U.S. patent application number 11/144011 was filed with the patent office on 2005-10-06 for method of producing powdery coating material.
Invention is credited to Koike, Nobuyuki, Kuwahara, Shojiro.
Application Number | 20050218550 11/144011 |
Document ID | / |
Family ID | 26611112 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050218550 |
Kind Code |
A1 |
Koike, Nobuyuki ; et
al. |
October 6, 2005 |
Method of producing powdery coating material
Abstract
Disclosed is a method of producing a powdery coating material by
using: a curable acrylic resin (A) having a number average
molecular weight of from 2,000 to 20,000 and a glass transition
temperature of from 30 to 90.degree. C. obtained by polymerizing a
starting monomer containing from 15 to 50 mol % of an unsaturated
compound which contains at least a glycidyl group and/or a
methylglycidyl group, and from 20 to 50 mol % of methyl
methacrylate; a curing agent (B) capable of being reacted with the
glycidyl group or the methylglycidyl group constituting the curable
acrylic resin (A); and an alcohol solvent (C) having a boiling
point under normal pressure of from 70 to 120.degree. C.; said
method comprising a kneading step of so kneading the curable
acrylic resin (A), the curing agent (B) and the alcohol solvent (C)
that at least the curing agent (B) is dissolved in the alcohol
solvent (C) at a temperature of not higher than 130.degree. C., and
a vapor-removing step of continuously vapor-removing the alcohol
solvent (C) under a reduced pressure at a temperature of not higher
than 130.degree. C.
Inventors: |
Koike, Nobuyuki; (Hiratsuka,
JP) ; Kuwahara, Shojiro; (Hiratsuka, JP) |
Correspondence
Address: |
Leonard W. Sherman
Sherman & Shalloway
415 N. Alfred Street
Alexandria
VA
22314
US
|
Family ID: |
26611112 |
Appl. No.: |
11/144011 |
Filed: |
June 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11144011 |
Jun 3, 2005 |
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10096437 |
Mar 13, 2002 |
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6933348 |
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Current U.S.
Class: |
264/138 ;
525/533; 525/55 |
Current CPC
Class: |
C09D 133/14 20130101;
C09D 133/14 20130101; C08L 2666/28 20130101 |
Class at
Publication: |
264/138 ;
525/055; 525/533 |
International
Class: |
B29B 009/00; C08L
063/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2001 |
JP |
2001-69685 |
Apr 25, 2001 |
JP |
2001-126989 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. A method of producing a powdery coating material by using: a
curable acrylic resin (A) having a number average molecular weight
of from 2,000 to 20,000 and a glass transition temperature of from
30 to 90.degree. C. obtained by polymerizing a starting monomer
containing from 15 to 50 mol % of an unsaturated compound which
contains at least a glycidyl group and/or a methylglycidyl group,
and from 20 to 50 mol % of methyl methacrylate in a polymerization
solvent selected from the group consisting of toluene, xylene and
an alcohol solvent having a boiling point under normal pressure of
from 70 to 120.degree. C. such that when the toluene or the xylene
is used as the polymerization solvent, said solvent is
vapor-removed prior to being kneaded with the curable acrylic resin
(A), a curing agent (B) and the alcohol solvent (D); the curing
agent (B) capable of being reacted with the glycidyl group or the
methylglycidyl group consisting the curable acrylic resin (A); and
the alcohol solvent (D) having a boiling point under normal
pressure of from 64 to 120.degree. C. wherein, the alcohol solvent
(D) is used in an amount of from 10 to 200 parts by weight per 100
parts by weight of the curing agent (B); said method comprising:
(I) the curable acrylic resin (A) and curing agent (B) are
continuously fed to a kneading step while side-feeding the solvent
(D) to said kneading step to continuously knead them together so
that at least the effect of homogeneous kneading enhances at 50 to
130.degree. C., or (II) the curable acrylic resin (A) is
continuously fed to the kneading step while side-feeding, to said
kneading step, a curing agent solution obtained by dissolving the
curing agent (B) in the alcohol solvent (D) to continuously knead
them together so that at least the effect of homogeneous kneading
enhances at 50 to 130.degree. C.; the alcohol solvent (D) is
continuously vapor-removed under a reduced pressure at 50 to
130.degree. C. in a vapor-removing step; and said kneading and said
vapor-removing of the alcohol solvent (D) are executed at such
rates that an average contact time between the curable acrylic
resin (A) and the alcohol solvent (D) is not longer than 5 minutes,
wherein the powdery coating material is obtained by pulverizing a
mixture of the curing agent (B) and the curable acrylic resin (A)
obtained by removing the alcohol solvent (D) therefrom.
17. A method of producing a powdery coating material according to
claim 16, wherein the alcohol solvent (D) is an alcohol having 1 to
4 carbon atoms or a mixture thereof.
18. A method of producing a powdery coating material according to
claim 16, wherein the apparatus used in the kneading step is a
monoaxial or biaxial extruder, or a monoaxial or biaxial
kneader.
19. A method of producing a powdery coating material according to
claim 16, wherein the apparatus used in the vapor-removing step is
a monoaxial or biaxial extruder, or a monoaxial or biaxial kneader
having at least one vapor-removing port.
20. A method of producing a powdery coating material according to
claim 16, wherein the kneading and the vapor-removing of solvent
are effected by using a single kneading/vapor-removing apparatus
having at least one vapor-removing port.
21. A method of producing a powdery coating material according to
claim 20, wherein the kneading/vapor-removing apparatus is a
monoaxial or biaxial extruder, or a monoaxial or biaxial kneader.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of producing a
powdery coating material comprising a curable acrylic resin.
[0003] 2. Description of the Related Art
[0004] Powdery coating materials do not generate volatile organic
substances during the baking, do not cause environmental problems
such as air pollution, and have, hence, been used in a wide field
of applications to substitute for the solution coating
materials.
[0005] As such powdery coating materials, there has been known an
acrylic powdery coating material containing, for example, a curable
acrylic resin having a glycidyl group and a curing agent as
represented by an aliphatic dibasic acid.
[0006] The powdery coating material is generally prepared by
dry-mixing a curable resin, a curing agent, additives for the
coating material and pigment, kneading and dispersing them by using
a melt kneader, followed by the pulverization and classification.
In heating and melt-kneading the curable resin and the curing agent
according to this method, however, it is necessary to suppress the
crosslinking reaction between the curable resin and the curing
agent. Therefore, limitation is imposed such as effecting the
kneading at a temperature lower than the melting point of the
curing agent, making it difficult to homogeneously disperse the
resin and the curing agent. Further, the film formed by using the
thus produced powdery coating material has problems concerning the
appearance and, particularly, lacking smoothness. Besides, the
pigment is poorly dispersed making it difficult to obtain a film
that exhibits vividness comparable to that of solution coating
materials.
[0007] In order to improve such problems, there have been proposed
methods of mixing a curable resin and a curing agent in a wet
manner, i.e., in a solvent (Japanese Unexamined Patent Publications
(Kokai) Nos. 25531/1979, 53729/1998, 302567/1999, 103866/2000).
[0008] Even with these methods, however, the curable resin and the
curing agent are not necessarily dispersed sufficiently
homogeneously, still leaving many problems such as the necessity of
vessels for dissolving starting coating materials, mixing devices
for mixing the solutions thereof, and a large apparatus for
vapor-removing/recovering large amounts of solvent.
