CA1044400A - Powdered coating composition and method - Google Patents

Abstract

Abstract of the Disclosure A coating, preferably a powder coating, composition comparising a polymerized resin having isocyanate reactive functionality and an organic polyisocyanate cross linking agent having at least one blocked isocyanate group and at least one isocyanate group that has been reacted with an agent that after curing of the coating composition is an internal plasticizing agent for the resin but prior to curing is an external plasticizing agent for the resin, wherein the poly-isocyanate is first reacted with the blocking agent and the product of the reaction is reacted with the plasticizing agent.

Description

::

~044~00 Background of the Invention - -The invention is concerned with a coating composition and in particular a powder coating composition. In particular, the coating composition is comprised of various segments which during the curing of these segments form a flexible adherent film upon the substrate. Most preferably, the powder is comprised of a polymerizèd acrylic resin and a cross-linking `~
agent having isocyanate reactivity.
The problems to be solved for prior coating compositions, especially powder paint coating compositions are that they had poor flow during cure and the films had poor gloss. In addition, there were high temperatures required for fusing, ;~
while the cross-linking reaction temperature was even higher, ,~
about 375-500F. Further the prior art materials had a temdency to cake in storage at low temperatures, such as 70-80F and that the coatings were brittle, lacked flexibility and adhesion.
The solution to these problems would be to have as pure a cros~-linking aqent a8 possible, which i8 compatible ~ ,::.

B&P 72096-M
iO4~4~0 with the polymerized resln. In addition, the cross-linking agent should impart flow at a desired low temperature as a solvent and act as an external plasticizing agent for the resin, yet be stable below desired storage temperature; it also should have functional groups which will cross link with the resin at as low a temperature as efficiently possible and after cross-linking will become part of film and act as an internal plasticizer.
U. S. 3,660,143 teaches a radiation curable paint binder having the addition product of a hydroxy functional acrylic rubber particle, a diisocyanate and a hydroxyalkyl acrylate and vinyl monomers.
U. S. 3,542,586 teaches a radiation cura ~e paint with a vinyl binder having pendant monoester groups.
U. S. 3,317,463 teaches the utilization of bloc~ed -isocyanate compositions (blocked with hindered phenols) in preparation of urethanes, while U. S. 3,583,943 teaches the blocking of an isocyanate group with a ketoxime. -U. S. 3,621,000 teaches a ~locked isocyanate with a bifunctional polyether.
U. S. 3,659,003 teaches a copolymerized acrylic resin which is reacted with a monoblocked diisocyanate to produce molding powders. The difficulty with all of the previous art is that there is not a simple means of incor- -porating a plasticizing effect into a cross linked -polymerized resin by a convenient processing step in the -- -formation of the resin film as has been described above.
Further the dif~iculty with all of the previouS
art i5 that there is not a simple means of formulating a powde~ composition which can rapidly be cured to the desired film at a low tem~erature.

- 2 -,, - , " , ,.

B&P 72096-M
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Summary of the Invention~
Due to the uniqueness of the coating composition especially powder coating composition of the present invention, one is able to obtain a cure at a low temperature resulting in an adherent film. Due to the need for a desired powder coating composition which can give a top coat quality as is needed in the truck and automobile industry, there has been a need for obtaining such low temperature cure of the film forming composition, yet eliminate caking of the powder.
The powder composition should have the ability of flowing p~ o the curing operation. If there were to be an agglomeration or caking of powder particles, it is prefe~red that this occur at as high a temperature as possible Yet in order to conserve energy in using less heat for the cure it is ~est that the powder composition have as low a curing or cross linking temperature as possible. There~ore, the softening point of the composition of the powder should be relatively narrow. Further, when employing a blocked isocyanate as a cross linking agent, it is preferred that when the iso-cyanate group unblocks, there should be little or no gas formation during the curing operation. To achieve these advantages, applicant's invention can be considered a coating composition especially a-powder coating composition comprising a polymerized resin having isocyanatP reactive functionality and an organic polyisocyanate cross linking ~gent having at least one bloc:ced isocyanate group and at least one isocyanate group that has been reacted with an agent that after curing of the coating composition is an internal plasticizing agent or the resin but prior to curing is an external plasticizing agent for the resin.

