Composition for etching treatment of resin material

Abstract

The present invention provides a composition for etching treatment of a resin material, the composition comprising an aqueous solution having a permanganate ion concentration of 0.2 mmol/L or more and a total acid concentration of 10 mol/L or more, and the aqueous solution satisfying at least one of the following conditions (1) to (3): (1) containing an organic sulfonic acid in an amount of 1.5 mol/L or more, (2) setting the divalent manganese ion molar concentration to 15 or more times higher than the permanganate ion molar concentration, and (3) setting the addition amount of an anhydrous magnesium salt to 0.1 to 1 mol/L. The composition for etching treatment of the present invention is a composition containing no hexavalent chromium and having excellent etching performance and good bath stability.

Claims

1. A composition for etching treatment of a resin material, the composition comprising an aqueous solution having a permanganate ion concentration of 0.2 mmol/L or more and a total acid concentration of 10 mol/L or more, and the aqueous solution satisfying at least one of the following conditions (1) to (3): (1) containing an organic sulfonic acid in an amount of 1.5 mol/L or more, (2) containing a divalent manganese ion in a molar concentration of 15 or more times higher than the permanganate ion molar concentration, and (3) containing an anhydrous magnesium salt in an amount of 0.1 to 1 mol/L.

2. The composition according to claim 1, wherein the permanganate ion is formed by subjecting a divalent manganese ion to electrolytic oxidation in the aqueous solution.

3. The composition according to claim 1, wherein the permanganate ion is formed by dissolving a permanganate salt in the aqueous solution.

4. The composition according to claim 1, wherein the aqueous solution satisfies condition (1), and the organic sulfonic acid is an aliphatic sulfonic acid having one to five carbon atoms.

5. The composition according to claim 1, wherein the aqueous solution satisfies condition (2), and the aqueous solution is prepared by adding a permanganate salt to an aqueous acid solution containing a divalent manganese ion.

6. The composition according to claim 1, wherein the aqueous solution satisfies condition (3), and the anhydrous magnesium salt is at least one member selected from the group consisting of anhydrous magnesium sulfate, anhydrous magnesium chloride, and anhydrous magnesium nitrate.

7. The composition according to claim 1, wherein the aqueous solution satisfies condition (3).

8. An etching treatment process of a resin material, comprising bringing the composition according to claim 1 into contact with a surface of a resin material to be treated.

9. A process for plating a resin material, comprising etching the resin material by the process of claim 8, then applying an electroless plating catalyst, and subsequently performing electroless plating.

10. A process for controlling the composition according to claim 1, the process comprising condensing the composition by heating when the volume of the composition is increased.

11. A process for controlling the composition according to claim 1, the process comprising blowing ozone gas into the composition when the permanganate ion concentration in the composition is decreased.

12. The composition according to claim 2, wherein the aqueous solution satisfies condition (1), and the organic sulfonic acid is an aliphatic sulfonic acid having one to five carbon atoms.

13. The composition according to claim 3, wherein the aqueous solution satisfies condition (1), and the organic sulfonic acid is an aliphatic sulfonic acid having one to five carbon atoms.

14. An etching treatment process of a resin material, comprising bringing the composition according to claim 2 into contact with a surface of a resin material to be treated.

15. An etching treatment process of a resin material, comprising bringing the composition according to claim 3 into contact with a surface of a resin material to be treated.

16. An etching treatment process of a resin material, comprising bringing the composition according to claim 4 into contact with a surface of a resin material to be treated.

17. An etching treatment process of a resin material, comprising bringing the composition according to claim 5 into contact with a surface of a resin material to be treated.

18. An etching treatment process of a resin material, comprising bringing the composition according to claim 6 into contact with a surface of a resin material to be treated.

19. A process for controlling the composition according to claim 2, the process comprising condensing the composition by heating when the volume of the composition is increased.

20. A process for controlling the composition according to claim 3, the process comprising condensing the composition by heating when the volume of the composition is increased.

21. A process for controlling the composition according to claim 4, the process comprising condensing the composition by heating when the volume of the composition is increased.

Description

DESCRIPTION OF EMBODIMENTS

(1) The Examples below describe the present invention in more detail.

Examples 1 to 6 and Comparative Examples 1 to 4

(1) Production of Composition for Etching Treatment

(2) Using an electrolytic cell separated into an anode chamber and a cathode chamber by a separating membrane, an aqueous solution (500 mL) containing a divalent manganese salt and an organic sulfonic acid according to the composition shown in Table or 2 was introduced into the anode chamber, and a 98% aqueous sulfuric acid solution (250 ml, 300 ml/L) was introduced into the cathode chamber.

