JP5610135B2 - Metal cleaning method - Google Patents

Description

  The present invention relates to a method for cleaning a metal, and more particularly to a method for cleaning a metal using a cleaning agent comprising an aqueous solution of an alkali metal silicate.

  Medical instruments, cooking utensils, heat exchangers and electronic components using copper-based metal materials, and parts using lightweight metal materials such as aluminum used in vehicles, aircraft, ships, etc., proteins, polysaccharides, lipids, In cleaning metal products that are susceptible to contamination by oils and fats or solvents, it is common to use alkaline cleaners that have a low environmental impact instead of chlorinated or chlorofluorocarbon organic solvents. In addition, for medical instruments, particularly surgical instruments, cleaning at 70 ° C. or higher using an alkaline detergent is preferred from the viewpoint of enhancing the cleaning effect, and it is a causative factor for mutant Creutzfeldt-Jakob disease. From the viewpoint of preventing contamination with infectious prion protein, washing at 90 ° C. or higher using an alkaline detergent is preferred (for example, Non-Patent Document 1).

  As a method for cleaning a metal product using an alkali cleaner, Patent Document 1 discloses a nonionic surfactant, an alkali metal silicate, hydroxide, carbonate or bicarbonate, and an acrylic copolymer. A method of immersing a metal product in an aqueous solution of a cleaning agent containing coalescence is described. Patent Document 2 describes a method in which a metal product is immersed in an aqueous solution of a cleaning agent containing an alkali metal hydroxide compound, a calcium compound, and a polycarboxylic acid or a salt thereof in a predetermined ratio.

  Although the cleaning method described in Patent Document 1 can be cleaned without corroding easily corroded metal products such as copper and tin, the temperature assumed for use is about 40 ° C. at most. In some cases, metal products may be corroded when cleaning at a high temperature of 70 ° C. or higher, particularly when cleaning at a high temperature of 90 ° C. or higher. On the other hand, the cleaning method described in Patent Document 2 can effectively clean metal products using light metals such as aluminum while suppressing the generation of scale and at the same time suppressing corrosion. A metal product using a metal can be cleaned while suppressing generation of scale, but it is difficult to suppress corrosion.

Takeshi Iwaki, Washing Disinfector's cleaning effect and prion effect, medical science, Vol. 76, no. 11 (2006), pages 784-791.

JP, 5-43897, A Claims, [0005], [0025], [0034], [0037] etc. JP, 2004-51761, A Claims, [0001], [0004], [0024], etc.

  An object of the present invention is to enable cleaning at a high temperature without corroding various metals while suppressing the generation of scale in the case of cleaning a metal using a cleaning agent comprising an aqueous solution of an alkali metal silicate. is there.

The present invention is a method for cleaning a metal using a cleaning agent composed of an aqueous solution in which an alkali metal silicate is dissolved in water substantially free of calcium ions . A step of preparing a cleaning liquid to which an additive comprising an aqueous solution containing a calcium salt and a scale dispersant is added, the calcium salt concentration being set to at least 20 mg / kg in terms of calcium carbonate; Immersing the metal in the washed liquid. Here, the additive is added to the cleaning agent so that the concentration of the scale dispersant in the cleaning liquid is not less than the concentration specified by the following formula (a) and not more than the concentration specified by the following formula (b). ing.

  The metal cleaned by the cleaning method of the present invention is, for example, a copper-based metal.

  Since the metal cleaning method according to the present invention includes the above-described steps, a cleaning agent composed of an aqueous solution of an alkali metal silicate is used, and cleaning is performed at a high temperature without corroding various metals while suppressing generation of scale. be able to.

The graph which shows the result of Experimental example 4. The graph which shows the result of Experimental example 5.

  The cleaning method of the present invention is a method for cleaning a metal using a cleaning agent. The metal that can be cleaned by this cleaning method is not particularly limited, and examples thereof include copper, tin, iron, zinc, magnesium, aluminum, and alloys thereof. In particular, the cleaning method of the present invention includes a medical instrument (for example, a surgical instrument such as a brain vera or Cusco), a cooking instrument, a heat exchanger (for example, a cupper) such as copper or a copper alloy (for example, brass). Heat exchangers such as heat pumps and cooling towers) and electronic parts, and various parts such as vehicles, aircraft and ships using lightweight metals such as aluminum and magnesium, etc., with proteins, polysaccharides, lipids, fats and oils, or solvents Suitable for cleaning metal products that are susceptible to contamination.

