 |
Description  |
|
|
This invention relates to a process for producing microcapsules enclosing
fine particles of a hydrophobic substance, more particularly to an
improved process for producing such microcapsules substantially without
entailing formation of large clusters of microcapsules.
Methods of producing microcapsules of complex hydrophilic colloid material
enclosing a hydrophobic substance are already known. The method of
producing such microcapsules disclosed in U.S. Pat. No. 2,800,457, for
example, comprises the steps of emulsifying and dispersing a hydrophobic
substance in an aqueous solution of a hydrophilic colloid material, mixing
with the dispersion an aqueous solution of another hydrophilic colloid
material, thereafter causing coacervation to deposit the colloid materials
around the hydrophobic substance by adjusting the pH of the resulting
dispersion and/or by diluting the dispersion with water, gelling the
colloid materials by cooling the dispersion to form microcapsules, and
hardening the microcapsules obtained by adjusting the pH of the dispersion
and by adding formaldehyde to the dispersion. The method disclosed in U.S.
Pat. No. 3,341,466 comprises the steps of emulsifying and dispersing a
hydrophobic substance in an aqueous solution of two hydrophilic colloid
materials, thereafter forming coacervate and gelling the same in the same
manner as above. However, in the preparation of microcapsules in which two
kinds of hydrophilic colloid materials are separated out as a complex
coacervated phase, the system which is unstable permits individual
capsules to agglomerate into bunches like grapes during gelling and
hardening steps, failing to give loose or unclustered capsules and
therefore to prevent clustering of capsules in the end product. Clustered
capsules produce troubles in various fields in which capsules are used.
For example, U.S. Pats. Nos. 2,730,456, 2,730,457, etc. disclose pressure
sensitive manifold papers utilizing electron donor-acceptor colour forming
reaction between (1) an electron donating organic chromogenic material
(hereinafter referred to as a "colour former") such as Crystal Violet
lactone, Malachite green lactone and like lactone dyes, benzoyl leuco
Methylene blue and like Methylene blue dyes, 3-diethylamino- 7-benzylamino
fluoran, 3-diethylamino-7-amino fluoran and like fluoran derivatives,
benzo-.beta.-naphtho spiropyran and like spiro compounds,
1-[bis(p-dimethylaminophenyl)methyl]pyrolidine and the auramine compounds,
etc. and (2) an electron accepting acidic reactant material (hereinafter
referred to as a "colour acceptor") such as kaolin, bentonite, acid clay,
zeolite, activated clay, attapulgite and like acidic clay,
p-phenylphenolformaldehyde resin, p-ter-butylphenol-acethylene resin and
like phenolic polymers, 3,5-di-(.alpha.-methylbenzyl) salicylic acid, zinc
3-phenyl-5-(.alpha., .alpha.'-dimethylbenzyl) salicylate and like aromatic
carboxylic acid and metal salts thereof, etc. With such manifold paper,
the colour former is enclosed in microcapsules which are provided on the
surface of paper in the form of a coating. If the coating contains
clusters of capsules, uneven distribution of the colour former will
result, leading to the drawback that the manifold paper gives an obscure
colour image when put to use or becomes markedly smudged during storage.
Furthermore when a coating composition containing clustered microcapsules
is applied to a substrate by air knife coater for the production of
pressure sensitive manifold paper, the capsules are classified by the air
pressure of the coater to form an irregular coating. When the manifold
paper obtained is used or stored, the same drawback as above is therefore
experienced. Similarly an attempt has been made to prepare an X-ray image
forming barium sulfate suspension having a low viscosity and good
stability by encapsulating barium sulfate with gelatin, gum arabic or the
like to render the barium sulfate readily dispersible in water. For this
purpose, it is greatly desired to prepare unclustered, barium
sulfate-enclosing capsules of uniform particle size distribution and to
make barium sulfate easily dispersible in water in stable manner, thereby
assuring that the X-ray image forming agent will be highly amenable to
intimate contact with the wall of the organ when put to use. Otherwise,
clusters of microcapsules might possibly lead to the serious result of
erroneous diagnosis. Accordingly, utmost care has been taken in
controlling the particle size distribution but, as already described, the
conventional method invariably permits capsules to cluster during gelling
and hardening steps and consequently results in uneven particle size
distribution of the capsules. Various troubles are therefore encountered.
