CA2215215A1

CA2215215A1 - Humidity-resistant bluish luster pigments

Info

Publication number: CA2215215A1
Application number: CA002215215A
Authority: CA
Inventors: Claus Kaliba; Harald Keller; Juan Antonio Gonzalez Gomez; Hermann Bidlingmaier; Raymond Ellinghoven; Raimund Schmid
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1996-09-30
Filing date: 1997-09-25
Publication date: 1998-03-30
Also published as: JPH10110116A; DE19640188A1; EP0832943A2; EP0832943B1; DE59712117D1; EP0832943A3; JP3847917B2

Abstract

Humidity-resistant bluish luster pigments Humidity-resistant bluish luster pigments based on titania-coated silicatic platelets heated in a reducing atmosphere are obtainable by reaction of the reduced platelets with a silane of the general formula I
RaSiXb where: I

R is a C1-C10-alkyl radical with substituted in the .omega.-position by a glycidoxy group, by an amino group, by a hydroxyl group or by a monoalkylamino group or an alkoxy radical whose alkyl chains may each contain up to 10 carbon atoms and may be interrupted by from 1 to 5 ether oxygen atoms or imino groups, the radicals R for a > 1 being identical or different;

X is C1-C4-alkoxy;

a is 1 or 2; and b is 2 or 3, subject to the proviso that a + b = 4.

Description

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 Humidity-resistant bluish luster pigments 5 The present invention relates to novel, humidity-resistant bluish luster pigments based on titania-coated platelets heated in a reducing atmosphere, obtainable by reaction of the reduced platelets with a silane of the general formula I

RaSiXb where:

R is a Cl-C10-alkyl radical substituted in the ~-position by a glycidoxy group, by an amino group, by a hydroxyl group or by a monoalkylamino group or an alkoxy radical whose alkyl chains may each contain up to 10 carbon atoms and may be interrupted by from 1 to 5 ether oxygen atoms or imino groups, the radicals R for a > 1 being identical or different;

X is a Cl-C4-alkoxy;

25 a is 1 or 2; and b is 2 or 3, subject to the proviso that a + b = 4.

The invention also relates to a process for producing these 30 pigments and to their use for coloring paints, inks, including printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations.

Reduced titania-coated mica pigments whose TiO2 coating includes 35 reduced titanium species (oxidation state of the titanium < 4 to 2) or has been completely converted into these reduced species have been known for some time as "dark" pearl luster pigments for the blue to black spectrum. Particularly bluish luster pigments are described in EP-A-332 071 and DE-A-195 11 697, which was 40 unpublished at the priority date of the present invention. These pigments are notable for good hiding, high color strength and high luster and are particularly interesting for automotive finishes. Frequently, however, they lack satisfactory humidity resistance.

CA 022l~2l~ l997-09-2 BASF Aktiengesellschaft 950283 O.Z. 0050/47376 DE-A-43 21 005 discloses unreduced, TiO2-coated mica pigments rendered suitable for use in waterborne paint systems by coating with a layer of the oxides of silicon, aluminum and cerium and in some cases also zirconium and the hydrolysis product of a 5 zirconium aluminate, of a metal acid ester or of an organofunctional silane as organic coupling reagent.

It is an object of the present invention to provide humidity-resistant bluish luster pigments which are based on 10 reduced titania-coated silicate platelets and have advantageous application properties.

We have found that this object is achieved by the luster pigments 1~ defined at the beginning.

The invention also relates to the thereby defined process for producing these luster pigments.

20 The invention further provides the use of the above-defined bluish luster pigments for coloring paints, inks, including printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations.

25 Suitable platelet-shaped silicatic substrate materials for the bluish luster pigments of the present invention include in particular light-colored or white micas, particularly preferably flakes of preferably wet-ground muscovite. It is of course also possible to use other natural micas, such as phlogopite or 30 biotite, artificial micas, talc and glass flakes.

The silicatic platelets are coated with a layer which consists essentially of titanium dioxide and may contain minor proportions 35 (generally < 5 % by weight) of further, preferably colorless, metal oxides such as zirconium dioxide, tin dioxide, aluminum oxide and silicon dioxide.

These pigments are generally known and commercially available 40 under the names Iriodin~ (E. Merck, Darmstadt), Flonac~ ~Kemira Oy, Pori, Finland) or Mearlin~ (Mearl Corporation, Ossining, New York).

