U.S. patent application number 09/767580 was filed with the patent office on 2001-08-30 for melt processible fluoropolymer composition.
Invention is credited to Kondo, Shosaku, Lee, Jeong C., Sato, Hajime.
Application Number | 20010018493 09/767580 |
Document ID | / |
Family ID | 18551315 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018493 |
Kind Code |
A1 |
Lee, Jeong C. ; et
al. |
August 30, 2001 |
Melt processible fluoropolymer composition
Abstract
A melt processible fluoropolymer composition comprising a
copolymer of tetrafluoroethylene with a perfluoro(alkyl vinyl
ether), which copolymer is a mixture of a first fluorocarbon resin
copolymer in which the alkyl group of the perfluoro(alkyl vinyl
ether) has at least 3 carbons, and a second fluorocarbon resin
copolymer in which the alkyl group of the perfluoro(alkyl vinyl
ether) has 1 and/or 2 carbons, and the components of the blend are
miscible in the amorphous regions and sometimes in the crystalling
regions.
Inventors: |
Lee, Jeong C.; (Shimizu
City, JP) ; Kondo, Shosaku; (Shimizu City, JP)
; Sato, Hajime; (Shimizu City, JP) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
18551315 |
Appl. No.: |
09/767580 |
Filed: |
January 23, 2001 |
Current U.S.
Class: |
525/200 ;
525/199 |
Current CPC
Class: |
C08L 27/18 20130101;
C08L 2205/02 20130101; C08L 27/18 20130101; C08L 2666/04
20130101 |
Class at
Publication: |
525/200 ;
525/199 |
International
Class: |
C08L 027/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2000 |
JP |
2000-25458 |
Claims
What is claimed is:
1. A melt processible fluoropolymer composition comprising: a) a
first copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl
ether) wherein the alkyl group of the perfluoro(alkyl vinyl ether)
has at least 3 carbons, and b) a second copolymer of
tetrafluoroethylene and perfluoro(alkyl vinyl ether) wherein the
alkyl group of the perfluoro(alkyl vinyl ether) has 1 and/or 2
carbons, wherein each said first copolymer and said second
copolymer has crystalline and amorphous regions, at least the
amorphous regions of said first copolymer and second copolymer
being miscible with one another as revealed by said composition
exhibiting a single .alpha.-transition temperature.
2. The melt processible fluoropolymer composition of claim 1,
wherein said first copolymer has a perfluoro(alkyl vinyl ether)
content within a range of about 0.5 to about 8% by weight, and said
second copolymer has a perfluoro(alkyl vinyl ether) content within
a range of about 1 to about 25% by weight.
3. The melt processible fluoropolymer composition of claim 1,
wherein the ratio of said first copolymer to said second copolymer
is from about 1:99 to about 99:1.
4. The melt processible fluoropolymer composition of claim 1,
wherein the ratio of said first copolymer to said second copolymer
is from about 10:90 to about 90:10.
5. The melt processible fluoropolymer composition of claim 1 which
exhibits only one crystallization temperature and one melting
point, as determined using a differential scanning calorimeter.
6. The melt processible fluoropolymer composition of claim 1
wherein the maximum viscosity difference of the component polymers
does not exceed 2000 Pa.multidot.s.
7. The melt processible fluoropolymer composition of claim 1
wherein the maximum viscosity difference of the component polymers
does not exceed 1500 Pa.multidot.s.
8. The melt processible fluoropolymer composition of claim 1
wherein the maximum viscosity difference of the component polymers
does not exceed 1000 Pa.multidot.s.
Description
FIELD OF THE INVENTION
[0001] This invention is in the field of blends of copolymers of
tetrafluoroethylene and perfluoro(alkyl vinyl ether) that are
miscible in amorphous regions and can be miscible in crystalline
regions as well.
BACKGROUND OF THE INVENTION
[0002] The melting points and crystallization temperatures of
tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (known
as TFE/PAVE or PFA) and tetrafluoroethylene-hexafluoropropylene
copolymers (FEP) are strongly influenced by the amount of PAVE or
HFP comonomer in the copolymer. An increase in the amount of
comonomer in the copolymer results in a decrease in the polymer
melting point.
