KR102625719B1 - Polarizer and display device using the same - Google Patents

Abstract

A polarizing plate having excellent durability under high temperatures and a display device using the same are provided. The polarizing plate according to the present invention is one in which protective film A is bonded to one side of the polarizer and protective film B is bonded to the other side, and the moisture permeability TA and TB of protective films A and B at 40°C 90%RH are as follows. Conditions (1) and (2) are simultaneously satisfied.
240g/m ² /day>TA>70g/m ² /day … (One)
70g/m ² /day≥TB … (2)

Description

Polarizer and display device using the same

The present invention relates to a polarizing plate and a display device using the same.

A polarizing plate used in a liquid crystal display device includes a polarizer in which an iodine compound or an organic dye is adsorbed to a polyvinyl alcohol (PVA) film, and the PVA film is stretched to orient the iodine compound or an organic dye. Since a polarizer formed using a PVA film has poor strength and water resistance, a protective film to protect the polarizer is bonded to both sides of the polarizer.

Conventionally, as a protective film for a polarizing plate, a hard coat film in which a hard coat layer is provided on one side of a triacetylcellulose (TAC) film has been generally used (for example, see Patent Document 1). However, the water vapor transmission rate of the hard coat film based on the TAC film was about 300 to 1000 g/m ² /day, and there was a problem that moisture absorption of the polarizer could not be sufficiently suppressed under high temperature and high humidity, causing deterioration of the polarizer. Therefore, in order to improve moisture resistance over protective films based on TAC films, various protective films using cycloolefin polymer (COP) or polyethylene terephthalate (PET) as a base material have been developed (for example, see Patent Document 2). ), the moisture permeability of the protective film has been reduced to about 5 to 100 g/m ² /day.

Japanese Patent Publication No. 2016-175991 Japanese Patent Publication No. 2006-30870

In recent years, the number of display devices mounted on vehicles has been increasing. Since display devices for vehicle mounting can be used in very harsh environments at high temperatures, polarizers are also required to have durability in high-temperature environments.

By using a protective film using a low moisture permeability substrate such as COP or PET, the intrusion of moisture into the polarizer from the outside of the polarizing plate can be sufficiently reduced. However, when the polarizing plate is exposed to a high temperature environment such as in a car, moisture contained in the base material of the protective film or moisture contained in the adhesive used to bond the protective film and the polarizer may penetrate into the inside of the polarizing plate and remain there. Therefore, it was found that this moisture causes deterioration of the polarizer.

Therefore, the purpose of the present invention is to provide a polarizing plate excellent in durability under high temperatures and a display device using the same.

The polarizing plate according to the present invention is one in which protective film A is bonded to one side of the polarizer and protective film B is bonded to the other side, and the moisture permeability TA and TB of protective films A and B at 40°C 90%RH are as follows. Conditions (1) and (2) are simultaneously satisfied.

240g/m ² /day>TA>70g/m ² /day … (One)

70g/m ² /day≥TB … (2)

Additionally, the display device according to the present invention is provided with the polarizing plate.

According to the present invention, a polarizing plate having excellent durability under high temperatures and a display device using the same can be provided.

1 is a cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment.

1 is a cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment.

The polarizing plate 10 includes a polarizer 1, a protective film A laminated on one side of the polarizer 1, and a protective film B laminated on the other side of the polarizer 1. The polarizer 1 is formed by adsorbing iodine or dye to a polyvinyl alcohol (PVA) film and orienting it. Since the PVA constituting the polarizer 1 is poor in strength and water resistance, protective films A and B are bonded to both sides of the polarizer 1.

Protective film A is a hard coat film in which a hard coat layer is laminated on one side of a TAC film. The hard coat layer is a functional layer that covers the flexible TAC film and provides hardness to the protective film A, and can be formed by applying and curing a coating liquid containing an ultraviolet curable material. It is preferable that the pencil hardness of protective film A (hard coat film) is 3H or more. Additionally, since the TAC film has low water vapor barrier properties (high moisture permeability), the moisture permeability of the protective film A is adjusted by the hard coat layer. Specifically, by mixing a hydrophobic material in the hard coat layer, the moisture permeability of the protective film A can be within the range described later. As a hydrophobic material contained in the hard coat layer, for example, cycloolefin polymer can be used. The TAC film of protective film A is bonded to the polarizer 1 using water glue (PVA aqueous solution).

