JP7101039B2 - Surface protection film for diffusion film and diffusion film with surface protection film - Google Patents

Description

INDUSTRIAL APPLICABILITY According to the present invention, a high adhesive force (initial adhesive force) can be exerted on a diffusion film having a rough surface, the adhesive does not easily proceed even with time or at a high temperature, and adhesive residue is less likely to occur when peeling from the diffusion film. The present invention relates to a surface protective film for a diffusion film. The present invention also relates to a diffusion film with a surface protection film including the surface protection film for the diffusion film.

Conventionally, a surface having a base material layer and an adhesive layer laminated on one surface 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. Protective films (generally sometimes referred to as protective tapes and the like) are widely used (for example, Patent Documents 1 to 3).
Among them, the surface protective film is used to protect the surface of an optical member for a liquid crystal display. Some optical members have an uneven shape on one side or both sides, such as a prism sheet and a diffusion film, and in order not to damage the uneven shape, the surface is surfaced prior to the use of the optical member. It is protected by a protective film.

Japanese Unexamined Patent Publication No. 1-129085 Japanese Unexamined Patent Publication No. 6-1958 Japanese Unexamined Patent Publication No. 8-12952

In recent years, with the thinning of liquid crystal displays, it has been proposed to make the surface of the diffusion film rougher than before so that the diffusion film will not be damaged even if it bites a foreign substance. For this reason, there is a problem that the surface protective film does not adhere to the diffusion film having a rougher surface than the conventional one, or that the surface protective film floats at the interface between the diffusion film and the surface protective film.

On the other hand, if a surface protective film having a high adhesive strength is used so that it can be attached to a diffusion film having a rougher surface than before, between the diffusion film and the adhesive layer of the surface protective film over time or at high temperature. There is a problem that the adhesive strength increases due to the increase in the contact area of the film, that is, the so-called adhesive diffusion progresses. In addition, due to the progress of adhesion, adhesive residue may be generated when the surface protective film is peeled from the diffusion film.

INDUSTRIAL APPLICABILITY According to the present invention, a high adhesive force (initial adhesive force) can be exerted on a diffusion film having a rough surface, the adhesive does not easily proceed even with time or at a high temperature, and adhesive residue is less likely to occur when peeling from the diffusion film. It is an object of the present invention to provide a surface protective film for a diffusion film. Another object of the present invention is to provide a diffusion film with a surface protection film including the surface protection film for the diffusion film.

The present invention is a surface protective film for a diffusion film for protecting the diffusion film by being attached to a diffusion film having a surface having an arithmetic average roughness (Ra) of 0.3 μm or more and 15 μm or less, and is a base material layer. The pressure-sensitive adhesive layer has a storage elasticity E'of 3.0 MPa or less at 25 ° C. and a storage elasticity E'at 100 ° C. of 0.4 MPa or more on the surface for a diffusion film. It is a protective film.
Hereinafter, the present invention will be described in detail.

The present inventors have studied a surface protective film for a diffusion film having a base material layer and an adhesive layer. Then, the present inventors adjust the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer to a specific range to have an adhesive force (initial adhesion) on a diffuse film having a rough surface. It was found that it is possible to suppress the adhesion progress over time or at high temperature while improving the force). The present inventors have adjusted the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer to a specific range when peeling the surface protective film for a diffusion film from the diffusion film. We have found that the adhesive residue of the film can be reduced, and have completed the present invention.

The surface protective film for a diffusion film of the present invention is intended to protect the diffusion film by being attached to a diffusion film having a surface having an arithmetic mean roughness (Ra) of 0.3 μm or more and 15 μm or less.
In a preferred embodiment of the present invention, the surface protective film for a diffusion film of the present invention has an arithmetic mean roughness (Ra) of 0.3 μm or more and 15 μm or less among the surfaces on both sides of the diffusion film. It is pasted against.

