KR20110076179A - Method for drying polarizing plate - Google Patents

Abstract

PURPOSE: A method for drying a polarization plate is provided to improve frequent generation of spots in a protection film asymmetry type polarization plate. CONSTITUTION: A protection film has moisture vapor permeability of 500g/m^2 at 40°C and 90%RH. The protection film is dried by a non-contact method so as to include a water-based adhesive of 40 weight%. The protection film is attached on the polarization plate by using the water-based adhesive. The polarization plate dried through the non-contact method is inserted between high-temperature rolls.

Description

Drying method of polarizing plate {METHOD FOR DRYING POLARIZING PLATE}

The present invention relates to a method of drying a polarizing plate that can improve unevenness due to polarizers that tend to occur in a protective film asymmetric polarizing plate.

The polarizing plate is widely used as a supply element of polarization in a liquid crystal display device, and as a detection element of polarization.

In general, a polarizing plate is a cellulose acetate type represented by a transparent protective film such as triacetylcellulose (TAC) through an adhesive on both sides of a polarizer made of polyvinylalcohol (PVA) -based resin in which a dichroic dye is adsorbed and oriented. The protective film has a laminated structure.

Recently, in order to express unusual optical properties, there has been an increasing number of polarizing plates on which protective films having different physical properties and the like are disposed on both surfaces of the polarizer. In particular, there are many cases of using a protective film having a low water vapor transmission rate. In this case, there is a problem in that staining due to the polarizer is severely generated when contact drying is carried out between the rolls.

In order to solve this problem, Korean Patent Laid-Open Publication No. 2006-80541 has proposed a technique that improves the appearance and file by adjusting the drying temperature range, but there is a limit that does not suppress the generation of spots due to the polarizer.

In order to express various optical characteristics through the liquid crystal display device, it is urgent to propose a method of suppressing occurrence of polarizer-derived stains in a drying step.

An object of the present invention is to provide a method for drying a polarizing plate that can improve the occurrence of frequent stains in the protective film asymmetric polarizing plate.

Another object of the present invention is to provide a method capable of reducing a defective rate of a polarizing plate by suppressing spots.

In the method for drying a polarizing plate according to the present invention, when the water-based adhesive is applied to a polarizing plate on which a protective film having a moisture permeability of 500 g / m ² · or less at 40 ° C. and 90% RH is bonded with an aqueous adhesive, the moisture of 40% or less of the adhesive weight is applied. Contactless drying to include; And contact drying by passing the non-contact dried polarizing plate between the hot rolls.

The protective film having a water vapor transmission rate of 500 g / m ² or less may include a polyester film, a styrene film, a polycarbonate film, a cycloolefin film, a polyolefin film, a vinyl chloride film, an amide film, and a sulfone film. , Polyether sulfone film, polyether ether ketone film, polyphenylene sulfide film, vinyl alcohol film, vinylidene chloride film, vinyl butyral film, allylate film, polyoxymethylene film, epoxy The acrylic film, the acrylic film, the urethane film, the acrylic urethane film, the epoxy film, the silicone film, and the acetyl cellulose film are selected from the group consisting of the surface treated films.

The polarizing plate may be provided with a protective film having a moisture permeability of 500 g / m ² · day or less on one side of the polarizer, and an acetyl cellulose protective film on the other side.

Here, the non-contact drying may be performed such that the water-based adhesive contains 20-40% of the weight of the adhesive when applied.

In addition, non-contact drying may be performed by hot air.

In addition, the non-contact drying may be carried out at a temperature of 50-80 ℃.

The time that the polarizing plate is in contact with the hot roll may be 35% or less of the total drying time after non-contact drying.

Here, the contact drying temperature may be 80 ℃ or more.

The present invention has an effect that can improve the stain generated when manufacturing a protective film asymmetric polarizing plate in an economical manner.

The present invention evenly spreads the moisture during drying, and by minimizing the roll contact with the polarizing plate has an effect that can prevent the film damage due to contact as well as the occurrence of stains.

