U.S. patent application number 14/346401 was filed with the patent office on 2014-08-21 for reinforced fiber/resin fiber composite, and method for manufacturing same.
The applicant listed for this patent is NATIONAL UNIVERSITY CORPORATION KYOTO INSTITUTE OF TECHNOLOGY. Invention is credited to Asami Nakai.
Application Number | 20140230634 14/346401 |
Document ID | / |
Family ID | 47914523 |
Filed Date | 2014-08-21 |
United States Patent
Application |
20140230634 |
Kind Code |
A1 |
Nakai; Asami |
August 21, 2014 |
REINFORCED FIBER/RESIN FIBER COMPOSITE, AND METHOD FOR
MANUFACTURING SAME
Abstract
A reinforced fiber/resin fiber composite is provided in which
the ratio and arrangement of a long fiber and a thermoplastic resin
fiber included in an intermediate material are accurately
controlled to simultaneously provide good impregnation
characteristics of the long fiber and good interfacial
characteristics between the long fiber and the thermoplastic resin.
A reinforced fiber/resin fiber composite (50) is provided which is
an intermediate material for a long-fiber reinforced thermoplastic
resin structure. The reinforced fiber (15) is a long fiber
extending in a longitudinal direction. The resin fiber (25)
includes at least two thermoplastic resin fibers. The at least two
thermoplastic resin fibers are arranged around the reinforced fiber
(15) to surround the reinforced fiber (15).
Inventors: |
Nakai; Asami; (Kyoto,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL UNIVERSITY CORPORATION KYOTO INSTITUTE OF
TECHNOLOGY |
Kyoto-shi, Kyoto |
|
JP |
|
|
Family ID: |
47914523 |
Appl. No.: |
14/346401 |
Filed: |
September 21, 2012 |
PCT Filed: |
September 21, 2012 |
PCT NO: |
PCT/JP2012/074200 |
371 Date: |
March 21, 2014 |
Current U.S.
Class: |
87/8 |
Current CPC
Class: |
C08J 5/047 20130101;
D07B 2201/1096 20130101; D07B 1/02 20130101; D10B 2403/02411
20130101; C08J 5/24 20130101; D04C 1/06 20130101; D10B 2505/02
20130101 |
Class at
Publication: |
87/8 |
International
Class: |
D07B 1/02 20060101
D07B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2011 |
JP |
2011-207258 |
Claims
1. A reinforced fiber/resin fiber composite which is an
intermediate material for a long-fiber reinforced thermoplastic
resin structure, wherein the reinforced fiber is a long fiber
extending in a longitudinal direction, the resin fiber includes a
polypropylene (PP) fiber and an acid-modified polypropylene (MAPP)
fiber, and the polypropylene (PP) fiber and the acid-modified
polypropylene (MAPP) fiber are arranged around the reinforced fiber
to surround the reinforced fiber.
2. The reinforced fiber/resin fiber composite of claim 1, wherein
the polypropylene (PP) fiber and the acid-modified polypropylene
(MAPP) fiber are braided at a predetermined angle with respect to
the longitudinal direction of the long fiber to form a braid around
the reinforced fiber.
3-7. (canceled)
8. A reinforced fiber/resin fiber composite which is an
intermediate material for a long-fiber reinforced thermoplastic
resin structure, wherein the reinforced fiber is a long fiber
extending in a longitudinal direction, the resin fiber includes a
polylactic acid (PLA) fiber and a polyoxymethylene (POM) fiber, and
the polylactic acid (PLA) fiber and the polyoxymethylene (POM)
fiber are arranged around the reinforced fiber to surround the
reinforced fiber.
9. The reinforced fiber/resin fiber composite of claim 8, wherein
the polylactic acid (PLA) fiber and the polyoxymethylene (POM)
fiber are braided at a predetermined angle with respect to the
longitudinal direction of the long fiber to form a braid around the
reinforced fiber.
10. A reinforced fiber/resin fiber composite which is an
intermediate material for a long-fiber reinforced thermoplastic
resin structure, wherein the reinforced fiber is a long fiber
extending in a longitudinal direction, the resin fiber includes at
least two thermoplastic resin fibers selected from the group
consisting of a polylactic acid (PLA) fiber, polyoxymethylene (POM)
fiber, acid-modified polypropylene (MAPP) fiber, polyphenylene
sulfide (PPS) fiber, and polyether ketone ketone (PEKK) fiber, and
the at least two thermoplastic resin fibers are arranged around the
reinforced fiber to surround the reinforced fiber.
11. The reinforced fiber/resin fiber composite of claim 10, wherein
the at least two thermoplastic resin fibers are braided at a
predetermined angle with respect to the longitudinal direction of
the long fiber to form a braid around the reinforced fiber.
12. A reinforced fiber/resin fiber composite which is an
intermediate material for a long-fiber reinforced thermoplastic
resin structure, wherein the reinforced fiber is a long fiber
extending in a longitudinal direction, the resin fiber includes at
least two thermoplastic resin fibers, the at least two
thermoplastic resin fibers are selected to have complementary
physical properties after thermoforming, and the at least two
thermoplastic resin fibers are arranged around the reinforced fiber
to surround the reinforced fiber.
13. The reinforced fiber/resin fiber composite of claim 12, wherein
the at least two thermoplastic resin fibers are braided at a
predetermined angle with respect to the longitudinal direction of
the long fiber to form a braid around the reinforced fiber.
Description
TECHNICAL FIELD
[0001] The present invention relates to reinforced fiber/resin
fiber composites which are an intermediate material for a
long-fiber reinforced thermoplastic resin structure, and methods
for manufacturing the same.
BACKGROUND ART
[0002] Fiber reinforced thermoplastic resins, which are a
combination of a thermoplastic resin and a fiber, have good
properties, i.e., light weight and high strength, and therefore,
are used in a variety of fields. For example, in transport
machines, such as automobiles, ships, aircrafts, etc., molded
products of fiber reinforced thermoplastic resins are used as a
portion of parts to improve fuel efficiency and safety.
