JPH037209B2 - - Google Patents

Description

[Detailed description of the invention]

A. Technical Field of the Invention The present invention relates to a method of treating a polymer sheet with low-temperature plasma. B. Prior art and its problems In recent years, studies have been conducted to modify the chemical properties, physical properties, mechanical properties, optical properties, electrical properties, surface structure, etc. of polymer sheet materials by low-temperature plasma treatment. It's becoming popular. In other words, low-temperature plasma treatment is being considered for the purposes of adhesion, friction properties, texture, gloss, antistatic properties, surface hardening, surface roughening, prevention of blocking, darkening of dyed products, and improvement of color fastness. There is. However, it is currently not widely used industrially due to high equipment costs and extremely high running costs. Considering the reasons why low-temperature plasma processing requires high equipment costs and running costs: 1) Processing time is required from several seconds to hundreds of seconds, so if you try to increase processing speed to increase production volume, you will end up with a long processing length. 2) Furthermore, the electric power required for discharging is extremely large, and most of the running costs are due to this electric power. Due to reasons such as. C. Purpose of the present invention The purpose of the present invention is to reduce the power required for this discharge, and for this purpose, it is necessary to confine the plasma to a certain extent, reduce discharge loss to unnecessary parts, and effectively apply it to the object to be treated. In addition to discovering that this is very effective, we have also discovered a low-temperature plasma treatment method that has low equipment costs and significantly reduces running costs. D Structure of the present invention In other words, the present invention provides low-temperature plasma treatment of a polymer sheet using an internal-electrode type low-temperature plasma generator in which a discharge electrode is located inside a can. The present invention relates to a plasma processing method characterized by insulating the can from the ground and keeping it in an ungrounded state. In the present invention, the polymer sheet-like material refers to a sheet-like material such as resin, molded product, film, cloth, etc. made of synthetic polymers, natural polymers, etc., but it does not necessarily have to be made of one type of polymer. Composite, bimetallic, bonded, blended, copolymerized, intertwisted,
It may be a mixed knit, a mixed weave, a mixed weave, etc., and may further contain an appropriate plasticizer, kneaded material, inorganic material, matting agent, etc. inside. Further, other polymeric substances, organic substances, inorganic substances, or a mixture thereof may be attached to the surface of the sheet-like material. Plasma is classified into two types: high-temperature plasma and low-temperature plasma, and the term "plasma" used in the present invention refers to low-temperature plasma. Low-temperature plasma is generated during discharge with an average electron energy of 10 eV (10 ⁴ ~
It is characterized by an electron density of 10 ⁹ to ^{10 12} cm ^-3 (10 ⁵ K) and is also called a non-equilibrium plasma because there is no equilibrium between the electron temperature and the gas temperature. Electrons, ions,
Atoms, molecules, etc. are mixed. Low-temperature plasma consists of gases such as argon, nitrogen, hydrogen, oxygen, etc. in a vacuum system of 0.01 to 10 Torr.
It is produced by continuously introducing air, carbon monoxide, carbon dioxide, etc. into the system and applying a voltage between the electrodes. The type of gas is selected depending on the processing purpose. Any frequency power source can be used to apply the voltage. 1K in terms of sustainability and uniformity of discharge
Hz to 10GHz is desirable. Also, in terms of plasma uniformity in the width direction of the electrode, 1KHz to 1MHz is preferable.
When the frequency exceeds 1 MHz, if the length of the electrode exceeds 1 m, processing spots tend to occur in the length direction. Furthermore, below 100 Hz, the edge effect of the electrode tends to occur, and arc discharge tends to occur at the edge part. Further, as the current, alternating current, direct current, biased alternating current, pulse waves, etc. can be used. Electrodes can be divided into internal electrode methods, which are placed inside the vacuum system, and external electrode methods, which are placed outside the vacuum system.With the external electrode method, as the equipment becomes larger, plasma moves particularly to the surface of the workpiece. During the process, the activity is lost or the plasma is scattered and the plasma concentration is diluted, resulting in little processing effect. On the other hand, with the internal electrode method, the discharge electrode can be installed near the object to be treated, so the treatment effect is greater than with the external electrode method. Electrode shapes can be divided into symmetrical and asymmetrical. In the case of a large plasma processing apparatus where the processing width of the object to be processed is large and therefore a large electrode is required, symmetrical electrodes have more disadvantages. For example, it is almost impossible to flow gas uniformly between large electrodes.
Furthermore, the electric field may be disturbed at the edge of the larger electrode,
