Reinforced plastics materials

© Beginning of patent period: 15.Feber 1974 Longest possible duration:

© Issued on: 25.November 1974 © Inventor:

© dependence:

OE 318909 © Pamphlets considered to delineate the state of the art:

FR-PS 1 565 738 - 2 -

Nr.318909

The invention relates to a method for producing a resin-impregnated strip or a

Train.

Plastic materials reinforced with fibers, especially glass fibers, have gained considerable technical importance and are used, for example, in the construction of aircraft, ships, buildings, pipes and storage vessels. The reinforced plastic materials may be prepared either according to the wet support method or according to the dry support method.

In the latter method, which is increasingly being used, a previously impregnated reinforcement generally referred to as a prepreg, ie, a preimpregnated material, is used, and the reinforcement in the form of a woven fabric of a fiber mat in chips or a highstrength tape a film impregnated with a resin contains. The resin is generally used as a composition which has been carefully formulated using the proper proportions of ingredients such as hardeners, fillers and catalysts. Often the resin component is a liquid and thermosetting and the treatment is carried out by pre-stretching the resin to a solid but fusible and curable B-stage during the preparation of the prepreg. A resin in the B-stage can then be fully cured, if desired, ie, after the prepreg or prepreg has been formed into the desired configuration. The use of prepregs has the advantage over the wet pad method that the manufacturer of fiber reinforced materials is freed from many of the problems associated with the storage and handling of the resin components, and generally a product is obtained which has a uniform distribution of the resin Resin has.

Known fiber reinforced plastic materials are less rigid than many metals and this has precluded their use in certain applications, for example in the manufacture of compressor blades in jet engines. Recently, however, carbon fibers have been used as reinforcing materials for plastics, giving the products high strength and rigidity combined with low weight. Other fibrous reinforcing materials used today include boron, silicon carbide, silicon nitride and aluminum oxide.

Carbon fibers are supplied in the form of tows or tow or as rovings with continuous fibers wound on a cylindrical bobbin without deliberate introduction of twist so that the fibers are more or less parallel. The cylindrically wound fiber cable on the cylindrical bobbin is generally known as a cross-wound bobbin. A typical fiber cable contains about 10,000 individual fibers.

Because carbon fibers are difficult to handle, for example, they are very light and brittle, methods which have been used successfully in the manufacture of resin impregnated fiberglass hands can not be used in the manufacture of resin impregnated carbon fiber tapes.

Web form carbon prepregs were prepared by dipping a number of fiber cables into a dilute solution of resin in a volatile solvent, placing the impregnated fiber tow side by side exactly parallel and without overlap, and then rolling the fiber tows to the same thickness with a heated roller. In another method, unimpregnated fiber cables are laid side by side, then covered with a resin film and rolled with a heated roller to form the film.

These processes are very slow and uneconomical, and attempts have therefore been made to produce continuous ribbons of impregnated carbon fibers from two or more fiber tows. The manufactured tape is generally between about 1 cm and 15 cm wide and has a thickness of about 0.1 cm or less. Consumers of these tapes have strict requirements. Thus, the band may not be trimmed at the edges and its width may not vary more than about 1.15 mm. There must be no voids between the individual fiber cables that form the band, and the fiber cables must be straight and free from wrinkles. The individual fiber cables forming the tape must be held together during subsequent processing operations and the density of the tape should be constant over the entire width.

The invention provides a process for the production of resin-impregnated tapes.

According to the invention, a method for producing a resin-impregnated belt or a web, by impregnating a plurality of fiber cables or Thick strands, in particular of carbon fibers with a solution of a first resin in a volatile solvent and juxtaposition of the fiber cables in the form of a band of substantially equal width, whereupon the solvent is substantially removed from the formed bands and a plurality of these bands are created, which is characterized a second resin is applied to the adjacent belts under the action of heat and / or pressure, wherein the second resin flows around the belts and a coherent resin-impregnated belt is formed.

In general, the second resin, caused by heating and applying pressure, is caused to flow around the aligned bands. When one or both of the resins are thermosetting, the conditions which cause the second resin to flow around the arranged bands may be chosen so that the - 3 -

No.3189O9 thermosetting resin is converted from the A-state into a solid, but still meltable B-step product.

