JP2009222430A - Evaluation method of surface state - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of a surface state, capable of easily evaluating the surface free energy of a microregion and becoming a similar evaluation as the measurement evaluation of the surface free energy by a usual contact angle measuring method, if the energy is the same as the sample. <P>SOLUTION: A mixed liquid of a polyhydric alcohol and water is dripped on a measuring sample 10 in a volume of 300 picoliter to measure a micro-contact angle. Thereafter, the micro-contact angle using the mixed liquid of the polyhydric alcohol and water is converted into a normal contact angle at the time of measurement using a usual amount (1 ml or larger), by employing a prepared linear regression curve and the surface state of the measuring sample 10 is evaluated, on the basis of this result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface state evaluation method particularly suitable for evaluating the surface free energy of a minute region.

  In recent years, magnetic disk devices (hard disk drives) have come to be used not only for computers but also for video recording devices such as hard disk video recorders, portable music playback devices, and the like. The magnetic disk device has a disk-shaped magnetic disk (magnetic recording medium) and a magnetic head. The magnetic head includes a recording element that magnetically records information on the magnetic disk, a reproducing element that reads information from the magnetic disk, and a slider that supports the recording element and the reproducing element. The slider is a rectangular parallelepiped member, and the recording element and the reproducing element are disposed on the end face of the slider.

  The magnetic head is arranged so that a surface called ABS (Air Bearing Surface; hereinafter referred to as an opposing surface) faces the magnetic disk. The magnetic head floats slightly from the surface of the magnetic disk by the air flow generated by the rotation of the magnetic disk, and in this state, information is written to the magnetic disk by the recording element and information is read from the magnetic disk by the reproducing element. In order to increase the recording density of the magnetic disk, it is necessary to reduce the distance between the magnetic disk and the magnetic head (hereinafter referred to as the flying height). In recent magnetic disk devices, the flying height of the magnetic head is as small as about 10 nm.

  By the way, a lubricant film having a thickness of about 1 nm is formed on the surface of the magnetic disk so that the magnetic disk is not damaged even if the magnetic head comes into contact with the magnetic disk for some reason (change in atmospheric pressure, vibration, etc.). ing. However, in recent magnetic disk devices in which the flying height of the magnetic head has become extremely small, a lubricant component or the like (hereinafter referred to as a pollutant) adheres to the facing surface of the magnetic head slider due to long-term use, and thereby the magnetic head The flying stability of the slider may be reduced. In order to avoid such problems, it is important to suppress the adhesion of contaminants to the surface of the magnetic head.

  Patent Document 1 describes a technique for forming a lubricating layer in which perfluoropolyether or the like is fixed to an opposing surface of a magnetic head by ultraviolet rays or the like in order to prevent the adhesion of contaminants. Further, as a method for measuring the surface free energy of the facing surface, a method is described in which the contact angle is measured with a microscope using two or more liquids and the surface free energy is obtained from the Fowke equation.

Patent Document 2 describes that the adhesion of outgas to the magnetic head is suppressed by lowering the surface energy of the magnetic head, and that the contact angle is measured using three or more liquids having different surface tensions. Yes. Patent Document 3 describes obtaining surface free energy of a solid surface from contact angle data of four or more kinds of liquids.
JP 2006-12377 A Japanese Patent Laid-Open No. 2005-221403 JP 2005-337781 A

  As described in Patent Document 2 described above, the adhesion of contaminants to the facing surface of the magnetic head is related to the surface free energy of the facing surface, and the lower the surface free energy, the less the contaminants adhere. In general, the surface free energy is obtained from a contact angle obtained by dropping a liquid such as water (probe liquid) on a sample. However, it is difficult to accurately obtain the surface free energy of the minute region of the facing surface of the magnetic head, and there is a problem that the surface state and quality control of the magnetic head cannot be controlled. This is due to the following two reasons.

  The first reason is that when the surface free energy of the minute region of the facing surface of the magnetic head is to be measured, the amount of probe liquid to be dropped needs to be reduced according to the spatial resolution to be measured. If the amount is reduced, the liquid evaporates in a very short time, and the contact angle changes greatly accordingly.

  The second reason is that the contact angle varies depending on the dropping amount of the probe liquid. Usually, when measuring the contact angle, about 1 microliter or more of probe liquid is dropped on the sample surface. In this case, the diameter of the droplet is several mm. However, when measuring the contact angle of a minute region, it is necessary to reduce the dropping amount of the probe liquid to, for example, several tens to several hundred picoliters. In this case, the diameter of the droplet is several tens of μm. In principle, the contact angle should be the same even if the drop amount of the probe liquid is different, but the contact angle actually changes depending on the drop amount of the probe liquid. Hereinafter, the contact angle measured by dropping a normal amount (1 microliter or more) of the probe liquid on the sample surface is called a normal contact angle, and a very small amount (several tens to several hundred picoliters) of the probe liquid is dropped on the sample surface. The contact angle measured in this way is called the minimum contact angle.

