JPH0472336A - Method of corona discharge treatment - Google Patents

Abstract

PURPOSE:To carry out the title discharge treatment of a resin molded product without producing defectives through such a way that a resin molded product is passed, by a carrying means, through the space between a pair of high voltage-applied electrodes facing to each other to make a corona discharge treatment and, when the product of the luminance between the electrodes and the passing time is below a set value, the system is put to shutdown. CONSTITUTION:A corona discharge is generated by applying high voltage from an electric source 9 on a pair of electrodes 7 and 8 facing to each other in a treatment tank l; concurrently, a resin molded product 6 is passed, by a carrying means 2 such as a belt conveyor, through the space between said electrodes 7 and 8 to activate the surface of said molded product 6 by the ozone generated by the corona discharge, thereby making a corona discharge treatment. In this case, when the product of (1) the luminance C between said electrodes 7 and 8 and (2) the time T necessary for said molded product 6's passing through the space between said electrodes 7 and 8 comes below a set value, it is determined that the surface activation of the resin molded product 6 is insufficient, and the voltage application on the electrodes 7 and 8 and the carriage of the molded product 6 are ensured to be put to shutdown, thus carrying out the objective corona discharge treatment of said resin molded product with the production of defectives prevented.

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] Generally, polyolefin resins such as polypropylene have few polar groups, so paints, adhesives, printing agents, etc. are difficult to adhere to the surface 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 held container) 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, water or other liquid is dripped onto the same surface and its contact angle is measured, or a wettability index standard solution is applied to the surface of the resin molded product and the state of liquid dripping on the coated surface is observed. The degree of activation of the product surface 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 determining the degree of activation based on the color of the discharge is not accurate enough to make a rough judgment. 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 if the surface activation is insufficient, it can be determined that the product is defective.

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 inventor conducted an experiment on the relationship between the brightness between the two electrodes and the time required for the resin molded product to pass between the two electrodes, and found that the product of the two becomes small. It has been found that the surface activity of resin molded products decreases as the temperature increases.

Therefore, in the present invention, a high voltage is applied between a pair of electrodes arranged opposite each other to generate a corona discharge, and 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 brightness between the two electrodes and the time required for the resin molded product to pass between the two electrodes is set in advance. When the value becomes smaller than the value, it is assumed that the surface activation of the resin molded product is insufficient.
The gist is a corona discharge treatment method in which the application of voltage between both electrodes and the conveyance of the resin molded article are stopped.

[Operation] When a high voltage is applied between a pair of electrodes and a 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 brightness between the two electrodes during corona discharge and the time required for the resin molded product to pass between the two electrodes becomes smaller than a preset value, the surface of the resin molded product is activated. If the voltage is insufficient, the voltage application between the two electrodes and the transport of the resin molded product 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 applied. This intermediate molded product 6 is made of polyolefin thermoplastic elastomer (TPE).

FIG. 1 is a diagram showing the configuration of a processing apparatus for carrying out the corona discharge treatment of this embodiment. The processing tank 1 of this processing apparatus is open on both the front and back sides (left and right in the figure), and a wooden shielding plate 1a is attached to the open rear part so as to be openable and closable. Further, in the processing tank 1, a heating converter 2 serving as a conveying means that is rotated by a motor M is disposed.

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 connected to the output side of the controller 4 which has a built-in microcomputer, and 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 activated. Or orbit in the six directions indicated by the arrows. Therefore, when the intermediate molded product 6 is supplied onto the belt 2a from the rear open portion 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 opposite to each other above and below the belt conveyor 2 in the processing tank 1, and the image electrodes 7 and 8 are connected to a power source 9, a high voltage transformer (not shown), and a second switch 10. It is connected.

The second switch IO 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. is generated and ozone (0
3) is now generated.

A luminance meter (LLIMINANCE METERB M- manufactured by Tokyo Kogaku Kikai Co., Ltd.) is installed at the front part of the processing tank 1.
5) 11 is installed. The focus of this brightness meter 11 is set on the grain of the inner surface of the shielding plate 1a, and in this state, the brightness meter 11 measures the brightness C (cd) between the picture electrodes 7 and 8.
/m) is detected. Further, at a position near the belt conveyor 2, the rotation speed S (m/min) of the belt 2a is displayed.
A speed detection sensor 12 is provided to detect the speed. These luminance meter 11 and speed detection sensor 12 are connected to the input side of the controller 4. Furthermore, on the output side of the controller 4, there is a display 13 that displays the luminance C between the picture electrodes 7 and 8 detected by the luminance meter 11 at any given time.
is connected.

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 obtained from the relational expression of TI2/S
is stored for each rotation speed S.

