JP2004076012A - Method for hydrophilizing surface of optical polymer material molded product by fluorination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for imparting hydrophilicity of the surface of fluorinated polyimide molded product. <P>SOLUTION: The method for surface hydrophilization of a fluorinated polyimide molded product comprises exposing the fluorinated polyimide molded product in 1-20% fluorine gas atmosphere for 1-30 min to make the molded product surface aqueous contact angle ≤70°. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for hydrophilizing a surface of a molded article of a polymer material used for optics.

In addition to excellent light transmittance, controllability of refractive index is required as the most important characteristic of optical materials. Particularly, polymers having excellent transparency include polymethyl methacrylate (PMMA), polycarbonate, polystyrene, epoxy resin, polyethylene terephthalate, and the like. These polymers have excellent characteristics unique to polymers, such as low cost, flexibility, and light weight, and are therefore used in various optical products such as lenses, optical filters, and windows. In addition, in the field of optical communication, use of these polymer materials as materials for various optical components such as optical fibers, optical waveguides, and optical filters is being studied.

In particular, polymer materials used for optical fibers and optical waveguides require precise refractive index controllability in order to control the optical waveguide characteristics. In order to confine light in the core in the optical waveguide, the refractive index of the clad needs to be smaller than the refractive index of the core. Therefore, the cladding material needs to have a low refractive index.

In a buried type step index (SI) type optical waveguide, it is necessary to precisely control the refractive index difference between the core and the clad in order to keep the waveguide mode of light constant. Therefore, precise refractive index controllability is required for the core material and the cladding material of the optical waveguide.

(4) A high-density optical waveguide wiring requires a bent optical waveguide having a small curvature, and for this purpose, a clad material having a low refractive index is required. Further, optical components such as optical couplers, splitters, optical multiplexers / demultiplexers, and the like are composed of curved waveguides having various curvatures, and thus materials for such optical components are required to have refractive index controllability in a wide range. In addition, the material for the optical component to be connected to the silica-based optical fiber needs to be close to the refractive index (1.46) of quartz in order to reduce the reflection of light at the connection interface. Since the refractive index is higher than that of quartz, it is necessary to reduce the refractive index of these polymer materials.

(4) As a method of reducing the refractive index of a polymer material, a method of introducing fluorine into a molecular structure is generally used. For example, to reduce the refractive index of an epoxy resin, as disclosed in Patent Document 1, by introducing a polyfluorinated substituent into a curing agent of the epoxy resin, the lowest refractive index among epoxy resins so far is achieved. did. Further, as disclosed in Patent Document 2, the refractive index control of a fluorine-containing polyimide which is an optical polymer material having excellent heat resistance is achieved by copolymerizing a polyimide having a high fluorine content and a polyimide having a low fluorine content. By doing so, it is possible to control the refractive index.

As described above, in a polymer material for an optical component, it is extremely important to reduce the refractive index of the material and to precisely control the refractive index. It is effective to introduce fluorine. However, in the conventional method, a raw material in which fluorine is introduced into a polymer molecule using a fluorine reagent has to be synthesized, and a polymer material must be manufactured using the raw material. There is a problem that the manufacturing process becomes complicated.

JP-A-61-44969 Japanese Patent No. 2640553 JP-A-8-302039 56th Fall Meeting of the Japan Society of Applied Physics, Preliminary Lectures 28a-ZT-6, 1995

The present inventors have noticed that a method capable of easily introducing fluorine into an optical polymer material for controlling the refractive index of the material has not been found, and have completed the present invention. That is, the present invention has been made to solve the above problems, and an object of the present invention is to introduce fluorine into an optical polymer material by a simple method to reduce the refractive index of the optical material and to reduce the refractive index. The purpose is to precisely control the rate.

By the way, the surface of a molded article made of a fluorinated polyimide has a tendency to water and oil repellency, so-called "wetting" is poor, and the adhesion with a metal surface or a metal oxide surface or the like with other organic optical materials. There was a problem. Ozone treatment, plasma treatment, excimer laser treatment, and the like have been performed on the surface of fluorinated polyimide in order to improve adhesion. It is also known that a fluorinated polyimide is made hydrophilic by reacting it with water under excimer laser irradiation (see Non-Patent Document 1). However, in such a method, the carbon-fluorine bond (CF bond) in the fluorinated polyimide is dissociated, so that the electrical advantage of the fluorinated polyimide or the optical advantage such as refractive index control may be lost. . Further, the conventional method has a problem in terms of equipment or cost, and also has a problem in that the size of the processing area is limited.

