Composite materials

Details Composite materials Composite materials

1999-05-03

2001-09-11

Cameron, Erma (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S388100, C427S388400, C427S389900

Reexamination Certificate

active

06287639

ABSTRACT:

The invention relates to composite materials characterized by a substrate and by a nanocomposite which is in functional contact with the substrate and is obtainable by surface modification of
a) colloidal inorganic particles with
b) one or more silanes of the general formula (I)
R
x
—Si—A
4−x
  (I)
where the radicals A are identical or different and are hydroxyl groups or groups which can be removed hydrolytically, except methoxy, the radicals R are identical or different and are groups which cannot be removed hydrolytically and x is 0, 1, 2 or 3, where x ≧1 in at least 50 mol % of the silanes;
under the conditions of the sol-gel process with a sub-stoichiometric amount of water, based on the hydrolysable groups which are present, with formation of a nanocomposite sol, and further hydrolysis and condensation of the nanocomposite sol, if desired, before it is brought into contact with the substrate, followed by curing, said substrate not being a glass or mineral fibre or a vegetable material.
The substrate may be of very different physical forms, and be, for example, particulate, flocculent, fibrous, strip-shaped, plate-shaped, foil-shaped, sheet-shaped or block-shaped, or have a layered structure, or be a shaped article of any desired shape. The term “particulate” includes powders, flours, granules, chips, slivers, globules, beads and generally any particle with a regular or irregular shape.
The nanocomposite, too, may be distributed in many different forms. It may, for example, cover the substrate entirely or partially, as a continuous coating or covering, or may be similar to a laminate between a number of substrates. Specific examples of composite materials of this type are fibre composites based on aramids or carbon fibres, metal substrates provided with high-temperature anti-corrosion layers, fibres, twines, yarns and semifinished products, such as wovens, knits, braids, non-wovens and felts, provided with a thermally stable impregnation, or shaped articles of glass or ceramic which are bonded (laminated) to a metal (e.g. aluminium) foil via the nanocomposite. The nanocomposite can also be employed as stiffening or reinforcement, diffusion barrier layer, extraction barrier layer, oxidation protection layer, electrical insulation layer or for levelling.
The nanocomposite can alternatively form discontinuous or punctiform contacts between a number of substrates and, for example, act as a matrix in bonding a particulate, flocculent or fibrous substrate, as for example in insulating materials.
Suitable substrate materials for the novel composite materials are many different inorganic or organic, natural or synthetic materials.
Examples of suitable substrate materials are non-metals, such as boron and silicon, and metals, such as iron, chromium, copper, nickel, aluminium, titanium, tin, zinc and silver, and corresponding alloys (e.g. brass, steel or bronze) in the form of powders, fibres, films, textiles, sheets and shaped articles; glass materials in the form of powders, flakes, sheets or shaped articles; ceramic materials in the form of powders, fibres, textiles, non-wovens, flakes, sheets and shaped articles; carbon (carbon black, graphite, fullerenes) in the form of powders, fibres, layers, sheets and shaped articles; oxides, such as SiO
2
, Al
2
O
3
, Fe
2
O
3
, Fe
3
O
4
, Cr
2
O
3
, CuO, Cu
2
O, In
2
O
3
, Mn
2
O
3
, PbO, PdO, SnO
2
, TiO
2
, ZnO and ZrO
2
, nitrides, such as BN, Si
3
N
4
and TiN, carbides, such as SiC, TiC and B
4
C, silicides, non-stoichiometric compounds (e.g. SiO
x
C
y
N
z
), composites and hybrid materials in the form of powders and fibres; preferably heat-resistant plastics, such as polyolefins, fluoropolymers, such as Teflon, homo- and copolymers of vinyl halides or vinyl esters, polycarbonates, polyesters, polyurethanes, aramids, polyamides, acrylic resins, silicones and ormocers in the form of fibres, granules, films, felts, textiles, non-wovens, sheets and shaped articles; natural fibres and materials of animal origin, such as wool, fur or leather; and minerals, such as montmorillonites, bentonites, mica, vermiculite, perlite, ferrite, spinels, e.g. magnetite or copper chromium spinel, barytes, fluorspar, asbestos, talc, aerogels, sands and clays.
