NO145511B - THERMO-CURSING POWDER COATS CONSISTING OF A POLYESTER AND A POLYEPOXY SIDE. - Google Patents

Description

The invention relates to electrical thermosetting coating product

in the form of a powder coating that is suitable for application by powder spraying methods and coating using a fluidized layer.

In general, thermosetting coating products take the form of

a solution of a synthetic resin in an organic solvent

part that serves as carrier. This solution is applied to the surface of the base material, which can be metal, wood, paper or textile, after which the solvent carrier evaporates and leaves

ter a synthetic resin film, which can then be subjected to heat curing.

The use of inorganic solvents as a carrier for the synthetic resin has the disadvantage that in most cases the solvents are flammable and can even lead to explosions.

down. In addition, some organic solvents are physiologically unacceptable as they are hazardous to the health of those who work with them. In addition, a lot of energy is required for the evaporation of the organic solvent and for the conditioning of the air that must carry away the solvent vapors from the oven where the coating is

the coated objects are burned.

For these reasons, it has been proposed to replace the organic solvents in whole or in part with water. The use of water as a carrier for the synthetic resin, however, necessitates the use of certain types of synthetic resins which may not give the finished coatings the necessary technological properties, e.g. flow, smoothing and shine.

Based on the disadvantages of previous methods, it is also proposed to use high-melting thermoplastic, non-curable

the coating products in the form of a homogeneous powder. This powder is mostly applied by the method known as the fluidized bed method. This method is essentially a dipping process, whereby the object to be coated is pre-

is heated to a temperature above the coating product's melting point and then introduced into a fluidized mass of coating product powder.

Powdery thermosetting coating products can be applied

applied to the substrate in the same way, but requires two heat treatments, first pre-heating of the object to be coated, and then hardening of the coating. Of

for this reason, the electrostatic powder spray application me-

tode has been developed, whereby only one heat treat-

ling, namely hardening, and this method has it

further advantage is that thinner layers (less than 100 ym) can be applied than with the fluidized layer method. Due to the relatively high viscosity of the molten powder, a coating is provided in one treatment that is significantly thicker than what can be achieved by the conventional coating methods where solutions of the coating material are used. Sharp edges or folds are also coated much better with the powder coating processes.

The composition of fusible, powdered coating products for use in powder spraying methods and fluidized bed processes places demands on film-forming materials that are totally different from those used in compositions for conventional coatings. It will be understood that the film-forming material must be a solid that can easily be converted into a free-flowing powder and that does not cake under normal storage conditions, and that the material must be able to melt at elevated temperatures below its breakdown or decomposition temperature.

In practice, the production of a thermoplastic powder coating has entailed much fewer difficulties than with a thermosetting powder coating. This is due to the fact that the thermoplastic powder coating hardens after application by simple cooling, while a thermosetting system must undergo cross-linking in order to achieve the desired film properties. For this purpose, it is necessary to introduce a curing agent, cross-linking agent or a catalyst into the system, which involves special problems.

To date, the most significant thermosetting powder coating systems are based entirely on epoxy resins whose main disadvantage is that they have poor outdoor durability.

There is therefore a constant need for a powdery, free-flowing, fusible, thermosetting coating product which is stable during storage, which can be used in electrostatic powder spray coating processes and which has a reduced epoxy resin content and therefore can be heat cured within an acceptable time to a uniform coating with satisfactory chemical and mechanical properties, and at an acceptable price.

From Norwegian patent application no. 296/70, heat-curable powdery coating compositions are known which consist of an alkoxylated polyamine aldehyde resin and a polyester. When using the known powdery coating compound, the hydroxyl groups in the polyester resin react during curing with the alkoxy groups in the alkoxylated polyamine aldehyde resin, whereby the alcohols are regenerated. The resulting condensation reaction leads to the formation of volatile reaction products, whereby a significant limitation of the film thickness is conditioned, as the volatile components produced by the condensation reaction above a certain film thickness can no longer escape sufficiently from the molten coating material and therefore lead to to the formation of blisters or surface irregularities.

