CA2055443A1 - System for adapting heat shrinkable fibrous structures to particular uses - Google Patents

Abstract

2055443 9112959 PCTABS00007 Composite product of adjacent interconnected layers of heat shrinkable fibers, made by heat shrink processing of interconnected such layers of differential shrinkage properties.

Description

W(~ 91/12959 2 0 ~ PCr/US91/011)34 me preserrt ~ tion rela~es to strucbural or filler devices ~ i.e., batts, bl~, r~ds, cylir~ers and sheets (and crther device fonns~ made of ~tic fibers ~bit~ high te~erature resista~x eS~ hi~h sb:er~ an~Jor high ~ulus of devices of ~e class dess~ibed abav~s and a~aratus an~ me~d combinations utilizing the ~ame in relation to acoustic, electrical and,/or t~mal in~ulatian; panlgling (a~3 a liT~, facing or frees stan~i~ panel); filter~; particle-s~i~;
filler; ~ re~æding; str~gthening and/or stifIening;
im~act/vibration absorbing; and/or other functions. The a~l f-- CllstamiZed adaptatian of the same to particulæ uses.

W O 91/12gS9 PCT/US91/01034

2~ 2-We have, in past patenting and cammercial activity, presented devices of the class first described above (an~ related ~ethcds and apparatus) wherein stretchr~, heat shrinkable, ncn-metallic fibers are used m parti~llar laid-up cc=str~otions and shrink prccessed to yield slabs, sheets or batts (or other structures) made up of self-bonded fibers. Ihe e~d product slabs, sheets or batts have a ~Ple~ted high density oompared to ~he original layup (but lcw c ~ to ~ valent thickne5s and equivalent porcsity ceramic or mtal or fiber-reinforced-matrix structcres). The fibers or a major portion thereof ~n any such devioe, are preferrably sel~cted from the group of heat shrin~olble polymers consisting of polyamids, polyimides, acrylics, polypropylene (and higher poly-olefins), polypb~nylene sulfide, polyetherimlde, aroma~ic ether ketanes an~l ~he lilce, wit~h up to five wei~t ~t c~tent of plasticizing materi~l in~ to suc3h fibers tprefe~rably } Gf olig~rs of ths fi~er's ba~;ic polymer species). Our prior w~rk is describ~d, e.g., in p~blished U.~ . Appl. 2217355, in non-pthe t ~ ks PYR~PEL, of Alba~r: ~ tianal ~orporation.

lhe disclosures of the forego m g referenced publications and other items are ~ orporated herein by reference as thc~gh set out a~ length herein.

It ~ an dbjec~ of the present invention ~o enhance ef~ecti~e utilization of d~vices of the class first cited above.

It is a further dbject o~ the invention to provide a system for matching mass production and custom t~;1Orin~ n ~ .

W O 9t/12959 PCT/US91/01034 2 ~

-3-It is a f ~ er object of the LnVention to prcvide a new class of dimensionally stable, flame resistant, high strength, light weight and insulating materials.

S~MWRY ~F T9E INUENIIoN

Ihe in~ention utilizes mLltiple layers, each made of heat shrinkable fibers of substantially differing shrinkage characteristics m distinct but oooperating groups, generally as adjacent layers made of different such fibers - i.e. layers A-B
using fibers a and b, respectively. The adjacent layers are interconnected, as hereinafter described, and then shrink processed together to yield a comçosite product with structurally distinc* adjaoent layers ~hat are compatible with each other and in tandem impart distinct characteristics to the composite p~uct.
Each component layer, group o~ layers, ox the like, experienses a processing essentlally as ~Gerrib3d Ln p~blished U.K. patent ap~lication 2217355. First, various ~ nt fiber katts are preFared by fiber carding, air layi~g, wet lay1ng ~r any cther batt-making p~soess known to the art. Second, layers are intcrconnectoi by reQrienting some of the fibers in each layer in thP z-direction by hesdlLng, hyG~centanglement or any cther process Xnown to the art. qbird, ~he felt structure comprised of m terconnected layers is restr~ined about its periphery an~ subjec~ed ~o a ~hermQl treatme~t sufficient to induce considerable fiber shrinkage especially among fibers oriented in the unrestramed z-direction. This prccess yields densified structur~s c~ntaining dense z-axis pillars of shrunken fibers that have bonded together ~t ~iber-t~-fiber cro6s over po~. .

