JPS639537B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for producing a polymer composite membrane having an asymmetric structure in the thickness direction by plasma polymerization, and more specifically, the concentration of the polymer formed by plasma polymerization is directed inward from one surface of the base polymer. The present invention relates to a method of manufacturing a monolithic, composite membrane with a progressively reduced texture. Conventionally, for polymer films with low surface energy, such as polyethylene, polypropylene, and Teflon films, when coating, laminating, printing, etc. are performed on these polymer films, the surface is treated to reduce the surface energy. In order to improve adhesion and printability by increasing the size or polarizing the surface, or to improve the antistatic properties of a polymer film, methods are often used to treat the surface to make it hydrophilic. It is being said. As a surface treatment method for this polymer film, methods such as corona discharge treatment, wet chromic acid treatment, flame treatment, hot air treatment, ozone or ultraviolet irradiation treatment are used to oxidize the surface, or to make the surface uneven. For this purpose, methods such as sandblasting and solvent treatment have been used. Furthermore, a method is also known in which a polymer coating having predetermined physical properties is formed on one or both surfaces of a polymer membrane by plasma polymerization (Japanese Unexamined Patent Application Publication No. 1983-1998-1).
Publication No. 131026). This method not only allows a relatively thin coating layer to be uniformly formed on the surface of the substrate without damaging it, but also allows the arbitrary formation of a surface coating with desired physical properties by appropriately selecting monomers to be plasma polymerized. This is an advantageous method in that it allows However, the coating layer formed by this method is simply laminated on a different base polymer by physical bonding force or weak chemical bonding force, so it cannot be used underwater or even in the atmosphere for long periods of time. It has the disadvantage that it peels off during use. The present inventors have conducted intensive research in order to overcome the above-mentioned drawbacks associated with surface coating of polymer membranes by plasma polymerization and to develop a method for forming a coating layer that firmly bonds the substrate. It was discovered that by plasma-treating the surface of a molecular membrane while infiltrating a plasma-polymerizable monomer from the back side, a composite membrane in which a plasma-polymerized polymer is integrally bonded to a base polymer can be obtained.Based on this knowledge, the present invention was developed. I arrived at the eggplant. That is, in the present invention, the plasma polymerizable monomer is infiltrated in a gaseous state from the back side of the polymer membrane substrate, and low-temperature plasma treatment is performed on the surface, so that the concentration of the plasma polymerizable polymer gradually decreases from the front side to the back side. The present invention provides a method for producing a polymer composite membrane having an asymmetric texture in the thickness direction, which is characterized by forming a composite membrane in which a plasma-polymerized polymer having a texture and a base polymer are integrated. In the polymer composite membrane obtained by the present invention, the plasma-treated surface consists of almost 100% plasma polymerized polymer, and the concentration gradually decreases toward the back surface, interpenetrating with the base polymer and integrating it. It has a structured organizational structure. The polymer membrane used in the method of the present invention may be a porous membrane, a homogeneous membrane, or even a laminate membrane, but it is necessary that the plasma polymerized monomer can diffuse through it. be. In addition, the polymer that forms this film is
Examples include polystyrene, polyvinyl acetate, silicone rubber, polyvinyl chloride, Teflon, polyethylene terephthalate, polypropylene, polyethylene, nylon, cellulose, polysulfone, polyacrylonitrile, polybutadiene, and copolymers thereof. The plasma-polymerizable monomers used in the method of the present invention are limited to those that can be volatilized by heating under reduced pressure, or those that are already gaseous. Examples of such monomers include volatile vinyl compounds, etc. , pyridine, ethyl acetate, phenol, benzaldehyde, tetramethyldisiloxane, pyrrole, ammonia and the like. These may be used alone or in combination.
You may use a mixture of two or more species. Furthermore, in the method of the present invention, in the plasma,
For example, the treatment may be performed while introducing a constant flow rate of a non-plasma polymerization gas such as hydrogen, argon, helium, etc., and this treatment can reduce the plasma intensity at the film location, thin film deposition from the plasma (thin film in normal plasma polymerization), etc. control becomes possible. In carrying out the method of the present invention, a general-purpose low-temperature plasma processing apparatus having a modified membrane holding mechanism as shown in FIG. 1 can be used, for example. In this figure, a circular polymer membrane 9 is held on a membrane holder 1 by an O-ring, and monomer gas at a constant pressure is supplied from a monomer gas inlet from a monomer container (or gas cylinder) 3 with a constant temperature bath. 10
is pressed by. Therefore, in some cases, the polymer membrane is reinforced with a coarse mesh. On the other hand, the plasma is excited at the radio wave coil 6 by the radio wave power supplied by the radio wave oscillator 5, and spreads to the radio wave coil 8. Furthermore, a non-plasma polymerizable gas is supplied from the non-plasma polymerizable gas introduction pipe 7 in order to adjust the film forming conditions as necessary. Monomer gas 10
diffuses within the polymer membrane 9, and a thin layer is formed on the plasma-contact surface of the polymer membrane by mutual penetration of the plasma-polymerized polymer and the polymer membrane polymer,
A polymer membrane with an asymmetric chemical structure is obtained. Compared to conventional plasma treatment methods, the method of forming a polymer film with an asymmetric chemical structure of the present invention has the following advantages: (1) The reaction rate of the monomer gas is high (2) The original chemical structure of the monomer is easily preserved (3) Less damage to the polymer membrane (4) The thickness of the surface layer, which is affected by the treatment, is relatively thick;
Moreover, its thickness can be controlled by controlling the pressure of the monomer gas and the membrane temperature. It has excellent characteristics such as no peeling or elution, and can be used, for example, to improve the adhesion, printability, antistatic properties, etc. of polymer films. Next, the present invention will be explained in more detail with reference to Examples. Example 1 After attaching a silicone rubber membrane with a thickness of 0.5 mm to the apparatus shown in Figure 1, first thoroughly deaerate both sides of the membrane.
Next, the vacuum chamber on the plasma processing vessel side is closed, and allylamine vapor is introduced as a monomer gas at room temperature (25°C). In addition, on the plasma container side 8, there is a
Flow argon gas at a pressure of 30 μmHg. Next, 40 W of radio wave (13.5 MHz) power is supplied to the coil 6, which has been matched in advance, to generate plasma. The pressure inside the reactor begins to rise after a while,
It will be about 84μmHg. This is due to the decomposition of the monomer gas passing through the membrane. Two types of treatment were performed, one for 8 minutes and one for 40 minutes, and the properties of the surface of the resulting treated silicone rubber membrane on the side that was in contact with the plasma were investigated by determining the contact angle of water and the stainability of Pontasilcamine. . For comparison, allylamine vapor was introduced from the inlet tube 7 at the same pressure as above and treated for 40 minutes while the side 10 in Fig. 1 was kept in a vacuum.
The surface properties of the treated silicone rubber film were investigated in the same manner as above (conventional method). These results are shown in Table 1.

