CA1293916C - Interleafed fiber-reinforced thermoplastic composite - Google Patents

Abstract

INTERLEAFED FIBER-REINFORCED THERMOPLASTIC COMPOSITE
ABSTRACT OF THE DISCLOSURE

Disclosed are interleafed fiber-reinforced thermoplastic composites formed by introducing a ductile interleaf block copolymer layer to a fiber-reinforced thermoplastic layer. Also disclosed are methods for producing such composites. These composites are useful in numerous applications where toughness, impact strength and resistance to delamination are desirable.

Description

~.~~3~ 1~

~ RD-15,981) This invention relate~ to thermoplastic composite laminates with ductile interleaves~ More particularly, it concerns laminate~ in whioh the the complimentary thermoplastic refiins and interleaf copolymer resins are co~patibilized to produce an integral, layered composite~
9~L3~
The production of light weight, shaped objects, such as auto body parts, which have high i~p~ct strength, that can be laid up or molded into co~ple~
shape~, and that will retain dimensional stability oYer a wide variety of use conditions has been an enduring goal o~ plastics researchers and manufacturers for several decades. Recently, great advances towards this goal have been made using reinforced plastics or composites, in which two or more layers of re~inou~
shesting, sometimes using fibrou~ reinforce~ent, are laminated together to form a lamina~ed co~posite wherein the physical propertie~ of the resulting laminate exceed what would bç e~pected considering the properties o~ the individual layers~
Some of the most encouraging re~ults have been achieved with laminates employing reinforced résin layers in conjunction with an unreinforced layer of a di~ferent re3in~ In the area o~ high performance co~posites, i.e., as for aircraft pan~l , U.S. Patent 4,539,253, to Hirschbuehler, et al, disclose an interleafed fiber re~in matrix co~position wherein a rein~orced ther~o~et epoxy resin sheet i~ layered with a fiber-rein~orced interleaf resin including a thermose~
epoxy and a rubbery vinyl addition polymer.
U.S. Patent 2,719,100 to ~anigan discloses a pEocess fo~ hea~-sealing thermoplastic laminates, that i8, bonding to~ether (by heat) the co~ponent layers of -2- ~D-15,981~

thermoplastic films, e.g., poly(ethylene terephthal~te), PET, by interposing a substantially amorphou~ ther~o-plastic film between adjacent layers o ten~ilized, i.e., stretched, film to be heat-se~led. T~e heat-sealing p~ocess results in a strong, light-weight bonded film useful for packaging. ~owever~ because the process requires tensilization to make the l~minated film, it is diffieult to produce such films having a thickness substantially greater than 0~007W in a continuous type of stretching apparatus. Thus, thickne~s is a limiti~g factor.
Kennedy, in U.S. Patent 3,357,874, describes a process for laminating polyester films and other "addends~ onto the surface of a shaped polyester article by treating the surface with an acid wash (e.g., 85~
sulfuric acid3, to leave the surface in an amorphous conditionO When the amorphous surface of the film is brought into contact with an addend material, a la~ina~e is formed having a strong interface adhesion between the component layers. However, the use of an acid treatme~t i-~ costly and makes the substrates difficult to ha~dle.
U.S. Patents 3,798,116 and 3,969,176, to Bassett, et al, de~cribe a method for preparing bonded polyester film~ having a bead ~ype heat seal between the plies o~ the composite film.
U.S. Patent 4,041,206, to Tsunashima, et al, teaches that PET or poly~butylene terephthalate), P~T, films can be laminated directly to a cry~talline poly~butylene terephthalate) or poly(hexylene terephthalate) copolyester blended with 10-~0 weight percen~ PET or P~T, said copolyester containing 50-~0 mole percent terephthalic acid units. The resulting films are transparent, tough, slippery and have excellent heat-adhe~ive properties, making ~hem useful in general packaging, pbotographic films and electriCal ~3~
_3 (RD-15,9Bl) insulation. However 9 no mention is made of the sui~ability of this system for reinforced, dimen~ionally stable objects.
U.S. Patent 4~314,002 to oizumi, et al~
di closes circui~ board laminates co~p~ising alterna~ing fiber-reinforced curable ther~oset re3in layer. and unreinforced cured resin layers in which the same or a di~ferent re~in may be used in ~oth types of layer~O
The reinforced layers, e.g., linter paper or kraft p~per impregnated with a thermoset resin, are separated by cured resin layers, forming an integral la~inate in which voids between layers due to c~ntraction during curing are eliminated.
U.S. 4,373,002 to Peterson-~oj di~closes a heat-sealable laminated material co~prising a layer o stretched crys~alline polye~ter and a layer of cyclohexane-modified, heat-3ealable amorphous polyester ~aterial, which layers are joined by lamination or coextrusion and then subjected to a joint stretching operation. Th0 resulting la~inate is heat-sealable and also exhibits high tensile strength.
The foregoing pate~ts de~onstrate that considerable work has been done in the area of re~in la~inates, both reinforced and unreinforced, which obtain ad~antageous propertie~ by promoting, in various ways, clo~e bonding between the re~pective layers, to give an integral composite. There is ~till a strong need, however, for reinforced co~posite~ utilizing thermopla~tic resins to produce articles h~ving high impact strength.
It ha~ now been surprisingly discovered that unique, interleafed fiber-reinforced ther~oplastic composites can be fo~med using layers of a fiber-rei~forced ther~oplastic re~in separated by layers of a duc~ile thermoplas~ic in~erleaf copoly~er resin~

