Fluorine-containing resin composition having improved thermal stability

A melt-processable fluorine-containing resin composition having an improved thermal stability which comprises (A) a tetrafluoroethylene copolymer, a chlorotrifluoroethylene homo- or co-polymer, or a vinylidene fluoride homo- or co-polymer and (B) a mixture, as a thermal stabilizer, of (a) an amine antioxidant, (b) an organosulfurous compound and at least one member selected from the group consisting of (c) carbon black and (d) metal powder of Group VIII of the Periodic Table. The composition can be advantageously processed without causing any trouble even at an optimum sintering temperature of the fluorine-containing resin.

BACKGROUND OF THE INVENTION 
The present invention relates to a melt-processable fluorine-containing 
resin composition having an excellent thermal stability, and more 
particularly to the composition comprising a tetrafluoroethylene 
(hereinafter referred to as "TFE") copolymer, a chlorotrifluoroethylene 
(hereinafter referred to as "CTFE") homo- or co-polymer or a vinylidene 
fluoride (hereinafter referred to as "VdF") homo- or co-polymer, and a 
thermal stabilizer, which has an improved thermal stability to 
high-temperature sintering and is processable under widen processing 
conditions with technical and economical advantages and also can provide 
an article having excellent physical properties. 
TFE copolymers and CTFE or VdF homopolymer and copolymers are 
melt-processable fluorine-containing resins having especially high thermal 
resistance among those put on the market, and for instance, as the former 
there are known TFE-hexafluoropropylene copolymer, perfluorovinyl 
ether-TFE copolymer, ethylene-TFE copolymer and ethylene-propylene-TFE 
copolymer and as the latter there are known CTFE and VdF homopolymers, 
ethylene-CTFE copolymer and VdF-TFE copolymer, etc. These melt-processable 
fluorine-containing resins have melt-flowability, that is, the melt 
viscosity of these resins is generally lower than 10.sup.6 poises at an 
optimum processing temperature and, therefore, they provide a film having 
less pinholes and voids as compared with polytetrafluoroethylene which has 
an excellent chemical and corrosion resistance but has not 
melt-flowability or melt-processability, since it has an extremely high 
melt viscosity of from 10.sup.10 to 10.sup.11 poises even at a processing 
temperature, i.e. about 380.degree. C. 
The thermal stability of these melt-processable resins at high temperatures 
in the vicinity of their sintering temperatures is, however, inferior to 
that of polytetrafluoroethylene, and this makes some troubles in 
processing. That is to say, when the resins are heated at a suitable 
sintering temperature of 340.degree. to 380.degree. C. for a time more 
than 30 minutes, the resins partially cause thermal deterioration, and 
particularly when the coated film is considerably thick, bubbles are 
formed in the film inevitably. This phenomenon is accelerated by the 
influence of oxygen in air. 
For this reason, in case of TFE-hexafluoropropylene resin, for instance, 
there are proposed (1) a process in which thickness of the coating per one 
application is controlled as small as possible (about 50.mu.) and the 
application and sintering procedures must be repeated many times until a 
sintered film reaches a desired thickness, and (2) a process in which a 
resin having a low molecular weight (of which melt viscosity is about 
0.5.times.10.sup.4 to about 7.times.10.sup.4 poises at 380.degree. C.) or 
a resin obtained by heat treatment of a high molecular weight resin (the 
melt viscosity of the high molecular weight resin is from about 
1.times.10.sup.5 to about 4.times.10.sup.5 poises at 380.degree. C.) is 
used for a coating composition so that the resin melts and flows at a 
lower temperature, and the coating is sintered at a lower temperature 
(320.degree. to 340.degree. C.) to give a sintered film. 
However, the above process (1) has the disadvantage that the formation of a 
film having a thickness necessary in general for corrosion resistant 
linings, i.e. about 600 to about 1,000.mu. requires much labor and time in 
application and sintering. 