The size of the silicate platelets is not critical per se and can 45 be adapted to the particular application. Typically, the platelets have average largest diameters of from about 1 to 200 ~m, in particular from about 5 to 100 ~m, and thicknesses of from CA 022l~2l~ l997-09-2~

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 about 0.1 to 1 ~m, in particular about 0.5 ~m. Their specific free surface area (BET) is customarily within the range from 1 to 15 m2/g, in particular from 3 to 12 m2/g.

5 The thickness of the TiO2 layer determines the reflection color of the substrate material and is preferably within the range from 50 to 100 nm (silver) or from 300 to 340 nm (bluei optical layer thicknesses).

To produce the luster pigments of the invention, the titania-coated silicate platelets serving as substrate material have been heated in a reducing gas atmosphere.

15 Examples of suitable reducing gases include ammonia gas, hydrogen, volatile hydrocarbons (especially Cl C4-alkanes) and mixtures thereof. All the gases are preferably used in a mixture with inert gases such as nitrogen (cf. DE-A-195 11 697, unpublished at the priority date of the present invention, and 20 the references cited therein, which include EP-A-322 071).

Preferred reducing gases are ammonia gas and mixtures of ammonia gas with volatile hydrocarbons such as methane, ethane and/or propane, for which a volume ratio of from about 95:5 to 70:30 is 25 advisable. The proportion of the particularly preferred reducing gas/inert gas mixtures which is accounted for bv nitrogen is preferably, respectively, up to 90 % by volume and within the range from 10 to 60 % by volume.

30 Suitable temperatures for the reduction are preferably within the range from 750 to 850~C when ammonia gas is used and preferably > 800 to 900~C when ammonia gas/hydrocarbon mixtures are used.

35 The reduction leads to the formation of reduced titanium species (lower titanium oxides such as Ti305, Ti2C3 down to Tio, titanium oxynitrides and also titanium nitride), which, owing to their blue absorption color, combine with the silvery- or blue-reflecting substrate platelets to produce particularly intensive bluish luster pigments.

The reduced titania-coated mica pigments are common knowledge and are also commercially obtainable under the name of Paliocrom~
(BASF, Ludwigshafen).

CA 022l~2l~ l997-09-2 BASF Aktiengesellschaft 950283 O.Z. 0050/47376 The humidity-resistant bluish luster pigments of the invention are advantageously obtainable by the manufacturing process of the invention by reacting the reduced titania-coated silicate platelets with a silane of the formula I

RaSiXb I.

Here suitable radicals R are alkyl radicals which generally 10 contain from 1 to 10, preferably 2 to 4, carbon atoms and are substituted in the ~-position by one of the following groups: a glycidoxy group, an amino group, a hydroxyl group or a monoalkylamino group or an alkoxy group, whose alkyl chains may each contain up to 10 (preferably up to 4) carbon atoms and may 15 be interrupted by from 1 to 5 ether oxygen atoms or imino groups.

Of these substituents, mono-(C1-C4-alkyl)amino groups with or without a substitution by an ether oxygen atom or an imino group in the alkyl radical are preferred, the glycidoxy group is 20 particularly preferred and the amino group is very particularly preferred.

If the silane I contains more than one alkyl radical R (a = 2), these alkyl radicals R can be identical or different. Preferably, 25 however, only one radical R is present (a = 1).

The radicals X are identical alkoxy radicals, which generally contain up to 4, preferably up to 2, carbon atoms.

Suitable silanes I contain at least 2 alkoxy radicals (b = 2), but preferably 3 alkoxy radicals (b = 3).

Since, according to the invention, the reaction of the reduced 35 silicate platelets preferably takes place with silane decomposed in the gas phase, particularly suitable silanes of the formula I
have a sufficiently high vapor pressure at temperatures < 500~C, preferably ~ 400~C, permitting simple vaporization.

40 Particularly preferred silanes conform to the formula Ia R'SiX'3 Ia 45 where R' is a propyl radical having a terminal amino group or a terminal glycidoxy group and X' is methoxy or ethoxy.

CA 022l~2l~ l997-09-2~

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 Examples of very particularly preferred silanes are 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane.

5 Examples of further suitable silanes are N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 2-aminoethyltriethoxysilane, 4-aminobutyltriethoxysilane and di(3-aminopropyl)diethoxysilane.

It lS also posslble to use mlxtures of the silanes I, of course.

Even very small quantities of silane I are sufficient to render the pigments of the invention humidity-resistant. It is customary 15 to use from 0.5 to 7 g, preferably from 2 to 5 g, of silane per 100 g of pigment.

The inventive reaction of the reduced silicate platelets with the silane I can be carried out wet-chemically at room temperature in 20 aqueous suspension. It is of course also possible to carry out the reaction at higher temperatures of up to 95~C, but this is generally not necessary.

