U.S. patent application number 14/435831 was filed with the patent office on 2015-10-15 for stampable sheet.
The applicant listed for this patent is TORAY INDUSTRIES, INC.. Invention is credited to Takafumi Hashimoto, Katsuhiro Miyoshi, Yoshihiro Naruse, Tetsuya Ohara, Takashi Shimada.
Application Number | 20150292146 14/435831 |
Document ID | / |
Family ID | 50544541 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150292146 |
Kind Code |
A1 |
Miyoshi; Katsuhiro ; et
al. |
October 15, 2015 |
STAMPABLE SHEET
Abstract
A stampable sheet includes discontinuous carbon fibers and a
thermoplastic resin as a matrix resin, wherein viscosity .eta. of
the stampable sheet in a state where the matrix resin in the
stampable sheet is molten is .eta.0.ltoreq..eta.<.eta.0
exp(0.20Vf)(Pas), and ratio Z of refined carbon fiber bundles (A)
in which Mn/(Ln.times.D) is less than 8.5.times.10-1 (mg/mm2) to
the total weight of carbon fibers in the stampable sheet is
10.ltoreq.Z<70 (wt %). The configuration makes it possible to
provide a stampable sheet provided with a controlled range of
conditions, and to achieve both high flowability during molding and
high mechanical properties after molding.
Inventors: |
Miyoshi; Katsuhiro; (Nagoya,
JP) ; Shimada; Takashi; (Otsu, JP) ;
Hashimoto; Takafumi; (Nagoya, JP) ; Ohara;
Tetsuya; (Otsu, JP) ; Naruse; Yoshihiro;
(Nagoya, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TORAY INDUSTRIES, INC. |
Tokyo |
|
JP |
|
|
Family ID: |
50544541 |
Appl. No.: |
14/435831 |
Filed: |
October 15, 2013 |
PCT Filed: |
October 15, 2013 |
PCT NO: |
PCT/JP2013/077973 |
371 Date: |
April 15, 2015 |
Current U.S.
Class: |
442/60 ;
442/179 |
Current CPC
Class: |
C08J 5/042 20130101;
B29K 2101/12 20130101; C08K 7/06 20130101; D06M 15/59 20130101;
B29B 11/16 20130101; C08J 5/06 20130101; B29C 70/12 20130101; D06M
2101/40 20130101; B29K 2307/04 20130101 |
International
Class: |
D06M 15/59 20060101
D06M015/59 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2012 |
JP |
2012-235635 |
Claims
1.-11. (canceled)
12. A stampable sheet comprising discontinuous carbon fibers and a
thermoplastic resin as a matrix resin, wherein viscosity .eta. of
said stampable sheet in a state where said matrix resin in said
stampable sheet is molten is
.eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.20Vf) (Pas), and a
proportion Z of refined carbon fiber bundles (A) in which
Mn/(Ln.times.D) is less than 8.5.times.10.sup.-1 (mg/mm.sup.2) to
the total weight of carbon fibers in said stampable sheet is
10.ltoreq.Z<90 (wt %), where .eta.: apparent viscosity of said
stampable sheet at a time when said matrix resin is molten (a
viscosity at a temperature of a solidification start temperature of
said matrix resin+50.degree. C.), Vf: carbon fiber content (%) per
unit volume of said stampable sheet, .eta..sub.0: hypothetical
resin viscosity of said matrix resin obtained by extending a
characteristic line up to a position of Vf=0% in a characteristic
chart which is obtained by changing said Vf and represents a
relationship between said Vf and the viscosity of said stampable
sheet, Mn: weight of carbon fiber bundles, Ln: fiber length of
carbon fibers, D: fiber diameter of carbon fibers.
13. The stampable sheet according to claim 12, wherein said
proportion Z of said carbon fiber bundles (A) to the total weight
of carbon fibers in said stampable sheet is 10.ltoreq.Z<70 (wt
%), a proportion Y of carbon fiber bundles (B) in which
Mn/(Ln.times.D) is 8.5.times.10.sup.-1 (mg/mm.sup.2) or more to the
total weight of carbon fibers is 30.ltoreq.Y<90 (wt %), an
average value X of Mn/Ln of said carbon fiber bundles (B) is
1.1.times.10.sup.-2.ltoreq.X.ltoreq.8.1.times.10.sup.-2 (mg/mm),
and said Y satisfies Y.ltoreq.100X+30.
14. The stampable sheet according to claim 12, wherein a standard
deviation .sigma. of a number of carbon fibers Xn forming a bundle
of said carbon fiber bundles (B) in said stampable sheet satisfies
50.ltoreq..sigma..ltoreq.400.
15. The stampable sheet according to claim 12, wherein said fiber
length Ln of carbon fibers in said stampable sheet is 5-25 mm.
16. The stampable sheet according to claim 12, wherein said matrix
resin comprises any one of polyamide, polypropylene and
polyphenylene sulfide.
17. The stampable sheet according to claim 12, wherein a single
fiber flexural stiffness of carbon fibers forming said carbon fiber
bundles (A) is 1.0.times.10.sup.-11 to 2.8.times.10.sup.-11
(Pam.sup.4).
18. The stampable sheet according to claim 12, wherein said
.eta..sub.0 satisfies
2.0.times.10.sup.2.ltoreq..eta..sub.0.ltoreq.5.0.times.10.sup.4
(Pas).
19. The stampable sheet according to claim 12, wherein said
viscosity .eta. of said stampable sheet is .eta..sub.0
exp(0.07Vf).ltoreq..eta.<.eta..sub.0 exp(0.20Vf)(Pas), and said
Vf is 5.ltoreq.Vf.ltoreq.70(%).
20. The stampable sheet according to claim 12, wherein a carbon
fiber aggregate in said stampable sheet comprises a carbon fiber
nonwoven fabric made by a carding method.
21. The stampable sheet according to claim 12, wherein said
viscosity .eta. of said stampable sheet is
.eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.07Vf)(Pas), and said
Vf is 5.ltoreq.Vf.ltoreq.70(%).
22. The stampable sheet according to claim 12, wherein a carbon
fiber aggregate in said stampable sheet comprises a carbon fiber
nonwoven fabric made by an air laid method.
23. The stampable sheet according to claim 13, wherein a standard
deviation .sigma. of a number of carbon fibers Xn forming a bundle
of said carbon fiber bundles (B) in said stampable sheet satisfies
50.ltoreq..sigma..ltoreq.400.
24. The stampable sheet according to claim 13, wherein said fiber
length Ln of carbon fibers in said stampable sheet is 5-25 mm.
25. The stampable sheet according to claim 14, wherein said fiber
length Ln of carbon fibers in said stampable sheet is 5-25 mm.
26. The stampable sheet according to claim 13, wherein said matrix
resin comprises any one of polyamide, polypropylene and
polyphenylene sulfide.
27. The stampable sheet according to claim 14, wherein said matrix
resin comprises any one of polyamide, polypropylene and
polyphenylene sulfide.
28. The stampable sheet according to claim 15, wherein said matrix
resin comprises any one of polyamide, polypropylene and
polyphenylene sulfide.
29. The stampable sheet according to claim 13, wherein a single
fiber flexural stiffness of carbon fibers forming said carbon fiber
bundles (A) is 1.0.times.10.sup.-11 to 2.8.times.10.sup.-11
(Pam.sup.4).
30. The stampable sheet according to claim 14, wherein a single
fiber flexural stiffness of carbon fibers forming said carbon fiber
bundles (A) is 1.0.times.10.sup.-11 to 2.8.times.10.sup.-11
(Pam.sup.4).
31. The stampable sheet according to claim 15, wherein a single
fiber flexural stiffness of carbon fibers forming said carbon fiber
bundles (A) is 1.0.times.10.sup.-11 to 2.8.times.10.sup.-11
(Pam.sup.4).
Description
TECHNICAL FIELD
[0001] This disclosure relates to a stampable sheet comprising a
carbon fiber composite material of carbon fibers and a
thermoplastic resin and, specifically, to a stampable sheet which
can achieve compatibility between high flowability and mechanical
properties when a molded article is made using the same.
