Note: Descriptions are shown in the official language in which they were submitted.
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HYBR!D PULTRUDED PRODUCTS AND
METHOD FOR THEIR MA-NUFACTURE
BACKGROUND OF THE INVENTION
The present invention comprises A pultruded product which
contains, in adclition to the usl1~1 glas!3 roving strands, a cellulosic m~t whioh
serves ~ R filler or rein~orcing filIer. The invention further comprises
method for making products OI the above type.
Pldtrusion i9 a process for contimlously forming reinforced
plastic materials hQving a uni~orm cross-sectional profile~ The word
"pultrusion" is a hybrid which combines the words "pull~' and "extrusion "
The product is literQlly pulled through a forming die. In it~ most usu~l form,
pultru~on involves ~eeding a multiplicity of ~iberglass roving strands, with
or without additional plies o~ glass mat o~ appropriate width9 into a
- pultrusion die. A resin, norm~lly a thermosetting material ~uch as a
polyester, is injected into the die where it is ~ ormly distributed among
the reinforcing materi~ls. Alternatively, the rein~orcing material may be
drawn through a resin bath prior to entry into the die. The die itsel~ is
heated. As the product is drawn from the die, the resin is either cured, or
very ne~rly cured. The endless product so formed is then cut to appropriate
length. M2ny variatlons of this general process haYe been developed as the
technology has matured.
Pultruded products are used in a great variety of applications. In
many places they have replaced metal1ic construction materials,
particularly those used in highly corrosive environments. Structural beam~,
~l~or gratings, handr~ils, ladders, and many simil~r products are now made
by a pultrusion process.
A general ba¢kground sn pultrusion is found in an article by
Martin, ~n~, pp. 317-318, McGraw-Hill~ Inc., New
York (1~86). Another good background discussion is found in U.S. Patent
4,252,696 issued to McQuarrie.
Despite the enormous versatility of the pultrusion method and
the many v~riations whi~ have been developed aro~nd it, it still has
limitations. In many cases it is necessary to overdesign products in order to
~ ensure uni~orm distribution o~ the glass reinfo~cement within the resin
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matrix. Products with low glass content tend to show are~s oi resin
separ~tion in which the reinforcing materi~l may be completely absent.
This resin separation is apt to occur even when high concentrations o~
mineral fillers are used with the resin. Pultruded produ~ts also tend to have
5 relatively h~gh density in comp~rison to many other plastic composites. This
results in a relatively high cost per unit volume of the finished product.
Further, because of the pr~blem of resin separation at low reir~orcing fiber
contents, it is very dimcult to make products less than about three
millimeters in thicknessJ even though they may not be required to have high
10 strengths. While some attempts have been made in the prior Qrt to address
these deficiencies, none have been particularly success~ul to the present
time.
Reference might be made at this point to a number o~ patents o~
general pertinence to the present invention. Cogswell et al, U.S. Patent
15 4,541,884, describe pulling a continuous tow or roving o~ ~ibers through a
mixture of a thermoplastic polymer and a volatile pl~ticizer. The presence
of the plastieizer reduces the melt viscosity to the point that uni~orm
impregnation of the reinforcing fibers is possible. After forming the
product, the pl~sticizer is volatilized. The inventors suggest th~t glass
20 ~iber, carbon fiber, jute ~nd high modulus synthetic polymer fibers can be
used for reinforcing. However, the reinforcing must h~ve su~icient
longitudinal strength to enaMe it to be drAwn through the viscous
impregnation bath. The inventors further note that at least 50% by volume
of the fibers must be aligned in the direction o~ draw.
Goppel et al, U.S. Patent 4,0287as77J make a pultruded product by
first taking an open cell foamed core material and impregn~ting it with a
therrnosetting resin. Th~ impregnated foam core is faced on one or both
sides with a resin free fibrous reinforcing layer. The assembly is then
molded in a pultrusion die where the resin ~ows from the îoam into the
30 reinforcement. The foam core is ultimately tot~lly collapsed in the process.
Cellulosic paper, cotton fabric, asbestos, nylon, and glass are disclosed as
reinforcing materi~lg.
