JPH08269363A - Coating material for interior finishing of cathode ray tube - Google Patents

Abstract

PURPOSE: To obtain an inexpensive coating material for interior finishing of a cathode ray tube by suspending and dispersing metal oxide particles, etc., coated with silica and alumina containing a specific amount of alumina into a water medium containing a dispersant and water glass, excellent in dispersion stability at a high temperature and long-term shelf stability. CONSTITUTION: Metal oxide particles such as titanium dioxide, iron oxide, etc., coated with silica and alumina having 20-60wt.%, preferably 30-50wt.% alumina content and graphite particles (preferably 0.05-0.1μm particle diameter) are suspended and dispersed into a water medium containing a dispersant and water glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating material for a cathode ray tube which contains water glass in a medium and in which metal oxide particles and graphite particles are dispersed.

[0002]

2. Description of the Related Art A conductive coating is applied to the inner surface of a funnel glass of a cathode ray tube. This conductive film is formed by applying a coating material containing conductive particles to the inner surface of the funnel portion, then drying and heating in air.

This paint is represented by graphite particles of a conductive material and iron oxide, titanium oxide, or silicon carbide for adjusting to an arbitrary electric resistance value in an aqueous medium containing water glass as an adhesive and a dispersant. The particles of the metal oxide or metal carbide to be used are suspended and dispersed. In addition to this, there is a paint in which only graphite particles of a conductive material are suspended and dispersed depending on the specifications of the CRT to be applied, but the spark current becomes relatively high as described in JP-B-63-45428. Therefore, it is common to use particles of graphite and metal oxides in combination. That is, graphite imparts conductivity and lowers the electric resistance value of the coating film, while metal oxides and the like function as fillers, while having the action of increasing the resistance value of the coating film like water glass as an adhesive. Therefore, the electrical resistance value and the adhesive strength of the coating film are controlled to predetermined values by adjusting the blending ratio of these.

Thus, it is very important for the interior paint of the cathode ray tube to disperse the metal oxide particles in the water-based paint and, in addition, to continue the dispersion to prolong the pot life of the paint. Is. Regarding the improvement of the dispersion stability of the components contained in the coating material for the interior of the cathode ray tube and the extension of the pot life, the applicant of the present invention has made various studies.
For example, the above-mentioned publication describes the following findings. This is because a composite powder having a negative charge as a whole is first prepared by granulating fine particles of graphite and a metal oxide using a surface treatment agent having a negative charge, and then the composite powder is mixed with a binder and a dispersion agent. It is made into a paint by suspending it in water containing the agent.

[0005]

In the work process of applying the paint to the inner surface of the cathode ray tube, the spray coating method and the brush coating method have been widely used in the past, but in recent years, the flow coating method has been used in order to improve the production technology. The so-called flow coating method is mainly used. For this reason, it is required that the applied paint has a low paint viscosity. That is, the viscosity of the coating material by the conventional coating method was 100 to 200 mPa · s, whereas the viscosity of the coating material for flow coating was 10 mPa · s.
・ Low as s. As a result, it becomes clear from the Stokes' equation which expresses the natural sedimentation state of the particles in the liquid that it becomes difficult to maintain the dispersion of the metal oxide particles in the paint.
Further, considering the effect on the storage environment, the above-mentioned conventional techniques are unsatisfactory, and further improvement in dispersibility is required.

Therefore, in view of the above background, an object of the present invention is to provide a coating composition containing water glass in which metal oxide particles and graphite particles are dispersed, which is excellent in dispersion stability particularly at high temperature and can be stored for a long time. The object is to provide a coating material that enables it and is easy to handle. Other purposes will be clarified in the following description.

[0007]

The above object, which is an essential part of the present invention, is to form silica particles in an aqueous medium containing a dispersant and water glass.
A paint for coating the inner surface of a cathode ray tube in which metal oxide particles and graphite particles coated with alumina are suspended and dispersed, wherein the content of alumina in the silica-alumina coating is 2
It is to adjust to 0 to 60% by weight.