Therefore, another object of the present invention is to introduce a fluorine into the surface of a molded article of a fluorinated polyimide by a simple method, without dissociating the carbon-fluorine bond in the fluorinated polyimide, to increase the hydrophilicity of the fluorinated polyimide. The purpose is to provide adhesiveness to the surface of a molded polyimide molded article.

The invention of the method for hydrophilizing the surface of a fluorinated polyimide molded article according to claim 1 is to immerse the molded article made of fluorinated polyimide in a fluorine gas atmosphere having a fluorine concentration of 0.01% to 20% for 1 minute to 30 minutes. Thereby, the water contact angle of the surface of the molded article made of the fluorinated polyimide is set to 70 ° or less.

Here, the fluorinated polyimide has the following structural formula:

Can be a fluorinated polyimide comprising a repeating unit represented by the formula:

The refractive index control method of the optical polymer material of the present invention can easily and widely control the refractive index of the optical polymer material as compared with the conventional refractive index control method by introducing fluorine, so that the optical fiber or It can be used for manufacturing various optical components such as formation of cladding of an optical waveguide.

Furthermore, by subjecting a molded article made of fluorinated polyimide to fluorination treatment, it is possible to control the hydrophilicity to an appropriate level.

In the present invention, the refractive index of the polymer material can be controlled by immersing the polymer material for optical use in a fluorine gas atmosphere. The refractive index of the polymer material can be precisely controlled to a desired value by appropriately selecting the fluorine gas concentration in the fluorine gas atmosphere, the temperature and the time of immersion in the fluorine gas atmosphere.

Here, the fluorine gas atmosphere means a gas containing a fluorine gas, for example, a mixed gas of a fluorine gas and a nitrogen gas. As the concentration of the fluorine gas in the fluorine gas atmosphere, a concentration necessary for obtaining a material having a desired refractive index is appropriately selected.

Examples of the polymer material used in the present invention include various polymer materials such as polyimide, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polyether sulfone which have excellent light transmittance. Polyimide is preferred from the viewpoints of properties and chemical stability, and fluorinated polyimide is preferred in view of high light transmittance.

For example, by immersing these polymer materials in various concentrations of fluorine gas diluted with nitrogen gas or the like at a predetermined temperature for a predetermined time, fluorine in the molecules is gradually increased from the surface of the polymer material toward the inside. The introduction takes place and the fluorine content of the material will increase. The depth of penetration of fluorine from the material surface and the fluorine content in the material after the fluorine treatment change depending on the concentration of the fluorine gas during the fluorine treatment, the fluorine treatment temperature, and the fluorine treatment time. There are no particular restrictions on these conditions, but when the fluorine concentration is high, when the treatment time is long, when the treatment temperature is high, the penetration depth of fluorine becomes deep, and the fluorine content of the polymer material after the fluorine treatment is increased. Rate is higher. Since the refractive index of the fluorinated portion decreases with an increase in the fluorine content, a material having a desired refractive index can be obtained by appropriately selecting the fluorine concentration, the processing temperature, and the processing time. However, if the fluorine concentration is extremely increased, or if the fluorine treatment is performed at an extremely high temperature for a long time, the molecules are degraded. Therefore, the usual fluorine treatment conditions include a fluorine concentration of 0.1 to 30% and a treatment temperature of 20%. ~ 150 ° C and a treatment time of 5-250 minutes are preferred.

に お い て In the present invention, fluorination treatment is performed to impart hydrophilicity to the surface of the fluorinated polyimide molded article. The fluorination treatment is preferably performed at room temperature in a fluorine gas atmosphere having a fluorine concentration of 0.01% to 20% for 1 minute to 30 minutes. By performing this treatment, the water contact angle on the surface of the fluorinated polyimide molded article can be reduced to 70 degrees or less and 30 degrees or more. Here, the water contact angle refers to the contact angle of a water drop when water is dropped on the surface of a fluorinated polyimide molded article. Further, in the present invention, the molded article means not only a molded article obtained by injection molding or the like but also all articles having a practically used shape such as a film, a plate, and a fiber. Specifically, a fluorinated polyimide film, a fluorinated polyimide coating film and the like are also included.

Since no change is observed even when the surface of the fluorinated polyimide molded article by such fluorination treatment is observed with a microscope, only the very thin upper layer portion of the molded article surface is fluorinated, and the surface is extremely thin. It is considered that C-F bonds coexisting coexisting in the part increase the surface energy and express the surface hydrophilicity.

