JP6454183B2 - Surface protective film and prism sheet with surface protective film - Google Patents

Description

The present invention relates to a surface protective film that can be unwound from a wound body with a small unfolding force and has a high adhesive force (initial adhesive force), but hardly develops an adhesive force over time or at high temperatures. 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 Protective films (sometimes generally referred to as protective tapes) are widely used (for example, Patent Documents 1 to 3).

In particular, in recent years, surface protective films have been used to protect the surface of optical members for liquid crystal displays. 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 general, it is effective to increase the blending amount of the tackifier in the pressure-sensitive adhesive layer in order to improve the adhesive strength. However, in the surface protective film, particularly when the adherend has a concavo-convex shape on the surface, an increase in adhesive force due to an increase in the contact area between the adherend and the adhesive layer over time or at high temperature. There is also a problem of so-called adhesive progress.

Japanese Patent Laid-Open No. 1-129085 JP-A-6-1958 Japanese Patent Laid-Open No. 8-12952

In order to achieve both improvement in adhesive strength (initial adhesive strength) and suppression of adhesive progress over time or at a high temperature, the present inventors reduce the elastic modulus of the adhesive layer to soften the adhesive layer, The improvement of the adhesiveness at the time of adhering the adhesive layer to the adherend was studied. By improving the adhesion at the time of pasting, the adhesive strength (initial adhesive strength) can be improved, and since the contact area between the adherend and the adhesive layer is large from the beginning of pasting, It is considered that the adhesion progress due to the increase of the contact area over time or at high temperature can be suppressed.
However, if the pressure-sensitive adhesive layer is too soft, a problem arises in that the force (deployment force) required for unwinding the surface protective film from the wound body (roll or original fabric) increases. Generally, the surface protection film is industrially manufactured as a wound body obtained by winding a long film into a roll shape. In FIG. 2, the schematic diagram which shows an example of the wound body by which the surface protection film was wound around the core is shown. It is known that the surface protection film made into such a wound body tends to increase the deployment force when the surface protection film is unwound from the wound body over time. It is required that it can be easily extended from the body.

An object of the present invention is to provide a surface protective film that can be drawn out from a wound body with a small unfolding force and has a high adhesive force (initial adhesive force), but hardly develops adhesive force over time or at high temperatures. . Moreover, an object of this invention is to provide the prism sheet with a surface protection film containing this surface protection film.

The present invention is a surface protective film having a base material layer and an adhesive layer, wherein the adhesive layer has a storage elastic modulus G ′ at −30 ° C. of 400 MPa or more and a storage elastic modulus G at 25 ° C. 'Is 5.5 MPa or less, the first styrene elastomer as the main component, and a second styrene elastomer having a storage elastic modulus G' at -30 ° C lower than that of the first styrene elastomer. It is a surface protective film to be contained.
The present invention is described in detail below.

The present inventors use two types of styrene-based elastomers having different storage elastic modulus G ′ at −30 ° C. for the pressure-sensitive adhesive layer of the surface protective film having the base material layer and the pressure-sensitive adhesive layer. It has been found that the pressure-sensitive adhesive layer can be softened by lowering the elastic modulus of the pressure-sensitive adhesive layer to such an extent that the developing force when the surface protective film is unwound from the roll is not increased.
That is, the inventors of the present invention provide a first styrene-based elastomer as a main component in the surface-protective film pressure-sensitive adhesive layer having a base material layer and a pressure-sensitive adhesive layer. By using a second styrene-based elastomer having a low storage elastic modulus G ′ at 30 ° C. and adjusting the storage elastic modulus G ′ at −30 ° C. and 25 ° C. of the pressure-sensitive adhesive layer to a specific range, a small unfolding force Surface protection that can be unwound from the wound body at the same time and at the same time has high adhesive strength (initial adhesive strength) due to its high adhesion when adhered to an adherend, but it is difficult for adhesive strength to progress even at high temperatures or over time The inventors have found that a film can be obtained and have completed the present invention.

The surface protective film of this invention has a base material layer and an adhesive layer. The pressure-sensitive adhesive layer has a storage elastic modulus G ′ at −30 ° C. of 400 MPa or more and a storage elastic modulus G ′ at 25 ° C. of 5.5 MPa or less.
By adjusting the storage elastic modulus G ′ at −30 ° C. and 25 ° C. of the pressure-sensitive adhesive layer to the above range, it can be fed out from the wound body with a small unfolding force, and at the same time when being applied to an adherend. Since the adhesiveness is high, a surface protective film having a high adhesive force (initial adhesive force), but hardly progressing with time or at high temperatures can be obtained.

In the pressure-sensitive adhesive layer, the lower limit of the storage elastic modulus G ′ at −30 ° C. is 400 MPa. When the storage elastic modulus G ′ at −30 ° C. is less than 400 MPa, the pressure-sensitive adhesive layer becomes too soft, and the developing force when the surface protective film is drawn out from the wound body is increased. The preferable lower limit of the storage elastic modulus G ′ at −30 ° C. is 450 MPa, and the more preferable lower limit is 500 MPa.
The upper limit of the storage elastic modulus G ′ at −30 ° C. is not particularly limited. However, if the elastic modulus of the pressure-sensitive adhesive layer is too high, the adhesive strength (initial adhesive strength) is decreased, or the adhesive strength is increased with time or at a high temperature. The preferred upper limit is 2000 MPa because of the progress.

The pressure-sensitive adhesive layer has an upper limit of storage elastic modulus G ′ at 25 ° C. of 5.5 MPa. When the storage elastic modulus G ′ at 25 ° C. exceeds 5.5 MPa, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to the adherend is reduced, and the adhesive strength (initial adhesion) Force) decreases, or adhesion progresses due to an increase in the contact area between the adherend and the pressure-sensitive adhesive layer over time or at a high temperature. The preferable upper limit of the storage elastic modulus G ′ at 25 ° C. is 5.4 MPa.
The lower limit of the storage elastic modulus G ′ at 25 ° C. is not particularly limited, but if the elastic modulus of the pressure-sensitive adhesive layer is too low, the adhesive force is too strong, or the unfolding force when the surface protective film is fed out from the wound body. The preferred lower limit is 3.0 MPa.

