JP4371333B2 - Phase plate production method, optical member, and liquid crystal display device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for accurately producing a retardation plate suitable for improving the viewing angle and contrast of a liquid crystal display device, and an optical member using the retardation plate.
[0002]
[Prior art]
Conventionally, as a method of producing a retardation plate that can compensate for a retardation due to birefringence of a liquid crystal cell and achieve an increase in viewing angle and an improvement in contrast of a liquid crystal display device, a heat shrinkable film is bonded to a thermoplastic film. A method of stretching under the action of the contraction force by heating has been known (Japanese Patent Laid-Open No. 5-157911). The heat-shrinkable film after such stretching treatment is peeled off from the obtained retardation plate.
[0003]
According to the above method, the disadvantage in terms of productivity and cost in the case of a uniaxially stretched film that needs to be laminated and used, and the heat resistance in the case of a biaxially stretched polystyrene film, etc. are poor, and thus it is used for forming a liquid crystal display device. You can overcome unsuitable points. However, in the conventional method, the shrinkage of the heat-shrinkable film is preceded and the adhesive interface is displaced or peeled off, and the retardation force of the retardation plate is difficult to control deformation due to insufficient shrinkage force on the thermoplastic film. There were poor problems.
[0004]
[Technical Problem of the Invention]
An object of the present invention is to develop a production method capable of efficiently transmitting the shrinkage force of a heat-shrinkable film to a thermoplastic film, easily controlling deformation, and obtaining a phase difference plate having excellent phase difference accuracy.
[0005]
[Means for solving problems]
The present invention, the shrinkage starting temperature relative to the initial dimensions Ti, the thermoplastic film when the glass transition temperature was Tg, of non-oriented heat-shrinkable film satisfying the Tg- 5 0 ≦ Ti thermoplastic film It is bonded to one side or both sides, and the thermoplastic film is stretched or shrunk in at least one longitudinal or lateral direction under the action of the shrinkage force of the heat-shrinkable film by heating, and then the heat-shrinkable film is peeled off. A method of manufacturing a retardation plate is provided.
[0006]
Further, the present invention is an optical member comprising a laminate of a retardation plate and a polarizing plate by the above manufacturing method, and the retardation plate or the polarizing plate by the above manufacturing method and at least one side of the liquid crystal cell. It is an object of the present invention to provide a liquid crystal display device characterized by having the liquid crystal display device.
[0007]
【The invention's effect】
According to the present invention, the shrinkage and peeling at the adhesive interface due to the shrinkage of the heat-shrinkable film can be suppressed, and the shrinkage force of the heat-shrinkable film can be efficiently imparted at a temperature at which the thermoplastic film is easily deformed. A heat-resistant retardation plate satisfying, for example, nx <nz characteristics, that is, nz>nx> ny refractive index characteristics required to compensate for birefringence and prevent changes in display color and contrast depending on viewing angle. Etc. can be obtained efficiently using a thermoplastic film of nx> ny. The above-mentioned nx and ny mean the in-plane main refractive index, and nz means the main refractive index in the thickness direction (the same applies hereinafter).
[0008]
As a result, it is possible to efficiently obtain a retardation plate having a highly adjusted retardation by easily controlling the deformation of the thermoplastic film under the action of the shrinkage force of the heat-shrinkable film. A liquid crystal display device excellent in viewing angle and contrast in which the phase difference due to birefringence is highly compensated can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Manufacturing process according to the invention, the shrinkage starting temperature relative to the initial dimensions Ti, when the glass transition temperature of the thermoplastic film was Tg, Tg- 5 0 shrinkable film satisfying the ≦ Ti unoriented heat Adhere to one or both sides of the plastic film, and after stretching or shrinking the thermoplastic film in at least one longitudinal or lateral direction under the action of the shrinkage force of the heat-shrinkable film by heating, the heat-shrinkable film is peeled off A phase difference plate is obtained.
[0010]
The thermoplastic film comprising a base of the retardation plate, a non-oriented film made of a light transmissive suitable thermoplastic resins are Ru is used. In particular, a film having a light transmittance of 75% or more, particularly 85% or more is preferable. Moreover, from the point which obtains the phase difference plate excellent in heat resistance, what consists of a polymer which shows the positive birefringence characteristic from which the refractive index of a extending | stretching direction becomes high is used preferably.
