JP2020100103A - Protective sheet and laminate - Google Patents

Abstract

To provide a protective sheet having excellent heat resistance, and a laminate including the protective sheet.SOLUTION: There is provided a protective sheet comprising a base material and an adhesive layer laminated on one side of the base material. When an elongation rate (%) measured by the tensile test at 23°C of the adhesive layer is defined as E1, an elongation rate (%) measured by the tensile test at 23°C of the adhesive layer which has been heated at 100°C for 30 minutes is defined as E2, the protective sheet has a ratio of the elongation rate E2 relatively to the elongation rate E1 (E2/E1) of 0.9 or more and 5 or less, and a loss tangent tanδ of 0.1 or more and 1 or less at 23°C in the adhesive layer which has been heated at 100°C for 30 minutes.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a protective sheet that can be suitably used for protecting the surface of an optical member and the like, and a laminate including the protective sheet.

Conventionally, in devices such as optical members and electronic members, a pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer is provided on the surface of the device in order to prevent scratches on the surface during processes such as processing, assembly, and inspection. , May be attached as a protective sheet. This protective sheet is peeled off from the device when protection is no longer required.

In the above-mentioned process, a process that exposes the device to a high temperature environment may be performed. In such a process, the protective sheet attached to the device is also heated. Therefore, the protective sheet is required to have a predetermined heat resistance. For example, even when the protective sheet is heated, it is required that the adhesiveness to the device can be maintained and unintentional peeling from the device does not occur. Further, even when the protective sheet is heated, good releasability can be maintained, and it is required that the protective sheet can be easily peeled from the device.

Patent Document 1 discloses a pressure-sensitive adhesive for a surface protection film, which is intended to achieve the heat resistance as described above. In particular, in Patent Document 1, a) 100 parts by weight of a (meth)acrylic acid alkyl ester containing a (meth)acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms as a main component, and b) a carboxyl group-containing compound 1 to 15 parts by weight of a polymerizable compound and 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms are added to a copolymer of a monomer mixture, and the carboxyl of the component b is added. Disclosed is a pressure-sensitive adhesive for a surface protective film, which comprises an equivalent amount or more of a cross-linking agent based on the base.

JP-A-11-256111

However, in recent years, the types of devices to be protected and the types of processing performed in the process have been diversified, and the conventional protective sheet as disclosed in Patent Document 1 has become insufficient in heat resistance. There is. In particular, in recent years, the surface on which the hard coat layer is provided has been increasingly protected, and when a conventional protective sheet is used for the surface of such a hard coat layer, the adhesion and peeling property after heat treatment are increased. It is difficult to achieve both.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a protective sheet having excellent heat resistance, and a laminate including the protective sheet.

In order to achieve the above-mentioned object, firstly, the present invention is a protective sheet comprising a base material and a pressure-sensitive adhesive layer laminated on one surface side of the base material, wherein the pressure-sensitive adhesive layer is stretched. The elongation rate (%) at 23° C. by the test is E _1, and the elongation rate (%) at 23° C. by the tensile test of the pressure-sensitive adhesive layer after heating the pressure-sensitive adhesive layer at 100° C. for 30 minutes is E ₂ when the said ratio of the elongation _E the elongation _{E 2} for _{1 (E} 2 / _{E 1)} is 0.9 or more and 5 or less, after the pressure-sensitive adhesive layer was heated at 100 ° C. 30 minutes The loss tangent tan δ of the pressure-sensitive adhesive layer at 23° C. is 0.1 or more and 1 or less, and the present invention provides a protective sheet (Invention 1).

In the protective sheet according to the above invention (Invention 1), the ratio (E ₂ /E ₁ ) of the elongation rate of the pressure-sensitive adhesive layer is within the above range, so that the pressure-sensitive adhesive layer is heated even when the protective sheet is heated. The above property is maintained, and while exhibiting good adhesion to the adherend, it can be favorably separated from the adherend at the time of peeling. Furthermore, when the loss tangent tan δ of the pressure-sensitive adhesive layer after heating is within the above range, even when the protective sheet is attached to the surface having fine irregularities such as the surface of the hard coat layer. The pressure-sensitive adhesive layer can appropriately follow the irregularities, and can achieve good adhesion and releasability at a high level even after heating.

In the above invention (Invention 1), the pressure-sensitive adhesive in the protective sheet is attached to the surface on the hard coat layer side in the resin plate with a hard coat layer, which comprises a resin plate and a hard coat layer laminated on one side of the resin plate. Regarding a laminate obtained by pasting the surface on the agent layer side, after the laminate is placed in an environment of 23° C. and 50% RH for 24 hours, the protective sheet is peeled off to expose the resin with the hard coat layer. The water contact angle (°) measured on the surface of the plate on the hard coat layer side was W ₁ , and the laminate was placed in an environment of 23° C. and 50% RH for 24 hours, and subsequently heated at 100° C. for 30 minutes. Then, after being placed in an environment of 23° C. and 50% RH for 30 minutes, the water contact angle measured on the surface of the resin plate with the hard coat layer exposed by peeling off the protective sheet. when the (°) was _{W 2,} the ratio of the water contact angle _{W 2} with respect to the water contact angle _{W 1 (W 2 / W 1} ) is 0.8 or more and 1.2 or less ( Invention 2).

In the above inventions (Inventions 1 and 2), the adhesive force of the protective sheet to the surface on the hard coat layer side in a resin plate with a hard coat layer, which comprises a resin plate and a hard coat layer laminated on one side of the resin plate. Is preferably 0.5 N/25 mm or more and 10 N/25 mm or less (Invention 3).

In the above inventions (Inventions 1 to 3), the protective sheet is provided for the surface on the hard coat layer side in the resin plate with a hard coat layer, which includes a resin plate and a hard coat layer laminated on one side of the resin plate. The adhesive force of the protective sheet to the hard coat layer constituting the laminate is 0.3 N/25 mm after heating the laminate obtained by pasting the surface on the side of the adhesive layer in 100° C. for 30 minutes. As described above, it is preferably 10 N/25 mm or less (Invention 4).

In the above inventions (Inventions 1 to 4), it is used for protecting the surface on the hard coat layer side in a resin plate with a hard coat layer comprising a resin plate and a hard coat layer laminated on one side of the resin plate. Preferably (Invention 5).

Secondly, the present invention comprises a resin plate with a hard coat layer, which comprises a resin plate and a hard coat layer laminated on one side of the resin plate, and the protective sheet (inventions 1 to 5). The pressure-sensitive adhesive layer side surface of the above is laminated on the hard coat layer side surface of the resin plate with the hard coat layer (Invention 6).

The protective sheet according to the present invention has excellent heat resistance. Moreover, the laminated body according to the present invention includes a protective sheet having excellent heat resistance.

Hereinafter, embodiments of the present invention will be described.
[Protection sheet]
The protective sheet according to the present embodiment includes a base material and an adhesive layer laminated on one surface side of the base material. A release sheet may be laminated on the pressure-sensitive adhesive layer side surface of the protective sheet according to the present embodiment in order to protect the pressure-sensitive adhesive layer until the protective sheet is used.

1. Physical Properties of Protective Sheet (1) Elongation Ratio In the protection sheet according to the present embodiment, the elongation ratio (%) at 23° C. of the pressure-sensitive adhesive layer measured by a tensile test is E ₁ , and the pressure-sensitive adhesive layer is heated at 100° C. for 30 minutes. elongation at 23 ° C. by the tensile test of the pressure-sensitive adhesive layer (%) in the case of the _{E 2,} the ratio of the elongation _{E 2} with respect to the elongation _{E 1 (E} 2 / _{E 1)} is, after 0 9 or more and 5 or less. When the above ratio (E ₂ /E ₁ ) is in this range, the pressure-sensitive adhesive layer in the present embodiment can maintain its properties well even when heated. Thereby, the protective sheet according to the present embodiment is prevented from being unintentionally peeled off from the adherend during the process and after the process is completed. On the other hand, when the protective sheet is to be peeled off from the adherend, the protective sheet does not stick too strongly to the adherend and can be easily peeled off.

