CA1336742C - Composites of stretch broken aligned fibers of carbon and glass reinforced resin - Google Patents

Abstract

A coating of a viscous lubricant applied prior to stretch-breaking permits forming slivers of stretch-broken carbon fibers. When an anti-static ingredient is added to the viscous lubricant cohesive slivers of stretch-broken glass fibers can be formed. Composites of matrix resin reinforced with these slivers exhibit high strength, tensile stiffness, and good formability.

Description

TITLE
Composites of Stretch Broken Aligned Fibers of Carbon Reinforced Resin Backqround of the Invention This invention relates to a process for stretch breaking carbon and glass filaments and using the stretch broken slivers therefrom to form a composite of either a matrix reinforced with carbon fibers or a matrix reinforced with glass fibers.
Composite sheets of either continuous filament carbon fiber reinforced resin or continuous filament glass fiber reinforced resin have been made. One technique is to prepare a warp of filaments as by winding on a frame, impregnating them with resins and hot pressing to form a thin flat sheet which is cut from the frame. Several such sheets are then cross lapped and again hot pressed to form the final reinforced composite product. Such products have high strength and stiffness.
Problems occur when attempts are made to produce deep drawn three dimensional articles by hot pressing continuous carbon or glass filament containing resin sheets. The articles in many instances exhibit uneven areas and wrinkles. The use of staple carbon or glass fibers as reinforcement substantially overcomes the above-stated problems but at a great sacrifice to strength and stiffness.
In a similar situation involving P-aramid fibers, a solution to the aforementioned problem was the use of certain stretch broken P-aramid fibers as disclosed by Fish and Lauterbach in U.S. Patent No.
4,552,805. However, because carbon and glass filaments exhibit little or not cohesive capability when processed according to known stretch-breaking processes, slivers of carbon or glass fibers have not been able to be formed by these known processes.

The present invention permits forming cohesive ~livers of stretch broken filaments of carbon and glass for use in forming a composite carbon or glas6 fiber reinforced re~in useful for deep drawing purposes with little sacrifice of ~trength and stiffness.
Summary of the Invention A cohesive filiver of stretch broken gla6s or carbon fibers having a high degree of axial alignment and a coating of a finish compri~ing a vi~cous lubricant and an anti-static ingredient. Composite~ of a matrix resin reinforced with such ~livers and ~haped ~tructures formed therefrom are al~o encompassed.
Brief Description of the Drawing Fig. 1 is a schematic illustration of a preferred embodiment apparatus for use with a continuous proce~s in the practice of the pre~ent invention.
Fig. 2 i5 a schematic illustration of apparatus for applying finish to a carbon or gla~ filament yarn.
Fig. 3 i5 a schematic illustration of apparatus for stretch-breaking a cohesive carbon or glass yarn.
Detailed Description of the Preferred Embodiment Referring to Fig. 1, the preferred embodiment generally includes a creel 10 for yarn eupply packages 12, a plurality of yarn tensioning bar~ generally designated 14, a finish applicator 16 comprised of a rotatable finish roll 18 emer~ed in a pan 20 filled with a liquid finish 22 a pair of grooved roller guides 24,26 are located between the finish applicator 16 and a Turbo Stapler 28 ~manufactured by the Turbo Machine Co., Lansdale, Pa.). The Turbo-Stapler include~ a pair of driven nip rolls 30,32 which firmly grip the tow band 34 that has been consolidated from the individual yarns in guide 29. The nip rolls 30,32 feed tow band 34 at a constant rate to a pair of front rolls 36,38 which also grip the tow band 34 and withdraw it from breaker bar~
39 and feed it as a sliver to a condensing guide 40 from which the sliver is fed to a windup (not shown) for packaging.
In operation, glass or carbon yarn 13 from individual packages 12 is fed from creel 10 over finish roll 18 where it is coated with finish 22. The yarns are con~olidated in guide 29, tensioned between rolls 30,32 and front rolls 36,38, then randomly broken by 6harply deflecting them laterally by the breaker bar6 39. The coating of finish on the yarn in the sliver i6 sufficient to enable the sliver to be pulled through guide 40 to the windup without disassociation of the fiber6 in the sliver.
While the continuous process illustrated in Fig. 1 is preferred, the application of finish to continuous filament carbon or glas6 fibers and the ~tretch-breaking of the coated filaments can be carried out in two steps; i.e., separate finish application and stretch-breaking processes, according to Fig~. 2 and 3 and as described ~ubsequently in Example 1. More particularly, in Fig. 2, glass or carbon yarn 13 from package 12 i5 fed over yarn tensioning bars 14' over finish roll 18 where it is coated with fini~h 22 and wound onto a bobbin 12' and allowed to dry. The yarn from bobbins 12' is then stretch-broken by breaker bars 39 (Fig. 3) in the turbo-6tapler as describcd above in connection with Fig. 1.
The finish used in this invention i6 a material that causes an interfilament viscou6 drag ~ufficiently high to permit the handling required to make a composite, such as winding and unwinding from a package.
More particularly, the finish used for the carbon fiber application is a m~xture of a one part of a ~uitable anti~tat and two part~ of a non-tacky viscou~ lubricant of a consistency to impart to the chopped sliver adequate cohesiveness (minimum of .01 gram6 per denier) without tackiness or without compromising the 1 33674~

