JP2021155593A - Tackiness agent for display device and tackiness sheet using the same - Google Patents

Abstract

To provide a tackiness agent for display devices which does not cause corrosion because of high hardness and not containing acrylic resin, and is difficult to be swollen or peeled even when a resin such as polycarbonate or the like is used under high temperature environment, or under high temperature/high humidity environment, and to provide a tackiness sheet using the tackiness agent.SOLUTION: A tackiness agent for display devices comprises an acrylic copolymer, the acrylic copolymer is a copolymer of the monomer composition containing at least ethyl acrylate and 4-acryloyl morpholine, in which the monomer composition does not contain acrylic acid and 2-ethylhexyl acrylate.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive for a display device and a pressure-sensitive adhesive sheet using the same.

Display devices such as liquid crystal displays and organic EL displays are configured by laminating various functional films and the like. In recent years, these display devices have been used for various purposes, and films having various functions are attached on the surface of a liquid crystal cell, the surface of an organic EL panel, or the outermost surface of a display screen according to the application. Is used.

For example, in a liquid crystal display, various functional films such as a polarizing plate and a retardation plate on the surface of a liquid crystal cell, and in an organic EL display, a polarizing plate on the surface of an organic EL panel are laminated and used.

In addition to car navigation, the installation rate of in-vehicle displays such as display audio and rear seat entertainment has increased as automobile equipment, and the use of display devices, especially touch panel display devices, has expanded to operate those display devices. ing. In the future, it is expected that button operations will disappear even around the dashboard of a car and touch panel operations will become the mainstream. On the outermost surface of such a display device, a shatterproof film is used on the outermost surface of the display screen to prevent the cover glass and glass substrate of the display screen from being damaged in an accident and noticing the occupants. Has been done.

In addition, for display devices used outdoors such as car navigation systems and smartphones, an antireflection film that does not reflect external light and can maintain the visibility of the display on the display device is attached to the outermost surface of the display device. There is.

These films are laminated and affixed using an adhesive, and are used in a high temperature or high temperature and high humidity environment when used outdoors, especially when used in an automobile. Durability in a high temperature and high humidity environment is required.

In Patent Document 1, a heat-resistant adhesive composition that does not cause swelling or peeling of an optical film even in a high temperature environment, has high durability even in a moist heat environment, has good reworkability, and can be used as an adhesive for an optical film. Things have been proposed.

Patent Document 2 proposes an acid-free adhesive that can be used for touch panels and the like and has excellent step-following property and blister resistance.

Japanese Unexamined Patent Publication No. 2008-308549 International Publication WO2015 / 132888

However, the adhesive of Patent Document 1 does not cause swelling or peeling of the optical film even in a high temperature environment, and has high durability even in a moist heat environment, but contains acrylic acid, and the adhesive is used. There was a risk of causing corrosion of laminates such as display devices. In addition, acrylic acid has reactivity and may react with other substances to generate gas, which may cause swelling or peeling of the optical film in a high temperature environment.

The pressure-sensitive adhesive of Patent Document 2 is a soft pressure-sensitive adhesive having a storage elastic modulus at 80 ° C. of 0.02 MPa to 0.10 MPa in order to have a step followability, although no acid is used and there is no problem of corrosion. It is characteristic that there is. When the adherend used for the outermost surface of the display device is plastic, especially polycarbonate having a higher water content than glass, the moisture contained in the adherend is gasified when used in a high temperature and high humidity environment. Since the adhesive is soft, there is a problem that it causes swelling and peeling.

Therefore, the present invention is for a display device that has high hardness, does not cause corrosion because it does not contain acrylic acid, and is less likely to swell or peel even when used for a resin such as polycarbonate in a high temperature environment or a high temperature and high humidity environment. It is an object of the present invention to provide the pressure-sensitive adhesive and a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive.

The present inventors have conducted diligent research and found that the above problems can be solved by using a pressure-sensitive adhesive having a specific composition, and have completed the present invention. That is, the present invention is as follows.

