JP7645758B2 - Evaluation method for surface treatment fillers - Google Patents

Description

The present invention relates to a new method for evaluating surface-treated fillers. More specifically, the present invention relates to a method for evaluating the filling ability of surface-treated fillers into resins by measuring the surface potential of the particles using a scanning probe microscope.

Resin composite materials, which are made by combining inorganic fillers with resins, are used in a wide range of fields. In order to improve the compatibility between the inorganic filler and the resin, it is common to use inorganic fillers that have been surface-treated (surface-treated fillers). By performing surface treatment, the filling ability of the inorganic filler into the resin is improved, making it easier to manufacture resin composite materials in which the inorganic filler is uniformly dispersed in the resin.

Surface treatment of inorganic fillers is achieved by reacting untreated inorganic fillers (untreated fillers) with a surface treatment agent, forming a coating derived from the surface treatment agent on the particle surfaces.

Even if a surface treatment operation is performed, if the surface treatment is not performed appropriately, for example, if the distribution of the coating is uneven and there are areas on the particle surface of the surface-treated filler that have not been sufficiently surface-treated, the filling ability of the surface-treated filler into the resin may not be sufficiently improved. Therefore, in the production of surface-treated fillers, it is important to check whether the surface treatment of the resulting surface-treated filler has been performed appropriately, and in particular to evaluate the uniformity of the coating, when considering surface treatment conditions and quality control.

Methods proposed for evaluating the surface treatment state of surface-treated fillers include those in Patent Documents 1 to 3, for example.

Patent document 1 discloses a method for evaluating the surface treatment state of a surface-treated filler by heating the surface-treated filler to burn off the coating derived from the surface treatment agent, which is an organic substance, and measuring the thermal changes that occur during this process.

Patent Document 2 discloses a method for evaluating the surface treatment state by observing the change in pH when acid is dropped into a suspension of a surface-treated filler (magnesium hydroxide). With this method, it is said that the more uniform the surface treatment and the less exposed surface of the particles, the faster the rate of pH decrease, making it possible to accurately evaluate the coating state.

In Patent Document 3, it is said that by immersing a surface-treated filler that has been surface-treated with a silane coupling agent (surface treatment agent) in alcohol, an alcohol containing the alkoxy group in the silane coupling agent is generated, and by quantifying this through gas chromatographic analysis, it is possible to quantitatively and accurately evaluate the reaction process and reaction rate between the particles and the silane coupling agent.

However, with conventional evaluation methods such as those described in Patent Documents 1 to 3, it is difficult to evaluate the distribution of the coating on a single surface-treated particle, and they are insufficient for evaluating the uniformity of the coating. Therefore, in the past, the only way to know the filling property of a surface-treated filler with high accuracy was to actually fill it into a resin, and if the resin was changed, it was necessary to perform the evaluation again, which was time-consuming.

JP 2001-85806 A JP 2003-83950 A JP 2004-108932 A

As described above, with conventional methods for evaluating surface-treated fillers, it is difficult to adequately evaluate the filling property while taking into account the uniformity of the coating on the particle surface, and it is difficult to evaluate the filling property of surface-treated fillers easily and with high accuracy. Therefore, the objective of the present invention is to provide a method for evaluating surface-treated fillers easily and with high accuracy.

The inventors conducted intensive research to solve the above problems and discovered that it is possible to evaluate the distribution of coatings by measuring the surface potential of surface-treated particles in a surface-treated filler using a scanning probe microscope, thereby enabling the filling property of the surface-treated filler to be evaluated easily and with high accuracy.

That is, the present invention is a method for evaluating a surface-treated filler, characterized by including a step of measuring the surface potential of surface-treated particles in the surface-treated filler with a scanning probe microscope. It is also preferable that the method further includes a step of measuring the surface potential of untreated particles in an untreated filler corresponding to the surface-treated filler, and/or a step of measuring the surface potential of a surface treatment agent corresponding to the surface-treated filler.

The evaluation method of the present invention makes it possible to easily evaluate the filling property of a surface-treated filler. This allows, for example, more efficient quality control than conventional methods.

