Attachment coating method

An attachment coating method including, mixing a conductive attachment into an insulating liquid, immersing an attachment target in the insulating liquid in which the attachment is mixed, and applying ultrasonic vibration to the insulating liquid in which the attachment target is immersed and causing friction between the attachment target and the attachment to charge the attachment target and the attachment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-252915, filed Dec. 15, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an attachment coating method to coat a target with an attachment.

2. Description of the Related Art

Jpn. Pat. Appln. KOKAI Publication No. 1-111899 discloses a technique for applying ultrasonic vibration for stirring in a technique of electrodeposition coating. Jpn. Pat. Appln. KOKAI Publication No. 2001-151828 discloses a technique for maintaining a high electric resistivity of a carrier fluid for the purpose of maintaining toner charge stability in a technique for printing a circuit pattern by an electrophotographic developing method.

BRIEF SUMMARY OF THE INVENTION

An attachment coating method including, mixing a conductive attachment into an insulating liquid, immersing an attachment target in the insulating liquid in which the attachment is mixed, and applying ultrasonic vibration to the insulating liquid in which the attachment target is immersed and causing friction between the attachment target and the attachment to charge the attachment target and the attachment.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of an attachment coating method is described with reference toFIG. 1toFIG. 3. In this embodiment, an attachment target undergoes the following steps and can be thereby uniformly coated with an attachment. A workpiece (attachment target) is coated with the attachment, for example, for the purpose of improving mold releasability when the workpiece is taken out of a mold.

An ultrasonic vibration generator11described below is used in the attachment coating method according to the embodiment. As shown inFIG. 1, the ultrasonic vibration generator11has a tank12, a bolt-clamped Langevin type transducer (BLT)13provided on the bottom of the tank12, and an electric power supply circuit which supplies electricity to the BLT13. In the ultrasonic vibration generator11, electricity is supplied to the BLT13from the electric power supply circuit, and ultrasonic vibration can be thereby applied to a liquid14retained in the tank12and to an attachment target15immersed in the liquid14. The frequency of the ultrasonic vibration actually applied to the liquid14and the attachment target15is determined by, for example, the resonant frequency of the BLT13on the output side, the material of the attachment target15, and the length of the attachment target15. The frequency of the ultrasonic vibration actually applied to the liquid14and the attachment target15can be measured, for example, by putting a hydrophone into the liquid14retained in the tank12and measuring its sound pressure (voltage).

A method of coating with an attachment16according to the present embodiment is described. This coating method includes a first step of mixing the attachment16into the liquid14, a second step of immersing the attachment target15in the liquid14, and a third step of applying ultrasonic vibration to the liquid14in which the attachment target15is immersed.

In the first step, first, the liquid14is put into the tank12of the ultrasonic vibration generator11. Molybdenum trioxide which is the attachment16is then mixed into the liquid14. The molybdenum trioxide is conductive. The attachment16has only to be a conductive material, and may be any conductive material other than molybdenum trioxide. A conductive material other than molybdenum trioxide is, for example, molybdenum disulfide.

In the first step, the liquid14is stirred with, for example, a stirring rod so that the molybdenum trioxide may be uniform in the liquid14. Alternatively, an operation switch of the ultrasonic vibration generator11may be turned on so that ultrasonic waves are applied to the liquid14in the tank12to stir the liquid14for mixing. An insulating lubricator (insulating lubricating oil) can be used as the liquid14to be put into the tank12. For example, an isoparaffinic hydrocarbon solvent can be used as the insulating lubricator. By way of example, a brand name “Daphne Alpha Cleaner L” manufactured by Idemitsu Kosan Co., Ltd. can be used. The insulating lubricator is not limited to the isoparaffinic hydrocarbon solvent, and other kinds of lubricators such as a naphthenic hydrocarbon solvent can be used. One example of a naphthenic hydrocarbon solvent is a brand name “Daphne cleaner” manufactured by Idemitsu Kosan Co., Ltd. The volume resistivity of “Daphne Cleaner” is 1.9×1013Ω·m. In general, when the volume resistivity of a liquid is 108Ω·m or more, this liquid can be considered to have insulating properties.

