JPS63278025A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the color phase irregularity and the variance of threshold voltage to improve the productivity by constituting a cell after grinding the first principal surface or first and second principal surfaces of a glass substrate. CONSTITUTION:In the production of a liquid crystal display device using the interference color due to double refraction, a process is provided where first principal surfaces 1a and 2a where display electrodes are formed of first and second substrates 1 and 2 constituting the cell or these first principal surfaces 1a and 2a and second principal surfaces 1b and 2b where polarizing plates 11 and 12 are stuck are ground by 1-3mum. Since the extent of grinding is set to 1-3mum, they are ground in a minimum grinding time and the flatness precision and the extent of warp of ground substrates are <=15mum and <=0.1% respectively. Thus, the variance of the gap is eliminated to stabilize various characteristics, and the grinding work of a thin plate glass is rationalized to improve the productivity.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention provides a liquid crystal display that utilizes interference color due to birefringence! ! Regarding the manufacturing method.

(Prior art) There are TN type, DS type, and GH type for liquid crystal display depending on the operation mode.
Although there are many types such as type, DAP type, and heat-containing type, TN type liquid crystal displays are used in most products, including wristwatches, trains, and measuring instruments. However, with the demand for increased display capacity and larger display area, problems such as insufficient contrast and narrow visual range have arisen in TN type liquid crystal displays, leading to the development of liquid crystal displays with new operating modes. was urgent.

In recent years, an SBE (super twisted bias fringe effect) type liquid crystal display, which is described in, for example, Japanese Patent Application Laid-Open No. 107020/1983, has been attracting attention as a liquid crystal display that meets such demands. S
The configuration of a BE type liquid crystal display is as follows: - Two transparent substrates each having a transparent electrode formed on at least one side are placed facing each other, subjected to alignment treatment such as oblique vapor deposition or rubbing, and the periphery is sealed to form a cell; A nematic liquid crystal is placed inside the cell. Nematic liquid crystals include cyclohexane, ester,
Biphenyl-based and pyridine-based liquid crystals are used.

A chiral agent is added to the nematic liquid crystal so that the molecular axes of the liquid crystal molecules range from 180° to 360', preferably 2
It is twisted between the upper and lower substrates at an angle of 70°. Further, the molecular axes of liquid crystal molecules have an inclination (pretilt) of more than 1° with respect to the plane of the substrate due to the action of an alignment layer on the substrate, and the distance between the opposing substrates is about 4 to 12#.

(Problems to be Solved by the Invention) The SBE type liquid crystal display requires an extremely high distance (gap) between opposing substrates, which must be kept within 0.1#. Even a slight unevenness in the gap causes a change in the threshold voltage, causing uneven lighting, and also causes noticeable color unevenness due to an interference phenomenon, degrading the display quality.

Conditions that affect gap accuracy include the flatness of the glass substrate that is the component, the dimensional accuracy of the spacer that determines the gap, and precise glass assembly conditions, but even if these conditions are satisfied, At the minimum, the flatness accuracy of the glass substrates should not exceed 0.14 for two substrates, and considering the tolerances of other conditions, it can be said that a flatness of about 0.03 IM1 is required.

In general, transparent substrates used in liquid crystal displays are usually relatively inexpensive soda lime glass substrates.

However, since this has a high degree of alkali elution, a transparent electrode is usually formed on an undercoat of 5I02 or the like as a blocking material. Furthermore, methods for producing soda-lime glass include, for example, the Colburn method and the float method, but both have unevenness due to the manufacturing method, and the flatness is limited to a flatness accuracy of 0.1 to 0.15 dust.

Therefore, when such a substrate is used in an SBE type liquid crystal display, the surface of the substrate is rough, so that the accuracy of the distance between the opposing substrates as described above cannot be obtained. For example, as an orientation treatment, SiO
When performing oblique evaporation, the desired tilt angle may not be obtained due to uneven evaporation, and unevenness in film thickness may occur during undercoating or when depositing a transparent conductive film, resulting in uneven color and threshold voltage. This caused unevenness and significantly reduced visibility.

The purpose of this invention is to streamline the polishing process of thin glass, which tends to be extremely expensive, and improve productivity by optimizing the flatness accuracy of the substrate and the amount of polishing.

[Structure of the Invention] (Means for Solving the Problems) The present invention is a method for manufacturing a birefringence control type liquid crystal display, in which display electrodes of first and second substrates constituting a cell are formed. The method includes a step of polishing the first principal surface on the side to which the polarizing plate has been applied, or the first principal surface and the second principal surface on the side to which the polarizing plate is attached, one to three times.

