JP7092625B2 - Removable sheet - Google Patents

Description

The present invention relates to a re-peelable sheet.

Conventionally, when manufacturing optical devices, electronic devices (for example, OLEDs, LCD modules, smartphones), etc., metal plates, painted metal plates, resin plates, glass plates, prism sheets, diffusion films, polarizing plates, touch panels, touch panels, etc. A removable removable sheet is used to protect the surface of a member such as a sensor (for example, Patent Documents 1 to 3). Such a re-peelable sheet is also generally referred to as a re-peelable tape, a surface protective film, a protective tape, or the like. The re-peelable sheet is also used for the purpose of temporarily adhering or temporarily fixing the members.

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

It is desirable that the re-peelable sheet exhibits sufficient adhesive strength depending on the intended use, and can be easily peeled off after use without leaving adhesive residue on the member or damaging the member. However, when assembling a member whose surface is protected by the re-peelable sheet, there is a problem that the re-peelable sheet is deteriorated by sebum and the edges are peeled off or the protective surface is contaminated due to frequent contact by human hands. There is.

An object of the present invention is to provide a re-peelable sheet which has excellent resistance to sebum and can be easily peeled off after use.

The present invention is a re-peelable sheet having an adhesive layer containing an acrylic copolymer, wherein the acrylic copolymer is an energy ray irradiation polymer type acrylic copolymer, and the acrylic copolymer is: Re-peelation containing a structural unit derived from a polyfunctional monomer, containing 30% by weight or more of a structural unit derived from a fluorine-containing (meth) acrylate, and having a 180 ° peeling adhesive force against a SUS plate of 2 N / 25 mm or less. It is a sheet.
Hereinafter, the present invention will be described in detail.

The present inventors use a fluorine-containing (meth) acrylate as the acrylic copolymer in a re-peelable sheet having an adhesive layer containing an acrylic copolymer, and peel off the re-peelable sheet by 180 ° with respect to a SUS plate. We have found that the resistance to sebum and the peelability after use can be improved by adjusting the adhesive strength to a certain value or less, and have completed the present invention.

The removable sheet of the present invention has a pressure-sensitive adhesive layer containing an acrylic copolymer. The acrylic copolymer contains 30% by weight or more of a structural unit derived from a fluorine-containing (meth) acrylate.
Since the acrylic copolymer contains a structural unit derived from the fluorine-containing (meth) acrylate, the molecule of the acrylic copolymer is due to the high water and oil repellency of fluorine itself and the dense packing of fluorine atoms. The infiltration of oleic acid (the main component of sebum) into the chain is suppressed. As a result, the swelling rate of the pressure-sensitive adhesive layer with respect to oleic acid, which is the main component of sebum, is lowered, and the resistance of the removable sheet to sebum is improved.

The fluorine-containing (meth) acrylate is not particularly limited, and is, for example, 2,2,2-trifluoroethyl (meth) acrylate, 2- (perfluorohexyl) ethyl (meth) acrylate, 2,2,3,3. 3-Pentafluoropropyl (meth) acrylate, 2- (perfluorobutyl) ethyl (meth) acrylate, 3-perfluorobutyl-2-hydroxypropyl (meth) acrylate, 3-perfluorohexyl-2-hydroxypropyl (meth) ) Acrylate, 3- (Perfluoro-3-methylbutyl) -2-hydroxypropyl (meth) acrylate, 1H, 1H, 3H-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate , 1H, 1H, 7H-dodecafluoroheptyl (meth) acrylate, 1H-1- (trifluoromethyl) trifluoroethyl (meth) acrylate, 1H, 1H, 3H-hexafluorobutyl (meth) acrylate, 1, 2, Examples thereof include 2,2-tetrafluoro-1- (trifluoromethyl) ethyl (meth) acrylate. Further, the fluorine-containing (meth) acrylate may be an acrylate having a trifluoromethyl group or a fluoro group at the α-position. The (meth) acrylate means that it may be an acrylate or a methacrylate. These fluorine-containing (meth) acrylates may be used alone or in combination of two or more. Of these, 2- (perfluorohexyl) ethyl (meth) acrylate and 2,2,2-trifluoroethyl (meth) acrylate are preferable because of their high resistance to sebum.