[0011]
Incidentally, examples of the polymer exhibiting positive birefringence described above include polycarbonate, polyvinyl alcohol, cellulose resin, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene resin, polysulfone, polyethersulfone, polypropylene. And the like.
[0012]
The thermoplastic film may be formed by an appropriate method such as a casting method such as a casting method or an extrusion method. A solution casting method such as a casting method is more preferable in that a film with less thickness unevenness, orientation strain unevenness and the like is obtained. The thermoplastic film can be used in a prescribed size for batch processing, or can be used as a long film for the purpose of continuous production.
[0013]
The thickness of the thermoplastic film can be appropriately determined depending on the retardation characteristics of the target retardation plate. In general, the thickness is 5 to 500 μm, especially 10 to 400 μm, especially 20 to 300 μm. Phase difference, Ru can be obtained as the product (△ n × L) refractive index difference (△ n) between the optical path length (L).
[0014]
A heat-shrinkable film that adheres to one or both sides of a thermoplastic film transmits the shrinkage force due to heating to the thermoplastic film and stretches the thermoplastic film in one or both directions in the vertical or horizontal direction under the action of the shrinkage force. Alternatively, it is intended to control the phase difference characteristics, particularly the refractive index in the thickness direction by shrinking, and in the present invention, the shrinkage start temperature based on the initial dimensions is Ti, and the glass transition temperature of the thermoplastic film is Tg. when the heat-shrinkable film satisfying the Tg- 5 0 ≦ Ti is used.
[0015]
That is, as shown in the curve illustrated in FIG. 1, in the heat-shrinking treatment of the heat-shrinkable film, the length is increased from the initial dimension due to the thermal expansion due to the temperature rise, and then the contraction starts and the dimension becomes shorter than the initial dimension. Shows behavior. In this case, in the present invention, the temperature at which the dimension becomes the same as the initial value after shrinkage after expansion is defined as the shrinkage start temperature Ti, and the Ti and the Tg of the thermoplastic film are expressed by the formula: Tg- 5 0 ≦ Ti A satisfactory heat shrinkable film is used.
[0016]
Efficient modification of the thermoplastic film by transmission of contractile force of a heat shrinkable film, Ru used heat-shrinkable film satisfying the Tg-50 ≦ Ti mentioned above from the viewpoint of turn sophistication of the phase difference controlling. Note that a heat-shrinkable film having a heat shrinkage force as uniform as possible over the entire surface of the film and excellent in surface smoothness is preferably used from the viewpoint of imparting a uniform orientation to the thermoplastic film.
[0017]
The heat-shrinkable film is not particularly limited as long as it satisfies the above-mentioned Ti condition. Therefore, the film is made of uniaxial or biaxial film made of a thermoplastic resin such as polyvinyl chloride, polyethylene, polypropylene, polyester, polystyrene or polyamide. An appropriate material such as a film that exhibits shrinkage by heat treatment can be used, and there is no particular limitation. In particular, those composed of a polymer exhibiting positive birefringence characteristics from the viewpoint of controllability of phase difference and the like are preferably used. The heat shrinkage force can be varied depending on the type of thermoplastic resin, stretching conditions such as the stretching ratio, and the like.
[0018]
The adhesion treatment between the thermoplastic film and the heat-shrinkable film can be performed by an appropriate method capable of transmitting the heat-shrink force of the heat-shrinkable film. An adhesive system through an adhesive layer is preferred from the viewpoint of easy separation after shrinkage treatment. The adhesive force between the heat-shrinkable film and the thermoplastic film can be determined as appropriate, but in general, based on the T-type peeling at room temperature, from the viewpoint of the transferability of heat-shrink force and easy separation after shrinkage treatment. 45 to 200 gf / 50 mm, especially 48 to 190 gf / 50 mm, especially 50 to 180 gf / 50 mm are preferable.
[0019]
The pressure-sensitive adhesive that forms the pressure-sensitive adhesive layer is not particularly limited, and for example, an appropriate material such as acrylic, silicone, polyester, polyurethane, polyether, or rubber can be used. In particular, those in which the adhesive force is hardly increased as much as possible by the heat shrinkage treatment of the heat shrinkable film are preferable.
