Reinforced plastics materials

(74) Agent: Regimbeau, Corre and Paillet.

(54) Reinforced plastic materials.

Invention of:

33) (32) (31

Conventional priority: Patent application filed in Great Britain on November 28, 1969, n. 58.434 / 1969 on behalf of Ciba (ARL) Limited.

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The present invention relates to reinforced plastics, in particular fiber-reinforced plastics, in the form of a strip, and to a process for manufacturing such materials.

Fiber-reinforced plastic materials, in particular glass fibers, have acquired considerable commercial importance, for example for use in the construction of aircraft, boats, buildings, pipelines and storage tanks. These reinforced plastic materials can be manu factured either by the wet lay-up technique (liquid assembly) or by the dry lay-up technique (dry assembly)

This latter method, which is increasingly used, involves a prepreg reinforcement material, generally called prepreg, and comprises reinforcement in the form of a fabric, a mat of non-oriented fibers or a unidirectional strip or sheet, impregnated with a resin. This resin is generally applied in the form of a composition which has been carefully formulated with the correct proportions of components such as hardeners, fillers and catalysts. Often the resin component is a liquid and is thermosetting, and the composition has been treated so that the resin is brought to the solid B state, but still fusible and hardenable, during the preparation of the prepreg. Such a resin in state B can then be completely cured when desired, for example when the prepreg has been put into the desired form. The advantage of using prepregs over the liquid assembly technique is that manufacturers of fiber-reinforced materials are relieved of many of the problems of storing and handling the resin components, and this method provides a product in which the resin is distributed more unifor lead.

Plastics reinforced with conventional fibers are less rigid than many metals, and this excludes their use in certain applications, for example in the manufacture of compressor blades of jet engines. However, carbon fibers have recently been used as reinforcement for plastic materials and products having high strength and high rigidity have been obtained joined to a

42131 low weight. Other fibrous reinforcing materials which are now used are boron, silicon carbide, silicon nitride and alumina.

The carbon fibers are supplied in the form of 5 cables or roving of continuous fibers wound together on a cylindrical sleeve without intentional twisting so that the fibers are more or less parallel. The cable wound cylindrically on the cylindrical sleeve is generally known as cheese. A typical cable contains around 10,000 individual fibers.

As carbon fibers are difficult to handle, for example because they are very light and fragile, it is not easy to apply the methods successfully used for the preparation of strips of glass fibers impregnated with resins, the preparation of strips of carbon fibers impregnated with resins.

Carbon fiber prepregs were prepared in sheet form by dipping a number of cables in a dilute resin solution in a volatile solvent, placing the impregnated cables vertically side by side, exactly parallel with no overlap, and then laminating cables by means of a heated rolling mill until the thickness is uniform. According to another method, non-impregnated cables are placed vertically, side by side, then they are covered with a resin film and laminated using a heated rolling mill to consolidate the sheet.

These methods are very slow and uneconomical and efforts have been made to continuously produce strips of impregnated carbon fibers from two or more cables. These strips are generally 1 to 15 cm wide and about 0.1 cm thick or less. The users of these tapes impose strict conditions. Thus the strips should not be cut on the edges and their width should not vary by more than about 1.25 mm; there should not be any gaps between the individual cables forming the strip; cables must be straight and not crease; the individual cables forming the strip must hold together during the subsequent handling operations and

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-32072299 the density of the strip must be constant over its entire width.

The present invention relates to a process and a device for the preparation of strips impregnated with resins.

According to one of its features, the invention provides a process for preparing a strip impregnated with a resin from a plurality of fiber cables, in particular carbon fibers, which comprises impregnating said fiber cables with a solution of a first resin in a volatile solvent, the placing of each of the cables in the form of a ribbon of substantially constant width, the elimination of practically all the solvent from each ribbon, edge-to-edge alignment of the impregnated ribbons, and contact of the upper and lower surfaces of the aligned ribbons with a second resin, preferably in the form of a continuous film, under conditions such that the second resin flows around the ribbons form a coherent band impregnated with resin.

