KR102748568B1 - Polarizing plate and optical display apparatus comprising the same - Google Patents

Abstract

A polarizing plate and an optical display device including the same are provided, which include a polarizer and a liquid crystal phase difference layer laminated on a lower surface of the polarizer, and further include an adhesive layer formed in direct contact with an upper surface or a lower surface of the liquid crystal phase difference layer, wherein the adhesive layer is formed of a thermosetting adhesive composition and has a thickness of 10 nm to 500 nm, and the liquid crystal phase difference layer has a rate of change in an in-plane direction phase difference of Equation 1 of 1% or less.

Description

Polarizing plate and optical display apparatus including the same {POLARIZING PLATE AND OPTICAL DISPLAY APPARATUS COMPRISING THE SAME}

The present invention relates to a polarizing plate and an optical display device including the same.

A light-emitting display device including an organic light-emitting display device may not include a polarizing plate. However, light incident from the outside may be reflected within the light-emitting display device, thereby deteriorating the screen quality of the display device and making it look bad. Accordingly, the light-emitting display device may include a polarizing plate for anti-reflection, thereby improving the screen quality and appearance.

In line with the trend toward thinning of light-emitting display devices, attempts are being made to thin polarizing plates as well. To this end, it is possible to consider using a liquid crystal phase difference layer in a polarizing plate. However, the liquid crystal phase difference layer has the problem of low adhesion to conventional adhesives.

When bonding a polarizer and a phase difference layer, a photocurable adhesive is used. However, in order to secure the desired adhesion, the thickness of the adhesive layer of the photocurable adhesive cannot be helped. In addition, the inventors of the present invention have confirmed that when a polarizing plate having an adhesive layer formed of a photocurable adhesive is left at a high temperature for a long period of time, the in-plane direction phase difference change rate of the liquid crystal phase difference layer increases, and the antireflection function cannot be properly implemented.

Meanwhile, development of foldable display devices that have a bending function added to the recent light-emitting display devices is also continuously progressing. Accordingly, polarizing plates are also required to have a bending function.

The background technology of the present invention is disclosed in Korean Patent Publication No. 10-2006-0103451, etc.

The purpose of the present invention is to provide a polarizing plate having a low rate of change in the in-plane direction phase difference of a liquid crystal phase difference layer when the polarizing plate is left at a high temperature for a long period of time.

Another object of the present invention is to provide a polarizing plate having excellent bending reliability.

Another object of the present invention is to provide a thin polarizing plate.

Another object of the present invention is to provide a polarizing plate having excellent adhesion between a polarizer and a liquid crystal phase difference layer and excellent adhesion between liquid crystal phase difference layers.

Another object of the present invention is to provide an optical display device including the above-described polarizing plate.

One aspect of the present invention is a polarizing plate.

1. A polarizing plate includes a polarizer and a liquid crystal phase difference layer laminated on a lower surface of the polarizer, and further includes an adhesive layer formed in direct contact with an upper surface or a lower surface of the liquid crystal phase difference layer, wherein the adhesive layer is formed of a thermosetting adhesive composition and has a thickness of 10 nm to 500 nm, and the liquid crystal phase difference layer has a change rate of an in-plane direction phase difference of the following equation 1 of 1% or less:

[Formula 1]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above equation 1,

A is the in-plane direction phase difference of the liquid crystal phase difference layer at a wavelength of 550 nm (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

2. In 1, the liquid crystal phase difference layer may contain a hydrophobic aromatic-containing liquid crystal compound.

In 3.1-2, the liquid crystal phase difference layer may have an in-plane phase difference of 100 nm to 220 nm or 225 nm to 350 nm at a wavelength of 550 nm.

In 4.1-3, the liquid crystal phase difference layer may have reverse wavelength dispersion.

In 5.1-4, the adhesion of the adhesive layer to the liquid crystal phase difference layer may be 0.5 N or more.

In 6.1-5, the adhesive layer may include at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.

In 7.1-6, the adhesive layer may be formed of a composition including a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group (-NH ₂ ) and/or a secondary amine group (-NH-); and at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.

In 8.7, the cross-linking agent may include a poly(ethyleneimine)-based cross-linking agent.

In 9.7, the polyphenol compound may include tannic acid.

In 10.7, the epoxy compound having the alkylene oxide group may include at least one of monoalkylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ether, monoalkylene glycol triglycidyl ether, and polyalkylene glycol triglycidyl ether.

In 11.7, 100 parts by weight of the polyvinyl alcohol-based resin, 0.1 to 50 parts by weight of the crosslinking agent, and 1 to 100 parts by weight of at least one of the polyphenol-based compound and the epoxy-based compound having an alkylene oxide group may be included.

In 12.1-11, the polarizing plate may include the adhesive layer, the liquid crystal phase difference layer, the second adhesive layer, and the second liquid crystal phase difference layer, which are sequentially laminated on the lower surface of the polarizer.

In 13.12, the second adhesive layer may be formed of at least one of a photocurable adhesive and a heat-curable adhesive.

In 14.13, the thermosetting adhesive may include a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group and/or a secondary amine group; and at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.

In 15.1-14, the polarizing plate may include a first adhesive layer, a liquid crystal phase difference layer, an adhesive layer, and a second liquid crystal phase difference layer, which are sequentially laminated on a lower surface of the polarizer.

In 16.15, the first adhesive layer may be formed of at least one of a photocurable adhesive and a heat-curable adhesive.

In 17.16, the second liquid crystal phase difference layer may have a change rate of the in-plane direction phase difference of the following equation 1-3 of 1% or less;

[Formula 1-3]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above equation 1-3,

A is the in-plane direction phase difference at a wavelength of 550 nm of the second liquid crystal phase difference layer (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the second liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

In 18.16, the thermosetting adhesive may include a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group and/or a secondary amine group; and at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.

In 19.1-18, a third protective layer may be further laminated on the upper surface of the polarizer.

Another aspect of the present invention is an optical display device.

An optical display device includes a polarizing plate of the present invention.

The present invention provides a polarizing plate having a low rate of change in the in-plane direction phase difference of a liquid crystal phase difference layer when the polarizing plate is left at a high temperature for a long period of time.

The present invention provides a polarizing plate having excellent bending reliability.

The present invention provides a polarizing plate having a thin thickness.

The present invention provides a polarizing plate having excellent adhesion between a polarizer and a liquid crystal phase difference layer and excellent adhesion between liquid crystal phase difference layers.

The present invention provides an optical display device including the above-described polarizing plate.

Figure 1 is an exploded view of a transfer-type liquid crystal phase difference film.
Figure 2 is a cross-sectional view of a polarizing plate of one embodiment of the present invention.
Figure 3 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.
Figure 4 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.
Figure 5 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.

The present invention will be described in detail with reference to the attached drawings and examples so that those skilled in the art can easily implement the invention. The present invention can be implemented in various different forms and is not limited to the examples described herein.

In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and the same names are used for identical or similar components throughout the specification. The length and size of each component in the drawings are for explaining the present invention, and the present invention is not limited to the length and size of each component described in the drawings.

In this specification, "upper" and "lower" are defined based on the drawing, and depending on the perspective, "upper" may be changed to "lower" and "lower" may be changed to "upper", and reference to "on" or "on" may include not only directly on but also cases where another structure is intervened. On the other hand, reference to "directly on" or "directly above" or "directly formed" indicates that there is no intervening other structure such as an intermediate.

In this specification, the “in-plane phase difference (Re)” is expressed by the following formula A:

[Formula A]

Re = (nx - ny) x d

(In the above formula A, nx and ny are the refractive index of the optical element in the slow axis direction and the refractive index of the optical element in the fast axis direction at the measurement wavelength, respectively, and d is the thickness of the optical element (unit: nm).)

In this specification, “polarization” means a value measured at a wavelength of 400 nm to 800 nm, specifically at a wavelength of 550 nm.

When describing a numerical range in this specification, “X to Y” means “X or more and Y or less” (X≤ ≤Y).

The present invention comprises a polarizer and a liquid crystal phase difference layer laminated on a lower surface of the polarizer, and further comprises an adhesive layer formed in direct contact with an upper surface or a lower surface of the liquid crystal phase difference layer, wherein the adhesive layer is formed of a thermosetting adhesive composition and has a thickness of 10 nm to 500 nm, and when the polarizer is left at a high temperature for a long period of time, the liquid crystal phase difference layer has an in-plane direction phase difference change rate of 1% or less as expressed by the following Equation 1:

[Formula 1]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above equation 1,

A is the in-plane direction phase difference of the liquid crystal phase difference layer at a wavelength of 550 nm (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

The above “formed by direct contact” means that no other adhesive layer, adhesive layer or point-of-contact adhesive layer is formed between the adhesive layer and the liquid crystal phase difference layer.

