KR101197160B1 - Composition for liquid crystal alignment film - Google Patents

Abstract

The present invention relates to a novel liquid crystal alignment film composition used in the manufacture of an optical film laminate applied to an LCD panel, wherein the composition for liquid crystal alignment film of the present invention is 1.0 to 5.0% by weight of polyvinyl alcohol or cellulose acetate, 0.01 to 1.0 It is characterized by consisting of a weight percent adhesion promoter, 0.01 to 1.0 weight percent reactive acrylate, 0.01 to 1.0 weight percent photoinitiator and the balance of the solvent.

This invention produced the liquid crystal aligning film of the coating system without an adhesion layer using the novel polymer composition mentioned above, and brought about the effect which remarkably reduces the thickness of an optical film laminated body.

Alignment film, optical film, liquid crystal

Description

Liquid crystal aligning film composition for optical film laminated bodies {COMPOSITION FOR LIQUID CRYSTAL ALIGNMENT FILM}

The present invention relates to a liquid crystal alignment film composition for an optical film laminate, and more particularly, to a liquid crystal alignment film composition for an optical film laminate applied to a liquid crystal display device.

A liquid crystal display generally includes an upper substrate on which a common electrode, a color filter, and the like are formed, a lower substrate on which a thin film transistor, a pixel electrode, and the like are formed, and a liquid crystal cell positioned between the upper substrate and the lower substrate. The liquid crystal display forms an electric field by applying different potentials to the pixel electrode and the common electrode, and the arrangement of the liquid crystal molecules in the liquid crystal cell is changed by the electric field, thereby adjusting the transmittance of light to express an image.

As such, a liquid crystal display using liquid crystal has been attracting attention as an alternative means of overcoming the disadvantages of the conventional brown because of its advantages of miniaturization, light weight, and low power consumption. It is attached and is used.

As described above, the liquid crystal display device has advantages in power, etc., compared to the conventional display device. However, since the liquid crystal molecules having anisotropy are used to implement the screen, the brightness and contrast ratio of the screen vary depending on the viewing angle.

In addition, since the liquid crystal display device is a light receiving device that does not emit light by itself, a light source (backlight unit) for providing light must be provided. In general, since light generated from the backlight of the liquid crystal display device passes through various paths before reaching the viewer's eye, the amount of light that can be observed from the eye is limited to a part of light emitted from the backlight. As a result, the light utilization efficiency of the backlight unit is reduced, and the brightness of the screen is reduced.

In the conventional liquid crystal display device, the above problems are solved by using a film laminate in which various optical films such as a compensation film and a retardation film are stacked. Here, the compensation film is a film having an anisotropy distribution opposite to that of the liquid crystal cell. When the compensation film is used, the delay difference of light according to the viewing angle of the liquid crystal cell is canceled to play a role of alleviating the problem caused by the anisotropy of the liquid crystal. . In addition, the retardation film is a film for changing the phase of the light, increases the light utilization efficiency, and serves to improve the brightness of the screen by improving the light characteristics.

Recently, many optical films using a curable liquid crystal are used as the optical films. In the case of the optical film using the liquid crystal, a liquid crystal alignment film for the basic alignment of the liquid crystal is required.

The liquid crystal alignment film is used for the basic alignment of the liquid crystal driven with respect to a specific mode, and was conventionally mainly used for the liquid crystal alignment of the liquid crystal cell. In general, the alignment layer is formed by a rubbing treatment by coating an imide-based polymer on the glass substrate, wherein the imide-based polymer is used as an alignment layer material with excellent liquid crystal alignment force and thermal stability and good chemical resistance. However, the imide-based polymer is not suitable for forming an alignment film for an optical film formed on a polymer film instead of a glass substrate because a high temperature heat treatment process of more than 200 degrees is required to form an alignment film. In addition, because the imide-based polymer is expensive, there is also a problem that the production cost is too high when used in a relatively high loss film process.

In view of these problems, conventionally, a polymer film has been prepared in advance, and anisotropy has been imparted by performing stretching or the like on the polymer film, and then an optical film laminate has been manufactured by laminating and bonding them using an adhesive. . However, in this case, the manufacturing process inevitably needs to be made of a film having a sufficient thickness, and the thickness of the optical film laminate becomes thick due to the presence of the adhesive layer, and as a result, there is a limit in the reduction of the weight and thickness of the LCD device. There is this.

 Therefore, an object of this invention is to provide the novel liquid crystal aligning film composition for optical film laminated bodies which are low in production cost, are suitable for an optical film, are formed by a coating method, and do not require an adhesion layer.

