U.S. patent application number 10/705650 was filed with the patent office on 2004-07-08 for zinc acrylate and method for production thereof.
Invention is credited to Hasegawa, Manabu, Saito, Yoshinori.
Application Number | 20040133023 10/705650 |
Document ID | / |
Family ID | 32677011 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040133023 |
Kind Code |
A1 |
Hasegawa, Manabu ; et
al. |
July 8, 2004 |
Zinc acrylate and method for production thereof
Abstract
Zinc acrylate excelling in flowability is provided. It is
produced by a method, characterized by dispersing zinc oxide in any
of (a) an aliphatic hydrocarbon solvent, (b) a mixed solvent formed
between an aliphatic hydrocarbon solvent and an aromatic
hydrocarbon solvent, and (c) a mixed solvent formed between an
aromatic hydrocarbon solvent and an alcohol and causing acrylic
acid to react with said zinc oxide in said solvent. The obtained
zinc acrylate refrains from undergoing secondary aggregation,
excels in disintegrability and, when kneaded in a rubber
composition, exhibits excellent dispersibility.
Inventors: |
Hasegawa, Manabu; (Tokyo,
JP) ; Saito, Yoshinori; (Chiba, JP) |
Correspondence
Address: |
Diane Dunn McKay, Esq.
Mathews, Collins, Shepherd & McKay, P.A.
Suite 306
100 Thanet Circle
Princeton
NJ
08540
US
|
Family ID: |
32677011 |
Appl. No.: |
10/705650 |
Filed: |
November 10, 2003 |
Current U.S.
Class: |
556/131 |
Current CPC
Class: |
C07C 51/412 20130101;
C07C 51/412 20130101; C07C 57/04 20130101 |
Class at
Publication: |
556/131 |
International
Class: |
C07F 003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2002 |
JP |
2002-327496 |
Claims
1. A method for the production of zinc acrylate, which comprises
dispersing zinc oxide in any of (a) an aliphatic hydrocarbon
solvent, (b) a mixed solvent formed between an aliphatic
hydrocarbon solvent and an aromatic hydrocarbon solvent, and (c) a
mixed solvent formed between an aromatic hydrocarbon solvent and an
alcohol and causing acrylic acid to react with said zinc oxide in
said solvent.
2. A method according to claim 1, wherein the reaction of said zinc
oxide with acrylic acid in said solvent is performed in the
presence of a higher fatty acid of 12-30 carbon atoms.
3. A method according to claim 1, wherein said aliphatic
hydrocarbon solvent is an alkane having 6-10 carbon atoms, said
alcohol is an alcohol having 1-8 carbon atoms, and said aromatic
hydrocarbon solvent is toluene or xylene.
4. Zinc acrylate forming the crystals thereof having a long axis of
not less than 5 .mu.m and an aspect ratio in the range of 1-30.
5. Zinc acrylate according to claim 4, further having a 50%
particle diameter of not less than 6 .mu.m.
6. Zinc acrylate according to claim 4, wherein the ratio of passage
of the crystals thereof through a sieve opening of 1 mm is not less
than 90%.
7. Zinc acrylate according to claim 4, wherein the solid
disintegrating load of the crystals thereof is not more than 1.0
kg/cm.sup.2.
8. Zinc acrylate according to claim 4, wherein the crystals thereof
have a degree of compaction of not more than 50%.
9. A zinc acrylate composition, comprising the zinc acrylate set
forth in any of claims 4-8 and a zinc salt of a higher aliphatic
acid of 12-30 carbon atoms.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method for the production of
zinc acrylate by the reaction of acrylic acid and zinc oxide by
virtue of the use of a specific mixed solvent and more particularly
to a method for the production of zinc acrylate which enables the
crystal form of zinc acrylate to be adjusted owing to the use of
the specific mixed solvent.
[0003] 2. Description of the Related Art
[0004] Zinc acrylate is a useful compound as a cross-linking agent
and is used as added in rubber composition to improve the
vulcanizability or used as a modifier for a varying synthetic
resin.
[0005] As a means to obtain zinc acrylate, a method which comprises
inducing acrylic acid to react with a zinc compound in an organic
solvent, distilling the reaction solution to expel the organic
solvent, and thereafter drying the residue of the distillation
(JP-B-58-14416) and a method which comprises filtering the reaction
solution to remove the organic solvent and thereafter drying the
residue of the filtration have been available. These methods,
however, are deficient in workability because their reaction
products stick tenaciously to the inner walls of their reaction
vessels and to the agitating elements or aggregate into clusters.
When the solvent is removed by decompression, the solvent contained
in the produced zinc acrylate is scattered and the produced zinc
acrylate is partly scattered as well to lower the yield thereof and
the economy of the production is heavily impaired because the
decomposition necessitates installation of extra devices for
separation and recovery, for example.
[0006] For the sake of using zinc acrylate by kneading it in a
rubber composition, numerous methods for coating the surface of
zinc acrylate particles by the addition of a higher fatty acid such
as stearic acid or a zinc salt thereof have been proposed
(JP-A-52-154436, JP-A-53-83834, JP-60-94434, and
JP-A-02-218639).
