CA2140301A1 - Process for preparing high-gloss fluorinated coatings - Google Patents

Abstract

Process for preparing high-gloss fluorinated coatings wherein Vinylidene fluoride copolymers having a melting temperature below about 160°C are used to prepare high-gloss pigmented powder coating products. Also observed was an improved corrosion resistance when substrates subject to corrosion were coated with the copolymers.

Description

-` 21~30~

EXPRESS MAIL #IR~A~8560~0 PATENT
Docket No.: F~29 PROOESS FOR PREPARING HIGH-GLOSS FLUORINATED COATINGS

CROSS REFERENCE TO REIATED APPLICATION
This applic~tion claims priority of previously filed copending Belgian appli~tiQn Serial Number 93870241~ enti~led T~oce~ for prep~,ng high gloss fluo-ulal~d co~
filed Dec...l~ 23, 1993; which previously filed applir~tinrl is hereby incorporated by reference herein.

BACKGROUND OF THE DNVENTION
The pr~senl invention relates to pi~T~ont~ powder co~tin~ products, based on vinylidene fluoride copolymers (hereinafter referred to as VdFC), for plepali~:lg high~loss fluorinated coatin~ and to a pr~)o~ for co~ting a ~ul~llate with a high-gloss pigmente~l VdFC puw~ler co~tin~. In particular, the preselll invention relates to the use of vinylidene fluoride copolymers in pi~n~nt~d puw~r coating products, for oblainin~ high~oss VdFC-based prote~iv~ co~;n~
~o~tin~ based on vinylidene fluoride homopolymers (hereinafter PVdF) are known to be very useful as prùl~ive co~tin~ for a variety of :iu~llales due to their good chemir~l and weather l~e~ n~ and to the thermal stability of PVdF. The general known te~llnique used for pr~pa~h~g PVdF co~ting~ iS to p-epare a dispersion of PVdF in a suitable solvent for application by known means onto the required substrate, and thereafter subjecting it to heat treatment.

-~ 214û301 The solvent used is generally known in the prior art as Hlatent solventn, and it is desclil~l therein as an or~ a~lic solvent which has no ~i~ifir~nt action on PVdF at room t~ lule, but which at an elev~lted temperature e~erts a sl~ffi~i~nt solvent action.
H~ r, although the known ~y~ lB may give good results, e,lv~o~ nt~l S pr~1ion laws throughout the world, but mainly in Europe and in the US~, are m~kin~
it incl~ingly ~liffrll1t to utilize solvent-based ~ysl~lls. Further, the leco~t;ly of the solvent is a costly pr~ lur~ Accor lin~,ly, there is a need in the art for solventless PVdF-based co~tin~ British Patent GB 2194539-A, to Labofina ~ r1os~ pi~rnf~.nt~l PVdF-based powder cli,.l;n~, products con~ e~Pnti~lly of vinylidene fluoride homopolymer (or 10 copolymer with at most 10 wt% of comonomer units), one or more c~mp~tible thermoplastic resins and one or more pigments. It also ~ ases a ~)rvce~ for preparing the products.
H~wevt:l, the gloss obtained is not acceplably high. GB 2194539-A is hereby incorporated by r~re European Patent No. EP 456018-A, to Elf ~tochem North America ~li~l~s 15 pign.ellLed p~..Jer co~tin~ of vinylidene fluoride/hexafluoropropene copolymers, the resin component colll~ g 50 90 wt% of said copolymers having a melt viscosiLy of 1~ kPoise [10~400 Pa-s] at 100 s-l and 232 C, said copolymers being chara~,i~d by a melting point in the range of about 160 oC to about 170CC (which closely approaches the melting point of PVdF), and 50 10 wt% of thermoplastic acrylic resin. The res~ltin~ co~tin~ are said to 20 be cha~acL~rid~d by il-lpr~ved flexibility, crack r~;~ and surface smoothness (as op~l to surface roughness or "orange peel" associatedwith the finish) while not requiring the inclusion of a flow-improving agen~ No information is reported about the gloss, e~cept 21~0301 that the thermoplastic acrylic resin is ~e~ ible for gloss durability. US. Patent s,æ9,460 to Evodex ~ ~ fluoropolymer-based ~wder co~tin~ 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.
S The inability of PVdF to produoe high-gloss co~tin~ is l~.CO~ in the art (see e.g., JOaCA ~(4), 145). Past a~ ~ to produce high-gloss fluorinated co~tin~ in<~
those de~clil~ad in US. Patent 3,944,689 which ~ osqs solvent~ased co~tin~ oo~ ~s;~ions based on vinylidene fluoride copolymers, co,nt~ining gloss~nh~n~ing solvents as ~n~ to that invention.
The plæellt invention aims at providing pi~n.onte l VdFC-based po.. ~er co~ting coll,~osilions for ple~)~ing high~loss co~tin~ High gloss C~ , as used herein, are co~tin~ having a gloss of more than 40 when measw~ accoldillg to ISO 2813 at an angle of 60 o; and pl~fel~bly a value of more than 50; and most prerer~bly a value of more than 60. Another object of this invention is to provide a pr~ for pr~ari~g high gloss 15 pi~n~nte-l VdFC-based co~tin~
It has ~w~u~isillgly been found that these compositir~ns~ when applied on ~ul~laLes subject to corrosion, provide i~ rov~d ~ ance t~ corrosion in c~ .ison to similar co~ ;ons based on PVdF.

