CA2010285A1

CA2010285A1 - Fiber composite

Info

Publication number: CA2010285A1
Application number: CA002010285A
Authority: CA
Inventors: Harri Dittmar; Ludwig Wahl; Giorgio Greening; Manfred Heym
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-02-17
Filing date: 1990-02-16
Publication date: 1990-08-17
Also published as: EP0383199A1; ATE70002T1; EP0383199B1; DE59000017D1; DE3904813A1; JPH02248212A

Abstract

Abstract of the Disclosures Fiber composites which are suitable for molding, for example into auto parts, are produced in n continuous process by briefly pressing fiber bundles and molten thermoplastics in a double belt press under a pressure of not less than 10 bar to impreg-nate the fiber bundles to such an extent that the indi-vidual filaments are completely wetted.

Description

LV~85 O Z 0050~40584 Fiber composite The pre~ent invention relate~ to a procsss for producing fiber composit~s from ~ thermoplastics matrix and unidirsctional, parallel reinforcing fibers 5Fiber composites based on thermoplastics are increasingly used in automotive con~tructlon It has therefore been nece~sary to develop cos~-effective, high-throughput proce~se~ for producing such compo~ite~
DEoC-2,948,235 describes a proces~ for producing 10a glass fiber reinforced shQet of thermopla~tic In this proce~s, fiber mat~ needled in a double belt pres~ and a molten thermoplastic are pressed and consolidated to-gether under a pressure of from 0 1 to 20 bar to form a fiber reinforced sheet The comparatively low pres~ure is 15sufficient to impregnate the loose glass mat~ all over without leaving air bubbles Since the fiber~ in the glas~ mat~ are non-oriented, the resulting composite~
have the same, albeit comparatlvely low, strength and stiffne~s properties ln all direction- o~ the plane of 20the sheet Compo-ite- formed from thermopla~tic- and uni-directional reinforcing f~her- are des~ribed in GB-A~ 85,586 They are produced by th ~atchwise pres-ing of layer- of thermopla-tic- fil~ and layers of 25parallel flber bundle~ a~ above the oftening temperature of the th -~pl~-tlc under pre-~ur-- of about 70 bar It i- found that pre--ing ti~e- of an hour or longer are requir d to brlnq about complete lmpregnation of the fib r layer~, le wetting of the individual filaments 30~king up th fib r bundle-EP-C-56,703 de-cribe- a continuou~ proce-s for producing a compo-ite~material fro~ a thermopla~jtlcs polymer and parallellzed reinforcing fibor~ in the form of reving- -35Th -- rovlng~ ar pull~d through the molten th r~opla-tlc- polym r by the pultru-ion t~chnlque To then compl-t- th impregnation and wettlng of the -: . ,. :.:
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individual filaments, the rovings mu~t be mechan~cally opened out by pulling them under ten~ion over spreader surf~ses and forcing the molten thermopla~tic between the individu~l filament~ by fulling Thi3 ha~ the consequence th~t only comparatively sm~ll throughput~ are obt~inable end that brokan ends occur In ~ddition, air bubbles rem~in in the product If the ~iscosity of the thermo-plastic i~ redueed by the ~ddition of a solvent or pl~ticizer, then tha product contains re~idue~ of these additive~
It is an ob~ect of the present invention to develop a continuous process for producing fiber compo-~ites whereby parallel, mechanically unconnected fiber bundles can be quickly and completely impregnated with a melt of a ther~opl~stic The fiber composites produced by the proce~s shall be free of air bubbles and ~hall be very stron~ and ~tlff ln the directlon of ~lign~ent of the reinforcing fibQrs and be very tough We have found that thi- ob~ect i~ achie~ed according to the pr -ent invention by cont~nuou-ly introduclng parallel, mechanlcally unconnected fiber bundle- and a thermoplastic lnto a double belt pre~, pre~ing und r a peclfic pre~ur of not le-~ than 10 b~r at more than lO C above the ~elting polnt of the thermopla-tic for a period of fro~ 20 ~econd- to 20 minute-, and coollng under pre--ure In ~ preferred ~mbodiment, ~ double belt press i8 used oealed off on all ldes Such apparatus 1~ descrlbed ln EP-A-212,232 There lt 1~ u-ed for producing ther~o-pl~tlcJ web- wlth or wlthout relnforcement fro~ woven te~tlle, gla-- fiber or metal fabrlc- or from bonded flber web- Comparatlvely low pre--ure- are ufficlent to obtaln completo impregnatlon of the fabrlc- or fiber web- Th publlcatlon mentloned doe- not provide any lndlcatlon that by employlng pre-~ure- ~bovo 10 bar it $8 al-o po~ible to obta~n co~plete impregnatlon of parallel fiber bundle-. In tho woven fabrlc~ u~ed in ~P-A-212,232, .. .. , ~ . . . , _ _ _ ~ ... _ . .. _ _ . _ _ .. _ _ _ _ . .. .. . . . . . . .. . .. . .