The liquid crystal aligning film composition of the present invention comprises 1.0 to 5.0% by weight of polyvinyl alcohol or cellulose acetate; 0.01 to 1.0 weight percent adhesion promoter; 0.01 to 1.0% by weight of reactive acrylate monomer; 0.01 to 1.0 wt% photoinitiator; And it comprises the remainder of the solvent, It is characterized by the above-mentioned.

Preferably, the adhesion promoter of the present invention is selected from the group consisting of polyvinylphenol and polyethyleneimine.

In addition, the reactive acrylate monomer of the present invention is pentaerythritol tri (meth) acrylate, triglycerol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, Pentaerythritol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) It is preferable to select 1 or more types from the group which consists of an acrylate, methoxyethyl (meth) acrylate, N, N- dimethylaminoethyl (methyl) acrylate, and butoxy triethylene glycol (meth) acrylate.

In addition, it is preferable to use methyl ethyl ketone or a mixed solvent of water and methanol as the solvent, and the methanol is preferably mixed in an amount of 1 to 50% by volume based on the total volume of the mixed solvent.

On the other hand, the composition of the present invention preferably has a solid content of 1.0 to 8.0% by weight.

This invention brought about the effect of remarkably reducing the thickness of a liquid crystal optical film laminated body by using a novel liquid crystal aligning film composition, and forming a film laminated body by a coating method without an adhesion layer.

In addition, the present invention has the effect of reducing the production cost by using an inexpensive polyvinyl alcohol or cellulose acetate polymer instead of expensive imide-based polymer.

Moreover, when the novel liquid crystal aligning film composition of this invention is used, the liquid crystal film excellent in the adhesiveness and stability between interfaces as well as the orientation of a liquid crystal can be manufactured.

The inventors of the present invention, as a result of repeated studies to achieve the above object, to develop a novel liquid crystal aligning film composition for an optical film laminate, which is low in production cost and capable of forming an optical film laminate having a thin thickness. Reached.

Hereinafter, the liquid crystal aligning film composition of this invention is demonstrated more concretely.

Composition

The novel liquid crystal aligning film composition of the present invention comprises polyvinyl alcohol or cellulose acetate, an adhesion promoter, a reactive acrylate monomer, a photoinitiator and a solvent.

Herein, the polyvinyl alcohol polymer or cellulose acetate polymer is used to induce liquid crystal alignment, and the content thereof is preferably about 1.0 to 5.0 wt% based on the total weight of the composition solution. If the content is less than 1.0% by weight, the thickness of the coated alignment film is formed to be lower than the appropriate thickness to lower the orientation force, and when the content exceeds 5.0% by weight, it is because the viscosity of the composition is too high to facilitate the thickness control. At this time, it is preferable that the polyvinyl alcohol has a hydrolysis of 87 to 89% and a molecular weight Mw of 10,000 to 120,000.

On the other hand, the adhesion promoter is added to improve the adhesion of the alignment layer, polyvinyl phenol (Poly (4-vinylphenol)) or polyethyleneimine (polyethyleneimine) may be used, the content of which is based on the total weight of the composition solution It is preferable that it is about 0.01 to 1.0 weight%. If the content is less than 0.01% by weight, the effect of adhesion promotion at the interface between the liquid crystal layers is not seen, and when it exceeds 1.0% by weight, the alignment ability of the liquid crystal coated on the upper side may be lowered.

The reactive acrylate monomer serves as a crosslinking agent, the content of which is preferably about 0.01 to 1.0% by weight based on the total weight of the composition solution. Like the adhesion promoter, when the content of the reactive acrylate monomer is less than 0.01% by weight, the effect of adhesion promotion at the interface between the liquid crystal layers is not seen, and when it exceeds 1.0% by weight, the alignment ability of the liquid crystal coated on the top This can be reduced.

The reactive acrylate monomers of the present invention are pentaerythritol tri (meth) acrylate, triglycerol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, pentaerythrate Lithol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate , Methoxyethyl (meth) acrylate, N, N-dimethylaminoethyl (methyl) acrylate, butoxytriethylene glycol (meth) acrylate, and the like.

As the photoinitiator, a water-soluble photoinitiator used for thin film coating may be used, and specific examples thereof include IRGACURE 500, IRGACURE 754, or IRGACRE 2959 manufactured by Ciba Specialty Chemicals. The content of the photoinitiator is preferably about 0.01 to 1.0% by weight. If the content is less than 0.01% by weight, the curing rate of the functional monomer is lowered, which is not preferable. If the content is more than 1.0% by weight, the unreacted photoinitiator lowers the alignment ability of the liquid crystal.

On the other hand, the solvent is preferably an organic solvent such as methyl ethyl ketone or a mixed solvent of water and methanol, wherein the mixing ratio of methanol is preferably about 1 to 50% by volume. In addition, in order to ensure appropriate coating properties, the solids content of the solution is preferably 1.0 to 8.0% by weight.

