Note: Descriptions are shown in the official language in which they were submitted.
~ft~ 36
TITI.E ~ THE INVENTION
Ornamental Articles Having Coating Membrane
BACKGROUND OF THE INVENTION
Field of the Invention
This invention is concerned with ornamental articles
having high resistivity to scratching, light, attack by various
chemicals, etc. More particularly, it relates to natural or
cultured pearls having such high resistivity which are suitable
for use in necklaces, chokers,~finger rings, brooches, ear rings,
necktie pins, cuff buttons and the likes.
Description of the Prior Art
Few of naturally occurring products can directly
used as ornamental articles. Such products are often sub~ected
to various processes, such as cutting, grinding and boring,
depending on their use to be applied, their forms and other
conditions when produced or f:ound in nature, etc.
Pearls are used an ornamental articles. Purely
naturally occurring pearls yield poorly. Most pearls are
produced by seeding nuclei to host shellfish such as pearl
oysters and growing square cylindrical layers, pearl layers
or the likes in a concentrical configuration. Improved methods
of producing such cultured pearls have been proposed: for
: ~ ~
example, Japanese Patent Application Laid-open No. 59-183638.
An 1mprovement~of the quality of cultured pearls has
already been attempted and put to practice by coating pearls
with an acrylic thermoplastic resin. However, there has not
36
yet been known a technique of making hard coatings on the
surface of pearls while maintaining their color tone and
luster which are characteristic to naturally occurring products.
Thus, ornamental materials such as pearls still involve an
inevitable drawback that they are readily scratched.
On the other hand, particularly with respect to
pearls, the survival rate of host shellfish has been improved
and pearls of good quality may now have been obtainable, by the
recently progressed techniques of pearl production by
cultivation. However, there has still been a problem of
damages caused by the contamination of sea water.
If host shellfish is taken up from sea water after
a short period immersion so as to improve the survival rate
of the shellfish, the pearls thus obtained are poor in the
luster due to the thin pearl layer and does not have the
characteristic pearl color. Conventionally~ such pearls are
dyed or coated with a thermoplastic resin in order to i~proving
the poor quality. However, such dye or coating membranes
exhibit poor resistance to acids, are discolored during the
use, or are easily scratched or even removed off upon collision
with metals or the likes due to their low hardness.
Such problems as described above have also been
found in other ornamental materials, such as corals.
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41~36
_UMMA RY O F THE I NVE NT I ON
This invention has been made to overcome the
foregoing drawbacks in the prior art and it is an object
thereof to provide ornamental articles of natural or cultured
high quality material, for example, pearl or coral, with
improved properties such as surface luster and resistivity
to scratch, light, chemicals, etc., by means of an outermost
layer having high hardness.
DESCRIPTION OF THE PREFERRED~ EM13ODIMENTS
This invention relates to ornamental articles having
excellent resistivity to scratch, light, chemicals, and the
llkè, particularly ~to pearls or the likes which further exhibit
improved luster, as well as to a process for the production
of such articles.
This inventlon provides an ornamental article
comprising a natural ornamental material and a coating membrane
of a curable composition based on organic materials whlch
is coated on the surface of said natural ornamental material
in a thickness from 0.01 ~m to 30 ~m.
Various kinds of materials may be used as the natural
ornamental materlals in the invention, so long as a coating
membrane can be applled onto the surface of~those materials.
Such materials~include, for example, pearl and~coral, but
are not llmlted to these~. Particularly, pearls are suitable
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materials for this invention in view of the surface hardness
and chemical resistance. "~atural materials" re~erred to
herein include those having more or less arti~icially treated
in some step of production thereof, for ~sxample,cultured
pearls. However, those artificially pearls obtained by glueing
guanines to glass beads are excluded from the natural materials.
In the case of natural or cultured pearls, it is
particul;arly preferable to be preliminarily bleached with
hydrogen peroxide or the like before applying a coating
membrane according to this invention, for the purpose of
increasing the luster ànd opaqueness and improving the adhesion
with the coating membrane.
According to thls invention, a curable composition
based on organic materials is coated on the surface of such
a natural ornamental material. Any curable composition may
be used in this invention so long as it can form three-
dimensional crosslinking. Thermosetting materials are
particularly preferred since they can be cured uniformly
and easily.
