WATER-ABSORBING EXFOLIATOR, METHOD FOR PRODUCING SAME, AND COSMETIC

Abstract

Provided is an exfoliator which absorbs water and exhibits suitable hardness, provides little skin stimulation, and has a favorable skin massaging effect. The exfoliator exhibits a pure-water absorption factor of at least 30 times, and exhibits a compression-breaking stress of 0.14-1.40 N upon absorbing water and swelling to 30 times the initial mass thereof.

Claims

1. A water-absorbing exfoliator comprising: a pure-water absorption factor of 30 times or more; and a compression-breaking stress of 0.14 to 1.40 N in a state that the water-absorbing exfoliator is swollen to have a mass 30 times of an initial mass of the water-absorbing exfoliator by absorbing water.

2. The water-absorbing exfoliator according to claim 1, having a structure in which a second polymer is infiltrated into a first polymer particle.

3. The water-absorbing exfoliator according to claim 1, wherein: the first polymer particle includes a polymer of a first monomer component including at least one of a monomer A or a salt of the monomer A, the second polymer includes a polymer of a second monomer component including at least one of a monomer B or a salt of the monomer B, and the monomer A has an acid dissociation index smaller than an acid dissociation index of the monomer B.

4. The water-absorbing exfoliator according to claim 3, wherein a difference between the acid dissociation index of the monomer B and the acid dissociation index of the monomer A (pKa) is 1.5 or more.

5. The water-absorbing exfoliator according to claim 4, wherein: the monomer A is an unsaturated sulfonic acid-based monomer, and the monomer B is a water-soluble ethylenically unsaturated monomer.

6. The water-absorbing exfoliator according to claim 1, having a granular shape, a substantially spherical shape, or a shape in which substantially spherical particles are aggregated.

7. A method for producing a water-absorbing exfoliator, the method comprising the steps of: preparing a first polymer particle; infiltrating a second monomer component that is to form a second polymer and includes at least one of a monomer B or a salt of the monomer B into the first polymer particle; and polymerizing the second monomer component infiltrated into the first polymer particle to form a structure in which the second polymer is infiltrated into the first polymer particle.

8. A cosmetic comprising the water-absorbing exfoliator according to claim 1.

Description

EXAMPLES

[0138] Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to Examples. The pure-water absorption factor, the compression-breaking stress, and the pKa were measured by the following methods. The exfoliator was evaluated by the following panelist evaluation method.

[0139] <Method of Measuring Pure-Water Absorption Factor>

[0140] The prepared water-absorbing exfoliator was classified into particles that passed through a JIS standard sieve having a mesh-opening of 250 m and remained on a JIS standard sieve having a mesh-opening of 150 m. In a 500 mL beaker, 500 g of pure water was weighed and put, and 0.250.0002 g of the water-absorbing exfoliator classified into particles having a size of 150 m to 250 m was dispersed in the pure water while the mixture was stirred at a stirring speed of 600 rpm with a magnetic stirrer bar (having a size of 8 mm30 mm without a ring) so that no lump was generated. The mixture was left for 30 minutes in a state of being stirred to swell the water-absorbing exfoliator sufficiently. Then, the mass Wa (g) of a JIS standard sieve having a mesh-opening of 75 m was measured in advance, and using the sieve, the contents of the beaker were filtered, and the sieve was left inclined by about 30 degrees with respect to the horizontal for 30 minutes to remove the excess water. The mass Wb (g) of the sieve containing the water-absorbing gel was measured, and the pure-water absorption factor was determined by the following formula.

Pure-water absorption factor (g/g)=[WbWa] (g)/mass of water-absorbing exfoliator (g)

