Method for evaluating keratin fibers

Abstract

To provide a novel method for evaluation for evaluating the hydrophilicity by using keratin fibers.SOLUTION: The method of evaluating keratin fiber 10 includes: dropping a droplet 20 having a diameter of at least 10 μm and not greater than the diameter of keratin fiber 10 onto a single fiber of keratin fiber 10; measuring the contact angle of the droplet 20 within 500 msec after droplet 20 lands; and evaluating the hydrophilicity of the keratin fiber 10 on the basis of the contact angle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating keratin fibers. [Background technology]

[0002] Patent Document 1 discloses a technology relating to a keratin fiber F layer damage repair agent. One method for confirming the F layer damage repair effect in Patent Document 1 is to arrange multiple hairs treated with the keratin fiber F layer damage repair agent evenly and without gaps, drop a 1 μL water droplet on the hairs, and measure the contact angle immediately afterward. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-059559 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the contact angle evaluation method disclosed in Patent Document 1 makes it difficult to evaluate the hydrophilicity of hair because droplets tend to spread between hair strands. Also, the contact angle evaluation method disclosed in Patent Document 1 provides evaluation results that reflect the average surface state of multiple hair strands used, making it difficult to evaluate the state of hydrophilicity of each individual hair fiber.

[0005] An object of the present disclosure is to provide a novel evaluation method capable of evaluating hydrophilicity using a single keratin fiber. [Means for solving the problem]

[0006] The method for evaluating keratin fibers disclosed herein involves dropping a droplet of liquid with a diameter of 10 μm or more and less than the diameter of the keratin fiber onto a single keratin fiber, measuring the contact angle of the droplet within 200 ms after landing, and evaluating the hydrophilicity of the keratin fiber based on the contact angle. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram illustrating a method for evaluating keratin fibers according to the first embodiment. [Figure 2] 1 is a graph showing the full plot until droplet disappearance. [Figure 3] This is a graph showing plots from immediately after droplet arrival to 200 ms and a linear approximation curve. [Figure 4] This is a graph showing plots from immediately after droplet arrival to 100 ms and a linear approximation curve. [Figure 5] This is a graph showing plots from immediately after droplet arrival to 900 ms and a linear approximation curve. [Figure 6] 1 is a graph showing the relationship between exposure period and initial contact angle. DETAILED DESCRIPTION OF THE INVENTION

[0008] A first embodiment of the present disclosure, which embodies the evaluation method for keratin fibers 10, will be described with reference to the drawings. In this specification, when a numerical range is described using "greater than or equal to" or "less than or equal to," the range includes both the lower limit and the upper limit unless otherwise specified. For example, the expression "10 or greater and 20 or less" includes both the lower limit of "10" and the upper limit of "20." In this specification, the upper and lower limits of each numerical range can be combined in any combination.

[0009] The evaluation method for the keratin fiber 10 of embodiment 1 is as shown in FIG. 1, in which a droplet 20 with a diameter of 10 μm or more and less than the diameter of the keratin fiber 10 is dropped onto a single fiber of the keratin fiber 10, the contact angle of the droplet 20 is measured within 200 ms after landing, and the hydrophilicity of the keratin fiber 10 is evaluated based on the contact angle.

[0010] This method involves preparing keratin fibers 10 to be evaluated. The keratin fibers 10 are not particularly limited. The keratin fibers 10 may be any of natural fibers derived from animals, such as hair, wool, and feathers, or blended fibers with these natural fibers. The blended fibers are not particularly limited and may be any of natural fibers, semi-synthetic fibers, and synthetic fibers. The blended fibers may include, for example, silk, flax, cotton, linen, lyocell, ramie, rayon, Tencel, triacetate, acrylic, nylon, polyester, etc.

[0011] The keratin fibers 10 to be evaluated may be untreated keratin fibers 10, keratin fibers 10 treated with purified water, or keratin fibers 10 that have undergone a specific treatment other than treatment with purified water. The residual chlorine concentration of the purified water is, for example, less than 0.05 ppm. Such purified water can be produced by filtering tap water through a water purification cartridge. The specific treatment may be a damaging treatment that can damage the keratin fibers 10, or a treatment treatment that improves the quality of the keratin fibers 10.

[0012] Keratin fibers 10 are composed of keratin proteins, and for example, the outermost layer is the cuticle, and inside that is a structure called the cortex, which accounts for the majority of hair. The epicuticle layer on the surface of the cuticle and the F-layer, which is bound to 18-methyleicosanoic acid, play a role in maintaining the hydrophobicity of the keratin fibers 10. Keratin fibers 10 are known to become hydrophilic when subjected to a damage treatment. The hydrophilization of keratin fibers 10 can cause problems such as poor feel, dryness, stiffness, and snagging. Therefore, understanding the hydrophilic state of keratin fibers 10 is important from the perspective of proposing appropriate care methods for keratin fibers 10 and preventing the progression of damage.