It is an object of the invention to provide a thermosetting powder coating with good powder stability which is suitable for application by powder spraying and fluidized bed coating, and which is produced by melting two resin components (1) and (2), preferably in an extruder, cooling and grinding down to a powder, where component (1), which makes up 75-96, preferably 85-92, % by weight of the mixture, essentially consists of a solid polyester resin (a), prepared from a dibasic, aromatic carboxylic acid and an alcohol component which includes: (a 1) from 0 to 100 mol% (based on the total alcohol component in the polyester) of an alcohol with the general formula: where R 1 and R 2 represent alkylene groups with from 2 to 4 carbon atoms, R 3 represents an alkylidene group with 3 or 4 carbon atoms or a cycloalkylidene group with 6 carbon atoms, or a carbonyl group, or a sulfone group, x and y are numbers that are each at least 1, the sum 4 5 of x and y not being greater than 6, and R and R represent a hydrogen atom or alkyl radical with from 1 to 6 carbon atoms; (a 2) from 0 to 40, preferably 0-20, mol% (based on the total alcohol component in the polyester) of a glycidyl ester of the general formula:

where R is a straight-chain or branched, saturated or unsaturated hydrocarbon radical with from 4 to 20 carbon atoms, preferably 4-10, or a substituted or unsubstituted benzene nucleus, and

(a 3) from 0 to 100, preferably 75-100, mol% (based on

the total alcohol component of the polyester) of at least one

divalent, aliphatic alcohol, the sum of the alcohol components (a 1), (a 2) and (a 3) being 100 mol%,

and this thermosetting powder coating is characterized in that the polyester resin (a) has a hydroxyl number from 15 to 50, preferably 15-40, and a softening point in the range between 60 and 130°C, and that this polyester is modified by reaction with a polybasic, organic carboxylic acid, so that the acid number in resin component (1)

has become from 30 to 100, preferably 40-80,

and that component (2), which constitutes 4-25, preferably 8-15, wt%

of the mixture, is a polyepoxy resin, where the molecule contains at least two epoxy groups.

In a preferred embodiment of the invention, the polyester resin (a) is modified by reaction with an anhydride of an aromatic, at least tribasic carboxylic acid. polyepoxy resin

the latter is preferably triglycidyl isocyanurate.

The thermosetting coating product according to the invention has good powder stability.

In the term "polybasic, organic carboxylic acid" as

is mentioned in claim 1's characteristic also includes the meaning "dibasic, organic carboxylic acid". Preferably, however, the anhydride of an aromatic, at least tribasic carboxylic acid is used, e.g. trimellitic anhydride. Also a mixture of the anhydride of an at least tribasic, aromatic carboxylic acid and up to 50 mol% (calculated on the mixture, of anhydrides) of an anhydride of a saturated or unsaturated, aliphatic or aromatic or cyclo-aliphatic, dibasic carboxylic acid, e.g. maleic anhydride or phthalic anhydride, can be used.

As the dibasic aromatic carboxylic acid in the acid component of the polyester resin can be used: orthophthalic acid, terephthalic acid, isophthalic acid, esters of these acids with lower aliphatic monohydric alcohols, e.g. methanol or ethanol. The dibasic, aromatic acids can be used either alone or in combination with each other. The preferred dibasic aromatic acid is terephthalic acid. In some cases, it has proven advantageous to use up to 10 mol%

(based on the total acid component) of a polybasic, aliphatic carboxylic acid, e.g. adipic acid, or of a tribasic, aromatic carboxylic acid, e.g. trimellitic acid or pyromellitic acid.

Examples of the diol-forming component (a 1) in the polyester resin include 2,2-di-(4-3-hydroxyethoxyphenyl)-propane; 2,2-di-

(4-3-hydroxyethoxyphenyl)-butane; 2,2-di-(4-hydroxypropoxyphenyl)-propane; 2,2-di-(3-methyl-4-3-hydroxyethoxyphenyl)-propane; the polyoxyethylene or polyoxypropylene ether of 4,4^-isopropylidene diphenol, where both phenolic groups are oxyethylated or oxypropylated and the average number of oxyethylene or oxypropylene groups is from 2 to 6, further di-(4-3-hydroxyethoxyphenyl) ketone and di- (4-3-Hydroxypropoxyphenyl)-ketone.

The preferred diols are 2,2-di-(4-3-hydroxyethoxyphenyl)-propane and 2,2-di-(4-hydroxypropoxyphenyl)-propane.

The alcohol component (a 2) in the polyester resin comprises glycidyl esters, and such that can be used include lauric acid glycidyl esters, benzoic acid glycidyl esters and glycidyl esters of saturated aliphatic monocarboxylic acids with tertiary or quaternary carbon atoms in the α-position to the carboxyl groups (available under the trade name "Versatic acids") . The latter glycidyl esters are preferred.