[0020]
The pressure-sensitive adhesive layer can be attached to one or both of the adhesive surfaces when the thermoplastic film and the heat-shrinkable film are bonded, and a retardation plate formed to be used in a state attached to the heat-shrinkable film in advance. It is preferable from the viewpoint of preventing the adhesive residue at the time of separation of the heat-shrinkable film and improving the production efficiency. That is, it is preferable from the viewpoint of production efficiency and the like that the adhesive layer is separated in a state accompanied with the heat-shrinkable film to prevent the adhesive layer from remaining on the formed retardation plate.
[0021]
Attaching the adhesive layer to the heat-shrinkable film can be done by applying a pressure-sensitive adhesive to the heat-shrinkable film and drying it, but the shrinkage characteristics of the heat-shrinkable film change due to the drying process. A method of transferring the pressure-sensitive adhesive layer provided on the separator to the heat-shrinkable film is preferable from the viewpoint of preventing the above.
[0022]
The separator can also be used as a protective cover for preventing contamination of the adhesive layer and the like until it is adhered as it is and the heat-shrinkable film is put to practical use. The heat-shrinkable film surface to which the adhesive layer is attached can be subjected to an appropriate surface treatment such as corona treatment for the purpose of improving the adhesion with the adhesive layer.
[0023]
As described above, the heat-shrinkable film can adhere one or two or more appropriate numbers to one or both sides of the thermoplastic film depending on the desired shrinkage force, etc. When the multilayer is adhered to the top, the heat-shrinkable films on the front and back sides and the upper and lower sides thereof may be the same, or may have different heat-shrinkage characteristics such as a heat-shrinkage rate.
[0024]
Shrinkage treatment of the heat-shrinkable film adhered to the thermoplastic film can be performed via an appropriate stretching machine such as a roll stretching machine, a tenter, or a biaxial stretching machine. The processing temperature is preferably in the vicinity of Tg of the thermoplastic film, in particular, within a temperature range within ± 20 ° C. of Tg, in particular, Tg or more from the viewpoint of increasing the accuracy of the phase difference due to the controllability of the processing operation.
[0025]
The treatment given to the thermoplastic film under the action of the shrinkage force of the heat-shrinkable film by heating is either stretching or shrinking, and may be appropriately determined according to the retardation plate to be formed. Moreover, the process to give may be any one of the vertical and horizontal directions (length direction and width direction) of a thermoplastic film, and may be both. In the case where the treatment is given in both directions, a combination in which the shrinkage treatment is given in one direction and the stretching treatment is given in the other direction can be used. The treatment given to the thermoplastic film under the action of the shrinkage force of the heat-shrinkable film described above can be performed in two or more steps.
[0026]
In the method according to the present invention, the refractive index nz in the thickness direction is controlled so that the phase difference in the direction related to the refractive index in the thickness direction is larger than the phase difference due to the refractive index difference (nx−ny) in the film plane. It can be advantageously used for manufacturing a large retardation plate. In general, the refractive index in the thickness direction can be controlled by a method of shrinking at least one of the thermoplastic film in the longitudinal and transverse directions. In particular, a retardation plate satisfying the refractive index characteristic of nz>nx> ny can be preferably used from the viewpoint of compensating the viewing angle characteristic due to the birefringence of the liquid crystal.
[0027]
When the necessary treatment is completed as described above, the heat-shrinkable film after the shrinkage treatment is peeled off from the formed retardation plate and separated. The obtained retardation plate can be used practically as it is, or it can be used practically as a phase-adjustment characteristic is adjusted by adding a stretching process or the like.
[0028]
A preferred retardation plate according to the present invention is not limited thereto, but the retardation due to birefringence and the variation of the orientation axis are as small as possible. In particular, in transmitted light perpendicular to the film surface (in the front direction). The phase difference variation is 10 nm or less, particularly 5 nm or less, and the alignment axis variation is 5 degrees or less, particularly 3 degrees or less.