Preferable examples of these curable compositions
include monomers, oligomers or prepolymers having poly-
functional acrylic group, melamine resins, epoxy resins,
polyurethane resins and the likes. Polyurethane resins include
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uretane-forming compositions comprising aliphatic, cyclo-
aliphatic or aromatic isocyanates and polyols, as well as
various kinds of modified resins capable of radical curing
by the introduction of double-bonds to the above-mentioned
compounds. Further, organopolysiloxane type compounds
obtained from organic-substituted silicon compounds can
be also used suitably.
Particularly, in case that the ornamental material
is natural or cultured pearl, the coating membrane is preferably
comprising the ~ollowing ingredients A and B,
A. Silicon compounds represented by the following general
formula (I) and/or hydrolysates thereof:
R1aR2bsi(oR3)4 (a+b) ____- (I)
where R1 and R2 independently represent alkyl group, alkenyl
group, aryl group or hydrocarbyl group containing halogen~
epoxy group, glycidoxy group, amino group, mercapto group,
methacryloxy group or cyano group, R3 represents C1 8 alkyl
group, alkoxyalkyl group, acyl group or aryl group, and ~ and
b represent respectively O or 1.
B. Epoxy resin compound.
Typical examples of the silicon compounds represented
by the foregoing formula (I) used as the ingredient A in this
inventiori include tetraalkoxy silanes, such as methyl silicate,
ethyl silicate, n-propyl silicate, iso-propyl silicate,
n-butyl silicate, sec-butyl silicate and t-butyl silicate,
and hydrolysates thereof, trialkoxysilanes, triacyloxysilanes or
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triphenoxysilanes such as methyltrimethoxysilane,
methyltriethoxysilane, methyltrimethoxyethoxysilane,
methyltriacetoxysilane, methyltributoxysilane,
ethyltrimethoxysilane, ethyltriethoxysilane,
vinyltrimethoxysilane, vinyltriethoxysilane,
vinyltriacetoxysilane, vinyltrimethoxyethoxysilane,
phenyltrimethoxysilane, phenyltriethoxysilane,
phenyltriacetoxysilane, ~-chloropropyltrimethoxysilane,
~-chloropropyltriethoxysilane,
r-chloropropyltriacetoxysilane,
3,3,3-trifluoropropyltrimethoxysilane,
~-methacryloxypropyltrimethoxysilane,
~-aminopropyltrimethoxysilane,
~-aminopropyltriethoxysilane,
~-mercaptopropyltrimethoxysilane,
~-mercaptopropyltriethoxysilane,
N~ aminoethyl)- y-aminopropyltrimethoxysilane,
~-cyanoethyltriethoxysilane,
methyltriphenoxysilane,
chloromethyltrimethoxysilane,
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3~i
chloromethyltriethoxysilane,
glycidoxymethyltrimethoxysilane,
glycidoxymethyltriethoxysilane,
a-glycidoxyethyltrimethoxysilane,
a-glycidoxyethyltriethoxysilane,
~-glycidoxyethyltrimethoxysilane,
~-glycidoxyethyltriethoxysilane,
a-glycidoxypropyltrimethoxysilane,
a-glycidoxypropyltriethoxysilane,
~-glycidoxypropyltrimethoxysilane,
~-glycidoxypropyltriethoxysilane,
~-glycidoxypropyltrimethoxysilane,
y-glycidoxypropyltriethoxysilane,
y-glycidoxypropyltripropoxysilane,
y-glycidoxypropyltributoxysilane,
~-glycidoxypropyltrimethoxyethoxysilane,
y-glycidoxypropyltriphenoxysilane,
a-glycidoxybutyltrimethoxysilane,
a-glycidoxybutyltriethoxysilane,
~-glycidoxybutyltrimethoxysilane,
~-glycidoxybutyltriethoxysilane,
y-glycidoxybutyltrimethoxysilane,
~-glycidoxybutyltriethoxysilane,
6-glycidoxybutyltrimethoxysilane,
~-glycidoxybutyltriethoxysilane,
(3,4-epoxycyclohexyl)methyltrimethoxysilane,~
" 1.2~836
(3,4-epoxycyclohexyl)methyltriethoxysilane,
~-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
~-(3,4-epoxycyclohexyl)ethyltriethoxysilane,
~-(3,4-epoxycyclohexyl)ethyltripropoxysilane,
~-(3,4-epoxycyclohexyl)ethyltributoxysilane,
~-(3,4-epoxycyclohexyl)ethyltrimethoxyethoxysilane,
~(3,4-epoxycyclohexyl)ethyltriphenoxysilane,
~-(3,4-epoxycyclohexyl)propyltrimethoxysilane,
y-(3,4-epoxycyclohexyl)propyltriethoxysilane,
~-(3,4-epoxycyclohexyl)butyltrimethoxysilane,
~-(3,4-epoxycyclohexyl)butyltriethoxysilane,
or the hydrolyzates thereo~, as well as dialkoxysilanes,
diphenoxysilanes or diacyloxysilanes such as
dimethyldimethoxysilane, phenylmethyldimethoxysilane,
dimethyldiethoxysilane, phenylmethyldiethoxysilane,
r-chloropropylmethyldimethoxysilane,
~-chloropropylmethyldiethoxysilane,
dimethyldiacetoxysilane,
~-methacryloxypropylmethyldimethoxysilane,
y-methacryloxypropylmethyldiethoxysllane,
y-mercaptopropylmethyldimethoxysilane,
~-mercaptopropylmethyldiethoxysilane,
~: .
