Method of and apparatus for manufacturing fiber-reinforced plastics articles

An apparatus used in connection with the construction of a duroplastic, fiber-reinforced article a fibrous web which includes continuously impregnating the web under subatmospheric pressure with a liquid, curable resin composition whose viscosity is gradually increasing. The prepreg thus obtained is covered on both its major surfaces by thin polymer sheets, then cut into the desired length, vacuum molded, pre-cured in the mold and finally cured outside the mold. Construction parts, car parts and boat bodies may thus be produced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing fiber-reinforced 
plastics articles, such as construction panels, boat hulls, roof tiles, 
car body parts, etc; by deep-drawing a planar prepeg comprising fibers 
impregnated with curable resins; and curing the said resins after 
deep-drawing of the prepeg. The invention also relates to a method of 
manufacturing said planar prepegs, and to a mold to be used for said 
deep-drawing. 
2. DESCRIPTION OF THE PRIOR ART 
Prepegs consisting of fiber mats which are impregnated by curable resins 
have been deep-drawn in open contoured mold dies having bore holes, by 
exerting a subatmospheric pressure, and subsequent UV-light curing, see 
U.S. Pat. No. 4,478,771 (Schreiber). However, these molds have serious 
drawbacks since the prepeg is drawn with a relatively great force towards 
the bore holes but with much weaker forces towards portions remote from 
those holes. Accordingly, uniform shaping of the web, especially at curved 
portions of the mold having small radii, will not occur. Vacuum deep-draw 
molds have also become known. Thus, Japanese patent publication 62-39218 
(Kasuga) discloses a vacuum forming mold composed of a mixture of sands 
and a furan resin. This mold has been designed for the deep-drawing of 
polypropylene sheets, thus an extensible, thermoplastic material, and it 
has been found that such molds cannot be used for the deep-drawing of 
prepregs. 
Fiber reinforced prepregs have been prepared by simply soaking of a fiber 
mat or other fiber arrangement in liquid resins. In order to keep the 
resin within the fiber mat and prevent it from leaking, the resin must 
have a relatively high viscosity. However, this very viscosity leads to 
leaving air bubbles within the mat. This causes a significant loss of 
strength in the cured prepreg. 
SUMMARY OF THE INVENTION 
Hence, it is a general object of the present invention to provide a new 
overall method for the manufacture of fiber-reinforced plastics articles. 
Another important object is to provide a new and useful vacuum mold for 
deep-drawing and curing of the resin impregnated, not yet cured prepreg 
sheets. 
A further object of the invention is to provide a new and useful apparatus 
or production line for the manufacture of fiber-reinforced plastics 
articles, both this production line and the aforesaid mold being provided 
for implementing the also aforesaid overall method. Still further objects 
of the invention are to provide a continuous method for making an 
impregnated prepreg ready for vacuum molding, as well as a continuously 
working apparatus for implementing this method. 
In its broadest aspect, the invention provides a method of manufacturing 
fiber-reinforced, cured plastics articles which can be carried out in a 
continuous manner and comprising two important inventive steps, namely the 
continuous production of a curable prepreg free from air voids or 
inclusions, and its shaping by deep-drawing and its precuring in a new, 
special vacuum mold. The invention further provides an apparatus for 
carrying out the first step mentioned above. 
The method of the invention comprises impregnating a fibrous web with a 
curable resin composition whose viscosity is gradually growing, under 
subatmospheric pressure in a vacuum tower which comprises a liquid resin 
composition whose level is raised in the tower due to a subatmospheric 
pressure applied to the interior of the tower. The impregnated fibrous web 
which has now become a so-called "prepreg" is then covered on both sides 
with a thin protecting polymer foil. These prepregs, cut to appropriate 
length, are then deep-drawn in the new vacuum mold where the molding or 
shaping surfaces are homogeneously provided with vacuum due to a shaping 
body made up of aluminum beads cemented together by a cured resin in such 
a manner that this body remains gas permeable. 
