EP0828693A1

EP0828693A1 - Sealing glass modifier for use with voc-free or low-voc vehicle

Info

Publication number: EP0828693A1
Application number: EP97917762A
Authority: EP
Inventors: Joseph Peer
Original assignee: Techneglas LLC
Current assignee: Techneglas LLC
Priority date: 1996-04-02
Filing date: 1997-04-01
Publication date: 1998-03-18
Also published as: JPH11507005A; MX9709381A; WO1997036836A1; KR19990022312A; EP0828693A4

Abstract

A sealing glass modifier that decreases the chemical reduction of PbO in a PbO-containing sealing glass to metallic lead during sealing or firing, and enables the sealing glass to be used in combination with a VOC-free or low-VOC vehicle. The modifier preferably comprises an inorganic nitrate that is thermally stable at the temperatures at which the sealing glass frit seals the glass surfaces together, but that can be reduced to a lower oxidation state when exposed to the reducing conditions. The modifier is added to the sealing glass system in an amount sufficient to prevent the PbO from being chemically reduced when the sealing glass is fired in the presence of reducing conditions at a temperature sufficient to seal the glass. Particularly preferred modifiers are Bi(NO3)3.5H2O and/or Zn(NO3)2.6H2O. The modifier may be incorporated as a component of the sealing glass. Alternatively, the modifier may be dissolved or dispersed in the vehicle.

Description

SEALING GLASS MODIFIER FOR USE WITH VOC-FREE OR LOW- VOC VEHICLE

BACKGROUND AND OBJECTS OF THE INVENTION

The present invention is concerned generally with sealing glass compositions, in

powdered form or admixed with a vehicle to form a sealing glass paste, for sealing glass

components such as television picture tubes. The invention renders a PbO-containing

sealing glass suitable for use in combination with a vehicle that includes much lower

levels of volatile organic compounds ("VOC") than conventional vehicles. The sealing

glass modifier of the present invention therefore allows the sealing process to be carried

our with low or no VOC emissions when the vehicle is volatilized during the sealing

process.

PbO-containing sealing glasses, and particularly PbO/B₂O₃/ZnO sealing glasses,

are commonly used commercially to seal the glass face plate to the glass funnel of a

cathode ray tube, such as a color television picture tube. Such sealing glasses have the

property of melting and flowing at low temperatures, i.e., usually below 500° C. and most

frequently between 440° C. and 475° C, which facilitates the wetting of the glass surfaces

to be sealed. These sealing glasses (sometimes referred to as "solder" glasses) are

customarily thermally devitrifiable or thermally crystallizable in nature. The devitrified or

crystallized glass has a melting point temperature that is higher than the fiber softening

point temperature of the original sealing glass. Seals produced using these sealing glasses

must have a suitable combination of properties to perform satisfactorily in television picture tubes and the like. These properties include appropriate thermal expansion

characteristics to avoid damage to the tube components, good flow to produce proper fillet

shape, good wetting to provide strong adhesive characteristics to the glass parts being

sealed, and good crystallization properties to allow formation of a strong crystallized seal

within a reasonable thermal soak time. The seals also must have good dielectric

characteristics to prevent failure of the tube when it is exposed to high voltages during

use.

Before the face plate and funnel are sealed together, each undergoes a number of

processing steps. These steps include the separate and successive application to the face

plate of green, blue and red phosphors by known techniques, with the phosphors being

present as a multiplicity of individual dots or stripes in an ordered arrangement on the

inner surface of the face plate. In some instances, a carbon or graphite background may

be applied to the inner surface of the face plate surrounding the phosphors and providing a

sharp contrast to the phosphors. A resinous or plastic film may be applied to the surface

of the phosphors, and the inner surface of the face plate is subsequently aluminized, i.e., a

thin aluminum film is deposited, so that an electrically conductive surface is formed. This

aluminized surface is connected to a metal stud on the inner surface of the face plate.

A number of different organic compounds usually are applied to the inner surface

of the face plate during the course of phosphor application and aluminization. As

described further below, these compounds must be subsequently volatilized or otherwise

removed from the face plate or face panel to decrease the natural tendency of the PbO

constituent in the sealing glass to be reduced to metallic lead during firing of the glass

seal. Such removal is accomplished by known take out or bake out processes.

SUBSTITUTE SHEET {RULE 26) After the preparatory face plate and funnel processing steps have been completed,

a sealing glass is applied to the mating edge surfaces of the funnel. The components are

assembled, fired in a nonreducing atmosphere at a temperature that is sufficiently elevated

to fuse the sealing glass (ie., about 425° C. to about 475° C), and then cooled, thereby

resulting in the formation of a strong, adherent hermetic bond of devitrified or crystallized

sealing glass between the face plate and funnel components.

After the face plate has been sealed to the funnel portion of the tube, the interior

confines of the tube are evacuated by applying a vacuum thereto. The tube must be heated

to a temperature within the range of about 300° C. to about 410° C. while being evacuated

to assure that all volatile substances, such as moisture and organic materials, are liberated

and withdrawn from the interior surfaces and confines of the tube. The application of heat

to the tube inevitably results in some relational shifting of the face plate, funnel and solder

glass seal with respect to each other. Thus, a strong devitrified seal is necessary to

withstand the creation or concentration of physical stresses in the vicinity of the seal

resulting from the relational shifting of parts during the heating operation and subsequent

cooling.

The PbO constituent in the sealing glass has a natural propensity or tendency to be

reduced to metallic lead during the course of heat sealing in a reducing atmosphere or in

the presence of organic vapors. This reduction of the PbO constituent tends to induce

dielectric breakdown in the resultant seal when the resultant seal is exposed to high

voltage conditions such as those existing within a color television tube during its

operation. Because the high voltages present in a television tube during its operation in a

television set range from about 25 kV to 45 kV or more for a color television tube, any dielectric breakdown in the seal between the funnel and face plate will provide a source of

tube malfunctions. A tube with appreciable amounts of metallic lead in its seal is

unacceptable for use, and is likely to be rejected when the tube undergoes a standard

voltage test conducted at the tube manufacturing plant. Consequently, special precautions

must be taken by television tube manufacturers to prevent any such reduction of PbO

during the sealing process. Seals in which the PbO constituent has been reduced are gray

or gray-black in color, indicating the presence of metallic lead, rather than the yellow

color that is characteristic of devitrified PbO glass.

