Fibroin-coated pigment and processes for producing same

A fibroin-coated pigment and two processes for producing the same are disclosed. The fibroin-coated pigment comprises a carrier pigment in the form of finely divided particles whose surfaces are substantially coated with a film of regenerated fibroin and is characterized in that at least 50% by weight of the regenerated fibroin is constituted of hot-water-insoluble fibroin having the .beta.-configuration.

BACKGROUND OF THE INVENTION 
This invention relates to a fibroin-coated pigment comprising a carrier 
pigment in the form of finely divided particles whose surfaces are 
substantially coated with a film of silk fibroin coagulated and 
precipitated from a solution thereof (hereinafter referred to as a film of 
regenerated fibroin) and having great utility in the manufacture of 
cosmetic preparations, coating compositions and the like, and to processes 
for producing the same. 
Conventionally, pigments for use in cosmetic preparations and coating 
compositions have several disadvantages. That is, when dispersed in water, 
such pigments are liable to aggregation and precipitation, and when 
dispersed in oil, their oil absorption properties are suppressed to such 
an extent that they are hardly wetted with oil, cannot be dispersed 
therein satisfactorily, and hence are apt to aggregate. Especially in the 
case of cosmetic preparations, such pigments remove moisture and grease 
from the skin and bring about a dehydrated, degreased or dried condition 
which may roughen the skin. Moreover, they lack adhesion to the skin, 
spreadability on the skin, smoothness and the like. Thus, the direct use 
of such pigments can hardly produce satisfactory cosmetic effects. 
Furthermore, it is said that, when calcium carbonate and the like adsorb 
moisture thereon, the pH of the skin surface becomes alkaline and tends to 
roughen the skin. 
In order to improve the properties of such pigments, a process for the 
production of a pigment having a silk-vinyl coating is disclosed in 
Japanese Patent Publication No. 250/'53. According to this process, a 
pigment (such as titanium oxide, zinc oxide, kaolin, talc, etc.) is mixed 
with a methanolic solution of polyvinyl acetate. While the resulting 
mixture is being stirred, a caustic potash solution containing fibroin is 
added thereto drop by drop to form and precipitate polyvinyl alcohol by 
the saponification of the polyvinyl acetate and, at the same time, to 
coagulate the fibroin by the action of the methanol. The white gelatinous 
precipitate so formed is heat-treated at 95.degree. C. in the 
water-methanol-caustic potash system, allowed to cool, separated from the 
liquid phase, neutralized with hydrochloric acid, washed with alcohol and 
water, and then dried under reduced pressure. 
However, the coated pigment obtained by this process has a coating composed 
of polyvinyl alcohol and fibroin. Though heat-treated (or crystalized), 
the polyvinyl alcohol tends to swell and dissolve in water. Accordingly, 
when water-base paints and cosmetics (such as face-powder fluid, cream and 
lotion) containing this coated pigment are stored for a long period of 
time, the polyvinyl alcohol may swell or dissolve. Moreover, when this 
coated pigment is dyed, the polyvinyl alcohol may dissolve in the dyeing 
solution and cause the surfaces of the pigment particles to be exposed 
partially. In consequence, the resulting coated pigment lacks in 
dispersibility in water and evenness of dyeability, and the final products 
(e.g., cosmetic preparations) containing it are poor in such properties as 
adhesion, spreadability, storage stability, etc. Furthermore, the fibroin 
present in the coating is denatured and hardened to a considerable degree 
because of the use of alkali in the production process and the heat 
treatment in the presence thereof, and it is not intimately mixed with the 
hard polyvinyl alcohol. Accordingly, the coating is apt to break as a 
result of intensive blending during the manufacture of coating 
compositions and cosmetic preparations (such as face powder and cheek 
rouge) in powder form. Moreover, this coated pigment is poor in such 
properties as feeling, adhesion to the skin, spreadability on the skin, 
oil absorption, dispersibility in oil, color fastness, etc., and is liable 
to undergo peeling-off of the coating and bleeding of the dye under the 
influence of water or sweat. In addition, the above-described process 
involves the use of large amounts of strong alkali (which is apt to 
denature fibroin) and methanol (which is toxic and dangerous) and requires 
a considerable number of troublesome operations, which makes it difficult 
to put this process into practice on an industrial scale. 
In Japanese Patent Publication No. 299/'52, a formulation for the 
production of a face powder is described as Example 4. According to this 
formulation, a portion of 1.385 g of a pigment is intimately mixed with 
5.0 g of a colloidal solution of fibroin (as a binder). Then, the 
remainder of the pigment and an appropriate amount of coloring matter are 
added to and blended with the resulting mixture. Finally, 35 g of perfume 
is incorporated therein to obtain a face powder. 
However, it is well known that, when such a small amount of binder (i.e., a 
colloidal solution of fibroin) is mixed with a large amount of pigment, 
the binder is only partially deposited on the surface of the pigment 
particles, and not over the entire surfaces of the pigment particles. Even 
if the pigment having the binder deposited thereon is dried (in air or by 
heating), the structure in which the surfaces of the pigment particles are 
uniformly coated with a film of fibroin is not created and, moreover, the 
fibroin is scarcely converted into that type of fibroin having the 
.beta.-configuration. Accordingly, this fibroin-loaded pigment and the 
face powder containing it are insufficient in such properties as adhesion 
to the skin, spreadability on the skin, and oil absorption, and the 
fibroin present on the surfaces of the pigment particles tends to cohere 
or peel off under the influence of water or sweat. Thus, they can hardly 
produce good cosmetic effects. 
In addition, silk powder (consisting of fibroin alone) has been used in 
cosmetic preparations in powder form, because of its silk-like feeling, 
good gloss, high ultraviolet-absorbing powder, moderate 
hydrophilic-lipophilic balance, good adhesion to the skin, and the like. 
However, silk powders produced by conventional grinding techniques, silk 
powders in granular form, and the like do not permit microscopically 
intimate mixing. Moreover, in order that the covering power and gloss of 
the pigment (e.g., talc, titanium oxide, mica, etc.) may be retained to a 
full extent, they must be used in an amount of no more than several 
percent. Accordingly, it is impossible to make good use of the excellent 
properties possessed inherently by fibroin. In order to utilize the 
properties of fibroin, the use of a microscopically intimate mixture in 
which the surfaces of finely divided particles of a pigment are masked (or 
coated) with fibroin particles is ideal. However, this is utterly 
infeasible in view of the particle shape and particle size of conventional 
silk powders. 
BRIEF SUMMARY OF THE INVENTION 
The above-described disadvantages of the prior art can be wholly overcome 
by this invention. Thus, it is an object of this invention to provide a 
fibroin-coated pigment which is very excellent in such properties as 
adhesion, spreadability, dispersibility, compatibility, covering power, 
oil absorption, hydrophilic-lipophilic balance, the ability to prevent the 
formation of oil droplets, feeling, skin-protecting ability, dyeability, 
coating stability, etc. and which is very useful in the manufacture of 
cosmetic preparations, coating compositions and the like. Another object 
of this invention is to provide processes for producing such a 
fibroin-coated pigment with industrial advantages. 
In accordance with one aspect of this invention, there is provided a 
fibroin-coated pigment comprising a carrier pigment in the form of finely 
divided particles whose surfaces are substantially coated with a film of 
regenerated fibroin, characterized in that at least 50% by weight of the 
regenerated fibroin is constituted of hot-water-insoluble fibroin having 
the .beta.-configuration. 
In accordance with another aspect of this invention, there is provided a 
process for producing a fibroin-coated pigment which comprises the steps 
of dissolving a degummed silk material in at least one solvent selected 
from the group consisting of an aqueous cupri-ethylenediamine solution, an 
aqueous ammoniacal solution of cupric hydroxide, an aqueous alkaline 
solution of cupric hydroxide and glycerol, an aqueous lithium bromide 
solution, an aqueous solution of the chloride, nitrate or thiocyanate of 
calcium, magnesium or zinc, and an aqueous sodium solution; dispersing a 
carrier pigment in the resulting fibroin solution having a fibroin 
concentration of from 3 to 20% by weight; adding a coagulating salt to the 
pigment-loaded fibroin solution to coagulate and precipitate (or 
regenerate) the fibroin; dehydrating and drying the resulting coagulum; 
and then pulverizing the dried product. 
