Trivalent chromium plating solution and chromium plating method using the same

Abstract

A trivalent chromium plating solution and a trivalent chromium plating method using the same. The trivalent chromium plating solution is characterized in that the trivalent chromium plating solution contains a trivalent chromium compound, a complexing agent, a conductive salt, and a pH buffer, and further contains an organic compound having 2 to 4 carbon atoms and more than 3 chlorine groups. Based on this, a trivalent chromium plating having improved corrosion resistance than existing trivalent chromium plating and having practicality can be obtained.

Description

Technical Field

[0001] The present invention relates to a trivalent chromium plating solution and a chromium plating method using the same. Background Art

[0002] Chromium plating is used as a decorative coating because of its silvery-white appearance. The chromium plating uses hexavalent chromium, but in recent years, due to the environmental impact of this hexavalent chromium, its use has been restricted, and the technology has shifted to using trivalent chromium.

[0003] However, trivalent chromium plating is inferior to hexavalent chromium plating in corrosion resistance. Therefore, there are reports of techniques for improving the corrosion resistance of trivalent chromium plating. For example, Patent Document 1 reports a technique for enhancing corrosion resistance in a calcium chloride environment.

[0004] However, this trivalent chromium plating has poorer corrosion resistance than hexavalent chromium plating in terms of CASS corrosion resistance and is not practical.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application No. 2012-521495 Summary of the invention

[0008] An object of the present invention is to provide a trivalent chromium plating having improved corrosion resistance compared with conventional trivalent chromium plating and having practicality.

[0009] The present inventors have conducted intensive studies to solve the above-mentioned problems and have found that a trivalent chromium plating obtained by adding a trivalent chromium plating solution having an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups has high corrosion resistance and is practical, thereby completing the present invention.

[0010] That is, the present invention is a trivalent chromium plating solution characterized in that the trivalent chromium plating solution containing a trivalent chromium compound, a complexing agent, a conductive salt, and a pH buffer further contains an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups.

[0011] In addition, the present invention is an additive for trivalent chromium plating solution, which contains an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups as an effective component.

[0012] Furthermore, the present invention is a method for plating chromium on an object to be plated, characterized in that the object to be plated is electroplated with the above-mentioned trivalent chromium plating solution.

[0013] Furthermore, the present invention is a method for improving the corrosion resistance of an object to be plated, characterized in that the object to be plated is electroplated with the above-mentioned trivalent chromium plating solution.

[0014] Furthermore, the present invention is a chromium-plated product obtained by electroplating an object with the above trivalent chromium plating solution.

[0015] The trivalent chromium plating solution of the present invention can obtain an appearance comparable to that of a plating layer using hexavalent chromium, although the plating layer uses trivalent chromium, and furthermore, the corrosion resistance is improved, thus having practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a figure which shows the result after performing a corrosion resistance test (CASS test) (Examples 1 to 5).

[0017] Figure 2 It is a figure which shows the result after performing a corrosion resistance test (CASS test) (Comparative Examples 1 and 2, Reference Example).

[0018] Figure 3 This is a diagram showing the results of a corrosion resistance test (CASS test) (Examples 6 to 8). DETAILED DESCRIPTION

[0019] The trivalent chromium plating solution of the present invention (hereinafter referred to as "the plating solution of the present invention") is a plating solution in which an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups is further contained in a trivalent chromium plating solution containing a trivalent chromium compound, a complexing agent, a conductive salt, and a pH buffer.

[0020] The organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups (hereinafter referred to as "organic compound") used in the plating solution of the present invention is not particularly limited, and examples thereof include chloral hydrate, trichloroethylene, trichloroacetic acid, trichloroacetyl cyanide, trichloroethanol, etc. These organic compounds can be used alone or in combination. Among these organic compounds, chloral hydrate and / or trichloroethylene are preferred, and chloral hydrate is more preferred. The content of the organic compound in the plating solution of the present invention is not particularly limited, and is, for example, 10 to 5000 mg / L, preferably 20 to 2000 mg / L, and more preferably 50 to 1000 mg / L.

