JPH05246776A - Method for chemical modifying mica surface - Google Patents

Abstract

PURPOSE:To form a modifying film having various characteristics on the surface of mica by allowing the surface of the mica to contact with a specific alkoxysilane derivative after irradiating with steam plasma. CONSTITUTION:A cleavaged flake of mica is provided in a reactor of a plasma treating device and the reactor is evacuated to 0.08mmHg degree of vacuum. steam is introduced at 78ml/min flow rate with argon as a carrier gas, high frequency voltage is impressed in 100 W out-put and plasma is irradiated for about 10 minutes. The flake of mica is picked up and transferred to a reactor for silanation treating, to the bottom of which the alkoxysilane derivative expressed by a formula (1) (e.g. dimethoxy-methyl-3,3,3-trifluoropropyl silane) is previously fed (in the formula, X is alkoxy group, each of R<1>-R<3> is substituted group except halogen). The silanating agent is vaporized by heating the reactor at about 80 deg.C and the flake of mica is brought into contact with the vapor and allowed to react. The flake of mica is cleaned with ethanol after continuing the reaction for 16 hours.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of modifying a mica surface so as to exhibit various characteristics in response to various needs.

[0002]

Mica is used as an additive to synthetic resins, paints and the like. The addition of mica improves the heat resistance and weather resistance of organic materials such as synthetic resins and paints, and also improves the mechanical strength. Further, when mica is added to cosmetics or the like, a product excellent in whiteness and gloss can be obtained.

When mica is used as an additive, it is necessary to adjust its affinity for the resin and medium. If the affinity is insufficient, the desired properties cannot be sufficiently improved by adding mica to synthetic resins, paints, cosmetics, etc., and some properties may be adversely deteriorated. For example,
In the case where the mica is added to the cosmetics, the mica easily causes aggregation or precipitation, and the quality stability cannot be maintained under storage conditions.

These drawbacks are solved by modifying the mica before addition to a surface state having a high affinity for resins, media and the like. For example, when the surface of mica is modified with a predetermined chemical substance, the surface characteristics change and the affinity for resins, media, etc. increases. However, it is not easy to modify the surface of mica, and the properties after modification are not stabilized.

Mica has a special cleavage plane that is not found in other substances. Attempts have been made to use mica in various fields by making use of an extremely smooth cleavage plane of molecular order. For example, evaluate the surface of a material on the nanometer scale.
When observing, a device such as a surface force direct measuring device or an atomic force microscope (AFM) is used. Although these measurement methods require a measurement substrate having an extremely smooth surface, the cleavage surface of the mica provides a surface suitable for the measurement substrate.

In order to widely apply mica used as a substrate for measurement to various objects, it is necessary to modify the surface of the mica to a state suitable for the object. Also in this case, since the cleavage surface of mica is chemically inactive like the additive, it is not possible to stably form a surface layer having predetermined characteristics.

An adsorption method has been adopted as a surface modification method. In the adsorption method, the property of the surface of mica having a negative charge is utilized to adsorb a predetermined compound on the surface of mica. For example, an ion exchange method for modifying the surface of mica by chemical modification is introduced in JP-A-63-3753. In this method, interlayer alkali ions of swelling mica are replaced by an ion exchange method, and a modified film ionically bonded is formed on the surface of the mica.

The LB method is also used for surface modification of mica. In the LB method, an amphipathic substance is spread on the liquid surface to form a monomolecular film, and the mica is immersed in and pulled up from the liquid to transfer the monomolecular film and accumulate it on the surface of the mica. Accumulable monolayers are limited to amphiphiles capable of forming monolayers on liquid surfaces. Therefore, the surface modification of mica by the LB method lacks general versatility and is not suitable for surface modification having properties that meet various needs.

In either method, the stability is insufficient depending on the type of medium, and the modified layer may peel off from the surface of the mica. In this respect, in order to prepare a modified surface that meets various needs and is excellent in stability, it is ideal to chemically modify the surface to form a modified layer covalently bonded to the surface of the mica. However, since the surface of mica is chemically inactive, it is generally difficult to form a chemically modified layer on the surface of mica.

As a method of modifying the surface of mica by covalent bonding, it is known to make the surface of mica hydrophobic with a chlorosilane compound in the Journal of Physical Chemistry (1989).
Year) Vol. 98, p. 6121. In this method, after activating the surface of mica with steam plasma, an alkylchlorosilane compound is reacted to covalently bond a hydrophobic alkyl group to the surface of mica.

[0011]

In the ion exchange method, the modifiable mica is limited to the swelling mica. Further, the substance used for modification is limited to a cationic compound, and the surface of mica cannot be modified with an anionic compound or a nonionic compound. Therefore, the ion exchange method is poor in versatility and cannot be surface-modified with properties that meet various needs. Moreover, the modified layer has insufficient stability depending on the type of medium.