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-20~0285 the par~llel fi~er~ are mechanically interconnected On uslng non-interconnected fiber bundles and deploying high pres~ure~ it was likely that tha fiber bundles would becom~ dislocated, destroying the par~llel arrange~ent s and h~nce reducing the lev01 of mechanical properties The pro~Qs~ accordlng to the pre~ent invent$on makes it po~sible to obtain complete and uniform i~pre~-nation of the fiber bundle~; that is, the molten thermo-plastic pQnetr~tes into the f~ber bundles, wetting and enveloping thQ individual filaments, even in the case of ~omparatively thick layer~, or tapes, 0 5 ~m or re in thickness In thi~ way it i- pos~ible to obtain high fiber contents of more than 50% by volume, which is otherwise only po~sible in a continuou~ method by impregnating with a solution of the thermopla~tic The fiber composite produced accordin~ to the present ln~ention preferably ha~ a fiber content of from 30 to ~0, in particular from 40 to 65, ~ by volume Tha compo-ite obtainod i~ free of holiday~ and ~ir bubble~ Thi~ m~ke- lt pos-ible to mold and pre~ the molding compound without employing the klnd of high pre-~uro- which would bo nece~-~ry if ~ir bubblo- h~d to be pre-~ed out Th proc--- according to the pre-ent in~ ntlon i8 c~rrled out on a doublo belt pre-- a- de-cribed for ex~mpl- ln EP-A-212,232 It 1- prefer~bly ~ealed off on ~ ide-, ao that no melt c~n e~c~pe at the id Thi~
can be acco~pli-hed by uitable e~ling m ~-ur -Tho reinforclng fiber~ can con~l-t of th~
cu-tomary ~terlal-, for e~mple gl~, c~rbon or Aro-m~tlc poly~mide-. Th y aro lntroducod into th~ double b lt pr -- ln the for~ of p~r~ll-l fiber bundlo-, either combin d lnto rorlng- or loo--ly lde by lde They ~re not mech~nlcally lnterconnect-d; that 1~, they ~r not ln th for of woven or knltt-d fabric Th b~l- ~ ight of tho flb r- 1- pr ferably 100-800 g m~~, ln p~stlcul~r ~ ,_,. , , , _ _ _ _ ~ _,,_ _. . . . .. . .. . . . . .. . ... . . . . . . .. . . ...

