GB1562629A - Phosphate pigments - Google Patents

Description

(54) PHOSPHATE PIGMENTS (71) We, NIPPON PAINT CO. LTD., a body corporate organised under the laws of Japan of No. 2-1-1, Oyodo-cho Kita, Oyodo-ku, Osaka-shi, Osaka-fu, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method for the preparation of phosphate pigments.

More particularly, it relates to a method for the preparation of phosphate pigments of fine and even particle size comprising zinc phosphate and iron phosphate.

Phosphate pigments such as zinc phosphate and iron phosphate have excellent corrosion-preventing properties and have been prepared for use in various paints. Since, however, the phosphate pigments (particularly zinc phosphate) prepared by conventional methods generally have a large particle size (e.g. ten to several tens of microns). they have to be pulverized with the aid of a special pulverizer into fine powders before being incorporated into paints. In addition. phosphate pigments as heretofore commercially available are relatively expensive.

When the surface of an iron substrate is subjected to phosphating with an aqueous solution containing phosphate ions and zinc ions. sludges comprising zinc phosphate and iron phosphate are unavoidably formed as by-products and have up to now been discarded.

However, a serious problem of environmental pollution arises from such discarding of sludges.

We have now found that, in certain conditions. such sludges from a phosphating process have a fine and even particle size and have properties such that they arc suitable for use as phosphate pigments. We have found that. if the treatment of an iron substrate with an aqueous solution comprising zinc phosphate is effected under acidic conditions. zinc phosphate and iron phosphate are produced in the form of particles having a fine and even particle size, which are utilizable as phosphate pigments. This is notable since conventional methods for the preparation of zinc phosphate or iron phosphate pigments have been carried out by the treatment of zinc or iron ions with phosphate ions under a neutral or basic pH condition to afford particles of large size.

The present invention provides a method for the preparation of a phosphate pigment which comprises collecting a sludge obtained as precipitate by phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions and mainly consisting of zinc phosphate and iron phosphate. sieving the collected sludge in the dispersed state in water to remove the particles of larger size and drying the sieved fine particles at a temperature not higher than 15() C to obtain a phosphate pigment powder.

According to the present invention, there is provided a method for the preparation of a phosphate pigment which comprises phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions whereby there is produced a sludge comprising a precipitate mainly consisting of zinc phosphate (ZN(PO4)2) and iron phosphate (FePO4), washing the collected sludge with water. dispersing the washed sludge in water, treating the resulting dispersion with an alhaline earth metal hydroxide. sieving the treated dispersion. collecting the dispersed particles and drying the collected particles at a temperature not higher than 15t1 C to obtain (l phosphate pigment powder.

As the Zn2±containing phosphate solution. there may be used any zinc phosphate solution conventionally employed for phosphating. We particularly prefer an aqueous solution of zinc phosphate containing soluble salt-forming ions such as nitrate ions (NO1 ), chlorate ions (Cl3-), nitrite ions (NO2-) or sodium ions (Na+) in a total concentration of not more than substantially 3% by weight. When the soluble salt-forming ions are included in a larger concentration, they are retained in the precipitate as formed, thus causing an unfavourable increase in the water absorption rate of the ultimate pigment product.A typical example of the Zn2±containing phosphate solutions may have a pH of from 1 to 4 and the following composition: Ionic components Contents (weight %) Zn2 0.02 - 1 Uni2+ not more than 0.1 Fe2+ not more than 0.07 Na+ not more than 1.0 PO43 0.1 - 3 NO2- 0.001 - 0.04 NO3- not more than 2 ClO3 not more than 0.8 As the iron material, there may be used scrap iron and/or steel products having any optional form such as plates, rods or pipes. These iron materials may be subjected, prior to use, to pre-treatments such as acid rinsing and degreasing to clean the surface, if necessary.

Reaction of the Zn-±containing phosphate solution on the iron material may be carried out by suitable methods such as dipping or spraying. The reaction temperature is usually from 10 to 100"C, preferably from 40 to 8() C.

