WO2012011678A2 - Method for fabricating a polarizer - Google Patents

Abstract

The present invention relates to a method for fabricating a polarizer, and more particularly, to a method for fabricating a polarizer which includes a cross-linking operation of immersing a polyvinyl alcohol-based film in a cross-linking aqueous solution containing a compound having an aldehyde group and a carboxy group. Accordingly, the film has excellent optical characteristics, and is prevented from being torn and wrinkled. In addition, the area of the film can be increased, and the thickness thereof can be decreased. Furthermore, the polarizer is highly stable dimensionally in the width and longitudinal directions thereof. Moreover, the characteristic odors of aldehydes are offset to thereby improve processability and productivity.

Description

Manufacturing method of polarizer

The present invention relates to a method of manufacturing a polarizer having excellent optical properties, preventing rupture and wrinkles of a film even when stretched at a high draw ratio, manufacturing a polarizer having high dimensional stability, and improving process handling and production efficiency.

In order to provide images with high brightness and excellent color reproducibility to various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP) and field emission display (FED), Constant research has been conducted. In particular, as the field of application of the image display device expands rapidly, the demand for large area and thinning of the polarizing plate is increasing, and at the same time, as the environment to be used is diversified, the dimensional stability is secured under various durability conditions. It turns out that it is an important factor in.

Conventionally, most polarizers are prepared by swelling, dyeing, crosslinking, stretching, washing, and drying a polymer film such as a polyvinyl alcohol (PVA) film, and in the crosslinking step, an inorganic crosslinking agent such as a boron compound is usually used. Was mainly used. However, when only the inorganic crosslinking agent is used, the crosslinking chain is short and the neck-in ratio is increased by the high stretching process, which causes the polarizer to become thick and narrow, resulting in breakage and heat resistance. Under the disadvantages of poor dimensional stability, process efficiency is also low.

In order to solve this problem, a method of using an organic crosslinking agent in addition to the boron compound has been proposed.

Japanese Laid-Open Patent Publication No. 2007-122050 discloses a method for producing a polarizer by stretching a film at a high draw ratio having a total cumulative draw ratio of 6 times or more in a bath containing dicarboxylic acid. In this method, however, fracture occurs due to the high stretching process, residual stress is generated in the film, and the dimensional stability is also drastically lowered. In addition, the flexibility and elongation is excessively increased so that the handleability is significantly deteriorated, such as wrinkles in the width direction immediately before the drying step such as water washing or complementary color step, resulting in a deterioration of the display quality.

In addition, Japanese Laid-Open Patent Publication No. 2008-158020 discloses a method of crosslinking treatment using trialdehyde. However, trialdehyde is easy to oxidize in the air due to its high reactivity and reducibility, and it is difficult to secure dimensional stability in the width direction and the length direction because the cross-linking reaction does not occur effectively. Hard to apply to

The present invention is to provide a method of manufacturing a polarizer that is excellent in optical properties, can prevent breakage and wrinkles of the film, as well as large area and thin film, and can increase the dimensional stability in the width direction and length direction do.

In addition, the present invention is to provide a method of manufacturing a polarizer that can improve the handling and production efficiency when applied to the actual process.

In addition, the present invention is to provide a polarizer manufactured by the manufacturing method.

In addition, the present invention is to provide a polarizing plate including the polarizer and an image display device provided with the polarizing plate.

In order to achieve the above object, a method of manufacturing a polarizer of the present invention includes a crosslinking step of immersing a polyvinyl alcohol-based film in an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group.

In addition, the compound having an aldehyde group and a carboxyl group may be an aliphatic compound or an alicyclic compound.

In addition, the aliphatic compound may be at least one selected from the group consisting of glyoxalic acid, 4-oxo-2-butenoic acid and 2-methyl-3-oxopropanoic acid.

In addition, the aliphatic compound may be glyoxalic acid.

In addition, the alicyclic compound is selected from the group consisting of 4-formyl-cyclohexanecarboxylic acid, 4-formyl-2-methyl-3-furancarboxylic acid and 5-formyl-3-isoxazole carboxylic acid. It may be one or more selected.

In addition, the alicyclic compound may be 4-formyl-cyclohexanecarboxylic acid.

In addition, the compound having an aldehyde group and a carboxyl group may be included in 0.5 to 10% by weight relative to 100% by weight of the aqueous solution for crosslinking.