200-600 g m~2 The f$ber strands can be from 10 to 150 cm, preferably from 30 to 100 cm, in width The fiber bundles can be drawn off as rovings from a conventional creel;
however, it i~ advantageouRly possible to u~e a warp beam made up directly of filament ends The thermoplastlc can be introduced into the double belt pre~s in various forms Preferably, it is introduced a~ an extruded melt; but $t can alss be introduced in the form o a film which is then melted in the intake zone of the press It is even possible to u~e thermoplastic~ fibers, in which case they are advanta-geously premixed with the reinforcing fibQrs to form a hybrid yarn It i~ finally al~o po~slble to apply the thermoplast$c to the fiber bundle ln powder form by ~prinkllng or from an agueous dispersion, in which case it is then necessary to evaporatQ the water before the fiber bundle i~ introduced into the double belt pre~s In the double belt pres~, the fiber bundles are impregnated with the thermopla~tic- ~elt This is done under a pressure of not le-~ than 10 bar, prefer~bly of from 20 to 100 bar The temperature ~hould be ~ufficient-ly hlgh for t~e thermoplastic to be pre-ent a~ a melt;
that 18, the temperaturs i- re th~n 10 C, preferably more than 20-120 C, abo~ the meltlng polnt of ths thermopla-tic The re~idence time on the double belt pra-- 1- fro~ 20 econd~ to 20 ~in~te~, preferably fro~
40 econd~ to 4 minute- ~h double belt pre-- ha~ a cooling zone in which the compo-ite i- cooled to below the ltlng polnt ~nd thereby con-olld~ted The compo-lte according to the pre~ent in~ention ia u$table for u-e a- a mold~ng co~pound fro~ which lt i- po--ible, by ~oldlng and pr~-ing, to produce ~tiruc-tural component- for u-e in varlou- ector-, for e~ample automobile-, port~ ~rtlcle-, furnlture, etc EXA~P~E
A gla~- flbor warp be~m h~vlng ~ ba~i- welght of 400 g/~ 1- arrangod on ~ braked unrolling tatlon .. .. ,. . :

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_ S - O.Z. 0050/40584 2G~02~35 upstream of a double belt presH. Two further br~ked unrolling stat~ons are creeled w~th polypropylene fllms.
The films are 60 ~m ln thickne~s and ~re made of an i~otactic polypropylene having a melt flow index of 40.
S ~he ~heet of fibars drawn off the warp be~m i~ par~lleli-zed with the aid of a reed posltloned a short distance upstream of the $ntake point of the double belt pre4s and introduced into the double belt prs~s in a par~llel arranqement betwaen the two ~heets of thermoplastic. The unidirect$onal gl~s fibers are completely impregnated with polypropylene in the heating zone at 50 bar and 240-C and ~t a speed of 1 m/min and cooled and fi~ed under pre~sure in th~ solidifying matrix in the ~ub-sequent cooling zone. The result obta$ned i~ a high-quality unidirectional tape havlng a fiber Yolume contentof 50% and a thi~kne~- of ~bout 0.3 mm. For productlon width~ of 1 m thi~ repre~Qnt- a throughput of 32 kg/h, wh$ch illu~trate~ the good economic~ of the production process .

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Claims

1. A process for producing a fiber composite from a thermoplastics matrix and unidirectional reinforcing fibers by impregnating the fibers with a thermoplastics melt, which comprises continuously introducing parallel, mechanically unconnected fiber bundles and a thermoplas-tic into a double belt press, pressing under a specific pressure of not less than 10 bar at more than 10°C above the melting point of the thermoplastic for a period of from 20 seconds to 20 minutes, and cooling under pres-sure.

2. A process as claimed in claim 1, wherein the thermoplastic is introduced into the double belt press as a melt.

3. A process as claimed in claim 1, wherein the thermoplastic is introduced into the double belt press as a film.

4. A process as claimed in claim 1, wherein the thermoplastic is introduced into the double belt press in fiber form, preferably in the form of a hybrid yarn with the reinforcing fiber.

5. A process as claimed in claim 1, wherein the thermoplastic is introduced into the double belt press as a powder applied to the reinforcing fibers by sprinkling or from an aqueous dispersion.

6. A process as claimed in claim 1, which is carried out on a double belt press sealed off on all sides.

Abstract of the Disclosures Fiber composites which are suitable for molding, for example into auto parts, are produced in a continuous process by briefly pressing fiber bundles and molten thermoplastics in a double belt press under a pressure of not less than 10 bar to impreg-nate the fiber bundles to such an extent that the indi-vidual filaments are completely wetted.