[0003] PAVE comonomers include perfluoro(propyl vinyl ether)
(PPVE), and perfluoro(ethyl vinyl ether) (PEVE), and
perfluoro(methyl vinyl ether) (PMVE). In comparison with TFE/PPVE,
the copolymers TFE/PEVE and TFE/PMVE have certain advantages. For
example, the PEVE and PMVE comonomers polymerize more rapidly than
PPVE, and polymerization is easier to control. Furthermore, PEVE
and PMVE are distributed more uniformly in the polymer molecules.
These features make them preferable to PPVE when higher comonomer
content is needed, as for example, when increased copolymer flex
life is desired. However, with higher comonomer content than
prior-art PPVE-containing PFAs, the TFE/PEVE and TFE/PMVE polymers
have lower melting points and lower maximum service temperatures
than TFE/PPVE PFAs. As a result, articles made from them have lower
use temperatures.
[0004] Examples are known in which the physical properties of a
fluoropolymer are optimized by admixture of other fluoropolymers.
U.S. Pat. No. 5,041,500 discloses heterogeneous blends of FEP with
TFE/PPVE. U.S. Pat. No. 5,179,167 discloses blending of low and
high molecular weight FEP or TFE/PPVE. Attempts have been made to
improve the blend properties by more uniform and intimate mixing of
the components: Macromolecules vol. 28, p. 2781 (1995); Journal of
Polymer Science: Polymer Physics vol. 37, p. 679 (1999)). Blends of
polytetrafluoroethylene (PTFE) with TFE/PPVE and of FEP with
TFE/PMVE were found to cocrystallize if the melt blends were
rapidly cooled with liquid nitrogen. However, under cooling
conditions characteristic of normal polymer melt processing, the
polymers of the blends crystallized separately, as shown by their
separate melting points in the blend.
[0005] There is a need for fluoropolymer blend compositions that
remain intimately blended after cooling, as evidenced by single
melting points and single .alpha.-transition temperatures.
SUMMARY OF THE INVENTION
[0006] It has been discovered that different melt processible
copolymers of tetrafluoroethylene and perfluoro(alkyl vinyl ether)
can be mixed together to produce a fluoropolymer composition in
which the components are miscible on a molecular level. In greater
detail, the melt processible fluoropolymer composition of the
present invention comprises: a) a first copolymer of
tetrafluoroethylene and perfluoro(alkyl vinyl ether) wherein the
alkyl group of the perfluoro(alkyl vinyl ether) has at least 3
carbons, and b) a second copolymer of tetrafluoroethylene and
perfluoro(alkyl vinyl ether) wherein the alkyl group of the
perfluoro(alkyl vinyl ether) has 1 and/or 2 carbons, wherein each
said first copolymer and said second copolymer has crystalline and
amorphous regions, at least the amorphous regions of said first
copolymer and second copolymer being miscible with one another as
revealed by said composition exhibiting a single .alpha.-transition
temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a graph showing the crystallization temperatures
(Tc) of PFA-C3/PFA-C2 blends and components. The cooling rate is
70.degree. C./minute.
[0008] FIG. 2 is a graph showing the independence of the melting
point (Tm) of a 40/60 PFA-C3/PFA-C2 blend of the method by which
the blend is mixed. The vertical broken lines mark the melting
points of the PFA-C2 and PFA-C3 components. The heating rate is
10.degree. C./minute.
DETAILED DESCRIPTION
[0009] Melt processible fluoropolymers are the general subject of
this patent. By melt processible is meant that the polymer can be
processed, that is fabricated into shaped articles such as films,
fibers, tubes, wire coating, and the like, by conventional
melt-extruding means. Melt processible polymers have melt
viscosities at their processing temperatures of no more than about
1.times.10.sup.6 Pa.multidot.s. Preferably the viscosity is in the
range of about 1.times.10.sup.2 to 1.times.10.sup.6 Pa.multidot.s,
more preferably in the range of about 1.times.10.sup.3 to
1.times.10.sup.5 Pa.multidot.s. Fluoropolymers are defined herein
as polymers in which at least some of the constituent monomers are
fluoromonomers. Fluoromonomers are fluoroolefins, which are defined
herein as olefins in which at least one of the substituents on the
doubly bonded carbon atoms is a fluorine atom. For the purposes of
this patent, fluoropolymers are further defined as having at least
about 35% by weight fluorine.
[0010] The fluoropolymers of this invention have both crystalline
and non-crystalline (also known as amorphous) regions or phases.
