JP2002221715A - Liquid crystal display device and liquid crystal display using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device for the use of a semi- transmission reflection type or a reflection type liquid crystal display of which the panel size is not larger than four inches using a plastic-substrate liquid crystal cell, and which is excellent in the resistance to heat and humidity. SOLUTION: The thickness of protective layer elements 2a, 2b, which are stuck on a polarizer 1 of a polarizing plate on the front side of the plastic- substrate liquid crystal cell, is set to be A, and the thickness of protective layer elements 5a, 5b, which are stuck on a polarizer 4 of a polarizing plate on the rear side, is set to be B, where the relationship between A and B is determined to be A/B<0.65. The absolute value of the amount of warp of the plastic-substrate liquid crystal cell can be thereby reduced to be not larger than 1.5 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized and medium-sized liquid crystal display device using a plastic substrate liquid crystal cell (hereinafter sometimes abbreviated as a plastic cell) used in a transflective or reflective liquid crystal display device. About.

[0002]

2. Description of the Related Art Liquid crystal display devices (hereinafter sometimes abbreviated as LCDs) are used in desktop electronic calculators, electronic timepieces, personal computers, word processors, and the like, and the demand has been rapidly increasing in recent years. . The use of LCDs is also expanding. In recent years, with the spread of portable information devices such as mobile phones and PDAs, the weight of liquid crystal display panels has been reduced,
There is a demand for a thinner liquid crystal display, and a liquid crystal display panel using a plastic substrate instead of a glass substrate has been developed and put into practical use for small and medium-sized liquid crystal displays.

However, in the case of a liquid crystal cell using a conventional glass substrate, even if the dimensions of the polarizing plate are changed in a heating and humidifying durability test, the glass is low in flexibility, so that warpage is hardly generated. In the case of a liquid crystal cell using a substrate, the flexibility of the plastic substrate is high, and the liquid crystal cell is deformed and warped due to the deformation of the polarizing plate. In particular, when stress is applied to the liquid crystal display element under humidification conditions, etc.
Due to the warpage, there is a problem that display unevenness occurs in a liquid crystal display, and a problem occurs in workability in an assembly process of a final product. In particular, the occurrence of warpage of | 1.5 | mm or more before and after the heating and humidification durability test is a serious problem.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention changes the thickness of the protective layer to be bonded to the polarizers of the front and rear polarizing plates and adjusts the thickness ratio within a certain range. It is an object of the present invention to provide a liquid crystal display element having excellent heat-humidification durability and having a small amount of warpage of the liquid crystal cell when the content is within the range.

[0005]

In order to achieve the above object, a liquid crystal display device of the present invention has a panel size of 4 inches or less used for a transflective or reflective liquid crystal display device using a plastic substrate liquid crystal cell. In the liquid crystal display device, the thickness A of the protective layer alone bonded to the polarizer of the front-side polarizing plate and the thickness B of the protective layer alone bonded to the polarizer of the rear-side polarizing plate with respect to the liquid crystal cell. Have the following relationship. A / B <0.65

[0006] By changing the thickness of the protective layer to be bonded to the polarizer of the polarizing plate between the front side and the rear side, and keeping the thickness ratio within the above range, the warpage of the plastic substrate liquid crystal cell can be eliminated. .

In the liquid crystal display element, the dimensional change rate C in the MD direction (longitudinal direction) of the polarizing plate alone on the front side after the liquid crystal display element is left for 120 hours under the conditions of 40 ° C. and 92% RH. And the MD of the rear polarizing plate alone
The dimension change rate D in the direction (vertical direction) preferably has the following relationship. C> D

One of the causes of warpage of a reflective liquid crystal display device using a plastic cell under humid conditions is that a semi-transmissive reflector or a reflector is used on the rear side of the cell. Due to the presence of this transflective plate or reflector, the structure of the front side and the rear side of the member bonded to the cell becomes asymmetric, and when the cell is left under humidification conditions, it differs on the front side and the rear side of the cell. Force is applied and the cell is warped. Therefore, when the dimensional change rate of the polarizing plate on the front side and the rear side of the cell under the humidifying condition has the above relationship, the warpage of the plastic cell which is generated due to the asymmetry is eliminated, and under the humidifying condition. Plastic cell (panel size 4)
Inch or less) | 1.5 | mm or less (± 1.5
mm or less).

