DE2206775B2 - TITANIUM DIOXIDE PIGMENTS WITH HIGH GRAYING STABILITY FOR RESIN COMPOSITIONS - Google Patents

Description

The invention relates to special titanium dioxide pigments coated with aluminum oxide aquat, a method for Production of titanium dioxide pigments with high graying stability for use in resin compositions after treatment with basic aluminum chloride solutions in the presence of an oxidizing effect Salts and the use of these pigments as additives for laminates on melamine-formaldehyde, Urea-formaldehyde or phenol-formaldehyde base.

It is known that resin compositions, especially melamine-formaldehyde, urea-formaldehyde and Phenol-formaldehyde resins, have found widespread industrial use. This is especially true for the field of laminates, under which laminates are understood in which the resin is individual Layers of, for example, wood, paper, polymers or glass fibers hold together and they like that Gives strength and hardness. Laminates in this form can be used to create scratch-resistant table tops, boards for furniture, Paneling, etc. are processed. Since the above-mentioned resin compositions are partly water-soluble are, they can be made opaque in a relatively simple manner by incorporating various pigments. This makes it possible to significantly expand their area of application.

A pigment that is excellently suited for this purpose is titanium dioxide. However, it has been for a long time known that titanium dioxide is photochemically active. Urea-formaldehyde-based, which are pigmented with titanium dioxide, leads to a steady UV exposure growing graying leading to a bluish-gray discoloration of the built-in titanium dioxide pigment. Attempts have therefore long been made to get through Post-treatment of rutile pigments to reduce their photoactivity. An effective reduction is however, this can only be achieved by costly and laborious sewing of the aftertreated pigments. Attempts have also been made for a long time to find pigments with sufficient photostability in laminate pressings without subsequent costly and laborious annealing, which can be done in a simple manner Way can be incorporated into resin molding compounds.

An inorganic post-treatment of titanium dioxide pigments with subsequent drying of the pigments is known and is described in German Offenlegungsschriften 15 92 956 and 15 92 945, for example. In these processes, the actual aftertreatment is carried out by neutralizing hydrolytically cleavable materials Salts with ammonia in an aqueous titanium dioxide pigment suspension before drying. The subsequent drying, which takes place at temperatures from 200 to 850 ° C is carried out, the neutralisa The volatilizable salts formed can be removed. The German Offenjegungsschrift 20 46 739 describes a method of coating metal oxide particles, wherein a hydrous metal oxide is precipitated from an aqueous solution on the particles. The precipitation solution is subjected to a special aging process. Show such aftertreated rutile pigments however, insufficient photostability in the above-mentioned resin systems

British patent 11 64 849 describes the aftertreatment of a pyrogenic TiOj pigment, the aqueous pigment suspension being mixed with a soluble silicon compound, a soluble aluminum compound and a neutralizing agent, whereby a water-containing aluminum silicate is precipitated on the pigment, which is then heated to a temperature from 200 to 650 ⁰ C is calcined. A water-containing aluminum silicate is precipitated in the TiOj suspension.

US Pat. No. 2,161,975 discloses a process for the aftertreatment of T1O2 pigments or hydrolysis sludges known with solutions of basic aluminum salts, followed by a filtration, careful washing followed by drying of the pigment. The pigments aftertreated in this way, however, show im Laminate test shows insufficient photostability in laminate pressings.

From US-patent specification 34 09 454 a process for the aftertreatment of TiO 2 pigments is known for the purpose of improved dispersibility with alkaline solutions inonisierbarer aluminum compounds at temperatures between 25 to 100 ⁰ C at a pH-value are acidified 7 to 7.8, wherein

at least 50% of the aluminum hydroxide precipitates out as boehmite after this known nanhbehandlungsverfahren predominantly a crystalline phase of defined composition is present on the pigment practically no anions incorporated

US Patent 2260177 describes a method to improve the pigment properties of titanium dioxide by contacting it with an aluminum salt solution Over a period of about 5 to 25 hours, followed by the addition of an alkaline Precipitant then follows in a second treatment period of about 1 to 2 hours Pigment is kept in contact with the mother liquor. The treated pigment is supported by the protruding Solution separated, washed out and dried ■

Belgian patent specification 6 61 398 relates to a method for treating a titanium dioxide pigment, in which adhesive amounts of at least two hydroxides or hydrated oxides or plural gels of Elements from the group aluminum, silicon, boron, titanium, antimony, zinc, magnesium, tin, lead and zirconium be precipitated in intimate association with the titanium dioxide pigment. The hydroxides or are advantageous hydrated oxides or plural gels by this known process by precipitating an aqueous Elutriation of the titanium dioxide pigment with at least one acidic compound of one Elements, such as aluminum, with at least one basic reacting compound, such as e.g. Sodium hydroxide, at pH levels 3 to 9. The angry ones Connections can include Chlorates, nitrites, nitrates, bromates, iodates of elements such as Include aluminum. The known methods are time-consuming and result in the As a rule not to pigments which have sufficient photostability in the above-mentioned resin systems.