In the second step, the attachment target15is immersed in the liquid in which the molybdenum trioxide is mixed as described above. The attachment target15is suspended with its top caught by support means, and can be thereby immersed in the liquid so that the attachment target15is floating from a bottom12A of the tank12as shown inFIG. 1. The attachment target15is metallic, and is made of one of the materials selected from the group consisting of titanium, a titanium alloy, and a stainless alloy. The attachment target15has a shape of, for example, a round bar, but may have any shape such as a quadratic prism shape, a spherical shape, a conical shape, or a quadrangular pyramid shape.

In the third step, ultrasonic vibration is applied to the liquid14and the attachment target15by the ultrasonic vibration generator11for a predetermined length of time. If the operation switch of the ultrasonic vibration generator11is turned on, an electric current is supplied to the BLT13from the electric power supply circuit, and ultrasonic vibration is then generated from the BLT13. The ultrasonic vibration is applied to the liquid14and the attachment target15. As a result, the attachment target15is negatively charged, and the attachment16is positively charged.

Furthermore, after the ultrasonic vibration is applied to the liquid14and the attachment target15in the third step, it is preferable to leave the state as it is (perform a leaving step) for a predetermined length of time. This leaving procedure can accelerate the sticking of the attachment16to the attachment target15. Specifically, the method of coating with the attachment16was conducted under conditions shown as Example inFIG. 4. The conditions according to the Example were compared with the conditions according to Comparative Examples 1 to 8 inFIG. 4as below to confirm the effectiveness of the method of coating with the attachment16according to the present embodiment (Example).

Example

In the Example, molybdenum trioxide was used as the attachment16. An isoparaffinic hydrocarbon solvent which was an insulating solvent was used as the liquid14. The application time of ultrasonic waves was 300 seconds. A leaving time after the application of the ultrasonic waves was 60 seconds. A compound frequency of 45 kHz, 90 kHz, and 135 kHz was used as the frequency of the ultrasonic waves applied to the liquid14and the attachment target15. The first to third steps and the leaving procedure that have been described above were conducted under the conditions according to the Example, so that the attachment target15could be uniformly coated with the attachment16as inFIG. 5. InFIG. 5, the right end is the side supported by the support means, and the left end is located close to the bottom12A of the tank12. As inFIG. 5, the attachment state was judged to be acceptable when the amount of the attachment16attached to the attachment target15was uniform and the thickness of the attachment16was also sufficient.

Furthermore, under the conditions according to the Example, the sound pressure of the ultrasonic waves applied to the liquid14and the attachment target15in the tank12of the ultrasonic vibration generator11was measured. The measurement results are shown inFIG. 6. In the graph ofFIG. 6, the measured sound pressure of the ultrasonic waves is indicated by a thin line waveform. The amplitude of the waveform indicates the intensity of the sound pressure. When the sound pressure was further decomposed by fast Fourier transform (FFT), a frequency component of 45 kHz, a frequency component of 90 kHz, and a frequency component of 135 kHz were respectively detected. Each of the frequency components is indicated by a black line inFIG. 6. A vertical axis of the black line indicating each of the frequency components indicates the intensity of each of the frequency components. FromFIG. 6, it can be found out that the respective frequency components of 45 kHz, 90 kHz, and 135 kHz are included at substantially equal ratios in the ultrasonic waves applied to the liquid14and the attachment target15. The frequency component of 45 kHz is the first frequency component of fundamental waves, and the frequency components of 90 kHz and 135 kHz are the second frequency components (harmonic components) which are integral multiples of (two times and three times) the frequency of the fundamental waves.

In the Example, it is considered that the attachment target15and the attachment16are electrostatically charged as in a hypothesis described below. That is, if ultrasonic vibration (which is first ultrasonic waves) is applied to the liquid14and the attachment target15, the attachment16actively moves, and the attachment target15also vibrates. Thus, the attachment16and the attachment target15are charged due to friction therebetween. The sound pressure is higher at antinode positions18of the ultrasonic vibration, so that the movement of the attachment16and the vibration of the attachment target15are stronger in the vicinity of the antinode positions18as indicated inFIG. 1and a sine curve corresponding to the first ultrasonic waves inFIG. 1. As a result, as shown inFIG. 2, the attachment16which has been charged in the vicinity of the antinode positions18is attracted and attached to the vicinity of the antinode positions18of the attachment target15which is also strongly charged. It is considered that the attachment16is attached to the attachment target15in accordance with such a principle (hypothesis).