Also, the above process (2) accompanies the formation of bubbles in a 
coated film when the thickness of the film per one application exceeds 
100.mu., even though the sintering has been conducted at a lower 
temperature (320.degree. to 340.degree. C.) Therefore, when it is desired 
to obtain a film having a thickness of more than 1,000.mu., the 
application and sintering must be repeated more than 10 times as in the 
process (1). Thus, the process (2) is also low in productivity and is not 
economical. Further, a low molecular weight resin is inferior in stress 
crack resistance and solvent crack resistance and is not desirable as a 
corrosion resistant material. Moreover, thermal resistance of such a resin 
is low, the allowable range for processing temperature and period of time 
are narrow, and the thermal deterioration may take place during the 
processing. And further such a low molecular weight resin is liable to 
occur runs during the processing. When a lining is made on an industrial 
scale for a large-sized substrate, for instance, having a length of more 
than one meter or a substrate having an irregular thickness, temperature 
distribution on the surface of the substrate and difference in heat 
history become, of course, large, and in such a case a uniform lining of 
good quality is hard to obtain by the process (2). 
Also, in case of ethylene-propylene-TFE copolymer and ethylene-CTFE 
copolymer, the bubble formation upon sintering after powder coating is not 
so much as TFE-hexafluoropropylene copolymer. However, when the sintering 
for a long time is required owing to the size and shape of a substrate to 
be coated, it accompanies deterioration of the resin, and as a result, the 
obtained film is discolored and also the durability to various 
environments and chemical reagents is remarkably impaired. 
There are known various processes for improving the thermal stability of 
these melt-processable fluorine-containing resins upon sintering. For 
instance, Japanese Unexamined Patent Publication Nos. 122155/1976 and 
122156/1976 disclose processes for improving the thermal stability of the 
resins by admixing two kinds of TFE-hexafluoropropylene copolymer with 
different melt viscosities which are thermally treated at a high 
temperature in the presence of steam. These processes require not only the 
thermal treatment of TFE-hexafluoropropylene copolymer at a high 
temperature of 340.degree. to 380.degree. C. for 2 to 5 hours, but also 
drying for several hours to remove moisture because of the thermal 
treatment in the presence of steam, and accordingly is not economical. 
It is also known to use, as a thermal stabilizer for ethylene-TFE 
copolymer, sulfates of metals of Group IV-A of the Periodic Table such as 
Sn and Pb as disclosed in Japanese Patent Publication No. 37980/1973; 
phosphates of alkali metals, barium or metals of Group IV-A of the 
Periodic Table as disclosed in Japanese Patent Publication No. 37981/1973; 
a combination of organo phosphites and phosphates of alkali metals, barium 
or metals of Group IV-A of the Periodic Table as disclosed in Japanese 
Patent Publication No. 38215/1973; and .alpha.-alumina as disclosed in 
Japanese Unexamined Patent Publication No. 87738/1974. However, these 
thermal stabilizers merely inhibit the discoloration by thermal 
degradation of ethylene-TFE copolymer in the sintering at 300.degree. C. 
within 30 minutes, and are not suitable for use in coating a substrate to 
be coated having a large size and a large heat capacity.

The present invention is more particularly described and explained by means 
of the following Examples and Comparative Examples, in which all parts are 
by weight unless otherwise noted. 
EXAMPLES 1 to 13 AND COMATIVE EXAMPLES 1 to 8 
A 50 liter kneader having four agitating blades (commercially available 
under the tradename "Speed Kneader" made by Showa Engineering Kabushiki 
Kaisha) was charged with 10 kg. of TFE-hexafluoropropylene 
(hexafluoropropylene being hereinafter referred to as "HFP") copolymer 
(TFE/HFP=88/12 by weight) having a particle size of 60 meshes pass and a 
prescribed amount of a thermal stabilizer shown in Table 1, and the 
agitating blades were rotated for 30 minutes at a speed of 1,500 r.p.m. to 
prepare a fluorine-containing resin composition in the form of powder. 
