EP2925819A1 - Pigment de dioxyde de titane - Google Patents

Pigment de dioxyde de titane

Info

Publication number
EP2925819A1
EP2925819A1 EP13808064.3A EP13808064A EP2925819A1 EP 2925819 A1 EP2925819 A1 EP 2925819A1 EP 13808064 A EP13808064 A EP 13808064A EP 2925819 A1 EP2925819 A1 EP 2925819A1
Authority
EP
European Patent Office
Prior art keywords
titanium dioxide
pigment
slurry
aluminum
containing compound
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13808064.3A
Other languages
German (de)
English (en)
Inventor
Kaarina HEIKKILÄ
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Venator Germany GmbH
Venator P&A Findland Oy
Original Assignee
Sachtleben Chemie GmbH
Sachtleben Pigments Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sachtleben Chemie GmbH, Sachtleben Pigments Oy filed Critical Sachtleben Chemie GmbH
Publication of EP2925819A1 publication Critical patent/EP2925819A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3692—Combinations of treatments provided for in groups C09C1/3615 - C09C1/3684
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3607—Titanium dioxide
    • C09C1/3653—Treatment with inorganic compounds
    • C09C1/3661—Coating
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K9/00—Use of pretreated ingredients
    • C08K9/04—Ingredients treated with organic substances
    • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L69/00—Compositions of polycarbonates; Compositions of derivatives of polycarbonates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3607—Titanium dioxide
    • C09C1/3684—Treatment with organo-silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/82—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by IR- or Raman-data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/16—Pore diameter
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/62—L* (lightness axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/63—Optical properties, e.g. expressed in CIELAB-values a* (red-green axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/64—Optical properties, e.g. expressed in CIELAB-values b* (yellow-blue axis)
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2237—Oxides; Hydroxides of metals of titanium
    • C08K2003/2241—Titanium dioxide

Definitions

  • the present invention relates to a titanium dioxide pigment. It further relates to a method for manufacturing said titanium dioxide pigment and to plastics con- taining said titanium dioxide pigment.
  • Titanium dioxide pigments are used in a number of applications. The most demanding applications from the viewpoint of product requirements are plastics produced at high temperatures and outdoor paint systems.
  • Engineering plastics are a line of thermoplastics which differ from standard plastics in their mechanical and thermal properties as well as in their chemical stability and optical properties.
  • Examples for engineering plastics are polycarbonate, polyamide, polyester, polyoxymethylene, acrylonitrile-butadiene- styrene, polyethylene terephthalate, polybuthylene terephthalate, acrylonitrile styrene acrylate, styrene acrylonitrile, polymethyl methacrylate, thermoplastic polyurethane as well blends of polycarbonate with above mentioned plastics.
  • the requirements for durability of titanium dioxide pigments in engineering plastics are high contrary to commodity plastics such as polyethylene, polypro- pylene, polyvinyl chloride, polystyrene or polyurethane.
  • Polycarbonate is commonly used in electronic components, construction materials, data storage and automotive, aircraft and security components as well as domestic appliances.
  • Polycarbonate is a predominantly amorphous, transparent, hard-elastic plastic with low water absorption.
  • Polycarbonate has useful features such as good mechanical properties, high toughness, temperature resistance and a high heat deflection temperature. Furthermore, it is easy to process. Many and diverse potential applications of polycarbonate confront this polymer with great challenges. The employment of additives and fillers is crucial in order to achieve the desired properties of products.
  • T1O2 pigment used in engineering plastics especially in polycarbonate
  • the requirements for a T1O2 pigment used in engineering plastics, especially in polycarbonate, comprises good optical properties, good processability, thermal and colour stability in the plastic matrix.
  • Most of the commercial pigments offered for use in polycarbonate do not fulfil these requirements, especially the excellent colour stability.
  • these pigments often are produced using special process steps with high energy consumptions and/or low capacity.
  • polycarbonate When polycarbonate is coloured with pigments or fillers, the nature of surface coating on the pigment/filler surface plays an important role. Type, thickness and density of the surface coating layer influences meaningfully several important properties including colour stability and optical properties of plastic matrix. Polycarbonate itself has very low water absorption. This is required also of the surface coated T1O2 pigment applied.
  • T1O2 pigments A major part of the commercial T1O2 pigments are surface coated with inorganic and organic agents. The reasons for this step are the improvement of dis- persibility, colour stability and hiding power. Those feature in coated T1O2 pigments are clearly better in comparison to uncoated T1O2 ones. In addition, plastics and paints containing surface coated T1O2 pigments have a better colour stability and weather durability than the corresponding systems pigmented with uncoated T1O2 pigments.
  • Hydrated oxides of silicon and aluminum are commonly used as inorganic coating substances in T1O2 pigments. Also some other chemicals are em- ployed in order to improve applicability of the T1O2 pigments for special purposes.
