JPH0251417A - Method for preventing caking of acidic ammonium fluoride - Google Patents

Abstract

PURPOSE:To easily and effectively prevent the caking of hygroscopic acidic ammonium fluoride by adding only a water-soluble vinyl compd. CONSTITUTION:Only a water-soluble high-molecular vinyl compd. is added to acidic ammonium fluoride (NH4F.HF) to prevent the caking of the fluoride. The vinyl compd. may be polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol acetal, polyacrylamide, polyacrylate or polyvinylpyrrolidone and the amt. of the compd. added is 0.1-5,000ppm, preferably 1-1,000ppm.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to acidic ammonium fluoride (NH4F-HF).
Concerning the anti-caking law. Acidic ammonium fluoride is used alone, as an aqueous solution, or as a mixture with dilute hydrofluoric acid, and is mainly used as a frosting agent for glass, a cleaning agent for metals, and an enotinting agent.

Acidic ammonium fluoride is a highly hygroscopic crystal that absorbs moisture at relative humidity of 50% or more, and solidifies during storage or transportation, making it extremely difficult to smoothly transfer it to a dissolution tank when used, for example. Therefore, it is strongly desired to have non-consolidating crystals.

[Prior art and problems] Conventionally, methods for preventing caking of hygroscopic solids include adding clay, white carbon, etc. to prevent contact between caking substances, and creating adsorption films on particle surfaces using surfactants, etc. and a method of adding a mixture of an anionic surfactant and a water-insoluble vinyl polymer compound to a caking substance (Japanese Patent Publication No. 11330/1983).
etc.

However, when clay, white carbon, etc. are added to acidic ammonium fluoride, there are disadvantages such as the liquid becomes cloudy or foreign matter gets mixed in when acidic ammonium fluoride is used as an aqueous solution or a mixed solution with dilute hydrofluoric acid. . Further, it is also undesirable that dust is generated when mixing clay and the like, which deteriorates the working environment. On the other hand, we also investigated methods using surfactants, but we were unable to find any that exhibited a stable anti-caking effect against acidic ammonium fluoride. Regarding the method of adding a mixture of an anionic surfactant and a water-insoluble vinyl polymer compound, the above publication describes
The reason why this effect is exerted is not stated, but according to other reports (for example, ammonium sulfate technology, 24(1)), urea, which is a caking substance, causes changes in temperature and humidity when the above mixture is added. In the process of repeated dissolution and recrystallization, the crystal habit changes, and urea grows into fine crystals.
It is believed that these fine crystals are easily destroyed by even the slightest mechanical stimulation, thereby preventing caking. However, the above-mentioned method requires a step of making the water-insoluble vinyl polymer compound water-soluble, and the presence of the surfactant causes problems in use.

[Knowledge related to problem solving] Water-soluble polymer compounds themselves have hygroscopic properties, so even if the hygroscopic particles are covered with this film, it is not possible to prevent particles from coagulating with each other due to their hygroscopic properties. previously thought. In fact, there are no known examples of using a water-soluble polymer compound alone as an anti-caking agent.

However, the present inventors have found that unexpectedly sufficient anti-caking effects can be achieved by adding a water-soluble vinyl polymer compound alone to acidic ammonium fluoride.

[Structure of the Invention] The present invention provides a method for preventing caking, which is characterized by adding a water-soluble vinyl polymer compound alone to acidic ammonium fluoride.

The water-soluble vinyl polymer compounds used in the practice of the present invention are vinyl polymers and compounds thereof, and specifically include polyvinyl acetate and saponified products thereof, polyvinyl alcohol and acetalized products thereof, polyacrylamide and parts thereof. Includes hydrolysates, polyacrylates, vinylpyrrolidone, etc.

The amount of the vinyl polymer compound added to the acidic ammonium fluoride is 0.1 to 5000 ppr based on the object to be treated.
m, preferably about 1 to 1,000 ρρm. When it is less than 0.1ρρ1, the anti-caking effect is insufficient. Even if it exceeds 5000 ppm, the anti-caking effect does not change much.

Acidic ammonium fluoride is commercially available in various forms such as crystals, powders, and flakes, but all have anti-caking effects. be done.

The coating of the water-soluble vinyl polymer compound prevents contact between acidic ammonium fluoride crystal particles, thereby preventing mutual aggregation of the particles.

Furthermore, when the crystal surface is coated with the water-soluble vinyl polymer compound, contact between the particle surface and the outside is prevented,
Even if changes in temperature and humidity, which are commonly considered to be the cause of caking, occur, changes in external conditions do not have much of an effect on the particle surface.

Therefore, it is thought that dissolution-recrystallization due to changes in the external environment is almost absent or significantly reduced.

Incidentally, when acidic ammonium fluoride crystals treated with partially saponified polyvinyl acetate etc. are stored for a long period of time and the surface of the crystal particles is observed under a microscope, no change in the crystal habit is observed, and only fine crystals are observed. No outbreaks have been seen, it takes! According to the investigation results, the conventional method using a combination of a surfactant and a water-insoluble vinyl polymer compound (Japanese Patent Publication No. 11330/1983)
It can be seen that the anti-caking effect of the present invention is achieved by a different effect from the above.

In addition, considering that the surfactant coating applied to acidic ammonium fluoride particles has almost no anti-caking effect,
The surfactant coating cannot suppress the hygroscopicity of the acidic ammonium fluoride particles. On the other hand, in the present invention, since the coating itself has a certain degree of hygroscopicity, the coating absorbs moisture that enters from the outside and absorbs moisture inside one particle. It is thought that this serves to prevent moisture from entering.

[Effects of the Invention] According to the method of the present invention, caking of acidic ammonium fluoride is easily and effectively prevented.

Unlike conventional methods that use a surfactant and vinyl polymer in combination, the method of the present invention uses a water-soluble vinyl polymer compound alone, so the process of dissolving the polymer and surfactant in the conventional method is eliminated. This is not necessary, and work efficiency is greatly improved. Further, since no surfactant is used, various disadvantages caused by the presence of surfactants (for example, after etching the glass, the surfactant remains on the glass surface and interferes with subsequent steps) can be avoided.

[Examples and Comparative Examples] Examples 1 to 5 of the present invention will be shown in comparison with comparative examples.
% or more) and a water-soluble vinyl polymer compound as an anti-caking agent, was placed in two plastic bags containing 1 kg of human milk. After sealing, each bag was loaded with 5 (10 kg/rn'). The bag was stored for 15 days in a work room with relative humidity of 60%.Then, the load was removed, one bag was opened gently, and the other bag was allowed to fall naturally from a height of 1m, and then opened and stored at a height of 5m. The lumps and powder were gently separated using a +l+ sieve, the weight of what remained on the sieve was taken as the remaining lump weight, and the remaining lump ratio (residual lump weight/total weight) was measured.The results are shown in the following table.

Comparative Example Example 1 except that no water-soluble vinyl polymer compound was added.
The remaining lump ratio was measured in the same manner as in 5. The results are shown in comparison in the table below.

Claims (1)

[Claims] A method for preventing caking of acidic ammonium fluoride, characterized by adding a water-soluble vinyl polymer compound alone as an anti-caking agent.