JP2009013310A - Method for modifying surface of fluororesin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for modifying a surface of a fluororesin molding that has little hazard of processing and little environmental load, enables introducing an active site and forming a hydrophilic membrane in a same apparatus, does not cause a problem such as complexity of processing, can impart fully easy adhesive quality, and enables exerting the easy adhesive quality stably even with time. <P>SOLUTION: This method for modifying the surface of the fluororesin molding comprises a step (1) of introducing the active site on the surface of the molding by irradiating plasma to the surface of the fluororesin molding, a step (2) of graft polymerizing a monomer to an active site of the surface of the molding by irradiating plasma in an atomspheric gas containing a water soluble monomer with an unsaturated bond as an essential component, and a step (3) of removing a homopolymer, derived from the monomer, deposited on the surface of the molding after the graft polymerization. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface modification method for modifying the surface of an inert fluororesin-based molded article and imparting easy adhesion to other materials.

Fluororesin moldings mainly composed of polytetrafluoroethylene (PTFE) have excellent properties such as heat resistance, chemical resistance, weather resistance, and electrical insulation. On the other hand, there is a problem that the surface is inactive, adhesives, paints, inks and the like are difficult to adhere, and it is difficult to obtain a composite with other materials.
In order to solve the above problems, attempts have been made to improve the surface of a fluororesin-based molded article to impart easy adhesion.
As one of such techniques, a method of activating by immersing a fluororesin-based molded article in a solution of metallic sodium dissolved in aqueous ammonia and introducing a hydrophilic group on the surface thereof is known. However, this method has a problem of causing a fire by using metallic sodium, and adverse effects on the environment due to the waste liquid after the surface activation treatment.

A technique for surface modification by performing plasma irradiation treatment under a pressure of 1.5 to 25 Pa on a fluororesin molding instead of metal sodium treatment is known (see Patent Document 1). In this technique, since metallic sodium is not used when performing surface modification, excellent easy adhesion can be imparted without causing problems in terms of safety and environment. However, this plasma irradiation treatment method has a problem that the activated site is deactivated with time, and the easy adhesion is gradually lowered.
A fluororesin composite having a graft layer of radically polymerizable monomer residues having a double bond by generating a radical by irradiating ultraviolet rays on a fluororesin-based molded article and then performing discharge polymerization in a monomer gas atmosphere There is also known a technique for obtaining (see Patent Document 2). In this technique, since a hydrophilic film composed of the graft layer of the monomer residue is formed on the surface of the molded product, inactivation with time does not occur as compared with the above method in which surface modification is simply performed by plasma irradiation. . However, this technique has a problem that the treatment is complicated in that it is necessary to use different apparatuses for ultraviolet irradiation and discharge polymerization in a monomer gas atmosphere.
JP 2003-261698 A Japanese Patent Laid-Open No. 10-226728

  Therefore, the problem to be solved by the present invention is to solve the problem of complicated processing by introducing the active sites and forming the hydrophilic film all in the same apparatus without causing the above-mentioned problems in safety and environment. And providing a method for modifying the surface of a fluororesin-based molded product, which can impart sufficient easy-adhesiveness and can stably exhibit this easy-adhesive property over time. is there.

  In order to solve the above problems, the present inventors have conducted intensive studies. As a result, in order to eliminate the complexity of processing by introducing active sites and forming a hydrophilic film with the same apparatus, it was considered to introduce active sites and form a hydrophilic film by plasma irradiation. However, in this case, sufficient easy adhesion could not be imparted to the surface of the molded product. Therefore, as a result of further studies, even when active sites were introduced by plasma irradiation and hydrophilic film formation was performed, the reason why sufficient adhesion was not yet exhibited was due to the homopolymer deposited on the surface of the molded product. I understood that. From this knowledge, it has been found that if the homopolymer deposited on the surface of the molded product is removed, a molded product exhibiting sufficient easy adhesion and excellent in stability over time of the easy adhesion can be obtained. As a result, the present invention was completed.

That is, the method for modifying the surface of a fluororesin-based molded product according to the present invention includes the step (1) of introducing active sites on the surface of the molded product by irradiating the surface of the fluororesin-based molded product with an unsaturated bond. A step (2) of graft-polymerizing the monomer at an active point on the surface of the molded article by plasma irradiation in an atmospheric gas having the water-soluble monomer as an essential component, and deposited on the surface of the molded article after the graft polymerization, And (3) removing the monomer-derived homopolymer.
The plasma irradiation in the step (1) is preferably performed in at least one atmospheric gas selected from helium, argon, nitrogen, carbon dioxide, ammonia, oxygen and hydrogen.