[0007] These methods, however, necessitate incorporation of a step
for coating the surface of particles of zinc acrylate by the
addition of such a high fatty acid as stearic acid or a zinc salt
thereof besides a step for effecting the reaction of acrylic acid
with a zinc compound and installation of devices appropriate for
such steps. Further, for the purpose of enabling the produced zinc
acrylate to be kneaded in a rubber composition, it is required to
be an impalpable powder having a particle size of not more than 325
mesh (44 .mu.m). Thus, these methods further necessitate a step for
pulverizing the produced zinc acrylate into an impalpable powder.
This step of pulverization not only calls for a huge labor but also
entails the possibility of deteriorating the working atmosphere and
inducing the problem of hygiene because zinc acrylate is unusually
liable to emit dust during and after the work of pulverization.
[0008] A method which produces zinc acrylate by using toluene as a
reaction solvent in the presence of an anionic surfactant, adding
acrylic acid and a higher fatty acid of 12 to 30 carbon atoms
thereto while dispersing zinc oxide therein, causing the zinc oxide
to react with the acrylic acid, and adding the product of this
reaction to the organic solvent has been also available. This
method can produce fine zinc acrylate. The produced zinc acrylate,
when kneaded in a rubber composition, very rarely induces cohesion
and aggregation, disperses uniformly, and brings the kneading to
completion
[0009] (Official Gazette of JP-A-09-202747).
[0010] When the higher fatty acid is reacted with acrylic acid in
the toluene which has zinc oxide dispersed therein, the product
aimed at must be dried after it has been separated from the organic
solvent because the reaction generates water of constitution. The
produced zinc acrylate is possibly aggregated during the course of
this drying. For the process of producing zinc acrylate, the step
of pulverization is indispensable because the presence of
aggregated clusters results in degrading the dispersibility.
[0011] The samples of zinc acrylate produced in Examples 1-4
inserted in the official gazette of JP-A-09-202747 invariably
contain particles exceeding 5001 .mu.m in diameter in proportions
exceeding 20% by weight of the whole particles and, in their
unaltered form, entail a disadvantage in failing to be smoothly
kneaded or satisfactorily dispersed without producing aggregated
clusters in rubber. They contain zinc acrylate particles of
diameters not more than 5 .mu.m in proportions in the range of
40-43% by weight while they contain the same particles of a
diameter of not more than 44 .mu.m in proportions in the range of
63-66% by weight. This fact indicates that the step of
pulverization is indispensable to the production of fine particles
of zinc acrylate possessing a fine and uniform particle diameter.
Thus, the desirability of developing zinc acrylate which can be
smoothly kneaded in a rubber composition and manifests satisfactory
dispersibility thereto has been commanding strong general
recognition. The methods known to the art, however, fall short of
fulfilling the demand.
[0012] The produced zinc acrylate, for the sake of ensuring safe
transportation and storage, is expected to avoid incurring repeated
aggregation even during a protracted storage and, for the sake of
facilitating transportation and storage, is expected to possess as
high build density as permissible. The conventional products of
zinc acrylate, however, are liable to incur aggregation during
storage and this aggregation constitutes one cause for degrading
the flowability of the compound at the time of use.
[0013] Regarding the process for the production of zinc acrylate,
while the adhesion of the reaction product to the inner wall of the
reaction vessel and to the agitation element mentioned above has
entailed such problems as degrading the workability and
jeopardizing the economy of the production, the problems have not
been satisfactorily coped with.
SUMMARY OF THE INVENTION
[0014] The present inventor has made a deliberate study of crystals
of zinc acrylate formed in the reaction solution and crystals of
zinc acrylate obtained after drying and has consequently found that
the crystals of the zinc acrylate taken out of the reaction
solution and then dried differ in shape from the crystals of the
zinc acrylate held in the reaction solution and that the crystals
of zinc acrylate in the reaction solution have the shape and size
thereof varied with the kind of the organic solvent which is used
as the reaction solvent for zinc acrylate. This invention has been
perfected as a result.
[0015] Specifically, this invention is aimed at providing a method
for the production of zinc acrylate which comprises dispersing zinc
oxide in any of (a) an aliphatic hydrocarbon solvent, (b) a mixed
solvent formed between an aliphatic hydrocarbon solvent and an
aromatic hydrocarbon solvent, and (c) a mixed solvent formed
between an aromatic hydrocarbon solvent and an alcohol and causing
the zinc oxide to react with acrylic acid in the solvent. By
finding that the crystal form of zinc acrylate varies with the kind
of reaction solvent and the degree of interfacial surface tension
of a solvent to water and adjusting the interfacial surface tension
of the reaction solvent to water, it is made possible to control
the crystal form of zinc acrylate and produce zinc acrylate
excelling in flowability.
[0016] This invention is also aimed at providing zinc acrylate the
crystals of which have a long axis of not less than 5 .mu.m and an
aspect ratio in the range of 1-30. By finding that the degree of
secondary aggregation is varied with the crystal size of zinc
acrylate and selecting the crystal size of zinc acrylate specified
above, it is made possible to repress the secondary aggregation and
secure easily the flowability necessary for excelling in
collapsibleness.
[0017] This invention is further aimed at providing a zinc acrylate
composition which comprises the zinc acrylate mentioned above and a
zinc salt of a higher fatty acid of 12-30 carbon atoms. The zinc
salt of higher fatty acid is added in the composition as a fluidity
retaining agent. The composition, even when kneaded in a rubber
composition, is capable of securing necessary dispersibility.