  • Titanium dioxide is an attractive pigment material for several applications. However, depending on the ambient conditions this material may suffer from oxidation state changes and/or photochemical reactions providing a greyish or yellowish colour hue.
  • T1O2 pigment Degradation reactions take place on the surface of T1O2 pigment in the presence of moisture and oxygen. Even after drying of the pigment/filler and the polycarbonate, OH groups in the surface of T1O2 pigment can cause damages in the polycarbonate during production and/or during its further processing.
  • titanium dioxide in photochemical degradation is twofold. By absorbing ultraviolet light it protects the polymer matrix. On the other hand due to its photo catalytical nature, chemical reaction can take place between titanium dioxide and polymer resulting in degradation of the matrix. In order to hinder or suppress these undesired changes a suitable coating combination is needed for the titanium dioxide material. In addition, chemical and thermal stability are required from the organic additives used. It is known that the addition of discordant siloxanes can counteract damaging or degrading of the polycarbonate in such cases. The high processing temperatures for the engineering plastics material complicate the colour stability issues. Processability at high temperatures set also requirements on the ⁇ 2 pigment.
  • Enhancing the colour stability may not lead to deterioration of the other desired properties of ⁇ 2 pigment applied like hiding power or dispersibility. Further issue is the required mechanical properties of the pigmented plastics material.
  • the applicant's previous patent EP 0406194 discloses a process for coating a T1O2 pigment with hydrated oxides of phosphorus, zirconium and aluminum.
  • the process comprises the following steps: (1 ) an acidic hydrolysable titanium compound, (2) a water soluble phosphate and (3) an acidic hydrolysable zirconium are added to the titanium dioxide pigment dispersion.
  • the slurry is made alkaline with base and (4) a water soluble hydrolysable alkaline aluminum compound is added.
  • the alkaline slurry formed is neutralized with an acid and the coated titanium dioxide pigment is recovered after filtration and washing.
  • US 2009/297852 A1 discloses a method for coating a T1O2 pigment, wherein an aqueous suspension of T1O2 base material is mixed with sodium hexameta- phosphate as dispersant.
  • the suspension obtained is disagglomerated using zirconium dioxide grinding media.
  • Aqueous sodium silicate solution is added to the suspension.
  • the obtained suspension is stirred and after stirring for 30 minutes, sodium silicate solution is added and finally AI2O3 in the form of sodium aluminate solution.
  • the pigment particle surface is usually additionally treated with an organic substance to improve dispersibility and processability as disclosed, for example, in US 7,01 1 ,703.
  • US 6,576,052 discloses titanium dioxide pigment wherein titanium dioxide particles are coated with an aluminum phosphate compound and a hydrolysate of an organo-silane compound without essentially increasing the water content of the pigment defined by Karl Fisher method.
  • This pigment is produced from aqueous titanium dioxide slurry whereto first e.g. orthophosphoric acid together with aluminum sulfate was added. Subsequently e.g. hexylmethoxysilane was added.
  • the method includes pH and temperature control during and after additions.
  • US 2010/01251 17 A1 discloses a surface-treated T1O2 pigment wherein a S1O2 layer, an AI2O3 layer and an organic layer are applied consecutively around the pigment particles.
  • the organic layer contains at least one compound from the group comprising H-siloxanes, silicone oils and organically functionalized pol- ysiloxanes.
  • An object of the present invention is to provide a pigmented plastics material which has a stable whiteness and low yellowish shade i.e. excellent colour stability and good mechanical properties.
  • a further object is to provide a titanium dioxide pigment which is suitable for use in said plastics material and able to provide the enhanced colour perfor- mance and stability.
  • a yet further object is to provide a process for the production of said titanium dioxide pigment having the improved optical characteristics and compatibility with said plastics material.
  • the present invention provides a titanium dioxide pigment as set out in claim 1 , and a method for coating titanium dioxide particles in order to produce said pigment as depicted by claim 12.
  • This titanium dioxide pigment is suitable for use in plastics materials.
  • the present invention further provides a plastic including said pigment as depicted by claim 17.
  • titanium dioxide pigments designed for demanding applications usually are surface coated with inorganic and organic agents. This is to enhance their dispersability, colour stability and hiding power in varying applications.
  • the performance of the surface coated pigment incorporated into a matrix such as binder depends on both the pigments characteristics and the matrix characteristics resulting in the overall visual appearance and stability thereof.
  • the discolouring of polycarbonate plastics due to production at high temperature is successfully hindered or suppressed using the coating of the present invention on the titanium oxide. It is possible to incorporate large enough quantities of the present pigment into plastics homogenously in order to result in the desired hiding power and colour intensity.
  • the compounded plastics show good processability, high enough thermostability and good mechanical properties.
  • the pigments of the present invention contain reduced amount of OH groups on the pigment surface detrimental to subsequent processing of engineering plastics.
  • the coating of the present invention offers an opportunity to use titanium oxide of varying origin.
  • the versatile solution provided by the inventive coating is able to overcome the fluctuations depending on the inherent properties of the varying titanium dioxide base material.
