JP2015074771A - Surface protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film that can obtain uniform adhesive strength and is easily drawn out from a wound body while maintaining sufficient adhesive strength.SOLUTION: A surface protective film of the present invention includes a polyolefin substrate layer and an adhesive layer. The adhesive layer contains a mixed styrene-based elastomer comprising at least a first styrene-based elastomer having a glass transition temperature of -40°C or more and a second styrene-based elastomer having a glass transition temperature of less than -40°C,and a tackifier. The hardness (Martens hardness) of the adhesive layer is 0.4 N/mmor less, and the loop tack is 0.2 N/25 mm or more and 1.0 N/25 mm or less.

Description

  The present invention relates to a surface protective film. In particular, the present invention relates to a surface protective film suitable for protecting the surface of an adherend having an uneven shape such as a prism sheet or a mat sheet.

A surface protective film is known which is laminated on the surface of a metal plate, a glass plate, a synthetic resin plate or the like and prevents the surface of these articles from being scratched or adhering to dust or the like.
As this type of surface protective film, there is a surface protective film formed by forming a pressure-sensitive adhesive layer made of a composition containing a block copolymer and a tackifying resin together with a polyolefin resin substrate by a coextrusion method or the like. It is disclosed (see Patent Documents 1 to 3).
The surface protective film can be laminated by a co-extrusion method, can achieve solvent-free pressure-sensitive adhesive, and is excellent in terms of environmental protection and safety and health during production. Moreover, since the manufacturing process can be simplified, it is economically superior.

When the surface protective film is stored or transported as a roll wound in a roll shape, the pressure-sensitive adhesive layer wound on the back surface of the base material may be strongly adhered to the base material.
As a result, the feeding of the surface protective film from the roll is hindered, and the efficiency of the sticking work to the adherend surface is reduced. Moreover, if it tries to force it out, a base material will be partially extended and deform | transformed, or an adhesive layer may peel partially, and there exists a possibility that it may become impossible to use as a surface protection film.

As described above, it is an object of the surface protective film to achieve both stable adhesive strength to the adherend and feeding property from the wound body.
In order to solve the above-mentioned problems, a technique for achieving both stable adhesive strength to the adherend and unwinding from the wound body by defining the hardness of the adhesive within a specific range has been studied (patent) References 4 and 5).

JP-A-61-103975 Japanese Patent No. 2713519 JP 2000-80336 A JP 2010-126711 A JP 2012-77244 A

On the other hand, the attachment of the surface protective film to the adherend is performed by superimposing the surface protective film fed from the wound body on the adherend and using a nip roll or the like on the adherend on which the surface protective film is superimposed. This is done by applying a predetermined pressure.
However, it is difficult to apply the same level of pressure across the entire width of the surface protection film drawn from the wound body, and uniform adhesive strength in the width direction can be obtained due to uneven pressure in the width direction at the time of application. There was no case.
Therefore, an object of the present invention is to provide a surface protective film that can obtain uniform adhesive strength and can be easily unwound from a roll while maintaining sufficient adhesive strength.

In order to solve the above-mentioned problems, the present inventors diligently studied the layer structure of the pressure-sensitive adhesive layer in order to obtain a pressure-sensitive adhesive layer that is not easily affected by the pressure at the time of attachment.
When the surface protective film is laminated on the adherend, the adhesive strength on the end side becomes higher than the vicinity of the center in the width direction of the surface protective film fed out from the roll due to uneven pressure of the nip roll. In many cases, uniform adhesive strength is not obtained in the entire region in the width direction.
This is presumed that the pressure during lamination is higher on the end side than in the vicinity of the central part in the width direction, and the contact area with the adherend becomes larger on the end side than in the vicinity of the central part in the width direction. Is done.
Moreover, since the pressure at the time of lamination differs depending on the adherend, the adhesive strength generated depending on the lamination conditions also differs.
Such uneven adhesive strength has been addressed by increasing the tackiness of the adhesive layer surface by increasing the hardness of the adhesive layer. However, in the above correspondence, the adjustment range of the adhesive strength is narrow, and it is difficult to obtain the feeding property from the wound body.