(3) Subsequently, electrolytic oxidation was performed at an anode current density of 5 A/dm.sup.2 by using a Pt/Ti plate as the anode and an SUS 316 plate as the cathode. With the energization rate in 10-Ah/L increments, the concentration of the permanganate ion in the aqueous solution in the anode chamber was quantified by redox titration using a 2.0 g/L aqueous ascorbic acid solution. After the analysis value of the permanganate ion concentration showed no change and remained constant, the aqueous solution was used as an etching treatment agent. Note that the analysis value (mmol/L) of permanganate ion shown in the tables is the value obtained after remaining constant.

(4) TABLE-US-00001 TABLE 1 Example Compound 1 2 3 4 5 6 Addition Manganese 7 70 35 70 amount sulfate (mmol/L) (II) Manganese 70 35 70 carbonate (II) Analysis value of 0.40 4.4 4.1 4.2 4.3 4.2 permanganate ion obtained after electrolytic oxidation (mmol/L) Addition Methane 10 10 6 8 2 4 amount sulfonic (mol/L) acid Ethane 4 sulfonic acid P-toluene 2 sulfonic acid Sulfuric 8 8 acid Phosphoric 2 acid Total acid concentration 10 10 10 10 12 12 (mol/L)

(5) TABLE-US-00002 TABLE 2 Comparative Example Compound 1 2 3 4 Addition Manganese 70 35 0.5 amount sulfate (II) (mmol/L) Manganese 70 35 carbonate (II) Analysis value of permanganate ion 0.7 4.2 4.0 0.03 obtained after electrolytic oxidation (mmol/L) Addition Methane 6 4 4 amount sulfonic acid (mol/L) Ethane 2 sulfonic acid P-toluene 2 sulfonic acid Sulfuric acid 8 8 Phosphoric acid Total acid concentration (mol/L) 6 8 8 12

(2) Production of Electroless Plating Film

(6) Flat plates (10 cm5 cm0.3 cm, surface area: about 1 dm.sup.2) made of ABS resin (trade name: UMG ABS3001M; produced by UMG ABS, Ltd.) were used as substrates to form electroless plating films according to the following method.

(7) The substrates were first immersed in an alkaline degreasing solution (an ACE CLEAN A-220 bath; produced by Okuno Chemical Industries Co., Ltd.) at 40 C. for five minutes and washed with water.

(8) Subsequently, the substrates were immersed in the compositions for etching treatment comprising aqueous solutions produced in Examples 1 to 6 and Comparative Examples 1 to 4. The etching conditions were an immersion temperature of 68 C. and an immersion time of 20 minutes.

(9) After the etching treatment, the substrates were immersed in sulfuric acid (300 ml/L) at 25 C. for one minute and washed with water to remove manganese salt from the surface.

(10) Subsequently, the substrates were immersed in a colloidal palladium-tin catalyst solution (a Catalyst C7 bath; produced by Okuno Chemical Industries Co., Ltd.) at 40 C. for 5 minutes and washed with water.

(11) Subsequently, the substrates were immersed in an activating solution (an aqueous solution containing 100 ml/1 of 35% hydrochloric acid) at 40 C. for five minutes, and washed with water.

(12) The substrates were then immersed in an electroless nickel plating solution (a Chemical Nickel SEP-LF bath; produced by Okuno Chemical Industries Co., Ltd.) at 40 C. for five minutes to form electroless nickel plating films.

(13) The bath stability of each composition for etching treatment used in the above process, and the coverage, appearance, and adhesion of each resulting plating film, were evaluated according to the following method. Table 3 shows the test results.

(14) (1) Bath Stability:

(15) The status of each composition for etching treatment was visually observed at regular time intervals after the preparation of the bath, and each composition was examined for the presence or absence of liquid decomposition, suspension, and sediment.

(16) (2) Coverage

(17) The area percentage of the substrate on which an electroless nickel plating film was formed was defined as coverage. Coverage was defined as 100% when the entire surface of the test piece was covered with the plating film.

(18) (3) Appearance:

(19) The appearance of the plating film was evaluated with the naked eye.

