KR20180136712A - Adhesive Composition and Adhesive Sheet Using the Same - Google Patents

Abstract

The present invention relates to an adhesive composition comprising an acrylic copolymer, a photopolymerizable monomer, a self-cleavage type photoinitiator, and a hydrogen drawing type photoinitiator. The adhesive composition is provided, whose stress relaxation ratio at 70°C after first photocuring at 600 mJ/cm^2 or lower is 0.2 or lower, and stress relaxation ratio at 70°C after second photocuring at 2000 mJ/cm^2 or more after the first photocuring is increased by 0.2 or more. The adhesive composition according to the present invention is excellent in step filling properties and durability.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a pressure-sensitive adhesive composition,

The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition, and more particularly, to a pressure-sensitive adhesive composition having excellent step difference filling and durability and a pressure-sensitive adhesive sheet using the same.

Among the pressure-sensitive adhesives, optically clear adhesives (OCA) having high transparency are used for interlayer adhesion for laminating components in a display device. Such optical transparent pressure-sensitive adhesives are required to have high transmittance and low haze and satisfy properties such as adhesiveness to various substrates, heat resistance and anti-wet heat resistance.

In recent years, a flexible display device capable of maintaining the display performance even if bent like paper by using a flexible material such as plastic instead of a conventional glass substrate with a non-flexibility is rapidly emerging as a next generation display device, Development of an optical transparent pressure-sensitive adhesive excellent in adhesion and durability is required.

Korean Patent Laid-Open No. 10-2014-0044269 discloses a (meth) acrylate having an alkyl group having 12 or more carbon atoms, a (meth) acrylate having an alkyl group having 1 to 8 carbon atoms and having a carbon number of 8 or less, A pressure-sensitive adhesive composition comprising a copolymer solution is disclosed. However, the pressure-sensitive adhesive composition containing such a solvent has a problem in that it is difficult to obtain the thickness of the pressure-sensitive adhesive layer at a level of several tens of micrometers. In addition, when applied to a flexible display device, the pressure-sensitive adhesive composition has a problem in that it is difficult to secure step coverage and durability.

Korean Patent Publication No. 10-2014-0044269

It is an object of the present invention to provide a pressure-sensitive adhesive composition of a solvent-free type excellent in step-fillability and durability.

Another object of the present invention is to provide a pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition.

Meanwhile, the present invention provides a pressure-sensitive adhesive composition comprising an acrylic copolymer, a photopolymerizable monomer, a self-cleavage type photoinitiator, and a hydrogen drawing type photoinitiator, wherein the pressure-sensitive adhesive composition has a primary sight at 600 mJ / Wherein the stress relaxation ratio at 70 캜 is 0.2 or less and the stress relaxation ratio at 70 캜 is increased by 0.2 or more after secondary light curing at 2,000 mJ / cm 2 or more after the primary light curing.

In one embodiment of the present invention, the acrylic copolymer is a copolymer comprising a high Tg monomer having a glass transition temperature (Tg) of 10 ° C to 100 ° C, a (meth) acrylate monomer containing an alkyl group having 1 to 12 carbon atoms, And a monomer having a functional group selected from an amine group.

On the other hand, the present invention provides a pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition according to the present invention is a pressure-sensitive adhesive composition comprising an acrylic copolymer, a photopolymerizable monomer, a self-cleavage type photoinitiator and a hydrogen-releasing type photoinitiator and is capable of primary curing without a separate solvent, Which is excellent in level difference filling and durability. Specifically, the pressure-sensitive adhesive composition according to the present invention exhibits a low stress relaxation ratio after primary light curing at low illuminance, so that the adherence of the adherend having a step difference is excellent, and the step after the secondary photo- The durability can be improved by restraining the force to unwind.

Hereinafter, the present invention will be described in more detail.