y-aminopropylmethyldimethoxysilane, ~ :~
y-aminopropylmethyldiethoxysilane, ~ ~
methylvinyldlmethoxysllane, me~thylvinyldiethoxysilane,
glycldoxymethylmethyldimethoxysilane,
: :
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3~i
glycidoxymethylmethyldiethoxysilane,
~-glycidoxyethylmethyldimethoxysilane,
a-glycidoxyethylmethyldiethoxysilane,
~-glycidoxyethylmethyldimethoxysilane,
~-glycidoxyethylmethyldiethoxysilane,
a-glycidoxypropylmethyldimethoxysilane,
~-glycidoxypropylmethyldiethoxysilane,
~-glycidoxypropylmethyldimethoxysilane,
~-glycidoxypropylmethyldiethoxysilane,
~-glycidoxypropylmethyldimethoxysilane,
y-glycidoxypropylmethyldiethoxysilane,
y-glycidoxypropyImethyldipropoxysilane,
~-glycidoxypropylmethyldibutoxysilane,
~-glycidoxypropylmethyldimethoxyethoxysilane,
y-glycidoxypropylmethyldiphenoxysilane,
~-glycidoxy~ropylethyldimethoxysilane,
~-glycidoxypropylethyldiethoxysilane,
Y-glycidoxypropylethyldipropoxysilane,
~-glycidoxypropylvinyldimethoxysilane,
Y-glycidoxypropylvinyldiethoxysilane,
~-glycidoxypropylphenyldimethoxysilane~ ~ .
y -glycidoxypropylphenyldiethoxysilane, or hydrolysates
thereof.
Two or more o~ these compounds can be
added t~gether. ParticuIarly, the organic silicon
compound containing epoxy group and glycidoxy group is
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preferable for the purpose of providing dyeability.
The epoxy resin compounds of the ingredient B include
those compounds which are generally used for paint and casting:
for example, polyolefinic epoxy resins synthesized by the
peroxidation process; cycloaliphatic epoxy resins such as
cyclopentadiene oxide, cyclohexene oxide and polyglycidyl
esters obtained from hexahydrophthalic acid with epichloro-
hydrin; polyglycidyl ethers obtained from polyvalent phenols,
such as bisphenol A, catechol and resorcinol, or polyfunctional
alcohols, such as (poly)ethylene glycol, (poly)propylene
glycol, neopentyl glycol, glycerin, trimethylolpropane,
pentaerythritol, diglycerol, and sorbitol, with epichloro-
hydrin; epoxidized vegetable oils; epoxy novolaks obtained
from novolak phenol resin and epichlorohydrin; epoxy
resins obtained from phenolphthalein and epichlorohydrin;
and copolymers of glycidyl methacrylate with acrylic
monomer such as methylmethacrylate or styrene.
Particularly, cycloaliphatic epoxy resins and
epoxy resins having aromatic rings are preffered in view
of the sweat-resistance and water proofness.
