Stock material or miscellaneous articles – Composite – Of quartz or glass
Patent
1994-09-29
1997-07-15
Ryan, Patrick
Stock material or miscellaneous articles
Composite
Of quartz or glass
428325, 428410, 428427, 428428, 428432, 428434, 428472, 428913, 65 3013, 65 3014, 65111, 65114, B32B 900
Patent
active
056481721
DESCRIPTION:
BRIEF SUMMARY
This invention concerns glass products, notably sheets of glass with a low alkalines content, notably of the borosilicate type.
The composition of these glasses is such that the sum of the alkaline oxides and alkaline-earth oxides is less than or equal to 15%, with a sodium oxide content less than or equal to 10%. These glasses have special applications, for example, in the field of reinforcing fibres or electronics.
The characteristics, notably the thermal behaviour, of these glasses make them interesting for serving as supports in the electronics sector. In particular, these glasses are used for the production of screens. In these applications it is necessary to protect the supported materials against the possible contaminations that may result from the migration of alkaline ions and alkaline-earth ions originating from the support. This is the case, for example, when the materials deposited on the glass substrate are of the semiconductor type and the migration of the mobile ions appreciably alters their essential qualities.
For avoiding this type of difficulty, in the electronics field, it has been proposed to use sheets of glassy the composition of which is virtually devoid of alkaline and alkaline-earth oxides. These glass-making compositions may be such that the sum of the alkaline oxides and alkaline-earth oxides, mainly sodium oxide, is between 500 and 1,000 ppm. These glass sheets server notably, as substrates for flat screens. used in electronics.
It is known that the alkaline oxides have an important influence upon the properties of the vitrifiable mixture; in particular, they enable the viscosity at a given temperature to be reduced and the melting of the mixture to be improved. For these reasons a glass-making composition having a low alkaline content presents many difficulties in processing.
Another solution to the problem of the migration in glasses containing alkaline ions and alkaline-earth ions is to deposit a surface film based upon silica. This deposition may be carried out by pyrolysis, CVD, deposition under vacuum etc. This technique does, however, require an excellent preparation of the surface of the glass sheet intended to be covered with this film, in order to remove any pollution. This preparation is time-consuming and meticulous. Furthermore, even an excellent preparation does not enable the risks of delamination, which will be discussed later, to be averted.
An objective of the invention is to propose a glass which, simultaneously, offers a certain facility of processing and does not allow the alkaline ions and/or alkaline-earth ions forming part of its composition to migrate.
Another objective of the invention is to propose a glass sheet capable of replacing the glass sheets in which the composition is virtually devoid of alkaline ions, for particular applications such as electronics.
Another objective of the invention is to propose the means of production of this glass.
The present invention concerns a sheet of glass having a low content of alkaline ions and alkaline-earth ions, at least one of the faces of which has a surface zone virtually devoid of alkaline ions.
A glass sheet according to this invention is constituted of a glass, in the composition by weight of which the sum of the alkaline and alkaline-earth oxides is less than or equal to 15% with a sodium oxides content less than or equal to 10%.
The alkaline oxides content is, preferably, according to this invention less than or equal to 8%. Although the use of glasses having a low content of alkalines is satisfactory according to this invention, this content must not be too low so that the glass can be processed, as will be explained later. It is necessary, in fact, for the glasses in question to have a sufficient ionic conduction at the processing temperatures envisaged. To obtain a satisfactory conduction, the content of alkaline ions is, preferably, not less than 0.1%. The content of alkaline ions is, with advantage, between 2 and 8%.
In view of the low alkaline content and in order to maintain relatively low fusi
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Database WPI Derwent Publications Ltd, London GB AN 86-141359.
Geoffroy Catherine
Jousse Didier
Vilato Pablo
Bahta Abraham
Ryan Patrick
Saint-Gobain Vitrage International
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