U.S. patent application number 10/251785 was filed with the patent office on 2003-06-05 for powder coating.
This patent application is currently assigned to Nippon Paint Co., Ltd.. Invention is credited to Aoki, Katsutoshi, Inagaki, Yasunori, Maruta, Masayuki, Sato, Yukiya, Tajima, Hisakazu, Tanaka, Shingo, Tohjo, Takehiko.
Application Number | 20030105244 10/251785 |
Document ID | / |
Family ID | 18282816 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030105244 |
Kind Code |
A1 |
Sato, Yukiya ; et
al. |
June 5, 2003 |
Powder coating
Abstract
The combination of powder coatings usable in a coating method
comprising mixing two or more powder coatings of which each color
is different, wherein each of the powder coatings fuses with each
other and is heat-cured, to thereby give a coating film having a
homogenous hue. A powder coating composition comprising two or more
powder coatings of which each color is different, wherein each of
the powder coatings fuses with each other and is heat-cured, to
thereby give a coating film having a homogenous hue. A coating
method comprising the steps of (a) applying to a substrate two or
more powder coatings, of which each color is different; (b) heating
to fuse with each other each of the two or more powder coatings
applied in step (a); and (c) curing the resulting fused product in
step (b), to give a coating film having a homogeneous hue.
Inventors: |
Sato, Yukiya; (Wakayama-shi,
JP) ; Tajima, Hisakazu; (Wakayama-shi, JP) ;
Aoki, Katsutoshi; (Wakayama-shi, JP) ; Tohjo,
Takehiko; (Tochigi-ken, JP) ; Inagaki, Yasunori;
(Wakayama-shi, JP) ; Maruta, Masayuki;
(Wakayama-shi, JP) ; Tanaka, Shingo; (Osaka,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Nippon Paint Co., Ltd.
Osaka
JP
|
Family ID: |
18282816 |
Appl. No.: |
10/251785 |
Filed: |
September 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10251785 |
Sep 23, 2002 |
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09580593 |
May 30, 2000 |
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09580593 |
May 30, 2000 |
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08978152 |
Nov 25, 1997 |
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6207768 |
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Current U.S.
Class: |
525/438 |
Current CPC
Class: |
Y10S 525/934 20130101;
C09D 5/032 20130101 |
Class at
Publication: |
525/438 |
International
Class: |
C08F 020/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 1996 |
JP |
8-334928 |
Claims
What is claimed is:
1. A coating method comprising the steps of: (a) applying to a
substrate two or more powder coatings, of which each color is
different; (b) heating to fuse with each other each of said two or
more powder coatings applied in step (a); and (c) curing the
resulting fused product in step (b), to give a coating film having
a homogeneous hue.
2. The coating method according to claim 1, wherein said step (c)
is carried out by heat-curing the resulting fused product in step
(b).
3. The coating method according to claim 1, wherein said step (c)
is carried out by irradiating light to the resulting fused product
in step (b).
4. A coating film or a coated substrate having a homogeneous hue
prepared by applying to a substrate two or more powder coatings, of
which each color is different, according to a combination of powder
coatings, wherein each of said powder coatings fuses with each
other and is heat-cured, to thereby give a coating film having a
homogenous hue.
5. A coating film or a coated substrate having a homogeneous hue
prepared by applying to a substrate two or more powder coatings, of
which each color is different, according to the coating method as
defined in claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a combination of two or
more powder coatings of which each color is different, a powder
coating composition comprising two or more powder coatings of which
each color is different, a coating method using two or more powder
coatings of which each color is different, a coating film or a
coated substrate prepared by applying to a substrate two or more
powder coatings according to the combination of powder coatings,
and a coating film or a coated substrate prepared according to the
coating method.
[0003] 2. Discussion of the Related Art
[0004] Conventionally, powder coatings have been prepared by adding
numerous color pigments to resins, curing agents, additives, mixing
the above components, melt-kneading the mixture, followed by
cooling, pulverization, and classification. Therefore, in these
powder coatings, the powder coatings have to be prepared for each
color needed, so that an enormous number of powder coating products
are needed.
[0005] By contrast, in order to simplify the toning process, there
has been proposed a powder coating prepared by forming a composite
of several kinds of colored powders.
[0006] However, when the powder coatings of which each color is
different are uniformly mixed upon use, in cases where of using the
mixed powder coatings with particle sizes exceeding 20 .mu.m, the
particles of the powder coatings of each color can be generally
distinguished by gross examination, thereby making it impossible to
obtain a coating film having a homogeneous hue.
[0007] On the other hand, as disclosed in Japanese Unexamined
Patent No. 4-504431, a method of forming a coating film of a
desired hue comprising mixing two or more color powders each having
an average particle size of 20 .mu.m or less has been proposed.
However, the yield tends to be lowered by down-sizing the particle
size to 20 .mu.m or less, and the particles are likely to be
agglomerated when they are in the order of 20 .mu.m or less, so
that the free flowability of the powder coatings becomes poor,
thereby giving rise to such problems as lack of handleability.
[0008] Also, a method of improving free flowability by granulating
powder coatings by adding a granulating agent solution has been
proposed. However, such processes require large number of
production steps, undesirably leading to increase in costs.
[0009] One object of the present invention is to provide a
combination of two or more powder coatings of which each color is
different, to thereby give a coating film having a homogeneous
hue.
[0010] Another object of the present invention is to provide a
powder coating composition comprising two or more powder coatings
of which each color is different, to thereby give a coating film
having a homogeneous hue.
[0011] A still another object of the present invention is to
provide a coating method using two or more powder coatings of which
each color is different, to thereby give a coating film having a
homogeneous hue.
[0012] A still another object of the present invention is to
provide a coating film or a coated substrate having a homogeneous
hue prepared by applying to a substrate two or more powder
coatings, of which each color is different, according to the
combination of powder coatings.
[0013] A still another object of the present invention is to
provide a coating film or a coated substrate having a homogeneous
hue prepared by applying to a substrate two or more powder
coatings, of which each color is different, according to the
coating method described above.
[0014] These and other objects of the present invention will be
apparent from the following description.
SUMMARY OF THE INVENTION
[0015] One aspect of the present invention is a combination of
powder coatings usable in a coating method comprising mixing two or
more powder coatings of which each color is different, wherein each
of the powder coatings fuses with each other and is heat-cured, to
thereby give a coating film having a homogenous hue.
[0016] Another aspect of the present invention is a powder coating
composition comprising two or more powder coatings of which each
color is different, wherein each of the powder coatings fuses with
each other and is heat-cured, to thereby give a coating film having
a homogenous hue.
[0017] A still another aspect of the present invention is a coating
method comprising the steps of:
[0018] (a) applying to a substrate two or more powder coatings, of
which each color is different;
[0019] (b) heating to fuse with each other each of the two or more
powder coatings applied in step (a); and
[0020] (c) curing the resulting fused product in step (b), to give
a coating film having a homogeneous hue.
[0021] A still another aspect of the present invention is a coating
film or a coated substrate having a homogeneous hue prepared by
applying to a substrate two or more powder coatings, of which each
color is different, according to the combination of powder coatings
described above.
[0022] A still another aspect of the present invention is a coating
film or a coated substrate having a homogeneous hue prepared by
applying to a substrate two or more powder coatings, of which each
color is different, according to the coating method as described
above.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The combination of powder coatings of the present invention
is a combination of powder coatings usable in a coating method
comprising mixing two or more powder coatings of which each color
is different, wherein each of powder coatings fuses with each other
and is heat-cured, to thereby give a coating film having a
homogenous hue.
[0024] Here, in the present specification, a coating film having a
"homogeneous" hue means that the hue of the formed coated film is
made homogenous to an extent that the colors of the mixed powder
coatings cannot be distinguished by gross examination. Also, "each
of powder coatings fuses" means that molten products of each of
powder coatings are mixed with each other, to have a substantially
homogenous state.
[0025] Each of the embodiments of the combination of the powder
coatings of the present invention will be detailed below.
[0026] First Embodiment
[0027] First Embodiment is a combination of two or more powder
coatings which have such properties that each of the powder
coatings does not have thermosetting properties alone at a
temperature of 250.degree. C., or less, and is heat-cured with
other powder coatings used in combination at a temperature of
250.degree. C. or less when mixed therewith.
[0028] The resins usable in the powder coatings in First Embodiment
include any of conventionally known resins without particular
limitation. In the present invention, it is desired to adjust the
fusing temperature of each of the usable resins such that
the-resins are together fused upon stoving. Since the fusing
temperature of the usable resins is adjusted, curing reaction takes
place after fusing together and homogeneously mixing the resins
upon stoving, thereby making it possible to obtain a coating film
having a homogeneous hue. The fusing temperature of the resins may
be adjusted by such methods, for instance, of adjusting the
chemical structure of the resins and of adjusting the molecular
weight distribution.
[0029] In First Embodiment, for instance, when two powder coatings
are respectively denoted by Powder Coating (i) and Powder Coating
(ii), each of which does not have thermosetting properties alone at
a temperature of 250.degree. C. or less, powder coatings having
properties described above can be obtained by suitably selecting a
combination of resins usable for Powder Coating (i) and resins
usable for Powder Coating (ii), and preparing each of powder
coatings according to each of embodiments detailed below.
[0030] In other words, the combinations of two or more powder
coatings of First Embodiment are roughly classified into two
embodiments:
[0031] (1) An embodiment where each of the resins contained in the
respective powder coatings is fused with each other to cause curing
reaction by the resins themselves at a temperature of 250.degree.
C. or less; and
[0032] (2) An embodiment where no curing reactions take place
between resins themselves at a temperature of 250.degree. C. or
less, but when adding a curing agent with the resin, the curing
agent being reactive with the counterpart resin, each of powder
coatings is cured with other powder coatings used in combination at
a temperature of 250.degree. C. or less.
[0033] (1) Embodiment Where Each of the Resins Contained in the
Respective Powder Coatings by the Resins Themselves to Cause Curing
Reaction
[0034] As mentioned above, in this embodiment, the resins contained
in the respective powder coatings are fused with each other,
thereby making it possible to cause curing reaction by the resins
themselves at a temperature of 250.degree. C. or less.
[0035] In Embodiment (1), the curing reaction is not carried out
until the resins usable in each of the powder coatings are melted
with each other upon stoving and uniformly mixed, in which curing
reaction one resin acts as a curing agent for the other resin.
Therefore, the resulting coating film obtained from such powder
coatings has a homogeneous hue. Accordingly, a suitable combination
of the functional groups in each resin must be selected so that one
resin has a functional group which can act as a curing agent for
the other resin.
[0036] Concrete examples of combinations of functional groups
capable of carrying out curing reaction include:
[0037] (I) combinations of one or more members selected from
carboxyl group, amino group, phenolic hydroxyl group, and acid
anhydride group, with one or more members selected from epoxy
groups, glycidyl groups, and groups having one or more unsaturated
bonds; and
[0038] (II) combinations of alcoholic hydroxyl group and an
isocyanate group.
[0039] In Embodiment (1), preference is given to combination (I).
In particular, combinations of one or more members selected from
carboxyl groups and amino groups with one or more members selected
from epoxy groups and glycidyl groups are more preferred.
[0040] Accordingly, the resins usable in each of powder coatings
have to be selected such that the combinations of the functional
groups owned by each resin may be as described above.
[0041] Here, when the powder coatings usable in this embodiment are
denoted by Powder Coating A and Powder Coating B, the combinations
of the resin usable in each of powder coatings are as follows.