The preparation of such B-stage materials requires great caution, because if the reaction is carried out too far, the resin is converted to the fully cured and infusible C-stage, and this is the

Makes tape worthless for further processing.

Preferably, the resins, especially the second resin, are selected so that the arranged bands are joined together without the second resin being converted to a B-stage product, ie, the second resin remaining primarily in the A-state. Tapes made in this way have a longer service life (shelf life) than those in which the resin was converted to a B-state product.

The apparatus for producing resin-impregnated strips of a plurality of fiber cables, in particular of carbon fibers, comprises:

Means for impregnating a plurality of fiber cables with a solution of the first resin, means for forming each fiber cable into the form of a band of substantially constant width, means for cutting the impregnated bands from which substantially all the solvent has been removed into an edge to arrange adjacent to edge relationship,

Means for contacting the upper and lower surfaces of the arranged bands with a second

Resin,

Means for causing the second resin to flow around the tapes to form a continuous resin impregnated tape therefrom, and

Devices to move the fiber cables through the device.

With reference to the drawings, an exemplary embodiment of the invention is given.

Fig. 1 is an overall side view showing a preferred apparatus according to the invention; Fig. 2 is a plan view of a bath which can be used to impregnate the carbon fiber cables; Fig. 3 is a plan view of one type of molding apparatus used to form the fiber tows, showing a section along lines 3'3 'in Fig. 3a; Fig. 4 is a plan view of a second type of forming apparatus, showing a section along the line 4 * 4 'in Fig. 4a; Fig. 5 is a plan view of a third type of molding apparatus, showing in Fig. 5a a section along the line 5'5 '; Fig. 6 is a section of the rolls used to place the strips in an adjacent edge-to-edge relationship; Fig. 7 is a section of the nip rolls used to cause the second resin to flow around the fibers of the belts arranged, and Fig. 8 is a view of a tubular impregnating bath tank.

With the exception of Fig. 8, the drawings show a device suitable for making tapes of seven fiber cables of carbon or other fibers, this being only an exemplary embodiment. The number of fiber cables depends on the width of the belt and the required fiber density.

Referring to Fig. 1, reels or packages of carbon fiber cables are hung in the frame -1- so as to be above the tank -2- containing the resin solution for impregnating the fiber cables. The reels are hung with their longitudinal axes parallel in a horizontal plane, so that the individual fiber cables can be guided to the impregnating without them tangle. The reels can rotate when the fiber cables are unwound from them. If desired, the fiber cables may be heated before entering the impregnating bath. This causes the fibers to be free of moisture and sometimes it helps to impregnate.

To effect a complete impregnation, the fiber cables are preferably passed under a freely rotatable roller -3- which is suspended near the bottom of the tank -2-. Instead of the roller -3- a solid rod with a smooth surface can be used.

After impregnation, the fiber tows from the tank -2- are passed through a former -4-, where each fiber tow is deformed into a ribbon, enforcing the expansion of the fiber tows, and wherein the resin receptacle (ie, adjusting the resin solution, from the fibers are taken) is measured. The tapes are passed from the mold device -4- to a drying apparatus, which may be a tube of suitable cross-section, and heated externally, for example by an electric heating mantle. This tube can lie in the horizontal or vertical plane. Preferably, the fiber cables in the dryer remain long enough to remove at least the major portion of the solvent, but the temperatures and heating time are selected so that no appreciable reaction occurs between the resin components. In Fig. 1, the drying apparatus includes a furnace -5- containing a vertical tube which is heated by an electric heating mantle, and the impregnated tape is conveyed from one side of the tube over a freely rotatable roller -7- over the Tube is suspended, led down to the other side of the tube. The tube should be sufficiently wide so that there is no danger of the impregnated bands contacting the heated sides. In order to prevent solvent from passing from the still solvent-wet belt on one side to the dry belt running along the other side, the tube may be equipped with a central, solvent-impermeable part -6-.

The dry impregnated tapes are then inserted into a device which they place in a - 4 -

No.318909 contiguous edge-to-edge relationship. This device may be in the form of channels separated by vertical guide rollers or guide pins, a comb or, as shown, by two grooved rollers -9 and 10. In Fig.l is shown how the tapes emerge from the lower part of the furnace and are fed via a roller -8- to the alignment device. This roller is not free to rotate, and thereby stress is generated in the fiber cables, and this causes the fibers to be arranged in parallel in the end belt.

