CA1100255A - Pigment preparation and use in coating compositions - Google Patents
Pigment preparation and use in coating compositionsInfo
- Publication number
- CA1100255A CA1100255A CA272,339A CA272339A CA1100255A CA 1100255 A CA1100255 A CA 1100255A CA 272339 A CA272339 A CA 272339A CA 1100255 A CA1100255 A CA 1100255A
- Authority
- CA
- Canada
- Prior art keywords
- silicofluoride
- zinc
- calcium
- chromate
- pigment
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/08—Anti-corrosive paints
- C09D5/082—Anti-corrosive paints characterised by the anti-corrosive pigment
- C09D5/084—Inorganic compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/08—Compounds containing halogen
- C01B33/10—Compounds containing silicon, fluorine, and other elements
- C01B33/103—Fluosilicic acid; Salts thereof
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/14—Compounds of lead
- C09C1/20—Lead chromate
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/28—Compounds of silicon
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/34—Compounds of chromium
- C09C1/343—Compounds of chromium containing silicon or associated with silicon containing material, except when silicon only occurs in a thin coating of the particles
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Paints Or Removers (AREA)
- Pigments, Carbon Blacks, Or Wood Stains (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
Abstract
Abstract of the Disclosure A new and useful pigment is prepared by reacting an inorganic sili-cofluoride and an inorganic calcium compound selected from the group con-sisting of calcium oxide, calcium hydroxide and calcium carbonate The product is especially useful in protective coating compositions which Are applied to metals in order to enhance adherence to and corrosion resistance of metals such as aluminum, zinc, magnesium, steel and alloys of said metals
Description
It is well known in the metal coating industry that there is a continuing need for coatings used for paint bonding and corrosion resistance.
This is especially true where the metal is steel, aluminum, magnesium, aluminum alloys and zinc surfaced articles including galvanized iron or steel, where such coatings are required in order to protect the articles against deterioration, In the past many such coatings have been suggested and used such as phosphate, zincate and anodized films but, in general, these coatings have left much to be desired because of various deficiencies including complex and often difficult operating procedures and high costs.
Chromate conversion coatings have been used with varying degrees of success. The effective protective ingredient in these coatings seems to be chromium in the hexavalent state It has long been recogni7ed that ]t would be desirable to coat metals with an organic film forming resinous composition which would not only be adherent to the metal but would also provide corrosion resistance. Unfortunately attempts to accomplish this result have not been very successful One of the objects of the present invention is to provide a new and useful type of water insoluble pigment which is especially useful in the preparation of emulsions of organic resinous film forming binders and which when applied to metals such as aluminum zinc, magnesium, steel and alloys of such metals and dried will form a coating on the metal which adheres to the metal and provides an unusual amount of corrosion resistance when the coated metal is subjected to salt spray tests.
Another object of the invention is to provide a new and improved process for preparing a water insoluble pigment of the type described.
Still another object of the invention is to provide new and improved coating compositions which can be applied to metals of the type described as a primer coating and which can thereafter be overcoated with a secondary ~'~
~Ol~Z55 coating or a top coating and particularly with water based paint emulsion coatings.
In accordance with the invention there is provided a pro-; cess of preparing a pigment which comprises mixing approximately equimolecular porportions of an inorganic silicofluoride and an inoxganic calcium compound selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate in water sufficient to form a thIck slurry of calcium silicofluoride, carrying out the mixing at a temperature that does not substan-tially exceed 9QF and while maintaining a pH within the range of about 5.0 to about 10.5, and grinding the resultant slurry to an average particle size of 0.5 to lO microns.
The process is preferably carried out at the temperature generated by the heat of reaction while maintaining a pH within the range of about 5.0 to about 10.5, preferably 7.0 to 7.5.
The inorganic silicofluoride used in practicing the in-vention is preferably fluosilicic acid (H2SiF6) which is available commercially as a 26% aqueous solution. However, other inorganic silicofluorides can be employed as, for example, zinc silico-fluoride, lead silicofluoride, manganese silicofluoride, sodium silicofluoride and potassium silicofluoride, magnesium silico-fluoride, and ot~ers.
In carrying out the process, a mixed pigment can be pre-pared by adding at least one chromium compound selected from the group consisting of chromic acid, strontium cHromate, zinc chrom-~ ate and lead chromate to the slurry of said inorganic calcium - compound and said inorganic silicofluoride, the quantity of said chromium compound being within the range of 0.05 to 50~ by weight of the total solids.
Coating compositions are prepared by mixin~ the calcium - silicofluoride pigment slurry in which the pigment particles are ~1(3 0255 usually in very fine form, e.g., an average particle size of 0.5 to 10 microns, or a mixed pigment containing calcium silico-fluoride and an inorgan~c chromium compound of the type prev-iously descri~ed wit~ emulsions of thermoplastic resins, thermo-setting resins, or mixtures of thermoplastic resins and thermo-setting resins in water where water is the cont;nuous phase, prefera~ly with the addition of at least one hexavalent inorganic chromium compound such as, for llC~(l Z55 - example, chromic acid or sodium dichromate, pigments and pigment extenders . other than calcium silicofluoride, driers such as naphthenates of cobalt, lead, magnesium, manganese, zinc and/or zirconium, coalescing agents, dis-persants, defoamers, surfactants and water soluble additives such as ammonium hydroxide, dimethylethanolamine and diethanolamine to enhance stability of the emulsion. Additional water is usually required over that normally present in commercial emulsions or resinous binders.
Preferred coating compositions coming within the scope of the invention consist essentially of the following:
Ingredients Weight %
(a) resin solids of at least one organic film : forming resin selected from the group consisting of thermoplastic resins., thermosetting resins, and mixtures thereof 10-60 (b) calcium silicofluoride 0.5-20 ~c) hexavalent inorganic chromium compound as Cr 0-10 ~d) pigments and pigment extenders other than ~b) 0-100 of resin ~e) dri.ers up to 0.5 of total solids ` ~f) coalescent agents 0.05-10 ~g) dispersants 0.05-6 ?o ~h) defoamers 0-0.05 ~i) surfactants 0.01-3 ~j) thickening agents ~viscosity and required trace to 10.0 by film thickness-determinants) weight of resin ~ ~k) water including water soluble additives 5-65 ~ A preferred type of thermoplastic resin emulsion is one containing 100% acrylic emulsion polymer comprising 46+0.5% by weight solids having a pH of 9 to 11 and weighing approximately 8.9 pounds per gallon. Such an . - ~ acrylic emulsion polymer is available commercially under the name Rhoplex MV-l, Ucar 4358.
A preferred thermosetting resin for use in the practice of the invention is an acrylic emulsion polymer containing 46+0.5% by weight solids rr~
~ -3-110~255 having a pH of 9.5 to 10.5 and weighing approximately 9 pounds per gallon.
