Concentrated magnetic particle dispersion and magnetic particle liquid for wet magnetic particle testing

Abstract

To provide thick magnetic particle dispersion fluid for wet magnetic particle flaw detection test which can maintain, a dispersion state without sedimentation and deposition of magnetic particles, for a long term, regardless of including an alga-proof agent, and by a method for diluting with water, the thick magnetic particle dispersion fluid, can adjust a magnetic particle solution including a proper amount of the alga proof agent, the adjusted magnetic particle solution capable of suppressing breeding of microbes, therefore the solution can suppress occurrence of unpleasant odor and an alga-like substance, and according to the thick magnetic particle dispersion fluid, even when reusing multiple times, the magnetic particle solution, the magnetic particles are hardly coagulated, therefore it is possible to perform accurate wet magnetic flaw detection test.SOLUTION: There is provided thick magnetic particle fluid for wet magnetic particle flaw detection test, comprising: 10 weight% or greater and 20 weight% or less; 5 weight% or greater and 15 weight% or less of a polyoxyalkylene-polystyrylphenyl ether type non-ion surfactant whose hydroxyl value is 69.5 or greater and 73.6 or less; 0.15 weight% or greater and 2.5 weight% or less of isothiazolinone-based inductor and / or triazine-based alga proof agent; and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a concentrated magnetic particle dispersion for wet magnetic particle testing that is diluted with water and used as a magnetic particle liquid for wet magnetic particle testing. More specifically, the concentrated magnetic particle dispersion contains an anti-algae agent, yet the magnetic particles remain dispersed for a long period of time without settling or settling, and a magnetic particle liquid containing an appropriate amount of anti-algae agent can be prepared by the simple method of diluting the concentrated magnetic particle dispersion with water. The prepared magnetic particle liquid inhibits the growth of microorganisms, thereby inhibiting the generation of unpleasant odors and algae-like substances, and is resistant to aggregation even when reused multiple times, making it possible to perform high-precision magnetic particle testing. [Background technology]

[0002] As is well known, magnetic particle testing methods are standardized in JIS-Z-2320, and this test method involves applying commercially available wet magnetic particle testing magnetic powder (conductive particles such as iron oxide particles or pure iron particles, with a synthetic resin binder such as cellulose acetate synthetic resin or vinyl butyral synthetic resin, to fluorescent pigments such as Lumogen Yellow 50790 (trade name: manufactured by BASF) or Festa A (trade name: manufactured by Swada) with an average particle diameter of 3 to 70 μm, volume-based distribution display (hereinafter the same), true specific gravity 2 g / cm) to a magnetized test object, for example, steel parts such as shafts, steel materials such as magnetic bodies or billets, or other magnetic bodies. 3 ~5g / cm 3 This is a test method in which a magnetic particle liquid prepared by dispersing the powder in a dispersion liquid such as water is brought into contact with the test object, causing the magnetic powder dispersed in the magnetic particle liquid to gather at open defects (fine cracks or pinholes on the surface or near the surface of the test object) to form a defect indication pattern, and this defect indication pattern is used to detect open defects on the surface (hereinafter this test method is referred to as "wet magnetic particle testing").

[0003] In wet magnetic particle testing on manufacturing lines for steel parts and steel materials, the testing fluid sprayed on the test object is collected and reused after the testing is completed.

[0004] Magnetic particle liquid is usually reused for about one week to one month and then replaced, but there are problems with microorganisms multiplying during reuse, causing unpleasant odors and the growth of algae-like substances.

[0005] Furthermore, if the magnetic powder is reused multiple times, there is a problem that the magnetic powder aggregates.

[0006] If the magnetic particles aggregate, the accuracy of the flaw detection test will decrease, the magnetic particles will adhere to the inside of the tanks and pipes that store the magnetic particle liquid, and the nozzles that spray the magnetic particle liquid will become clogged.

[0007] By adding an anti-algae agent such as methylisothiazolinone to the magnetic powder liquid, it is possible to inhibit the growth of microorganisms and the aggregation of magnetic powder, but if the amount of anti-algae agent added is too small, the effect of inhibiting the growth of microorganisms is low, and if too much is added, the magnetic powder will aggregate, which is a problem.

