JPH03139603A - Optical phase difference plate - Google Patents

Abstract

PURPOSE:To facilitate production and to lessen a change with time by tightly adhering and forming two kinds of optical phase difference films to one sheet on both sides of a tacky adhesive agent layer and specifying the retardation of the sheet. CONSTITUTION:The 1st optical phase difference film 2 formed by unidirectionally stretching a compsn. consisting of a polyvinylidene fluoride resin and polymethyl methacrylate resin at >=55/45 and <=85/15 mixing ratios by weight and the 2nd optical phase difference film 3 formed by unidirectionally stretching a polycarbonate resin are tightly adhered and formed to one sheet on both sides of the tacky adhesive agent layer 4. The retardation of the sheet is maintained within the range of 500 to 650nm. The optical phase difference plate 1 is formed in such a manner, by which the change of the DELTAnd of the two optical phase difference films with time is nearly offset and the change characteristics of the DELTAnd over the entire part of the optical phase difference plate 1 with time is stabilized; in addition, the production is facilitated.

Description

[Detailed Description of the Invention] [Summary] Regarding optical retardation plates, the purpose of this invention is to realize optical retardation plates that are easy to manufacture and stable with little change over time. A first optical retardation film formed by stretching in one direction a composition in which the mixing ratio of methacrylate resin is 55/45 or more and 85/15 or less by weight;
A second optical retardation film formed by stretching a polycarbonate resin in one direction is closely formed into a single thin plate with an adhesive layer sandwiched therebetween, and the retardation of the thin plate is 500 to 650 nm. The optical retardation plate is configured to be maintained within the range of . Further, the optical retardation plate and the polarizing plate are closely formed into a single thin plate with an adhesive layer in between to form a composite optical retardation plate.

[Industrial application field]

The present invention provides an optical retardation plate, in particular, stable aging characteristics. Furthermore, the present invention relates to an inexpensive optical retardation plate.

In recent years, various office automation equipment, including personal computers and word processors, have become widespread. In particular, recently there has been a demand for portable, lightweight equipment, and as a result, liquid crystal display devices that are thin, lightweight, low power and low cost have become preferred as display devices.

Although liquid crystal display devices have the above-mentioned advantages, conventional O
It had the disadvantage of inferior display quality compared to CR, T and plasma displays. In order to improve this display quality, various improvements have been made, and black and white liquid crystal display devices using STN liquid crystals have been developed and are now in practical use. In addition, there is a demand for the development of a liquid crystal display device with long-term quality stability, and there is a strong demand for improvements in various components used therein, such as optical retardation plates for color compensation.

[Conventional technology]

Conventionally, the most commonly used liquid crystal display device is a simple matrix type that uses TN type liquid crystal, but as the display screen becomes larger, the contrast deteriorates and the viewing angle becomes smaller. It becomes unbearable for practical use.

On the other hand, in order to realize a large screen, for example, a 640 x 400 pixel class display, 5TN (Su
(per twisted nematic) type liquid crystals have come into use. This STN type liquid crystal has a twisted arrangement of liquid crystal molecules of 240° to 270°, which is larger than the 90° of the conventional TN type liquid crystal, thereby significantly improving contrast and display capacity characteristics.

However, as a result of the use of birefringence in this STN liquid crystal, the screen is colored, for example, the background in positive image display becomes yellow-green, making it difficult to see. To deal with this, various countermeasures have been considered, and the STN display is black and white.
type liquid crystal display devices have been developed and have come into practical use in some cases. Typical examples are shown below.

FIG. 8 is a diagram (part 1) showing a conventional monochrome liquid crystal display panel. In the figure, 6 is a lower polarizing plate, 5' is an upper polarizing plate disposed orthogonally to the lower polarizing plate 6, 7 is a display liquid crystal panel, 8 is a compensation liquid crystal panel, 71.72 is a glass substrate, and 73.74 is a liquid crystal panel for compensation. Drive electrodes 75 are formed on opposing inner surfaces of glass substrates 71 and 72 to form an X-Y matrix, and 75 is an STN liquid crystal layer. However, drive electrodes 73 and 74 are not formed in the compensation liquid crystal panel 8, and the liquid crystal panel 8 is made exactly the same as the display liquid crystal panel 7, except that the twist direction, that is, the twist direction of the liquid crystal molecules is reversed. has been done. Note that 9 is an observer.

Now, when light is incident from below, it becomes linearly polarized light by the lower polarizing plate 6, and when it passes through the STN liquid crystal layer 75 of the display liquid crystal panel 7, it becomes elliptically polarized light with wavelength dependence. Therefore, if you observe it through the upper polarizing plate 5', it will appear colored, but since the compensating liquid crystal panel 8 with the same twist angle and opposite twist to the display liquid crystal panel 7 is arranged, By doing so, the phase difference at each wavelength is canceled out, and the light becomes linearly polarized light again, and the wavelength dependence of the transmitted light is eliminated, resulting in a black and white display.