In addition, the storage elastic modulus G ′ at −30 ° C. and 25 ° C. of the pressure-sensitive adhesive layer is, for example, a viscoelastic spectrometer such as DVA-200 (manufactured by IT Measurement & Control Co., Ltd.) and is used in a constant speed temperature rising tensile mode. It can be determined by measuring the dynamic viscoelastic spectrum of the pressure-sensitive adhesive layer under conditions of 10 ° C./min and 10 Hz.

In order to adjust the storage elastic modulus G ′ at −30 ° C. and 25 ° C. of the pressure-sensitive adhesive layer to the above range, the pressure-sensitive adhesive layer includes a first styrene elastomer as a main component and the first styrene. And a second styrene elastomer having a storage elastic modulus G ′ at −30 ° C. lower than that of the elastomer.
By using such two kinds of styrene elastomers having different storage elastic moduli G ′ at −30 ° C., the elasticity of the pressure-sensitive adhesive layer is not increased to the extent that the developing force when the surface protective film is unwound from the wound body is increased. The pressure-sensitive adhesive layer can be softened by reducing the rate. As a result, it can be fed out from the wound body with a small unfolding force, and at the same time has a high adhesive force (initial adhesive force) due to its high adhesiveness when affixed to the adherend, but it also has an adhesive force over time or at high temperatures. A surface protective film that is difficult to develop is obtained.

The storage elastic modulus G ′ at −30 ° C. of the first styrene-based elastomer is not particularly limited as long as it is higher than that of the second styrene-based elastomer, but the preferable lower limit is 100 MPa, and the preferable upper limit is 2000 MPa, more preferable. The lower limit is 200 MPa, and the more preferable upper limit is 1500 MPa.
The glass transition temperature Tg of the first styrenic elastomer is not particularly limited, but the preferred lower limit is −50 ° C., the preferred upper limit is −10 ° C., the more preferred lower limit is −40 ° C., and the more preferred upper limit is −15. ° C.
The glass transition temperature Tg of the first styrene-based elastomer is, for example, 10 ° C./min, 10 Hz in a constant speed temperature rising tension mode using a viscoelastic spectrometer such as DVA-200 (made by IT Measurement Control Co., Ltd.). The dynamic viscoelastic spectrum of the first styrenic elastomer can be measured under the conditions described above and obtained from the peak of tan δ.
The storage elastic modulus G ′ of the pressure-sensitive adhesive layer at −30 ° C. and 25 ° C. is adjusted by adjusting the storage elastic modulus G ′ at −30 ° C. and the glass transition temperature Tg of the first styrene elastomer. Can be easily adjusted to the above range.

The first styrene-based elastomers have the general formula [A-B] a copolymer having a structure represented by n ¹ (I) or its hydrogenated product, the general formula A-B-A or (A-B ) It is preferable to contain a copolymer (II) having a structure represented by x ¹ -Y ¹ or a mixture thereof with a hydrogenated product.
A: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit, wherein the content of the aromatic alkenyl compound unit in the entire aromatic alkenyl polymer represented by A is 70% by weight or more B: Aromatic alkenyl-conjugated diene copolymer randomly containing an aromatic alkenyl compound unit and a conjugated diene compound unit n ¹ : an integer of ^{1 to} 3 x ¹ : an integer of 1 or more Y ¹ : a coupling agent residue 1 styrene elastomer, the aromatic alkenyl-conjugated diene copolymer represented by B contains an aromatic alkenyl compound unit in addition to the conjugated diene compound unit, so that the first styrene elastomer is The storage elastic modulus G ′ at −30 ° C. is relatively high. When the said adhesive layer contains such a 1st styrene-type elastomer, the surface protection film of this invention can be drawn out from a wound body with a small expansion | deployment force.

The aromatic alkenyl polymer represented by A is an aromatic alkenyl polymer containing an aromatic alkenyl compound unit.
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.

In the aromatic alkenyl polymer represented by A, the content of the aromatic alkenyl compound unit in the whole aromatic alkenyl polymer represented by A is 70% by weight or more.
By making the content rate of the said aromatic alkenyl compound unit 70 weight% or more, the thermoplasticity of the said adhesive layer can be improved and recycling of a 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 aromatic alkenyl-conjugated diene copolymer represented by B is an aromatic alkenyl-conjugated diene copolymer containing an aromatic alkenyl compound unit and a conjugated diene compound unit randomly.
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.
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.

The aromatic alkenyl-conjugated diene copolymer represented by B is the content of the aromatic alkenyl compound unit in the entire aromatic alkenyl-conjugated diene copolymer represented by B (the aromatic alkenyl compound is When it is only styrene, it is preferable that it is also called "styrene content") 10 to 35 weight%, and the content rate of the said conjugated diene compound unit is 65 to 90 weight%. When the content of the aromatic alkenyl compound unit is lower than the above range, the pressure-sensitive adhesive layer becomes too soft, and the developing force when the surface protective film is unwound from the wound body may be increased. When the content of the aromatic alkenyl compound unit is higher than the above range, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to the adherend is lowered, and the adhesive strength (initial adhesive strength) ) May decrease, or the adhesion progress may increase due to an increase in the contact area between the adherend and the pressure-sensitive adhesive layer over time or at a high temperature. As for the content rate of the said aromatic alkenyl compound unit, 13 to 33 weight% is more preferable, and 16 to 30 weight% is still more preferable.
The aromatic alkenyl-conjugated diene copolymer represented by B may contain a repeating unit other than the aromatic alkenyl compound unit and the conjugated diene compound unit.

