U.S. patent application number 10/531876 was filed with the patent office on 2006-01-26 for prepreg and method of manufacturing the prepreg.
This patent application is currently assigned to Mitsubishi Rayon Co., Ltd.. Invention is credited to Shirou Asada, Kimihiro Ikezaki, Akihiro Ito, Hisao Koba, Kazutami Mitani, Koki Wakabayashi.
Application Number | 20060020074 10/531876 |
Document ID | / |
Family ID | 32170775 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060020074 |
Kind Code |
A1 |
Asada; Shirou ; et
al. |
January 26, 2006 |
Prepreg and method of manufacturing the prepreg
Abstract
The present invention relates to a prepreg which is free from
the phenomenon that air is trapped between layers to generate
voids, has good handling characteristics and can produce molded
articles having any complicated shape and also relates to a method
of producing the prepreg. A reinforced-fiber sheet is impregnated
with a matrix resin so as to form a continuous resin layer at least
in the inside thereof, and then, a protective film having an
irregular surface is applied to at least one surface of the
reinforced-fiber sheet impregnated with the matrix resin such that
the irregular surface faces the reinforced-fiber sheet. In this
state, the prepreg is allowed to leave at 30 to 60.degree. C. under
the atmosphere for 12 hours or more. The resulting prepreg (1) is
provided with a continuous resin layer (3a) which exists therein,
wherein at least one surface of one side of the prepreg is
constituted of a resin-impregnated part (3b) where the impregnated
resin substantially exists and a fiber part (2a) where no resin
substantially exists.
Inventors: |
Asada; Shirou; (Aichi,
JP) ; Koba; Hisao; (Aichi, JP) ; Ito;
Akihiro; (Aichi, JP) ; Mitani; Kazutami;
(Aichi, JP) ; Ikezaki; Kimihiro; (Aichi, JP)
; Wakabayashi; Koki; (Aichi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Mitsubishi Rayon Co., Ltd.
6-41, Konan 1-chome, Minato-ku
Tokyo
JP
108-8506
|
Family ID: |
32170775 |
Appl. No.: |
10/531876 |
Filed: |
October 23, 2002 |
PCT Filed: |
October 23, 2002 |
PCT NO: |
PCT/JP02/11013 |
371 Date: |
April 19, 2005 |
Current U.S.
Class: |
524/494 ;
427/402; 524/495 |
Current CPC
Class: |
B29C 37/0075 20130101;
C08J 5/24 20130101; B29B 15/10 20130101; C08K 9/08 20130101 |
Class at
Publication: |
524/494 ;
427/402; 524/495 |
International
Class: |
C08K 3/40 20060101
C08K003/40; C08K 3/04 20060101 C08K003/04 |
Claims
1. A prepreg produced by impregnating a reinforced-fiber sheet with
a matrix resin, wherein the prepreg comprises a continuous resin
layer which exists in an inside thereof, and at least one surface
of one side thereof is constituted of a resin-impregnated part
where an impregnated resin substantially exists and a fiber part
where an impregnated resin does not substantially exist.
2. The prepreg according to claim 1, wherein the one surface of the
one side thereof has a sea-island structure in which the fiber part
constitutes a sea portion and the resin-impregnated part
constitutes an island portion.
3. The prepreg according to claim 2, wherein an area of the island
portion is 1 to 80% of a total area of the one surface of the one
side thereof.
4. The prepreg according to claim 1, wherein a protective film
having an irregular surface is applied to at least one surface of
one side of the reinforced-fiber sheet impregnated with the matrix
resin.
5. The prepreg according to claim 2, wherein a center distance
between adjacent island portions is 1 to 10 mm.
6. A method of producing a prepreg, comprising: impregnating a
reinforced-fiber sheet with a matrix resin so as to form a
continuous resin layer at least in an inside thereof; and applying
a protective film having an irregular surface to at least one
surface of one side of the reinforced-fiber sheet impregnated with
the matrix resin.
7. The method of producing the prepreg according to claim 6,
wherein only a convex portion of the irregular surface is brought
into contact with the reinforced-fiber sheet impregnated with the
matrix resin.
8. The method of producing the prepreg according to claim 6,
comprising keeping the viscosity of an impregnated resin at 10000
Poise or less for 4 hours or more in a situation where the
protective film is applied to the reinforced-fiber sheet.
9. The method of producing the prepreg according to claim 6,
comprising keeping a temperature at 30 to 150.degree. C. for 4
hours or more in a situation where the protective film is applied
to the reinforced-fiber sheet.
10. The method of producing the prepreg according to claim 6,
wherein the irregular surface of the protective film is formed of a
number of independent convex portions.
11. The method of producing the prepreg according to claim 10,
wherein the irregular surface of the protective film is disposed
with dispersing a number of convex portions uniformly on a surface
of the film.
12. The method of producing the prepreg according to claim 10,
wherein a center distance between the adjacent convex portions is 1
to 10 mm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a prepreg used when
producing a fiber-reinforced composite molded article and to a
method of producing the prepreg, and, particularly, to a prepreg
used preferably for vacuum bagging molding and to a method of
producing the prepreg.
BACKGROUND ART
[0002] A prepreg used in the production of a fiber-reinforced
composite molded article is usually provided with its one side
supported by releasable paper coated with silicone for the purpose
of retaining the shape thereof. Also, the other side of the prepreg
is covered with a protective film such as a polyethylene film to
retain the tack of the prepreg or to prevent foreign substances
such as dust from adhering thereto.
