Wrinkle finish powder coatings

The use of an amine salt of trifluoromethanesulfonic acid as a catalyst for the curing of hydroxyl-functional resins provides a wrinkle finish. The hydroxy-function may be present in polyesters, epoxies, and acrylate or methacrylate resins, among others. The polyester resins which are able to provide such a finish have a hot plate melt flow of at least about 50 mm but if it is more than 150 mm, the gel time of the resin must not be more than about 280 seconds. The minimum gel time in the case of polyesters is about 30 seconds.

TECHNICAL FIELD 
This invention relates to coatings applied by fusion coating processes and 
more particularly to coating powders that yield wrinkle finishes upon 
curing. It relates still more particularly to such powders made from 
thermosettable hydroxy-functional resins. 
BACKGROUND OF THE INVENTION 
The coating compositions of this invention are dry, free flowing powders 
that may be used in fusion coating processes. "Fusion coating processes" 
are herein defined as those coating processes in which a coating powder is 
distributed over a substrate (which may be hot or cold) and heat, supplied 
from the substrate or an external source, fuses the powder into a 
continuous film. Examples of fusion coating processes include fluidized 
bed, electrostatic spraying, hot flocking, and cloud chambers. When the 
coating powder is based upon heat curing resins, as is the case of the 
hydroxy-functional resins of this invention, sufficient heat in excess of 
that required to fuse the powder must be available to cure the coating and 
fully develop its physical and chemical properties. 
Wrinkle finishes are desired in many applications and are commonly applied 
to office equipment such as typewriters, staplers, dictating equipment, 
file cabinets, and the like. In addition to being aesthetically pleasing, 
these finishes have certain utilitarian functions: they hide surface 
defects of a substrate even when applied in thin films and, having a low 
gloss, they do not show scratches. Wrinkle finishes, as contemplated for 
the purposes of this invention, are reticulated, i.e., made up of a 
pattern of raised veins across the surface and are exemplified by 
interconnected star-burst patterns, mosaics, and by patterns similar to 
that of an alligator hide. 
Wrinkle finish coatings conventionally are applied from solvent-based 
paints, usually using two coats, to establish a compound system in which 
the surface sets up first. When the rest of the coating cures, the 
resulting shrinkages deform the previously set surface and cause a fine 
wrinkle pattern to develop on the surface of the coating. 
Epoxy resin-based powder coatings having wrinkle finishes are taught in 
U.S. Pat. No. 4,341,819. The wrinkle pattern is achieved by means of a 
special curing agent, methylene disalicylic acid, acting upon the epoxy 
groups of the resin. Because of the rather poor weatherability of epoxy 
resin coatings, these wrinkle-finish coatings are used almost exclusively 
on surfaces protected from the weather and are very popular for interior 
uses. 
SUMMARY OF THE INVENTION 
Accordingly, it is the object of this invention to provide a coating powder 
which will yield a coating having a low gloss and a randomly developed 
wrinkle pattern on its surface. 
It is another object of this invention to provide a coating powder adapted 
to give a weatherable wrinkle finish. 
It is another object of this invention to provide a method for generating a 
wrinkle finish on a powder coating made from a hydroxy-functional resin. 
It is yet another object of this invention to provide a wrinkle finish on 
an article having a powder coating based on a hydroxy-functional resin. 
These and other objects of this invention are achieved through the use of 
an amine salt of trifluoromethanesulfonic acid as the catalyst for curing 
a hydroxy-functional resin, the essence of the coating powder.

