CA1147085A - Particulate pigment compositions - Google Patents

Abstract

Ferrill Case 4 Canada PARTICULATE PIGMENT COMPOSITIONS

Abstract of the Disclosure Pigmented compositions which are readily dispersible in oleoresinous vehicle systems are described. The com-positions comprise by weight from 25 to 95% pigment and 5 to 75% of certain water-insoluble, friable thermoplastic polyester resins having a hydroxyl value of at least 50 mg/KOH per gram and a Ring and Ball softening point of at least 60°C. Particularly preferred polyester resins are the condensation products of an aromatic dicarboxylic acid, anhydride or ester, an aromatic monocarboxylic acid and an aliphatic polyol containing at least three hydroxy-methyl groups.

Description

~7~85 The invention relates to readily dispersible solid colorants hav-ing broad compatibility with oleoresinous vehicle systems, and m~re part-icularly to particulate, non-agglomerating pigm~ent compositions which are readily dispersible in industrial type oleoresinous vehicles and provide therewith colored films or coatings having outstanding gloss, hardness and durability.
It is kno~n that pigments can be after-treated with organic sub-stances to change the surface characteristics of the pigments. Substances which have been proposed include, among others, liquid, non-drying fatty acid modified alkyd resins (U.S. patents, 2,479,836 to HQback et al and 3,728,142 to Rudolph et al), diglycol terephthalates or linear oligomers of terephthalic acid and ethylene glycol (U.S. patent 3,607,335 to Belde et al), low melting polylactones having terminal hydroxyl groups (U.S. patent 3,754,956 to ~urrant et al), and viscous carba~yesters having acid values up to about 140 derived from trimellitic acid and a fatty alcohol or a hydroxy terminated fatty acid ester (U.S. patent 4,028,128 to ~bertson). Pigm~nts which have been after-treated with more than about 10~ by weight of the pig-m~nt of the above liq,uid, oily or viscous resins are sticky and agglomerating and require special handling and storage tec~miques. Further, the resulting pigment compositions are not sufficien,tly cc~patible with the wide variety of oleoresinous vehicles presently available to the trade to warrant broad com-mercial acceptan,ce an,d hence are of limited utility.
me use of liquid pigment dispersions as colorants for paints and inks is also known and Stansfield et al describe in U.S. patent 3,778,287 dispersions of inorganic 7`~38S

pigments, lakes or toners in organic liquids containing dissolved therein polyesters having acid values up to 100 derived from certain hydroxy-contain-ing, saturated or unsaturated aliphatic carboxylic acids. While liquid color-ants offer the distinct advantage of being more readily incorporated into the medium to be colored than dry pigments, their commercial significance is ser-iously limited due to the problems of handling and storing potentially haz-ardous liquid chemicals. Thus, from an economical and safety standpoint, it is desirable to have the colorants in a dry, storage stable form which is readily dispersible in a wide variety of coating media without detriment to any of the desirable properties of coatings produced therefrom.
Now, in accordance with this invention, it has been found that solid particulate pigment compositions which meet the above objectives, can be produced in a stable, non-agglomerating form and that such compositions exhi-bit excellent dispersibility characteristics in air drying, baking type and thermosettable oleoresinous vehicle systems and providetherewith colored films of outstanding gloss, hardness and durability. Accordingly, the pre-sent invention relates to a solid particulate pigment composition which is readily dispersible in oleoresinous vehicle systems and comprises by weight from 25 to 95% of at least one pigment and from 5 to 75% of at least one water-insoluble,friable thermoplastic polyester resin having a hydroxyl value of at least 50 mg. KO~l~gram of resin and a Ring and Ball softening point of at least G0C. The preferred compositions of this invention are pigment concen-trates comprising from 30 to 85% and most preferably from 35 to 75% of pig-ment, from 10 to 70% and most preferably from 15 to 65% of the polyester resin, and from about 1 to about 15% and most preferably from about 3 to about 10% of a cationic surfactant or surfactant combination.
Thus, this invention provides a solid particulate granular pigment composition which is readily dispersible in oleoresinous vehicle systems and and consists essentially of from 25 to 95% by weight of at least one pigment, from 1 to 15% of a cationic surfactant or surfactant combination and from 5

- 2 -.