3~

_4~ ~RD-lS,981) The composites of the present invention are distinguished from foregoing composite~ in that the interleaf block copolymer resin is compatible with the fibee-reinforced thermoplastic resin ss as to undergo a co-crystalliza~ion or co vitrifica~ion, resulting in chemical interlayer bonding which has not been seen in prior art laminates~
Such co-cry tallization is achieved without any of the surface treatment techniques (acid treatment, tensilization, precuring, etc.) seen in prior processes.
The intelleaf copolymer resin form-R a ductile~
tough, rubbery layer, and, in th2 final co~posite o~ the invention, will form a diffuse interface with the fiber-reinforced, or "~inder~, resin. The final thermoplastic composites have high impact strength and high resistan.e to delamination.
While not intending to be bound by any theory of operation, it is believed that the following factors may be i~portant in providing the advantageous r~ults obtained with the present inventiono (i) Adhesion between the reinforced substrate and the interlayer occurs because the binder resin in the substrate and the hard blocks (hereinafter (a)) in the block copolymer of the interlayer mix with a negative Gibbs free energy. This may be a consequence of a co-crystalli2ability or of some o~her thermodynamic driving force, such as negative mixing enthalpy or positive entropic energy.
(ii) The soft block3 (hereina~ter (b)) in the block copolymer of t~e interlayer al~ay~ have low Tg, in fact alwa~s les~ than 25~C and typically les-~ than -~0C. This does not guarantee that they will be incompatible with the binder resin in the composite substrate, thus demixing during cool down. They mus~ be chosen on rigorous thermodynamic considerations to insure demixing.

3~

_5- ` (RD-15,9Bl) C~
The drawing illustra~es in perspective v1e~ a detail o~ an interlea~ed, fiber-reinforced thermoplastic composite of this inven~ion, showing the different layers included therein.
6Y~` ~9~
Provided in acccordance with the pres@nt invention are laminated fiber-reinforced thermopla~tic GOmpOS i te5 comprising:
~1) at least one fiber-reinforced layer comprising reinorcing filaments coated with at least one thermoplastic binder resin, and on at least one surface of said fiber-reinforced layer~
(2) a~ le st one interleaf layer comprising a block copolymer resin comprising polymer segments of (a) a least one thermoplastic resin co-crystallizable or co;vitrifiable with said binder resin, and (b) a~ leas~ one co-resin having a gla~s transition temperature (~g) substantially lower than said co-crystallizable thermsplastic resin.
Al~o contemplatad herein is a proce~s for producin~
laminated fiber-rein~orced thermoplastic composite~
comprising:
(1) forming a fiber-reinforced thermoplastic resin substrate co~prising fibrou~ reinforcement coated ~ith at least one thermoplastic binder resin, (2) introducin~ on at least one sur~ace of said sub~trate an interleaf layer comprising a block copolymer resin compri~ing polymer segments of (a) at least one thermoplastic r~sin co-crystallizable or co-vitriflable with said binder resin, and 3 t~;