In accordance with still another aspect of this invention, there is 
provided a process for producing a fibroin-coated pigment which comprises 
the steps of dissolving a degummed silk material in at least one solvent 
selected from the group consisting of an aqueous cupri-ethylenediamine 
solution, an aqueous ammoniacal solution of cupric hydroxide, an aqueous 
alkaline solution of cupric hydroxide and glycerol, an aqueous lithium 
bromide solution, an aqueous solution of the chloride, nitrate or 
thiocyanate of calcium, magnesium or zinc, and an aqueous sodium 
thiocyanate solution; dialyzing the resulting fibroin solution; dispersing 
a carrier pigment in the resulting aqueous fibroin solution having a 
fibroin concentration of from 3 to 20% by weight; subjecting the 
pigment-loaded aqueous fibroin solution to at least one treatment for 
coagulating and precipitating (or regenerating) the fibroin, the treatment 
being selected from the group consisting of the addition of a coagulating 
salt, aeration, coagulation at the isoelectric point, exposure to 
ultrasonic waves, and agitation at high shear rate; dehydrating and drying 
the resulting coagulum; and then pulverizing the dried product. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The fibroin-coated pigment of this invention comprises a carrier pigment in 
the form of finely divided particles whose surfaces are substantially 
coated with a film of regenerated fibroin, and the film of regenerated 
fibroin usually forms a substantially uniform coating on the pigment 
particles. In addition, it is characterized by the fact that at least 50% 
by weight, preferably from 80 to 100% by weight, and most preferably from 
90 to 100% by weight of the regenerated fibroin is constituted of 
hot-water-insoluble fibroin having the .beta.-configuration. If the 
hot-water-insoluble fibroin content is less than 50% by weight, the 
fibroin becomes extremely hydrophilic. As a result, the fibroin-coated 
pigment undergo agglomeration or cohesion under the influence of water or 
sweat to form secondary particles (i.e., they gather together to form 
coarse particles). Moreover, the film is apt to peel off when the 
dispersion medium is water (e.g., in the case of water-base paints and 
cosmetics), and the dispersibility is apt to decrease when the dispersion 
medium is oil (e.g., in the case of oil-base paints and cosmetics). 
Furthermore, when applied to the skin, the fibroin-coated pigment is poor 
in such properties as spreadability, feeling, etc. 
The term "hot-water-insoluble fibroin" as used herein means that type of 
fibroin which cannot be dissolved by boiling it in hot water at 
100.degree. C. for 15 minutes. This hot-water-insoluble fibroin is 
characterized by the fact that the hydrogen bonding between fibroin 
molecules represents essentially the .beta.-configuration. 
The film of regenerated fibroin generally has a degree of crystallinity of 
at least 10% and preferably from 20 to 43%, though it may vary slightly 
according to the conditions of the production process. 
The degree of crystallinity of the film of regenerated fibroin present in 
the fibroin-coated pigment of this invention is generally lower than the 
degrees of crystallinity (ranging from about 50 to about 55%) of natural 
silk thread and degummed silk materials, and markedly higher than the 
degree of crystallinity of the films of regenerated fibroin obtained by 
prior art processes such as those described in Japanese Patent Publication 
Nos. 250/'53 and 299/'52. Moreover, the hot-water-insoluble fibroin 
content (or the rate of .beta.-configuration) of regenerated fibroin 
present in the fibroin-coated pigment of this invention is much higher 
than the hot-water-insoluble fibroin contents of the regenerated fibroins 
obtained by the aforesaid prior art processes. 
The film of regenerated fibroin is present in an amount of from 2 to 100% 
by weight and preferably from 5 to 50% by weight based on the weight of 
the carrier pigment. If the amount is less than 2% by weight, the desired 
structure in which the surfaces of finely divided particles of a carrier 
pigment is substantially coated with a film of regenerated fibroin cannot 
be created. Accordingly, it is difficult to endow the fibroin-coated 
pigment with satisfactorily good properties such as adhesion, 
spreadability, dispersibility, covering power, skin-protecting ability, 
feeling, etc. On the other hand, if the amount is greater than 100% by 
weight, the fibroin-coated pigment may tend to decrease in covering power. 
The film of regenerated fibroin generally has a thickness of from 0.01 to 
50.mu.. 
The regenerated fibroin present in the fibroin-coated pigment of this 
invention has an average molecular weight of not less than 50,000 and 
preferably from 80,000 to 150,000. 
The fibroin-coated pigment of this invention has a maximum particle 
diameter of from 0.05 to 100.mu., preferably from 0.05 to 60.mu., and most 
preferably from 0.1 to 30.mu.. If the maximum particle diameter is greater 
than 100.mu., the fibroin-coated pigment tends to become poor in such 
properties as adhesion to the skin, affinity for the skin, spreadability 
on the skin, etc. 
The carrier pigment which is used in the fibroin-coated pigment of this 
invention can be any of the well-known pigments for use in cosmetic 
preparations and coating compositions, including white pigments, color 
pigments, extender pigments, pearlescent pigments and the like. Typical 
examples thereof are talc, kaolin, mica, calcium carbonate, titanium 
oxide, zinc oxide, micaceous titanium, magnesium carbonate, iron oxides, 
zinc stearate, magnesium stearate, magnesium silicate and organic 
pigments. These pigments may be used alone or in combination. The carrier 
pigment generally has a maximum particle diameter of from 0.03 to 100.mu.. 
As stated before, the fibroin-coated pigment of this invention is 
characterized by the fact that the film of regenerated fibroin forms a 
substantially uniform coating on the pigment particles. Accordingly, the 
fibroin-coated pigment can be colored evenly, brightly and fadelessly with 
dyestuffs for silk such as acid dyes, metallized dyes, etc., and it can 
also be used effectively used as a colored pigment. 
The manner in which the surface of finely divided particles of the carrier 
pigment is coated with the film of regenerated fibroin can be observed by 
dyeing the fibroin-coated pigment with Tartrazine NS (C.I. Acid Yellow 23) 
known as an acid dye or Shirlastain A (Imperial Chemical Industry Co., 
Ltd.) known as a dye for identification of silk, and then examining the 
evenly and brightly colored particles microscopically in comparison with 
uncoated and hence uncolored particles of the same pigment. More 
specifically, the fibroin-coated pigment of this invention is dyed in a 
bright yellow color with Tartrazine NS and in a dark brown color wth 
Shirlastain A, while the carrier pigment is not dyed at all. 
Also as stated before, the fibroin-coated pigment of this invention has the 
structure in which the surfaces of finely divided particles of a carrier 
pigment are substantially coated with a film of regenerated fibroin, and 
takes the form of a fine powder. Accordingly, the fibroin-coated pigment 
per se is markedly excellent in such properties as adhesion to the skin, 
spreadability, feeling, moisture retention, buffer capacity, covering 
power, hydrophilic-lipophilic balance, skin-protecting ability, etc. Thus, 
the fibroin-coated pigment of this invention can overcome the 
disadvantages of conventional pigments, i.e., the problems of dehydration, 
degreasing or drying of the skin, of alkalification of the skin surface, 
and the like, and can keep the skin intact. 
In addition, the film of regenerated fibroin has a high rate of 
.beta.-configuration because at least 50% by weight of the regenerated 
fibroin is constituted of hot-water-insoluble fibroin having the 
.beta.-configuration, and has a moderate degree of molecular orientation. 
Accordingly, when used in water-base or oil-base coating compositions and 
cosmetic preparations, the fibroin-coated pigment of this invention is 
also markedly excellent in such properties as the uniformity of 
dispersion, the ability to prevent the formation of oil droplets, 
stability, compatibility with inorganic powder materials, color fastness, 
the ability to control the moisture content of the skin, etc. Thus, the 
fibroin-coated pigment of this invention does not present the 
above-described phenomena, such as agglomeration or cohesion, the 
formation of secondary particles, peeling-off of the coating, etc., under 
the influence of water or sweat. 
As described above, the fibroin-coated pigment of this invention has great 
utility in the manufacture of cosmetic preparations and coating 
compositions, and can thereby produce beneficial cosmetic and coating 
effects. 
In accordance with this invention, the fibroin-coated pigment having the 
aforesaid meritorious features can be produced by either of the 
above-described two processes. 
The solvent for fibroin which is used in the practice of this invention can 
be an aqueous cupri-ethylenediamine solution, an aqueous ammoniacal 
solution of cupric hydroxide (Schweitzer's reagent), an aqueous alkaline 
solution of cupric hydroxide and glycerol (Roe's reagent), an aqueous 
lithium bromide solution, an aqueous solution of the chloride, nitrate or 
thiocyanate of calcium, magnesium or zinc, or an aqueous sodium 
thiocyanate solution. However, it is preferable to use an aqueous solution 
of the chloride or nitrate of calcium or magnesium, because of its low 
cost and convenience for use. The concentration of these solutions may 
vary according to the type of solute used, temperature and the like. Where 
an aqueous solution of a metal salt is used, its concentration is 
generally from 10 to 80% by weight, preferably from 20 to 70% by weight, 
and most preferably from 25 to 60% by weight. 
