KR20210044446A - Composition of Pressure Sensitive Adhesives for Flat Panel Display - Google Patents

Abstract

The present invention relates to an adhesive composition for a flat panel display. According to the present invention, an adhesive which is used in a flat panel display and satisfies optical performance, cutting properties, folding properties, and step absorption rate while satisfying basic physical properties is manufactured by using a specific (meth)acrylic copolymer and a curing agent composition.

Description

Composition of Pressure Sensitive Adhesives for Flat Panel Display

In the present invention, in OCA, which is an adhesive used in a flat panel display, for a composition composed of a (meth)acrylic copolymer, a curing agent and other additives, while satisfying the basic physical properties of the adhesive, in particular, folding characteristics and printing step absorption rate are It's all about making great products.

Flat panel displays (FPD) include a plasma display panel (PDP), a liquid crystal display (LCD), and an organic electro-Luminescence display (OLED). A flat panel display device consists of a combination of a display panel and various optical films, and the optical film includes a polarizer, a phase difference film, an anti-glare film, and a wide view angle compensation film. film), a contrast enhanced film, and a conductive film.

When these optical films are laminated to each other or attached to a display panel, an optically transparent point/adhesive agent is used. When an adhesive is used, a so-called OCR (Optically clear resin) or LOCA (Liquid OCA) is used to produce a non-continuous process in which a liquid resin is applied and photocured. OCR is mainly applied to a large area, and is not limited by the thickness and printing step (Ink step), but there is a risk of yellowing and has a disadvantage of relatively low productivity due to a discontinuous process. When an adhesive is used, it is a so-called OCA (Optical clear adhesive), contrary to OCR, it is difficult to apply a large area and fill in the printing steps, and out-gassing removal and aging processes are required, but rolls It is easy to process due to roll to roll production, and has the advantage of high productivity. The camps of OCR and OCA are studying each other's strengths and weaknesses in a complementary aspect.

As the physical property required for OCA, it is the first adhesive that has adequate adhesive strength and high durability in the environment of heat/heat resistance and moisture resistance. In the second optical aspect, the transmittance should be high, the haze should be low, and the refractive index should be high to ensure visibility. The third aspect of workability is that there is no occurrence of steaming when cutting/punching in a desired shape, and because of good rework, peeling should occur at high/low temperature or room temperature. As a fourth aspect of functional addition, it must have chemical resistance from substances intruding from the human body and from the outside, exhibit sufficient adhesive strength even where the surface energy of the film to be used is low, and have a low dielectric constant for touch sensitivity.

In addition, recently, flexible display devices are being developed competitively. In a flexible display device, since the device itself is bent, rolled, or folded, panels and various optical films included in the device are also subjected to strong stress. OCA used for this is also required to have a folding characteristic against strong stress. Since the process of folding and unfolding a flexible display is repeated countless times, it must have flexibility in that there are no appearance problems (bubbles, peeling, streaks, cracks, etc.) depending on the deformation.Especially, each film becomes hard at low temperatures, so that the peeling between layers does not appear. It should have good adhesion.

A print step exists in a display panel or a functional optical film, which distorts the light of the bezel and causes uneven stress distribution on the panel, which can cause so-called marks (= mura). OCA has a weaker printing step filling property than OCR, so many studies have been conducted on this. The printing step has increased as the FPD develops (20㎛~70㎛), but since the FPD has become thinner, the step absorption rate (%; overcome thickness and adhesive thickness) rather than simply expressing the performance of overcoming printing step by the overcome thickness (㎛). It would be more appropriate to express it as a ratio).

In order to overcome the printing step, there is a limit to simply lowering the softness of the adhesive. Here, there may be methods such as using a resin having a relatively low molecular weight and low Tg, or lowering the content of the curing agent to achieve a low crosslinking density. However, in this case, it is not free from problems such as hardening shrinkage, leveling, and steaming during punching.

Accordingly, there is a case where a relatively flexible OCA product is attached to the adherend through the primary curing and a method of being settled through the secondary curing is sometimes used. In the published patents 1020180063165 and 1020170049674, by using a monomer containing a photocurable benzophenone group, it does not participate in the reaction in the first photocuring of a long wavelength, thereby overcoming the printing step in a state of low crosslinking degree, By performing photocuring, the pressure-sensitive adhesive is settled while increasing the degree of crosslinking. This can be obtained by placing a site capable of reacting radical hydrogen absorption (Hydrogen abstraction) reaction in the resin in the second photocuring, unlike the photoinitiator of the cleavage type used for the first photocuring.

In addition, in the registered patent 1019348250000, a double photocurable adhesive is manufactured using a polyfunctional ketoprofenyl material containing a benzophenone group. This solves the problem of reducing reliability such as out-gassing by using a photocuring agent containing a benzophenone group capable of hydrogen absorption reaction without containing a photoreactive site on the resin.

