Note: Descriptions are shown in the official language in which they were submitted.
-- 21402~9 ~`
I~XPRESS MAIL #HB090~9~0~ PATENT
Docket No.: F 631
FLUORINATED POWDER COATINGS HAVING IMPROVED GLOSS
CROSS REFERENOE TO RELATED APPLICATION
S This application claims priority of previously filed cop~o.ndin~ Belgian application,
Serial Number 93870243.8, ~ntitl~l "Fluorinated powder co~tin~ having regulable gloss",
filed December 23, 1993; which previously filed appli~tiQn is hereby incorporated in its
enlir~ly by referenc~
BACKGROUND OF THE INVENTION
The pr~selll invention related to fluorinated powder co~ting produc~;, based on
certain vinylidene fluoride terpolymers (hereinafter referred to as VdFT), for preparing
fluorinated co~tin~ having controllable gloss and to a process for co~tin~ a substrate with
a pi~nente~l fluorinated c~ting having controllable gloss. In particular, the pr~se
invention relates to the use of certain vinylidene fluoride terpolymers in pi~n~.nte~ powder
lS co~tin~ products, for obt.~ining fluorinated pr~leclive co~tin~ having controllable gloss
propertie~
C~o~tin~ based on vinylidene fluoride h~ mopolymers (hereinafter PVdF) are knownto be very useful as pro~liv~ co~tin~ for a variety of ~u~lla~es due to their good chemi~
and weather re~ nç~ and to the thermal stability of PVdF. The general known te~hni~lue
used for plep~ing PVdF coA~ ~ is to plepale a dispersion of PVdF in a suitable solvent
for application by known means onto the r~uired substrate, and thereafter subjecting it to
heat treatment.
- - -
` 214029~
The solvent used is generally known in the prior art as "latent solventn, and it is
desclil~l therein as an (jlgdlliC solvent which has no si~nifir~nt action on PVdF at room
l~lll~ralule, but which at an ele~ated lell~alule exerts a s -fficient solvent action.
Ho.._~_r, although the known ~ ellls may give good results, envir~nm~ont~l
S pr~)teclion laws throughout the world, but mainly in Europe and in the US~, are m~king
it increasingly d;ffl~`ult to utilize solvent-based ~y~ll~ Further, the r~co~.y of the solvent
is a costly pr~lule. Accor~ gly, there is a need in the art for solventless PVdF-based
c~tin~
British Patent GB 2194539-A, to Labofina ~i~l~s pigmented PVdF~ased powder
10 co~ting products c~n~ ing e~nti~lly of vinylidene fluoride homopolymer (or copolymer
with at most 10 wt% of comonomer units), one or more comp~tible thermoplastic resins and
one or more pigrnPnt~ It also ~ r1Qs~ a pr~ for p.ep~illg the pro~luc~. Hc..._~_r, the
gloss obtained is not easily controlled at an ~ t~ble level.
Eur~ Patent No. 456018-A, to ~t~h~m North America d ~ pi~n~nte~
15 powder co~tin~ of vinylidene fluoride/h~fluQropropene copolymers, the resin component
colllpl~ing 50 90 wt% of said copolymers having a melt vi~ ily of 1~ kPoise [100 400
Pa-s] at 100 s-l and 2320C, said copolymers being ch~acl~.i~ by a m~ltin~ point in the
range of about 1600C to about 1700C (which closely appl ,~ches the m-o1ti~ point of
PVdF), and 50 10 wt% of thermoplastic ac~lic resin. The resultin~ co~tin~ are said to be
20 chara.;l~i;æd by i~ ,r~t;d fle~nbility, crack r~~ ~ and surface ~moothnP~ (as oppose~l
to surface rou~hn~ or "orange peel" ~ te 1 with the finish) while not requiring the
inclusion of a flow~ ring agent. No information is reported about the gloss, not to
2~ 9 0299 --
m~nti~-n gloss re~l~tion, except that the thermoplætic acrylic resin is re~o~ib!,~-for gloss
durability.