Although not particularly limited, as described below, the polarizing plate of the present invention can preferably be used as an anti-reflection polarizing plate for a light-emitting display device. The anti-reflection polarizing plate can provide an anti-reflection function through a polarizing function by a polarizer and a predetermined range of in-plane directional phase difference by a liquid crystal phase difference layer. When the polarizing plate is left at a high temperature for a long period of time and the in-plane directional phase difference of the liquid crystal phase difference layer has a high change rate, the polarizing plate cannot have the reliability of providing an anti-reflection function.

In the range of the change rate of the in-plane direction phase difference of the above formula 1, the polarizing plate can properly implement the anti-reflection function even after being left at a high temperature for a long period of time, so that even when applied to an optical display device, it can provide an excellent appearance and excellent screen quality, and can improve the reliability of the optical display device. Preferably, the change rate of the above formula 1 can be 0% to 1%.

The liquid crystal phase difference layer prevents reflection of external light by circularly polarizing or helping to circularly polarize linearly polarized light emitted after passing through a polarizer, thereby implementing an anti-reflection function, thereby improving the appearance and screen quality.

In one specific example, the liquid crystal phase difference layer may have an in-plane phase difference of 100 nm to 220 nm, specifically 100 nm to 180 nm, for example, a λ/4 phase difference, at a wavelength of 550 nm. In this range, the reflectivity for external light can be lowered, thereby obtaining an effect of improving screen quality.

In another specific example, the liquid crystal phase difference layer may have an in-plane phase difference of 225 nm to 350 nm, specifically 225 nm to 300 nm, for example, a phase difference of λ/2, at a wavelength of 550 nm. In this range, the reflectivity for external light can be lowered, thereby obtaining an effect of improving screen quality.

In another specific example, the liquid crystal phase difference layer may exhibit reverse wavelength dispersion. The reverse wavelength dispersion means that Re(450) < Re(550) < Re(650). Here, Re(450), Re(550), and Re(650) represent in-plane direction phase differences of the liquid crystal phase difference layer at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

The liquid crystal phase difference layer can have a thickness of 0.1 ㎛ to 10 ㎛, for example, 1 ㎛ to 5 ㎛. In the above range, the polarizing plate can be made thin and the target phase difference can be implemented.

The liquid crystal phase difference layer may have low adhesion to an adhesive layer or polarizer formed with a conventional polarizing plate adhesive composition. The low adhesion may be due to the liquid crystal phase difference layer being formed with a liquid crystal composition. In one specific example, the liquid crystal phase difference layer may contain a hydrophobic aromatic-containing liquid crystal compound. In one specific example, the aromatic-containing liquid crystal compound may be a polymer, oligomer or monomer comprising a unit composed of an aromatic ring capable of imparting liquid crystal properties and a polymerizable functional group. The polymerizable functional group may be a (meth)acryloyl group, an epoxy group or a vinyl ether group, and may be cured by heat or light to increase the strength of the liquid crystal phase difference layer.

The liquid crystal phase contrast layer can be formed of a composition containing the above-described aromatic-containing liquid crystal compound. The composition may further contain additives such as a leveling agent, a polymerization initiator, an alignment aid, a heat stabilizer, a lubricant, a plasticizer, an antistatic agent, etc., and the detailed types thereof can be referred to those known to those skilled in the art.

The inventor of the present invention confirmed that when a polarizing plate is left at a high temperature for a long period of time, delamination occurs between the polarizer and the liquid crystal phase difference layer or between the liquid crystal phase difference layer and the adhesive layer, or the rate of change in the in-plane phase difference of the liquid crystal phase difference layer increases, so that the anti-reflection function cannot be properly implemented. It was also confirmed that an adhesive layer or a pressure-sensitive adhesive layer with high adhesion to the liquid crystal phase difference layer can increase the rate of change in the in-plane direction phase difference of the liquid crystal phase difference layer when a polarizing plate is left at a high temperature for a long period of time.

The polarizing plate of the present invention has excellent bending reliability at room temperature or high temperature and/or high temperature and high humidity. Accordingly, the polarizing plate of the present invention can provide excellent bending reliability even when used in a flexible optical display device. In one specific example, since the polarizing plate has excellent bending reliability, a rectangular specimen having a length x width (MD x TD, 200 mm x 150 mm) was manufactured so that the absorption axis direction of the polarizer is in the 45° direction (diagonal direction), and the manufactured specimen was folded and unfolded so that the liquid crystal phase difference layer was on the inside and the polarizer was on the outside at room temperature so that the radius of curvature was 3 mm, and the number of times this was performed was considered one. When the first number of times cracks or interlayer lifting occurred at the folding portion was evaluated, no cracks or interlayer lifting occurred even after 200,000 or more times. However, a non-flexible optical display device including the polarizing plate of the present invention is not excluded from the scope of the present invention.

A change rate of 1% or less in the in-plane direction phase difference of the above formula 1 and a bending reliability can be implemented by an adhesive layer formed by a thermosetting adhesive composition described below.

Hereinafter, the heat-curing adhesive composition (hereinafter referred to as “adhesive composition”) is described.

The adhesive composition comprises a polyvinyl alcohol-based resin; a crosslinker having a primary amine group (-NH ₂ ) and/or a secondary amine group (-NH-); and at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.

An adhesive layer formed by the above adhesive composition can provide a change rate of the in-plane direction phase difference of the above formula 1 of 1% or less and excellent bending reliability. This can increase the reliability of the anti-reflection function of an optical display device and enable its use in flexible applications.

In addition, the adhesive composition can also provide excellent adhesion between the liquid crystal phase difference layer with low adhesiveness and the polarizer. As described above, the liquid crystal phase difference layer has low adhesiveness. In order to increase the adhesion of the liquid crystal phase difference layer, a method of surface treatment, such as corona treatment, can be considered, but the inventors have confirmed that there are limitations.

When the adhesive layer is formed with a photocurable adhesive composition, the thickness of the adhesive layer becomes thick, and when the polarizing plate is left at high temperature for a long period of time, the change rate of the in-plane directional phase difference of Equation 1 may exceed 1%, and the bending reliability is poor. Although it is not clear, when the adhesive layer is formed with a heat-curable adhesive composition, since high-temperature processing conditions have already been applied in the process of forming the adhesive layer, even if the polarizing plate is left at high temperature for a long period of time after being manufactured, the change rate of the in-plane directional phase difference is likely to be low. On the other hand, when the adhesive layer is formed with a photocurable adhesive composition, since light is irradiated in the process of forming the adhesive layer, additional heat processing is provided to the polarizing plate if it is left at high temperature for a long period of time after being manufactured, and thus the change rate of the in-plane directional phase difference may be high.

The above-described excellent adhesion can be realized by including all of a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group and/or a secondary amine group; and at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group. In this regard, the polyvinyl alcohol-based resin provides excellent adhesion to a polarizer by reacting with the crosslinking agent, and can also provide excellent adhesion to a liquid crystal phase difference layer by reacting with the polyvinyl alcohol-based resin, the polyphenol-based compound, and the crosslinking agent.

In addition, the adhesive composition can provide excellent adhesion to both the front and back surfaces of the liquid crystal phase difference layer. In one specific example, the adhesion of the adhesive layer to the liquid crystal phase difference layer can be 0.5 N or more, specifically 1 N to 10 N. In this range, there can be no peeling and/or lifting between the polarizer and the liquid crystal phase difference layer or between the liquid crystal phase difference layers.

The surface and back surface of the liquid crystal phase difference layer are described with reference to Fig. 1. Fig. 1 is an exploded view of a transfer type liquid crystal phase difference film.

Referring to FIG. 1, a transfer-type liquid crystal phase difference film includes a base film (1) and a liquid crystal phase difference layer (2) formed on one surface of the base film (1).

The transfer type liquid crystal phase difference film can be manufactured by forming an alignment film on one side of a base film (1) (the upper side of the base film in FIG. 1), coating a composition for forming a liquid crystal phase difference layer on the alignment film, orienting it, and then curing it. The side (the lower side of the liquid crystal phase difference layer in FIG. 1) (3) that was in contact with the alignment film of the liquid crystal phase difference layer is called the 'back side', and the side (the upper side of the liquid crystal phase difference layer in FIG. 1) (4) that was not in contact with the alignment film is called the 'surface'. Unlike the surface, the back side originates from the part of the base film (1) where the alignment film was formed, and thus may have different physical properties than the surface.

The substrate film (1) may include a conventional resin film known to those skilled in the art. For example, the substrate film may include a cellulose ester film such as triacetyl cellulose (TAC). The upper surface of the substrate film, i.e., the surface on which the alignment film is formed, may or may not be subjected to a release treatment.

The alignment film can be formed of a composition including, but not limited to, a polycarboxylic acid compound, an anhydride compound of a polycarboxylic acid, a diamine compound, etc.