- 3 -~09~44QO
A further feature of the invention is therefore dlrected towards a unique cross-linking agent having at least one blocked isocyanate group and at least one isocyanate group that has been reacted with an agent that after curing of the coating composition is an internal plasticizing agent for the resin but prior to curing is an external plastici~ing agent for the resin.
In one particular aspect the present invention provides a solvent resistant coating composition comprising (i) a polymerized resin having isocyanate reactive functionality and (ii) an organic polyisocyanate cross linking agent derived from isophorone diisocyanate, a blocking agent and an agent that after curing of the coatlng composition is an internal plastici~ing agent for the resin, wherein the isophorone diisocyanate is first reacted with the blocking agent and the isocyanate group - con- -taining product of that reaction is reacted with the plasticizing ~ -agent, the plasticizing agent containing at least two isocyanate reactive groups and the cross linking agent containing at least ~ -two blocked isocyanate groups, A, Description of Preferred Embodiments ---The present invention is concerned with a coating - - -composition preferably a powder coating composition which may be applied to a desirable substrate which on heating would form a hard adherent film. The powder that is employed in the present r~
case generally is a very fine powder, havlng a range of particle size, from about 0.1 to about 250 microns, preferably 1 to ~50 -microns and more preferably from about 10 to 100 microns, pre-ferably having an average diameter of less than 35 microns, While the invention is primarily directed towards a coating composition, the preferred embodiment is a powder coating compos- --ition and the two will be used interchangeably.
The substrate that the coating is applied on may be unprimed metal, plastic, glas.s and the li~e. It is to be - ~ ;

, " , , . '.

44(~0 appreciated that on non-conduct-Lve surfaces, a conductive deposit such as carbon or metal may be placed thereon, prior to applying the coating of the present invention. This is especially true if the powders are to be electrostatlcally deposited on a charged substrate, If one did not wish to apply such a conductive làyer, it would be possible to heat the substrate so taht the particles may adhere thereto. It has been found that desirable top coat qualities can be obtained when a metallic substrate is employed.
While the metallic substrate may be cleaned with normal cleaning techniques such as a chlorinated hydrocarbon, alkali and the like, the powder may be applied directly onto the metallic sub-strate .'"~ ~ , jl/r i _4a~

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without the use of a normal phosphate corrosion resistant coating compositions. In some instances, however, it has been found desirable to obtain long time corrosion resistance with powder coatings to apply a phosphate corrosion~ resistant coating composition onto the metallic substrate.
Generically a component of the coating composition is a polymerized resin having i~ocyanate reactive functionality.
In other words, the resin is already polymerized but has oendant functional ~roups, which groups may react with the isocyanate group from the cross linking age`nt. The cross linking would occur during the curing (normally by heating) of the powder coating. By "isocyanate reactive functionality" is meant that the composition has a reactive group which may react with an isocyanate group.
Examples of polymerized resins having isocyanate reactive functionality preferably are thermosetting resins although thermoplastic resins may also be employed. A pre-ferred polymerized resin is one containing pendant groups that hav e replaceable hydrogen atoms such as those hydrogens which are present in a hydroxyl group, an amino group (a primary or secondary amino), a mercapto group, an amido group and the like. While Applicant does not wish to be tied to any theory of the invention, it is believed tha~t the hydrogen atoms will shift from the aforementioned groups to the unblocked isocyanate group during cure or there may be an ester interchange of carbonyl addition reaction whereby the isocyanate group is not reformed ~ut rather an intermediate is formed, The polymerized resin is preferably a linear polymer.
The resin may be a polymerized ethylenically unsaturated material, such as acrylics, methacrylics, vinyls, polyesters, -and the like. The preferred polymerized resin is one where the monomer is of the formula t[Rl-o-~o)cl-A-[c(o)o-Rln wherein n and t are 0 or l and n + t is from 1-2; ~herein A is alkenyl .. . .