In addition, the compound having an aldehyde group and a carboxyl group may be included in 0.8 to 6% by weight based on 100% by weight of the aqueous solution for crosslinking.

In addition, the boron compound may contain 1 to 10% by weight based on 100% by weight of the aqueous solution for crosslinking.

In addition, the weight ratio of the compound having an aldehyde group and a carboxyl group to 1 part by weight of the boron compound may be 0.1 to 5.

In addition, the crosslinking step may be repeatedly performed two or more times.

In addition, the crosslinking step may be repeatedly performed two or more times using an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group and a boron compound.

In addition, the crosslinking step may be repeated two or more times the first crosslinking step using an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group, and the second crosslinking step using an aqueous solution for crosslinking containing a boron compound.

In addition, a second crosslinking step may be performed after the first crosslinking step, or a first crosslinking step may be performed after the second crosslinking step.

In addition, the present invention includes a polarizer produced by the above production method.

In addition, the present invention includes a polarizing plate in which a protective film is laminated on at least one surface of the polarizer.

In addition, the present invention includes an image display device provided with the polarizing plate.

According to the present invention, by applying an organic crosslinking agent containing a carboxyl group and an aldehyde group simultaneously in the compound, the optical properties are excellent and the breakage of the film does not occur even when the film is stretched at a high draw ratio, and thus the durability and the flexibility and stretchability of the film are improved. It is possible to manufacture a polarizer in which wrinkles are also prevented.

In addition, the present invention enables a large area and a thin film of the polarizer and at the same time improves the dimensional stability in the longitudinal direction (lateral direction) as well as the width direction (vertical direction).

In addition, the present invention can improve the handleability when applied to the actual process by offsetting the odor unique to the aldehyde group, it is possible to manufacture the polarizer in a stable and high production efficiency process.

The present invention relates to a method of manufacturing a polarizer having excellent optical properties, preventing rupture and wrinkles of a film even when stretched at a high draw ratio, manufacturing a polarizer having high dimensional stability, and improving process handling and production efficiency.

Hereinafter, the present invention will be described in detail.

The method of manufacturing a polarizer of the present invention includes a crosslinking step of immersing a polyvinyl alcohol-based film in an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group.

In the present invention, the polarizer means a conventional iodine-based polarizer in which iodine is adsorbed and oriented on the polymer film.

The polymer film for preparing the polarizer is not particularly limited as long as it is a dichroic material, that is, a film that can be dyed by iodine, and specifically, a polyvinyl alcohol film, a partially gumified polyvinyl alcohol film; Hydrophilic polymer films such as polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, partially gumified film thereof and the like; Or a polyene alignment film such as a dehydrated polyvinyl alcohol-based film, a dehydrochloric acid-treated polyvinyl alcohol-based film, or the like. Among them, polyvinyl alcohol-based films are preferred in that they are excellent in effect of enhancing uniformity in polarization degree and excellent in dyeing affinity for iodine.

Usually, the method of manufacturing a polarizer includes a swelling step, a dyeing step, a crosslinking step, an stretching step, a washing step and a drying step, and are mainly classified by the stretching method. For example, a dry drawing method, a wet drawing method, or the hybrid drawing method which mixed the said two types of drawing methods, etc. are mentioned. Hereinafter, the manufacturing method of the polarizer of the present invention will be described using the wet stretching method as an example, but is not limited thereto.

The remaining steps except the drying step are performed in a state in which a polyvinyl alcohol-based film is immersed in a constant temperature bath filled with at least one solution selected from several kinds of solutions.

In addition, the order of the steps and the number of repetitions are not particularly limited, and the steps may be performed simultaneously or sequentially, and some steps may be omitted. For example, the stretching step may be performed before the dyeing step or after the dyeing step, or may be performed simultaneously with the swelling step or the dyeing step.

The swelling step is immersed in a swelling tank filled with an swelling aqueous solution before dyeing the unstretched polyvinyl alcohol-based film, to remove impurities such as dirt or antiblocking agent deposited on the surface of the polyvinyl alcohol-based film, and polyvinyl alcohol It is a step for improving the physical properties of the polarizer by swelling the system film to improve the stretching efficiency and to prevent dyeing unevenness.