An embodiment of the present invention is a pressure-sensitive adhesive composition comprising an acrylic copolymer, a photopolymerizable monomer, a self-cleavage type photoinitiator, and a hydrogen drawing type photoinitiator, And a stress relaxation ratio at 70 캜 after photocuring is 0.2 or less and a stress relaxation ratio at 70 캜 is increased by 0.2 or more after secondary photocuring at 2,000 mJ / cm 2 or more after the primary photocuring.

After the primary photocuring, the stress relaxation ratio (S / R ratio) at 70 캜 was measured by photocuring the pressure-sensitive adhesive composition at a light quantity of 600 mJ / cm 2 or less, for example, 500 mJ / Sec and a modulus of elasticity after 300 seconds can be measured and then found by the following equation (1).

[Equation 1]

Stress relaxation ratio = elasticity rate after 300 seconds / elasticity rate after 1 second

The stress relieving ratio at 70 캜 after the secondary photocuring is obtained by photocuring the primary photocured adhesive composition at a light quantity of 2,000 mJ / cm 2 or more, for example, 3,000 mJ / cm 2, The elastic modulus after one second and the elastic modulus after 300 seconds can be measured, and then the elastic modulus can be obtained by the following equation (1).

If the stress relieving ratio at 70 캜 after the first photocuring of the pressure-sensitive adhesive composition is more than 0.2, the step difference filling property may be deteriorated. When the stress relaxation ratio at 70 캜 after the secondary photo-curing is increased to less than 0.2, that is, between the stress relaxation ratio at 70 캜 after the first photo-curing and the stress relaxation ratio at 70 캜 after the secondary photo- If the difference is less than 0.2, the durability may be lowered.

In one embodiment of the present invention, the acrylic copolymer is a component that plays a role in controlling the viscosity-to-elasticity balance of the pressure-sensitive adhesive composition, and includes a high Tg monomer having a glass transition temperature (Tg) (Meth) acrylate monomer having an alkyl group, and a monomer having a functional group selected from a hydroxyl group, a carboxyl group and an amine group.

The high Tg monomer having a glass transition temperature (Tg) of 10 ° C to 100 ° C is a component for imparting elasticity to an acrylic copolymer to improve adhesion to various substrates, and includes t-butyl (meth) acrylate, methyl methacrylate (Meth) acrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobonyl Benzyl methacrylate, 3,3,5-trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octylacrylamide, etc. These may be used alone or in combination of two or more. The (meth) acrylate means acrylate and methacrylate.

The high Tg monomer is preferably contained in an amount of 30 to 50% by weight based on 100% by weight of the total monomer used in the production of the acrylic copolymer. When the content is less than 30% by weight, it may be difficult to secure durability. When the content is more than 50% by weight, it may be difficult to secure adhesion.

The (meth) acrylate monomer having an alkyl group of 1 to 12 carbon atoms is a monomer having a glass transition temperature (Tg) lower than -10 ° C. Specific examples thereof include n-butyl acrylate, 2-ethylhexyl acrylate, Methyl acrylate, n-propyl acrylate, isopropyl acrylate, pentyl acrylate, n-octyl acrylate, nonyl acrylate, decyl acrylate and dodecyl acrylate. Of these, 2-ethylhexyl acrylate Dodecyl acrylate, or mixtures thereof. These may be used alone or in combination of two or more.

The (meth) acrylate monomer having an alkyl group of 1 to 12 carbon atoms is preferably contained in an amount of 40 to 60% by weight based on 100% by weight of the total monomers used in the production of the acrylic copolymer. When the content is less than 40% by weight, the adhesive strength is not sufficient. When the content is more than 60% by weight, the cohesive strength may be lowered.

The monomer having a functional group selected from a hydroxyl group, a carboxyl group and an amine group is a polymerizable compound having a hydrophilic functional group selected from a hydroxyl group, a carboxyl group and an amine group in the molecule.

Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl , Hydroxypropyleneglycol (meth) acrylate, hydroxyalkylene glycol (meth) acrylate having 2 to 4 carbon atoms in the alkylene group, (Meth) acrylate, 4-hydroxybutyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, 7-hydroxyheptyl vinyl ether, 8-hydroxyoctyl vinyl ether, Nonyl vinyl ether, and 10-hydroxydecyl vinyl ether. Of these, 2-hydroxyethyl (meth) acrylate is preferable.

Examples of the monomer having a carboxyl group include monovalent acids such as (meth) acrylic acid and crotonic acid; Dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and monoalkyl esters thereof; 3- (meth) acryloylpropionic acid; A succinic anhydride ring-adduct adduct of 2-hydroxyalkyl (meth) acrylate in which the alkyl group has 2 to 4 carbon atoms, a succinic anhydride ring-adduct of a hydroxyalkylene glycol (meth) acrylate having 2 to 4 carbon atoms in the alkylene group , And compounds obtained by ring-opening addition of succinic anhydride to caprolactone adducts of 2-hydroxyalkyl (meth) acrylates having 2-3 carbon atoms in the alkyl group. Of these, methacrylic acid is preferable.

Examples of the monomer having an amine group include N, N- (dimethylamino) ethyl (meth) acrylate, N, N- (diethylamino) ethyl Acrylate, and the like.

The monomer having a functional group selected from a hydroxyl group, a carboxyl group and an amine group is preferably contained in an amount of 1 to 15% by weight based on 100% by weight of the total monomer used in the production of the acrylic copolymer. When the content is less than 1% by weight, cohesive failure tends to occur at the time of temperature rise, and when it is more than 15% by weight, flow properties at the time of temperature rise may be lowered.

The acrylic copolymer may further contain other polymerizable monomers other than the monomers in an amount not lowering the physical properties such as adhesion, durability and adhesion, for example, 10% by weight or less based on the total amount.

The method of producing the acrylic copolymer is not particularly limited, and bulk polymerization, emulsion polymerization or suspension polymerization, which are conventionally used in the art, can be used, and bulk polymerization is preferred. A polymerization initiator usually used in polymerization, a chain transfer agent for controlling the molecular weight, and the like can be used.

In one embodiment of the present invention, the acrylic copolymer may be a partial polymer partially polymerized with the above-mentioned monomer mixture.

These partial polymerizates exhibit a syrup shape (viscous liquid phase) in which a polymer formed from a part of the monomer mixture and unreacted monomers coexist. Accordingly, the polymeric syrup may be referred to as a partial polymer of such an aspect.

The method of partially polymerizing the monomer mixture is not particularly limited, and various polymerization methods can be appropriately selected and used. For example, a photopolymerization or thermal polymerization method can be used.

In one embodiment of the present invention, the partial polymer of the acrylic copolymer, i. E. The polymer syrup, may have a glass transition temperature (T _g ) of less than 25 ° C, typically less than 0 ° C. When the glass transition temperature (T _g ) of the partial polymer of the acrylic copolymer is less than 25 캜, the viscosity of the pressure-sensitive adhesive composition may be appropriate. For this purpose, the type and / or content of the monomers can be appropriately controlled.

The acrylic copolymer may be contained in an amount of 10 to 40% by weight based on 100% by weight of the total amount of the acrylic copolymer and the photopolymerizable monomer. If the content is less than 10% by weight, the primary photopolymerization may be difficult due to a large amount of residual photopolymerizable monomer. If the content is more than 40% by weight, the molecular weight of the polymer may be low.

In one embodiment of the present invention, the acrylic copolymer has a weight average molecular weight (in terms of polystyrene) measured by Gel Permeation Chromatography (GPC) of 10,000 or more, typically 20,000 or more, for example, 20,000 to 2,000,000 Lt; / RTI > If the weight average molecular weight of the acrylic copolymer is less than 10,000, it may be difficult to outgassing and migrating the binary copolymer.

