit include a repeating unit derived from an aromatic alkenyl compound. Of these, styrene is preferred because of its high copolymerizability with the conjugated diene compound.

By setting the content of the vinyl bond derived from the conjugated diene compound to 50 mol% or more, an adhesive layer having an excellent balance between tack and adhesive strength can be formed. The content of vinyl bonds derived from the conjugated diene compound is preferably 50 to 90 mol%, more preferably 60 to 80 mol%.
The “content ratio” of vinyl bonds means the total content ratio of 1,2-vinyl bonds and 3,4-vinyl bonds calculated by the Morello method using an infrared absorption spectrum.

The aromatic alkenyl-conjugated diene copolymer represented by C contains an aromatic alkenyl compound unit and a conjugated diene compound unit, and the content of the aromatic alkenyl compound unit is 50 wt% or more and 95 wt%. Is an aromatic alkenyl-conjugated diene copolymer.
When the styrene-based elastomer contains the aromatic alkenyl-conjugated diene copolymer represented by C, the adhesive strength with time of the surface protective film can be improved.
Examples of the aromatic alkenyl compound unit include the same aromatic alkenyl compound units as those contained in the aromatic alkenyl polymer represented by A described above. Examples of the conjugated diene compound unit include the same conjugated diene compound units as those contained in the conjugated diene polymer represented by B described above.

By setting the content of the aromatic alkenyl compound unit to 50% by weight or more and less than 95% by weight, the adhesive strength with time of the surface protective film can be improved. The minimum with the preferable content rate of the said aromatic alkenyl compound unit is 60 weight%, and a more preferable minimum is 70 weight%.
Further, the content of the aromatic alkenyl compound unit is preferably changed in a taper shape in the aromatic alkenyl-conjugated diene copolymer represented by C, that is, gradually increases or decreases continuously. Thereby, the time-dependent adhesive force of the surface protective film can be further improved.

Although the content rate of the said conjugated diene compound unit is not specifically limited, 5 weight% or more and less than 50 weight% are preferable. The upper limit with more preferable content rate of the said conjugated diene compound unit is 30 weight%.

The aromatic alkenyl-conjugated diene copolymer represented by C may contain a repeating unit other than the aromatic alkenyl compound unit and the conjugated diene compound unit.

The copolymer having the structure represented by the general formula ABC or the hydrogenated product thereof may be used alone or in combination of two or more.
Although there is no restriction | limiting in particular in the weight average molecular weight of the copolymer which has a structure represented by the said general formula ABC, or its hydrogenated substance, A preferable minimum is 30,000 and a preferable upper limit is 500,000. When the weight average molecular weight is less than 30,000, the copolymer or its hydrogenated product is removed from the copolymer or its hydrogenated product, and the copolymer or its hydrogenated product adheres to the production equipment in the drying step. Industrial production of the hydrogenated product may be difficult. When the weight average molecular weight exceeds 500,000, the solubility of the copolymer or its hydrogenated product in a solvent or the heat melting property is deteriorated, and it may be difficult to process the pressure-sensitive adhesive. The more preferable lower limit of the weight average molecular weight is 80,000, the more preferable upper limit is 300,000, the still more preferable lower limit is 100,000, and the more preferable upper limit is 200,000.

In the copolymer having the structure represented by the general formula A-B-C or a hydrogenated product thereof, the hydrogenated product has excellent heat resistance and weather resistance. Therefore, the general formula AB- The double bond (unsaturated bond) of the conjugated diene compound unit in the copolymer having a structure represented by C is preferably 80% or more, more preferably 90% or more, and still more preferably 95% or more saturated by hydrogenation. It is preferably converted to a bond.
The hydrogenation ratio (hydrogenation rate) means a hydrogenation rate calculated from ¹ H-NMR spectrum at 270 MHz using carbon tetrachloride as a solvent.

In the copolymer having the structure represented by the general formula ABC or the hydrogenated product thereof, the content of the aromatic alkenyl compound unit in the copolymer or the entire hydrogenated product has a preferable lower limit. 5% by weight and the preferred upper limit is 50% by weight. When the content of the aromatic alkenyl compound unit is less than 5% by weight, an appropriate holding force may not be imparted to the pressure-sensitive adhesive layer, or the pressure-sensitive adhesive layer may become too soft. When the content rate of the said aromatic alkenyl compound unit exceeds 50 weight%, the initial stage adhesive force or temporal adhesive force of a surface protective film may fall. The minimum with more preferable content rate of the said aromatic alkenyl compound unit is 30 weight%.