In this specification, inorganic fillers that have been surface-treated with a surface treatment agent are referred to as "surface-treated fillers," and inorganic fillers before the surface treatment of the surface-treated fillers or inorganic fillers with equivalent manufacturing conditions are referred to as "untreated fillers corresponding to the surface-treated fillers" (sometimes simply referred to as "untreated fillers"). Furthermore, particles in surface-treated fillers are referred to as "surface-treated particles," and particles in untreated fillers are referred to as "untreated particles." Organic matter derived from the surface treatment agent present on the surface of surface-treated particles is referred to as a "coating," and the raw material for forming the coating is referred to as a "surface treatment agent corresponding to the surface-treated filler" (sometimes simply referred to as a "surface treatment agent").

There are no particular limitations on the surface-treated filler to be evaluated by the evaluation method of the present invention, and the evaluation method of the present invention can be applied to, for example, surface-treated silica, alumina, aluminum nitride, boron nitride, and the like. The particle size of the surface-treated filler is not particularly limited, but since a small particle size makes evaluation difficult and a large particle size requires a long time for evaluation, the particle size is preferably 0.5 μm to 100 μm, and more preferably 1.0 μm to 10 μm.

The surface treatment agent is not particularly limited, and known agents can be used, such as silane coupling agents. The difference between the surface potential of the surface treatment agent and the surface potential of the untreated inorganic filler is preferably 100 mV or more, and more preferably 120 mV or more. As described later, the greater the difference in surface potential between the surface treatment agent and the untreated inorganic filler, the easier it is to evaluate the surface-treated filler with high accuracy.

A scanning probe microscope is a device that evaluates the surface condition of a measurement object by scanning a probe along the surface of the measurement object and detecting the interaction between the probe and the measurement object. The measurement of the surface potential using a scanning probe microscope involves applying a DC voltage to the measurement sample to charge it, then applying an AC voltage to the probe to scan the sample surface and detect the electrostatic force acting between the sample and the probe, thereby measuring the surface potential at each position of the measurement object. Since the surface potential of a surface-treated particle is usually different between the part where a coating is present and the part where no coating is present, by measuring the surface potential of the particle using such a scanning probe microscope, it becomes possible to distinguish between the part where a coating is present and the part where no coating is present on the particle surface. This makes it possible to evaluate the state of the coating on the particle surface. The surface potential of the surface-treated filler is evaluated by appropriately picking up and measuring the surface-treated particles in the surface-treated filler. There is no particular limit to the number of surface-treated particles to be picked up, but since the evaluation accuracy can be improved by measuring a larger number of particles, it is preferable to pick up 5 or more particles per 500 g of filler, and more preferably 10 or more particles.

The scanning probe microscope used in the evaluation method of the present invention is not particularly limited as long as it is capable of measuring the surface potential of particles.

The type of probe used in the evaluation method of the present invention is not particularly limited as long as it can measure the surface potential of the particles, but in order to obtain high resolution, it is preferable that the radius of curvature of the probe tip is 5 to 100 nm. It is also preferable to use a probe with a conductive coating on the tip. Examples of conductive coatings include Au coating, Pt coating, PtIr coating, PtSi coating, and diamond coating.

In the evaluation method of the present invention, the method of placing the measurement sample on the scanning probe microscope is not particularly limited as long as the above measurement can be performed. For example, the measurement can be performed by dispersing particles in a volatile solvent to prepare a dispersion, dropping the dispersion on a conductive substrate, and volatilizing the volatile solvent to prepare a measurement substrate, and then fixing the measurement substrate to the sample stage of the scanning probe microscope using a conductive paste. The volatile solvent is not particularly limited as long as it can disperse the particles to be measured and does not react with the particles. For example, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, and butanol, ketones such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone, ethers such as diethyl ether, dioxane, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and tetrahydrofuran, alkanes such as hexane, 2-methylpentane, heptane, cyclohexane, octane, 2,2,4-trimethylpentane, and petroleum ether, esters such as ethyl formate, butyl formate, ethyl acetate, propyl acetate, and butyl acetate, benzene, toluene, xylene, and naphthalene can be used. The conductive substrate may be, for example, a highly oriented pyrolytic graphite (HOPG) substrate or a conductively coated mica substrate. The conductive paste may be a resin having conductive particles dispersed therein, such as an epoxy resin having silver particles, gold particles, platinum particles, or the like dispersed therein.