  • Figure 1 shows the colour brightness values (L * ) measured from PC plates pigmented with reference pigments (A and C) and with the pigment according to the present invention (B) as discussed in table 7.
  • Figure 2 shows colour tone values (b * ) measured from PC plates pigmented with reference pigments (A and C) and with the pigment according to the present invention (B) as discussed in table 7.
  • FIG. 3 depicts two alternative processing schemas according to the present invention. Detailed description of the invention
  • the titanium dioxide particles to be coated may originate from any desired manufacturing process.
  • the titanium dioxide originates from the commercial sulfate process or from the commercial chloride process. These processes are described in detail in Volume I of Pigment Handbook, publ. John Wiley & Sons (1988) pp. 1 1 -16.
  • the use of the surface coating of the present invention renders the origin of the titanium dioxide particle less relevant and the differences based on process technology may thus be levelled.
  • a method for processing a titanium dioxide pigment comprising the subsequent steps from a to h.
  • the preferred processing schemas are illustrated in figure 3.
  • the feed of the T1O 2 core particles comprises discharge from the calciner of a sulfate process. In another embodiment the feed of the T1O 2 core particles comprises burner discharge from a chloride process.
  • an aqueous suspension of titanium dioxide core particles is provided and the suspension is subjected to elevated temperature, preferably to at least 30 °C.
  • the titanium dioxide core particles are at least 85%, more preferably 95% and most preferably 98 %, by weight of rutile form.
  • the feed is advantageously wet milled.
  • the aqueous suspension slurry has preferably a concentration from 300 to 1500 g T1O 2 /I, more preferably from 500 to 1200, and most preferably 700 - 1000 g ⁇ 2/ ⁇ water.
  • the temperature of the slurry is preferably elevated to at least 30 °C, more preferably the elevated temperature is from 30 °C to 100 °C, most preferably from 40 °C to 80 °C, such as from 50 °C to 70 °C.
  • the reactivity of the inorganic surface coating compounds is in- creased by increasing the reaction temperature. However, in a reaction temperature approaching 100 °C the evaporation of water becomes excessive and energy consumption is unfavourably increased.
  • the pH of the titanium dioxide slurry is at this point adjusted to preferably more than 8, more preferably to more than 9. If the increasing pH causes increase in viscosity dispersing agents may further be added into the slurry.
  • the dispersants are selected from the group of water soluble silicon compounds, such as sodium metasilicate, and/or amino alcohols, such as monoisopropanolamine.
  • the amount of the dispersing agent is preferably about 0.1 to 0.4 % by weight for the silicon compound calculated as S1O2, or by weight of the amino alcohol. If the T1O2 core originates from the chloride process, typically, there is no need to add dispersants.
  • a silicon containing compound is introduced into said slurry the pH of which is made alkaline, preferably the pH is at least 1 1 .
  • the silicon containing compound is preferably alkaline water soluble silicate, more preferably an alkali metal silicate, most preferably water glass.
  • This silicon containing compound is preferably added as an aqueous solution into the suspension or slurry of the titanium dioxide particles.
  • the concentration of the silicon containing compound in an aqueous solution is preferably from 50 to 300 g/l calculated as S1O2, more preferably from 50 to 150 g/l.
  • step c the pH of said slurry, obtained from step b, is adjusted step by step to a value of preferably about 6 for precipitating the silicon containing layer onto said titanium dioxide core.
  • Adjustment of the pH from the alkaline value, pref- erably to about 6, is performed by an acid, preferably an inorganic acid, such as sulfuric acid (H 2 SO 4 ).
  • Adjusting the pH from an alkaline value, preferably to below about 9.5 leads to precipitation resulting in gel like, dense amorphous silicon oxyhydrate i.e. gelatinous precipitate.
  • step by step is meant that at least two different approaches may be used.
  • this process step is performed in a batch type vessel i.e. reactor.
  • the pH is gradually adjusted as a function of time by addition of the reaction chemicals and/or pH controlling agents such as acids or bases.
  • the process step is performed in continuous mode. The slurry is continuously transferred from one vessel to another for gradually changing the pH of the transported slurry at each vessel.
  • an aluminum containing compound is introduced into the slurry from step c.
  • This slurry contains titanium dioxide core particles coated with the amorphous, dense, silicon oxyhydrate layer.
  • the aluminum containing compound to be introduced is preferably an acidic aluminum salt, more preferably a salt selected from the group consisting of aluminum sulfate, alu- minum chloride and alkali aluminate, most preferably this salt is aluminum sulfate.
  • the aluminum containing compound is added as an aqueous solution having a concentration from 50 to 300 g/l calculated as AI2O3, preferably from 50 to 200 g/l.
  • the pH of the aluminum containing compound in aqueous solution is acidic or, if alkali aluminate is introduced, pH is kept at less than 4 by adding acid simultaneously.