  Since a high level of technology is required to measure the contact angle of a minute region, for example, a normal contact angle measurement method (hereinafter referred to as a normal contact angle measurement method) that can be easily measured for inspecting the surface state of a magnetic disk. ), And the surface free energy is measured by a method suitable for measuring the minimum contact angle (hereinafter referred to as the minimum contact angle measurement method) in the micro area of the surface of the magnetic head. Use properly is desired. For that purpose, if the samples have the same surface free energy, a minimum contact angle measurement method that requires the same value as that measured by the normal contact angle measurement method is required.

  From the above, the object of the present invention is to evaluate the surface state, which can easily evaluate the surface free energy of a minute region and is the same evaluation as that measured by the normal contact angle measurement method if the surface free energy is the same sample. Is to provide a method.

  According to one aspect of the present invention, a step of measuring a minimum contact angle by dropping a probe liquid made of polyhydric alcohol or a mixed liquid of polyhydric alcohol and water onto a measurement sample in a volume of 300 picoliters or less; The linear regression equation showing the correlation between the minimum contact angle when measured using the probe solution of 300 picoliters or less and the normal contact angle when measured using water of 1 microliter or more is used. A method for evaluating a surface state, comprising: converting a minimum contact angle of a probe liquid into a normal contact angle of water; and evaluating a surface state of the measurement sample based on a conversion result of the water into a normal contact angle. Provided.

  In the present invention, a polyhydric alcohol or a mixed liquid of polyhydric alcohol and water that is difficult to evaporate and has the same chemical structure as water is used as the probe liquid. And the contact angle (minimum contact angle) of a micro area | region is measured using this probe liquid, and the measurement result is converted into the normal contact angle of water. Thereby, the surface state of a micro area can be evaluated by comparing with the contact angle measured by a general normal contact angle measurement method.

  In order to convert the minimum contact angle measured using a polyhydric alcohol or a mixed solution of polyhydric alcohol and water into a normal contact angle of water, the surface energy is previously placed on a plurality of standardized samples having different surface energies. The probe solution is dropped at a volume of 300 picoliters or less to measure the minimum contact angle, and water is dropped onto the standardized samples at a volume of 1 microliter or more to measure the normal contact angle. A linear regression equation obtained by linear regression analysis of the measurement result of the angle and the measurement result of the normal contact angle is used.

  In order to calculate the surface free energy by the Fowke equation, it is necessary to measure the contact angle using two or more kinds of probe liquids. The above-mentioned polyhydric alcohol or a mixed liquid of polyhydric alcohol and water is used as the first probe liquid, and a hydrocarbon-based liquid such as diiodomethane or hexadecane is used as the second probe liquid. By converting the measured minimum contact angle into a normal contact angle, the surface free energy of the micro area can be calculated.

  When the present invention is used for manufacturing a magnetic head, the surface free energy of the facing surface facing the magnetic recording medium (magnetic disk) is controlled to be 15 mN / m to 30 mN / m when measured by the above method. It is preferable to do.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a method for measuring a contact angle. First, the light source 13 is disposed on the side of the sample 10, and the camera (CCD) 14 is disposed on the opposite side of the light source 13 with the sample 10 interposed therebetween. Then, a probe liquid is dropped from the capillary 11 onto the sample 10.

  As a result, the light from the light source 13 is blocked by the liquid droplets 12 to form a shadow. The camera 14 photographs the shadow of the droplet 12 and measures the contact angle of the droplet 12 based on the image.

  The capillary 11 is made of a glass tube with a very thin tip. In this embodiment, a capillary having an inner diameter of 5 to 30 μm is used for measurement of a minimum contact angle using a very small amount (300 picoliters or less) of a probe liquid, and a normal contact angle using a probe liquid of 1 to 100 microliters or more. For the measurement, a capillary with an inner diameter of 0.15 to 1.2 mm is used.

2A is a side view of the magnetic head, and FIG. 2B is a bottom view of the magnetic head. The magnetic head 30 includes a slider 6 made of a ceramic material such as Al ₂ O ₃ —TiC (Altic), for example, and a recording / reproducing element 5 disposed on the end face of the slider 6. In FIGS. 2A and 2B, the recording element and the reproducing element are schematically shown as the recording / reproducing element 5, but a known single-pole head is used as the recording element. For example, a known MR (Magneto Resistive) element, GMR (Giant Magneto Resistive) element or TMR (Tunnel Magneto Resistive) element is used as the element.

  Convex portions 1 to 4 are formed on the opposing surface of the slider 6 in a predetermined pattern as shown in FIG. These convex portions 1 to 4 are provided for adjusting the air flow generated by the rotation of the magnetic disk and ensuring the flying stability of the magnetic head 30 (slider 6). The magnitude | size of the convex parts 1, 2, and 3 is 0.5 mm x 0.5 mm or less, for example. Moreover, the height D of the convex parts 1-4 is about 2 micrometers, for example. In order to avoid the occurrence of inconvenience due to contaminants adhering to the facing surface of the magnetic head, it is important to grasp the surface free energy of these convex portions 1 to 4. In order to suppress the adhesion of contaminants to the magnetic head, the surface free energy of the facing surface of the magnetic head (slider) calculated by the Fowke equation is preferably 15 mN / m to 30 mN / m. It is preferable that the surface free energy on the magnetic head side is lower than the surface free energy of the magnetic disk.