Many proposals are made for prevention of capsules from clustering. For
example, Japanese Pat. No. 315,171 discloses a method in which a thickener
such as magnesium silicate, tragacantha, glycerin or the like is used in
emulsifying step to sufficiently deposit a hydrophilic colloid material
around fine particles of hydrophobic material. However, this method is
still unable to fully inhibit clusters of capsules and to obtain
unclustered capsules. It is also known to add a copolymer of vinyl methyl
ether and maleic anhydride, serving as an agglomeration inhibitor, to two
kinds of hydrophilic colloid materials for the preparation of
microcapsules (Japanese Pat. No. 288,452), or to similarly use pectin,
pectic acid, pectinic acid or the like as a shock preventing agent
(Japanese Patent Publication No. 16,168/1972). Although considerably
effective in suppressing clustering of microcapsules, these methods
require an additional cumbersome step of incorporating the above-mentioned
substances, consequently entailing an increase in the equipment cost due
to the modification of the existing equipment or to the installation of
new equipment as well as a substantial increase in the processing cost for
the cumbersome procedure.
Accordingly, the main object of this invention is to provide a novel
process for producing microcapsules free of the drawbacks of the
conventional methods described above.
Another object of this invention is to provide a process for producing
microcapsules substantially free from clustered capsules by using existing
equipment.
Still another object of this invention is to provide a process for
producing microcapsules substantially free from clustered capsules by a
simple operation.
Other objects and features of this invention will become apparent from the
following description.
In a process for producing microcapsules of complex hydrophilic colloid
material enclosing fine particles of a hydrophobic substance, the present
invention provides the improvement characterized in that an acid-treated
gelatin and at least one of carboxy-modified cellulose derivatives are
used as the hydrophilic colloid materials, the amount of the cellulose
derivative being 1/7 to 1/40 the amount of the gelatin by weight, the
cellulose derivative having an average polymerization degree of 50 to
1,000 and a carboxyl substitution degree of 0.4 to 1.5 and that the
coacervation of colloid material solution is effected at a pH of 4.8 to
6.0.
Our researches have revealed that when the acid-treated gelatin and the
above-specified carboxy-modified cellulose derivative are used as
hydrophilic colloid materials, with the pH of the dispersion maintained at
the specified value for coacervation, microcapsules are prevented from
clustering into grape-like bunches during gelling and hardening steps and
unclustered capsules are easily available eventually. The present
invention has the great advantage that unclustered capsules can be
prepared with extreme ease without using an agglomeration inhibitor or
shock preventing agent and with an existing equipment, simply by using an
acid-treated gelatin as one of the hydrophilic colloid materials and a
carboxy-modified cellulose derivative as the other hydrophilic colloid
material. Thus with the use of the specified hydrophilic colloid materials
and further with the use, for example, of oily material as a hydrophobic
substance having a colour former dissolved or dispersed therein or of
barium sulfate as a hydrophobic substance, it has become possible to very
easily unclustered microcapsules having outstanding properties for use in
pressure sensitive manifold sheet or for the production of X-ray image
forming agent.
Firstly, the present invention is characterized by the use of acid-treated
gelatin and carboxy-modified cellulose derivative in an amount of 1/7 to
1/40, preferably of 1/8 to 1/20, the amount of acid-treated gelatin by
weight. If the amount of carboxy-modified cellulose derivative is more
than 1/7 or less than 1/40 the amount of acid-treated gelatin based on
weight, it is no longer possible to obtain unclustered capsules. It has
not been known to use two kinds of hydrophilic colloid materials in such
an extremely unbalanced relative ratio. In fact this is entirely
inconceivable from the prior art of encapsulation in which two known
hydrophilic colloid materials are used for coacervation. Further various
hardening agents such as formaldehyde, glyoxal and glutaraldehyde are
usually used to strengthen the wall of capsule obtained, chiefly through
the reaction of such hardening agent with gelatin. Accordingly, in the
hardening reaction of the capsule wall in the gelatin-gum arabic system in
a conventional method as disclosed in U.S. Pat. No. 2,800,457, it is known
that gum arabic does not participate in the reaction but is released from
the capsule wall (Kogyo Kagaku Zasshi, Vol. 73, No. 8 (1970), pages 1,755
to 1,758), whereas with conventional methods, the hydrophilic colloid
material to be used in combination with gelatin must be employed in an
amount almost equal to the amount of gelatin. (For example, U.S. Pat. No.
2,800,457 states that gelatin and gum arabic are used in the same amount).
