TWI851620B - Polarizing film, polarizing film, laminated polarizing film, image display panel and image display device - Google Patents

Abstract

The present invention is a polarizing film, which is formed by iodine adsorption directed onto a polyvinyl alcohol film; the iodine concentration of the polarizing film is 6% by weight or more; and in the presence of an inert gas, the peak temperature of the maximum intensity of water detected under the conditions of a temperature increase rate of 10°C/min and a temperature increase range of 40°C to 350°C is 200°C or more. The polarizing film has a good initial polarization degree and is excellent in suppressing the coloring of the polarizing film and the reduction of the monomer transmittance in a high temperature environment.

Description

Polarizing film, polarizing film, laminated polarizing film, image display panel and image display device

The present invention relates to a polarizing film, a polarizing film, a laminated polarizing film, an image display panel and an image display device.

Invention background

In the past, polarizing films used in various image display devices such as liquid crystal display devices or organic EL display devices used polyvinyl alcohol films that have been dyed (containing dichroic substances such as iodine or dichroic dyes) in order to have both high transmittance and high polarization. The polarizing film is manufactured by subjecting the polyvinyl alcohol film to various treatments such as swelling, dyeing, crosslinking, and stretching in a bath, then washing and drying. In addition, the aforementioned polarizing film is usually made into a polarizing film (polarizing plate) with a protective film such as cellulose triacetate bonded to one or both sides using an adhesive.

The aforementioned polarizing film can be laminated with other optical layers to form a laminated polarizing film (optical laminate) for use as needed. The aforementioned polarizing film or the aforementioned laminated polarizing film (optical laminate) is laminated between an image display unit such as a liquid crystal unit or an organic EL element and a front transparent plate (window layer) on the viewing side or a front transparent component such as a touch panel through an adhesive layer or a bonding agent layer to form the above-mentioned various image display devices for use (Patent Document 1).

In recent years, the various image display devices are used in mobile devices such as mobile phones and tablet computers, as well as in vehicle-mounted image display devices such as car navigation devices or rear-view camera recorders, and their uses are becoming more and more extensive. Therefore, the image display devices are required to have high durability in harsher environments (such as high temperature environments) than previously required, and an image display device is proposed for the purpose of ensuring the above durability (Patent Document 2).

Prior art literature

Patent Literature

Patent document 1: Japanese Patent Publication No. 2014-102353

Patent document 2: Japanese Patent Publication No. 2018-101117

Invention content

When a polarizing film or a laminated polarizing film using an iodine-based polarizing film is exposed to a high temperature environment, the polyvinyl alcohol constituting the polarizing film will be polyene-converted due to a dehydration reaction, causing the polarizing film to be colored and having a problem of reduced monomer transmittance.

After active research, the inventors of the present invention have found that the iodine contained in the iodine-based polarizing film will promote polyene formation in a high temperature environment. Therefore, if you want to suppress the decrease in monomer transmittance caused by the coloring of the polarizing film in a high temperature environment, it is effective to reduce the iodine concentration (content) in the polarizing film. However, on the other hand, it is difficult to obtain a polarizing film with a high iodine concentration and good polarization.

In view of the above circumstances, the purpose of the present invention is to provide a polarizing film with a high iodine concentration and good initial polarization, and the polarizing film is excellent in suppressing the coloring of the polarizing film and causing the decrease of the monomer transmittance in a high temperature environment.

Furthermore, the purpose of the present invention is to provide a polarizing film, a laminated polarizing film, an image display panel and an image display device using the above-mentioned polarizing film.

That is, the present invention relates to a polarizing film, which is formed by iodine adsorption directed onto a polyvinyl alcohol-based film; the iodine concentration of the polarizing film is 6% by weight or more; and, in the presence of an inert gas, the peak temperature of the maximum intensity of water detected under the conditions of a temperature increase rate of 10°C/min and a temperature increase range of 40°C to 350°C in the outgassing analysis method is 200°C or more.

Furthermore, the present invention relates to a polarizing film, wherein a transparent protective film is bonded to at least one side of the aforementioned polarizing film.

Furthermore, the present invention relates to a laminated polarizing film, wherein the aforementioned polarizing film is bonded to an optical layer.

Furthermore, the present invention relates to an image display panel, in which the aforementioned polarizing film or the aforementioned laminated polarizing film is bonded to the image display unit.

Furthermore, the present invention relates to an image display device, which has a front transparent component on the polarizing film or laminated polarizing film side of the aforementioned image display panel.

Although the details of the mechanism of action of the polarizing film of the present invention are still unclear, we speculate as follows. However, the present invention is not limited to the explanation of the mechanism of action.

The polarizing film of the present invention is an iodine-based polarizing film formed by iodine adsorption and orientation on a polyvinyl alcohol-based film; the iodine concentration is 6% by weight or more; and, in the presence of an inert gas, the peak temperature of the maximum intensity of water detected under the conditions of a temperature increase rate of 10°C/min and a temperature increase range of 40°C to 350°C is 200°C or more. As mentioned above, the iodine-based polarizing film will undergo polyeneization due to the dehydration reaction of polyvinyl alcohol in a high temperature environment, but the polarizing film of the present invention sets the temperature at which the dehydration reaction occurs to the high temperature side, that is, the peak temperature of the maximum intensity of water detected (observed) by the outgassing analysis method is set to 200°C or more, thereby being able to suppress the polarizing film from being colored and causing a decrease in the monomer transmittance in a high temperature environment. Furthermore, although the polarizing film of the present invention sets the iodine concentration in the polarizing film above a certain range, so that the peak temperature of the maximum intensity of water detected (observed) by the outgassing analysis method can be controlled above 200°C, the initial polarization degree is still good.

On the other hand, the inventors of the present invention observed that the polarizing film produced free radicals after exposing the polarizing film formed by iodine adsorbing oriented iodine on the polyvinyl alcohol film to a high temperature environment for a certain period of time. The timing of the polarizing film being colored due to polyeneization is very similar to the timing of the generation of the free radicals. This fact shows that the polyeneization of the polarizing film will produce free radicals. Therefore, for the polarizing film, if the temperature at which the above-mentioned dehydration reaction occurs is to be set to the high temperature side, that is, if the peak temperature of the maximum intensity of water detected (observed) by the outgassing analysis method is to be set to above 200°C, it is advisable to make the polarizing film contain a compound with free radical capture function.

Furthermore, as the panels of image display devices become thinner, from the perspective of preventing the panel of a polarizing film or a laminated polarizing film from warping when heated, the polarizing film of the present invention can be used as a thin polarizing film.

Figure 1 is an example of a graph showing the peak value of water detected in the outgassing analysis method using an iodine-based polarizing film as a sample.

The form used to implement the invention

<Polarizing film>

The polarizing film of the present invention is an iodine-based polarizing film formed by iodine adsorption directed onto a polyvinyl alcohol-based film; its iodine concentration is 6% by weight or more; and, in the outgassing analysis method, in the presence of an inert gas, at a heating rate of 10°C/min and a heating range of 40°C to 350°C, the peak temperature of the maximum intensity of water detected is above 200°C.

The aforementioned polyvinyl alcohol (PVA) film can be used without particular limitation as long as it is light-transmissive in the visible light region and can disperse and absorb iodine. In addition, the thickness of the PVA film generally used as the original plate should be about 1~100μm, and about 1~50μm is more preferred, and the width should be about 100~5000mm.

As the material of the aforementioned polyvinyl alcohol-based film, polyvinyl alcohol or its derivatives can be cited. The derivatives of the aforementioned polyvinyl alcohol can be exemplified by polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and their alkyl esters, modified by acrylamide, etc. The average polymerization degree of the aforementioned polyvinyl alcohol is preferably about 100 to 10,000, preferably about 1,000 to 10,000, and preferably about 1,500 to 4,500. In addition, the saponification degree of the aforementioned polyvinyl alcohol is preferably about 80 to 100 mol%, and preferably about 95 mol% to 99.95 mol. In addition, the aforementioned average polymerization degree and the aforementioned saponification degree can be obtained in accordance with JIS K 6726.

The aforementioned polyvinyl alcohol film may also contain additives such as plasticizers or surfactants. Examples of the aforementioned plasticizers include polyols such as glycerol, diglycerol, triglycerol, ethylene glycol, propylene glycol, polyethylene glycol, and their condensates. The amount of the aforementioned additive used is not particularly limited, but for example, it is preferably less than 20% by weight in the polyvinyl alcohol film.