[0009] U.S. Pat. No. 6,309,572 discloses a method of producing a
powder coating material in which a curable acrylic resin is
prepared in methanol and the obtained resin solution is wet-mixed
with a curing agent. Methanol has a low boiling point and is
vapor-removed easily. However, when methanol is used in the process
for producing the acrylic resin and in the process for the powder
coating material, methanol contacts with a glycidyl group and/or a
methyl glycidyl group contained in the acrylic resin for a long
time during being heated. In the result, the ring of the glycidyl
group or the methyl glycidyl group is opened by methanol,
therefore, the anti-blocking property of the obtained powder
coating material and the mechanical property of the film are
impaired.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a method
of producing an acrylic powdery coating material, which is capable
of homogeneously dispersing a curable resin and a curing agent
using simple means and of forming a film featuring excellent
smoothness and luster at a low cost.
[0011] According to the first embodiment the present invention,
there is provided a method of producing a powdery coating material
by using:
[0012] a curable acrylic resin (A) having a number average
molecular weight of from 2,000 to 20,000 and a glass transition
temperature of from 30 to 90.degree. C. obtained by polymerizing a
starting monomer containing from 15 to 50 mol % of an unsaturated
compound which contains at least a glycidyl group and/or a
methylglycidyl group, and from 20 to 50 mol % of methyl
methacrylate;
[0013] a curing agent (B) capable of being reacted with the
glycidyl group or the methylglycidyl group constituting the curable
acrylic resin (A); and
[0014] an alcohol solvent (C) having a boiling point under normal
pressure of from 70 to 120.degree. C.;
[0015] said method comprising a kneading step of so continuously
kneading the curable acrylic resin (A), the curing agent (B) and
the alcohol solvent (C) that at least the curing agent (B) is
dissolved in the alcohol solvent (C) at a temperature of not higher
than 130.degree. C., and a vapor-removing step of continuously
vapor-removing the alcohol solvent (C) under a reduced pressure at
a temperature of not higher than 130.degree. C.
[0016] According to the second embodiment of the present invention,
there is further provided a method of producing a powdery coating
material by using:
[0017] a curable acrylic resin (A) having a number average
molecular weight of from 2,000 to 20,000 and a glass transition
temperature of from 30 to 90.degree. C. obtained by polymerizing a
starting monomer containing from 15 to 50 mol % of an unsaturated
compound which contains at least a glycidyl group and/or a
methylglycidyl group, and from 20 to 50 mol % of methyl
methacrylate;
[0018] a curing agent (B) capable of being reacted with the
glycidyl group or the methylglycidyl group constituting the curable
acrylic resin (A); and
[0019] an alcohol solvent (D) having a boiling point under normal
pressure of from 64 to 120.degree. C.;
[0020] wherein, the alcohol solvent (D) is used in an amount of 10
to 200 parts by weight per 100 parts by weight of the curing agent
(B);
[0021] (I) the curable acrylic resin (A) and the curing agent (B)
are continuously fed to a kneading step while side-feeding the
alcohol solvent (D) to said kneading step to continuously knead
them together at 50 to 130.degree. C., or (II) the curable acrylic
resin (A) is continuously fed to the kneading step while
side-feeding, to said kneading step, a curing agent solution
obtained by dissolving the curing agent (B) in the alcohol solvent
(D) to continuously knead them at 50 to 130.degree. C.;
[0022] the alcohol solvent (D) is continuously vapor-removed under
a reduced pressure at 50 to 130.degree. C. in a vapor-removing
step; and
[0023] said kneading and said vapor-removing of the alcohol solvent
(D) are executed at such rates that an average contact time between
the curable acrylic resin (A) and the alcohol solvent (D) is not
longer than 5 minutes.
[0024] The present invention has a distinguished feature in the use
of a curable acrylic resin (A) which is a curable resin that is
solid at normal temperature and contains, as a constituent unit, an
unsaturated monomer containing a glycidyl group and/or a
methylglycidyl group (the first and the second embodiments), and an
alcohol solvent (C) having a boiling point under normal pressure of
from 70 to 120.degree. C. (the first embodiment) or an alcohol
solvent (D) having a boiling point of from 64 to 120.degree. C.
(the second embodiment) as a dispersing medium for the wet-mixing.
That is, by using the curable acrylic resin (A), the curing agent
(B) and the alcohol solvent (C) or (D) in combination, it is
allowed to homogeneously disperse and mix the resin (A) and the
curing agent (B), and to obtain an acrylic powdery coating material
capable of forming a film maintaining excellent smoothness and
luster. This combination makes it easy to conduct the continuous
mixing for homogeneously dispersing the resin (A) and the curing
agent (B) and the vapor-removing of the alcohol solvent by using an
in-line mixer, a small extruder or a kneader. Namely, the acrylic
powdery coating material can be produced without using a large
kneader or a large solvent-removing apparatus, further offering a
great advantage in economy. Moreover, since additives for the
coating material, such as pigment and the like, can be
homogeneously dispersed, there is obtained an acrylic powdery
coating material capable of forming a film having sharpness.
[0025] In the first and the second embodiments of the present
invention, the alcohol solvent (particularly, the alcohol solvent
(C)) can be also used as a solvent for polymerization at the time
of producing the curable acrylic resin (A). The alcohol solution of
the curable acrylic resin (A) that is obtained may be used in a
form that can be put to the wet-mixing. Further, the alcohol
solvent may be side-fed at the time of kneading the curing agent
(B) and the curable acrylic resin (A). Or, a curing agent solution
(alcohol solution) obtained by dissolving the curing agent (B) in
the alcohol solvent may be side-fed at the time of kneading the
curable acrylic resin (A).
[0026] In the present invention, the side-feed stands for feeding a
substance that is to be kneaded into the kneading apparatus through
a separate throw port (second throw port) located downstream of a
throw port (first throw port) that is communicated with a main feed
line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIGS. 1 to 8 are diagrams illustrating preferred examples of
the kneading/vapor-removing process employed by the production
method of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Alcohol Solvents:
[0029] The solvent used for the wet-mixing in the present invention
is an alcohol solvent (C) having a boiling point under normal
pressure of from 70 to 120.degree. C. (the first, embodiment) or an
alcohol solvent (D) having a boiling point under normal pressure of
from 64 to 120.degree. C. (the second embodiment). As the alcohol
solvent (C), there can be exemplified an alcohol having 2 to 4
carbon atoms such as ethanol, n-propanol, isopropanol, n-butanol,
isobutanol, sec-butanol, and tert-butanol. As the alcohol solvent
(D), there can be further exemplified methanol in addition to those
exemplified as the alcohol solvent (C). These solvents can be
easily vapor-removed by reducing the pressure, and are easily
vapor-removed by using an extruder or a kneader that will be
described later.
[0030] Among these alcohol solvents, the present invention selects
the one which is capable of at least dissolving the curing agent
(B). The alcohol solvent can be used in one kind or in a mixture of
two or more kinds.
[0031] It is further allowable to use other solvents in small
amounts (e.g., not more than 50 parts by weight per 100 parts by
weight of the alcohol solvent) so far as they do not impair the the
function for homogeneously dispersing the curable acrylic resin (A)
and the curing agent (B) and so far as they can be
vapor-removed.
[0032] In the present invention (the first and the second
embodiments), the alcohol solvents may be fed, via the first throw
port, to the kneading apparatus together with other components.
Also, the alcohol solvent can be side-fed to the kneading
apparatus.