The thickness of the TAC film used for protective film A is not particularly limited, but is preferably 25 to 100 μm. In addition, the film thickness of the hard coat layer is not particularly limited, but is preferably 2 to 15 μm. However, as long as the moisture permeability of the protective film A is within the range described later, the thickness of the TAC film and the film thickness of the hard coat layer can be appropriately changed.

Protective film B is a low moisture permeability film and can be made of any one of cycloolefin polymer, polyethylene terephthalate, and polymethyl methacrylate. Protective film B is bonded to the polarizer 1 via an ultraviolet curable adhesive. The thickness of protective film B is not particularly limited, but is preferably 10 to 100 μm.

Additionally, in a display device equipped with a display panel and a polarizing plate, the protective film B is disposed on the display panel side, and the hard coat layer of the protective film A is disposed on the viewing side (opposite to the display panel).

The TAC film of the polarizer 1 and the protective film A is bonded using water glue as an adhesive. Therefore, even after going through the drying process, moisture may be contained in the adhesive layer and the TAC film. For example, if both protective films A and B are composed of films with low moisture permeability, the intrusion of moisture from the outside is suppressed, but in very high temperature environments such as inside a car in the summer, moisture is contained in the adhesive layer and/or TAC film. Since the existing moisture continues to remain in the polarizer 10, it leads to deterioration of the polarizer 1. Therefore, in the polarizing plate 10 according to the present embodiment, the moisture permeability of the protective film A and the moisture permeability of the protective film B are differentiated, and the moisture permeability of the protective film A and the moisture permeability of the protective film B are set to specific ranges, respectively, so that the adhesive and/ Alternatively, deterioration of the polarizer 1 due to moisture derived from the TAC film is suppressed.

Specifically, if the moisture permeability of protective films A and B at 40°C and 90%RH are TA and TB, respectively, TA and TB simultaneously satisfy the following conditions (1) and (2). In addition, both the moisture permeability TA and TB are values measured based on JIS Z 0208:1976.

240g/m ² /day>TA>70g/m ² /day … (One)

70g/m ² /day≥TB … (2)

By simultaneously satisfying the above conditions (1) and (2), the intrusion of moisture into the inside of the polarizing plate from the outside is suppressed, and when exposed to a high temperature environment of, for example, 85°C, the adhesive layer and/or protective fill A Moisture generated from the TAC film can be discharged to the outside.

The moisture permeability TA of the protective film A is preferably 180 g/m ² /day or more. In this case, since the amount of hydrophobic material contained in the hard coat layer can be reduced in order to adjust the moisture permeability of the protective film A, the surface hardness of the hard coat layer is excellent. In addition, since the protective film B is intended to completely block the ingress and egress of moisture, it is preferable that the moisture permeability TB of the protective film B is small.

As described above, the polarizing plate 10 according to the present embodiment is a protective film of the polarizer 1, and includes a protective film A having a moisture permeability that satisfies the above condition (1), and a moisture permeability that satisfies the above condition (2). It is provided with a protective film B having. In this configuration, the protective film B disposed on the display panel side substantially blocks moisture from entering and exiting. On the other hand, the protective film A disposed on the viewing side suppresses the intrusion of moisture into the polarizing plate 10 from the outside, but enables the release of moisture generated inside the polarizing plate 10. Therefore, when the polarizing plate 10 according to the present embodiment is used in a high temperature environment, moisture generated inside the polarizing plate 10 does not remain, thereby suppressing deterioration of the polarizer and maintaining the polarizing plate 10 over a longer period of time. ) It becomes possible to maintain optical performance.

The TAC film of the protective film A is bonded to the PVA film of the polarizer 1 using water glue (PVA aqueous solution) as an adhesive. In order to ensure adhesion between the TAC film and the PVA film, saponification treatment is performed on the protective film A before bonding. However, when saponification treatment is performed, the contact angle of not only the surface of the TAC film but also the surface on the opposite side decreases, leading to an increase in the moisture permeability of the protective film A. It is believed that the reason why the moisture permeability of the protective film A increases is because the contact angle of the surface opposite to the TAC film becomes small, making it difficult to repel water, that is, making it easy to let water pass through. As a result of examination by the inventor of the present application, if the contact angle after saponification of the surface (hard coat layer surface) opposite to the bonding surface of the protective film A to the polarizer (TAC film surface) is more than a predetermined value, the moisture permeability of the protective film A is sufficiently increased. I figured out what I could do lower.