In the method of hydrophobizing the surface of mica with a chlorosilane compound, it is not possible to synthesize a stable chlorosilane derivative containing a functional group such as an amino group or a mercapto group because the reactivity of the chlorosilane group is high. The functional groups that can be introduced into are limited. Therefore, it is unsuitable as a method for introducing various functional groups having properties corresponding to various needs.

The present invention has been devised in order to solve such a problem. By contacting the surface of mica after steam plasma irradiation with an alkoxysilane derivative capable of synthesizing derivatives of various functional groups, functionalization is achieved. The purpose is to chemically modify the surface of mica under stable conditions, regardless of the type of the group, and to impart properties that meet various needs.

[0014]

In order to achieve the object, in the chemical modification method of the present invention, the surface of mica is irradiated with steam plasma, and then catalytically reacted with an alkoxysilane derivative represented by the general formula [I]. It is characterized by However, in the general formula [I], X is an alkoxy group, R ¹ ,
R ² and R ³ represent a substituent other than a halogen element.

[0015]

[Chemical 2]

The steam plasma is generated by evacuating the inside of the reaction vessel, introducing steam, applying a high frequency or DC voltage, and discharging. As the discharge electrode, an electrode of capacitive coupling type, parallel plate type or the like is used. When the voltage is applied with a high frequency alternating current, if the high frequency output is too large, the effect of surface activation by plasma irradiation is reduced. Also, if the plasma irradiation time is too long,
The effect of surface activation by plasma irradiation is reduced. Water vapor can be introduced into the reaction zone by using an inert gas such as argon or helium as a carrier gas.

Substituents R ¹ , R ² and R in formula [I]
^At least one of the ^three is a substituent that is less susceptible to hydrolysis than the alkoxy group X because it needs to remain as a substituent for modifying the surface of the mica after the reaction. If all of the substituents R ¹ , R ² and R ³ are more susceptible to hydrolysis than the alkoxy group X, they first react with and depart from the hydroxyl groups on the surface of the mica, and the desired modified layer is not formed.

Specific examples of the substituents R ¹ , R ² and R ³ include linear or branched alkyl groups and phenyl groups. Also, one of the substituents R ¹ , R ² and R ³ is R
^{When 1} is a linear or branched alkyl group, a phenyl group or the like, the other substituents R ² and R ³ may be alkoxy groups.

The alkyl group, phenyl group and the like may further have other substituents at arbitrary positions. Examples of the substituent include a halogen atom, amino group, mercapto group, alkoxy group, aryloxy group, epoxy group, vinyl group, cyano group, isocyanate group, aryl group, pyridyl group, imidazole group, acyl group, acylamino group, sulfone group. There are amide groups and the like.

As the alkoxysilane derivative represented by the general formula [I], for example, the silane compounds listed in Tables 1 to 3 are used.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

The method of reacting the alkoxysilane derivative of the general formula [I] on the surface of the mica includes immersing the mica in a dilute solution prepared by using an appropriate solvent for the alkoxysilane derivative, and vaporizing the vapor of the alkoxysilane derivative into the mica. A method of contacting with the surface or the like can be adopted. The reaction between the alkoxysilane derivative and the mica surface suppresses the contamination of the mica surface, the reaction between the polymerized alkoxysilane derivative and the mica surface, and the like, from the viewpoint of producing a smooth and highly controlled modified surface, A method using vapor of an alkoxysilane derivative is preferable.

The vapor of the alkoxysilane derivative can be obtained by evaporating the alkoxysilane derivative as it is or by dissolving or dispersing it in a suitable solvent. At this time, the type and concentration of the solvent can be changed according to the reactivity of the alkoxysilane derivative with respect to the surface of the mica. Further, if necessary, the contact reaction can be carried out under reduced pressure.

On the other hand, the method of immersing mica in a dilute solution prepared by using an appropriate solvent for the alkoxysilane derivative modifies the surface of the mica under milder conditions than the method of contacting with the vapor of the alkoxysilane derivative. can do. Therefore, considering the advantages of the vapor contact method and the dipping method, a modification method is adopted according to the purpose.

As a method for evaluating the presence or absence of modification of the surface modified mica and the modification method, Fourier transform infrared spectroscopy (F
T-IR), X-ray photoelectron spectroscopy (XPS) and the like. Among them, X-ray photoelectron spectroscopy (XPS) is suitable as an evaluation method for surface-modified mica because it is possible to detect elements in the modification layer present in a trace amount on the surface of mica with high sensitivity. ..

For surface-modified mica, the amount of modification can be evaluated using X-ray photoelectron spectroscopy (XPS).
However, in the case of a substance having a layered structure such as mica, it is necessary to determine the degree of contribution of a given atom to the X-ray photoelectron signal in consideration of the distance from the surface of the atom and the mean free path of photoelectrons.