[0042] Combination 1:
[0043] Resin in Powder Coating A
[0044] Acrylic resin having one or more members selected from
carboxyl groups and amino groups; and
[0045] Resin in Powder Coating B
[0046] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0047] Combination 2:
[0048] Resin in Powder Coating A
[0049] Polyester resin having one or more carboxyl groups; and
[0050] Resin in Powder Coating B
[0051] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0052] Combination 3:
[0053] Resin in Powder Coating A
[0054] Polyester-polyamide resin having one or more members
selected from carboxyl groups and amino groups; and
[0055] Resin in Powder Coating B
[0056] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0057] Combination 4:
[0058] Resin in Powder Coating A
[0059] Polyamide resin having one or more members selected from
carboxyl groups and amino groups; and
[0060] Resin in Powder Coating B
[0061] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0062] Combination 5:
[0063] Resin in Powder Coating A
[0064] Resin having one or more phenolic hydroxyl groups; and
[0065] Resin in Powder Coating B
[0066] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0067] Combination 6:
[0068] Resin in Powder Coating A
[0069] Acid anhydride resin having one or more acid anhydride
groups; and
[0070] Resin in Powder Coating B
[0071] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0072] Combination 7:
[0073] Resin in Powder Coating A
[0074] Aminopolyacrylamide resin having one or more amino groups;
and
[0075] Resin in Powder Coating B
[0076] At least one member selected from epoxy resin having one or
more epoxy groups, acrylic resin having one or more glycidyl
groups, and resin having one or more unsaturated bonds.
[0077] Combination 8:
[0078] Resin in Powder Coating A
[0079] Melamine resin having one or more alkoxy groups; and
[0080] Resin in Powder Coating B
[0081] At least one member selected from polyester resin, acrylic
resin, polyol resin, and urethane resin, each having one or more
hydroxyl groups.
[0082] Combination 9:
[0083] Resin in Powder Coating A
[0084] Urethane resin having one or more isocyanate groups; and
[0085] Resin in Powder Coating B
[0086] At least one member selected from polyester resin, acrylic
resin, polyol resin, and urethane resin, each having one or more
hydroxyl groups; and acrylic resin, polyamide resin,
polyester-polyamide resin, and aminopolyacrylamide resin, each
having one or more amino groups.
[0087] Combination 10:
[0088] Resin in Powder Coating A
[0089] At least one member selected from acrylic resin, polyamide
resin, polyester-polyamide resin, and aminopolyacrylamide resin,
each having one or more amino groups; and
[0090] Resin in Powder Coating B
[0091] At least one member selected from polyester resin and
acrylic resin, each having one or more carboxyl groups.
[0092] Combination 11:
[0093] Resin in Powder Coating A
[0094] Acid anhydride resin having one or more acid anhydride
groups; and
[0095] Resin in Powder Coating B
[0096] At least one member selected from polyester resin, acrylic
resin, polyol resin, and urethane resin, each having one or more
hydroxyl groups.
[0097] Among them, from the viewpoint of giving good strength of
the resulting coating film, at least one of Powder Coating A and
Powder Coating B contains one or more resins selected from acrylic
resins having one or more members selected from carboxyl groups and
amino groups, polyester resins having one or more carboxyl groups,
polyester-polyamide resins having one or more members selected from
carboxyl groups and amino groups, polyamide resins having one or
more members selected from carboxyl groups and amino groups, resins
having one or more phenolic hydroxyl groups, and acid anhydride
resins having one or more acid anhydride groups; and another powder
coating contains one or more resins selected from epoxy resins
having one or more epoxy groups, acrylic resins having one or more
glycidyl groups, and resins having one or more unsaturated bonds.
The above-exemplified resins may be prepared by any conventional
methods without particular limitation.
[0098] Incidentally, in Embodiment (1), in a case where the resins
are used in the above combinations, curing agents may be optionally
used, though not essential. In a case where a curing agent is used,
the usable curing agents may be any of various conventionally known
curing agents without limitation, provided that a combination of a
resin and a curing agent mixed in the same powder coating has to be
suitably selected such that the powder coating does not have
thermosetting properties alone at a temperature of 250.degree. C.
or less.
[0099] Specifically, in Embodiment (1), the resins and the curing
agents in the powder coating have to be selected such that
combinations of the resins and the curing agents in the powder
coatings are:
[0100] Powder Coating A=Resin A+Curing Agent B'; and
[0101] Powder Coating B=Resin B+Curing Agent A',
[0102] wherein Resins A, B denote resins in Powder Coatings A, B,
respectively; Curing Agent A' denotes a curing agent reactive with
Resin A but unreactive with Resin B; and Curing Agent B' denotes a
curing agent reactive with Resin B but unreactive with Resin A.
[0103] In this embodiment, a curing agent reactive with a resin
contained in one powder coating is contained in the other powder
coating. As described above, since a curing agent and a resin
unreactive therewith are contained in a single powder coating, a
powder coating which does not have thermosetting properties alone
at a temperature of 250.degree. C. or less can be prepared.
[0104] In addition, in another embodiment where a curing agent is
used, a curing agent may be contained in only one of the powder
coatings.
[0105] Powder Coating A=Resin A; and
[0106] Powder Coating B=Resin B+Curing Agent A',
[0107] wherein Resins A, B and Curing Agent A' are as defined
above.
[0108] Incidentally, in the present invention, the ratio of Resin A
and Resin B in Powder Coatings A and B depends upon the amount of
functional groups being present in the resins, and it is desired
that the ratio is in the range of 0.8 to 1.2 in terms of the
equivalency ratio of functional groups.
[0109] Also, the amount of the usable curing agents in the present
invention may be of the level required for conventional
thermosetting reaction. The amount may depend upon the amount of
the functional groups being present in the resins, and it is
desired that the molar ratio of the functional groups in the curing
agents to that in the resin is from 0.8 to 1.2 in terms of the
equivalency ratio of functional groups contained therein.
[0110] In this embodiment, curing reaction proceeds by the reaction
between Resin A and Resin B and the reaction between Resin A and
Curing Agent A'.
[0111] In the present invention, examples of combinations of the
resins and the curing agents which are reactive to cause curing
reaction at a temperature of 250.degree. C. or less, each listed
below as either Resin A [Curing Agent A'] or Resin B [Curing Agent
B'], include an organopolysiloxane [an aminoxysilane compound], an
organopolysiloxane [an alkoxysilane compound], a silicone polymer
[a tin compound], a polysulfide polymer [lead dioxide], a urethane
resin [an acrylic oligomer], a urethane resin [a polyol compound],
a urethane prepolymer [a polyol compound], a polyester resin [a
polyepoxy compound], a polyester resin [a poly(acid anhydride)
compound], a polyester resin [a polyamine compound], a polyester
resin [a melamine compound], a polyester resin having one or more
hydroxyl groups at terminus [an alkoxy compound], a polyester resin
having one or more carboxyl groups [triglycidyl isocyanurate
(hereinafter simply referred to as "TGIC")], a polyester resin
having one or more amino groups at terminus [TGIC], a polyester
resin having one or more amino groups at terminus [a modified
melamine compound], a polyester resin having one or more phenolic
hydroxyl groups [TGIC], an unsaturated polyester resin having one
or more hydroxyl groups other than phenolic hydroxyl groups at
terminus [a melamine compound], an unsaturated polyester resin
having one or more hydroxyl groups other than phenolic hydroxyl
groups at terminus [2,4,6-triaminopyridine], an epoxy resin [a
polyamine compound], an epoxy resin [a poly(acid anhydride)
compound], an epoxy resin [a diamine compound], an epoxy resin
[2,4,6-triaminopyridine], an epoxy resin [a, polycarboxylic acid
compound], an acrylic resin having one or more glycidyl groups
[2,4,6-triaminopyridine], an acrylic resin having one or more amino
groups [TGIC], a polyamide resin [a polycarboxylic acid compound],
a polyamide resin having one or more amino groups at terminus
[TGIC], a polyester-polyamide resin [a polycarboxylic acid
compound], a polyester-polyamide resin [TGIC], a novolak resin
[TGIC], an alkoxy resin [a polyol compound], and the like. Here,
examples of the diamine compounds include dihydrazide adipate, and
the like.
[0112] Accordingly, concrete examples of combinations of the resins
and the curing agents in Powder Coating A and Powder Coating B
include the following without being limited thereto:
[0113] Combination 1:
[0114] Powder Coating A
[0115] Resin A: Polyamide resin having one or more amino groups at
terminus;
[0116] Powder Coating B
[0117] Resin B: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups; and
[0118] Curing
[0119] Agent A': TGIC.
[0120] Combination 2:
[0121] Powder Coating A
[0122] Resin A: Polyester-polyamide resin having one or more amino
groups at terminus;
[0123] Powder Coating B
[0124] Resin B: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups; and
[0125] Curing
[0126] Agent A': TGIC.
[0127] Combination 3:
[0128] Powder Coating A
[0129] Resin A: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups;
[0130] Powder Coating B
[0131] Resin B: Polyamide resin having one or more amino groups at
terminus; and
[0132] Curing
[0133] Agent A': 2,4,6-Triaminopyridine.
[0134] Combination 4:
[0135] Powder Coating A
[0136] Resin A: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups;
[0137] Powder Coating B
[0138] Resin B: Polyester-polyamide resin having one or more amino
groups at terminus; and
[0139] Curing
[0140] Agent A': 2,4,6-Triaminopyridine.
[0141] Combination 5:
[0142] Powder Coating A
[0143] Resin A: Acrylic resin having one or more amino groups;
[0144] Powder Coating B
[0145] Resin B: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups; and
[0146] Curing
[0147] Agent A': TGIC.
[0148] (2) Embodiment Where No Curing Reactions Take Place Between
the Resins Themselves at a Temperature of 250.degree. C. or
Less
[0149] As mentioned above, in this embodiment, no curing reactions
take place between the resins themselves, and by using a curing
agent with a resin in each of the two powder coatings, powder
coatings are fused with each other, thereby causing curing reaction
at a temperature of 250.degree. C. or less.
[0150] Therefore, when the powder coatings usable in Embodiment (2)
are respectively denoted by Powder Coating C and Powder Coating D,
it is essential that the resin usable in Powder Coating C and the
resin usable in Powder Coating D are selected such that no curing
reactions take place even when these resinous components are melted
and mixed at a temperature of 250.degree. C. or less.
[0151] Specifically, in Embodiment (2), the resins and the curing
agents in the powder coating have to be selected such that
combinations of the resins and the curing agents in the powder
coatings are:
[0152] Powder Coating C=Resin C+Curing Agent D'; and
[0153] Powder Coating D=Resin D+Curing Agent C',
[0154] wherein Resins C, D denote resins in Powder Coatings C, D
respectively, provided that no curing reactions take place between
Resin C and Resin D at a temperature of 250.degree. C. or less;
Curing Agent C' denotes a curing agent reactive with Resin C but
unreactive with Resin D; and Curing Agent D' denotes a curing agent
reactive with Resin D but unreactive with Resin C.
[0155] In this embodiment, a curing agent reactive with a resin
contained in one powder coating is contained in the other powder
coating. As described above, since a curing agent and a resin
unreactive therewith are contained in a single powder coating, a
powder coating which does not have thermosetting properties alone
at a temperature of 250.degree. C. or less can be prepared.
[0156] Combinations of resins and curing agents which react with
each other to cause curing reaction at a temperature of 250.degree.
C. or less are not particularly limited as long as the
above-described relationships are satisfactorily met.
[0157] Therefore, concrete examples of combinations of resins and
curing agents in Powder Coatings C and D include the following,
without being limited thereto.
[0158] Combination 1:
[0159] Powder Coating C
[0160] Resin C: Polyester resin having one or more hydroxyl groups
at terminus;
[0161] Curing
[0162] Agent D': TGIC;
[0163] Powder Coating D
[0164] Resin D: Polyester-polyamide resin having one or more amino
groups at terminus; and
[0165] Curing
[0166] Agent C': Alkoxy compound.
[0167] Combination 2:
[0168] Powder Coating C
[0169] Resin C: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups;
[0170] Curing
[0171] Agent D': Alkoxy compound;
[0172] Powder Coating D
[0173] Resin D: Polyester resin having one or more hydroxyl groups
other than phenolic hydroxyl groups at terminus; and
[0174] Curing
[0175] Agent C': Diamine compound.
