JP3864211B2 - Surface modification method of fluoropolymer moldings using vacuum ultraviolet laser - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a surface treatment method for a fluoropolymer molded article. More specifically, the present invention irradiates a vacuum ultraviolet fluorine laser in a system containing water (water vapor), improves the structural characteristics and functionality of the surface without leaving impurities such as residues on the polymer surface, and performs laser irradiation. The present invention relates to a novel surface treatment method in which only the surface is selectively hydrophilized.
[0002]
[Prior art]
The polymer surface reaction using an excimer laser that oscillates high-intensity pulsed light in the ultraviolet region has been actively studied from both the basic and applied aspects as a precise surface treatment and surface processing method for polymers.
In particular, fluoropolymers represented by polytetrafluoroethylene have high thermal and chemical stability and are of wide industrial interest. However, the surface free energy is so low that the surface is It has water and oil repellency, has poor surface adhesion, and has limited application fields. Therefore, in order to improve surface adhesion while maintaining various characteristics of the molded product itself, it has been studied to introduce polar groups by various surface modification methods.
The present inventors have previously reported a surface treatment method for a fluoropolymer molded article by excimer laser irradiation (Patent No. 1966682 (Patent Publication No. 07-005773)). This is a technique of hydrophilizing the surface of a molded article by irradiation with an ArF excimer laser or a KrF excimer laser in the presence of hydrazines. However, in this method, there is a problem in using hydrazines which are careful in handling for work safety as reagents.
[0003]
In addition, as a surface modification technique of a fluorine-based polymer using an ultraviolet excimer laser, a method using a silicon derivative or the like (Kasai et al., JP 07-179636), a method using a boron derivative or the like (Murahara et al. JP-A 06-329818, JP-A 06-293837), a method using a metal belonging to Group II of the periodic table (Okada et al., JP 06-240026), an aromatic UV-absorbing compound, etc. Examples include a method (Nishii et al., JP 07-207049), a method using a fluororesin mixed with a boron derivative powder (five colors, JP 06-220229), and the like. In these methods, since there is no absorption of fluoropolymer at the wavelength of the ultraviolet excimer laser, laser irradiation is performed in a state where a reagent that has absorption at this wavelength and can effectively modify the polymer surface coexists. is there. However, these methods have problems such as physical damage to the polymer surface and sufficient care in handling the reagents.
In recent years, research on surface modification technology using vacuum ultraviolet light having a wavelength of 190 nm or less has been activated with the development of new light sources. As a technique for modifying the surface of the fluoropolymer using a xenon excimer lamp with a wavelength of 172 nm, a method using water (Hiramoto et al., JP 07-179629 A), a method using an aqueous boron compound solution (Hiramoto et al., JP-A-07-179628), irradiation in the atmosphere (Kasai, JP-A-08-165369), a method using a condensed layer (Tsutsui, JP-A-09-188773), and the like. In these methods, it is stated that the surface modification proceeds after the C—F bond of the fluorine-based polymer surface layer is cut by irradiation with vacuum ultraviolet light and the polymer surface is activated.
[0004]
However, these methods using vacuum ultraviolet lamps have disadvantages such as the fact that the intensity of the light source is weak, so that long-time irradiation is required to obtain the desired modification characteristics, and position-selective surface modification is not possible. There is. Further, as a technique for modifying the surface of the fluoropolymer by irradiation with a fluorine laser having a wavelength of 157 nm, a method using an alcohol aqueous solution (Inasaki, JP 06-279590), a method using silica particles (Eguchi et al., Special Examples include surface modification methods using reagents and fine particles such as Kaihei 10-249271). It is stated that surface modification proceeds after the C—F bond of the resin surface layer is cut by irradiation with fluorine laser and the polymer surface is activated.
On the other hand, research on microfabrication using a vacuum ultraviolet laser has been conducted in a vacuum or in an inert gas. Ceramics (Ohara et al., JP 09-048684 A), oxide thin films (Kitahara et al. No. 09-048698), water / oil repellent nozzle plate (Aoki, JP 10-278278), quartz glass / polytetrafluoroethylene (Wada et al., JP 06-0779478), and the like. These studies are techniques for removing (etching) the surface layer of the workpiece by laser irradiation, and are different from the surface modification method for hydrophilizing the surface of the workpiece.
