JP6545488B2 - Adhesive sheet - Google Patents

Description

  The present invention relates to an adhesive sheet.

  BACKGROUND ART Various mobile electronic devices such as mobile phones and tablet terminals in recent years are provided with a display (display) using a display panel having a liquid crystal element, a light emitting diode (LED element), an organic electroluminescence (organic EL) element and the like. .

  In such a display, a protective plate is usually provided on the front side of the display panel. An air gap is provided between the protective plate and the display panel so that the deformed protective plate does not collide with the display panel even when the protective plate is deformed by an external force.

  However, when the air gap as described above, that is, the air layer is present, the reflection loss of light due to the refractive index difference between the protective panel and the air layer and the refractive index difference between the air layer and the display module is large. There is a problem that the image quality is degraded.

  Therefore, it has been proposed to improve the image quality of the display by filling the space between the protective plate and the display panel with an adhesive.

  However, in the conventional pressure sensitive adhesive, when the display is placed under high temperature and humidity, there is a problem that the generation of air bubbles and the transparency decrease.

  Therefore, attempts have been made to suppress the generation of air bubbles and the decrease in transparency by adding a low molecular weight polymer to the adhesive main component (see, for example, Patent Document 1).

  However, a frame-like printing layer may be present as a step on the display panel side of the protective plate, and the pressure-sensitive adhesive layer described in Patent Document 1 can not follow this step, and adhesion in the vicinity of the step The agent layer floats, which causes a problem of light reflection loss. For this reason, the adhesive sheet excellent in both foaming resistance and level | step difference tracking property is calculated | required.

JP 2002-327160 A

  An object of the present invention is to provide a pressure-sensitive adhesive sheet excellent in foam resistance (blister resistance) and step followability.

Such an object is achieved by the present invention of the following (1) to ( 3 ).
(1) A pressure-sensitive adhesive sheet used to bond a protective plate and a display panel,
A monomer having a carboxyl group, and an acrylic polymer having a (meth) acrylic acid alkyl ester as a constituent monomer and having a weight average molecular weight of 200,000 or more and 900,000 or less ;
An epoxy crosslinking agent as a thermal crosslinking agent,
Formed of a pressure-sensitive adhesive composition comprising a hydrogen abstraction type photoinitiator,
The acrylic polymer is substantially free of radically unsaturated double bonds, and
The pressure-sensitive adhesive composition is substantially free of a self-cleavage type photoinitiator .
The content of the monomer having a carboxyl group in the acrylic polymer is 8% by mass or more and 20% by mass or less,
The content of the (meth) acrylic acid alkyl ester in the acrylic polymer is 50% by mass or more and 92% by mass or less,
A pressure-sensitive adhesive sheet, wherein a thickness of a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is 50 μm or more .
(2) A pressure-sensitive adhesive sheet used to bond a protective plate and a display panel,
An acrylic polymer having a hydroxyl group-containing monomer and a (meth) acrylic acid alkyl ester as a constituent monomer and having a weight average molecular weight of 200,000 or more and 900,000 or less;
An isocyanate crosslinking agent as a thermal crosslinking agent,
Formed of a pressure-sensitive adhesive composition comprising a hydrogen abstraction type photoinitiator,
The acrylic polymer is substantially free of radically unsaturated double bonds, and
The pressure-sensitive adhesive composition is substantially free of a self-cleavage type photoinitiator.
The content of the monomer having a hydroxyl group in the acrylic polymer is 10% by mass to 25% by mass,
The content of the (meth) acrylic acid alkyl ester in the acrylic polymer is 50% by mass or more and 90% by mass or less,
A pressure-sensitive adhesive sheet, wherein a thickness of a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is 50 μm or more.

( 3 ) The adhesive sheet as described in (1) or (2) above, wherein the addition amount of the hydrogen extraction photoinitiator with respect to 100 parts by mass of the acrylic polymer is 0.1 part by mass or more and 5.0 parts by mass or less.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesive sheet excellent in foaming resistance (blister-proof performance) and level | step difference flattery can be provided.

It is sectional drawing which shows an example of the display which bonded the protective plate and the display panel using the adhesive sheet of this invention.

Hereinafter, the present invention will be described in detail based on preferred embodiments.
<1> Adhesive sheet FIG. 1: is sectional drawing which shows an example of the display which bonded the protective plate and the display panel using the adhesive sheet of this invention. In the following description, the upper side in the drawings is referred to as "upper" or "upper", and the lower side is referred to as "lower" or "lower".