The alcohol component (a 3) in the polyester resin comprises dihydric aliphatic alcohols, e.g. 2,2-dimethylpropanediol-1,3, propylene glycol-1,2, 1,4-cyclohexanedimethanol and ethylene glycol, as these alcohols may contain functional groups other than hydroxyl groups, e.g. diethylene glycol. The dihydric aliphatic alcohols can be used either alone or in combination with each other.

It has in some cases been found advantageous to use up to 10 mol% (based on the total alcohol component) of aliphatic trihydric or polyhydric alcohols, e.g. trimethylolpropane and pentaerythritol. In any case, however, the sum of the alcohol components (a 1), (a 2), (a 3) and, optionally, the aliphatic trihydric or polyhydric alcohol is 100 mol%.

The polyester resins are produced by the general techniques used in the production of polyester resins. They can conveniently be prepared by heating all reaction partners, with stirring, to a temperature of 240°C, while an inert gas (e.g. nitrogen) is passed continuously through the reaction mixture to remove the water formed during the esterification reaction, or the lower alcohol in the reesterification reactions. at the end of the esterification reaction, the pressure is lowered to approx. 100 mm Hg, and some glycol is distilled off.

In general, the polyester resin is first melted with stirring in an inert gas atmosphere. The anhydride of the polyvalent organic carboxylic acid is then added, and the mixture is heated for approx. 1-15 hours, preferably 1-3 hours, at approx. 180-250°C, preferably 180-210°C. The reaction product is then cooled to approx. 140° and poured into shallow containers for solidification. After cooling, the reaction product is crushed into small pieces and ground, preferably in a pin-plate mill, to a free-flowing powder with the desired particle size range (approximately 20-150 µm). The resulting free-flowing powder can be subjected to a sieving treatment to adjust the desired average particle size to the specific application area.

The polyepoxy resins used in the thermosetting coating products according to the invention as a cross-linking agent for the solid, modified polyester resin are compounds or mixtures of compounds, where the molecules contain at least 2 epoxy groups.

Preferably, the average number of epoxy groups contained in the molecule of the polyepoxy resin is 3 or more. Particularly desirable for the purposes of the invention is triglycidyl isocyanurate, although several other well-known polyepoxy resins can be used, provided that they contain at least two epoxy groups in their molecule and that in combination with the solid, modified polyester resins they lead to thermosetting coating products with good powder stability as defined in the following .

When producing the product according to the invention, 75 to 96% by weight, preferably 85 to 90%, based on the total mixture, of the powdered modified polyester resin is mixed with 4 to 25% by weight, preferably 8 to 15% by weight, based on the total mixture, of a polyepoxy resin with at least two epoxy groups at a temperature just above its melting points, i.e. at a temperature of approx. 100°C, e.g. in an extruder, cooled to solidify the mixture and then crushed and ground in a suitable mixer,

e.g. a pin plate mill, to a free-flowing powder with a particle size range of approximately 20-150 µm. The free-flowing powder thus obtained can be subjected to a sieving treatment to adjust the desired average particle size to it. specific type of application.

When filler and pigment components are used, an alternative method is to melt the polyepoxy resin and polyester resin, add the filler and pigment components while mixing in an extruder, cool the resulting mixture for solidification, and then crush and grind it into a free-flowing powder of the desired particle size range.

The homogeneous, powdery coating products that are obtained can also include various well-known functional modifiers, e.g. painting aids, curing agents or accelerators, flow control agents, surfactants, heat-stable organic or inorganic pigments, inert fillers, inhibitors, abrasives and plasticizers in the usually effective proportions.

After applying the coating products to the substrate, the coatings are cured at a temperature of from approx. 120 to approx. 250°C for a period of up to approx. 60 minutes. The hardening treatment is preferably carried out for 10 to 40 minutes at 150-200°C.

In the following, the invention will be described by means of examples. In all examples relating to the production of the final coating product, the product was pigmented with such an amount of titanium dioxide that a weight ratio between pigment and binder of 1:2 was provided. In all examples and in the accompanying claims, all softening points of the polyester and modified polyester resins were determined by a modified version of the ball and ring method according to ASTM E 28-58 T. The method is modified so that the first temperature noted is the temperature at which the ball begins to move, and the last temperature is the temperature at which the ball reaches the bottom plate. On the basis of the application as a powder coating, it has been found advantageous for the evaluation of the properties of the polyester resin to be modified, to use these numbers rather than those indicated in the above

for the mentioned ASTM specification.