Tadewald, in U.S. Patent 4,207,129, describes a pultruded
product which is a conductive or semi-conductive sheet. As Q first step in
35 its manufacture, a resin is admixed with a semiconductive powder, such as
acetylene black, and a refractory inorganic oxide. This niixture is
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impregnated into ~ supporting material which may include a heavy
absorptive paper about 0.020 inches in thickness. Th~ resin in the
impregnated product i8 then B-staged. At this time ~onductive elements
such as copper foil strips may be included. The B-staged rnaterial is then
5 encapsulnted with glass rovings and/or serim and furtheP impregnated with a
polyester resin in a conventional pultrusion process.
Cellulosic materials have ~ound very little use in any cap~city in
reimorced plastic materials based on polyester resins. They have had a long
standing reputation, not without sonne justification, for causing soft cures
10 and tacky surf~ces. This has been particularly true for products based on
wood fiber which have not been chemically modified. Gregory et al, in U.~.
3,361,690, describe the use of l:~ouglas-fir bark fiber as a reini'orcing
material for polyeste~based bulk molding compounds. Gehr, in U.S.
3,248~4~7, describe~ the use oi' similar compounds in melamine overlaid
15 reinforced plastic moldings. However, the bark ~iber products appear to be
- an exception to the problems encountered with other eell~ose based
materials.
Notwithstanding the well established bias against them~ the
present inventor has found that cellulose~based mats can be successfully
20 used in pultruded products made with a wide variety o~ impregnating resins.
Apparently the present success i~ due at least in part to the iact that it has
been found critical to maintain a moisture content at or below about 1% in
the cellulosic product.
SUMMARY OF THE INVlENTION
The present invention comprises a method of making a composite
pultruded product and the product resulting from the use of the process.
The product contains a plurality of longitudinally oriented, essentialIy
parallel glRss roving strands in association with a celluloisic mat. Both the
30 roving strands and the cellulosic mat are completely encased within a resin
matrix. The glass roving strands comprise from 10-45%, the cellulosic mat
between 5 and 40%, and the resin 40-70% of the product, all measured by
volume.
The cellulosic mat serves as a filler or reinforcing filler to help
35 maintain uni~orm resin distribution within the product. This mat will
typicalIy be formed of short fibers having a length distribution within the
range o~ about 1-l0 mm, more typically about 1-3 mm~
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The furnish of the cellulosic mat c~n be selected from defibered
whole wood, thermomechanical pulps, an~l chemical pulps such as those
made by the kraft or sulphite process. The mats can be formed from the fibers
using conventional wet or dry processes. It is within the scope of the
invention to include up to about 20% by weight of noncellulosic fibers in the
mat. These fibers include glass fibers or polyolefin fibers such as polyethyleneor polypropylene, or mixtures of any of these.
It is a critical aspect of the invention that prior to fo~ning the
pultruded product, the cellulosic mat should be dried to a maximum of about
1% moisture content.
The resin matri~ of the product may be chosen from thermo-
setting or thermoplastic resins. In the case of thermosetting resins these will
usually be chosen from unsaturated polyester, epoxy, methacrylate, or
phenolic types. Where thermoplastic resins are u~sed, they may be either
polyethylene or polypropylene, acrylonitrile-butadiene-styrene, acetal,
polyamide, polyimide, and polyester. Other types of thermoplastic resins may
also be used. Mixtures of thermosetting and thermoplastic resins are also
acceptable.
The process may be either a conventional pultrusion type or a
pulforming type in which a thermosetting resin matrix is only partially cured
within the pultrusion die. Further curing of the pultrucled product is carried
out in a second die. It should be considered within the scope of the invention
to use the pulfonning process with a thermoplastic resin, a thermosetting
type, or mixtures of the two.
The method further includes preimpregnating t~e cellulosic
mat with resin prior to incorporation with the glass roving strands in the
pultrusion die. The matrix resin may be added to the glass roving and
cellulosic mat either in the pultrusion die itself or in an open bath prior to
the pultrusion die.
The product may include glass ntats as well as glass roving and
it is within the scope of the process to support the cellulosic mat on a glass
fiber mat or between glass fiber mats as it is supplied to the pultrusion die.
It is an object of the present invention to provide a novel
pultruded product.