When the ratio _(E 2 _/ E ₁₎ is less than 0.9, when the protective sheet is heated, cohesion of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is lost greatly. As a result, the adhesion to the adherend is lowered, and the protective sheet is unintentionally peeled off from the adherend. From this viewpoint, the ratio (E ₂ /E ₁ ) is preferably 0.95 or more, and particularly preferably 1.0 or more.

If the ratio (E ₂ /E ₁ ) exceeds 5, the adhesiveness of the pressure-sensitive adhesive layer to the adherend will be excessively increased after heating, and the protective sheet after use can be easily removed from the adherend. It becomes difficult to peel it off. From this viewpoint, the ratio (E ₂ /E ₁ ) is preferably 3 or less, particularly preferably 2 or less, and further preferably 1.2 or less.

In the protective sheet according to the present embodiment, the elongation rate E ₁ is preferably 100% or more, more preferably 120% or more, particularly preferably 150% or more, and further 200% or more. Is preferred. Further, the elongation rate E ₁ is preferably 1000% or less, particularly preferably 600% or less, and further preferably 300% or less. When the elongation rate E ₁ is within these ranges, the ratio (E ₂ /E ₁ ) can be easily adjusted to the above range.

In the protective sheet according to the present embodiment, the elongation rate E ₂ is preferably 90% or more, more preferably 100% or more, particularly preferably 120% or more, and further 150% or more. Is preferable and 200% or more is the most preferable. The elongation rate E ₂ is preferably 1000% or less, particularly preferably 600% or less, and further preferably 300% or less. When the elongation rate E ₂ is within these ranges, it becomes easy to adjust the ratio (E ₂ /E ₁ ) within the above range.

The details of the method for measuring the elongation rate E ₁ and the elongation rate E ₂ described above are as described in the test examples described later.

(2) Loss tangent tan δ
In the protective sheet according to the present embodiment, the loss tangent tan δ at 23° C. of the adhesive layer after heating the adhesive layer at 100° C. for 30 minutes is 0.1 or more and 1 or less. When the loss tangent tan δ is in the above range, the pressure-sensitive adhesive layer after heating can favorably follow the fine structure existing on the surface of the adherend. For example, there may be fine irregularities on the surface of the antiglare hard coat layer, but the pressure-sensitive adhesive layer after heating can appropriately follow such irregularities, and therefore, it is appropriate. It exhibits adhesiveness. As a result, the protective sheet according to the present embodiment can achieve both excellent adhesion and releasability at a high level even when it is attached to the surface having fine irregularities.

When the loss tangent tan δ is less than 0.1, when the protective sheet is heated, the ability of the pressure-sensitive adhesive layer to follow the fine structure of the adherend surface is significantly reduced. This causes a problem that the protective sheet attached to the surface having fine irregularities is unintentionally peeled off. From this viewpoint, the loss tangent tan δ is preferably 0.12 or more, and particularly preferably 0.15 or more.

Further, when the loss tangent tan δ exceeds 1, the handleability, productivity and processability of the pressure-sensitive adhesive layer will be significantly reduced. From this viewpoint, the loss tangent tan δ is preferably 0.5 or less, and particularly preferably 0.3 or less.

In the protective sheet according to the present embodiment, the loss tangent tan δ at 23° C. of the pressure-sensitive adhesive layer (that is, the loss tangent tan δ at 23° C. of the pressure-sensitive adhesive layer that has not been heated as described above) is 0.1 or more. Is particularly preferable, 0.12 or more is particularly preferable, and 0.15 or more is further preferable. The loss tangent tan δ is preferably 1 or less, more preferably 0.5 or less, and further preferably 0.3 or less. When the loss tangent tan δ at 23° C. of the pressure-sensitive adhesive layer is within these ranges, it becomes easy to adjust the loss tangent tan δ at 23° C. of the pressure-sensitive adhesive layer after heating to the above range.

The details of the method for measuring the loss tangent tan δ of the pressure-sensitive adhesive layer at 23° C. before and after the above-described heating are as described in the test examples described later.

(3) Storage elastic modulus In the protective sheet according to the present embodiment, the adhesive layer has a storage elastic modulus at 23° C. of preferably 0.01 MPa or more, particularly preferably 0.08 MPa or more, and further It is preferably 0.12 MPa or more. The storage elastic modulus is preferably 2 MPa or less, more preferably 1 MPa or less, particularly preferably 0.8 MPa or less, and further preferably 0.4 MPa or less.

Moreover, in the protective sheet according to the present embodiment, the storage elastic modulus at 23° C. of the pressure-sensitive adhesive layer after heating the pressure-sensitive adhesive layer at 100° C. for 30 minutes is preferably 0.01 MPa or more, and particularly, 0. The pressure is preferably 08 MPa or more, more preferably 0.12 MPa or more. The storage elastic modulus is preferably 2 MPa or less, more preferably 1 MPa or less, particularly preferably 0.8 MPa or less, and further preferably 0.4 MPa or less.

When the storage elastic moduli before and after the above-mentioned heating are in the above-mentioned ranges, respectively, it becomes easy to adjust the loss tangent tan δ at 23°C of the above-mentioned heated adhesive layer within the above-mentioned range. The details of the method for measuring the storage elastic modulus before and after heating are as described in the test examples described later.

(4) Water contact angle In the protective sheet according to the present embodiment, after being adhered to a predetermined adherend and placed under predetermined conditions, the exposed surface of the adherend exposed by peeling off the protective sheet is: It preferably exhibits a water contact angle as described below.

First, the pressure-sensitive adhesive layer-side surface of the protective sheet is attached to the hard-coat layer-side surface of the resin plate with a hard-coat layer that includes a resin plate and a hard-coat layer laminated on one side of the resin plate. The laminated body formed by the combination is referred to as a first laminated body.

Then, after the first laminate is placed in an environment of 23° C. and 50% RH for 24 hours, the protective sheet is peeled off from the first laminate to expose the hard coat layer in the resin plate with the hard coat layer. The water contact angle (°) measured on the side surface is W ₁ .

In addition, the first laminated body is placed in an environment of 23° C. and 50% RH for 24 hours, subsequently heated at 100° C. for 30 minutes, and further placed in an environment of 23° C. and 50% RH for 30 minutes. The water contact angle (°) measured on the surface of the resin plate with a hard coat layer, which is exposed by peeling the protective sheet from the first laminate, is W ₂ .

In this case, the ratio of the water contact angle _{W 2} for the water contact angle _{W 1 (W 2 / W 1} ) is preferably not less than 0.8 and preferably, in particular 0.88 or more, more It is preferably 0.98 or more. Further, the ratio (W ₂ /W ₁ ) is preferably 1.2 or less, particularly preferably 1.1 or less, and further preferably 1.05 or less. When the ratio (W ₂ /W ₁ ) is in these ranges, the pressure-sensitive adhesive layer according to the present embodiment effectively suppresses changes in properties before and after heating, and thus, according to the present embodiment. Even when the protective sheet is heated, it becomes easy to achieve both excellent adhesion and releasability with respect to the adherend.

Further, the water contact angle W ₁ is preferably 40° or more, more preferably 50° or more, particularly preferably 60° or more, and further preferably 68° or more. Further, the water contact angle W ₁ is preferably 90° or less, particularly preferably 80° or less, and further preferably 72° or less. By setting the water contact angle W ₁ in these ranges, it becomes easy to adjust the ratio (W ₂ /W ₁ ) to the range described above.

Further, the water contact angle W ₂ is preferably 40° or more, more preferably 50° or more, particularly preferably 60° or more, and further preferably 70° or more. Further, the water contact angle W ₂ is preferably 95° or less, particularly preferably 85° or less, and further preferably 75° or less. By setting the water contact angle W ₂ in these ranges, it becomes easy to adjust the ratio (W ₂ /W ₁ ) to the range described above.

Next, a laminated body obtained by laminating the pressure-sensitive adhesive layer-side surface of the protective sheet to one surface of the glass plate is used as a second laminated body.

Then, after the second laminated body is placed in an environment of 23° C. and 50% RH for 24 hours, the protective sheet is peeled off from the second laminated body, and water measured on the exposed surface of the glass plate is exposed. The contact angle (°) is W ₃ .

In addition, after the second laminate is placed in an environment of 23° C. and 50% RH for 24 hours, subsequently heated at 100° C. for 30 minutes, and further placed in an environment of 23° C. and 50% RH for 30 minutes, The water contact angle (°) measured on the exposed surface of the glass plate exposed by peeling the protective sheet from the second laminate is W ₄ .