  • the addition of the aluminum containing compound results in further decrease of pH of the slurry, preferably the pH of the slurry is decreased to a value of less than 4, more preferably to a value less than 3.
  • the decrease of the pH of the slurry may be assisted by addition of an acid, preferably a mineral acid, most preferably sulfuric acid, if necessary.
  • step e the pH of said slurry is increased to a neutral value, preferably to at least 5, more preferably to at least 6, most preferably to at least 7, such as 7.5.
  • the pH is required to be below 9, preferably below 8.5 in order to avoid dissolution of the aluminum coating.
  • This adjustment is made by addition of an alkali solution, preferably a hydroxide or carbonate solution or mixture thereof, most preferably by addition of a mixture thereof to enhance the favourable structural formation of the Al compound produced.
  • Increasing the pH value of the slurry leads to precipitation of aluminum oxyhydrate onto the surface of the titanium dioxide core particle coated with the silicon oxyhydrate.
  • the silicon oxyhydrate and aluminum oxyhydrate coated titanium dioxide particle is washed at this stage (step e * ) for removal of excess soluble species such as sodium or sulfate ions.
  • a phosphorus containing layer is introduced in between these two layers. The amount of phosphorus is low ena- bling two different treatment approaches as depicted by figure 3 solid and dashed lines comprising steps f and g or f * and g * .
  • a phosphate containing compound is introduced into said slurry at a pH range from 6 to 8.5.
  • the phosphate containing compound is preferably a water soluble phosphate salt, phosphoric acid or disodium hydrogen phosphate, more preferably an alkaline phosphate salt, most preferably sodium hexametaphosphate.
  • the amount of the phosphate containing compound to be added is small, preferably resulting in P 2 O 5 amount less than 3 % by weight of the pigment. This small amount does neither essentially change the pH of the slurry nor provide a disturbing amount of additional salts.
  • step g the resulting coating layer is let to mature during an extended mixing period of preferably at least 15 min, more preferably at least 30 min, partially dependent on the volume of the product to be coated.
  • the resulting slurry thus obtained from step f is filtered after step g. The removal of excess water and soluble salts by filtering results in formation of a suspension cake.
  • the filtrate is washed with water to remove excess salts (step g).
  • the filtrated and optionally washed suspension cake preferably has a solids content of more than 20 % by weight, preferably more than 30 %, more preferably more than 35, such as over 40 %.
  • the removal of salts by washing is preferably performed by either consequently washing the filtrate cake for at least 10 times, preferably 15 times with an amount of water comparable with the filtered amount. Or, the amount of salts may be monitored and the washing is guided by the analysis result.
  • steps a to e are applied as described above.
  • step f * the resulting coating layer consisting of dense silica and alumina is let to mature, preferably during an extended mixing period of at least 15 min, more preferably at least 30 min, partially dependent on the volume of the product to be coated.
  • the silica-alumina coated ⁇ 2 pigment is filtered and washed.
  • step g * the phosphate containing compound is added and after mixing, preferably for 15 min, aluminum oxyhydrate reacts with phosphate containing chemical forming aluminum phosphate. No further filtering or washing steps are needed before drying. See the dashed line in figure 3 for this processing schema.
  • the precipitated phosphate is reacting with the surface of the aluminum oxyhydrate layer on the par- tides forming a mixed aluminum phosphorus compound and/or aluminum phosphate. Due to the thinness of the formed layers it is difficult to characterize these layers even qualitatively from the multilayered particles formed. Simulation tests have been performed to study the reactions and their outcome. These studies have shown aluminum and phosphorus to react resulting in a precipitate having e.g. different porosity properties than pure aluminum precipitate.
  • the density of the resulting titanium dioxide pigment surface comprising a core particle consisting of titanium dioxide having a multilayer coating thereon comprising a silicon containing compound layer, an aluminum containing compound layer, a phosphorus containing compound layer is increased compared to a titanium dioxide pigment surface without the phosphorus containing compound layer.
  • This density change can be seen in the varying properties of the pigment, such as in filtra- tion and washing times during the production process, and in specific surface area (BET) values, total pore volume and average pore radius of the coated pigment.
  • the filtration time is increased at least 60 %, preferably from 60 to 70 %.
  • the washing time is increased at least 70 %, preferably from 70 to 80%, as depicted in more de- tail by e.g. the results of example 1 .
  • the specific surface area (BET) is decreased at least by 30 %, preferably from 30 to 45 %, more preferably from 35 to 40%.
  • the total pore volume is decreased at least by 45 %, preferably from 45 to 70 %, more preferably from 50 to 65 %.
  • the average pore radius is decreased at least by 25%, preferably from 25 to 35 %, more preferably from 30 to 35 %. The differences become less pronounced when a further organic coating is provided on the pigment particle surface which levels out the density of the coating.
  • an organosilane compound is introduced.
  • organosilane compound is according to one embodiment introduced to said filtrated suspension free of soluble salts.
