U.S. patent application number 12/244676 was filed with the patent office on 2009-05-14 for prepreg, intermediate material for forming frp, and method for production thereof and method for production of fiber-reinforced composite material.
This patent application is currently assigned to Mitsubishi Rayon co., Ltd.. Invention is credited to Kazuya Goto, Akihiro Ito, Kazuki Koga, Tadayoshi Saitou, Tsuneo Takano, Kouki Wakabayashi.
Application Number | 20090123717 12/244676 |
Document ID | / |
Family ID | 30773719 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090123717 |
Kind Code |
A1 |
Goto; Kazuya ; et
al. |
May 14, 2009 |
PREPREG, INTERMEDIATE MATERIAL FOR FORMING FRP, AND METHOD FOR
PRODUCTION THEREOF AND METHOD FOR PRODUCTION OF FIBER-REINFORCED
COMPOSITE MATERIAL
Abstract
An FRP is produced using a prepreg comprising reinforcing fiber,
a sheet-like reinforcing fiber substrate containing reinforcing
fiber, and a matrix resin, wherein the matrix resin is impregnated
into the sheet-like reinforcing fiber substrate and also covers one
surface of the sheet-like reinforcing fiber substrate, and the
matrix resin impregnation ratio is within a range of 35% to 95%; a
prepreg comprising reinforcing fiber, a sheet-like reinforcing
fiber substrate containing reinforcing fiber, and a matrix resin,
wherein the matrix resin exists on both surfaces of the sheet-like
reinforcing fiber substrate, and the portion inside the sheet-like
reinforcing fiber substrate into which the matrix resin has not
been impregnated is continuous; or a prepreg comprising reinforcing
fiber, a sheet-like reinforcing fiber substrate containing
reinforcing fiber, and a matrix resin, wherein at least one surface
exhibits a sea-and-island-type pattern comprising resin-impregnated
portions (island portions) where the matrix resin is present at the
surface and fiber portions (sea portions) where the matrix resin is
not present at the surface, the surface coverage ratio of the
matrix resin on those surfaces with said a sea-and-island-type
pattern is within a range of 3% to 80%, and the weave intersection
coverage ratio for the island portions, represented by a formula
(1) shown below, is at least 40%, displays excellent external
appearance, with no internal voids or surface pinholes, even when
molded is conducted using only vacuum pressure. Island portions
weave intersection coverage ratio (%)=(T/Y).times.100 (1) (wherein,
T represents a number of island portions that cover weave
intersections, and Y represents a number of weave intersections
within said reinforcing fiber woven fabric on said surface with
said sea-and-island-type pattern).
Inventors: |
Goto; Kazuya; (Irvine,
CA) ; Koga; Kazuki; (Aichi-ken, JP) ; Saitou;
Tadayoshi; (Aichi-ken, JP) ; Ito; Akihiro;
(Aichi-ken, JP) ; Takano; Tsuneo; (Aichi-ken,
JP) ; Wakabayashi; Kouki; (Otake-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Mitsubishi Rayon co., Ltd.
Tokyo
JP
|
Family ID: |
30773719 |
Appl. No.: |
12/244676 |
Filed: |
October 2, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10521433 |
Jan 14, 2005 |
|
|
|
PCT/JP03/09176 |
Jul 18, 2003 |
|
|
|
12244676 |
|
|
|
|
Current U.S.
Class: |
428/213 ;
156/182; 156/242; 442/179 |
Current CPC
Class: |
D06M 15/55 20130101;
B29C 70/086 20130101; Y10T 442/2049 20150401; Y10T 442/2861
20150401; B29C 70/465 20130101; Y10T 442/2926 20150401; Y10T
442/2992 20150401; B29C 70/081 20130101; B29C 70/22 20130101; B29K
2101/12 20130101; Y10T 442/2361 20150401; Y10T 442/2984 20150401;
B29C 70/546 20130101; B32B 5/022 20130101; Y10T 156/10 20150115;
Y10T 442/2951 20150401; B29C 70/342 20130101; B32B 2260/023
20130101; B32B 5/26 20130101; B32B 2363/00 20130101; Y10T 428/2495
20150115; Y10T 428/249921 20150401; Y10T 442/2008 20150401; B29B
15/122 20130101; B32B 2305/076 20130101; Y10T 442/20 20150401; B29K
2063/00 20130101; C08J 5/24 20130101; B32B 2262/106 20130101; Y10T
442/2139 20150401; Y10T 442/3854 20150401; Y10T 428/2481 20150115;
B29K 2101/10 20130101 |
Class at
Publication: |
428/213 ;
442/179; 156/182; 156/242 |
International
Class: |
B32B 5/10 20060101
B32B005/10; B32B 37/06 20060101 B32B037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2002 |
JP |
2002-210123 |
Aug 12, 2002 |
JP |
2002-234861 |
Sep 18, 2002 |
JP |
2002-271850 |
Dec 5, 2002 |
JP |
2002-353759 |
Mar 10, 2003 |
JP |
2003-63166 |
Claims
1. A prepreg comprising reinforcing fiber, a sheet-like reinforcing
fiber substrate containing reinforcing fiber, and a matrix resin,
wherein said matrix resin is impregnated into said sheet-like
reinforcing fiber substrate and also covers one surface of said
sheet-like reinforcing fiber substrate, and a matrix resin
impregnation ratio is within a range of 35% to 95%.
2. A prepreg comprising reinforcing fiber, a sheet-like reinforcing
fiber substrate containing reinforcing fiber, and a matrix resin,
wherein said matrix resin exists on both surfaces of said
sheet-like reinforcing fiber substrate, and a portion inside said
sheet-like reinforcing fiber substrate into which said matrix resin
has not been impregnated is continuous.
3. A prepreg comprising a sheet-like reinforcing fiber substrate
formed from a reinforcing fiber woven fabric, and a matrix resin,
wherein at least one surface displays a sea-and-island-type pattern
comprising resin-impregnated portions (island portions) where said
matrix resin is present at said surface, and fiber portions (sea
portions) where said matrix resin is not present at said surface, a
surface coverage ratio of said matrix resin on surfaces with said
sea-and-island-type pattern is within a range of 3% to 80%, and a
weave intersection coverage ratio for said island portions,
represented by a formula (1) shown below, is at least 40%: Island
portions weave intersection coverage ratio (%)=(T/Y).times.100 (1)
(wherein, T represents a number of island portions that cover weave
intersections, and Y represents a number of weave intersections
within said reinforcing fiber woven fabric on said surface with
said sea-and-island-type pattern).
4. A prepreg according to any one of claim 1 through claim 3,
wherein said matrix resin is a thermosetting resin composition.
5. A prepreg according to claim 4, wherein said thermosetting resin
composition is curable by holding at 90.degree. C. for 2 hours.
6. A prepreg according to claim 4, wherein a minimum viscosity of
said thermosetting resin composition is no more than 1000
poise.
7. A prepreg according to claim 4, wherein said thermosetting resin
composition comprises epoxy resin as a primary component.
8. A prepreg according to claim 4, wherein said thermosetting resin
composition also contains a thermoplastic resin, and said
thermoplastic resin is not dissolved within said thermosetting
resin composition.
9. A prepreg according to claim 8, wherein said thermoplastic resin
comprises short fibers of thermoplastic resin with a length of 1 to
50 mm.
10. A prepreg according to claim 9, wherein said short fibers of
thermoplastic resin have a size of no more than 300 tex.
11. A prepreg according to any one of claim 1 through claim 3,
wherein said reinforcing fibers are carbon fiber and/or glass
fiber.
12. A prepreg according to any one of claim 1 through claim 3,
wherein said sheet-like reinforcing fiber substrate has a fiber
weight within a range of 200 g/m.sup.2 to 1500 g/m.sup.2.
13. A prepreg according to any one of claim 1 through claim 3,
wherein said sheet-like reinforcing fiber substrate is in a form
selected from the group consisting of unidirectional materials,
woven fabrics, knit fabrics, braided fabrics, mat materials,
non-woven fabrics, and stitched sheets.
14. A prepreg according to any one of claim 1 through claim 3,
wherein said sheet-like reinforcing fiber substrate has a thickness
of at least 200 .mu.m.
15. A process for producing a prepreg, comprising the steps of
applying a matrix resin on a resin support sheet, bonding a matrix
resin-coated surface of said resin support sheet to both surfaces
of a sheet-like reinforcing, fiber substrate, and pressing a
laminate of said resin support sheets and said sheet-like
reinforcing fiber substrate under temperature conditions ranging
from room temperature to 40.degree. C. in order to cause said
matrix resin to impregnate said sheet-like reinforcing fiber
substrate, thus forming a prepreg in which an interior of said
sheet-like reinforcing fiber substrate comprises a continuous
portion that has not been impregnated with said matrix resin.
16. A process for producing a prepreg, comprising the steps of
applying a matrix resin on a resin support sheet, bonding a matrix
resin-coated surface of said resin support sheet to one surface of
a reinforcing fiber woven fabric, bonding a protective film to
another surface of said reinforcing fiber woven fabric,
subsequently applying heat and/or pressure in order to cause said
matrix resin to impregnate said reinforcing fiber woven fabric,
thus forming a prepreg in which a surface of said reinforcing fiber
woven fabric facing said protective film displays a
sea-and-island-pattern comprising resin-impregnated portions
(island portions) where said matrix resin is present at said
surface and fiber portions (sea portions) where said matrix resin
is not present at said surface.
17. A process for producing a prepreg according to claim 16,
wherein a thermosetting resin composition containing a
thermoplastic resin that is not dissolved within said thermosetting
resin composition is also applied uniformly to said matrix
resin-coated surface.
18. An intermediate material for FRP molding comprising a prepreg
containing reinforcing fibers and a matrix resin, and a substrate
containing essentially no impregnated thermosetting resin
composition, which is provided on at least one side surface of said
prepreg, wherein a ratio (B)/(A) between a thickness (A) of said
prepreg and a thickness (B) of said substrate is within a range of
0.1 to 2.5.
19. A prepreg according to claim 18, wherein said matrix resin is a
thermosetting resin composition.
20. An intermediate material for FRP molding according to claim 18,
wherein said substrate containing essentially no impregnated
thermosetting resin composition contains a fibrous thermoplastic
resin.
21. An intermediate material for FRP molding according to claim 18,
wherein said substrate containing essentially no impregnated
thermosetting resin composition is a non-woven cloth of a
thermoplastic resin.
22. An intermediate material for FRP molding according to claim 18,
wherein said substrate containing essentially no impregnated
thermosetting resin composition contains reinforcing fibers.
23. An intermediate material for FRP molding according to claim 22,
wherein said reinforcing fibers are identical to said reinforcing
fibers incorporated within said prepreg.
24. An intermediate material for FRP molding according to claim 22,
wherein said reinforcing fibers are positioned at a different angle
to said reinforcing fibers incorporated within said prepreg.
25. An intermediate material for FRP molding according to claim 22,
wherein said reinforcing fibers are different from said reinforcing
fibers incorporated within said prepreg.
26. An intermediate material for FRP molding according to claim 18,
wherein said matrix resin is one of an epoxy resin composition and
a phenol resin composition.
27. An intermediate material for FRP molding according to claim 18,
wherein said reinforcing fibers incorporated within said prepreg
are carbon fiber and/or glass fiber.
28. A process for producing an intermediate material for FRP
molding, comprising the steps of preparing a prepreg using a
lacquer-type process, and bonding a substrate containing
essentially no impregnated thermosetting resin composition to at
least one surface of said prepreg.
29. A process for producing a fiber-reinforced composite material,
comprising the steps of laminating a prepreg according to any one
of claim 1 through claim 3, and conducting molding using vacuum bag
molding.
30. A process for producing a fiber-reinforced composite material,
comprising the steps of laminating an intermediate material for FRP
molding according to claim 18, and conducting molding using vacuum
bag molding.
31. A process for producing a fiber-reinforced composite material,
wherein prepregs according to any one of claim 1 through claim 3
are laminated with identical side surfaces of said prepregs facing
to identical directions.
32. A process for producing a fiber-reinforced composite material,
wherein an intermediate material for FRP molding according to claim
18 is laminated with identical side surfaces of said intermediate
material facing to identical directions.
33. A process for producing a fiber-reinforced composite material
according to claim 29, wherein in said vacuum bag molding process,
primary curing is conducted for at least 10 minutes at a primary
curing temperature of no more than 150.degree. C., and molding is
then conducted at a temperature that is equal to, or greater than,
said primary curing temperature.
34. A process for producing a fiber-reinforced composite material
according to claim 31, wherein in said vacuum bag molding process,
primary curing is conducted for at least 10 minutes at a primary
curing temperature of no more than 150.degree. C., and molding is
then conducted at a temperature that is equal to, or greater than,
said primary curing temperature.
35. A process for producing a fiber-reinforced composite material
according to claim 29, comprising the steps of deaerating said
prepreg under conditions including a temperature within a range of
room temperature to 50.degree. C., and a pressure of no more than
50 Torr, and conducting molding by raising temperature to a molding
temperature, while said pressure is maintained at no more than 50
Torr.
36. A process for producing a fiber-reinforced composite material
according to claim 35, wherein a rate of temperature increase
during said raising of temperature to said molding temperature is
set to no more than 1.degree. C./minute when it starts from a point
at least 20.degree. C. below said molding temperature.
Description
TECHNICAL FIELD
[0001] The present invention relates to a prepreg that functions as
an intermediate material for FRP molding.
BACKGROUND ART
[0002] Fiber-reinforced composite materials (hereafter also
abbreviated as FRP) are lightweight, while offering good strength
and high rigidity, and are consequently widely used in a variety of
applications from sports and leisure through to industrial
applications such as vehicles and aircraft. In recent years, with
the fall in the cost of carbon fiber, the use of carbon fiber
reinforced composite materials (hereafter abbreviated as CFRP),
which are even more lightweight and offer even higher levels of
strength and rigidity, within industrial applications has also
become more widespread.
[0003] Amongst these potential industrial applications, CFRPs used
for structural members within train bodies and aircraft frames are
typically produced by autoclave molding, using an intermediate
material known as a prepreg. The reason for this preference is that
by conducting the molding under high pressure using an autoclave,
not only can the occurrence of voids within the molded product be
reduced, enabling the strength of the molded product to meet
expectations, but the occurrence of surface pinholes can also be
suppressed, enabling the production of a molded product with a
favorable external appearance.
[0004] However, autoclave facilities are extremely expensive, which
not only acts as a large barrier to new entrants, but also means
that once autoclave facilities are purchased, the size of the
molded products is restricted by the size of the autoclave, meaning
the production of larger products is effectively impossible.
[0005] In order to avoid these problems, the development of
autoclave-free, low cost molding is also progressing, and
representative examples of such molding include oven molding under
either vacuum conditions or normal atmospheric conditions (also
known as vacuum bag molding). Oven molding does not require the
application of pressure, meaning the molding can be conducted
without the need for a proper pressure-resistant vessel such as an
autoclave, and molding can be conducted simply with a furnace for
raising the temperature. Molding can also be conducted with a
simple device comprising an adiabatic board and a hot air heater.
However, because these processes do not involve the application of
pressure, residual voids tend to remain within the molded product,
the strength of the molded product is inferior to that of a molded
product produced in an autoclave, and pinhole formation is also a
problem.