The method for producing the copolymer having the structure represented by the general formula ABC or the hydrogenated product thereof is not particularly limited. For example, the step of synthesizing the aromatic alkenyl polymer represented by the above A (A), a step (b) of synthesizing a copolymer having an AB structure by polymerizing a conjugated diene compound with the aromatic alkenyl polymer represented by A, and the AB structure. And a step (c) of synthesizing a copolymer having an A-B-C structure by polymerizing an aromatic alkenyl compound and a conjugated diene compound with respect to the copolymer having s. Furthermore, you may perform the process (d) which hydrogenates with respect to the copolymer which has the said ABC structure.
In particular, in the step (c), first, a conjugated diene compound is added to the copolymer having the AB structure to start polymerization, and the polymerization of the conjugated diene compound is in progress. Further, it is preferable to add an aromatic alkenyl compound (sequential polymerization). As a result, the content of the aromatic alkenyl compound unit changes in a tapered shape in the aromatic alkenyl-conjugated diene copolymer represented by C, that is, a copolymer that gradually increases or decreases, or a copolymer thereof. A hydrogenated product can be produced, and the adhesive strength with time of the surface protective film can be further improved.

Specific examples of the phenol resin include terpene phenol resins, alkylphenol resins, rosin-modified phenol resins, phenol-modified coumarone indene resins, phenol-modified formaldehyde resins, t-butylphenol resins, and t-butylphenol acetylene resins. . These phenol resins may be used independently and may use 2 or more types together. Of these, terpene phenol resins and hydrogenated products of terpene phenol resins are preferred.

Although content of the said phenol resin is not specifically limited, The preferable minimum with respect to 100 weight part of said styrene-type elastomers is 5 weight part, and a preferable upper limit is 50 weight part. When the content of the phenol resin is less than 5 parts by weight, the initial adhesive force or the temporal adhesive force of the surface protective film may be lowered. When the content of the phenol resin exceeds 50 parts by weight, the adhesive may remain (adhesive residue) on the surface of the adherend when the surface protective film is peeled off from the surface of the adherend. The minimum with more preferable content of the said phenol resin is 10 weight part, and a more preferable upper limit is 40 weight part.

The pressure-sensitive adhesive layer may contain additives such as a mold release agent, a softening agent, an antioxidant, and an adhesion progressing prevention agent, as necessary, for the purpose of controlling the adhesive force.

Although the thickness of the said adhesive layer is not specifically limited, A preferable minimum is 1 micrometer and a preferable upper limit is 40 micrometers. When the thickness of the pressure-sensitive adhesive layer is less than 1 μm, the initial pressure-sensitive adhesive force or the time-dependent pressure-sensitive adhesive force of the pressure-sensitive adhesive layer may be lowered. When the thickness of the pressure-sensitive adhesive layer exceeds 40 μm, it may be difficult to remove the surface protective film when peeling the surface protective film from the surface of the adherend. The minimum with more preferable thickness of the said adhesive layer is 2 micrometers, and a more preferable upper limit is 30 micrometers.

Although the said base material layer is not specifically limited, It is preferable to contain polyolefin resin.
Examples of the polyolefin resin include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-α-olefin copolymer, ethylene-ethyl acrylate copolymer, and ethylene-vinyl acetate copolymer. And polypropylene (homopolymer, random copolymer, block copolymer) and the like.
These can be used alone or in combination of two or more. Moreover, polyolefin which has a substituent may be sufficient as polyolefin, and resin other than polyolefin may be added. Furthermore, the end material of the polyolefin base material layer and the end material of the surface protection film which were produced in the manufacturing process of the surface protection film may be added.

The base material layer may be a single layer or a layer having two or more multilayer structures having different compositions.

The base material layer is within the range not impairing the effects of the present invention, additives such as antistatic agents, mold release agents, antioxidants, weathering agents, crystal nucleating agents, resins such as polyolefins, polyesters, polyamides, elastomers, etc. You may contain a modifier.