Generally, the second resin is made to flow around the aligned ribbons, by heating or applying pressure. When one or both resins are thermosetting, the conditions applied to run the second resin around the aligned ribbons can be chosen so that the thermosetting resin is transformed from state A to state B, solid but still fusible . The formation of state B requires great care because if the transformation is pushed too far, the resin is transformed into state C, insoluble and infusible, completely hardened, and this makes the strips unusable for subsequent treatments.

Preferably therefore, the resins and in particular the second resin, are chosen so that the aligned ribbons are linked together without the second resin being transformed into state B, that is to say that the second resin remains predominantly in state A. The tapes produced in this way have a longer storage life than those in which the resin has been transformed into state B.

The invention also relates to a device for the preparation of strips impregnated with resin from a plurality of fiber cables, in particular carbon fibers, which

42131 includes:

means for impregnating a plurality of fiber cables with a solution of a first resin,

means for putting each of the cables in the form of a ribbon of substantially constant width,

means for aligning edge to edge the impregnated ribbons from which practically all the solvent has been removed,

means for bringing the upper and lower surfaces of the aligned ribbons into contact with a second resin,

means for making the second resin flow around the ribbons in order to form a coherent band impregnated with resin, and

- means for advancing the cables through the. device.

The invention will be better understood with the aid of the additional description which follows, with the accompanying drawing, in which:

Figure 1 is an overall schematic elevational view showing a preferred embodiment of a device according to the invention;

Figure 2 is a plan view of a bath which can be used to impregnate the cables with carbon fibers;

Figure 3 is a plan view of a type of cable shaping device, and Figure 3a is a sectional elevation along lines 3 * 3'j Figure 4 is a plan view of a second type of shaping device, and Figure 4a is a sectional elevation along the line 4 * 4 ';

Figure 5 is a plan view of a third type of shaping device, and Figure 5a is a sectional elevation along the line 5'5 ';

Figure 6 is an elevational view of rollers for aligning the ribbons edge to edge;

Figure 7 is an elevational view of pinch rollers which cause the casting of the second resin around the fibers of the aligned ribbons and Figure 8 shows in elevation a tubular impregnation bath.

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With the exception of FIG. 8, the drawings illustrate a device making it possible to form strips from seven cables of carbon fibers or other fibers. It is understood that this only serves to illustrate the invention. The number of cables used depends on the width of the strip and the density of the fiber required.

In Figure Ί, the coils or sleeves (cheese) of carbon fiber cables are suspended from a frame 1 so that they are above a tank 2 containing a resin solution for impregnating the cables . The coils are suspended, their longitudinal axes being parallel in a horizontal plane so that the individual cables can arrive in the impregnation bath without intertwining. The coils can rotate freely as the cables are unwound. If desired, the cables can be heated before entering the impregnation bath 2; this eliminates any moisture and sometimes helps with impregnation.

To ensure complete impregnation, the cables pas20 preferably lie under an idler roller 3 suspended near the bottom of the tank 2. Instead of roller 3, it is also possible to use a fixed bar with a smooth surface.

After impregnation, the cables pass from the tank 2 through a shaping device. 4 which puts each cable.

in the form of a ribbon by preventing the spreading of the cables and by adjusting the resin setting (that is to say by controlling the amount of resin solution retained by the fibers). The ribbons pass from the shaping device 4 to a drying device which can be a tube of suitable section, heated from the outside, for example by an electric heating jacket. This tube can be horizontal or vertical. The cables preferably remain in the dryer long enough to remove most of the solvent, but the temperature and the heating time should be such that there is no appreciable reaction between the components of the resin.

In FIG. 1, the drying device consists of an oven 5 comprising a vertical tube heated by an electric heating che70 42131. The impregnated ribbons rise on one side of the tube, pass over an idler roller 7, suspended above the tube, and descend on the other side. The tube should be wide enough that the impregnated ribbons will not touch the heated walls. To avoid the passage of the solvent from the ribbons still containing solvent ascending on one side, to the dry ribbons descending from the other side, the tube is provided with a central separation 6 impermeable to solvent.