In the liquid crystal display device, the thickness A of the protective layer alone of the front polarizing plate is 20 to 20.
0 μm, and the thickness B of the protective layer alone of the rear polarizing plate is 7
It is preferably from 0 to 220 μm.

In the liquid crystal display device, it is preferable that the dimensional change C is 0.6 to 1.6% and the dimensional change D is 0.1 to 0.6%. When the dimensional change rate is out of the above range, the warpage of the plastic substrate liquid crystal cell becomes 1.5 mm or more.

In the liquid crystal display device, it is preferable that a retardation plate is laminated on the front and / or rear polarizing plates. By stacking the retardation plates, coloring caused by birefringence of the liquid crystal layer of the STN liquid crystal display device can be compensated.

Further, in the liquid crystal display device, it is preferable that a reflector or a transflector is laminated on the rear polarizer. By laminating the transflective plate or the reflective plate, the balance between the forces applied to the front side and the rear side is improved, and the amount of warpage of the plastic cell can be reduced.

In the liquid crystal display device, from the viewpoint of suppressing display unevenness in the liquid crystal display, the plastic substrate liquid crystal cell after leaving the liquid crystal display device at 40 ° C. and 92% RH for 120 hours. The amount of warpage is |
1.5 | mm or less, particularly 1.0 m
m or less.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a transflective or reflective liquid crystal display device using a plastic substrate liquid crystal cell, wherein a liquid crystal display element having a panel size of 4 inches or less is used. Thickness of one side of the protective layer to be bonded to both sides (thickness of a single protective layer) A and thickness of one side of the protective layer to be bonded to both sides of the polarizer of the rear polarizing plate (thickness of the single protective layer) A / B <0.6
By setting the value to 5, it is possible to provide a liquid crystal display element having a small amount of warpage of the liquid crystal cell.

In the present invention, the relationship between the thickness A of the protective layer of the polarizing plate on the front side and the thickness B of the protective layer on the polarizing plate on the rear side is such that when A / B is too small, the front side and the rear side are different. It is particularly preferable that 0.2 <A / B <0.65, since the thickness difference between the respective polarizing plates becomes too large, the behavior difference between the polarizing plates also becomes large, and the warpage tends to increase.

Further, the liquid crystal display device of the present invention is used at 40 ° C.
Dimensional change rate C in the MD direction (longitudinal direction) of the front polarizing plate alone after standing for 120 hours under the condition of 92% RH
And the dimensional change rate D in the MD direction (longitudinal direction) of the rear polarizing plate alone preferably has a relationship of C> D. The smaller the dimensional change, the better.
The dimensional change in the MD direction (vertical direction) of the polarizing plate alone is generally 0.1 to 1.6%. Therefore, in the present invention, the dimensional change rate C on the front side is preferably in the range of 0.6 to 1.6%, and the dimensional change rate D on the rear side is preferably in the range of 0.1 to 0.6%.

Next, the structure of the liquid crystal display device of the present invention will be described. FIG. 1 is a cross-sectional view illustrating a configuration example of the liquid crystal display element of the present invention. In FIG. 1, 1 is a polarizer of a front-side polarizing plate, 2a and 2b are protective layers of a front-side polarizing plate, 3 is a plastic substrate, 4 is a polarizer of a rear-side polarizing plate, 5
Reference numerals a and 5b denote protective layers of the rear polarizer, 6 denotes a front polarizer, 7 denotes a liquid crystal cell, and 8 denotes a rear polarizer.

The polarizing plate used in the present invention is obtained by laminating a transparent protective film serving as a protective layer on both sides of a polarizer made of a dichroic substance-containing polyvinyl alcohol-based polarizing film or the like via an appropriate adhesive layer. Become.

