KR20120088399A - Method of Manufacturing Acrylic Adhesive Composition for Polarizing Plate - Google Patents

Abstract

PURPOSE: A manufacturing method of acrylic adhesive for polarizers is provided to manufacture EB curing type adhesives having an improved durable reliability under high temperature and high moisture conditions. CONSTITUTION: A manufacturing method of acrylic adhesive for polarizers comprises the following steps: manufacturing a copolymer by solution polymerizing acrylic monomers including carboxy group and (meth) acrylic monomers including C1-4 alkyl groups and (meta) acrylic monomers including the C4-12 alkyl groups; and performing cross linkages by irradiating the copolymer with electron beam. The acrylic monomers including C4-12 alkyl groups are n-butyl acrylates. The (meat) acrylic monomer including the C1-4 alkyl groups is 2- hydroxyl ethyl (meta) acrylate.

Description

Method of manufacturing acrylic adhesive for polarizing plate by electron beam irradiation {Method of Manufacturing Acrylic Adhesive Composition for Polarizing Plate}

The present invention relates to a manufacturing method through electron beam irradiation of the acrylic pressure-sensitive adhesive composition for polarizing plates.

A pressure-sensitive adhesive is a material with viscoelastic properties that can adhere strongly even under a small pressure for a short time. Such pressure-sensitive adhesives are used in various fields such as wood, medical, and electronics. Among the materials used as the material of the pressure-sensitive adhesive is the acrylic pressure-sensitive adhesive is most used. Acrylic adhesives have high transparency and do not easily oxidize in air or yellow due to sunlight as compared to other adhesives. Acrylic pressure-sensitive adhesives are generally prepared by polymerizing together monomers having a low glass transition temperature to increase the tackiness and monomers having a high glass transition temperature to increase the cohesion. However, the acrylic pressure-sensitive adhesive having a linear structure has a disadvantage in that it cannot be used at a high temperature, thereby increasing the heat resistance by introducing a crosslinked structure.

Pressure sensitive adhesives (PSAs) for polarizing plates serve to bond the liquid crystal panel and the polarizing plate. Polarizer adhesives account for only about 0.05% of LCD panel prices. However, it requires a high level of reliability because it has a very important influence on the quality of LCD panels such as image quality loss, reliability, and productivity due to bubbles in the LCD panel compared to the weight ratio.

Acrylic adhesive for polarizing plates is used in various forms, such as solution type, emulsion type, hot melt type, and liquid curing type. The most commonly used solution type adhesives and emulsion type adhesives use the same monomers, but solution type adhesives can obtain lower molecular weight adhesives than emulsion type adhesives. In order to have it, it is necessary to compensate using a crosslinking agent.

In the pressure-sensitive adhesive for polarizing plates, it is difficult to achieve both adhesion durability and light leakage prevention, and this is a major problem. Moreover, in manufacturing processes, such as a liquid crystal display device, when joining a polarizing plate to optical components, such as a liquid crystal cell, it is necessary to peel a polarizing plate and to reuse an expensive liquid crystal cell after time after joining, such as a bonding position being deviated. There is a case. Therefore, the adhesive strength with the polarizing plate increases with time, which requires a pressure-sensitive adhesive having excellent durability in the long term, and a pressure-sensitive adhesive that can be easily peeled from the liquid crystal cell even after a certain time after bonding through the adhesive applied to the polarizing plate. It is becoming. This is a problem contrary to reinforcing adhesion for imparting adhesive durability, and satisfying this simultaneously is a problem.

Until now, the improvement of thermosetting adhesives has been studied for acrylic adhesive resin compositions that can minimize stress concentration, development of acrylic adhesives for polarizing plates with positive photoelastic coefficient, and acrylic adhesive compositions for polarizing plates with polymers having excellent compatibility with plasticizers. The research on the manufacture of pressure-sensitive adhesives with excellent blending and durability, research on adhesive products for polarizing plates having excellent characteristics such as durability, cutting properties and reworking properties have been conducted. However, such a thermosetting pressure-sensitive adhesive takes a long time to cure, if the heat resistance is weak, such as plastics had a problem that is difficult to use.