As the aqueous solution for swelling, water (pure water, deionized water) can be usually used alone, and when a small amount of glycerin or potassium iodide is added thereto, the processability can be improved together with the swelling of the polymer film. It is preferable that content of glycerin is 5 weight% or less with respect to 100 weight% of aqueous solutions for swelling, and content of potassium iodide is 10 weight% or less.

It is preferable that the temperature of a swelling tank is 20-45 degreeC, More preferably, it is 25-40 degreeC.

The execution time (swelling tank dipping time) of the swelling step is preferably 180 seconds or less, and more preferably 90 seconds or less. When the immersion time is within the above range, the swelling can be prevented from becoming saturated due to excessive swelling, preventing breakage due to softening of the polyvinyl alcohol-based film, and the adsorption of iodine is uniform in the dyeing step, thereby improving the degree of polarization. .

The stretching step may be performed together with the swelling step, wherein the stretching ratio is preferably about 1.1 to 3.5 times.

In addition, the swelling step may be omitted, and swelling may be performed simultaneously in the following dyeing step.

The dyeing step is a step of adsorbing iodine to the polyvinyl alcohol-based film by immersing the polyvinyl alcohol-based film in a dye bath filled with a dichroic material, for example, an aqueous solution for dyeing containing iodine.

The dyeing aqueous solution may include water, a water-soluble organic solvent or a mixed solvent and iodine thereof. The content of iodine is preferably 0.4 to 400 mmol / L, more preferably 0.8 to 275 mmol / L, and most preferably 1 to 200 mmol / L, based on 100% by weight of the aqueous solution for dyeing. In order to further improve dyeing efficiency, iodide may be further included as a dissolution aid. As iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. may be used alone or in combination of two or more thereof. Of these, potassium iodide is preferred in view of its high solubility in water. The content of iodide is preferably 0.010 to 10% by weight, more preferably 0.100 to 5% by weight based on 100% by weight of the aqueous solution for dyeing.

It is preferable that the temperature of a dye bath is 5-42 degreeC, More preferably, it is 10-35 degreeC. In addition, the immersion time of the polyvinyl alcohol-based film in the dyeing tank is not particularly limited, preferably 1 to 20 minutes, more preferably 2 to 10 minutes.

The drawing step may be performed together with the dyeing step, in which case the cumulative drawing ratio is preferably 1.1 to 4.0 times. In this specification, "cumulative draw ratio" represents the value of the product of draw ratios in each step.

The crosslinking step is a step of fixing the adsorbed iodine molecules by immersing the dyed polyvinyl alcohol-based film in an aqueous solution for crosslinking so that the dyeability by physically adsorbed iodine molecules is not lowered by the external environment. Dichroic dyes are not frequently eluted in a moisture resistant environment, but iodine is often dissolved or sublimed depending on the environment when the crosslinking reaction is unstable, so sufficient crosslinking reaction is required. In addition, in order to orient all polyvinyl alcohol molecules and iodine molecules located between the molecules to improve optical properties, the crosslinking step is important because it generally has to be drawn at the largest draw ratio in the crosslinking step.

In the present invention, by using a compound having an aldehyde group and a carboxy group at the same time as the organic crosslinking agent in the crosslinking step, it gives a long crosslinking and flexibility. In particular, by using an organic crosslinking agent having both an aldehyde group and a carboxyl group in the compound, wrinkle problems caused by the use of a compound containing only a carboxyl group can be prevented through an aldehyde crosslinking reaction, so that the thin film and the large area can be formed, thereby increasing the material utilization rate and dimensional stability. Can improve. In addition, it is possible to suppress the reaction between aldehydes generated when using a compound containing only an aldehyde group to increase the efficiency of the crosslinking reaction and to offset the aldehyde-specific odor through mutual reaction with the carboxyl group, which is advantageous when applied to the actual process. In addition, the crosslinking reaction is enhanced and the fixing efficiency of iodine is increased to improve the optical properties, and the breakage is suppressed, thereby improving the process handling and production efficiency.

The aqueous solution for crosslinking may include water, which is a solvent, and an organic crosslinking agent, and further include an organic solvent that is mutually soluble with water.

The organic crosslinking agent is a compound having an aldehyde group and a carboxyl group in the compound, and an aliphatic compound or an alicyclic compound may be used. The alicyclic compound has a higher iodine fixation efficiency than the aliphatic and is preferable for improving the optical durability of the polarizer.