Although FIG. 9 uses a compensation liquid crystal panel 8 with a conventional monochrome display liquid crystal display spring reversely twisted, in reality, the twist angles of the display liquid crystal panel 7 and the compensation liquid crystal panel 8 do not necessarily have to be equal. The phase difference of the light of each wavelength transmitted through the display liquid crystal panel 7, that is, the retardation R (=Δ
Black and white display is possible by compensating for nd (here, Δn: refractive index change, d: layer thickness). For example, in the plastigram of birefringence that does not have a twist angle, 2' is an optical retardation plate, for example, when a mixed composition of polyvinylidene fluoride resin and polymethyl methacrylate resin is stretched in one direction. This optical retardation film has already been proposed by the present inventors (Japanese Patent Application No. 01-058295).

Note that the same reference numerals are given to the same parts as those explained in the drawings of the conventional example.

Further, since the operating principle is the same as that of y except that the compensating liquid crystal panel 8 in FIG. 6 is replaced with an optical retardation plate 2', detailed explanation will be omitted.

[Problems to be Solved by the Invention] However, the method using the compensation liquid crystal panel 8 shown in FIG. There is a problem that this will lead to an increase in prices and increase in prices.

On the other hand, the method of using an optical retardation plate 2'' is effective in reducing weight and cost and has recently been widely used, but there are still many points to be improved.

For example, FIG. 7 is a diagram showing the aging characteristics of a conventional optical retardation plate, in which the vertical axis shows And (retardation) measured using light with a wavelength of 600 nm, and the horizontal axis shows the aging time during the test. The sample has already been proposed by the present inventors (Japanese Patent Application No. 01-058295), and is formed by stretching a mixed composition of polyvinylidene fluoride resin and polymethyl methacrylate resin in one direction. This is an optical retardation film. The test conditions were as follows: The sample was left in a constant temperature bath at 700C, and at the time of measurement, it was taken out to room temperature, cooled, and then carried out using a condensator of a polarizing microscope.

As shown in the figure < , from before 200H, A
nd shows a large change of +20 nm or more, and in such a case, the background color may change from white to yellow-green.

In general, in monochrome LCD devices, the tolerance for changes in And is strict, about ±10 nm. A solution was needed.

[Means to solve the problem]

The above problem is that the mixing ratio of polyvinylidene fluoride resin and polymethyl methacrylate-1 resin is 55/4 by weight.
A first optical retardation film 2 formed by stretching a composition of 5 or more and 85/15 or less in one direction, and a second optical retardation film 3 formed by stretching a polycarbonate resin in one direction. are closely formed into a single thin plate with the adhesive layer 4 in between, and the retardation of the thin plate is 50.
This problem can be solved by constructing an optical retardation plate that maintains the wavelength within the range of 0 to 650 nm. moreover,
By forming a composite optical retardation plate by closely forming the optical retardation plate 1 and the polarizing plate 5 into a single thin plate with the adhesive layer 4 in between, rationalization effects such as a reduction in the number of parts can be achieved. can be raised.

[Effect]

The first optical retardation film 2 is formed by stretching a mixed composition (polymer blend) of polyvinylidene fluoride resin and polymethyl methacrylate resin in one direction. Since a certain polyvinylidene fluoride (PVDF) crystallizes along the stretching axis direction and the birefringence increases, And increases with the passage of time.

On the other hand, the second optical retardation film 3 formed by stretching polycarbonate-1/based resin in one direction is originally amorphous, and molecular orientation occurs during the stretching process, resulting in birefringence. However, during high-temperature storage, the molecular orientation relaxes, the birefringence decreases, and the And
becomes smaller over time.

Therefore, according to the present invention, if the above two optical retardation films 2 and 3 are integrated with the transparent adhesive layer 4 in between to form the optical retardation plate 1, the And of both optical retardation films can be The changes are canceled out, and the temporal change characteristics of And of the optical retardation plate 1 as a whole are extremely stabilized.

〔Example] FIG. 1 is a diagram showing an embodiment of the present invention.

In the figure, ■ is an optical retardation plate, 2 is a first optical retardation film, and for example, the mixing ratio of polyvinylidene fluoride resin and polymethyl methacrylate resin is 55/4 by weight.
A composition of 5 or more and 85/15 or less was stretched 20% in one direction at 1000C to form a transparent film with a thickness of 100 μm.

3 is a second optical retardation film, which is formed by, for example, stretching polycarbonate resin by 40% in one direction at 1700 G to form a transparent film with a thickness of 100 μm.

4 is an adhesive layer, for example, a layer of transparent acrylic adhesive with a thickness of about 15 μm, and the optical retardation films 2 and 3 are bonded together to prevent air bubbles from entering. It's no good.

For the first optical retardation film, a so-called polymer blend, a mixture of polyvinylidene fluoride resin and polymethyl methacrylate resin having a composition range already proposed by the present inventors, may be used. For example, patent application Senkyu-058295).

That is, the light transmittance, which is particularly important in determining the characteristics of the optical retardation film, and the degree of stretching for providing birefringence will be described below.

