CALCIUM CARBONATE TREATED WITH FATTY ACIDS, MANUFACTURE AND USE

Abstract: Precipitated calcium carbonate, having an average particle size of from about 0.01 micron to about 0.1 micron, and a specific surface area of from about 10 m<2>/g to about 100 m<2>/g, surface treated with at least one high molecular weight unsaturated fatty acid, such as erucic acid, or a combination of at least one high molecular weight unsaturated fatty acid, and at least one high molecular weight saturated fatty acid, wherein the preferred combination of a high molecular weight unsaturated fatty acid and a high molecular weight saturated fatty acid is oleic acid and erucic acid, respectively, and processes for the preparation of such material are disclosed. A method for the addition of such surface-treated calcium cabonate to polyvinyl chloride plastisols to increase the baked adhesion of the plastisol to a metal surface and to reduce the baking temperature at which the plastisol formulation is baked onto the metal surface is also disclosed.

Description: Calcium carbonate treated with fatty adds, manufacture and use Background of the Invention This invention broadly relates to treated filler materials, more particularly, to surface-treated calcium carbonate, and still more particularly to calcium carbonate surface-treated with a high molecular weight unsaturated fatty acid for use as filler in polyvinyl chloride plastisols to improve the baked adhesion to electrocoated metal surfaces at low bake temperatures. Polyvinyl chloride (PVC) plastisols are generally composed of finely divided PVC resin, plasticizers and fillers; for particular application they may contain small amounts other additives such as stabilizer, pigments or colorants, and adhesion promoting compounds. The components of a plastisol are combined and mixed to form a fluid which may be applied to a substrate (e.g. cloth or metal) or formed into shapes or articles (e.g. gloves) . After this, the plastisol is heated, which results in the complete diffusion of plasticizer into the resin particles (gelation) over the temperature range of from about 50°C to about 170°C, and in the melting of the polymer over the temperature range of from about 120°C to about 180°C. When the melted (fused) plastisol is then allowed to cool below about 50°C, it forms a flexible, tough and chemical- resistant solid. In the automotive industry, PVC plastisols may be used as undercoatings, chip guards and as sealants for the seams of welded metal parts. The body work and underside of autos are generally electrocoated primed sheet metal; plastisols for these applications must adhere well to the electrocoated metal and must have good abrasion and impact resistance to perform their protective and sealant functions. Since PVC homopoly er has relatively poor inherent adhesion to electrocoated metal, vinyl acetate copolymers which have fast gelation times and low fusion temperatures are substituted for a portion of the homopolymer resin. Because copolymers undergo quicker viscosity aging (increase in viscosity) and develop lower ultimate impact strength properties than homopolymers, the amount of homopolymer they can replace is limited. Therefore organic adhesion promoting compounds are often added to automotive type plastisols. Recently there has been a trend in the automotive industry to bake PVC plastisols at lower temperatures (i.e. about 120°C) than was formerly the practice (i.e. 140- 150°C) . This energy-cost saving step, in which the paint coating is often baked simultaneously with the plastisol, has put the processing temperature near to the minimum needed for fusion. Since complete fusion is necessary for the development of optimum physical properties, including adhesion, the use of lower bake temperatures has made plastisol formulation more critical. Calcium carbonate is used in PVC plastisols in the forms of ground limestone and precipitated calcium carbonate (PCC) . Ground limestone is added as a filler, primarily to reduce the volume cost of the plastisol. Precipitated calcium carbonate is used to increase the low shear viscosity and thixotropy of the fluid plastisol and to increase the impact resistance of the baked product. Surface treatment of the calcium carbonate with stearic acid or salts of stearic acid is widely practiced for decreasing the plasticizer absorption and increasing the compatibility of the calcium