[0141] <Method of Measuring Compression-Breaking Stress>

[0142] The prepared water-absorbing exfoliator was classified into particles that passed through a JIS standard sieve having a mesh-opening of 250 m and remained on a JIS standard sieve having a mesh-opening of 150 m. In a 10 mL beaker, 3.0 g of pure water was weighed and put, and 0.100.0002 g of the classified water-absorbing exfoliator was added in the pure water while the mixture was stirred with a magnetic stirrer bar (having a size of 4 mm11 mm without a ring). The mixture was left for 2 minutes in a state of being stirred, then the stirring was stopped, and the mixture was left for another 30 minutes to swell the water-absorbing exfoliator to 30 times by mass to obtain a water-absorbing gel. Using a compact compression/tensile tester (Eztest/CE manufactured by SHIMADZU CORPORATION), the load required to break one particle of the water-absorbing gel was measured in accordance with the following operations and conditions. One particle of the water-absorbing gel was placed on the center of the measuring table, an indenter was lowered from above the water-absorbing gel at a constant speed (displacement speed) shown in the conditions described below, and while a graph of the load against the moving distance of the indenter was displayed, the variation of the load was recorded. When the indenter comes into contact with the water-absorbing gel, the repulsive force of the water-absorbing gel increases the load. When the water-absorbing gel is broken, the repulsive force is decreased to decrease the load. Based on the fact, the indenter was moved until the increase in the load caused by lowering the indenter stopped and then the load was decreased (Examples 1, 2, and 3 and Comparative Example 2). In the case that the load was not decreased, the indenter was lowered until the load reached the load limit of the load cell in accordance with the conditions (Comparative Example 1). The maximum load immediately before the decrease in the load occurred was measured and regarded as the yield load of the water-absorbing gel. This yield load was determined to be the load required to break the water-absorbing gel. The yield load of each of three particles of the water-absorbing gel was measured using a load cell A or a load cell B (the load cell A was used in Comparative Example 1, and the load cell B was used in Examples 1 to 3 and Comparative Example 2), and the compression-breaking stress (N) was determined from the average of the measured values. The value of the compression-breaking stress is one of the indexes showing the strength of the crosslinked polymer, and the higher the compression-breaking stress is, the more difficult the water-absorbing gel tends to be to break.

[0143] The conditions of the load cell used in measuring the load are as follows.

[0144] Upper limit and lower limit of quantification of load cell A: 20 (N) and 0.4 (N)

[0145] Upper limit and lower limit of quantification of load cell B: 2 (N) and 0.04 (N)

[0146] Displacement speed: 0.5 (mm/min)

[0147] Load limit (upper limit) of load cell A set as measurement condition: 15.0 (N)

[0148] Load limit (upper limit) of load cell B set as measurement condition: 1.5 (N)

[0149] Indenter: 15 (mm)

[0150] <Method of Measuring pKa>

[0151] To 20.4 g of the monomer whose pKa was to be measured, 29.6 g of ion-exchanged water was weighed and added in a 100 mL glass beaker, and the mixture was mixed for 5 minutes while stirred with a magnetic stirrer bar (having a size of 8 mm30 mm without a ring) to prepare 40.8% by mass of an aqueous solution. In a 100 mL glass beaker, 2.4 g of the aqueous solution and 50.0 g of physiological saline were weighed and put, and the mixture was stirred with a magnetic stirrer bar (having a size of 8 mm30 mm without a ring) to prepare an aqueous solution for measurement. The aqueous solution for measurement was adjusted to 17 C. until immediately before the measurement. The acid dissociation index was measured using an automatic titrator (COM-1600) manufactured by HIRANUMA SANGYO Co., Ltd. While the aqueous solution for measurement was stirred, 0.025 mL of 0.1 M sodium hydroxide was dropped every 10 seconds, and the pH of the aqueous solution for measurement was measured in each dropping. The acid dissociation index pKa of the monomer was determined using the Henderson-Hasselbalch equation from the concentration of the aqueous solution for measurement, the amount of the dropped sodium hydroxide, and the measured pH.

[0152] <Panelist Evaluation Method>

[0153] A cosmetic was prepared using the exfoliator. Specifically, the exfoliator was classified into particles that passed through a JIS standard sieve having a mesh-opening of 250 m and remained on a JIS standard sieve having a mesh-opening of 150 m. Next, components 1 and 2 were first mixed so as to have the following composition, the mixture was heated to 70 C. and stirred to obtain a uniform mixed liquid. Next, the following components 3 to 6 were added to the obtained mixed liquid, and the mixture was stirred to prepare an emulsion cosmetic (cream).

[0154] (Composition of Cosmetic)

[0155] Component 1. Polysorbate: 60 3 g

[0156] Component 2. Purified water: 66 g

[0157] Component 3. Mineral oil: 10 g

[0158] Component 4. Isopropyl myristate: 10 g

[0159] Component 5. Caprylic/capric triglyceride: 10 g

[0160] Component 6. Exfoliator: 1 g

[0161] Next, 10 panelists evaluated the massage effect and the skin irritation due to the hardness when the obtained cosmetic was applied to the hand and the hand was massaged. The evaluation criteria are as follows, and the average of the evaluation points of 10 panelists is shown in Table 1.