[0033] When the alcohol solvent is side-fed, the curable acrylic
resin (A) and/or the curing agent (B) may be dissolved in the
alcohol solvent to prepare an alcohol solution, and the kneading
may be conducted by side-feeding the thus prepared alcohol
solution. Namely, the alcohol solution of the curable acrylic resin
(A) and the curing agent (B) may be thrown, the alcohol solution of
the curable acrylic resin (A) and the alcohol solution of the
curing agent (B) may be thrown, or the curable acrylic resin (A)
and the alcohol solution of the curing agent may be thrown, into
the kneading apparatus to effect the wet-mixing.
[0034] The alcohol solution of the curable acrylic resin (A) may be
prepared by dissolving the curable acrylic resin (A) that has been
obtained in advance in the alcohol solution, or by polymerizing by
using the alcohol solvent as a polymerization-solvent. When brought
into contact with the curable acrylic resin (A) under the heated
condition for extended periods of time, however, "methanol" used in
the second embodiment may open the ring of the glycidyl group and
the methylglycidyl group. Therefore, when the alcohol solvent
contacts with the resin (A) for longer than 5 minutes at higher
than 80.degree. C. (for example, the alcohol solution of the resin
(A) is used, or the alcohol solvent is used as the polymerization
solvent), it is desired to avoid the use of methanol. Because of
the same reason, it is also desired to avoid the use of methanol in
case the contact with the resin lasts for longer than 3 minutes at
not lower than 100.degree. C. Curable acrylic resin (A):
[0035] The curable acrylic resin (A) which is solid at normal
temperature (20.degree. C.) and is used as a resin component of the
powdery coating material in the first and second embodiments of the
present invention, is obtained by polymerizing a starting monomer
which contains 15 to 50 mol %, preferably, from 25 to 45 mol % of a
glycidyl group and/or methylglycidyl group-containing unsaturated
compound (hereinafter called glycidyl acrylic compound) and 20 to
50 mol %, preferably 25 to 45 mol %, of methyl methacrylate, and
has a number average molecular weight of from 2,000 to 20,000 and a
glass transition temperature of from 30 to 90.degree. C.
[0036] With respect to the starting monomer, when the glycidyl
acrylic compound is used in an amount of smaller than 15 mol %, the
obtained coating film exhibits decreased corrosion resistance and
hardness. When the amount of its use exceeds 50 mol %, on the other
hand, the storage stability of the powdery coating material
decreases, the film smoothness decreases, and the appearance
decreases. When methyl methacrylate is used in an amount of smaller
than 20 mol %, the obtained film exhibits decreased weatherability,
and decreased grade of appearance (decreased transparency and
decreased feeling of thickness). When the amount of its use exceeds
50 mol %, on the other hand, the obtained film exhibits decreased
smoothness and degraded appearance.
[0037] Accordingly, the curable acrylic resin (A) contains 15 to 50
mol % and, preferably, 25 to 45 mol % of a constituent unit
stemming from the glycidyl acrylic compound and, further, contains
20 to 50 mol %, and preferably, 25 to 45 mol % of a constituent
unit stemming from methyl methacrylate. As required, further, the
curable acrylic resin (A) may contain constituent units stemming
from other unsaturated compounds. The curable acrylic resin (A)
containing these constituent units exhibits effects same as those
described above.
[0038] The curable acrylic resin (A) is obtained by, for example,
copolymerizing the glycidyl group and/or methylglycidyl
group-containing unsaturated compound (glycidyl acrylic compound),
methyl methacrylate and, as required, other unsaturated
compounds.
[0039] Though not limited thereto only, examples of other
unsaturated compounds used, as required, for the copolymerization
of the glycidyl acrylic compound and methyl methacrylate include
methyl acrylate, ethyl methacrylate, ethyl acrylate, n-butyl
methacrylate, n-butyl acrylate, i-butyl methacrylate, i-butyl
acrylate, t-butyl methacrylate, t-butyl acrylate, -2-ethylhexyl
methacrylate, 2-ethylhexyl acrylate, lauryl methacrylate, lauryl
acrylate, cyclohexyl methacrylate, cyclohexyl acrylate,
2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate,
caprolactone-modified 2-hydroxyethyl methacrylate,
caprolactone-modified 2-hydroxyethyl acrylate, styrene,
.alpha.-methylstyrene, acrylonitrile, acrylamide and
methacrylamide.
[0040] There is no particular limitation on the amount of use of
the above other unsaturated compounds provided the amount of
constituent units stemming from the glycidyl acrylic compound and
the methyl methacrylate lies within the above-mentioned ranges. In
general, however, the amount of the other unsaturated compound lies
in a range of from 20 to 60 mol % per the whole monomers.
[0041] Copolymerization of the glycidyl acrylic compound and the
methyl methacrylate is conducted by dispersing or dissolving these
compounds in the polymerization-solvent together with the
polymerization initiator such as azobisisobutylonitrile and
polymerizing them under the conditions of 50 to 150.degree. C.
under normal pressure to 20 MPa. After the polymerization, the
polymerization-solvent is removed to obtain a desired curable
acrylic resin (A) which is solid at normal temperature.
[0042] As the polymerization-solvent, there can be used an aromatic
hydrocarbon solvent such as toluene or xylene, or the
above-mentioned solvent for the wet-mixing. In the present
invention, however, there can be preferably used a solvent for the
wet-mixing (i.e., alcohol solvent (C) having a boiling point under
normal pressure of from 70 to 120.degree. C.) except methanol. The
solvent for the wet-mixing is lowly compatible with the resin that
is obtained and has a low boiling point, and can be easily removed.
As compared to the aromatic hydrocarbon solvent such as toluene,
further, the solvent for the wet-mixing easily dissolves the curing
agent (B). Methanol should not be used as the
polymerization-solvent since it is reactive with the glycidyl
acrylic compound and may cause side reactions during the
polymerization reaction.
[0043] The polymerization-solvent is, usually, used in such an
amount that the concentration thereof is from 10 to 90% by weight
in the whole polymerization reaction components (inclusive of the
polymerization-solvent).
[0044] It is desired that the copolymerization is conducted until
the degree of polymerization becomes not smaller than 98%,
preferably, not smaller than 99% and, most preferably, not smaller
than 99.5%. When the degree of polymerization is low, a laborious
work is required for removing the unreacted monomers.
[0045] It is desired that the thus obtained curable acrylic resin
(A) which is solid at normal temperature has a number average
molecular weight in a range of from 2,000 to 20,000, preferably,
from 2,500 to 10,000 and, more preferably, from 3,000 to 8,000, and
has glass transition temperature in a range of from 30 to
90.degree. C., preferably, from 35 to 80.degree. C. and, more
preferably, from 40 to 70.degree. C. When the number average
molecular weight and the glass transition temperature are smaller
than the above-mentioned ranges, the powdery coating material that
is obtained exhibits decreased preservation stability and the film
formed from the coating material may lose flexibility. When the
number average molecular weight and the glass transition
temperature are larger than the above-mentioned ranges, on the
other hand, the curable acrylic resin (A) is less blended with the
alcohol solvent for the wet-mixing, making it difficult to obtain a
powdery coating material of a homogeneous composition or to form a
film having excellent smoothness.
[0046] In the present invention, the number average molecular
weight is measured by the gel permeation chromatography (GPC). The
sample is a tetrahydrofuran solution in which the resin is
dissolved in an amount of 0.3 parts per 100 parts by weight of the
tetrahydrofuran, and is measured by the GPC, e.g., by the GPC,
Model 8020, manufactured by Toso Co., and the number average
molecular weight is calculated as polystyrene.
[0047] Further, the glass transition temperature (.degree. C.) is
measured by the DSC method (differential scanning calorimetric
method, raising the temperature at a rate of 10.degree. C./min.),
and a glass transition temperature. (Tmg) at an intermediate point
is regarded to be the glass transition temperature (Tg).