  FIG. 3 is a schematic diagram showing the probe liquid 12 dropped on the sample 10. Here, the probe liquid 12 is dropped using a capillary 11 having an inner diameter of 5 μm. Note that the outer surface (surface) of the capillary 11 is subjected to water repellent treatment in order to drop a very small amount of the probe liquid 12, and the water repellent treatment will be described later.

  FIG. 4 is a diagram showing a change in the radius of the droplet over time, with time on the horizontal axis and the radius of the droplet on the vertical axis. FIG. 5 is a diagram showing the change over time in the contact angle of the droplet, with time on the horizontal axis and contact angle on the vertical axis. However, here, as shown in FIG. 3, water (pure water) is dropped onto the sample 10 using a capillary 11 having an inner diameter of 5 μm.

  FIG. 4 shows that when water is used as the probe liquid, the radius of the droplet decreases in a very short time. This indicates that water is rapidly evaporating from the droplet. Moreover, it can be seen from FIG. 5 that the contact angle changes in a short time, and especially the change in the contact angle immediately after dropping is large. 4 and 5, when water is used as the probe liquid, it can be considered that the height of the droplet is rapidly decreased by evaporation of water immediately after the dropping, and as a result, the contact angle is rapidly decreased. That is, when water is used as the probe liquid, it is difficult to accurately measure the contact angle of a minute region and the reproducibility is poor.

  Therefore, it is conceivable to use a liquid that is less likely to evaporate than water as the probe liquid. However, in order to make the contact angle (minimum contact angle) of a minute region correspond to the contact angle (normal contact angle) measured by the normal contact angle measurement method, it is necessary to use a liquid having a chemical structure similar to water. is important. Hereinafter, a liquid having a chemical structure similar to that of water is referred to as a water-like liquid.

  In the present embodiment, a mixed liquid of water and a polyhydric alcohol is used as the water-like liquid. In order to take correspondence between the minimum contact angle and the normal contact angle, a plurality of types of samples having different surface free energies are prepared.

  Then, a water-like liquid is dropped on the first sample in an amount of 300 picoliters or less, and then the minimum contact angle A1 of the droplet on the first sample is measured. In addition, after dropping a normal amount (1 microliter or more) of water on the first sample, the normal contact angle B1 of the droplet on the first sample is measured.

  Similarly, after a water-like liquid is dropped on the second sample in an amount of 300 picoliters or less, the minimum contact angle A2 of the droplet on the second sample is measured. Further, after dropping a normal amount of water on the second sample, the normal contact angle B2 of the droplet on the second sample is measured. For other samples, after dropping a water-like liquid in an amount of 300 picoliters or less, the minimum contact angle An (n is an integer) of the droplet is measured, and after dropping a normal amount of water, the normal contact angle of the droplet Bn is measured.

  Thereafter, the measurement results of these contact angles are plotted on a graph to obtain a linear regression equation represented by the following equation (1).

Y = a × X + b (1)
However, X is a minimum contact angle, Y is a normal contact angle, and a and b are both coefficients.

  After obtaining a linear regression equation in this way, about 300 picoliters of a water-like liquid is dropped on an arbitrary sample, and the minimum contact angle A is measured. Using the equation (1), a normal amount of water is contacted. Convert to angle (normal contact angle) B. Thereby, the contact angle of a micro area can be measured repeatedly with good accuracy and good reproducibility. In this embodiment, for example, a magnetic head using a surface state of a magnetic disk measured by a normal contact angle measurement method using water as a probe liquid, and a water-like liquid (mixed liquid of water and polyhydric alcohol) as a probe liquid. It is possible to evaluate the surface condition of the minute region of the facing surface of the same surface by the same standard. As a result, the surface state of the magnetic disk and the magnetic head can be controlled and managed with high accuracy.

  In the present embodiment, a mixed liquid of water and a polyhydric alcohol is used as the probe liquid. The reason will be described below.

  According to Young's equation, what characterizes the contact angle of water is the surface tension of the water, the surface tension of the solid, and the interfacial tension of the solid and water. Of these, the properties of water are reflected in the surface tension of water and the interfacial tension of solids and water. Therefore, when the minimum contact angle is measured using a liquid that has a chemical structure similar to water and does not easily evaporate as the probe liquid, the correlation with the normal contact angle measured using water as the probe liquid is good. There is expected.