  The pressure-sensitive adhesive sheet (pressure-sensitive adhesive sheet 11) of the present invention is used to bond the protective plate 21 and the display panel 22 as shown in FIG.

  The pressure-sensitive adhesive sheet of the present invention is formed of a pressure-sensitive adhesive composition containing an acrylic polymer having a functional group, a thermal crosslinking agent, and a hydrogen abstraction photoinitiator.

  Moreover, in the adhesive sheet of this invention, the acrylic polymer which has a functional group does not contain a radically unsaturated double bond substantially.

  In the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive composition is substantially free of a self-cleavage type photoinitiator.

  By having the above characteristics, when there is a level difference on the bonding surface of the protective plate or the display panel, the adhesive sheet can follow the level difference, and after storage under durability (high temperature and high humidity) conditions Even in this case, it is possible to maintain the state following the level difference (hereinafter, may be referred to as "level difference following property"). In addition, by directly crosslinking acrylic polymers with a hydrogen extraction type photoinitiator, even after storage under durable (high temperature and high humidity) conditions, the adhesive sheet and the bonding surface of the protective plate or display panel It is possible to prevent the generation of voids or air bubbles therebetween (hereinafter, sometimes referred to as "foam resistance").

  The protective plate 21 preferably has a step (printing step) 3 on the side in contact with the adhesive sheet 11, as shown in FIG. The height of the step 3 is preferably 5 to 50 μm and more preferably 10 to 30 μm from the viewpoint of concealing the wiring and the like of the display panel while considering the thinning of the display 23. Moreover, a glass plate, a plastic plate, etc. are mentioned preferably for the protective plate 21. Among them, a plastic plate which is easy to foam when attached to a pressure-sensitive adhesive sheet and is exposed to a durable condition is particularly preferable because the foam resistance of the pressure-sensitive adhesive sheet according to the present embodiment can be further exhibited. As a plastic board, an acrylic board, a polycarbonate board, etc. are mentioned, for example. The thickness of the protective plate 21 is preferably 0.1 to 3 mm, and particularly preferably 0.3 to 1.5 mm.

Hereinafter, each component which comprises an adhesive composition is demonstrated in detail.
1. Acrylic polymer having functional group The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet contains an acrylic polymer having a functional group. By using an acrylic polymer having a functional group, it can be easily crosslinked by a thermal crosslinking agent. In addition, radicals generated by the hydrogen abstraction type photoinitiator extract hydrogen bonded to carbon such as a main chain skeleton in the acrylic polymer, generate radicals in the acrylic polymer, and directly crosslink the acrylic polymers. it can.

  The acrylic polymer is crosslinked in the pressure-sensitive adhesive sheet by a thermal crosslinking agent and a hydrogen-abstracting photoinitiator described later to form a three-dimensional network structure.

  The acrylic polymer is not particularly limited, but it is preferable to use a (meth) acrylic acid ester copolymer. In the present specification, (meth) acrylic acid means both acrylic acid and methacrylic acid. Other similar terms are also the same.

  The acrylic polymer preferably has at least one selected from the group consisting of a carboxyl group and a hydroxyl group as a functional group. By having such a functional group, crosslinking can be performed more reliably by the thermal crosslinking agent. In addition, it is presumed that hydrogens bonded to carbon such as the main chain skeleton in the acrylic polymer are easily extracted by radicals generated by the hydrogen extraction photoinitiator.

  The content of the carboxyl group-containing monomer in the acrylic polymer is preferably 8% by mass or more, and more preferably 10% by mass or more. Moreover, it is preferable that it is 20 mass% or less, and, as for content of the monomer which has a carboxyl group in an acryl polymer, it is more preferable that it is 15 mass% or less. As a result, it is presumed that an appropriate three-dimensional network structure is formed, and the foam resistance and step followability of the resulting pressure-sensitive adhesive sheet can be more effectively improved. On the other hand, when the content of the monomer having a carboxyl group is less than the lower limit value, the transparency may be reduced due to the whitening of the pressure-sensitive adhesive sheet after storage under high temperature and high humidity durability conditions. In addition, when the content of the monomer having a carboxyl group exceeds the upper limit value, sufficient adhesiveness may not be obtained.

  Examples of the monomer having a carboxyl group include, for example, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, citraconic acid, etc. Can be used in combination. Among these, it is preferable to use acrylic acid from the viewpoint of the reactivity with the thermal crosslinking agent and the copolymerizability with other monomers.