Consequently a high proportion of the hydrophilic colloid material is left
out of the hardening reaction, this making it impossible to completely
strengthen the capsule wall and therefore leading to the drawback that,
when exposed to a high humidity, capsules rupture spontaneously or permit
the enclosed substance to seep therethrough. When such capsules are used,
for example, in pressure sensitive manifold sheet, the sheet becomes
smudged during storage or handling and suffers various troubles in
practical use. Further in the production of pressure sensitive manifold
sheet, the capsule-containing aqueous dispersion prepared is usually
applied, along with additives when so desired, to paper, plastic or like
substrate. The manifold sheet therefore has the drawback that the gum
arabic, remaining unreacted during hardening, interferes with colour
forming reaction and reduces the density of the colour formed. Thus, to
render the capsules fully serviceable, it has been desired to increase the
gelatin content thereof to the highest possible extent. This invention
provides microcapsules having a high gelatin content. In fact the capsules
prepared according to this invention can be readily hardened through usual
hardening reaction, are fully resistant to high humidities and have a high
copying ability when used in pressure sensitive manifold sheet without
interfering with the colour forming reaction.
The process of this invention has another important feature that
acid-treated gelatin and carboxy-modified cellulose derivative in the
above-specified proportions are subjected to coacervation at a pH of from
4.8 to 6.0. With known methods, gelatin and another colloid material are
coacervated usually at an adjusted pH value of 3.0 to 4.5, for example, as
disclosed in Japanese Pat. No. 521,609, whereas according to this
invention the coacervate obtained tends to agglomerate and unclustered
capsules are unavailable if the pH value is lower than 4.8 even at
temperatures not lower than the gelling point of the gelatin used.
Conversely, at pH values of above 6.0, capsules agglomerate during cooling
and hardening steps and unclustered capsules are not obtainable. Thus only
when the pH of the system is adjusted to the limited range of 4.8 to 6.0,
loose and unclustered capsules can be obtained free of any adhesion and
agglomeration throughout the entire process for the production of
capsules. Indeed such unexpected effect and advantage are attainable only
by using acid-treated gelatin and carboxy-modified cellulose derivative in
the specified proportions given above and by conducting coacervation in
the limited pH range. Unclustered capsules can be prepared more
inexpensively and by a simplified process according to this invention as
compared with conventional methods with which it is necessary to use an
additional material such as agglomeration inhibitor or shock preventing
agent. Researches have yet to be made to determine why the use of
hydrophilic colloid materials in the specified proportions in the limited
pH range gives unclustered capsules without permitting agglomeration.
Generally the process of this invention is practiced in the following
manner. First, acid-treated gelatin is dissolved in water in the known
manner to produce an aqueous solution thereof. The water may be warmed to
a temperature higher than the gelling point of the gelatin so as to obtain
a solution of higher concentration. The acid-treated gelatin to be used in
this invention is any of those heretofore employed for the production of
microcapsules in the prior art. Such gelatin is usually prepared by
treating collagen with an inorganic acid such as sulfuric acid or
hydrochloric acid and extracting the treated collagen from mildly hot
water. Preferable among acid-treated gelatins thus obtained are those
having an isoelectric point of about 7 to 9 and jelly strength of about 70
to 250 g.Bloom, especially of 90 to 200 g.Bloom, as determined by jelly
strength meter of the Bloom type according to PAGI method. The
concentration of the aqueous solution of gelatin, which is not
particularly different from that in the prior art, is usually 0.25 to 10
wt.%, preferably 1 to 5 wt.% Subsequently, the hydrophobic substance to be
encapsulated is emulsified in the aqueous solution of gelatin. Useful as
the hydrophobic substance is any of those conventionally used as such and
is not particularly limited, insofar as it is substantially insoluble in
water, is not so reactive with the capsule forming materials used and with
another substance to be encapsulated as to be objectionable to the novel
process of this invention, and is wettable with the coacervate formed.
Example of such substances are fish oil, lard, whale oil, beef tallow and
like animal oils, olive oil, peanut oil, linseed oil, soybean oil, castor
oil and like vegetable oils, petroleum, kerosene, xylene, toluene and like
mineral oils, alkyl-substituted diphenylalkane, alkyl-substituted
naphthalene, diphenylethane, methyl salicylate and like synthetic oils
which are insoluble or substantially insoluble in water. In addition to
these liquids, further examples are water-insoluble metal salts and metal
oxides such as barium sulfate, fibrous materials such as asbestos,
cellulose, water-insoluble synthetic polymeric materials, minerals,
pigments, glasses, perfumes, spices, sterilizer compositions,
physiological compositions, fertilizer compositions, etc. When
microcapsules are used for example for pressure sensitive manifold sheet,
the above-mentioned liquid substance is used with a colour former such as
Crystal Violet lactone, etc. dissolved or dispersed therein.