Since the fluorinated polyimide already has many CF3 groups before the fluorination treatment, it cannot be determined from the Fls spectrum in the surface measurement by X-ray electron spectroscopy (ESCA). 1A and 1B show Cls spectra of ESCA. FIG. 1A shows the Cls spectrum of ESCA for the fluorinated polyimide before the reaction, and FIG. 1B shows the Cls spectrum of ESCA for the fluorinated polyimide after the reaction. However, ESCA is a measurement of an extremely thin layer of about 50 angstroms from the surface of the molded article.

From FIGS. 1 (a) and 1 (b), the absorption at 281.87 eV corresponding to a C—H bond or a C—C bond is greatly reduced before and after the reaction, and corresponds to a C ＝ O bond or a C—N bond. The change in absorption at 284.10 eV does not change much before and after the reaction. Further, the absorption at 285.92 eV corresponding to the CF bond and 287.73 eV corresponding to the CF2 bond greatly increased before and after the reaction, and the absorption at 290.21 eV corresponding to the CF3 bond hardly changed.

FIG. 2 shows the NMR spectrum of the polyimide molded article after the fluorination treatment. From FIG. 2, the F signal bonded to the benzene ring, which was not present in the polyimide before the fluorination treatment, appeared at -180 PPM, and the F signal corresponding to the CF2 bond of the cyclohexane ring appeared at -70 to -80 PPM. I understood.

When fluorinated polyimide is held under a predetermined concentration of fluorine gas atmosphere under predetermined conditions, a fluorine affinity state is formed on the surface of the fluorinated polyimide, and the fluorine atoms are attracted very quickly by the interaction between the fluorine atoms. And a new CF bond is introduced. Since the hydrogen bond between the imide bonds is strong, the surface energy of the fluorinated polyimide is small. However, in an extremely thin layer on the surface, distortion is caused by the newly formed CF bond, and a part of the regular hydrogen bond is formed. Is disconnected. Breakage of hydrogen bonds between imides on such a surface increases the surface energy and decreases the surface tension and the contact angle. The adjustment of the contact angle by the fluorination treatment can be realized only in the fluorinated polyimide. The fluorinated polyimide preferably used in such a reaction is not particularly limited. For example, a fluorinated polyimide having the following structural formula is preferable.

(4) When a molded article made of ordinary polyimide that has not been fluorinated is subjected to a fluorination treatment, the above-mentioned effect cannot be obtained because the surface hydrophilicity is too high to control the hydrophilicity. This is because in non-fluorinated polyimides, there are no fluorine bonds, so the fluorination reaction occurs irregularly, so that the hydrogen bonds are broken in various ways, and the fluorination proceeds, crossing the desired hydrophilic surface. This results in a water-soluble surface capable of free hydrogen bonding.

A technique of hydrophilizing polypropylene or the like with fluorine is known (see Patent Literature 3), but this is the case where there is no fluorine bond in the object to be fluorinated. That is, the chemical structure of the surface-treated polypropylene and the fluorinated polyimide are completely different from each other, and the mechanism of surface hydrophilicity is completely different. Is limited.

(4) The method for controlling the refractive index of the optical polymer material of the present invention will be specifically described below with reference to examples. However, the following embodiments are merely examples, and the present invention is not limited to these embodiments. In each example, the introduction of fluorine into the molecules of the polymer material was confirmed by X-ray photoelectron spectroscopy (ESCA). The refractive index is measured using a prism coupling, at a wavelength of 633 nm, in a TE mode (polarization mode of light parallel to the film surface of the material) and in a TM mode (polarization mode of light perpendicular to the film surface of the material). It was measured.

Control 1
The following repeating unit

ESCA analysis was performed on a fluorinated polyimide film having a molecular structure of The ratio of the total number of fluorine atoms in the polymer structure (hereinafter, referred to as “total fluorine atom ratio” or “total F ratio”), and C—C, C—N, C ＝ O, C—F, CF 2, and CF 3 The ratio of the number of each bond in the polymer structure (hereinafter referred to as “each bond ratio”) was obtained. Table 1 shows the results. Further, the refractive index of the fluorinated polyimide film having a molecular structure composed of the above repeating units was measured. Table 1 shows the results.