As a result of the reaction, the iron material is dissolved in the form of ferrous ion (Fe2+), which is then oxidized to ferric ion (Fe3+ ). The ferric ion forms a phosphate together with a zinc ion (Zn2+), with an increase in pH at the surface of the iron material owing to etching, and the resulting phosphate precipitates. The precipitate mainly consists of a mixture of Zn3(PO4)2 and FePO4 and may also contain Zn2Fe(PO4)2. The precipitate comprises fine particles most of which have a particle size of from l to 7 p. Such a precipitate has substantially the same composition as that of the sludge formed as the by-product in conventional methods for zinc phosphate treatment of iron materials.

The precipitate may be collected by filtration and washed with water. The collected material frequently contains water-soluble phosphate ions and. when used as a pigment, shows an unfavourably high water absorption rate. In order to eliminate such an unfavourable water absorption property. it is desirable to treat the collected material with an alkaline earth metal hydroxide such ás slaked lime to make the phosphate ions insoluble in water. In this case. the treatment may be carried out. for instance, by adding slaked lime to an aqueous dispersion of the collected material in a proportion of from 0.05 to 1 mole of the former to 1 mole (in terms of PnOs) of the total phosphate ions in the latter, and reacting them at a temperature of from 1 to 100"C. preferably of from 1 to 30"C.

The material treated with slaked lime may be collected from its dispersion by filtration, but it is preferred to sieve the material in a dispersed state in water, for example, with the aid of a 100 mesh (Tyler Standard) sieve. By this sieving. it become possible to redisperse the material easilv as particles having a uniform particle size. and further to remove impurities such as dusts and sands contained in the original precipitate. The removal of those impurities which mav act as nuclei promoting the formation of course pigment particles prevents the productionof pigments of a large particle size, and makes the application of any crushing operation to pigments unnecessarv.

The material thus collected is dried bv a conventional procedure to obtain a pigment. A preferred drying temperature is not more than 15()'C. In particular. in case of a precipitate which has been subjected to treatment with an alkaline earth metal hydroxide and sieving, drying at a temperature not more than 15()'C can afford a pigment comprising fine particles of 1 to 7 tt, and therefore subsequent pulverization is unnecessary. Even in the case of a precipitate which has not been subjected to treatment with an alkaline earth metal hydroxide and to sieving, it is still possible to obtain pigments of fine and even particle size by drying at a temperature not higher than substantially 15() C. However, a longer period of time is required for drying.When drying is carried out at a temperature higher than substantially 1500C, an aggregation of pigment particles occurs so that the application of pulverization procedure becomes necessary.

The thus prepared phosphate pigment of the invention mainly consists of zinc phosphate and iron phosphate. The weight ratio of zinc to iron in the phosphate pigment is usually from 1: 0.5 - 6.

The advantages attained by the present invention are summarized as follows: (1) Sludge, formed as a by-product in a zinc phosphate treatment of iron products, is used as the phosphate pigment of the invention. Consequently, the present invention is not only useful for preventing environmental pollution owing to the sludge but also contributes to the reduction of pigment cost.

(2) Pigments having a low content of water-soluble materials and a low water absorption rate can be obtained by employing the slaked lime treatment of the precipitate.

At the same time, the pigments can be used for various kinds of paints because the slaked lime treatment is itself a neutralization treatment.

(3) Pigments requiring substantially no pulverization can be obtained by sieving the precipitate in the dispersed state in water.

(4) Pigments containing no pigment aggregates can be obtained by drying the preciptate at a temperature not higher than 150"C.

(5) Pigments have a fine and even particle size of from 1 to 7 y so that they are easily dispersible. Thus, pigments comprising zinc phosphate and iron phosphate which have a good dispersibility and corrosion preventing property can be obtained.

The invention is illustrated in the following Examples wherein the percentage(s) and part(s) are by weight.