Since the aromatic alkenyl-conjugated diene copolymer represented by B can constitute a pressure-sensitive adhesive layer having a good balance between tack and adhesive strength, the vinyl bond content is 50 to 90%. Is preferable, and it is more preferable that it is 60 to 80%.
The “vinyl bond content” means the total content of 1,2-vinyl bonds and 3,4-vinyl bonds calculated by the Morello method using an infrared absorption spectrum.

The copolymer (I) has a structure represented by the general formula [AB] n ¹ (n ¹ : an integer of ^{1 to} 3).
Specific examples of the structure represented by the general formula [A-B] n ¹ include, for example, A-B, A-B-A-B, and A-B-A-B-A-B. Examples include the structure. Especially, from the viewpoint of improving the adhesive strength and material strength of the pressure-sensitive adhesive layer, a structure represented by AB or AB-AB is preferable, and a structure represented by AB is more preferable. A and B may be the same or different in each repetition. These copolymers (I) may be used independently and may use 2 or more types together.
From the viewpoint of reliably exhibiting the effect of the aromatic alkenyl-conjugated diene copolymer represented by B, the copolymer (I) is an aromatic alkenyl-conjugated diene copolymer represented by B at the terminal. The coalescence preferably accounts for 2% by weight or more of the entire copolymer (I).

The copolymer (II) has a structure represented by the general formula A-B-A or (A-B) x ¹ -Y ¹ (x ¹ is an integer of 1 or more, Y ^{1 is a} coupling agent residue). Have
In other words, having the structure represented by the general formula (AB) x ¹ -Y ¹ means having the structure in which the copolymer (I) is coupled by Y ¹ . Therefore, since the mixture of the said copolymer (I) and the said copolymer (II) can be synthesize | combined with the same reaction kettle (one pot), from an industrial viewpoint, the said general formula (AB) x ¹ -Y ¹ is preferred. If x ¹ is 3 or more, the copolymer (II) is a so-called star polymer. x ¹ is preferably 2 to 4 from the viewpoint of suppressing side reactions during the production of the copolymer (II) and controlling the physical properties of the copolymer (II).
From the viewpoint of surely exerting the effect of the aromatic alkenyl polymer represented by A, the copolymer (II) is obtained by converting the terminal aromatic alkenyl polymer represented by A to the copolymer (II). ) It preferably accounts for 2% by weight or more of the whole.

Examples of the coupling agent from which the coupling agent residue represented by Y ¹ is derived include methyldichlorosilane, dimethyldichlorosilane, methyltrichlorosilane, butyltrichlorosilane, tetrachlorosilane, and halogen compounds (for example, dibromoethane, tetra Chlorotin, butyltrichlorotin, tetrachlorogermanium, bis (trichlorosilyl) ethane), epoxy compounds (eg, epoxidized soybean oil), carbonyl compounds (eg, diethyl adipate, dimethyl adipate, dimethyl terephthalic acid, diethyl terephthalic acid) ), Polyvinyl compounds (for example, divinylbenzene), polyisocyanates, and the like. Of these, methyldichlorosilane, dimethyldichlorosilane, methyltrichlorosilane, and tetrachlorosilane are preferred because they are easily available industrially and have high reactivity.

The weight average molecular weight of the copolymer (I) or hydrogenated product thereof is preferably 30,000, a preferred upper limit is 500,000, a more preferred lower limit is 80,000, a more preferred upper limit is 300,000, and further preferred. The lower limit is 100,000, and the more preferable upper limit is 200,000.
As for the weight average molecular weight of the said copolymer (II) or its hydrogenated product, a preferable minimum is 50,000, a preferable upper limit is 500,000, and a more preferable upper limit is 300,000.
When the weight average molecular weight is smaller than the above range, the copolymer or its hydrogenated product adheres to the production equipment in the step of desolvating the copolymer or its hydrogenated product and drying it, or the copolymer or its Industrial production of hydrogenated products may be difficult. When the weight average molecular weight is larger than the above range, the solubility of the copolymer or its hydrogenated product in the solvent or the heat melting property is deteriorated, and it may be difficult to process the pressure-sensitive adhesive.

Since the hydrogenated product of the copolymers (I) and (II) provides excellent heat resistance and weather resistance, the double of the conjugated diene compound unit in the copolymer (I) or (II). Preferably 80% or more of bonds (unsaturated bonds), more preferably 90% or more, and still more preferably 95% or more are converted to saturated bonds by hydrogenation.
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 first styrenic elastomer, the weight ratio of the copolymer (I) or hydrogenated product thereof to the copolymer (II) or hydrogenated product thereof is 90:10 to 10:90. preferable. If the weight of the copolymer (I) or the hydrogenated product thereof is smaller than the above range, the pressure-sensitive adhesive layer may be lifted from the surface of the adherend, and the surface protective film may be peeled off. If the weight of the copolymer (I) or its hydrogenated product is larger than the above range, the adhesive remains on the surface of the adherend when the surface protective film is peeled off from the surface of the adherend (adhesive residue). ) To contaminate the surface of the adherend. The weight ratio of the copolymer (I) or hydrogenated product thereof to the copolymer (II) or hydrogenated product thereof is more preferably 50:50 to 15:85.

In the first styrene elastomer, the total weight of the aromatic alkenyl polymer represented by A and the total amount of the aromatic alkenyl-conjugated diene copolymer represented by B in the entire mixture. The ratio is preferably 15:85 to 45:55. If the weight of the total amount of the aromatic alkenyl polymer represented by A is smaller than the above range, an appropriate holding force may not be imparted to the pressure-sensitive adhesive layer. When the weight of the total amount of the aromatic alkenyl polymer represented by A is larger than the above range, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to an adherend is reduced. Adhesive strength (initial adhesive strength) may decrease, or adhesion may increase due to an increase in the contact area between the adherend and the adhesive layer over time or at high temperatures. The weight ratio of the total amount of the aromatic alkenyl polymer represented by A and the total amount of the aromatic alkenyl-conjugated diene copolymer represented by B is more preferably 10:90 to 40:60.