The liquid crystal phase difference layer (2) can be formed of a composition containing the aromatic-containing liquid crystal compound described above.

The back surface and the surface of the liquid crystal phase difference layer (2) may have different water contact angles depending on the presence or absence of the alignment film. Depending on the order of the polarizing plate manufacturing process, the types of the base film and the alignment film among the transfer-type liquid crystal phase difference films, the thickness of the liquid crystal phase difference layer, and the type of liquid crystal included in the liquid crystal phase difference layer, the surface or the back surface of the liquid crystal phase difference layer may be adhered to the polarizer. Therefore, it is necessary to form an adhesive layer having excellent adhesiveness on both the surface and the back surface of the liquid crystal phase difference layer. The adhesive composition of the present invention can form an adhesive layer having excellent adhesiveness on both the surface and the back surface of the liquid crystal phase difference layer.

In one specific example, the back surface and the surface of the liquid crystal phase difference layer may have different water contact angles at 25°C after the corona treatment. For example, the back surface of the liquid crystal phase difference layer may have a water contact angle of 50° to 70° at 25°C after the corona treatment, and the surface of the liquid crystal phase difference layer may have a water contact angle of 70° to 90° at 25°C after the corona treatment. The 'corona treatment' means corona treatment at a speed of 10 mpm and an output of 1000 W. The 'water contact angle' can be measured by a conventional method known to those skilled in the art.

Below, each component of the adhesive composition is described in detail.

Aqueous solvent

The adhesive composition may further include an aqueous solvent. The aqueous solvent may facilitate application of the adhesive composition to form a thin adhesive layer.

The aqueous solvent may be, but is not limited to, water, including ultrapure water, distilled water, etc. The aqueous solvent may be included as a residual amount in the adhesive composition.

Polyvinyl alcohol resin

Polyvinyl alcohol-based resin is a vinyl-based polymer, and when a polyvinyl alcohol-based polarizer is included as a polarizer, it can have superior adhesive strength to other adhesive resins.

The polyvinyl alcohol-based resin may include polyvinyl alcohol or a derivative thereof obtained by saponifying polyvinyl acetate, or a saponified product of a copolymer with a monomer having copolymerizability with vinyl acetate, or a modified polyvinyl alcohol-based resin obtained by acetylating, urethane-izing, etherifying, grafting or phosphoric acid esterifying polyvinyl alcohol. These may be included alone or in a mixture of two or more. Monomers having the above copolymerizability include unsaturated carboxylic acids or esters thereof such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth)acrylic acid, alpha-olefins such as ethylene and propylene, (meth)allylsulfonic acid, monoalkyl maleates, disulfonic acid soda alkyl maleates, N-methylolacrylamide, acrylamide alkyl sulfonic acid alkali salts, N-vinylpyrrolidone, N-vinylpyrrolidone derivatives, etc.

In one specific example, the polyvinyl alcohol-based resin may include a polyvinyl alcohol-based resin containing an acetoacetyl group. The polyvinyl alcohol-based resin containing an acetoacetyl group may help improve the water resistance of the adhesive layer.

In one specific example, the degree of acetoacetyl group modification of the polyvinyl alcohol-based resin may be 1 mol% to 30 mol%, for example, 1 mol% to 10 mol%. In the above range, sufficient reaction sites with the crosslinking agent may be provided, thereby improving adhesive strength and increasing the water resistance of the polarizing plate. The method for producing the polyvinyl alcohol-based resin containing an acetoacetyl group is not particularly limited. For example, a method of dispersing the polyvinyl alcohol-based resin in acetic acid and adding diketene may be considered, but is not limited thereto.

The average degree of polymerization and degree of saponification of the polyvinyl alcohol-based resin are not particularly limited, and the average degree of polymerization can be 100 to 3,000, and the average degree of saponification can be 85 mol% to 100 mol%. In the above range, the adhesive strength between the polarizer and the liquid crystal phase difference layer can be further improved.

The polyvinyl alcohol-based resin may be included in an amount of 1 to 20 parts by weight, specifically 1 to 10 parts by weight, per 100 parts by weight of the aqueous solvent. In the above range, the adhesive strength of the adhesive layer can be improved, and the viscosity of the adhesive composition does not increase rapidly, so that the processability can be excellent.

Crosslinking agent having primary amine group and/or secondary amine group

A crosslinking agent having a primary amine group and/or a secondary amine group can provide adhesion by reacting with a polyvinyl alcohol-based resin, preferably a polyvinyl alcohol-based resin containing an acetoacetyl group. The crosslinking agent can help improve adhesion by forming a hydrogen bond with at least one of the polyphenol-based compounds and the epoxy-based compounds having an alkylene oxide group described below.

The crosslinking agent may be linear, branched or dendritic and may have multiple primary amine groups and/or secondary amine groups to provide adhesion to the adhesive layer. In addition, the crosslinking agent was selected from among multiple crosslinking agents used in water-based adhesives for polarizing plates because it can achieve all of the above-described effects of the present invention when combined with at least one of the polyphenol-based compounds and the epoxy-based compounds having alkylene oxide groups, which are described below.

In one specific example, the cross-linking agent having a primary amine group or a secondary amine group may include at least one of ethyleneimine-based cross-linking agents. The 'ethyleneimine-based cross-linking agent' may include a cross-linking agent synthesized by treating ethyleneimine by at least one of a known method, such as ring opening, polymerization, or derivatization. Specifically, the ethyleneimine-based cross-linking agent may include a poly(ethyleneimine)-based cross-linking agent.

The poly(ethyleneimine)-based cross-linking agent may include a linear, branched, or dendritic compound having a primary amine group and/or a secondary amine group at the terminal and a secondary amine group and/or a tertiary amine group in the main chain. The primary amine group and/or the secondary amine group can increase adhesion by reacting with a functional group of the polyvinyl alcohol-based resin, specifically, a hydroxyl group or an acetoacetyl group.

The poly(ethyleneimine) crosslinking agent may include a crosslinking agent having an ethylene group (-CH ₂ CH ₂ -) linked to a secondary amine group and/or a tertiary amine group and having a primary amine group and/or a secondary amine group at the terminal, as is known to those skilled in the art.

The weight average molecular weight of the above crosslinking agent is not particularly limited, but can be from 1 million to 1 million. Within the above range, the effect of the adhesive layer of the present invention can be well achieved.

The crosslinking agent may be included in an amount of 0.1 to 50 parts by weight, specifically 0.5 to 10 parts by weight, more specifically 1 to 10 parts by weight, or 1 to 5 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol-based resin. In the above range, the adhesion of the adhesive layer may be improved.

The crosslinking agent: at least one of the following polyphenol compounds and epoxy compounds having an alkylene oxide group may be included in the adhesive composition at a weight ratio of 1:1 to 1:20, specifically 1:1 to 1:15, and more specifically 1:1 to 1:10. In the above range, excellent adhesive strength can be achieved even at ultra-low temperatures, and excellent durability and bending reliability can be achieved at high temperatures and high humidity.

polyphenol compounds

The polyphenol compound can provide a change rate of the in-plane phase difference of the above formula 1 of 1% or less and excellent bending reliability.

The polyphenol compound may include a compound having multiple hydroxyl groups in multiple aromatic rings. The polyphenol compound may form an affinity bond with the aromatic rings of the liquid crystal phase difference layer, and may provide a higher bonding force between the polarizer and the liquid crystal phase difference layer by matching the hydroxyl group arrangement of the acetoacetylated polyvinyl alcohol resin. In addition, the polyphenol compound may be easily dissolved in an aqueous solvent due to the multiple hydroxyl groups.

The polyphenol compound may include tannic acid. Tannic acid has a pKa of 6, and can effectively implement the effects of the present invention when combined with the acetoacetylated polyvinyl alcohol resin and crosslinking agent of the present invention.

The polyphenol compound may be included in an amount of 1 to 100 parts by weight, specifically 1 to 50 parts by weight, and more specifically 3 to 35 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol resin. In the above range, excellent adhesion can be achieved even at ultra-low temperatures, and excellent durability and bending reliability can be achieved at high temperatures and high humidity.

Epoxy compound having an alkylene oxide group

An epoxy compound having an alkylene oxide group can provide a change rate of the in-plane phase difference of the above formula 1 of 1% or less and excellent bending reliability.

Meanwhile, since the liquid crystal phase difference layer is formed of the above-described hydrophobic aromatic ring liquid crystal compound, there may be a problem that the water-based adhesive is not well applied. However, an epoxy compound having an alkylene oxide group can solve the above-described problem. In one specific example, the epoxy compound having an alkylene oxide may be a non-aromatic compound that does not have an aromatic group. In addition, the epoxy compound reacts with the crosslinking agent by the epoxy group, and the crosslinking agent reacts with the polyvinyl alcohol resin, thereby ultimately providing an adhesive layer having high adhesion.

