KR19990087342A - Sealed glass suspension - Google Patents

Abstract

The present invention relates to a sealing glass material comprising a glass frit and a medium, wherein the medium is an aqueous solution of a cellulosic polymer and a method for producing the sealing glass material.

Description

Sealed glass suspension

The present invention relates in part to a sealing glass material free of volatile organic compounds and comprising an aqueous solution of a cellulosic polymer and a sealing glass frit.

The present invention relates to a fused glass seal which is a fired product of the seal glass material.

The present invention relates to a suspension of sealing glass frit in a medium free of volatile organic compounds.

Glass that melts at relatively low temperatures has long been used to bond metal, glass and ceramic components by fusion sealing. Initially, the seal has the properties of glass. Lead glasses, in particular lead zinc borate, have been commonly used.

The sealing technique has been developed by the discovery that the glass can be crystallized in a controlled manner by heat treatment. This combined with the efficacy of low temperature molten glass with strong sealing in the crystalline state.

More recently, non-lead glass consisting essentially of tin, zinc and phosphorous oxides has been proposed as an alternative to conventional lead zinc borate glass. U.S. Patent 5,246,890 (Aitken et al.) Discloses an example of such phosphate glass.

In forming a seal with the sealing glass, it was customary to use the glass in the form of particles known as glass frits. The glass frit is mixed with the medium and the binder to form a suspension or paste. The mixture is applied to the sealing surface, for example by extrusion.

Many organic vehicles and binders have been proposed. The combination of nitrocellulose and amyl acetate is commonly used for the manufacture of commercial cathode ray tubes.

Many organic vehicles and binders have been proposed. The combination of nitrocellulose and amyl acetate is commonly used for the manufacture of commercial cathode ray tubes.

Recently, environmental attention has been drawn to the desirability of avoiding the use of volatile organic compounds (VOCs) as much as possible. The areas of dominant interest are sealing glass pastes used in a variety of applications as LCD panels, cathode ray tubes and contrast products.

It is an object of the present invention to provide a sealed glass suspension which avoids the use of volatile glass compounds while satisfying current process descriptions for paste dispersion, seal strength, electrical properties and hermeticity in seals. It is another object of the present invention to provide such suspensions with soft consistency. It is another object of the present invention to provide a sealing glass material having rheological properties that provides good flowability and easy dispersion. Still another object of the present invention is to provide a sealing glass material having acceptable electrical properties when fired to form a seal.

In view of the present invention, it is essential to distinguish between volatile and non-volatile organic compounds. The former evaporates characteristically at or near room temperature and enters the air in gaseous, organic form.

The latter acceptable does not evaporate in the glass form. Rather, the only evaporated material is water.

The figures in the accompanying drawings are representative graphs illustrating the properties of the materials of the present invention.

The present invention begins with an effort to eliminate the need for volatile organics in the manufacture of fusion seal materials. It has been found that some substitutes are necessarily compatible with the glass frit currently available. In addition, it will be necessary to maintain significant rheological properties to enable the application of such materials with the methods and apparatus of the present invention.

It has been found that the desired object can be achieved with a water soluble, cellulosic binder using water or methanol as solvent. Although any soluble cellulosic binder could be used, we worked with a side chain functional type filled with Alpha Metals (AMV). The material contains about 1.25% polymer solids dispersed in water as a solvent.

Sealing pastes are readily prepared by adding low melt glass frit to the water soluble cellulose medium. The term "low melting" glass frit means in this field a medium-temperature sealed glass that softens to form a seal therewith at a sealing temperature of about 400-450 ° C. and to wet the sealing surface. The glass has a softening point of 400-450 ° C.

Commercial applications have generally been developed from lead borosilicate glasses containing zinc oxide. The glass may consist essentially of 70-80% PbO, 10-14% ZnO, 6-12% B ₂ O ₃ , 0-3% SiO ₂ and 0-3% BaO. Conventional glass is marketed by Corning Incorporated, Code 7590 having a composition consisting of about 75% PbO, 12% ZnO, 9% B ₂ O ₃ , 2% SiO ₂ and 2% BaO. to be.