[0006] In recent years, a variety of measures for overcoming these
problems have been proposed. For example, WO 00/27632 discloses
technology relating to materials comprising a resin layer and a
reinforcing fiber layer, which display minimal void generation, and
enable the production of molded products with extremely clean
surfaces, even when used with oven molding. However, with this
technology, almost all of the resin is impregnated during molding,
and depending on the molding conditions, portions of the resin that
display unsatisfactory impregnation can occur, leading to the
occurrence of internal voids and surface pinholes. Furthermore,
because the surface is almost free from resin and is extremely dry,
workability problems such as difficulty in bonding the product to
the molding die can also be a concern.
DISCLOSURE OF INVENTION
[0007] An object of the present invention is to provide an
intermediate material, which retains the level of workability
associated with conventional prepregs, while enabling the
production of a FRP with no internal voids or surface pinholes, but
with excellent external appearance, using molding at only vacuum
pressure, without the use of an autoclave.
[0008] A first aspect of the present invention is a prepreg
comprising reinforcing fiber, a sheet-like reinforcing fiber
substrate containing reinforcing fiber, and a matrix resin, wherein
the matrix resin is impregnated into the sheet-like reinforcing
fiber substrate and also covers one surface of the sheet-like
reinforcing fiber substrate, and the matrix resin impregnation
ratio is within a range of 35% to 95%.
[0009] Furthermore, a second aspect of the present invention is a
prepreg comprising a matrix resin, and a sheet-like reinforcing
fiber substrate, wherein the prepreg comprises reinforcing fiber, a
sheet-like reinforcing fiber substrate containing reinforcing
fiber, and a matrix resin, wherein the matrix resin exists on both
surfaces of the sheet-like reinforcing fiber substrate, and the
portion inside the sheet-like reinforcing fiber substrate into
which the matrix resin has not been impregnated is continuous.
[0010] Furthermore, a third aspect of the present invention is a
prepreg comprising a sheet-like reinforcing fiber substrate formed
from a reinforcing fiber woven fabric, and a matrix resin, wherein
at least one surface displays a sea-and-island-type pattern
comprising resin-impregnated portions (island portions) where the
matrix resin is present at the surface and fiber portions (sea
portions) where the matrix resin is not present at the surface, the
surface coverage ratio of the matrix resin on surfaces with the
sea-and-island-type pattern is within a range of 3% to 80%, and the
weave intersection coverage ratio for the island portions, as
represented by a formula (1) below, is at least 40%.
Island portions weave intersection coverage ratio
(%)=(T/Y).times.100 (1)
(wherein, T represents the number of island portions that cover
weave intersections, and Y represents the total number of weave
intersections of the reinforcing fiber fabric on the surface with
the sea-and-island-type pattern).
[0011] Furthermore, a fourth aspect of the present invention is an
intermediate material for FRP molding comprising a prepreg
containing reinforcing fiber and a matrix resin, and a substrate
containing essentially no impregnated thermosetting resin
composition, which is provided on at least one side of the prepreg,
wherein the ratio (B)/(A) between the thickness (A) of the prepreg,
and the thickness (B) of the substrate is within a range of 0.1 to
2.5.
[0012] Using the aspects described above, the level of workability
associated with conventional prepregs can be retained, while FRP
with no internal voids or surface pinholes, but with excellent
external appearance can be produced using molding at only vacuum
pressure, without the use of an autoclave.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic illustration of a prepreg that uses a
sheet with the fibers aligned unidirectionally as the sheet-like
reinforcing fiber substrate, viewed in a cross section cut
perpendicularly to the direction of the fibers.
[0014] FIG. 2 is a schematic illustration of a prepreg that uses a
plain weave fabric as the sheet-like reinforcing fiber substrate,
viewed in a cross section cut perpendicularly to the warp.
[0015] FIG. 3 is a schematic illustration showing one example of a
prepreg according to a second embodiment of the present
invention.
[0016] FIG. 4 is a schematic illustration of a prepreg of a
comparative example, wherein the matrix resin has been supplied
from one surface.
[0017] FIG. 5 is a schematic illustration of a prepreg of another
comparative example, wherein although the matrix resin has been
supplied from both sides, portions that have not been impregnated
with the matrix resin do not exist in a continuous state.
[0018] FIG. 6 is a schematic illustration showing the surface of a
prepreg according to a third embodiment of the present
invention.
[0019] FIG. 7 is a schematic illustration of a comparative example,
showing the surface of a prepreg wherein a island portions weave
intersection coverage ratio is low.
[0020] FIG. 8 is an example of a graph showing the results of
measuring the dynamic modulus of elasticity of a matrix resin, as
well as a method of determining the value of Tg from such a
graph.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] As follows is a description of the composition of the
present invention.
[0022] A first embodiment of the present invention is a prepreg
comprising a sheet-like reinforcing fiber substrate formed from
reinforcing fiber that has been impregnated with a matrix resin,
wherein only one surface of the sheet-like reinforcing fiber
substrate is covered with the matrix resin, and the resin
impregnation ratio is within a range of 35% to 95%. There are no
particular restrictions on the fiber used in the sheet-like
reinforcing fiber substrate used within this first embodiment of
the present invention, and examples of suitable fibers include
carbon fiber, glass fiber, aramid fiber, high-strength polyethylene
fiber, boron fiber, and steel fiber. Carbon fiber is preferred as
it results in more favorable properties for the generated FRP,
particularly in terms of reduced weight and favorable mechanical
properties such as high strength and high rigidity.
[0023] Furthermore, there are also no particular restrictions on
the form of the sheet-like reinforcing fiber substrate used in the
prepreg of this first embodiment, and suitable examples include
plain weave fabric, twill fabric, satin weave fabric, stitched
sheets such as non-crimped fabric (NCF) wherein fiber bunches are
layered, either unidirectionally or at various angles, and then
stitched to prevent the layers coming apart, as well as non-woven
fabric, mats, and unidirectional materials in which a bundle of
reinforcing fibers is aligned unidirectionally. Of these, woven
fabrics and stitched sheets, which offer superior levels of
handling, are preferred.
[0024] Furthermore, there are also no particular restrictions on
the matrix resin used in the prepreg of the first embodiment, and
either thermosetting resins or thermoplastic resins can be used,
although from the viewpoints of the handling of the prepreg, such
as the tack and drape characteristics, and the moldability,
thermosetting resins are preferred. Examples of suitable
thermosetting resins include epoxy resins, phenol resins, vinyl
ester resins, unsaturated polyester resins, bismaleimide resins, BT
resins, cyanate ester resins, and benzoxazine resins, although in
terms of handling properties and the properties of the resulting
cured product, epoxy resins, bismaleimide resins, BT resins, and
cyanate ester resins are preferred, and of these, epoxy resins are
particularly desirable.
[0025] A prepreg of the first embodiment is completely covered with
resin on one surface, and the resin impregnation ratio must fall
within a range of 35% to 95%. When molding is conducted without the
use of an autoclave, under only vacuum pressure, the inclusion of a
deaeratingdeaerating circuit is very important, although this
requirement has already been well identified in the conventional
technology. In this description, the deaeratingdeaerating circuit
refers to the portions within the prepreg that have not been
impregnated with resin, and these portions act as air pathways.
However, if this deaeratingdeaerating circuit is too large, then
the deaeratingdeaerating circuit can remain even after molding, and
can cause internal voids and surface pinholes. As a result of
investigating the most appropriate size for the
deaeratingdeaerating circuit in a prepreg, the inventors of the
present invention discovered that provided the resin impregnation
ratio falls within a certain preferred range, a satisfactory
deaerating circuit can be ensured, while satisfactory resin
impregnation can still be achieved during molding, and they were
consequently able to complete the present invention.
[0026] This resin impregnation ratio is described below in more
detail with reference to the drawings. FIG. 1 is a schematic
illustration of a prepreg 10 with a reinforcing fiber substrate in
which the fibers are aligned unidirectionally, viewed in a cross
section cut perpendicularly to the direction of the fibers. The
matrix resin is supplied from underneath in FIG. 1, and the matrix
resin 1 impregnates upwards into the sheet-like reinforcing fiber
substrate. In FIG. 1, the portion into which the matrix resin 1 has
impregnated is shown by the diagonal shading. In FIG. 1, the matrix
resin is supplied from underneath, but in the present invention,
the matrix resin can also be supplied from above, and then allowed
to impregnate down into the substrate. The cross section is
inspected across at least 80% of the width of the sheet-like
reinforcing fiber substrate, and the highest point to which the
resin has penetrated is determined (or in those cases where the
resin is supplied from above, the lowest point of penetration is
determined). In FIG. 1, the point A represents the highest point
for the resin. If the average thickness of the sheet-like
reinforcing fiber substrate is termed t.sub.1, and the distance
from the bottom edge of the sheet-like reinforcing fiber substrate
to the point A is termed a, then the impregnation ratio can be
represented by a formula (3) shown below.
Resin impregnation ratio=a/t.sub.1.times.100(%) (3)
[0027] The average thickness t.sub.1 of the sheet-like reinforcing
fiber substrate can be determined in the manner described below.
The length of the line joining the bottom edge 10a and the top edge
10b in a cross section through the prepreg 10 (this line is deemed
the thickness line) is taken as the thickness of the sheet-like
substrate. This thickness is measured at 10 random points, and the
average of the thickness values is calculated and used as the
average thickness t.sub.1 of the sheet-like reinforcing fiber
substrate. In the case of a sheet-like reinforcing fiber substrate
in which the fibers are aligned unidirectionally, the outer
contours of the substrate essentially coincide with the thickness
line.
[0028] Furthermore, in order to determine the highest point reached
by the matrix resin 1, the substrate is best viewed in a cross
section perpendicular to the direction of the reinforcing fibers,
and consequently in the case of a multiaxial stitched sheet,
wherein unlike the sheet-like reinforcing fiber substrate of the
FIG. 1 in which the fibers are aligned unidirectionally, the fibers
are layered in all different directions, a cross sectional
photograph can be taken through a cross section at any suitable
angle.
[0029] The cut can be performed with a sharp blade such as a razor
blade, and is made with a single cut. The photograph is preferably
taken at a magnification of 50 to 100.times..
[0030] Next is a description of a case in which the sheet-like
reinforcing fiber substrate is a woven fabric 20. FIG. 2 shows a
method of determining the resin impregnation ratio in those cases
where a plain weave fabric is used as the sheet-like reinforcing
fiber substrate. In the case of a woven fabric, the matrix resin 1
moves along the open portions 21 in the weave, meaning the resin
impregnation ratio is best observed at a cross-section through
those open portions 21. In a similar manner to that described for
the reinforcing fiber substrate in the FIG. 1 where the fibers were
aligned unidirectionally, the highest point B to which the matrix
resin 1 has penetrated is determined from the cross section of FIG.
2. If the distance from the bottom edge 20a of the sheet-like
reinforcing fiber substrate to the point B is termed b, the length
of the line joining the bottom edge 20a and the top edge 20b of the
sheet-like reinforcing fiber substrate is deemed the thickness of
the sheet-like reinforcing fiber substrate, and the average
thickness is termed t.sub.2, then the resin impregnation ratio can
be determined by a formula (4) shown below. The average thickness
t.sub.2 is measured using a similar method to that described for
the case of a reinforcing fiber substrate in which the fibers are
aligned unidirectionally, although in the case of a woven fabric,
the outer contours of the sheet-like reinforcing fiber substrate do
not coincide with the thickness line (see FIG. 2).
Resin impregnation ratio=b/t.sub.2.times.100(%) (4)
[0031] The resin impregnation ratio in a prepreg according to the
first embodiment is preferably within a range of 35% to 95%. If the
resin impregnation ratio is less than 35%, then the resin is unable
to completely fill the non-impregnated portions during molding,
meaning internal voids and surface pinholes remain following
molding. If the resin impregnation ratio is at least 40%, then
internal voids and surface pinholes tend not to remain following
molding, and ratios of at least 50% are particularly preferred. In
contrast, if the resin impregnation ratio exceeds 95%, then the
formation of a deaerating circuit can no longer be ensured, which
can also cause residual internal voids and surface pinholes. If the
resin impregnation ratio is no more than 90%, then it is easier to
ensure an adequate deaerating circuit, and resin impregnation
ratios of no more than 80% are particularly preferred.
[0032] Furthermore, a prepreg of the present invention must have at
least one surface completely covered with resin. The prepreg is
used either by sticking to a molding die, or by generating a
multi-ply laminate of the prepreg, and consequently the prepreg
requires a suitable level of tackiness. A prepreg of the present
invention has at least one surface completely covered with resin,
and consequently has a suitable level of tackiness and superior
handling properties.
[0033] Furthermore, the weight of the sheet-like reinforcing fiber
substrate in a prepreg according to the first embodiment is
preferably at least 400 g/m.sup.2. A prepreg of the first
embodiment contains a deaerating circuit, but during molding the
resin penetrates to all corners of the sheet-like reinforcing fiber
substrate, enabling the formation of a completely impregnated
molded product with no internal voids or surface pinholes, and
consequently the prepreg is suited to sheet-like reinforcing fiber
substrate with a certain level of thickness. In terms of weight,
sheet-like reinforcing fiber substrates with a weight of at least
400 g/m.sup.2 are preferred. Weights of at least 600 g/m.sup.2 are
even more desirable, and weights of at least 700 g/m.sup.2 are
particularly preferred.
[0034] Furthermore, the thickness of the sheet-like reinforcing
fiber substrate in a prepreg of the first embodiment is preferably
at least 200 .mu.m. A prepreg of the first embodiment can yield a
favorable molded product with no internal voids at atmospheric
pressure, even if the fluidity of the matrix resin is poor.
Accordingly, a favorable molded product can be achieved even if the
sheet-like reinforcing fiber substrate is considerably thick, and
in actual fact, the effects of the present invention are manifested
most markedly with thicker substrates. The effects are particularly
marked for thick materials where the thickness of the sheet-like
reinforcing fiber substrate is at least 300 .mu.m. The thickness is
determined by dividing the mass per unit of surface area of the
sheet-like reinforcing fiber substrate by the density of the
reinforcing fibers.
[0035] In those cases where the matrix resin of a prepreg of the
first embodiment is a thermosetting resin composition, the
thermosetting resin composition preferably comprises a
thermoplastic resin that is not dissolved within the thermosetting
resin composition. This thermoplastic resin is preferably in the
form of short fibers, and the length of those short fibers is
preferably within a range of 1 to 50 mm. Furthermore, the size of
the fibers is preferably no more than 300 tex.
[0036] When prepregs of this first embodiment are laminated and
molded, then during the molding process, the short fibers of
thermoplastic resin within the thermosetting resin composition are
filtered by the reinforcing fibers that make up the sheet-like
reinforcing fiber substrate, and end up positioned at the surface
of each of the laminated sheet-like reinforcing fiber substrates,
namely, positioned between the layers of the laminate. This
improves the interlayer peeling resistance markedly, providing a
superior interlayer reinforcement effect.
