CN102965656B - Low-temperature drying passivant and passivation method for hot-dip galvanized steel sheet - Google Patents

Abstract

The invention relates to the technical field of surface treatment of hot-dip galvanized steel sheets, and specifically discloses a low-temperature drying passivator for hot-dip galvanized steel sheets, which includes water and the following components: nano-SiO ₂ , water-based acrylic resin, Organic phosphonic acid is 40-80g/L, ammonium fluotitanate or titanyl sulfate is 5-15g/L, ammonium metavanadate is 10-20g/L, and the pH value can be adjusted to 4-5 with diethylamine. The invention also discloses a passivation method, which mainly refers to coating the passivation agent on the hot-dip galvanized steel sheet by spraying or roller coating on the production line of the hot-dip galvanized steel sheet, and the drying temperature of the sheet only needs to be 70°C about. The passivating agent and the passivating method of the present invention not only have simple formula, readily available raw materials and convenient use, but also have good passivating effect, low drying temperature, and are healthy and environment-friendly.

Description

Low-temperature drying passivator and passivation method for hot-dip galvanized steel sheet

technical field

The invention belongs to the technical field of surface treatment of steel plates, in particular to a passivator for hot-dip galvanized steel plates.

Background technique

Hot-dip galvanizing is the most commonly used protective cathodic protection method for cold-rolled steel sheets, but the galvanized layer is easily corroded in the air (especially in humid air). In order to prevent the corrosion of the galvanized layer, passivation treatment is required. The traditional passivation method is to coat the surface of the hot-dip galvanized steel sheet with a hexavalent chromium passivation agent, and form a passivation layer containing hexavalent chromium salt after drying. , but hexavalent chromium is toxic and carcinogenic, which not only affects human health, but also easily causes harm to the environment, and it will be gradually eliminated by the market. The ROHS directive issued by the European Union clearly restricts the use of hexavalent chromium. In the prior art, in order to reduce the harm of hexavalent chromium, a trivalent chromium passivator has appeared, but when trivalent chromium is used as a passivator, not only the passivation effect is not as ideal as hexavalent chromium, but also it will Converting to hexavalent chromium also has the potential risk of harming the environment and human health. Therefore, it will be an inevitable trend in the development of this technical field to replace chromium passivating agent with chromium-free passivating agent.

Existing chromium-free passivators either use molybdate or rare earth metal salts as the main component, but these passivators are expensive, and the passivation effect is not ideal, and they cannot fully meet the requirements of the cold environment. Demand for hot-dip galvanizing lines in rolling mills. In addition, the drying temperature of the existing passivation agent is relatively high during use, which not only increases the energy consumption and the use cost of the passivation agent, but also deteriorates the operating environment of the passivation process, which is not conducive to the safe production of the passivation operation . So far, there has not been a chromium-free passivator that is truly satisfactory and has a good market prospect in this technical field.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a hot-dip galvanized steel sheet with simple formula, easy-to-obtain raw materials, low drying and curing temperature, convenient use, good passivation effect, health and environmental protection. The passivating agent also correspondingly provides a method for passivating the hot-dip galvanized steel sheet by the passivating agent.

In order to solve the above-mentioned technical problems, the technical solution proposed by the present invention is a low-temperature drying passivator for hot-dip galvanized steel sheets. The passivator includes water (preferably deionized water) and components with the following concentrations:

Nano SiO ₂ 40g/L～80g/L,

Water-soluble acrylic resin 40g/L～80g/L,

Organic phosphonic acid 40g/L～80g/L,

Ammonium fluotitanate and/or titanyl sulfate 5g/L～15g/L, and

Ammonium metavanadate 10g/L～20g/L. the

The above-mentioned low-temperature drying passivator for hot-dip galvanized steel sheet, also preferably contains diethylamine for adjusting the pH value of the passivator in the passivator, and the pH value of the passivator is preferably 4 ~5.

The above-mentioned low-temperature drying passivation agent for hot-dip galvanized steel sheets, the passivation agent is preferably a chromium-free passivation agent. The passivating agent may also not contain expensive molybdates or rare earth metal compounds.

In the above-mentioned low-temperature drying passivator for hot-dip galvanized steel sheets, the average particle size of the nano-SiO ₂ is preferably 10nm-100nm.

The above-mentioned low-temperature drying passivator for hot-dip galvanized steel sheets, the organic phosphonic acid preferably refers to hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, ethylidene One or more of organic phosphonic acids such as diamine tetramethylene phosphonic acid, polyaminopolyether methylene phosphonic acid, etc.