An aqueous solution of carboxy-modified cellulose derivative is then added
to the resulting emulsion, and the mixture is uniformly stirred. Usable as
the carboxy-modified cellulose derivative in this invention are
carboxymethyl cellulose, carboxyethyl cellulose, .alpha.-dicarboxyethyl
cellulose, etc., which are obtained by the reaction of OH, ONa, CH.sub.2
OH or CH.sub.2 ONa groups on the glucose rings of cellulose with
halogenated lower aliphatic carboxylic acid such as monochloroacetic acid,
monobromoacetic acid, monofluoroacetic acid, monochloropropionic acid or
monochlorosuccinic acid. Also useful are carboxymethylhydroxyethyl
cellulose, carboxymethylhydroxypropyl cellulose, carboxymethylmethyl
cellulose, carboxyethylmethyl cellulose, carboxyethylhydroxyethyl
cellulose, carboxymethylbenzyl cellulose, etc., which are obtained by
substituting methyl, ethyl, propyl, butyl or like C.sub.1- 4 alkyl,
hydroxyethyl, hydroxypropyl or like C.sub.2- 4 hydroxyalkyl or benzyl for
some of the unsubstituted hydroxyl groups of the above-mentioned
compounds, the degree of substitution being such that the compounds
obtained still retain the characteristics of carboxy-modified cellulose
derivatives. Among these compounds, carboxymethyl cellulose is preferable
for the formation of unclustered capsules. These compounds are used singly
or at least two of them may be used conjointly.
The carboxy-modified cellulose derivatives to be used in this invention
must have a carboxyl substitution degree (hereinafter referred to as
"substitution degree") of 0.4 to 1.5, preferably 0.6 to 1.2. With
substitution degrees of above 1.5, the system are electrostatically out of
balance, failing to give unclustered capsules as desired, whereas if the
substitution degree is less than 0.4, the cellulose derivative has a very
low solubility in water. Furthermore useful cellulose derivatives must
have an average polymerization degree of 50 to 1,000 preferably of 70 to
500, because if the average polymerization degree is lower than 50, it is
difficult to effect coacervation and unclustered capsules are not
available, whereas if the degree exceeds 1,000, the phase separated out is
unable to fully enclose the fine particles of hydrophobic substance as
desired. Incomplete capsules will therefore result. Usually the cellulose
derivatives are used in the form of an aqueous solution of alkali metal
salt or ammonium salt. As already described, the carboxy-modified
cellulose derivative is used in an amount of 1/7 to 1/40, preferably of
1/8 to 1/20, the amount of the acid-treated gelatin by weight.
Alternatively, the hydrophobic substance to be encapsulated may be first
emulsified in the aqueous solution of carboxy-modified cellulose
derivative and the aqueous solution of acid-treated gelatin may be then
added to the resulting emulsion, or a solution having dissolved
carboxy-modified cellulose and acid-treated gelatin therein may be first
prepared and then the hydrophobic substance may be emulsified in the
resulting solution. The steps so far described are conducted usually above
the gelling point of the acid-treated gelatin used.
The resulting mixture of the two kinds of colloid materials is then
adjusted to a pH of 4.8 to 6.0 and is thereafter cooled to a temperature
lower than the gelling point of the acid-treated gelatin used.
Alternatively, after the solution having dissolved therein
carboxy-modified cellulose and acid-treated gelatin is adjusted to a pH of
4.8 to 6.0 for coacervation, the hydrophobic substance may be added
thereto as in the process disclosed in U.S. Pat. No. 3,341,466. The
adjustment of pH of the solution can be made, as known in the art, by the
addition in the form of a solution of, for example, a base such as sodium
hydroxide, potassium hydroxide and like alkali metal hydroxides, ammonium,
pyridine, trimethylamine and like organic bases, etc., or an acid such as
acetic acid, citric acid and like carboxylic acids, hydrochloric acid,
sulfuric acid, nitric acid and like inorganic acids, etc., as required. To
the resulting system thus obtained is further added, for example, an
aqueous solution of formaldehyde, glyoxal or glutaraldehyde according to
the usual process to harden the gelled coacervate. Prior to or after the
addition of formaldehyde solution to the system, the pH of the system may
be adjusted to a higher value with the addition of a base for improving
the hardness of the coacervate.