[0003] As a type of fiber reinforced thermoplastic resin, fiber
reinforced plastics (FRPs), which are a molded product of a
thermoplastic resin to which a short fiber is added, have been well
known. In recent years, a long-fiber reinforced thermoplastic
resin, which is a combination of a thermoplastic resin and a long
fiber (e.g., a reinforced fiber, such as a carbon fiber etc.), has
attracted attention. As used herein, the term "long fiber" refers
to a fiber extending in the longitudinal direction (so-called a
"fiber"). The long-fiber reinforced thermoplastic resin has a
number of advantages: (1) very good impact resistance; (2) good
recyclability because it can be melted by heat; (3) the ability to
be quickly molded because molding of it does not involve chemical
reaction; (4) the ease of storage of an intermediate material
(prepreg) before molding because chemical reaction has already been
ended; (5) the ease of changing shape or attachment by being melted
by heat; etc. Therefore, the long-fiber reinforced thermoplastic
resin is expected as a very useful material in the future.
[0004] On the other hand, in the long-fiber reinforced
thermoplastic resin, the thermoplastic resin has a very high melt
viscosity, and therefore, it is disadvantageously difficult to
impregnate the long fiber with the thermoplastic resin. As the
impregnation characteristics of the resin decrease, the molded
product cannot exhibit sufficient strength. Also, it is important
for the long-fiber reinforced thermoplastic resin to improve
interfacial characteristics between the long fiber and the
thermoplastic resin. If the interfacial characteristics are
insufficient, the long fiber and the thermoplastic resin are likely
to come off the adhesion surface therebetween, so that the molded
product is likely to be damaged. Here, generally, as the
impregnation characteristics of the thermoplastic resin with
respect to the long fiber become better, the interfacial
characteristics between the long fiber and the thermoplastic resin
become worse. For example, when the surface of the long fiber is
modified by acid modification etc. in order to improve the
interfacial characteristics, the contact angle of the thermoplastic
resin with respect to the long fiber increases (i.e., the
wettability of the long fiber surface deteriorates), and as a
result, the impregnation characteristics become worse. Thus, there
is a trade-off relationship between the impregnation
characteristics and the interfacial characteristics. When a
long-fiber reinforced thermoplastic resin structure is manufactured
using the long-fiber reinforced thermoplastic resin, it is
desirable to simultaneously provide as good impregnation
characteristics and interfacial characteristics as possible.
[0005] In order to maintain good interfacial characteristics
between the long fiber and the thermoplastic resin while improving
the impregnation characteristics of the thermoplastic resin with
respect to the long fiber, it may be effective to modify the form
of the intermediate material used for manufacture of the long-fiber
reinforced thermoplastic resin structure. In the intermediate
material phase, the arrangement and mixture of the long fiber and
the thermoplastic resin can be adjusted before thermoforming, and
therefore, it is easy to control characteristics of the long-fiber
reinforced thermoplastic resin structure, which is a final product.
As used herein, the term "intermediate material" refers to a
composite or mixture of the long fiber and the thermoplastic
resin.
[0006] Conventionally, as an intermediate material for the
long-fiber reinforced thermoplastic resin structure, for example, a
"carbon fiber reinforced thermoplastic resin tape" has been
developed which is a tape-like molded product of a carbon fiber
(long fiber) impregnated with a thermoplastic resin (see, for
example, Patent Document 1). In Patent Document 1, opened carbon
fiber strands are immersed in a melted thermoplastic resin bath to
impregnate a carbon fiber with a thermoplastic resin, and then, the
resin-impregnated carbon fiber is passed through a nozzle for
molding, whereby a thin and long carbon fiber reinforced
thermoplastic resin tape is formed. In an example application, the
carbon fiber reinforced thermoplastic resin tape is wound around
the surface of a target structure and is then cooled to solidify.
As a result, the structure is reinforced.
[0007] As another intermediate material for a long-fiber reinforced
thermoplastic resin structure, a "commingled yarn for a composite
material (composite material commingled yarn)" is known in which a
continuous reinforced fiber bundle (long fiber) is commingled with
a continuous thermoplastic resin fiber bundle (see, for example,
Patent Document 2). In Patent Document 2, a non-twisted continuous
reinforced fiber bundle and a non-twisted continuous thermoplastic
resin fiber bundle are opened before being commingled together, to
obtain a composite material commingled yarn. The composite material
commingled yarn is, for example, processed into woven or knitted
fabric.
CITATION LIST
Patent Literature
[0008] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2007-118216 [0009] Patent Document 2: Japanese
Unexamined Patent Application Publication No. H09-324331
SUMMARY OF INVENTION
Technical Problem
[0010] However, the carbon fiber reinforced thermoplastic resin
tape of Patent Document 1 and the composite material commingled
yarn of Patent Document 2 have the following technical and economic
problems.
[0011] In the carbon fiber reinforced thermoplastic resin tape of
Patent Document 1, long fiber strands impregnated with a
thermoplastic resin extend generally in parallel in the
longitudinal direction. Therefore, the mixture ratio of the long
fiber and the thermoplastic resin are generally uniform
irrespective of the position of the tape. When such an intermediate
material having a generally uniform mixture ratio is used, the
composition of the long-fiber reinforced thermoplastic resin
structure as a final product cannot be accurately controlled in a
position-dependent manner. It is also difficult to control the
composition, and therefore, it may be difficult to simultaneously
achieve good impregnation characteristics of the long fiber and
good interfacial characteristics between the long fiber and the
thermoplastic resin. Moreover, a structure to which the carbon
fiber reinforced thermoplastic resin tape is applicable is limited
to those having a flat surface or a simple curved surface. This is
because it is difficult to tightly attach the carbon fiber
reinforced thermoplastic resin tape to a structure having a
complicated surface. In addition, the carbon fiber reinforced
thermoplastic resin tape is likely to have excessive stiffness due
to its structure and has poor tackiness. Therefore, it is not easy
to handle the carbon fiber reinforced thermoplastic resin tape.