The crystalline region is such that on analysis using differential
scanning calorimetry (DSC), the polymer has an observable melting
point and a heat of melting, sometimes referred to as the heat of
fusion, of at least about 3 J/g.
[0011] It has been discovered that when TFE/PPVE is blended with
TFE/PEVE and/or TFE/PMVE, the components are miscible at the
molecular level in the amorphous region and can be miscible in the
crystalline region as well, which means that they form a uniform
and intimate mixture that is maintained after melt processing
regardless of how the molten blend is cooled to ambient
temperature, that is, to about 15.degree. C. to 20.degree. C.
[0012] It is therefore an object of the invention to provide melt
processible fluoropolymer compositions in which the constituent
components are miscible in amorphous regions. As will be described
herein, the constituent components can also be miscible in
crystalline regions as well. More specifically, the object is to
provide such compositions that have physical properties superior to
those of a single PFA. The object of the invention is most
particularly to provide melt processible fluoropolymer compositions
which have an improved flex life and a higher melting point than
the lower-melting PFA component, and which confer upon
melt-fabricated articles made therefrom a higher maximum service
temperature.
[0013] The TFE/PAVE copolymer used in the invention is composed of
a first copolymer (A) (hereinafter referred to as "PFA-C3") in
which the alkyl group of the PAVE has at least 3 carbons, and
preferably from 3 to 10 carbons, and which more preferably is PPVE;
and a second copolymer (B) in which the alkyl group of the PAVE is
methyl (PFA-C1) and/or ethyl (PFA-C2). One or more of the first
copolymer (A) and one or more of the second copolymer (B) may be
used. Compositions of this type include blends of PFA-C3 in
copolymer (A) with blends of PFA-C 1 and PFA-C2 in copolymer (B).
Use can also be made of a copolymer containing two or more
perfluoro(alkyl vinyl ethers), each having different alkyl groups.
For example, TFE/PPVE might be blended with the terpolymer
TFE/PEVE/PMVE.
[0014] PFA-C3 is preferably a copolymer having a PAVE content of
about 0.5 to about 8% by weight, preferably about 2 to about 6%,
and more preferably about 3 to about 5%. PFA-C1 and PFA-C2 are each
preferably copolymers having PAVE contents of about 1 to about 25%
by weight, and more preferably about 1 to about 20% by weight. If
the PAVE content of PFA-C1 or PFA-C2 differs too much from the PAVE
content of PFA-C3, the copolymers may be immiscible in the
crystalline regions. To obtain a composition in which the
constituent copolymers are miscible in the crystalline regions, it
is preferable that PFA-C1 and PFA-C2 differ in PAVE content from
PFA-C3 by no more than about 10% by weight, preferably by no more
than about 8%, and more preferably by no more than about 6%. The
PAVE content (weight %) of PFA-C3 will preferably be less than the
PAVE content of PFA-C2 or of PFA-C1, or the admixture of both. As
will be described in the examples, when PFA-C3 copolymer having a
PPVE content of about 4% by weight or less is used, the admixture
of PFA-C1 or PFA-C2 copolymer having a PMVE or PEVE content of
about 1 to about 12% by weight gives a composition in which the
constituent copolymers are miscible in both crystalline and
amorphous regions. However, the admixture of PFA-C 1 or PFA-C2
copolymer having a PMVE or PEVE content of more than about 12 to
25% by weight shows phase separation in the crystalline regions
during cooling, so that the components are miscible only in
amorphous regions in the cooled blend.
[0015] When the components of the cooled blend are miscible in the
amorphous region, a single .alpha.-transition temperature, as
determined with a dynamic mechanical analyzer (DMA), appears
between the temperatures of the .alpha.-transitions of the blend
components. When the components of the cooled blend are miscible in
the crystalline region, the melting point (the principal
endothermic peak that appears as the solid blend is heated to melt
it) and crystallization temperature (the principal exothermic peak
that appears as the molten blend is cooled), as determined with a
differential scanning calorimeter (DSC), each appears as a single
temperature between the respective values of the components of the
mixture. There are cases where the compositions of the invention
are miscible only in amorphous regions and cases where miscibility
extends to both amorphous regions and crystalline regions. The
latter condition is preferred for better improvement of the maximum
service temperature of the low-melting component.
