KR20080093508A - Manufacturing method of acryl pressure sensitive adhesive for polarizing film - Google Patents

Abstract

A method for preparing an acrylic pressure sensitive adhesive for suitable for the preparation of a polarizer is provided to improve light permeability and wettability. A method for preparing an acrylic pressure sensitive adhesive comprises the steps of firstly polymerizing 30-50 wt% of an organic solvent, 20-30 wt% of a polymerization initiator, 55-65 wt% of an acrylic main monomer and 35-45 wt% of an acrylic functional group monomer; adding 15-20 wt% of an organic solvent, 10-15 wt% of a polymerization initiator, 35-45 wt% of an acrylic main monomer and 35-45 wt% of an acrylic functional group monomer to the first polymerization product for the second polymerization; adding 15-20 wt% of the organic solvent and 60-75 wt% of the polymerization initiator to the second polymerization product for the third polymerization; adding 25-40 wt% of a solvent to it to prepare a liquid acrylic resin; irradiating an ultrasonic wave to the liquid acrylic resin; and adding a curing agent or a coupling agent to it to prepare an acrylic pressure sensitive adhesive. The ratio of the organic solvent, an acrylic main monomer and an acrylic functional group monomer is 1.7-1.9 : 1.0 : 0.05-0.7 by weight.

Description

Manufacturing method of acrylic adhesive for polarizing film {Manufacturing method of acryl pressure sensitive adhesive for polarizing film}

1 is a view showing a cross section of a general polarizing film.

Explanation of symbols on the main parts of the drawings

1: polarizing film 4: adhesive

2,2 ′: Transparent protective film 5: Release film

3: base film

The present invention relates to a method for producing an acrylic resin-based pressure-sensitive adhesive suitable for manufacturing a polarizing film.

In general, a polarizing film is used in a liquid crystal display (hereinafter referred to as LCD) or a plasma display (plasma display projector) (hereinafter referred to as PDP) to uniformize the distribution of light in the traveling direction.

The polarizing film used for LCD or PDP is composed of a base film 3 and a transparent protective film (2) (2 ') containing a polarizing material, as shown in Figure 1, the transparent protective film, such as triace cellulose A hydrophilic polymer material is used, and the base film uses a lipophilic polymer material such as polyvinyl alcohol and combines the two films so that physical properties do not vary depending on directions.

In addition, the transparent protective film (2 ') is prepared by attaching a release film (5), when the polarizing film to adhere to the LCD or PDP is used to peel off the release film.

The present invention relates to a method for producing an adhesive used when attaching the release film (5) to the transparent protective film (2 ').

Since the adhesive is used in a state where it is attached to the polarizing film, various optical and physical properties are required.

For example, not only optical characteristics such as transmittance in the visible region, uniform light transmittance, stability to heat and light, but also workability should be easy, and physical properties such as resistance to pressing marks in the manufacturing process are required.

In the polarizing film, when the adhesive is applied, press marks are likely to occur in the pressure-sensitive adhesive layer for sheet loading and roll. When the depressing mark occurs, the refraction or reflection of the light may appear, and the light escaping phenomenon (light escape) occurs to increase the defective rate.

Copolymers such as silicone, acrylic, and polyurethane are frequently used in the production of pressure-sensitive adhesives. Among them, acrylic pressure-sensitive adhesives are widely used because they have easy workability, excellent transparency and cohesion, and easy control of viscosity and molecular weight.

Acrylic adhesive is excellent for cohesion and transparency, suitable for display and can adjust the wettability (wetability) to be easy to apply to the film. When the pressure-sensitive adhesive has excellent spreadability with respect to the adherend, productivity is improved and work efficiency is improved. Also, make sure that foreign matter does not occur as much as possible and consider the resistance to heat and light when using it for display purposes. In addition, the spreadability is good when the viscosity is low.

Recently, acrylic adhesives are mainly prepared by solution polymerization, but are not satisfactory in light transmittance and wettability.

The acrylic pressure-sensitive adhesive for polarizing film aims to increase the cohesive force and increase the uniform light transmittance. Cohesive force increases when the molecular weight is high, but the transmittance has excellent light transmittance when the molecular weight is low. Since cohesion and light transmittance have opposite relations, pressure-sensitive adhesives that satisfactorily satisfy both must be prepared. In general, the molecular weight as an adhesive should have a high molecular weight of several tens to millions to impart cohesion and lack of strength. Cohesion here means cohesion between the pressure-sensitive adhesives.

The cohesive force of the acrylic polymer is determined by the degree of crosslinking of the polymer. When the polymer causes crosslinking, the cohesive force is proportional to the gel content of the polymer because the polymer is converted from the sol state to the gel state.