Sealing glasses typically are applied to the mating edge surfaces of the funnel in

paste form. The paste is made by combining the sealing glass with a vehicle that holds

the glass frit in a ribbon form for a period of time sufficient to enable the resultant paste to

be applied to one of the mating pieces, e.g., in the case of a color television tube, the

funnel, and the mating pieces, e.g., the face plate and funnel, to be joined and sealed. The

vehicle constituents must be pyrolyzable when they are subjected to a temperature below

the temperature at which the sealing glass frit is fired and must leave only an

inappreciable amount, if any, of residue in the fired frit.

Conventional vehicles generally comprise a binder and a solvent. The only binder

that has achieved widespread commercial success in vehicles for PbO-containing sealing

glasses, such as the PbO/B₂O₃/ZnO sealing glasses, is nitrocellulose (usually as a 1 to

1.4% solution in amyl acetate or butyl acetate). Although other compounds, such as ethyl

cellulose and hydroxypropyl cellulose, may be used as binders for PbO-containing sealing

glasses, nitrocellulose is particularly preferred because it tends to decrease the reduction

of the PbO constituent to metallic lead during the sealing process. As described further below, this contributes to the formation of satisfactory seals between the tube

components.

Amyl acetate and butyl acetate are the preferred solvents for use in sealing glass

vehicles because they volatilize rapidly from the extruded ribbon, thus permitting the

ribbon to be fired more quickly to seal the adjoining glass surfaces. They also are

excellent solvent for nitrocellulose. Ethylene glycol methyl ether also is a suitable binder

solvent, either alone or in admixture with the amyl acetate. Ethylene glycol ethyl ether,

methyl amyl acetate, ethyl hexyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl

acetate and diethylene glycol monobutyl ether acetates are other examples of the many

binder solvents that may be used. The amount of solvent in the paste will depend upon

the desired paste consistency, but will usually comprise about five to about fifteen weight

percent of the paste.

The amount of vehicle necessary for the paste is the amount that will maintain the

sealing glass frit in a wet form, extrudable as a bead or ribbon that holds its extruded

shape for the necessary length of time. The ribbon must be wide enough to produce an

effective and acceptable seal but less than the width of the funnel edge to avoid excess

paste being squeezed out from between the adjoining surfaces of the funnel and face plate

during the sealing process. However, the ribbon The width of the extruded ribbon and

the weight of the ribbon being extruded for a given length may vary appreciably over time

during the course of application of a single batch of paste. Thus, the operator of the

dispensing apparatus must carefully monitor the ribbon and adjust the volume of the paste

being extruded as needed to keep the width and the weight of the ribbon substantially

uniform from the orifice of the dispensing apparatus onto and completely about the periphery of the funnel edge. The weight ratio of sealing glass solids (including refractory

fillers, nucleating agents, and any modifiers) to vehicle is usually in the range of about

8.0:1 to about 16.0: 1, and preferably about 1 1.0: 1 to about 13.0: 1 , for conventional

vehicles. Preferably, the paste obtained by combining the vehicle with the sealing glass is

reasonably stable for at least three to four hours or more so that the paste can be made in

acceptably large quantities.

Because use of nitrocellulose as a binder for PbO-containing sealing glasses tends

to decrease the reduction of the PbO constituent to metallic lead during the sealing

process, seals formed from pastes that employ nitrocellulose as a binder are less

susceptible to dielectric breakdown caused by the reduction of PbO to metallic lead. The nitrocellulose is thought to provide a source of oxygen during heating of the sealing glass

that decreases the likelihood and extent of PbO reduction. Other binders do not offer the

advantage of decreasing the tendency of the PbO in the sealing glass to be reduced to

metallic lead. For example, the thermal decomposition of hydroxypropyl cellulose results

in the liberation of organic compounds that are capable of chemically reducing PbO to

metallic lead. The devitrified seals formed by these other binders is gray or gray-black,

indicating the presence of metallic lead in the seal.

Attempts have been made to overcome the tendency of the PbO constituent in

seals formed by these other binders to be reduced during the sealing process. One such

method, described in United States Letters Patent No. 3,973,975 to Francel et al., involves

the addition to the PbO-containing sealing glass frit and the sealing glass paste made

therefrom of a sufficient amount of a powder of a higher oxide of a cation that is

thermally stable at the temperatures at which the sealing glass frit seals the glass surfaces together, but that can be reduced to a lower oxide of the cation when exposed to the

reducing conditions. Any reducing agent in contact with such a sealing glass during the

time the sealing glass is melting and sealing will tend to reduce the higher oxide of the

metal to the lower oxide rather than reducing the PbO in the sealing glass to metallic lead.

The addition of certain oxides, nitrates, and other oxidizing agents to the sealing glass in amounts from at least 0.1 to about 1.5% by weight of the sealing glass were shown to

decrease the reduction of the PbO in the sealing glass to metallic lead and to permit the

substitution of a non-nitrocellulose binder, such as hydroxypropyl cellulose, for a portion

of the nitrocellulose binder. However, the addition of such oxidizing agents to the sealing

glass frit did not eliminate the need for the use of at least some nitrocellulose binder.

Notwithstanding these efforts, all commercially successful vehicles for PbO-

containing sealing glasses include nitrocellulose, which in turn requires the use of a

volatile organic compound as a solvent for the nitrocellulose. None of the known vehicles

for PbO-containing sealing glasses solves the problem of VOC emissions that result from

volatilization of the vehicle.

Thus, there exists a need in the art for a sealing glass system for use as a solder

glass for sealing the face plate to the funnel portion of a color television tube that is

capable of being used with a VOC-free or low-VOC vehicle, and particularly an aqueous

vehicle. (As used herein, the term "low-VOC vehicle" includes VOC-free formulations.)

As with conventional sealing glass systems, the novel system must be resistant to

substantial chemical reduction of PbO in the glass to metallic lead when the sealing glass

is exposed to reducing conditions during sealing or firing and produce a seal having

suitable dielectric and other properties. This invention aids in fulfilling these needs in the art by providing a sealing glass

modifier that decreases the chemical reduction of PbO to metallic lead in a VOC-free or

low-VOC sealing glass system when the sealing glass is exposed to reducing conditions

during sealing or firing. As used herein, the term "modifier" means any substance that

can be used in an amount sufficient to prevent the PbO from being chemically reduced

when the glass frit is being fired in the presence of reducing conditions at a temperature

sufficient to seal the glass without having a substantial adverse effect on the properties of

the sealing glass paste or the fired glass seal. The modifier comprises an inorganic nitrate

that is thermally stable at the temperatures at which the sealing glass frit seals the glass

surfaces together, but that can be reduced to a lower oxidation state when exposed to the

reducing conditions. Any reducing agent in contact with the modified sealing glass

system during the time the sealing glass is melting and sealing will tend to reduce the

inorganic nitrate to its lower oxidation state rather than reducing the PbO in the sealing

glass to metallic lead. Preferably, the inorganic nitrate is Bi(NO₃)₃ 5H₂O and/or Zn(NO₃)₂

6RO.