For a better understanding of the invention, Examples are given below to
which, however, the invention is not limited in any way. All parts and
percentages used in the Examples and Comparison Examples are by weight
unless otherwise indicated. In the Examples and Comparison Examples,
microcapsules and pressure sensitive manifold paper prepared are evaluated
by identifying the defects and determining the characteristic values as
stated below:
1. Clustered microcapsules in microcapsule dispersion:
The diameter of the largest cluster of microcapsules and the number of
clusters per 100 capsules produced are microscopically determined.
2. Tests of microcapsules for use in pressure sensitive manifold paper:
To the microcapsule dispersion obtained in each of Examples and Comparison
Examples are added 100 parts of 20% aqueous solution of oxidized starch
and 15 parts of cellulose powder to prepare a colour former coating
composition, which is applied in an amount of 5 g/m.sup.2 when dried, to a
paper substrate weighing 40 g/m.sup.2 to obtain transfer sheets (top
sheets). A colour acceptor coating composition is separately prepared from
100 parts of acidic clay, 10 parts of 20% aqueous solution of sodium
hydroxide, 40 parts of 50% styrene-butadiene copolymer latex (styrene:
butadiene = 60 : 40), 50 parts of 1% aqueous solution of sodium alginate
and 200 parts of water. The colour acceptor coating composition is then
applied, in an amount of 6 g/m.sup.2 when dried, to a paper substrate
weighing 40 g/m.sup.2 to obtain copy sheets (bottom sheets). The same
colour former coating composition as above is applied, in an amount of 5
g/m.sup.2 when dried, to the rear surface of each of the same copy sheets
prepared in the same manner as above to obtain middle sheets.
The three kinds of sheets thus prepared are tested in the following manner.
i. Colour forming ability
The transfer sheet is superposed on the copy sheet with the coatings facing
each other, and the set of sheets is subjected to pressure of 600
kg/cm.sup.2 to form a colour mark on the copy sheet. The density of the
mark is measured by HITACHI SPECTRO PHOTOMETER, Model-124 (manufactured by
HITACHI, LTD., Japan) at a light wavelength of 610 m.mu.. The result is
given in terms of absorbancy (D.sub.1).
ii. Resolving power
Seven middle sheets are fitted together in layers with the colour former
coatings facing the colour acceptor coatings respectively, and the pile of
sheets is pressed by electric typewriter. The sharpness of the colour
characters formed on the colour acceptor coating on the lowermost sheet is
inspected with the unaided eye and evaluated according to the following
criteria:
A: Excellent
B: Good
C: Acceptable
D: Reject
iii. Pressure resistance
The transfer sheet is superposed on the copy sheet with the coatings facing
each other, and the set of sheets is subjected to pressure of 40
kg/cm.sup.2 to form a colour mark on the copy sheet. The density of the
mark is measured by the same spectrophotometer as above at a light
wavelength of 610 m.mu.. The result is given in terms of absorbancy
(D.sub.2), which relates to smudging caused in the course of coating and
winding-up operations for the production of middle sheet or when the sheet
is cut or printed. The lower the value, the less is the susceptibility of
manifold paper to smudging.
iv. Frictional smudge resistance
The transfer sheet is superposed on the copy sheet with the coating facing
each other, and the transfer sheet is moved back and forth five times over
a distance of 5 cm at a speed of 450 cm/min. while applying pressure of 55
g/cm.sup.2 to the transfer paper on its uncoated surface. The colour
smudge formed on the copy sheet is inspected with the unaided eye and
evaluated according to the following criteria:
A: Excellent
B: Good
C: Acceptable
D: Reject
v. Fogging characteristics
Expressed in terms of D.sub.2 /D.sub.1 x 100, namely the ratio of the
colour density produced at pressure of 40 kg/cm.sup.2 to that produced at
pressure of 600 kg/cm.sup.2. The higher the value, the more susceptible is
the manifold paper to fogging, hence less amenable to processing.
EXAMPLE 1
To 225 parts of water is added 25 parts of acid-treated gelatin
(isoelectric point: 8, jelly strength: 180 g.sup.. Bloom), and after
leaving the mixture at 10.degree. C 1 hour, 530 parts of water is added
thereto. The mixture is then heated at 60.degree. C to prepare a solution.
Separately, 2 parts of Crystal Violet lactone and 1 part of benzoyl leuco
Methylene Blue are dissolved in 30 parts of kerosene and 70 parts of
isopropylnaphthalene, and the solution is heated to 60.degree. C and then
added to the gelatin solution. The mixture is stirred to prepare an
emulsion containing oily droplets 5 to 10 .mu. in mean particle size.