The water-soluble monomer having an unsaturated bond is preferably one having at least one functional group selected from a carboxyl group, an amino group, a sulfone group, a hydroxyl group and an amide group.
The removal of the homopolymer is preferably performed by washing the surface of the molded product after the graft polymerization with a solvent.

According to the surface modification method for a fluororesin-based molded product according to the present invention, the risk of processing and the environmental load are small, the introduction of active sites and the formation of a hydrophilic film can be performed in the same apparatus. In addition to the advantage that there is no problem of complexity, sufficient easy adhesion can be imparted, and this easy adhesion can be stably exhibited over time.
If the plasma irradiation in the step (1) is performed in at least one kind of atmospheric gas selected from helium, argon, nitrogen, carbon dioxide, ammonia, oxygen and hydrogen, excellent etching efficiency is exhibited.
If the water-soluble monomer having an unsaturated bond has at least one functional group selected from a carboxyl group, an amino group, a sulfone group, a hydroxyl group and an amide group, the surface of the fluororesin-based molded article has high hydrophilicity. It is preferable because it is imparted and the easy adhesion is further improved.

  If the removal of the homopolymer is carried out by washing the surface of the molded product after the graft polymerization with a solvent, the removal of the homopolymer can be carried out simply, safely and at low cost.

Hereinafter, the method for modifying the surface of a fluororesin-based molded product according to the present invention will be described in detail, but the scope of the present invention is not limited thereto, and the scope of the present invention is not impaired except for the following examples. And can be changed as appropriate.
The fluororesin-based molded product targeted by the present invention is a molded product containing a fluororesin as a main component, and the fluororesin is not particularly limited and may be a homopolymer of a monomer containing fluorine or other monomer. And a copolymer thereof may be used. Specifically, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), Examples thereof include chlorotrifluoroethylene-ethylene (ECTFE), tetrafluoroethylene-ethylene (ETFE), tetrafluoroethylene-hexafluoropropylene (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA).

It does not specifically limit as a shaping | molding form of the said fluororesin type molded object, For example, molded objects, such as a sheet form, a film form, and plate shape, are mentioned.
The surface modification method for a fluororesin-based molded product according to the present invention is a method for modifying the surface of a fluororesin-based molded product as described above, and includes an active site introduction step (step (1)), graft polymerization, and the like. A process (process (2)) and a homopolymer removal process (process (3)) are included. Each step will be specifically described below.
[Step (1): Active site introduction step]
Step (1) is a step of introducing active sites on the surface of the fluororesin-based molded product, and as a specific means for achieving this, plasma irradiation (hereinafter, in order to distinguish from plasma irradiation in step (2), (Hereinafter referred to as “first plasma irradiation”). When active sites are introduced by the first plasma irradiation, if etching is performed and unevenness is formed on the surface (roughening), the mechanical adhesive force of the fluororesin-based molded product increases. More preferred.

The atmospheric gas used for the first plasma irradiation is not particularly limited, and examples thereof include helium, argon, nitrogen, carbon dioxide, ammonia, oxygen, hydrogen, air, water vapor, and carbon tetrafluoride. From the viewpoint of etching efficiency, at least one atmospheric gas selected from helium, argon, nitrogen, carbon dioxide, ammonia, oxygen and hydrogen is preferable.
Although it does not necessarily limit as a pressure at the time of 1st plasma irradiation, For example, it is preferable to set it as 1-100 Pa. If it is less than 1 Pa, it takes time to repeat the decompression and release to the atmosphere, and the production efficiency may be deteriorated. If it exceeds 100 Pa, the treatment efficiency may be lowered from the viewpoint of introducing active sites. More preferably, it is 5-70 Pa, More preferably, it is 10-50 Pa.

