Nanocomposite for thermal insulation

Details Nanocomposite for thermal insulation Nanocomposite for thermal insulation

1999-11-12

2002-11-12

Lovering, Richard D. (Department: 1712)

Stock material or miscellaneous articles

Composite

Of quartz or glass

C106S018120, C106S490000, C252S062000, C516S100000, C516S101000, C428S404000, C428S921000

Reexamination Certificate

active

06479156

ABSTRACT:

The present invention relates to a nanocomposite for thermal insulation (e.g., fireproofing), in particular, to a preferably transparent nanocomposite that is suitable as a filler for insulation glass assemblies.
Particularly when in contact with their solution phase, known solvent-containing inorganic gels show ageing phenomena that manifest themselves in shrinking in combination with haze, blistering as well as possibly cracking. Said signs of ageing are often summarized under the term syneresis, and in the literature they are explained by progressive condensation reactions and phase separation.
A gelled dispersion of SiO
2
particles in water, for example, can be prepared by concentrating diluted colloidal silica sol solutions. Upon gelation, the individual SiO
2
particles initially develop hydrogen bonding between them until Si—OH groups condense to form Si—O—Si bonds that cannot be cleaved anymore. Due to said rigid Si—O—Si bonds the gel becomes increasingly brittle and finally breaks under the influence of the capillary forces of the contained solvent and due to tensile stress caused by the shrinkage of the gel body.
It is known that reactive groups can be shielded by surface charges so that said syneresis-active groups are separated from each other. A well-known example thereof is the stabilization of SiO
2
with bases such as tetramethylammonium hydroxide. Said surface modification by charges is effective in preventing syneresis, however at the expense of a lack of immobilization since there is not sufficient interaction between the particles. Additionally, only relatively diluted solutions can be prepared in this manner since, if the particles come too close to each other, the shielding by charges breaks and a spontaneous gel formation occurs, resulting in a loss of the blocking of said syneresis.
For certain applications, e.g., as transparent filling between (fire protection) panes, it is necessary to employ gels which stay clear, without the ageing phenomena mentioned above, for extended periods of time. It is also important that said gels exactly maintain their shape when being filled into, e.g., spaces of complex shape in door or wall units made of different materials. Here it is also of particular importance that even at relatively high solids contents, no ageing phenomena due to solvents may occur. This is difficult because the natural ageing process via solution phases, which proceeds according to the Ostwald mechanism, usually cannot be avoided. However, high solids contents are necessary if such systems are to be used as heat protection. Upon the action of heat a foam having fine pores which acts as insulation is formed, as is known in the case of waterglass. A sufficiently high insulation effect as it is, e.g., required in the case of a fire (see, e.g., DIN 4102) can in turn only be realized by very thick fillings or multiple pane assemblies, which result in a very high weight of the system and thus limit the possible applications thereof.
The present invention, therefore, was based on the problem of providing gel systems which make it possible to obtain a sufficiently high solids content, while being absolutely free of syneresis, as well as layer thicknesses (as heat protection) which are significantly below the present state of the art and also provide long-term transparency, which is particularly indispensable in the case of transparent walls.
It has now surprisingly been found that transparent, solid gel materials which do not show ageing phenomena can be prepared by combining nanoscaled particles of inorganic solids with specific organic compounds which shield the groups that are responsible for said syneresis but at the same time develop sufficiently strong bonding forces which are necessary to form a mechanically stable gel body.
Due to the use of particles in the nm range, light scattering is so minimal that sufficient transparency can be ensured. Furthermore, the matrix structure at the interface with the particle is altered and, due to its high proportion, plays a decisive role in the overall properties of the system.
By employing the principle described above, solid and colorless nanocomposite gels which are stable against syneresis may thus be prepared by dispersing inorganic (preferably oxidic) particles in the presence of suitable substances which, on the one hand, protect syneresis-active groups of said colloidal particles and, on the other hand, still effect a certain degree of crosslinking of the particles.
Thus, an object of the present invention is a nanocomposite for thermal insulation, said nanocomposite being obtainable by combining
(A) at least 35% by wt. of nanoscaled, optionally surface-modified particles of inorganic compound;
(B) 10-60% by wt. of compound having at least two functional groups capable of reacting and/or interacting with the surface groups of said nanoscaled particles (A);
(C) 1-40% by wt. of water and/or inorganic solvent which has no or only one functional group as defined above under (B); the above percentages being based on the sum of said components (A), (B) and (C); as well as
(D) 0-10% by wt., based on said nanocomposite, of additives.
Preferably, the nanocomposite just defined is a transparent material which in its final state is present as a rigid (solidified), solid gel.
In the following, the materials constituting the nanocomposite according to the present invention will be described in more detail.
Component (A) consists of nanoscaled particles of inorganic compound. As used in the present specification and in the claims, the term “nanoscaled particles” refers to particles having an (average) particle size of up to 200 nm, preferably up to 100 nm and particularly up to 50 nm. A particularly preferred particle size ranges from 1-20 nm. For producing said nanocomposite said particles are to be employed in an amount of at least 35%, preferably at least 40%, and particularly at least 45% by wt., based on said components (A), (B) and (C).
Generally, said particles are particles of inorganic oxidic compounds, particularly of oxides of the elements aluminum, silicon, phosphorus, boron, tin, zinc, titanium, zirconium, tungsten, and the alkali and alkaline earth metals as well as of the mixed oxides of any of the oxides just mentioned, (mixed) oxides of Si, Al, Ti and/or Zr being preferred, and SiO
2
and mixed oxides thereof being particularly preferred. However, according to the present invention, inorganic compounds different from oxides, such as carbides, nitrides, silicides, borides and the like, may also be employed.
Said particles may either be employed as such or may also only be formed in situ by suitable processes (well-known to the person skilled in the art).
Furthermore, said particles may optionally be surface-modified. The surface modification of nanoscaled (particularly oxidic) particles is known from the prior art and described, e.g., in DE-A-42 12 633.
As described above, component (B) of the nanocomposite of the present invention serves to shield said nanoscaled particles of component (A) in a manner such that, on the one hand, ageing phenomena due to interparticular reactions may be avoided in said nanocomposite and, on the other hand, the particles will still be sufficiently bonded to each other (crosslinked) so that a solid, mechanically stable gel body is provided.
Component (B) accounts for 10 to 60% by wt., based on the components (A), (B) and (C) of the nanocomposite of the present invention. Preferably, component (B) is employed in an amount of from 15 to 45% and particularly 20 to 35% by wt., 20 to 30% by wt. of component (B) being particularly preferred.
Component (B) consists of one or more, particularly one, compound (preferably of organic or inorganic/organic nature) having at least two, preferably at least three (and in most cases less than 50) functional groups capable of reacting and/or interacting with surface groups present on the surface of said nanoscaled particles (A). The surface groups of said nanoscaled particles (A) are either those which are present due to the inorgani

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