Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-05-08
2004-05-25
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S450000, C428S448000, C428S698000, C428S209000, C428S702000, C428S913000, C428S690000, C427S255180, C427S255190, C427S255280, C427S255600, C427S255700
Reexamination Certificate
active
06740416
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aerogel substrate comprising an aerogel layer and a functional layer formed on a surface of the aerogel layer and a process for the production of the substrate.
BACKGROUND ART
An aerogel, particularly a silica aerogel has characteristic properties such as a heat insulating property, an electrically insulating property, a low refractive index and a low dielectric constant. Studies have been made to apply the aerogel to various fields using its properties. For example, a highly functional substrate can be manufactured by forming a thin film of a silica aerogel on a surface of a plate member such as a glass plate and so on and further forming a functional thin film on a surface of the silica aerogel thin film. For example, in the case where an electrically conductive metal (such as copper) thin film is formed as the functional thin film on the surface of the silica aerogel thin film and a circuit is formed with the electrically conductive metal thin film, a circuit board can be obtained in which the low dielectric constant of the silica aerogel is utilized.
The silica aerogel is prepared by hydrolyzing an alkoxysilane (which is referred to also as a silicon alkoxide or an alkyl silicate) followed by polycondensation of the alkoxysilane to obtain a gel compound, and drying the gel compound in the presence of a dispersion medium under supercritical conditions exceeding a critical point of the solvent, as disclosed in U.S. Pat. Nos. 4,402,927, 4,432,956 and 4,610,863. Further, as disclosed in Japanese Patent Kokai Publications Nos. 5-279011 and 7-138375, a hydrophobing treatment (a treatment for making a silica aerogel hydrophobic) improves moisture resistance of the silica aerogel and prevents deterioration of characteristic properties of the silica aerogel.
DISCLOSURE OF INVENTION
In order to produce a highly functional substrate using an aerogel such as a silica aerogel, it is required that a functional thin film is formed uniformly on a surface of the aerogel. However, it is difficult to form the thin film uniformly on the surface of the aerogel since the aerogel is a porous material. For this reason, a highly functional substrate in which an aerogel is used has not currently been put to its practical use.
The present invention has been accomplished in the light of the circumstances as described above, of which object is to provide an aerogel substrate which comprises an aerogel layer and a functional layer formed uniformly on a surface of the aerogel layer, and a process for producing the aerogel substrate.
In the first aspect, the present invention provides an aerogel substrate which comprises an aerogel layer, an intermediate layer which is formed on at least one surface of the aerogel layer and a functional layer which is formed on a surface of the intermediate layer, the functional layer being formed on the surface of the intermediate layer without penetration of a material constituting the functional layer into the aerogel layer.
“Without penetration of a material constituting the functional layer into the aerogel layer” means that penetration of the material(s) which constitutes the functional layer into the aerogel layer through pores in the aerogel layer does not occur during and after formation of the functional layer. Such functional layer constitutes the aerogel substrate as a uniform layer (e.g. a thin uniform film) of which surface is continuous with a small surface roughness and performs a predetermined function well.
The aerogel substrate of the present invention is obtained by making the intermediate layer as a layer which prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer. “Preventing the material(s) which constitutes the functional layer from penetrating into the aerogel layer” means preventing the material(s) which forms the functional layer from penetrating into the aerogel through the pores in the aerogel layer during and after the formation of the functional layer. In the case where the formation of the functional layer involves a material which does not remain in the functional layer ultimately (for example, a solvent which evaporates by drying), the intermediate layer prevents also the penetration of such material. Therefore, the functional layer which is formed on the surface of the intermediate layer is a uniform layer (e.g. a thin uniform film) of which surface is continuous with a small surface roughness.
It is not necessarily needed that the intermediate layer completely prevents the penetration of the material(s) which constitutes the functional layer into the aerogel layer. As long as the functional layer is formed so uniformly that it can perform a desired function depending on its use or the like, it is acceptable that only a small amount of the material(s) constituting the functional layer penetrates into the aerogel layer. For example, in the case where the intermediate layer is not continuous in a part thereof and micropores (such as pinholes) are formed in the intermediate layer, even if the material(s) constituting the functional layer penetrates into the aerogel layer through the micropores, such penetration is accepted as long as the functional layer is formed uniformly as a whole and performs the desired function.
Alternatively, the aerogel substrate according to the present invention may be constructed by combining a specific intermediate layer with a specific aerogel layer and further selecting a specific material(s) which constitutes the functional layer (such as specific material(s) including a material (such as a solvent to be evaporated by drying) which is used only in the step of forming the functional layer), so that the material(s) constituting the functional layer may penetrate into the intermediate layer, but cannot penetrate into the aerogel layer from the intermediate layer. Such aerogel substrate is realized, for example, by making properties of the intermediate layer different from those of the aerogel layer so that the material(s) constituting the functional layer has an affinity for the intermediate layer and does not have an affinity for the aerogel layer.
In any aerogel layer, the intermediate layer may be a layer which is separately formed on a surface of the aerogel layer, or a layer which is formed by transmuting a part of the aerogel layer. The intermediate layer which is formed by the transmutation of the aerogel layer is substantially inseparably unified with the aerogel layer which is not transmuted, but it is not included in the “aerogel layer” which constitutes the aerogel substrate of the present invention. However, in the case where the intermediate layer is formed by the transmutation of the surface of the aerogel layer, “a surface of the aerogel layer” refers to a surface of the intermediate layer so far as a particular mention is not made.
Any one of the aerogel substrates of the present invention can be said to be a functional substrate of which functional layer can perform a predetermined function. In this specification, the term “substrate” is used in a sense as including a plate member (including a plate, a sheet and a film) of which thickness dimension is considerably smaller than the other dimensions, and a rectangular solid and a cube which have a thickness dimension which is of generally the same order as those of the other dimensions. The substrate includes a plate, a rectangular solid and a cube in which a part of surface is curved. Therefore, each layer which constitutes the aerogel substrate may be in the form of a plate, a sheet, a film, a rectangular solid, or a cube depending on the final form of the aerogel substrate.
The embodiments of the aerogel substrates according to the present invention will be described below.
In the first aspect of the present invention, the first embodiment of the aerogel substrate is an aerogel substrate comprising a hydrophobic aerogel layer, a hydrophilic layer which is formed by subjecting at least one surface of the hydrophobic aerogel layer to a hydroph
Kawano Kenji
Sonoda Kenji
Tsubaki Kenji
Yokogawa Hiroshi
Yokoyama Masaru
Jones Deborah
Matsushita Electric & Works Ltd.
Xu Ling
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