BACKGROUND
[0002] A carbon fiber composite material comprising carbon fibers
and a thermoplastic resin is used to manufacture various molded
articles because high mechanical properties can be obtained.
Specifically, when a stampable sheet comprising a carbon fiber
composite material of carbon fibers and a thermoplastic resin is
used for molding, because a rapid molding is possible by heat press
molding, such a use is considered to be suitable for molding of
mass-production articles.
[0003] With respect to conventional stampable sheets, in a
stampable sheet wherein a paper or nonwoven fabric comprising
carbon fibers is impregnated with a resin (for example, JP
2002-212311 A), although the mechanical properties of the stampable
sheet are excellent, the flowability at the time of molding is low
and moldability is poor. This is because the carbon fibers, which
are reinforcing fibers, are dispersed and therefore stress is hard
to be concentrated and, while the reinforcing effect due to the
carbon fibers is sufficiently exhibited, the carbon fibers are
crossed to each other to restrict their movements and therefore the
carbon fibers become hard to be moved. In general, when carbon
fibers are placed in a resin, the viscosity increases sharply and
it becomes difficult to flow. Further, when the fiber length of
carbon fibers in a resin is too long, the viscosity also tends to
increase.
[0004] On the other hand, in an SMC (Sheet Molding Compound) in
which a resin is impregnated into cut carbon fiber bundles,
although the flowability is high and moldability is excellent, the
mechanical properties are poor. This is because a stress is liable
to be concentrated at end portions of the carbon fibers because the
carbon fibers are formed in a bundle and, therefore, it is
difficult to exhibit high mechanical properties, but the carbon
fibers can move easily because they do not form networks, and
therefore a good flowability can be obtained at the time of molding
(for example, JP 2010-163536 A).
[0005] Further, separately from the above-described JP 2002-212311
A and JP 2010-163536 A, various technologies have been proposed
with the aim of achieving high mechanical properties of a
manufactured molded article and a good flowability at the time of
molding. For example, in JP 2011-178890 A, a composite material is
proposed wherein the proportion of specified carbon fiber bundles
relative to the total amount of fibers in a carbon fiber composite
material is suppressed, and the average number of fibers in the
respective specified carbon fiber bundles is controlled in a
specified range. However, in such a carbon fiber composite material
as described in JP 2011-178890 A wherein the carbon fiber bundles
in the carbon fiber composite material are thin, the proportion of
the bundles is small and the carbon fibers are refined, although
the mechanical properties of a molded article manufactured using
the same are excellent, the flowability at the time of molding is
low and the moldability is poor. This is because the carbon fibers,
which are reinforcing fibers, are sufficiently dispersed and
therefore stress is hard to be concentrated, and while the
reinforcing effect due to the carbon fibers is sufficiently
exhibited, the carbon fibers are crossed to each other to restrict
their movements and therefore the carbon fibers become hard to be
moved.
[0006] On the other hand, in JP 2011-178891 A, a composite material
is proposed wherein the proportion of specified carbon fiber
bundles in a carbon fiber composite material relative to the total
amount of fibers, similar to that described above, is set higher,
and the average number of fibers in the respective specified carbon
fiber bundles is controlled in another specified range. However, in
such a carbon fiber composite material as described in JP
2011-178891 A wherein the carbon fiber bundles are thick and the
proportion of the bundles is great, although the flowability at the
time of manufacturing a molded article using the same is high and
moldability is excellent, the followability in molding of carbon
fibers to a small-shape part is poor, the mechanical properties are
low and variation in the mechanical properties is great. Namely,
whereas the carbon fibers can move easily since they do not form
networks, because the carbon fiber bundles are thick, the
followability of carbon fibers is poor when a component having
small member parts is molded, stress is liable to be concentrated
at end portions of the carbon fibers and, therefore, it is
difficult to obtain high mechanical properties.
[0007] Accordingly, it could be helpful to provide a stampable
sheet having a controlled range of conditions which can satisfy
both a high flowability at the time of molding and high mechanical
properties after molding, that have not been achieved by the
conventional stampable sheet comprising a carbon fiber paper or
nonwoven sheet or by the conventional SMC.
SUMMARY
[0008] We thus provide a stampable sheet comprising discontinuous
carbon fibers and a thermoplastic resin as a matrix resin,
characterized in that a viscosity .eta. of the stampable sheet in a
state where the matrix resin in the stampable sheet is molten is
.eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.20Vf) (Pas), and a
proportion Z of refined carbon fiber bundles (A), in which
Mn/(Ln.times.D) is less than 8.5.times.10.sup.-1 (mg/mm.sup.2), to
the total weight of carbon fibers in the stampable sheet is
10.ltoreq.Z<90 (wt %) where, .eta.: apparent viscosity of the
stampable sheet at a time when the matrix resin is molten (a
viscosity at a temperature of a solidification start temperature of
the matrix resin+50.degree. C.), Vf: carbon fiber content (%) per
unit volume of the stampable sheet, .eta..sub.0: hypothetical resin
viscosity of the matrix resin obtained by extending a
characteristic line up to a position of Vf=0% in a characteristic
chart which is obtained by changing the Vf and represents a
relationship between the Vf and the viscosity of the stampable
sheet, Mn: weight of carbon fiber bundles, Ln: fiber length of
carbon fibers, D: fiber diameter of carbon fibers.
[0009] In such a stampable sheet, the configuration of the
stampable sheet is controlled particularly to satisfy both a good
flowability and high mechanical properties at a good balance by
comprehensive consideration of the following factors: a factor that
the melt viscosity of a composite material (namely, the viscosity
.eta. of a stampable sheet in a state where its matrix resin is
molten) increases sharply when carbon fibers are placed in its
matrix resin of a thermoplastic resin; a factor that, although the
flowability at the time of molding decreases when the viscosity
increases, reduction of the flowability can be suppressed by
increasing the rate of the amount of carbon fiber bundles in which
carbon fibers are in a bundle form, and thus it is possible to
realize a good flowability; a factor that, if the rate of carbon
fiber bundles becomes too high, although a good flowability can be
obtained, it becomes difficult to obtain high mechanical properties
of a molded article; and a factor that the controlled range of form
of carbon fiber bundles in view of good flowability does not always
equal to the controlled range of form of carbon fiber bundles in
view of high mechanical properties.
[0010] More concretely, when the viscosity .eta. of the stampable
sheet is .eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.20Vf)(Pas),
although it is higher than the viscosity of the resin alone as a
natural result, the viscosity .eta. is suppressed to become too
high and thus a good flowability at the time of molding can be
secured. The viscosity .eta. is preferably
.eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.13Vf)(Pas), and more
preferably .eta..sub.0.ltoreq..eta.<.eta..sub.0
exp(0.10Vf)(Pas). Further, refined carbon fiber bundles (A) in
which Mn/(Ln.times.D) is less than 8.5.times.10.sup.-1
(mg/mm.sup.2) are carbon fiber bundles which have a relatively high
degree of refinement and are likely to exhibit high mechanical
properties. When a proportion Z of such refined carbon fiber
bundles (A) to the total weight of carbon fibers is
10.ltoreq.Z<90 (wt %), it becomes possible to exhibit high
mechanical properties at a good balance while securing a good
flowability as described above.
[0011] Further, in the above-described stampable sheet, it is
further possible to employ a configuration wherein the proportion Z
of refined carbon fiber bundles (A), in which Mn/(Ln.times.D) is
less than 8.5.times.10.sup.-1 (mg/mm.sup.2), to the total weight of
carbon fibers is 10.ltoreq.Z<70 (wt %), that a proportion Y of
refined carbon fiber bundles (B), in which Mn/(Ln.times.D) is
8.5.times.10.sup.-1 (mg/mm.sup.2) or more, to the total weight of
carbon fibers is 30.ltoreq.Z<90 (wt %), an average value X of
Mn/Ln of the carbon fiber bundles (B) is
1.1.times.10.sup.-2.ltoreq.X.ltoreq.8.1.times.10.sup.-2 (mg/mm),
and the Y satisfies Y.gtoreq.100X+30.
