JP2014065663A - Gypsum dissolution agent and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive gypsum dissolution liquid capable of dissolving deposited gypsum without causing damage to containers, tools or the like for mixing, application, or processing, the gypsum dissolution liquid solving the problem in which many of the conventional gypsum dissolution liquid agents are alkaline solution whose pH is 8 or more, and pH of some removers is 13 or more, and they are safer for operators than strong acids, decreasing the risk of corroding stainless steel materials, but there is a risk of corroding containers, tools or the like made of non-ferrous metal such as aluminium which is vulnerable to alkali.SOLUTION: The gypsum dissolution agent contains chelating agent, organic acid, alkali agent, and water, and has a pH of 7.5-8.0.

Description

  TECHNICAL FIELD The present invention relates to a gypsum dissolving agent for dissolving gypsum adhering to containers, instruments, and the like for kneading, application, and processing in work / art and dental applications, and a method for producing the same.

  Gypsum has been widely used since the past because it is inexpensive, fast-curing, and can maintain its hardness when it is "shaped" for work, art and dental use. However, gypsum adhering to containers, instruments to be kneaded, coated, processed is hard to peel off due to its high hardness and high hardness, and there is a risk of damaging the containers, instruments if removed physically such as by shaving.

  Since the composition of gypsum is calcium sulfate, heating with strong acid such as hydrochloric acid or perchloric acid will dissolve gypsum easily, but the gas generated from hydrochloric acid and perchloric acid is dangerous for the safety of workers. In addition, stainless steel used in many appliances cannot be used because of corrosion caused by hydrochloric acid and perchloric acid. For this reason, a mechanism for dissolving a gypsum by extracting a calcium ion contained in the gypsum by using a chelating agent as a main component is reported (for example, Patent Document 1), and a solution using this mechanism is sold.

  However, most of the gypsum solution for sale sold on the market is an alkaline solution having a pH of 8 or higher, and some removing agents have a pH of more than 13. The safety of workers is superior to that of strong acids. Although the risk of corrosion is reduced, it may corrode containers and instruments made of non-ferrous metals such as aluminum which is weak against alkali.

Further, ethylenediaminetetraacetic acid is often used as a calcium ion chelating agent, but has a high chelating effect (CV (Chelation
Since the acid type (with a large value) has low water solubility, it is necessary to neutralize with an alkali and convert it to the sodium salt type. Although there is information that a lot of ethylenediaminetetraacetic acid trihydrogen sodium salt is used in actual products, using ethylenediaminetetraacetic acid sodium salt type improves water solubility but decreases CV and lowers the chelating effect (CV is 0.65 times the acid type) Therefore, if the gypsum dissolution effect is expected, it is necessary to add about 1.5 times the amount.
The solubility of the chelating agent in water is approximately 0.1 wt% (pH 7) and 25 wt% (pH 9), and it has been found that it decreases with a decrease in pH. Therefore, the amount of the aqueous solution having a pH of about 8 is limited, so an expensive acid type must be added. See Patent Document 1.

JP 2006-292407 A

  Therefore, an inexpensive gypsum dissolving agent capable of dissolving adhering gypsum without damaging kneading, coating and processing containers and instruments, and a method for producing the same.

  As a result of intensive studies, the present inventors have completed the gypsum solubilizer of the present invention and a method for producing the same, and are characterized by a chelating agent, an organic acid, It has an alkaline agent and water, and the pH is 7.5 to 8.0. In the production method, a chelating agent and an organic acid are mixed with water adjusted to pH 8 to 9, and finally It exists in the point which adjusts pH to 7.5-8.0.

The chelating agent used here is preferably ethylenediaminetetraacetic acid sodium salt or a hydrate thereof. One of the features is the use of an inexpensive sodium salt type.
The chelating agent (calcium ion chelating agent) used in the present invention is ethylenediaminetetraacetic acid sodium, ethylenediaminetetraacetic acid trihydrogensodium salt, ethylenediaminetetraacetic acid dihydrogensodium salt, ethylenediaminetetraacetic acid monosodium salt sodium trihydrogenate and the like. Salts and their hydrates. In particular, ethylenediaminetetraacetic acid tetrasodium, such as Kirest 400 (trade name, manufactured by Kirest Co., Ltd.) and Trilon B (trade name, BASF JAPAN) are excellent in solubility in water and are easy to handle.
The mixing amount (concentration in the dissolving agent) of these chelating agents is 10 to 25 wt%, preferably 15 to 20 wt%.