[0021] Furthermore, the organic compound can be used as an additive for trivalent chromium plating solution by using it as an effective component. This additive for trivalent chromium plating solution can be added to an existing trivalent chromium plating solution.

[0022] The trivalent chromium compound used in the plating solution of the present invention is not particularly limited, and includes, for example, basic chromium sulfate, chromium sulfate, chromium chloride, chromium sulfamate, chromium acetate, etc., preferably basic chromium sulfate and chromium sulfate. These trivalent chromium compounds may be combined alone or in combination of two or more. The content of the trivalent chromium compound in the plating solution of the present invention is not particularly limited, and for example, as metal chromium, it is 1 to 25 g / L, preferably 1 to 15 g / L.

[0023] The complexing agent used in the plating solution of the present invention is not particularly limited, and for example, aliphatic monocarboxylic acids or salts thereof such as formic acid, ammonium formate, potassium formate, etc., aliphatic dicarboxylic acids or salts thereof such as succinic acid, maleic acid, malic acid, citric acid, triammonium citrate, etc., carboxylic acids or salts thereof having two or more hydroxyl groups and two or more carboxyl groups such as tartaric acid, ammonium tartrate, sodium tartrate, etc., etc., can be listed. These complexing agents can also be combined in one or more than two. The content of the complexing agent in the plating solution of the present invention is not particularly limited, and for example, it is 0.1 to 50 g / L, preferably 1 to 30 g / L.

[0024] The conductive salt used in the plating solution of the present invention is not particularly limited, and examples thereof include sulfates such as potassium sulfate, ammonium sulfate, and sodium sulfate, chlorides such as potassium chloride, ammonium chloride, and sodium chloride, and aminosulfonates such as potassium sulfamate, ammonium sulfamate, and sodium sulfamate. In addition, these conductive salts are used as respective groups, for example, sulfates, chlorides, and the like. Among these conductive salts, sulfates or chlorides are preferred. These conductive salts may also be combined in one or more. The content of the conductive salt in the plating solution of the present invention is not particularly limited, and is, for example, 100 to 500 g / L, preferably 150 to 300 g / L.

[0025] The pH buffer used in the plating solution of the present invention is not particularly limited, and includes boric acid, sodium borate, potassium borate, phosphoric acid, dipotassium hydrogen phosphate, etc. Among them, boric acid and sodium borate are preferred. These pH buffers can also be combined in one or more. The content of the pH buffer in the plating solution of the present invention is not particularly limited, for example, 25 to 200 g / L, preferably 50 to 100 g / L.

[0026] The plating solution of the present invention may further contain ascorbic acid, sodium ascorbate, hydrogen peroxide, polyethylene glycol, tin salt, and the like. The tin salt is tin sulfate, tin chloride, and the like.

[0027] The pH of the plating solution of the present invention is not particularly limited as long as it is acidic, but is preferably, for example, 2 to 4.5, and more preferably 2.5 to 4.0.

[0028] When the conductive salt of the plating solution of the present invention is a sulfate, a carboxylic acid or a salt thereof having two or more hydroxyl groups and two or more carboxyl groups is preferably used as a complexing agent. As this complexing agent, for example, carboxylic acids such as tartaric acid, and salts of the above carboxylic acids such as ammonium tartrate, Rochelle salt, and sodium tartrate can be cited. Among these complexing agents, tartaric acid or ammonium tartrate is preferred, and ammonium tartrate is more preferred. These complexing agents can also be combined in one or more than two. The content of the carboxylic acid or its salt in the plating solution of the present invention is not particularly limited, and is, for example, 0.1 to 90 g / L, preferably 1 to 60 g / L. In addition, in the present invention, the hydroxyl group in the carboxyl group is not counted as a hydroxyl group.

