JP2005337781A - Measuring method of surface free energy of solid and measuring instrument therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method of the surface free energy of a solid so constituted as to reduce the irregularity of a measuring result and capable of easily judging the reliability of the measuring result. <P>SOLUTION: The contact angle of the solid to be measured with a liquid known in the respective components of surface free energy is measured and surface free energy of the solid is measured using the numerical formula 7 due to an extended Fowkes theory. The surface free energy is calculated from the contact angle data due to at least four liquids. In the formula, γL is the surface free energy of the liquid represented by γ<SP>a</SP>L+γ<SP>b</SP>L+γ<SP>c</SP>L, γ<SP>a</SP>L is the dispersion component of the surface free energy of the liquid, γ<SP>b</SP>L is a dipole component of the surface free energy of the liquid, γ<SP>c</SP>L is a hydrogen bond component of the surface free energy of the liquid, γ<SP>a</SP>S is the dispersion component of the surface free energy of the solid, γ<SP>b</SP>S is the dipole component of the surface free energy of the solid, γ<SP>c</SP>S is the hydrogen bond component of the surface free energy of the solid and θ is a contact angle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a highly reliable solid surface free energy measuring method and a solid surface free energy measuring apparatus.

  Ninoaki Kitasaki, Toshio Hata et al., In Non-Patent Document 1, regarding the surface free energy (synonymous with surface tension), Fowkes's theory of nonpolar intermolecular forces is further based on polar or hydrogen-bonded intermolecular forces. It is reported that the surface free energy of each substance can be obtained from three components according to this extended Fowkes theory.

This theory is based on the following three assumptions.
-Assumption 1
The surface free energy of a solid (organic substance) is expressed as the sum of three different components as shown in Equation 1 below.
<Formula 1>
γ = γ ^a + γ ^b + γ ^c
In Formula 1, γ ^a represents a dispersion component (nonpolar wetting), γ ^b represents a dipole component (wetting by polarity), and γ ^c represents a hydrogen bonding component (wetting by hydrogen bonding).

-Assumption 2-
Each surface free energy that decreases as a result of contact between two substances can be expressed as the sum of the geometric mean of the corresponding surface free energies, as shown in Equation 2 below. On the other hand, when there is no corresponding component, it is considered that there is no interaction between the components.

-Assumption 3-
Standard substances are classified into the following three types.
TypeA γ = γ ^a type: a liquid and solid saturated hydrocarbons.
Type B γ = γ ^a + γ ^b type: liquids and solids other than Type A and Type C.
Type C γ = γ ^a + γ ^b + γ ^c type: Liquids and solids that are soluble in water or have low interfacial tension with water (γ ¹² <30 mN / m) and have hydrogen bonds.

Non-Patent Document 1 describes surface free energy data for standard materials of Type A to C as shown below.
[Surface free energy of Type A]

（ ）：標準偏差 [Surface free energy of Type B]

( ):standard deviation

（ ）：標準偏差 [Surface free energy of Type C]

( ):standard deviation

また、物質が固体と液体である場合、図１に示すように、液滴が固体表面上で接触角θを保って平衡に達しているとすると、下記数式５で表されるヤングの式が成立する。
＜数式５＞
γ_ｓ＝γ_SL＋γ_Lｃｏｓθ Based on these assumptions 1 to 3, the surface free energy of the solid can be obtained as follows.
First, adhesion energy _{W 12} of material 1 and material 2 is represented by the following Equation 3.
<Formula 3>
W ₁₂ = γ ₁ + γ ₂ −γ ₁₂
Next, from Equation 2 above, Equation 3 becomes Equation 4 below.

Further, when the substance is a solid and a liquid, as shown in FIG. 1, assuming that the droplet has reached the equilibrium while maintaining the contact angle θ on the solid surface, the Young's formula expressed by the following formula 5 is obtained. To establish.
<Formula 5>
γ _s = γ _SL + γ _L cos θ

Therefore, the relationship shown by the following formula 6 is established between the contact angle and the adhesive energy W _{sL based on} the formula 3 and the formula 5.
<Formula 6>
W _SL = γ _L (1 + cos θ)

  Then, the following formula 7 representing the extended Fowkes theory is obtained from the formula 4 and the formula 6.