As a general technical idea, the present invention also provides a method for passivating the hot-dip galvanized steel sheet with the above-mentioned low-temperature drying passivator, which mainly refers to the use of scraper coating on the production line of the hot-dip galvanized steel sheet The passivating agent is applied to the hot-dip galvanized steel sheet by spraying or rolling, and the drying panel temperature (PMT) is above 70°C, and the drying panel temperature is more preferably lower than 80°C.

In the above-mentioned low-temperature drying passivator for hot-dip galvanized steel sheet, because it does not contain phosphoric acid and phytic acid, and because the water absorption of organic phosphonic acid is lower than phosphoric acid or phytic acid, the passivator of the present invention is easier to dry , in addition, the preferred pH regulator diethylamine of the present invention is also more volatile, through the optimal adjustment and improvement of the formula of the present invention, the passivator of the present invention can make the passivation effect on the premise of improving the original passivation effect When the drying temperature is significantly reduced, the energy consumption and cost are reduced accordingly.

Compared with the prior art, the present invention has the advantages that: the passivating agent of the present invention not only has simple formula, easy-to-obtain raw materials, and is convenient to use, but also has better passivation effect and lower drying and curing temperature. In the preferred technical scheme, the passivating agent of the present invention can completely contain no heavy metal chromium that is harmful to the environment and human health, and the passivating agent of the present invention can also completely contain molybdate or rare earth with higher cost Metal compounds have the characteristics of high quality, low price, environmental protection and health, and have broad application prospects.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the following examples are only preferred examples and do not limit the protection scope of the present invention.

Example:

First, degrease the surface of the hot-dip galvanized steel sheet that has not undergone any passivation treatment but is protected by oiling after off-line, rinse it with tap water, rinse it with distilled water or deionized water, dry it with hot air and wait for passivation .

Based on the technical solution of the present invention, this example describes 16 groups of passivators of the present invention, and the formulations of each group of passivators are shown in Table 1 below (the total amount prepared in each example is 1 L).

Table 1: List of formulation ingredients for various examples

Example number Organic phosphonic acid g/L Nano SiO ₂ g/L Water-soluble acrylic resin g/L Ammonium Fluotitanate g/L Titanyl sulfate g/L Ammonium metavanadate g/L 1 60 60 40 0 10 15 2 40 60 40 10 0 15 3 80 60 40 10 0 15 4 60 40 40 10 0 15 5 60 80 40 10 0 15 6 60 60 40 10 0 15 7 60 60 80 10 0 15 8 60 60 60 5 0 15 9 60 60 40 15 0 15 10 60 60 40 0 10 10 11 60 60 40 0 10 20 12 60 40 40 0 15 15 13 60 60 40 0 10 15 14 60 60 40 0 10 15 15 60 60 40 0 10 15 16 80 40 40 0 10 15

Note: In the above table 1, the organic phosphonic acid selected in Examples 1-11 is hydroxyethylidene diphosphonic acid, the organic phosphonic acid selected in Example 12 is aminotrimethylene phosphonic acid, and the organic phosphonic acid selected in Example 13 It is diethylenetriaminepentamethylene phosphonic acid, the organic phosphonic acid selected in embodiment 14 is ethylenediamine tetramethylene phosphonic acid, and the organic phosphonic acid selected in embodiment 15 and embodiment 16 is polyamino polyether sub Methylphosphonic acid.

In each group of passivating agents listed in the above examples, diethylamine is used to adjust the pH value of each passivating agent to the range of 4 to 5, and each group of passivating agents is a chromium-free passivating agent. All do not contain molybdate or rare earth metal compound, and the average particle diameter of nano- _SiO2 in each group of passivators is in the range of 10nm to 100nm.

The laboratory passivation of the above-mentioned hot-dip galvanized steel sheets to be passivated is carried out with 0# scraper rod of British RK Company (about 4 μm after wet film), and dried in a hot air oven at a temperature of about 70 °C. Then cut passivated galvanized steel sheets with a size of 150mm×75mm as test pieces for the performance testing of the following items, including neutral salt spray test, cold workability test, X-scribing test, and solvent resistance test. The performance is evaluated by the percentage of corrosion area for 72 hours; at the same time, the blackening resistance test and the yellowing resistance test are also carried out, and the performance is evaluated by the degree of color change. In the case of a dry film thickness of 0.4 μm to 0.8 μm (dry film weight of 0.5g/m ² to 1.0g/m ² ), the white etching area of the neutral salt spray test is less than 3% after 72 hours.