[0029]
The retardation plate according to the present invention can be preferably used as a single layer or the same kind or different kind of laminate for compensation of retardation due to birefringence for the purpose of increasing the viewing angle of a liquid crystal cell or improving contrast. In practical use, for example, an adhesive layer provided on one or both sides of a retardation plate, a polarizing plate, or a protective layer made of an isotropic transparent resin layer or glass layer is bonded via the adhesive layer. It can also be applied as an optical member of an appropriate form such as a laminated one.
[0030]
Lamination with the polarizing plate or the like can be performed by a method of laminating separately in the manufacturing process of the liquid crystal display device, but by laminating in advance, the liquid crystal display has excellent quality stability and laminating workability. There is an advantage that the manufacturing efficiency of the apparatus can be improved. An appropriate adhesive or the like can be used for bonding. In particular, an adhesive layer such as those exemplified above, particularly an acrylic layer is preferably used from the viewpoint of heat resistance and optical characteristics.
[0031]
For the adhesive layer, for example, natural or synthetic resins, glass fibers or glass beads, fillers or pigments made of metal powder or other inorganic powders, colorants, antioxidants, etc. Additives can also be blended. Moreover, it can also be set as the contact bonding layer which contains microparticles | fine-particles and shows light diffusibility.
[0032]
As the polarizing plate laminated with the retardation plate, an appropriate one may be used. Examples thereof include hydrophilic films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polarizing films made of polyene-oriented films such as those obtained by adsorbing iodine and / or dichroic dyes on a conductive polymer film, polyvinyl alcohol dehydrated products, and polyvinyl chloride dehydrochlorinated products. .
[0033]
The polarizing plate may have a transparent protective layer on one side or both sides of the polarizing film. Further, the polarizing plate may be a reflective type or a transflective type having a reflective layer, a half mirror, or the like. The reflective polarizing plate is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side) and displays a liquid crystal display that can omit the incorporation of a light source such as a backlight. It has an advantage that the display device can be easily thinned.
[0034]
The transparent protective layer can be appropriately formed as a polymer coating layer, a laminate of protective films, etc., and a polymer excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, etc. is preferably used for the formation. It is done. Examples include polyester resins, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, acrylic resins, urethane resins, acrylic urethane resins, Examples thereof include thermosetting resins such as epoxy and silicone resins, and ultraviolet curable resins. The surface of the transparent protective layer may be formed in a fine concavo-convex structure by containing fine particles.
[0035]
In addition, the reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one side of the polarizing plate via a transparent resin layer, if necessary. One surface of a transparent resin layer such as a treated protective film provided with a foil or a vapor deposition film made of a reflective metal such as aluminum, or the surface of the transparent resin layer containing fine particles, a vapor deposition method or plating Examples thereof include those provided with a metal reflection layer by an appropriate method such as a method. The transflective polarizing plate can be obtained by making the reflective layer a transflective type such as a half mirror.
[0036]
In addition, when laminating the retardation plate and the polarizing plate, the arrangement angle of the optical axes such as the transmission axis and the fast axis is not particularly limited and can be determined as appropriate. By the way, when applied to an STN type liquid crystal cell, it is often arranged at an oblique crossing angle such as 45 degrees, and when applied to a TN type liquid crystal cell, it is arranged at a substantially parallel or substantially orthogonal crossing angle. There are many.
[0037]
As described above, the retardation plate can be used by laminating two or more of them. This is for the purpose of improving the compensation effect, and in this case, in the present invention, the phase difference plate according to the present invention and other phase differences are used. It can also be set as a laminated body with a board. As the retardation plate, for example, an appropriate one such as a uniaxial or biaxial stretched film exemplified by the above thermoplastic film, a discotic or nematic liquid crystal alignment plate, or the like can be used.
[0038]
Each layer such as the above-mentioned retardation plate, polarizing plate, transparent protective layer, and adhesive layer is composed of, for example, an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex salt compound. UV absorption ability can also be provided by a method of treating with.
[0039]
The phase difference plate according to the present invention is a TN type, STN type, etc., such as compensation for compensation of a perspective direction retardation that prevents a decrease in contrast in the front direction, compensation compensation for a phase difference between the front direction and the perspective direction. It can be preferably used for compensation of viewing angle characteristics due to birefringence in various liquid crystal cells such as π type.