In the evaluation method of the present invention, a DC voltage is applied to the particles to be measured to charge them, and then an AC voltage is applied to the probe while scanning the sample surface to detect the electrostatic force acting between the sample and the probe. To do this, it is first necessary to obtain a topography image (height image) of the particle by scanning the surface of the particle to be measured with the probe. There are no particular limitations on the method for obtaining the topography image, but it can be performed, for example, by a method such as tapping mode in which the probe is vibrated to scan the sample surface.

Tapping mode is a method in which a cantilever with a probe attached to the tip is vibrated at the resonant frequency while scanning the particle surface. Measurements in tapping mode can obtain not only a topographical image, but also a phase image of the particle surface. It is believed that the phase image can also be used to estimate the distribution of coatings, and by combining it with surface potential measurements, it is expected that a wealth of information on surface-treated fillers can be obtained, making it one of the preferred methods for obtaining topographical images.

Next, the particles to be measured are charged by applying a DC voltage. There are no particular restrictions on the conditions for applying the DC voltage, and it is sufficient to apply the voltage under conditions that provide a good observation image; for example, the applied voltage may be 100 to 1000 mV.

Then, while applying an AC voltage to the probe, the scanning position is determined based on the data of the topography image of the particle to be measured, and the probe is scanned while electrically connected to the sample stage so that a surface potential image is obtained, and the electrostatic force acting between the sample and the probe is detected, making it possible to measure the surface potential of the particle. The scanning position is not particularly limited as long as it is a position where the probe and the particle do not come into contact and an electrical connection can be obtained between the sample and the probe, but the shorter the distance between the probe and the particle, the higher the sensitivity is, but the more difficult it is to adjust the probe position, so in the present invention, it is preferable to control the probe position to 5 nm to 300 nm from the surface of the particle, and more preferably to control it to 50 nm to 200 nm.

In the evaluation method of the present invention, the distribution of surface potential on the surface of the particle can be measured by scanning the probe over the entire surface of the particle using the above-mentioned method and measuring the surface potential at each position. From this distribution of surface potential, the distribution of the coating can be evaluated.

Although it is not clear why the surface treatment state of particles can be evaluated using the evaluation method of the present invention, the inventors speculate as follows. That is, since the surface potential of untreated particles and the surface potential of a surface treatment agent are usually different, the surface potential of the part of a surface-treated particle where a coating of the surface treatment agent is present will be different from that of an untreated particle. Therefore, it is presumed that it becomes possible to evaluate the state of the coating on the particle surface from the surface potential.

The filling property of the surface-treated filler can be evaluated based on the surface potential, for example, from a histogram showing the frequency of the surface potential. Specifically, it can be evaluated based on, for example, the most frequent value of the surface potential in the histogram.

When evaluating using the most frequent value of the surface potential, if the untreated filler and the type of surface treatment agent are the same, it can be said that there is a correlation between the filling property and the most frequent value of the surface potential, and this can be used for evaluation. For example, if the surface potential of a surface-treated filler whose filling property is known is measured in advance and the most frequent value of the surface potential that gives high filling property is identified, then it is possible to easily predict the filling property of the filler by measuring the surface potential of a newly manufactured surface-treated filler and determining the most frequent value.

If the surface potential of the untreated filler corresponding to the surface-treated filler is also measured, this is a preferred form since it is possible to obtain more detailed information. For example, when comparing untreated filler and surface-treated filler using the same surface treatment agent, the greater the difference between the mode of the surface potential of the surface-treated filler and the mode of the surface potential of the untreated filler, the more sufficiently the surface treatment has been performed, the more uniform the distribution of the coating is, and the better the filling properties can be evaluated.