[0012] In particular, flowability of the stampable sheet can be
further improved by controlling the proportion Y of carbon fiber
bundles (B) in which Mn/(Ln.times.D) is 8.5.times.10.sup.-1
(mg/mm.sup.2) or more, namely, carbon fiber bundles (B) which have
a relatively low degree of refinement and are likely to exhibit
high flowability, to the total weight of carbon fibers; the average
value X of Mn/Ln of the carbon fiber bundles (B); and the range of
the relationship between Y and X. To realize the compatibility
between high flowability and mechanical properties more securely, a
more preferred range of the average value X of Mn/Ln of the carbon
fiber bundles (B) is
1.5.times.10.sup.-2.ltoreq.X.ltoreq.5.5.times.10.sup.-2
(mg/mm).
[0013] Further, to realize the compatibility between high
flowability and mechanical properties, it is preferred that a
standard deviation .sigma. of a number of fibers
x.sub.n=Mn/(Ln.times.F) forming a bundle of the above-described
carbon fiber bundles (B) is 50.ltoreq..sigma..ltoreq.400, where, F
is a fineness of carbon fibers, and the calculation methods of the
number of fibers x.sub.n and the standard deviation .sigma. will be
described later. If the above-described standard deviation .sigma.
is lower than 50, the flowability is deteriorated, and if the
above-described standard deviation .sigma. is more than 400, the
mechanical properties are deteriorated, and the dispersion of the
mechanical properties becomes great.
[0014] The above-described standard deviation .sigma. is more
preferably 100.ltoreq..sigma..ltoreq.380, and further preferably
150.ltoreq..sigma..ltoreq.360.
[0015] Further, as aforementioned, since the viscosity is likely to
become high and the flowability is likely to be lowered if the
fiber length of carbon fibers becomes too long, in the stampable
sheet, it is preferred that the fiber length of carbon fibers Ln in
a stampable sheet is 5 to 25 mm.
[0016] In the stampable sheet, although the kind of the matrix
resin comprising thermoplastic resin is not particularly
restricted, it is preferred to be any of polyamide, polypropylene
and polyphenylene sulfide from the viewpoint of moldability.
[0017] Further, in the stampable sheet, to realize a good
flowability more securely while realizing high mechanical
properties, it is preferred that a single fiber flexural stiffness
of carbon fibers forming the above-described carbon fiber bundles
(A) is 1.0.times.10.sup.-11 to 2.8.times.10.sup.-11
(Pam.sup.4).
[0018] To realize a further high flowability, the above-described
.eta..sub.0 is preferably
2.0.times.10.sup.2.ltoreq..eta..sub.0.ltoreq.5.0.times.10.sup.4
(Pas). If .eta..sub.0 becomes lower than 2.0.times.10.sup.2, there
is a fear that the resin may become brittle and the properties may
be lowered, and if .eta..sub.0 becomes greater than
5.0.times.10.sup.4, there is a fear that the viscosity may become
high even when the gradient of the characteristic line is small and
therefore the flowability may deteriorate.
[0019] To realize the compatibility between high flowability and
mechanical properties more securely, the viscosity .eta. of a
stampable sheet is preferably .eta..sub.0
exp(0.07Vf).ltoreq..eta.<.eta..sub.0 exp(0.20Vf)(Pas), and the
Vf is preferably 5.ltoreq.Vf.ltoreq.70(%).
[0020] Further, when the viscosity .eta. of a stampable sheet is
.eta..sub.0 exp(0.07Vf).ltoreq..eta.<.eta..sub.0
exp(0.20Vf)(Pas), it is preferred that carbon fiber aggregates in
the stampable sheet comprise a carbon fiber nonwoven fabric made by
carding method.
[0021] Alternatively, to realize a higher flowability, the
viscosity .eta. of the above-described stampable sheet is
preferably .eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.07Vf)
(Pas), and the Vf is preferably 5.ltoreq.Vf<70(%).
[0022] Furthermore, when the viscosity .eta. of the above-described
stampable sheet is .eta..sub.0.ltoreq..eta.<.eta..sub.0
exp(0.07Vf)(Pas), it is preferred that carbon fiber aggregates in
the stampable sheet comprise a carbon fiber nonwoven fabric made by
air laid method.
[0023] Thus, in the stampable sheet, it becomes possible to provide
an excellent stampable sheet wherein both an excellent flowability
at the time of molding and high mechanical properties of a molded
article can be achieved, and wherein the mechanical properties are
in a narrow range of variation.
BRIEF EXPLANATION OF THE DRAWINGS
[0024] FIG. 1 is a characteristic chart showing concepts of
viscosity and solidification start temperature of a resin.
[0025] FIG. 2 is a characteristic chart showing a concept of
determination of viscosity.
[0026] FIG. 3 is a schematic diagram showing an example of a
carding machine.
[0027] FIG. 4 is a schematic diagram showing an example of an air
laid machine.
EXPLANATION OF SYMBOLS
[0028] 1: carding machine [0029] 2: cylinder roll [0030] 3: take-in
roll [0031] 4: doffer roll [0032] 5: worker roll [0033] 6: stripper
roll [0034] 7: feed roll [0035] 8: belt conveyer [0036] 9:
discontinuous carbon fibers [0037] 10: sheet-like web [0038] 20:
air laid machine [0039] 21: drum [0040] 22: pin cylinder [0041] 23:
wire [0042] 24: suction box
DETAILED DESCRIPTION
[0043] Hereinafter, our stampable sheets will be explained in
detail together with Examples and Comparative Examples.
[0044] First, the viscosity .eta. of the stampable sheet in a state
where the matrix resin in the stampable sheet is molten is
.eta..sub.0.ltoreq..eta.<.eta..sub.0 exp(0.20Vf)(Pas). As shown
in FIG. 1 as a concept diagram with respect to the characteristics
of the stampable sheet, when the temperature becomes high, the
matrix resin melts at a certain temperature and the viscosity
exhibits an approximately constant value at a temperature higher
than the certain temperature. This temperature at which the matrix
resin begins to melt can be perceived as a solidification start
temperature of the matrix resin during a step of lowering the
temperature from the molten state. Therefore, the stampable sheet
viscosity .eta., which exhibits an approximately constant value
regardless of the temperature change as described above, is defined
as a viscosity at a temperature of the solidification start
temperature of the matrix resin+50.degree. C., and the stampable
sheet viscosity .eta., which can be thus perceived, is defined in
the above-described range using the viscosity .eta..sub.0 of the
matrix resin. The viscosity no of the matrix resin can be
determined as shown in FIG. 2. Namely, when the viscosity .eta. of
a stampable sheet is measured (measured points: indicated as black
square points) in relation to the Vf (carbon fiber content (%) per
unit volume of the stampable sheet), as shown in FIG. 2, an
approximately linear characteristic line can be obtained in a
semilogarithmic graph. The value at which the characteristic line
crosses the vertical axis of viscosity .eta. when the
characteristic line is extended up to a position of Vf=0% can be
obtained as a hypothetical resin viscosity of the molten resin
(namely, it is a viscosity of the matrix resin alone determined by
the characteristic line of the viscosity .eta.). The range of the
viscosity .eta. of a stampable sheet is defined as described above
relative to the thus determined viscosity no of the matrix resin.
Namely, the range of the viscosity .eta. of a stampable sheet is a
range depicted as a region R surrounded by the line of the
viscosity .eta..sub.0 of the matrix resin (depicted as a dotted
line) and the characteristic line of the viscosity .eta. (depicted
as a solid line) in FIG. 2.