(Function) This invention sets the amount of polishing to 1 to 3 polishes based on the results of experiments, thereby increasing the flatness accuracy of the substrate to be polished to 0.154 or less and warping to 0.1% or less with the minimum polishing time. The characteristics can be stabilized without any uneven gaps.

(Example) The details of this invention will be explained below with reference to the drawings.

The glass substrates used in liquid crystal displays are made of inexpensive soda-lime glass, and there are various manufacturing methods, but the most common are the Colburn method and the float method, and we investigated these two methods. . Furthermore, what is hereinafter referred to as flatness accuracy is a value obtained by averaging the difference between the highest and lowest parts observed over the entire surface of the substrate when, for example, the needle of a stylus meter is moved by 2 m.

Of the two types of glass substrate manufacturing methods mentioned above, in the Colburn method, molten glass is pulled up vertically and then bent horizontally using a roller called a bending roller to form a thin plate. What determines the flatness of glass is
The flatness of the bending roller in contact with the molten glass results in the presence of extremely fine waves in the glass. As a result, the flatness accuracy of the general Colburn method is as high as 0.7m, and even if a better one is selected based on manufacturing know-how and selection, it is 0.1 to 0.151I.
Ir1 is said to be the limit.

On the other hand, in the float method, molten glass is poured onto molten tin.
Determine the flatness on the free interface of tin.

Since it is a free interface, the flatness is better than the Colburn method, but when it is pulled at a predetermined speed to make a thin plate, undulations parallel to the pulling direction occur, and as a result, the flatness accuracy of ordinary glass is 0°1 to 0. It is said to be .154.

Regardless of the glass manufacturing method, color unevenness and display unevenness occurred when used in a liquid crystal display with this level of flatness accuracy.

In particular, glass produced by the Colburn process exhibits characteristic phenomena such as disordered color unevenness, and glass produced by the float process exhibits stripes of color unevenness at a corrosion pitch of 1.5 to 2.0.

Therefore, by solving these phenomena, 0.037! In order to obtain flatness accuracy of #m or less, we considered applying a polishing technique used for Si wafers, glass masks, lenses, etc. This polishing is not just a matter of cutting, but there are various processing components. That is, if the amount of polishing is simply increased, the flatness will improve, but if the amount of polishing is increased, the glass thickness will change, which will affect the total thickness of the product and the manufacturing process. For example, machining time becomes longer,
In this invention, when considering the amount of polishing, the following three points are taken into consideration.

■Glass thickness ■Warp of the glass to be polished ■Flatness accuracy of the glass to be polished Among these, (■) can be polished to approximately 1.11 JM for large glass plates used as substrates for liquid crystal display devices, where multi-piece molding is common. It is necessary to consider whether or not the polishing amount and the polishing time are determined by these values, so they are necessary parameters.

Table 1 below shows the observed results of the display when a cell was constructed using glass manufactured by the Colburn method and polished on one side.

*O, etc. are the evaluation results at cell time: 0: Good O: Very good △: Slightly poor This was done using the same type of double-sided polishing machine. The size of the glass is 300 mm square, which is the maximum size that can be polished with a polishing machine, and the thickness is 1 mm, which is the commonly used thickness. IJllll>0.5 when looking at the thinner side
5 m, 0.77 Ill, 1.1 mm. Warpage is expressed as a value expressed as a percentage of the longitudinal dimension of the glass (300,) and the ratio of the maximum height of the glass to the lowest length, and those less than 0.1%, 0.1%, 0.15 %
It was made into a thing. Flatness accuracy is 0 for Colburn method glass.
．． 4m, 0.2u11.0-15g! 11 and 0.
1 piece, float method glass 0.1571111
．． 0.15! II and 0.081111, and the amount of polishing was 0.5mm and 1mms2 while measuring.
m and 31m.

A birefringent liquid crystal display was constructed using these substrates, and the color unevenness of the cell was confirmed as well as the polishing time.

As can be seen from the same table, even though the polishing conditions were changed for 'Mo9' with a glass thickness of 0.55 mm, all of them were damaged and could not be polished, whereas there was not much difference between 0.7jllI and 1.1jIII. There isn't. In addition, in the case of the glass having the best flatness accuracy, a glass warpage of 0.1% or less is extremely good, and if it exceeds 0.1%, it may be damaged or the thickness may be unevenly reduced, which is not good.

Although there is almost no difference between the Colburn method and the float method, it was found that the float method was slightly more difficult to remove and took 1 to 2 minutes longer to achieve the desired amount of polishing. In the case of double-sided polishing, there were two polished surfaces, so the polishing time took twice as long.