Example 1 [Part I] An aqueous phosphate solution (pH. 2.9) having the composition shown in Table 1 below was sprayed onto a steel plate at 60"C under a spraying pressure of 1.1 kg/cm2: Table 1 Component Concentration ion (%) Zn2+ 0.1 Na+ 0.3 Ni2+ 0.02 Pro43 1.0 NO3- 0.5 NO2- 0.008 When 70g of iron were dissolved out. the spraving was stopped. and the precipitate was collected, washed with water and dried to obtain 195 g of a phosphate pigment. of which the composition was as shown in Table 2 below:: Table 2 Component Content (2/3) Zn2* 10.4 Fe3+ 25.6 Ni2+ 0.02 Nat 0.05 POj3 58.0 NO3- 3.0 water 3.0 Separately, 100 g of the precipitate formed in the same manner as above were washed with water and then treated by either one of the following procedures to give a phosphate pigment having the properties and composition shown in Table 3 below: Procedure A: To the precipitate (100 g). water (5,000 g) was added and stirred to make a dispersion (pH, 6.0). which was passed through a 100 mesh (Tyler Standard) sieve in approximately 20 minutes. The amount of the residue retained on the sieve was extremely small. The precipitate was then washed with water and dried at 105 C for 6 hours to yield a phosphate pigment (hereinafter referred to as "Pigment A").

Procedure B: To the precipitate (100 g). a solution of slaked lime (10 g) in water (400 g) was added and stirred at 30 C for about 30 minutes to make a dispersion (pH, 7.8). which was passed through a 100 mesh sieve in about 20 minutes. The amount of the residue on the sieve was extremely small. The precipitate was then washed with water and dried at 1050C for 6 hours to yield a phosphate pigment (hereinafter referred to as "Pigment B").

Procedure C: To the precipitate (100 g), a solution of slaked lime (10 g) in water (400 g) was added and stirred at 30"C for about 30 minutes to make a dispersion (pH 7.8). The supernatant liquor was removed bv decantation. and the collected precipitate was dried at 1050C for 6 hours and passed thrdugh a 100 mesh sieve to yield a phosphate pigment (hereinafter referred to as "Pigment C".) Previous crushing of the dried product was needed. since otherwise the sieving took a long time and the amount of residue on the sieve was large.

For comparison. the properties and composition of the zinc phosphate pigment obtained by the following procedure as described in Japanese Patent Publication No. 2005/1974 are shown in Table 3: zinc oxide (500 g). finely pulverized silica (25 g) and water (4.500 g) were mixed together to make a slurry. and a 5':i aqueous solution of sodium hexametaphosphate (50 ml) was added thereto. An equivalent amount of 75c phosphoric acid to zinc oxide was added to the mixture, and the pH was adjusted to 6.0. The resulting mixture was filtered, and the collected cake was dried at 110"C for 2() hours and then crushed to give a zinc phosphate pigment (hereinafter referred to as Pigment 1").

Table 3 Pigment A B C 1 Pigment Colour white to pale pale white property yellow yellow yellow Water-soluble material 1.2 0.45 0.44 0.8 (%) Water content (%) 2.0 1.7 1.9 1.2 Average particle size ( ) about 5 1 to 3 about 5 2 to 5 (containing coarse particles) Dispersibility 1) good excellent good good Precipitation property 2) good excellent good excellent Pigment PO43- 52.4 52.1 51.3 40.3 composition NO3- 1.0 0.8 1.1 (%) Fe3+ 23.1 15.1 14.8 Zn2+ 9.6 11.0 12.1 41.8 Na+ 1.4 2.1 2.2 Ca2+ 0 5.0 5.5 Water content (including 12.1 14.0 13.0 16.2 Water of crystallization Notes: 1) The pigment was incorporated into a paint, and the size of particles dispersed therein was measured by means of a grind gauge.A particle size of less than 10 zit was judged as "excellent," and that of 10 to 20 Ft was judged as "good".