The controller 4 controls the luminance C (cd/rn') detected by the luminance meter 11 and the passing time T (
minutes). Then, the controller 4 compares the calculated value with a preset value B, and if the former calculated value is greater than or equal to the latter set value B, the controller 4 closes both the switches 5 and 10 and sets the calculated value to When the value B 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 stop the rotation of the belt conveyor 2. Note that the set value B in this embodiment is 0.04 cd/rr?・minutes, and this set value B 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 ■
A method of leaving the intermediate molded product 6 in trichloroethane vapor (approximately 74°C) for a predetermined time (approximately 20 seconds);
■ Spraying method (for about 20 seconds), ■ Spraying the intermediate molded product 6 in trichloroethane vapor (about 74°C) for a predetermined time (about 20 seconds)
There is a method in which warmed trichloroethane is sprayed onto the intermediate molded product 6 for a predetermined period of time (about 20 seconds) after the molded product is left standing. After the washing with trichloroethane is completed, the intermediate molded product 6 is dried (90° C. for 15 minutes) to evaporate adhering trichloroethane.

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

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. 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 brightness C between the picture electrodes 7 and 8 is detected by the brightness meter 11, and the belt conveyor 2
The rotation speed S of the belt 2a is detected by the speed detection sensor I2. The controller 4 takes in the detected brightness C and circulating speed S at each time, and calculates the product of the transit time T and the brightness C corresponding to the circulating speed S. Then, the value calculated as above and the set value B (in this case 0.0
4cd/rn'·min). At this time, if the calculated value is greater than or equal to the set value B, both the switches 5 and 10 are kept closed.

By the way, if for some reason the rotational speed S of the bell 2a of the belt conveyor 2 decreases or the brightness C decreases, the set value B ( If it becomes smaller than 0.04 cd/r+ (min), the surface activation of the intermediate molded product 6 is considered insufficient.
The controller 4 has a first switch 5 and a second switch 10.
Outputs a control signal to open the door. 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, thereby preventing the occurrence of defective products.

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, the intermediate molded product 6
acrylic urethane paint is applied to the
After being allowed to stand for 30 minutes, it was reacted and cured at 85°C for 30 minutes.

Then, a coating film is formed on the surface of the intermediate molded product 6.

Here, (brightness C) x (passing time T) and intermediate molded product 6
An experiment was conducted to examine the relationship with the degree of surface activation. The results are shown in Table-1. In this experiment, the degree of activation of the surface of the intermediate molded product 6 was used to determine the adhesion of the coating film to the surface.

In this adhesion test, cuts were made in the coating film in the shape of the base plate to form 1-00 pieces of the coating film, and industrial tape was attached to these pieces, and when the tape was peeled off, intermediate forming Item 6
It counts the number of pieces of paint that peel off from the surface. For reference, Table 1 also shows the contact angle (°) when a water droplet is dropped on the surface of the intermediate molded product 6 that has been subjected to the corona discharge treatment.

As is clear from Table 1, when the product of transit time T and luminance C is greater than 0.04 cd/m・min, no paint film flakes are peeled off;゜04cd/
Some parts of the paint film were peeled off under the m. This is because the surface of the intermediate molded product 6 is not activated to a sufficient level when the product of the transit time T and the brightness C is 0.04 cd/m. Therefore, the transit time T and the luminance C
The degree of activation of the surface of the intermediate molded product 6 due to the corona discharge treatment can be accurately determined by multiplying by the product .

In this way, according to this embodiment, it is possible to determine 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 brightness C, and if it has not been sufficiently activated, In this case, the application of voltage between the picture electrodes 7 and 8 and the conveyance of the intermediate molded product 6 are stopped, thereby preventing the occurrence of defective products due to insufficient activation. I can do it. Therefore, it is no longer necessary to confirm the degree of activation, such as measuring the contact angle of water droplets or the like or observing the dripping state of the index standard solution, as in the prior art, after the corona discharge treatment.

In the embodiment described above, 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. As a result of conducting the same experiment as in Table 1 above, the luminance C and the transit time T
The preferred upper limit of the product is 2.0 cd/m2.min, and it has been found that if it exceeds 50 cd/m2.min, there is a risk of aging of the coating film surface. From this, the upper limit setting value is set to 50cd/rrl''', and the product is 0.
．． When it is out of the range of 04 to 50 cd/m2・min,
By stopping the voltage application between the picture electrodes 7 and 8 and the driving of the belt conveyor 2, 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.

Furthermore, the shielding plate 1a may be made of a material other than books, such as an iron plate, and in this case, it is necessary to have a pattern on the inner surface.

"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 insufficient activation of the surface of resin molded products. 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 corona discharge treatment.

[Brief explanation of the drawing]

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, C.
... Luminance, T... Passage time. Patent applicant Toyoda Gosei Co., Ltd.

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 brightness between the two electrodes (7, 8) and the resin molded article (6) and the time required to pass between the electrodes (7, 8) becomes smaller than a preset value, the surface activation of the resin molded product (6) is deemed to be insufficient. Both electrodes (7, 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).