TWI467213B - Method of preparing a protective film for a polarizing plate - Google Patents

Description

Method for preparing polarizing plate protective film

The invention relates to a method for preparing a polarizing plate protective film, in particular to a method for preparing a polarizing plate protective film capable of adjusting a phase retardation value of a polarizing plate protective film during preparation.

The main function of the polarizing plate in a liquid crystal display (LCD) is to control the polarization direction of a specific light wave to generate polarized light. The polyvinyl alcohol (PVA) film in the polarizing plate has a good iodine absorption tensile property to make the PVA film. After adsorbing iodine, it is stretched with mechanical external force to allow the iodine molecules to be linearly aligned along the extending direction. However, the iodine molecule is easily combined with the moisture in the air, and the PVA film which is insufficient in moisture resistance and heat resistance is liable to cause edge shrinkage due to the influence of the temperature of the panel backlight, so that the PVA film is protected and supported. The polarizing plate protective film is attached to the upper and lower sides of the PVA film.

Cellulose is the most abundant polymer found in nature. Cellulose acetate is obtained by reacting natural cellulose with acetic anhydride. It has high transparency, low optical heterogeneity, good solvent resistance and heat resistance. It is suitable as a substrate for a polarizing plate protective film. Acetic acid The degree of cellulose acetate determines its properties. For example, the degree of acetic acidization of cellulose triacetate (TAC) is about 59-62%, and the degree of acetic acid of cellulose diacetate (DAC). It is about 50~58%, both of which have high transparency, but TAC has higher heat resistance and is more suitable as a protective substrate for polarizing plates.

The display quality of the liquid crystal display is affected by the phase retardation value of the polarizer protective film. The phase retardation value is an optical property related to the thickness of the refractive index coefficient in the x, y, and z directions of the film surface, and the phase retardation value can be divided into a phase retardation value (Re) in the planar direction and a phase retardation value (Rth) in the thickness direction, and the calculation method thereof As follows: Re = (Nx-Ny) × d

Rth=[(Nx+Ny)/2-Nz]×d, where the refractive index of the direction of the slow axis of the plane of the Nx film (the direction in which the light travels slowly); the direction of the phase of the phase in the plane of the Ny film (refractive index in the direction in which the light travels faster); refractive index in the thickness direction of the Nz film; d film thickness.

The method of adjusting the phase retardation value of the protective film of the polarizing plate of the cellulose halide is disclosed in the Republic of China Patent Publication No. 200801097, which is to extend the direction of the protective film of the polarizing plate by a stretching ratio of 1.0 to 2.0 times, and The vertical direction of this direction is extended by a stretching ratio of 1.01 to 2.5 times to adjust the required phase delay value. In the case of manufacturing a polarizing plate protective film whose base material is a cellulose resin, the polarizing plate protective film is stretched at a stretching ratio of 0.8 to 2.0 in one direction, and is positive in the direction. The plane direction of the intersection, from 1.01 to 2.5 The stretching ratio is stretched, whereby Re and Rth fall within the desired range.

However, at present, the method of adjusting the phase retardation value of the protective film of the polarizing plate by the extension process is such that if the stretching ratio is too small during the stretching process, a sufficient phase difference cannot be obtained, and if the stretching ratio is too large, the protective film of the polarizing plate is generated. The situation of the break. Further, when the film is stretched in the uniaxial direction, the thickness of the protective film of the polarizing plate is likely to fluctuate. When the film thickness is excessively changed, a phase difference is formed on the protective film, and when it is applied to a liquid crystal display device, There are problems such as color spots in the display, and the phase delay value of the polarizing plate protective film is adjusted by the extension process, and the manufacturing process is cumbersome and high in cost.

Therefore, it is possible to find a way to replace the extension process so that during the process of preparing the polarizing plate protective film, when the phase retardation value is adjusted, there is no breakage of the polarizing plate protective film, excessive film thickness variation, cumbersome process and high cost, etc. The problem that will arise when the process adjusts the phase delay value has become the goal of current research.