The curable composition in this irîvention can
contain non-crosslinking materials, inorganic compounds
and other curable ma~erials within such a range as not
significantly reduclng the coating performance and the
transparency. Various physical properties such as adhesion
with pearls, chemical resistivity, surface hardness, durability
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and dyeability can be improved by the combination of these
additives.
The preferable examples of the organic materials
described above include vinyl copolymers including acrylic
types, polyester polymers (including alkyd resins) and cellulose
polymers. The inorganic materials can include metal aIkoxides
represented by the following general formula (II),
M(OR)C (II)
where R represents alkyl group, acyl group or alkoxyalkyl
group, M represents silicon, titanlum, zirconium, antimony,
tantalum, germanium or aluminium, and c represents the same
value as the valence of the metal M, and/or hydrolysates
thereof, and finely particulate metal oxides, particulaly,
colloidally dispersed sols thereof.
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Preferable examples of colloidally dispersed sols may
include, for example, silica sol, titania sol, zirconia sol~
antimony oxide sol and alumina sol. Particularly, silica sol
is preferable ~for the improvement of the adhesion to the
substrate pearls, and~titania sol or antimony oxide sol is
preferable for the improvement of the refractive index
of coating membrane,~that;is,; for the~1mpro~ement~of the luster
due to the increase of light reflection at the surface.
Réference is then made to the method of coating
a natural material with the curable composltion and curing
the composit~ion~in thls~invention. The surface of the
natural material is coat~ed with the composition in liquid
rorm, and then the composition is cured.
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The liquid composition can be applied to the
ornamental material by any coating means employed in the
ordinary coating works, and it is preferably carried out,
for example, by~dip c~ating~ curtain coating and float
coating with air or gas stream. In the latter case, the
coated material is drie~d as lt is floating. Further, when
the ornamental material such as pearl is bored in the
fabrication step, they are preferably supported by a
supporting means (e.g.~, a ~ig)~at the bored holes and then
coated by dip coating. ~;
The coating composltion thus coated can be cured
by the action of curable functlonal~group, for example,
double bonds ln the polymer or oligomer, which are curable
bD radiation rays such as ultraviolet ray, electron ray
and gamma ray. ~
However, the heat curing is partlcularly preferable
for the entire~and uniform curing~i~n thls~invention.
The heating can be carried~out,~fo~r example,~by~hot blow,
;infrared~ray;and~the~ ke~. The~usable heating temperature~
ranges generally~from ro~om~temperature to 150C, and more
preferably, from 40 ~to lZ0~C, while it lS depending on the
coating Gompositio~n~ employed. ~Curing or drying would be
;ins~ufficient at the lower temperature,~and heat decomposition
or cracking may be~resulted at the higher~temperature.
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In case that the silicon compound of the ingredient A
is cured by heating, the hydrolysate is preferably used
in order to carry out the curing more entirely with lower
curing temperature.
The hydrolysates are produced by adding to the
material purified water or an aqueous solution of hydrochloric
acid, acetic acid or sulfuric acid, and stirring. Further,
the degree of hydrolysis can be easily controlled by
ad~usting the addition amount of water or acid solution.
For the hydrolysis, it is particularly preferable to add
purified water or aqueous acidic solution in an amount of
from 1 to 3 times by mole greater than the moIar amount of
-oR3 groups in the~general formula (I) in view of the promotion
of curing.
While the hydrolysis can be carried out in the
absence of any solvent since alcohol or the like ls formed
during hydrolysis~ it is also possible to carry out hydrolysis
after mixing an organic silicon compound with a solvent
in order to perform the hydrolysis more uniformly. Further,
it is also pos~sible to use the hydrolysate from which
: .
an appropriate~amount of alcohol or the like produced
dur;ing hydrolysis;has be~en removed by heating and/or reduclng
pressure depending on the purposes, or an appropriate solvent
:
may be added after the hydrolysis~ The examples of above
mentioned solvents include alcohols, esters, ethers, ketones
and halogenated hydrocarbons or aromatic hydrocarbons such as
.,, "
13
toluene and xylene. These solvents can be also used as
a mixture of two or more of them if required. Furthermore,
it is also possible to promote the hydrolyzing reaction or
other reactions, such as preliminary condensation, by
heating to temperatures higher than room temperature depending
on the purposes. Alternatively~ it is of course possible
to carry out the hydrolysis while maintaining the reactants
at temperatures lower than room temperature in order to
suppress the preliminary condensation.