In the aforementioned polarizing film, from the perspective of making the initial polarization of the polarizing film good, the aforementioned iodine concentration (content) is 6 weight % or more. In the aforementioned polarizing film, from the perspective of improving the initial polarization of the polarizing film, the aforementioned iodine concentration (content) is preferably 7 weight % or more, and 8 weight % or more is more preferred, and from the perspective of controlling the peak temperature of the maximum intensity of water detected by the outgassing analysis method to be above 200°C, it is preferably 12 weight % or less, and 10 weight % or less is more preferred.

The polarizing film has a peak temperature of the maximum intensity of water detected by the outgassing analysis method in the presence of an inert gas at a heating rate of 10°C/min and a heating range of 40°C to 350°C of 200°C or more. The polarizing film sets the temperature at which the dehydration reaction of polyvinyl alcohol occurs at a high temperature, that is, the peak temperature of the maximum intensity of water detected by the outgassing analysis method is set at 200°C or more, thereby suppressing the coloring of the polarizing film and causing a decrease in the transmittance of the monomer in a high temperature environment. On the other hand, when the peak temperature of the maximum strength of the above water is lower than 200°C, it will be difficult to control the change in the single transmittance of the polarizing film before and after the heating durability test (95°C × 750 hours) to be above 0% and below 5%. The above heating durability test is used as a high-temperature durability index required for low-end automotive displays.

Figure 1 is an example of a graph showing the peak value of water detected by the above-mentioned outgassing analysis method. The peak temperature of the maximum intensity of water detected is above 200°C.

In addition, the above-mentioned evolved gas analysis method is an analysis method that directly connects the gas chromatograph and the mass spectrometer with an inactive metal capillary, and monitors the gas generated when the sample is heated in real time. It is generally called EGA/MS method, EGA/TOFMS method, etc.

系化合物等具有自由基捕捉功能之化合物(例如抗氧化劑等)。由可易將會發生多烯化之脫水反應的溫度設定在高溫側之觀點來看，前述具有自由基捕捉功能之化合物例如宜為具有氮氧自由基或氮氧基之化合物。 The aforementioned polarizing film preferably contains a compound having a free radical scavenging function. We speculate that the aforementioned compound having a free radical scavenging function can capture free radicals generated by heating the polyvinyl alcohol of the polarizing film, and set the temperature at which the dehydration reaction of polyene formation occurs to a high temperature side. The aforementioned compound having a free radical scavenging function can be exemplified by hindered phenol series, hindered amine series, phosphorus series, sulfur series, benzotriazole series, diphenyl ketone series, hydroxylamine series, salicylate series, tris(III) series, and the like.

Compounds having a free radical scavenging function such as a nitroxide free radical or a nitroxide radical are preferably compounds having a free radical scavenging function, for example, from the viewpoint that the temperature of the dehydration reaction of polyene formation can be easily set at a high temperature.

The aforementioned compounds having nitroxide radicals or nitroxide groups can be N-oxyl compounds (compounds having CN(-C) ^-O as a functional group ( ^O represents an oxygen radical)) from the viewpoint of having a relatively stable radical at room temperature and in the air, and known compounds can be used. Examples of N-oxyl compounds include compounds having an organic group having the following structure.

[Chemical formula 1]

(In the general formula (1), ^R1 represents an oxygen free radical, ^R2 to ^R5 independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents 0 or 1.) In addition, the left side of the dotted line in the general formula (1) represents an arbitrary organic group.

Compounds having the above-mentioned organic groups include, for example, compounds represented by the following general formulas (2) to (5).

(In the general formula (2), R ¹ to R ⁵ and n are the same as above, R ⁶ represents a hydrogen atom or an alkyl group, acyl group or aryl group having 1 to 10 carbon atoms, and n represents 0 or 1).

[Chemical formula 3]

(In the general formula (3), ^R1 to ^R5 and n are the same as above, and ^R7 and ^R8 independently represent a hydrogen atom or an alkyl group, acyl group or aryl group having 1 to 10 carbon atoms).

(In the general formula (4), ^R1 to ^R5 and n are the same as above, and ^R9 to ^R11 independently represent a hydrogen atom or an alkyl group, acyl group, amino group, alkoxy group, hydroxyl group or aryl group having 1 to 10 carbon atoms).

(In the general formula (5), ^R1 to ^R5 and n are the same as above, and ^R12 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, an amino group, an alkoxy group, a hydroxyl group or an aryl group).

In the aforementioned general formulae (1) to (5), ^R2 to ^R5 are preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms, from the viewpoint of easy availability. In the aforementioned general formula (2), ^R6 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom, from the viewpoint of easy availability. In the aforementioned general formula (3), ^R7 and ^R8 are preferably independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom, from the viewpoint of easy availability. In the aforementioned general formula (4), ^R9 to ^R11 are preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, from the viewpoint of easy availability. In the aforementioned general formula (5), ^R12 is preferably a hydroxyl group, an amino group, or an alkoxy group, from the viewpoint of easy availability. In the above general formulas (1) to (5), n is preferably 1 from the viewpoint of ease of acquisition.

In addition, the aforementioned N-oxyl compounds include N-oxyl compounds described in Japanese Patent Publication No. 2003-64022, Japanese Patent Publication No. 11-222462, Japanese Patent Publication No. 2002-284737, International Publication No. 2016/047655, etc.

Furthermore, from the perspective of being able to efficiently capture free radicals generated in the polyene reaction, the molecular weight of the aforementioned compound having a free radical capturing function is preferably 1000 or less, and preferably 500 or less, and even more preferably 300 or less.

From the perspective of being able to efficiently penetrate the polarizing film together with water during the manufacture of the polarizing film, being able to be impregnated into the polarizing film at a high concentration, and being able to be impregnated in a short time when a thicker polyvinyl alcohol film is used, thereby improving the productivity of the polarizing film, the above-mentioned compound having a free radical scavenging function is preferably soluble in 1 part by weight or more relative to 100 parts by weight of water at 25°C, and more preferably soluble in 2 parts by weight or more relative to 100 parts by weight of water at 25°C, and even more preferably soluble in 5 parts by weight or more relative to 100 parts by weight of water at 25°C.

In addition, the aforementioned compounds having nitroxide free radicals or nitroxide groups include, for example, the following compounds.

(In general formula (6), R represents a hydrogen atom or an alkyl group, acyl group or aryl group having 1 to 10 carbon atoms).

From the perspective of suppressing the coloring of the polarizing film under a high temperature environment and causing a decrease in the transmittance of the monomer, when the polarizing film contains the compound having a free radical scavenging function, the content of the compound having a free radical scavenging function in the polarizing film is preferably 0.005% by weight or more, preferably 0.01% by weight or more, and more preferably 0.02% by weight or more. From the perspective of appearance, it is preferably 15% by weight or less, preferably 12% by weight or less, and more preferably 10% by weight or less.

<Polarizing film manufacturing method>

The manufacturing method of the polarizing film can be obtained by subjecting the polyvinyl alcohol-based film to any swelling step and washing step, and at least a dyeing step, a crosslinking step, and a stretching step. The content of the iodine contained in the polarizing film can be controlled by the concentration of the iodine and iodide such as potassium iodide contained in any of the treatment baths in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step, and the treatment temperature and treatment time of the treatment baths.

Furthermore, when manufacturing a polarizing film containing the aforementioned compound having a free radical scavenging function, it is sufficient as long as the aforementioned swelling step, the aforementioned washing step, the aforementioned dyeing step, the aforementioned cross-linking step, and the aforementioned stretching step contain the aforementioned compound having a free radical scavenging function in any one of the aforementioned treatment baths. The concentration of the aforementioned compound having a free radical scavenging function contained in any of the aforementioned treatment baths will be affected by the number of treatments, treatment time, treatment temperature, etc. of each treatment and cannot be determined in general. However, from the perspective of being able to efficiently control the content of the aforementioned compound having a free radical scavenging function in the polarizing film, it is usually preferably 0.01% by weight or more, preferably 0.05% by weight or more, and preferably 0.1% by weight or more, and preferably 30% by weight or less, preferably 25% by weight or less, and preferably 20% by weight or less.