  The surface tension of water is 72.8 mN / m, and the breakdown is 21.8 mN / m for the dispersed component and 51.0 mN / m for the polar component. The nature of water is that the proportion of polar components is large, which is attributed to having hydroxyl groups. For example, diiodomethane having no hydroxyl group has a surface tension of 50.8 mN / m, the breakdown of which is 49.5 mN / m for the dispersed component and 1.3 mN / m for the polar component, and the proportion of the polar component is small. . Hexadecane also has no hydroxyl group, but the surface tension of hexadecane is 27.6 mN / m, and the breakdown is 27.6 mN / m for the dispersed component and 0 mN / m for the polar component. In this example, it can be seen that the dispersed component is derived from hydrocarbons such as methylene group and methyl group.

  As a liquid having a chemical structure similar to water, there is an alcohol having a hydroxyl group. However, with monohydric alcohols, the alkyl chain must be lengthened to prevent evaporation. As a result, the proportion of the dispersed component is increased and the similarity with water is impaired.

  On the other hand, divalent or trivalent alcohols such as ethylene glycol (divalent alcohol) and glycerin (trivalent alcohol) have a short alkyl chain and a large number of hydroxyl groups, and thus have a strong similarity to water. Moreover, since these alcohols have a high boiling point, they are difficult to evaporate. Therefore, it is conceivable to use a polyhydric alcohol as the water-like liquid.

  As a result of various experiments and examinations by the inventors of the present application, it has been found that when polyhydric alcohol and water are mixed, the similarity to water becomes stronger and evaporation is also suppressed. Therefore, in this embodiment, a mixed liquid of divalent or trivalent alcohol and water is used as the probe liquid used for measuring the minimum contact angle.

(Experiment 1)
FIG. 6 is a diagram showing the results of measuring changes in the minimum contact angle over time for three types of liquids having different mixing ratios of glycerin and water, with time on the horizontal axis and the minimum contact angle on the vertical axis. is there. Here, the minimum contact angle is measured by dropping a mixed solution onto a plurality of samples having different surface free energies using a capillary having an inner diameter of 5 μm.

  As can be seen from FIG. 6, when the mixed solution contains 75% water (glycerin: water = 1: 3 (however, volume ratio, the same applies hereinafter)), the change in the minimum contact angle with time is relatively large. However, when the water content is 50% (glycerin: water = 1: 1) or less, the change with time of the minimum contact angle is small.

  FIG. 7 shows the measurement results of changes in droplet height over time in three types of liquids with different mixing ratios of glycerin and water, with time on the horizontal axis and the height of the droplet on the vertical axis. FIG. As can be seen from FIG. 7, when the content of water in the mixed liquid is 50% or less, the change in the height of the droplets with time is suppressed.

  FIG. 8 shows the results of measuring changes in the radius of the droplet over time in three types of liquids having different mixing ratios of glycerin and water, with time on the horizontal axis and the radius of the droplet on the vertical axis. FIG. As can be seen from FIG. 8, when the water content in the mixed solution is 50% or less, the change in the radius of the droplet over time is suppressed.

  From these FIG. 6 to FIG. 8, in the mixed liquid of glycerin and water, the amount of evaporation from the droplets can be reduced by setting the water content to 50% or less. It can be seen that the change in height and droplet radius over time is reduced.

(Experiment 2)
Hereinafter, the results of actually measuring the minimum contact angle and the normal contact angle and obtaining the linear regression equation will be described.

  First, a plurality of magnetic disks having a DLC (Diamond-Like-Carbon) protective film formed on the surface were prepared. Of these magnetic disks, Fomblin Z25 manufactured by Solvay Solexis Co. was applied to a thickness of about 1.5 nm as a lubricant. Thereafter, these magnetic disks (a magnetic disk not coated with a lubricant and a magnetic disk coated with a lubricant) are irradiated with ultraviolet light having a wavelength of 172 nm for 0 seconds to 20 seconds, and a plurality of surface free energies different from each other. A sample was prepared.

  Next, a mixed solution of glycerin and water (glycerin: water = 3: 1) was dropped on these samples (magnetic disks) using a capillary having an inner diameter of 30 μm, and the normal contact angle was measured. Further, a mixture of glycerin and water (glycerin: water = 3: 1) was dropped on these samples using a capillary having an inner diameter of 5 μm, and the minimum contact angle was measured.

  Before the measurement, the surface of the sample was washed with Vertrel XF (solvent) manufactured by Mitsui Fluoro DuPont.

FIG. 9 is a diagram in which the measurement results are plotted with the minimum contact angle on the horizontal axis and the normal contact angle on the vertical axis. FIG. 9 shows that the contact angle varies depending on the amount of the probe liquid dropped even on the sample surface having the same surface free energy. When a linear regression equation was obtained from the measurement results, it was Y = 0.916X + 2.2115. The square value (R ² ) of the correlation coefficient R is 0.9981, and there is a strong correlation between the normal contact angle and the minimum contact angle measured using a mixture of glycerin and water as the probe liquid. It was confirmed that there is sex. In order to convert the contact angle with good accuracy using the linear regression equation, it is considered that the square value (R ² ) of the correlation coefficient R needs to be 0.98 or more.