2 a ~ PC~/US91/01034 It is an important difference compar~d to our prior sLngle layer prccess mg (or process~ng of sta~ked, but not i ~ nnected, similar layers), that in mLlti-layer processing according to the present in~ention (processing of Lntenc~nn3c~rd layexs of different shrinkage ch~racteristics), the two adjacent layers are Lnter-nedled to a substantial ex~ent. m at is, fiber~directing, bar*ed or fluted needles pass throu3h the thi ~ es of both layers and in a high density of needle penetrations thrcugh the stacXed layers.
The modes of differentiating and otherwise controlling shrinkage characteristics and respective end product properties are fiber composition selection, fiber preparation and history, including pre-stretcbing and heat treatments, type and frequency of the z-axis pillars, and thickness an~ (x, y) fiber density of the original layers. Of ~hese, the m~st significant m~de is the type of fiber and frequency of z-axis pillars. Physical restraint of some portions of the layers during shrinkage (e.g., hQlding side edges of sheet materials in a frame during heating) and heat t ~ tment conditions are also very significant control method~.
Ihe inNention can be applied to in-situ pro*uction of curved end pro~ucts, e.g., as pipe wrappings us m g the piFe itself as a mandrel during prcce5sing, or used for other shaped or flat end produc~s.
The invention can be aF~lied in mLltiples of basic m~dules for greater fle ~ ility of design. For example, consider a non-wcven nedlefelt fabric's c~mpcnent layers A and B of thicknesses of l/2 inch each as l ~ d up and n ~ ad, with A shrinkable to l/8 inch and B not ahrinkable under common shrink processing. It is also feasible to provide such a felt wherein A an~ B æ e bo~h shrinkable but to different degrees of shrinkage, e.g. a 2:l thicknss shrinkage of one such layer and 5:1 of the other.) Instead of the basic single mLdLle A-B composite described above, çne can make A-B~i-B~A or B~A-i-E-A four layer/two m~wle composites, or A-B-i-A or B-A-i-B tlIree layer/two module WO 91/12959 PCr/US91/01U34 2 û ~ 3 c~osites, w~ere i is an i~lterwn~ion means ~ a~ an adhesive or a further array of lig~t dsnsity of i~
needled fibers ~etwe~ two basic modules. ~ee or ~re m~les can be pr~vided ~n a single pr~t. ~ ~aboration of the basic A-B pattern enlarges the range of c~i~s pr~ts ' pr~perties (e.~., stiffness, th~mal ins~latic~ ar~ or acalstic insulation) that can be provid6d. It is also possible, but less prePerred because of complexlty of control, to provide expanded modular composite units of re than two layers per mcdNle, e.g.
A-B-A, ~-B~C in a sincle such mcdLle or a nLltimcdular arrays, e.g. A-2~A-i-A-B-A-i-A-B~C with a first ~ e layer n~dule, seoond three layer module, etc.
While the discussion of the invention hereinafter is explained in terms of utilization of polyimide as the heat shrinXable polymer fiber to be use, it will be ~nder~tood that cther hea~ shri ~ le ~bers can be e~pl~yed, mcluding polyamides, polyesters, acrylics, polypropylene and higher polyolefins), polyphenylene sulfide, polyetherimlde, aromatic ether ketanes and the like.
Ihe oompocite produsts can be subjected to moldiny, bendin~, piercing, c^~ting, assembly and other manufacturing or installation steps after heat shrink proce~ g as outlined above.
Alternatively some of such steps can be integrat3d wlth heat shrink pmoessir~.
Other Qbjects, feat~res, and advantages will ke apparent from the foll ~ de*ailed dæ ription of preferred embodimYnts taken in conjunction wlth the acocmpanyin~ drawing in which:

FIGS. 1 an~ 2 are block diagrams of practioe of tw~
preferred embod~ s o~ the mvention.

WO 91/12959 PCr/US91/01034 E :tGS . 3-l ar~ 3-2 are phc~ icr~graF~s of cross-sections of material produced as irxlica~ IGS. 1 and 2, re~ectively;
and FIG. 4 is a cr~s~-section ~sc~etric sket~h of two co~ple~nentary pieces produced in accordance with the FIG. 1 en~il~nt, mold0d and ass~led.

~2~D ~E~P~C~ OF }~ ~

The follaw~n~ two non-limit~r~ examples ;llustra~e practice of the illvention in two (A-B) and three (A-B-C) layer versions.