If desired, the aqueous suspension of the silicate platelets may 25 have added to it a nonionic surfactant to further coat the surface of the silicate platelets and provide particularly low-dusting pigments. Examples of surfactants which are preferred here are poly-C2-C3-alkylene glycols, especially polyethylene glycols having an average molecular weight from 200 to 800 and 30 polypropylene glycols having an average molecular weight from 400 to 1000, but also mixed polyethylene/polypropylene glycols.
Suitable surfactant quantities are customarily in the range from 2 to 10 g per 100 g of pigment.

An advantageous way of carrying out the process is to charge a stirred reaction vessel with an aqueous suspension of the reduced silicate platelets and to add an aqueous solution of the silane, which optionally may also comprise the surfactant, or else neat 40 silane with stirring.

The pigment which is being reacted with the silane is advantageously isolated by spray drying. However, it is also possible to filter the pigment off and dry it in a drying 45 cabinet. But in this case it is advisable first to exchange the remaining water against a low boiling, water-miscible organic solvent to forestall clumping of the pigment platelets during CA 022l~2l~ l997-09-2~

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 drying. Examples of suitable solvents are acetone and Cl-C4-alcohols such as methanol and ethanol.

It is also possible to introduce the silicate platelets without 5 water into a solids mixer equipped with additional deagglomerating means and spray an aqueous solution of the silane and optionally of the surfactant onto the pigment platelets with stirring and deagglomeration.

A preferred embodiment of the process of the invention comprises reacting the reduced silicate platelets with gaseous (vaporized) silane (chemical vapor deposition, CVD).

15 The CVD variant is preferably likewise carried out in the presence of water (water vapor).

An advantageous reactor which can be used for this process variant is a fluidized bed reactor in which the reduced silicate 20 platelets are fluidized with an inert gas, preferably nitrogen, and optionally heated to a temperature of up to 300~C, preferably within the range from 150 to 300~C. The vaporized silane and the water vapor are then introduced by means of inert carrier gas streams (various subsidiary streams of fluidizing gas) from 25 upstream vaporizer vessels via separate nozzles.

A particularly suitable apparatus for the CVD variant is a solids mixer equipped with additional deagglomerating means and upstream vaporizers (e.g., thin-film evaporators) for silane and water 30 which are likewise flushed by an inert gas passing through them.
Examples of preferred solids mixers are mixers having plough share stirrers and vertical shaft mixers, each equipped with a stator/rotor beater.

The vaporizer temperatures naturally depend on the boiling point of the substance to be vaporized. Other factors are the flow rate of the inert gas stream directed through the vaporizer and the desired silane concentration in the reactor. In the case of 40 3-aminopropyltriethoxysilane, for example, suitable vaporizer temperatures range from about 70 to 150~C when a fluidized bed reactor is used and from about 150 to 300~C when the reaction is carried out in a solids mixer (at carrier gas streams from about ~00 to 200 l/h).

CA 022l~2l~ l997-09-2 BASF Aktiengesellschaft 950283 O.Z. 0050/47376 When a fluidized bed reactor is used, the concentration of the vaporized silane is advantageously ' 3 % by volume, preferably within the range from 0.001 to 0.5 % by volume, based on the total quantity of gas in the reactor. If the reaction is carried 5 out in the presence of water vapor, at least the amount of water vapor which is stoichiometrically necessary to hydrolyze the silane should be used, but preference is given to an excess from 10 to 100 times.

10 When the reaction is carried out in a solids mixer, the silane concentration in the carrier gas stream is generally within the range from 0.1 to 6 g/l, preferably within the range from 0.5 to 4 g/1. If water vapor is added, an excess of from 1 to 10 times is preferred here. And it is advisable, after the silane 15 vaporization has ended, to add further water vapor to ensure a complete hydrolysis of any adsorbed silane to reactive silanol intermediate.

20 Customary reaction times for the CVD process variant typically range from 2 to 10 h when a solids mixer is used and up to 20 h when a fluidized bed reactor is used.

The bluish luster pigments of the invention are notable for 25 advantageous application properties, especially high humidity resistances, and it is especially the pigments which have been reacted with the silane in a solids mixer which also show excellent dispersibility in varnishes.

30 They are advantageously useful for many purposes, such as coloring of plastics, glasses, ceramic products, decorative cosmetic preparations, inks, including printing inks, especially varnishes, especially to prepare automotive finishes.

35 For these applications, the pigments of the invention can also be advantageously used in admixture with transparent and hiding white, color and black pigments.