A rectangular frame having a size of 10 cm..times.5 cm. was placed on an 
aluminum plate, and the composition in the form of powder was placed in 
the frame in an amount calculated on the basis of the specific gravity of 
the obtained film after sintering so that the film may have a thickness of 
50.mu., 100.mu., 150.mu., 200.mu., 300.mu. or 600.mu.. After removing the 
frame gently, the composition on the aluminum plate was sintered in an 
electric oven at a temperature of 370.degree..+-.5.degree. C. for 2 hours. 
The above procedures were repeated to give 7 films having different 
thickness on each composition. 
After the completion of the sintering, appearance of the obtained film was 
observed, and it was represented on Table 1 according to the following 
criteria. 
.times.: State of bubble formation of the film having a thickness of 
100.mu. obtained in Comparative Example 1 in which no thermal stabilizer 
was used. In that case, an infinite number of bubbles having a diameter of 
1 to 2 mm. were present, and this state of bubble formation was made 
standard on determining the state of bubble formation of other films. 
.times..times.: State of bubble formation being inferior to the above 
standard film 
.DELTA.: State of bubble formation being improved to some extent as 
compared with the standard film 
: Only several bubbles being present 
: No bubble being observed 
Although the films were prepared by a method different from usual powder 
coating method in order to adjust exactly the thickness of the films, the 
above sintering conditions are approximately the same as those applied to 
the practical powder coating, and it was also confirmed that the state of 
bubble formation well corresponded to that in the practical powder 
coating. 
The results are shown in Table 1. 
The thermal stabilizers A to P shown in Table 1 are as follows: 
A: 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine 
B: cobalt powder having a particle size of 1 to 2.mu. 
C: zinc salt of 2-mercaptobenzothiazole 
D: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine and 
cobalt powder having a particle size of 1 to 2.mu. (6:1 by weight) 
E: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine and 
zinc salt of 2-mercaptobenzothiazole (1:1 by weight) 
F: Mixture of di-.beta.-naphthyl-p-phenylenediamine and zinc salt of 
2-mercaptobenzoimidazole (2:1 by weight) 
G: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine, zinc 
salt of 2-mercaptobenzothiazole and iron powder having a particle size of 
not more than 40.mu. (3:3:2 by weight) 
H: Mixture same as the above mixture G excepting the use of cobalt powder 
having a particle size of 1 to 2.mu. instead of iron powder 
I: Mixture same as the above mixture G excepting the use of nickel powder 
having a particle size of 325 meshes pass instead of iron powder 
J: Mixture of phenyl-.beta.-naphthylamine, 2-mercaptobenzoimidazole and 
iron powder having a particle size of not more than 40.mu. (3:3:2 by 
weight) 
K: Mixture same as the above mixture J excepting the use of nickel powder 
having a particle size of not more than 40.mu. instead of iron powder 
L: Mixture same as the above mixture J excepting the use of cobalt powder 
having a particle size of 1 to 2.mu. instead of iron powder 
M: Mixture of di-.beta.-naphthyl-p-phenylenediamine, zinc salt of 
2-mercaptobenzoimidazole and cobalt powder having a particle size of 1 to 
2.mu. (3:3:1 by weight) 
N: Mixture of tetramethylthiuram disulfide, monooctyldiphenylamine, 
dioctyldiphenylamine and nickel powder having a particle size of not more 
than 40.mu. (2:0.5:0.5:0.5 by weight) 
O: Mixture of dibutyl tin mercaptide (commercially available under the 
tradename "AP-52" made by Tokyo Fine Chemical Kabushiki Kaisha), 
diphenyl-p-phenylenediamine and cobalt powder having a particle size of 1 
to 2.mu. (4:2:1 by weight) 
P: Mixture of dibutyl tin mercaptide (commercially available under the 
tradename "AP-52" made by Tokyo Fine Chemical Kabushiki Kaisha), 
phenylcyclohexyl-p-phenylenediamine and nickel powder having a particle 
size of not more than 40.mu. (3:3:1 by weight) 
TABLE 1 
__________________________________________________________________________ 
Thermal 
stabilizer State of film 
Amount 
Kind (PHR) 
50.mu. 
100.mu. 
150.mu. 
200.mu. 