[0013] Damage treatments include, for example, treatment using residual chlorine water, heat treatment using a hair iron or the like, chemical treatment using permanents, permanent hair dyes, bleach, etc., friction treatment using brushing, etc., and ultraviolet irradiation treatment. The hypochlorous acid concentration of residual chlorine water is not particularly limited and may be, for example, 0.1 ppm to 20 ppm, or even 1 ppm. Note that a hypochlorous acid concentration of 1 ppm is approximately equal to the residual chlorine concentration of ordinary tap water. When the residual chlorine concentration of residual chlorine water is 0.02 ppm or more and 2 ppm or less, it can be measured using the diethylparaphenylenediamine method. The diethylparaphenylenediamine method is also called the DPD method. When the residual chlorine concentration of residual chlorine water exceeds 2 ppm, it can be measured using the DPD method after dilution with ultrapure water so that the residual chlorine concentration after dilution is 0.05 ppm or more and 2 ppm or less.

[0014] The diameter of the keratin fiber 10 is not particularly limited. The diameter of the keratin fiber 10 is the maximum length in a direction perpendicular to the longitudinal direction of the fiber. For example, the keratin fiber 10 has a substantially circular cross section in a direction perpendicular to the longitudinal direction of the fiber. Symbol d1 in FIG. 1 represents the diameter of the keratin fiber 10. When the keratin fiber 10 is hair, the diameter is, for example, 40 μm or more and 150 μm or less. The diameter of the keratin fiber 10 can be calculated by analyzing an image of the keratin fiber 10 viewed from a direction perpendicular to the longitudinal direction of the fiber.

[0015] In this method, a droplet 20 of a predetermined diameter is dropped onto a single fiber of keratin fiber 10, and the contact angle of the droplet 20 is measured within 200 milliseconds after landing. The symbol θ in FIG. 1 represents the contact angle of the droplet 20. The contact angle of the droplet 20 can be measured, for example, using the following measuring device. One example of the measuring device is a device that deposits a fine droplet 20 ejected from an inkjet printer at a predetermined position on an object, captures the wetting and spreading of the droplet after landing from a direct sideways direction using a high-speed camera, and analyzes the contact angle at each time from the captured video. Note that the contact angle of the droplet 20 may be measured using other measuring devices as long as the effects of the present disclosure are not impaired.

[0016] Specifically, in this method, a predetermined amount of test liquid is dropped onto the upper surface of the keratin fiber 10. The test liquid is preferably water, and more preferably any one of ultrapure water, ion-exchanged water, reverse osmosis water, and distilled water. The dropped test liquid spreads on the surface of the keratin fiber 10 according to the wettability of the surface, forming droplets 20 on the upper surface of the keratin fiber 10. The droplets 20 have a substantially circular shape when viewed from above. The amount of test liquid dropped is appropriately adjusted so that the diameter of the droplets 20 falls within a predetermined range. The amount of test liquid dropped is, for example, 10 pL or more and 100 pL or less. When the hydrophilicity of two or more types of keratin fibers 10 is to be evaluated relatively, it is preferable that the amount of test liquid dropped be the same for each keratin fiber 10.

[0017] The diameter of the droplets 20 is 10 μm or more, and from the viewpoint of ensuring an evaluation area on the keratin fiber 10, it is preferably 20 μm or more, and more preferably 30 μm or more. Measurements by the present inventors have shown that when the keratin fiber 10 is hair, the exposed length per cuticle is approximately 10 μm. It is considered that if the diameter of the droplets 20 is equal to or greater than the above-mentioned lower limit, it is possible to evaluate, for example, the state of the cuticle. The diameter of the droplets 20 is equal to or less than the diameter of the keratin fiber 10, and, taking into account the accuracy of the droplet position, is preferably equal to or less than 0.95 times the diameter, and more preferably equal to or less than 0.9 times the diameter. That is, the diameter of the droplets 20 is equal to or greater than 10 μm and equal to or less than the diameter of the keratin fiber 10, preferably equal to or greater than 20 μm and equal to or less than 0.95 times the diameter of the keratin fiber 10, and more preferably equal to or greater than 30 μm and equal to or less than 0.9 times the diameter of the keratin fiber 10. The diameter of the droplet 20 can be calculated by analyzing an image of the droplet 20 viewed from above immediately after it has landed. The diameter of the droplet 20 may also be calculated by analyzing an image of the droplet 20 viewed from the side immediately after it has landed.