[0037] In order to ensure an efficient manifestation of this
interlayer reinforcement effect, the thermoplastic resin preferably
exist as fibers. If other shapes such as fine particles are used
instead of the aforementioned short fibers, then the thermoplastic
resin is not efficiently filtered by the sheet-like reinforcing
fiber substrate during the molding process, and migrates into the
interior of the sheet-like reinforcing fiber substrate together
with the thermosetting resin during the impregnation process,
meaning efficient interlayer reinforcement can not be achieved.
[0038] Accordingly, the thermoplastic resin is preferably in the
form of short fibers. In addition, the length of these fibers is
preferably within a range of 1 to 50 mm. If the length of the short
fibers is less than 1 mm, then the fibers penetrate into the
interior of the sheet-like reinforcing fiber substrate, in a
similar manner to fine particles, making it difficult to achieve an
efficient improvement in the interlayer peeling resistance.
Considering the fact that a certain size is necessary, fibers with
a length of at least 3 mm are particularly preferred. In contrast,
if the length of the fibers exceeds 50 mm, then the fibers become
overly long, preparation of the thermosetting resin composition
becomes extremely problematic, and dispersing the fibers uniformly
through the thermosetting resin composition also becomes difficult,
which causes an undesirable deterioration in the uniformity of the
interlayer reinforcement. Fiber lengths of no more than 30 mm are
particularly preferred.
[0039] Furthermore in those cases where the thermoplastic resin
exists as short fibers, the size of those fibers is preferably no
more than 300 tex. The short fibers of the thermoplastic resin may
exist either as filaments formed from single strands of fiber, or
as multifilaments comprising a plurality of individual fiber
strands. If the size of the fibers exceed 300 tex, then the
thickness of the layer formed by the accumulated short fibers
between the substrate layers becomes overly thick, and there is a
danger of the short fibers interfering with the reinforcing fibers
of the sheet-like reinforcing fiber substrates, causing bending of
the reinforcing fibers, and an undesirable deterioration in the
mechanical strength of the molded composite material. Fiber sizes
of no more than 100 tex are even more desirable, and sizes of no
more than 50 tex are particularly preferred. There are no
particular restrictions at the fine end of the size scale, and
satisfactory effects can be achieved for sizes of at least 1
tex.
[0040] Examples of suitable thermoplastic resins include
polyaramid, polyester, polyacetal, polycarbonate, polyphenylene
oxide, polyphenylene sulfide, polyallylate, polyimide,
polyetherimide, polysulfone, polyamide, polyamide-imide, and
polyetheretherketone. Furthermore, elastomers can also be used
favorably instead of the thermoplastic resin. Examples of suitable
elastomers include synthetic rubbers such as butyl rubber, isoprene
rubber, nitrile rubber, and silicon rubber, as well as natural
rubbers such as latex.
[0041] The quantity of the thermoplastic resin within the
thermosetting resin composition is preferably within a range of 1
to 100 parts by mass per 100 parts by mass of the thermosetting
resin composition. If the quantity of the thermoplastic resin is
less than 1 part by mass, then the effect of the invention in
improving the FRP interlayer peeling resistance weakens
undesirably. Quantities of the thermoplastic resin of at least 5
parts by mass are even more desirable, and quantities of at least
10 parts by mass are particularly preferred. In contrast, if the
quantity exceeds 100 parts by mass, then the proportion of the
thermoplastic resin becomes overly high, which can cause a
deterioration in the impregnation of the matrix resin into the
sheet-like reinforcing fiber substrate, and the quantity of the
matrix resin relative to the sheet-like reinforcing fiber substrate
can become too high, causing an undesirable deterioration in the
FRP mechanical strength.
[0042] Although there are no particular restrictions on the process
for producing a prepreg according to the first embodiment, a
production process in which a resin is supplied, using a hot melt
method, to one surface of a sheet-like reinforcing fiber substrate
comprising reinforcing fibers, and the structure is then heating
and pressed, causing the resin to migrate through to a position
close to the opposite surface of the substrate is preferred. In
such a process, the heating temperature and the pressure applied
during the pressing step are adjusted to control the degree of
migration of the resin and the manner of the migration, thus
adjusting the resin impregnation ratio to a value within a range of
35% to 95%. The hot melt method is a prepreg production process in
which no solvent is used, and the viscosity of the resin is lowered
by raising the temperature of the resin, thereby causing the resin
to impregnate the substrate, and amongst the possible forms of the
hot melt method that can be used for producing a prepreg, a double
film process, in which the resin is supplied from both the upper
and lower surfaces of the sheet-like reinforcing fiber substrate is
usually preferred in terms of the impregnation results. However, in
the first embodiment, because one surface of the prepreg must be
available for forming the deaerating circuit and can therefore not
be impregnated with resin, the double film process is not suitable
as the process for producing a prepreg according to the first
embodiment. As described above, a single film process in which the
resin is supplied from one surface of the sheet-like reinforcing
fiber substrate is preferred.
[0043] The matrix resin in a prepreg of the first embodiment is a
thermosetting resin composition, and in those cases where the
composition also comprises a thermoplastic resin that has not been
dissolved in the thermosetting resin composition, the thermoplastic
resin is preferably blended into the composition during the mixing
and preparation of the thermosetting resin composition, and the
resulting composition is then converted to a film form, and
impregnated into the sheet-like reinforcing fiber substrate.
[0044] A second embodiment of the present invention is a prepreg
comprising a sheet-like reinforcing fiber substrate and a matrix
resin, wherein the matrix resin exists on both surfaces of the
sheet-like reinforcing fiber substrate, and the portion inside the
sheet-like reinforcing fiber substrate into which the matrix resin
has not been impregnated is continuous.
[0045] There are no particular restrictions on the reinforcing
fibers used in the sheet-like reinforcing fiber substrate used in a
prepreg of this second embodiment, and examples of suitable fibers
include carbon fiber, graphite fiber, aramid fiber, silicon carbide
fiber, alumina fiber, boron fiber, high-strength polyethylene
fiber, PBO fiber, and glass fiber, and these fibers can be used
either singularly, or in mixtures of two or more different types of
fiber. Of these reinforcing fibers, either carbon fiber which
offers superior specific strength and inelasticity, or glass fiber
which offers more favorable cost performance, is preferred.
[0046] Furthermore, there are also no particular restrictions on
the form of the sheet-like reinforcing fiber substrate used in the
prepreg of this second embodiment, and suitable examples include
unidirectional materials in which the reinforcing fibers are
aligned unidirectionally, woven fabrics, knit fabrics, braided
fabrics, stitched sheets wherein multiple fabrics are laminated,
either unidirectionally or in various directions, and then
stitched, as well as mats and non-woven fabrics comprising short
fibers. Of these, woven fabrics, stitched sheets, mats and
non-woven fabrics offer superior levels of stability for the
sheet-like reinforcing fiber substrate, and because an intermediate
material for FRP molding of the present invention offers superior
handling properties, it is preferred as the sheet-like reinforcing
fiber substrate.
[0047] In a prepreg according to the second embodiment, the portion
inside the sheet-like reinforcing fiber substrate into which the
matrix resin has not been impregnated must be a continuous portion.
In the second embodiment, this non-impregnated portion functions as
the deaerating circuit, and the existence of this deaerating
circuit means that the molded FRP can be formed without internal
voids and surface pinholes. However, if this deaerating circuit is
segmented by the matrix resin, then the air that is enclosed by the
matrix resin becomes extremely difficult to remove, and can give
rise to internal voids and surface pinholes.
[0048] The following method can be used for determining whether or
not the portion inside the sheet-like reinforcing fiber substrate
into which the matrix resin has not been impregnated is continuous.
First, the prepreg is cut at a right angle to the lengthwise
direction of the prepreg. The cut is performed in a single action,
using an NT cutter or the like. If a number of cutting strokes are
used, then the surface of the cut becomes undesirably messy. The
two edges of the cut surface in the width direction are trimmed
off, with 10% of the width dimension removed from each edge. The
entirety of the remaining 80% portion across the width direction is
then inspected to confirm that the portion into which the matrix
resin has not been impregnated is continuous. The inspection is
preferably conducted using a magnifying glass or the like.
[0049] FIG. 3 shows a prepreg 30 formed from a sheet-like
reinforcing fiber substrate comprising matrix resin-impregnated
layers 31 that have been impregnated with a matrix resin 1, and a
matrix resin non-impregnated layer 32. This figure represents an
example where, when the matrix resin 1 is impregnated, the matrix
resin non-impregnated layer 32 is formed as a continuous layer.
[0050] In contrast, FIG. 5 shows a prepreg 50 formed from a
sheet-like reinforcing fiber substrate comprising matrix
resin-impregnated layers 51 that have been impregnated with a
matrix resin 1, and a matrix resin non-impregnated layer 52. This
figure represents an example where, when the matrix resin 1 is
impregnated, the matrix resin non-impregnated layer 52 is formed in
a non-continuous manner.
[0051] There are no particular restrictions on the matrix resin
used in a prepreg of the second embodiment, and both thermosetting
resins and thermoplastic resins can be used, although from the
viewpoints of the handling of the prepreg, such as the tack and
drape characteristics, and the moldability, thermosetting resins
are preferred. Examples of suitable thermosetting resins include
epoxy resins, phenol resins, vinyl ester resins, unsaturated
polyester resins, bismaleimide resins, BT resins, cyanate ester
resins, and benzoxazine resins. In terms of handling properties and
the properties of the resulting cured product, epoxy resins,
bismaleimide resins, BT resins, and cyanate ester resins are
preferred, and of these, epoxy resins are particularly
desirable.
[0052] Furthermore, the weight of the sheet-like reinforcing fiber
substrate in a prepreg according to the second embodiment is
preferably at least 400 g/m.sup.2. A prepreg of the second
embodiment contains a deaerating circuit, but during molding the
resin penetrates to all corners of the sheet-like reinforcing fiber
substrate, enabling the formation of a completely impregnated
molded product with no internal voids or surface pinholes.
Consequently the prepreg is suited to sheet-like reinforcing fiber
substrate with a certain level of thickness. In terms of weight,
sheet-like reinforcing fiber substrates with a weight of at least
200 g/m.sup.2 are preferred. Weights of at least 600 g/m.sup.2 are
even more desirable, and weights of at least 700 g/m.sup.2 are
particularly preferred.
[0053] Furthermore, the thickness of the sheet-like reinforcing
fiber substrate in a prepreg of the second embodiment is preferably
at least 200 .mu.m. A prepreg of the second embodiment can yield a
favorable molded product with no internal voids at atmospheric
pressure, even if the fluidity of the matrix resin is poor.
Accordingly, a favorable molded product can be achieved even if the
sheet-like reinforcing fiber substrate is considerably thick, and
in actual fact, the effects of the present invention are manifested
most markedly with thicker substrates. The effects are particularly
marked for thick materials where the thickness of the sheet-like
reinforcing fiber substrate is at least 300 .mu.m. The thickness is
determined by dividing the mass per unit of surface area of the
sheet-like reinforcing fiber substrate by the density of the
reinforcing fibers.
[0054] In those cases where the matrix resin of a prepreg of the
second embodiment is a thermosetting resin composition, the
thermosetting resin composition preferably comprises a
thermoplastic resin that is not dissolved within the thermosetting
resin composition. This thermoplastic resin is preferably in the
form of short fibers, and the length of those short fibers is
preferably within a range of 1 to 50 mm. Furthermore, the size of
the fibers is preferably no more than 300 tex.
[0055] When prepregs of this second embodiment are layered and
molded, then during the molding process, the short fibers of
thermoplastic resin within the thermosetting resin composition are
filtered by the reinforcing fibers that make up the sheet-like
reinforcing fiber substrate, and end up positioned at the surface
of each of the laminated sheet-like reinforcing fiber substrates,
namely, positioned between the layers of the laminate. This
improves the interlayer peeling resistance markedly, providing a
superior interlayer reinforcement effect.
[0056] In order to ensure an efficient manifestation of this
interlayer reinforcement effect, the thermoplastic resin preferably
exist as fibers. If other shapes such as fine particles are used
instead of these thermoplastic resin short fibers, then the
thermoplastic resin is not efficiently filtered by the sheet-like
reinforcing fiber substrate during the molding process, and
migrates into the interior of the sheet-like reinforcing fiber
substrate together with the thermosetting resin during the
impregnation process, meaning efficient interlayer reinforcement
can not be achieved.
[0057] Accordingly, the thermoplastic resin is preferably in the
form of short fibers. In addition, the length of these fibers is
preferably within a range of 1 to 50 mm. If the length of the short
fibers is less than 1 mm, then the fibers penetrate into the
interior of the sheet-like reinforcing fiber substrate, in a
similar manner to fine particles, making it difficult to achieve an
efficient improvement in the interlayer peeling resistance.
Considering the fact that a certain size is necessary, fibers with
a length of at least 3 mm are particularly preferred. In contrast,
if the length of the fibers exceeds 50 mm, then the fibers become
overly long, preparation of the thermosetting resin composition
becomes extremely problematic, and dispersing the fibers uniformly
through the thermosetting resin composition also becomes difficult,
which causes an undesirable deterioration in the uniformity of the
interlayer reinforcement. Fiber lengths of no more than 30 mm are
particularly preferred.
[0058] Furthermore, in those cases where the thermoplastic resin
exists as short fibers, the size of those fibers is preferably no
more than 300 tex. The short fibers of the thermoplastic resin may
exist either as filaments formed from single strands of fiber, or
as multifilaments comprising a plurality of individual fiber
strands. If the size of the fibers exceed 300 tex, then the
thickness of the layer formed by the accumulated short fibers
between the substrate layers becomes overly thick, and there is a
danger of the short fibers interfering with the reinforcing fibers
of the sheet-like reinforcing fiber substrates, causing bending of
the reinforcing fibers, and an undesirable deterioration in the
mechanical strength of the molded composite material. Single fiber
sizes of no more than 100 tex are even more desirable, and sizes of
no more than 50 tex are particularly preferred. There are no
particular restrictions at the fine end of the single fiber size
scale, and satisfactory effects can be achieved for sizes of at
least 1 tex.
[0059] Examples of suitable thermoplastic resins include
polyaramid, polyester, polyacetal, polycarbonate, polyphenylene
oxide, polyphenylene sulfide, polyallylate, polyimide,
polyetherimide, polysulfone, polyamide, polyamide-imide, and
polyetheretherketone. Furthermore, elastomers can also be used
favorably instead of the thermoplastic resin. Examples of suitable
elastomers include synthetic rubbers such as butyl rubber, isoprene
rubber, nitrile rubber, and silicon rubber, as well as natural
rubbers such as latex.
[0060] The quantity of the thermoplastic resin within the
thermosetting resin composition is preferably within a range of 1
to 100 parts by mass per 100 parts by mass of the thermosetting
resin composition. If the quantity of the thermoplastic resin is
less than 1 part by mass, then the effect of the invention in
improving the FRP interlayer peel resistance weakens undesirably.
Quantities of at least 5 parts by mass are even more desirable, and
quantities of at least 10 parts by mass are particularly preferred.
In contrast, if the quantity exceeds 100 parts by mass, then the
proportion of the thermoplastic resin becomes overly high, which
can cause a deterioration in the impregnation of the matrix resin
into the sheet-like reinforcing fiber substrate, and the quantity
of the matrix resin relative to the sheet-like reinforcing fiber
substrate can become too high, causing an undesirable deterioration
in the FRP mechanical strength.