DETAILED DESCRIPTION OF THE INVENTION 
Trifluoromethanesulfonic acid, also known as triflic acid, is one of the 
strongest of all known monoprotic acids. It is about 427 times as strong 
as nitric acid but it is not an oxidizing agent and is extremely stable to 
high temperatures. It is available as FC-28 from the 3M Company. By itself 
or in an aqueous glycol ether solution, the acid does not act as a 
wrinkle-producing catalyst in the curing of the powder coating composition 
on a bare metal surface. However, an amine salt of the acid, called an 
amine triflate, does cause a remarkably abrupt dulling of the surface of 
the molten powder and the formation of a skin within seconds of fusion, 
followed by a slumping of the skin as the resinous mass is cured beneath 
it. For the purposes of this invention, the meaning of the term amine 
shall include ammonia as well as amines having the formula R.sub.x N 
wherein R is an alkyl group, preferably one having from 1 to 4 carbon 
atoms, and x is from 1 to 3. Examples include methyl-, dimethyl-, and 
trimethylamine, ethylamine, propylamine, dipropylamine, butylamine, and 
dibutylamine. The diethylamine salt is a preferred catalyst for the 
wrinkle-forming curing process of this invention. The amine salts are 
suitably used as solutions in a mixture of water and a polar organic 
solvent such as a glycol ether. The diethylamine triflate is available 
from 3M as FC-520 Resin Catalyst, a 60% solution in a 50/50 mixture of 
water and diethyleneglycol monoethyl ether. A starburst type wrinkle is 
achieved with the hydroxy-functional polyester even though the amine 
triflate has a pH on the order of about 4.5. For an attractive alligator 
finish on such polyester-based coatings, it is preferred that the pH is 
from about 6.5 to about 10; an excess of the amine over the stoichiometric 
amount being used in making the salt alkaline. Nevertheless, the alligator 
finish is achieved on the epoxy resin-based coatings even when the 
catalyst does not contain excess amine. When four different lots of FC-520 
salt which were effective catalysts for the epoxy alligator finish were 
diluted with equal amounts of water, the resulting solutions had pH values 
of 4.7-4.9. In general, then, the pH may be from about 4.5 to about 10 or 
even higher although a large excess of amine may be harmful to other 
desirable properties of the coating. 
The amount of active catalyst is from about 0.05 to about 1 part per 
hundred parts by weight of the resin (phr); the term resin herein means 
the combination of the hydroxy-functional resin and the curing agent. 
Preferably, the active catalyst is used in an amount ranging from about 
0.2 to about 0.8 phr. The types and amounts of filler and pigment used are 
to be taken into account when determining the level of catalyst for a 
particular formulation of the coating powder of this invention, as will be 
seen below. 
The curing agent in the coating composition of this invention is preferably 
one that splits out a volatile by-product of the curing reaction. 
Aminoplasts, particularly the melamine/formaldehyde resins, urea/glyoxal 
condensation products, and the alkoxylated derivatives of each are 
examples of such a curing agent. Hexamethoxymethyl melamine and 
tetramethoxymethyl glycouril exemplify the preferred curing agents. A 
curing agent in solid form is preferred for convenience in formulation. 
The tetramethoxymethyl glycouril, available from American Cyanamid under 
its trademark and number POWDERLINK 1174, is a solid. The amount of curing 
agent may be from about 4% to about 20% by weight of the resin, but 
preferably it is from about 5 to about 7%. 
The wrinkle finish powder coatings are derived from hydroxy-functional 
resins exemplified by hydroxy-functional polyesters, epoxy resins (through 
the secondary hydroxyl group in each unit), hydroxy-functional acrylate 
and methacrylate resins, cellulose esters such as cellulose 
acetate/butyrate, and polyvinylbutyral. 
The polyester resin is predominantly hydroxyl in functionality; its acid 
number is preferably about 12 or less and, even more preferably, not more 
than about 5. The hydroxyl number, on the other hand, is preferably from 
about 25 to about 50, as conventionally reported. The amount of curing 
agent used depends on the hydroxyl number; as the number goes up, so does 
the amount of curing agent. 
The epoxy resins are exemplified by the diglycidyl ether condensation 
polymers resulting from the reaction of epichlorohydrin with a bisphenol 
in the presence of an alkaline catalyst. Bisphenol A is most commonly used 
but the bisphenols B, F, G and H are also suitable. By controlling the 
operating conditions and varying the ratio of the reactants, products of 
various equivalent weights can be made. For the purposes of this 
invention, the epoxide equivalent weight (EEW) may be from about 600 to 
about 2000 and the hydroxyl equivalent weight may be from about 300 to 
about 400. These are available from a wide variety of commercial sources. 
The GT-series of bisphenol A epoxies from Ciba-Geigy, including 7004, 
7013, 7014, 7074, and 7097 are examples of useful epoxy resins in this 
invention. Shell Chemical Co. also supplies suitable epoxy resins under 
its Epon trademark. 
Epoxy/polyester hybrids are also contemplated for use in this invention. 
The hydroxyl function is contributed by the epoxy resin. Acid functional 
polyester resins specifically designed for curing with bisphenol A epoxy 
resins have an acid number of from about 35 to about 75 (equivalent weight 
about 750-1600) and are generally used at a stoichiometric ratio .+-.10% 
with the epoxy. The weight ratio of epoxy to polyester is typically from 
about 50:50 to about 30:70. 