The surface potential of the surface-untreated filler may be measured according to the above-mentioned method for measuring the surface potential of particles.
In addition, when the surface potential of the surface treatment agent is also measured, it is also possible to evaluate the filling property by comparing the mode of the surface potential of the surface treatment agent with the mode of the surface potential of the surface treatment filler. For example, when comparing an untreated filler with a surface-treated filler using the same surface treatment agent, the closer the difference between the mode of the surface potential of the surface-treated filler and the mode of the surface potential of the surface treatment agent is, the more sufficiently the surface treatment is performed, the more uniform the distribution of the coating is, and the better the filling property can be evaluated.

The surface potential of the surface treatment agent can be measured by placing a surface treatment agent measurement sample on a scanning probe microscope and measuring it in the same way as for particles. The surface treatment agent measurement sample can be prepared, for example, by dissolving the surface treatment agent in a volatile solvent, dropping a solution prepared by dissolving the surface treatment agent in a volatile solvent onto a conductive substrate, and volatilizing the volatile solvent. The volatile solvent is not particularly limited as long as it can measure the surface potential of the surface treatment agent, and examples of the volatile solvent include alcohols such as methanol, ethanol, propanol, isopropyl alcohol, and butanol, ketones such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone, ethers such as diethyl ether, dioxane, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and tetrahydrofuran, alkanes such as hexane, 2-methylpentane, heptane, cyclohexane, octane, 2,2,4-trimethylpentane, and petroleum ether, esters such as ethyl formate, butyl formate, ethyl acetate, propyl acetate, and butyl acetate, benzene, toluene, xylene, and naphthalene. The conductive substrate can be a conductive substrate equivalent to that used when measuring particles.

The evaluation method of the present invention makes it possible to evaluate the filling property of a surface-treated filler without actually filling it into a resin. Therefore, by using the evaluation method of the present invention, it becomes possible to easily evaluate the manufactured surface-treated filler, which contributes to simplifying the inspection.

The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The samples used for evaluation are as follows.

Aluminum nitride powder A1: Aluminum nitride powder (non-surface-treated aluminum nitride powder, average particle size 1 μm, manufactured by Tokuyama Corporation)
B1 to B3: A1 treated with an alkyl silane coupling agent S1 according to the following surface treatment method. Note that B1 to B3 differ in the amount of silane coupling agent used in the surface treatment.
C1 to C3: A1 treated with a methacrylic silane coupling agent S2 according to the following treatment method. Note that C1 to C3 differ in the amount of silane coupling agent used in the surface treatment.
D1 to D3: A1 treated with an epoxy-based silane coupling agent S3 according to the following treatment method. Note that D1 to D3 differ in the amount of silane coupling agent used in the surface treatment.
E1 to E3: A1 treated with a phenyl-based silane coupling agent S4 according to the following treatment method. Note that E1 to E3 differ in the amount of silane coupling agent used in the surface treatment.

<Surface treatment method for aluminum nitride powder>
500 g of aluminum nitride powder A1, a predetermined amount of silane coupling agent, and 600 g of isopropyl alcohol were placed in a glass eggplant flask and stirred with a fluororesin stirring blade for 30 minutes. After removing the isopropyl alcohol under reduced pressure with a rotary evaporator, the mixture was dried under reduced pressure at 100° C. to obtain a surface-treated aluminum nitride powder. The obtained surface-treated aluminum nitride powder weighed about 500 g.

<Measurement of the surface potential of the filler>
0.005 g of filler and 10 g of ethanol were placed in a 50 mL screw tube bottle and irradiated with ultrasonic waves for 15 minutes in an ultrasonic bath to prepare a sample dispersion. The prepared sample dispersion was collected with a dropper, dropped on a 10 mm square HOPG substrate, and then dried at 80°C to remove the ethanol to obtain a measurement substrate. The obtained measurement substrate was fixed to the sample stage of a scanning probe microscope (Bruker's Dimension Icon) using a conductive paste (silver particles dispersed in epoxy resin). Next, particles with a particle size of 1 μm to 10 μm were selected, and a roughness image of the particles was obtained by tapping mode. Next, the applied voltage was set to 500 mV, the distance between the probe and the particle was set to 100 nm, and the surface potential of the particles was measured. The probe used had a tip curvature radius of 25 nm and was coated with Pt-Ir. The same procedure was carried out for 20 particles, and from the results of all the measured particles, a histogram was obtained with the horizontal axis representing the surface potential and the vertical axis representing the frequency, and the most frequent value of the surface potential was determined.