The arranged tapes are then fed into a device where resin films are continuously applied to their lower and upper surfaces, and then the resin is caused to flow around the fibers to form a coherent structure. Preferably, this is accomplished in one step, wherein the means for applying the resin film and the means for causing the resin to flow around the fibers include two forming rolls (11 and 12) which are heated and resiliently urged against each other when the aligned ribbons are introduced into the nip between the rolls together with a resin film, the resin flows around the fibers, forming a coherent impregnated ribbon. The tape is wound on a spool -15- for storage until needed. It is generally necessary to wind a peelable intermediate layer together with the tape to avoid sticking between the adjacent layers. The resin may have a strippable backing sheet, for example of polyethylene or paper, on the side opposite that which is brought into contact with the arranged ribbons. These sheets can either be removed after the tape has been formed on rolls -11 and 12- or they can be left on the tape to act as a removable interlayer. In the apparatus shown in Fig. 1, the reel -15- is driven by an electric motor, which is not shown, which is capable of maintaining a selected constant speed. The movement of this reel pulls the fibers through the device.

Fig. 2 shows a mold of the impregnating bath. The container may be made of any suitable material, such as metal, glass, plastics or glass reinforced plastics. As mentioned above, the fiber cables can be passed under a freely rotatable roller -3- suspended near the bottom of the tank to effect complete impregnation. This roll is preferably grooved, as shown in Fig. 2, and each fiber cable passes through the roll in a separate groove. The grooves should preferably have in their base area the same width as the proportion of the width that each fiber cable contributes to the total width of the end band. For example, if 7 fiber cables are arranged in a side-by-side arrangement to form a belt having a width of 7 cm, then each fiber cable contributes 1 cm to the total width of the belt and the grooves in the roller are 1 cm in their base wide. By passing around the roller, the fiber cables are slightly flattened and this facilitates the passage of the fiber cables through the device through which they pass as they exit the impregnating bath while continuing to stretch smoothly and removing the excess solvent of the resin. In general, the apparatus is such that, although the fiber tows are considerably flattened, the tapes which are produced are thicker than the finished tape, the thickness of which can be regulated by rolls -11 and 12-.

The molding apparatus may have slots through which the fiber cables pass and which are cut or formed in metal, glass or other suitable material. Preferably, the length of each slot is equal to the proportion of the width that contributes each fiber cable in the end band. In Fig. 2, the molding apparatus includes a series of slots (21) cut in a metal sheet -22- which can form a partial cover of the tank -2-. The upper and lower ends of the slots may be rounded. The forming devices may also be hollow cones, the upper ends of which are flattened to form the necessary slot-like openings, and the lower ends of which have a circular cross-section and terminate in correspondingly shaped nozzles cut into the lid of the tank -2-. A nozzle of this type, connected to a tubular impregnating bath, is shown in FIG.

The molding apparatus may also be in the form of two hard surfaces between which the impregnated fiber cables are passed and which surfaces have means to limit lateral expansion, ie to regulate the width of the bands. Preferably, the restriction devices are arranged so that the width of each band is equal to the proportion of the width that contributes each band to the total width of the end panel. The restriction devices may be rods attached to the surfaces or grooves cut into the surfaces. The surfaces and rods can be made of hard material with a long service life, which can be made very smooth, for example of glass or a metal, such as brass or steel.

One type of this molding apparatus is shown in Figs. 3 and 3a. Two plates -31 and 32- which are separated by a distance equal to or greater than the thickness of the strip to be produced are held vertically above the impregnating bath. The fiber strands pass through the plates and are separated and confined by a series of rods -33- connected to the plate -32- and pass through holes in the plate -31-. The distance between the plates can be regulated by moving the plate along the bars.

- 5

Nr.318909

A second type of molding apparatus is shown in Figs. 4 and 4a. Two plates -41 and 42- are located horizontally above each other above the impregnation bath. Each plate has bars -43 on one side_O44-, which is preferably separated by the proportion of the width that each fiber cable contributes. The removal of these plates is not critical and, if desired, they can be moved horizontally so that they are not in the same vertical plane. Each fiber cable -40- is passed from the bath next to the plate -41- between a pair of rods -43-, then between the plates and finally over the end -2- of the plate -42- between a pair of rods -44- , The ends of plates -41 and 42- between the bars may be rounded.

