JP5749554B2 - Evaluation method for stickiness of cosmetics - Google Patents

Description

  The present invention relates to a method capable of objectively evaluating the degree of stickiness when cosmetics are applied to the skin.

  Improving the feeling of use when a cosmetic such as a beauty essence is applied to the skin is an important factor for increasing the commercial value of the cosmetic. One of the feelings of use of cosmetics is the non-stickiness when the cosmetics are applied. Various prescription cosmetics have been proposed for the purpose of reducing the stickiness when applied. However, since the degree of stickiness varies from person to person, the evaluation is generally a sensory evaluation by a well-developed development engineer (a skilled development engineer who has over 5 years of experience in cosmetics development). Was the main. Skilled development engineers are very familiar with this type of evaluation because they evaluate various cosmetics on a daily basis. However, since the accumulation of experience of individual evaluation results belongs to each evaluator, it cannot be objectively digitized or generalized, and the evaluation of stickiness is not analyzed corresponding to the mechanical properties of cosmetics. For this reason, there have been problems such as inability to obtain knowledge about the structure of cosmetics that controls stickiness, and the inability to evaluate materials whose safety has not been confirmed.

  As a method for objectively evaluating the stickiness of cosmetics, the cosmetics are dropped on a movable plate having a horizontal upper surface, and the movable plate is reciprocated while the probe is in contact with the upper surface of the movable plate. There has been proposed a method for measuring a horizontal force exerted on the surface (see Patent Document 1). In this method, a roller-like contact is attached to the tip of the probe, and the contact is rolled without slipping on the movable plate with the cosmetic interposed therebetween. And the degree of stickiness is evaluated from the change of rolling power, utilizing the sticky force of cosmetics acting as rolling resistance.

  In Patent Document 2, a force perpendicular to both roll axis planes generated on the roll axis during elongation or splitting of the cosmetic applied to the roll surface is formed between the nips formed by two rolls. A method for measuring and evaluating the stickiness of the cosmetic is described.

  In Patent Document 3, a cylindrical mortar and a columnar upper ridge are used, and the mortar is filled with a viscoelastic substance, and when the viscoelastic substance is compressed with an upper ridge, A method for evaluating the shape-retaining property, lubricity, and spinnability of the viscoelastic material based on the amount of the viscoelastic material attached to the upper eyelid is described.

JP-A-11-281559 JP 2005-106731 A JP-A-8-247916

  The degree of stickiness of the cosmetic material becomes a problem during or after the cosmetic material is applied to the skin. When the cosmetic is applied to the skin, the moisture in the cosmetic is lost by evaporation or penetration into the skin, resulting in the destruction of the emulsion and the structural change. Therefore, in order to evaluate the stickiness of cosmetics, cosmetics in a state after such a structural change should be targeted. Furthermore, in the method described in the previous patent document, a dedicated device is required to evaluate the degree of stickiness, but it is desirable that the degree of stickiness can be evaluated with a general-purpose device.

  Accordingly, an object of the present invention is to provide a method for objectively evaluating the degree of stickiness when a cosmetic is applied to the skin, which has not been performed so far. Another object of the present invention is to provide a method for objectively evaluating the degree of stickiness with a more general-purpose rheometer.

  As a result of intensive studies, the present inventors have evaluated the milky cosmetic material after volatilizing water under mild conditions, and according to the properties of the milky cosmetic material after volatilization. It has been found that by appropriately selecting the evaluation parameter, it is possible to accurately evaluate the degree of stickiness when the emulsion cosmetic is applied to the skin. The present invention has been made based on this finding.

That is, the present invention is based on the rheological properties of the cosmetic after leaving the milky cosmetic in an atmosphere at room temperature (15 to 35 ° C.) to volatilize the moisture, and the cosmetic is applied to the skin. A method for evaluating the stickiness of a milky cosmetic composition for evaluating the degree of stickiness,
The evaluation method includes a step of classifying rheological properties for evaluating the degree of stickiness according to the state of the cosmetic after volatilizing moisture,
The case classification provides a method for evaluating stickiness of a milky cosmetic composition comprising the following (A) and (B).