[0045] Next, although the carbon fibers are not particularly
restricted, high-strength and high-elastic modulus carbon fibers
can be used, and one kind of carbon fibers may be used or two or
more kinds of carbon fibers may be used together. In particular,
carbon fibers such as PAN-based, pitch-based and rayon-based ones
can be exemplified. From the viewpoint of the balance between the
strength and the elastic modulus of a molded article to be
obtained, PAN-based carbon fibers are more preferable. The density
of carbon fibers is preferably 1.65 to 1.95 g/cm.sup.3, and more
preferably 1.70 to 1.85 g/cm.sup.3. If the density is too high, the
lightness in weight of a carbon fiber-reinforced plastic obtained
is poor and, if too low, there is a possibility where the
mechanical properties of a carbon fiber-reinforced plastic obtained
become low.
[0046] Further, the carbon fibers are preferably formed as a bundle
from the viewpoint of productivity, and it is preferred that the
number of single fibers in the bundle is many. The number of single
fibers for the carbon fiber bundle can be 1,000 to 350,000, and in
particular, it is preferably 10,000 to 100,000. However, the carbon
fiber bundle is required to satisfy our conditions.
[0047] The single fiber flexural stiffness of carbon fibers is, as
aforementioned, preferably 1.0.times.10.sup.-11 to
2.8.times.10.sup.-11 Pam.sup.4, and more preferably
1.0.times.10.sup.-11 to 1.5.times.10.sup.-11 Pam.sup.4. Such a
single fiber flexural stiffness in the above-described range makes
it possible, in the process of manufacturing carbon fiber
aggregates described later, to stabilize the quality of carbon
fiber aggregates obtained.
[0048] Further, for the purpose of improving the adhesive property
between carbon fibers and a matrix resin and the like, it is
preferred that the carbon fibers are surface treated. As a method
of the surface treatment, there are electrolytic treatment, ozone
treatment, ultraviolet treatment and the like. Further, for the
purpose of preventing the fuzz generation of carbon fibers,
improving the convergence of carbon fibers, improving the adhesive
property between carbon fibers and a matrix resin, and the like, a
sizing agent may be provided to the carbon fibers. As a sizing
agent, a compound having a functional group such as an epoxy group,
a urethane group, an amino group, and a carboxyl group can be used,
and one kind or two or more kinds of these compounds may be
used.
[0049] Further, as a sizing treatment, a treatment method is
employed wherein a liquid containing a sizing agent (a sizing
liquid) is provided after drying wet carbon fiber bundles which are
wetted by water and have a moisture content of about 20 to about 80
wt % by generally known surface treatment process and washing
process.
[0050] Although the method of providing a sizing agent is not
particularly restricted, for example, typical examples of the
method include a method of dipping the fibers into a sizing liquid
via rollers, a method of bringing the fibers into contact with a
roller adhered with a sizing agent, and a method of spraying an
atomized sizing agent. Further, although any of a batch type and a
continuous type may be employed, a continuous type is preferred
because it provides a good productivity and helps to minimize the
degree of variation. At that time, so that the adhesion amount of
the effective components of the sizing agent relative to the carbon
fibers can become uniform within an adequate range, it is preferred
to control the concentration and the temperature of the sizing
agent, the tension of the yarns and the like. Further, it is more
preferred to vibrate the carbon fibers by a ultrasonic wave at the
time of providing the sizing agent.
[0051] Although the temperature and the time for drying should be
adjusted depending upon the adhesion amount of the compound, from
the viewpoints of completely removing the solvent used for
providing the sizing agent, shortening the time required for the
drying, on the other hand, preventing the heat deterioration of the
sizing agent and preventing the carbon fiber bundles from being
grown stiff and being deteriorated with the bundle spreading
property, the temperature for drying is preferably 150.degree. C.
or higher and 350.degree. C. or lower, and more preferably
180.degree. C. or higher and 250.degree. C. or lower.
[0052] The adhesion amount of a sizing agent relative to the mass
of only the carbon fibers is preferably 0.01 mass % or more and 10
mass % or less, more preferably 0.05 mass % or more and 5 mass % or
less, and further preferably 0.1 mass % or more and 5 mass % or
less. If less than 0.01 mass %, the effect for improving the
adhesive property is hardly exhibited. If more than 10 mass %,
there is a possibility where the properties of a molded article may
be reduced.
[0053] A thermoplastic resin is used as a matrix resin. The
material of the thermoplastic matrix resin is not particularly
restricted, and it can be appropriately selected within a range
that does not greatly reduce the mechanical properties of the
carbon fiber-reinforced plastic as a molded article. For example, a
polyolefin-based resin such as polyethylene or polypropylene, a
polyamide-based resin such as nylon 6 or nylon 6,6, a
polyester-based resin such as polyethylene terephthalate or
polybutylene terephthalate, or a resin such as a polyphenylene
sulfide, a polyetherketone, a polyethersulfone, or an aromatic
polyamide, can be used. Among them, the thermoplastic resin
preferably comprises any of polyamide, polypropylene and
polyphenylene sulfide.
[0054] Typical examples of the process of obtaining carbon fiber
aggregates include carding and air laid. The carding means an
operation of arranging the direction of discontinuous fibers or
unraveling fibers by applying a shear force in an approximately
same direction to the aggregates of discontinuous carbon fibers
with a comb-like member. Generally, it is performed using a carding
machine equipped with a roll having many needle-like projections on
the surface and/or a roll wound with a metallic wire having saw
blade-like projections.
[0055] When such a carding is carried out, it is preferred to
shorten the time (residence time) during which carbon fibers are
present in the carding machine, for the purpose of preventing the
carbon fibers from being folded. More specifically, it is preferred
to transfer the carbon fibers existing on the wires wound onto a
cylinder roll of a carding machine to a doffer roll in minimal
time. Therefore, to accelerate such a transfer, it is preferred to
rotate the cylinder roll at a high rotational speed, for example,
250 rpm or higher. Further, for the same reason, it is preferred
that the surface speed of the doffer roll is set at a high speed,
for example, 10 m/min. or higher.
[0056] The process of carding the carbon fiber bundles is not
particularly restricted, and a general one can be used. For
example, as shown in FIG. 3, carding machine 1 mainly comprises a
cylinder roll 2, a take-in roll 3 provided at an upstream side and
closely to the outer circumferential surface of the cylinder roll
2, a doffer roll 4 provided closely to the outer circumferential
surface of the cylinder roll 2 at a downstream side which is a side
opposite to the side of the take-in roll 3, a plurality of worker
rolls 5 provided closely to the outer circumferential surface of
the cylinder roll 2 between the take-in roll 3 and the doffer roll
4, stripper rolls 6 provided closely to the worker rolls 5, a feed
roll 7 provided closely to the take-in roll 3, and a belt conveyer
8.
[0057] Discontinuous carbon fiber bundles 9 are supplied to belt
conveyer 8, and the carbon fiber bundles 9 are introduced onto the
outer circumferential surface of cylinder roll 2 through the outer
circumferential surface of feed roll 7 and then through the outer
circumferential surface of take-in roll 3. Up to this stage, the
carbon fiber bundles 9 are refined and become floc-like aggregates
of carbon fiber bundles. Although a part of the floc-like
aggregates of carbon fiber bundles introduced onto the outer
circumferential surface of cylinder roll wind around the outer
circumferential surface of worker rolls 5, these carbon fibers are
stripped off by stripper rolls 6 and returned again onto the outer
circumferential surface of the cylinder roll 2. Many needles,
projections exist at standing conditions on the outer
circumferential surfaces of the respective rolls of feed roll 7,
take-in roll 3, cylinder roll 2, worker rolls 5 and stripper rolls
6, and in the above-described steps, by the operation of the
needles, the carbon fiber bundles are refined into
predetermined-condition bundles, and oriented to some extent. The
carbon fiber bundles, refined into predetermined-condition bundles
through such steps, move onto the outer circumferential surface of
doffer roll 4 as a sheet-like web 10 which is one form of the
carbon aggregates.