<Measurement of surface potential of surface treatment agent>
A drop of the silane coupling agent was collected with a dropper, dropped onto a 10 mm square HOPG substrate, and heated at 100°C to obtain a measurement substrate. The measurement substrate obtained was fixed to the sample stage of a scanning probe microscope (Bruker: Dimension Icon) with conductive paste. Next, the amplitude and gain of the vibrated probe were adjusted so that a roughness image could be obtained. Next, the applied voltage was set to 500 mV, the distance between the probe and the particle was set to 100 nm, and the surface potential of the particle was measured. The probe used had a tip curvature radius of 25 nm and was coated with Pt-Ir. From the measurement results, a histogram was obtained with the horizontal axis representing the surface potential and the vertical axis representing the frequency, and the most frequent value of the surface potential was obtained.

<Evaluation of Filler Filling Properties>
The two-liquid addition reaction type silicone resin and the filler were kneaded using a foam remover (manufactured by Thinky Corporation) and the maximum amount of filler was confirmed to evaluate the filler filling property. The evaluation results are shown in order of the maximum amount of filler filled.

Example 1
According to the measurements of the surface potentials of the above fillers and surface treatment agents, the surface potentials of fillers A1, B1 to B3, and surface treatment agent S1 were determined. In addition, the loading property of B1 to B3 was evaluated. As shown in Table 1, the results indicate that the loading property is higher as the mode of the surface potential of the surface-treated filler moves away from the mode of the surface potential of the untreated filler (A1) and approaches the mode of the surface potential of the silane coupling agent (S1).

Example 2
According to the measurements of the surface potential of the above fillers and surface treatment agents, the surface potentials of fillers A1, C1 to C3, and surface treatment agent S2 were determined. In addition, the filling property of C1 to C3 was evaluated. The results are shown in Table 1. It was shown that the higher the filling property, the more the mode of the surface potential of the surface-treated filler moves away from the mode of the surface potential of the untreated filler (A1) and approaches the mode of the surface potential of the silane coupling agent (S2).

Example 3
According to the measurements of the surface potential of the above fillers and surface treatment agents, the surface potentials of fillers A1, D1 to D3, and surface treatment agent S3 were determined. In addition, the filling property of D1 to D3 was evaluated. The results are shown in Table 1. It was shown that the more the mode of the surface potential of the surface-treated filler moves away from the mode of the surface potential of the untreated filler (A1) and approaches the mode of the surface potential of the silane coupling agent (S3), the higher the filling property.

Example 4
According to the measurements of the surface potential of the above fillers and surface treatment agents, the surface potentials of fillers A1, E1 to E3, and surface treatment agent S4 were determined. In addition, the filling property of E1 to E3 was evaluated. The results are shown in Table 1. It was shown that the more the mode of the surface potential of the surface-treated filler moves away from the mode of the surface potential of the untreated filler (A1) and approaches the mode of the surface potential of the silane coupling agent (S4), the higher the filling property.

The above results show that there is a correlation between the surface potential of the surface-treated filler and its ability to fill into resin, and that the filling ability of the filler can be evaluated by measuring the surface potential of the surface-treated filler using a scanning probe microscope.

Claims (1)

A method for evaluating the filling property of a surface-treated filler into a resin, comprising a step of measuring the surface potential of particles of the surface -treated filler and particles of an untreated filler and/or a surface treatment agent corresponding to the surface-treated filler using a scanning probe microscope, and is characterized by comparing the most frequent values of the surface potential in a histogram showing the frequency of the surface potential of the particles of the surface-treated filler and particles of an untreated filler and/or a surface treatment agent corresponding to the surface-treated filler.