[0176] Combination 3:
[0177] Powder Coating C
[0178] Resin C: Alkoxy resin;
[0179] Curing
[0180] Agent D': TGIC;
[0181] Powder Coating D
[0182] Resin D: Polyester-polyamide resin having one or more amino
groups at terminus; and
[0183] Curing
[0184] Agent C': Polyol compound.
[0185] Combination 4:
[0186] Powder Coating C
[0187] Resin C: Epoxy resin having one or more epoxy groups and/or
acrylic resin having one or more glycidyl groups;
[0188] Curing
[0189] Agent D': Melamine compound;
[0190] Powder Coating D
[0191] Resin D: Polyester resin having one or more hydroxyl groups
other than phenolic hydroxyl groups at terminus; and
[0192] Curing
[0193] Agent C': Diamine compound.
[0194] Combination 5:
[0195] Powder Coating C
[0196] Resin C: Unsaturated polyester resin having one or more
hydroxyl groups other than phenolic hydroxyl groups at
terminus;
[0197] Curing
[0198] Agent D': TGIC
[0199] Powder Coating D
[0200] Resin D: Polyester resin having one or more phenolic
hydroxyl groups; and
[0201] Curing
[0202] Agent C': Melamine compound.
[0203] Combination 6:
[0204] Powder Coating C
[0205] Resin C: Urethane prepolymer having one or more --NCO groups
at terminus;
[0206] Agent D': TGIC;
[0207] Powder Coating D
[0208] Resin D: Polyester-polyamide resin having one or more amino
groups at terminus; and
[0209] Agent C': Polyol compound.
[0210] Incidentally, in the combinations of the epoxy resins and
the polyester resins, depending upon the kinds of the functional
groups owned by the polyester resins, in some cases curing reaction
may take place by using a curing agent together with the resin as
shown in Table 2, in addition to the combinations where curing
reaction takes place between the resins themselves described
above.
[0211] The resins usable in the powder coatings in First Embodiment
are as described above, among which in both Embodiments (1) and
(2), particular preference is given to the resins each having two
or more functional groups per molecule which can participate in a
thermosetting reaction from the aspect of improving the strength in
the resulting coating film. When the resin mentioned above is used,
the strength of the resulting coating film can be remarkably
improved.
[0212] In the present invention, concrete examples of the
functional groups which can participate in the thermosetting
reaction include carboxyl group, amino group, hydroxyl group,
glycidyl group, isocyanate group, and the like.
[0213] In the present invention, the number of functional groups
per molecule in the resin can be calculated from at least one value
of an acid value, an amine value, a hydroxyl value, an oxirane
value, and the like, and a number-average molecular weight measured
by using gel permeation chromatography (GPC).
[0214] In the powder coatings in First Embodiment, depending upon
each of the embodiments, suitably selected curing agents may be
used in addition to the resin as described above. Also, colorants,
various additives, and the like may be further optionally added
thereto.
[0215] The colorants usable in the present invention may be any of
known ones without particular limitation, which may be suitably
selected depending upon the desired tone. Concrete examples thereof
include titanium oxide, carmine 6B, carbon blacks, copper
phthalocyanine, acetoacetic acid arylamide-based monoazo yellow
pigments, dis-azo yellows, pigment reds, and the like. The amount
thereof is preferably from about 5 to about 60 parts by weight,
based on 100 parts by weight of the resin.
[0216] The additives usable in the present invention may be any of
known ones usable in the composition of powder coatings without
particular limitation. Examples thereof include levelling agents,
such as acrylate polymers, crosslinking accelerators, such as
various catalysts and organotin compounds, pinhole preventives,
such as benzoin. Each of the additives may be preferably added in
an amount of from about 0.1 to about 5 parts by weight, based on
100 parts by weight of the resins.
[0217] The powder coating usable in the present invention may be
prepared by melt-kneading each of the above components using an
extruder. After cooling the resulting kneaded mixture, it is
subjected to physical pulverization using pulverizing devices, such
as hammer mills and jet mills, and then the pulverized product is
classified using classifiers, such as air classifiers and
micron-classifiers, to give powder coatings of desired average
particle sizes. Also, in the present invention, flowability
controlling agents, such as silica, alumina, titania, and zirconia
may be further added to the surface of the powder coating.
[0218] It is desired that the average particle size of the powder
coating usable in the present invention is 1 .mu.m or more,
preferably 5 .mu.m or more, from the viewpoint of inhibiting
agglomeration of the powder coating particles and uniformly mixing
the two or more powder coatings. Also, it is desired that the
average particle size is 50 .mu.m or less, preferably 30 .mu.m or
less, from the viewpoint of inhibiting excessive thickening of the
resulting coating film. Here, the average particle size of the
powder coatings may be measured by Coulter counter method. Also, in
the present invention, since the homogeneous coating film can be
prepared by fusing the powder coatings upon mixing and applying the
powder coatings, the powder coatings having average particle sizes
of 20 to 50 .mu.m may be used without any problems.
[0219] In the present invention, it is desired that the
triboelectric charges of the powder coatings are controlled within
a desired range. Methods for controlling triboelectric charges
include a method by adjusting acid values, amine values, etc. of
the resin; a method by adjusting charges and amounts of the
colorants; a method by adding various additives, such as quaternary
ammonium salts, dyes, and metallic soaps; and a method by adjusting
the amounts of such agents as silica, alumina, titania, and
zirconia, the agents being added to adjust flowability. For
instance, in a case where a resin having a high acid value is used
as a raw material, negative triboelectric charges increase.
[0220] In the present invention, an example of a method for
measuring triboelectric charges of each of powder coatings is as
follows. First, a powder coating is applied using the coating
machine and the substrate to be coated under working conditions,
such as applied voltage, amount of coating feed, and the like.
After air blowing-off of the powder from the substrate, a
difference in voltage owing to the efflux of electric charges from
the substrate and the amount of the powder coatings removed are
measured. Alternatively, as a simple method, the triboelectric
charge is measured by a blow-off method when each of the powder
coatings is mixed with various powder coatings having particle
sizes larger than that of the powder coating to be tested.
[0221] In the present invention, it is desired that each of
differences in triboelectric charges of two or more powder coatings
mixed is 5.0 .mu.C/g or less. In other words, in a case, for
example, where three kinds of powder coatings A, B, and C are
mixed, each of the differences in the triboelectric charges between
A and B, between B and C, and between A and C is preferably 5.0
.mu.C/g or less. When the difference in the triboelectric charges
is 5.0 .mu.C/g or less, the concentration of the electric lines of
forces at the edge portion of the substrate to be coated can be
avoided during coating, so that those having high triboelectric
charges are unlikely to be agglomerated at the edge portion,
thereby making it possible to obtain a coating film having a
homogeneous hue.
[0222] The powder coatings usable in First Embodiment described
above have such properties that each of the powder coatings does
not have thermosetting properties alone at a temperature of
250.degree. C. or less, and is heat-cured with other powder
coatings used in combination at a temperature of 250.degree. C. or
less when mixed therewith. In other words, each of powder coatings
is melted and sufficiently uniformly mixed and then heat-cured
during the stoving process, thereby making it possible to give a
coating film having a homogenous hue.
[0223] The powder coatings usable in First Embodiment feature in
the adjustment of each of the powder coatings such that each of the
powder coatings does not have thermosetting properties alone at a
temperature of 250.degree. C. or less. Since conventionally known
powder coatings cause thermosetting reaction by themselves at a
temperature of 250.degree. C. or less, when mixing two or more
powder coatings and applying them to a substrate, the resins usable
in each of the powder coatings are fused and immediately cured
during the stoving process, so that it is practically impossible to
obtain a uniform mixture by mixing the two or more powder coatings.
Consequently, the particles in each of the powder coatings are
visualized by gross examination after curing reaction, so that the
resulting coating film does not have a homogenous hue.
[0224] By contrast, in Embodiment (1) where curing agents are not
essential, by mixing the two or more powder coatings having such
properties that each of the powder coatings does not have
thermosetting properties alone at a temperature of 250.degree. C.
or less and is heat-cured with other powder coatings used in
combination at a temperature of 250.degree. C. or less when mixed
therewith and applying the powder coatings to a substrate, the
curing reaction is not carried out until the resins usable in each
of the powder coatings are melted with each other upon stoving and
uniformly mixed, in which curing reaction one resin acts as a
curing agent for the other resin. Therefore, the resulting coating
film obtained from such powder coatings has a homogeneous hue.
[0225] On the other hand, in Embodiment (2) where curing agents are
used, a resin and a curing agent contained in a single powder
coating are selected such that they are unreactive with each other.
Therefore, no curing reaction takes place by a single powder
coating, and by fusing two or more powder coatings during stoving,
curing reaction is caused by the action of a curing agent contained
in a counterpart powder coating, so that the resulting coating film
having a homogeneous hue can be obtained. This is because the
curing agent reactive with a resin contained in one powder coating
is contained the other powder coating, which is different from
prior art where the resin and the curing agent which are reactive
with each other are contained in the same powder coating, so that
the initiation of the curing reaction may be delayed, the curing
reaction occurring only after the resins are uniformly fused with
each other.
[0226] In First Embodiment, the two or more powder coatings may be
used in combination referring to the embodiment for the combination
of the resins described above, and in the combination of these
powder coatings, it is desired that a difference in melt
viscosities of the two or more powder coatings is not more than 20
pa.multidot.s, preferably not more than 15 pa.multidot.s, more
preferably not more than 10 pa.multidot.s, at a temperature
corresponding to 90% of a curing initiation temperature of a
mixture of the two or more powder coatings of which each color is
different from the viewpoints of obtaining excellent gloss and
strength in the resulting coating film. In other words, in a case,
for example, where three kinds of powder coatings A, B, and C are
mixed, each of the differences in the melt viscosities between A
and B, between B and C, and between A and C is preferably not more
than 20 pa.multidot.s.
[0227] In the present invention, the curing initiation temperature
of the mixture of powder coatings is obtained from the kickoff of
the exothermic peak measured when using a differential scanning
calorimeter ("DSC Model 210," manufactured by Seiko Instruments,
Inc.), and heating at a heating rate of 10.degree. C./min.
[0228] In the present invention, the melt viscosities of the powder
coatings may be measured by DYNAMIC ANALYZER "RDA-II" (manufactured
by Rheometrics, Inc.) under the following measurement
conditions:
1 Geometry: Parallel plate (radius: 12.5 mm) Frequency: 62.8
rad/sec Strain: 2%
[0229] In the present invention, methods of adjusting melt
viscosities of the powder coatings include any general methods for
adjusting melt viscosities of resins. For instance, the melt
viscosities of the resins may be adjusted by controlling the
backbone structure, the molecular weight, the molecular weight
distribution, the crosslinking degree, and the like, of the resins.
Alternatively, the melt viscosities of the powder coatings may be
adjusted by adding such additives as fillers, and the like.
[0230] Second Embodiment
[0231] Second Embodiment is a combination of two or more powder
coatings where a difference between a softening point of a powder
coating having the highest softening point and a curing initiation
temperature of a mixture of the two or more powder coatings is not
less than 10.degree. C., preferably not less than 20.degree. C.,
more preferably not less than 30.degree. C.
[0232] The powder coatings usable in Second Embodiment are not
particularly limited as long as the softening point and the curing
initiation temperature are as defined in this embodiment.
Specifically, in the combinations of the two or more powder
coatings in this embodiment, not only the powder coatings in First
Embodiment are usable, but also any of conventionally employed
powder coatings are usable, to give a coating film having a
homogeneous hue. In other words, any combinations of known powder
coatings which are heat-cured alone at a temperature of 250.degree.