The impregnated dry ribbons then pass through a device which aligns them edge to edge. This device can be in the form of channels separated by vertical guide walls or dowels, a comb or, as shown in the drawing, two grooved rollers 9 and 10. As shown in Figure 1, the ribbons emerge from the base from the oven and pass into the alignment device by a roller 8. This roller is not free to rotate, this creates tension in the cables and helps to keep the fibers parallel in the final strip.

The aligned ribbons then pass through a device in which a continuous film of resin is applied to their upper and lower surfaces and the resin is poured around the fibers to form a coherent structure. This is preferably done in one phase. The means for applying the continuous resin film and the means for flowing the resin around the fibers comprise two rollers (11 and 12) heated and repelled relative to each other so that when the aligned ribbons are introduced into the space between the rollers with the resin film, the latter flows around the fibers, forming a coherent impregnated strip. The strip is wound on a reel 15 for storage. It is generally necessary to wrap with the strip a detachable intermediate layer to prevent adhesion between the adjacent layers. The resin may comprise a peelable support sheet, for example of polyethylene or paper, on the face opposite to that which is brought into contact with the aligned ribbons. These sheets can either be removed when the strip has been formed by the rollers 11 and 12 or remain on the strip to serve as a detachable intermediate layer. In the device of Figure 1, the coil 15 is driven by an electric motor

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-72072299 (not shown) capable of maintaining a chosen constant speed. The movement of this spool pulls the fibers through the entire device.

FIG. 2 illustrates an embodiment of the impregnation bath 5. The tank can be made of any suitable material such as metal, glass, plastic or plastic reinforced with glass fibers. As mentioned above, the cables can pass under the idler roller 3 suspended near the bottom of the tank to ensure complete impregnation. This roller preferably has grooves, as shown in Figure 2 and each cable passes around the roller in a separate groove. The grooves at their base preferably have the same width as that corresponding to each cable in the final strip. So, for example, if you line up seven cables side by side to form a strip 7 cm wide, each cable will then contribute 1 cm to the total width of the strip, and the grooves of the roll are 1 cm wide at their base.

The cables are flattened to a certain extent by passing around the roller and this facilitates the passage of the cables through the shaping device, where they pass leaving the impregnation bath, and where they are subjected to a new flattening and the excess resin being removed.

Generally, the shaping device is such that, although the cables are considerably flattened, the ribbons produced are thicker than the final strip, the thickness of which can be adjusted by the rollers 11 and 12.

The shaping device may have slots, through which the cables pass, these slots being cut or formed in metal, glass or any other suitable material. Preferably, the width of the slot will be equal to that assumed by each cable in the final strip. In FIG. 2, the shaping device consists of a series of slots 21 cut out from a metal sheet 22 which can partially form the cover of the tank 2. The upper and lower edges of the slots can be rounded. The shaping device can also consist of hollow cones, the upper end of which has been flattened to form openings like a slit, and the lower end has a circular section and engages in size orifices. corresponding cut from the cover of the .cuve 2. A nozzle of this type, attached to a tubular impregnation bath, is shown in FIG. 8.

The shaping device can also take the form of two hard surfaces between which the impregnated cables pass, the surfaces having means to prevent lateral spreading, that is to say to keep the width of the tapes constant. Preferably, these means are arranged in such a way that the width of each ribbon is equal to the width that the ribbon has in the final strip. These means may be dowels fixed on the surfaces, or grooves hollowed in the surfaces. The surface and the dowels are formed from a hard material which can take a polished finish, for example glass or a metal such as brass or steel.

One type of such a shaping device is shown in Figures 3 and 3a. Two plates 37 and 32, separated by a distance equal to or greater than the required strip thickness, are held vertically above the impregnation bath. The cables pass between the plates and are kept separated by a series of pins 33 fixed to the plate 32 and passing through orifices in the plate 37. The distance between the plates can be adjusted by moving the plate 37 along the pins.