~6~ l 5 , 9 ~ ~ ) (b) at least one polymer h~ving a Tg substantiallly lower than s~ld co-crystallizable resin, and ~3~ consolidating said fiber-reinfor~ed substrate and said interleaf layer unde~ su~ficient heat and pressure to ef~eot co-crystallization or co-vitrification of said thermoplastic coocrystallizable re~i~ at the interface between said substrate and said interleae layer, suoh that an integral composite is obtained.
ETAILED DESCRIPTION OF T~E INV~TION
The novel ther~oplastic composites of this invention use complemen~ary pairs of thermoplastic resins, which can be engineered to make integral, toughg fiber-reinforced, thermoplastic laminates with ductile interleaf layers. It is known that layers o~ a duotile resin included between fiber-rein~orced plies of a composite can augmen~ th~ survivability of such composi~es during tran~verse impact loading or other deformation modes associated with interply delamination.
~owever, the exact nature of the re~in, the thickne~s of the interleaf layer, and the quality of the bonding at the interface between the interleaf layer and other layers oP the la~inate are critical to the successful perfor~ance of the finished co~posite. In the pre3ent invention, for the first time, co~tinuous interlayer co-crystallization or co-vitrification leads to a type of diffuse bond between the reinforced layers and the interleaves, giving the finished composites of the present invention exceptional resistance to transverse impact loading and resistance to shear and chemical delamination.
The thermopla~tic resins in the ductile interleaves and the binder resins of the reinforced layers ~ust be ~co~plementary,~ i.e., the binder re~in and at least one segment of the interleaf copolymer must ~2~ 6 -7~ (~D-15,9~1) be diffusible in one another in the molten state, and upon crystallization or vitrification of the binder resin and the co--dif~usibl~ interleaf copolymer segment, they form a diffuse, continuous interlayer bond. The interleaf copolymer mus~ also include non~di~fusible segmen~s, which will prevent the total dissolution o~
the interleaf resin into the binder layer, thus maintaining the interleaf as a separateO ~uctile layer even with substantial intermixing (co-dif~usion) of the binder resin and other co-polymer segments. It i~ not critical that either the binder resin or the co-di~fusible components of the interleaf copolymer be crystallizable resinc, as long as the two polymers exhibit a high degree of chemical compatibility, resulting in a diffuse, continuous interlayerO The term ~co-crystalli~a-tion~, when referring to ~he interaction and bonding between the binder resin and the co-diffusible ~egments of the interleaf copoly~er, i~ expre~sly intended to cover not only cases where both components are co-crystallizable, bu~ also cases where they are co-vitrifiable due to other ther~odynamic consideration~.
The binder resin and interleaf copolymer may be selected from a wide variety of known resins that would be complementary a~ described above, or may be ~5 specifically syntheqized with laminated composites of the present in~ention in mind. Among such resins, given illustratively, are aromatic polyesters, polyamides and polyurethanes. The polyesters preferred for use herein include poly(l,4-bu~ylene terephthalate) and poly(ethylene tereph~halate) with minor amoun~s of polyes~ers derived from an aliphatic or cycloaliphatic diol, or mixture~
thereof, containing from 3 to about 10 carbon atom~ and at least one aromatic dicarboxylic acid. Preferred polyesters are derived from an aliphatic diol and an aroma~ic dicarboxylic acid have repeating units of the following general formula:

~3~

-B- (RD-15,g81) O =~ C--~ CE12 ) n ~ ~ C--/~

wherein n is an integer~ preferably 2 or 4, e.g., poly(l,4-butylene terephthalate~.
Also contemplated herein are the above polyester with additional amoun~s of polyol~ and~or acids in the amounts of from 0.5 to 50 weight percent based on the total resin compo3ition~ The acids can be aliphatic or cycloaliphatic with the number of carbon atoms covering the sa~e range. Polyalkylene ether glycols can also be used where the alkylene portion ha~
from 2 to 10 carbon atom~ and the entire ylycol ~ortion varies in molecular weight from 100 to 10,000. All such polye~ters can be made following the teachings of, for example, U.S. Patents 2,465,319 7 3~047,539 and 4,556,688.
lS When employed a~ the binder re~in for a composite to be used in the temperature range of from about 40 to about +150C, PBT exhibits a combination of modulus and toughne~s which ~ake it particularly preferred.
In for~ing the composites of this invention, the binder re~in, which may be crystalline or semi-crystalline or amorphous, i~ juxtaposed with a suitable fibrous reinforc~ment, eOg.~ a fabric, roving, yarn, tow, mat or tape o~ unidirectionally aligned continuous rein~orcing ~ilaments. The reinforcement can comprise a wide variety o~ materials including but not limi~ed ~o carbon, glass, graphite, cellulose, polyaramid, silicon carbide, boron, polyester, rayon, polybenzimidazole, polybenæothiazole and m~al-coated polybenzothiazole.
For sheet-like la~inates according to th2 inven~ion, the reinforcing material will pre~erably be ~29~

-9 (RD~15,981) woven into a f abric or a Elat, non-woven mat. Pre~erred as a rein~orcing fabric of high strength rein~orcing filaments is ~AGNAMI~E~ A370 (~ercule , Inc.~, a balanced 8-harness satin weave of ~000-count tows n ~ercules MAGNAMITE~ ~S4, high strength ca~bon fibers.
Tha fibrous reinforcement is juxtaposed with the binder resin by any of a number of w011 known method~, su~h as coating9 dipping, spraying, co-extrusion, wetting, etc~ Fo~ the purposes herei~, the term ~coatingU will encompass all known methods by which the reinforcement and binder resin are permanently juxtaposed, this in~ludes embodiments wherein the ~ibrous reinforcement is surface coated, as well as instance wherein the ~ibrous rein~orcement, in whatever form, is thorougly coated and impregnated with the binder resin. In cases wh~re the binder resin is in the form of a sheet or film, it is preferred to layer the fibrous reinfo~cement with the binder resin ~il~ and join the resin and reinforcement components under pre~sure, with heat if desired, e.g., 50-300C.
In preparing the interl~af film copoly~er, the thermoplastic resin segment can comprise a number o polymers, including by way o~ example, aromatic polyesters, polya~ides and polyurethanes. Almost any kind of thermoplastic re~in i~ suitable for incorporation into the interleaf copolymer t provided it is comple~e~ary with the binder re3in, that is to say, they are mutually co-diffu~ible in the amorphous state and are co-cry~tallizable or co-vitrifiable as defined above.
The second polymer seg~ent of the interleaf copoly~er c n also compr$se a ~umber of compounds.
Typically, thi~ polymer will have a glass transition temperature, Tg, substantially lower than the interleaf copolymer segment which is codiffusible with the binder resin. This ~elastomeric~ copoly~er segment, the ~so~t~

-10- (RD~15,981) segment is selected to be phase separable ~rom the "hard~ blocks preven~ing total dissolution o~ the interleaf into ~he binder resln at lamination temperatures, ensuring ~he pre~ence of a distinct S interleaf layer. Preferred as interleaf copolymer~ are poly~etherimide es~ers), such as General Electric Company's LOMOD J resin and copolymers of PBT and polytetrahydrofuran (PT~F), such as DuPont'~ ~YTR~L
thermoplastic elastomer. Segment length and overall degree of polymeri~ation of the interleaf copolymer may be varied by known techni~ues t in order to obtain particular desired properties.
In a preferred embodiment, PBT of the formula (~ ~f~ OC~2C~2C~2C~2o)p is employed as the binder resin coating a fabric or mat of reinforcing filaments, and an interlea~ copoly~er film comprising segmented PBT and PT~F is employed h~ving the formula O ~` O
( (C ~ cocEl~c~2cEl2c~2o)X(CE~2CE~2C~2C~2)y)c~

