Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
1999-11-12
2001-09-18
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
Reexamination Certificate
active
06291070
ABSTRACT:
The present invention relates to nanostructured moulded articles and layers as well as to processes for their production. Particularly, the present invention relates to nanostructured moulded articles and layers which can be produced by means of a wet chemical process.
Nanostructured materials have been known for quite a while. They are usually prepared by densification of nanoscaled particles having diameters in the lower nanometer range by a suitable process (see, e.g., H. Gleiter, Nanocrystalline Materials, Pergamon Press, Oxford, 1989). This is done mostly under high pressure, taking advantage of the high diffusion rates in the outer districts of the nanoscaled particles. Under the action of pressure (and as the case may be, simultaneous action of elevated temperatures) a densification to form dense articles takes place thereby. Corresponding wet chemical processes such as, e.g., the sol-gel process usually result in porous gels since, although due to the high surface activity of the particles a bonding thereof takes place, a tight joining together of the particles and a filling of the gussets does not occur. Materials prepared by such processes are uniform, i.e., they have interfacial phases the composition whereof is not (significantly) different from that of the particle phase (only the gaseous phase of the environment may be additionally present).
It has now surprisingly been found that if said nanoscaled particles are provided with polymerizable and/or polycondensable organic surface groups and said surface groups are polymerized and/or polycondensed, systems of nanostructured materials equivalent or even superior to those which have so far been prepared via the dry route are available via the wet chemical route. Particularly, highly transparent materials are also available via said route since due to the small distances between the particles (one to a few nm) the correlation lengths for the Raleigh scattering are not reached.
Subject of the present invention thus is a process for the production of nanostructured moulded articles and layers comprising the following steps:
a) provision of a free-flowing composition which contains solid nanoscaled inorganic particles having polymerizable and/or polycondensable organic surface groups;
1) introduction of the composition of step a) into a mould; or
2) application of the composition of step a) onto a substrate;
c) polymerization and/or polycondensation of said organic surface groups of said solid inorganic particles with formation of a cured moulded article or a cured layer.
It may be advantageous in many cases to conduct, subsequent to the above step c), a thermal post-treatment of said cured moulded article or said cured layer, respectively, preferably at a temperature ranging from 60 to 150° C., particularly from 80 to 130° C.
Alternatively or in addition thereto, a (further) thermal densification of said moulded article or said layer, respectively, at a temperature of at least 250° C., preferably at least 400° C. and particularly at least 500° C., may be effected. In the case of a layer on a substrate thermal densification may naturally only be carried out if the substrate material can resist such high temperatures without impairment, as this is the case with, e.g., glass and many metals and metal alloys, respectively (but also with some plastics).
In some cases it may be recommendable to carry out a (further) thermal densification at temperatures ranging from 800 to 1500° C., preferably 1000 to 1400° C.
(Post-)treatment at temperatures of at least 350° C. generally makes it possible to utilize said solid nanoscaled inorganic particles as firm precursor for the production of an exclusively inorganic solid.
In the present description and the appended claims the term “solid nanoscaled inorganic particles” is to denote particles having a mean particle size (a mean particle diameter) not exceeding 200 nm, preferably not exceeding 100 nm and particularly not exceeding 70 nm. A particularly preferred range of particle sizes is from 5 to 50 nm.
The solid nanoscaled inorganic particles may consist of any material but preferably they consist of metals and particularly of metal compounds such as (optionally hydrated) oxides, such as ZnO, CdO, SiO
2
, TiO
2
, ZrO
2
, CeO
2
, SnO
2
, Al
2
O
3
, ln
2
O
3
, La
2
O
3
, Fe
2
O
3
, Cu
2
O, Ta
2
O
5
, Nb
2
O
5
, V
2
O
5
, MoO
3
or WO
3
; chalcogenides such as sulfides (e.g. CdS, ZnS, PbS and Ag
2
S), selenides (e.g. GaSe, CdSe and ZnSe) and tellurides (e.g. ZnTe or CdTe), halides such as AgCl, AgBr, Agl, CuCl, CuBr, Cdl
2
and PbI
2
; carbides such as CdC
2
or SiC; arsenides such as AlAs, GaAs and GeAs; antimonides such as InSb; nitrides such as BN, AIN, Si
3
N
4
and Ti
3
N
4
; phosphides such as GaP, InP, Zn
3
P
2
and Cd
3
P
2
; phosphates, silicates, zirconates, aluminates, stannates and the corresponding mixed oxides (e.g. those having a perovskite structure such as BaTiO
3
and PbTiO
3
).
Preferably, the solid nanoscaled inorganic particles employed in step a) of the process according to the present invention are those of oxides, sulfides, selenides and tellurides of metals and mixtures thereof. Particularly preferred according to the present invention are nanoscaled particles of SiO
2
, TiO
2
, ZrO
2
, ZnO, Ta
2
O
5
, SnO
2
and Al
2
O
3
(in any modification, particularly in the form of boehmite, AlO(OH)) as well as mixtures thereof.
Since the nanoscaled particles employable according to the present invention cover a broad range of refractive indices, the refractive index of a moulded article or a layer, respectively, can conveniently be set at the desired value by appropriately selecting said nanoscaled particles.
The production of the nanoscaled solid particles employed according to the present invention may be effected in usual manner, e.g., by flame pyrolysis, plasma processes, condensation processes in the gas phase, colloid techniques, precipitation processes, sol-gel processes, controlled nucleation and growth processes, MOCVD processes and (micro)emulsion processes. Said processes are described in detail in the literature. Particularly, metals (for example following the reduction of the precipitation processes), ceramic oxide systems (by precipitation from solution) but also salt-like or multicomponent systems may, for example, be used. The salt-like or multicomponent systems also encompass semiconductor systems.
The preparation of said solid nanoscaled inorganic particles provided with polymerizable and/or polycondensable organic surface groups may on principle be carried out via two different routes, i.e., on the one hand by surface modification of preformed solid nanoscaled inorganic particles and, on the other hand, by preparation of said solid nanoscaled inorganic particles using one or more compounds having such polymerizable and/or polycondensable groupings. Said two approaches will be explained in more detail further below and in the examples.
Said organic polymerizable and/or polycondensable surface groups may be any groups known to the skilled person which can undergo a radical, cationic or anionic, thermal or photochemical polymerization or thermal or photochemical poly-condensation (optionally in the presence of a suitable initiator or catalyst, respectively). Surface groups which are preferred according to the present invention are those having a (meth)acrylic, acrylic, vinylic or epoxy group, (meth)acrylic and epoxy groups being particularly preferred. Among the polycondensable groups hydroxy, carboxy and amino groups may particularly be cited, said groups making it possible to obtain ether, ester and amide linkages between said nanoscaled particles.
According to the present invention it is also preferred that said organic groups present on the surfaces of said nanoscaled particles and comprising said polymerizable and/or polycondensable groups have a relatively low molecular weight. In particular, the molecular weight of said (purely organic) groups should not exceed 500 and preferably not exceed 300, particularly preferred not exceed 200. Of course this
Arpac Ertugrul
Krug Herbert
Mueller Peter
Oliveira Peter W.
Schmidt Helmut
Boykin Terressa M.
Heller Ehrman White & McAuliffe LLP
Institut fur Neue Materialien gemeinnutzige GmbH
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