Hydroxy-functional acrylate and methacrylate polymers are exemplified by 
the homopolymers and copolymers of hydroxyethyl and hydroxypropyl acrylate 
and methacrylate. Comonomers include alkyl esters of acrylic and 
methacrylic acid wherein the alkyl group contains from 1 to 8 carbon 
atoms, styrene, ethylene, propylene, and vinyl monomers. The hydroxyl 
equivalent weight is from about 600 to about 1400. They are available from 
the Polymer Division of S.C. Johnson & Son, Inc. 
Mixtures of the hydroxy-functional resins are also useful in the practice 
of this invention. 
An essential property that must be considered when formulating a coating 
powder is the ability of the powder to fuse into a continuous and void 
free film. As a guide to formulation chemists, two relatively simple test 
procedures have been established to measure the ability of a coating 
powder to fuse over a substrate. One of these is gel time which provides a 
measure of the reactivity of a given system; the other is the hot plate 
melt flow (HPMF) test which is a combined measure of both the reactivity 
and melt viscosity of the coating powder. It is generally true that the 
gel time and the HPMF are a function of the molecular weight and 
functionality of the resin, the nature of the curing agent, and the 
activity of the catalyst. The HPMF and melt viscosity are also influenced 
by fillers which generally increase the viscosity depending on the amount 
used, the particle size, the surface area and the surface chemistry of the 
fillers. 
For each 100 parts by weight of the resin, from 0 to about 100 parts by 
weight of fillers and pigments may be added to the formulation. Silica, 
mica, talc, and diatomaceous earth are examples of the fillers. Alkaline 
fillers, however, such as the sodium potassium aluminum silicate sold 
under the MINEX trademark seem to interfere with the catalytic action of 
the amine triflates. The presence of even a substantially neutral salt 
like barium sulfate requires an additional amount of the catalyst. Even 
so, the following pigments exemplify those contemplated in this invention: 
carbon black, titanium dioxide, nickel-titanium oxide, 
nickel-antimony-titanium oxide, ferrite yellow oxide, ferric oxides, raw 
sienna, phthalocyanine blue, phthalocyanine green, ultramarine blue, 
toluidine red, parachlor red, and organic maroons. Titanium dioxide also 
interferes to some extent with the catalyst and that is taken into account 
in formulating the coating composition. The various grades of titanium 
oxide have varying effects on the appearance of the finish. A very 
pronounced alligator finish may be obtained on a white coating when an 
alkaline-reacting titanium oxide having an alumina/silica coating such as 
that designated R-902 by Dupont is used. Also, titanium oxides by SCM 
Pigments called Zopaque RCL-2 and RCL-9 permit an alligator finish. An 
organic-coated titania designated R-101 by Dupont also permits a very 
desirable finish. On the other hand, an alumina-coated titanium oxide 
designated R-900 by Dupont greatly slows the cure and an organically 
treated, silica-encapsulated titanium oxide designated Zopaque RCL-6 by 
SCM can prevent the formation of a wrinkle finish almost entirely. The 
effect of R-960 titania (Dupont), which has a silica/alumina coating, on 
the wrinkle may be minimized by using lesser amounts of the pigment. 
Other ingredients may be useful for particular compositions. Flow or 
leveling agents are useful to promote the formation of a continuous 
coating. These are exemplified by polyacrylic esters, non-ionic 
fluorinated alkyl ester surfactants, non-ionic alkylarylpolyether 
alcohols, and silicones. Benzoin is useful as a bubble release agent. 
Melt mixing is the preferred method for making the coating powders. The dry 
ingredients are weighed into a batch mixer and are mixed with a a medium 
intensity horizontal plow mixer or a lesser intensity tumble mixer; in the 
latter case care must be taken that all ingresients are thoroughly 
distributed. When liquids are to mixed into the powder, a high intensity 
impeller mixer such as a Henschel or Wellex mixer is advantageous. Mixing 
times range from about 1 to about 3 minutes for the high intensity mixers 
to about 30-60 minutes for the tumble mixers. The premix is then further 
mixed and compounded as the resin is melted in either a single screw or a 
twin screw extruder for about 0.5 to 1 minute. The extrudate is cooled 
quickly and broken into small chips suitable for grinding. 
The coating powder is applied to substrates by conventional means, 
including the electrostatic fluidized beds, electrostatic spray guns, and 
triboelectric guns. Hot flocking may also be used. 