Although it does not necessarily limit as a power supply output at the time of 1st plasma irradiation, For example, it is preferable to set it as 10-1000W. If it is less than 10 W, the treatment time may be prolonged, and if it exceeds 1000 W, the material strength of the treated substrate surface may be deteriorated. More preferably, it is 10-600W, More preferably, it is 20-400W.
The plasma excitation electric field frequency of the power source for the first plasma irradiation is not particularly limited, and direct current, alternating current, radio wave, microwave, or the like can be used. Among these, a 13.56 MHz RF power source can be preferably used.
The time of the first plasma irradiation varies depending on the pressure, the atmospheric gas, and the temperature. When the pressure, the atmospheric gas, and the temperature in the above-described ranges are employed, the time is usually 5 seconds to 60 minutes. Preferably, it is 10 seconds to 20 minutes. If it is less than 5 seconds, the introduction of active sites may not be sufficiently achieved, and if it exceeds 60 minutes, the material strength of the treated substrate surface may be deteriorated.

By such first plasma irradiation, active sites are formed on the surface of the fluororesin-based molded product. The said active point is a site | part which is formed in the surface of an inactive fluororesin molding, and shows the reactivity with the water-soluble monomer used at the process (2) mentioned later.
[Step (2): Graft polymerization step]
Step (2) is a step of graft-polymerizing a monomer having a water-soluble monomer as essential to the active site introduced onto the surface of the fluororesin-based molded product in the step (1), and a specific method for achieving this. As a specific means, plasma irradiation in an atmospheric gas that requires a water-soluble monomer having an unsaturated bond (hereinafter referred to as “second plasma irradiation” in order to distinguish it from plasma irradiation in step (1)). ).

The atmospheric gas used for the second plasma irradiation requires a water-soluble monomer having an unsaturated bond. When this monomer chemically bonds with the active sites on the surface of the fluororesin-based molded product and polymerizes, the monomer is graft-polymerized on the surface of the molded product. As a result, a hydrophilic film made of the graft polymer is formed on the surface of the molded product, the surface of the fluororesin-based molded product is hydrophilized, and easy adhesion is exhibited. In order to improve the speed and efficiency of graft polymerization, a rare gas such as argon or helium may be mixed as an atmospheric gas. In addition, it is preferable to mix water vapor or the like as the atmospheric gas because the hydrophilicity can be further improved.
The water-soluble monomer is not particularly limited as long as it has a hydrophilic functional group for easy adhesion, and examples thereof include a carboxyl group, an amino group, a sulfone group, a hydroxyl group, and an amide group. It is preferable to have at least one functional group selected from Specifically, 2-propyn-1-ol, 2-propen-1-ol, 2-methyl-3-butyn-2-ol, acrylic acid, methacrylic acid, allyl alcohol, methyl methacrylate, allylamine, acrylamide, etc. It can be illustrated. In addition, the unsaturated bond in the monomer is preferably a triple bond rather than a double bond because it can be polymerized under relatively relaxed conditions and a crosslinked structure can be constructed. Although it does not specifically limit as a monomer which has a triple bond, For example, 2-propyn-1-ol etc. can be illustrated. A monomer can be used combining these 1 type (s) or 2 or more types.

Although it does not necessarily limit as a pressure at the time of 2nd plasma irradiation, For example, it is preferable to set it as 1-100 Pa. If it is less than 1 Pa, it may take too much time to form the hydrophilic film, and if it exceeds 100 Pa, the formation efficiency of the hydrophilic film may be too low. More preferably, it is 10-75 Pa, More preferably, it is 25-75 Pa, Most preferably, it is 35-50 Pa. In 35-50 Pa, the remarkable improvement of adhesive strength can be anticipated by the homopolymer removal process mentioned later.
Although it does not necessarily limit as a polymerization monomer temperature at the time of 2nd plasma irradiation, For example, it is preferable to set it as 0-100 degreeC. Since the monomer is liquid even when the temperature is lower than 0 ° C. or higher than 100 ° C., the vaporization rate is not stable, and it may take time to reach a constant internal pressure. More preferably, it is 20-40 degreeC. If it is 20-40 degreeC, the stable gas flow rate can be obtained.