~1~03~1 SUMMARY OF THE INVENTION
Ac~ lgly, the pl æ-ll invention provides a pi~ .-e~ cl VdFC-based powder c4~tin~product for ple~ing high-gloss co~tin~, c~ g ~nli~11y Of:
(a) a resin component Con~e~ ~n~;~lly of S (i) from 60 to 90 wt% of one or more vinyUdene fluoride copolymers having a melting tempel~lul~ below about 160 C;
(ii) from 40 to 10 wt% of one or more CU~ ;1J1C resins; and, (b) from 1 to 35 parts byweight of one or more pi~mentc per 100 parts byweight of the resin component The plesent invention further provides a ~r~i for the use of vinylidene fluoridecopolymers having a m~olting ~l"~elalul~ below about 160 oC in pi~.~nl~1 powder c~ti~
products for providing high gloss protective co~tin~, c~pable of exhibiting gloss values that exceed 50, and even 60.
The pr~el1l invention ~d~lition~lly r~ s a pr~ for l)lepa~n~, high-gloss fluorinated co~tin~, ch~a~;ler~d in co-llplising the steps of:
(1) Providing a pi~nen~e-l polyvinylidene fluoride copolymer-based powder compo~sition co~-e;~ e~nti~lly of:
(a) a resin c~rnponent con~ -g f~.nti~lly of:
(i) from 60 to 90 wt% of one or more vinylidene fluoride copolymers having a rn~1tin.~ Iempe,alule below about 160~
(ii) from 40 to 10 wt% of one or more c~...r~ible resins; and, 214~.~01 (b) from 1 to 35 parts by weight of one or more pigm~Pnt~ per 100 parts by weight of the resin component;
(V applying the po..der to a ~ul~LIaL~, and, (3) ~ul,je~ g the c~ting on the ~ul~LlaLe to heat tre~tmPnt-S The present invention also provides for the use of vinylidene fluoride copolymers having a mPlting Lel"~l ~Lur~ below about 160 oC in pi~m~.ntP~l ~.. Jer co~tin~ productsfor application on siu~L~a~es subject to corrosion.

DESCRIPTION OF THE PREFERRED EMBODIMEN~
The vinylidene copolymers used herein are the copolymers p~ e~ from 70 to 99%
by weight of vinylidene fluoride (VdF) monomers with 1 to 30% by weight of one or more fluorinated com~l~omers such as tetrafluoroethylene (l~), chlor~l,irluoroelllylene, vinyl fluoride, hexafluoropropene (HFP), and CF3~F2-CF=CF2; and having a melting tempe ralure below about 160 C, prefe~ ably below 150 C and most pr~re, ably below 140 oC
Preferred copolymers are pr~ar~d from 75 to 95% by weight of vinylidene fluoridemonomer, preferably more than 80 wt % and most preferably more than 90 wt%. Preferred comonomPrs are l~`~ and HFP.
In one of the ~I~Çc.led embo~1impn~ VdF/HFP copolymers are used, said copolymers having a me.ltin~ tempe,dlu,e (Tm) of about 107 + 68 e~ l4lX wherein X is the amount of HFP monomPr, ~.*,l~ in % by weight, in the copolymer as c~lc~ ted by NMR data by the method of Pianca et al. (Polymer ~, 224-30, 1987). Such copolymers are known in the art and need not be described in greater detail. They are characterized by a 21~030~