ASTM Specification D-3451 defines a procedure for measuring gel time in 
which a small quantity of powder is dropped onto a hot plate at a given 
temperature, e.g. 205.degree. C. (400.degree. F.) and stroked with a 
tongue depressor until continuous and readily breakable filaments are 
formed when the depressor is lifted from the sample. The elapsed time for 
this to occur is measured in seconds and is the gel time. Although gel 
time, by itself, is not an indicator of whether a certain resin 
composition of this invention will provide a wrinkled finish to the 
coating made therefrom, the minimum gel time for compositions of this 
invention is preferably about 30 seconds. 
To obtain the desired wrinkle finish, the HPMF of the hydroxy-functional 
polyester powder coating composition should be at least about 50 but if it 
is more than 150 mm when measured at 375.degree. F. (190.degree. C.), the 
gel time must not be greater than about 280 seconds. If these two 
properties do not fall within these limits, the desired wrinkle finish of 
this invention is not obtained. In this test a pellet of powder having a 
diameter of 12.7 mm and 6 mm thick is placed on a hot plate set at 
375.degree. F. (190.+-.2.degree. C.) at an inclination angle of 
35.degree.. The pellet melts and runs down the plate. The length of the 
flow is measured in millimeters. The distance the coating flows is 
dependent on the initial melt viscosity, the rate of reaction, the 
temperature at which the test is conducted, and the type and amount of 
catalyst. 
As will be seen in the follwing examples, the gel times for the bisphenol A 
epoxy resins are on the order of about twice those of the 
hydroxy-functional polyesters whereas the HPMF is about the same order of 
magnitude. 
In the examples of hydroxy-functional polyester coating powders that 
follow, the correlation between the HPMF, the gel time, and the production 
of a wrinkle finish is apparent. 
EXAMPLES 1-7 
Coating powders were prepared in accordance with this invention by 
initially blending at high speed the POWDERLINK 1174 curing agent and the 
polyester resin identified in Table I in weight ratios of 6:94 in Examples 
1-4; 8:92 in Example 5; and 10:90 in Examples 6 and 7; along with the 
following ingredients: 
______________________________________ 
phr 
______________________________________ 
RESIFLOW P-67 flow agent 
1.4 
Benzoin 0.8 
Bartex 65 barium sulfate 
30 
Titanium dioxide (R-960) 
0.4 
Black pigment 0.76 
Red pigment 1.5 
Yellow pigment 3.6 
Diethylamine triflate (FC-520) 
0.6 
______________________________________ 
The blend was then melt-mixed in a Buss extruder whose front zone was 
maintained at 180.degree. F. and whose rear zone was unheated. The 
extrudate was then chipped and ground with 0.2% by weight of colloidal 
alumina (Degussa) to a fine powder that passed through a 60 mesh screen 
(U.S. Standard). 
Precleaned steel test panels (from "Q" Panel Co.) measuring 
3".times.6".times.0.032" (7.6.times.15.2.times.0.08 cm) were coated using 
standard electrostatic spray techniques and baked in an oven at about 
400.degree. F. (205.degree. C.) for 15 minutes to give a coating having a 
thickness of from about 2.5 to about 4.0 mils. The 60.degree. gloss for 
each panel was 8.2 % or less. Other properties are given in Table I. 
TABLE I 
______________________________________ 
Gel 
Polyester OH Acid Visc time HPMF 
Ex. No. 
Resin* # # mPa secs mm Wrinkle 
______________________________________ 
1 Arakote 30 -- 4500 55 87 Yes 
3109 
2 AN 745 30 5 7100 41 77 Yes 
3 Ruco 112 30 -- 4500 35 72 Yes 
4 Crylcoat 30 -- 6500 38 54 Yes 
2392 
5 Ruco 121 41 5 4000 40 74 Yes 
6 Morton*** 47 12 2200 39 81 Yes 
7** Morton*** 47 12 2200 65 126 Yes 
______________________________________ 
*Arakote 3109 is sold by CibaGeigy 
AN 745 is sold by Hoechst Celanese 
Ruco 112 and 121 are sold by Ruco Polymer Corporation 
Crylcoat 2392 is sold by UCB 
**Catalyst level reduced to 0.2 phr 
***Captive product of assignee; not commercially available 
COMATIVE EXAMPLES A-D 
The general procedures of Example 1 were repeated except for the 
substitution of the polyester resins shown in Table II for that of Example 
1. As is shown in the table, none of these powder coating compositions 
produced a wrinkle finish. The weight ratios of curing agent to resin were 
6:94 for Examples A,B, and E; and 8:92 for Examples C & D. 