The organic acid used in the present invention has a carboxylic acid group at the end and is not limited as long as it is generally blended with a cleaning agent. For example, malic acid, citric acid, lactic acid, oxalic acid, Examples include tartaric acid and benzoic acid. In particular, malic acid and citric acid having a high chelating effect exhibit a synergistic effect on gypsum dissolution when used in combination with ethylenediaminetetraacetic acid sodium salt.
The mixing amount (concentration in the dissolving agent) of these organic acids is preferably 1 wt% to 5 wt%, and more preferably 2 to 3.5 wt%. This is because it is desirable to contain 10 wt% to 20 wt% of the amount of chelating agent. If it is less than 10%, the gypsum dissolving power decreases in proportion to the content. If it exceeds 20%, the solubility in water with the chelating agent has an upper limit, and there is a risk that it will be undissolved or co-precipitated in a low temperature range.

  The alkali agent may be a normal one. For example, sodium hydrogen carbonate, sodium hydroxide, potassium hydroxide and the like. The mixing ratio may be determined by the final pH or the like, but is usually 1 to 5 wt%.

  What added water to this is a necessary component of the solubilizer of the present invention, but other components such as a fragrance, a colorant and the like may be mixed therein without departing from the spirit of the present invention. Furthermore, the necessary components of the present invention may be mixed in any way, and an alkali agent and an organic acid may be added in several portions.

The gypsum solubilizing agent according to the present invention is finally adjusted to pH 7.5 to 8.0. What is necessary is just to adjust this with the mixing ratio of each component.
When the pH of the dissolving agent itself exceeds 8.0, the gypsum solubility starts to decrease, and when the pH exceeds 9.0, the gypsum hardly dissolves. This is because the chelate formation reaction is affected by the pH, and when the pH is increased, the coordination bond of the OH group becomes dominant to the metal ion, and the generated hydroxide tends to polymerize. It is presumed that this is because it is difficult to bond with the metal ion through the OH group.
On the other hand, when the pH is lower than 7.5, the added sodium hydrogen carbonate starts to react and carbon dioxide gas is generated.

Next, the manufacturing method of the present invention will be described.
As described above, the components of the present invention may be mixed in any order, but there is a method in which water is first prepared and components are sequentially added thereto. Then, the first water whose pH is adjusted to 8-9 is used. This is the invention of claim 4.
The water adjusted to pH 8-9 is water adjusted to pH 8-9 by adding an alkali such as potassium hydroxide or sodium hydroxide. Ion exchange water, reverse osmosis membrane water (RO water), distilled water, and tap water are all targets.

According to the present invention, it has become possible to provide a gypsum solution characterized by using an inexpensive chelating agent and an organic acid and further suppressing the corrosion of metal equipment by making the pH neutral.
Furthermore, it is used as a removing agent and a dissolving agent for gypsum used for art and dentistry, but it is used in gypsum applications and in plants where gypsum is produced by chemical reaction. Since there is no concern about corrosion of pipes, pipes, and devices, it can be used widely.

It is a graph which shows the relationship between pH and solubility.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples. A chelating agent, an organic acid, and an alkali agent were blended in an arbitrary ratio, and gypsum was dissolved to evaluate dissolution performance.
The blending ratio is as shown in Table 1.

Table 1 will be described in detail.
In Example 1, 74% by weight of ion-exchanged water adjusted to pH 8.8, 20% by weight of Kirest 400 as a chelating agent, 3% by weight of malic acid (special reagent grade, manufactured by Kanto Chemical Co.) as an organic acid, sodium bicarbonate (reagent) 3 wt% of a special grade (manufactured by Kanto Chemical Co., Inc.) was prepared and mixed and stirred in this order.
Stirring is a method generally used when mixing solutions, and any method such as a method of rotating a stirring bar using magnetic force and a method of adding a stirring blade into the liquid and stirring can be used. There is no need to use a method.