In the acrylic copolymer, the lower limit of the content of the constituent unit derived from the fluorine-containing (meth) acrylate is 30% by weight. When the content is 30% by weight or more, the infiltration of oleic acid into the molecular chain of the acrylic copolymer is suppressed, and the resistance of the removable sheet to sebum is improved. The preferable lower limit of the content is 40% by weight, and the more preferable lower limit is 45% by weight.
The upper limit of the content of the constituent unit derived from the fluorine-containing (meth) acrylate is not particularly limited, but the preferable upper limit is 90% by weight. When the content is 90% by weight or less, the pressure-sensitive adhesive layer does not become too hard, and the pressure-sensitive adhesive force suitable for peeling can be exhibited. A more preferable upper limit of the content is 80% by weight.

The acrylic copolymer preferably further contains a structural unit derived from a monomer having a crosslinkable functional group.
Since the acrylic copolymer contains a structural unit derived from the monomer having a crosslinkable functional group, the chains of the acrylic copolymer are crosslinked when a crosslinking agent is used in combination. At that time, the gel fraction of the pressure-sensitive adhesive layer can be adjusted by adjusting the degree of cross-linking.

Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, a glycidyl group, an amino group, an amide group, a nitrile group and the like. Of these, a hydroxyl group or a carboxyl group is preferable because the gel fraction of the pressure-sensitive adhesive layer can be easily adjusted.
Examples of the monomer having a hydroxyl group include (meth) acrylate having a hydroxyl group such as 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate. Examples of the monomer having a carboxyl group include (meth) acrylic acid. Examples of the monomer having a glycidyl group include glycidyl (meth) acrylate. Examples of the monomer having an amide group include acrylamide, hydroxyethyl acrylamide, isopropyl acrylamide, and dimethylaminopropyl acrylamide. Examples of the monomer having a nitrile group include acrylonitrile. These crosslinkable functional groups may be used alone or in combination of two or more.

In the acrylic copolymer, the content of the structural unit derived from the monomer having a crosslinkable functional group is not particularly limited, but the preferable lower limit is 2% by weight, the preferable upper limit is 25% by weight, and the more preferable lower limit is 5. By weight%, a more preferred upper limit is 20% by weight.
Further, among the monomers having a crosslinkable functional group, the content of the structural unit derived from the (meth) acrylate having a hydroxyl group such as 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate is particularly high. The preferred lower limit is 2% by weight, and the more preferable lower limit is 5% by weight.
When these contents are within the above range, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive layer to a relatively high range, and the 180 ° peeling adhesive force of the re-peelable sheet to the SUS plate will be described later. Since it is easy to adjust to a specific range, the peelability of the re-peelable sheet after use is further improved.

The acrylic copolymer can be further used as a methyl (meth) acrylate, an ethyl (meth) acrylate, a propyl (meth) acrylate, a butyl (meth) acrylate, a cyclohexyl (meth) acrylate, 2 as long as the effect of the present invention is not impaired. -Contains structural units derived from ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, vinyl acetate and the like. May be good.
Among them, from the viewpoint of adjusting the gel fraction of the pressure-sensitive adhesive layer to a relatively high range, it is preferable to contain a structural unit derived from acrylic (meth) acrylate having an acrylic group having 4 or more carbon atoms. Further, it is more preferable to contain a structural unit derived from an acrylic (meth) acrylate having an acrylic group having 8 or more carbon atoms (for example, 2-ethylhexyl (meth) acrylate).

When the acrylic copolymer is an energy ray (for example, ultraviolet) irradiation polymerization type acrylic copolymer, the acrylic copolymer may be further divided into divinylbenzene, trimerol propantri (meth) acrylate and the like. It is preferable to contain a structural unit derived from the polyfunctional monomer of. Since the acrylic copolymer contains a structural unit derived from the polyfunctional monomer, it becomes easy to adjust the gel fraction of the pressure-sensitive adhesive layer in a relatively high range, and the peeling sheet is pulled by 180 ° with respect to the SUS plate. Since it becomes easy to adjust the peeling adhesive strength to a specific range as described later, the peelability of the removable sheet after use is further improved.