Polyolefin, which has been used to adjust the hardness as a constituent component of the adhesive layer, is a harder material than the styrene-based elastomer. For this reason, it is difficult to obtain uniform adhesive strength depending on the uneven shape of the adherend surface and the lamination conditions.
Therefore, in order to obtain a constant contact area under any lamination condition, conventionally, the polyolefin which was a constituent component of the adhesive layer is not used, and the hardness adjustment is performed only with the styrene-based elastomer. The hardness was adjusted to be lower than before.
Further, for the tackiness per unit area, the tackiness of the pressure-sensitive adhesive layer was adjusted by controlling the glass transition temperature, styrene content, and diblock content of the styrene elastomer.
Specifically, it is composed of a mixed styrene elastomer mixed with at least two components having different glass transition temperatures and a tackifier, so that the hardness of the pressure-sensitive adhesive is softer than before and is attached to the adherend. It has been found that it is possible to maintain the same feedability as before while being hardly affected by the pressure at the time of attaching.

The present invention provides the following surface protective film.
That is, the surface protective film of the present invention is a surface protective film provided with a polyolefin-based substrate layer and an adhesive layer, and the adhesive layer is a first styrene system having a glass transition temperature of −40 ° C. or higher. A mixed styrene elastomer containing at least an elastomer and a second styrene elastomer having a glass transition temperature of less than −40 ° C. and a tackifier, and the hardness (Martens hardness) of the adhesive layer is 0.4 N / mm ² or less, and loop tack is 0.2 N / 25 mm or more and 1.0 N / 25 mm or less.

  In the surface protective film of the present invention, the first styrene elastomer has a styrene content of 5% by mass to 30% by mass, a diblock copolymer content of 30% by mass or less, and a glass transition temperature of −40 ° C. It is preferably 20 ° C. or lower.

  In the surface protective film of the present invention, the second styrene elastomer has a styrene content of 5% by mass to 30% by mass, a diblock copolymer content of 50% by mass or less, and a glass transition temperature of −100 ° C. It is preferable that it is less than -40 degreeC above.

  In the surface protective film of the present invention, the thickness of the adhesive layer is preferably 10 μm or less.

  In the surface protective film of the present invention, the adhesive layer is preferably laminated by a coextrusion method.

  In the surface protective film of the present invention, the external haze of the base material layer is preferably 20% or less.

  According to the surface protective film of the present invention, it is possible to provide a surface protective film that is controlled to have a uniform adhesive strength without being affected by the laminating conditions at the time of lamination to an adherend. In addition, even when the back surface of the base material layer forming the surface protective film is smooth while maintaining sufficient adhesion strength to adherends having protrusions on the surface, it is more than necessary as a wound product. It is possible to provide a surface protective film that can be easily drawn out without causing the surfaces of the layer and the base material layer to adhere firmly.

In an Example, the figure which shows typically the outline | summary of the test which measures a loop tack.

  Embodiments of the present invention will be described below.

  The surface protective film of this embodiment is a film which protects the surface of the adherend having an uneven shape, and includes a base material layer and an adhesive layer.

[Configuration of base material layer]
As the base material layer, any sheet or film generally used as a support for a surface protective film can be used without any particular limitation. For example, a film formed of a polyolefin-based material is preferable. .

  Examples of the polyolefin-based material that can be used as the base material layer include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, ethylene- Examples thereof include ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-n-butyl acrylate copolymer, polypropylene (homopolymer, random copolymer, block copolymer) and the like. In addition, these polyolefin-type materials may be used independently and may be used as a mixture and composition by arbitrary combinations. In particular, block copolymer polypropylene (hereinafter sometimes abbreviated as “BPP”) is preferable as the material of the base material layer. By using BPP, the surface of the base material layer is roughened, and the drawability is further improved, and the tear strength and impact strength are improved.

Moreover, you may mix | blend additives, such as a pigment, anti-aging agent, a stabilizer, and an ultraviolet absorber, with a base material layer as needed.
Furthermore, the base material layer is not limited to a single layer and may be formed of a plurality of layers. The total thickness of the base layer composed of a single layer or a plurality of layers is, for example, 20 μm or more and 100 μm or less, preferably 30 μm or more and 80 μm or less.

As the base material layer of this embodiment, a film having an external haze of 20% or less can be used. In general, a small external haze means that the surface is smooth and contributes to the transparency of the base material layer and also the surface protective film. However, in the conventional surface protection film, it is necessary to increase the roughness of the surface of the base material layer in consideration of the drawability from the roll product, and as a result, the transparency of the base material layer and the surface protection film is required. It was a sacrifice. In the present embodiment, as will be described later, by setting the hardness of the adhesive layer and the loop tack within a predetermined range, a transparent film having an external haze of 20% or less is used as a base material layer to obtain a wound product. Even in some cases, it is possible to exhibit excellent payout performance.
In addition, the external haze of a base material layer can be measured based on JISK7105, for example.