Such a resin is available commercially under the name Rhoplex AC-604.
Examples of other suitable resins are those sold under the names Rhoplex B-5 and Rhoplex AC-33X; Ucar 878,4550.
While the foregoing resins are preferred in the practice of the invention, the invention in its broadest aspects is not limited to these particular resins. The types of resins used are many, e,g., vinyl, polyester, epoxy and acrylic, either simple or modified, or mixed; cross linking additives such as, for example, melamine resins, methylated urea formaldehyde and synthetic type rubber type resins can be used.
Typical examples of resin combinations are thermoplastic ~e.g., B Rhoplex MV-1)-thermosetting (e.g, Rhoplex~AC-604); thermoplastic ~e.g., Rhoplex~
MN-l)-thermosetting ~e.g., Rhoplex~AC-604)-thermosetting ~Epoxy~PR-808);
thermopl~astic ~e.g , Rhoplex~ MV-l)-thermosetting ~e.g., Rhoplex~B-5)-thermo-setting ~e.g., Rhoplex~E-1046)-cross linking ~e.g., Uformite~ M83, a melamine resin); and thermoplastic ~e.g., Rhoplex~MV-1)-thermosetting ~e.g., Rhoplex~
B-5)-thermosetting ~e.g., Rhoplex~AC-33x and Rhoplex~E-1046)-cross linking ~e,g., HYCAR CTBN, Uformite M-83, and Beetle~65), Cymel~303.
The various resins are formulated into emulsions in a conventional manner by mixing them in water with various additives including dispersion agents, surfactants, defoamers, coalescing agents, coupling agents, flow control agents, pH control agents and viscosity control agents. The variety of these additives is quite large in number and while the end product produced will have somewhat different chemical and physical characteristics depending upon the particular additives, except to the extent herein described, the invention is not limited to particular additives. Examples of suitable coupling agents normally employed in making such emulsions are isopropyl alcohol, N-butyl alcohol, and tertiary butyl alcohol. Examples of suitable coalescing agents are butyl Cellosolve, butyl carbitol and tributyl phosphate.
Hydrolyzable esters ana water soluble substances detract from shelf life and ~r ~
water and vapor insensitivity.
The preferred pH control materials are ammonium hydroxide, dimethyl-ethanolamine, and diethanolamine. These substances are alkaline as contrasted with the aqueous solutions of the dichromates which are acidic. Tertiary amines such as dimethylethanolamine are preferred from the standpoint of enhancing the stability of the resultant emulsions with which the hexavalent chromium compounds have been incorporated, Diethanolamine also gives good results. The use of ammonium hydroxide is also effective but with the stability somewhat less. However, the use of ammonium hydroxide has the advantage that it decomposes more easily after the emulsion coating composition has been applied to a substrate and during the curing process. For this -~ reason it is usually desirable to add the hexavalent chromium as ammonium dichromate. It is also customary to use the pH control agents in the form of aqueous solutions, for example, ammonium hydroxide as a 28% aqueous solution and the amines diluted in equal weight proportions li.e., 1:1) with water.
Examples of thickening agents are polyacrylic acid and salts :- B thereof, for example, the sodium and ammonium salts such as Acryso fGS, Acrysol G-llO and Acrysol ~ S-?4; cellulose (methyl, carboxy methyl, hydroxy methyl and ethyl cellulose-l,OOO to 150,000 CPS); silicas; silicates.
Examples of pigment dispersants, stabilizers and surfactants are those materials sold commercially under the names Tamol~731, Tamo~ 850, Triton CF-10 which is a water soluble nonionic oxyethylated benzyl ether of octyl phenol, Trito ~ -114 which is an oxyethylated octyl phenol, and Ethoxylan ~ which is lanolin reacted with ethylene oxide.
As shownby the foregoing description of the preferred coating composition, the use of pigments and pigment extenders other than calcium silicofluoride is optional. Among the preferred optional pigments and ~ extenders are lead silicate, chromate pigments (e.g., Oncor~-M50 which has a - ~ yellow-brown color), potassium zinc chromate, magnesium silicofluoride, titanium dioxide, and strontium chromate. As pigment extenders hydrophilic and hydrophobic silicas, synthetic talc and silicates can be employed, with the hydrophilic silicas being preferred.
In preparing the calcium silicofluoride pigment, the reaction between the inorganic silicofluoride such as fluosilicic acid and the inorganic calcium compound is exothermic and the mixing container is preferably jacketed and water cooled. Usually the temperature should be above that giving ice crystal formation and not above 90F., preferably around 70-80F, In order to control the pH chromic acid can be used to neutralize the slurry and thereby produce a chromium containing pigment If it is desired to prepare the calcium silicofluoride pigment without chromium, another inorganic acid, e g., phosphoric acid, can be used to control the pH.
It is usually desirable to adjust the viscosity of the final coating composition to a Zahn #1 viscosity of 10-35 seconds or a Zahn #2 viscosity of 15-50 seconds. This can be done by adjusting the water content and by the use of thixotropic agents or thickeners which are well known in the art.
A given emulsion coating composition might be modified depending upon the type of application, i e., roll coating, spray coating, immersion and squeegee applications, electrostatic applications and other methods of application Where the emulsion coating composition contains both thermoplastic resins and thermosetting resins the weight ratio of thermoplastic resins to thermosetting resins is preferably within the range of 6:1 to 3:1, the ratio however, can be altered at will The more thermosetting resin used the less the water and vapor sensitivity and extensibility If a cross linking agent is employedj the amount is preferably at least 25% by weight of the resin to be cross linked Where pigments are added the weight ratio of pigment to resinous binder is usually within the range of 5:95 to 40:60, although it can be as low as 1:99.
In the application of the coating compositions to a substrate such 110~255 as a metal, those skilled in the art will recognize that cleaning and preparation of the metal is qui~e important and may involve the usual cleaning methods, deoxidizing of the substrate, rinising and drying.
After the emulsion coating composition is applied to a substrate, e,g., steel, aluminum, magnesium, or a 7inc surfaced substrate, it is dried or allowed to dry and cured, for example, at 400F. for from 30 seconds to three minutes or 600F from 20 to 90 seconds, or 1-6 seconds using an intense infra-red air blown unit at 2000F. The time of heating is longer at lower temperatures and shorter at the higher temperatures. The time-temperature - 10 relationship is preferably controlled to give a final coating having a pencil - hardness of H to 2H
The wet thickness of the applied coating is usually within the range - of 0.05 mil to 10 mils (a mil equalling 0 001 inch) A preferred thickness of the wet coating is within the range of 0.1 to 0.3 mil. The greater the thickness of film the greater wi~l be the difficulty of acquiring a uniformly - "cured" film.
