JP4982397B2 - Non-fibrous potassium titanate - Google Patents

Description

  The present invention relates to potassium titanate used for plastics, friction materials, paints, lubricants, heat-resistant materials, heat-insulating materials, paper additives, etc., and particularly non-fibrous titanic acid with an emphasis on shape characteristics related to hygiene. Regarding potassium.

  Potassium titanate has a fiber shape and has been put into practical use in the fields of plastics, paints, friction materials, and the like, and is widely used. However, fibrous powders are bulky, have poor fluidity, and are difficult to handle. Furthermore, the fibrous powder is liable to generate dust and has a problem in the working environment.

  For example, the carcinogenicity of asbestos has become a problem, but there is a view that the cause is related to the fibrous shape. According to Stanton's hypothesis, fibers having a fiber diameter of 0.25 μm or less and a length of 8 μm or more are highly tumorigenic. In the World Labor Organization (ILO), fibers having a diameter of 3 μm or less, a length of 5 μm or more, and a ratio of length to diameter of 3: 1 or more are used as inhalable fibers.

  Although it is not clear about the possibility that potassium titanate fibers may affect the health of the respiratory system or the like, in any case it is desirable that there are few inhalable fibers.

The fine particle alkali titanate is an aggregate of spherical particles, and has a powder size of 0.01 to 0.5 μm confirmed by an electron microscope and a specific surface area by a BET method of about 100 m ² / g or more (for example, (See Patent Document 1).

According to Patent Document 1, the alkali titanate disclosed in many documents and patents is usually in the form of a fiber having a major axis of several μm to several tens of μm, and the specific surface area is as small as 20 m ² / g or less. There are known a dissolution method, a hydrothermal method, a flux method, a melt method, and the like. However, Patent Document 1 discloses a surface-active fine-particle alkali titanate that cannot be obtained by these conventional techniques.

  This powder is obtained by adding an aqueous solution of titanium tetrachloride to an aqueous solution in which an organic carboxylic acid is dissolved, adding an alkali metal hydroxide to an aqueous suspension of a reaction condensate of hydrated titanium oxide-organic acid to be produced, and having a pH of 8 or more. It is obtained by reacting at a temperature of 50 ° C. or higher and 100 ° C. or lower.

This powder is an aggregate of several tens to several hundreds of spherical particles.
JP-A-4-280815

As potassium titanate, potassium titanate (K ₂ O · 2TiO ₂ ), potassium titanate (K ₂ O · 4TiO ₂ ), potassium titanate (K ₂ O · 6TiO ₂ ), potassium potassium titanate ( K ₂ O · 8TiO ₂ ) is known. Among these, what is directly produced | generated by heat synthesis is a thing of the composition of 2, 4, or 6 titanate. Potassium dititanate or potassium tetratitanate has a fiber shape easily by heating, but potassium hexatitanate originally does not grow in a fibrous form. However, when the Ti source and the K source, which are the initial raw materials, are heated, the first melting is potassium oxide generated from the K source, so that the initial melting portion is rich in potassium. 4 Potassium titanate is produced. When heating is further continued, the surrounding titanium oxide is taken in, but there is a part that leaves the fiber shape grown in the initial stage.

  An object of the present invention is to provide a potassium titanate crystal in which particles having an inhalable fiber shape are substantially zero.

The present invention has been intensively developed to achieve the above object, and is a powder obtained by pulverizing a slightly sintered sintered product of prismatic crystals of non- fibrous potassium titanate , Non-fibrous potassium titanate characterized in that the particles have a diameter of 3 μm or less, a length of 5 μm or more, and particles having a length to diameter ratio of 3: 1 or more are prismatic crystals having a number ratio of 3% or less. I will provide a.

  Here, as the criteria for determining the fiber property, the diameter of crystal shape, the length, and the ratio of length to diameter are listed, but the limitation on the shape of non-fibrous potassium titanate in terms of hygiene is still clear. There were no specific provisions, and the provision was made with reference to the inhalable fibers of ILO. Then, the standard that the number ratio corresponding to this rule is 3% or less was set and judged. As for this number ratio, the standard from the viewpoint of hygiene is not yet definite, and the inventors have uniquely determined in the present invention, sufficiently considering safety from a probabilistic viewpoint.

  On the other hand, it is conceivable to finely pulverize potassium titanate as a means for reducing the ratio of inhalable fibers of commercially available potassium titanate fibers. However, potassium titanate is bulky and has poor fluidity, making it difficult to supply, causing problems such as adhering to the wall of the supply channel and blocking it, and a significant increase in cost. It is difficult.

  Whereas the limit of the respirable fiber ratio by pulverization at the laboratory level is about 5%, the present invention has been achieved by the production method capable of reducing the number ratio to 3% or less.

Potassium titanate having such characteristics can be produced by the following means. That is, the Ti source powder that produces TiO ₂ by firing and the K source powder that produces K ₂ O are mixed at a molar ratio of TiO ₂ : K ₂ O of 5.5: 1 to 6.5: 1. By the method for producing potassium titanate, the temperature of the article to be heated is fired at a heating rate of 20 ° C./min or higher from 800 ° C. to the target maximum temperature 1000-1300 ° C., and the fired product is crushed after cooling. Can be manufactured.

As the Ti source, titanium oxide, hydrous titanium oxide or the like can be used, and as the K source, carbonate, hydrogen carbonate, nitrate, sulfate or the like can be used. Even when a Na source that generates Na ₂ O by heating is used instead of the K source, sodium hexatitanate having the same characteristics as potassium hexatitanate is produced, so that it is also possible to apply a Na source.