[0048] The curable acrylic resin (A) which is solid at normal
temperature is fed to a kneading step as will be described later.
When the above-mentioned alcohol solvent for the wet-mixing is used
as a polymerization-solvent, the alcohol solution of the curable
acrylic resin (A) which is the product of polymerization can be
directly fed to the kneading step without removing the
polymerization-solvent.
[0049] Curing Agent (B):
[0050] The curing agent (B) used in the present invention is
reactive with the glycidyl group in the above-mentioned curable
acrylic resin (A). Though not limited thereto only, examples of the
curing agent (B) include dibasic acids or anhydrides thereof such
as azelaic acid, nonanoic diacid, sebacic acid, dodecanoic diacid,
adipic acid, maleic acid, isophthalic acid, naphthalenedicarboxylic
acid, succinic anhydride, phthalic anhydride and itaconic
anhydride; polybasic acids or anhydrides thereof such as
trimellitic acid, pyromellitic acid, trimellitic anhydride and
pyromellitic anhydride; amine or diamine compounds such as
metaphenylene diamine, metaxylene diamine, dicyan diamide,
aliphatic amine and alicyclic amine; amide compounds; melamine
compounds; hydrazine compounds; maleimide compounds; and cyanate
compounds, which can be used in a single kind or in a combination
of two or more kinds. Among them, a dibasic acid and, particularly,
a dodecanoic diacid can be preferably used in the present
invention.
[0051] The curing agent (B) is usually used in an amount of from
0.7 to 1.3 equivalents, preferably, from 0.8 to 1.2 equivalents
and, more preferably, from 0.8 to 1.1 equivalents per the glycidyl
group and/or the methylglycidyl group in the curable acrylic resin
(A). Additives for the coating material:
[0052] In the method of producing the powdery coating material of
the present invention, there can be used, as required, known
additives for the coating material, such as melt
fluidization-adjusting agent, pinhole-preventing agent, ultraviolet
ray absorber, antioxidant, curing catalyst, plasticizer,
anti-blocking agent, powder fluidization-imparting agent and
de-foaming agent in addition to the above-mentioned curable acrylic
resin (A) and the curing agent (B).
[0053] The additives for the coating material are used in such
amounts as to exhibit predetermined functions without spoiling
properties such as film-forming property of the powdery coating
material. For example, the additives are used in an amount of from
0.1 to 10 parts by weight par 100 parts by weight of the curable
acrylic resin (A). Pigments:
[0054] The present invention further uses a pigment depending upon
the use of the powdery coating material. Though not limited thereto
only, the pigment may be titanium oxide, red iron oxide,
phthalocyanine blue, phthalocyanine green, carbon black or iron
oxide.
[0055] The pigment is usually used in an amount of not larger than
200 parts by weight per 100 parts by weight of the curable acrylic
resin (A). Mixing/kneading:
[0056] In the present invention, the above-mentioned curable
acrylic resin (A), curing agent (B), additives which are, as
required, used for the coating material and pigment, are
continuously wet-kneaded in the presence of the above-mentioned
alcohol solvent (alcohol solvent (C) or (D)) for the wet-mixing
and, then, the alcohol solvent is continuously vapor-removed under
a reduced pressure. The continuous kneading and the removal of
solvent may be conducted at normal temperature or being heated at
not higher than 130.degree. C. When the continuous kneading and the
removal of solvent is conducted under a heated condition, the
heating temperature is set to be not higher than the cross-linking
reaction temperature of the resin and the curing agent. As will be
described later, further, when the alcohol solvent is side-fed
alone or as an alcohol solution of the curing agent (for example,
the second embodiment), it is desired to conduct the kneading being
heated at 50 to 130.degree. C. to enhance the effect of homogeneous
kneading.
[0057] In the first embodiment of the present invention, the amount
of the alcohol solvent used here is in a range of from 10 to 1000
parts by weight, i.e., the amount of the alcohol solvent in the
kneaded composition which is a mixture of the curable acrylic
resin. (A), curing agent (B) and alcohol solvent, is from 10 to
1000 parts by weight per 100 parts by weight of the curing agent.
When the alcohol solution of the resin (A) is used the curing agent
(B) is dissolved in the alcohol solvent, it is desired that the
amount of the alcohol solvent in the kneaded composition is in a
range of from 50 to 1000 parts by weight per 100 parts by weight of
the curing agent. In the second embodiment of the present
invention, when the alcohol solvent or the alcohol solution of the
curing agent (B) is side-fed, the amount of the alcohol can be
smaller (10 to 200 parts by weight per 100 parts by weight of the
curing agent) than that of the above-mentioned case to exhibit a
sufficient degree of wet dispersion enabling the solvent to be
easily removed.
[0058] When the amount of supplying the alcohol solvent is smaller
than the above-mentioned range, the effect of homogeneous kneading
by the alcohol solvent decreases. When the amount of supplying the
alcohol solvent is larger than the above range, on the other hand,
it becomes necessary to use a large kneading/vapor-removing
apparatus causing disadvantage in economy. When the alcohol solvent
(except methanol) is used as the polymerization-solvent and the
alcohol solution of the obtained curable acrylic resin (A) is
directly used, it is recommended that the amount of the
polymerization-solvent that. is used satisfies the above-mentioned
conditions.
[0059] The above-mentioned continuous kneading and the removal of
solvent can be carried out by using a kneading/vapor-removing
apparatus that continuously conduct the kneading and the removal of
alcohol component volatilized due to a reduction in the pressure.
It is further allowable to couple a continuous kneading apparatus
and a vapor-removing apparatus in cascade to conduct the continuous
kneading and the removal of solvent.
[0060] The curable. acrylic resin (A), curing agent (B), additives
used, as required, for the coating material and pigment can be
separately thrown into the kneading/vapor-removing apparatus or to
the continuous kneading apparatus. They, however, may be mixed
together in advance and may, then, be thrown. Before being thrown,
though not being limited thereto, they can be mixed together by
using the Henscel's mixer or the tumbler.
[0061] In the first and the second embodiments, the alcohol solvent
can be directly side-fed to the kneading/vapor-removing apparatus
or to the continuous kneading apparatus without being mixed to
other components. As described already, further, the alcohol
solvent can be used as the alcohol solution of the curable acrylic
resin (A). Or, the alcohol solution of the curing agent (B) may be
prepared by using the alcohol solvent, and may be side-fed.
[0062] In this case, the curing agent (B) may have been completely
dissolved in the alcohol solvent or may have been dissolved only
partly. When the kneading is conducted in a state where the curing
agent (B) is completely dissolved, the curing agent is
homogeneously dispersed in the form of fine particles of not larger
than 4 .mu.m in the powdery coating material obtained by
vapor-removing the solvent. When the alcohol solvent is side-fed,
on the other hand, part of the curing agent is not often dissolved.
In this case, too, the curing agent is dispersed in the form of
fine particles of from about 3 to about 8 .mu.m in the powdery
coating material that is obtained.
[0063] Further, the additives used, as required, for the coating
material and the pigment may be mixed into the curable acrylic
resin (A) or into the alcohol solution of the curable acrylic resin
(A) so as to be continuously mixed. Or, they may be continuously
mixed being dissolved or dispersed in the curing agent (B) or in
the alcohol solution of.the curing agent (B).
[0064] In the present invention, there is no particular limitation
on the structure of the kneading/vapor-removing apparatus provided
it is equipped with hoppers for stably feeding the components
(starting materials for the powdery coating material), metering
feeders and metering pumps, and is capable of vapor-removing the
solvent under a reduced pressure. In general, however, there is
used a monoaxial or biaxial extruder or a monoaxial or biaxial
kneader.