Furthermore, Inazaki No. 06-228343 by Inazaki describes a method for surface modification of a fluororesin by ArF excimer laser irradiation in the presence of water having an electrical resistivity of 100 MΩ · cm or higher, and mentions the use of a fluorine laser in this. Has been. In the present invention, it is stated that the surface of the fluororesin is made hydrophilic by using ultra-high purity water having an electrical resistivity exceeding 100 MΩ · cm.
However, the production of ultra-high-purity water having an electrical resistivity exceeding 100 MΩ · cm requires a very advanced technique and has a drawback of requiring a large production cost.
[0005]
[Problems to be solved by the invention]
An object of this invention is to provide the method of producing the site | part which hydrophilized the surface of the fluorine-type polymer molded article position-selectively. An object of this invention is to provide the more effective surface treatment processing method of a synthetic resin molded product.
[0006]
[Means for Solving the Problems]
As a result of intensive studies on the surface processing method of the vacuum ultraviolet laser polymer, the inventors of the present invention, when irradiated with a vacuum ultraviolet laser in a system containing water or water vapor with an electrical resistivity of 20 MΩ · cm or less, The inventors have found that it is possible to replace the fluorine atom with a hydroxyl group or a hydrogen atom to make only the laser irradiated surface hydrophilic, and based on these findings, various studies have been made and the present invention has been made.
That is, the present invention provides a fluoropolymer characterized by irradiating a fluorine-based polymer molded article with a vacuum ultraviolet fluorine laser having a wavelength of 157 nm in the presence of water or water vapor to hydrophilize the surface of the polymer molded article. A surface modification method for the surface of a molded product is provided.
Next, the present invention will be described in detail. The polymer molded product herein refers to a material such as a film, a sheet, a fiber, a fiber reinforced resin, a resin molded product, etc., and does not necessarily need to be a molded product as a final product, and the shape is not limited.
Examples of the water used in the present invention include water (H ₂ O) having an electrical resistivity of 20 MΩ · cm or less and its isotopes (such as heavy water). Typical examples include deionized water, distilled water, and ultrafiltered water.
Since vacuum ultraviolet light, which is a high-energy photon, is used in the present invention, a large amount of reactive species are generated by high-energy photons even when using low-purity water containing a small amount of impurities. Will not have any adverse effect.
The reaction between this fluoropolymer molded product and water molecules will be described. First, when water molecules are irradiated with a vacuum ultraviolet laser, the water molecules absorb vacuum ultraviolet light and water in an electronically excited state is generated. At this time, the light absorption coefficient (absorption cross section) of water molecules at a wavelength of 157 nm is about 10 ⁴ cm ⁻¹ in liquid water (JLWeeks et al., Radiation Research, vol.19, pp.559-567 (1963)). ), About 3 × 10 ⁻¹⁸ cm ² in gaseous water (JMHeller et al., Journal of Chemical Physics, vol. 60, No. 9, pp. 3483-3486 (1974)), so an argon fluorine excimer laser (wavelength 193 nm Absorption coefficient of water about 10 ⁻¹ cm ⁻¹ ), krypton fluorine excimer laser (wavelength 248 nm; absorption coefficient of water 10 ⁻² cm ⁻¹ or less), and xenon excimer lamp (wavelength 172 nm; absorption coefficient of water about 10 ^It can be seen that it has a greater absorption than the light source wavelength longer than that of a fluorine laser such as ² cm ⁻¹ ). Such a large absorption at 157 nm is extremely important in securing the amount of active species generated necessary for surface modification.
[0007]
Next, water in an electronically excited state generated by irradiation with vacuum ultraviolet light is decomposed into a reaction intermediate such as a hydrogen atom or a hydroxyl group with a high quantum yield. At a wavelength of 157 nm, the quantum yield is about 0.6 (N. Getoff et al., Photochemistry and Photobiology, vol. 8, pp. 167-178 (1968)). This quantum yield is also wavelength-dependent, similar to the absorption coefficient, and decreases significantly on the long wavelength side. For example, it is 0.4 at 172 nm and 0.2 at 193 nm. Thus, when a 157 nm laser is used, the photolysis reaction of water molecules can be performed with high efficiency due to the synergistic effect of its high absorption rate and quantum yield compared to other light sources.