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or alkenylene of from 2 to 8 carbon atoms or a substitutent thereof, wherei~ the substitutent may be chloro, carboxy or cyano; it is to be appreciated that A may be branched or straight chain; and R and R may be t'he same or different and may be hydrogen, alkyl of from 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms, hydroxy substituted alkyl of from 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms, and even more preferably 2 to 5 carbon atoms, a primary or secondary amino substituted alkyl of from 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms; wherein the substitutent on the amino group is an alkyl group or a hydroxyl aklyl group of from 1 to 6 carbon atoms; mercapto substituted alkyl group of from 1 to 6 carbon atoms; mer,capto subsLiL~Led alkyl of from 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms;
alkyl thio alkylene of up to 20 carbon atoms, preferably up to 8 carbon atoms and a group of up to 8 carbon atoms containing an oxipane ring, most preferably, 3 carbon atoms as glycidyl.
Of the abo~e monomers, the most preferred are those n+t = 1, especially acrylics, methacrylics, and the like.
Of the above monomers, suitable examples of acids are a~rylic, methacrylic, itaconic, ethacrylic, maleic, fumarici and the like; suitable examples of alkyl esters are where the alkyl group is methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl, hexyl, ethylhexyl, octyl, decyl, dodecyl, and the like;
suitable examples of hydroxy substituted alkyl is hydroxyl ethyl, hydroxypropyl, hydroxy butyl, hydroxyl pentyl, hydroxy hexyl, hydroxyl octyl, hydroxy decyl, hydroxyl dodecyl, and the like;
suitable examples of aminoalkyl are amino methyl, amino ethyl, amino propyl, amino butyl, amino pentyl, amino -, B&P 72096-M
~044400 hexyl, amino octyl, amino decyl, amino dodecyl wherein the amino group is a primary amino or a secondary amino and the substitutent on the amino is an alkyl group of from 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms; suit-able examples of a mercapto alkyl are methyl mercapto, ethyl mercapto, propyl mercapto, butyl mercapto, pentyl mercapto, hexyl mercapto, octyl mercapto, decyl mercapto, dodecyl mercapto, and the like; in like manner the alkoxy alkyl and the alkyl thio alkyl groups may be methoxy methyl, ethoxy methyl, ethoxy ethyl, methyl thiomethyl, ethyl thio-ethyl, and the like.
It is to be appreciated that while the polymerized resin may be a homopolymer, it is most desirable to utilize a mixture of monomers to give various properties to the coating composition of the film such as improved chip resistance, chalking resistance, adherence, gloss, flexibility, dura-bility, hardness, flow, caking resistance and solvent resistance.
A preferred polymerizable monomer mixture is one having a major anount of esters (R or Rl in above formula is alkyl or su~stituted alkyl where the substitutent is non-functional or non-reactive) (about 50 to 90~); a minor amount (about 0.1 to 5%) of an acid (R or Rl is hydrogen), and a significant amount (about 5 to 25%) of a functionally substituted alkyl (R or Rl is an alkyl group having a sub-stitutent which has isocyanate reactive functionality).
In a~dition, other copolymerizable monomers, having an ethylenically unsaturated group, may be added to the mix-ture ;n ~nor amounts ~from about 0.1 to 10%) such as ali-phatic or aromatic vinyls (e,g, vinyl chloxide~ Yln toluene, styrene and the like).

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All that is required for the polymerized resin is that it have pendant isocyanate reactlve functional groups, such as those recited above.
The polymerization reaction of the aforementioned monomers employs standard polymerization techni~ue using catalysts, promoters and the like. A preferred process is solution polymerization in various organic solvents.
Since the composition is to be utilized preferably as a powder coating composition, the temperature for curing shouldbe at as low a temperature as possible. Therefore it is preferred that the molecular weight of the polymerized resin be relatively low, such as, from about 10,000 to about 75,000 with as little deviation from the num~er average as possible. In other words, to obtain such a cure, the range of molecular weight for a given copolymer should be as narrow as possible, yet still within the above range.
It should be pointed out tha~ the low molecular weight resin is to achieve desirable flow, film appearance, less "orange peel" appearance and the like. A narrow molecular weight distribution permits a high caking temperature for powder, better flow, better gloss appearance and better compatibility with the other components of the powder composition~
Cross Lin~ing Agent The cross linking agent that is employed as a component of the powder coating composition is a poly-functional organic isocyanate cross linking agent wherein at least one isocyanate group is a blocked isocyanate group and at least one isocyanate group has been reacted with an agent that after curing of the coating composition i5 an internal plasticizing agent for the resin but prior to , . i , . . .. .. .. . . . . . .