First, the contact angle is measured with a Type A liquid, and γ _S ^a is obtained from Equation 7. Next, the contact angle is measured with a Type B liquid, and γ _S ^b is obtained from Equation 7. At this time, γ _S ^a and γ _S ^b may be obtained from simultaneous data of two types of Type B liquid. Finally, the contact angle is measured with a Type C liquid, and γ _S ^c is obtained from Equation 7. Thus, each component of the solid surface free energy can be obtained. Further, each component of the surface free energy of the solid can also be obtained from the data of three kinds of liquids in which γ _L ^b or γ _L ^c is not 0 in all liquids, using a ternary simultaneous equation.

However, when each component of the surface free energy of the solid is determined by the above method, the square root of each component of the surface free energy (such as √γ _S ^b ) may become negative due to the calculation. For example, √ When γ _S ^b becomes negative, it is forced to square and γ _S ^b is not obtained, and γ _S ^b = 0.

  As described above, the method for measuring the surface free energy of a solid from the contact angle data of three types of liquids greatly differs depending on the combination of the liquids used for the measurement, and the measurement using which combination of liquids. There is a problem of not knowing whether to trust the result. In addition, since the value of the contact angle changes due to the influence of the surface shape of the sample, the accurate surface free energy may not be measured in some cases. However, the conventional method cannot measure the accurate surface free energy. Even if not, it is difficult to judge this.

Japan Adhesion Association Paper 8 (3), 131-141 (1972)

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention is less affected by contact angle measurement errors, has little variation in measurement results due to the combination of liquids used for measurement, and further, can measure the surface free energy of a solid that can easily determine the reliability of the measurement results. It is an object to provide a method and an apparatus for measuring the surface free energy of a solid.

ただし、前記数式中、γ_Ｌは、γ^ａ _Ｌ＋γ^ｂ _Ｌ＋γ^Ｃ _Ｌで表される液体の表面自由エネルギーを表す。γ^ａ _Ｌは、液体の表面自由エネルギーの分散成分を表す。γ^ｂ _Ｌは、液体の表面自由エネルギーの双極子成分を表す。γ^Ｃ _Ｌは、液体の表面自由エネルギーの水素結合成分を表す。γ^ａ _Ｓは、固体の表面自由エネルギーの分散成分を表す。γ^ｂ _Ｓは、固体の表面自由エネルギーの双極子成分を表す。γ^Ｃ _Ｓは、固体の表面自由エネルギーの水素結合成分を表す。θは、接触角を表す。
＜２＞ 接触角データから表面自由エネルギーを算出する際に、Ｒ-２乗値（重相関係数）を求める前記＜１＞に記載の固体の表面自由エネルギー測定方法である。
＜３＞

Ｒ−２乗値が一番大きくなる場合の結果を固体の表面自由エネルギーとする前記＜１＞から＜２＞のいずれかに記載の固体の表面自由エネルギー測定方法である。
＜４＞ Ｒ−２乗値が０．８以上であるとき、測定結果の信頼性があると判断する前記＜１＞から＜３＞のいずれかに記載の固体の表面自由エネルギー測定方法である。
＜５＞ 拡張Ｆｏｗｋｅｓ理論におけるＴｙｐｅＢの液体とＴｙｐｅＣの液体のみを用いる前記＜１＞から＜４＞のいずれかに記載の固体の表面自由エネルギー測定方法である。
＜６＞ 拡張Ｆｏｗｋｅｓ理論におけるＴｙｐｅＢの液体２種以上、ＴｙｐｅＣの液体２種以上を用いる前記＜１＞から＜５＞のいずれかに記載の固体の表面自由エネルギー測定方法である。
＜７＞ 測定対象である固体の表面が平滑である前記＜１＞から＜６＞のいずれかに記載の固体の表面自由エネルギー測定方法である。
＜８＞ 前記＜１＞から＜７＞のいずれかに記載の固体の表面自由エネルギー測定方法を用い、固体の表面自由エネルギーの解析を行うプログラムを記録したことを特徴とする記録媒体である。
＜９＞ 前記＜８＞に記載の記録媒体を具備することを特徴とする固体の表面自由エネルギー測定装置である。 Means for solving the problems are as follows. That is,
<1> A method of measuring the contact angle between a solid to be measured and a liquid whose surface free energy components are known, and measuring the surface free energy of the solid using the following formula 7 based on the extended Fowkes theory. A surface free energy measuring method for a solid, characterized in that surface free energy is obtained by linear regression from contact angle data of four or more liquids.