In order to shorten the curing time of the thermosetting adhesive and to increase the curing efficiency, the development of the photocurable adhesive is progressing. Photocurable adhesives include UV curable and electron beam curable adhesives. UV curable adhesives are less affected by shortening the curing time and substrate selection compared to thermosetting. It is necessary, the thickness of the coating film is extremely limited, it is difficult to apply to the opaque material, there was a problem that the yellowing phenomenon and polymerization proceeds to deteriorate when stored for a long time.

The present invention was devised to solve the problems of the conventional method for producing a pressure-sensitive adhesive for polarizing plates, such as thermosetting, ultraviolet curing, and the like, and devised a manufacturing method through electron beam curing, and to provide an optimized monomer composition and composition ratio for electron beam curing. There is this.

In order to solve the above object, in the present invention by solution polymerization of the (meth) acrylic monomer containing an alkyl group having 4 to 12 carbon atoms, the (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms and the acrylic monomer containing a carboxyl group 1 step of preparing a copolymer; And it provides a method for producing a pressure-sensitive adhesive for a polarizing plate comprising two steps of irradiating an electron beam to the copolymer prepared above.

The electron beam curable pressure sensitive adhesive prepared in the present invention can replace the thermosetting pressure sensitive adhesives currently used in the manufacture of polarizing plates for LCD panels, and can dramatically shorten the curing time compared to the thermosetting pressure sensitive adhesives, thereby dramatically improving the productivity and workability of the polarizing plate. Can be improved. The electron beam curable pressure sensitive adhesive prepared in the present invention has a low initial adhesive force and excellent re-peeling characteristics, and has excellent durability durability under high temperature and high humidity conditions.

1 is a graph showing the amount of change in gel fraction according to the electron beam irradiation amount of Experimental Example 1.
2 is a graph showing the amount of change in expansion ratio according to the electron beam irradiation amount of Experimental Example 1.
3 is a graph showing the adhesive force measurement results of Experimental Example 2.
4 is a graph showing the creep measurement results of Experimental Example 3. FIG.

The present invention is a step of preparing a copolymer by solution polymerization of a (meth) acrylic monomer containing an alkyl group having 4 to 12 carbon atoms, a (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms and an acrylic monomer containing a carboxyl group ; And a two step of crosslinking by irradiating the prepared copolymer with an electron beam.

In the present invention, the (meth) acrylic monomer refers to not only a methacryl monomer but also an acrylic monomer. In addition, in the present invention, the polymer refers to both “homopolymer” or “copolymer”.

It is preferable that the (meth) acrylic monomer including the alkyl group having 4 to 12 carbon atoms is n-butyl acrylate (n-Butyl Acrylate, n-BA).

The (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms and the acrylic monomer including a carboxyl group have a function of increasing curing efficiency during electron beam curing, thereby enabling the preparation of an adhesive by electron beam curing.

Specifically, the (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms is preferably 2-hydroxy ethyl (meth) acrylate (2-HEMA).

In addition, the acrylic monomer containing the carboxyl group is preferably acrylic acid (Acrylic Acid, AA).

85 to 94.9% by weight of the (meth) acrylic monomer containing an alkyl group having 4 to 12 carbon atoms, 5 to 10% by weight of the (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms, and an acrylic monomer containing a carboxyl group. It is preferable to mix | blend 0.1-5 weight% and superpose | polymerize. Durability reliability and heat-resistant light leakage of the pressure-sensitive adhesive prepared within the above range can be improved.

