JPS63132971A - Composition containing light stable pigment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to pigment compositions, particularly pigment compositions containing titanium dioxide.

Titanium dioxide is widely used as a pigment for various purposes. This pigment is generally used in latex, acrylic, vinyl acetate, alkyd, polyester, polystyrene, polymethyl methacrylate (PMMA), polyvinyl chloride (pvC)
), used as emulsions or dispersions in combination with binders such as melamine, cellulose, and/or cellulose derivatives to produce finished products such as painted boards, colored plastics, or paper, e.g. as pigments. Used in white paint, interior and exterior paint for houses, automobile paint, and coating materials. To industrially produce titanium dioxide, first extract titanium ores such as ilmenite (FeTie) with concentrated sulfuric acid to form a sulfate solution, evaporate the water and concentrate, and then
SO4 is removed as a precipitate, hydrolyzed to precipitate titanium dioxide hydrate, and this is roasted at 800 to 1000°C,
It was like a cake. The agglomerated cake is mechanically broken down into fine particles suitable for use. Although titanium dioxide obtained by this aromatic process has been used for a long time, it has been associated with some serious problems. These problems are generally related to the relatively wide particle size distribution and impurities, particularly iron, left in the titanium dioxide during manufacturing. These impurities are
It is generally uniformly distributed within the titanium dioxide particles. Efforts have been made to reduce this iron content, and an industrial tolerance limit of 200 ppm (by weight) has been established for this iron. (Barr Rechmann, Bunsen Physical Chemistry Report, 71
Vol. 277-285, 1967).

The above impurities strongly absorb a portion of visible light, so
It greatly reduces the reflectivity of the titanium dioxide particles, causing their color to deviate substantially from "white". Therefore, great efforts have been focused on removing these impurities. A wide particle size distribution also reduces the visible light scattering efficacy of the pigment. Particles with a diameter of 0.2-0.3 μm show the highest scattering efficiency in the visible region.

To alleviate these problems, a method for producing titanium dioxide has been developed that is more uniform and pure than previous methods.

This method is described in Kirk Ozmer's Encyclopedia of Chemical Chemistry, Volume 3, Volume 23, 143.
~149 pages, U.S. Patent No. 2,833,627, No. 4,
No. 462,979, and other patents mentioned in this latter patent (all of which are therefore incorporated by reference), titanium tetrachloride was combined with oxygen at 150
It consists of a process of reacting in a flame at 0°C to generate particulate "soot". The resulting titanium dioxide is not only substantially more pure, but also has uniform, appropriately sized particles,
That is, it takes the form of particles of 0.18 to 0.26 μm. In this method, particles of the appropriate size are directly obtained, thereby eliminating the cost of mechanical processing and associated costs.

Although this improved process for producing titanium dioxide substantially improves purity, degradation of the binder due to exposure to sunlight still occurs.

To improve its performance, titanium dioxide is coated with a layer of a passivating dielectric 1, for example silicon dioxide or aluminum oxide. (In general, materials with a resistance to electron or hole transport of about 10' ohms or more are desirable.) prevent.

This application increases stability, but at the cost of
1) Coating costs are extra, and 2) the coating film reduces reflectance.

Nevertheless, the stability of titanium dioxide with such coatings is well accepted.

It is currently widely used as a commercial product.

It has been found that in the case of titanium dioxide produced by the soot method, ie, the chloride method, which does not require grinding of agglomerated particles, its photochemical activity can be reduced without coating it. This stability in the absence of a coating is achieved by quenching the photo-generated charges in the titanium dioxide before they chemically react with the substances adsorbed on the surface of the titanium dioxide pigment particles. Ru. This result may be due to 1) the introduction of more electron and vacancy traps in the lattice or on the surface of the titanium dioxide particles than are already present in the synthesized titanium dioxide, and/or 2) Obtained by suppressing reduced substances. Surprisingly, even though submicron particles do have traps due to their high area/mass ratio, further increasing the concentration of traps surprisingly increases stability significantly. .

There are several ways to achieve the above goals. Methods that may be used include grinding, milling, or crushing for longer periods of time, ie breaking up the crystal structure for at least one day.

and/or high temperature treatment in an oxidizing medium such as air or oxygen.

For some applications, the latter method is preferred because the treatment does not reduce the particle size of the titanium dioxide. However, in either case, the stability of the pigment composition is maintained without the costs associated with coating.