fiber-matrix adhesion in the final composite. The antistat portion of the mixture could be reduced or even eliminated if the reinforcing fiber is electrically conductive (e.g., carbon fibers).
A suitable viscous lubricant is polyethylene glycol (400 mol wt) monolaurate and a lauric amide while a suitable antistat is mixed mono and di-phosphate esters of C8-C12 fatty alcohols neutralized with diethanol amine.
Preferably, the percent finish on fiber is in the range of from about 0.3% to about 0.5% by weight.
Formable planar and shaped non-planar composites are contemplated by the present invention.
For the formable composites, that is, those composites that can be formed into shaped non-planar three-dimensional structures at elevated temperatures (where necessary), matrix resins of the thermoplastic variety or of the not fully cured thermoset type may be employed.
In the latter case the thermosettable resin is cured after the composite has been shaped. Suitable thermoplastic resins include polyesters (including copolyesters), e.g., polyethylene terephthalate, Kodar~
PETG copolyester 6763 (Eastman Kodak); polyamides, e.g., nylon 6,6; polyolefins, e.g., polypropylene; also included are the high temperature resins such as an amorphous polyamide copolymer based upon bis (para-aminocyclohexyl) methane, a semi-crystalline polyamide homopolymer also based on bis(para-aminocyclohexyl) methane, and polyetheretherketone. Thermosetting resins that are useful include phenolic resins, epoxy resins and vinyl ester resins.
The ratio of reinforcement to matrix can vary, but preferably is between 40% to 75% by volume. The average fiber lengths also may vary but preferably range from about 1/2 to about 6 inches in lenqth with a random overlap distribution. About B5 percent of the fiber6 are aligned within +10 degrees, preferably +5 degrees of the axial direction.
The composite may be made by a variety of procedures. Thus, a 6tretch broken sliver may be wound on a frame covered with a film of thermoplastic resin to form a warp. The warp of stretch-brokcn sliver, however, can be made by any technique known to those skilled in the art, e.g., by creeling or beaming. A
preform is obtained when another film of thermopla6tic resin is placed over the warp to form a sandwich which is heated in a vacuum bag and then removed from the frame. Several of such preforms may be stacked while offset to provide multi-directionality and then the ~tack may be heated under pressure to form a compo6ite rtructure.
Other techniques for applying matrix polymer include sprinkling of powdered resin on the sliver warp followed by heating to melt the resin, flowing liquid resin over the 61iver warp, intermingl~ng thermopla~tic fiber with the sliver warp and then heating to melt the thermoplastic fiber thereby forming the matrix resin, calendering the warp between layers of matrix film, etc.
Test Procedures Composite Tensile The composite tensile te6ts followed the general procedure described in ASTM Te~t D 3039-76 entitled "Standard Test Method for Tensile Properties of Fiber--Resin Composites. n Short Beam Shear The 6hort beam shear tests followed the general procedure described in ASTM Method D 2344-76 entitled, "Standard Test Method for Apparent Interlaminar Shear Strength of Parallel Fiber Composites by Short Beam Method" with the following exception, the loading nose was 1/16 inch radius instead of 1/8 i~ch.
Sliver Cohesion The yarn to be tested for sliver cohesion was S placed in the clamps of an ~nstron*ten6ile testing machine set to a gauge length of 17 inches, a cros6head speed of 10 inches per minute and a chart speed of 12 inches per minute. The crosshead was started to apply tension to the sample and the maximum force in grams indicated on the chart was recorded and divided by the sliver denier to give the sliver cohesion.
Finish on Yarn Finish on yarn i6 determined in a method wherein weighed ~pecimens are extracted gravimetrically with prescribed solvent(6) at room temperature, the solvent containing dissolved fini6h and any other materials which may wash off the specimens, is transferred to a preweighed container and evaporated.
The extractable residue is weighed. Percentage extractables based on extractable-free specimen weight is calculated. Aerothane (l,l,l-trichloroethane) is u~ed as the solvent for all finish material6 except glycerine and methanol is used as the solvent for that material.
High Temperature Tensile Drawing The sample to be tested was placed in the clamps of an Instron tensile testing machine get to a particular gauge length and a crosshead speed depending on the sample. A thermocouple was attached the surface of the sample midway between the clamps and an 8 inch long electrically heated cylindrical oven was placed around the sample leaving a one inch space between the bottom of the oven and the lower clamp. The open ends of the oven were plugged with insulation material to prevent convective heat loss and heating of the clamps.
* denotes trade mark The oven was turned on and the sample heated to reduce its viscosity to permit drawing (temperature determined by the viscosity, time, temperature data of the matrix material. Samples made with thermosetting matrix resins must be tested in their uncured state.). The sample was held at this temperature for 15 minutes to ~nsure thermal equilibrium. The crosshead was then started and allowed to run until the heated section of the sample was drawn 50%. The oven was removed and the sample inspected to determine whether it had broken.
Fiber Orientation A photomicrograph of the surface of the composite (enlarged 240X) was prepared. The angle between each fiber axis and the axial direction of the composite was measured with a protractor on the photomicrograph and tabulated. The percentage of fibers with an angle within + 5 degrees of the axial direction was reported.