Therefore, considering the polishing time and other factors from these results, the optimal polishing conditions are: ■ Flatness accuracy ≦ 0.15 immediately ■ Warpage of glass material 50.1% ■ Polishing amount 1 to 3 dust ■ Glass thickness 0.7 to It is considered to be 1.1 μs.

FIG. 1 is a sectional view showing an embodiment of the present invention, and will be explained according to the manufacturing process. First, two pieces of soda lime glass (1,
The first and second substrates (1) were polished by polishing the main surfaces of 1 m thick and with a flatness accuracy of 0.15 m for about 7 minutes using an Oska single-pole polishing machine.

(2) is obtained. In the first and second substrates (1) and (2), the first principal surfaces (1a) and (2a) were polished, and the amount of polishing was approximately 2 mm. Next, the first and second! ! Board (1).

On the first principal surface (la) and (2a) of (2), undercoat II (3) consisting of, for example, 5fOa, respectively,
(4) and, for example, I To (Indium Tin
0xide) Color conductive electrodes (5) and (6) are sequentially formed. Next, the first and second substrates (1), (
2), conductive electrodes (
Alignment layers (7) and (8) made of polyimide, for example, are formed to cover 3) and (4), respectively. The first and second substrates (1) and (2) are approximately 71 cm long with their respective first principal surfaces (1a) and (2a) facing each other.
The periphery except for the portion that will become the injection port for the liquid crystal is sealed with a sealing agent (9) made of, for example, an ultraviolet curing adhesive so that the distance is maintained at a distance of mm. Next, a nematic liquid crystal (10) added with a chiral agent is injected between the first and second substrates (1) and (2)', and then the injection port is sealed. In this way, the nematic liquid crystal (1G)
The molecular axes of the substrates (1) and (2) are sandwiched between the first and second substrates (1) and (2) due to the action of the chiral agent.
2) with a twist of 1800° to 360°, for example, 270°, and due to the action of the alignment layers (7) and (8), 1 to the plane of the first and second substrates (1) and (2). The second main surface (1b
) side includes a polarizing plate (11) and a second main surface (2) of the second substrate (2).
A polarizing plate (12) and a reflecting plate (13) are attached to the 2b) side. Here, the arrangement angle of the polarizing plates (11) and (12) is
The transmission axes of the polarizing plates (11) and (12) are aligned with the first substrate (1)
With respect to the orientation direction of , the angles are set to be about 30 degrees clockwise and about 20'' clockwise, respectively.

In this example, by using the first and second substrates (1) and (2) whose first principal surfaces (1a) and (2a) have been polished, the flatness accuracy on the substrate surfaces is improved. It is possible to reduce the uneven deposition that occurs when depositing an undercoat and the uneven deposition that occurs when depositing ITO, and at the same time reduce the uneven deposition during oblique vapor deposition during alignment processing, and also reduce the distance between opposing substrates. We were able to improve the accuracy of As a result, the completed liquid crystal display had reduced color unevenness and threshold voltage unevenness, and was able to improve visibility.

Until now, the first principal surface (1a), (2
Although we have described an example in which only the a) side was polished, the first principal surface (1
It goes without saying that even if both surfaces of a), (2a) and the second main m(1b), (2b) are polished, similar effects can be obtained.

[Effects of the Invention] The present invention is a method for manufacturing a liquid crystal display using interference color due to birefringence, and includes
By configuring the cell after polishing the second main surface, it was possible to improve the visibility due to visual sensation, which was insufficient in the past.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention. (1)...First board (2)...Second board

Claims (3)

[Claims] (1) First and second electrodes with conductive electrodes formed on the first main surface side
a substrate, the molecular axis being 1 with respect to the plane of the first and second substrates;
a nematic liquid crystal having an inclination larger than
A method for manufacturing a liquid crystal display including a polarizing plate on the main surface side, comprising the step of polishing the first main surface of the first and second substrates or the first and second main surfaces together by 1 μm to 3 μm. A method for manufacturing a liquid crystal display device, characterized in that: (2) The first and second substrates are soda lime glass formed by a Colburn method or a float method, and have a flatness accuracy of 0.15 μm or less and a warpage of 0.1% or less. 2. The method for manufacturing a liquid crystal display according to item 1. (3) The thickness of the first and second substrates before polishing is 0.7 m.
2. The method of manufacturing a liquid crystal display according to claim 1, wherein the thickness is 1.1 mm to 1.1 mm.