JP5048964B2 - Surface protection film - Google Patents

Description

  The present invention relates to a surface protective film used for preventing adhesion of dust to the surface of an adherend and scratching of the surface of the adherend, and more specifically, a surface on which a pressure-sensitive adhesive layer is laminated on a polyolefin substrate. It relates to a protective film.

  In order to protect the article or member, a surface protective film may be temporarily attached to the surface of the article or member. The surface protective film is used, for example, in various adherends such as a synthetic resin plate, a metal plate, a decorative plywood, or various nameplates to prevent the surface from being soiled or damaged during processing and transportation. It is used.

  This type of surface protective film has a structure in which an adhesive layer is laminated on a film substrate. In general, a film made of a thermoplastic resin is used as the film substrate.

  By the way, the surface protective film is generally temporarily attached to the surface of the adherend by hand bonding, and is peeled off from the surface of the adherend when used. Therefore, the surface protective film has 1) sufficient initial adhesive strength, 2) good adhesive strength with time, and less adhesive strength with time, and 3) from the adherend. There is a demand for easy peeling and no adhesive residue on the adherend after peeling.

  Patent Document 1 below discloses a surface protective film in which a pressure-sensitive adhesive layer is laminated on the surface of a base material, and polyisobutylene is used as the pressure-sensitive adhesive layer. Here, it is shown that the performance of the surface protective film can be improved by using polyisobutylene for the pressure-sensitive adhesive layer.

On the other hand, Patent Document 2 below specifies a block copolymer having at least two terminal polymer blocks A and at least one intermediate polymer block B, a tackifier resin, and a softener. A pressure-sensitive adhesive composition is disclosed. Block A is a polymer block essentially derived from an aromatic vinyl compound, and block B is a polymer block essentially derived from isobutylene. According to Patent Document 2, it is said that, by this configuration, even when exposed to a high temperature of 70 ° C., the adhesive force hardly decreases and is stable against heat, and further excellent in stability against ultraviolet rays.
JP-A-6-73352 Japanese Examined Patent Publication No. 7-57865

  However, the surface protective film described in Patent Document 1 is excellent in the stability over time of the adhesive strength of the pressure-sensitive adhesive layer and the peeling workability, but the SP value is very low, so that the SP value such as an acrylic plate is used. The initial adhesive strength with a high adherend was not sufficient. That is, there was room for improvement in the initial adhesive strength of 1).

  On the other hand, the pressure-sensitive adhesive composition of Patent Document 2 was developed not only as a surface protective film for protecting articles and members as described above, but mainly for use in various pressure-sensitive adhesive tapes and pressure-sensitive adhesive sheets. . That is, even when this pressure-sensitive adhesive composition is applied to a surface protective film, the performance required for the surface protective film cannot be sufficiently satisfied. For example, when a surface protective film is formed using the pressure-sensitive adhesive composition of Patent Document 2, the adhesive strength with time may be inferior, and the adhesive strength may vary with time. In addition, it is inevitable that peeling from the adherend is extremely difficult after the surface protective film is applied to the adherend, or even if it can be peeled off, adhesive residue is left on the adherend after peeling.

  By the way, the surface protective film may be stored outdoors in winter in a state temporarily attached to the adherend. However, in the surface protective film described in Patent Document 1, the surface protective film tends to peel from the adherend when stored at a very low temperature such as outdoors in winter.

  Therefore, in addition to having the above performances 1) to 3), 4) the surface protective film was temporarily attached to the adherend and stored at a very low temperature as outdoors in winter. Even in such a case, there has been a strong demand for a surface protective film capable of sufficiently maintaining the temporary attachment state between the surface protective film and the adherend.

  The object of the present invention is to provide an excellent initial adhesive force to an adherend, excellent stability over time of the adhesive force, can be easily peeled off from the adherend, and can be applied to the adherend in view of the current state of the prior art described above. Then, even if it is stored outdoors in winter and exposed to low temperatures, it is intended to provide a surface protective film that hardly peels off from the adherend.