In this case, the ratio of the water contact angle W ₄ for the water contact angle _{W 3 (W 4 / W 3} ) is preferably 1 or more, preferably in particular 2 or more, more is 3 or more It is preferable. Further, the ratio (W ₄ /W ₃ ) is preferably 6 or less, particularly preferably 5 or less, and further preferably 4 or less. When the ratio (W ₄ /W ₃ ) is within these ranges, the pressure-sensitive adhesive layer in the present embodiment effectively suppresses changes in properties before and after heating, and thus the present embodiment is concerned. Even when the protective sheet is heated, it becomes easy to achieve both excellent adhesion and releasability with respect to the adherend.

Further, the water contact angle W ₃ is preferably 5° or more, particularly preferably 10° or more, and further preferably 15° or more. Further, the water contact angle W ₃ is preferably 60° or less, more preferably 50° or less, particularly preferably 40° or less, and further preferably 30° or less, Most preferably, it is 20° or less. By setting the water contact angle W ₃ in these ranges, it becomes easy to adjust the ratio (W ₄ /W ₃ ) to the range described above.

Further, the water contact angle W ₄ is preferably 30° or more, particularly preferably 40° or more, and further preferably 50° or more. The water contact angle W ₄ is preferably 95° or less, more preferably 85° or less, particularly preferably 75° or less, and further preferably 60° or less. When the water contact angle W ₄ is within these ranges, it becomes easy to adjust the ratio (W ₄ /W ₃ ) within the above range.

The details of the method for measuring the water contact angles W ₁ , W ₂ , W ₃ and W ₄ described above are as described in the test examples described later.

(5) Adhesive force In the protective sheet according to the present embodiment, the adhesive force to the surface on the hard coat layer side of the resin plate with the hard coat layer, which includes the resin plate and the hard coat layer laminated on one side of the resin plate. Is preferably 0.5 N/25 mm or more, particularly preferably 0.7 N/25 mm or more, and further preferably 0.9 N/25 mm or more. Further, the adhesive strength is preferably 10 N/25 mm or less, more preferably 5 N/25 mm or less, particularly preferably 2 N/25 mm or less, and further preferably 1.5 N/25 mm or less. Is preferred. When the adhesive force is 0.5 N/25 mm or more, the protective sheet easily adheres well to the resin plate with the hard coat layer, and it is possible to effectively prevent unintended peeling during a process or the like. .. Further, when the adhesive force is 10 N/25 mm or less, the protective sheet can be more easily peeled from the resin plate with the hard coat layer.

Further, in the protective sheet according to the present embodiment, in the protective sheet with respect to the surface on the hard coat layer side in the resin plate with a hard coat layer, which comprises a resin plate and a hard coat layer laminated on one side of the resin plate, The adhesive force of the protective sheet to the hard coat layer constituting the laminate is 0.3 N/25 mm or more after heating the laminate obtained by pasting the surface of the adhesive layer side at 100° C. for 30 minutes. It is preferably 0.5 N/25 mm or more, and more preferably 0.65 N/25 mm or more. Further, the adhesive strength is preferably 10 N/25 mm or less, particularly preferably 5 N/25 mm or less, and further preferably 2 N/25 mm or less. When the adhesive strength is 0.3 N/25 mm or more, the protective sheet easily adheres well to the resin plate with the hard coat layer even after heating, which effectively prevents unintended peeling after the heat treatment. It can be suppressed to. Further, when the adhesive force is 10 N/25 mm or less, the protective sheet can be more easily peeled from the resin plate with the hard coat layer even after heating.

Further, in the protective sheet according to the present embodiment, the adhesive force to the glass plate is preferably 0.1 N/25 mm or more, particularly preferably 0.2 N/25 mm or more, and further 0.3 N/25 mm The above is preferable. Further, the adhesive strength is preferably 10 N/25 mm or less, more preferably 5 N/25 mm or less, particularly preferably 2 N/25 mm or less, and further 0.8 N/25 mm or less. Is preferred. When the adhesive force is 0.1 N/25 mm or more, the protective sheet easily adheres well to the glass plate, and unintentional peeling during the process or the like can be effectively suppressed. Moreover, when the adhesive force is 10 N/25 mm or less, the protective sheet is more easily peeled from the glass plate.

In addition, in the protective sheet according to the present embodiment, the laminated body obtained by laminating the pressure-sensitive adhesive layer-side surface of the protective sheet to one surface of the glass plate is heated at 100° C. for 30 minutes, and then the laminated body is formed. The adhesive force of the protective sheet to the constituent glass plate is preferably 0.1 N/25 mm or more, particularly preferably 0.2 N/25 mm or more, and further preferably 0.5 N/25 mm or more. .. Further, the adhesive force is preferably 10 N/25 mm or less, more preferably 5 N/25 mm or less, particularly preferably 2 N/25 mm or less, and further preferably 1 N/25 mm or less. .. When the adhesive strength is 0.1 N/25 mm or more, the protective sheet easily adheres well to the glass plate even after heating, and can effectively prevent unintended peeling after the heat treatment. Becomes Further, when the adhesive force is 10 N/25 mm or less, the protective sheet can be more easily peeled from the glass plate even after heating.

The details of the above-mentioned four methods of measuring the adhesive force are as described in the test examples described later.

(6) Rate of change in total light transmittance of adherend In the protective sheet according to the present embodiment, a laminate obtained by laminating the protective sheet on the adherend is placed under an environment of 23° C. and 50% RH. It was assumed that the protective sheet was peeled off from the laminate after being left for 24 hours, heated at 100° C. for 30 minutes, and further allowed to stand at room temperature by standing for 30 minutes in an environment of 23° C. and 50% RH. In this case, with respect to the total light transmittance measured for the adherend before attaching the protective sheet to the adherend, the change in the total light transmittance measured for the adherend after the heating and peeling. The ratio is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and further preferably 0% (that is, total light transmittance does not change). .. When the rate of change described above is 5% or less, the adherend protected by the protective sheet according to the present embodiment easily exhibits desired performance. The details of the method for measuring the total light transmittance described above are as described in the test examples described later.

2. Each member constituting the protective sheet (1) Base material The base material in the present embodiment is not particularly limited as long as the pressure-sensitive adhesive layer can be laminated, and preferably the use of the protective sheet according to the present embodiment. Depending on the one used. For example, when the device is exposed to a high temperature environment in the state where the protective sheet according to the present embodiment is attached, the base material has heat resistance to an applied temperature (for example, 90 to 150° C.). Is preferred. Further, when performing a light emission inspection of the device via the protective sheet according to the present embodiment, it is preferable to use, as the base material, a material that is transparent to the light of the wavelength used in the inspection. ..

Specific examples of the base material include polyesters such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate, cellulose such as diacetyl cellulose, triacetyl cellulose and acetyl cellulose butyrate, polyolefins such as polyethylene and polypropylene, polyimides and polyethers. Imide, polycarbonate, polymethylpentene, polyphenylene sulfide, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polystyrene, polysulfone, polyetheretherketone, polyethersulfone, fluororesin, polyamide, acrylic resin A plastic film made of a resin such as a norbornene-based resin, a cycloolefin resin, or a liquid crystal polymer is preferable. In addition, these plastic films may be a film composed of a single layer or a film in which a plurality of layers of the same kind or different kinds are laminated.

In the base material, the surface on which the pressure-sensitive adhesive layer is laminated may be subjected to a surface treatment by an oxidation method or a textured method, or a primer treatment for the purpose of improving the adhesion with the pressure-sensitive adhesive layer. Examples of the oxidation method include corona discharge treatment, plasma discharge treatment, chromium oxidation treatment (wet type), flame treatment, hot air treatment, ozone, and ultraviolet irradiation treatment, and examples of the roughening method include a sand blast method, A thermal spraying method and the like can be mentioned. These surface treatment methods are appropriately selected depending on the type of substrate.

Although the thickness of the substrate is not particularly limited, it is preferable that the protective sheet has a thickness that can sufficiently achieve the protective function. For example, the thickness of the base material is preferably 10 μm or more, particularly preferably 25 μm or more, and further preferably 38 μm or more. Further, the thickness of the base material is preferably 200 μm or less, particularly preferably 175 μm or less, and further preferably 150 μm or less.

(2) Pressure-sensitive adhesive layer The pressure-sensitive adhesive that constitutes the pressure-sensitive adhesive layer in the present embodiment satisfies the above-mentioned ratio (E ₂ /E ₁ ), and the loss tangent tan δ after heating is in the above-mentioned range, and further protects The sheet is not particularly limited as long as it has predetermined adhesiveness and peelability. In particular, as the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer, acrylic pressure-sensitive adhesives, silicone pressure-sensitive adhesives, rubber pressure-sensitive adhesives and urethane pressure-sensitive adhesives are preferable. Adhesives are preferred.

The acrylic pressure-sensitive adhesive is preferably one obtained from a pressure-sensitive adhesive composition containing the (meth)acrylic acid ester polymer (A) (hereinafter sometimes referred to as "pressure-sensitive adhesive composition P"). The adhesive composition P preferably contains a crosslinking agent (B) in addition to the (meth)acrylic acid ester polymer (A). In addition, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Further, the term "polymer" includes the concept of "copolymer".

(2-1) (Meth)acrylic acid ester polymer (A)
The (meth)acrylic acid ester polymer (A) preferably contains a (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. As a result, good tackiness is easily exhibited. The alkyl group may be linear or branched.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group and having 1 to 20 carbon atoms in the alkyl group is preferable from the viewpoint of adhesiveness. .. Examples of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and (meth)acrylic. Acid n-butyl, (meth)acrylic acid n-pentyl, (meth)acrylic acid n-hexyl, (meth)acrylic acid 2-ethylhexyl, (meth)acrylic acid isooctyl, (meth)acrylic acid n-decyl, (meth ) N-dodecyl acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate and the like can be mentioned. Among them, from the viewpoint of further improving the tackiness, an alkyl acrylate having an alkyl group having 3 to 8 carbon atoms is preferable, and at least one of n-butyl acrylate and 2-ethylhexyl acrylate is particularly preferably used. In addition, these may be used individually and may be used in combination of 2 or more type.

The (meth)acrylic acid ester polymer (A) preferably contains 40% by mass or more, and preferably 60% by mass or more, of a (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. It is particularly preferable to contain 80% by mass or more. When the lower limit of the content of the (meth)acrylic acid alkyl ester is the above, the (meth)acrylic acid ester polymer (A) can exhibit suitable tackiness. Further, the (meth)acrylic acid ester polymer (A) preferably contains 99% by mass or less, and particularly 95% by mass or less of a (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. It is preferable that the content is 92 mass% or less. When the upper limit of the content of the (meth)acrylic acid alkyl ester is the above, a suitable amount of another monomer component such as a reactive functional group-containing monomer is introduced into the (meth)acrylic acid ester polymer (A). It will be easy.

The (meth)acrylic acid ester polymer (A) contains, as a monomer unit constituting the polymer, a reactive group-containing monomer having a reactive group capable of reacting with the crosslinking agent (B) in the molecule. Is preferred. The reactive group derived from this reactive group-containing monomer reacts with the cross-linking agent (B) to form a cross-linked structure (three-dimensional network structure), and a pressure-sensitive adhesive having a desired cohesive force is obtained.

As the reactive group-containing monomer, a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxy group in the molecule (carboxy group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer) ) And the like are preferred. Among these, at least one of a hydroxyl group-containing monomer and a carboxy group-containing monomer, which have excellent reactivity with the crosslinking agent (B) and have little adverse effect on the adherend, is particularly preferable.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and (meth ) Hydroxyalkyl esters of (meth)acrylic acid such as 3-hydroxybutyl acrylate and 4-hydroxybutyl (meth)acrylic acid. Among them, 2-hydroxyethyl (meth)acrylate from the viewpoint of the reactivity of the hydroxyl group in the obtained (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and the copolymerizability with other monomers. 2-hydroxyethyl methacrylate is preferable from the viewpoint that the formed pressure-sensitive adhesive layer easily satisfies the above-described ratio (E ₂ /E ₁ ) regarding the elongation rate and the loss tangent tan δ. These may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid and citraconic acid. Among them, acrylic acid is preferable from the viewpoint of the reactivity of the carboxy group in the obtained (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and the copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include aminomethacrylate (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains a reactive group-containing monomer as a monomer unit constituting the polymer at a lower limit of 1% by mass or more, and preferably 2% by mass or more. Is more preferable, and it is particularly preferable to contain 4% by mass or more. When the reactive group-containing monomer is a carboxy group-containing monomer, it is preferably contained in an amount of 8% by mass or more. The (meth)acrylic acid ester polymer (A) preferably contains a reactive group-containing monomer as a monomer unit constituting the polymer in an amount of 25% by mass or less as an upper limit, and 18% by mass or less. It is more preferable that the content is 12% by mass or less. In addition, when the reactive group-containing monomer is a hydroxyl group-containing monomer, it is preferable to further contain 8% by mass or less. When the (meth)acrylic acid ester polymer (A) contains the reactive group-containing monomer in the above-mentioned amount as a monomer unit, a favorable crosslinked structure is formed in the obtained pressure-sensitive adhesive, and a desired cohesive force is easily obtained. As a result, the formed pressure-sensitive adhesive layer easily satisfies the above-described ratio (E ₂ /E ₁ ) regarding the elongation rate and the loss tangent tan δ.

It is also preferable that the (meth)acrylic acid ester polymer (A) contains a monomer having an alicyclic structure in the molecule (an alicyclic structure-containing monomer) as a monomer unit constituting the polymer. Since the alicyclic structure-containing monomer is bulky, it is presumed that the alicyclic structure-containing monomer is present in the polymer to widen the interval between the polymers, and the adhesive obtained has a predetermined flexibility. This makes it easier for the pressure-sensitive adhesive layer to satisfy the ratio (E ₂ /E ₁ ) and the loss tangent tan δ regarding the elongation rate described above.

The carbon ring of the alicyclic structure in the alicyclic structure-containing monomer may have a saturated structure or may partially have an unsaturated bond. Further, the alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure such as a bicyclic ring or a tricyclic ring. From the viewpoint of making the distance between the obtained (meth)acrylic acid ester polymers (A) appropriate and imparting a predetermined flexibility to the pressure-sensitive adhesive, the alicyclic structure is a polycyclic alicyclic structure ( It is preferably a polycyclic structure). Furthermore, in consideration of the compatibility of the (meth)acrylic acid ester polymer (A) with other components, the polycyclic structure is particularly preferably a bicyclic ring to a tetracyclic ring. Further, from the viewpoint of imparting predetermined flexibility in the same manner as above, the carbon number of the alicyclic structure (refers to all carbon numbers in the part forming the ring, and when a plurality of rings are present independently, Is preferably 5 or more, and particularly preferably 7 or more. On the other hand, although the upper limit of the number of carbon atoms in the alicyclic structure is not particularly limited, it is preferably 15 or less, and particularly preferably 10 or less from the viewpoint of compatibility as in the above.

Specific examples of the alicyclic structure-containing monomer include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, and (meth)acrylic. Examples thereof include dicyclopentenyl acid and dicyclopentenyloxyethyl (meth)acrylate, with isobornyl (meth)acrylate being preferred. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer, it must contain 0.5% by mass or more of the alicyclic structure-containing monomer. It is preferable that the content is 1% by mass or more, and more preferably 2% by mass or more. Further, the (meth)acrylic acid ester polymer (A) preferably contains 10% by mass or less, particularly 8% by mass or less, of an alicyclic structure-containing monomer as a monomer unit constituting the polymer. Is preferable, and it is more preferable that the content is 5% by mass or less. When the content of the alicyclic structure-containing monomer is within the above range, the obtained pressure-sensitive adhesive layer can more easily satisfy the above-mentioned ratio (E ₂ /E ₁ ) with respect to the elongation rate and the loss tangent tan δ.