Examples 1 to 6
The fluorinated polyimide film of Control 1 was subjected to fluorination under the treatment conditions shown in Table 1 to obtain fluorinated polyimide films of Examples 1 to 6. For each of the obtained fluorinated polyimide films of Examples 1 to 6, ESCA analysis of the film surface was performed, and the total fluorine atom ratio, and the CC, CN, C = O, CF, CF2, CF3 Each binding ratio was obtained. Further, the refractive index of the fluorinated polyimide film was measured. Table 1 summarizes these results.

Control 2
ESCA analysis was performed on a commercially available polyimide film (Kapton H film manufactured by Du Pont-Toray Co., Ltd.), and the total fluorine atom ratio and the bond ratios of CC, CN, C = O, CF, CF2, and CF3 were determined. Was measured. Table 1 shows the results. Further, the refractive index of this polyimide film was measured. Table 1 shows the results.

Examples 7 to 11
The polyimide film of Control 2 was subjected to a fluorine treatment under the processing conditions shown in Table 1 to obtain polyimide films of Examples 7 to 11. ESCA analysis of the film surface of each of the obtained films of Examples 7 to 11 was performed, and the total fluorine atom ratio and the bonding ratios of CC, CN, C = O, CF, CF2, and CF3 were determined. Obtained. Further, the refractive index of this polyimide film was measured. Table 1 summarizes these results.

Control 3
ESCA analysis was performed on a commercially available PMMA film to obtain a total fluorine atom ratio and bond ratios of CC, CN, C = O, CF, CF2, and CF3. Table 1 shows the results.

Examples 12 to 15
Fluorine treatment was performed on the PMMA film of Control 3 under the conditions shown in Table 1 to obtain PMMA films of Examples 12 to 15. For each of the obtained films of Examples 12 to 15, ESCA analysis of the film surface was performed, and the total fluorine atom ratio and the bond ratios of CC, CN, C = O, CF, CF2, and CF3 were determined. Got. Table 1 shows the results.

Control 4
ESCA analysis was performed on a commercially available polyethersulfone film (TALPA), and the total fluorine atom ratio, and the bond ratios of CC, CN, C = O, CF, CF2, and CF3 were measured. Table 1 shows the results.

Examples 16 to 17
The polyethersulfone film of Control 4 was subjected to fluorine treatment under the conditions shown in Table 1 to obtain the polyethersulfone films of Examples 16 to 17. ESCA analysis of the film surface of each of the obtained films of Examples 16 to 17 was performed, and the total fluorine atom ratio and the bonding ratios of CC, CN, C = O, CF, CF2, and CF3 were determined. Obtained. Table 1 shows the results.

Control 5
ESCA analysis was performed on a commercially available PET film, and the total fluorine atom ratio and the bond ratios of CC, CN, C = O, CF, CF2, and CF3 were measured. Table 1 shows the results.

Examples 18 to 22
The PET film of Control 5 was treated with fluorine under the treatment conditions shown in Table 1 to obtain PET films of Examples 18 to 22. ESCA analysis of the surface of each of the obtained films of Examples 18 to 22 was performed to obtain the total fluorine atom ratio and the bond ratios of CC, CN, C = O, CF, CF2, and CF3. Was. Table 1 shows the results.

関係 FIG. 3 shows the relationship between the exposure time (treatment time) to the fluorine gas and the fluorine content of the polyimide obtained in Control 1 and Examples 1-4. From this result, it was found that the fluorine content of the polyimide increased as the treatment time increased, and the fluorination reaction reached a saturated state in a very short time. FIG. 4 shows the relationship between the processing time for the fluorine gas obtained in Control 1 and Examples 1 to 4 and the refractive index of the polyimide. From this result, it became clear that the refractive index of the polyimide gradually decreased as the processing time increased, and the refractive index of the polyimide could be easily controlled by changing the processing time.

(5) Next, FIG. 5 shows the relationship between the processing temperature of the fluorine gas obtained in Examples 1, 3 and Examples 5 to 6 and the fluorine content of the polyimide. From this result, it was found that when the treatment temperature was increased, the fluorine content of the polyimide was increased. FIG. 6 shows the relationship between the processing temperature of the fluorine gas obtained in Example 1, Example 3, and Examples 5 to 6 and the refractive index of polyimide. From FIG. 6, it has become clear that the refractive index of polyimide can be easily controlled by changing the temperature since the refractive index of polyimide gradually decreases as the processing temperature of fluorine gas increases. 5 and 6 that the longer the processing time is, as described above, that is, the film containing 10 minutes has a higher fluorine content than the film having a processing time of 1 minute.

In addition, it can be seen from Control 2 and Examples 7 to 13, Control 3 and Examples 12 to 15, Control 5 and Examples 18 to 22 that the longer the treatment time, the higher the fluorine content.