In addition, the epoxy compound having the alkylene oxide group can form a uniform adhesive layer by allowing the adhesive composition to be well applied to the liquid crystal phase difference layer at a predetermined thickness when the adhesive composition is applied to the liquid crystal phase difference layer.

An epoxy compound having an alkylene oxide group may include a linear or branched compound having an alkylene oxide group repeating unit in the compound molecule and an epoxy group at a side chain and/or terminal.

The above 'alkylene oxide group' may be *-[-O-R-]-* (* is a linking moiety, R is a straight-chain or branched-chain alkylene group having 2 to 4 carbon atoms). For example, the above alkylene oxide group may be an ethylene oxide group, an n-propylene oxide group, an iso-propylene oxide group, etc. The above 'epoxy group' may be an epoxide group, a glycidoxy group, etc. In one specific example, the epoxy compound having an alkylene oxide group may include a compound of the following chemical formula 1, but is not limited thereto:

[Chemical Formula 1]

R ¹ -[-OR-]nOR ²

(In the above chemical formula 1,

R is a straight or branched alkylene group having 2 to 4 carbon atoms,

R ¹ and R ² are each independently an epoxide group or an epoxide group-containing group,

n is an integer from 1 to 30).

The above epoxide group-containing group can be a glycidyl group or a glycidoxy group.

For example, the epoxy compound having an alkylene oxide group may include one or more of monoalkylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ether, monoalkylene glycol triglycidyl ether, and polyalkylene glycol triglycidyl ether, for example, ethylene glycol diglycidyl ether; poly(ethylene glycol) diglycidyl ether including di(ethylene glycol) diglycidyl ether, tri(ethylene glycol) diglycidyl ether, and the like; propylene glycol diglycidyl ether; and poly(propylene glycol) diglycidyl ether, but is not limited thereto.

Preferably, the epoxy compound having an alkylene oxide group may include at least one of poly(ethylene glycol) diglycidyl ether and poly(propylene glycol) diglycidyl ether. Poly(ethylene glycol) diglycidyl ether and poly(propylene glycol) diglycidyl ether can increase the bending reliability even at a lower radius of curvature.

The epoxy compound having an alkylene oxide group may be included in an amount of 1 to 100 parts by weight, specifically 1 to 50 parts by weight, and more specifically 3 to 35 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol-based resin. In the above range, the adhesion of the adhesive layer may be improved.

The adhesive composition may further include conventional additives in addition to the polyvinyl alcohol-based resin; a crosslinker having a primary amine group and/or a secondary amine group; and one or more polyphenol-based compounds and epoxy-based compounds having an alkylene oxide group. For example, the additives may include one or more of a UV absorber, a heat stabilizer, a plasticizer, a surfactant, a reaction inhibitor, an adhesion improver, a thixotropic agent, a conductivity agent, an antioxidant, a leveling agent, and a stabilizer, but are not limited thereto.

Hereinafter, a polarizing plate according to one embodiment of the present invention will be described with reference to Fig. 2.

Referring to FIG. 2, the polarizing plate includes a polarizer (100), a first adhesive layer (300), a first liquid crystal phase difference layer (200), and a third protective layer (400). A third protective layer (400) is laminated on the upper surface of the polarizer (100), and a first adhesive layer (300) and a first liquid crystal phase difference layer (200) are sequentially laminated from the polarizer (100) on the lower surface of the polarizer (100).

The first adhesive layer (300) has a thickness of 10 nm to 500 nm and is formed in direct contact with the first liquid crystal phase difference layer (200).

The first liquid crystal phase difference layer (200) has a change rate of the in-plane phase difference of the following equation 1-1 of 1% or less:

[Formula 1-1]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above formula 1-1,

A is the in-plane direction phase difference at a wavelength of 550 nm of the first liquid crystal phase difference layer (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the first liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

In the range of the change rate of the in-plane direction phase difference of the above formula 1-1, the polarizing plate can implement an anti-reflection function even after being left at a high temperature for a long period of time, so that it can provide an excellent appearance and excellent screen quality even when applied to an optical display device. Preferably, the change rate of the above formula 1-1 can be 0% to 1%.

In one specific example, A in the above formula 1-1 may be 100 nm to 220 nm, specifically 100 nm to 180 nm, and B in the above formula 1-1 may be 95 nm to 205 nm, specifically 110 nm to 170 nm.

Polarizer

The polarizer (100) linearly polarizes light incident from the outside and transmits it to the first liquid crystal phase difference layer (200) or linearly polarizes light incident from the first liquid crystal phase difference layer (200) and emits it, thereby preventing reflection of external light and implementing an anti-reflection function, thereby improving the appearance and screen quality.

The polarizer (100) may have a polarization degree of 99% or more, specifically 99.90% to 99.995%. In the above range, it may help to implement an anti-reflection function.

The polarizer (100) may include a conventional polarizer known to those skilled in the art. For example, the polarizer may include a polarizer made of a polyvinyl alcohol (PVA)-based resin film or a polypropylene (PP)-based resin film. Specifically, the polarizer may be a polyvinyl alcohol-based polarizer in which at least one of iodine and a dichroic dye is adsorbed onto a polyvinyl alcohol-based resin film, or a polyene-based polarizer made by dehydrating a polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin film may have a saponification degree of 85 mol% to 100 mol%, specifically 98 mol% to 100 mol%. The polyvinyl alcohol-based resin film may have a polymerization degree of 1,000 to 10,000, specifically 1,500 to 10,000. With the above saponification degree and polymerization degree, a polarizer can be made. Polarizers can be manufactured by conventional methods known to those skilled in the art.

The polarizer (100) may have a thickness of 5 ㎛ to 30 ㎛, specifically 5 ㎛ to 25 ㎛. In the above range, it may be used in a polarizing plate and may implement a thinning effect of the polarizing plate.

1st liquid crystal phase difference layer

The first liquid crystal phase difference layer (200) prevents reflection of external light by circularly polarizing the linearly polarized light emitted after the external light passes through the polarizer (100), thereby implementing an anti-reflection function, thereby improving the appearance and screen quality.

In one specific example, the first liquid crystal phase difference layer (200) may have an in-plane phase difference (Re) of 100 nm to 220 nm, specifically 100 nm to 180 nm, for example, a λ/4 phase difference, at a wavelength of 550 nm. In the above range, the reflectivity for external light may be lowered, thereby obtaining an effect of improving screen quality.

In another specific example, the first liquid crystal phase difference layer (200) may have an in-plane phase difference (Re) of 225 nm to 350 nm, specifically 225 nm to 300 nm, for example, a phase difference of λ/2, at a wavelength of 550 nm. In the above range, the reflectivity for external light can be lowered, thereby obtaining an effect of improving screen quality.

In one specific example, the first liquid crystal phase difference layer (200) may exhibit reverse wavelength dispersion. The reverse wavelength dispersion means that Re(450) < Re(550) < Re(650). Here, Re(450), Re(550), and Re(650) represent in-plane direction phase differences of the first liquid crystal phase difference layer at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

The first liquid crystal phase difference layer (200) may have a thickness of 0.1 ㎛ to 10 ㎛, for example, 1 ㎛ to 5 ㎛. In the above range, the polarizing plate can be made thin and the target phase difference can be implemented.

The first liquid crystal phase difference layer (200) can be formed using the liquid crystal composition described above.

Although not shown in FIG. 2, an adhesive layer or bonding layer may be formed on the lower surface of the first liquid crystal phase difference layer (200) so as to bond the polarizing plate to a panel for an optical display device, etc. The adhesive layer or bonding layer may be formed of a (meth)acrylic composition known to those skilled in the art, but is not limited thereto.

First adhesive layer

The first adhesive layer (300) is formed between the polarizer (100) and the first liquid crystal phase difference layer (200), and can adhere the polarizer (100) and the first liquid crystal phase difference layer (200) to each other.

The first adhesive layer (300) can be formed by directly contacting the polarizer and the first liquid crystal phase difference layer, respectively. The first adhesive layer (300) can simultaneously provide a change rate of the in-plane direction phase difference of Equation 1-1 of 1% or less and bending reliability.

The inventor of the present invention confirmed that simply increasing the adhesion of the first adhesive layer (300) to the polarizer or liquid crystal phase difference layer cannot simultaneously provide a change rate of 1% or less in the in-plane direction phase difference of the above formula 1-1 and bending reliability.

The first adhesive layer (300) has a thickness of 10 nm to 500 nm. Specifically, it may be 50 nm to 500 nm, and more specifically, 50 nm to 200 nm. In the above range, a thinning effect of the polarizing plate can be obtained.

The first adhesive layer (300) is formed using the thermosetting adhesive composition described above. Through this, the first adhesive layer can be made thin, and the change rate of the in-plane direction phase difference of Equation 1-1 after the polarizing plate is left at a high temperature for a long period of time can be 1% or less, and the bending reliability can be improved. The details of the thermosetting adhesive composition are substantially the same as described above.