It is preferred that the weight average molecular weight of the copolymer prepared in step 1 be 500,000 to 5 million. If the weight average molecular weight is 500,000 or more, the adhesion durability with the adherend, the adhesion durability reliability under high temperature, and high humidity are sufficient, and it is preferable because the lifting or peeling phenomenon may not occur. In consideration of the internal cohesion force and the durability of the pressure-sensitive adhesive, the weight average molecular weight is more preferably between 1 million and 2 million, and particularly preferably from 1.2 million to 1.4 million considering the viscosity and the coating process. In addition, the polydispersity index (PDI) representing the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the copolymer prepared in step 1 is preferably 5 or less. When the molecular weight distribution exceeds 5, a ringing phenomenon occurs in a coating or the like, and there may be a problem in that the lifting or peeling phenomenon occurs due to the surface migration of low molecules at high temperature and high humidity.

In the second step, the electron beam energy used for curing the pressure-sensitive adhesive composition is preferably 0.5 ~ 10 MeV. If the energy exceeds 10 MeV, the temperature of the instantaneous composition is increased to affect the foaming of the pressure-sensitive adhesive composition and the degree of polarization of the polarizing film, if less than 0.5 MeV, it may not be sufficiently cured. . Moreover, it is preferable that irradiation dose is 10-200 kGy. If it is less than 10 kGy, hardening does not proceed, leaving a residue when re-peeling. Low crosslinking density causes heat light leakage phenomenon. If it exceeds 200 kGy, it affects productivity and increases the internal cohesiveness. In addition, it affects the transmittance and the degree of polarization of the polarizing plate.

In the present invention, the high molecular weight acrylic polymer is crosslinked by an electron beam so as not to leave residues of the low molecular weight, thereby preventing the surface migration of the low molecular weight body. Improve the light leakage phenomenon effectively.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are merely to illustrate the present invention, but it should be understood that the present invention is not limited thereto.

Example  1 to 3 and Comparative example

n-BA, 2-HEMA, AA were used as the basis of the copolymer, and the acrylic pressure-sensitive adhesive for electron beam curable polarizing plates was prepared through solution polymerization while varying the content of 2-HEMA and AA. Nitrogen gas was refluxed and mixed with n-BA, 2-HEMA, and AA in a 1 L reactor equipped with a cooling device to facilitate temperature control, according to the composition shown in Table 1 below. Thereafter, 120 parts by weight of ethyl acetate (EAc) was added as a solvent based on 100 parts by weight of the monomer. In order to remove oxygen, the mixture was stirred slowly while purging nitrogen gas for 60 minutes to induce the mixture to be uniformly mixed, and then maintained at 60 ° C. while maintaining the temperature at 60 ° C. To 0.05 parts by weight diluted in ethyl acetate was added and reacted for about 8 hours. After the reaction, the high molecular weight acrylic resin was properly diluted to provide a coating process and physical properties, and the solid content was measured, and the molecular weight and viscosity were measured.

Code n-BA
(weight%) 2-HEMA
(weight%) AA
(weight%) Mw (× 10 ^-4 )
(g / mol) PDI
(Mw / Mn) Solid contents
(%) Viscosity
(cP) Example 1 94.5 5 0.5 140 2.45 18 2170 Example 2 89.5 10 0.5 135 2.63 23 2130 Example 3 84.5 15 0.5 125 2.14 18 1250 Comparative example 100 0 0 140 1.62 17 1520

The prepared pressure-sensitive adhesive was coated on a release film at 25 μm using a micrometer adjustable film applicator. Next, put in an oven at 90 ℃ dried for 5 minutes to remove the solvent. After the transfer to the polarizing film was carried out by curing the electron beam irradiation with the release surface facing up. The cured sample was measured by cutting to fit the characteristic analysis specimen and adhered to the glass plate. In the case of electron beam curing, the irradiation dose was crosslinked by 10, 20, 30, 40, 50, 100 kGy (Equipment name: ELV-8, electron beam energy: 1.0 ~ 2.5 MeV)

Experimental Example  One : Gel fraction  And expansion ratio

The pressure-sensitive adhesive samples prepared in Examples 1 to 3 and Comparative Examples and cured while varying the electron beam irradiation amount were placed in toluene, stored at room temperature for 3 days, and dried until they reached a certain weight to calculate the gel content and expansion ratio. Obtained.

