PLATE-LIKE PVD ALUMINUM PIGMENT WITH A PROTECTIVE ENCAPSULATION AND METHOD FOR MANUFACTURING A PLATE-LIKE PVD ALUMINIUM PIGMENT WITH A PROTECTIVE ENCAPSULATION

Abstract

The invention is directed to a plate-like PVD aluminum pigment with a protective encapsulation, wherein said protective encapsulation comprises a) a continuous encapsulating silicon oxide containing coating (a), wherein said silicon oxide containing coating comprises at least 60 wt.-% silicon oxide, based on the total weight of said silicon oxide containing coating, and b) a layer (b) of metal oxide, wherein said metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, tungsten oxide hydrate and mixtures thereof, and c) optionally an outer organic-chemical modification layer. The invention is further directed to method for producing the plate-like metal pigment as well as the use thereof.

Claims

1. An encapsulated pigment comprising a plate-like PVD aluminum pigment and a protective encapsulation disposed on the PVD aluminum pigment, wherein the protective encapsulation comprises: a continuous encapsulating silicon oxide containing coating, wherein the silicon oxide containing coating comprises at least 60 wt.-% silicon oxide, based on the total weight of the silicon oxide containing coating, and a layer of metal oxide, wherein the metal oxide includes one or more of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, and tungsten oxide hydrate.

2. The encapsulated pigment according to claim 1, wherein the PVD aluminum pigment has a median diameter d.sub.50 in the range of 2 to 30 μm.

3. The encapsulated pigment according to claim 1, wherein the PVD aluminum pigment has a median thickness h.sub.50 in the range of 15 to 75 nm.

4. The encapsulated pigment according to claim 1, wherein the metal oxide includes 0.01 to 0.4 wt.-% molybdenum and 0.01 to 0.8 wt.-% tungsten, calculated as elemental molybdenum and elemental tungsten and based on the weight of the uncoated PVD aluminum pigment.

5. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating amounts to 8 wt.-% to 25 wt.-%, based on the weight of the uncoated PVD aluminum pigment.

6. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating has an average thickness in a range of 15 to 60 nm.

7. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating consists of silicon oxide.

8. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating comprises up to 100 wt-% of compounds comprising organic groups forming a hybrid silicon oxide/organic coating, based on the weight of the silicon oxide containing coating.

9. The encapsulated pigment according to claim 8, wherein the organic groups comprise one or more of organic oligomers and organic polymers.

10. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating comprises a mixture of silicon oxide and organofunctional silanes, the organofunctional silanes acting as network modifiers and having the formula
R.sub.(4-z)Si(X).sub.z  (I) wherein, z is an integer from 1 to 3, R comprises one or more of an unsubstituted, unbranched or branched alkyl chain having 1 to 24 C atoms, an aryl group having 6 to 18 C atoms, and an arylalkyl group having 7 to 25 C atoms, and X comprises one or more of a halogen group and an alkoxy group.

11. The encapsulated pigment according to claim 1, wherein the protective encapsulation further comprises an outer organic-chemical modification layer comprising at least one organofunctional silane.

12. A method for manufacturing the encapsulated pigment according to claim 1, the method comprising: encapsulating the PVD aluminum pigment with the silicon oxide containing coating and then coating the encapsulated PVD aluminum pigment with the layer of the metal oxide.

13. A method for manufacturing the encapsulated pigment according to claim 1, the method comprising: coating the PVD aluminum pigment with the layer of the metal oxide and subsequently encapsulating the coated PVD aluminum pigment with the silicon oxide containing coating.

14. A method for manufacturing an encapsulated pigment, the method comprising: performing a sol-gel process including contacting a plate-like PVD aluminum pigment with a soluble silicon alkoxide compound dissolved in a solvent to form an plate-like PVD aluminum pigment encapsulated with a substantially continuous silicon oxide containing coating, contacting the encapsulated plate-like PVD aluminum pigment with a soluble metal compound dissolved in a solvent to envelop the encapsulated plate-like PVD aluminum pigment with a metal oxide, wherein the metal of the soluble metal compound includes at least one selected from molybdenum and tungsten.

15. An aqueous formulation comprising the encapsulated pigment according to claim 1.

16. (canceled)

17. The encapsulated pigment according to claim 1, wherein the protective encapsulation further comprises an outer organic-chemical modification layer.

18. The encapsulated pigment according to claim 1, wherein the silicon oxide containing coating consists of silicon dioxide.

19. The encapsulated pigment according to claim 10, wherein the silicon oxide containing coating comprises a mixture of silicon dioxide and the organofunctional silanes.

20. The method for manufacturing an encapsulated pigment according to claim 14, further comprising forming an outer organic-chemical modification layer comprising at least one organofunctional silane.