In one embodiment of the present invention, the photopolymerizable monomer is a component that acts as a dispersion medium for the acrylic copolymer and can be polymerized by the action of a photoinitiator. The photopolymerizable monomer is polymerized during the first photocuring and is substantially absent in the second photocuring.

The photopolymerizable monomer may be a monomer used in the production of the acrylic copolymer.

That is, the photopolymerizable monomer is preferably a high Tg monomer having a glass transition temperature (Tg) of 10 to 100 ° C, a (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms, a hydroxyl group, a carboxyl group and an amine group A monomer having a functional group, or the like can be used.

Examples of the monomer having a functional group selected from a high Tg monomer having a glass transition temperature (Tg) of 10 ° C to 100 ° C, a (meth) acrylate monomer containing an alkyl group having 1 to 12 carbon atoms, and a hydroxyl group, a carboxyl group and an amine group The same materials as those used for the acrylic copolymer may be used.

In one embodiment of the present invention, the self-cleavage type photoinitiator is a photoinitiator capable of generating radicals by cleavage of its single bond to form a radical at 600 mJ / cm 2 or less, for example, about 100 to 500 mJ / Can be activated at a low light amount condition of 200 to 500 mJ / cm < 2 >.

Examples of the self-cleavage type photoinitiator include 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethane-1-on, 4-phenoxydichloroacetophenone, 4- 2-methyl-1-phenylpropan-1-one, 1- (4-isopropylenephenyl) -2-hydroxy- (2-hydroxy-2-propyl) ketone, 2- (4-dodecylphenyl) Methyl-1- (4- (methylthio) phenyl) -2-morpholinopropane-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, (2-hydroxy-2-propyl) ketone, 4-benzoyl-4 ' -Methyldiphenyl sulfide, and the like, and particularly, 1-hydroxycyclohexyl phenyl ketone And 2,2-dimethoxy-1,2-diphenylethan-1-one are preferred.

The self-cleavage type photoinitiator may be used in an amount of 0.1 to 1.0 part by weight based on 100 parts by weight of the total amount of the acrylic copolymer and the photopolymerizable monomer. When the self-clearing photoinitiator is used within the above range, it can exhibit an appropriate degree of curing.

In one embodiment of the present invention, the hydrogen-drawing type photoinitiator is a photoinitiator which is capable of forming an excited complex with a photo-excited initiator and a hydrogen donor in the system to transfer hydrogen of the hydrogen donor, and is distinguished from the self-cleavage type photoinitiator . The hydrogen-releasing photoinitiator can be activated at a high light amount of 2,000 mJ / cm 2 or more, for example, about 2,000 to 5,000 mJ / cm 2, preferably 3,000 to 4,000 mJ / cm 2.

The hydrogen-releasing-type photoinitiator can be used again as a reaction initiator since it is returned to a ground state even if it is excited once, and not reacted in the initiator. As a result, as compared with the self-cleavage type photoinitiator, the hydrogen-releasing photoinitiator tends to remain as an active species even after the reaction. Therefore, it is suitable for use as a reaction initiator when crosslinked (secondary photo-curing) by irradiating ultraviolet rays after bonding.

Examples of the hydrogen-drawing type photoinitiator include benzophenone, 2-ethyl anthraquinone, methyl benzoyl peroxide, benzoyl benzoic acid, methyl benzoyl benzoate, 4-phenylbenzophenone, hydroxybenzophenone, 3,3'-dimethyl- Benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, thioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 9,10-phenanthrenequinone and the like can be used, and benzophenone, 2-ethyl anthraquinone and methyl benzoyl peroxide are preferable Do.

The hydrogen-releasing photoinitiator may be used in an amount of 0.5 to 5.0 parts by weight based on 100 parts by weight of the total amount of the acrylic copolymer and the photopolymerizable monomer. If the amount of the hydrogen-releasing photoinitiator is less than 0.5 parts by weight, the secondary curing degree may be lowered. If the amount of the hydrogen-releasing photoinitiator is more than 5.0 parts by weight, durability may be deteriorated by the residual photoinitiator.