The present invention can contribute to the development of a liquid crystal display device having various optical characteristics.

The present invention is a non-contact drying of the polarizing plate bonded to the protective film is a water-based adhesive protective film having a water vapor transmission rate of 500g / m ² · days or less at 40 ℃ and 90% RH so that the water-based adhesive contains 40% or less of the weight of the adhesive It relates to a drying method of the polarizing plate that can improve the defect rate in the protective film asymmetric polarizing plate that is easy to cause stains resulting from the polarizer by passing through the step and contact-dried between the non-contact dried polarizing plate between the hot rolls.

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

In the polarizing plate of the present invention, a protective film having a water vapor transmission rate at 40 ° C. and 90% RH of 500 g / m ² · day or less is bonded with an aqueous adhesive. One of the protective films includes a case where the moisture permeability is 500 g / m ² · day or less, and the two protective films have a moisture permeability of 500 g / m ² · day or less.

The polarizer is a dichroic dye adsorbed on the stretched polyvinyl alcohol-based film. The polyvinyl alcohol-based resin constituting the polarizer can be produced by saponifying a polyvinyl acetate-based resin. As an example of polyvinyl acetate type resin, the copolymer etc. with vinyl acetate and the other monomer copolymerizable with this besides the polyvinyl acetate which is a homopolymer of vinyl acetate are mentioned. Specific examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, acrylamides having an ammonium group, and the like. In addition, the polyvinyl alcohol-based resin may be modified, for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of saponification of the polyvinyl alcohol-based resin may be 85 to 100 mol%, preferably 98 mol% or more. In addition, the degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

A protective film having a water vapor transmission rate of 500 g / m ² · day or less at 40 ° C. and 90% RH means that the protective film is made of a material having a lower moisture permeability than a triacetyl cellulose film that is usually used as a protective film. It is mechanically weak and serves to protect it. When the retardation film performs the role of a polarizer protective film, the retardation film is also considered to belong to the protective film of the present invention.

For example, polyester polymers, such as polyethylene terephthalate (PET) resin, polyethylene naphthalate, acrylic polymers, such as polymethylmethacrylate, styrene polymers, such as polystyrene and an acrylonitrile-styrene copolymer (AS resin), and polycarbonate Amides such as cycloolefin-based resins (COP) or polyolefins having a norbornene structure, polyolefin-based polymers such as ethylene-propylene copolymers, vinyl chloride-based polymers, nylon and aromatic polyamides Type polymer, sulfone type polymer, polyether sulfone type polymer, polyether-ether ketone type polymer, polyphenylene sulfide type polymer, vinyl alcohol type polymer, vinylidene chloride type polymer, vinyl butyral type polymer, allylate type polymer, poly Oxymethylene-based polymers, epoxy-based polymers, blends of these polymers A film made of a resin which is used alone or in combination with a blend polymer, acrylic, urethane, acrylic urethane, epoxy, silicone, and the like, or acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose. Includes films that have been surface treated (liquid crystal coating, AG, LR treatment, etc.).

On one side of the polarizer, a protective film having a moisture permeability of 500 g / m ² · day or less at 40 ° C. and 90% RH is used, and on the other side, a polarizing plate equipped with an acetylcellulose-based protective film may also be prepared by the present invention.

Although it is preferable that the thickness of a protective film is thin, when too thin, intensity | strength falls and it is inferior to workability, On the other hand, when too thick, problems, such as transparency fall or the hardening time required after lamination | stacking arise, etc. do. Therefore, the suitable thickness of a protective film is about 5-200 micrometers, for example, Preferably it is about 10-150 micrometers, More preferably, it is about 20-100 micrometers.

The protective film may contain appropriate one or more additives. Specific examples of the additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, colorants, flame retardants, nucleating agents, antistatic agents, pigments, colorants, and the like.