(20) (4) Peel Strength Measurement

(21) The electrolessly plated test pieces were subjected to electroplating using a copper sulfate plating bath at a current density of 3 A/dm.sup.2 and a temperature of 25 C. for 120 minutes to form copper plating films. The samples thus obtained were dried at 80 C. for 120 minutes and allowed to stand to cool to room temperature. Thereafter, a cut with a width of 10 mm was made in each plating film, and the plating film was pulled in a direction vertical to the resin using a tensile tester (AUTOGRAPH AGS-J 1 kN; produced by Shimadzu Corp.) to determine the peel strength.

(22) (5) Heat Cycle Test

(23) After each electroless nickel plating film was formed under the above conditions, electroplating was performed using a copper sulfate plating bath to a thickness of 10 to 15 m, a nickel plating bath to a thickness of 10 m, and a chrome plating bath to a thickness of 0.2 to 0.3 m, thus preparing test pieces. Using these test pieces, three heat cycles were carried out, each cycle consisting of maintaining the test pieces at 30 C. for one hour, at room temperature for 30 minutes, and at +80 C. for one hour. The test pieces were then checked for appearance by naked eye and evaluated according to the following criteria.

(24) A: No change observed; excellent appearance.

(25) B: Cracking occurred.

(26) C: Blistering of the plating occurred.

(27) : Not evaluated

(28) TABLE-US-00003 TABLE 3 Peel Heat Bath Cover- Appear- strength cycle stability age (%) ance (N/cm) test Example 1 Sediment 100 Good 6.9 A generated five days after bath preparation Example 2 Sediment 100 Good 10.8 A generated five days after bath preparation Example 3 Sediment 100 Good 10.3 A generated five days after bath preparation Example 4 Sediment 100 Good 10.5 A generated five days after bath preparation Example 5 Sediment 100 Good 12.2 A generated seven days after bath preparation Example 6 Stable 100 Good 12.4 A seven days after bath preparation Comparative Sediment 10 Poor Unmea- Example 1 generated surable 12 hours after bath preparation Comparative Sediment 50 Poor 1.7 Example 2 generated three days after bath preparation Comparative Sediment 45 Poor 1.5 Example 3 generated 16 hours after bath preparation Comparative Stable 100 Good 3.3 C Example 4 seven days after bath preparation

Examples 7 to 12 and Comparative Examples 5 to 8

(29) Etching treatment was performed in the same manner as in Examples to 6 and Comparative Examples to 4 except that aqueous solutions in which components including a permanganate salt and an organic sulfonic acid shown in Table 4 or 5 were dissolved were used as compositions for etching treatment to form electroless plating films. Each aqueous solution was prepared by simultaneously adding a permanganate salt and an acid in amounts shown in Table 4 or 5 to water for dissolution. The permanganate ion concentration shown in the table was measured after the produced composition for etching treatment was kept for one hour at 68 C. to stabilize the permanganate ion concentration.

(30) TABLE-US-00004 TABLE 4 Example Compound 7 8 9 10 11 12 Addition Potassium 7 70 35 70 amount permanganate (mmol/L) (VII) Sodium 70 35 70 permanganate (VII) Analysis value of 0.42 4.2 4.4 4.0 4.2 4.0 permanganate ion obtained after stabilization (mmol/L) Addition Methane 10 10 6 8 2 4 amount sulfonic acid (mol/L) Ethane 4 sulfonic acid P-toluene 2 sulfonic acid Sulfuric acid 8 8 Phosphoric acid 2 Total acid concentration 10 10 10 10 12 12 (mol/L)

(31) TABLE-US-00005 TABLE 5 Comparative Example Compound 5 6 7 8 Addition Potassium 70 35 0.5 amount permanganate (VII) (mmol/L) Sodium 70 35 permanganate (VII) Analysis value of permanganate ion 0.1 4.5 4.0 0.03 obtained after stabilization (mmol/L) Addition Methane 6 4 4 amount sulfonic acid (mol/L) Ethane 2 sulfonic acid P-toluene 2 sulfonic acid Sulfuric acid 8 8 Phosphoric acid Total acid concentration (mol/L) 6 8 8 12

(32) The bath stability of each composition for etching treatment used in the above process, and the coverage, appearance, and adhesion of each formed plating film, were evaluated in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 4. Table 6 below shows the test results.