The diffusion film has a surface having an arithmetic mean roughness (Ra) of 0.3 μm or more and 15 μm or less.
When the arithmetic mean roughness (Ra) is within the above range, the surface of the diffusion film becomes rougher than before, and it is less likely to be damaged even when a foreign substance is caught. Further, when the arithmetic mean roughness (Ra) is 15 μm or less, stress concentration can be suppressed and the diffusion film is less likely to be damaged.
The surface protective film for a diffusing film of the present invention can exert a high adhesive force (initial adhesive force) even on such a diffusing film having a rough surface, and is difficult to adhere even with time or at a high temperature, and diffuses. Adhesive residue is unlikely to occur when peeling from the film. Since the surface protective film for a diffusion film of the present invention can exert a higher adhesive force (initial adhesive force) and is difficult to adhere, the arithmetic mean roughness (Ra) is preferably 0.5 μm or more and 13 μm or less, preferably 1 μm. More preferably, it is 10 μm or less.

The maximum height roughness (Rz) of the diffusion film is not particularly limited, but 1 μm or more and 50 μm or less are preferable, and 2 μm or more and 40 μm are preferable from the viewpoint of reducing the damage caused by the biting foreign matter while maintaining the diffusion function. The following are more preferable.

The arithmetic mean roughness (Ra) is a value based on JIS B0601: 2013, and a line is drawn at the center of the cross-sectional curve on the surface of the diffusion film, and the total area of the curve obtained by the center line is drawn. Means divided by the length. The maximum height roughness (Rz) is a value based on JIS B0601: 2013, and means a numerical value of the highest peak within the range of the reference length of the cross-sectional curve of the surface of the diffusion film. do. The arithmetic mean roughness (Ra) and the maximum height roughness (Rz) can be measured using, for example, the surf test SJ-310 (manufactured by Mitutoyo).

The surface protective film for a diffusion film of the present invention has a base material layer and an adhesive layer.
The base material layer is not particularly limited, but it is preferable to contain a polyolefin resin from the viewpoint of simultaneously improving transparency, rigidity and heat resistance.
The polyolefin resin is not particularly limited, and conventionally known polyolefin resins can be used, and examples thereof include polypropylene (PP) resin and polyethylene (PE) resin.

Examples of the polypropylene resin include homopolypropylene, random polypropylene, block polypropylene and the like. Examples of the polyethylene resin include high-pressure low-density polyethylene, linear low-density polyethylene, and high-density polyethylene. Of these, polypropylene resin is preferable from the viewpoint of transparency, rigidity and heat resistance, and homopolypropylene or a copolymer of propylene and at least one α-olefin is more preferable.

The base material layer is an additive such as an antistatic agent, a mold release agent, an antioxidant, a weathering agent, a crystal nucleating agent, and a resin such as a polyolefin, a polyester, a polyamide, and an elastomer, as long as the effect of the present invention is not impaired. It may contain a modifier.

The thickness of the base material layer is not particularly limited, but a preferable lower limit is 20 μm and a preferable upper limit is 200 μm. When the thickness of the base material layer is within this range, the handleability is excellent. From the viewpoint of further improving the handleability, the more preferable lower limit of the thickness of the base material layer is 25 μm, and the more preferable upper limit is 188 μm.

The pressure-sensitive adhesive layer has a storage elastic modulus E'at 25 ° C. of 3.0 MPa or less and a storage elastic modulus E'at 100 ° C. of 0.4 MPa or more.
By adjusting the storage elasticity E'at 25 ° C. and the storage elasticity E'at 100 ° C. of the pressure-sensitive adhesive layer within the above ranges, the surface protective film for a diffusion film of the present invention can be used with respect to a diffusion film having a rough surface. It is possible to exert a high adhesive force (initial adhesive force), it is difficult for the adhesive to advance even over time or at a high temperature, and it is difficult for adhesive residue to occur when it is peeled off from the diffusion film.