The present invention provides a method other than 1) coating a charged substance or a reduced substance in titanium dioxide with a continuous phase of a high-resistance dielectric; (b) by a method selected from the group consisting of: oxidizing most of the reduced substance;

and 2) combining the titanium dioxide with a binder, thereby increasing the stability of the titanium dioxide and binder composition without substantially reducing its reflectance. An object of the present invention is to provide a method of forming a composition.

The present invention combines titanium dioxide with materials such as latex, acrylic, vinyl acetate, alkyd, polyester, polystyrene, P
Includes the titanium dioxide used as a pigment in compositions with which it can interact with binders such as MMA, PVC, melamine, cellulose, cellulose derivatives, etc. (
The binder used in the present invention is an organic polymer, a material containing it, or a polymer precursor in which the pigment is dispersed or suspended. ) Thus, the present invention relates to pigment compositions containing titanium dioxide, for example high purity titanium dioxide, and a binder. (The titanium dioxide used in the present invention may be in the rutile or anatase form.) For such compositions, it is generally preferred to use titanium dioxide having a particle size within the range of 0.1 to 1.0 μm.
Particles larger than 1 μm and particles smaller than 0.1 μm are
This is not desirable because the light scattering efficiency per unit weight is low.

(Particles outside this size range are not advantageous, but do not exclude them from the scope of the invention.) As stated above.

Particles of desired size are easily produced by the interaction of titanium tetrachloride and oxygen.

To improve stability, charge (vacancies and electrons) and T
reduced substances such as i'' and adsorbed substances, e.g. 1) water and most importantly adsorbed organic substances which react with the vacancies, and 2) substances such as oxygen which react with the electrons. , the interaction with , must be suppressed,
This suppression is achieved by causing the vacancies to react with electrons and annihilating both, before the vacancies and electrons react with the adsorbed substance on the particle surface. , and also for the reasons below.

Further hindering electron-vacancy annihilation, e.g. Ti3
4″, Ti″+ and oxygen vacancy (Oxy-gan
This is achieved by removing reduced substances such as 1attic vacancies). Electrons and holes react well by providing traps for each. Generally, it is desirable to create electron and hole traps with a surface concentration of 10"/a1 or more, more preferably 4 X 12"71 or more, or a volume concentration of 1017/am3; however, if the surface concentration is 3X1014 /aJ or volume concentration is 3
Above X 10"/cm, further improvements do not seem to be obtained and a one-color change is observed. One method of introducing the desired concentration of traps is by mechanical stress, i.e., by agglomeration. This is a method such as milling, crushing, crushing, etc. that not only disperses but also breaks down 10% or more of the individual pigment particles of micron size or smaller by applying stress. Milling for at least 1 day, more preferably 21 days, produces a sufficient concentration of traps for both electrons and holes.The milling method provides the desired concentration of traps, but at the same time reduces particle size. Upon grinding, the particle size is reduced from 0.2 μm to 0.1 μm.

If particle size reduction is undesirable in a particular application,
Other methods of introducing traps, ie, inducing electron-vacancy annihilation, can be used.

In particular, by limiting the presence of reduced substances such as Ti", Ti", oxygen vacancies, etc., it is possible to induce the disappearance of vacancies and electrons. This phenomenon is explained based on the alignment of the Fermi level in TiO□ with the electrochemical potential of the environment. As illustrated in Fig. 2, the original Ti
The Fermi level in Ox (Tie, which does not contain reduced substances) is at approximately the same electrochemical potential as in one representative environment, 0,/H20. Therefore, no bending of the energy band at the interface between TiO□ and the environment occurs, Tie.

If there is a reduced substance in the
The result will be as shown in the figure. Therefore, when the Fermi level and the electrochemical potential of the environment are made equal at the interface between the 0□/Hz O environment and Tie2, the energy band is bent as shown in FIG. Since the bending of the energy band does not occur in the original TiO□, the electrons are
There is no barrier for O to reach the interface with the environment, and there is no barrier for the vacancy to disappear at this interface. In contrast, in TiO□ containing reduced material, as shown in FIG. 4, there is a substantial barrier to electrons, preventing them from reaching the T i O,/environment interface. This barrier to electrons conversely promotes the migration of vacancies to the interface. In this way, the vacancies are preferentially directed towards the interface, and the annihilation of these degradation-inducing vacancies, such as photo-generated vacancies, is limited, which is undesirable.

Another possible way to create the desired concentration of traps is to form dopant sites. but,
This dopant must not cause energy band bending as shown in FIG. For example, good stability is obtained by incorporating iron, manganese, or cobalt as dopants in T i O, in a reducing environment such as an aqueous solution containing methyl viologen cations and methyl viologen radical cations. However, the effect of dopants in environments with relatively low electrochemical potentials, such as oxidizing environments, is not clear.