According to German Offenlegungsschrift 20 57 337, salts are used as aftertreatment substances The pigments treated in this way are, however, partly due to the considerable solubility of the halogenated oxygen acids in water for incorporation into the discussion here standing resin systems are only insufficiently suitable.

US Pat. No. 3,427,278 describes resin systems which contain titanium dioxide pigments and which are photochemical are inert. These resin systems incorporate 0.1 to 5% of nitrate. This method has the disadvantage that the added nitrates are water-soluble and in the case of hydrolytic cleavage polymerizing on the Resins work and make processing more difficult due to the hardening of the resin.

The present invention thus provides titanium dioxide pigments coated with aluminum oxide aquat, characterized in that they contain 0.5 to about 10 _{% by weight of aluminum oxide aquat (based on TiO 2} ) and 0.3 to 1.5% by weight .-% of nitrate. Ntrit contain peroxydisulfate, perborate or percarbonate or a mixture of these anions (based on the resulting pigment).

The invention relates to a process for the preparation of coated with an alumina-Aqua layer titanium dioxide pigments is also high Vergrauungsbeständigkeit by treating an aqueous TiOrPigmentsuspension with a solution of a basic aluminum chloride, which is characterized in that the TKVPigmentsuspension at temperatures between 25 and 200 ⁰ C dried is applied to the TiOrPigment 0.5 to about 10 wt .-% aluminum oxide aquat and wherein the suspension nitrates, nitrites, peroxydisulfates, peroxide addition compounds or mixtures of these salts for the incorporation of 0.3 to 13 wt .-% of their anions (based on ΤΪΟ2) can be added to the aluminum oxide aquat layer.

In the process according to the invention, the inorganic aftertreatment does not take place before the drying, but rather through the drying. The oxidizing salts present in the suspension in the liquid phase should not be removed by the drying but mostly incorporated into the aluminum oxide aquat formed during the drying process. For the purposes of the invention, aluminum oxide aquat is understood to mean the gel which is formed when the basic aluminum salt solutions are concentrated in the course of drying and in which most of the oxidizing salts are incorporated. The drying can take place at relatively low temperatures between 25 and 200 ^° C., in practice between approximately 80 and 120 ^° C. The pigment suspension can be dried in any desired manner, for example in a drying cabinet, thin-film evaporator, belt dryer, drum dryer and by spray drying. Before drying, there is no precipitation of oxide aqua in the presence of the aqueous titanium dioxide suspension

The basic aluminum salts which can be used for the process according to the invention dissolve in water with the formation of particles of colloidal size. The term "basic" is not intended to be one alkaline reaction of these aluminum compounds in water, but only to express that, from a formal stoichiometric view, predominantly OH anions are present in these aluminum salts. For the purposes of the present invention, compounds in which there is a ratio of aluminum cations can be used to chloride anion of values from 0.5 to 5, preferably from 1.0 to 3.0, exists (without taking into account of OH as an anion).

Examples of these compounds are Alj (OH) SCI (cation / anion ratio 2) and Al (OH) ₂ CI (cation / anion ratio 1).

According to the method according to the invention, the titanium dioxide pigment is slurried in water and mashed with the solution of one of the basic aluminum chlorides mentioned, whereby a pigment suspension is formed, the pH of which, depending on the pigment type, basicity and amount of aluminum chloride, is between about 4.0 and 7.0, preferably between 5.0 and 6.5. Additional salts with oxidizing anions are introduced into this system (pigment suspension + basic aluminum salt). In the context of the invention, such oxidizing compounds are salts which contain the anions nitrate, nitrite and peroxydisulfate and peroxide addition compounds such as sodium perborate, NaBo ₂ · H2O2, sodium percarbonate Na ₂ COa · 3H ₂ O ₂ . The cations of these salts are preferably alkali cations, alkaline earth cations and ammonium cations. Mixtures of such oxidizing compounds can also be used for aftertreatment.