It is another object of the invention to provide a pultrusion
process which incl~ldes feeding a cellulose-based mat along with glass
reinforcing roving.
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It Is nnother ob~ect to provide Q gllQ8S pultrusion process ~nd
resulting product wh{eh may hnve relntively lower gla~ content while
m~intainin~ unl~orm resin distribution.
These ~nd many other ob~ect~ w~1 become re~dily ~pparent to
S those skilled in the art upon readin~ the following det~iled description taken
in conjunction with the dr~wir~,
BRI13~ DE~CRIPT113N OF THE DRAWIP~GS
Pigure 1 is a diagrammQtic repre~entflt~on o~ the m~or elemerlts
o~ the present pultrusion process.
~igure 2A-D show representQtive cros3~ectlon~l viewY o~ n
pultruded rod.
Figure 3 shows ~ cross-section~l repre3ent~tion o~ n flQt
pultruded product.
DESCRIPTION OP TE~E PREFERRED EMBODIMENT~
ConYentionnl pultruded products normally consist of a resin
matrix, typically a polyester resin, ~nd glass reinforcing ~ibers. The
rein~orcing ~ibers are usually pre~en$ ns roving but the product may contain
gla~s m~t as well. The roving provides longitudinal 5trength ror both the
proces~ and the produ~t, wherea~ the m~t proYid~ a measure o~ tr~nsverse
strength. The percentage of glass fiber in mo~t pul~uded products ranges
~rom 50 70~6 by weig~ht or about 35-55% by volume. Pultruded products
have a relQtiYely high density, USuQ]ly in the range of about 1700 kg/m3.
In the present {nvention a cel~ ic mat is used In addition to, or
to substitute ~or, some of the glass 3~iber, c~eating a hybrid product. The use
of the cellulo5ie mat can r@duce density and ~t ot the produ~t. It al~o
~: enàbles the production of products h~ving relaffvely lower percent~ges of
gl~æ than ~n now be m~de with gsod uni~ormity.
In m~ny cases thin p~lel5, in the range o~ ~bout 3 mm thick,
must be subst~nti~lly over designed in the glass fiber component bec2use it
is not practical to pultrude through thinner dies. However, i~ the glass fiber
content i9 reducedj resin rich area~ may ~orm whi~h have poor physical
properties ~md, ~dditionQlly~ may cause jamming in the die. The addition of
the low den3ity cellul~sic mat ean maintain composition integrity arld
provides ~ ms3ns o~ reducing the ~iberglas3 content while overcoming the
befor~mentioned limitations.
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The cellulosic mat may be formed as an air laid felt or it may be
made as a wet l~lcl product as, for example, on a conventional paper machine.
If made as an air laid felt, the mat will normally be precompressed to reduce
bulk ~ncl improve strength and handling characteristics. The mat may
include up to 20% by weight of a noncellulosic fiber such as glass or
polyolefin. However, they are prepared, the mats must be ~ried to a low
moisture content, in the range of 1% moisture or below, prior to inclusion in
the pultruded product.
Figure 1 is representative of the pultrusion process of the
present invention. A fiberglass roving supply 1 is maintained in a
conventional creel. A sufficient number of roving strands 2 are drawn from
the creels into a preformer 6. The appropriate form of cell~tlosic mat is
supplied as rolls 3, 3' from which the mat 4, 4' is led through dryers 5 to
preformer 6. The preformed raw material 7 is then directed to the pultrusion
die 10. An appropriate resin, usually a Hlled polyester, is supplied to the die
by pump 9. The die will normally have electrical heaters which are
connected to an electrical supply 8. The cured pultruded profile 11 is drawn
from the die by pullers 12 to a cutoff saw 13.
Alternatively one or more of the rovings or mats supplied to
the pultrusion die may be preimpregnated with resin in bath 9'. Bath 9' may
be located either before or after former 6. The product may also be post
formed in a die 14, as in a pulforming process. The post forming die 14 will
usually be heated and may be incorporated in the puller mechanism 12 or
may be separate, as is shown in the drawing.
It should be considered within the scope of the invention to
carry the fiber mat into the pultrusion dies supported on a glass or other type
mat. Thus, in Figure 1, mat 4 might be cellulose fiber and mat 4' glass roving.