[0003] However, when one side or both sides of prepreg are covered
with these sheet-like materials such as releasable paper and
protective film, the resin contained in the prepreg is deviated to
the sheet-like material side by the interaction such as surface
tension on the sheet-like material, which makes both surfaces of
the prepreg resin-rich.
[0004] The prepreg with both surfaces being resin-rich has the
characteristics that even if the sheet-like material is peeled off
after the prepreg is cut into a desired pattern to process the
prepreg into a composite molded product to be intended, the state
that the surfaces of the prepreg are resin-rich is left unchanged
just after the sheet-like material is peeled off. If these prepregs
with resin-rich surfaces are merely laminated in plural, air is
trapped between two prepregs.
[0005] If the prepreg is cured in such a state that air is trapped
between these prepregs, the obtained molded article is inferior in
integration. Alternatively, the traces of the trapped air form
voids, which become stress-concentrated portions under some stress
and therefore the function of the prepreg is impaired: for example,
the strength required for a composite molded article is obtained
insufficiently.
[0006] In order to avoid such a disadvantage, it is necessary to
prevent air from being trapped between the laminated prepregs.
There is, for example, a method in which when laminating prepregs
by using, for example, an auto lay-up machine, prepregs are pressed
to each other under heating and pressure to let the air out of the
space between prepregs to laminate. However, this auto lay-up
machine is very expensive, which also affects the price of a
resulting composite molded product. Also, this auto lay-up machine
is not suitable for use in the case of laminating in a complicated
form and is therefore limited in its use. For these reasons, the
current operation of laminating prepregs is still actually carried
out by operators manually.
[0007] Therefore, a method is proposed in which talc is stuck to
the surface of a prepreg to prevent resins from being stuck
plane-wise directly to each other on the surfaces of the prepregs,
thereby reducing the stickiness of the resin itself to prevent air
trapping. This method of sticking talc is effective to reduce tack
characteristics of a prepreg. However, it merely reduces the tack
characteristics, and because the talc is finally contained in a
molded article, an unintended increase in weight is brought about
in the case of producing a large molded product. Also, it is
desirable to stick the talc evenly in consideration of the
mechanical characteristics of a molded article. In this method,
however, there is the case where spotting is caused to localize the
talc. In this case, there is a fear that the mechanical
characteristics of a molded article are deteriorated.
[0008] In another method of preventing layer voids as disclosed in
theses "Production of void free composite parts without debulking"
and "Degree of impregnation of prepregs--Effects on prosity" made
public in the 31st (held in Apr. 7 to 10, 1986) and the 32nd (held
in Apr. 6 to 9, 1987) International SAMPE Symposium respectively, a
prepreg is adopted in which a reinforced-fiber sheet is not
impregnated entirely with resin but one surface of the
reinforced-fiber sheet is locally impregnated with the resin. It is
described in these theses that this prepreg in which one surface
thereof is locally impregnated with the resin can prevent the
generation of voids because, when this prepreg is cured, conduits
are formed which permit the escape of the air and volatile
materials trapped between layers when laminating plural
prepregs.
[0009] This prepreg in which one surface of a reinforced-fiber
sheet is locally impregnated with the resin is produced using a
method in which a reinforced-fiber sheet is interposed between
releasable paper coated with the resin weighed in advance and
releasable paper non-coated with the resin, followed by fastening
and pressing from both sides.
[0010] Meanwhile, in a method disclosed in Japanese Patent
Laid-Open Publication No. 2-227212, a number of concave grooves
along the molding direction of a prepreg are formed on the surface
of the prepreg impregnated sufficiently with resin by using a
roller having a irregular portion in its circumferential direction.
It is described in this publication that in the case of molding by
vacuum bagging molding in which a plurality of the above prepregs
are laminated in the condition that the direction of the concave
grooves are fixed, the concave grooves on the surface of the
prepreg function as conduits allowing the escape of the air and
volatile materials trapped between layers and it is therefore
possible to prevent the generation of layer voids.
[0011] However, in the case of the prepreg in which the resin is
localized on one surface thereof and which is produced by the above
double-film method, the releasable paper non-coated with the resin
must be peeled off to use the prepreg in the state of a structure
constituted of a prepreg and the releasable paper which is coated
with resin and supports the prepreg. At this time, the releasable
paper which is non-coated with the resin is in direct contact with
the reinforced fibers. Therefore, when the releasable paper is
peeled off, single yarns are drawn from the reinforced-fiber sheet
and these drawn single yarns entangle other single yarns,
resultantly bringing about the disadvantage that an opening is
formed in the entangled part, which is sometimes a serious defect
of a product.
[0012] Also, no resin exists on the other surface of the prepreg
and therefore, when prepregs are laminated in such a manner that
the sides on which no resin exists are made to face each other,
they cannot be laminated in the condition that these sides are
stuck to each other, leading to inferior handling characteristics
of the prepreg.
[0013] When the upper side and lower side are laminated such that
the upper side concave groove intersects with the lower side
concave groove in the method in which the concave groove is formed
on the surface of the prepreg as disclosed in Japanese Patent
Laid-Open Publication No. 2-227212, the shapes of the concave
grooves are kept, so that the concave grooves serve as air
conduits, allowing the trapped air to flow, resulting in the
production of a void-free molded article. However, when the upper
and lower layers are laminated such that the concave grooves are
substantially parallel to each other, the concave groove on the
surface of the prepreg is easily clogged with the backside material
of the prepreg laminated thereon and therefore the air is trapped
on the contrary with the result that voids are easily formed.