By drying the titanium dioxide pigment suspension according to the invention at relatively low temperatures, the basic aluminum salts become in

Oxide gels are converted to the individual titanium dioxide pigment particles envelop. The additionally present, oxidizing agents are incorporated into this covering layer Built-in salts

The production of the basic aluminum chlorides according to the invention can be carried out in any manner according to the known manufacturing processes (see Gmelins Handbuch & Anorg. Chemie, 8th edition, No. 35, Al, part B, p. 117-125, 156ff, 205f [1934]) for basic aluminum salt solutions, for example by dissolving of aluminum metal in a deficit of hydrochloric acid or by peptization of A3 (OH) 3 in Acid deficiency. Since the aluminum salts used according to the invention are basic salts acts (i.e. salts with a deficit of acid anions), When it dries on the pigment, practically no large amounts of foreign salts or free acid. By drying the titanium dioxide pigment suspension the added basic aluminum salts are converted into oxide gels that envelop individual titanium dioxide pigment particles and, in particular, oxidize those present in the system fix acting anions. As a result of the low drying temperatures, there is no risk of Change in the particle size spectrum of the pigment. For the method according to the invention there is a certain if also a low salt or electrolyte content of the pigment is characteristic, which is desirable for the invention Obtain pigments with excellent laminate stability.

According to the method according to the invention, titanium dioxide suspensions can be used in very wide concentration ranges from an extremely liquid to paste-like consistency (5 to 80 percent by weight of TiO ₂ , based on the weight of the suspension); the most appropriate suspension concentration depends primarily on the evaporation process.

By drying the pigment suspensions, amounts of 0.5 to about 10 percent by weight of aluminum oxide aquat can be deposited on the TiO2 pigment particles according to the method according to the invention, but within the meaning of the invention, optimal results are already achieved with 2 to 5 percent by weight of Al2O3 (based on TiO ₂ ) obtain. At the same time as the coating with aluminum oxide aquat, the oxidizing salts are incorporated into the coating, the resulting pigment containing between 0.3 and 1.5 percent by weight of the oxidizing anions.

The presence of the oxidizing salts results only in combination with the drying up of the Alumina aquats on T1O2 pigments to pigments with optimal graying stability. A purely mechanical additive, for example by rubbing or mixing or milling of aluminum salts individually or in combination with the mentioned oxidizing active salts leads to TiO2 pigments, which due to a high content of free electrolyte deteriorate have pigmentary properties and because of the lack of effectiveness of the oxidizing additives too have a poorer graying stability. So it happens with the direct mixing of as a result Hydrolysis of acidic, stoichiometric or basic aluminum salt solutions with TiOk pigments and subsequent incorporation into resin compositions based on melamine-formaldehyde at a momentary Polymerization of the resin mass, which becomes rock hard and can no longer be processed. Likewise leads to the addition of oxidizing substances described above, if not according to the invention Process can be partially built into the aluminum oxide aquat gel and thus firmly attached to the TiOr surface due to the lack of contact with the pigment surface and the sensitivity against thermal stress, water and solvents alone not to TiOz pigments with good Graying stability

In order to modify the pigment properties, the post-treatment process according to the invention can be followed by further post-treatment steps known per se (e.g. additional precipitation of SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , SnO ₂ , MgO, ZnO, phosphates etc. or organic post-treatment with amines , Hydroxyalkanes, epoxides, etc.) can be connected or connected upstream.

Any TiOr pigments which are produced either by the chloride or the sulfate process can be used for the process according to the invention. Particularly suitable are TiO ₂ pigments with a rutile structure which already have an aluminum oxide-modified surface, that is to say e.g. B. by burning TiCU in the presence of AICI3 or by calcining a TiOr hydrolysis sludge in the presence of Al ₂ Os, but the invention is not limited to these types of pigments

The TiOr pigments post-treated according to the invention only with aluminum oxide aquat in the presence of small amounts of oxidizing salts have a higher brightness, a greater bluish cast and, in some cases, a considerably higher brightening _{power than the TiO 2} pigments post-treated and _{post-annealed with SiO 2} and Al _{2 Os.} They show excellent graying stability in laminate pressings. Laminates based on melamine-formaldehyde, urea-formaldehyde or phenol-formaldehyde can _{advantageously contain the TiO 2} pigments treated according to the invention in amounts of 10 to 40 percent by weight.

To test the stability of the laminate, various TiO ₂ rutile pigments were used to produce laminate pressings (laminates). The procedure was as follows:

100 g of a melamine-formaldehyde resin was made into a paste with 60 ml of distilled water of 60 to 7O ⁰ C with the aid of a glass rod and stirred until complete dissolution of the melamine resin with a glass stirrer while adding 50 ml of ethanol. The solution obtained lasts only one day.

