Note: Descriptions are shown in the official language in which they were submitted.
~z~s~
FIBER REINFORCED RESIN MOLDED ARTICLES FOR ELECTROMAGNETIC
WAVES AND METHOD FOR PRODUCTION THEREOF
. ,
ACKGROUND OF THE INVENTION
(i) Field of the Invention:
This invention relates to a fiber reinforced resin
molded article for electromagnetic waves. More particu-
larly, this invention relates to a fiber reinforced resin
(hereinafter sometimes referred to as FRP) molded article
which contains an electroconductive nonwoven fabric-resin
composite layer having a flat or curved surface and
provides the properties of uniformly reflecting and
shielding VHF or shorter electromagnetic waves, and to a
method ~or production thereof. Some molded articles of
tne present invention are especially useful as antennas
for receiving or transmitting electromagnetic waves in the
range of VHF to EHF.
(ii) Description of the Prior Art:
Hitherto, for providing resin molded articles with
electromagnetic wave-reflecting properties (hereinafter
referred to as EMWR properties) or electromagnetic wave-
shielding properties (hereinafter referred to as EMWS
properties or EMI shielding properties), there have been
conducted coating of substrate articles with electrocon-
ductive paints; application of metallic materials on the
substrate articles by means of flame spraying, chemical
plating, vapor deposition, spattering, or ion-plating;
. .
~ 2~S9!~7
addition of electroconductive fillers, Metal foils, rnetal
fibers, metal ribbons or metal flakes to the molding
resins; and the like. The application oE these materials
to thermo-setting resin articles, however, had some troubles
with respect to performances, stability, costs and/or
processability of the resulting products. For example
coating with electroconductive paints caused oxidative
deterioration, formation of cracking and peeling, etc.
The flame spraying of metals required a large apparatus with
high cost, needed a pre-treatment step, and also causedjtoxic
metal vapors. In the chemical plating, the plastics to be
plated are restricted to ABS resin and some other similar
resins, and also a costly apparatus is required.
In the case of a parabola antenna for reflecting
electromagnetic waves, such antennas of metal (normally of
aluminum) have been fabricated carefully with high cost and
can hardly be repaired when the reflective surface thereof
was once damaged.
In the case of a parabola antenna made of FRP, the
reflective surface thereof having uniformly electroconductive
surface is required in order to obtain necessary performances.
In this connection, it has been considered that an electro~
conductive nonwoven fabric can not be used successfully for
the above mentioned purpose in a compression molding method,
because the fibers of the nonwoven fabrics are moved or
broken by the molding pressure and ununiform flow of a resin
component, etc. and an ununiform reflective surface is
produced. Thus, an FRP plate having the EMWR or EMWS
lS~7
properties, wherein a sheet molcling compound containing a
larqe amoun-t of an electroconductive short fiber is used
instead of the nonwoven fabric, has been produced by
compresslon molding. The performance of this FRP plate
containing such short fiber and no nonwoven fabric, however,
is unstable because the electroconductive short fiber is
dispersed ununiformly throughout the FRP body by the
compression molding step to give an ununiform reflective
surface. See, for example, CONDUCTIVE POLYMER (1981),
pages 49-55, Plenum Publishing Corporation, New York.
Even when an extremely large amount of the short fiber and
resin materials are used regardless of high costs, the
resulting FRP plate contains a very thick, ununiformly
dispersed electroconductive layer which may fail to eY~hibit
uniformly reflecting properties.
A hand lay-up molding method has problems in both
precise surface characteristics and productivity. An
injection molding method suffers from precise surface charac-
teristics of the resulting product. Such inferior surface
characteristics as waviness on the surface caused by
shrinkage upon hardening of resin materials have adverse
effects on reflective loss of electromagnetic waves and
reflecting properties as well as on antenna performances.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an FRP
molded article for electromagnetic waves having the properties
of uniformly reflecting and shielding VHF or shorter electro-
~Z~'~L5~7
magnetic waves, and a method for production thereof.Another object of the present invention is to provide the
above mentioned molded article onto the surface of which a
protective and/or decorative resin layer is further applied,
and a method for production thereof. A further object of
the present invention is to provide antennas (e.g., of a
parabolic shape) composed of the molded article having a
curved, e.g. concave, reflective surface for receiving or
transmitting electromagnetic waves. Other objects and
features of the present invention will become apparent from
the following description.