[0018] According to the method contemplated by this invention for
the production of zinc acrylate, the crystal form of zinc acrylate
to be obtained can be adjusted by varying the kind of a reaction
solvent to be used. The crystals of zinc acrylate vary their
flowability and fixability with their crystal form. In this
invention, the zinc acrylate to be produced is enabled to secure
the flowability aimed at by changing the kind of a reaction solvent
thereby adjusting the crystal form. The zinc acrylate produced by
this invention is restrained from forming secondary aggregation
and, even when their crystals are mutually bound, is enabled to
disintegrate the bound crystals and regain flowability. When the
zinc acrylate is kneaded as a vulcanizer as in a rubber
composition, it is enabled to serve as a species of zinc acrylate
excelling in dispersibility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a diagram illustrating a method for determining a
solid disintegrating load of sample zinc acrylate produced in
working examples and comparative examples.
[0020] FIG. 2 is a diagram illustrating the crystal form of zinc
acrylate produced in Example 1.
[0021] FIG. 3 is a diagram illustrating the crystal form of zinc
acrylate.
[0022] FIG. 4 is a diagram illustrating the crystal form of zinc
acrylate produced in Comparative example 1.
[0023] FIG. 5 is a diagram illustrating the crystal form of zinc
acrylate produced in Example 4.
[0024] FIG. 6 is a diagram illustrating the crystal form of zinc
acrylate produced in Comparative Example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The first aspect of this invention is directed toward a
method for the production of zinc acrylate, which comprises
dispersing zinc oxide in any of (a) an aliphatic hydrocarbon
solvent, (b) a mixed solvent formed between an aliphatic
hydrocarbon solvent and an aromatic hydrocarbon solvent, and (c) a
mixed solvent formed between an aromatic hydrocarbon solvent and an
alcohol and causing acrylic acid to react with said zinc oxide in
said solvent.
[0026] As a means to produce zinc acrylate, a method which
synthesizes this compound by inducing the reaction of acrylic acid
and zinc oxide in toluene is generally followed. The reason for
using toluene as the reaction solvent is that the water of
constitution which occurs in the reaction of acrylic acid and zinc
oxide as represented by the following formula can be easily
eliminated by azeotropic distillation and that the reaction
performed in this manner affords fine zinc acrylate.
ZnO+2CH.sub.2.dbd.CHCOOH.fwdarw.CH.sub.2.dbd.CHCOO--Zn--OOCHC.dbd.CH.sub.2-
+H.sub.2O
[0027] When the kind of reaction solvent is changed in the
production of zinc acrylate, however, the crystal form of zinc
acrylate in the reaction solution is varied from that of the zinc
acrylate produced (a) when an aliphatic hydrocarbon solvent is used
alone, (b) when a mixed solvent formed between an aliphatic
hydrocarbon solvent and an aromatic hydrocarbon solvent is used,
and (c) when a mixed solvent formed between an aromatic hydrocarbon
solvent and an alcohol is used. This difference may be explained by
a supposition that since the formation and growth of crystals of
zinc acrylate mainly occurs in the water constituted by the
reaction, the crystal form of zinc acrylate can be varied by
varying the interfacial tension exhibited by the solvent to the
water. In fact, when the solvent having an interfacial tension of
35-40 dynes/cm (20.degree. C.) to water added to the solvent having
an interfacial tension of 50-55 dynes/cm (20.degree. C.) to water
is increased, the crystals become gradually slender. In contrast,
when the solvent having an interfacial tension of not more than 10
dynes/cm added to the solvent having an interfacial tension of
35-40 dynes/cm (20.degree. C.) to water is increased, the crystals
become gradually grow in bulkiness. For example, the zinc acrylate
which is obtained by using toluene, one kind of aromatic
hydrocarbon solvent having an interfacial tension of 36 dynes/cm
(20.degree. C.) to water assumes a slender crystal form as compared
with the zinc acrylate produced with a solvent having an intefacial
tension of 50-55 dynes/cm (20.degree. C.) to water. Since the
slender crystals are liable to be cut in the reaction solution, the
produced zinc acrylate assumes the shape of slender crystals. This
zinc acrylate tends to undergo secondary aggregation and form
aggregated clusters after it is separated from the solution. Thus,
the conventional zinc acrylate is actually clusters of secondary
aggregation of zinc acrylate. When heptane which is one kind of
aliphatic hydrocarbon solvent having an interfacial tension of 51
dynes/cm (20.degree. C.) to water is used, the crystals extracted
from the reaction solution and dried avoid undergoing secondary
aggregation, though they become thicker and longer than those
obtained by using toluene. As a result, the zinc acrylate at the
time of actual use assumes a small particle diameter and excels in
flowability, represses solidification and, when suffered to form
cohering clusters, exhibits excellent disintegrability. This zinc
acrylate renders the storage and transportation thereof convenient
because it has a high bulk density. Thus, this invention has
decided to vary the crystal form of zinc acrylate and produce zinc
acrylate excelling in flowability and disintegrability by using (a)
an aliphatic hydrocarbon solvent, (b) a mixed solvent formed
between an aliphatic hydrocarbon solvent and an aromatic
hydrocarbon solvent, and (c) a mixed solvent formed between an
aromatic hydrocarbon solvent and an alcohol. Now, this invention
will be described in detail below.