[0008] In production lines where speeding up production is required, it is difficult to add a step of weighing out the appropriate amount of anti-algae agent and adding it to the magnetic powder liquid. Therefore, it is desirable to be able to add the anti-algae agent to the concentrated magnetic powder dispersion liquid before diluting it with water, and then simply dilute it to prepare a magnetic powder liquid containing the appropriate amount of anti-algae agent.

[0009] However, if an anti-algae agent is added in advance to a concentrated magnetic powder dispersion so that the appropriate amount is obtained when diluted, the magnetic powder will settle or precipitate within a few hours to a few days, making it difficult to store for long periods of time.

[0010] Therefore, there is a need for the development of a concentrated magnetic particle dispersion that can be stored for a long period of time without the magnetic particles settling or settling, even when an anti-algae agent is added, and that inhibits the growth of microorganisms and is less likely to produce unpleasant odors or algae-like substances, even when diluted and prepared and reused multiple times over the course of about a month, and that does not cause the magnetic particles to aggregate and thereby reduce the accuracy of flaw detection tests. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2019-128292 [Patent Document 2] Patent Publication No. 2009-109424 [Patent Document 3] Patent Publication No. 10-332644 Summary of the Invention [Problem to be solved by the invention]

[0012] Patent Document 1 describes a concentrated magnetic particle dispersion for wet magnetic particle testing, in which the magnetic particles remain dispersed without settling or settling even after being left standing at 40°C for 90 days, by using a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant with an HLB value of 10 to 12 and an average molecular weight of 750 to 950 as a dispersant.

[0013] However, the concentrated magnetic powder dispersion described in Patent Document 1 suppresses the settling of magnetic particles in the concentrated magnetic powder dispersion within a certain range of HLB values ​​and average molecular weights, and therefore there is a problem in that the magnetic particles will settle within a few days when an anti-algae agent is added.

[0014] Patent Document 2 describes a concentrated magnetic particle dispersion for wet magnetic particle testing, in which magnetic particles remain dispersed without settling or settling even after being left standing at 40°C for 90 days, by using a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant and an anionic surfactant as dispersants.

[0015] However, the concentrated magnetic particle dispersion described in Patent Document 2 also has a problem in that the electrostatic repulsion is increased by mixing a certain ratio of an anionic surfactant with a polyoxyalkylene polystyryl phenyl ether type nonionic surfactant, thereby suppressing settling and sedimentation, and therefore adding an anti-algae agent will cause the magnetic particles in the concentrated magnetic particle dispersion to settle or precipitate within a few days.

[0016] Patent Document 3 describes a concentrated magnetic particle dispersion that uses an alkyl ether-type nonionic surfactant with an HLB of 10 to 12 and alcohol as a dispersant, and in which the magnetic particles do not settle or precipitate even when left standing for at least two months.

[0017] However, when an anti-algae agent is added to the concentrated magnetic particle dispersion liquid described in Patent Document 3, there is a problem in that the magnetic particles settle and precipitate within a few days.

[0018] The inventors of the present invention have set solving the above-mentioned problems as a technical task, and as a result of numerous trial and error trials and experiments, have discovered a concentrated magnetic particle dispersion for wet magnetic particle testing, which contains 10% by weight or more and 20% by weight or less of magnetic powder, 5% by weight or more and 15% by weight or less of a nonionic surfactant, 0.15% by weight or more and 2.5% by weight or less of an anti-algae agent, and water, wherein the anti-algae agent is an isothiazolinone derivative and / or a triazine anti-algae agent, and the nonionic surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having a hydroxyl value of 69.5 or more and 73.6 or less. If this is done, despite the presence of an anti-algae agent, the magnetic particles will not settle or precipitate for a long period of time, such as more than one month, even when left to stand at a high temperature of 40°C, and the magnetic particle liquid prepared by diluting the concentrated magnetic particle dispersion liquid of the present invention with water will inhibit the growth of microorganisms and will be less likely to produce unpleasant odors or algae-like substances, even if reused multiple times over a period of about one month.Furthermore, since the magnetic particles are less likely to agglomerate, high-precision flaw detection tests can be carried out, and the magnetic particles will not adhere to the tanks that store the magnetic particle liquid or the piping that transports the magnetic particle liquid, and the magnetic particle liquid will be less likely to clog the nozzles that spray the magnetic particle liquid.This is a remarkable finding that has enabled the achievement of the above technical objectives. [Means for solving the problem]

[0019] The above technical problems can be solved by the present invention as follows.