7~8S

to 75% of at least one water-insoluble, non-crystalline, friable, thermo-plastic polyester resin having a hydroxyl value of at least 50 mg. KOH/gram of resin and a Ring and Ball softening poin~ of from about 65 to 100C which polyester resin is the condensation product of ~1) an aroma~ic dicarboxylic acid, an aromatic dicarboxylic anhydrlde or an aromatic dicarboxylic acid ester, (2) an aromatic monocarboxylic acid and (3) an aliphatic polyol con-taining at least three hydroxymethyl groups.
Pigments which can be used in accordance with this invention are any of the solid colorants normally used in the industry for the coloring of paints, inks or plastics. These include the colored inorganic and organic prime - 2a -~7~35 pigments, extender pigments, metallic pigments, the væious finely-divided channel and furnaoe blacks and the like. The pigments can be in the form of dried lump, wet cake, a slurry of the pigment in water or a suitable organic solvent, or the pigment slurry resulting from its synthesis. Presscakes æe preferred where possible as these avoid the aggregation that normally occurs during drying of the pigment. Typical pigments include the organic pigments such as the diarylide yellows~ the phthalocyanine blues and greens, the quinacridone reds and violets, dioxazine violet, carbon black, and the like;
and inorganic pi~ments such as the cadmium reds and yellows, the lead chro-mate colors including pure lead chromate as well as solid solutions contain-ing lead chromate and lead sulfate and/or lead molybdate, iron oxide yellows and reds, titanium dioxide and the like.
The polyester resins employed in this invention æe water-insoluble, non-crystalline thermoplastic polymers which are friable at roQm temperature, have a Ring and sall softening point above about 60C., preferably from about 65 to about loo&., and contain hydroxyl functionality. me hydroxyl func-ti~nality of the resin is described herein as hydroxyl value, which value is the number of milligrams of potassium hydro~cide which will neutralize the quantity of acetic anhydride requured to acetylate one gram of resin. me polyesters of this invention have hydroxyl values of at least 50 and prefer ably from about 75 to about 150 and æe formed in known manner by the conden-sation reaction of a di boxylic acid, anhydride or ester and a mono-cæboxylic acid with greater than an equivalent amount of an aliphatic polyol containing at least three hydroxymethyl ~roups. The dicarboxylic acid con~
ponent can be a saturated or unsaturated aliphatic, alicyclic or æomatic acid, anhydride or ester and is preferably phthalic anhydride, o-phthalic acid, terephthalic acid, isophthalic acid or dimethyl terephthala-te. me dicarboxylic ad d component usually provides less than 50 mole ~ of the total acid components of the reaction product. The monocarboxylic acid comonent can likewise be aliphatic or aromatic and is preferably an arcmatic acid such "~

