Glass manufacturing – Processes – Forming product or preform from molten glass
Reexamination Certificate
2000-09-15
2003-07-22
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
Forming product or preform from molten glass
C065S026000, C065S030130, C065S031000, C065S060500, C065S060530, C065S060700, C065S060100, C065S126000, C065S187000, C065S191000, C065SDIG009, C427S011000, C427S133000, C427S230000
Reexamination Certificate
active
06595029
ABSTRACT:
The invention relates to a process for the production of internally-hardened glass tubes, devices for performing the process as well as uses of the tubes that are produced according to the process.
For numerous applications of glass tubes or of glass molded elements that are formed from glass tubes (semifinished products), high chemical resistance is necessary.
Hollow glass molded elements, which require an elevated chemical resistance of the inside surface, are, for example, those
for chemical plant production
which are used for flowmeters for chemically aggressive media
for analytical purposes (e.g., burette tubes, titration cylinders, etc.)
for reagent glasses for special purposes
for sheathings for measurement electrodes in aggressive media
for lighting purposes, e.g., halogen lamps
for discharge lamps
which are used as components for biotechnological reactors, and
which are used as containers for medical purposes (e.g., ampoules, vials, syringe bodies, cylinder ampoules, etc.).
It is known to produce glass tubes from silica glass (quartz glass, SiO
2
glass) as semifinished products for shaping hollow glass molded elements, which have a very high chemical resistance. Such tubes are very production-intensive and costly, however, because of the high melting point of the SiO
2
glass; they can also be produced only with limited optical quality and are not well suited for mass production. In addition, such tubes can be deformed only with very special devices, since, on the one hand, the deformation temperatures are very high, and, on the other hand, the temperature range in which deformations are possible is very small.
Semifinished product-glass tubes made of silica glass therefore cannot be produced with sufficient quality and economic efficiency for mass applications.
Predominantly low-melting glasses, e.g., borosilicate glasses or soda-lime glasses are therefore used for industrial glass tube products. The latter can be advantageously economically produced and deformed as tubes.
Processes that increase the chemical resistance of the inside surface of such glass tubes made of low-melting glass are already known.
Processes in which the glass surface is chemically leached out are known.
In this respect, a correspondingly aggressive gas, typically SO
2
or HCl gas, is introduced into the still hot glass tube, which results in surface reactions and reduction of the alkali content in the surface.
Such dealkalizing processes are described in, e.g., H. A. Schaeffer et al.; Glastechn. Ber. 54 (1981) No. 8, pp. 247-256. The drawbacks of these processes are that mainly toxic gases are used, whereby the glass surface still can contain traces of these aggressive reaction gases according to the chemical treatment, and that the glass surface structure is damaged, which results in an increased surface area and in active centers of the surfaces. The use of such aggressive gases from environmental standpoints and worker-safety conditions is also disadvantageous. During deformation of such leached-out glass tubes, particles from the porous, damaged surface can dissolve. A washing process for removing the reaction products is also necessary before the leached-out glass tubes are used. This washing process makes necessary a subsequent drying and disposability of the reaction products, i.e., it increases the costs for the production of semifinished-product-glass tubes.
U.S. Pat. No. 3,314,772 describes another process for dealkalization of low-melting glass by fluorination using fluorine-containing compounds, e.g., aqueous HF solutions, which has the same typical main drawbacks as the other previously described processes for dealkalization.
To avoid the drawbacks of the dealkalization process, it is also known to provide tube-like glass containers that consist of low-melting glass, which are used especially as packaging for pharmaceutical materials, on their inside surface with a silicon oxide (SiO
2
) layer, which is comparable in its inertness to a quartz glass surface (M. Walther, “Packaging of Sensitive Parenteral Drugs in Glass Containers with a Quartz-like Surface” from Pharmaceutical Technology Europe, May 1996, Vol. 8, No. 5, pages 22-27.