Yet another type of this molding apparatus is shown in Figures 5 and 5a. This contains two grooved rods -51 and 52- which are mounted horizontally above the impregnating bath. They are mounted so that they do not rotate, but can be adjusted to each other to give a more or less large degree of winding for the fiber strands -50-. The width of the grooves -53- in each bar is preferably equal to the proportion of the width that each band contributes to the final web.

Returning to Fig. 1, the fiber cables can be passed directly into the impregnating bath and drawn around the roller -3, but the very light carbon fibers tend to flourish in the resin solution in an uncontrolled, irregular manner. This inclination may result in uneven fiber density belts and so it is preferable to introduce each fiber cable into the bath through an entrance opening which regulates and locks the fibers as they pass the roller -3. The entrance opening may be a gap or gap between two teeth of a comb or a small circular cavity cut in a metal plate or other suitable material. Particularly good results have been obtained with circular eyes -23- sunk into the cavities cut in the metal plate -24- as shown in FIG. The eyelets may be made of hard, wear-resistant, very smooth material such as ceramic, metal or glass. The distribution of the openings over the surface of the tank and their separation depends on the width and density of the desired band.

Instead of passing the cable strands through a bath, each fiber cable can be passed through a separate impregnating solution, for example, held in a U-shaped tube as shown in FIG. As shown therein, the impregnating bath contains a glass tube -81- which, for example, has an inner diameter of about 2 cm and is bent by a radius of about 5 cm. The nozzle includes a flattened glass tube -82- having a conically shaped end portion -83-, the outer surface of which is adapted to fit within a corresponding flange -84- attached to the end of the U-shaped tube.

Preferably, rollers -7 and 8- at the top and the outside of the drying tower, as shown in Fig.l, are grooved in the same manner as roller -3-. The impregnated dry tapes leaving the roller may, as mentioned above, be arranged in an adjacent side-by-side arrangement by channeling them down through channels so that the tapes at the end of the channels in the same horizontal plane in the desired relationship. However, in a preferred embodiment, the arraying of the dry ribbons is accomplished using two grooved surfaces, the width of the grooves and the raised surfaces between the grooves being equal to the width fraction each band contributes to the total width of the end web and the grooves are aligned on a surface with the raised surfaces between the grooves of the second surface so that the bands passing through the grooves of one surface, in an adjacent side-by-side relationship with the bands passing through the grooves of the second surface. The grooved surfaces may be in the form of two comb-like structures made of metal, but it is preferable to use grooved rollers (9 and 10). Figure 6 shows in the part a pair of rollers with which one can form a web of seven bands.

The upper roller -9- has four grooves -61- which are separated by three protruding parts -62-. The width of each groove and each protruding part is preferably equal to the width of each band. The lower roller -10- has three grooves -63- which are separated by two protruding parts -64-, the protruding parts and the grooves have the same width as that of the upper roller. The grooves of the lower roll are in the same vertical plane as the protruding parts of the upper roll and the protruding parts of the lower roll are in the same vertical plane as the grooves of the upper roll.

The seven belts leaving the roller -8- are split, with four passed through the upper roller -9- in the four grooves -61- and three through the lower roller -10- in the three grooves -63-.

The rollers -9 and 10 are as close as possible to the rollers -11 and 12-, so that the belts leaving the rollers -9 and 10 rapidly enter the nip of the rollers -11 and 12-, where they are pressed in the contiguous side-to-side relationship.

The rollers -11 and 12- may each have flat surfaces, but preferably a roller adjacent to the rollers -9 and 10 has a groove all around as wide as the required width in FIG.

No. 3,189,909 of the end web, while the other roll has a mating protrusion part that fits into this groove. Such rollers are shown in FIG. The gap between the groove

--71- and the projection or the shoulder -72- is preferably adjusted so that one can produce tapes with different thicknesses.

When the arranged belts pass from the rollers -9 and 10 into the nip of the rollers -11 and 12-, a continuous resin film is applied to the upper and lower surfaces of the spools -13 and

14 - (see Fig.l) attached. One or heath of the rollers - 11 and 12 - can be heated to the

Flow of the resin to support the fibers. Preferably, the continuous resin films contain a peelable support surface that passes through the nip of rollers -11 and 12- and prevents the resin from sticking to the rollers. If the resin films do not contain backing sheets, devices should be provided to prevent the resin and / or tape from sticking to the rolls. For example, one may coat the rolls with a material which does not stick to the resin, or one may provide a suitable intermediate layer, for example in the form of a loop, which continuously passes between the rolls and the constituents of the strip.

