GB2142654A

GB2142654A - Pigmentation of aluminium mold material

Info

Publication number: GB2142654A
Application number: GB08317946A
Authority: GB
Inventors: Akira Nomura; Yoshikazu Shimoda
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-06-27
Filing date: 1983-07-01
Publication date: 1985-01-23
Also published as: IT8321980A0; AU1629483A; IT1169452B; GB8317946D0; DE3324565A1

Abstract

Four convey frames (1, 2, 3, 4) each have suspended therefrom a number of arrayed aluminium mold materials having anodic oxide films. The first and third convey frames (1, 3) constitute a first conduction 3 unit (U1) and the second and fourth convey frames (2, 4) constitute a second conduction unit (U2). The mold materials suspended from the four convey frames are simultaneously immersed in an electrolytic bath (6) containing a metal salt. Electrodes (E1, E2, E3) are arranged at positions to the left and right of and at a central position of the four convey frames so that two arrays of mold materials oppose each other between each pair of electrodes. Anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis are sequentially performed for each conduction unit, such that the to conduction units (U1, U2) cannot be conducted simultaneously. <IMAGE>

Description

SPECIFICATION Method for Pigmentation of Aluminum Mold Material The present invention relates to a method for pigmentation of a mold material of aluminum or an alloy thereof (to be simply referred to as an aluminum mold material hereinafter).

According to a conventional method for electrolytic pigmentation of an aluminum mold material, a number of such materials are mounted on one or two convey frames. However, with this method, the number of aluminum mold materials which may be treated simultaneously is limited.

Accordingly, mass-production of aluminum mold materials is difficult. It is also difficult to obtain aluminum mold materials which are pigmented uniformly to a dark tone and which have a good appearance.

The present invention has been made in consideration of this situation and has for its object to provide a method for electrolytic pigmentation of an aluminum mold material, wherein four convey frames, each having a number of aluminum mold materials suspended therefrom, are simultaneously conveyed and immersed in an electrolytic bath so that a large number of aluminum mold materials may be treated simultaneously and uniformly, without excessively increasing the size of such an apparatus.

In order to achieve the above and other ends, there is provided according to the present invention a method for pigmentation of an aluminum mold material, comprising the steps of simultaneously conveying four convey frames, each of which has suspended therefrom a number of arrayed aluminum or aluminum alloy mold materials having anodic oxide films, first and third convey frames constituting a first conduction unit, and second and fourth convey frames constituting a second conduction unit; simultaneously immersing the mold materials suspended from said four convey frames in an electrolytic bath containing a metal salt; arranging electrodes at positions to the left and right of and at a central position of said four convey frames so that two arrays of mold materials oppose each other between each pair of said electrodes; and sequentially performing anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis for each of said conduction units such that said conduction units cannot be conducted simultaneously, thereby performing electrolytic pigmentation.

The single drawing is a view showing an example of electrolytic pigmentation according to a method of the present invention.

According to the present invention, four convey frames from which a number of arrayed aluminum mold materials having anodic oxide films are suspended are simultaneously conveyed by, for example, a crane or a conveyor and simultaneously immersed in an electrolytic bath.

The prior anodic oxidation is performed by the electrolytic oxidation of aluminum mold materials 6 m long in an aqueous solution of sulfuric acid, chromic acid, oxalic acid or the like. Electrodes are arranged inside an electrolytic pigmentation cell as shown in the drawing; electrodes El and E3 are arranged at positions just inside the electrolytic pigmentation cell and near the cell walls, that is, to the left and right of the four frames, and an electrode E2 is arranged at the central position of the four frames. The cell walls may be used as the electrodes El and E3.

Furthermore, two electrodes may be arranged at the central position of the four electrodes so as to be paired with each of the electrodes El and E3.

When two electrodes are arranged at the central position of the four frames, pigmentation films may be formed with greater uniformity. The first and third frames are paired to constitute a conduction unit, and the second and fourth frames are paired to constitute another conduction unit. As may be seen from the drawing, aluminum mold materials Al and A3 suspended from the first and third convey frames, that is, convey frames 1 and 3, respectively, are electrically connected to constitute a conduction unit Ul, and aluminum mold materials A2 and A4 suspended from the second and fourth convey frames, that is, convey frames 2 and 4, respectively, are electrically connected to constitute a conduction unit U2.

These conduction units U1 and U2 define an electrical connection such that when one of them is conductive the other is not conductive. For example, the method of the present invention may be performed in the following manner. First, anodic direct current electrolysis of the aluminum mold materials Al and A3 of the conduction unit U1 is performed at a voltage of 15 to 25 V.