1. Neutral salt spray test: The passivated hot-dip galvanized steel sheet is subjected to a neutral salt spray test according to GB/T10125-1997, and the corrosion resistance of the passivation film is evaluated by the surface white etching area.

2. Cold workability test: Cup punch the passivated hot-dip galvanized steel sheet, and then conduct a neutral salt spray test to test the cold workability of the passivation film.

3. X-scribing test: Scribe the passivated hot-dip galvanized steel sheet diagonally with a blade to scratch the passivation film, and then conduct a neutral salt spray test to detect passivation after X-scribing Corrosion resistance under film damage conditions.

4. Solvent resistance test: Wipe the passivated hot-dip galvanized steel sheet with absorbent cotton and ethanol for 10 times, observe the surface changes, and then conduct a neutral salt spray test to test the solvent resistance of the passivation film.

5. Blackening resistance test: put the passivated hot-dip galvanized steel sheet in a constant temperature and humidity box, and conduct a blackening resistance test at 70°C×80% relative humidity to detect the blackening resistance of the passivation film The test piece is hung on the automatic rotating frame in the humidity and heat test chamber, and the automatic rotating frame performs forward and reverse rotation at the same interval.

6. Anti-yellowing test: Bake the passivated hot-dip galvanized steel sheet at 220°C for 30 minutes, and compare the color change of the baking sheet. The test is carried out in an oven.

After passivating the hot-dip galvanized steel sheet to be passivated with each group of passivating agents in the above embodiments, the performance tests of the passivation effect are shown in Table 2 below.

Table 2: Performance test results of hot-dip galvanized steel sheets after passivation

Example number Neutral salt spray test cold workability X-dash Solvent resistance Anti-yellowing Resistance to blackening 1 <3% <3% <3% <5% mild mild 2 <3% <3% <3% <5% mild mild 3 <3% <3% <3% <5% mild mild 4 <3% <3% <3% <5% mild mild 5 <3% <3% <3% <5% mild mild 6 <3% <3% <3% <5% mild mild 7 <3% <3% <3% <5% mild mild 8 <3% <3% <3% <5% mild mild 9 <3% <3% <3% <5% mild mild 10 <3% <3% <3% <5% mild mild 11 <3% <3% <3% <5% mild mild 12 <3% <3% <3% <5% mild mild 13 <3% <3% <3% <5% mild mild 14 <3% <3% <3% <5% mild mild 15 <3% <3% <3% <5% mild mild 16 <3% <3% <3% <5% mild mild

Note: The percentages in Table 2 above indicate the percentage of corrosion area after 72 hours of neutral salt spray test.

Claims (5)

1. a low-temperature drying passivator for hot-dip galvanized steel sheet, characterized in that, the passivator includes water and the following concentration of components: Nano SiO ₂ 40g/L～80g/L, Water-soluble acrylic resin 40g/L～80g/L, Organic phosphonic acid 40g/L～80g/L, Ammonium fluotitanate and/or titanyl sulfate 5g/L～15g/L, and Ammonium metavanadate 10g/L～20g/L; The organic phosphonic acid includes amino trimethylene phosphonic acid, hydroxyethylidene diphosphonic acid, diethylene triamine pentamethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, polyamino polyether group methylene phosphonic acid at least one of acids; The drying plate temperature of the low-temperature drying passivator is above 70°C and below 80°C. 2. the low-temperature drying passivator for hot-dip galvanized steel sheet according to claim 1, is characterized in that, also contains the diethylamine that is used to regulate passivator pH value in the passivator, so The pH value of the passivating agent is 4-5. 3. the low-temperature drying passivating agent for hot-dip galvanized steel sheet according to claim 1 or 2, is characterized in that, described passivating agent is chrome-free passivating agent, and does not contain in the described passivating agent Molybdates or rare earth metal compounds. 4. The low-temperature drying passivator for hot-dip galvanized steel sheets according to claim 1 or 2, characterized in that the average particle diameter of the nano-SiO ₂ is 10nm-100nm. 5. A method for passivating a hot-dip galvanized steel sheet with the low-temperature drying passivator described in any one of claims 1 to 4, the method mainly refers to adopting on the production line of the hot-dip galvanized steel sheet The passivating agent is applied to the hot-dip galvanized steel sheet by scraping, spraying or roller coating, and the temperature of the drying plate is above 70°C; the temperature of the drying plate is lower than 80°C.