JP7303931B2 - Evaluation method of coating film of composition for skin application - Google Patents

Description

The present invention relates to a method for evaluating coatings of compositions for application to skin.

Knowing the physical properties and rheological properties of a coating film formed by applying a coating composition to an object in a dry state is an important matter from the viewpoint of objectively judging the feeling of use of the composition. . However, since the dried coating film is thin and soft or brittle, it is not easy to measure its physical properties and rheological properties.

For the purpose of measuring the viscoelasticity of a coating composition during the drying process, Patent Document 1 discloses a viscoelasticity measuring device having a rotating shaft and a circular body concentrically attached to the tip of the rotating shaft. A fixture has been proposed. The circular body is formed of an annular body and a support that supports the annular body on the rotating shaft. According to this document, the viscoelasticity of a sample containing a volatile component can be measured continuously and accurately even in a process in which the sample changes, such as volatilization or curing.

Patent Document 2 describes a method for objectively and reproducibly evaluating the degree of stickiness of a cosmetic, in which an emulsion cosmetic is allowed to stand in the atmosphere at room temperature (15 to 35° C.) and moisture is measured. A method has been proposed for evaluating the degree of stickiness of a cosmetic when applied to the skin, based on the rheological properties of the cosmetic after volatilization. In this method, the rheological properties for evaluating the degree of stickiness are classified into (A) and (B) according to the state of the emulsion cosmetic after the moisture is volatilized. (A) When the kneaded product of the cosmetic after volatilization of water has an appearance of a mixture of liquid and solid, the loss tangent tan δ is measured as a rheological property after kneading. (B) When the kneaded product of the cosmetic after the volatilization of water is in the form of grease or rice cake, the first normal stress difference _N1 is measured as the rheological property after kneading.

JP 2010-078444 A JP 2012-229962 A

In order to accurately measure the physical properties of the coating film of the coating composition, it is ideal to measure the coating film itself formed on the object. However, in reality, such measurement is extremely difficult. Therefore, there is a demand for a measurement method that is more similar to the actual coating film.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for accurately measuring the rheological properties of a dry film of a coating composition.

The present invention is a coating film evaluation method for evaluating the properties of a coating film of a composition for skin application using a rotational rheometer,
The rotational rheometer comprises a viscoelasticity measuring instrument,
The viscoelasticity measuring device includes a rotating shaft, an annular body, and radially extending from the tip of the rotating shaft, connecting the rotating shaft and the annular body, and concentrically fixing the annular body to the rotating shaft. and a connector that
The skin application composition is placed between the lower plate and the viscoelasticity measuring device, and the skin application composition is applied to the skin while the viscoelasticity measuring device is in contact with the skin application composition. Apply a strain within the linear strain of the composition for application, and continuously measure the rheological properties of the composition for application to skin while volatilization of volatile components from the composition for application to skin and after volatilization is almost complete. death,
Evaluate the performance of the coating film of the skin application composition based on the linear rheological properties of the skin application composition while the volatile components are volatilizing, or after the volatilization of the volatile components is substantially completed. In the above, a method for evaluating the coating film of the composition for skin application is provided, which evaluates the performance of the coating film of the composition for skin application based on the rheological properties of the composition for skin application in the linear strain region or the nonlinear strain region. It is something to do.

The present invention also provides a coating film evaluation method for evaluating the properties of a coating film of a composition for skin application using a rotational rheometer,
The rotational rheometer comprises a viscoelasticity measuring instrument,
The viscoelasticity measuring device includes a rotating shaft, an annular body, and radially extending from the tip of the rotating shaft, connecting the rotating shaft and the annular body, and concentrically fixing the annular body to the rotating shaft. and a connector that
The composition for skin application is placed between the lower plate and the viscoelasticity measuring device, and the composition for skin application is applied to the composition for skin application while the viscoelasticity measuring device is in contact with the composition for skin application. Applying a strain within the linear strain of the skin application composition and continuing to apply the strain while volatile components are volatilized from the skin application composition,
During volatilization of the volatile component, or after volatilization is almost completed, the liquid is brought into contact with the skin application composition,
subsequently applying a strain within the linear strain of the skin application composition to the skin application composition to measure the rheological properties of the skin application composition;
Provided is a method for evaluating a coating film, wherein the performance of the coating film of the skin application composition after contact with the liquid is evaluated based on the rheological properties.

