Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2003-04-07
2004-09-14
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
C106S287150, C427S419500, C428S412000, C428S447000
Reexamination Certificate
active
06790273
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to compositions comprising inorganic UV absorbers and to coatings produced from them for the long-term protection of materials, especially plastics, against photochemical degradation.
Many materials such as plastics or natural substances (wood) must, for use outdoors, be protected against photochemical degradation by means of an appropriate coating. Appropriate primarily for this purpose is coating of the surface in a wet-chemical operation, although in the case of substantially two-dimensional substrates such as sheets of plastic it is also possible to achieve corresponding protection by coextrusion (on both sides) of a plastic which contains UV absorber. The wet-chemical application of a coating, particularly of an inorganic coating, however, has the advantage that it generally also enhances the chemical resistance and scratch resistance of the plastic. Coextrusion, although not providing these advantages, is nevertheless much easier to implement from a technical standpoint.
Both in the (wet-chemically) applied coatings and in the coextruded coats, it is common to use organic UV absorbers, which usually provide satisfactory protection of the underlying material (see, for example, Paint & Coatings Industry 2001, July, 64-76). In the case of very prolonged exposure to UV radiation (sunlight), however, organic UV absorbers are slowly degraded and so lose their protective effect. Through effects of weathering (humidity, high temperatures), moreover, there may be a loss of UV absorber through migration and leaching.
In contrast, inorganic UV absorbers such as titanium dioxide, cerium dioxide or zinc oxide, for example, do not have the disadvantages mentioned for organic UV absorbers. They are not photochemically degraded, and are neither leached out nor discharged under thermal loads.
If the particle size of the inorganic UV absorbers used is small enough, it is possible to produce highly transparent coatings from them. In principle, organic and inorganic binders can be used for this purpose. One example of the incorporation of nano-cerium dioxide into polyacrylates, which are then used as adhesion promoters on thermoplastics, is given in EP 0 732 356 A2. Because of the high surface area of titanium dioxide, cerium dioxide and zinc oxide nano-particles, however, there are frequent instances of photochemical damage and, ultimately, degradation of the matrix surrounding the inorganic UV absorbers. This then leads, among other consequences, to a loss of adhesion between coating and substrate (plastic).
This degradation can be prevented by using inorganic binders, especially sol-gel materials. The predominantly inorganic matrix is undamaged in the majority of cases by the photoactivity of the said nanoparticles.
Some UV protection formulations based on titanium dioxide, cerium dioxide and zinc oxide nanoparticles in sol-gel materials are now state of the art. For instance, U.S. Pat. No. 4,799,963 describes transparent coating compositions composed of partly hydrolysed (organic) alkoxides of the formula R
x
M(OR)
z
and colloidal cerium dioxide, where R is an organic radical, x can be 0 but is smaller than z, and M stands for Si, Al, Ti or Zr or mixtures thereof. The compositions described in U.S. Pat. No. 4,799,963 have the disadvantage, however, that the mixtures of the organosilanes CH
3
Si(OC
2
H
5
)
3
and (CH
3
)
2
Si(OC
2
H
5
)
2
, Example 1, or of CH
3
Si(OCH
3
)
3
and (CH
3
)
2
Si(OC
2
H
5
)
2
, Example 2, have solids contents of only about 6% by weight of nano-CeO
2
, calculated on the basis of the fully hydrolysed and condensed methylalkoxy-silanes. When Si(OC
2
H
5
)
4
is used, in Example 3, the fraction of nano-CeO
2
achieved is indeed much higher, but the coatings produced therefrom are so brittle that they can be applied only to glass and not to plastic.
Additionally, by using the functional organosilane 3-glycidyloxypropyltrimethoxy-silane, Example 4, the amount of nano-CeO
2
in the solids can be raised only to about 13% by weight. Since the coatings described can only be applied in limited film thicknesses (cracking, flaking), the protection effect against relatively long-wave UV radiation (above about 300 nm) is so low, owing to the restricted amount of nano-CeO
2
, that the substrate is not durably protected. Sunlight contains only UV radiation above about 300 nm, and so the protection effect above this figure is essential for all exterior applications.
DE-A 198 58 998 describes further coating compositions containing nano-CeO
2
, which in addition to epoxy-functional silanes further comprise particulate boehmite, another hydrolysable silicon compound, and a hydrolysable aluminium compound. Although according to the examples it was possible to realize nano-CeO
2
contents of up to 25% in the coating compositions provided, and although weathering (Suntest) of correspondingly coated polycarbonate (Makrolon® 2808) exhibits a certain UV protection effect, the yellowing indices (YI) achieved are all above 3.5 and are therefore still too high for many applications.
EP 0 947 520 A1 describes mixtures of polyfunctional organosilanes with compounds containing aluminium and/or boron, which mixtures may further comprise inorganic particles such as particles, for example, of the oxides of the elements B, Al, Si, Ti, Zr and Ce. There is no reference whatsoever, however, to the suitability of such coatings for UV protection. In combination with nano-CeO
2
, moreover, the great mechanical hardness and accompanying brittleness of the coatings gives them a strong propensity towards stress cracking under weathering, so making them unsuitable for exterior applications.
It is an object of the present invention, therefore, to provide UV protection formulations which following application to an appropriate substrate, such as plastic, can be cured to give transparent coatings and exhibit an effective and long-term UV protection effect while at the same time being highly stable to weathering.
DESCRIPTION OF THE INVENTION
It has now surprisingly been found that through the use of polyfunctional organosilanes it is possible to prepare UV protection formulations containing more than 15% by weight of nano-CeO
2
and that these formulations, even with a nano-CeO
2
content of 30% by weight or more, can be cured to give transparent coatings which display an effective and long-term UV protection effect while at the same time being highly stable to weathering.
The present invention accordingly provides compositions comprising, calculated on the basis of the solids, with complete hydrolysis and condensation,
A) 30-85% by weight of at least one polyfunctional organosilane and
B) 15-70% by weight of nano-CeO
2
,
the compositions containing less than 0.1% by weight, preferably 0%, of an element from main group three of the periodic table or compounds of these elements.
The present invention further provides a process for preparing UV protection formulations containing 30-85% by weight of at least one polyfunctional organosilane and 15-70% by weight of nano-CeO
2
, and also provides for their use for coating surfaces, especially surfaces of plastics.
Suitable polyfunctional organosilanes which may be used in UV protection formulations of the invention are monomers, oligomers and/or polymers, characterized in that at least 2 silicon atoms with hydrolysable and/or condensation-crosslinking groups are attached by way of, in each case, at least one SiC bond to a structural unit which links the silicon atoms. Due to their ready compatibility with nano-CeO
2
, polyfunctional organosilanes having at least 3, preferably at least 4, silicon atoms with hydrolyzable and/or condensation-crosslinking groups are particularly suitable for the UV protection formulations of the invention. Particularly suitable hydrolyzable groups are alkoxy or aryloxy groups, mention being made preferably of alkyloxy groups, such as methyloxy, ethyloxy, propyloxy or butyloxy. Condensation-crosslinking groups are, in particular, silanol groups (Si—OH). Linking structural uni
Bayer Aktiengesellschaft
Brunsman David
Gil Joseph C.
LandOfFree
Compositions comprising inorganic UV absorbers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compositions comprising inorganic UV absorbers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compositions comprising inorganic UV absorbers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3258397