Although the thickness of the said base material layer is not specifically limited, A preferable minimum is 10 micrometers and a preferable upper limit is 100 micrometers. When the thickness of the base material layer is less than 10 μm, the protective performance as a surface protective film may be lowered. When the thickness of the base material layer exceeds 100 μm, the base material layer may remain wound. The minimum with more preferable thickness of the said base material layer is 20 micrometers, and a more preferable upper limit is 90 micrometers.

The method for producing the surface protective film of the present invention is not particularly limited. For example, another layer is formed on a layer obtained in advance by T-die molding or inflation molding by a known lamination method such as extrusion lamination or extrusion coating. A method of laminating, and a method of laminating each of the obtained films by dry lamination after each layer is made into a film, are mentioned above. From the viewpoint of productivity, the substrate layer and the pressure-sensitive adhesive layer are mentioned. Coextrusion molding in which each of the above materials is supplied to a multilayer extruder for molding is preferred, and T-die molding is more preferred from the viewpoint of thickness accuracy.

The surface protective film of the present invention may be used for protecting the surface of an adherend having a smooth surface, or may be used for protecting the surface of an adherend having an uneven shape on the surface.
The adherend having an uneven shape on the surface is not particularly limited, and examples thereof include optical members for liquid crystal displays such as prism sheets and diffusion films. Among these, the surface protective film of the present invention is preferably used by being attached to the prism layer of the prism sheet, and is manufactured by a soft mold method using a prism layer of a self-recovering prism sheet or a resin mold. More preferably, it is used by being affixed to the prism layer of the prism sheet thus prepared, and particularly preferably, it is affixed to the prism layer of the self-healing prism sheet. The surface protective film of the present invention has a high adhesive force (initial adhesive force) even with respect to a self-recovering prism sheet and the like, and can maintain a high adhesive force even if time passes.
In FIG. 1, the schematic diagram which shows an example of the state by which the surface protection film of this invention was affixed on the self-recovery prism sheet is shown. In FIG. 1, the surface protective film 1 is attached to the prism layer 7 of the self-healing prism sheet 4 having the prism layer 7 on the surface of the transparent film 6. The surface protective film 1 has a base material layer 2 and an adhesive layer 3.

A prism sheet with a surface protective film in which the surface protective film of the present invention is attached to the prism layer of the self-healing prism sheet is also one aspect of the present invention.
The self-healing prism sheet refers to a prism sheet that can elastically recover the concavo-convex shape even when the concavo-convex shape of the prism layer (prism surface) is deformed in a very small region at the time of manufacturing a liquid crystal display. JIS R1639 When the weight is removed after the prism sheet is deformed to a weight of 20 gf according to −5, it means a prism sheet whose deformation cannot be confirmed 3 seconds after the weight is removed.

According to the present invention, it is possible to provide a surface protective film that has a high adhesive force (initial adhesive force) with respect to a self-recovering prism sheet and the like and can maintain a high adhesive force even after a lapse of time. Moreover, according to this invention, the prism sheet with a surface protection film containing this surface protection film can be provided.

It is a schematic diagram which shows an example of the state by which the surface protection film of this invention was affixed on the self-recoverable prism sheet.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Synthesis example 1 of styrene elastomer (ABC structure))
(A) Synthesis of aromatic alkenyl polymer represented by A In a nitrogen-substituted reaction vessel, 500 parts by weight of degassed and dehydrated cyclohexane, 7.5 parts by weight of styrene as an aromatic alkenyl compound and 5 parts by weight of tetrahydrofuran Was added, and 0.10 parts by weight of n-butyllithium was added at a polymerization initiation temperature of 40 ° C. to carry out temperature rising polymerization.

(B) Synthesis of copolymer having AB structure After the polymerization conversion rate of styrene reached almost 100%, the reaction solution was cooled to 15 ° C., and then 85 weight of 1,3-butadiene as a conjugated diene compound Part was added, and further temperature rising polymerization was performed. When a partly extracted polymer was calculated by the Morero method using an infrared absorption spectrum, the content of vinyl bonds derived from the conjugated diene compound was 50 mol%.