carbonate. PCC, treated with stearic acid or salts of stearic acid, manufactured by Pfizer Inc. , New York, and commercially available under the name Ultra-Pflex, was tested in a polyvinyl chloride plastisol of the type used in the automotive industry for performance with respect to rheology and adhesion. The plastisols made with Ultra-Pflex had unacceptably poor baked adhesion to electrocoated metal when the bake temperature was around 120°C. It was then decided to experiment with different combinations of PCC treated with other materials to determine whether there would be improvement in baked adhesion at low baking temperature by using such other treated PCC's as a functional filler material in PVC plastisols. Further work involving pre-surface-treating the PCC with high molecular weight unsaturated fatty acid or a combination of a high molecular weight unsaturated fatty acid and a high molecular weight saturated fatty acid, has resulted in the discovery of the present invention. Summary of the Invention It has been discovered that unexpectedly, the addition to a polyvinyl chloride plastisol of a precipitated calcium carbonate which has been pre-surface treated with a high molecular weight unsaturated fatty acid or a combination of a high molecular weight unsaturated fatty acid and a high molecular weight saturated fatty acid, greatly increases the baked adhesion of the overall composition to an electrocoated metal surface, especially when the baking process is conducted at a low baking temperature in the range of from about 115°C to about 125°C. Detailed Description of the Invention The PCC for surface treatment according to preferred embodiments of the present invention has an average particle size of from about 0.01 to about 0.1 micron, and preferably about 0.07 micron. The PCC has a specific surface area in the range of from about 10 m 2 /g to about 100 πr/g, depending on the corresponding average particle size. For PCC with an average particle size of 0.07 micron, the specific surface area is from about 18 m : /g to about 22 m 2 . ' .,. The C filler material is surface treated according to the present invention with at le.'.st one high molecular weight (C>20) unsaturated fatty acid or a combination of at least one high molecular weight (C>18) unsaturated fatty acid and at least one high molecular weight (C>20) saturated fatty acid. It has been discovered that when the PCC is surface- treated with a high molecular weight unsaturated fatty acid alone, the fatty acid must have a carbon content of at least C=20 in order to provide both the desired adhesion and rheological properties. However, when the PCC is surface- treated with a combination of at least one high molecular weight unsaturated fatty acid at at least one high molecular weight saturated fatty acid, it is possible to utilize an unsaturated fatty acid having a somewhat lower carbon content of at least C-18 to provide adhesion, as long as the high molecular weight saturated fatty acid has a carbon content of at least C=20, to provide the rheological properties. While use of unsaturated fatty acids having a carbon content lower than C=18 still affords a fair amount of adhesion in the PVC plastisol to which the calcium carbonate coated with such acid has been added, it has been found that the rheological properties of a PVC plastisol incorporating a calcium carbonate coated with a less than C 18 unsaturated fatty acid become less and less acceptable with decreasing carbon content. The high molecular weight unsaturated fatty acid, when utilized alone, is selected from the group consisting of erucic acid (cis-13-docosenoic acid) , gadoleic acid (9 cis-eicosenoic acid) , brassidic acid (13 trans-docosenoic acid) , selacholeic acid (15 cis- tetrasenoic acid), ximenic acid (17 cis-hexacosenoic acid), lu egueic acid (21 cis-triacon-tenoic acid) , and combinations thereof. Where a high molecular weight unsaturated fatty acid is used in combination with the unsaturated fatty acid, it is possible to utilize an unsaturated fatty acid selected from the above indicated group and further including oleic acid (C^) . It has been found, according to the present invention, that erucic acid (cis-13-docosenoic acid) is preferred as the unsaturated fatty acid when used alone. The high molecular weight saturated fatty acid is selected from the group consisting of arachidic acid (C 20 ) , behenic acid (C 22 ) , lignoceric acid (C 24 ) , cerotic acid (C 26 ) , montanic acid (C 28 ) , and combinations thereof. A preferred combination of a high molecular weight unsaturated fatty acid and a high molecular weight saturated fatty acid is oleic acid and behenic acid. The PCC is surface-treated with the unsaturated fatty acid or acids or combination of unsaturated and saturated fatty acids to the extent of from about 1.0 weight percent to about 3.5 weight percent based on the weight of the calcium carbonate. Preferably, the fatty acid surface treatment is present in an amount of about 2.0 weight percent to about 2.5 weight percent, based on the weight of calcium carbonate. Surface treatment of the PCC with the unsaturated or combination of unsaturated and saturated fatty acids according to the present invention is accomplished by either a dry process or a wet process. In the dry process, ultrafine precipitated calcium carbonate at room temperature is first dry-mixed alone until the frictional heating produced by mixing causes an increase in the temperature of the PCC to about 80°C. At that point, a sufficient amount of at least one high molecular weight unsaturated fatty acid or a combination of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid, is added to the PCC to produce a coating of the fatty acid on the PCC of from about 1.0 to about 3.5 weight percent based on the weight of PCC. Mixing of the PCC and the fatty acid is continued until the temperature rises to about 105°C due to frictional heating, or at least five minutes have elapsed since addition of the fatty acid. The coated ultrafine PCC is then ready for milling to any desired degree of fineness, using, for example, a Mikroato izer mill (Mikropul Division, Hosokawa Micron International, Inc., Summit, N.J.). In the wet process, ultrafine precipitated calcium carbonate is first mixed with water to form a slurry. Preferably, the PCC is as a centrifuge paste containing about 40.1% by weight of calcium carbonate. The PCC-water slurry is heated to 85°C and agitated for about one hour to produce a homogeneous mixture. A sodium salt solution of a at least one high molecular weight unsaturated fatty acid or a combination of sodium salt solutions of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid is then added to the slurry, with agitation, over a period of about 5 minutes. The resulting new slurry is agitated for about one hour at a temperature around 85°C and is then dewatered, such as by filtration, dried at a temperature around 110°C and milled, such as with a Mikroatomizer mill. Preferably, the high molecular weight fatty acid is erucic acid. A sodium erurate solution is prepared by saponifying erucic acid with an excess of sodium hydroxide. Erucic acid is a solid at room temperature. In the dry mixing process, the PCC and the erucic acid are combined and homogenized in a high intensity mixer, such as a Henschel type mixer (Rheinstahl Henschel AG, Kassel, W. Germany) or a Welex type mixer (Gunther Pappen eier GmbH, Detmold, W. Germany) . The components are mixed sufficiently long to allow complete melting of the erucic acid and its uniform adsorption by the calcium carbonate. The calcium carbonate is then deagglomerated in a high speed mill such as a Mikroatomizer mill. Addition of an effective amount of an erucic acid surface-treated PCC filler to a PVC plastisol, namely, an amount of from about 10 weight percent to about 30 weight percent, based on the weight of the plastisol, and preferably, from about 15 weight percent to about 20 weight percent, based on the weight of the plastisol, has been found to greatly increase the baked adhesion of the filled plastisol to an electrocoated metal, particularly when the baking step is performed at a low temperature in the range of from about 110°C to about 140°C, and preferably at about 120°C. While not wishing to be limited to a particular theory, it is believed that addition of a precipitated calcium carbonate treated with a high molecular weight i saturated fatty acid or a combination of a high molecular weight unsaturated fatty acid and a high molecular weight saturated fatty acid to a polyvinyl chloride plastisol improves the rheological properties and adhesion of the plastisol to an electrocoated metal surface because the high molecular weight of the coating agent on the PCC has a beneficial effect on the product rheology, and because the