The silk material which is used in the practice of this invention can be 
cocoons, raw silk, waste cocoons, raw silk waste, bisu, unreelable 
cocoons, silk fabric waste, bourette or the like. Prior to use, the silk 
material is degummed or freed from sericin by any conventional procedure. 
This can be done, for example, by washing the silk material in warm water 
containing a surface-active agent or an enzyme, as required, and then 
drying it. 
The fibroin solution which is used in the practice of this invention is a 
solution obtained by dissolving an appropriate amount of the degummed silk 
material in the above-defined solvent for fibroin. More specifically, 
employing a suitable apparatus such as kneader, the degummed silk material 
is added to the solvent and made into a homogeneous solution at a 
temperature of from 60.degree. to 95.degree. C. and preferably from 
70.degree. to 85.degree. C. Where the coagulation step is to be carried 
out by the addition of a coagulating salt (according to the first process 
of this invention), the resulting fibroin solution may be used directly, 
that is, without subjecting it to dialysis. However, where the coagulation 
step is to be carried out by other means (according to the second process 
of this invention), the fibroin solution must be dialyzed prior to use. It 
is more preferable to dialyze the fibroin solution in case of the addition 
of a coagulating salt. 
In the dialysis step, it is desirable to remove the salt and other 
contaminants almost completely by means of a dialyzer using semipermeable 
membranes or hollow fibers, typically made of cellulose acetate. In order 
that a stabler gel of fibroin may be rapidly formed on the surfaces of 
finely divided particles of the carrier pigment, there must be a proper 
correlation between the volume of the fibroin solution to be dialyzed and 
the surface area of the dialysis membrane. More specifically, the dialysis 
step should desirably be carried out by the use of a multilayer membrane 
structure or bundled hollow-fiber structure satisfying the condition 
expressed by 
##EQU1## 
where the priming volume means the internal volume within the dialysis 
tubes or between the layers of dialysis membrane. The above-defined ratio 
preferably has a value of not less than 30 and most preferably a value of 
not less than 50. 
In order to satisfy the aforesaid condition, it is necessary to keep the 
spacing between the layers of dialysis membrane at 2 mm or less in the 
case of a multilayer membrane structure or to keep the diameter of hollow 
fibers at 4 mm or less in the case of a bundled hollow-fiber structure. 
The aqueous fibroin solution resulting from this dialysis step has a very 
low residual salt concentration of from 0.03 to 0.06% by weight, so that 
the purity of fibroin can preferably be maintained at a high level. 
The aqueous fibroin solution resulting from the dialysis step is adjusted, 
either by concentration or by dilution, to a predetermined fibroin 
concentration. 
The fibroin solution or aqueous fibroin solution which is used in the 
practice of this invention should have a fibroin concentration of from 3 
to 20% by weight, preferably from 4 to 15% by weight, and most preferably 
from 5 to 10% by weight. If the fibroin concentration is less than 3% by 
weight, an uneconomically long time is required for the coagulation of the 
fibroin solution or aqueous fibroin solution and a uniform gel of fibroin 
is not formed on the surfaces of finely divided particles of the carrier 
pigment. On the other hand, if the fibroin concentration is greater than 
20% by weight, it may be difficult to dehydrate the resulting coagulum in 
a subsequent dehydration step. Furthermore, if the fibroin concentration 
is outside the aforesaid range, the resulting film of regenerated fibroin 
may be low in hot-water-insoluble fibroin content (or the rate of 
.beta.-configuration) and, therefore, the resulting fibroin-coated pigment 
tends to agglomerate, form secondary particles, or undergo peeling-off of 
the coating under the influence of sweat or water used as a dispersion 
medium. 
While a required amount of the fibroin solution or aqueous fibroin solution 
is being stirred, the above-defined carrier pigment is added thereto and 
dispersed therein to form a homogeneous suspension. Then, this suspension 
is subjected to a coagulation step. 
The amount of fibroin solution or aqueous fibroin solution used may vary 
according to the fibroin concentration thereof, the amount of regenerated 
fibroin desired, and the like. However, the fibroin solution or aqueous 
fibroin solution is generally used in an amount of not less than 100% by 
weight, preferably not less than 300% by weight, and most preferably from 
500 to 1,000% by weight based on the weight of the carrier pigment. If the 
amount is less than 100% by weight, the film of regenerated fibroin is 
only partially deposited on the surfaces of the pigment particles and is 
incapable of coating them to a substantial degree. Accordingly, the 
resulting fibroin-coated pigment is hardly endowed with satisfactorily 
good properties such as adhesion to the skin, spreadability, covering 
power, evenness of dyeability, skin-protecting ability, dispersibility, 
hydrophilic-lipophilic balance, etc. Generally speaking, larger amounts of 
the fibroin solution or aqueous fibroin solution produce better results. 
However, the use of too large amounts of the fibroin solution or aqueous 
fibroin solution uneconomically increases the required amount of a 
coagulating agent and the like. 
As stated before, the coagulation step for the pigment-loaded fibroin 
solution is carried out by the addition of a coagulating salt. In case of 
the pigment-loaded aqueous fibroin solution, however, the coagulation step 
is carried out by subjecting it to a treatment selected from the group 
consisting of the addition of a coagulating salt, aeration, coagulation at 
the isoelectric point, exposure to ultrasonic waves, agitation at high 
shear rate, and combinations thereof. 
The coagulating salt can be any salt that coagulates the fibroin present in 
the pigment-loaded fibroin solution or aqueous fibroin solution. Typical 
examples thereof are sodium chloride, potassium chloride, sodium sulfate, 
potassium sulfate, ammonium sulfate, sodium nitrate, potassium nitrate and 
the like. The coagulating salt may be added as such or in the form of an 
aqueous solution. The coagulating salt is used in an amount of from 2 to 
10% by weight based on the weight of the water present in the coagulation 
system. 
Aeration is carried out by bubbling air through the pigment-loaded aqueous 
fibroin solution according to any suitable technique. For each liter of 
the pigment-loaded aqueous fibroin solution, air is generally fed at a 
rate of at least 0.1 l/min. The aeration time is generally 10 minutes or 
more, though it may vary according to the feed rate of air. 
Coagulation at the isoelectric point is carried out by adding an inorganic 
acid (such as hydrochloric acid, sulfuric acid, etc.) or an organic acid 
(such as acetic acid, citric acid, etc.), with stirring, to the 
pigment-loaded aqueous fibroin solution until its pH reaches 4.5. Then, 
this pigment-loaded aqueous fibroin solution is usually allowed to stand 
at room temperature for a period of 10 minutes or more. 
Exposure to ultrasonic waves is carried out by placing the pigment-loaded 
aqueous fibroin solution in an ultrasonic wave generator and exposing it, 
with stirring, to ultrasonic waves which generally have a frequency of 30 
kHz or more. The fibroin is coagulated by continuing this treatment at 
room temperature for a period of 1 hour or more. 
The fibroin can also be coagulated and precipitated simply by agitating the 
pigment-loaded aqueous fibroin solution. However, this agitation must be 
carried out at a high shear rate which is generally 50/sec or more and 
preferably 100/sec or more. The agitation time required for gelation is 
generally 1 hour or more, though it may vary according to the fibroin 
concentration of the aqueous fibroin solution, the shear rate employed, 
and the like. 
During this agitation at high shear rate, methyl alcohol, ethyl alcohol, 
isopropyl alcohol or acetone may be added to the pigment-loaded aqueous 
fibroin solution in order to increase the rate of .beta.-configuration of 
the regenerated fibroin to 90% or more. The amount of alcohol or acetone 
added is suitably from 1 to 100% by weight based on the weight of the 
pigment-loaded aqueous fibroin solution. However, the addition of such a 
water-soluble organic solvent is not a requisite for this invention. 
After the pigment-loaded fibroin solution or aqueous fibroin solution has 
been subjected to one or more of the above-described treatments for 
coagulating the fibroin, the resulting coagulum (consisting of the carrier 
pigment coated with a gel of regenerated fibroin) is dehydrated for the 
purpose of separating it from the liquid phase (consisting of water and 
other components). This dehydration step is preferably carried out by the 
use of a centrifuge, and the gel of regenerated fibroin present on the 
surfaces of the pigment particles is generally dehydrated to a water 
content of the order of from 100 to 500% by weight based on its dry 
weight. The dehydrated coagulum can then be easily dried to the absolute 
dry state. This drying step is carried out at a temperature of from 
60.degree. to 120.degree. C. under normal or reduced pressure. 
The dried product (consisting of aggregates of the pigment particles coated 
with a film of regenerated fibroin) is easily pulverized by the use of a 
pulverizer such as hammer mill, jet mill, etc. The particle size should 
generally be adjusted to a maximum particle diameter of from 0.05 to 
100.mu., preferably from 0.05 to 60.mu., and most preferably from 0.1 to 
30.mu.. 