The present invention (1)
Adhesive for display devices
The pressure-sensitive adhesive contains an acrylic copolymer and contains
The acrylic copolymer is a copolymer of a monomer composition containing at least ethyl acrylate and 4-acryloyl morpholine.
The monomer composition is a pressure-sensitive adhesive for display devices, which is characterized by not containing acrylic acid and 2-ethylhexyl acrylate.
The present invention (2)
^{The display device adhesive has a Martens hardness of 0.3 N / mm 2 to} 0.55 N / measured according to ISO 14577-1: 2002 when the display device adhesive is a sheet having a thickness of 25 μm. The pressure-sensitive adhesive for a display device according to the invention (1), characterized in that it is ^{mm 2.}
The present invention (3)
The pressure-sensitive adhesive for a display device according to the invention (1) or (2) is a pressure-sensitive adhesive sheet laminated on a base material.

According to the present invention, a display device that has high hardness, does not cause corrosion because it does not contain acrylic acid, and is less likely to swell or peel even when used for a resin such as polycarbonate in a high temperature environment or a high temperature and high humidity environment. It is an object of the present invention to provide a pressure-sensitive adhesive for use and a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive.

Without any notice in the present specification, the term "acrylic" shall include "methacryl", and the term "acrylate" shall include "methacrylate". Further, in the present specification, the fact that the composition does not contain a certain component means that the content of a certain component in the composition is unavoidably equal to or less than the amount present.

Hereinafter, the pressure-sensitive adhesive for a display device of the present invention and the pressure-sensitive adhesive sheet using the pressure-sensitive adhesive will be described.
1. 1. Adhesive for display devices 1-1. Composition of Adhesive for Display Devices The adhesive of the present invention contains an acrylic copolymer.

The acrylic copolymer can be obtained by copolymerizing a monomer composition containing an acrylic monomer.

The monomer composition according to the present invention is characterized by containing at least ethyl acrylate and 4-acryloyl morpholine, and not containing acrylic acid and 2-ethylhexyl acrylate.

The other acrylic monomer contained in the monomer composition is not particularly limited as long as the effect of the present invention is not impaired, and a known monomer can be included. Examples of the monomer include methyl acrylate, n-butyl acrylate, i-butyl acrylate, n-octyl acrylate, i-octyl acrylate, n-nonyl acrylate, i-nonyl acrylate, n-decyl acrylate, n-dodecyl acrylate, and stearyl. Linear or branched alkyl esters of acrylic acids such as acrylates;
Linear or branched alkyl acrylic monomers of methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-dodecyl methacrylate, stearyl methacrylate;
2-Hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 3-methyl-3-hydroxybutyl acrylate, 1,1-dimethyl-3-butyl acrylate, 1,3-dimethyl -3-Hydroxybutyl acrylate, 2,2,4-trimethyl-3-hydroxypentyl acrylate, 2-ethyl-3-hydroxyhexyl acrylate, glycerin monoacrylate, polypropylene glycol monoacrylate, polyethylene glycol monoacrylate, poly (ethylene glycol) Lupropylene glycol) Hydroxyl-containing acrylic monomers such as monoacrylate, N-methylolacrylamide, allyl alcohol, and metalryl alcohol;
Monohydroxyethyl Acrylate Acrylate, Monohydroxyethyl Maleate Acrylate, Monohydroxyethyl Fumarate Acrylate, Monohydroxyethyl Acrylate Acrylate, 1,2-Dicarboxycyclohexane Monohydroxyethyl Acrylate, Dimer Acrylic Acid, ω-carboxy-Polycaprolactone Carboxyl group-containing acrylic monomer such as monoacrylate;
Glycidyl group-containing acrylic monomers such as glycidyl acrylate, 3,4-epoxycyclohexylmethyl acrylate, glycidyl vinyl ether, 3,4-epoxycyclohexylvinyl ether, glycidylallyl ether, and 3,4-epoxycyclohexylallyl ether;
Acrylamide, methacrylamide, N-methylacrylamide, N-ethylacrylamide, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, N-propoxymethylacrylamide, N-butoxymethylacrylamide, N-tert-butylacrylamide, N-octylacrylamide , N-substituted amide group-containing acrylic monomer such as diacetone acrylamide;
Tertiary amino group-containing acrylic monomers such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, and dimethylaminopropyl acrylamide; and the like, and various derivatives thereof can be included. These can be used alone or in combination of two or more.