where p, q, x and y are variables adjusted to obtain an appropriate balance between modulus, ductility and toughne~s. Because the PBT segments of the copolymer can co-crystall~ze with the PB~ binder resin and due to interlayer-diffu~ion of PBT components in th~ binder resin and the copolymer, the in~erface between ~hem is broadened by diffusion at lamination temperatures above the melting poin~ of P~T, and a continuous inter~ayer adhesion is promoted. At the same time, the PT~F
segments in the copolymer prevent the to~al dissolu~ion ~2~3~

~ (RD-15,9~1) of the interlea~ resin into the binder re~in, due to a positive heat of solution between the dissimilar species.
The interleaf copolymer may also be prepared using conventional methods known to those skilled in the art. The copolymer may be advanta~eou~ly extruded a~ a film with a par~icular desired ~hickne~ or may be thinned to a lesser thickness using a conventional compre~sion molding press.
Tempera~ures and pressure for ~or~ing the thermoplastic interleafed composites will be varied according to the selec~ed resin and targeted applicakion~
The fiber-reinforced thermoplastic layer and interleaf film copolymer can be joined using technique~
w~ll known in the art, such as lamination, casting, coating, or spraying the interleaf onto a reinforced fiber-resin substrate.
For la~inated, p~nel-like composites of thl~
invention, any sequence o~ fiber-rein~orced ther~oplastic 29 sheets and interleaf copolymer film can be used. That is to say, the layers can be laid up in alternating layers, in any orien~ation, to any number of desired layers. As one illustration, given in the drawing, three plies are depicted. T~e corner of a sheet-like composite accoeding to the invention is depicted, wherein a woven fabric of rein~orcing filaments is used a~ the fibrous reinforcement~ The filaments of warp 1 are interwoven to form a sheet with the ~ilament~ 0 weft 2, and are coated with binder resin, e.g., P~T, to form integral fiber-reinforced layers 3 and 4.
Interlayer film 5 is sandwiched between reinforced layers 3 and 4, and after consolida~ion under pressure, an inte~ral composite is formed. The rein~orced layers may be arranged in any ori~n~ation to take advantage of the physical properties of the reinforcing fila~en~s ~;293~3~6 -12- (RD-15 ,981 ) or the physical characteristics of the weaYe, in the case of a woven reinforcing fabric. Those skilled in the art will appreciate the wide variety of layups that 5 are contemplated by the present invention,.