  The ion-exchanged water whose pH has been adjusted is ion-exchanged water that has been adjusted beforehand with sodium hydroxide (special grade reagent, manufactured by Kanto Chemical Co., Inc.) so that the pH becomes 8.8. The pH of the solution after mixing and stirring was 7.7.

  In Example 2, 73 wt% ion-exchanged water adjusted to pH 8.8, 20 wt% Trilon B as a chelating agent, 3.5 wt% citric acid (special grade reagent, manufactured by Kanto Chemical Co., Ltd.) as an organic acid, and sodium bicarbonate 3.5 wt% was prepared and mixed and stirred in this order. The pH of the solution after mixing and stirring was 7.6.

  Comparative Example 1 is 60 wt% reverse osmosis membrane water adjusted to pH 6.7, 15 wt% 48% sodium hydroxide, and 20 wt% Kirest 110 (trade name, manufactured by Kirest Co., Ltd .: ethylenediaminetetraacetic acid type) as a chelating agent. 5 wt% of sodium hydrogen carbonate was prepared and mixed and stirred in this order. The pH of the solution after mixing and stirring was 8.7.

  Comparative Example 2 is prepared by preparing 75 wt% of ion-exchanged water adjusted to pH 8.8, 20 wt% of cherest 400 as a chelating agent, 1.5 wt% of malic acid as an organic acid, and 3.5 wt% of sodium hydrogen carbonate, Mixing and stirring were performed in this order. The pH of the solution after mixing and stirring was 8.5.

  In Comparative Example 3, 71 wt% of ion-exchanged water adjusted to pH 8.8, 20 wt% of Kirest 400 as a chelating agent, phosphoric acid (reagent special grade, manufactured by Kanto Chemical Co., Ltd.) instead of malic acid for comparison with Example 1 6 wt% and sodium hydrogen carbonate 3 wt% were prepared and mixed and stirred in this order. The pH of the solution after mixing and stirring was 7.7.

  In Comparative Example 4, 75 wt% of ion-exchanged water adjusted to pH 8.8, 25 wt% of Kirest 400 as a chelating agent, and 5 wt% of sodium hydrogen carbonate were prepared and mixed and stirred in this order. The pH of the solution after mixing and stirring was 9.5.

The results of the gypsum dissolution test using these solutions are shown in Table 2. In this gypsum dissolution test, water 6 (weight ratio) is mixed with commercially available calcined gypsum (dental calcined gypsum, Yoshino Gypsum Sales Co., Ltd.) 10 and kneaded well. In this test, the solution is put into a 20 g container after drying and solidification, and the solubility of gypsum after 1 hour, 6 hours and 12 hours is measured. The solubility indicates the initial gypsum weight as 100, and the weight reduction rate is shown as solubility.

  It can be seen from Table 2 that gypsum dissolves rapidly and well in Examples, and Comparative Examples have low solubility except for Comparative Example 1 and Comparative Examples 3 and 4 cannot be used very much.

Next, in order to evaluate the corrosiveness of the test solution, 20 g of each of Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 were collected in a disposable aluminum foil cup, and the state was confirmed over time. The results are shown in Table 3. Here, ○: Abnormalities such as corrosion are not seen in the cup, △: Part of the cup is damaged (dissolution such as foaming is seen), ×: Problems such as damage to the cup and spilled solution occur Represents.

  From this table, it can be seen that there is almost no corrosiveness in the examples, and that all the comparative examples are corrosive.

  Finally, the relationship between the solubility of the present invention and pH was examined. Using the solubilizer of Example 2, the final pH was variously changed to measure the solubility. The result is shown in FIG. It is the data for 3 hours after immersion. From this figure, it can be seen that the pH is preferably 7.5 to 8.0.

Claims (4)

  A gypsum solubilizer having a chelating agent, an organic acid, an alkaline agent, and water, and having a pH of 7.5 to 8.0.   The gypsum solution according to claim 1, wherein the content of each component is 60 to 80 wt% water, 10 to 30 wt% chelating agent, 1 to 5 wt% organic acid, and 1 to 10 wt% alkaline agent.   The gypsum solution according to claim 1 or 2, wherein the chelating agent is sodium ethylenediaminetetraacetate.   A method for producing a gypsum dissolving agent, comprising mixing a chelating agent and an organic acid in water adjusted to pH 8 to 9, and finally adjusting pH to 7.5 to 8.0.

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