JPH0718463A - Chemical conversion treatment - Google Patents

Abstract

PURPOSE:To provide chemical conversion treatment by which the variation of unit chemical conversion coating weight in the respective regions of a body to be treated is reduced even if there are a highly reactive region and a lowly reactive region on the body. CONSTITUTION:A body 2 to be treated is dipped in a treating tank 1 to form a chemical conversion coating. In this process, a cold body or a hot body 12 is confronted with a specified region between the region of the body 2 highly reactive to a chemical conversion soln. and the region lowly reactive to the soln., the soln. temp. close to the specified region is made different from that at the other regions by utilizing the heat dissipation from the hot body, and the variation of chemical conversion coating weight at the respective regions of the body 2 is reduced. Consequently, the film thickness on the respective regions of the body is uniformized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical conversion treatment method for forming a chemical conversion treatment film on an automobile body or other metal body as a pretreatment for a coating process or a plating process.

[0002]

2. Description of the Related Art Conventionally, in a coating process for an automobile body or the like, a chemical conversion treatment film is formed as a pretreatment for electrodeposition coating for undercoating an automobile in order to improve the adhesion and corrosion resistance of the coating film. In this pretreatment method, first, an automobile body is transported to a degreasing process by using a hanger conveyor or the like, sufficiently degreased with an alkaline degreasing agent or sodium orthosilicate, and then transported to a surface conditioning process, where the body is titanium salt. The titanium colloid is precipitated by immersing it in a colloidal liquid made of a component such as sodium phosphate and the like, and then the body is conveyed to a chemical conversion treatment step to form a phosphoric acid treatment film on its surface. .

[0003]

However, since this phosphoric acid-treated coating is formed by utilizing the solubility of the steel sheet surface, the surface properties of the steel sheet have a great influence on the coating formation. That is, in an automobile body, the chemical conversion reactivity of the flat part is good, but the reactivity of the plate-bonding part having irregularities is poor. Therefore, conventionally, the chemical conversion treatment is performed by setting the reaction temperature and reaction time according to the plate-bonding part. Since it is carried out, an excessive chemical conversion film is attached to the flat surface portion, which may not only unnecessarily consume the treatment liquid but also adversely affect the coating process such as an increase in the amount of the coating used in the subsequent coating process.

In recent years, in order to reduce the weight and to provide a window in the roof part, a vehicle body having a composite structure in which an aluminum material is included in a part of a body of a steel sheet has been proposed. Since the material has a lower reactivity to the chemical conversion treatment liquid than the steel plate, an additive such as NaF (sodium fluoride) is added to the treatment liquid to increase the reactivity of the aluminum material portion. The reactivity of the steel plate portion other than the material forming portion is also increased, and as a result, an excessive chemical conversion film is attached to that portion, and the same drawbacks as described above are derived.

In view of the above-mentioned drawbacks of the prior art, the present invention makes the film thickness of the chemical conversion film uniform at each part of the object to be processed even when the object has a highly reactive part and a poorly reactive part. In other words, it is an object of the present invention to provide a chemical conversion treatment method capable of reducing variation in the weight of the chemical conversion coating per unit.

[0006]

FIG. 3 shows a steel plate for an automobile body (material SP
(CC and SGACC) is a relationship between the coating weight and temperature obtained by immersing (CC and SGACC) in a phosphoric acid conversion treatment solution for a predetermined time. As is clear from this figure, the coating weight increases with increasing temperature. It is understood that the rising curve is small up to 45 ° C, but the rising curve becomes large above 45 ° C.

The present invention was created on the basis of such findings, and is characterized in that the article to be treated is immersed in the treatment liquid tank to form a chemical conversion coating on the surface of the article to be treated. In the chemical conversion treatment method, a cold or hot body is disposed so that the cold body or the hot body can be faced to a predetermined site on either one of the site having good reactivity and the site having poor reactivity with the chemical conversion solution of the object to be treated, The temperature of the treatment liquid in the vicinity of a predetermined portion is relatively different from that of the other portions by utilizing the heat radiation from the heat treatment, so that the weight of the chemical conversion coating varies among the respective portions of the object to be treated. It is intended to reduce. In this case, when the object to be treated is an automobile body, the temperature of the treatment liquid around the highly reactive portion should be about 45 ° C or lower, and the temperature of the treatment liquid around the poorly reactive portion should be about 45 ° C or higher. It is better to have a relative temperature difference.

[0008]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 1
(A) shows a chemical conversion treatment liquid tank used in a pretreatment process for automobile body painting according to the first embodiment of the present invention, in which an object to be treated 2 is provided above the treatment liquid tank 1 in which a treatment liquid 1a is stored. A conveyer 3 is installed to carry the material into and out of the treatment liquid tank 1 while supporting the object 2 to be treated in the treatment liquid 1a in the treatment liquid tank 1. A plurality of article support jigs 5 to be conveyed are arranged at intervals. Further, as shown in FIG. 1 (B), a pipe line 6 which is opened at an appropriate position for circulating the treatment liquid is arranged along the longitudinal direction, and the pipe line 6 includes a pump 8 and a heat exchanger. 9 is connected to the processing liquid tank 1 so that the processing liquid 1a in the processing liquid tank 1 is circulated in the processing liquid tank 1 via the pipe line 6 while being constantly maintained at a constant temperature by the heat exchanger 9.