  • the organosilane compound is added into the suspension if optionally no additional filtration is needed after addition of a phosphate containing compound.
  • the obtained coated titanium dioxide pigment product is dried. Typically, the product is dried using spray or belt dryer. The final pigment product may be ground, preferably by a jet mill with moderate efficiency.
  • the amounts of silicon, aluminum, phosphorus and organosilane compounds to be used are in comparison with the amount of titanium dioxide pigment preferably from 0.5 to 6 % by weight calculated as S1O2, more preferably from 1 .0 to 4.0 %, most preferably from 1 .5 to 3.0 %, for the silicon containing com- pound; preferably from 0.5 to 6 % by weight calculated as AI2O3, more preferably from 1 .0 to 4.0 %, most preferably from 1 .5 to 3.0 %, for the aluminum containing compound; preferably from 0.1 to 3.0 % by weight calculated as P2O 5 , more preferably from 0.15 to 2.5 %, most preferably from 0.2 to 1 .5 %, for the phosphorus containing compound; and preferably from 0.02 to 2.0 % by weight of carbon, more preferably from 0.05 to 1 .5 %, most preferably from 0.1 to 1 .2 %, for the organosilane compound.
  • the process of the present invention leads to a coated T1O2 pigment having improved colour stability and, optionally, provides better mechanical properties in the application tests compared to the tested commercially available pigments.
  • the process is independent of the process for the titanium dioxide core particles i.e. sulfate or chloride process and the operational mode of the inorganic coating process i.e. continuous or batch surface coating.
  • the inorganic surface coating chemicals are commonly available and the handling of used silicon, aluminium and phosphorous compounds is well known and thus safe. No additional thermal treatment is needed after the coating process. The amount of OH groups is found to be low thus promoting the stability in the pol- ycarbonate application.
  • the manufactured pigment is well suited for use in pigmentation of engineering plastics, especially polycarbonate plastics.
  • a titanium dioxide pigment is provided.
  • this pigment is made by the above described method.
  • the titanium dioxide pigment of the present invention comprises a core particle consisting of titanium dioxide having a multilayer coating thereon.
  • This multilayer coating comprises silicon containing compound layer, an aluminum containing compound layer, a phosphorus containing compound layer and an out- er organosilane layer in this order on the surface of said core.
  • the silicon containing compound layer of the titanium dioxide pigment of the present invention comprises silicon-oxygen compound, preferably amorphous silicon oxyhydroxide.
  • the amount of silicon containing compound is preferably from 0.5 to 6.0 % by weight of said pigment, more preferably from 1 .0 to 4.0 %, most preferably from 1 .5 to 3.0 % calculated as S1O2.
  • the silicon oxyhydroxide is manufactured preferably from water glass by precipitation from the alkaline pH side.
  • the aluminum containing compound layer of the titanium dioxide pigment of the present invention residing on top of the silicon gel layer comprises an alu- minum-oxygen compound, preferably aluminum oxyhydrate.
  • This aluminum oxyhydrate is preferably manufactured from aluminum sulfate.
  • the total aluminum content of the pigment comprising the aluminum containing compound layer is from 0.5 to 6.0 % by weight of said pigment, more preferably from 1 .0 to 4.0 %, most preferably from 1 .5 to 3.0 % calculated as AI2O3 and referred to the total pigment amount.
  • the phosphorus containing layer on top of the silicon oxyhydrate and the aluminum containing layer of the titanium dioxide pigment according to the present invention comprises preferably aluminum phosphate.
  • the aluminum containing layer fur- ther comprises aluminum phosphate and/or an alkaline phosphate salt.
  • the phosphate layer deposited after aluminum oxyhydrate layer may at least partly react with the aluminum oxyhydrate layer or at least the surface of said layer.
  • the aluminum containing layer and the phosphorus containing layer may become intermixed at least at the interphase providing a mixed layer and said layers overlap at least partly with each other.
  • at least part of the aluminum containing compound layer is converted into aluminum phosphate during manufacture.
  • the amount of phosphorus in the titanium dioxide pigment of the present in- vention is preferably from 0.1 to 3.0 % by weight, preferably from 0.2 to 2.5 %, more preferably from 0.3 to 1 .5 %.
  • the phosphorus containing layer is preferably manufactured from sodium hexametaphosphate.
  • an organosilane layer On top of the titanium dioxide core coated with the silicon, aluminum and phosphorus containing layers an organosilane layer is provided.
  • This outer layer comprises preferably siloxane or alkyl silane compound, more preferably an amino-functional oligosiloxane or alkoxy alkyl silane, preferably ethoxy alkyl silane, such as ethoxy octyl silane.
  • the amount of said organosilane layer is preferably from 0.05 to 1 .5% by weight of the pigment calculated as carbon content, preferably from 0.1 to 1 .2 %.
  • the titanium dioxide pigment according to the present invention has a titanium dioxide core which is preferably in rutile form.
  • the core titanium dioxide crystal size i.e.