In the present invention, the polarizer and the protective films are bonded with an aqueous adhesive. The aqueous adhesive basically comprises a polyvinyl alcohol resin, a crosslinking agent and water.

Polyvinyl alcohol-based resin, which is one of the components of the aqueous adhesive, is a vinyl polymer resin and is excellent in adhesion with a polyvinyl alcohol-based polarizer. In order to improve the durability of the polarizing plate, a polyvinyl alcohol resin containing acetoacetyl group is preferable, and a carboxyl group-modified polyvinyl alcohol resin containing a highly reactive functional group is preferable in order to improve the adhesiveness and moisture-heat resistance of the adhesive composition.

The degree of polymerization and the degree of saponification of the polyvinyl alcohol-based resin are not particularly limited. It is preferable that the average degree of polymerization is 100 to 3,000 and the average degree of saponification is 85 to 100 mol% in consideration of adhesion.

The crosslinking agent may be a conventional crosslinking agent to improve the water resistance and durability of the adhesive. Specific examples of the crosslinking agent include aldehyde compounds such as formaldehyde, glyoxal, and glutaraldehyde as organic crosslinking agents; Methylol group-containing compounds such as urea resin, guanamine resin and methylolmelamine; Glycidyl group-containing compounds such as amino resins, water-soluble epoxy resins, and polyaminopolyamide-epichlorohydrin; Amine compounds such as ethylenediamine, hexamethylenediamino, methaxylenediamine, 1,3-bisaminocyclohexane, polyoxyalkylenediamine, polyamine; Hydrazide compounds such as adipic acid hydrazide, carbodiazide, and polyacrylic acid hydrazide; Isocyanate compounds, such as polyisocyanate and block isocyanate; Hydrazine compounds; Boron compounds such as boric acid and borax as acid anhydrides and inorganic crosslinking agents; Zirconium compounds, such as chlorohydroxyoxo zirconium, zirconyl nitrate, and zircosol; Titanium compounds such as tetra alkoxychiterate and water-soluble titanium compounds; Aluminum compounds such as aluminum sulfate, aluminum chloride and aluminum nitrate; Phosphoric acid compounds such as phosphite ester and bisphenol A-modified polyphosphoric acid; And a silicon compound having a reactive functional group such as an alkoxy group or glycidyl group.

The aqueous adhesive composition may include 1 to 10 parts by weight of a polyvinyl alcohol-based resin, and 1 to 100 parts by weight of a crosslinking agent based on 100 parts by weight of polyvinyl alcohol-based resin (based on solids content) based on 100 parts by weight of water. When the content of the crosslinking agent is less than 1 part by weight based on 100 parts by weight of the polyvinyl alcohol-based resin, the heat and moisture resistance may be weak, and when the content of the crosslinking agent is greater than 100 parts by weight, the adhesive strength may be lowered.

The adhesive for bonding the polarizer and the protective film is applied to either side of the polarizer and the protective film or both. The coating operation is not particularly limited, and various methods such as a roll method, a spray method, and a dipping method can be used. It is preferable to apply the adhesive layer so that the thickness of the adhesive layer formed after drying in consideration of the content of solid content is 10 to 1000 nm, preferably 40 to 600 nm. If the thickness is less than 10nm, the adhesion may be poor, if the thickness is greater than 1000nm it may be difficult to uniformly apply the adhesive or the appearance of the thickness unevenness. In addition, when the polarizer and the protective film is bonded, the tension may be applied to the protective film, but the tension is preferably as low as possible because the deformation is applied to the protective film.

After applying the adhesive, the polarizer and the protective film are bonded by a roll laminator or the like. After bonding the polarizer and the protective film, a drying process is performed to form an adhesive layer comprising a coating dry layer.

The drying process of the present invention is 40% or less of the weight of the adhesive when the aqueous adhesive is applied to the polarizing plate bonded with a water-based adhesive protective film having a water vapor transmission rate of 500 g / m ² · or less at 40 ℃ and 90% RH, preferably 20 Non-contact drying to contain -40% moisture and contact-drying the non-contact dried polarizing plate through a hot roll.

