JPS5944328B2 - Method for purifying green-emitting phosphor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying a green-emitting phosphor, and in particular, a method for purifying a green-emitting phosphor in which a blue-emitting phosphor made of silver-activated zinc sulfide is mixed in the green-emitting phosphor. The present invention relates to a method for purifying a phosphor that increases the color purity of the phosphor.

The luminescent screen of a color picture tube emits the three primary colors of light: red,
It consists of three types of electron beam-emitting phosphors, blue and green, arranged regularly in a dot-like or stripe-like trio. This arrangement is achieved by applying a photoresist in which phosphors are suspended to a luminescent screen, exposing it to an appropriate light source through a shadow mask, and developing it, and this operation is performed sequentially for each phosphor. It is done. By the way, the phosphor used in color picture tubes is very expensive, so for the purpose of cost reduction, the surplus phosphor recovered from each development process has traditionally been used as the least expensive of the three types. Furthermore, all materials are recycled, except for the blue-emitting phosphor, which tends to discolor when recycled.

When such recycling is carried out, the recovered phosphor becomes contaminated with the phosphor of the previous coating order, i.e.
There is a problem in that previously formed dots or stripes of the phosphor and some of the deposits on the face plate get mixed into the recovered phosphor and accumulate over repeated use. In the early days, the phosphors were applied in the order of green → blue → red, so blue and red-emitting phosphors were contaminated by the phosphors in the previous order, but green-emitting phosphors were was not contaminated.

Therefore, the purification treatment for removing the contaminated phosphor from the recovered phosphor only had to be applied initially to the recovered red-emitting phosphor, which was mainly contaminated with the blue-emitting phosphor. however,
Recently, the order of applying phosphors has been changed from blue to green to red due to various reasons, and the recovered green-emitting phosphor, which had no problems before this change, is applied first to form the blue color. It has become contaminated by luminescent phosphors.

Currently, there is no known purification method to remove the blue-emitting phosphor from the recovered green-emitting phosphor, so the content of the blue-emitting phosphor that accumulates and increases with repeated collection and reuse is limited to a certain level. When the value reached , the recovered green-emitting phosphor had to be discarded. In the process of developing a purification method that would enable repeated use of recovered green-emitting phosphors, the inventors discovered that silver-activated zinc sulfide (ZnS:Ag), commonly used as the blue component of luminescent screens, We focused on the fact that the blue-emitting phosphor often causes a development called discoloration, which changes from blue to green, during the manufacturing process of color picture tubes, and as a result of investigating the cause of this, we found that the blue-emitting phosphor is It was found that when heated to a high temperature of 200° C. or higher after reacting with copper ions, an exchange reaction between silver and copper, which is an activator, occurs and the material changes into a green-emitting phosphor.

If the above knowledge is applied to a method for purifying a recycled color-emitting phosphor, instead of physically or chemically removing the blue-emitting phosphor that is present as an impurity component in this phosphor, The inventors have discovered that a purification method based on a completely new perspective is possible, in which a blue-emitting phosphor itself is changed into a green-emitting phosphor, and the present invention has been achieved. That is, the present invention is characterized in that a blue-emitting phosphor made of silver-activated zinc sulfide, which is present as an impurity in a green-emitting phosphor, is reacted with copper ions. The method of the present invention can be applied to all green-emitting phosphors that are not easily affected by copper ions; is the target.

The amount of copper ions to be reacted is determined by
) is preferably in the range of 0.2 to 1.2 mol %; if the amount is too low, the recovery of purity will be too small, and if the amount is too high, the brightness of the green-emitting phosphor will be significantly reduced.

After reacting the mixed blue-emitting phosphor with copper ions,
In order to convert this into a green-emitting phosphor, it is necessary to heat it to a high temperature of over 200°C, but in the color picture tube manufacturing process, it is inevitably heated to a high temperature of over 400°C. No heating is required.

Further, the amount of the blue-emitting phosphor mixed in the color-emitting phosphor of the recorded color can be easily determined by measuring the emission spectrum or emission chromaticity. Hereinafter, this invention will be explained in detail with reference to Examples.