Further separately, 5% aqueous solution of carboxymethyl cellulose
(average polymerization degree: 150, substitution degree: 0.6) is
prepared, and 50 parts of the solution (amount of the carboxymethyl
cellulose: 1/10 the amount of the gelatin by weight) is added to the
emulsion with stirring to obtain a system having a pH of 4.3. The system
is adjusted to a pH of 5.5 with a 5% aqueous solution of sodium hydroxide
and then cooled to 10.degree. C. After adding 25 parts of 10% aqueous
solution of formaldehyde to the system, the mixture is left to stand for 5
minutes. Adjustment of the mixture to a pH of 10 with dropwise addition of
10% aqueous solution of sodium hydroxide gives a dispersion of highly
hardened capsules. Microscopic inspection of the dispersion reveals that
it contains loose and unclustered capsules with uniform particle size
distribution and entirely free from clusters. The pressure sensitive
manifold paper prepared with the use of the capsule dispersion gives a
colour image of uniform and high density and is free of any smudging when
stored for a long period of time. Table 1 shows the characteristics of the
microcapsule dispersion and the properties of the manifold paper prepared
with the use of the dispersion, along with the results achieved in
Examples 2 to 7 and Comparison Examples 1 and 2.
EXAMPLE 2
In 530 parts of water is dissolved 2.5 parts of carboxymethyl cellulose
(polymerization degree: 150, substitution degree: 0.6), and the solution
is heated to 60.degree. C. A mixture of 30 parts of kerosene and 70 parts
of isopropylnaphthalene having dissolved therein 2 parts of Crystal Violet
lactone and 1 part of benzoyl leuco Methylene Blue is added to the
solution to prepare an emulsion, which is then adjusted to a pH of about 7
with dropwise addition of 10% aqueous solution of sodium hydroxide. To the
emulsion is thereafter added 250 parts of 10% aqueous solution of
acid-treated gelatin (isoelectric point: 8, jelly strength: 150 g.sup..
Bloom) at 60.degree. C. Adjustment of the resulting system to a pH of 5.5
with a 10% acetic acid, cooling of the system and addition of formaldehyde
solution are followed by the same procedure as in Example 1 to obtain a
capsule dispersion.
EXAMPLE 3
To 700 parts of water are added 25 parts of acid-treated gelatin
(isoelectric point: 8, jelly strength: 130 g.sup.. Bloom) and 2.5 parts of
carboxymethyl cellulose (average polymerization degree: 150, substitution
degree: 0.6), and the mixture is heated to 60.degree. C to prepare a
solution having a pH of 4.7. To the solution thereafter adjusted to a pH
of 5.5 with a 5% aqueous solution of sodium hydroxide is added a mixture
consisting of 30 parts of kerosene, 70 parts of isopropylnaphthalene, 2
parts of Crystal Violet lactone and 1 part of benzoyl leuco Methylene Blue
to formulate an emulsion, which is cooled to 10.degree. C and further
treated in the same manner as in Example 1, whereby a capsule dispersion
is prepared.
EXAMPLES 4 TO 7
Various capsule dispersions are prepared by the process of this invention
following the same procedure as in Example 1 except that acid-treated
gelatin and carboxymethyl cellulose are used in the proportions listed in
Table 1.
COMPARISON EXAMPLES 1 AND 2
Two kinds of capsule dispersions are prepared in the same manner as in
Example 1 except that acid-treated gelatin and carboxymethyl cellulose are
used in the proportions given in Table 1.
Table 1
__________________________________________________________________________
Capsule
Propor-*.sup.1
dispersion Pressure sensitive manifold paper
tion of Maximum
Number*.sup.2 Pres-
Frictional
carboxy- diameter
of Colour
Resolv-
sure smudge
Fogging
methyl of clus-
clus- forming
ing resist-
resist-
charac-
cellulose ters (.mu.)
ters ability
power
ance ance teristics
__________________________________________________________________________
Ex. 1
1/10 -- 0 0.96 A 0.05 A 5.2
Ex. 2
1/10 -- 0 0.96 A 0.05 A 5.2
Ex. 3
1/10 -- 0 0.95 A 0.05 A 5.3
Comp.
Ex. 1
1/6 50 15 0.97 D 0.23 D 23.7
Ex. 4
1/7 15 1 0.95 A 0.08 B 8.4
Ex. 5
1/15 -- 0 0.97 A 0.05 A 5.2
Ex. 6
1/20 -- 0 0.96 A 0.05 A 5.2
Ex. 7
1/40 15 3 0.96 B 0.09 B 9.4
Comp.
