Low temperature burnout screen printing frit vehicle

Details Low temperature burnout screen printing frit vehicle Low temperature burnout screen printing frit vehicle

2001-02-26

2001-10-23

Brunsman, David (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Carbohydrate or derivative containing

Reexamination Certificate

active

06306208

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to sealing compositions and in particular to vehicles and pastes for use in the screen printing of glass frit.
BACKGROUND OF THE INVENTION
Bernot et al, U.S. patent application Ser. No. 08/986,253, filed Dec. 5, 1997, now U.S. Pat. No. 6,058,780 entitled, (as amended), “Capacitive Pressure Sensor Housing Having a Ceramic Base” which is assigned to the assignee of this application, discloses a glass ceramic capsule comprised of a cover and a header also referred to as a base that together define an interior chamber. A capacitive pressure sensor is mounted within the chamber. The header is ceramic while the cover is either ceramic or metallic. The cover and header are sealed together with glass frit.
Typically, the glass frit is made into a paste using a vehicle which is a combination of a solvent and a binder. The paste is then applied onto the surfaces to be bonded by either brushing or ink-jetting. A critical requirement for the vehicle is that it have a low temperature burnout capability. It needs to completely bum out before the glass frit softens (i.e. melts) which occurs at about 350° C. (662° F.). One vehicle currently used is amyl-acetate (a solvent) containing a small amount of nitrocellulose (a binder). This vehicle meets the temperature requirement because the nitrocellulose burns out well below 350° C. (662° F.).
A disadvantage to the brushing or ink-jetting methods is that with these methods it is difficult to control the thickness and uniformity of the glass frit as it is applied. Using a screen-printing method to apply the glass frit paste would provide both performance and cost advantage over these other methods because the screen printing method produces a more uniform frit coating layer with easily controlled thickness and can be economically applied in large scale batch production. However, the current vehicle of amyl-acetate and nitrocellulose is not suitable for a screen-printing method because the evaporation rate of amyl-acetate is too fast creating an unstable paste whose thickness is difficult to control. Further, other commercially available screen-printing vehicles do not burn out completely at temperatures below 350° C. (662° F.).
Accordingly, there is a need for a low-evaporation rate, low temperature burnout vehicle that can be used in the formation of a glass frit paste that can be used in a screen printing process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a glass frit paste that can be used in a screen printing process and a method for making the paste.
Another object of the present invention is to provide a vehicle that can be used in the formation of the glass frit paste and a method for making such a vehicle.
To make the glass frit paste nitrocellulose is dissolved in a high vapor pressure solvent of the nitrocellulose to make a solution. A portion of the solution is then mixed with alpha-terpineol to form a vehicle. Glass frit is mixed with the vehicle and then ground to form the paste. During the grinding step most of the high vapor pressure solvent evaporates. The resulting paste has a composition comprising about 0.3-12.0 wt. % nitrocellulose, about 0.5-2.0 wt. % of a high vapor pressure solvent of said nitrocellulose, about 14.0-25.0 wt. % alpha-terpineol, and the remainder glass frit.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A vehicle for use in a screen printing method in applying a glass frit paste comprises alpha-terpineol, nitrocellulose and a solvent of nitrocellulose, such as amyl-acetate or ethylene glycol monoethyl ether. The solvent is transitional in that it mostly evaporates during the paste making process where the vehicle is mixed with glass frit. The use of the solvent is nonetheless essential because the binder, nitrocellulose, does not dissolve in alpha-terpineol. Due to its low-evaporation rate, the resulting paste is stable in open air and suitable for screen-printing. The vehicle bums out at temperatures below 300° C. (572° F.).
The process to make the vehicle and paste consists of the following steps which preferably occur at room temperature and pressure. First nitrocellulose is dissolved in a high vapor pressure solvent such as amyl-acetate or ethylene glycol monoethyl ether to make a solution. The nitrocellulose preferably constitutes 1 to 15 wt. % of the solution. Next, the solution is mixed with alpha-terpineol. The ratio of solution to alpha-terpineol can range from 1 part solution to five parts alpha-terpineol to 6 parts solution to 1 part alpha-terpineol. The mixing of solution and alpha-terpineol forms the vehicle. The vehicle is then mixed and ground with a glass frit at a ratio that ranges from 2 parts vehicle to 1 part frit to 1 part vehicle to 8 parts frit. A dispersing agent may also be added at this point in the process. The result is the paste. In the preferred embodiment the paste is comprised of about 0.1-18.0 wt. % nitrocellulose; about 0.0-3.0 wt. % of a high vapor pressure solvent; about 8.0-40.0 wt. % alpha-terpineol; and the remainder glass frit In a more preferred embodiment the paste is comprised of about 0.3-12.0 wt. % nitrocellulose; about 0.5-1.9 wt. % of a high vapor pressure solvent; about 14.0-25.0 wt. % alpha-terpineol; and the remainder glass frit. The particular glass frit used is selected to match the expansion properties of the components that are to be sealed together. Examples of such frits are lead borosilicate, copper aluminoborate, lead aluminosilicate, lead zinc borate, zinc borosilicate, zinc bismuthsilicate, alkali zincsilicate, alkali titaniumsilicate and the like. During the mixing and grinding process, the high vapor pressure solvent, (amyl-acetate or ethylene glycol monoethyl ether), mostly evaporates, that is less than 3 wt. % of the solvent is left in the paste after the process is complete.


REFERENCES:
patent: 3966449 (1976-06-01), Foster et al.
patent: 4456549 (1984-06-01), Kano et al.
patent: 4460622 (1984-07-01), Yamaoka et al.
patent: 4567059 (1986-01-01), Yamaoka et al.
patent: 4612433 (1986-09-01), Nagaoka et al.
patent: 4880665 (1989-11-01), Adler et al.
patent: 5242867 (1993-09-01), Lin et al.
patent: 5443786 (1995-08-01), Yokoyama et al.
patent: 5691254 (1997-11-01), Sakamoto et al.
patent: 5702996 (1997-12-01), Kawakami et al.
patent: 5766741 (1998-06-01), Kawakami et al.
patent: 5801108 (1998-09-01), Huang et al.
patent: 5840107 (1998-11-01), Salibay
patent: 6248680 (2001-06-01), Xue et al.
patent: 0092601 (1983-11-01), None
patent: 60137848 (1985-07-01), None
International Search Report dated Sep. 15, 2000.

Affiliated with

Also associated with

Rating

Low temperature burnout screen printing frit vehicle does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Low temperature burnout screen printing frit vehicle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low temperature burnout screen printing frit vehicle will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2617700