21. A method for manufacturing an encapsulated pigment, the method comprising: contacting a plate-like PVD aluminum pigment with a soluble metal compound dissolved in a solvent to obtain a plate-like PVD aluminum pigment coated with a metal oxide, wherein the metal of the soluble metal compound includes one or more selected from molybdenum and tungsten, and performing a sol-gel process including contacting the coated plate-like PVD aluminum pigment with a soluble silicon alkoxide compound dissolved in a solvent to encapsulate the coated plate-like PVD aluminum pigment with a substantially continuous silicon oxide containing coating.

22. The method according to claim 21 further comprising forming an outer organic-chemical modification layer comprising at least one organofunctional silane.

Description

EXAMPLES

[0170] The following examples are given only for illustration of the invention. The examples are not to be construed as limiting the scope of the invention. The scope of the invention is defined only by the appended claims.

A Preparations

[0171] Experiments were done according to the following recipes. In Table 1 it is indicated which of the examples is based on which recipe. The amounts of molybdenum or of tungsten acid can be depicted from Table 1.

1.1. Preparation of a Peroxomolybdic Acid Solution:

[0172] 5 g powdered molybdic acid (molybdenum(VI)oxide hydrate, MoO.sub.3*H.sub.2O) were dissolved at room temperature under stirring in 15 g of an aqueous 30% H.sub.2O.sub.2-solution until a clear yellow solution evolved.

1.2 Preparation of a Peroxotungsten Acid Solution (According to P. C. Murrau, Anal. Chem., 1961, 33 (8), Pp 1125-1126):

[0173] 0.5 g metallic tungsten was dissolved at room temperature under stirring in 4.5 g of an aqueous 30% H.sub.2O.sub.2-solution until a clear yellow solution evolved.

Example A1 (Invention)

[0174] 150 g of a commercially available PVD aluminum pigment (Metalure W-52012 IL; Eckart GmbH; containing 30 g aluminum and residues of polyvinyl pyrrolidone vinylacetate used as release coat) were dispersed under stirring in 450 g isopropanol in a chemical reactor.

[0175] A defined amount (see table 1) of peroxomolybdenum acid solution prepared according to section 1.1 was added and stirred for 30 min. The dispersion was heated to 70° C. and stirred for further 25 min. Then 18.8 g TEOS (tetraethoxysilane) and 18.8 g water were added and stirred for 1 h. Then 4.5 g of a 25-wt-% solution of ammonia in water was dosed within 1 h to the reaction mixture. After 7 h of reaction period 1.2 g Dynasylan Octeo were added and subsequently 0.4 g Dynasylan AMMO were added. The reaction mixture was stirred for further 120 min. The dispersion was cooled down to room temperature and filtered using a Büchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

Example A2 (Invention)

[0176] 150 g of a commercially available PVD aluminum pigment (Metalure W-52012 IL; containing 30 g aluminum and residues of release coat) were dispersed under stirring in 365 g isopropanol in a jacketed 1 L glassreactor. The dispersion was heated to 70° C. and stirred for further 25 min. Then 18.8 g TEOS and 18.8 g water were added and the dispersion was stirred for 1 h. Then 4.5 g of a 25-wt-% solution of ammonia in water was dosed within 1 h to the reaction mixture. After 7 h of reaction period a defined amount (see table 1, column 5) of peroxomolybdenum acid solution prepared according to Section 1.1 was added and stirred for 30 min. Then 1.2 g Dynasylan Octeo and subsequently 0.4 g Dynasylan AMMO were added. The reaction mixture was stirred for further 120 min. The dispersion was cooled down to room temperature and filtered using a Büchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

Example A3 (Invention)

[0177] Like Example A1 except that peroxotungsten acid solution prepared according to Section 1.2 was used instead of the peroxomolybdenum acid solution. Amounts are defined in table 1.

Example A4 (Invention)

[0178] Like Example A2 except that peroxotungsten acid solution prepared according to Section 1.2 was used instead of the peroxomolybdenum acid solution. Amounts are defined in table 1.

Comparative Example 2 (without Treatment of Peroxomolybdenum or Peroxotungsten Acid Solution)

[0179] 150 g of a commercially available PVD aluminum pigment (Metalure W-52012 IL; containing 30 g aluminum and residues of release coat) was dispersed under stirring in 365 g isopropanol. The dispersion was heated to 70° C. and stirred for further 45 min. Then 18.8 g TEOS and 18.8 g water were added and stirred for 1 h. Then 4.5 g of a 25-wt-% solution of ammonia in water was dosed within 1 h to the reaction mixture. After 5 h of reaction period 1.2 g Dynasylan Octeo and subsequently 0.4 g Dynasylan AMMO were added. The reaction mixture was stirred for further 120 min. The dispersion was cooled down to room temperature and filtered using a Büchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

Example B1 (Invention)

[0180] 300 g of a commercially available PVD aluminum pigment dispersion (Metalure A-41010 BG; Eckart GmbH; containing 30 g aluminum and residues of polyacrylate used as release coat) were dispersed under stirring in 300 g isopropanol.