Example I

In a suitable reaction vessel equipped with a thermometer,

tubes, separation column and inert gas inlet pipe, it was

carried 2816 g (9 g mol) of the dieter of ethylene glycol and bisphenol A,

480 g (2 g mol) of "Cardura E" (glycidyl ester

of branched-chain monocarboxylic acid with from 9 to 11 carbon atoms) and 1660 g (10 g mol) of terephthalic acid. The contents of the vessel were heated to a temperature of approx. 180-250°C and maintained at this temperature with stirring, whereby the water from the esterification reaction was removed from the reaction mass by bubbling nitrogen gas through it. The heating was continued until an acid number of 7 was reached. The obtained polyester had a softening point of 78-96°C and a hydroxyl number of 30. 1000 g of this polyester resin was heated in a reaction vessel of the same type as described above, to 200-210° C, while nitrogen gas was bubbled through the molten mass. Then 103 g (0.53 g mol) of the anhydride of trimellitic acid were added with stirring, after which the resulting mixture was heated for 3 hours at 200-210°C until an acid number of approx. 62 to 63. The heating was stopped, the product obtained was cooled and solidified. The obtained modified polyester resin had . an acid number of 62.8, a hydroxyl number of 0 and a softening point of 99-111.5°C. The product shall hereafter be referred to as "acid A".

Examples II and III

In the same apparatus as described in example I, it was produced two other polyester resins using the ingredients listed in Table I. The acid numbers (ST), hydroxyl number (OH number)

and softening points (MP) in °C for these polyester resins are also listed in Table I.

-i-jj i- Ir-£PEGBA.,f .diejter-, ayx et.yvlengl.y-koxl,«.qgr ,-bJLs-f ejipl, ;A,3^^ ,' . -'j:;.l.£.!!:3<2>\;o<T>JiSl in ^-tereph^thalic acid,:) ^pso/Moa ,nirnsvooaii v-.; ' Modified ,- polye. ster resins; . (o >!31.:>• oo -pni.t) ~'c .i '.C J . (2a-).-:rl-0p 0.v,g, Lay rpplyes,ter has pik sen f rar: ek sempeli ;M-.^bie. tPRPj^ ;* ^q heated -in- the same apparatus-: and,, in, ;the same -way .^as.:besk-revetj.ci; :example:lT.:I with..86,,;.Q, ;g,j(-Q->£4.5, >g-,;mpl-k-.ay*^hydr.dLd.et , ay0 tr4mej .'ljits.yre;,-j hv.pr-yed-, it was .achieved^"en; mpdif isejr-t;.-pplye^_ter.ha-rp4ks,> .4, de_t;-f øljgendej angifctx \ -v as "acid (Ek", -syretal-lr -5.1.,. hydroxyl.tal lf ,-5and my kn4ngs point-;;; 9.6", 6-vj - 114°C. (3a) 1250 g of the polyester resin from Example III was heated in the same apparatus and in the same way as in example I with 141.3 g. <: . -i::>i-. i.'.£•-.• v j Jtt-j y.p. •< " :\ ''S. i i. ua. p Ot er.-nn la i- J c.O ■ (0.74 g mol) of the anhydride of trimellitic acid, whereby it was obtained ' :3vb ! .v .isvc/itas - ; /.-..'co r/..-.': ifirøovoos c--J Y!>i ::••'/x*<> "i-"' a modified polyester resin, hereinafter indicated as "acid C ", acid number 69, hydroxyl number 0 and softening point 82.0-99.5 C. c- .f c>' w-,c ci; in; in c:-. iqi: rn ''3"' •• ., f; :' :r:- i:.J ~ ! .•:* ■. c->P.r t:''C v n.'c Example, . iy .-t.; .,,, ,..v,r r.i.-r,- . rf< v.-. ^Ic-uv? o>!;.l •••••» n;;;: i About rv'; .

r^^ed^h-jelp^av/^" acid ,A." became:. it -for,emstilt:T et^fbei.egningsprodu.k.t/''; , by -i; ^_en;,_ex^rude^::. ;_å;,-blend- 8.0, g-.ay .-pulvjBrd^.erti^sy.re^A"../. 4;;1,5vi.g; .. Ti02 and 15 g of a powdered polyglycidyl ether of orthocrespl -Æor-.-: malaldehyde-novolac, with epoxy equivalent weight5* of 225 and mp... 73°C (Durran's mercury metpde, described by Gardner and ^Sward in~"<p>å~iift Testing Manual" ,"' in 2. uiq., "1962, p/368)'' and 0.3 wt%, based on r. ' oxøitoti.jvicv; i no .-.i ''-; '>"-'■-': •;'' -■'j^c-.j. > '3 v L:;q u c« jonsiu <> D j "acid A", of tris-(2 ,4 ,6-dimethylaminomethyl)-phenol', a hardening catalyst ("DMP-30").