In the first styrene elastomer, the content of aromatic alkenyl compound units in the entire mixture (also referred to as “total styrene content” when the aromatic alkenyl compound is only styrene) has a preferred lower limit of 30. The preferred upper limit is 50% by weight. When the content of the aromatic alkenyl compound unit is less than 30% by weight, an appropriate holding force cannot be imparted to the pressure-sensitive adhesive layer, or the pressure-sensitive adhesive layer becomes too soft, and the surface from the wound body becomes too soft. The deployment force when paying out the protective film may increase. When the content of the aromatic alkenyl compound unit exceeds 50% by weight, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to the adherend is lowered, and the adhesive strength (initial adhesive strength) ) May decrease, or the adhesion progress may increase due to an increase in the contact area between the adherend and the pressure-sensitive adhesive layer over time or at a high temperature. The minimum with more preferable content rate of the said aromatic alkenyl compound unit is 33 weight%, and a more preferable upper limit is 45 weight%.

The method for producing the first styrenic elastomer is not particularly limited. For example, the copolymer (I) and the copolymer (II) are produced by block polymerization and mixed, and then necessary. There is a method in which hydrogenation is performed accordingly to obtain a mixture of the copolymer (I) or a hydrogenated product thereof and the copolymer (II) or a hydrogenated product thereof.
Moreover, as a method for producing the first styrene-based elastomer, when the copolymer (II) has a structure represented by the general formula (AB) x ¹ -Y ¹ , [AB] A first step of synthesizing a copolymer having the following structure by block polymerization, and coupling a part of the copolymer having the structure of [AB] with a coupling agent, and (AB) x ¹ how a second step of synthesizing a copolymer having a structure of -Y ¹ (coupling method) may be mentioned. When performing hydrogenation product further performs hydrogenated the copolymer having the above [A-B] copolymer and the having the structure of ^{(A-B) x 1 -Y} 1 of structure You may perform a 3rd process.
In the above coupling method, since the mixture of the copolymer (I) and the copolymer (II) can be synthesized in the same reaction kettle (one pot), the production process is simple and the production cost is low. Thus, the weight ratio of the copolymer (I) or hydrogenated product thereof to the copolymer (II) or hydrogenated product thereof can be controlled by the type or amount of the coupling agent.

The storage elastic modulus G ′ at −30 ° C. of the second styrenic elastomer is not particularly limited as long as it is lower than the first styrenic elastomer, but the preferred lower limit is 1 MPa, and the preferred upper limit is 100 MPa, more preferred. The lower limit is 5 MPa.
The glass transition temperature Tg of the second styrene elastomer is not particularly limited, but the preferred lower limit is −60 ° C., the preferred upper limit is −20 ° C., the more preferred lower limit is −50 ° C., and the more preferred upper limit is −30 ° C. is there.
The storage elastic modulus G ′ of the pressure-sensitive adhesive layer at −30 ° C. and 25 ° C. is adjusted by adjusting the storage elastic modulus G ′ at −30 ° C. and the glass transition temperature Tg of the second styrene elastomer. Can be easily adjusted to the above range.

The second styrenic elastomer includes a copolymer (III) having a structure represented by the general formula [C-D] n ² or a hydrogenated product thereof, and a general formula C-D-C or (C-D ) A copolymer (IV) having a structure represented by x ² —Y ² or a mixture thereof with a hydrogenated product thereof, wherein the content of aromatic alkenyl compound units in the whole mixture is 15% by weight or less. Preferably there is.
C: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit, wherein the content of the aromatic alkenyl compound unit in the entire aromatic alkenyl polymer represented by C is 70% by weight or more D: A conjugated diene polymer containing a conjugated diene compound unit, wherein the content of the conjugated diene compound unit in the whole conjugated diene polymer represented by D is 85% by weight or more n ² : an integer of 1 to 3 x ² : integer Y ² or more Y ² : coupling agent residue In the second styrene elastomer, the content of the conjugated diene compound unit in the whole conjugated diene polymer represented by D is 85% by weight or more. The second styrenic elastomer has a high storage elastic modulus G ′ at −30 ° C. because the content of the aromatic alkenyl compound unit in the entire mixture is low and 15% by weight or less. Is relatively low. When the pressure-sensitive adhesive layer contains such a second styrenic elastomer, the elastic modulus of the pressure-sensitive adhesive layer is lowered to such an extent that the development force when the surface protective film is drawn out from the wound body is not increased. The agent layer can be softened.

The aromatic alkenyl polymer represented by C is an aromatic alkenyl polymer containing an aromatic alkenyl compound unit.
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.
In the aromatic alkenyl polymer represented by C, the content of the aromatic alkenyl compound unit in the whole aromatic alkenyl polymer represented by C is 70% by weight or more.
The aromatic alkenyl polymer represented by C may contain a repeating unit other than the aromatic alkenyl compound unit, and examples of the repeating unit other than the aromatic alkenyl compound unit include those represented by A described above. And the same repeating units as those contained in the aromatic alkenyl polymer.

The conjugated diene polymer represented by D is a conjugated diene polymer containing a conjugated diene compound unit.
Examples of the conjugated diene compound unit include the same conjugated diene compound units as those contained in the aromatic alkenyl-conjugated diene copolymer represented by B described above. Moreover, when the said conjugated diene compound unit contains a butylene unit, the minimum with preferable content rate of the butylene unit in the said conjugated diene compound unit is 60 weight%. When the content of the butylene unit is less than 60% by weight, the low-temperature elastic modulus of the pressure-sensitive adhesive layer may be lowered, and the developing force when the surface protective film is drawn out from the wound body may be increased. A more preferred lower limit of the content of butylene units in the conjugated diene compound unit is 65% by weight.