Note that, in order to manufacture the carbon fiber reinforced
thermoplastic resin tape, it is necessary to use dedicated
equipment, such as a thermoplastic resin bath, a nozzle for
molding, etc., leading to an increase in cost.
[0012] Also, in the composite material commingled yarn of Patent
Document 2, the continuous reinforced fiber bundle and the
continuous thermoplastic resin fiber bundle are only simply
commingled together, and therefore, it is difficult to accurately
control the mixture ratio of both of the fibers along the
longitudinal direction. Therefore, also in Patent Document 2, it is
not possible to simultaneously achieve good impregnation
characteristics of the long fiber and good interfacial
characteristics between the long fiber and the thermoplastic resin.
Also, the reinforced fiber is likely to be damaged due to friction
during opening of the continuous reinforced fiber bundle or
commingling of the continuous reinforced fiber bundle and the
continuous thermoplastic resin fiber bundle. When the composite
material commingled yarn is processed into woven or knitted fabric,
each fiber is likely to be damaged. Moreover, when the composite
material commingled yarn is manufactured, a portion of the fiber
strands may be cut or come off, etc., to be lost during opening and
commingling, resulting in a decrease in the yield of the final
product.
[0013] Thus, at present, a reinforced fiber/resin fiber composite
has not yet been developed which is an optimum intermediate
material including a reinforced fiber and a resin fiber for
manufacture of a long-fiber reinforced thermoplastic resin
structure. With the above circumstances in mind, the present
invention has been made. It is an object of the present invention
to provide a reinforced fiber/resin fiber composite (intermediate
material) in which the ratio and arrangement of a long fiber and a
thermoplastic resin fiber are accurately controlled in order to
simultaneously achieve different physical properties (e.g.,
impregnation characteristics, interfacial characteristics, etc.) of
the reinforced fiber and the resin fiber. It is another object of
the present invention to provide a method for efficiently and
reliably manufacturing such a reinforced fiber/resin fiber
composite at low cost.
Solution to Problem
[0014] To achieve the object, a reinforced fiber/resin fiber
composite according to the present invention has the following
characteristic features.
[0015] The reinforced fiber/resin fiber composite is a reinforced
fiber/resin fiber composite which is an intermediate material for a
long-fiber reinforced thermoplastic resin structure, in which
[0016] the reinforced fiber is a long fiber extending in a
longitudinal direction,
[0017] the resin fiber includes at least two thermoplastic resin
fibers, and
[0018] the at least two thermoplastic resin fibers are arranged
around the reinforced fiber to surround the reinforced fiber.
[0019] As described in the "BACKGROUND ART" section, in order to
obtain a high-performance long-fiber reinforced thermoplastic resin
structure, it is important to maintain good interfacial
characteristics between the long fiber and the thermoplastic resin
while improving impregnation characteristics of the long fiber. To
do so, it may be effective to modify the form of the reinforced
fiber/resin fiber composite which is an intermediate material.
[0020] In this regard, in the reinforced fiber/resin fiber
composite having this configuration, when the long fiber extending
in the longitudinal direction is used as the reinforced fiber, and
the at least two thermoplastic resin fibers are used as the resin
fiber, the at least two thermoplastic resin fibers are arranged
around the reinforced fiber to surround the reinforced fiber. In
other words, a hybrid resin fiber including the at least two
thermoplastic resin fibers is provided around the long fiber. When
the reinforced fiber/resin fiber composite having such a form is
processed by thermoforming, then if the at least two thermoplastic
resin fibers are suitably selected, the reinforced fiber can be
reliably impregnated to the inside thereof with the thermoplastic
resin, for example, when the thermoplastic resin fiber surrounding
the reinforced fiber is melted, and at the same time, interfacial
characteristics between the reinforced fiber and the thermoplastic
resin can be improved. As a result, the reinforced fiber and the
thermoplastic resin can be prevented from coming off the interface
therebetween. Note that melting of the thermoplastic resin fiber
during thermoforming, which is a type of so-called in-situ polymer
blend, can be easily carried out.
[0021] In the reinforced fiber/resin fiber composite of the present
invention, the at least two thermoplastic resin fibers are
preferably braided at a predetermined angle with respect to the
longitudinal direction of the long fiber to form a braid around the
reinforced fiber.
[0022] In order to improve the performance of the long-fiber
reinforced thermoplastic resin structure, it may be effective to
accurately control the composition of the long-fiber reinforced
thermoplastic resin structure. For example, if the mixture ratio of
the reinforced fiber and the thermoplastic resin or the composition
ratio of the at least two thermoplastic resins can be flexibly
controlled along the longitudinal direction of the reinforced
fiber, the long-fiber reinforced thermoplastic resin structure as a
final product can be manufactured in a form suitable for the
purpose of use ("made-to-order" manufacture).
[0023] In this regard, in the reinforced fiber/resin fiber
composite having this configuration, the at least two thermoplastic
resin fibers are braided at a predetermined angle with respect to
the longitudinal direction of the long fiber (reinforced fiber) to
form a braid around the reinforced fiber. In other words, the at
least two thermoplastic resin fibers are braided around the
reinforced fiber using a "braiding technique" which is known as a
traditional craft. In the braiding technique, strands (fiber) can
be braided into various arrangement patterns by modifying the
braiding pattern. Therefore, if the braiding technique is applied
to the reinforced fiber/resin fiber composite, the mixture ratio of
the reinforced fiber and the thermoplastic resin, or the
composition ratio of the at least two thermoplastic resins, can be
flexibly controlled, depending on the pattern in which strands are
braided. In addition, if the braiding technique is used, strands
(fiber) are not opened, and therefore, the fiber is not likely to
be damaged.