[0018] This method measures the contact angle of the droplet 20 within 500 ms after landing. The contact angle can be calculated, for example, by photographing the formed droplet 20 from the side with a high-speed camera and analyzing images of the droplet 20 at each time point from the captured video. The measurement temperature is typically 5°C or higher and 45°C or lower, for example, 23°C. The measurement atmosphere is, for example, air. The humidity during measurement is, for example, 20% RH or higher and 70% RH or lower.

[0019] When evaluating single fibers of keratin fibers 10, the inventors discovered a new finding: the change in contact angle over time increases as the time after droplet landing increases. For example, the contact angles of the samples shown in the graph of FIG. 2 show a significant change over time, repeating rapid increases and decreases, from approximately 600 ms after droplet landing. While the reason for this significant change in contact angle over time is unclear, it is presumed that the influence of the stick-slip phenomenon caused by the pinning effect increases when the time after droplet landing exceeds a certain time. The inventors focused on the time after droplet landing when the contact angle of the droplet 20 remains stable, and developed the technology of the present disclosure for evaluating the hydrophilicity of keratin fibers 10 based on the contact angle at 500 ms or less after droplet landing.

[0020] This method measures the contact angle of the droplet 20 500 msec or less after landing, and evaluates the hydrophilicity of the keratin fibers 10 based on the contact angle. This method can improve the accuracy of the evaluation by excluding the contact angle of an unstable droplet 20 that lands more than 500 msec after landing from the evaluation of hydrophilicity.

[0021] The time for measuring the contact angle in this method can be appropriately set within a range of 0 ms to 500 ms after droplet landing. For example, the time for measuring the contact angle may be set within a specific range within a range of 0 ms to 500 ms after droplet landing. From the viewpoint of improving evaluation accuracy, the contact angle may be measured multiple times within a range of 0 ms to 500 ms after droplet landing. The interval for measuring the contact angle is not particularly limited. For example, the interval for measuring the contact angle may be 0.1 ms to 10 ms, 0.2 ms to 5 ms, or 0.3 ms to 1 ms. The interval for measuring the contact angle can be determined, for example, by conducting a preliminary test, so that the hydrophilicity of the keratin fiber 10 to be evaluated can be adequately evaluated.

[0022] A first aspect of this method is a method for evaluating the hydrophilicity of keratin fibers 10 by obtaining a linear approximation that indicates the relationship between the time after droplet landing and the contact angle in the range from immediately after droplet landing to 104 ms to 500 ms. A second aspect of this method is a method for evaluating the hydrophilicity of keratin fibers 10 by calculating the average value of the contact angle in the range from 4 ms to 20 ms after droplet landing.

[0023] For example, in a first embodiment of the present method, at least two types of keratin fibers 10 are prepared from untreated keratin fibers 10, keratin fibers 10 treated with purified water, and keratin fibers 10 that have been subjected to a specific treatment other than treatment with purified water. For each of the two types of keratin fibers 10, a linear approximation equation is obtained that shows the relationship between the time after droplet landing and the contact angle in the range from immediately after droplet landing to a point in time of 104 msec to 500 msec. The hydrophilicity of the two types of keratin fibers 10 is evaluated based on the slope of the linear approximation equation for one keratin fiber 10 and the slope of the linear approximation equation for the other keratin fiber 10.

[0024] The treatment using purified water is, for example, a treatment in which the keratin fibers 10 are exposed to purified water at a predetermined temperature for a predetermined time per day for a predetermined exposure period. A specific treatment is, for example, a treatment using residual chlorine water. The treatment using residual chlorine water is, for example, a treatment in which the keratin fibers 10 are exposed to residual chlorine water at a predetermined temperature for a predetermined time per day for a predetermined exposure period. The predetermined water temperature is assumed to be the temperature of a typical shower water, and may be, for example, 10°C to 60°C, or 20°C to 50°C. The predetermined time is assumed to be the average daily shower time for a typical person, and may be, for example, 3 minutes to 10 minutes. The predetermined exposure period may be, for example, 1 month to 12 months. Such treatment can be suitably performed using a liquid exposure device for keratin fibers 10 described in Japanese Patent Application No. 2022-184111 filed by the applicant of the present application.