lower . . ,P11 iil~o point for a given con~ of HFP c~monomer~ While not wishing to be bound by a theory, it would appear that the high gloss does not result dir~ly from the lower melting ~ alUI'~ be~All~ the melt flow index, which reflects the melt vi~oo~iiLy,;is ~ n~ ;Ally independent of the melting ~-~ a~u~ In any case, one skilled in the art would 5 not have ex~ted that a lower melting point would be responsible for a higher gloss.
~n~, it is known from US. Patent 4,179,542 that the use of fluxing agents (i.e~ hi-gh boiling latent solvents for PVdF) lower the obsel ved mPlting point of PVdF at t~lllpelalur~
above 60 ~C, while the powder co~ting c~nll)osiLions f~ Qsed in EP 284996 A to PPG and c4-.~Ai~-in~ more than 40% of a such agent are not r~l~ed to have a high gloss.
In another preferred emb~lim~pnt~ VdF/HFP copolymers are us_d, said copolymers having polydispersity values Uz lower than 1.0, preferably equal to about 0.9, and Un lower than 1.7, p,~re.dbly lower than 1.6, most preferably lower than 1.5. As used herein, Uz is equal to (MJMW)-1 and Un is equal to (MW/Mn)-1, wherein Mz is the z-av~lage mo',~ul~r weight, Mn the number-average molecular weight and Mw the weight-a~e.age molecular weight; all molecular weights being del~llllil~ed by GPC (gel permlo~tinn chromalo~dj)hy).
In a third ~r~re,led embodiment, the copolymers used have a tensile modulus lower than 800 MPa, preferably lower than 600 MPa, most preferably lower than 400 MPa, when d acconlil~g to ASTM D 638.
In a fourth prefelled embocliment~ the copolymers used have a melt ~iscosily g~eater than about 400 Pa-s measured at 100 sec~l and 232OC using ASTM D-3825 test method, plefe.ablygl~l~r than about 400 Pa-s at 100 sec~l and 240 oC but sm~llP-r than about 1300 21~0301 Pa-s at 100 sec~l and 232 oC, and most plef~ably gr~l~r than about 600 Pa-s at 100 sec~
and 240 C but sm7.11er than about 1000 Pa-s at 100 sec~l and 2320C
rlerell~d VdFC resins are those having a weight-a~ molecular weight (~s de~~ ed by GPC) in the range of from 50,000 to 270,000, most p,efe,ably from 90,000 S to 160,000 and a melt flow index (acoordinig to ASTM D-1238 at 230 oC with a S kg weight) of from 5 to 30 g/lOmin, most preferably from 6 to 20 g/lOmin. -The VdFC is mi~d with one or more cr~.~y~ 1e resins, pr~relably of the acrylic type. Acrylic resins are known in the art and need not be described here ~lthou~h a description may be found in French Patent FR 2,636,959A (from line 18 of page 3 to line 14 of page 4). As examples of thermoset~in~ acrylic resin, there are those described in US.
4,659,768 to DeSoto, particularly under the denomin~ti~ ns "E~perim~nt~l resin" and "c~llllol resinN. H.~ ~, it has been found that it is adv~nt~ous to use a thermoplastic acrylic resin, and most a lv~ a~ to use a thermoplastic polym~lllyl"leth~r~ylate (PMMA) resin.
A plere.l~ed thermoplastic PMMA resin is one obt~in~ by (co)polymerization of at least 75 wt% of an allyl meth~ ate~ the other com~ nomers being one or more o~i~finir~lly ale~ comonome~, preferably of the alkyl (meth)acrylate type. Tbiese esters are formed by the re~rtion of the acrylic or meth~rrylic acid wit-h- suitable alcohols, for example, methyl alcohol, ethiyl alcohol, propyl alcohol, butyl alcohol and 2-ethylhexyl ~lroho!
Generally, tbie larger the alcohol portion of thie ester, the softer and more flexible the r~l~1t~nt resin. Also, generally, the methacrylic esters form harder films thian thie coll~onding acrylic esters Examples of such resins include polymethylme1h~rrylate, copolymers of methylmethacrylate with ethyl acrylate, butyl methacrylate, isobutyl ~1~0301 me~ ,ylate, acrylic acid or meth~l~rylate acid, and the like. The most preferred PMMA
resins are those which eYhibit a vi~cosily of from 7 to 17 P in 40% solution in a 95:5 by weight Il~ixLwe of toluene and ethyiene gly-col methyl ether.
The weight ratio of the VdFC to the c~ r~ible resin may vary widely from 90:10 to 60:40, preferably from 75 25 to 65 35, and most preferably of about 70 30.
The resin component may ~iti~)n~llyc~ in minor amounts of the usual addiLiv~s, for example, W al~,l~~ h~ion promoters, flow promoters and/or ~nti~)xid~nt~ As sug~l~l in US. Patent 5,229,460, an ~nti-Yi-l~nt maybe utili7~1 to enhance heat stability and provide pr~Le~ion a~inst thermal degr~d~t3On and discoloration of the c02~ti~ film due to ~ive ~Illpela~ures incurred during heat curing. Another usual additive is a flow promoting agent which, although not ~nti~l to the invention, helps obtain a high quality of co~ti~ surface l~quir~d in the industry. Flow promo~in~ agents generally inrlud~ acrylic resins having a relatively low molecular weight (eg., M,V of about 20,000). The amount of flow promoting agent may vary from 0 to 3 wt% based on the total weight of the mixLule, but the ~mount preferably used is less than about 1 wt% based on the total weight of the codLing product. The use of Kynar ADS ~ as ~ul~l;~ ule for a flow promoting agent is known in the art from U.S. Patent 5,229,460.
Use of pigments in the co~ting composition is p.er~lable. Indeed, if no pigmellt is used, a cl~arcoa~ or v~lli~ll can be obtained; however, the resulting co~tin~ is unevenly milky, which is undesirable. Further, such clear~od~ have a lesser ~ nce to high~ ,pelalules, and most impo-~llly, they insufficiently absorb ultraviolet light which co~ s to the degradation of the primer when primers are used. The use of ultrafine titanium ~ Y ~ to absorb ult,raviolet light is commercially known.
When pigrnont~ are to be used, any pigment or col~ination of pigmPnt~ may be s~ ~ The choioe of pigments should pleferably be made in accor~lce with what~is known in the art for PVdF-based coating~ The ~mount of pigment used may vary widely S ac~rding to its hiding power. For example, a white topcoat pr~pa~ ,lusiv~ly with ni...~ .1 ~de may r~uire up to about 35 wt% of pigment Other pigment,s with better hiding pr~p~. lies may require lower amounts.
The pr~ of preparing the powder co~ting product col.lplises the steps of:
(a) melt-mixing the VdFC, the col.lpa~il)le resin compollents and the pigm~nt~;
(b) formingpellets; and, (c) grinding the pellets.
Melt-mixing is normally carried out by extrusion. ~truding and granulating the r~lllting "~i~Lule can be acajlllplished bythe usual procedures which are easily de~ ed by one skilled in the ar~ In particular, a single or double screw extruder is utili7~1 at a pr~ ~n,~lalur~ of from 150 oC to 190 oC The ~limpn~ions of the pellets are usuaUy about 3 mm in ~ meter and 2 mm in length.
Grinding the pellets is done by any suitable means which allows suitable sized particles to be obtaine~ Techniques are known to those skiUed in the art and need not be desclil~d in detail. For example, US. Patent 5,229,460 corlt~ins a ~ nn of the state 20 of the art of grinding fluoropolymer-based thermoplastic blends and the infl~len~ of the cooling step t,hereon.