Example 1 Four bobbins of 2000 denier continuous filament carbon fiber (3K AS-4 from Hercules ~nc.) were prepared for stretch-breaking by applying a finish composed of two parts of a lubricant ~polyethylene glycol monolaurate and a lauric amide) and one part of an antistat (mixed mono and diphosphate esters of C8-C12 fatty alcohols neutralized with diethanol amine). The finish was applied by running the continuous filament carbon fiber, one bobbin at a time, at 75 yards/minute over a finish roll which was wet with a 4% aqueous emulsion of the lubricant-antistat mixture (Fig 2). The four bobbins were allowed to stand overnight to evaporate the water. Finish level after drying was 0.33%.
The four bobbins of carbon fiber were stretch-broken on a Turbo-stapler (Turbo Machine Co., Lansdale, PA) as ~hown in Fig 3. The 6urface 6peed of the roll~ ~30,32) wa~ 3S.4 yards/minute and the turface 6peed of the front roll~ (36,38) wa~ 110 yards/minute.
The tip speed of the breaker bars (39) was 71 yards/minute. The resulting sliver wa~ 2422 denier and had a cohesion value of 0.18 grams/denier which was 6ufficient to allow winding without twi6t on a cylindrical paper tube u~ing a Leesona*type 959 winder.
The average fiber length of fifty measurement6 of this 61iver was 3.2 inches (shortest 0.7 inch, longest 5.6 inches).
A warp was prepared from this sliver by winding it from the paper tube, 25 ends to the-inch on a 16 inch square metal plate. A 2.0 mil thick film of lS thermoplastic re6in (an amorphous polyamide copolymer based on bis~para-aminocyclohexyl) methane) was placed on the frame before winding the 61iver and another was added after winding was complete. The entire sandwich was vacuum bagged at 280-C for lS minute~ after which time it was cut from the plate. Thi6 product, called a preform was now a well-impregnated, relatively stiff matrix/6tretch-broken 61iver 6andwich, in which all the 61ivers were aligned in one direction.
Twelve of the~e preform6 were 6tacked on top of 2S one another with all the fibers in the same direction.
Thi6 6tack wa6 heated ~n a mold at 305C at 500 pounds per square inch for 3S minute6 to make a well-consolidated plate 93 mil6 thick and fiber volume fraction of SS%. Short beam shear test6 conducted on O.S inch wide strip6 cut from this plate gave a value of 13,700 pounds per ~quare inch. It wa~ concluded that the presence of the finish did not adver~ely affect the adhesion of the fiber to the matrix polymer.
A 6econd plate was made from ten of the6e 3S preforms by stackinq them so that the direction of the * denotes trade ~ark stretch-broken fibers were offset by 45 degrees in a clockwise direction in successive layers. The bottom plane of the fifth layer was considered a reflecting plane and the next five layers were stacked 60 that the warp directions of the stretch-broken sliver were mirror images of the top five layers with respect to that plane. This sandwich was molded as above to make a well consolidated plate with a fiber volume fraction of 55%.
This plate was heated to 322C and molded into a hemisphere with a radius of 3 inches. The plate conformed very well to the shape of the mold and it was concluded that the product was deep drawable without wrinkles.
Example 2 A sliver of stretch-broken glass fiber was prepared by the method in Example 1 except that 6700 denier continuous filament glass fiber was u6ed (T-30 P353B from Owens-Corning Fiberglass) and the finish was applied by spraying a 10% aqueous emulsion on the fiber.
The emulsion was pumped to the spray nozzle at 5 cc. per minute and the air pres6ure used was 3 psi. The yarn was pulled past the spray head at 55 yards per minute by a pair of nip rolls and wound on a cylindrical paper tube. After drying, the finish level was 0.35%.
Stretch-broken sliver was prepared from two finish treated continuous filament bobbins and had a cohesion of 0.09 grams per denier which was adequate for winding as in Example 1. Further, the finish controlled static generation in the stretch-breaking process to an acceptable level. The average fiber length of fifty measurements of this sliver was ~.4 inches (6hortest 1.0 inch, longest 10.2 inches).
A unidirectional plate was made from this sliver and PETG film (Kodar PETG copolyester 6763, Eastman Kodak) by the method of Example 1 cxcept that the sliver spacing was 26 ends per inch, the film thickness was 3.0 mils and 8 layers of preform were used to 55% fiber volume fraction. Short beam shear tests on 0.5 inch wide strips cut from this plate gave a result of 5,400 pounds per square inch. It wa6 concluded that the presence of the finish did not affect the adhesion of the fiber to the matrix polymer.
Example 3 A sample of carbon fiber sliver was prepared using the stretch-breaking process of Example 1 except that finish was not pre-applied to the continuous fiber and two bobbins were used instead of four. The two ends of carbon fiber were contacted by a felt pad saturated with glycerine which was placed between thc tension guide and the infeed roll. Glycerine level on the sliver was 0.5%. The average fiber length of fifty measurements of this sliver was 3.2 inches (shortest 0.6 inch, longest 7.9 inch). Cohesion was measured as a function of time vs. the sliver from Example 1 with the following results.
Cohesion, grams per denier Days Glycerine Example 1 1 .58 .15 9 .79 .24 16 .02 .25 22 .02 .25 .02 .21 Example 4 Glycerine treated sliver from Example 3 was made into a warp, preforms and a unidirectional plate by the method of Example 1. The end count was 12 per inch, the film was 3.0 mil thick PETG (Rodar PETG copolyester 6763 from Eastman Rodak) and 6 preforms were stacked to make the plate which was 40% fiber volume fraction. The plate was cut into 0.5 inch strip6, provided with aluminum tabs and subjected to tensile te6ts at 8 inch guage length with the following results:

Tensile strength, psi. 127,400 Modulus, psi. 11,600,000 It was concluded that the product had very high strength and modulus. The uniformity of orientation of the fibers on the surface of thi~ plate were measured from a photomicrograph and it was found that 85% of the fibers were within + 5 degrees of the axial direction.
Example 5 Continuous filament 2000 denier carbon fiber was made into a warp, preforms and a unidirectional plate. The end count was 12 per inch, the film was 3.0 mil thick PETG (Kodar PETG copolye~ter 6763 from Eastman Rodak) and 16 preforms were stacked to make the plate which was 40% fiber volume fraction. The plate was cut into 0.5 inch strips, provided with aluminum tab~ and subjected to tensile tests at 8 inch guage length with the following results:
Tensile strength, psi. 139,800 Modulus, psi. 11,600,000 It was concluded that the product of Example 4 exhibited the strength and stiffness expected of continuous filament carbon fiber. The product of Example 4, although made of stretch-broken di6continuou~ staple fiber, came within 90% of the ~trength and 6tiffness of the continuous filament product. This excellent performance i~ believed due to the high degree of order of the ~tretch-broken fibers.
Example 6 Stretch broken glass sliver was prepared by the method of Example 2 except that finish was not pre-applied to the continuous fiber. Instead, the fiber being 6upplied to the Turbo-stapler was sprayed periodically with Jif-Job*antistatic spray (Schafco, ~ancaster, PA). The roll and breaker bar speeds were one-half the values in Example 2. The average fiber * denotes trade mark 1~ 1 33674~
length of fifty measurements of this sliver was 3.1 inches (shortest 1.0 inch, longest 5.8 $nch). This sliver was made into a warp, preforms and a unidirectional plate by the method of Example 1. The end count was 21 per inch, the film was 3.0 mil thick PETG (Rodar PETG copolyester 6763 from Eastman Rodak) and 5 preforms were ~tacked to make the plate which was 40% fiber volume fraction. The plate was cut into 0.5 inch strips, provided with aluminum tabs and subjected to tensile tests at 8 inch guage length with the following results:
Tensile strength, psi. 67,200 Modulus, psi. 4,950,000 It was concluded that the product had very high strength and modulus.
Example 7 Continuous filament 6700 denier glass fiber was made into a warp, preforms and a unidirectional plate.
The end count was 13 per inch, the film was 3.0 mils thick PETG (Rodar0 PETG copolyester 6763 from Eastman Rodak) and 5 preforms were stacked to make the plate which was 40% fiber volume fraction. The plate was cut into 0.5 inch strips, provided with aluminum tabs and subjected to tensile tests at 8 inch guage length with the following results:
Tensile strength, psi. 67,900 Modulus, p8i. 5,460,000 It was concluded that the product of Example 6 exhibited the ~trength and stiffness expected of continuous filament glass fiber. The product of Example 6, although made of discontinuous staple fiber, came within 90% of the strength and stiffness of the continuou~
filament product.