[Configuration of adhesive layer]
The adhesive layer contains a mixed styrene elastomer and a tackifier.

[Mixed styrene elastomer]
The mixed styrene elastomer blended in the adhesive layer contains at least a first styrene elastomer and a second styrene elastomer.
The first styrene-based elastomer and the second styrene-based elastomer are, for example, block copolymers represented by the following general formula (1) or general formula (2).
A-B-A (1)
AB (2)
A is preferably a styrene copolymer block, B is an ethylene-propylene copolymer, a butadiene copolymer block, an isoprene copolymer block, or a polymer block obtained by hydrogenating these.

The styrene content of the first styrene elastomer is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less.
Moreover, 5 mass% or more and 30 mass% or less are preferable, and, as for the styrene content of a 2nd styrene-type elastomer, 10 mass% or more and 25 mass% or less are more preferable.

The styrene content is determined, for example, by the following method.
The block copolymer composition contained in the adhesive layer of the surface protective film is dissolved in a small amount of hexane, and then excess acetone is added to separate the acetone insoluble and soluble components. (Spectrum) measurement is performed, and the integral intensity ratio of the spectrum is calculated.

The content of the diblock copolymer of the first styrene elastomer is preferably 30% by mass or less, and more preferably 20% by mass or less.
Further, the content of the diblock copolymer of the second styrene elastomer is preferably 50% by mass or less, and more preferably 1% by mass or more and 40% by mass or less.

The content of the diblock copolymer is determined by, for example, the following method.
The block copolymer composition contained in the adhesive layer of the surface protective film was dissolved in tetrahydrofuran (THF), and GS5000H and G4000H liquid chromatograph columns manufactured by Tosoh Corporation were each provided in two stages, for a total of four stages. Are connected in series, and high performance liquid chromatography is performed using THF as a mobile phase under the conditions of a temperature of 40 ° C. and a flow rate of 1 mL / min. The peak area corresponding to the coupling component, that is, the diblock copolymer is determined from the obtained chart. The percentage of this peak area relative to the total peak area is taken as the content of the diblock copolymer.

  The glass transition temperature of the first styrene elastomer is −40 ° C. or more and 20 ° C. or less, and the glass transition temperature of the second styrene elastomer is −100 ° C. or more and less than −40 ° C. Among these, the glass transition temperature of the first styrene elastomer is more preferably −40 ° C. or more and 0 ° C. or less. Moreover, as for the glass transition temperature of a 2nd styrene-type elastomer, -80 degreeC or more and less than -40 degreeC are more preferable.

A glass transition temperature is calculated | required by the following method, for example.
After the block copolymer composition contained in the adhesive layer of the protective film is dissolved in a small amount of hexane, excess acetone is added to separate the acetone-insoluble and soluble components. The insoluble matter is heated at a rate of 20 ° C./min from room temperature with a differential scanning calorimeter, and the heat generation amount is measured to create an endothermic curve. Two extension lines are drawn on the endothermic curve, and the glass transition temperature is obtained from the intersection of the 1/2 straight line between the extension lines and the endothermic curve.

The content of the vinyl-polyisoprene block is determined, for example, by the following method.
The raw material pellet of the adhesive layer is dissolved in deuterated chloroform, NMR (nuclear magnetic resonance spectrum) measurement is performed, and the integral intensity ratio of the spectrum is calculated.
The first styrene elastomer and the second styrene elastomer may or may not be hydrogenated.

[Tackifier]
The tackifier to be blended in the adhesive layer is selected as the constituent part B of the block copolymer represented by A-B-A in the general formula (1) or A-B in the general formula (2). Resins that are compatible with each other can be preferably employed. As such a resin, for example, an aliphatic hydrocarbon resin, a terpene resin, a coumarone / indene resin, an aromatic hydrocarbon resin, a rosin resin and the like are preferably used.
Moreover, you may mix | blend additives, such as softeners, such as a liquid polymer and paraffin oil, a filler, a pigment, anti-aging agent, a stabilizer, and a ultraviolet absorber, with the adhesion layer.

  A desirable ratio of the tackifier added to the adhesive layer is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the mixed styrene-based elastomer. When the blending amount of the tackifier is less than 1 part by mass, the adhesive strength becomes weak, and for example, the adhesive strength to an adherend having a protrusion may be weakened and peeled off. On the other hand, when the compounding amount of the tackifier exceeds 50 parts by mass, the adherend may be contaminated by bleed and the cohesive force may be reduced. Moreover, since the adhesive strength between the adhesive layer and the smooth base material layer having a low external haze (the back surface of the wound body) is increased, there is a possibility that the drawability from the wound body product is lowered.