- The quantity of the cured coating can be tested in a number of ways. One such test is the salt spray test where a mist or fog of an aqueous - solution containing 5% sodium chloride or acetic acid acidified sodium chloride is applied to coated panels over a predetermined time period Another type of test is the Q-Panel Humidity Panel Test in which the coated panel is subjected to humidities of 90 to 100% at temperatures of from 100F. to 190F, with drying in cyclical periods, the cycles being timed at 0 to 60 minutes under high humidity conditions and 0 to 60 minutes under drying conditions or in variation in 10 minute units of time Another test which is perhaps the most strenuous of all involves boiling the coated panels in distilled water for 30 minutes, 60 minutes or 120 minutes. The area being tested may or may not be impac~ed or bent, Usually a pencil hardness test is made before and after the test ~allowing 5 to 15 minutes recovery at room temperature). Observation can be made for lla~2ss resistance to solvation of coating, chalking of coating and water absorption.
A good film or coating should be capable of returning to its original condition after this test.
Other tests can be conducted to determine resistance to over-bake cure using pencil hardness, impact tests and bend tests. Continuity of film can be determined by using the Preece or modified Preece tests with acidified copper sulfate solution, As previously indicat~d the composition of the emulsion to be applied as a coating may vary somewhat depending upon the nature of the substrate.
~hus, in applying the emulsion coating compositions to aluminum (this term also includes aluminum alloys) experience has shown that excellent reSults are obtained either with high or low hexavalent chromium contents and either at low pH's or high pH's, although the pH is preferably within the range from 5,8 to 10.5. On the other hand, when the emulsion coating compositions are applied to steel, the pH should be below 7Ø In the treatment of galvanized iron or steel (i.e., zinc surfaced articles), it is preferable to have the hexavalent chromium present in amounts such that a coating of the emulsion coating composition on the substrate contains not more than 10 micrograms per square inch of hexavalent chromium, as Cr, and the pH is preferably 6.8 to 8.0 for best results, If too much hexavalent and active chromium is present it reacts with the zinc forming zinc chromates which tend to form a powder and give poor adhesion where a finishing top coat is applied.
The application of the emulsion coating compositions to magnesium (which includes magnesium alloys) is similar to that for aluminum although magnesium is very sensitive to low pH values below 5Ø
The invention will be further illustrated but is not limited by the following example in which the quantities are given in parts by weight unless otherwise indicated.
EXAMPLE
A pigment was prepared by mixing together in water 1 pound of slaked B lime (CaOH)2,-1 liter of water and 15 ml of a surfactant (Triton CF-10) to form a paste. 26% fluosilicic acid was then slowly added with thorough mixing until a pH of 8.0 was obtained. The reaction was highly exothermic and the mixer was water cooled. Thereafter, chromic acid was added until the pH
was 7.0~ This gave a pigment containing hexavalent chromium. If the addition of chromium is not desired, another acid such as phosphoric is used to neutralize the composition to the desired pH of 7.0, immediately before using --this is a catalyst addition. The pH value can be altered.
In either case the resultant composition was then ground in a ball mill and about 1/2 pound of synthetic talc was used to reduce gloss.
One to two pounds of titanium dioxide were then added ~duPont~966 TiO2). A premix was prepared by mixing together 500 ml of tributyl phosphate, -~ 100 ml of a defoaming agent (NOPCO~NXZ), 1 gallon of propylene glycol and 75 gra~s of a pigment dispersant and stabilizer (Tamo ~830) added to the foregoing composition. The resultant mixture was milled until no fish eyes, agglomerates or large particles appeared on a ground gauge and the particles had a size within the range of 0.5 to 5 microns.
1000 ml of thermoplastic acrylic emulsion polymer (Rhoplex MV-l) was then added and milled with the pigment until all of the pigment particles were uniformly coated.
In a slow paddle wheel mixer 5 gallons of the aforesaid thermo-: plastic acrylic emulsion polymer was mixed with 2 gallons of water and the pigmented mixture slowly added thereto. Thereafter a dilute solution of sodium dichromate containing 1% to 10% by weight hexavalent chromium, as Cr, was added dropwise to the peripheral portion of the rotating mixture until a pH of 7.6 to 7.8 had been obtained. $
A diluted thickening agent was then added (Acrysol G-llO) until a viscosity reading of 25/30 seconds was obtained using a Zahn No. 2 cup.
This is especially true where the metal is steel, aluminum, magnesium, aluminum alloys and zinc surfaced articles including galvanized iron or steel, where such coatings are required in order to protect the articles against deterioration, In the past many such coatings have been suggested and used such as phosphate, zincate and anodized films but, in general, these coatings have left much to be desired because of various deficiencies including complex and often difficult operating procedures and high costs.
Chromate conversion coatings have been used with varying degrees of success. The effective protective ingredient in these coatings seems to be chromium in the hexavalent state It has long been recogni7ed that ]t would be desirable to coat metals with an organic film forming resinous composition which would not only be adherent to the metal but would also provide corrosion resistance. Unfortunately attempts to accomplish this result have not been very successful One of the objects of the present invention is to provide a new and useful type of water insoluble pigment which is especially useful in the preparation of emulsions of organic resinous film forming binders and which when applied to metals such as aluminum zinc, magnesium, steel and alloys of such metals and dried will form a coating on the metal which adheres to the metal and provides an unusual amount of corrosion resistance when the coated metal is subjected to salt spray tests.
Another object of the invention is to provide a new and improved process for preparing a water insoluble pigment of the type described.
Still another object of the invention is to provide new and improved coating compositions which can be applied to metals of the type described as a primer coating and which can thereafter be overcoated with a secondary ~'~
~Ol~Z55 coating or a top coating and particularly with water based paint emulsion coatings.
In accordance with the invention there is provided a pro-; cess of preparing a pigment which comprises mixing approximately equimolecular porportions of an inorganic silicofluoride and an inoxganic calcium compound selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate in water sufficient to form a thIck slurry of calcium silicofluoride, carrying out the mixing at a temperature that does not substan-tially exceed 9QF and while maintaining a pH within the range of about 5.0 to about 10.5, and grinding the resultant slurry to an average particle size of 0.5 to lO microns.
The process is preferably carried out at the temperature generated by the heat of reaction while maintaining a pH within the range of about 5.0 to about 10.5, preferably 7.0 to 7.5.
The inorganic silicofluoride used in practicing the in-vention is preferably fluosilicic acid (H2SiF6) which is available commercially as a 26% aqueous solution. However, other inorganic silicofluorides can be employed as, for example, zinc silico-fluoride, lead silicofluoride, manganese silicofluoride, sodium silicofluoride and potassium silicofluoride, magnesium silico-fluoride, and ot~ers.
In carrying out the process, a mixed pigment can be pre-pared by adding at least one chromium compound selected from the group consisting of chromic acid, strontium cHromate, zinc chrom-~ ate and lead chromate to the slurry of said inorganic calcium - compound and said inorganic silicofluoride, the quantity of said chromium compound being within the range of 0.05 to 50~ by weight of the total solids.