  The content of the monomer having a hydroxyl group in the acrylic polymer is preferably 10% by mass or more, and more preferably 15% by mass or more. Moreover, it is preferable that it is 25 mass% or less, and, as for content of the monomer which has a hydroxyl group in an acryl polymer, it is more preferable that it is 20 mass% or less. As a result, it is presumed that an appropriate three-dimensional network structure is formed, and the foam resistance and step followability of the resulting pressure-sensitive adhesive sheet can be more effectively improved. On the other hand, when the content of the monomer having a hydroxyl group is less than the lower limit value, the transparency may be reduced due to the whitening of the pressure-sensitive adhesive sheet after storage under high temperature and high humidity durability conditions. In addition, when the content of the monomer having a hydroxyl group exceeds the upper limit value, sufficient adhesiveness may not be obtained.

  Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, And (meth) acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate. Among these, it is preferable to use 2-hydroxyethyl (meth) acrylate or 4-hydroxybutyl (meth) acrylate from the viewpoint of the reactivity with a thermal crosslinking agent and the copolymerizability with other monomers.

  In addition, the acrylic polymer may have a monomer other than the monomer having a functional group as a structural unit.

  As such a monomer, it is preferable to use (meth) acrylic acid alkyl ester, and it is more preferable to use (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group. Thereby, the adhesiveness of an adhesive sheet can be made favorable.

  Examples of the (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group include methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, N-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate And myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate and the like. Among them, from the viewpoint of further improving adhesiveness, (meth) acrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl group are preferable, and n-butyl (meth) acrylate or 2-ethylhexyl (meth) acrylate is particularly preferable preferable.

  The content of the (meth) acrylic acid alkyl ester in the acrylic polymer is preferably 50% by mass or more, and more preferably 70% by mass or more. Further, the upper limit of the content of the (meth) acrylic acid alkyl ester in the acrylic polymer is determined in relation to the blending amount of the monomer having a carboxyl group or the monomer having a hydroxyl group. Specifically, when a monomer having a carboxyl group is blended, the upper limit of the content of the (meth) acrylic acid alkyl ester is preferably 92% by mass or less, and particularly preferably 90% by mass or less. On the other hand, when the monomer having a hydroxyl group is blended, the upper limit of the content of the (meth) acrylic acid alkyl ester is preferably 90% by mass or less, and more preferably 80% by mass or less.

  The polymerization mode of the acrylic polymer may be a random copolymer or a block copolymer.

  The weight average molecular weight of the acrylic polymer is preferably 200,000 or more, more preferably 400,000 or more. The weight average molecular weight of the acrylic polymer is preferably 900,000 or less, more preferably 700,000 or less. Thereby, the adhesive sheet excellent in level | step difference follow-up property is obtained. On the other hand, when the weight average molecular weight of the acrylic polymer is less than the lower limit value, the cohesion of the pressure-sensitive adhesive may be insufficient to deteriorate the foam resistance. On the other hand, when the weight average molecular weight of the acrylic polymer exceeds the above upper limit value, the solubility in the solvent decreases. As a result, it may be difficult to form a relatively thick adhesive sheet. 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.

  Acrylic polymers as described above are substantially free of radically unsaturated double bonds. As a result, the pressure-sensitive adhesive sheet becomes rich in stress relaxation properties, and is particularly excellent in step followability. Furthermore, the radical generated by the hydrogen abstraction type photoinitiator is not consumed by the radically unsaturated double bond, and efficiently contributes to the hydrogen abstraction reaction of the main chain skeleton of the acrylic polymer. It is presumed to promote crosslinking, and the foaming resistance of the resulting pressure-sensitive adhesive sheet is also excellent.

2. Thermal Cross-Linking Agent The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet contains a thermal cross-linking agent.

  The thermal crosslinking agent is not particularly limited as long as it reacts with the functional group of the acrylic polymer, and, for example, an isocyanate crosslinking agent, an epoxy crosslinking agent, an amine crosslinking agent, a melamine crosslinking agent, an aziridine crosslinking agent, A hydrazine type crosslinking agent, an aldehyde type crosslinking agent, an oxazoline type crosslinking agent, a metal alkoxide type crosslinking agent, a metal chelate type crosslinking agent, a metal salt type crosslinking agent, an ammonium salt type crosslinking agent and the like can be mentioned.

  Among the above-mentioned, when using the acrylic polymer which has a carboxyl group as a functional group, it is preferable to use an epoxy-type crosslinking agent. Thereby, the three-dimensional network structure by acrylic polymer can be formed more efficiently.