[0065] As the monoaxial extruder, there is used the one equipped
with a rotary shaft having a high shearing shape (such as screw,
the Torester type, the Maddock type or of the torpedo type) and a
known kneading portion of the notch type or the dulmadge type. As
the biaxial extruder, there is preferably used the one equipped
with a pair of screw shafts which rotate in the different
directions or in the same direction and possess the kneading
function. It is desired that either extruder has a vapor-removing
port (vent) for removing the volatile components and is capable of
vapor-removing the alcohol solvent through the vent under a reduced
pressure. When the extruder has a plurality of vent, in particular,
the degrees of reduction in the pressure can be separately set in
the respective vapor-removing zones to accomplish excellent
vapor-removing performance as the degree of reduction in the
pressure increases toward the downstream side in the extruder.
Further, the solvent or the solution is fed into the kneading zone
upstream of the vent. When there are provided a plurality of vents,
the solvent or the solution can be fed into any kneading zone, and
can be fed from one place or from two or more places being divided
from each other. The extruder having such a structure can be
represented by, for example, TEM-37BS manufactured by Toshiba Kikai
Co.
[0066] It is further desired that the kneader that can be used as
the kneading/vapor-removing apparatus is of a structure having at
least one vapor-removing port (vent), two stirrer shafts arranged
in line in the transverse direction in the barrel of the main body,
each shaft having a screw and a paddle and being rotated in the
same direction at an equal speed, so that the starting materials
fed from an upper portion at one end of the barrel are fed into the
kneading zone by the screws so as to be kneaded by the paddles, and
that the kneaded product is continuously discharged from the lower
portion, from the side surface or from the front portion on the
other side of the barrel. This kneader can be represented by SC
processor or KRC kneader manufactured by Kurimoto Tekkosho Co.
[0067] The kneading/vapor-removing apparatus of either type is
capable of homogeneously kneading the starting materials of the
powdery coating material by supplying the above-mentioned alcohol
solvent into the kneading zone.
[0068] When used being coupled together in cascade, the continuous
kneading apparatus and the vapor-removing apparatus are the
above-mentioned monoaxial or biaxial extruders or kneaders. The
in-line mixer can be used when the resin solution and the curing
agent solution are to be mixed together. When the above-mentioned
extruder, kneader or in-line mixer is used as the continuous
kneading apparatus, no vent is necessary. In this case, further,
the vapor-removing apparatus has the kneading function, and at
least some of the above-mentioned alcohol solvent (C) or (D) can be
thrown into the vapor-removing apparatus.
[0069] Accordingly to the present invention, the alcohol solvent is
vaporized and is removed as the vapor thereof being heated under a
reduced pressure in the vapor-removing apparatus until the
concentration of the nonvolatile components becomes not lower than
98.5% by weight and, preferably, not lower than 99.0% by weight.
When the concentration of the nonvolatile components becomes lower
than the above value, the anti-blocking property may not be
improved.
[0070] As will be understood from the foregoing description, the
continuous kneading and the removal of the alcohol can be conducted
according to a variety of patterns depending upon the apparatus
that is used. Described below are some of the representative
patterns.
[0071] When, for example, the alcohol solution of the curable
acrylic resin (A) obtained by the polymerization in the presence of
the alcohol solvent is directly used, the continuous kneading and
the removal of the alcohol can be conducted according to the
following pattern. The alcohol solvent used in this case is the
alcohol solvent (C) having a boiling point under normal pressure of
from 70 to 120.degree. C. Methanol shall not be used.
[0072] {circle over (1)} Referring to FIG. 1, use is made of the
above-mentioned kneading/vapor-removing apparatus 13. An alcohol
solution 4 of the curable acrylic resin (A) and the curing agent
(B) denoted by 2 are fed into the kneading/vapor-removing apparatus
13 to continue the kneading and to remove alcohol solvent through
the vents 14, and to take out the kneaded composition 6 from the
kne.ading/vapor-removing apparatus 13. In this case as shown in
FIG. 2, it is allowable to prepare a curing agent solution 5 by
dissolving the curing agent (B) in the alcohol solvent, and to feed
the curing agent solution 5 and the alcohol solution 4 of the
curable acrylic resin (A) to the kneading/vapor-removing apparatus
13. In this case, it is desired that the total weight of the
alcohol solvent lies within the above-mentioned range.
[0073] {circle over (2)} Referring to FIG. 3, the above-mentioned
continuous kneading apparatus 11 and a vapor-removing apparatus 20
are coupled together in cascade. The alcohol solution 4 of the
curable acrylic resin (A) and the curing agent (B) denoted by 2 are
fed into the continuous kneading apparatus 11 to continue the
kneading. The obtained kneaded product is fed from the continuous
kneading apparatus 11 into the vapor-removing apparatus 20, the
alcohol solvent (C) is vapor-removed through the vents 14, and the
kneaded composition 6 is taken out from the vapor-removing
apparatus 20. In this case, too, it is allowable to prepare a
curing agent solution 5 by dissolving the curing agent (B) in the
alcohol solvent (C), and to feed the curing agent solution. 5 and
the alcohol solution 4 of the curable acrylic resin (A) to the
continuous kneading apparatus 11 as shown in FIG. 4 like that of
the above-mentioned pattern {circle over (1)}.
[0074] When the curable acrylic resin (A) that has been prepared in
advance (from which the polymerization-solvent has been removed) is
used, the continuous kneading and the removal of the alcohol can be
executed by the following pattern. In this case, methanol can be
used in addition to the above-mentioned alcohol solvent (C).
Namely, there can be used the alcohol solvent (D) having a boiling
point under normal pressure of from 64 to 120.degree. C.
[0075] {circle over (3)} Referring to FIG. 5, use is made of the
kneading/vapor-removing apparatus 13 same as the one used in the
pattern {circle over (1)}. The curable acrylic resin (A) denoted by
1 and the curing agent (B) denoted by 2 are fed to the
kneading/vapor-removing apparatus 13 to continue the kneading. The
alcohol solvent 3 is directly side-fed into the
kneading/vapor-removing apparatus 13 to effect the kneading and the
removal of the alcohol solvent through the vents 14, and to take
out the kneaded mixture 6 from the kneading/vapor-removing
apparatus 13. In this case, too, it is allowable to prepare a
curing agent solution 5 by dissolving the curing agent (B) in the
alcohol solvent, and to side-feed the curing agent solution 5 into
the kneading/vapor-removing apparatus 13 as shown in FIG. 6.
[0076] {circle over (4)} Referring to FIG. 7, use is made of the
continuous kneading apparatus 11 and the vapor-removing apparatus
20 coupled in cascade like in the pattern {circle over (2)}. The
curable acrylic resin 1 and the curing agent 2 are fed into the
continuous kneading apparatus 11 to continue the kneading. The
alcohol solvent 3 is directly side-fed into the continuous kneading
apparatus 11 to effect the kneading and the removal of the alcohol
solvent through the vents 14, and to take out the kneaded
composition from the solvent-removing apparatus 20. In this case,
too, it is allowable to prepare a curing agent solution 5 by
dissolving the curing agent (B) in the alcohol solvent, and to
side-feed the curing agent solution 5 into the continuous kneading
apparatus 11 as shown in FIG. 8.
[0077] In any one of the above-mentioned patterns {circle over (1)}
to {circle over (4)}, the pigment and the additives used as
required for the coating material are usually fed being mixed in
advance into the curable acrylic resin (A) or into the alcohol
solution of the curable acrylic resin (A). They, however, may be
fed being dissolved or dispersed in the alcohol solution of the
curing agent (B).