Thus in accordance with the present invention, there is
provided an FRP molded article for electromagnetic waves
having the properties of uniformly reflecting and shielding
electromagnetic waves, which comprises or consists essentially
of a compression-molded crosslink-cured resin-fiber material
laminated structure having a plane or curved reflective
surface co~prisinga surface layer, an intermediate layer
and a substrate layer; said surface layer being an electro-
conductive nonwoven fabric-cured resin composite layer having
an effective layer thickness of at least about 0.005mm; said
intermediate layer being a woven fabric-cured resin composite
layer having an effective layer thickness of at least about
0.005mm, said fabric having a mesh size of not larger than
about 5 mesh ; and said substrate layer being an FRP layer.
As necessary, there is also provided the above mentioned
molded article having a top protective and/or decorative
5~7
resin layer on the nonwoven fabric-resin composite layer.
The top resin layer may contain pigment.
The above mentioned molded article for electromagnetic
waves of the present invention can be advantageously
produced according to the present method for production which
comprises steps of placing, on a mold having a desired
molding surface, an effective amount of an electroconductive
nonwoven fabric for the surface layer and then an effective
amount of a woven fabric for the intermediate layer, the non-
woven fabric and/or the woven fabric of which may be impreg-
nated (e.g. in the form of a prepreg) with a liquid
crosslink-curable resin composition or may not ; placing
thereon a mixture of a reinforcing fiber material and a liquid
crosslink-curable resin composition for the substrate layer,
the compound viscosity of the resin composition being not
more than about S x 108 cps ; and then compressing the
laminated materials under a molding pressure of about 25 to
about 100 kgf/cm2 and at a mold closi`ng speed of not more
than about 2~0 mm/minute and curing the resin composition ;
whereby the flow of the liquid resin composition into the
nonwoven fabric layer in the course of compression is
substantially controlled in such a direction that the liquid
resin composition passes through the interstices of the ~oven
fabric to prevent the nonwoven fabric from ununiformly
dispersing and/or fracturing. The above mentioned pro-
tective and/or decorative surface resin layer can be provided
either by applying the top resin layer onto the molded
article or by applying a resin material onto a molding
~L2~L459~7
surface of the mold and -then molding the article.
Incidentally, the liquid crosslink-curable resin compo-
sition to be used in the present invention normally comprises
a crosslinkable resin, a copolymeri~able monomer or a
compound for addition polymeri~ation, and preferably a
hardening agent such as a catalyst, which may further contain
a thickener such as magnesium oxide, a releasing agent and
an optional component such as fillers. This resin compo-
sition is generally referred to as "compound". The term
"compound viscosity" herein means the viscosity of such a
resin composition measured by means of a B-type Helipath
viscometer supplied by Brookfield Engineering Laboratories,
U.S.A.
Incidentally, the term "mesh" herein means the number
of openings per linear inch of the woven fabric.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of the molded
article consisting of surface, intermediate and substrate
layers according to the present invention. FIG. 2 is a
schematic cross-sectional view of the present molded article
having a protective and/or decora-tive top resin layer thereon.
FIG. 3 is a schematic plane view showing a fractured nonwoven
fabric according to a comparative example 4 herein.
DETAILED DESCRIPTION OF THE INVENTION
The term "the molded article having properties of
uniformly reflecting and shielding electromaynetic waves"
-- 6
~Z44S47
usecl ht-~rein Ineans that the molc1etl artiele has a substantially
smooth reElective surface for electromagnetic ~1aves, has the
property ol regularly reflecting e]ectrornaclnetic waves
without rorlning ~ ase tiifference such as phase lacJ o~ the
~7aves in a pretleterllined tiirection, and also hclS the property
of preventing penetration of e~leetroinagl1etie waves the~retlrrough
~7ithout substantially irregular refleetion of the waves.