The amount of the ingredient A and B used in this
invention are preferably from 1 to lOOO parts by weight of
the ingredient B based on 100 parts by weight of the
ingredient A in view of the surface hardness, water proofness
~` and the like, although it should be determined depending
on the curing conditions, the quality of natural pearls
as the material to be coated, and the desired properties
to be provided;.
The coating composition for forming membranes in
this lnvention can contain various types of surface active
agents for the~purp~ose of lmproving the flow wpon coating,
thereby improving~the smoo~thness of the coat-in~g membranes
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36
and reducing the friction coefficient at the surface of the
coating membrane. Block or graft copolymers of dimethyl-
siloxane and alkylene oxide, fluorine type surface active agents
are particularly effective. It is also possible to color
the coating membrane by dispersing dyes or pigments therein,
and to improve the practical properties of the coating composition
such as coatability, adhesion with the substrate and other
physical properties by dispersing fillers or dissolving
organic polymers therein. Furthermore~ it is also possible
to add UV-absorbent for the purpose of improving the weather
proofness and add an anti-oxidant for the purpose of improving
the heat resistance.
For curing the coating composition according to this
inv~ention, it is possible to use various kinds of curing
agents in combination in order to promote the curing and
enabling the curing at low temperature. As the curing agent,
various kinds of epoxy resin curing agents or organic silicon
resin curing agents can be used.
Preferable examples of these curing agents include
various kinds of organic acid and acid anhydrides thereof,
nitrogen-containing organic compounds~ metal complex compounds
and metal alkoxides, as well as various kinds of salts
such as organic carboxylates, carbonates and perchlorates of metals
and radical polymerization initiators such as peroxides and
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azobis-isobutyronitrile.
These curing agents may be used as a mixture of two or
more o~ them. Among these curing agents, aluminium chelate
compounds mentioned below are particularly useful for the
purpose of this invention in view of the stability of composition
and the coloration of membrane after coating.
The aluminium chelate compounds mentioned herein are,
for example, those aluminium chelate compounds represented
by the following general formula (III),
AlXnY3-n ------- (III)
where X represents OL (L is a lower alkyl group), Y is at
least one ligand selected from the ligands derived from
the compounds represented by the general formula :
Ml COCH2COM2 ..
(where M1 and M2 represent individually lower alkyl group)
and the ligands derived from the compounds represented by
the genearal formula :
M3CoC~2CooM4
(where M3 and M4 repressnt individually lower alkyl group)
and n is O, 1 or 2.
Among the aluminium chelate compounds represented by
the general formula (III), particularly preferable examples
of the curing agent for this invention, in view of the
solubility to the composition, stability and e~fect as the
curing agent, include alumlnium acetylacetonatej aluminium
bis-ethylacetoacetatemonoacetylacetonate, aluminium
di-n-butoxidemonoethylacetoacetate, aluminium di-isopropoxide-
monomethylacetoacetate and the llke. They can be used as
a mixture of two or more of them.
_ 16
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The coating composition for this invention can be diluted
with various kinds of solvents in order to improve the workability,
to control the thickness of coating membrane, etc., and
various diluting solvents can be used depending on the purposes,
for example, water, alcohol, ester, ether, halogenated hydrocarbon,
dimethylformamide, dimethylsulfoxide and the like. A mixed
solvent may be also used as required.
When the composition contains finely particulate inorganic
oxide, water, alcohol, dimethylformamide, ethylene glycol,
diethylene glycol, triethylene g]ycol, benzyl alcohol, phenethyl
alcohol, phenylcellosolve and the like are particularly preferable
in view of the dispersability and the like.
The thickness of coating~membrane comprising the curable
composition based on organic materials thus formed should be
.. ..
from!O.O1 ~m to 30 ~m. The thickness of the membrane herein
.
means the average thlckness at the surface of ornamental product.
If the thickness of coating membrane is less than~O.01 ~m,
no substantial effect can be obtained and thus no me~it of
this invention can be obtained.
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While on the other hand, if the thickness exceeds 3C ~m,
there may be resulted problems such as exfoliation and crack
of coating membrane due to the difference in the heat
coefficient between the coating membrane and the ornamental
material as the substrate. Further, a thicker coating
will cause the ununiformity of coating, and the loss in
production thereby.