,:[.; ,'J.') r - V <*>tI 0 •• i vi"'^ 3 H 1V' i' :) 1 K X 'l;i:r) :. M .; : i-. V Ot- The extrudate was broken up and ground into a powder

.• i..': U[!;d;..;, idi' - å: r. vi,:.; oi';3:;n^;;i)ic; obn^iTTin:?:;^J ~ viv 'Vi.-.: - r. ::• :•>'-• ••■ of which 80-90% had eh particle size of between 70 and 100 pm-The powdery, pigmented resin mixture was' applied to 1 mm thick plates • of mild steel by the electrostatic spray coating-- r. ^;-ij!v~ br)R"i i. is i .? ■' i v- • ^ f Jvi >e:~) " ' ^ :v l: . a ■:: L ; '. Q''." J ningsmetdde, in such a way that upon subsequent curing at 180 C

in 30 minutes a uniform coating was formed with a thickness of

":.::i:>risq 3T>cj«j nc po ITV-V1 nn-n icrn7'.«^/.£- ;>n9Pf; ■ hr.c- ru-.:^j.c,7 r.i!

about. 80 etc.

"Epoxyekyjivalentyekten";.-.^ def i-neres .as. the weight;..ay-; ,pplyeppksynr resin x qram "containing 1 chemical gram equivalent of epoxy.

The epoxy equivalent weight is determined -yed^ \å , dissolve-^en. try on, 1.; g.ray,,-. ; the polyepoxy resin in 25 ml of 0.2N pyridinium chloride in pyridine. Afterwards; f?røvén;i;'é'r "uproar >; '-bppvå'fmés '-1'øshi-rig'eW -under 'ti-lbakéløVs-kjølirig; i.,-.25;-minutes-!.; The solution is cooled and 5.0 ml of methanol and 15 drops of phenolphthalein indicator are added. The excess of pyridinium chloride is discarded. i'lb'å'ke <?>iSéd- ^0>'<;>5N'<c>mé<t>6arioI<i>i-'s}e''NaOH<>> ti-11- rdisa : yj 1 endpointx.lEppksy^ekyiyalentye yed afr:man:.;ta;r.viVtV.;i..^..... consideration that one HCi molecule is equivalent to one epoxy group.

Example V

A coating product was prepared by mixing in an extruder at 105°C 88 g of powdered "acid A" and 12 g of powdered triglycidyl isocyanurate, which had an epoxy equivalent weight of 102 and a melting point of 95-115°C (ring and ball method). In this product, 80-90% had a particle size of between 70 and 100 ym. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick sheets of mild steel by the electrostatic spray coating method, in such a way that upon subsequent curing at 180°C for 30 minutes, a uniform coating with a thickness of approx. 40 etc.

Example VI

A coating product was prepared by mixing in an extruder at 105°C 90 g of powdered "acid B" and 10 g of the powdered

te triglycidyl isocyanurate which is discussed in example V. In this product, 80-90% of the particles had a particle size of 70-100 um. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick mild steel panels by the electrostatic spray coating method, in such a way that upon subsequent curing at 150°C for 30 minutes, a uniform coating with a thickness of approx. 70. etc.

Example VII

A coating product was prepared by mixing in an extruder at 100°C 88 g of powdered "acid C" and 12 g of the powdered triglycidyl isocyanurate described in Example V. In this product, 80-90% of the particles had a particle size of 70 -100 etc. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick mild steel panels by the electrostatic spray coating method, in such a way that upon subsequent curing at 150°C for 30 minutes, a uniform coating of thick

look at approx. 70 etc.

The resin compositions of Examples IV-VII and the coated panels

of mild steel obtained in these examples was then examined with respect to its powder stability and mechanical properties. The "powder stability" stated in this description and in the accompanying claims is determined as follows:

50 g of the pigmented, powdery, free-flowing product (of which 80-90% of the particles had a particle size of 70-100 µm) was heated in a beaker at 40°C for 7 days. If the resin particles were not sintered together and the powder was still completely free-flowing, the powder stability was given the designation excellent (E). If the powder only contained some particles that were sintered together and formed soft lumps, the powder stability was designated as moderate (M), and if particles were sintered together, the powder stability was designated as poor (B). The "flexibility" was determined on the basis of the samples of 1 mm thick mild steel plates, on which a quantity of the powdery resin mixture was applied by the electrostatic spray coating method, and these were then cured. The flexibility was designated as acceptable (P) or failed (F), depending on whether or not the coated steel plate could be bent 180° over a 19.2 mm diameter mandrel without damage to the coating. If the film developed cracks or fissures, it was designated as a failure. The "shock resistance" indicated was measured with the "Erichsen Schlagprufgerat" according to the German specification DIN 53.156 with the tests indicated under "flexibility". The "hardness" indicated was measured as "Pendelharte nach Konig" according to DIN 53.157 on the samples indicated under "flexibility". The results are set out in Table II below.