As the monomer constituting the acrylic copolymer, a more preferable monomer differs depending on the content of the fluorine-containing (meth) acrylate.
When the content of the structural unit derived from the fluorine-containing (meth) acrylate in the acrylic copolymer is 40% by weight or less, the acrylic copolymer is a methyl (meth) acrylate or an ethyl (meth) acrylate. It is preferable to contain a structural unit derived from. By containing these, the swelling rate of the pressure-sensitive adhesive layer with respect to oleic acid, which is the main component of sebum, is lowered, and the resistance of the removable sheet to sebum is improved. When methyl (meth) acrylate or ethyl (meth) acrylate is used, the gel fraction described later is preferably 95% by weight or more. With such a configuration, it is possible to maintain the re-peelability by suppressing an excessive increase in the adhesive strength while making the re-peelable sheet resistant to sebum. In this case, for example, the gel fraction can be increased by increasing the content of the structural unit derived from the monomer having a crosslinkable functional group (for example, 5% by weight or more).
In the acrylic copolymer, when the content of the structural unit derived from the fluorine-containing (meth) acrylate exceeds 40% by weight and is less than 80% by weight, the acrylic copolymer is derived from a highly polar monomer. It is preferable that the content of the constituent unit is 5% by weight or less. With such a configuration, it is possible to suppress an excessive increase in adhesive strength and maintain removability. Examples of the highly polar monomer include methyl (meth) acrylate and ethyl (meth) acrylate.
In the acrylic copolymer, when the content of the structural unit derived from the fluorine-containing (meth) acrylate is 80% by weight or more, the acrylic copolymer has a glass transition point of the homopolymer of −60 ° C. or lower. It is preferable to contain a structural unit derived from the monomer. With such a configuration, the removable sheet can be given an appropriate tack feeling to improve the wettability to the adherend, and the removable sheet can be easily handled. Examples of the monomer having a glass transition point of the homopolymer having a glass transition point of −60 ° C. or lower include 2-ethylhexyl (meth) acrylate and octyl (meth) acrylate.

The weight average molecular weight of the acrylic copolymer is not particularly limited, but from the viewpoint of adjusting the gel fraction of the pressure-sensitive adhesive layer to a relatively high range, a larger molecular weight is preferable, a preferable lower limit is 700,000, and a more preferable lower limit is It is one million. The upper limit of the weight average molecular weight of the acrylic copolymer is not particularly limited, but the preferable upper limit is 2 million, and the more preferable upper limit is 1.2 million.
The weight average molecular weight can be adjusted by the polymerization conditions (for example, the type or amount of the polymerization initiator, the polymerization temperature, the monomer concentration, etc.).

In order to synthesize the acrylic copolymer, the monomer from which the structural unit is derived may be radically reacted in the presence of a polymerization initiator. The polymerization method is not particularly limited, and a conventionally known method can be used. Examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like. Of these, solution polymerization is preferable because it is easy to synthesize.

When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether and the like. These reaction solvents may be used alone or in combination of two or more.

The above-mentioned polymerization initiator is not particularly limited, and examples thereof include organic peroxides and azo compounds.
Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5. -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples thereof include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

Further, when the acrylic copolymer is an energy ray (for example, ultraviolet) irradiation polymerization type acrylic copolymer, in order to synthesize the acrylic copolymer, the monomer from which the structural unit is derived is lighted. The radical reaction may be carried out in the presence of the polymerization initiator.
The photopolymerization initiator is not particularly limited, and is, for example, acetophenone, 4,4'-dimethoxybenzyl, dibenzoyl, benzoylphenylcarbinol, benzophenone, 2-benzoylbenzoic acid, 2,2-dimethoxy-1,2-diphenylethane. Examples thereof include -1-one and 1-hydroxy-cyclohexyl-phenyl-ketone. These photopolymerization initiators may be used alone or in combination of two or more.

The pressure-sensitive adhesive layer preferably contains a cross-linking agent in addition to the acrylic copolymer.
When the acrylic copolymer contains a structural unit derived from a monomer having a crosslinkable functional group, a crosslinked structure can be constructed between the chains of the acrylic copolymer by the crosslinking agent. At that time, the gel fraction of the pressure-sensitive adhesive layer can be adjusted by adjusting the degree of cross-linking.

The above-mentioned cross-linking agent is not particularly limited, and examples thereof include an isocyanate-based cross-linking agent, an aziridine-based cross-linking agent, an epoxy-based cross-linking agent, and a metal chelate-type cross-linking agent. Of these, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferable.
In the pressure-sensitive adhesive layer, the content of the cross-linking agent is not particularly limited, but the preferable lower limit is 0.01 parts by weight, the preferable upper limit is 10 parts by weight, and the more preferable lower limit is 0 with respect to 100 parts by weight of the acrylic copolymer. .1 part by weight, more preferably 5 parts by weight.