Specifically, the contact angle CA after saponification on the surface opposite to the bonding surface of the protective film A satisfies the following condition (3). In addition, the contact angle CA after saponification is determined by immersing the protective film A in a 2.0N sodium hydroxide aqueous solution at 50°C for 60 seconds, then washing with pure water for 30 seconds and drying in an oven at 100°C for 60 seconds, as determined in JISR 3257:1999. It is a value measured based on the standard.

70°≤CA≤120° … (3)

When the contact angle CA after saponification on the surface opposite to the bonding surface of the protective film A is less than 70°, the water vapor permeability of the protective film A increases (moisture permeation becomes easier). The higher the contact angle CA after saponification on the side opposite to the bonding surface, the lower the moisture permeability of protective film A can be. However, in the case of protective film A provided with a hard coat layer on the TAC film, the hard coat layer on the side opposite to the bonding surface is The contact angle of the surface is less than 120°. In addition, the contact angle CA after saponification of the surface opposite to the bonding surface varies depending on the mixing ratio of the hydrophobic compound in the binder component used to form the coating film laminated on the TAC film, the type of leveling agent used in the coating solution, etc. It can be adjusted. Since the contact angle CA after saponification on the surface opposite to the bonding surface of the protective film A satisfies the above condition (1), the moisture permeability of the protective film A can be lowered while ensuring adhesion between the protective film A and the polarizer 1. .

[Example]

Hereinafter, a detailed embodiment of the present invention will be described.

A. Examples 1 to 7 and Comparative Examples 1 to 4

(Example 1)

Composition 1 shown in Table 1 as a coating solution for forming a hard coat layer was applied to a 40 ㎛ thick TAC film (product name: TJ40UL manufactured by Fujifilm) using a wire bar coater, dried, and then 100 mJ of ultraviolet ray was applied to the coating film. It was irradiated and cured at an exposure dose of /cm ² to produce protective film A (hard coat film) according to Example 1. The film thickness after curing of the hard coat layer was set to the value shown in Table 2. Additionally, a COP film with a thickness of 5 μm was used as protective film B.

After bonding a polarizer to the TAC film side of protective film A using water glue and drying it, bonding the protective film to the polarizer using an ultraviolet curing adhesive, and curing the ultraviolet curing adhesive by irradiating ultraviolet rays, according to Example 1. Got a polarizer.

(Examples 2 to 7)

Polarizing plates according to Examples 2 to 7 were produced in the same manner as Example 1, except that the compositions 2 to 7 shown in Table 1 were used as the coating liquid for forming the hard coat layer.

(Comparative Example 1)

As a coating liquid for forming a hard coat layer, Composition 8 shown in Table 1 was used, and a polarizing plate according to Comparative Example 1 was produced in the same manner as in Example 1, except that the exposure amount of ultraviolet rays was 75 mJ/cm ² .

(Comparative Example 2)

A polarizing plate according to Comparative Example 2 was produced in the same manner as in Example 1, except that Composition 9 shown in Table 1 was used as a coating liquid for forming a hard coat layer.

(Comparative Example 3)

A polarizing plate according to Comparative Example 3 was produced in the same manner as in Example 1, except that a PMMA film with a thickness of 40 μm was used as the protective film A.

(Comparative Example 4)

A polarizing plate according to Comparative Example 4 was produced in the same manner as in Example 1, except that a COP film with a thickness of 5 μm was used as the protective film A.

(Water permeability)

The moisture permeability TA of protective film A and the moisture permeability TB of protective film B before bonding to the polarizer were measured under conditions of 40°C and 90%RH based on JIS Z 0208:1976.

(Polarization degree after high temperature and high humidity durability test)

The polarizing plates of Examples 1 to 7 and Comparative Examples 1 to 4 were placed in a constant temperature bath at 85°C and 85%RH, and the degree of polarization was measured 240 hours and 500 hours after introduction. In addition, the degree of polarization was calculated by performing visibility correction using a 2-degree field of view (C light source) of “JIS Z 8701” to the value measured by an absorption photometer with an integrating sphere (“V7100” manufactured by Nippon Bunko Co., Ltd.). Calculated.