[0020] The present invention is a concentrated magnetic particle dispersion for wet magnetic particle testing, which contains 10% by weight or more and 20% by weight or less of magnetic powder, 5% by weight or more and 15% by weight or less of a nonionic surfactant, 0.15% by weight or more and 2.5% by weight or less of an anti-algae agent, and water, wherein the anti-algae agent is an isothiazolinone derivative and / or a triazine anti-algae agent, and the nonionic surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having a hydroxyl value of 69.5 or more and 73.6 or less.

[0021] The present invention also relates to the concentrated magnetic particle dispersion for wet magnetic particle testing, wherein the isothiazolinone derivative is one or a mixture of two or more selected from the group consisting of methylisothiazolinone, chloromethylisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, and benzisothiazolinone.

[0022] The present invention also relates to the concentrated magnetic particle dispersion for wet magnetic particle testing, wherein the triazine-based anti-algae agent is hexahydro-1,3,5 tris(2-hydroxyethyl) 1,3,5 triazine.

[0023] The present invention also relates to the concentrated magnetic particle dispersion for wet magnetic particle testing, wherein the polyoxyalkylene polystyrylphenyl ether type nonionic surfactant is one or a mixture of two or more surfactants selected from polyoxyethylene polystyrylphenyl ether and polyoxyethylene polyoxypropylene polystyrylphenyl ether.

[0024] The present invention also relates to the concentrated magnetic particle dispersant for wet magnetic particle testing, wherein the polyoxyalkylene polystyrylphenyl ether type nonionic surfactant has an average molecular weight of 750 or more and 950 or less.

[0025] The present invention also relates to the concentrated magnetic particle dispersion for wet magnetic particle testing, wherein the nonionic surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having an average molecular weight of 750 to 950 and a hydroxyl value of 69.5 to 73.6, which is a mixture of one or more polyoxyalkylene polystyrylphenyl ether type nonionic surfactants having an average molecular weight of 750 to 950 and one or more polyoxyalkylene polystyrylphenyl ether type nonionic surfactants having a hydroxyl value of 55 to 85 and an average molecular weight of 750 to 950.

[0026] The present invention also provides a magnetic particle liquid for wet magnetic particle testing, which is obtained by diluting the above-mentioned concentrated magnetic particle dispersion with water. [Effects of the Invention]

[0027] The present invention uses a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant with a hydroxyl value of 69.5 or more and 73.6 or less as a dispersant, and therefore is a concentrated magnetic particle dispersion that, despite containing an isothiazolinone derivative and / or a triazine anti-algae agent, is able to maintain a dispersed state without the magnetic particles settling or precipitating even when left standing at a high temperature of 40°C for more than one month.

[0028] Furthermore, if the surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant with a hydroxyl value of 69.5 or more and 73.6 or less and an average molecular weight of 750 or more and 950 or less, the magnetic particles will be even more concentrated and less likely to settle or precipitate.

[0029] Furthermore, since the concentrated magnetic particle dispersion liquid of the present invention contains an isothiazolinone derivative and / or a triazine anti-algae agent, it is possible to prepare a magnetic particle liquid containing an appropriate amount of anti-algae agent by the simple method of diluting it with water, without having to weigh out and add the appropriate amount of anti-algae agent to the magnetic particle liquid at the site of the wet magnetic particle inspection test.

[0030] Furthermore, the prepared magnetic powder liquid can inhibit the growth of microorganisms even if it is reused multiple times over a period of more than one month, and is therefore a magnetic powder liquid that can inhibit the occurrence of unpleasant odors and algae-like substances.

[0031] Furthermore, since the magnetic powder liquid of the present invention contains an isothiazolinone derivative and / or a triazine anti-algae agent, it is possible to suppress the aggregation of magnetic powder, and therefore it is a magnetic powder liquid that can be used to perform high-precision wet magnetic particle inspection tests even if it is reused multiple times over a period of one month or more.

[0032] Furthermore, since the magnetic powder is less likely to agglomerate, it is less likely to adhere to the tanks that store the magnetic powder liquid or the piping that transports it, and the nozzles that spray it onto the test object are less likely to clog, making this a magnetic powder liquid that offers excellent work efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0033] The concentrated magnetic particle dispersion of the present invention contains magnetic particles, a nonionic surfactant as a dispersant, an anti-algae agent, and water.