[0029] In addition, when the conductive salt of the plating solution of the present invention is a sulfate, it is preferred that a carboxylic acid or its salt having more than 2 carboxyl groups and a carbon number of more than 4 is also used in combination with the above-mentioned complexing agent. As the carboxylic acid or its salt having more than 2 carboxyl groups and a carbon number of more than 4, for example, carboxylic acids such as adipic acid, phthalic acid, pimelic acid, sebacic acid, and salts of the carboxylic acids can be cited. These complexing agents can also be combined in one or more, preferably phthalic acid and / or adipic acid. The content of the carboxylic acid or its salt having more than 2 carboxyl groups and a carbon number of more than 4 in the plating solution of the present invention is not particularly limited, and within the range of the content of the carboxylic acid or its salt having more than 2 hydroxyl groups and more than 2 carboxyl groups, a part of it can be a carboxylic acid or its salt having more than 2 carboxyl groups and a carbon number of more than 4. By using the above-mentioned carboxylic acid or its salt having more than 2 carboxyl groups and a carbon number of more than 4, the corrosion resistance is improved even if the chromate treatment described later is not performed.

[0030] When the conductive salt of the plating solution of the present invention is a sulfate, it is preferred to further contain a sulfur-containing organic compound. The sulfur-containing organic compound used in the plating solution of the present invention is not particularly limited, and examples thereof include saccharin or its salts, sulfur-containing organic compounds having an allyl group, carboxylic acids having a carboxamidinothio group and dehydration products thereof, thiourea, sodium thiocyanate, and the like.

[0031] Examples of saccharin or a salt thereof include saccharin and sodium saccharate, among which sodium saccharate is preferred.

[0032] Examples of the sulfur-containing organic compound having an allyl group include sodium propylene sulfonate, allylthiourea, ammonium 2-methylpropylene sulfonate, and allyl isothiocyanate. Among them, sodium propylene sulfonate and / or allylthiourea are preferred.

[0033] Examples of the carboxylic acid having a carboxyamidinylthio group and its dehydration product include a carboxylic acid having a carboxyamidinylthio group represented by the general formula (1) and a dehydration product of a carboxylic acid having a carboxyamidinylthio group represented by the general formula (2).

[0034]

Chemical formula 1

[0035]

[0036] In formula (1), n ​​represents an integer of 1 to 5, preferably 1 to 2.

[0037]

Chemical formula 2

[0038]

[0039] In formula (2), m represents an integer of 1 to 2.

[0040] Specific examples of carboxylic acids having a amidinothio group and dehydration products thereof include {[amino(imino)methyl]thio}acetic acid, 3-{[amino(imino)methyl]thio}propionic acid, 2-iminothiazolidin-4-one, and 2-amino-5,6-dihydro-4H-1,3-thiazin-4-one.

[0041] These sulfur-containing organic compounds may be used alone or in combination of two or more. Among the above sulfur-containing organic compounds, saccharin or its salts and one or more selected from the group consisting of sulfur-containing organic compounds having an allyl group, carboxylic acids having a carboxamidinothio group and / or their dehydration products are preferred, and a combination of sodium saccharate and sodium propylene sulfonate is particularly preferred. The content of the sulfur-containing organic compound in the plating solution of the present invention is not particularly limited, and is, for example, 0.5 to 10 g / L, preferably 2 to 8 g / L.

[0042] It is particularly preferred in the plating solution of the present invention that when sulfate is used as the conductive salt, a carboxylic acid or its salt having two or more hydroxyl groups and two or more carboxyl groups is used as the complexing agent, and as the sulfur-containing organic compound, saccharin or its salt is used in combination with one or more selected from the group consisting of a sulfur-containing organic compound having an allyl group, a carboxylic acid having a guanidinethio group and / or its dehydration reaction products.