The present invention is a surface protective film in which an adhesive layer comprising an adhesive composition containing a rubber-based resin component and a tackifier resin is laminated on a polyolefin-based substrate, and the rubber-based resin component is a styrene-based film It is a styrene elastomer comprising a block copolymer of a polymer block (A) and an olefin polymer block (B), and the polystyrene-reduced weight average molecular weight measured by GPC of the styrene elastomer is in the range of 30000-400000. The tackifying resin is paraffinic process oil, liquid polyisobutylene or liquid hydrogenated terpene resin, and the tackifying resin is blended in the range of 5 to 70 parts by weight with respect to 100 parts by weight of the rubber-based resin component. The shear storage modulus of the pressure-sensitive adhesive layer at a frequency of 10 Hz is 3 × 10 ⁷ Pa or less at −30 ° C. The shear storage modulus at 10 Hz is in the range of 5 × 10 ^{4 to} 5 × 10 ⁶ Pa at 23 ° C.

In another specific aspect of the surface protective film according to the present invention, the shear storage modulus of the pressure-sensitive adhesive layer at a frequency of 10 Hz is 2 × 10 ⁵ Pa or more at 70 ° C.

In the surface protective film according to the present invention, the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition containing the specific rubber-based resin component and the tackifying resin described above is laminated on the polyolefin-based substrate, and the frequency of the pressure-sensitive adhesive layer Since the shear storage modulus at 10 Hz is 3 × 10 ⁷ Pa or less at −30 ° C. and the shear storage modulus at 10 Hz is in the range of 5 × 10 ^{4 to} 5 × 10 ⁶ Pa at 23 ° C., The initial adhesive strength is excellent, and the stability of the adhesive strength over time is enhanced. In addition, the adhesive layer of the surface protective film has sufficient adhesive strength even when it is exposed to low temperatures after being affixed to an adherend and stored outdoors in winter, etc. And the adherend can be sufficiently maintained.

  In addition, when the surface protective film of the present invention is used for protecting the surface of an adherend such as a synthetic resin plate, a metal plate, a decorative plywood or various nameplates, the surface of the adherend is stained during processing and transportation. Can be effectively prevented from adhering and the surface of the adherend from being damaged.

  When the rubber-based resin component is a styrene-based elastomer composed of a block copolymer of a styrene-based polymer block (A) and an olefin-based polymer block (B), and the block (B) is polyisobutylene Further, the initial adhesive strength to the adherend and the temporal stability of the adhesive strength are more excellent.

When the shear storage modulus at a frequency of 10 Hz of the pressure-sensitive adhesive layer is 2 × 10 ⁵ Pa or more at 70 ° C., it is more excellent in the stability of the adhesive force over time, and the fluctuation of the adhesive force over time can be suppressed. .

  Details of the present invention will be described below.

As a result of earnestly examining the surface protective film in which the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition containing the rubber-based resin component and the tackifier resin is laminated on the polyolefin-based substrate, the above-mentioned specific The pressure-sensitive adhesive layer is composed of a rubber-based resin component, and the shear storage elastic modulus at a frequency of 10 Hz of the pressure-sensitive adhesive layer is 3 × 10 ⁷ Pa or less at −30 ° C. The shear storage elastic modulus at 10 Hz is 5 × at 23 ° C. It was found that if the range of 10 ^{4 to} 5 × 10 ⁶ Pa was used, the above-described problem could be achieved, and the present invention was made.

  In the surface protective film according to the present invention, a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition containing a rubber-based resin component and a tackifier resin is laminated on a polyolefin-based substrate. The rubber resin component is a block copolymer of a styrene polymer block (A) and an olefin polymer block (B), a random copolymer block of styrene polymer block (A) and styrene and olefin. A block copolymer with (B ′) and / or a styrene-based elastomer having a hydrogenated product thereof as a main skeleton. In other words, the styrene elastomer is a styrene elastomer of the following (1), (2) or (3).

(1) A styrene elastomer having a main skeleton of a block copolymer of a styrene polymer block (A) and an olefin polymer block (B). Here, more specific examples of the olefin polymer block (B) include a conjugated diene polymer block and an isobutylene polymer block. The styrene-based elastomer is not particularly limited as long as the (A)-(B) block copolymer is a main skeleton. For example, AB, ABA, (AB) _n or (A _-B) copolymers thereof represented by like _n X. In addition, n is an integer greater than or equal to 1, and X is a residue by a coupling agent.

  (2) A styrene elastomer having a main skeleton of a block copolymer of a styrene polymer block (A) and a random copolymer block (B ′) of styrene and an olefin such as conjugated diene or isobutylene. Examples of such a styrene elastomer include the following (2-1) to (2-4).