Non-contact drying does not require the polarizing plate to be dried under certain conditions if the aqueous adhesive can be made to contain 40% or less, preferably 20-40%, moisture of the adhesive when applied. The degree of non-contact drying is confirmed through the moisture content of the water-based adhesive as described above, and the water content of the water-based adhesive may be 40% or less of the total weight (100% by weight) of the water-based adhesive when the water-based adhesive is applied. For example, the moisture content change of the water-based adhesive due to non-contact drying is from 98% by weight to 40% by weight or less, preferably 20-40% by weight after drying.

As the non-contact drying method, for example, the drying temperature may be performed at 80 ° C. or lower, preferably 50 to 80 ° C., using hot air. The drying time may be usually 20 to 1200 seconds, but it is preferable that the drying time is as short as possible in order to improve productivity.

In the present invention, by going through the above steps before drying with a high-temperature roll it is possible to prevent the sublimation of the dichroic iodine contained in the polarizer and the stain due to the dry imbalance. In non-contact drying, a roll including a guide roll or the like is used to prevent contact with the polarizing plate.

After non-contact drying, the polarizing plate containing 40 wt% or less of moisture is contact dried while passing between hot rolls. Due to the non-contact drying step, the time for contacting the rolls during contact drying is shortened.

The time that the polarizer is in contact with the roll is directly related to the occurrence of spots. If the contact time is 35% or less in the absence of the non-contact step, no staining of the polarizing plate occurs. It is desirable to reduce the roll contact time as much as possible so that the final moisture content of the polarizing plate is 1-10% by weight.

The contact drying temperature is preferably 80 ° C. or higher, such as 80-130 ° C.

In the polarizing plate of the present invention, a surface coating layer such as a hard coating layer, an antireflection layer, an antifouling layer, a diffusion layer, and an antiglare layer may be further laminated on the other side of the protective film not bonded with the polarizer. In addition, the optical functional film may be further laminated by the pressure-sensitive adhesive layer.

The hard coating layer is performed to prevent damage to the surface of the polarizing plate, for example, a cured coating film having excellent hardness, sliding properties, etc. formed by a system for adding a suitable ultraviolet curable resin such as a silicone resin to the surface of the protective film. have. In addition, the antireflection layer is performed for the purpose of preventing external light from being reflected from the surface of the polarizing plate. The antireflective layer can be achieved by forming an antireflective film according to the prior art. In addition, the anti-stick layer is performed for the purpose of preventing the protective film from being in close contact with the adjacent layer. The anti-glare layer is performed to prevent the visual perception of light transmitted through the polarizer from being inhibited by external light reflected from the surface of the polarizing plate, for example, a roughening system or a transparent particle mixing system using sand blasting, embossing, or the like. Etc., the micro-corrugated structure can be imparted to the surface of the protective film. Transparent particles have an average particle size of 0.5 to 20㎛, specific examples include particles made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like. In addition, the transparent particles may use inorganic fine particles having conductivity or organic fine particles made of a crosslinked or uncrosslinked granular polymer or the like. The transparent particles are 2 to 70 parts by weight, preferably 5 to 50 parts by weight with respect to 100 parts by weight of the resin. The anti-glare layer containing the transparent fine particles may be provided as the protective film itself or as a coating layer applied to the surface of the protective film. The anti-glare layer can also function as a diffusion layer (viewing angle compensation function, etc.) that expands the viewing angle by diffusing light transmitted through the polarizing plate.

The polarizing plate manufactured by the manufacturing method of the present invention can be used in a liquid crystal display device. The liquid crystal display device may be manufactured by peeling a release film of a pressure-sensitive adhesive polarizing plate and then attaching an adhesive layer to a liquid crystal panel.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is apparent that the embodiments are merely examples of the present invention and do not limit the scope of the present invention. It is natural that modifications and variations of the embodiments fall within the scope of the present invention without departing from the basic technical spirit of the present invention.