As the polarizer (polarizing film), for example, a film made of a polyvinyl alcohol polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol and having a thickness of 75 μm or less is subjected to swelling treatment, iodine, dichroic dye, or the like. Dyeing treatment with a dichroic substance comprising, stretching treatment, cross-linking treatment, in an appropriate order and method,
A dried product can be used. The steps of dyeing, crosslinking and stretching do not need to be performed separately but may be performed simultaneously. In general, any material that transmits linearly polarized light when natural light is incident thereon may be used. In particular, a material having excellent light transmittance and degree of polarization is preferable. The thickness of the polarizer is 2 to 35 μm, especially 7
-30 μm is preferred.

Examples of the polyvinyl alcohol polymer include a polymer obtained by polymerizing vinyl acetate and then saponified, and a polymer obtained by copolymerizing vinyl acetate with a small amount of a copolymerizable monomer such as unsaturated carboxylic acid and unsaturated sulfonic acid. No. The average degree of polymerization is 5 in terms of the solubility of the film in water.
It is preferably from 100 to 10,000, more preferably from 1000 to 60
The saponification degree is preferably at least 75 mol%, more preferably at least 98 mol%.

As a protective film material to be a transparent protective layer provided on both sides of the polarizer (polarizing film), an appropriate transparent film can be used. Above all, a film made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include, for example, a polyester resin, an acetate resin, a polynorbornene resin, a polyethersulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, an acrylic resin, or an acrylic resin. Thermosetting or ultraviolet-curable resins such as urethane, urethane, epoxy, and silicone resins. Above all, an acetate resin is preferable from the viewpoint of transparency, and a triacetyl cellulose film whose surface is saponified with an alkali or the like is particularly preferable from the viewpoint of polarization characteristics and durability.

The thickness of the protective layer alone on both sides of the polarizer of the polarizing plate is 20 to 200 μm on the front side,
Preferably it is 30 to 120 μm. When the thickness is less than 20 μm, the durability decreases, and when it exceeds 200 μm, the transparency decreases. On the other hand, the width on the rear side is 70 to 220 μm, preferably 50 to 120 μm. If it is less than 70 μm, durability becomes a problem, and if it exceeds 220 μm, insufficient transmittance becomes a problem.

When a protective layer is provided on both sides of the polarizer, the protective layer may be made of a different polymer on the front and back sides, or may be made of a different polymer on the front and rear sides. .

The transparent protective film used for the protective layer is
As long as the object of the present invention is not impaired, a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion or anti-glare, or the like may be performed. The hard coat treatment is performed for the purpose of preventing scratches on the polarizing plate surface and the like.
A cured film excellent in hardness, slipperiness and the like made of a suitable ultraviolet-curable resin such as a urethane-based, acrylic-based, or epoxy-based resin can be formed by a method of adding to the surface of the transparent protective film.

On the other hand, the anti-reflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, anti-sticking is performed to prevent adhesion between adjacent layers, and anti-glare treatment is performed to prevent external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate. For example, the transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a roughening method by a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Fine particles may be used, or organic fine particles composed of crosslinked or uncrosslinked polymer particles or the like may also be used.
The amount of the transparent fine particles used is 2 per 100 parts by mass of the transparent resin.
It is generally from 70 to 70 parts by weight, especially from 5 to 50 parts by weight.

The anti-glare layer containing the transparent fine particles can be provided as the transparent protective film itself or as a coating layer on the surface of the transparent protective film. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle. The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer, and the like can be provided as an optical layer made of a sheet or the like provided with these layers, separately from the transparent protective film.

The bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive composed of a vinyl alcohol polymer, boric acid or boric acid may be used. It can be carried out via an adhesive or the like comprising at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as sand, glutaraldehyde, melamine, and oxalic acid. This makes it difficult for the film to be peeled off due to the influence of humidity or heat, and can have excellent light transmittance and degree of polarization. Such an adhesive layer is formed as a coating and drying layer of an aqueous solution, and at the time of preparing the aqueous solution, other additives and a catalyst such as an acid can be blended as necessary.