The cleaning agent used in the present invention is an aqueous solution in which an alkali metal silicate is dissolved in water. The alkali metal silicate is a compound represented by a general formula of M ₂ O · nSiO ₂ and has a cleaning action on a metal. In the general formula, M represents sodium (Na) or potassium (K), and n is a real number of 1 to 4. The alkali metal silicate may be a hydrate. Two or more alkali metal silicates may be used in combination. The water used to prepare the aqueous solution of the cleaning agent is tap water, industrial water, softened water from which hardness components (calcium ions and magnesium ions) are removed by treating these waters with an ion exchange resin, and ions Purified water such as exchange water, distilled water, reverse osmosis water, and pure water. Among these waters, preferred are water substantially free of hardness components such as softened water and distilled water, particularly water substantially free of calcium ions.

The concentration of the alkali metal silicate in the cleaning agent is usually set so that the concentration when the cleaning liquid is prepared by adding the additives described later is 100 to 600,000 mg / kg in terms of silica (SiO ₂ ). Is preferable, and it is more preferable to set to 500 to 300,000 mg / kg.

  The cleaning agent can also be prepared by dissolving an alkali metal hydroxide and a silicon compound in water. In this case, the alkali metal hydroxide dissolved in water reacts with the silicon compound to produce the required alkali metal silicate, and the desired cleaning agent is obtained.

  The alkali metal hydroxide used here is usually potassium hydroxide or sodium hydroxide. In addition, silicon dioxide, sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, sodium metadisilicate, potassium metadisilicate, sodium orthosilicate, and potassium orthosilicate may be used as the silicon compound. it can. The usage-amount of an alkali metal hydroxide and a silicon compound is set so that the density | concentration of the alkali metal silicate produced | generated in aqueous solution may become the above-mentioned density | concentration.

  When the metal is cleaned by the method of the present invention, a cleaning solution is prepared from the above-described cleaning agent. In the preparation of this cleaning solution, a predetermined additive is added to the cleaning agent. The additive used here consists of an aqueous solution containing a calcium salt and a scale dispersant.

  Examples of calcium salts that can be used include calcium hydroxide, calcium acetate, calcium chloride, calcium carbonate, calcium bromide, calcium iodide, and calcium nitrate. Of these, water-soluble ones such as calcium acetate, calcium chloride, calcium bromide, calcium iodide and calcium nitrate are preferred. Two or more calcium salts may be used in combination.

  The concentration of the calcium salt in the additive can be appropriately set within a range not exceeding the solubility.

  The scale dispersant is for suppressing the generation of scale in the metal to be cleaned. Usually, the acrylic polymer, acrylate polymer, acrylic copolymer, acrylate copolymer Polymer, maleic acid polymer, maleate polymer, maleic acid copolymer, maleate copolymer, phosphinocarboxylic acid polymer, phosphinocarboxylate polymer, phosphinocarboxylic acid copolymer and phosphinocarboxylic acid copolymer A polymer, particularly a water-soluble polymer, such as a finocarboxylate copolymer, which can suppress adhesion and deposition to an object to be cleaned by dispersing scale crystal nuclei in a solution. Two or more kinds of scale dispersants may be used in combination.

Examples of monomers constituting the above-mentioned various copolymers that can be used as a scale dispersant include acrylic acid and salts thereof, acrylic acid esters, methacrylic acid and salts thereof, methacrylic acid esters, acrylonitrile, acrylamide, and maleic acid. And salts thereof, maleic anhydride, itaconic acid, styrene, styrenesulfonic acid and salts thereof, vinylpyrrolidone, vinyl acetate, isobutene, 2-acrylamido-2-methylpropanesulfonic acid, methallylsulfonic acid and salts thereof, vinylsulfonic acid And salts thereof, allylsulfonic acid and salts thereof, and carbon monoxide, which can be selected according to the type of copolymer.