Heating titanium dioxide in an oxygen atmosphere above 350'C, more preferably above 550°C, limits the reaction of the charge with substances such as water and adsorbed organic materials. This heat treatment completely ensures that essentially all the Ti, including the Ti present on the surface, is completely oxidized to Ti4+, thus limiting the adsorption of water and other substances to the surface and, more importantly, , which ensures the annihilation of electrons and vacancies 6 Heating in a reducing environment 1, for example hydrogen, then produces the opposite effect, limiting the annihilation of electrons and vacancies. Similarly, heating to 550 °C in an inert environment such as nitrogen and in the presence of adsorbed organic materials results in Ti
A reduced substance like 3+ is produced. A similar effect is seen at temperatures above 800° C. in an inert atmosphere, but in the absence of adsorbed organic substances.

Also, when heated in an air or oxygen atmosphere at such temperatures, but only if the first cooling is sufficiently rapid to prevent vacancy ripening1, e.g., only if quenched in a cold fluid. , the same result is seen. Thus, heating the pigment to 350-800°C in an oxidizing atmosphere increases the photostability of the paint, but heating it similarly in the presence of a reducing agent in an inert environment or at extremely high temperatures heating increases instability.

Although a suitable method of electron and vacancy annihilation has been disclosed, the improved stability is independent of the method used to produce this effect, provided that a sufficient number of effective traps or annihilation means are introduced into the pigment. The same degree of stability improvement can be obtained as long as the For example, if Ti3+ and other reduced materials are substantially eliminated, stability is enhanced because annihilation is enhanced. The following examples demonstrate 1) an advantageous method of removing photogenerated harmful charges, 2) the results obtained by this removal, and 3) reducing the adsorption of substances that react with these charges, e.g. Top and internal T
The results obtained by ensuring complete oxidation of all i to coordinate Ti4+ and oxygen are illustrated.

Example 1 Rutile titanium dioxide commercially available as DuPont R101 pigment from EI DuPont was obtained. This pigment had an average particle size of 0.2 μm, a narrow particle size distribution, and a triethanolamine coating that accounted for about 1% of the weight of each particle. Experiments were conducted using the purchased titanium dioxide and titanium dioxide particles corroded with a strong mineral acid. This acid corrosion was carried out by immersion in 3 molar boiling sulfuric acid for 15 minutes. (We also conducted a separate corrosion experiment in boiling hydrochloric acid at a 3 molar concentration, but found that the results did not change depending on the acid used.) After cooling to room temperature,
Filter the reaction mixture.

Five washes were performed with deionized water.

The treated particles and untreated particles were each separated into 6mm diameter and 6mm length.
mm high-density alumina cylinder fills half of the cylinder 5
The mixture was placed in a 00 mA polyethylene jar and pulverized. In each milling operation, 100 g of titanium dioxide and 350 mQ of deionized water were placed in the jar. 12 jars
After rotation in the Orpm and milling for 1 day, 2 days, 1 week, and 3 weeks, the resulting slurry samples were removed for testing.

150 g of ground pigment sample was mixed with 2.5XIO-3 molar concentration of methyl viologen (composed of dichloride) and 3
×−2 molar concentration of ethylenediaminetetraacetic acid (
Its photoactivity was measured by suspending it in an aqueous solution containing disodium EDTA. This suspension was buffered to pH 6.0 and kept under a nitrogen atmosphere. The vacancies generated by light irradiation directly oxidize EDTA. The electrons reduce methylviologen to a blue methylviologen radical, which is quantified by spectroscopy by following the change in absorption at 602 nm. This change in absorption is directly proportional to the photochemical reaction rate. The light source used to irradiate the composition was a 250 watt xenon/mercury lamp. Corning 7-51 and 0-51 light beams from this lamp
Filters are used to select active rays with wavelengths of 360 to 40.
It was limited to a range of 0 nm.

The size of pigment particles obtained by varying the grinding time was measured using the Branauer, Emmett, and Teller (BET) gas adsorption/desorption method.

As a result of this measurement, the average particle size was 0.2μ after 21 days of grinding.
It was observed that the thickness decreased from m to 0.1 μm. The reduction in photoactivity is shown in the figure as a function of milling time, as can be seen, the photoactivity was reduced to 9% of the initial value. When the ground sample was heated to 550°C in air for 2 hours, the photoactivity further decreased to 6% of the initial value, but when heated at 550°C for 2 hours in a nitrogen atmosphere, the photoactivity decreased to the initial value. The value increased from 9% to 15%. However, this is only true if organic compounds such as triethanolamine or cyclohexanone are adsorbed on the particle surface.

