JPH09176632A - Method for recycling recovered phosphor slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recycling a recovered phosphor slurry whereby three impurities are efficiently and almost completely removed from the slurry under well considered conditions and thus a phosphor having good characteristics is recovered. SOLUTION: This method for recovering a phosphor from a recovered red rare-earth oxysulfide phosphor slurry comprises the first step wherein an oxidizing agent in an amt. of 0.5-5.0wt.% of the solids in the slurry and an alkali in an amt. of 0.01-0.1 N based on the slurry are added to the slurry, which is then treated in warm water, the second step wherein the slurry is washed with water and treated at a pH of 1.0-3.0, and the third step wherein the slurry is washed with water and then treated in warm water at a pH of 5 or higher in the presence of a chelating agent in an amt. of 0.00001-10wt.% of the solids in the slurry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention processes a red rare earth oxysulfide phosphor slurry collected in a manufacturing process of a fluorescent film of a color picture tube to obtain a regenerated phosphor having characteristics equivalent to those of a new product. Regarding the method.

[0002]

2. Description of the Related Art For a phosphor screen of a color picture tube, green, blue, and red phosphors are mixed with polyvinyl alcohol and ammonium dichromate at a predetermined ratio to prepare a phosphor slurry. The phosphor slurry is applied to the entire surface of the face plate on which a black matrix has been formed in advance by carbon by a suitable application method such as spin coating.
Ultraviolet rays are radiated through a shadow mask, an aperture grill or the like to cure a predetermined portion, and then development with warm water is performed on the phosphors of three colors to form a phosphor screen of dots or stripes in a predetermined array.

The phosphor slurries recovered in this process include those that are shaken off from the face plate in the coating process and those that are washed off with the developing hot water in the developing process. The former can reach 70 to 80% or more of the coating amount, depending on the coating method. Among these recovered phosphor slurries, particularly expensive red phosphors containing rare earth elements need to be recovered and recycled.

However, the recovered phosphor slurry mainly contains the following three types of components as impurities. First,
Polyvinyl alcohol or chromate which is a constituent of the slurry is wrapped around a phosphor to be solidified and insolubilized. Second
Also, contaminants such as phosphors of other emission colors. The recovery slurry of the red phosphor contains a green light emitting phosphor and a blue light emitting phosphor as other light emitting color phosphors. Third, as metallic impurities, contaminants such as stainless fine powder from structures such as spin coaters and recovery machines.

If such a phosphor is reused as it is, the insoluble polyvinyl alcohol, which is the first impurity, may cause crushing of particles or pinholes in the fluorescent film, resulting in uniform fluorescence. It is difficult to form the surface. Further, because of the phosphor of the other emission color which is the second impurity, the phosphor of the other emission color is contained in the red pixel, which causes a light emission failure. When the method of dissolving and removing the other-color phosphor is used, if zinc ions, which are the parent ions of the other-color phosphor, remain in the phosphor slurry, the coating sensitivity is greatly affected, such as a change in coating sensitivity.

Further, since the red phosphor is applied last in the application process, the red slurry is applied on the existing green or blue pixel. Therefore, if copper or copper compound in the metallic impurities contained as the third impurities remains even in a very small amount, so-called copper spot defects occur on the phosphor screen. This means that a trace amount of copper or a copper compound is mixed in a part of the blue pixel to cause a color change from the original blue light emission to green light emission. Specifically, a green spot is generated in the blue pixel portion, which causes a defective color of the blue pixel.
In other words, if copper or a copper compound is mixed in the red phosphor coating slurry even in a very small amount, the color of the blue pixel is mixed with copper or the copper compound on the blue pixel already coated during the coating process. Cause defects. This green discoloration is caused by a slight amount of copper mixed in the blue phosphor ZnS: Ag and ZnS:
It is considered that this is because the composition changes to Cu or ZnS: Cu, Ag.

Various methods have been conventionally proposed as a method for regenerating the red-collected phosphor slurry for removing the above components.

For example, as a method for removing the residual polyvinyl alcohol which is the first impurity, Japanese Patent Publication No. 59-7
Japanese Patent No. 747 discloses a method in which an alkali is added to the phosphor slurry to raise the liquid temperature to 60 ° C. or higher.

As a method for dissolving and removing the residual polyvinyl alcohol and the second impurity phosphor of another color, Japanese Patent Publication No. 54-12270 discloses a phosphor slurry containing an oxidizing agent such as alkali peroxide. Japanese Patent Publication No. 54158/1979 discloses a method of adding an alkaline solution having a pH of 12 or more, for example, a dihalogenate such as sodium dichlorate (NaClO) to the recovered phosphor slurry. No. 5883, the phosphor slurry contains an alkali of 0.5 N or less and 1.0 to 10.0.
% Oxidant is added.