(A) When the cosmetic material after volatilization of moisture is kneaded and the appearance of the cosmetic material after kneading is a mixture of a liquid and a solid, the cosmetic material after kneading is lost as a rheological property. The tangent tan δ is measured, and the degree of stickiness when the cosmetic is applied to the skin is evaluated based on the loss tangent tan δ.
(B) The cosmetic material after volatilizing water is kneaded, and when the cosmetic material after kneading has a grease-like or wrinkle-like shape, the first normal as rheological characteristics of the cosmetic after kneading The stress difference N ₁ is measured, and the degree of stickiness when the cosmetic is applied to the skin is evaluated based on the normal stress difference N ₁ .

  According to the present invention, the degree of stickiness of a milky cosmetic can be evaluated objectively and with good reproducibility.

FIG. 1 is a schematic diagram showing a structural example of a parallel plate cell in a rheometer. FIGS. 2 (a) and (b) show the relationship between the degree of stickiness at the start of application and the loss tangent tan δ of the milky cosmetic material, which was subjected to sensory evaluation by several specialist panelists on several commercially available milky cosmetic materials. It is a graph which shows. 3 (a) and 3 (b) show the relationship between the degree of stickiness after application and the loss tangent tan δ of the milky cosmetic material, which was subjected to sensory evaluation by a specialized panelist for several types of commercially available milky cosmetic materials. It is a graph to show. 4 (a) and 4 (b) show the degree of stickiness at the start of application and sensory evaluation of several commercially available emulsion cosmetics by the expert panelist, and the first normal stress difference of the emulsion cosmetics. is a graph showing the relationship between N _1. 5 (a) and 5 (b) show the degree of stickiness after application, which was evaluated by a specialized panelist for several types of commercially available emulsion cosmetics, and the first normal stress difference N of the emulsion cosmetics. ₃ is a graph showing a relationship with ₁ .

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The present invention relates to a method capable of objectively evaluating the degree of stickiness when an emulsion cosmetic is applied to the skin and after being applied to the skin. Stickiness generally refers to a touch with stickiness or adhesion on the skin surface during or after the cosmetic is applied to the skin. In general, cosmetics with a large degree of stickiness are often perceived by the user if the feeling of use is not good, but there are also users who obtain a feeling of use by perceiving stickiness.

Cosmetics to be evaluated in the present invention are liquid cosmetics in a category generally called emulsion. These cosmetics generally have a viscosity (shear rate of 1 s ⁻¹ ) at 25 ° C. of 0.1 to 50 Pa · s. Further, the cosmetics to be evaluated in the present invention include, for example, O / W emulsions and W / O emulsions.

  In the evaluation method of the present invention, the milky cosmetic material itself (that is, the milky cosmetic material in a state where the container is filled) is not subjected to the evaluation, but is in a state similar to the state applied to the skin. Emulsion cosmetics are subject to evaluation. In order to realize such a state, in the present invention, the moisture from the emulsion cosmetic is volatilized as a pretreatment for evaluation. In order to volatilize the water, for example, a milky cosmetic may be sucked under reduced pressure. In this way, water can be volatilized in a short time. However, the volatilization of moisture due to vacuum suction may be accompanied by the volatilization of oily components, etc., and as a result, the state of the emulsion cosmetic in which the moisture has volatilized may be significantly different from the state applied to the skin. . Therefore, in the present invention, a mild volatilization condition in which only moisture is mainly volatilized is adopted, and the state of the milky cosmetic composition in which moisture is volatilized is made as close as possible to the state applied to the skin. For this purpose, in the present invention, the milky cosmetic is left in a room temperature atmosphere to evaporate moisture. The room temperature here means 15 to 35 ° C. Since this volatilization condition is close to the condition in which moisture is lost from the milky cosmetic applied to the skin, the state of the milky cosmetic that volatilized water is close to that applied to the skin.

In relation to temperature, atmospheric humidity can affect the volatilization of moisture from milk cosmetics. From this viewpoint, it is desirable to set the humidity in the atmosphere to 20 to 80% RH. The time for which the milky cosmetic is allowed to stand in the air varies depending on the temperature / humidity of the atmosphere and the thickness of the milky cosmetic when dried, but the change in the residual rate per day ((sample weight on the day before the measurement day / initial Drying until (sample weight) − (sample weight on measurement day ÷ initial sample weight)) is less than 0.004 is preferable because the correlation with the sticky sensory evaluation becomes high. For example, the remaining rate change can be set to the above numerical value by setting the drying days to about 10 to 14 days. When leaving the milky cosmetic in the atmosphere, place it thinly in a shallow container such as a petri dish (the cross-sectional area of the container is about 50 to 120 cm ² ), and breathable cover etc. It is desirable to cover with. It is preferable that the depth of the milky cosmetic to be put in the shallow container is 0.5 to 3 mm. In addition, although there exists a range in the temperature, humidity, and drying days mentioned above, if it is in the range of this width | variety, the dry cosmetics with the favorable reproducibility of an evaluation result will be obtained.