2i40301 The finixhed powder should c~,llp,~e particles of size and shape suitable for achieving c~..x(~( flow Lllr(ju~l- the appli~tiQn eqllirment~ and to obtain a c~-.xlA"~ c~A~
thirlrn~: It is preÇe.l~d that the shape of the particles be as spherical as possible and their size be as uniform as possible l~-~se the resultin~ powder will have better flow prope, Lies.
S R~g_rdil~g the size of the particles, the grinding step is followed by a sieving step for el; - i~ -g the largest size particles, i.e~ those particles ~Y.~lin~ about three times the desired thi~n~x of the co~ting On the other hand, ~ixiv~ly small particles are to be avoided I~Ause they are a hazard to health and they tend to block ll al~l L lines during application.
It is preferable to use a h~mmer mill to grind the pçll~" wherein a rotating shaft carries h~mmers which break the pellets on fixed shapes in the casing of the h~mmer mill, and h~mm~r them through a sieve lining at the bottom of the mill. Sieve openings of about 0~ mm have been found particularly approp,iate.
The r~ul~ing ~w~r may be applied on the ~ul~sLlale by any means suitable for 15 achieving an even di~llilwlion of the particles, using for example, an ele~ ~lic spray appli~tio~ a~palalu~, whereby the particles reoeive an electrical charge and then are ayed onto an opposilely charged ~ul~ le. Alternative te~hniques include cloud rh~mbers, fluidized beds, even triboele~tric co~;ng, and the like. ~uch tef~hniques are well known in the industry and need not be described in great detail.
~0 The VdFC~ased powder is preferably applied over a suitable primer co~tin~, e.g., those known in the art as primers for similar fluorinated co~tin~