[Table] When the surface of the silicone rubber film treated for 40 minutes using the method of the present invention in contact with plasma was observed using an optical microscope, it was found that the treated layer was a layer on the extreme surface that was highly stained by an acidic dye (pontasilcamine). It had a two-layer structure, with a relatively thick pale pink layer underneath, and the thickness of the layers was about 3μ and 20μ, respectively. Furthermore, the dyeability was maintained even after washing with an aqueous surfactant solution and methanol and then immersing in water for one week. Furthermore, the dyeing property remained unchanged even though it was immersed in acetone for a long time to cause swelling. Note that no staining or contact angle change was observed on the surface that was not in contact with the plasma. Example 2 Using a polyethylene terephthalate (PET) membrane, allylamine and pyridine vapors were introduced as plasma polymerization monomer gases at room temperature, and plasma treatment was performed for 20 minutes in the same manner as in Example 1. The PET film thickness is 55 μm, the radio wave power is 15 W, and the initial pressure on the plasma container side is 14 μm.
Hg was 27μmHg. The properties of the surface of the obtained treated PET film on the side that was in contact with the plasma were investigated in the same manner as in Example 1. For comparison, a conventional treatment as shown in Example 1 was performed using pyridine, and the surface properties of the resulting treated PET film were similarly investigated. These results are shown in Table 2.