Table 2 shows the measured values of the moisture permeability TA of protective film A used in Examples 1 to 7 and Comparative Examples 1 to 4, the moisture permeability TB of protective film B, and the polarization degree of the polarizer (initial value, before and after the high temperature and high humidity durability test). represents.

For the polarizing plates according to Examples 1 to 7, the moisture permeability TA of protective film A and the moisture permeability TB of protective film B satisfy the above conditions (1) and (2), and were placed in a constant temperature bath at 85°C and 85%RH for 500 hours. Also, it showed a high value of polarization degree. The test results of the degree of polarization after the high-temperature, high-humidity endurance test for Examples 1 to 7 show that even when exposed to high temperature and high humidity, deterioration of the polarizer due to moisture entering the inside of the polarizing plate from the outside, protective film A and/or the protective film This means that no deterioration of the polarizer due to moisture contained in the adhesive for joining A has occurred.

In the polarizing plates of Comparative Examples 1 and 2, the moisture permeability TA of the protective film A is high, exceeding the upper limit of the above condition (1). The polarizing plates of Comparative Examples 1 and 2 had lower polarization degrees than those of Examples 1 to 7 after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours. In addition, when the polarizing plates according to Comparative Examples 1 and 2 were placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the deterioration of the polarizer progressed too much, and the amount of light transmitted through the polarizing plate (i.e., the amount of leaked light) became too large. , the degree of polarization could not be measured. From the comparison between Comparative Examples 1 and 2 and Examples 1 to 7, in the polarizing plates of Comparative Examples 1 and 2, it is believed that the polarizer deteriorated as a result of moisture entering the inside of the polarizing plate from the protective film A under high temperature and high humidity. .

In the polarizing plates of Comparative Examples 3 and 4, the moisture permeability TA of the protective film A is lower than the lower limit of the above condition (1). The polarizing plates of Comparative Examples 3 and 4 also had lower polarization degrees after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours than those in Examples 1 to 7. In addition, when the polarizing plates according to Comparative Examples 3 and 4 were placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the deterioration of the polarizer progressed too much, and the amount of light transmitted through the polarizing plate (i.e., the amount of leaked light) became too large. , the degree of polarization could not be measured. From the comparison between Comparative Examples 3 and 4 and Examples 1 to 7, in the polarizing plates of Comparative Examples 3 and 4, penetration of moisture into the inside of the polarizing plate was suppressed under high temperature and high humidity, but protective film A and/or protective film A It is thought that the polarizer deteriorated due to moisture contained in the adhesive for bonding.

B. Examples 8 to 10 and Comparative Example 5

A coating solution for forming a hard coat layer containing a polymerizable compound as a binder component, a solvent, a leveling agent, and a photopolymerization initiator was adjusted, and the adjusted coating solution for forming a hard coat layer was applied to a TAC film (product name: TJ40) with a thickness of 40 ㎛. (manufactured by Fujifilm Corporation) using a wire bar coater so that the film thickness after curing was 7 μm. After drying the coating film, the coating film was cured by irradiating ultraviolet rays at an exposure dose of 100 mJ/cm ² to produce protective film A (hard coat film). In each of Examples 8 to 10 and Comparative Example 5, by varying the mixing ratio of the hydrophobic compound (polymerizable compound having a hydrophobic functional group) in the polymerizable compound used in the coating liquid for forming the hard coat layer, the saponification results shown in Table 1 were obtained. Then, the contact angle was adjusted. Additionally, a COP film with a thickness of 5 μm was used as protective film B.

After the protective film A was immersed in a 2.0N sodium hydroxide aqueous solution at 50°C for 60 seconds, the protective film A was washed with pure water for 30 seconds and dried in an oven at 100°C for 60 seconds. The contact angle of the hard coat layer surface of protective film A after saponification treatment was measured using a contact angle meter (“LSE-B100” manufactured by NiCK) based on JIS R 3257:9999. The solvent used in the contact angle measurement is pure water.