[Surface protection film]
In the surface protective film of the present embodiment, the adhesive layer has a hardness (Martens hardness) of 0.4 N / mm ² or less. Since the hardness is too high when it exceeds 0.4 N / mm ² , for example, when the adherend has a protrusion, the ease of following the uneven shape of the adherend is different, so the pressure bonding at the time of pasting Depending on conditions, there is a possibility that uniform adhesive strength in the width direction cannot be obtained.
Further, if the hardness of the adhesive layer exceeds 0.4 N / mm ² , it is difficult to follow the uneven shape of the adherend when the pressure in the pressure bonding condition at the time of attachment is too low, so that sufficient adhesive strength is obtained. Cannot be obtained and the film may be peeled off from the adherend.
The hardness of the adhesive layer can be adjusted by, for example, the hardness and blending ratio of the first styrene elastomer and the second styrene elastomer to be blended in the adhesive layer.

  In the surface protective film of this embodiment, the loop tack when the adhesive layer is used as the adherend is 0.2 N / 25 mm or more and 1.0 N / 25 mm or less. When the loop tack is less than 0.2 N / 25 mm, the adhesive force of the adhesive layer is insufficient, and the film may peel from the adherend. When the loop tack exceeds 1.0 N / 25 mm, the adhesive strength of the adhesive layer is strong, the adhesive strength between the adhesive layer and the back surface of the base material layer becomes too strong, and the feedability from the roll product may be reduced. This is not preferable because of its properties. The loop tack of the adhesive layer can be adjusted by, for example, the diblock amount of the mixed styrenic elastomer to be blended in the adhesive layer and the blending amount of the tackifier.

The thickness of the adhesive layer is preferably 10 μm or less. More preferably, they are 1 micrometer or more and 5 micrometers or less. Here, the thickness of the adhesive layer does not necessarily have a lower limit, but if the thickness is less than 1 μm, the tip may be damaged when the adherend has a protrusion. In addition, the adhesive strength may be reduced, and peeling from the adherend may occur. When the thickness of the pressure-sensitive adhesive layer exceeds 10 μm, the pressure-sensitive adhesive strength is increased, and there is a possibility that an adhesive residue may be generated at the time of peeling from the adherend. Moreover, since the adhesive strength with the back surface of a base material layer becomes strong, there exists a possibility that the drawing | feeding-out property from a roll product may fall.
Therefore, practically, the preferable thickness of the pressure-sensitive adhesive layer is 1 μm or more and 5 μm or less.

The base material layer and the adhesive layer in the surface protective film of the present embodiment are not particularly specified, but are preferably laminated by a coextrusion method. According to the co-extrusion method, the base material layer and the adhesive layer can be laminated at a time without using any solvent, and the surface protective film can be formed by a relatively simple production apparatus. Moreover, the manufacturing cost of the surface protective film can be reduced at a low cost by simplifying the manufacturing process. Furthermore, in the surface protective film formed by the co-extrusion method, the interlayer strength between the surface of the base material layer and the adhesive layer is strong, and the possibility that adhesive residue is generated at the time of peeling from the adherend is reduced. The coextrusion method may be a feed block method or a multi-manifold method.
Further, the surface protective film of this embodiment can be used for the purpose of protecting the surface of adherends such as metal plates, glass plates and synthetic resin plates. In particular, the apex angles of these adherends are 80 ° to 100 °. Up to 20 μm to 80 μm in height can be suitably used for prism sheets having protrusions having a substantially triangular cross section.

[Effect of the embodiment]
According to the above-described embodiment, the following effects can be achieved.
According to the surface protective film of this embodiment, the hardness (Martens hardness) of the adhesive layer is 0.4 N / mm ² or less, and the loop tack is 0.2 N / 25 mm or more and 1.0 N / 25 mm or less. Since the hardness and loop tack of the pressure-sensitive adhesive layer are adjusted within the above range, it is possible to provide a surface protective film controlled to have a uniform pressure-sensitive adhesive strength without being affected by the lamination conditions during lamination to the adherend. .
Further, the mixed styrene elastomer was configured to include at least a first styrene elastomer having a glass transition temperature of −40 ° C. or higher and a second styrene elastomer having a glass transition temperature of less than −40 ° C. With the above configuration, it is possible to achieve both an appropriate adhesive strength and a good feeding property from the wound product.
Moreover, since it is not particularly necessary to greatly roughen the back surface of the base material layer, the surface protection film can be made highly transparent.