C. or less may be encompassed by this embodiment, provided that a
difference between a softening point of a powder coating having the
highest softening point and a curing initiation temperature of a
mixture of the two or more powder coatings is not less than
10.degree. C., to give a coating film having a homogeneous hue.
[0233] In Second Embodiment, by adjusting the difference between a
softening point of a powder coating having the highest softening
point and a curing initiation temperature of a mixture of the two
or more powder coatings within the above-specified range, each of
the powder coatings is sufficiently melted and mixed to initiate
curing reaction, so that a coating film having a homogeneous hue
can be obtained even when the powder coatings having average
particle sizes of 20 .mu.m or more are used.
[0234] The curing initiation temperature of the powder coatings may
be obtained in the same manner as described above.
[0235] The softening point of the powder coating is measured by a
method according to ASTM E28-67.
[0236] Examples of conventionally known powder coatings include
those comprising resins, curing agents, additives, colorants, and
the like. As for the resins, any of conventionally known resins may
be usable without particular limitation. Examples of the resins
include non-reactive resins, such as polyethylenes, nylon resins,
vinyl chloride, and the like; and reactive resins, such as epoxy
resins, polyester resins, acrylic resins, and the like. Among them,
preference is given to the polyester resins, the epoxy resins, and
the acrylic resins. Also, even in cases where known powder coatings
are used, it is desired that resins each having two or more
functional groups per molecule which can participate in the
thermosetting reaction are used from the viewpoint of improving the
strength of the resulting coating film.
[0237] In Second Embodiment, it is desired that the powder coatings
are stoved until the curing reaction is sufficiently terminated in
a temperature range of 70 to 130% of an exothermic peak temperature
for curing reaction of the powder coatings to be stoved.
[0238] The term "exothermic peak temperatures for curing reaction"
refers to a temperature at a peak value of the exothermic curve
measured when using a differential scanning calorimeter. Here, the
exothermic peak temperature can be obtained at a peak value of the
exothermic curve measured when using a differential scanning
calorimeter ("DSC Model 210," manufactured by Seiko Instruments,
Inc.), and heating at a heating rate of 10.degree. C./min. The time
required until the curing reaction is terminated can be obtained
from the time required for terminating the exothermic peak using
the differential scanning calorimeter set by the stoving
temperature.
[0239] As described above, there are the two embodiments in the
combination of the powder coating of the present invention. In
either embodiment, it is desired that the curing temperature of the
mixture of two or more powder coatings used in combination is less
than 250.degree. C., preferably 230.degree. C. or less, more
preferably 200.degree. C. or less, from the viewpoint of inhibition
of thermal decomposition and cost reduction.
[0240] In the present invention, the curing temperature may be
calculated from the exothermic peak top temperature measured when
the differential scanning calorimeter ("DSC Model 210,"
manufactured by Seiko Instruments, Inc.) is used, and the
temperature is raised at a heating rate of 10.degree. C./min.
[0241] Further, the present invention provides a powder coating
composition containing two or more powder coatings used in
combination as described above.
[0242] In other words, the powder coating composition of the
present invention comprises two or more powder coatings of which
each color is different, wherein each of the powder coatings fuses
with each other and is heat-cured, to thereby give a coating film
having a homogenous hue.
[0243] When the two or more powder coatings are mixed to give a
desired hue, the mixing proportions may be suitably selected
depending upon the desired hue. The methods for preparing powder
coating compositions comprising mixing powder coatings may be any
of conventionally known methods, including such dry-blending
methods using a high-speed agitator, such as a Henschel mixer and a
Super Mixer.
[0244] By mixing and applying two or more powder coatings used in
combination according to the present invention to a substrate or by
applying a powder coating composition of the present invention to a
substrate, a coating film having a homogeneous hue can be
obtained.
[0245] Incidentally, in the present specification, the term "mixing
and applying" means that the two or more powder coatings are mixed
and applied to a substrate. The term "applying" used in the present
specification refers to a series of treatments for forming a
coating film comprising applying the powder coatings to a substrate
by various methods described below, and then stoving at a
temperature of 100.degree. to 200.degree. C.
[0246] In the case where the two or more powder coatings are mixed
and applied, the powder coatings usable in the combination may be
previously mixed, or the two or more powder coatings may be applied
using an electron gun, while mixing the two or more powder
coatings. Here, the method of previously mixing the powder coatings
may be the same one as described above.
[0247] Also, the means of coating are not particularly limited, and
examples of the coating methods include coating methods using
electrostatic sprayers, fluidized bed coating methods, plastic
flame spraying methods, and the like.
[0248] The coating film and the coated substrate prepared by
applying to a substrate two or more powder coatings according to
the combination of powder coatings of the present invention each
has a homogeneous hue, even when each of powder coatings has
different color.
[0249] Next, the coating method of the present invention will be
described below.
[0250] The coating method of the present invention comprises the
steps of:
[0251] (a) applying to a substrate two or more powder coatings, of
which each color is different;
[0252] (b) heating to fuse with each other each of the two or more
powder coatings applied in step (a); and
[0253] (c) curing the resulting fused product in step (b), to give
a coating film having a homogeneous hue.
[0254] In one embodiment of the coating method of the present
invention, step (c) is carried out by heat-curing the resulting
fused product in step (b).
[0255] In this embodiment, not only the powder coatings usable in
First Embodiment but also any of generally known powder coatings
may be used. In other words, the powder coatings usable herein may
be those which may or may not be cured alone at a temperature of
250.degree. C. or less, and each of powder coatings fuses with each
other and is heat-cured in a well-melted state. In this embodiment,
in the case where the powder coatings usable in the combination of
the present invention are used, this embodiment would be
substantially the same as the embodiment for the coating method
described above, in which case it is characterized in that the
powder coatings are preheated and fused prior to thermosetting.
[0256] Step (a) in this embodiment comprises applying to a
substrate two or more of the above powder coatings, of which each
color is different. When applying these powder coatings, the powder
coatings may be previously mixed to prepare a mixture of the two or
more powder coatings, or each of powder coatings may be
independently used. The method for applying the powder coatings and
the method for previously mixing two or more powder coatings may be
the same as above. The amount of each of the powder coatings used
in mixed colors is suitably selected depending upon the desired hue
obtained by mixing colors.
[0257] Step (b) comprises heating to fuse with each other each of
the two or more powder coatings applied in step (a). In the present
invention, prior to step (c), the two or more powder coatings
applied to the substrate may be heated and fused, to thereby obtain
a coating film having a homogeneous hue.
[0258] It is desired that the heating temperature of the powder
coatings in step (b) mentioned above is less than the curing
initiation temperature of the applied powder coatings, preferably
at a temperature lower than the curing initiation temperature by
2.degree. C. or more, more preferably at a temperature lower than
the curing initiation temperature by 5.degree. C. or more, from the
aspect of fusing the powder coatings without undergoing curing
reaction and sufficiently mixing the two or more powder
coatings.
[0259] It is desired that heating of the powder coatings in step
(b) mentioned above is carried out in a length sufficient for
fusing the powder coatings. The fusing state of the powder coatings
can be determined by gross examination.
[0260] Step (c) in this embodiment comprises heat-curing the
resulting fused product in step (b), to give a coating film having
a homogeneous hue.
[0261] It is desired that step (c) mentioned above is carried out
at a temperature 70% or more, preferably 80% or more, of the
exothermic peak temperature for curing reaction from the viewpoint
of reaction efficiency, and it is desired that step (c) is carried
out at a temperature 130% or less, preferably 110% or less, of the
exothermic peak temperature for curing reaction from the viewpoint
of cost reduction and inhibition of decomposition of the
ingredients.
[0262] Here, the exothermic peak temperature for curing reaction
may be obtained by the method described above.
[0263] The time for curing the powder coatings is not particularly
limited, and it is desired that the time therefor is from 10 to 40
minutes.
[0264] In another embodiment of the coating method of the present
invention, step (c) is carried out by irradiating light to the
resulting fused product in step (b). In other words, photosetting
reaction is used in place of thermosetting reaction.
[0265] Step (a) in this embodiment comprises applying to a
substrate two or more of the above powder coatings, each of which
color is different, and this step may be carried out in the same
manner as in step (a) of one embodiment described above.
[0266] Step (b) comprises heating to fuse with each other each of
the two or more powder coatings applied in step (a). In the present
invention, the two or more powder coatings applied to the substrate
may be heated and fused prior to step (c), to thereby obtain a
coating film having a homogeneous hue.
[0267] It is desired that the heating temperature of the powder
coatings in step (b) mentioned above is 90% or more, preferably 95%
or more, of the highest softening point among the resins contained
in the powder coatings from the viewpoint of melt viscosities, and
it is desired that the heating temperature is 150% or less,
preferably 130% or less, of the highest softening point among the
resins contained in the powder coatings from the viewpoint of cost
reduction and thermal decomposition.
[0268] In the present invention, the softening points of the resins
usable in the powder coatings are measured by a method according to
ASTM E28-67.
[0269] The heating time of the powder coatings in step (b)
mentioned above is not particularly limited, and it is desired that
the heating time is from 10 to 40 minutes.
[0270] By carrying out step (b) mentioned above, the resins, the
photoinitiator, and the like can be sufficiently mixed.
[0271] Step (c) in this embodiment comprises curing the fused
product obtained in step (b) by irradiating light to the resulting
fused product, to thereby form a coating film having a homogeneous
hue.
[0272] This embodiment is advantageous in that a low-temperature
stoving can be made possible in the formation of the coating film
by utilizing photosetting reaction, which comprises curing the
powder coatings by irradiating light. As a result, the powder
coating to such materials as wood, plastics, and the like having
low heat resistance can be made possible, which in turn leads to
reduction of the running costs.
[0273] Step (c) mentioned above is carried out, for instance, by
irradiating light using an ultraviolet light (UV), an electron
beam, and the like. Among these methods, from the viewpoint of cost
reduction and handleability, preference is given to a method of
irradiating light using the ultraviolet light (UV).
[0274] In this embodiment, in the case where step (c) is carried
out by irradiating the ultraviolet light (UV), it is desired that a
photoinitiator is added to the usable powder coating together with
the additives mentioned above.
[0275] The time for curing the powder coatings is not particularly
limited, and it is desired that the time therefor is from 30
seconds to 10 minutes.
[0276] The powder coatings usable in the coating method of this
embodiment may be any of conventionally used ones without
particularly limitation, as long as the powder coatings each
comprises a resin, a photoinitiator, additives, a colorant, and the
like.
[0277] The resins usable in the powder coatings may be any of
conventionally known ones without particular limitation as long as
the resins can be cured by irradiating light. Concrete examples
thereof include polyester acrylate resins, epoxy acrylate resins,
epoxy methacrylate resins, urethane acrylate resins, polystyryl
methacrylate resins, polyether methacrylate resins, polyol resins,
and the like, among which preference is given to the epoxy acrylate
resins.
[0278] Concrete examples of the photoinitiators include benzoin
propyl ether, benzoin isopropyl ether, benzoin ethyl ether, benzil,
dimethyl ketal, isopropyl thioxanthone, 2-methyl thioxanthone,
2,4-diethyl thioxanthone, benzophenone, benzoin benzoate, and the
like, among which preference is given to benzoin isopropyl
ether.
[0279] It is desired that the amount of the photoinitiator
mentioned above is from about 1 to about 15 parts by weight, based
on 100 parts by weight of the resin.
[0280] Examples of the additives mentioned above may be the same
ones as those listed above, and it is desired that each of the
additives is added in an amount of from about 0.1 to about 5 parts
by weight, based on 100 parts by weight of the resin.
[0281] Examples of the colorants mentioned above may be the same
ones as those listed above, and it is desired that the amount of
the colorants is about 5 to 60 parts by weight, based on 100 parts
by weight of the resin.
[0282] The powder coatings usable in this embodiment may be
prepared in the same manner as above using the resins, the
photoinitiators, the additives, the colorants, and the like
mentioned above.