[0028] The aliphatic hydrocarbon solvents which are usable in this
invention are cyclic or chain alkanes optionally possessing a
branch of 1-14 carbon atoms such as pentane, isopentane, hexane,
isohexane, heptane, isoheptane, octane, isooctane, nonane,
isononane, cyclohexane, cycloheptane, cyclooctane, and cyclononane.
Among other aliphataic hydrocarabon solvents mentioned above, the
alkanes of 6-8 carbon atoms such as hexane, heptane, and octane are
used advantageously. The reason for the preference of these alkanes
is that they facilitate removal of water from the system by virtue
of azeotropy. These aliphatic hydrocarbon solvents may be used
either singly or in the form of a mixed solvent. Optionally, they
may be used in the form of a mixed solvent using any of the
aromatic hydrocarbon solvents which will be more specifically
described herein below. The aliphatic hydrocarbon solvents
mentioned above have interfacial tension of not more than 55
dynes/cm to water. The crystals of zinc acrylate obtained such a
solvent are thicker and longer than the crystals obtained when
toluene is used as the reaction solvent. The crystals in the
reaction solvent, therefore, are not broken very copiously. The
crystals, even after they are taken out of the reaction solvent and
dried, do not cohere very much and, even when they undergo
secondary aggregation, enable the coherent masses to be easily
disintegrated. Further, the use of the solvent mentioned above
brings such advantages of production as reducing the load exerted
on the agitation element and reducing the adhesion to the reaction
vessel.
[0029] The aromatic hydrocarbon solvent which has the interfacial
tension of not more than 40 dynes/cm to water and is used as mixed
with the aliphatic hydrocarbon solvent mentioned above is at least
one member selected from the group consisting of toluene, xylene,
mesitylene, cumene, cymene, styrene, benzene, and ethylbenzene.
Among other aromatic hydrocarbon solvents enumerated above, toluene
and xylene are used particularly advantageously. The reason for the
preference of these members is that they facilitate the removal of
water from the system by virtue of azeotropy. The mixing ratio of
the aliphatic hydrocarbon solvent and the aromatic hydrocarbon
solvent is a matter of arbitrary decision in this invention. In the
light of the fact that the crystal form of zinc acrylate varies
with this mixing ratio and from the point of view of restraining
zinc acrylate from undergoing secondary aggregation, however, the
ratio by weight of the aliphatic hydrocarbon solvent and the
aromatic hydrocarbon solvent is preferably in the range of 10:0 to
6:4 and more preferably in the range of 10:0 to 8:2. Particularly,
the crystal form varies with the amounts of the aromatic
hydrocarbon solvent and the aliphatic hydrocarbon solvent to be
incorporated; the crystals grow thick when the amount of such an
aliphatic hydrocarbon solvent heptane to be incorporated is large
and they grow slender when the amount of the aromatic hydrocarbon
solvent to be incorporated is large. Besides the degree with which
the second aggregation occurs on the crystals after they are washed
varies with the kind of the solvent to be used and the secondary
aggregation can be repressed by adding to the amount of the
aliphatic hydrocarbon solvent to be incorporated. Particularly by
controlling the ratio of the solvents within the range mentioned
above, it is made possible to obtain crystals of zinc acrylate
which hardly break, repress solidification, and allow easy
disintegration of masses of secondary aggregation if any suffered
to form.
[0030] The alcohols which are usable in this invention are alcohols
of 1-8 carbon atoms optionally containing a branch preferably. The
alcohols are methanol, ethanol, propanol, isopropanol, butanol,
isobutanol, pentanol, hexanol, heptanol, and octanol. Among other
alcohols mentioned above, isopropanol, butanol, isobutanol, and
isopentanol are used particularly advantageously. The reason for
their preference is that they facilitate the removal of water from
the system by means of azeotropy. Such an alcohol as has an
interfacial tension of not more than 10 dynes/cm to water is used
as mixed with the aromatic hydrocarbon solvent mentioned above. The
mixing ratio of the alcohol and the aromatic hydrocarbon solvent is
a matter of arbitrary decision in this invention and the crystal
form of zinc acrylate varies with the mixing ratio. Particularly
when the amount of the alcohol to be incorporated increases, the
crystals are enabled to gain in growth even in the solvent outside
the process of synthetic reaction and the crystal form thereof is
enabled to become so thick as to render breakage of the crystals
difficult to occur. As a result, the zinc acrylate is restrained
from undergoing secondary aggregation. The ratio by weight of the
alcohol and the aromatic hydrocarbon solvent is preferably in the
range of 10:0 to 1:9 and more preferably in the range of 10:0 to
3:7 in this invention. The reason for this range is that an
addition to the weight ratio of the alcohol allows the crystals to
grow and the crystal form to become so thick as to render breakage
thereof difficult to occur.
[0031] Now, one mode of preferred embodiment of this invention with
respect to the production of zinc acrylate will be described
below.
[0032] The method of this invention obtains zinc acrylate by
causing zinc oxide to react with acrylic acid and meanwhile
dispersing the zinc oxide in the reaction solvent mentioned above.
The solvent may allow the reaction of acrylic acid with zinc oxide
to proceed in the further presence of a higher fatty acid having
12-30 carbon atoms.
[0033] Specifically, a reaction vessel furnished with a stirring
device having a fully satisfactory capacity of agitation and a
device for thermal treatment is charged with a prescribed amount of
the solvent mentioned above and made to add zinc oxide therein as
kept stirred meanwhile to prepare a suspension.