According to the present invention, it is possible to measure the rheological properties of a dry coating film, which has been difficult to measure because it is soft or brittle, and to objectively evaluate the composition based on the rheological properties. becomes possible.

FIG. 1(a) is a plan view of a viscoelasticity measuring instrument used in the present invention, and FIG. 1(b) is a cross-sectional view taken along line bb in FIG. 1(a). FIG. 2 is a schematic diagram showing the rheological measurement of the composition for skin application. FIG. 3(a) is a graph showing changes over time in storage elastic modulus G′ and loss elastic modulus G″ measured for a commercially available liquid foundation, and FIG. 3(b) is for the same liquid foundation. 4 is a graph showing changes over time in measured loss tangent tan δ. FIG. 4 is a graph showing the relationship between the rate of change in storage elastic modulus due to drying and the sensory evaluation. FIG. 5(a) is a graph showing the angular frequency dependence of the storage elastic modulus G′ and the loss elastic modulus G″ within the linear strain region after volatilization of volatile components measured for a commercially available liquid foundation. FIG. 5(b) is a graph showing the angular frequency dependence of the loss tangent tan δ within the linear strain region after volatilization of volatile components measured for the same liquid foundation. FIG. 6 is a graph showing the strain dependence of shear stress up to the nonlinear strain region after volatilization of volatile components, measured for a commercially available liquid foundation. Yield-onset strain and yield-onset stress are the strain and stress, respectively, at which the stress-strain dependence begins to depart from the linear strain region. FIG. 7 is a graph showing the relationship between lower values of yield initiation stress or yield stress and sensory evaluation. FIG. 8(a) is a graph showing temporal changes in the storage elastic modulus G′ and the loss elastic modulus G″ within the linear strain region before and after the addition of artificial sebum, measured for a commercially available liquid foundation. 8(b) is a graph showing temporal changes in loss tangent tan δ within the linear strain region before and after adding artificial sebum, measured for the same liquid foundation. FIG. 9 shows the strain dependence of shear stress up to the nonlinear strain region after the addition of artificial sebum and after the change in the storage elastic modulus G' value has generally subsided, measured for a commercially available liquid foundation. is a graph showing As in FIG. 6, yield-onset strain and yield-onset stress are the strain and stress, respectively, at the point where the stress-strain dependence begins to depart from the linear strain region. FIG. 10 is a graph showing the relationship between lower values of yield initiation stress or yield stress and sensory evaluation.

The present invention will be described below based on its preferred embodiments. TECHNICAL FIELD The present invention relates to a method for evaluating the performance of a coating film formed by applying a composition for skin application to the skin from a rheological point of view. For this purpose, in the present invention, the rheological properties of the coating film are measured using a rotational rheometer. The composition for application to the skin to be evaluated in the present invention is a composition intended to be applied to the skin and containing a liquid component. Such compositions for skin application broadly include cosmetics called lotions, lotions, creams, milky lotions, quasi-drugs, pharmaceuticals, and the like. Compositions for skin application to be evaluated in the present invention include, but are not limited to, various non-Newtonian fluids such as O/W emulsions and W/O emulsions.

The "performance of the coating film" referred to in the present invention includes, for example, the cosmetic performance related to skin sensations such as a feeling of tightness and moistness received from the coating film, and the durability of the coating film, such as the difficulty of removing the coating film from rubbing. Cosmetic performance related to the physical properties of the coating film, such as the resistance to water and oils and fats, and the resistance to twisting of the coating film. The "tight feeling" is the feeling that the stretch of the skin is regulated by the formation of the coating film. "Difficulty in removing the coating film" means the difficulty in breaking the coating film structure when an external force is applied to the coating film. The term "resistance to twisting" refers to how little change in coating thickness distribution over time occurs when the coating is in contact with water or oil compared to before contact.

In the present invention, a rotational rheometer is used to measure the rheological properties of the coating film. This rotational rheometer is equipped with a viscoelasticity measuring tool. As shown in FIGS. 1(a) and 1(b), this viscoelasticity measuring instrument 1 includes a rotating shaft 2, an annular body 3, and radially extending from the tip of the rotating shaft 2. and a connecting portion 4 that connects and concentrically fixes the annular body 3 to the rotating shaft 2 . A plurality of notches 5 are formed in the measuring tool 1 by the rotating shaft 2 , the annular body 3 and the connecting portion 4 .