[0043] The preparation method of the plating solution of the present invention described above is not particularly limited. For example, it can be prepared in the following manner: add and mix a trivalent chromium compound, a complexing agent, a conductive salt, and a pH buffer in water at 40 to 60° C., and after dissolution, add and mix an organic compound having 2 to 4 carbon atoms and more than 3 chlorine groups, add and mix a sulfur-containing organic compound as needed, and finally adjust the pH value with sulfuric acid, ammonia water, etc.

[0044] The plating solution of the present invention, like the conventional chromium plating solution, can be used to electroplate the object to be plated with chromium by electroplating the object to be plated with the plating solution of the present invention, and the electroplating can improve the corrosion resistance.

[0045] The electroplating conditions are not particularly limited. For example, the liquid temperature is 30 to 60°C, the anode is carbon or iridium oxide, and the cathode current density is 2 to 20 A / dm 2 , electroplating can be carried out for 1 to 15 minutes.

[0046] As the object to be plated, for example, metals such as iron, stainless steel, and brass, and resins such as ABS and PC / ABS can be cited. In addition, before the object to be plated is treated with the plating solution of the present invention, it can be previously subjected to copper plating, nickel plating, and the like.

[0047] When the object to be plated is nickel-plated, it is preferred to set 3 or 4 layers of nickel plating in accordance with the conventional method. If it is 3 layers, the layers can be set in the order of semi-gloss nickel plating, glossy nickel plating, and microporous nickel plating. At this time, the potential difference of each layer is not particularly limited. For example, it is preferred that the potential difference of glossy nickel plating to semi-gloss nickel plating is -200 to -60mV, and the potential difference of microporous nickel plating to glossy nickel plating is 20 to 100mV. If it is 4 layers, the layers can be set in the order of semi-gloss nickel plating, high-sulfur nickel plating, glossy nickel plating, and microporous nickel plating. At this time, the potential difference of each layer is not particularly limited. For example, it is preferred that the potential difference of glossy nickel plating to semi-gloss nickel plating is -200 to -60mV, the potential difference of high-sulfur nickel plating to glossy nickel plating is -50 to -5mV, and the potential difference of microporous nickel plating to glossy nickel plating is in the range of 20 to 100mV.

[0048] The chrome-plated product thus obtained has improved corrosion resistance. Here, improved corrosion resistance means that the rating (RN) is improved in accordance with JIS H8502.

[0049] Furthermore, chromate treatment may be performed during the chrome plating, thereby further improving the corrosion resistance.

[0050] The conditions for chromate treatment are not particularly limited. For example, the liquid temperature is 25 to 70°C, the anode is an insoluble anode such as a lead-tin alloy, and the cathode current density is 0.1 to 1 A / dm 2 , electroplating for 1 minute is sufficient.

[0051] [Example]

[0052] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples at all.

[0053] Embodiments 1 to 5

[0054] Trivalent chromium plating:

[0055] The trivalent chromium compound, complexing agent, conductive salt, and pH buffer described in Table 1 are added and mixed into water at 60°C. After dissolving, organic compounds with carbon numbers of 2 to 4 and 3 or more chlorine groups and sulfur-containing organic compounds are added and mixed. Finally, the pH value is adjusted with sulfuric acid, ammonia water, etc. to prepare a trivalent chromium plating solution. For ABS resin, copper plating ("CU-BRITE EP-30" manufactured by JCU Corporation, semi-gloss nickel plating ("CF-24T" manufactured by JCU Corporation), glossy nickel plating ("HI-BRITE#88" manufactured by JCU Corporation), and microporous nickel plating ("MP-NI 308" manufactured by JCU Corporation) are implemented at the liquid temperature described in Table 1 at a current density of 10A / dm 2The chrome plating was carried out under the conditions of 3 minutes under the conditions of 100 °C and 100 °C to obtain a test piece. The CASS test (JIS H8502) was carried out on this test piece. The microscope photograph of the test piece after 80 hours of CASS test shows Figure 1 and 2 The classification (RN) described in the figure is evaluated by the total corrosion rate. The chromate treatment was performed using "EBACHR O-500" manufactured by JCU Co., Ltd. at a liquid temperature of 40°C and a cathode current density of 0.2 A / d for 1 minute.