The pressure-sensitive adhesive layer may contain additives such as plasticizers, emulsifiers, softeners, fillers, pigments, dyes, and other resins, if necessary.

The gel fraction of the pressure-sensitive adhesive layer is preferably 80% by weight at the lower limit.
When the gel fraction is 80% by weight or more, the peelability after use of the re-peelable sheet is improved. A more preferable lower limit of the gel fraction is 85% by weight, and a further preferable lower limit is 90% by weight.
The upper limit of the gel fraction is not particularly limited, but a preferable upper limit is 98% by weight. When the gel fraction is 98% by weight or less, the re-peelable sheet can exhibit sufficient adhesive strength. A more preferable upper limit of the gel fraction is 95% by weight.
In addition, the "gel fraction" in this specification is the weight of the pressure-sensitive adhesive layer after being immersed in ethyl acetate and dried as compared with the weight of the pressure-sensitive adhesive layer before being immersed in ethyl acetate as shown in the following formula (1). It is a value expressed as a percentage of.
Gel fraction (% by weight) = 100 x (W ₂ -W ₀ ) / (W ₁ -W ₀ ) (1)
(W ₀ : Weight of substrate, W ₁ : Weight of removable sheet test piece before dipping in ethyl acetate, W ₂ : Weight of removable sheet test piece after dipping in ethyl acetate, drying)

The pressure-sensitive adhesive layer may have a swelling rate (also referred to as "oleic acid swelling rate") of 100% by weight or more and 130% by weight or less after being immersed in oleic acid at 60 ° C. and a humidity of 90% for 24 hours. preferable. A more preferable upper limit of the oleic acid swelling rate is 120% by weight, and a further preferable upper limit is 115% by weight.
The "oleic acid swelling rate" in the present specification refers to the pressure-sensitive adhesive layer after being immersed in oleic acid and dried with respect to the weight of the pressure-sensitive adhesive layer before being immersed in oleic acid as shown in the following formula (2). It is a value expressed as a percentage of the weight. In the presence of elution of the adhesive component into oleic acid, the oleic acid swelling rate is less than 100% by weight.
Oleic acid swelling rate (% by weight) = 100 × (W ₅ -W ₃ ) / (W ₄ -W ₃ ) (2)
(W ₃ : Weight of substrate, W ₄ : Weight of removable sheet test piece before oleic acid immersion, W ₅ : Weight of removable sheet test piece after oleic acid immersion, drying)

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit is 1 μm and the preferred upper limit is 50 μm. When the thickness of the pressure-sensitive adhesive layer is 1 μm or more, the adhesive strength of the pressure-sensitive adhesive layer is improved. When the thickness of the pressure-sensitive adhesive layer is 50 μm or less, the processability of the removable sheet is improved.

The re-peelable sheet of the present invention has an upper limit of 180 ° peeling adhesive strength with respect to the SUS plate of 2N / 25 mm.
When the 180 ° peeling adhesive force to the SUS plate is 2N / 25 mm or less, the peelability after use of the re-peelable sheet is improved. The preferred upper limit of the 180 ° peeling adhesive force with respect to the SUS plate is 1 N / 25 mm, and the more preferable upper limit is 0.5 N / 25 mm.
The lower limit of the 180 ° peeling adhesive force with respect to the SUS plate is not particularly limited, but the preferable lower limit is 0.005 N / 25 mm. If the 180 ° peeling adhesive force to the SUS plate is 0.005 N / 25 mm or more, the re-peelable sheet can exhibit sufficient adhesive force. A more preferable lower limit of the 180 ° peeling adhesive force with respect to the SUS plate is 0.01 N / 25 mm.

The "180 ° peeling adhesive strength to the SUS plate" in the present specification can be measured as follows.
First, the re-peelable sheet test piece is placed on the SUS plate so that the adhesive layer faces the SUS plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min. The test piece and the SUS plate are bonded together, and then allowed to stand at 23 ° C. for 24 hours to prepare a test sample. According to JIS Z0237, a tensile test in the 180 ° direction is performed at a peeling speed of 300 mm / min, and the 180 ° peeling adhesive force (N / 25 mm) is measured.