[Example]

1. Experiments to Identify Conditions and Mechanisms Related to Speckle Generation Due to Polarizers

(1) Influence by the difference of drying temperature and moisture content

A polarizer is placed between two protective films having a water vapor permeability of 500 g / m ² · day or less, a water-based adhesive is introduced at each interface, and non-contact drying is carried out in an oven set at 80 ° C. and 100 ° C., respectively, to confirm the occurrence of stains. The polarizer origin stain in the state was confirmed.

Time / temperature 100 ℃ 80 ℃ Moisture content (%) Stain or not Moisture content (%) Stain or not Undried 3.82 X 4.85 X 1 minute Before drying 4.65 X 3.86 X after drying 4.33 X 3.40 X 5 minutes Before drying 4.49 X 5.11 X after drying 2.66 X 3.25 X 10 minutes Before drying 5.14 X 5.06 X after drying 2.76 X 2.75 X

As shown in the above table, staining did not occur even when the polarizing plate was dried at a high temperature of 100 ° C. as well as 80 ° C., and there was no difference in whether staining occurred depending on the initial moisture content of the polarizing plate. Therefore, it was judged that spots due to the polarizer did not occur depending on the drying temperature or the initial moisture content. In addition, since the polarizing plates had a water content of less than 10%, staining due to polarizers did not occur even when they were in contact with the thermal rolls, respectively.

(2) Influence by contact heating time after application of water-based adhesive

A polarizer was put between two protective films having a water vapor transmission rate of 500 g / m ² · day or less, and an aqueous adhesive was added to each interface, and then immediately placed between 110 ° C. hot rolls to check for spots while adjusting the roll rotational speed. Since the length of the drying furnace was the same, when the roll rotation speed was slow, it could be seen that roll contact time was long.

Roll Rotational Speed (rpm) Moisture content (%) Roll contact time / residence time with drying Stain or not 2 5.17 50% Ο 5 5.14 20% X

As shown in the above table, staining occurred according to the time of contact with the hot roll, and the longer the contact time was, the more severe the staining was confirmed. Based on the above experiments, it was found that staining occurs when the roll contact time exceeds 35% of the residence time at a high temperature of 80 ° C. or higher.

(3) the mechanism of staining

In order to confirm whether the stain generated above is due to the polarizer, the protective film was removed from the polarizing plate, and the single transmittance (%) and the color value of each spot were measured (see FIG. 2).

Measuring position Group transmittance (%) color Group a Group b Dark parts 7.42 -0.59 1.53 light 14.66 -0.93 2.3

According to the above results, there was a difference in the local moisture content of the contact portion of the roll showing the difference in the color value and the transmittance of iodine. High water content part is due to the amount of more water becomes a lower transmittance than the low-water content portions iodine sublimation is slow in the drying step, I ₃ ^- relative compared ^to-a is weak to water, I ₅ as the water is dried It was judged that the amount was reduced to decrease the b value.

2. Initial moisture content setting experiment to prevent staining

(1) Preparation of polarizer

A 75 μm-thick polyvinyl alcohol (PVA) film having a degree of polymerization of 2,400 and a saponification degree of 99.9 mol% or more was uniaxially stretched by about 6 times in the previous step, and the weight ratio of iodine / potassium iodide / distilled water was 0.05 / 5. Dyeing step immersed for 60 seconds in an aqueous solution of 30 ℃ / 100, then crosslinking step immersed for 300 seconds in a 53 ℃ aqueous solution having a weight ratio of potassium iodide / boric acid / distilled water for 8.5 / 8.5 / 100, distilled water of 40 ℃ A polarizer having iodine adsorbed on a PVA film was prepared through a washing step of washing for 20 seconds and a drying step of drying at 70 ° C.

