CA1323160C

CA1323160C - Hybrid pultruded products and method for their manufacture

Info

Publication number: CA1323160C
Application number: CA000575708A
Authority: CA
Inventors: Frank C. Beall
Original assignee: Weyerhaeuser Co
Current assignee: Weyerhaeuser Co
Priority date: 1987-09-04
Filing date: 1988-08-25
Publication date: 1993-10-19
Anticipated expiration: 2010-10-19
Also published as: WO1989001863A1

Abstract

HYBRID PULTRUDED PRODUCTS AND
METHOD FOR THEIR MANUFACTURE

ABSTRACT OF THE DISCLOSURE
The present invention is a composite pultruded product and the method for its manufacture. The product is made with a plurality of longitudinal glass roving strands. In addition, a cellulosic mat is used in association with the roving. The mat serves as a filler, or reinforcing filler, to ensure uniform resin distribution within the product even when the glass content is significantly reduced. The method can be carried out on convention pultrusion equipment with little or no modification. The cellulose fiber mats may be either air laid or wet laid and should have an ultimate moisture of 1% or less before being incorporated into the pultruded product.

Description

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 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 .

, 1 323 1 6() 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~

.
, 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.
~.
,, ~ ., .

.

1 ~23 1 60 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.

:: :

.

6 1 323 1 ~0 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.
.

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.
'~ ,:

.
, ~ ~ .

~ 323 1 60 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.

~`' . ' : ' .

1 3231 bO

E a~ ¦ c~ ,, o 3 ~ ~ ~r~ CD C'~ ~ C"

O ~
a V 0 u~ O ~ ~ ~ ~
~o ~ V C~

C V ~ G C:1 O O O O
a ~ ~ ~ 0~ ~ ~ _, V
¢
v ~1 c~ , ~.', ", , c~

o E ~31 o ~ ~ u~
~ ~ I - ,, ~
P~

e~

C~

o G ¦

~ , ' ' ' , :-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~.

*Trade-mark ~ ~ `

:: . .
.
.

1 3~3 1 60 l~P 1 16û57 10 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.

:

:; . : :

:

: ~ : . ~,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composite pultruded product which comprises:
a plurality of longitudinally oriented essentially parallel glass roving strands;
and a parallel oriented cellulosic mat interlayered between the roving strands, said cellulosic mat having a moisture content of 1% or less;
both the roving strands and the cellulosic mat being completely saturated with and enclosed within a resin matrix; and wherein the glass roving strands comprise from 10 - 45%, the cellulosic mat 5 -40 %, and the resin 40 - 70% of the product, all measured by volume.

2. The product of claim 1 in which the cellulosic mat is air laid prior to incorporation into the product.

3. The product of claim I in which the cellulosic mat is wet formed and dried prior to incorporation into the product.

4. The product of claim 1 in which the cellulosic mat is selected from defibered wood, thermomechanical pulps, chemical pulps, and mixtures thereof.

5. The product of claim 1 in which the cellulosic mat is combined with up to 20% by weight of noncellulosic fibers.

6. The product of claim 5 in which the noncellulosic fibers are selected from polyolefin fibers, glass fibers, and mixtures thereof.

7. The product of claim 1 in which the resin matrix is a thermosetting resin.

8. The product of claim 7 in which the resin matrix is selected from polyester, epoxy, methylacrylate, and phenolic resins.

9. The product of claim 1 in which the resin matrix is a thermoplastic resin.

10. The product of claim 9 in which the resin matrix is selected from polyethylene, polypropylene, acrylonitrile-butadiene-styrene, acetal, polyamide,polyimide, and polyester resins, and mixtures thereof.

11. The product of claim 1 in which the resin matrix is a mixture of thermosetting and thermoplastic resins.

12. The product of claim 1 which further contains up to 25% by volume of a glass fiber mat.

13. A method of making a composite pultruded product which comprises:
providing a heated pultrusion die;
supplying a plurality of essentially parallel continuous glass roving reinforcing strands to the die;
further supplying in parallel a cellulosic mat to the die, said mat having a density of no greater than about 0.45 g/cc and a basis weight in the range of about 100 -600 g/m2;
drying said cellulosic mat to a moisture content of 1% or less;
impregnating the roving and dried cellulosic mat with a thermosetting resin;
supporting said cellulosic mat on and enclosing said cellulosic mat within said roving strands; and drawing the impregnated materials through the heated die to form a pultruded product whereby the cellulosic mat reduces the density of the product while serving to maintain uniform resin distribution throughout the pultruded product.

14. The method of claim 13 wherein the resin is a thermosetting type which is essentially fully cured in the die.

15. The method of claim 13 wherein the resin is a thermosetting type which is only partially cured within the pultrusion die and further curing the pultruded product in a second die.

16. The method of claim 13 wherein the resin is a thermoplastic type.

17. The method of claim 16 in which the pultruded product is post formed in a second die.

18. The method of claim 13 which includes preimpregnating the cellulosic mat with resin prior to incorporation with the glass roving strands.

19. The method of claim 13 which includes impregnating the roving and cellulosic mat with resin in the pultrusion die.

20. The method of claim 13 which includes impregnating the roving and cellulosic mat with resin in an open bath prior to the pultrusion die.

21. The method of claim 13 which further includes supporting the cellulosic mat on a glass fiber mat as it is supplied to the pultrusion die.