When the storage elastic modulus E'at 25 ° C. of the pressure-sensitive adhesive layer is 3.0 MPa or less, the adhesiveness of the pressure-sensitive adhesive layer when attached to the diffusion film is high, and the pressure-sensitive adhesive layer has high adhesive strength (initial stage). Adhesive strength) can be exhibited. From the viewpoint that the pressure-sensitive adhesive layer can exhibit a higher adhesive force (initial adhesive force), the storage elastic modulus E'at 25 ° C. of the pressure-sensitive adhesive layer is preferably 2.9 MPa or less, more preferably 2.8 MPa or less. 2.7 MPa or less is more preferable.
The lower limit of the storage elastic modulus E'at 25 ° C. of the pressure-sensitive adhesive layer is not particularly limited, but from the viewpoint of suppressing the adhesive strength of the pressure-sensitive adhesive layer from becoming too high and causing poor peeling when peeling from the diffusion film. , 0.5 MPa or more is preferable, and 0.7 MPa or more is more preferable.

When the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer is 0.4 MPa or more, the adhesion progress is suppressed over time or at high temperature, and the adhesive residue when the surface protective film for the diffusion film is peeled off from the diffusion film. Is also reduced. The storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer is set from the viewpoint of further suppressing the adhesion progress over time or under high temperature and further reducing the adhesive residue when the surface protective film for the diffusion film is peeled off from the diffusion film. , 0.45 MPa or more is preferable. Further, from the same viewpoint, 0.5 MPa or more is more preferable, 0.55 MPa or more is further preferable, 0.6 MPa or more is even more preferable, 0.65 MPa or more is particularly preferable, and 0.7 MPa or more is very preferable.
The upper limit of the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 3 MPa or less, more preferably 2 MPa or less, from the viewpoint of suppressing the occurrence of floating at the interface with the diffusion film.

The storage elastic modulus E'of the pressure-sensitive adhesive layer is, for example, a viscoelastic spectrometer (for example, DVA-200 manufactured by IT Measurement Control Co., Ltd.) at 10 ° C./min and 10 Hz in a constant speed temperature rise tension mode. The dynamic viscoelastic spectrum of the pressure-sensitive adhesive layer can be measured and obtained under the above conditions.

The resin (base resin) that is the main component of the pressure-sensitive adhesive layer is not particularly limited, and examples thereof include styrene-based elastomers, acrylic-based elastomers, urethane-based elastomers, and olefin-based elastomers. Among them, a styrene-based elastomer is preferable because it can exhibit a high adhesive force (initial adhesive force) and the storage elastic modulus E'can be easily adjusted by the styrene content.

The method for adjusting the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer is not particularly limited, and the type of the base resin can be selected or the base resin can be selected. Examples thereof include a method of using another resin in combination with the above-mentioned resin and a method of cross-linking the above-mentioned base resin.

In order to adjust the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer within the above ranges, the base resin has a hardness of 35 to 50 shore / 10 seconds. It is preferable to select. If a base resin having a hardness in such a range is selected and used, the storage elastic modulus E'at 25 ° C. of the pressure-sensitive adhesive layer can be adjusted to the above range relatively easily by using it in combination with a tackifier. can. A more preferable upper limit of the hardness of the base resin is 47 shore / 10 seconds.

When a styrene-based elastomer is used as the base resin, the styrene content in the primary structure of the styrene-based elastomer is also a guide for selecting the base resin. Although there are exceptions depending on the secondary structure and tertiary structure, the styrene-based elastomer having a styrene content of 15% by weight or less in the primary structure tends to increase the storage elastic modulus E'at 25 ° C. as the styrene content increases. When used, the storage elastic modulus E'at 25 ° C. of the pressure-sensitive adhesive layer can be easily adjusted to 3.0 MPa or less.

As a more specific method for adjusting the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer within the above ranges, for example, the general formula (AB) as a base resin is used. ) A method using a radial styrene-based elastomer having a structure represented by _nC can be mentioned.

The radial type styrene-based elastomer is a branched styrene block copolymer having a structure in which a plurality of styrene block copolymers are radially projected around a coupling agent, and is represented by the general formula (AB) _n C. It has the structure represented.
In the general formula, A represents an aromatic alkenyl polymer block, B represents a conjugated diene polymer block, C represents a component derived from a coupling agent, and n represents an integer of 2 or more. n is usually an integer of 8 or less from the viewpoint of suppressing gelation of the radial styrene-based elastomer.
When n is 3, it is called a 3-branch type, and when n is 4, it is also called a 4-branch type.