[0016] The mixing proportions of PFA-C3 with PFA-C1 or PFA-C2 vary
with the intended use, although the weight ratio is preferably from
about 1/99 to about 99/1, and more preferably from about 10/90 to
about 90/10. For example, when PFA-C3 is used as the high-melting
component, by mixing it with up to about 40% by weight of PFA-C1 or
PFA-C2 as the low-melting component, the flex life can be
dramatically improved without undue sacrifice of the high heat
deflection temperature of PFA-C3.
[0017] Various additives may be added to the inventive composition
insofar as the objects of the invention are not defeated. Examples
of such additives include ultraviolet absorbers, antistatic agents,
pigments and inorganic fillers.
[0018] The inventive composition may be prepared using any ordinary
method to mix the PFA-C3 with PFA-C1 and/or PFA-C2. Examples of
suitable methods include mixing aqueous dispersions, mixing organic
solvent-based dispersions, and melt blending. Mixing to achieve
molecular miscibility occurs most readily when the viscosities of
the component PFAs are identical or nearly so. The melt viscosities
of the component polymers should not differ by more than about 5000
Pa.multidot.s, preferably not more than about 2000 Pa.multidot.s,
more preferably not more than about 1500 Pa.multidot.s, and most
preferably not more than about 1000 Pa.multidot.s. If more than two
polymers are blended, the maximum viscosity difference, that is the
difference between the two components that are farthest apart in
viscosity, should not exceed the above values.
[0019] The mixing of aqueous dispersions is the preferred
method.
EXAMPLES
[0020] Examples are given below by way of illustration. The methods
used for evaluating physical properties in the examples and
comparative examples are described below.
[0021] 1. Measurement of Crystallization Temperature and Melting
Point with a Differential Scanning Calorimeter:
[0022] A differential scanning calorimeter (DSC) is used for
determining whether the melt processible fluoropolymer composition
forms cocrystals and is therefore miscible in the crystalline
region. The fluoropolymer composition is heated to a temperature at
least 50.degree. C. higher than the melting point of the
high-melting component and held there for a time, for example held
at 360.degree. C. for 10 minutes, in order to completely melt the
crystals. The composition is then cooled at a rate of 70.degree.
C./min and the crystallization temperature is determined as the
minimum of the exothermic peak. After crystallization, the
composition is heated at 10.degree. C./min and the melting point is
determined as the maximum of the endothermic peak. It will be
recognized that this method uses the convention by which
endothermic peaks are taken as descending to a minimum, exothermic
peaks as rising to a maximum.
[0023] When a single crystallization temperature peak appears
between the crystallization temperatures of the components and a
single melting peak appears between the melting points of the
components, the mixture is judged to be miscible in the crystalline
region and to have formed cocrystals. Occasionally two melting
peaks may appear in a specimen in which the PFA is crystallized
after having first been melted. The small peak on the
high-temperature side is attributable to molecular chains similar
to PTFE, that is, PFA chains having a low PAVE content. In such
cases, the larger peak is regarded as the melting point of the
composition.
[0024] 2. Measurement of a-Transition Temperature with Dynamic
Mechanical Analyzer:
[0025] A Perkin Elmer Model 7e dynamic mechanical analyzer (DMA) is
used for determining whether a melt processible fluoropolymer
composition is miscible in the amorphous region. The general method
for determining dynamic mechanical properties of plastics is given
in ASTM D 4065-95. Standard terminology for the analysis is given
in ASTM D 4092-96. A test specimen (3.5 mm wide, 8 mm long, 1.3 mm
thick) is formed from the melt processible fluoropolymer
composition, and the temperature dependence of tan .delta. is
measured in the dynamic mechanical analyzer 3-point bending mode at
a frequency of 1 Hz and a temperature rise rate of 5.degree.
C./min. Constant stress is applied. The amplitude of the bending is
typically about 20 .mu.m when the temperature is 15.degree. C. The
analysis is typically carried out over a temperature range of about
15.degree. C. to 150.degree. C. The .alpha.-transition temperature
(the highest temperature transition) is determined as the peak
temperature on the tan .delta. curve.
[0026] When a single .alpha.-transition temperature proportional to
the blend ratio of copolymers in the composition appears between
the a-transition temperatures for the two components, the mixture
is considered to be miscible in the amorphous region. Because the
a-transition temperature of PFA is regarded as similar to the
glass-transition temperature of an ordinary polymer, the appearance
of a single .alpha.-transition temperature proportional to the
ratio of the mixture indicates that the components are mixed at the
molecular level in the amorphous region.