  In the present invention, the cosmetic after the milky cosmetic is allowed to stand and the water is volatilized under the above-described conditions (hereinafter, the cosmetic in this state is referred to as “post-drying cosmetic”). Measure rheological properties. By the way, when the milky cosmetic is allowed to stand under the above-described conditions to evaporate water, the structure of the milky cosmetic is changed due to this, and the state is different from that before standing. As a result of the examination by the present inventors, the state of the cosmetic after standing can be classified into several types by lightly kneading the cosmetic after drying with a spatula or the like. Specifically, it has been found that (A) the appearance of the kneaded product of the dry cosmetic is roughly classified into a type that is a mixture of a liquid and a solid and a type that is not (B). Here, lightly kneading means that the dried product is collected with a spatula or the like and kneaded to an extent that it looks together without gaps.

  It has also been found that the type (B) of the milky cosmetic is further roughly divided into two types depending on the state after kneading after standing. Specifically, the kneaded product kneaded after standing is roughly divided into (B-1) a grease-like product and (B-2) a hook-like product. Grease-like is a viscous fluid-like shape, and cocoon-like is a state with little stickiness and elasticity (an attempt to recover the shape while viewing even if the sample is deformed). is there.

In the present invention, as described above, the stickiness of the emulsion cosmetic is evaluated based on the rheological properties of the cosmetic after drying, and the rheological properties for evaluating the stickiness according to the state of the kneaded product of the cosmetic after drying, That is, as a result of the study by the present inventors, it was found that stickiness can be accurately evaluated by dividing the case into the case of (A) and the case of (B). Specifically, in the case of the type (A) emulsion cosmetic, loss tangent tan δ is adopted as the rheological characteristic, and stickiness is evaluated based on this value. On the other hand, in the case of the type (B) emulsion cosmetic, the first normal stress difference N ₁ is adopted as the rheological property, and stickiness is evaluated based on this value. Details of the measurement method of these rheological properties are as described below.

Emulsified cosmetic which corresponds to (B) in its entirety rather than not have a correlation between the first normal stress difference N ₁ and sensory evaluation, the case analysis in properties after kneading After drying cosmetics As a result of the study by the present inventors, it was found that there is a correlation between the normal stress difference N ₁ and the sensory evaluation among the groups. That is, in the group of the emulsion cosmetics of (B-1), a correlation is recognized between the first normal stress difference N ₁ and the sensory evaluation. Similarly, in the group of (B-2) of the emulsified cosmetic, a correlation between the first normal stress difference N ₁ and sensory evaluation is observed.

  For the measurement of rheological properties, a rheometer, which is a device used for measuring viscoelasticity of objects, is used. A cell that mounts a measurement sample on a rheometer and applies strain or stress to the sample to perform rheology measurement includes (i) a parallel plate cell in which the measurement sample is placed between circular parallel plates, and (ii) a circular There are types such as a cone plate type cell in which a measurement sample is arranged between a flat plate and a conical cone plate, and (iii) a concentric cylinder rotating type (queet) cell in which a measurement sample is arranged in the gap between two coaxial cylinders. Are known. In the present invention, these cells can be used without any particular limitation. In particular, in the present invention, by using a parallel plate type or cone plate type cell, the degree of stickiness of the cosmetic can be evaluated with high accuracy and reproducibility with a small amount of measurement sample of about several ml. Although the case where a parallel plate type cell is used will be described below, the same applies to the cone plate type.

  In the parallel plate type cell, as shown in FIG. 1, a lower plate 1 and an upper plate 2 are used as two parallel plates. In general, one plate is fixed, and the other plate can be rotated or vibrated. The opposing plate surfaces of the lower plate 1 and the upper plate 2 are parallel to each other. A set of the lower plate and the upper plate is referred to as a cell in the present invention.