Aliphatic compounds are, for example, oxoethanoic acid of formula 1, 4-oxo-2-butenoic acid of formula 2, 2-methyl-3-oxopro of formula 3 Panoic acid (2-methyl-3-oxopropanoic acid) etc. can be used individually or in mixture of 2 or more types. Among them, glyoxalic acid represented by the general formula (1), which is an aliphatic compound having one aldehyde group and one carboxyl group at both terminals, is more preferable.

[Formula 1]

[Formula 2]

[Formula 3]

The alicyclic compound is, for example, 4-formyl-cyclohexanecarboxylic acid of Formula 4, 4-formyl-2-methyl-3-furancarboxylic acid of Formula 5 (4- formyl-2-methyl-3-furancarboxylic acid) and 5-formyl-3-isoxazolecarboxylic acid of formula 6 may be used alone or in combination of two or more thereof. Among these, 4-formyl-cyclohexanecarboxylic acid represented by general formula (4) is more preferable.

[Formula 4]

[Formula 5]

[Formula 6]

The content of the compound having an aldehyde group and a carboxyl group is preferably 0.5 to 10% by weight, more preferably 0.8 to 6% by weight based on 100% by weight of the aqueous solution for crosslinking. If the content is less than 0.5% by weight, the effect of organic crosslinking is insignificant, which makes it difficult to impart flexibility. If the content is more than 10% by weight, the effect of organic crosslinking is excessively activated, which may cause wrinkles due to high flexibility, and handling and production efficiency. Can be lowered.

In addition, the present invention may include an inorganic crosslinking agent together with an organic crosslinking agent, thereby providing a short crosslink and stiffness characteristic of the inorganic crosslinking agent.

The inorganic crosslinking agent may be a boron compound such as boric acid and sodium borate. The content of the boron compound is preferably 1 to 10% by weight, more preferably 2 to 6% by weight relative to 100% by weight of the aqueous solution for crosslinking. If the content is less than 1% by weight, the rigidity of the film is lowered and the neck-in ratio is too small, which may cause wrinkles in the process, and when the content is more than 10% by weight, the rigidity may be increased, resulting in fracture. It can inhibit activity.

Most preferably, the mixture is used such that the weight ratio of the boron compound and the compound having one aldehyde group and one carboxyl group is 1: 0.1 to 1: 5, particularly preferably 1: 0.3 to 1: 3.

In addition, the aqueous solution for crosslinking may further include a small amount of iodide in order to prevent the uniformity of the degree of polarization in the plane of the polarizer and the desorption of the iodine salted. Iodide may be the same as the one used in the dyeing step, the content may be 0.05 to 15% by weight with respect to 100% by weight of the aqueous solution for crosslinking, preferably 0.5 to 11% by weight.

The temperature of the crosslinking bath is 20 to 70 ° C., and the immersion time of the polyvinyl alcohol-based film in the crosslinking bath may be 1 second to 15 minutes, and preferably 5 seconds to 10 minutes.

The crosslinking step may be repeated two or more times. For example, two or more crosslinking steps using a compound having an aldehyde group and a carboxyl group, and two or more crosslinking steps using a compound having an aldehyde group and a carboxyl group and a boron compound are possible. In addition, a crosslinking step in which a first crosslinking step using only a boron compound and a second crosslinking step using a compound having an aldehyde group and a carboxyl group is two or more times is also possible. In this case, a second crosslinking step may be performed after the first crosslinking step, or a first crosslinking step may be performed after the second crosslinking step. That is, when the step of crosslinking with an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group is included in the scope of the present invention. At this time, the order of the crosslinking step is not particularly limited.

The stretching step may be performed together with the crosslinking step, and in this case, the stretching step is preferably such that the total cumulative stretching ratio is 3.0 to 8.0 times.

As described above, the stretching step may be performed together with the swelling step, the dyeing step, and the crosslinking step, or may be performed as an independent stretching step using a separate drawing tank filled with an aqueous solution for drawing after the crosslinking step.

The washing step is a step of removing the unnecessary residue such as a crosslinking agent attached to the polyvinyl alcohol-based film in the previous steps by immersing the polyvinyl alcohol-based film completed crosslinking and stretching in a washing tank filled with an aqueous solution for washing.

The aqueous solution for washing may be water, and further iodide may be added thereto.

It is preferable that the temperature of a water washing tank is 10-60 degreeC, More preferably, it is 15-40 degreeC.