Example 1 Copper, aluminum-activated zinc sulfide recovered from the development process of green-emitting phosphor stripes in the manufacturing process of a color picture tube phosphor surface forming blue-emitting phosphor stripes first and green-emitting phosphor stripes second. When we investigated the emission spectrum of a green-emitting phosphor made of (ZnS:Cu:Al), we found that its chromaticity point was point B on the CIE chromaticity diagram in Figure 1. ) was found to contain 1.0% by weight of a blue-emitting phosphor.

This time, 20 kg of color-emitting phosphors were collected at 100 f. 6.5cc of 10% copper sulfate solution was suspended in pure water and stirred.
(ZnS: equivalent to 0.2 mol % with respect to Ag) was added. After stirring for 1 hour, the phosphor was allowed to settle and the supernatant liquid was removed.

Pure water was added again to make the mixture 1001, and the mixture was stirred for about 30 minutes. After repeating this operation three times to thoroughly wash the phosphor, ▲
The mixture was filtered and dried at 40°C. The thus purified color emitting phosphor was applied to the fluorescent surface of a color picture tube, and after undergoing heat treatment at approximately 400°C in the normal color picture tube manufacturing process, its chromaticity was measured. The condition had recovered to point C in Figure 1. The chromaticity of a green-emitting phosphor made of copper and aluminum-activated zinc sulfide with no color contamination is A in Figure 1.
The chromaticity of point C was close to this value, and there was no change in brightness. Therefore, there was no problem with reuse. Example 2 Similar to Example 1, copper, gold, and aluminum activated zinc sulfide (Zn
When we investigated the emission spectrum of a green-emitting phosphor made of silver-activated zinc sulfide (S:Cu:Au:A1), we found that its chromaticity was at point P in Figure 1.
:Ag) was found to be mixed in by 1.5% by weight.

Suspend color-emitting phosphor 20k9 recorded in this episode in 1001 pure water, and while stirring, 59 cC of 10% copper sulfate solution (
ZnS (corresponding to 1.2 mol % based on Ag) was added. After stirring for 1 hour, sedimentation and washing with pure water were repeated four times, followed by filtration and drying at 40°C.

The thus purified color emitting phosphor was applied to the fluorescent surface of a color picture tube, and after undergoing heat treatment at about 400°C in the normal color picture tube manufacturing process, its chromaticity was measured. It had recovered to point Q in the figure. The chromaticity of a green-emitting phosphor made of copper, gold, and aluminum-activated zinc sulfide with no color contamination is point O in Figure 1, and the chromaticity at point Q is O.
It was very close to the point. Further, the brightness was about 95% of the original phosphor, and there was no problem in practical use. As is clear from the above examples, according to the method of the present invention, the blue-emitting phosphor mixed in the green-emitting phosphor can be easily converted into the green-emitting phosphor, thereby eliminating color contamination. This makes it possible to repeatedly use the color-emitting phosphor over a long period of time, which is of great industrial value.

[Brief explanation of drawings]

The drawing is a CIE chromaticity diagram showing the respective chromaticities of the green-emitting phosphor before and after the purification process and the uncontaminated green-emitting phosphor in the example of the present invention. A is uncontaminated, B is before the purification treatment in Example 1, C
are the chromaticity points of green-emitting phosphors made of copper and aluminum-activated zinc sulfide, respectively, after the purification treatment in Example 1, O is the uncontaminated one, and P is the Q before the purification treatment in Example 2. are copper and copper after the purification treatment in Example 2, respectively.
This is the chromaticity point of a green-emitting phosphor made of gold and aluminum-activated zinc sulfide.

Claims (1)

[Scope of Claims] 1. Containing a blue-emitting phosphor made of silver-activated zinc sulfide as an impurity, a green-emitting phosphor containing zinc sulfide or zinc cadmium sulfide as a matrix and copper as a main activator; A method for purifying a green-emitting phosphor characterized by reacting ions. 2 The amount of copper ions to be reacted is 0 relative to silver activated zinc sulfide.
．． The method for purifying a green-emitting phosphor according to claim 1, wherein the amount is 2 to 1.2 mol %.