[0008]

[Function] In order to suspend and disperse metal oxide particles such as titanium oxide and iron oxide in an aqueous medium, it is effective to apply silica coating, alumina coating, or silica-alumina coating to the surface of the metal oxide particles. It is well known that (for example, "Titanium oxide-Physical properties and applied technology" Seino
Gakuji, pages 29-30). As also described here, silica in the coating contributes to hydrophilicity, and alumina imparts lipophilicity and improved weather resistance. Besides this,
For example, in Japanese Unexamined Patent Publication No. 53-33228, when titanium dioxide is used in a coating composition, a titanium dioxide pigment obtained by continuously coating high-density, amorphous silica on titanium dioxide and further depositing alumina on the surface thereof is used. It is described that the properties and the color retention of the coating film are improved. Although this prior art specifies the treatment method of titanium dioxide pigment,
It does not specify the properties of paints made with an alkaline medium containing water glass in the medium or the specific application of the paint.

The present invention relates to a metal oxide particle such as titanium oxide or iron oxide coated with silica / alumina in an aqueous solution containing an alkali silicate anion, particularly an aqueous solution containing silicate anion, that is, an aqueous medium containing water glass, and graphite. In a coating material for a cathode ray tube in which particles are suspended and dispersed, the content of alumina in the silica-alumina coating is 20 to 6
It is 0% by weight. In this case, the alumina content is more preferably 30 to 50% by weight. Alumina has the effect of suppressing the dissolution of silica, but if its content exceeds 60% by weight, the water containing water glass is suspended in the same manner as when suspended in an alkaline aqueous solution such as KOH aqueous solution or NaOH aqueous solution. Even in the medium, particles aggregate and settle due to the low surface charge of alumina.

On the contrary, when the alumina content in the silica-alumina coating is less than 20% by weight, in other words, when the silica content is 80% by weight or more, agglomeration and sedimentation of particles due to the binding of the silica-alumina coating occur. This is because the solubility of silica in water glass is much higher than that of alumina, and is a phenomenon that occurs when the paint is left for a long time or when the storage environment changes in temperature.

That is, when the silica content in the silica-alumina coating is high, the silica component in the coating is dissolved as silicate in water glass, and the ion micelle concentration of the silicate in the aqueous solution is locally increased. In this way, the aqueous solution having an increased ionic micelle concentration is unstable in terms of concentration equilibrium, and is deposited as silica on the surface of particles existing in the liquid. When this phenomenon continues, binding between dispersed particles easily occurs, as described above, particles agglomerate and settle, the dispersion stability of the coating, which is the object of the present invention, and the extension of the pot life can be achieved. It is thought to disappear.

[0012]

EXAMPLES The present invention will now be described in more detail by way of examples. (Preparation of paint) Particle size of 0.05 to 0.1 μm as conductive material
Graphite particles crushed to some extent, eight types of titanium oxide particles (T1 to T8) and seven types of iron oxide particles (F1 to F1 shown in Table 1
F7) was used as dispersed particles, carboxymethyl cellulose (Carboxy Methyl Cellulose, hereinafter abbreviated as CMC) as a dispersant, potassium silicate as a binder, and water as a medium were prepared as coating materials. These materials were added at the following mixing ratios and sufficiently stirred using a stirrer to prepare each suspension. Graphite particles 3.0 parts by weight Metal oxide particles 18.0 parts by weight CMC 0.3 parts by weight Potassium silicate 8.7 parts by weight Water 70.0 parts by weight

Then, these suspensions were dispersed in a ball mill to obtain a coating material for the interior of the cathode ray tube. In addition, Japanese Patent Publication No. 63-4542 previously invented by the applicant.
Those using the composite conductive particles described in Japanese Patent No. 8 were also prepared and compared at the same time.

(Evaluation of coating material) When the coating material is left at a high temperature, the dispersion state of the dispersed particles changes, and the viscosity decreases as the coating temperature rises, and the dispersed particles tend to settle. Therefore, dispersion stability at high temperature is an important issue from the viewpoint of maintaining the pot life of the paint for a long period of time without being affected by the environment. Therefore, for this examination and evaluation, each paint produced was allowed to stand for 3 weeks at 50 ° C. and the sedimentation state of the dispersed particles contained therein was investigated. Specifically, the paint was poured into a 100 ml screw tube, sealed tightly, and allowed to stand for 3 weeks in a constant temperature bath kept at 50 ° C. After standing, the sedimentation rate from the thickness (or height) of the sediment in the tube and the height of the poured paint, sedimentation rate (%) = (thickness (or height) of the sediment in the tube)
÷ Height of paint in tube) x 100. Then, in this study, it was judged that the paint with less sediment had better dispersibility at high temperature. The results are shown in Table 1.