In contrast, as shown inFIG. 3, if ultrasonic waves (which are second ultrasonic waves) that are twice as high in frequency as, for example, the first ultrasonic waves are simultaneously input, antinode positions19of the ultrasonic vibration of the second ultrasonic waves can be located in parts corresponding to node positions22of the first ultrasonic vibration as indicated inFIG. 3and sine curves corresponding to the second ultrasonic waves inFIG. 3. Thus, the attachment target15can be more evenly and more uniformly coated with the attachment16than in the example shown inFIG. 1.

In the Example, the ultrasonic waves of the fundamental frequency (45 kHz), the ultrasonic waves of the frequency (90 kHz) which is twice as high as the fundamental frequency, and the ultrasonic waves of the frequency (135 kHz) which is three times as high as the fundamental frequency are simultaneously input, so that the attachment16can be uniformly attached to the attachment target15as shown inFIG. 5.

Comparative Example 1

In Comparative Example 1, boron nitride which is an insulator was used as the attachment16. In other respects, the first to third steps and the leaving procedure were conducted under exactly the same conditions as those according to the Example. As a result, the attachment16was not at all attached to the attachment target15as shown inFIG. 7. Thus, the attachment state was judged to be unacceptable. In Comparative Example 1, boron nitride was not charged, so that the attachment16was not attached to the attachment target15.

Comparative Example 2

In Comparative Example 2, ethanol of 86.4 volume percent concentration was used as the liquid14into which the attachment16was mixed. Ethanol of 86.4 volume percent concentration is a conductor. In other respects, the first to third steps and the leaving procedure were conducted under exactly the same conditions as those according to the Example. As a result, the attachment16was not at all attached to the attachment target15as inFIG. 7. Thus, the attachment state was judged to be unacceptable. In Comparative Example 2, it was considered that the attachment16was not successfully charged because the charging of the attachment16diffused to the surrounding conductive liquid14(ethanol).

Comparative Example 3

In Comparative Example 3, the time of the application of ultrasonic waves in the third step was 10 seconds. In other respects, the first to third steps and the leaving procedure were conducted under exactly the same conditions as those according to the Example. As a result, the attachment16was thinly attached to the attachment target15as shown inFIG. 8. The amount of the attachment16attached to the attachment target15in Comparative Example 3 was apparently smaller than that in the Example. Thus, the attachment state was judged to be thin. In Comparative Example 3, it could be considered that the attachment16and the vibration of the attachment target15were insufficiently charged because the time of the application of ultrasonic waves was too short in the third step.

Comparative Example 4

In Comparative Example 4, the leaving procedure was not conducted after the application of ultrasonic waves in the third step, and the attachment target15was pulled out of the conductive liquid14immediately after the completion of the application of ultrasonic waves. In other respects, the first to third steps were conducted under exactly the same conditions as those according to the Example. As a result, the attachment16was not at all attached to the attachment target15as inFIG. 7. Thus, the attachment state was judged to be unacceptable. In Comparative Example 4, it was considered that there was not enough time for the attachment16to be attracted and attached to the attachment target15after the attachment16and the attachment target15had been charged because the leaving procedure was not conducted. Therefore, it was considered that the attachment16was not successfully attached.

Comparative Example 5

In Comparative Example 5, the frequency of the ultrasonic waves applied to the liquid14and the attachment target15is only the fundamental frequency (45 kHz). In other respects, the first to third steps and the leaving procedure were conducted under exactly the same conditions as those according to the Example. As a result, the attachment target15was coated with the attachment16so that thickly attached parts and thinly attached parts alternate as shown inFIG. 9. Thus, the attachment state was judged to be uneven.

Under the conditions according to Comparative Example 5, the sound pressure of the ultrasonic waves actually applied to the liquid14and the attachment target15in the tank12was measured by a hydrophone. In the graph ofFIG. 10, the sound pressure of the ultrasonic waves is indicated by a thin line waveform. The amplitude of the waveform indicates the intensity (voltage) of the sound pressure. When the sound pressure was decomposed by fast Fourier transform (FFT), a frequency component of 45 kHz was detected. The frequency component of 45 kHz is indicated by a black line inFIG. 10. Thus, it was found out that the ultrasonic waves of the fundamental frequency (45 kHz) were only input in Comparative Example 5.