In the present invention, the above-described cell is used to measure the angular frequency dependence of the loss tangent tan δ or the shear rate dependence of the first normal stress difference N ₁ for the measurement sample to be evaluated. The measurement temperature is preferably 20 to 35 ° C. and more preferably 25 to 32 ° C. in consideration of the environment when the milky cosmetic is applied. The relative humidity of the environment is preferably 30 to 65% RH. The angular frequency measurement of the loss tangent tan δ was measured in the linear strain range after waiting for a sufficient time for the influence of the mounting operation on the sample structure to disappear after mounting the sample on the cell. The measurement time was set at a time at which at least two sine waves could be applied to the measurement sample at each measurement point. In consideration of obtaining necessary data and the performance of a commercially available rheometer, the angular frequency is preferably 6.28 × 10 ^{−3 to} 100 s ⁻¹ , more preferably 0.01 to 62.8 s ⁻¹ . Since the shear rate dependence of the first normal stress difference N ₁ is a measurement in a non-linear region, the value obtained depends on the measurement conditions. In the present invention, after the mount operation to the cell, after waiting for a sufficient time for the influence of the mount operation to disappear, the shear rate between 0.001 and 1000 s ^-1 is changed from the low shear rate side to the high shear rate side. Measurement was performed at a shear rate of 19 points. In addition, the measurement shear rate was set to be a point obtained by dividing the logarithm between 0.001 and 1000 s ⁻¹ by 19 logarithms, and the measurement time at each shear rate was divided by 19 logarithms from 30 seconds to 3 seconds. Set to be time.

  The loss tangent tan δ is represented by a ratio G ″ / G ′ between the storage elastic modulus G ′ and the loss elastic modulus G ″, and is an index representing how much energy is absorbed when the milky cosmetic is deformed.

The normal stress is a stress generated in a direction perpendicular to the direction in which the shear is applied when rotational deformation is applied to the measurement object made of a viscoelastic fluid. The normal stress is not grasped by itself, but is grasped by a difference from the shear stress. That is, assuming that the flow direction is 1 and the shear direction is 2 in a simple shear flow, the normal stress difference is the first normal stress difference N ₁ (= σ ₁₁ −σ ₂₂ ), and the second normal stress difference N ₂ ( = Σ ₂₂ −σ ₃₃ ) and the third normal stress difference N ₃ (= σ ₃₃ −σ ₁₁ ). Of these normal stress differences, in the present invention, the first normal stress difference N ₁ is employed as a measure of normal stress. The reason for adopting the first normal stress difference N ₁ as a measure of normal stress is that (i) many phenomena caused by rheological characteristics can be explained as the effect of N ₁ , and (ii) easy with a commercially available rheometer This is because N ₁ can be measured.

  As the rheometer, since the measurement conditions can be easily set, a strain control type is easy to use, but a stress control type may also be used. In the present invention, the stress control type MCR300 or MCR500 manufactured by Paar Physica was used, and the measurement was performed in the strain control mode.

According to the evaluation method of the present invention, when designing cosmetics having various degrees of stickiness, the prescription of the components constituting the cosmetics is adjusted using the loss tangent tan δ or the first normal stress difference N ₁ as a guide. Thus, since an appropriate cosmetic can be designed, the design can be simplified or shortened. As a specific method, for example, in order to obtain a milky cosmetic material with a low degree of stickiness, in order to reduce the loss tangent tan δ or the first normal stress difference N ₁ , What is necessary is just to adjust prescription or the preparation conditions of milky cosmetics. When adjusting the prescription of the components constituting the emulsion cosmetic, for example, the amount of the liquid oil and the balance of the water-soluble polymer, the balance of the liquid oil and the solid fat, the balance of the active agent and the polyol may be adjusted. .

The present inventors have further studied from the viewpoint of further enhancing the correlation between the sensory evaluation result and the loss tangent tan δ or the first normal stress difference N ₁ and more objectively evaluating the stickiness. It has been found that it is advantageous to appropriately control the surface roughness of the surface in contact with the sample in the cell used for viscoelasticity measurement (hereinafter referred to as “sample contact surface”). Specifically, the sample contact surface of the cell used for the viscoelasticity measurement is generally a smooth surface having a small surface roughness value. However, in the evaluation method of the present invention, the upper plate, which is a plate in contact with the upper part of the sample, is used. It has proved advantageous to use a cell whose surface is intentionally roughened. In this specification, the surface roughness refers to the centerline surface roughness Ra specified in JIS B0601.