The coating of the inside surface of the formed glass molded element is carried out in this case by chemical deposition of oxidic coating material from its gas phase, especially using a vacuum-supported plasma-CVD process (PECVD=plasma-enhanced chemical vapor deposition), and especially using a pulsed plasma (PICVD=plasma-pulse-chemical-vapor deposition).
In the known case (DE 296 09 958 U1), the finish-formed containers, i.e., the glass molded elements themselves, are coated inside. As a result, each glass form container per se, matched to its form, must be subjected to an expensive coating process.
A feature of the invention is now to harden glass tubes that produce the semifinished product for the various hollow glass molded elements in a simple way on their inside surface.
In a tube-drawing process that is known in the art for the production of glass tubes, a coated drawing tool is used, for example in the Danner process as disclosed in U.S. Pat. No. 1,218,598; a coated Danner mandrel, or in the Vello process a coated Vello needle (see Heinz G. Pfaender, “Schott Guide to Glass,” Chapman & Hall, pp. 93-94 (1996 edition)) whereby the improvement is a coating that releases coating material to the glass surface upon contact with the inside surface of the tube that is produced.
By this “doping,” the inside surface of the finished tube is hardened. It is passivated and has an elevated chemical resistance.
The release of the coating material should achieve a sufficient effect such that at least 1.5 &mgr;g/(m
2
s) of the coating surface is released from the coating. The general release rate of the coating surface can be from about 1.5−about 15 &mgr;g/(m
2
s), the preferred release rate of the coating surface can be≧about 5.0 &mgr;g/(m
2
s), and the optimal release rate of the coating surface can be about 15 &mgr;g/(m
2
s). This is ensured by the material that is used and its surface composition.
Suitable coating materials are inorganic materials, e.g., nitrides or preferably oxides, which are themselves sufficiently inert against water, acid or lye attack and in which sufficient diffusion and solution processes on the coating/glass interfaces occur at the temperatures and viscosities in this process step (about 700° C.-1400° C. and about 10
3.3
dPas-10
7.3
dPas). In the case of glasses with a transformation temperature of T
9
<500° C., only very small diffusion and solution amounts are produced because of the low process temperatures, and no significant degree of concentration of the coating material occurs on the inside tube surface. Since the time of contact between glass and coating is limited, coating materials with relatively high diffusion coefficients are effective.
Preferred materials have diffusion coefficients of at least 1×10
−13
m
2
/s at operating temperature. The diffusion coefficients that are indicated for the materials relate to a temperature range of about 800° C. to about 1200° C., which is in the range of the operating temperatures (see above: temperatures in the process step): e.g., ZrO
2
: ≈3.8×10
−11
; with concentration proportions of about 0.1-5% by weight of RN, R
3
N
4
, RO
2
, RO, R
2
O
3
, doped SiO
2
: ≈7.7×10
−11
; Al
2
O
3
: ≈1×10
−13
. Especially suitable are ZrO
2
, Al
2
O
3
, SiO
2
, MgO and mixtures thereof, mullite, mixtures of the above-mentioned oxides with about 0.1-20% by weight of RO
2
, RO, R
2
O
3
, RN, R
3
N
4
, e.g., with Y
2
O
3
, or spinel (MgAl
2
O
4
) where R is Y, Ca, Mg, K, Si, Al, B, Ti, Mn, or Co. Coatings that consist of ZrO
2
or with proportions of ZrO
2
, especially with proportions of at least 5% by weight of ZrO
2
, are especially preferred.
The coating can be applied with the commonly used processes to the drawing tool, which include, i.a., ceramic materials such as chamotte, sillimanite, zirconium oxide, zirc
Dick Erhard
Fischer Erich
Fuchs Roland
Colaianni Michael
Millen White Zelano & Branigan P.C.
Schott Spezialglas GmbH
LandOfFree
Process for devices for the production of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for devices for the production of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for devices for the production of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3076168