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curing is an external plasticizing agent for the resin. By "internal plasticizing agent" is meant a material which is a separate chemical entity or a portion of another chemical entity which imparts a plasticizing effect to the resin, i.e., imparts flexibility, workability and abîlity to flow, and which after cure the agent is chemically bonded to the polymerized resin. By "external plasticizing agentn is meant a material which is a separate chemical entity or a portion of another chemical entity which imparts a plasticizing effect to the resin, i.e., imparts flexibility, workability and ability to flow, ana which is not chemically bonded to the polymerized resin. The distinct advantage of employing a blocked isocyante is that during the curing of the powder coating composition, the isocyanate group will become unblocked and the isocyanate group may be reacted with the isocyanate reactive functional groups which are pendant from the polymerized resin.
By "blocked Isocyanate" is meant to mean an iso-cyanate group which has been reacted with a blocking as-nt which reaction product is stable at ambient temperatures and pressures and stable up about 50 degrees Centigrade, for periods of time, and which is compatible with the poly-merized resin having isocyanate reactive functionality.
During the curing of the powder coating composition, the blocked isocyanate becomes unblocked d~ring baking, such as from about 125 to about 200 degrees C., which unblocked isocyanate groups are then reactive with the pendant iso-cyanate reactive functional groups in the polymerized resin.

In preparing the ~socyanate cross linking agent a polyfunctional organic isocyanate is employed. Any of the . .. .. ...

lV444~0 polyfunctional isocyanate materials may be employed, such as, the alkyl and cycloalkyl isocyanates preferably containing from l to 8 carbon atoms, such as ethylene diisocyanate, propylene diisocyanate, butylene diisocyanate, hexylene diisocyanate, cyclohexylene diisocyanate, isophorone diiso-cyanate, and the like; aromatic diisocyanates such as phenylene diisocyanate, toluene diisocyanate, such as the 2,4- and 3,6- toluene diisocyanate, biphenylene diisocyan-ates wherein the pheyl ring may be substituted with hydroxyl groups, alkyl groups alkoxy groups, and the like, wherein the alkyl groups are up to 4 carbon atoms. Other isocyanates that may be employed are:
polymethylene phenyl polyisocyanate;
polyphenylene polyisocyanate;
Desmodur-N (trademark of Bayer for poly-isocyanate materials); . : .

Hylene W (trademark of Du Pont for polyiso-cyanate materials, such as, methylene-bis- ~.

4-phenyl isocyanate); ~ ' methylene-bis-(cyclohexyl isocyanate);
ethylene-bis-(cyclohexyl isocyanate);
N (CH2CH2CH2NC0)3;
S (CH2CH2CH2NC0)2;
0 (CH2CH2CH2NC0)2;
2,5 - diisocyanato - 1,3,4, - oxadiazole;
(CH3)2 SI - (isocyanatocyclohexyl);
Bis - ( 4 - isocyanatocyclohexyl ether;) Bis - (4 - isocyanatocyclohexyl sulfonei) Bis - (4 - isocyanatocyclohexyl sulfide.) .
For a listing of suitabl~ isocyanates, reference is made to U.S. 3,217,463. ~ . .

ph/ - 10 -. ,; , . , , . ~ .

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In order to impart both external and internal plasticizing effects, preferably the agent is reacted with one isocyanate group of the polyisocyanate. Suitable isocyanate reactive agents are: saturated aliphatic glycols or polyhydric alkanes or cycloalkanes, such as butylene glycol, 1,6 aihydroxy octane;
1,7 - dihydr~yyoctane; 1,10 - dihydroxy decane; 1,12 -dihydroxydodecane; 2,2,2, - trimethylolpentane; pentaery-thritol; 1,3,5, - trihydroxypentane; 2,4,6, - trihydrQxy-hexane; neopentyl glycol (2,2 - dimethyl - 1,3 - dihydroxy propane); 2,2,4 - trimethyl - i,3 - pentanediol; 1,4 cyclo-hexanedimethanol; and the like; polyoxyalkylene glycol wherein the alkylene is from 2 to 4 carbon atoms, such as, polyoxyethylene glycol, polyoxy propylene glycol, po~yoxybutylene glycol, of a molecular weight of up to 500; polyhydric materials having the repeating linXage -[CH2-CHtCH2OH]n wherein n ranges from 1 to 10; polyaminocompounds, such as, 1,4-diamino butane;
1,6 -diamino-hexane; 1,8 - diaminododecane; it is to be appreciated that the amino compounds should be primary or secondary amines having at least one reactive hydrogen; a substitutent may be attached to the nitrogen; the substitutent may be an alkyl -group or hydroxy alkyl group of from 1 to 6 carbon atoms.
Suitable examplçs of mercapto compounds are: 1,4 - di mercapto pentane; 1,6 - di mercapto hexane; 1,8 - di mercapto octane; 1,10 - di mercapto decane; 1,12 - di mer-capto dodecane.
Sui~able examples of amido compounds that may be employed are 1,4 - di amido butane; 1,6 - di amido hexane; --1,8 - di amido octane; 1, io - di amido decane; 1,12 - di amido dodécane It is to be appreciated that a hydrogen attached to the amido group may be replaced ~y an alkyl or hydroxy alkyl thereby having at least one replaceable hydrogen which may be reacted from the amido group.