Therefore, the object of the present invention is to provide a replacement extension process for adjusting the phase retardation value in the process of preparing a polarizing plate protective film without causing breakage of the polarizing plate protective film and excessive film thickness variation. A method of preparing a polarizing plate protective film with a problem of simple process and low cost.

Therefore, the method for preparing a polarizing plate protective film of the present invention comprises the following steps: (1) preparing a protective film solution comprising cellulose acetate, magnetic particles and a solvent; and (2) applying the protective film solution to a substrate. Forming a film; And (3) providing a magnet and moving the magnet in a predetermined direction such that the magnetic particles in the film are affected by the magnetic field of the magnet to cause orientation of the film.

The effect of the present invention is that the magnetic particles in the film are affected by the magnetic field of the magnet to cause orientation of the film, whereby the phase retardation value of the protective film of the polarizing plate can be easily adjusted without further adjustment by the stretching process. Therefore, the method of the present invention does not have problems such as breakage of the polarizing plate protective film, excessive variation in film thickness, cumbersome process, and high cost.

The present invention will be described in detail below. The cellulose acetate of the step (1) may be any cellulose acetate type which is suitable for use as a substrate for a polarizing plate protective film. Preferably, the cellulose acetate is selected from the group consisting of cellulose acetate. A cellulose triacetate, a cellulose diacetate, a cellulose acetate propionate, a cellulose acetate butyrate, or a combination thereof. In a particular embodiment of the invention, the cellulose acetate is cellulose triacetate.

Preferably, the cellulose acetate is contained in an amount of from 5 to 30% by weight based on 100% by weight of the protective film solution of the step (1).

The magnetic particles of the step (1) may be any conventional metal particles having magnetic properties. Preferably, the magnetic particles are selected from the group consisting of iron, cobalt, nickel, or a combination thereof. In a particular embodiment of the invention, the magnetic particles are iron.

Preferably, the content of the magnetic particles ranges from 0.005 to 0.3% by weight based on 100% by weight of the protective film solution of the step (1). When the magnetic When the content of the particles is less than 0.005 wt%, the content of the magnetic particles in the film is too small, so that when the phase retardation value of the protective film of the polarizing plate is adjusted, the phase retardation value can be changed little; if the magnetic property is When the particle content is more than 0.3% by weight, the light transmittance of the polarizing plate protective film is lowered. More preferably, the content of the magnetic particles ranges from 0.005 to 0.15 wt%.

Preferably, the magnetic particles of the step (1) have a particle size ranging from 5 to 400 nm. When the particle diameter of the magnetic particle is more than 400 nm, the light transmittance of the polarizing plate protective film is lowered due to the excessive particle diameter of the magnetic particle; when the particle diameter range of the magnetic particle is less than 5 nm Since the magnetic particles are difficult to produce, the acquisition is difficult, and thus the preparation of the polarizing plate protective film is affected. More preferably, the magnetic particles of the step (1) have a particle size ranging from 20 to 100 nm.

The solvent of the step (1) may be a solvent conventionally used for preparing a protective film for a polarizing plate. Preferably, the solvent is selected from the group consisting of dichloromethane, chloroform, methanol, acetone, or a combination thereof. In a particular embodiment of the invention, the solvent is a combination of dichloromethane and methanol.

Preferably, the magnet of the step (3) can be any material having a magnetic field size ranging from 1000 to 8000 gauss. More preferably, the magnet is selected from the group consisting of a samarium cobalt magnet, a neodymium iron boron magnet, an alnico magnet, a ferrite magnet, a neodymium iron boron magnet, or a combination thereof. In a particular embodiment of the invention, the magnet is a neodymium iron boron magnet (the magnetic field is about 4600 Gauss).

Preferably, the method for preparing a polarizing plate protective film of the present invention, after the step (3), further comprises a step (4) of drying the film.

The present invention will be further illustrated by the following examples, but it should be understood that this embodiment is intended to be illustrative only and not to be construed as limiting.