[0014] The present invention has been made to solve the above
conventional problem and it is an object of the present invention
to provide a prepreg which is free from a phenomenon that air is
trapped between the layers of the prepreg to generate voids when
the prepregs are laminated to produce a molded product, has
excellent handling characteristics and can produce a molded product
having any complicated shape and also to provide a method of
producing the prepreg.
DISCLOSURE OF THE INVENTION
[0015] In order to solve the above problem, the fundamental
structure of the present invention is a prepreg produced by
impregnating a reinforced-fiber sheet with a matrix resin, being
characterized in that the prepreg comprises a continuous resin
layer which exists in an inside thereof, and at least one surface
of one side thereof is constituted of a resin-impregnated part
where an impregnated resin substantially exists and a fiber part
where an impregnated resin dose not substantially exist.
[0016] The aforementioned reinforced-fiber sheet means sheets in
which reinforced fibers such as carbon fibers and glass fibers are
arranged in the same directions and reinforced-fiber woven/knit
fabrics or nonwoven fabrics.
[0017] In the prepreg of the present invention, a fiber part where
an impregnated resin dose not substantially exist is formed on at
least one surface of the prepreg. Therefore, a plurality of the
aforementioned prepregs are laminated manually without using an
expensive apparatus such as an auto lay-up machine and also without
carrying out debulking. Even when these prepregs are cured by a
conventional method, for example, a vacuum bagging molding method,
no void is generated between layers and a molded article provided
with desired mechanical strength can be obtained.
[0018] This is because the aforementioned fiber part on one surface
of the prepreg serves as a conduit through which the air trapped
between layers and volatile materials produced during molding are
allowed to escape. It is to be noted that the aforementioned fiber
part is filled with the resin because the resin around the fiber
part flows to the fiber part until the resin is completely cured
during molding.
[0019] Moreover, the aforementioned one surface is sufficiently
impregnated with the resin and therefore a resin-impregnated part
where an impregnated resin substantially exists is formed. The
adhesion between the upper and lower layers when these layers are
laminated is properly obtained, which improves the handling
characteristics of the prepreg.
[0020] The present invention may take a sea-island structure in
which the aforementioned fiber part constitutes a sea portion and
the aforementioned resin-impregnated part constitutes an island
portion.
[0021] Such a structure in which the fiber part constitutes a sea
portion and the resin-impregnated part constitutes an island
portion permits the escape of the air and volatile materials
trapped between layers to the outside efficiently and effectively.
Preferably, the area of the island portion is 1 to 80%, and more
preferably 2 to 50% of the total area of the one surface of the one
side of the prepreg.
[0022] When the area of the island portion is less than 1% of the
total area of the one surface, there is a fear that the adhesion
between the upper and lower layers when these layer are laminated
is insufficient and it is therefore difficult to handle the
prepreg. Also, when the area of the island portion exceeds 80% of
the total area of the one surface, the fiber part is instantly
clogged by the fluidization of the surrounding resin when molding,
so that the air and volatile materials trapped between layers are
allowed to escape incompletely, arousing a fear that remaining air
forms voids inside of a molded article.
[0023] Preferably, the center distance between adjacent island
portions is 1 to 10 mm, and more preferably 2 to 5 mm. When the
island portions are formed such that the center distance between
the adjacent island portions is in the above range, the air and
volatile materials trapped between layers are allowed to escape
externally smoothly and completely.
[0024] The fundamental structure adopted to produce such a prepreg
in the present invention is based on a method of producing a
prepreg, the method comprising impregnating a reinforced-fiber
sheet with a matrix resin so as to form a continuous resin layer at
least in an inside thereof; and applying a protective film having
an irregular surface to at least one surface of one side of the
reinforced-fiber sheet impregnated with the matrix resin.
[0025] Further preferably, only a convex portion of the irregular
surface is brought into contact with the reinforced-fiber sheet
impregnated with the matrix resin. Although no particular
limitation is imposed on the material of the reinforced fiber which
may be used in the present invention, carbon fibers, glass fibers,
alamide fibers, boron fibers and steel fibers and the like may be
used as the reinforced fiber. Among these fibers, carbon fibers are
preferably used because of good mechanical characteristics after
molding. As this carbon fibers, both polyacrylonitrile (PAN) type
carbon fibers and pitch type carbon fibers may be used.
[0026] The reinforced-fiber sheet used in the present invention is
not particularly limited in its shape and arrangement. Examples of
the reinforced-fiber sheet include those put in the form of a
sheet, cloth (woven fabric), tow, mat, knit or sleeve, in which
long fibers are arranged in the same direction.
[0027] Also, no particular limitation is imposed on the material of
the protective film and the material of the protective film may be
changed appropriately corresponding to the type of matrix resin in
consideration of the adhesion to the matrix resin. For example, a
polyethylene film which is conventionally used may be used as the
protective film.
[0028] Moreover, there is no particular limitation to the type of
matrix resin. As the resin used in the present invention,
thermosetting resins are preferable. Examples of the thermosetting
resins include epoxy resins, polyester resins, vinyl ester resins,
phenol resins, maleimide resins, polyimide resins and BT resins
(manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.) obtained by
combining a cyanate ester with a bismaleimide resin. It is
preferable to use epoxy resins.
[0029] As the epoxy resin, a bisphenol A-type epoxy resin,
bisphenol F-type epoxy resin, biphenyl type epoxy resin,
naphthalene type epoxy resin, dicyclopentadiene type epoxy resin
and fluorenone type epoxy resin which are difunctional resins and
combinations of these resins may be preferably used.