In the conjugated diene polymer represented by D, the content of the conjugated diene compound unit in the whole conjugated diene polymer represented by D is 85% by weight or more.
When the content of the conjugated diene compound unit is less than 85% by weight, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to the adherend is lowered, and the adhesive strength (initial adhesive strength) ) May decrease, or the adhesion progress may increase due to an increase in the contact area between the adherend and the pressure-sensitive adhesive layer over time or at a high temperature.

The conjugated diene polymer represented by D may contain a repeating unit other than the conjugated diene compound unit. As the repeating unit other than the conjugated diene compound unit, for example, the fragrance represented by A described above. Examples thereof include the same aromatic alkenyl compound units as those contained in the group alkenyl polymer.
The conjugated diene polymer represented by D is a content of the aromatic alkenyl compound unit in the whole conjugated diene polymer represented by D (when the aromatic alkenyl compound is only styrene, “styrene content” The preferred upper limit is also 15% by weight, the more preferred upper limit is 13% by weight, and the still more preferred upper limit is 11% by weight.
The conjugated diene polymer represented by D may further contain a repeating unit other than the conjugated diene compound unit and the aromatic alkenyl compound unit.

Since the conjugated diene polymer represented by the above D can constitute a pressure-sensitive adhesive layer having a good balance between tack and adhesive strength, the vinyl bond content is preferably 50 to 90%, preferably 60 to More preferably, it is 80%.

The copolymer (III) has a structure represented by the general formula [CD] n ² (n ² : an integer of 1 to 3).
Specific examples of the structure represented by the general formula [C-D] n ² include C-D, C-D-C-D, and C-D-C-D-C-D. Examples include the structure. Among these, from the viewpoint of improving the adhesive strength and material strength of the pressure-sensitive adhesive layer, a structure represented by CD or CDCD is preferable, and a structure represented by CD is more preferable. C and D may be the same or different in each repetition. These copolymers (III) may be used alone or in combination of two or more.
From the viewpoint of surely exhibiting the effect of the conjugated diene polymer represented by D, the copolymer (III) is a conjugated diene polymer represented by D at the end of the copolymer (III) as a whole. It is preferable to occupy 2% by weight or more.

The copolymer (IV) has the general formula C-D-C or ^{(C-D) x 2 -Y} 2 (x 2: 1 or more integer, ^{Y 2:} Coupling agent residue) structure represented by Have
The general formula and having a ^{(C-D) x 2 -Y} 2 represented by the structure, in turn, means having a structure in which the copolymer (III) was coupled by ^{Y 2.} Therefore, since the mixture of the said copolymer (III) and the said copolymer (IV) can be synthesize | combined with the same reaction kettle (one pot), from the industrial viewpoint, the said general formula (C-D) x ² -Y ² is preferred. If x ² is 3 or more, the copolymer (IV) is a so-called star polymer. x ² is the copolymer (IV) to inhibit side reactions during production, from the viewpoint of controlling the physical properties of the copolymer (IV), preferably 2-4.
From the viewpoint of reliably exhibiting the effect of the aromatic alkenyl polymer represented by C, the copolymer (IV) is obtained by converting the terminal aromatic alkenyl polymer represented by C to the copolymer (III). ) It preferably accounts for 2% by weight or more of the whole.
Examples of the coupling agent from which the coupling agent residue represented by Y ² is derived include the same coupling agents as those from which the coupling agent residue represented by Y ¹ described above is derived.

The weight average molecular weight of the copolymer (III) or hydrogenated product thereof is preferably 30,000, a preferable upper limit is 500,000, a more preferable lower limit is 80,000, a more preferable upper limit is 300,000, and further preferable. The lower limit is 100,000, and the more preferable upper limit is 200,000.
As for the weight average molecular weight of the said copolymer (IV) or its hydrogenated substance, a preferable minimum is 50,000, a preferable upper limit is 500,000, and a more preferable upper limit is 300,000.
When the weight average molecular weight is smaller than the above range, the copolymer or its hydrogenated product adheres to the production equipment in the step of desolvating the copolymer or its hydrogenated product and drying it, or the copolymer or its Industrial production of hydrogenated products may be difficult. When the weight average molecular weight is larger than the above range, the solubility of the copolymer or its hydrogenated product in the solvent or the heat melting property is deteriorated, and it may be difficult to process the pressure-sensitive adhesive.

Since the hydrogenated product of the copolymers (III) and (IV) provides excellent heat resistance and weather resistance, the double of the conjugated diene compound unit in the copolymer (III) or (IV) is obtained. Preferably 80% or more of bonds (unsaturated bonds), more preferably 90% or more, and still more preferably 95% or more are converted to saturated bonds by hydrogenation.

In the second styrenic elastomer, the weight ratio of the copolymer (III) or hydrogenated product thereof to the copolymer (IV) or hydrogenated product thereof is 90:10 to 10:90. preferable. If the weight of the copolymer (III) or hydrogenated product thereof is smaller than the above range, the pressure-sensitive adhesive layer may be lifted from the surface of the adherend, and the surface protective film may be peeled off. When the weight of the copolymer (III) or hydrogenated product thereof is larger than the above range, the adhesive remains on the surface of the adherend (adhesive residue) when the surface protective film is peeled off from the surface of the adherend. ) To contaminate the surface of the adherend. The weight ratio of the copolymer (III) or hydrogenated product thereof to the copolymer (IV) or hydrogenated product thereof is more preferably 50:50 to 15:85.

