JPH05247254A - Surface treatment method for polyolefin resin foam - Google Patents

Abstract

(57) [Summary] [Purpose] Without generating pinholes or avatars,
To provide a surface treatment method for improving the wettability of a polyolefin resin foam. [Structure] A high voltage is applied to an electrode placed in the air to cause discharge, and the surface of the foam is subjected to a non-polar discharge treatment by utilizing the difference in electrostatic capacitance between the gas and the polyolefin resin foam to wet the surface. A method for treating the surface of a polyolefin-based resin foam, which is characterized by improving its properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a polyolefin resin foam, and more particularly to a surface treatment method for improving the wettability of the foam surface without generating pinholes or avatars.

[0002]

2. Description of the Related Art Polyolefin resin foams are used in a wide variety of fields as heat insulating materials, cushioning materials and the like. For example, in the field of automobile interior molded products, it is used as a heat insulating material such as a ceiling, a door inner surface material, an instrument panel, a cooler cover, and a cushion material.

By the way, when the polyolefin resin foam is used for automobile interior moldings and the like, it is used as a composite material by laminating it with a skin material such as a soft polyvinyl chloride sheet. This composite material is heated by an infrared heater or the like, set on a molten aggregate such as a polypropylene resin sheet, and pressed in that state to obtain a molded product having a predetermined shape. To laminate
The skin material is extrusion laminated onto the foam using an adhesive or using an extruder.

When laminating a skin material, the polyolefin resin foam has poor wettability and poor adhesiveness with an adhesive or a skin material. Therefore, surface treatment is performed in advance to improve the wettability of the surface. .. Conventionally, corona discharge treatment is known as a surface treatment method for improving the wettability of a polyolefin resin foam.

Corona discharge treatment has hitherto been widely used as a surface treatment method for plastic molded products such as films. However, a high voltage electrode is provided with grounds facing each other within a certain distance, and a linear corona is provided between them. A common two-electrode system is generally used in which an object to be processed is passed between an electrode and a ground.
However, when such a close two-electrode corona discharge treatment is applied to the surface treatment of a polyolefin resin foam, a pinhole is generated on the foam surface, or a discharge current passes through the inside of the foam to form a bubble film. To be destroyed,
It is difficult to increase the degree of treatment and impart sufficient wettability. Moreover, when the foam film inside the foam is broken, when the film is heated in the laminating process with the skin material, the broken part shrinks to cause a surface defect called avatar. When corona discharge treatment is performed on a raw foam material having pinholes, the foam film inside the foam material is significantly broken.

Conventionally, it has been proposed to perform the corona discharge treatment of a foam body not in the air but in an oxygen-lean atmosphere to improve the treatment degree. However, in such a method, it is necessary to replace the atmosphere of the corona discharge treatment with nitrogen, so that the running cost is increased and the occurrence of avatar or the like cannot be prevented.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface treatment method which improves the wettability of a polyolefin resin foam without generating pinholes or avatars. As a result of intensive studies to overcome the problems of the prior art, the inventors of the present invention perform surface treatment of a polyolefin resin foam by a non-polar discharge method instead of a corona discharge treatment by the conventional proximity two-electrode method. As a result, they have found that the wettability can be easily improved without generating pinholes and avatars, and have completed the present invention based on the findings.

[0008]

According to the present invention, a high voltage is applied to an electrode placed in the air to cause discharge, and the difference in capacitance between the gas and the polyolefin-based resin foam is used to form the foam. Provided is a surface treatment method for a polyolefin-based resin foam, which comprises subjecting the surface of the body to non-polar discharge treatment to improve the wettability of the surface.

The present invention will be described in detail below. The non-polar discharge method used in the present invention has a different discharge mechanism from the normal proximity two-electrode discharge method, and performs the surface treatment of the object to be processed without disposing the ground electrode. In the corona treatment by the conventional proximity two-electrode system, the high-voltage electrode is opposed to the earth within a certain distance, and an insulator having certain electric characteristics is coated on the earth side in order to create a uniform discharge state. A linear corona is created according to the impedance between the high-voltage electrode and ground, and the object to be processed is passed between this electrode and ground to perform surface treatment.

On the other hand, in the non-polar discharge method, the surface treatment of the object to be processed is carried out by utilizing the difference in the electrostatic capacitance between the gas and the object to be processed, without using the earth electrode facing the discharge electrode.
When a high voltage is applied to the electrodes installed in the air, the discharge is performed in the direction of the circumference of 360 degrees. At this time, when an object having a density equal to or higher than the surrounding gas approaches the electrode within a certain distance, the discharge concentrates in the direction of the object having a high molecular density.
By utilizing this non-polar discharge phenomenon, the surface treatment of the object is performed.

The non-polar discharge method utilizes a difference in electrostatic capacitance between a gas and a polymer object which is an object to be treated.
Capable of non-polar discharge treatment without arranging a ground electrode,
(2) There is no limitation on the shape or size of the object to be processed, (3)
Since local concentrated discharge is unlikely to occur, there is an advantage that the object to be treated is not damaged by burning and (4) pinholes are not generated as in the normal corona discharge treatment.