[0034] The zinc oxide is preferred to have a high degree of purity.
It nevertheless may contain zinc hydroxide as an impurity. Though
the amount of the zinc oxide to be added in the reaction solvent is
variable with the kind of a solvent to be used, it is preferably in
the range of 1-7 times, more preferably 1-5 times, and particularly
preferably 1.3-4.5 times, the amount of zinc oxide as reduced to
ratio by weight. If the amount of the solvent is unduly large, the
excess may possibly result in degrading the purity because the
unaltered reactants are localized in the upper part of the reaction
solution. When the amount of the solvent is decreased, the reaction
solution is enabled to increase its viscosity and consequently
entail such advantages as homogenizing itself, enhancing the
efficiency of agitation, and exalting the purity of zinc acrylate.
Moreover, since the viscosity is raised and uniformized as well,
the adhesion of the reaction solution to the agitation element
during the course of kneading is lessened. If the amount of the
solvent exceeds 5 times the weight of zinc oxide, the excess will
result in decreasing the effect of improving the purity mentioned
above. Conversely, if the amount falls short of 1 times the weight
of zinc oxide, the shortage will possibly result in rendering the
agitation difficult.
[0035] Subsequently, the reaction solution retained by cooling when
necessary at a temperature in the range of 10-70.degree. C.,
preferably 15-50.degree. C., adds acrylic acid therein and causes
it to undergo a necessary reaction to form zinc acrylate. The
amount of acrylic acid to be used does not need to be particularly
restricted but is only required to be enough for inducing the
expected reaction with zinc oxide fully satisfactorily. It is
generally in the range of 50-250 parts by weight and preferably in
the range of 50-200 parts by weight based on 100 parts by weight of
zinc oxide. If the acrylic acid is used in an unduly large amount,
the excess acrylic acid may be removed by distillation together
with the organic solvent and the water formed by the reaction
during the separation and recovery of zinc acrylate. The acrylic
acid to be used in this invention may be in any of the forms
possibly assumed thereby. Optionally, it may somewhat contain
water. Preferably, it is in a form not diluted with water. Further,
the acrylic acid may be made to contain a polymerization inhibitor
such as hydroquinone or hydroquinone monomethyl ether.
Incidentally, the time for adding acrylic acid and the duration of
the reaction may be suitably selected within a length of time
falling in the range of 0.5-10 hours, preferably 2-7 hours.
[0036] This invention may form a zinc salt of higher fatty acid in
advance of the addition of acrylic acid by preparing the suspension
mentioned above by dispersing zinc oxide in the reaction solvent,
retaining the temperature of the suspension at a level in the range
of 10-70.degree. C., preferably 30-50.degree. C., and meanwhile
adding a higher fatty acid therein and causing it to undergo the
expected reaction. In this case, the time for the addition of the
higher fatty acid and the duration of the reaction may be suitably
selected within a length of time falling in the range of 0.5-10
hours, preferably 1-5 hours. When the zinc acrylate is synthesized
in the presence of a higher fatty acid, the amounts of the acrylic
acid and the higher fatty acid to be used are adjusted so that the
content of zinc acrylate may fall in the range of 60-98% by weight,
preferably 70-95% by weight. More specifically, the amount of the
higher fatty acid to be used does not need to be particularly
restricted but is only required to be enough to induce the reaction
with zinc oxide fully satisfactorily and can be decided within the
range of the purpose of use of zinc acrylate. It is generally in
the range of 0-150 parts by weight, preferably in the range of
10-100 parts by weight based on 100 parts by weight of zinc oxide.
If the amount of the higher fatty acid to be used exceeds 150 parts
by weight, the excess will bring an adverse effect of putting the
characteristic properties of zinc acrylate to wastage.
[0037] As concrete examples of the higher fatty acid of 12-30
carbon atoms which is used advantageously in this invention, lauric
acid, myristic acid, palmitic acid, stearic acid, behenic acid,
oleinic acid, and linolic acid may be cited. These higher fatty
acids may be used either singly or in the form of a mixture of two
or more members. Among other higher fatty acids enumerated above,
palmitic acid and stearic acid are used particularly favorably.
Such a higher fatty acid maybe used in its unmodified form or in
the form of a solution prepared in advance by using either the same
organic solvent as used in the reaction or acrylic acid. It may be
otherwise used, when necessary, in the form dissolved by
heating.
[0038] This invention allows the higher fatty acid to be added in
the system together with an anionic surfactant or a nonionic
surfactant. In this invention, the amount of the anionic surfactant
or nonionic surfactant to be used does not need to be particularly
restricted but is only required to be enough for enabling the
reaction of zinc oxide, acrylic acid, and a higher fatty acid of
12-30 carbon atoms to proceed efficiently. Properly, it is in the
range of 0-15 parts by weight, preferably 0.03-6 parts by weight,
based on 100 parts by weight of the zinc oxide. When the use of
such a surfactant is elected, the surfactant may be used as added
in advance in the same organic solvent as used for the reaction and
mixed together therein.