Still other objects and advantages of the invention will be pointed out 
specifically or will become apparent from the following description of 
examples and specific embodiments taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In the past, curable prepregs have generally been manufactured by soaking 
within a trough a fibrous mat, vleece or other analoguous material in a 
liquid curable resin composition, then, removing the resin impregnated 
material from said trough, and covering it at least on one of its two 
faces by a plastic sheet. This method is cumbersome, long-lasting and 
inaccurate. According to U.S. Pat. No. 4,478,771, already mentioned above, 
a prepreg is manufactured from a homogeneous fill of 450 g/m.sup.2 glass 
fibers and by an impregnation with 1'340 g/m.sup.2 of styrene containing 
unsaturated polyester resin between two thin soft-polyethylene or 
polyvinylidene chloride foils As a viscosity increase agent, 2.6% of 
powdery cellulose aceto=butyrate is dissolved in the resin-styrene 
mixture, and the original viscosity thereof, namely 6 poise (=0,6 Pa s) is 
raised to 100 poise (=10 Pa s), see Example 1 of the said patent. 
However, it has now been found that the soaking of the fibrous material in 
the high viscosity resin composition leaves an appreciable amount of air 
bubbles within the fibrous material due to the high viscosity of the resin 
composition. This leads to serious losses in the strength and resistance 
to fracture of the cured plastics articles. Furthermore, the known method 
is not a continuous one, said soaking taking a rather long time, and the 
viscosity enhancer used in the prior art is also detrimental to final 
strength values since it is not compatible with the cured resin 
composition. 
In contrast thereto, the method of the invention does not show these 
draw-backs. During the soaking step, the viscosity of the resin 
composition is kept to a relatively low value, and during the molding 
step, the viscosity of the resin composition enclosed within the prepreg 
forming fibrous material has raised to a high value. This important 
feature is achieved, according to the invention, by incorporating into the 
starting resin composition a reactive viscosity enhancer capable of 
gradually raising the viscosity of the mixture. Furthermore, the soaking 
step is carried out at subatmospheric pressure in order to remove air from 
the fibrous material as completely as possible. The soaking may further be 
enhanced, if necessary in special cases, by incorporating a fiber wetting 
agent into the resin composition. 
The fibrous material may be chosen at will. The fibers may be of organic or 
inorganic origin; examples thereof are cotton, wool, polyester, 
polyurethane, polyamide, polyolefin, acrylic materials, glass, asbestos, 
carbon. Glass fibers, alone or in mixture with polyester fibers, are 
presently preferred. The fibers are used in the form of mattings, vleeces 
or fabrics; at present, roving fabrics or roving layer stratums, layered 
at 45.degree. to the travelling direction and stitched together, being 
preferred. These stratums are known and commercially sold. 
The curable resin composition to be used for making the prepreg of this 
invention comprises any curable resin, e.g. based on epoxy, urethane or 
ester resins and furthermore a monomeric crosslinking agent such as 
styrene and its derivatives or any other vinyl compound or olefin 
derivatives. A mixture of an unsaturated polyester and styrene is 
preferred. This composition may be cured by heat, radiation such as UV, or 
according to radical copolymerization. Depending upon the curing method to 
be selected, appropriate initiators or initiator systems may be added, 
e.g. UV sensitizers, cobalt or manganese salts, peroxy compounds etc. The 
impregnating, curable resin as well as the curing promoters to be added 
are well known to the men skilled in the art and need not be described in 
detail here. 
The viscosity enhancer with retarded activity which is preferably used 
according to the invention, in the case of a polyester-styrene basic 
composition, is ultrafinely divided active magnesium oxide, magnesium 
hydroxide or a mixture thereof. For example, if about 1% by weight of this 
magnesium preparation is added to said resin composition having an 
original viscosity of about 1 Pa.s at 20.degree. C., the viscosity after 3 
hours is about 10 Pa.s and after 5 hours about 1'000 Pa.s. Furthermore, 
said MgO or Mg(OH).sub.2 is well compatible with the resin composition 
before and after curing. 
Thus, the present invention, in one of its particular aspects, provides a 
sophisticated method of manufacturing a curable prepreg, and the inventive 
idea is to impregnate a fibrous, web-like material with a relatively low 
viscous curable resin composition. The impregnation is easy, complete end 
quick and is enhanced by the application of subatmospheric pressure In a 
subsequent step, the impregnated web is processed for shaping as will be 
described below. During this processing step, the viscosity of the curable 
resin composition has acquired a ten to thousand fold value compared to 
the initial viscosity so that there will virtually no leakage of the resin 
from the prepreg. Viscosity itself as well as the speed of viscosity 
increase may be controlled; thus, a lower initial viscosity may be 
obtained by the addition of more styrene to the resin composition and/or 
by the application of heat, and the increase of viscosity may be speeded 
up by heating the resin or the impregnated prepreg. 