The washing step may be omitted and may be performed whenever previous steps such as dyeing step, crosslinking step or stretching step are completed. In addition, it may be repeated one or more times, and the number of repetitions is not particularly limited.

The drying step is a step of obtaining a polarizer having excellent optical properties by drying the washed polyvinyl alcohol-based film and further improving the orientation of the iodine molecules dyed by neck-in by drying.

As a drying method, methods such as natural drying, air drying, heat drying, far infrared drying, microwave drying, and hot air drying may be used. Recently, microwave drying for activating and drying only water in a film is newly used. Drying is mainly used. For example, hot air drying may be performed at 20 to 90 ° C. for 1 to 10 minutes. The drying temperature is preferably low in order to prevent deterioration of the polarizer, more preferably 80 ° C. or less, and most preferably 60 ° C. or less.

As described above, the method of manufacturing a polarizer of the present invention uses a compound having an aldehyde group and a carboxyl group as an organic crosslinking agent, and together with a boron compound as an inorganic crosslinking agent to increase the fixing efficiency of iodine, thereby providing excellent optical properties, Breakage does not occur, wrinkles are prevented, and dimensional stability is excellent not only in the width direction but also in the longitudinal direction, so that a large area and a thin film of the polarizer are possible. In addition, it is easy to handle in the process and can improve the production efficiency, it is advantageous when applied to the process to offset the odor peculiar to the aldehyde.

The present invention provides a polarizer manufactured by the above method.

In addition, the present invention provides a polarizing plate in which a protective film is laminated on at least one surface of the polarizer.

The protective film is not particularly limited as long as the film is excellent in transparency, mechanical strength, thermal stability, moisture shielding, and isotropy. Specifically, polyester-based resin, such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate; Cellulose resins such as diacetyl cellulose and triacetyl cellulose; Polycarbonate resins; Acrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene resins such as polystyrene and acrylonitrile-styrene copolymers; Polyolefin resins such as polyethylene, polypropylene, cyclo-based or norbornene-structured polyolefins, ethylene propylene copolymers; Vinyl chloride-based resins; Polyamide resins such as nylon and aromatic polyamide; Imide resin; Polyether sulfone resin; Sulfone resins; Polyether ketone resins: sulfide polyphenylene resins; Vinyl alcohol-based resins; Vinylidene chloride-based resins; Vinyl butyral resin; Allyl resins; Polyoxymethylene resin; And films composed of thermoplastic resins such as epoxy resins, and the like, and films composed of blends of the above thermoplastic resins may also be used. Moreover, you may use the film which consists of thermosetting resins or ultraviolet curable resins, such as (meth) acrylic-type, urethane type, epoxy type, and silicone type. Among these, especially the cellulose type film which has the surface saponified by saponification by alkali etc. is preferable in consideration of polarization characteristic or durability. In addition, the protective film may have a function of the following optical layer.

In the present invention, the structure of the polarizing plate is not particularly limited, and various kinds of optical layers capable of satisfying required optical properties may be laminated on the polarizer. For example, a structure in which a protective film for protecting the polarizer is laminated on at least one surface of the polarizer; A structure in which surface treatment layers such as a hard coating layer, an antireflection layer, an anti-sticking layer, a diffusion preventing layer, and an anti-glare layer are stacked on at least one surface or a protective film of the polarizer; It may have a structure in which an alignment liquid crystal layer or another functional film is laminated on at least one surface of the polarizer or a protection film. In addition, a phase difference including a wavelength plate (including a λ plate) such as an optical film, a reflector, a semi-transmissive plate, a 1/2 wave plate, or a quarter wave plate, such as a polarization conversion device used to form various image display devices At least one of the plate, the viewing angle compensation film, and the brightness enhancement film may be laminated with an optical layer. In more detail, a polarizing plate having a structure in which a protective film is laminated on one surface of a polarizer, the reflective polarizing plate or semi-transparent polarizing plate having a reflector or a transflective reflector laminated on the laminated protective film; An oval or circular polarizing plate in which retardation plates are stacked; A wide viewing angle polarizer on which a viewing angle compensation layer or a viewing angle compensation layer is stacked; Or the polarizing plate in which the brightness improving film was laminated | stacked is preferable.

Such a polarizing plate may be a pressure sensitive adhesive polarizing plate having an adhesive layer formed on one surface thereof.