The adhesive composition is a thermosetting composition and can form a first adhesive layer by thermal curing. For example, the thermal curing is not particularly limited and can be performed at least once at, for example, 40° C. to 100° C. for 1 minute to 60 minutes.

Third layer of protection

The third protective layer (400) is formed on the upper surface of the polarizer (100) to protect the polarizer (100) or provide additional functions to the polarizing plate.

In one specific example, the third protective layer (400) may have an in-plane phase difference of 0 nm to 100 nm, specifically 0 nm to 30 nm, at a wavelength of 550 nm. In the above range, it may be easy to provide an anti-reflection effect.

The third protective layer (400) may include a conventional optically transparent protective film or protective coating layer known to those skilled in the art. For example, the protective film may include at least one of a cellulose ester resin including triacetyl cellulose (TAC), a cyclic polyolefin resin including amorphous cyclic polyolefin, a polycarbonate resin, a polyester resin including polyethylene terephthalate (PET), a polyethersulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, an acyclic-polyolefin resin, a polyacrylate resin including polymethyl methacrylate resin, a polyvinyl alcohol resin, a polyvinyl chloride resin, and a polyvinylidene chloride resin.

The third protective layer (400) has a thickness of 5 ㎛ to 200 ㎛, specifically 30 ㎛ to 120 ㎛, and in the case of a protective film type, it can be 10 ㎛ to 100 ㎛, and in the case of a protective coating layer type, it can be 1 ㎛ to 50 ㎛. It can be used in a polarizing plate within the above range.

Although not shown in FIG. 2, a functional coating layer such as a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, etc. may be additionally formed on the upper surface of the third protective layer (400) to provide additional functions to the polarizing plate.

In addition, although not shown in FIG. 2, the third protective layer (400) may be adhered to the polarizer (100) by an adhesive layer. At this time, the adhesive layer may be formed of the adhesive composition for the polarizing plate of the present invention described above, or may be formed of a water-based adhesive or a photocurable adhesive known to those skilled in the art.

Hereinafter, a polarizing plate of another embodiment of the present invention will be described with reference to FIG. 3.

Referring to FIG. 3, the polarizing plate includes a third protective layer (400), a polarizer (100), a first adhesive layer (300a), a first liquid crystal phase difference layer (200), a second adhesive layer (600), and a second liquid crystal phase difference layer (500).

A third protective layer (400) is laminated on the upper surface of the polarizer (100), and a first adhesive layer (300a), a first liquid crystal phase difference layer (200), a second adhesive layer (600), and a second liquid crystal phase difference layer (500) are sequentially laminated on the lower surface of the polarizer (100).

The second adhesive layer (600) has a thickness of 10 nm to 500 nm and is formed in direct contact with each of the first liquid crystal phase difference layer (200) and the second liquid crystal phase difference layer (600).

The first liquid crystal phase difference layer (200) has a change rate of the in-plane phase difference of the following equation 1-2 of 1% or less:

[Formula 1-2]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above equation 1-2,

A is the in-plane direction phase difference at a wavelength of 550 nm of the first liquid crystal phase difference layer (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the first liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

In the range of the change rate of the in-plane direction phase difference of the above formula 1-2, the polarizing plate can implement an anti-reflection function even after being left at a high temperature for a long period of time, so that it can provide an excellent appearance and excellent screen quality even when applied to an optical display device. Preferably, the change rate of the above formula 1-2 can be 0% to 1%.

In one specific example, A in the above formula 1-2 may be 225 nm to 350 nm, specifically 225 nm to 300 nm, and B in the above formula 1-2 may be 220 nm to 355 nm, specifically 220 nm to 305 nm.

The second liquid crystal phase difference layer (500) has a change rate of the in-plane direction phase difference of Equation 1-3 below of 1% or less:

[Formula 1-3]

Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100

(In the above equation 1-3,

A is the in-plane direction phase difference at a wavelength of 550 nm of the second liquid crystal phase difference layer (unit: nm)

B is the in-plane direction phase difference (unit: nm) of the second liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.

In the range of the change rate of the in-plane direction phase difference of the above formula 1-3, the polarizing plate can implement an anti-reflection function even after being left at a high temperature for a long period of time, so that it can provide an excellent appearance and excellent screen quality even when applied to an optical display device. Preferably, the change rate of the above formula 1-3 can be 0% to 1%.

In one specific example, A in the above formula 1-3 may be 100 nm to 220 nm, specifically 100 nm to 180 nm, and B in the above formula 1-3 may be 95 nm to 205 nm, specifically 110 nm to 170 nm.

The third protective layer (400), polarizer (100), and first liquid crystal phase difference layer (200) are each substantially the same as described in FIG. 2 above.

Second liquid crystal phase difference layer

The second liquid crystal phase difference layer (500) can improve screen quality by preventing reflection of external light by circularly polarizing the linearly polarized light emitted after the external light passes through the polarizer (100).

In one specific example, the second liquid crystal phase difference layer (500) may have an in-plane phase difference of 225 nm to 350 nm, specifically 225 nm to 300 nm, for example, a phase difference of λ/2, at a wavelength of 550 nm. In the above range, the reflectivity for external light may be lowered, thereby obtaining a screen quality improvement effect. In another specific example, the second liquid crystal phase difference layer (500) may have an in-plane phase difference of 100 nm to 220 nm, specifically 100 nm to 180 nm, for example, a phase difference of λ/4, at a wavelength of 550 nm. In the above range, the reflectivity for external light may be lowered, thereby obtaining a screen quality improvement effect. In yet another specific example, the second liquid crystal phase difference layer (500) may have reverse wavelength dispersion.

The second liquid crystal phase difference layer (500) can be formed using the liquid crystal composition described above. Although not shown in Fig. 3, an adhesive layer or bonding layer can be formed on the lower surface of the second liquid crystal phase difference layer (500) so that the polarizing plate can be adhered to a panel for an optical display device, etc.

Second adhesive layer

The second adhesive layer (600) is formed between the first liquid crystal phase difference layer (200) and the second liquid crystal phase difference layer (500), and can adhere the first liquid crystal phase difference layer (200) and the second liquid crystal phase difference layer (500) to each other.

The second adhesive layer (600) has a thickness of 10 nm to 500 nm. Specifically, it may be 50 nm to 500 nm, and more specifically, 50 nm to 200 nm. In the above range, a thinning effect of the polarizing plate can be obtained.

The second adhesive layer (600) is formed using the thermosetting adhesive composition described above. Through this, the second adhesive layer can be made thin, and the rate of change in the in-plane direction phase difference of Equations 1-2 and 1-3 after the polarizing plate is left at a high temperature for a long period of time can be 1% or less, and the bending reliability can be improved. Details of the thermosetting adhesive composition are substantially the same as described above. The second adhesive layer (600) can be formed by thermal curing including, but not limited to, treatment at 40° C. to 100° C. for 1 minute to 60 minutes at least once.

First adhesive layer

The first adhesive layer (300a) may be formed of a typical photocurable adhesive known to those skilled in the art. The photocurable adhesive may include an epoxy compound or a (meth)acrylic compound, and a photoinitiator. The epoxy compound or the (meth)acrylic compound, and the photoinitiator may be selected from typical types known to those skilled in the art and used. At this time, the first adhesive layer (300a) may have a thickness of 1 µm to 10 µm, for example, 1 µm to 5 µm. In the above range, the adhesive strength between the first liquid crystal phase difference layer and the second liquid crystal phase difference layer can be secured, and the thickness of the polarizing plate can be reduced. In another specific example, the first adhesive layer (300a) may be formed of a typical water-based thermosetting adhesive known to those skilled in the art. For example, the water-based thermosetting adhesive may include a polyvinyl alcohol-based resin and a crosslinking agent. At this time, the first adhesive layer (300a) may have a thickness of 10 nm to 500 nm, for example, 50 nm to 200 nm. In the above range, a thinning effect of the polarizing plate can be obtained.

The present invention also includes a polarizing plate in which a first adhesive layer is formed of the thermosetting adhesive composition for a polarizing plate of the present invention described above. At this time, the first adhesive layer may have a thickness of 10 nm to 500 nm, for example, 50 nm to 200 nm. In the above range, a thinning effect of the polarizing plate can be obtained, and the effects of the present invention can be better implemented.

Hereinafter, a polarizing plate according to another embodiment of the present invention will be described with reference to FIG. 4.