A second type of such a shaping device is shown in Figures 4 and 4A. The two plates 47 and 4-2 are maintained, spaced apart from each other horizontally, above the impregnation bath. Each plate carries on one side of the pins 43 or 44 which are preferably separated by the width that the cable assumes in the strip. The distance between the plates is not critical and the plates can be moved horizontally, if desired, so that they are no longer in the same vertical plane. Each cable 40 rises from the bath to the plate 47, between a pair of pins 43, then between the plates, then over the edge of the plate 42 between a pair of pins 44. The edges of the plates 47 and 42 between the dowels can be rounded.

Yet another type of such a formatting device

42Ί3Ι is illustrated in Figures 5 and 5a · It includes two grooved bars 51 and 52 mounted and spaced horizontally above the impregnation bath, the bars do not rotate but they can be adjusted one relative to the other so as to create a greater or lesser degree of winding of the cables 50. the width of the grooves 53 in each bar is preferably equal to that assumed by each ribbon in the final strip.

Returning to FIG. 1, the cables can pass directly into the impregnation bath and rotate around the roller 3, but the very light carbon fibers tend to float in the resin solution in an uncontrollable and irregular manner. This tendency can lead to bands having an uneven fiber density, and it is therefore preferred to pass each cable in the bath through an inlet opening which makes it possible to control and retain the fibers during their passage towards the roll 3 · L The entry opening can be the space between two teeth of a comb or a small circular orifice cut from a metal plate or any other suitable material. Particularly good results are obtained when using circular eyelets 23 placed in orifices cut out from the metal plate 24 as seen in FIG. 2.

Eyelets can be made of any suitable hard, very smooth material such as ceramic, metal, or glass. The distribution of the openings above the surface of the tank and their spacing depends on the width and the density of the desired strip.

Instead of all the cables passing through a single bath, each cable can pass through a separate impregnation solution contained for example in a U-shaped tube like that which is represented in FIG. 8: the impregnation bath comprises a glass tube 81 having for example an internal diameter of approximately 2 cm and being curved along a radius of approximately 5 cm. The nozzle comprises a flattened glass tube 82 having one end formed as a cone 83, the external surface of which is lapped to fit into the corresponding lapped female part 84 which is at the end of the U-shaped tube.

Preferably, the rollers 7 and 8 at the top and bottom of the drying tower as shown in FIG. 1 have grooves / u * 4 ZI □ I like the roll 3. The dried impregnated ribbons leaving the roll 8 can, as indicated above, be aligned edge to edge, by passing through channels so that at the end of the channels, the ribbons are located in the same horizontal plane with the desired arrangement. However, in a preferred embodiment, the alignment of the dry ribbons is carried out by means of two grooved surfaces, the width of the grooves and that of the projections between the grooves being equal to the width that each ribbon will assume in the final strip, and the grooves on one of the surfaces being aligned on the projections between the grooves of the second surface so that the ribbons, passing through the grooves of one of the surfaces are aligned side by side with the ribbons passing through the grooves of the second surface. The grooved surface can have a structure like a metal comb, but it is preferable to use two grooved rollers (9 and 10). Figure 6 shows in. cut a pair of rollers to form a strip from seven ribbons.

The upper roller 9 has four grooves 61 separated by three projections 62. The width of each groove and each projection esb preferably equal to the width of each ribbon. The lower roller 10 has three grooves 63 separated by two projections 64, the projections and the grooves being the same width as in the upper roller. The grooves of the lower roller are in the same vertical plane as the projections of the upper roller, and the projections of the lower roller are in the same vertical plane as the grooves of the upper roller.

The seven ribbons leaving the roll 8 are divided; four pass on the upper roller 9 in the four grooves 61, and three pass under the lower roller 10 in the three grooves 63 ·.