[0025] In the first aspect of this method, "immediately after landing" can be set, for example, within the range of 0 ms to 20 ms after landing. Specifically, the contact angle at 0 ms after landing may indicate that the state of the droplet 20 is not stable. Therefore, the contact angle for obtaining the linear approximation formula may be calculated from the contact angle at the second measurement, excluding the contact angle at 0 ms after landing. For example, if the contact angle is measured at 4 ms intervals from 0 ms after landing, a linear approximation formula showing the relationship between the time after landing and the contact angle in the range from 4 ms after landing to 104 ms to 500 ms may be obtained.

[0026] Figure 3 is a graph showing plots and linear approximation curves for each sample from immediately after droplet landing to 200 ms. Details of each sample will be explained later. In the following explanation, the "slope of the linear approximation equation" refers to the absolute value of the ratio of the increase in "contact angle (°)" to the increase in "time (msec)" in Figure 3.

[0027] For the keratin fibers 10 treated with residual chlorine water for 1 month, 3 months, and 6 months, the slope of the linear approximation equation increases as the exposure period to residual chlorine water increases. A larger slope of the linear approximation equation indicates a faster rate at which the contact angle of the droplet 20 decreases. The increase in the rate of decrease is presumably due to a change in the behavior of the droplet 20 on the keratin fibers 10 caused by an increase in the hydrophilicity of the keratin fibers 10, which changes the balance between the evaporation of the droplet 20 and its absorption into the keratin fibers 10.

[0028] In the first aspect of this method, when the slope of the linear approximation equation of the keratin fiber being evaluated is small relative to the reference value, the keratin fiber can be evaluated as having low hydrophilicity, i.e., hydrophobicity, and when the slope is large, the keratin fiber can be evaluated as having high hydrophilicity. Specifically, in the Examples described below, samples measured for a time period of 0 ms to 120 ms, 4 ms to 120 ms, 4 ms to 200 ms, or 4 ms to 500 ms can be evaluated as follows: The reference value can be set to |-0.045|. When the slope of the linear approximation equation is |-0.045| or greater, the sample can be evaluated as having high hydrophilicity. When the slope of the linear approximation equation is less than |-0.045|, the sample can be evaluated as having low hydrophilicity.

[0029] In addition, for the measurement time of 4 ms to 500 ms, the sample treated with residual chlorine equivalent to one month had a linear approximation slope of |-0.0500|, which can be evaluated as having high hydrophilicity. The samples treated with purified water equivalent to one month, three months, and six months had linear approximation slopes of |-0.0353|, |-0.0334|, and |-0.0333|, respectively, which can be evaluated as having low hydrophilicity. On the other hand, the contact angle at 0 ms for the sample treated with residual chlorine equivalent to one month was 85.93°. The contact angles at 0 ms for the samples treated with purified water equivalent to one month, three months, and six months were 87.71°, 90.84°, and 87.66°, respectively. In other words, the contact angles at 0 ms for the sample treated with residual chlorine equivalent to one month were similar to those for the samples treated with purified water equivalent to one month, three months, and six months. Therefore, the difference in hydrophilicity between the sample treated with residual chlorine for one month and the samples treated with purified water for one month, three months, and six months cannot be detected based solely on the contact angle at 0 msec. Thus, the first embodiment of the present invention has the potential to evaluate hydrophilicity more accurately than an embodiment that evaluates hydrophilicity based solely on the contact angle at 0 msec.

[0030] In the first embodiment of this method, when the slopes of the linear approximation equations of two types of keratinous fibers 10 are approximately equal, the two types of keratinous fibers 10 can be evaluated as having approximately equal hydrophilicity. When the slope of the linear approximation equation of one of the two types of keratinous fibers 10 is greater than the slope of the linear approximation equation of the other keratinous fiber 10, the hydrophilicity of one keratinous fiber 10 can be evaluated as being higher than the hydrophilicity of the other keratinous fiber 10.

[0031] For example, in a second embodiment of the present method, at least two types of keratin fibers 10 are prepared from untreated keratin fibers 10, keratin fibers 10 treated with purified water, and keratin fibers 10 that have been subjected to a specific treatment other than treatment with purified water. For each of the two types of keratin fibers 10, the contact angle is measured at least twice, with an interval of at least 4 milliseconds between 4 milliseconds and 20 milliseconds after droplet application. The average value of the measured contact angles is calculated, and the hydrophilicity of the two types of keratin fibers 10 is evaluated based on the average value of one keratin fiber 10 and the average value of the other keratin fiber 10.

[0032] In the second embodiment of this method, the explanations regarding the treatment using purified water and the specific treatment are the same as those in the first embodiment of this method. In the second embodiment of this method, the number of times the contact angle is measured may be two, preferably three, more preferably four, and even more preferably five. Hereinafter, the average value of the contact angle in the range of 4 ms to 20 ms after landing is also simply referred to as the "initial contact angle."