Therefore, there is a need for the development of a pressure-sensitive adhesive having excellent cohesion, light transmittance, and productivity to increase productivity.

An object of the present invention is to provide a method for producing a pressure-sensitive adhesive for polarizing film having excellent light transmittance in the visible light region and having a wettability suitable for application to a film form.

In the polymerization step of producing an acrylic resin by heating and solution polymerization of an acrylic monomer and a polymerization initiator in an organic solvent, the inventors separately perform stepwise polymerization of an organic solvent, an acrylic monomer and a polymerization initiator to obtain an acrylic resin solution. After irradiating the ultrasonic wave (ultrasonic waves) to the acrylic resin solution obtained in the present invention by adding a curing agent and a coupling agent to prepare an acrylic adhesive, it was confirmed that an acrylic adhesive for polarizing film having improved light transmittance and wettability can be obtained. It was completed.

The present invention relates to a method for producing an acrylic pressure-sensitive adhesive for polarizing film excellent in light transmittance and wettability.

The present invention will be described in detail with reference to the following Examples.

Example  One

 <Production of Acrylic Resin>

 Inject 45 g of ethyl acetate (solvent) into a reactor equipped with a nitrogen gas reflux device, a temperature controller and a thermometer to control the exothermic reaction, and 10 g of 2-ethylhexyl acrylate, 20 g of butyl acrylate and 1.5 g of acrylic acid. Add 0.02 g of benzoyl peroxide (hereinafter referred to as BPO) and stir for 30 minutes. Then dropping by the amount of Feed 1 described in the following [Table 1] for 2 hours and 30 minutes, injecting the solvent and BPO stirred in Feed 2, and injecting only the solvent in Feed 3 for 80 hours, 6 hours 30 minutes The polymerization reaction is carried out to obtain an acrylic resin. The conversion rate of the monomers into the polymer was 98%.

TABLE 1

Initial charge Feed 1 (g) Feed 2 (g) Feed 3 (g) Total (g) EAc ^{1 )} 45 15 19 30 109 2-EHA ^{2 )} 10 15 25 BA ^{3 )} 20 30 50 AA ^{4 )} 1.5 2.0 3.5 BPO ^{5 )} 0.02 0.01 0.045 0.075 Polymerization time  30min dropping: 2hr dropping: 30min 30min 30min 2hr 30min Cumulative time 30min 3hr 6hr 6hr 30min   1) EAc: ethyl acetate (solvent) 2) 2-EHA: 2-ethylhexyl acrylate 3) BA: butyl acrylate 4) AA: acrylic acid 5) BPO: benzoyl peroxide (polymerization initiator)

<Production of Acrylic Adhesive>

 100 g of the acrylic resin prepared in the above step was irradiated with an ultrasonic wave having a strength of 40 W for 30 minutes using an ultrasonic generator (model name 5510E-DTH), and 1.2 g of diphenylmethane diisocyanate (isocyanate-based curing agent); 1 g of methacryloxypropyltrimethoxy silane, which is a silane coupling agent, was uniformly mixed to prepare an acrylic pressure-sensitive adhesive.

The physical properties of the light transmittance, wettability, peel off bubble generation, and glass transfer of the acrylic adhesive obtained here were tested by the following method, and the results are shown in the following [Table 2].

An acrylic adhesive composition containing 0.1 to 0.5 parts by weight of a silane coupling agent and 0.5 to 1.2 parts by weight of an isocyanate or epoxy curing agent is suitable for 100 parts by weight of an acrylic polymer having an average molecular weight of 1,500,000 to 2,000,000 and a Tg of -40 ° C. or less. The content of 0.05 to 0.09 parts by weight of the polymerization should be carried out at an appropriate temperature according to the type of initiator.

In the above embodiment, the acrylic monomer may be butyl acrylate, methyl acrylate, ethyl methyl acrylate, propyl acrylate, acrylic acid, 2-ethylhexyl acrylate, etc., and appropriate monomer selection and ratio according to the glass transition temperature are required. . In the case of the silane coupling agent, vinyl trimethoxy silane, vinyl triethoxy silane, methacrylate silane, 3-aminopropyl triethoxy silane, and N-phenyl-3-aminopropyl trimethoxy silane may be used. Consider the compatibility of the copolymer and the light transmittance, and to improve the adhesiveness to the liquid crystal cell should be used as much as possible.

The curing agent may be an isocyanate compound or an epoxy compound. Isocyanate compounds include diphenylmethane isocyanate, xylene diisocyanate, isophorone diisocyanate, toluene diisocyanate and the like, and epoxy-based polyethylene glycol diglycidyl ether, diglycidyl ether and trimethylol propane triglycidyl ether. There is this.