21~0301 After the co~ing has been applied to the substrate, it must be subjected to a heat treatment. The coated ~ ale is passed into a heated oven wherein the co~tin~ is baked, preferably at a ~ l~.alule of from 150 to 2~0 oC, preferably of from 160 to 190 C The l~lll~,elalul~ used in this step should be higher than the meltin~ point of the powder, which S melting point is easily del~-lllined ~I;~ent~lly~ eg with an oven having a tempelalule gradient. On the other hand, ~x~iv~ly high tempe.~lul~s have a yellowing effect on the finished co~ting. The duration of the heating step is determined by any suitable method known in the art, taking into ac~unL that an i1lsufflcient duration is detrimental to the surface hardness and to the gloss. One of the advantageous results of this invention is that 10 high gloss can be obtained without the need to bake at relatively high tempe~alur~, conll~y to the expectations of those skilled in the art Finally, the co~ting and its substrate can be either cooled slowly in air or qu~nrh~l in water.
It is su l.lisillg that high-gloss co~tin~ can be obt~ined from VdFC-based powder co~in~, in view of the conllaly te~rhin~ of US. Patent 3,944,689 to the effect that gloss-enhancing solvents are ~nti~l It has also been observed that the re~s -ltin~ co~tin~ unexpectedly have better m~h~nit~l properties.
In order to further illu~ le the invention, the following examples are given which 20 are intended for illu~LIali~ pUl~O~S only and not to limit the scope of the invention.

2~40301 Example 1 and C~ )drdLiv~ Ex~nple B
The following powder co~ting c~ on was pr~pared.
- fluorinated polymer 64.8 pbw (parts by weight) - acrylicpolymer 27.9 pbw - Lil~~ l dioxide 0.7 pbw - pi~nent~ 6.6 pbw -100.0 The mixture of pigments was selected to yield a red color co,l~onding to RAL
3004; it col1s~L~d of 5.1 pbw of Bayferroxu~ 130BM (iron oxide), 1.0 pbw of Quindo 4 Violet RV 6951 (organic pigment) and 05 pbw of Kronos 4 ~ 2160 (titanium dioxide).
The flow ill,~r~v~;r was a low molecular weight copoly-mer of 30 wt% of ethyl acrylate monornçr and 70 wt% of 2-ethylhexy1 acry1ate m~nomçr, having a v~co~ily of about 1.06 Pa-s at 98.9~C
The acrylic polymer is a commercially available thermoplastic copolymer of 70 wt%
methyl me~ . . ylate monomer and 30 wt% of ethyl acrylate monomer, having a viscosi~y of about 12 P in 40% solution in a 95 5 by weight mixture of toluene and ethylene glycol methy1 ether.
In FY~n~rle 1, the fluorinated polymer is a copoly-mer of vinylidene fluoride and 20 hexafluoropropene having the following characteristics:
- VDF/HFP molar ratio: 93:7 (NMR determin~tion according to Pianci et al., Polymer ~, 224, 1987) 21~0301 - melt flow index: 85g/10 min (ASTM D-1238; 2300C, 2.16 kg) - melt ~li~ily: 850 Pa-s (ASTM D-3835; 240 oC, 100 s~l) - molecular weight (GPC):
Mn = 49,000 M,v = 112,000 Mz = 217,000 S - tensile properties (ASTM D 638 on a 2mm thick pr~æd sheet):
- tensile stress at yield 16 MPa -- u1tim~te tensile strength 34 MPa - elongation at yield 14 %
- elongation at break 650 %
modulus 360 MPa - flexural ~rope,lies (ASTM D-790 on a 4mm thick ~l~ed sheet):
- m~X;~ - Ioad 30 MPa - modulus 380 MPa - DSC ..... ......P~ nt~ (ASTM D-3418):
- n~e1ting point 134 oc - fusion heat 23 J/g - cryst~lli7~tion point 97OC
cryst~lli7~tion heat 25 J/g - brittleness tempel~lu,~ (ASTM D-746 A): -23 oc In co~ raLivc~ Example A, the fluorinated polymer was a vinylidene fluoride homopolymer commercially available from ATOCHEM NORTH AMERICA under the tr~ n~me KYNAR 710.