~7~3~S

as benzoic acid, the lower aIkyl substituted benzoie aeids and most prefer-ably the para substituted alkyl benzoic acids wherein ~le aIkyl group eon-tains 1 to 6 carbon atoms. Particularly preferred is p-t-butyl benzoic acid.
me aliphatic polyols are the tri or higher polyols eontaining at least three hydroxymethyl groups and preferably are trim~ethylol ethane, trimethylol pro-pane, pentaerythritol, dipentaerythritol or tripentaerythritol. me eonden-sation reaction is preferably earried out by heating the acid and aleohol components to temperatures in excess of about 150&. in the presenee of a small amount of an acid eatalyst sueh as an organie sulfonie aeid or a basie catalyst such as a metal oxide, and the reaction is continued until a pro-duet is obtained having a relatively low acid value, usually less than abou~
15. m e acid value of the resin is the number of milligrams of potassium hydroxide required to neutralize one gram of the resin.
Optionally, and sueh is usually preferred, the composition can also eontain a small amount, as for example, from about 1 to about lS% and prefer-ably from about 3 to about 10% by weight of the eclmposition of a water-insoluble, oil-soluble cationie surfaetant or surfaetant eombination to en-hance pigment dispersion. Preferred eationic surfaetants are the substituted tertiary amines whieh are heterocyclie tertiary amines sueh as the alkyl imidazolines and oxazollnes, the polyethoxylated tertiary amines, primary amines such as dehydroabietylamine and ~-tallow trimethylene diamine and quaternc~ry ammanium oompounds sueh as the quaternary c~m~onium chlorides de-rived from adduets of C12 to C18 fatty aeid amines and about 2 to 15 moles of ethylene oxide. Qne of the preferred imidazolines is 1-(2-hydroxyethyl)-2-n-heptadecenyl-2-imidazoline. m e cationie surfaetants are eapable of forming water-soluble salts with various acids and being eonverted to a water-insoluble, oil-soluble form by reaetion with alkali or anionie surfaetantsO
As their acetate salts they are exoellent surfaetants with good solubility in water. me water-insoluble, oil-soluble form of sueh surfaetants, as for example, eomplexes of the above amine surfaetants with anionie surfactants ~a7~85 are also useful provided a stoichio~etric excess such as at least 10% and preferably 10 to 70% molar exoess of the cationic surfactant is present.
Typical anionic surfactants include sodium oleate, sodium laurate, sodium palmitate, sodium stearate, sodium naphthenate, sulfonated castor oil, sul-fonated petroleum, sulfonated tall oil, sodium butyl naphthalene sulfonate, wood rosins and the like. Particularly useful are the commercially available anionic surfactants such as Tergitol 4 (the sodium sulfate derivative of 7-ethyl-2-methyl-4-undecanol), Igepon AC-78 (the coconut oil acid ester of sodium isethionate), Aerosol 22 (tetrasodium-N-(1,2-dicarboxyethyl)-N-octa-decyl sulfosuccinamate), the sodium salt of hydrogenated wood rosin and the sodium alkyl a~yl sulfonates.
The choice and amount of surfactant will, of course, vary depending upon a number of f.actors which include the HLB value of the surfactant or surfactant cc~bination and the surface characteristics of the pigment.
Generally, when present, the amount of surfactant will range from about 1 to about 15% and more preferably from about 3 to about 10% by weight of the cc~r position, and the a~ount will be such that the resin to surfactant weight ratio is at least 2:1 and preferably within the range from about 2.5:1 to about 6:1.
The compositions of this invention can be for~ed in any convenient manner for intimately mixing a pigment with a norm~lly solid resin, as for example, by ball milling in a dry state, pebble milling in aqueous medium, high speed stirring in the presen oe of a solvent for the resin, and the like, and then removing any aqueous medium or solvent. Conveniently, the composi-tions are prepared by forming an aqueous dispersion of the pigment, prefer-ably by stirring the pigment in water in the presenoe of a water-soluble or water-dispersible cationic or anionic surfactant which is convertible to an oil-soluble, water-insoluble form, adding the resin to the aqueous dispersion, agitating the aqueous pigment-resin slurry at a te~,perature above the soften-ing temperature of the resin, usually at about 5 to about 35C. above the softening point of the resin, until the pigment transfers from the aqueous phase to the resin phase and an essentially pigment-free water phase is formed, adjusting the temperature of the slurry to a range at which the resin is a solid and recovering the resulting product. If granules are preferred, and such is usually the case when dealing with finely divided pigments which tend to be dusty in nature, the temperature of the agitated pigment-resin slurry is adjusted to a range above the softening point of the resin which provides a sufficiently high resin viscosity to achieve controlled coales-oence of the particles and granulation in the desired particle size range, cooling water is added to adjust the temperature to the desired range or heating is discontinued and the slurry is permitted to cool slowly to below the softening point of the resin. Optionally, the resin can ke added as a solution in an organic solvent and the pigment flushed from the aqueous phase to the resin phase by precipitating the surfactant or by removal of the sol-vent to form a colored non-aqueous phase in the form of small pigment granu-les.
Recovery of the product is conventional. For example, the slurry can be centrifuged or dewatered by running the batch through any suitable type of filtering apparatus such as a filter press, screen, etc, and the part-ially dewatered product can then be washed and dried using trc~y driers,vacuum drisrs, etc. Recovery can also be accomplished conveniently by spray drying or drum drying. Prior to or following drying, the product can be ground to a pcwder form, if desired.
The particulate pigment compositions of this invention are of exoe ptionally high quality and uniformity, are readily dispersible in oleore-sinous vehicle systems and provide with such systems enamels whi~h give films or coatings of outstanding color strength, gloss and transparency. They are ideally suited for use in industrial type oleoresinous vehicles such as the conventional air drying alkyd enamels, the bc~king type alkyd-melamine enamels and the thermosetting type acrylic-melamine enamels, with which they provide films or coatings of outstanding gloss, h æ dness and durability.