The pressure-sensitive adhesive composition according to one embodiment of the present invention may contain the hydrogen-releasing photoinitiator in an amount of 1 to 5 parts by weight based on 1 part by weight of the self-clearing photoinitiator. If the hydrogen-releasing photoinitiator is included in an amount of less than 1 part by weight based on 1 part by weight of the self-clearing photoinitiator, the secondary curability may be lowered. If the hydrogenation-type photoinitiator is included in an amount exceeding 5 parts by weight, durability may be deteriorated by the residual photoinitiator.

The pressure-sensitive adhesive composition according to one embodiment of the present invention may contain, in addition to the above components, a silane coupling agent, a tackifier resin, a tackifier resin, a tackifier resin or the like to control the adhesion, cohesion, viscosity, elastic modulus, glass transition temperature, , An antioxidant, a corrosion inhibitor, a leveling agent, a surface lubricant, a dye, a pigment, a defoaming agent, a filler, a light stabilizer, and an antistatic agent.

The pressure-sensitive adhesive composition according to one embodiment of the present invention comprises a self-cleavage type photoinitiator and a hydrogen-releasing type photoinitiator and includes an excess amount of a hydrogen-releasing type photoinitiator relative to the self-cleavable type photoinitiator, Leaving room for the photocuring reaction.

For example, the first photo - curing is performed by activating the self - cleavable photoinitiator at a low light intensity of less than 600 mJ / cm 2, and then the second photo curing is performed by activating the hydrogen photoinitiator at a light intensity of 2,000 mJ / Can be performed.

The pressure-sensitive adhesive composition according to an embodiment of the present invention can be applied not only to a conventional flat panel display but also to a flexible display, and specifically to a display panel, a polarizer, a touch panel, a cover glass, a bezel, .

The pressure-sensitive adhesive composition according to one embodiment of the present invention is flexible so as to leave the ultraviolet ray reactivity, that is, allow further curing, in the state before the primary curing and the secondary curing, And even if foreign matter or the like is present on the adhesive interface, it is possible to sufficiently follow these irregularities, and the step difference filling property is excellent. Therefore, when the two display constituting members are laminated through the pressure sensitive adhesive sheet before the secondary curing, each display constituting member can be brought into close contact with each other, and ultraviolet ray crosslinking (secondary curing) It can be surely bonded. Therefore, two display constituent members are laminated through the pressure-sensitive adhesive sheet before secondary curing, and then ultraviolet rays are irradiated from the side of at least one display constituent member, and the pressure-sensitive adhesive sheet is secondarily cured by ultraviolet crosslinking, It is possible to ensure durability by ensuring sufficient adhesion and cohesion by crosslinking.

One embodiment of the present invention relates to a pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition.

The pressure-sensitive adhesive sheet according to one embodiment of the present invention is a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition according to the present invention on a base film, or a pressure-sensitive adhesive layer formed from the pressure- .

Examples of the base film include a polyolefin film, a polyester film, an acrylic film, a styrene film, an amide film, a polyvinyl chloride film, a polyvinylidene chloride film and a polycarbonate film. Powder or the like.

The thickness of the base film is preferably 30 to 80 mu m. When the thickness is less than 30 mu m, the substrate film is susceptible to poor adhesion, etc. When the thickness is more than 80 mu m, the shrinkage rate under a severe condition is large and the possibility of flooding is high.

The pressure-sensitive adhesive layer can be formed by coating a pressure-sensitive adhesive composition on one base film. The coating method is not particularly limited as long as it is a method known in the art. For example, a bar coater, an air knife, a gravure, a reverse roll, a kiss roll, a spray, a blade, a die coater, a casting, . Specifically, the pressure-sensitive adhesive composition may be coated on a single base film to a predetermined thickness, or the pressure-sensitive adhesive composition may be sandwiched between two base films, pressed to a predetermined thickness, and cured.