[0027] Those skilled in the art will recognize that other
temperature transitions, specifically the .gamma.-transition, are
sometimes referred to as glass-transition temperatures (see for
example, S. V. Gangal in The Encyclopedia of Polymer Science and
Engineering, vol. 16, p. 604; John Wiley and Sons, New York).
However, the a-transition temperature is the higher of the two and
is of greater interest when polymer use properties under normal
conditions are being considered.
[0028] 3. Flex Life:
[0029] A specimen (0.2 mm thick, 15 mm wide, 110 mm long) is
compression molded from the melt processible fluoropolymer
composition, and the flex life of the specimen is measured by the
MIT method under a 1 kg load. The MIT method is described in ASTM D
2176. A Toyoseiki K. K. MIT Folding Endurance Machine is used.
[0030] 4. Melt Flow Rate and Viscosity:
[0031] Melt flow rate (MFR) in units of g/10 minutes and, as
disclosed herein, is determined according to the general method of
ASTM D 1238, at 372.degree. C. and under a 5 kg load. Melt
viscosity (MV) in units Pa.multidot.s is calculated from the melt
flow rate using Equation (1):
MV=53150.div.MFR (1)
[0032] 5. Polymers:
[0033] The polymers used in the examples are commercial products
where indicated. Otherwise, they are made according to the methods
disclosed in U.S. Pat. No. 5,760,151.
EXAMPLES 1 TO 4, COMPARATIVE EXAMPLES 1 AND 2
[0034] Dispersions of PFA-C3 (PFA 345J, produced by DuPont-Mitsui
Fluorochemicals Co., Ltd.; melt flow rate (MFR) 5 g/10 min; MV
10600 Pa.multidot.s, melting point 308.degree. C.) containing 3.5%
by weight of perfluoro(propyl vinyl ether) (PPVE) and of PFA-C2
(produced by DuPont-Mitsui Fluorochemicals Co., Ltd.; MFR 23 g/10
min, MV 2300 Pa s, melting point 296.degree. C.) containing 5.7% by
weight of perfluoro(ethyl vinyl ether) (PEVE) are mixed in the
proportions shown in Table 1, stirred and coagulated, then washed
and dried to give a specimen. Specimens are also made in the same
way from each of the starting materials. FIG. 1 shows the
crystallization temperatures (Tc) of the components and the blends.
Table 1 summarizes the crystallization temperature and the melting
point measurements of the specimens.
[0035] As is apparent from FIG. 1 and Table 1, a single
crystallization peak for the mixture appears between the
crystallization temperatures of the two components (PFA-C3,
267.degree. C.; PFA-C2, 250.degree. C.) at a temperature
proportional to the ratio of the components, and a single melting
point proportional to the ratio appears between the melting points
of the components (PFA-C3, 308.degree. C.; PFA-C2, 296.degree. C.)
during the heating scan. Accordingly, it is concluded that the
mixture is miscible in the crystalline regions and forms
cocrystals. In Table 1, the melting point of the
PFA-C3/PFA-C2=60/40 mixture (Example 2) is 305.degree. C., which is
about 9.degree. C. higher than the melting point of the
lower-melting component PFA-C2.
[0036] Using test pieces compression-molded from each of the above
specimens, the .alpha.-transition temperature is measured with a
dynamic mechanical analyzer. The results are summarized in Table 1.
The PFA-C3/PFA-C2 mixtures exhibit a single .alpha.-transition
temperature between the .alpha.-transition temperatures of the
components and proportional to the ratio of components. This
indicates that the composition is miscible in the amorphous
regions. Furthermore, the maximum service temperature of the PFA-C2
is increased by the blending, and mechanical strength is maintained
at temperatures greater than that of the PFA-C2 alone. The heat
deflection temperature of the PFA-C2 is also increased by the
blending. At the same time, the flex life of the blend is improved
over that of PFA-C3 by itself.
1 TABLE 1 Comp. Comp. Ex.1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 2 PFA-C3 (wt
%) 100 80 60 40 20 0 (3.5 wt % PPVE) PFA-C2 (wt %) 0 20 40 60 80
100 (5.7 wt % PEVE) Crystallization 267 263 260 257 255 250
temperature (.degree. C.) Melting point (.degree. C.) 308 307 305
303 300 296 .alpha.-Transition 82 80 79 78 77 77 temperature
(.degree. C.)