Further, in addition to these acrylic monomers, a monomer other than the acrylic monomer copolymerizable with the acrylic monomer can be included. The monomer other than the acrylic monomer is not particularly limited as long as it does not inhibit the effect of the present invention, and examples thereof include N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylacetamide, acrylonitrile, styrene, and vinyl acetate. can. These can be used alone or in combination of two or more.

The acrylic copolymer can be obtained by radically reacting the monomer composition in the presence of a polymerization initiator. The radical reaction method is not particularly limited, and examples thereof include living radical polymerization and free radical polymerization. According to the living radical polymerization, a copolymer having a more uniform molecular weight and composition as compared with the free radical polymerization can be obtained, the formation of low molecular weight components and the like can be suppressed, and the cohesive force of the pressure-sensitive adhesive layer is increased. can do. Further, the polymerization method is not particularly limited, and a conventionally known method can be used. For example, solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like can be mentioned. Of these, solution polymerization is preferable because it is easy to synthesize.

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

The polymerization initiator is not particularly limited as long as it does not inhibit the effect of the present invention, and for example, an organic peroxide, an azo compound or the like can be used. Examples of organic peroxides include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, and 2,5-dimethyl. -2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobuty Rate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate and the like can be mentioned.
Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These can be used alone or in combination of two or more.

In the case of living radical polymerization, examples of the polymerization initiator include an organic tellurium polymerization initiator. The organic telluride polymerization initiator is not particularly limited as long as it does not inhibit the effect of the present invention, and those generally used for living radical polymerization can be used. Examples thereof include organic telluride compounds and organic telluride compounds. be able to. Also in living radical polymerization, in addition to the organic tellurium polymerization initiator, an azo compound can be used as the polymerization initiator for the purpose of promoting the polymerization rate.

The acrylic copolymer can be further crosslinked with a crosslinking agent for the purpose of appropriately adjusting the gel fraction. The cross-linking agent is not particularly limited as long as the effect of the present invention is not impaired, and for example, an isocyanate-based cross-linking agent, an aziridine-based cross-linking agent, an epoxy-based cross-linking agent, a metal chelate-type cross-linking agent and the like can be used. These can be used alone or in combination of two or more. Of these, the isocyanate-based cross-linking agent has appropriate reactivity and is preferable from the viewpoint of productivity.

The isocyanate-based cross-linking agent is not particularly limited as long as it does not inhibit the effect of the present invention, and is, for example, toluenediisocyanate (TDI), methylenediphenyldiisocyanate (MDI), naphthalenediocyanate, xylylene diisocyanate, polypeptide polyisocyanate (crude MDI). Aromatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, aliphatic polyisocyanates such as dicyclohexamethanediisocyanate; cyclohexane 1,4-diisocyanate, isophorone diisocyanate (IPDI), hydrogenated xylylene diisocyanate, hydrogenated bis (isocyanate) Examples thereof include alicyclic polyisocyanates such as natophenyl) methane and bicycloheptanetriisocyanate; isocyanurate compounds; bullet-type compounds; and modified products thereof. These can be used alone or in combination of two or more. It is preferable to contain an isocyanurate compound in that the pressure-sensitive adhesive has a higher hardness and further excellent heat resistance and heat-moisture resistance are imparted. As a result, it is possible to obtain an adhesive that is less likely to swell or peel.