The modifier of the present invention may be incorporated as a component of the

sealing glass frit. The modified frit glass comprises a PbO-containing glass frit having a

sealing or firing temperature within the temperature range of about 420° C. to about 460°

C, and a modifier in an amount sufficient to prevent the PbO in the sealing glass from

being chemically reduced when the glass frit is fired in the presence of reducing

conditions at a temperature sufficient to seal the glass. The invention includes a sealing

glass paste comprising the above-described modified frit in combination with a VOC-free

or low-VOC vehicle. The modifier also may be dissolved or dispersed in a sealing glass vehicle for a

PbO-containing glass. The modified vehicle comprises a VOC-free or low-VOC vehicle

and a modifier in an amount sufficient to prevent the PbO in the sealing glass from being

chemically reduced when the glass is fired in the presence of reducing conditions at a

temperature sufficient to seal the glass. The invention further includes a sealing glass

paste comprising the above-described modified vehicle in combination with a PbO-

containing glass frit having a sealing or firing temperature with the temperature range of

about 420° C. to about 460° C.

In addition, the invention includes a method of sealing a face plate to the funnel of

a cathode ray tube using a PbO-containing sealing glass in a VOC-free or low-VOC

vehicle, under conditions capable of reducing the PbO to metallic lead, comprising the

steps of :

A. Applying between the sealing edges of the face plate and funnel portions a sealing

amount of the sealing glass composition of this invention; and

B. Subjecting the applied sealing glass composition to a sealing temperature within

the sealing temperature range of between about 420° C. and about 460° C. for a period of

time sufficient to fuse said sealing glass composition and form a seal to and between the

sealing edges of the face plate and funnel portions.

Further, this invention includes a method of sealing a face plate to the funnel of a

cathode ray tube using a PbO-containing sealing glass in a VOC-free or low-VOC vehicle,

in the presence of conditions capable of reducing the PbO to metallic lead, comprising the

steps of A. Combining the sealing glass with a modifier in an amount sufficient to prevent the PbO from being chemically reduced when the sealing glass is fired at a

temperature sufficient to seal the glass;

B. Applying a sealing amount of the modified sealing glass between the sealing edges

of the face plate and funnel portions; and

C. Subjecting the applied sealing glass composition to a sealing temperature within

time sufficient to fuse said sealing glass composition and form a seal to and between the sealing edges of the face plate and funnel portions.

Still further, this invention provides a method of sealing a face plate to a funnel of

a cathode ray tube using a PbO-containing sealing glass, in the presence of conditions

capable of reducing the PbO to metallic lead, comprising the steps of:

A. Combining a low-VOC vehicle with a modifier in an amount sufficient to prevent

the PbO from being chemically reduced when the sealing glass is fired at a temperature

sufficient to seal the glass;

B. Combining the modified vehicle with a sealing glass to form a sealing glass paste;

C. Applying a sealing amount of the modified sealing glass paste between the sealing

edges of the face plate and funnel portions; and

D. Subjecting the applied sealing glass composition to a sealing temperature within

sealing edges of the face plate and funnel portions.

These and other objects of the present invention will be apparent from the

specification that follows and the appended claims. SUMMARY OF THE INVENTION

The foregoing objectives are achieved in a sealing glass modifier that enables a

PbO-containing sealing glass to be used in combination with a VOC-free or low-VOC

vehicle by decreasing the chemical reduction of PbO in the sealing glass to metallic lead

during sealing or firing. The modifier preferably comprises an inorganic nitrate that is

thermally stable at the temperatures at which the sealing glass frit seals the glass surfaces

together, but that can be reduced to a lower oxidation state when exposed to the reducing

conditions. Any reducing agent in contact with such a modified sealing glass system

during the time the sealing glass is melting and sealing will tend to reduce the inorganic

nitrate to its lower oxidation state rather than reducing the PbO in the sealing glass to

metallic lead. Particularly preferred modifiers are Bi(NO₃)₃ 5H₂O and/or Zn(NO₃)₂

6H₂0. The modifier is added to the sealing glass system in an amount sufficient to

prevent the PbO from being chemically reduced when the sealing glass is fired in the

presence of reducing conditions at a temperature sufficient to seal the glass. The

invention includes the use of a modifier in a sealing glass system to decrease the reduction

of PbO during firing and sealing, a sealing glass incoφorating the modifier, a sealing

glass paste including the modified sealing glass, a vehicle incoφorating the modifier, a

sealing glass paste including the modified vehicle, the methods of making the modified

sealing glass, the modified vehicle, and the related pastes, and the methods of sealing the

tube components using the modified sealing glass and the modified vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a sealing glass modifier that decreases the

chemical reduction of PbO in a PbO-containing sealing glass to metallic lead during

sealing or firing, and enables the sealing glass to be used in combination with a VOC-free

or low-VOC vehicle. The modifier preferentially comprises bismuth nitrate and/or zinc

nitrate in an amount sufficient to prevent the PbO from being chemically reduced when

the sealing glass is fired in the presence of reducing conditions at a temperature sufficient

to seal the glass.

A. Sealing Glass

Lead-zinc-borate solder glasses are preferred in practicing this invention. Such

glasses are well-known in the solder glass art, and examples can be found in United States

Letters Patent No. 4,589,899 to Hudacek. The solder glasses useful in the practice of this

invention also are referred to herein as the "base glass."

The lead-zinc-borate glasses suitable for use in the present invention typically

have the oxide composition (as calculated from raw batch starting materials) specified in

Table 1 , expressed in weight percent, and wherein the total content of all oxides is 100%.

TABLE 1. PREFERRED BASE GLASS COMPOSITION

Oxides Usual Range Preferred Range Preferred Values

PbO 70-80 73-77 75.0

B₂O₃ 5-1 1 7-10 8.5

ZnO 9-16 10-14 12.5

SiO₂ 0- 5 1- 3 2.0

BaO 0- 3 1.5- 2.5 2.0 13

The particularly preferred base glass composition set forth above in the "Preferred

Values" column is especially well-suited for color television picture tube applications.

Other conventional glass making oxides such as CaO, CuO, Bi₂0₃, Na,0, K₂0,

Li,0, CdO, and Fe₂0₃ can be included. However, it is preferred in many instances not to

employ these constituents, but rather to provide compositions that consist essentially only

of those constituents set forth in Table 1 , above.

The particle size of the glass frit is not particularly critical to the practice of the

present invention, and any conventional particle size distribution can be employed.