...~ ~ .

~.7`~35 Having described the invention generally, the following examples are given to illustrate specific embodiments thereof. All parts and percent-ages are by weight unless otherwise specified.
Example 1 A vessel equipped with an agitator and heating means was charged with light chrome yellow pigment presscake containing 224 parts (dry basis) of Pigment Yellow 34 (CI No. 77603) and sufficient water to provide a charge Pqual to 1660 parts by volume. The agitator was turned on, and the charge was heated to 55C., following which time 9.6 parts of a coconut oil ester of sodium isethionate (0.023 equivalent of anionic surfactant), a sufficient amount of a 5% aqueous sodium carkonate solution to adjust the pH of the slurry to 7.0 and 72.0 parts of a powdered aromatic polyester resin were a~ded to the slurry. Agitation was continued while maintaining the tem~era-ture of the slurry at 55&., for 5 minutes. The polyester resin had a soft-ening point (Ring and Ball method) of about 82C., an acid value of about 14 and a hydrcxyl value of about llO and was prepared by the condensation reac-tion of 0.9 mole o-phthalic anhydride and 2.3 moles of p-t-butyl kenzoic acid with 1.7 m~les of trimethylol ethane. Next 48.0 parts of an aqueous solution containing 12.0 parts of dehydroabietyL~mine (0.038 equi~alent of cationic surfactant) and 2.4 parts of glacial acetic acid were added, the pH of the slurry was adjusted to 6.5, and the slurry was heated to 90C. and maintained at 90 to 95&. with agitation for 2 hours. Water at 25C. was added to ad-just the volume to 3500 parts and the slurry was agitated for an additional 2 mlnutes. me batch was ~hen run out onto a 40 mesh screen and the de-watered material was dried in an oven at 70&. me product was 235 parts (73.8% yield) of a non-sticky granular pigment composition containing about 70.5% of the lead chromate, 22.7% of the polyester resin and 6.8% of the sur-factant ..

~7~35 combination, based on the weight of the composition. The granules were non-dusting, essentially spherical, free-flowing particles, the majority of which had a diameter between about 1 and about 2 millimeters.
The dispersibility characteristics of the pigment composition of this example were evaluated in an air-drying alkyd enamel as follows.
A yellow enamel paste formulation was prepared by stirring 170.2 parts of the granules of this example with 47.2 par~s of a commercial soya-linseed, medium oil alkyd resin ~Aroplaz 1445-M50)* and 32.8 parts of mineral spirits for 15 minutes using a small Cowles dispersing blade at 5000 rpm, adding 306 parts of sand ~20-30 mesh) and continuing stirring for an addi-tional 15 minutes using a sand mill type impeller blade. Following removal of the sand, the paste gave a Hegman gauge reading greater than 7. An enamel was produced from the above paste by stirring 68.6 parts of the paste with 54.9 parts of the Aroplaz resin, 25.3 parts of mineral spirits, 1.0 part of lead drier and 0.2 part of cobalt dried until uniform and adjusting the viscosity to 20-25 sec., #4 Zahn cup. The enamel was then sprayed onto standard test panels ~size 3 x 9") to ~Tive a coating thickness of 0.7 mil and the panels were dried at room temperature for 48 hours. The resulting panels had a smooth, glossy, bright yellow surface. Exposure in a Cleveland humidity cabinet for 24 hours at 66C. did not significantly alter the smooth, glossy surface of the panels. When the panels were tested in a Weatherometer, the color after 100 hours was a trace darker than a non-exposed panel, and was deemed fully satisfactory.
The pigment composition of this example was also evaluated in a baking-type alkyd-melamine enamel. In this evaluation, a yellow paste was prepared by 3-roll milling a mixture con~aining 62.8 parts of the granules of this example and 40.0 parts of a commercial general purpose, nonoxidizing short oil alkyd resin ~Koppers Rezyl 99-5)*, using three passes. An enamel was prepared from the above paste by stirring 67.0 parts of the paste with 29.5 parts oE the alkyd resin, 27.7 parts of a commercial * Trade Mark ~r~