The weight average molecular weight of the acrylic copolymer is not particularly limited as long as the effect of the present invention is not impaired, but is, for example, 300,000 to 2 million, preferably 400,000 to 1.5 million. When the weight average molecular weight is in such a range, the hardness, heat resistance, and heat resistance and moisture resistance of the pressure-sensitive adhesive are good. As a result, it is possible to obtain an adhesive that is less likely to swell or peel. As a method for measuring the weight average molecular weight, a known measuring method can be used, and for example, a method based on JIS K7252-1: 2008 "Method for determining the average molecular weight and molecular weight distribution of a polymer by plastic-size exclusion chromatography". Can be measured by.

The glass transition temperature (hereinafter referred to as Tg) of the acrylic copolymer can be −50 ° C. to −10 ° C., preferably −40 ° C. to −15 ° C., and more preferably −30 ° C. to −15 ° C. When the Tg is in such a range, the adhesive can be made harder and the adhesiveness to the outermost surface of the display device can be made high. As a result, it is possible to obtain an adhesive that is less likely to swell or peel. As a method for measuring Tg, a known measuring method can be used, and for example, it can be measured by a method based on JIS K7121-1987 “Method for measuring transition temperature of plastic”.

The pressure-sensitive adhesive of the present invention may contain other components. Other components are not particularly limited as long as the effects of the present invention are not impaired, and are, for example, coupling agents, leveling agents, cross-linking aids, plasticizers, softeners, fillers, antistatic agents, anti-aging agents, and the like. It may contain various additives that are common in the field of pressure-sensitive adhesive compositions, such as UV absorbers, antioxidants, light stabilizers, and surfactants. As for such various additives, conventionally known ones can be used by a conventional method and do not particularly characterize the present invention, and thus detailed description thereof will be omitted.

1-2. Martens hardness of the display device for pressure-sensitive adhesive properties Martens hardness present invention display adhesive agent is not particularly ^limited, it is possible to ^{0.3N / mm 2 ~0.55N / mm 2} , 0 .4 N / mm ^{2 to} 0.5 N / mm ² is preferable, and 0.45 to 0.5 N / mm ² is more preferable. When the Martens hardness of the adhesive for the display device is within the applicable range, it is possible to obtain sufficient hardness for adhesion to the base material / adherend and suppression of swelling, and for the display device of the present invention. The storage elastic modulus of the pressure-sensitive adhesive at 80 ° C. is higher than the storage elastic modulus of the pressure-sensitive adhesive of Patent Document 2 at 80 ° C., which is 0.02 MPa to 0.10 MPa, and swelling or peeling occurs. It becomes possible to suppress it. Martens hardness can be measured according to ISO 14577-1: 2002.

Here, swelling is a phenomenon in which when an adhesive is used as an adhesive sheet, gas is generated from the adhesive or an adherend in a high temperature environment or a high temperature and high humidity environment, and the generated gas forms bubbles and swells. To say. In addition, peeling means that when the swelling becomes severe, not only the swelling occurs, but also the state where the adhesive is peeled off from the adherend and the adhesive can follow the stress change of the base material / adherend. It means the state of being peeled off from the base material / adherend.

1-3. Method for Producing Adhesive for Display As for the method for preparing the adhesive, a method for producing an acrylic copolymer using living radical polymerization by a solution polymerization method, which is a preferable example, will be described. A monomer composition is prepared by mixing a monomer as a raw material and an organic solvent such as toluene or ethyl acetate. The monomer composition is placed in a closed container and heated to a predetermined temperature (for example, 40 ° C. to 90 ° C.) with a nitrogen barge and stirring. A predetermined polymerization initiator is added dropwise to the predetermined monomer composition, and heating and stirring are continued until the reaction is completed to obtain an acrylic copolymer. At this time, the weight average molecular weight can be adjusted by adjusting the type of solvent, heating temperature, and the like.

The blending amount of ethyl acrylate in the monomer composition of the raw material can be 25% by mass to 45% by mass when all the monomer components in the monomer composition are 100% by mass.

The blending amount of 4-acryloyl morpholine in the monomer composition of the raw material can be 5% by mass to 15% by mass when all the monomer components in the monomer composition are 100% by mass.