[0061] In those cases where the matrix resin used in a prepreg of
the second embodiment is a thermosetting resin composition, the
thermosetting resin composition is preferably able to be cured at
90.degree. C. for 2 hours, and even more preferably at 80.degree.
C. for 2 hours. A prepreg of the second embodiment can yield a
favorable molded product with no internal voids at atmospheric
pressure, even if the fluidity of the thermosetting resin
composition that functions as the matrix resin is poor, and
consequently, the invention is suited to comparatively low
temperature curing of the thermosetting resin composition.
[0062] On the other hand, prepregs must typically display favorable
handling characteristics at room temperature. Two major factors in
determining the handling characteristics are the tack (the degree
of stickiness) and the drape characteristics (the flexibility), and
in order to optimize the tack and drape characteristics, the
thermosetting resin composition that functions as the matrix resin
must have a viscosity that falls within a certain range. If the
viscosity of the thermosetting resin composition is too low, then
the tackiness is too powerful, making handling extremely difficult,
whereas if the viscosity is too high, then the tackiness is overly
weak, and the drape characteristics can effectively disappear,
which also makes handling very difficult. Hence, in order to ensure
favorable handling characteristics for the prepreg, the
thermosetting resin composition must have a viscosity that falls
within an appropriate range. Accordingly, if a thermosetting resin
composition cures at lower temperatures, then this means that the
composition is capable of curing while still at a relatively higher
viscosity, and is consequently suitable as a thermosetting resin
composition for a prepreg of the second embodiment, which is
capable of yielding a favorable molded product even with
comparatively poor fluidity.
[0063] A determination as to whether or not the thermosetting resin
composition can be cured in 2 hours at 90.degree. C. can be
performed in the following manner. Namely, either the thermosetting
resin composition by itself, or a sheet-like reinforcing fiber
substrate that has been impregnated with the thermosetting resin
composition is molded for 2 hours at 90.degree. C. in an oven. If
the external appearance suggests that the resulting cured product
has definitely cured, then the composition is deemed to be curable
in 2 hours at 90.degree. C. A determination as to whether or not a
thermosetting resin composition can be cured in 2 hours at
80.degree. C. can be conducted in a similar manner. In those cases
where determining whether or not the composition has cured is
difficult, the Tg value of the molded product is measured, and the
composition is deemed to have cured if the Tg value is at least
30.degree. C.
[0064] Typically, when an intermediate material for FRP molding
such as a prepreg is produced, the process for impregnating the
matrix resin into the sheet-like reinforcing fiber substrate
involves applying a thin coating of a thermosetting resin
composition on the surface of a release sheet or a polyolefin film
or the like, and then supplying the thermosetting resin composition
on the surface of a reinforcing fiber substrate to achieve
impregnation. These impregnation processes can be broadly
classified into single film processes in which the resin
composition is supplied and impregnated from only one surface of
the reinforcing fiber substrate, and double film processes in which
the resin composition is supplied and impregnated from both
surfaces of the reinforcing fiber substrate. In the second
embodiment, supply of the resin composition using a double film
process is extremely desirable. The reason for this preference is
that the second embodiment assumes the use of thermosetting resin
compositions that are capable of curing at low temperatures,
namely, thermosetting resin compositions with comparatively low
fluidity. FIG. 3 and FIG. 4 are schematic illustrations showing the
prepregs obtained when the same quantity of resin is supplied to
sheet-like reinforcing fiber substrates of identical thickness,
using a double film process and a single film process
respectively.
[0065] FIG. 3 shows a prepreg 30 comprising matrix
resin-impregnated layers 31 and a matrix resin non-impregnated
layer 32, formed by impregnating a matrix resin 1 from both
surfaces of a sheet-like reinforcing fiber substrate.
[0066] FIG. 4 shows a prepreg 40 comprising a matrix
resin-impregnated layer 41 and a matrix resin non-impregnated layer
42, formed by impregnating a matrix resin 1 from one surface of a
sheet-like reinforcing fiber substrate.
[0067] As is evident from FIG. 3 and FIG. 4, if prepregs of the
second embodiment are produced by either a single film process or a
doable film process, then the prepreg produced by the double film
process tends to have a wider non-impregnated layer 42 than the
prepreg produced by the single film process. As a result, using a
double film process is preferred, as it enables a reduction in the
quantity of thermosetting resin composition that must migrate in
order to fill the deaerating circuit during the molding step, thus
ensuring that the deaerating circuit is completely filled prior to
the completion of curing.
[0068] When the matrix resin is supplied to the sheet-like
reinforcing fiber substrate, it is preferably stuck to the
substrate at room temperature, without heating. However, in those
cases where the viscosity of the matrix resin at room temperature
is very high, the resin may be heated slightly to improve the level
of fluidity. However even in such cases, in order to ensure that a
continuous resin non-impregnated portion such as that described
below is left inside the substrate, any heating is preferably
conducted at no more than 40.degree. C., and even more preferably
at no more than 30.degree. C.
[0069] In those cases where the matrix resin for a prepreg
according to the second embodiment is a thermosetting resin
composition, and that composition comprises a thermoplastic resin
that is not dissolved within the thermosetting resin composition,
the thermoplastic resin is preferably blended into the composition
during the mixing and preparation of the thermosetting resin
composition, and the resulting composition is then converted to a
film form, and impregnated into the sheet-like reinforcing fiber
substrate.
[0070] A prepreg according to a third embodiment of the present
invention comprises a matrix resin impregnated into a reinforcing
fiber woven fabric, wherein at least one surface displays a
sea-and-island-type pattern comprising resin-impregnated portions
(island portions) where the matrix resin is present at the surface
and fiber portions (sea portions) where the matrix resin is not
present at the surface, the surface coverage ratio of the matrix
resin on surfaces with the sea-and-island-type pattern is within a
range of 3% to 80%, and the weave intersection coverage ratio for
the island portions, as represented by a formula (5) shown below,
is at least 40%.
Island portions weave intersection coverage ratio
(%)=(T/Y).times.100 (5)
(wherein, T represents the number of island portions that cover
weave intersections, and Y represents the total number of weave
intersections of the reinforcing fiber fabric on the surface with
the sea-and-island-type pattern).
[0071] A prepreg of the third embodiment is formed by impregnating
a reinforcing fiber woven fabric with a matrix resin. Suitable
examples of the reinforcing fibers used in forming the woven fabric
include carbon fiber, glass fiber, aramid fiber, boron fiber, metal
fiber, PBO fiber, and high-strength polyethylene fiber, although of
these, carbon fiber is particularly preferred as it results in more
favorable mechanical properties following molding, and is also very
lightweight. Furthermore, suitable examples of the form of the
woven fabric include plain weave fabric, twill fabric, satin weave
fabric, stitched sheets in which long fibers that have been aligned
unidirectionally are stitched together, and blind weave. Woven
fabrics in which the warp and the woof use different fibers can
also be used.
[0072] Furthermore, a reinforcing fiber woven fabric used in the
third embodiment preferably displays a fiber weight of no more then
1500 g/m.sup.2. If the fiber weight exceeds 1500 g/m.sup.2, then
the density of the reinforcing fibers becomes overly high, and
achieving a fabric with superior mechanical properties becomes
difficult. Fiber weights of no more than 1000 g/m.sup.2 are even
more desirable. There are no particular restrictions on the lower
limit for the fiber weight. However, the weight is preferably at
least 50 g/m.sup.2, and even more preferably 75 g/m.sup.2 or
greater. If the fiber weight is less than 50 g/m.sup.2, then in
those cases where a large FRP is required, the number of layers of
prepreg must be increased significantly, which can lead to cost
increases.
[0073] There are no particular restrictions on the matrix resins
that can be used in a prepreg according to the third embodiment,
and suitable resins include thermosetting resins such as epoxy
resins, polyester resins, vinyl ester resins, phenol resins,
maleimide resins, polyimide resins, and BT resins comprising a
combination of a cyanate and a bismaleimide resin, as well as
thermoplastic resins such as acrylic resins and
polyetheretherketones. Matrix resins that improve the strength of
the product FRP are preferred, and of the above resins, epoxy
resins are particularly preferred, as their superior adhesion to
reinforcing fibers improves the mechanical properties of the
product FRP.
[0074] Specific examples of suitable epoxy resins include
bifunctional resins such as bisphenol A epoxy resins, bisphenol F
epoxy resins, bisphenol S epoxy resins, biphenyl epoxy resins,
naphthalene epoxy resins, dicyclopentadiene epoxy resins, fluorene
epoxy resins, and modified resins thereof; and trifunctional or
greater polyfunctional epoxy resins such as phenol novolac epoxy
resins, cresol epoxy resins, glycidylamine epoxy resins such as
tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol and
tetraglycidylamine, glycidyl ether epoxy resins such as
tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxymethane), as
well as modified resins thereof; and combinations of one or more of
the above resins can also be used as the matrix resin.
[0075] The above epoxy resin compositions may also contain curing
agents such as diphenylmethane, diaminodiphenylsulfone, aliphatic
amines, imidazole derivatives, dicyandiamide, tetramethylguanidine,
thiourea adducts of amines, carboxylic acid hydrazides, carboxylic
acid amides, polyphenol compounds, polymercaptans, and boron
trifluoride ethyl amine complex, or materials obtained by
preliminary reaction between an epoxy resin and a portion of one of
the above curing agents. In addition, by also blending in a curing
catalyst such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea or
phenyldimethylurea, the curing time can be shortened, thereby
shortening the molding time.
[0076] In addition, in those cases where the matrix resin in the
third embodiment is a thermosetting resin composition, the minimum
viscosity for the thermosetting resin composition is preferably no
more than 1000 poise. If a high-viscosity thermosetting resin
composition with a minimum viscosity exceeding 1000 poise is used,
then the fluidity of the thermosetting resin composition
deteriorates. In a prepreg of the third embodiment, the
thermosetting resin composition fills the deaerating circuit, which
has been complete the role, during molding, but if the fluidity of
the thermosetting resin composition is poor, then the molding
process may finish before this filling step is complete, meaning
there is a danger that any portions of residual deaerating circuit
will form internal voids. In order to prevent this occurring, the
weight of the resin must be increased, resulting in an undesirable
increase in cost. Accordingly, lower minimum viscosity values are
preferred, and values of no more than 500 poise are particularly
desirable.
[0077] In the third embodiment, the minimum viscosity refers to the
lowest viscosity value observed when the temperature of the
thermosetting resin is raised from room temperature at a rate of
5.degree. C./minute. The minimum viscosity of the thermosetting
resin composition can be determined by measuring the dynamic
viscoelasticity of the composition, while the temperature is raised
from room temperature at a rate of 5.degree. C./minute.
[0078] In a prepreg of the third embodiment, at least one surface
displays a sea-and-island-type pattern comprising resin-impregnated
portions (island portions) where the resin composition is present
at the surface and fiber portions (sea portions) where the resin
composition is not present at the surface, and the surface coverage
ratio of the resin on surfaces with the sea-and-island-type pattern
is within a range of 3% to 80%.
[0079] First is a description of the sea-and-island-type pattern,
with reference to the drawings. FIG. 6 is a schematic illustration
showing the surface of a prepreg according to a third embodiment of
the present invention, wherein a resin composition has been
impregnated into one surface of a plain weave reinforcing fiber
woven fabric to form a sea-and-island-type pattern. The surface of
the woven fabric 60 produced from woven reinforcing fibers
comprises island portions 61 and sea portions 62. Of the island
portions 61, those that exist in isolation at a single weave
intersection 64 are labeled as island portions 61a, and those that
are linked with adjacent island portions are labeled as island
portions 61b. By forming the island portions 61 in this type of
scattered arrangement across the surface, the sea portions 62 act
as the deaerating circuit during molding of the prepreg. The
spacing between adjacent weave intersections 64 is labeled as the
distance 63.
[0080] In a prepreg of the third embodiment, the surface coverage
ratio of the resin on those surfaces with the sea-and-island-type
pattern must fall within a range of 3% to 80%. Here, the surface
coverage ratio refers to the ratio of the area of the island
portions 61 relative to the surface area of the entire surface with
the sea-and-island-type pattern.
[0081] If this surface coverage ratio is less than 3%, then the
tackiness of the sea-and-island-type patterned surface of the
prepreg is overly poor, causing a deterioration in the prepreg
handling properties. In contrast, if the surface coverage ratio
exceeds 80%, then the deaerating circuit for the prepreg is almost
completely blocked off, which can cause internal voids and surface
pinholes. In terms of achieving a favorable balance between
tackiness and the size of the deaerating circuit, surface coverage
ratios of 5% or more is preferred, and 60% or less is particularly
preferred.
[0082] Furthermore, in a prepreg of the third embodiment, the weave
intersection coverage ratio for the island portions 61 on the
sea-and-island-type patterned surface, as represented by a formula
(6) below, is at least 40) %.
Island portions weave intersection coverage ratio
(%)=(T/Y).times.100 (6)
[0083] T represents the number of island portions that cover weave
intersections, and Y represents the total number of weave
intersections of the reinforcing fiber woven fabric on the surface
with the sea-and-island-type pattern. In the third embodiment, a
weave intersection 64 refers to an intersection between the warp
and the woof.
[0084] For example, in FIG. 6, the number of island portions 61
covering weave intersections 64 of the reinforcing fiber fabric is
11, namely T=11. On the other hand, in this figure Y=15, meaning
that in the example shown, the island portions weave intersection
coverage ratio is (11/15).times.100=73%.
[0085] In contrast, FIG. 7 represents a case where the surface of
the woven fabric 60 contains a larger proportion of linked island
portions 61b. In FIG. 7, the island portions weave intersection
coverage ratio of island portions 61 is calculated from T=3 and
Y=15, and yields a value of (3/15).times.100=20%.
[0086] When calculating the number T of island portions that cover
weave intersections in the present invention, resin-impregnated
portions 65 that do not cover a weave intersection of the
reinforcing fiber fabric are not counted.
[0087] When the resin surface coverage ratio is within the range
from 3% to 80%, if the weave intersection coverage ratio for the
island portions 61 is less than 40%, then as shown in FIG. 7, the
probability of the existence of a sea portion 62 that is totally
enclosed by an island portion 61 on the sea-and-island-type
patterned surface increases. In such a case, the air that reaches
the fabric surface through the deaerating circuit during molding
has no where to escape, increasing the likelihood of undesirable
pinhole formation.
[0088] In those cases where both surfaces of the fabric are
sea-and-island-type patterned surfaces, the surface coverage ratio
must be within a range of 3% to 80% on both surfaces, and the weave
intersection coverage ratio for the island portions 61 is
preferably at least 40% on both surfaces.
[0089] In terms of productivity and the like, the most preferred
process for producing a prepreg according to the third embodiment
is a process in which a resin composition is applied to a resin
support sheet, this matrix resin supported on the resin support
sheet is bonded to one surface of a reinforcing fiber woven fabric,
a protective film is affixed to the other surface of the
reinforcing fiber woven fabric to prevent the adhesion of any
foreign matter, and heating and/or pressure is then used to
impregnate the matrix resin into the reinforcing fiber woven
fabric, thus forming a prepreg wherein the surface of the
reinforcing fiber woven fabric on the side of the protective film
displays a sea-and-island-type pattern comprising resin-impregnated
portions (island portions) where the matrix resin is present at the
surface, and fiber portions (sea portions) where the resin
composition is not present at the surface.