In particular, when a washing step is performed after the dyeing step, the crosslinking step and the stretching step, the washing step can easily adjust the content of the iodine or the compound having a free radical scavenging function to a desired range from the viewpoint that the iodine or the compound having a free radical scavenging function can be dissolved from the polyvinyl alcohol film or adsorbed onto the polyvinyl alcohol film, taking into account the treatment conditions of the dyeing step, the crosslinking step and the stretching step.

Furthermore, each treatment bath in the aforementioned swelling step, the aforementioned dyeing step, the aforementioned crosslinking step, the aforementioned extension step, and the aforementioned washing step may also contain additives such as zinc salts, pH adjusters, pH buffers, and other salts. Examples of the aforementioned zinc salts include zinc halides such as zinc chloride and zinc iodide; inorganic zinc salts such as zinc sulfate and zinc acetate, etc. Examples of the aforementioned pH adjusters include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, or strong bases such as sodium hydroxide and potassium hydroxide. Examples of the aforementioned pH buffers include carboxylic acids such as acetic acid, oxalic acid, and citric acid, and their salts, or inorganic weak acids such as phosphoric acid and carbonic acid, and their salts. The aforementioned other salts include chlorides such as sodium chloride, potassium chloride, barium chloride, nitrates such as sodium nitrate and potassium nitrate, sulfates such as sodium sulfate and potassium sulfate, and alkaline metal and alkaline earth metal salts.

The aforementioned swelling step is a treatment step of immersing the polyvinyl alcohol film in a swelling bath, which can remove dirt and anti-caking agents on the surface of the polyvinyl alcohol film, and can swell the polyvinyl alcohol film to inhibit uneven dyeing. The aforementioned swelling bath can generally use water, distilled water, pure water and other media with water as the main component. The aforementioned swelling bath can also be appropriately added with surfactants, alcohols, etc. according to general methods.

The temperature of the aforementioned swelling bath is preferably about 10~60℃, preferably about 15~45℃, and more preferably about 18~30℃. In addition, since the swelling degree of the polyvinyl alcohol-based film will be affected by the temperature of the swelling bath, the immersion time in the aforementioned swelling bath cannot be determined in a general manner, but is preferably about 5~300 seconds, preferably about 10~200 seconds, and more preferably about 20~100 seconds. The aforementioned swelling step can be performed only once, or multiple times as needed.

The aforementioned dyeing step is a treatment step of immersing the polyvinyl alcohol film in a dyeing bath (iodine solution), which can make iodine adsorb and orient the polyvinyl alcohol film. The aforementioned iodine solution is generally preferably an iodine aqueous solution, and contains iodine and iodide as a dissolving aid. In addition, the aforementioned iodide can be: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among them, potassium iodide is preferred from the perspective of controlling the potassium content in the aforementioned polarizing film.

In the dyeing bath, the iodine concentration is preferably about 0.01 to 1% by weight, and preferably about 0.02 to 0.5% by weight. In the dyeing bath, the iodide concentration is preferably about 0.01 to 20% by weight, and preferably about 0.05 to 10% by weight, and more preferably about 0.1 to 5% by weight.

The temperature of the dyeing bath is preferably about 10~50℃, preferably about 15~45℃, and more preferably about 18~30℃. In addition, since the degree of dyeing of the polyvinyl alcohol film is affected by the temperature of the dyeing bath, the immersion time in the dyeing bath cannot be determined in a general way, but is preferably about 10~300 seconds, and more preferably about 20~240 seconds. The dyeing step can be performed only once, or multiple times as needed.

The crosslinking step is a treatment step of immersing the polyvinyl alcohol film in a treatment bath (crosslinking bath) containing a boron compound. The polyvinyl alcohol film can be crosslinked by the boron compound to adsorb iodine molecules or dye molecules to the crosslinked structure. The boron compound can be boric acid, borate, borax, etc. The crosslinking bath is generally an aqueous solution, but it can also be a mixed solution of an organic solvent miscible with water and water. In addition, from the perspective of controlling the potassium content in the polarizing film, the crosslinking bath preferably contains potassium iodide.

In the crosslinking bath, the concentration of the boron compound is preferably about 1 to 15% by weight, preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight. In addition, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15% by weight, preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight.

The temperature of the crosslinking bath is preferably about 20-70°C, and preferably about 30-60°C. In addition, since the degree of crosslinking of the polyvinyl alcohol-based film is affected by the temperature of the crosslinking bath, the immersion time in the crosslinking bath cannot be determined in a general manner, but is preferably about 5-300 seconds, and preferably about 10-200 seconds. The crosslinking step can be performed only once, or multiple times as needed.

The aforementioned stretching step is a processing step of stretching the polyvinyl alcohol film in at least one direction by a predetermined ratio. Generally speaking, the polyvinyl alcohol film is uniaxially stretched along the conveying direction (long side direction). The aforementioned stretching method is not particularly limited, and any method of wet stretching method and dry stretching method can be adopted. The aforementioned stretching step can be performed only once or multiple times as needed. The aforementioned stretching step can be performed at any stage in the manufacture of the polarizing film.

The treatment bath (stretching bath) of the wet stretching method can generally use water or organic solvents miscible with water and water mixed solutions and other solvents. From the perspective of controlling the potassium content in the polarizing film, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15 weight%, preferably about 2 to 10 weight%, and more preferably about 3 to 6 weight%. In addition, from the perspective of suppressing film breakage during stretching, the treatment bath (stretching bath) preferably contains the boron compound. At this time, the concentration of the boron compound in the stretching bath is preferably about 1 to 15 weight%, preferably about 1.5 to 10 weight%, and more preferably about 2 to 5 weight%.

The temperature of the stretching bath is preferably about 25-80°C, preferably about 40-75°C, and more preferably about 50-70°C. In addition, since the stretching degree of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, the immersion time in the stretching bath cannot be determined in a general manner, but is preferably about 10-800 seconds, and more preferably about 30-500 seconds. In addition, the stretching treatment of the wet stretching method can also be performed simultaneously with any one or more of the swelling step, the dyeing step, the crosslinking step, and the washing step.

The aforementioned dry stretching method may include, for example, an inter-roll stretching method, a heated roll stretching method, a compression stretching method, etc. In addition, the aforementioned dry stretching method may also be performed simultaneously with the aforementioned drying step.

The total stretching ratio (cumulative stretching ratio) applied to the aforementioned polyvinyl alcohol-based film can be appropriately set according to the purpose, and is preferably about 2 to 7 times, preferably about 3 to 6.8 times, and more preferably about 3.5 to 6.5 times.

The aforementioned cleaning step is a treatment step of immersing the polyvinyl alcohol film in a cleaning bath, which can remove foreign matter remaining on the surface of the polyvinyl alcohol film. The aforementioned cleaning bath can generally use a medium with water as the main component, such as water, distilled water, and pure water. In addition, from the perspective of controlling the potassium content in the aforementioned polarizing film, the aforementioned cleaning bath can also contain potassium iodide. At this time, the concentration of potassium iodide in the aforementioned cleaning bath is preferably about 1 to 10 weight%, preferably about 1.5 to 4 weight%, and more preferably about 1.8 to 3.8 weight%.

The temperature of the aforementioned cleaning bath is preferably about 5~50℃, preferably about 10~40℃, and more preferably about 15~35℃. In addition, since the degree of cleaning of the polyvinyl alcohol-based film will be affected by the temperature of the cleaning bath, the immersion time in the aforementioned cleaning bath cannot be determined in general, but is preferably about 1~100 seconds, preferably about 2~50 seconds, and more preferably about 3~20 seconds. The aforementioned swelling step can be performed only once, or multiple times as needed.

The manufacturing method of the polarizing film of the present invention may also include a drying step. The aforementioned drying step is a step of drying the polyvinyl alcohol-based film washed in the aforementioned washing step to obtain a polarizing film, and a polarizing film with a desired moisture content can be obtained by drying. The aforementioned drying can be performed by any appropriate method, such as natural drying, air drying, and heating drying.

The aforementioned drying temperature is preferably about 20~150℃, and preferably about 25~100℃. In addition, because the drying degree of the polarizing film will be affected by the drying temperature, the aforementioned drying time cannot be determined in general, but is preferably about 10~600 seconds, and preferably about 30~300 seconds. The aforementioned drying step can be performed only once, or multiple times as needed.

From the perspective of improving the initial polarization degree of the polarizing film, the thickness of the polarizing film is preferably 1 μm or more, and preferably 2 μm or more, and from the perspective of preventing panel warping, it is preferably 15 μm or less, preferably 10 μm or less, and preferably 8 μm or less. In particular, in order to obtain a polarizing film with a thickness of about 8 μm or less, the following method for manufacturing a thin polarizing film can be applied, wherein the thin polarizing film uses a laminate of a polyvinyl alcohol resin layer formed on a thermoplastic resin substrate as the polyvinyl alcohol film.

<Manufacturing method of thin polarizing film>

The manufacturing method of the thin polarizing film includes the following steps: forming a polyvinyl alcohol resin layer (PVA resin layer) containing a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate to form a laminate; and sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrinking treatment on the laminate. In particular, in order to obtain a polarizing film with high optical properties, a two-stage stretching method combining an air-assisted stretching treatment (dry stretching) and an underwater stretching treatment in a boric acid aqueous solution is selected.

The method for making the aforementioned laminate may adopt any appropriate method, for example, a method of applying a coating liquid containing the aforementioned PVA resin on the surface of the aforementioned thermoplastic resin substrate and drying it. The thickness of the aforementioned thermoplastic resin substrate is preferably about 20~300μm, and preferably about 50~200μm. The thickness of the aforementioned PVA resin layer is preferably about 3~40μm, and preferably about 3~20μm.

From the perspective of being able to absorb water and significantly reduce the extension stress, and thus achieve high-rate extension, the water absorption of the thermoplastic resin substrate should be about 0.2% or more, and preferably about 0.3% or more. On the other hand, from the perspective of preventing the dimensional stability of the thermoplastic resin substrate from being significantly reduced, which may cause the appearance of the resulting polarizing film to deteriorate, the water absorption of the thermoplastic resin substrate should be about 3% or less, and preferably about 1% or less. In addition, the water absorption can be adjusted, for example, by introducing a modified base into the constituent material of the thermoplastic resin substrate. The water absorption is a value obtained in accordance with JIS K 7209.

From the viewpoint of suppressing the crystallization of the PVA resin layer and fully ensuring the elongation of the laminate, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably below about 120°C. Furthermore, considering that the thermoplastic resin substrate can be plasticized by water and can be well elongated in water, the glass transition temperature (Tg) is preferably below about 100°C, and more preferably below about 90°C. On the other hand, from the viewpoint of preventing the thermoplastic resin substrate from deforming during coating and drying of the coating liquid and producing a good laminate, the glass transition temperature of the thermoplastic resin substrate is preferably above about 60°C. In addition, the aforementioned glass transition temperature can be adjusted by, for example, heating the crystallized material that can introduce the modified group into the aforementioned thermoplastic resin substrate. The aforementioned glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

The aforementioned thermoplastic resin substrate can be made of any appropriate thermoplastic resin. Examples of the aforementioned thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among them, norbornene resins and amorphous (non-crystalline) polyethylene terephthalate resins are preferred. In addition, from the perspective that the thermoplastic resin substrate not only has extremely excellent elongation but also can suppress crystallization during elongation, it is more suitable to use amorphous (non-crystalline) polyethylene terephthalate resins. Amorphous (non-crystalline) polyethylene terephthalate resins include copolymers containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, or copolymers containing cyclohexanedimethanol or diethylene glycol as glycols.

Before forming the PVA resin layer, the aforementioned thermoplastic resin substrate may be subjected to surface treatment (e.g., corona treatment, etc.), or an easy-to-adhere layer may be formed on the thermoplastic resin substrate. By performing the above treatment, the adhesion between the thermoplastic resin substrate and the PVA resin layer may be improved. Furthermore, the aforementioned thermoplastic resin substrate may have been stretched before forming the PVA resin layer.

The aforementioned coating liquid is a solution in which a PVA-based resin is dissolved in a solvent. Examples of the aforementioned solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trihydroxymethylpropane, amines such as ethylenediamine and diethylenetriamine, and water is preferred. These can be used alone or in combination of two or more. From the perspective of forming a uniform coating film that adheres closely to the thermoplastic resin substrate, the PVA-based resin concentration of the aforementioned coating liquid is preferably about 3 to 20 parts by weight relative to 100 parts by weight of the solvent.

From the perspective of enhancing the orientation of polyvinyl alcohol molecules by stretching, the coating liquid is preferably mixed with a halogen. The halogen can be any appropriate halogen, such as iodide and sodium chloride. The iodide can be potassium iodide, sodium iodide and lithium iodide, and potassium iodide is preferred. The concentration of the halogen in the coating liquid is preferably about 5 to 20 parts by weight, and more preferably about 10 to 15 parts by weight, relative to 100 parts by weight of the PVA resin.

Furthermore, additives may be mixed into the aforementioned coating liquid. Examples of the aforementioned additives include plasticizers such as ethylene glycol or propylene glycol; surfactants such as non-ionic surfactants, etc.

The coating method of the aforementioned coating liquid can adopt any appropriate method, such as roller coating, spin coating, wire rod coating, dip coating, mold coating, curtain coating, spray coating, scraper coating (comma coating, etc.), etc. In addition, the drying temperature of the aforementioned coating liquid is preferably above 50°C.

The aforementioned in-air auxiliary stretching treatment step can stretch the thermoplastic resin substrate while inhibiting crystallization, so the laminate can be stretched at a high rate. The stretching method of the aforementioned in-air auxiliary stretching treatment can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxially stretching the laminate by passing it between rollers with different circumferential speeds). From the perspective of obtaining high optical properties, free-end stretching is preferred.

The stretching ratio of the aforementioned air-assisted stretching should be about 2 to 3.5 times. The aforementioned air-assisted stretching can be performed in one stage or in multiple stages. When it is performed in multiple stages, the stretching ratio is the product of the stretching ratios of each stage.

The stretching temperature of the aforementioned air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin substrate, the stretching method, etc. For example, it is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, and preferably above the aforementioned glass transition temperature (Tg) + 10°C, and more preferably above the aforementioned glass transition temperature (Tg) + 15°C. On the other hand, from the perspective of inhibiting the rapid progress of crystallization of the PVA resin, thereby inhibiting the adverse conditions caused by crystallization (for example, hindering the orientation of the PVA resin layer due to stretching), the upper limit of the stretching temperature is preferably about 170°C.

It is also possible to perform an insolubility treatment after the aforementioned air-assisted extension treatment and before the dyeing treatment or the underwater extension treatment as needed. The aforementioned insolubility treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the insolubility treatment, the PVA-based resin layer can be given water resistance to prevent the orientation of the PVA from being reduced when immersed in water. The concentration of the boric acid aqueous solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubility treatment bath is preferably about 20 to 50°C.

The dyeing treatment is performed by dyeing the PVA resin layer with iodine. The adsorption method may include: a method of immersing the PVA resin layer (laminated body) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA resin layer, and a method of spraying the dyeing solution onto the PVA resin layer, etc., and preferably, a method of immersing the PVA resin layer (laminated body) in a dyeing solution containing iodine.

The amount of iodine mixed in the aforementioned dyeing bath is preferably about 0.05~0.5 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, the aforementioned iodide is preferably mixed in the iodine aqueous solution. The amount of the aforementioned iodide mixed relative to 100 parts by weight of water is preferably about 0.1~10 parts by weight, and more preferably about 0.3~5 parts by weight. In order to inhibit the dissolution of the PVA resin, the liquid temperature of the dyeing bath is preferably about 20~50°C. In addition, from the perspective of ensuring the transmittance of the PVA resin layer, the immersion time is preferably about 5 seconds to 5 minutes, and preferably about 30 seconds to 90 seconds. From the perspective of obtaining a polarizing film with good optical properties, the content ratio of iodine and iodide in the iodine aqueous solution is preferably about 1:5~1:20, and more preferably about 1:5~1:10.

A crosslinking treatment may be performed after the dyeing treatment and before the underwater stretching treatment as required. The aforementioned crosslinking treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing the crosslinking treatment, the PVA-based resin layer can be given water resistance, and the orientation of the PVA can be prevented from being reduced when immersed in high-temperature water during the subsequent underwater stretching. The boric acid concentration of the boric acid aqueous solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when performing the crosslinking treatment, it is preferable to further mix the aforementioned iodide in the crosslinking bath during the crosslinking treatment. By mixing the aforementioned iodide, the dissolution of iodine adsorbed on the PVA-based resin layer can be suppressed. The mixing amount of the aforementioned iodide is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. The liquid temperature of the crosslinking bath (boric acid aqueous solution) should be around 20~50℃.

The aforementioned underwater stretching treatment is performed by immersing the laminate in a stretching bath. Through the underwater stretching treatment, the laminate can be stretched at a temperature lower than the glass transition temperature (typically about 80°C) of the aforementioned thermoplastic resin substrate or PVA resin layer, and the PVA resin layer can be stretched at a high rate while inhibiting crystallization. The stretching method of the aforementioned underwater stretching treatment can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxially stretching the laminate by passing it between rollers with different circumferential speeds), and free-end stretching is preferred from the perspective of obtaining high optical properties.

The aforementioned underwater stretching treatment is preferably performed by immersing the laminate in a boric acid aqueous solution (boric acid aqueous stretching). By using a boric acid aqueous solution as a stretching bath, the PVA-based resin layer can be given the rigidity to withstand the tension during stretching and the water resistance of being insoluble in water. The boric acid concentration of the boric acid aqueous solution is preferably 1 to 10 parts by weight, and preferably 2.5 to 6 parts by weight relative to 100 parts by weight of water. In addition, iodide can also be mixed in the aforementioned stretching bath (boric acid aqueous solution). The liquid temperature of the stretching bath is preferably about 40 to 85°C, and preferably about 60 to 75°C. The immersion time of the laminate in the stretching bath is preferably about 15 seconds to 5 minutes.

The stretching ratio of the aforementioned underwater stretching should be about 1.5 times or more, and about 3 times or more is even better.

In addition, the total elongation ratio of the laminate should be about 5 times or more, and preferably about 5.5 times or more relative to the original length of the laminate.

The aforementioned drying and shrinking treatment can be performed by heating the entire area or by heating the conveying roller (so-called using a heating roller). It is preferred to use both. By using a heating roller to dry the laminate, the heat curling of the laminate can be effectively suppressed, and a polarizing film with excellent appearance can be manufactured. Moreover, the laminate can be dried while being kept flat, so that not only curling but also wrinkling can be suppressed. Furthermore, during the drying and shrinking treatment, the optical properties of the polarizing film obtained can be improved by shrinking it in the width direction. From this point of view, the shrinkage rate in the width direction of the laminate obtained by the drying and shrinking treatment should be about 1-10%, and preferably about 2-8%.

Drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, and the contact time with the heating roller. The temperature of the heating roller is preferably about 60~120℃, preferably about 65~100℃, and more preferably 70~80℃. From the perspective of increasing the crystallization degree of the thermoplastic resin to effectively suppress curling, the conveyor rollers are generally set at about 2~40, and preferably about 4~30. The contact time (total contact time) between the laminate and the heating roller is preferably about 1~300 seconds, preferably 1~20 seconds, and more preferably 1~10 seconds.

The heating roller can be installed in a heating furnace or in a general manufacturing line (at room temperature). It is best to install it in a heating furnace equipped with an air supply mechanism. By using the heating roller for drying and hot air drying together, the rapid temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be around 30~100℃. In addition, the hot air drying time should be around 1~300 seconds.

It is advisable to perform a cleaning treatment after the water stretching treatment and before the drying shrinkage treatment. The aforementioned cleaning treatment is typically performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

Furthermore, when manufacturing a thin polarizing film containing the aforementioned compound having a free radical scavenging function, it is sufficient as long as the aforementioned compound having a free radical scavenging function is contained in any one or more of the treatment baths in the dyeing treatment, the underwater extension treatment, the insolubilization treatment, the crosslinking treatment, and the washing treatment. The concentration of the aforementioned compound having a free radical scavenging function contained in any of the aforementioned treatment baths will be affected by the number of treatments, the treatment time, the treatment temperature, etc. of each treatment, so it cannot be determined in general. However, from the perspective of being able to efficiently control the content of the aforementioned compound having a free radical scavenging function in the polarizing film, it is usually preferably 0.01% by weight or more, and preferably 0.05% by weight or more, and preferably 0.1% by weight or more, and preferably 30% by weight or less, and preferably 25% by weight or less, and preferably 20% by weight or less.

In particular, when cleaning is performed, the content of the aforementioned iodine or the aforementioned compound having a free radical scavenging function can be easily adjusted to the desired range by the cleaning process, taking into account the treatment conditions of the dyeing process, the underwater stretching process, etc., from the perspective that the iodine or the aforementioned compound having a free radical scavenging function can be dissolved from the polyvinyl alcohol film or can be adsorbed to the polyvinyl alcohol film.

<Polarizing film>

The polarizing film of the present invention is a transparent protective film laminated on at least one side of the aforementioned polarizing film.

The transparent protective film is not particularly limited, and various transparent protective films that can be used for polarizing films can be used. The material constituting the transparent protective film can be, for example, a thermoplastic resin with excellent transparency, mechanical strength, thermal stability, moisture barrier, isotropy, etc. Examples of the aforementioned thermoplastic resin include cellulose ester resins such as cellulose triacetate, polyester resins such as polyethylene terephthalate or polyethylene naphthalate, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon or aromatic polyamide, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic or cyclic polyolefin resins having a norbornene structure (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. In addition, the transparent protective film may use a hardening layer formed by a thermosetting resin or UV-hardening resin such as (meth) acrylic, urethane, acrylic urethane, epoxy, or silicone. Among them, cellulose ester resins, polycarbonate resins, (meth) acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

The thickness of the aforementioned transparent protective film can be appropriately determined, but generally from the perspective of strength or handling, workability, thinness, etc., it is preferably about 1~500μm, and about 1~300μm is preferred, and about 5~100μm is more preferred.

When the aforementioned transparent protective film is laminated to both sides of the aforementioned polarizing film, the transparent protective films on both sides may be the same or different.

The aforementioned transparent protective film can use a phase difference plate with a front phase difference of 40nm or more and/or a thickness direction phase difference of 80nm or more. The front phase difference is usually controlled in the range of 40~200nm, and the thickness direction phase difference is usually controlled in the range of 80~300nm. When a phase difference plate is used as the aforementioned transparent protective film, the phase difference plate can also function as a transparent protective film, so it can be thinned.

As the aforementioned phase difference plate, for example, a birefringent film made by uniaxial or biaxial stretching of a polymer material, an oriented film of a liquid crystal polymer, an oriented layer of a liquid crystal polymer supported by a film, etc. There is no particular restriction on the thickness of the phase difference plate, which is generally about 20 to 150 μm. In addition, the aforementioned phase plate can also be used by attaching it to a transparent protective film without phase difference.

The aforementioned transparent protective film may also contain any appropriate additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, coloring agents, etc. In particular, when the aforementioned transparent protective film contains ultraviolet absorbers, the light resistance of the polarizing film can be improved.

The surface of the transparent protective film not bonded to the polarizing film may be provided with a functional layer such as a hard coating layer, an anti-reflection layer, an anti-adhesion layer, a diffusion layer or an anti-glare layer. In addition, the functional layers such as the hard coating layer, the anti-reflection layer, the anti-adhesion layer, the diffusion layer or the anti-glare layer may be provided on the protective film itself or separately provided as an individual body from the protective film.

The aforementioned polarizing film and the aforementioned transparent protective film, or the aforementioned polarizing film and the aforementioned functional layer are generally bonded together through an adhesive layer or a bonding agent layer.

The adhesive forming the aforementioned adhesive layer can be applied to various adhesives that can be used for polarizing films, such as rubber adhesives, acrylic adhesives, silicone adhesives, urethane adhesives, vinyl alkyl ether adhesives, polyvinyl alcohol adhesives, polyvinyl pyrrolidone adhesives, polyacrylamide adhesives, cellulose adhesives, etc. Among them, acrylic adhesives are preferred.

The method of forming the adhesive layer can be exemplified by the following methods: applying the aforementioned adhesive to a separation piece that has been subjected to a peeling treatment, drying it to form an adhesive layer, and then transferring it to a polarizing film, etc.; applying the aforementioned adhesive to a polarizing film, etc., and drying it to form an adhesive layer. The thickness of the aforementioned adhesive layer is not particularly limited, for example, it is about 1 to 100 μm, and preferably about 2 to 50 μm.

The adhesive forming the aforementioned adhesive layer can be applied to various adhesives that can be used for polarizing films, such as isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, water-based polyesters, etc. These adhesives are usually used as adhesives composed of aqueous solutions (water-based adhesives) and contain 0.5~60% by weight of solid components.

The aforementioned water-based adhesive may also contain a crosslinking agent. The aforementioned crosslinking agent can generally be used as a compound having at least two functional groups in one molecule that are reactive with the components of the polymer etc. constituting the adhesive, such as alkylene diamines; isocyanates; epoxides; aldehydes; hydroxymethyl urea, hydroxymethyl melamine and other amine-formaldehydes. The amount of the crosslinking agent mixed in the adhesive is generally about 10 to 60 parts by weight relative to 100 parts by weight of the components of the polymer etc. constituting the adhesive.

烷二醇二丙烯酸酯、EO改質二甘油四丙烯酸酯等多官能單體。又，陽離子聚合硬化型接著劑亦可使用具有環氧基或氧雜環丁烷基之化合物。具有環氧基之化合物只要是分子內具有至少2個環氧基者，則無特別限制，可使用一般已知的各種硬化性環氧化合物。 In addition to the above-mentioned adhesives, active energy ray-curing adhesives such as ultraviolet-curing adhesives and electron beam-curing adhesives can also be mentioned. Examples of the active energy ray-curing adhesives include (meth)acrylate adhesives. Examples of the curable components of the (meth)acrylate adhesives include compounds having a (meth)acryloyl group and compounds having a vinyl group. Examples of the compounds having a (meth)acryloyl group include alkyl (meth)acrylates such as chain alkyl (meth)acrylates having 1 to 20 carbon atoms, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates; (meth)acrylates containing a hydroxyl group; (meth)acrylates containing an epoxy group such as glycidyl (meth)acrylate, and the like. The (meth)acrylate adhesive may also contain nitrogen-containing monomers such as hydroxyethyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, (meth)acrylamide, (meth)acrylamide, and (meth)acryloyl frankincense. The (meth)acrylate adhesive may contain tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclotrihydroxymethylpropane methyl acrylate, dimethoxy propane methyl acrylate, and the like as a crosslinking component.

Polyfunctional monomers such as alkylene glycol diacrylate and EO-modified diglycerol tetraacrylate can be used. In addition, the cationic polymerization curing adhesive can also use compounds having an epoxy group or an oxycyclobutane group. The compound having an epoxy group is not particularly limited as long as it has at least two epoxy groups in the molecule, and various generally known curable epoxy compounds can be used.

The aforementioned bonding agent may also contain appropriate additives as required. The aforementioned additives may include silane coupling agents such as silane coupling agents, titanium silane coupling agents, bonding promoters such as ethylene oxide, ultraviolet absorbers, anti-degradation agents, dyes, processing aids, ion scavengers, antioxidants, adhesives, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, etc.

The adhesive can be applied to either the transparent protective film side (or the functional layer side) or the polarizing film side, or both. After lamination, a drying step is performed to form an adhesive layer consisting of a coated dry layer. After the drying step, ultraviolet rays or electron beams may be irradiated as needed. The thickness of the adhesive layer is not particularly limited. When a water-based adhesive is used, it is preferably about 30 to 5000 nm, and preferably about 100 to 1000 nm. When a UV curing adhesive or an electron beam curing adhesive is used, it is preferably about 0.1 to 100 μm, and preferably about 0.5 to 10 μm.

The aforementioned transparent protective film and the aforementioned polarizing film or the aforementioned polarizing film and the aforementioned functional layer can also be laminated via intermediate layers such as a surface modification treatment layer, an easy-adhesion agent layer, a barrier layer, and a refractive index adjustment layer.

The surface modification treatment for forming the aforementioned surface modification layer may include, for example, corona treatment, plasma treatment, primer treatment, saponification treatment, etc.

The easy-bonding agent forming the aforementioned easy-bonding layer may include, for example, various resin forming materials having the following skeletons: polyester skeleton, polyether skeleton, polycarbonate skeleton, polyurethane skeleton, polysilicone system, polyamide skeleton, polyimide skeleton, polyvinyl alcohol skeleton, etc. The aforementioned easy-bonding layer is usually provided on the protective film in advance, and the easy-bonding layer side of the protective film is laminated with the polarizing film by the aforementioned adhesive layer or the aforementioned bonding agent layer.

The aforementioned barrier layer is a layer that has the function of preventing impurities such as oligomers or ions dissolved from a transparent protective film from migrating (invading) into the polarizing film. The aforementioned barrier layer can be any layer that is transparent and can prevent impurities dissolved from a transparent protective film. Materials that form the barrier layer include urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, epoxy-based forming materials, etc.

The aforementioned refractive index adjustment layer is a layer provided to suppress the decrease in transmittance due to reflection between layers with different refractive indices such as the aforementioned transparent protective film and polarizing film. The refractive index adjustment material forming the aforementioned refractive index adjustment layer may include, for example, a forming agent including various resins and additives such as silica, acrylic, acrylic-styrene, and melamine.

The polarization degree of the aforementioned polarizing film is preferably above 99.98%, and preferably above 99.99%.

<Laminated polarizing film>

The laminated polarizing film (optical laminate) of the present invention is the aforementioned polarizing film bonded to an optical layer. The aforementioned optical layer is not particularly limited, and for example, one or more layers such as a reflective plate and a semi-transmissive plate, a phase difference plate (including 1/2 and 1/4 wavelength plates), a viewing angle compensation film, etc. can be used to form an optical layer of a liquid crystal display device, etc. As the aforementioned laminated polarizing film, there can be cited, for example: a reflective polarizing film or a semi-transmissive polarizing film formed by laminating a reflective plate or a semi-transmissive reflective plate on the aforementioned polarizing film, an elliptical polarizing film or a circular polarizing film formed by laminating a phase difference plate on the aforementioned polarizing film, a wide viewing angle polarizing film formed by laminating a viewing angle compensation film on the aforementioned polarizing film, or a polarizing film formed by laminating a brightness enhancement film on the aforementioned polarizing film.

The polarizing film or one or both sides of the laminated polarizing film may also be provided with an adhesive layer for bonding image display units such as liquid crystal units or organic EL elements to other components such as transparent plates or touch panels on the front of the visual side. The adhesive layer is preferably an adhesive layer. There is no particular restriction on the adhesive forming the adhesive layer, and an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based polymer or a rubber-based polymer may be appropriately selected for use. In particular, an adhesive such as an acrylic polymer having excellent optical transparency, exhibiting moderate wettability, cohesion and adhesion, and having excellent weather resistance and heat resistance may be appropriately used.

The adhesive layer can be attached to one or both sides of the polarizing film or the laminated polarizing film by an appropriate method. The adhesive layer can be attached by the following methods, for example: preparing an adhesive solution and directly attaching it to the polarizing film or the laminated polarizing film by an appropriate unfolding method such as a casting method or a coating method; forming an adhesive layer on a separated part and transferring it to the polarizing film or the laminated polarizing film. The thickness of the adhesive layer can be appropriately determined according to the purpose of use or the bonding force, and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. As described above, the polarizing film or the laminated polarizing film having an adhesive layer on at least one side thereof is referred to as a polarizing film with an adhesive layer or a laminated polarizing film with an adhesive layer.

In order to prevent the exposed surface of the adhesive layer from being contaminated, it is advisable to temporarily attach and cover it with a separating piece before it is actually used. This can prevent the adhesive layer from being contaminated in the usual handling state. As the separating piece, for example, a suitable sheet such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, mesh, foam sheet or metal foil and a laminate thereof, which is coated with a suitable stripping agent such as a polysilicone system, a long-chain alkyl system, a fluorine system or molybdenum sulfide as needed, can be used.

<Image display panel and image display device>

The image display panel of the present invention is a device having the aforementioned polarizing film or the aforementioned laminated polarizing film bonded to the image display unit. Furthermore, the image display device of the present invention is a device having a front transparent component on the polarizing film or laminated polarizing film side (visual side) of the aforementioned image display panel.