(Experiment 3)
FIG. 10 shows a normal contact angle measured using water as a probe liquid on the horizontal axis, and a normal measurement measured using a mixed liquid of glycerin and water (glycerin: water = 3: 1) as the probe liquid on the vertical axis. It is a figure which shows the result of having taken the contact angle and investigated the correlation of both. In the measurement of the contact angle, a plurality of magnetic disks in which the surface free energy was changed by changing the irradiation amount of ultraviolet rays as in Experiment 2 were used as samples.

From FIG. 10, there is a good correlation between the normal contact angle measured using water as the probe liquid and the normal contact angle measured using a mixture of glycerin and water. It was confirmed that the normal contact angle measured using the mixed solution can be accurately converted to the normal contact angle measured using water. When a linear regression equation was obtained from the measurement results shown in FIG. 10, Y = 1.1048X-17.825 was obtained. The square value (R ² ) of the correlation coefficient R is 0.9817, confirming that there is a strong correlation between the normal contact angle of water and the normal contact angle of a mixture of glycerin and water. It was done.

  As described above, since the conversion between the normal contact angle and the minimum contact angle can be accurately performed for the mixed liquid of glycerin and water, the minimum contact angle of the mixed liquid of glycerin and water is set to the water. The normal contact angle can be accurately converted. Therefore, the surface state of the magnetic disk and the surface state (surface free energy) of the minute region of the magnetic head (slider) can be accurately evaluated based on a common criterion of water contact angle.

(Experiment 4)
Next, the results of examining the correlation between the normal contact angle and the minimum contact angle using diiodomethane having no hydroxyl group will be described. In the measurement of the contact angle, a plurality of magnetic disks whose surface free energy was changed by changing the irradiation amount of ultraviolet rays as in Experiment 2 were used as samples.

  FIG. 11 is a diagram showing measurement results of the normal contact angle and the minimum contact angle of diiodomethane. FIG. 11 shows the correlation between the normal contact angle and the minimum contact angle of diiodomethane.

As shown in FIG. 11, even when diiodomethane is used as the probe liquid, the normal contact angle and the minimum contact angle do not match. However, there is a good correlation between the normal contact angle and the minimum contact angle, and conversion between the normal contact angle and the minimum contact angle is possible using a linear regression equation. When a linear regression equation was obtained from the measurement results shown in FIG. 11, Y = 1.0404X + 3.2849. The square value (R ² ) of the correlation coefficient R was 0.9934, and it was confirmed that there was a strong correlation between the normal contact angle and the minimum contact angle of diiodomethane.

  As described in Patent Document 1, the surface free energy is calculated by the Fowke equation by measuring the contact angle using two types of probe liquids. In this case, it is preferable to use a liquid having a large polar component and a liquid having a large dispersed component. In the present embodiment, a mixed liquid of polyhydric alcohol and water is used as a liquid having a large polar component, and diiodomethane is used as a liquid having a large polarization component. Therefore, by measuring the minimum contact angle of the liquid mixture of water and glycerin and the minimum contact angle of diiodomethane in the minute region of the opposing surface of the magnetic head (slider), and converting it to the normal contact angle of water and diiodomethane, the magnetic head It is possible to accurately evaluate the surface state of the minute region and the surface state of the magnetic disk medium with a common physical quantity called surface free energy.

  In the above Experiment 4, diiodomethane is used as the liquid having a small polar component, but other hydrocarbon-based liquids such as hexadecane may be used.

(Experiment 5)
FIG. 12 is a diagram showing the results of examining the correlation between water, with the normal contact angle of water on the horizontal axis and the normal contact angle of a mixture of ethylene glycol (divalent alcohol) and water on the vertical axis. It is. In addition, the ratio (volume ratio) of ethylene glycol and water in a liquid mixture is 1: 1. Further, in the measurement of the contact angle, a plurality of magnetic disks in which the surface free energy was changed by changing the irradiation amount of ultraviolet rays as in Experiment 2 were used as samples. However, the irradiation time of ultraviolet rays was 1 second to 30 seconds.

From FIG. 12, there is a good correlation between the normal contact angle measured using water as the probe liquid and the normal measurement angle measured using a mixture of ethylene glycol and water. It was confirmed that the normal contact angle measured using a mixed solution with water can be accurately converted to the normal contact angle measured using water. When the linear regression equation was obtained from the measurement results shown in FIG. 12, it was Y = 1.0749X-18.145. Further, the square value (R ² ) of the correlation coefficient R is 0.9951, and there is a strong correlation between the normal contact angle of the mixture of ethylene glycol and water and the normal contact angle of water. Was confirmed.

(Experiment 6)
FIG. 13 is a diagram showing the results of examining the correlation between a normal contact angle on the horizontal axis and a minimum contact angle on the vertical axis, and using a mixture of ethylene glycol and water as the probe liquid. is there. In addition, the mixing ratio (volume ratio) of ethylene glycol and water in the mixed solution is 1: 1. Further, in the measurement of the contact angle, a plurality of magnetic disks in which the surface free energy was changed by changing the irradiation amount of ultraviolet rays as in Experiment 2 were used as samples.