As such, research on basic performance, optical performance, processing performance, and functional performance as a pressure-sensitive adhesive is in progress for OCA, and in particular, development of a pressure-sensitive adhesive composition that can be free from folding stress and printing step is required.

The present invention is to provide a pressure-sensitive adhesive composition having excellent folding characteristics and free from printing steps by providing a flexible crosslinked structure (network) in OCA (Optical clear adhesives) used in flat panel display devices.

In the current OCA, a relatively flexible double-sided adhesive obtained through the first photocuring is attached to the flat panel display to fill in the printing step, and the second photocuring is performed once again to go through the process of mounting. At this time, when the first photocuring, the crosslinking degree must be in the range of 30-50% to fill the printing step, and the second photocuring must have a crosslinking degree of 60% or more to satisfy the durability in the display device. The problem here is that in the range of 30-50% of crosslinking degree after the first photocuring, the modulus is so low that it is practically difficult to handle as an adhesive, and this is a hassle of lowering the temperature in storage/transport and punching. There may be a lot of money and cost increase.

Accordingly, in the present invention, while satisfying durability only by primary curing, the crosslinked chain is reversibly released by heat, thereby inducing a reaction to occur, thereby overcoming the printing step. This reversible reaction is a known matter and intends to use a Diels-Alder (DA) reaction that is used in various fields. The DA reaction is a reaction in which conjugated dienes and doenophiles form cycloene. Due to its characteristic, it is a reversible reaction when the temperature is raised above 80℃. Is that this happens. The phenomenon in which the cycloene part is separated by heat again allows the reverse reaction as if the lock is opened, so that even though the DA reaction is a thermosetting reaction, it shows the behavior of thermoplasticity, so that the folding characteristics and the printing step can be filled.

In addition, in order to further satisfy the folding characteristics, a relatively high molecular weight (meth)acrylic copolymer is used in the present invention. The higher the molecular weight, the greater the entanglement effect, so that similar crosslinking can be increased and the content of the curing agent can be relatively lowered, so that the crosslinked structure of the adhesive becomes more flexible, so that it is possible to effectively cope with external stress.

The OCA produced by the present invention uses a curing agent having a specific DA reaction linkage, so even if it has a relatively high degree of crosslinking to satisfy durability, it is irreversible when a temperature of 80 to 120°C is applied. The crosslinking is released through the reaction, so that OCA can be obtained free from the printing step.

In addition, since it has a flexible thermoplastic structure while satisfying the basic physical properties of OCA, it has good folding characteristics, and a flexible display made using it may not have any appearance problems.

In addition, the manufacturing process can be simplified because it is possible to manufacture OCA free of printing steps only by the first heat curing without the current first and second photocuring processes.

The present invention is not limited to the examples shown below, but may be implemented in various forms, and the OCA composition according to the present invention is (A) solvent-type (meth)acrylic copolymer 100 parts by weight, (B) DA reaction It consists of 0.01 to 0.5 molar equivalents of curing agent containing linkage and other additives as needed.

(A) Solvent type (meth)acrylic copolymer

The expression (meth) referred to below is for expressing both the acrylic monomer and the methacrylic monomer used in the copolymer, and does not mean only the methacrylic monomer. The solvent-type (meth)acrylic copolymer is a mixture of a (meth)acrylic resin copolymer and a solvent, and the polymerization method is made by solution polymerization and a resin made by bulk polymerization is used as a solvent. It may be diluted with.

The monomer used in the (meth)acrylic copolymer is not particularly limited, and general ones may be used, and the following examples may be given for the main monomer, polar monomer, and functional monomer.

The main monomer has an alkyl group of 1 to 8 carbon atoms and is selected from the group having no polarity. Examples of such monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, ethylhexyl (meth) acrylate, and isooctyl (meth) acrylate. have. The content of the main monomer is 50% or more for the copolymer, and if it is less than 50%, the glass transition temperature (Tg) is too high as a pressure-sensitive adhesive, so it is difficult to express sufficient adhesion and wettability.

Here, it may contain a monomer having a polarity capable of copolymerizing with a main monomer and a functional monomer. Here, the polar monomer provides a reaction site with the curing agent, and a large number of polar monomers remaining without reacting with the curing agent are largely involved in the expression of adhesion. Such monomers include monomers containing carboxyl groups such as (meth)acrylic acid, carboxyethyl (meth)acrylate, maleic acid, and fumaric acid, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl Monomers containing hydroxy groups such as (meth)acrylate and hydroxybutyl (meth)acrylate, monomers containing glycidyl groups such as glycidyl (meth)acrylate, acrylamide, dimethylacrylamide, di And monomers containing an amine group such as ethyl acrylamide and butoxymethyl acrylamide. The content of polar monomer is less than 30% of the copolymer, and if it is more than 30%, the viscosity is too high during the polymerization process, making it difficult to obtain the desired high molecular weight and high conversion rate. It is difficult to express the performance as

It may also contain a functional monomer capable of copolymerizing with a main monomer and a polar monomer. Examples of adhesive functionality include control of refractive index, addition of chemical resistance, control of dielectric constant, addition of adhesion to substrates (polyolefin, polycarbonate, polyimide) with low surface energy (LSE), addition of moisture barrier function, etc. This can be.