Typically, the particle size of the glass frit will be such that about 100% of the particles

pass a 100 mesh (U.S. Standard Sieve Series) screen, and at least about 60% of the particles pass a 400 mesh screen.

It is also preferred that the base glass used in the practice of this invention have the

following properties:

A. A glassy edge of about 360° C. to about 390° C, preferably about 370° C, as

determined by a gradient boat test;

B. A devitrification edge of about 390° C. to about 425° C, preferably about 415° C,

as determined by a gradient boat test;

C. A button flow of about 1.050 to about 1.120 inches diameter, preferably about

1.080 inches diameter; and

D. A rod stress within the tensional stress range of about 0 p.s.i. to about 1000 p.s.i.,

preferably about 300 p.s.i. to about 800 p.s.i., especially about 500 p.s.i. The terms

"gradient boat test," "button flow" and "rod stress value" have the same meanings and are determined according to the same procedures set forth in United States Letters Patent No.

4,058,387 to Nofziger.

The results described herein relate to the use of the particularly preferred base

glass. However, it is believed that any PbO-containing glass frit having a sealing or firing

temperature within the temperature range of about 420° C. to about 460° C. can be used with satisfactory results.

B. Vehicle

A VOC-free vehicle that reasonably satisfies the requirements that the vehicle be

capable of holding the solder glass frit in a ribbon form for a sufficient length of time for

satisfactory application to the funnel surface, and that the resultant paste be stable enough

that it can be made in quantities suitable for use in commercial tube manufacture, is

vehicle A9065, available from Alpha Metals, Inc., Jersey City, New Jersey. This VOC-

free vehicle is a colorless liquid comprising 97-98% water and less than 2% cellulose. It

has a specific gravity of about 1.00 to about 1.01 and a pH in the range of about 5.0 to

about 8.0. The weight ratio of sealing glass solids (including refractory fillers, nucleating

agents, and modifiers) to vehicle is usually in the range of about 6.0:1 to about 12.0:1, and

preferably about 8.0: 1 to about 8.5:1, for a VOC-free or low-VOC vehicle such as vehicle

A9065.

The results described herein relate to sealing glass systems that make use of

vehicle A9065. However, it is contemplated that the invention may be practiced with

other VOC-free or low-VOC vehicles having similar properties. C. Modifier

As described above, the modifier of the present invention preferably comprises an

inorganic nitrate that is thermally stable at the temperatures at which the sealing glass frit

seals the glass surfaces together, but that can be reduced to a lower oxidation state when

exposed to the reducing conditions. The modifier is added to the sealing glass system in

an amount sufficient to prevent the PbO from being chemically reduced when the sealing

glass is fired in the presence of reducing conditions at a temperature sufficient to seal the

glass.

Bi(NO₃)₃ 5H₂0 and/or Zn(NO₃)₂ 6H₂0 are the particularly preferred modifiers.

These modifiers are effective in decreasing the chemical reduction of PbO during firing

and sealing of the glass without causing any substantial adverse effect on the rheology of

the sealing glass paste or on the sealing properties of the base glass.

The effectiveness of a modifier in decreasing the reduction of PbO usually can be

determined visually by comparing the colors of fired frits with and without the modifier.

The formation of free lead or a lower oxide of lead during firing is characterized by a gray

or black color appearing in the fired frit unless, of course, the modifier itself is black or

gray in color. In all cases, analytical tests can be used to determine the presence of

metallic lead, and therefore, the effectiveness of the modifier. The effectiveness of the

modifier also may be shown by dielectric tests of the resultant seal.

Modifier candidates initially were assessed by examining the visual rheology of

modified paste samples and the color of the corresponding glass frits after firing. The test

samples were prepared by incoφorating a modifier (in an amount equal to about 1 % by

weight of the base glass) in the particularly preferred PbO-containing glass frit described above. The modified base glass samples were then combined with VOC-free vehicle

A9065 by hand mixing in a weight ratio of about 8.3: 1. After the sample rheology was

assessed, the samples were fired at a temperature of about 420° C. to about 460° C. The

samples were compared to a base glass control, which was similarly combined with the

VOC-free vehicle A9065 in a weight ratio of about 8.3: 1 and fired at a temperature of

about 420° C. to about 460° C. The results of these tests are provided in Table 2.

17

TABLE 2. VISUAL ASSESSMENT OF MODIFIERS

Modifier Color Visual Rheologv

Control (unmodified Gray Medium gelation base glass)

PbO, Red orange Slight or no change

Pb(N0₃)₂ Ivory with beige splotches Initially broke gel structure and gradually returned

PbA Orange-yellow Completely gelled

Bi(NO₃), 5H₂O Yellow Initially broke gel structure

Ca(NO₃)₂ 4H₂0 Orange-yellow No change

BaO₂ Orange, porous Gelled

C₄H₄O₄ Black, porous No change

Zn(NO₃)₂ 6H₂O Yellow Slight gel

Of the compounds tested, Bi(NO₃)₃ 5H₂O and Zn(NO₃)₂ 6H₂O were the most

effective in decreasing the reduction of PbO to metallic lead, as evidenced by the yellow

color of the fired frits. Pb₃O₄ and Ca(NO₃)₂ 4H₂0 appeared to be somewhat less effective

in decreasing PbO reduction during firing of the frit. C₄H₄O₄ was not effective in

decreasing the reduction of PbO to metallic lead during firing, as evidenced by the black

color of the fired frit.

Both BaO₂ and Pb₃O₄ (which were among the most preferred additives in

decreasing the reduction of PbO in conventional nitrocellulose binder systems) exhibited

unsatisfactory visual rheology in the VOC-free vehicle system. The C₄H₄O₄ seal had a

porous appearance, which is indicative of low seal strength and an increased likelihood of

dielectric breakdown.

Further tests were conducted to determine the amount of the modifier necessary to

achieve the desired decrease in PbO reduction. In these tests, varying amounts of modifiers were incoφorated into the preferred PbO base glass, and the modified glasses

were combined with vehicle A9065 and fired as described above. After firing, the color

of the modified frits were evaluated. The results of these tests are shown in Table 3.

TABLE 3. EFFECTIVE AMOUNTS OF MODIFIERS

Sample Compound Available Decompositi Hand Mix Color

No. Oxygen on Point Rheologv

(%) C C) (at 1%) 1.0% 0.25% 0.1%

1 PbO₂ 6.69 290 no effect red-orange orange gray- orange co 2 Pb(NO₃)₂ 14.5 470 thin/thicken pale yellow beige

CD CO 3 Pb₃O 2.33 500 ' thicken orange gray- beige m co 4 Bi(NO₃)₃ 5H₂O 14.84 500 thin/thicken yellow pale gray- yellow orange

5 Ca(NO₃)₂ 4H₂O 20.33 132 no effect orange* - pale gray- bumpy yellow- orange ro beige

6 BaO₂ 9.45 800 thicken orange- porous

7 C₄H₄O₄ ? ? no effect black-porous

8 Zn(NO₃)₂ 6H₂O 19.72 ? slight yellow- pale gray- thickener orange yellow orange

*May have been affected by samples 6 and 7.