The annular body 3 consists of a continuous torus as shown in FIG. 1(a). The annular body 3 has a hanging wall 6 hanging down in the direction opposite to the direction in which the rotating shaft 2 extends over the entire circumference of the annular body 3 . The hanging wall 6 has the same height over the entire circumference of the annular body 3 .

The outer diameter of the annular body 3 is preferably about 25 mm or more and 75 mm or less. The width of the annular body 3 in plan view is preferably about 0.5 mm or more and 3 mm or less. It is preferable that the thickness of the annular body 3 in a side view is about 1 mm or more and 6 mm or less. It is preferable that the width of the connecting portion 4 in a plan view is about 0.5 mm or more and 20 mm or less. It is preferable that the thickness of the connecting portion 4 in a side view is about 0.5 mm or more and 2 mm or less. Although the number of connecting portions 4 is four in FIG. 1A, the number is not limited to this and can be selected within the range of, for example, three or more and eight or less. Depending on the width and the number of the connecting portions 4, the ratio of the area of the notch portion 5 to the apparent area of the ring-shaped body 3 in plan view can be about 70% or more and 97% or less.

In order to measure the viscoelasticity of the composition for skin application, as shown in FIG. The skin application composition 8 is placed so that the lower portion of the depending wall 6 and the upper surface of the skin application composition 8 are in contact. The facing surface 9 of the lower plate 7 is arranged in parallel with the viscoelasticity measuring instrument 1 . The inner diameter of the lower plate 7 is preferably 2 mm to 6 mm larger than the outer diameter of the annular body 3 of the viscoelasticity measuring instrument 1 .

In the viscoelasticity measurement of the composition for application to skin, the composition for application to skin 8 is applied to the composition for application to skin 8 while the lower portion of the hanging wall 6 of the viscoelasticity measuring instrument 1 is in contact with the composition for application to skin 8. Give a distortion within the linear distortion of the object 8. The strain “within linear strain” is a strain within a range in which a directly proportional relationship is established between the strain and the stress when strain is applied to the composition for application on skin 8 . In order to apply distortion to the composition 8 for application to skin, the lower plate 7 is fixed and the viscoelasticity measuring instrument 1 is rotated or vibrated around the rotating shaft 2 . In the following description, the combination of the lower plate 7 and the viscoelasticity measuring device 1 is also called a "cell" in the present invention.

The distance between the facing surface 9 of the lower plate 7 and the lower end of the hanging wall 6 of the viscoelasticity measuring instrument 1 is preferably set to 0.3 mm or more and 1 mm or less from the viewpoint of improving the reproducibility of measurement. The skin application composition is filled between the lower plate 7 and the viscoelasticity measuring device 1 within this range, and the lower end of the hanging wall 6 of the viscoelasticity measuring device 1 is brought into contact with the skin application composition 8 . This contact should be such that the lower end surface of the hanging wall of the viscoelasticity measuring device 1 continuously touches the skin application composition 8 while the viscoelasticity measuring device 1 is rotating or vibrating. It is not necessary that the entire depending wall of 1 is immersed in the skin application composition 8 .

Even if this cell shape is used, rheological measurements using a rotational rheometer can be performed in the same way as when using a normal cell. However, in calculating the rheological parameters from the stress value, strain value, and strain rate value obtained by measurement, the contribution of the influence of the cell notch 5 is unknown. Each rheological parameter was calculated assuming a plate-shaped cell). Therefore, all rheological parameters (stress, strain, storage modulus, loss modulus, viscosity modulus) except loss tangent of dynamic viscoelasticity measurements in the specification are apparent values.

The environment in which the composition for skin application 8 is distorted by the cell is not particularly limited as long as the temperature and humidity are in consideration of the living environment and acceleration during drying measurement. Specifically, the temperature is 20° C. or higher and 50° C. or lower, and the humidity may be controlled as necessary.