Ex. 2
1/50 60 20 0.95 D 0.27 D 28.4
__________________________________________________________________________
Note:
*.sup.1 Based on the weight of acid-treated gelatin.
*.sup.2 Per 100 capsules.
Table 1 indicates that the dispersions prepared in Examples contain loose
and unclustered capsules with uniform particle size distribution and
almost free from clusters. The manifold papers prepared are also
satisfactory in various properties. With Comparison Examples, the
dispersions contain many clusters of capsules and it is impossible to
obtain unclustered capsules with uniform particle size distribution. The
manifold papers prepared with use of such dispersions are not satisfactory
for use.
EXAMPLE 8
A capsule dispersion is formulated in the same manner as in Example 1
except that acid-treated gelatin (isoelectric point: 7.8, jelly strength:
180 g.sup.. Bloom) and carboxymethyl cellulose (average polymerization
degree: 500, substitution degree: 0.7) are used. Table 2 shows the
characteristics of the capsule dispersion and the properties of the
manifold paper prepared with the use of the dispersion, along with the
results achieved in Examples 9 to 12 and Comparison Examples 3 to 5.
EXAMPLES 9 TO 12
Various capsule dispersions are prepared in the same manner as in Example 8
except that carboxymethyl celluloses of varying average polymerization
degrees and substitution degrees are used as listed in Table 2.
COMPARISON EXAMPLES 3 TO 5
Various capsule dispersions are prepared in the same manner as in Example 8
except that carboxymethyl celluloses of varying average polymerization
degrees and substitution degrees are used as listed in Table 2.
Table 2
__________________________________________________________________________
Carboxymethyl Capsule Pressure sensitive manifold paper
cellulose dispersion Colour
Average Maximum
Number*
form- Pres-
Frictional
Fogg-
polymeri- Substi-
diameter
of ing Resolv-
sure smudge
ing
zation tution
of clus-
clus-
abili-
ing resist-
resist-
charac-
degree degree
ters (.mu.)
ters ty power
ance ance teristic
__________________________________________________________________________
Ex. 8
500 0.7 -- 0 0.96
A 0.05 A 5.2
Comp.
Ex. 3
300 0.3 80 50 0.97
D 0.30 D 30.9
Ex. 9
200 0.4 15 1 0.97
B 0.08 B 8.3
Ex. 10
200 1.0 -- 0 0.96
A 0.04 A 4.2
Ex. 11
50 1.5 15 1 0.96
B 0.08 B 8.3
Comp.
Ex. 4
150 2.0 40 20 0.97
D 0.19 D 19.6
Ex. 12
800 1.2 20 2 0.95
B 0.09 B 9.5
Comp.
Ex. 5
1200 0.9 100 80 0.98
D 0.32 D 32.7
__________________________________________________________________________
Note:
*Per 100 capsules.
As will be apparent from Table 2, the dispersions prepared in Examples
contain loose and unclustered capsules with uniform particle size
distribution and free from clusters. The manifold papers prepared using
the dispersions are also found fully serviceable for practical use. The
dispersions obtained in Comparison Examples all contain many clusters of
capsules and it is impossible to obtain unclustered capsules with uniform
particle size distribution. The manifold papers prepared with the use of
such dispersions are therefore found to be unserviceable in any way.
EXAMPLES 13 AND 14
Capsule dispersions are formulated in the same manner as in Example 1
except that coacervation is effected at varying pH values as listed in
Table 3. The capsule dispersions are microscopically inspected, and
pressure sensitive manifold papers are prepared using the dispersions and
then tested. Table 3 also shows the results as well as the corresponding
results achieved in Comparison Examples 6 and 7 to follow.
COMPARISON EXAMPLES 6 AND 7
Capsule dispersions are prepared in the same manner as in Example 1 except
that coacervation is effected at pH values outside the range specified in
the present invention.
As will be apparent from Table 3, the dispersions of Examples contain loose
and unclustered capsules with uniform particle size distribution and
almost free from clusters, whereas those of Comparison Examples both
contain many clusters of capsules and it is impossible to obtain
unclustered capsules with uniform particle size distribution.
Table 3
__________________________________________________________________________
Capsule dispersion
Pressure sensitive manifold paper
Maximum dia-
Number*
Colour Frictional
Fogging
pH meter of
of forming
Resolving
Pressure
smudge
charac-
value
clusters (.mu.)
clusters
ability
power resistance
resistance
teristics
__________________________________________________________________________
Comp. Ex.