Acrylic pressure-sensitive adhesive in the present invention is composed of an acrylic polymer, isocyanate curing agent, silane coupling agent and has a suitable physical properties as a pressure-sensitive adhesive for the display and prepares the adhesive in consideration of the wetness improvement and light transmittance not previously used.

Acrylic adhesive polymerization can be prepared by solution polymerization, bulk polymerization and emulsion polymerization. In the case of bulk polymerization, it is difficult to control high viscosity and reaction heat, and emulsion polymerization has excessive impurities and weak transparency compared to solution polymerization. On the other hand, in the case of solution polymerization, transparency, viscosity and molecular weight can be controlled, and working conditions can be easily used as an adhesive for a display.

In the present invention, the experimental procedure follows the radical polymerization reaction step, and the ratio of the solvent, the main monomer, and the functional monomer is based on 1.7 to 1.9: 1: 0.05 to 0.09, and the initiator is prepared according to the above-described content, and the step is the first step in 4 steps. (Solvent 35-50%, Initiator 20-30%, Jumonomer 35-45%, Functional monomer 35-45%), Feed 1 (Solvent 15-20%, Initiator 10-15%, Main monomer 55-65%, Preparation of adhesive by dividing functional monomer 55 ~ 65%), Feed 2 (solvent 15 ~ 20%, initiator 60 ~ 75%) and Feed 3 (solvent 25 ~ 40%). If it is not, the physical properties are somewhat lowered, and the three properties (holding force, initial adhesive force, cohesion force) as general adhesives are not satisfied as well as for display adhesives.

In the polymerization process for producing acrylic resin, the organic solvent, the acrylic monomer, and the polymerization initiator are dividedly added and the polymerization process is carried out step by step, so that the gel content of the acrylic resin is increased as compared to the batch polymerization method, thereby increasing the cohesive force of the adhesive. .

The present invention polymerizes for 6 hours and 30 minutes by adding an acrylic monomer and an initiator by solution polymerization, and the initiator uses BPO (benzoyl peroxide). BPO (benzoyl peroxide) is more compatible with acrylic copolymers than initiators such as AIBN (2,2-azobis (isobutyronitile)), has excellent light transmittance in the visible range, and has relatively high reactivity and polymerization. The time can be shortened and it is efficient in a process. In the case of AIBN, chromophores and chromophores are present, which may interfere with light transmission, and thus are not suitable as adhesives for displays. BPO (benzoyl peroxide) is used in an amount of 0.05 to 0.1 parts by weight based on 100 parts by weight of an acrylic monomer. If too small, the viscosity increases and the workability decreases. When used in a large amount, the molecular weight decreases, which may affect cohesion.

When the acrylic adhesive is ultrasonicated, the viscosity is lowered and the wettability of the film is improved. Although the influence of temperature can not be ignored during the ultrasonic treatment, high wettability cannot be obtained only by the temperature, and the intermolecular entanglement is reduced to have better wettability. The ultrasonic treatment was performed at 40 to 60W, and when the ultrasonication was too high or the ultrasonication was performed for a long time, the viscosity was increased, the wettability was reduced, and the molecular structure could be deformed, thereby inhibiting the inherent properties of the acrylic adhesive.

A silane coupling agent and an isocyanate curing agent are used in the acrylic polymer prepared by the solution polymerization. First, the silane coupling agent is used as an inorganic surface treatment and an inorganic-organic adhesion improving agent, and induces an improvement in adhesion to the liquid crystal cell, which is an adhesive, and also has a light transmittance. Increase. Isocyanate curing agents are chemical crosslinks that perform crosslinking between molecules and increase cohesion. In the present invention, methacryloxypropyltrimethoxy silane having excellent reactivity with the acrylic copolymer is used, and 0.5 to 1.2 parts by weight is used with respect to 100 parts by weight of the acrylic polymer. And the isocyanate is mixed with 0.5 to 1.2 parts by weight with respect to 100 parts by weight of the acrylic polymer using tolylene diisocyanate, and adjusts the degree of crosslinking according to the content of the isocyanate with a gel content of 38% to 98%.

In the present invention, an acrylic polymer is prepared by using an acrylic monomer and an initiator by solution polymerization, and an ultrasonic treatment is performed to increase the wettability and to prepare an acrylic adhesive including a curing agent and a silane coupling agent.

Ultrasonic irradiation of the solution-based acrylic polymer is thought to function to release the aggregation state between molecules. The stronger the aggregation state between molecules, the higher the viscosity and the poor workability. The lower the viscosity, the better the workability.