[0090] The heating conditions used within this process preferably
employ a temperature that ensures that the viscosity of the matrix
resin reaches no more than 5000 poise, whereas the pressure
conditions preferably use a linear pressure of 49 to 780 kPa, thus
ensuring a prepreg with a satisfactory deaerating circuit. In the
case of an epoxy resin composition, the temperature required to
ensure a viscosity of no more than 5000 poise is typically within a
range of 40 to 80.degree. C.
[0091] The protective film used in the process for producing a
prepreg according to the third embodiment preferably displays
favorable releasability relative to the matrix resin, and suitable
examples include release sheets or polyethylene film that have been
surface-treated with silicone.
[0092] Furthermore, the resin support sheet can also use a resin
film formed from a polyolefin and a release sheet or the like. In
addition, when the matrix resin is applied to the resin support
sheet, a process can be used which employs a resin support sheet
with an irregular surface, so that when the matrix resin is applied
to this resin support sheet, and the matrix resin-coated surface of
the resin support sheet and the reinforcing fiber woven fabric are
stuck together, only the matrix resin applied to the convex
portions of the resin support sheet is transferred to, and
impregnated into the reinforcing fiber woven fabric, thus
generating a sea-and-island-type pattern.
[0093] If a prepreg of the third embodiment is produced using this
process, then the matrix resin is impregnated into the reinforcing
fiber woven fabric mainly at the weave intersections points, and is
exuded out at the weave intersections on the opposite surface (the
protective film side) of the fabric, impregnating the reinforcing
fibers in the vicinity of the surface. As a result, this process
results in almost no island portions that do not cover weave
intersections.
[0094] Furthermore, in a different process from that described
above, the matrix resin can be applied directly to the surface of
the reinforcing fiber woven fabric that is to become the
sea-and-island-type patterned surface, either uniformly or in a
non-uniform manner, or by sticking a resin support sheet to the
surface, and in a similar manner to that described above, this
process also causes the matrix resin to impregnate into the fabric
along the weave intersections, so that following impregnation,
almost all of the matrix resin is connected to an island portion
that covers a weave intersection.
[0095] However, although production is possible using this
alternative process, adjusting the impregnation conditions (the
temperature and pressure conditions) to ensure a favorable surface
coverage ratio and a favorable island portions weave intersection
coverage ratio requires considerable skill.
[0096] In other words, regardless of the process used to produce a
prepreg according to the third embodiment, during impregnation the
matrix resin penetrates into the interior of the woven fabric along
the weave intersections from the surface, and exudes from the weave
intersections on the opposite surface, meaning the number of island
portions that do not cover weave intersections is essentially
nil.
[0097] A fourth embodiment of the present invention is an
intermediate material for FRP molding in which a substrate
containing essentially no impregnated thermosetting resin
composition is bonded to at least one side of a prepreg comprising
a matrix resin and reinforcing fibers, wherein the ratio (B)/(A)
between the thickness (A) of the prepreg, and the thickness (B) of
the substrate is within a range of 0.1 to 2.5.
(Matrix Resin)
[0098] There are no particular restrictions on the matrix resin
used in the fourth embodiment, although from the viewpoints of the
handling of the prepreg, such as the tack and drape
characteristics, and the moldability, thermosetting resin
compositions are preferred. Examples of the thermosetting resin
that forms the main component of the thermosetting resin
composition include epoxy resins, phenol resins, bismaleimide
resins, BT resins, cyanate ester resins, and benzoxazine resins,
although epoxy resins are preferred, as their superior adhesion to
reinforcing fibers improves the mechanical properties of the
product FRP. Furthermore, phenol resins are also preferred, as not
only do they display excellent flame retardancy, but they are also
ideally suited to lacquer-type prepreg production processes.
(Reinforcing Fibers)
[0099] There are no particular restrictions on the reinforcing
fibers used in the prepreg of this fourth embodiment, and any
reinforcing fibers that offer high strength and high elasticity can
be used, including glass fiber, carbon fiber, aramid fiber, boron
fiber, and PBO fiber. Of these, reinforcing fibers that use either
glass fiber or carbon fiber are preferred, as they offer excellent
balance between elasticity and strength, and yield FRPs with
excellent mechanical properties.
(Production Process for Prepreg)
[0100] The process for producing a prepreg used in the fourth
embodiment may utilize the hot melt process described above,
although even when a prepreg that has been produced by a lacquer
process is used, oven molding is still capable of producing a
molded product with no internal voids or surface pinholes, meaning
the effects of the present invention are particularly significant
for prepregs produced by a lacquer process.
[0101] A lacquer process is a prepreg production process in which
the reinforcing fibers are impregnated with a thermosetting resin
composition that has been diluted with a solvent, and the solvent
is subsequently removed. Suitable methods for impregnating the
reinforcing fibers with the solvent solution include immersing the
reinforcing fibers in the thermosetting resin composition solution,
or applying the solution to a roller and then transferring the
solution to the reinforcing fibers using the roller. However,
effecting the impregnation by immersing the reinforcing fibers in
the solution provides superior impregnation of the thermosetting
resin composition solution into the reinforcing fibers, and is
consequently preferred. Furthermore, suitable methods for removing
the solvent include warm or hot air dryers, or drying under reduced
pressure, although warm air drying is the most preferred in terms
of productivity.
(Prepreg and Substrate)
[0102] An intermediate material for FRP molding according to the
present invention comprises an aforementioned prepreg with a
substrate containing essentially no impregnated thermosetting resin
composition bonded to at least one side of the prepreg. By allowing
this substrate to function as a deaerating circuit, any internal
air pockets can be removed easily during molding, meaning the
substrate performs an important role in preventing the occurrence
of internal voids and surface pinholes within the molded product.
If a substrate is bonded to both surfaces of a prepreg, then the
deaerating circuit is larger than that generated when a substrate
is bonded to only one surface, which can offer advantages in some
cases. However, the loss of tackiness on both surfaces can cause a
deterioration in productivity, and as such, in most cases, a
substrate is preferably only bonded to one surface, and the other
surface is left with the prepreg exposed, thus retaining favorable
tackiness.
[0103] As described above, in an intermediate material for FRP
molding according to the fourth embodiment, the substrate acts as a
deaerating circuit during molding, acting as a pathway for guiding
air out of the structure during the molding process. However,
during molding, the substrate must also become impregnated with the
matrix resin that is impregnated within the reinforcing fibers, so
that following molding, a single integrated body molded product is
obtained that contains no internal voids or surface pinholes. As a
result, the substrate must comprise sufficient air gaps to function
satisfactorily as the deaerating circuit, but must also have a
quantity of air gaps that can be completely filled by the matrix
resin during the molding process. Accordingly, the quantity of air
gaps within the substrate must be matched with the prepreg used in
the fourth embodiment of the present invention. As a result of
careful investigations, it was discovered that a favorable quantity
of air gaps could be achieved by controlling the ratio between the
respective thickness values for the prepreg and the substrate.
Specifically, the ratio (B)/(A) between the thickness (A) of the
prepreg, and the thickness (B) of the substrate must be within a
range of 0.1 to 2.5. As described above, the substrate must
comprise sufficient air gaps to function satisfactorily as the
deaerating circuit, but those air gaps must be completely filled by
the matrix resin during the molding process. The lower limit of the
above range is even more preferably 0.15 or greater, and most
preferably 0.2 or greater. If the ratio is less than 0.1, then
ensuring sufficient air gaps for the substrate to function
satisfactorily as the deaerating circuit becomes difficult, and air
can remain trapped following molding. On the other hand, the upper
limit of the above range is even more preferably no more than 1.5,
and is most preferably 1.1 or less. If the ratio exceeds 2.5, then
the air gaps may not be completely filled during the molding
process, meaning residual air may be left following molding.
(Measurement of the Thickness of the Prepreg and the Substrate)
[0104] In this description, the thickness (A) of the prepreg and
the thickness (B) of the substrate refer to values measured using
vernier calipers. During measurement, care must be taken to ensure
that the vernier calipers are pressed against the prepreg or the
substrate so that the thickness does not vary. Particularly in the
case of the substrate, if there is a concern that, even with the
vernier calipers pressed against the substrate, the measurement
error during measurement is overly large, then a photograph is
preferably taken of the substrate cross section and enlarged, so
that measurements can be conducted with minimal error. In addition,
in those cases where a substrate is bonded to both surfaces of the
prepreg, the sum of the individual thickness values for the two
substrates is used as the thickness value (B).
(Substrate Construction)
[0105] Suitable examples of the material used for forming the
substrate include fibrous thermoplastic resins and reinforcing
fibers. The use of fibrous thermoplastic resins is preferred as it
enables an improved interlayer reinforcement effect to be achieved
when layers of the intermediate material for FRP molding are
laminated. Suitable examples of such materials include nylon,
polyester, polyethylene, and polypropylene, and provided a
deaerating circuit can be ensured, the material may be a net-like
material, a material in which rods or fibers of the thermoplastic
resin are aligned unidirectionally, or a laminated material in
which these materials are overlaid at different angles. However, in
order to best ensure an efficient deaerating circuit, the
thermoplastic resin is most preferably in the form of a fibrous
material, and suitable materials include woven fabrics formed from
fibers, as well as materials in which the fibers are aligned
unidirectionally and non-woven fabrics. Of these, non-woven fabrics
are particularly desirable as they offer ready formation of the
deaerating circuit.
[0106] Furthermore, the material for the substrate can also use
non-thermoplastic resin fibers, and reinforcing fibers are
particularly favorable. In those cases where reinforcing fibers are
used as the material for the substrate, the same reinforcing fibers
that were used to form the prepreg can be used, although different
fibers may also be used.
[0107] In those cases where the same reinforcing fibers as those
used in the prepreg are used, the substrate can be bonded to the
prepreg so that the angle of alignment of the reinforcing fibers in
the substrate matches the angle of alignment of the reinforcing
fibers in the prepreg. However, bonding the two together so that
the respective angles of alignment are different enables the
lamination step during quasi-isotropic lamination or the like to be
conducted with greater ease, and is consequently preferred.
Quasi-isotropic lamination involves laminating layers with the
angles of alignment set to
[-45.degree./0.degree./45.degree./90.degree.], so that overall, the
FRP is isotropic and displays no anisotropy in terms of the FRP
properties.
[0108] On the other hand, different reinforcing fibers from those
used in the prepreg can be used for forming the substrate. In such
cases, a hybrid FRP can be produced with considerable ease, which
is ideal. For example, an FRP produced using an intermediate
material in which glass fiber is used as the reinforcing fibers for
forming the prepreg, and carbon fiber is used as the reinforcing
fibers for forming the substrate becomes a glass/carbon fiber
hybrid FRP, enabling optimal design of the cost performance
balance. In this case, as was described above, the respective
angles of alignment of the reinforcing fibers of the substrate and
the reinforcing fibers of the prepreg may be either the same or
different.
(Molding Using Prepregs or Intermediate Materials for FRP Molding
According to the Present Invention)
[0109] When a FRP is produced using either a prepreg or an
intermediate material for FRP molding according to the present
invention, vacuum bag molding is the most preferred process,
although molding using an autoclave or press molding can also be
used.
[0110] In a process for producing FRP according to the present
invention, primary curing is preferably conducted for at least 10
minutes at a primary curing temperature of no more than 150.degree.
C., and then the curing is preferably completed at a temperature
equal to, or greater than, the primary curing temperature.
Processes in which the primary curing is conducted at a temperature
of no more than 100.degree. C. are particularly preferred as a
resin mold can be used instead of a metal mold, and heating can be
conducted using solely steam, which provide significant cost
reductions.
[0111] In addition, following the primary curing and subsequent
removal from the mold, the product is preferably subjected to
further curing at a temperature either equal to, or higher than,
the primary curing temperature, thus enabling a further reduction
in the high-temperature molding time.
[0112] A prepreg or intermediate material for FRP molding according
to the present invention provides a deaerating circuit during
molding, meaning air from the voids can be guided out through the
deaerating circuit and expelled outside the FRP, thus making these
materials ideally suited to vacuum bag molding and oven
molding.
[0113] Regardless of whether or not oven molding is used, when
molding is conducted using a prepreg or an intermediate material
for FRP molding according to the present invention, the prepreg or
FRP molding intermediate material is preferably laminated, and then
placed under a vacuum, so that the air contained within the prepreg
or FRP molding intermediate material can be completely removed
before the temperature is raised. Specifically, a degree of vacuum
of no more than 600 mmHg is preferred, and a degree of vacuum of no
more than 700 mmHg is even more desirable. If the temperature is
raised before satisfactory deaerating has been completed, then the
viscosity of the matrix resin may fall too far, causing the
deaerating circuit to become undesirably blocked before the air
within the prepreg or FRP molding intermediate material has been
completely removed. Furthermore, if the process atmosphere is
returned to normal pressure in the middle of the molding process,
then there is a danger that air that has already been removed may
penetrate back into the interior of the prepreg or FRP molding
intermediate material, and as a result, the vacuum is preferably
maintained throughout the molding process.
[0114] In addition, when molding is conducted using a prepreg or an
intermediate material for FRP molding according to the present
invention, the structure is preferably held for at least 1 hour,
prior to curing, and while the viscosity of the matrix resin is no
more than 10,000 poise, before the curing step is conducted. During
this holding period, the matrix resin can migrate, making it easier
to force the air out of the molded product. Holding the structure
while the viscosity of the matrix resin is no more than 5000 poise
before the curing step is even more desirable. Furthermore, holding
the structure in this state for at least 2 hours before curing is
also particularly preferred.
[0115] A preferred process for molding a FRP using either a prepreg
or a FRP molding intermediate material according to the present
invention involves raising the temperature from a temperature at
least 20.degree. C. below the molding temperature to the molding
temperature at a rate of no more than 1.degree. C./minute. The
raising of the temperature is initiated once the vacuum has been
established, and is conducted with the vacuum state maintained,
although during the temperature raising step, if the resin starts
to move very suddenly, then small quantities of residual air can
become trapped in the cured product under vacuum conditions,
namely, under reduced pressure conditions of no more than 50 Torr,
and this trapped air can cause residual interlayer voids and
surface pinholes.
[0116] Consequently, it is very important to control the speed of
movement of the resin during the temperature raising step, to
ensure that any last small quantities of residual air are expelled
from the molded product. In order to achieve this aim, the rate of
temperature increase can be kept low, although at very low
temperatures, the viscosity of the matrix resin is high, and the
movement of the air is too slow, meaning an extremely long time
would be required for the matrix resin to impregnate right into the
corners of the sheet-like reinforcing fiber substrate, causing a
problematic deterioration in productivity.
[0117] Because the viscosity of the resin reaches its minimum value
near typical molding temperatures, slowing the rate of temperature
increase to no more than 1.degree. C./minute from a temperature at
least 20.degree. C. below the molding temperature produces a
favorable effect, and is consequently preferred. Lowering the rate
of temperature increase to no more than 1.degree. C./minute from a
temperature at least 30.degree. C. below the molding temperature is
even more preferred, and lowering the rate from a temperature at
least 40.degree. C. below the molding temperature is particularly
desirable. Furthermore, slowing the rate of temperature increase to
no more than 0.7.degree. C./minute is even more preferred, and to
no more than 0.5.degree. C./minute is particularly desirable.