FIG. 1 shows schematically an apparatus for the manufacture of the prepreg 
of this invention. In a known manner, such prepregs are enclosed between 
two thin sheets of plastic which is inert to resin, styrene and the 
additives of the resin composition. 
Supply rolls or supply unit 50 contain windings of the starting fibrous 
material web 94. Although any fibrous web may be used, this material 94 
will be designed herein as "roving stratus" according to a preferred 
embodiment. This roving stratus has a thickness of about 2 to 5 mm and may 
have a web width of up to 2 meters. If the final cured article should have 
a greater thickness than that of one web, more than one supply roll 50 can 
be provided, and two or more stratus webs are then combined on deflection 
roller 52. 
The liquid resin composition 54 is contained in a trough 56. Two deflection 
rollers 58, 60 are horizontally mounted within the trough 56. An 
impregnating tower 62 having an inversed U-shaped cross section is fixed 
in such a manner within and above trough 56 that the rim 64 of the 
inversed U opening is beneath the level 66 of the liquid resin composition 
54. At the top of the tower 62, a vacuum connection tube 68 is provided, 
and a freely running or driven deflection roller 70 is mounted within the 
top portion of the tower 62. A displacement body 72 my be provided in the 
axial middle section of the tower 62. 
A pair of parallel, cooperating, positively driven compression rollers 74, 
76 are mounted outside the tower 62 and trough 56. In the space above 
roller 74, a supply roll 78 for a thin polyvinylalcohol (PVA) foil 96 is 
provided, and in the space below roller 76, another supply roll 80 for PVA 
foil 92 is provided. A supporting table 82 is horizontally mounted in 
front of the roller nip between the compression rollers 74, 76. At an 
appropriate distance from those compression rollers, a cutter knife 84, 
having about the width of table 82, is shown to hung over the table 82. 
Furthermore, a transverse heating source 86 may be mounted above the front 
portion of table 82. 
The apparatus shown in FIG. 1 is operated as follows; features and details 
of the method according to the invention will become apparent from the 
following description. 
First of all, roving stratus web 94 is drawn from the supply roll 50, 
passed around deflection rollers 52, 58, 70, 60 in the manner shown in 
FIG. 1, then between compression rollers 74, 76 whose nip is opened for 
this purpose. PVA foil 96 is unwound from supply roll 78 and placed around 
compression roller 74 upon stratus web 94. PVA foil 92 is unwound from 
supply roll 80 and placed around compression roller 76 under stratus web 
94. Thus, a sandwich 90 is formed comprising basic PVA sheet or foil 92, 
roving stratus web 94 and overlying PVA sheet 96, see FIG. 1A. 
Then, liquid curable resin composition 54 is poured into trough 56. A 
subatmospheric pressure is established within tower 62 by applying it to 
the connection tube 68. Thus, if this vacuum is correctly selected, the 
level of the liquid resin in trough 56 will raise in the interior of tower 
62 to a certain height and form a higher level, about at 98. Displacement 
body 72 (an optional part of the apparatus) serves to limit the amount of 
resin within tower 62. 
Now, a driving force is applied to compression rollers 74 and 76 whose nip 
has meanwhile be adjusted to the value of about the desired thickness of 
the prepreg 90. The rotation of rollers 74 and 76 (see arrows) draws the 
two foils 96 and 92 and the intermediate roving stratus web 94 from the 
corresponding supply rolls 78, 80 and 50, respectively, and supplies the 
prepreg 80 over the table 82 where it may be cut by the knife 84 into 
appropriate lengths 91. 
The impregnation within trough 56 and tower 62 will occur as follows. 