The resulting fibroin-coated pigment, which is characterized by the fact 
that at least 50% by weight of the regenerated fibroin is constituted of 
hot-water-insoluble fibroin, is excellent in such properties as 
hydrophilic-lipophilic balance, the ability to prevent the formation of 
oil droplets, moisture retention, water resistance, dispersibility in 
water or oil, etc. and is scarcely liable to the formation of secondary 
particles, cohesion, excessive swelling and the like under the influence 
of water or sweat. However, the regenerated fibroin can further be 
insolubilized in hot water (i.e., its hot-water-insoluble fibroin content 
or rate of .beta.-configuration can further be enhanced) and, therefore, 
the aforesaid properties thereof can further be improved by the 
application of a wet heat treatment as described below. 
The wet heat treatment can be carried out according to either of the 
following two procedures. That is, the product resulting from the drying 
or pulverizing step may be heat-treated with saturated steam at a 
temperature of 50.degree. C. or above and preferably from 80.degree. to 
120.degree. C. alternatively, prior to the drying step, the coagulum may 
be heat-treated at a temperature of 50.degree. C. or above in an aqueous 
solution of a neutral salt such as sodium chloride potassium chloride, 
sodium sulfate, potassium sulfate, ammonium sulfate, sodium nitrate, etc. 
or in an organic solvent such as acetone, alcohol, etc. By the application 
of this wet heat treatment, not only the regenerated fibroin can further 
be insolubilized in hot water (i.e., its rate of .beta.-configuration can 
further be enhanced) as described above, but also its degree of 
crystallinity can further be increased, so that the resulting 
fibroin-coated pigment is likely to be excellent in such properties as 
hydrophilic-lipophilic balance, the ability to prevent the formation of 
oil droplets, dispersibility in various dispersion media, coating 
stability, color fastness, etc. 
This invention is further illustrated by the following examples. In these 
examples, parts and percentages are by weight, except for the percentages 
representing degrees of crystallinity. 
With respect to the fibroin-coated pigments obtained in these examples, the 
amount (%) of regenerated fibroin present on the pigment particles, the 
hot-water-insoluble fibroin content (%) of the regenerated fibroin, and 
the degree of crystallinity (%) of the film of regenerated fibroin were 
determined according to the following procedures. 
1. Amount (%) of Regenerated Fibroin Present on Pigment Particles 
The nitrogen content (%) of a sample (of a fibroin-coated pigment to be 
tested) is determined by the Kjeldahl method [J. Kjeldahl: Z. anal. Chem., 
22, 366 (1883)]. From this nitrogen content, the regenerated fibroin 
content (%) of the sample is calculated according to the following 
equation: 
EQU Regenerated Fibroin Content (%) of Sample=Nitrogen Content 
(%).times.(100/16) 
Then, this regenerated fibroin content of the sample is converted into the 
amount (%) of regenerated fibroin present on the pigment particles. 
2. Hot-water-insoluble Fibroin Content (%) of Regenerated Fibroin 
A 10-g sample (absolute dry weight) of a fibroin-coated pigment to be 
tested is boiled in 1 l of hot water at a temperature of 100.degree. C. 
for a period of 15 minutes, and the absolute dry weight of the undissolved 
portion of the sample is measured. Thus, the weight of the dissolved 
fraction of the regenerated fibroin is determined. Then, the 
hot-water-insoluble fibroin content (%) is calculated according to the 
following equation: 
##EQU2## 
where W stands for the weight of the regenerated fibroin present in the 
sample and w for the weight of the dissolved fraction of the regenerated 
fibroin. If the carrier pigment is more or less soluble in hot water, it 
is boiled under the same conditions to determine its solubility, which is 
used to correct the weight of the dissolved fraction of the regenerated 
fibroin. 
3. Degree of Crystallinity (%) of Film of Regenerated Fibroin 
Employing the reflection method, the X-ray diffraction intensity curve of a 
sample powder is automatically recorded over an angle range of 
2.delta.=10.degree.-35.degree. C. Then, the fibroin intensity curve is 
derived by subtracting the diffraction peaks attributable to the carrier 
pigment from the above X-ray diffraction intensity curve. The area under 
this fibroin intensity curve is denoted by Xs. On the other hand, a 
reference powder containing amorphous fibroin and the carrier pigment in 
the same proportion as that of the sample powder is prepared, and the 
X-ray diffraction intensity curve thereof is obtained in the same manner 
as described above. The area under the similarly derived amorphous fibroin 
intensity curve is denoted by Xa. Then, the degree of crystallinity (%) is 
calculated according to the following equation: 
##EQU3## 
The amorphous fibroin is prepared by pouring a 5% (w/w) aqueous fibroin 
solution on a Teflon plate, drying it at a temperature of 50.degree. C., 
and then grinding the resulting film at low temperatures.

EXAMPLE 1 
Spun silk waste was used as the starting material for the production of a 
fibroin-coated pigment. One hundred parts of spun silk waste was added to 
a solution of 30 parts of marseille soap in 3,000 parts of water, stirred 
at 95.degree.-98.degree. C. for 3 hours to reduce its gum content to 0.1% 
or less, washed with water, and then dried in hot air at 80.degree. C. An 
aqueous solution containing 8% of ethylenediamine and 6% of cupric 
hydroxide (i.e., a cupri-ethylenediamine solution) was prepared, and 10 
parts of the spun silk waste degummed and dried as above was dissolved in 
100 parts of the cupri-ethylenediamine solution by stirring at room 
temperature for 5 minutes. The resulting solution was immediately adjusted 
to pH 6.8 with 10% acetic acid and then diluted with water to prepare a 5% 
fibroin solution. 
To 100 parts of this 5% fibroin solution was added 10 parts of talc having 
a maximum particle diameter (or major diameter) of 10-20.mu.. The 
resulting mixture was vigorously stirred at room temperature to form a 
homogeneous suspension. While this suspension was being vigorously 
stirred, 20 parts of a 30% aqueous solution of sodium sulfate was added 
thereto and mixed therewith to coagulate and precipitate (or regenerate) 
the fibroin on the surfaces of the talc particles. The coagulum so formed 
was separated by filtration, washed thoroughly with water until the 
washings no longer contained sulfate ions, dehydrated by centrifugation, 
and then dried at 105.degree. C. The resulting product was pulverized in a 
hammer mill to obtain a fibroin-coated pigment having a particle diameter 
of 10-30.mu.. When this fibroin-coated pigment was dyed with a 2% aqueous 
solution of the acid dye Tartrazine NS and then examined under an optical 
microscope, the entire surfaces of the particles were found to be brightly 
and evenly colored in yellow. This demonstrates that the particles of the 
talc used as the carrier pigment were uniformly coated with a film of 
regenerated fibroin. (When talc alone was dyed under the same conditions, 
it was not colored at all.) 
When determined according to the above-described procedures, the amount of 
regenerated fibroin present on the talc particles was 50.1% based on the 
weight of the talc, and the hot-water-insoluble fibroin content of the 
regenerated fibroin was 50.2% based on the weight of the regenerated 
fibroin. Moreover, the film of regenerated fibroin had a degree of 
crystallinity of 10.1%, while a powder of the degummed spun silk waste had 
a degree of crystallinity of 51%. 
Then, the above fibroin-coated pigment (Test Run 1), talc having 3% of a 
conventional fibroin powder (or silk powder) blended therewith (Control 
Run 1), talc having 50.1% of the same fibroin powder blended therewith 
(Control Run 2), and talc alone (control Run 3) were subjected to 
practical performance tests for the purpose of evaluating their 
performance as a cosmetic preparation (e.g., face powder). These tests 
were conducted by a panel of 10 skilled examiners. The results thus 
obtained are summarized in Table 1. 
TABLE 1 
______________________________________ 
Mois- Ad- Spread- 
Oil 
ture hesion ability 
Ab- 
Powder Reten- to the on the sorp- Feel- 
Covering 
Sample tion Skin Skin tion ing Power 
______________________________________ 
Test Run 1 
.circleincircle. 
.circle. 
.circle. 
.circleincircle. 
.circleincircle. 
.circle. 
Control 
Run 1 .DELTA. .DELTA. .circle. 
.DELTA. 
.circle. 
.circle. 
Control 
Run 2 .circleincircle. 
.circle. 
X .circleincircle. 
X X 
Control 
Run 3 X X .DELTA. 
X .circle. 
.circleincircle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X) 
Thus, the fibroin-coated pigment produced in accordance with this invention 
were very good or good in such properties as moisture retention, adhesion 
to the skin, spreadability on the skin, oil absorption and feeling, and 
proved to be very useful as a base material for cosmetic preparations such 
as face powder, etc. 