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Example 1
A cellulosic mat having a 400 g/m2 basis weight, a density of
about 60 kg/m3 and a thickness between 6 and 7 mm was cut into strips 12
mm wide. The mat was a standard Euro Hospital product No. 001.400. This
is comprised of an air lai~ bleached softwood pulp fiber supported on a
single tissue layer and containing approximately 20% Pulpex polyolefin
fiber. Pulpex is ~ trademark of Hercules, Inc., Wilmington, Delaware. The
mat was supplied by Dry-Formed Processes, ~.B., Oerkelljunga, Sweden.
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The pultrusion die, which produced a 9.7 mm diameter rod, was initially
strw~g with 17 strands of E-glQss roving weighing 5 g/m. The trials were run
by removing strands of roving and substituting strips of cellulose mat in the
sequence shown in the following table. The resin was a standard pultrusion
5 grade polyester obtQined from Nordic Supply, Aalesund, Norway,
The produets made are represented in Figure 2 where rods
generally indiçated at 20, 22, 24 and 26 were made respectively with 0,1, 2,
and 3 strips of cellulosic mat. The plass fiber rovings are indicated at 27
within the resin matrix 29. The ce~llulosic mat strips 28 were positioned
10 approximately as is shown in the drawing.
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While the higher usag0s ot cellulose mat r~sult in Q signiiicant
reduction in strength, a ma~or redu~tion in product density Is ~Iso achieved.
This effects a signii~icRnt cost redu~tion in a product where the high
5 strengUl were not required.
Example 2
In this example a nat pu]ltruded produet WQ~ made having a cross
section a x 150 mm. Thl~ product WEI~ normally mad~ with 39% glas~ rovlng,
16% gla~ mat în two layers, and 4'j~6 resin, flll rnea3ured by volume~ The
roving was E-glass having a weight o~ 5 g/m as wa3 u~ed in the previous
example. The glass mats each had Q basis wclght ot 1050 g/m2.
Two types o~ cellulosic mat and two types o~ resin were used in
making the products o~ the example. The ~irst eellulosic mat WQS a Euro
15 Hospital mat a~ described above. The other w~s alr laid ~rom mech~nically
defibered ~ouglas-~r mixed with 15% Pulpex 2 polyethylene fiber~ and
i~ormed to Q 400 g/m~ basis weight. Thi~ mat had a d~nsity o~ about
67 kg/m2 ~nd n thi~kness oi 6 mm~
The fiber mRts were cut into strips 150 mm wide by 600 mm
20 long. The glass was distributed with roving top and bottom end eellulosic
mats in the center, a~ shown in Figure 3. Here the nat pro~iled product 30
h~s glas3 roving 32 ~t top ~nd bottom and two cellulosic mQts 34 within a
re~in matri~c 36. For the te~t, ~fter achieving steady-state operation with
the conventfon~l materi~s, the glQ3s m~ts were ~ut and substituted with th~
25 fiber mats on a on~to-one basis. The ~iber mat~ were previously dried to ~
moisture content below 1%. The volumetric eontriblltion o~ the cellulo~ic
mats to the dtimate product was ~bout the same a~ that ol~ the orJgin~
gla~ rov~
A first set o~ tr~ with the two types o2 cell~o~iic mat wa9
30 c~rried out with the polye~ter resin described in the previo~ example. A
second set of trials w~ then made using ~ phenolic resin. The re~in
employed W115 Norsophen 1701 used with catQlyst 3100. l'hese products are
available from CdP Chimie North America, Inc~., Lerchmont, New York.
The products made with both types ot cellulosic m~t ~nd w~th
35 both resir~ were excellent in appe~rance1 The cellulosic mats ~ed into t1~
pultrusion die smoothly ~nd with no tendenicy to famming. There wa~ no
evidence o~ blistering, delamin~ion, or incomplete cure in ~ny o~ the
pliltruded produce~.
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Having thus described the best mode known to the inventor of
practicing his invention3 it will be readily apparent to those skilled in the art
that many variations can be made from the described example without
departing ~rom the spirit oi the invlention. Thus, the invention i~ to be
5 considered as being limited only by the following claims.
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