[0024] Also, in the braiding technique, when a plurality of strands
(fiber) are braided, the arrangement of the strands (fiber), and
tension exerted on the strands (fiber), can be controlled on a
strand-by-strand basis. Therefore, the reinforced fiber/resin fiber
composite having this configuration is particularly effective in
accurately controlling the structure and composition of the
long-fiber reinforced thermoplastic resin structure as a final
product. Therefore, if the braiding technique is used, the physical
properties of each resin fiber can be imparted, in a desired form,
to the long-fiber reinforced thermoplastic resin structure after
thermoforming.
[0025] In the reinforced fiber/resin fiber composite of the present
invention, the at least two thermoplastic resin fibers are
preferably selected to have complementary physical properties after
thermoforming.
[0026] In the reinforced fiber/resin fiber composite having this
configuration, if thermoforming is performed using the at least two
thermoplastic resin fibers, the physical properties of the fibers
complement each other. A high-performance long-fiber reinforced
thermoplastic resin structure which has a good balance between the
physical properties of the fibers can be obtained.
[0027] In the reinforced fiber/resin fiber composite of the present
invention, the at least two thermoplastic resin fibers are
preferably selected from the group consisting of a polylactic acid
(PLA) fiber, polyamide (PA) fiber, polycarbonate (PC) fiber,
polyoxymethylene (POM) fiber, polypropylene (PP) fiber,
acid-modified polypropylene (MAPP) fiber, polyethylene (PE) fiber,
polyphenylene sulfide (PPS) fiber, polyether ether ketone (PEEK)
fiber, and polyether ketone ketone (PEKK) fiber.
[0028] In the reinforced fiber/resin fiber composite having this
configuration, the at least two thermoplastic resin fibers are
selected from the group consisting of a polylactic acid (PLA)
fiber, polyamide (PA) fiber, polycarbonate (PC) fiber,
polyoxymethylene (POM) fiber, polypropylene (PP) fiber,
acid-modified polypropylene (MAPP) fiber, polyethylene (PE) fiber,
polyphenylene sulfide (PPS) fiber, polyether ether ketone (PEEK)
fiber, and polyether ketone ketone (PEKK) fiber. Therefore, if
thermoforming is performed using the selected two thermoplastic
resin fibers, a high-performance long-fiber reinforced
thermoplastic resin structure which has advantages of the fibers
can be obtained.
[0029] In the reinforced fiber/resin fiber composite of the present
invention, the at least two thermoplastic resin fibers are
preferably a polypropylene (PP) fiber and an acid-modified
polypropylene (MAPP) fiber.
[0030] In the reinforced fiber/resin fiber composite having this
configuration, the at least two thermoplastic resin fibers are a
polypropylene (PP) fiber and an acid-modified polypropylene (MAPP)
fiber. In a long-fiber reinforced thermoplastic resin structure
obtained from this combination, the interfacial characteristics
between the reinforced fiber and the thermoplastic resin can be
improved while the impregnation characteristics of the
thermoplastic resin with respect to the reinforced fiber are
maintained good.
[0031] In the reinforced fiber/resin fiber composite of the present
invention, the at least two thermoplastic resin fibers are
preferably a polylactic acid (PLA) fiber and a polyoxymethylene
(POM) fiber.
[0032] In the reinforced fiber/resin fiber composite having this
configuration, the at least two thermoplastic resin fibers are a
polylactic acid (PLA) fiber and a polyoxymethylene (POM) fiber. In
a long-fiber reinforced thermoplastic resin structure obtained from
this combination, the toughness of the structure can be reinforced
while the interfacial characteristics between the reinforced fiber
and the thermoplastic resin are improved.
[0033] In order to achieve the above object, a method for
manufacturing a reinforced fiber/resin fiber composite according to
the present invention has the following characteristic
features.
[0034] The method is a method for manufacturing a reinforced
fiber/resin fiber composite which is an intermediate material for a
long-fiber reinforced thermoplastic resin structure, in which the
reinforced fiber is a long fiber extending in a longitudinal
direction, and
[0035] the resin fiber includes at least two thermoplastic resin
fibers, and
[0036] the method includes: [0037] a preparing step of causing the
at least two thermoplastic resin fibers to be on standby around the
reinforced fiber; and [0038] a braiding step of continuously
braiding the at least two thermoplastic resin fibers at a
predetermined angle with respect to the longitudinal direction to
surround the reinforced fiber.
[0039] According to the method for manufacturing the reinforced
fiber/resin fiber composite having this configuration, advantages
similar to those of the reinforced fiber/resin fiber composite
described above can be obtained.
[0040] Specifically, a hybrid resin fiber including the at least
two thermoplastic resin fibers is provided around the long fiber.
When the reinforced fiber/resin fiber composite having such a form
is processed by thermoforming, then if the at least two
thermoplastic resin fibers are suitably selected, the reinforced
fiber can be reliably impregnated to the inside thereof with the
thermoplastic resin, for example, when the thermoplastic resin
fiber surrounding the reinforced fiber is melted, and at the same
time, interfacial characteristics between the reinforced fiber and
the thermoplastic resin can be improved. As a result, the
reinforced fiber and the thermoplastic resin can be prevented from
coming off the interface therebetween. Note that melting of the
thermoplastic resin fiber during thermoforming, which is a type of
so-called in-situ polymer blend, can be easily carried out.
[0041] Moreover, the method for manufacturing the reinforced
fiber/resin fiber composite having this configuration employs a
"braiding technique" which is known as a traditional craft. In the
braiding technique, strands (fiber) can be braided into various
arrangement patterns by modifying the braiding pattern. Therefore,
if the braiding technique is applied to the reinforced fiber/resin
fiber composite manufacturing method, the mixture ratio of the
reinforced fiber and the thermoplastic resin, or the composition
ratio of the at least two thermoplastic resins, can be flexibly
controlled, depending on the pattern in which strands are braided.
In addition, if the braiding technique is used, strands (fiber) are
not opened, and therefore, the fiber is not likely to be
damaged.