These functional monomers include aliphatic (Aliphatic) monomers with a long side chain, such as decyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate, and cyclopentyl (meth) acrylic. Monomers containing cycloaliphatic rings such as acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, glycidyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydro Hetero-cyclic rings such as loperfuryl (meth)acrylate, acryloyl morpholine, dihydrodicyclopentadienyl (meth)acrylate, vinylpyridine, vinyl caprolactam, and vinylpyrrolidone Monomer containing, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyl (meth) acrylate, phenylethyl (meth) acrylate, naphthyl (meth) acrylate, styrene, methyl styrene, vinyl Monomers containing aromatic rings such as phenol, monomers containing ether groups such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, vinyl acetate, vinyl pivalate, vinyl And monomers containing an acetate group such as neodocanoate and vinyl propionate, and a monomer containing a nitrile group such as (meth)acrylonitrile. These functional addition monomers use 40% or less of the copolymer, and if it exceeds 40%, the basic performance as a pressure-sensitive adhesive may be impaired.

The molecular weight of the (meth)acrylic copolymer is in the range of 500,000 to 2 million in terms of weight average molecular weight (Mw).If it is less than 500,000, durability/environmental reliability of the adhesive may be deteriorated. It is difficult to remove all air bubbles during the curing/drying process because the amount of solvent used to achieve an appropriate viscosity is too high, which causes a product appearance defect.

In order to control the molecular weight of the (meth)acrylic copolymer, a chain transfer agent (= molecular weight control agent) can be used during polymerization, and the boiling point (Bp; = boiling point) is higher than the set temperature during polymerization (thiol group (-SH group)). ) Or an organic compound having a hydroxyl group (-OH) group, it is not particularly limited, and it is advantageous to have a thiol group for use efficiency The amount of the chain transfer agent is 0.01 to 0.1 parts by weight compared to the (meth)acrylic monomer. In this case, there is no effect, and when it exceeds 0.1 part by weight, the molecular weight becomes too low.

Chain transfer agents having such a thiol group include alkyl mercaptans such as butyl mercaptan, hexyl mercaptan, octyl mercaptan, and dodecyl mercaptan, thiophenols such as phenyl mercaptan and benzyl mercaptan, thioglycolic acid, mercaptopropionic acid, And mercaptans containing a carboxyl group such as thiosalicylic acid, mercaptans containing a hydroxyl group such as mercaptoethanol and mercaptopropanediol, and polyfunctional mercaptans such as pentaerythritol tetrakismercaptopropionate.

In addition, it is preferable that the glass transition temperature (Tg) of the (meth)acrylic copolymer is in the range of -65 to -20°C. The lower the Tg, the lower the storage modulus (G') of the adhesive, resulting in better relatively flexible physical properties, but should be within an appropriate range in terms of durability and functionality as an adhesive. If the Tg is less than -65℃, it is a temperature that is difficult to reach as a pressure-sensitive adhesive in view of the Tg of the monomer homopolymer, and if it is more than -20℃, the adhesive strength and wetting property of the pressure-sensitive adhesive begin to deteriorate.

A known solvent may be used for the solvent-type (meth)acrylic copolymer. Diluting solvents that can be used to adjust the viscosity after polymerization and reduce the surface roughness during the curing/drying process include ethyl acetate (EAc), toluene (TOL), xylene, methyl ethyl ketone (MEK), acetone, and Isopropyl alcohol (IPA), and the like. However, when selecting a solvent in terms of polymerization, a chain transfer coefficient must be considered, and ethyl acetate is preferable in terms of increasing the molecular weight and conversion rate.

The total solid content (TSC) of the solvent-type (meth)acrylic copolymer can be found in the relationship between the appropriate viscosity required for coating and the molecular weight to satisfy the physical properties of the product. Viscosity is expressed in the form of an exponential curve for TSC and molecular weight change, and when two of the three are fixed, the other one is determined naturally. The solid content concentration proposed in the present invention is present in 10 to 40%, on the contrary, 60 to 90% is occupied by the solvent. For reference, the appropriate viscosity required for coating may vary depending on the thickness of the coating film, the coating speed, and the type of coating equipment, and is generally in the range of 100 to 20,000 centipoas (cP), mainly 1,000 to 5,000 cP. .