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1~)44~00 The isocyanate group can be "blocked" wherein the isocyanate group is reacted with a material which subsequently, under the application of heat, will decompose which then may enter into a reaction with the pendant functional group of the polymerized monomer such as with a hydroxyl group to give a ure-thane or an amino group to give a urea or an amido to give a group of the structure;
-N(H)C(O)-N-C(O)-. A suitable list of blocking agents are those recited in U.S. 2,982,754 or 3,499,852. Some blocking agents that may be employed are phenols, alcohols, caprolac tam, al-doximes or ketoximes. Preferably the blocking agent is a ke-toxime. Suitable ketoximes are those recited in U.S. 3,583,943. ~,;
The preferred ketoxime are dialkyl ketoximes, such as the dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, di-isobutyl ketoxime and the like.
In the preparation of the cross linking agent at least one of the isocyanate groups of the polyfunctional is-ocyanate is reacted with an isocyanate reactive compound which will induce or impart the desirable effects during the curing step and after cure. The use of a blocking agent adds to the ~uick curing step of the present powder.
It is to be appreciated that any plasticizing agent having a replaceable hydrogen from a functional group may be used providing the functional group is reactive with one of the isocyanate groups of the polyfunctional organic isocyanate ma- -terial. It is preferred that the plasticizing agent have two -functional groups and possibly three functional groups which -may react with the polyisocyanate. -Preparation of Cross-Linking Agent ~
.
a) Polyisocyanate and blocking agent X
b) X and Polyfunctional plasticizing agent Y

ph/ - 12 -~ B&P 72096-M
1~44400 wherein X contains a blocked isocyanate group and at leas. one unreacted isocyanate group; and Y contains the blocked isocyanate group and a group resulting from reaction with the plasticizing agent.
As can be seen, the plasticizing agent is a poly-functional material which is reactive with the isocyanate group of the polyfunctional isocyanate. The preferred plasticizing agent that may be employed is one containing at least 4 carbon atoms wherein the functional groups have isocyanate reactivity and are separated by at least 1 carbon atom. Preferably, the -plasticizing agent has at least 6 carbon atoms to about 20 carbon atoms.
Suitable polyfunctional plasticizing agents are those that may contain any one or a mixture of the following groups;
hydroxyl,mercapto, amido, amino groups and the like. It is to be appreciated that the functional groups that are present on the plasticizing agent may be mixed, that is, contain hydroxyl and amino, or hydroxyl and mercapto or both hydroxyl and the like. Preferably, the functional groups are both hydroxyl groups. For a recital o~ the desirable agents, see the afore-mentioned isocyanate reactive agents. The plasticizing agent may itself be the reaction product of various organic reactions, such as the ester resulting from the reaction of a polyhydroxyl material and an acid, its anhydride or a dibasic acid. Suitable -polyhydric materials are described above. Suitable aci~
dibasic acids and their anhydrides may have up to 12 carbon atoms such as oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelic acid and sebacic acid.
one preferred ester is that resulting from reacting neopentyl glycol and 2,2 - dimethyl, 3 - hydroxy proprionic acid, having the structure HO-CH2-C(CH3)2-cH2-o-c(o)-c(c~3)2 CH2 The primary properties of the plasticizing agent is that it , ", . .