  • the primary particle size is preferably from 120 to 700 nm, preferably from 150 to 300 nm, more preferably from 170 to 250 nm.
  • the core titanium dioxide has preferably a specific surface area (BET) value less than 40 m 2 /g, more preferably less than 25 m 2 /g, most preferably less than 10 m 2 /g.
  • the titanium dioxide pigment according to the present invention has preferably a total pore volume of less than 150 ⁇ 3 ⁇ , preferably less than 50 ⁇ 3 ⁇ , at the surface.
  • the average pore radius is preferably less than 200 A, more preferably less than 150 A, most preferably less than 100 A.
  • Moisture of the titanium dioxide pigments in accordance to this invention is preferably less than 0.4 %, more preferable less than 0.3 %, most preferable less than 0.25 %.
  • a following method for measuring the photo activity of titanium dioxide pigments The pigment sample is exposed to visible light or ultra violet light radiation. Decomposition of gaseous molecules such as isopropanol to acetone and CO2 or intermediates is determined using FTIR. The values of acetone formation for the samples of the present invention T1O2 pigment is less than 150 ppm/h, preferable less than 100 ppm/h and more preferable less than 50 ppm/h.
  • plastics comprising a titanium dioxide pigment according to the present invention as described above or manufactured as described above.
  • the plastics of the present invention is preferably engineering plastics, more preferably selected from the group of polycarbonate, polyoxymethylene, poly- amide, polyester and acrylonitrile-butadiene-styrene, acrylonitrile-butadiene- styrene, polyethylene terephthalate, polybuthylene terephthalate, acrylonitrile styrene acrylate, styrene acrylonitrile, polymethyl methacrylate and thermoplastic polyurethane.
  • the plastics is polycarbonate or a blend of above mentioned plastics therewith.
  • the amount of the titanium dioxide pigment is from 1 to 20 % by weight of the pigmented plastics, preferably from 1 .5 to 10 %, more preferably from 1 .5 to 5 %.
  • the titanium dioxide pigment is included into a plastics, preferably plastics comprising polycarbonate, masterbatch, which may be further processed into various plastics compositions and articles or end products.
  • a polycarbonate article pigmented with the titanium dioxide pigment according to the present invention shows good optical properties in view of colour stability and whiteness.
  • the colour tone b * values of the polycarbonate articles such as plates pigmented with the titanium dioxide pigment according to the present invention are increased less than 8 %, but preferably less than 5 %.
  • An improvement in brightness L * values of the plates are observed.
  • the decrease in L * value is less than at least 0.4 %, preferably less than 0.2 %, is obtained.
  • Colour coordinate values of the plates given as x,y,z decreased less than 1 % for x, less than 1 % for y and less than 1 .5 % for z. This indicates a shift to a whiter colour hue compared to commercially available PC plates with pigments or compared to PC plates with pigments without the phosphorus containing layer.
  • An indication for the good mechanical properties PC plates pigmented with various titanium dioxide pigments are attained by the melt flow index test.
  • the fourth aspect of the present invention provides processing of the pigmented plastics.
  • the plastics are first dried in a drier, preferably SOMOS drier, for a few hours, such as 3 h, at a temperature over 100 °C.
  • a drier preferably SOMOS drier
  • the desired amount of titanium dioxide pigment of the present invention in ground form is added into the plastics powder and mixed to ensure good uniformity of the pigment throughout the plastics matrix.
  • This mixture is heated in the moulding process to a temperature of at least 250 °C, preferably at least 300 °C, to enable fusion of the plastics.
  • the titanium dioxide pigment is required to withstand the moulding temperature of the plas- tics.
  • the weight ratio of the pigment to plastics may be at least 1 .5:100, preferably 2:100.
  • finely micronized titanium dioxide powder is mixed less than a minute with polycarbonate plastics and subsequently injection moulded at a temperature of about 300 °C in order to provide a pigmented plate.
  • a titanium dioxide pigment was prepared by surface coated titanium dioxide particles using the following sequence.
  • Titanium dioxide slurry was prepared according to EP 0406194 B2. This preparation method provides rutile titanium dioxide particles having an appropriate particle size and a specific surface area (BET) value of less than 10 m 2 /g.
  • BET specific surface area
  • the wet milled T1O2 slurry having a concentration of 220 g T1O2/I was intro- prised into a 10 I vessel with a jacket heater.
  • the obtained 1500 g batch of ⁇ 2 was heated to 70 °C while continuously stirring with a laboratory stirrer. Mixing was continued during the whole surface coating sequence in order to ensure an even distribution of the treatment chemicals.
  • the pH of the slurry was increased to a value more than 1 1 by addition of 2.1 % by weight calcu- lated as S1O2 of sodium water glass solution.
  • the resulting slurry was mixed for 5 min. Next, pH of the slurry was decreased with sulfuric acid stepwise to 6 with sulfuric acid within 60 min.