[0034] (Magnetic powder) The magnetic powder in the present invention is preferably fluorescent magnetic powder in which the particle surfaces of magnetically conductive particles (such as iron tetroxide particles or pure iron particles) are coated with a synthetic resin (cellulose acetate synthetic resin or vinyl butyral synthetic resin) binder and a fluorescent pigment (Lumogen Yellow 50790 (manufactured by BASF) or Festa A (manufactured by Swada)).

[0035] The magnetically conductive particles have a median diameter of 3 μm to 70 μm and a true specific gravity of 2 g / cm 3 ~5g / cm 3 The following is preferred.

[0036] The fluorescent magnetic powder may be a commercially available product. Examples of commercially available products include magnetic particles for wet magnetic particle testing, Super Magna LY-10, Super Magna LY-20, and Super Magna LY-20P (all manufactured by Marktec Co., Ltd.).

[0037] The content of magnetic powder in the concentrated magnetic powder dispersion is 10% by weight to 20% by weight.

[0038] If it is less than 10% by weight, a large amount of magnetic powder dispersion liquid is required when preparing the magnetic powder liquid, resulting in poor work efficiency, and if it exceeds 20% by weight, the dispersion stability will deteriorate and there is a risk that the magnetic powder will settle or precipitate if left standing for a long period of time.

[0039] (nonionic surfactants) The present invention contains a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant (hereinafter sometimes referred to as "nonionic surfactant") as a dispersant.

[0040] Examples of nonionic surfactants include, but are not limited to, polyoxyethylene polystyrylphenyl ether and polyoxyethylene polyoxypropylene polystyrylphenyl ether.

[0041] The nonionic surfactants may be used alone or in combination of two or more.

[0042] The hydroxyl value of the nonionic surfactant is preferably 69.5 to 73.6, and more preferably 72.0 to 73.5.

[0043] If the hydroxyl value is less than 69.5 or more than 73.6, the magnetic particles will not be able to maintain a dispersed state for a long period of time when an isothiazolinone derivative and / or a triazine anti-algae agent is added, and will settle or precipitate.

[0044] The average molecular weight of the nonionic surfactant is preferably 750 to 950.

[0045] If the average molecular weight is less than 750, the viscosity will be too low, and there is a risk that the viscosity will not be sufficient to disperse and retain the magnetic powder in the concentrated magnetic powder dispersion, resulting in sedimentation or settling.If the average molecular weight exceeds 950, the viscosity will be too high, which will reduce the efficiency of the weighing process when preparing the magnetic powder liquid.

[0046] In the present invention, the surfactant may be a single nonionic surfactant having a hydroxyl value of 69.5 to 73.6 and an average molecular weight of 750 to 950, or a nonionic surfactant prepared by mixing nonionic surfactants so as to have a hydroxyl value of 69.5 to 73.6 and an average molecular weight of 750 to 950.

[0047] (anti-algae agent) The concentrated magnetic particle dispersion of the present invention contains an isothiazolinone derivative and / or a triazine anti-algae agent as an anti-algae agent.

[0048] Examples of isothiazolinone derivatives include, but are not limited to, methylisothiazolinone, chloromethylisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, and benzisothiazolinone.

[0049] An example of a triazine-based algae control agent is hexahydro-1,3,5 tris(2-hydroxyethyl) 1,3,5 triazine, but the agent is not limited to this.

[0050] In the present invention, the isothiazolinone derivatives may be used alone or in combination of two or more.

[0051] The triazine-based anti-algae agents may be used alone or in combination of two or more.

[0052] Also, the isothiazolinone derivative and the triazine anti-algae agent may be used in combination.

[0053] The content of the anti-algae agent in the present invention is 0.15% by weight to 2.5% by weight, and more preferably 0.75% by weight to 2.5% by weight.

[0054] If the anti-algae agent is less than 0.15% by weight, the effect of inhibiting microbial growth in the prepared magnetic powder liquid will be too low, and there is a risk of microbial growth; if the amount is more than 2.5% by weight, there is a risk that the magnetic particles will settle or precipitate when stored for a long period of time, and there is also a risk that the magnetic particles in the prepared magnetic powder liquid will aggregate.

[0055] The viscosity of the concentrated magnetic powder dispersion in the present invention is preferably 1000 mPa·s to 5000 mPa·s, and more preferably 1000 mPa·s to 3000 mPa·s.

[0056] This is because it is useful for the weighing work of filling the manufacturing vessel and preparing the magnetic powder liquid.