Thus, the rnoldecl article .aeeording to the present inventio
ean be advantageously used, by utilizing its uniforlnly
refleeting proper:ty, as a curved or plane refleeting sheet
or board for eleetromagnetic t7aves sueh as reflecting antennas
as well as a plane or eurved shielding sheet or l~oard ~7hieh
~oes not eause irregular reflection of electromagnetic ~aves
in an undesirable direction. The present molded artieles for
electron~agnetic waves are useful for electrolllagnetic waves in
the range of VHI' to E~, and especially useful for electro-
macJnetic ~:7aves havincJ a wave length OL abOUt 100 ~illz to about
lO0 GHz but are not always restricted to sueh a ~7ave lensth.
The electroconductive nonwoven fabric nentioned above
generally means a nonwoven abrie of inorganie, metallie or
organie fibers having eleetroeonduetivity o~ at least about
l x lO ohm-lem~l, preferably about l x lQ2 ohm~lem~l or
more, more preferably about l 7' 103 ohln~lem~l or more.
'~he fibers or the non~over. fabric include, for example,
metal fibers, carbcn fibers, inorganic or organic fibers
surface-coatetl fuLly or partly ~itlt1 a rnetal (e.g. with
about 5 to about 5~ by weig}1-t of metal), electro-
conductive synthetic fibers and mixtures thereof, whiclt1 are
generally commercially availablt-~. The non~oven fabric of
45~7
metal-coated ylass fibers is normally employed. The
diameter of the electroconductive fibers is preferably as
small as possible for the EMWR and EMWS performances, and
is generally less than about 30 microns in diameter. The
above mentioned metal is exemplified by aluminum, nickel,
silver, copper, zinc, an alloy thereof, and the like.
Incidentally, the nonwoven fabric may contain some non-
electroconductive fibers if the electroconductivity is
not substantially impaired.
The amount of the electroconductive nonwoven fabric to
be used is required to be as dense as to prevent penetration
of electromagnetic waves therethrough. The nonwoven fabric-
resin composite layer should have an effective layer thickness
of at least about 0.005 mm. The upper limit of the amount
thereof to be used is not especially restricted, but the
larger amount is uneconomical. When the nonwoven fabric is
not impregnated with the liquid resin composition in advance,
the amount of the nonwoven fabric to be used is such that the
resin composition can permeate into the ~abric satisfactorily
in the course of compression molding. Thus, the thickness
of the nonwoven fabric-resin layer is generally in the range
OL about 0.005 to about 1 mm and typically in the range of
about 0.01 to about 0.2 mm. In this connection, the
thickness of nonwoven fabric materials to be used prior to
compression molding will be approximately in the range of
0.01 to 3 mm when not impregnated with the resin composition
and in the range of 0.01 to 2 mm when impregnated. For
example, such thickness corresponds to about 25 to about
-- 8
-
~24~59t7
900 g/m2 ancl preferably 50 to 300 g/m2 in the case of a
metal-coated glass fiber nonwoven fabric ancl to about 2~ to
about 400 g/m2 and preferably 30 to 200 g/m2 in the case of
a carbon fiber nonwoven fabric. These are referred to as
an effective layer thickness and an effective amount herein,
respectively.
Incidentally, when the electroconductive nonwoven layer
is replaced by an electroconductive woven fabric, the satis-
factory properties of uniformly reflecting and shielding
electromagnetic waves can hardly be obtained presumably
because of uneven surface of the woven fabric, interstices
of the woven fabric , and the like.