12.5 g of ground TiO ₂ pigment are weighed into a beaker, 100 g of the resin solution are added and mixed with an Ultraturrax (7500 to 8000 revolutions per minute) for 5 minutes.

After transferring the dispersion into a porcelain dish, four strips of filter paper (Whatman No. 3) are half immersed one after the other, the soaked adhesive is fastened in a paper clip and then the other adhesive is dipped Glass rod stripped over the bowl. The paper clips to hang with the soaked strips in a wire rack and let them dry for 20 minutes at 100 ⁰ C. After cooling, the paper strips are pulled through unpigmented resin solution and stripped off as before

the samples in a drying cabinet preheated ^{to 138 °} C. for 20 minutes. The four strips of each sample are placed on top of one another, labeled and placed between two clean, chrome-plated steel plates. The samples are pressed in a hydraulic two-column laboratory hand press preheated to 149 ° C. with heating and cooling options at a pressure of 105 kg / cm ² for 13 minutes. The heating is then switched off while maintaining the pressure and the water cooling is put into operation for 3 to 4 minutes to cool down to 40 ^{° C.} After 40 ° C has been reached , the press can be opened and the pair of plates with the sample can be removed.

On the finished pigmented laminate panels, the brightness before exposure and the percentage Graying determined after exposure.

For this purpose, the emission of the plates was first determined with an electrical reflectance photometer using a standardized green filter (Ry filter) on the lower half of the plate. The determined remission value Ry is a measure of the brightness. The upper half of the plate was then covered with an aluminum foil in order to later see the contrast between the exposed and unexposed area. The covered side was placed on the edge of a turntable (3 revolutions / minute) and, after the samples had been exposed for 4 hours with 6 Ultra-Vitalux lamps (circular arrangement 10 cm from the turntable), the Ry value was measured at the same point on the sample as before exposure. The expression

R y before - Ry after exposure) 100
Ry before exposure

35

specified.

In addition to the lightness and percentage graying of the laminate panels, the lightening power of the pigment powder according to DIN 53 192 and its blue cast were measured. The measure of the blue cast was the difference, referred to as the gray value, of the remissions of the blue and red filters (R _x - R _x ) on a gray paste rub-out with Ry = (35 ± 0.2)%. A more positive gray value indicates a greater blue tint or a higher degree of fineness of the pigment.

The lightening power and the gray value were determined after grinding the pigment for 60 minutes in a pulverizer. The pigments described were incorporated into laminate pressings after grinding for 15 minutes in this mill.

The invention is to be explained in more detail by the following examples:

Comparative example

Example 2 of U.S. Patent No. 22 60 177 was followed using aluminum nitrate solution at temperature of 30 ° C and gates ^ 0 ⁰ C

For this purpose, 300 g of a TiO _r pigment ground in a Raymond mill were suspended in 1200 ml of water. 122 g of an aluminum nitrate solution were added to the suspension

(22 g Al (NOj) ₃ 9H ₂ O +100 ml water)

The mixture was added at 30 ⁰ C (70 ⁰ C) then heated stirred for 16 hours, and thereafter back to 30 ° C (70 ⁰ Q heated with ammonia water was then made of the pH to 7.4, followed by stirring for 2 hours was. the treated pigment was then filtered off. was the pigment not washed, the filter cake contained corresponding to a solids content of 60% naturally the total amount of nitrate that corresponds to the remaining 40% moisture content in the filter cake, this value was 0.56% nO ₃ The following values were obtained when washing in stages:

Test at 30 ° C

500 ml water: 0.06% nitrate
2000 ml water: 0.03% nitrate

Test at 70 ° C

500 ml water: 0.04% nitrate
2000 ml water: 0.02% nitrate

example 1

To 125 g of a _{pigment calcined in the presence of Al 2} O ₃ (0.7 percent by weight, based on TiO ₂ ) and then ground in a Raymond mill, a solution of 1.25 g of sodium nitrite NaNO ₂ in 50 ml was added after mashing in 900 ml of H2O H ₂ O added After a further momentary addition of a solution of 7.0 g of the commercially available basic aluminum salt

Al ₂ (OH) ₅ Cl • 3H ₂ O

in 50 ml H2O the pH of the pigment slurry was 5.3. After 1 hour stirring the pigment suspension in 4 mm thick layer was poured onto plates for 24 hours in an oven at 8O ⁰ C dried Percent graying in the laminate test was at an initial reflectance of 83% 2.4. The lightening power according to DIN 53 192 and the gray value were 730 and 3.6, respectively. The pigment contained 3.1 percent by weight Al ₂ O ₃ (based on TiO ₂ ) and 0.65 percent by weight NO ₂ (based on TiO ₂ ).