$he following examples illustrate tha novel methods and composites of the present invention and are not to be construed to limit the scope of the appended 10 claims in any manner.
Pre~aration of Fiber-Reinforced Sheets A faber-reinforced thermoplastic sheet wa~
prepared using poly(l, 4-butylene terephthalate ), VALOX~
310, General Electric Company, as the binder resin and woven high strength, high modulus carbon fibers, ~AGNAMIT~ A370, ~ercules, Inc., as the reinforcing substrate. ~AGN~ITE A370 is a balanced 8-harne~s satin weave of 3000-count tows of MAGNA~ITE- AS4 high strength, carbon fibers. The carbon fiber fabric was 20 heated to 450C in flowinq nitrogen to re~ove any sizing .
A fiber-resin co~posite sheet was prepared using carbon fiber fabric cut to 1~.0 x 11.4 cm in size.
The swatches were cut with tha sides parallel to the warp and weft of the fabric. The 14.0 cm dimension wa~
always parallel to the warp direction, Because of the particular weave, the front and back sides of the fabric appeared differently, with one side having fibers primarily in the warp direction. This side was designated the ~s~rong~ qides the other side was designated as the Uweaka side.
A sym~etric lay-up using four layers of carbon ~iber fabric and two extruded film layers of the PBT
resin was assembled. The average PBT film thickness was 0.0337 cm. T~e six layer~, viewed fro~ the top, were ~93~l6 13 (RD-15,981) assembled in a mat~ched die, positive-pre3sure, tool-steel mold in the following sequence: fabric ~weak)~P~T film/fabric (weak)/ fabric (strong)/PBT
filmffab~ic (~trong)~ The inner mold walls were treated w~th FREKOTE~ 44 mold relea~e agent according to the manufacturer's ins~ructioAs.
Th~ cold mold was placed between the platen~ of a 445 kN pre s (Pasadena ~ydraulics Inc.~. Th~ platens were made to lightly clamp the mold for positive heat transfer. To facilitate rapid heating, the platen~ we~e preheated elec~rically to 260C. ~hen the mold temperature, according to an e~bedded therMocouple, had reached 200C, co~pre~sive loading was introduced gradually until 250C, when the maxi~um force of l8 kN
was reached. The hot mold was quickly trans~erred to a Waba h high-produc~ion pre~s with water-cooled pla~en~, where the mold was allowed to cool under load control at 19 k~ After cooling9 the compo-~ite was removed from the mold.
The resultant fiber-resin composite sheet had glossy, s~ooth suEface~. When dropped on a h~rd surface, the composite produced a glassy ring. A
section was taken using a Buehler saw, and the section wa~ embedd~d in pott$ng epoxy and polished using 3tandard m~tallurglcal polishing technique~. There wa3 complete wettlng of the fabric surface and no interfaci~l cracking.
Another section w~ cut and trea~ed at 500C
in flowing nitrogen to ash th~ binder resinO T~e fiber weight fraction was 74.4~. Differential scanning calorimetry on sha~ed composi~e fragments in~icated the re~in in the PBT composite to be 36.2% crystalline.
Combining these measuremen~s, the fiber volu~e frac~ion was calculated to be 67.6~.

~'~9~

-14- (~D-15t9~1) An interlea film wa~ p~epared Prom a thermoplastic elastomer, copoly(ethermide ester), LO~OD
~-200 (&eneral Electric Co~pany~. The thermoplastic elasto~er wa~ an extruded fil~ with an average thick~e~
of 0.036 c~ S~o~io~ of film were thinned down to abou~ 0.011 cm using 222 kN of force in the 445 kN
Pasadena Hydraulics press. Th~ fllm wa~ placed between heavy gage aluminu~ foil sheets coated with polytetra-fluoroethylene (PTFE), also k~own a~ Dupont's T~LON~resin, the platens were preheated to 190C, and the foil/film/foil sandwich was left under load or 100 seconds.

Three thin fiber-reinforced PBT composite sheets were made according to the above procedure, except that each composite was made from two carbonofiber swatch*s and one P3T film. The swatche-~ were oriented weak/strong and the stacking seque~ce was ~abric/~ilm/
fabric. The three thin co~posi1 e~ were interleaved in a cold matched-die, posit~ve-pres3ure mold with three of the pre-thinned poly(etherimide e~ter) fil~3 in the following unsymmetrical sequence: composite/
interlea~/composite~in~erleaf/composite/interleaf. The molding conditions were the same as used to produce the fiberresin composite sheet~.
The lamina~ed composite plaque obtained had a smooth, high-gloss surface finish. T~e plaque wa~ fourld to contain approximately 15S poly(etherimide ester) by VolU~2. A glassy ring was produced by dropping the plaque on a hard sur~ace.
Specimens of the PBT/poly(etherimide ester) laminated composite la~inates were placed in 1,1,2-trichloroethane at 2SC. The polyletherimide ~9~6 RD-15981 ester) dissolved very quickly whereas the PBT showed no apparent solvation after several house. An embedded and polished section oE the laminated composite was exposed to circulating 1,1,2-trichloroethane at 25C
for several hours, then dried in air. Microsaopic examination revealed long thin areas, outside of the flattened, impregnated fiber tows, where the unreinforced poly(etherimide ester) had been extracted. A polished section was examined before trichioroethane extraction showed no evidence of delamination between the interleaf regions and the impregnated carbon fiber fabric.
Many obvious variations will suggest themselves to those skilled in the art in light of the above detailed description. For example, instead of using poly(1,4-butylene terephthalate) as the thermoplastic resin, other resins, e.g., polyamide or polyurethane, can be used. Instead of fabric comprising reinforcing carbon fibers, other fibers, such as glass, cellulose, graphite, polyaramide, silicon carbide, boron, polyester, rayon, polybenzimidazole, polybenzothiazole, metal coated poly(benzothiazole) or mixtures of any of the foregoing can be substituted. In the place of the complementary thermoplastic resin of the interleaf copolymer, other resins can instead be employed as long as they are co-diffusible and co-crystallizable or co-vitrifiable with the thermoplastic binder resin. For the polymer (b) used in the interleaf copolymer, other polymers, instead of poly(ethermide ester), can be employed so long as the interleaf copolymer as a whole leads to the formation of the impact and delamination resistant, integral composites such as described above. Instead of laminating the plies and interleaf films to form planar 1~3~91~i -16 - (Rl:1~15 ~981 ) l~mislates ~ the interl~af can be in'crodu~ed onto the reinforced th2~moplastlc ply by ca~ting 9 coating c~r spraying, and shaped article~ of two or mult:Lple layer~
can be made.
S All such variation~ are with.irl the full intend~d ~cope of the appended claim~a