The (meth)acrylic acid ester polymer (A) may contain a monomer other than the above-mentioned monomer as a monomer unit constituting the polymer. Examples of such a monomer include non-crosslinkable acrylamides such as acrylamide and methacrylamide, methoxyethyl (meth)acrylate, (meth)acrylic acid alkoxyalkyl esters such as ethoxyethyl (meth)acrylate, and (meth)acrylic acid. Examples thereof include (meth)acrylic acid esters having a non-crosslinkable tertiary amino group such as N,N-dimethylaminoethyl acrylate and N,N-dimethylaminopropyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

Among the above, the (meth)acrylic acid ester polymer (A) preferably contains acrylamide as a monomer unit constituting the polymer, and particularly preferably contains N-(butoxymethyl)acrylamide. When the (meth)acrylic acid ester polymer (A) contains acrylamide as a monomer unit constituting the polymer, the obtained pressure-sensitive adhesive easily forms a desired crosslinked structure, and thus has a suitable cohesive force. Will be things. This makes it easier for the obtained pressure-sensitive adhesive layer to satisfy the above-described ratio (E ₂ /E ₁ ) regarding the elongation rate and the loss tangent tan δ.

When the (meth)acrylic acid ester polymer (A) contains acrylamide as a monomer unit constituting the polymer, it preferably contains 0.5% by mass or more, and particularly 1% by mass or more of the acrylamide. It is preferable that the content is 1.5% by mass or more. The (meth)acrylic acid ester polymer (A) preferably contains 10% by mass or less of acrylamide as a monomer unit constituting the polymer, more preferably 8% by mass or less, and particularly 5% by mass. The content is preferably not more than mass%, more preferably not more than 3 mass%. When the content of acrylamide is within the above range, the obtained pressure-sensitive adhesive is more likely to form a desired crosslinked structure and has a suitable cohesive force. This makes it easier for the obtained pressure-sensitive adhesive layer to satisfy the above-described ratio (E ₂ /E ₁ ) of the elongation rate and the loss tangent tan δ.

The (meth)acrylic acid ester polymer (A) is preferably a linear polymer. By being a linear polymer, entanglement of molecular chains is likely to occur, and a pressure-sensitive adhesive having a desired cohesive force is easily formed.

Further, the (meth)acrylic acid ester polymer (A) is preferably a solution polymerized product obtained by a solution polymerization method. By being a solution polymer, a high molecular weight polymer is easily obtained, and a pressure-sensitive adhesive having a desired cohesive force is easily formed.

The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

The lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 20,000 or more, particularly preferably 60,000 or more, and further preferably 120,000 or more. The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 1,000,000 or less as an upper limit, more preferably 750,000 or less, and particularly preferably 500,000 or less. Further, it is preferably 250,000 or less. When the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is within the above range, the formed pressure-sensitive adhesive layer satisfies the above-mentioned ratio (E ₂ /E ₁ ) for the elongation rate and the loss tangent tan δ. It will be easy. In addition, the weight average molecular weight in this specification is the value of standard polystyrene conversion measured by the gel permeation chromatography (GPC) method.

In addition, in the said adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used individually by 1 type, and may be used in combination of 2 or more type.

(2-2) Crosslinking agent (B)
The cross-linking agent (B) cross-links the (meth)acrylic acid ester polymer (A) when the pressure-sensitive adhesive composition P is heated, thereby forming a good three-dimensional network structure in the obtained pressure-sensitive adhesive. It is possible. Thereby, the cohesive force of the obtained pressure-sensitive adhesive is improved, and the pressure-sensitive adhesive layer to be formed easily satisfies the above-mentioned ratio (E ₂ /E ₁ ) with respect to the elongation rate and the loss tangent tan δ.

The cross-linking agent (B) may be any as long as it reacts with the reactive group of the (meth)acrylic acid ester polymer (A), and examples thereof include an isocyanate cross-linking agent, an epoxy cross-linking agent, and an amine cross-linking agent. , Melamine-based crosslinking agent, aziridine-based crosslinking agent, hydrazine-based crosslinking agent, aldehyde-based crosslinking agent, oxazoline-based crosslinking agent, metal alkoxide-based crosslinking agent, metal chelate-based crosslinking agent, metal salt-based crosslinking agent, ammonium salt-based crosslinking agent, etc. Are listed. Among the above, when the reactive group contained in the (meth)acrylic acid ester polymer (A) is a hydroxyl group, it is preferable to use an isocyanate cross-linking agent excellent in reactivity with the hydroxyl group. When the reactive group contained in the polymer (A) is a carboxy group, it is preferable to use an epoxy-based cross-linking agent having excellent reactivity with the carboxy group. The crosslinking agent (B) may be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate. And their biurets, isocyanurates, and adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane and castor oil. Among them, from the viewpoint of reactivity with hydroxyl groups, it is preferable to use at least one of trimethylolpropane-modified aromatic polyisocyanate, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate.

Examples of the epoxy crosslinking agent include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether. , 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl aniline, diglycidyl amine and the like. Of these, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane is preferable from the viewpoint of reactivity with the carboxy group.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.1 part by mass or more, and particularly 1 part by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). It is preferably not less than 1 part by mass, more preferably not less than 2.5 parts by mass. Further, the content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and further preferably 5 parts by mass or less. When the content of the cross-linking agent (B) is within the above range, the obtained pressure-sensitive adhesive layer can more easily satisfy the ratio (E ₂ /E ₁ ) with respect to the elongation rate and the loss tangent tan δ described above.

(2-3) Other Additives In the adhesive composition P, if desired, various additives commonly used in acrylic adhesives, for example, silane coupling agents, ultraviolet absorbers, antistatic agents, and tackifiers. Agents, antioxidants, light stabilizers, softening agents, fillers, refractive index adjusting agents, rust preventives and the like can be added. In addition, the below-mentioned polymerization solvent and diluting solvent shall not be contained in the additive which comprises an adhesive composition.

(2-4) Preparation of Adhesive Composition P Adhesive composition P is a (meth)acrylic acid ester polymer (A) produced by producing a (meth)acrylic acid ester polymer (A). It can be produced by mixing the cross-linking agent (B) with other additives as desired.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by an ordinary radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method, optionally using a polymerization initiator. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like, and two or more kinds may be used in combination.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more kinds may be used in combination. Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane1-carbonitrile), 2 , 2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate) , 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl) Propane] and the like.

Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxy. Examples thereof include dicarbonate, t-butylperoxyneodecanoate, t-butylperoxybivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.

In the polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

After the (meth)acrylic acid ester polymer (A) is obtained, the solution of the (meth)acrylic acid ester polymer (A) is added to the crosslinking agent (B), optionally other additives, and optionally a diluting solvent and Additives are added and mixed sufficiently to obtain a tacky composition P (coating solution) diluted with a solvent. Incidentally, in any of the above components, when using a solid one, or when precipitation occurs when mixed with other components in the undiluted state, that component alone in advance in a diluent solvent. It may be dissolved or diluted and then mixed with other components.

Examples of the diluent solvent include hexane, heptane, aliphatic hydrocarbons such as cyclohexane, toluene, aromatic hydrocarbons such as xylene, methylene chloride, halogenated hydrocarbons such as ethylene chloride, methanol, ethanol, propanol, butanol, Alcohols such as 1-methoxy-2-propanol, acetone, methyl ethyl ketone, ketones such as 2-pentanone, isophorone and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve solvents such as ethyl cellosolve are used.

The concentration and viscosity of the coating solution prepared in this way are not particularly limited as long as they can be coated, and can be appropriately selected depending on the situation. For example, the pressure-sensitive adhesive composition P is diluted to a concentration of 10 to 60% by mass, preferably 20 to 30% by mass. In addition, when obtaining a coating solution, addition of a diluting solvent or the like is not a necessary condition, and a diluting solvent may not be added as long as it has a viscosity such that the adhesive composition P can be coated. In this case, the adhesive composition P is a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer (A) as a diluting solvent.

(2-5) Physical Properties of Adhesive Layer etc. The gel fraction of the adhesive layer is preferably 60% or more, particularly preferably 70% or more, and further preferably 80% or more. Further, the gel fraction of the pressure-sensitive adhesive layer is preferably 100% or less, particularly preferably 98% or less, and further preferably 95% or less. When the gel fraction of the pressure-sensitive adhesive layer is in the above range, the pressure-sensitive adhesive layer to be formed is likely to satisfy the above-mentioned ratio (E ₂ /E ₁ ) for the elongation rate and the loss tangent tan δ.