Recently, lead-free glass has been proposed. For example, SnO-ZnO-P ₂ O ₅ glass groups are disclosed in the aforementioned patents of Aitken et al. These glasses are lead-free and have a composition containing 25-50 mole percent P ₂ O ₅ with SnO and ZnO such that the molar ratio of SnO: ZnO is 1: 1 to 5: 1. They can contain up to 20 mole percent of modified oxides comprising up to 5 mole percent SiO ₂ , up to 20 mole percent B ₂ O ₃ , up to 5 mole percent alkaline earth metal oxides, and up to 5 mole percent Al ₂ O ₃ And may further contain a seal adhesion promoter selected from up to 5 mol% WO ₃ , up to 5 mol% MoO ₃ , up to 0.10 mol% Ag metal and mixtures and 1-15 mol% R ₂ O and 1 To 5 mole% of zircon and / or zirconia.

The present invention has been developed for the use of lead borosilicate glass. However, this also indicates that it is effective to use lead-free glass, as described in Aitken et al.

Pastes can be readily prepared by adding the medium to the glass frit. The frit can be dispersed in the medium by mixing with a Hobart shaker, although a high speed mixer can be used to form a softer paste. The ratio of glass frit to mediator was 6: 1 to 10: 1 with the resulting soft paste after mixing.

As a result, it is necessary to take into account the rheological properties necessary to disperse the paste onto the sealing surface. In order to disperse on a narrow surface, such as the edge of a CRT panel, this is a common particle for injection molding the paste through a small opening. It may be compressed through a hole, syringe or automatic disperser.

The rheological properties of the paste, ie the viscosity or flow properties for dispersing the object, are measured using a Rheometrics Dynamic Analyzer. This is a parallel plate mechanism in which one of the plates vibrates. A sample of material is placed between the plates and the viscosity is measured as the rate of vibration increases.

The single view in the accompanying drawings is a graph showing the viscosity measurements measured on the dynamic analyzer. Viscosity is shown in logs on the longitudinal axis and vibration frequency is shown in units of radians / second (rad / s) on the horizontal axis.

Curve A shows the flowability of a paste prepared by mixing 6 parts by weight of Code 7590 glass with the 1 part by weight of cellulosic medium received. This decreases when shear stress is applied, resulting in a thinner, more flowable paste. Similar measurements were made on current commercially available pastes in which the glass frit is dispersed in a medium of nitrocellulose dissolved in amyl acetate. The curve is substantially lower than curve A, resulting in different viscous properties. It is clear that the material of curve A cannot be prepared properly using the particles currently used in commercial materials.

This creates the need to modify the paste in some manner suitable for embodiments of the present invention. Initially, attempts were made to dilute the paste by further addition of the medium. The addition of these mediators showed no significant effect. A flow curve consistent with that shown in curve A was obtained on the modified material. They did not show any significant change.

As a further study, the desired downward of the flow curve of the paste of curve A can be achieved. Surprisingly, this is accomplished by prediluting the medium with a solvent such as methanol or water. Effectively, this reduces the proportion of polymer solids in the medium by one hundredth. It was found that doubling the amount of solvent, reducing the polymer solids to about 0.6% mediator, produced a paste with fluidity similar to the paste of the present invention.

Curve C is based on measurements on paste prepared using media diluted with water. The amount of solvent in the medium was doubled such that the medium contained 0.6% solids in the form of cellulose polymer. The paste prepared using the diluted medium consisted of 1 part by weight of the diluted medium and 6 parts by weight of Code 7590 glass frit. The corresponding mixture in which the medium was diluted with methanol rather than water is similar to curve C, but gives a slightly higher shaped curve. Curve D is based on a paste containing 10 parts by weight of glass frit in 1 part by weight of medium. In this case, the mediator is diluted with methanol to provide 0.6% polymer solids in the mediator.

Another consideration in making a fusion seal is the color of the fired seal. Dark color indicates the possibility of reduced lead. As a result, yellow or orange is preferred and can be used as qualitative process control.

When the paste with a 6: 1 frit-mediated ratio was calcined, the color of the seal was brownish olive. Electrical test methods showed acceptable properties. Nevertheless, it is necessary to alleviate the fear by improving the seal color.

The higher frit-mediated ratio was found to result in improved color. In addition, various oxidants may be added in a minimum amount sufficient to enhance color. Such oxidizing agents include peroxides, persulfates and sulfates. Preferably we used potassium persulphate.