In the second styrenic elastomer, the weight ratio of the total amount of the aromatic alkenyl polymer represented by C in the entire mixture to the total amount of the conjugated diene polymer represented by D is 5: 95-15: 85 is preferable. If the weight of the total amount of the aromatic alkenyl polymer represented by C is smaller than the above range, an appropriate holding force may not be imparted to the pressure-sensitive adhesive layer. When the weight of the total amount of the aromatic alkenyl polymer represented by C is larger than the above range, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when sticking the pressure-sensitive adhesive layer to the adherend is lowered, Adhesive strength (initial adhesive strength) may decrease, or adhesion may increase due to an increase in the contact area between the adherend and the adhesive layer over time or at high temperatures. The weight ratio of the total amount of the aromatic alkenyl polymer represented by C and the total amount of the conjugated diene polymer represented by D is more preferably 7:93 to 13:87.

In the second styrenic elastomer, the content of aromatic alkenyl compound units in the entire mixture (when the aromatic alkenyl compound is only styrene is also referred to as “total styrene content”) is 15% by weight or less. is there. When the content of the aromatic alkenyl compound unit exceeds 15% by weight, the pressure-sensitive adhesive layer becomes hard and the adhesiveness when the pressure-sensitive adhesive layer is attached to the adherend is lowered, and the adhesive strength (initial adhesive strength) ) May decrease, or the adhesion progress may increase due to an increase in the contact area between the adherend and the pressure-sensitive adhesive layer over time or at a high temperature. The content of the aromatic alkenyl compound unit is preferably 13% by weight or less, and more preferably 11% by weight or less.

The method for producing the second styrene-based elastomer is not particularly limited, and examples thereof include the same method as the method for producing the first styrene-based elastomer described above.

In the pressure-sensitive adhesive layer, the weight ratio of the first styrene elastomer to the second styrene elastomer is not particularly limited, but the second styrene elastomer is used with respect to 100 parts by weight of the first styrene elastomer. The preferred lower limit of the content of is 15 parts by weight, the preferred upper limit is 140 parts by weight, the more preferred lower limit is 20 parts by weight, and the more preferred upper limit is 90 parts by weight. By adjusting to such a weight ratio, the elastic modulus of the pressure-sensitive adhesive layer can be lowered and the pressure-sensitive adhesive layer can be made soft so as not to increase the developing force when the surface protective film is drawn out from the wound body.
Note that the first styrene elastomer is “main component” means that the first styrene elastomer of the first styrene elastomer out of a total of 100 parts by weight of the first styrene elastomer and the second styrene elastomer. It means that the content is 50 parts by weight or more.

The pressure-sensitive adhesive layer may further contain a tackifier.
Although the said tackifier is not specifically limited, It is preferable that a softening point is 80 degreeC or more, and it is more preferable that it is 90-140 degreeC. Examples of the tackifier include petroleum resins such as aliphatic copolymers, aromatic copolymers, aliphatic aromatic copolymers, and alicyclic copolymers, coumarone-indene resins, terpene resins, Examples include terpene phenol resins, rosin resins such as polymerized rosin, (alkyl) phenol resins, xylene resins, and hydrogenated products thereof. Moreover, you may use the tackifier marketed as a mixture with polyolefin resin. These tackifiers may be used alone or in combination of two or more. In addition, in order to improve the peelability, weather resistance, and the like of the pressure-sensitive adhesive layer, the tackifier is preferably a hydrogenated product.
The tackifier is preferably compatible with the aromatic alkenyl-conjugated diene copolymer represented by B in the first styrenic elastomer.

The content of the tackifier is not particularly limited, and is appropriately adjusted to the extent that the adhesive does not remain on the surface of the adherend (no adhesive remains) when the surface protective film is peeled off from the surface of the adherend. However, a preferred lower limit for the total of 100 parts by weight of the first styrenic elastomer and the second styrenic elastomer is 2 parts by weight, a preferred upper limit is 30 parts by weight, and a more preferred upper limit is 20 parts by weight.

The pressure-sensitive adhesive layer may further contain a release agent.
When the pressure-sensitive adhesive layer contains the release agent, the surface protective film can be fed out from the wound body with a smaller developing force. The release agent is not particularly limited. For example, fatty acid amide, polyethyleneimine long chain alkyl graft product, soybean oil-modified alkyd resin (for example, Arakawa Chemical Industries, trade name “Arachid 251”, etc.), tall oil-modified Examples thereof include alkyd resins (for example, trade name “Arachid 6300” manufactured by Arakawa Chemical Industries, Ltd.), fluorine-containing compounds having a polyfluorohydrocarbon group and a polyoxyethylene group.

The content of the release agent is not particularly limited, but the preferred lower limit for the total of 100 parts by weight of the first styrene elastomer and the second styrene elastomer is 0.5 parts by weight, and the preferred upper limit is 3 parts by weight. There is a more preferred upper limit of 2.5 parts by weight.

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

Although the thickness of the said adhesive layer is not specifically limited, A preferable minimum is 3 micrometers and a preferable upper limit is 30 micrometers. When the thickness of the pressure-sensitive adhesive layer is less than 3 μm, the pressure-sensitive adhesive strength of the pressure-sensitive adhesive layer may be reduced. When the thickness of the pressure-sensitive adhesive layer exceeds 30 μm, it may be difficult to remove the surface protective film when peeling the surface protective film from the surface of the adherend. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm, and the more preferable upper limit is 20 μm.

Although the said base material layer is not specifically limited, It is preferable to contain polyolefin resin.
The said polyolefin resin is not specifically limited, A conventionally well-known polyolefin resin can be used, For example, a polypropylene (PP) resin, a polyethylene (PE) resin, etc. are mentioned.

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

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 25 micrometers and a preferable upper limit is 200 micrometers. When the thickness of the base material layer is less than 25 μm, the surface protective film may be easily broken during handling. When the thickness of the base material layer exceeds 200 μm, the base material layer may remain wound. The more preferable lower limit of the thickness of the base material layer is 50 μm, and the more preferable upper limit is 188 μm.