EXAMPLE 2 
Spun silk waste was degummed in the same manner as described in Example 1 
and used as the starting material for the production of a fibroin-coated 
pigment. One hundred parts of a 50% aqueous solution of calcium chloride 
was prepared by dissolving 82 parts of calcium chloride 
(CaCl.sub.2.4H.sub.2 O) in 18 parts of water, and then heated to 
110.degree. C. Thereafter, 10 parts of the degummed spun silk waste was 
added, with stirring, to the calcium chloride solution over a period of 5 
minutes and dissolved therein completely by stirring for an additional 30 
minutes. The resulting fibroin-calcium chloride solution was cooled and 
then desalted by dialysis. More specifically, the fibroin-calcium chloride 
solution was placed in a cellulose tube having an internal diameter of 7-8 
cm and a length of 1 m, its both ends were sealed, and the tube was 
immersed in running water for 15-25 hours, whereby the salt concentration 
of the solution was reduced to 0.01% or less. After completion of the 
dialysis, the resulting aqueous fibroin solution had a fibroin 
concentration of 5.1%. 
While 50 parts of this aqueous fibroin solution was being stirred, 10 parts 
of titanium oxide having a particle diameter of 0.1-10.mu. was added 
thereto and dispersed therein to form a homogeneous suspension. In order 
to coagulate and precipitate the fibroin (i.e., in order to effect 
gelation of the fibroin), this suspension was intensively agitated at room 
temperature by means of such an agitator as to give a shear rate of 
100/sec. Initially, the coagulation system was in the form of an aqueous 
fibroin solution having titanium oxide suspended therein. In the course of 
2-3 hours' agitation, the fibroin gradually coagulated and precipitated on 
the surfaces of the titanium oxide particles. Ultimately, the whole system 
formed a mass of gel. This mass of gel was dehydrated by means of a 
centrifuge and then dried at 105.degree. C. Thereafter, the resulting 
product was pulverized in a jet mill until its particle diameter was 
reduced to 0.1-0.5.mu., and then subjected to a wet heat treatment (for 
insolubilizing the regenerated fibroin in hot water) comprising exposure 
to saturated steam at 110.degree. C. for 5 minutes. When the 
fibroin-coated pigment thus obtained was dyed in the same manner as 
described in Example 1 and then examined microscopically, the entire 
surfaces of the particles were found to be brightly and evenly colored in 
yellow. This demonstrates that the particles of the titanium oxide used as 
the carrier pigment were uniformly coated with a film of regenerated 
fibroin. (When the film of regenerated fibroin present on the titanium 
oxide particles was removed by dissolving it in the aforesaid solvent, and 
then dyed under the same conditions, the particles were not colored at 
all.) 
When determined according to the above-described procedures, the amount of 
regenerated fibroin present on the titanium oxide particles was 25.2% 
based on the weight of the titanium oxide, and the hot-water-insoluble 
fibroin content of the regenerated fibroin was 88.4% based on the weight 
of the regenerated fibroin. Moreover, the film of regenerated fibroin had 
a degree of crystallinity of 27.0%. 
Then, the above fibroin-coated pigment (Test Run 2), titanium oxide having 
3% of a conventional fibroin powder blended therewith (Control Run 4), 
titanium oxide having 25.2% the same fibroin powder blended therewith 
(Control Run 5), and titanium oxide alone (Control Run 6) were subjected 
to practical performance tests for the purpose of evaluating their 
performance as a face powder. These tests were conducted in the same 
manner as described in Example 1. The results thus obtained are summarized 
in Table 2. 
TABLE 2 
______________________________________ 
Mois- Ad- Spread- 
Oil 
ture hesion ability 
Ab- 
Powder Reten- to the on the sorp- Feel- 
Covering 
Sample tion Skin Skin tion ing Power 
______________________________________ 
Test Run 2 
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.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Control 
Run 4 .DELTA. X .circle. 
.DELTA. 
.circle. 
.circleincircle. 
Control 
Run 5 .circle. 
.circle. 
X .circle. 
.DELTA. 
X 
Control 
Run 6 X X .circle. 
X X .circleincircle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X). 
Thus, the fibroin-coated pigment produced in accordance with this invention 
was very good in such properties as moisture retention, adhesion to the 
skin, spreadability on the skin, oil absorption and feeling, and proved to 
be markedly excellent as compared with the blends of a conventional 
fibroin powder and the uncoated carrier pigment or with the uncoated 
carrier pigment alone. 
EXAMPLE 3 
Spun silk waste was degummed in the same manner as described in Example 1 
and used as the starting material for the production of fibroin-coated 
pigments. A 50% aqueous solution of zinc chloride was prepared by 
dissolving anhydrous zinc chloride (ZnCl.sub.2) in water, and then heated 
to 70.degree. C. Employing the same procedure as described in Example 2, 
the degummed spun silk waste was added thereto and dissolved therein to 
prepare a fibroin-zinc chloride solution having a fibroin concentration of 
10%. Thereafter, the procedure of Example 1 was repeated except that the 
above solution was used as the coating solution, calcium carbonate, mica 
or red iron oxide as the carrier pigment, and a 35% aqueous solution of 
ammonium sulfate as the coagulating agent. When the fibroin-coated 
pigments thus obtained were dyed in the same manner as described in 
Example 1, the entire surfaces of the particles were found to be brightly 
and evenly colored in yellow, as was the case with the fibroin-coated 
pigment of Example 1. This demonstrates that, in all of the above 
fibroin-coated pigments, the particles of the carrier pigment were coated 
with a film of regenerated fibroin in a substantially uniform manner. 
For the fibroin-coated pigment using calcium carbonate as the carrier 
pigment (Test Run 3), the amount of regenerated fibroin was 98.8%, the 
hot-water-insoluble fibroin content was 68%, and the degree of 
crystallinity was 20%. For the fibroin-coated pigment using mica as the 
carrier pigment (Test Run 4), the amount of regenerated fibroin was 99.1%, 
the hot-water-insoluble fibroin content was 85.3%, and the degree of 
crystallinity was 15.3%. For the fibroin-coated pigment using red iron 
oxide as the carrier pigment (Test Run 5), the amount of regenerated 
fibroin was 98.2%, the hot-water-insoluble fibroin content was 92.1%, and 
the degree of crystallinity was 30.3%. 
Then, the above fibroin-coated pigments (Test Runs 3, 4 and 5), calcium 
carbonate having 98.8% of a fibroin powder blended therewith (Control Run 
7), calcium carbonate alone (Control Run 8), mica having 99.1% of a 
fibroin powder blended therewith (Control Run 9), mica alone (Control Run 
10), red iron oxide having 98.2% of a fibroin powder blended therewith 
(Control Run 11), and red iron oxide alone (Control Run 12) were subjected 
to practical performance tests for the purpose of evaluating their 
performance as a cosmetic preparation (e.g., face powder). These tests 
were conducted in the same manner as described in Example 1. The results 
thus obtained are summarized in Table 3. 
TABLE 3 
______________________________________ 
Mois- Ad- Spread- 
Oil 
ture hesion ability 
Ab- 
Powder Reten- to the on the sorp- Feel- 
Covering 
Sample tion Skin Skin tion ing Power 
______________________________________ 
Test Run 3 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
Control 
Run 7 .circleincircle. 
.circle. 
X .DELTA. 
.circle. 
X 
Control 
Run 8 X X .circle. 
X .DELTA. 
.circleincircle. 
Test Run 4 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Control 
Run 9 .circleincircle. 
.circle. 
X .circle. 
.DELTA. 
X 
Control 
Run 10 X X .circleincircle. 
X .DELTA. 
.circle. 
Test Run 5 
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.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Control 
Run 11 .circleincircle. 
.circle. 
X .circle. 
.DELTA. 
X 
Control 
Run 12 X X X X X .circle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X). 
Thus, all of the fibroin-coated pigments produced in accordance with this 
invention were very good in such properties as moisture retention, 
adhesion to the skin, spreadability on the skin, oil absorption and 
feeling, and proved to be markedly excellent as compared with the blends 
of a fibroin powder and the uncoated carrier pigments or with the uncoated 
carrier pigments alone. 