  Examples of epoxy-based crosslinking agents 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 etc. are mentioned, It can be used combining 1 type, or 2 or more types among these.

  Moreover, when using the acrylic polymer which has a hydroxyl group as a functional group among the above-mentioned, it is preferable to use an isocyanate type crosslinking agent. Thereby, the three-dimensional network structure by acrylic polymer can be formed more efficiently.

The isocyanate crosslinking agent contains at least a polyisocyanate compound.
Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and the like And biuret bodies thereof, isocyanurate bodies, and adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, castor oil and the like.

  The content of the thermal crosslinking agent in the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet is preferably 0.01 parts by mass or more, and 0.03 parts by mass or more with respect to 100 parts by mass of the acrylic polymer. More preferable. In addition, the content of the thermal crosslinking agent in the pressure-sensitive adhesive composition is preferably 2.0 parts by mass or less, and more preferably 1.0 parts by mass or less with respect to 100 parts by mass of the acrylic polymer. Thereby, the acrylic polymer can be crosslinked more efficiently.

3. Hydrogen abstraction type photoinitiator The adhesive composition which constitutes an adhesive sheet contains hydrogen abstraction type photoinitiator.

  The hydrogen abstraction photoinitiator has a function of generating radicals. Then, the generated radicals extract hydrogen bonded to carbon such as a main chain skeleton in the acrylic polymer, thereby generating radicals in the acrylic polymer and directly crosslinking the acrylic polymers.

  Examples of hydrogen abstraction type photoinitiators include aromatic ketones such as acetophenone, benzophenone, P, P'-dimethoxybenzophenone, P, P'-dichlorobenzophenone, P, P'-dimethylbenzophenone and acetonaphthone. . In addition, aromatic aldehydes such as terephthalaldehyde and quinone aromatic compounds such as methylanthraquinone may be mentioned. One of these may be used alone, or two or more of these may be used in combination. Among the above hydrogen abstraction type photoinitiators, it is preferable to use a compound containing benzophenone in particular, from the viewpoint of the ease of radical generation.

  The amount of hydrogen extraction photoinitiator added to 100 parts by mass of the acrylic polymer is preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more. In addition, the addition amount of the hydrogen extraction photoinitiator with respect to 100 parts by mass of the acrylic polymer is preferably 5.0 parts by mass or less, and more preferably 2.0 parts by mass or less. Thereby, acrylic polymers can be directly crosslinked more efficiently. On the other hand, depending on the type of the acrylic polymer, the crosslinking may not proceed sufficiently if the addition amount of the hydrogen abstraction type photoinitiator is less than the lower limit value. In addition, when the addition amount of the hydrogen abstraction type photoinitiator exceeds the upper limit value, the hydrogen abstraction type photoinitiator which does not contribute to the reaction may be increased, and the adhesiveness may not be obtained sufficiently.

  In addition, the adhesive composition which comprises an adhesive sheet does not contain a self-cleavage type photoinitiator substantially. This makes it possible to prevent the radicals generated in the hydrogen abstraction type photoinitiator from reacting and disappearing with the radicals generated in the self-cleavage type photoinitiator, and it is possible to crosslink acrylic polymers directly more reliably.

4. Other Components In the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet, various additives generally used in acrylic pressure-sensitive adhesives as required, for example, silane coupling agents, antistatic agents, tackifiers, oxidation Inhibitors, ultraviolet light absorbers, light stabilizers, fillers, refractive index modifiers and the like can be added. The pressure-sensitive adhesive composition is substantially free of a compound containing a radically unsaturated double bond such as a multifunctional acrylate, from the viewpoint of preventing the disappearance of radicals other than the purpose of the hydrogen abstraction type photoinitiator. Is preferred. Here, “substantially free” is preferably less than 1% by mass, particularly preferably less than 0.1% by mass, with respect to the entire pressure-sensitive adhesive composition. In addition, the below-mentioned polymerization solvent and dilution solvent are the components which dilute the above-mentioned adhesive composition etc., Comprising: It does not correspond to the component which constitutes adhesive composition itself.

<2> Production of Pressure-Sensitive Adhesive Composition The pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive sheet produces an acrylic polymer, and mixes the obtained acrylic polymer, a thermal crosslinking agent, and a hydrogen-abstraction type photoinitiator. It can be produced by adding an additive if desired.

  The acrylic polymer can be produced by polymerizing a mixture of monomers constituting the polymer by a conventional radical polymerization method.