(33) TABLE-US-00006 TABLE 6 Peel Heat Bath Cover- Appear- strength cycle stability age (%) ance (N/cm) test Example 7 Sediment 100 Good 6.1 A generated five days after bath preparation Example 8 Sediment 100 Good 10.1 A generated five days after bath preparation Example 9 Sediment 100 Good 10.8 A generated five days after bath preparation Example 10 Sediment 100 Good 10.8 A generated five days after bath preparation Example 11 Sediment 100 Good 11.9 A generated seven days after bath preparation Example 12 Stable 100 Good 12.2 A seven days after bath preparation Comparative Decomposition Not evaluated Example 5 immediately after bath preparation Comparative Sediment 50 Poor 1.6 Example 6 generated 12 hours after bath preparation Comparative Sediment 50 Poor 1.3 Example 7 generated eight hours after bath preparation Comparative Stable 100 Good 3.3 C Example 8 seven days after bath preparation

(34) As is clear from the results, the compositions for etching treatment of Examples 1 to 12 each having a permanganate ion concentration of 0.2 mmol/L or more, an organic sulfonic acid concentration of 1.5 mol/L or more, and a total acid concentration of 10 mol/L or more were confirmed to have good stability in both cases, i.e., when produced by the electrolyzing method (Examples 1 to 6) and when produced by direct addition of a permanganate salt (Examples 7 to 12). Further, plating films obtained by performing etching treatment using these compositions had high coverage, good appearance, and excellent adhesion.

(35) In contrast, the compositions for etching treatment of Comparative Examples 1 to 3 and 5 to 7 having a total acid concentration below 10 mol/L had poor bath stability in both cases, i.e., when produced by the electrolyzing method (Comparative Examples 1 to 3) and when produced by direct addition of a permanganate salt (Comparative Examples 5 to 7), and the resulting films had poor coverage and adhesion.

(36) Although the compositions for etching treatment of Comparative Examples 4 and 8 had an organic sulfonic acid concentration of 1.5 mol/L or more and a total acid concentration of 10 mol/L or more, etching performance was poor due to the low concentration of the permanganate salt, and the resulting films had poor adhesion.

Examples 13 to 18 and Comparative Examples 9 to 12

(1) Production of Composition for Etching Treatment

(37) Aqueous solutions (500 mL) having the composition shown in Table 7 or 8 were prepared. Specifically, an acid component (methanesulfonic acid and/or sulfuric acid) and a divalent manganese salt (manganese sulfate and/or manganese carbonate) in amounts shown in Table 7 or 8 below were added to water to prepare aqueous acid solutions containing these components. Subsequently, a permanganate salt (potassium permanganate and/or sodium permanganate) was added to each aqueous solution in an amount shown in the table. The resultant was kept at 68 C. for one hour and stabilized, and then used as a composition for etching treatment. Tables 7 and 8 show the results of the permanganate ion concentration in the bath after stabilization, the concentration being obtained by redox titration using an aqueous ascorbic acid solution.

(38) TABLE-US-00007 TABLE 7 Example Compound 13 14 15 16 17 18 Addition Manganese 6 100 50 100 amount sulfate (II) (mmol/L) Manganese 75 25 75 carbonate (II) Potassium 0.4 5 2.5 5 permaganate (VII) Sodium 5 2.5 5 permanganate (VII) Analysis value of 0.4 4.5 4.9 4.4 4.5 4.7 permanganate ion obtained after stabilization (mmol/L) Addition Methane 10 2 4 amount sulfonic acid (mol/L) Sulfuric acid 10 10 12 8 8 Total acid concentration 10 10 12 10 10 12 (mol/L)

(39) TABLE-US-00008 TABLE 8 Comparative Example Compound 9 10 11 12 Addition Manganese 8 25 amount sulfate (II) (mmol/L) Manganese 25 100 2 carbonate (II) Potassium 0.8 5 0.1 permaganate (VII) Sodium 5 permanganate (VII) Analysis value of permanganate ion 0.4 2.5 3.4 0.1 (mmol/L) Addition Methane 6 6 amount sulfonic acid (mol/L) Sulfuric acid 8 12 Total acid concentration (mol/L) 6 6 8 12

(40) The bath stability of each composition for etching treatment used in the above process, and the coverage, appearance, and adhesion of each resulting plating film, were evaluated in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 4. Table 9 shows the test results.