In the polymerization of the (meth)acrylic copolymer, a known azo type initiator and a peroxide type initiator may be used as the initiator. Examples of azo initiators include azobisisobutylonitrile, azobisdimethylvaleronitrile, azobismethoxydimethylvaleronitrile, azobismethylbutylonitrile, azobiscyclohexanecarbonitrile, dimethylazobismethylpropionate, There may be azobisbutylmethylpropionamide, and the like, and the peroxide initiators include dibenzoyl peroxide, dilauryl peroxide, dicumyl peroxide, dibutyl peroxide, butyl peroxybenzoate, and cyclohexanone peroxide. There may be. In the polymerization of the (meth)acrylic copolymer, the amount of initiator used is 0.01 to 0.5 parts by weight compared to the (meth)acrylic monomer, and if it is less than 0.01 parts by weight, it is difficult to initiate a smooth polymerization, and if it exceeds 0.5 parts by weight, the desired molecular weight is reached. You won't be able to. In addition, the initiator may be dividedly added in order to evenly disperse the polymerization exotherm during the reaction time.

In the polymerization of the (meth)acrylic copolymer, it is also possible to use a polymerization inhibitor (Inhibitor) at the end of the reaction for a stable polymerization reaction. The polymerization inhibitor is not particularly limited as long as it can absorb the generated radicals such as hydroquinone, methoxyphenol, or derivatives thereof to perform a termination reaction.

(B) DA-reactive linkage-containing curing agent

The functional group curing agent varies depending on the type of functional group in the resin. For example, when carboxylic acid (-COOH) is a functional group in the resin, an epoxy or aziridine-based curing agent is used, and when a hydroxyl group (-OH) is a functional group in the resin, an isocyanate-based curing agent is used. . However, when the (meth)acrylic copolymer for OCA contains carboxylic acid, it may affect metal panels used in flat panel displays and indium tin oxide (ITO) films. Therefore, the OCA pressure-sensitive adhesive is of an acid-free type, a hydroxyl functional group is used in the copolymer, and an isocyanate-based curing agent is suitable.

In the present invention, a specific isocyanate curing agent is produced by including a DA reaction linkage in the isocyanate curing agent generally used. The isocyanate-based curing agent used at this time is aliphatic (Aliphatic), alicyclic (Cyclic), aromatic (Aromatic) type, and can have from bifunctional to polyfunctional, all of which vary depending on the reactivity and use. can do.

Aliphatic isocyanate curing agents include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HMDI), decamethylene diisocyanate, dimethylpentane diisocyanate, trimethylhexamethylene diisocyanate, undecane triisocyanate, Trimethylhexamethylene diisocyanate, decamethylene diisocyanate, butene diisocyanate, butadiene diisocyanate, undecane tridiisocyanate, diisocyanate methylcaproate... It is selected from the group consisting of, etc. It is also possible to use a plurality of one or more.

Alicyclic isocyanate curing agents include isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bisisocyanate ethylcyclohexene dicarboxylate, norbornane diisocyanate, dimethyl Dicyclohexylmethane diisocyanate... It is selected from the group consisting of, etc. It is also possible to use a plurality of one or more.

Aromatic isocyanate curing agents include 1,3-bis (isocyanatomethyl) benzene (m-XDI), 1,4-bis (isocyanatomethyl) benzene (p-XDI), and 1,4-bis (2-iso Cyanato propan-2-yl) benzene (m-TMXDI), 1,3-bis (2-isocyanato propan-2-yl) benzene (p-TMXDI), 1,3-bis (isocyanatomethyl) -4-methylbenzene, 1,3-bis(isocyanatomethyl)-4-ethylbenzene, 1,3-bis(isocyanatomethyl)-4,5-dichlorobenzene, 1,3-bis( Isocyanatomethyl)-2,4,5,6-tetrachlorobenzene... It is selected from the group consisting of, etc. It is also possible to use a plurality of one or more.

The DA reaction is a reaction in which conjugated diene and dienopyl react to form cycloene. Here, the conjugated dineene includes chemicals represented by Formula A and derivatives containing them, and the dienopye includes chemicals represented by Formula B and derivatives containing them.

Formula A

Formula B

Examples of the precursor material containing the DA reaction linkage are described by Formula C, and compounds having various structures selected from Formulas A and B may be formed. Here, an isocyanate curing agent having a DA reaction linkage can be synthesized as in the example of Formula D by reacting an isocyanate curing agent to participate in the curing reaction.

Formula C

Formula D

The role of the curing agent having the DA reaction linkage is as shown in the following formula (E). Since the hydroxyl group of the (meth)acrylic copolymer reacts with the isocyanate reactor of the curing agent to undergo a urethane curing reaction, and the DA reaction linkage can be reversibly released, dibonding/bonding may occur again when subjected to heat treatment.