(C) Synthesis of copolymer having ABC structure After the polymerization conversion of 1,3-butadiene reached almost 100%, the reaction solution was brought to 80 ° C., and then 0.375 as a conjugated diene compound. Part by weight, 7.125 parts by weight as an aromatic alkenyl compound were added, and further temperature rising polymerization was performed. After the polymerization conversion rate reached almost 100%, hydrogen gas was allowed to stand for 10 minutes while being supplied at 0.4 MPa-Gauge pressure. When a partly taken out polymer was analyzed by GPC, the weight average molecular weight was about 200,000.

(D) In a hydrogenation reaction vessel, 0.03 part by weight of diethylaluminum chloride and 0.06 part by weight of bis (cyclopentadienyl) titanium furfuryloxychloride were added and stirred. The hydrogenation reaction was started at a hydrogen gas supply pressure of 0.7 MPa-Gauge and a reaction temperature of 80 ° C. When the absorption of hydrogen was completed, the reaction solution was returned to room temperature and normal pressure, and extracted from the reaction vessel. A hydrogenated product of a copolymer having a BC structure was obtained.

(Synthesis example 2 of styrene elastomer (ABA structure))
(A) Synthesis of aromatic alkenyl polymer represented by A In a nitrogen-substituted reaction vessel, 500 parts by weight of degassed and dehydrated cyclohexane, 7.5 parts by weight of styrene as an aromatic alkenyl compound and 5 parts by weight of tetrahydrofuran Was added, and 0.10 parts by weight of n-butyllithium was added at a polymerization initiation temperature of 40 ° C. to carry out temperature rising polymerization.

(B) Synthesis of copolymer having AB structure After the polymerization conversion rate of styrene reached almost 100%, the reaction solution was cooled to 15 ° C., and then 85 weight of 1,3-butadiene as a conjugated diene compound Part was added, and further temperature rising polymerization was performed. When a partly extracted polymer was calculated by the Morero method using an infrared absorption spectrum, the content of vinyl bonds derived from the conjugated diene compound was 50 mol%.

(C) Synthesis of copolymer having ABA structure After the polymerization conversion of 1,3-butadiene reached almost 100%, the reaction solution was brought to 80 ° C, and then styrene 7 as an aromatic alkenyl compound. .5 parts by weight was added, and further temperature-programmed polymerization was performed. After the polymerization conversion rate of styrene reached almost 100%, it was left for 10 minutes while supplying hydrogen gas at a pressure of 0.4 MPa-Gauge. When a partly taken out polymer was analyzed by GPC, the weight average molecular weight was about 200,000.

(D) In a hydrogenation reaction vessel, 0.03 part by weight of diethylaluminum chloride and 0.06 part by weight of bis (cyclopentadienyl) titanium furfuryloxychloride were added and stirred. The hydrogenation reaction was started at a hydrogen gas supply pressure of 0.7 MPa-Gauge and a reaction temperature of 80 ° C. When the absorption of hydrogen was completed, the reaction solution was returned to room temperature and normal pressure, and extracted from the reaction vessel. A hydrogenated product of a copolymer having a B-A structure was obtained.

Example 1
100 parts by weight of the styrenic elastomer (ABC structure) obtained in Synthesis Example 1, 20 parts by weight of a tackifier (trade name “YS Polystar TH130”, terpene phenol resin, manufactured by Yashara Chemical Co., Ltd., softening point 130 ° C.) Were mixed with stirring using a lab plast mill twin screw extruder to prepare an adhesive composition.
Co-extrusion molding is performed by the T-die method using polyolefin resin (trade name “J715M”, polypropylene, manufactured by Prime Polymer Co., Ltd.) as the raw material for the base material layer, and the adhesive composition obtained above as the raw material for the adhesive layer. A surface protective film having a substrate layer of 36 μm and an adhesive layer of 4 μm was obtained.

(Example 2)
Surface protective film in the same manner as in Example 1 except that 20 parts by weight of a tackifier (trade name “YS Polystar TH130”, terpene phenol resin, manufactured by Yashara Chemical Co., Ltd., softening point 130 ° C.) was changed to 30 parts by weight. Got.

(Examples 3 and 4)
20 parts by weight of a tackifier (trade name “YS Polystar TH130”, terpene phenol resin, manufactured by Yashara Chemical Co., Ltd., softening point 130 ° C.) A surface protective film was obtained in the same manner as in Example 1 except that the softening point was 115 ° C. and the weight was changed to 30 parts by weight and 40 parts by weight.