Example 2

40 kg of the pigment described in Example 1 were mixed with 13.21 of water and 9.81 of a solution of the commercially available basic aluminum salt

Al ₂ (OH) ₅ Cl • 3H ₂ O

stirred to a flowable suspension. The solution of the basic aluminum salt contained 1 mol of Al ₂ O ₃ per liter. To the TiOrSuspension 169 g of ammonium peroxydisulfate (NH ^ ₂ S was further added in the form Einei solution in 41 H ₂ O ₂ O ₈ was stirred purpose.:. Long setting constant conditions for a further hour after The pigment suspension was now in Fora a homogeneous, non- The sludge was then ^{spray-dried at an inlet temperature of 160 °} C. In the laminate test, the pigment had an initial remission of 85% and a percentage graying of 2%. the gray white 3.7 The TiOr pigment contained 3.0 percent by weight of At ₂ O ₃ (based on TiO ₂ ) and 035% S ₂ O ₈ (based on TiO ₂ ).

Example 3 Example 2 is repeated with the following modification Instead of an aqueous solution of Ammoniumperor

disulfate (NH ₄ J ₂ S ₂ O ₈ becomes a solution of 360 g of NaNC added to the aqueous pigment suspension. Tuesday

Lightening power of the pigment according to DIN 531!

709609 / '

was 740, the gray value 3.8. The TiOrPigment contained 3.0 percent by weight (based on TiO ₂ ) Al ₂ O ₃ and 0.66 percent by weight (based on TiO ₂ ) NO ₃ . The percentage graying of the laminate compression was 1.2%.

Example 4

A solution of the composition AJ (OH) aCl was prepared by dissolving Al grit in a deficit of HCt. It contained 0.84 mol of Al ₂ O ₃ per liter. 125 g of the TiOr pigment mentioned in Example 1

were mashed with 900 ml of H ₂ O and 36.5 ml of the basic ammonium chloride solution. A solution of 2.0 g of NaBO ₂ · H ₂ Oj in 100 ml of H ₂ O was added to the aqueous suspension, after which the pH was 6 , 1 set. The pigment suspension was dried in a vacuum rotary evaporator at 60 ^° C. The pigment incorporated into a laminate compression had a percentage graying of 2.1% (initial remission 84%). The pigment contained 3.1

ίο percent by weight AI2O3 and 123 percent by weight (BO ₂ - · H ₂ O ₂ ), based on TiO ₂ .

Claims (6)

Patent claims: 1. Titanium oxide pigments coated with aluminum oxide aquat, characterized in that they contain 0.5 to about 10% by weight of aluminum oxide aquat (based on TiO ₂ ) and 0.3 to 1.5% by weight of nitrate , Nitrite, peroxidisulfate, perborate or percarbonate or a mixture of these anions (based on the resulting pigment; contain.> O 2. A process for the preparation of coated with an alumina-Aqua layer Titaiuiioxidpigmenten high Vergrauungsbeständigkeit by Behändem an aqueous TiQrPigmentsuspension with a solution of a basic aluminum is umchlorids, characterized in that the TiOR pigment suspension is dried at temperatures between 25 and 200 ⁰ C, wherein 0.5 to about 10% by weight of aluminum oxide aquat are applied to the TiOi pigment and the suspension contains nitrates, nitrites, peroxydisulfates, peroxide addition compounds or mixtures of these salts for the incorporation of 03 to 1.5% by weight of their anions ( based on T1O2) can be added to the aluminum oxide aquat layer. 3. The method according to claim 2, characterized in that the basic aluminum chloride compounds used are those which have a ratio of aluminum cation [Al ³⁺ ] to chloride anion of 0.5 to 5.0. 4. The method according to any one of claims 2 to 3, characterized in that a compound of the approximate stoichiometric composition Al ₂ (OH) ₅ Cl is used as the basic aluminum chloride. 5. The method according to any one of claims 2 to 4, characterized in that the drying of the suspension at temperatures between 8O ⁰ C and 120 ⁰ C is carried out. 6. Use of titanium dioxide pigments according to claim 1 as an additive for laminates Melamine-formaldehyde, urea-formaldehyde or phenol-formaldehyde-based in an amount of 10 to 40% by weight, based on the laminates. 45