The aforementioned image display unit can be, for example, a liquid crystal unit or an organic EL unit. The aforementioned liquid crystal unit can use any one of, for example, a reflective liquid crystal unit that uses external light, a transmissive liquid crystal unit that uses light from a light source such as a backlight, and a semi-transmissive and semi-reflective liquid crystal unit that uses both light from the outside and light from the light source. When the aforementioned liquid crystal unit uses light from a light source, the image display device (liquid crystal display device) will also configure a polarizing film on the side of the image display unit (liquid crystal unit) opposite to the visual side, and will configure a light source. The polarizing film on the light source side and the liquid crystal unit should be bonded together through an appropriate adhesive layer. The driving method of the aforementioned liquid crystal unit can use any mode such as VA mode, IPS mode, TN mode, STN mode or bent orientation (π type).

The aforementioned organic EL unit can be suitably used, for example, in which a transparent electrode, an organic light-emitting layer and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting body (organic electroluminescent body). The aforementioned organic light-emitting layer is a laminate of various organic thin films, for example, the following various layer structures can be adopted: a laminate of a hole injection layer composed of triphenylamine derivatives and a light-emitting layer composed of fluorescent organic solids such as anthracene; a laminate of these light-emitting layers and an electron injection layer composed of perylene derivatives; or a laminate of a hole injection layer, a light-emitting layer and an electron injection layer, etc.

The front transparent component disposed on the visual side of the aforementioned image display unit can be, for example, a front transparent plate (window layer) or a touch panel. The aforementioned front transparent plate can use a transparent plate with appropriate mechanical strength and thickness. For example, the transparent plate can use a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate. The aforementioned touch panel can use various touch panels such as resistive film type, capacitive type, optical type, ultrasonic type, or a glass plate or transparent resin plate with a touch sensing function. When a capacitive touch panel is used as the aforementioned front transparent component, it is advisable to set a front transparent plate composed of glass or a transparent resin plate closer to the visual side than the touch panel.

The polarizing film of the present invention has good initial polarization and is excellent in suppressing the coloring of the polarizing film and reducing the transmittance of the single body in a high temperature environment. Therefore, the polarizing film of the present invention, and the polarizing film, laminated polarizing film, image display panel and image display device using the polarizing film are suitable for use in vehicle-mounted image display devices such as automobile navigation devices or rear-view monitors.

Implementation example

The present invention is described in more detail with the following examples, but the present invention is not limited to these examples.

<Implementation Example 1>

<Production of polarizing film>

The thermoplastic resin substrate is a long strip of amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100μm) with a water absorption rate of 0.75% and a Tg of about 75℃. One side of the resin substrate is subjected to a corona treatment. 13 parts by weight of potassium iodide is added to 100 parts by weight of a PVA resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetyl acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") in a ratio of 9:1 to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was subjected to free-end uniaxial stretching 2.4 times in the longitudinal direction (long side direction) between rollers of different peripheral speeds in an oven at 130°C (air-assisted stretching treatment). Then, the laminate was immersed in an insoluble bath (boric acid aqueous solution with a boric acid concentration of 4.0 wt%) at a liquid temperature of 40°C for 30 seconds (insoluble treatment). Next, the polarizing film is immersed in a dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 relative to 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds (dyeing treatment). It is then immersed in a crosslinking bath (an aqueous solution with a potassium iodide concentration of 3.0% by weight and a boric acid concentration of 5.0% by weight) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). Then, the laminate is immersed in a boric acid aqueous solution (boric acid concentration of 4.0% by weight) at a liquid temperature of 70°C, while uniaxially stretching is performed in the longitudinal direction (long side direction) between rollers with different peripheral speeds to achieve a total stretching ratio of 5.5 times (underwater stretching treatment). The laminate was then immersed in a cleaning bath at a liquid temperature of 20°C (aqueous solution containing 3% potassium iodide by weight and 1.0% by weight of the compound represented by the following general formula (9) as a compound having a free radical scavenging function) (cleaning treatment). Thereafter, it was dried in an oven maintained at 90°C while being in contact with a SUS heating roller whose surface temperature was maintained at 75°C for about 2 seconds (drying shrinkage treatment). Through the above procedure, a polarizing film with a thickness of 5μm was formed on the resin substrate. In addition, the peak temperature of the maximum intensity of water detected by the outgassing analysis method of the obtained polarizing film was 204°C, and the content of the compound represented by the following general formula (9) in the polarizing film was 0.3% by weight.

[Method for determining iodine concentration (weight %) in polarizing film]

For the polarizing film, an X-ray fluorescence analyzer (Rigaku Corporation, trade name "ZSX-PRIMUS IV", measuring diameter: ψ20 mm) was used to obtain the iodine concentration (weight %) using the following formula.

Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kcps/μm) In addition, the coefficient used to calculate the concentration will vary depending on the measuring device, but the coefficient can be obtained using an appropriate calibration curve.

[Escape gas analysis method]

The polarizing film was introduced into a heating furnace type pyrolyzer (manufactured by Frontier Laboratories, PY-2020iD), and the generated gas was directly introduced into a TOFMS (manufactured by JEOL, JMS-T100GCV) for the evolved gas analysis (EGA/TOFMS) method.

[Measurement conditions]

Heating conditions: 40℃→+10℃/min→350℃

Interface: Inactive fused silica tube, 2.5m×0.15mm id

Carrier gas: He (1.0mL/min)

Injection temperature: 300℃

Inlet: split ratio 20:1

Interface temperature: 300℃

Mass Analyzer: TOFMS

Ionization method: EI method

Mass range: m/z=18

[Method for determining the content (weight %) of compounds with free radical scavenging function in polarizing films]

About 20 mg of polarized film was taken and quantified, dissolved in 1 mL of water by heating, and then diluted with 4.5 mL of methanol. The obtained extract was filtered through a membrane filter, and the concentration of compounds with free radical scavenging function in the filter was measured using HPLC (ACQUITY UPLC H-class Bio manufactured by Waters).

<Production of polarizing film>

The adhesive used was an aqueous solution containing acetylacetyl-containing polyvinyl alcohol resin (average degree of polymerization 1,200, saponification degree 98.5 mol%, acetylacetylization degree 5 mol%) and hydroxymethyl melamine in a weight ratio of 3:1. A 30 μm thick transparent protective film (manufactured by Japan Catalyst, moisture permeability 125 g/(m ² ‧24h)) made of (meth) acrylic resin (modified acrylic polymer with lactone ring structure) was bonded to the surface of the polarizing film obtained above on the opposite side to the resin substrate (image display unit side) using a roll laminator. Next, the resin substrate was peeled off, and a transparent protective film with a thickness of 47 μm was formed on a triacetate cellulose film (manufactured by Fuji Film, trade name "TJ40UL") using the following UV curing adhesive using a roll laminator.

(Moisture permeability: 380g/(m ² ‧24h)) is laminated to the peeled surface (visual side) as a transparent protective film, and then UV light is irradiated from the transparent protective film surface to cure the adhesive, thereby producing a polarizing film.

[Evaluation of polarization]

The polarization degree of polarizing film can be measured using a spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The specific method for measuring the polarization degree is to measure the parallel transmittance (H0) and orthogonal transmittance (H90) of the polarizing film, which can be obtained by the formula: Polarization degree (%) = {(H0-H90)/(H0+H90)}1/2×100. The parallel transmittance (H0) is the transmittance value of the parallel type multilayer polarizing film, which is made by stacking two identical polarizing films so that the absorption axes of both sides are parallel. In addition, the orthogonal transmittance (H90) is the transmittance value of the orthogonal multilayer polarizing film, which is made by stacking two identical polarizing films so that the absorption axes of both sides are orthogonal. In addition, these transmittances are the Y values obtained by calibrating the light performance with the 2-degree field of view (C light source) of JIS Z 8701-1982. The results are listed in Table 1.