(2) Preparation of protective film

One side of a norbornene-based film (Japan Zeon, trade name "ZEONOR", 50 µm) was corona-treated at a discharge amount of 1000 w · min / m 2 to prepare a protective film having a water vapor transmission rate of 250 g / m 2 · day.

In addition, a triacetyl cellulose film having a water vapor permeability of 900 g / m 2 · day subjected to a saponification process having a thickness of 80 μm was prepared.

(3) Preparation of Polarizing Plate

When the norbornene-based film and / or triacetyl cellulose film is bonded to both sides of the polarizer prepared above with an aqueous adhesive, and then contactlessly dried at 80 ° C. or less, when the moisture content of the polarizing plate (initial moisture of the injected aqueous adhesive is 100% by weight) The samples of Examples 1-3 and Comparative Examples 1-2, each having a weight of 20%, 30%, 40%, 50%, and 65% by weight, respectively, were prepared according to the rate at which the moisture was reduced by drying. .

(4) Water content setting to prevent spots

The samples of Examples 1-3 and Comparative Examples 1-2 were each put between hot rolls at 110 ° C., and the staining in each sample was checked while maintaining the contact time with the hot rolls at 30% during the residence time. . The results are shown in Table 4 below.

division Moisture content (%) Smudges occur Example 1 20 X Example 1 30 X Example 1 40 X Comparative Example 1 50 Ο Comparative Example 2 65 Ο

As shown in the above table, staining did not occur when the moisture content of the polarizing plate before contacting the roll was 40% by weight or less, and staining occurred when the moisture content was more than 40% by weight. Among these, the photographs of stains of Example 1 and Comparative Example 1 are as shown in FIGS. 3 and 4.

The present invention can be effectively applied to the field of producing high quality polarizers by clearly identifying the cause of staining in the drying process of the polarizer and adjusting the total amount of water and its distribution in a simple and easy manner before drying at high temperatures.

1 is a diagram conceptually illustrating a method of drying a polarizing plate of the present invention.

2 is a diagram of a schematic image and measurement point of a spot generating polarizer.

3 is a photograph of a polarizing plate of Example 1. FIG.

4 is a photograph of a polarizing plate of Comparative Example 1. FIG.

Claims (8)

Non-contact drying the polarizing plate on which the protective film having a water vapor transmission rate at 40 ° C. and 90% RH of 500 g / m ² · day or less is bonded with the water-based adhesive so that the water-based adhesive contains water of 40% or less of the adhesive weight when the water-based adhesive is applied; And contact-drying the non-contact dried polarizing plate through a hot roll. The protective film of claim 1, wherein the protective film having a water vapor transmission rate of 500 g / m ² · day or less includes a polyester film, a styrene film, a polycarbonate film, a cycloolefin film, a polyolefin film, a vinyl chloride film, an amide film, Sulfone film, polyether sulfone film, polyether ether ketone film, polyphenylene sulfide film, vinyl alcohol film, vinylidene chloride film, vinyl butyral film, allylate film, polyoxymethylene A method for drying a polarizing plate, which is a film selected from the group consisting of a film, an epoxy film, an acrylic film, a urethane film, an acrylic urethane film, an epoxy film, a silicon film, and an acetyl cellulose film. The method of claim 1, wherein the polarizing plate is provided with a protective film having a moisture permeability of 500 g / m ² · or less on one surface of the polarizer and an acetyl cellulose protective film on the other surface. The method of claim 1, wherein the non-contact drying is performed such that the water-based adhesive contains 20-40% of the weight of the adhesive when applied. The method of claim 1 or 4, wherein the non-contact drying is performed by hot air. The method of claim 1, wherein the non-contact drying is performed at a temperature of 50-80 ° C. 6. The method according to claim 1, wherein the time that the polarizing plate is in contact with the hot roll is 35% or less of the total drying time after non-contact drying. The method for drying a polarizing plate according to claim 1, wherein the contact drying temperature is 80 ° C. or higher.

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