From FIG. 13, even when a mixed liquid of ethylene glycol and water is used as the probe liquid, there is a good correlation between the normal contact angle and the minimum contact angle, and the normal contact angle is calculated using a linear regression equation. And the minimum contact angle is possible. When a linear regression equation was obtained from the measurement results shown in FIG. 13, Y = 1.1437X−26.872 was obtained. Further, the square value (R ² ) of the correlation coefficient R is 0.9959, and it is confirmed that there is a strong correlation between the normal contact angle and the minimum contact angle of the mixture of ethylene glycol and water. It was done.

  From the above experimental results, it can be concluded that a mixed liquid of polyhydric alcohol and water is appropriate as the water-like liquid used for the measurement of the contact angle of the minute region. Examples of the polyhydric alcohol include diethylene glycol (divalent alcohol) in addition to the above-described glycerin and ethylene glycol. However, the polyhydric alcohol is easily dissolved in water and should not be separated.

(Comparative example)
Hereinafter, as a comparative example, a case will be described in which a mixed liquid of formaldehyde and water that does not contain a hydroxyl group, is capable of hydrogen bonding, and is easily dissolved in water is used as the probe liquid.

FIG. 14 is a diagram showing the results of examining the correlation between a normal contact angle on the horizontal axis and a minimum contact angle on the vertical axis when a mixed liquid of formaldehyde and water is used as the probe liquid. . In addition, the mixing ratio (volume ratio) of formaldehyde and water is formaldehyde: water = 1: 1. When the linear regression equation was obtained from FIG. 14, it was Y = 1.1874X−25.795. However, the square value (R ² ) of the correlation coefficient R was 0.9693. As described above, in order to convert the contact angle with high accuracy, the square value (R ² ) of the correlation coefficient R is considered to be 0.98 or more. It can be said that it is not suitable for the measurement of the contact angle.

  The reason why the correlation between the normal contact angle and the minimum contact angle of the mixed liquid of formaldehyde and water is not sufficient is considered that formamide does not have a hydroxyl group similar to polyhydric alcohol or water.

(Surface free energy calculation method)
If the surface free energy of the solid sample is γ _S , the surface free energy of the liquid sample is γ _L , the contact angle between the solid sample and the liquid is θ _SL , and the interface free energy between the solid sample and the liquid is γ _SL , the following (2 The Young's formula shown in the formula is established.

γ _S = γ _L · cos θ _SL + γ _SL (2)
Further, adhesion work W _SL liquid is energy stabilized by adhering to the solid surface according to equation (3) below Dupre.

γ _S + γ _L = W _SL + γ _SL (3)
The following Young-Dupre equation (4) is derived from the above two equations, and the adhesion work is obtained from the surface free energy of the liquid and the contact angle.

W _SL = γ _L (1 + cos θ _SL ) (4)
When the geometrical mean rule of each component of the surface free energy is applied to this bonding work, the following equation (5) is established.

W _SL = 2√ (γ _Sd · γ _Ld ) + 2√ (γ _Sh · γ _Lh ) (5)
Here, d and h mean a dispersion component and a hydrogen bond component, respectively.

  If two kinds of liquids (i, j) are used, the following relational expression (6) is established for the bonding work.

従って、２種類の液体の接触角を実測し接着仕事求めれば次の関係式（７）から固体の表面自由エネルギーを各成分毎に求めることができる。この関係式（７）をFowke式と呼ぶ。またこの関係式（７）より、表面自由エネルギーγ=γ^d＋γ^hが求められる。

Therefore, if the contact angles of two types of liquids are measured to determine the adhesion work, the solid surface free energy can be determined for each component from the following relational expression (7). This relational expression (7) is called a Fowke expression. Further, from this relational expression (7), the surface free energy γ = γ ^d + γ ^h is obtained.

すなわち、水類似液体を用いて求めた極小接触角とジヨードメタンを用いて求めた極小接触角とにより、磁気ヘッドの微小領域の表面自由エネルギーを計算することが可能となる。

That is, the surface free energy of the micro area of the magnetic head can be calculated from the minimum contact angle obtained using the water-like liquid and the minimum contact angle obtained using diiodomethane.

(Water repellent treatment)
When measuring the minimum contact angle, the liquid is dropped onto the surface of the sample through a small glass capillary. There are commercially available capillaries with inner diameters of 5 μm, 30 μm, 50 μm, etc., but when diiodomethane is dropped using a capillary with an inner diameter of 5 μm, the diiodomethane 15 becomes the glass wall surface of the capillary 11 as shown in FIG. It adheres to and cannot be dripped. This is because the surface tension of diiodomethane is low and the surface tension of glass acts as an attractive force. Therefore, it is necessary to apply some treatment to the surface of the glass to lower the surface tension.