21~0~01 The r~l11ting l~lixluies were extruded under the following con~lition~, giving pellets of 3 mm in diameter and about 2 mm in length:
twin screw extruder - screw rotation: 200 rpm 5 - load: 85%
- ~lll~dlU~e profile: 1650C at hopper exit, rising to 1900C in the middle of the screw, and 180 C at the end of the screw, - t~"lpelalwe of the material at the exit: 180 oC
The pellets were cooled in liquid nil,ogell down to about -150 oC, then milled at a 10 temp~lalu,~ of about -100 C in a h~mmçr mill and sieved to ~limin~te particles larger than about 150 ~Lm. In the h~mmçr mill, a rotation shaft carries h~mm.ors which break the pellets on fixed shapes in the casing of the h~mm.or mill and hammer them through a sieve lining at the bottom of the mill. The particle siæ distribution was measured: 99% of the particles had a siæ below 90 ,~n and 40% below 32 ~n. Only 5% had a size below 15 ,~n.
The res -ltin~ pow~ was applied by an elecLI~Lalic spray process on both sides of a 1 mm thick chrom~te~l alu",inum plate previously covered by a 50 ,um layer of an epoxy primer. The epoxy primer had been plepa~d and applied accordillg to Example 1 of Applicants' European Patent, No. 404752~
The coated ~u~llate was then heated 9 lui~ules at 220OC (object tempelalu,e), 20 giving a 50 ~m top co~ting Gloss me~ en~ were made at an angle of 60 C according to ISO 2813.
- Example 1: 60 p~r;~ v~ FY~mPIe A: 31 1iti~n~l me~u~nlents were made with the c4~ , of Example 1:
Example 1 Comp. EY A
-direct impact r~ nce > 150 kg.cm 40 kg.cm ASTM D-2794 S - ~ e impact resi~ oe >150 kg.cm 25 kg.cm ASTM D-2794 -adherence GTO GTO ISO 2409 --flexibility(conir~l mandrel) 0 mm 2mm ISO 6860 -flexibility (Erichsen) > 10 mm 6 mm ISO 1510 gloss ret~ntion after 2000 h AWOM 75.2% 90% ASTM G 26 -gloss retention after 5000 h QWB 88.7% 88% ECCA-T10 -acid salt spray corrosion (2000 h) none none ASTM B-287 -Kesternich 20 cycles (2 L SO~) none none DIN 5018 -filiform corrosion (1000 h) 0-3 mm 0-2 mm DIN 65472 Example 2 and Col-lpalativ~ Example B
20 Example 1 and C~ ativ~ Example A were repeated, except that the following white pigment powder composition was prepared (RAL 9010) - fluorinated polymer 54.9 pbw -acrylic polymer 233 pbw -flow improver 0.7 pbw 21~0301 tilal)iulll dioxide 21.1 pbw 100.0 GIQSS m~ cnlents were made aco~r~iing to ISO 2813: ;
Example 2 Comp. Ex B
atan angleof 600 62 38 ~d-lition~l me~ ---ent~ were made with the co~ti~ of l~ample 2: --direct impact r~ ce 140 kg.cm ASTM D-2794 ,e~ e impact ~ n~ >150 kg.cm ASTM D-2794 -adherence GTO ISO 2409 -flexibility (conical mandrel) 0 mm ISO 6860 -flexibility (Erichsen) > 10 mm ISO 1510 -gloss ret~ntion after 2000 h AWOM 88.8% ASTM G-26 -gloss retentiQn after 5000 h QWB 109% ECCA-T10 -acid salt spray corrosion (2000 h) none ASTM B-287 -Kesternich 20 cycles ( 2 L SO~) none DIN 50018 -Hoek van Holland t~ (1 year) 117% EC~CA-T19 gloss retention l~amples 3 and 4. and Comparative Examples C and D
Example 2 was repeated, except that vinylidene fluoride-hexafluor~proplelle copolymers 20 were used that had the following characteristics (detelluilled as mentioned in Example 1):

2~0~01 E~L2 Ex 3 E5L4 Comp.C CompD Units - VDF/HFP molar ration: 93:7 93:7 955 96:4 96:4 -~melt flow index 85 2.2 2.2 85 2.2 g/10 min - molecular ~.~i~ls Mn 49 56 65 42 51 x 1000 S M,~ 112 134 135 113 143 x 1000 Mz 217 251 245 227 336 x 1000 -- tensile propel ~ies:
- tensile stress at yield 16 16 26 31 31 MPa tim~te tensile strength 34 45 43 24 33 MPa 10- e1~n~ti~n atyield 14 10 10 %
n~tion at break 650 700 480 400 400 %
mod~ 360 350 750 1000 1000 MPa - fle~ural p~ope~
-m~llu.,l load 30 49 40 MPa 15-- modulus 380 970 1000 MPa - DSC me~ r~lllents:
- mPltin~point 134 131 146 160 160 oC
- fusion heat 23 23 40 38 38 J/g - cryst~lli7~ti~n point 97 93 101 119 119 oC
20- cryst~lli7~tion heat 25 24 34 35 35 J/g - brittl~on~ tempelaLule -23 -15 -17 oC