Although it does not necessarily limit as a power supply output at the time of 2nd plasma irradiation, For example, it is preferable to set it as 10-300W. If it is less than 10 W, stable plasma may not be generated. If it exceeds 300 W, the production cost increases, which is not preferable. More preferably, it is 15-200W, More preferably, it is 15-100W.
The plasma excitation electric field frequency of the power source for the second plasma irradiation is not particularly limited, and direct current, alternating current, radio wave, microwave, or the like can be used. Among these, a 13.56 MHz RF power source can be preferably used.
The time of the second plasma irradiation varies depending on the pressure, the atmospheric gas, and the temperature. When the pressure, the atmospheric gas, and the temperature in the above-described ranges are employed, the time is usually 10 seconds to 20 minutes. Preferably it is 1 to 20 minutes. If it is less than 10 seconds, a sufficient amount of graft polymer may not be formed on the surface of the molded product. If it exceeds 20 minutes, it takes time to remove the homopolymer in the step (3) described later, and the production efficiency is increased. May be worse.

The monomer gas used in this step (2) is, for example, a trap is inserted between the processing vessel and the gas exhaust pump during gas exhaust, or more simply, methanol and dry ice are used. By cooling the gas and liquefying it, it is possible to prevent it from being released into the atmosphere.
[Step (3): Homopolymer removal step]
Step (3) is a step of removing the monomer-derived homopolymer deposited on the surface of the molded product after the graft polymerization. That is, the monomer used in step (2) is chemically bonded to the active site of the fluororesin-based molded product and polymerized. In addition to such graft polymerization, self-polymerization produces a homopolymer. There is something to do. This homopolymer is deposited on the surface of the molded product after the graft polymerization, but not only contributes to the surface activation of the molded product, that is, easy adhesion, but prevents the surface activation.

In this step (3), the homopolymer is removed, but it is not necessary to completely remove all the homopolymer deposited on the surface of the molded article, and the removal is suitable for the purpose of suppressing the decrease in surface activation due to the homopolymer. Good. Specifically, the homopolymer removal may be performed under the following conditions.
Although it does not specifically limit as a method for removing a homopolymer, It is preferable because it is simple and highly efficient to wash | clean the surface of the molded object after graft polymerization with a solvent.
In the case of the method of washing with a solvent, the method is not particularly limited. For example, a simple method of immersing a molded product after graft polymerization in a solvent can be employed. Furthermore, if heating, ultrasonic treatment, etc. are performed, the cleaning efficiency is improved. Although not particularly limited, for example, the cleaning can be efficiently performed if the cleaning temperature is 25 to 100 ° C. and the cleaning time is 1 minute or more.

Although it does not specifically limit as said solvent, For example, polar solvents, such as water and alcohol, can be used preferably. In consideration of removing the solvent later, a low boiling point solvent that can be easily removed by drying is preferred.
The surface of the fluororesin-based molded product that has undergone the steps (1), (2), and (3) as described above is activated and easy adhesion is imparted. Therefore, it can be easily bonded to adhesives, paints, inks, and the like, and in particular, composites with various materials can be obtained through the adhesives.
It does not specifically limit as said adhesive agent, What is necessary is just to select a thing suitable for a to-be-adhered body suitably. For example, when importance is attached to heat resistance, an epoxy type or polyimide type is preferable.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
The measuring method in an Example is shown below.
<Adhesive strength>
With respect to the surface-treated fluororesin-based molded product, the adhesive strength with other materials was measured as follows.
By applying an epoxy adhesive (trade name “Bond E Set”, manufactured by Konishi Co., Ltd.) to the surface of the surface-modified fluororesin-based molded product, bonding with SUS304, and treating at 100 ° C. for 30 minutes The adhesive was heat cured. This was subjected to a 90-degree peel strength test at a temperature of 25 ° C., and the adhesive strength was measured.

[Example 1]
As a fluororesin-based molded product, polytetrafluoroethylene (PTFE) molded into a sheet shape of 25 mm long × 60 mm wide × 1 mm thick was prepared. The first and second plasma irradiations were performed on the surface of the molded product under the following conditions with the configuration shown in FIG.
<First plasma irradiation conditions>
Pressure: 27 Pa, atmospheric gas: oxygen, RF power source for plasma generation: Noda RF Technologies, power output: 300 W, irradiation time: 10 minutes <Second plasma irradiation conditions>
Pressure: 40 Pa, atmosphere gas: 2-propyn-1-ol, RF power source for plasma generation: manufactured by Samco, power output: 20 W, irradiation time: 10 seconds Next, a molded product after graft polymerization by second plasma irradiation Was washed by immersion in water at 25 ° C. for 20 minutes to remove the homopolymer deposited on the surface of the molded product.