[0057] (magnetic powder liquid) The concentrated magnetic particle dispersion of the present invention can be diluted with water to prepare a magnetic particle liquid for wet magnetic particle testing.

[0058] The magnetic powder liquid preferably contains 0.5 g to 2.0 g of magnetic powder per 1 L of water.

[0059] Tap water can be used for dilution.

[0060] The magnetic powder content in the magnetic powder liquid is preferably 0.05% to 0.2% by weight, the nonionic surfactant content is 0.18% to 0.72% by weight, and the anti-algae agent content is preferably 0.075% to 0.5% by weight.

[0061] The magnetic powder liquid may contain 2 to 8% by weight of a commercially available antifoaming agent (for example, antifoaming agents KS-537, KS-538, and KM-75 (manufactured by Shin-Etsu Chemical Co., Ltd.)).

[0062] Additionally, a rust inhibitor (for example, sodium nitrite) may be added as appropriate.

[0063] Each of the above-mentioned components is weighed out within the above-mentioned blending ratio range, with the remainder being water. A stainless steel tank is first charged with the dispersant, antifoaming agent, rust inhibitor (if any) and water, and the mixture is stirred at room temperature (approximately 25°C) for 15 minutes using a propeller-type electric mixer. After continuing to stir, magnetic powder is added and the mixture is stirred for a further 60 minutes to obtain a magnetic powder liquid. [Example]

[0064] The present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited thereto.

[0065] Tap water, dispersant, algae inhibitor, antifoaming agent, and rust inhibitor were added to a stainless steel tank as shown in Table 2, and stirred at room temperature (approximately 25°C) for 15 minutes using a propeller-type electric mixer.While continuing to stir, Super Magna LY-10 magnetic powder for wet magnetic particle testing (manufactured by Marktec Co., Ltd.) was then added, and the mixture was stirred for a further 60 minutes to produce concentrated magnetic particle dispersions for the Examples and Comparative Examples.

[0066] In each of the Examples and Comparative Examples, nonionic surfactants A to M shown in Table 1 were used as dispersants.

[0067] Anti-algae agents include Fineside C-14BT, Fineside HS-20M, Fineside LC-430M (manufactured by Tokyo Fine Chemical Co., Ltd.), Sunlight IP-50, Sunlight IP-51, Sunlight PX (manufactured by Sanwa Kasei Co., Ltd.), Statect 150 (manufactured by Nissin Chemical Research Institute Co., Ltd.), Levanax BA-200 (manufactured by Shoei Chemical Co., Ltd.), and sodium omadine 40% (manufactured by Lonza Japan Co., Ltd.). BIOSOL-LIQUID (manufactured by Osaka Kasei Co., Ltd.) was used.

[0068] The antifoaming agent used was KS-537 (manufactured by Shin-Etsu Chemical Co., Ltd.), and sodium nitrite was used as a rust inhibitor.

[0069] The ingredients of each anti-algae agent are listed in Table 4.

[0070] [Table 1]

[0071] [Table 2]

[0072] (evaluation) 200 g of each was placed in a transparent glass beaker, and the mouth of each beaker was covered with aluminum foil with a small hole punched in it.The beakers were then placed in a thermostatic chamber with the liquid temperature maintained at 40°C and left to stand for an hour.The state of the dispersion was then visually observed, and a state in which there was no supernatant or precipitate was evaluated as ``○'', and a state in which 10% or more by volume of supernatant had formed and clear separation had occurred in appearance was evaluated as ``×''.

[0073] For the 5°C test, the same conditions as for the 40°C test were used, except that the liquid temperature in the beaker was kept at 5°C in the refrigerator.

[0074] The viscosity was measured using a digital rotational viscometer, Viscoride One L (Fungilab) at 20°C and 6 rpm.

[0075] A concentrated magnetic particle dispersion was weighed out in an amount that would result in 0.5 g of magnetic particles per liter of water, then poured into water and mixed and stirred to prepare a test liquid. The state of aggregation was observed after one month.

[0076] Those in which no agglomeration was observed or there was a small amount of agglomeration but it did not affect flaw detection were rated as ◯, and those in which there was little effective magnetic powder and a lot of agglomeration or only agglomerates were rated as x.

[0077] The results are shown in Table 3.