The acrylic pressure-sensitive adhesive reduces the defect rate, improves the production efficiency, and does not deform when subjected to light or heat, and thus is suitable for the display field, thereby expanding its use range.

Comparative example  One

<Production of Acrylic Resin>

109 g of ethyl acetate (solvent) is injected into a reactor equipped with a nitrogen gas reflux device, a temperature control device and a cooling device for controlling the exothermic reaction, and 25 g of 2-ethylhexyl acrylate, 50 g of butyl acrylate and silver acrylate. 3.5 g, A75N (2,2-azobis (isobutyronitile)) 0.075g is stirred at 80 ℃ for 6 hours 30 minutes. The conversion of monomers to polymers was 90%.

TABLE 2

Total (g) EAc ^{1 )} 109 2-EHA ^{2 )} 25 BA ^{3 )} 50 AA ^{4 )} 3.5 AIBN ^{5 )} 0.075 Polymerization time 6 hours 30 minutes   1) EAc: ethyl acetate 2) 2-EHA: 2-ethylhexyl acrylate 3) BA: butyl acrylate 4) AA: acrylic acid 5) AIBN: azobis isobutyrol nitrile

<Production of Acrylic Resin Adhesive>

 An acrylic pressure-sensitive adhesive was prepared by uniformly mixing 1.2 g of an isocyanate-based curing agent and 1 g of methacryloxypropyltrimethoxy silane, which is a silane coupling agent, to 100 g of the acrylic resin prepared in the above process.

Comparative example  2

<Production of Acrylic Resin>

109 g of ethyl acetate (solvent) was injected into a reactor equipped with a reflux device, a temperature controller and a thermometer for controlling the exothermic reaction, and nitrogen gas, 25 g of 2-ethylhexyl acrylate, 50 g of butyl acrylate, and acrylic acid. Silver 3.5g, 0.075g BPO (benzoyl peroxide) is stirred at 80 ℃ for 6 hours 30 minutes. The conversion of monomers to polymers was 90%.

TABLE 3

Total (g) EAc ^{1 )} 109 2-EHA ^{2 )} 25 BA ^{3 )} 50 AA ^{4 )} 3.5 BPO ^{5 )} 0.075 Polymerization time 6 hours 30 minutes   1) EAc: ethyl acetate 2) 2-EHA: 2-ethylhexyl acrylate 3) BA: butyl acrylate 4) AA: acrylic acid 5) BPO: benzoyl peroxide

<Production of Acrylic Resin Adhesive>

An acrylic pressure-sensitive adhesive was prepared by uniformly mixing 1.2 g of isocyanate-based curing agent and 1 g of methacryloxypropyltrimethoxy silane, which is a silane coupling agent, to 100 g of the acrylic resin prepared in the above process.

Comparative example  3

<Production of Acrylic Resin>

109 g of ethyl acetate solvent is injected into a reactor equipped with a reflux device, a temperature controller and a thermometer for controlling the exothermic reaction, and nitrogen gas, 25 g of 2-ethylhexyl acrylate, 50 g of butyl acrylate, and 3.5 of acrylic acid. g, BPO (benzoyl peroxide) 0.075g is stirred at 80 ℃ for 8 hours. The conversion of monomers to polymers is 96%.

TABLE 4

Total (g) EAc ^{1 )} 109 2-EHA ^{2 )} 25 BA ^{3 )} 50 AA ^{4 )} 3.5 BPO ^{5 )} 0.075 Polymerization time 6 hours 30 minutes   1) EAc: ethyl acetate 2) 2-EHA: 2-ethylhexyl acrylate 3) BA: butyl acrylate 4) AA: acrylic acid 5) BPO: benzoyl peroxide

<Production of Acrylic Adhesive>

 An acrylic adhesive was prepared by uniformly mixing 1.2 g of an isocyanate curing agent and 1 g of methacryloxypropyltrimethoxy silane, which is a silane coupling agent, to 100 g of the acrylic adhesive prepared in the above process.

In preparing an acrylic adhesive by polymerizing an acrylic monomer, various kinds of acrylic monomers are generally mixed and used in consideration of physical properties such as adhesiveness, flexibility, cohesion, and strength related to the use of the adhesive.

In this field, the acrylic monomer forming the main chain of the pressure-sensitive adhesive resin is called the main monomer, and the acrylic monomer used in connection with the physical property control having the -OH and -COOH columns is called the functional monomer.

In the above examples and comparative examples, the main monomer is butyl acrylate and 2-ethylhexyl acrylate and acrylic acid are functional group acrylates.