[0283] As for the powder coatings usable in this embodiment, those
powders having an average particle size of from 1 to 50 .mu.m,
preferably from 5 to 30 .mu.m may be used, as in the case of the
powder coatings usable in First Embodiment. In particular, it is
highly desired that the average particle size is from 10 to 20
.mu.m from the viewpoint of handleability.
[0284] Incidentally, it is desired that the powder coatings usable
in this embodiment also have their triboelectric charges controlled
in the given ranges as in the case of the powder coatings in First
Embodiment described above. It is desired that each of differences
in triboelectric charges of two or more powder coatings mixed is
5.0 .mu.C/g or less.
[0285] As described above, in various embodiments for the coating
methods of the present invention, the powder coatings are fused by
heating upon stoving and then uniformly mixing, which results in
effecting thermosettingreaction. Therefore, the coating film and
the coated substrate have a homogeneous hue, the coating film and
the coated substrate being prepared by applying to a substrate two
or more powder coatings, of which each color is different,
according to the coating method described above. In the present
invention, since a homogeneous hue can be obtained by the above
mechanisms, a homogeneous hue can be obtained even if the particle
size of the powder coatings is larger than 20 .mu.m.
[0286] According to the present invention, it is made possible to
obtain a coating film having a homogeneous hue by mixing colors of
powders having different tones. Therefore, by furnishing several
tones of powders including those with primary colors, powders with
all sorts of tones can be obtained, so that it is no longer
necessary to prepare a large number of tones as conventionally
required.
EXAMPLES
[0287] The present invention will be explained in further detail by
means of the following working examples, without intending to limit
the scope of the present invention thereto in any manner.
[0288] In the following working examples, acid values of the
resulting resins, average particle sizes and softening points of
the powder coatings, curing initiation temperatures and exothermic
peak temperatures for curing reaction of mixtures of the powder
coatings were evaluated by each of the following methods:
[0289] Acid Value
[0290] Measured by a method according to JIS K0070.
[0291] Average Particle Size
[0292] The average particle size is measured using a
Coulter-Muitisizer (manufactured by Coulter K. K.).
[0293] Softening Point
[0294] Measured by a method according to ASTM E28-67.
[0295] Curing Initiation Temperature
[0296] Obtained from the kickoff of the exothermic peak measured
when using a differential scanning calorimeter ("DSC Model 210,"
manufactured by Seiko Instruments, Inc.), and heating at a heating
rate of 10.degree. C./min.
[0297] Exothermic Peak Temperatures for Curing Reaction
[0298] Temperature obtained at the peak of the exothermic curve
measured when using a differential scanning calorimeter ("DSC Model
210," manufactured by Seiko Instruments, Inc.), and heating at a
heating rate of 10.degree. C./min.
[0299] Also, gloss, pencil hardness, and solvent resistance of the
resulting coating films were evaluated by the following
methods.
[0300] Gloss
[0301] Measured by using a glossmeter "GM-60" (manufactured by
Minolta Co., Ltd.) by a method according to ASTM 3363-74.
[0302] Pencil Hardness
[0303] Measured by a method according to JIS K5400 8.4.
[0304] Solvent Resistance
[0305] Acetone is applied to a piece of tissue paper, and the
coating film is rubbed therewith backward and forward ten times.
The thicknesses of the coating films before and after the test are
measured by a method according to JIS K5400 3.5. The solvent
resistance is evaluated as the difference of the thicknesses before
and after the test obtained above.
Resin Preparation Example 1-1
[0306] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 750 g (2 mol) of ethylene oxide adduct of
bisphenol A and 438.6 g (3 mol) of adipic acid, and the ingredients
were heated to 230.degree. C. and reacted. Thereafter, 272.4 g (2
mol) of m-xylylenediamine was added to the above mixture to form a
polyamide.
[0307] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester-polyamide resin. The resulting resin had an
amine value of 100 KOH mg/g. Here, the amine value is measured by a
method according to ASTM D2073-66. This resulting resin is referred
to as "Binder Resin 1-A."
Resin Preparation Example 1-2
[0308] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 750 g (2 mol) of ethylene oxide adduct of
bisphenol A, 166 g (1 mol) of terephthalic acid, and 292.4 g (2
mol) of adipic acid, and the ingredients were heated to 230.degree.
C. and reacted. Thereafter, 272.4 g (2 mol) of m-xylylenediamine
was added to the above mixture to form a polyamide.
[0309] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester-polyamide resin. The resulting resin had an
amine value of 80 KOH mg/g. Here, the amine value is measured by a
method according to ASTM D2073-66. This resulting resin is referred
to as "Binder Resin 1-B."
Resin Preparation Example 1-3
[0310] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 186 g (3 mol) of ethylene glycol, 728 g (7
mol) of neopentyl glycol, 1494 g (9 mol) of terephthalic acid, and
192 g (1 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0311] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 52.4 KOH mg/g. This resulting resin is referred to as
"Binder Resin 1-C."
Resin Preparation Example 1-4
[0312] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 186 g (3 mol) of ethylene glycol, 728 g (7
mol) of neopentyl glycol, and 1743 g (10.5 mol) of terephthalic
acid, and the ingredients were heated to 220.degree. C. and
reacted.
[0313] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 52.5 KOH mg/g. This resulting resin is referred to as
"Binder Resin 1-D."
Preparation Example 1-1 of Powder Coating
[0314]
2 Epoxy Resin (Solid Epoxy Resin 100 parts by weight manufactured
by Mitsui Petrochemical Industries, Ltd.) Dis-azo Yellow ("PIGMENT
YELLOW ECY-210," 8 parts by weight manufactured by Dainichiseika
Color & Chemicals MFG. Co., Ltd.) Levelling Agent ("ACRONAL
4F," 1 part by weight manufactured by BASF)
[0315] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 27 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-1).
Preparation Example 1-2 of Powder Coating
[0316]
3 Polyester-Polyamide Resin 100 parts by weight (Binder Resin 1-A;
amine value: 100 KOH mg/g) Carmine 6B ("SUMIKAPRINT CARMINE 6BC," 8
parts by weight manufactured by Sumitomo Chemical Co., Ltd.)
Levelling Agent ("ACRONAL 4F," 1 part by weight manufactured by
BASF)
[0317] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 29 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-2).
Preparation Example 1-3 of Powder Coating
[0318]
4 Polyester-Polyamide Resin 100 parts by weight (Binder Resin 1-B;
amine value: 80 KOH mg/g) Copper Phthalocyanine 6 parts by weight
("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS, LTD.)
Levelling Agent ("ACRONAL 4F," 1 part by weight manufactured by
BASF)
[0319] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 28 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-3).
Preparation Example 1-4 of Powder Coating
[0320]
5 Polyester Resin ("ER-8107," 40 parts by weight manufactured by
Nippon Ester Co., Ltd., acid value = 32.5 KOH mg/g) Polyester Resin
("ER-8100," 54 parts by weight manufactured by Nippon Ester Co.,
Ltd., acid value = 65.8 KOH mg/g) TGIC ("ARALDITE PT810," 18 parts
by weight manufactured by Ciba Geigy AG) Dis-azo Yellow ("PIGMENT
YELLOW ECY-210," 8 parts by weight manufactured by Dainichiseika
Color & Chemicals MFG. Co., Ltd.) Levelling Agent ("ACRONAL
4F," 1 part by weight manufactured by BASF) Benzoin 0.5 parts by
weight
[0321] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 27 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-4).
Preparation Example 1-5 of Powder Coating
[0322]
6 Polyester Resin ("ER-8107," 40 parts by weight manufactured by
Nippon Ester Co., Ltd., acid value = 32.5 KOH mg/g) Polyester Resin
("ER-8100," 54 parts by weight manufactured by Nippon Ester Co.,
Ltd., acid value = 65.8 KOH mg/g) TGIC ("ARALDITE PT810," 18 parts
by weight manufactured by Ciba Geigy AG) Carmine 6B ("SUMIKAPRINT
CARMINE 6BC," 8 parts by weight manufactured by Sumitomo Chemical
Co., Ltd.) Levelling Agent ("ACRONAL 4F," 1 part by weight
manufactured by BASF) Benzoin 0.5 parts by weight
[0323] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 28 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-5).
Preparation Example 1-6 of Powder Coating
[0324]
7 Polyester Resin ("ER-8107," 40 parts by weight manufactured by
Nippon Ester Co., Ltd., acid value = 32.5 KOH mg/g) Polyester Resin
("ER-8100," 54 parts by weight manufactured by Nippon Ester Co.,
Ltd., acid value = 65.8 KOH mg/g) TGIC ("ARALDITE PT810," 18 parts
by weight manufactured by Ciba Geigy AG) Copper Phthalocyanine 6
parts by weight ("CYANINE BLUE-KRS," manufactured by SANYO COLOR
WORKS, LTD.) Levelling Agent ("ACRONAL 4F," 1 part by weight
manufactured by BASF) Benzoin 0.5 parts by weight
[0325] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 29 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-6).
Preparation Example 1-7 of Powder Coating
[0326]
8 Epoxy Resin (Solid Epoxy Resin 100 parts by weight manufactured
by Mitsui Petrochemical Industries, Ltd.) Melamine Compound
("Resimene 747," 39 parts by weight manufactured by Monsanto)
Carmine 6B ("SUMIKAPRINT CARMINE 6BC," 8 parts by weight
manufactured by Sumitomo Chemical Co., Ltd.) Levelling Agent
("ACRONAL 4F," 1 part by weight manufactured by BASF)
[0327] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 29 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-7).
Preparation Example 1-8 of Powder Coating
[0328]
9 Polyester Resin ("ER-6620," 100 parts by weight manufactured by
Nippon Ester Co., Ltd., acid value = 0.8 KOH mg/g, hydroxyl value =
42.9 KOH mg/g) Dihydrazide adipate 9 parts by weight Dis-azo Yellow
("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("ACRONAL 4F," 1 part by weight manufactured by BASF)
[0329] The same procedures as in Preparation Example 1-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 28 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-8).
Preparation Example 1-9 of Powder Coating
[0330]
10 Epoxy Resin ("EPICOAT 1044AF," 100 parts by weight manufactured
by YUKA SHELL EPOXY KABUSHIKI KAISHA) Dis-azo Yellow ("PIGMENT
YELLOW ECY-210," 8 parts by weight manufactured by Dainichiseika
Color & Chemicals MFG. Co., Ltd.) Levelling Agent ("ACRONAL
4F," 1 part by weight manufactured by BASF)
[0331] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 25 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-9).
Preparation Example 1-10 of Powder Coating
[0332]
11 Polyester Resin 100 parts by weight (Binder Resin 1-C) Carmine
6B ("SUMIKAPRINT CARMINE 6BC," 8 parts by weight manufactured by
Sumitomo Chemical Co., Ltd.) Levelling Agent ("ACRONAL 4F," 1 part
by weight manufactured by BASF)
[0333] The same procedures as in Preparation Example 1-9 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 25 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (1-10).
Preparation Example 1-11 of Powder Coating
[0334] The same procedures as in Preparation Example 1-10 of Powder
Coating were carried out except for using Binder Resin 1-D in place
of Binder Resin 1-C for a polyester resin, to give a powder having
an average particle size of 28 .mu.m. To 100 parts by weight of the
resulting powder, 0.3 parts by weight of silica "AEROSIL R972"
(manufactured by Nippon Aerosil Co., Ltd.) were added, and the
mixture was uniformly blended using a Henschel mixer, to give
Powder Coating (1-11).
Preparation Example 1-12 of Powder Coating
[0335] The same procedures as in Preparation Example 1-10 of Powder
Coating were carried out except for using "ER-8123" (manufactured
by Nippon Ester Co., Ltd.) in place of Binder Resin 1-C for a
polyester resin, to give a powder having an average particle size
of 28 .mu.m. To 100 parts by weight of the resulting powder, 0.3
parts by weight of silica "AEROSIL R972" (manufactured by Nippon
Aerosil Co., Ltd.) were added, and the mixture was uniformly
blended using a Henschel mixer, to give Powder Coating (1-12).