U S. Patent S,229,460 to EvodeK -1:~1as~ fluoropolymer-bæed powder co~ ~ which
may be based on PVdF or on a copolymer with at leæt 80 wt% of vinylidene fluoride and
S up to 20 wt% of at leæt one other fluorine-bæed mon~ mer. No inform~tirn is reported
about the gloss nor about gloss reg~llati~
There is, ho~.,er, a certain demand for co~tin&~ exhibiting very low gloss, which
cannot be obtained pr~l.lly. Accor~dhlgly, there is a need for a pl~ for regulating the
gloss of fluorinated powder co~tin~:.
An object of the plesell~ invention is to provide VdFT-bæed powder co~ting
composition~ capable of providing easily controllable low gloss co~tin~ Controllable gloss
co~tin~, as used herein, are co~tin~: whose gloss can be ~ ted from values from above
40, prefela~ly above 50 and most preferably above 60, down to values below 30, prer~ly
below 20 (all values being me~ ed accor~hlg to ISO 2813 at an angle of 60 o), while still
15 having a good surface smoothnes~
Another object of the pr~selll invention is to provide VdFT-based powder co~ti~
co...~ilion~ c~pable of providing low gloss co~tin~- Low gloss c~tin~;, as used herein,
are co~tin~ having a gloss below 30, plere.ably below 20 (all values being ~-.f~h..-~d
accordhlg to ISO 2813 at an angle of 60 o)~ while still having a good surface sm~
A further object is to provide a proc~ for pl~h~g controllable gloss VdFT~ased
CO~tin~
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Still another object is to provide a pr~s for pr~p~iug low-gloss VdFT-based
c~,.~ s.
SUMMARY OF THE INVENTION
Accor~ ly, the pl~nl invention provides a pu..~ ng product c~n~ g
5 ~.nti~lly of:
(a) a resin c~n~pon~,nt c~ l;~ e~nti~lly of:
(i) from 60 to 90 wt% of one or more low m~lti~ point fluorine-based
terpolyme~;
(ii) from 40 to 10 wt% of one or more co,ll~,a~le resins; and,
(b) from 1 to 35 parts byweight of one or more pi~m~,nt~ per 100 parts byweight
of the resin component.
The present invention further provides a proc~ for pr~p~illg ~lin&~ from the
powder c~ p products of the invention, ~nti~lly chal~c~.i~ by a sq1~tinn of the
baking ~ pe.alul~
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The low m~.lting point fluorine-based terpolymers used herein made from t,hree
monomers so1e~t~1 from the group OQ~ ;ng of vinylidene fluorine (VdF),
lell alluor~e~-ylene (TFE), chlor~l irluoroe~lylene, vinyl fluoride, hexafluol ~pr~pene (HFP),
and CF3-CF2-CF=CF2; and having a me1ting tempelalule below about 150C, preferably
below 120 ~C and most plerelably below 100 oC Preferably the terpolymer is made from
a majority of VdF copolymerized with TFE and HFP; the most preferred terpolymers are
21 10293
prepared from 65 to 85 wt% of VdF monom~r units with from 7.5 to 17.5 wt% of each of
TFE and HFP. The melt vis~ily of the terpolymer should preferably be of from 9,000 to
15,000 dPa s, most pleÇelably from 11,000 to 13,000 dPa s, all ...f~ cd at 125 oc
The VdFC is m~ed with one or several c~ ible resins, p.~fe.dluly of the acrylic
S type. Acrylic resins are known in the art and need not be d~cril~l here; a descli~tion may
be found in French Patent 2,636,959-A to ~to~h~om (see line 18 of page 3 to line 14 of page
4). As examples of thermoæfflng acrylic resin, there are those described in US 4,659,768
to DeSoto, particularly under the denomin~ti~n~ "Experirn~nt~l resin" and "control resin".