The woven fabric for the intermediate layer is to
control the flow of the liquid resin composition into the
nonwoven fabric layer in the course of compression molding
for preventing the nonwoven fabric from ununiform dispersion,
waviness and/or fracture. In other words, the intermediate
woven fabric layer is to control the flow of the resin
composition in such a direction that the liquid composition
passes through the interstices of the woven fabric and to
prevent the liquid composition from flowing substantially
laterally along the nonwoven fabric. Thus, it is required
that the woven fabric has such thickness ~molded thickness
of at least about 0.005 mm) and strength (e~g. tensile
strength of at least about 16 kgf/inch) as to control the
above mentioned flow of the liquid resin composition. It
is desired that the woven fabric has the interstices having
a mesh size of smaller than about 10 mesh and preferably
g
~2~4S~
smaller than about 16 mesh, because when the interstice is
too coarse the above mentioned control of the Elow becomes
difficult. The mesh size, however, should not be so small
as to lmpede the flow of the liquid composition.
Incidentally, the woven fabric should preferably have some
flexibility so that it can compress the nonwoven fabric
u.-liformly. There can be used ordinary inorganic, organic
or metallic woven fabrics having the above mentioned mesh
sizes which produce the intermediate layer having molded
thickness in the range of generally about 0.005 to about 2 mm
and typically about 0.01 to about 1 mm. In this connection,
the thickness of the woven fabric materials to be used prior
to compression molding will be approximately in the range of
0.01 to 2 mm. For example, such thickness generally
corresponds -to about 25 to about 400 g/m2 and preferably 60
to 200 g/m2 in the case of ordinary woven fabrics. These
are referred to as an effective layer thickness and an
effective amount herein, respectively. Incidentally, such
woven fabrics have a thread count of generally 11 to 60 and
typically 19 to 40 threads/25 mm.
There can be used reinforcing fiber materials of inorganic,
organic or metallic substance mixed or impregnated with a
liquid crosslinkable resin composition for the above mentioned
substrate layer. The fiber materials may be in the form of
short fibers, bulky fibers, nonwoven fabrics, woven fabrics
having coarse interstices or mixtures thereof, although low-
cost short fibers can be generally used with satisfactory
results. Normally, a so-called sheet molding compound or
-- 10 --
~;~4454~7
bulk molding compound, hereinafter reEerred to as SMC or BMC,
can be used advantageously. Incidentally, the SMC means
glass fiber chopped to about 1 inch, impregnated with a
crosslinkable resin composition and stored ln the form of
sheet. The sMC means glass fiber chopped to about ~ - ~ inch,
impregnated with a crosslinkable resin composition and stored
in the form of bulk. The amount to be used of the fiber
material impregnated with the resin composition is such as
to provide the present molded article with satisfactory
strength. The amount to be used is, for example, such as
to get the molded thickness of the substrate layer of at least
about 1.0 mm. The upper limit thereof will depend on the
dimensions of the molded article, which will be readily
selected by those skilled in the art. In general, the
amount of the fiber material impregnated with the resin com-
position to be used for the substrate layer will be such as
to get the molded thickness of the substrate layer in the
range of about 1 to about 10 mm. As necessary, the molded
thickness of the substrate layer can be larger than about
10 mm.
The crosslinkable resin to be used in the present
invention means a resin component which can form a crosslink-
cured resin by application thereto of heat ~e~g. about 80
to about 200C), a catalyst and/or a high-energy ionizing
radiation (e.g. gamma rays, electron beams, etc.). The
crosslinkable resins encompass (i) an ethylenically unsatu-
rated resin containing a multiplicity of ethylenical double
bonds which is substantially dissolved in an ethylenically
~124~5~7
unsaturated monomer, (ii) an addition-polymerizable multl-
functional resin and a compound for addition polymerization
such as acid anhydrides, alcohols, amines or mercaptans,
and the like.