I: A-B M~DULE (two layers) An A-B mod~le was p ~ as a flat sheet comprised of two different polyimide fiker layers.

: Ihe fiber chosen for use in the A-layer was 2.2 dtex, 60mm high-shrink Lenzin~ P84 staple fiber. Ihe fiber chosen ~or use in th~ B- la~er was 5.5 dtex, 6omm low-shrink lenzin~ P84 staple polyimide fiber. ~oth f~bers are oommercially available. High-chrink P~4 fiber was carded and lightly needled approx. 500 penetratio~s/square m.) to form a batt welghting 7 aunoa/square yard I~w ~hrir~c P84 fiber was- similarly pr~cess~ into a batt weighir~ 13 oz/square yar~.

A laysr of the high shrird~ P84 3~att was r~dled a tatal of 6, 000 penetratio~s/square in. to a final thi~kness of o. 09" . A
layer of th~ low sh~iTik P84 batt was attached to the hig~ shrir~c fe:Jt b~ ~lir~ ~ ~e la. ~hri~c ba~t i~to ~he hlgh ~hrinl;
layer at 250 p~ra~ians/square in~h. Ihe resulting tw~layer W O 91/12959 PCT/US91/01~34 2Q~44~

felt had a thickness of 0.33 inch, a basis weight of 18 ounce/square yard, an~ a density of 4.5 lb./cubic foot The layered felt was restrained in the plane of the fabric using a rigid metal frame. Ihe ~ ned felt was subjected to a thermal treatment of one hsur at 630 degrees F. The resulting structure was a flat sheet of 0.28 inch thickness ccmprised of a thin dense and flexurercapable but essentially rigid layer ~Layer ~) joined to a thick lofty non-rigid (compar~d ~ A) layer (Layer B). lhe thickness and density of each layer and th~ complete structure are repor~ed in Table I-l.

I~BLE I-l (m.)(lb/cu. ft) Layer A 0.04 10.2 Layer B 0024 5.0 Mkdule A-B 0.28 5.7 Ihus Iayer A had essentially a 2:l thickness shrinXa~.e (from, 0.09 inch to 0.04 inch) while layer B had min ;_.l shrlnkage. Such a praduc~ is useful in ~hermal insulat.~n æ~arded primarily by Layer B with special bene~it in assem~ly anl prctection due to thc high shrink layer.

m e foregoing processing is repre~ented by the block diagram of FIG. l.

WO 91/1~9~9 PCr/US91/01034 EX~ II. A-B~ ~ (~hree layer) An A-B C mo~le was pr~pared as a flat sheet cc~rised of three differ~t layer~ of polyi~n~de fi~xr.
lhe fiber cho~en for use ~n A- and C- layers was 2.2 ~c, 60 mm high~;hrin)c ~enz~r~ P84 staple fiber. I~e fiber chosen for use in Layer B was 5 ~ 5 ~c, 60 mm., la~shrir~c ~z~ng P84 staple fiber. High shrink P8~ fiber was car~ed and li~htly needl~d (~t 500 p~etratians/sq~are ~.) ~o form batt~ of 4 and 10 oz/~e yar~l. Law ~3hrir~c P84 fiber was co~verted ~nto a lightly ne~led batt weigl~ 18 a~e/s~3uare yard.
Two pieces of lcw shrir~c batt were needled together to form ~yer B. ISis was acca~lish~d by passin~ the batts tl~ a needle loam twioe at 250 p~2etrations/ ~ are in ~ per pass. The high shrink fiber layers were attached in ~ ate operations. m e

4 cunce/s ~ yard high shrink ba~t was placed on Layer B an~
attached by nedling through the high shrink fiber into the low shrink fiber at 250 penetrations/square inch for~ing Layer A. The 10 cunce/square yard high shrink b~tt was placed on the other side of Layer B and needled ~ h the high shrink fiber into the low shrink f~ber layer at 250 pene~rations/square inch. Ihe resulting three-layer felt had a basis weight of 52 ounce/square yard and a total thi ~ of 0.85".
~ he laycred felt was restralrei in the plane o~ the fabric using a rigid me*al frame. The restrlined felt was subjected to a ~hermal trea~ment of cne hour at 630 degrees F.
lhe resulting stru~*ure was a flat sheet cc~prised of three layers diffP~ing in thickness and d~nsity as reported Ln Table II-2. In this mGdule, the d~nsity of the different laye~s did nok differ greatly, but the th~n hlgh shrink fiber layers (Iayers A and C) provided smooth even ~urfa~

W O9t/12~59 PCr/US91/OtO34 ~9~ 2~5a~4~

l~ELE II-2 mickness Density Layer A 0.04 9.1 Layer B 0.31 lO.0 Layer C 0.07 10.9 M~ULE A-B~C 0.42 10.1 The foregoing processing is represented by the block diagram of FIG. 2.