However, in the formula, gamma _L represents the surface free energy of the liquid represented by ^{_{γ a L + γ b L +}} γ C L. γ ^a _L represents a dispersion component of the surface free energy of the liquid. γ ^b _L represents a dipole component of the surface free energy of the liquid. γ ^C _L represents the hydrogen bond component of the surface free energy of the liquid. γ ^a _S represents a dispersion component of the surface free energy of the solid. γ ^b _S represents the dipole component of the surface free energy of the solid. γ ^C _S represents a hydrogen bond component of the surface free energy of the solid. θ represents the contact angle.
<2> The solid surface free energy measurement method according to <1>, wherein an R-square value (multiple correlation coefficient) is obtained when calculating the surface free energy from contact angle data.
<3>

The solid surface free energy measurement method according to any one of <1> to <2>, wherein the result when the R-square value is the largest is the surface free energy of the solid.
<4> The solid surface free energy measurement method according to any one of <1> to <3>, wherein the measurement result is determined to be reliable when the R-square value is 0.8 or more. .
<5> The solid surface free energy measurement method according to any one of <1> to <4>, wherein only the Type B liquid and the Type C liquid in the extended Fowkes theory are used.
<6> The solid surface free energy measurement method according to any one of <1> to <5>, wherein two or more Type B liquids and two or more Type C liquids in the extended Fowkes theory are used.
<7> The solid surface free energy measuring method according to any one of <1> to <6>, wherein the surface of the solid to be measured is smooth.
<8> A recording medium on which a program for analyzing the surface free energy of a solid is recorded using the method for measuring the surface free energy of a solid according to any one of <1> to <7>.
<9> A solid surface free energy measuring apparatus comprising the recording medium according to <8>.

  In the solid surface free energy measuring method of the present invention, the surface free energy is obtained by linear regression from the contact angle data of four or more liquids, thereby averaging the influence of deviation from the true value of the contact angle. The influence of the measurement error of the contact angle on the measurement result of free energy can be reduced.

  According to the present invention, conventional problems can be solved, and the influence of contact angle measurement error can be reduced by obtaining the surface free energy of a solid by linear regression from the contact angle data of four types of liquids. The reliability of the measurement result can be easily determined.

(Measurement method of surface free energy of solid)
In the method for measuring the surface free energy of a solid according to the present invention, the contact angle between the solid to be measured and a liquid whose components of the surface free energy are known is measured using the following formula 7 based on the extended Fowkes theory. In the method of measuring surface free energy, surface free energy is obtained by linear regression from contact angle data of four or more liquids.

ただし、前記数式７中、γ_Ｌは、γ^ａ _Ｌ＋γ^ｂ _Ｌ＋γ^Ｃ _Ｌで表される液体の表面自由エネルギーを表す。γ^ａ _Ｌは、液体の表面自由エネルギーの分散成分を表す。γ^ｂ _Ｌは、液体の表面自由エネルギーの双極子成分を表す。γ^Ｃ _Ｌは、液体の表面自由エネルギーの水素結合成分を表す。γ^ａ _Ｓは、固体の表面自由エネルギーの分散成分を表す。γ^ｂ _Ｓは、固体の表面自由エネルギーの双極子成分を表す。γ^Ｃ _Ｓは、固体の表面自由エネルギーの水素結合成分を表す。θは、接触角を表す。