  The polymerization of the monomers constituting the acrylic polymer can be carried out by a solution polymerization method or the like, using a polymerization initiator, if desired. As a polymerization solvent, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone etc. are mentioned, for example, You may use 2 or more types together.

  As a polymerization initiator, an azo compound, an organic peroxide, etc. are mentioned, You may use 2 or more types together. As an azo compound, for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane 1-carbonitrile), 2 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis (2-methyl propionate) 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 peroxy dicarbonate, di-n-propyl peroxy dicarbonate, di (2-ethoxyethyl) peroxy Dicarbonate, t-butyl peroxy neodecanoate, t-butyl peroxy bivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like can be mentioned.

  In addition, in the said superposition | polymerization process, the weight average molecular weight of the polymer obtained can be adjusted by mix | blending chain transfer agents, such as 2-mercapto ethanol.

<3> Production of Pressure-Sensitive Adhesive Sheet The pressure-sensitive adhesive sheet 11 can be produced, for example, as follows.

First, a release sheet is prepared.
Next, the coating liquid of the said adhesive composition is apply | coated to the peeling surface of a peeling sheet. In addition, the said coating liquid is prepared by diluting with a dilution solvent so that it may become a viscosity suitable for the said adhesive composition to apply | coat. When the pressure-sensitive adhesive composition has an appropriate viscosity for application, the addition of the dilution solvent may be omitted. Here, examples of the dilution 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. The dilution solvent can also be used as the above-mentioned polymerization solvent.

  And an application layer is obtained by passing through the above-mentioned application and drying processing (heat processing). The resulting coated layer may be subjected to additional heat treatment as necessary to further promote the thermal crosslinking of the pressure-sensitive adhesive composition, and then the acrylic polymers are directly crosslinked (photo-crosslinking) by irradiation with active energy rays. ) To obtain an adhesive sheet.

  Here, an active energy ray means what has an energy quantum in electromagnetic waves or a charged particle beam, and an ultraviolet ray, an electron beam, etc. are specifically mentioned. Among the active energy rays, ultraviolet rays which are easy to handle are particularly preferable.

  In addition, you may overlap the peeling surface of another peeling sheet on the exposed adhesive surface of an adhesive sheet as needed.

  As a method for applying the coating solution of the pressure-sensitive adhesive composition, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method and the like can be used.

  The thermal crosslinking of the pressure-sensitive adhesive composition can be carried out by heat treatment (including drying treatment). This heat treatment can be combined with the drying treatment after the application of the pressure-sensitive adhesive composition. The heating temperature of the heat treatment is preferably 50 ° C. or more, more preferably 70 ° C. or more. Moreover, it is preferable that it is 150 degrees C or less, and, as for the heating temperature of heat processing, it is more preferable that it is 120 degrees C or less. The heating time is preferably 10 seconds or more, more preferably 50 seconds or more. The heating time is preferably 10 minutes or less, more preferably 2 minutes or less. In addition, after heat processing or after active energy ray irradiation, a curing period (for example, normal temperature, about 1 to 2 weeks) can be provided as needed.

Moreover, an adhesive sheet can also be manufactured as follows.
First, prepare two release sheets.

  The coating liquid of the said adhesive composition is apply | coated to the peeling surface of one prepared peeling sheet, and a coating layer is obtained by making it dry (heating). In addition, thermal crosslinking will be accelerated | stimulated by the said drying. Next, thermal crosslinking is further promoted by performing additional heat treatment as necessary on the obtained coated layer, and then the active energy ray irradiation is performed to photocrosslink the pressure-sensitive adhesive composition, 1. Form an adhesive layer. Moreover, the coating liquid of the said adhesive composition is apply | coated to the peeling surface of the other peeling sheet, and a coating layer is obtained by making it dry, and heat processing is performed with respect to the obtained coating layer as needed. Thereafter, active energy ray irradiation is performed to photocrosslink the pressure-sensitive adhesive composition, thereby forming a second pressure-sensitive adhesive layer. Then, the first pressure-sensitive adhesive layer-attached release sheet and the second pressure-sensitive adhesive layer-attached release sheet are pasted together so that the two pressure-sensitive adhesive layers contact each other, and this is used as a pressure-sensitive adhesive sheet. In addition, after this, a curing period (for example, normal temperature, about 1 to 2 weeks) can be provided as needed.

  In addition, instead of separately forming the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer and then obtaining the pressure-sensitive adhesive sheet, the respective application layers are brought into contact with each other and then collectively irradiated with active energy rays. You may obtain an adhesive sheet by this.