The aromatic alkenyl polymer block represented by A is a repeating unit derived from an aromatic alkenyl compound.
Examples of the aromatic alkenyl compound include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, divinylbenzene, 1,1-diphenylethylene, vinylnaphthalene, vinylanthracene, N, and so on. Examples thereof include N-diethyl-p-aminoethylstyrene and vinylpyridine. Of these, styrene is preferable because it is industrially easily available.

The conjugated diene polymer block represented by B is a repeating unit derived from the 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-octadien, and 1,3-hexadiene. , 1,3-Cyclohexadiene, 4,5-diethyl-1,3-octadien, 3-butyl-1,3-octadien, myrcene, chloroprene and the like. These conjugated diene compounds may be used alone or in combination of two or more. Of these, 1,3-butadiene and isoprene are preferable because they have high polymerization reactivity and are easily available industrially.

The coupling agent used as a raw material for the component derived from the coupling agent represented by C is a polyfunctional compound that radially bonds the linear styrene block copolymer.
Examples of the coupling agent include silane compounds such as silane halide and alkoxysilane, tin compounds such as tin halide, epoxy compounds such as polycarboxylic acid esters and epoxidized soybean oil, and acrylics such as pentaerythritol tetraacrylate. Examples thereof include esters and divinyl compounds such as epoxysilane and divinylbenzene. More specific examples include, for example, trichlorosilane, tribromosilane, tetrachlorosilane, tetrabromosilane, methyltrimethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, and the like. Examples thereof include tetrachlorotin and diethyladipate.

The pressure-sensitive adhesive layer preferably further contains a pressure-sensitive adhesive.
The tackifier also plays a role of blending with the base resin and adjusting the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer within the above ranges.
Examples of the tackifier include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic aromatic copolymers, and alicyclic copolymers, kumaron-inden-based resins, and terpene-based resins. Examples thereof include terpene phenol-based resins, rosin-based resins such as polymerized rosins, (alkyl) phenol-based resins, xylene-based resins, and hydrogenated products thereof. Further, a commercially available tackifier may be used as a mixture with the polyolefin resin. These tackifiers may be used alone or in combination of two or more. Above all, the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer can be easily adjusted to the above range, and the adhesive residue when the surface protective film for a diffusion film is peeled from the diffusion film is further reduced. Resin is preferred. Among the petroleum-based resins, an aliphatic copolymer, an aromatic copolymer, an aliphatic aromatic copolymer and an alicyclic copolymer are more preferable, and an alicyclic copolymer is further preferable. When the tackifier is an aliphatic copolymer, an aromatic copolymer, an aliphatic aromatic copolymer or an alicyclic copolymer, the tackifier may be saturated or unsaturated. From the viewpoint of reducing adhesive residue, it is preferably saturated.
The tackifier preferably has a softening point of 80 ° C. or higher. By using a tackifier having a softening point of 80 ° C. or higher, when the surface protective film for a diffusion film of the present invention is used as a wound body, the unfolding force when the surface protection film for a diffusion film is unwound does not increase too much. Can be done. The softening point of the tackifier is more preferably 90 to 140 ° C, further preferably 100 to 140 ° C, even more preferably 110 to 140 ° C, and 120 to 140 ° C. Is particularly preferable.

The content of the pressure-sensitive adhesive is particularly limited as long as the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. of the pressure-sensitive adhesive layer can be adjusted within the above ranges by using in combination with the base resin. Not done. The preferable lower limit of the content of the tackifier with respect to 100 parts by weight of the base resin is 5 parts by weight, the preferable upper limit is 80 parts by weight, the more preferable lower limit is 20 parts by weight, and the more preferable upper limit is 60 parts by weight.