Formula E

상기의 이소시아네이트 가교제의 사용량은 (메타)아크릴 공중합체 내에 있는 수산기와의 몰비로 설명될 수 있다. 이론적으로 수산기와 이소시아네이트를 모두 반응시키기 위해서는 수산기 몰수에 대해, 2관능 이소시아네이트의 경우는 1/2, 3관능 이소시아네이트의 경우는 1/3, 4관능 이소시아네이트의 경우는 1/4 몰의 사용량이 필요하다. 하지만 관능기가 많을수록 가교에 참여하는 비율은 약간씩 줄어들며, 이는 관능기-관능기가 반응하기 위해 필요한 공간이 부족해지기 때문이며 이를 입체 장애(Steric hindrance)효과라고 한다. 이러한 입체 장애 효과 때문에 관능기가 많은 이소시아네이트 경화제일수록 몰비보다 약간 더 사용하게 된다. 그러나 이소시아네이트 경화제의 사용량은 접착력, 모듈러스, 인성(Toughness), 가공성 등의 제품의 물성에 관여하는 가교도의 조절을 위해, 수산기에 대한 몰수보다 적은 0.01~0.5 당량 사이에서 사용하게 된다. 여기서 0.01 당량 미만에서 사용하게 되면 가교도가 너무 낮아 점착제로써의 물성 확보가 어려우며, 0.5 당량 초과하여 사용하게 되면 점착제의 가교도가 너무 높아 소성 변형에 대한 회복이 충분하지 않게 되고 결국 폴딩 특성이 떨어지게 된다.

The amount of the isocyanate crosslinking agent used may be described in terms of the molar ratio of the hydroxyl groups in the (meth)acrylic copolymer. Theoretically, in order to react both hydroxyl groups and isocyanates, it is necessary to use 1/2 in the case of difunctional isocyanate, 1/3 in the case of trifunctional isocyanate, and 1/4 mol in the case of tetrafunctional isocyanate, based on the number of moles of hydroxyl groups. . However, as the number of functional groups increases, the ratio of participation in the crosslinking decreases slightly, and this is because the space required for the functional group-functional group to react becomes insufficient, and this is called a steric hindrance effect. Because of this steric hindrance effect, the isocyanate curing agent with many functional groups is used slightly more than the molar ratio. However, the amount of isocyanate curing agent used is between 0.01 and 0.5 equivalents, which is less than the number of moles of hydroxyl groups, in order to control the degree of crosslinking, which is involved in the physical properties of the product such as adhesion, modulus, toughness, and workability. Here, if it is used in less than 0.01 equivalent, the degree of crosslinking is too low to secure physical properties as a pressure-sensitive adhesive, and if it is used in excess of 0.5 equivalent, the degree of crosslinking of the pressure-sensitive adhesive is too high, so that recovery against plastic deformation is not sufficient, resulting in poor folding characteristics.

It is preferable that the degree of crosslinking of the pressure-sensitive adhesive obtained from the pressure-sensitive adhesive composition is 50 to 70%. If it is less than 50%, the step absorption rate may be high, but durability/cutting/folding characteristics are not good, and if it is more than 70%, physical properties such as folding characteristics and step absorption rate are not good.

Other additives can be added to the pressure-sensitive adhesive composition of the present invention. Other additives include tackifier, silane coupling agent, leveling agent, wetting agent, anti-oxidant, anti-static agent, It is also possible to use a flame retardant or the like alone or two or more depending on the purpose.

The thickness of the pressure-sensitive adhesive obtained from the pressure-sensitive adhesive composition may be in the range of 5 to 250 μm, and in the case of OCA, a thickness of 20 μm to 200 μm is preferable. The thicker the thickness, the larger the print step that can be overcome, but it is more appropriate to express the step absorption rate (%; the ratio of the step overcome thickness and the adhesive thickness). When the thickness is less than 5 μm, stress cannot be relieved during bending and breakage is easy. When the thickness is more than 250 μm, there is a problem of removing air bubbles during curing, and when repeatedly folded, it becomes agglomerated and causes wrinkles.

The storage modulus (G') of the pressure-sensitive adhesive layer of the present invention may be in the range of 0.03 to 0.1 MPa at room temperature. If the storage modulus is less than 0.03Mpa, steaming may occur during storage/transport and punching, and if it exceeds 0.1Mpa, it becomes relatively hard, making it difficult to overcome the printing step.