[0030] Further, tri- or more or polyfunctional epoxy resins may be
used. As these polyfunctional epoxy resins, a phenol novolac type
epoxy resin, cresol type epoxy resin, glycidylamine type epoxy
resins such as tetraglycidyldiaminodiphenylmethane,
triglycidylaminophenol and tetraglycidylamine, glycidyl ether type
epoxy resins such as tetrakis(glycidyloxyphenyl)ethane and
tris(glycidyloxymethane) and combinations of these resins are
preferably used.
[0031] It is preferable to add a hardener to the matrix resin in
the present invention. Examples of the hardener include aromatic
amines such as diphenylmethane and diaminodiphenylsulfone,
aliphatic amines, imidazole derivatives, dicyandiamide,
tetramethylguanidine, thiourea addition amines, carboxylic acid
anhydrides such as a methylhexahydrophthalic acid anhydride,
carboxylic acid hydrazide, carboxylic acid amide, polyphenol
compounds, novolac resins, polymercaptan and Lewis acid complexes
such as trifluoride ethylamine complex.
[0032] Also, microcapsulated materials of these hardeners may be
preferably used to improve the preserving stability of the prepreg.
These hardeners may be combined with a proper hardening promoter to
improve hardening activity. Preferable examples of the combination
include a combination of dicyandiamide with a urea derivative such
as 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) or an imidazole
derivative as the hardening promoter and a combination of a
carboxylic acid anhydride or novolac resin with a tertiary amine as
the hardening promoter.
[0033] Also, these epoxy resin and hardener or a material obtained
by pre-reacting a part of these materials may also be compounded in
the matrix resin composition. There is the case where this method
is effective to control the viscosity and to improve the preserving
stability.
[0034] Further, in addition to the above structural elements of the
matrix resin, a thermoplastic resin may be compounded for the
purpose of controlling the viscosity of the resin and the handling
characteristics of the prepreg. In this case, an appropriate resin
is selected in consideration of the compatibility with the epoxy
resin and taking into account avoiding an adverse influence on the
physical properties of a composite material when it is made into
the composite material. Preferable examples of the resin include a
polyvinylformal, polyvinylbutyral, polyethylene oxide,
polymethylmethacrylate, polyamide, polyester, polyether sulfone,
polysulfone, polyetherimide and polyinmide and the like. Also, two
or more of these resins may be combined.
[0035] Also, rubber particles, soluble rubbers or rubbers having a
core-shell structure may be contained as additives. These additives
are partly dissolved at least in a mother resin or are not
dissolved but exist in the state of particles. In order to obtain a
high-quality prepreg in the present invention, the particles are
preferably pulverized or dissolved in advance so that particles
having a particle diameter of about 50 .mu.m or more are
substantially not contained when these rubber materials exist in
the state of particles.
[0036] In the production method of the present invention, first,
the reinforced-fiber sheet is impregnated with the matrix resin by
a conventional method. For example, the matrix resin is applied
evenly to the surface of releasable paper and the reinforced-fiber
sheet is applied to the surface of the resin to impregnate the
sheet with the resin. In the prepreg produced by this method, the
reinforced-fiber sheet is impregnated with the matrix resin in the
condition that the matrix resin is localized on one side of the
reinforced-fiber sheet, namely on the surface of the sheet on the
side of the releasable paper.
[0037] Alternatively, the reinforced-fiber sheet may be sandwiched
from both sides thereof by releasable paper coated evenly with the
matrix resin to impregnate the reinforced-fiber sheet with the
resin. The prepreg obtained by this method is entirely impregnated
evenly with the resin. If the reinforced-fiber sheet is impregnated
with the resin by these conventional methods, a continuous resin
layer is formed at least in the inside.
[0038] Next, the irregular surface of the protective film having
the irregular surface is applied to at least one of the surfaces of
the prepreg. In the case where, for example, the releasable paper
is applied to only one surface, it is preferable to apply the
protective film to the other fiber-rich surface. Also, when the
releasable paper is applied to both surfaces, at least the
releasable paper applied to one surface is peeled off and the
protective film is applied to the exposed surface.
[0039] The protective film is applied to the reinforced-fiber sheet
in the condition that the convex portion thereof is in close
contact with the sheet impregnated with the resin and the concave
portion thereof is far from the sheet. At this time, the resin
included in the reinforced-fiber sheet is attracted to the
protective film side by surface tension at the portion where the
convex portion of the protective film is in close contact with the
sheet and that portion is resin-rich with the result that a
resin-impregnated part where an impregnated resin substantially
exists is formed. On the other hand, the position corresponding to
the concave portion of the protective film is distant from the
reinforced-fiber sheet impregnated with the resin and therefore the
aforementioned surface tension does not act, so that the resin
moves to the convex side or to the inside of the prepreg with the
result that the position corresponding to the concave portion is a
fiber part where an impregnated resin dose not substantially
exist.
[0040] In the method of producing such a prepreg, an excellent
prepreg whose surface is constituted of the aforementioned
resin-impregnated part and the fiber part and is therefore free
from the generation of voids during molding can be easily produced
by only altering the protective film, which is usually applied to
the surface of the prepreg when the prepreg is stored and conveyed,
into the film having an irregular surface. Because an outstandingly
big-scale apparatus is not required in this method, it has no
influence on its production cost.