First, the roving web 94 enters the trough 56 downstream of roller 52 and 
upstream of roller 58. It receives a first impregnation with resin 54 by a 
merely soaking phenomenon. Then, the web 94 travels upwardly in direction 
of deflection roller 70. When the web 94 leaves the resin level at 98, the 
subatmospheric pressure or vacuum within the upper part of the tower 62 
removes virtually all air bubbles and other air pockets from the 
pre-impregnated roving web (see FIG. 1). After having been turned by 
180.degree. on the deflecting roller 70, the web 95 travels downwardly and 
re-enters the liquid resin composition at 98. During its travel across the 
resin toward deflection roller 60 and still afterwards, the hollow, 
airless spaces in web 95 are now completely filled by the liquid resin. 
The web is deflected by roller 60 and finally leaves the resin bath in a 
fully impregnated state. 
Just before entering the roller nip between compression rollers 74 and 76, 
the underside of web 95 is covered by the PVA sheet 92 unwound from supply 
roll 80, and the upper side is covered by the PVA sheet 96 unwound from 
supply roll 78. Thus, compression rollers 74, 76 will not come into direct 
contact with the resin impregnated web 95. The nip between rollers 74, 76 
is controlled to a value corresponding to the desired final thickness of 
the prepreg 90. 
Since the viscosity of the impregnating resin increases with time, the 
prepreg 90 thus obtained will not substantially leak and loose resin. In 
order to rapidly increase resin viscosity before cutting the continuous 
prepreg 90 by knife 84 in appropriate lengths 91, a heating device 86 may 
be proved to accelerate the speed of viscosity increase. 
The prepreg pieces 91 are now ready for shaping and curing into the final 
articles. It should be noted that the viscosity increasing additive will 
raise the viscosity of the resin finally to about 1,000 fold its original 
value, and the final viscosity, attained after about 5 hours, will not 
increase further nor will the very curing of the resin take place. Prepreg 
pieces 91 may thus be kept even several days before shaping and curing. 
FIG. 2 to 5 illustrate a mold of the invention. This mold, generally 
designed as 1, comprises an edge 2 and a mold interior 3. Generally, the 
base 23 of the mold interior is not level and is adapted to the shape of 
the article to be manufactured. As can be seen from FIG. 3 and 4, the 
lower mold portion 1 is made from a porous material 5 whose manufacture is 
another aspect of this invention and will be described in detail later. 
This porous material is formed from aluminum beads 6, especially spheric 
ones (FIG. 5) which are cemented together by a resin layer 7 in such a 
manner that the whole body 5 still has a substantial porosity and is air 
permeable. The aluminum spheres may have diameters comprised between 0.1 
and 4 mm or even more. 
According to the invention, the size of the aluminum spheres or beads may 
be different in the mold. Thus, the main body of mold 1 may be filled with 
coarse beads (of course always bound together by a resin) 5A, etc. The 
average diameter of the beads decreases layerwise toward the inner surface 
23. The fineness of the uppermost bead layer (e.g. 5C in FIG. 4) is 
selected in function of the desired surface quality or finish of the 
article to be shaped. Thus, if a high surface quality is desired, layer 5C 
should comprise the finest aluminum beads, e.g. from 0.1 to 0.5 mm. To the 
contrary, if no special finish of the article to be manufactured is 
desired, layer 5C and, optionally, also layer 5B may be omitted. 
Only the shaping surfaces 23, 24 of the mold are air permeable, i.e. 
aluminum bead layer 5C is uncovered. All other surfaces of the mold are 
covered by an air-tight housing or casing 15 which thus envelops the 
entire lower mold portion 1 with the exception of the mold interior 3. 
Conduit 10 is made of a different material from aluminum, and air 
permeable cover 11 takes up thermal dilation differences between the 
aluminum granules or beads and conduit 10. The lower mold portion 1 
contains an annular, circumferential conduit 10, generally arranged 
parallel to the outer contours of the mold, see FIG. 2 where it is 
schematically represented by a dashed line. A connection 8 connects 
conduit 10 to the exterior of the mold and serves to connect conduit 10 to 
a vacuum source (not shown). Another connection 9 of the conduit 10 serves 
to connect the latter to a compressed air source (not shown). Conduit 10, 
which contributes to the mechanical stability of the mold, is a metal 
pipe, generally of steel, of any desired cross sectional shape and size. 