[Modification]
In addition, this invention is not limited to the above-mentioned embodiment, The change in the range which can achieve the objective of this invention, improvement, etc. are included in this invention.
In the present embodiment, the surface protective film provided with the base material layer and the adhesive layer is exemplified, but the present invention is not limited thereto, and for example, another functional layer such as an ultraviolet absorbing layer may be provided. In this case, the adherend surface can be protected not only from physical contact but also from other factors such as ultraviolet rays.
Moreover, you may mix | blend a mold release material with a base material layer. Thereby, when it is made into a wound body, better unwinding property is obtained without contaminating the adhesive layer. Examples of the release material include a resin obtained by graft polymerization of siloxane to olefin.
In addition, specific materials and configurations in the implementation of the present invention may be other materials and configurations as long as the object of the present invention can be achieved.

  Next, the present invention will be described in more detail with reference to examples and comparative examples. In addition, this invention is not restrict | limited to the description content of these Examples at all.

[Example 1]
69.0% by mass of styrene elastomer A shown below, 6.0% by mass of styrene elastomer B, 11.5% by mass of styrene elastomer C, and 13.5% by mass of tackifier were mixed. Thus, an adhesive layer material was obtained.
This adhesive layer material and mRPP (trade name Wintech WFW-4, manufactured by Nippon Polypro Co., Ltd.), which is a base material, are formed by a two-layer coextrusion method, the adhesive layer thickness is 1 μm, and the base material layer thickness is 39 μm. Thus, coextrusion was performed by a feed block method to obtain a surface protective film.

The styrene elastomer and tackifier used for the adhesive layer are shown below.
Styrene elastomer A: Styrene content is 20% by mass, diblock copolymer content is 0% by mass, glass transition temperature is −15 ° C. (Kuraray Co., Ltd., trade name Hibler 7125)
Styrene elastomer B: styrene content is 13% by mass, diblock copolymer content is 0% by mass, glass transition temperature is −32 ° C. (Kuraray Co., Ltd., trade name HIBLER 7311)
Styrene elastomer C: styrene content is 13% by mass, diblock copolymer content is 30% by mass, glass transition temperature is −50 ° C. (product name: G1657, manufactured by Kraton Polymer Co., Ltd.)
・ Tackifier (trade name Alcon P-140, manufactured by Arakawa Chemical Co., Ltd.)

[Example 2]
As the adhesive layer material, 21.7% by mass of styrene elastomer A, 9.4% by mass of styrene elastomer B, 50.2% by mass of styrene elastomer C, and 18.7% by mass of tackifier, respectively. A surface protective film was obtained in the same manner as in Example 1 except that the mixture was used.

[Comparative Example 1]
The adhesive layer material is 26.6% by mass of styrene elastomer A, 50.2% by mass of styrene elastomer C, and 4.5% by mass of mRPP (trade name Wintech WFW-4, manufactured by Nippon Polypro Co., Ltd.) as the polyolefin. And the surface protection film was obtained like Example 1 except having used what mixed 18.7 mass% of tackifiers, respectively.

[Comparative Example 2]
As the adhesive layer material, 13.6% by mass of styrene elastomer A, 57.7% by mass of styrene elastomer C, 10.0% by mass of polyolefin, and 18.7% by mass of tackifier A surface protective film was obtained in the same manner as in Example 1 except that was used.

[Comparative Example 3]
As the adhesive layer material, 54.3% by mass of styrene elastomer A, 29.7% by mass of styrene elastomer B, 2.4% by mass of polyolefin, and 13.6% by mass of tackifier are mixed. A surface protective film was obtained in the same manner as in Example 1 except that was used.

〔Evaluation method〕
About each film of the Example and comparative example which were mentioned above, various characteristics were evaluated by the method shown below. The results are shown in Table 1.

(1) Hardness of adhesive layer (Martens hardness)
Martens hardness was measured using an ultra-micro hardness meter (HM2000 manufactured by Fischer Instruments Co., Ltd.) with a test force of 1 mN and a load speed of 0.05 mN / sec.