<Use raw materials and instruments>

Cellulose triacetate (TAC): purchased from Eastman Chemical Company, the degree of acetic acidization is 43.48%.

Dichloromethane: purchased from the company Panreac, with a purity of 99%.

Methanol: purchased from SIGMA-ALDRICH, with a purity of 99.8%.

Nano magnetic iron powder: purchased from Yongsheng Materials Technology Co., Ltd., spherical powder with a purity greater than 99.5%.

Adjustable wet film applicator: ZEHNTNER ZUA2000, purchased from Quanhua Technology Co., Ltd.

Phase difference high speed inspection machine: RE-100, purchased from Otsuka Technology Co., Ltd.

Ultraviolet-visible spectrometer: JASCO V-550, purchased from Shangwei Technology Co., Ltd.

NdFeB magnets: 13cm long, 2cm wide, 1.5cm thick, purchased from Guishi Enterprise Co., Ltd.

<Example 1>

Preparation of polarizing plate protective film (triacetate content of 9.95 Wt%, nano magnetic iron powder content is 0.1605wt%, there are magnets used in the film making process)

Step (1): 50.4 g of dichloromethane is taken, 5.6 g of methanol is added with stirring, and 0.1 g of nano magnetic iron powder (magnetic particles, average particle diameter of 46.4 nm) is further added, and the nano magnetic iron powder is uniformly dispersed. After adding 6.2 g of cellulose triacetate, sealing and stirring for 3 hours, and allowing to stand for 48 hours, a protective film solution was obtained.

Step (2): placing the protective film solution obtained in the step (1) on a 1 cm thick glass substrate, and then using a tunable wet film coater (adjusting the thickness to 1000 μm) at a speed of 1 cm per second. The protective film solution is applied to the glass substrate along a predetermined direction to form a film.

Step (3): providing a neodymium iron boron strong magnet to be in close contact with the back surface of the glass substrate (ie, the substrate is opposite to the side of the film), and the predetermined direction when the protective film solution is coated along the step (2) Slowly moving at a speed of 1 cm per second, the nano magnetic iron powder in the film is affected by the magnetic field of the NdFeB magnet, so that the film is oriented.

Step (4): the film treated in the step (3) is allowed to stand at room temperature for 2 hours, and then subjected to film removal to obtain a film thickness of 70 μm and a cellulose triacetate content of 9.95 wt%. A polarizing plate protective film having a nano magnetic iron powder content of 0.1605 wt%.

<Example 2>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.97 wt%, the content of nano magnetic iron powder was 0.0161 wt%, and a magnet was used in the film formation process)

The procedure of Example 2 is the same as that of Example 1, except that step (1) of Example 2 is to add 0.01 g of nano magnetic iron powder having an average particle diameter of 46 nm, and finally to obtain a film thickness of 70 μm and triacetic acid. A polarizing plate protective film having a cellulose content of 9.97 wt% and a nano magnetic iron powder content of 0.0161 wt%.

<Example 3>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.97 wt%, the content of nano magnetic iron powder was 0.0129 wt%, and a magnet was used in the film formation process)

The procedure of Example 3 is the same as that of Example 1, except that the step (1) of Example 3 is to add 0.008 g of nano magnetic iron powder having an average particle diameter of 45.5 nm, and finally to obtain a film thickness of 70 μm, three. A polarizing plate protective film having a cellulose acetate content of 9.97 wt% and a nano magnetic iron powder content of 0.0129 wt%.

<Example 4>

Preparation of polarizing plate protective film (triacetate content of 9.97 wt%, nano magnetic iron powder content of 0.0096% by weight, using magnets during film formation)

The procedure of Example 4 is the same as that of Example 1, except that step (1) of Example 4 is to add 0.006 g of nano magnetic iron powder having an average particle diameter of 45 nm, and finally to obtain a film thickness of 70 μm and triacetic acid. A polarizing plate protective film having a cellulose content of 9.97 wt% and a nano magnetic iron powder content of 0.0096 wt%.

