Coating material for multifunctional superphobic layers

Details Coating material for multifunctional superphobic layers Coating material for multifunctional superphobic layers

2001-09-06

2004-09-07

Moore, Margaret G. (Department: 1712)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C106S287100, C106S287130, C106S287160, C106S425000, C106S432000, C106S436000, C428S447000, C524S588000, C524S858000, C528S035000

Reexamination Certificate

active

06787585

ABSTRACT:

The present invention is directed to coating materials which can be used to produce layers which are not only extremely oil- and water-repellent but also IR-reflective. The coating materials are particularly suitable as paints, e.g., as interior paints or masonry paints.
Easy-clean, dirt-repellent or self-cleaning layers are known in a number of variants. For example, there are purely hydrophobic coating systems which are based on nonpolar coating materials. Where not only an oil/fat-repellent but also a water-repellent finish is required, fluorine components are generally employed. Thus, DE-A-41 18 184 reported that layers containing fluorine or fluorosilane may exhibit anti-adhesion (hydrophobic/oleophobic) effects. Additionally, U.S. Pat. No. 5,760,126 describes fluorine-containing coatings, which are water-based.
One self-cleaning effect of surfaces has become known as the “lotus effect”. It is based on the presence of certain, defined surface structures of hydrophobic materials and is modeled on nature, which brings about the dripping of water from the leaves of plants in a similar way (see EP 772 514 B1). Moreover, it has been reported that a combination of oleophobic and hydrophobic properties can be achieved by means of fractal structures which are disposed in the form of fluorosilane-treated Eloxal layers on aluminum.
The theory of wetting predicts that, at liquid contact angles on the substrate surface of more than 90°, roughening of the surface leads to reduced wetting. Below 90°, increased wetting occurs. For applications on transparent substrates such as glass, for example, roughnesses in the nm range are needed. For example, B. S. Hong et al., in Proc. 2nd Int. Conf. on Coatings on Glass (ICCG), Saarbrücken, 1998, pages 388 to 392 investigated a controlled separation of sol-gel systems for the purpose of generating nanoroughnesses and made use of its effect on wetting properties. In the Werkstoffwoche 99 Euromat session “Properties and Technological Applications of Nanostructured Materials”, S. Sepeur et al. reported on the effect of the surface roughness of perfluorinated nanocomposite materials with high scratch resistance. The incorporation of silicon dioxide particles with a diameter of 230 nm significantly increased the hydrophobic and oleophobic properties of the surface. Instead of producing surface roughnesses by influencing the properties of the material, surfaces may also be structured by techniques such as embossing or the like. For instance, D. Sporn et al., in Specktrum der Wissenschaft, page 20-22, 1997, reported on ultrafine structures for antireflection coating which were “taken as seen from the eye of the moth”.
Coating materials with low emissivity in the region of thermal radiation have been disclosed by G. Hugo in DE 44 18 214 C2. In that document, a binder with high transparency in the range from 3 to 50 &mgr;m has incorporated into it a pigment which likewise possesses a high transparency within this range, but where the refractive index of the binder is different than that of the particles in the stated region of thermal radiation. Pigments proposed particularly include the fluorides, chlorides, selenides and sulfides of metals. The IR reflection maximum can be adjusted by way of the particle size and by the combination of pigments (DE 195 01 114 A1 and 196 50 300 A1). Pigment from brown rutile has also been described as exhibiting a high degree of infrared reflectiveness. DE 198 56 171 discloses the use of functional pearlescent pigments in transparent media which are suitable as coatings for the outside of buildings and which have angle-selective transmission and/or reflection properties in the visible region. The effect of IR-reflective pigments on the heat balance of buildings and in connection with military applications has been described by L. V. Wake in J. Oil Color Chem. Assoc., pages 78 to 81 (1990). Heat reflection may also be achieved through the use of hollow ceramic beads in a polymer matrix. Products having such ingredients are already being marketed for interior coatings; they are said to save up to 10% of heating costs.
DE 196 39 783 A1 to Merck, Hüls AG, describes metal oxide-coated pigments especially for water-based coating systems. The pigments have the structure of platelets atop whose topmost metal oxide layer there is an outer layer comprising certain oxides and/or mixed oxides. As the aqueous coating system, oligomeric silane systems are described. These systems develop silicon-functional hydroxyl groups which form chemical bonds with the hydroxyl groups of the pigment surfaces. The pigments do not have reflection properties in the infrared region.
U.S. Pat. No. 4,311,623 proposes the incorporation of zinc sulfide and other pigments into silicon-alkyd resins.
DE 197 26 862 A1 describes a process for producing a transparent protective layer, having reflecting properties in the infrared region, which can be used to coat transparent polymer plates or glass plates used in refrigeration or freezing apparatus. The protective layer is preferably of two-part construction, in which a thin metal sulfide layer is applied to the polymer or glass and overcoated with a so-called ORMOCER. An alternative proposal is to incorporate an additive having reflecting properties directly into such an ORMOCER.
It is an object of the present invention to provide coating materials from which coatings having excellent oleophobicity/hydrophobicity and, at the same time, heat-reflective properties can be produced. The materials should be suitable for processing by wet coating techniques and should preferably be self-curing, in order that they may be used as paints (e.g masonry or interior paints). Desirably, furthermore, they are solvent-free or contain only a small fraction of solvent. Where solvents are needed, they should as far as possible be nontoxic and environmentally friendly/readily biodegradable.
It has surprisingly been found that this object can be achieved through the provision of coating materials which comprise IR-reflective pigments having dimensions in the range from about 1 to 50 &mgr;m or hollow beads having the same dimensions.
Before they are applied to the intended substrate, the coating materials should possess a viscosity at which they may be applied with conventional means such as rollers or brushes, by spraying, or otherwise. They must be or should be relatively mobile, such that following application the pigment particles in the near-surface layers are covered by a binder layer which is extremely thin, forms a stochastic surface structure, and yet is sufficiently thick to retain weathering stability. Viscosities like that possessed, for example, by honey when stored in the cold (i.e., which are sticky as honey), on the other hand, should be avoided. The coating material may be adjusted to an adequate viscosity where appropriate by separating off or adding solvent and/or dispersion medium (preferably water). In this way it is possible to dispense with additional surface structuring operations such as embossing or the like.
The dirt repellency properties (oleophobicity and hydrophobicity) of the layers formed from the coating material are improved still further by the binder of the coating materials and, respectively, of the coatings comprising at least one optionally organically polymerizable/polymerized silane of the formula (I)
X
a
R
b
SiR
1
4−a−b
  (I)
in which
X is a hydrolyzable group,
R is optionally substituted alkyl, alkenyl, aryl, alkylaryl or arylalkyl,
R
1
is an organic radical which is attached to the silicon via carbon and carries a reactive group, especially one able to enter into organic reactions,
a is an integer from 1 to 3, and
b is an integer from 0 to 2,
or a (partial) condensate of this silane. Such (partially) condensed, optionally organically modifiable/modified silanes have been described in large numbers; the condensates, alone or in a mixture with further (partly) hydrolyzed metal compounds and/or organic components, are frequently referred to collectively as ORMOCERS®. P

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