JPH0725908B2 - Corona discharge treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a corona discharge treatment method for activating the surface of a resin molded product made of a polyolefin resin such as polypropylene.

[Prior Art] Generally, a polyolefin resin such as polypropylene has a small number of polar groups, and therefore a paint, an adhesive, a printing agent or the like is unlikely to adhere to the surface of a molded article made of the resin. Therefore, when coating or the like is applied to the surface of the resin molded product, corona discharge treatment is performed as a pretreatment to activate the surface and improve the adhesion.

This corona discharge treatment includes a pair of electrodes that are arranged to face each other,
It is carried out in a processing tank provided with a conveying means (for example, a belt conveyor) arranged between both electrodes. That is, while the resin molded product is being transported by the transport means, a high voltage is applied between both electrodes to generate corona discharge, and the ozone generated by the corona discharge activates the surface of the resin molded product.

With this method, it cannot be confirmed whether or not the surface of the resin molded product was sufficiently activated during the corona discharge treatment. for that reason,
After the treatment, dripping a liquid such as water on the surface to measure the contact angle, or applying a wetting index standard liquid to the surface of the resin molded product, and observing the liquid-drained state on the coated surface,
The degree of activation of the surface of the resin molded product is judged. These methods focus on the fact that when the surface of a resin molded product is activated, its surface tension changes. There is also a method of visually observing the discharge state during the corona discharge treatment and roughly determining the degree of activation by the color of the discharge.

[Problems to be Solved by the Invention] However, the methods for measuring the contact angle and the method for observing the liquid breakage of the exponential standard solution are both performed after the corona discharge treatment. Occurrence of defects cannot be prevented. Further, the method of observing the degree of activation by the color of discharge can make a rough judgment but lacks accuracy. Therefore, it is expected that a method that accurately grasps the degree of activation of the surface of the resin molded product during the corona discharge treatment and can judge that a defective product has occurred when the surface activation is insufficient.

The present invention has been made in view of the above-mentioned circumstances, and its object is to prevent the occurrence of defective products due to insufficient activation of the surface of the resin molded product. It is to provide an electric discharge treatment method.

[Means for Solving the Problem] As a result of an experiment conducted by the present inventor on the relationship between the ozone concentration between both electrodes and the time required for a resin molded product to pass between both electrodes, the product of both is small. It has been found that the surface activity of the resin molded product is lowered as much as possible.

Therefore, according to the present invention, a high voltage is applied between a pair of electrodes arranged to face each other to generate corona discharge, and a resin molding product is conveyed by a conveying means to pass between both electrodes to generate corona discharge. In the corona discharge treatment method in which the surface of the resin molded product is activated by the ozone, the product of the ozone concentration between the electrodes and the time required for the resin molded product to pass between the electrodes is set in advance. When the value becomes smaller than the specified value, the surface activation of the resin molded product is considered to be insufficient, and the corona discharge treatment method that stops the voltage application between both electrodes and the conveyance of the resin molded product Is.

[Operation] When a high voltage is applied between the pair of electrodes to generate corona discharge, ozone is generated by the corona discharge. At this time, ozone bonds with molecules on the surface of the resin molded product to generate, for example, a carbonyl group, and activates the surface of the resin molded product. When the product of the ozone concentration during this corona discharge and the time required for the resin molded product to pass between the electrodes becomes smaller than a preset value, it is determined that the surface activation of the resin molded product is insufficient. The voltage application between both electrodes and the conveyance of the resin molded product are stopped.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a large number of unpainted intermediate molded products 6 formed through the injection molding process, which is one of the manufacturing processes for automobile mudguards, are resin molded products, and prior to coating these intermediate molded products 6. Corona discharge treatment shall be applied. The intermediate molded product 6 is made of a polyolefin-based thermoplastic elastomer (TPE).

FIG. 1 shows a processing apparatus for carrying out corona discharge processing according to the present embodiment, and a belt conveyor 2 as a transfer means which is driven by a motor M to rotate in a processing tank 1 whose front and rear surfaces are open. ing. A first switch 5 is connected between the motor M and a power supply 3 that supplies electric power to the motor M. The first switch 5 is connected to the output side of a controller 4 having a built-in microcomputer. When the first switch 5 is closed by a control signal from the controller 4, the motor M is activated and the belt 2a of the belt conveyor 2 is driven. Circles in the direction of arrow A. Therefore, the rear side of the processing tank 1 (first
When the intermediate molded product 6 is supplied onto the belt 2a from the open portion (on the right side of the drawing), the intermediate molded product 6 is conveyed forward by the circulation of the belt 2a.

In the processing tank 1, a pair of electrodes 7 and 8 are arranged opposite to each other above and below the belt conveyor 2, and a power source 9 is provided between the electrodes 7 and 8.
The high voltage transformer (not shown) and the second switch 10 are connected to each other. The second switch 10 is connected to the output side of the controller 4, and when the second switch 10 is closed by a control signal from the controller 4,
A high voltage is applied between both electrodes 7 and 8, corona discharge is generated, and ozone (O ₃ ) is generated.

In the front part of the processing tank 1, the ozone concentration C (p
pm) ozone concentration meter (EG EBARA CORPORATION)
-2001B or EG-2001R) 11 is installed. Also,
At a position near the belt conveyor 2, a speed detection sensor 12 for detecting the orbital speed S (m / min) of the belt 2a.
Is provided. The ozone concentration meter 11 and the speed detection sensor 12 are connected to the input side of the controller 4. In addition, an ozone concentration meter is provided on the output side of the controller 4.
A display 13 is connected to display the ozone concentration C between the electrodes 7 and 8 detected by 11 at each time.

In the memory built in the controller 4, the time required for the intermediate molded product 6 on the belt 2a to pass between the electrodes 7 and 8 for each orbiting speed S of the belt 2a of the belt conveyor 2 The time T is associated and stored. That is, assuming that the front-rear length of the belt conveyor 2 is 1, the passage time T obtained by the relational expression T = 1 / S is stored for each orbital speed S.

The controller 4 has a passage time T (minutes) corresponding to the ozone concentration C (ppm) detected by the ozone concentration meter 11 and the orbital speed S (m / min) detected by the speed detection sensor 12.
Calculate the product of and. Then, the controller 4 compares the calculated value with a preset setting value B, and when the former calculated value is equal to or larger than the latter set value B, both the switches 5 and 10 are closed to calculate the calculated value. Is smaller than the set value B, both switches 5 and 10 are opened to stop the voltage application between the electrodes 7 and 8 and the circulatory drive of the belt conveyor 2. The set value B in this embodiment is 20 pp.
m · minute, and the set value B is a value determined based on the experimental result described later.

Next, a method of subjecting the surface of the intermediate molded product 6 to corona discharge treatment using the above-mentioned processing apparatus will be described.

First, a pretreatment of washing the intermediate molded product 6 with trichloroethane is performed so that the surface of the intermediate molded product 6 is surely subjected to corona discharge treatment. As a cleaning method at this time,
Method of leaving the intermediate molded product 6 in the steam of trichloroethane (about 74 ° C.) for a predetermined time (about 20 seconds), spraying warmed trichloroethane onto the intermediate molded product 6 for a predetermined time (about 20 seconds), steam of trichloroethane ( There is a method in which the intermediate molded product 6 is allowed to stand for a predetermined time (about 20 seconds) in about 74 ° C., and then warmed trichloroethane is sprayed onto the intermediate molded product 6 for a predetermined time (about 20 seconds). After washing with the trichloroethane, dry the intermediate molded product 6 (90
(° C x 15 minutes) and evaporate the attached trichloroethane.

Next, the intermediate molded product 6 is loaded into the processing device. In this processing device, the passage time T is 3.7 minutes (the orbital speed S of the belt 2a of the belt conveyor 2 is 1 m / min), and the ozone concentration C is 20 to 9
It is preset to 0 ppm. When a start switch (not shown) of the processing device is turned on, the controller 4
Outputs a control signal for closing the first switch 5 and the second switch 10. Based on this control signal, both switches 5,
When 10 is closed, the belt conveyor 2 is orbitally driven and a high voltage is applied between both electrodes 7 and 8. Corona discharge is generated between the electrodes 7 and 8 by the voltage application, and ozone is generated accordingly. At this time, ozone bonds with molecules on the surface of the intermediate molded product 6 to generate, for example, a carbonyl group, and the surface of the intermediate molded product 6 is activated.

When the processing device is operating, the ozone concentration C between the electrodes 7 and 8 is detected by the ozone concentration meter 11, and the circulation speed S of the belt 2a of the belt conveyor 2 is detected by the speed detection sensor 12. The controller 4 takes in the detected ozone concentration C and the orbiting speed S at each occasion, and calculates the product of the passage time T corresponding to the orbiting speed S and the ozone concentration C. Then, the value calculated as described above and the set value B
(In this case, 20 ppm / min). At this time, if the calculated value is greater than or equal to the set value B, both switches 5 and 10 are held in the closed state.

By the way, the circulation speed S of the belt 2a of the belt conveyor 2 is lowered or the ozone concentration C is decreased for some reason, and the product of the ozone concentration C and the passage time T of the intermediate molded product 6 is a set value. When it becomes smaller than B (20 ppm · minute), the surface activation of the intermediate molded product 6 is insufficient, and the controller 4 outputs a control signal for opening the first switch 5 and the second switch 10. When both switches 5 and 10 are opened, the voltage application between the electrodes 7 and 8 and the circulation of the belt conveyor 2 are stopped. Therefore, the operation of the processing device is automatically stopped, and the generation of defective products is prevented.

The intermediate molded product 6 that has been normally subjected to the corona discharge treatment is transferred to the coating process. Intermediate molded product 6 in this process
Acrylic urethane-based paint is applied to the product, left at room temperature for about 10 minutes, and then cured by reaction at 80 ° C for 40 minutes. Then,
A coating film is formed on the surface of the intermediate molded product 6.

Here, an experiment was conducted on the relationship between (ozone concentration C) × (passing time T) and the degree of activation of the surface of the intermediate molded product 6.
The results are shown in Table-1. In this experiment, as the degree of activation of the surface of the intermediate molded product 6, the adhesion of the coating film to the surface was examined. In this adhesion test, the coating film is cut into a grid pattern to form 100 coating film pieces, an industrial tape is adhered to this, and then the tape is peeled off. This is to count the number of coating film pieces that are peeled off from. Also,
For reference, Table 1 also shows the contact angle (°) when a water droplet is dripped on the surface of the intermediate molded product 6 that has been subjected to corona discharge treatment.

As is clear from Table-1, transit time T and ozone concentration C
When the product was less than 19 ppm · min, the coating film pieces did not peel at all, whereas when the product was less than 19 ppm · minute, the coating film pieces peeled off. This is because the surface of the intermediate molded product 6 is not activated to a sufficient level when the product of the passage time T and the ozone concentration C is 19 ppm · min or less. Therefore, the product of the passage time T and the ozone concentration C makes it possible to accurately grasp the degree of activation of the surface of the intermediate molded product 6 by the corona discharge treatment.

On the other hand, there is a certain degree of correlation between the contact angle when a water drop is dropped on the intermediate molded product 6 and the coating film adhesion. That is, when the contact angle increases, the coating film adhesion tends to deteriorate. However, as can be seen from Table-1, when the contact angle is 98 °, the coating film pieces are not peeled at all, whereas when the contact angle is 94 °, two coating film pieces are peeled off. Not clear.

As described above, according to the present embodiment, it is possible to determine during the processing whether the surface of the intermediate molded product 6 is sufficiently activated by the product of the passage time T and the ozone concentration C, and it is not sufficiently activated. In this case, since the voltage application between both electrodes 7 and 8 and the conveyance of the intermediate molded product 6 are stopped, it is possible to prevent the occurrence of defective products due to insufficient activation. can do. Therefore, in the prior art, the work of confirming the degree of activation, such as measuring the contact angle of water droplets or the like after the corona discharge treatment and observing the liquid drop state of the index standard liquid, becomes unnecessary.

In the above embodiment, only the lower limit value for stopping the voltage application between the electrodes 7 and 8 and the driving of the belt conveyor 2 is set, but the upper limit value may be set together. As a result of the same experiment as in Table 1, it was found that when the product of ozone concentration C and passage time T exceeded 610 ppm · min, cracks were formed on the coating film surface. From this, the upper limit setting value
If the product is out of the range of 20 to 610 ppm · min and the voltage application between both electrodes 7 and 8 and the driving of the belt conveyor 2 are stopped, the defective product is generated. It can be prevented more reliably.

In addition to the mudguard, the present invention can also be applied to resin molded articles such as automobile bumpers and automobile moldings that require painting, bonding, printing, etc. after molding.

[Effects of the Invention] As described in detail above, according to the corona discharge treatment method of the present invention, it is possible to prevent occurrence of defective products due to insufficient activation of the surface of the resin molded product. You can Therefore, it is not necessary to confirm the degree of activation such as measuring the contact angle or observing the liquid state of the exponential standard solution after the corona discharge treatment.

[Brief description of drawings]

FIG. 1 shows an embodiment embodying the present invention, and is a diagram showing the structure of a processing apparatus used for performing corona discharge processing. 2 ... Belt conveyor as transport means, 6 ... Intermediate molded product as resin molded product, 7, 8 ... Electrode, C ... Ozone concentration, T ... Passing time.

Claims (1)

[Claims] 1. A high voltage is applied between a pair of electrodes (7, 8) facing each other to generate a corona discharge, and a resin molding (6) is conveyed by a conveying means (2). Electrode (7,
8) in which the surface of the resin molded product (6) is activated by ozone generated by the corona discharge, the ozone concentration between the electrodes (7, 8), When the product of the time required for the resin molded product (6) to pass between both electrodes (7, 8) becomes smaller than a preset value, the surface activation of the resin molded product (6) fails. Sufficiently, both electrodes (7,
A corona discharge treatment method characterized in that the voltage application between 8) and the conveyance of the resin molded product (6) are stopped.