[0078] The kneaded composition obtained by removing the alcohol as
described above is, as required, pulverized, classified into a
predetermined particle size and is used as a powdery coating
material. Depending upon the cases, further, a solvent that
dissolves the resin only is added to the obtained kneaded
composition which is, then, spray-dried to obtain a powdery coating
material of nearly a spherical shape making it possible to obtain a
smooth film. The volatile solvent used in this case may,
preferably, be acetone or the like.
[0079] In the thus obtained acrylic powdery coating material, the
curing agent (B), the additives used, as required, for the coating
material and the pigment are homogeneously dispersed in the curable
acrylic resin (A). In particular, the curing agent is existing as
fine particles. This powdery coating material makes it possible to
obtain a film that exhibits smooth surface and beautiful appearance
that could not be accomplished thus far.
EXAMPLES
[0080] The invention will now be concretely described by way of
Reference Examples, Examples and Comparative Examples to which
only, however, the invention is in no way limited as a matter of
course. In these Examples, further, the blended amounts are all by
weight.
[0081] Properties of the powdery coating materials were evaluated
in a manner as described below. Concentration of nonvolatile
components (% by weight):
[0082] The powdery coating material in an amount of 2 g was dried
at 140.degree. C. for 30 minutes, and the weight-holding factors
(%. by weight) were calculated before and after the drying.
[0083] Particle Diameter (.mu.m):
[0084] The volume average particle diameters of the powdery coating
material and of the starting material of the curing agent were
measured by using a laser diffraction scattering particle size
distribution-measuring instrument, Model LA-910, manufactured by
Horiba Seisakusho Co.
[0085] Anti-Blocking Property:
[0086] The powdery coating material in an amount of 30 g was
introduced into a cylindrical container of a diameter of 2 cm, and
a mass of the powdery coating material after preserved at
40.degree. C. for 7 days was evaluated on the following basis.
[0087] .largecircle.--No mass or no aggregation is recognized in
the powdery coating material.
[0088] .DELTA.--Mass is recognized to some extent in the powdery
coating material, which, however, is so weakly aggregated that it
cannot be nipped by figers.
[0089] X--Mass is recognized in the powdery coating material but
can be nipped.
[0090] Film Appearance (Smoothness):
[0091] The powdery coating material was electrostatically applied
onto a steel plate treated with zinc phosphate, cured in an oven
heated at 160.degree. C. for 20 minutes, and the formed film was
evaluated for its smoothness by eyes.
[0092] .largecircle.--Very smooth without dent or ruggedness.
[0093] .DELTA.--Smoothness is slightly poor containing dents and
ruggedness.
[0094] X--Smoothness is poor containing dents and ruggedness to a
considerable degree.
[0095] Film Thickness:
[0096] The film thickness after being applied and cured, was
measured by using LZ-300C manufactured by Kett Electric Laboratory
Co.
[0097] Center Line Mean Roughness Ra:
[0098] The surface of the film after being applied and cured was
measured by using a probe-type surface roughness meter, SURFCOM,
manufactured by Tokyo Seimitsu Co., and was expressed as an average
value of ruggedness. Cut off was 0.8 mm. The smaller the value, the
more smooth the film is.
[0099] Luster (60.degree.):
[0100] The surface of the film after being applied and cured was
measured for its 60.degree. mirror surface reflection factor (%) in
compliance with JIS K5400, 7.6.
[0101] Measurement of Particle Diameter of the Curing Agent After
Kneaded:
[0102] A strand obtained by extruding the powdery coating material
composition after kneaded was buried in the molten polyester resin.
The polyester resin was cured at normal temperature, and the
surface of the sample was polished. The polished surface of the
sample was photographed by using a polarized
microscope,OPTIPHOT-POL manufactured by Nikon Co. and the particle
diameter was measured by eyes (the curing agent is crystalline and
appears in a bright color, enabling the particle diameter to be
measured). Film vividness: Appearance of the film was judged by
eyes.
[0103] .largecircle.: Color tone is homogeneous, and image
representation is excellent.
[0104] .DELTA.: Color tone is slightly unhomogeneous, and image
representation is slightly poor.
[0105] X: Image representation is poor.
[0106] (Using an Alcohol Solution of the Resin)
Example 1
[0107] 120 Parts of isopropanol were fed into a reactor equipped
with a thermometer, a stirrer, a reflux cooler, a pressure adjustor
using nitrogen and a bottom drain pipe, and were heated at
110.degree. C., and to which were further added:
[0108] 40 parts of methyl methacrylate,
[0109] 30 parts of glycidyl methacrylate,
[0110] 15 parts of styrene,
[0111] 15 parts of n-butyl methacrylate, and
[0112] 4 parts of t-amylperoxyisononanoate,
[0113] over a period of two hours, and were maintained at the above
temperature for three hours to obtain an alcohol solution of a
curable acrylic resin (hereinafter called resin solution).
[0114] Separately,
[0115] 22 parts of dodecanoic diacid (curing agent),
[0116] 0.6 parts of benzoin, and
[0117] 0.6 parts of PL-540 (fluidity adjusting agent manufactured
by Kusumoto Kasei Co.),
[0118] were mixed together to prepare a curing agent-containing
mixture.
[0119] The resin solution and the curing agent-containing mixture
prepared above were homogeneously mixed together within a short
period of time by using a continuous biaxial kneader maintained at
70.degree. C. to obtain a kneaded composition.
[0120] The above kneaded composition was then passed into an
extruder equipped with a vent for removing the solvent maintained
at 90.degree. C. and coupled to the continuous biaxial kneader in
cascade thereby to vapor-remove the solvent and to obtain a powdery
kneaded composition.
[0121] The powdery kneaded composition was pulverized by using a
shock-type pulverizer and was further classified to obtain a
powdery coating material having an average particle diameter of 25
.mu.m.
[0122] The thus obtained powdery coating material was
electrostatically applied onto a steel plate treated with zinc
phosphate and was cured in an oven heated at 160.degree. C. for 20
minutes to form a film. The thus formed film was evaluated for its
properties. Table 1 shows the results together with the properties
of the obtained curable acrylic resin.
Example 2
[0123] A resin solution was prepared in the same manner as in
Example 1 but using the polymerization-solvent in an amount of 70
parts and the t-amylperoxyisononanoate in an amount of 6 parts.
[0124] A powdery coating material was prepared in the same manner
as in Example 1 but using the above resin solution, preparing an
alcohol solution of the curing agent (hereinafter called curing
agent solution) by using the above resin solution and by adding 50
parts of methanol to the curing agent-containing mixture,
wet-mixing them together by using an in-line mixer and feeding the
mixture into the extruder with a vent. The powdery coating material
and a film formed therefrom were evaluated for their properties.
Table 1 shows the results together with the properties of the
obtained curable acrylic resin.
Example 3
[0125] An acrylic resin solution was prepared in the same manner as
in Example 1 but using 120 parts of ethanol as the
polymerization-solvent and changing the polymerization temperature
into 90.degree. C.
[0126] A powdery coating material was prepared in the same manner
as in Example 2 but using the above acrylic resin solution and
adding 50 parts of ethanol to the curing agent-containing mixture.
The powdery coating material and a film thereof were evaluated for
their properties. Table 1 shows the results together with the
properties of the obtained curable acrylic resin.
Example 4
[0127] A curable acrylic resin solution was prepared in the same
manner as in Example 1 but using 33 parts of tert-butanol as the
polymerization-solvent and changing the polymerization temperature
into 110.degree. C.