- co,.l;,-g prope.Lies:
- gloss (ISO 2813, 600) 62 70.8 48.4 37.6 28.6 .~

A few other prope. Lies were me~sured and found to be idçntic~l for E~amples 3 and 4, and (~ alive Examples C and D:
S - direct impact (ASTM D-2794) 100 kg.cm -- l~vt;l~e impact (ASTM D-2794) > 100kg.cm - adherence (ISO 2409) GTO
- conical mandrel (ISO 6860 ASTM D-552) 0 mm Example S
Example 1 was repeated except that the following composition was prepared:
- fluorinated polymer 62.2 pbw - ac~lic polymer 265 pbw - flow hnp~v~r 0.8 pbw - pigments 10.5 pbw and that the fluorinated poly-mer and pi~mçnt~ used were as follows:
The fluo,illaLed polymer was a co~ l,el~ially available copolymer of vinylidene fluoride and lel~alluoroelllylene having the following characteri~ics as shown on the terhnic~l d~t~h~t - mçlting point læ - 126 C (ASTM D-3418) - fusion heat 12.5 - 20.9 I/g (ASTM D-3417) ~1~0301 - tensile plopc.lies (ASTM D-638 and D-1708 at 25 oC):
- tensile stress at yield 145 - 18.6 MPa tirn~te tensile strength 32.4 - 44.8 MPa - elon~tion at break 500 - 800 %
S - modulus 414 - 552 MPa The ~ Lur~ of pi~r Pnt~ wæ sele~t~ to yield a brown color, it col-s~ ed of 1.9 pbw of Flalnml~ 101 (carbon black), 2.5 pbw of Sheperd brown 49 (organic pigment), 3.4 pbw of Bayfellu,~ 180 (iron oxide) and 2.7 pbw of Tipaque~ TY200 (chromium tit~n~te.).
The gloss was measure~ according to ISO 2813 at an angle of 60 o; a value of 56 was olusel ved.

Examples 6 and 7 and Cc~ aLive Examples E and F
The following white-pigment powder co~tin~ composition wæ ple~ ed:
- fluorinated polymer54.9 pbw - acrylic polymer 233 pbw - flow imp~ . 0.7 pbw - titanium dioxide 21.1 pbw 100.0 The fluorinated polymer, the acrylic polymer and the flow illlpluv~r were identical 20 to those of Examples 1 and 5 (respectively, for Examples 6 and 7) and in Col~lpalative ~1~0301 Example A (for C'~ aLi~l~ Examples E and F). The powders were ple~a~ed as described above.
In ~cample 6 and ~4...p~aLive Example E, the res~1ting ~wd~l~ were applied by an el~t.o~ldlic spray proc~i on both sides of a 1 mm thick Sen~17imir steel plate having a 5 25 ,~un thick zinc layer, covered by a 50 ,~n layer of an epoxy primer. The epoxy primer had been pr~ d and applied accor~h g to Example 1 of Applicants' patent EP-404752-A.
In Example 7 and Comparative Example F, the powder co~tin&~ were applied on both sides of a 1 mm thick thermally galvani~ed steel plate having a 40 ~n thick zinc layer, co.~.ed by a 50 ,~n layer of the epoxy primer described hereabove.
In Examples 6 and 7, the coated ~ul~LIales were then heated 15 minutes at 200 oC
(air tempe.alule), giving 80 ,~n thick top oo~tin~
In (~(j.np~alive Examples E and F, the coated ~ul~lla~es were then heated 15 minutes at 230 ~C (air temperature), giving 80 ~n thick top co:ltin~
The co~tin~ obtained show a good r~;i~lce to corrosion. That property is 15 determined by ASTM-B-117 (salt spray) test method, using panels coated on both sides and evaluated according to ASTM D-714 (blister formation). The p~ne1~ previously notched with two cl~ed lines, are subjected to a salt spray (50 g/l NaCl) at a tempelalule of 35 oC
for lO00 hours. The following results were obtained:
Example6 Example7 Comp.E~cE Comp.E~LF Test Used - 600 gloss 62 60 38 38 IS0 2813 - salt spray none none 7-12 mm 308 mm ASTM B-117 corrosion 21~0301 Example 8 Example 2 was repe~tell using an ~ nt~1 VDF-copolymer sold under the name Kymar RC 10062 by Elf-Atochem and having the following cha~a(;lu~Lics:
VDF-HFP ratio (NMR) 94:6 Melting point 142-145 oC
Gloss of the white CQ~ ,. 65 palalive Examples G. H and I
Example 2 was repeated, except that vinylidene fluoride-hexafluor~ropene copolymers that had the following characteristics were used:
MEI HOD COMP E~G COMP E~CH COMP EX I UNrrS
VDF/HFP molar rado NMR ~ ~ t~ 96:4 98 2 95:5 acco~ing to Pianca et aL Polymer ~, 224, 1987 Specific gravity AS~M D792 1.76-1.78 1.76-1.78 1.76-1 %0 Melt viscosity ASIM D3835 2300-2700 2300 2700 L~1700 Pa-s (232 C, 100 s-l) Melt ~ow rate ASTM D1238 - - 25-65 g/10 min (230 'C, 5.0kg) ASTM D1238 ~7 3-7 - g/10 min (230 C, 12 Skg) Meltingtem~~ ASTM D3418 140-145 155 160 140-145 C
Tensile plu~ i~ ASTM D638 tensileyield str~ngth 20-27 34 20-24 MPa tensile br~alcstr~ 24-41 39 37-45 MPa break elon~ti- n 400-600 400 400-700 %
tensile modulus 483-620 793 - MPa Fle~ral modulus ASTM D790 620~27 1158 655-793 MPa ~14~3~1 Co~g P~es Gloss IS028L3(60' angle) 6.6 38.1 12.4 ~lsually, the co~tin~ obtained from these copolymers were glossy but, because of a very bad flow, the r~cordhlg of this property according to the ISO method yielded low value~
The qu~ntific~tion of the flow at 220 C of VDF~opolymers wæ al~lllpt~d accor.dhlg to a method developed for phenolic resins ~DIN 16916 part 2):
Copolymer of Example 1 41.7 mm 8 12.8 mm 9 15.0 mm 10 14.8 mm In the foregoing examples and ~.littell description, the following units were abbreviated as indicated:
~lscosities Energy Poise - P Joules - J
Pæcal-seconds - Pa-s Joules per gram - J/g Decipæcal-seconds - dPa-s l~lillip~ l-seconds - mPa-s Pr~ur~ and Force Me~ seconds - MPa-s Pascals - Pa Me~p~ - MPa ~03Ql The following p~tPnt~ are hereby incorporated by reference into this application:
EP 404752A; US 4,659,768; and GB 2194539A; US 5,229,460.
FR 2636959A;