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, but is used when protecting the surface of an adherend having an uneven shape on the surface. However, the adhesiveness at the time of sticking to an adherend is high and the adhesive strength (initial adhesive strength) is high, but the adhesive strength does not easily increase even with aging or high temperature.
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 a prism sheet (also referred to as a diffusion film). Especially, it is preferable that the surface protection film of this invention is affixed and used for a prism sheet. Furthermore, the surface protective film of the present invention is more preferably used by being attached to the matte layer of a prism sheet having a prism layer on the front surface and a matte layer on the back surface. Note that the matte layer is a layer that has been subjected to a matte treatment, and has a concavo-convex shape (for example, a concavo-convex shape with a pitch of about 20 μm) on the surface (also referred to as a mat surface).
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 prism sheet is shown. In FIG. 1, the surface protective film 1 is attached to the mat layer 5 of the prism sheet 4 having the prism layer 7 on the front surface of the transparent film 6 and the mat layer 5 on the back surface. 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 mat layer of the prism sheet having a prism layer on the front surface and a mat layer on the back surface is also one aspect of the present invention.
The prism sheet is not particularly limited as long as it has a prism layer on the front surface and a mat layer on the back surface, and examples thereof include a prism sheet that is usually used as an optical member for a liquid crystal display.

According to the present invention, it is possible to provide a surface protective film that can be unwound from a wound body with a small unfolding force and has a high adhesive force (initial adhesive force), but is less likely to develop an adhesive force over time or at high temperatures. . 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 prism sheet. It is a schematic diagram which shows an example of the wound body by which the surface protection film was wound around the core.

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

<First styrenic elastomer>
Elastomer 1 (a) (Glass transition temperature (Tg): -28 ° C., storage elastic modulus (G ′) at −30 ° C .: 342 MPa, total styrene content: 35 wt%, styrene content represented by A 15% by weight, styrene content in the whole aromatic alkenyl-conjugated diene copolymer represented by B: 20% by weight)
Elastomer 1 (b) (Glass transition temperature (Tg): −8 ° C., storage elastic modulus (G ′) at −30 ° C .: 1220 MPa, total styrene content: 45% by weight, styrene content represented by A 15% by weight, styrene content in the whole aromatic alkenyl-conjugated diene copolymer represented by B: 30% by weight)

<Second Styrenic Elastomer>
Elastomer 2 (a) (trade name “DR1321P”, styrene-ethylenebutylene copolymer, manufactured by JSR, glass transition temperature (Tg): −33 ° C., storage elastic modulus at −30 ° C. (G ′): 92 MPa )
Elastomer 2 (b) (trade name “DR8630P”, styrene-ethylenebutylene copolymer, manufactured by JSR, glass transition temperature (Tg): −35 ° C., storage elastic modulus (G ′) at −30 ° C .: 36 MPa )
Elastomer 2 (c) (trade name “DR1320P”, styrene-ethylenebutylene copolymer, manufactured by JSR, glass transition temperature (Tg): −32 ° C., storage elastic modulus (G ′) at −30 ° C .: 93 MPa )
Elastomer 2 (d) (styrene-ethylene butylene copolymer, glass transition temperature (Tg): −44 ° C., storage elastic modulus (G ′) at −30 ° C .: 8 MPa, total styrene content: 9% by weight, Styrene content represented by C: 9% by weight)

Example 1
Elastomer 1 (a) 100 parts by weight, elastomer 2 (a) 20 parts by weight, tackifier (trade name “Arcon P125”, alicyclic saturated hydrocarbon resin, Arakawa Chemical Industries, softening point 125 ° C.) 5 parts by weight with respect to 100 parts by weight as a total, and 1 part by weight with respect to 100 parts by weight of the total amount of a release agent (trade name “Alflow H50TF”, ethylene bis-stearic amide (EBSA), manufactured by NOF Corporation) Part and an antioxidant (trade name “IRGANOX 1010”, manufactured by BASF) were mixed in an amount of 1 part by weight with respect to a total of 100 parts by weight of the elastomer to obtain a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer.
Co-extrusion by T-die method using polyolefin resin (trade name “J715M”, polypropylene resin, manufactured by Prime Polymer Co., Ltd.) as the raw material of the base material layer and the adhesive composition obtained above as the raw material of the adhesive layer Thus, a surface protective film having a substrate layer of 55 μm and an adhesive layer of 5 μm was obtained.
About the pressure-sensitive adhesive layer of the obtained surface protective film, using a viscoelastic spectrometer (DVA-200, manufactured by IT Measurement Control Co., Ltd.) The elastic spectrum was measured, and the storage elastic modulus G ′ at −30 ° C. and 25 ° C. was measured.

(Examples 2 to 12, Comparative Examples 1 to 7)
As shown in Table 1 or 2, a surface protective film was obtained in the same manner as in Example 1 except that the content of the first styrene-based elastomer, the second styrene-based elastomer, or the additive was changed. About the adhesive layer of the obtained surface protection film, it carried out similarly to Example 1, and measured the storage elastic modulus G 'in -30 degreeC and 25 degreeC.

<Evaluation>
The following evaluation was performed about the surface protection film obtained by the Example and the comparative example. The results are shown in Tables 1 and 2.