Examples, Comparative Examples

1. Polymerization of (meth)acrylic copolymer

A jacketed 5-neck 2-liter glass reactor equipped with a stirrer, nitrogen gas inlet tube, temperature sensor, condenser, and drain line, and 360 g of 2-ethylhexyl acrylate (2-EHA) as a monomer. , Iso-bonyl acrylate (IBOA) 120g, 2-Hydroxyethyl acrylate (2-HEA) 120g, chain transfer agent n-dodecyl mercaptan (n-dodecyl mercaptan; n -DDM) 0.06g and 810g of ethyl acetate (EAc) as a solvent are added. In order to remove dissolved oxygen, nitrogen purging was performed at room temperature for 30 minutes, and the reactor temperature was raised to 60°C. When stabilized at the set temperature, 6 g of an initiator azobisisobutylonitrile (2,2'-Azobis (isobutyronitrile); AIBN) dissolved in EAc at 5 wt% in advance is added to initiate the reaction. 3 hours after the start of the smooth reaction, 6 g of AIBN was additionally added and the set temperature was raised to 70° C., so that monomers that have not yet participated in the reaction also participate in the polymerization. After 8 hours from the start of the reaction, 240 g of EAc was added as a diluent to lower the viscosity, the reactor temperature was cooled to room temperature, and a reactant was obtained through the outlet. The composition and results of the obtained solvent-type (meth)acrylic copolymers C1 to 6 are summarized in Table 1. In addition, EAc was further diluted in the obtained (meth)acrylic copolymer for an appropriate viscosity required for coating, and the viscosity was adjusted to 2000 cP.

2. Measurement of solid content

0.1~0.3g of the reactant was added dropwise to the previously weighed aluminum dish, weighed, dried in a forced convection oven at 150° C. for 30 minutes, weighed, and calculated by the volatilization-gravity method.

3. Measurement of viscosity

In a Brookfield LV-type viscometer, the relative viscosity was measured at Spindle No 3, 20 rpm, 25°C.

4. Measurement of molecular weight

Use the mobile phase tetrahydrofuran (THF) in gel permeation chromatography (GPC) (manufactured by Agilent), and measure at a mobile phase speed of 1 ml/min, and a column and detector temperature of 40° C., A calibration curve was drawn with a polystyrene standard sample to measure the relative weight average molecular weight (Mw) and molecular weight distribution (Polydispersity index; PDI) values of the sample.

5. Synthesis of precursor material containing DA reaction linkage

First, to make the compound containing the DA reaction linkage, 18 g (0.1416 mol) of hydroxymethyl pyrroledione (1-(Hydroxymethyl)pyrrole-2,5-dione) was added to a 100 ml round bottom flask equipped with a condenser. After completely dissolving in 45 ml of (Anhydrous dioxane), 13.89 g (0.1416 mol) of perfuryl methanol (2-Furylmethanol) was added, followed by stirring at room temperature for 24 hours to proceed the reaction. Thereafter, the generated precipitate was filtered and washed several times with diethylether to obtain 2,7-bis(hydroxymethyl)-4,7a-dihydro-3aH-4,7-epoxyisoindole-1,3-dione. The obtained DA reaction linkage-containing precursor material was used for synthesis of a curing agent.

6. Synthesis of curing agent containing DA reaction linkage

Hardener X1

In order to synthesize the isocyanate curing agent with the precursor material containing the DA reaction linkage obtained above, 0.01 molar equivalent of dibutyltin dilaurate (DBTDL) based on 1 equivalent of the precursor compound synthesized in a 100 ml round-bottom flask. ) Was added and 2 equivalents of isophorene diisocyanate (IPDI), which is an alicyclic isocyanate, was added in methyl ethyl ketone (MEK), and then reacted at 40° C. for 5 hours. Thereafter, the reaction product was precipitated in diethyl ether, washed and filtered to obtain a curing agent X1 containing a DA reaction linkage as shown in Chemical Formula F.

Formula F

Hardener X2

2 equivalents of hexamethylene diisocyanate (HMDI), an aliphatic isocyanate, were added to 1 equivalent of the precursor material containing the DA reaction linkage, and the reaction was carried out in the same manner as in Example 1 to obtain a curing agent X2 as shown in Chemical Formula G. .

Formula G

Hardener X3

To 1 equivalent of the precursor material containing the DA reaction linkage, 2 equivalents of 1,3-bis (isocyanatomethyl) benzene (m-XDI), which is an aromatic isocyanate, were added, and the reaction was carried out in the same manner as in Example 1, and the formula Curing agent X3 as shown in H was obtained.

Formula H

Hardener X4

2 equivalents of 1,3-bis(1-isocyanato-1-methylethyl)benzene (m-TMXDI), an aromatic isocyanate, were added to 1 equivalent of the precursor material containing the DA reaction linkage, the same as in Example 1. The reaction was carried out to obtain a curing agent X4 as shown in the formula (I).

Formula I

7. Preparation of adhesive

Apply to the surface of polyethylene terephthalate (PET) with a thickness of 50 μm subjected to silicone release treatment on the surface so that the coating film thickness after drying becomes 100 μm, and heat curing at 100°C for 2 minutes and 150°C for 3 minutes in a forced convection oven. An adhesive film was obtained.

8. Measurement of adhesion

The substrate was made of SUS304 on a universal physical property analyzer (manufactured by Stable micro systems, Texture analyzer TAXT plus), and the adhesive length was 150 mm, the width was 25 mm, and the peel rate was 300 mm/min at room temperature, and the peel angle was 180º.