Claims (11)

1. Powder coating composition for preparing high-gloss coatings, consisting essentially of:
(a) a resin component essentially consisting of:
(i) from 60 to 90 wt% of at least one vinylidene fluoride copolymer having a melting temperature below about 160°C;
(ii) from 40 to 10 wt% of at least one compatible resin; and (b) from 1 to 35 parts by weight of at least one pigment per 100 parts by weight of the resin component.

2. The composition for preparing high-gloss coatings according to claim 1, wherein the copolymers are prepared with 75 to 95 wt% of vinylidene fluoride monomer, and 25 to 5 wt% of at least one comonomer selected from tetrafluoroethylene and hexafluoropropene.

3. The composition for preparing high gloss coatings according to either of claims 1 and 2 wherein the copolymers have a melting point below l50°C.

4. The composition for preparing high-gloss coating according to either of claims 1 or 2, wherein the copolymers have a tensile modulus lower than 600 MPa.

5. The composition for preparing high-gloss coatings according to either of claims 1 or 2, wherein the copolymers have a melt viscosity greater than about 400 Pa-s at 100 sec-1 and 232°C, but smaller than about 1000 Pa-s at 100 sec-1 and 232°C.

6. The composition for preparing high-gloss coatings according to either of claims 1 or 2, wherein the copolymers are copolymerized with hexafluoropropene and have polydispersity values Uz equal to about 0-9, and Un lower than 1.6.

7. The composition for preparing high-gloss coatings according to either of claims 1 or 2, wherein the copolymers are copolymerized with hexafluoropropene and have a melting temperature TM of about 107+68e0.141X, wherein X is the weight percentage of hexafluoropropene in the copolymer as calculated from NMR data by the method of Pianca et al.

8. The composition for preparing high-gloss coatings according to claim 7, wherein the compatible resin is thermoplastic polymethylmethacrylate.

9. The composition for preparing high-gloss coating according to claim 8, wherein the weight ratio of copolymer to resin is about 70:30.

10. The use of vinylidene fluoride copolymers having a melting temperature below about 160°C in pigmented powder coating compositions for providing high-gloss coatings.

11. The use according to claim 10, wherein the composition consists essentially of the composition according to claim 9.