***

FIGS. 3-l and 3-2 are photomicrographs of transverse sections. at 8 and lO x magm fication, respectively, of a two-layer lammate produced substan~ially as in Example 1 above (3~ d of a thxee layer lami~ate praduced Yu~dlle1al~y as in ~ le 2 ~above ~3-2). Z-axis pillars are seen in FIG. 3-l within la~ers A and B, i.e. ZAl, ZA2, ZBl, ZB2 an~ ~ 2-axis pillars are also abservable Z~Bl. Penetraticn is net n*cess~rily thrcugh the full thickness of either or both layers. Similarly, Z-axis pillaxs are indicated for FIG. 3 2, i.e. ZAl, ZBl, ZCl, Z~B, ZECl.
The fibers are preferably polyImides an~ more particularly polymers oomposed of strotor~l units of the general form~la:

WO 91/129~9 PCr/US91tO1034 o o (o o o 'or where R is:
c~3 (~II) ~3 .' ~

W O 91/1~959 PCT/lJS91/01034 i 2 ~ 4 ~
M~nor amounts (preferably not re than 5 w~i~ht per oent) of plasticizin~ material can ke included in the fiber. Such plasticizer~ may be solvents ~or the polymer (e.g., dimethylformamide, n-~ethyl pyrrolidone or dimethyl a oetamide as solvents for polyimide) and~or lcw molecular weight olig~mers of the same polymer.

Ihe lay-up of fibers involves separat m g an~ dispersing the fibers in web6 by fib~r carding, air lay ~ , wet lay m g or some othRr process known to the art and stabilizi~g these waks by light needling (tacking) or scme o~her m~ans kno~n to the art to form katts. One or more shRe~s of a selected oo~position are used to form a layer and these are combined via needling, hLdroentanglement or scme other prooess knc~n to the art for c#mbi ~ fibrcus webe. Fibrcus layers (ea~h oomprised o~ sheets or groupe of attached sheets) are oombined m a ;=bse3uYnt step u~ m g needl1ng, hydroentanglem~nt or some other process to form layered felts ~uitable for use m this invention. Ihe type and extent of the neadl ~ pnocess (or other process designed to reorient fiber in the z-direction) deeen=ines the loca~icn and characteristic5 of the z-axis n~dle tracks which span layers of fibers ori ~ in the x- and y-directions. Ihe z-axis needle tracks, which will oor~espond to pillars m the thermally treated products, are usually of higher densiti~s (frequencies of oocurenae) than the sheet areas EurrooDding each such pillar, normally in a ratio of 2:1 to 3:1.

The degree of needling (no. of penetrations) is correlatable to the stiffness of the resultant pro*uct after shrinXing, wl~h a higher nedling leading to a greater stiffn2ss or tension and in oo~pression.

The heat treatment of layered felts required for W O 9t/12~59 PCT/US91/01n4 preparatian of devices herein described can be ex0cut0d us mg a variety of well known restrainin~ devices and h~ating devices.
RestrairLuYg devices include but are nct limit2d to tenter fran~s and welded clamp m ~ frames. Heatiny devices mclude any number of ovens and presses capable of uniformly heating the frame ~d felt to a tençerature su~ficient to in*uce shrinkage. Clamping and thermal treatments may be execut3d as batch or cont m uous processes. In any case, the thrmal treatment m~st be con~ucted above the glass transition temperature of the fiber. In the case of the lenz mg P84 used in EXamples I a~d II, thermal treatments in excess of 600 F are requir3d. Heating rate and treatment time m~st be specified in oonsiderati~n of the fiber t ~ , module weight and thickness, an~ characteristics of the cla~pm g device and heatmg devioe.