[0040]
The liquid crystal display device using the retardation plate can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a retardation plate for optical compensation, and a polarizing plate and an illumination system as necessary, and incorporating a drive circuit. In the present invention, there is no particular limitation except that the retardation plate according to the present invention is used for optical compensation, and is provided on at least one side of the liquid crystal cell together with a polarizing plate, if necessary, and can be based on the conventional one.
[0041]
Therefore, a liquid crystal display device in which a polarizing plate is arranged on one or both sides of a liquid crystal cell, a transmission type or a reflection type using a backlight, a reflection plate or a semi-transmission type reflection plate in an illumination system, or a reflection / transmission type An appropriate liquid crystal display device can be formed. In the case of a liquid crystal display device using a polarizing plate, the retardation plate for optical compensation is preferably arranged between the liquid crystal cell and the polarizing plate, particularly the polarizing plate on the viewing side, from the viewpoint of the compensation effect. In the arrangement, the optical member described above can also be used.
[0042]
In the above description, the components for forming the liquid crystal display device may be laminated and integrated, or may be in a separated state. In forming the liquid crystal display device, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer and a protective plate can be appropriately disposed. Such an element can also be used for forming a liquid crystal display device in the form of the above-described optical member formed by laminating with a retardation plate.
[0043]
The retardation plate according to the present invention and the optical member using the retardation plate exhibit birefringence such as TN type and STN type for the purpose of compensating for the phase difference due to the birefringence of the liquid crystal cell, such as widening the viewing angle and improving the contrast. It can be preferably used for various display devices such as TFT type and MIM type using a liquid crystal cell. In that case, as the retardation plate for optical compensation, one that compensates for the phase difference due to the birefringence of the liquid crystal cell over a wide viewing angle range is preferably used.
[0044]
【Example】
Example 1
A 20% by weight solution of methylene dichloride in polycarbonate having a molecular weight of about 80,000 consisting of a polycondensate of phosgene and bisphenol A is continuously cast on a steel drum, which is peeled off and dried in order to obtain a thickness of 60 μm. A long polycarbonate film having a phase difference of approximately 0 is obtained, and a heat-shrinkable film having a Tg of 145 ° C. is bonded to both sides of the film having a Tg of 145 ° C. via an acrylic adhesive layer attached thereto. The heat-shrinkable film was peeled off together with the adhesive layer by applying a shrinkage treatment of 5% in the transverse direction at 160 ° C. to obtain a retardation plate continuously.
[0045]
Comparative Example A retardation film was obtained in the same manner as in Example 1 except that a heat-shrinkable film having a Ti of 65 ° C. was used.
[0046]
In the above, in Example 1, the polycarbonate film was efficiently deformed to obtain a retardation plate having the desired retardation, but in the comparative example, the heat-shrinkable film was first contracted by heating. Deviation and peeling occurred on the adhesive surface, and the desired phase difference could not be imparted due to insufficient transmission of contractile force. Further, polarizing plates were arranged on both sides of the TN type liquid crystal cell via the phase difference plate obtained in Example 1, and the display characteristics due to the contrast in the front direction and the change in viewing angle were examined. There was no change in display characteristics, and the liquid crystal display device was of high display quality with excellent visibility.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a shrinkage start temperature Ti

Claims (4)

The initial size as a reference to the shrinkage starting temperature Ti, when the glass transition temperature of the thermoplastic film was Tg, Tg- 5 0 shrinkable film satisfying the ≦ Ti on one or both sides of the thermoplastic film of non-oriented A phase difference plate characterized in that the heat-shrinkable film is peeled off after being stretched or shrunk in at least one longitudinal or lateral direction under the action of the shrinkage force of the heat-shrinkable film by heating. Manufacturing method. The manufacturing method according to claim 1, wherein the heat-shrinkable film and the thermoplastic film are made of a polymer exhibiting positive birefringence characteristics. An optical member comprising a laminate of a retardation plate and a polarizing plate produced by the production method according to claim 1. A liquid crystal display device comprising a retardation plate or a polarizing plate produced by the manufacturing method according to claim 1 or 2 and a polarizing plate on at least one side of a liquid crystal cell.

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