The pressure-sensitive adhesive layer may contain additives such as a softening agent, an antioxidant, an anti-adhesive agent, and a mold release agent, if necessary, for the purpose of controlling the adhesive strength and the like.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit is 2 μm and the preferred upper limit is 30 μm. When the thickness of the pressure-sensitive adhesive layer is within this range, sufficient adhesive strength to the diffusion film and handleability can be achieved at the same time. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 2.5 μm, and the more preferable upper limit is 20 μm.

The method for producing the surface protective film for a diffusion film of the present invention is not particularly limited, and for example, another known laminating method such as extrusion lamination or extrusion coating is performed on a layer previously obtained by T-die molding or inflation molding. A method of laminating the layers of the above can be mentioned. Further, a method in which each layer is independently formed into a film and then the obtained films are laminated by dry lamination, a method in which the resin constituting each layer is coextruded by a T-die method, and the like can be mentioned. Among them, coextrusion molding in which each material of the base material layer and the pressure-sensitive adhesive layer is supplied to a multi-layer extruder for molding is preferable from the viewpoint of productivity, and T-die molding is more preferable from the viewpoint of thickness accuracy. ..

A diffusion film with a surface protective film comprising a diffusion film having a surface having an arithmetic average roughness (Ra) of 0.3 μm or more and 15 μm or less and a surface protective film for a diffusion film of the present invention attached to the diffusion film is also available. It is also one of the present inventions. The maximum height roughness (Rz) of the diffusion film is not particularly limited, but 1 μm or more and 50 μm or less are preferable, and 2 μm or more and 40 μm are preferable from the viewpoint of reducing the damage caused by the biting foreign matter while maintaining the diffusion function. The following are more preferable.

According to the present invention, it is possible to exert a high adhesive force (initial adhesive force) on a diffusion film having a rough surface, it is difficult for the adhesive to proceed even with time or at a high temperature, and when it is peeled off from the diffusion film, adhesive residue remains. It is possible to provide a surface protective film for a diffusion film that is unlikely to occur. Further, according to the present invention, it is possible to provide a diffusion film with a surface protection film including the surface protection film for the diffusion film.

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

<Diffusion film>
In the examples and comparative examples, the following five types of diffusion films were used as adherends.
Diffusion film 1: Arithmetic mean roughness (Ra) 8 μm, maximum height roughness (Rz) 45 μm
Diffusion film 2: Arithmetic mean roughness (Ra) 1 μm, maximum height roughness (Rz) 5 μm
Diffusion film 3: Arithmetic mean roughness (Ra) 4 μm, maximum height roughness (Rz) 21 μm
Diffusion film 4: Arithmetic mean roughness (Ra) 0.2 μm, maximum height roughness (Rz) 0.9 μm
Diffusion film 5: Arithmetic mean roughness (Ra) 16 μm, maximum height roughness (Rz) 55 μm
Diffusion film 6: Arithmetic mean roughness (Ra) 0.5 μm, maximum height roughness (Rz) 2 μm
Diffusion film 7: Arithmetic mean roughness (Ra) 0.5 μm, maximum height roughness (Rz) 0.9 μm
Diffusion film 8: Arithmetic mean roughness (Ra) 13 μm, maximum height roughness (Rz) 55 μm

The scratch resistance (easiness of scratching) of the diffusion film was evaluated as follows.
The diffusion film was cut into a size of 100 mm × 200 mm, and placed on a friction coefficient measuring machine (AB-401, manufactured by Tester Sangyo Co., Ltd.) with the surface (diffusion surface) to which the surface protective film was attached facing upward. The same diffusion film was cut out to a size of 63 mm × 126 mm, the surface (diffusion surface) to which the surface protective film was attached was attached to a sliding piece (63 mm × 63 mm), and this was layered on the diffusion film placed on the friction coefficient measuring machine. .. A load of 1200 gf was applied from the top of the slip piece, and a load cell was pulled at a feed rate of 100 mm / min to apply friction between the two diffusion films. The presence or absence of scratches on the diffusion surface of the diffusion film placed on the friction coefficient measuring machine was visually observed.
◯: No scratches on the diffusion surface Δ: 1 to 5 scratches on the diffusion surface ×: More than 5 scratches on the diffusion surface

<Base resin>
In Examples and Comparative Examples, the resins shown in Table 1 (resins 1 to 4) were used as the base resin. The method for synthesizing the resins 1 and 2 is as follows.