unsaturation of the coating agent on the PCC improves the bake adhesion of the plastisol to the metal surface and enables the plastisol to set at a lower baking temperature than heretofore utilizable with the plastisol alone. An amine type adhesion promoter may also be added to the surface-treated PCC-PVC plastisol mixture to further improve the baked adhesion of the mixture to a metal surface. When an amine type adhesion promoter is used, it is added to the surface-treated PCC-PVC plastisol mixture in an amount of from about 0.8 weight percent to about 1.0 weight percent, based on the weight of the PCC-PVC plastisol mixture. The amine type adhesion promoter is selected from the group consisting of amino-a ides, such as Euretek 550, 556, 580 and 600, manufactured by Sherex Corp., Dublin, OH, and amino functional silanes, as manufactured by Union Carbide Corp., Danbury, CT. The nature of the present invention may be more fully understood in light of the following non-limiting examples. Example 1 Preparation of Ultrafine PCC Surface-treated with Various Levels of Erucic Acid bv Dry-Method Samples of ultrafine PCC were surface treated with erucic acid in amounts of 1.5%, 2.0% 2.25%, and 2.5% by weight, based on the weight of PCC. The samples were prepared by surface-treating ultrafine PCC which had previously been synthesized, dewatered and dried. The source of the PCC was from the Pfizer Inc. plant at Adams, MA. The dried samples of Ultrafine PCC were surface-treated with the erucic acid at the various levels in a laboratory scale Welex high intensity mixer. The Ultrafine PCC was first placed int he Welex mixer and mixed alone at a blade speed of 3800 rpm until the temperature reached 80°C. At that point, erucic acid (Prifrac 2990, Unichema Chemicals Inc. , Chicago, IL) was added and mixing was continued at 3800 rpm until the temperature of the batch reached 105°C or five minutes had elapsed from the time of the erucic acid addition. The amounts of each ingredient for the various samples are shown in Table I. Table I deagglomerated in a Mikroatomizer Mill (Mikropul Div. , Hosokawa Micron International, Inc. , Summit, NJ) . Example 2 Evaluation of Samples of Erucic Acid surface-treated PCC in PVC Plastisol The samples of Ultra fine PCC surface-treated with various levels of erucic acid, prepared in Example 1, were added to a polyvinyl chloride plastisol of the type used in the automotive industry to evaluate the properties of the material as to adhesion and rheology. Each of the surface treated PCC samples of Example 1 was evaluated in the PVC plastisol formulation shown in Table II. Table II PVC Plastisol Formulation Containing Erucic Acid Treated Ultrafine PCC. Component Amount (gms) Weight Percent PVC Resin Oxychem 6338 220 31.94 (Occidental Chemical Co., Pottstown, PA) Plasticizer, Santicizer 220 31.94 711 (Monsanto Co., St. Louis, MO) Adhesion Promoter, 5.36 0.78 Euretek 580 Sherex Chemical Co., Dublin, OH) Calcium Oxide, Technical 9.90 1.44 grade (Fisher Scientific Co. , Fairlawn, NJ) Limestone, Vicron 25-11 110 15.97 (Pfizer Inc. , NY, NY) Mineral Spirits, 13.5 1.96 Industrial grade Erucic acid surface-treated 110 15.97 PCC(Samples 1-4, from Table I) Total 688.76 100.00 The plastisol formulations were mixed using a Ross double planetary mixer (Charles Ross and Son Co. , Hauppauge, NY) . The resin plasticizer, calcium oxide and adhesion promoter were placed in the mixing bowl and mixed at 55 rpm for three minutes. The limestone and erucic acid treated ultrafine PCC were added and mixing continued at 55 rpm for twenty minutes. The mineral spirits were then added and mixing continued at 55 rpm for five minutes under vacuum. Water was circulated through the jacket of the mixing bowl throughout the mixing procedure. Each of the final plastisol formulations was packed in a can and stored 24 hours at 72°F. After this conditioning period, the viscosity of each batch was measured using a Brookfield Model HBT Viscometer using the TE spindle and the Model D Helipath stand (Brookfield Engineering Laboratories, Stoughton, MA) . The results are shown in Table III. Table HI Immediately after the viscosity measurements were completed, the adhesion properties of each plastisol were measured. A 0.050 ± 0.002 inch thick film, of each sample of plastisol was applied to an ED 3060 (PPG Automotive Products Inc., Cleveland, OH) electrocoated metal test panel. The film was