  In the present invention, the surface roughness Ra is measured using, for example, a surface roughness measuring machine (surfcom-590A, manufactured by Tokyo Seimitsu Co., Ltd.). The measuring element was a maker model 0102501 conical diamond with a conical angle of 90 degrees, and the radius of curvature at the tip was 5 μm. The measurement conditions were a measurement length of 4.0 mm, a measurement speed of 0.3 mm / s, and a cutoff wavelength of 0.8 mm.

  For example, when the cell having the form shown in FIG. 1 is used as the cell used in the evaluation method of the present invention, (a) Of the lower plate 1 and the upper plate 2, only the upper plate 2 has a surface roughness of the sample contact surface. By increasing the value, the value of the surface roughness of the sample contact surface of the lower plate 1 can be decreased (that is, the same as the surface roughness of the conventional sample contact surface). (B) The surface roughness values of the sample contact surfaces of both the lower plate 1 and the upper plate 2 can be increased. In the case of (b), the value of the surface roughness of the sample contact surface of the lower plate 1 and the value of the surface roughness of the sample contact surface of the upper plate 2 may be the same or different.

  In any of the cases (a) and (b), the surface roughness value on the sample contact surface having a large surface roughness value is 1 to 10 μm, particularly 3 to 7 μm, expressed by Ra. It is preferable to set to. The area of the sample contact surface of the lower plate 1 and the upper plate 2 is not critical in the present invention as long as an appropriate torque output can be obtained, and commercially available rheometer parts may be used as they are.

  Particularly in the case of (a), the surface roughness value at the sample contact surface having a small surface roughness value is smaller than the surface roughness value at the sample contact surface having a large surface roughness value. On the condition, it is preferable to set it to 0.01 to 0.5 μm, particularly 0.08 to 0.2 μm in terms of Ra. On the other hand, when a cone plate type cell is used as the cell, the sample contact surface of the cone of the flat plate and the cone plate is used as a sample contact surface having a large surface roughness value, that is, a surface in contact with the upper portion of the sample. This is necessary due to the structure of the rheometer.

  In order to set the surface roughness of the lower plate 1 and the upper plate 2 to a desired value, a standard parallel plate or a sandblasted parallel plate may be purchased from the list of optional parts of the rheometer used. For example, the plate surface may be subjected to sandblasting to roughen the plate surface, or conversely, the plate surface may be smoothed by polishing using an abrasive.

  As described above, typical cosmetics to be evaluated in the present invention are O / W emulsions and emulsions made of W / O emulsions. As a general prescription of the O / W emulsion, the oil component is 1 to 50% by mass, the polyol component is 0.1 to 20% by mass, the activator component is 0.01 to 10% by mass, and the polymer component is 0 to 10%. The prescription | regulation which is a mass% and the remainder is water is mentioned. On the other hand, as a general prescription of W / O emulsion, water is 1 to 60% by mass, polyol component is 0.1 to 20% by mass, activator component is 0.1 to 10% by mass, and solid fat component is 0. The formulation which is -20 mass% and the remainder is an oil-based component is mentioned.

  About 14 g of each of the 14 types of commercially available emulsions was put in a glass petri dish with a diameter of 90 mm, and each emulsion was dried at a temperature of 25 ° C. and a relative humidity of 50% RH for 14 days until the residual rate of change was less than 0.004. . The dried product was collected with a Teflon (registered trademark) spatula and kneaded until it was gathered without gaps. Among the 14 types of emulsions, there were 5 types of (A) type emulsions and 9 types of (B) type emulsions. Among the nine types of (B) type emulsions, there were seven types of emulsions that exhibited the (B-1) type of grease, and two types of emulsions that exhibited the (B-2) type of emulsion. The rheological properties of each dried product were measured by the method described above. Specifically, a rheological property was measured by using a parallel plate type cell having a diameter of 25 mm, setting Ra of the lower plate to 0.14 μm, and setting Ra of the upper plate to 5.5 μm.