EXAMPLE 5
[0037] To investigate the crystallization rate dependence of the
melting point, specimens prepared from the PFA-C3/PFA-C2=40/60 (by
weight) mixture used in Example 3 are held at 360.degree. C. for 10
minutes and the crystals completely melted, following which
crystallization is induced at cooling rates of 5.degree. C./min,
10.degree. C./min, 20.degree. C./min, and 70.degree. C./min. The
melting points are then measured at a heating rate of 10.degree.
C./min. The results are summarized in Table 2.
[0038] It is apparent from Table 2 that, over a broad range of
cooling conditions, the 40/60 mixture exhibits a single melting
point (about 304.degree. C.) between the melting points of both
components (PFA-C3, 308.degree. C.; PFA-C2, 296.degree. C.). Hence,
the components of this blend cocrystallize regardless of the
cooling conditions. The fact that cocrystals form whether cooling
is rapid or gradual means that a uniform and intimate mixture can
easily be formed in ordinary melt fabrication processes.
Extraordinary care need not be taken to ensure that phase
separation of the components does not occur under certain cooling
conditions.
2 TABLE 2 Example 5 PFA-C3 (wt %) - (PPVE content, 3.5 wt %) 40
PFA-C2 (wt %) - (PEVE content, 5.7 wt %) 60 Melting point (.degree.
C.) (cooling rate, 5.degree. C./min) 305 Melting point (.degree.
C.) (cooling rate, 10.degree. C./min) 304 Melting point (.degree.
C.) (cooling rate, 20.degree. C./min) 304 Melting point (.degree.
C.) (cooling rate, 70.degree. C./min) 303
EXAMPLE 6
[0039] To determine if miscibility is affected by the blending
method, melt blending is carried out with an R-60 internal melt
kneader (manufactured by Toyo Seiki Seisaku-sho Co., Ltd.) using
the polymers described in Examples 1 to4, in the same weight ratio
(40/60) as in Example 3. FIG. 2 summarizes the results obtained by
DSC measurements of the resulting composition carried out in the
same fashion as in Example 3. For comparison, the dispersion-mixing
results from Example 3 are included.
[0040] As is apparent from FIG. 2, only one melting point (Tm)
appears between the melting points of the components PFA-C3 and
PFA-C2. This shows that the melt blend exists in a uniform,
intimately mixed state, and the melting point in this case is
essentially the same as that of a dispersion mixture of the same
composition. Thus, it is apparent that the PFA-C3 and PFA-C2
cocrystallize regardless of mixing methods. A small melting peak
appears near 310.degree. C. on the melting curve, but, as is stated
above, this arises from the melting of PFA-C3 chains having a low
PAVE content. Because a small melting peak is also seen near
310.degree. C. after the crystallization of pure PFA-C3, this peak
is clearly not the melting peak of the cocrystal. The large peak
near 303.degree. C. is the melting peak of the cocrystal.
[0041] This example demonstrates that the compositions of this
invention do not require special mixing means for their production.
Standard mixing methods are acceptable.
EXAMPLES 7 TO 10, COMPARATIVE EXAMPLE 3
[0042] Specimens of PFA-C3/PFA-C2 mixtures are prepared by the
dispersion mixing process in the same manner as in Examples 1 to 4
except that a copolymer (manufactured by DuPont-Mitsui
Fluorochemicals, Co., Ltd.; MFR 9.7 g/10 min, MV 5700
Pa.multidot.s) containing 13.3% by weight of PEVE is used as
PFA-C2. Melting point measurements (DSC) and .alpha.-transition
temperature measurements (DMA) are carried out on the resulting
compositions. The same measurements are also carried out on the
PFA-C2 alone. The results are summarized in Table 3.
[0043] As is apparent from Table 3, unlike the results obtained in
Examples 1 to 4 using PFA-C2 containing 5.7% by weight of PEVE, two
melting points (PFA-C3: near 308.degree. C.; PFA-C2: near
254.degree. C.) corresponding to the melting points of the
respective components are observed in these mixtures. Also, because
the specimen composed solely of PFA-C2 has a high PEVE, the melting
point is low and the degree of crystallinity is low. As a result,
because the melting point difference between the two components is
about 54.degree. C. and the crystallization temperature difference
is about 45.degree. C., during crystallization of the mixture the
higher melting component PFA-C3 crystallizes first, after which the
PFA-C2 solidifies within the already formed matrix of solid PFA-C3.