The ethylenically unsaturated resins include, for
example, an unsaturated polyester resin, an allyl resin such
as diallyl phthalate polymers, a pendant-type unsaturated
resin such as vinyl ester resins, and mixtures thereof. The
reactive unsaturated monomers to substantially dissolve these
resins include, for example, vinyl monomers such as styrene
monomers, acrylonitrile, vinyl acetate and acrylic monomers ;
allyl monomers such as diallyl phthalate, and mixtures thereof.
The ratio of the resins to the monomers to be used is generally
in the range of about 80/20 to about 40/60 by weight. The
polymerization agents therefor are exemplified by a radical
polymerization catalyst such as organic peroxides, a redox
catalyst and, if used, a polymerization accelerator such as
organic amines, mercaptans or metal naphthenate.
The addition-polymerizable multifunctional resins
include, for example, an epoxy resin such as ~lycidyl epoxide
resins, which are used together with a substantially stoichio-
metric amount of a compound for addition polymerization such
as acid anhydrides.
The above mentioned crosslink-curable resins, polymer-
ization catalysts, polymerization accelerators, compounds
for addition polymerization are well known and can be readily
selected by those skilled in the art. Incidentally, the
above mentioned polymerization catalyst and accelerator can
- 12 -
L54t7
be normally used in effective amounts oE less than about 2%
by weight oE the liquid crosslinkable resin, respectiveiy.
The dose of the ionizing radiation, if used, is generally
in the range of about 103 to about 107 rads. The period
for compression molding will be generally about 3 to about
20 minutes.
Because the dimensional stability and the like are
especially irnportant for the present molded article, it is
preferred to use a suitable thermoplastic resin in the form
of a solution or suspension as an anti-shrinkage agent as a
mixture with the crosslinkable resin, the ratio of the
liquid thermoplastic resin to the liquid crosslinkable resin
being generally about 35/65 to about 5/95 by weight. These
anti-shrinkage thermoplastic resins include, for example, a
polymer or copolymer of one or more monomers selected from
styrene, vinyl acetate, an acrylate, a methacrylate,
caprolactone, ethylene, etc., and mixtures thereof. These
thermoplastic resins are normally used in the forrn of a
solution or suspension in an ethylenically unsaturated
monomer such as a vinyl monomer.
~ hen a protective or decorative resin layer is applied
onto the electroconductive nonwoven fabric layer of the
present molded article, the thickness of the top resin
layer is generally in the range of about 0.015 to about 0.3 mm.
Such resin layer can be produced by coating with a resin
paint, flame coating or electrostatic coating with resin
powder, etc. on the molded article or by application of a
resin surfacing agent onto the surface of a mold prior to
:3L2~S~
compression molding. These are well known in the art.
The process for producing the molded article in accordance
wi-th the present invention comprises carrying out compression
molding of the laminated materials in a mold at a molding
pressure of about 25 to about lO0 kgf/cm2 and at a mold
closing speed of not more than 240 mm/minute and preferably
not more than about 120 mm/minute. Ununiform dispersion
and fracture of the nonwoven fabric may take place if the
molding pressure or mold closing speed is over the above
defined ranges. The molding process, which satisfies the
above mentioned conditions, is easily understood by those
skilled in the art and can be readily carried out by means
of conventional compression molding machines. For example,
a matched-die molding machine can be advantageously used for
efficient production of the molded articles. Incidentally,
in the present molding process, means such as nuts and bolts
for installation of antenna equipment and/or supporting
members can be readily embedded in the molded articles.
The typical embodiments of the present invention will
be further explained with reference to attached drawings as
necessary. It is to be understood that the present
invention should not be restricted by these examples.
Incidentally, the amounts and percentages used herein are
by weight unless otherwise specified.