As shown in Table 3, the Bi(NO₃)₃ 5H₂0 and Zn(NO₃)₂ 6H₂O modifiers achieved

satisfactory results when incoφorated into the base glass in amounts ranging from about

0.25% to about 1% by weight of the base glass. Pb0₂ and Ca(N0₃)₂ 4H₂O also achieved

satisfactory results in these amounts based on the color of the fired frits. However, the fired

frit containing Ca(NO,)₂ 4H₂0 had a bumpy appearance, indicating that the molten paste

flow was not uniform.

Pb₃0₄, Pb(NO₃)₂ and BaO₂ in an amount equal to 1% by weight of the base glass

produced seals with a satisfactory color. The fired BaO₂ frit, however, had a porous

appearance indicative of low seal strength. C,R,O₄ did not yield satisfactory results at any of

the levels tested and had a porous appearance at the 1% level. None of the tested

compounds achieved satisfactory results in an amount equal to 0.1% by weight of the base

glass.

Selected compounds from Table 3 that passed the initial screening, namely, Pb0₂,

Pb(NO₃)₂, Bi(NO₃)₃ 5H₂0, Ca(NO₃)₂ 4H₂0 and Zn(N0₃)₂ 6H₂0, were further subjected to

differential thermal analysis (DTA) to assess their crystallization behavior. Samples of base

glass were combined with both a conventional vehicle (Vehicle F1016, 1.25% nitrocellulose

in amyl acetate, in a weight ratio of about 12.5: 1) and vehicle A9065 (in a weight ratio of

about 8.3:1). The vehicles were driven off the samples by heat at about 300° C. to yield

Sample Nos. 1 and 2, respectively. The modified blend samples were prepared by

incorporating the modifier, combining the modified base glass with vehicle A9065 in a

weight ratio of about 8.3: 1, and driving the vehicle off by heat at about 300° C. as described

above for Sample No. 2. The DTA results for the modified blend samples were compared to those for the

base sealing glass powder (Sample #8), which was used as the base glass in all samples, and

the samples prepared from the base glass with the conventional vehicle (Sample #1) and

with vehicle A9065 (Sample Ul). The DTAs on all of the dried pastes and the sealing glass

powder (Sample #8) were conducted using the following thermal cycle: increasing the

temperature at a rate of about 10° C. /minute to about 440° C, and holding at this

temperature for 60 minutes or until the thermal curve was complete. The results of these

tests are shown in Table 4.

A satisfactory modifier should result in little, if any, change in the DTA

crystallization characteristics of the modified glass compared to the unmodified sealing

glass powder (Sample #8). As can be seen from Table 4, dried paste using the standard

vehicle system (Sample #1) showed only slight differences between the DTA peak and

DTA completion time when compared to sealing glass powder (Sample #8).

Unmodified dried paste using the VOC-free vehicle Alpha A9065 (Sample #2) showed

a slightly faster DTA peak and DTA completion than sealing glass powder (Sample

#8).

Dried paste using a PbO₂ modifier (Sample #2) showed a significantly faster

DTA peak time and a significantly slower completion time compared to sealing glass

powder (Sample #8). This sample also exhibited unsatisfactory crystallization behavior

as evidenced by the absence of a sharp peak and a smooth curve from peak to

completion on the DTA plot for this sample. Dried paste using a Pb(NO₃)₂ modifier

showed a significantly faster DTA peak time and completion time than sealing glass

powder (Sample #8). These results indicate an unsatisfactorily fast crystallization rate

for the Pb(NO₃)₂ - modified paste.

Dried paste using either Bi(NO₃)₃ 5H₂O (Sample # 5) or Zn(NO₃)₂ 6H₂O

(Sample #7) as the modifier showed only very slight differences in the DTA peak time

or DTA completion time compared to sealing glass powder (Sample #8). These

modifiers exhibited the least influence on the DTA crystallization characteristics of the

sealing glass powder. Dried paste using a Ca(NO₃)₂ 4H₂O modifier (Sample #6)

showed a slightly slower DTA peak time and DTA completion time than sealing glass

powder (Sample #8). The amount of the modifier used to prevent or decrease the chemical reduction

of the PbO will depend, among others things, upon the relative effectiveness of the

modifier and the conditions to which the sealing glass is exposed during sealing and

firing. The foregoing description of the relative effectiveness of modifiers, when

employed with the particularly preferred base glass, can be used as a guide for this

purpose. The effective amount of the modifier typically will be in the range of about

0.05 to about 5 weight percent of the sealing glass, and preferably in an amount of

about 0.1 to about 1.0 weight percent of the sealing glass. Although amounts in excess

of 1.0 weight percent were not tested, it is believed that higher amounts also will yield

satisfactory results; provided, however, that these amounts are not so high that they

adversely affect the other properties of the sealing glass system. Optimum performance

of the sealing glass is obtained when the modifier is added in an amount that is not

greatly in excess of the effective amount. This minimizes adverse effects on the

rheology of the sealing glass paste and the sealing properties (including crystallization

behavior) of the base glass.

The particularly preferred modifiers Bi(NO₃)₃ 5H₂O and Zn(NO₃)₂ 6H₂O are

typically employed in an amount of about 0.25 to about 1 weight percent of the sealing

glass composition, and preferably about 0.3 to about 0.5 weight percent, when used

with the particularly preferred base glass and Alpha Metals vehicle A9065 in a ratio of

about 8.3:1. With improved low-VOC vehicles, however, it is expected that

satisfactory results may be achieved by using the modifier of the present invention in an

amount as low as about 0.05% by weight of the base glass. Commercial grades of the preferred modifiers have been found to be suitable for

use in this invention. These modifiers of the present invention have been found to

perform satisfactorily in the hydration states specified above; however, the hydration

states are not thought to be critical, and it is expected that these modifiers would yield

satisfactory results in other hydration states as well.

One way in which the modifier may be used in a sealing glass system is by

substituting the modifier for a portion of the frit. Optimum results may be obtained by

reducing the particle size of the modifier and distributing it evenly throughout the

sealing glass powder. This may be accomplished, for example, using the two-step

process described below. In the first step, about 10% to about 20% of the modifier in

sealing glass powder is blended in a twin shell or rotocone blender for about 5 to about

15 minutes. In the second step, the blended material from Step 1 is placed into a

ceramic lined ball mill with ceramic grinding media and ground for about 5 to about 30

minutes. The material from Step 2 is referred to as a modifier masterblend. A desired

amount of the modifier masterblend may be uniformly dispersing in the final sealing

glass product, for example, using a rotocone blender.