Thereafter, alternating current electrolysis of the aluminum mold materials Al and A3 of the conduction unit U1 is performed at a voltage of 10 to 25 V. Further, cathodic direct current electrolysis of the aluminum mold materials Al and A3 of the coriduction unit U1 is performed at a voltage of 1 5 to30 V. Then, the aluminum mold materials A2 and A4 of the conduction unit U2 are subjected to electrolytic pigmentation in accordance with similar procedures.

From the viewpoint of economy and simple structure of the apparatus, power for electrolysis shouid preferably be supplied from a single power supply or the respective power supplies for both conduction units. However, power supplies may be arranged separately for the respective convey frames.

Referring to the accompanying drawing, an electrolytic pigmentation cell 5 holds an electrolytic bath 6 containing a metal salt therein.

The metal salt to be contained in the electrolytic bath 6 may be one or more water-soluble salts such as nickel salt, cobalt salt, copper salt, tin salt, silver salt or the like. Depending upon the kind of water-soluble salt or salts used, an additive such as sulfuric acid, boric acid, a metal hydroxide such as nickel hydroxide, metal carbonate or ammonia, is added in a suitable amount so as to adjust the conductance and the pH of the electrolytic bath.

Furthermore, an additive such as citric acid, succinic acid, tartaric acid or the like may also be added as needed. An example of the bath composition containing nickel sulfate as a major component may be: 150 to 180 9/l of nickel sulfate hexahydrate, and 5 to 50 g/l of boric acid. The temperature of the electrolytic bath is controlled to be between the ordinary temperature and 400 C, and the pH is adjusted to be within the range of 2 to 5.5 and preferably within the range of 3 to 4.5. The electrodes may comprise aluminum or a metal of the same type as that which is used for the electrolyte, such as nickel, tin or copper. The surface area ratio (counter electrode ratio) of the electrodes and the mold materials is within the range of 2:1 to 1:50 and preferably within the range of 1:5 to 1:10.The current density and electrolysis time for anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis may vary in accordance with the composition of the electrolytic bath, the counter electrode ratio, the distance between the counter electrodes, the number of the aluminum mold materials to be treated, and so on. However, in anodic direct current electrolysis, the maximum current density is preferably 0.1 to 1.5 A/dm2 and the electrolysis time is preferably 1 to 1 5 seconds. In alternating current electrolysis, the maximum current density is preferably 0.1 to 2.0 A/dm2 and the electrolysis time is preferably 1 to 30 seconds. In the cathodic direct current electrolysis, the maximum current density is preferably 0.1 to 1.0 A/dm2 and the electrolysis time is preferably 30 to 240 seconds.

Alternating current electrolysis and cathodic direct current electrolysis are generally performed in the same electrolytic cell in which anodic direct current electrolysis is performed. However, a separate electrolytic cell may be prepared and may be used for alternating current electrolysis and cathodic direct current electrolysis. When the three electrolysis treatments are performed in a single electrolytic cell, a switch may be provided for the power supply, and the power supply may be switched for each electrolysis treatment.

The electrolysis pigmentation treatment according to the present invention has the function of providing the alternating current electrolysis, which results in the formation of satisfactory pigmentation films. However, if it is desired to form a film which is denser in color, the respective conduction units need not be simultaneously subjected to electrolytic pigmentation; a cycle of anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis may be performed repeatedly for performing the electrolysis treatment. According to the present invention, when anodic direct current electrolysis is performed, after the aluminum mold materials are immersed in an electrolytic bath, they may be kept in a nonconduction state for a predetermined period of time before the electrolysis is begun.In this case, the predetermined period of time is preferably 60 seconds or longer. When such a nonconduction period is adopted, more uniform pigmentation may be achieved. Furthermore, when a switch is to be made from alternating current electrolysis to cathodic direct current electrolysis, another nonconduction period may be adopted. When alternating current electrolysis is performed in a large scale industrial electrolytic cell, an induced current tends to flow. In order to prevent this, a nonconduction period is preferably adopted. This nonconduction period is 1 second or longer and preferably 1 5 seconds or longer.

Similarly, when a switch is to be made from anodic direct current electrolysis to alternating current electrolysis, still another nonconduction period is adopted. This nonconduction period is 5 seconds or longer and preferably 10 seconds or longer.

According to the method of the present invention, after anodic direct current electrolysis, alternating current electrolysis and cathodic direct current electrolysis are sequentially performed for one conduction unit, the same cycle of electrolysis treatments may be performed for the other conduction unit. Alternatively, it is also possible to perform anodic direct current electrolysis and alternating current electrolysis for one conduction unit and then to perform the same electrolysis treatments for the other conduction unit. In this case, cathodic direct current electrolysis is then performed for the former conduction unit, and is thereafter performed for the latter conduction unit.According to the method of the present invention, better results are obtained if cathodic direct current electrolysis is performed at a voltage which is higher than that of anodic direct current electrolysis.

After the electrolytic pigmentation treatment, the aluminum mold materials are subjected to sealing and painting as needed.