The thickness of the pressure-sensitive adhesive layer may be 30 to 2,000 mu m, preferably 50 to 1,500 mu m. If the thickness of the pressure-sensitive adhesive layer is less than 30 mu m, it may be difficult to cushion the impact generated from the outside. If the thickness is more than 2,000 mu m, the optical performance may be deteriorated.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention may be one that is first cured at 600 mJ / cm 2 or less, or a second cured at 600 mJ / cm 2 or less and then 2,000 mJ / cm 2 or more after primary curing .

Specifically, the pressure-sensitive adhesive sheet according to one embodiment of the present invention is formed by applying a pressure-sensitive adhesive composition on one base film and forming a pressure-sensitive adhesive sheet having a pressure of 600 mJ / cm 2 or less, for example, about 100 to 500 mJ / cm 2, m < 2 > / m < 2 >. The pressure-sensitive adhesive sheet according to one embodiment of the present invention is formed by applying a pressure-sensitive adhesive composition on one base film and forming a pressure-sensitive adhesive layer having a pressure of 600 mJ / cm 2 or less, for example, about 100 to 500 mJ / cm 2, / Cm < 2 >, and then irradiated with ultraviolet light of 2,000 mJ / cm 2 or more, for example, about 2,000 to 5,000 mJ / cm 2, preferably 3,000 to 4,000 mJ / Or may be formed by light curing.

The secondary photocuring may be performed before or after adhering to the adherend.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention exhibits a low stress relaxation ratio after primary light curing, so that the adherence of an adherend having a step difference is excellent, and the step after secondary light curing, It is possible to suppress the force and improve the durability.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention may be subjected to surface treatment of the pressure-sensitive adhesive layer before bonding to improve adhesion.

The surface treatment method is not particularly limited, and the surface of the pressure-sensitive adhesive layer can be activated by a method such as corona discharge treatment, plasma treatment, ultraviolet irradiation, electron beam irradiation, or an anchoring agent application.

Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Experimental Examples. It should be apparent to those skilled in the art that these examples, comparative examples and experimental examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example  1: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

50 parts by weight of ethylhexyl acrylate, 40 parts by weight of isobornyl acrylate and 10 parts by weight of 2-hydroxyethyl acrylate were placed in a 1-liter glass reactor, and 0.3 part by weight of 1-hydroxycyclohexyl phenyl ketone relative to 100 parts by weight of the monomer And then photopolymerized to obtain a mixture of 25 parts by weight of an acrylic copolymer syrup having a viscosity of 5,000 cP and a solid content of 25% by weight, that is, an acrylic copolymer and 75 parts by weight of a photopolymerizable monomer. To 100 parts by weight of a mixture of the acrylic copolymer and the photopolymerizable monomer, 0.5 part by weight of 1-hydroxycyclohexyl phenyl ketone was added as a self-cleavage type photoinitiator, and 1.0 part by weight of benzophenone was added as a hydrogenation photoinitiator. .

The pressure-sensitive adhesive composition was formed into a film having a thickness of 150 μm on a release film coated with a silicone release agent and irradiated with light (TL Lamp, UV) at a light quantity of 500 mJ / cm 2 to prepare a first UV-cured pressure-sensitive adhesive sheet.

Example  2: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

A pressure-sensitive adhesive composition and a first UV-cured pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that 2-ethyl anthraquinone was used instead of benzophenone as a hydrogen-drawing type photoinitiator.

Example  3: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

A pressure-sensitive adhesive composition and a primary UV-cured pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that methyl benzoyl formate was used instead of benzophenone as the hydrogen-drawing type photoinitiator.

Example  4: Production of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

Except that 2,2-dimethoxy-1,2-diphenylethane-1-one was used instead of 1-hydroxycyclohexyl phenyl ketone as a self-cleavage type photoinitiator. A first UV-cured pressure-sensitive adhesive sheet was prepared.