After washing with water and air-drying for 20 minutes, a fluororesin-based molded product to which the surface modification method of the present invention was applied was obtained.
[Example 2]
Among the second plasma irradiation conditions, a fluororesin-based molded product to which the surface modification method of the present invention was applied was obtained in the same manner as in Example 1 except that the irradiation time was changed to 1 minute.
Example 3
Of the second plasma irradiation conditions, a fluororesin-based molded product to which the surface modification method of the present invention was applied was obtained in the same manner as in Example 1 except that the irradiation time was changed to 10 minutes.
Example 4
Among the second plasma irradiation conditions, a fluororesin-based molded product to which the surface modification method of the present invention was applied was obtained in the same manner as in Example 1 except that the irradiation time was changed to 20 minutes.

[Comparative Examples 1-4]
The molded product after graft polymerization was washed by immersing it in water at 25 ° C. for 20 minutes, and the same process as in Examples 1 to 4 was performed except that the step of removing the homopolymer deposited on the surface of the molded product was not performed. Surface modification was performed to obtain fluororesin-based molded products of Comparative Examples 1 to 4.
[Comparative Example 5]
Comparative Example 5 was obtained by performing only the first plasma irradiation on the surface of the fluororesin-based molded product under the same conditions as in Example 1.
[Comparative Example 6]
Comparative Example 6 was obtained by performing only the second plasma irradiation on the surface of the fluororesin-based molded product under the same conditions as in Example 4.

[Evaluation]
The adhesive strengths of the fluororesin-based molded products according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured by the method described above, and the results were determined based on the presence or absence of the first plasma irradiation, the irradiation time of the second plasma irradiation, Table 1 shows the presence or absence of the homopolymer removal step.

From the results shown in Table 1, the following can be understood.
(1) As apparent from a comparison between Examples 1 to 4 and Comparative Examples 1 to 4, there is a difference in adhesive strength depending on whether or not the homopolymer is removed. In particular, when the irradiation time of the second plasma irradiation is 1 minute to 20 minutes, that is, in the comparison between Examples 2 to 4 and Comparative Examples 2 to 4, the difference is significant. Further, Comparative Example 5 in which only the introduction of active sites was performed, and Comparative Example 6 in which only the plasma irradiation was performed on the surface of the fluororesin-based molded article in a water-soluble monomer gas having a double bond were Examples 1-4. Compared with, the adhesive strength is small and lacks practicality.
(2) Summarizing the above results, as in the surface modification method of the fluororesin-based molded product according to the present invention, a series of introduction of active sites and graft polymerization using plasma irradiation, and removal of homopolymers. It turns out that only the fluororesin-type molded product which passed through the process shows the outstanding adhesive strength, and the remarkable synergistic effect by combining each process is recognized.

  The method for modifying the surface of a fluororesin-based molded product according to the present invention is, for example, by modifying the surface of a fluororesin-based molded product that is difficult to adhere to an adhesive, paint, ink, etc., and imparting easy adhesion, It can be suitably used as a method for obtaining a fluororesin-based molded product that can be easily combined with other materials.

It is the figure which showed the structure for performing the plasma irradiation in an Example.

Claims (4)

  By irradiating the surface of the fluororesin-based molded product with plasma, the step (1) of introducing active sites on the surface of the molded product, and by irradiating with plasma in an atmospheric gas that requires a water-soluble monomer having an unsaturated bond, A step (2) of graft-polymerizing the monomer at an active point on the surface of the molded product, and a step (3) of removing a homopolymer derived from the monomer deposited on the surface of the molded product after the graft polymerization. Surface modification method for resin-based molded products.   The surface irradiation of the fluororesin-based molded product according to claim 1, wherein the plasma irradiation in the step (1) is performed in at least one atmosphere gas selected from helium, argon, nitrogen, carbon dioxide, ammonia, oxygen and hydrogen. Quality method.   The fluororesin-based molding according to claim 1 or 2, wherein the water-soluble monomer having an unsaturated bond has at least one functional group selected from a carboxyl group, an amino group, a sulfone group, a hydroxyl group and an amide group. Method for surface modification of objects. The method for modifying the surface of a fluororesin-based molded product according to any one of claims 1 to 3, wherein the removal of the homopolymer is performed by washing the surface of the molded product after the graft polymerization with a solvent.

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