FIGS. 2A and 2B are graphs showing the relationship between loss tangent tan δ measured for five types of commercially available cosmetic emulsions corresponding to the type of (A) and sensory evaluation. FIG. 2A shows measured values of loss tangent tan δ at an angular frequency of 0.1 s ⁻¹ , and FIG. 2B shows measured values at an angular frequency of 1 s ⁻¹ . The measurement environment is 25 ° C. and 55% RH. Moreover, sensory evaluation is a thing at the time of application | coating to the skin of milky cosmetics. As is clear from these results, it was surprisingly found that there was a first-order negative correlation between the two. However, no clear correlation was recognized between the other rheological properties such as storage elastic modulus G ′, loss elastic modulus G ″, viscosity η, first normal stress difference N _1, and sensory evaluation. On the other hand, for the milky cosmetics corresponding to the type (B), the same graphs as in FIGS. 2 (a) and (b) were prepared, but there is a clear correlation between the loss tangent tan δ and the sensory evaluation. In other words, it was difficult to evaluate the stickiness of all types of emulsion cosmetics with a single rheological property, and the horizontal axis in FIGS. Means that the larger the numerical value, the lower the degree of stickiness, and the same applies to FIGS.

  3 (a) and 3 (b) were obtained in the same manner as FIGS. 2 (a) and 2 (b) except that sensory evaluation was performed after 5 minutes had elapsed after applying the milky cosmetic material to the skin. It is a graph. As is apparent from the results shown in FIGS. 3A and 3B, even after the milky cosmetic is applied to the skin, there is a correlation between the loss tangent tan δ and the sensory evaluation.

  From the results shown in FIGS. 2 and 3, it can be evaluated that the smaller the loss tangent tan δ of the kneaded product of the cosmetic after drying, the lower the degree of stickiness of the emulsion cosmetic. Moreover, it can be evaluated that the greater the loss tangent tan δ, the higher the degree of stickiness of the emulsion cosmetic.

4 (a) and (b) are described above, (B) type applicable to commercial nine cosmetic measured first normal stress difference N ₁ and the relationship between the sensory evaluation emulsion as a target of It is a graph which shows. FIG. 4 (a) shows the measured value of the first normal stress difference N ₁ at a shear rate of 464s ⁻¹ , and FIG. 4 (b) shows the measured value at a shear rate of 1000s ⁻¹ . The measurement environment is 25 ° C. and 55% RH. Moreover, sensory evaluation is a thing at the time of application | coating to the skin of milky cosmetics. As is clear from these results, there is a first-order negative correlation between the two. However, as in the case of the emulsion cosmetic of type (A) described above, other rheological properties such as storage elastic modulus G ′, loss elastic modulus G ″, viscosity η, etc., and sensory evaluation No clear correlation was observed, and the correlation with the loss tangent tan δ observed in the case of the type (A) emulsion cosmetic was not clearly observed. For the milky cosmetics corresponding to the type of), even if the same graphs as in FIGS. 4A and 4B are prepared, it is still clear between the first normal stress difference N ₁ and the sensory evaluation. There was no correlation.

Figure noted in 4 (a) and FIG. 4 (b), the emulsified cosmetic for the type of (B) is a correlation between all of the first normal stress difference N ₁ and sensory evaluation In the group classified according to the properties after kneading the cosmetic after drying, there is a correlation between the normal stress difference N ₁ and the sensory evaluation. As described above, the emulsion cosmetics corresponding to the type (B) are the properties after the drying and kneading of the cosmetics, and are (B-1) grease-like and (B-2) bowl-like. Divided into things. And in the group of milky cosmetic of (B-1), the correlation between the first normal stress difference N ₁ and sensory evaluation is observed. Similarly, in the group of (B-2) of the emulsified cosmetic, a correlation between the first normal stress difference N ₁ and sensory evaluation is observed.

5 (a) and 5 (b) were obtained in the same manner as FIGS. 4 (a) and 4 (b) except that sensory evaluation was performed after 5 minutes had elapsed after the milky cosmetic was applied to the skin. It is a graph. As is apparent from the results shown in FIGS. 5A and 5B, the first normal stress difference N ₁ and the sensory evaluation among the grease-like groups even after the milky cosmetic was applied to the skin. There is a correlation between the first normal stress difference N ₁ and the sensory evaluation in the saddle-shaped group.

From the results shown in FIGS. 4 and 5, it can be evaluated that the smaller the first normal stress difference N ₁ of the kneaded product of the cosmetic after standing, the lower the degree of stickiness of the emulsion cosmetic. In addition, it can be evaluated that the greater the first normal stress difference N ₁ is, the higher the degree of stickiness of the emulsion cosmetic.