Comparative Example  1: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

A pressure-sensitive adhesive composition and a first UV-cured pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that benzophenone, a hydrogen-releasing photoinitiator, was used in an amount of 0.2 part by weight.

Comparative Example  2: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

A pressure-sensitive adhesive composition and a first UV-cured pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that 2.0 parts by weight of 1-hydroxycyclohexyl phenyl ketone as a self-cleavage type photoinitiator was used.

Experimental Example  One:

The physical properties of the pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

(1) Stress relaxation ratio (S / R Ratio )

The stress relieving ratios of the first UV-cured pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples and the second UV-cured pressure-sensitive adhesive sheets obtained by the second UV-curing were measured under the following conditions by the elastic modulus after 1 sec and the elastic modulus after 300 sec And determined by the following formula (1). The secondary UV curing was performed by light irradiation (TL lamp, UV) at a light quantity of 3,000 mJ / cm 2.

[Equation 1]

S / R Ratio = elastic modulus after 300 seconds / elastic modulus after 1 second

Measuring instrument: Rheometer MCR-302, PP25 (25mmΦ)

Measurement conditions: Strain 25%, Axial force 1N

Thickness: 500 탆 (5 sheets of 100 탆 overlap)

Temperature: 70 占 폚 (stabilization 10 min)

(2) Stepped burial castle

The releasing film on one side of the pressure-sensitive adhesive sheet was peeled off and bonded to a polyethylene terephthalate film (PET100) having a thickness of 100 占 퐉 to prepare a pressure-sensitive adhesive sheet having PET100 bonded on one side. The test piece was cut into a length of 50 mm and a width of 40 mm. Separately, a polyethylene terephthalate film (PET100) having a thickness of 100 占 퐉 was cut to a length of 50 mm and a width of 40 mm. Next, a polyethylene terephthalate film (PET50) having a thickness of 50 占 퐉 was cut to a length of 40 mm and a width of 30 mm. The release film on the other side of the pressure sensitive adhesive sheet was peeled off, and the cut PET 50 was placed on the peeled pressure sensitive adhesive sheet and bonded to another PET 100 prepared above (PET100 / pressure sensitive adhesive sheet / PET50 / PET100). This was autoclaved at a temperature of 50 ° C and a pressure of 0.5 MPa for 20 minutes, and then irradiated with a metal halide lamp at 3 J / cm 2 to prepare a sample. Thereafter, the film was allowed to stand in an atmosphere at a temperature of 80 占 폚 for 24 hours, and the PET 50 portion was observed with a visual observation, and the filling property of a step of 50 占 퐉 thickness was evaluated by the following evaluation criteria.

<Evaluation Criteria>

○: There is no mixing of air bubbles

△: There is some air bubbles

X: There is a lot of air bubbles

(3) Durability (heat resistance, Wet heat )

The release films on one side of the pressure-sensitive adhesive sheet prepared in Examples and Comparative Examples were peeled off, corona-treated on the side of the pressure-sensitive adhesive, and adhered to 40 占 퐉 COP film were cut into a size of 90 mm x 170 mm, After peeling, it was adhered to a glass substrate (110 mm x 190 mm x 0.7 mm) and irradiated with a metal halide lamp at 3,000 mJ / cm 2 to prepare a specimen. At this time, the applied pressure was 5 kg / cm &lt; 2 &gt;, and the clean room operation was performed so that bubbles or foreign matter would not occur. The heat resistance characteristics were observed for 500 hours at a temperature of 100 ° C. and then observed for occurrence of bubbles or peeling. The resistance to moisture and heat was measured at 85 ° C. and 85% RH for 500 hours, Respectively.

<Evaluation Criteria>

Ⓞ: No bubbles or peeling.