The thickness of the pressure-sensitive adhesive layer is preferably 3 μm or more, particularly preferably 8 μm or more, and further preferably 16 μm or more. Moreover, the thickness of the pressure-sensitive adhesive layer is preferably 50 μm or less, particularly preferably 40 μm or less, and further preferably 30 μm or less. When the thickness of the pressure-sensitive adhesive layer is in the above range, it becomes easy to adjust the pressure-sensitive adhesive force of the protective sheet according to the present embodiment to the range described above, and the adhesion to the adherend and the releasability are improved. It becomes easy to be compatible.

(3) Release Sheet When the protective sheet according to the present embodiment includes a release sheet, the release sheet is not particularly limited as long as it does not adversely affect the pressure-sensitive adhesive layer. For example, a polyethylene film , Polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer Resin films, ethylene/(meth)acrylic acid copolymer films, ethylene/(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, fluororesin films and the like are used. Further, these crosslinked films are also used. Furthermore, these laminated films may be used. Among the above, a polyethylene terephthalate film having excellent handleability is preferable.

The surface of the release sheet that contacts the pressure-sensitive adhesive layer may be subjected to a release treatment. Examples of the release agent used in the release treatment include fluorine-based, alkyd-based, silicone-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

The thickness of the release sheet is not particularly limited, but is usually preferably 15 μm or more, and particularly preferably 25 μm or more. The thickness is usually preferably 100 μm or less, and particularly preferably 75 μm or less.

3. Method for Producing Protective Sheet The method for producing the protective sheet according to this embodiment is not particularly limited, and a conventional method can be used. For example, first, the adhesive composition P (or a coating solution obtained by diluting it with a solvent) is applied onto one surface of a substrate by a die coater, a curtain coater, a spray coater, a slit coater, a knife coater or the like. To form a coating film. After that, by drying the coating film, a protective sheet having a pressure-sensitive adhesive layer provided on a substrate can be obtained.

When the adhesive composition P contains the crosslinking agent (B), the above-mentioned drying conditions (temperature, time, etc.) may be changed in order to form a crosslinked structure with a desired existing density, or a heat treatment May be separately provided. In order to allow the crosslinking reaction to proceed sufficiently, after laminating the pressure-sensitive adhesive layer on the substrate by the above method or the like, the resulting protective sheet is allowed to stand for several days in an environment of 23° C. and 50% relative humidity, for example. You may perform curing.

As another production example of a protective sheet, an adhesive composition P (or a coating solution obtained by diluting it with a solvent) is applied onto the release surface of a release sheet to form a coating film, and then the coating film is formed. A protective sheet may be obtained by forming a pressure-sensitive adhesive layer by drying and then transferring the formed pressure-sensitive adhesive layer onto one surface of the substrate.

4. Use of Protective Sheet The protective sheet according to the present embodiment can be used to protect an object such as a device. In this case, during a process such as device processing, assembly, and inspection, a protective sheet is attached to a predetermined surface of the device, so that the surface can be prevented from being damaged.

The device is not particularly limited, but examples thereof include an optical member and an electronic member. Specific examples of such optical members and electronic members include a resin plate with a hard coat layer including a resin plate and a hard coat layer laminated on one side of the resin plate, a glass plate, and the like.

As described above, the protective sheet according to the present embodiment maintains the properties of the pressure-sensitive adhesive layer even when it is heated, and exhibits good adhesion to an adherend, but also peels off. When it is carried out, it can be favorably peeled from the adherend. Therefore, the protective sheet according to the present embodiment is suitable for use in a device that is subjected to heat treatment while being protected by the protective sheet.

Further, the protective sheet according to the present embodiment, as described above, when bonded to the surface having fine irregularities, the pressure-sensitive adhesive layer can appropriately follow the irregularities, and even after heating. Good adhesion and releasability can be compatible at a high level. Therefore, the protective sheet according to the present embodiment is preferably used for a resin plate with a hard coat layer, which generally has fine irregularities on the surface.

[Laminate]
The laminate according to the present embodiment includes a resin plate with a hard coat layer including a resin plate and a hard coat layer laminated on one side of the resin plate, and the above-mentioned protective sheet. The surface of the protective sheet on the side of the pressure-sensitive adhesive layer is laminated on the surface of the resin plate with the hard coat layer on the side of the hard coat layer.

As described above, the protective sheet maintains the properties of the pressure-sensitive adhesive layer even when heated, and shows good adhesion to the adherend, but when peeled, the adherend Can be peeled off satisfactorily. Furthermore, when it is attached to a surface having fine irregularities, the pressure-sensitive adhesive layer appropriately follows the irregularities, and even after heating, good adhesion and releasability are compatible at a high level. can do.

Therefore, in the laminate according to the present embodiment, the protective sheet is appropriately adhered to the surface on the hard coat layer side of the resin plate with the hard coat layer, and even when the laminate is heated. Unintentionally peeling off the protective sheet from the resin plate with the hard coat layer is suppressed. On the other hand, when the protective sheet is peeled off, it can be favorably peeled off from the resin plate with the hard coat layer.

The embodiments described above are described to facilitate the understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above-described embodiment is intended to include all design changes and equivalents within the technical scope of the present invention.

For example, another layer may be interposed between the base material and the pressure-sensitive adhesive layer in the protective sheet, and another layer is laminated on the surface of the base material opposite to the pressure-sensitive adhesive layer side. It may have been done.

Hereinafter, the present invention will be described more specifically with reference to Examples and the like, but the scope of the present invention is not limited to these Examples and the like.

[Example 1]
1. Preparation of (meth)acrylic acid ester polymer n-butyl acrylate 70 parts by mass, 2-ethylhexyl acrylate 20 parts by mass, isobornyl acrylate 3 parts by mass, 2-hydroxyethyl methacrylate 5 parts by mass and N-(butoxymethyl). ) 2 parts by mass of acrylamide were copolymerized to prepare a (meth)acrylic acid ester polymer. The weight average molecular weight (Mw) of this (meth)acrylic acid ester polymer was measured by the method described later and was 150,000.

2. Preparation of Adhesive Composition 100 parts by mass of (meth)acrylic acid ester polymer obtained in the above step 1 (solid content conversion value; the same applies hereinafter), and 3.5 parts by mass of hexamethylene diisocyanate as an isocyanate crosslinking agent. Were mixed, sufficiently stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an adhesive composition having a solid content concentration of 25% by mass.

3. Production of protective sheet The coating solution of the adhesive composition obtained in the above step 2 was coated on one side of a polyethylene terephthalate film (Mitsubishi Chemical Corporation, product name "PET38 T-100", thickness: 38 µm) with a knife coater. A coating layer was formed by coating. Then, the coating layer was heat-treated at 90° C. for 1 minute to form a pressure-sensitive adhesive layer having a thickness of 20 μm. Thus, a protective sheet including the base material and the pressure-sensitive adhesive layer was obtained.

[Examples 2 to 4, Comparative Example 1]
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1 except that the composition of the (meth)acrylic acid ester polymer and the type of the cross-linking agent were changed as shown in Table 1.

Here, the above-mentioned weight average molecular weight (Mw) is the weight average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement).
<Measurement conditions>
・GPC measuring device: HLC-8320 manufactured by Tosoh Corporation
・GPC column (passed in the following order): Tosoh TSK gel superH-H
TSK gel super HM-H
TSK gel superH2000
・Measuring solvent: Tetrahydrofuran ・Measuring temperature: 40°C

[Test Example 1] (Measurement of gel fraction)
The protective sheets obtained in Examples and Comparative Examples were cut into a size of 80 mm×80 mm, the adhesive layer was wrapped in a polyester mesh (Tetron mesh #200), and the mass was weighed with a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. The mass at this time is M1.

Next, the pressure-sensitive adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23° C.) for 24 hours. Then, the adhesive was taken out, air-dried for 24 hours in an environment of temperature 23° C. and relative humidity 50%, and further dried in an oven at 80° C. for 12 hours. After drying, the mass was weighed with a precision balance, and the mass of the mesh alone was subtracted to calculate the mass of the adhesive alone. The mass at this time is M2. Then, the gel fraction (%) was calculated by the calculation of (M2/M1)×100. The results are shown in Table 1.