EXAMPLE 4 
A series of fibroin solutions were prepared in the same manner as described 
in Example 2. However, instead of being dissolved in the calcium chloride 
solution, 10 parts each of the degummed spun silk waste (having a degree 
of crystallinity of 52%) was dissolved in 100 parts each of Schweitzer's 
reagent (Test Run 6), a 70% aqueous solution of lithium bromide (Test Run 
7), an aqueous solution of magnesium chloride (Test Run 8), a 70% aqueous 
solution of calcium nitrate (Test Run 9), a 58% aqueous solution of 
magnesium nitrate (Test Run 10), a 50% aqueous solution of calcium 
thiocyanate (Test Run 11), a 50% aqueous solution of sodium thiocyanate 
(Test Run 12) and a 50% aqueous solution of magnesium thiocyanate (Test 
Run 13). These fibroin solutions were dialyzed in the same manner as 
described in Example 2, and the resulting aqueous fibroin solutions were 
adjusted to a fibroin concentration of 5.0%. While 50 parts of each of 
these aqueous fibroin solutions was being stirred, 10 parts of zinc oxide 
having a particle diameter of 0.1-10.mu. was added thereto and dispersed 
therein to form a homogeneous suspension. Then, this suspension was 
exposed to ultrasonic waves having a frequency of 47 kHz for 3 hours, 
whereby the fibroin was coagulated and precipitated on the surfaces of the 
zinc oxide particles. The coagulum so formed was dehydrated by 
centrifugation, dried, and then pulverized in the same manner as described 
in Example 1. Thereafter, the resulting powder was subjected to a wet heat 
treatment comprising exposure to saturated steam at 90.degree. C. for 30 
minutes. When the fibroin-coated pigments thus obtained were dyed in the 
same manner as described in Example 1, the entire surfaces of the 
particles were found to be brightly colored in yellow, as was the case 
with the fibroin-coated pigments of Examples 1 and 3. This demonstrates 
that, in all of the above fibroin-coated pigments, the particles of the 
zinc oxide used as the carrier pigment were uniformly coated with a film 
of regenerated fibroin. 
With respect to the above fibroin-coated pigments, the amount of 
regenerated fibroin present on the zinc oxide particles, the 
hot-water-insoluble fibroin content of the regenerated fibroin, and the 
degree of crystallinity of the film of regenerated fibroin were 
determined. The results thus obtained are summarized in Table 4. In 
addition, they were subjected to practical performance tests for the 
purpose of evaluating their performance as a cosmetic preparation (e.g., 
face powder). The results thus obtained are summarized in Table 5. 
TABLE 4 
______________________________________ 
Amount of Hot-water-insoluble 
Fibroin- Regener- Fibroin Content 
Degree 
coated ated Fi- [or Rate of .beta.- 
of Crystalinity 
Pigment broin (%) Configuration] (%) 
(%) 
______________________________________ 
Test Run 6 
10.1 85.1 28 
Test Run 7 
10.2 81.6 29 
Test Run 8 
30.4 90.6 28 
Test Run 9 
10.0 82.5 30 
Test Run 10 
50.4 95.7 27 
Test Run 11 
25.4 96.1 29 
Test Run 12 
25.3 97.0 30 
Test Run 13 
25.2 95.4 30 
______________________________________ 
TABLE 5 
______________________________________ 
Mois- Ad- Spread- 
Oil 
Fibroin- ture hesion ability 
Ab- Cover- 
coated Reten- to the on the sorp- Feel- 
ing 
Pigment tion Skin Skin tion ing Power 
______________________________________ 
Test Run 6 
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.circle. 
.circleincircle. 
Test Run 7 
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.circle. 
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.circleincircle. 
Test Run 8 
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.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Test Run 9 
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.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circleincircle. 
Test Run 10 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
Test Run 11 
.circle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circleincircle. 
.circle. 
Test Run 12 
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.circleincircle. 
.circleincircle. 
.circle. 
.circleincircle. 
.circle. 
Test Run 13 
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.circleincircle. 
.circleincircle. 
.circle. 
.circleincircle. 
.circle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X). 
EXAMPLE 5 
An aqueous solution having a fibroin concentration of 5.1% was prepared in 
the same manner as described in Example 2. While three 100-l portions of 
this aqueous fibroin solution were being stirred, 20 kg each of titanium 
oxide having a particle diameter of 0.1 to 10.mu. was added thereto and 
dispersed therein to form homogeneous suspensions. Then, these suspensions 
were subjected, with stirring, to one of the following treatments: 
(1) Coagulation at the isoelectric point (Test Run 14) 
The suspension was adjusted to pH 4.5 (isoelectric point) by adding 0.1 N 
sulfuric acid thereto drop by drop, and then allowed to stand at room 
temperature for 10 minutes. 
(2) Exposure to ultrasonic waves (Test Run 15) 
A 30 kHz ultrasonic wave generator was attached to the inside wall of the 
vessel in which the suspension was placed, and operated at room 
temperature for 1 hour. 
(3) Aeration (Test Run 16) 
Using a pipe, air was fed at a rate of 10 l/min. and bubbled through the 
suspension for 10 minutes. 
In every case, the suspension formed a coagulum consisting of the pigment 
particles coated with a gel of regenerated fibroin. This coagulum was 
dehydrated by means of a centrifuge and then dried in hot air at 
105.degree. C. Thereafter, the resulting product was pulverized in a jet 
mill until its particle diameter was reduced to 5-40.mu., and then 
subjected to a wet heat treatment comprising exposure to saturated steam 
at 120.degree. C. for 30 minutes. 
With respect to the fibroin-coated pigments thus obtained, the 
hot-water-insoluble fibroin content (or rate of .beta.-configuration) of 
the regenerated fibroin was 94.0% in case of coagulation at the 
isoelectric point, 99% in case of exposure to ultrasonic waves, and 85.5% 
in case of aeration. The degree of crystallinity as determined by X-ray 
diffraction analysis was 31% in case of coagulation at the isoelectric 
point, 33% in case of exposure to ultrasonic waves, and 42% in case of 
aeration. The amount of regenerated fibroin present on the pigment 
particles was 24.5% (based on the weight of the carrier pigment) in case 
of coagulation at the isoelectric point, 25.0% in case of exposure to 
ultrasonic waves, and 24.2% in case of aeration. 
When the above fibroin-coated pigments were dyed with Tartrazine NS and 
then examined microscopically, the entire surfaces of the particles were 
found to be brightly and evenly colored in yellow. This demonstrates that, 
in all of these fibroin-coated pigments, the particles of the titanium 
oxide used as the carrier pigment were coated with a film of regenerated 
fibroin in a substantially uniform manner. 
Then, the above fibroin-coated pigments were subjected to practical 
performance tests for the purpose of evaluating their performance as a 
cosmetic preparation. These tests were conducted in the same manner as 
described in Example 2. The results thus obtained are summarized in Table 
6. 
TABLE 6 
______________________________________ 
Mois- Ad- Spread- 
Oil 
ture hesion ability 
Ab- Cover- 
Type of Reten- to the on the sorp- Feel- 
ing 
Treatment 
tion Skin Skin tion ing Power 
______________________________________ 
Coagulation 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
at the 
Isoelectric 
Point 
Exposure to 
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.circleincircle. 
.circleincircle. 
.circleincircle. 
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.circleincircle. 
Ultrasonic 
Waves 
Aeration .circleincircle. 
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.circleincircle. 
.circleincircle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X). 
EXAMPLE 6 
A fibroin solution having a fibroin concentration of 10% was prepared in 
the same manner as described in Example 1, and then analyzed in the same 
manner as described in Example 2. Thereafter, the resulting aqueous 
fibroin solution (having a fibroin concentration of 5.0%) was worked up 
according to the procedure of Example 2. With respect to the 
fibroin-coated pigment (Test Run 17) thus obtained, the 
hot-water-insoluble fibroin content (or rate of .beta.-configuration) of 
the regenerated fibroin was 84.1%, the degree of crystallinity as 
determined by X-ray diffraction analysis was 31%, and the amount of 
regenerated fibroin present on the titanium oxide particles was 25.1% 
based on the weight of the titanium oxide. 
On the other hand, the above-described procedure was repeated except that 
the wet heat treatment of the pulverized product was omitted. With respect 
to the fibroin-coated pigment (Test Run 18) thus obtained, the 
hot-water-insoluble fibroin content was 54.1%, the degree of crystallinity 
was 23%, and the amount of regenerated fibroin was 25.1% based on the 
weight of the titanium oxide. 
When these fibroin-coated pigments were dyed in the same manner as 
described in Example 1 and then examined microscopically, the entire 
surfaces of the particles were found to be brightly and evenly colored in 
yellow. This demonstrates that, in both these fibroin-coated pigments, the 
particles of the titanium oxide used as the carrier pigment were coated 
with a film of regenerated fibroin in a substantially uniform manner. 
Then, the above fibroin-coated pigments were subjected to practical 
performance tests for the purpose of evaluating their performance as a 
cosmetic preparation. These tests were conducted in the same manner as 
described in Example 2. The results thus obtained are summarized in Table 
7. 