  The molar ratio of 5.5: 1 to 6.5: 1 is to match the molar ratio of the final product, preferably 6: 1, but not necessarily stoichiometric and not the above. If it is within the range of the molar ratio, it is a range in which potassium hexatitanate is produced as long as it is confirmed by X-ray diffraction measurement.

  Firing is performed at a temperature increase rate of 20 ° C./min or more from 800 ° C. to a target maximum temperature 1000 to 1300 ° C. The reason why the temperature range from 800 ° C. to the target temperature is rapidly heated is to suppress the formation of 2 or 4 potassium titanate. The upper limit of this temperature range is preferably up to 1200 ° C. in consideration of the melting point of potassium hexatitanate.

  The rate of temperature increase in the region below 800 ° C. may be either slow or rapid, but since the region above 800 ° C. is rapidly heated, it is practical to rapidly heat the region below 800 ° C. accordingly.

  The reason for setting the temperature rising rate to 20 ° C./min or more is that it is difficult to suppress the formation of 2 or 4 potassium titanate at less than 20 ° C./min. The upper limit of the heating rate is restricted from the viewpoint of equipment, and is determined by protection of refractories, restrictions on equipment maintenance, restrictions from an economic viewpoint, and the like.

When the Ti source and K source powders are mixed at a molar ratio of TiO ₂ / K ₂ O in a ratio of 5.5: 1 to 6.5: 1, and this is heated and fired, the rate of temperature rise is as described above. Is slow, it promotes fiber growth of potassium dititanate and potassium tetratitanate in the previously melted potassium-rich phase, and does not become the desired non-fibrous form. Therefore, rapid heating is performed so that potassium dititanate and potassium tetratitanate easily pass through a temperature range where growth is easy. As a result, the growth rate of potassium dititanate and potassium titanate is suppressed by a rapid temperature increase of 20 ° C./min or higher to a temperature increase rate of 1200 ° C., and the desired non-fibrous potassium 6 titanate is obtained. Obtainable. Since the calcined product of potassium titanate thus calcined is slightly sintered, after cooling, it is crushed to an appropriate particle size by a pulverizer to obtain a product.

  Potassium titanate has physical properties such as high whiteness, low Mohs hardness, low thermal conductivity, and high refractive index, and has properties as a substance excellent in heat resistance, chemical resistance, and sliding properties. Therefore, it can be used for plastics, friction materials, paints, lubricants, heat-resistant materials, heat-insulating materials, paper additives and the like in addition to the use as a reinforcing fiber. Furthermore, while the fibrous powder is bulky and poor in fluidity and difficult to handle, the potassium titanate of the present invention has a wide range of applications in that these drawbacks are improved.

  In the application, it is possible to perform a surface treatment such as a coupling treatment in accordance with the purpose.

  Further, it has been found that when the non-fibrous potassium titanate powder of the present invention is used as a friction material, it exhibits stable friction performance from a low temperature to a high temperature as compared with the conventional potassium titanate powder. The reason for this is not clear, but since the potassium titanate powder of the present invention has low fiber properties compared to the conventional potassium titanate powder, the side-side crystal plane and bottom-side crystal of potassium titanate that is a prismatic crystal. The surface is considered to be due to the average arrangement of the friction material sliding portions.

  The non-fibrous potassium titanate of the present invention is potassium titanate such that particles in the region defined as fibers are considered substantially zero. Although this material cannot be expected to have much reinforcing property among the properties of conventional fibrous potassium titanate, it is widely accepted as a raw material for various applications that can be used safely and hygienically. It is a material and has a great contribution.

The melting point of each product of potassium titanate is potassium dititanate 965 ° C
4 Potassium titanate 1114 ° C
6 Potassium titanate 1370 ° C
The crystal growth occurs at a slightly lower temperature than these melting points. Therefore, the shape derived from potassium dititanate or potassium titanate is suppressed by passing the crystal growth temperature range of potassium dititanate and potassium titanate at a rate of temperature rise as high as possible of 20 ° C./min. The non-fibrous non-fibrous potassium titanate of the invention can be obtained.

Titanium oxide powder and potassium carbonate powder are blended so that the molar ratio of TiO ₂ : K ₂ O is 6: 1, this raw material is mixed for 10 minutes with a blender, and this mixed powder is an electric furnace with a temperature program controller. Then, the temperature was raised from 800 ° C. to 1130 ° C. under conditions of 7 ° C./min, 20 ° C./min, and 30 ° C./min, respectively, held for 20 minutes, and then pulverized with an impact mill.

  An electron microscopic image of the obtained potassium titanate powder was subjected to image analysis processing, and from the diameter and length of each particle, the diameter was 3 μm or less, the length was 5 μm or more, and the ratio of length to diameter was 3: 1 or more. When the number ratio of the particles was calculated, the results shown in Table 1 were obtained.

  For comparison, the number ratio of particles having a diameter of 3 μm or less, a length of 5 μm or more, and a ratio of length to diameter of 3: 1 or more was also obtained for two types of typical commercially available potassium titanate fibers. This is also shown in Table 1.

Claims (1)

A powder obtained by pulverizing a slightly sintered sintered product of prismatic crystals of non- fibrous potassium titanate, and the particles of the powder have a diameter of 3 μm or less, a length of 5 μm or more, and a length and a diameter Non-fibrous potassium titanate, wherein particles having a ratio of 3: 1 or more are prismatic crystals having a number ratio of 3% or less.