JP7645759B2 - 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 surface-treated fillers by scanning the particle surface while vibrating a probe at a predetermined amplitude using a scanning probe microscope to obtain a phase image.

Resin composite materials, which are a composite of inorganic filler and resin, are used in a wide range of fields, such as heat dissipation materials. 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-treated fillers are obtained by reacting inorganic fillers that have not been surface-treated (untreated fillers) with a surface treatment agent, and forming a coating derived from the surface treatment agent on the surfaces of the particles.

Here, when the inorganic filler is a thermally conductive filler to be mixed into the heat dissipation material, surface treatment to enhance the filling property is an effective method for obtaining a resin composite material with high thermal conductivity. However, if the surface treatment is not performed appropriately, for example, if the coating derived from the surface treatment agent is not uniformly distributed on the particle surface, the effect of the surface treatment may not be fully exerted. For example, if the distribution of the coating is uneven and there are parts that are not surface-treated, the compatibility with the resin is not sufficiently improved, making it difficult to obtain high filling property. In addition, if an excessive layer of coating is present on the particle surface of the thermally conductive filler, the excessive layer of coating may interrupt the heat path, and the thermal conductivity of the resin composition may not be improved as much as expected even if the filling property is increased. Therefore, in the production of surface-treated thermally conductive filler, it is important to confirm whether the surface treatment of the obtained surface-treated filler is performed appropriately, and in particular, to evaluate it taking into account the distribution of the coating on the particle surface.

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

Patent Document 1 discloses a method for evaluating the surface treatment state of a surface-treated filler by heating the 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 the 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 this is quantified by gas chromatographic analysis, the reaction process and reaction rate between the filler and the silane coupling agent can be quantitatively and accurately evaluated.

However, with conventional evaluation methods such as those described in Patent Documents 1 to 3, it is not possible to confirm the distribution of the coating, making it difficult to adequately perform evaluations that take into account the distribution of the coating in the surface-treated filler. Therefore, in order to know with high accuracy the adverse effect that an excess layer of coating in the above-mentioned surface-treated thermally conductive filler has on thermal conductivity, for example, the only way is to actually manufacture a resin composite material and measure its thermal conductivity, which is a time-consuming evaluation.

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

As mentioned above, it was difficult to adequately evaluate the distribution of the coating using conventional methods for evaluating the state of surface treatment. Therefore, the objective of the present invention is to provide an evaluation method that can evaluate the distribution of the coating in surface-treated fillers, and in particular the uniformity of the coating.

The inventors conducted extensive research to solve the above problems and discovered that it is possible to evaluate the distribution of coatings by scanning the particle surfaces of surface-treated particles while vibrating the probe of a scanning probe microscope at a predetermined amplitude to obtain a phase image.

That is, the present invention is a method for evaluating a surface-treated filler, which includes a step of scanning the particle surface of the surface-treated thermally conductive filler while vibrating the probe of a scanning probe microscope at a predetermined amplitude to obtain a phase image.

The evaluation method of the present invention allows for easy evaluation of the distribution of coatings in surface-treated fillers. As a result, for example, it is possible to evaluate the presence or absence of an excess layer of coating in a surface-treated thermally conductive filler, and to more easily select surface-treated thermally conductive fillers that may not provide high thermal conductivity in a resin composite material using the surface-treated thermally conductive filler.

In this specification, a filler that has been surface-treated with a surface treatment agent is referred to as a "surface-treated filler," and a filler before the surface treatment of the surface-treated filler or a filler manufactured under the same conditions is referred to as an "untreated filler corresponding to the surface-treated filler" (sometimes simply referred to as an "untreated filler"). Furthermore, particles in a surface-treated filler are referred to as "surface-treated particles," and particles in an untreated filler are referred to as "untreated particles." The organic matter derived from the surface treatment agent present on the surface of the 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 any known agent can be used, such as a silane coupling agent.

A scanning probe microscope is a device that evaluates the surface condition of a measurement object by scanning the surface of the measurement object while moving the probe to trace it and detecting the interaction between the probe and the measurement object. In the evaluation method of the present invention, the particle surface of the surface-treated particle is scanned while the probe is vibrated at a predetermined amplitude, and a phase image is obtained. When comparing the phase when the sample surface is scanned with the phase when the probe is vibrated at a predetermined amplitude, the phase delay due to the adsorption of the probe to the particle surface is large when a soft part is scanned, and the phase delay is small when a hard part is scanned, so the degree of hardness of the part can be evaluated from the obtained phase image. And, since the part of the surface-treated particle where a lot of coating is present is soft, it is presumed that the distribution of coating on the particle surface can be evaluated from the phase image obtained by this measurement.