Experimental Method

Iii. Light transmittance

The glass substrate (50mm x 50mm x 5mm) is coated with an adhesive to 100μm to measure the transmittance in the visible range.

Ii. Wettability

The adhesive is coated on a glass substrate (50mm × 50mm × 5mm) with 100μm, and water is dropped to measure and evaluate the relative wetting energy more than 5 times.

Iii. Peel-off Evaluation

 After forming a pressure-sensitive adhesive having a thickness of 30μm on the polarizing plate, and attaching a protective film and a release film on each side of the polarizing plate. The polarizing plate of the laminated structure is cut to a size of 25 mm x 75 mm and laminated on a glass substrate and left for 48 hours at 80 ° C. to observe whether or not a part is peeled off the glass substrate.

Iii. Bubble outbreak

 After forming a pressure-sensitive adhesive having a thickness of 30μm on the polarizing plate, and attaching a protective film and a release film on each side of the polarizing plate. The polarizing plate is constantly cut into a size of 25 mm x 75 mm, laminated on a glass substrate, left at 80 ° C. for 48 hours, and observed for bubble generation on the glass substrate.

Iii. Glass Warrior

 After forming a pressure-sensitive adhesive having a thickness of 30μm on the polarizing plate, and attaching a protective film and a release film on each side of the polarizing plate. The polarizing plate is constantly cut into a size of 25 mm × 75 mm, laminated on a glass substrate, left at 25 ° C. for 48 hours, detached from the glass substrate, and observed for remaining on the glass substrate.

[Table 5] Comparison of physical properties of the prepared pressure-sensitive adhesive

Measure Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Light transmittance (%) 98 88 91 91 Wetting (mN / m) 18.4 15.6 15.3 14.9 Peelability radish radish radish radish Bubble radish U U radish Glass Transfer radish radish U radish

According to the said Table 5, in the case of the acrylic adhesive of Example 1 which concerns on this invention, it has a physical property superior to the thing of a comparative example, and is preferable as an adhesive for polarizing plates. Particularly, in Comparative Example 1, bubbles are generated and free transcription occurs, and molecular weight is also very low, which greatly increases the defect rate.

Acrylic adhesive for polarizing film produced by the method of the present invention has an excellent light transmittance and wettability.

Claims (3)

In the method for producing a liquid acrylic resin by heat-polymerizing an acrylic monomer and a polymerization initiator in an organic solvent and adding and mixing a curing agent or a coupling agent to the acrylic resin solution, Initial polymerization is carried out when the weight ratio of the organic solvent, the acrylic main monomer and the acrylic functional monomer is 1.7 to 1.9: 1.0: 0.05 to 0.07, and the polymerization initiator is added to the acrylic main monomer to prepare the acrylic resin by adding 0.1 to 0.2 wt%. 30 ~ 50wt% of organic solvent, 20 ~ 30wt% of polymerization initiator, 55 ~ 65wt% of acryl main monomer, 35 ~ 45wt% of functional group monomer based on total requirement in stage, and organic 15-20 wt% of solvent, 10-15 wt% of polymerization initiator, 35-45 wt% of acryl main monomer, 35-45 wt% of acryl functional group monomer were added to polymerize in two stages, 15-20 wt% of organic solvent, 60-75 wt of polymerization initiator % Was added to polymerize in three stages, and 25-40 wt% of solvent was added thereto to divide the raw material input into multiple stages to prepare a solution acrylic resin by stepwise polymerization. The solution acrylic resin was irradiated with ultrasonic waves, and then a curing agent and Add and mix coupling agent Method for producing an acrylic pressure-sensitive adhesive for the film. The method of claim 1, The organic solvent is ethyl acetate, the acryl main monomer is selected from butyl acrylate, methyl acrylate, methyl ethyl acrylate and propyl acrylate, and the acrylic functional monomer is selected from acrylic acid and 2-ethylhexyl acrylate, and a polymerization initiator Is a benzoyl peroxide, the curing agent is selected from an isocyanate compound or an epoxy compound, and the coupling agent is a method for producing an acrylic pressure-sensitive adhesive for polarizing film, which is a silane compound. The method of claim 2, Isocyanate compound is selected from diphenylmethane diisocyanate, xylene diisocyanate, isophorone diisocyanate or toluene diisocyanate, epoxy compound is selected from polyethylene glycol, diglycidyl ether or trimethylolpropane, triglycidyl ether A method for producing an acrylic pressure-sensitive adhesive for polarizing film wherein the silane compound is selected from vinyltrimethoxysilane, vinyltriethoxysilane, methacrylatesilane or methacryloxypropyl, and trimethoxysilane.

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