[0162] (Evaluation Criteria for Massage Effect)

[0163] 1 Exfoliator is not tangible and massage effect is low

[0164] 2 Exfoliator is slightly tangible and massage effect is slightly low

[0165] 3 Exfoliator is tangible and massage effect is normal

[0166] 4 Exfoliator is suitably tangible and massage effect is slightly high

[0167] 5 Exfoliator is particularly suitably tangible and massage effect is high

[0168] (Evaluation Criteria for Skin Irritation Due to Hardness)

[0169] 1 Irritation due to hardness of exfoliator is too strong

[0170] 2 Irritation due to hardness of exfoliator is strong

[0171] 3 Irritation due to hardness of exfoliator is slightly strong

[0172] 4 Irritation due to hardness of exfoliator is slightly weak

[0173] 5 Irritation due to hardness of exfoliator is weak

Example 1

[0174] A 2 L round-bottom cylindrical separable flask having an inner diameter of 110 mm equipped with a reflux condenser, a nitrogen gas introduction tube, and, as a stirrer, a stirring blade having two stages each having four inclined paddle blades having a blade diameter of 50 mm was prepared. In the flask, 293 g of n-heptane was put as a hydrocarbon dispersant, 0.74 g of a maleic anhydride-modified ethylene/propylene copolymer (manufactured by Mitsui Chemicals, Inc., Hi-WAX 1105A) was added as a polymer dispersant and dissolved by heating while the mixture was stirred, and then the mixture was cooled to 58 C.

[0175] In a 500 mL Erlenmeyer flask, 82.69 g (0.399 mol, pKa: 1.4) of 2-acrylamido-methylpropanesulfonic acid whose acid dissociation index (pKa) was previously measured by the above-described method was put as a monomer A, and 68.59 g of ion-exchanged water was added to prepare an aqueous solution. While the aqueous solution was cooled from the outside, 51.60 g of a 30% by mass sodium hydroxide aqueous solution was dropped to neutralize 97 mol % of the monomer A, then, 0.08 g of hydroxylethyl cellulose (manufactured by Sumitomo Seika Chemicals Company, Limited, HEC AW-15F) as a thickener, 2.19 g of a 5% by mass 2,2azobis(2-aziminopropane) dihydrochloride aqueous solution as an azo-based compound, 3.20 g of a 3% by mass N,N-methylenebisacrylamide aqueous solution as an internal cross-linking agent, and 32.40 g of ion-exchanged water were added, and the solutes were dissolved to prepare an aqueous solution containing, as the first monomer component, the monomer A and its sodium salt.

[0176] Then, the aqueous solution, prepared as described above, containing the first monomer component was added to the separable flask, and the mixture was stirred at a stirring speed of 300 rpm for 10 minutes while nitrogen was passed through the system at a rate of 0.2 L/min. Separately, in 6.62 g of n-heptane, 0.74 g of sucrose stearate having an HLB of 3 (manufactured by Mitsubishi-kagaku Foods Corporation, RYOTO Sugar Ester S-370) as a surfactant was dissolved by heating to prepare 7.36 g of a surfactant solution. The surfactant solution was further added to the aqueous solution containing the first monomer component, the atmosphere inside the system was sufficiently replaced with nitrogen while the mixed solution was stirred at a stirring speed of 550 rpm for 20 minutes, then the separable flask was immersed in a water bath at 70 C. to raise the temperature, and polymerization was performed for 26 minutes.

[0177] After the first stage polymerization, 110 g of n-heptane was added to the system, the stirring speed was changed to 1,000 rpm, then the reaction solution was heated in an oil bath at 125 C., and 121.15 g of water was removed out of the system by azeotropic distillation of n-propane and water while n-heptane was refluxed. Then, n-heptane was evaporated, and the resulting product was dried to obtain a dried product of the crosslinked polymer (first polymer particle).

[0178] JIS standard sieves having a mesh-opening of 425 m, 300 m, 250 m, 180 m, 106 m, 75 m, and 45 m, and a saucer were combined in this order from the top. In the combined uppermost sieve, 10 g of the first polymer particles were put and rubbed on sieves by hand in order from the sieve having the largest mesh-opening to disentangle the partially observed agglomeration of the first polymer particles.

[0179] Using ROBOT SIFTER RPS 205 manufactured by Seishin Enterprise Co., Ltd., under the conditions of a sound wave intensity of 40 W/m.sup.2, a frequency of 80 Hz, a pulse interval of 1 second, and a classification time of 2 minutes, JIS standard sieves for ROBOT SIFTER having a mesh-opening of 425 m, 300 m, 250 m, 180 m, 106 m, 75 m, and 45 m were combined from the top, and the disentangled first polymer particles were put in a filling container of the apparatus and classified. After the classification, the mass of the first polymer particle remaining on each sieve was calculated as a mass percentage based on the total amount, and the particle size distribution was obtained. Based on the particle size distribution, the mass percentages on the sieves were accumulated in descending order by the particle diameter to plot the relationship between the mesh-opening of the sieve and the accumulated value of the mass percentage of the water-absorbing resin remaining on the sieve on a logarithmic probability paper. The plotted points on the probability paper were connected with a straight line to obtain a particle diameter corresponding to 50% cumulative percentage by mass as the median particle diameter. As a result, the median particle diameter of the obtained first polymer particle was 83 m.