  FIG. 16 is a diagram showing the relationship between the baking temperature and the contact angle of glass coated with a fluorine-based coating agent, with the baking temperature on the horizontal axis and the contact angle on the vertical axis. Here, Garako from Soft 99 and EGC-1720 from 3M are used as the fluorine-based coating agent. After applying the fluorine-based coating agent to the glass, it was heated to the temperature indicated by the horizontal axis, and then water was dropped on the glass to measure the contact angle. In the experiments conducted by the inventors of the present application, diiodomethane could be dropped from a capillary having an inner diameter of 5 μm when the contact angle of water was 105 ° or more. FIG. 17 shows a state immediately before diiodomethane is dropped from a capillary having an inner diameter of 5 μm.

  For this reason, it is preferable to apply a fluorine-based coating agent as a water repellent to the capillary used for measuring the minimum contact angle, and to bake at a predetermined temperature.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1) Measuring a minimum contact angle by dropping a probe solution made of polyhydric alcohol or a mixed solution of polyhydric alcohol and water on a measurement sample in a volume of 300 picoliters or less;
The probe using a linear regression equation showing the correlation between the minimum contact angle when measured using the probe liquid of 300 picoliters or less and the normal contact angle when measured using water of 1 microliter or more. Converting the minimal contact angle of the liquid into a normal contact angle of water;
And a step of evaluating a surface state of the measurement sample based on a result of conversion of the water into a normal contact angle.

(Appendix 2) The linear regression equation is
The probe solution is dropped on a plurality of standardized samples having different surface energies in a volume of 300 picoliters or less to measure a minimum contact angle, and water is stored on the plurality of standardized samples in a volume of 1 microliter or more. The method for evaluating a surface condition according to appendix 1, wherein a normal contact angle is measured by dripping and a linear regression analysis is performed on the measurement result of the minimum contact angle and the measurement result of the normal contact angle.

(Appendix 3) Measuring a minimum contact angle by dropping a hydrocarbon-based liquid on a measurement sample in a volume of 300 picoliters;
Linear regression equation showing the correlation between the minimum contact angle measured using the hydrocarbon-based liquid of 300 picoliters or less and the normal contact angle measured using the hydrocarbon-based liquid of 1 microliter or more Converting the minimum contact angle of the hydrocarbon-based liquid into a normal contact angle using
And a step of evaluating the surface state of the measurement sample based on the conversion result of the hydrocarbon-based liquid into a normal contact angle.

(Appendix 4) The linear regression equation is
The hydrocarbon liquid is dropped in a volume of 300 picoliters or less on a plurality of standardized samples having different surface energies to measure a minimum contact angle, and the hydrocarbon liquid is placed on the plurality of standardized samples. The surface according to appendix 3, which is obtained by measuring a normal contact angle by dropping in a volume of 1 microliter or more, and performing linear regression analysis on the measurement result of the minimum contact angle and the measurement result of the normal contact angle. State evaluation method.

(Appendix 5) A step of measuring a minimum contact angle by dropping a probe solution made of polyhydric alcohol or a mixture of polyhydric alcohol and water on a measurement sample in a volume of 300 picoliters or less;
The first linear regression equation showing the correlation between the minimum contact angle when measured using the probe solution of 300 picoliters or less and the normal contact angle when measured using water of 1 microliter or more is used. Converting the minimal contact angle of the probe liquid into a normal contact angle of water;
Dropping a hydrocarbon-based liquid on the measurement sample in a volume of 300 picoliters and measuring a minimum contact angle;
A second correlation indicating a correlation between a minimum contact angle when measured using the hydrocarbon-based liquid of 300 picoliters or less and a normal contact angle when measured using the hydrocarbon-based liquid of 1 microliter or more. Converting a minimal contact angle of the hydrocarbon-based liquid into a normal contact angle using a linear regression equation;
The step of obtaining the surface free energy of the measurement sample using the normal contact angle of the water converted by the first linear regression equation and the normal contact angle of the hydrocarbon-based liquid converted by the second linear regression equation A method for evaluating a surface state, comprising:

  (Appendix 6) The surface state evaluation method according to any one of appendices 3 to 5, wherein the hydrocarbon liquid is diiodomethane or hexadecane.

  (Supplementary note 7) The surface state evaluation according to any one of supplementary notes 1 to 5, wherein a capillary having a contact angle of water of 105 degrees or more on the surface is used for dropping a liquid of 300 picoliters or less. Method.

  (Supplementary note 8) The surface state evaluation method according to supplementary note 7, wherein the surface of the capillary is subjected to water repellent treatment.

(Supplementary note 9) In the magnetic head for a magnetic recording apparatus,
A magnetic head, wherein the surface free energy of the facing surface facing the magnetic recording medium is controlled to be 15 mN / m to 30 mN / m when measured by the method described in Appendix 5.