The blending amount of the monomers other than ethyl acrylate and 4-acryloyl morpholine in the monomer composition of the raw material may be 40% by mass to 70% by mass when all the monomer components in the monomer composition are 100% by mass. can. The amount of the monomer to be blended can be freely adjusted depending on the glass transition temperature and hardness of the desired hard acrylic copolymer (or pressure-sensitive adhesive).

If necessary, a cross-linking agent is added to the obtained acrylic copolymer and heated to complete the cross-linking reaction while evaporating the organic solvent. The heating temperature (for example, 60 ° C. to 120 ° C.) and the heating time (drying time) can be freely selected depending on the type of the cross-linking agent, the type and concentration of the organic solvent used. In this way, the gel fraction can be adjusted to obtain a pressure-sensitive adhesive having a predetermined hardness. As a result, it is possible to obtain an adhesive that is less likely to swell or peel.

The amount of the cross-linking agent added can be 0.1 parts by mass to 10 parts by mass, preferably 0.3 parts by mass to 5 parts by mass, more preferably 0.3 parts by mass, when the acrylic copolymer is 100 parts by mass. Is 0.5 parts by mass to 3 parts by mass. Within such a range, a pressure-sensitive adhesive having high hardness and excellent heat resistance and moisture resistance can be formed.

When the pressure-sensitive adhesive is a pressure-sensitive adhesive sheet, an acrylic copolymer can be applied onto a base material and laminated. An adhesive sheet can be formed by heating this laminated sheet to evaporate the organic solvent. When a cross-linking agent is added, a mixture of an acrylic copolymer and a cross-linking agent may be applied before coating and heated to complete the cross-linking reaction. The heating conditions can be freely selected depending on the type of the cross-linking agent, the type and concentration of the organic solvent used.

Examples of the method for forming the adhesive into a sheet include a comma coater, a blade coater, a lip coater, a rod coater, a squeeze coater, a reverse coater, a transfer coater, a gravure coater, a spray coater, a screen printing method, and a curtain coat method. Examples include a spray coating method and a roll coating method, which may be applied directly to the surface of the layer to be laminated, or may be applied to the surface of a release sheet or the like in the form of a sheet and then transferred to the surface of the layer to be laminated. A method of laminating can be mentioned.

The base material is not particularly limited as long as the effects of the present invention are not impaired, and for example, a polarizing plate, a film containing a hard-coded layer (scattering prevention film), an antireflection film, and the like can be used.

The thickness of the base material is not particularly limited, but can be, for example, 1 μm to 100 μm, and 25 μm to 50 μm is more preferable. Due to the high hardness of the pressure-sensitive adhesive of the present invention, the base material used in the present invention can be made thinner than the conventionally used base material.

The thickness of the pressure-sensitive adhesive is not particularly limited, but can be, for example, 1 μm to 50 μm, preferably 5 μm to 40 μm, and preferably 10 μm to 30 μm.

1-4. Applications of Adhesives for Display Devices Adhesives for display devices can be used for laminating polarizing plates and retardation plates on the surface of liquid crystal cells in liquid crystal displays, and polarizing plates on the surface of organic EL panels in organic EL displays. ..
It can also be used as an adhesive for an anti-scattering film or an anti-reflection film used on the outermost surface of the display screen of a display device.

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

<Production of Acrylic Copolymer Solution of Example 1>
In a flask equipped with a thermometer, a stirrer, a reflux cooling tube, and a nitrogen introduction tube, 50 parts by mass of n-butyl acrylate (BA), 30 parts by mass of ethyl acrylate (EA), and 15 parts by mass of 4-acryloyl morpholine (ACMO). 5 parts by mass of 2-hydroxyethyl acrylate (2HEA), 0.1 part by mass of azobisisobutyronitrile, 100 parts by mass of ethyl acetate, nitrogen was introduced from the nitrogen introduction tube, and the inside of the flask was filled with nitrogen. Then, the polymerization reaction was carried out for 8 hours while heating at 65 ° C. to obtain an acrylic copolymer solution. Ethyl acetate was added to this acrylic copolymer solution so that the solid content was 30% to obtain an acrylic copolymer solution 1 having a glass transition temperature of −29.7 ° C. and a weight average molecular weight (Mw) of 900,000. The specific formulation is shown in Table 1.