[0033] 6 is a graph showing the relationship between the exposure period and the initial contact angle for each sample. The exposure period of 0 months in the water purification treatment graph and the residual chlorine water treatment graph corresponds to the sample of untreated keratin fiber 10. Details of each sample will be described later.

[0034] The keratin fibers 10 treated with residual chlorine water tend to have a smaller initial contact angle when exposed to residual chlorine water for more than one month. A smaller initial contact angle indicates higher hydrophilicity. The decrease in the initial contact angle is presumed to be due to the increased hydrophilicity of the keratin fibers 10, which makes it easier for the droplets 20 to wet and spread on the keratin fibers 10.

[0035] In the second aspect of this method, if the initial contact angle of the keratin fiber being evaluated is small relative to the reference value, it can be evaluated as having high hydrophilicity, and if it is large, it can be evaluated as having low hydrophilicity, i.e., hydrophobicity. Specifically, each sample measured for a measurement time of 4 ms to 20 ms in the "(4) Consideration of evaluation based on initial contact angle" in the Examples described below can be evaluated as follows: The reference value for the slope of the initial contact angle can be set to 80°. If the slope of the linear approximation is 80° or more, the sample can be evaluated as having high hydrophilicity. If the slope of the linear approximation is less than 80°, the sample can be evaluated as having low hydrophilicity.

[0036] In the second embodiment of this method, when the initial contact angles of two types of keratinous fibers 10 are approximately equal, the two types of keratinous fibers 10 can be evaluated as having approximately equal hydrophilicity. When the initial contact angle of one of the two types of keratinous fibers 10 is smaller than the initial contact angle of the other keratinous fiber 10, the hydrophilicity of one keratinous fiber 10 can be evaluated as being higher than the hydrophilicity of the other keratinous fiber 10.

[0037] As described above, the method for evaluating keratinous fibers 10 of embodiment 1 involves dropping a droplet 20 having a diameter of 10 μm or more but less than the diameter of the keratinous fiber 10 onto a single fiber of the keratinous fiber 10, measuring the contact angle of the droplet 20 within 500 ms after landing, and evaluating the hydrophilicity of the keratinous fiber 10 based on the contact angle. This method for evaluating keratinous fibers 10 allows evaluation of a single fiber of the keratinous fiber 10, and therefore does not require consideration of the effect of the droplet spreading between the keratinous fibers 10, as is the case with, for example, a method for evaluating a plurality of keratinous fibers 10 arranged uniformly and without gaps. Furthermore, this embodiment is groundbreaking in that it allows evaluation of the state of hydrophilicity of each single fiber of the keratinous fiber 10.

[0038] Conventionally, keratin fibers 10 treated with residual chlorine water have been less damaged than keratin fibers 10 treated with bleach, making it difficult to evaluate their hydrophilicity. The evaluation method for keratin fibers 10 of embodiment 1 is particularly useful in that it can also evaluate the hydrophilicity of keratin fibers 10 treated with residual chlorine water.

[0039] The first aspect of this method obtains a linear approximation that shows the relationship between the time after droplet landing and the contact angle in the range of 104 ms to 500 ms from immediately after droplet landing, and evaluates the hydrophilicity of the keratin fibers 10. The first aspect of this method can take into account a wide range of contact angles from immediately after droplet landing to at least 104 ms, so it can adequately capture changes in the contact angle over time. Furthermore, the first aspect of this method does not include contact angles beyond 500 ms after droplet landing in the evaluation, so high evaluation accuracy can be expected.

[0040] In a second aspect of the present method, the contact angle is measured at least twice at intervals of at least 4 ms between 4 ms and 20 ms after droplet landing, and the average of the measured contact angles is calculated to evaluate the hydrophilicity of the keratin fibers 10. There is a concern that droplets 20 less than 4 ms after landing may not be stable due to the impact of the drop. Since the second aspect of the present method does not include contact angles less than 4 ms after landing in the evaluation, high evaluation accuracy can be expected. Furthermore, since the second aspect of the present method evaluates contact angles in the range of 4 ms to 20 ms after droplet landing, the influence of changes in the contact angle over time due to the disappearance of the droplets 20 can be reduced. [Example]

[0041] The present disclosure will be described in more detail below with reference to examples, although the scope of the present disclosure is not limited to these examples.

[0042] 1. Preparation of keratin fiber samples to be evaluated To understand the changes in hair over time caused by showering with tap water containing residual chlorine, hair was exposed to residual chlorine water using the keratin fiber liquid exposure device described in Japanese Patent Application No. 2022-184111. For comparison, hair was exposed to purified water using the same keratin fiber liquid exposure device. The diameter of the hair was 84 μm.