(2-1) Block (A) and block (B ′) combined: AB ′ block copolymer (2-2) Tapered block in which styrene and styrene among conjugated dienes and isobutylene gradually increase (C ): A B′-C block copolymer (2-3) A styrene polymer block (A) instead of the tapered block (C): AB′-A block copolymer Combined (2-4) Repeated (2-1) to (2-3) and those bonded at an arbitrary ratio: (AB ′) _n , (AB ′) _n X, (A− _B'-C) n X, such as _{(A-B'-A) n} X.

  In addition, n is an integer greater than or equal to 1, and X is a residue by a coupling agent.

  (3) A styrene elastomer having the hydrogenated product of (1) or (2) as a main skeleton.

  Examples of the olefin used to form the olefin polymer block (B) or the random copolymer block (B ′) of the styrene elastomer include isobutylene, ethylene, butylene, and preferably isobutylene is used. .

  The olefin polymer block (B) is preferably polyisobutylene.

  In the above (2) styrene elastomer or (3) styrene elastomer having a hydrogenated product of (2) as the main skeleton, the content ratio of the constituent components of styrene and conjugated diene or isobutylene as an olefin is: The ratio is preferably 5:95 to 60:40, more preferably 7:93 to 40:60. When the content of styrene is less than 5% by weight, the cohesive strength of the pressure-sensitive adhesive layer is lowered, and there is a possibility that adhesive residue may be generated on the adherend when the surface protective film is peeled off. May be difficult to attach to the adherend.

  In the styrene elastomer of (3) having the main skeleton of the styrene elastomer of (2) and its hydrogenated product, in the configuration including the block (C), the block in the constitution of all monomers constituting the styrene elastomer The total of the styrene content ratio, which is the sum of the styrene content in (A) and the styrene content in the block (C), is preferably in the range of 3 to 50 wt%, more preferably in the range of 5 to 40 wt%. Is in the range of 5 to 25% by weight. When the total content of styrene in the block (A) and the block (C) is less than 3% by weight in the total monomers, the cohesive force of the pressure-sensitive adhesive layer is reduced, and the adhesive remains on the adherend when the surface protective film is peeled off. When the amount exceeds 50% by weight, the adhesive strength of the pressure-sensitive adhesive layer is insufficient, and sticking to the adherend may be difficult. The styrene content ratio in the block (A) in the constitution of all monomers constituting the styrene elastomer is preferably 3% by weight or more, more preferably 3 to 20% by weight.

  When the rubber-based resin component has an unsaturated double bond derived from an olefin, the unsaturated double bond is preferably as small as possible from the viewpoint of improving heat resistance and weather resistance, and hydrogenated as necessary. Is preferred. In this sense, a rubber-based resin component using isobutylene in which an unsaturated bond does not remain after completion of addition polymerization as an olefin is preferably used.

  In the styrene elastomer of (3) having a hydrogenated product of the styrene elastomer of (1) and (2) as a main skeleton, in the conjugated diene polymer block as the olefin polymer block (B), or with styrene It is preferable that at least 80% of the double bond of the conjugated diene moiety in the random copolymer block (B ′) with the conjugated diene that is an olefin is saturated by hydrogenation. A more preferable ratio of hydrogenation is 90% or more, and further preferably 95 to 100%. When the proportion of hydrogenation is less than 80%, heat resistance and weather resistance may be inferior.

  The weight average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography) of the styrene elastomer is preferably in the range of 30,000 to 400,000, more preferably in the range of 50,000 to 200,000. When the weight average molecular weight is less than 30000, the cohesive force of the pressure-sensitive adhesive layer is lowered, and thus, adhesive residue may be generated on the adherend when the surface protective film is peeled off. When the weight average molecular weight exceeds 400,000, the adhesive strength is insufficient, and troubles such as an increase in solution viscosity and melt viscosity may occur during the preparation of the pressure-sensitive adhesive composition and the production of the surface protective film.

  In this invention, in addition to the said rubber-type resin component, tackifying resin is further mix | blended with the adhesive composition which comprises an adhesive layer.

  Although it does not specifically limit as said tackifying resin, When it adds to a rubber-type resin component, what satisfies the range which the shear storage elastic modulus of the adhesive layer mentioned above is used preferably. Examples of such tackifier resins include terpene resins, paraffinic process oils, naphthenic process oils, aromatic process oils, castor oil, tall oil, natural oils, and liquid polyisobutylene resins. Specifically, as the terpene resin, Yashara Chemical Co., Ltd., trade name: Clearon, as the paraffinic process oil, Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil, as the liquid polyisobutylene resin, manufactured by BASF, Product name: Glysopearl, etc. These may be used independently and 2 or more types may be used together.