[Evaluation of single body transmittance in high temperature environment]

The polarizing film obtained above was cut into a size of 5.0×4.5 cm in such a way that the absorption axis of the polarizing film was parallel to the long side, and a glass plate (simulating the image display unit) was attached to the protective film surface on the image display unit side of the polarizing film through a 20μm thick acrylic adhesive layer, and then an autoclave was treated at 50℃ and 0.5MPa for 15 minutes to produce a laminate. The obtained laminate was placed in a hot air oven at a temperature of 95℃ for 750 hours, and the single body transmittance (ΔTs) before and after being put into (heated) was measured. The single body transmittance was measured using a spectrophotometer (Japan Scope Co., Ltd., product name "V7100") and evaluated according to the following standards. In addition, the measurement wavelength was 380~700nm (every 5nm). The results are listed in Table 1.

ΔTs(%)=Ts ₇₅₀ -Ts ₀

Here, _Ts0 is the single transmittance of the laminate before heating, and _Ts750 is the single transmittance of the laminate after heating for 750 hours. The above-mentioned ΔTs(%) is preferably 5≧ΔTs(%)≧0, and more preferably 3≧ΔTs(%)≧0.

[Evaluation panel warp]

The polarizing film was cut into a size of 145×105mm in such a way that the absorption axis of the polarizing film was parallel to the long side, and a glass plate with a thickness of 0.4mm and a size of 155×115mm was attached to the protective film surface on the image display unit side of the polarizing film through a 20μm thick acrylic adhesive layer. The obtained glass (simulated panel) sample with polarizing film was placed in a hot air oven at 85℃ for 5 hours, and then placed in a normal temperature and humidity environment for 1 hour, and the warp of the glass was evaluated. The warp refers to the warp of the glass and the lower side of the polarizing plate in a convex shape. The results are listed in Table 1.

○: The amount of warp is less than 1.0mm

×: Curvature is more than 1.0 mm

<Implementation Example 2>

<Production of polarizing films and polarizing films>

When preparing the polarizing film, the iodine concentration of the dyeing bath was adjusted to 6.3% by weight of the iodine concentration of the polarizing film obtained. Otherwise, the polarizing film and polarizing film were prepared in the same manner as in Example 1. The peak temperature of the maximum intensity of water detected by the outgassing analysis method in the obtained polarizing film was 207°C, the content of the compound represented by the above general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 5μm.

<Implementation Example 3>

<Production of polarizing films and polarizing films>

A polyvinyl alcohol film having an average polymerization degree of 2,400, a saponification degree of 99.9 mol% and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a 20°C swelling bath (water bath) for 30 seconds between rollers with different peripheral speed ratios for swelling, while being stretched 2.2 times in the conveying direction (swelling step), and then, the film was immersed in a 30°C dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 relative to 100 parts by weight of water) with a concentration adjusted so that the iodine concentration of the final polarizing film is 6.1% by weight, and was dyed therein for 30 seconds, while being stretched 3.3 times in the conveying direction based on the original polyvinyl alcohol film (polyvinyl alcohol film that has not been stretched in the conveying direction at all) (dyeing step). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution of 3.5 wt % boric acid, 3.0 wt % potassium iodide and 3.6 wt % zinc sulfate) at 40° C. for 28 seconds and stretched to 3.6 times the original polyvinyl alcohol film in the transport direction (crosslinking step). The obtained polyvinyl alcohol film was then immersed in a stretching bath (aqueous solution containing 4.5% by weight of boric acid, 5.0% by weight of potassium iodide and 5.0% by weight of zinc sulfate) at 64°C for 60 seconds, and stretched to 6.0 times the original polyvinyl alcohol film in the transport direction (stretching step), and then immersed in a cleaning bath (aqueous solution containing 2.3% by weight of potassium iodide and 1.0% by weight of the compound represented by the following general formula (6) having a free radical scavenging function) at 27°C for 10 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 40°C for 30 seconds to produce a polarizing film. The peak temperature of the maximum intensity of water detected by the outgassing analysis method in the obtained polarizing film is 209°C, the content of the compound represented by the above general formula (9) in the polarizing film is 0.2% by weight, and the thickness of the polarizing film is 12μm.

Next, the connective agent is an aqueous solution containing an acetylacetyl-containing polyvinyl alcohol resin (average degree of polymerization 1,200, saponification degree 98.5 mol %, acetylacetylation degree 5 mol %) and hydroxymethyl melamine in a weight ratio of 3:1. Using the adhesive, a 30 μm thick transparent protective film made of (meth) acrylic resin (modified acrylic polymer having a lactone ring structure) (manufactured by Japan Catalyst, moisture permeability: 125 g/(m ^{2 ‧24h)) was laminated to one side (image display device unit side) of the polarizing film obtained above by a roll laminator, and a 47 μm thick transparent protective film (moisture permeability: 380 g/(m 2 ‧24h} )) formed with HC on a triacetyl cellulose film (manufactured by Fujifilm, trade name "TJ40UL") was laminated to the other side. ‧24h)) is laminated to the other side (visual side), and then heated and dried in an oven (temperature is 90℃, time is 10 minutes), thus producing a polarizing film with transparent protective films laminated on both sides of the polarizing film.

<Implementation Example 4>

<Production of polarizing films and polarizing films>

When preparing the polarizing film, the iodine concentration of the dyeing bath is adjusted to a final iodine concentration of 7.9 wt% in the polarizing film, and the compound represented by the above general formula (8) is added to the bath in the washing step at a concentration of 1.0 wt% to replace the compound represented by the above general formula (9) as a compound having a free radical scavenging function. Otherwise, the polarizing film and polarizing film are prepared in the same manner as in Example 1. The peak temperature of the maximum intensity of water detected by the outgassing analysis method in the obtained polarizing film is 206°C, the content of the compound represented by the above general formula (8) in the polarizing film is 0.3 wt%, and the thickness of the polarizing film is 5 μm.

<Comparison Example 1>

<Production of polarizing films and polarizing films>

When preparing the polarizing film, the iodine concentration of the dyeing bath was adjusted to 8.5% by weight of the iodine concentration of the polarizing film obtained, and the compound represented by the above general formula (9) was not added to the cleaning bath as a compound having a free radical scavenging function. Otherwise, the polarizing film and polarizing film were prepared in the same manner as in Example 1. The peak temperature of the maximum intensity of water detected by the outgassing analysis method in the obtained polarizing film was 193°C, the content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 5μm.

<Comparison Example 2>

<Production of polarizing films and polarizing films>

When preparing the polarizing film, the iodine concentration of the dyeing bath was adjusted to 5.6% by weight of the iodine concentration of the polarizing film obtained, and the compound represented by the above general formula (9) was not added to the cleaning bath as a compound having a free radical scavenging function. Otherwise, the polarizing film and polarizing film were prepared in the same manner as in Example 1. The peak temperature of the maximum intensity of water detected by the outgassing analysis method in the obtained polarizing film was 203°C, the content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 5μm.

The polarizing films of the above-mentioned examples and comparative examples were used to perform the above-mentioned [Evaluation of polarization degree], [Evaluation of single-body transmittance in a high temperature environment], and [Evaluation of panel warp]. The results are listed in Table 1.

Claims (9)

A polarizing film, characterized in that it is formed by iodine adsorption directed onto a polyvinyl alcohol film; the iodine concentration of the polarizing film is 6% by weight or more; the polarizing film contains 0.02% by weight or more of a compound having a free radical scavenging function, the molecular weight of the compound having a free radical scavenging function is 1000 or less, and can dissolve more than 1 part by weight relative to 100 parts by weight of water at 25°C; the peak temperature of the maximum intensity of water detected by the polarizing film in the presence of an inactive gas in an outgassing analysis method is 200°C or more under the conditions of a heating rate of 10°C/min and a heating range of 40°C to 350°C. For example, the polarizing film in claim 1 has a thickness of less than 15μm. As in the polarizing film of claim 1 or 2, the aforementioned compound having a free radical scavenging function is a compound having a nitroxide free radical or a nitroxide radical. A polarizing film, characterized in that a transparent protective film is laminated on at least one side of the polarizing film of any one of claims 1 to 3. For example, the polarizing film in claim 4 has a polarization degree of 99.98% or more. A laminated polarizing film, characterized in that: the polarizing film as claimed in claim 4 or 5 is bonded to an optical layer. An image display panel, characterized in that: a polarizing film as in claim 4 or 5 or a laminated polarizing film as in claim 6 is bonded to the image display unit. An image display device, characterized in that: a front transparent component is provided on the polarizing film or laminated polarizing film side of the image display panel as in claim 7. The image display device of claim 8 is used for vehicle-mounted purposes.