  Examples of the salt of the monomer constituting the polymer include alkali metal salts such as sodium and potassium, ammonium salts, and amine salts such as triethylamine salt, triethanolamine salt, and diisopropylamine salt. Metal salts are preferred.

  The weight average molecular weight of the above-mentioned polymer used as a scale dispersant is usually preferably from 100 to 100,000, more preferably from 1,000 to 10,000. When the molecular weight is less than 100 or exceeds 100,000, there is a possibility that a sufficient scale dispersion effect cannot be obtained.

  The density | concentration of the scale dispersing agent in an additive can be suitably set in the range which does not exceed solubility.

  The additive can be prepared by dissolving a calcium salt and a scale dispersant in water. The water used here is usually purified water such as ion-exchanged water, distilled water, reverse osmosis water, and pure water. However, water containing hardness components, that is, calcium ions and magnesium ions, such as tap water, should be added. In this case, the calcium ion concentration may be increased.

  Adjust the amount of additive added to the cleaning solution so that the concentration of the scale dispersant is not less than the concentration specified by the following formula (a) and not more than the concentration specified by the following formula (b). To prepare. In each formula, the calcium salt concentration means the concentration of ionic and nonionic (for example, dispersed colloidal) calcium salts that are not sequestered by a chelating agent or the like. This calcium salt concentration means a concentration in terms of calcium carbonate. For example, when calcium chloride (formula amount: 111) is used in the additive, the formula amount of calcium carbonate is 100. Therefore, when the concentration of calcium chloride is multiplied by 0.9, it can be expressed as a concentration in terms of calcium carbonate. .

  The cleaning solution is set so that the calcium salt concentration is at least 20 mg / kg in terms of calcium carbonate at the same time. The significance of this calcium salt concentration is the same as the calcium salt concentration in formulas (a) and (b).

  The calcium salt concentration of the cleaning liquid can be usually adjusted by calcium ions as a hardness component contained in water when the calcium salt contained in the additive and water containing a hardness component are used at the time of preparation of the additive. Moreover, it can also adjust by adding the water containing a hardness component further to a washing | cleaning liquid.

  In the cleaning liquid, if the concentration of the scale dispersant and the calcium salt concentration do not satisfy the above conditions, cleaning while simultaneously suppressing corrosion and scale generation of the object to be cleaned, especially suppressing corrosion and scale generation of the object to be cleaned at the same time. However, it may be difficult to clean at a high temperature of 70 ° C. or higher.

  If the cleaning liquid is left for a long time after preparation, the function of the scale dispersant may be impaired due to the influence of the alkali metal silicate. For this reason, it is preferable to prepare the cleaning liquid when cleaning the object to be cleaned.

  In cleaning the object to be cleaned, the object to be cleaned is immersed in the prepared cleaning liquid, and left for a predetermined time while stirring the cleaning liquid as necessary. At this time, the cleaning liquid can be heated. The heating temperature can be set to, for example, a high temperature of 70 ° C. or higher and lower than the boiling temperature of the cleaning liquid. Moreover, it is preferable that the metal product after immersion is usually dried after being rinsed with purified water from which hardness components have been removed, such as distilled water or softened water.

  In the cleaning method of the present invention, it is possible to effectively remove proteins, polysaccharides, lipids, fats and oils, solvents and other dirt adhered to the object to be cleaned while suppressing the corrosion of the object to be cleaned. It can suppress that a scale generate | occur | produces in the to-be-washed | cleaned material after drying. Furthermore, when the object to be cleaned is a medical instrument such as a surgical instrument, the object to be cleaned can be immersed in a cleaning liquid set at a high temperature of 90 ° C. or higher, so that it may adhere to the medical instrument. Infectious prion protein can be removed at the same time. Therefore, the cleaning method of the present invention is particularly suitable as a method for cleaning a medical instrument, particularly a medical instrument made of a copper-based metal.

<Experimental example>
The component materials and test pieces of the cleaning liquid used in the following experimental examples are as follows.