The method of adjusting the 180 ° peeling adhesive force to the SUS plate within the above range is not particularly limited, but the method of adjusting the gel fraction of the pressure-sensitive adhesive layer to the above-mentioned relatively high range is preferable.
In order to adjust the gel fraction of the pressure-sensitive adhesive layer to a relatively high range as described above, for example, the acrylic copolymer has a monomer having the crosslinkable functional group (particularly, having the hydroxyl group (in particular, the hydroxyl group). It is preferable to contain a structural unit derived from (meth) acrylate) or a structural unit derived from the above-mentioned polyfunctional monomer. Further, the acrylic copolymer has an acrylic (meth) acrylate having an acrylic group having 4 or more carbon atoms, preferably an acrylic (meth) acrylate having an acrylic group having 8 or more carbon atoms (for example, 2-ethylhexyl (for example, 2-ethylhexyl). It is also preferable to contain a structural unit derived from (meth) acrylate). It is also preferable to increase the molecular weight of the acrylic copolymer, and the preferable lower limit of the weight average molecular weight is 700,000, and the more preferable lower limit is 1 million. Further, it is preferable not to add a tackifier such as a rosin-based resin or a terpene-based resin to the pressure-sensitive adhesive layer.

The re-peelable sheet of the present invention may be a support type having a base material or a non-support type having no base material. In the case of the support type, the pressure-sensitive adhesive layer may be formed on one side of the base material, or the pressure-sensitive adhesive layer may be formed on both sides.

The base material is not particularly limited, and examples thereof include a polyolefin resin film such as a polyethylene film and a polypropylene film, and a polyester resin film such as a PET film. Further, examples thereof include an ethylene-vinyl acetate copolymer film, a polyvinyl chloride resin film, a polyurethane resin film, a polyethylene foam sheet, a polyolefin foam sheet such as a polypropylene foam sheet, and a polyurethane foam sheet. Of these, PET film is preferable. Further, from the viewpoint of impact resistance, a polyolefin foam sheet is preferable.
Further, as the base material, a base material printed in black to prevent light transmission, a base material printed in white to improve light reflectivity, a base material vapor-deposited with metal, or the like can also be used.

The method for producing the re-peelable sheet of the present invention is not particularly limited, and for example, when the re-peelable sheet of the present invention has a base material and adhesive layers on both sides of the base material, the following methods can be mentioned.
First, a solvent is added to an acrylic copolymer, a cross-linking agent or the like if necessary to prepare a solution of the acrylic pressure-sensitive adhesive a. The obtained solution of the acrylic pressure-sensitive adhesive a is applied to the surface of the base material, and the solvent in the solution is completely dried and removed to form the pressure-sensitive adhesive layer a. Next, the release film is superposed on the formed pressure-sensitive adhesive layer a so that the release-treated surface faces the pressure-sensitive adhesive layer a. Next, a release film different from the release film is prepared, a solution of the acrylic adhesive b is applied to the release-treated surface of the release film, and the solvent in the solution is completely dried and removed. A laminated film having an adhesive layer b formed on the surface of the release film is produced. The obtained laminated film is laminated on the back surface of the base material on which the pressure-sensitive adhesive layer a is formed so that the pressure-sensitive adhesive layer b faces the back surface of the base material to prepare a laminated body. Then, by pressurizing the laminate with a rubber roller or the like, it is possible to obtain a re-peelable sheet having pressure-sensitive adhesive layers on both sides of the base material and having the surface of the pressure-sensitive adhesive layer covered with a release film.

Further, two sets of laminated films are prepared in the same manner, and these laminated films are laminated on both sides of the base material so that the adhesive layer of the laminated film faces the base material to prepare a laminated body. By pressurizing this laminate with a rubber roller or the like, a re-peelable sheet having adhesive layers on both sides of the base material and having the surface of the adhesive layer covered with a release film may be obtained.

The use of the removable sheet of the present invention is not particularly limited, but it is preferably used for surface protection of a member of an electronic device. More specifically, the removable sheet of the present invention is, for example, a metal plate, a painted metal plate, a resin plate, a glass plate, a prism sheet, when manufacturing an electronic device (for example, an OLED, an LCD module, a smartphone). It can be preferably used to protect the surface of a member such as a diffusion film, a polarizing plate, a touch panel, and a touch sensor.
Since the re-peelable sheet of the present invention has excellent resistance to sebum, even when it is frequently touched by human hands, deterioration by sebum may cause the edges to peel off or the protective surface to be contaminated. Can be prevented.