250.mu. 
300.mu. 
600.mu. 
__________________________________________________________________________ 
Com. 
Ex. 1 
-- -- .circle. 
X XX XX XX XX XX 
Com. 
Ex. 2 
A 2 .circleincircle. 
.circle. 
.circle. 
X X XX XX 
Com. 
Ex. 3 
B 2 .circleincircle. 
X X XX XX XX XX 
Com. 
Ex. 4 
C 2 .circleincircle. 
.circle. 
.circle. 
X X XX XX 
Com. 
Ex. 5 
D 2 .circleincircle. 
.circle. 
.circle. 
X X XX XX 
Com. 
Ex. 6 
E 1 .circleincircle. 
.circle. 
.circle. 
X X X XX 
Com. 
Ex. 7 
E 2 .circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
X XX 
Com. 
Ex. 8 
F 2 .circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
.circle. 
XX 
__________________________________________________________________________ 
Ex. 1 
G 1 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
X 
Ex. 2 
G 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Ex. 3 
H 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Ex. 4 
I 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Ex. 5 
J 1 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
X 
Ex. 6 
K 1 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
X 
Ex. 7 
L 1 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
X 
Ex. 8 
M 0.5 
.circleincircle. 
.circle. 
.circle. 
.DELTA. 
X X XX 
Ex. 9 
M 1 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.DELTA. 
X 
Ex. 10 
M 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
Ex. 11 
N 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
XX 
Ex. 12 
O 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
Ex. 13 
P 2 .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
__________________________________________________________________________ 
EXAMPLES 14 TO 17 AND COMATIVE EXAMPLES 9 TO 14 
The procedures of the preceding Examples were repeated except that CTFE 
homopolymer, VdF homopolymer or VdF-TFE copolymer (VdF:TFE=87:13 by 
weight) as a melt-processable fluorine-containing resin and a thermal 
stabilizer were employed as shown in Table 2 and the sintering was 
conducted under conditions as shown in Table 2. 
The results of observation of the sintered films are shown in Table 2, in 
which the state of film was judged according to the following criteria. 
a: No bubble being observed 
b: A few bubbles being observed 
c: Several bubbles being observed 
d: Considerable number of bubbles being observed all over the film 
e: Noticeable amount of bubbles being observed all over the film 
TABLE 2 
__________________________________________________________________________ 
Sintering 
Thermal stabilizer 
Fluorine-containing 
condition 
State of film 
Kind 
Amount (PHR) 
resin .degree.C. 
hour 
400 .mu. 
600 .mu. 
__________________________________________________________________________ 
Com. Ex. 9 
-- -- CTFE homopolymer 
300 
5 d e 
Com. Ex. 10 
-- -- VdF homopolymer 
260 
3 c d 
Com. Ex. 11 
-- -- VdF-TFE copolymer 
260 
3 c d 
Com. Ex. 12 
A 2 CTFE homopolymer 
300 
5 c e 
Com. Ex. 13 
B 2 CTFE homopolymer 
300 
5 d e 
Com. Ex. 14 
C 2 CTFE homopolymer 
300 
5 c e 
__________________________________________________________________________ 
Ex. 14 G 2 CTFE homopolymer 
300 
5 a a 
Ex. 15 M 2 CTFE homopolymer 
300 
5 a b 
Ex. 16 M 2 VdF-TFE copolymer 
260 
3 a b 
Ex. 17 O 2 VdF homopolymer 
260 
3 a a 
__________________________________________________________________________ 
EXAMPLE 18 
A mixture of (1) 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)-diphenylamine, 
(2) zinc salt of 2-mercaptobenzothiazole and (3) cobalt powder having a 
particle size of 1 to 2.mu. (3:3:1 by weight) was added as a thermal 
stabilizer to 10 kg. of finely divided TFE-HFP copolymer (TFE/HFP=85/15 by 
weight) having a particle size of 60 meshes pass in an amount of 0.5 part, 
1 part or 2 parts per 100 parts of the copolymer, and they were blended in 
the same manner as in Example 1. The above procedures were repeated to 
give three compositions containing 0.5 part, 1 part and 2 parts of the 
thermal stabilizer mixture respectively, per 100 parts of the copolymer. 