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lrV4440o gives the desired plasticizing effect in the cross-linking agent during the curing step and after the film is cured.
Other suitable polyhydric materials which may react with a polyisocyanate are polyhydric hydantoin materials generally of the structure R3 R6 ~ ~ = O
0'~
wherein R5 and R6 may be the same or different and may be hydrogen, alkyl o~ l to 6 carbon atoms, hydroxyl alkyl of l to 6 carbon atoms, phenyl and the like.
R3 and R4 may be the same or different and may be hydrogen, alkyl of ~rom l to 6 carbon atoms, hydroxy alkyl of from l to 6 carbon atoms, polyoxyalkylene of from 2 to 4 carbon atoms per alkylene group with a terminal hydroxy group; repeating units of _l OCH2-cH(cH2OH) ] n where n ranges from 1 to 10, and the like. It is to be appreci-ated that the hydantoin materials must contain at least two hydroxyl groups. Normally these compounds are prepared by reacting dimethyl hydantoin (R5 and R6 are methyl and R3 and R4 are hydrogen) with the appropriate hydroxy inducing material, such as, epichlorohydrin, ethylene oxide, propylene oxide, butylene oxide and the like. The reaction product of epichloro-hydrin may require hydrolysis to remove the chloro groups. In gèneral "polyhydric hydantoin" derivatives may be said to contain the basic S membered ring structure recited above (regardless of R3-6 substituents with at least two hydroxy groups in the molecule.
It has also been determined that a bis hydantoin derivative may also be employed, i.e., the appropriate hydroxy derivative of methylene-bis-(substituted hydantoin).

The preferred hydantoin is where R5 and R6 are both methyl and R3 and R4 are both-C2H4OH. A second preferred hydantoin is when R5 and R6 are both methyl and R3 ~.nd R4 are both-CH2OH.

, Described below is the reaction sequence which is the preferred embodiment wherein X and Xl are organic moieties and G
is residue of-the b~ocking~agent. The most preferred plasticizing embodiment, a diol, is described.
1. OCN-X-NCO + H-G
OCN-X-NHC (0) -G
2. 2 OCN-X-NHC (0) -G + HO-Xl-OH
Xll-0-(0) C-NH-X-NHC (0) -G]2 The sequence is preferrèd becausè of the substantial variations in reactivity of the -NCO groups of the poly-isocyanate. Because the final powder composition should have a rapid cure, the blocking agent will be released at the appropriate temperature preferably above 250 F.
Since the first reacted -NCO group of the polyfunctional isocyanate reactant is the most reactive ana is now un-blocked (250F), it can rapidly cross link with the isocyanate reactive groups pendant from the polymerized resin, thereby giving a rapid cure.
A further distinct advantage of the cross linking agent of the present invention is that it is very stable due to the blocked isocyanate, especially when exposed to the atmosphere. This is particularly important for a powder coating composition in that there is improved shelf life and the powder,will not cake during handling.
The cross-linking agent and polymerized resin that is prepared according to the above procedures may be used as a paint base for application onto a suitable substrate after appro-priate dilution with ian organic solvent. In addition~
however, the paint (solvent plus film former i.e. polymer-ized rssin + cross linking agent) may be used in the preparation of powder paint particles according to the lV444~0 process described in U.S. 3,737,401, Method of Making Powder Paint.
The preferred method of making powder particles of the present invention is to prepare the particles by the precipitation process of U.S. 3,737,401. In that process finely divided droplets are formed of film former plus organic solvent for the film former. When the liquid paint is brought into contact with a second solvent which is a non-solvent for the film former but is mutually solvent (partially miscible) with the first solvent the droplets are formed. The powder particles are precipitated when the first solvent is removed from the drop-lets by dilution therefrom during contact with a solvent in which the first solvent is miscible. A preferred pair of sol- ~
vents is an organic solvent (a ketone) for the film former and -water. For a further discussion of preparation of powder par- ~
ticles, see Canadian Patent Application Serial No.224,285 ~ -filed April 10, 1975. ~ ~
Other components may be added to the liquid prior to ~ -forming the powder particles, such as pigments, fillers, or-ganic dyes and lakes, plasticizing and flow control agents, catalysts to accelerate cure rate, antistatic agents and the like. A preferred additional plasticizing agent that may be blended in with the cross linking agents is an ester resulting ~ -from the reaction of a saturated aliphatic triol having up to 12 carbon atoms tabout 2 parts by weight) with a long chain monobasic fatty acid (having at least 5 carbon atoms - about 2 parts by weight), which reaction product is then reacted with `
an aromatic or a saturated aliphatic dibasic acid or anhydride (about 1 part) resulting in a ph - 16 -B&P 72096-M
~)44400 composition having excess, preferably 50% excess, of hydroxyl groups. This plasticizing-agent's hydroxyl groups may react with the unblocked isocyanate groups of the cross linking agent during cure of the powder.
It should be further appreciated that other soluble plasticizing agents may be added to make up the film forming components in order to react with excess unreacted unblock d isocyanate groups. Therefore these additional agents need .
only have as a requirement the ability to have isocyanate reactive functionality (having groups which contain replaceable hydrogen atoms, such as those described above) and impart their plasticizing properties to the resin.
Any of the above recited plasticizing agents may be employed. Preferred materials are polyhydric materials such as cellulosics (cellulose acetate, cellulose acetate butyrate), alkane polyols, polyhydric lactones and lactams having rings of S to 7 members, polyhydric hydantoin materials and 'he like.
Based on film forming constituents, totaling 1.00%
by weight, powder compositions of the present invention can be described as follows:
polymerized resin 30 - 75%