The composition for skin application 8 is given constant and continuous strain within the range of linear strain by the viscoelasticity measuring instrument 1, and the rheological properties are continuously measured. During this time, volatile components such as water and an organic solvent gradually volatilize from the skin coating composition 8 . Even while the volatile components are volatilizing, a constant strain within the linear strain range is continuously applied, and the rheological properties are continuously measured. The rheological properties may be observed as such or their changes may be observed. For example, changes in rheological properties over time and the relationship between one rheological parameter and another rheological parameter (for example, the relationship between shear stress and loss tangent) can be mentioned. Further, "while the volatile components are volatilizing" refers to the state until the residual rate of the volatile components contained in the composition for skin application 8 is reduced to about 10 to 1% by mass. The residual rate (% by mass) is defined as ((W1-W3)-(W1-W2))×100/(W1-W3). W1 is the mass of the skin application composition 8 before the start of measurement by the rotational rheometer. W2 is the mass of the skin application composition 8 when volatilization of volatile components is almost complete. W3 is the weight of the skin application composition 8 when completely dried.

In the present invention, as described above, the linear rheological properties of the composition for skin application are measured while the composition for skin application 8 is distorted and the volatile components are volatilized from the composition for application on skin 8 . The performance of the skin application composition 8 is then evaluated based on the linear rheological properties. Linear rheological properties include, for example, stress in the linear strain region, storage modulus or loss modulus, or loss tangent, or changes thereof over time. Based on these linear rheological properties, the performance of the coating film formed by applying the skin coating composition 8 to the skin, for example, the skin sensation resulting from the coating film, is evaluated. FIG. 3(a) shows changes over time in the storage elastic modulus G′ and loss elastic modulus G″ of a commercially available liquid foundation as an example of the skin application composition 8 using the cell configuration shown in FIGS. The measurement results are shown.Fig. 3(b) shows the results of measuring the change over time of the loss tangent tan δ of the same liquid foundation.The measurement was carried out at 40°C and open to the atmosphere.Liquid A frequency of 2 Hz and an apparent strain of 0.01% were applied to the foundation.As shown in FIG. In other words, as the volatile components volatilize from the liquid foundation, it becomes harder. Also, as shown in FIG. 3(b), the loss tangent tan δ decreases over time. In other words, the liquid foundation becomes solid as the volatile components volatilize.

The measurement shown in FIG. 3(a) was also performed for the same type of liquid foundation commercially available from multiple companies. In addition, regarding the coating film formed by applying each liquid foundation to the face, the lack of a tight feeling was sensory evaluated by three expert panelists on a scale of 1 to 5 (1 point: the most tight feeling). 5 points: the least tight feeling), and the average value was calculated. Then, the change rate of the storage elastic modulus G' measured with a rotational rheometer (residual rate of volatile components at the end of measurement: about 5% by mass) and the sensory evaluation values were plotted on a graph, as shown in FIG. The results shown were obtained. In the figure, G' (dry-initial)/initial on the horizontal axis is the difference between the storage elastic modulus G' at the end of volatilization of the volatile component and the storage elastic modulus G' at the start of measurement. is a value divided by the storage elastic modulus G'. As is clear from the results shown in the figure, it is found that there is a high correlation between the change rate of the storage elastic modulus G' and the sensory evaluation of the tight feeling. From this result, based on the change over time of the storage elastic modulus G' of the composition 8 for application to skin, it was found that the skin sensation of tightness, which is one of the skin sensations caused by the coating film formed by applying the composition 8 for application to skin, was observed. It can be seen that the lack of feeling can be evaluated objectively.

Although not shown in FIG. 4, the loss elastic modulus G″ obtained by the measurement shown in FIG. 3(a) and the loss tangent tan δ obtained by the measurement shown in FIG. It also had a high correlation with the sensory evaluation of feeling.

The rotational rheometer used for the above measurements was MCR301 manufactured by Anton Paar. The outer diameter of the annular body 3 in the viscoelasticity measuring instrument 1 was set to 60 mm. The width of the annular body 3 in plan view was set to 2 mm. The thickness of the annular body 3 in side view was set to 4.5 mm. The width of the connecting portion 4 in plan view was set to 2 mm. The thickness of the connecting portion 4 in side view was set to 2 mm. The number of connecting portions 4 is four. The distance between the facing surface 9 of the lower plate 7 and the lower end surface of the hanging wall 6 of the viscoelasticity measuring instrument 1 was set to 0.5 mm. These conditions were also adopted for the measurements described below.