Further, as a method for removing copper or a copper compound which is the third impurity, Japanese Patent Laid-Open No. 3-217483
Japanese Patent Laid-Open Publication No. 2003-242242, a recovered phosphor slurry containing a chelating agent, an oxidizing agent,
And a method of treating in an aqueous solution containing an alkaline agent.

[0011]

However, any of the above-mentioned methods is a method of removing only one or two of the three kinds of impurities, and it is possible to completely remove all three kinds of impurities. Was not sufficient to obtain a good regenerated phosphor that was obtained for the first time.

The present invention solves the above-mentioned drawbacks, efficiently and almost completely removes the three main impurities contained in the recovered phosphor slurry, and regenerates a phosphor having good phosphor characteristics. It is an object of the present invention to provide a reproduction processing method in which the respective removal conditions are mutually considered.

[0013]

The present invention provides a method for regenerating a phosphor slurry recovered in a coating step, wherein at least the above-mentioned three types of impurities, namely polyvinyl alcohol, dichromates, phosphors of other colors, and It is a regeneration method for removing metallic impurities, and is characterized by comprising the following three steps.

The first step is mainly intended to remove the solidified and insolubilized polyvinyl alcohol which is the first impurity. However, depending on the processing conditions of this step, another color phosphor which is the second impurity removed in the next second step,
Further, the removal efficiency of the metallic impurities that are the third impurities removed in the third step has a great influence. Therefore, this first step is very important for efficiently and almost completely removing the three types of impurities.

The second step mainly aims to remove the phosphor of another color which is the second impurity oxidized in the first step. However, depending on the processing conditions of this step, the removal efficiency of the metallic impurities that are the third impurities removed in the next third step is affected.

In the third step, copper ions are generated from the metallic impurities, which are the third impurities which have been oxidized to a certain extent in the first and second steps and become highly soluble, and at the same time chelated by a chelating agent to be dissolved and removed. The main purpose is things. A chelating agent is a substance that catches and chelates metal ions in a solution even in an extremely small amount, and removes them. Therefore, the phosphor ions of the other color that have not been completely removed in the second step and are also chelated at the same time are almost completely removed.

These three steps are mutually related to the efficiency of removing impurities, and the condition for removing one or two kinds of impurities out of three kinds is to remove all three kinds of impurities. It is not a suitable condition to do. Therefore, in order to remove these three kinds of impurities efficiently and almost completely, it is necessary to determine the processing conditions of the first to third steps as one set.

The inventors of the present invention have proposed a conventional method for removing impurities of one type or two types, respectively.
Since it is not necessarily suitable for efficiently and almost completely removing all three types of impurities, the combination of the processing conditions of these first to third steps is considered to be particularly important, and as a result of numerous studies, The present invention has been completed by finding a method for efficiently and almost completely removing three kinds of impurities.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the first step, an oxidizing agent and an alkali are added to a recovered phosphor slurry and treated as hot water.
The oxidizer is 0.5 to the dry solid content in the slurry.
Add 5.0 wt% and use HClO and HB as oxidizers
Dihalogen acids and salts thereof such as rO, HIO, NaClO, HClO ₃ , HBrO ₃ , HIO ₃ , NaClO ₃ , K
Halogen-oxygen acids such as ClO ₃ and salts thereof, HClO ₄ ,
Examples thereof include halogen acids such as KClO ₄ , NaIO ₄ and salts thereof, and NaClO is particularly desirable. 0.01 to 0.1 N (0.125 wt% to 1.25 wt% based on the dry solid content) of alkali is added to the phosphor slurry, and NaOH, KOH, LiOH, NH ₄ O is used as the alkali.
At least one of H can be used. Also,
The regeneration treatment is preferably performed at 45 ° C. or higher.

Here, the alkali promotes the oxidizing action of the oxidizer and destroys the structure of the polyvinyl alcohol, so that the phosphors of other colors are oxidized and can be dissolved and removed in the next second step, and the metal is used. Used to oxidize certain impurities to some extent. Therefore, if it is 0.01 N or less, the oxidation effect is not sufficiently exerted, and the polyvinyl alcohol is not sufficiently removed,
The phosphors of other colors cannot be sufficiently oxidized, cannot be sufficiently removed in the next second step, and the oxidation of metallic impurities is insufficient.
On the other hand, if it is 0.1 N or more, the oxidizing effect is too strong, and the metallic impurities are remarkably oxidized and dissolved in the next second step, and at the same time become insoluble sulfides. Removal efficiency deteriorates. Further, the oxidation of the surface of the matrix red phosphor becomes remarkable, and the phosphor characteristics such as a decrease in brightness become insufficient.