[0041] In the production method of the present invention which
utilizes the contact with the irregular surface of the protective
film and the surface tension of the resin, the development of a
sea-island structure comprising the resin-impregnated part and the
fiber part on the surface of the prepreg is a phenomenon which
depends on the viscosity of the resin with time.
[0042] This implies that the viscosity of the matrix resin is kept
at 10000 Poise or less for 4 hours or more in the situation where
the protective film is applied to the reinforced-fiber sheet. This
also implies that the temperature of the matrix resin is kept at 30
to 150.degree. C. for 4 hours or more in the situation where the
protective film is applied to the reinforced-fiber sheet.
[0043] If the impregnated resin is put in the state that it has a
viscosity of a fixed value or less or put at a fixed temperature
for 4 hours or more, the resin is moved sufficiently to the surface
which is in contact with the convex portion to thereby form a
resin-impregnated part and a fiber part distinctly.
[0044] Generally, the viscosity of the resin is dropped by raising
the temperature to be kept at this time. Although this viscosity of
the resin differs depending on the type of matrix resin, the
temperature to be kept is preferably designed to be 30.degree. C.
or more. When the temperature is too high, there are the cases
where the curing reaction of the resin becomes so fast that plenty
of time required for the movement of the resin is not secured and
where the tack characteristics of the prepreg when the prepreg is
afterward stored at ambient temperature is impaired. Therefore, the
temperature to be kept is made to be preferably 150.degree. C. or
less.
[0045] The irregular surface of the protective film is formed of a
number of independent convex portions. The use of the protective
film having such an irregular surface ensures the formation of a
prepreg having a surface provided with a resin-impregnated part
constituting an island portion and with a fiber part constituting a
sea portion.
[0046] Further preferably, the irregular surface of the protective
film is disposed with dispersing a number of convex portions
uniformly on a surface of the film. The uniform dispersion of the
convex portions leads to uniform presence of resin-impregnated
parts relative to fiber parts on the surface of the obtained
prepreg. Molded products formed from the prepregs resultantly have
uniform resin density and fiber density. Although the convex
portions are desirably dispersed uniformly for the above reason,
these convex portions may be dispersed nonuniformly, of course.
[0047] Further preferably, a center distance between the adjacent
convex portions is 1 to 10 mm, and more preferably 2 to 5 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] FIG. 1 is a plan view of a prepreg in a preferred embodiment
of the present invention.
[0049] FIG. 2 is a sectional view taken along the line II-II in
FIG. 1.
[0050] FIG. 3 is an explanatory view showing a bagging method.
[0051] FIG. 4 is a graph showing curing conditions.
[0052] FIG. 5 is a graph showing curing conditions.
[0053] FIG. 6 is a graph showing curing conditions.
BEST MODE FOR CARRYING OUT THE INVENTION
[0054] Embodiments of the present invention will be explained in
detail with reference to the drawings.
[0055] FIG. 1 is a plan view of a prepreg in a preferred embodiment
of the present invention and FIG. 2 is a sectional view taken along
the line II-II in FIG. 1.
[0056] The prepreg 1 is constituted of a reinforced-fiber sheet 2
and a matrix resin 3 with which the sheet 2 is impregnated. As the
reinforced-fiber sheet, sheets in which reinforced fibers such as
carbon fibers and glass fibers are arranged in the same direction
and woven or nonwoven fabrics of reinforced fibers may be used.
[0057] The prepreg 1 is impregnated with the resin 3 locally on the
backside thereof and a continuous resin layer 3a exists therein.
Further, on the surface of the prepreg 1, the resin is sufficiently
impregnated in the reinforced-fiber sheet and the prepreg 1 is
constituted of a resin-impregnated part 3b where an impregnated
resin substantially exists and a fiber part 2a where the resin dose
not substantially exist and the above reinforced fiber is
exposed.
[0058] The prepreg 1 has a sea-island structure in which the above
fiber part 2a constitutes a sea portion and the above
resin-impregnated part 3b constitutes an island portion, wherein
the resin-impregnated part 3b exists independently. In this
embodiment, the surface of the resin-impregnated part 3b has a
rhomboid shape and the resin-impregnated parts 3b are regularly
arranged herringbone-wise at equal intervals. The center distance
between the adjacent resin-impregnated parts 3b is preferably 1 to
10 mm. Further, the area of the resin-impregnated part 3b which is
the island portion is preferably 1 to 80% of the total surface
area. In this case, the shape and arrangement of this
resin-impregnated part 3b may be properly altered in its design
corresponding to the fluidity and tack characteristics of the
resin.
[0059] The production of the prepreg having such a structure
comprises, first, impregnating one surface of the reinforced-fiber
sheet with the matrix resin in such a manner as to form a
continuous resin layer at least in the inside of the prepreg. For
example, a fixed amount of the matrix resin is applied to the
surface of the releasable paper, the reinforced-fiber sheet is
supplied to the surface of the matrix resin and then the
reinforced-fiber sheet is made to be impregnated with the resin
using a means of passing a press roll, whereby a prepreg
impregnated with the resin locally on one surface side can be
obtained.
[0060] Alternatively, the reinforced-fiber sheet may be sandwiched
from both sides thereof by releasable paper coated evenly with the
matrix resin of a fixed amount and then, for example, a means of
passing a press roll is used, whereby a prepreg impregnated with
the resin on the entire surface thereof can be obtained.