From these results, the method for controlling the refractive index of the optical polymer material of the present invention allows the introduction of fluorine into the molecule by a very simple operation of immersing the polymer material in fluorine gas. It became clear that this method can reduce the refractive index of the polymer material. Further, it has been clarified that the refractive index of the material can be precisely controlled by changing the fluorine treatment conditions.

Example 23
A fluorinated polyimide solution was formed into a film by spin coating to obtain a film having a thickness of 16 μm. The water contact angle of the obtained film was measured. The obtained fluorinated polyimide film was placed in a nickel container, and the inside of the container was evacuated. Next, a mixed gas of 0.4% F2 / 99.6% N2 was introduced into the container at room temperature. The relationship between the processing time in a fluorine gas atmosphere and the fluorine content of the polyimide is similar to that shown in FIG. 3, and the fluorine content of the polyimide increases as the processing time increases, and the fluorination reaction is saturated in a very short time. State had been reached. The film was taken out for a processing time of 1, 5, 10, or 30 minutes, and the water contact angle on the film surface was measured. The results are shown below.

Treatment time Untreated water contact angle 84.1 degrees 1 minute 73.5 degrees 5 minutes 70.3 degrees 10 minutes 70.5 degrees 30 minutes 69.0 degrees

When a commercially available polyimide resin film (Kapton) was treated in the same manner as in Example 23 instead of the fluorinated polyimide, the water contact angle before the treatment was 71 °, but the water contact angle was 1 minute after the treatment time. It was observed that the surface gradually dissolved in water at 9.0 degrees. When the fluorine treatment was further continued for 1 hour, the water contact angle increased, albeit slightly, to 18.9 degrees.

Example 24
Fluorine treatment was performed in the same manner as in Example 23 except that the fluorine gas composition was changed to 1.0% F2 / 99.0% N2. At a treatment time of 1 minute, the water contact angle reached 56 degrees. In addition, the water contact angle was 61.9 degrees when the treatment time was 10 minutes.

Example 25
Fluorine treatment was performed in the same manner as in Example 23 except that the fluorine gas composition was changed to 8.0% F2 / 92.0% N2. At a treatment time of 10 minutes, the water contact angle was 48 degrees.

Example 26
Fluorine treatment was performed in the same manner as in Example 23 except that the fluorine gas composition was changed to 0.01% F2 / 99.99% N2. At a treatment time of 30 minutes, the water contact angle was 70.0 degrees.

Example 27
In Example 23, a fluorine treatment was performed in the same manner as in Example 23 except that the fluorine gas composition was changed to 20.0% F2 / 80.0% N2. At a treatment time of 1 minute, the water contact angle reached 50.0 degrees. In addition, the water contact angle was 40.0 degrees when the treatment time was 5 minutes.

As is apparent from Examples 23 to 27, a molded article made of a fluorinated polyimide useful as an organic optical material was treated for a short time in a dilute fluorine gas atmosphere at room temperature to obtain a CF bond. It was possible to control the surface of the molded article to an appropriate degree of hydrophilicity extremely easily without cutting and without apparently changing the physical properties.

(A) is a diagram of the ESCA spectrum of the fluorinated polyimide before the reaction, and (b) is a diagram of the ESCA spectrum of the fluorinated polyimide after the reaction. It is a diagram which shows the NMR spectrum of the polyimide molded article after a fluorination process. 4 is a graph showing the relationship between the processing time in a fluorine gas atmosphere and the fluorine content in polyimide. 5 is a graph showing the relationship between the processing time in a fluorine gas atmosphere and the refractive index of polyimide. 4 is a graph showing the relationship between the processing temperature in a fluorine gas atmosphere and the fluorine content in polyimide. 4 is a graph showing the relationship between the processing temperature in a fluorine gas atmosphere and the refractive index of polyimide.

Claims (2)

By immersing the fluorinated polyimide molded article in a fluorine gas atmosphere having a fluorine concentration of 0.01% to 20% for 1 minute to 30 minutes, the water contact angle of the surface of the fluorinated polyimide molded article can be reduced. A method for hydrophilizing a surface of a fluorinated polyimide molded product, wherein the surface is made 70 ° or less. The fluorinated polyimide has the following structural formula:

2. The method for hydrophilizing the surface of a fluorinated polyimide molded article according to claim 1, wherein the fluorinated polyimide is a fluorinated polyimide comprising a repeating unit represented by the formula:

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