  As a method for applying the coating solution of the pressure-sensitive adhesive composition, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method and the like can be used. The conditions of the heat treatment for the applied pressure-sensitive adhesive composition are as described above.

  The thickness of the pressure-sensitive adhesive sheet as described above (value measured according to JIS K7130, the same applies hereinafter) is preferably 10 μm or more, more preferably 30 μm or more, from the viewpoint of level difference followability. More preferably, it is 50 μm or more. The thickness of the pressure-sensitive adhesive sheet is preferably 1000 μm or less, more preferably 400 μm or less, and still more preferably 300 μm or less, from the viewpoint of processability. The pressure-sensitive adhesive sheet may be formed as a single layer or may be formed by laminating a plurality of layers.

  Further, the haze value (value measured according to JIS K 7136: 2000) of the pressure-sensitive adhesive sheet according to the present embodiment is preferably 1.0% or less, and particularly preferably 0.8% or less. Is preferably 0.6% or less. When the haze value is 1.0% or less, the transparency is very high, which is suitable as a pressure-sensitive adhesive sheet used between the protective plate and the display panel.

  The gel fraction of the pressure-sensitive adhesive sheet according to this embodiment is preferably 15 to 90%, more preferably 25 to 80%, and particularly preferably 45 to 60%. Foam resistance may fall that a gel fraction is less than 15%. On the other hand, if the gel fraction exceeds 90%, the step following performance may be lowered. In addition, the measuring method of a gel fraction is as showing to the test example mentioned later.

  Moreover, it is preferable that it is 15 N / 25 mm or more, and, as for the adhesive force of the adhesive sheet concerning this embodiment, it is more preferable that it is 20 N / 25 mm or more. By having an adhesive force of 15 N / 25 mm or more, the protective plate and the display panel are firmly joined, and the effect of excellent stability in durability conditions and the like is obtained. The upper limit of the adhesive strength is not particularly limited, but is preferably about 50 N / 25 mm or less in consideration of the peelability and the like of the release sheet to be protected. In addition, the measuring method of adhesive force is as showing to the test example mentioned later.

  As mentioned above, although the suitable embodiment of the adhesive sheet of this invention was described, this invention is not limited to these.

  For example, in the embodiment described above, the protective plate has been described as having a printing step, but the pressure-sensitive adhesive sheet of the present invention can also be applied to a sheet having no printing step.

  Hereinafter, the present invention will be more specifically described by way of examples and the like, but the scope of the present invention is not limited to these examples and the like.

1. Preparation of Pressure-Sensitive Adhesive Sheet (Example 1)
(1) Preparation of Acrylic Polymer 90 parts by mass of n-butyl acrylate and 10 parts by mass of acrylic acid were copolymerized to prepare an acrylic polymer which is a (meth) acrylic acid ester copolymer. When the molecular weight of this acrylic polymer was measured by the method mentioned later, it was 500,000 of weight average molecular weight (Mw).

(2) Preparation of Pressure-Sensitive Adhesive Composition 100 parts by mass (solid content conversion value; the same below) of the acrylic polymer obtained in the above step (1) and an epoxy-based crosslinking agent (manufactured by Japan Polyurethane Co., Ltd., product name “TC-5 Solid content: 100% by mass), 0.03 parts by mass, benzophenone (manufactured by Kanto Chemical Co., Ltd.) 0.5 parts by mass as a hydrogen extraction type photoinitiator, and 3-glycidoxypropyl as a silane coupling agent An adhesive with a solid content concentration of 36 mass% by mixing with 0.25 parts by mass of trimethoxysilane (product name "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.), sufficiently stirring and diluting with methyl ethyl ketone An application solution of the composition was obtained.

(3) Production of pressure-sensitive adhesive sheet A heavy release type release sheet (made by Lintec Co., product name "SP-PET 752150") obtained by peeling the coating solution of the obtained pressure-sensitive adhesive composition on one side of a polyethylene terephthalate film with a silicone release agent. The coated layer was formed by applying a knife coater to the release-treated surface and drying treatment at 100 ° C. for 2 minutes.

  Similarly, the coating solution of the obtained pressure-sensitive adhesive composition is peeled off from a light-peelable release sheet (made by Lintec Co., product name "SP-PET 382120"), one side of a polyethylene terephthalate film being release-treated with a silicone release agent. The coated layer was formed on the surface by applying a knife coater and drying treatment at 100 ° C. for 2 minutes.