[0118] Furthermore, when prepregs or FRP molding intermediate
materials according to the present invention are laminated, then in
those cases where the upper and lower surfaces of the prepregs or
FRP molding intermediate materials can be obviously distinguished,
arranging the layers with the same surface of each layer facing in
the same direction enables a more reliable establishment of the
deaerating circuit, and is consequently preferred.
EXAMPLES
[0119] In the series of examples 1 to 7 and comparative examples 1
to 3 described below, a matrix resin was prepared by uniformly
mixing the resin constituents described below. The mixing
conditions were as follows. All of the components except for DICY7
and DCMU99 were mixed uniformly in a kneader set to 100.degree. C.,
and the temperature of the kneader was then lowered to 50.degree.
C., the DICY7 and DCMU99 were added, and mixing was continued to
generate a uniform mixture.
<Matrix Resin Composition>
[0120] Epikote 828 (a bisphenol A epoxy resin, manufactured by
Japan Epoxy Resins Co., Ltd.) 40 parts by mass
[0121] Epikote 1001 (a bisphenol A epoxy resin (solid at room
temperature), manufactured by Japan Epoxy Resins Co., Ltd.) 40
parts by mass
[0122] Epiclon N740 (a phenol novolac epoxy resin, manufactured by
Dainippon Ink and Chemicals, Incorporated) 20 parts by mass
[0123] DICY7 (dicyandiamide, manufactured by Japan Epoxy Resins
Co., Ltd.) 5 parts by mass
[0124] DCMU99 (3,4-dichlorophenyl-N,N-dimethylurea, manufactured by
Hodogaya Chemical Co., Ltd.) 5 parts by mass
[0125] Furthermore, the materials used in each of the examples and
comparative example, and the methods used for evaluation are
described below.
<Short Fibers of Thermoplastic Resin>
[0126] Nylon 12 was subjected to melt spinning to generate a short
fiber with a size of 200 tex, and these fibers were then cut to a
length of 5 mm to complete preparation of the short fibers.
Hereafter, these are referred to simply as short fibers.
<Compressive Strength after Impact>
[0127] Measurement of the compressive strength after impact was
measured in accordance with the SACMA recommended method SRM2-88,
and involved measuring the compressive strength following
application of a 270 lb-in impact.
<Method of Measuring Tg>
[0128] Using a RDA-700 device manufactured by Rheometrics Inc., or
a viscoelastic spectrometer with equivalent functionality, the
temperature was raised from approximately 0.degree. C. at a rate of
2.degree. C./minute, and the dynamic modulus of elasticity (G') of
the sample was measured. The results of the measurements were
graphed with temperature along the horizontal axis and logarithm of
G' along the vertical axis as shown in FIG. 8, a tangent L1 was
drawn from the glass region and another tangent L2 was drawn from
the transition region, and the temperature corresponding with the
point of intersection C of the two tangents was used as Tg (see
FIG. 8).
<Minimum Viscosity>
[0129] Using a dynamic analyzer (RDA-200) manufactured by
Rheometrics, Inc., viscosity measurements were conducted from room
temperature (23.degree. C.) to 150.degree. C. using a rate of
temperature increase of 5.degree. C./minute and an angular velocity
of 10 rad/second. The lowest value observed for the viscosity
during this test was recorded as the minimum viscosity for the
resin composition.
<Surface Coverage Ratio>
[0130] A smooth and transparent polyethylene film of thickness 20
.mu.m was bonded to a sea-and-island-type patterned surface of a
prepreg by application of a metal heated roll press under
conditions including a temperature of 40.degree. C., a pressure of
1 atom, and a roll speed of 5 m/minute. The surface was then
photographed using a CCD camera of at least 2 megapixels, and an
image analysis system (detailed fine image analysis "IP1000")
manufactured by Asahi Engineering Co., Ltd. was used to determine
the surface area covered by the thermosetting resin, by measuring
the surface area of those regions where the thermosetting resin had
stuck to the polyethylene film causing a change in coloring, and
the ratio of this surface area relative to the total surface area
of the prepreg was then used to determine the surface coverage
ratio.
<Island Portions Weave Intersection Coverage Ratio>
[0131] In the same manner as described above for the measurement of
the surface coverage ratio, a smooth and transparent polyethylene
film of thickness 20 .mu.m was bonded to a prepreg by application
of a metal heated roll press under conditions including a
temperature of 40.degree. C., a pressure of 1 atm, and a roll speed
of 5 m/minute. The coated prepreg was then cut into a 10
cm.times.10 cm square, the surface of the prepreg to which the
polyethylene film had been bonded was photographed using a CCD
camera, and the aforementioned image analysis system was used to
determine the number of individual regions (T: the number of
islands) where the thermosetting resin had stuck to the
polyethylene film causing a change in coloring.
[0132] Subsequently, the polyethylene film was peeled off, the
surface of the prepreg was photographed again with the CCD camera,
and an image analyzer was used to measure the number of weave
intersections (Y) within the reinforcing fiber woven fabric on the
sea-and-island-patterned surface. The island portions weave
intersection coverage ratio was then calculated from the formula
(1).
<Evaluation of FRP External Appearance (for the Existence of
Pinholes)>
[0133] Using the method described below, a piece of chalk was
pressed against the surface of the produced flat sheet of FRP and
used to coat the entire surface of the sheet. The surface was then
wiped lightly with a dry cloth or the like, making any pinholes
very visible, and enabling an evaluation of whether or not any
pinholes exist.
<Evaluation of FRP Voids>
[0134] Following evaluation for pinholes, the flat sheet of FRP was
cut through the center in a direction perpendicular to the
thickness direction, and the cross section was photographed at
20.times. magnification. An evaluation of whether or not any voids
exist was then made by inspecting the cross section photograph.
<Evaluation of Tackiness>
[0135] Under an atmosphere at a temperature 23.degree. C. and a
humidity of 50%, a steel plate of thickness 2 mm that had been
treated with a releasing agent was stood up vertically with respect
to the ground, and a prepreg that had been cut to a size of 10
cm.times.10 cm was stuck to the surface of the steel plate. If the
prepreg remained attached to the steel plate with no signs of
peeling after 1 minute, then the surface tackiness of the prepreg
was adjudged to be favorable.
Example 1
[0136] The matrix resin was applied uniformly to a release sheet at
a resin weight of 430 g/m.sup.2, thus forming a resin film. This
resin film was supplied to a piece of carbon fiber cloth TRK510,
manufactured by Mitsubishi Rayon Co., Ltd. (fiber weight 646
g/m.sup.2, 2/2 twill) from the bottom surface of the cloth, thus
impregnating the carbon fiber cloth with the resin. The temperature
during impregnation vas 60.degree. C., and the pressure was
adjusted to complete the preparation of a prepreg. When the resin
impregnation ratio of the thus produced prepreg was measured, the
result was 90%, thus confirming the prepreg as conforming to the
present invention.
[0137] Next, using the release sheet side of the thus produced
prepreg of the present invention as the tool side (a stainless
steel plate), a 4-ply laminate was formed at 0.degree. C. The
layers from the second layer up were arranged so that the release
sheet side of the prepreg faced the opposite side of the previous
layer. Vacuum bag molding was conducted, and a 30 cm square panel
was subjected to oven molding. The operation of laminating the
prepregs presented absolutely no problems.
[0138] The molding conditions used for the prepreg laminate were as
follows. Namely, the temperature was raised from room temperature
to 50.degree. C. at a rate of 3.degree. C./minute, the laminate was
then held at 50.degree. C. for 30 minutes under reduced pressure at
20 Torr to allow deaerating, and subsequently, with the reduced
pressure state maintained at 20 Torr, the temperature was raised to
120.degree. C. at a rate of 1.degree. C./minute. The temperature
was then held at 120.degree. C. for 1 hour, thus yielding a 30 cm
square panel.
[0139] The thus obtained panel had no surface voids, and when the
panel was cut through the center and the resulting cross section
was inspected, no internal voids were visible.
Comparative Example 1
[0140] With the exception of altering the impregnation temperature
to 70.degree. C., a prepreg was prepared in the same manner as the
example 1. When the cross-section of the prepreg was inspected, it
was found that the resin had migrated right through to the opposite
surface from the release sheet, producing a resin impregnation
ratio of 100%. This prepreg was then laminated, and a panel was
molded in the same manner as the example 1. The operation of
laminating the prepregs presented absolutely no problems, but the
surface of the molded panel contained pinholes. Furthermore, when a
central cross section of the panel was inspected in the same manner
as the example 1, a plurality of internal voids was observed.
Comparative Example 2
[0141] A resin film was prepared in the same manner as the example
1, and a prepreg was then formed. However, the impregnation of the
carbon fiber cloth with the resin was conducted at room
temperature, with only pressure being applied. Almost no
impregnation occurred, and absolutely no resin was visible at the
opposite surface to where the resin was supplied. When the resin
impregnation ratio of the thus produced prepreg was measured, the
result was 30%. This prepreg was then laminated, and a panel was
molded in the same manner as the example 1. The lamination was
conducted with the release sheet side of the prepregs facing the
tool surface.
[0142] A small number of pinholes were identified in the surface of
the thus produced panel, and when a central cross section of the
panel was inspected in the same manner as the example 1, internal
voids were also observed.
[0143] A piece of carbon fiber cloth TR3110 (number of filaments
3000, plain weave, weight 200 g/m.sup.2, manufactured by Mitsubishi
Rayon Co., Ltd.) was impregnated with the same resin composition as
that used in the example 1, thus forming a prepreg of the present
invention. When the resin impregnation ratio was measured, the
result was 70%. A 16-ply laminate of this prepreg was formed using
an alignment pattern of
[0.degree./45.degree./90.degree./-45.degree./0.degree./45.degree./90.degr-
ee./-45.degree./-45.degree./90.degree./45.degree./0.degree./-45.degree./90-
.degree./45.degree./0.degree.], and a 1 m square panel was molded.
The lamination was conducted with the release sheet side of the
prepregs facing the tool surface. The operation of laminating the
prepregs presented absolutely no problems.
[0144] Under the molding conditions used, the temperature was
raised from room temperature to 45.degree. C. at a rate of
5.degree. C./minute, the laminate was then held at 45.degree. C.
for 60 minutes under reduced pressure at 7 Torr to allow
deaerating, and subsequently, the temperature was raised to
80.degree. C. at a rate of 2.degree. C./minute, and from 80.degree.
C. to 120.degree. C. at a rate of 0.7.degree. C./minute. The
temperature was then held at 120.degree. C. for 1 hour, thus
yielding a 1 m square panel.
[0145] The thus obtained panel had no surface pinholes, and when
the interior was inspected in the same manner as the example 1, no
internal voids were visible.
Example 4
[0146] An epoxy resin composition #830 manufactured by Mitsubishi
Rayon Co., Ltd. was used as the matrix resin. Using this resin, a
resin film was prepared in the same manner as the example 1, and
this was then impregnated into a TRK510. The impregnation
temperature was set to 50.degree. C. When the resin impregnation
ratio of the thus obtained prepreg was measured, the result was
(60%, thus confirming the prepreg as conforming to the present
invention. Using this prepreg, a molded product was molded. A
wooden female mold was used as the molding die. An 8-ply laminate
was formed using an alignment pattern of
[0.degree./45.degree./90.degree./-45.degree./-45.degree./90.degree./45.de-
gree./0.degree.], with the release sheet side of the prepreg facing
the tool surface, and subsequently prepregs arranged so that the
release sheet side faced the opposite side of the previous layer.
The operation of laminating the prepregs presented absolutely no
problems.
[0147] Under the molding conditions used, the temperature was
raised from room temperature to 45.degree. C. at a rate of
2.degree. C./minute, the laminate was then held at 45.degree. C.
under reduced pressure at 2 Torr for 4 hours to allow deaerating,
and subsequently, the temperature was raised to 80.degree. C. at a
rate of 0.5.degree. C./minute. The temperature was then held at
80.degree. C. for 2 hours, thus yielding a molded product.
[0148] The thus obtained molded product had no surface pinholes,
and when the product was cut open and the exposed cross section was
inspected, no internal voids were visible.
Example 5
[0149] Using the resin used in the example 1, and using a
non-crimped fabric Quadraxial-Carbon-Gelege (+45.degree.: Carbon
267 g/m.sup.2, 0.degree.: Carbon 268 g/m.sup.2, -45.degree.: Carbon
267 g/m.sup.2, 90.degree.: Carbon 268 g/m.sup.2, stitching: PES 6
gm.sup.2, weight 1076 g/m.sup.2) manufactured by Saertex Co., Ltd.
as a sheet-like reinforcing fiber substrate, a prepreg was prepared
in the same manner as the example 1. However, the resin weighting
was 717 g/m.sup.2. When the resin impregnation ratio was measured,
the result was 75%, thus confirming the prepreg as conforming to
the present invention. A 2-ply laminate was prepared with the
prepreg surfaces facing in the same direction, and a FRP was then
molded. The molding was conducted under the same molding conditions
as the example 1. The thus obtained molded product displayed no
internal voids and no surface pinholes.
Example 6
[0150] 8.1 parts by mass of the short fibers were added to 100
parts by mass of the thermosetting resin, and then mixed uniformly
in a kneader at 50.degree. C., thus yielding a thermosetting resin
composition.
[0151] Using a roll coater, this resin composition was applied to a
release sheet with a resin weight of 133 g/m.sup.2. This resin film
was supplied at room temperature to one surface of a piece of
carbon fiber cloth TR3110, a sheet-like reinforcing fiber substrate
manufactured by Mitsubishi Rayon Co., Ltd. (fiber weight 200
g/m.sup.2, plain weave), and a prepreg of the present invention was
prepared by heating to 40.degree. C., applying pressure from a
roller, and ensuring that the resin did not migrate from the supply
surface right through to the opposite surface. When the resin
impregnation ratio of the thus produced prepreg was measured, the
result was 60%.
[0152] A 24-ply laminate of this prepreg was formed with the fiber
alignment direction (of the warp) set to
[45.degree./0.degree./-45.degree./90.degree./45.degree./0.degree./-45.deg-
ree./90.degree./45.degree./0.degree./-45.degree./90.degree./90.degree./-45-
.degree./0.degree./45.degree./90.degree./-45.degree./0.degree./45.degree./-
90.degree./-45.degree./0.degree./45.degree.], and oven molding was
used to mold a 500 mm.times.500 mm panel. Under the molding
conditions used, following lamination of the prepregs, the laminate
was first placed under vacuum, and was then heated for 2 hours at
50.degree. C., and then a further 2 hours at 80.degree. C., before
being returned to normal pressure and held for 1 hour at
130.degree. C., thus yielding a CFRP panel. The rate of temperature
increase used was 0.5.degree. C./minute, and the rate of cooling
following the 1 hour at 130.degree. C. was 2.degree. C./minute.
[0153] The thus obtained CFRP panel had no pinholes and displayed
an extremely favorable external appearance. Furthermore, when the
panel was cut though the center, no internal voids were visible.