2) The pigment was incorporated into a paint, and the viscosity was measured after 12 days by means of Ford Cup No. 4. A viscosity of more than 78 seconds was judged as "excellent" and that of 75 to 60 seconds was judges as "good".

[Part II] A paint composition was prepared according to the following procedure using Pigment B, Pigment 1, aluminium silicate known as an extended pigment (hereinafter referred to as "Pigment 2") or titanium oxide (hereinafter referred to as "Pigment 3"): titanium oxide (20 parts), the pigment (5 parts) and an oil-free polyester paint (trade name "Orga TO777" manufactured by Nippon Paint Co. Ltd.) (75 parts) were kneaded in a ball mill for about 16 hours to make a paint composition.

The paint composition was applied onto an iron plate previously phosphated with an aqueous solution of zinc phosphate "Granodine (Trade Mark) 16N-2" manufactured by Nippon Paint Co., Ltd.) by either one of the following coating procedures: Coating Procedure A: Onto the phosphated iron plate, a maleinized natural oil type electrodeposition paint (trade name "Power Coat 6600" manufactured by Nippon Paint Co., Ltd.) was applied to make an undercoat film of 20 Ft thick, and baking was effected at 17ü C for 30 minutes. The paint composition as prepared above was sprayed onto the baked plate to make a second-coating film of 20 It thick, and baking was effected at 140"C for 30 minutes. Finally, a melamine alkyd type paint (trade name "Orga TO626" manufactured by Nippon Paint Co., Ltd.) was sprayed onto the resulting plate to make a top coating film 30 Ft thick, followed by baking at 140"C for 30 minutes.

Coating Procedure B: The coating was carried out in the same manner as in Coating Procedure A but omitting the top coating.

Coating Procedure C: Onto the phosphated iron plate. the paint composition as prepared above was applied by spraying to make a coating film 20 u thick, and then baking was carried out at 140"C for 30 minutes.

The state of the paint composition and the properties of the coating film are shown in Table 4 below.

Table 4 Pigment B 1 2 3 State of Pigment dispersi- less than 10 less than 10 less than 10 less than 10 paint bility 3) composition Storage stability 4) 41/83 41/78 61/111 41/64 Coating Gloss of coating 85 89 55 90 film surface formed by property Coating Procedure B 5) Gloss of coating 96 97 98 96 surface formed by Coating Procedure A 6) Dissolution per- 3.8 3.1 2.6 3.5 centage (%) *7) Water absorption 2.2 2.1 2.1 1.9 rate (%) *8) Salt spray test less than 1.0 less than 1.0 less than 1.0 less than 1.0 (mm) *9) Water resistance@10 excellent excellent good good Adhesion property 11) excellent excellent good good Notes: 3) The particle size of the dispersed pigment particles was measured by means of a grind gauge. All the paints had a particle size of less than 10 with a good dispersibility.

4) The viscosities of the paint were tested by means of Ford Cup No. 4 at 20 C immediately after the preparation of the paint (upper numerals) and 12 days thereafter (lower numerals). The viscosity was expressed by second.

5) & 6) The gloss of the coating surface was measured by means of a gloss-meter.

7) The dissolution percentage of the coating film formed by Coating Procedure B was determined by dipping the plate in warm water (50 C) for 4 days, drying at 110 C and calculating from the weights before dipping and after drying.

8) The water absorption rate of the coating film formed by Coating Procedure B was determined by dipping the plate in warm water (50"C) for 4 days and calculating from the weights before and after dipping.

9) The coating film formed by Coating Procedure C was cut crosswise with a knife. A 50% aqueous sodium chloride solution was sprayed onto the surface and after 6 days the degree of blistering was measured (the width of the blistering part from the cut line).

10) The coated plate cross-cut as above was dipped in warm water (50"C) for 1 day. and the blistering of the coating surface was judged visually.