cross lin~ing agent with plasticizing agent reacted there- -with 70 - 25%

Additional plasti-cizer 0 - 10% preferably at least 1%
The powder composition.can also be described as the ratio of various reactive groups.

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l.C~49t400 A. polymerized resin 0.7 - 1.5 isocyanate reactive groups B. cross linking agent 0,8 - 1.5 isocyanate groups C. Plasticizing agent (prior to reaction with cross linking agent) 0.8 - 1.1 isocyanate reactive groups The total of B + C should have excess NCO groups in order to be reactive with the polymerized resin.
Having described the invention above, other embodiments of the invention are described below. All temperatures are in degrees F. and all percentages are percentages by weight unless otherwise indicat~d.
Example 1.
An acrylic resin formulation was prepared by adding to an organic ketone solvent one part of acrylic acid, one part of ethylhexylacrylate, six parts ethylhexylmethacrylate, twenty parts of ethylmethacrylate, five parts of hydroxy propyl meth-acrylate; the solution was polymerized with an azocatalyst at about 80C.
The cross-linking agent was prepared by adding to an organic ketone solvent one part of isophorone diisocyanate, one part of methyl ethyl oxime until reaction is completed.
Then one half part of 1,6 - hexanediol was added until the -reaction was completed. Dibutyl tin oxide was added to complete the reaction.
A solution was then prepared comprising a 2 to 1 ratio of acrylic polymerized resin to cross-linking agent.
Carbon pigments were added at the ratio of 1 part of pigment per 25 parts of acrylic resin and powdered particles were produced in accordance with U.S. 3,737,401 by agitating .

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1~)444~10 the film forming solution ana then adding it to a mixture of liquid water and the ketone at which point the droplets began to occur. Then the solution is added to substantial additional amounts of water to effect the precipitation of the powder by dilution of the ketone from the droplets.
The powder was then separated from the liquid by being filtered, washed and~dried.
The particles had diameters ranging,between 5 and 50 microns.
A cleaned steel panel was used as the substrate upon which the particles were electrostatically sprayed. The film was cured to a hard, adherent, high gloss finish by baking the panel at about 325F.
Example 2 Following the procedure of Example ~1, excess iso-_ya,.-~e was employed (50% excess) in the preparation of the cross linking agent. Prior to the precipitation from ~he -gitated medium, an additional plasticizing agent was added (0.1 part per part acrylic resin). The second plasticizing agent is the reaction product of trimethylol propane (2 parts) pelargonic acid (2 parts)and phthalic anhydride (1 part). The powder was formed in the same manner as Example ~1. The powder particles were electrostatically sprayed on to a steel panel and then cured by subjecting the panel to heat of about 325F. The film was hard and adherent and can be characterized as having a high gloss top coat quality.
Example 3.
The procedure of Example #2 was followed except that capryl lactone diol (one part per 10 parts of acrylic resin) /

,, , ' B&P 72096-M
1~4~QO
was added prior to the precipitation. Equivalent films on steel were obtained.
Example 4 The procedure of Example 1 was employed in manufacturing the resin and the powder except that the following formulation was employed to prepare the cross linking agent.
Material #Equivalents Isophorone diisocyanate 7.6 O C 2 ( )2 2- 2.0 HO CH~ - (CH3)2 -C
Trimethylol Propane 2.0 Methyl isobutyl ketoxime 3.64 The films produced according to this example are, substantially equivalent to those of Example.l.
Example 5.
The procedure of E~ample 1 was employed in manufacturing the resin and the powder, except that the following formulation was employed to prepare the cross linking agent.