(2) Loop tack The loop tack was measured using a device in which an Imada digital force gauge ZP-5N was mounted on an Imada vertical electric measurement stand MV-500NII-L550. Specifically, it is as follows.
The adhesive layer of the film cut out to a width of 25 mm and a length of 300 mm is fixed to the digital force gauge crosshead with the adhesive layer on the outside, and the crosshead is lowered to the acrylic plate on the stage until the contact length is 5 mm and held for 3 seconds. After that, the digital force gauge value was corrected to zero, peeled at a pulling speed of 0.3 m / min, and the resistance value (N / 25 mm) at that time was measured. FIG. 1 schematically shows the outline of the test.

(3) Adhesive strength Under conditions of a linear pressure of 0.04 MPa and 2 m / min, the film has a surface roughness Ra of 0.40 μm, Ry of 2.3 μm, and Rz of 1.6 μm (surface roughness evaluation equipment Tokyo Seimitsu Co., Ltd.) It was press-bonded to a polycarbonate resin mat sheet (manufactured by Handy Surf E-35B) and stored at 23 ° C. for 24 hours. Then, using a tensile tester, peeling was performed at a tensile speed of 0.3 m / min and a 180 ° C. peel, and the resistance value (N / 25 mm) at that time was measured.
Further, the adhesive strength was measured in the same manner as described above except that the pressure bonding conditions (linear pressure 0.4 MPa) were changed.
Further, when the adhesive strength under the linear pressure of 0.4 MPa and 2 m / min is less than 2 times compared to the adhesive strength under the conditions of the linear pressure of 0.04 MPa and 2 m / min, These cases are shown as x in Table 1.

(4) Feeding strength Under the conditions of a linear pressure of 0.38 MPa and 2 m / min, the pressure-sensitive adhesive surface of the film and the back surface of the base material layer were pressure-bonded and stored at 23 ° C. for 5 minutes. Then, using a tensile tester, peeling was performed at a tensile speed of 0.3 m / min and 90 ° peel, and the resistance value (N / 25 mm) at that time was measured. Table 1 also shows the case of less than 0.2 N / 25 mm as ◯ and the case of 0.2 N / 25 mm or more as x.

(5) Haze The total haze of the film was measured according to JIS K 7105 using a haze meter (HZ-1 manufactured by Suga Test Instruments Co., Ltd.). The external haze of the base material layer was determined using the following method.
Measure the haze in advance by sandwiching only silicone oil (trade name SH200 manufactured by Toray Dow Corning Silicone Co., Ltd.) between two glass plates (Hz1), and then sandwich the film with the adhesive layer coated with silicone oil. Then, the haze was measured (Hz2), then the haze was measured by sandwiching a film coated on both sides with silicone oil (Hz3), and the external haze (Hz4) of the base material layer was determined from the following formula.
Hz4 = (Hz2-Hz1)-(Hz3-Hz1)
The case where the external haze was 20% or less was rated as ◯, and the case where it exceeded 20% was rated as x.

  Especially this invention can be utilized as a suitable surface protection film in order to protect the surface of the to-be-adhered body which has uneven | corrugated shape on the surfaces, such as a prism sheet and a mat sheet.

Claims (6)

A surface protective film comprising a polyolefin-based substrate layer and an adhesive layer,
The adhesive layer is
A first styrene elastomer having a glass transition temperature of −40 ° C. or higher, a mixed styrene elastomer containing at least a second styrene elastomer having a glass transition temperature of less than −40 ° C., and a tackifier,
The surface protective film, wherein the adhesive layer has a hardness (Martens hardness) of 0.4 N / mm ² or less and a loop tack of 0.2 N / 25 mm or more and 1.0 N / 25 mm or less. In the surface protection film according to claim 1,
The first styrene elastomer is
Styrene content is 5 mass% or more and 30 mass% or less,
The content of the diblock copolymer is 30% by mass or less,
A glass transition temperature is −40 ° C. or higher and 20 ° C. or lower. In the surface protection film according to claim 1 or 2,
The second styrene elastomer is
Styrene content is 5 mass% or more and 30 mass% or less,
The content of the diblock copolymer is 50% by mass or less,
The surface protective film characterized by having a glass transition temperature of −100 ° C. or higher and lower than −40 ° C. In the surface protection film according to any one of claims 1 to 3,
The thickness of the said adhesion layer is 10 micrometers or less. The surface protection film characterized by the above-mentioned. In the surface protection film according to any one of claims 1 to 4,
The surface-protective film, wherein the adhesive layer is laminated by a coextrusion method. In the surface protection film according to any one of claims 1 to 5,
The external haze of the base material layer is 20% or less.

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