<Production of Acrylic Copolymer Solutions of Examples 2-4 and Comparative Examples 1-2>
The acrylic copolymer solutions of Examples 2 to 4 and Comparative Examples 1 and 2 were obtained in the same manner as in the production of the acrylic copolymer solution of Example 1 except that the amounts of each monomer shown in Table 1 were used. .. The specific formulation is shown in Table 1.

<Production of Acrylic Copolymer Solution of Comparative Example 3>
Acrylic acid (AA) was further added to the flask as a monomer, and the amounts of each monomer shown in Table 1 were adjusted. An acrylic copolymer solution of Example 3 was obtained. The specific formulation is shown in Table 1.

<Adhesive sheets of Examples 1 to 4 and Comparative Examples 1 to 3>
Table 2 shows polyisocyanate (manufactured by Tosoh Corporation, trade name: Coronate HX) in the obtained acrylic copolymer solutions of Examples and Comparative Examples with respect to 100 parts by mass of the solid content of the acrylic copolymer solution. The mixture was added in the indicated amount to prepare an adhesive coating solution.
The pressure-sensitive adhesive coating liquid is applied to a 38 μm peeling PET so that the film thickness after drying is 25 μm, dried, and the dried surface of the pressure-sensitive adhesive coating liquid is bonded with an 80 μm TAC film. The adhesive sheets of each Example and Comparative Example were obtained by curing for one week in an environment of a temperature of 23 ° C. and a humidity of 55%. The peeling PET of the adhesive sheet was peeled off to prepare a test sample.

<Evaluation method>
The following evaluation results are shown in Table 2.
(Martens hardness)
Martens hardness was measured using a micro-pressing hardness tester (manufactured by Elionix Inc.) only for the pressure-sensitive adhesive layer of the obtained pressure-sensitive adhesive sheets of Examples and Comparative Examples. For the measurement, a load / unloading test was performed using a Berkovich indenter with a load of 0.5 mN, and the Martens hardness was calculated.

(Reliability test)
Each of the obtained test samples was cut into a size of 80 × 100 mm, bonded to a 1.0 m-thick polycarbonate plate (NF2000 manufactured by Mitsubishi Gas Chemical Company, Inc.) with a laminator, and then the following tests were performed.

(High temperature resistance test)
The sample for the polycarbonate plate bonding test was put into a constant temperature bath at 105 ° C. for 1000 hours, and the appearance of the sample after the test was visually evaluated.

(High temperature and high humidity test)
The sample for the polycarbonate plate bonding test was put into a constant temperature and humidity chamber at 85 ° C. and 85% for 1000 hours, and the appearance of the sample after the test was visually evaluated.

The evaluation items and criteria of the above reliability test are as follows.
・ Swelling ○: None △: Swelling to the extent that it does not hinder the appearance ×: Swelling to the extent that it does not hinder the appearance There is a degree of peeling

From the above, all of Examples 1 to 4 of the present invention withstood the high temperature resistance test and the high temperature and high humidity resistance test, whereas Comparative Examples 1 to 3 satisfied all of these evaluation criteria unlike the examples. I couldn't.

Claims (3)

Adhesive for display devices
The pressure-sensitive adhesive contains an acrylic copolymer and contains
The acrylic copolymer is a copolymer of a monomer composition containing at least ethyl acrylate and 4-acryloyl morpholine.
A pressure-sensitive adhesive for a display device, wherein the monomer composition does not contain acrylic acid and 2-ethylhexyl acrylate. ^{The display device adhesive has a Martens hardness of 0.3 N / mm 2 to} 0.55 N / measured according to ISO 14577-1: 2002 when the display device adhesive is a sheet having a thickness of 25 μm. characterized in that it is a mm ^2, the display device for pressure-sensitive adhesive of claim 1. An adhesive sheet in which the adhesive for a display device according to claim 1 or 2 is laminated on a base material.