Example 2 Treated pigments and untreated pigments were placed separately in a quartz boat and heated for 550 min in a gentle stream of air or nitrogen gas.
℃ for 2 hours.

These samples were allowed to cool down to room temperature at a cooling rate of 1° C. per minute, or were rapidly cooled in liquid nitrogen. Changes in photoactivity were measured as described in Example 1. Pigments adsorbing triethanolamine (both slow and rapidly cooled) showed a two-fold increase in photoactivity when heated under a nitrogen atmosphere. Both treated and untreated pigments
After heating in air, the photoactivity is reduced to 1/6 to 1/7, i.e., 15% of the initial value, regardless of whether it is slowly cooled or rapidly cooled.
decreases to Further heating of a pigment heated in air under a nitrogen atmosphere does not increase photoactivity, nor does corrosion of a pigment heated in air in boiling mineral acid increase photoactivity.

Example 3 The pigment described in Example 1 was boiled for 15 minutes in 3 molar hydrochloric acid. The photoactivity of this pigment was measured in the same manner as in Example 1 and showed a 6-fold increase. Boiling this acid-treated pigment in 3 molar tetramethylammonium hydroxide does not change the photoactivity, BE
According to T measurements, the surface area of the pigment is neither increased nor decreased by this acid treatment.

Example 4 Pigment purchased from the manufacturer mentioned in Example 1 was heated in air to 550°C for 2 hours.

Next, the photochemical activity of this pigment was determined by quantifying the amount of hydrogen peroxide produced. In this test, 90% water by volume
The pigment was suspended in a solution containing 10% by volume of isopropyl alcohol, and 0.1 molar sodium acetate/acetate buffer. The pH of this solution was 5.1.

Add 2 g of pigment to 15 mN of this solution, and mix this mixture with 1
Irradiation was performed using a 00 Watt medium pressure mercury lamp (λmax: 336 nm). The concentration of hydrogen peroxide in the mixture was analyzed for irradiation times from 0 to 20 minutes. This analysis is 2.5m
m samples were taken and filtered through a 0.45 μm pore size filter, and the filtrate contained an acetate buffer (0.1 molar, pH 5.1) and 0-dianisidine (0.3 mmolar). Add 1 mA of the solution, then the enzyme horseradish peroxidase solution (60 units per mm)
100 μQ was added, and the absorbance of the solution at a wavelength of 500 nm was measured. This absorbance is proportional to the concentration of hydrogen peroxide. A comparison of undenatured pigments (as purchased) and those heated in air at 550°C for 2 hours revealed that the photochemical activity of the pigments heated in air was 175 times lower than that of the as-purchased pigments. Ta.

Example 5 The pigment heated as in Example 4 in air was then heated in forming gas (96% nitrogen, 4% hydrogen) at 550°C for 2 hours. After heating, the pigment exhibited a slight bluish tinge.The photochemical activity of this pigment in a normal atmosphere (air) was measured in the same manner as in Example 4. This activity was 20 times that of the oxidized pigment (ie, 4 times that of the as-purchased pigment).

Example 6 The triethanolamine-coated pigment of Example 1 was heated in nitrogen at 550° C. for 2 hours, and then its photochemical activity in air was measured in the same manner as in Example 4. This activity was 25 times higher than that of the original pigment as purchased.

[Brief explanation of the drawing]

FIG. 1 illustrates the results obtained by the present invention, and FIGS. 2 to 4 are explanatory diagrams of processes related to the present invention.

Claims (1)

[Claims] 1.1) Methods other than coating a charged substance or a reduced substance in titanium dioxide with a continuous phase of a high resistance dielectric,
(a) a step of reducing by one method selected from the group consisting of a method of providing a trap to capture electrons and vacancies; and (b) a method of oxidizing most of the reduced substance; and 2) A method of forming a composition comprising the step of combining the titanium dioxide with a binder, thereby increasing the stability of the titanium dioxide and binder composition without substantially reducing its reflectance. 2. The method of claim 1, wherein said trap is applied by crushing said titanium dioxide. 3. The method of claim 1, wherein oxidation of said reduced material is carried out by heating to about 350° C. in an oxidizing environment. 4. The method of claim 1, wherein said composition comprises a paint or a coating material. 5. The method of claim 1, wherein said composition comprises paper. 6. The method of claim 1, wherein said composition comprises plastic. 7. A composition comprising titanium dioxide and a binder, wherein the titanium dioxide is heated in an oxidizing environment at a temperature within the range of 350°C to 800°C.