(41) TABLE-US-00009 TABLE 9 Peel Heat Bath Cover- Appear- strength cycle stability age (%) ance (N/cm) test Example 13 Sediment 100 Good 7.1 A generated five days after bath preparation Example 14 Sediment 100 Good 10.4 A generated five days after bath preparation Example 15 Sediment 100 Good 11.3 A generated five days after bath preparation Example 16 Sediment 100 Good 10.5 A generated five days after bath preparation Example 17 Sediment 100 Good 11.2 A generated seven days after bath preparation Example 18 Stable 100 Good 12.1 A seven days after bath preparation Comparative Sediment 30 Poor 0.9 Example 9 generated 12 hours after bath preparation Comparative Sediment 40 Poor 1.7 Example 10 generated 12 hours after bath preparation Comparative Sediment 80 Poor 5.9 Example 11 generated 24 hours after bath preparation Comparative Stable 10 Poor Unmea- C Example 12 seven days surable after bath preparation

(42) As is clear from the results, the compositions for etching treatment of Examples 13 to 18 each having a permanganate ion concentration of 0.2 mmol/L or more, a divalent manganese ion molar concentration 15 times or more higher than the permanganate ion molar concentration, and a total acid concentration of 10 mol/L or more were confirmed to have good stability. Further, plating films obtained by performing etching treatment using these compositions had high coverage, good appearance, and excellent adhesion.

(43) In contrast, the compositions for etching treatment of Comparative Examples 9 to 11 having a total acid concentration below 10 mol/L had poor bath stability, and the resulting films had poor coverage and adhesion.

(44) Although the composition for etching treatment of Comparative Example 12 had a divalent manganese ion molar concentration 15 times or more higher than the permanganate ion molar concentration, and had a total acid concentration of 10 mol/L or more, etching performance was poor due to the low permanganate ion concentration, and the resulting film had remarkably poor coverage.

Examples 19 to 24

(1) Production of Composition for Etching Treatment

(45) Aqueous solutions (500 mL) each having the composition shown in Table 10 were prepared. Specifically, an acid component (methanesulfonic acid and/or sulfuric acid) and an anhydrous magnesium salt (anhydrous magnesium sulfate, anhydrous magnesium chloride, or anhydrous magnesium nitrate) in amounts shown in Table 10 below were added to water to prepare aqueous acid solutions containing these components. Subsequently, a permanganate salt (potassium permanganate and/or sodium permanganate) was added to each aqueous solution in an amount shown in the table. The resultant was kept at 68 C. for one hour and stabilized, and then used as a composition for etching treatment. Table 10 shows the results of the permanganate ion concentration in the bath after stabilization, the concentration being obtained by redox titration using an aqueous ascorbic acid solution.

(46) TABLE-US-00010 TABLE 10 Example Compound 19 20 21 22 23 24 Addition Manganese 6 100 50 amount sulfate (II) (mmol/L) Manganese 75 25 75 carbonate (II) Potassium 70 0.4 5 2.5 permaganate (VII) Sodium 5 2.5 5 permanganate (VII) Analysis value of 4.5 0.4 4.6 4.9 4.8 4.7 permanganate ion obtained after stabilization (mmol/L) Addition Methane sulfonic 10 2 amount acid (mol/L) Sulfuric acid 12 10 10 12 8 Anhydrous 0.5 0.2 magnesium sulfate Anhydrous 0.2 0.5 0.2 magnesium chloride Anhydrous 0.2 magnesium nitrate

(47) The bath stability of each composition for etching treatment used in the above process, and the coverage, appearance, and adhesion of each resulting plating film were evaluated in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 4. Table 11 shows the test results.

(48) TABLE-US-00011 TABLE 11 Peel Heat Bath Cover- Appear- strength cycle stability age (%) ance (N/cm) test Example 19 Sediment 100 Good 10.1 A generated seven days after bath preparation Example 20 Stable 100 Good 11 A seven days after bath preparation Example 21 Stable 100 Good 11.1 A seven days after bath preparation Example 22 Stable 100 Good 10.9 A seven days after bath preparation Example 23 Stable 100 Good 11.8 A seven days after bath preparation Example 24 Stable 100 Good 11.2 A seven days after bath preparation

(49) As is clear from the results, the compositions for etching treatment of Examples 19 to 24 each having a permanganate ion concentration of 0.2 mmol/L or more and a total acid concentration of 10 mol/L or more, and having an addition amount of anhydrous magnesium salt of 0.1 to 1 mol/L were confirmed to have good stability. Further, plating films obtained by performing etching treatment using these compositions had high coverage, good appearance, and excellent adhesion.

Example 25

(50) The composition for etching treatment containing components in amounts shown in Table 12 was prepared in the same manner as in Examples 7 to 12, and the specific gravity of the composition immediately after bath preparation was measured.