Example 1-1
[0336] 50 parts by weight of Powder Coating (1-1) and 50 parts by
weight of Powder Coating (1-2) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous vermilion color.
Example 1-2
[0337] 50 parts by weight of Powder Coating (1-1) and 50 parts by
weight of Powder Coating (1-3) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
Example 1-3
[0338] 50 parts by weight of Powder Coating (1-7) and 50 parts by
weight of Powder Coating (1-8) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film was homogeneous vermilion color.
Example 1-4
[0339] 50 parts by weight of Powder Coating (1-1) and 50 parts by
weight of Powder Coating (1-2) were blended using a Henschel mixer
to prepare a powder coating composition. After a six-month period
storage (under conditions of ambient temperature, normal pressure,
and normal humidity), in the same manner as in Example 1-1, the
resulting composition was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film was homogeneous vermilion color, as in the case
of Example 1-1.
Example 1-5
[0340] 50 parts by weight of Powder Coating (1-9) and 50 parts by
weight of Powder Coating (1-10) were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
167.degree. C. Also, the melt viscosities of each of the powder
coatings at 150.degree. C., the temperature corresponding to 90% of
the curing initiation temperature, were 5 pa.multidot.s and 15
pa.multidot.s, respectively, the difference thereof being 10
pa.multidot.s. The resulting mixture was applied to a degreased
steel substrate using an electrostatic sprayer, and the coated
steel substrate was stoved at 180.degree. C. for 20 minutes to form
a coating film. The formed coating film was homogeneous vermilion
color.
[0341] The resulting coating film had a gloss of 76, and a pencil
hardness of 2H.
Example 1-6
[0342] 50 parts by weight of Powder Coating (1-9) and 50 parts by
weight of Powder Coating (1-11) were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
167.degree. C. Also, the melt viscosities of each of the powder
coatings at 150.degree. C., the temperature corresponding to 90% of
the curing initiation temperature, were 5 pa.multidot.s and 11
pa.multidot.s, respectively, the difference thereof being 6
pa.multidot.s. The resulting mixture was applied to a degreased
steel substrate using an electrostatic sprayer, and the coated
steel substrate was stoved at 180.degree. C. for 20 minutes to form
a coating film. The formed coating film was homogeneous vermilion
color.
[0343] The resulting coating film had a gloss of 82, and a pencil
hardness of H.
Example 1-7
[0344] 50 parts by weight of Powder Coating (1-9) and 50 parts by
weight of Powder Coating (1-12) were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
167.degree. C. Also, the melt viscosities of each of the powder
coatings at 150.degree. C., the temperature corresponding to 90% of
the curing initiation temperature, were 5 pa.multidot.s and 34
pa.multidot.s, respectively, the difference thereof being 29
pa.multidot.s. The resulting mixture was applied to a degreased
steel substrate using an electrostatic sprayer, and the coated
steel substrate was stoved at 180.degree. C. for 20 minutes to form
a coating film. The formed coating film was homogeneous vermilion
color.
[0345] The resulting coating film had a gloss of 50, and a pencil
hardness of HB, having somewhat poorer gloss and pencil hardness
when compared with those of Examples 1-5 and 1-6.
Comparative Example 1-1
[0346] 50 parts by weight of Powder Coating (1-4) and 50 parts by
weight of Powder Coating (1-5) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate in
the same manner as in Example 1-1 to form a coating film. The
resulting coating film had an uneven vermilion color.
Comparative Example 1-2
[0347] 50 parts by weight of Powder Coating (1-4) and 50 parts by
weight of Powder Coating (1-6) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate in
the same manner as in Example 1-1 to form a coating film. The
resulting coating film had an uneven green color.
[0348] As is clear from the above results in Examples 1-1 to 1-7
and Comparative Examples 1-1 and 1-2, in the case of Comparative
Examples 1-1 and 1-2 where two powder coatings each containing a
polyester resin are blended and applied, no homogeneous hues can be
obtained in the resulting coating film because each of the powder
coatings is independently cured. On the other hand, in the case of
Examples 1-1 to 1-7 where a powder coating containing an epoxy
resin and a powder coating containing a polyester-polyamide resin
or a polyester resin are blended and applied, each of the powder
coatings does not have thermosetting properties alone, and each of
the powder coatings is melted and sufficiently blended and then
heat-cured during the stoving process to carry out curing reaction,
thereby making it possible to give a coating film having a
homogeneous hue. Also, in the case of Example 1-3 where a powder
coating comprises the resin and a curing agent, a coating film with
a homogeneous hue can be obtained. Further, even in a case of
Example 1-4 where a composition comprising two powder coatings is
used, a coating film with a homogeneous hue can be similarly
obtained. Moreover, in cases of Examples 1-5 and 1-6, since the
differences in the melt viscosities at a temperature of 90% of the
curing initiation temperature of the mixture of the usable coating
powders are adjusted within 20 pa.multidot.s, coating films with
further improved gloss and pencil hardness can be obtained when
compared with Example 1-7.
Resin Preparation Example 2-1
[0349] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 124 g (2 mol) of ethylene glycol, 520 g (5
mol) of neopentyl glycol, 830 g (5 mol) of terephthalic acid, and
1152 g (6 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0350] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 83.4 KOH mg/g.
[0351] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2800) and the
acid value was 4.2. This resulting resin is referred to as "Binder
Resin 2-A."
[0352] Incidentally, the number-average molecular weight and the
number of functional groups per molecule were obtained by methods
detailed below.
[0353] Number-Average Molecular Weight
[0354] Measured by GPC. More concretely, a column
("GMHXL+G3000HXL," manufactured by Tosoh Corporation) is stabilized
in a thermostat at 40.degree. C. Chloroform was flowed as an eluent
through the column at a flow rate of 1 ml/minute, and 100 .mu.l of
a chloroform solution of a sample adjusted to a sample
concentration of from 0.05 to 0.5% by weight was poured into the
column to measure molecular weight distribution. The number-average
molecular weight of the sample was calculated from the retention
time of the peaks based on the calibration curve obtained by using
several monodisperse polystyrenes as standards.
[0355] Number of Functional Groups
[0356] The number of functional groups per molecule is calculated
from the number of moles of functional groups per gram obtained
from the acid value (KOH mg/g) and the number of moles per gram
obtained from the number-average molecular weight. Specifically, as
shown below, using A and B values obtained below from Equations (1)
and (2), the number of functional groups per molecule can be
calculated by Equation (3).
A(mol/g)=Acid Value(KOH mg/g)/56100 (1)
B(mol/g)=1/Number-Average Molecular Weight (2)
Number of Function Groups=A/B (3)
Resin Preparation Example 2-2
[0357] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 124 g (2 mol) of ethylene glycol, 520 g (5
mol) of neopentyl glycol, 830 g (5 mol) of terephthalic acid, and
768 g (4 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0358] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 66.4 KOH mg/g.
[0359] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2700) and the
acid value was 3.6. This resulting resin is referred to as "Binder
Resin 2-B."
Resin Preparation Example 2-3
[0360] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 124 g (2 mol) of ethylene glycol, 520 g (5
mol) of neopentyl glycol, 1743 g (9 mol) of isophthalic acid, and
576 g (3 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0361] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached
100.degree. C., to give a polyester resin. The resulting resin had
an acid value of 52.5 KOH mg/g.
[0362] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2570) and the
acid value was 2.4. This resulting resin is referred to as "Binder
Resin 2-C."
Resin Preparation Example 2-4
[0363] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 155 g (2.5 mol) of ethylene glycol, 624 g (6
mol) of neopentyl glycol, 134 g (1 mol) of trimethylolpropane, and
1660 g (10 mol) of terephthalic acid, and the ingredients were
heated to 220.degree. C. and reacted.
[0364] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 95.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 53.1 KOH mg/g.
[0365] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2770) and the
acid value was 2.6. This resulting resin is referred to as "Binder
Resin 2-D."
Resin Preparation Example 2-5
[0366] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 124 g (2 mol) of ethylene glycol, 520 g (5
mol) of neopentyl glycol, and 1660 g (10 mol) of terephthalic acid,
and the ingredients were heated to 220.degree. C. and reacted.
[0367] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 44.5 KOH mg/g.
[0368] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2020) and the
acid value was 1.6. This resulting resin is referred to as "Binder
Resin 2-E."
Resin Preparation Example 2-6
[0369] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 124 g (2 mol) of ethylene glycol, 520 g (5
mol) of neopentyl glycol, 1494 g (9 mol) of terephthalic acid, and
192 g (1 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0370] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 90.degree.
C., to give a polyester resin. The resulting resin had an acid
value of 43.6 KOH mg/g.
[0371] Also, the number of functional groups per molecule
calculated from the number-average molecular weight (2300) and the
acid value was 1.8. This resulting resin is referred to as "Binder
Resin 2-F."
Preparation Example 2-1 of Powder Coating
[0372]
12 Epoxy Resin ("EPICOAT 1003F," 100 parts by weight manufactured
by YUKA SHELL EPOXY KABUSHIKI KAISHA) Copper Phthalocyanine 8 parts
by weight ("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS,
LTD.) Levelling Agent ("MODAFLOW POWDER 2000," 1 part by weight
manufactured by Monsanto)
[0373] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 24 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-1).
[0374] Incidentally, the number of functional groups per molecule
of the epoxy resin used, as calculated from the number-average
molecular weight (1559) and the epoxy equivalency (768 g/equiv),
was 2.0.
Preparation Example 2-2 of Powder Coating
[0375]
13 Polyester Resin 100 parts by weight (Binder Resin 2-A) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0376] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-2).
Preparation Example 2-3 of Powder Coating
[0377]
14 Polyester Resin 100 parts by weight (Binder Resin 2-B) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0378] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 26 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-3).
Preparation Example 2-4 of Powder Coating
[0379]
15 Polyester Resin 100 parts by weight (Binder Resin 2-C) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0380] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 27 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-4).
Preparation Example 2-5 of Powder Coating
[0381]
16 Polyester Resin 100 parts by weight (Binder Resin 2-D) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0382] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 25 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-5).
Preparation Example 2-6 of Powder Coating
[0383]
17 Polyester Resin 100 parts by weight (Binder Resin 2-E) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0384] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 22 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-6).
Preparation Example 2-7 of Powder Coating
[0385]
18 Polyester Resin 100 parts by weight (Binder Resin 2-F) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0386] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 28 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-7).
Preparation Example 2-8 of Powder Coating
[0387]
19 Epoxy Resin ("EPICOAT 1055," 100 parts by weight manufactured by
YUKA SHELL EPOXY KABUSHIKI KAISHA) Copper Phthalocyanine 8 parts by
weight ("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS,
LTD.) Levelling Agent ("MODAFLOW POWDER 2000," 1 part by weight
manufactured by Monsanto)
[0388] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 26 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (2-8).
[0389] Incidentally, the number of functional groups per molecule
of the epoxy resin used, as calculated from the number-average
molecular weight (1607) and the epoxy equivalency (872 g/equiv),
was 1.8.
Example 2-1
[0390] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-2) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0391] The resulting coating film had a pencil hardness of 2H and a
solvent resistance of 0 .mu.m.
Example 2-2
[0392] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-3) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0393] The resulting coating film had a pencil hardness of 2H and a
solvent resistance of 0 .mu.m.
Example 2-3
[0394] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-4) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0395] The resulting coating film had a pencil hardness of H and a
solvent resistance of -1 .mu.m.
Example 2-4
[0396] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-5) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0397] The resulting coating film had a pencil hardness of H and a
solvent resistance of -1 .mu.m.
Example 2-5
[0398] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-6) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0399] The resulting coating film had a pencil hardness of B and a
solvent resistance of -17 .mu.m.