Processing spots are likely to occur. Therefore, it has been found that asymmetric electrodes are preferable for large-scale plasma processing equipment. The shape of the electrode on the side that does not come into contact with the object to be processed can be arbitrarily selected from one or more cylinders or rods with a polygonal cross section with an acute angle, but the processing effect also depends on the number of electrodes. is different, and if it is too small, the processing effect will be small. The shape is preferably cylindrical. In addition, the shape of the electrode on the side that comes into contact with the object to be processed can be drum-shaped, plate-shaped, or modified shapes thereof, but the shape and combination thereof are not limited to these. It's not something you can do. Further, the material of the electrode can be metal such as stainless steel, copper, iron, aluminum, etc., and it may be coated with glass, ceramics, etc., if necessary. Naturally, these electrodes may be water-cooled if necessary, and the cooling temperature is appropriately selected depending on the object to be treated. The cooling water is desirably water with as few impurities as possible, but this is not particularly the case when electrical leakage due to these impurities is not a serious problem. Next, the gas to be introduced into the vacuum thread should be introduced as far as possible from the exhaust port of the vacuum pump and distributed as necessary. This is important in the sense of avoiding short passes of the gas within the vacuum system, and is also important in order to prevent processing spots on the object to be processed. The degree of vacuum for generating low-temperature plasma is usually 0.01 to 10 Torr, but according to the results of studies by the present inventors, 0.05 to 1.0 Torr is preferable. When the degree of vacuum becomes 0.05 Torr or less, the mean free path of ions and electrons increases and the energy of accelerated particles increases, but the total number of accelerated particles that reach the object to be processed is small, and processing efficiency is not good. Moreover, in order to maintain the temperature below 0.05 Torr while introducing gas into a large processing chamber, a vacuum pump with a very large displacement is required, which is not desirable considering the equipment cost. When the degree of vacuum becomes 1 Torr or more, the mean free path of ions, electrons, etc. becomes small, the energy of accelerated particles becomes small, and processing efficiency deteriorates even though the total number of accelerated particles is large. Thinking in this way, the mean free path of an accelerated particle, in other words, the degree of vacuum P that determines the distance over which a charged particle is accelerated by an electric field and the number of accelerated particles, and the degree of vacuum P that determines the number of accelerated particles, and the accelerated particle loses its energy or activity. It is conceivable that some kind of optimal relationship exists between the distance d between the electrodes, which determines the probability that the process can be reached without any change. As a result of considering this point, we found that 1≦d≦10 (cm) and 0.05<P・
It has been found that the processing efficiency is particularly good when the degree of vacuum and the distance between the electrodes satisfy d<5 (Torr×cm). In other words, the processing efficiency was good when d was set small when the pressure was high, and when d was set large when the pressure was low. Furthermore, regarding the relative position of the sheet-like material placed between the electrodes, it is better to place the sheet-like material in contact with one of the electrodes for better processing efficiency. In addition, if you do not want to apply too much tension to the sheet-like material or do not want to wrinkle the sheet-like material, use a type that allows the sheet-like material and the electrode to move together, for example, by touching the sheet-like material on a drum electrode. It is desirable that the sheet-like material be moved while rotating the drum. In fact, minute wrinkles often cause processing spots. If there is no need to pay much attention to tension or wrinkles, the sheet-like material may be placed in contact with the plate electrode, and the sheet-like material may be slid and moved on the electrode. However, when a sheet-like material is placed in contact with one of the electrodes, it has the disadvantage that the treatment effect can only be obtained on the surface that is not in contact with the electrode surface. Of course, after single-sided treatment, double-sided treatment is possible by passing through a place where the electrodes are arranged inversely to the sheet material. In normal cases, the processing effect on only one side is often sufficient, so this type is desirable from the viewpoint of processing efficiency. However, it is impossible to increase the processing effect on both sides by 1.
If it is desired to obtain the effect using only a pair of electrodes, a sheet-like material may be placed between the two electrodes, and the sheet-like material may be moved. In this case, the processing effect is generally smaller than when it is placed in contact with the electrode. Considering this phenomenon in terms of discharge characteristics, it can be explained by the voltage drop characteristics between the two electrodes. It is said that the voltage drop characteristic between both electrodes is large near the electrodes, and small near the middle of both electrodes.This voltage drop is proportional to the strength of the electric field, and the voltage drop is large near the electrodes. This is probably because the larger portion can give more energy to the charged particle. Next, from the point of view of uniformity of processing, both electrodes must be held in parallel and must be arranged at right angles to the traveling direction of the polymeric sheet-like material to be treated. If this condition is not satisfied, processing unevenness will occur in the width direction of the sheet-like material. Furthermore, the width of both electrodes must be at least 5 cm longer than the width of the polymer sheet to be treated. This is to eliminate electric field non-uniformity at the ends of the electrodes. If this length is less than 5 cm, the processing effect in the width direction of the sheet-like material, particularly on both sides, will be different from that