The polarizing plate can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, a reflector, a transflector, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 板 wavelength plate), a viewing angle compensation film, and a brightness enhancement film For example, one or more appropriate optical layers that may be used for forming a liquid crystal display device or the like can be used. A polarizing plate comprising the above-described polarizer and protective layer, an elliptically polarizing plate or a circularly polarizing plate further having a retardation plate laminated thereon, and a polarizing plate comprising the above-mentioned polarizer and protective layer further laminated with a viewing angle compensation film. Polarizing plate, or a polarizing plate in which a brightness enhancement film is further laminated on the above-mentioned polarizing plate comprising a polarizer and a protective layer. In particular, a polarizing plate comprising the above-described polarizer and a protective layer, an elliptically polarizing plate or a circularly polarizing plate further laminated with a retardation plate, or a reflective polarizing plate further laminated with a reflecting plate or a transflective reflecting plate. A transflective polarizing plate is preferred.

The phase difference plate is used to change linearly polarized light into elliptically polarized light or circularly polarized light, change elliptically polarized light or circularly polarized light into linearly polarized light, or change the polarization direction of linearly polarized light. A so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate for changing to elliptically polarized light or circularly polarized light or for changing elliptically or circularly polarized light to linearly polarized light. 1/2 wavelength plate (also called λ / 2 plate)
Is usually used to change the polarization direction of linearly polarized light.

Specific examples of the retardation plate include a birefringent film obtained by stretching a film made of a polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylates and polyamides, and a liquid crystal polymer. And an alignment layer of a liquid crystal polymer supported by a film. Examples of the obliquely oriented film include, for example, a film obtained by bonding a heat shrinkable film to a polymer film and subjecting the polymer film to a stretching treatment and / or a shrinking treatment under the action of the shrinkage force caused by heating, or a liquid crystal polymer obliquely oriented. And the like. The thickness of the film can be appropriately determined according to the phase difference or the like according to the purpose of use, but is generally 1 mm or less, preferably 1 to 500 μm, particularly preferably 5 to 3 μm.
00 μm.

An elliptically polarizing plate compensates (prevents) coloring (blue or yellow) caused by birefringence of a liquid crystal layer of a super twisted nematic (STN) type liquid crystal display device to provide a monochrome display without the coloring. It is used effectively for such purposes. Further, the one in which the three-dimensional refractive index is controlled is preferable because coloring which occurs when the screen of the liquid crystal display device is viewed from an oblique direction can be compensated (prevented). The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflection type liquid crystal display device for displaying an image in color, and also has an antireflection function.

The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a direction slightly oblique rather than perpendicular to the screen. As a suitable viewing angle compensation film, a film obtained by coating a discotic liquid crystal on a triacetyl cellulose film or the like, or a retardation plate is used.
For the ordinary retardation plate, a polymer film having birefringence uniaxially stretched in the plane direction is used,
The retardation plate used as a viewing angle compensating film includes a birefringent polymer film that is biaxially stretched in a plane direction or a refractive index in a thickness direction that is uniaxially stretched in a plane direction and also stretched in a thickness direction. For example, a bidirectionally stretched film such as an obliquely oriented polymer film having a controlled thickness is used. As described above, as described above, for example, as described above, a heat-shrinkable film is adhered to a polymer film, and the polymer film is stretched or / and shrunk under the action of the heat-induced shrinkage. Oriented ones are exemplified. As the raw material polymer for the retardation plate, the same polymer as the polymer described for the retardation plate is used. The same applies to lamination with a polarizing plate.

As a brightness enhancement film, for example, a property of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropy. Indicating a cholesteric liquid crystal layer,
In particular, one that reflects either left-handed or right-handed circularly polarized light and transmits other light, such as an oriented film of a cholesteric liquid crystal polymer or one in which the oriented liquid crystal layer is supported on a film substrate. Is used.

Next, a reflective or transflective liquid crystal display device using a reflective polarizer or a transflective polarizer will be described. FIG. 2 is a sectional view showing a configuration example of the reflection type liquid crystal display element of the present invention. In FIG. 2, 1 is a polarizer of a front-side polarizing plate, 2a and 2b are protective layers of a front-side polarizing plate, 3 is a plastic substrate, 4 is a polarizer of a rear-side polarizing plate, and 5a and 5b are rear-side. , A front side polarizing plate, 7 a liquid crystal cell, 8 a rear side polarizing plate, 9
Denotes a retardation plate and 10 denotes a reflection plate.