The generated active species hydrogen atom has high chemical reactivity with the fluorine atom. Therefore, when a fluoropolymer molded product is put in a reaction vessel, a reaction occurs in which fluorine atoms and hydrogen atoms react on the surface of the molded product, and a carbon-fluorine bond is broken to generate hydrogen fluoride molecules. The reactivity of carbon atoms in the polymer main chain is improved (H. Niino et al., Applied Surface Science, vol. 96-98, pp. 550-557 (1996)). The carbon atom from which the fluorine atom has been released immediately undergoes a reaction in which a hydrogen atom or a hydroxyl radical generated by photolysis of another water molecule is substituted on the surface of the molded product. Therefore, polymer molecular chains having hydrogen atoms and hydroxyl groups are formed on the surface of the molded product, and surface hydrophilization is observed.
As described above, when a vacuum ultraviolet fluorine laser having a wavelength of 157 nm is used, water with high work safety can be decomposed with high efficiency, and a large amount of active species effective for surface modification of fluororesin can be generated. I understand that. In addition, since the lifetime of the reaction intermediate generated by this method is not so long, a substitution reaction occurs only on the surface portion irradiated with the laser beam, and a position-selective surface reaction is performed.
[0008]
In the method of the present invention, it is preferable that the intensity of the vacuum ultraviolet laser is lower than the threshold intensity at which ablation occurs (about 100 mJ / cm ² / pulse or less), and the higher the gas pressure of water vapor, the more effective (Saturated vapor pressure at room temperature: about 25 Torr). However, it is important that the active species is sufficiently supplied to the surface portion of the molded product to be modified. As described above, since the fluororesin has a large absorption at a wavelength of 157 nm, even if the laser is irradiated from the back surface of the resin film, most of the laser is absorbed inside, which is effective for surface modification. Not right. In addition, since water and water vapor also have absorption at a wavelength of 157 nm, when a large amount of water is present between the formed product and the laser device, the laser cannot reach the vicinity of the molded product and is generated by laser irradiation. The active species cannot react with the surface of the molded product, and surface modification is not achieved. For example, since the water vapor concentration at 25 Torr, which is the saturated vapor pressure at room temperature, is about 8 × 10 ¹⁷ molecules · cm ⁻³ , the absorption coefficient is about 2 cm ⁻¹ and the thickness of the water vapor layer is controlled to about 0.5 mm. Thus, the active species can be supplied to the surface of the formed product. In addition, as a method of introducing water vapor into the reaction vessel, it is possible to use only water vapor alone, but the reaction vessel contains a gas having no absorption at a wavelength of 157 nm, such as nitrogen gas or rare gas (argon, helium, etc.). It is also possible to introduce to.
[0009]
It was confirmed by X-ray photoelectron spectroscopy (XPS) and surface contact angle measurement that the surface of polytetrafluoroethylene (PTFE) film irradiated with fluorine laser in a system containing water molecules was substituted with a hydroxyl group. It was. A carbon C1s peak and a fluorine F1s peak were detected from the PTFE surface before the laser treatment.
At this time, the atomic ratio of carbon and fluorine was 1: 2. A new oxygen O1s peak was observed from the laser-treated sample surface, and the proportion of fluorine atoms decreased compared to the pretreatment surface. Furthermore, the contact angle with water also changed from 130 degrees to 70 degrees, and it became clear that the surface was made hydrophilic.
These experimental results indicate that the fluorine atoms in the surface layer of the molded product are substituted with hydrogen atoms or hydroxyl groups by laser treatment. It has become possible to hydrophilize the surface of a fluoropolymer molded article by such a simple and rapid method. Fluoropolymer molded products whose surface has been modified by hydroxyl groups have increased surface free energy while maintaining various bulk properties, and therefore improved surface adhesion while taking advantage of the advantages of fluoropolymers. It is possible to expand the range of application to improvement of surface wettability, improvement of dye adsorption, application to medical materials, and cell growth substrates.
[0010]
It is also possible to perform functional group conversion by a chemical reaction between a hydroxyl group and another reagent. For example, when a chemical treatment with an organic acid anhydride such as acetic anhydride is performed, an acetyl group is added to the hydroxyl group, and the surface exhibits lipophilicity due to the effect of the terminal methyl group.
Further, in the present invention, surface treatment is performed only on a desired irradiated portion by irradiating a laser beam that has passed through a mask (such as a metal plate pattern) corresponding to a portion of the polymer film to be modified. Is possible. On the other hand, the fluorine laser beam has a larger beam shape compared to other laser beams such as a helium-neon laser and a YAG laser. Can easily handle large area processing. In particular, in the present invention, water molecules react by a non-thermal photochemical reaction by a vacuum ultraviolet laser, so that the surface treatment is performed extremely effectively without any thermal damage in the periphery other than the irradiated part. Can do.
