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...
Reexamination Certificate
2003-02-06
2004-08-03
Wu, David W. (Department: 1713)
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...
C524S570000, C524S493000, C524S437000, C524S438000, C524S492000, C525S526000
Reexamination Certificate
active
06770705
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to novel curable film-forming compositions containing submicron-sized particles and having improved chip resistance.
BACKGROUND OF THE INVENTION
Substrates coated with film-forming compositions, particularly those used in automotive applications, are subject to surface defects that occur during the assembly process as well as damage from numerous environmental elements. Such defects incurred during the assembly process include paint defects in the application or curing of the various coating layers. Damaging environmental elements include acidic precipitation, exposure to ultraviolet radiation from sunlight, high relative humidity and high temperatures, defects due to contact with objects causing scratching of the coated surface, and defects due to impact with small, hard objects resulting in chipping of the coating surface.
Typically, a harder, more highly crosslinked film may exhibit improved scratch resistance, but it is less flexible and much more susceptible to chipping and/or thermal cracking due to embrittlement of the film resulting from a high crosslink density. A softer, less crosslinked film, while not prone to chipping or thermal cracking, is susceptible to scratching, waterspotting, and acid etch due to a low crosslink density of the cured film.
A spray-applied chip resistant coating layer is often present in multi-layered coating composites for motor vehicles. The chip resistant layer protects the surface of the substrates from losing paint through chipping during manufacturing and when the vehicle is hit with solid debris, such as gravel and stones. The art for achieving chip resistance from spray applied primer coatings has postulated that reducing the differential in impact energy between the multiple coating layers should improve chip resistance of the coating. This is especially applicable when coating layers have excessive difference of hardness between them. This reduction in the differential would lessen delamination between the coatings, such as between an undercoat and an intermediate coat or between a topcoat and an intermediate coat.
Prior art attempts to improve the chip resistance of coatings have included the addition of hard micron- and submicron-sized particles such as colloidal silica to relatively soft resinous compositions. Japanese Kokai Number Hei 5-15533 discloses a coating composition comprising an alkyd resin and aminoplast crosslinking agent, to which is added ultrafine particles of silica. Such particles typically have highly active (and reactive) surfaces, often due to surface treatments, and as a result the particles tend to agglomerate during production thereof or during incorporation into the coating composition. Agglomeration of the particles prevents high loading of the particles into a coating composition because the viscosity of the composition increases unacceptably. Additionally, agglomeration of the particles may affect the optical properties of the coating, reducing the gloss and clarity thereof because of light scattering.
It would be desirable to provide a chip resistant curable film-forming composition using novel particle technology without detrimentally affecting appearance properties of the composition.
SUMMARY OF THE INVENTION
In accordance with the present invention, a curable film-forming composition is provided comprising in a medium (i) 10 to 90 percent by weight based on the total weight of solids in the film-forming composition of a crosslinking agent; (ii) 10 to 90 percent by weight based on the total weight of solids in the film-forming composition of a polymer containing a plurality of functional groups reactive with the crosslinking agent; and (iii) at least 20 percent by volume based on the total volume of the film-forming composition of particles having a mean particle size less than 100 nm. A cured composition comprising the crosslinking agent of (i) and the polymer of (ii) has a cured softening point of less than 30° C. The particles of component (iii) further have a hardness value greater than 5 on the Moh hardness scale, and have an affinity for the medium sufficient to keep the particles suspended therein. The affinity of the particles for the medium is greater than the affinity of the particles for each other, thereby preventing agglomeration of the particles within the medium.
Also provided is a coated substrate comprising a substrate on which the curable film-forming compositions described above are applied and cured to form a cured coating; the cured coating having a thickness of at least 5 microns. The coating shows excellent chip resistance, superior sandability and resistance to scratching, water spotting and acid etch.
DETAILED DESCRIPTION
Other than in any operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
Film-forming compositions of the present invention comprise 10 to 90 percent by weight of a crosslinking agent as component (i). Examples of suitable crosslinking agents include any known crosslinking agents useful in liquid curable film-forming compositions such as aminoplasts, polycarboxylic acids and anhydrides, polyisocyanates, polyols, and polyepoxides.
Aminoplasts are obtained from the reaction of formaldehyde with an amine or amide. The most common amines or amides are melamine, urea, or benzoguanamine. However, condensates with other amines or amides can be used. While the aldehyde used is most often formaldehyde, other aldehydes such as acetaldehyde, crotonaldehyde, and benzaldehyde may be used.
The aminoplast contains methylol groups and usually at least a portion of these groups are etherified with an alcohol to modify the cure response. Any monohydric alcohol may be employed for this purpose including methanol, ethanol, and isomers of butanol and hexanol.
Most often, the aminoplasts are melamine-, urea-, or benzoguanamine-formaldehyde condensates etherified with an alcohol containing from one to four carbon atoms.
Examples of polycarboxylic acids that are suitable for use as the crosslinking agent (i) in the composition of the present invention include those described in U.S. Pat. No. 4,681,811, at column 6, line 45 to column 9, line 54. Suitable polyanhydrides include those disclosed in U.S. Pat. No. 4,798,746, at column 10, lines 16-50, and in U.S. Pat. No. 4,732,790, at column 3, lines 41 to 57.
Polyisocyanate crosslinking agents may be used in the composition of the present invention and are typically at least partially capped. Usually the polyisocyanate crosslinking agent is a fully capped polyisocyanate with substantially no free isocyanate groups. T
Kutchko Cynthia
McCollum Gregory J.
Munro Calum H.
O'Dwyer James B.
Vanier Noel R.
PPG Industries Ohio Inc.
Sastri Satya B
Uhl William J.
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