<Comparative Example 1>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.95 wt%, the content of nano magnetic iron powder was 0.1605 wt%, and no magnet was used in the film formation process)

Step (1): 50.4 g of dichloromethane was taken, 5.6 g of methanol was added with stirring, and 0.1 g of nano magnetic iron powder (magnetic particles, average particle diameter of 45.4 nm) was added thereto, and the mixture was stirred and uniformly dispersed with nano magnetic iron. After the powdering, 6.2 g of cellulose triacetate was added, sealed and continuously stirred for 3 hours, and then allowed to stand for 48 hours to obtain a protective film solution.

Step (2): placing the protective film solution obtained in the step (1) on a 1 cm thick glass substrate, and then using a tunable wet film coater (adjusting the thickness to 1000 μm) at a speed of 1 cm per second. The protective film solution is applied to the glass substrate along a predetermined direction to form a film.

Step (3): the film obtained in the step (2) is allowed to stand at room temperature for 2 hours, and then subjected to film removal to obtain a film thickness of 70 μm and a cellulose triacetate content of 9.95 wt%. A polarizing plate protective film having a magnetic iron powder content of 0.1605% by weight.

<Comparative Example 2>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.97 wt%, the content of nano magnetic iron powder was 0.0161 wt%, and no magnet was used in the film formation process)

The procedure of Comparative Example 2 was the same as that of Comparative Example 1, except that the step (1) of Comparative Example 2 was to add 0.01 g of nano magnetic iron powder having an average particle diameter of 45.3 nm, and finally to obtain a film thickness of 70 μm, three. Polarizing plate having a cellulose acetate content of 9.97 wt% and a nano magnetic iron powder content of 0.0161 wt% Protective film.

<Comparative Example 3>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.97 wt%, the content of nano magnetic iron powder was 0.0129 wt%, and no magnet was used in the film formation process)

The procedure of Comparative Example 3 was the same as that of Comparative Example 1, except that the step (1) of Comparative Example 3 was to add 0.008 g of nano magnetic iron powder having an average particle diameter of 45.4 nm, and finally to obtain a film thickness of 70 μm, three. A polarizing plate protective film having a cellulose acetate content of 9.97 wt% and a nano magnetic iron powder content of 0.0129 wt%.

<Comparative Example 4>

A polarizing plate protective film was prepared (the content of cellulose triacetate was 9.97 wt%, the content of nano magnetic iron powder was 0.0096% by weight, and no magnet was used in the film formation process)

The procedure of Comparative Example 4 was the same as that of Comparative Example 1, except that the step (1) of Comparative Example 4 was the addition of 0.006 g of nano magnetic iron powder having an average particle diameter of 47 nm, and finally a film thickness of 70 μm and triacetic acid was obtained. A polarizing plate protective film having a cellulose content of 9.97 wt% and a nano magnetic iron powder content of 0.0096 wt%.

<Comparative Example 5>

Preparation of polarizing plate protective film (triacetate content of 9.97 wt%, no nano magnetic iron powder, no magnet used in the film making process)

The procedure of Comparative Example 5 was the same as that of Comparative Example 1, except that the step (1) of Comparative Example 5 was not added with any nano magnetic iron powder, and finally a film was obtained. A polarizing plate protective film having a thickness of 70 μm and a cellulose triacetate content of 9.97 wt%.

<Measurement and Analysis of Phase Delay Value of Polarizing Plate Protective Film>

The polarizing plate protective films obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were cut into a film having a size of 10 cm × 10 cm. The film was placed in a phase difference high-speed inspection machine, the refractive index was set to 1.5 (refractive index of cellulose triacetate), and the plane direction phase retardation value Re and the thickness direction phase retardation value Rth were measured by a halogen lamp source having a wavelength of 550 nm. The results obtained are shown in Table 1 below.