The surface to be coated is preferably cleaned by removal
of contamination with a surface active agent, degreasing
with an organic solvent and vapor cleaning with freon etc.
Further, it is also effective to apply various types of
pretreatment for the purpose of;improving the adhesion
and durability. As the pretreatment, the chemical tre~atment
with an acid or alkali in suitable concentration is particularly
< :
preferable.
While there are various types of combinations as the
embodiment of this lnvention, in one of the preferable
embodiments, a coated ornamental artlcle is obtained by the
step of dyeing ornamental material such as cultured pearl with
reactive dye such as cationic dye and of coating it with the
curable composition.
In another preferable embodiment of' this i.nvention, an
ornamental article i8 coated with the curable composition
:
containing the dyes for dyeing or coloring. Where the ornamental~
~ ~ material is pearl,;~dye containing at least one fluoresce;nt dye
; is ~particularly preferable, and those dyes~having maximum
absorption at the wavelènth from 500 640 nm, more preferably
from 540 - 600 ~nm, are used for getting high quality feeling.
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EXAMPLES
This invention will now be described by way of the
following examples for better understanding of the ~eatures
of the invention, but this invention is no way restricted
only to these~examples.
Example 1
(1) Preparation of Coating Composition
Into a reactor containing a rotator and 95.3 g of
y-glycidoxypropyltrimethoxysilane, 21.8 g of 0.01 N
hydrochloric acid solution was added dropwise at 10C under
stirring with a magnetic stirrer. The stirring was continued
for additional 30 minutes to obtain a hydrolysateO
To the hydrolysate obtained above, 216 g of methanol,
216 g of dimethylformamide, 0.5 g of a fluorine type
surface active agent and 67.5 g of bisphenol A epoxy resin
(Epikote~ 827: product manufactured by Shell Chemical
Chemical Co.) were added, and then, 270 8 Of a colloidal sol
of antimony pentoxide (Antimony pentoxide~ A-2550:
product manufactured by Nissan Kagaku Co., 60 nm in average
particle size) and 13.5 g of aluminium acetyl acetonate
were added. The mixture was stirred sufficiently to obkain
a coating oomposition.
t2) Coating of Pearls
Bleached and bored cultured pearls at 2 years stage
(5 mm in diameter) were coated with the coating composition
prepared in (~lj above by manual dip coating, and then dried
for 20 minutes in a hot blow drier at 50C as the primary
drying and further heated to dry in a hot blow reoycling
drier at 50C for 20 hours to obtain pearls having coating
membranes. Coating thickness was 2.5 ~m.
A -~ :
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Example 2
(1) Preparation of Coating Composition
To 92.2 g of hydrolysate prepared in the same manner
as in Example 1 (1), 130.2 g of N,N-dimethylformamide and
then 35.5 g of novolak type epoxy resin (Epikote~ 152:
product manufactured by Shell Chemical Co.) were added.
Further, 236 g of colloidal silica dispersed in methanol was added,
and then 0.7 g of a sillcone type surface active agent and
7.1 g of aluminium acetylacetonate were added. The mixture
was stirred sufficiently to obtain a coating compositlon.
(2) Coating of Pearls
All of the same procedures as those of Example 1 (2) were
repeated except that the drying temperature was 90C, to obtain
pearls having coaking membranes. Coati~g thickness was 1.8 ~m.
Evaluation
The pearls having coating membranes obtained in Examples
1 and 2 had improved luster and higher quality as
compared with pearls without coating. Among all, those
containing the colloidal sol of antimony pentoxide in the
coating composition had the best luster, a clear color
and high quality.
When the pearls obtained in Examples 1 and 2 were slightly
rubbed with ~inger nails, no scratch was observed in them. This
showed hlgh hardness of surfaces thereof.
Furthermore~ when the pearls obtained Examples 1 and 2
were immersed in distilled water at 40C for one hour, both
of them possessed the coating~membranes after the immersion,
which showed excellent water proofness as well.
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Example 3
(1) Preparation of Coating Composition
lnto a beaker containing 50.01 parts of ~-
glycidoxypropyltrimethoxysilane, 11.5 parts of 0.01 N
hydrochloric acid was added dropwise at 10C to carry out
hydrolysis. The stirring was continued for additional
30 minutes to obtain hydrolysate.