The term fibrous substrates is taken to mean either individual fibres, including hollow fibres and whiskers, or corresponding fibre bundles, threads, ropes, twines and yarns or semifinished products, such as wovens, knits, braids, textiles, non-wovens, felts, webs and mats. Concrete examples of these are carbon fibres, fabrics made from cotton and synthetics, metal fibres and metal fabrics.
The nanocomposite employed according to the invention is prepared by surface modification of colloidal inorganic particles (a) with one or more silanes (b), if desired in the presence of other additives (c) under the conditions of the sol-gel process.
Details of the sol-gel process are described in C. J. Brinker, G. W. Scherer: “Sol-Gel Science—The Physics and Chemistry of Sol-Gel-Processing”, Academic Press, Boston, San Diego, New York, Sydney (1990) and in DE 1941191, DE 3719339, DE 4020316 and DE 4217432.
Here, specific examples of the silanes (b) which can be employed according to the invention and of their radicals A which are hydrolytically removable and their radicals R which are not hydrolytically removable are given.
Preferred examples of groups A which are removable hydrolytically are hydrogen, halogen (F, Cl, Br and I, in particular Cl and Br), alkoxy (in particular C
2-4
-alkoxy, such as ethoxy, n-propoxy, isopropoxy and butoxy), aryloxy (in particular C
6-10
-aryloxy, such as phenoxy), alkaryloxy (e.g. benzyloxy), acyloxy (in particular C
1-4
-acyloxy, such as acetoxy and propionyloxy) and alkylcarbonyl (e.g. acetyl). Radicals A which are likewise suitable are amino groups (e.g. mono- or dialkyl-, -aryl- and -aralkylamino groups having the abovementioned alkyl, aryl and aralkyl radicals), amide groups (e.g. benzamido) and aldoxime or ketoxime groups. Two or three radicals A may also together form a moiety which complexes the Si atom, as for example in Si-polyol complexes derived from glycol, glycerol or pyrocatechol. Particularly preferred radicals A are C
2-4
-alkoxy groups, in particular ethoxy. Methoxy groups are less suitable for the purposes of the invention, since they have an excessively high reactivity (short processing time of the nanocomposite sol) and can give nanocomposites and/or composite materials with insufficient flexibility.
The abovementioned hydrolysable groups A may, if desired, carry one or more usual substituents, for example halogen or alkoxy.
The radicals R which are not hydrolytically removable are preferably selected from the group consisting of alkyl (in particular. C
1-4
-alkyl, such as methyl, ethyl, propyl and butyl), alkenyl (in particular C
2-4
-alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (in particular C
2-4
-alkynyl, such as acetylenyl and propargyl), aryl (in particular C
6-10
-aryl, such as phenyl and naphthyl) and the corresponding alkaryl and arylalkyl groups. These groups may also, if desired, have one or more usual substituents, for example halogen, alkoxy, hydroxy, amino or epoxide groups.
The abovementioned alkyl, alkenyl and alkynyl groups include the corresponding cyclic radicals, such as cyclopropyl, cyclopentyl and cyclohexyl.
Particularly preferred radicals R are substituted or unsubstituted C
1-4
-alkyl groups, in particular methyl and ethyl, and substituted or unsubstituted C
6-10
-alkyl groups, in particular phenyl.
It is also preferable that x in the above formula (I) is 0, 1 or 2, particularly preferably 0 or 1. It is also preferable if x=1 in at least 60 mol %, in particular at least 70 mol %, of the silanes of the formula (I). In particular cases, it may be even more favourable if x=1 in more than 80 mol %, or even more than 90 mol % (e.g. 100 mol %), of the silanes of the formula (I).
The novel composite materials may be prepared, for example, from pure methyltriethoxysilane (MTEOS) or fr

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