(51) TABLE-US-00012 TABLE 12 Addition amount Sodium permanganate (VII) 0.07 (mol/L) Methane sulfonic acid 4 Sulfuric acid 8 Specific gravity (immediately after bath preparation) 1.58

(52) The composition for etching treatment was allowed to stand in an atmosphere at 25 C. for 48 hours, and heat condensation was performed on the bath whose volume was increased to 109% based on the volume immediately after bath preparation. The specific gravity of the composition after the heat condensation was then measured. According to the measured specific gravity, the ratio of the volume of the composition after heating treatment was obtained based on the volume of the composition immediately after bath preparation (100%). Table 13 shows the results.

(53) In the table, dry-air blowing shown in the column of heating conditions is a treatment of blowing dry air, which had been prepared by using silica gel and calcium chloride, at a flow rate of 1.0 L/m into the composition for etching treatment. Heating treatment was performed under atmospheric pressure or reduced pressure of 0.07 MPa.

(54) TABLE-US-00013 TABLE 13 Heating conditions Temper- Treatment Atmos- ature time Dry-air phere Specific Volume ( C.) (hour) blowing (MPa) gravity (%) Before treatment (bath allowed to stand at 25 C. for 1.53 109 48 hours) Test 70 60 Without 0.10 1.58 100 Example 1 dry-air (atmos- blowing pheric pres- sure) Test 0.07 1.59 98 Example 2 Test Dry-air 0.10 1.59 98 Example 3 blowing (atmos- pheric pres- sure) Test 0.07 1.61 95 Example 4 Test 90 6 Without 0.10 1.58 100 Example 5 dry-air (atmos- blowing pheric pres- sure)

(55) As is clear from the above results, as compared with the specific gravity before heating treatment, the specific gravity obtained after heating treatment at a temperature of 70 C. or more increased, and an effect of condensing the composition for etching treatment, the volume of which was increased by moisture absorption, was acknowledged. In addition, a tendency was observed in which the concentration efficiency increased as the treating temperature was high, and the combination use of dry-air blowing or heating treatment under reduced pressure was confirmed to ensure efficient condensation.

Example 26

(56) The test solution containing components in amounts shown in Table 14 was prepared.

(57) TABLE-US-00014 TABLE 14 Addition amount Manganate sulfate (II) 0.07 (mol/L) Methane sulfonic acid 4 Sulfuric acid 8

(58) Using a commercially available ozone generation device, ozone gas was blown into the test solution (1 L) for one hour, and the concentration of permanganate ion generated in the bath was obtained by ascorbic acid titration. The yield of ozone gas was 200 mg/h or 1000 mg/h, and the blowing amount was 2 L/min.

(59) Ozone gas was blown by using either of the following methods: a method of blowing ozone gas by using a glass tube with a tip diameter of 1.5 mm (general bubbling) or a method of blowing ozone gas in microbubble form by providing the end of the glass tube with pumice having a diameter of about 30 m (microbubbling).

(60) As a comparative test, the concentration of permanganate ion obtained by blowing air at an air flow rate of 2 L/min for one hour in place of ozone gas was measured in the bath. Table 15 blow shows the results.

(61) TABLE-US-00015 TABLE 15 Ozone Treatment Permanganate yield temperature ion concentra- (mg/H) ( C.) Bubbling method tion (mg/L) Test 200 25 General bubbling 1.5 Example 1 Test Microbubbling 7.5 Example 2 Test 50 Microbubbling 12 Example 3 Test 70 Microbubbling 15 Example 4 Test 1000 25 General bubbling 7.5 Example 5 Test Microbubbling 37.5 Example 6 Test 50 Microbubbling 60 Example 7 Test 70 Microbubbling 75 Example 8 Comparative 0 (air 25 General bubbling 0 Test stirring) Example 1 Comparative Microbubbling 0 Test Example 2 Comparative 50 Microbubbling 0 Test Example 3 Comparative 70 Microbubbling 0 Test Example 4

(62) The above results clearly indicated that the permanganate ion was generated by blowing ozone gas into the aqueous solution containing manganese sulfate, methane sulfonic acid, and sulfuric acid. In particular, the yield of permanganate ion was greatly increased by increasing the bath temperature and blowing ozone gas as microbubbles.

(63) In contrast, a permanganate ion was not generated when air was blown as microbubbles in place of ozone gas.

(64) The results confirmed that when the permanganate ion concentration is reduced with use, the concentration can be increased by blowing ozone gas.