The molded article A in FIG. l shows a molded FRP sheet
having laminated structure for uniformly reflecting or
shielding electromagnetic waves, consisting of an FRP
substrate layer l, a woven fabric composite intermediate
- 14 -
-
5~7
layer 2 formed on the substrate layer 1, and an electro~
conductive surface layer 3, consistlng of an electroconductive
nonwoven fabric-resin composite, formed on the intermedi.ate
layer ~. The molded article B in FIG. 2 shows a molded
FRP sheet for uniformly reflecting and shielding electro-
m,3gnetic waves, consisting of the above mentioned article A
and a protective or decorative top resin l.ayer 4 formed on
the electroconductive surface layer 3. It should be noted
that, in the present molded articles as shown in FIGS. 1 and
2, the layers 1 and 2 and especially the electroconductive
layer 3 have the distinct laminated layer structure by the
presence of the woven fabric intermediate layer 2.
The molded article A can be produced, for example, by
placing an electroconductive nonwoven fabric (25 to goo g/m2
in the case of a metal-coated glass fiber nonwoven fabric)
on a mold, placing thereon a woven fabric having dimensions
of 95% or more of an electroconductive-layer area required,
and further either (i) placing thereon an SMC or sMC having
a compound viscosity of not more than 5 x 108 cps to cover
50% or more of the area of the article to be molded or (ii)
pouring thereon a high viscosity crosslink-curable resin
composition containig a reinforcing fiber material, and
then heating under compression:in a prewarmed mold at a
curing temperature (e.g. lower than about 160C), a molding
pressure of 25 to 100 kgf/cm2 and a mold closing speed of
not more than 240 mm/minute.
In order to produce the molded article B having a top
resin layer 4 on the electroconductive layer 3, the top
- 15 -
~Z~547
resin layer can be applied either by coating it on the
electroconductive layer of the molded article ~ or by coating
it on the surface of a mold prior to the compression molding
(i.e. so-called in-mold coating). In the case of the in-mold
coating, a resin surfacing agent comprising polyester resin,
acrylic resin, urethane resin or the like is applied by
means of electrostatic powder coating onto a mold which has
been preheated to a temperature as high as a molding tempera-
ture of the SMC or BMC, and then the above mentioned compression
molding is carried out. Such top resin layer can also be
applied onto the substrate layer if so desired. More
specifically, the thickness of the top layer 4 is generally
in the range of 0.05 to about 0.3 mm. ~he material thereof
consists essentially of, for example, polyester resin and
toluidine isocyanate and/or diallyl phthalate, etc.
Incidentally, the top layer 4 plays a role of protecting the
electroconductive layer, preventing mar thereon and increasing
weathering properties, as well as enhancing attractive
appearance and coloring.
In the following examples, a solution of an unsaturated
polyester resin in styrene monomer was used as a main
component of the liquid crosslink-curable resin composition.
The highly reactive polyester resin is produced from 1 mol
isophthalic anhydride, 3 mols maleic anhydride and 4.5 mols
propyrene glycol, and has one double bond per molecular
weight of about 300. Similar unsaturated polyester resin
is exemplified by "Polymar 6819" of Takeda Yakuhin Ko~yo
K.K., Japan. About 60% of the unsaturated polyester resin
- 16 -
S~7
was dissolved in about ~0~ of styrene monomer to ad-just its
viscosity to about lO poises (25C). As an anti-shrinkage
agent, was used a solution of about 30% of polystyrene
~Dialex HF-77 from Mitsubishi Monsanto K.K., Japan) dissolved
in about 70~ of styrene monomer. Incidentally, the mixing
ratio of the crosslinkable resin solution to the anti-
shrinkage resin solution is normally in the range of about
70/30 to about 90/lO.
Example 1
There was used an SMC for the substrate layer 1 composed
of 50 parts of 1 inch glass fiber and a liquid crosslinkable
resin composition consisting essentially of 75 parts of the
above mentioned unsaturated polyester solution, 25 parts of
the above mentioned anti-shrinkage polystyrene resin solution,
100 parts of calcium carbonate, 1 part of t-butyl perbenzoate
polymerization catalyst, 6 parts of zinc stearate releasing
agent and 2 parts of magnesium oxide thickener. As the
material for the woven ~abric layer 2 was used a plain weave
fabric of glass fiber 120 g/m2 having a mesh size of about
20 mesh. As the material for the electroconductive layer 3
was used a prepreg consisting of a 500 g/m2 nonwoven fabric
of glass fiber coated with 25% by weight of aluminum and the
above mentioned liquid crosslinkable resin composition.