The contribution of an element in the oriented sample to the X-ray photoelectron signal is generally represented by the formula (1). However, I
_d is the contribution to the X-ray photoelectron signal by the atom A at the depth d from the sample surface, n _d is the number of the element A at the depth d, λ is the mean free path of the photoelectrons from the element A, θ represents the extraction angle of photoelectrons. Therefore, the photoelectron intensity of the element A can be theoretically obtained by integrating I _d in the depth direction. I _d = n _d · exp (−dλ / sin θ) (1)

For example, muscovite is known to have a layered structure as shown in FIG. Applying equation (1) based on this structure, the contribution of each atom in the unmodified mica to the XPS signal is calculated. The calculated value obtained shows high agreement with the measured value.

It is assumed that the mica surface is coated with a density modified compound. Applying equation (1) to this chemically modified mica surface gives the elemental ratio on the modified surface under this assumption. Then, by fitting the density assumed so that the obtained element ratio is close to the actually measured value, the amount of the reacted silane compound per unit surface area can be obtained.

In this way, when the contribution of the X-ray photoelectrons to the signal is obtained using the equation (1) and compared with the actual data, the number of reactive molecules per unit surface area, and thus the coverage can be obtained. .. By this analysis method, the atomic concentration of mica having an oriented layered structure can be accurately grasped.

An actual analysis example will be described below. [Analysis Example] Muscovite flakes were subjected to steam plasma treatment under the following conditions. The cleaved muscovite flakes were placed in the reaction vessel of the plasma processing apparatus, and the vessel was evacuated to 0.08 mmHg. Then, using argon as a carrier gas, a flow rate of 78
Steam was introduced at ml / min. A high frequency voltage was applied at an output of 100 W and plasma was irradiated for 10 minutes.

The composition of muscovite treated with steam plasma was
It was measured by X-ray photoelectron spectroscopy (XPS). Further, the composition was calculated from the crystal structure of muscovite using the formula (1). The measured and calculated values are shown in comparison with Table 4.

[0035]

[Table 4]

As is clear from Table 4, the measured values by X-ray photoelectron spectroscopy (XPS) agree with the calculated values obtained from the crystal structure of muscovite using the formula (1). This indicates that the atomic concentration in the oriented sample such as the mica surface can be relatively accurately obtained by the equation (1).

Next, the surface of the mica was chemically modified with the compound 1. Chemical modification was performed on mica irradiated with steam plasma.
It was carried out by contacting with vapor of Compound 1 at 0 ° C. for 16 hours.

In this case, the surface of the mica is 1.3 per 1 nm ^2.
Assuming that each of the compounds was modified with Compound 1, the calculated value and the actually measured value were almost the same as shown in Table 2. Therefore,
The density of the silane compound at this time was defined as the modification amount. In addition,
For the mean free path of photoelectrons, see the Journal of Colloid
and Interface Science (1987) Volume 119 Volume 1
From page 55, λ = 3.0 nm.

[0039]

[Table 5]

[0040]

When the mica surface is irradiated with water vapor plasma, active hydroxyl groups are generated on the mica surface. Since this hydroxyl group is formed on the surface of a very smooth mica, it restricts the approach of the reactants from the side and the rear, and provides a two-dimensional reaction field having a directivity in the reaction direction.

Since the alkoxysilane derivative of the general formula [I] has a lower reactivity than the chlorosilane derivative,
It is possible to introduce into the molecule a functional group such as a mercapto group or an amino group that cannot be present in a chlorosilane derivative. Therefore, when modifying the surface of a mica irradiated with water vapor plasma with an alkoxysilane derivative, it is possible to prepare a mica surface modified with various functional groups that cannot be introduced when a chlorosilane derivative is used. Moreover,
Since the modified layer is formed in a unique reaction field formed by irradiation with water vapor plasma, a smooth modified surface having a desired function and reflecting the smoothness peculiar to the mica surface can be stably obtained. In particular, when the surface of the mica irradiated with steam plasma is reacted with the alkoxysilane derivative vapor of the general formula [I], polymerization on the surface is less likely to occur, and a more controlled modified surface can be produced.

The surface modification method of the present invention can be applied to any of natural mica, synthetic mica, swelling mica, non-swelling mica, particulate mica and the like. Further, the functional group in the alkoxysilane derivative of the general formula [I] can be utilized to further modify the surface-modified mica with another compound. Furthermore, it is also possible to mold the surface-modified fine particulate mica into a film.

The surface-modified mica is used as an additive to synthetic resins and heat-resistant paints in order to improve heat resistance, weather resistance and mechanical strength of organic materials. When added to cosmetics, ceramics, etc., whiteness, gloss, etc. are improved. It is also used in applications such as catalyst materials and optical materials. It is also used as a substrate when evaluating and observing the surface of a substance on the nanometer scale. At this time,
By selecting an alkoxysilane derivative represented by the general formula [I] having a substituent having predetermined characteristics, surface-modified mica can be obtained according to various needs.