Conduit 10 has a plurality of apertures or borings 19 directed to the mold 
interior. Conduit 10 is thermally insulated against aluminum bead layer 5A 
by an air permeable cover 11, preferably a fiber mat. The mold further 
comprises a cover 12 (FIG. 3) which may be a plain panel or simply a frame 
whose shape and size is adapted to those of the mold. A circumferential 
holding ring 13 is fixed to the underside of cover 12 in such a manner 
that it will come to rest on those upper surface portions of lower mold 
portion 1 which are covered by the casing 15. 
The mold is manufactured according to this invention in the following 
manner. 
First, an appropriate casing 15 is provided and then equipped with the 
annular conduit 10. This conduit 10 (which is fixed within the casing 15 
merely by the connection studs 8 and 9) is then enveloped by the isolation 
mat 11. 
The cross-sectional shape as well as the material of the conduit 10 are 
selected such as to stiffen the mold and to increase its stability. Since 
normally a steel pipe is used for the conduit 10, the isolation 11 is 
necessary to take up the differences in the thermal expansion coefficients 
of iron and aluminum. The thickness of the isolation mat 11 is about 3 to 
5 mm. 
Then, a blend is made from aluminum beads and a binder resin. This resin is 
a special, cold hardening, heat resistant polyester resin, normally 
designed for the use in polymer concrete, and which should be thixotropic 
such as to cement the aluminum beads together but not subject to the 
formation of drops which could obliterate the porous layer or layers 5. 
An important feature of this invention is the choice of the correct ratio 
of aluminum beads to the binder resin since this ratio will determine the 
strength and mechanical resistance of the mold, on one hand, and its 
porosity to air on the other hand. If too much of the resin is used, the 
mold is mechanically very resistant but perhaps not sufficiently air 
permeable. To the contrary, if too resin is used, air permeation will be 
excellent but mechanical resistance too poor. Furthermore, said inventive 
ratio will depend upon the size of the aluminum beads. 
Now, the inventor has found that this ratio of aluminum beads to resin, 
expressed by weight, should be selected in the ranges according to the 
following table: 
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Weight ratio ranges of aluminum to resin 
aluminum beads 
resin weight Preferred weight 
diameter 
weight general preferred 
ratio 
(mm) (g) (g) (g) aluminum/resin 
______________________________________ 
0.1-0.5 100 30-60 50 1:0.5 
0.6-1.5 100 20-50 30 1:0.3 
1.5-3 100 15-30 20 1:0.2 
3-4 100 10-25 15 1:0.15 
______________________________________ 
The blend made up of aluminum beads and binder resin is then poured into 
the casing 15 and distributed therein according to the shape of the cured 
prepreg article to be formed. A totally exact shaping is not necessary 
since the mold may be brought in shape after the curing of the binder 
resin by machining, grinding or other well known suitable techniques. This 
is an important advantage of the invention. 
When the said blend is distributed in the casing 15, the mold is put aside 
for the curing of the resin which will be accomplished after some hours. 
Finally, a mold is obtained as shown in FIG. 2 to 4. FIG. 5 shows an 
enlarged portion of the structure of the mold. Aluminum beads 6 are evenly 
covered by a resin layer 4. At the contact sites of the beads, resin 
binding locations 7 assure a solid cementing of adjacent beads. 
When the mold is to contain different sizes of aluminum beads, it will be 
manufactured by a stepwise method. First, the undermost layer 5A 
comprising relatively coarse aluminum beads (see FIG. 4) is produced as 
described above. When this layer is at least partially cured, a second 
layer 5B of medium size aluminum beads is introduced into casing 15 over 
the surface of the layer 5A, and afterwards, if necessary, a layer 5C of 
the finest beads. Layer 5B may also be omitted. Finally, interior 3 of the 
mold (surfaces 23,24) is given the desired shape by machining. The mold is 
now ready for use. 
Referring now to FIG. 6 and 7, two steps of the manufacturing method of 
shaped articles are illustrated. For the details of the mold, see FIG. 2 
to 5. 
The mold 1 is put horizontally, and a prepreg 90, having been prepared as 
described above, is laid with its lower surface (polymeric film layer 92) 
on the upper surface 15A of the casing 15. This step is shown in FIG. 6. 