The scanning probe microscope used in the evaluation method of the present invention is not particularly limited as long as it can perform the above measurements.

The type of probe used in the evaluation method of the present invention is not particularly limited, but in order to obtain high resolution, it is preferable that the radius of curvature of the probe tip is 5 to 100 nm.

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 liquid, dropping the dispersion liquid on a mica 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 with conductive carbon tape. 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.

In the evaluation method of the present invention, a cantilever holder with a cantilever having a probe at its tip is attached to a scanning probe microscope, and the cantilever is then vibrated at its resonant frequency. The height displacement and phase shift of the cantilever when scanning the sample surface are detected and imaged, making it possible to confirm the change in phase of the sample surface. The amplitude and gain of the probe can be adjusted so that a roughness image of the particles can be obtained.

In the evaluation method of the present invention, the probe is scanned over the entire surface of the surface-treated particles in the surface-treated filler, thereby making it possible to confirm the distribution of hardness on the surface of the surface-treated particles, and to evaluate the uniformity of the coating from this hardness distribution. There are no particular limitations on the method for evaluating the hardness distribution of the surface-treated particles from the obtained data, but it can be done, for example, by checking a phase image that shows the phase delay in contrast.

The properties of the surface-treated filler can be understood by measuring multiple particles in the surface-treated filler. There is no particular limit to the number of surface-treated particles measured to understand the properties of the surface-treated filler, but since measuring a larger number of particles can improve evaluation accuracy, it is preferable to measure 5 or more particles per 500 g of filler, and more preferably 10 or more particles.

By carrying out the evaluation method of the present invention, a roughness image of the particle surface can also be obtained at the same time. Since areas where an excess of coating material is present are often higher than the surrounding area, evaluation using the roughness image may also be carried out.

The evaluation method of the present invention makes it possible to evaluate the uniformity of the coating on the particle surface of surface-treated fillers. This makes it easier than ever to control the quality of surface-treated fillers and to consider manufacturing conditions.

By evaluating the uniformity of the coating using this evaluation method, it is possible to select fillers that may not be highly packed because part of the particle surface is not surface-treated and therefore does not blend well with the resin, or fillers that may have an excessive layer of coating that reduces thermal conductivity. This makes it possible to efficiently control the quality of surface-treated fillers. Specifically, for example, when both high packing and high thermal conductivity are required for a thermally conductive filler to be filled into resin, this evaluation method is used, and if the distribution of the coating is uneven, it can be determined that at least one of the high packing and high thermal conductivity is likely to be insufficient and does not meet the requirements.

For example, if a thermally conductive filler requires high thermal conductivity but the expected amount of filling into the resin is small and high filling is not necessary, a filler with a part of the particle surface that is not surface-treated and does not blend well with the resin and does not provide high filling will meet the requirement, while a filler with an excessive layer of coating that causes a decrease in thermal conductivity will not meet the requirement. In such a case, it is difficult to distinguish between these two states using only the evaluation method of the present invention, but the accuracy of the judgment can be increased by combining an evaluation that can confirm that a sufficient amount of coating is present on the surface-treated filler (for example, the carbon amount or M value of the surface-treated filler) with the evaluation method of the present invention. Specifically, for fillers that are determined to have an uneven coating in the present evaluation, the surface treatment state is evaluated based on the carbon content and M value, and if the surface is sufficiently treated, it is determined that the filler does not meet the requirements for high packing, but does not have high thermal conductivity due to the presence of an excessive coating layer, and if the surface is not sufficiently treated, part of the particle surface is not surface treated, resulting in uneven distribution of the coating, and it is possible to determine that the filler meets the requirements for high thermal conductivity, as there is no excessive coating layer.

In addition, after confirming that sufficient coating is present on the particle surface and high packing properties can be obtained through evaluation of the carbon content and M value of the surface-treated filler, the evaluation method of the present invention can be used to select fillers that may have an excessive layer of coating that may cause a decrease in thermal conductivity.

The present invention will be specifically explained 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, 2: A1 treated with an alkyl silane coupling agent S1 according to the following surface treatment method. The carbon amounts of B1 and B2 measured by a carbon analyzer are equivalent.
C1, 2: A1 treated with an epoxy-based silane coupling agent S2 according to the following surface treatment method. The carbon amounts of C1 and C2 measured by a carbon analyzer are equivalent.
D1, 2: A1 treated with a methacrylic silane coupling agent S3 according to the following surface treatment method. The carbon amounts of D1 and D2 measured by a carbon analyzer are equivalent.
E1, 2: A1 treated with a phenyl-based silane coupling agent S4 according to the following surface treatment method. The carbon amounts of E1 and E2 measured by a carbon analyzer are equivalent.