[0056]

Table 1

[0057] Plating solution composition Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Reference example Basic chromium sulfate g / L 64 64 64 64 64 64 64 - Chromium trioxide g / L - - - - - - - 250 Sulfuric acid (98%) g / L - - - - - - - 2.5 Malic acid g / L 15 - - - - 15 - - Ammonium tartrate g / L - 30 30 30 30 - 30 - Adipic acid g / L - - - 1 - - - - Sodium sulfate g / L 35 - - - - 35 - - Potassium sulfate g / L 140 150 150 150 150 - 150 - Ammonium sulfate g / L 30 20 20 20 20 30 20 - Boric acid g / L 90 80 80 80 80 90 80 - Sodium saccharate g / L 2.5 4 4 4 4 2.5 4 - Thiourea mg / L 10 - - - - 10 - - Sodium propylene sulfonate (36%) mL / L - 2 2 2 2 - 2 - Chloral hydrate (810g / L) mL / L 0.1 0.1 0.1 0.1 - - - - Trichloroethylene mL / L - - - - 26 - - - Plating solution pH 3.4 3.4 3.4 3.4 3.4 3.4 3.4 - Liquid temperature℃ 60 55 55 55 55 60 45 40 Chromate treatment none none have none none none have -

[0058] The results of the CASS test show that the corrosion resistance is improved by including an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups in the trivalent chromium plating solution. In addition, even without chromate treatment, a highly corrosion-resistant film equivalent to hexavalent chromium plating can be obtained for the plating solution of the present invention.

[0059] Embodiments 6 to 8

[0060] Trivalent chromium plating:

[0061] The trivalent chromium compound, complexing agent, conductive salt, and pH buffer described in Table 2 are added and mixed into water at 60°C. After dissolving, organic compounds with carbon numbers of 2 to 4 and 3 or more chlorine groups and sulfur-containing organic compounds are added and mixed. Finally, the pH value is adjusted with sulfuric acid, ammonia water, etc. to prepare a trivalent chromium plating solution. For ABS resin, copper plating ("CU-BRITE EP-30" manufactured by JCU Corporation, semi-gloss nickel plating ("CF-24T" manufactured by JCU Corporation), glossy nickel plating ("HI-BRITE#88" manufactured by JCU Corporation), and microporous nickel plating ("MP-NI 308" manufactured by JCU Corporation) are implemented at the liquid temperature described in Table 2 at a current density of 10A / dm 2 The chrome plating was carried out under the conditions of 3 minutes under the conditions of 100 °C and 100 °C to obtain a test piece. The CASS test (JIS H8502) was carried out on this test piece. The microscope photograph of the test piece after 80 hours of CASS test shows Figure 3 The classification (RN) was evaluated based on the total corrosion rate. The results are shown in Table 2.

[0062]

Table 2

[0063] Plating solution composition Example 6 Example 7 Example 8 Comparative Example 3 Basic chromium sulfate g / L 19.5 19.5 19.5 19.5 Ammonium tartrate g / L 3 3 3 3 Potassium sulfate g / L 150 150 150 150 Boric acid g / L 70 70 70 70 Sodium saccharate g / L 3 3 3 3 {[Amino(imino)methyl]thio}acetic acid mg / L 50 - 20 50 2-Imino-thiazolidin-4-one mg / L - 50 30 - Chloral hydrate (810g / L) mL / L 0.25 0.25 0.25 - Plating solution pH 3.7 3.7 3.7 3.7 Liquid temperature℃ 55 55 55 55 Chromate treatment none none none none Classification (RN) 9 9 9 8

[0064] The results of the CASS test show that the corrosion holes in Example 6 are smaller than those in Comparative Example 3. The same results can be obtained in Examples 7 and 8. From the above, it can be seen that the corrosion resistance can be improved by adding an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups to the trivalent chromium plating solution.