In mixtures having a PFA-C3 content of 60% or more, crystallization
of the PFA-C2 is hindered, and no melting peak for PFA-C2
appears.
[0044] In the other PFA-C3/PFA-C2 mixtures in these examples,
because of the wide difference in the crystallization temperatures
of the components and the high PAVE content of PFA-C2, the
high-melting component PFA-C3 crystallizes first, resulting in
phase separation between the crystal phases of the components, and
the appearance of two melting points, which correspond to the
melting points of the components. Therefore, the above blend is not
miscible in the crystalline regions. However, a single
.alpha.-transition temperature appears at a point between the
.alpha.-transition temperatures of the two components and
proportional to the composition, indicating miscibility in the
amorphous regions. The heat deflection temperature of the PFA-C2 is
increased by the blending.
3 TABLE 3 Comp. Comp. Ex. 1 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 3 PFA-C3
(wt %) - 100 80 60 40 20 0 (3.5 wt % PPVE) PFA-C2 (wt %) - 0 20 40
60 80 100 (13.3 wt % PEVE) PFA-C3 melting point 308 307 307 307 306
-- (.degree. C.) High temperature side PFA-C2 melting point -- no
no 251 253 254 (.degree. C.) peak peak Low temperature side
.alpha.-Transition temp. 82 77 68 65 61 61 (.degree. C.)
EXAMPLES 11 TO 15, COMPARATIVE EXAMPLE 4
[0045] PFA-C3 (PFA 340J, from DuPont-Mitsui Fluorochemicals Co.,
Ltd.; MFR 13.0 g/10 min, MV 4100 Pa.multidot.s) containing 3.9% by
weight of PPVE and PFA-C2 (DuPont-Mitsui Fluorochemicals Co., Ltd.;
MFR 14.3 g/10 min, MV 3700 Pa.multidot.s) containing 6.7% by weight
of PEVE, or PFA-C2 (DuPont-Mitsui Fluorochemicals Co., Ltd.; MFR
10.1 g/10 min, MV 5250 Pa.multidot.s) containing 14.5% of PEVE are
melted and mixed by the same method as in Example 6 and in the
mixing ratios shown in Table 4. Test pieces compression-molded from
the resulting mixtures are subjected to flex life measurements by
the MIT method. Because flex life is strongly dependent upon
molecular weight (or MFR), components having similar melt flow
rates are selected for these examples. The flex lives of test
pieces composed only of PFA-C3 are also measured. The results are
summarized in Table 4.
[0046] As is apparent from Table 4, the flex life of PFA-C3 is
improved by admixture of PFA-C2. Moreover, at the same ratios, the
use of PFA-C2 having a higher PEVE content increases the relative
proportion of the amorphous region, thereby increasing the flex
life. That is, PFA-C2 with higher PEVE is a more effective blend
component. The blends of Examples 11 to 13, which are miscible in
both the amorphous and the crystalline regions, exhibit increased
deflection temperature and maintain their mechanical properties to
higher temperatures compared to PFA-C2. Examples 14 and 15, which
are miscible in the amorphous regions but not in the crystalline
regions, exhibit increased deflection temperature compared to
PFA-C2.
4 TABLE 4 Comp. Ex. 4 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 PFA-C3 100
90 80 70 90 80 (wt %) - (3.9 wt % PPVE) PFA-C2 0 10 20 30 (wt %) -
(6.7 wt % PEVE) PFA-C2 10 20 (wt %) - (14.5 wt % PEVE) Flex life
29,000 32,000 42,000 55,000 76,000 120,000 (cycles)
[0047] Because they are miscible in amorphous regions, the melt
processible fluoropolymer compositions according to the present
invention have desirable properties, including enhanced mechanical
properties such as flex life, and lower permeability to gases and
chemicals. Moreover, by suitably selecting the constituent
components, there can be obtained compositions that will
cocrystallize after conventional melt fabrication, regardless of
the cooling conditions and mixing method. The cocrystallized
composition thus obtained will have a melting point situated
between the melting point of the lower-melting PFA and the melting
point of the higher-melting PFA. Accordingly, this is an effective
means for improving the maximum service temperature of the
lower-melting component while taking advantage of its contribution
to product properties, such as improved flex life.
* * * * *