When a test specimen was cut from the panel and the compressive
strength after impact was measured, the result was an extremely
high 262 MPa.
Comparative Example 3
[0154] A prepreg was prepared in the same manner as the example 6.
However, during the step for integrating the resin film with the
sheet-like reinforcing fiber substrate, the level of impregnation
was increased, so that almost no non-impregnated portions remained
on the opposite surface to the surface from which the resin was
supplied. The resin impregnation ratio was 100%.
[0155] The thus obtained prepreg was laminated and molded in the
same manner as the example 6, yielding a CFRP panel. This CFRP
panel displayed pinholes, and the external appearance was poor.
Furthermore, when the panel was cut through the center, a plurality
of internal voids was visible. When the compressive strength after
impact was measured for this panel, the result was low, and 222
MPa.
Example 7
[0156] With the exception of using a unidirectional, sheet-like
reinforcing fiber substrate (with a fiber weight of 200 g/m.sup.2)
for stitching-reinforcement formed by stitching unidirectionally
aligned TR50S-12L fibers with polyester fiber, a prepreg of the
present invention was formed in exactly the same manner as the
example 6. The resin impregnation ratio of the thus obtained
prepreg was 45%.
[0157] The thus obtained prepreg was laminated and molded in the
same manner as the example 6, yielding a CFRP panel. When the panel
was cut through the center, no internal voids were visible. When
the compressive strength after impact was measured for this panel
in the same manner as the example 6, the result was a very high 325
MPa.
Comparative Example 4
[0158] A prepreg was prepared in the same manner as the example 7.
However, during the step for integrating the resin film with the
sheet-like reinforcing fiber substrate, the level of impregnation
was increased, so that resin exuded from the opposite surface to
the surface from which the resin was supplied. The resin
impregnation ratio was 100%.
[0159] The thus obtained prepreg was laminated and molded in the
same manner as the example 7, yielding a CFRP panel. When this
panel was cut through the center, internal voids were visible. When
the compressive strength after impact was measured for this panel
in the same manner as the example 6, the result was 283 MPa,
considerably lower than that observed for the example 7.
Example 8
[0160] (A) A carbon fiber cloth TRK510 (fiber weight 646 g/m.sup.2,
2/2 twill, thickness 355 .mu.m), manufactured by Mitsubishi Rayon
Co., Ltd., was used as the sheet-like reinforcing fiber substrate,
and
[0161] (B) an epoxy resin #830, manufactured by Mitsubishi Rayon
Co., Ltd., which can be cured by heating at 80.degree. C. for 2
hours, was used as a curable resin composition.
[0162] The curable resin composition (B) was applied to a release
sheet with a resin weight of 175 g/m.sup.2. One of these release
sheets was then bonded to both the top and bottom surfaces of the
sheet-like reinforcing fiber substrate (A), with both of the
curable resin composition surfaces facing inwards. The bonding was
conducted at room temperature, with the tackiness of the curable
resin composition (B) used to effect the bonding. When the thus
obtained FRP molding intermediate material of the present invention
was cut open and the interior was inspected, it was found that the
portions into which the curable resin composition had not
impregnated existed as a continuous portion.
[0163] A 10-ply laminate of the thus produced prepreg of the
present invention was prepared, with the prepregs aligned in the
same direction, and a 800 mm.times.800 mm CFRP panel was molded.
Under the molding conditions used, atmospheric pressure was first
confirmed as having fallen to no more than 700 mmHg, and the
temperature was then raised from room temperature at a rate of
1.degree. C./minute, and held at 50.degree. C. for 3 hours, before
the temperature increase was resumed and heating was continued at
80.degree. C. for 2 hours, thus curing the laminate. The viscosity
of the #830 resin at 50.degree. C., measured using a DSR200 device
manufactured by Rheometrics, Inc., with a rate of temperature
increase of 2.degree. C./minute, was 3500 poise.
[0164] The surface of the produced CFRP panel displayed absolutely
no pinholes. Furthermore, when the FRP panel was cut though the
center and the cut cross section was inspected, no internal voids
were visible.
Comparative Example 5
[0165] A prepreg was prepared using the same material as the
example 8. However, the resin was applied at a weight of 350
g/m.sup.2, and was bonded to only one surface of the sheet-like
reinforcing fiber substrate (A). The thus obtained FRP molding
intermediate material was molded in the same manner as the example
1, thus yielding a FRP panel.
[0166] Although no pinholes were observed in the surface of the
produced CFRP panel, when the panel was cut though the center and
the cut cross section was inspected, a plurality of small internal
voids was visible.
Comparative Example 6
[0167] A prepreg was prepared using the same material as the
example 8. The resin was applied at a weight of 175 g/m.sup.2 in
the same manner as the example 8, but rather than simply bonding
the resin to both surfaces of the sheet-like reinforcing fiber
substrate (B), the structure was passed twice through a fusing
press under conditions of 60.degree. C., 0.1 MPa, and a speed of 25
cm/minute, thus ensuring good impregnation. When the thus produced
prepreg was cut though the center and the cut cross section was
inspected, the curable resin composition had impregnated right into
the center of the substrate, and although a few portions with no
curable resin composition were visible, each of these
non-impregnated portions was partitioned off by the curable resin
composition.
[0168] The produced prepreg was molded in the same manner as the
example 8, yielding a FRP panel, but the surface of the thus
obtained FRP panel contained a plurality of pinholes. Furthermore,
when the panel was cut though the center and the cut cross section
was inspected, a large number of variously sized internal voids
were visible.
Example 9
[0169] A prepreg was prepared in the same manner as the example 8.
However, an epoxy resin composition that was capable of being cured
by heating at 80.degree. C. for 2 hours, formed by uniformly mixing
the resin components listed below at a temperature of 55.degree.
C., was used as the curable resin composition (B), and when this
curable resin composition (B) was applied to the release sheet, a
resin weight of 215 g/m.sup.2 was used.
[0170] Epikote 1001 (a bisphenol A epoxy resin (solid at room
temperature), manufactured by Japan Epoxy Resins Co., Ltd.) 70
parts by mass
[0171] Epiclon N740 (a phenol novolac epoxy resin, manufactured by
Dainippon Ink and Chemicals, Incorporated) 20 parts by mass
[0172] Novacure HX3722 (a microcapsule based latent curing agent,
manufactured by Asahi Kasei Corporation) 10 parts by mass
[0173] Omicure 94 (an amine based curing agent, manufactured by PTI
Japan Co., Ltd.) 5 parts by mass
[0174] Using the thus produced prepreg, a CFRP panel was produced
in the same manner as the example 8. The surface of the produced
CFRP panel displayed absolutely no pinholes. Furthermore, when the
CFRP panel was cut though the center and the cut cross section was
inspected, no internal voids were visible. In addition, when the
flexural strength of the product CFRP panel was measured in
accordance with ASTM D790, a high strength value of 680 MPa was
obtained.
Comparative Example 7
[0175] A prepreg was prepared in the same manner as the example 9.
However, following bonding of the resin film, the structure was
passed twice through a fusing press under conditions of 60.degree.
C., 0.1 MPa, and a speed of 25 cm/minute, thus ensuring good
impregnation. When the thus produced prepreg was cut, and the cut
cross section was inspected, the matrix resin had impregnated right
into the center of the substrate, and although a few portions with
no matrix resin were visible, each of these non-impregnated
portions was partitioned off by the matrix resin, and no continuous
non-impregnated portion existed.
[0176] Using the produced prepreg, a CFRP panel was produced in the
same manner as the example 9. The surface of the thus obtained CFRP
panel contained a plurality of pinholes. Furthermore, when the
panel was cut through the center and the cut cross section was
inspected, a large number of variously sized internal voids were
visible. Furthermore, when the CFRP panel was cut though the center
and the cut cross section was inspected, no internal voids were
visible. In addition, when the flexural strength of the product
CFRP panel was measured in accordance with ASTM D790, a value of
420 MPa, which was lower than that observed for the example 9, was
obtained.
Example 10
[0177] An epoxy resin composition (#340, manufactured by Mitsubishi
Rayon Co., Ltd., minimum viscosity 20 poise) was applied uniformly
to a release sheet wherein one surface thereof is release-treated,
using a roll coater, at a weight of 133 g/m.sup.2. A carbon fiber
woven fabric manufactured by Mitsubishi Rayon Co., Ltd. (TRK510
(fiber weight: 646 g/m.sup.2)) was then bonded to the resin
composition side of this resin support sheet. Another release sheet
that had undergone release-treatment in the same manner as
described above was then overlaid on the carbon fiber fabric side
such that a release-treated surface is provided on the fabric. The
resulting structure was then pressed and heated by passage through
a pair of heated rollers at 40.degree. C., thus forming a
prepreg.
[0178] The thus obtained prepreg had a resin composition surface
coverage ratio of 3%, and the weave intersection coverage ratio for
the island portions of the resin composition that existed at the
surface was 60%. Furthermore, evaluation of the workability
revealed that the prepreg displayed favorable tackiness, and stuck
favorably to a steel plate.
[0179] Using this prepreg, a FRP was produced in the manner
described below. 10 prepreg sheets that had been cut to dimensions
of 20 cm long.times.20 cm wide were laminated. This laminate was
provided on a steel base plate (thickness 2 mm), the surface of
which had been treated with a releasing agent. Subsequently, a
polytetrafluoroethylene film containing holes of 2 mm diameter at
10 cm intervals, a nylon cloth of weight 20 g/m.sup.2, and a glass
fiber non-woven fabric of weight 40 g/m.sup.2 were placed in
sequence on top of the laminate. The resulting structure was then
covered and sealed using a nylon film. The space sealed within the
outer nylon film was then placed under reduced pressure, and while
the pressure was maintained at no more than 600 mmHg, the
temperature was raised from room temperature to 130.degree. C. at a
rate of 2.degree. C./minute, and was then held at 130.degree. C.
for 2 hours, thus yielding a FRP.
[0180] When the thus produced FRP was subjected to the evaluations
described above, it was found that the surface on the base plate
side of the molded FRP had a favorable external appearance with no
pinholes, and a cross section photograph revealed no visible
interlayer or intralayer voids.
Examples 11 to 14
[0181] Using the same resin composition and reinforcing fiber woven
fabric as those used in the example 10, a series of
fiber-reinforced fabric prepregs with the respective surface
coverage ratios shown in Table 1 were prepared by conducting a
plurality of repetitions of pressing and heating with a roller
heated to 40.degree.. Each of the prepregs had an island portions
weave intersection coverage ratio of 60%.
[0182] Evaluation of these prepregs in the same manner as the
example 10 revealed that all of the prepregs had favorable handling
properties, and the produced FRPs all had favorable external
appearances, and no voids.
Examples 15 and 16
[0183] Prepregs were prepared in the same manner as the example 11,
but with the conditions altered to produce a resin composition
surface coverage ratio of 40%. The number of repetitions of the
impregnation step using the heated roll press was adjusted to
produce island portions weave intersection coverage ratios of 100%
and 50% respectively. Evaluation of these prepregs in the same
manner as the example 10 revealed that both of the prepregs had
favorable handling properties, and the produced FRPs both had
favorable external appearances, and also displayed no interlayer or
intralayer voids.
Examples 17 to 21
[0184] With the exceptions of altering the temperature during
impregnation to 60.degree. C. in the case of the example 17,
increasing the minimum viscosity of the epoxy resin composition as
shown in Table 2 in the case of the examples 18 and 19, and
altering the weight of the carbon fiber fabric as shown in Table 2
in the case of the examples 20 and 21, prepregs were prepared in
the same manner as the example 10. All of the prepregs displayed
favorable tackiness, and the produced FRPs all had favorable
external appearances, and displayed no voids.
Examples 22 and 23
[0185] With the exceptions of altering the minimum viscosity to
1100 poise in the case of the example 22, altering the fiber weight
to 1600 g/m.sup.2 in the case of the example 23, and setting the
other values as shown in Table 2, prepregs were prepared in the
same manner as the example 10. The tackiness of these prepregs was
good. On the other hand, the FRPs produced from these prepregs did
contain internal voids, although FRPs with no pinholes were
obtained.
Example 24
[0186] With the exception of applying the resin composition on the
release sheet with a uniform weighting per unit of surface area of
266 g/m.sup.2, preparation was conducted in the same manner as the
example 10, up to and including the heating and pressing using a
pair of heated rollers. The resin support sheet was then peeled
off, TR3110 was bonded to the same surface, and then a similar
release sheet to that described above was overlaid on the side of
the just bonded TR3110. The resulting structure was then pressed
and heated again by passage through the pair of heated rollers at
40.degree. C., and the overlaid release sheet was peeled off,
yielding a prepreg in which both sides displayed a
sea-and-island-pattern.
[0187] The surface coverage ratio of the thus obtained prepreg,
totaled across both surfaces, was 50%, and the island portions
weave intersection coverage ratio was 60%. This prepreg also stuck
favorably to a steel sheet, and was adjudged to have a good level
of tackiness. Furthermore, when this prepreg was used to conduct
the molding evaluations described above, the molded FRP had a
favorable external appearance with no surface pinholes, and no
internal voids were observed.
Comparative Examples 8 to 10
[0188] With the exceptions of altering the surface coverage ratios,
the island portions weave intersection coverage ratios, and the
fiber weights to the values shown in Table 3, prepregs were
prepared in the same manner as the example 9 and then evaluated.
The evaluation results showed that the comparative example 8, which
had a lower surface coverage ratio than the example 10, displayed
only weak tackiness, and had poor handling properties. In contrast,
the comparative example 9, which had an overly high surface
coverage ratio when compared with the example 10, and the
comparative example 10, which had a lower island portions weave
intersection coverage ratio than the example 10, produced molded
products with pinholes and interlayer voids, meaning products with
satisfactory external appearances and mechanical characteristics
could not be obtained.
[0189] A thermosetting resin composition acetone solution used in
the examples 25 to 30 and the comparative examples 11 to 14
employed an acetone solution containing 60% by mass of the epoxy
resin composition, and was prepared by dissolving an epoxy resin
composition (solid at room temperature), comprising the
constituents listed below, in acetone to generate a homogenous
solution (hereafter referred to simply as the epoxy solution).
<Epoxy Resin Composition>
[0190] Epikote 828 (a bisphenol A epoxy resin (liquid at room
temperature), manufactured by Japan Epoxy Resins Co., Ltd.) 50
parts by mass
[0191] Epikote 1004 (a bisphenol A epoxy resin (solid at room
temperature), manufactured by Japan Epoxy Resins Co., Ltd.) 30
parts by mass
[0192] Epiclon N740 (a phenol novolac epoxy resin, manufactured by
Dainippon Ink and Chemicals, Incorporated) 20 parts by mass
[0193] DCMU99 (3,4-dichlorophenyl-N,N-dimethylurea, manufactured by
Hodogaya Chemical Co., Ltd.) 5 parts by mass
Example 25
[0194] A carbon fiber woven fabric Pyrofil TRK510 that used carbon
fiber for both the warp and the woof (manufactured by Mitsubishi
Rayon Co., Ltd., 2/2 twill fabric, fiber weight 646 g/m.sup.2,
thickness 0.57 mm) was impregnated by immersion in the epoxy
solution, and was then dried by warm air drying at 40.degree. C. to
remove the solvent, thus yielding a prepreg with a resin content of
46.7% by mass (a resin weight of 564 g/m.sup.2). When the thickness
of the prepreg was measured with vernier calipers, the measured
thickness (A) was 0.85 mm. Using a carbon fiber woven fabric
Pyrofil TR3110 that used carbon fiber for both the warp and the
woof (manufactured by Mitsubishi Rayon Co., Ltd., plain weave,
fiber weight 200 g/m.sup.2, thickness (B)=0.23 mm) as a substrate,
the substrate was bonded to one surface of the prepreg so that the
warp and woof were aligned in the same direction as in the prepreg,
thus forming an intermediate material for FRP molding. This
intermediate material displayed a (B)/(A) ratio of 0.27, the
overall fiber weight of the entire intermediate material was 846
g/m.sup.2, and the resin content was 40% by mass.