Example 2-6
[0400] 50 parts by weight of Powder Coating (2-1) and 50 parts by
weight of Powder Coating (2-7) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color.
[0401] The resulting coating film had a pencil hardness of B and a
solvent resistance of -10 .mu.m.
Example 2-7
[0402] 50 parts by weight of Powder Coating (2-8) and 50 parts by
weight of Powder Coating (2-2) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film was homogeneous green color.
[0403] The resulting coating film had a pencil hardness of HB and a
solvent resistance of -7 .mu.m.
Example 2-8
[0404] 50 parts by weight of Powder Coating (2-7) and 50 parts by
weight of Powder Coating (2-8) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film was homogeneous green color.
[0405] The resulting coating film had a pencil hardness of 2B and a
solvent resistance of -30 .mu.m.
[0406] As is clear from the above results in Examples 2-1 to 2-8,
when the powder coatings containing two or more functional groups
per molecule which can participate in the thermosetting reaction
are used, it is found that the coating films having excellent
pencil hardness and solvent resistance can be obtained.
Resin Preparation Example 3-1
[0407] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 155 g (2.5 mol) of ethylene glycol, 624 g (6
mol) of neopentyl glycol, 134 g (1 mol) of trimethylolpropane, and
1743 g (10.5 mol) of terephthalic acid, and the ingredients were
heated to 220.degree. C. and reacted.
[0408] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 95.degree.
C. The resulting resin had an acid value of 52.9 KOH mg/g. This
resulting resin is referred to as "Binder Resin 3-A."
Resin Preparation Example 3-2
[0409] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 186 g (3 mol) of ethylene glycol, 728 g (7
mol) of neopentyl glycol, 1743 g (9 mol) of isophthalic acid, and
1920 g (10 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0410] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached
100.degree. C. The resulting resin had an acid value of 52.0 KOH
mg/g. This resulting resin is referred to as "Binder Resin
3-B."
Preparation Example 3-1 of Powder Coating
[0411]
20 Epoxy Resin ("EPICOAT 1003F," 100 parts by weight manufactured
by YUKA SHELL EPOXY KABUSHIKI KAISHA) Copper Phthalocyanine 8 parts
by weight ("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS,
LTD.) Levelling Agent ("MODAFLOW POWDER 2000," 1 part by weight
manufactured by Monsanto)
[0412] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (3-1). Powder Coating (3-1) had a
softening point of 98.degree. C.
Preparation Example 3-2 of Powder Coating
[0413]
21 Polyester Resin 100 parts by weight (Binder Resin 3-A) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0414] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (3-2). Powder Coating (3-2) had a
softening point of 93.degree. C.
Preparation Example 3-3 of Powder Coating
[0415] The same procedures as in Preparation Example 3-1 of Powder
Coating were carried out except for using "EPICOAT 1004AF"
(manufactured by YUKA SHELL EPOXY KABUSHIKI KAISHA) in place of
"EPICOAT 1003F" (manufactured by YUKA SHELL EPOXY KABUSHIKI KAISHA)
for an epoxy resin, to give a powder having an average particle
size of 23 .mu.m. To 100 parts by weight of the resulting powder,
0.3 parts by weight of silica "AEROSIL R972" (manufactured by
Nippon Aerosil Co., Ltd.) were added, and the mixture was uniformly
blended using a Henschel mixer, to give Powder Coating (3-3).
Powder Coating (3-3) had a softening point of 99.degree. C.
Preparation Example 3-4 of Powder Coating
[0416] The same procedures as in Preparation Example 3-2 of Powder
Coating were carried out except for using Binder Resin 3-B in place
of Binder Resin 3-A for a polyester resin, to give a powder having
an average particle size of 22 .mu.m. To 100 parts by weight of the
resulting powder, 0.3 parts by weight of silica "AEROSIL R972"
(manufactured by Nippon Aerosil Co., Ltd.) were added, and the
mixture was uniformly blended using a Henschel mixer, to give
Powder Coating (3-4). Powder Coating (3-4) had a softening point of
101.degree. C.
Preparation Example 3-5 of Powder Coating
[0417]
22 Polyester Resin 100 parts by weight (Binder Resin 3-A) TGIC
("ARALDITE PT810," 15 parts by weight manufactured by Ciba Geigy
AG) Copper Phthalocyanine 8 parts by weight ("CYANINE BLUE-KRS,"
manufactured by SANYO COLOR WORKS, LTD.) Levelling Agent ("MODAFLOW
POWDER 1 part by weight 2000," manufactured by Monsanto) Benzoin
0.5 parts by weight
[0418] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (3-5). Powder Coating (3-5) had a
softening point of 97.degree. C.
Preparation Example 3-6 of Powder Coating
[0419] The same procedures as in Preparation Example 3-5 of Powder
Coating were carried out except for using Dis-azo Yellow ("PIGMENT
YELLOW ECY-210," manufactured by Dainichiseika Color &
Chemicals MFG. Co., Ltd.) in place of Copper Phthalocyanine
("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS, LTD.)
[0420] for a pigment, to give a powder having an average particle
size of 23 .mu.m. To 100 parts by weight of the resulting powder,
0.3 parts by weight of silica "AEROSIL R972" (manufactured by
Nippon Aerosil Co., Ltd.) were added, and the mixture was uniformly
blended using a Henschel mixer, to give Powder Coating (3-6).
Powder Coating (3-6) had a softening point of 97.degree. C.
Preparation Example 3-7 of Powder Coating
[0421] The same procedures as in Preparation Example 3-1 of Powder
Coating were carried out except for using "YDCN-704" (manufactured
by TOHTO KASEI CO., LTD.) in place of "EPICOAT 1003F" (manufactured
by YUKA SHELL EPOXY KABUSHIKI KAISHA) for an epoxy resin, to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (3-7). Powder Coating (3-7) had a
softening point of 96.degree. C.
Preparation Example 3-8 of Powder Coating
[0422] The same procedures as in Preparation Example 3-6 of Powder
Coating were carried out except for using Binder Resin 3-B in place
of Binder Resin 3-A for a polyester resin, to give a powder having
an average particle size of 23 .mu.m. To 100 parts by weight of the
resulting powder, 0.3 parts by weight of silica "AEROSIL R972"
(manufactured by Nippon Aerosil Co., Ltd.) were added, and the
mixture was uniformly blended using a Henschel mixer, to give
Powder Coating (3-8). Powder Coating (3-8) had a softening point of
100.degree. C.
Example 3-1
[0423] 50 parts by weight of Powder Coating (3-1) [softening point:
98.degree. C.] and 50 parts by weight of Powder Coating (3-2)
[softening point: 93.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
135.degree. C., and the difference between the softening point of
Powder Coating (3-1), the higher softening point, and the curing
initiation temperature of the resulting mixture was 37.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color. Incidentally,
the resulting mixture had an exothermic peak temperature for curing
reaction of 175.degree. C.
[0424] Also, by using a differential scanning calorimeter "DSC
Model 210" (manufactured by Seiko Instruments, Inc.), since an
exothermic peak, obtained after raising the temperature from room
temperature to 180.degree. C. and then keeping at 180.degree. C.,
disappeared in no more than 15 minutes from initiation of the
temperature rise, it is considered that the curing reaction is
sufficiently terminated under the above stoving conditions.
[0425] The resulting coating film had a gloss of 80 and a pencil
hardness of H.
Example 3-2
[0426] 50 parts by weight of Powder Coating (3-3) [softening point:
99.degree. C.] and 50 parts by weight of Powder Coating (3-4)
[softening point: 101.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
148.degree. C., and the difference between the softening point of
Powder Coating (3-4), the higher softening point, and the curing
initiation temperature of the resulting mixture was 47.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color. Incidentally,
the resulting mixture had an exothermic peak temperature for curing
reaction of 184.degree. C.
[0427] The resulting coating film had a gloss of 89 and a pencil
hardness of 2H.
Example 3-3
[0428] 50 parts by weight of Powder Coating (3-1) [softening point:
98.degree. C.] and 50 parts by weight of Powder Coating (3-4)
[softening point: 101.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
133.degree. C., and the difference between the softening point of
Powder Coating (3-4), the higher softening point, and the curing
initiation temperature of the resulting mixture was 32.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color. Incidentally,
the resulting mixture had an exothermic peak temperature for curing
reaction of 176.degree. C.
[0429] The resulting coating film had a gloss of 86 and a pencil
hardness of H.
Example 3-4
[0430] 50 parts by weight of Powder Coating (3-5) [softening point:
97.degree. C.] and 50 parts by weight of Powder Coating (3-6)
[softening point: 97.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
108.degree. C., and the difference between the softening point of
Powder Coating (3-5) and Powder Coating (3-6) and the curing
initiation temperature of the resulting mixture was 11.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had a homogeneous green color. Incidentally,
the resulting mixture had an exothermic peak temperature for curing
reaction of 148.degree. C.
[0431] The resulting coating film had a gloss of 88 and a pencil
hardness of 2H.
Comparative Example 3-1
[0432] 50 parts by weight of Powder Coating (3-2) [softening point:
93.degree. C.] and 50 parts by weight of Powder Coating (3-7)
[softening point: 96.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
100.degree. C., and the difference between the softening point of
Powder Coating (3-7), the higher softening point, and the curing
initiation temperature of the resulting mixture was 4.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had an inhomogeneous hue to be confirmed to
have yellow particles and cyan particles.
[0433] The resulting coating film had a gloss of 70 and a pencil
hardness of HB.
Comparative Example 3-2
[0434] 50 parts by weight of Powder Coating (3-4) [softening point:
101.degree. C.] and 50 parts by weight of Powder Coating (3-7)
[softening point: 96.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
105.degree. C., and the difference between the softening point of
Powder Coating (3-4), the higher softening point, and the curing
initiation temperature of the resulting mixture was 4.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had an inhomogeneous hue to be confirmed to
have yellow particles and cyan particles.
[0435] The resulting coating film had a gloss of 61 and a pencil
hardness of H.
Comparative Example 3-3
[0436] 50 parts by weight of Powder Coating (3-5) [softening point:
97.degree. C.] and 50 parts by weight of Powder Coating (3-8)
[softening point: 100.degree. C.] were blended using a Henschel
mixer. The resulting mixture had a curing initiation temperature of
108.degree. C., and the difference between the softening point of
Powder Coating (3-8), the higher softening point, and the curing
initiation temperature of the resulting mixture was 8.degree. C.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had an inhomogeneous hue to be confirmed to
have yellow particles and cyan particles.
[0437] The resulting coating film had a gloss of 80 and a pencil
hardness of 2H.
[0438] As is clear from above results in Examples 3-1 to 3-4 and
Comparative Examples 3-1 to 3-3, since a difference between the
softening point of the powder coating having the highest softening
point and a curing initiation temperature of a mixture of two or
more powder coatings is not less than -10.degree. C., in Examples
3-1 to 3-4, each of the resulting coating films has a homogeneous
hue, and also has excellent gloss and pencil hardness. On the other
hand, in Comparative Examples 3-1 to 3-3, since the difference is
less than 10.degree. C., each of the resulting coating films having
a homogeneous hue cannot be obtained, though sufficient levels in
gloss and pencil hardness can be obtained.
Resin Preparation Example 4-1
[0439] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 155 g (2.5 mol) of ethylene glycol, 624 g (6
mol) of neopentyl glycol, 134 g (1 mol) of trimethylolpropane, and
1743 g (10.5 mol) of terephthalic acid, and the ingredients were
heated to 220.degree. C. and reacted.
[0440] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached 95.degree.
C. The resulting resin had an acid value of 52.9 KOH mg/g. This
resulting resin is referred to as "Binder Resin 4-A."