(Component material)
Alkali metal hydroxide: potassium hydroxide silicon compound: sodium calcium silicate salt: calcium chloride scale dispersant: maleic acid copolymer (trade name “Belclean 283” manufactured by BioLab Water Additive Co., Ltd .: solid content 50% by weight)
Water: distilled water

(Test pieces)
Copper specimen:
A copper test piece (C1220) polished with # 400 abrasive paper was washed with water, degreased with acetone, then dried and weighed.
Copper alloy specimen:
A copper alloy specimen (C2801) polished with # 400 abrasive paper was washed with water, degreased with acetone, then dried and weighed.
Aluminum specimen:
An aluminum test piece (A1050) immersed in nitric acid (4 + 1) at room temperature for about 10 minutes was washed with water, degreased with acetone, then dried and weighed.
Aluminum alloy specimen:
An aluminum alloy specimen (A2024) immersed in nitric acid (4 + 1) at room temperature for about 10 minutes was washed with water, degreased with acetone, then dried and weighed.

Experimental example 1
An alkali metal hydroxide, a silicon compound, a calcium salt, and a scale dispersant are dissolved in water. The alkali metal hydroxide concentration is 260 mg / kg, the silicon compound concentration (silica conversion concentration) is 720 mg / kg, and the calcium salt concentration (carbonic acid). A cleaning liquid comprising an aqueous solution having a calcium equivalent concentration of 26 mg / kg and a scale dispersant concentration (solid content concentration) of 20 mg / kg was prepared. The silicon compound concentration (concentration in terms of silica) is that the formula amount of sodium silicate (Na ₂ SiO ₃ ) is 122 whereas the formula amount of silica (SiO ₂ ) is 60, so the concentration of sodium silicate Is obtained by multiplying by 0.49.

Experimental example 2
An alkali metal hydroxide, a silicon compound and a scale dispersant are dissolved in water, and the alkali metal hydroxide concentration is 260 mg / kg, and the silicon compound concentration (silica conversion concentration: determined by the same method as in Experimental Example 1) is 720 mg. / Kg and a cleaning liquid composed of an aqueous solution having a scale dispersant concentration (solid content concentration) of 20 mg / kg was prepared.

Experimental example 3
An alkali metal hydroxide, a calcium salt and a scale dispersant are dissolved in water. The alkali metal hydroxide concentration is 260 mg / kg, the calcium salt concentration (calcium carbonate equivalent concentration) is 26 mg / kg, and the scale dispersant concentration (solid content). A cleaning solution consisting of an aqueous solution having a concentration of 20 mg / kg was prepared.

Evaluation of experimental examples 1 to 3 (cleaning status)
About the washing | cleaning liquid of Experimental example 1, the washing | cleaning condition was evaluated using the TOSI washing | cleaning evaluation indicator by a PEREG GmbH. Specifically, the indicator was immersed in the cleaning liquid, and the cleaning liquid was heated to 80 ° C. with stirring, and then the indicator was rinsed with distilled water. And the residual protein of the indicator was confirmed visually and evaluated according to the following criteria. The results are shown in Table 3.

Level 0: It has been completely cleaned and the soiled parts have been completely decomposed and removed.
Level 1: There is very little white residue.
Level 2: There is a white residue.
Level 3: There is a red residue.

(Corrosion status)
About the washing | cleaning liquid of Experimental Examples 1-3, the corrosion condition was evaluated using each above-mentioned test piece. Specifically, the cleaning liquid was heated to adjust the temperature to 78 to 80 ° C., and flowed so that the flow rate was 0.9 to 1.1 m / s in the pipe. And each test piece fastened to the fixing metal fitting was immersed in the cleaning liquid flowing in the pipe and cleaned for 6 hours. Thereafter, the degree of corrosion (mdd) was determined from the weight difference between the test pieces before and after cleaning, and was rated according to the criteria shown in Table 1. The results are shown in Table 3.