The reflection plate is provided on a polarizing plate to form a reflection type polarizing plate. The reflection type polarizing plate is usually provided on the back side of a liquid crystal cell, and is provided from the viewing side (display side). A liquid crystal display device of a type that reflects and displays incident light can be formed, and there is an advantage that a built-in light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced.

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 provided on one side of the polarizing plate via the transparent protective film or the like as necessary. Specific examples thereof include a transparent protective film that has been matted as necessary, and a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one surface.

Further, a reflective polarizing plate having a reflective layer on which the fine uneven structure is reflected on the transparent protective film having a fine uneven structure on the surface by containing fine particles may be used. The reflection layer having the fine surface irregularity structure has the advantage of diffusing incident light by irregular reflection, preventing directivity and glaring appearance, and suppressing unevenness in brightness and darkness. The formation of the reflective layer of the fine uneven structure reflecting the fine uneven structure on the surface of the transparent protective film is performed by, for example, making the metal transparent by an appropriate method such as an evaporation method such as a vacuum evaporation method, an ion plating method, or a sputtering method, or a plating method. It can be performed by a method of directly attaching to the surface of the protective film.

In addition, the reflecting plate may be used as a reflecting sheet in which a reflecting layer is provided on an appropriate film conforming to the transparent protective film, instead of directly attaching to the transparent protective film of the polarizing plate described above. it can. Since the reflection layer of the reflection plate usually contains a metal, the use form in which the reflection surface is covered with a film, a polarizing plate, or the like is intended to prevent a decrease in the reflectance due to oxidation and to maintain the initial reflectance over a long period of time. It is preferable from the viewpoint of avoiding separately providing a protective layer.

On the other hand, a transflective polarizing plate can be obtained by forming a transflective reflective layer such as a half mirror that reflects and transmits light on the reflective layer.
The transflective polarizing plate is provided on the back side of the liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, a liquid crystal display device of a type that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and is used for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. Useful. As the transflective plate, a half mirror made of a metal film, a synthetic resin plate containing a pearl pigment, or the like can be used.

The polarizing plate and the retardation plate, the reflecting plate or the semi-transmissive reflecting plate can be laminated by a method of sequentially laminating the polarizing plate and the transflective plate in the manufacturing process of the liquid crystal display device. Excellent in quality stability and laminating workability,
There is an advantage that the manufacturing efficiency of the liquid crystal display device can be improved. For the adhesive layer, for example, an appropriate material such as an acrylic, silicone, polyester, polyurethane, polyether, or rubber can be used. Among them, acrylic is preferable in terms of heat resistance and optical characteristics. The system type is preferably used. When laminating the polarizing plate and the retardation plate, the arrangement angle of the optical axis such as the transmission axis and the fast axis is not particularly limited, and can be appropriately determined.

Further, the polarizing plate may be formed by laminating a polarizing plate and two or more optical layers, such as a polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate and retardation plate may be used. An optical member in which two or three or more optical layers are laminated can be formed by a method in which the optical members are sequentially laminated separately in a manufacturing process of a liquid crystal display device or the like. This has the advantage that the stability of quality and the workability of assembling are excellent and the manufacturing efficiency of a liquid crystal display device or the like can be improved. In addition, an appropriate bonding means such as the above-mentioned adhesive layer can be used for lamination.

An optical member such as the above-mentioned polarizing plate may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed with an appropriate pressure-sensitive adhesive, such as an acrylic resin, according to the related art. In particular, from the viewpoint of preventing foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of liquid crystal cell warpage, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. It is preferable that the pressure-sensitive adhesive layer is low and has excellent heat resistance.
In addition, an adhesive layer or the like which contains fine particles and exhibits light diffusibility can be used. The adhesive layer may be provided on a necessary surface if necessary.For example, if mention is made of a protective layer of a polarizing plate comprising a polarizer and a protective layer, if necessary, an adhesive layer may be provided on one or both sides of the protective layer. May be provided. The adhesive layer may be made of any suitable material such as acrylic, silicone, polyester, polyurethane, polyether, and rubber.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until the adhesive layer is put to practical use for the purpose of preventing contamination and the like. The separator is formed by a method of providing a release coat with a suitable release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary, on a suitable thin leaf according to the transparent protective film or the like. be able to.