Resin Preparation Example 4-2
[0441] A three-liter four-necked flask equipped with a thermometer,
a stainless stirring rod, a reflux condenser, and a nitrogen inlet
tube was charged with 186 g (3 mol) of ethylene glycol, 728 g (7
mol) of neopentyl glycol, 1743 g (9 mol) of isophthalic acid, and
1920 g (10 mol) of trimellitic anhydride, and the ingredients were
heated to 220.degree. C. and reacted.
[0442] The degree of polymerization was monitored from a softening
point measured by the method according to ASTM E28-67, and the
reaction was terminated when the softening point reached
100.degree. C. The resulting resin had an acid value of 52.0 KOH
mg/g. This resulting resin is referred to as "Binder Resin
4-B."
Preparation Example 4-1 of Powder Coating
[0443]
23 Epoxy Resin ("YDCN-704," 100 parts by weight manufactured by
TOHTO KASEI CO., LTD.) Copper Phthalocyanine 8 parts by weight
("CYANINE BLUE-KRS," manufactured by SANYO COLOR WORKS, LTD.)
Levelling Agent ("MODAFLOW POWDER 2000," 1 part by weight
manufactured by Monsanto)
[0444] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (4-1). Powder Coating (4-1) had a
softening point of 96.degree. C.
Preparation Example 4-2 of Powder Coating
[0445]
24 Polyester Resin 100 parts by weight (Binder Resin 4-A) Dis-azo
Yellow ("PIGMENT YELLOW ECY-210," 8 parts by weight manufactured by
Dainichiseika Color & Chemicals MFG. Co., Ltd.) Levelling Agent
("MODAFLOW POWDER 2000," 1 part by weight manufactured by
Monsanto)
[0446] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (4-2). Powder Coating (4-2) had a
softening point of 93.degree. C.
Preparation Example 4-3 of Powder Coating
[0447]
25 Polyester Resin 100 parts by weight (Binder Resin 4-A) TGIC
("ARALDITE PT810," 15 parts by weight manufactured by Ciba Geigy
AG) Copper Phthalocyanine 8 parts by weight ("CYANINE BLUE-KRS,"
manufactured by SANYO COLOR WORKS, LTD.) Levelling Agent ("MODAFLOW
POWDER 1 part by weight 2000," manufactured by Monsanto) Benzoin
0.5 parts by weight
[0448] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (4-3). Powder Coating (4-3) had a
softening point of 97.degree. C.
Preparation Example 4-4 of Powder Coating
[0449]
26 Polyester Resin 100 parts by weight (Binder Resin 4-B) TGIC
("ARALDITE PT810," 15 parts by weight manufactured by Ciba Geigy
AG) Dis-azo Yellow ("PIGMENT YELLOW 8 parts by weight ECY-210,"
manufactured by Dainichiseika Color & Chemicals MFG. Co., Ltd.)
Levelling Agent ("MODAFLOW POWDER 1 part by weight 2000,"
manufactured by Monsanto) Benzoin 0.5 parts by weight
[0450] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23 .mu.m. To 100 parts by
weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (4-4). Powder Coating (4-4) had a
softening point of 100.degree. C.
Example 4-1
[0451] 50 parts by weight of Powder Coating (4-1) and 50 parts by
weight of Powder Coating (4-2) were blended using a Henschel mixer,
and the resulting mixture was applied to a degreased steel
substrate using an electrostatic sprayer, and the coated steel
substrate was kept standing at 98.degree. C. for 10 minutes to
sufficiently heat and melt the applied powder coatings. Thereafter,
the coated steel substrate was stoved at 180.degree. C. for 20
minutes to form a coating film. The formed coating film had a
homogeneous green color. Incidentally, the applied powder coatings
had a curing initiation temperature of 100.degree. C. and an
exothermic peak temperature for curing reaction of 160.degree.
C.
[0452] The resulting coating film had a gloss of 90 and a pencil
hardness of H.
Example 4-2
[0453] 50 parts by weight of Powder Coating (4-3) and 50 parts by
weight of Powder Coating (4-4) were blended using a Henschel mixer,
and the resulting mixture was applied to a degreased steel
substrate using an electrostatic sprayer, and the coated steel
substrate was kept standing at 104.degree. C. for 20 minutes to
sufficiently heat and melt the applied powder coatings. Thereafter,
the coated steel substrate was stoved at 180.degree. C. for 20
minutes to form a coating film. The formed coating film had a
homogeneous green color. Incidentally, the applied powder coatings
had a curing initiation temperature of 108.degree. C. and an
exothermic peak temperature for curing reaction of 145.degree.
C.
[0454] The resulting coating film had a gloss of 90 and a pencil
hardness of 2H.
Comparative Example 4-1
[0455] 50 parts by weight of Powder Coating (4-1) and 50 parts by
weight of Powder Coating (4-2) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had an inhomogeneous hue, a part of which
yellow particles and cyan particles were observed.
[0456] The resulting coating film had a gloss of 70 and a pencil
hardness of HB.
Comparative Example 4-2
[0457] 50 parts by weight of Powder Coating (4-3) and 50 parts by
weight of Powder Coating (4-4) were blended using a Henschel mixer.
The resulting mixture was applied to a degreased steel substrate
using an electrostatic sprayer, and the coated steel substrate was
stoved at 180.degree. C. for 20 minutes to form a coating film. The
formed coating film had an inhomogeneous hue to be confirmed by
gloss to have yellow particles and cyan particles.
[0458] The resulting coating film had a gloss of 80 and a pencil
hardness of 2H.
[0459] As is clear from the above results in Examples 4-1 and 4-2
and Comparative Examples 4-1 and 4-2, when compared with
Comparative Examples 4-1 and 4-2 where the applied powder coatings
to form a coating film are directly stoved, in Examples 4-1 and
4-2, since the coating film is formed by heating and melting the
applied powder coatings, and then stoving the powder coatings to
carry out curing reaction, the resulting coating film has a
homogeneous hue and also has excellent gloss and pencil
hardness.
Preparation Example 5-1 of Powder Coating
[0460]
27 Epoxy Acrylate Resin ("RIPOXY VR-40," 98 parts by weight
manufactured by Showa Kobunshi; softening point: 75.degree. C.)
Benzoin Isopropyl Ether 2 parts by weight ("NISSOCURE IBPO,"
manufactured by Nippon Soda Co., Ltd.) Titanium Oxide ("TIPAQUE
CR-90," 30 parts by weight manufactured by ISHIHARA SANGYO KAISHA,
LTD.) Levelling Agent ("ACRONAL 4F," 1 part by weight manufactured
by BASF)
[0461] The above components were previously blended using a Super
Mixer, and the resulting mixture was kneaded using a Buss
Ko-kneader (manufactured by Buss (Japan) Ltd.). The kneaded mixture
was cooled, the cooled product was pulverized using a pulverizer
"PJM" (manufactured by Nippon Pneumatic MFG, Co., Ltd.), to give a
powder having an average particle size of 23.7 .mu.m. To 100 parts
by weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (5-1).
[0462] Incidentally, the softening points of the epoxy acrylate
resins used in each of Powder Coatings (5-1) to (5-3) are measured
by a method according to ASTM E28-67.
[0463] Powder Coating (5-1) was applied to a degreased steel plate
using an electrostatic sprayer. A capacitor having an electric
capacitance (C) of 0.047 pF was connected between the coating
object and the ground. The powder coating applied to the surface of
the object was removed by air-blowing. The mass (M) of the powder
coating removed from the coating surface was obtained by measuring
the masses of the coating object before and after the removal of
powder coating, and calculating the difference of the masses. The
mass (M) was found to be 0.0283 g. The difference in voltage (V) in
the capacitor owing to the efflux of electric charges (Q=CV) caused
by the removal of the powder coating was measured using an
electrometer "TR 8411" (manufactured by Advantest Corporation). The
difference in voltage was found to be +4.58 V. From the values
obtained, the triboelectric charge (Q/M) was calculated, and the
triboelectric charge was found to be -7.6 .mu.C/g.
Preparation Example 5-2 of Powder Coating
[0464]
28 Epoxy Acrylate Resin ("RIPOXY VR-40," 96 parts by weight
manufactured by Showa Kobunshi; softening point: 75.degree. C.)
Benzoin Isopropyl Ether 4 parts by weight ("NISSOCURE IBPO,"
manufactured by Nippon Soda Co., Ltd.) Carmine 6B ("SUMIKAPRINT
CARMINE 6BC," 8 parts by weight manufactured by Sumitomo Chemical
Co., Ltd.) Levelling Agent ("ACRONAL 4F," 1 part by weight
manufactured by BASF)
[0465] The same procedures as in Preparation Example 5-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 25.6 .mu.m. To 100 parts
by weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (5-2).
[0466] The same procedures as in Preparation Example 5-1 of Powder
Coating were carried out to obtain the triboelectric charge of
Powder Coating (5-2). The triboelectric charge was found to be -8.1
.mu.C/g.
Preparation Example 5-3 of Powder Coating
[0467]
29 Epoxy Acrylate Resin ("RIPOXY VR-40," 96 parts by weight
manufactured by Showa Kobunshi; softening point: 75.degree. C.)
Benzoin Isopropyl Ether 4 parts by weight ("NISSOCURE IBPO,"
manufactured by Nippon Soda Co., Ltd.) Dis-azo Yellow ("PIGMENT
YELLOW ECY-210," 8 parts by weight manufactured by Dainichiseika
Color & Chemicals MFG. Co., Ltd.) Levelling Agent ("ACRONAL
4F," 1 part by weight manufactured by BASF)
[0468] The same procedures as in Preparation Example 5-1 of Powder
Coating were carried out using the above components, to give a
powder having an average particle size of 25.1 .mu.m. To 100 parts
by weight of the resulting powder, 0.3 parts by weight of silica
"AEROSIL R972" (manufactured by Nippon Aerosil Co., Ltd.) were
added, and the mixture was uniformly blended using a Henschel
mixer, to give Powder Coating (5-3).
[0469] The same procedures as in Preparation Example 5-1 of Powder
Coating were carried out to obtain the triboelectric charge of
Powder Coating (5-3). The triboelectric charge was found to be -8.8
.mu.C/g.
Example 5-1
[0470] 10 parts by weight of Powder Coating (5-1), 45 parts by
weight of Powder Coating (5-2), and 45 parts by weight of Powder
Coating (5-3) were blended using a Henschel mixer. The resulting
mixture was applied to a degreased steel substrate using an
electrostatic sprayer, and the coated steel substrate was kept
standing at 85.degree. C. for 20 minutes to sufficiently heat and
melt the applied powder coatings. Thereafter, the powder coatings
were cured by adjusting an UV accumulation amount to 250
mJ/cm.sup.2 to form a coating film. The formed coating film had a
homogeneous vermilion color.
[0471] The resulting coating film had a gloss of 85, and a pencil
hardness of HB.
Comparative Example 5-1
[0472] 10 parts by weight of Powder Coating (5-1), 45 parts by
weight of Powder Coating (5-2), and 45 parts by weight of Powder
Coating (5-3) were blended using a Henschel mixer. The resulting
mixture was applied to a degreased steel substrate using an
electrostatic sprayer, and the coated steel substrate was placed in
an atmosphere of 85.degree. C., and concurrently the powder
coatings were cured by adjusting an UV accumulation amount to 250
mJ/cm.sup.2 to form a coating film. The formed coating was
confirmed by gross examination to have color separation.
[0473] The resulting coating film had a gloss of 25, and a pencil
hardness of B.
[0474] As is clear from the above results in Example 5-1 and
Comparative Example 5-1, when compared with Comparative Example 5-1
where the heating and the curing of the coating powders to form a
coating film were concurrently carried out, in Example 5-1, since
the coating film is formed by heating and melting the applied
powder coatings, and then curing the powder coatings, the resulting
coating film has a homogenous hue and also has excellent gloss and
pencil hardness.
[0475] The present invention being thus described, it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the invention, and all such modifications as would be obvious to
one skilled in the art are intended to be included within the scope
of the following claims.
* * * * *