Claims (38)

1. An interleafed fiber-reinforced thermoplastic composite comprising:
(1) at least one fiber-reinforced layer comprising reinforcing filaments coated with at least one thermoplastic binder resin, and on at least one surface of said fiber-reinforced layer, (2) at least one interleaf layer comprising a block copolymer resin comprising polymer segments of (a) at least one thermoplastic resin which is either (i) co-crystallizable or (ii) co-vitrifiable with said binder resin, and (b) at least one co-resin having a glass transition temperature substantially lower than said segment (a).

2. A composite as defined in Claim 1 wherein the composite comprises multiple alternating fiber-reinforced and interleaf layers.

3. A composite as defined in Claim 1 wherein the composite is shaped.

4. A composite as defined in Claim 1 wherein said thermoplastic binder resin is selected from aromatic polyester, polyimide, polycarbonate, polyamide and polyurethane, or mixtures thereof.

5. A composite as defined in Claim 4 wherein said thermoplastic binder resin comprises an aromatic polyester.

6. A composite as defined in Claim 5 wherein said aromatic polyester is poly(1,4-butylene terephthalate).

-18- (RD-15,981)

7. A composite as defined in Claim 1 wherein said reinforcing filaments are selected from cellulose, carbon, glass, graphite, polyaramide, silicon carbide, boron, rayon, polybenzimidazole, polybenzothiazole, and metal-coated polybenzothiazole filaments, or combinations of any of the foegoing.

8. A composite as defined in Claim 7 wherein said reinforcing filaments are in the form of a fabric, mat, tow, roving, braid or unidirectional alignment.

9. A composite as defined in Claim 1 wherein the thermoplastic resin segment (a) of the interleaf copolymer is selected from aromatic polyester, polyimide, polycarbonate, polyamide and polyurethane.

10. A composite as defined in Claim 9 wherein said thermoplastic resin segment (a) comprises an aromatic polyester.

11. A composite as defined in Claim 10 wherein said aromatic polyester comprises poly(1,4-butylene terephthalate).

12. A composite as defined in Claim 1 wherein said co-resin segment (b) of the interleaf copolymer is selected from poly(etherimide ester) or poly(alkylene ether ester).

13. A composite as defined in Claim 12 wherein said co-resin segment (b) comprises poly(etherimide ester).

14. A composite as defined in Claim 12 wherein said co-resin segment (b) comprises poly(alkylene ether ester).

15. A composite as defined in Claim 14 wherein said poly(alkylene ether ester) comprises poly(tetramethylene ether terephthalate).

16. A composite as defined in Claim 1 wherein said interleaf copolymer comprises poly(1,4-butylene -19- (RD-15,981) terephthalate-co-ethermide ester).