Example 8 A preform of stretch broken carbon fiber 61iver in an epoxy resin ~Hercules 3501-6) was made by the following procedure:
1) The frozen resin was thawed at room tcmperature, then heated to 180F for 15 minutes.

2) A film of resin was cast onto release paper then chilled to 40F to stop the polymerlzation reaction and the exposed surface was covered`with polyester film for protection.

3) The paper-resin-film ~andwich was wound on a 7-foot diameter drum and the polyester film removed.

4) 2300 denier graphite sliver made by the process of Example 1 was wound on the exposed resin at 9 ends per inch for a total width of 10.5 inches. The average fiber length of fifty measurements of thi~
~liver was 3.2 inches (shortest 0.7 inch, longest 5.6 inches).

5) The polyester film was removed from a second paper-resin-film sandwich and wound over the graphite layer on the drum to make a paper-resin-graphite-resin-paper sandwich.

6) The sandwich was unwound from the drum and vacuum bagged flat at 140F for 10 minutes to force the resin into the graphite layer, then frozen for later use. The thickness of the resin-graphite part of this sandwich was 7 mils.
A unidirectional compo6ite strip made by ~tacking together ten layers of 3/4-inch wide and 14-inch long strips (fiber direction parallel to the 14-inch dimension) of the graphite-resin preform was vacuum bagged for two minutes. One inch on either end of the strip was partially cured by heating it to 120C
for two hours while keeping the middle 12 inches of the strip cold with dry ice. At a guage length of 11 inches and a cros6head speed of 5 inches per minute, a high temperature tensile drawing test was conducted at 124C
on the 14 inch long by 0.75 inch wide 6trip which 6howed the composite could be drawn 50% without breaking, predicting a high degree of formability.
A composite plate was made from 10 layers of the 6andwich from step 6 above by removing the release paper, cutting the graphite-resin preform into sheet6 and stacking them so that the direction of the stretch-broken fibers were offset by 45 degrees in a clockwise direction in successive layers. The bottom plane of the fifth layer was considered a reflecting plane and the next five layers were stacked 60 that the warp directions of the stretch-broken sliver were mirror images of the top five layers with respect to that plane. This sandwich was vacuum-bagged at ambient temperature for 2 minutes to stick the layers together.
This plate was molded into a hemispherc with a radius of 3 inches and cured in the mold at 175C for 2 hours.
The plate conformed very well to the shape of the mold and it was concluded that the product was formable.
Example 9 Four bobbins of 2000 denier continuous filament carbon fiber (3K AS-4~from Hercules ~nc.) were stretch-broken on a Turbo-stapler (Turbo Machine Co., Lansdale, PA) set up as shown in Fig 1. A 10% aqueous solution of the finish described in Example 1 was applied with a wetted roll. The surface speed of the intermediate rolls was 17.7 yards/minute and the surface speed of the front rolls was 55 yards/minute. The tip speed of the breaker bars was 35.5 yards/minute. The resulting sliver was 2250 denier. The average fiber length of fifty measurements of this sliver was 3.3 inches (shortest O.B inch, longest 5.5 inches).