applied to a 2-inch wide by 3 inch long rectangular area of the panel. The panels were then placed in an oven at 120°C for 30 minutes. After removal from the oven, the panels were allowed to stand at room temperature for 30 minutes. At that time, two parallel slits were made in the plastisol film 0.5 inch apart and through the entire width of the film. A spatula was used to lift a small piece of the strip thus formed and an attempt was made to slowly pull the test strip from the metal test panel. If the strip could be entirely removed leaving no residue on the panel, the adhesion was rated poor. If the strip tore before detaching from the panel, the adhesion was rated excellent (i.e. greater than the cohesion of the plastisol). The results of this test for the various samples is shown in Table IV. SampleNo. Adhesion RelativeAdhesion (Interpretation of results) Table IV shows that although all of the erucic acid surface treated PCC containing PVC plastisol formulations according to the present invention demonstrated superior baked adhesion to an electrocoated metal surface, the adhesion increased with increasing amount of erucic acid on the PCC. Example 3 Wet Coating Calcium Carbonate with Erucic Acid Three gallons of tap water and 5,095 grams of ultrafine precipitated calcium carbonate centrifuge paste containing 40.1% by weight of calcium carbonate were combined in a stainless steel container to form a first slurry. The components were heated to 85°C with agitation and further agitated for about 1 hour at 85°C after which a sodium erucate solution was added with agitation over a period of about 5 minutes, forming a second slurry. The sodium erucate solution was prepared by saponifying erucic acid with an excess of sodium hydroxide. 53.12 grams of erucic acid (Prifrac 2990, Unichema Chemicals Inc., Chicago, 111.) were added with agitation to 3090 ml of tap water which had been heated to 85°C. 12.58 grams of 50% (weight/weight) sodium hydroxide aqueous solution, representing a 5% excess of NaOH was added. The resultant solution was agitated for one hour at 85°C before addition to the PCC slurry. The second slurry was agitated for one hour at 85°C after which it was dewatered by filtration, dried at 110 °C and milled with a Mikroatomizer mill.

Claims: CLAIMS 1. A composition characterized by calcium carbonate surface-treated with at least one high molecular weight unsaturated fatty acid or at least one high molecular wight unsaturated fatty acid in combination with at least one high molecular weight saturated fatty acid. 2. The composition according to claim 1 further characterized by the calcium carbonate having an average particle size of from about 0.01 to about 0.1 micron. 3. The composition according to claim 1 further characterized by the calcium carbonate having a specific surface area of from about 10 m 2 /g to about 100 m 2 /g. 4. The composition according to claim 1 further characterized by the condition that when at least one high molecular weight unsaturated fatty acid is utilized alone, it is selected from the group consisting of erucic acid (cis-13-docosenoic acid) , gadoleic acid (9 cis-eicosenoic acid) , brassidic acid (13 trans-docosenoic acid) , selacholeic acid (15 cis-tetrasenoic acid) , ximenic acid (17 cis-hexacosenoic acid) , lumegueic acid (21 cis-tri- acontenoic acid) , and combinations thereof; and when at least one high molecular weight unsaturated fatty acid is utilized in combination with at least one high molecular weight saturated fatty acid, the unsaturated fatty acid is selected from the group consisting of oleic acid, erucic acid (cis-13-docosenoic acid) , gadoleic acid (9 cis-eico¬ senoic acid) , brassidic acid (13 trans-docosenoic acid) , selacholeic acid (15 cis-tetrasenoic acid) , ximenic acid (17 cis-hexacosenoic acid) , lumegueic acid (21 cis-tri- acontenoic acid) , and combinations thereof. 5. The composition according to claim 4 further characterized by the high molecular weight unsaturated fatty acid being erucic acid. 6. The composition according to claim 1 further characterized by the high molecular weight saturated fatty acid being selected from the group consisting of arachidic acid (C 20 ) , behenic acid (C 22 ) , lignoceric acid (C 24 ) , cerotic acid (C 6 ) , ontanic acid (C 28 ) , and combinations thereof. 