An adhesive layer is a layer formed using acrylic resin, silicone resin, styrene resin, polyester resin, rubber resin, or urethane resin as an adhesive resin. Among these, acrylic pressure-sensitive adhesive resins having excellent optical transparency, cohesiveness and viscosity / adhesiveness, low hygroscopicity and remarkable durability such as weather resistance and heat resistance are preferable. The thickness of the pressure-sensitive adhesive layer can be appropriately adjusted according to the purpose of use and rework, it is usually 1 to 500㎛, preferably 5 to 200㎛, more preferably 10 to 100㎛.

The polarizing plate of the present invention can be applied to various image display devices such as electroluminescent display devices, plasma display devices, field emission display devices as well as ordinary liquid crystal display devices.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

EXAMPLE

Examples 1 to 10 Aliphatic Compounds

Example 1

A transparent unstretched polyvinyl alcohol film (VF-PS 70 µm, Kuraresa) having a degree of saponification of 99.9% or more was swelled by immersion in water (deionized water) at 30 ° C. for 2 minutes, followed by 3.5 mmol / L of iodine and potassium iodide 2 It was dyed by immersion for 4 minutes in an aqueous solution for dyeing at 30 ℃ containing weight%. At this time, it was stretched 1.3 times and 1.4 times in the swelling and dyeing step, respectively. Subsequently, the mixture was immersed in a 50 ° C. first and second aqueous solution for crosslinking containing 10% by weight of potassium iodide, 3.5% by weight of boric acid, and 1% by weight of glyoxalic acid for 2 minutes and 1 minute, respectively. At this time, in the first and second crosslinking steps, the total draw ratio was stretched to 3.75 times so that the total cumulative draw ratio was 6.8 times. After crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 70 ° C. for 4 minutes to prepare a polarizer.

A triacetyl cellulose (TAC) film was laminated on both surfaces of the prepared polarizer to prepare a polarizing plate.

Example 2

In the same manner as in Example 1, 3 wt% glyoxalic acid was used in the first and second aqueous solution for crosslinking.

Example 3

5 wt% glyoxalic acid was used in the same method as Example 1 except that the first and second aqueous solutions for crosslinking were used.

Example 4

In the same manner as in Example 1, 0.5 wt% glyoxalic acid was used in the first and second crosslinking aqueous solutions.

Example 5

In the same manner as in Example 1, 10 wt% glyoxalic acid was used in the first and second aqueous solution for crosslinking.

Example 6

The same method as in Example 1 was performed except that the second crosslinking step was omitted and the draw ratio was extended to 3.75 times in the first crosslinking step.

Example 7

The same method as in Example 1 was performed, but the first crosslinking step was omitted and the stretching ratio was extended to 3.75 times in the second crosslinking step.

Example 8

The same method as in Example 1 was carried out, but the second crosslinking step was omitted, and 5 wt% of glyoxalic acid was used in the first crosslinking step, and the stretching ratio was extended to 3.75 times.

Example 9

In the same manner as in Example 1, 3% by weight of boric acid and 3% by weight of glyoxalic acid were used in the first and second aqueous solutions for crosslinking.

Example 10

The same method as in Example 1, except that the first cross-linking solution containing 10% by weight of potassium iodide in the first cross-linking step, 3.5% by weight boric acid, 10% by weight of potassium iodide in the second cross-linking step, glyc A second crosslinking aqueous solution containing 1% by weight of oxalic acid was used.

Examples 11-18 Alicyclic Compounds

Example 11

A transparent unstretched polyvinyl alcohol film (VF-PS 70 µm, Kuraresa) having a degree of saponification of 99.9% or more was swelled by immersion in water (deionized water) at 30 ° C. for 2 minutes, followed by 3.5 mmol / L of iodine and potassium iodide 2 It was dyed by immersion for 4 minutes in an aqueous solution for dyeing at 30 ℃ containing weight%. At this time, it was stretched 1.3 times and 1.4 times in the swelling and dyeing step, respectively. Subsequently, they were immersed in a 50 ° C. first and second aqueous crosslinking solution containing 10% by weight of potassium iodide, 3.5% by weight of boric acid, and 1% by weight of 4-formyl-cyclohexanecarboxylic acid for 2 minutes and 1 minute, respectively. Crosslinked. At this time, in the first and second crosslinking steps, the total draw ratio was stretched to 3.75 times so that the total cumulative draw ratio was 6.8 times. After crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 70 ° C. for 4 minutes to prepare a polarizer.