Examples VIII and IX

In the same apparatus as described in example I, two other polyester resins were produced using the ingredients indicated in table III. The same abbreviations as in table I have been used.

Modified polyester resins ■x j t-^- --^ -

(8a) 100.0:-g of woven polyeVtérfia^pikVeW^ira^:,ej?gf vfifnD'feheated in sanune ca'pparaturi o'g:: ipå-«:santoe^nfå£e* Vsbin- x£ example ~T méc3 97 g"'1'-"

(0, 5,-. g-),mol)in the avuan anhydride of- ^frlmelWt sy£é' ltu hVorrvéd "it llile'vobtained a modified:Jpolye'stefhårpiks>::"in: dfefc*ffj8irgen<J'e aWgitV ^as' '"acid'b'"",' acid number. 'SjV^.ogC.myknl-ng^spurik-ti^O^MO^C^ 'TOt; '3av^-I(? '-^ -iCl Mt-(9a) 1000 g of pol-yes"tér^arpiVse!rr^Va-ekVrix<1>" was "heated" in the same apparatus and to the same extent-ft/as in example I with 126 g ( . pu>n<k>YH9T-l"0"<4>o<,>C"; |

Final coating products I •»- j :. n... t, l4.

(8b) By means of "acid D" ;it became! produced a. coating-i..,- i ■,: r ,•-I o r-S i :.n-,ri; sno:sc^.).;-:i;f product by in ;one extruder' at 116 C mixing 100 g of powdered "acid D" and 11;',X ..g_Åy„dat.pul-veriser-efe- -trigly discussed in Example V. In this product, more than 90% had a particle size between 70 and 100 µm. The powder form-in-ge7--i'ri"tt'=''''<::::>' strewn,-^pigmented^ plates .of ^soft-steel5 -at that"<;>élék't/ fosSatiské^^ tode, on eh :s-l-ik"^måté^at'-vé^d -followingVhdfé': h'éTd'ing vedi26u°c"i io mi-'0 nuts an even coating formed with a thickness of approx. . 70-80 pm.-The powder stability and mechanical properties were as follows:

(9b) With the help of "acid E", a coating product was prepared by mixing in an extruder at 105°C 645 g of powdered "acid E" and 105 g of the powdered triglycidyl isocyanurate mentioned in example V. In this product, more than 90% of the particles a particle size of 70-100 ym. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick sheets of mild steel by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes, a uniform coating with a thickness of approx. 70-80 etc. The powder stability and mechanical properties were as follows:

Example X

It was prepared in the same apparatus as described in example I

a polyester resin of 9 mol neopentyl glycol, 1 mol 1,6-hexanediol,

1 mol "Cardura E" and 10 mol terephthalic acid. The polyester obtained had an acid number of 8.3, a hydroxyl number of 38.3 and a softening point of 86-103°C.

750 g of this polyester was heated in the same apparatus <p>g on

the same way as described in example I with a mixture of 49.0 g of trimellitic anhydride and 102.0 g of maleopimaric anhydride, whereby a modified polyester resin was obtained, hereinafter referred to as "acid F", acid number 65.6 and softening point 92-108 °C.

With the aid of "acid F" a coating product was produced at i

an extruder at 105°C to mix 860 g of powdered "acid F" and 140 g of the powdered triglycidyl isocyanurate as described in Example V. In this product, more than 90% of the particles had a particle size of 70-loo ym. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick mild steel plates by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes, a uniform coating with a thickness of approx. 50-60 etc. The powder stability and mechanical properties were as follows:

Example XI

It was prepared in the same apparatus as described in example I

a polyester resin of 5 mol ethylene glycol, 3 mol neopentyl glycol,

1 mol of 1,4-cyclohexanedimethanol, 2 mol of "Cardura E" and 10 mol of terephthalic acid. The obtained polyester had an acid number of 9.3, a hydroxyl number of 32.5 and a softening point of 74-83°C. 1824 g of this polyester was heated in the same apparatus and in the same manner as described in Example I with 218.9 g of trimellitic anhydride, whereby a modified polyester resin was obtained, hereinafter referred to as "acid G", acid number 66 and softening point 96- 117.5°C. With the aid of "acid G" a coating product was prepared by mixing 580 g of powdered "acid G" and 170 g of powdered diglycidyl terephthalate in an extruder at 100°C. In this product, more than 90% of the particles had a particle size of 70-100 µm. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick sheets • of mild steel by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C

in 20 minutes a uniform coating with a thickness of approx. 50 to 60 ym. The powder stability and mechanical properties were as follows:

Example XII

In the same apparatus as described in example I, a polyester resin was produced from 6 mol ethylene glycol, 3 mol neopentyl glycol,

1 mol of diethylene glycol, 1 mol of "Cardura E" and 10 mol of terephthalic acid. The obtained polyester had an acid number of 6.4, a hydroxyl number of 36.5 and a softening point of 81-97°C. 750 g of this polyester was heated in the same apparatus and in the same way as described in example I with

93.9 g of trimellitic anhydride, whereby a modified polyester resin was obtained, hereinafter referred to as "acid H", acid number 83.3 and softening point 94-104°C. With the help of "acid H", a coating product was produced by mixing 600 g of powder in an extruder at 100°C -

sert "acid H" and 66 g of powdered triglycidyl isocyanurate. In this product, more than 90% of the particles had a particle size of 70-100 um. The powdery, free-flowing, pigmented resin mixture was applied to 1 nm thick sheets of mild steel by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes, a uniform coating of thickness approx. 50 to 60 ym. The powder stability and the mechanical

characteristics were as follows:

Examples XIII-XV

In the same apparatus as described in Example I, three other polyester resins were produced using the ingredients indicated in Table IV - The same abbreviations as in Table I are used.

Modified polyester resins

(13a) 1000 g of the polyester resin from example XIII was heated in the same apparatus and in the same manner as described in example IX with a mixture of 58.5 g of trimellitic anhydride and 30.5 g of succinic anhydride, whereby a modified polyester resin was obtained, hereinafter referred to as "acid K", with an acid value of 50.1 and a softening point of -93-114°C.

(14a) 750 g of the polyester resin from example XIV was heated in the same apparatus and in the same manner as described in example I with a mixture of 126 g of trimellitic anhydride and 4 g of maleic anhydride, whereby a modified polyester resin was obtained,

hereinafter referred to as "acid L", with an acid number of 94 and a softening point of 112-126°C.

(15a) 750 g of the polyester resin from example XV was heated in the same apparatus and in the same manner as described in example I with a mixture of 41 g of trimellitic anhydride and 14 g of maleic anhydride, whereby a modified polyester resin was obtained, hereinafter stated as "acid M", with acid number 36 and softening point 87-115°C.

Final coating products

(13b) With the aid of "acid K", a coating product was prepared by mixing in an extruder at 115°C 440 g of powdered "acid K" and 60 g of the powdered triglycidyl isocyanurate mentioned in Example V. In this product, more than 90% of the particles have a particle size of 70-100 ym. The powdered, free-flowing, pigmented resin mixture was applied to 1 mm thick mild steel sheets by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes, a uniform coating of thickness approx. 50 to 60 ym. The powder stability and mechanical properties are indicated in table V.

(14b) With the aid of "acid L" a coating product was produced by mixing in an extruder at 120°C 625 g of powdered "acid L" and 75 g of the powdered triglycidyl isocyanurate mentioned in example V. r this product, more than 9u% of the particles had a particle size of 70-100 ym. The powdery, free-flowing, pigmented resin mixture was applied to 1 mm thick mild steel sheets by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes, a uniform coating of 60 to 70 µm thickness was formed . The powder stability and mechanical properties were as follows in Table V.

(15b) With the help of "acid M", a coating product was prepared by mixing in an extruder at 115°C 630 g of powdered "acid K" and 120 g of the powdered triglyceride isocyanate mentioned in example V. In this product, more than 90% of the particles a par-tickel size of approx. 70-1UU etc. The powdered free-flowing pigmented resin mixture was applied to 1 mm thick mild steel plates by the electrostatic spray coating method, in such a way that upon subsequent curing at 200°C for 10 minutes a uniform coating of thickness approx. 50 to 60 ym. The powder stability and mechanical properties were as in Table V.

Example XVI

In the apparatus and by the method described in example I, the following ingredients were reacted to form an intermediate hydroxyl-terminated polyester:

The resin was then divided into two portions:

one portion was further reacted with phthalic anhydride (Example XVIA) and the other portion with hexahydrophthalic anhydride (Example XVIB).