Therefore, according to the non-polar discharge method, even if the surface treatment of the polyolefin resin foam is performed, pinholes and avatars are not generated, and the wettability can be easily improved. Moreover, with respect to the change with time of the wettability after the treatment, the treatment by the non-polar discharge method has a feature that the wettability is less deteriorated as compared with the case of the corona discharge treatment by the conventional adjacent two-electrode method. ing.

As the polyolefin resin foam, polyethylene (low density, medium to high density, linear low density, etc.),
Foams of various polyolefin resins such as ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polypropylene, and blends of two or more of these can be used. These foams may be crosslinked foams.

The degree of surface treatment of the polyolefin resin foam can be appropriately determined according to the purpose, but the wetting index (according to JIS K-6768) is 30 dyn / c.
It is preferable that the treatment degree is m or more, preferably 35 dyn / cm or more, and more preferably 40 dyn / cm or more. According to the conventional proximity two-electrode type corona discharge treatment,
Wetting index of polyolefin resin foam surface 40dyn
If the treatment rate is not less than / cm, a large number of pinholes are generated and avatars are easily formed. However, according to the non-polar discharge method, even if the treatment rate is not less than 40 dyn / cm,
There are no pinholes or avatars.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1] Low density polyethylene resin (M
I = 2.5, density 0.922) crosslinked foam (thickness 7 m
m, width about 1650 mm, foaming ratio about 30 times), and surface treatment was carried out by the non-polar discharge method. Using a non-polar discharge type processor manufactured by Kasuga Electric Co., Ltd., non-polar discharge treatment was performed so that the degree of treatment of the surface of the foam was 48 dyn / cm (output voltage 175 V, treatment speed 5 m / min).

The degree of surface treatment was based on JIS K-6768 (wetting test method for polyethylene and polypropylene films), and the wetting index was determined. No pinholes were observed on the surface of the treated foam.
Further, the treated foam was placed in an oven at 120 ° C. for 1 minute, and the presence or absence of the avatar phenomenon due to the contraction of bubbles was observed. As a result, the occurrence of avatar was not observed.

[Comparative Example 1] Using the same foam as that used in Example 1, corona discharge treatment was performed by a conventional proximity two-electrode system. Using a proximity two-electrode type corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., non-polar discharge treatment was performed so that the treatment degree of the surface of the foam was 38 dyn / cm (output voltage 110 V, treatment speed 20 m / min. ). Generation of pinholes was observed on the surface of the foam after the treatment, and further, when the treatment was performed by increasing the output voltage to 150 V so that the wetting index was 40 dyn / cm, avatars were generated.

With respect to the treated foams obtained in Example 1 and Comparative Example 1, the change with time of the wetting index was measured. The results are shown in Figure 1. As is apparent from FIG. 1, the foamed body 1 surface-treated by the non-polar discharge method can have a high degree of treatment and, at the same time, maintains a high wetting index.

[Example 2] Low-density polyethylene resin (M
I = 2.0, density 0.921) crosslinked foam (thickness 4.
6 mm, a width of about 1350 mm, and a foaming ratio of about 31 times) were used for the surface treatment by a non-polar discharge method. Two types of foams were used, one with a normal surface condition and one with a rough surface condition.

Using a non-polar discharge type processor manufactured by Kasuga Electric Co., Ltd., the surface treatment degree of the above two kinds of foams is 48d.
A non-polar discharge treatment was carried out so that it would be yn / cm (output voltage 175 V, treatment speed 5 m / min). Each treated foam was placed in an oven at 120 ° C. for 1 minute, and the presence or absence of the avatar phenomenon due to the contraction of bubbles was observed. No avatar was observed.

[Comparative Example 2] Using the same foam (having a normal surface state) as used in Example 2, an output voltage of 150 V was applied by a proximity two-electrode corona discharge processor manufactured by Kasuga Electric Co., Ltd. Then, the treatment speed was changed to 10 m / min and 30 m / min to obtain foams having different treatment degrees. Each of the treated foams was placed in an oven at 120 ° C. for 1 minute, and the presence or absence of the avatar phenomenon due to the shrinkage of bubbles was observed. As a result, the wetting index was 42 dyn / cm at the processing speed of 10 m / min, but there were many pinholes and avatars were generated. In addition, a processing speed of 30 m / min and a wetting index of 40 dyn /
cm, but there were some pinholes and avatars occurred.

As described above, according to the conventional proximity two-electrode type corona discharge treatment, when the wetting index is improved, pinholes and avatars are generated, so that it is difficult to improve the treatment degree.

[0024]

EFFECTS OF THE INVENTION According to the present invention, there is no risk of pinholes, avatars, etc., and therefore the wettability of foam (the degree of treatment)
Can be improved. Moreover, since there are no pinholes, the appearance is also good.

[Brief description of drawings]

FIG. 1 is a graph showing changes over time in the wetting index of the foam (1) treated by the non-polar discharge method of Example 1 and the foam (2) treated by the proximity two-electrode method of Comparative Example 1. ..

Claims (1)

[Claims] 1. A high voltage is applied to an electrode placed in the air to cause discharge, and the surface of the foam is subjected to non-polar discharge treatment by utilizing the difference in capacitance between the gas and the polyolefin resin foam.
A surface treatment method for a polyolefin resin foam, which is characterized by improving the wettability of the surface.