(Synthesis of resin 1)
In a nitrogen-substituted reaction vessel, 500 parts by weight of degassed and dehydrated cyclohexane, 15 parts by weight of styrene and 5 parts by weight of tetrahydrofuran were charged, and 0.13 parts by weight of n-butyllithium was added at the polymerization initiation temperature of 40 ° C. Then, temperature-heating polymerization was carried out to obtain an aromatic alkenyl polymer block (block A).
After the polymerization conversion of the aromatic alkenyl polymer block reaches approximately 100%, the reaction solution is cooled to 15 ° C., then 85 parts by weight of 1,3-butadiene is added, and further heating polymerization is performed to carry out conjugated diene. A polymer block (block B) was obtained.
After the polymerization conversion reached almost 100%, 0.06 part by weight of trichlorosilane was added as a coupling agent, and a coupling reaction was carried out. After the coupling reaction was completed, hydrogen gas was supplied at a pressure of 0.4 MPa-Gauge and left for 10 minutes.

Then, 0.03 part by weight of diethylaluminum chloride and 0.06 part by weight of bis (cyclopentadienyl) titanium furfuryloxychloride were added to the reaction vessel, and the mixture was stirred. The hydrogenation reaction was started at a hydrogen gas supply pressure of 0.7 MPa-Gauge and a reaction temperature of 80 ° C., and when the absorption of hydrogen was completed, the reaction solution was returned to normal temperature and pressure, and the reaction solution was taken out from the reaction vessel to obtain radial styrene. A block copolymer (AB) _3C was obtained.
When a partially extracted polymer was analyzed by GPC, the weight average molecular weight was about 98,000 and the dispersity was 1.1.
Moreover, the hardness of the obtained radial type styrene block copolymer was measured using the durometer GS-719N (manufactured by TECLOCK).

(Synthesis of resin 2)
Radial styrene block copolymer (AB) _4C was obtained by the same synthesis method as in Resin 1 except that tetrachlorosilane was used as the coupling agent.
When a partially extracted polymer was analyzed by GPC, the weight average molecular weight was about 130,000 and the dispersity was 1.1.

<Adhesive enhancer>
In the examples and comparative examples, the tackifiers (TF1 and 2) shown in Table 2 were used as the tackifiers.

(Example 1)
As a base resin, 100 parts by weight of resin 1 and 30 parts by weight of TF1 were blended to obtain a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer.
Co-extrusion molding by the T-die method using a polyolefin resin (trade name "J715M", polypropylene resin, manufactured by Prime Polymer Co., Ltd.) as a raw material for the base material layer and the pressure-sensitive adhesive composition obtained above as a raw material for the pressure-sensitive adhesive layer. Then, a surface protective film having a thickness of 2.5 μm for the pressure-sensitive adhesive layer and a thickness of 60 μm for the entire surface protective film was obtained.
For the pressure-sensitive adhesive layer of the obtained surface protection film, a viscoelastic spectrometer (DVA-200 manufactured by IT Measurement Control Co., Ltd.) was used, and dynamic viscoelasticity was performed under the conditions of 10 ° C./min and 10 Hz in a constant-speed temperature rise tension mode. The elastic spectrum was measured, and the storage elastic modulus E'at 25 ° C. and the storage elastic modulus E'at 100 ° C. were measured.

A 25 mm wide surface protective film was attached to the diffusion film 1 at an environment of 23 ° C. and a relative humidity of 50% RH at a pasting pressure of 3 Pa and a rate of 3 m / min to obtain a diffusion film with a surface protective film.