[0065] Example 9

[0066] Trivalent Chrome Plating Bath:

[0067] The trivalent chromium compound, complexing agent, conductive salt and pH buffer described in the following compositions 1 to 3 are added and mixed into water at 50°C. After dissolution, an organic compound having 2 to 4 carbon atoms and more than 3 chlorine groups is added and mixed. Finally, the pH value is adjusted with hydrochloric acid, ammonia water, etc. to prepare a trivalent chromium plating solution.

[0068] <Composition 1>

[0069]

[0070]

[0071] <Composition 2>

[0072]

[0073] <Composition 3>

[0074]

[0075] Embodiments 10 to 11

[0076] Trivalent chromium plating:

[0077] The trivalent chromium compound, complexing agent, conductive salt, and pH buffer described in Table 3 are added and mixed into water at 60°C. After dissolving, an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups is added and mixed. Finally, the pH value is adjusted with hydrochloric acid and ammonia water to prepare a trivalent chromium plating solution. For ABS resin, copper plating (JCU "CU-BRITE EP-30", semi-gloss nickel plating (JCU "CF-24T"), glossy nickel plating (JCU "HI-BRITE #88"), and microporous nickel plating (JCU "MP-NI 308") are performed at the liquid temperature described in Table 3 at a current density of 10A / dm 2The chromium plating was carried out under the above conditions for 3 minutes to obtain a test piece. The CASS test (JIS H 8502) was carried out on the test piece. The classification (RN) after 80 hours of the CASS test was evaluated by the total corrosion rate. The results are shown in Table 3. In addition, the chromate treatment was carried out using "EBACHRO-500" manufactured by JCU Co., Ltd. at a liquid temperature of 40°C and a cathode current density of 0.2A / dm 2 The conditions were carried out for 1 minute.

[0078]

Table 3

[0079] Plating solution composition Example 10 Embodiment 11 Comparative Example 4 Comparative Example 5 Basic chromium sulfate g / L 64 64 64 64 Ammonium formate g / L 16 16 16 16 Sodium chloride g / L 70 70 70 70 Potassium chloride g / L 140 140 140 140 Ammonium chloride g / L 85 85 85 85 Ammonium bromide g / L 6 6 6 6 Boric acid g / L 67 67 67 67 Chloral hydrate (810g / L) mL / L 0.8 0.8 - - Plating solution pH 2.7 2.7 2.7 2.7 Liquid temperature℃ 32 32 32 32 Chromate treatment none have none have Classification (RN) 9 9.3 8 9

[0080] The results of the CASS test show that the corrosion resistance is improved by including an organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups in the trivalent chromium plating solution.

[0081]

Industrial Applicability

[0082] The trivalent chromium plating solution of the present invention can be used for various purposes similar to plating using hexavalent chromium.

[0083] above

Claims

1. A trivalent chromium plating solution, characterized in that: In the trivalent chromium plating solution containing trivalent chromium compounds, complexing agents, conductive salts, and pH buffers, there are also organic compounds with carbon numbers of 2 to 4 and more than 3 chlorine groups. Among them, the organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups is chloral hydrate and / or trichloroethylene, The trivalent chromium compound is selected from one or more of basic chromium sulfate, chromium sulfate, chromium chloride, chromium sulfamate, and chromium acetate. The conductive salt is one or more sulfates selected from potassium sulfate, ammonium sulfate, and sodium sulfate, or one or more chlorides selected from potassium chloride, ammonium chloride, and sodium chloride. The complexing agent is selected from one or more of aliphatic monocarboxylic acid, aliphatic dicarboxylic acid, carboxylic acid having two or more hydroxyl groups, two or more carboxyl groups, or salts thereof. The pH buffer is selected from one or more of boric acid, sodium borate, potassium borate, phosphoric acid, and dipotassium hydrogen phosphate. The pH is 2.5-4.

5.