The sensory evaluation method performed in creating the correlation diagrams of FIGS. 2 to 5 is as follows. Evaluation was performed by 10 to 13 professional evaluators who were trained to perform sensory evaluation.
[Evaluation of non-stickiness]
10 to 13 professional evaluators apply each evaluation sample taken on the fingertip to the arm and spread it thinly (referred to as “during application” in FIGS. 2 and 4) and 5 minutes after the application operation In FIG. 3 and FIG. 5, “after application” was evaluated for the presence and degree of stickiness when the fingertips in contact with the arm skin were released. A 9-level evaluation was performed with 0 as the standard product. A non-sticky sample was +4, and a very non-sticky sample was -4. The results obtained from each expert evaluator were averaged to obtain a sticky score. Regarding score values +4, +3, +2, and +1, 100%, 90%, 80%, and 70% of respondents (general panelists) answered that they were not sticky. For -3 and -4, 70%, 80%, 90% and 100% of respondents (general panelists) answered that they were sticky.

Based on the results shown in FIG. 2 to FIG. 5, the present inventors further studied. In the case of (A), the results of the sensory evaluation of the degree of stickiness by a specialized panelist and the common use of the loss tangent tan δ The correlation with the numerical values is good when the angular frequency when measuring the loss tangent tan δ is preferably in the range of 0.01 to 10 s ⁻¹ , more preferably in the range of 0.05 to 5 s ^−1. Was found to be obtained. On the other hand, for the case of (B) is the result of the degree of sensory evaluation of stickiness, correlation between the first common logarithm of the normal stress difference N _1, when measuring a first normal stress difference N ₁ range of preferably the angular frequency 100~1000s ^-1, more preferably when the range of 200~1000s ^-1, was found to give good results.

1 Lower plate 2 Upper plate

Claims (8)

Based on the rheological properties of the cosmetic after leaving the milky cosmetic in an atmosphere of room temperature (15-35 ° C.) and volatilizing water, the degree of stickiness when the cosmetic is applied to the skin is determined. A method for evaluating the stickiness of an emulsion cosmetic to be evaluated,
The evaluation method includes a step of classifying rheological properties for evaluating the degree of stickiness according to the state of the cosmetic after volatilizing moisture,
The method for evaluating stickiness of an emulsion cosmetic comprising the following cases (A) and (B).
(A) When the cosmetic material after volatilization of moisture is kneaded and the appearance of the cosmetic material after kneading is a mixture of a liquid and a solid, the cosmetic material after kneading is lost as a rheological property. The tangent tan δ is measured, and the degree of stickiness when the cosmetic is applied to the skin is evaluated based on the loss tangent tan δ.
(B) Kneading the cosmetic material after volatilizing moisture, and kneading the cosmetic material when it is not a mixture of liquid and solid and is in the form of a grease or a bowl for the cosmetic after the first normal stress difference N ₁ measured as rheological properties, based on the normal line stress difference N ₁ to evaluate the degree of stickiness at the time of application to the cosmetic skin. In the case of (A), the evaluation method according to claim 1, wherein the degree of stickiness when the cosmetic is applied to the skin is evaluated based on the loss tangent tan δ at an angular frequency of 0.01 to 10 s ^-1 .   In the case of (A), the evaluation method according to claim 1 or 2, wherein the smaller the tan δ value is, the lower the stickiness degree is, and the larger the tan δ value is, the higher the stickiness degree is. For (B), based on the first normal stress difference N ₁ at the angular frequency 100~1000s ^-1, evaluation method according to claim 1 for evaluating the degree of stickiness at the time of application of the cosmetics of the skin. In the case of (B), it is evaluated that the degree of stickiness is lower as the first normal stress difference N ₁ is smaller, and the degree of stickiness is higher as the normal stress difference N ₁ is larger. Evaluation method. The evaluation method according to claim ₁ , wherein tan δ and the first normal stress difference N ₁ are measured using a rheometer having a parallel plate type or cone plate type cell.   The evaluation method according to any one of claims 1 to 6, wherein the measurement cell in the rheometer uses a sample contact surface of the upper plate having a surface roughness of 1 to 10 µm.   The evaluation method according to any one of claims 1 to 7, wherein the emulsion cosmetic comprises an O / W emulsion or a W / O emulsion.

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