[0061] In the case of the prepreg impregnated with the resin
locally at least on one surface of the prepreg having a continuous
resin layer at least in the inside, a protective film having an
irregular surface is applied to the reinforced-fiber sheet such
that the aforementioned irregular surface faces other surface side
opposite to the side impregnated locally with the resin. At this
time, only the convex portion of the irregular surface of the
protective film is in close contact with the reinforced-fiber
sheet.
[0062] In the situation where the protective film is applied to the
reinforced-fiber sheet impregnated with the resin, the viscosity of
the resin is kept at 1000 Poise or less for 4 hours or more, or the
temperature is kept at 30 to 60.degree. C. for 4 hours or more. In
the reinforced-fiber sheet, the resin inside of the sheet is moved
to the surface side by its surface tension at the portion where the
convex portion is in close contact therewith.
[0063] As a result, on the surface of the reinforced-fiber sheet 1,
as shown in FIG. 1, the portion with which the convex portion is in
close contact is the resin-impregnated part 3b where the resin is
sufficiently impregnated and the impregnated resin substantially
exists and the portion corresponding to the concave portion of the
protective film which the protective film is not in close contact
with the resin is the fiber part 2a where the resin dose not
substantially exist.
[0064] Such movement of the resin due to surface tension is
observed even in a reinforced-fiber sheet which is entirely
impregnated with the resin and the resin substantially exists on
the entire surface. In the case of applying a protective film with
irregular surface to the surface on which the resin exists
entirely, the resin around a portion where the convex portion of
the protective film is in close contact with the sheet moves to the
portion on the reinforced-fiber sheet. The portion which is in
close contact with the convex portion is sufficiently impregnated
with the resin and becomes a resin-impregnated part where the
impregnated resin substantially exists and the part surrounding the
resin-impregnated part becomes a fiber part where no resin
substantially exists.
[0065] As the protective film, a polyethylene film which is
conventionally used as a protective film is preferably used.
However, this film may be altered corresponding to the type of
matrix resin taking the adhesion to the matrix resin into
account.
[0066] The protective film preferably has at least one irregular
surface in which, particularly, the convex portions form island
portions in the concave portion as a sea portion where each convex
portion exists isolatedly. Further, the convex portions are
preferably arranged uniformly and regularly.
[0067] Also, the area of the convex portions is 1 to 80% and
preferably 4 to 50% of the total area of the protective film. Also,
the center distance between adjacent convex portions is 1 to 10 mm
and preferably 2 to 5 mm.
[0068] Specific examples of the present invention and comparative
examples will be hereinafter explained.
[0069] It is to be noted that in the following examples, a
polyethylene embossed film with irregularities on the surface
thereof is used as a protective film with irregular surface. In the
irregular pattern of the embossed film, rhomboid convex portions
having diagonal lengths of 4 mm.times.2 mm are arranged
herringbone-wise at intervals of 0.5 mm.
[0070] The area of a resin-impregnated part where the impregnated
resin substantially exists was measured in the following
manner.
[0071] The resulting prepreg was set to the Microscope VH-6000
manufactured by KEYENCE CORPORATION and the field of view was set
to 13 mm (width).times.13 mm (length) (magnification: 25) to
observe the prepreg reflected on a display. The outline of the
resin-impregnated part where the impregnated resin substantially
exists on the part of 9 mm.times.7 mm in the filed of view was
traced by a cursor on the display to input the outline to a
calculator for calculating the total area. It is to be noted that
the magnification was set to 25 and a scale was placed within the
field of view to calibrate prior to the measurement.
EXAMPLE 1
[0072] An epoxy resin composition having the composition A shown in
Table 1 was prepared. This resin was applied uniformly to
releasable paper such that the areal weight of the resin was 108
g/m.sup.2, to prepare a resin film. Also, a reinforced-fiber sheet
was a sheet-like product obtained by arranging carbon fibers (trade
name: TR30S, manufactured by Mitsubishi Rayon Co., Ltd., tensile
elastic modulus: 235 GPa) in the same direction. The resin film and
the reinforced-fiber sheet were used to manufacture a uni-direction
prepreg in which the areal weight of carbon fiber (hereinafter
referred to as "FAW") was 200 g/m.sup.2 and the resin content
(hereinafter referred to as "RC") was 35%.
[0073] The aforementioned embossed film was applied to the prepreg
such that the irregular surface of the embossed film is faced to
the surface side of the prepreg, which was then placed in an
atmosphere kept at 80.degree. C. for 4 hours.
[0074] The resin was penetrated into the inside of the prepreg at
the position corresponding to the concave portion of the embossed
film on the surface of the resulting prepreg and this position was
a fiber part where no resin substantially existed on the surface of
the prepreg. Also, the position corresponding to the convex portion
of the embossed film on the surface of the prepreg was sufficiently
impregnated with the resin and constituted a resin-impregnated part
which was resin-rich and the impregnated resin substantially
existed. It was confirmed that tacking characteristics allowing
laminating works sufficiently were secured in such a prepreg.
[0075] As shown in FIG. 3, a releasable film 5 comprising a
copolymer of tetrafluoroethylene and ethylene was arranged and
laminated on both sides of a prepreg stack 4 obtained by laminating
eight prepregs obtained as described above such that the directions
of the fibers of these prepregs were
-45.degree./90.degree./+45.degree./0.degree./0.degree./+45.degree./9-
0.degree./-45.degree., respectively.
[0076] This laminate was placed on a base plate 6 comprising a
5-mm-thick aluminum thin plate coated with a releasing agent.
Moreover, a surface breather 7 made of glass fiber woven fabric and
a bagging film 8 made of nylon were laminated in this order on the
upper surface of the laminate, followed by bagging and then cured
in the condition shown in FIG. 4.