A warp was prepared from this sliver by winding it, 27 ends to the inch ~n a 18 inch square metal plate.
A 3.0 mil thick film of thermoplastic resin (PETG
copolyester) was placed on the frame before winding the sliver and another was added after winding was complete. The entire 6andwich was vacuum bagged at 220C for 15 minutes after which time it was cut from the frame. This product, called a preform was now a well-impregnated, relatively stiff matrix/stretch-broken sliver sandwich, in which all the sliver6 were aligned in one direction.
Seven of these preforms were stacked on top of one another with all the fibers in the 6ame direction.
This stack was heated in a mold at 200C at 400 pounds per square inch for 30 minutes to make a well-consolidated plate 82 mils thick and fiber volume fraction of 50%. High temperature tensile drawing tests at a guage length of 10 inches and cros6head speed of 10 inches per minute conducted at 262C on 12 inch long by 0.75 inch wide strips cut from this plate with the fiber direction parallel to the 12 inch dimension 6howed the composite could be drawn 50% without breaking, predicting a high degree of formability.
Example 10 Two bobbins of 6700 denier continuous filament glass fiber ~T-30 P353B from Owens-Corning Fiberglass) were stretch-broken on a Turbo-stapler (Turbo Machine Co~, Lansdale, PA) set up as 6hown in Fig 1. A 10%
aqueous 601ution of the finish described in Example 1 was applied with a wetted roll. The surface ~peed of the intermediate rolls was 17.7 yards/minute and the surface speed of the front rolls was 55 yards/minute.
The tip speed of the breaker bars was 35.5 yards/minute.
The resulting sliver was 4100 denier. The average fiber length of fifty measurements of this sliver was 3.4 inches (shortest 0.9 inch, longest 8.7 inches).

A warp was prepared from this 61iver by winding it, 22 ends to the inch pn a 18 inch square metal plate.
A 3.0 mil thick film of thermoplastic resin (PETG
copolyester) was placed on the frame before winding the sliver and another was added after winding was complete.
The entire ~andwich was vacuum bagged at 220C for 15 minutes after which time it was cut from the frame.
This product, called a preform was now a well-impregnated, relatively stiff matrix/stretch-broken 61iver ~andwich, in which all the sliver6 were aligned in one direction.
Seven of these preforms were stacked on top of one another with all the fibers in the same direction.
This stack was heated in a mold at 200C at 400 pounds per 6quare inch for 30 minutes to make a well-consolidated plate ~2 mils thick and fiber volume fraction of 50%. High temperature tensile drawing test6 at a guage length of 10 inches and cros6head ~peed of 10 inches per minute conducted at 262C on 12 inch long by 0.75 inch wide strips cut from this plate with the fiber direction parallel to the 12 inch dimension showed the composite could be drawn 50% without breaking, predicting a high degree of formability.
Example 11 Sliver from Example 10 was re-broken to reduce the fiber length by passing it through two set6 of elastomer coated nip rolls with a separation of 2.50 inches between the nips. The surface 6peed of the second set of rolls was 10 yards per minute and the ~urface 6peed of the first set of roll~ was 7.1 yards per minute giving a draft of 1.4. Denier of this re-broken sliver was 5371 and the average fiber length of fifty measurements of this sliver was 1.57 inches (shorte6t 0.5 inch, longest 3.6 inches~.