Gel fraction (%) = B / A X 100-Formula (1)

Expansion ratio = C / B-equation (2)

In the above formulas (1) and (2)

A represents the mass of the acrylic pressure-sensitive adhesive composition, B represents the dry mass of the insoluble fraction of the acrylic pressure-sensitive adhesive after immersing the pressure-sensitive adhesive sample in toluene at room temperature for 3 days, and C is inflated by toluene after 3 days of immersion in toluene at room temperature. The mass of the insoluble fraction.

In the prepared pressure-sensitive adhesive polymer chain, an active point is formed by an electron beam, thereby causing a crosslinking reaction. The polymer network structure formed by the crosslinking reaction is left insoluble in the solvent. The amount of the polymer network becomes a gel fraction and indicates the degree of crosslinking density of the pressure sensitive adhesive. In addition, the crosslinking density can be evaluated by obtaining the expansion ratio.

1 and 2 show the change in the gel fraction and the expansion ratio according to the electron beam irradiation amount. As shown in FIG. 1, Examples 1 to 3 to which 2-HEMA and acrylic acid are added show higher crosslinking concentrations than the comparative example. 2 shows the expansion ratio of the pressure-sensitive adhesive, but as the content of 2-HEMA, which is a hydrogen donor, increases, the lower the expansion ratio, the higher the crosslinking density. Since the irradiation dose of 50 kGy or more affects the polarization degree of the polarizing film, the irradiation dose was set to 50 kGy and the characteristics were analyzed.

Experimental Example  2: adhesive force ( Peel strength )

After irradiating the polarizing plate coated with the pressure-sensitive adhesive layer with an electron beam at 50 kGy, crosslinking was carried out, and the one end in the longitudinal direction of the glass plate and the polarizing plate was aligned with the adhesive face of the polarizing plate laminated with the pressure-sensitive adhesive layer down on the washed glass plate, The polarizing plate was placed at the center in the width direction of the glass plate, leaving the remaining approximately 125 mm portion of the polarizing plate, and a release film was peeled off on the adhesive surface of the remaining portion. Next, the roller was reciprocated twice at a speed of about 300 mm / min on the polarizing plate, and then pressed for 2 hours at 50 ° C. Thereafter, the remaining portion of the polarizing plate was folded back to 180 ° and peeled off about 25 mm. Then, the polarizing plate was inserted into the upper slot and the glass plate into the lower slot, and the polarizing plate was pulled off at a speed of 300 mm / min. The average value was recorded four times by reading the force value between 20 mm and 80 mm from the start of the pull-out. At least three sheets were repeated and the average value of the measured forces was obtained.

The adhesive force when the electron beam irradiation amount is 50 kGy is shown in FIG. In the case of the comparative example without the addition of acrylic acid showed a low adhesive strength of less than 100g / 25mm low defect force, it can be seen that in the case of Examples 1 to 3 with the addition of acrylic acid showed a higher adhesion. In addition, it can be seen that the adhesion tends to increase as the content of 2-HEMA increases.

Experimental Example  3: creep resistance ( Creep resistance )

The adhesive-coated polarizing plate (15mm × 120mm) was attached to a glass substrate with an area of 15mm × 15mm as in Experimental Example 2, and then stored at room temperature for 3 days. The prepared specimens were bitten in the same manner as in the measurement of adhesive force, and then subjected to a constant force of 2250 gf to measure the distance pushed for 1000 seconds three times to obtain an average value.