[0077] Here, the periphery of a releasable film 4 arranged on both
sides of a prepreg stack 4 except for a part thereof was sealed
with a highly viscous resin. A braid 9 made of glass fiber was
disposed and a glass yarn 10 was disposed in the inside thereof in
the unsealed opening portion to promote the exhaust of air, to draw
off the air from the film 4 in advance. Then, the composite
material was sealed with a seal agent 11, leaving all the periphery
of the base plate 6 and bagging film 8.
[0078] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, any void which had an influence on
the strength of the composite material was not observed between the
layers of the prepreg.
EXAMPLE 2
[0079] A uni-direction prepreg having a FAW of 200 g/m.sup.2 and a
RC of 35% was manufactured in the same manner as in Example 1
except that an epoxy resin composition was altered to the
composition B shown in Table 1. The aforementioned embossed film
was applied to the prepreg such that the irregular surface of the
embossed film is faced to the surface side of the prepreg, which
was then kept in an atmosphere at a temperature of 50.degree. C.
for 12 hours.
[0080] The obtained prepreg had the same structure as in Example 1
and had good tacking characteristics.
[0081] The resulting prepreg was observed by Microscope VH-6000
manufactured by KEYENCE CORPORATION to find that the area ratio of
a resin-impregnated part where the impregnated resin substantially
exists was 30.4%.
[0082] Then, the obtained eight prepregs were laminated in the same
manner as in Example 1, subjected to bagging carried out as shown
in FIG. 3 and cured in the condition shown in FIG. 5.
[0083] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, any void which had an influence on
the strength of the composite material was not observed between the
layers of the prepreg.
EXAMPLE 3
[0084] A uni-direction prepreg having a FAW of 200 g/m.sup.2 and a
RC of 35% was manufactured in the same manner as in Example 1
except that an epoxy resin composition was altered to the
composition C shown in Table 1. The aforementioned embossed film
was applied to the prepreg such that the irregular surface of the
embossed film is faced to the surface side of the prepreg, which
was then kept in an atmosphere at a temperature of 130.degree. C.
for 10 hours.
[0085] The obtained prepreg had the same structure as in Example 1
and had good tacking characteristics.
[0086] Then, the obtained eight prepregs were laminated in the same
manner as in Example 1, subjected to bagging carried out as shown
in FIG. 3 and cured in the condition shown in FIG. 6.
[0087] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, any void which had an influence on
the strength of the composite material was not observed between the
layers of the prepreg.
EXAMPLE 4
[0088] An epoxy resin composition having the composition A shown in
Table 1 was prepared. This resin was applied uniformly to
releasable paper such that the areal weight of the resin was 54
g/m.sup.2, to prepare a resin film. Also, a reinforced-fiber sheet
obtained by arranging carbon fibers (trade name: TR30S,
manufactured by Mitsubishi Rayon Co., Ltd., modulus of elasticity
in tension: 235 GPa) sheet-wise in the same directions was put
between the above resin films and pressed from both sides thereof.
The sheet was heated to manufacture a uni-direction prepreg having
a FAW of 200 g/m.sup.2 and a RC of 35%.
[0089] The aforementioned embossed film was applied to the prepreg
such that the irregular surface of the embossed film is faced to
the surface side of the prepreg, which was then placed in an
atmosphere kept at 80.degree. C. for 4 hours.
[0090] The obtained prepreg had the same structure as in Example 1
and had good tacking characteristics.
[0091] Eight prepregs obtained as described above were laminated
such that the directions of the fibers of these prepregs were
-45.degree./90.degree./+45.degree./0.degree./0.degree./+45.degree./90.deg-
ree./-45.degree., respectively, subjected to bagging as shown in
FIG. 3 and then cured in the condition shown in FIG. 4.
[0092] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, any void which had an influence on
the strength of the composite material was not observed between the
layers of the prepreg.
EXAMPLE 5
[0093] An epoxy resin composition having the composition A shown in
Table 1 was applied uniformly to releasable paper to prepare a
resin film having a resin areal weight of 133 g/m.sup.2. This resin
film and a carbon fiber cloth TR3110 manufactured by Mitsubishi
Rayon Co., Ltd. were used to obtain a cloth prepreg in which no
resin substantially existed on the surface side and the resin was
impregnated locally on the backside, the prepreg having a FAW of
200 g/m.sup.2 and a RC of 40%.
[0094] An embossed film was applied to the surface of the prepreg,
which was then kept in an atmosphere at 80.degree. C. for 5 hours.
After that, when the embossed film was peeled off, the resin was
penetrated into the inside of the prepreg at the position
corresponding to the concave portion of the embossed film on the
surface of the prepreg and a fiber part where no resin
substantially existed was formed on the surface of the prepreg.
Also, the position corresponding to the convex portion of the
embossed film on the surface of the prepreg was sufficiently
impregnated with the resin and constituted a resin-impregnated part
which was resin-rich and the impregnated resin substantially
existed and the retention of tack enough to carry out a laminating
operation was confirmed.
[0095] Using the prepregs, an 8-ply prepreg was formed by
lamination, subjected to bagging as shown in FIG. 3 and cured in
the condition shown in FIG. 4. Then, the section of the composite
material was observed, to find that no void was observed between
layers.