○: Bubbles or peeling <5

?: 5 pieces? Bubbles or peeling <10 pieces

X: 10 pieces &lt; bubble &

Example Comparative Example One 2 3 4 One 2 Acrylic copolymer (parts by weight) 25 25 25 25 25 25 The photopolymerizable monomer (parts by weight) 75 75 75 75 75 75 Self-healing type
1-hydroxycyclohexyl phenyl ketone 0.5 0.5 0.5 0.5 2.0 2,2-dimethoxy-1,2-diphenylethan-1-one 0.5 Hydrogen extraction type
Benzophenone 1.0 1.0 0.2 1.0 2-Ethylanthraquinone 1.0 Methyl benzoyl formate 1.0 The stress relaxation ratio (70 DEG C) After primary UV curing 0.08 0.11 0.04 0.06 0.06 0.22 After secondary UV curing 0.31 0.33 0.35 0.32 0.10 0.31 Difference in stress relaxation ratio 0.23 0.22 0.31 0.26 0.15 0.14 Stepped burial castle ○ ○ ○ ○ ○ × durability Heat resistance ○ ○ ○ ○ × ○ Wet heat ○ ○ ○ ○ × ○

As can be seen in Table 1, the pressure-sensitive adhesive compositions of Examples 1 to 4 exhibited a stress relaxation ratio at 70 ° C after primary UV curing of 0.2 or less, a stress relaxation ratio at 70 ° C after primary UV curing, It was confirmed that the difference between the stress relaxation ratios at 70 캜 after UV curing was 0.2 or more, and the step difference filling property and the durability were excellent. However, in the pressure-sensitive adhesive compositions of Comparative Examples 1 and 2, the stress relaxation ratio at 70 占 폚 after the primary UV curing is more than 0.2, or the stress relaxation ratio at 70 占 폚 after the primary UV curing, The difference between the stress relaxation ratios was less than 0.2, and it was confirmed that at least one of step difference filling property and durability was poor.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Do. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

Claims (9)

A pressure-sensitive adhesive composition comprising an acrylic copolymer, a photopolymerizable monomer, a self-cleavage type photoinitiator, and a hydrogen drawing type photoinitiator, wherein the pressure-sensitive adhesive composition has a viscosity of less than 600 mJ / Wherein the stress relaxation ratio is 0.2 or less and the stress relaxation ratio at 70 占 폚 is increased by 0.2 or more after secondary light curing at 2,000 mJ / cm2 or more after the primary light curing. The acrylic copolymer according to claim 1, wherein the acrylic copolymer has a high Tg monomer having a glass transition temperature (Tg) of 10 to 100 캜, a (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms, and a hydroxyl group, Is a copolymer of a monomer having a functional group selected from the group consisting of a methacrylate group and a methacrylate group. The photopolymerizable monomer according to claim 1, wherein the photopolymerizable monomer has a high Tg monomer having a glass transition temperature (Tg) of 10 to 100 ° C, a (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms and a hydroxyl group, And a monomer having a functional group selected from the group consisting of a hydroxyl group and a hydroxyl group. The pressure-sensitive adhesive composition according to claim 1, wherein the self-cleavage type photoinitiator is at least one selected from 1-hydroxycyclohexyl phenyl ketone and 2,2-dimethoxy-1,2-diphenylethane-1-one. The pressure-sensitive adhesive composition according to claim 1, wherein the hydrogen-releasing photoinitiator is at least one selected from benzophenone, 2-ethyl anthraquinone, and methyl benzoyl formate. The pressure-sensitive adhesive composition according to claim 1, which comprises 1 to 5 parts by weight of the hydrogen-generating photoinitiator per 1 part by weight of the self-clearing photoinitiator. A pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition according to any one of claims 1 to 6. The pressure-sensitive adhesive sheet according to claim 7, wherein the pressure-sensitive adhesive sheet is primary light-cured at 600 mJ / cm 2 or less. The pressure-sensitive adhesive sheet according to claim 7, wherein the pressure-sensitive adhesive sheet is secondarily photo-cured at a pressure of 2,000 mJ / cm 2 or more after primary curing at 600 mJ / cm 2 or lower.