The treatment liquid tank 1 is located slightly above the pipe line 6 on the side facing the plate matching portion 2a of the automobile body 2.
Two fluid pipes 12 are arranged in parallel along the longitudinal direction, and a fluid heated to a predetermined temperature by the heat exchanger 11 is circulated in the fluid pipes 12 via a pump 15. The heat exchanger 11 has a heat pump 2 and other warmers 2.
The heat medium heated by 0 makes it possible to circulate through the heat exchange pipe in the exchanger 11, and the controller 29 controls the heater 20 based on the temperature detected by the thermistor 21 provided near the fluid pipe 12. The temperature of the fluid flowing through the fluid pipe 12 can be controlled accurately by controlling the temperature of the fluid pipe 12.

In such a structure, for example, a known chemical conversion treatment liquid containing manganese oxide, nickel oxide and the like in a predetermined amount in a phosphate conversion treatment liquid is used, and the treatment liquid temperature in the treatment liquid tank 1 is set to 40. The temperature was set to ˜43 ° C., and the car body using the steel plate of SPCC material was subjected to the chemical conversion treatment by the above-described pretreatment process procedure in the conventional state in which the treatment liquid was not heated from the fluid pipe 12. The weight of the chemical conversion coating on the site varied with 2.05 to 2.56 (g / m ² ). Next, when a heat medium heated to about 50 ° C. was circulated from the fluid pipe 12 to raise the temperature of the treatment liquid around the plate-matching portion 2a, the chemical conversion treatment was performed under the same conditions as described above. The conversion coating weight is 2.30-2.
The variation was 56 (g / m ² ), which was significantly reduced.

Next, the car body 1 made of SGAC steel plate was subjected to chemical conversion treatment under the same conditions as above, with and without heating of the treatment liquid from the fluid pipe 12, and in the former case, The weight of the chemical conversion coating at each site is
Although it was 3.11 to 3.51 (g / m ² ), in the latter case, the weight of the conversion coating film at each site was 3.31.
-3.56 (g / m < ² >), the variation was significantly reduced.

FIG. 3 shows another embodiment in which the temperature of the treatment liquid around the door is lowered contrary to the above, and as shown in FIG. 3A, the treatment liquid storage portion is located at a position facing the door portion 2b of the automobile body 2. , The cooling fluid pipes 13 are arranged in a comb shape, and the fluid pipes 13
In addition, the fluid cooled to a predetermined temperature by the heat exchanger 11 is circulated through the pump 24. The heat exchanger 11 is connected to a heat pump or other cooler 25, and the cooler 25 is controlled based on the temperature detected by the thermistor 21 provided between the fluid pipe and the door portion 2b to control the fluid pipe 13. Through the door portion 2b of the automobile body 2
The surrounding temperature is configured to be accurately controlled so as to have a temperature difference with respect to other parts.

In this structure, the temperature of the processing liquid in the processing liquid tank 1 is set to around 46 to 50 ° C.
In the state in which a low coolant temperature of about 37 to 40 ° C. is circulated in 2 to reduce the temperature of the processing solution around the door portion 2a side where the planar processing solution has good reactivity, an automobile body made of a steel plate of SPCC material is used. When each of the automobile bodies using the steel sheet of SGAC material was subjected to the chemical conversion treatment under the same conditions as described above, the variation in the weight of the chemical conversion coating in each part was significantly reduced as in the above-mentioned example.

[0014]

As described above, according to the present invention, the temperature of the processing liquid in the processing liquid tank is controlled by partially giving a temperature difference, and thus the flat surface portion and the uneven portion of the object to be processed, and further the aluminum material. And a portion where the treatment liquid easily reacts, such as a composite-structured object having portions with different materials such as a steel plate,
Even if there is a site that is difficult to react, it is possible to reduce the variation in the weight of the chemical conversion coating in each site of the object to be treated. Further, the present invention can be applied not only as a coating process but also as a chemical conversion treatment method for a plating process. It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a schematic view showing a chemical conversion treatment bath for automobile body pre-coating treatment according to a first embodiment of the present invention, (A) is a front view thereof, and (B) is a central sectional view thereof.

FIG. 2 is a schematic view showing a chemical conversion treatment bath for automobile body pre-treatment according to another embodiment of the present invention, in which (A) is a front view thereof and (B) is a central sectional view thereof.

FIG. 3 is a graph showing the relationship between coating weight and temperature in chemical conversion treatment.

[Explanation of symbols]

 5 article support 2 object to be treated 1 treatment liquid tank 11 heat exchanger 12 hot body 13 cold body

Claims (2)

[Claims] 1. A chemical conversion treatment method of forming a chemical conversion treatment film on the surface of an object to be treated by immersing the object to be treated in a treatment liquid tank, wherein a portion of the object to be treated that has a high reactivity with the chemical conversion solution. A cold or hot body is placed so as to be able to face any one of the predetermined areas with poor reactivity, and the heat of the heat body is used to dissipate the temperature of the treatment liquid in the vicinity of the predetermined area. A chemical conversion treatment method characterized in that a variation in the weight of the chemical conversion coating per unit in each part of the object to be treated is reduced by making a relative temperature difference compared with the temperature of the treatment liquid. 2. When the object to be treated is an automobile body, the temperature of the treatment liquid around the highly reactive portion is about 45 ° C. or less, and the temperature of the treatment liquid around the poorly reactive portion is about 45 ° C. or more. The chemical conversion treatment method according to claim 1, wherein a relative temperature difference is provided.