The materials for the electroconductive layer, the woven
fabric layer and the substrate layer were placed on a mold
in this order and subjected to compression molding under the
conditions shown in the Table below. ~here was thus obtained
5~7
a plane FRP molded sheet 1 m x 1 m x 6 mm. Neither waviness
nor fracture of the nonwoven fabric in the electroconductive
layer 3 was observed with respect to the resulting molded
sheet. The reflection loss of the resulting molded sheet
was found to be a very small value of 0.2 dB or less when
12 GHz electromagnetic wave was used.
Example 2
The process of Example 1 was repeated except that the
viscosity of the liquid crosslinkable resin composition, the
molding pressure and the mold closing speed were changed as
shown in the table below. ~hë~e was thus obtained a plane
FRP molded sheet 1 m x 1 m x 3 mm. Neither waviness nor
fracture of the nonwoven fabric layer was observed. The
reflection loss was as small as 0.2 dB or less.
Example 3
The process of Example 1 was repeated except that there
was used a mold having a molding surface of a convex paraboloid
of revolution. There was thus obtained a molded FRP sheet
with a shape of the corresponding concave paraboloid of
revolution which has the dimensions of 600 mm diameter and
6 mm thickness and also has the surface of a concave paraboloid
of revolution represented by an expression of y2+z2=4 Fd x
wherein Fd (focal distance) is 360 mm. ' Neither waviness nor
fracture of the nonwoven fabric was observed. The gain
with the resulting molded sheet used as a parabola antenna
was 37 dB.
SgL7
Example ~ (Comparative)
The process of Example 1 was repeated except that the
woven fabric for the layer 2 was not used to obtain a plane
FRP sheet. The nonwoven fabric of the resulting molded
sheet was fractured and ununiformly dispersed to form about
50% by area of non-electroconductive portions. The fractured
nonwoven fabric 5 and the space 6, where the nonwoven fabric
is absent, of the resulting nonwoven fabric layer 3' are
schematically shown in FIG. 3.
Example 5 (Comparative)
A plane molded FRP sheet 1 m x 1 m x 3 mm was produced
in a process similar to that of Example 1 except that a prepreg of
120 g/m2 glass fiber woven fabric was used for the woven
fabric layer and the molding was carried out as shown in
Table below by a hand lay-up method instead of compression
molding. The results are summarized below.
Example 6 (Comparative)
The process of Example 1 was repeated except that the
120 g/m2 woven fabric for the intermediate layer was not
used, and a prepreg consisting of a 860 g/m2 glass fiber
woven fabric having a coarse mesh size of about 3 mm square
and the above mentioned liquid crosslinkable resin composition
was used instead of the SMC for the substrate layer. Some
uneven thickness was observed in the electroconductive layer
of the resulting FRP sheet. Moreover, about 30~ by area of
non-electroconductive portions were formed on the resulting
- 19 -
~Z~45~7
electroconductive layer.
The conditlons used and the results of the above describeA
Examples are summarized in the followincJ.
TABLE
~ vi5c05ity of
fabric of molding liquld resin mold closing moldin~ r~lding
Ex. elecbxxxx~uctive pressure c~sition s~ t~xrature time,
Nos. layer, q/~f-k~f~cm2 cpsr,m/minute C---- min~te
EX. 1 500 ~o 5i~ 10650 1~10
EX. 2 250 80 5 x 107100 150 3
E~. 3 500 ~o 5 ~ 10650 1~0
E~. 4 500 ~0 5 x 10650 140 4
Ex. 5 500 0 1 x 103 0 40 2~0
~x. 6 500 40 5 x 10550 1~0 6
As clear from the Examples~ both th~ uneven t11ichness and
surface wavinass of the electroconductive layers were generated
in Examples 4 through 6. In EXamples 4 and 6, the electro-
conductive nonwoven fabrics were dispersed and ununiformly
distributed by the action of ununiform flow of tlle liquid
resin composition, and considerable non-electroconductive
portions were formed in the electroconductive layers. The
defects have seriously adverse effects on the inaccuracy of
reflective mirror surface and thus on an'cenna periormances.