  Then, the coated layer on the heavy release type release sheet and the coated layer on the light release type release sheet are pasted so that both coated layers come into contact with each other, and ultraviolet rays are irradiated under the following conditions. A pressure-sensitive adhesive sheet (thickness of the pressure-sensitive adhesive sheet: 50 μm) sandwiched between two release sheets was produced. The thickness is a value measured according to JIS K7130 using a constant-pressure thickness measuring device (product name “PG-02” manufactured by Techlock Co., Ltd.).

[UV irradiation conditions]
-Light source: High pressure mercury lamp-Light quantity: 500 mJ / cm ²
-Illuminance: 200mW / cm ²

(Examples 2 to 6, Comparative Examples 1 to 6)
The adhesion was carried out in the same manner as in Example 1 except that the proportions of the respective monomers constituting the acrylic polymer, the type and amount of the thermal crosslinking agent, and the type and amount of the hydrogen abstraction type photoinitiator were changed as shown in Table 1. The sheet was manufactured. In Comparative Example 1, ultraviolet irradiation was not performed.

  Table 1 shows the composition and the like of the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive sheet of each of the examples and the comparative examples.

  In Table 1, n-butyl acrylate is “BA”, 2-hydroxyethyl acrylate is “HEA”, acrylic acid is “AA”, 2-ethylhexyl acrylate is “2EHA”, and methyl methacrylate is “MMA”. The epoxy-based crosslinking agent is referred to as "epoxy-based", and the isocyanate-based crosslinking agent (trimethylolpropane-modified tolylene diisocyanate, manufactured by Nippon Polyurethane Co., Ltd., trade name "Corronate L") as "isocyanate-based".

2. Evaluation [adhesive strength measurement]
The light-peelable release sheet on the pressure-sensitive adhesive sheet obtained in each example and each comparative example is peeled off, and the exposed adhesive surface is a polyethylene terephthalate film having an easy-adhesion layer (manufactured by Toyobo Co., Ltd., PET A4300, thickness: 100 μm) It stuck to the easily bonding layer of The laminate was cut into a width of 25 mm and a length of 100 mm, and this was used as a sample. The heavy release type release sheet was peeled off from the sample, and the exposed adhesive surface was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.).

  Then, after standing for 24 hours under conditions of normal pressure, 23 ° C., 50% RH, using a tensile tester (Orientech Co., Ltd., product name “Tensilon”), according to JIS Z0237: 2009, peeling speed The adhesion (N / 25 mm) was measured under the conditions of 300 mm / min and a peeling angle of 180 °.

[Evaluation of foam resistance]
The light-peelable release sheet of the pressure-sensitive adhesive sheet obtained in each example and each comparative example is peeled off, and the exposed adhesive surface is a polyethylene terephthalate film provided with a transparent conductive film made of tin-doped indium oxide (ITO) on one side It was bonded to a transparent conductive film manufactured by IKEDA CO., LTD., An ITO film, and having a thickness of 125 μm. Next, the heavy release type release sheet of the pressure-sensitive adhesive sheet is peeled off, and the exposed adhesive surface is a polymethyl methacrylate (PMMA) acrylic plate (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "Eupiron sheet MR200", thickness: A laminate was obtained by pasting with 1 mm).

  The obtained laminate was autoclaved at 50 ° C. and 0.5 MPa for 30 minutes, and then left at normal pressure, 23 ° C., 50% RH for 15 hours. Then, it was stored for 72 hours under the endurance condition of 85 ° C. and 85% RH. Thereafter, it was visually confirmed whether the pressure-sensitive adhesive layer had bubbles, floating or peeling, and the foam resistance was evaluated according to the following criteria.

A: There were no bubbles, lifting and peeling.
B: Only bubbles having a diameter of 0.2 mm or less were generated.
C: Bubbles with a diameter of more than 0.2 mm, floating or peeling occurred.

[Step followability evaluation]
UV curable ink (product name "POS-911 black" manufactured by Teikoku Ink Co., Ltd.) on the surface of a glass plate (manufactured by NSG Precision, product name "Corning glass Eagle XG, 90 mm long x 50 mm wide x 0.5 mm thick) ) Was screen-printed in a frame shape (outline: 90 mm long × 50 mm wide, 5 mm wide) such that the coating thickness was 30 μm. Next, UV light is irradiated (80 W / cm ² , metal halide lamp 2 lamps, lamp height 15 cm, belt speed 10 to 15 m / min) to cure the printed UV curable ink, and print step (high step) Step (30 μm) was produced.