[0195] The prepreg side surface of the thus obtained FRP molding
intermediate material was stuck to a molding die, and a 3-ply
laminate was then formed by overlaying the intermediate materials
with the same angle of alignment and the same surfaces facing the
same direction, and the thus formed 500 mm.times.500 mm flat sheet
was then subjected to oven molding. The molding conditions were as
follows. Namely, under a vacuum of no more than 5 Torr, the
temperature was raised from room temperature to 50.degree. C. at a
rate of 3.degree. C./minute, held at 50.degree. C. for 3 hours, and
then raised to 120.degree. C. at a rate of 0.5.degree. C./minute,
and subsequently held at 120.degree. C. for 2 hours, thus yielding
a FRP panel.
[0196] Despite being formed by oven molding, as shown in Table 4,
the thus obtained FRP panel displayed no surface pinholes, and when
the FRP panel was cut through the center and the interior was
inspected, no internal voids were visible.
Example 26
[0197] With the exceptions of altering the resin content to 57.1%
by mass (a resin weight of 861 g/m.sup.2) and setting the thickness
(A)=1.1 mm, a prepreg was prepared in the same manner as the
example 25. Using a reinforcing fiber woven fabric (TRK510,
thickness (B)=0.57 mm) as a substrate, which is same with those
used in the prepreg, the substrate was bonded to one surface of the
prepreg, with the direction of alignment of the reinforcing fibers
inclined 45.degree. relative to that of the prepreg, thus forming
an intermediate material for FRP molding. This intermediate
material displayed a (B)/(A) ratio of 0.52, the overall fiber
weight of the entire intermediate material was 1292 g/m.sup.2, and
the resin content was 40% by mass.
[0198] The thus obtained FRP molding intermediate material was
laminated with the angle of alignment of the warp fibers set to
[-45.degree./0.degree./45.degree./90.degree./90.degree./45.degree./0.degr-
ee./-45.degree.], and was then oven molded in the same manner as
the example 24, yielding a FRP panel. In this example, because the
intermediate material was a 0.degree./45.degree. double layered
structure, a 4-ply laminate of intermediate material units was
formed.
[0199] As shown in Table 4, the thus obtained FRP panel displayed
no surface pinholes, and when the FRP panel was cut through the
center and the interior was inspected, no internal voids were
visible.
Example 27
[0200] With the exceptions of replacing the TRK510 with roving
glass cloth WR800 manufactured by Nitto Boseki Co., Ltd., and
altering the resin content to 53.3% by mass (a resin weight of 450
g/m.sup.2) and the thickness (A)=0.71 mm, a prepreg was prepared in
the same manner as the example 25. A sheet of Pyrofil TR3110 was
then bonded to one surface of the prepreg so that the warp and woof
were aligned in the same direction as in the prepreg, thus forming
a glass fiber/carbon fiber hybrid FRP molding intermediate material
((B)/(A)=0.32).
[0201] A 4-ply laminate was then formed by overlaying the thus
obtained intermediate material with the same angle of alignment and
the same surfaces facing the same direction, and the laminate was
then subjected to oven molding in the same manner as the example
25, yielding a glass fiber/carbon fiber hybrid FRP. By using an
intermediate material of the present invention, a hybrid FRP was
able to be molded with considerable ease.
[0202] As shown in Table 4, the thus obtained FRP panel displayed
no surface pinholes, and when the FRP panel was cut through the
center and the interior was inspected, no internal voids were
visible.
Example 28
[0203] With the exceptions of altering the resin content to 51.9%
by mass (a resin weight of 697.5 g/m.sup.2), and setting the
thickness (A)=0.96 mm, a prepreg was prepared in the same manner as
the example 25. Using Pyrofil TR3110 as the substrate, substrates
were bonded to both the upper and lower surfaces of the prepreg so
that the warp and woof were aligned in the same direction as in the
prepreg, thus yielding an intermediate material for FRP molding.
This intermediate material displayed a (B)/(A) ratio of 0.24, the
overall carbon fiber weight of the entire intermediate material was
1064 g/m.sup.2, and the resin content was 40% by mass.
[0204] A 10-ply laminate was then formed by overlaying the thus
obtained intermediate material of the present invention, with the
same angle of alignment and the same surfaces facing the same
direction, and the laminate was then subjected to oven molding in
the same manner as the example 25, yielding a FRP panel.
[0205] As shown in Table 4, the thus obtained FRP panel displayed
no surface pinholes, and when the FRP panel was cut through the
center and the interior was inspected, no internal voids were
visible.
Example 29
[0206] With the exceptions of replacing the epoxy resin with a
phenol resin methanol solution Phenolite 5900 (approximately 60% by
mass) manufactured by Dainippon Ink and Chemicals, Incorporated,
and altering the resin content to 57.1% by mass (a resin weight of
861 g/m.sup.2) and the thickness (A)=1.1 mm, a prepreg was prepared
in the same manner as the example 25. A sheet of Pyrofil TR3110 was
then bonded to one surface of the prepreg so that the carbon fibers
were aligned in the same direction as in the prepreg, thus yielding
an intermediate material for FRP molding. This intermediate
material displayed a (B)/(A) ratio of 0.21, the overall carbon
fiber weight of the entire intermediate material was 1292
g/m.sup.2, and the resin content was 40% by mass.
[0207] A 3-ply laminate was then formed by overlaying the thus
obtained intermediate material with the same alignment, and the
resulting 1000 mm.times.1000 mm FRP panel was then subjected to
oven molding. The molding was conducted under a vacuum of no more
than 5 Torr, and the temperature was raised from room temperature
to 90.degree. C. at a rate of 0.5.degree. C./minute, and then held
at 90.degree. C. for 20 hours.
[0208] As shown in Table 4, the thus obtained FRP panel displayed
no surface pinholes, and when the FRP panel was cut through the
center and the interior was inspected, no internal voids were
visible.
Comparative Example 11
[0209] This comparative example presents an example in which a
substrate is not bonded to the prepreg. With the exceptions of
setting the resin content to 40.0% (a resin weight of 431
g/m.sup.2), and the thickness (A)=0.73 mm, a prepreg was prepared
in the same manner as the example 25.
[0210] Without bonding any substrates, an 8-ply laminate was formed
using only the prepreg, with the prepreg alignments set to
[-45.degree./0.degree./45.degree./90.degree./90.degree./45.degree./0.degr-
ee./-45.degree.], and the resulting laminate was then subjected to
oven molding in the same manner as the example 24, thus yielding a
FRP panel.
[0211] As shown in Table 4, the thus obtained FRP panel contained a
plurality of surface pinholes, and when the FRP panel was cut
through the center and the interior was inspected, a plurality of
internal voids was also visible.
Comparative Example 12
[0212] With the exceptions of altering the resin content to 40.5%
(a resin weight of 430 g/m.sup.2), and the thickness (A)=0.74 mm, a
prepreg was prepared in the same manner as the example 25. A sheet
of glass cloth H20 F5 104 (thickness (B)=0.04 mm) manufactured by
Unitika Glass Fiber Co., Ltd. was then bonded to the prepreg as the
substrate, yielding an intermediate material for FRP molding. This
intermediate material displayed a (B)/(A) ratio of 0.05.
[0213] This FRP molding intermediate material was subjected to oven
molding in the same manner as the example 25, yielding a FRP panel.
As shown in Table 4, the thus obtained FRP panel contained surface
pinholes, and when the FRP panel was cut through the center and the
interior was inspected, internal voids were also visible.
Comparative Example 13
[0214] With the exceptions of altering the resin content to 32.0%
(a resin weight of 300 g/m.sup.2), and the thickness (A)=0.62 mm, a
prepreg was prepared in the same manner as the example 25. A
polyester fiber non-woven fabric (fiber weight 132 g/m.sup.2,
thickness (B)=1.7 mm) was bonded to the prepreg, yielding an
intermediate material for FRP molding. This intermediate material
displayed a (B)/(A) ratio of 2.74.
[0215] This FRP molding intermediate material was subjected to oven
molding in the same manner as the example 25, yielding a FRP panel.
As shown in Table 4, the surface of thus obtained FRP panel
contained a plurality of resin non-impregnated portions, and when
the FRP panel was cut through the center and the interior was
inspected, a plurality of internal voids was also visible.
Example 30
[0216] Carbon fibers Pyrofil TR50S-12L manufactured by Mitsubishi
Rayon Co., Ltd. were aligned unidirectionally with a fiber weight
of 190 g/m.sup.2, and the same method as the example 25 was then
used to prepare a prepreg with a resin content of 30.2% by mass (a
resin weight of 82.3 g/m.sup.2), and a thickness (A)=0.18 mm. A
non-woven fabric comprising nylon 12 fibers (fiber weight 20
g/m.sup.2) with a thickness (B)=0.32 mm was bonded to one surface
of the prepreg, yielding an intermediate material for FRP molding
((B)/(A)=1.78).
[0217] A 24-ply laminate was then formed by overlaying the thus
obtained FRP molding intermediate material with the alignment of
the carbon fibers set to
[-45.degree./0.degree./45.degree./90.degree.] 3s (wherein, 3s means
a laminate produced by repeating the lamination repeating unit 3
times is then bonded to another laminate which is a mirror image.
In other words, the initial 12-ply laminate is arranged with the
carbon fiber side facing the die, and the subsequent 12-ply
laminate is then arranged with the carbon fiber side facing the
opposite direction to the die.) The resulting laminate was
subjected to oven molding in the same manner as the example 24,
yielding a FRP panel.
[0218] The thus obtained FRP panel contained no pinholes in either
the surfaces or between the layers, and when the FRP panel was cut
through the center and the interior was inspected, no internal
voids were visible. A CAI (residual compressive strength after
impact) measurement was performed for the panel. The CAI
measurement was conducted in accordance with the SRM2-88 method of
SACMA. The applied impact was 1500 inch-pounds/inch. The result of
the CAI measurement on the panel was 350 MPa, a high value for a
FRP.
Comparative Example 14
[0219] With the exceptions of altering the resin content to 35.0%
(a resin weight of 102.3 g/m.sup.2), and setting the thickness
(A)=0.19 mm, a prepreg was prepared in the same manner as the
example 25. A 24-ply laminate was produced using only the thus
obtained prepreg, with the alignment set to
[-45.degree./0.degree./45.degree./90.degree.] 3s, and the resulting
laminate was subjected to oven molding in the same manner as the
example 25, thus forming a FRP panel.
[0220] The thus obtained FRP panel had a few surface pinholes and
interlayer voids, and when the FRP panel was cut through the center
and the interior was inspected, internal voids were also visible.
Furthermore, when a CAI measurement was conducted on the panel, the
result was a comparatively low 210 MPa.
TABLE-US-00001 TABLE 1 Example Example Example Example Example
Example Example 10 11 12 13 14 15 16 Surface coverage ratio (%) 3
20 40 60 80 40 40 Island portions weave 60 60 60 60 60 40 100
intersection coverage ratio (%) Minimum viscosity (poise) 20 20 20
20 20 20 20 Fiber weight of reinforcing 650 650 650 650 650 650 650
fiber fabric (g/m.sup.2) External appearance No No No No No No No
(existence of pinholes) Existence of voids No No No No No No No
Tackiness Good Good Good Good Good Good Good
TABLE-US-00002 TABLE 2 Example Example Example Example Example
Example Example Example 17 18 19 20 21 22 23 24 Surface coverage
ratio (%) 60 60 60 60 60 60 60 50 Island portions weave 50 50 50 50
50 60 60 60 intersection coverage ratio (%) Minimum viscosity
(poise) 20 950 100 500 500 1100 500 20 Fiber weight of reinforcing
650 650 650 50 1500 650 1600 400 fiber fabric (g/m.sup.2) External
appearance No No No No No No No No (existence of pinholes)
Existence of voids No No No No No Yes Yes No Tackiness Good Good
Good Good Good Good Good Good
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative example
8 example 9 example 10 Surface coverage ratio (%) 2 81 70 Island
portions weave 60 60 35 intersection coverage ratio (%) Minimum
viscosity (poise) 20 20 20 Fiber weight of reinforcing 650 650 650
fiber fabric (g/m.sup.2) External appearance No No Yes (existence
of pinholes) Existence of voids Yes Yes Yes Tackiness Poor Good
Good
TABLE-US-00004 TABLE 4 Example Example Example Example Example
Example Comparative Comparative Comparative Comparative 25 26 27 28
29 30 example 11 example 12 example 13 example 14 Prepreg TRK510
TRK510 WR800 TRK510 TRK510 TR50S- TRK510 TRK510 TRK510 TR50S-
reinforcing 12L 12L fibers Prepreg matrix Epoxy Epoxy Epoxy Epoxy
Phenol Epoxy Epoxy Epoxy Epoxy Epoxy resin resin resin resin resin
resin resin resin resin resin resin Prepreg resin 46.7 57.1 53.3
51.9 57.1 30.2 40.0 40.5 32.0 35.0 content (%) Substrate TR3110
TRK510 TR3110 TR3110 TR3110 Non- None H20 Non- None woven woven
fabric of fabric of nylon 12 polyester fiber fiber Prepreg 0.85 1.1
0.71 0.96 1.1 0.18 0.73 0.74 0.62 0.19 thickness (mm) (A) Substrate
0.23 0.57 0.23 0.23 0.23 0.32 -- 0.04 1.7 -- thickness (mm) (B)
(B)/(A) 0.27 0.52 0.32 0.24 0.21 1.78 -- 0.05 2.74 -- Pinholes and
No No No No No No Yes Yes Yes Yes voids in FRP molded product
TRK510: carbon fiber woven fabric Pyrofil TRK510, manufactured by
Mitsubishi Rayon Co., Ltd. TR3110: carbon fiber woven fabric
Pyrofil TR3110, manufactured by Mitsubishi Rayon Co., Ltd. WR800:
roving glass cloth WR800, manufactured by Nitto Boseki Co., Ltd.,
TR50S-12L: Unidirectional material comprising carbon fibers Pyrofil
TR50S-12L, manufactured by Mitsubishi Rayon Co., Ltd. H20: glass
cloth H20 F5 104, manufactured by Unitika Glass Fiber Co., Ltd.
INDUSTRIAL APPLICABILITY
[0221] The level of workability associated with conventional
prepregs is retained, while a FRP with no internal voids or surface
pinholes, and with excellent external appearance, can be produced
using molding using only vacuum pressure, without the use of an
autoclave.
* * * * *