[0128] A powdery coating material was prepared in the same manner
as in Example 2 but using the above acrylic resin solution and
adding 50 parts of ethanol to the curing agent-containing mixture.
The powdery coating material and a film thereof were evaluated for
their properties. Table 1 shows the results together with the
properties of the obtained curable acrylic resin.
Comparative Example 1
[0129] An acrylic resin solution was prepared in the same manner as
in Example 1 but using 100 parts of xylene as the
polymerization-solvent and changing the polymerization temperature
into 125.degree. C., and a powdery coating material was also
prepared in the same manner. Table 2 shows the evaluated results of
properties of the powdery coating material and of the film.
[0130] In this case, xylene was not completely vapor-removed in the
extruder, the curing agent was not homogeneously dispersed, and the
blocking properties and the film properties were inferior.
Comparative Example 2
[0131] A powdery coating material was prepared in the same manner
as in Comparative Example 1 but adding dodecanoic diacid and 50
parts of isopropanol. Table 2 shows the evaluated results of
properties of the powdery coating material and of the film
thereof.
Comparative Example 3
[0132] A powdery coating material was prepared in the same manner
as in Example 3 but adding 180 parts of isopropanol to the curing
agent-containing mixture. Table 2 shows the evaluated results of
properties of the powdery coating material and of the film
thereof.
Comparative Example 4
[0133] A powdery coating material was prepared in the same manner
as in Example 1 but using 300 parts of isopropanol as the
polymerization-solvent. Table 2 shows the evaluated results of
properties of the powdery coating material and of the film
thereof.
Comparative Example 5
[0134] A powdery coating material was prepared in the same manner
as in Example 1 but using 150 parts of 1-pentanol as the
polymerization-solvent. Table 2 shows the evaluated results of
properties of the powdery coating material and of the film
thereof.
[0135] The solvent was not completely vapor-removed in the
extruder, and the blocking properties and the film properties were
inferior.
1 TABLE 1 Ex- Ex- Ex- Ex- ample 1 ample 2 ample 3 ample 4 Curable
acrylic resin Number average molecular weight 4500 5200 4700 4800
Tg (.degree. C.) 51 51 50 50 Powder Paint Non-volatile
concentration (wt %) 99.5 99.6 99.8 99.5 Particle diameter (.mu.m)
34 29 30 28 Anti-blocking property .largecircle. .largecircle.
.largecircle. .largecircle. Film thickness (.mu.m) 45 45 43 42 Film
appearance (smoothness) .largecircle. .largecircle. .largecircle.
.largecircle. Luster (60.degree.) 95 94 93 92 Center line average
surface 0.06 0.05 0.05 0.06 roughness Ra (.mu.m) Particle diameter
of curing agent Average diameter of starting 20 20 20 20 material
(.mu.m) Particle diameter after <1 <1 <1 <1 kneading
(.mu.m)
[0136]
2 TABLE 2 Comparative Comparative Comparative Comparative
Comparative Example 1 Example 2 Example 3 Example 4 Example 5
Curable acrylic resin Number average molecular weight 5400 5400
5300 4900 5500 Tg (.degree. C.) 51 51 51 51 51 Powder Paint
Non-volatile concentration (wt %) 97.8 97.2 98.2 98.0 97.8 Particle
diameter (.mu.m) 31 23 25 20 23 Anti-blocking property X X .DELTA.
.DELTA. X Film thickness (.mu.m) 52 53 49 52 48 Film appearance
(smoothness) X X .DELTA. .DELTA. X Luster (60.degree.) 88 85 87 85
84 Center line average surface 0.15 0.09 0.11 0.11 0.12 roughness
Ra (.mu.m) Particle diameter of curing agent Average diameter of
starting 20 20 20 20 20 material (.mu.m) *Particle diameter after
9.about.13 3.about.7 <1 <1 1.about.3 kneading (.mu.m) *the
particle diameter of curing agent after kneading shows the particle
diameter range in more than 90% particles
Reference Example 1
[0137] 100 Parts (parts by weight, the same holds hereinafter) of
xylene were fed into a reactor equipped with a thermometer, a
stirrer, a reflux cooler, a pressure adjustor using nitrogen and a
bottom drain pipe, and were heated at 115.degree. C., and to which
were further added:
[0138] 40 parts of methyl methacrylate,
[0139] 30 parts of glycidyl methacrylate,
[0140] 15 parts of styrene,
[0141] 15 parts of n-butyl acrylate, and
[0142] 4 parts of azobisisobutylonitrile,
[0143] over a period of four hours, and were maintained at the
above temperature for six hours to obtain a resin solution.
[0144] The obtained resin solution was distilled off at 200.degree.
C. under a reduced pressure (0.13 kPa) until no solvent was
distilled off, and was, then, cooled to obtain a curable acrylic
resin which was solid at normal temperature.
[0145] The resin possessed a number average molecular weight of
5100 and a glass transition temperature Tg of 51.degree. C.
[0146] 50 Parts of the obtained curable acrylic resin were coarsely
pulverized by using a pulverizer, and to which were added and
dry-blended:
[0147] 11 parts of dodecanoic diacid (curing agent),
[0148] 0.3 parts of surface adjusting agent (PL-540 manufactured by
Kusumoto Kasei Co.), and
[0149] 0.3 parts of benzoin,
[0150] in order to prepare a starting mixture for preparing an
acrylic powdery coating material.
Reference Example 2
[0151] A starting mixture for preparing an acrylic powdery coating
material was prepared in quite the same manner as in Reference
Example 1 but without using the curing agent.
[0152] (Side-Feeding of Alcohol)
Example 5
[0153] A three-vent biaxial extruder, TEM-37BS (manufactured by
Toshiba Kikai Co.), was used as a kneading/vapor-removing
apparatus.
[0154] That is, the starting mixture for preparing the acrylic
powdery coating material obtained in Reference Example 1 was fed to
the kneading/vapor-removing apparatus and was extruded at a
cylinder temperature of 90.degree. C., at a screw rotational speed
of 170 rpm and at a rate of 61.6 kg/h.
[0155] Here, methanol was fed at a rate of 3 kg/h into a first
kneading zone downstream of the starting material feed port of the
kneading/vapor-removing apparatus, and the volatile component was
partly removed through a first vent on the downstream side adjusted
at 53 kPa while continuously kneading the starting material for
obtaining the acrylic powdery coating material. Then, the kneading
and removal of solvent were conducted through a second kneading
zone, a second vent (6.7 kPa), a third kneading zone and a third
vent (0.67 kPa) thereby to obtain a kneaded composition.
[0156] By using the kneaded composition, a powdery coating material
was produced in the same manner as in Example 1. The powdery
coating material and a film thereof were evaluated for their
properties. The results were as shown in Table 3.
Example 6
[0157] A powdery coating material was produced in the same manner
as in Example 5 but using, as a solvent, isopropanol instead of
methanol. The powdery coating material and a film thereof were
evaluated for their properties. The results were as shown in Table
3.
Example 7
[0158] A powdery coating material was produced in the same manner
as in Example 5 but feeding the solvent at a rate of 6 kg/h instead
of 3 kg/h. The powdery coating material and a film thereof were
evaluated for their properties. The results were as shown in Table
3.
Example 8
[0159] A powdery coating material was produced in the same manner
as in Example 5 but feeding the solvent at a rate of 4 kg/h into
the first kneading zone and feeding the solvent at a rate of 2 kg/h
into the second kneading zone. The powdery coating material and a
film thereof were evaluated for their properties. The results were
as shown in Table 3.