According to the present invention, it is possible to provide a re-peelable sheet which is excellent in resistance to sebum and can be easily peeled off after use.

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

( Reference example 1)
(1) Production of acrylic copolymer (solution polymerization)
Ethyl acetate was added as a polymerization solvent to the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing nitrogen to start reflux. Subsequently, as a polymerization initiator, a polymerization initiator solution obtained by diluting 0.1 part by weight of azobisisobutyronitrile with ethyl acetate 10-fold was put into a reaction vessel, and 64.5 parts by weight of butyl acrylate, 2,2. 30 parts by weight of 2-trifluoroethyl acrylate, 5 parts by weight of 2-hydroxyethyl acrylate, and 0.5 part by weight of acrylic acid were added dropwise over 2 hours. After completion of the dropping, the polymerization initiator solution obtained by diluting 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator with ethyl acetate 10-fold was put into the reaction vessel again, and the polymerization reaction was carried out for 4 hours to carry out the acrylic co-weight. A coalescence-containing solution was obtained.

(2) Production of Removable Sheet A cross-linking agent (isocyanate-based cross-linking agent, Coronate L-45, manufactured by Tosoh Corporation) was added to the obtained acrylic copolymer-containing solution by 2 parts by weight with respect to 100 parts by weight of the acrylic copolymer. In addition, a pressure-sensitive adhesive solution was prepared. This pressure-sensitive adhesive solution was applied to a PET film having a thickness of 75 μm and subjected to a mold release treatment so that the thickness of the pressure-sensitive adhesive layer after drying was 35 μm, and then dried at 110 ° C. for 5 minutes. This pressure-sensitive adhesive layer was transferred to a corona-treated PET film having a thickness of 50 μm as a base material and cured at 40 ° C. for 48 hours to obtain a re-peelable sheet.

(3) Measurement of gel fraction The re-peelable sheet was cut into a flat rectangular shape of 20 mm × 40 mm to prepare a test piece, and the weight was measured. After immersing the test piece in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate and dried under the condition of 110 ° C. for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1).
Gel fraction (% by weight) = 100 x (W ₂ -W ₀ ) / (W ₁ -W ₀ ) (1)
(W ₀ : Weight of substrate, W ₁ : Weight of test piece before immersion in ethyl acetate, W ₂ : Weight of test piece after immersion in ethyl acetate, drying)

(4) Measurement of 180 ° Peeling Adhesive Strength on SUS Plate The re-peelable sheet was cut into strips having a width of 25 mm to prepare test pieces, and the release film was peeled off to expose the adhesive layer. This test piece is placed on a SUS plate so that the adhesive layer faces the SUS plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min to reciprocate the test piece and SUS. The plates were bonded together and then allowed to stand at 23 ° C. for 24 hours to prepare a test sample. According to JIS Z0237, a tensile test in the 180 ° direction was performed at a peeling speed of 300 mm / min, and a 180 ° peeling adhesive force (N / 25 mm) was measured.

( Reference Examples 2 to 5, Comparative Examples 1 to 4)
A re-peelable sheet was obtained in the same manner as in Reference Example 1 except that the composition of the acrylic copolymer was changed as shown in Tables 1 and 2.

(Example 6)
(1) Manufacture of re-peelable sheet (ultraviolet irradiation polymerization)
In the reaction vessel, 29 parts by weight of 2-ethylhexyl acrylate, 70 parts by weight of 2- (perfluorohexyl) ethyl acrylate, and 0.1 weight of 2,2-dimethoxy-1,2-diphenylethane-1-one as a photopolymerization catalyst. Added a part. After bubbling with nitrogen, the viscosity of the reaction solution (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 23 ° C.) was about 8000 mPa. It was irradiated with ultraviolet rays until it became s. Then, 1 part by weight of trimethylolpropane triacrylate was added to the reaction solution to prepare a syrup.
The prepared syrup was applied to a release-treated PET film having a thickness of 75 μm so that the thickness of the pressure-sensitive adhesive layer after drying was 35 μm, and then bonded to a corona-treated PET film having a thickness of 50 μm as a base material. .. A re-peelable sheet was obtained by irradiating the PET film surface of this laminated sheet with ultraviolet rays having an illuminance of 5 mW / cm ² for 5 minutes with a black light (manufactured by Toshiba Corporation).