[0044]

【Example】

-Example 1-Preparation of sample 1 of the present invention : The cleaved mica flakes are placed in a reaction vessel of a plasma processing apparatus, and the degree of vacuum in the vessel is 0.08 m.
Exhausted to mHg. Then, steam was introduced at a flow rate of 78 ml / min using argon as a carrier gas. Output 1
A high frequency voltage was applied at 00 W and plasma treatment was performed for 10 minutes.

After the container was evacuated to 0.08 mmHg again, the mica flakes irradiated with the steam plasma were taken out,
As a silanizing agent, dimethoxymethyl-3,3,3-trifluoropropylsilane was transferred to a silanization reaction container which was previously placed at the bottom.

By heating the reaction vessel to 80 ° C.,
The silanizing agent was evaporated, and the mica flakes were contacted and reacted with the vapor. After continuing the reaction for 16 hours, the mica flakes were washed with ethanol.

Preparation of Comparative Example Sample 1 : A mica thin piece was subjected to the same silanization treatment as that of Sample 1 of the present invention without irradiating with steam plasma to prepare Comparative Example Sample 1.

Preparation of Comparative Example Sample 2 : 3,3,3-trifluoropropylmethyldichlorosilane was used as the silanizing agent without irradiation with steam plasma, and the mica flakes were contacted with the vapor of the silanizing agent for 1 hour. Then, Comparative Example Sample 2 was prepared.

Evaluation of modification amount : The surface of the prepared sample was analyzed using an X-ray electron spectrometer. Based on the analysis result, the modification amount was evaluated according to the above-mentioned analysis example. The evaluation results are shown. As is apparent from Table 6, Sample 1 of the present invention
It can be seen that the amount of modification markedly increases in comparison with Comparative sample 1 which is not subjected to the plasma treatment.

[0050]

[Table 6]

In the comparative example sample 2 modified with chlorosilane, the amount of modification was remarkably increased as compared with the sample 1 of the present invention using the alkoxysilane derivative. However, the occupied area of the reacted alkoxysilane derivative (0.25-0.3n
Considering m ² ), the modification amount of 10.1 / nm ² means that the excess alkoxysilane derivative reacts with the surface of the mica.

On the other hand, the modification amount of 1.3 nm ² in the sample 1 of the present invention indicates that the modification film of about a monomolecular layer is formed on the surface of the mica. This indicates that in Sample 1 of the present invention, more uniform chemical modification was performed, and a chemically modified surface reflecting the smoothness peculiar to the surface of the mica was formed.

Example 2-Preparation of Inventive Samples 2 and 3 : Under the same conditions as those of Inventive Sample 1, steam plasma was irradiated on the surface of the mica.
In the present invention sample 2, the compound 4 of Table 1 was used, and in the present invention sample 3, the compound 5 was also used as the silanizing agent. In each case, the silanizing agent was placed in the reaction vessel without dilution, and the silanizing agent was evaporated by heating the reaction vessel to 80 ° C. Mica after plasma irradiation was treated with the silanizing agent vapor and 16
After the completion of the reaction, the silanized mica flakes were washed with ethanol after the reaction.

Preparation of sample 4 of the present invention : Sample 4 of the present invention was prepared by immersing the mica flakes subjected to the same plasma treatment as in Example 1 in a 1% hexane solution of compound 5 heated to 40 ° C. did. The modification amount of each produced sample was evaluated by the same analysis method as in Example 1. The evaluation results are shown in Table 7.

[0055]

[Table 7]

As is apparent from Table 7, it is understood that the present invention can produce mica modified with various functional groups. Further, from the modification amount of the sample 3 of the present invention, when the silanization treatment is performed by the dipping method, the modification can be performed under milder conditions, and even when a silane compound unstable at high temperature is used, the surface of the mica can be easily obtained. It is understood that can be chemically modified.

[0057]

As described above, in the present invention, by bringing an alkoxysilane derivative into contact with the surface of a mica irradiated with water vapor plasma, the surface of the mica which is originally inactive and has no affinity for other substances is chemically treated. Mica is produced that has been modified and has a modified surface with properties that meet a variety of needs. The modified film formed on the mica surface has excellent stability,
Moreover, a modified film having a monolayer thickness can be produced. The chemically modified mica is used in various fields as various additives, catalyst materials, optical materials, surface measurement substrate materials and the like.

[Brief description of drawings]

Fig. 1 Cross-section model of muscovite and the positional relationship of each atom in the layer

Claims (1)

[Claims] 1. A method for chemically modifying the surface of a mica, which comprises irradiating the surface of the mica with steam plasma and then contacting the same with an alkoxysilane derivative represented by the general formula [I]. [Chemical 1]