However, in Equation 7, gamma _L represents the surface free energy of the liquid represented by ^{_{γ a L + γ b L +}} γ C L. γ ^a _L represents a dispersion component of the surface free energy of the liquid. γ ^b _L represents a dipole component of the surface free energy of the liquid. γ ^C _L represents the hydrogen bond component of the surface free energy of the liquid. γ ^a _S represents a dispersion component of the surface free energy of the solid. γ ^b _S represents the dipole component of the surface free energy of the solid. γ ^C _S represents a hydrogen bond component of the surface free energy of the solid. θ represents the contact angle.

  Here, the formula 7 of the extended Fowkes theory is

とおくと、下記数式８に示すようになる。
＜数式８＞
ｙ＝ａｘ_１＋ｂｘ_２＋ｃｘ_３

Then, the following formula 8 is obtained.
<Formula 8>
y = ax ₁ + bx ₂ + cx ₃

Each component (a, b, c) of the surface free energy of the solid can be obtained by linear regression from contact angle data (y; x1, x2, x3) by the standard substance. The conventional method of obtaining from three types of liquid contact angle data obtains three unknowns from three equations. Therefore, if the contact angle of one liquid greatly deviates from the true value due to some influence, the obtained surface free energy of the solid is greatly affected.
In the method for measuring the surface free energy of a solid from the contact angle data with four or more liquids according to the present invention, the influence of deviation from the true value of the contact angle is averaged, and the contact angle of the measurement result of the surface free energy is calculated. The influence of measurement error can be reduced.
Here, the measurement of the contact angle is not particularly limited and can be appropriately selected according to the purpose. For example, the contact angle can be measured by a general droplet method, a meniscus method, or the like. A detailed description of the measurement method is described in “Wet Technology Handbook: Basics, Measurement Evaluation, Data” (supervised by Ikuo Ishii, Junji Koishi, Mitsuo Tsunoda, Publisher: Techno System Co., Ltd.)

-Calculation method by linear regression-
The calculation method by linear regression is as follows. That is,
Assuming that there is contact angle data for n types (n ≧ 3) of liquid, it is expressed by the following mathematical formula 9.
<Formula 9>
yi = ax _i1 + bx _i2 + cx _i3
However, i represents 1 to n.

The error ε is expressed by Equation 10 below.
<Formula 10>
εi = yi− (ax _i1 + bx _i2 + cx _i3 )
However, i represents 1 to n.

前記数式１１が最小になるように（ａ，ｂ，ｃ）を決める。最小の条件は、下記数式１２〜１４に示す通りである。 The sum of squares of this error is expressed by Equation 11 below.

(A, b, c) is determined so that the formula 11 is minimized. The minimum conditions are as shown in the following formulas 12-14.

前記数式１３より、下記数式１６が求まる。

前記数式１４より、下記数式１７が求まる。

From the equation 12, the following equation 15 is obtained.

From Equation 13, the following Equation 16 is obtained.

From the equation 14, the following equation 17 is obtained.

  Next, (a, b, c) is obtained by solving the ternary simultaneous equations expressed by the mathematical formula 15, the mathematical formula 16, and the mathematical formula 17. The surface free energy of the solid can be obtained by squaring each of (a, b, c). However, in this case, any of a, b, and c may be negative. Since a, b, and c are the square roots of the surface free energy of the solid, it is physically strange that this is negative. Therefore, the above calculation must be solved under the conditions of a ≧ 0, b ≧ 0, and c ≧ 0.