  It is preferable that the said tackifying resin is mix | blended in 5 to 70 weight part with respect to 100 weight part of rubber-type resin components, More preferably, it is 20 to 50 weight part. When the tackifying resin is less than 5 parts by weight, the shear storage modulus may be too high, and the adhesive force to the adherend may be insufficient. When the tackifying resin exceeds 70 parts by weight, the cohesive force of the pressure-sensitive adhesive layer is insufficient, and it may be difficult to peel off the adherend after temporarily attaching the surface protective film, and the adhesive remains on the adherend after peeling. May occur.

In the surface protective film according to the present invention, the shear storage modulus at a frequency of 10 Hz of the pressure-sensitive adhesive layer is 3 × 10 ⁷ Pa or less at −30 ° C.

  When the surface protective film is temporarily attached to the adherend and stored outdoors in winter, the temperature of the surface protective film may be lower than 0 ° C. In this case, in the conventional surface protective film, the adhesive force of the surface protective film is lowered, and the surface protective film may be peeled off naturally from the adherend.

  As a result of intensive studies, the present inventors have found that the natural peeling phenomenon of the surface protective film when stored outdoors in winter correlates with the adhesive force between the adhesive layer and the adherend at −5 ° C. I found it. Specifically, the peeling speed dependency of the adhesive strength between the adhesive layer and the adherend at −5 ° C. is evaluated, and if it is rubbery peeling in a region where the peeling speed is 30 mm / min or less, it is outdoors in winter. It was clarified that the surface protective film does not peel off from the adherend when it is stored, and the temporary attachment state can be sufficiently maintained.

Furthermore, it has been found that the adhesive force between the pressure-sensitive adhesive layer and the adherend at −5 ° C. is closely related to the shear storage modulus at −30 ° C., and has led to the present invention. That is, the present inventors found for the first time that the shear storage modulus at −30 ° C. is closely related to the natural peeling phenomenon of the surface protective film when stored outdoors in winter. In the present invention, by setting the shear storage modulus at −30 ° C. to a specific value, that is, 3 × 10 ⁷ Pa or less, the surface protective film is peeled off from the adherend when stored outdoors in winter. It was found that the temporary wearing state can be sufficiently maintained.

Therefore, at the time of filing the present application, the configuration in which the shear storage modulus at −30 ° C. was 3 × 10 ⁷ Pa or less resulted in rubber-like peeling at −5 ° C. in a region where the peeling speed was 30 mm / min or less, and the surface protective film Those skilled in the art also expect that the temporary attachment state with the adherend can be sufficiently maintained, in other words, that it has the effect of suppressing the natural peeling phenomenon of the coating film protective film when stored outdoors in winter. I didn't get it. That is, the structure having a shear storage modulus of 3 × 10 ⁷ Pa or less at −30 ° C. expresses an effect having unpredictability for those skilled in the art.

On the other hand, the shear storage elastic modulus at a frequency of 10 Hz of the pressure-sensitive adhesive layer needs to be in the range of 5 × 10 ^{4 to} 5 × 10 ⁶ Pa at 23 ° C. When the shear storage elastic modulus is outside this range, the surface protective film may be naturally peeled off from the adherend during transportation due to insufficient adhesive force, or the workability during peeling may be poor.

  That is, by setting the shear storage elastic modulus at −30 ° C. at a frequency of 10 Hz and the shear storage elastic modulus at 23 ° C. within the above specific range, the surface protective film has particularly good initial adhesive strength and is outdoor in winter. Thus, the temporary protective state can be sufficiently maintained without the surface protective film being peeled off from the adherend when stored.

In the surface protective film which concerns on this invention, it is preferable that the shear storage elastic modulus in 10 Hz of an adhesive layer is 2 * 10 < ⁵ > Pa or more at 70 degreeC. If the shear storage elastic modulus is less than 2 × 10 ⁵ Pa at 70 ° C., the adhesive force may vary with time.

  Although the thickness of an adhesive layer is not specifically limited, The range of 3-50 micrometers is desirable. If the thickness of the pressure-sensitive adhesive layer is less than 3 μm, the adhesive strength may be insufficient, and if it exceeds 50 μm, there is no advantage and it is economically disadvantageous.