[0181] A defined amount (see table 1) of peroxomolybdenum acid solution prepared according to Section 1.1 was added and stirred for 30 min. The dispersion was heated to 70° C. and stirred for further 45 min. 21.4 g TEOS and 21.4 g water were added and stirred for further 1 h. Then 6 g of a 25-wt-% solution of ammonia in water was dosed within 1 h to the reaction mixture. After 7 h of reaction period 5 g Hydrosil 2909 were added. The reaction mixture was stirred for further 2 h and then was cooled down to room temperature and filtered using a Buchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

Example B2 (Invention)

[0182] 300 g of a commercially available PVD aluminum pigment dispersion (Metalure A-41010 BG; containing 30 g aluminum and residues of polyacrylate used as release coat) were dispersed under stirring in 300 g isopropanol.

[0183] 21.4 g TEOS and 21.4 g water were added and stirred for further 1 h. Then 4.5 g of a 25-wt-% solution of ammonia in water were dosed within 1 h to the reaction mixture. After 5 h of reaction period a defined amount (see table 1, column 5) of peroxomolybdenum acid solution prepared according to 1.1 was added and stirred for 30 min. Then 5 g Hydrosil 2776 were added. The reaction mixture was stirred for further 2 h and then was cooled down to room temperature and filtered using a Büchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

Example B3 (Invention)

[0184] Like Example B1 except that peroxotungsten acid solution prepared according to Section 1.2 was used instead of the peroxomolybdenum acid solution. Amounts are defined in table 1.

Example B4 (Invention)

[0185] Like Example B2 except that peroxotungsten acid solution prepared according to Section 1.2 was used instead of the peroxomolybdenum acid solution. Amounts are defined in table 1.

Comparative Example 1 (without Treatment of Peroxomolybdenum of Peroxotungsten Acid Solution)

[0186] 300 g of a commercially available PVD aluminum pigment dispersion (Metalure A-41010 BG; containing 30 g aluminum and residues of polyacrylate used as release coat) were dispersed under stirring in 300 g isopropanol.

[0187] 21.4 g TEOS and 21.4 g water were added and stirred for further 1 h. Then 5 g of a 25-wt-% solution of ammonia in water was dosed within 1 h to the reaction mixture. After 5 h of reaction period 5 g Hydrosil 2776 were added. The reaction mixture was stirred for further 1 h and then was cooled down to room temperature and filtered using a Büchner funel isolating the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

B Test Methods

[0188] The samples were tested with respect to their hydrolysis stabilities according to the following method according to Volkswagen test TL 226, § 3.12.1 for coatings in automotive interior: 10 g of the dispersions of the coated PVD pigments were dispersed in 2.5 g butylglycol with the aid of 0.5 g of a dispersing additive. 70 g of an aqueous acrylate binder system were added and the pH was adjusted to a range of 7.6 to 8.0. The basecoat should have a viscosity of in a range of 80 to 120 mPas measured at a shear rate of 1000 1/s with a Brookfield viscosimeter. If necessary the viscosity can be adjusted by further addition of water. A plastic substrate (ABS/PC Blend) was coated with this basecoat using a Langguth (Erichsen GmbH, model 480) under the following spraying conditions:

pistol conditions: 1.1.0/4 runs
drying time: 10 min room temperature and 15 min at 80° C.

[0189] The thickness of this base coat was about 2 to 4 μm. A clearcoat was sprayed on top of this base coat with pistol parameter 2.1.2 in two runs and dried for 30 min at 80° C.

[0190] The coated substrates were stored for 48 hours at 80° C.

[0191] Then the coated substrates were subjected at 90° C. and a humidity of >96% for 72 hours in a desiccator. The treated substrates were dried and the L*a*b* coordinates were measured at i=5 angles of 15°, 25°, 45°, 75° and 110° (cis-configuration) in comparison to untreated substrates (Byk-Mac, Byk Instruments, Geretsried, Germany). A ΔE* was obtained for these angles and averaged according to the following formula:

[00001]$\begin{array}{cc}\Delta .Math.E^{\star }=\frac{\sqrt{\underset{i}{\overset{110.Math.°}{.Math.}}.Math..Math.\left(\Delta .Math.E_i^2+\Delta .Math.a_i^2+\Delta .Math.b_i^2\right)}}{5}& \left(\mathrm{II}\right)\end{array}$

wherein i are the angles of measurement and the ΔE.sub.i, Δa.sub.i and Δb.sub.i are the differences of the coordinates between treated and not treated substrates at the specific angle i.