  Since S (a, b, c) is quadratic with respect to a, b, and c, when any of a, b, and c becomes negative, for example, when c becomes negative Obtains (a, b) such that c = 0 and S (a, b, 0) is minimized. Here, when b becomes negative, b is further set to 0, and a is obtained so that S (a, 0, 0) is minimized. However, when c becomes negative, there are cases where S becomes smaller when b = 0 and when (a, c) is calculated so that S (a, 0, c) is minimized. Therefore, actually, when any of a, b, and c becomes negative, a = 0, b = 0, c = 0, a = b = 0, a = c = 0, b = c = 0, a ≧ 0, b ≧ 0, c ≧ 0, and those with the smallest S best match the contact angle data in the range of a ≧ 0, b ≧ 0, c ≧ 0 The solution to

前記数式１１及び前記数式１８からＳが最小の場合、Ｒ−２乗値は最大となる。
なお、ａ，ｂ，及びｃのいずれかが負になった場合、従来のように、負になったものを０とすることが考えられるが、これは上記のことからわかるように、接触角データに最もよく合致する解ではない。 Further, the R-2 power value can be obtained from Equation 18 below.

When S is the minimum from Equation 11 and Equation 18, the R-squared value is the maximum.
When any of a, b, and c becomes negative, it is conceivable that the negative value becomes 0 as in the prior art, but as can be seen from the above, the contact angle It is not the solution that best fits the data.

  As described above, when the surface free energy of a solid is obtained from linear regression, an R-2 power value (multiple correlation coefficient) is calculated. If the R-square value is close to 1, all the contact angle data is in Equation 7 of the extended Fowkes theory, and it can be determined that the obtained surface free energy of the solid is highly reliable. That is, the measurement reliability can be easily determined from the R-2 power value. In this case, if the R-2 power value is 0.8 or more, it can be determined that the measurement result is reliable. If it is determined that the R-square value is small and the reliability is low, it is considered that the contact angle cannot be measured accurately. As a cause of this, in many cases, the surface shape of the sample has an effect, and it is necessary to devise a sample form that reduces the surface roughness and voids. Examples of a method for producing a sample with less surface roughness and voids include a casting method for resins and the like, and compression molding and heat melting for others.

As a standard substance used in the method for measuring the surface free energy of a solid according to the present invention, each component of the surface free energy is four or more known liquids, and γ _L ^b or γ _L ^c does not become zero in all liquids. If it is a combination, there will be no restriction | limiting in particular, According to the objective, it can select suitably.
Examples of liquids having known components of the surface free energy include those shown in Tables 1 to 3 above. However, it is necessary that the reference material does not cause extended wetting. Extended wetting is a phenomenon in which wetting spreads spontaneously when a droplet is placed on a solid, and in this case, the contact angle cannot be measured. The Type A liquids listed in Table 1 for many solids (organic substances) are not preferred because they cause extended wetting.

Therefore, the combination of standard substances for measuring the surface free energy of the solid (organic substance) is preferably a combination containing two or more types of Type B liquids and two or more types of Type C liquids without using Type A liquids. Examples of the Type B liquid include diiodomethane, α-bromonaphthalene, and Type C liquids such as glycerin, diethylene glycol, and formamide.
In the measurement of the surface free energy of the solid, the value obtained depends on the combination of the liquids used for the measurement. However, the combination of two or more Type B liquids and two or more Type C liquids shows almost the same value. Stabilize.

  The solid to be measured in the solid surface free energy measuring method of the present invention preferably has a smooth surface. Examples of the method for preparing a sample having a smooth surface include molding on a film by a casting method if it is a resin, and compression molding or heat melting if it is a powder.

  As described above, the solid surface free energy measurement method of the present invention is less affected by the measurement error of the contact angle, there is little variation in measurement results due to the combination of liquids used for measurement, and the reliability of the measurement results It is possible to provide a method for measuring the surface free energy of a solid that can be easily determined, and can be widely applied to fields such as surface treatment, surface modification, adhesive, painting, and coating.

(recoding media)
By using the recording medium programmed with the calculation process in the solid surface free energy measuring method of the present invention, the surface free energy of the solid can be easily obtained by a computer.
There is no restriction | limiting in particular as said recording medium, According to the objective, it can select suitably, For example, FD, CD, MO, MD, DVD etc. are mentioned.