To a beaker containing 106.5 parts of bisphenol A type
epoxy resin (Epicoat 827: a trade name of product manufactured
by Shell Chemical Co.), 309.4 parts of N,N-dimethylformamide
was added and the mixture was stirred to obtain a solution.
Then, the sllane hydrolysate obtained above was added and
the mixture was stirred. Further, 0.8 parts of a silicone
surface~active agent and 7.1 parts of aluminium acetylacetonate
were added and the mixture was stirred sufficiently to obtain
a coating composition.
(2) Coating o~ Pearls
Bleached and bored cultured pearls at 2 years stage
(5 mm in diameter) were coated with the coating composition
prepared in (1) above by float coating with an air stream at 90C
and dried for 20 minutes. Further, they were heated to dry in
a hot blow recycling drier at 90C for 20 hours to obtain pearls
having coating membranes. Coating thickness was 2.0 ~m.
Evaluation
The pearl~obtained in Example 3 had significantly
improved luster and high quality as compared with pearls
without coating. When it was immersed in distilled water
at 40C to observe the state of coating membranes,
.
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no separation of the membrane was observed af'ter immersion of
one hour and the pearl possessed coating membrane even after
immersion of additional 10 hours to show excellent water
proofness.
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Example 4
.
A coating composition was prepared in the same manner
as in Example 3 except that the epoxy resin was a hydrogenated
bisphenol A epoxy resin (Epiclon 750: product
manufactured by Dainihon Ink K.K.) and that N,N-dimethylformamide
was replaced with ethanol. As a result, a coated,pearl of
substantially same grade with that of Example 3 could be obtalned
even in case that the heating temperature was lowered to 50C.
Coating thickness was 1.5 ~m.
Example 5
A coating composition was prepared by addi~ng 90 ppm of
a fluorescent cationic dye ~Cathilon Brilliant Pink~ CD-BH:
product manufactured by Hodogaya Kagaku Industry R.XO~
absorption maximum at 562 nm) to the coating composition of Example 4.
The coating composition was applied to pearls which had been
sub~ected to bleaching only, and cured in the same manner as Example 4.
Thus obtained pearls had pinky fluorescent color and very high
quality feeling. The properties of coating membrane were
substantially same with those of Example 4.
Example 6
All of the same procedures as those o~ Example 4 were
carried out except that pearls were dyed wlth a pink cationic
dye before the coating. Thus obtained pearls had more clear
pink color and higher quality in addition to the properties
of pearls of Example 4.
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Example 7
(1) Preparation of Coating Composition
Into a beaker containing 12I.5 parts of y-
glycidoxypropyltrimethoxysilane, 27.7 parts of 0.01 N
hydrochloric acid was added dropwise at 10C to carry out
hydrolysis. The stirring was continued for additional
30 minutes to obtain hydrolysate. Then, 142.4 parts of
methanol, 5.4 parts of a silicone surface active agent and
4.29 parts of aluminium acetylacetonate were added to the
hydrolysate and the mixture was stirred sufficlently to obtain
a coating composition.
(2) Coating of Pearls
Bleached and bored cultured pearls at 2 years stage were
coated with the coating composition prepared in (1) above by
manual dip coating. Then, they were heated to dry in a hot blow
recycling drier at 50C for 24 hours to obtain pearls having
coating membranes.
Evaluation
The pearl obtained in Example 7 had significantly improved
luster and high quality as compared with pearls withouk coating.
When it was~ground for 30 minutes with an abrasive comprising
a major amount of rock salt, no change of the membrane was
observed after abrasion to show excellent abrasion resistance.
Coating thickness~ was about 2.5 ~m.
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Comparison Example 1
All of the same procedures as those of Example 7 were
repeated except that a coating composition was prepared by
adding 854 parts of methanol to the coating composition of
Example 7 and stirring the mlxture sufficiently.
The coating thickness of thus obtalned pearl was
~0.005 ~m, and no improvement of luster or quality was observed
as compared with pearls wlthout coating.
Comparison Example 2
All of the same procedures as those of Example 7 were
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repeated except that 10 % solid content of acrylic resin
solution in methylisobutyl ketone was used as a coating
:
composition.~
`~ While~some improvement o luster could be observed,
the coating membranes were completeIy removed off after 10
~,~ minutes of abrasion test to show very poor durability thereof.
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