The resin film may be a thermosetting or thermoplastic resin or a mixture of these two types.

Suitable resins that can be processed into films, including, if necessary, a curing agent, can be simple thermosetting resins, such as an epoxy resin (ie, a substance containing on average more than one 1,2-epoxy group in the molecule), a resole, which is formed from a phenol such as phenol itself and an aldehyde such as formaldehyde, an unsaturated polyester, a silicone resin, a melamine resin or a furan resin or mixtures of the thermosetting resins. Preferably, they also contain a thermoplastic resin which is not thermosetting. Examples of such compositions are: resoles having as a thermoplastic ingredient, a polyvinyl acetate or a nylon; a novolak formed from a phenol such as phenol itself and formaldehyde or another aldehyde, with a neoprene rubber or an acrylonitrile rubber; and epoxy resins with a phenoxy resin (ie a polyarylene polyhydroxy polyether substantially free of 1,2-epoxy groups, which is a dihydric alcohol interpolymer with either a diglycidyl ether of a dihydric phenol or with epichlorohydrin, and repeating units of the formula - OR OCH, CHCHτ | z is OH, where R is an arylene group), a polysulfone (ie a polymer containing repeating units of the formula - RSO 2 - wherein R has the definition given above), or a copolymer of an α-olefin hydrocarbon and a Q! -olefin with an ester of a carboxylic acid.

Suitable thermoplastic resin compositions may contain only a thermoplastic resin such as a polycarbonate, a polyoxymethylene, a polyimide, a poly (benzimidazole) or a polyamide or they may contain a mixture of thermoplastic resins.

As already indicated, these resins are preferably used in the form of films, in general, powders are inconvenient to use, especially with carbon fibers and other light, brittle fibers. They are processed into movies in a familiar way. Handling a resin film is often easier if it has a sticky surface. This can be made by coating the film with a substance which causes tackiness during storage of the film at room temperature, but which itself becomes a hard, insoluble, infusible resin under the conditions used in the subsequent processing steps of the tape , harden. In many cases, however, the films of thermosetting resin compositions, even those containing a thermoplastic non-thermosetting resin, have suitable tackiness even under the conditions used for impregnating the carbon fibers.

The resin used in the impregnating bath may be the same as or different from the second resin. It can often be of a different kind. One can thus use an epoxy resin to impregnate the fiber cables while the second resin can be a mixture of a phenolic resole with a polyvinyl acetal.

All suitable volatile solvents can be used to prepare the impregnation solutions. Of course, the drying apparatus must be operated at a temperature sufficiently high to remove substantially all of the solvent from the belt.

The concentration of the non-volatile resinous compounds in the impregnating solution depends strongly on the desired total resin content of the tape and the proportion of the amount applied in the form of a film during the second resin treatment. The cheapest resin fractions that can be applied at each stage can be easily determined by experiment. In general, optimum results are obtained when the major portion of the resin is applied as a second resin. Preferably, fewer are used

No.318909 as 40% by volume, in particular less than 25% by volume, of the total resin present in the end strip during the first, ie the impregnation, step. The smallest amount of resin in the first

In the first stage, in practice, the level is about 5% and preferably at least

Vol .-% appropriate.

The speed at which the fiber tows are pulled through the device depends to some extent on the size of the inlet openings and the holes in the nozzles. Good results were obtained at a speed of 1 to 10 m / min, in particular at a speed of 0.6 to 1.2 m / min.

Carbon fiber ribbons made by the process of the present invention can be used directly as they are made, or the ribbons can be applied side by side to make a large sheet. In any event, laminated products can be made by cutting portions of the tape or web into the desired shape, stitching the webs together and consolidating them using heat and pressure. In order to give the product greater strength, some leaflets may be cut so that when they lie on top of each other, the carbon fibers are at an angle to those in the adjacent leaflet.

The following example illustrates the invention. Unless otherwise indicated, parts are parts by weight.