The rollers 9 and 10 are placed as close as possible to the rollers 11 and 12, so that the ribbons leaving the rollers 9 and 10 pass quickly into the slot between the rollers 11 and 12 where they are pressed side by side against each other au35. be. . .

The rollers 11 and 12 may each have a flat surface but it is preferable that one of the rollers adjacent to the rollers 9 and 10 has a circumferential groove which has the width

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- Ti2072299 of the final strip while the other roller has a projection which engages in the groove. Such rollers are illustrated in Figure 7. The space between the groove 71 and the projection 72 is preferably adjustable so that strips of different thicknesses can be produced.

As the aligned ribbons pass from rollers 9 and 10 into the space between rollers 11 and 12, continuous films of resin are applied to the upper surface and to the lower surface from the reels 13 and 14 (see Figure 1) . One or both rollers 11 and 12 can be heated to run the resin around the fibers. Preferably, the continuous resin films have a detachable backing sheet which passes through the space between the rollers 11 and 12 and prevents the resin from adhering to the rollers. If the resin films do not have a backing sheet, means must be provided to prevent the resin and / or the strip from sticking to the rollers, such as a coating with a material which does not stick to the resin, or by continuously passing an intermediate sheet, for example in the form of a loop, between the rollers and the components of the strip.

The resin film can be a thermosetting or thermoplastic resin or a mixture of the two types.

Suitable resins which can be made into films, including, if necessary, a curing agent, can be unique thermosetting resins, such as an epoxy resin (i.e. a product having on average more than one epoxy group per molecule) a resole formed by the action of 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 a mixture of thermosetting resins. Preferably, they also contain a thermoplastic resin which is not hardenable by heat. Examples of such compositions are: resoles with, as thermoplastic component, a polyvinylacetal or a polyamide; a novolak formed with a phenol such as phenol itself and formaldehyde or another aldehyde, with a neoprene or acrylonitrile rubber; and epoxy resins with a phenoxy resin (i.e. a polyarylene polyether poly / u

-JI hydroxy, substantially free of epoxy groups which is a copolymer of a diphenol with a diglycidyl ether of a diphenol or with epichlorohydrin and which contains the recurring units of formula -OROCH ^ CHCHg- in which E is a

OH arylene group) a polysulfone (i.e. a polymer containing the repeating units represented by the formula -RSOg-, where E is an arylene group), or a copolymer of an α-olefinic hydrocarbon and a α-olefin which is an ester of a carboxylic acid.

Suitable thermoplastic resin compositions may contain only a thermoplastic resin, such as a polycarbonate, polyoxymethylene, polyimide, poly (benzimidazole), or polyamide, or may contain a mixture of these thermoplastic resins. As already mentioned, these resins are preferably applied in the form of films. Powders are generally not suitable for this use, especially with carbon fibers or other light and fragile fibers. They are transformed into films in a known manner. Handling a resin film is often easier if it has a sticky surface.

For this purpose, the film can be coated with a substance which retains its tacky effect during storage of the film at room temperature but which is hardened into a hard resin, insoluble, infusible under the conditions in which the strips are subsequently treated. Often films of a thermosetting resin composition, even those containing a non-heat-curable thermoplastic resin already have one. sticky effect under the conditions used to impregnate carbon fibers.

the resin used for the impregnation bath may be the same as the second resin or may be different. It may even be of a different type. Thus an epoxy resin can be used to impregnate the cables, while the second resin can be a mixture of a phenolic resole with a polyvinyl acetal.

Any suitable volatile solvent can be used for the impregnation solution. Obviously the drying device must

42131 be at a temperature high enough to substantially remove any solvent from the tape.

The concentration of non-volatile resinous substances in the impregnation solution depends largely on the total resin content desired in the strip and the proportion of what will be applied as a film in the second treatment. The best proportions of resins to be applied in each phase can be easily determined by tests. In general, the best results are obtained when a higher proportion is used for the second resin. Therefore preferably less than 40%, in particular less than 25%, by volume of the total resin present in the final strip is applied during the first phase, that is to say during the impregnation. The minimum proportion to be applied in the first phase is in practice around 5% and preferably at least 10% by volume.