Example 9
[0160] A continuous biaxial kneader, KRC Kneader, Model S1
(manufactured by Kurimoto Tekkojo Co., screw diameter of 25 mm) was
used as a continuous kneading apparatus, and a monoaxial extruder,
TP20 (manufactured by Thermoplastic Kogyo Co., screw diameter of 20
mm) was used as a vapor-removing apparatus being coupled to the
kneader in cascade.
[0161] The starting mixture for producing the powdery coating
material obtained in Reference Example 1 was fed at a rate of 2
kg/h into the hopper of the kneader by using a metering feeder,
methanol was fed at a rate of 120 g/h into the body of the kneader,
and the mixture was continuously kneaded at a cylinder temperature
of 90.degree. C. and at a screw rotational speed of 100 rpm.
[0162] The kneaded composition was directly fed into the
vapor-removing apparatus adjusted at a cylinder temperature of
90.degree. C. and a screw rotational speed of 100 rpm to remove the
solvent under the condition of a vent pressure of 1 kPa. Here, the
average contact time between the curable acrylic resin and the
methanol at 90.degree. C. was one minute.
[0163] A powdery coating material was produced from the kneaded
composition from which the solvent has been vapor-removed in the
same manner as in Example 5. The powdery coating material and a
film thereof were evaluated for their properties. The results were
as shown in Table 3.
Comparative Example 6
[0164] A powdery coating material was produced in the same manner
as in Example 5 but kneading the starting material of acrylic
powdery coating material without feeding methanol. The powdery
coating material and a film thereof were evaluated for their
properties to find that they lacked smoothness and luster. The
results were as shown in Table 4.
Comparative Example 7
[0165] A powdery coating material was produced in the same manner
as in Example 5 but feeding toluene instead of methanol. The
powdery coating-material and a film thereof were evaluated for
their properties to find that they lacked smoothness and luster.
The results were as shown in Table 4.
Comparative Example 8
[0166] A powdery coating material was produced in the same manner
as in Example 5 but feeding a starting mixture for preparing the
powdery coating material into the kneader at a rate of 200 g/h,
feeding methanol at a rate of 12 g/h and turning the screw of the
kneader at a speed of 10 rpm. The average contact time between the
curable acrylic resin and the methanol at 90.degree. C. was 12
minutes. The,powdery coating material and a film thereof were
evaluated for their properties. The results were as shown in Table
4.
3 TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Powder
paint Non-volatile concentration (wt %) 99.8 99.7 99.6 99.9 99.8
Average particle diameter (.mu.m) 25 23 24 28 25 Anti-blocking
property .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Film thickness (.mu.m) 42 40 43 38 42 Film appearance
(smoothness) .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Center line average surface 0.06 0.07
0.07 0.06 0.06 roughness Ra (.mu.m) Particle diameter of curing
agent Average diameter of starting 20 20 20 20 20 material (.mu.m)
*Particle diameter after 3.about.7 4.about.8 1.about.5 3.about.7
3.about.7 kneading (.mu.m) *the particle diameter of curing agent
after kneading shows the particle diameter range in more than 90%
particles
[0167]
4 TABLE 4 Com- Com- parative Comparative parative Example 1 Example
2 Example 3 Powder paint Non-volatile concentration (wt %) 99.8
99.7 99.8 Average particle diameter (.mu.m) 25 25 24 Anti-blocking
property .largecircle. .largecircle. X Film thickness (.mu.m) 44 45
45 Film appearance (smoothness) X X .DELTA. Center line average
surface 0.15 0.14 0.13 roughness a (.mu.m) Particle diameter of
curing agent Average diameter of starting 20 20 20 material (.mu.m)
*Particle diameter after 10.about.16 10.about.15 3.about.8 kneading
(.mu.m) *the particle diameter of curing agent after kneading shows
the particle diameter range in more than 90% particles
[0168] (Side-Feeding the Curing Agent Solution)
Example 10
[0169] By using the kneading/vapor-removing apparatus used in
Example 5, the starting mixture for preparing the acrylic powdery
coating material obtained in Reference Example 2 was fed to the
above apparatus and was extruded at a cylinder temperature of
90.degree. C., at a screw rotational speed of 170 rpm and at a rate
of 50.6 kg/h.
[0170] There was further prepared a curing agent solvent comprising
11 parts by weight of dodecanoic diacid and 19 parts by weight of
methanol and heated at 80.degree. C.
[0171] While the starting mixture for preparing the acrylic powdery
coating material was being fed, the curing agent solvent was fed at
a rate of 30 kg/h into the first kneading zone downstream of the
starting material feed port of the kneading/vapor-removing
apparatus, and the volatile component was partly removed through
the first vent on the downstream side adjusted at 53 kPa while
continuously kneading the starting material for preparing the
acrylic powdery coating material. Then, the kneading and the
removal of solvent were conducted through the second kneading zone,
the second vent (6.7 kPa), the third kneading zone and the third
vent (0.67 kPa) thereby to obtain a kneaded composition.
[0172] By using the kneaded composition from which the solvent has
been removed, a powdery coating material was produced in the same
manner as in Example 1. The powdery coating material and a film
thereof were evaluated for their properties. The results were as
shown in Table 5.
Example 11
[0173] A powdery coating material was produced in the same manner
as in Example 10 but using a curing agent solvent prepared by using
isopropanol instead of methanol. The powdery coating material and a
film thereof were evaluated for their properties. The results were
as shown in Table 5.
5 TABLE 5 Example 10 Example 11 Powder paint Non-volatile
concentration (wt %) 99.8 99.7 Average particle diameter (.mu.m) 25
23 Anti-blocking property .largecircle. .largecircle. Film
thickness (.mu.m) 40 43 Film appearance (smoothness) .largecircle.
.largecircle. Center line average surface 0.07 0.07 roughness Ra
(.mu.m) Particle diameter of curing agent Average diameter of
starting 20 20 material (.mu.m) *Particle diameter after <1
<1 kneading (.mu.m) *the particle diameter of curing agent after
kneading shows the particle diameter range in more than 90%
particles
[0174] (Using a Pigment)
Example 12
[0175] A powdery coating material was produced in the same manner
as in Example 1 but adding 25 parts of titanium oxide to the
starting mixture for preparing the acrylic powdery coating material
of Reference Example 1. The powdery coating material and a film
thereof were evaluated for their properties. Table 6 shows the
results together with the properties of the obtained curable
acrylic resin.
Comparative Example 9
[0176] A powdery coating material was produced in the same manner
as in Comparative Example 6 but adding 25 parts of titanium oxide
to the starting mixture for preparing the acrylic powdery coating
material of Reference Example 1. The powdery coating material and a
film thereof were evaluated for their properties. Table 6 shows the
results together with the properties of the obtained curable
acrylic resin.
6 TABLE 6 Comparative Example 12 Example 9 Powder paint Number
average molecular weight 4600 5000 Resin Tg (.degree. C.) 51 51
Non-volatile concentration (wt %) 99.7 98.0 Particle diameter
(.mu.m) 32 25 Anti-blocking property .largecircle. .DELTA. Film
thickness (.mu.m) 49 49 Film appearance (smoothness) .largecircle.
.DELTA. Luster (60.degree.) 92 85 Sharpness .largecircle. X
Particle diameter of curing agent Average diameter of starting 20
20 material (.mu.m) *Particle diameter after <1 10.about.16
kneading (.mu.m) *the particle diameter of curing agent after
kneading shows the particle diameter range in more than 90%
particles
* * * * *