[0039] The zinc acrylate thus obtained may be separated and
recovered from the reaction solution by a known method such as, for
example, a method which comprises separating the water formed by
the reaction and the organic solvent in the reaction vessel by
filtration and drying the residue of the filtration at a
temperature in the range of 10-70.degree. C. When the reaction
vessel happens to be a kneader blender which is furnished with a
stirrer fitted with raking blades, a method which separates and
recovers the zinc acrylate by keeping the reaction solution stirred
in its original form and distilling it at a temperature in the
range of 10-70.degree. C., preferably 15-50.degree. C., while
reducing the pressure when necessary till the excess acrylic acid,
the organic solvent, and the water formed by the reaction are
expelled, and drying the residue of the distillation is adopted
favorably from the point of view of simplifying the equipment. The
time spent for the distillation and the drying in this case can be
properly selected in the range of 1-20 hours, depending on the
temperature prevalent therein.
[0040] The second aspect of this invention is directed toward zinc
acrylate the crystals of which have a long axis of not less than 5
um and an aspect ratio in the range of 1-30 and zinc acrylate the
crystals of which have a long axis of not less than 5 .mu.m, an
aspect ratio in the range of 1-30, and a 50% particle diameter of
not less than 6 um. The conventional zinc acrylate has resulted
from the reaction using toluene as the reaction solvent. In the
reaction solution, therefore, it forms slender crystals. The
crystals of zinc acrylate, owing to the slenderness of crystal
form, tend to break in the reaction solution and undergo secondary
aggregation after they have been dried. When the fine crystals do
not undergo secondary aggregation, they are so bulky as to
inconvenience their storage and transportation. In the meantime,
such fine aggregates tend to solidify as under a physical pressure
exerted during the course of transportation and the solidified
aggregates are not easily disintegrated and, prior to actual use,
are required to be released from the consolidation. The zinc
acrylate contemplated by this invention is in the form of crystals
having a long axis preferably not less than 5 .mu.m and more
preferably falling in the range of 5-500 .mu.m and particularly
preferably in the range of 5-100 .mu.m, an aspect ratio preferably
in the range of 1-30, more preferably 1-15, and particularly
preferably 1-8, and a 50% particle diameter preferably not less
than 6 .mu.m and more preferably falling in the range of 6-100
.mu.m and particularly preferably 10-50 .mu.m. If the crystals are
unduly fine, the excess fineness will be at a disadvantage in
inducing the crystals to form aggregated clusters, fail to be
uniformly kneaded with a rubber composition, manifest no
satisfactory dispersibility therein, and deteriorate the working
atmosphere on account of their liability to be scattered. The zinc
acrylate of this invention acquires such a quality as permits
repression of secondary aggregation after drying, excels in
dispersibility, secures fluidity consequently, and enjoys high
bulkiness enough to convenience transportation and storage.
Incidentally, the long axis and the aspect ratio of the crystals of
zinc acrylate indicated in the specification of the subject patent
application are such numerical values as are obtained of the
crystals of zinc acrylate after the crystals have been dried to a
water content of not more than 0.5%.
[0041] The zinc acrylate of this invention possesses such a quality
as not easily sustaining breakage because the crystals thereof are
thick and long as compared with those of the zinc acrylate obtained
when toluene is used as a solvent. Thus, the crystals rarely
succumb to further division even when they are exposed to a
physical stimulation with an ultrasonic wave for the purpose of
repressing zinc acrylate from undergoing secondary aggregation
after the reaction or allowing the secondarily aggregated clusters
of zinc acrylate to return to their original form of crystals. This
invention, therefore, is further capable of providing zinc acrylate
the crystals of which have a long axis of not less than 5 .mu.m, an
aspect ratio in the range of 1-30 and a 50% particle diameter of
not less than 6 .mu.m. This crystal form can be obtained by
dispersing what is obtained by the method of production according
to the second aspect of this invention with an ultrasonic wave
having a frequency in the range of 30-50 kHz for 15 minutes.
Incidentally, the 50% particle diameter used in this invention is
to be determined by the method of determination described in the
working examples cited herein below.
[0042] This invention further requires the zinc acrylate after the
drying mentioned above to pass a sieve opening of 1 mm at a ratio
of not less than 90%, preferably not less than 92%, and
particularly preferably not less than 95%. The zinc acrylate has
its crystal form vary with the kind of a reaction solvent to be
used and also has its crystals after the drying vary in the degree
of secondary aggregation. This secondary aggregation can be
discerned by the ratio of passage of the relevant crystals through
a sieve opening of 1 mm. When toluene was used as the reaction
solvent, the ratio of passage through a sieve opening of 1 mm was
lower than 70%. This invention attains a ratio of passage of not
less than 95% and this fact indicates that the zinc acrylate may
well be rated as a product succumbing very rarely to secondary
aggregation. The zinc acrylate of this quality can be produced by
the method of production contemplated by the first aspect of this
invention.
[0043] Further, the zinc acrylate of this invention has a solid
disintegrating load of not more than 1.0 kg/cm.sup.2, preferably
not more than 0.5 kg/cm.sup.2, and particularly preferably not more
than 0.3 kg/cm.sup.2. The solid disintegrating load, namely the
load required for disintegrating the solidified mass of zinc
acrylate, signifies the ease of disintegration which increases in
accordance as the magnitude thereof decreases. The reason for this
invention to set the solid disintegrating load at a level of not
more than 1.0 kg/cm.sup.2 is that the disintegration of a given
solid becomes extremely difficult when this solid disintegrating
load is larger than 1.0 kg/cm.sup.2. Incidentally, the term "solid
disintegrating load" as used in the present invention represents a
magnitude determined by the method of determination described in
the working example cited herein below.