  The rating for the degree of corrosion is based on the ratings A, B, and C described in page 3 of the Industrial Materials Handbook (Nikkan Kogyo Shimbun, first edition published on October 30, 1981). B3 is subdivided into three stages. The weight of the test piece after washing was measured as follows. For copper test pieces and copper alloy test pieces, wipe the test pieces after washing with gauze, immerse them in about 10% sulfuric acid at room temperature for 5 minutes, wash them with water, further degrease them with acetone and dry them. It was measured. For aluminum test pieces and aluminum alloy test pieces, wipe the test pieces after washing with gauze, immerse them in nitric acid (4 + 1) at room temperature for 10 minutes, wash with water, degrease them with acetone, and dry them. Was measured.

(Presence / absence of scale)
About the washing | cleaning liquid of Experimental Examples 1-3, the presence or absence of scale generation | occurrence | production was determined with the amount of floating substances after preparing a washing | cleaning liquid. Specifically, a fixed volume of the prepared cleaning liquid was allowed to stand for 2 hours, and then filtered through a membrane filter, and the amount of suspended solids captured by the filter was measured. Here, the amount of suspended solids and the visual determination result of scale generation on the test piece in the corrosion state evaluation have a relationship as shown in Table 2. For this reason, when the amount of suspended solids was less than 4 mg / L, no scale was generated, and when it was 4 mg / L or more, it was determined that scale was generated. The results are shown in Table 3.

Experimental Example 4
An alkali metal hydroxide, a silicon compound, a calcium salt, and a scale dispersant were dissolved in water to prepare a cleaning solution. Here, the alkali metal hydroxide concentration is set to 260 mg / kg, the silicon compound concentration (silica conversion concentration: determined by the same method as in Experimental Example 1) is set to 720 mg / kg, and the calcium salt and scale dispersion are set. Thirteen types of cleaning liquids were prepared in which the calcium salt concentration (calcium carbonate equivalent concentration) and scale dispersant concentration (solid content concentration) were set as shown in Table 4 by changing the amount of the agent used.

  About each washing | cleaning liquid, the corrosion condition was investigated by the method similar to evaluation of Experimental Examples 1-3. The results are shown in Table 4 and FIG. FIG. 1 is a graph of the results in Table 4.

  According to Table 4 and FIG. 1, in the case where the cleaning liquid contains the scale dispersant so that the calcium salt concentration is 20 mg / kg or more and the concentration of the scale dispersant is equal to or less than the concentration defined by the formula (b). It is difficult to cause corrosion on the test piece.

Experimental Example 5
An alkali metal hydroxide, a silicon compound, a calcium salt, and a scale dispersant were dissolved in water to prepare a cleaning solution. Here, the alkali metal hydroxide concentration was set to 260 mg / kg, the silicon compound (silica conversion concentration: determined by the same method as in Experimental Example 1) was set to 720 mg / kg, and the calcium salt and the scale dispersant Twelve types of cleaning liquids were prepared in which the calcium salt concentration (calcium carbonate equivalent concentration) and the scale dispersant concentration (solid content concentration) were set as shown in Table 5 by changing the amount used.

  About each washing | cleaning liquid, the presence or absence of scale generation | occurrence | production was investigated by the method similar to evaluation of Experimental Examples 1-3. The results are shown in Table 5 and FIG. FIG. 2 is a graph of the results in Table 5.

  According to Table 5 and FIG. 2, in the case where the cleaning liquid contains the scale dispersant such that the calcium salt concentration is 20 mg / kg or more and the concentration of the scale dispersant is equal to or higher than the concentration defined by the formula (a). It is difficult to attach the scale to the test piece.

Claims (2)

A method for cleaning a metal using a cleaning agent comprising an aqueous solution in which an alkali metal silicate is dissolved in water substantially free of calcium ions ,
A step of preparing a cleaning solution in which an additive comprising an aqueous solution containing a calcium salt and a scale dispersant is added to the cleaning agent, the calcium salt concentration being set to at least 20 mg / kg in terms of calcium carbonate; ,
Immersing the metal in the cleaning liquid set at 70 ° C. or higher,
The additive is added to the cleaning agent so that the concentration of the scale dispersant in the cleaning liquid is not less than the concentration specified by the following formula (a) and not more than the concentration specified by the following formula (b). Being
Metal cleaning method.

  The metal cleaning method according to claim 1, wherein the metal is a copper-based metal.

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