A triacetyl cellulose (TAC) film was laminated on both surfaces of the prepared polarizer to prepare a polarizing plate.

Example 12

In the same manner as in Example 11, 0.5 wt% of 4-formyl-cyclohexanecarboxylic acid was used in the first and second crosslinking aqueous solutions.

Example 13

In the same manner as in Example 11, 6% by weight of 4-formyl-cyclohexanecarboxylic acid was used in the first and second aqueous solution for crosslinking.

Example 14

In the same manner as in Example 11, 10 wt% of 4-formyl-cyclohexanecarboxylic acid was used in the first and second crosslinking aqueous solutions.

Example 15

In the same manner as in Example 11, 3% by weight of boric acid and 3% by weight of 4-formyl-cyclohexanecarboxylic acid were used in the first and second aqueous solutions for crosslinking.

Example 16

The same method as in Example 11, except that the first cross-linking solution containing 10% by weight of potassium iodide in the first crosslinking step, 3.5% by weight boric acid, 10% by weight of potassium iodide in the second crosslinking step, 4 A second cross-linked aqueous solution containing 1% by weight of formyl-cyclohexanecarboxylic acid was used.

Example 17

The same method as in Example 11, except that 1% by weight of 4-formyl-2-methyl-3-furancarboxylic acid instead of 4-formyl-cyclohexanecarboxylic acid in the first and second aqueous solution for crosslinking Was used.

Example 18

In the same manner as in Example 11, 1 wt% of 5-formyl-3-isoxazolecarboxylic acid was used in place of 4-formyl-cyclohexanecarboxylic acid in the first and second crosslinking aqueous solutions. .

Comparative Example 1

The same method as in Example 1, except that glyoxalic acid was not used in the first and second aqueous solutions for crosslinking.

Comparative Example 2

The same method as in Comparative Example 1 was carried out, but the second crosslinking step was omitted and the drawing ratio was extended to 3.75 times in the first crosslinking step.

Comparative Example 3

In the same manner as in Example 1, 3 wt% glyoxal was used in place of glyoxalic acid in the first and second crosslinking aqueous solutions.

Comparative Example 4

In the same manner as in Example 1, 3% by weight of adipic acid was used in place of glyoxalic acid in the first and second aqueous solution for crosslinking.

Comparative Example 5

In the same manner as in Example 1, 1.5 wt% glyoxal and 1.5 wt% adipic acid were used in place of glyoxalic acid in the first and second crosslinking aqueous solutions.

TABLE 1

Test Example

The physical properties of the polarizers prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

1. Optical characteristics (polarization, transmittance)

The prepared polarizer was cut to a size of 4 cm × 4 cm and measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO). At this time, the degree of polarization is defined by the following equation (1).

[Equation 1]

Polarization degree (P) = [(T ₁ -T ₂ ) / T ₁ + T ₂ )] ^1/2

(Wherein T ₁ is parallel transmittance obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T ₂ is orthogonal transmittance obtained when the pair of polarizers are arranged in the state where the absorption axes are orthogonal to each other) .

2. Thickness (㎛)

The thickness of the produced polarizer was measured 10 points with respect to the width direction using the film thickness gauge (MS-5C, Nikon), and it represented by the average value.

3. Neck rate (%)

It is represented by the ratio of the initial disk width of the polyvinyl alcohol film and the width of the prepared polarizer, it was calculated by the following formula (2).

[Equation 2]

Neck In Rate (%) = (L ₁ -L ₂ ) / (L ₁ ) × 100

(In formula, L <_1> is the initial disk width length of an unstretched polyvinyl alcohol-type film, and L <_2> is the width length of the produced polarizer).

4. Dimensional stability

The polarizer thus prepared was cut into a size of 1 cm × 3 cm in the width direction (longitudinal direction, TD) and the longitudinal direction (lateral direction, MD), and then left to stand at a heat resistant condition of 24 hours at 80 ° C. The dimensions before and after the heat resistance condition were measured using a two-dimensional measuring instrument, and calculated based on the following equation (3).

[Equation 3]

% Change in dimension = (P ₁ -P ₂ ) / (P ₁ ) × 100

(Wherein P ₁ is the length of the initial polarizer, P ₂ is the length of the polarizer after standing under heat-resistant conditions).