The resins used were the following:

Epoxy resin A; was a polyglycidyl ether prepared in a known manner from 2,2-bis- (4-hydroxyphenyl) -propane and epichlorohydrin in the presence of an alkali. It had an epoxide content in the range of 5.0 to 5.2 equiv / kg and a viscosity at 21 ° C in the range of 200 to 400 poise.

Epoxy Resin B "was a polyglycidyl ether prepared in a similar manner, but having a 1,2-epoxide content in the range of 0.25 to 0.42 equiv / kg and having a softening point (Durrans) in the range of 145 to 155 ° C ,

Epoxy Resin C "was a polyglycidyl ether prepared in a similar manner, but with a 1,2-epoxide content in the range of 1.9 to 2.2 equiv / kg and a softening point (Durrans) in the range of 64 to 76 ° C.

Example: Epoxy Resin A (100 parts), Epoxy Resin C (100 parts) and dicyandiamide (10 parts) were dissolved in methoxyethanol (2000 parts by volume) to form an impregnating solution.

Epoxy Resin A (80 parts) and Epoxy Resin B (100 parts) were heated in a Z-blade mixer at 150 ° C. When the mixture became homogeneous, it was cooled to 100 ° C, and a ground mixture containing 20 parts of Epoxy Resin A and 10 parts of dicyandiamide was incorporated. The mixture was poured into a film having a thickness of 0.1 mm in thickness.

The impregnating solution was placed in a bath partially covered with a metal lid containing seven inlet ports. These openings contained 0.4 cm diameter circular ceramic eyelets inserted in holes cut into the metal lid. A freely rotatable roller with seven grooves running around it with a width of 0.363 cm was placed near the bottom of the bath.

Above the side of the bath remote from the entrance openings were two brass plates as shown in Fig. 4 attached. The plates, each 1.3 cm wide and 14.5 cm long, were equipped on one side, as shown, with 8 steel rods that were 1 cm long and 0.363 cm apart. The plates were 2 cm apart and mounted horizontally over the side of the bath so that the lower plate bars faced the side of the bath equipped with the inlet openings and the upper plate bars pointed in the opposite direction.

A drying tower mounted vertically above these panels was 305 cm high and equipped with a central vertical divider. He was heated with an electric heating tape wrapped around him. A freely rotatable roller 9.0 cm in diameter and with grooves running around it, each 0.363 cm wide, was placed over the tower and a similar roller was placed under it.

Seven fiber cables were passed through the entrance openings into the impregnating bath under the roller in the bath and out of the bath through the horizontal plates where they were formed into strips. Each fiber tow was kept separate from the next and tied by causing it to lie in a groove of the roll and by passing it through a gap between two of the steel pins connected to the plates.

The bands, still kept separate, were led down on one side of the drying tower via the grooved roller on the head and on the other side of the drying tower. The tower was kept at a constant temperature of 70 ° C.

The ribbons were then separated and fed to two grooved rolls as in FIG. The rollers, which were mounted so that their axes lagn in a horizontal plane, were 5.50 cm away. The rolls, as shown, had grooves around them, with the grooves and protruding parts each being 0.353 cm wide. Immediately adjacent to these rolls was a pair of heated rolls with a gap as shown in Fig. 7 attached. The groove in the lower roll and the protruding part of the upper roll were each 2.54 cm wide. The rollers were pressed together by adjustable springs.

- 8th -

Nr.3189O9

Four of the 7 bands were in alternate order from the roller at the bottom of the tower in the

Grooves in the upper roller passed while three intermediate belts were passed into the grooves of the lower roller. In this way, the 7 belts were brought together in side-by-side arrangement and formed a 2.54 cm wide belt which was fed almost immediately into the groove of the heated nip rollers. At the

As the tape entered the nip, it was contacted at the top and bottom surfaces with a continuous resin film 2.54 cm wide and backed by a release paper on the back.

The nip rollers were heated to 70 ° C and the springs were adjusted so that the belt 3.56 X IO '² cm thick.

The belt was wound on a spool operated at such a speed that the fiber cables passed through the device at a speed of 0.6 m / min. The paper on the back of the two resin films was not removed, leaving the paper on the back as a removable intermediate layer.

Laminates formed by superimposing strips of the strip so produced could be obtained by heating for 1 hour at 170 ° C and a pressure of 7 kg / cm² be consolidated.