[0042] Also, in the braiding technique, when a plurality of strands
(fiber) are braided, the arrangement of the strands (fiber), and
tension exerted on the strands (fiber), can be controlled on a
strand-by-strand basis. Therefore, the method for manufacturing the
reinforced fiber/resin fiber composite having this configuration is
particularly effective in accurately controlling the structure and
composition of the long-fiber reinforced thermoplastic resin
structure as a final product. Therefore, if the braiding technique
is used, the physical properties of each resin fiber can be
imparted, in a desired form, to the long-fiber reinforced
thermoplastic resin structure after thermoforming.
BRIEF DESCRIPTION OF DRAWINGS
[0043] FIG. 1(a) is a schematic diagram showing an example braiding
machine for manufacturing a reinforced fiber/resin fiber composite
according to the present invention, and FIG. 1(b) is an external
view of the reinforced fiber/resin fiber composite.
[0044] FIG. 2 is a schematic cross-sectional view of a reinforced
fiber/resin fiber composite for describing a pattern in which a PP
fiber and an MAPP fiber (braiding fibers) are braided with respect
to a carbon fiber (axial fiber), showing a double-layer arrangement
(FIG. 2(a)) and an alternate arrangement (FIG. 2(b)).
[0045] FIG. 3 shows a photograph of an external appearance of a
carbon fiber/resin fiber composite of an example in which two
thermoplastic resin fibers are braided with respect to a carbon
fiber, and a diagram showing a structure thereof.
[0046] FIG. 4 shows photographs of cross-sections of test pieces
having a double-layer arrangement and an alternate arrangement,
indicating changes in their impregnated states depending on the
molding time.
[0047] FIG. 5 shows example image data for calculating the
unimpregnation ratio of a carbon fiber, indicating a cross-section
of a test piece before image processing (FIG. 5(a)) and that after
image processing (FIG. 5(b)).
[0048] FIG. 6 is a graph plotted to show a relationship between the
unimpregnation ratio and molding time of each of test pieces having
the double-layer and alternate arrangements.
[0049] FIG. 7 is a graph of measurement data (load-flexure curve)
of each test piece which was obtained by a three point bending
test.
DESCRIPTION OF EMBODIMENTS
[0050] Embodiments of a reinforced fiber/resin fiber composite
according to the present invention and a method for manufacturing
the composite will now be described with reference to FIGS. 1 to 6.
Note that the present invention is not intended to be limited to
configurations described in the embodiments below and the
accompanying drawings.
[0051] <Reinforced Fiber/Resin Fiber Composite>
[0052] A reinforced fiber/resin fiber composite according to the
present invention which is an intermediate material for a
long-fiber reinforced thermoplastic resin structure is provided in
the form of a composite or mixture including a long fiber and a
thermoplastic resin fiber. The long fiber includes a multifilament,
which is a group of monofilaments. The multifilament is a thin and
long fiber extending in the longitudinal direction. The long fiber
may, for example, be a reinforced fiber (e.g., a carbon fiber,
glass fiber, aramid fiber, etc.).
[0053] The thermoplastic resin fiber includes at least two fibers.
It is desirable to select a combination of thermoplastic resin
fibers which have complementary physical properties after
thermoforming. For example, a combination of thermoplastic resin
fibers is selected so that good impregnation characteristics and
good interfacial characteristics are simultaneously provided by
thermoforming. For example, a polypropylene (PP) fiber, which is
representative of a thermoplastic resin fiber, has good resin
impregnation characteristics and slightly poor interfacial
characteristics (e.g., interfacial shear strength). On the other
hand, if a PP fiber is modified with an acid to form an
acid-modified polypropylene (MAPP) fiber, the interfacial
characteristics are improved, and at the same time, the wettability
deteriorates, and therefore, the thermoplastic resin impregnation
characteristics decrease. Therefore, a PP fiber and an MAPP fiber
are combined into a new hybrid resin fiber having both types of
characteristics. In the hybrid fiber, the fibers offset mutual
lacks of physical properties, so that good impregnation
characteristics and good interfacial characteristics are
simultaneously achieved, and therefore, a material having both good
impregnation characteristics and good interfacial characteristics
can be provided.
[0054] In the reinforced fiber/resin fiber composite of the present
invention, at least two thermoplastic resin fibers are provided
around the long fiber (reinforced fiber) to surround the long fiber
in order to form a hybrid. As used herein, the term "surround" with
respect to the long fiber means that the at least two thermoplastic
resin fibers are provided on the surface of the long fiber,
overlapping each other, so that all or a portion of the surface of
the long fiber is concealed from the outside. The term "provided
around" or "arranged around" with respect to the long fiber means
that, in a cross-sectional view of the fiber, the outlines of the
at least two thermoplastic resin fibers are in contact with or
close to the outline of the long fiber. The arrangement of the at
least two thermoplastic resin fibers with respect to the long fiber
is not limited to an arrangement in which the at least two
thermoplastic resin fibers extend generally in parallel to the long
fiber in the longitudinal direction. Alternatively, for example,
the at least two thermoplastic resin fibers may extend at a
predetermined angle with respect to the long fiber, may be bent or
curved and extend while gradually changing the position, or may be
randomly positioned. In other words, the hybrid resin fiber
including the at least two thermoplastic resin fibers only needs to
be provided around the long fiber. These arrangements of the at
least two thermoplastic resin fibers with respect to the long fiber
may be implemented by a variety of techniques. The hybrid fiber is
effectively obtained by using a "braiding technique" which will
next be described.
[0055] <Braiding Technique>
[0056] A braiding technique is known as a Japanese traditional
craft, in which a plurality of thin threads (braiding fiber
strands) are interwoven into a fabric which is strong and has a
beautiful woven pattern. In the present invention, a braided fabric
is provided in which at least two thermoplastic resin fibers which
are braiding fibers are arranged around a reinforced fiber which is
an axial fiber. Specifically, the at least two thermoplastic resin
fibers are interwoven at a predetermined angle with respect to the
longitudinal direction of the reinforced fiber to form a braid in
which the at least two resin fibers are braided around the
reinforced fiber.