Each composition was applied to a steel plate having a thickness of 8 mm. 
which was previously preheated to 400.degree. C., by a powder spraying 
method in such an amount as to give, after sintering, a film having a 
thickness of about 500.mu.. 
The obtained coated plate was placed in a hot air circulating electric 
oven, and was sintered under varied temperature and time conditions to 
determine critical sintering condition under which a film leaving no 
traces of bubbles could be obtained. 
The results are shown in FIG. 1, in which curves 1, 2 and 3 show the cases 
containing the thermal stabilizer mixture in amounts of 0.5, 1 and 2 
parts, respectively, per 100 parts of the copolymer. 
EXAMPLE 19 
The procedures of Example 18 were repeated except that a mixture containing 
the components (1), (2) and (3) in a weight ratio of 3:3:2 was employed as 
the thermal stabilizer and two compositions containing 1 part and 2 parts 
of the thermal stabilizer mixture respectively, per 100 parts of the 
copolymer were prepared. 
Each composition was applied to a steel plate having a thickness of 8 mm. 
which was previously preheated to 400.degree. C., by a powder spraying 
method, and after provisionally sintering the coated plate in an electric 
oven at 370.degree. C. for 20 minutes, the plate was taken out from the 
oven and was immediately applied again with the composition by a powder 
spraying method so that the total thickness of a film obtained after 
sintering became about 1,000.mu.. 
Each thus obtained coated plate was sintered in the same manner as in 
Example 18 to determine critical sintering condition under which a film 
leaving no traces of bubbles could be obtained. 
The results are shown in FIG. 2, in which curves 4 and 5 show the cases 
containing the thermal stabilizer mixture in amounts of 1 and 2 parts, 
respectively, per 100 parts of the copolymer. 
EXAMPLE 20 
The procedures of Example 18 were repeated except that 15 parts of a glass 
fiber powder having an average diameter of 10.mu. and an average fiber 
length of 60.mu. was further employed per 100 parts of the copolymer in 
addition of the copolymer and the thermal stabilizer mixture. 
The results are shown in FIG. 3, in which curves 6 and 7 show the cases 
containing the thermal stabilizer mixture in amounts of 1 and 2 parts, 
respectively, per 100 parts of the copolymer. 
It is observed from the comparison of FIG. 3 with FIG. 1 that the thermal 
stabilization effect cannot be impaired by the addition of additives such 
as pigments and reinforcing agents. 
EXAMPLES 21 TO 28 AND COMATIVE EXAMPLES 15 TO 19 
A 50 liter kneader having four agitating blades (commercially available 
under the tradename "Speed Kneader" made by Showa Engineering Kabushiki 
Kaisha) was charged with 10 kg. of TFE-HFP copolymer (TFE/HFP=88/12 by 
weight) having a particle size of 60 meshes pass and a thermal stabilizer 
as shown in Table 3, and the agitating blades were rotated for 30 minutes 
at a speed of 1,500 r.p.m. to prepare a fluorine-containing resin 
composition in the form of powder. 
A rectangular frame having a size of 10 cm..times.5 cm. was placed on an 
aluminum plate, and the composition in the form of powder was placed in 
the frame in such an amount as to give, after sintering, a film having a 
thickness of 600.mu.. After removing the frame gently, the composition on 
the aluminum plate was sintered in an electric oven at a temperature of 
350.degree. C., 360.degree. C., 370.degree. C. or 380.degree. C. for 2 
hours. 
The above procedure was repeated on every compositions. 
After the completion of the sintering, the state of the film was observed 
and judged according to the same criteria as described in Examples 14 to 
17. 
The results are shown in Table 3. 