A ~warp~ was prepared from this sliver by winding it , 17 ends to the inch on a 18 inch square metal plate. A 3.0 mil thick film of thermoplastic resin (PETG copolyester) was placed on the frame before winding the sliver and another wa~ added after winding was complete. The entire sandwich was vacuum bagged at 220C for 15 minutes after which time it was cut from the frame. This product, called a preform was now a well-impregnated, relatively stiff matrix/6tretch-broken sliver sandwich, in which all the slivers were aligned in one direction.
Seven of these preforms were stacked on top of one another with all the fibers in the ~ame direction.
This stack was heated in a mold at 200C at 400 pounds per square inch for 30 minutes to make a well-consolidated plate 80 mils thick and fiber volume fraction of 50%. High temperature tensile drawing tests at a guage length of 10 inches and cro~shead speed of 10 inches per minute conducted at 262C on 12 inch long by 0.75 inch wide strips cut from this plate with the fiber direction parallel to the 12 inch dimension showed the composite could be drawn 50% without breaking, predicting a high degree of formability.
Example 12 Sliver from Example 9 was re-broken to reduce the fiber length by passing it through two set6 of elastomer coated nip rolls with a separation of 2.50 inches between the nips. ~he surface speed of the second set of rolls was 10 yards per minute and the surface speed of the first set of roll6 was 7.1 yards per minute giving a draft of 1.4. Denier of this re-broken sliver was 4623 and the average fiber length of fifty measurements of this sliver was 1.33 inches ~6hortest 0.6 inch, longest 3.1 inches).

A warp was prepared from thi6 61iver by winding it, 13 ends to the inch on an 18 inch 6quare metal plate. A 3.0 mil thick film of thermoplastic resin (PETG copolye6ter) was placed on the frame before winding the 61iver and another was added after winding was complete. The entire sandwich wa6 vacuum bagged at 220C for 15 minutes after which time it wa6 cut from the frame. This product, called a preform was now a well-impregnated, relatively stiff matrix/~tretch-broken sliver sandwich, in which all the sliver6 were aligned in one direction.
Seven of these preforms were 6tacked on top of one another with all the fiber6 in the same direction.
This 6tack was heated in a mold at 200C at 400 pounds per 6quare inch for 30 minutes to make a well-consolidated plate 80 mils thick and fiber volume fraction of 50%. High temperature ten6ile drawing test6, at a guage length of 10 inches and a cro66head speed of 10 inches per minute, conducted, at 262C, on 12 inch long by 0.75 inch wide strip6 cut from thi6 plate with the fiber direction parallel to the 12 inch dimension 6howed the composite could be drawn 50%
without breaking, predicting a high degree of formability.
Example 13 A pre-laminate was prepared from gla6s fiber from Example 2 by a continuou6 proce66 as follows:
46 ends of sliver were fed from a creel into a 6 inch wide warp which was 6andwiched between two 1.0 mil PET
poly(ethylene terephthalate) films to give a pre-laminate of 55% fiber volume fraction. A release film of Rapton* polyimide was placed on each 6ide of thi6 sandwich to prevent 6ticking of molten PET to hot 6urface6. This sandwich was then passed at 10 feet per minute through the nip of two steel roll6 heated to 278C to tack the assembly together.
* denotes trade mark A composite plate was made from this pre-laminate by removing the release film, trimming the excess PET from the edges and placing strips of pre-laminate in layers in a 16 inch 6quare mold. Each 5 layer was made up of side-by side strip6 of pre-laminate to reach the required 16 inch width.
A plate was made from 10 layer6 of pre-laminate by arranging them 80 that the direction of the stretch-broken fiber~ were offset by 45 degrees in a 10 clockwise direction in successive layers. The bottom plane of the fifth layer wa6 considered a reflecting plane and the next five layers were 6tacked ~o that the warp directions of the 6tretch-broken sliver were mirror images of the top five layers with respect 15 to that plane. This 6andwich was molded as ln Ex~mple 2 to make a well-consolidated composite plate with a fiber volume fraction of 55%. Thi6 plate was heated to 280C
and molded into a hemisphere with a radiu6 of 3 inches.
The plate conformed very well to the ~hape of the mold 20 and it was concluded that the product wa6 formable.
Example 14 A plate was made from 10 layers of pre-forms made by the method of Example 11 by arranging them in a 16 inch square mold 60 that the direction of the 25 ~tretch-broken fibers were offset by 45 degree6 $n a clockwi6e direction in 6uccessive layer6. The bottom plane of the fifth layer was considered a reflecting plane and the next five layers were 6tacked so that the warp directions of the 6tretch-broken 61iver were mirror 30 images of the top five layers with respect to that plane. This 6andwich was molded as in Example 2 to make a well-consolidated composite plate with a fiber volume fraction of 55%. This plate was heated to 280C and molded into a hemisphere with a radius of 3 inches. The 35 plate conformed very well to the shape of the mold and it was concluded that the product was formable.