[0058] As for air laid, it is not particularly restricted too, and
a general method can be used. Examples of general air laid
processes include Honshu Paper process, Kroyer process, Danweb
process, J&J process, KC process, Scott process and the like
(refer to "Base and application of non-woven fabric" (Non-woven
fabric seminar in Japan Fibrous Machine Society, published in
1993)). More specifically, the examples include a process having a
step of introducing cut carbon fiber bundle single materials or cut
carbon fiber bundles and thermoplastic resin fibers into a tube, a
step of blowing compressed air to refine fibers, and a step of
obtaining carbon fiber aggregates which are dispersed and fixed;
and a process having a step of refining cut carbon fiber bundle
single materials or cut carbon fiber bundles and thermoplastic
resin fibers by a refining means (for example, a pin cylinder) to
form a carbon fiber nonwoven fabric as carbon fiber aggregates.
[0059] FIG. 4 is a schematic configuration diagram showing an
example of an air laid machine. In FIG. 4, air laid machine 20 has
drums 21 rotated in directions reverse to each other, each formed
in a cylinder shape and having small holes, pin cylinders 22
provided in the respective drums 21, wires 23 running under the
drums 21, and suction box 24 provided under the wires 23. When
carbon fiber bundle single materials or carbon fiber bundles and
thermoplastic resin fibers are supplied to air laid machine 20,
these fibers are air transported to drums 21 together with a large
amount of air, they are refined by pin cylinders 22 in drums 21,
discharged from the small holes, and they drop onto wires 23
running thereunder. The air used for the air transportation is
sucked into suction box 24, and only refined carbon fiber bundle
single materials or refined carbon fiber bundles and thermoplastic
resin fibers are left on wires 23 to form a carbon fiber nonwoven
fabric.
[0060] The carbon fiber aggregates, as referred to herein, mean
aggregates in a state where discontinuous carbon fiber bundles are
refined and oriented by the above-described carding or air laid,
and in which their configuration is maintained by entanglement or
friction between fibers. Examples of such carbon fiber aggregates
include a thin sheet-like web and a nonwoven fabric made of
laminated webs that are, when necessary, entangled or adhered
together.
[0061] The carbon fiber aggregates may comprise only carbon fiber
bundle single materials, or may include carbon fiber bundles and
thermoplastic resin fibers. It is preferred to add thermoplastic
resin fibers because it makes it possible to prevent carbon fibers
from fracturing in the carding or air laid process. Carbon fibers
are difficult to twine around and liable to break, because they are
rigid and brittle. Therefore, carbon fiber aggregates consisting of
only carbon fibers have potential problems that they are liable to
be cut off and the carbon fibers are liable to fall out. Carbon
fiber aggregates containing thermoplastic resin fibers, which are
flexible, resistant to breakage and liable to twine, make it
possible to form carbon fiber aggregates having a high uniformity.
When carbon fiber aggregates include thermoplastic resin fibers,
the ratio of carbon fiber content in the carbon fiber aggregates is
preferably 20-95 wt %, more preferably 50-95 wt %, and further
preferably 70-95 wt %. If the ratio of carbon fiber content is too
low, it becomes difficult to obtain high mechanical properties when
manufacturing carbon fiber composite material. On the other hand,
if the ratio of carbon fiber content is too high, the
above-described effect to promote the uniformity of carbon fiber
aggregates cannot be obtained.
[0062] When carbon fiber aggregates contain thermoplastic resin
fibers, the fiber length of thermoplastic resin fibers are not
particularly limited as long as it is in a desired range such as
configuration preservation of carbon fiber aggregates and
prevention of fallout of carbon fibers. In general, thermoplastic
resin fibers having a fiber length of approximately 10-100 mm can
be used. The fiber length of thermoplastic resin fibers can be
determined in relation to the fiber length of carbon fibers. For
example, a greater tension is applied to a fiber having a longer
fiber length at the time of elongating carbon fiber aggregates.
Therefore, when aligning carbon fibers in the longitudinal
direction of carbon fiber aggregates by applying tension to carbon
fibers, it is possible to configure the fiber length of the carbon
fibers to be longer than the fiber length of thermoplastic resin
fibers. In the opposite case, it is possible to configure the fiber
length of the carbon fibers to be shorter than the fiber length of
thermoplastic resin fibers.
[0063] Further, it is preferred to provide a crimp to the
above-described thermoplastic resin fibers for the objective of
enhancing the effect of tangle due to the thermoplastic resin
fibers. The degree of the crimp is not particularly limited as long
as it is in a desired range and, generally, thermoplastic resin
fibers having a number of crimps of approximately 5 to 25 crests
per 25 mm and a rate of crimp of approximately 3 to 30% can be
used.
[0064] The material for such thermoplastic resin fibers is not
particularly restricted, and it can be selected suitably within a
range that does not greatly reduce the mechanical properties of the
carbon fiber composite material. For example, it is possible to use
fibers which are prepared by spinning a resin such as a
polyolefin-group resin such as polyethylene or polypropylene, a
polyamide-group resin such as nylon 6 or nylon 6,6, a
polyester-group resin such as polyethylene terephthalate or
polybutylene terephthalate, a polyetherketone, a polyethersulfone
or an aromatic polyamide. It is preferred that such a material for
thermoplastic resin fibers is appropriately selected in accordance
with the combination with a matrix resin. In particular,
thermoplastic resin fibers prepared using the same resin as a
matrix resin, a resin having a compatibility with a matrix resin or
a resin having a high adhesive property with a matrix resin is
preferred, because the mechanical properties of a carbon
fiber-reinforced plastic are not lowered. For example, the
thermoplastic resin fibers are preferred to be composed of at least
one kind of fibers selected from the group consisting of polyamide
fibers, polyphenylene sulfide fibers, polypropylene fibers,
polyetheretherketone fibers and phenoxy resin fibers.
[0065] When a matrix resin is impregnated into the carbon fiber
aggregates, a method may be employed wherein carbon fiber
aggregates containing thermoplastic resin fibers are prepared and
the thermoplastic resin fibers contained in the carbon fiber
aggregates are used as the matrix resin as they are, or a method
may also be employed wherein carbon fiber aggregates not containing
thermoplastic resin fibers are used as a raw material, and a matrix
resin is impregnated at an arbitrary stage for producing a carbon
fiber composite material. Further, even when carbon fiber
aggregates containing thermoplastic resin fibers are used as the
raw material, a matrix resin can be impregnated at an arbitrary
stage of producing a carbon fiber composite material. In such a
case, a resin forming thermoplastic resin fibers and a matrix resin
may be an identical resin, and may be resins different from each
other. When the resin forming thermoplastic resin fibers and the
matrix resin are different from each other, it is preferred that
both resins have a compatibility or a high affinity.
[0066] When the stampable sheet comprising the carbon fiber
composite material is produced, a thermoplastic resin as a matrix
resin is impregnated into the above-described carbon fiber
aggregates, and the impregnation step for manufacturing the carbon
fiber composite material can be carried out using a press machine
having a heating function. The press machine is not particularly
restricted as long as it can realize temperature and pressure
required for impregnation of the matrix resin, a usual press
machine having a plane-like platen moved vertically, or a so-called
double belt press machine having a mechanism to run a pair of
endless steel belts can be used. In such an impregnation step,
after the matrix resin is prepared in a sheet-like form such as a
film, a nonwoven fabric or a woven fabric, it is laminated with the
carbon fiber aggregates and, at that condition, the matrix resin
can be melted and impregnated using the above-described press
machine. Further, a method can also be employed wherein
discontinuous fibers are prepared using a matrix resin, by mixing
them and inorganic fibers at a step for making carbon fiber
aggregates, carbon fiber aggregates containing the matrix resin and
the inorganic fibers are prepared, and the carbon fiber aggregates
are heated and pressed using the press machine and the like.
[0067] The carbon fiber content Vf (%) per unit volume of a
stampable sheet comprising carbon fiber composite material is
preferably 5.ltoreq.Vf<80(%), more preferably
5.ltoreq.Vf.ltoreq.70(%), and further preferably
10.ltoreq.Vf.ltoreq.50(%). If the value of Vf becomes less than 5%,
there is a fear that the reinforcing effect by the carbon fibers
may become small. Further, if the value of Vf becomes 80% or more,
it becomes difficult to secure high flowability and there is a fear
that it may become difficult to mold the stampable sheet.