[0043] Residual chlorine water and purified water were stored in separate storage containers in the keratin fiber liquid exposure device described above. For the residual chlorine water, tap water was filtered through a LIXIL JF-43 water purification cartridge to remove residual chlorine, resulting in raw water. Sodium hypochlorite was added to adjust the residual chlorine concentration to 1 ppm, approximately the same as that of typical tap water. For the purified water, the same tap water was filtered through the above water purification cartridge to remove residual chlorine. The residual chlorine concentration of the purified water was less than 0.05 ppm. The residual chlorine concentrations of the residual chlorine water and purified water were measured using a HACH HACH2470 pocket residual chlorine meter. The temperature of the residual chlorine water and purified water was set at 40°C. The exposure time for the residual chlorine water and purified water was 5 minutes per day. The exposure time for the residual chlorine water and purified water was set to 1 month, 3 months, or 6 months.

[0044] 2. Measurement of contact angle over time To measure contact, a device was used to deposit a fine droplet ejected from an inkjet printer onto a designated location on the object. The droplet's wetting and spreading were then filmed from the side with a high-speed camera. The video footage was then used to analyze the contact angle at each time point. 36 pL of ultrapure water was dropped onto each sample. The droplet diameter immediately after landing was between 30 μm and 45 μm for all samples. In other words, the droplet diameter immediately after landing was greater than 10 μm and less than the diameter of a human hair. The droplet was filmed from the side with a high-speed camera, and the contact angle at each time point was analyzed from the video footage. The shutter speed was set to 4 ms. Measurements were performed on four hairs per sample, and the average was used as the contact angle for that sample.

[0045] 3.Results (1) Change in contact angle over time The measurement results are shown in the graphs in Figures 2 to 5. In each graph, the horizontal axis represents the time (msec) after droplet landing, and the vertical axis represents the contact angle (°) of the droplet. The plot "- (horizontal bar)" represents the results for untreated samples, i.e., samples exposed to residual chlorine water and purified water for 0 months. The plot "● (black circle)" represents the results for samples treated with purified water equivalent to 1 month, i.e., samples exposed to purified water for 1 month. The plot "▲ (black triangle)" represents the results for samples treated with purified water equivalent to 3 months, i.e., samples exposed to purified water for 3 months. The plot "■ (black square)" represents the results for samples treated with purified water equivalent to 6 months, i.e., samples exposed to purified water for 6 months. The plot "○ (open circle)" represents the results for samples treated with residual chlorine water equivalent to 1 month, i.e., samples exposed to residual chlorine water for 1 month. The plot "△ (open triangle)" represents the results for samples treated with residual chlorine water equivalent to 3 months, i.e., samples exposed to residual chlorine water for 3 months. The plots "□, open squares" show the results of samples treated with residual chlorine water for six months, i.e., samples exposed to purified residual chlorine water for six months.

[0046] In the graph in Figure 2, the droplets disappeared in 1300 ms or more for the untreated sample and the samples treated with purified water for 1 month, 3 months, and 6 months. The droplets disappeared in less than 1300 ms for the samples treated with residual chlorine water for 1 month, 3 months, and 6 months. The initial contact angle decreased with increasing exposure time for the residual chlorine water treatment. Furthermore, the change in the contact angle over time for all samples increased, and the droplets became unstable.

[0047] (2) Evaluation based on the slope of the linear approximation Since it was deemed difficult to evaluate hydrophilicity from the contact angle of an unstable droplet, we investigated the optimal measurement time range for obtaining a first-order approximation equation. The measurement time ranges were set to 4 ms to 40 ms, 4 ms to 100 ms, 0 ms to 120 ms, 4 ms to 120 ms, 4 ms to 200 ms, 4 ms to 500 ms, 0 ms to 740 ms, 4 ms to 740 ms, and 4 ms to 900 ms, and a first-order approximation equation was obtained and the slope was calculated. The results are shown in Table 1.

[0048] [Table 1]

[0049] The stability of droplets over time was examined for each measurement time range using the following criteria: "A" is the coefficient of determination R obtained from the linear approximation equation obtained by the least squares method for each sample. 2 is sufficiently large, indicating excellent stability over time. "B" is the coefficient of determination R obtained from the linear approximation equation obtained by the least squares method for each sample. 2 "C" is the coefficient of determination R obtained from the linear approximation equation obtained by the least squares method for each sample. 2 The results are shown in Table 1.