<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.

<Filler Evaluation Method>
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 onto a 10 mm square mica substrate, and then dried at 80 ° C to remove ethanol to obtain a measurement substrate. The obtained measurement substrate was fixed to the sample stage of a scanning probe microscope (manufactured by Bruker: Dimension Icon) using double-sided tape. Next, particles with a particle size of 1 μm to 10 μm were selected, and the cantilever was scanned with a probe while vibrating at a resonant frequency to obtain a height image and a phase image. The amplitude and gain of the probe were adjusted so that a roughness image of the particles was obtained. After obtaining phase images for 10 particles, evaluation was performed using the obtained phase images.

<Evaluation of thermal conductivity>
A resin composite material was prepared by kneading 1 g of a two-liquid addition reaction type silicone resin and 5 g of a filler in an agate mortar. The thermal conductivity of the prepared resin composite material was measured by a laser flash method to evaluate the thermal conductivity of the resin composite material.

Example 1
When fillers B1 and B2 were evaluated according to the above-mentioned filler evaluation method, filler B1 had fewer locations where phase lag was observed than filler B2. Furthermore, when the thermal conductivity of resin composite materials containing these fillers was evaluated according to the above-mentioned thermal conductivity evaluation, the resin composite material using filler B1 had a higher thermal conductivity than the resin composite material using filler B2.
Fillers B1 and B2 had the same amount of carbon measured by a carbon analyzer, so it was believed that the amount of coating was the same and that both had sufficient surface treatment. However, according to the evaluation method of the present invention, differences were observed in the phase images, and it was believed that filler B2 had a lower uniformity of coating. When a resin composition was actually produced and its thermal conductivity was evaluated, the resin composition using filler B2, which showed a phase delay, showed a lower thermal conductivity.
Therefore, it can be said that the evaluation method of the present invention makes it possible to select fillers that may have an excessive coating layer that may cause reduced thermal conductivity from fillers that have a sufficient coating on the particle surface.

Example 2
When fillers C1 and C2 were evaluated according to the above-mentioned filler evaluation method, filler C1 had fewer locations where phase lag was observed than filler C2. Furthermore, when the thermal conductivity of resin composite materials containing these fillers was evaluated according to the above-mentioned thermal conductivity evaluation, the resin composite material using filler C1 had a higher thermal conductivity than the resin composite material using filler C2.
Therefore, as in Example 1, it can be said that the evaluation method of the present invention made it possible to select fillers that may have an excessive coating layer that may cause a decrease in thermal conductivity from fillers that have a sufficient coating on the particle surface.

Example 3
Fillers D1 and D2 were evaluated according to the above-mentioned filler evaluation method, and filler D1 had fewer locations where phase lag was observed than filler D2. Furthermore, when the thermal conductivity of resin composite materials containing these fillers was evaluated according to the above-mentioned thermal conductivity evaluation, the resin composite material using filler D1 had a higher thermal conductivity than the resin composite material using filler D2.
Therefore, as in Example 1, it can be said that the evaluation method of the present invention made it possible to select fillers that may have an excessive coating layer that may cause a decrease in thermal conductivity from fillers that have a sufficient coating on the particle surface.

Example 4
When fillers E1 and E2 were evaluated according to the above-mentioned filler evaluation method, filler E1 had fewer locations where phase lag was observed than filler E2. Furthermore, when the thermal conductivity of resin composite materials containing these fillers was evaluated according to the above-mentioned thermal conductivity evaluation, the resin composite material using filler E1 had a higher thermal conductivity than the resin composite material using filler E2.
Therefore, as in Example 1, it can be said that the evaluation method of the present invention made it possible to select fillers that may have an excessive coating layer that may cause a decrease in thermal conductivity from fillers that have a sufficient coating on the particle surface.

Claims (1)

A method for evaluating a surface-treated filler, comprising the steps of: scanning the particle surface of the surface-treated filler while vibrating a probe with a predetermined amplitude using a scanning probe microscope; obtaining a phase image showing a phase delay in contrast ; and using the phase image to confirm the distribution of surface hardness of the surface-treated particles in the surface-treated filler, and to evaluate the uniformity of the coating .