17. A composite as defined in Claim 1 wherein said interleaf copolymer comprises poly(1,4-butylene terephthalate-co-tetramethylene ether).

18. A composite as defined in Claim 1 wherein said thermoplastic binder resin comprises poly(1,4-buty-lene terephthalate), said reinforcing filaments are carbon fibers, and said interleaf copolymer comprises poly(1,4-butylene terephthalate-co-etherimide ester).

19. A process for preparing an interleafed fiber-reinforced thermoplastic composite comprising:
(1) forming a fiber-reinforced thermoplastic resin substrate comprising fibrous reinforcement coated with at least one thermoplastic binder resin, (2) introducing on at least one surface of said substrate an interleaf layer comprising a block copolymer resin comprising polymer segments of (a) at least one thermoplastic resin which is either (i) co-crystallizable or (ii) co-vitrifiable with said binder resin, and (b) at least one polymer having a glass transition temperature substantially lower than said segment (a), and (3) consolidating said fiber-reinforced substrate and said interleaf layer under sufficient heat and pressure to effect either (i) co-crystallization or (ii) co-vitrification of said thermoplastic co-crystallizable or co-vitrifiable resin at the interface between said substrate and said interleaf layer, such that an -20- (RD-15,981) integral composite is obtained.

20. A process as defined in Claim 19 wherein the integral composite comprises multiple alternating fiber-reinforced and interleaf layers.

21. A process as defined in Claim 19 wherein the integral composite is shaped.

22. A process as defined in Claim 19 wherein said thermoplastic binder resin is selected from aromatic polyester, polyimide, polycarbonate, polyamide and polyurethane, or mixtures thereof.

23. A process as defined in Claim 22 wherein said thermoplastic binder resin comprises an aromatic polyester.

24. A process as defined in Claim 23 wherein said aromatic polyester is poly(1,4-butylene terephthalate).

25. A process as defined in Claim 19 wherein said reinforcing filaments are selected from cellulose, carbon, glass, graphite, polyaramide, silicon carbide, boron, rayon , polybenzimidazole, polybenzothiazole, and metal-coated polybenzothiazole filaments, or combinations of any of the foregoing.

26. A process as defined in Claim 25 wherein said reinforcing filaments are in the form of a fabric, mat, tow, roving, braid or unidirectional alignment.

27. A process as defined in Claim 19 wherein the thermoplastic resin segment (a) of the interleaf copolymer is selected from aromatic polyester, polyimide, polycarbonate, polyamide and polyurethane.

28. A process as defined in Claim 27 wherein said thermoplastic resin segment (a) comprises an aromatic polyesters

29. A process as defined in Claim 28 wherein said aromatic polyester comprises poly(1,4-butylene terephthalate).

30. A process as defined in Claim 19 wherein said co-resin segment (b) of the interleaf copolymer is selected from poly(etherimide ester) or poly(alkylene ether ester).

31. A process as defined in Claim 30 wherein said co-resin segment (b) comprises poly(etherimide ester)

32. A process as defined in Claim 30 wherein said co-resin segment (b) comprises poly(alkylene ether ester).

33. A process as defined in Claim 32 wherein said poly(alkylene ether) comprises poly(tetramethylene ether terephthalate).

34. A process as defined in Claim 19 wherein said interleaf copolymer comprises poly(1,4-butylene) terephthalate-co-ethermide ester).

35. A process as defined in Claim 19 wherein said interleaf copolymer comprises poly(1,4-butylene terephthalate-co-tetramethylene ether).

36. A process as defined in Claim 19 wherein said thermoplastic binder resin comprises poly(1,4-butylene terephthalate), said reinforced filaments are carbon fibers and said interleaf copolymer comprises poly(1,4-butylene terephthalate-co-etherimide ester).

37. A process as defined in Claim 19 wherein said fiber-reiforced thermoplastic substrate is formed by laminating a thermoplastic resin film on said fibrous reinforcement.

38. A process as defined in Claim 19 wherein said interleaf copolymer forms a film and is introduced to the fiber-reinforced substrate by lamination.