Referring to FIG. 4, the polarizing plate includes a third protective layer (400), a polarizer (100), a first adhesive layer (300), a first liquid crystal phase difference layer (200), a second adhesive layer (600a), and a second liquid crystal phase difference layer (500). The polarizing plate of FIG. 2 is substantially the same as the polarizing plate of FIG. 2, except that the second adhesive layer (600a) and the second liquid crystal phase difference layer (500) are sequentially laminated on the lower surface of the first liquid crystal phase difference layer (200). The second liquid crystal phase difference layer (500) can be formed of the liquid crystal composition described in FIG. 3. The second adhesive layer (600a) can be formed of the composition for the first adhesive layer described in FIG. 3.

Hereinafter, a polarizing plate according to another embodiment of the present invention will be described with reference to FIG. 5.

Referring to FIG. 5, the polarizing plate includes a third protective layer (400), a polarizer (100), a first adhesive layer (300), a first liquid crystal phase difference layer (200), and a fourth phase difference layer (700).

A third protective layer (400) is laminated on the upper surface of the polarizer (100), and a first adhesive layer (300), a first liquid crystal phase difference layer (200), and a fourth phase difference layer (700) are sequentially laminated on the lower surface of the polarizer (100). It is substantially the same as the polarizing plate of Fig. 2, except that a fourth phase difference layer (700) is further formed on the lower surface of the first liquid crystal phase difference layer (200).

The fourth phase difference layer (700) can further improve the anti-reflection function of the polarizing plate. In one specific example, the first liquid crystal phase difference layer (200) can exhibit reverse wavelength dispersion.

The fourth phase difference layer (700) may include a positive C layer where nz>nx≒ny (where nx, ny, and nz are refractive indices of the fourth phase difference layer in the slow axis direction, the fast axis direction, and the thickness direction, respectively, at a wavelength of 550 nm). In one specific example, the fourth phase difference layer (700) may have a thickness direction phase difference of -300 nm to -10 mm, for example, -200 nm to -30 nm, at a wavelength of 550 nm. The fourth phase difference layer (700) may have an in-plane phase difference of 0 nm to 10 nm, for example, 0 nm to 5 nm, at a wavelength of 550 nm. In the above range, a reflectivity reduction effect may be realized.

The fourth phase difference layer (700) can be a polymer film or a coating layer. If the fourth phase difference layer (700) is a polymer film, it can be adhered to the first liquid crystal phase difference layer (200) by an adhesive layer, for example, the second adhesive layer described above. If the fourth phase difference layer (700) is a coating layer, it can be adhered to the first liquid crystal phase difference layer (200) without an adhesive layer or by an adhesive layer.

Hereinafter, a method for manufacturing a polarizing plate of the present invention will be described.

A method for manufacturing a polarizing plate may include the steps of applying an adhesive composition for a polarizing plate of the present invention to a surface or back surface of a liquid crystal phase difference layer to form a coating layer, laminating the coating layer with a polarizer, and curing the adhesive composition for a polarizing plate to adhere the polarizer and the liquid crystal phase difference layer.

The method for manufacturing a polarizing plate may include the steps of applying the adhesive composition for a polarizing plate of the present invention to the surface or back surface of a liquid crystal phase difference layer to form a coating layer, laminating the coating layer and the liquid crystal phase difference layer, and curing the adhesive composition for a polarizing plate to adhere the liquid crystal phase difference layer and the liquid crystal phase difference layer. Before applying the adhesive composition for a polarizing plate to the surface or back surface of the liquid crystal phase difference layer, the adhesive strength may be increased by performing corona treatment on the surface or back surface of the liquid crystal phase difference layer, respectively.

The above application can be performed by a conventional method known to those skilled in the art. For example, it can include, but is not limited to, a die coater, a bar coater, etc. The above curing can include thermally curing the coating layer. Thermal curing is not particularly limited and can be performed at least once at, for example, 40° C. to 100° C. for 1 minute to 60 minutes.

The optical display device of the present invention includes the polarizing plate of the present invention.

For example, the optical display device may include, but is not limited to, a light-emitting display device including an organic light-emitting display device, a liquid crystal display device, and the like. For example, the optical display device may include a flexible optical display device.

Hereinafter, the configuration and operation of the present invention will be described in more detail through examples of the present invention. However, the following examples are intended to help understanding of the present invention, and the scope of the present invention is not limited to the following examples.

A. Third protective layer: COP film (G+, Zeon, hard coating layer formed on the upper surface, thickness: 28㎛)

B. First liquid crystal phase difference film: A liquid crystal phase difference film (Fujifilm, QLAA218, with an absorption axis aligned at an angle of 17.5° with respect to the MD of the TAC film) having a liquid crystal phase difference layer (having a phase difference of λ/2 at a wavelength of 550 nm) formed on the lower surface of a base film (TAC film, thickness: 80 ㎛)

C. Second liquid crystal phase difference film: A liquid crystal phase difference film (Fujifilm, QLAB, TAC film, thickness: 80 ㎛) having a liquid crystal phase difference layer (having a phase difference of λ/4 at a wavelength of 550 nm) formed on the upper surface of a base film (TAC film, thickness: 80 ㎛) (the absorption axis is oriented at an angle of 77.5° with respect to the MD of the film)

D. Corona treatment: Corona irradiation at 10mpm speed and 1000W output using a corona treatment device (AFS Corporation).

Example 1

<Third layer treatment>

The lower surface of the third protective layer was subjected to the above-described corona treatment.

<Polarizer manufacturing>

A polyvinyl alcohol film (Mitsubishi Chemical Co., polymerization degree: 2800, thickness: 20 μm) was dyed by immersing it in a 0.3% iodine aqueous solution. The film was stretched along the MD axis at a stretching ratio of 5.0 times. The stretched polyvinyl alcohol film was immersed in a 3% boric acid aqueous solution and a 2% potassium iodide aqueous solution to perform color correction. A polarizer (thickness: 7 μm) was manufactured by drying it at 50°C for 4 minutes.

<Manufacturing of photocurable adhesive for polarizing plates>

A photocurable adhesive for a polarizing plate was manufactured by mixing 80 parts by weight of an epoxy compound 2021P (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate, Daicel), 20 parts by weight of an epoxy compound EX141 (phenyl glycidyl ether, Nagase Chemtec), and 5 parts by weight of a cationic polymerization initiator CPI100P (SanApro).

<Manufacture of water-based thermosetting adhesive composition for polarizing plates>

3 parts by weight of acetoacetylated polyvinyl alcohol-based resin (Mitsubishi Chemical Co., Ltd., Z200, acetoacetylated polyvinyl alcohol resin, average degree of polymerization: 1200, degree of saponification: 99 mol%, degree of acetoacetylation modification: 5 mol%) was dissolved in 100 parts by weight of water at 95°C, and stirred for 60 minutes. The obtained solution was completely cooled to room temperature, and 0.1 part by weight of a poly(ethyleneimine)-based crosslinking agent (Japan Catalyst Co., Ltd., SP018, having a primary amine group and/or a secondary amine group) and 0.15 parts by weight of tannic acid (Daejung Chemicals Co., Ltd., 100% solids) were sequentially added, mixed together, and stirred with a magnetic stirrer to prepare an aqueous thermosetting adhesive composition for a polarizing plate.

<Manufacturing of polarizing plates>

The surface of the first liquid crystal phase difference film B was subjected to the above-described corona treatment.

3 parts by weight of polyvinyl alcohol-based resin (Mitsubishi Chemical Co., Ltd., Z200, acetoacetylated polyvinyl alcohol resin, average degree of polymerization: 1200, degree of saponification: 99 mol%, degree of acetoacetylation modification: 5 mol%) was dissolved in 100 parts by weight of water at 95°C, and stirred for 60 minutes. The obtained solution was completely cooled to room temperature, and 0.1 parts by weight of a poly(ethyleneimine)-based crosslinking agent (Japan Catalyst Co., Ltd., SP018) and 0.5 parts by weight of a zirconium compound (Zircosol-ZN, water as a solvent, Jeil Heewon Chemical Industry Co., Ltd.) were sequentially added, mixed together, and stirred with a magnetic stirrer to prepare an adhesive for a polarizing plate.

The upper surface of the polarizer manufactured above was coated with the adhesive for a polarizing plate manufactured above to a predetermined thickness, and the lower surface of a third protective layer was laminated on the obtained coating layer.

Then, the prepared water-based thermosetting adhesive composition for polarizing plates was coated on the lower surface of the polarizer to a predetermined thickness, and the surface side of the first liquid crystal phase difference film B was laminated on the obtained coating layer. At this time, the MD of the polarizer and the MD of the TAC film among the first liquid crystal phase difference film B were aligned with each other. Then, by leaving it in a 50°C oven for 1 minute and in an 85°C oven for 3 minutes, a laminate was manufactured in which the third protective layer / adhesive layer / polarizer / first adhesive layer / first liquid crystal phase difference film (liquid crystal phase difference layer / TAC film) were laminated in that order.