FIG. 1 is a schematic diagram showing a method for measuring a contact angle. 2A is a side view of the magnetic head, and FIG. 2B is a bottom view of the magnetic head. FIG. 3 is a schematic diagram showing the probe liquid dropped on the sample. FIG. 4 is a diagram showing a change with time of the radius of the droplet. FIG. 5 is a diagram showing the change with time of the contact angle of the droplet. FIG. 6 is a diagram showing the results of measuring changes in the minimum contact angle over time for three types of liquids having different mixing ratios of glycerin and water. FIG. 7 is a diagram showing the results of measuring the temporal change in the height of the droplets in three types of liquids having different mixing ratios of glycerin and water. FIG. 8 is a diagram showing the results of measuring changes in the radius of the droplet over time in three types of liquids having different mixing ratios of glycerin and water. FIG. 9 is a diagram showing the relationship between the minimum contact angle and the normal contact angle of a mixed liquid of glycerin and water. FIG. 10 is a diagram showing the results of examining the correlation between the contact angle of a mixed liquid of glycerin and water and the contact angle of water. FIG. 11 is a diagram showing measurement results of the normal contact angle and the minimum contact angle of diiodomethane. FIG. 12 is a diagram showing the results of examining the correlation between the normal contact angle of a mixed liquid of ethylene glycol and water and the normal contact angle of water. FIG. 13 is a diagram showing the results of examining the correlation between the normal contact angle and the minimum contact angle of a mixed liquid of ethylene glycol and water. FIG. 14 is a diagram showing the results of examining the correlation between the normal contact angle and the minimum contact angle of a mixed liquid of formaldehyde and water. FIG. 15 is a diagram showing a state in which diiodomethane adheres to the glass wall surface of the capillary and cannot be dropped. FIG. 16 is a diagram showing the relationship between the baking temperature and the contact angle of glass coated with a fluorine-based coating agent. FIG. 17 is a view showing a state immediately before water is dropped from a capillary having an inner diameter of 5 μm.

Explanation of symbols

1-4 ... convex part 5 ... recording / reproducing element,
6 ... Slider,
10 ... Sample,
11 ... capillary,
12 ... droplet,
13 ... light source,
14 ... Camera,
15 ... diiodomethane,
30: Magnetic head.

Claims (5)

A step of dropping a probe liquid composed of polyhydric alcohol or a mixed liquid of polyhydric alcohol and water onto a measurement sample in a volume of 300 picoliters or less and measuring a minimum contact angle;
Using the linear regression equation showing the correlation between the minimum contact angle when measured using the probe liquid of 300 picoliters or less and the normal contact angle when measured using water of 1 microliter or more, the probe is used. Converting the minimal contact angle of the liquid into a normal contact angle of water;
And a step of evaluating a surface state of the measurement sample based on a result of conversion of the water into a normal contact angle. The linear regression equation is
The probe solution is dropped on a plurality of standardized samples having different surface energies in a volume of 300 picoliters or less to measure a minimum contact angle, and water is stored on the plurality of standardized samples in a volume of 1 microliter or more. The surface condition evaluation method according to claim 1, wherein a normal contact angle is measured by dripping and a linear regression analysis is performed on the measurement result of the minimum contact angle and the measurement result of the normal contact angle. Dropping a hydrocarbon-based liquid on the measurement sample in a volume of 300 picoliters and measuring a minimum contact angle;
Linear regression equation showing the correlation between the minimum contact angle measured using the hydrocarbon-based liquid of 300 picoliters or less and the normal contact angle measured using the hydrocarbon-based liquid of 1 microliter or more Converting the minimum contact angle of the hydrocarbon-based liquid into a normal contact angle using
And a step of evaluating the surface state of the measurement sample based on the conversion result of the hydrocarbon-based liquid into a normal contact angle. The linear regression equation is
The hydrocarbon liquid is dropped in a volume of 300 picoliters or less on a plurality of standardized samples having different surface energies to measure a minimum contact angle, and the hydrocarbon liquid is placed on the plurality of standardized samples. 4. The method according to claim 3, wherein a normal contact angle is measured by dropping at a volume of 1 microliter or more, and the measurement result of the minimum contact angle and the measurement result of the normal contact angle are obtained by linear regression analysis. Evaluation method of surface condition. A step of dropping a probe liquid composed of polyhydric alcohol or a mixed liquid of polyhydric alcohol and water onto a measurement sample in a volume of 300 picoliters or less and measuring a minimum contact angle;
The first linear regression equation showing the correlation between the minimum contact angle when measured using the probe solution of 300 picoliters or less and the normal contact angle when measured using water of 1 microliter or more is used. Converting the minimal contact angle of the probe liquid into a normal contact angle of water;
Dropping a hydrocarbon-based liquid on the measurement sample in a volume of 300 picoliters and measuring a minimum contact angle;
A second correlation showing a correlation between a minimum contact angle when measured using the hydrocarbon-based liquid of 300 picoliters or less and a normal contact angle when measured using the hydrocarbon-based liquid of 1 microliter or more. Converting a minimal contact angle of the hydrocarbon-based liquid into a normal contact angle using a linear regression equation;
The step of obtaining the surface free energy of the measurement sample using the normal contact angle of the water converted by the first linear regression equation and the normal contact angle of the hydrocarbon liquid converted by the second linear regression equation A method for evaluating a surface state, comprising:

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