While the above description relates to measuring the rheological properties of the composition for skin application 8 while the volatile components contained in the composition for skin application 8 volatilize, in the present invention, It is also possible to measure the rheological properties of the skin application composition 8 after volatilization of the volatile components is almost completed, and to evaluate the performance of the coating film formed from the skin application composition 8 . Specifically, after the volatile components are volatilized from the skin application composition 8 and the residual rate of the volatile components is less than 10% by mass, the skin application composition 8 is continuously distorted or distorted. It is also possible to apply strain again after completing the above, and evaluate the performance of the coating film of the composition for skin application 8 based on the rheological properties of the composition for application to skin 8 .

Specifically, after the volatilization of the volatile components contained in the composition for application to skin 8 is almost completed, the composition for application to skin 8 changes in rheological properties in a linear strain region or a nonlinear strain region, and the skin is The performance of the coating film of coating composition 8 can be evaluated. FIG. 5(a) shows the angular frequency dependence of the storage elastic modulus G′ and loss elastic modulus G″ of a commercially available liquid foundation as an example of the skin application composition 8 using the cell configuration shown in FIGS. 5(b) shows the results of measuring the angular frequency dependence of the loss tangent tan δ of the same liquid foundation.In these measurements, the liquid foundation contains After volatilization of the volatile components is almost completed, the angular frequency dependence of the rheological parameters in the linear strain region of the liquid foundation is obtained.The measurement was performed in an environment of 40° C. and open to the atmosphere. , Strain within the linear strain region was given within the angular frequency range of 628 to 0.000628 s ^−1.By combining these results with various sensory evaluations of the coating film by specialized panelists, the properties of the coating film were objectively evaluated. can be evaluated objectively.

FIG. 6 shows strain dependence of shear stress measured for the same liquid foundation as the liquid foundation used in the measurements shown in FIGS. 5(a) and (b) using the cell configuration shown in FIGS. results are shown. In this measurement, after volatilization of the volatile components contained in the liquid foundation is almost complete, the strain dependence of the shear stress when measuring up to the nonlinear strain region of the liquid foundation is obtained. The measurement was performed at 40° C. under open air. The liquid foundation was subjected to shear rates ranging from 0.0001 to 1000 s ⁻¹ , gradually increasing from a low rate.

The measurements shown in FIG. 6 were also carried out for the same type of liquid foundation commercially available from multiple companies. In addition, regarding the coating film formed by applying each liquid foundation to the face, three expert panelists sensory evaluated the difficulty of removing the coating film by rubbing with fingers on a scale of 1 to 5. (1 point: most easily removed, 5 points: most difficult to remove), and the average value was calculated. Then, the yield stress was obtained from the relationship between the shear stress and the strain measured by the rotational rheometer, and the yield stress value and the sensory evaluation value were plotted on a graph, and the results shown in FIG. 7 were obtained. . As is clear from the results shown in the figure, it is found that the value of yield stress and the sensory evaluation of the resistance to rubbing of the coating film have a high correlation. From this result, based on the stress-strain characteristics of the composition for skin application 8 after the volatile components have mostly volatilized, the durability of the coating film formed by applying the composition for skin application 8 to the skin, rubbing It can be seen that it is possible to objectively evaluate the difficulty of removing the coating film from the surface.

The correlation shown in FIG. 7 is based on the yield stress obtained from the stress-strain characteristics of the skin application composition 8 after the volatile components have generally volatilized, but the physical property values other than the yield stress, A correlation with sensory evaluation may be obtained. Physical property values other than the yield stress include, for example, the yield initiation stress shown in FIG. "Yield onset stress" is the point at which the stress-strain dependence begins to depart from the linear strain region.

The description so far relates to measuring the rheological properties of the skin application composition 8 while volatilizing the volatile components contained in the skin application composition 8 or after the volatilization is substantially completed. Alternatively, during volatilization of the volatile components or after the volatilization is almost completed, the skin coating composition 8 is brought into contact with a liquid, and then the rheological properties of the skin coating composition 8 are measured. good. Liquid contact assumes a situation in which the coating film formed from the skin coating composition 8 absorbs water such as sweat or oil such as sebum. In other words, it is assumed that the coating film is permeated with sweat or sebum, and the liquid is a substance that it is desired to know whether it affects the mechanical properties of the coating film. From this point of view, the liquid to be brought into contact with the skin application composition 8 includes water, a single substance of oil components constituting human sebum, or a mixed oil. The temperature of the liquid that is brought into contact with the skin application composition 8 is preferably the same as the temperature of the environment in which the rheological properties are measured.

