Coating processes – Solid particles or fibers applied – Uniting particles to form continuous coating with...
Reexamination Certificate
1998-11-20
2001-04-24
Buttner, David J. (Department: 1712)
Coating processes
Solid particles or fibers applied
Uniting particles to form continuous coating with...
C524S520000, C525S199000
Reexamination Certificate
active
06221429
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention related to fluorinated powder coating products, based on certain vinylidene fluoride terpolymers (hereinafter referred to as VdFT), for preparing fluorinated coatings having controllable gloss and to a process for coating a substrate with a pigmented fluorinated coating having controllable gloss. In particular, the present invention relates to the use of certain vinylidene fluoride terpolymers in pigmented powder coating products, for obtaining fluorinated protective coatings having controllable gloss properties.
Coatings based on vinylidene fluoride homopolymers (hereinafter PVdF) are known to be very useful as protective coatings for a variety of substrates due to their good chemical and weather resistance and to the thermal stability of PVdF. The general known technique used for preparing PVdF coatings is to prepare a dispersion of PVdF in a suitable solvent for application by known means onto the required substrate, and thereafter subjecting it to heat treatment.
The solvent used is generally known in the prior art as “latent solvent”, and it is described therein as an organic solvent which has no significant action on PVdF at room temperature, but which at an elevated temperature exerts a sufficient solvent action.
However, although the known systems may give good results, environmental protection laws throughout the world, but mainly in Europe and the USA, are making it increasingly difficult to utilize solve-based systems. Further, the recovery of the solvent is a costly procedure. Accordingly, there is a need in the art for solventless PVdF-based coatings.
British Patent GB 2194539-A, to Labofina discloses pigmented PVdF-based powder coating products consisting essentially of vinylidene fluoride homopolymers (or copolymer with at most 10 wt % of comonomer units), one or more compatible thermoplastic resins and one or more pigments. It also discloses a process for preparing the products. However, the gloss obtained is not easily controlled at an acceptable level.
European patent No. 456018-A, to Atochem North America discloses pigmented powder coatings of vinylidene fluoride/hexafluoropropene copolymers, the resin component comprising 50-90 wt % of said copolymers having a melt viscosity of 1-4 kPoise [100-400 Pa-s] at 100 s
−1
and 232° C., said copolymers being characterized by a melting point in the range of about 160° C. to about 170° C. (which closely approaches the melting point of PVdF), and 50-10 wt % of thermoplastic acrylic resin. The resulting coatings are said to be characterized by improved flexibility, crack resistance and surface smoothness (as opposed to surface roughness or “orange peel” associated with the finish) while not requiring the inclusion of a flow-improving agent. No information is reported about the gloss, not to mention gloss regulation, except that the thermoplastic acrylic resin is responsible for gloss durability.
U.S. Pat. No. 5,229,460 to Evodex discloses fluoropolymer-based powder coatings which may be based on PVdF or on a copolymer with at least 80 wt % of vinylidene fluoride and up to 20 wt % of at least one other fluorine-based monomer. No information is reported about the gloss nor about gloss regulation.
There is, however, a certain demand for coatings exhibiting very low gloss, which cannot be obtained presently. Accordingly, there is a need for a process for regulating the gloss of fluorinated powder coatings.
An object of the present invention is to provide VdFT-based powder coating compositions capable of providing easily controllable low-gloss coatings. Controllable gloss coatings, as used herein, are coatings whose gloss can be adjusted from values from above 40, preferably above 50 and most preferably above 60, down to values below 30, preferably below 20 (all values being measured according to ISO 2813 at an angle of 60°), while still having a good surface smoothness.
Another object of the present invention is to provide VdFT-based powder coating compositions capable of providing low-gloss coatings. Low-gloss coatings, as used herein, are coatings having a gloss below 30, preferably below 20 (all values being measured according to ISO 2813 at an angle of 60°), while still having a good surface smoothness.
A further object is to provide a process for preparing controllable gloss VdFT-based coatings.
Still another object is to provide a process for preparing low-gloss VdFT-based coatings.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a powder coating product consisting essentially of:
(a) a resin component consisting essentially of:
(i) from 60 to 90 wt % of one or more low melting point fluoride-based terpolymers;
(ii) from 40 to 10 wt % of one or more compatible resins; and
(b) from 1 to 35 parts by weight of one or more pigments per 100 parts by weight of the resin component.
The present invention further provides a process for preparing coatings from the powder coating products of the invention, essentially characterized by a selection of the baking temperatures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The low melting point fluorine-based terpolymers used herein are made from three monomers selected from he group consisting of vinylidene fluorine (VdF), tetrafluoroethylene (TFE), chlorotrifluoroethylene, vinylfluoride, hexafluoropropene (HFP), and CF
3
—CF
2
—CF═CF
2
; and having a melting temperature below about 150° C., preferably below 120° C. and most preferably below 100°. Preferably the terpolymer is made from a majority of VdF copolymerized with TFE and HFP; the most preferred terpolymers are prepared from 65 to 85 wt % of VdF monomer units with from 7.5 to 17.5 wt % of each of TFE and HFP. The melt viscosity of the terpolymer should preferably be of from 9,000 to 15,000 dPa-s, most preferably from 11,000 to 13,000 dPa-s, all measured at 125° C.
The VdFC is mixed with one or several compatible resins, preferably of the acrylic type. Acrylic resins are known in the art and need not be described here; a description may be found in French Patent 2,636,959-A to Atochem (see line 18 of page 3 to line 14 of page 4). As examples of thermosetting acrylic resin, there are those described in U.S. Pat. No. 4,659,768 to Tortorello, particularly under the denominations “Experimental resin” and “control resin”. However, it has been found that it is advantageous to use a thermoplastic acrylic resin, and most advantageous to use a thermoplastic polymethylmethacrylate (PMMA) resin. A preferred thermoplastic PMMA resin is that obtained by (co)polymerization of at least 75 wt % of an alkyl methacrylate, the other comonomers being one or several olefinically unsaturated comonomers, preferably of the alkyl (meth)acrylate type. These esters are formed by the reaction of the acrylic or methacrylic acid with suitable alcohols, for example, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol and 2-ethylhexyl alcohol. Generally, the larger the alcohol portion of the ester, the softer and more flexible the resultant resin. Also, generally, the methacrylic esters form harder films than the corresponding acrylic esters. Examples of such resins include polymethylmethacrylate, copolymers of methylmethacrylate with ethyl acrylate, butyl methacrylate, isobutyl methacrylate, acrylic acid or methacrylate acid, and the like. The most preferred PMMA resins are those which exhibit a viscosity of from 7 to 17 P in 40% solution in a 95:5 by weight mixture of toluene and ethylene glycol methyl ether.
The weight ratio of the VdFC to the compatible resin may vary widely from 90:10 to 60:40, preferably from 75:25 to 65:35, most preferably of about 70:30.
The resin component may additionally contain minor amounts of the usual additives, such as an antioxidant, a flow promoting agent, a UV absorber, and/or an adhesion promoter. As suggested in U.S. Pat. No. 5,229,460, an antioxidant may be utilized to enhance heat stability and provide protection against thermal degradation and discoloration of the coating film due to excessive heat at high curing temper
Gillard Michel
Rijkse Ludwig Karl
Verwey Edwin
Buttner David J.
Fina Research S.A.
Jackson William D.
Wheelington Jim D.
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