  In the surface protective film according to the present invention, if necessary, a stabilizer such as a light-proofing agent and an antioxidant, an adhesion progressing preventing agent, and the like may be added to the pressure-sensitive adhesive layer as long as the pressure-sensitive adhesive performance is not impaired.

  The light stabilizer is not particularly limited, and examples thereof include salicylic acid series, benzophenone series, benzotriazole series, cyanoacrylate series light stabilizers such as hindered amine series, and antioxidants include phenol. System (monophenol type, bisphenol type, polymer type phenol type), sulfur type, phosphorus type and the like.

  Examples of the anti-adhesion progress agent include fatty acid amides, polyethyleneimine long-chain alkyl grafts, soybean oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 251”, etc.), tall oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 6300”, etc.).

  The surface protective film according to the present invention has a structure in which a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition configured as described above is laminated on a polyolefin-based substrate.

  The polyolefin constituting the polyolefin-based substrate is not particularly limited, and polyolefins such as polypropylene and polyethylene, polyolefins mixed with olefin-based elastomers, and the like can be used.

  In the base material, it is optional to add known additives usually blended in this field. Examples of additives include stabilizers such as light-proofing agents and antioxidants that can be added to the pressure-sensitive adhesive layer, as well as lubricants, antistatic agents, rust preventives, and pigments.

  Although the thickness of the said polyolefin-type base material changes with purposes of use, 20-100 micrometers is preferable. If the thickness is 20 μm or less, the protective performance of the adherend may not be sufficiently exhibited, or the handling property may be inferior. If the thickness is 100 μm or more, the waist is too strong and the followability at the time of pasting deteriorates, or floats or peels off after pasting. May easily occur.

  The method for producing the surface protective film is not particularly limited, but for example, a method of laminating and integrating the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer and the composition constituting the polyolefin-based substrate, Or the method of laminating | stacking an adhesive composition on the polyolefin-type base material formed into a film, and laminating | stacking and integrating etc. is mentioned.

  As a method of laminating and integrating the polyolefin base material and the pressure-sensitive adhesive composition by coextrusion, a known method such as an inflation method or a T-die method can be used. As a method for laminating the pressure-sensitive adhesive composition on a polyolefin-based substrate, a solution coating method for coating a pressure-sensitive adhesive solution, a dry lamination method, an extrusion coating method using a T-die, or the like is used. Among these, a co-extrusion method using a T-die is preferable because quality can be improved and production can be made economically. Further, when the solution coating method is performed, in order to increase the bonding strength between the base material layer and the pressure-sensitive adhesive layer, it is preferable to apply a primer to the polyolefin base material in advance to perform surface treatment.

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

(Materials used)
[Rubber resin component]
SIBS (1); manufactured by Kaneka Co., Ltd., product number: Shibster 073T, block copolymer of styrene and isobutylene (styrene content in all monomers: 30% by weight)
SIBS (2); manufactured by Kaneka Co., Ltd., product number: Shibster 072T, block copolymer of styrene and isobutylene (styrene content in all monomers: 20% by weight)
SEBS (1); manufactured by Kraton Polymer Co., Ltd., product number: Kraton G1657, block copolymer of styrene and ethylene / butylene (styrene content ratio in all monomers: 13% by weight)
SEBS (2); manufactured by Asahi Kasei Co., Ltd., product number: Tuftec H1052, block copolymer of styrene and ethylene / butylene (styrene content in all monomers: 20% by weight)

[Tackifying resin]
Diana process oil P-430; Idemitsu Kosan Co., Ltd., paraffinic process oil Glysopearl V190; BASF, liquid polyisobutylene resin Glysopearl V500; BASF, liquid polyisobutylene resin Clearon LH; Yasuhara Chemical Co., liquid hydrogenated terpene resin Alcon P125; Arakawa Chemical Industries, hydrogenated petroleum resin

Example 1
A rubber-based pressure-sensitive adhesive composition containing 100 parts by weight of SIBS (1) as a styrene-based elastomer as a rubber-based resin component and 20 parts by weight of Diana Process Oil P-430 as a tackifier resin was prepared. A rubber-based pressure-sensitive adhesive layer made of this pressure-sensitive adhesive composition and a layer made of polypropylene (a block polypropylene manufactured by Sun Allomer Co., Ltd., PB170A) are coextruded by a T-die method, and a rubber having a thickness of 10 μm is formed on a polypropylene substrate having a thickness of 50 μm. A surface protective film having a laminated pressure-sensitive adhesive layer was obtained.