The thermal stabilizers shown in Table 2 are as follows: 
E: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine and 
zinc salt of 2-mercaptobenzothiazole (1:1 by weight) 
Q: Mixture of di-.beta.-naphthyl-p-phenylenediamine and zinc salt of 
2-mercaptobenzothiazole (1:1 by weight) 
R: Mixture of dibutyl-tin-mercaptide and 
phenylcyclohexyl-p-phenylenediamine (1:1 by weight) 
As is clear from Table 3, the state of the sintered films obtained from the 
compositions of the invention was very good as compared with the film 
obtained in Comparative Examples. The bubble formation is well inhibited 
so as to give the smooth surface and no deterioration of the resin itself 
is observed. 
TABLE 3 
__________________________________________________________________________ 
Thermal stabilizer State of film 
Amount 
Amount of carbon 
Kind (PHR) 
black (PHR) 
350.degree. C. 
360.degree. C. 
370.degree. C. 
380.degree. C. 
__________________________________________________________________________ 
Ex. 21 
E 2 0.01 a a c d 
Ex. 22 
E 2 0.03 a a b d 
Ex. 23 
E 2 0.1 a a a b 
Ex. 24 
E 2 1.0 a a b b 
Ex. 25 
E 2 2.0 a a c d 
Ex. 26 
E 2 5.0 a b c d 
Ex. 27 
Q 2 0.1 a a b d 
Ex. 28 
R 22 0.1 a a b c 
__________________________________________________________________________ 
Com. 
Ex. 15 
-- -- -- d e e e 
Com. 
Ex. 16 
E 2 -- a c e e 
Com. 
Ex. 17 
Q 2 -- a c e e 
Com. 
Ex. 18 
R 2 -- a b c e 
Com. 
Ex. 19 
-- -- 2.0 d e e e 
__________________________________________________________________________ 
EXAMPLES 29 to 32 
The procedures of Examples 21 to 28 were repeated except that the thermal 
stabilizers shown in Table 4 were employed, in order to observe the 
synergistic effect by the use of carbon black. 
The results are shown in Table 4. 
The thermal stabilizers shown in Table 4 are as follows: 
S: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine, 
2-mercaptobenzothiazole and cobalt powder having a particle size of 1 to 
2.mu. (3:3:2 by weight) 
T: Mixture of phenyl-.beta.-naphthylamine, 2-mercaptobenzothiazole and tin 
powder having a particle size of not more than 74.mu. (3:3:2 by weight) 
As is clear from Table 4, the thermal stability is further improved by the 
use of carbon black powder. 
TABLE 4 
__________________________________________________________________________ 
Thermal stabilizer State of film 
Amount 
Amount of carbon 
Kind (PHR) 
black (PHR) 
350.degree. C. 
360.degree. C. 
370.degree. C. 
380.degree. C. 
__________________________________________________________________________ 
Ex. 29 
S 2 -- a a a c 
Ex. 30 
T 2 -- a b d e 
Ex. 31 
S 2 0.05 a a a a 
Ex. 32 
T 2 0.1 a a b c 
__________________________________________________________________________ 
EXAMPLES 33 TO 51 AND COMATIVE EXAMPLES 20 TO 25 
A melt-processable fluorine-containing resin composition in the form of 
powder was prepared in the same manner as in Example 1 except that a 
fluorine-containing resin having a particle size of 60 meshes pass and a 
thermal stabilizer were employed as shown in Table 5. 
The composition was placed in a fluidized bed, and the powder was 
fluidized. A steel plate having a thickness of 10 mm. which was previously 
preheated to 380.degree. C. was then dipped to adhere the powder to the 
plate. The powder adhered to the plate was then sintered under a condition 
shown in Table 5 to give a test specimen having a film of 300.+-.50.mu. in 
thickness. 
The thus obtained test specimen was placed in an autoclave containing high 
pressure saturated steam, and steam resistance test was carried out. The 
high pressure steam resistance of the film was judged according to the 
following criteria. 
: No change 
.DELTA.: Whitening (a large number of fine hair cracks being observable by 
a microscope of about 40 magnifications) 
.times.: Occurrence of cracks observable by the naked eye 
The results of the high pressure steam resistance are shown in Table 5 
together with the results of Comparative Examples where no thermal 
stabilizer was employed. 