(Examples 2 to 12, Comparative Examples 1 to 7)
A surface protective film and a diffusion film with a surface protective film were obtained in the same manner as in Example 1 except that the diffusion film, the tackifier and the base resin were changed as shown in Table 3.

<Evaluation>
The diffusion films with surface protective films obtained in Examples and Comparative Examples were evaluated as follows. The results are shown in Table 3.

(1) Initial adhesive strength The diffusion film with a surface protective film was left for 30 minutes in an environment of 23 ° C. and a relative humidity of 50% RH. After being left to stand, the surface protective film was peeled off from the diffusion film in the 180 ° direction at a tensile speed of 300 mm / min according to JIS Z0237, and the initial adhesive strength was measured. In addition, the initial adhesive strength was determined according to the following criteria.
⊚: 5 gf / 25 mm or more, 15 gf / 25 mm or less ○: 3 gf / 25 mm or more and less than 5 gf / 25 mm, or more than 15 gf / 25 mm and 30 gf / 25 mm or less ×: less than 3 gf / 25 mm or more than 30 gf / 25 mm

(2) Adhesive promotion rate The diffusion film with the surface protective film was left in a temperature environment of 50 ° C. for 1 week. After standing, the diffusion film with a surface protective film was taken out to room temperature, and after being left for another 60 minutes, the surface protective film was peeled off from the diffusion film at a tensile speed of 300 mm / min in the 180 ° direction in accordance with JIS Z0237, and adhered over time. The force was measured.
Using the obtained initial adhesive force and adhesive force over time, the rate of change from the initial adhesive force to the adhesive force over time (adhesive progress rate) was calculated by the following formula and evaluated according to the following criteria.
Rate of change (adhesive progress rate) (%) = (adhesive strength over time / initial adhesive strength) x 100
⊚: 200% or less ○: More than 200% and 300% or less ×: More than 300%

(3) Diffusion film with adhesive residue surface protective film was left in a temperature environment of 50 ° C. for 1 week. After standing, the diffusion film with a surface protective film was taken out to room temperature and left for another 60 minutes, and then the surface protection film was peeled off from the diffusion film in the 180 ° direction at a tensile speed of 300 mm / min in accordance with JIS Z0237. The presence or absence of contamination on the surface of the diffusion film was visually observed.
⊚: No contamination on the surface of the diffusion film ○: There is some contamination on the surface of the diffusion film due to the generation of adhesive residue (1% or less of the total area).
X: Contamination due to the generation of adhesive residue is observed on the surface of the diffusion film.

According to the present invention, it is possible to exert a high adhesive force (initial adhesive force) on a diffusion film having a rough surface, it is difficult for the adhesive to proceed even with time or at a high temperature, and when it is peeled off from the diffusion film, adhesive residue remains. It is possible to provide a surface protective film for a diffusion film that is unlikely to occur. Further, according to the present invention, it is possible to provide a diffusion film with a surface protection film including the surface protection film for the diffusion film.

Claims (3)

A surface protective film for a diffusion film for protecting the diffusion film by being attached to a diffusion film having a surface having an arithmetic average roughness (Ra) of 0.3 μm or more and 15 μm or less.
It has a base material layer and an adhesive layer,
The pressure-sensitive adhesive layer has a storage elastic modulus E'at 25 ° C. of 3.0 MPa or less and a storage elastic modulus E'at 100 ° C. of 0.4 MPa or more, and is represented by the general formula (AB) nC. A surface protective film for a diffusion film, which comprises a radial type styrene-based elastomer having a structure .
A: Aromatic alkenyl polymer block
B: Conjugated diene polymer block
C: Ingredients derived from the coupling agent
n: Integer greater than or equal to 2 It is characterized by comprising a diffusion film having a surface having an arithmetic average roughness (Ra) of 0.3 μm or more and 15 μm or less, and a surface protective film for a diffusion film according to claim 1 attached to the diffusion film. Diffusion film with surface protection film. The diffusion film with a surface protective film according to claim 2 , wherein the diffusion film has a surface having a maximum height roughness (Rz) of 1 μm or more and 50 μm or less.