(Examples 2-7 and Comparative Examples 1-3)
A surface protective film was obtained in the same manner as in Example 1 except that the types and blending ratios of the rubber-based resin component and tackifying resin used were changed as shown in Tables 1 and 2 below.

(Evaluation of Examples and Comparative Examples)
The (1) shear storage elastic modulus of the rubber-based pressure-sensitive adhesive layer in each obtained surface protective film was determined as follows. Further, (2) low temperature adhesive strength, (3) initial adhesive strength, (4) initial peel strength, and (5) aging adhesive strength of each surface protective film were evaluated as follows.

(1) Shear storage elastic modulus The shear storage elastic modulus of the rubber-based pressure-sensitive adhesive layer was measured at a frequency of 10 Hz and a heating rate of 6 ° C./min with a dynamic viscoelasticity spectrum measurement device (IT Measurement Control Co., Ltd., product number: DVA200). It measured in the range of -50 degreeC-+150 degreeC, and calculated | required the shear storage elastic modulus in -30 degreeC, 23 degreeC, and 70 degreeC.

(2) Low-temperature adhesive strength From the rubber adhesive layer side, the surface protective film was placed on an acrylic plate (Kuraray Co., Ltd., Paragrass cast plate, thickness 2 mm) in an environment of room temperature 23 ° C. and relative humidity 65%. Using a 2 kg pressure-bonded rubber roller, it was attached at a speed of 300 mm / min and left in that state for 30 minutes. Next, after leaving in a thermostatic bath at -5 ° C. for 30 minutes, 180-degree peeling at a width of 25 mm was performed at each speed of 0.3, 3, 30, 300 and 500 mm / min. The peeling form of the adhesive layer of the surface protective film at this time was evaluated according to the following evaluation criteria.

[Evaluation criteria for low-temperature adhesive strength]
○: Rubber peeled off (rubbery)
Δ: Vibration peeling (stick-slip)
X: Glassy peeling (Glassy)

(3) Initial adhesive force The surface protective film was affixed on the acrylic board similarly to the case of the evaluation of the low temperature adhesive force of said (2). After leaving in that state for 30 minutes, a 180 degree peel strength at a width of 25 mm was measured at a speed of 300 mm / min. The peel strength measured in this manner was taken as the initial adhesive strength.

(4) Initial peeling force The surface protective film was affixed on the acrylic board similarly to the case of the evaluation of the low temperature adhesive force of said (2). After leaving in that state for 30 minutes, the 180 degree peel strength at a width of 25 mm was measured at a speed of 30 m / min. The peel strength measured in this way was taken as the initial peel force.

(5) Adhesive strength with time The surface protective film was affixed to an acrylic plate in the same manner as in the evaluation of the low temperature adhesive strength of (2) above. In this state, it was left in a gear oven at 70 ° C. for 7 days, and further left for 24 hours in an environment at room temperature of 23 ° C. and relative humidity of 65%. Thereafter, the 180 degree peel strength at 25 mm width of the surface protective film was measured at a speed of 300 mm / min.

  The results are shown in Tables 1 and 2 below.

Claims (2)

A pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing a rubber-based resin component and a tackifier resin is a surface protective film laminated on a polyolefin-based substrate,
The rubber-based resin component is a styrene- based elastomer composed of a block copolymer of a styrene-based polymer block (A) and an olefin-based polymer block (B), and the block (B) is polyisobutylene,
The polystyrene-reduced weight average molecular weight measured by GPC of the styrenic elastomer is in the range of 30,000 to 400,000.
The tackifying resin is paraffinic process oil, liquid polyisobutylene or liquid hydrogenated terpene resin,
The tackifying resin is blended in the range of 5 to 70 parts by weight with respect to 100 parts by weight of the rubber-based resin component,
The pressure-sensitive adhesive layer has a shear storage modulus at a frequency of 10 Hz of 3 × 10 ⁷ Pa or less at −30 ° C., and a shear storage modulus at 10 Hz in the range of 5 × 10 ^{4 to} 5 × 10 ⁶ Pa at 23 ° C. A surface protective film characterized by that. 2. The surface protective film according to claim 1, wherein the pressure-sensitive adhesive layer has a shear storage elastic modulus of 2 × 10 ⁵ Pa or more at 70 ° C. at a frequency of 10 Hz.