Note: Descriptions are shown in the official language in which they were submitted.
::
~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
.
10444Q0
. . .
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~
~ B&P 72096-M
1044400
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
-- 5 -- -
.. . .
i~4~0 B&P 72096-M
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 -,
-- 6 --
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).
_ 7 _
1044~0 B&P 72096-~
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
--8--
, . i , . . .. .. .. . . . . . .
-
:
1044~0 B&P 72096-M
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 -
. ,; , . , , . ~ .
B&P 72096-M
1044400
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.
.
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
- 13 -
, ", . .
~ B~P 72096-M
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
R5
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.
- 14 -
,
1044400
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
- 15 -
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.
- 17 -
B&P 72096-M
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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B&P 72096-M
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)
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/
,, , '
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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