[Test Example 2] (Measurement of adhesive strength)
After the protective sheets prepared in Examples and Comparative Examples were cut into a size having a width of 25 mm and a length of 120 mm, the pressure-sensitive adhesive layer side surface thereof was a polycarbonate having a hard coat layer made of polymethylmethacrylate as one material. The resin plate (manufactured by Mitsubishi Gas Chemical Co., Inc., product name "HMRS52T", thickness: 2.0 mm, hereinafter sometimes referred to as "resin plate with hard coat layer") is attached to the surface on the hard coat layer side, and Was used as a sample for measuring the adhesive strength.

After leaving the above-mentioned adhesive force measurement sample in an environment of 23° C. and 50% RH for 24 hours, the protective sheet was peeled off using a tensile tester at a peeling angle of 180° and a peeling speed of 0.3 m/min. The adhesive strength (N/25 mm) was measured. The measured value was taken as the adhesive strength of the resin plate with the hard coat layer before heating. The results are shown in Table 2.

The adhesive strength measurement sample obtained in the same manner as above was left for 24 hours in an environment of 23° C. and 50% RH, then heated at 100° C. for 30 minutes, and further in an environment of 23° C. and 50% RH. Let stand for 30 minutes. As a result, the adhesive strength of the adhesive strength measurement sample whose temperature returned to room temperature was measured in the same manner as above. The results are shown in Table 2 as the adhesive strength of the resin plate with the hard coat layer after heating.

Further, using the adhesive strength measurement sample obtained by changing the resin plate with the hard coat layer to soda lime glass, the adhesive strength to the glass plate before and after heating was measured in the same manner as above. These results are also shown in Table 2.

In addition, the measurement result of the adhesive strength marked with "*1" in Table 2 is the result measured as follows. That is, in the measurement of the adhesive force, when the protective sheet was peeled from the adhesive force measurement sample, the adhesive layer was separated from the base material and only the adhesive layer remained on the glass plate. However, when only the pressure-sensitive adhesive layer was peeled at the above-described peeling angle and peeling speed, the pressure-sensitive adhesive layer was appropriately peeled and the adhesive strength could be measured. Therefore, the adhesive strength with "*1" is the adhesive strength measured in this way.

[Test Example 3] (Measurement of water contact angle)
The surface of the protective sheet produced in Examples and Comparative Examples on the side of the pressure-sensitive adhesive layer is a resin plate with a hard coat layer, and a polycarbonate resin plate having a hard coat layer made of polymethylmethacrylate as a material (Mitsubishi Gas The product was attached to the surface on the hard coat layer side in the product "HMRS52T", thickness: 2.0 mm, manufactured by Kagaku Co., and this was used as a water contact angle measurement sample.

After leaving the water contact angle measurement sample in an environment of 23° C. and 50% RH for 24 hours, the protective sheet was peeled off, and the exposed surface of the resin plate with the hard coat layer on the hard coat layer side was fully automatic contact angle. The water contact angle (°) was measured under the following conditions using a measuring instrument (Kyowa Interface Science Co., Ltd., product name “DM-701”). The results are shown in Table 2 as the water contact angle W ₁ of the resin plate with the hard coat layer before heating.
・ Droplet volume of purified water: 2 μl
・Measurement time: 3 seconds after dropping ・Image analysis method: θ/2 method

In addition, the water contact angle measurement sample obtained in the same manner as above was left for 24 hours in an environment of 23° C. and 50% RH, then heated at 100° C. for 30 minutes, and further in an environment of 23° C. and 50% RH. And allowed to stand for 30 minutes. As a result, the water contact angle of the water contact angle measurement sample whose temperature returned to room temperature was measured in the same manner as above. The results are shown in Table 2 as the water contact angle W ₂ of the resin plate with the hard coat layer after heating. Further, the ratio (W ₂ /W ₁ ) of the water contact angle W ₁ to the water contact angle W ₂ measured as described above was calculated. The results are also shown in Table 2.

Further, using a water contact angle measurement sample obtained by changing the resin plate with the hard coat layer to soda lime glass, the water contact angle W _{3 of the} glass plate before heating and the water contact angle W _{3 of the} glass plate before heating were used in the same manner as above. The water contact angle W ₄ of the glass plate was measured, and the ratio (W ₄ /W ₃ ) was calculated. These results are also shown in Table 2.

The water contact angle measurement results marked with "*2" in Table 2 are the results measured as follows. That is, when measuring this water contact angle, when the protective sheet is peeled from the water contact angle measurement sample, the adhesive layer separates from the substrate and only the adhesive layer remains on the glass plate. It was Therefore, the water contact angle of the exposed surface of the glass plate exposed by peeling only the pressure-sensitive adhesive layer from the glass plate was measured as described above, and the result is shown in Table 2 with "*2". ..

[Test Example 4] (Measurement of total light transmittance)
All of polycarbonate resin plates (made by Mitsubishi Gas Chemical Co., Inc., product name "HMRS52T", thickness: 2.0 mm) having a hard coat layer made of polymethylmethacrylate as a resin plate with a hard coat layer on one side. The light transmittance (%) was measured according to JIS K7361-1:1997 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000"). The results are shown in Table 2 as the total light transmittance of the resin plate with the hard coat layer before sticking the protective sheet (before sticking).

Then, the surface of the pressure-sensitive adhesive layer side of the protective sheet produced in Examples and Comparative Examples, was stuck to the surface of the hard coat layer side in the resin plate with the hard coat layer, this sample for total light transmittance measurement And The sample for measuring total light transmittance was allowed to stand in an environment of 23° C. and 50% RH for 24 hours, then heated at 100° C. for 30 minutes, and further left to stand in an environment of 23° C. and 50% RH for 30 minutes. The total light transmittance (%) was measured in the same manner as above for the resin plate with the hard coat layer obtained by peeling and removing the protective sheet from the total light transmittance measurement sample in which the temperature returned to room temperature. The results are shown in Table 2 as the total light transmittance of the resin plate with the hard coat layer after heating with the protective sheet attached and peeling the protective sheet (after heat peeling).

Further, the resin plate with a hard coat layer was changed to soda lime glass, and the total light transmittance (%) was measured in the same manner as above. The total light transmittance of the glass plate before sticking and the glass plate after heat peeling were measured. The total light transmittance of These results are also shown in Table 2.

[Test Example 5] (Measurement of storage elastic modulus and loss tangent tan δ)
A release sheet obtained by subjecting one side of a polyethylene terephthalate film to a release treatment with a silicone-based release agent from the coating solution of the adhesive composition prepared in Examples and Comparative Examples (manufactured by Lintec Co., product name “SP-PET381130”, thickness: 38 μm) was coated on the peeled surface with a knife coater. The obtained coating film is heated in an environment of 90° C. for 1 minute to heat the coating film, and a 40 μm-thick adhesive layer for testing formed from each adhesive composition is laminated on a release sheet. A plurality of the resulting pressure-sensitive adhesive sheets were prepared.

Using the obtained pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer for testing was stuck to a thickness of 800 μm to obtain a pressure-sensitive adhesive layer laminate. The laminate was punched into a circle having a diameter of 10 mm to obtain a viscoelasticity measurement sample of the pressure-sensitive adhesive layer. The viscoelasticity measurement sample was left in an environment of 23° C. and 50% RH for 24 hours, and then, using a viscoelasticity measurement apparatus (manufactured by TA Instruments, product name “ARES”), A strain having a frequency of 1 Hz was applied to the viscoelasticity measurement sample, the storage elastic modulus and the loss elastic modulus at −50 to 150° C. were measured, and the storage elastic modulus (MPa) and the loss tangent tan δ at 23° C. were calculated from these values. .. These results are shown in Table 3 as the storage elastic modulus and loss tangent tan δ before heating.

The viscoelasticity measurement sample obtained in the same manner as above was left for 24 hours in an environment of 23° C. and 50% RH, then heated at 100° C. for 30 minutes, and further in an environment of 23° C. and 50% RH. After the temperature of the sample was returned to room temperature by allowing it to stand for a minute, the storage elastic modulus (MPa) and the loss tangent tan δ were calculated in the same manner as above. These results are shown in Table 3 as storage elastic modulus and loss tangent tan δ after heating.