Coating compositions are prepared by mixin~ the calcium - silicofluoride pigment slurry in which the pigment particles are ~1(3 0255 usually in very fine form, e.g., an average particle size of 0.5 to 10 microns, or a mixed pigment containing calcium silico-fluoride and an inorgan~c chromium compound of the type prev-iously descri~ed wit~ emulsions of thermoplastic resins, thermo-setting resins, or mixtures of thermoplastic resins and thermo-setting resins in water where water is the cont;nuous phase, prefera~ly with the addition of at least one hexavalent inorganic chromium compound such as, for llC~(l Z55 - example, chromic acid or sodium dichromate, pigments and pigment extenders . other than calcium silicofluoride, driers such as naphthenates of cobalt, lead, magnesium, manganese, zinc and/or zirconium, coalescing agents, dis-persants, defoamers, surfactants and water soluble additives such as ammonium hydroxide, dimethylethanolamine and diethanolamine to enhance stability of the emulsion. Additional water is usually required over that normally present in commercial emulsions or resinous binders.
Preferred coating compositions coming within the scope of the invention consist essentially of the following:
Ingredients Weight %
(a) resin solids of at least one organic film : forming resin selected from the group consisting of thermoplastic resins., thermosetting resins, and mixtures thereof 10-60 (b) calcium silicofluoride 0.5-20 ~c) hexavalent inorganic chromium compound as Cr 0-10 ~d) pigments and pigment extenders other than ~b) 0-100 of resin ~e) dri.ers up to 0.5 of total solids ` ~f) coalescent agents 0.05-10 ~g) dispersants 0.05-6 ?o ~h) defoamers 0-0.05 ~i) surfactants 0.01-3 ~j) thickening agents ~viscosity and required trace to 10.0 by film thickness-determinants) weight of resin ~ ~k) water including water soluble additives 5-65 ~ A preferred type of thermoplastic resin emulsion is one containing 100% acrylic emulsion polymer comprising 46+0.5% by weight solids having a pH of 9 to 11 and weighing approximately 8.9 pounds per gallon. Such an . - ~ acrylic emulsion polymer is available commercially under the name Rhoplex MV-l, Ucar 4358.
A preferred thermosetting resin for use in the practice of the invention is an acrylic emulsion polymer containing 46+0.5% by weight solids rr~
~ -3-110~255 having a pH of 9.5 to 10.5 and weighing approximately 9 pounds per gallon.
Such a resin is available commercially under the name Rhoplex AC-604.
Examples of other suitable resins are those sold under the names Rhoplex B-5 and Rhoplex AC-33X; Ucar 878,4550.
While the foregoing resins are preferred in the practice of the invention, the invention in its broadest aspects is not limited to these particular resins. The types of resins used are many, e,g., vinyl, polyester, epoxy and acrylic, either simple or modified, or mixed; cross linking additives such as, for example, melamine resins, methylated urea formaldehyde and synthetic type rubber type resins can be used.
Typical examples of resin combinations are thermoplastic ~e.g., B Rhoplex MV-1)-thermosetting (e.g, Rhoplex~AC-604); thermoplastic ~e.g., Rhoplex~
MN-l)-thermosetting ~e.g., Rhoplex~AC-604)-thermosetting ~Epoxy~PR-808);
thermopl~astic ~e.g , Rhoplex~ MV-l)-thermosetting ~e.g., Rhoplex~B-5)-thermo-setting ~e.g., Rhoplex~E-1046)-cross linking ~e.g., Uformite~ M83, a melamine resin); and thermoplastic ~e.g., Rhoplex~MV-1)-thermosetting ~e.g., Rhoplex~
B-5)-thermosetting ~e.g., Rhoplex~AC-33x and Rhoplex~E-1046)-cross linking ~e,g., HYCAR CTBN, Uformite M-83, and Beetle~65), Cymel~303.
The various resins are formulated into emulsions in a conventional manner by mixing them in water with various additives including dispersion agents, surfactants, defoamers, coalescing agents, coupling agents, flow control agents, pH control agents and viscosity control agents. The variety of these additives is quite large in number and while the end product produced will have somewhat different chemical and physical characteristics depending upon the particular additives, except to the extent herein described, the invention is not limited to particular additives. Examples of suitable coupling agents normally employed in making such emulsions are isopropyl alcohol, N-butyl alcohol, and tertiary butyl alcohol. Examples of suitable coalescing agents are butyl Cellosolve, butyl carbitol and tributyl phosphate.
Hydrolyzable esters ana water soluble substances detract from shelf life and ~r ~
water and vapor insensitivity.
The preferred pH control materials are ammonium hydroxide, dimethyl-ethanolamine, and diethanolamine. These substances are alkaline as contrasted with the aqueous solutions of the dichromates which are acidic. Tertiary amines such as dimethylethanolamine are preferred from the standpoint of enhancing the stability of the resultant emulsions with which the hexavalent chromium compounds have been incorporated, Diethanolamine also gives good results. The use of ammonium hydroxide is also effective but with the stability somewhat less. However, the use of ammonium hydroxide has the advantage that it decomposes more easily after the emulsion coating composition has been applied to a substrate and during the curing process. For this -~ reason it is usually desirable to add the hexavalent chromium as ammonium dichromate. It is also customary to use the pH control agents in the form of aqueous solutions, for example, ammonium hydroxide as a 28% aqueous solution and the amines diluted in equal weight proportions li.e., 1:1) with water.
Examples of thickening agents are polyacrylic acid and salts :- B thereof, for example, the sodium and ammonium salts such as Acryso fGS, Acrysol G-llO and Acrysol ~ S-?4; cellulose (methyl, carboxy methyl, hydroxy methyl and ethyl cellulose-l,OOO to 150,000 CPS); silicas; silicates.
Examples of pigment dispersants, stabilizers and surfactants are those materials sold commercially under the names Tamol~731, Tamo~ 850, Triton CF-10 which is a water soluble nonionic oxyethylated benzyl ether of octyl phenol, Trito ~ -114 which is an oxyethylated octyl phenol, and Ethoxylan ~ which is lanolin reacted with ethylene oxide.
As shownby the foregoing description of the preferred coating composition, the use of pigments and pigment extenders other than calcium silicofluoride is optional. Among the preferred optional pigments and ~ extenders are lead silicate, chromate pigments (e.g., Oncor~-M50 which has a - ~ yellow-brown color), potassium zinc chromate, magnesium silicofluoride, titanium dioxide, and strontium chromate. As pigment extenders hydrophilic and hydrophobic silicas, synthetic talc and silicates can be employed, with the hydrophilic silicas being preferred.
In preparing the calcium silicofluoride pigment, the reaction between the inorganic silicofluoride such as fluosilicic acid and the inorganic calcium compound is exothermic and the mixing container is preferably jacketed and water cooled. Usually the temperature should be above that giving ice crystal formation and not above 90F., preferably around 70-80F, In order to control the pH chromic acid can be used to neutralize the slurry and thereby produce a chromium containing pigment If it is desired to prepare the calcium silicofluoride pigment without chromium, another inorganic acid, e g., phosphoric acid, can be used to control the pH.
It is usually desirable to adjust the viscosity of the final coating composition to a Zahn #1 viscosity of 10-35 seconds or a Zahn #2 viscosity of 15-50 seconds. This can be done by adjusting the water content and by the use of thixotropic agents or thickeners which are well known in the art.
A given emulsion coating composition might be modified depending upon the type of application, i e., roll coating, spray coating, immersion and squeegee applications, electrostatic applications and other methods of application Where the emulsion coating composition contains both thermoplastic resins and thermosetting resins the weight ratio of thermoplastic resins to thermosetting resins is preferably within the range of 6:1 to 3:1, the ratio however, can be altered at will The more thermosetting resin used the less the water and vapor sensitivity and extensibility If a cross linking agent is employedj the amount is preferably at least 25% by weight of the resin to be cross linked Where pigments are added the weight ratio of pigment to resinous binder is usually within the range of 5:95 to 40:60, although it can be as low as 1:99.
In the application of the coating compositions to a substrate such 110~255 as a metal, those skilled in the art will recognize that cleaning and preparation of the metal is qui~e important and may involve the usual cleaning methods, deoxidizing of the substrate, rinising and drying.
After the emulsion coating composition is applied to a substrate, e,g., steel, aluminum, magnesium, or a 7inc surfaced substrate, it is dried or allowed to dry and cured, for example, at 400F. for from 30 seconds to three minutes or 600F from 20 to 90 seconds, or 1-6 seconds using an intense infra-red air blown unit at 2000F. The time of heating is longer at lower temperatures and shorter at the higher temperatures. The time-temperature - 10 relationship is preferably controlled to give a final coating having a pencil - hardness of H to 2H
The wet thickness of the applied coating is usually within the range - of 0.05 mil to 10 mils (a mil equalling 0 001 inch) A preferred thickness of the wet coating is within the range of 0.1 to 0.3 mil. The greater the thickness of film the greater wi~l be the difficulty of acquiring a uniformly - "cured" film.
- The quantity of the cured coating can be tested in a number of ways. One such test is the salt spray test where a mist or fog of an aqueous - solution containing 5% sodium chloride or acetic acid acidified sodium chloride is applied to coated panels over a predetermined time period Another type of test is the Q-Panel Humidity Panel Test in which the coated panel is subjected to humidities of 90 to 100% at temperatures of from 100F. to 190F, with drying in cyclical periods, the cycles being timed at 0 to 60 minutes under high humidity conditions and 0 to 60 minutes under drying conditions or in variation in 10 minute units of time Another test which is perhaps the most strenuous of all involves boiling the coated panels in distilled water for 30 minutes, 60 minutes or 120 minutes. The area being tested may or may not be impac~ed or bent, Usually a pencil hardness test is made before and after the test ~allowing 5 to 15 minutes recovery at room temperature). Observation can be made for lla~2ss resistance to solvation of coating, chalking of coating and water absorption.
A good film or coating should be capable of returning to its original condition after this test.
Other tests can be conducted to determine resistance to over-bake cure using pencil hardness, impact tests and bend tests. Continuity of film can be determined by using the Preece or modified Preece tests with acidified copper sulfate solution, As previously indicat~d the composition of the emulsion to be applied as a coating may vary somewhat depending upon the nature of the substrate.
~hus, in applying the emulsion coating compositions to aluminum (this term also includes aluminum alloys) experience has shown that excellent reSults are obtained either with high or low hexavalent chromium contents and either at low pH's or high pH's, although the pH is preferably within the range from 5,8 to 10.5. On the other hand, when the emulsion coating compositions are applied to steel, the pH should be below 7Ø In the treatment of galvanized iron or steel (i.e., zinc surfaced articles), it is preferable to have the hexavalent chromium present in amounts such that a coating of the emulsion coating composition on the substrate contains not more than 10 micrograms per square inch of hexavalent chromium, as Cr, and the pH is preferably 6.8 to 8.0 for best results, If too much hexavalent and active chromium is present it reacts with the zinc forming zinc chromates which tend to form a powder and give poor adhesion where a finishing top coat is applied.
The application of the emulsion coating compositions to magnesium (which includes magnesium alloys) is similar to that for aluminum although magnesium is very sensitive to low pH values below 5Ø
The invention will be further illustrated but is not limited by the following example in which the quantities are given in parts by weight unless otherwise indicated.
EXAMPLE
A pigment was prepared by mixing together in water 1 pound of slaked B lime (CaOH)2,-1 liter of water and 15 ml of a surfactant (Triton CF-10) to form a paste. 26% fluosilicic acid was then slowly added with thorough mixing until a pH of 8.0 was obtained. The reaction was highly exothermic and the mixer was water cooled. Thereafter, chromic acid was added until the pH
was 7.0~ This gave a pigment containing hexavalent chromium. If the addition of chromium is not desired, another acid such as phosphoric is used to neutralize the composition to the desired pH of 7.0, immediately before using --this is a catalyst addition. The pH value can be altered.
In either case the resultant composition was then ground in a ball mill and about 1/2 pound of synthetic talc was used to reduce gloss.
One to two pounds of titanium dioxide were then added ~duPont~966 TiO2). A premix was prepared by mixing together 500 ml of tributyl phosphate, -~ 100 ml of a defoaming agent (NOPCO~NXZ), 1 gallon of propylene glycol and 75 gra~s of a pigment dispersant and stabilizer (Tamo ~830) added to the foregoing composition. The resultant mixture was milled until no fish eyes, agglomerates or large particles appeared on a ground gauge and the particles had a size within the range of 0.5 to 5 microns.
1000 ml of thermoplastic acrylic emulsion polymer (Rhoplex MV-l) was then added and milled with the pigment until all of the pigment particles were uniformly coated.
In a slow paddle wheel mixer 5 gallons of the aforesaid thermo-: plastic acrylic emulsion polymer was mixed with 2 gallons of water and the pigmented mixture slowly added thereto. Thereafter a dilute solution of sodium dichromate containing 1% to 10% by weight hexavalent chromium, as Cr, was added dropwise to the peripheral portion of the rotating mixture until a pH of 7.6 to 7.8 had been obtained. $
A diluted thickening agent was then added (Acrysol G-llO) until a viscosity reading of 25/30 seconds was obtained using a Zahn No. 2 cup.
2 gallons of an acrylic thermosetting polymer (Rhoplex~AC-604) were then added and the mixture was mixed slowly for at least 6 hours.
_ 9 _ A coating of the foregoing emulsion was applied to both 3003 aluminum sheet and spangle hot dip galvanized sheet to a wet thickness of 0.2 mil using a draw bar. The coated hot dip galvanized sheet was preheated to 160F, for 30 seconds and cured at 600F. for 75 seconds. The coated aluminum sheet was preheated at 160F. for 30 seconds and cured at 600F. for 60 seconds, In each case the resultant coatings had a pencil hardness of 2H/H.
The hot dip galvani~ed coated sheet withstood the impact of 80 to 100"-pounds and the coated aluminum sheet withstood impact of 30"-pounds.
~ The aluminum sheet after being bent withstood an edge impact of 60"-pounds.
- 10 The impact value ~lbs/sq.in.) is that just before metal or crystal fracture occurs, thus, this value must be a variable.
Salt spray tests on both sheets were conducted to failure. The coated hot dip galvanized sheet ran 400 to 600 hours and the coated aluminum sheet ran over 1000 hours. On embossed aluminum sheeting a coating of the foregoing emulsion applied as previously described gave very superior results on sharply rounded areas as tested by the modified Preece copper sulfate test, Coated panels prepared as previously described will adhere to B finishing coats including, for example, polyester (e.g., PPG-JJ-487 Duracron~, acrylic ~e.g., PPG llW30, Duracron 100, duPont 876-5461, 876-559 and 876-5484), polyvinyl chloride ~e.g., Sherwin-Williams G-77WC198), modified silicone ~e.g., 64X423), modified polyester ~e.g., Dexstar~5XlOOA), modified epoxy ~e.g., Dexstar 9X165), and aqueous resin coatings ~e.g., Armorcote~ll White).
Since all of the chromate-type primers have a decided color, when-ever a top coating is to be white or pastel in color, there is produced a decided color detraction after the baking operation. To offset this effect rutile titanium dioxide is incorporated and sometimes the addition of a blue pigment dispersible in water ~e.g., Hercules Imperial A-984, or X2925) to 30improve the final color effect for whites, blues and greens. For other 11(~(~25S
shades some comparable color pigments akin to the desired color tone can be added. These tend to block out or hide the color effect of the active chro-mates contained in the prime coating.
As will be apparent from the foregoing description, the emulsion conating compositions prepared in accDrdance with the invention can contain a wide variet~ of ingredients in various proportions. In general, however, these compositions fall into two main categories depending upon whether the resinous binder is a thermoplastic resin or a combination of thermoplastic and thermo-setting resins. Where the resinous binder is solely a thermoplastic resin, the composition of the emulsion is preferably as follows:
Thermoplastic resin Ce.g.~ Rhoplex MV-l) 50-95% CVl.) Water 45-0 % CVol.) Dilute inorganic chromate solution Ce.g., Enough to give a pH
- Na2Cr2O7) of 5.5-9.0 Drier (e.g., cobalt naphthenate) 0.05-0.5% of total solids ~wt.) Pigment Ce.g., CaSiF6, or chromate containing CaSiF6 0.5-20% Cwt.) CoalesciRg agents Ce.g., tributyl phosphate) 0.5-3% of the resin ~vol.) B Surfactant CTriton~CF10) Trace to 0.1% of resin (wt.) Thickening Agent CAcrysol G-llO)- Trace to 10.0% of ~as film thickness requires~ resin Cwt.) Titanium dioxide 0-5% Cwt.) Dispersing agent ~e.g., Tamol~850~ 0-5.0% of pigment Cwt.) In the case of a composition containing both thermoplastic and thermo-setting resins a preferred composition contains:
Thermoplastic resin Ce.g., Rhople~MV-l) 15-60% Cvol.) Thermosetting resin (e.g., Rhople *AC-604) 10-60% Cvol.) Water 10-4% Cvol.) Dilute chromate solution ~Na2Cr2O7~NH4OH; Enough to gi~e pH
CrO3~NHAOH; CNH4)2Cr2O7/NH4OH - diluted:20 pts of 6.8 9.5 water/ I part solld]
Pigment ~e.g., CaSiF or chromate containing CaSiF6~ 0.5-20% Cwt.) D~er ~e~g~, eQbalt napht~enate~ 0.05-0.5% of total solids (wt.) Coalescing agents ~e.g., tri~utrl phosphate~ 0.5~3% o the resin (vol.) B Surfactant (Triton CF10) Trace to 0.1% of resin (wt.) Thickening agent (Acrysol G-llO)- Trace to 10.0% of ~as film thickness requires) resin twt.) Titanium dioxide 0-5% ~wt.) Dispersing agent (e.g., Tamol~850) 0-5.0% of pigment (wt.) In these compositions ammonium hydroxide, dimethylethanolamine, or diethanolamine are added with or without the thickener to obtain a desired viscosity which is within the range of 20 to 45 seconds on a Zahn No. 1 cup and 17 to 35 seconds on a Zahn No. 2 cup. The method of application and desired dry-film thickness will determine the viscosity value, along with the equipment for curing such applied film.
Certain catalysts can be incorporated to: increase the speed of cure, and/or lower the "cure" temperature. Such materials are, for example, thio-cyanates (provided iron is not present to cause discoloration), toluene sul-fonic acid, and phosphoric acid. It is suggested that if such be used, this along with other additives such as water, for viscosity control, should`be added just prior to mixing (at usage station).
Also, it is desirable to keep the organic film-coating mixture at a pH value of 8.0 to 8.5 and make the final adjustment along with the aforemen-tioned additions. This affords a more accurate pH control for whatever the desired pH value may be. For best results a pH of at least 7 is desirable -- because at acidic pH's the composition may set up prematurely to a mass which ; cannot be applied as a coating.
In the foregoing description reference has been made to the use of calcium silicofluoride as an inorganic pigment for use in compositions forming a protective coating on metals such as aluminum, zinc, magnesium, steel and alloys of such metals, with or without the addition of hexavalent chromium.
It has been noted that when such compositions are applied to aluminum, appar-ently oxide formation on the surface of the aluminum does not occur after a coating composition containing the calcium silicofluoride is dried at tem-3Q ReX~tu~es c~ ~t lea~t 2aO~F~ and usually~w~thin the range of 4Q0F~ to 600F.
~ OY~
. .
1~0025S
; The resultant coating with or without the film forming organic resin will not wash off with water and prov~des a protective coating at a thickness of 0.05-10 mils, especially within the range of 0.1-0.3 mil which is unusually resis-tant to corrosion, as tested by conventional salt spray testing methods a~nd is especially resistant to corrosion caused by humidity. It is believed th~at this is attributable in part at least to the calcium silicofluoride breaking~', down in situ thereby creating a condition which interferes with the electrical action that normally produces corrosion.
Where the protective coating composition containing the calcium silicofluoride is applied to zinc surfaced articles and steel, it is desirable to include in the composition 0.01-10 weight per cent, as Cr, of a hexavalent inorganic chromium compound. Of course, the chromium compound can also be in-cluded in a composition of the same type that is applied to aluminum but the behavior of the composition as applied to aluminum is somewhat different from - the behavior as applied to steel and zinc surfaced articles such as galvanized iron or steel.
As previously pointed out, it is desirable to apply the compositions containing calcium silicofluoride to a metal of the type described after the metal has been cleaned. In this connection, especially good resullts have been obtained where the cleaning composition is of the type described in United States Patent 3,840,841 which contains boron compounds. This may be attribut-able to interaction between a boron containing coating and the calcium silico-fluoride containing coating.
While calcium silicofluoride has been referred to herein as a pigment, it will be apparent from the foregoing description that it is not necessarily inert and could also be called an activator when employed in protective coating : compositions for metals in accordance with the invention.
It will be apparent that other variations can be made without de-parting from the spirit and scope of the invention.
_ 9 _ A coating of the foregoing emulsion was applied to both 3003 aluminum sheet and spangle hot dip galvanized sheet to a wet thickness of 0.2 mil using a draw bar. The coated hot dip galvanized sheet was preheated to 160F, for 30 seconds and cured at 600F. for 75 seconds. The coated aluminum sheet was preheated at 160F. for 30 seconds and cured at 600F. for 60 seconds, In each case the resultant coatings had a pencil hardness of 2H/H.
The hot dip galvani~ed coated sheet withstood the impact of 80 to 100"-pounds and the coated aluminum sheet withstood impact of 30"-pounds.
~ The aluminum sheet after being bent withstood an edge impact of 60"-pounds.
- 10 The impact value ~lbs/sq.in.) is that just before metal or crystal fracture occurs, thus, this value must be a variable.
Salt spray tests on both sheets were conducted to failure. The coated hot dip galvanized sheet ran 400 to 600 hours and the coated aluminum sheet ran over 1000 hours. On embossed aluminum sheeting a coating of the foregoing emulsion applied as previously described gave very superior results on sharply rounded areas as tested by the modified Preece copper sulfate test, Coated panels prepared as previously described will adhere to B finishing coats including, for example, polyester (e.g., PPG-JJ-487 Duracron~, acrylic ~e.g., PPG llW30, Duracron 100, duPont 876-5461, 876-559 and 876-5484), polyvinyl chloride ~e.g., Sherwin-Williams G-77WC198), modified silicone ~e.g., 64X423), modified polyester ~e.g., Dexstar~5XlOOA), modified epoxy ~e.g., Dexstar 9X165), and aqueous resin coatings ~e.g., Armorcote~ll White).
Since all of the chromate-type primers have a decided color, when-ever a top coating is to be white or pastel in color, there is produced a decided color detraction after the baking operation. To offset this effect rutile titanium dioxide is incorporated and sometimes the addition of a blue pigment dispersible in water ~e.g., Hercules Imperial A-984, or X2925) to 30improve the final color effect for whites, blues and greens. For other 11(~(~25S
shades some comparable color pigments akin to the desired color tone can be added. These tend to block out or hide the color effect of the active chro-mates contained in the prime coating.
As will be apparent from the foregoing description, the emulsion conating compositions prepared in accDrdance with the invention can contain a wide variet~ of ingredients in various proportions. In general, however, these compositions fall into two main categories depending upon whether the resinous binder is a thermoplastic resin or a combination of thermoplastic and thermo-setting resins. Where the resinous binder is solely a thermoplastic resin, the composition of the emulsion is preferably as follows:
Thermoplastic resin Ce.g.~ Rhoplex MV-l) 50-95% CVl.) Water 45-0 % CVol.) Dilute inorganic chromate solution Ce.g., Enough to give a pH
- Na2Cr2O7) of 5.5-9.0 Drier (e.g., cobalt naphthenate) 0.05-0.5% of total solids ~wt.) Pigment Ce.g., CaSiF6, or chromate containing CaSiF6 0.5-20% Cwt.) CoalesciRg agents Ce.g., tributyl phosphate) 0.5-3% of the resin ~vol.) B Surfactant CTriton~CF10) Trace to 0.1% of resin (wt.) Thickening Agent CAcrysol G-llO)- Trace to 10.0% of ~as film thickness requires~ resin Cwt.) Titanium dioxide 0-5% Cwt.) Dispersing agent ~e.g., Tamol~850~ 0-5.0% of pigment Cwt.) In the case of a composition containing both thermoplastic and thermo-setting resins a preferred composition contains:
Thermoplastic resin Ce.g., Rhople~MV-l) 15-60% Cvol.) Thermosetting resin (e.g., Rhople *AC-604) 10-60% Cvol.) Water 10-4% Cvol.) Dilute chromate solution ~Na2Cr2O7~NH4OH; Enough to gi~e pH
CrO3~NHAOH; CNH4)2Cr2O7/NH4OH - diluted:20 pts of 6.8 9.5 water/ I part solld]
Pigment ~e.g., CaSiF or chromate containing CaSiF6~ 0.5-20% Cwt.) D~er ~e~g~, eQbalt napht~enate~ 0.05-0.5% of total solids (wt.) Coalescing agents ~e.g., tri~utrl phosphate~ 0.5~3% o the resin (vol.) B Surfactant (Triton CF10) Trace to 0.1% of resin (wt.) Thickening agent (Acrysol G-llO)- Trace to 10.0% of ~as film thickness requires) resin twt.) Titanium dioxide 0-5% ~wt.) Dispersing agent (e.g., Tamol~850) 0-5.0% of pigment (wt.) In these compositions ammonium hydroxide, dimethylethanolamine, or diethanolamine are added with or without the thickener to obtain a desired viscosity which is within the range of 20 to 45 seconds on a Zahn No. 1 cup and 17 to 35 seconds on a Zahn No. 2 cup. The method of application and desired dry-film thickness will determine the viscosity value, along with the equipment for curing such applied film.
Certain catalysts can be incorporated to: increase the speed of cure, and/or lower the "cure" temperature. Such materials are, for example, thio-cyanates (provided iron is not present to cause discoloration), toluene sul-fonic acid, and phosphoric acid. It is suggested that if such be used, this along with other additives such as water, for viscosity control, should`be added just prior to mixing (at usage station).
Also, it is desirable to keep the organic film-coating mixture at a pH value of 8.0 to 8.5 and make the final adjustment along with the aforemen-tioned additions. This affords a more accurate pH control for whatever the desired pH value may be. For best results a pH of at least 7 is desirable -- because at acidic pH's the composition may set up prematurely to a mass which ; cannot be applied as a coating.
In the foregoing description reference has been made to the use of calcium silicofluoride as an inorganic pigment for use in compositions forming a protective coating on metals such as aluminum, zinc, magnesium, steel and alloys of such metals, with or without the addition of hexavalent chromium.
It has been noted that when such compositions are applied to aluminum, appar-ently oxide formation on the surface of the aluminum does not occur after a coating composition containing the calcium silicofluoride is dried at tem-3Q ReX~tu~es c~ ~t lea~t 2aO~F~ and usually~w~thin the range of 4Q0F~ to 600F.
~ OY~
. .
1~0025S
; The resultant coating with or without the film forming organic resin will not wash off with water and prov~des a protective coating at a thickness of 0.05-10 mils, especially within the range of 0.1-0.3 mil which is unusually resis-tant to corrosion, as tested by conventional salt spray testing methods a~nd is especially resistant to corrosion caused by humidity. It is believed th~at this is attributable in part at least to the calcium silicofluoride breaking~', down in situ thereby creating a condition which interferes with the electrical action that normally produces corrosion.
Where the protective coating composition containing the calcium silicofluoride is applied to zinc surfaced articles and steel, it is desirable to include in the composition 0.01-10 weight per cent, as Cr, of a hexavalent inorganic chromium compound. Of course, the chromium compound can also be in-cluded in a composition of the same type that is applied to aluminum but the behavior of the composition as applied to aluminum is somewhat different from - the behavior as applied to steel and zinc surfaced articles such as galvanized iron or steel.
As previously pointed out, it is desirable to apply the compositions containing calcium silicofluoride to a metal of the type described after the metal has been cleaned. In this connection, especially good resullts have been obtained where the cleaning composition is of the type described in United States Patent 3,840,841 which contains boron compounds. This may be attribut-able to interaction between a boron containing coating and the calcium silico-fluoride containing coating.
While calcium silicofluoride has been referred to herein as a pigment, it will be apparent from the foregoing description that it is not necessarily inert and could also be called an activator when employed in protective coating : compositions for metals in accordance with the invention.
It will be apparent that other variations can be made without de-parting from the spirit and scope of the invention.
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process of preparing a pigment which comprises mixing approximately equimolecular proportions of an inorganic silicofluoride and an inorganic calcium compound selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate in water sufficient to form a thick slurry of calcium silicofluoride, carrying out the mixing at a temperature that does not substantially exceed 90°F. and while maintaining a pH within the range of about 5.0 to about 10.5, and grinding the resultant slurry to an average particle size of 0.5 to 10 microns.
2. A process as claimed in claim 1 in which said mixing is carried out at a temperature in the range of 70 to 80°F.
3. A process as claimed in claim 1 in which said mixing is carried out at a pH of approximately 7.0 to 7.5.
4. A process as claimed in claim 1 in which the inorganic silico-fluoride is H2SiF6.
5. A process as claimed in claim 1 in which the inorganic silico-fluoride is selected from the group consisting of zinc silicofluoride, lead silicofluoride, manganese silicofluoride, sodium silicofluoride and potassium silicofluoride, and magnesium silicofluoride.
6, A process as claimed in claim 1 in which a quantity of at least one chromium compound selected from the group consisting of chromic acid, strontium chromate, zinc chromate and lead chromate is added to said slurry, said quantity being 0.05% to 50% by weight of the total solids.
7. A process as claimed in claim 6 in which said chromium compound is chromic acid.
8. A process as claimed in claim 6 in which said chromium compound is strontium chromate.
9. A pigment comprising calcium silicofluoride having an average particle size of 0.5 to 10 microns.
10. A pigment comprising a finely divided intimate mixture of calcium silicofluoride and at least one chromium compound selected from the group consisting of chromic acid, strontium chromate, zinc chromate and lead chromate, the quantity of said chromium compound Being within the range of 0.05% to 50% by weight of the total solids, said finely divided intimate mixture Having an average particle size of 0.5 to 10 microns.
11. A pigment as claimed in claim 10 wherein said chromium compound is chromic acid.
12. A pigment as claimed in claim 10 wherein said chromium compound is strontium chromate.
13. A coating composition comprising an organic resinous film forming binder and a product as claimed in claim 9 in suf-ficient amount to enhance adherence to a metal from the group consisting of aluminum, zinc, magnesium and steel.
14. A coating composition comprising an organic resinous film forming binder and a product as claimed in claim 10 in suf-ficient amount to enhance adherence to and corrosion resistance of a metal from the group consisting of aluminum, zinc, magnes-ium and steel.
15. A coating composition comprising an organic resinous film forming Binder and a product as claimed in claim 11 in suf-ficient amount to enhance adherence to and corrosion resistance of a metal from the group consisting of aluminum, zinc, magnes-ium and steel.
16. A coating composition comprising an organic resinous film forming binder and a product as claimed in claim 12 in suf-ficient amount to enhance adherence to and corrosion resistance of a metal from the group consisting of aluminum, zinc, magnes-ium and steel.
17. A coating composition as claimed in claim 13 consisting essentially of:
18. A coating composition as claimed in claim 17 containing 0.01 - 10%, as Cr, of the hexavalent inorganic chromium compound.
19. A composition as claimed in claim 17 or 18 in which the hexavalent inorganic chromium compound is selected from the group consisting of chromic acid, strontium chromate, zinc chromate and lead chromate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/660,173 US4154620A (en) | 1974-09-12 | 1976-02-23 | Pigment preparation and use in coating compositions |
| US660,173 | 1976-02-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100255A true CA1100255A (en) | 1981-05-05 |
Family
ID=24648461
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,339A Expired CA1100255A (en) | 1976-02-23 | 1977-02-22 | Pigment preparation and use in coating compositions |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1100255A (en) |
| DE (1) | DE2707486A1 (en) |
| FR (1) | FR2341629A1 (en) |
| NL (1) | NL188897C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6083373A (en) * | 1998-07-10 | 2000-07-04 | Ppg Industries Ohio, Inc. | Electrodeposition baths containing calcium salts |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US789671A (en) * | 1904-09-14 | 1905-05-09 | Julius Alois Reich | Process of making alkaline fluosilicates. |
-
1977
- 1977-02-21 DE DE19772707486 patent/DE2707486A1/en active Granted
- 1977-02-22 CA CA272,339A patent/CA1100255A/en not_active Expired
- 1977-02-22 FR FR7705048A patent/FR2341629A1/en active Granted
- 1977-02-23 NL NLAANVRAGE7701938,A patent/NL188897C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| DE2707486A1 (en) | 1977-08-25 |
| NL188897B (en) | 1992-06-01 |
| DE2707486C2 (en) | 1988-03-31 |
| FR2341629A1 (en) | 1977-09-16 |
| NL188897C (en) | 1992-11-02 |
| FR2341629B1 (en) | 1982-10-08 |
| NL7701938A (en) | 1977-08-25 |
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