Example 15 Continuous filament 2000 denier carbon fiber was made into a warp, preforms and a unidirectional plate by the method of Example 1. The cnd count was 25 per inch, the film was 2.0 mil thick film of thermoplastic resin (an amorphous polyamide copolymer based on bis(para-aminocyclohexl) methane). Seven preforms were stacked to make the plate which was 55 mils thick and 55% fiber volume fraction. The plate was cut into 0.5 inch strips, provided with aluminum tabs and subjected to tensile tests at 8 inch gauge length with the following results:
Tensile strength, psi. 243,200 Modulus, psi. 18,200,000 It was concluded that the product had very high strength and modulus.
Example 16 A warp was prepared from sliver from example 9 by winding it, 21 ends to the inch on a 18 $nch square metal plate. A 2.0 mil thick film of thermoplastic resin (an amorphous polyamide copolymer based on bis(para-aminocyclohexl) methane) was placed on the frame before winding the sliver and another was added after winding was complete. The entire ~andwich was vacuum bagged at 280C for 20 minutes after which time $t was cut from the frame. This product, called a preform was now a well-impregnated, relatively stiff matrix/stretch-broken sliver sandwich, in which all the slivers were aligned in one direction.
Seven of these preforms were stacked on top of one another with all the fibers in the same direction.
This stack was heated in a mold at 305C at 600 pounds per 6quare inch for 40 minutes to make a well-consolidated plate 5B mils thick and fiber volume fraction of 55%. One half inch strips cut from this plate were subjected to tensile tests at 8 inch gauge length with the following result6:
Tensile strength, psi 246,000 Modulus, psi 18,800,000 The uniformity of orientation of the fibers on the surface of this plate were measured from a photomicrograph and it was found that 92% of the fibers were within + 5 degrees of the axial direction. The product of this example, although made of discontinuous staple fiber, was equivalent to the strength and modulus of continuous filament fiber (Example 15).
Example 17 Continuous filament 6700 denier glass fiber was made into a warp, preforms and a unidirectional plate by the method of Example 1. The end count was 15.5 per inch, the film was 3.0 mil thick PET (poly(ethylene terephthalate)) and 5 preforms were stacked to make the plate which was 55% fiber volume fraction. The plate was cut into 0.5 inch strips, provided with aluminum tabs and subjected to tensile tests at 8 inch gauge length with the following results:
Tensile strength, psi. 156,000 Modulus, psi. 7,300,000 It was concluded that the product of Example 17 exhibited the strength and stiffnes6 expected of continuous filament glass fiber.
Example 18 A unidirectional plate was made from pre-laminate from Example 13 by stacking 5 layers in a mold with all slivers in the same direction and heating in a press as in the reference example to give a final thickness of 103 mils. One-half inch strips cut from this plate were subjected to tensile tests at 8 inch gauge length with the following results:
Tensile Strength, psi 86,800 Modulus, psi 5,900,000 It was concluded that strength and modulus of the product of this example, although not as high as those from continuous filament glass (Example 17) were far superior to those of randomly oriented glass composites of equivalent fiber volume fraction reported in the literature (ref. B.D. Agawarl, L.J. Broutman, "Analysis and Performance of Fiber Composites" p. 92) which are:
Tensile Strength, psi 23,000 Modulus, psi 2,400,000 This is a divisional application based on Canadian Serial No. 616,305 filed February 5, 1992, which was a division of Canadian Serial No. 554,032 filed December 10, 1987.

Claims (5)

1. A cohesive sliver of stretch broken carbon fibers having a coating of finish thereon, said finish comprising a viscous lubricant, said sliver having a cohesion of at least .01 grams/denier.

2. The sliver of Claim 1, wherein said finish comprises polyethylene glycol monolaurate and lauric amide.

3. A sliver of Claim 1 wherein the percent finish on the sliver is from about 0.3 to about 0.5% by weight.

4. A sliver of Claim 2 wherein the percent finish on the sliver is from about 0.3 to about 05.%, by weight.

5. In a process for preparing a sliver of stretch broken fibers that includes the steps of feeding yarn or tow continuous filaments into a tensioning zone, and tensioning said filaments to their breaking tension causing them to break, the improvement comprising:
feeding yarn or tow of carbon fibers into said tensioning zone and applying a finish comprising polyethylene glycol monolaurate and lauric amide.