A sealing glass paste of the present invention may be prepared by mixing the

modified sealing glass blend with a VOC-free or low-VOC vehicle, in conventional

manner. The weight ratio of sealing glass solids (including refractory fillers, nucleating

agents, and modifiers) to vehicle is usually in the range or about 7.0:1 to about 13.0:1,

and preferably about 8.0: 1 to about 8.5: 1. A mixing time of not more than about thirty

minutes is recommended to prolong the useful life of the paste. The modified vehicle of this invention may be prepared by dissolving an

appropriate amount of the Zn(NO₃)₂ 6H₂0 modifier into the commercially available

A9065 vehicle, and using the vehicle to prepare a sealing glass paste in the

conventional manner. This is a particularly easy and economical way to incorporate the

modifier into the sealing glass system. Although the Zn(NO₃)₂ 6H₂O modifier is

preferred for preparation of a modified vehicle because of its solubility in the vehicle, it

also is possible to prepare the modified vehicle by dispersing the appropriate quantity

of Bi(NO₃)₃ 5H₂O in the vehicle. However, the Bi(NO₃)₃ 5H₂O-containing vehicle

requires agitation before use in preparation of a sealing glass paste to rehomogenize the

vehicle and provide a uniform distribution of the Bi(NO₃)₃ 5H₂O dispersed therein.

The amount of modifier added to the vehicle to create the modified vehicle generally

will be in the range of about 0.005% to about 0.1% by weight of the vehicle.

Another sealing glass paste of the present invention may be prepared by mixing

the modified vehicle, prepared as described above, with the base sealing glass. As with

the other sealing glass paste, the weight ratio of sealing glass solids to vehicle is usually

in the range or about 7.0: 1 to about 13.0:1, and preferably about 8.0: 1 to about 8.5: 1,

and a mixing time of not more than about thirty minutes is recommended.

The present invention includes a method of sealing a face plate to the funnel of

steps of :

A. Applying between the sealing edges of the face plate and funnel portions a

sealing amount of the sealing glass composition of this invention; and B. Subjecting the applied sealing glass composition to a sealing temperature within

the sealing temperature range of between about 420° C. and about 460° C. for a period

of time sufficient to fuse said sealing glass composition and form a seal to and between

the sealing edges of the face plate and funnel portions.

Further, this invention includes a method of sealing a face plate to the funnel of

steps of :

A. Combining the sealing glass with a modifier in an amount sufficient to prevent

sufficient to seal the glass;

B. Applying a sealing amount of the modified sealing glass between the sealing

edges of the face plate and funnel portions; and

the sealing edges of the face plate and funnel portions.

Still further, this invention provides a method of sealing a face plate to a funnel

portion of a cathode ray tube, such as a color television tube, with a PbO-containing

sealing glass, comprising the steps of:

A. Combining a VOC-free or low-VOC vehicle with a modifier in an amount

sufficient to prevent the PbO from being chemically reduced when the sealing glass is

fired at a temperature sufficient to seal the glass; B. Combining the modified vehicle with a sealing glass to form a sealing glass

paste;

C. Applying a sealing amount of the modified sealing glass paste between the

sealing edges of the face plate and funnel portions; and

the sealing edges of the face plate and funnel portions.

At present, sealing glass pastes made with a VOC-free vehicle such as A9065

from Alpha Metals do not achieve the rheology and shelf life characteristics (with or

without the presence of modifiers) of sealing glass paste made with conventional

vehicles comprising nitrocellulose in amyl or butyl acetate. Typical pastes made with

the conventional vehicle system have a stable rheology for about 0.5 to about 8 hours

after mixing in a typical tube manufacturing plant. The shelf life of such pastes is

usually up to about 48 hours after mixing. Pastes made with a VOC-free vehicle such

as A9065, with or without modifiers, currently are stable up to about 2 hours after

mixing. The shelf life of these VOC-free pastes does not exceed about 4 hours unless

additional vehicle is added to the paste with subsequent mixing. In short, available

VOC-free pastes have commercially useful, but not optimal rheology and shelf-life

characteristics. Nevertheless, it is believed that some tube manufacturers may be

willing to adjust their mixing and dispensing processes to accommodate these

characteristics of VOC-free pastes because of the environmental benefits of VOC-free

sealing glass systems. Although specific embodiments of the invention have been described herein in

detail, it is understood that variations may be made thereto by those skilled in the art

without departing from the spirit of the invention or the scope of the appended claims.

Claims

What is claimed is:

1. A modifier for use in combination with a PbO-containing sealing glass

and a low-VOC sealing glass vehicle for sealing the face plate to the funnel of a

cathode ray tube, said modifier decreasing the chemical reduction of the PbO-

constituent in the sealing glass during firing of the sealing glass.

2. The modifier according to Claim 1, wherein the amount of the modifier

used is at least about 0.05 percent of the weight of the sealing glass.

3. The modifier according to Claim 1, wherein the amount of the modifier

used is about 0.05 to about 5.0 weight percent of the sealing glass.

4. The modifier according to Claim 1 , wherein the amount of the modifier

is about 0.05 to about 1.0 weight percent of the sealing glass.

5. The modifier according to Claim 1 , wherein the amount of the modifier

is about 0.1 to about 0.5 weight percent of the sealing glass.

6. The modifier according to Claim 1 , wherein the amount of the modifier

is about 0.25 to about 0.5 weight percent of the sealing glass.

7. The modifier according to Claim 1, wherein the amount of the modifier

is about 0.3 to about 0.8 weight percent of the sealing glass.

8. The modifier according to Claim 1 , wherein said modifier comprises

bismuth nitrate.

9. The modifier according to Claim 1 , wherein said modifier comprises

Bi(N0₃)₃ 5H₂0.

10. The modifier according to Claim 9, wherein the amount of

Bi(N0₃)₃ 5H₂O is at least about 0.05 percent of the weight of the sealing glass.

11. The modifier according to Claim 9, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.05 to about 5.0 weight percent of the sealing glass.

12. The modifier according to Claim 9, wherein the amount of

Bi(NO,)j 5H₂O is about 0.05 to about 1.0 weight percent of the sealing glass.

13. The modifier according to Claim 9 wherein the amount of

Bi(NO₃)₃ 5H₂O. is about 0.1 to about 0.5 weight percent of the sealing glass.