The timing of bringing the liquid into contact with the skin coating composition 8 can be selected depending on the purpose, such as during drying or when volatilization reaches a residual rate of about 10% by mass or less. In addition, when the liquid is brought into contact with the skin application composition 8 during volatilization of the volatile component or after the volatilization is almost completed, the amount of the liquid to be contacted is the same as that of the skin at the beginning of drying (that is, when drying starts). From the viewpoint of improving the accuracy of evaluation, it is preferably 30% by mass or more and 200% by mass or less with respect to the mass of the coating composition 8 .

During the volatilization of the volatile components or after the volatilization is almost complete, even after the composition for skin application 8 is brought into contact with the liquid, the composition for skin application 8 is continuously distorted within a linear strain to strain the composition. The presence or absence of changes in the rheological properties of the skin application composition 8 is determined. For example, FIG. 8(a) shows changes over time in the storage elastic modulus G′ and loss elastic modulus G″ of a commercially available liquid foundation as an example of the composition for skin application 8 using the cell structure shown in FIGS. 8(b) shows the results of measuring the change over time of the loss tangent tan δ of the same liquid foundation.The measurement was performed at 40° C. in an environment open to the atmosphere. A distortion of 0.01% at a frequency of 2 Hz was applied to the liquid foundation, and when the residual rate of volatile components was 6% by mass, the liquid foundation was subjected to 40% by mass of artificial sebum was added in. The artificial sebum is a pseudo-substance of human sebum composed of oleic acid: squalane: triglyceride (olive oil) = 2: 3: 3. Fig. 8 (a) shows As can be seen, the storage modulus G' and the loss modulus G'' are decreased by the addition of the artificial sebum. In other words, when the liquid foundation comes into contact with the artificial sebum, the properties of the coating film change. Moreover, as shown in FIG. 8(b), the loss tangent tan δ increases with the addition of artificial sebum. In other words, when the liquid foundation comes into contact with the artificial sebum, the properties of the coating film change. By combining these results with various sensory evaluations of the coating film by expert panelists, it is possible to objectively evaluate the properties of the coating film, for example, the resistance to twisting of the coating film against perspiration and sebum.

The results shown in FIGS. 8( a ) and 8 ( b ) show that the rheological properties of the composition 8 for skin application changed over time by bringing the liquid into contact with the composition 8 for skin application. However, after the change in rheological properties over time is almost completed, the performance of the coating film of the composition for skin application 8 is measured based on the rheological properties when measuring up to the linear strain region or the nonlinear strain region of the composition for skin application 8. can also be evaluated. For example, based on the frequency dependence of the storage elastic modulus or loss elastic modulus or loss tangent in the linear strain region of the composition for skin application 8 after the change in rheological properties due to contact with a liquid is almost completed, the skin application It is possible to evaluate the resistance to twisting of the coating film formed by applying the composition to the skin. In the present invention, "almost completed the time-dependent change in rheological properties" means the point in time when the rate of change of the storage elastic modulus G' falls below a predetermined value. The predetermined value can be changed in the absolute value range of 5% to 0% depending on the purpose of evaluation. In particular, it is preferable from the viewpoint of obtaining good reproducibility that "the time-dependent change in the rheological properties is almost completed" is the time when the rate of change in the storage elastic modulus G' is less than 1%/min in absolute value. .

In the present invention, the composition for application to skin 8 is evaluated based on the stress-strain characteristics when measured up to the nonlinear strain region of the composition for application to skin 8 after the time-dependent change in rheological properties due to contact with a liquid is almost complete. It is possible to evaluate the resistance to twisting formed by applying to the skin. For example, FIG. 9 shows strain dependence of shear stress measured for the same liquid foundation as the liquid foundation used in the measurements shown in FIGS. 8(a) and (b) using the cell configuration shown in FIGS. sex results are shown. In this measurement, when the residual rate of volatile components contained in the liquid foundation is 6% by mass, 40% by mass of artificial sebum is added to the initial measurement mass of the liquid foundation, and then distortion within the linear strain region and when the rate of change in storage elastic modulus after contact with artificial sebum falls below 1% / min in absolute value, the strain dependence of shear stress when measuring up to the nonlinear strain region of the liquid foundation is obtained. . The measurement was performed at 40° C. in an environment open to the atmosphere. The liquid foundation was continuously subjected to a linear strain of 0.01% at a frequency of 2 Hz, and after the rate of change in storage elastic modulus after contact with artificial sebum fell below 1% / min in absolute value, 0.0001 to 1000 s A stepwise addition of ⁻¹ shear flow was applied to strain up to the nonlinear strain regime.