(Measurement device for solid surface free energy)
The solid surface free energy measuring apparatus of the present invention comprises the recording medium of the present invention, and further includes other means such as a recording means and a control means as required.
Examples of the recording means include a printer, a liquid crystal screen, a display device such as a CRT, and the like.
The control means is not particularly limited as long as the movement of each means can be controlled, and can be appropriately selected according to the purpose. Examples thereof include devices such as a sequencer and a computer.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Example 1)
About polystyrene as a measuring object, the contact angle was measured using a total of four kinds of liquids, i.e., diiodomethane, α-bromonaphthalene, which is a liquid of Type B, glycerin, which is a liquid of Type C, and diethylene glycol.
Specifically, polystyrene was dissolved in tetrahydrofuran (THF), and the solution was deposited on a polyethylene terephthalate (PET) film by a casting method to prepare a sample having a smooth surface. The contact angle was measured using an automatic contact angle meter (Kyowa Interface Science Co., Ltd., CA-W). The results are shown in Table 4.

表４の接触角の測定結果と各液体の表面自由エネルギーを上記数式１５〜数式１７に代入し、３元連立方程式を解いた。その結果、下記表５に示すようにｂ及びｃが負となった。

The measurement results of the contact angles and the surface free energy of each liquid in Table 4 were substituted into the above formulas 15 to 17 to solve the ternary simultaneous equations. As a result, b and c were negative as shown in Table 5 below.

  Next, a = 0, b = 0, c = 0, a = b = 0, a = c = 0, b = c = 0, and calculation was performed for each case. The results are shown in Table 6.

表６の結果から、ａ≧０，ｂ≧０，ｃ≧０であり、かつＲ−２乗値が一番大きくなるのはｃ＝０の場合である。したがってポリスチレンの表面自由エネルギーはｃ＝０の場合のａ，ｂ，及びｃを自乗することにより、下記表７に示すように求めることができる。

From the results of Table 6, a ≧ 0, b ≧ 0, c ≧ 0, and the R-2 power value is largest when c = 0. Therefore, the surface free energy of polystyrene can be obtained as shown in Table 7 below by squaring a, b, and c when c = 0.

(Example 2)
The surface free energy was measured for polymethyl methacrylate (PMMA), polystyrene, and polyethylene terephthalate (PET) as measurement objects.
Polymethyl methacrylate (PMMA) and polystyrene were dissolved in tetrahydrofuran (THF), and the solution was deposited on a polyethylene terephthalate (PET) film by a casting method to prepare a sample having a smooth surface. For polyethylene terephthalate (PET), a polyethylene terephthalate (PET) film was used.
A total of 5 types of diiodomethane, α-bromonaphthalene, which is a liquid of Type B, and glycerin, diethylene glycol, and formamide, which are liquids of Type C, were used as standard substances. The contact angle was measured using an automatic contact angle meter (Kyowa Interface Science Co., Ltd., CA-W).
The surface free energy was calculated from the measured contact angle data using the method of the present invention. At that time, the surface free energy was calculated by changing the combination of liquids. The results are shown in Table 8.

(Comparative Example 1)
In Example 2, the surface free energy was calculated in the same manner as in Example 2 from the contact angle data of three types of liquids (diiodomethane, α-bromonaphthalene, diethylene glycol). The results are shown in Table 9.

From the results shown in Table 8, it can be determined that Example 2 is more than 0.9 in all of R-2 power values, and the measurement results are reliable. Moreover, in the combination of the liquid in Example 2, it is calculated | required that the calculated surface free energy of the solid becomes substantially the same value.
On the other hand, from the results in Table 9, it can be seen that in Comparative Example 1, the surface free energy obtained by the combination of liquids varies. In particular, in polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET), the polar component γb varies greatly depending on the combination of liquids.

(Example 3)
The surface free energy of zinc stearate as a measurement object was measured. Since zinc stearate is a powder, a sample was prepared so as to have a smooth surface by compression molding.
As standard substances, four liquids of diiodomethane, α-bromonaphthalene, glycerin, and diethylene glycol were used. The contact angle was measured using an automatic contact angle meter (Kyowa Interface Science Co., Ltd., CA-W). The results are shown in Table 10.