14. The modifier according to Claim 9, wherein the amount of

Bi(NO₃)₃ 5H₂0 is about 0.2 to about 0.5 weight percent of the sealing glass.

15. The modifier according to Claim 9, wherein the amount of

Bi(N0₃)₃ 5H_:O is about 0.3 to about 0.8 weight percent of the sealing glass.

16. The modifier according to Claim 1 , wherein said modifier comprises

zinc nitrate.

17. The modifier according to Claim 1 , wherein said modifier comprises

Zn(NO₃)₂ 6H₂O.

18. The modifier according to Claim 16, wherein the amount of Zn(NO₃)₂

6H₂O is at least about 0.05 percent of the weight of the sealing glass.

19. The modifier according to Claim 16, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.05 to about 5.0 weight percent of the sealing glass.

20. The modifier according to Claim 16, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.05 to about 1.0 weight percent of the sealing glass.

21. The modifier according to Claim 16, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.1 to about 0.5 weight percent of the sealing glass.

22. The modifier according to Claim 16, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.25 to about 0.5 weight percent of the sealing glass.

23. The modifier according to Claim 16, wherein the amount of Zn(NO₃),

6H₂0 is about 0.3 to about 0.8 weight percent of the sealing glass.

24. The modifier according to Claim 1 , said modifier further causing the

seal formed between the face plate and the funnel to exhibit acceptable dielectric

properties.

25. A composition in powdered form for sealing the face plate and the

funnel of a cathode ray tube, said composition comprising:

a crystallizable PbO/ZnO/B₂O₃ glass; and

a modifier, said modifier decreasing the chemical reduction of the PbO-

constituent in the crystallizable glass during sealing of the cathode ray tube components.

26. The composition according to Claim 25, wherein said modifier

comprises bismuth nitrate.

27. The composition according to Claim 25, wherein said modifier

comprises Bi(NO₃)₃ 5H₂O.

28. The composition according to Claim 25, wherein the amount of

Bi(NO₃) 5H₂O is at least about 0.05 percent of the weight of the crystallizable glass.

29. The composition according to Claim 25, wherein the amount of

Bi(NO₃), 5H,O is about 0.05 to about 5.0 weight percent of the crystallizable glass.

30. The composition according to Claim 25, wherein the amount of

Bi(NO,)₃ 5H₂O is about 0.05 to about 1.0 weight percent of the crystallizable glass.

31. The composition according to Claim 25 wherein the amount of

Bi(NO₃)₃ 5H₂0 is about 0.1 to about 0.5 weight percent of the crystallizable glass.

32. The composition according to Claim 25, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.25 to about 0.5 weight percent of the crystallizable glass.

33. The composition according to Claim 25, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.3 to about 0.8 weight percent of the crystallizable glass.

34. The composition according to Claim 25, wherein said modifier

comprises zinc nitrate.

35. The composition according to Claim 25, wherein said modifier

comprises Zn(NO₃)₂ 6H₂O.

36. The composition according to Claim 35, wherein the amount of

Zn(NO₃)₂ 6H₂O is at least about 0.05 percent of the weight of the crystallizable glass.

37. The composition according to Claim 35, wherein the amount of

Zn(N0₃)_: 6H₂O is about 0.05 to about 5.0 weight percent of the crystallizable glass.

38. The composition according to Claim 35, wherein the amount of

Zn(N0₃)₂ 6H₂0 is about 0.05 to about 1.0 weight percent of the crystallizable glass.

39. The composition according to Claim 35, wherein the amount of

Zn(NO₃)₂ 6H₂O is about 0.1 to about 0.5 weight percent of the crystallizable glass.

40. The composition according to Claim 35, wherein the amount of

Zn(N0₃)₂ 6H₂O is about 0.25 to about 0.5 weight percent of the crystallizable glass.

41. The composition according to Claim 35, wherein the amount of

Zn(N0₃)₂ 6H₂O is about 0.3 to about 0.8 weight percent of the crystallizable glass.

42. The composition according to Claim 25, wherein said PbO/ZnO B₂O₃

glass comprises the following ingredients in approximate percent by weight:

Ingredient Percent Bv Weight

PbO 70 to 80

ZnO 5 to 11

B₂0₃ 9 to 16

SiO₂ O to 5

43. A vehicle for use in combination with a PbO-containing sealing glass for

sealing the face plate to the funnel of a cathode ray tube, said vehicle comprising:

a low-VOC liquid; and a modifier, said modifier decreasing the chemical reduction of the PbO-

constituent in the sealing glass during firing of the sealing glass.

44. The vehicle according to Claim 43, wherein said modifier is dissolved in

the low-VOC liquid.

45. The vehicle according to Claim 44, wherein said modifier is Zn(NO₃)

6H₂O.

46. The vehicle according to Claim 45, wherein said Zn(NO₃)₂ 6H₂O is

present in the vehicle in an amount from about 0.005 to about 0.1 weight percent of the

vehicle.

47. The vehicle according to Claim 43, wherein said modifier is dispersed in

the low-VOC liquid.

48. The vehicle according to Claim 47, wherein said modifier is

Bi(NO₃)₃ 5H₂O.

49. The vehicle according to Claim 48, wherein said Bi(NO₃)₃ 5H₂0 is

vehicle.

50. A sealing glass paste for sealing the face plate and the funnel of a

cathode ray tube, said composition comprising:

a crystallizable PbO/ZnO/B₂O₃ glass in powdered form;

a modifier, said modifier decreasing the chemical reduction of the PbO-

constituent in the crystallizable glass during sealing of the cathode ray tube

components; and

a low-VOC liquid capable of holding the powdered glass in ribbon form for a

period of time sufficient to enable the resultant paste to be applied to a surface of one of

the cathode ray tube components.

51. The sealing glass paste according to Claim 50, wherein said modifier

comprises Zn(NO₃)₂ 6H₂O.

52. The sealing glass paste according to Claim 51 , wherein the amount of

Zn(N0₃)₂ 6H₂0 is at least about 0.05 percent of the weight of the powdered glass.

53. The sealing glass paste according to Claim 51 , wherein the amount of

Zn(N0₃)₂ 6H₂O is about 0.05 to about 5.0 weight percent of the powdered glass.

54. The sealing glass paste according to Claim 51 , wherein the amount of

Zn(N0₃)_: 6H₂O is about 0.05 to about 1.0 weight percent of the powdered glass.

55. The sealing glass paste according to Claim 51. wherein the amount of

Zn(N0₃); 6H₂0 is about 0.1 to about 0.5 weight percent of the powdered glass.

56. The sealing glass paste according to Claim 50, wherein the modifier is

soluble in the low-VOC liquid.