9. Measurement of heat-resistant holding power

When the pressure-sensitive adhesive was left in an oven at 85° C. for 1 hour with a load of 500 g on the substrate SUS304 with an area of 1×1 cm, the pushed distance was measured.

10. Measurement of gel content

The degree of crosslinking during thermal curing of an adhesive is a reaction that creates a new functional group by reacting a functional group to a functional group (e.g., a hydroxyl group + an isocyanate group → a urethane group), so infrared spectroscopy (IR) or nuclear magnetic resonance analysis (Nuclear magnetic) There may be a method to check the presence or absence of a functional group by spectroscopy (NMR), etc., but it is not possible to measure how much of the crosslinked structure is introduced, and the degree of crosslinking can be determined by measuring the gel fraction, which is an alternative factor. The weight of the prepared pressure-sensitive adhesive sample is measured, and it is swelled by impregnating it with ethyl acetate or toluene solvent for 24 hours at room temperature. The swollen adhesive was poured into a 200 mesh wire mesh, filtered, and dried in a forced convection oven at 80° C. for 1 hour and weighed again. At this time, the portion dissolved in the solvent was referred to as sol, and the portion remaining after being filtered and dried was referred to as gel, and the gel fraction was measured by the gravimetric method.

11. Measurement of optical properties

The transmittance and haze values were measured in a transmission mode in the visible range (wavelength 400 to 700 nm) using a spectrophotometer (manufactured by Jasco, V-650).

12. Measurement of storage modulus

Using a rheology dynamic analyzer (manufactured by TA, ARES-G2), the adhesive was laminated to a thickness of 1 mm and then punched into a diameter of 8 mm to prepare a sample. Frequency 1 rad/sec, strain 10%, temperature rise rate 5°C Measured at /min.

13. Measurement of permittivity

It measured under 400KHz condition using an LCR meter (manufactured by Agilent, E4980A).

14. Measurement of refractive index

Using an Abbe refractometer (manufactured by Kruss optronic, AR4), the refractive index of the pressure-sensitive adhesive was measured while maintaining at 25°C through a constant temperature water bath.

15. Evaluation of Cutting

When the adhesive was cut with a flat plate on a simple Thomson cutter, it was visually checked whether there was any glue leftover or agglomeration of the glue on the side of the blade or the adhesive cutting surface.

O: There is no glue leftover or agglomeration of glue on the cutting surface of the knife or adhesive, X: Yes

16. Evaluation of folding characteristics

Using a Tension-free U-shape folding machine (manufactured by Yuasa) (evaluation standard: IEC627156-6-1 (durability test for flexible materials)) folded 10,000 times at -20℃ The unfolding was repeated and the presence or absence of defects such as air bubbles, peeling, streaks, cracks, etc. was visually checked.

O: No defects such as air bubbles, peeling, streaks, cracks, etc. were found, △: slightly recognized, X: clearly recognized

17. Evaluation of step absorption rate

The performance of overcoming the printing level difference is evaluated through the printing level difference absorption rate of the following equation, and the average is calculated by performing 5 pieces per sample.

Step Absorption Rate (%) = (Maximum Print Step Overcome/Thickness of Adhesive)X100

In order to measure the print step that can be overcome, using printing ink on a flat glass plate, 2 degree printing with a length of 50 mm and a width of 5 mm (average height of printing step 10㎛), 4 degree printing (average height of printing step 20㎛), 6 degree A glass plate for evaluating a printing step was prepared by printing (average print step height 30 µm), 8-degree print (print step average height 40 µm), and 10-degree print (print step average height 50 µm).

The release paper on one side of the prepared pressure-sensitive adhesive was removed and attached to the hard-coated surface of the polarizing plate, and then the release paper on the other side was removed and attached to the glass plate for evaluating the printing step. After attaching, autoclave treatment (50℃, 30min, 0.5Mpa) and check for defects. The overcoming of the printing step according to the present invention is that the DA reaction linkage has variability depending on the temperature, so in order to check this effect, it was left in an oven at 80°C for 24 hours and then taken out to determine the presence or absence of defects at 100 times the magnification of the optical microscope Reconfirm/evaluate.

O: No air bubbles in the print step, X: Air bubbles remain in the print step

The conditions and results of Examples 1 to 5 and Comparative Examples 1 to 4 are summarized in Table 2.

[Examples 1 to 5]

A pressure-sensitive adhesive was prepared by using the (meth)acrylic copolymers C1, C3, C4, C5, C6 polymerized above, and adding 0.05 equivalents of the curing agent X1 to X4 containing the DA reaction linkage. It was found that the basic performance and optical performance such as transmittance/haze were excellent, and at the same time, the cutting property, folding property, and step absorption rate were all high.