[0057] FIG. 1(a) is a schematic diagram showing an example braiding
machine 100 for manufacturing a reinforced fiber/resin fiber
composite 50 of the present invention. FIG. 1(b) is an external
view of the reinforced fiber/resin fiber composite 50. As shown in
FIG. 1(a), the braiding machine 100 includes axial fiber supply
units 10 which supply an axial fiber strand (reinforced fiber) 15
to a core fiber (reinforced fiber) 40 which is a core of a braided
fabric (the reinforced fiber/resin fiber composite 50), and
braiding fiber supply units 20 which supply a braiding fiber strand
(resin fiber) 25 to the core fiber 40. Prior to formation of a
braided fabric, for preparation, the braiding fiber supply units 20
are on standby around the axial fiber supply unit 10. The axial
fiber supply units 10 and the braiding fiber supply units 20 are
provided in pairs. In FIG. 1(a), the axial fiber supply units 10
are each paired with one braiding fiber supply unit 20.
Alternatively, the axial fiber supply unit 10 may be each combined
with a plurality of braiding fiber supply units 20. The number of
the braiding fiber supply units 20 may be suitably set based on the
structural design of the reinforced fiber/resin fiber composite 50.
The axial fiber supply unit 10 is connected to a roving (not shown)
into which the reinforced fiber is wound, and outputs the
reinforced fiber unwound from the roving through a tip portion 11
as the axial fiber strand 15. The braiding fiber supply unit 20
includes a spindle 21 around which the braiding fiber strand 25 is
wound, and an unwinding bar 22 through which the braiding fiber
strand 25 pulled out of the spindle 21 is passed. The braiding
fiber supply unit 20 revolves around the corresponding axial fiber
supply unit 10. In this case, the relative positions of the spindle
21 and the unwinding bar 22 as viewed from above change. As a
result, the braiding fiber strand 25 wound around the spindle 21 is
continuously released from the spindle 21 through the unwinding bar
22. The released braiding fiber strands 25 are collected to
surround the axial fiber strands 15, and the axial fiber supply
units 10 and the braiding fiber supply units 20 move on a braiding
orbit 30, so that the braiding fiber strands 25 are braided at a
braiding angle .theta. with respect to the longitudinal direction
of the axial fiber strands 15, and therefore, a braid is formed.
The braid formed by the axial fiber strands 15 and the braiding
fiber strands 25 surrounds the core fiber 40. Thus, the reinforced
fiber/resin fiber composite 50 (also referred to as a "hybrid fiber
composite") as a braided fabric shown in FIG. 1(b) in which the
braiding fiber strands 25 are braided at the braiding angle .theta.
with respect to the axial fiber strands 15 is continuously formed
around the core fiber 40. The resultant reinforced fiber/resin
fiber composite 50 is processed by thermoforming directly or after
being arranged in a desired shape, to obtain the desired long-fiber
reinforced thermoplastic resin structure. Melting of the resin
fiber during thermoforming, which is a type of so-called in-situ
polymer blend, can be easily carried out.
[0058] In the braiding technique, the pattern in which the braiding
fiber strands 25 are braided with respect to the axial fiber
strands 15 may be modified to provide various arrangement patterns
of the braiding fiber strands (thermoplastic resin fiber) 25.
Therefore, If the braiding technique is applied to the reinforced
fiber/resin fiber composite 50 of the present invention, the
mixture ratio of the reinforced fiber and the thermoplastic resin,
and the composition ratio of the thermoplastic resin melted by
heat, can be flexibly controlled by the pattern in which the
strands are braided. As a result, the long-fiber reinforced
thermoplastic resin structure as a final product can be
manufactured in a form suitable for the purpose of use
("made-to-order" manufacture). Also, if the braiding technique is
used, the fibers are not opened, and therefore, are not likely to
be damaged. Moreover, in the braiding technique, when a plurality
of braiding fiber stands are braided, the arrangement of the
braiding fiber strands, and tension exerted on the braiding fiber
strands, can be controlled on a strand-by-strand basis. Therefore,
the braiding technique is particularly effective in accurately
controlling the structure and composition of the long-fiber
reinforced thermoplastic resin structure as a final product.
Therefore, if the braiding technique is used, the physical
properties of each resin fiber can be imparted, in a desired form,
to the long-fiber reinforced thermoplastic resin structure after
thermoforming.
EXAMPLES
[0059] Examples relating to the reinforced fiber/resin fiber
composite (hybrid fiber composite) of the present invention which
is manufactured using the above braiding technique will be
described. In the examples, a carbon fiber is used as the long
fiber which is a reinforced fiber, and a polypropylene (PP) fiber
and an acid-modified polypropylene (MAPP) fiber which is obtained
by modifying a PP fiber by maleic acid are used as the
thermoplastic resin fibers. As described above, a PP fiber has good
resin impregnation characteristics and slightly poor interfacial
characteristics (e.g., interfacial shear strength). On the other
hand, an MAPP fiber has slightly poor resin impregnation
characteristics and good interfacial characteristics. Therefore,
attempts have been made to braid a PP fiber and an MAPP fiber on
the surface of a carbon fiber using the braiding technique to
obtain a hybrid fiber composite, thereby simultaneously achieving
good impregnation characteristics of the thermoplastic resin into
the carbon fiber and good interfacial characteristics between the
carbon fiber and the thermoplastic resin.
[0060] [Pattern of Braiding for Reinforced Fiber/Resin Fiber
Composite]
[0061] FIG. 2 is a schematic cross-sectional view of the reinforced
fiber/resin fiber composite 50 for describing a pattern in which a
PP fiber 25a and an MAPP fiber 25b (the braiding fiber strands 25)
are braided with respect to a carbon fiber 15a (the axial fiber
strand 15). In this example, 16 strands of the PP fiber 25a and 16
strands of the MAPP fiber 25b were braided with respect to one
strand of the carbon fiber 15a to obtain a carbon fiber/PP
fiber/MAPP fiber composite (hybrid fiber composite) which is an
intermediate material for a long-fiber reinforced thermoplastic
resin structure. The resin fibers were braided in two patterns
shown in FIGS. 2(a) and 2(b). In FIG. 2(a), only the PP fiber
strands 25a are braided as a first layer to surround the surface of
the carbon fiber 15a, and next, only the MAPP fiber strands 25b are
braided as a second layer on the first layer. The braiding pattern
of FIG. 2(a) is referred to as "double-layer arrangement." In FIG.