57. The sealing glass paste according to Claim 50, wherein said modifier

comprises Bi(NO₃)₃ 5H₂O.

58. The sealing glass paste according to Claim 57, wherein the amount of

Bi(N0₃)₃ 5H,O is at least about 0.05 percent of the weight of the powdered glass.

59. The sealing glass paste according to Claim 57, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.05 to about 5.0 weight percent of the powdered glass.

60. The sealing glass paste according to Claim 57, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.05 to about 1.0 weight percent of the powdered glass.

61. The sealing glass paste according to Claim 57, wherein the amount of

Bi(NO₃), 5H₂O is about 0.1 to about 0.5 weight percent of the powdered glass.

62. A method of making a sealing glass paste for sealing the face plate and

the funnel of a cathode ray tube, said method comprising the steps of: providing a crystallizable PbO/ZnO/B₂O₃ glass in powdered form;

providing a modifier, said modifier decreasing the chemical reduction of the

PbO-constituent in the crystallizable glass during sealing of the cathode ray tube

components;

incorporating said modifier into said powdered glass to form a sealing glass

blend; and

mixing said sealing glass blend with a VOC-free vehicle, said vehicle holding

the sealing glass blend in ribbon form for a period of time sufficient to enable the

resultant paste to be applied to a surface of one of the cathode ray tube components.

63. The method according to Claim 62, wherein the modifier comprises

Zn(N0₃)₂ 6H₂O.

64. The method according to Claim 63, wherein the amount of Zn(NO₃)₂

6H₂O is at least about 0.05 percent of the weight of the powdered glass.

65. The method according to Claim 63, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.05 to about 5.0 weight percent of the powdered glass.

66. The method according to Claim 63, wherein the amount of Zn(NO₃)₂

6H₂O is about 0.05 to about 1.0 weight percent of the powdered glass.

67. The method according to Claim 63, wherein the amount of Zn(NO₃)₂

6H,0 is about 0.1 to about 0.5 weight percent of the powdered glass.

68. The method according to Claim 62, wherein the modifier comprises

Bi(N0₃)₃ 5H₂O.

69. The method according to Claim 68 wherein the amount of

Bi(NO₃)j 5H₂O is at least about 0.05 percent of the weight of the powdered glass.

70. The method according to Claim 68, wherein the amount of

71. The method according to Claim 68, wherein the amount of

72. The method according to Claim 68, wherein the amount of

Bi(NO₃)₃ 5H₂O is about 0.1 to about 0.5 weight percent of the powdered glass.

73. The method according to Claim 62, wherein the weight ratio of sealing

glass solids to vehicle is in the range of about 7.0:1 to about 13.0:1.

74. The method according to Claim 62, wherein the weight ratio of sealing

glass solids to vehicle is in the range of about 8.0:1 to about 8.5: 1.

75. The method according to Claim 62, wherein the step of incoφorating

the modifier into the powdered glass includes the step of grinding the modifier and the

powdered glass.

76. The method according to Claim 62, wherein the mixing time is less than

about thirty minutes.

77. A method of making a sealing glass paste for sealing the face plate and

the funnel of a cathode ray tube, said method comprising the steps of:

providing a low-VOC vehicle, said vehicle capable of holding a powdered

sealing glass in ribbon form for a period of time sufficient to enable the resultant paste

to be applied to a surface of one of the cathode ray tube components;

combining said vehicle with a modifier to form a modified vehicle, said

modifier decreasing the chemical reduction of the PbO-constituent in the crystallizable

glass during sealing of the cathode ray tube components;

providing a powdered PbO/ZnO B₂O₃ sealing glass; and

mixing said modified vehicle and said sealing glass to form a paste.

78. The method according to Claim 77, wherein the step of combining the

vehicle with the modifier further includes the step of:

dissolving an appropriate quantity of the Zn(NO₃)₂ 6H₂O modifier in the

vehicle.

79. The method according to Claim 77, wherein the step of combining the

vehicle with the modifier further includes the steps of:

dispersing an appropriate quantity of Bi(N0₃)₃ 5H₂0 in the vehicle; and

agitating the modified vehicle before combining it with the sealing glass.

80. A method of sealing the face plate to the funnel of a cathode ray tube

using a PbO-containing sealing glass in a low VOC vehicle, under conditions capable

of reducing the PbO to metallic lead, comprising the steps of:

preparing a modified sealing glass composition;

applying between the sealing edges of the face plate and funnel portions a

sealing amount of the sealing glass composition; and

subjecting the applied sealing glass composition to a sealing temperature within

the sealing edges of the face plate and funnel portions.

81. The method according to Claim 80, wherein the step of preparing a

modified sealing glass composition comprises the steps of:

providing a crystallizable PbO/ZnO/B₂O₃ glass in powdered form;

providing a modifier, said modifier decreasing the chemical reduction of the

components; incoφorating said modifier into said powdered glass to form a sealing glass

blend; and

mixing said sealing glass blend with a VOC-free vehicle, said vehicle holding

82. The method according to Claim 81 , wherein the modifier comprises

Zn(N0₃)₂ 6H₂O in an amount from about 0.3 to about 1.0 weight percent of the

powdered glass.

83. The method according to Claim 81 , wherein the modifier comprises

Bi(NO₃)₃ 5H₂O in an amount from about 0.3 to about 1.0 weight percent of the

powdered glass.

84. A method of sealing a face plate to the funnel of a cathode ray tube

of reducing the PbO to metallic lead, comprising the steps of :

combining the sealing glass with a modifier in an amount sufficient to prevent

sufficient to seal the glass;

applying a sealing amount of the modified sealing glass between the sealing

edges of the face plate and funnel portions; and subjecting the applied sealing glass composition to a sealing temperature within

the sealing edges of the face plate and funnel portions.

85. A method of sealing the face plate to the funnel of a cathode ray tube

with a PbO-containing sealing glass, comprising the steps of:

combining a low-VOC vehicle with a modifier in an amount sufficient to

prevent the PbO from being chemically reduced when the sealing glass is fired at a

temperature sufficient to seal the glass; combining the modified vehicle with a sealing glass to form a sealing glass

paste;

applying a sealing amount of the sealing glass paste between the sealing edges

of the face plate and funnel portions; and

the sealing edges of the face plate and funnel portions.

86. The method according to Claim 85, wherein the modifier comprises

Zn(NO₃)₂ 6H₂O in an amount from about 0.005 to about 0.1 weight percent of the

vehicle.

87. The method according to Claim 85, wherein the modifier comprises

Bi(NO₃)₃ 5H₂O in an amount from about 0.005 to about 0.1 weight percent of the

vehicle.