[Comparative Example 1]

The molecular weight of the (meth)acrylic copolymer was reduced (C2), and the crosslinking degree and storage modulus were low, so the step absorption rate was high, but it was found to be poor in cutability and folding characteristics.

[Comparative Example 2]

Instead of the use of the curing agent containing the DA reaction linkage, the commonly used IPDI curing agent was used. Other characteristics were largely the same, but the folding characteristics and the step absorption rate were low.

[Comparative Example 3]

The amount of the curing agent containing the DA reaction linkage was reduced to less than the range, and the step absorption rate was high due to low crosslinking and storage modulus, but it was found to be poor in basic performance as an adhesive, cutting ability, and folding characteristics.

[Comparative Example 4]

The amount of the curing agent containing the DA reaction linkage was increased to exceed the range, and the folding characteristics and the step absorption rate were poor due to high crosslinking and storage elasticity.

Code Monomer (wt%) TSC
(%) Mw
(X10 ⁴ ) PDI Visc.
(cP) Tg
(℃) 2-EHA 2-HEA IBOA LA CHMA THFA PhEA C1 60 20 20 17.5 130 3.2 3380 -35.1 C2 60 20 20 36.0 40 3.0 3250 -35.1 C3 60 20 20 21.5 110 3.1 3420 -45.0 C4 60 20 20 18.5 100 3.3 3360 -36.0 C5 60 20 20 18.5 120 3.2 3300 -45.1 C6 60 20 20 18.0 120 3.2 3130 -43.4

No polymer
Kinds Hardener
Kinds Hardener
Content (equivalent) Adhesion (gf/in) Heat resistant
Holding power (mm) Degree of crosslinking (%) Transmittance (%) Haze
(%) G'(Mpa) permittivity Refractive index Cutability Folding characteristics Step
Water absorption (%) Example One C1 X1 0.05 3450 3 60 99+ 1.0- 0.052 3.7 1.490 O O 30 2 C3 X2 0.05 3500 3 58 99+ 1.0- 0.048 3.6 1.484 O O 30 3 C4 X3 0.05 3400 3 55 99+ 1.0- 0.051 3.6 1.486 O O 30 4 C5 X4 0.05 3600 3 57 99+ 1.0- 0.052 3.8 1.487 O O 30 5 C6 X1 0.05 3300 3 58 99+ 1.0- 0.055 3.5 1.499 O O 30 Comparative example One C2 X1 0.05 4300
Residue leaving out 45 99+ 1.0- 0.026 3.7 1.488 X X 40 2 C1 IPDI 0.05 3500 3 61 99+ 1.0- 0.060 3.7 1.490 O △ 20 3 C1 X1 0.005 Bulk destruction leaving out 15 99+ 1.0- 0.018 3.8 1.486 X X 40 4 C1 X1 0.6 2300 leaving out 75 99+ 1.0- 0.120 3.7 1.491 O X 18

Claims (10)

(A) Based on 100 parts by weight of the solvent-type (meth)acrylic copolymer
(B) 0.01 to 0.5 molar equivalent of specific functional group type curing agent
Adhesive composition, characterized in that consisting of and adhesive using the The pressure-sensitive adhesive using a curing agent according to claim 1, wherein the specific functional group type curing agent contains a Diels-Alder (DA reaction) linkage. The curing agent for a pressure-sensitive adhesive using a compound selected from a chemical substance represented by Chemical Formula A and its derivatives as the raw material of the conjugated dienes of the DA reaction according to claim 1
Formula A

The curing agent for pressure-sensitive adhesives according to claim 1, wherein the raw material for dienophiles of the DA reaction is a chemical substance represented by Formula B and a compound selected from its derivatives.
Formula B

The curing agent for an adhesive using a compound selected from chemical substances and derivatives thereof in which the DA reaction linkage of claim 1 is represented by Chemical Formula C.
Formula C

The pressure-sensitive adhesive composition according to claim 1, wherein the amount of the curing agent having the DA reaction linkage is contained in a ratio of 0.01 to 0.5 equivalent to the molar ratio of hydroxyl groups of the (meth)acrylic copolymer. The pressure-sensitive adhesive composition according to claim 1, wherein the weight average molecular weight (Mw) of the copolymer in the (meth)acrylic syrup is between 500,000 and 2 million. The pressure-sensitive adhesive composition according to claim 1, wherein the glass transition temperature (Tg) of the copolymer in the (meth)acrylic syrup is between -65 and -20°C. A pressure-sensitive adhesive having a storage modulus of elasticity in the range of 0.03 to 0.1 MPa of the pressure-sensitive adhesive prepared using the pressure-sensitive adhesive composition of claim 1 A pressure-sensitive adhesive having a crosslinking degree of 50 to 70% of the pressure-sensitive adhesive prepared using the pressure-sensitive adhesive composition of claim 1