  • the resulting slurry was filtered for 3 - 5 min and washed with 20 litres of ion- exchanged water for 1 - 2 h in order to remove water soluble salts. This results in a suspension with a solids content of about 40 % by weight.
  • Amino functional siloxane compound (several commercial providers, e.g. from Wacker or Momentive) is added into the suspension the amount of which is adjusted by determining the carbon content. A value of 0.4 % of carbon was aimed at.
  • the resulting suspension was dried in an air circulation oven for 20 h at 105 °C. The dried powder was then jet-grounded in a laboratory jet mill using a moderate efficiency.
  • a pigment without phosphorus was manufacture according to Example 1 whereby no water soluble hexametaphosphate, Calgon, was added during the surface coating.
  • Table 1 shows selected analyses of silica-alumina coated T1O2 vs. silica- alumina-phosphorus coated T1O2. Table 1 .
  • a titanium dioxide pigment was prepared by modifying the surface coating of ti- tanium dioxide particles using the following sequence.
  • the silica-alumina surface coated T1O2 slurry having a concentration of 35 w-% was introduced into a 10 I vessel with a jacket heater.
  • the preparation of silica- alumina surface coating was prior carried out according to the sequence presented in Example 1 .
  • a 1500 g batch of T1O2 slurry was heated to 70 °C while continuously stirring with a laboratory stirrer. Mixing was continued during the whole modified surface coating sequence in order to ensure an even distribution of the treatment chemical .
  • Water soluble hexametaphosphate, Calgon (0.5 % by weight calculated as P2O5), was introduced into the slurry having a pH value of 8. The pH value was not adjusted.
  • a pigment without phosphorus was manufacture according to Example 2 whereby no water soluble hexametaphosphate (Calgon) was added.
  • Table 2 shows selected analyses of silica-alumina coated ⁇ 2 vs. silica- alumina-phosphorus coated ⁇ 2.
  • the example 3 was prepared according to the same procedure as the example 1 with the exception that no organic additive was used.
  • the suspension was dried in a circulation oven for 4 h at 300 °C.
  • the dried powder was not jet milled.
  • a pigment without phosphorus was manufactured according to Example 3 whereby no water soluble hexametaphosphate, Calgon, was added during the surface treatment.
  • Table 3 shows selected analyses of silica-alumina coated T1O2 vs. silica- alumina-phosphorus coated T1O2 when no organic additive is used. Table 3.
  • Filtration and washing times were determined using the following procedure: Two different kinds of filter papers were wetted and placed into filtering funnels. Suction was put on. From a 10 litre vessel the surface coated pigment slurry was decanted into four filtering funnels. During filtration a cake was built on the filter paper. The time was taken down. This is called a filtration time. Five litre of ion-exchanged water was decanted stepwise into each filtering funnel. When no visible water was available, the time was taken down. This is called a washing time. The results of the filtration and washing times of Example 1 and 2 are presented in table 3. The long filtration and washing times of Example 2 (silica, alumina and alumina-phosphate coated T1O2 pigment) indi- cates a dense coating.
  • Table 4 shows filtration and washing times of silica-alumina coated T1O2 vs. silica-alumina-phosphorus coated T1O2. Table 4.
  • T1O2 pigments Specific surface of area, total pore volume and average pore radius of T1O2 pigments were determined according to BET (Braunauer-Emmet-Teller) theory using a NOVA 3200 device.
  • Table 5 shows specific surface area, total pore volume and average pore radius of silica-alumina coated T1O2 vs. silica-alumina-phosphorus coated T1O2.
  • Example 1 Specific surface area (BET), total pore volume and average pore radius values in Table 5 show, that the T1O2 pigment prepared with a silica, alumina and alumina-phosphate layers (Example 1 ) provides a denser coating than the reference T1O2 pigment having only a coating consisting of silica and alumina. Therefore the colour stability in polycarbonate matrix of the Example 1 T1O2 pigment is improved.
  • the phosphorus chemical was added into the silica-alumina coated, filtered and washed slurry without additional washing step (Example 2), the effect on specific surface area of ⁇ 2 pigment was about the same.
  • Table 6 shows specific surface area, total pore volume and average pore radi- us of silica-alumina coated T1O2 vs. silica-alumina-phosphorus coated T1O2 when no organic additive is used.
  • T1O2 pigment prepared with a silica, alumina and alumina-phosphate layers (Example 3) provides a denser coating than the reference T1O2 pigment having only a coating consisting of silica and alumina (Comparative Example 3) .
  • T1O2 pigments were tested by preparing polycarbonate injection mouldings with a pigmentation level of 2 % by weight.
  • the polycarbonate used was Makrolon 2405 PC from Bayer. Polycarbonate was dried using SOMOS dryer at 120 °C for 3 h. 784.0 g of polycarbonate (98.0 %) and 16.0 g of T1O2 pigment (2.0 %) were mixed using a shaker for 30 s. Plates were pressed using injection moulding equipment Engel ES240/40HL. Optical properties (X, Y Z and Yl as well as L * , a * and b * values) of plates pigmented with ⁇ 2 pigments were measured with Hunterlab Ultrascan XE (Table 7 and 8).