[0078] [Table 3]

[0079] Each anti-algae agent was added to the concentrated magnetic powder dispersion of Example 6 to a concentration of 0.5% by weight, and after leaving it to stand at room temperature for one month, the dispersibility was evaluated by observation.

[0080] Those in which no agglomeration was observed or there was a small amount of agglomeration but it did not affect flaw detection were rated as ◯, and those in which there was little effective magnetic powder and a lot of agglomeration or only agglomerates were rated as x.

[0081] The results are shown in Table 4.

[0082] [Table 4]

[0083] As shown in Tables 3 and 4, it has been proven that the concentrated magnetic particle dispersion of the present invention is a concentrated magnetic particle inspection liquid in which magnetic particles do not settle or precipitate for a long period of time, such as one month, even when an anti-algae agent is added. [Industrial Applicability]

[0084] The concentrated magnetic particle dispersant for wet magnetic particle testing of the present invention contains an anti-algae agent, yet the magnetic particles can maintain a dispersed state without settling or sedimentation even when stored at high temperatures such as 40°C for a long period of time, such as one month or more. Furthermore, since it contains an anti-algae agent, a magnetic powder liquid containing the appropriate amount of anti-algae agent can be prepared by the simple method of diluting it with water, so there is no need to weigh out the appropriate amount of anti-algae agent and add it to the magnetic powder liquid at the magnetic particle testing site. Furthermore, since the prepared magnetic powder liquid contains an appropriate amount of anti-algae agent, even if it is reused multiple times over a long period of time, such as more than one month, it is possible to suppress the growth of microorganisms and prevent the occurrence of unpleasant odors and algae-like substances.Furthermore, since the magnetic powder is difficult to agglomerate, high-precision wet magnetic particle inspection testing can be performed even with magnetic powder liquid that has been reused multiple times. In addition, since the magnetic particles are less likely to agglomerate, the magnetic particles are less likely to adhere to tanks or pipes that store the magnetic particle liquid, and the concentrated magnetic particle dispersion liquid for wet magnetic particle testing can be used to prepare a magnetic particle liquid that is less likely to clog the nozzles that spray the magnetic particle liquid. Therefore, the present invention has high industrial applicability.

Claims

1. A concentrated magnetic particle dispersion for wet magnetic particle testing containing 10% by weight or more and 20% by weight or less of magnetic powder, 5% by weight or more and 15% by weight or less of a nonionic surfactant, 0.15% by weight or more and 2.5% by weight or less of an anti-algae agent, and water, wherein the anti-algae agent is an isothiazolinone derivative and / or a triazine anti-algae agent, and the nonionic surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having a hydroxyl value of 69.5 or more and 73.6 or less.

2. 2. The concentrated magnetic particle dispersion for wet magnetic particle testing according to claim 1, wherein the isothiazolinone derivative is one or a mixture of two or more selected from the group consisting of methylisothiazolinone, chloromethylisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, and benzisothiazolinone.

3. 3. The concentrated magnetic particle dispersion for wet magnetic particle testing according to claim 1, wherein the triazine-based anti-algae agent is hexahydro-1,3,5 tris(2-hydroxyethyl) 1,3,5 triazine.

4. 4. A concentrated magnetic particle dispersion for wet magnetic particle testing according to claim 1, wherein the polyoxyalkylene polystyrylphenyl ether type nonionic surfactant is one or a mixture of two or more surfactants selected from polyoxyethylene polystyrylphenyl ether and polyoxyethylene polyoxypropylene polystyrylphenyl ether.

5. 5. A concentrated magnetic particle dispersant for wet magnetic particle testing according to claim 1, wherein the polyoxyalkylene polystyrylphenyl ether type nonionic surfactant has an average molecular weight of 750 or more and 950 or less.

6. The nonionic surfactant is a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having an average molecular weight of 750 or more and 950 or less, and a hydroxyl value of 69.5 or more and 73.6 or less, which is a mixture of one or more of a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having an average molecular weight of 750 or more and 950 or less, and a polyoxyalkylene polystyrylphenyl ether type nonionic surfactant having a hydroxyl value of 55 or more and 85 or less, and an average molecular weight of 750 or more and 950 or less. The concentrated magnetic particle dispersion for wet magnetic particle testing according to any one of claims 1 to 5.

7. A magnetic particle liquid for wet magnetic particle testing, obtained by diluting the concentrated magnetic particle dispersion liquid according to any one of claims 1 to 6 with water.

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