2(b), the PP fiber strands 25a and the MAPP fiber strands 25b are
alternately braided as a first layer to surround the surface of the
carbon fiber 15a, and next, the PP fiber strands 25a and the MAPP
fiber strands 25b are alternately braided as a second layer in a
manner similar to that of the first layer. The braiding pattern of
FIG. 2(b) is referred to as "alternate arrangement." FIG. 3 shows a
photograph of an external appearance of the carbon fiber/resin
fiber composite of this example in which two thermoplastic resin
fibers having different properties are braided with respect to a
carbon fiber, and a diagram showing a structure thereof.
[0062] [Evaluation of Impregnation Characteristics]
[0063] The impregnation characteristics of a long-fiber reinforced
thermoplastic resin structure (also referred to as a "hybrid
structure") obtained by processing a carbon fiber/resin fiber
composite (hybrid fiber composite) by thermoforming was evaluated
by cross-sectional observation using a microscope.
[0064] Initially, carbon fiber/resin fiber composites having the
double-layer arrangement and the alternate arrangement were each
processed by thermoforming to obtain test pieces of a long-fiber
(carbon fiber) reinforced thermoplastic resin structure (hybrid
structure). The thermoforming for each test piece was performed
under conditions that the molding temperature was 200.degree. C.,
the molding pressure was 10 MPa, and the molding time was 5 min, 10
min, 20 min, and 40 min. Next, a cross-section of each test piece
was observed to evaluate how much (or how little) the carbon fiber
was impregnated with the thermoplastic resin. FIG. 4 shows
photographs of cross-sections of the test pieces having the
double-layer and alternate arrangements, indicating changes in
their impregnated states depending on the molding time. A numerical
value described at the right corner of each photograph represents
the unimpregnation ratio of the carbon fiber. The unimpregnation
ratio is calculated by a procedure described below.
[0065] FIG. 5 shows example image data for calculating the
unimpregnation ratio of the carbon fiber. FIGS. 5(a) and 5(b) show
cross-sections of a test piece before and after image processing,
respectively. The cross-sectional image of the carbon fiber (a
bundle of fiber strands) of FIG. 5(a) is binarized by image
processing using a predetermined threshold, to obtain the
cross-sectional image of FIG. 5(b) having an impregnated region S1
indicated by a white region and an unimpregnated region S2
indicated by a black region. The unimpregnation ratio (%) is
calculated using the values of S1 and S2 obtained from the
cross-sectional image of FIG. 5(b) by:
the unimpregnation ratio (%)=S2/(S1+S2) (1)
[0066] FIG. 6 is a graph plotted to show a relationship between the
unimpregnation ratio and molding time of each of the test pieces
having the double-layer and alternate arrangements. As can be seen
from FIG. 6, in both of the double-layer and alternate
arrangements, the unimpregnation ratio of the thermoplastic resin
with respect to the carbon fiber gradually decreases with molding
time. In other words, it was observed that the carbon fiber is more
sufficiently impregnated with the thermoplastic resin with an
increase in the molding time. By comparison of the double-layer and
alternate arrangements, it was found that the double-layer
arrangement has impregnation characteristics better than those of
the alternate arrangement. In particular, it was found that if the
carbon fiber/resin fiber composite having the double-layer
arrangement is subjected to thermoforming for 20 min or more,
preferably 40 min or more, the carbon fiber can be impregnated to
substantially the center thereof with the thermoplastic resin.
[0067] [Evaluation of Interfacial Characteristics]
[0068] A three point bending test was conducted using a flexure
tester on a long-fiber reinforced thermoplastic resin structure
(hybrid structure) which is obtained by processing a carbon
fiber/resin fiber composite (hybrid fiber composite) by
thermoforming, to evaluate the interfacial characteristics thereof.
Mechanical characteristics in the longitudinal direction of the
long-fiber reinforced thermoplastic resin structure were measured
using the three point bending test. The interfacial characteristics
can be indirectly estimated to be better with an increase in the
values of the modulus of elasticity and strength.
[0069] Long-fiber reinforced thermoplastic resin structures in the
shape of a plate having a length of 50 mm, a width of 20 mm, and a
thickness of 2 mm were produced as test pieces by thermoforming. As
the test pieces, molded products of carbon fiber/resin fiber
composites having the double-layer and alternate arrangements of
FIG. 2 were prepared. As control test pieces, molded products of a
carbon fiber/PP fiber composite and a carbon fiber/MAPP fiber
composite were prepared. The test pieces were produced by
thermoforming under conditions that the molding temperature was
200.degree. C., the molding pressure was 10 MPa, and the molding
time was 5 min, 10 min, 20 min, and 40 min. Next, a load was
applied to each test piece at the center of the span distance of 32
mm at a crosshead speed of 1 mm/min. The three point bending test
was continued until the test piece was broken. FIG. 7 is a graph of
measurement data (load-flexure curve) of each test piece which was
obtained by the three point bending test. The modulus of elasticity
in bending E (MPa) and flexural stress .sigma. (MPa) of each test
piece were estimated using the following expressions (2) and (3)
based on the measurement data. The maximum value of the flexural
stress .sigma. is defined as a flexural strength. Note that these
calculations were performed using a technique complying with JIS
K7017.
E=L.sup.3/(4bh.sup.3)(.DELTA.F/.DELTA.S) (2)
.sigma.=3FL/(2bh.sup.2) (3)
[0070] L: the distance between supporting points (mm)
[0071] b: the width of the test piece (mm)
[0072] h: the thickness of the test piece (mm)
[0073] F: load (N)
[0074] .DELTA.S: the difference (mm) between flexures S' and S''
corresponding to flexural strains .epsilon.'=0.0005 and
.epsilon.''=0.0025
[0075] .DELTA.F: the difference (N) between loads F' and F'' in S'
and S'', respectively
[0076] The test result is shown in Table 1 below.