Among the first liquid crystal phase difference films, the TAC film was peeled from the laminate to expose the back surface of the liquid crystal phase difference layer. The back surface was subjected to the corona treatment described above.

The photocurable adhesive for polarizing plates manufactured as described above was applied to the back surface of the above-described liquid crystal phase difference layer to a predetermined thickness, and the surface side of the second liquid crystal phase difference film was laminated on the obtained coating layer. At this time, the MD of the polarizer and the MD of the TAC film in the second liquid crystal phase difference film were aligned with each other. Then, UV was irradiated at 100 mJ/cm ² from the second liquid crystal phase difference film side with a metal halide lamp, and after leaving it at room temperature for 1 day, the TAC film in the second liquid crystal phase difference film was peeled off. Through this, a polarizing plate was manufactured in which third protective layer / adhesive layer (thermosetting adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (thermosetting adhesive layer containing tannic acid, thickness: 100 nm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photocurable adhesive layer, thickness: 3 ㎛) / second liquid crystal phase difference layer (λ/4 phase difference) was laminated in this order.

Example 2

<Manufacture of water-based thermosetting adhesive composition for polarizing plates>

3 parts by weight of acetoacetylated polyvinyl alcohol-based resin (Mitsubishi Chemical Co., Ltd., Z200, acetoacetylated polyvinyl alcohol resin, average degree of polymerization: 1200, degree of saponification: 99 mol%, degree of acetoacetylation modification: 5 mol%) was dissolved in 100 parts by weight of water at 95°C, and stirred for 60 minutes. The obtained solution was completely cooled to room temperature, and 0.1 part by weight of a polyethyleneimine-based crosslinking agent (Japan Catalyst Co., Ltd., SP018, having a primary amine group and/or a secondary amine group) and 0.1 part by weight of poly(ethylene glycol) diglycidyl ether (EX821, Nagase Chemtech Co., Ltd.) as an epoxy compound were sequentially added, mixed together, and stirred with a magnetic stirrer to prepare an aqueous thermosetting adhesive composition for a polarizing plate.

Except that the aqueous thermosetting adhesive composition for a polarizing plate containing the epoxy-based compound manufactured above was used instead of the aqueous thermosetting adhesive composition for a polarizing plate containing tannic acid in Example 1, a polarizing plate was manufactured by laminating third protective layer / adhesive layer (thermosetting adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (thermosetting adhesive layer containing an epoxy-based compound, thickness: 110 nm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photocurable adhesive layer, thickness: 3 µm) / second liquid crystal phase difference layer (λ/4 phase difference) in that order.

Example 3

Referring to Example 1, a polarizing plate was manufactured by laminating third protective layer/adhesive layer (thermo-curable adhesive layer, thickness: 100 nm)/polarizer/first adhesive layer (photo-curable adhesive layer, thickness: 3 μm)/first liquid crystal phase difference layer (λ/2 phase difference)/second adhesive layer (thermo-curable adhesive layer containing tannic acid, thickness: 100 nm)/second liquid crystal phase difference layer (λ/4 phase difference) in that order.

Comparative Example 1

3 parts by weight of polyvinyl alcohol-based resin (Mitsubishi Chemical Co., Ltd., Z200, acetoacetylated polyvinyl alcohol resin, average degree of polymerization: 1200, degree of saponification: 99 mol%, degree of acetoacetylation modification: 5 mol%) was dissolved in 100 parts by weight of water at 95°C, and stirred for 60 minutes. The obtained solution was completely cooled to room temperature, and 0.1 parts by weight of a poly(ethyleneimine)-based crosslinking agent (Japan Catalyst Co., Ltd., SP018) and 0.5 parts by weight of a zirconium compound (Zircosol-ZN, water as a solvent, Jeil Heewon Chemical Industry Co., Ltd.) were sequentially added, mixed together, and stirred with a magnetic stirrer to prepare an adhesive for a polarizing plate.

Except that the first adhesive layer was manufactured using the above-mentioned adhesive for a polarizing plate, a polarizing plate was manufactured by laminating, in the following order, a third protective layer / adhesive layer (thermosetting adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (thermosetting adhesive layer free of epoxy compound having tannic acid and alkylene oxide groups, thickness: 100 nm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photocurable adhesive layer, thickness: 3 μm) / second liquid crystal phase difference layer (λ/4 phase difference) in the same manner as in Example 1.

Comparative Example 2

에서 6시간 반응시켜, 중량 평균 분자량 170만의 아크릴계 중합체를 함유하는 용액을 얻었다. 또한, 이 아크릴계 중합체를 함유하는 용액에 메틸에틸케톤을 첨가하여 고형분 농도를 20％의 아크릴계 중합체 용액을 얻었다. 상기 아크릴계 중합체 용액의 고형분 100부에 대해 이소시아네이트계 가교제(Soken社의 L-45)를 0.3부를 가교제로 투입하고, 실란 커플링제(신에쯔社의 KMB-403)을 0.05부 투입하여 점착제 용액을 제조했다. 상기 점착제 용액을, 박리 처리한 폴리에틸렌테레프탈레이트 필름(두께 38㎛)으로 이루어지는 이형 시트의 표면에, 건조 후의 두께가 15㎛로 되도록 도포하고, 건조하여, 점착제층을 형성하였다.In a reaction vessel equipped with a condenser, a nitrogen introduction tube, a thermometer and a stirring device, 100 parts of n-butyl acrylate, 2 parts of acrylic acid, 0.2 parts of 2-hydroxyethyl acrylate and 0.3 parts of 2,2'-azobisisobutyronitrile were added together with ethyl acetate to prepare a solution. The solution was stirred under a nitrogen gas atmosphere and stirred for 60

By reacting for 6 hours in a solution containing an acrylic polymer having a weight average molecular weight of 1.7 million, a solution was obtained. In addition, methyl ethyl ketone was added to the solution containing the acrylic polymer to obtain an acrylic polymer solution having a solid content concentration of 20%. With respect to 100 parts of the solid content of the acrylic polymer solution, 0.3 parts of an isocyanate crosslinking agent (L-45 of Soken) was added as a crosslinking agent, and 0.05 parts of a silane coupling agent (KMB-403 of Shinetsu) was added to prepare an adhesive solution. The adhesive solution was applied to the surface of a release sheet made of a polyethylene terephthalate film (thickness: 38 μm) that had been subjected to a peeling treatment so that the thickness after drying became 15 μm, and dried to form an adhesive layer.

A polarizing plate was manufactured by laminating third protective layer / adhesive layer (thermo-curable adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (acrylic adhesive layer, thickness: 15 μm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photo-curable adhesive layer, thickness: 3 μm) / second liquid crystal phase difference layer (λ/4 phase difference) in the same manner as in Example 1, except that the first adhesive layer was manufactured using the above-mentioned manufactured adhesive layer.

Comparative Example 3

A photocurable adhesive for a polarizing plate was manufactured by mixing 80 parts by weight of an epoxy compound 2021P (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate, Daicel), 20 parts by weight of an epoxy compound EX141 (phenyl glycidyl ether, Nagase Chemtec), and 5 parts by weight of a cationic polymerization initiator CPI100P (SanApro).

Except that the first adhesive layer was manufactured using the photocurable adhesive for the polarizing plate manufactured above, a polarizing plate was manufactured in which the third protective layer / adhesive layer (thermocurable adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (photocurable adhesive layer, thickness: 3 μm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photocurable adhesive layer, thickness: 3 μm) / second liquid crystal phase difference layer (λ/4 phase difference) were laminated in the same order as in Example 1.

Comparative Example 4

A photocurable adhesive for a polarizing plate was manufactured by mixing 80 parts by weight of an epoxy compound 2021P (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate, Daicel), 20 parts by weight of an epoxy compound EX141 (phenyl glycidyl ether, Nagase Chemtec), and 5 parts by weight of a cationic polymerization initiator CPI100P (SanApro).

Except that the first adhesive layer was manufactured using the photocurable adhesive for the polarizing plate manufactured above, a polarizing plate was manufactured in which the third protective layer / adhesive layer (thermocurable adhesive layer, thickness: 100 nm) / polarizer / first adhesive layer (photocurable adhesive layer, thickness: 0.5 μm) / first liquid crystal phase difference layer (λ/2 phase difference) / second adhesive layer (photocurable adhesive layer, thickness: 3 μm) / second liquid crystal phase difference layer (λ/4 phase difference) were laminated in the same order as in Example 1.

The following physical properties were evaluated for the polarizing plates of the examples and comparative examples, and the results are shown in Table 1 below.

(1) Folding test: A rectangular specimen with a length x width (MD x TD, 200 mm x 150 mm) was manufactured so that the polarizing plates manufactured in the examples and comparative examples had the absorption axis of the polarizer at a 45-degree angle (diagonal direction). The specimens manufactured above were folded and unfolded at room temperature with the second liquid crystal phase difference layer on the inside and the third protective layer, the COP film, on the outside so that the radius of curvature was 2 mm, and the number of times this was done was considered one. The first number of times cracks or interlayer lifting occurred at the folded portion was evaluated.