In this manner, the method of the present invention can provide aluminum mold materials which are uniformly pigmented to a dark tone and which have a good appearance. This is considered to be due to the following reasons.

If all the convey frames are treated in a single group and are conducted simultaneously, a current simultaneously flows to the adjacent mold materials Al and A2 and to the adjacent mold materials A3 and A4. This causes electric repulsion between these adjacent pairs of mold materials and renders the resistances of the anodic oxide films nonuniform. Accordingly, the current density becomes unstable, and uniform adsorption of metal ions is prevented due to the repulsion of the metal ions. Then, nonpigmented regions are formed on surfaces a, b, c and d as shown in the drawing, respectively.

In contrast to this, according to the method of the present invention, the first and third convey frames are paired to form one conduction unit, while the second and fourth convey frames are paired to form the other conduction unit. Then, aluminum mold materials which are not adjacent to each other are subjected to anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis under predetermined conditions. This allows removal of any impurities which may have become attached to or adsorbed in anodic oxide films and renders the resistances of these films uniform.Furthermore, since first the aluminum mold materials Al and A3 and then the aluminum mold materials A2 and A4 are subjected to the electrolysis treatments, the overall quality of the anodic oxide films may be improved in synergism with the prevention of the formation of nonpigmented regions. For these reasons, the current density is made stabie, and the distribution of the metal ions within the electrolytic bath becomes uniform. Deposition of a metal or a metal oxide in the anodic oxide film becomes uniform and easy, resulting in an increased amount of deposition and a higher conductance. Conventionally, irregular pigmentation tends to occur between two surfaces of an aluminum mold material when these two surfaces are at different distances from the electrode.Despite this, according to the method of the present invention, an aluminum mold material which is uniformly pigmented may be obtained.

The method of the present invention is thus suitable for mass-production wherein four convey frames are conveyed simultaneously and a number of aluminum mold materials are subjected to electrolytic pigmentation. The problem of irregular pigmentation which tends to arise in mass-production is eliminated, and treatment of several times the number of aluminum mold materials as was conventionally possible is thus realized. In summary, the method of the present invention allows efficient production of aluminum mold materials which are uniformly pigmented to a dark tone and which have a good appearance, produces a high throwing power, and allows simultaneous electrolytic pigmentation of a large number of aluminum mold materials.

In addition to the advantages enumerated above, the present invention can provide the following advantages. Specifically, the method of the present invention is less subject to the effects of impurities which may be contained in the electrolytic bath, so that inferior pigmentation from this cause may be prevented and the allowable range of the amount of impurities is widened. Accordingly, when an electrolytic bath is prepared, the quality of water before treatment need not be strictly checked, and a large ion exchanger is not required, resulting in an industrially advantageous method. When a large number of aluminum mold materials are to be pigmented, a pair of electrodes is conventionally arranged for each frame suspending therefrom a number of aluminum mold materials.In contrast to this, with the method of the present invention, uniformly pigmented films may be obtained with a smaller number of electrodes. Accordingly, the apparatus for practicing the method may be reduced in size and effective electrolysis may be performed.

The present invention will now be described by way of its examples.

Example Arrays each consisting of a number of aluminum mold materials were suspended from convey frames 1, 2, 3 and 4 shown in the drawing. The four frames 1 to 4 were simultaneously conveyed by a crane to perform degreasing, etching and neutralization treatments. Thereafter, the aluminum mold materials were immersed in an anodic oxidation bath and were subjected to direct current electrolysis for formation of anodic oxide films in a bath of 1 80 g/l of an aqueous solution of sulfuric acid at a current density of 1.3 A/dm2, an electrolysis time of 30 minutes and a bath temperature of200C. After being rinsed with water, the convey frames 1 to 4 were simultaneously conveyed to an electrolytic pigmentation cell 5 and the aluminum mold materials Al to A4 were simultaneously immersed in an electrolytic bath 6 held therein.

The arrangement of electrodes El, E2, and E3 was as shown in the drawing. The composition and conditions of the electrolytic bath 6 were as shown below: Nickel sulfate hexahydrate 1 50 g/l Boric acid 50 g/l pH 3.7 Temperature 350C One example of impurities 60 ppm of Na ions The convey frames 1 and 3 and the convey frames 2 and 4 were electrically connected to constitute conduction units U1 and U2, respectively. After a nonconduction period of 5 seconds, a direct current was supplied to the conduction unit U1 to perform anodic direct current electrolysis at a voltage of 1 8 V for an electrolysis time of 10 seconds, with aluminum mold materials Al and A3 of the conduction unit U1 serving as anodes.After another nonconduction period of 1 5 seconds, an alternating current was supplied to the conduction unit U1 to perform alternating current electrolysis at a voltage of 20 V for an electrolysis time of 10 seconds. After still another nonconduction period of 10 seconds, a direct current was supplied to the conduction unit U1 again to perform cathodic direct current electrolysis at a voltage of 20 V for an electrolysis time of 60 seconds, with the mold materials Al and A3 serving as cathodes. Power supply connection was then switched to the conduction unit U2 and aluminum mold materials A2 and A4 of the conduction unit U2 were subjected to electrolytic pigmentation under the same conditions as were the mold materials Al and A3.The current density for each electrolysis step was about 0.3 to 0.02 A/dm2, 0.8 to 0.6 Ndm2, and 0.3 to 0.05 A/dm2, respectively.