[0180] Acrylic acid (pKa: 4.1) whose acid dissociation index (pKa) was previously measured by the above-described method was prepared as the monomer B and dissolved in ion-exchanged water to prepare 384.6 g of an 80% by mass acrylic acid aqueous solution (containing 4.27 mol of acrylic acid). The aqueous solution was put in a 2 L round-mouth wide plastic container, and while the aqueous solution was cooled from the outside, 416.7 g (3.20 mol) of a 30% by mass sodium hydroxide aqueous solution was dropped to neutralize 75 mol % of the acrylic acid aqueous solution. In this container, 6.42 g of a 5% by mass 2,2azobis(2-aziminopropane) dihydrochloride aqueous solution as an azo-based compound, 6.17 g of a 1% by mass N,N-methylenebisacrylamide aqueous solution as an internal cross-linking agent, and 164.78 g of ion-exchanged water were added, and the solutes were dissolved to prepare an aqueous solution containing, as the second monomer component, the monomer B and its sodium salt. In the aqueous solution containing the second monomer component, 15 g of the first polymer particle was immersed and sufficiently swollen in a refrigerator for 14 hours. The swollen first polymer particle and the excess aqueous solution containing the second monomer component were separated using a sieve having a mesh-opening of 38 m. The swollen first polymer particle absorbed 363.69 g of the aqueous solution containing the second monomer component.

[0181] A 2 L round-bottom cylindrical separable flask having an inner diameter of 110 mm equipped with a reflux condenser, a nitrogen gas introduction tube, and, as a stirrer, a stirring blade having two stages each having four inclined paddle blades having a blade diameter of 50 mm was prepared. In the flask, 293 g of n-heptane was put as a hydrocarbon dispersant, 0.74 g of a maleic anhydride-modified ethylene/propylene copolymer (manufactured by Mitsui Chemicals, Inc., Hi-WAX 1105A) was added as a polymer dispersant and dissolved by heating while the mixture was stirred at a stirring speed of 300 rpm, and then the mixture was cooled to 60 C.

[0182] After the cooling to 60 C., 7.36 g of a surfactant solution, that was prepared by dissolving 0.74 g of sucrose stearate having an HLB of 3 (manufactured by Mitsubishi-kagaku Foods Corporation, RYOTO Sugar Ester S-370) as a surfactant in 6.62 g of n-heptane by heating, was further added, and the mixture was stirred for 10 minutes.

[0183] After the stirring, 362.02 g of the swollen first polymer particle was added to the system, and the atmosphere inside the system was sufficiently replaced with nitrogen at a rate of 0.2 L/min while the mixture was stirred at a stirring speed of 1,000 rpm for 30 minutes. Then, the flask was immersed in a water bath at 80 C. to raise the temperature, the second stage polymerization was performed for 66 minutes, and the second monomer component infiltrated into the first polymer particle was polymerized to obtain a water-absorbing exfoliator having a structure in which the second polymer was infiltrated into the first polymer particle.

[0184] After the second stage polymerization, the reaction solution was heated in an oil bath at 125 C., 171.8 g of water was removed out of the system by azeotropic distillation of n-heptane and water while n-heptane was refluxed, then n-heptane was distilled, and the resulting product was dried to obtain a dried product of the water-absorbing exfoliator. The dried product was passed through a sieve having a mesh-opening of 850 m to obtain 144.22 g of a dried water-absorbing exfoliator.

[0185] JIS standard sieves having a mesh-opening of 425 m, 250 m, 180 m, 106 m, 75 m, and 45 m, and a saucer were combined in this order from the top. In the combined uppermost sieve, 50 g of the water-absorbing exfoliator was put and shaken for classification for 10 minutes using a ro-tap shaker. After the classification, the mass of the water-absorbing exfoliator remaining on each sieve was calculated as a mass percentage based on the total amount, and the particle size distribution was obtained. Based on the particle size distribution, the mass percentages on the sieves were accumulated in descending order by the particle diameter to plot the relationship between the mesh-opening of the sieve and the accumulated value of the mass percentage of the water-absorbing exfoliator remaining on the sieve on a logarithmic probability paper. The plotted points on the probability paper were connected with a straight line to obtain a particle diameter corresponding to 50% cumulative percentage by mass as the median particle diameter. As a result, the median particle diameter of the water-absorbing exfoliator at this time was 174 m.