TABLE-US-00001 TABLE 1 Test No. Test piece Elastic modulus (GPa)
Strength (MPa) 1 carbon fiber/resin 50.2 314 fiber (double layer) 2
carbon fiber/resin 32.3 232 fiber (alternate) 3 carbon fiber/PP
fiber 18.2 110 4 carbon fiber/MAPP fiber 48.6 352
[0077] As can be seen from the above result, the long-fiber
reinforced thermoplastic resin structures (hybrid structures)
formed of the carbon fiber/resin fiber composite having the
double-layer arrangement (Test No. 1) and the carbon fiber/resin
fiber composite having the alternate arrangement (Test No. 2) have
a modulus of elasticity and strength much greater than those of the
long-fiber reinforced thermoplastic resin structure (non-hybrid
structure) formed of the carbon fiber/PP fiber composite (Test No.
3). In particular, the carbon fiber/resin fiber composite of the
double-layer arrangement (Test No. 1) has a modulus of elasticity
and strength similar to those of the carbon fiber/MAPP fiber
composite (Test No. 4). Therefore, if a carbon fiber/resin fiber
composite which includes a hybrid of a PP fiber and an MAPP fiber
as the resin fiber is processed by thermoforming, a
high-performance long-fiber reinforced thermoplastic resin
structure having a sufficient strength in the long fiber direction
(longitudinal direction) can be obtained with as high interfacial
characteristics as those of a carbon fiber/MAPP fiber composite
while reducing a decrease in the impregnation characteristics due
to the MAPP fiber.
Other Embodiments
[0078] (1) The at least two resin fibers included in the carbon
fiber/resin fiber composite (hybrid fiber composite) may be a
combination of other materials in addition to a PP fiber and an
MAPP fiber described in the above embodiment. Example resin fiber
composites having a combination of resin fibers, and their
complementary physical properties (physical properties which can be
simultaneously achieved), are described as follows.
[0079] [1] A polylactic acid (PLA) fiber/a polyoxymethylene (POM)
fiber: interfacial characteristics and impregnation
characteristics/toughness
[0080] [2] A polypropylene (PP) fiber/a polyamide (PA) fiber (nylon
fiber): impregnation characteristics/interfacial adhesiveness, low
cost/interfacial adhesiveness
[0081] [3] A polyamide (PA) fiber/a polyoxymethylene (POM) fiber:
interfacial adhesiveness/abrasion resistance and slidability
[0082] [4] A polypropylene (PP) fiber/a polyoxymethylene (POM)
fiber: impregnation characteristics/abrasion resistance and
slidability
[0083] [5] A polyamide (PA) fiber/a polyphenylene sulfide (PPS)
fiber: interfacial adhesiveness/heat resistance, interfacial
adhesiveness/impregnation characteristics
[0084] [6] A polypropylene (PP) fiber/a polycarbonate (PC) fiber:
impregnation characteristics/impact resistance
[0085] [7] A polyamide (PA) fiber/a polycarbonate (PC) fiber:
interfacial adhesiveness/impact resistance
[0086] In addition, the at least two resin fibers included in the
resin fiber composite may, for example, be a thermoplastic resin
fiber, such as a polyethylene (PE) fiber, polyether ether ketone
(PEEK) fiber, polyether ketone ketone (PEKK) fiber, etc. Examples
of complementary physical characteristics of the thermoplastic
resin fibers include, in addition to the above characteristics,
water absorbance, fatigue resistance, chemical resistance, solvent
resistance, frame resistance, electrical characteristics, cold
resistance, weather resistance, etc.
[0087] (2) A hybrid fiber composite produced by the braiding
technique may have a variety of structures depending on the
intended long-fiber reinforced thermoplastic resin structure. There
are traditional braids, such as a square braid, flat braid,
circular braid, etc. A hybrid fiber composite may be constructed on
the basis of these braids. For example, when a pillar which is a
part of the body of an automobile is manufactured, a reinforced
fiber/resin fiber composite which is an intermediate material is
produced in the form of a ribbon-like flat braid, and is wound into
an annular shape. As a result, a hollow pillar having a light
weight and a high strength can be manufactured.
[0088] (3) In the above embodiment, a braided fabric (reinforced
fiber/resin fiber composite) is produced using the core fiber 40
and the axial fiber strand 15 which are a reinforced fiber and the
braiding fiber strand 25 which is a resin fiber. The fiber types of
the core fiber 40, the axial fiber strand 15, and the braiding
fiber strand 25 are not particularly limited, and may be suitably
determined, depending on the reinforced fiber/resin fiber composite
to be produced. For example, the axial fiber strand 15 may be a
reinforced fiber while the core fiber 40 and the braiding fiber
strand 25 may be a resin fiber.
INDUSTRIAL APPLICABILITY
[0089] The reinforced fiber/resin fiber composite of the present
invention serves as an intermediate material for a long-fiber
reinforced thermoplastic resin structure, and is preferably
applicable to the fields of automobiles, ships, aircrafts, etc.
REFERENCE SIGNS LIST
[0090] 10 AXIAL FIBER SUPPLY UNIT [0091] 11 TIP PORTION [0092] 15
AXIAL FIBER STRAND (REINFORCED FIBER) [0093] 15a CARBON FIBER
[0094] 20 BRAIDING FIBER SUPPLY UNIT [0095] 21 SPINDLE [0096] 22
UNWINDING BAR [0097] 25 BRAIDING FIBER STRAND (RESIN FIBER) [0098]
25a PP FIBER [0099] 25b MAPP FIBER [0100] 40 CORE FIBER (REINFORCED
FIBER) [0101] 50 REINFORCED FIBER/RESIN FIBER COMPOSITE [0102] 100
BRAIDING MACHINE
* * * * *