[0011]
As the laser in the present invention, a vacuum ultraviolet laser that oscillates the absorption wavelength of water molecules is suitable, and a fluorine laser (wavelength: 157 nm) is particularly preferred. In addition, it is also effective to convert laser fundamental wavelength light into laser light in the vacuum ultraviolet region by a nonlinear optical effect or the like. The fluence of the laser varies depending on the type of polymer, but a high-intensity laser having a pulse width of about 0.1 mJ / pulse or more as a nanosecond is desirable. In the present invention, the target fluorine-based synthetic resin may be amorphous, crystalline, aromatic, or non-aromatic. For example, polytetrafluorinated ethylene, polyhexafluorinated propylene, Any of polyfluorinated vinylidene, polytrifluorinated ethylene chloride resin, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene tetrafluorinated ethylene copolymer, or copolymers or cocondensates thereof Or a synthetic resin made of a mixture thereof.
[0012]
(Examples) Next, the present invention will be described in more detail based on examples.
Example 1 A polytetrafluoroethylene film was set in a reaction vessel using calcium fluoride as a window material, and a fluorine laser was applied at a room temperature and a steam atmosphere (25 Torr) with a pulse of 100 Hz with an intensity of 4 mJ · cm ⁻² · pulse ^−1. The surface treatment film was obtained by repeating irradiation for 60 seconds. At this time, water vapor was obtained from deionized water having an electrical resistivity of 2 MΩ · cm.
It was found that the contact angle of the surface with water decreased from 130 degrees to 90 degrees by laser irradiation, and the surface became hydrophilic. In addition, X-ray photoelectron spectroscopy (XPS) of the sample surface after laser treatment shows a new O1s peak for oxygen in addition to the peak derived from carbon and fluorine, and the intensity of the F1s peak for fluorine is the C1s peak for carbon. Decreased compared to The atomic ratio of the sample surface before laser treatment is carbon: fluorine: oxygen = 1.0: 2.0: 0.0, whereas carbon: fluorine: oxygen = 1.0: 1 after laser treatment. .6: 0.05. From the above experimental results, it was confirmed that hydroxyl groups were introduced on the surface.
[0013]
Example 2 A polytetrafluoroethylene film is set in a reaction vessel using calcium fluoride as a window material, and a fluorine laser is applied at 100 Hz with an intensity of 4 mJ · cm ⁻² · pulse ⁻¹ at room temperature in a water vapor atmosphere (25 Torr). The surface treatment film was obtained by repeating irradiation for 100 seconds. At this time, water vapor was obtained from deionized water having an electrical resistivity of 2 MΩ · cm.
It was found that the contact angle of the surface with water decreased from 130 degrees to 70 degrees by laser irradiation, and the surface became hydrophilic. In addition, X-ray photoelectron spectroscopy (XPS) of the sample surface after laser treatment shows a new O1s peak for oxygen in addition to the peak derived from carbon and fluorine, and the intensity of the F1s peak for fluorine is the C1s peak for carbon. Decreased compared to From the above experimental results, it was confirmed that hydroxyl groups were introduced on the surface.
Comparative Example 1 A polytetrafluoroethylene (PTFE) film was set in a reaction vessel using calcium fluoride as a window material, and a fluorine laser was applied at a pulse of 100 Hz with an intensity of 4 mJ · cm-2 · pulse-1 in a vacuum atmosphere at room temperature. The surface treatment film was obtained by repeating irradiation for 100 seconds. The contact angle of the surface with water before and after the laser treatment did not change up to 130 degrees, and it was found that the presence of water was indispensable together with the laser irradiation for the hydrophilized surface treatment.
[0014]
【The invention's effect】
According to the present invention, the surface treatment method of a fluoropolymer molded product using a vacuum ultraviolet laser is very effective because the laser is excellent in energy and position controllability, so that a precise and uniform hydrophilic group can be obtained. Hydrophilization surface treatment by introduction can be performed only on the pattern formation site by laser irradiation.

Claims (1)

The polytetrafluoroethylene molded article, a vacuum ultraviolet fluorine laser with a wavelength of 157nm was irradiated with 4 mJ · ^{cm -2} · pulse ^-1 or less intensity in the presence of less water or steam electrical resistivity of 20 M.OMEGA · cm, said poly A method for modifying the surface of a polytetrafluoroethylene molded article, wherein only the irradiated portion of the surface of the tetrafluoroethylene molded article is hydrophilized.