2. The trivalent chromium plating solution according to claim 1, wherein The conductive salt is one or more sulfates selected from potassium sulfate, ammonium sulfate, and sodium sulfate. It also contains sulfur-containing organic compounds.

3. The trivalent chromium plating solution according to claim 2, wherein: The complexing agent is a carboxylic acid or a carboxylate having two or more hydroxyl groups and two or more carboxyl groups. The sulfur-containing organic compound is a combination of saccharin or a saccharin salt and one or more selected from the group consisting of: A sulfur-containing organic compound having an allyl group, a carboxylic acid containing a carboxamidylthio group and / or a dehydration product of the carboxylic acid.

4. The trivalent chromium plating solution according to claim 3, wherein The carboxylic acid having more than two hydroxyl groups and more than two carboxyl groups or the carboxylate thereof is tartaric acid or ammonium tartrate.

5. The trivalent chromium plating solution according to claim 3 or 4, wherein: The sulfur-containing organic compound having an allyl group is sodium propylene sulfonate and / or allylthiourea.

6. A trivalent chromium plating solution, characterized in that: In the trivalent chromium plating solution containing trivalent chromium compounds, complexing agents, conductive salts, and pH buffers, there are also organic compounds with carbon numbers of 2 to 4 and more than 3 chlorine groups. Among them, the organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups is chloral hydrate and / or trichloroethylene, The trivalent chromium compound is selected from one or more of basic chromium sulfate, chromium sulfate, chromium chloride, chromium sulfamate, and chromium acetate. The conductive salt is one or more sulfates selected from potassium sulfate, ammonium sulfate, and sodium sulfate, and further contains a sulfur-containing organic compound. The sulfur-containing organic compound is saccharin or a saccharin salt and a combination of one or more selected from the group consisting of: A sulfur-containing organic compound having an allyl group, a carboxylic acid containing a carboxamidinothio group and / or a dehydration product of the carboxylic acid, The complexing agent is one or two of a carboxylic acid or a carboxylate having two or more hydroxyl groups and two or more carboxyl groups, and one or two of a carboxylic acid or a carboxylate having two or more carboxyl groups and a carbon number of four or more. The pH buffer is selected from one or more of boric acid, sodium borate, potassium borate, phosphoric acid, and dipotassium hydrogen phosphate. The pH is 2.5-4.

5.

7. The trivalent chromium plating solution according to claim 6, wherein: The carboxylic acid having 2 or more carboxyl groups and 4 or more carbon atoms or the carboxylate thereof is phthalic acid and / or adipic acid.

8. The trivalent chromium plating solution according to claim 6, wherein: The carboxylic acid having more than two hydroxyl groups and more than two carboxyl groups or the carboxylate thereof is tartaric acid or ammonium tartrate.

9. The trivalent chromium plating solution according to any one of claims 6 to 8, wherein The sulfur-containing organic compound having an allyl group is sodium propylene sulfonate and / or allylthiourea.

10. A use of an additive, which is the use of the additive as an additive for the trivalent chromium plating solution according to claim 1 or 6, wherein: The additive has an organic compound with 2 to 4 carbon atoms and more than 3 chlorine groups as an effective ingredient. The organic compound having 2 to 4 carbon atoms and 3 or more chlorine groups is chloral hydrate and / or trichloroethylene.

11. A method for chromium plating an object, characterized in that: An object to be plated is electroplated using the trivalent chromium plating solution according to any one of claims 1 to 9.

12. The chromium plating method for an object to be plated according to claim 11, wherein: After the object is electroplated, it is subjected to chromate treatment.

13. A method for improving the corrosion resistance of a plated object, characterized in that: An object to be plated is electroplated using the trivalent chromium plating solution according to any one of claims 1 to 9.

14. The method for improving the corrosion resistance of a plated object according to claim 13, wherein: After the object is electroplated, it is subjected to chromate treatment.

15. A chrome-plated product obtained by electroplating an object to be plated with the trivalent chromium plating solution according to any one of claims 1 to 9.

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