TABLE 7 
______________________________________ 
Mois- Ad- Spread- 
Oil 
Fibroin- ture hesion ability 
Ab- Cover- 
coated Reten- to the on the sorp- Feel- 
ing 
pigment tion Skin Skin tion ing Power 
______________________________________ 
Test Run 17 
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.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Test Run 18 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circleincircle. 
.circleincircle. 
______________________________________ 
Note: 
The above properties were rated as very good (.circleincircle.), good 
(.circle.), somewhat poor (.DELTA.) or poor (X). 
EXAMPLE 7 
Spun silk waste was degummed in the same manner as described in Example 1, 
and the resulting powder had a degree of crystallinity of 52%. A series of 
fibroin solutions having the fibroin concentrations indicated in Table 8 
were prepared by dissolving the degummed spun silk waste in aqueous zinc 
chloride solutions having the concentrations indicated in Table 8. 
While the specified amount (Table 8) of each of these fibroin solutions was 
being stirred, 10 parts of talc (as used in Example 1) was added thereto 
and dispersed therein to form a homogeneous suspension. Then, this 
suspension was mixed with a concentrated aqueous solution containing the 
same amount of ammonium sulfate as that of zinc chloride present in the 
fibroin solution used, whereby the fibroin was coagulated (or 
regenerated). The coagulum so formed was heat-treated at 70.degree. C. for 
20 minutes in the same concentrated aqueous solution of ammonium sulfate, 
washed with water, and then dehydrated by centrifugation. When the fibroin 
concentration was in the range of 3-20% as taught by this invention, a 
homogeneous mass of gel was formed. Upon dehydration by centrifugation, 
this mass of gel was broken to pieces having a size of several millimeters 
or less. However, when the fibroin concentration was less than 3% or 
greater than 20% as in the Control Runs, a white precipitate was formed 
instead of a homogeneous mass of gel. This precipitate was so sticky that 
it could hardly be separated by conventional filtration under reduced 
pressure. Moreover, when it was placed in a cloth bag and then 
centrifuged, it agglomerated and cohered to form a bulky mass which was 
very difficult of dehydration and drying. The dehydrated mass of gel was 
then dried in a hot-air oven kept at 90.degree.-100.degree. C. or a vacuum 
dryer kept at 70.degree. C. to obtain a fine granular product of 
fibroin-coated pigment. Subsequently, this granular product was pulverized 
in a jet mill to obtain a fine powder of fibroin-coated pigment consisting 
of nearly globular particles, 98% or more of which had a diameter of 
6-30.mu.. 
The data are summarized in Table 8. 
TABLE 8 
__________________________________________________________________________ 
Amount 
Amount 
of of Degree 
Zinc Fibroin Regener- 
Fibroin 
of 
Chloride 
Concen- 
Rate of 
ated Fi- 
Solution 
Crystal- 
Concentra- 
tration 
.beta.-Configu- 
broin 
Used linity 
tion (%) 
(%) ration (%) 
(%) (Parts) 
(%) 
__________________________________________________________________________ 
Control Run 13 
10 1 5 9.9 100 8 
Test Run 19 
10 3 58 9.9 33 15 
Test Run 20 
10 4 59 11.3 30 20 
Test Run 21 
10 6 60 17.1 30 25 
Test Run 22 
10 10 61 30.0 30 27 
Test Run 23 10 
15 63 44.1 30 26 
Test Run 24 
10 20 59 59.0 30 29 
Control Run 14 
20 1 16 9.8 100 8 
Test Run 25 
20 3 62 9.7 33 18 
Test Run 26 
20 4 63 11.6 30 25 
Test Run 27 
20 6 66 17.8 30 29 
Test Run 28 
20 10 68 29.9 30 28 
Test Run 29 
20 15 69 44.5 30 27 
Test Run 30 
20 20 62 59.0 30 20 
Control Run 15 
40 1 13 9.8 100 7 
Test Run 31 
40 3 65 9.9 33 20 
Test Run 32 
40 4 70 11.9 30 25 
Test Run 33 
40 6 71 17.6 30 30 
Test Run 34 
40 10 72 29.8 30 29 
Test Run 35 
40 20 69 74.0 37 27 
Control Run 16 
40 25 5 74.5 30 8 
Control Run 17 
60 1 1 9.8 100 5 
Test Run 36 
60 3 67 9.8 33 18 
Test Run 37 
60 4 68 11.5 30 25 
Test Run 38 
60 6 69 17.5 30 29 
Test Run 39 
60 10 72 29.5 30 28 
Test Run 40 
60 20 68 74.0 37 29 
Control Run 18 
60 25 6 74.3 30 8 
Control Run 19 
80 1 5 9.8 100 5 
Test Run 41 
80 3 59 9.9 33 19 
Test Run 42 
80 4 62 11.5 30 23 
Test Run 43 
80 6 63 17.5 30 25 
Test Run 44 
80 10 68 30.0 30 27 
Test Run 45 
80 15 72 44.5 30 27 
Test Run 46 
80 20 70 74.0 37 29 
Control Run 20 
80 25 5 74.4 30 8 
Control Run 21 
3 3 -- -- -- -- 
Control Run 22 
90 10 43 29.1 30 7 
__________________________________________________________________________ 
Note: 
When the zinc chloride concentration was less than 10% the degummed spun 
silk waste was not dissolved even after a long period of time (i.e., 24 
hours or more). 
EXAMPLE 8 
Spun silk waste was degummed in the same manner as described in Example 1 
and used as the starting material for the production of fibroin-coated 
pigments. A series of fibroin solutions were prepared by dissolving 10 
parts of the degummed spum silk waste in 100 parts each of aqueous calcium 
chloride solutions having the concentrations indicated in Table 9. 
Then, these fibroin solutions were desalted by passing each of them through 
a dialyzer of the hollow-fiber type at a rate of 1 l/hr. The dialyzer 
comprised 2,000 hollow fibers of regenerated cellulose having an internal 
diameter of 200.mu., a membrane thickness of 20.mu., and a length of 500 
mm, both ends of these hollow fibers being bundled and sealed without 
blocking up their bores. In this case, the ratio of membrane surface area 
(cm.sup.2) to priming volume (cm.sup.3) had a value of 100. The resulting 
aqueous fibroin solutions had a fibroin concentration of 3.5-7.1% and a 
residual calcium chloride concentration of 0.01-0.063%. 
The molecular weight of the fibroin contained in each of these aqueous 
fibroin solutions was determined by gel permeation chromatography. Thus, 
it was found that, when the calcium chloride concentration was greater 
than 80% as in Control Runs 32 and 33, the molecular weight was reduced to 
the order of 40,000. 
The above aqueous fibroin solutions were adjusted, either by concentration 
or by dilution, to the respective fibroin concentrations indicated in 
Table 9. While the specified amount (Table 9) of each of the aqueous 
fibroin solutions was being stirred, 10 parts of talc was added thereto 
and dispersed therein to form a homogeneous suspension. This suspension 
was agitated at room temperature and at such a high speed as to give a 
shear rate of the order of 100/sec. Typically, in the course of 2-3 hours' 
agitation, the fibroin gradually precipitated and ultimately formed a mass 
of gel comprising an aggregation of small pieces of gel. However, when the 
fibroin concentration was less than 3% or greater than 20% as in the 
Control Runs, a white precipitate was formed instead of a homogeneous mass 
of gel. This precipitate was so sticky that it could hardly be separated 
by conventional filtration under reduced pressure. Moreover, when it was 
placed in a cloth bag and then centrifuged, it agglomerated and cohered to 
form a bulky mass which was very difficult of dehydration and drying. The 
above mass of gel was dehydrated by means of a centrifuge and then dried 
at 105.degree. C. Thereafter, the resulting product was pulverized in a 
jet mill and then subjected to a wet heat treatment comprising exposure to 
saturated steam at 110.degree. C. for 15 minutes. The fine powder thus 
obtained consisted of nearly globular particles, 98% or more of which had 
a diameter of 5-30.mu.. 
The data on the amount of aqueous fibroin solution used, fibroin 
concentration, average molecular weight, the rate of .beta.-configuration, 
and the degree of crystallinity are summarized in Table 9. 