(2) Measurement of gel fraction The re-peelable sheet was cut into a flat rectangular shape of 20 mm × 40 mm to prepare a test piece, and the weight was measured. After immersing the test piece in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate and dried under the condition of 110 ° C. for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1).
Gel fraction (% by weight) = 100 x (W ₂ -W ₀ ) / (W ₁ -W ₀ ) (1)
(W ₀ : Weight of substrate, W ₁ : Weight of test piece before immersion in ethyl acetate, W ₂ : Weight of test piece after immersion in ethyl acetate, drying)

(3) Measurement of 180 ° Peeling Adhesive Strength on SUS Plate The re-peelable sheet was cut into strips having a width of 25 mm to prepare test pieces, and the release film was peeled off to expose the adhesive layer. This test piece is placed on a SUS plate so that the adhesive layer faces the SUS plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min to reciprocate the test piece and SUS. The plates were bonded together and then allowed to stand at 23 ° C. for 24 hours to prepare a test sample. According to JIS Z0237, a tensile test in the 180 ° direction was performed at a peeling speed of 300 mm / min, and a 180 ° peeling adhesive force (N / 25 mm) was measured.

(Examples 7 to 9, Comparative Example 5)
A re-peelable sheet was obtained in the same manner as in Example 6 except that the composition of the acrylic copolymer was changed as shown in Tables 1 and 2.

<Evaluation>
The re-peelable sheets obtained in Reference Examples, Examples , and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

(1) Evaluation of resistance to sebum The re-peelable sheet was cut into a width of 25 mm and a length of 100 mm to prepare a test piece, and the release film was peeled off to expose the pressure-sensitive adhesive layer. This test piece is placed on a SUS plate so that the adhesive layer faces the SUS plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min to reciprocate the test piece and SUS. The plates were bonded together and then allowed to stand at 23 ° C. for 24 hours to prepare a test sample.
When this test sample was immersed in an oleic acid bath at 60 ° C. and 90% humidity for 50 hours, the case where the test piece was peeled off from the SUS plate was marked with x, and the case where it was not peeled off was marked with ◯.

(2) Evaluation of peelability The release film of the re-peelable sheet was peeled off to expose the pressure-sensitive adhesive layer. This test piece is placed on a thin glass plate having a thickness of 0.5 mm so that the adhesive layer faces the glass plate, and then a 2 kg rubber roller is reciprocated once on the test piece at a speed of 300 mm / min. Then, the test piece and the glass plate were bonded together, and then allowed to stand at 23 ° C. for 24 hours to prepare a test sample.
In this test sample, when the test piece was peeled off under the condition that the peeling speed was 300 mm / min and the tensile direction was 90 ° with one end of the glass plate fixed, the case where the glass plate was cracked was ×, and there was no cracking. The case was marked as ○.

According to the present invention, it is possible to provide a re-peelable sheet which is excellent in resistance to sebum and can be easily peeled off after use.

Claims (6)

A re-peelable sheet having an adhesive layer containing an acrylic copolymer.
The acrylic copolymer is an energy ray irradiation polymerization type acrylic copolymer.
The acrylic copolymer contains a structural unit derived from a polyfunctional monomer and contains 30% by weight or more of a structural unit derived from a fluorine-containing (meth) acrylate.
A re-peelable sheet characterized by having a 180 ° peeling adhesive force against a SUS plate of 2N / 25 mm or less. The removable sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a gel fraction of 80% by weight or more. The removable sheet according to claim 1 or 2, wherein the acrylic copolymer contains 2% by weight or more of a structural unit derived from (meth) acrylate having a hydroxyl group. The removable sheet according to claim 1, 2 or 3, wherein the structural unit derived from the polyfunctional monomer contains at least one selected from the group consisting of divinylbenzene and trimethylolpropane tri (meth) acrylate. The removable sheet according to claim 1, 2, 3 or 4, which is used for surface protection of a member of an electronic device. A re-peelable sheet having an adhesive layer containing an acrylic copolymer.
The acrylic copolymer is an energy ray irradiation polymerization type acrylic copolymer.
The acrylic copolymer contains a structural unit derived from a polyfunctional monomer and contains 30% by weight or more of a structural unit derived from a fluorine-containing (meth) acrylate.
The 180 ° peeling adhesive strength to the SUS plate is 2N / 25mm or less.
Used to protect the surface of electronic device components
A re-peelable sheet characterized by that.