In order to obtain air tightness between prepreg 90 and upper mold surface 
15A, the cover 12 is laid upon the upper polymeric foil 96 of the prepreg 
in such a manner that the holding ring 13, which may be made of a 
resilient material having, however, a smooth and non-frictional surface, 
slightly presses the prepreg 90 on the upper mold surface 15A, just by the 
weight of the cover 12. If this weight is not sufficient to assure 
air-tightness between surfaces 15A and 92, the load of the cover 12 may be 
increased by conventional means. 
Now, the connection tube 8 is connected to a vacuum source (not shown), and 
vacuum is applied to the mold space 3. The air in space 3 passes by the 
voids between the aluminum beads 6 (FIG. 5) through the porous mold 
material 5, then through the porous isolation layer 11 of the conduit 10, 
the holes 19 of the conduit 10, and finally through conduit 10 and 
connection tube 8. As a result of the suction and the fact that the 
prepreg 90 lies in an air-tight condition on the upper, non-porous mold 
surface 15A, the prepreg is drawn by the vacuum into the mold interior 3 
and is finally pressed by the surrounding atmosphere into intimate contact 
with the inner molding surfaces 23, 24, see FIG. 7. The prepreg molds in a 
smooth and homogeneous manner to all contours and all surfaces of the 
porous portion of the mold 1; this perfect molding would not take place if 
there were only some or even a plurality of holes in an otherwise 
air-tight molding surface. 
The fact that the circumferential holding ring 13 only guarantees 
airtightness between the prepreg 90 and the upper airtight mold surface 
15A but does not prevent a horizontal relative movement of prepreg and 
mold surface, all the more that ring 13 has a smooth surface, in other 
words that ring 13 is no clamping ring, allows the prepreg 90 to slide 
during vacuum molding over the mold surface 15A to cope for the length 
demand during molding. This condition can be seen by comparing FIG. 6 and 
7. 
After the molding step, the prepreg can be cured. Preferably, curing is 
accomplished during the vacuum is still applied to the mold. Cover 12 can 
be remain on the mold if that cover is a frame; normally, it will be 
removed. Curing is initiated by application of energy such as hot air, 
ultraviolet light, electron beams, infrared light, etc. to the molded 
prepreg from above. 
The prepreg 90 may gently be warmed before vacuum molding if it is too 
stiff. This warming can be performed by any one of the energy sources just 
described. After curing, the vacuum is removed from connection tube 8, air 
is allowed to fill the mold body, and the prepreg may be removed from the 
mold. In principle, it can be removed even in a pre-cured state, and final 
curing may be effected outside the mold. Molded prepreg removal may be 
assisted by blowing compressed air into the mold body through connection 
tube 8 or 9. After complete curing, polymeric foils 92 and 96 may be 
peeled from the cured prepreg 94. 
It is important for the invention that aluminum is used for the body 5 of 
the mold. In fact, there is a problem associated with thermal expansion of 
the mold and the prepreg to be formed. 
As it has already been mentioned above, the curing of the prepreg is 
normally accomplished by the application of thermal energy or such an 
energy which is transformed into heat within the prepreg. If the mold has 
another thermal expansion coefficient than the prepreg, the shaped and 
cured article would have other dimensions than those of the mold after 
cooling. This effect is well known to the man skilled in the art, and 
until now, complicated calculations had to be made in order to give the 
cold mold dimensions which differ from those of the article, and these 
calculations are necessarily only approximate since the real temperature 
of curing may change from one curing to another. 
Thus, it has been found that a mold material should be used which allows to 
manufacture the mold with exactly the same dimensions as those of the 
finally cured plastics article; it has further been found that this 
condition can be fulfilled if the material of the mold has the same 
thermal expansion properties than those of the prepreg. 
The following is a list of thermal expansion coefficients, the unity being 
1/K (or 1/.degree. C.): 
______________________________________ 
prepreg, vleece, mat 
28 .times. 10.sup.-6 *) 
prepreg, vleece mat, 
25 .times. 10.sup.-6 *) 
insoluble binder 
prepreg, roving mat 15-20 .times. 10.sup.-6 *) 
aluminum 20-24 .times. 10.sup.-6 
(alloys included) 
______________________________________ 
*)source: BASF Kunststoffe, prospectus "Palatal A410" August 1978 
For comparison, the thermal expansion coefficients of other materials are 
given below: 
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steel 12 .times. 10.sup.-6 
sand 0.5-1 .times. 10.sup.-6 (estimated form quartz) 
copper 17 .times. 10.sup.-6 
magnesium 26 .times. 10.sup.-6 
silver 20 .times. 10.sup.-6 
______________________________________ 
Thus, only magnesium, silver or a copper alloy could replace the aluminum 
according to the invention. Of course, aluminum is the optimum since 
copper and silver are too heavy and magnesium too sensitive to oxidation. 