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer which form the polarizing plate and the optical member are made of, for example, a salicylate compound, a benzophenone compound, a benzotriazole compound or a cyanoacrylate compound. Compounds having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorbent such as a compound or a nickel complex compound may be used.

The liquid crystal display device using the plastic substrate liquid crystal cell of the present invention is used for forming a transflective or reflective liquid crystal display device. Therefore, the liquid crystal cell used in the liquid crystal display element of the present invention is appropriately, for example, an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twisted nematic type or a super twisted nematic type, etc. A liquid crystal cell of any type may be used. When polarizing plates or optical members are provided on both sides of the liquid crystal cell, they may be the same or different as long as the requirements of the present invention are satisfied. Further, in forming the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, and a backlight can be arranged at appropriate positions. Next, the present invention will be specifically described with reference to examples.

[0047]

EXAMPLE 1 A polyvinyl alcohol film having a thickness of 75 μm was immersed in a dyeing bath containing iodine and potassium iodide, and then subjected to a dyeing treatment and a stretching treatment of about three times, followed by addition of boric acid and potassium iodide. The stretching treatment and the crosslinking treatment were performed in the bath so that the total stretching ratio became 5 times. Then dried, 27μ thickness
m polarizers were obtained. An adhesive composed of a 7% by mass aqueous solution of polyvinyl alcohol is applied to both surfaces of the polarizer, and a 50 μm-thick triacetyl cellulose film saponified with an aqueous solution of caustic soda is attached to the adhesive surface of the polarizer used on the front side. Then, an 80 μm-thick triacetyl cellulose film saponified with an aqueous solution of caustic soda was attached to the bonding surface of the polarizer used on the rear side to produce two polarizing plates. An adhesive having a thickness of 25 μm was applied to one side of each polarizing plate in order to attach the polarizing plate to the cell.
Next, two pieces of the produced polarizing plate were cut out to a size of 3 inches, and P was obtained by depositing silver on one side of a polarizing plate used on the rear side.
A transflective layer made of an ET film was laminated to produce a transflective polarizing plate. A liquid crystal display cell (3 inches, plastic substrate thickness: 400 μm) using a plastic cell substrate is prepared, a polarizing plate or a circular polarizing plate is bonded to the front side, and a transflective polarizing plate or The circularly polarizing plate was bonded so that the transflective layer was on the side opposite to the cell.

Example 2, Comparative Examples 1-2 The same procedures as in Example 1 were carried out except that the thickness of the triacetylcellulose film to be bonded to the front-side polarizing plate and the rear-side polarizing plate was changed as shown in Table 1. Experiments.

The performance of the liquid crystal display devices produced in the examples and comparative examples was evaluated by the following methods. Table 1 shows the results.

[Dimensional change rate] The polarizing plate produced by the above method was cut into a size of 50 mm x 50 mm (the number of test pieces: 2), and humidified under the conditions of a temperature of 40 ° C and a humidity of 92% RH.
It was left for 20 hours. The dimension (Lb) in the longitudinal direction (MD) of the test piece before the test and the dimension (Lb) in the longitudinal direction (MD) after the test
a) was measured, and the dimensional change (%) was determined from the following equation. Dimensional change rate = [(La−Lb) / Lb] × 100

[Amount of Warpage] With the polarizing plate adhered to the liquid crystal cell, the liquid crystal cell was left under the conditions of 40 ° C. and 92% RH for 120 hours, and the amount of warpage (mm) of the liquid crystal cell after the test was measured.

[0052]

[Table 1] Thickness of protective layer (μm) Thickness ratio MD direction warpage of polarizing plate Front side Rear side A / B Dimensional change rate (%) (mm)(A) (B) Front side Rear side Example 1 50 80 0.62 0.473 0.240 -1.28 Example 2 40 80 0.50 0.562 0.229 -1.09 Comparative Example 1 80 80 1.00 0.227 0.232 -1.94 Comparative Example 2 80 40 2.00 0.267 0.541 -2.58

As is clear from the results shown in Table 1, the liquid crystal display device of the present invention has a thickness A of the protective layer to be bonded to the polarizer of the front polarizer of the liquid crystal cell and a polarizer of the rear polarizer. A / B <
The combination satisfies 0.65. In addition, the dimensional change rate of the front-side polarizing plate and the rear-side polarizing plate under the humidifying condition is larger on the front side, and the relation of front-side polarizing plate warpage> rear-side polarizing plate warpage is obtained. I have. As a result, in the liquid crystal display cell using the plastic cell substrate, the absolute value of the amount of warpage of the liquid crystal cell after the test for 120 hours under humid conditions was 1.0 l. It turns out that it is as small as 5 mm or less.