The above mentioned defects obserued in Comparative Examples
through 6 were not found at all in Examples 1 through 3 of
the present invention. It is to be noted that these cle~ects
have béen eliminated by the use of the woven fabric as the
intermediate layer 2, whereby the electroconductive layer 3
having uniform layer structure can be securely formed.
- 20 -
~Z~9~S47
Incidentally, the electromagnetic wave-reflecting
performances were measured in the following way by using
12 x 109 Hz (i.e. 12 GHz) electromagnetic wave. For the
molded artlcle having a parabolic reflective surface, the
electromagnetic wave-reflecting performance thereof is
determined in accordance with Japanese Industrial Standard
(JIS) C 6103 "Testing method for a television antenna".
For the molded article having a plane reflective surface, the
reflecting performance is determined by an apparatus wherein
a horn-type antenna for generating and receiving an electro-
magnetic wave is equipped in horizontal direction and a
reflecting plate (30 x 30 cm) is set vertically and in a!
fashion movable horizontally. Thus, the reflection loss is
obtained from the resulting reflection in comparison with
that of an polished aluminum plate (the loss of which is
evaluated as 0 dB).
In the latter testing method, when the reflection loss is
0.2 dB or less, it can be understood by those skilled in the
art that the gain to be obtained by using the present molded
article as such an offset-type parabola antenna as given in
JIS C5103 is as follows :
diameter of parabora gain with 12GHz
antennas m.m. electromaqnetic wave
600 35 dB or more
750 37 - ~
900 39 _ ~I _
1,000 40 - " -
1,200 41 - " -
These gain values are quite satisfactory for practical uses.
5~7
The preferable conditions in the process for production
of the present molded ar-ticles are given below.
(1) The SMC has been normally cured to s-stage. It is
necessary that the compound viscosity of the liquid resin
composition thereof containing no reinforcing fiber is not
more than 5 x 108 cps. It is especially preferred that the
compound viscosity is~in the range of 5 x 106 to 5 x 107 cps.
(2) It is preferred that the molding pressure is in the range
of 40 to 80 kgf/cm .
(3) It is preferred that the mold closing speed is in the
range of 50 to 200 mm/minute.
(4) The dimensions of an electroconductive nonwoven fabric or
a prepreg thereof to be placed on a mold should be as large
as to be about 100% of a required electroconductive area.
In the same way, the dimensions of an woven fabric or a
prepreg thereof for the intermediate layer should be prefer-
ably as large as to be about 100% of the required electro-
conductive area.
(5) The dimensions of SMC or BMC to be placed on the woven
fabric layer material should be preferably about 50% to
about 90% of the mold area.
Incidentally, the lamination of these materials for the
surface layer, the intermediate layer and the substrate layer
prior to compression molding can be conducted either in the
mold or outside of the mold.
As described above in detail, the molded articles according
to the present invention provide a high-precision molded F~P
- 22 -
~'~49~S47
sheet or board for uniformly reflecting and shielding electro-
magnetic waves. For example, there are thus provided a
parabola antenna or an offset-type parabola antenna having
very excellent performances. A molded article having very
small inaccuracy of reflective mirror surface can be obtained,
because the electroconductive layer can be uniformly formed
in a single layer and `the electroconductive region is not
distributed throughout a molded article as observed in such
conventional FRP products. Moreover, the cost, processability,
precision of the product, use life, productivity and the like
of the present molded articles have been markedly improved
in comparison with those of conventional products and
processes for production thereof.
- 23 -