In Comparative Example 5, the frequency of the ultrasonic waves to be input was only the fundamental frequency (45 kHz), and it was therefore considered that charging was insufficient at the node positions22of the ultrasonic vibration so that the coating amount of the attachment16was smaller at the node positions22as shown inFIG. 9.

Comparative Example 6

In Comparative Example 6, the frequency of the ultrasonic waves applied to the liquid14and the attachment target15is only a frequency (170 kHz) different from the fundamental frequency. In other respects, the first to third steps and the leaving procedure were conducted under exactly the same conditions as those according to the Example. As a result, the attachment target15was coated with the attachment16so that thickly attached parts and thinly attached parts alternate as shown inFIG. 11. The intervals of the thickly attached part and the thinly attached part were smaller than the pitch according to Comparative Example 5 inFIG. 9. Thus, the attachment state according to Comparative Example 6 was judged to be uneven.

In Comparative Example 6, the frequency of the ultrasonic waves to be input was only the frequency of 170 kHz, and it was therefore considered that charging was insufficient at the node positions22of the ultrasonic vibration so that the coating amount of the attachment16was smaller at the node positions22as shown inFIG. 11.

However, it was considered that in Comparative, Example 6, the frequency was higher than in Comparative Example 5, and the intervals of the antinode position18and the node position22were therefore smaller, so that the thick parts and thin parts alternate at a smaller pitch.

Comparative Example 7

In Comparative Example 7, the first to third steps were conducted under the same conditions as those according to the Example. After the end of the third step, the leaving procedure was conducted such that a voltage of −1000 V was left applied to the attachment target15for 60 seconds. As a result, as shown inFIG. 12, the attachment16was thickly attached to the surface of the attachment target15. The attachment amount of the attachment16according to Comparative Example 7 was greater than the attachment amount according to the Example. Thus, the attachment state of the attachment16was judged to be thick.

Comparative Example 8

In Comparative Example 8, the first to third steps were conducted under the same conditions as those according to the Example. After the end of the third step, the leaving procedure was conducted such that a voltage of +1000 V was left applied to the attachment target15for 60 seconds. As a result, as inFIG. 8, the attachment16was thinly attached to the surface of the attachment target15.

From the results according to Comparative Examples 7 and 8, the attachment amount of the attachment16increased if the negative voltage was applied to the attachment target15after the input of ultrasonic waves in the third step, whereas the attachment amount of the attachment16decreased if the positive voltage was applied to the attachment target15after the input of ultrasonic waves in the third step. These results proved that there was a phenomenon in which by the input of ultrasonic waves, the attachment16was positively charged and the attachment target15was negatively charged at the same time. Thus, it is understood that the hypothesis described above is substantially correct.

According to the present embodiment and the Example, the method of coating with the attachment16includes the steps of mixing the conductive attachment16into the insulating liquid14, immersing the attachment target15in the insulating liquid14in which the attachment16is mixed, and applying ultrasonic vibration to the insulating liquid14in which the attachment target15is immersed and causing friction between the attachment target15and the attachment16to charge the attachment target15and the attachment16.

According to this configuration, by a simple method of applying ultrasonic vibration, the attachment target15and the attachment16can be charged, and the attachment16can be uniformly attached to the attachment target15. Thus, the coating step can be simplified, and the quality of the attachment target15coated with the attachment16can be improved.

The attachment coating method includes the step of leaving for a predetermined length of time after the step of charging. According to this configuration, the attachment target15can be surely coated with the attachment16, and the quality of the attachment target15coated with the attachment16can be improved.

In this case, the ultrasonic vibration includes a first frequency component having the frequency of fundamental waves, and second frequency components having frequencies which are integral multiples of the frequency of the fundamental waves and which are different from each other. According to this configuration, the antinode positions of the second ultrasonic waves can be located at the node positions of the ultrasonic vibration of the fundamental waves. Thus, the attachment target15can be uniformly coated with the attachment16, and the quality of the attachment target15coated with the attachment16can be further improved.

The present invention is not limited to the embodiment described above, and modifications can be suitably made without departing from the spirit thereof.