~ ~r ~7~8 5 fast curing, general purpose melamine-formaldehyde type resin ~Koppers Melamine* resin 61-8, 55% solid) and 24.9 parts of xylene and adjusting the viscosity to 20 seconds, #4 Ford cup using xylene. The enamel was then sprayed on test panels and the panels were baked for 30 minutes at 121C.
The resulting panels ~ad a smooth, glossy, bright yellow surface which gave a Sward hardness test value of 48. Exposure in a Cleveland humidity cabinet for 24 hours at 66C. did not significantly alter the smooth, glossy surface of the panels. When the panels were tested in a Weatherometer, the color after 100 hours was a trace darker than a nonexposed panel and was deemed fully satisfactory. Control panels were also prepared in the same manner as above except that-the paste was formed using 46 parts of Pigment Yellow 34J and the enamel was formed using 56.1 parts of paste, 46.5 parts of the alkyd resin, 29.1 parts of the melamine resin and 17.4 parts of xylene to provide an enamel of equal solids content. Evaluation of the control panels in the same manner as above showed that the panel was smooth and glossyJ that the Sward hardness test value was 20 and that the surface and color characteristics were not significantly altered by the humidity and Weatherometer tests.
Example 2 The procedure of example 1 was repeated except that a molybdate orange pigment presscake containing 224 parts ~dry basis) of Pigment Red ~04 ~CI No. 77605) was substi~uted for the light chrome yellow pigment presscakeJ 60.0 parts of the polyester resin were used and the final pH adjustment was to a value of 6~0. The product of this example ~91.6% yield) was in the form of nondustingJ free-flowing granules containing 73.3% of the orange pigmentJ 19.7% of the polyester resin and 7.0% of the surfactant combination. When the granules were dispersed in the air drying alkyd enamel and coated panels were prepared therefrom and evaluated in the same manner as Example 1J the panels had a smooth, glossy, bright, red toned orange surface which was not significantly altered by the humidity test * Trade Mark _g_ ~.,~

and which was only slightly darker after 200 hours of exposure in the ~Yea~herometer.
The pigment composition of this example was also evaluated in a ther~osetting type acrylic-melamine enamel as follows. An orange paste was prepared by 3-roll milling a ~ixture containing 61.4 parts of the granules of this example and 22.5 parts of a commercial acrylic resin solution (Acryloid AT-56*, 50% solids) using three passes. An enamel was prepared from the above paste by stirring 55.9 parts of the paste with 37.2 parts of the acrylic resin solution, 24.8 parts of a commercial melamine-formaldehyde type resin (Uformite MM-47*, 60% solids), 3.6 parts of an aromatic petroleum solvent ~Solvesso 100*), 4.9 parts of butanol and 19.6 parts of xylene and adjusting the viscosity to 20 seconds, #4 Ford cup using xylene. The enamel was then sprayed on test panels and the panels were heated for 30 minutes at 121C. Control panels were also pre-pared in the same manner except that the paste was formed using 45 parts of Pigment Red 104, and the enamel was formed using 45 parts of the paste, 57.6 parts of the acrylic resin solùtion, 26.0 parts of the melamine-formalde-hyde resin, 3.6 parts of the aromatic petroleum solvent, 3.6 parts of butanol and 10 parts of xylene to provide an enamel of equal solids content. Visual comparison of the test panels ~prepared with the enamel containing the pig-ment composition of this example) and the control panels showed that the tes~ panels were more deeply colored, and slightly less glossy than the control panels. The ~ward hardness test value for the test panels was 44, as compared with 28 for the control panel.
Example 3 A vessel equipped with agitator and heating means was charged with 1600 parts by volume of a slurry containing 85.5 parts (dry weight) of copper phthalocyanine Pigment Green 7 (CI 74260) and water, agitation was commenced and the slurry was heated to 55C. Next, 38.0 parts of an aqueous solution containing 30% of the commercial anionic surfactant Alkanol WXN