The second step is a step in which the phosphor in the phosphor slurry treated in the first step is washed well with water, and further diluted with a strong acid to maintain the pH at 1.0 to 3.0. Examples of the acid include dilute sulfuric acid, dilute hydrochloric acid and dilute nitric acid, and dilute sulfuric acid is particularly desirable. First when the pH is over 3.0
The efficiency of ionizing and dissolving and removing the other color phosphor oxidized in the step is not preferable. On the other hand, if the pH is 1.0 or less, the surface of the phosphor is dissolved by an acid, which lowers the brightness and the coating properties, which is not preferable.

In the third step, the phosphor is sufficiently washed in the phosphor slurry treated in the second step, and then a chelating agent is added to treat the phosphor as warm water while keeping the pH at 5 or higher. At this time, an oxidizing agent may be added if necessary.

The amount of the chelating agent added is 0.00001 wt% to 10 wt% with respect to the dry solid content in the slurry, and is changed depending on the content of copper or copper compound in the recovered phosphor slurry. As chelating agents, ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (ID
A), nitrilotriacetic acid (NTA), tetraethylenepentamine (TEPA) and the like can be mentioned, with tetraethylenepentamine being particularly desirable. Here, it is desirable to add the chelating agent in an amount capable of chelating several times to several thousand times the expected copper ion content. It is preferably used in the range of 0.01 wt% to 0.1 wt% with respect to the ordinary recovered phosphor slurry.

The pH of the phosphor slurry is adjusted to 5 or more, but there is no particular limitation as the pH adjusting agent. When the pH is less than 5, the ability of the above chelating agent to chelate copper ions, zinc ions and the like is drastically reduced. It is desirable to treat at a pH of 10 or higher. Then, the treatment is preferably performed at 30 ° C. or higher.

It is desirable to add an oxidizing agent, but
Condition is 2.0 wt% with respect to the dry solid content in the slurry
It is added as follows, and as the oxidizer, it was added in the first step.
The listed oxidizing agents HClO, HBrO, HIO, Na
Dihalogen acids such as ClO and its salts, HClO_Three, H
BrO_Three, HIO_Three, NaClO_Three, KClO_Three, Etc. halo
Gen-oxygen acid and its salt, HClO_Four, KClO_Four, NaI
O_Four, Halogen acids and their salts, and H_TwoO_Two, Na_Two
O_Two, K_TwoO_TwoAnd peroxides such as H _TwoO_TwoHope
Good. Here, if the oxidizing agent is 2.0 wt% or more, the phosphor mother
Body slightly oxidized and dissolved, producing yttrium ions
The chelating agent also kills yttrium ions
To reduce the efficiency of chelating copper ions
Is not preferred. Preferably less than 0.1 wt%
It is good to use in the range.

[0026]

【Example】

(Example 1) First, as a first step, the recovered phosphor slurry (500 g in dry weight) was placed in a 3 liter beaker, 1500 ml of pure water was added, and the mixture was heated in a water bath with good stirring to 65 ° C. 10% N while holding
24 ml (0.04 N) of aqueous aOH solution and 10 parts of NaClO
After adding 0 ml (12.5% of available chlorine, 2.5 wt% as the amount of chlorine to the dry solid content) and stirring for 2 hours, the phosphor was allowed to settle well and the supernatant was discharged.

Next, in the second step, pure water was introduced into the above beaker, decantation was repeated 3 times to wash the phosphor well, and 1500 ml of pure water was introduced to adjust the pH to 2. After stirring for 1 hour while maintaining at 5, the phosphor was allowed to settle well and the supernatant was discharged.

Finally, in the third step, pure water was introduced into the above beaker and decantation was repeated 3 times to thoroughly wash the phosphor, then 1000 ml of pure water was introduced and heated in a water bath. , 10% while maintaining at 55 ℃
After adjusting the pH to 11 with an aqueous NaOH solution, tetraethylenepentamine (TEPA) as a chelating agent was added to 3.
25 g was added and stirred for 3 hours. After that, the phosphor is allowed to settle well, the supernatant is discharged, pure water is introduced into the beaker and stirred, and the decantation is repeated 4 times to thoroughly wash the phosphor, and then the phosphor is dehydrated and filtered. did.

Table 1 shows the powder characteristics and coating characteristics of the regenerated phosphor thus obtained. As is clear from Table 1, the phosphor obtained here had the same characteristics as the new phosphor, and was a good phosphor from which the impurities in the recovered phosphor slurry were removed.