4.5 150 100 0.98 D 0.35 D 35.7
6
Ex. 13 4.8 12 1 0.97 B 0.07 B 7.2
Ex. 14 6.0 12 1 0.95 B 0.07 B 7.4
Comp. Ex.
6.5 200 70 0.98 D 0.34 D 34.5
7
__________________________________________________________________________
Note:
*Per 100 capsules
EXAMPLES 15 TO 22
Capsule dispersions are prepared in the same manner as in Example 1 except
that in place of carboxymethyl cellulose various carboxy-modified
cellulose derivatives are used in ratios relative to acid-treated gelatin
as listed in Table 4 and that coacervation is effected at varying pH
values given in the same table. Table 4 shows the results of microscopic
inspection of the capsule dispersions obtained and Table 5 shows the
results of tests conducted for the pressure sensitive manifold papers
produced with the use of the dispersions.
As will be apparent from Table 4, the dispersions of Examples contain loose
and unclustered capsules with uniform particle size distribution and
almost free from clustered capsules.
Table 4
__________________________________________________________________________
Carboxy-modified cellulose Capsule dispersion
derivative Maximum
Average diameter
polymeri-
Substi- of Number*.sup.2
zation
tution pH clusters
of
Kind degree
degree
Ratio*.sup.1
value
(.mu.)
clusters
__________________________________________________________________________
Ex. 15
Carboxyethyl
300 0.9 1/9 5.5 15 1
cellulose
Ex. 16
Carboxyethyl
100 1.2 1/18 5.2 15 1
cellulose
Ex. 17
Carboxymethyl-
150 0.4 1/10 4.9 18 2
hydroxyethyl
cellulose
Ex. 18
Carboxymethyl-
100 1.5 1/15 5.8 15 3
hydroxyethyl
cellulose
Ex. 19
Carboxymethyl-
80 1.0 1/7 5.0 12 2
hydroxyethyl
cellulose
Ex. 20
Carboxymethyl-
500 0.7 1/10 5.5 15 1
hydroxypropyl
cellulose
Ex. 21
Methylcarboxy-
200 1.3 1/15 5.3 18 1
methyl
cellulose
Ex. 22
Carboxymethyl-
100 1.5 1/10 4.8 18 2
benzyl
cellulose
__________________________________________________________________________
Note:
*.sup.1 Based on the weight of acid-treated gelatin.
*.sup.2 Per 100 capsules.
Table 5
______________________________________
Pressure sensitive manifold paper
Colour Resolv- Frictional
Fogging
forming ing Pressure smudge charac-
ability power resistance
resistance
teristics
______________________________________
Ex. 15 0.89 B 0.07 B 7.8
Ex. 16 0.90 B 0.07 B 7.8
Ex. 17 0.88 A 0.08 B 9.1
Ex. 18 0.89 B 0.08 B 9.0
Ex. 19 0.86 A 0.07 B 8.1
Ex. 20 0.89 B 0.07 B 7.9
Ex. 21 0.87 B 0.09 B 9.2
Ex. 22 0.91 B 0.08 B 9.9
______________________________________
EXAMPLE 23
In 100 ml of water is dissolved 20 g of acid-treated gelatin (isoelectric
point: 8, jelly strength: 90 g.sup.. Bloom). Addition of 5 ml of Turkey
red oil and 160 g of barium sulfate is followed by stirring to formulate a
suspension, which is dispersed in 1.7 liters of aqueous solution of 2 g of
carboxymethyl cellulose (average polymerization degree: 150, substitution
degree: 0.6) at 60.degree. C with stirring. Subsequently, the dispersion
is adjusted to a pH of 5.3 and then cooled to 10.degree. C. Ten ml of 10%
aqueous solution of formaldehyde is then added to the dispersion. The
mixture is left to stand for 5 minutes and is thereafter adjusted to a pH
of 9 with dropwise addition of 10% aqueous solution of sodium hydroxide.
The system is heated to 40.degree. C to completely harden the coacervate
formed. The microcapsules obtained have uniform particle size distribution
which is substantially in coincidence with that of barium sulfate when the
increments of particle sizes corresponding to the film thicknesses of
capsules are excluded.
The capsules are isolated, washed and then formulated into an aqueous
dispersion in usual manner for use as an X-ray image forming agent. The
dispersion has high stability free of settling even when stored for a long
period | | |