11) The coating surface formed by Coating Procedure B was cross-cut and dipped in warm water (50 C) for 3 days. The adhesion property of the cut surface was judged by sticking an adhesive tape to the surface and tearing off the tape.

From Tables 3 and 4, it is understood that the content of water-soluble materials is largely decreased by the slaked lime treatment. When the precipitate is sieved in a dispersion state and then dried, the sieving can be carried out in a relatively short time and the pigments obtained have a uniform particle size, and further pulverization of the pigments can be omitted. Moreover. it is apparent that the pigments of the present invention, i.e. Pigments A, B and C, have performances equal to, or superior to, those of Pigments 1, 2 and 3.

Example 2 Sludges, which were formed as by-produts in the phosphating process for the treatment of automobile bodies with a phosphate solution (pH, 3.0) containing 0.07% of Zn2+, 0.3% of Na+, 0.015% of Ni2-, 1.05% of PO43-, 0.2% of NO3-, 0.008% of NO2-, 0.2% of ClO3and 0.1% of Cl- and mainly consisting of zinc phosphate and iron phosphate, were collected. The collected sludges were treated as in Example 1, Part I. Procedure B, to make a phosphate pigment having the following properties: colour, pale yellow; water-soluble material content. 0.25%; water content, 1.6%; average particle size, 1 to 3 . The ion contents of the phosphate pigment were as follows; PO43-, 50.3%; Fe3+, 20.0%; Zn2+, 7.5%; Ca2+, 5.7%.

In the same manner as in Example 1. Part II. a paint composition was prepared by the use of the phosphate pigment. The state of the paint composition and the properties of the coating film were examined. and the following results were obtained: State of paint composition: pigment dispersibilitv. less than 10 It: storage stability, 40/85.

Properties of coating film; gloss of coating surface formed by Coating Procedure B. 84; gloss of coating surface formed by Procedure A. 98; dissolution percentage, 3,7%; water absorption rate. 2.0%; salt spray test, less than 1.0mm; water resistance, excellent; adhesion property. excellent.

From the above results. it is apparent that the sludges obtained as a by-product in a phosphating process are utilizable as phosphate pigments for paints. Since the sludges are originally a waste material, the phosphate pigments obtainable therefrom are available at an extremely low cost even if the transportation cost and the processing cost are taken into account.

WHAT WE CLAIM IS: 1. A method for the preparation of a phosphate pigment which comprises collecting a sludge obtained as precipitate by phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions and mainly consisting of zinc phosphate and iron phosphate. sieving the collected sludge in the dispersed state in water to remove the particles of larger size and drying the sieved fine particles at a temperature not higher than 1500C to obtain a phosphate pigment powder.

2. A method according to Claim 1. wherein the collected sludge is dispersed in water and then treated with an alkaline earth metal hydroxide.

3. A method according to Claim 2. wherein the alkaline earth metal hydroxide is slaked lime.

4. A method for the preparation of a phosphate pigment which comprises phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions whereby there is produced a sludge comprising precipitate mainly consisting of zinc

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Notes:

   3) The particle size of the dispersed pigment particles was measured by means of a grind gauge. All the paints had a particle size of less than 10 with a good dispersibility.

   4) The viscosities of the paint were tested by means of Ford Cup No. 4 at 20 C immediately after the preparation of the paint (upper numerals) and 12 days thereafter (lower numerals). The viscosity was expressed by second.

   5) & 6) The gloss of the coating surface was measured by means of a gloss-meter.

   7) The dissolution percentage of the coating film formed by Coating Procedure B was determined by dipping the plate in warm water (50 C) for 4 days, drying at 110 C and calculating from the weights before dipping and after drying.

   8) The water absorption rate of the coating film formed by Coating Procedure B was determined by dipping the plate in warm water (50"C) for 4 days and calculating from the weights before and after dipping.

   9) The coating film formed by Coating Procedure C was cut crosswise with a knife. A 50% aqueous sodium chloride solution was sprayed onto the surface and after 6 days the degree of blistering was measured (the width of the blistering part from the cut line).