[0068] Next, Examples and Comparative Examples will be
explained.
[0069] First, the properties and determination methods used in the
Examples and Comparative Examples will be explained.
(1) Method of Determining Bundles
[0070] A sample with a size of 100 mm.times.100 mm was cut out from
a carbon fiber composite material and, thereafter, the sample was
heated in an electric furnace heated at 500.degree. C. for about 1
hour to burn off organic substances such as the matrix resin. After
cooling to room temperature, the mass of the residual carbon fiber
aggregates was determined and, thereafter, carbon fiber bundles
were all extracted from the carbon fiber aggregates by a pincette.
With respect to all the extracted carbon fiber bundles, using a
balance capable of measuring up to a degree of 1/10,000 g, the
weigh Mn and the length Ln of each carbon fiber bundle are
determined. After the determination, for each bundle, Mn/Ln,
Mn/(Ln.times.D) and x.sub.n=Mn/(Ln.times.F) are calculated, where D
is a diameter of carbon fibers, F is a fineness of carbon fibers,
and x.sub.n is a number of fibers forming a carbon fiber bundle.
The determination is carried out at a condition where fiber bundles
in which the value of Mn/(Ln.times.D) is less than
8.5.times.10.sup.-1 mg/mm.sup.2 are referred to as carbon fiber
bundles (A) and the total weight of the carbon fiber bundles (A) is
referred to as M.sub.A. Further, the determination is carried out
at a condition where carbon fiber bundles in which Mn/(Ln.times.D)
is 8.5.times.10.sup.-1 mg/mm.sup.2 or more are referred to as
carbon fiber bundles (B), the total weight of the carbon fiber
bundles (B) is referred to as M.sub.B and the total number of the
bundles is referred to as N.sub.B. For fiber bundles refined to a
degree at which the bundles cannot be extracted by a pincette, the
weight thereof was determined in the lump at the last. Further,
when the fiber length is so small that determination of weight
becomes difficult, the fiber length may be classified at an
interval of about 0.2 mm and the weights of a plurality of
classified bundles may be determined in the lump, and an average
value thereof may be used. After classifying and determining all
bundles, for the carbon fiber bundles (A),
Z=M.sub.A/(M.sub.A+M.sub.B).times.100 (wt %) is calculated to
obtain the ratio Z of carbon fiber bundles (A) to the total weight
of carbon fibers. Next, for the carbon fiber bundles (B),
Y=M.sub.B/(M.sub.A+M.sub.B).times.100 (wt %),
X=.SIGMA.(Mn/Ln)/N.sub.B, x=.SIGMA.{Mn/(Ln.times.F)}/N.sub.B and
.sigma.={1/N.sub.B.times..SIGMA.(x.sub.n-x).sup.2}.sup.1/2 are
calculated to obtain the ratio Y of carbon fiber bundles (B) to the
total weight of carbon fibers, the average value X of Mn/Ln in
carbon fiber bundles (B), the average value x of number of fibers
forming a fiber bundle, and the standard variation .sigma. of
number of fibers forming a fiber bundle.
(2) Viscosity
[0071] The viscosity is determined using APA2000 (supplied by ALPHA
TECHNOLOGIES, Inc.) as follows: a sample having a size of 4.3
cm.sup.3 is interposed between parallel plates, the temperature is
raised to a temperature of the melting point +60.degree. C., the
viscosity is measured under conditions where the frequency is 1 Hz
and the strain is 5% while cooling down the temperature at a speed
of 10.degree. C./min. and, thereafter, the viscosity of the sample
is determined as a value of viscosity (Pas) at the solidification
start temperature at which the viscosity begins to increase
sharply.
(3) Vf (Carbon Fiber Content in Stampable Sheet)
[0072] A sample of about 2 g was cut off from a molded article of a
stampable sheet and the mass thereof was determined. Thereafter,
the sample was heated in an electric furnace heated at 500.degree.
C. for one hour to burn off organic substances such as matrix
resin. After cooling to room temperature, the mass of the residual
carbon fibers was determined. The rate of the mass of the carbon
fibers to the mass of the sample before being burned off with
organic substances such as matrix resin was determined, and it was
defined as the percentage content of carbon fibers.
(4) Flexural Strength
[0073] A flexural strength was determined on the basis of
JIS-K7171. For the flexural strength, the CV value (coefficient of
variation [%]) was also calculated. When the CV value was less than
5%, the variance of the flexural strength was small and judged as
`good (.smallcircle.)` and, when the CV value was 5% or more, the
variance of the flexural strength was large and judged as `bad
(x)`
(5) Single Fiber Flexural Stiffness (Pam.sup.4)
[0074] It was calculated by Single fiber flexural
stiffness=E.times.I.
[0075] Here, E: single fiber elastic modulus, I: geometrical moment
of inertia.
[0076] The cross section of a fiber was supposed as a true circle,
the geometrical moment of inertia I was determined from the fiber
diameter D, and the flexural stiffness was determined from the
single fiber tensile elastic modulus E and the geometrical moment
of inertia I.
(6) Evaluation of Flowability [Flow Test (Stamping Molding)]
[0077] After two sheets of carbon fiber composite materials each
having a size of 100 mm.times.100 mm.times.2 mm were preheated at
240.degree. C., the two sheets were stacked and placed on a press
table heated at 80.degree. C., and pressed at 10 MPa for 30
seconds. The area of the sheet after this pressing A2 and the area
before the pressing A1 were measured, and A2/A1 was determined as a
flowability (%).
EXAMPLES
[0078] First, carbon fibers and carbon fiber bundles (before
cutting) used in Examples and Comparative Examples will be
explained.
Carbon Fiber (1) and Carbon Fiber Bundle:
[0079] A continuous carbon fiber bundle having a fiber diameter of
7 .mu.m, a tensile elastic modulus of 230 GPa, a single fiber
flexural stiffness of 2.71.times.10.sup.-11 Pam.sup.4 and a number
of filaments of 12,000.
Carbon Fiber (2) and Carbon Fiber Bundle:
[0080] A continuous carbon fiber bundle having a fiber diameter of
5.5 .mu.m, a tensile elastic modulus of 294 GPa, a single fiber
flexural stiffness of 1.32.times.10.sup.-11 Pam.sup.4 and a number
of filaments of 12,000.
Example 1
[0081] The carbon fiber bundle (1) was cut at a fiber length of 25
mm, the cut carbon fiber bundles and nylon 6 short fibers (fineness
of short fiber: 1.7 dtex, cut length: 51 mm, number of crimps: 12
crests per 25 mm, rate of crimp: 15%) were mixed at a mass ratio of
90:10, and the mixture was introduced into a carding machine. The
web having come out was cross wrapped to form sheet-like carbon
fiber aggregates comprising carbon fibers and nylon 6 fibers and
having an areal weight of 100 g/cm.sup.2. In the obtained carbon
fiber aggregates, the ratio Z of carbon fiber bundles (A) to the
total weight of carbon fibers was 85 wt %, the ratio Y of carbon
fiber bundles (B) to the total weight of carbon fibers was 15 wt %,
the average value X of Mn/Ln was 0.01 mg/mm, the average value x of
number of fibers forming a fiber bundle was 144 and the standard
variation .sigma. of number of fibers forming a fiber bundle was
88.
[0082] The winding direction of the sheet-like carbon fiber
aggregates was referred to as 0.degree., sheets of the carbon fiber
aggregates were stacked and, further, after a nonwoven fabric
comprising nylon resin ("CM1001", .eta.r=2.3, supplied by Toray
Industries, Inc.) was stacked so that the volume ratio of the
carbon fibers to the thermoplastic resin fibers became 20:80 as the
whole of the stacked carbon fiber aggregates, the whole was nipped
by stainless plates, and after preheating at 250.degree. C. for 90
seconds, it was hot pressed at 250.degree. C. for 180 seconds while
being applied with a pressure of 1.0 MPa. Then, it was cooled to
50.degree. C. at the pressed condition to obtain a flat plate of
carbon fiber composite material having a thickness of 2 mm. When
the flexural strengths in 0.degree. and 90.degree. directions were
determined relative to the 0.degree. direction of the surface layer
of the obtained flat plate, the average value of the flexural
strengths in 0.degree. and 90.degree. directions was 365 MPa, and
the CV value was less than 5%.