CA 022l~2l~ l997-09-2 BASF Aktiengesellschaft 950283 O.Z. 0050/47376 Examples A) Preparation of luster pigments of the invention Example 1 In an approximately 50 l capacity Lodige mixer equipped with a plough share stirrer, a stator/rotor beater, 3 separate gas feed 10 lines and 2 upstream thin-film evaporators, 4 kg of a silverily reflecting titania-coated mica pigment which have been reduced with ammonia gas at 800~C were reacted with 3-aminopropyltriethoxysilane in the presence of water vapor and nitrogen. A 300 l/h stream of nitrogen was passed through the 15 silane vaporizer, which was heated to 170~C, and a 160 l/h stream of nitrogen was passed through the water vaporizer, which was heated to 85~C. In this way, 218 g of silane and 52 g of water were introduced into the reactor over 65 min. On completion of the silane vaporization, water vapor was subsequently introduced 20 for a further 80 min, so that a total of 117 g of water were added.

The pigment obtained had a carbon content of 0.8 % by weight.
Classification < 50 !lm left an oversize of 2 % by weight.
Example 2 In the mixer of Example 1, 4 kg of the mica pigment of Example 1 30 were reacted with 3-aminopropyltriethoxysilane in the presence of water vapor and nitrogen. Two 200 l/h streams of nitrogen introduced 120 g of silane from the vaporizer heated to 240~C and 16 g of water from the vaporizer heated to 110~C, over 10 min. On completion of the silane vaporization, water vapor was 35 subsequently introduced for a further 50 min, so that a total of 95 g of water were added.

The pigment obtained had a carbon content of 0.5 % by weight.
Classification < 50 ~m left an oversize of 0.7 % by weight.
Example 3 In a fluidized bed reactor made of glass with a diameter of 16 cm and a height of 100 cm, equipped with a glass frit bottom, filter 45 socks suspended from the top and cleaned by a nitrogen jet and two gas inlet nozzles mounted on the side above the frit bottom, 600 g of the mica pigment of Example 1 were heated to 200~C under CA 022l~2l~ l997-09-2~

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 fluidization with a total of 1700 l/h of nitrogen. ~art of the fluidizing gas (400 1/h of nitrogen) was passed through an upstream 3-aminopropyltriethoxysilane vaporizer heated to 80~C, while a further portion of the fluidizing gas (300 l/h of 5 nitrogen) was passed through an upstream water vaporizer heated to 40~C. In total, 35 g (37 ml) of silane were introduced.

The pigment obtained had a carbon content of 0.5 % by weight.
Classification < 50 ~m left an oversize of 0.5 % by weight.

Example 4 In the fluidized bed reactor of Example 3, 600 g of the mica 15 pigment of Example 1 were heated to 200~C under fluidization with a total of 1800 l/h of nitrogen, 400 l/h of which was passed through an upstream 3-aminopropyltriethoxysilane vaporizer heated to 100~C, while 400 l/h of nitrogen were passed through an upstream water vaporizer heated to 40~C. In total, 70 g (74 ml) of 20 silane were introduced.

The pigment obtained had a carbon content of l.1 % by weight.
Classification < 50 ~m left an oversize of 0.3 % by weight.

25 Example 5 In a stirred vessel, a suspension of 100 kg of the mica pigment of Example 1 in 850 l of water was admixed with a solution of 30 5 kg of 3-aminopropyltriethoxysilane in 50 l of water. The water was then removed by spray drying, the suspension at a pressure of 4.5 bar, a tower inlet temperature of 320~C and a tower outlet temperature of 110~C at a rate of 130 kg/h.

35 The pigment obtained gave rise to an oversize of 0.6 % by weight in a < 50 ~m classification.

Example 6 ~ A suspension of 20 g of the mica pigment of Example 1 in 200 ml of water was admixed with 0.4 g of 3-aminopropyltrimethoxysilane ~y stirring. The water was then removed by spray drying in a laboratory unit, the suspension being sprayed at a tower inlet temperature of 230~C and a tower outlet temperature of 95~C at a 45 rate of 0.5 kg/h.

CA 022l~2l~ l997-09-2~

BASF Aktiengesellschaft 950283 O.Z. 0050/47376 The pigment obtained had a carbon content of 0.3 % by weight.
Classification < 50 ~m left an oversize of 0.5 % by weight.

Example 7 Example 6 was repeated to react 20 g of the mica pigment of Example 1 with 0.4 g of 3-glycidoxypropyltrimethoxysilane.