Huwevt:r, it has been found that it is advantageous to use a thermoplastic acrylic resin, and
10 most adv~nt~o~l~ to use a thermoplastic polymethylmeth~ylate (PMMA) resin. A
preferred thermoplastic PMMA resin is that obt~ined by (co)polymerization of at least
75 wt% of an alkyl meth~rrylate, the other c~monrrners being one or several o~^~inir~lly
un~t-lrated comonomers, prerelably of the allyl (meth)acrylate type. These esters are
formed by the re~tion of the acrylic or memarrylic acid with suitable alcohols, for ~mrl~,
15 methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol and 2-ethylhe~yl alcohol.
Generally, the larger the alcohol portion of the ester, the softer and more fl~bl~ the
reslllt~nt resin. Also, generally, the meth~ylic esters form harder films than the
c~ll~onding acry1ic este~ Examples of such resins inrlucle polymelllyl~ th?~glate,
copolymers of methylmethacrylate with ethyl acry1ate, butyl m~h~ylatÆ, isol~utyl
20 methac~glate, acry1ic acid or methacry1ate acid, and the like. The most preferred PMMA
resins are those which exhibit a v~co~ity of from 7 to 17 P in 40% solution in a 95:5 by
weight mixture of toluene and ethylene gly-col methyl ether.
2~4~293
The weight ratio of the VdFC to the ~r~ .le resin may vary widely from 90:10
to 60:40, pref~ly from 75:25 to 6535, most p.~rel~dbly of about 7030.
The resin co,llpollent may A~lition~lly c~>ntAin minor ~m~ln~ of the usual addi~ive~,
such as an antioxidant, a flow promoting agents, a W absorber, and/or an lhe~sion
S promoter. As s~ ~l in U S. Patent 5,Z2'9,460, an ~nti~ YidAnt may be utili7f~1 to çnh,~n~
heat stability and provide pr~tion against thermal degrA-1~tion and ~li~o~oration of the
co~ting film due to e~iv~ heat at high curing le",~latur~ also, the use of Kynar ADS
as s~ lu(e for flow promoting agent is ~lis~lc)sed
The use of pigments in the coAting colllposilion is ~ ~.able. Indeed, if no pigment
is used, a clear~oat or varnish can be obtained; h<,~ r, the r~sulting ooA~ing is unevenly
milky, which is undesirable. Fur~er, such cl~d~ have a lesser ~ nc~ to high
tempe. atul~s, and most impo. ~Illy, they in~llffl.~ien~ly absorb ultraviolet light which would
contribute to the degradation of the primer (if any). The use of ultrafine ~ niu... dioAide
to absorb ultraviolet light is known commercially.
When pi~,æl,ls are Ic~lui~d, any pig,llelll or co,lll,.-l~tiQn of pigments may be
utili7f~fl, and the choice of pigments should plerelably be made in accor~lce with what is
known in the art for PVdF-based coAtin~- The amount of pigment used may vary widely
accor~ ; to its hiding power. For example, a white topco~l pr~pa~ lu~i~,ely with
li~liulll dioYAide may r~ up to about 35 w~% of pigment Other pi~n~.n~ with better
20 hiding properties may r~uir~ lower amounts.
The process of pr~pal ing the powder co~ting product CO1ll~ es the steps of:
(a) melt-mixing the VdFC, the compatible resin components and the pigments;
~1~029g
(b) fG~ ingpellets; and,
(c) grinding the pellets.
Melt-mixing is normally carried out by extrusion. E~truding and gr~n~ tin~ the
reslllting I~ ure is performed by the usual procedures which are easily determined by one
S skilled in the art. In particular, a single or double screw extruder is utili7fxl at a p,~ g
tempelalu-e of from 100 oc to 130 oc The ~im.on~ ns of the pellets are usually about 3
mm in ~ r and 2 mm in length.
Grinding the pellets is done by any suitable means which allows suitable si_ed
particles to be obtained, which techniques are known to those skilled in the art and need
not be described in detail. For example, U.S. Patent 5,229,460 contains a ~ ~;on of the
state of the art of grinding fluoropolymer-based thermoplastic blends and the influence of
the cooling step thereon.
The finished powder should colll~,lise particles of si_e and shape suitable for
achieving col~lL flow through the application e~uipllællt, mainly in order to obtain a
15 con~l~n~ thickness of co~ting. It is preferred that the shape of the particles be as spherical
as possible and their si_e as uniform as possible so that the rçsl~lting powder will have better
flow pr~,bel Li~ Rega~di~lg the size of the particles, the grinding step is co~ ed with a
sieving step for elimin~ting the largest si7e particles, i~, those particles ~y.~ling about
t~hree times the desir~d thir1~nf~ of the co~tin~ On the other hand, ~i~ly small
20 particles are to be avoided bec~ e they are a hazard to health and they tend to block
transport lines during application.
2~a299
The pler~r~ method of grinding utiliæs a h~ .-Pr mill ~.he.eill a r~la~lg shaft
carries ha"l~ which break the pellets on fixed shapes in the casing of the hqmmer mill,
and h~ Pr them ~ U~h a sieve lining at the bottom of the mill. Sieve openin~ of about
0~ mm have been found particularly appr~pliate.
SThe re~l-lting powder may be applied on the ~ul~llate by any means suitable forachieving an even d~LIibulion of the particles, such as, for example, an elP~lic spray
applic~tiorl app~alu~, whereby the particles reo~ e an electrical charge and then are
ay~d onto an oppositely charged ~ul~l~ale. Alternative t~hni~lues include cloud
chambe~, fluidiæd beds, even triboelectric co~tin~, and the like. Such terhniques are well
10known in the industry and need not be described in great detail.
The VdFC-based p~wder is p.c:fielably applied over a suitable primer co~tin~,
commercially available for similar fluorinated co~tin~, in~ in~ solvent-based "flash" or
powder primers.
After the co~ting has been applied to the substrate, it must be subject to heat
15treatment. The coated ~ul~llale is passed into a heated oven wherein the co~ting is baked.
An ~;enti~l fealule of the ~)r~c~ of the invention is the sol~tion of the t~ alul~
enabling control of gloss. The ~Illpe.aLule to be se1~cted for obl~ining a s~i~lr gloss
(within experimt-nt~1 variations) is easily d~l,l,lilled by one skilled in the art using an oven
with a tempelalule gradient such as is ~;ull~lllly used in the c~tin~: industry and need not
20be described further. This feature is based on the ol~~ lion that the gloss obtained with
the co~ osilions of the invention first increase, then decrease to a low value (as definecl
herein).
21~0~99
Finally, the co~ting and its ~ ale can either be cooled slowly in air or qu~on~h~d
in water.
In order to further illu~l-dle the invention, the following example is given which;is
intended to be illu~llalive only and not to limit the scope of the invention. The example
shows that the desil~d gloss, from high values to low values, can be obtained by s~ecting
a baking tempeld~ure between about 140C (ie~ about 50oC above the melting
tempel alur~) to about 220 oC (i.e., well below the hi~h~t tenlperdlule at which the polymer
is stable). It also shows that better me~h~nic~l properties can be obtained that with PVdF.
Example 1
The following white-pigmented powder co~ting composition was pr~pdred:
- fluorinated polymer 54.9 pbw (parts by weight)
- acrylic polymer 243 pbw
- li~liulll dioxide 21.1 pbw
100.0
The fluorinated polymer is a terpolymer con~ g of about 75 wt% of VdF monomer
units and about 12.5 wt% of each of HFP and TFE monomer units (as ~lelell,lilled from
NMR data by the method of Pianca et al. in Polymer ~, æ4, 1987); said polymer having
the following properties accolding to its te~hnir~l d~t~heet-
-melting point about90 C ASTM D-3418
-specific gravity 1.846 g/cm3 ASTM D-792
2140299
-refractive inde~ (nD25) 1384 ASTM D-524
-tensile ~ng~l @ yield 8 MPa ASTM D~82
-tensile strength @ break 15 MPa ASTM D-882
~lon~tion @ break 990 % ASTM D 882
S -tensile modulus 130 MPa ASTM D-882
-solution vi~i~y 20 mPa-s Bro~ 1 LV
(20 wt% in MEK at 25 oC) #1 spindle @ 30 rpm
-stability up to 316 C
The acrylic polymer is a commercially available thermoplastic copolymer of 70 wt%
10 methyl methacrylate monomer and 30 wt% of ethyl acrylate monomer, having a vi~cosi~y of
about 12 P in 40% solution in a 9S S by weight mixture of toluene and ethylene glycol
methyl ether, cont~ining 3 wt% (relative to the total acrylic polymers) of a low molecular
weight copolymer which colllprised 30 wt% ethyl acrylate monomer and 70 wt% 2-ethylhexyl
acrylate monomer, having a viscosi~y of about 1.06 Pa-s at 98.9 oC.
The r~l.lltin~ mixtures were extruded under the following conditions, giving pellets
of 3 mm in ~ meter and about 2 mm in length:
- twin screw extruder
- screw rotation: 200 rpm
- load: 85%
- tempe~a~ul~ profile: 100C at hopper exit, rising to 1300C in the middle of the
screw, then llS oC up to the end of the screw,
- tempelaLul-e of the material at the exit: 115~
2140299
The pellets were cooled in liquid nitrogen down to about -150 oC, then ground at a
tempeldlul~ of about -100 oC in a h~mtn~r mill and sieved to çlimin~te particles larger than
about 150 ,~n. In the hammer mill, a rotation shaft carries hammers which break the pelle~ts
on fixed shapes in the casing of the h~mm.o.r mill and hammer them through a sieve lining
S at the bottom of the h~mm~r mill. The particle size di~LIiluuLion was me~ red and 99%
of the parhcles had a size below 90 ,~an, with 40% below 32 ,~n. Only 5% had a size below
15 ,~n.
The rçs~llting ~wd~l~ were applied by an ele~;l,~laLic spray process on both sides
of a 1 mm thick rolled steel plate previously covered by a 50 ,um layer of an epoxy primer.
10 The epoxy primer had been prepaled and applied accordillg to Example 1 of Applicants'
European Patent, No. 404752A
Two coated ~ul~LIaLes were then heated 20 ll~inll(~ in a tempe,alure-gradient oven,
giving top c~tin~ of 80 ,~n thickness
The following results were obtained in the two separate determin~tiorl~:
lS L
TeL4~ uu~ ( C) 121 126 131 138 144 157 164 171 179
Gloss (60-CISO-2813) 49 56 59 62 60 61 SS 51 44 30
II.
Temperature ( C) 149 158 168 177 188 199 210 æ 235 249
Glcss (60 C IS0-2813) 59 50 41 26 20 18 18 16 16 16
21~0299
A further coated sul~Llale was baked at 200OC for 10 minutes and the following
properties were m~ ~l after cooling:
- direct impact > 100 kg.cm ASTM D-2794
e impact > 100 kg cm ASTM D-2794
S - flexibility (conical mandrel) 0 mm ISO 6860
- flexibility (Erichsen) 7.7 mm ISO 1510 -
- adherence 0 GT ISO 2409
In the fo,eg~ g examples and written de~.i~tion, ~e following units were
abbreviated as in ~ tef1
~1scosities Energy
Poise - P Joules - J
Pascal seconds - Pa-s Joules per gram - J/g
;p~l seconds - dPa-s Pr~ure and Force
~lillir~ l seconds - mPa-s Pascals - Pa
Me~ l-seconds - MPa-s Megapascals - MPa
The following p~tent~ are hereby incorporated by l~rerellce into this appli~ti- n
FR 2,636,959 - Atochem
US 5 ~29,460
EP 404752~
12