COMPARATIVE EXAMPLE 1
[0096] An epoxy resin composition having the composition A shown in
Table 1 was used and applied uniformly to releasable paper such
that the areal weight of the resin was 54 g/m.sup.2, to prepare a
resin film. Also, a reinforced-fiber sheet obtained by arranging
carbon fibers (trade name: TR30S, manufactured by Mitsubishi Rayon
Co., Ltd.) sheet-wise in one direction was put between the above
resin films and pressed from both sides thereof to impregnate the
sheet with the resin. Thereafter, the upper releasable paper was
peeled off to obtain an uni-direction prepreg having a FAW of 200
g/m.sup.2 and a RC of 35%.
[0097] A polyethylene film with a smooth surface was applied to the
side of the prepreg to which the releasable paper was not stuck,
which was then placed in an atmosphere kept at 80.degree. C. for 5
hours.
[0098] In the obtained prepreg, the resin was uniformly impregnated
in the inside of the carbon fiber tow and the resin existed
uniformly also on the surface of the prepreg. The tack was strong
and the surface of the prepreg was sticky.
[0099] Using the above prepregs, the polyethylene film with a
smooth surface was peeled off and immediately, eight prepregs
obtained as described above were laminated such that the directions
of the fibers of these prepregs were
-45.degree./90.degree./+45.degree./0.degree./0.degree./+45.degree./90.deg-
ree./-45.degree., respectively, subjected to bagging as shown in
FIG. 3 and then cured in the condition shown in FIG. 4.
[0100] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, a great number of voids was observed
between the layers of the prepreg.
COMPARATIVE EXAMPLE 2
[0101] A uni-direction prepreg having a FAW of 200 g/m.sup.2 and a
RC of 35% was obtained in the same manner as in Comparative Example
1 except that an epoxy resin composition having the composition B
shown in Table 1 was used. A polyethylene film with a smooth
surface was applied to the side of the prepreg to which the
releasable paper was not stuck, which was then placed in an
atmosphere kept at 50.degree. C. for 12 hours.
[0102] In the obtained prepreg, the resin was uniformly impregnated
in the inside of the carbon fiber tow and the resin existed
uniformly also on the surface of the prepreg. The tack was strong
and the surface of prepreg was sticky.
[0103] The prepregs were treated in the same manner as in
Comparative Example 1. Namely, the polyethylene film with a smooth
surface was peeled off and immediately, eight prepregs obtained as
described above were laminated such that the directions of the
fibers of these prepregs were
-45.degree./90.degree./+45.degree./0.degree./0.degree./+45.degree./90.deg-
ree./-45.degree., respectively, subjected to bagging as shown in
FIG. 3 and then cured in the condition shown in FIG. 5.
[0104] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, a great number of voids were observed
between the layers of the prepreg.
COMPARATIVE EXAMPLE 3
[0105] A prepreg was manufactured in the same manner as in
Comparative Example 1 except that an epoxy resin composition having
the composition C shown in Table 1 was used. A polyethylene film
with a smooth surface was applied to the side of the prepreg to
which the releasable paper was not stuck, which was then placed in
an atmosphere kept at 130.degree. C. for 10 hours.
[0106] In the obtained prepreg, the resin was uniformly impregnated
in the inside of the carbon fiber tow and the resin existed
uniformly also on the surface of the prepreg. The tack was strong
and the surface of prepreg was sticky.
[0107] The prepregs were treated in the same manner as in
Comparative Example 1. Namely, the polyethylene film with a smooth
surface was peeled off and immediately, eight prepregs obtained as
described above were laminated such that the directions of the
fibers of these prepregs were
-45.degree./90.degree./+45.degree./0.degree./0.degree./+45.degree./90.deg-
ree./-45.degree., respectively, subjected to bagging as shown in
FIG. 3 and then cured in the condition shown in FIG. 6.
[0108] The section of the resulting plate composite material was
abraded to observe the section by using an optical microscope at a
magnification of 50. However, a great number of voids were observed
between the layers of the prepreg.
COMPARATIVE EXAMPLE 4
[0109] An epoxy resin composition having the composition A shown in
Table 1 was applied uniformly to releasable paper to prepare a
resin film having a resin areal weight of 133 g/m.sup.2. This resin
film and a carbon fiber cloth TR3110 manufactured by Mitsubishi
Rayon Co., Ltd. were used to obtain a cloth prepreg in which the
entire carbon fiber cloth was impregnated with the resin.
[0110] A polyethylene film having a smooth surface without any
irregularity was applied to the surface of the prepreg, which was
then kept in an atmosphere at 80.degree. C. for 5 hours.
[0111] When the film was peeled off from the cloth prepreg obtained
in this manner, the entire surface of the prepreg was covered with
the resin. The tack was strong and the surface of the prepreg was
sticky.
[0112] Using the prepregs, an 8-ply prepreg was formed by
lamination in the same manner as in Example 4, subjected to bagging
as shown in FIG. 3 and cured in the condition shown in FIG. 4.
Then, the section of the composite material was observed, to find
that many voids were observed between layers. TABLE-US-00001 TABLE
1 Resin composition Manufacturer A B C Ep828 Yuka-Shell Epoxy Co.,
Ltd. 60 60 60 Ep1001 Yuka-Shell Epoxy Co., Ltd. 40 40 40
Dicyanamide Yuka-Shell Epoxy Co., Ltd. 5 Dichloromethyl HODOGAYA
CHEMICAL CO., LTD. 5 urea HX3613 Asahi Kasei Epoxy Co., Ltd. 10
Seika Cure S WAKAYAMA SEIKA KOGYO CO., 30 LTD. Unit: Part by
weight
* * * * *