The measurements shown in FIG. 9 were also performed for the same type of liquid foundation commercially available from multiple companies. In addition, regarding the coating film formed by applying each liquid foundation to the face, three specialized panelists evaluated the resistance to sebum sagging in the same manner as the sensory evaluation shown in FIG. value was calculated. Then, the yield start stress and the yield stress were obtained from the relationship between the shear stress and the strain measured by the rotational rheometer, and the lower values of the yield start stress and the yield stress and the sensory evaluation values were plotted on a graph. , the results shown in FIG. 10 were obtained. As is clear from the results shown in the figure, it can be seen that the lower values of the yield initiation stress and the yield stress have a high correlation with the sensory evaluation of resistance to sebum twisting. From this result, based on the stress-strain characteristics of the skin application composition 8 in contact with artificial sebum, the durability of the coating film formed by applying the skin application composition 8 to the skin, which is the resistance to sebum. It can be seen that the difficulty can be objectively evaluated.

As described in detail above, according to the present invention, it is possible to measure the rheological properties of dry coating films, which have been difficult to measure because they are soft or brittle. In addition, it becomes possible to objectively evaluate the composition based on the rheological properties. Therefore, according to the evaluation method of the present invention, it is possible to know the properties of the coating film formed from the composition for skin application without sensory evaluation. In addition, the evaluation results obtained by the method of the present invention can be used as a guideline when, for example, developing a new composition for skin application.

Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the above-described embodiment, the liquid foundation was taken as an example of the composition 8 for skin application, and the results of measuring the rheological properties were shown, but the present invention can be applied to compositions for skin application other than liquid foundation. .

REFERENCE SIGNS LIST 1 viscoelasticity measuring device 2 rotating shaft 3 annular body 4 connecting portion 5 notch portion 6 hanging wall 7 lower plate (dish-shaped)
8 Skin application composition

Claims (3)

A coating film evaluation method for evaluating the properties of a coating film of a composition for skin application using a rotational rheometer,
The rotational rheometer comprises a viscoelasticity measuring instrument,
The viscoelasticity measuring device includes a rotating shaft, an annular body, and radially extending from the tip of the rotating shaft, connecting the rotating shaft and the annular body, and concentrically fixing the annular body to the rotating shaft. and a connector that
The skin application composition is placed between the lower plate and the viscoelasticity measuring device, and the skin application composition is applied to the skin while the viscoelasticity measuring device is in contact with the skin application composition. continuously measuring the rheological properties of the skin application composition while the composition for application is strained within linear strain and volatile components are volatilized from the composition for application on skin;
While the volatile component volatilizes, the performance of the coating film of the composition for skin application is evaluated based on the change over time of the storage elastic modulus, loss elastic modulus, or loss tangent in the linear strain region of the composition for skin application. Evaluation method of the coating film of the composition for skin application to be evaluated. 2. The evaluation method according to claim 1, wherein the lack of tautness is evaluated as the performance of the coating film of the composition for application to skin. A coating film evaluation method for evaluating the properties of a coating film of a composition for skin application using a rotational rheometer,
The rotational rheometer comprises a viscoelasticity measuring instrument,
The viscoelasticity measuring device includes a rotating shaft, an annular body, and radially extending from the tip of the rotating shaft, connecting the rotating shaft and the annular body, and concentrically fixing the annular body to the rotating shaft. and a connector that
The skin application composition is placed between the lower plate and the viscoelasticity measuring device, and the skin application composition is applied to the skin while the viscoelasticity measuring device is in contact with the skin application composition. Apply a strain within the linear strain of the composition for application, and continuously measure the rheological properties of the composition for application to skin while volatilization of volatile components from the composition for application to skin and after volatilization is almost complete. and
After volatilization of the volatile component is almost completed, the composition for skin application is measured based on the angular frequency dependence of the storage elastic modulus, loss elastic modulus, or loss tangent in the linear strain region of the composition for skin application. A method for evaluating a coating film of a composition for application to the skin, which evaluates the performance of the coating film.

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