As can be seen from Table 1, in Examples 1 to 4 in which nano magnetic iron powder and magnet were used at the same time, the phase retardation value Re in the plane direction of Examples 1 to 4 was compared with Comparative Example 5 in which the nano magnetic iron powder and the magnet were not used. It will increase significantly with the increase of nano magnetic iron powder content, and the thickness direction phase retardation value Rth will also decrease significantly with the increase of nano magnetic iron powder content, confirming the method of the present invention. It is indeed possible to effectively increase the plane direction phase retardation value Re of the polarizing plate protective film and reduce the thickness direction phase retardation value Rth of the polarizing plate protective film in the process of preparing the polarizing plate protective film. Specifically, in Example 1, which has a large content of nano magnetic iron powder, compared with Examples 2 to 4 in which the content of nano magnetic iron powder is small, Example 1 (nano magnetic iron powder content is 0.1605 wt%). ) The light transmittance is low.

In Comparative Examples 1 to 4 in which nano magnetic iron powder was added but no magnet was used, the phase retardation value Re in the plane direction of Comparative Examples 1 to 4 was compared with Comparative Example 5 in which the nano magnetic iron powder and the magnet were not used. The increase of the content of magnetic iron powder in rice is only slightly increased, and the phase retardation value Rth in the thickness direction decreases only slightly with the increase of the content of nano magnetic iron powder; and the comparative examples 1 to 4 which do not use magnets respectively have the same nanometer. The magnetic iron powder content is compared with Examples 1 to 4 using magnets. In Comparative Examples 1 to 4, as the nano magnetic iron powder content increases, the plane direction retardation value Re increases in the plane direction and the thickness direction phase retardation value Rth decreases. None of the examples 1 to 4 are obvious, and it is confirmed that the comparative examples 1 to 4 in which the magnet is not used, the influence of the amount of the nano magnetic iron powder on the phase retardation values Re and Rth is not the same as the examples 1 to 4 using the magnet. It is also remarkable that the method of the present invention can effectively adjust the phase retardation value of the protective film of the polarizing plate during the preparation of the protective film of the polarizing plate when the nano magnetic iron powder and the magnet are simultaneously used.

In summary, since the nano magnetic iron powder (magnetic particles) in the film is affected by the magnetic field of the NdFeB magnet, the film is oriented, whereby the phase retardation of the polarizing plate protective film can be easily adjusted. Therefore, there is no problem that the polarizing plate protective film is broken, and the film thickness is excessively changed. Moreover, the process is simple and the cost is low, so the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes and modifications made by the patent application scope and the patent specification of the present invention are still It is within the scope of the patent of the present invention.

Claims (10)

A method for preparing a polarizing plate protective film comprises the following steps: (1) preparing a protective film solution comprising cellulose acetate, magnetic particles and a solvent; and (2) forming a protective film solution on a substrate a film; and (3) providing a magnet and moving the magnet in a predetermined direction such that magnetic particles in the film are affected by the magnetic field of the magnet to cause orientation of the film. The method of claim 1, wherein the cellulose acetate of the step (1) is selected from the group consisting of cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, or Combination of the foregoing. The method of claim 1, wherein the magnetic particles of the step (1) are selected from the group consisting of iron, cobalt, nickel, or a combination thereof. The method of claim 1, wherein the solvent of the step (1) is selected from the group consisting of dichloromethane, chloroform, methanol, acetone, or a combination thereof. The method according to claim 1, wherein the cellulose acetate is contained in an amount of from 5 to 30% by weight based on 100% by weight of the protective film solution of the step (1). The method according to claim 1, wherein the content of the magnetic particles is from 0.005 to 0.3% by weight based on 100% by weight of the protective film solution of the step (1). The method of claim 6, wherein the content of the magnetic particles ranges from 0.005 to 0.15 wt%. The method of claim 1, wherein the magnetic particles of the step (1) The particle size ranges from 5 to 400 nm. The method of claim 8, wherein the magnetic particles of the step (1) have a particle size ranging from 20 to 100 nm. The method of claim 1, after the step (3), further comprising the step (4) of drying the film.