5. Tensile Strength (MPa)

The tensile strength applied to the polyvinyl alcohol film before drying when drawn to the final cumulative draw ratio in a crosslinking bath was measured using a roll with a load cell attached thereto. At this time, if it is 10MPa or more, the risk of breakage is considered large.

6. Wrinkle occurrence evaluation

The wrinkles occurring in the polyvinyl alcohol film from the crosslinking step to just before the drying step were visually observed.

<Evaluation Criteria>

X: No wrinkles occur.

○: wrinkles occur.

7. Optical durability evaluation

After the polarizers prepared in Examples and Comparative Examples were left for 3 hours at a temperature of 60 ° C. and a humidity of 90%, the polarization degree of the polarizers was measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO Co., Ltd.) The difference of degree of polarization after 3 hours was also compared.

<Evaluation Criteria>

◎: polarization difference ≤ 1.5%

○: 1.5% <polarization difference ≤ 3%

×: 3% <polarization difference (poor)

TABLE 2

As shown in the above table, the polarizers of Examples 1 to 18 prepared by crosslinking with an aqueous solution for crosslinking containing an aldehyde group and a compound having a carboxyl group according to the present invention have excellent optical properties as compared with those of Comparative Examples 1 to 5 and a film. It was confirmed that there was no breakage and wrinkle generation phenomenon, and the handleability was good, and the dimensional stability and optical durability in the longitudinal direction as well as the width direction were excellent.

In addition, the optical durability of Examples 11 to 18 prepared by crosslinking with an aqueous solution for crosslinking containing an alicyclic compound compared to Examples 1 to 10 prepared by crosslinking with an aqueous solution for crosslinking containing an aliphatic compound having an aldehyde group and a carboxyl group. It was confirmed that the polarizer was better.

Claims (17)

1. A method of manufacturing a polarizer comprising a crosslinking step of immersing a polyvinyl alcohol-based film in an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group.
2. The method of claim 1, wherein the compound having an aldehyde group and a carboxyl group is an aliphatic compound or an alicyclic compound.
3. The method of claim 2, wherein the aliphatic compound is at least one member selected from the group consisting of glyoxalic acid, 4-oxo-2-butenoic acid and 2-methyl-3-oxopropanoic acid.
4. The method of claim 3, wherein the aliphatic compound is glyoxalic acid.
5. The cycloaliphatic compound of claim 2, wherein the alicyclic compound is 4-formyl-cyclohexanecarboxylic acid, 4-formyl-2-methyl-3-furancarboxylic acid, and 5-formyl-3-isoxazole carboxylic acid. The manufacturing method of the polarizer which is 1 or more types chosen from the group which consists of.
6. The method of claim 1, wherein the alicyclic compound is 4-formyl-cyclohexanecarboxylic acid.
7. The method of claim 1, wherein the compound having an aldehyde group and a carboxyl group is included in an amount of 0.5 to 10 wt% based on 100 wt% of the aqueous solution for crosslinking.
8. The method of claim 7, wherein the compound having an aldehyde group and a carboxyl group is contained in an amount of 0.8 to 6 wt% based on 100 wt% of the aqueous solution for crosslinking.
9. The method of claim 1, wherein the boron compound 1 to 10% by weight based on 100% by weight of the aqueous solution for crosslinking.
10. The method according to claim 9, wherein the weight ratio of the compound having an aldehyde group and a carboxyl group to 1 part by weight of the boron compound is 0.1 to 5.
11. The method of claim 1, wherein the crosslinking is repeated two or more times.
12. The method of claim 11, wherein the crosslinking is repeated two or more times using an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group and a boron compound.
13. The method according to claim 11, wherein the crosslinking step is a first crosslinking step using an aqueous solution for crosslinking containing a compound having an aldehyde group and a carboxyl group, and the second crosslinking step using an aqueous solution for crosslinking containing a boron compound is repeated two or more times Method of manufacturing a polarizer.
14. The method of claim 13, wherein a second crosslinking step is performed after the first crosslinking step or a first crosslinking step is performed after the second crosslinking step.
15. The polarizer manufactured by the manufacturing method of any one of Claims 1-14.
16. Polarizing plate laminated protective film on at least one surface of the polarizer of claim 15.
17. An image display device provided with a polarizing plate of claim 16.