As is clear from the results, the films prepared from the compositions of 
the invention containing thermal stabilizers have a high durability to 
superheated steam, while the films containing no thermal stabilizer as 
shown in Comparative Examples are thermally deteriorated in part under a 
severe sintering condition and is colored and this causes lowering of the 
stress crack resistance in superheated steam. 
Thermal stabilizers shown in Table 5 are as follows: 
U: Mixture of zinc salt of 2-mercaptobenzothiazole, 
phenyl-.beta.-naphthylamine and cobalt powder having a particle size of 1 
to 2.mu. (2:1:1 by weight) 
V: Mixture of copper dimethyldithiocarbamate, 
4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine and cobalt powder 
having a particle size of 1 to 2.mu. (3:3:1 by weight) 
W: Mixture of zinc salt of 2-mercaptobenzoimidazole, 
phenyl-.beta.-naphthylamine and nickel powder having a particle size of 
not more than 40.mu. (3:3:2 by weight) 
X: Mixture of zinc salt of ethylphenyldithiocarbamate, 
di-.beta.-naphthylphenylenediamine and nickel powder having a particle 
size of not more than 40.mu. (2:4:1 by weight) 
Y: Mixture of 4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine, 
2-mercaptobenzoimidazole and cobalt powder having a particle size of 1 to 
2.mu. (2:4:1 by weight) 
Z: Mixture of zinc salt of 2-mercaptobenzoimidazole, 
di-.beta.-naphthyl-p-phenylenediamine and nickel powder having a particle 
size of 1 to 2.mu. (3:3:1 by weight) 
TABLE 5 
__________________________________________________________________________ 
Fluorine-containing resin 
Sintering 
Thermal stabilizer 
High pressure steam resistance 
Kind condition 
Amount 
Amount of 
120.degree. C. 
140.degree. C. 
160.degree. C. 
160.degree. C. 
(molar ratio) 
.degree.C. 
hour 
Kind 
PHR carbon black 
40 days 
7 days 
1 day 
7 days 
__________________________________________________________________________ 
Com. 
E/P/TFE = 
Ex. 20 
17.0/6.5/76.5 
290 
0.5 
-- -- -- .DELTA. 
.DELTA. 
-- X 
Com. 
E/P/TFE = 
Ex. 21 
17.0/6.5/76.5 
270 
2 -- -- -- X X -- X 
__________________________________________________________________________ 
Ex. 33 
E/P/TFE = 
17.0/6.5/76.5 
270 
2 U 1 -- .circle. 
.circle. 
-- .DELTA. 
Ex. 34 
E/P/TFE = 
17.0/6.5/76.5 
270 
4 U 1 -- .circle. 
.circle. 
-- .DELTA. 
Ex. 35 
E/P/TFE = 
17.0/6.5/76.5 
270 
6 U 1 -- .DELTA. 
.circle. 
-- .DELTA. 
Ex. 36 
E/P/TFE = 
17.0/6.5/76.5 
270 
2 V 2 -- .circle. 
.circle. 
-- .DELTA. 
Ex. 37 
E/P/TFE = 
17.0/6.5/76.5 
300 
2 V 1 -- .circle. 
.circle. 
-- .DELTA. 
Ex. 38 
E/P/TFE = 
17.0/6.5/76.5 
270 
2 U 1 0.05 .circle. 
.circle. 
-- .circle. 
Ex. 39 
E/P/TFE = 
17.0/6.5/76.5 
270 
4 V 1 0.1 .circle. 
.circle. 
-- .circle. 
Ex. 40 
E/P/TFE = 
17.0/6.5/76.5 
300 
2 Z 1 0.1 .circle. 
.circle. 
-- .circle. 
__________________________________________________________________________ 
Com. 
E/TFE = 
Ex. 22 
19.8/80.2 
320 
1 -- -- -- .circle. 
.circle. 
X X 
Com. 
E/TFE = 
Ex. 23 
19.8/80.2 
320 
2 -- -- -- .circle. 
.circle. 