[0186] The obtained water-absorbing exfoliator was classified into particles that passed through a JIS standard sieve having a mesh-opening of 500 m and remained on a JIS standard sieve having a mesh-opening of 106 m.

[0187] In a 2 L round-bottom cylindrical separable flask having an inner diameter of 110 mm equipped with a fluorine resin anchor-shaped stirring blade having a blade diameter of 90 mm, 30 g of the classified water-absorbing exfoliator was put, a solution, that was prepared by mixing 0.02 g of ethylene glycol diglycidyl ether and 0.3 g of propylene glycol that are post-crosslinking agents, 1.0 g of ion-exchanged water, and 0.3 g of isopropanol, was dropped while the mixture was stirred at 500 rpm, and the mixture was stirred for another 1 minute. The polymer was spread on a fluorine resin-coated tray having a bottom surface of 2620 cm and a depth of about 5 cm, and the tray was allowed to stand in a hot air dryer (manufactured by ADVANTEC CO., LTD., FV-320) set at 180 C. for 40 minutes. Thus, the water-absorbing exfoliator was crosslinked with the post-crosslinking agent and then passed through a sieve having a mesh-opening of 500 m to obtain 29 g of the water-absorbing exfoliator having a structure in which the second polymer was infiltrated into the first polymer particle.

[0188] Then, the pure-water absorption factor and the compression-breaking stress of the prepared water-absorbing exfoliator were measured by the above-described method, and the water-absorbing exfoliator was evaluated by panelists. The results are shown in Table 1.

Example 2

[0189] A water-absorbing exfoliator was prepared in the same manner as in Example 1, except that the addition amount of the 3% by mass N,N-methylenebisacrylamide aqueous solution that was the internal cross-linking agent of the first polymer particle was changed to 3.38 g in Example 1.

[0190] Then, the pure-water absorption factor and the compression-breaking stress of the prepared water-absorbing exfoliator were measured by the above-described method, and the water-absorbing exfoliator was evaluated by panelists. The results are shown in Table 1.

Example 3

[0191] A water-absorbing exfoliator was prepared in the same manner as in Example 1, except that the addition amount of the 3% by mass N,N-methylenebisacrylamide that was the internal cross-linking agent of the first polymer particle was changed to 3.60 g in Example 1.

[0192] Then, the pure-water absorption factor and the compression-breaking stress of the prepared water-absorbing exfoliator were measured by the above-described method, and the water-absorbing exfoliator was evaluated by panelists. The results are shown in Table 1.

Comparative Example 1

[0193] A low-density polyethylene fine particle manufactured by Sumitomo Seika Chemicals Company, Limited (flow beads CL8007, low-density polyethylene spherical particle, particle diameter: 0.6 mm) was prepared and used as the exfoliator in Comparative Example 1.

[0194] Then, the pure-water absorption factor and the compression-breaking stress of the prepared exfoliator were measured by the above-described method, and the exfoliator was evaluated by panelists. When the exfoliator was evaluated by panelists, a cosmetic was prepared without classification of the low-density polyethylene fine particles because the particle diameter of the low-density polyethylene fine particle was not increased owing to water absorption. The results are shown in Table 1.

Comparative Example 2

[0195] A water-absorbing resin particle manufactured by Sumitomo Seika Chemicals Company, Limited (AQUA KEEP SA50II, acrylic acid polymer partial sodium salt crosslinked product, particle diameter: 256 m) was prepared and used as the water-absorbing exfoliator in Comparative Example 1.

[0196] Then, the pure-water absorption factor and the compression-breaking stress of the prepared water-absorbing exfoliator were measured by the above-described method, and the water-absorbing exfoliator was evaluated by panelists. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Pure-water Compression- Skin absorption breaking Massage irritation due factor (g/g) stress (N) effect to hardness Example 1 140 0.24 4 5 Example 2 114 0.38 5 5 Example 3 103 0.51 5 4 Comparative No water 15 N or more 4 1 Example 1 absorption (upper limit or more) Comparative 739 0.09 2 5 Example 2

[0197] As is clear from the results shown in Table 1, it can be found that the water-absorbing exfoliators in Examples 1 to 3 exhibit suitable hardness by absorbing water, provide little skin irritation, and have a favorable skin massage effect.