[0044] The zinc acrylate of this invention is further preferred to
have a degree of compaction of not more than 50%. The term "degree
of compaction" as used herein means the numerical value which is
obtained by testing a given sample for loose apparent relative
density and solid apparent relative density and calculating the
following formula using the results of the test.
Degree of compaction (%)=[100(solid apparent relative density-loose
apparent relative density)]/(Solid apparent relative density)
[0045] These numerical values can be measured by a powder property
measuring device made by Hosokawa Micron K.K. and sold under the
model designation of "Powder Tester PT-N Type." The degree of
compaction is the factor most deeply related to the rheological
characteristics of powder. In the case of a zinc acrylate
composition, the flowability of the composition is degraded when
the degree of compaction exceeds 50% so that the composition, when
left standing at rest in the hopper for a long time, will be
released with unusual difficulty.
[0046] The third aspect of this invention is directed toward a zinc
acrylate composition comprising the zinc acrylate of the second
aspect of this invention and a zinc salt of higher fatty acid of
12-30 carbon atoms. The zinc salt of the higher fatty acid
mentioned above is incorporated in the composition as a dispersing
agent for zinc acrylate and this incorporation enables the zinc
acrylate to secure its fluidity further. This higher fatty acid may
be the same as mentioned in the first aspect of this invention. The
mixing ratio of the zinc acrylate and the zinc salt of the higher
fatty acid is such that the zinc salt of higher fatty acid is
contained at a proportion in the range of 0-40% by weight, more
preferably 5-30% by weight, and particularly desirably 10-20% by
weight in the zinc acrylate composition. If this proportion to the
rubber composition exceeds 40% by weight, the excess will prevent
the zinc salt from being fully satisfactorily cross-linked to the
butadiene rubber resulting from the addition of the zinc salt to
the rubber composition. Conversely, if this proportion falls short
of 5% by weight, the shortage, the effect of the added zinc salt in
enhancing the flowability of zinc acrylate will not be sufficient.
In the calculation of the content of the zinc salt of the higher
fatty acid, when the zinc acrylate contemplated by the second
aspect of this invention has been produced while the higher fatty
acid is continuously added to the reaction system during the course
of the production, the total amount of the zinc salt of the higher
fatty acid contained in the zinc acrylate composition and the newly
added or formed zinc salt of the higher fatty acid will be regarded
as the content.
[0047] The zinc acrylate of this invention can be restrained from
succumbing to secondary aggregation and from yielding to
solidification as well. When it happens to solidify at all, the
solid masses are easily disintegrated. Thus, it is enabled to
secure necessary flowability at the time of its actual use. When it
is kneaded as a vulcanizer in a rubber composition, therefore, it
manifests excellent dispersibility. Heretofore, for the purpose of
repressing the degradation of flowability by secondary aggregation,
it has been customary to pulverize the produced crystals of zinc
acrylate by compression, impulse, friction, or shearing. The zinc
acrylate and the zinc acrylate composition according to this
invention obviate the necessity for such a pulverizing treatment
because they are restrained from such aggregation.
EXAMPLES
[0048] Now, this invention will be described more specifically
below with reference to working examples.
Example 1
[0049] In a jacketed kneader having an inner volume of 10 L and
made of SUS-316, 1,140 g of heptane was placed as a solvent and 407
g of zinc oxide was added and they were stirred together till they
formed a suspension. While the inner temperature of the kneader
holding the suspension was retained at a temperature in the range
of 5-30.degree. C., 739 g of acrylic acid was gradually added to
the suspension over a period of three hours till the temperature
reached 40.degree. C. At 40.degree. C., the ensuant reaction was
continued for four hours. Then, while the inner pressure of the
kneader was gradually lowered and the inner temperature was raised
to 50.degree. C. till the pressure reached 20 Torrs, the reaction
solution was distilled for five hours to expel the reaction product
and the heptane. Consequently, 1,037 g of zinc acrylate was
obtained.
[0050] The crystal forms of zinc acrylate obtained before and after
drying in working examples and comparative examples are shown in
Table 1. The crystals of zinc acrylate after the drying were tested
for long axis, aspect ration, ratio of passage through a sieve
opening of 1 mm, 50% particle diameter, solid disintegrating load,
and degree of compression. The results are shown in Table 2. The
crystal form before the drying is shown in FIG. 2.
[0051] (Method for Determination of Solid Disintegrating Load)
[0052] The solid disintegrating load was determined by the
following method depicted in FIG. 1.
[0053] First, 2 g of zinc acrylate was accurately weight out,
introduced into a disk molding cylinder 1, and topped by a disk
molding lid 2. A 3 kg weight 3 was left standing on the lid 2 for
one hour for solidifying the sample to obtain a dislike sample 4.
Then, the sample 4 was tested for disintegrating load by the use of
a powder property measuring device made by Hosokawa Micron K.K. and
sold under the model designation of "Powder Tester PT-N Type." The
test was carried out in an aluminum bag displaced with nitrogen to
prevent the same from absorbing moisture from the external
environment.
[0054] (Determination of 50% Particle Diameter)
[0055] About 10 g-100 mg of a sample was dispersed in Aisopaa H
with an ultrasonic wave having a frequency in the range of 30-50
kHz to prepare a dispersion medium. With the aid of a laser
diffraction/scattering type particle diameter distribution tester
using Aisopaa H (made by Nikkiso K.K. and sold under the trademark
designation of "MICROTRAC HRA MODELNO. 9320-.times.100), a given
sample was tested for 50% particle diameter at a temperature of
25.degree. C. and a humidity of 50% RH.