near the center, which is undesirable. In the present invention, moving the sheet material means that this device can continuously move and process the polymer sheet material in the atmosphere into the vacuum system, and the polymer sheet material can be moved into the preliminary vacuum system. It refers to those that can be arranged and moved to the processing chamber, and furthermore, those that have a polymer sheet-like material partitioned and arranged in the processing chamber, but in short, any material that can be moved continuously can be used. E Functions of the Present Invention It will also be described that the discharge electrode and its discharge circuit are insulated from the grounded can body and are in an ungrounded state. A conventional low-temperature plasma generator is schematically drawn as shown in Fig. 1. Here, 1 is a polymer sheet, 2 and 3 are electrodes, 4 is a power source, 5 is a can body (metal), and 6 is a transformer. When the device becomes larger, the can body is made of metal such as stainless steel, but in this case, the electrode potential in contact with the sheet and the potential of the can body are the same as the ground potential, so the can body also acts as an electrode and discharges. covers the entire inside of the can. Therefore, the amount of plasma acting on the sheet is small, and a very large amount of discharge power is required. As the discharge power is increased to increase efficiency, the discharge current flows through the can body, and the proportion of current flowing through the electrodes in contact with the sheet decreases. For this reason, plasma cannot be used effectively, the cost of discharging power to obtain the desired processing effect is very high, the running cost is also high, and the processing time must be extended, making it difficult to miniaturize the equipment and increasing equipment costs. Therefore, it was difficult to be adopted industrially for processing polymer sheet materials with a width of 1 m or more. The present inventors have been researching the effective use of plasma for many years and have developed a device as shown schematically in FIG. 2. The symbols are the same as in FIG. That is, the feature of this system is that the discharge electrode and the discharge circuit are insulated from the grounded can body and are in an ungrounded state. In this case, the potential of the electrode in contact with the sheet and the potential of the can body (earth potential since it is grounded) are different, the can body does not act as an electrode, and discharge mainly occurs between the two electrodes. Therefore, the plasma acts on the sheet without being effectively diluted, and the processing effect is significantly improved.At the same time, the processing effect is significantly greater with less discharge power than the method shown in Figure 1, and the desired effect can be achieved in a short time. As a result, the device can be made smaller, in other words, the equipment cost can be reduced, and the running cost can also be reduced to a fraction of the cost since the discharge power is small. F. Effects of the present invention As described above, the present invention can improve the treatment effect with less discharge power during low-temperature plasma treatment of polymer sheet-like materials, and therefore can significantly reduce running costs. , which is extremely effective in practice. The plasma processing method of the present invention is particularly effective for surface roughening processing, etc., which requires a relatively long processing time among plasma processing. This will be explained below using examples. Examples and Comparative Examples Surface roughening treatment (etching treatment), which requires the longest processing time among plasma treatments, will be described. 15 mμ of colloidal silica was applied by the dip-nip method at 0.05 wt% to a black-dyed black dyed product made of polyester filament as a polymer sheet and dried at 100℃, and 3% silica in
A chili-menjo ossified grain containing 27% alkali loss was used which had already roughened its surface. In Example 1, the plasma generating device is an asymmetrical electrode consisting of an internal electrode type bar and drum as shown in FIG. Bar diameter is 22mm, length is
We used 60 800mm stainless steel pipes. The drum has a diameter of 1000mm and a width of
Made of 600mm stainless steel, both electrodes are controlled by water cooling at 30℃. The polymer sheet material can be unwound and wound up in the discharge treatment chamber, and since the drum is rotatable, it can be moved in contact with the drum electrode. In Comparative Example 1, FIG. 3 shows the results when the drum electrode was grounded, whereas in Example 1 the drum electrode was kept ungrounded. Further, as Example 2, the results obtained when the apparatus shown in FIG. 4 was used are shown. FIG. 4 shows an asymmetric electrode consisting of an internal electrode type bar and plate. The bar is a stainless steel pipe with a diameter of 20 mm and a length of 800 mm, and the plate is made of stainless steel with a length of 500 mm and a width of 600 mm, and both electrodes are water-cooled and controlled at 30°C. The polymer sheet can contact the plate electrode and move on the plate. Comparative Examples 2 and 3 are shown in FIG. 4, which shows the results when the only difference from Example 2 was that the plate electrode was grounded. The power supply for Examples 1 and 2 and Comparative Examples 1, 2, and 3 is an AC 110KHz 40KVA AC frequency power supply, and the output is
I used a vacuum tube system that can add up to 20KW. Plasma discharge conditions are oxygen gas 30
/hr, the degree of vacuum was 0.15 Torr, and the distance between the electrodes was 5 cm, so P×d=0.75 Torr cm. The effect of surface roughening (etching) treatment was evaluated using L ^* of L ^* ab system. The discharge power consumption rate was calculated from the power supply input power required to set L ^* to a predetermined value after plasma treatment.