Further, the evaluation for the homogenizing treatment required for the water-based coating material for the interior of the cathode ray tube will be described. As described in the section of the problem to be solved by the invention, in recent cathode ray tube manufacturing processes, a flow coating method is mainly used as a coating method of a paint for forming an interior coating. In this flow coating method, the conductive paint that has flowed out excessively is recovered and flow coated again. Therefore, a part of the paint is circulated several times and is subjected to a homogenization (stirring) process in the tank of the paint pool. However, if this stirring treatment is received for a long time, the coating on the surface of the metal oxide is destroyed, the electric charge on the surface of the metal oxide is changed, and aggregation due to electric attraction occurs. As an experimental examination of this phenomenon, the paint was treated with a stirrer rotating at a speed of 400 rpm for 6 hours, after which the paint was gently poured into a screw tube and the sedimentation state was observed when left for 10 minutes.
The state of sedimentation was calculated from the sedimentation rate (%) = (thickness (or height) of sediment in the pipe / height of paint in the pipe) × 100, as in the case of standing at high temperature.

[0016]

[Table 1]

In Table 1, the amount of alumina in the coating (%)
Indicates Al2O3 / (Al2O3 + SiO2). The sedimentation rate (%) of 50 ° C. indicates the thickness of the precipitate / height of the entire coating after standing at 50 ° C. for 3 weeks. The sedimentation rate (%) agitation indicates the thickness of the precipitate / height of the total paint when the mixture is agitated for 6 hours under the condition of an agitator-400 rotations / minute and left standing for 10 minutes. The composite conductive particles are the composite conductive particles described in JP-B-63-45428. The remarks are classified into examples and comparative examples according to the evaluation results.

The test results are shown in Table 1. First,
As shown in Table 1, when the sedimentation rate was 50 ° C. after 3 weeks, the difference in the sedimentation rate was remarkable when the alumina content was in the range of 20 to 60% by weight, and the difference in the sedimentation rate was remarkable. The paints of Examples 1 to 9 above are much better than others in dispersion stability at high temperatures. In addition, the sedimentation rate after agitation treatment for 6 hours and standing for 10 minutes had a tendency similar to that described above. That is, in the case of titanium oxide, the alumina content in the silica-alumina coating was less than 20% by weight (Comparative Example 1) and 86% by weight (Comparative Example 2), and iron oxide was less than 20% by weight ( Comparative Example 5) and those exceeding 63% by weight (Comparative Example 6), uncoated titanium oxide (Comparative Example 3) and iron oxide (Comparative Example 7), and composite conductive particles described in JP-B-63-45428. The coating material of (Comparative Example 4) has a large amount of sedimentation, and Examples 1 to 5 (titanium oxide; T2, T3, T4, which are within the range)
T5, T6 paints) and Examples 6-9 (iron oxide; F2, F
3, F4, F5 paints) have a small amount of sedimentation. Particularly, when the alumina content is about 30 to 50% by weight, the dispersion stability becomes the best. And
The difference in sedimentation rate is remarkable between the two, and it can be seen from Table 1 that the paints of Examples 1 to 9 are also very excellent in terms of the homogenization treatment required for paints for interiors of cathode ray tubes.

As described above, in the coating containing water glass in which the metal oxide particles and the graphite particles are dispersed, silica.
It has been found that useful results can be obtained simply by adjusting the alumina content in the alumina coating to a specified range. For this reason, the coating composition of the present invention can maintain a stable dispersed state under a temperature environment or an environment such as a homogenizing treatment for a long time.

[0020]

As described above, the coating material for the interior of a cathode ray tube according to the present invention is not easily affected by the storage environment, can be stored for a long period of time, and can be supplied as a coating material which is easy to handle. . In addition, since the coating material of the present invention does not require the spray-drying step for producing the composite conductive particles, which is the technology owned by the present applicant, the coating material can be supplied at a low cost.

Claims (1)

[Claims] 1. A paint for coating the inner surface of a cathode ray tube in which silica-alumina-coated metal oxide particles and graphite particles are suspended and dispersed in an aqueous medium containing a dispersant and water glass, A coating material for an interior of a cathode ray tube, wherein the content of alumina in the silica-alumina coating is 20 to 60% by weight.