Example 2
[0056] Zinc acrylate was obtained by following the procedure of
Example 1 while using a 4:1 mixed solvent of heptane:toluene in the
place of heptane. The crystal form of zinc acrylate before drying
is shown in FIG. 3.
Comparative Example 1
[0057] Zinc acrylate was obtained by following the procedure of
Example 1 while using toluene in the place of heptane. The crystal
form of this zinc acrylate before drying is shown in FIG. 4.
Example 3
[0058] Zinc acrylate was obtained by following the procedure of
Example 1 while using a 1:1 mixed solvent of toluene:isopropanol
(IPA) in the place of heptane. The crystal form of this zinc
acrylate before dying is shown in FIG. 5.
Comparative Example 2
[0059] Zinc acrylate was obtained by following the procedure of
Example 1 while using isopropanol in the place of heptane. The
crystal form of this zinc acrylate before drying is shown in FIG.
6
Example 4
[0060] Zinc acrylate was obtained by following the procedure of
Example 1 while using 814 g of heptane in the place of 1,140 g of
heptane. The crystal form and the purity of zinc acrylate as shown
in Table 3.
Example 5
[0061] Zinc acrylate was obtained by following the procedure of
Example 1 while using 692 g of heptane in the place of 1,140 g of
heptane.
Example 6
[0062] Zinc acrylate was obtained by following the procedure of
Example 1 while using 571 g of heptane in the place of 1,140 g of
heptane.
1 TABLE 1 Crystal form (.mu.m) Solvent Before drying After drying
Example 1 Heptane 7 .times. 15 7 .times. 15 Example 2
Heptane:toluene = 4:1 6 .times. 40 6 .times. 25 Comparative Toluene
1 .times. 20 1 .times. 3 Example 1 Example 3 Toluene:IPA = 1:1 7
.times. 120 7 .times. 50 Comparative IPA 8 .times. 100 8 .times. 30
Example 2
[0063]
2 TABLE 2 Long Ratio of axis 50% passage Solid Degree of Particle
through sieve disintegrating of crystal Aspect diameter opening of
1 mm load compaction Solvent (.mu.m) ratio (.mu.m) (%)
(kg/cm.sup.2) (%) Example 1 Heptane 15 2.1 11.0 95 0.2 39.9 Example
2 Heptane:Toluene = 4:1 25 4.2 20.3 96 0.3 39.7 Comparative Toluene
3 3 5.5 69 1.7 55.2 Example 1 Example 3 Toluene:IPA = 1:1 50 7.1
30.5 96 0.1 39.9 Comparative IPA 30 3.8 11.8 96 0.2 37.4 Example
2
[0064]
3 TABLE 3 Amount of Crystal form Purity solvent (.mu.m) (%) Example
1 2.8 times 7 .times. 15 96.9 Example 4 2.0 times 8 .times. 18 97.4
Example 5 1.7 times 8 .times. 18 98.2 Example 6 1.4 times 8 .times.
18 98.7
[0065] (Results)
[0066] As shown in Table 1, sole use of heptane did not cause the
produced zinc acrylate to change its crystal form before and after
the drying treatment. It means that the drying treatment inflicted
no breakage in the crystals. In contrast, the use of toluene which
found popular use heretofore resulted in causing the crystals of
zinc acrylate to sustain breakages at a plurality of points in the
direction of long axis owing to the drying treatment and the
crystals after the drying assumed a thin and short crystal form.
The breakage in the direction of long axis by the drying treatment
was observed as well in a solvent system containing IPA. Since the
use of an IPA-containing solvent resulted in adding to the
thickness of crystal, the crystals in this solvent eventually
acquired a long-axis length 20 .mu.m in excess of the length of the
crystals of zinc acrylate formed heretofore in toluene.
[0067] The ratio of passage through a sieve opening of 1 mm shown
in Table 2 approximates closely to the crystal form which the zinc
acrylate product assumes when it is put to actual use and it is the
numerical value that reflects the degree of secondary aggregation.
When toluene was used alone, the ratio of passage was caused by
secondary aggregation to fall below 90%. Since the crystals
produced in this case assumed a very fine form after the drying
treatment, the pulverizing treatment given thereafter to the
crystals enabled the crystals to acquire the same ratio of passage
through a sieve opening as the crystals obtained when other solvent
was used. This invention excels in respect that it obtains zinc
acrylate exhibiting an excellent ratio of passage through the sieve
opening without going through such a pulverizing step.
[0068] The crystals of the zinc acrylate whose ratio of passage
through a sieve opening of 1 mm (%) excessed 90% had a low solid
disintegrating load (kg/cm.sup.2) and, therefore, were highly
vulnerable to breakage. This fact indicates that the crystals,
though suffered to undergo secondary aggregation, were easily
separated asunder and enabled to secure flowability. When the
crystals showed a low solid disintegrating load (kg/cm.sup.2), they
showed a low degree of compaction and excelled in flowability.
[0069] As shown in Table 3, when the amount of the solvent was 1.4
times that of zinc oxide, the produced zinc acrylate enjoyed an
exalted purity and the crystals thereof had a thick form measuring
8.times.18 .mu.m.
* * * * *