   10) The coated plate cross-cut as above was dipped in warm water (50"C) for 1 day. and the blistering of the coating surface was judged visually.

   11) The coating surface formed by Coating Procedure B was cross-cut and dipped in warm water (50 C) for 3 days. The adhesion property of the cut surface was judged by sticking an adhesive tape to the surface and tearing off the tape.

   From Tables 3 and 4, it is understood that the content of water-soluble materials is largely decreased by the slaked lime treatment. When the precipitate is sieved in a dispersion state and then dried, the sieving can be carried out in a relatively short time and the pigments obtained have a uniform particle size, and further pulverization of the pigments can be omitted. Moreover. it is apparent that the pigments of the present invention, i.e. Pigments A, B and C, have performances equal to, or superior to, those of Pigments 1, 2 and 3.

   Example 2 Sludges, which were formed as by-produts in the phosphating process for the treatment of automobile bodies with a phosphate solution (pH, 3.0) containing 0.07% of Zn2+, 0.3% of Na+, 0.015% of Ni2-, 1.05% of PO43-, 0.2% of NO3-, 0.008% of NO2-, 0.2% of ClO3and 0.1% of Cl- and mainly consisting of zinc phosphate and iron phosphate, were collected. The collected sludges were treated as in Example 1, Part I. Procedure B, to make a phosphate pigment having the following properties: colour, pale yellow; water-soluble material content. 0.25%; water content, 1.6%; average particle size, 1 to 3 . The ion contents of the phosphate pigment were as follows; PO43-, 50.3%; Fe3+, 20.0%; Zn2+, 7.5%; Ca2+, 5.7%.

   In the same manner as in Example 1. Part II. a paint composition was prepared by the use of the phosphate pigment. The state of the paint composition and the properties of the coating film were examined. and the following results were obtained: State of paint composition: pigment dispersibilitv. less than 10 It: storage stability, 40/85.

   Properties of coating film; gloss of coating surface formed by Coating Procedure B. 84; gloss of coating surface formed by Procedure A. 98; dissolution percentage, 3,7%; water absorption rate. 2.0%; salt spray test, less than 1.0mm; water resistance, excellent; adhesion property. excellent.

   From the above results. it is apparent that the sludges obtained as a by-product in a phosphating process are utilizable as phosphate pigments for paints. Since the sludges are originally a waste material, the phosphate pigments obtainable therefrom are available at an extremely low cost even if the transportation cost and the processing cost are taken into account.

   WHAT WE CLAIM IS: 1. A method for the preparation of a phosphate pigment which comprises collecting a sludge obtained as precipitate by phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions and mainly consisting of zinc phosphate and iron phosphate. sieving the collected sludge in the dispersed state in water to remove the particles of larger size and drying the sieved fine particles at a temperature not higher than 1500C to obtain a phosphate pigment powder.

   2. A method according to Claim 1. wherein the collected sludge is dispersed in water and then treated with an alkaline earth metal hydroxide.

   3. A method according to Claim 2. wherein the alkaline earth metal hydroxide is slaked lime.

   4. A method for the preparation of a phosphate pigment which comprises phosphating an iron substrate with an acidic aqueous solution containing zinc ions and phosphate ions whereby there is produced a sludge comprising precipitate mainly consisting of zinc

   phosphate and iron phosphate, washing the collected sludge with water, dispersing the washed sludge in water, treating the resulting dispersion with an alkaline earth metal hydroxide, sieving the treated dispersion. collecting the dispersed particles and drying the collected particles at a temperature not higher than 15û C to obtain a phosphate pigment powder.

   5. A method for the preparation of a phosphate pigment substantially as hereinbefore described.

   6. A phosphate pigment prepared by a method as claimed in any of Claims 1 to 5.

   7. A paint composition comprising at least one phosphate pigment as claimed in Claim 6.