◎ If cracks and interlayer lifting do not occur even after more than 200,000 cycles

○ If cracks or interlayer lifting occur after 100,000 to 200,000 repetitions

△ If cracks or interlayer lifting occur after 50,000 to 100,000 repetitions

If cracks or delamination occurred at less than 50,000 cycles, it was evaluated as ⅹ.

(2) Adhesion force (unit: N): The polarizing plates manufactured in the examples and comparative examples were cut to a size of 100 mm x 25 mm (MD x TD) of the polarizer to manufacture samples. Cellophane tape (length x width, 150 mm x 25 mm) was attached to the liquid crystal phase difference layer side of the above-mentioned sample so that 50 mm remained, to manufacture specimens for measuring the peeling force. The third protective layer side of the above-mentioned specimen was attached to the grab of a texture analyzer (TA, TX C model) that measures the peeling force, and the cellophane tape of the above-mentioned specimen was fixed to the lower grab of the peeling force measuring device. When the first liquid crystal phase difference layer was peeled from the first adhesive layer at a peeling temperature of 25°C, a peeling speed of 300 mm/min, and a peeling angle of 180°, the average peeling force over the length section was evaluated. Example 3 evaluated the average peeling force when the second liquid crystal phase difference layer was peeled from the second adhesive layer.

(3) Rate of change in in-plane directional phase difference (unit: %): For the polarizing plates of the examples and comparative examples, the in-plane directional phase difference (phase difference A) of the liquid crystal phase difference layer was measured at a wavelength of 550 nm using a phase difference measuring device AXOSCAN (Axometry). After leaving the polarizing plates at 80°C for 250 hours, the in-plane directional phase difference (phase difference B) of the liquid crystal phase difference layer was measured at a wavelength of 550 nm using the same method as above. The measured phase differences A and B were used to calculate the rate of change in the in-plane directional phase difference using the above formula for calculating the rate of change in the in-plane directional phase difference.

type thickness Folding test Adhesion Rate of change of phase difference in the plane direction First adhesive layer Second adhesive layer First adhesive layer Second adhesive layer 1st liquid crystal phase difference layer Second liquid crystal phase difference layer Example 1 Heat curing adhesive layer
(including tannic acid) Photocurable adhesive layer 100nm 3㎛ ◎ 2N 0.6% - Example 2 Heat curing adhesive layer
(including epoxy compounds having alkylene oxide groups) Photocurable adhesive layer 110nm 3㎛ ◎ 2.3N 0.6% - Example 3 Photocurable adhesive layer Heat-curing adhesive layer (containing tannic acid) 3㎛ 100nm ◎ 1N 0.7% 0.7% Comparative Example 1 Thermosetting adhesive layer (excluding epoxy compounds having tannic acid and alkylene oxide groups) Photocurable adhesive layer 100nm 3㎛ ⅹ
Due to reduced adhesion
delamination 0.2N Unable to measure due to delamination - Comparative Example 2 Acrylic adhesive layer Photocurable adhesive layer 15㎛ 3㎛ ⅹCrack occurrence 5N 5.2% - Comparative Example 3 Photocurable adhesive layer Photocurable adhesive layer 3㎛ 3㎛ ○ 1N 3.6% - Comparative Example 4 Photocurable adhesive layer Photocurable adhesive layer 0.5㎛ 3㎛ ⅹ
Due to reduced adhesion
Excited 0.3N 9.0% -

*In Table 1 above, “-” indicates that the result was not measured.

As shown in Table 1 above, the polarizing plate of the present invention exhibited a low in-plane phase difference change rate of the liquid crystal phase difference layer even after being left at a high temperature for a long period of time, and also had excellent bending reliability. Therefore, although not shown in Table 1, the polarizing plate of the present invention is easy to implement an anti-reflection function even after being left for a long period of time, and can be used in a flexible display device.

However, in Comparative Examples 1 to 4, in which the adhesive layer formed by directly contacting the liquid crystal phase difference layer is not the adhesive layer of the present invention, interlayer peeling occurred between the polarizer and the liquid crystal phase difference layer, or the in-plane phase difference change rate of Equation 1 significantly exceeded 1%. In particular, in Comparative Examples 2 and 3, although the adhesion between the polarizer and the liquid crystal phase difference layer was excellent, the in-plane phase difference change rate of Equation 1 significantly exceeded 1%, confirming that there is a limit to lowering the in-plane phase difference change rate simply by increasing the adhesion.

Simple modifications or changes of the present invention can be easily implemented by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (20)

A polarizer comprising a liquid crystal phase difference layer laminated on a lower surface of the polarizer, and further comprising an adhesive layer formed by directly contacting an upper surface or a lower surface of the liquid crystal phase difference layer, wherein the liquid crystal phase difference layer contains a hydrophobic aromatic-containing liquid crystal compound,
The adhesive layer is formed of a thermosetting adhesive composition and has a thickness of 10 nm to 500 nm, and the adhesive layer includes at least one of a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.
The above liquid crystal phase difference layer is a polarizing plate in which the change rate of the in-plane direction phase difference of the following equation 1 is 1% or less:
[Formula 1]
Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100
(In the above equation 1,
A is the in-plane direction phase difference of the liquid crystal phase difference layer at a wavelength of 550 nm (unit: nm)
B is the in-plane direction phase difference (unit: nm) of the liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.
delete A polarizing plate in claim 1, wherein the liquid crystal phase difference layer has an in-plane phase difference of 100 nm to 220 nm or 225 nm to 350 nm at a wavelength of 550 nm.
A polarizing plate in claim 1, wherein the liquid crystal phase difference layer has reverse wavelength dispersion.
A polarizing plate, wherein in the first paragraph, the adhesion of the adhesive layer to the liquid crystal phase difference layer is 0.5 N or more.
delete A polarizing plate in claim 1, wherein the adhesive layer is formed of a composition comprising a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group (-NH ₂ ) and/or a secondary amine group (-NH-); and at least one of the polyphenol-based compound and the epoxy-based compound having an alkylene oxide group.
A polarizing plate in claim 7, wherein the cross-linking agent includes a poly(ethyleneimine)-based cross-linking agent.
A polarizing plate in claim 7, wherein the polyphenol compound contains tannic acid.
A polarizing plate in claim 7, wherein the epoxy compound having an alkylene oxide group includes at least one of monoalkylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ether, monoalkylene glycol triglycidyl ether, and polyalkylene glycol triglycidyl ether.
A polarizing plate comprising, in claim 7, 100 parts by weight of the polyvinyl alcohol-based resin, 0.1 to 50 parts by weight of the crosslinking agent, and 1 to 100 parts by weight of at least one of the polyphenol-based compound and the epoxy-based compound having an alkylene oxide group.
In the first paragraph, the polarizing plate comprises the adhesive layer, the liquid crystal phase difference layer, the second adhesive layer, and the second liquid crystal phase difference layer, which are sequentially laminated on the lower surface of the polarizer.
A polarizing plate in claim 12, wherein the second adhesive layer is formed of at least one of a photocurable adhesive and a heat-curable adhesive.
A polarizing plate in claim 13, wherein the thermosetting adhesive comprises at least one of a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group and/or a secondary amine group; and a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.
In the first paragraph, the polarizing plate includes a first adhesive layer, the liquid crystal phase difference layer, the adhesive layer, and a second liquid crystal phase difference layer, which are sequentially laminated on the lower surface of the polarizer.
A polarizing plate in claim 15, wherein the first adhesive layer is formed of at least one of a photocurable adhesive and a heat-curable adhesive.
In the 16th paragraph, the second liquid crystal phase difference layer is a polarizing plate in which the change rate of the in-plane direction phase difference of the following equation 1-3 is 1% or less:
[Formula 1-3]
Rate of change of phase difference in the plane = {｜B - A｜/ A} x 100
(In the above equation 1-3,
A is the in-plane direction phase difference at a wavelength of 550 nm of the second liquid crystal phase difference layer (unit: nm)
B is the in-plane direction phase difference (unit: nm) of the second liquid crystal phase difference layer at a wavelength of 550 nm after leaving the polarizing plate at 80°C for 250 hours.
A polarizing plate in claim 16, wherein the thermosetting adhesive comprises at least one of a polyvinyl alcohol-based resin; a crosslinking agent having a primary amine group and/or a secondary amine group; and a polyphenol-based compound and an epoxy-based compound having an alkylene oxide group.
A polarizing plate in accordance with claim 1, wherein a third protective layer is further laminated on the upper surface of the polarizer.
An optical display device comprising a polarizing plate according to any one of claims 1, 3 to 5, and 7 to 19.