[Table] The polymer sheet materials used in Examples 1 and 2 and Comparative Examples 1 and 2 are materials that are about three times easier to etch than the normal polyester fibers used in Comparative Example 3. The processing speed is Comparative Example 1,
In case 2, the speed is very slow at 3 m/min, and the discharge power consumption is high. In the case of Examples 1 and 2, the processing speed is around 5 m, which is about twice the speed, and the discharge power consumption rate is 1/3 to 1/2 in the case of Comparative Examples 1 and 2, which reduces running costs. It can be seen that it is possible to reduce the processing time and downsize the processing equipment (only about half the processing length is required).

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional low-temperature plasma generator, and FIG. 2 is a schematic diagram of a low-temperature plasma generator according to the present invention. 3 and 4 are schematic diagrams of examples of apparatus for carrying out the method of the present invention. DESCRIPTION OF SYMBOLS 1... Polymer sheet-like material, 2, 3... Electrode, 4... Power source, 5... Can body, 6... Transformer.

Claims (1)

[Claims] 1. When subjecting a polymer sheet to low-temperature plasma treatment using an internal electrode type low-temperature plasma generator in which the discharge electrode is located inside the can, the discharge electrode and discharge circuit are insulated from the grounded can; A plasma processing method characterized by maintaining the plasma in a non-grounded state.