X X 
__________________________________________________________________________ 
Ex. 41 
E/TFE = 
19.8/80.2 
320 
2 U 1 -- .circle. 
.circle. 
.circle. 
.DELTA. 
Ex. 42 
E/TFE = 
19.8/80.2 
320 
1 W 2 -- .circle. 
.circle. 
.circle. 
.DELTA. 
Ex. 43 
E/TFE = 
19.8/80.2 
320 
2 W 0.5 
-- .circle. 
.circle. 
.DELTA. 
.DELTA. 
Ex. 44 
E/TFE = 
19.8/80.2 
320 
2 W 2 -- .circle. 
.circle. 
.circle. 
.circle. 
Ex. 45 
E/TFE = 
19.8/80.2 
320 
1 X 2 -- .circle. 
.circle. 
.circle. 
.DELTA. 
Ex. 46 
E/TFE = 
19.8/80.2 
320 
2 U 1 0.05 .circle. 
.circle. 
.circle. 
.circle. 
Ex. 47 
E/TFE = 
19.8/80.2 
320 
2 V 1 0.05 .circle. 
.circle. 
.circle. 
.circle. 
Ex. 48 
E/TFE = 
19.8/80.2 
320 
2 Z 1 0.05 .circle. 
.circle. 
.circle. 
.circle. 
__________________________________________________________________________ 
Com. 
E/CTFE = 
Ex. 24 
19.5/80.5 
250 
0.5 
-- -- -- .DELTA..about..circle. 
.DELTA..about..circle. 
.DELTA. 
X 
Com. 
E/CTFE = 
Ex. 25 
19.5/80.5 
260 
1 -- -- -- .DELTA. 
.DELTA. 
X X 
__________________________________________________________________________ 
Ex. 49 
E/CTFE = 
19.5/80.5 
260 
1 Y 1 -- .circle. 
.circle. 
.circle. 
.DELTA. 
Ex. 50 
E/CTFE = 
19.5/80.5 
260 
1 Y 2 -- .circle. 
.circle. 
.circle. 
.circle. 
Ex. 51 
E/CTFE = 
19.5/80.5 
260 
1 Y 3 -- .circle. 
.circle. 
.circle. 
.DELTA. 
__________________________________________________________________________ 
(Note)- 
E: Ethylene 
P: Propylene 
EXAMPLES 52 TO 54 AND COMATIVE EXAMPLE 26 
In a ball mill, 200 parts of xylene, 350 parts of cyclohexane, 300 parts of 
finely divided TFE-HFP copolymer (TFE/HFP=86/14 by weight) having a 
particle size of not more than 70.mu. pass and a prescribed amount of, as 
a thermal stabilizer, a mixture of 
4,4'-bis(.alpha.,.alpha.'-dimethylbenzyl)diphenylamine, zinc salt of 
2-mercaptobenzothiazole and cobalt powder having a particle size of 1 to 
2.mu. (3:3:1 by weight) were blended for 24 hours to give a dispersion of 
resin and stabilizer in organic solvent. 
The obtained dispersion was sprayed to aluminum plates to give coated 
plates having coatings of various thicknesses. After drying the coatings 
in an infrared dryer maintained at about 100.degree. C., the coated plates 
were placed in a hot air circulating type electric oven and then sintered 
at 365.degree. C. for 1.5 hours. Limit thickness to bubble formation being 
capable of providing a good sintered film leaving no traces of bubbles was 
then judged. 
The results are shown in Table 6. 
As is clear from the results shown in Table 6, fluorine-containing resin 
compositions in the form of dispersion of the present invention can be 
coated more thickly as compared with the dispersion not containing thermal 
stabilizer obtained in Comparative Example 26. 
TABLE 6 
______________________________________ 
Thermal stabilizer 
Limit thickness to 
Amount bubble formation in 
(PHR) sintered film (.mu. ) 
______________________________________ 
Com. 
Ex. 26 -- 70 to 80 
Ex. 52 0.5 180 to 200 
Ex. 53 1 &gt;300 
Ex. 54 2 &gt;300 
______________________________________