In Table 1, the coating characteristics (∘) of the coating characteristics indicate that they have the same characteristics as the new phosphor, and (x) indicates the unusable level. The relative luminance is a value obtained by drying the obtained regenerated fluorescent substance and setting the luminance of a new product as 100%. Further, the Zn content rate and the Cu content rate are
The obtained regenerated phosphor was completely dissolved in hot nitric acid and chemically analyzed.

(Comparative Example 1) -No third step The characteristics of the regenerated phosphor obtained by performing the first step and the second step in the same manner as in Example 1 and omitting the third step are shown in Table 1. As can be seen from Table 1, this phosphor had a high Cu content and was a poor phosphor.

(Comparative Example 2) -No second step Table 1 shows the characteristics of the regenerated phosphor obtained by performing the first step and the third step in the same manner as in Example 1 and omitting the second step. As can be seen from Table 1, this phosphor had a high Zn content and a high Cu content, and was a poor phosphor.

(Example 2) -Third step Addition of oxidizing agent Regenerated fluorescence obtained by the same process as in Example 1 except that 12 ml of 35% H ₂ O ₂ was added as an oxidizing agent in the third step. The body characteristics are shown in Table 1. As can be seen from Table 1, this phosphor had a very low Cu content and was a good regenerated phosphor.

(Comparative Example 3) -First step Highly concentrated alkali Characteristics of regenerated phosphor obtained by the same treatment as in Example 1 except that 120 ml (0.2 N) of 10% NaOH was used in the first step. Is shown in Table 1. As can be seen from Table 1, this phosphor was a poor regenerated phosphor because of its insufficient relative brightness and high Cu content.

(Comparative Example 4) -Second Step High pH The characteristics of the regenerated phosphor obtained by the same treatment as in Example 1 except that the pH of the slurry was adjusted to 4.0 in the second step are shown in Table 1.
Shown in As can be seen from Table 1, this phosphor had a high Zn content and a high Cu content and was a defective regenerated phosphor.

[0036]

[Table 1]

[0037]

As described above, according to the method of the present invention, the phosphor recovered by treating the first step with an alkaline solution having an appropriate oxidizing power using an oxidizing agent At the same time as decomposing and removing the solidified / insolubilized chromate and polyvinyl alcohol contained in the slurry, it also serves as a pretreatment to oxidize other color phosphors and dissolve and remove them in the next second step, and also to some extent metallic impurities. Oxidation can promote the removal by copper ionization and chelation in the third step.

Next, by treating with a dilute strong acid in the second step, it is possible to dissolve and ionize and remove the other color phosphor oxidized in the first step, and to remove metallic impurities as follows. Ionization can be promoted in the third step.

Finally, in the third step, the pH is adjusted by using a chelating agent to chelate and remove the ionized copper ions, and at the same time, the zinc ions, which are the host of the other color phosphor remaining in the solution, are removed. Can be chelated at the same time and removed almost completely. At this time, if necessary, if an oxidizing agent having an extremely weaker oxidizing power than that of the first step is used, the removal efficiency is further improved.

Claims (4)

[Claims] 1. A method of regenerating a red rare earth oxysulfide recovery phosphor slurry, comprising: a) 0.5 wt% to 5.0 wt% of an oxidizing agent in the recovered phosphor slurry with respect to a dry solid content in the slurry. And a first step of adding an alkali in the range of 0.01 N to 0.1 N to the slurry solution and treating it in warm water, b) washing the phosphor slurry with water and then adjusting the pH to 1.0 to
Second step of treating while maintaining at 3.0, c) After washing the phosphor slurry with water, a chelating agent is added in the range of 0.00001 wt% to 10 wt% with respect to the dry solid content in the slurry to adjust the pH to 5 A method characterized in that the respective steps of the above-mentioned third step of treating in warm water are performed in this order. 2. The oxidizing agent used in the first step is H
ClO, HBrO, HIO, NaClO and other dihalogen acids and salts thereof, HClO ₃ , HBrO ₃ , HIO ₃ , N
at least one selected from the group consisting of halogen oxygen acids such as aClO ₃ and KClO ₃ and salts thereof, and halogen acids such as HClO ₄ , KClO ₄ , NaIO ₄ and salts thereof, and the like;
The method of claim 1 which is a seed. 3. The method according to claim 1, wherein an oxidizing agent is added in the third step. 4. The oxidizing agent is HClO, HBrO, H
Dihalogen acids such as IO and NaClO and their salts, HC
lO ₃ , HBrO ₃ , HIO ₃ , NaClO ₃ , KCl
Halogen-oxygen acid such as O ₃ and its salt, HClO ₄ , KC
4. At least one selected from the group consisting of halogen acids such as 10 ₄ , NaIO ₄ and the like and salts thereof, and peroxides such as H ₂ O ₂ , Na ₂ O ₂ and K ₂ O _2. The method described.