After bonding the TAC film surface (bonding surface) of protective film A and the polarizer using water glue and drying it, bonding the protective film to the polarizer using an ultraviolet curing adhesive, and curing the ultraviolet curing adhesive by irradiating ultraviolet rays to form a polarizer. got it

The moisture permeability of protective films A and B of Examples 8 to 10 and Comparative Example 5 and the degree of polarization after the constant temperature and humidity durability test of the polarizing plate were measured in the same manner as Example 1. In Table 3, contact angle CA after saponification of protective film A used in Examples 8 to 10 and Comparative Example 5, moisture permeability TA, moisture permeability TB of protective film B, and polarization degree of polarizer (initial value, before and after high temperature and high humidity durability test) Indicates the measured value.

The polarizing plates according to Examples 8 to 10 had a contact angle CA of 70° or more and 120° or less after saponification on the surface of the hard coat layer. In addition, the moisture permeability TA of protective film A and the moisture permeability TB of protective film B satisfied the above conditions (1) and (2). Therefore, the polarizing plates according to Examples 8 to 10 showed high polarization degree values even after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours. The test results of the degree of polarization after the high temperature and high humidity endurance test for Examples 8 to 10 show that even when exposed to high temperature and high humidity, deterioration of the polarizer due to moisture entering the inside of the polarizing plate from the outside, protective film A and/or adhesive ( This means that no deterioration of the polarizer due to moisture contained in the water paste has occurred.

In the polarizing plate according to Comparative Example 5, the contact angle CA after saponification on the surface of the hard coat layer was below the lower limit of the above condition (1), and the water vapor permeability TA of the protective film A was increased to exceed the upper limit of the above condition (2). Therefore, the degree of polarization of the polarizing plate according to Comparative Example 5 after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours was lower than that of Examples 8 to 10. In addition, when the polarizing plate according to Comparative Example 5 was placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the deterioration of the polarizer progressed too much, and the amount of light passing through the polarizing plate (i.e., the amount of leaked light) became too large, and the polarization degree measurement could not be made. From the comparison between Comparative Example 5 and Examples 8 to 10, it is believed that in the polarizing plate according to Comparative Example 5, the polarizer was deteriorated as a result of moisture entering the inside of the polarizing plate from the protective film A under high temperature and high humidity.

From the above, it was confirmed that according to the present invention, even when exposed to a very harsh environment of high temperature and high humidity for a long time, deterioration of the polarizer can be suppressed and the optical performance of the polarizing plate can be maintained.

The present invention can be used as a polarizing plate for display devices, and is particularly suitable as a polarizing plate for display devices used in high-temperature environments such as vehicle-mounted applications.

1: Polarizer
10: Polarizer
A, B: Protective film

Claims (7)

It is a polarizer in which protective film A is bonded to one side of the polarizer and protective film B is bonded to the other side,
The moisture permeability TA and TB of the protective films A and B at 40°C 90%RH simultaneously satisfy the following conditions (1) and (2),
A polarizing plate, characterized in that the contact angle CA after saponification on the surface of the protective film A opposite to the bonding surface to the polarizer satisfies the following condition (3).
240g/m ² /day>TA>70g/m ² /day … (One)
70g/m ² /day≥TB … (2)
70°≤CA≤120° … (3) According to paragraph 1,
A polarizing plate wherein the protective film A is a hard coat film in which a hard coat layer is laminated on one side of a triacetylcellulose film. According to paragraph 2,
A polarizing plate wherein the hard coat film has a pencil hardness of 3H or more. According to any one of claims 1 to 3,
A polarizing plate wherein the protective film B is a film containing any one of cycloolefin polymer, polyethylene terephthalate, and polymethyl methacrylate. A display device including a polarizer,
The polarizing plate is comprised of protective film A bonded to one side of the polarizer and protective film B bonded to the other side, and the moisture permeability TA and TB of the protective films A and B at 40°C 90%RH are as follows. Conditions (1) and (2) are met simultaneously,
A display device characterized in that the contact angle CA after saponification on the surface of the protective film A opposite to the bonding surface to the polarizer satisfies the following condition (3).
240g/m ² /day>TA>70g/m ² /day … (One)
70g/m ² /day≥TB … (2)
70°≤CA≤120° … (3) delete delete

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