TABLE 9 
__________________________________________________________________________ 
Amount 
Amount of 
Average 
of Degree 
Calcium 
Fibroin 
Aqueous 
Molecu- 
Regener- 
Rate of 
of 
Chloride 
Concen- 
Fibroin 
lar ated .beta.-Configu- 
Crystal- 
Concentra- 
tration 
Solution 
Weight 
Fibroin 
ration 
linity 
tion (%) 
(%) Used(parts) 
(.times. 10.sup.4) 
(%) (%) (%) 
__________________________________________________________________________ 
Control Run 23 
10 1 100 10.1 9.7 27 8 
Test Run 47 
10 3 33 10.1 9.7 71 30 
Test Run 48 
10 4 30 10.1 11.4 79 31 
Test Run 49 
10 6 30 10.1 17.4 82 32 
Test Run 50 
10 10 30 10.1 29.2 84 33 
Test Run 51 
10 15 30 10.1 44.3 81 34 
Test Run 52 
10 20 37 10.1 73.5 79 34 
Control Run 24 
20 1 100 9.7 9.7 37 8 
Test Run 53 
20 3 33 9.7 9.7 75 31 
Test Run 54 
20 4 30 9.7 11.5 86 31 
Test Run 55 
20 6 30 9.7 17.2 90 32 
Test Run 56 
20 10 30 9.7 29.5 96 34 
Test Run 57 
20 20 37 9.7 73.6 93 32 
Test Run 58 
20 20 30 9.7 74.3 20.5 7 
Control Run 25 
40 1 100 8.6 9.8 40 8 
Test Run 59 
40 3 33 8.6 9.8 79 31 
Test Run 60 
40 4 30 8.6 11.6 83 33 
Test Run 61 
40 6 30 8.6 17.8 93 33 
Test Run 62 
40 10 30 8.6 29.5 98 34 
Test Run 63 
40 20 37 8.6 73.8 94 32 
Control Run 26 
40 25 30 8.6 74.8 23 8 
Control Run 27 
60 1 100 8.5 9.8 42 9 
Test Run 64 
60 3 33 8.5 9.8 80 30 
Test Run 65 
60 4 30 8.5 11.8 83 32 
Test Run 66 
60 6 30 8.5 17.8 92 33 
Test Run 67 
60 10 30 8.5 29.6 95 33 
Test Run 68 
60 20 37 8.5 73.5 93 31 
Control Run 28 
60 25 30 8.5 74.8 26.8 7 
Control Run 29 
80 1 100 8.4 9.7 37 8 
Test Run 69 
80 3 33 8.4 9.7 71 30 
Test Run 70 
80 4 30 8.4 11.5 79 31 
Test Run 71 
80 6 30 8.4 17.2 81 32 
Test Run 72 
80 10 30 8.4 29.3 83 33 
Test Run 73 
80 15 30 8.4 44.2 85 33 
Test Run 74 
80 20 37 8.4 63.5 79 32 
Control Run 30 
80 25 30 8.4 74.1 35 7 
Control Run 31 
3 -- -- -- -- -- -- 
Control Run 32 
90 1 100 4.2 9.6 39 8 
Control Run 33 
90 25 30 4.2 74.1 36 8 
__________________________________________________________________________ 
Note: 
In Control 31, the degummed spun silk waste was not dissolved. 
EXAMPLE 9 
The fibroin-coated pigments obtained in Examples 7 and 8 were subjected to 
practical performance tests for the purpose of evaluating their 
performance as a cosmetic preparation. These tests were conducted in the 
same manner as described in Example 1. 
Thus, it was found that the fibroin-coated pigments of Test Runs 19, 24, 
25, 30, 31, 35, 36, 40 and 41 (Group 1) had nearly as good performance as 
the product of Test Run 1 in Example 1. Moreover, the fibroin-coated 
pigments of Test Runs 20-23, 26-29, 32-34, 37-39, 47 and 74 (Group 2) were 
better in adhesion to the skin, spreadability on the skin, and the like 
than those of the aforesaid Group 1. Furthermore, the fibroin-coated 
pigments of Test Runs 48-73 (Group 3) had as good performance as the 
product of Test Run 2 in Example 2, and were still better than the 
fibroin-coated pigments of the aforesaid Group 2. 
On the other hand, the fibroin-coated pigments of Control Runs 13-20 and 
23-33 were good () in moisture retention and covering power, but somewhat 
poor (.DELTA.) in adhesion to the skin, spreadability on the skin, and 
feeling. Thus, they were inferior in performance to the fibroin-coated 
pigments of the aforesaid Groups 1-3. Moreover, the fibroin-coated 
pigments of these Control Runs had the disadvantage that, whether they are 
used alone or in combination with untreated pigments, they cohered or 
agglomerated under the influence of water, formed secondary particles, and 
gave a sticky feeling. 
EXAMPLE 10 
A mixture of 20 parts of liquid paraffin, 5 parts of ceresin, 5 parts of 
lanolin, 10 parts of microcrystalline wax, and 31.2 parts of isopropyl 
myristate was melted, with stirring, by heating it to 90.degree. C. To the 
resulting melt was added 32 parts of a pigment. This mixture was kneaded 
well, poured into a mold, and then cooled. The oil-base foundation thus 
obtained was allowed to stand at a relative humidity of 90% and a 
temperature of 40.degree. C., and then observed visually to examine the 
presence or absence of oil droplet formation on its surface. 
Thus, it was found that, when the pigment consisted of 40 parts of a 
fibroin-coated pigment selected from the products of Test Runs 1-74 or 31 
parts of the fibroin-coated pigment mixed with 0:3 part of red iron oxide 
and 0.7 part of yellow iron oxide, no oil droplet formation was noted. 
Moreover, the uniformity of dispersion of the pigment was satisfactorily 
good. 
On the other hand, when the pigment consisted of 40 parts of a 
fibroin-coated pigment selected from the products of Control Runs 13-35 or 
31 parts of the fibroin-coated pigment mixed with 0.3 part of red iron 
oxide and 0.7 part of yellow iron oxide, a considerable degree of oil 
droplet formation was noted, and the uniformity of dispersion of the 
pigment was relatively poor. 
Furthermore, when the pigment consisted of 40 parts of titanium oxide or 
talc or 31 parts of titanium oxide or talc mixed with 0.3 part of red iron 
oxide and 0.7 part of yellow iron oxide, a considerable degree of oil 
droplet formation was also noted, and the uniformity of dispersion of the 
pigment was significantly poorer than in the oil-base foundations made in 
accordance with this invention. 
EXAMPLE 11 
With respect to the fibroin-coated pigments of Test Runs 2 and 14-18 and 
untreated titanium oxide, the measurement of oil absorption was made 
according to the milling method described in JIS-K5101. Thus, it was found 
that the oil absorption was 55.6% for the product of Test Run 2, 58.9% for 
the products of Test Runs 14 and 15, 57.5% for the product of Test Run 16, 
57.1% for the product of Test Run 17, and 53% for the product of Test Run 
18. On the other hand, the oil absorption of untreated titanium oxide was 
36.1%. 
COMATIVE EXAMPLE 1 
The procedure described in Example 4 of Japanese Patent Publication No. 
299/'52 was repeated except that the aqueous fibroin solution of Test Run 
62 (having a fibroin concentration of 10%) or that of Test Run 63 (having 
a fibroin concentration of 20%) was used as the colloidal solution of 
fibroin, and the coloring matter and perfume were omitted. More 
specifically, a pigment was thoroughly mixed with either of the aqueous 
fibroin solutions, and the resulting mixture was dried at 70.degree. C. 
With respect to the treated pigments thus obtained, the amount of 
regenerated fibroin present on the pigment particles were 0.36% for the 
former and 0.72% for the latter. The hot-water-insoluble fibroin content 
(or rate of .beta.-configuration) of the regenerated fibroin was 0% for 
either of them, indicating that all (100%) of the regenerated fibroin was 
constituted of that type of fibroin having .beta.-configuration. In 
consequence, when these treated pigments were dyed with a 2% aqueous 
solution of Tartrazine NS at 100.degree. C. for 10 minutes, all of the 
regenerated fibroin was dissolved in the dye bath. 
In addition, the above treated pigments were dyed with Shirlastain A at 
40.degree. C. for 20 minutes and then examined under an optical 
microscope. Thus, it was found that the fibroin was only partially 
deposited on the surfaces of the pigment particles and, therefore, they 
were not substantially coated with a film of regenerated fibroin. 
Then, with respect to the above treated pigments, the measurement of oil 
absorption was made in the same manner as described in Example 11. Thus, 
the oil absorption was found to be 37.9% for the former and 39.9% for the 
latter. Moreover, when evaluated in the same manner as described in 
Example 10, these treated pigments showed no ability to prevent the 
formation of oil droplets and fairly poor dispersibility in oil. 
Furthermore, in order to evaluate their performance as a consmetic 
preparation, these treated pigments were tested in the same manner as 
described in Example 1. Thus, they were found to be somewhat poor 
(.DELTA.) in moisture retention, adhesion to the skin, spreadability on 
the skin, and feeling. Although their covering power was rated as good (), 
it showed no improvement and seemed to be significantly poorer than that 
of the fibroin-coated pigments of Test Runs 1-74.