Example XVIA

1500 g of the intermediate product was heated to 185°C, and then 190 g of phthalic anhydride (with an acid value of 750 mg KOH/g and aniline value of 409 mg KOH/g) was added. The mixture was stirred for an additional 1 hour at 185°C and was then cooled. The resin thus produced had the following characteristics:

This resin was used with additional ingredients listed below to produce a powder coating using an extruder whose jacket was heated to a temperature of 110°C. The mixture was ground to a fine powder.

After application and storage for 10 minutes at 200°C, a coating was obtained which had the following characteristics:

Example XVIB

The second portion of the intermediate product, 1500 g, was likewise heated to 185°C, and then 198 g of hexahydrophthalic anhydride (with an acid number of 728 mg KOH/g and aniline number of 389 mg KOH/g) was added. The mixture was stirred for an additional 1 hour at 185°C and then cooled. The resin thus produced had the following characteristics:

Using this resin, a powder coating was produced using an extruder as indicated above:

After application, a coating was obtained which had the following characteristics:

Example XVII

Using the same apparatus as described in example

column I, a polyester resin was prepared from 10 mol of neopentyl glycol and 11 mol of tetrahydrophthalic acid. The obtained polyester had an acid number of 7.5 mg KOH/g, a hydroxyl number of

40 mg KOH/g and a softening point of approx. 56-63°C.

1000 g of this polyester resin was heated in co-

with apparatus and in the same manner as described in Example I, with 257.9 g of hexachlorophthalic anhydride, and as a result a modified polyester resin was obtained which had an acid number of 34 and a softening point of 74-78°C.

By means of this modified polyester resin was

a coating preparation was prepared by mixing 660 g of it with 90 g of triglycidyl isocyanurate in an extruder at 105°C. More than 90% of the particles in this product had a particle size of 70-100 um.

The pulverized, free-flowing, pigmented resin powder was then applied by the electrostatic spray coating method to 1 mm thick mild steel plates in such a way that upon subsequent curing at 200°C for 10 minutes a uniform coating was obtained which had a thickness of approx. 50-60yum.

The powder stability and the mechanical properties of the coating turned out to be:

Claims (3)

1. Thermosetting powder coating with good powder stability which is suitable for application by powder spraying and fluidized bed coating, and which is produced by melting two resin components (1) and (2), preferably in an extruder, cooling and grinding to a powder, where component (1), which makes up 75-96, preferably 85-92, % by weight of the mixture, essentially consists of a solid polyester resin (a), prepared from a dibasic, aromatic carboxylic acid and an alcohol component comprising: (a 1) from 0 to 100 mol% (based on the total alcohol component in the polyester) of an alcohol with the general formula: where R 1 and R 2 represent alkylene groups with from 2 to 4 carbon atoms, R represents an alkylidene group with 3 or 4 carbon atoms or a cycloalkylidene group with 6 carbon atoms, or a carbonyl group, or a sulfone group, x and y are numbers that are each at least 1, wherein the sum 4 5 of x and y is not greater than 6, and R and R represent a hydrogen atom or alkyl radical with from 1 to 6 carbon atoms; (a 2) from 0 to 40, preferably 0-20, mol% (based on the total alcohol component in the polyester) of a glycidyl ester of the general formula: where R is a straight-chain or branched, saturated or unsaturated hydrocarbon radical with from 4 to 20 carbon atoms, preferably 4-10, or a substituted or unsubstituted benzene nucleus, and (a 3) from 0 to 100, preferably 75-100, mol% (based on the total alcohol component of the polyester) of at least one divalent, aliphatic alcohol, the sum of the alcohol components (a 1), (a 2) and (a 3) being 100 mol%, characterized in that the polyester resin (a) has a hydroxyl number from 15 to 50, preferably 15-40, and a softening point in the range between 60 and 130°C, and that this polyester has been modified by reaction with a polybasic, organic carboxylic acid, so that the acid number in resin component (1) has become from 30 to 100, preferably 40-80, and that component (2), which constitutes 4-25, preferably 8-15, wt% of the mixture, is a polyepoxy resin, the molecule containing at least two epoxy groups. 2. Thermosetting powder coating as specified in claim 1, characterized in that the polyester resin (a) is modified by reaction with an anhydride of an aromatic, at least tribasic carboxylic acid. 3. Thermosetting powder coating as stated in claim 1, characterized in that the polyepoxide resin is triglycidyl isocyanurate.