[0050] For each measurement time range, the ability to detect damage, i.e., evaluate hydrophilicity, was evaluated using the following criteria. "A" indicates that there was a sufficient difference between the slope of the linear approximation equation obtained by the least squares method for the samples treated with residual chlorine water for three and six months and the slope of the linear approximation equation obtained by the least squares method for the other samples, making it particularly suitable for evaluating hydrophilicity. "B" indicates that there was a difference between the slope of the linear approximation equation for the samples treated with residual chlorine water for three and six months and the slope of the linear approximation equation for the other samples, making it suitable for evaluating hydrophilicity. "C" indicates that there was variation in the slope of the linear approximation equation obtained by the least squares method, making it difficult to detect a difference between the slope of the linear approximation equation for the samples treated with residual chlorine water for three and six months and the slope of the linear approximation equation for the other samples, making it unsuitable for evaluating hydrophilicity.

[0051] These results indicate that the measurement time ranges of 4 ms to 120 ms, 4 ms to 200 ms, and 4 ms to 500 ms are particularly suitable for evaluating hydrophilicity. The upper limit of the measurement time range was determined to be between 120 ms and 500 ms, and the following hydrophilicity evaluation was carried out.

[0052] (3) Evaluation results based on the slope of the linear approximation At measurement times of 0 ms to 120 ms, 4 ms to 120 ms, and 4 ms to 200 ms, the slopes of the linear approximation equations for untreated samples, samples treated with purified water equivalent to 1 month, 3 months, and 6 months, and samples treated with residual chlorine water equivalent to 1 month were all less than |-0.045|. The untreated samples, samples treated with purified water equivalent to 1 month, 3 months, and 6 months, and samples treated with residual chlorine water equivalent to 1 month can be evaluated as having low hydrophilicity, i.e., hydrophobicity. On the other hand, the slopes of the linear approximation equations for samples treated with residual chlorine water equivalent to 3 months and 6 months were all greater than |-0.045|. The samples treated with residual chlorine water equivalent to 3 months and 6 months can be evaluated as having high hydrophilicity.

[0053] At measurement times of 4 ms or more and 500 ms or less, the slope of the linear approximation equation for the untreated samples and the samples treated with purified water for 1 month, 3 months, and 6 months was less than |-0.045|. The untreated samples and the samples treated with purified water for 1 month, 3 months, and 6 months can be evaluated as having low hydrophilicity, i.e., hydrophobicity. On the other hand, the slope of the linear approximation equation for the samples treated with residual chlorine water for 1 month, 3 months, and 6 months was greater than |-0.045|. The samples treated with residual chlorine water for 1 month, 3 months, and 6 months can be evaluated as having high hydrophilicity.

[0054] The graph in Figure 3 shows plots and linear approximation curves from immediately after droplet application up to 200 ms. In Figure 3, the slope of the linear approximation equation for the untreated sample is approximately the same as the slope of the linear approximation equation for the samples treated with purified water for one month, three months, and six months. Therefore, the samples treated with purified water for one month, three months, and six months can be evaluated as having approximately the same hydrophilicity as the untreated sample.

[0055] In Figure 3, the slope of the linear approximation equation for the samples treated with residual chlorine water for 3 months and 6 months is larger than the slope of the samples treated with purified water for 3 months and 6 months. The slope of the linear approximation equation for the samples treated with residual chlorine water for 3 months and 6 months is larger than the slope of the linear approximation equation for the untreated sample. Therefore, the samples treated with purified water for 3 months and 6 months can be evaluated as having lower hydrophilicity than the samples treated with residual chlorine water for 3 months and 6 months.

[0056] (4) Evaluation based on initial contact angle We hypothesized that hydrophilicity could be evaluated from the initial contact angle, i.e., the contact angle near 0 ms in the graph of Figure 2, and investigated the optimal measurement time range for calculating the initial contact angle. The measurement time ranges were set to 0 ms to 20 ms, 4 ms to 20 ms, 4 ms to 60 ms, 4 ms to 100 ms, and 4 ms to 120 ms, and contact angle measurements were extracted at five approximately equal intervals within these ranges. The average of the five contact angles was calculated. The results are shown in Table 2. As a result, we found that a time range of 4 ms to 20 ms was suitable for evaluating hydrophilicity.

[0057] [Table 2]

[0058] To determine the appropriate number of measurements for calculating the average value, the following were calculated: a value extracted from only one of five measurement points in the time range of 4 ms to 20 ms, an average value calculated from two arbitrary points, an average value calculated from three arbitrary points, and an average value calculated from four arbitrary points. These values were then compared with the average value of the five points. As a result, it was found that within the time range of 4 ms to 20 ms, an average value of two or more points can evaluate hydrophilicity equivalently to an average value of five points.