Material #Equivalents isophoronediisocyanate 5.0 1,3 - (2-hydroxyeths~l) - 5,5 -dimethylhydantoin 2.5 methylisobutylketoxime 2.5 The films produced according to this example are superior to those produced according to Example 1.

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Claims (19)

WHAT WE CLAIM IS:-

1. A solvent resistant coating composition comprising (i) a polymerized resin having isocyanate reactive functionality and (ii) an organic polyisocyanate cross linking agent derived from isphorone diisocyanate, a blocking agent and an agent that after curing of the coating composition is an internal plasticizing agent for the resin, wherein the isophorone diisocyanate is first reacted with the blocking agent and the isocyanate group -containing product of that reaction is reacted with the plasticizing agent, the plasticizing agent containing at least two isocyanate reactive groups and the cross linking agent containing at least two blocked isocyanate groups

2. A composition as claimed in claim 1 further comprising an organic solvent for the composition.

3. A composition 25 claimed in claim 1 wherein the isocyanate reactive functionality of the polymerized resin is selected from hydroxy, primary amino, secondary amino, mercapto, mono-N-substituted amido and unsubstituted amido.

4. A composition as claimed in any of Claims 1-3 wherein the polymerized resin is any one or more of acrylic resin, methacrylic resin, vinyl resin, polyester resin and epoxy resin.

5. A composition as claimed in claim 1 wherein the polymerized resin is formed from a polymerizable monomer of the formula {R1-O(O)C}t A{C(O)OR}n wherein n and t are 0 or 1 and n + t is from 1 to 2;
A is alkenyl, alkenylene of from 2-8 carbonatoms or a substituted derivative thereof, wherein the subsituent may be chloro, alkoxy or cyano; and R and R1 may be the same or different, and are independently selected from hydrogen, alkyl of from 1 to 20 carbon atoms, hydroxy substituted alkyl from 1 to 20 carbon atoms, a primary or secondary amino substituted alkyl of from 1 to 20 carbon atoms, and mercapto substituted alkyl of from 1 to 20 carbon atoms.

6. A composition as claimed in claim 5 wherein t is O and A
is alkenyl or substituted alkenyl.

7. A composition as claimed in claim 6 wherein R is hydroxy alkyl of up to 20 carbon atoms.

8. A composition as claimed in claim 7 wherein R has from 2 to 8 carbon atoms.

9. A composition as claimed in claim 6 wherein R is amino substituted alkyl of up to 20 carbon atoms.

10. A composition as claimed in claim 9 wherein R has 2 to 8 carbon atoms.

11. A composition as claimed in claim 5 wherein the plasticizing agent prior to reaction with the isocyanate contains a group independently selected from hydroxyl, mercapto, primary amino, secondary amino, unsubstituted amido and mono-N-substituted amido.

12. A composition as claimed in claim 11 wherein the plasticizing agent is a hydroxy containing alkane.

13. A composition as claimed in claim 11 wherein the plasticizing agent is an ester formed by reacting an organic carboxylic compound and a saturated polyhydric organic compound.

14. A composition as claimed in Claim 1 in which the composition is in powder form.

15. A composition as claimed in claim 14 wherein the powder particles range in size from 0.1 to 250 microns.

16. A composition as claimed in Claim 5 further comprising an effective plasticizing amount of a second internal plasticizing agent having excess hydroxyl groups, said second internal plasticizing agent being the reaction product of a saturated aliphatic triol having up to 12-carbon atoms, a fatty acid having at least five carbon atoms and an aromatic or saturated aliphatic dibasic acid or anhydride.

17. A composition as claimed in claim 6 , 11 or 16 wherein the polymerized resin is formed from a mixture of at least two monomers; the first monomer being an ester wherein R is an alkyl group of from 2 to 8 carbon atoms, and the second monomer is an ester wherein R is selected from hydroxy alkyl, primary amino alkyl and secondary amino alkyl, wherein the alkyl group is from 2 to 8 carbon atoms.

18. A composition as claimed in any of claims 1, 5 or 11 wherein the plasticizing agent prior to reaction with the diisocyanate compound is a polyhydric hydantoin.

19. A method of painting comprising the steps of applying the powder coating composition as claimed in claim 14 to a substrate, and forming a continuous film on the substrate by heating the coated substrate.