[Test Example 6] (Measurement of elongation by tensile test)
A release sheet obtained by subjecting one side of a polyethylene terephthalate film to a release treatment with a silicone-based release agent from the coating solution of the adhesive composition prepared in Examples and Comparative Examples (manufactured by Lintec Co., product name “SP-PET381130”, thickness: 38 μm) was coated on the peeled surface with a knife coater. The obtained coating film is heated at 90° C. for 1 minute to heat the coating film, and a 25 μm-thick test adhesive layer formed from each adhesive composition is laminated on a release sheet. A plurality of the resulting pressure-sensitive adhesive sheets were prepared.

Using the obtained pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer for testing was stuck to a thickness of 500 μm. In addition, at the time of this bonding, the bonding was repeated while leaving the outermost release sheet, thereby obtaining a laminate composed of a pressure-sensitive adhesive layer having a thickness of 500 μm and one release sheet. After that, the laminate was cut into a size of 10 mm×75 mm to obtain a sample for measuring elongation.

After leaving the obtained sample for elongation measurement in an environment of 23° C. and 50% RH for 24 hours, a tensile tester (manufactured by Orientec Co., product name “Measurement site” has a size of 10 mm×20 mm). Tensilon”). Then, in a 23° C., 50% RH environment, elongation was performed at a tensile speed of 200 mm/min, and the elongation at break (%) was measured. The results are shown in Table 3 as the elongation rate E ₁ before heating.

Moreover, the sample for elongation rate measurement obtained in the same manner as above was left for 24 hours in an environment of 23° C. and 50% RH, then heated at 100° C. for 30 minutes, and further heated in an environment of 23° C. and 50% RH for 30 minutes. After the temperature of the sample was returned to room temperature by allowing it to stand for a minute, the elongation at break (%) was measured in the same manner as above. The results are shown in Table 3 as the elongation rate E ₂ after heating. Further, the ratio (E ₂ /E ₁ ) of the extension rate E ₁ to the extension rate E ₂ measured as described above was calculated. The results are also shown in Table 3.

[Test Example 7] (Evaluation of adhesion after heating)
The surface of the protective sheet prepared in Examples and Comparative Examples on the pressure-sensitive adhesive layer side is a resin plate with a hard coat layer, a polycarbonate resin plate having a hard coat layer made of polymethylmethacrylate as a material (Mitsubishi Gas The product was attached to the surface on the hard coat layer side in the product "HMRS52T" manufactured by Kagaku Co., Ltd., thickness: 2.0 mm, and this was used as a sample for adhesion evaluation.

By leaving the above-mentioned adhesiveness evaluation sample in an environment of 23° C. and 50% RH for 24 hours, heating it at 100° C. for 30 minutes, and further leaving it to stand in an environment of 23° C. and 50% RH for 30 minutes. The temperature of the adhesive strength measurement sample was returned to room temperature. Regarding the adhesion evaluation sample, the state of the interface between the protective sheet and the resin plate with the hard coat layer was visually confirmed, and the adhesion of the protective sheet after heating was evaluated based on the following criteria. The results are shown in Table 3.
⊚: No floating or bubbles were generated, and the protective sheet was in good contact with the resin plate with the hard coat layer.
◯: Although the floating and air bubbles were slightly generated, the protective sheet was sufficiently adhered to the resin plate with the hard coat layer.
X: Lifting occurred on the entire surface, and the protective sheet was peeled off from the resin plate with the hard coat layer.

Furthermore, the adhesion of the protective sheet after heating was evaluated in the same manner as above using a sample for evaluation of adhesion obtained by changing the resin plate with a hard coat layer to soda lime glass. The results are also shown in Table 3.

[Test Example 8] (Evaluation of peelability after heating)
For the examples (Examples 1 to 4) that were evaluated as “⊚” or “◯” in Test Example 7 above, the protective sheet was peeled off from the adhesion evaluation sample after evaluation in Test Example 7 above, in which case Regarding the state of peeling, the peelability of the protective sheet after heating was evaluated based on the following criteria. The results are shown in Table 3.
⊚: Can be easily peeled off.
◯: Peeling was possible although some force was required for peeling.
X: Could not be peeled off.

Regarding the evaluation results marked with "*3" in Table 3, when the protective sheet was peeled off from the adhesion evaluation sample, the adhesive layer was separated from the base material and only the adhesive layer was on the glass plate. Although it remained, it means that only the pressure-sensitive adhesive layer could be peeled off from the glass plate thereafter.

The abbreviations in Table 1 are as follows.
[Composition of acrylic ester polymer]
BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate IBXA: isobornyl acrylate HEMA: 2-hydroxyethyl methacrylate BMAA: N-(butoxymethyl)acrylamide AA: acrylic acid HEA: 2-hydroxyethyl acrylate [crosslinking Agent)
Isocyanate system: Hexamethylene diisocyanate Epoxy system: 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane

As is clear from Tables 2 and 3, the protective sheets produced in the examples were excellent in releasability even after being subjected to heat treatment, while exhibiting good adhesion to the adherend. ..

The protective sheet according to the present invention is suitable as a protective sheet for protecting the surface of an optical member or the like.

Claims (6)

A protective sheet comprising a base material and an adhesive layer laminated on one surface side of the base material,
The elongation rate (%) of the pressure-sensitive adhesive layer at 23° C. in the tensile test is E _1, and the elongation rate of the pressure-sensitive adhesive layer at 23° C. in the tensile test after heating the pressure-sensitive adhesive layer at 100° C. for 30 minutes the (%) in the case of the _{E 2,} the ratio of the elongation _{E 2} with respect to elongation _{E 1 (E} 2 / _{E 1)} is 0.9 or more and 5 or less,
A protective sheet, wherein the loss tangent tan δ at 23° C. of the pressure-sensitive adhesive layer after heating the pressure-sensitive adhesive layer at 100° C. for 30 minutes is 0.1 or more and 1 or less. The surface of the protective sheet on the side of the pressure-sensitive adhesive layer is attached to the surface of the resin plate with a hard coat layer that includes a resin plate and a hard coat layer laminated on one side of the resin plate. About the laminated body
After the laminate was placed in an environment of 23° C. and 50% RH for 24 hours, water contact measured on the surface of the resin plate with the hard coat layer, which was exposed by peeling off the protective sheet, was measured. The angle (°) is W ₁ ,
The laminate is placed in an environment of 23° C. and 50% RH for 24 hours, subsequently heated at 100° C. for 30 minutes, placed in an environment of 23° C. and 50% RH for 30 minutes, and then the protective sheet is peeled off. When the water contact angle (°) measured on the hard coat layer side surface of the resin plate with the hard coat layer thus exposed is W ₂ ,
Protective sheet according to claim 1, the ratio of the water contact angle _{W 2 (W 2 / W 1} ) is 0.8 or more and a is 1.2 or less with respect to the water contact angle _{W 1.} In the resin plate with a hard coat layer, which comprises a resin plate and a hard coat layer laminated on one side of the resin plate, the adhesive force of the protective sheet to the surface on the hard coat layer side is 0.5 N/25 mm or more and 10 N or more. It is /25 mm or less, The protective sheet of Claim 1 or 2 characterized by the above-mentioned. The surface of the protective sheet on the side of the pressure-sensitive adhesive layer is attached to the surface of the resin plate with a hard coat layer that includes a resin plate and a hard coat layer laminated on one side of the resin plate. The adhesive strength of the protective sheet with respect to the hard coat layer constituting the laminate after heating the laminate obtained by heating at 100° C. for 30 minutes is 0.3 N/25 mm or more and 10 N/25 mm or less. The protective sheet according to claim 1, wherein the protective sheet is a protective sheet. It is used for protecting the surface on the side of the hard coat layer in a resin plate with a hard coat layer comprising a resin plate and a hard coat layer laminated on one side of the resin plate. 4. The protective sheet according to any one of 4 above. A resin plate with a hard coat layer comprising a resin plate and a hard coat layer laminated on one side of the resin plate,
A protective sheet according to any one of claims 1 to 5,
A pressure-sensitive adhesive layer-side surface of the protective sheet is laminated on the hard-coat layer-side surface of the resin plate with a hard-coat layer.