  A light-peelable release sheet was peeled off from the pressure-sensitive adhesive sheet obtained in each example and each comparative example, and the exposed adhesive surface was a polyethylene terephthalate film (product name “PET A4300” manufactured by Toyobo Co., Ltd., thickness) : 100 μm) of the easily adhesive layer. Next, the heavy release type release sheet was peeled off to expose the adhesive surface. Then, using the laminator (product name "LPD 3214" manufactured by Fuji Plastic Co., Ltd.), the laminate is laminated on each stepped glass plate so that the adhesive layer covers the entire printing surface in a frame shape, and this is used as a sample for evaluation. did.

  The obtained evaluation sample was autoclaved under conditions of 50 ° C. and 0.5 MPa for 30 minutes, and then stored under endurance conditions of 85 ° C. and 85% RH for 72 hours. Thereafter, it was visually confirmed whether or not there were air bubbles in the adhesive sheet (in particular, in the vicinity of the step due to printing), and the step following property was evaluated according to the following criteria.

A: There were no bubbles.
B: There were almost no air bubbles.
C: Air bubbles were remarkable.

[Measurement of gel fraction]
The pressure-sensitive adhesive sheet obtained in each example and each comparative example is cut into a size of 80 mm × 80 mm, the light release type release sheet and the heavy release type release sheet are peeled off, and the adhesive sheet in which both adhesive surfaces are exposed Obtained. The said adhesive sheet was wrapped in polyester mesh (mesh size 200), the mass was measured with a precision balance, and the mass of only the adhesive sheet was computed by deducting the mass of the said mesh alone. The mass at this time is M1.

Next, the pressure-sensitive adhesive sheet wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23 ° C.) for 24 hours. Thereafter, the pressure-sensitive adhesive sheet was taken out, air-dried for 24 hours in an environment at a temperature of 23 ° C. and a relative humidity of 50%, and further dried in an oven at 80 ° C. for 12 hours. After drying, the mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. The mass at this time is M2. The gel fraction (G1 (%)) is represented by (M2 / M1) × 100.
The results are shown in Table 2.

  As apparent from Table 2, the pressure-sensitive adhesive sheet of the present invention was excellent in foam resistance and step followability. On the contrary, in the comparative example, sufficient results were not obtained.

3 Printed steps 11 Adhesive sheet 21 Protective plate 22 Display panel 23 Display

Claims (3)

A pressure-sensitive adhesive sheet used to bond a protective plate and a display panel,
A monomer having a carboxyl group, and an acrylic polymer having a (meth) acrylic acid alkyl ester as a constituent monomer and having a weight average molecular weight of 200,000 or more and 900,000 or less ;
An epoxy crosslinking agent as a thermal crosslinking agent,
Formed of a pressure-sensitive adhesive composition comprising a hydrogen abstraction type photoinitiator,
The acrylic polymer is substantially free of radically unsaturated double bonds, and
The pressure-sensitive adhesive composition is substantially free of a self-cleavage type photoinitiator .
The content of the monomer having a carboxyl group in the acrylic polymer is 8% by mass or more and 20% by mass or less,
The content of the (meth) acrylic acid alkyl ester in the acrylic polymer is 50% by mass or more and 92% by mass or less,
A pressure-sensitive adhesive sheet, wherein a thickness of a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is 50 μm or more . A pressure-sensitive adhesive sheet used to bond a protective plate and a display panel,
An acrylic polymer having a hydroxyl group-containing monomer and a (meth) acrylic acid alkyl ester as a constituent monomer and having a weight average molecular weight of 200,000 or more and 900,000 or less ;
An isocyanate crosslinking agent as a thermal crosslinking agent,
Formed of a pressure-sensitive adhesive composition comprising a hydrogen abstraction type photoinitiator,
The acrylic polymer is substantially free of radically unsaturated double bonds, and
The pressure-sensitive adhesive composition is substantially free of a self-cleavage type photoinitiator .
The content of the monomer having a hydroxyl group in the acrylic polymer is 10% by mass to 25% by mass,
The content of the (meth) acrylic acid alkyl ester in the acrylic polymer is 50% by mass or more and 90% by mass or less,
A pressure-sensitive adhesive sheet, wherein a thickness of a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is 50 μm or more . The pressure-sensitive adhesive sheet according to claim 1 or 2 , wherein the addition amount of the hydrogen extraction photoinitiator with respect to 100 parts by mass of the acrylic polymer is 0.1 parts by mass or more and 5.0 parts by mass or less.

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