[Table] As can be seen from this table, the PET film treated by the method of the present invention using pyridine and allylamine did not differ much from the untreated film in terms of water contact angle, but pontasilcamine staining was not observed. Ta. In addition, conventionally treated with pyridine
The PET membrane did not exhibit any staining properties, and furthermore, the membrane was significantly colored (yellowing) during processing. Furthermore, when the surface of the PET film treated by the method of the present invention was observed using an optical microscope, the thickness of the treated layer was considerably thinner than that of the silicone rubber film, and was several μm thick.
It was moderately hot. The thinness of this layer is probably the reason why the dyeing results in a much lighter color. Also, although the treated layer appeared to consist of only one layer, it is unclear whether there is a thin layer that cannot be observed with an optical microscope. Example 3 Using a silicone rubber membrane (0.5 mm thick), vinyl methyl ether and vinyl acetate vapor were introduced as monomer gases at room temperature, and plasma treatment was performed for 30 minutes in the same manner as in Example 1. Note that the radio wave power was 15 W, and the initial pressure on the plasma container side was 15 μmHg and 13 μmHg, respectively. The obtained treated silicone rubber film showed no yellowing that was observed in the film treated by the conventional method. Furthermore, the surface tackiness that silicone rubber originally had was significantly reduced, and the treated surface had a smooth feel. In addition, the reflection infrared spectrum of the film treated with vinyl acetate showed an increase in absorption of carbonyl groups, clearly indicating the formation of polymer. Example 4 Using a Teflon porous membrane, plasma treatment was performed in the same manner as in Example 1 under the conditions of argon 27 μmHg, pyridine 10 μmHg, and radio frequency power 20W. However, plasma excitation was performed in a repeating manner of 0.5 seconds ON and 5 seconds OFF to avoid continuous contact with plasma. For comparison, a conventional plasma treatment was performed with both sides of the film in a vacuum. FIG. 2 shows a scanning electron micrograph of the Teflon membrane surface. FIG. 2A shows the surface of an untreated Teflon film, B shows the surface of the Teflon film treated by the method of the present invention, and C shows the surface of the Teflon film treated by the conventional method. As can be seen from this photo, each fiber in the plasma-treated fibers is thicker than the untreated fibers due to the plasma polymerized film attached. Further, the surface of the film treated by the method of the present invention retains its original surface structure well, whereas the treatment by the conventional method causes significant non-uniformity of the treated layer and deformation due to strain force.
This is thought to be because in the former case, a plasma polymerized film is formed almost evenly around each fiber, so the strain forces caused by this film balance out and prevent deformation.On the other hand, in the conventional treatment, It is presumed that this is because the plasma polymerized film is concentrated on the surface area.

[Brief explanation of the drawing]

FIG. 1 shows one of the apparatuses for carrying out the method of the present invention.
To illustrate an example, FIG. 1A is an explanatory cross-sectional view of the apparatus, and FIG. 1B is an enlarged cross-sectional view of a membrane holder in the apparatus. In the figure, 1 is a membrane holder, 3 is a monomer container with a constant temperature bath, 5 is a radio wave oscillator, 6 is a radio wave coil, 7 is a non-plasma polymerizable gas introduction tube, 8 is a plasma reactor, and 9 is an O-ring. The circular polymer membrane is thus held, and 10 is a monomer gas introduction part. Figure 2 is a scanning electron micrograph of the surface of a Teflon porous membrane, in which A is the untreated Teflon membrane surface, B is the Teflon membrane surface treated by the method of the present invention, and C is the Teflon membrane surface treated by the conventional method. This is an example of a Teflon film surface made of

Claims (1)

[Claims] 1. By performing low temperature plasma treatment on the surface while infiltrating the plasma polymerizable monomer in gaseous form from the back surface of the polymer membrane substrate, a plasma structure is created in which the concentration of the plasma polymerized polymer gradually decreases from the front surface to the back surface. A method for producing a polymer composite membrane having an asymmetric tissue structure in the thickness direction, characterized by forming a composite membrane in which a polymerized polymer and a base polymer are integrated.