Further, the liquid crystal display device manufactured in Example 1 was mounted to form a liquid crystal display device. As a result, in this display device, since the amount of warpage of the liquid crystal cell due to the heating history was small, even when used for a long time, almost no color loss at the end of the panel or variation in hue in the panel surface was observed.

[0055]

As described above, according to the present invention,
In a medium-sized or small-sized transflective or reflective liquid crystal display device using a plastic substrate liquid crystal cell, the thickness A of one side of the protective layer (the thickness of the protective layer alone) bonded to both sides of the polarizer of the front-side polarizer, and the rear By setting the relationship between the thickness B of one side of the protective layer to be bonded to both sides of the polarizer of the side polarizing plate (thickness of the protective layer alone) B and A / B <0.65, the heating and humidification durability is good. The warpage of the plastic cell can be eliminated. Therefore, workability in a final product assembling process is improved, and display unevenness such as a variation in hue in a liquid crystal display panel surface and a change in panel hue can be eliminated. Therefore, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a liquid crystal display device of the present invention.

FIG. 2 is a sectional view showing a reflective liquid crystal display device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizer of front-side polarizing plate 2a, 2b Protective layer of front-side polarizing plate 3 Plastic substrate 4 Polarizer of rear-side polarizing plate 5a, 5b Protective layer of rear-side polarizing plate 6 Front-side polarizing plate 7 Liquid crystal cell 8 Rear side Polarizing plate 9 Retardation plate 10 Reflector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 324 G09F 9/00 324 (72) Inventor Seri Yoshikawa 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation F-term (reference) 2H049 BA02 BA03 BA06 BA27 BB03 BB33 BB43 BB51 BB63 BC03 BC14 BC22 2H090 JB03 JD12 KA05 KA08 LA06 LA09 LA16 2H091 FA08X FA08Z FA11X FA11Z FA21X FA26XFA31 FA31XFA31X LA30 5G435 AA04 AA12 AA13 AA17 BB12 CC12 EE33 FF03 FF05 GG09

Claims (7)

[Claims] 1. A liquid crystal display element having a panel size of 4 inches or less used in a transflective or reflective liquid crystal display device using a plastic substrate liquid crystal cell, wherein a polarizing plate on a front side with respect to the liquid crystal cell is polarized. A liquid crystal display device, wherein the thickness A of the protective layer alone to be bonded to the polarizer and the thickness B of the protective layer alone to be bonded to the polarizer of the rear polarizing plate have the following relationship. A / B <0.65 2. The liquid crystal display device is operated at 40 ° C. and 92% RH.
The dimensional change rate C in the MD direction (longitudinal direction) of the front polarizing plate alone and the dimensional change rate D in the MD direction (longitudinal direction) of the rear polarizing plate alone after standing for 120 hours under the conditions. Has the following relationship: C> D 3. The thickness A of the protective layer alone of the front-side polarizing plate is 20 to 200 μm, and the thickness B of the protective layer alone of the rear-side polarizing plate is 70 to 220 μm. 3. The liquid crystal display device according to 2. 4. The liquid crystal according to claim 1, wherein the dimensional change rate C is 0.6 to 1.6%, and the dimensional change rate D is 0.1 to 0.6%. Display element. 5. The liquid crystal display device according to claim 1, wherein a retardation plate is laminated on the front and / or rear polarizing plates. 6. The liquid crystal display device according to claim 1, wherein a reflection plate or a transflective plate is laminated on the rear polarizing plate. 7. The liquid crystal display device is operated at 40 ° C. and 92% RH.
The liquid crystal display device according to any one of claims 1 to 6, wherein the amount of warpage of the plastic substrate liquid crystal cell after standing for 120 hours under the conditions is | 1.5 mm | or less.