7a sodium alkyl aryl sulfonate) wsre added, the Ph was adjusted to 6.0 * Trade Mark 7^~35 using dilute acetic acid and agitation was continued or 30 minutes at 55C.
Next, 114.0 parts of tbe polyester resin of Example l were added to the slurry, agitation was continued for 5 minutes at 55~., 80.8 parts of an aque-ous solution containing lO.l parts of the commercial cationic surfactant Duomeen T *(N-tallow trimethylenediamine) and 7.3 parts of 100~ acetic acid were added gradually and the p~l was adjusted to 7.1 using a dilute solution of sodium carbonate. The slurry was heated to 90~C. and agitated for 2 hours at 90-95C., and then cold water was added to reduce the volume to 3500 parts.
Following run out of the slurry onto a 40 mesh screen and drying of the resulting granules, the product of this example was 154 parts (70% yield~ of free-flowing, non-dusting granules containing 38.7~ of pigment, 51.7% of the polyester resin and 9.7% of the surfactant coli~ination, based on the weight of the product.
The dispersability characteristics of the pigment composition of this example were evaluated in a vinyl lacquer as follows: A green paste formulation was prepared by stirring 21.~ parts of the granules of this exam-ple with 75 parts of a coating solution containing 35~ of a vinyl chloride-acetate copolymer (86~14, weight ratia), 32.5% of xylene and 32.5% of methyl ethyl ketone for 30 minutes using a small Cowles dispersing blade at 5000 r.p.m. and gradually adding 33.5 parts of a solvent mixture of xylene and methyl ethyl ketone (50:50) over the 30-minute period. A lacquer was produced from the above paste by stirring 43 parts of the paste with 70.1 parts of the solvent mixture and 2.6 parts of dioctyl phthalate for 30 minutes. The lac-quer gave a Hegman gauge reading of 7-l/2 and upon microscopic examination showed that dispersion quality was excellent and that essentially all of the pigment particles were below 2 microns in size. When the lacquer was drawn-down on aluminum coated paper to a film thickness of 1.5 mil, the film had good color intensity and was exceptionally bright and transparent.
A control lacquer was prepared as above except that 8.3 parts of a commercial Pigment Green 7 toner and 13.1 *Trademark .~

7~85 -]2-:
parts of the polyester of Examp].e ]. were substituted for the L
2l.4 parts of the granu.les of this example. The control ,~
. lacquer gave a Hegman gauge reading of 6 and upon micro- r scopic examination showed a very large number of particles S in the size range of 10-25 microns. The draw-down on alumi-num possessed a color intensity substantially equa]. to that .~ of the test lacquer but was considerably less bright and less transparent.

.
., . ':
,.

. ~ .

.. .. . . .. . ~

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A solid particulate granular pigment composition which is readily dispersible in oleoresinous vehicle systems and consists essentially of from 25 to 95% by weight of at least one pigment, from 1 to 15% of a cationic sur-factant or surfactant combination and from 5 to 75% of at least one water-insoluble, non-crystalline, friable, thermoplastic polyester resin having a hydroxyl value of at least 50 mg. KOH/gram of resin and a Ring and Ball soft-ening point of from about 65° to 100°C which polyester resin is the condensa-tion product of (1) an aromatic dicarboxylic acid, an aromatic dicarboxylic anhydride or an aromatic dicarboxylic acid ester, (2) an aromatic monocarboxy-lic acid and (3) an aliphatic polyol containing at least three hydroxymethyl groups.

2. The composition of claim 1 wherein the polyester resin has a hydro-xyl value of 75 to 150.

3. The composition of claim 2 wherein the polyester is the condensation product of phthalic anhydride, p-t-butyl benzoic acid and trimethylol ethane.

4. The composition of claim 3 wherein the pigment is an inorganic pigment.

5. The composition of claim 4 wherein the pigment is a lead chromate-containing pigment.

6. The composition of claim 3 wherein the pigment is an organic pigment.

7. The composition of claim 6 wherein the pigment is a copper phthalo-cyanine pigment.