[0059] Based on these results, it was determined that it was optimal to measure at least twice, with an interval of at least 4 ms between 4 ms and 20 ms after the droplets landed, and the following hydrophilicity evaluation was carried out.

[0060] The graph in Figure 6 shows the relationship between the exposure period (months) for either purified water or residual chlorine water and the initial contact angle (°). The initial contact angle was calculated as the average of five contact angles measured at intervals of at least 4 ms between 4 ms and 20 ms after droplet landing.

[0061] (5) Evaluation results based on initial contact angle The untreated samples, samples treated with purified water for 1 month, 3 months, and 6 months, and samples treated with residual chlorine water for 1 month all had initial contact angles of 80° or more. The untreated samples, samples treated with purified water for 1 month, 3 months, and 6 months, and samples treated with residual chlorine water for 1 month can be evaluated as having low hydrophilicity, i.e., hydrophobicity. On the other hand, the samples treated with residual chlorine water for 3 months and 6 months all had initial contact angles less than 80°. The samples treated with residual chlorine water for 3 months and 6 months can be evaluated as having high hydrophilicity.

[0062] 6, the contact angle of the untreated sample (i.e., the sample exposed to the purified water treatment for 0 months) is approximately equal to the contact angle of the samples exposed to the purified water treatment for 1 month, 3 months, and 6 months. Therefore, the samples exposed to the purified water treatment for 1 month, 3 months, and 6 months can be evaluated as having approximately the same hydrophilicity as the untreated sample.

[0063] In Figure 6, the contact angles of the samples exposed to residual chlorine water treatment for 3 months and 6 months are smaller than the contact angles of the samples exposed to purified water treatment for 3 months and 6 months, respectively. Therefore, the samples exposed to residual chlorine water treatment for 3 months and 6 months can be evaluated as being less hydrophilic than the samples exposed to purified water treatment for 3 months and 6 months.

[0064] 4. Summary The above examples provided a novel evaluation method that can evaluate hydrophilicity using a single keratin fiber. [Explanation of symbols]

[0065] 10...keratin fiber, 20...droplet

Claims

1. A method for evaluating keratin fibers, comprising dropping a liquid droplet having a diameter of 10 μm or more and less than the diameter of the keratin fiber onto a single fiber of the keratin fiber, measuring the contact angle of the liquid droplet within 500 msec after the droplet has landed, and evaluating the hydrophilicity of the keratin fiber based on the contact angle.

2. The method for evaluating keratin fibers according to claim 1, further comprising obtaining a linear approximation that indicates the relationship between the time after droplet landing and the contact angle in a range from immediately after droplet landing to a point of 104 ms or more and 500 ms or less for the keratin fibers, and evaluating the hydrophilicity of the keratin fibers.

3. At least two types of keratin fibers are prepared from untreated keratin fibers, keratin fibers treated with purified water, and keratin fibers that have been subjected to a specific treatment other than the treatment with purified water; For each of the two types of keratin fibers, a linear approximation formula is obtained that shows the relationship between the time after droplet landing and the contact angle in a range from immediately after droplet landing to a time of 104 msec or more and 500 msec or less; The method for evaluating keratinous fibers according to claim 1, wherein the hydrophilicity of the two types of keratinous fibers is evaluated based on the slope of the linear approximation equation of one of the two types of keratinous fibers and the slope of the linear approximation equation of the other of the two types of keratinous fibers.

4. 2. The method for evaluating keratin fibers according to claim 1, wherein the contact angle of the keratin fibers is measured at least twice at intervals of at least 4 ms within a range of 4 ms to 20 ms after the droplet has landed, and the average of the measured contact angles is calculated to evaluate the hydrophilicity of the keratin fibers.

5. At least two types of keratin fibers are prepared from untreated keratin fibers, keratin fibers treated with purified water, and keratin fibers that have been subjected to a specific treatment other than the treatment with purified water; For each of the two types of keratin fibers, the contact angle is measured at least twice at intervals of at least 4 ms within a range of 4 ms to 20 ms after the droplet has landed; The method for evaluating keratinous fibers according to claim 1, wherein the average value of the measured contact angles is calculated, and the hydrophilicity of the two types of keratinous fibers is evaluated based on the average value of one of the keratinous fibers and the average value of the other of the two types of keratinous fibers.

6. The method for evaluating keratinous fibers according to claim 3 or 5, wherein the specific treatment is a treatment of exposing the keratinous fibers to residual chlorine water.

Images