It has been found that the flowability of the paste can be further adjusted by the addition of a gelling agent to the medium before adding the glass frit. In particular, this is still sparse at very low viscosities at higher shear stresses, while the material is deformed to have a higher viscosity at low shear stresses. This is highly desirable since it allows for easy preparation of the paste after it has been deposited on the sealing surface, allowing it to quickly set so that the material does not flow or fall off. As a result, the fluidity of the paste of the present invention can be made to be very consistent with the embodiment of the present invention.

Materials containing clay gelling agents were prepared in the following manner. 100 g of medium was diluted with 100 g of water. Thereafter, 7.7 g of clay-type rheology modifier was added to the diluted medium. The modifier is commercially available as Bentone LT from Rheox, Inc. The mixture was then heated at 38 ° C. and mixed with a high-speed disperser for about 90 minutes to produce a uniform pregel blend.

The seal paste was then prepared by adding 14.28 g of the pregel to 36.26 g of diluted medium. It was stirred rapidly for about 20 minutes. Thereafter, 500 g of Code 7590 frit was added in a small amount to the mixture. Following the addition of the frit, the mixture was stirred to a creamy concentration prior to being used for the sealing object.

A series of tests was conducted to determine the effect of the invention with lead-free, SnO-ZnO-P ₂ O ₅ glass frit. In molar units, a glass having a composition of 31.5% P ₂ O ₅ , 1.5% B ₂ O ₃ , 14.6% ZnO, 51.2% SnO and 0.7% Al ₂ O ₃ and 0.5% WO ₃ was selected. . Four blends of 74 g glass frit, 6 g alumina and 20 g zircon each were prepared. Two batches were mixed with acceptable cellulose media to form the paste. The frit: mediator was 4.8: 1 in one mixture and 6.7: 1 in the other mixture. The other two blends were each mixed with a medium diluted 1: 1 with water to form a paste. In each of the pastes, the frit: median ratio was 4.8: 1.

The flowability characteristics of the resulting four pastes were analyzed as described above using a rheometryless dynamic analyzer. The two pastes containing the medium produced a viscosity curve comparable to that shown by curve A in the figure. The other two pastes made with the diluted medium produced a viscosity curve comparable to that shown in curves C and D in the figure. This indicates that the advantages of the present invention can be obtained with both conventional lead-borate frits and novel lead-free frits.

Claims (16)

Sealing glass frit and a medium, the medium being an aqueous solution of a cellulosic polymer. The sealing glass material of claim 1, wherein the glass frit is lead borosilicate. The glass frit of claim 1, wherein the glass frit is in weight percent based on oxide, 70-80% PbO, 10-14% ZnO, 6-12% B ₂ O ₃ , 0-3% SiO ₂ and 0 Sealed glass material, characterized in that consisting essentially of -3% BaO. The sealing glass material of claim 3, wherein the glass frit consists essentially of 75% PbO, 12% ZnO, 9% B ₂ O ₃ , 2% SiO _2, and 2% BaO. The sealed glass material of claim 1, wherein the glass frit is a lead-free material and is SnO-ZnO-P ₂ O ₅ glass. The method of claim 5, wherein the glass frit essentially consists of 25-50 mol% P ₂ O ₅ and SnO and ZnO, and the molar ratio of SnO: ZnO is 1: 1 to 5: 1. Glass material. The sealing glass material of claim 1, wherein the material comprises the glass frit and the medium in a weight ratio of 5: 1 to 10: 1. The sealed glass material of claim 1, wherein the cellulose polymer solids content in the media is 1% or less. 9. The sealed glass material of claim 8, wherein the solids content in the media is about 0.6%. The sealing glass material of claim 1, wherein the material further comprises a gelling agent. 11. The sealed glass material of claim 10, wherein the gelling agent is clay. Preparing a water soluble cellulosic polymer solution having a solids content of cellulosic polymer of 1% or less, and the medium in an amount of frit-to-mediated ratio of at least 6: 1 and not exceeding 12: 1 A method of making the sealing glass material of claim 1, comprising adding the sealing glass frit to a. 13. The process of claim 12 wherein the aqueous solution of cellulose polymer containing about 1.2% solids is diluted with water or methanol to a solids content of 1% or less. The method of claim 13 wherein the solids content is halved by dilution with water or methanol. The method of claim 13, wherein a gelling agent is added to a portion of the diluted medium, the clay is dispersed in the medium, pregel is added to the medium by mixing, and the glass frit is added to the mixture of pregel and medium. The method characterized in that the addition. The method of claim 15 wherein the gelling agent is clay.