表１０の結果から、Ｒ−２乗値が０．４７３と小さく信頼性が低い結果となった。これはサンプルが十分に平滑でなく、また、測定中に液体がサンプルにわずかながら染み込んでいることが観察され、正確な接触角が測定できなかったためであると考えられる。

From the results of Table 10, the R-2 power value was as small as 0.473, and the reliability was low. This is considered to be because the sample was not sufficiently smooth, and it was observed that the liquid slightly permeated the sample during the measurement, and an accurate contact angle could not be measured.

Example 4
In Example 3, the measurement was performed in the same manner as in Example 3 except that after the zinc stearate was melted by heat and then slowly cooled and solidified, a sample having a sufficiently smooth surface was produced. The results are shown in Table 11.

表１１の結果から、Ｒ−２乗値が０．８９７と大きくなり信頼性のある結果が得られた。これはサンプルの表面が十分に平滑であり、液体の染み込みもなかったためと考えられる。
実施例３及び４の結果から、Ｒ−２乗値により測定がうまくいったかどうかを容易に判断することができる。

From the results in Table 11, the R-2 power value was increased to 0.897, and a reliable result was obtained. This is presumably because the surface of the sample was sufficiently smooth and liquid did not penetrate.
From the results of Examples 3 and 4, it can be easily determined whether or not the measurement is successful by the R-2 power value.

  In the solid surface free energy measuring method of the present invention, the surface free energy of the solid is obtained by linear regression from the contact angle data of four or more liquids, so that the influence of the measurement error of the contact angle is small, and the measurement can be performed. Variations in measurement results due to the combination of liquids used can be reduced and can be widely applied to fields such as surface treatment, surface modification, adhesives, painting, and coating.

FIG. 1 is a diagram illustrating a state in which when a substance is a solid and a liquid, a droplet has reached equilibrium on the surface of the solid while maintaining a contact angle θ.

Claims (9)

A method of measuring the contact angle between a solid to be measured and a liquid whose surface free energy components are known, and measuring the surface free energy of the solid using the following formula 7 based on the extended Fowkes theory. A method for measuring the surface free energy of a solid, characterized in that the surface free energy is obtained by linear regression from the above contact angle data with a liquid.

However, in the formula, gamma _L represents the surface free energy of the liquid represented by ^{_{γ a L + γ b L +}} γ C L. γ ^a _L represents a dispersion component of the surface free energy of the liquid. γ ^b _L represents a dipole component of the surface free energy of the liquid. γ ^C _L represents the hydrogen bond component of the surface free energy of the liquid. γ ^a _S represents a dispersion component of the surface free energy of the solid. γ ^b _S represents the dipole component of the surface free energy of the solid. γ ^C _S represents a hydrogen bond component of the surface free energy of the solid. θ represents the contact angle.   The method for measuring the surface free energy of a solid according to claim 1, wherein an R-square value (multiple correlation coefficient) is obtained when calculating the surface free energy from the contact angle data.

The method for measuring the surface free energy of a solid according to claim 1, wherein the result when the R-square value is the largest is the surface free energy of the solid.   The solid surface free energy measuring method according to any one of claims 1 to 3, wherein when the R-square value is 0.8 or more, it is determined that the measurement result is reliable.   The method for measuring the surface free energy of a solid according to claim 1, wherein a Type B liquid and a Type C liquid in the extended Fowkes theory are used.   6. The solid surface free energy measuring method according to claim 1, wherein two or more Type B liquids and two or more Type C liquids in the extended Fowkes theory are used.   The solid surface free energy measuring method according to claim 1, wherein the surface of the solid to be measured is smooth.   A recording medium on which a program for analyzing the surface free energy of a solid is recorded using the method for measuring the surface free energy of a solid according to claim 1. A solid surface free energy measuring apparatus comprising the recording medium according to claim 8.

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