As a result of this treatment, uniformly pigmented films of a bronze-like color were formed on the mold materials Al, A2, A3 and A4. The Na ions did not cause any adverse effect such as inferior pigmentation when they were contained in the bath in an amount of 60 ppm.

Comparative Example 1 After forming anodic oxide films on aluminum mold materials Al to A4 of convey frames 1 to 4, respectively, in accordance with procedures similar to those used in the Example described above, the aluminum mold materials Al to A4 were simultaneously immersed in an electrolytic bath 6 similar to that used in the Example, and the convey frames 1 and 3 and the convey frames 2 and 4 were electrically connected to constitute conduction units U1 and U2, respectively. A direct current was supplied to the conduction unit U1 first so as to perform anodic direct current electrolysis of the mold materials Al and A3 at a voltage of 23 V for an electrolysis time of 10 seconds. Subsequently, the mold materials Al and A3 were subjected to cathodic direct current electrolysis at a voltage of 20 V for an electrolysis time of 45 seconds.The power supply connection was then switched to the conduction unit U2, and the mold materials A2 and A4 were subjected to electrolysis under the same conditions as were the mold materials Al and A3. As a result, spalling occurred, and properly pigmented films were not obtained.

Comparative Example 2 After forming anodic oxide films on aluminum mold materials Al to A4 of convey frames 1 to 4, respectively, in accordance with procedures similar to those in the Example described above, the aluminum mold materials Al to A4 were simultaneously immersed in an electrolytic bath 6 similar to that used in the Example, and the convey frames 1 to 4 were electrically connected. The mold materials Al to A4 were then simultaneously subjected to a cycle of anodic direct current electrolysis at 10 V for 10 seconds, alternating current electrolysis at 5 V for 5 seconds and cathodic direct current electrolysis at 20 V for 60 seconds.

Spalling and irregular pigmentation occurred, and properly pigmented films were not obtained.

Claims

1. A method for pigmentation of an aluminum mold material, comprising the steps of: simultaneously conveying four convey frames, each of which has suspended therefrom a number of arrayed aluminum or aluminum alloy mold materials having anodic oxide films, first and third convey frames constituting a first conduction unit, and second and fourth convey frames constituting a second conduction unit; simultaneously immersing the mold materials suspended from said four convey frames in an electrolytic bath containing a metal salt; arranging electrodes at positions to the left and right of and at a central position of said four convey frames so that two arrays of mold materials oppose each other between each pair of said electrodes; and sequentially performing anodic direct current electrolysis, alternating current electrolysis, and cathodic direct current electrolysis for each of said conduction units such that said conduction units cannot be conducted simultaneously, thereby performing electrolytic pigmentation.

2. A method according to claim 1, wherein the anodic direct current electrolysis at a voltage of 1 5 to 25 V, the alternating current electrolysis at a voltage of 10 to 25 V, and the cathodic direct current electrolysis at a voltage of 1 5 to 30 V are sequentially performed.

3. A method according to claim 1 , wherein the metal salt contained in the electrolytic bath is at least one water-soluble salt selected from the group consisting of nickel salt, cobalt salt, copper salt, tin salt and silver salt.

4. A method according to claim 3, wherein the electrolytic bath further contains at ieast one additive selected from the group consisting of sulfuric acid, boric acid, a metal hydroxide, a metal carbonate, ammonia, citric acid, succinic acid, and tartaric acid.

5. A method according to claim 1, wherein a ratio of surface areas of said electrodes and the mold materials is within a range of 2:1 to 1:50.

6. A method according to claim 1 ,wherein a nonconduction period is adopted before the step of performing the anodic direct current electrolysis, the alternating current electrolysis, and the cathodic direct current electrolysis.

7. A method according to claim 1, wherein a nonconduction period is adopted between the anodic direct current electrolysis and the alternating current electrolysis.

8. A method according to claim 1, wherein a nonconduction period is adopted between the alternating current electrolysis and the cathodic direct current electrolysis.

9. A method according to claim 1 , wherein the cathodic direct current electrolysis is performed at a voltage higher than a voltage of the anodic direct current electrolysis.

10. A method for pigmentation of aluminum mold material, substantially as hereinbefore described with reference to the accompanying drawing.