TABLE II 
______________________________________ 
Gel 
Polyester 
OH Acid Visc time HPMF 
C. Ex. 
Resin # # mPa secs mm Wrinkle 
______________________________________ 
A Ruco 111 23 4 6500 24 49 No 
B Crylcoat 30 -- -- 29 46 No 
3493 
C Ruco 118 41 13 7500 25 28 No 
D XP 3932 40 13 4000 29 46 No 
E* Arakote 30 -- 4500 298 150+ No 
3109 
______________________________________ 
*Formulation contained only 0.1 phr of the FC520 catalyst and 50 phr of 
barium sulfate 
COMATIVE EXAMPLES F-Q 
Here, the general procedures of Example 1 were followed except for the 
substitution of the catalysts shown in Table III. A s shown, none of these 
other catalysts, including cyclamic acid, provided a fused coating having 
a wrinkle finish. 
TABLE III 
______________________________________ 
Gel 
time HPMF 
C. Ex. 
Catalyst* Type secs. mm Wrinkle 
______________________________________ 
F Nacure 4167 
phosphate 300+ 150+ No 
G Nacure 5225 
dodecyl- 79 88 No 
benzene 
sulfonic 
acid salt 
H Nacure 3525 
dinonyl- 66 77 No 
naphthalene 
disulfonic 
acid salt 
J Nacure 2500 
p-toluene 54 79 No 
sulfonic 
acid salt 
K Nacure XP330 
zinc salt of 
31 39 No 
dinonyl- 
naphthalene 
sulfonic acid 
L Nacure XP350 
sulfonic 69 61 No 
acid ester 
M Cycat 4045 amine blocked 
54 79 No 
aromatic 
sulfonic acid 
N Cycat 4040 strong acid 
25 26 No 
O Cycat 600 organic acid 
22 18 No 
P Cycat 296-9 
acid 300+ 54 No 
Q Cyclamic -- 40 57 No 
acid 
______________________________________ 
*Nacure is a trademark of King Industries 
Cycat is a trademark of American Cyanamid 
Cyclamic acid is a product of Abbott Laboratories 
EXAMPLES 8-14 
The general procedure of Examples 1-7 was repeated except that benzoin was 
not used, 40 parts of the Bartex 65 filler was used, only 0.5 part of the 
amine triflate was used, and the epoxy resin identified in Table V was 
used. The weight ratio of the resin to the Powderlink 1174 curing agent is 
also given in the table. 
TABLE V 
______________________________________ 
Gel 
Ex. Epoxy eq wt 
epoxy time HPMF 
No. Resin Ratio (OH) eq wt secs mm Wrinkle 
______________________________________ 
8 GT-7013 6:94 .about.400 
650- 300+ 67 yes 
* 725 
9 GT-7074 7:93 323 950- 130 56 alli- 
* gator 
10 GT-7074 8:92 323 950- 134 55 alli- 
* 1175 gator 
11 GT-7097 8:92 303 1667 104 56 alli- 
* 2000 gator 
12 GT-7097 9:91 303 same 82 59 alli- 
* gator 
13 GT-7097 10:90 303 same 88 61 alli- 
* gator 
14 Epon 6:94 .about.325 
875- 300+ 63 yes 
2004** 975 
______________________________________ 
*Ciba-Geigy 
**Epon is a trademark of Shell Chemical Co. 
poor cure 
EXAMPLE 15 
Ruco 112 polyester (94 parts), Powderlink 1174 curing agent (6 parts), 
Resiflow P-67 and Uraflow B flow agents (1.4 and 0.8 parts, respectively), 
Bartex 65 filler (40 parts), Raven #22 carbon black (3 parts), and the 
dibutylamine salt of triflic acid (0.4 part, pH=9.3) were blended in a 
Henschel blender at 2200 rpm for 1 minute. The blend was then melt mixed 
in an extruder having a front zone at 180.degree. F. and an unheated rear 
zone. The extrudate was then mixed with 0.2% by weight of alumina "C" and 
ground in a high speed, 12 pin grinder to a 60 mesh size. The gel time of 
the resulting coating powder was 99 seconds and the HPMF was 92 mm. A 
Q-panel electostatically coated with about 2.5 to 4.0 mils of the powder 
was heated at 400.degree. F. for 15 minutes. A wrinkle finish was 
achieved. 
EXAMPLE 16 
The general procedure of Example 15 was repeated except that the pH of the 
dibutylamine salt was 8.3. A wrinkle pattern substantially identical to 
that of Example 15 was achieved.