[0083] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was 150%,
viscosity .eta. was 5.0.times.10.sup.5 Pas and .eta..sub.0 was
1.5.times.10.sup.4 Pas. The conditions and the results of the
determinations and the evaluations are shown in Table 1.
Example 2
[0084] A flat plate of carbon fiber composite material was obtained
in a manner similar to that of Example 1 except that the carbon
fiber bundle (1) was cut at a fiber length of 15 mm, carbon fiber
aggregates in which the ratio Z of carbon fiber bundles (A) to the
total weight of carbon fibers was 65 wt %, the ratio Y of carbon
fiber bundles (B) to the total weight of carbon fibers was 35 wt %,
the average value X of Mn/Ln was 0.017 mg/mm, the average value x
of number of fibers forming a fiber bundle was 246 and the standard
variation .sigma. of number of carbon fibers forming a fiber bundle
was 110 were stacked to obtain a flat plate of carbon fiber
composite material having a thickness of 2 mm. When the flexural
strengths in 0.degree. and 90.degree. directions were determined
relative to the 0.degree. direction of the surface layer of the
obtained flat plate, the average value of the flexural strengths in
0.degree. and 90.degree. directions was 360 MPa, and the CV value
of the flexural strength was less than 5%.
[0085] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was 170%,
viscosity .eta. was 3.0.times.10.sup.5 Pas and .eta..sub.0 was
1.5.times.10.sup.4 Pas.
Examples 3 to 6
[0086] They were carried out under conditions similar to Example 2
except that the average value X of Mn/Ln, the average value x of
number of fibers forming a fiber bundle, the standard variation
.sigma. of number of fibers forming a fiber bundle, the Vf and the
like were changed from Example 2. The results were shown in Table
1.
Example 7
[0087] It was carried out in a manner similar to Example 6 except
that a melt flow nonwoven fabric comprising nylon resin ("CM1041",
.eta.r=4.3, supplied by Toray Industries, Inc.) was used, carbon
fiber aggregates in which the ratio Z of carbon fiber bundles (A)
to the total weight of carbon fibers was 55 wt %, the ratio Y of
carbon fiber bundles (B) to the total weight of carbon fibers was
45 wt %, the average value X of Mn/Ln was 0.027 mg/mm, the average
value x of number of fibers forming a fiber bundle was 390 and the
standard variation .sigma. of number of fibers forming a fiber
bundle was 250 were stacked, and a flat plate of carbon fiber
composite material having a thickness of 2 mm was obtained. When
the flexural strengths in 0.degree. and 90.degree. directions were
determined relative to the 0.degree. direction of the surface layer
of the obtained flat plate, the average value of the flexural
strengths in 0.degree. and 90.degree. directions was 350 MPa, and
the CV value of the flexural strength was less than 5%.
[0088] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was 230%,
viscosity .eta. was 5.5.times.10.sup.4 Pas and .eta..sub.0 was
1.8.times.10.sup.4 Pas.
Example 8
[0089] It was carried out in a manner similar to Example 6 except
that the fiber length L of carbon fibers was changed. The results
were shown in Table 1.
Example 9
[0090] It was carried out in a manner similar to Example 1 except
that the carbon fiber bundle (2) was cut at a fiber length of 15
mm, carbon fiber aggregates in which the ratio Z of carbon fiber
bundles (A) to the total weight of carbon fibers was 50 wt %, the
ratio Y of carbon fiber bundles (B) to the total weight of carbon
fibers was 50 wt %, the average value X of Mn/Ln was 0.025 mg/mm,
the average value x of number of fibers forming a fiber bundle was
585 and the standard variation .sigma. of number of carbon fibers
forming a fiber bundle was 350 were stacked, and a flat plate of
carbon fiber composite material having a thickness of 2 mm was
obtained. When the flexural strengths in 0.degree. and 90.degree.
directions were determined relative to the 0.degree. direction of
the surface layer of the obtained flat plate, the average value of
the flexural strengths in 0.degree. and 90.degree. directions was
400 MPa, and the CV value of the flexural strength was less than
5%.
[0091] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was 300%,
viscosity .eta. was 2.0.times.10.sup.4 Pas and no was
1.5.times.10.sup.4 Pas.
Example 10
[0092] It was carried out in a manner similar to Example 9 except
that the fiber length L, the ratio of carbon fiber bundles (B), the
average value X of Mn/Ln, the average value x of number of fibers
forming a fiber bundle and the standard variation .sigma. of number
of fibers forming a fiber bundle were changed. The results were
shown in Table 1.
Example 11
[0093] The carbon fiber bundle (1) was cut at a fiber length of 15
mm, the cut carbon fiber bundles and nylon 6 short fibers (fineness
of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass
ratio of 80:20, and the mixture was introduced into an air laid
machine. The nonwoven fabric having come out was heat treated to
form sheet-like carbon fiber aggregates comprising carbon fibers
and nylon 6 fibers and having an areal weight of 200 g/cm.sup.2. In
the obtained carbon fiber aggregates, the ratio Z of carbon fiber
bundles (A) to the total weight of carbon fibers was 30 wt %, the
ratio Y of carbon fiber bundles (B) to the total weight of carbon
fibers was 70 wt %, the average value X of Mn/Ln was 0.028 mg/mm,
the average value x of number of fibers forming a fiber bundle was
400 and the standard variation .sigma. of number of fibers forming
a fiber bundle was 315.
[0094] The winding direction of the sheet-like carbon fiber
aggregates was referred to as 0.degree., sheets of the carbon fiber
aggregates were stacked, and further, after a nonwoven fabric
comprising co-polymerized nylon resin ("E3500", supplied by Toray
Industries, Inc.) was stacked so that the volume ratio of the
carbon fibers to the thermoplastic resin fibers became 20:80 as the
whole of the stacked carbon fiber aggregates, the whole was nipped
by stainless plates, and after preheating at 250.degree. C. for 90
seconds, it was hot pressed at 250.degree. C. for 180 seconds while
being applied with a pressure of 1.0 MPa. Then, it was cooled to
50.degree. C. at the pressed condition to obtain a flat plate
(stampable sheet) of carbon fiber composite material having a
thickness of 2 mm. When the flexural strengths in 0.degree. and
90.degree. directions were determined relative to the 0.degree.
direction of the surface layer of the obtained flat plate, the
average value of the flexural strengths in 0.degree. and 90.degree.
directions was 330 MPa, and the CV value was less than 5%.
[0095] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was 370%,
viscosity .eta. was 1.1.times.10.sup.4 Pas and .eta..sub.0 was
3.0.times.10.sup.3 Pas. The conditions and the results of the
determinations and the evaluations are shown in Table 2.
Examples 12 to 13
[0096] They were carried out in a manner similar to Example 11
except that the Vf was changed. The results were shown in Table
2.
Examples 14 to 16
[0097] They were carried out in a manner similar to Example 1
except that the ratio Z of carbon fiber bundles (A) to the total
weight of carbon fibers, the ratio Y of carbon fiber bundles (B),
the average value X of Mn/Ln, the average value x of number of
fibers forming a fiber bundle, the standard variation .sigma. of
number of fibers forming a fiber bundle, the Vf, the resin and the
like were changed from Example 1. The results were shown in Table
2.
Comparative Example 1
[0098] The carbon fiber bundle (1) was cut at a fiber length of 15
mm, the cut carbon fiber bundles were uniformly dispersed on a
matched die mold having a size of 300 mm.times.300 mm, a nylon
resin melt blow nonwoven fabric ("CM1001", .eta.r=2.3, supplied by
Toray Industries, Inc.) was stacked so that the volume ratio of the
carbon fibers to the thermoplastic resin fibers became 20:80, and
carbon fiber aggregates in which the ratio Z of carbon fiber
bundles (A) to the total weight of carbon fibers was 1 wt %, the
ratio Y of carbon fiber bundles (B) to the total weight of carbon
fibers was 99 wt %, the average value X of Mn/Ln was 0.55 mg/mm,
the average value x of number of fibers forming a fiber bundle was
7944 and the standard variation .sigma. of number of fibers forming
a fiber bundle was 955 were stacked to obtain a flat plate of
carbon fiber composite material having a thickness of 2 mm. When
the flexural strengths in 0.degree. and 90.degree. directions were
determined relative to the 0.degree. direction of the surface layer
of the obtained flat plate, the average value of the flexural
strengths in 0.degree. and 90.degree. directions was 200 MPa, and
the CV value was more than 5%. The result was shown in Table 3.
Comparative Example 2
[0099] It was carried out in a manner similar to Example 1 except
that the carbon fiber bundle (1) was cut at a fiber length of 15
mm, carbon fiber aggregates in which the ratio Z of carbon fiber
bundles (A) to the total weight of carbon fibers was 95 wt %, the
average value X of Mn/Ln was 0.01 mg/mm, the average value x of
number of fibers forming a fiber bundle was 140 and the standard
variation .sigma. of number of carbon fibers forming a fiber bundle
was 40 were stacked to obtain a flat plate of carbon fiber
composite material having a thickness of 2 mm. When the flexural
strengths in 0.degree. and 90.degree. directions were determined
relative to the 0.degree. direction of the surface layer of the
obtained flat plate, the average value of the flexural strengths in
0.degree. and 90.degree. directions was 365 MPa, and the CV value
of the flexural strength was less than 5%.
[0100] When a sample having a size of 100 mm.times.100 mm was cut
out from the obtained flat plate and the flow test and the
viscosity determination test were performed, flowability was only
120%, viscosity .eta. was 5.0.times.10.sup.5 Pas and no was
1.5.times.10.sup.4 Pas.
TABLE-US-00001 TABLE 1 Exam- Exam- Exam- Exam- Exam- Exam- Exam-
Exam- Exam- Exam- Examples ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple
7 ple 8 ple 9 ple 10 Carbon fiber Carbon Carbon Carbon Carbon
Carbon Carbon Carbon Carbon Carbon Carbon fiber fiber fiber fiber
fiber fiber fiber fiber fiber fiber (1) (1) (1) (1) (1) (1) (1) (1)
(2) (2) Single fiber [Pa m.sup.4] 2.71 .times. 2.71 .times. 2.71
.times. 2.71 .times. 2.71 .times. 2.71 .times. 2.71 .times. 2.71
.times. 1.32 .times. 1.32 .times. flexural stiffness 10.sup.-11
10.sup.-11 10.sup.-11 10.sup.-11 10.sup.-11 10.sup.-11 10.sup.-11
10.sup.-11 10.sup.-11 10.sup.-11 D: fiber diameter [.mu.m] 7 7 7 7
7 7 7 7 5.5 5.5 L: fiber length [mm] 25 15 15 15 15 15 15 25 15 10
Z: ratio of carbon [%] 85 65 65 65 65 55 55 55 50 45 fiber bundles
(A) Y: ratio of carbon [%] 15 35 35 35 35 45 45 45 50 55 fiber
bundles (B) X: average value [mg/mm] 0.01 0.017 0.024 0.024 0.024
0.027 0.027 0.027 0.025 0.026 of Mn/Ln Resin CM1001 CM1001 CM1001
CM1001 CM1001 CM1001 CM1041 CM1001 CM1001 CM1001 Vf [%] 20 20 20 10
30 20 20 20 20 20 Flowability [%] 150 170 200 240 150 255 230 200
300 320 Flexural strength [MPa] 365 360 350 280 470 345 350 350 400
390 JIS-K7171 CV value [%] .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. .eta..sub.0
[Pa s] 1.5 .times. 1.5 .times. 1.5 .times. 1.5 .times. 1.5 .times.
1.5 .times. 1.8 .times. 1.5 .times. 1.5 .times. 1.5 .times.
10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4
10.sup.4 10.sup.4 10.sup.4 .eta. [Pa s] 5.0 .times. 3.0 .times. 1.6
.times. 6.0 .times. 8.0 .times. 5.0 .times. 5.5 .times. 8.0 .times.
2.0 .times. 1.9 .times. 10.sup.5 10.sup.5 10.sup.5 10.sup.4
10.sup.5 10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4 x: average of
[number 144 246 350 350 350 390 390 390 585 608 number of of
bundle-forming fibers] fibers .sigma.: standard [number 88 110 230
230 230 250 250 250 350 360 variation of fibers]
TABLE-US-00002 TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- Examples
ple 11 ple 12 ple 13 ple 14 ple 15 ple 16 Carbon fiber Carbon
Carbon Carbon Carbon Carbon Carbon fiber fiber fiber fiber fiber
fiber (1) (1) (1) (1) (1) (1) Single fiber [Pa m.sup.4] 2.71
.times. 2.71 .times. 2.71 .times. 2.71 .times. 2.71 .times. 2.71
.times. flexural stiffness 10.sup.-11 10.sup.-11 10.sup.-11
10.sup.-11 10.sup.-11 10.sup.-11 D: fiber diameter [.mu.m] 7 7 7 7
7 7 L: fiber length [mm] 15 15 15 15 15 15 Z: ratio of carbon [%]
30 30 30 60 60 60 fiber bundles (A) Y: ratio of carbon [%] 70 70 70
40 40 40 fiber bundles (B) X: average value [mg/mm] 0.028 0.028
0.028 0.022 0.022 0.022 of Mn/Ln Resin E3500 E3500 E3500 E3500
E3500 E3500 Vf [%] 20 25 30 20 25 30 Flowability [%] 370 345 300
300 280 260 Flexural strength [MPa] 330 375 440 360 405 475
JIS-K7171 CV value [%] .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .eta..sub.0 [Pa s] 3.0
.times. 3.0 .times. 3.0 .times. 3.0 .times. 3.0 .times. 3.0 .times.
10.sup.3 10.sup.3 10.sup.3 10.sup.3 10.sup.3 10.sup.3 .eta. [Pa s]
1.1 .times. 1.5 .times. 2.1 .times. 1.1 .times. 1.5 .times. 2.1
.times. 10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4 10.sup.4 x:
average of [number 400 400 400 318 318 318 number of of
bundle-forming fibers] fibers .sigma.: standard [number 315 315 315
200 200 200 variation of fibers]
TABLE-US-00003 TABLE 3 Comparative Examples Comparative Comparative
Example 1 Example 2 Carbon fiber Carbon fiber (1) Carbon fiber (1)
Single fiber flexural stiffness [Pa m.sup.4] .sup. 2.71 .times.
10.sup.-11 .sup. 2.71 .times. 10.sup.-11 D: fiber diameter [.mu.m]
7 7 L: fiber length [mm] 15 15 Z: ratio of carbon fiber [%] 1 95
bundles (A) Y: ratio of carbon fiber [%] 99 5 bundles (B) X:
average value of Mn/Ln [mg/mm] 0.55 0.550.01 Resin CM1001 CM1001 Vf
[%] 20 20 Flowability [%] 320 120 Flexural strength J1S-K7171 [MPa]
200 365 CV value [%] X O .eta..sub.0 [Pa s] 1.5 .times. 10.sup.-4
1.5 .times. 10.sup.-4 .eta. [Pa s] 1.6 .times. 10.sup.-4 8.5
.times. 10.sup.-5 x: average of number of [number 7944 140
bundle-forming fibers of fibers] .sigma.: standard variation
[number 955 40 of fibers]
INDUSTRIAL APPLICATIONS
[0101] The stampable sheet can be applied for manufacturing any
carbon fiber reinforced molded article required with combination of
high flowability and mechanical properties and few variations in
mechanical properties, that have not been achieved by the
conventional technologies.
* * * * *