Sand and steel, normal mold materials, cannot be used. 
The method of the invention will further be illustrated by a working 
example which is an illustration only and will not limit the invention 
thereto. 
EXAMPLE 
To 100 kg of "Palatal A410", a styrene containing, medium reactive 
isophthalic acid polyester resin, supplied by BASF, Ludwigshafen, Germany, 
500 g of "Luvatol" were added and thoroughly dispersed in the resin. 
Luvatol is a 50% by weight paste of reactive MgO/Mg(OH).sub.2 having a 
solids fineness below 30 .mu.m and a viscosity of 8 to 12 Pa.s at 
20.degree. C. The resin "Palatal A410" has a starting viscosity of 
1.35.+-.0.15 Pa.s at 20.degree. C., and the styrene content is 43.+-.2% by 
weight. Furthermore, a UV sensitizer is added to the resin. A glass roving 
web in the form of a stratum comprising four mat layers each arranged at 
45.degree. C. to the other and stitched together, the width of the web 
being 1 m, is fed into the apparatus shown in FIG. 1. The resin mixture is 
poured into the trough 56 and subatmospheric pressure (about 0.2 bar) is 
applied to tube 68 so that the resin mounts by about 2 m within the tower 
62. A polyvinylalcohol foil having a width of about 1.2 m and a thickness 
of about 0.15 to 0.2 mm is unwound from supply rolls 78 and 80 and 
combined with the stratum 95 between rollers 74 and 76 as already 
described above. 
The "sandwich" made up of stratum 95 and foils 92 and 96 is now advanced 
with a speed of about 3 m/min. When the leading end of resin impregnated 
stratum 94 has reached the knife 84, the unimpregnated length is cut off, 
and further pieces of about 2 m each are cut off during the containing 
advance of the web 90. 
The inner stratum 94 of the web 90 is impregnated without visible air 
inclusions at a rate of about 40 to 50% by weight of resin. Its viscosity 
is found to be about 15 Pa.s and it does not leak from the stratum 94. 
Manufacture of a shaped article 
One of the prepregs described above is laid on the upper surface of the 
mold in the manner shown in FIG. 6. The cover 12 is laid upon the prepreg 
90 after warming up the prepreg by an infrared radiator from above (not 
shown) to about 50.degree. C. 
Then, as it has already been described in detail above, the prepreg is 
shaped within the mold. The applied vacuum was about 0.2 bar (0.8 bar 
subatmosperic). The cover 12 is removed, and a pre-curing is effected by 
overhead irradiation wish an UV lamp array (not shown) supplying an UV 
rays power of about 2'000 W/cm.sup.2 during 15 to 20 seconds. 
The precured prepreg is removed from the mold by cutting the vacuum and 
introducing a superatmospheric pressure of about 2.5 bar through tube 9. 
The shaped and precured prepreg is lifted, seized and put aside. After 
passing a conventional hardening tunnel under continued UV radiation, the 
plastic foils 92 and 96 are peeled off, and the cured article is cut into 
size. In this way, construction elements are obtained. 
The fact that curing is divided into pre-curing and final hardening is due 
to the phenomenon of exothermic reaction. If a total curing would be 
effected under the conditions described for pre-curing, the reaction heat 
thus produced would weaken or even destroy the prepreg and also affect the 
mold. 
In this Example, about 60 to 70 shaped articles could be produced per hour 
at reasonable, low cost. All articles had the same mechanical properties, 
and the dimension tolerances were lower than 0.2%. These features could 
not be obtained by known methods with analoguous prepregs and other molds. 
Whereas the manufacturing process has been described in the Example as a 
continuous one, the man skilled in the art will be aware that step 2 may 
be executed in a discontinuous manner. 
While the invention has been disclosed in relation to preferred or special 
embodiments thereof, it will become apparent to those skilled in the art 
that numerous modifications and variations can be made within the scope 
and spirit of the invention as claimed in the claims.