Composition preparation method

The liquid crystal aligning film composition of the present invention comprises the above-mentioned 1.0 to 5.0 wt% polyvinyl alcohol or cellulose acetate, 0.01 to 1.0 wt% adhesion promoter, 0.01 to 1.0 wt% reactive acrylate monomer in an organic solvent or a mixed solvent of water and methanol And 0.01 to 1.0% by weight of photoinitiator.

film Laminate  Manufacturing method

The curable liquid crystal film laminate generally uses a polymer film of polyester, cellulose acetate, or polyvinyl alcohol as a substrate. The surface of the substrate is generally rubbed with a rubbing cloth to induce liquid crystal alignment, and an optically anisotropic material is laminated on the rubbed substrate to form a film layer. In this case, as the optically anisotropic material, a liquid crystal mixture in the form of an acrylate that can be polymerized by a photoreaction is usually used, and in particular, a liquid crystal mixture having a single axis, horizontal alignment, easily mixed with an organic solvent, and having good coating properties may be used. desirable.

After coating the liquid crystal mixture, the first laminated film is produced by drying and UV curing, and the liquid crystal aligning film composition solution prepared by the above method is coated on the surface of the laminated film. There is no particular limitation on the coating method, but in order to form a thin and uniform alignment layer, it is preferable to coat by the solution cast method.

When the alignment layer coating step is completed, the alignment layer is dried in a drying oven. It is preferable that drying temperature is 80-100 degreeC, and it is preferable that drying time is about 1 minute-about 5 minutes. The drying temperature is an important factor in the alignment position attitude of the liquid crystal, and may not be properly aligned in a region outside the proper temperature section. In addition, if the drying does not occur sufficiently may cause stains, the drying is preferably carried out for 1 minute or more, the drying time is enough so that the drying time is limited to 1 to 5 minutes.

Next, a UV curing step for curing the crosslinking agent is performed. What is necessary is just to perform UV hardening according to a normal liquid crystal hardening method.

Next, since the formed alignment film does not yet have anisotropy in a specific direction, it is necessary to perform a rubbing treatment in a desired direction in order to impart anisotropy to the alignment film. The rubbing treatment is performed by mechanically rubbing the surface of the alignment film using a rubbing cloth such as rayon. When liquid crystal molecules are applied onto the alignment layer by the rubbing treatment, the liquid crystal molecules interact with the surface of the polymer to be aligned in the rubbing direction.

As described above, the liquid crystal mixture solution is further laminated on the rubbed alignment layer, dried, and cured to form a secondary laminated film layer, thereby manufacturing a film laminate. If necessary, an alignment film is formed on the secondary laminated film by the same method as described above, and the liquid crystal mixture is further laminated on the alignment film to form a film laminate in which a plurality of liquid crystal films are laminated.

The present invention can be used as a film using a curable liquid crystal, irrespective of its kind, that is, a semi-transmissive reflective polarizing plate, an optical retardation film, a compensation film, and the like, and the curable liquid crystal used is also not limited in form. However, when the objective of manufacturing the liquid-crystal film laminated body oriented horizontally on a plane is aimed, more excellent effect can be acquired.

Since the liquid crystal alignment film composition of the present invention uses a coating method, it is possible to form an optical film laminate having a thin thickness compared to the conventional optical film laminate, which is adhesive, and relatively low-cost polyvinyl alcohol or cellulose acetate polymer Because of this, the production cost is reduced.

desirable Example

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention. However, the following examples are merely examples of the present invention, and the present invention is not limited by the following examples.

[ Synthetic example ]

The alignment film composition consisting of 74.0% by weight of polyvinyl alcohol, 5.0% by weight of polyvinylphenol, 14.0% by weight of pentaerythritol triacrylate, and 7.0% by weight of photoinitiator (Irgacure 2959) is mixed with water and methanol in 3: 2 (% by volume). 5 wt% of the total solution was dissolved in the prepared solvent to prepare an alignment layer solution.

[ Example ]

Example  One: Acromatic  1/4 Phase difference  film Of the laminate  Produce

The surface of the polymer substrate made of polyester material was rubbed using a winding roll. Rayon was used as a rubbing cloth for rubbing.

Thereafter, the liquid crystal solution in which the cyano biphenyl acrylate monomer was dissolved in a toluene solvent at 25% by weight was coated on the surface of the polymer substrate by a solution cast method. At the time of coating, the thickness of the liquid crystal layer was controlled to about 1 μm to form a quarter wavelength retardation film layer. The coated isotropic liquid crystal layer was dried in a drying oven for 1 minute at a temperature of 25 ° C. and fixed with a liquid crystal quarter wavelength retardation film layer oriented in a constant direction. The fixed film layer was then cured by UV curing to form a solid quarter-wave retardation film layer.