[0192] The test was well passed with a ΔE* of below 2.0. At a ΔE* in a range of 2 to 5 the test was passed. A ΔE* in a range of over 5 to 15 means a partial passing in the sense that the pigments may be incorporated into certain 2-coat system coatings in an application which exhibit a not too high criticality.

[0193] If ΔE* is above 15 the test is not passed.

[0194] Method of Determining the Content of Mo or W:

[0195] 200 mg of the coated pigments were dissolved in a mixture of 10 ml of nitric acid (65%) diluted with about 10 ml water and 2 ml hydrofluoric acid (40%) which was heated below their boiling points. The concentration of molybdenum or tungsten was measured with optical emission spectroscopy (ICP-OES). Every sample was prepared twice and five single measurements were made and averaged. All preparations and measurements were made using housing materials compatible with hydrofluoric acid.

[0196] Furthermore the concentration of elemental silicon was measured using an internal scandium standard. The concentration was calculated as SiO.sub.2.

TABLE-US-00001 TABLE 1 Summary of experimental parameters of Examples and Comparative Examples and Hydrolysis test results Mo or W Metal of Mo- or W- content/wt-% metal compound (based on oxide and Basis-PVD wt -% ratio SiO.sub.2/ dryed powder Underlying order of pigment to Al in wt.-% of total Hydrolysis Hydrolysis Example receipe addition Metalure solution to Al pigment) test/ΔE* test note Comparative — A-41010 BG — — 24.4 not example 1: passed Example 1 B1 Mo before A-41010 BG 0.250 15.3 0.01 2.7 passed SiO2 Example 2 B1 Mo before A-41010 BG 0.025 16.2 <0.01 4.9 passed SiO2 Example 3 B1 Mo before A-41010 BG 0.125 17.2 0.01 1.9 well SiO2 passed Example 4 B1 Mo before A-41010 BG 0.500 17.0 0.28 2.5 passed SiO2 Example 5 B1 Mo before A-41010 BG 1.250 16.3 2.6 passed SiO2 Example 6 B1 Mo before A-41010 BG 2.500 16.4 0.27 2.4 passed SiO2 Example 7 B2 Mo after A-41010 BG 0.250 17.5 2.8 passed SiO2 Comparative A — W-52012 IL 0 — 25.9 not example 2: passed Example 8 A1 Mo before W-52012 IL 0.25 0.8 well SiO2 passed Example 9 A2 Mo after W-52012 IL 0.25 1.2 well SiO2 passed Example 10 A3 W before W-52012 IL 1.125 15 0.05 0.6 well SiO2 passed Example 11 A3 W before W-52012 IL 2.25 0.07 0.9 well SiO2 passed Example 12 A3 W before W-52012 IL 0.75 0.04 0.7 well SiO2 passed Example 13 A3 W before W-52012 IL 1.5 0.05 0.4 well SiO2 passed Example 14 A4 W after W-52012 IL 0.75 <0.01 2.1 passed SiO2 Example 15 A4 W after W-52012 IL 1.5 0.05 1.1 well SiO2 passed Example 16 B3 W before A-41010 BG 0.25 16.3 <0.01 14.8 partially SiO2 passed Example 17 B3 W before A-41010 BG 0.5 16.3 <0.01 4.9 passed SiO2 Example 18 B4 W after A-41010 BG 0.25 16.5 <0.01 14.9 partially SiO2 passed Example 19 B4 W after A-41010 BG 0.5 16.2 0.01 7.5 partially SiO2 passed

CONCLUSIONS

[0197] All the inventive Examples exhibited a significantly increased stability in the hydrolysis test compared to the respective Comparative Examples 1 and 2 which did not pass the test. Generally the Mo-oxide/SiO.sub.2 coated systems had a high stability (Examples 1 to 9). The order of the metal oxide coating didn't seem to have a significant effect.

[0198] The W-oxide/SiO.sub.2 coatings exhibited a very good stability for the W-52012 PVD-Al-pigment which had a thickness h.sub.50 determined by SEM of about 40 nm (Examples 10 to 13). The W-oxide/SiO.sub.2 coating is slightly better than the SiO.sub.2/W-oxide coating. For the thinner PVD-Al-pigments (A-41010; thickness h.sub.50 determined by SEM about 32 nm) exhibiting a higher specific surface more tungsten material must be chosen to obtain an acceptable stability. At a lower amount the test is just partially passed. The hydrolysis test results for those Examples having a coating with a first layer of W-oxide followed by a silica coating were slightly better that for those Examples having the reversed order of coatings.