Nanocomposite coatings

Details Nanocomposite coatings Nanocomposite coatings

2002-05-13

2004-11-09

Wyrozebski, Katarzyna (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S450000, C524S448000, C524S155000, C524S127000

Reexamination Certificate

active

06815489

ABSTRACT:

This invention relates to a composition for forming a coating, and to a coating formed from such composition.
In the literature, it has already been proposed several times to incorporate a layered inorganic filler, such as a clay, into a coating. A difficulty here, however, is that compositions for coatings are normally based on polymeric systems in a diluent. These polymeric systems often have a hydrophobic character, whereas the filler has a more hydrophilic character. This makes the two components intrinsically immiscible.
There are different, more and less successful procedures known for alleviating the problem of the intrinsic immiscibility of the two materials. In most cases, to that end, an ion exchange is carried out, whereby ions between the sheets of the layered filler are exchanged for ions which have an organic character, which makes them compatible with the polymeric matrix.
Although in publications on this subject it is mentioned in most cases that the above-described method for uniting the layered filler and a polymeric matrix relates to both polymeric bulk materials and coatings, in practice only the issues involved in bulk materials are addressed.
In the case of coatings, there is, in addition to the above-outlined problem of the intrinsic immiscibility, another problem. After application, a composition for a coating should cure into a solid coating. This not only requires that the diluent evaporates, but also that a curing reaction occurs. This reaction is mostly initiated and/or catalyzed by heat, oxygen, addition of an extra reactant (crosslinking agent) or light (UV radiation). Of course, the presence of the layered filler should not disturb the curing process. It has been found that this problem has not been adequately resolved yet in the prior art.
In European patent application 0 791 556 a water-dispersible organic clay complex is described, in which a quaternary ammonium ion is present in the interlamellar space of an expansible phyllosilicate. The ammonium ion comprises an oxypropylene unit and an oxyethylene unit. The complex is used for controlling the rheology of a water-based coating agent.
The international patent application 98156598 relates to a barrier coating consisting of an elastomer and a dispersed, layered filler in a liquid carrier. The coating is used in particular in (car) tires. In order to enable proper dispersion of the filler, which is preferably vermiculite, and the elastomer, in the liquid carrier, use is made of a surfactant. Examples of suitable surfactants that are mentioned are known wetting agents, antifoam agents, emulsifiers, dispersing agents and the like. Preferably, nonionic surfactants are used.
The object of the present invention is to provide a coating composition comprising a layered, functional inorganic filler, a polymeric matrix and a diluent, which does not have the disadvantages of the known compositions. What is contemplated in particular is that the composition, after being applied, cures to form a coating having very good properties, in particular barrier properties. It is then desirable that the filler has no or hardly any adverse effect on the curing reaction of the composition. What is further contemplated is for the filler to be homogeneously dispersed through the composition.
Surprisingly, it has presently been found that these objects can be achieved by subjecting the layered, inorganic filler to an ion exchange with a modifier before incorporating the filler in a composition for a coating, which modifier comprises at least two ionic groups, which groups are separated from each other by at least four atoms. Thus, the invention relates to a method for preparing a composition for a coating, wherein a layered, inorganic filler is subjected to an ion exchange with a modifier, which modifier comprises at least two ionic groups, which groups are separated from each other by at least four atoms, and wherein the modified filler, together with a polymer, is dispersed in a diluent.
What is achieved according to the invention by the use of the specific modifier is that the layered inorganic filler together with the polymer is homogeneously dispersed in the diluent. Further, it has been found that the modified filler substantially does not have any adverse effect on the curing of the composition when it has been applied for forming a coating. The cured layer has particularly favorable properties, such as a reduced permeability to gases and liquids, and an improved heat resistance. Further, the coating has been found to possess improved surface properties (resistance to scratches and the like), without this affecting the bonding of the layer to a substrate or the flexibility of the layer.
The layered inorganic filler which is used according to the invention can be both cationic and anionic in nature. In principle, any anionic or cationic filler obtained synthetically or from a natural source can be used. Suitable examples can be selected from the classes of clays and layered double hydroxides.
Eminently suitable are clay types based on layered silicates, such as layered phyllosilicate which is made up of magnesium and/or aluminum silicate layers each about 7-12 Å thick. Particularly preferred are smectite-type clay minerals such as montmorillonite, saponite, hectorite, fluorohectorite, beidellite, nontronite, vermiculite, halloysite and stephanite. These materials impart very favorable mechanical properties and an increased thermal stability to a coating.
A suitable clay type preferably has a cation exchange capacity of 30 to 250 milliequivalents per 100 grams. When that capacity is higher than the upper limit mentioned, it proves to be difficult to finely disperse the clay at a molecular level because of the strong mutual interaction of the layers of clay. When the cation exchange capacity is lower than the lower limit mentioned, the clay proves to be difficult to modify in that the interaction with the modifier is small. Preferably, a clay is used having a cation exchange capacity of from 50 to 200 milliequivalents per 100 grams.
Another layered, inorganic filler that can be used according to the invention is a layered double hydroxide (LDH). This material is a so-called anionic clay, consisting of small crystalline sheets of dimensions of a few nanometers, between which anions are located. By these anions are meant anions other than hydroxyl groups. A layered double hydroxide can be both natural and synthetic in nature. For a description of possible methods of preparation for a synthetic layered double hydroxide, reference is made to U.S. Pat. Nos. 3,539,306 and 3,650,704.
Preferably, the layered double hydroxide has a large contact surface and an ion exchange capacity of 0.5 to 6 milliequivalents per gram. An LDH preferably used is a hydrotalcite or a hydrotalcite-like material, because these materials can be easily prepared synthetically, while the desired properties can be eminently controlled.
Found to be uncommonly suitable are hydrotalcites that satisfy the formula (I):
[M
1-x)
2+
M
x
3+
(OH)
2
] [A
x/y
y−
.n H
2
O]  (I),
wherein M
2+
is a bivalent cation, M
3+
is a trivalent cation, x is a number between 0.15 and 0.5, y is 1 or 2, n is a number from 1 to 10, and A is an anion selected from the group consisting of Cl—, Br—, NO
3
—, SO
4
2
— and CO
3
2
—. The bivalent cation is preferably selected from the group of bivalent magnesium, zinc, nickel, iron, copper, cobalt, calcium and manganese ions and combinations of these bivalent cations. Most preferably, the bivalent cation is a magnesium, zinc or calcium ion or a combination thereof. The trivalent cation is preferably selected from the group of trivalent aluminum, chromium, iron, cobalt and manganese ions and combinations of these trivalent cations. Most preferably, the trivalent cation is an aluminum, chromium or iron ion or a combination thereof
It is preferred that the filler, when it is being processed according to the invention, contains substantially no agglomerates of sheets which f

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