Thereafter, the alignment film solution prepared by the synthesis example was coated on the 1/4 wavelength retardation film layer by the solution cast method. The coated alignment layer solution was dried at 80 ° C. to form a polymer film layer, and the polymer film layer was rubbed with a rubbing cloth such that the alignment angle with the quarter-wave retardation film formed at the bottom was 60 degrees to form an alignment layer. The thickness of the formed alignment film was about 300 nm.

Next, in order to form a 1/2 wavelength retardation film again on the alignment layer, a 1/2 wavelength retardation film having a thickness of 1.6 μm was formed under the same conditions as the 1/4 wavelength retardation film.

Through the above process, an achromatic quarter-wave retardation film laminate in which a quarter-wave retardation film, an alignment film, and a half-wave retardation film were laminated in order from the bottom was obtained on the polymer substrate.

The thickness of the film laminate obtained by the example was about 3 μm except for the lowermost polymer substrate, and as a result, the anisotropic polymer film, which had a thickness of about 100 μm, was provided by the adhesive. It was confirmed that the ultra-thin achromatic quarter-wave retardation film laminate, which is only 3% of the thickness of the achromatic quarter-wave retardation film laminate, can be obtained.

[ Comparative example ]

An alignment layer solution was prepared by dissolving an alignment layer composition composed of polyvinyl alcohol alone at 4.0 wt% based on the total weight of the solution in a solvent in which water and methanol were mixed at 3: 2 (vol%).

A retardation film laminate was produced in the same manner as in Example 1 using the alignment film solution. The retardation film laminate thus produced is shown in FIG. 2.

Experimental Example  : Measurement of Layer Bonding Performance

The retardation film laminate prepared in Example and the retardation film laminate prepared in Comparative Example were transferred from the polyester film substrate on the adhesive-treated glass substrate, respectively, and then the interlayer bonding force of the retardation film was tested using an adhesive tape.

The interlayer bonding force was measured by attaching a strong adhesive tape to the surface of the film transferred to the glass plate with the same area (20 × 50 mm), and then applying a constant force to compare the degree of peeling.

3 is a photograph showing whether the tape peeled off after the bonding force test for the retardation film laminate prepared in Example, Figure 4 is a photograph showing whether the peeling tape after the bonding force test for the retardation film laminate prepared by the Comparative Example. to be. The section indicated by the dotted line is the section where the tape was peeled off. As shown in Figure 3 and 4, it can be seen that when using the alignment film composition of the present invention, the interlayer bonding force is much better than when using the conventional PVA alignment film composition.

On the other hand, Figures 5 and 6 are measured by using a polarizing microscope in the polarizer orthogonal state of the film specimens of the Examples and Comparative Examples, respectively, the more uniform and the liquid crystal alignment, the darker and brighter (small white point on the photo) appears. 5 and 6, it can be seen that the film specimen of the example is superior to the orientation force compared to the film specimen of the comparative example.

1 is a cross-sectional view showing a typical transflective LCD structure divided into layers,

2 is a cross-sectional view showing a layer arrangement method of an optical film laminate according to the present invention,

3 is a photograph showing the tape peeling after the laminate of the alignment film and the liquid crystal film formed by the alignment film composition of the present invention,

4 is a photograph showing the tape peeling of the laminate of the alignment film and the liquid crystal film formed by the conventional alignment film composition.

5 is a photograph of a film laminate specimen prepared according to an example, measured with a polarization microscope,

FIG. 6 is a photograph of a film laminate specimen prepared by a comparative example, measured with a polarization microscope.

<Key Symbols in Drawing>

1: polarizing film 2: retardation film

3: liquid crystal layer 4: reflecting plate

5: retardation film 6: polarizing film

7: Backlight 8: 1/2 wavelength retardation film

9: polymer alignment film 10: 1/4 wavelength retardation film

Claims (6)

1.0 to 5.0 weight percent polyvinyl alcohol or cellulose acetate; 0.01 to 1.0 weight percent polyvinylphenol; 0.01 to 1.0 weight percent pentaerythritol tri (meth) acrylate; 0.01 to 1.0 wt% photoinitiator; And The liquid crystal aligning film composition for optical film laminated bodies which consisted of the remainder of solvent. delete delete The method of claim 1, As said solvent, the mixed solvent of water and methanol is used, The liquid crystal aligning film composition for optical film laminated bodies characterized by the above-mentioned. 5. The method of claim 4, The methanol is mixed in an amount of 1 to 50% by volume based on the total volume of the mixed solvent, the liquid crystal aligning film composition for an optical film laminate. The method of claim 1, Solid content of the said composition is 1.0-8.0 weight%, The liquid crystal aligning film composition for optical film laminated bodies characterized by the above-mentioned.

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