Figure 4 is a diagram showing the relationship between light transmittance and polyvinylidene fluoride resin weight ratio, and shows the practically required light transmittance of 90%.
In order to obtain the above, the polyvinylidene fluoride resin weight ratio is 5.
The composition may be 5/45 or more and 85/15 or less.

In addition, Figure 5 is a diagram showing the relationship between the degree of stretching and the weight ratio of polyvinylidene fluoride resin. A composition having a vinylidene resin weight ratio of 55/45 or more and 85/15 or less is sufficient.

From the above points, the composition of the first optical retardation film of the present invention is such that the mixing ratio of polyvinylidene fluoride resin and polymethyl methacrylate resin is 55/45 or more and 85 or more by weight.
/15 or less.

FIG. 2 is a diagram showing another embodiment of the present invention.

In the figure, numeral 5 denotes a polarizing plate, which is made of, for example, an iodine-doped oriented vinyl alcohol film with a thickness of about 200 μm. In this embodiment, the adhesive layer 4 described above is coated on the upper surface of the second optical retardation film 3 of the optical retardation plate 1 of the embodiment shown in FIG. A polarizing plate 5 is attached.

FIG. 3 is a diagram showing the temporal change characteristics of the embodiment of the present invention.

The vertical axis, horizontal axis, test conditions 5 and measurement conditions are the same as those explained in FIG. 5 above. As shown in the figure, even when the optical retardation plate 1 according to the embodiment of the present invention is left at high temperatures for a long period of time, the change in Δnd over time is extremely small and falls within the range of ±10 nm, which is the required condition for black-and-white liquid crystal display devices. I understand that.

FIG. 6 is a diagram showing the structure of a black-and-white liquid crystal display panel using an embodiment of the present invention. In FIG. 2, ■ is an optical retardation plate according to the present invention.

Note that the same reference numerals are given to the same parts as those explained in the above drawings, and the explanation of the same parts will be omitted.

It can be easily understood from the above that a black and white display can be obtained with the configuration shown in this figure. It goes without saying that even if the composite optical retardation plate 10 shown in FIG. 2 is used instead of the optical retardation plate 1 and the upper polarizing plate 5 shown in the figure, a completely similar liquid crystal display device with black and white display can be obtained. In this case, it goes without saying that further rationalization effects such as a reduction in the number of parts and the number of assembly steps can be obtained.

Furthermore, the same effect can be obtained even if the order of overlapping the optical retardation films 2 and 3 is reversed.

The embodiments described above are merely examples, and it goes without saying that preferred materials and configurations, or combinations thereof, may be used as long as they comply with the spirit of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, the first optical retardation film 2 is formed by stretching a mixed composition (polymer blend) of polyvinylidene fluoride resin and polymethyl methacrylate resin in one direction. The increase in retardation R (Δnd) during high temperature storage of the second optical retardation film 3 formed by stretching polycarbonate resin in one direction during high temperature storage
d) can be offset by the reduction of d), and the high-temperature aging change of - optical retardation plates 1 or - composite optical retardation plates 10 can be reduced, so long-term color stability is guaranteed and black-and-white display is possible. This greatly contributes to improving the quality stability and reliability of liquid crystal display devices.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing another embodiment of the present invention, Fig. 3 is a diagram showing the temporal change characteristics of the embodiment of the present invention, and Fig. 4 is a diagram showing light transmission. Figure 5 is a diagram showing the relationship between the drawing ratio and the polyvinylidene fluoride resin weight ratio, Figure 6 is a diagram showing the relationship between the stretching degree and the polyvinylidene fluoride resin weight ratio, and Figure 6 is a diagram showing the relationship between the drawing ratio and the weight ratio of the polyvinylidene fluoride resin. Figure 7 is a diagram showing the structure of a black-and-white liquid crystal display panel; Figure 7 is a diagram showing the aging characteristics of a conventional optical retardation plate; Figure 8 is a diagram showing an example of a conventional black-and-white liquid crystal display panel (part 1). ), FIG. 9 is a diagram (part 2) showing an example of a conventional black and white liquid crystal display panel. In the figure, 1 is an optical retardation plate, 2 is a first optical retardation film, 3 is a second optical retardation film, 4 is an adhesive layer, 5 is a polarizing plate, 5' is an upper polarizing plate, and 6 is a 7 is a display liquid crystal panel; 8 is a compensation liquid crystal panel; 10 is a composite optical retardation plate. 5 6 <-(uu>'; lp op, uv 0 0 0 0 size ■ c<-0

Claims (1)

[Claims] (1) The mixing ratio of polyvinylidene fluoride resin and polymethyl methacrylate resin is 55/45 or more and 85 by weight.
The first film formed by stretching a composition of /15 or less in one direction
The optical retardation film (2) and the second optical retardation film (3) formed by stretching a polycarbonate resin in one direction are combined into an adhesive layer (4).
An optical retardation plate characterized in that the retardation of the thin plate is maintained within a range of 500 to 650 nm. (2) A composite optical retardation device characterized in that the optical retardation plate according to claim (1) and the polarizing plate (5) are closely formed into a single thin plate with an adhesive layer (4) in between. Board.