10 The pigment obtained had a carbon content of 0.5 % by weight.

Example 8 In a 250 1 capacity Lodige mixer equipped with a plough share 15 stirrer and a stator/rotor beater, 44.2 kg of the mica pigment of Example 1 were sprayed with a mixture of 3.3 kg of 3-aminopropyltriethoxysilane, 2.4 kg of a polypropylene glycol having an average molecular weight of 600 and 0.2 kg of water with stirring and deagglomeration.

The pigment obtained had a carbon content of 1.0 % by weight.

B) Evaluation of luster pigments of the invention To evaluate the humidity resistance of the pigments in paint, the first step was to prepare the painted test panels as follows: for each pigment, 4 g were stirred into 96 g of a polyester mix varnish having a solids content of 21 % by weight and dispersed 30 using a propeller stirrer at 1500 rpm for 15 min. Thereafter each base coating was adjusted to a spray viscosity of 18 sec in DIM
cup 4 (DIN 53 211) and sprayed both onto an unprimed aluminum panel and onto an automotive body panel (paint build: bonded substrate (zinc phosphated steel)/cathodic 35 electrocoating/polyester-acetobutyrate primer). Following a short flashoff time, a one-component clear varnish based on acrylate/melamine resin (47 % by weight solids, adjusted to 23 sec DIN 4) was applied on top, wet on wet. After 30 minutes flashoff at room temperature, each panel was baked at 130~C for 40 30 min.

The humidity behavior was subsequently evaluated according to the Cleveland Humidity Test (DIN ISO 6270) and the water immersion test (ISO 2812-2; May 1982).

CA 022l~2l~ l997-09-2 BASF Aktiengesellschaft 950283 O.Z. 0050/47376 In the humidity test, the painted panels were placed in a Cleveland Condensing Humidity Cabinet (Condensation Tester Q C-T
from The Q-Panel Company; Cleveland, Ohio, USA). The fully deionized water bath was adjusted to 70~C and the panels were 5 continuously bedewed for 24 h at l00 % relative humidity.

In the water immersion test, the painted panels were placed for 24 h in a water bath heated to 80~C following 24 hour aging at room temperature.

On completion of the exposure, the panels were each dried off and without delay evaluated for a color change against the gray scale of EN 20105-A02. On this scale, coatings without a change in 15 color are rated 5 and coatings which have turned white all over are rated l.

In the same way, the luster change was evaluated against the relative evaluation scale of ISO 4628/l. On this scale, which 20 likewise ranges from 0 to 5, a rating of 0 means no loss of luster and a rating of 5 means very pronounced loss of luster.

The results of these investigations are reported in the table below, which also shows the results, by way of comparison (C), 25 for a starting pigment prior to reaction with the silane.

Table 30 Pigment Cleveland Humidity Test Water Immersion Test of Example Color change Luster change Color change Luster change CA 0221~21~ 1997-09-2

Claims

1. Humidity-resistant bluish luster pigments based on titania-coated silicatic platelets heated in a reducing atmosphere, obtainable by reaction of the reduced platelets with a silane of the general formula I

RaSiXb I
where:

R is a C1-C10-alkyl radical with or without substituted in the .omega. position by a glycidoxy group, by an amino group, by a hydroxyl group or by a monoalkylamino group or an alkoxy radical whose alkyl chains may each contain up to 10 carbon atoms and may be interrupted by from 1 to 5 ether oxygen atoms or imino groups, the radicals R for a > 1 being identical or different;

X is C1-C4-alkoxy;

a is 1 or 2; and b is 2 or 3, subject to the proviso that a + b = 4.

2. Luster pigments as claimed in claim 1, wherefor the reduced platelets are reacted with a silane of the general formula Ia R'SiX'3 Ia where R' is a propyl radical having a glycidoxy or an amino substituent in the terminal position, and X' is methoxy or ethoxy.

3. Luster pigments as claimed in claim 1, wherefor the reduced platelets are reacted with the silane in the presence of water or water vapor.

4. Luster pigments as claimed in claim 1, wherefor the reduced platelets are reacted with vaporized silane.

5. Luster pigments as claimed in claim 1, wherefor the reduced platelets are reacted with vaporized silane in a fluidized bed reactor.

6. Luster pigments as claimed in claim 1, wherefor the reduced platelets are reacted with the silane in a solids mixer equipped with deagglomerating means and with upstream vaporizers for the silane and optionally water.

7. Luster pigments as claimed in claim 1, wherefor the titania-coated silicatic platelets have been heated in a reducing atmosphere comprising ammonia gas, hydrogen or volatile hydrocarbons or mixtures thereof.

8. A process for producing humidity-resistant bluish luster pigments as claimed in claim 1.

9. The use of humidity-resistant bluish luster pigments as claimed in claim 1 for coloring paints, inks, including printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations.