JPH03296538A - Corona discharge treatment - Google Patents

Abstract

PURPOSE:To perform corona discharge treatment while preventing the formation of rejects due to the insufficient surface activation of a resin molding by stopping the application of a voltage and the traveling when the product of the noise level during corona discharge and the time necessary for the resin molding to pass between the electrodes is decreased. CONSTITUTION:The memory built in a controller 4 stores the relationship between the traveling speed S of the belt 2a of a belt conveyor 2 and the time T necessary for the intermediate molding 6 to pass between the electrodes 7 and 8. This controller 4 computes the product of a level L detected by a noise meter 11 and a pass time T (min) corresponding to a traveling speed S (m/min) detected by a speed detecting sensor 12. The controller 4 compares the computed value with the set value B, and when it is larger than the set value B, switches 5 and 10 are shut, and when it is smaller than the set value B, the switches 5 and 10 are opened to stop the application of a voltage and the traveling of the belt conveyor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a corona discharge treatment method for activating the surface of a resin molded article made of a polyolefin resin such as polypropylene.

[Prior Art] In general, polyolefin resins such as polypropylene have few polar groups, so paints, adhesives, printing agents, etc. are difficult to adhere to the surfaces of molded products made of the same resins. Therefore, when painting or the like is applied to the surface of the resin molded article, a corona discharge treatment is performed as a pretreatment to activate the surface and improve adhesion.

This corona discharge treatment involves a pair of electrodes placed opposite each other,
The processing is carried out in a processing tank equipped with a conveying means (for example, a belt conveyor) disposed between both electrodes.

That is, a high voltage is applied between both electrodes while the resin molded product is transported by the transport means to generate corona discharge, and the surface of the resin molded product is activated with ozone generated by the corona discharge.

With this method, it cannot be confirmed whether the surface of the resin molded article has been sufficiently activated during the corona discharge treatment. Therefore, after treatment, liquid such as water is dripped onto the surface of the resin molded product and its contact angle is measured, or a wettability index standard solution is applied to the same surface and the state of dripping on the coated surface is observed.
The degree of activation of the surface of a resin molded product is determined. These methods focus on the fact that when the surface of a resin molded article is activated, its surface tension changes. Another method is to visually observe the discharge state during the corona discharge treatment and roughly judge the degree of activation based on the color of the discharge.

[Problem to be Solved by the Invention] However, the method of measuring the contact angle and the method of observing the dripping of the index standard solution described above are both performed after corona discharge treatment, and due to their nature, corona discharge treatment It is not possible to prevent defects from occurring at times. Furthermore, the method of looking at the degree of activation based on the color of the discharge allows for a rough judgment, but lacks accuracy. Therefore, it is expected that a method will be developed that can accurately determine the degree of activation of the surface of a resin molded product during corona discharge treatment and determine that a defective product has occurred if the surface activation is insufficient.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to prevent the occurrence of defective products due to insufficient activation of the surface of resin molded products. An object of the present invention is to provide a discharge treatment method.

Means for Solving the Problem] The present inventor conducted an experiment on the relationship between the noise level during corona discharge and the time required for a resin molded product to pass between both electrodes, and found that the product of the two is small. (Indeed, we found that the surface activity of resin molded products decreases.

Therefore, the present invention generates a corona discharge by applying a high voltage between a pair of electrodes arranged opposite to each other, and at the same time, a resin molded article is conveyed by a conveying means to pass between the two electrodes, and the corona discharge is generated by the corona discharge. In a corona discharge treatment method in which the surface of a resin molded product is activated with ozone, the product of the noise level during the corona discharge and the time required for the resin molded product to pass between the two electrodes is set in advance. The gist of the corona discharge treatment method is to stop the application of voltage between both electrodes and the transportation of the resin molded product when the surface activation of the resin molded product becomes smaller than the specified value. It is.

[Operation] When a high voltage is applied between a pair of electrodes and corona discharge occurs, ozone is generated by this corona discharge. At this time, ozone combines with molecules on the surface of the resin molded article to generate, for example, carbonyl groups, thereby activating the surface of the resin molded article. When the product of the noise level during this corona discharge and the time required for the resin molded product to pass between the two electrodes becomes smaller than a preset value, it is assumed that the surface activation of the resin molded product is insufficient. , the voltage application between both electrodes and the transport of the resin molded product 9 are stopped.

[Example] Hereinafter, an example embodying the present invention will be described based on the drawings. In this embodiment, a large number of unpainted intermediate molded products 6 formed through an injection molding process, which is one of the manufacturing processes for automobile mudguards, are resin molded products, and prior to painting of these intermediate molded products 6. Corona discharge treatment shall be performed. This intermediate molded product 6 is made of polyolefin thermoplastic elastomer (TPE).

FIG. 1 shows a processing apparatus for performing the corona discharge treatment of this embodiment, and a belt conveyor 2 as a conveyance means driven by a motor M is disposed inside a processing tank L with both front and rear sides open. ing. A first switch 5 is connected between the motor M and a power source 3 that supplies power to the motor M.

The first switch 5 is a controller 4 with a built-in microcomputer.
When the first switch 5 is closed by the control signal from the controller 4, the motor M is connected to the output side of the motor M.
is activated, and the belt 2a of the belt conveyor 2 is rotated in the direction of arrow C. Therefore, when the intermediate molded product 6 is supplied onto the bell 2a from the open rear side (right side in FIG. 1) of the processing tank 1, the intermediate molded product 6 is conveyed forward by the rotation of the belt 2a.

A pair of electrodes 7 and 8 are disposed facing each other above and below the belt conveyor 2 in the processing tank 1, and between the image electrodes 7 and 8 there is a power supply 9, a high voltage transformer (not shown), and a second switch IO. is connected.

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 the picture electrodes 7 and 8, causing corona discharge. Occurs and ozone (03)
is now generated.

A sound level meter 11 is attached to the front part of the processing tank 1 to detect the noise level L (dB) with A characteristic during corona discharge. Further, a speed detection sensor 12 is disposed near the belt conveyor 2 to detect the rotational speed S (m/min) of the belt 2a. These sound level meter 11 and speed detection sensor 12 are connected to the input side of the controller 4. A display 13 is connected to the output side of the controller 4 to display the current noise level L detected by the sound level meter 11.

The memory built into the controller 4 stores the time required for the intermediate molded product 6 on the belt 2a to pass between the picture electrodes 7 and 8 (hereinafter referred to as the passing time) for each rotational speed S of the belt 2a of the belt conveyor 2. (referred to as time) are stored in association with each other. In other words, the front and rear length of the belt conveyor 2 is l.
Then, the transit time T determined by the relational expression T1/S is stored for each rotation speed S.

This controller 4 calculates the product of the noise level L (dB) detected by the sound level meter 11 and the transit time T (minutes) corresponding to the orbiting speed S (m/minute) detected by the speed detection sensor 12. . Then, the controller 4 compares the calculated value with a preset setting value B, and if the calculated value is equal to or higher than the setting value 8, the controller 4
is closed, and if the calculated value is smaller than the set value B, both switches 5 and 10 are opened to stop the voltage application between the picture electrodes 7 and 8 and the rotational drive of the belt conveyor 2. Note that the setting value B in this example is 80 dB.
This is a value determined based on the experimental results described later.

Next, a method of applying corona discharge treatment to the surface of the intermediate molded product 6 using the treatment apparatus will be described.

First, in order to ensure that the surface of the intermediate molded product 6 is subjected to the corona discharge treatment, the intermediate molded product 6 is pretreated by cleaning with trichloroethane. The cleaning method at this time is ■
Intermediate molded product 6 in trichloroethane vapor (approximately 74°C)
(about 20 seconds), ■ Spraying warmed trichloroethane onto the intermediate molded product 6 for a predetermined time (about 20 seconds), ■ Spraying trichloroethane vapor (about 7 seconds),
There is a method in which the intermediate molded product 6 is left for a predetermined time (about 20 seconds) in a temperature of 4° C.) and then heated trichloroethane is sprayed onto the intermediate molded product 6 for a predetermined time (about 20 seconds). After the washing with trichloroethane is finished, the intermediate molded product 6
Dry (90°C x 15 minutes) to evaporate adhering trichloroethane.

Next, the intermediate molded product 6 is put into a processing device.

In this processing device, the passing time T is set in advance to 3.7 minutes (the rotation speed S of the belt 2a of the belt conveyor 2 is 1 m/min), and the noise level L of corona discharge is set in advance to 97 to 106 dB. 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 IO. When both switches 5 and 10 are closed based on this control signal, the belt conveyor 2 is rotated and a high voltage is applied between the picture electrodes 7 and 8. Corona discharge occurs between the picture electrodes 7 and 8 due to the voltage application, and ozone is generated accordingly. At this time, ozone is released into the intermediate molded product 6.
For example, carbonyl groups are generated by bonding with molecules on the surface,
The surface of the intermediate molded product 6 is activated.

When the processing device is in operation, the noise level L of the discharge sound generated due to corona discharge is detected by the sound level meter 11, and the rotation speed S of the belt 2a of the belt conveyor 2 is detected by the speed detection sensor 12. Ru. The controller 4 takes in the detected noise level L and circulating speed S at each time, and calculates the product of the transit time T corresponding to the circulating speed S and the noise level L. Then, the value calculated as described above is compared with the set value B (80 dB·min in this case). At this time, if the calculated value is equal to or greater than the set value B, both the switches 5 and 1o are kept closed.

By the way, due to some reason, the rotational speed S of the belt 2a of the belt conveyor 2 decreases, or corona discharge does not occur sufficiently, and the product of the noise level L and the passing time T becomes the set value B (80 dB・min). If the surface activation of the intermediate molded product 6 is insufficient, the controller 4
outputs a control signal for opening the first switch 5 and the second switch IO. When both switches 5 and 10 are opened, the application of voltage between the picture electrodes 7 and 8 and the rotation of the belt conveyor 2 are stopped. Therefore, the operation of the processing device is automatically stopped, and the occurrence of defective products is prevented.

Note that the intermediate molded product 6 that has been successfully subjected to the corona discharge treatment is transferred to a coating process. In this process, an acrylic urethane paint is applied to the intermediate molded product 6, and approximately 1
After being allowed to stand for 0 minutes, it is reacted and cured 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 (passing time T) x (noise level L) and the degree of activation of the surface of the intermediate molded product 6.

The results are shown in Table-1. In this experiment, the degree of activation of the surface of the intermediate molded product 6 was determined, and the adhesion of the coating film to the surface was investigated. In this adhesion test, 100 pieces of the coating film were formed by making cuts in the shape of the substrate, and then an industrial tape was attached to these pieces, and when the tape was then peeled off, the intermediate molded product 6 The number of pieces of paint that peel off from the surface is counted. For reference, Table 1 also shows the contact angle (0) when a water droplet is dropped on the surface of the intermediate molded product 6 that has been subjected to corona discharge treatment.
Also listed.

Table-1 As is clear from Table-1, passing time T and noise level L
When the product was larger than 78 dB·min, the paint film pieces did not come off at all, whereas for the same type, the paint film pieces peeled off under 78 dB·min.

This means that the product of transit time T and noise level L is 78 dB・
The amount indicates that the surface of the intermediate molded product 6 is not activated to a sufficient level.

Therefore, the degree of activation of the surface of the intermediate molded product 6 due to the corona discharge treatment can be accurately determined by the product of the passage time T and the noise level L.

On the other hand, there is a certain degree of correlation between the contact angle when a water droplet is dropped on the intermediate molded product 6 and the coating film adhesion. That is, as the contact angle increases, coating film adhesion tends to deteriorate. However, as can be seen from Table 1, when the contact angle is 98°, no coating film peels off at all, while when the contact angle is 94°, two pieces of the coating film peel off, etc. The angle is not clear.

In this way, in this embodiment, it is determined during processing whether or not the surface of the intermediate molded product 6 has been sufficiently activated based on the product of the transit time T and the noise level L of the discharge sound, and whether or not the surface of the intermediate molded product 6 has been sufficiently activated is determined. If not, the application of voltage between the picture electrodes 7 and 8 and the conveyance of the intermediate molded product 6 are stopped. Therefore, it is possible to prevent the occurrence of defective products due to insufficient activation. Therefore, it is no longer necessary to confirm the degree of activation by measuring the contact angle of water droplets or observing the dripping state of the index standard solution after the corona discharge treatment.

In the above embodiment, only the lower limit value for stopping the voltage application between the picture electrodes 7 and 8 and the driving of the belt conveyor 2 was set, but the upper limit value may also be set. That is, as a result of conducting an experiment similar to that shown in Table 1 above, it was found that when the product of the noise level L and the transit time T exceeds 720 dB·min, cracks appear on the surface of the coating film. From this,
The upper limit setting value is 720 dB・min, and the product is 80 to 7.
If the voltage application between the picture electrodes 7 and 8 and the driving of the belt conveyor 2 are stopped when the voltage is out of the range of 20 dB·min, the occurrence of defective products can be more reliably prevented.

In addition to the mudguards described above, the present invention can also be applied to resin molded products that require painting, adhesion, printing, etc. after molding, such as automobile bumpers and automobile moldings.

[Effects of the Invention] As detailed above, according to the corona discharge treatment method of the present invention, it is possible to prevent the occurrence of defective products due to the surface of the resin molded product not being sufficiently activated. Can be done. Therefore, it is not necessary to confirm the degree of activation by measuring the contact angle or observing the dripping state of the index standard solution after the corona discharge treatment.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and is a diagram showing the configuration of a processing apparatus used for performing corona discharge treatment. 2... Belt conveyor as a conveyance means, 6... Intermediate molded product as a resin molded product, 7, 8... Electrode, L.
...Noise level, T...Passage time.

Claims (1)

[Claims] 1. A high voltage is applied between a pair of electrodes (7, 8) arranged opposite to each other to generate a corona discharge, and a conveying means (
2), transport the resin molded product (6) and connect both electrodes (7, 8).
In the corona discharge treatment method, the surface of the resin molded article (6) is activated by the ozone generated by the corona discharge, the noise level during the corona discharge and the resin molded article (6) When the product of the time required to pass between the two electrodes (7, 8) becomes smaller than a preset value, the surface activation of the resin molded product (6) is considered insufficient, and the surface activation of the resin molded product (6) is determined to be insufficient. , 8)
A corona discharge treatment method characterized by stopping the application of voltage between the steps and the conveyance of the resin molded product (6).