(1) An initial adhesive prism sheet (a diffusion film which is an acrylic film having an arithmetic average roughness Ra (JIS B 0601-1994) of 0.32 μm) was prepared as an adherend. A 25 mm wide surface protective film was attached so as to cover the mat surface of the adherend, thereby preparing a test piece. The pasting was performed by pressing at a speed of 300 mm / min using a 2 kg pressure-bonded rubber roller in an environment of 23 ° C. and a relative humidity of 50% RH. The obtained test piece was left for 30 minutes in an environment of 23 ° C. and a relative humidity of 50% RH. After standing, according to JIS Z0237, the surface protective film was peeled from the adherend in a 180 ° direction at a tensile speed of 300 mm / min, and the initial adhesive strength was measured. Further, the initial adhesive strength was determined according to the following criteria.
◎ (excellent) 0.15N / 25mm or more and less than 0.4N / 25mm ○ (good) 0.1N / 25mm or more and less than 0.15N / 25mm,
Or 0.4N / 25mm or more and less than 0.5N / 25mm x (defect) Less than 0.1N / 25mm or 0.5N / 25mm or more

(2) A time-dependent adhesive prism sheet (a diffusion film which is an acrylic film having an arithmetic average roughness Ra (JIS B 0601-1994) of 0.32 μm) was prepared as an adherend. A 25 mm wide surface protective film was attached so as to cover the mat surface of the adherend, thereby preparing a test piece. The pasting was performed by pressing at a speed of 300 mm / min using a 2 kg pressure-bonded rubber roller in an environment of 23 ° C. and a relative humidity of 50% RH. The obtained test piece was left in a temperature environment of 50 ° C. for 168 hours. After leaving, the test piece is taken out to room temperature and left for another 60 minutes. Then, according to JIS Z0237, the surface protective film is peeled off from the adherend in a 180 ° direction at a tensile speed of 300 mm / min, and the adhesive strength with time is measured. did. Moreover, the adhesive strength with time was determined according to the following criteria.
◎ (excellent) 0.15N / 25mm or more and less than 0.4N / 25mm ○ (good) 0.1N / 25mm or more and less than 0.15N / 25mm,
Or 0.4N / 25mm or more and less than 0.5N / 25mm x (defect) Less than 0.1N / 25mm or 0.5N / 25mm or more

(3) Adhesion progress rate Using the initial adhesive force and the temporal adhesive force obtained in the above (1) and (2), the rate of change from the initial adhesive force to the temporal adhesive force (adhesive progress rate) was calculated by the following equation. .
Rate of change (adhesion progress rate) (%) = (adhesive force with time / initial adhesive force) × 100
◎ (Excellent) 200% or less ○ (Good) Over 200% and less than 300% × (Defect) 300% or more

(4) Unfolding force A surface protective film was wound around a paper core having an inner diameter of 3 inches to produce a wound body having a width of 50 mm. Based on JIS Z0237, the surface protection film was rewound from the wound body at a rewinding speed of 20 m / min, and the high-speed rewinding force was measured. The measured value obtained is the deployment force.
◎ (excellent) Less than 0.05N / 25mm ○ (good) 0.05N / 25mm or more and less than 0.07N / 25mm × (defect) 0.07N / 25mm or more

According to the present invention, it is possible to provide a surface protective film that can be unwound from a wound body with a small unfolding force and has a high adhesive force (initial adhesive force), but is less likely to develop an adhesive force over time or at high temperatures. . 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 protection film 2 Base material layer 3 Adhesive layer 4 Prism sheet 5 Mat layer 6 Transparent film 7 Prism layer 8 Surface protection film 9 Core

Claims (7)

A surface protective film having a base material layer and an adhesive layer,
The pressure-sensitive adhesive layer has a storage elastic modulus G ′ at −30 ° C. of 400 MPa or more and a storage elastic modulus G ′ at 25 ° C. of 5.5 MPa or less, the first styrene elastomer as the main component, A second styrenic elastomer having a storage elastic modulus G ′ at −30 ° C. lower than that of the first styrenic elastomer,
The first styrene-based elastomers have the general formula [A-B] a copolymer having a structure represented by n ¹ (I) or its hydrogenated product, the general formula A-B-A or (A-B ) copolymer having the structure represented by x ¹ -Y ¹ (II) or a front surface protective film you characterized by containing a mixture of a hydrogenated product thereof.
A: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit, wherein the content of the aromatic alkenyl compound unit in the entire aromatic alkenyl polymer represented by A is 70% by weight or more B: An aromatic alkenyl-conjugated diene copolymer containing an aromatic alkenyl compound unit and a conjugated diene compound unit at random n ¹ : an integer of ^{1 to} 3 x ¹ : an integer of 1 or more Y ¹ : a coupling agent residue A surface protective film having a base material layer and an adhesive layer,
The pressure-sensitive adhesive layer has a storage elastic modulus G ′ at −30 ° C. of 400 MPa or more and a storage elastic modulus G ′ at 25 ° C. of 5.5 MPa or less, the first styrene elastomer as the main component, A second styrenic elastomer having a storage elastic modulus G ′ at −30 ° C. lower than that of the first styrenic elastomer,
The second styrene-based elastomer of the general formula [C-D] and copolymer (III) or its hydrogenated product having a structure represented by ^{n 2,} the general formula C-D-C or (C-D ) A copolymer (IV) having a structure represented by x ² -Y ² or a mixture thereof with a hydrogenated product thereof, wherein the content of aromatic alkenyl compound units in the whole mixture is 15% by weight or less. front surface protective film you wherein there.
C: An aromatic alkenyl polymer containing an aromatic alkenyl compound unit, wherein the content of the aromatic alkenyl compound unit in the entire aromatic alkenyl polymer represented by C is 70% by weight or more D: A conjugated diene polymer containing a conjugated diene compound unit, wherein the content of the conjugated diene compound unit in the whole conjugated diene polymer represented by D is 85% by weight or more n ² : an integer of 1 to 3 x ^2: 1 or more integer ^{Y 2:} coupling agent residue The surface protective film according to claim 1 , wherein the pressure-sensitive adhesive layer further contains a tackifier. The surface-protecting film according to claim 3 , wherein the tackifier has a softening point of 80 ° C. or higher. The surface protective film according to claim 1, 2, 3, or 4 , wherein the pressure-sensitive adhesive layer further contains a release agent. 6. The surface protective film according to claim 1, wherein the surface protective film is used by being attached to the mat layer of a prism sheet having a prism layer on the front surface and a mat layer on the back surface. A surface protective film according to claim 1, 2 , 3, 4, 5 or 6 attached to the mat layer of a prism sheet having a prism layer on the front surface and a mat layer on the back surface. Prism sheet with protective film.

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