Significant bondir~ oc~rs at fiber cross over points in the shrinka~le fiber layer. I~e ext~t arx3 str~h of bo~s is nat related to the de~ree of shrir~age per se, but is related to for~e a~plication ~hic;h often correlates to degree of fihrirJcage, but not ~rlvariably. ~he ten~erab~res of heat shrinkage are not surficient to ~use the ~ss~ng fibers or o~herwise bond th~
withaIt si~ultar~s a~plicatian of suitable force.

Ihere can be syr~gistic usage of the in~ed layers erein ane is used to ~ nstraln ~ e o~her esse~tially laterally of their parallel (almost common) plane(s). for example, if an inter-needled mrdule A-B with A of high shrinkage and B of lower shrinkage (or no shrink) characteristics is wrapped around a pipe or cther cylin~rical or a m former. Ihen shrinkage of A will constrain B to establish a higher density of ~ and lower thickness than wculd occur in a planar format.

Complex parts can also be formed after heat shrink prccess m ~. FIG. 4 is a part-sec~ion and part isometric view of W O 91/129~9 PCr/US91/01034 2~5~ ~

a pair of oomplementary molded parts which tQgether form a pipe eIbow. Ihe upper piece is 10 and has a low shrinkage layer lOA
and high shrinkage layer 10~. The lower piece is 20 and hAs a law shrinkage layer 2QA and a high shrinkage layer 20B. Each ~art as molded from a sheet ~orm, subsequent to heat shrink processing of the sheets per se, has side flanges (121, for Fart 10~ 2 æ for part 20) and a curved central portion (16 for part 10, 26 for part 20). Ihe flanges are n ~ down at their outer edges while thickness o~ layers lQ~, lOB, 2Q~, 20B is cther essentially unmodified by molding. Ihe moldiny ef~ects a glaze-like surface o~ the faces 12F, 22F, 14F, 22F of the ~lange portions. The flanges are Fer~anertly assembled by adhesive kcnding an~/or by fastener means (bolts, clamps or clips, etc.) ~he elbow can ke supported on a base, by hanger means or ky ducts assembled to iks ope mngs I and II (e.g., by insertion of duct ends into such eIbow ope mngs or okher ccuplin~s).
Ihe molding is done under light forces at a temperature just above the glass transition temperature of the fiber ccmpo=ents of the p~rts.

It will ncw k~ apparent to those skilled. m the art tha~ other e~xxliments, improvements, details, and uses can be made oonsistent wlth the letter and spirit of ~he forego mg ~;crlosure an~ within the ~oope of this paten~, which is li~ited only by the foll ~ claims, crnstrued in acoordance with the patent law, including the doctrine of equivalents.

~ hat is claimed is:

Claims (12)

1. A structural or filler article of manufacture comprising one or more pairs of adjacent layers of heat-shrinkable fibers of different shrink characteristics in the respective layers which have been heat treated together to produce a differential degree of fiber shrinkage from layer to layer and consequent differential densification of the layers, the layers of at least one adjacent pair of layers being Z-axis linked by spanning pillars of Z-oriented fiber groups that span the layers.

2. Article as in claim 1 wherein the adjacent layers are of flat sheet form.

3. Article as in claim 1 wherein the adjacent layers are of curved sheet form.

4. Article as in claim 1 as made with a layer of essentially no shrinkage and a shrinkable layer connected thereto.

5. Article as in claim 1 as made with two heat shrinkable layers of substantially different shrinkage characteristics.

6. Article as in claim 1 comprising a single pair of adjacent such layers.

7. Article as in claim 1 comprising a triad of such layers.

8. Article as in any of claims 1, 6 or 7, comprising multiple modular sets of adjacent such layers in combination and co-acting to jointly provide composite properties, the modular sets being loosely bonded in comparison to the interlayer bonding of layers within each modular set.

9. Article as in claim 1 wherein the fibers are of a composition selected from the class represented by structure I
and including structures II through IV.

10. A process of utilizing heat shrinkable fibers to establish a controlled multi-density structure, comprising the steps of:

(a) establishing adjacent layers of heat shrinkable fibers of differing shrink characteristics, (b) establishing lateral interpenetration of fibers from one of said layers into the other, to form a laminate, and (c) restraining the laminate from shrinkage in at least one lateral dimension and heating the laminate above the glass transition temperature of fiber components of at least one of the layers.

11. Process of claim 10 wherein the laminate is heated above the glass transition temperature of both the adjacent layers.

12. Process of claim 10 wherein the laminate is molded subsequent to its heat shrink processing.