In Examples 1 to 3, as the crosslinking density was increased in association with the gel fraction and the expansion ratio, it was confirmed that the pushed distance (creep) value was significantly lowered. This creep property affects the light leakage phenomenon. As the creep value decreases, the light leakage phenomenon improves. Comparing Examples 1 to 3 in FIG. 4, it can be seen that the creep value is lowered as 2-HEMA is added. In the case of the comparative example, the adhesion with the glass substrate was remarkably poor, and creep measurement was impossible.

Experimental Example  4 : Durability Reliability  And Heat-resistant spring

As in Experiment 2, a pressure-sensitive adhesive coated polarizing plate (120 mm × 100 mm) was attached to a glass substrate by applying a pressure of about 5 kg / cm ² . In order to determine the heat and humidity characteristics of these specimens, the presence of air bubbles or lifting was observed after 500 hours at 60 ° C. and 95% relative humidity. Heat resistance was observed for 500 hours at the temperature of 85 ℃ and 105 ℃ after the occurrence of bubbles or lifting phenomenon. The evaluation criteria for durability were determined as follows.

○: No bubbles or uplift

△: weak bubble or lifting phenomenon

×: Strong bubbles or excitement

Using the same specimen as the endurance reliability was attached to the glass substrate with the optical absorption axis crossed on both sides. In order to confirm the heat-resistant light leakage characteristics, after the light was left at 85 ° C. for 500 hours, it was visually identified whether the light leaked out from the dark room. Heat resistance light gland characteristics were evaluated based on the following criteria.

○: Light leaks out

△: Some light leaks out

×: The part where light leaks out is strong

The results of evaluating the durability reliability and heat resistance light leakage phenomenon by the above method are shown in Table 2 below. As compared with the comparative examples, it was confirmed that Examples 1 to 3 were superior in durability reliability and heat resistance light leakage phenomenon. Due to the addition of a portion of acrylic acid, the durability was improved due to the increase in adhesion due to the improvement of adhesion with the glass substrate, and it is considered that it may help to improve the heat leakage phenomenon by increasing the crosslinking efficiency by the electron beam.

division Example 1 Example 2 Example 3 Comparative example Endurance
responsibility 60 ℃, 95% × ○ ○ × 85 ℃ △ ○ ○ × 105 ℃ △ ○ ○ × Heat resistant
Light fountain 85 ℃ △ ○ ○ ×

Claims (7)

Preparing a copolymer by solution polymerization of a (meth) acrylic monomer including an alkyl group having 4 to 12 carbon atoms, a (meth) acrylic monomer including an alkyl group having 1 to 4 carbon atoms and an acrylic monomer including a carboxyl group; And
2 steps of crosslinking by irradiating the prepared copolymer with an electron beam;
The manufacturing method of the adhesive for polarizing plates containing a.
The method according to claim 1, wherein the (meth) acrylic monomer containing an alkyl group having 4 to 12 carbon atoms is n-butyl acrylate.
The method for producing a pressure-sensitive adhesive for polarizing plates according to claim 1, wherein the (meth) acrylic monomer containing an alkyl group having 1 to 4 carbon atoms is 2-hydroxyethyl (meth) acrylate.
The method for producing a pressure sensitive adhesive for polarizing plate according to claim 1, wherein the acrylic monomer containing a carboxyl group is acrylic acid.
According to claim 1, wherein the (meth) acrylic monomer containing an alkyl group having 4 to 12 carbon atoms of 80 to 94.9% by weight, 5 to 15% by weight of the (meth) acrylic monomer containing an alkyl group of 1 to 4 carbon atoms, carboxyl group 0.1 to 5% by weight solution polymerization of an acrylic monomer containing a method for producing a pressure-sensitive adhesive for a polarizing plate.
The method for manufacturing a pressure-sensitive adhesive for polarizing plates according to claim 1, wherein the copolymer prepared in step 1 has a weight average molecular weight of 500,000 to 5 million.
The method of claim 1, wherein the electron beam irradiation irradiates 10 to 200 kGy of 0.5 to 10 MeV electron beams.

Images