  • Table 7 and figures 1 and 2 show the colour values measured from PC plates pigmented with silica-alumina coated T1O2 (fig. 1 B and 2B) vs. silica-alumina- phosphorus coated T1O2 (fig. 1A and fig. 2A) in comparison to values measured from commercial samples (fig. 1 C and 2C).
  • Example 1 81.7 86.5 87.5 94.5 - 0.5 j 3.7 6.2
  • Comparative example 1 80.7 85.5 86.0 94.1 - 0.5 j 4.0 6.7 commercial sample 79.5 84.0 84.7 93.4 - 0.2 j 3.9 6.9
  • Example 7 The results presented in Table 7 demonstrate that the b * value of polycarbonate plate pigmented with the pigment prepared according to the invention (Example 1 ) is lower e.g. improved in comparison to that of comparative ex- ample 1 and that of Control plate containing commercial titanium pigment (commercial sample). There is also a clear improvement in the L * value. These results indicate that by using the coating treatment of Example 1 (2.1 % by weight calculated as S1O2, 2.3 % by weight calculated as AI2O3 and 0.5 % by weight calculated as P2O5) gives improved colour stability of polycarbonate plate.
  • Table 8 shows colour values measured from PC plates pigmented with silica- alumina coated T1O2 vs. silica-alumina-phosphorus coated T1O2. Table 8.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Pigments, Carbon Blacks, Or Wood Stains (AREA)

Abstract

La présente invention concerne un procédé pour le traitement d'un pigment de dioxyde de titane et lesdits pigments et leurs utilisations. Le procédé comprend les étapes d'obtention d'une suspension aqueuse de particules de cœur de dioxyde de titane à une température élevée, et l'introduction d'un composé contenant du silicium dans ladite bouillie dont le pH est rendu alcalin, et la diminution du pH de ladite bouillie à une valeur d'environ 6 pour précipiter la couche contenant du silicium sur ledit cœur de dioxyde de titane, et l'introduction de façon subséquente d'un composé contenant de l'aluminium dans ladite bouillie dont le pH est acide, et l'augmentation du pH de ladite bouillie à une valeur neutre. Subséquemment, un composé contenant un phosphate est introduit dans ladite bouillie, la bouillie résultante est filtrée en un gâteau de suspension, et un composé organosilane est introduit dans ladite suspension et le produit de pigment obtenu est séché. Facultativement, un composé contenant un phosphate est ajouté après filtration et lavage dans une bouillie de pigment revêtue par silice-alumine. Une stabilité de couleur améliorée est obtenue dans des matières plastiques de polycarbonate plaquées préparées à l'aide des pigments de dioxyde de titane mentionnés ci-dessus.
EP13808064.3A 2012-11-28 2013-11-27 Pigment de dioxyde de titane Withdrawn EP2925819A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20126250A FI125473B (en) 2012-11-28 2012-11-28 Titanium dioxide pigment
PCT/FI2013/051112 WO2014083242A1 (fr) 2012-11-28 2013-11-27 Pigment de dioxyde de titane

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CN104194409A (zh) * 2014-08-13 2014-12-10 攀钢集团钛业有限责任公司 一种耐高温钛白粉及其制备方法和用途
CA2979852A1 (fr) * 2015-04-13 2016-10-20 The Chemours Company Tt, Llc Particules thermoresistantes de dioxyde de titane et formation d'objets froids
CA3019838A1 (fr) 2016-03-29 2017-10-05 Venator P&A Finland Oy Procede de traitement de particules de dioxyde de titane, particule de dioxyde de titane et ses utilisations
EP3626885A1 (fr) * 2018-09-21 2020-03-25 Kronos International, Inc. Pigment stratifié ayant des propriétés d'espacement et une grande stabilité au ternissement par les uv
CN114621607B (zh) * 2020-12-11 2023-06-06 中信钛业股份有限公司 一种耐高温通用工程塑料专用型二氧化钛颜料的制备方法

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US20050129634A1 (en) * 2003-12-16 2005-06-16 Frerichs Scott R. Passivated nano-titanium dioxide particles and methods of making the same
MY153667A (en) * 2006-01-30 2015-03-13 Kronos Int Inc Titanium dioxide pigment particles with doped, dense sio2 skin and methods for their manufacture
DE102006004344B4 (de) * 2006-01-30 2008-11-13 Kronos International, Inc. Titandioxid-Pigment mit hoher Opazität und Verfahren zur Herstellung
DE102008026300A1 (de) * 2008-06-02 2009-12-03 Kronos International, Inc. Verfahren zur Oberflächenbeschichtung von anorganischen Festkörperpartikeln, insbesondere Titandioxid-Pigmentpartikel

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WO2014083242A1 (fr) 2014-06-05
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