7. The composition according to claim l further characterized by the high molecular weight unsaturated fatty acid being oleic acid and the high molecular weight saturated fatty acid being behenic acid. 8. The composition according to claim l further characterized by the high molecular weight unsaturated fatty acid or combination of high molecular weight saturated fatty and high molecular weight saturated fatty acid being from about l.o weight percent to about 3.5 weight percent, based on the weight of calcium carbonate. 9. The composition according to claim 8 further characterized by the high molecular weight unsaturated fatty acid or combination of high molecular weight unsaturated fatty acid and high molecular weight saturated fatty acid being from about 2.0 weight percent to about 2.5 weight percent, based on the weight of calcium carbonate. 10. A process for preparing calcium carbonate surface- treated with at least one high molecular weight unsaturated fatty acid or a combination of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid, characterized by the steps of: a) dry-mixing an ultrafine precipitated calcium carbonate to raise the temperature thereof due to frictional heating to about 80°C; b) adding to the calcium carbonate a sufficient amount of at least one high molecular weight unsaturated fatty acid or a combination of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid, to ultimately produce a desired level of fatty acid coating on the calcium carbonate; c) mixing the calcium carbonate and fatty acid until the temperature thereof increases to about 105°C due to frictional heating and continuing said mixing for at least 5 minutes from the time of addition of the fatty acid to the calcium carbonate; and d) milling the fatty acid-coated calcium carbonate. 11. A process for preparing calcium carbonate surface- treated with at least one high molecular weight unsaturated fatty acid or a combination of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid, characterized by the steps of: a) mixing an ultrafine precipitated calcium carbonate with water to form a first slurry; b) heating the first slurry to a temperature of about 85°C while agitating the slurry; c) adding to the first slurry, with continuous agitation, a sufficient amount of a saponified sodium salt solution of at least one high molecular weight unsaturated fatty acid or combination of at least one high molecular weight unsaturated fatty acid and at least one high molecular weight saturated fatty acid, to ultimately produced a desired level of fatty acid coating on a calcium carbonate, to form a second slurry; d) maintaining the temperature of the second slurry at about 85°C and further agitation for about one hour to homogenize the second slurry; e) dewatering the second slurry; f) drying the dewatered second slurry at a temperature of about 110°C; and g) milling the dried second slurry. 12. A method for improving the rheological properties of polyvinyl chloride plastisols and increasing their baked adhesion to coated metal surfaces, particularly at low bake temperature, characterized by forming a mixture by adding to said plastisol and homogeneously mixing therewith, an effective amount of calcium carbonate has been surface- treated with a high molecular weight unsaturated fatty acid or a high molecular weight unsaturated fatty acid in combination with a fatty acid ester, applying said mixture to a coated metal surface, and baking at a temperature in the range of from about 115°C to about 150°C. 13. The method according to claim 12 further characterized by the amount of surface-treated calcium carbonate being from about 10 weight percent to about 30 weight percent, based on the weight of the plastisol. 14. The method according to claim 13 further characterized by the amount of surface-treated calcium carbonate being from about 15 weight percent to about 20 weight percent, based on the weight of the plastisol. 15. The composition according to claim 1 further characterized by from about 0.8 percent by weight to about 1.0 percent by weight of an amine-containing adhesion promoter. 16. The composition according to claim 15 further characterized by the amine-containing adhesion promoter being selected from the group consisting of amino-amides and a ino-functional silanes.

Inventors: BAUER ROGER E, MATHUR KRISHNA K, BAUER, ROGER, E., MATHUR, KRISHNA, K.
Applicants: PFIZER, PFIZER INC.
Application year: 1991
Main classification: C09C1
IPC codes: C08K9, C09C1, C09C3