(Comparative Examples 1-4)
Examples 1-4 with the exception that the styrene elastomer (ABC structure) obtained in Synthesis Example 1 was changed to the styrene elastomer (ABA structure) obtained in Synthesis Example 2. In the same manner, a surface protective film was obtained.

(Comparative Examples 5 and 6)
20 parts by weight of a tackifier (trade name “YS Polystar TH130”, terpene phenol resin, manufactured by Yashara Chemical Co., Ltd., softening point 130 ° C.), and a tackifier (trade name “AP100”, petroleum resin, manufactured by Arakawa Chemical Industries, Ltd., softened) A surface protective film was obtained in the same manner as in Example 1 except that the point was changed to 20 parts by weight and 40 parts by weight.

<Evaluation>
The following evaluation was performed about the surface protection film obtained by the Example and the comparative example. The results are shown in Table 1.

(1) The initial adhesive strength surface protective film was cut to a width of 25 mm. The cut surface protective film is applied to a prism layer (prism surface) of a self-recovering prism sheet (thickness 130 μm, made of acrylic resin, having a prism layer with a pitch 50 μm and a height 25 μm) at room temperature 23 ° C. and relative humidity 50%. Then, it was pasted at a speed of 300 mm / min using a 2 kg pressure-bonded rubber roller. After leaving in that state for 30 minutes, in accordance with JIS Z0237, the surface protective film was peeled off at a speed of 300 mm / min, and the 180-degree peel strength was measured.
○ More than 0.07N / 25mm △ More than 0.04N / 25mm and 0.07N / 25mm or less × 0.04N / 25mm or less

(2) The time-dependent adhesive force surface protective film was cut into a width of 25 mm. The cut surface protective film is applied to a prism layer (prism surface) of a self-recovering prism sheet (thickness 130 μm, made of acrylic resin, having a prism layer with a pitch 50 μm and a height 25 μm) at room temperature 23 ° C. and relative humidity 50% Then, it was pasted at a speed of 300 mm / min using a 2 kg pressure-bonded rubber roller. In this state, after standing at 23 ° C. for 2 weeks, the surface protective film was peeled off at a speed of 300 mm / min in accordance with JIS Z0237, and the 180-degree peel strength was measured.
○ More than 0.07 N / 25 mm Δ More than 0.04 N / 25 mm and 0.07 N / 25 mm or less × 0.04 N / 25 mm or less In Table 1, “floating” means that the surface protection film is from the surface of the self-recovering prism sheet. Indicates that it has lifted and peeled off.

The self-healing prism sheet used in the above (1) and (2) is in accordance with JIS R1639-5. When the weight is removed after the prism sheet is deformed until the weight is 20 gf, the weight is removed. When observed using an optical microscope (magnification 500 times) after 3 seconds, no deformation was confirmed.

According to the present invention, it is possible to provide a surface protective film that has a high adhesive force (initial adhesive force) with respect to a self-recovering prism sheet and the like and can maintain a high adhesive force even after a lapse of time. Moreover, according to this invention, the prism sheet with a surface protection film containing this surface protection film can be provided.

DESCRIPTION OF SYMBOLS 1 Surface protective film 2 Base material layer 3 Adhesive layer 4 Self-healing prism sheet 6 Transparent film 7 Prism layer

Claims (3)

A surface protective film having a base material layer and an adhesive layer,
The pressure-sensitive adhesive layer contains a styrene elastomer and a phenol resin,
The surface protection film, wherein the styrene elastomer is a copolymer having a structure represented by a general formula ABC or a hydrogenated product thereof.
A: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit at a content of 80% by weight or more B: Containing a conjugated diene compound unit at a content of 50% by weight or more and containing 50 vinyl bonds derived from the conjugated diene compound Conjugated diene polymer C contained at a content of at least mol%: an aromatic alkenyl compound unit and a conjugated diene compound unit, wherein the content of the aromatic alkenyl compound unit is 50 wt% or more and less than 95 wt% Certain aromatic alkenyl-conjugated diene copolymers The surface protective film according to claim 1, wherein the surface protective film is used by being attached to a prism layer of a self-recovering prism sheet. A prism sheet with a surface protective film, wherein the surface protective film according to claim 1 or 2 is attached to a prism layer of the self-healing prism sheet.

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