The speed at which the cables are pulled through the device depends to some extent on the size of the inlet openings and the nozzles. Good results are obtained with speeds of 0.1 to 10 meters per minute, in particular 0.6 to 1.2 meters per minute.

The carbon fiber strips produced by the process of the invention can be used directly, or placed side by side to produce a larger sheet. In all cases, a laminated product can be produced by cutting sections of the strip or sheets to the desired size, stacking the sheets and consolidating them by heat and pressure. To give greater strength, the laminates can be cut so that when stacked, the carbon fibers form an angle with those of the adjacent layer.

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

The resins used are the following: Epoxy Resin A is a polyglycidyl ether, prepared in a known manner from bis- (4-hydroxyphenyl) -2,2 propane and epichlorohydrin in the presence of alkali, having a level epoxides between 5, θ and 5.2 equivalents per kg, and a viscosity at 21 ° C of 200-400 poises;

Epoxy Resin B is a polyglycidyl ether pre2072299 similarly adorned but having an epoxide content of between 0.25 and 0.42 equivalent per kg, and a softening point (Durrans) located between 145 and 155 ° G .

Epoxy Resin C is a polyglycidyl ether prepared in a similar way but having an epoxide content of between 1.9 and 2.2 equivalents per kg and a softening point (Durrans) located between 64 and 76 ° C.

Example

100 parts of Epoxy Resin A, 100 parts of Epoxy Resin C and 10 parts of dicyandiamide are dissolved in 2000 parts (by volume) of methoxyethanol to form an impregnation solution.

80 parts of Epoxy Resin A and 100 parts of Epoxy Resin B are heated to 150 ° C. in a mixer with Z-blades. When the mixture is homogeneous, the wave is cooled to 100 ° C. and a ground mixture of 20 parts is incorporated. of Epoxy Resin A and 10 parts of dicyandiamide. Poured from the mixture of 0.1 mm thick films.

The impregnation solution is placed in a bath partially covered with a cover which contains seven inlet openings. These openings include circular ceramic eyelets with a diameter of 0.4 cm, placed in holes cut through the metal cover. A freely rotatable roller having seven circumferential grooves with a width of 0.363 cm is mounted near the bottom of the bath.

Above the side of the bath opposite the entry openings are suspended two brass plates as shown in the figure

4. These plates, each 1.3 cm wide and 14.5 cm long, are provided on one side as shown in the figure, with eight steel dowels 1 cm long and spaced 0.363 cm apart. These plates are 2 cm apart and are hung horizontally above the side of the bath so that the pegs on the bottom plate point to the side of the bath with the inlet openings and the pegs on the top plate point in the direction opposite.

A drying tower, mounted vertically above these plates is 3θ5 cm high and is provided with a vertical central separator. It is heated using a ribbon .chauf70 42131 electrical wire wrapped around it. A freely rotating roller, 9.0 cm in diameter, and having seven grooves, each 0.363 cm wide, is suspended above the tower and a similar roller is suspended below the tower.

Seven cables pass through the openings in the impregnation bath under the roller suspended in the bath and exit the bath through the horizontal plates where they are formed into ribbons. Each cable is kept separate from its neighbor and is forced to take its shape because it is forced to adapt to the groove in the roll and pass through the space between the steel dowels fixed on the plates .

The ribbons, each still kept separate, pass up one side of the drying tower over the grooved roller at the top, then down to the other side.

The temperature is kept constant at 7Ο ° θ ·

The ribbons are then separated and pass over two grooved rollers according to FIG. 6. The rollers which are suspended with their axes in a horizontal plane are spaced apart by 5.50 cm. They have grooves, as shown in the drawing, the grooves and projections each having a width of 0.363 cm. Immediately against these rollers is a pair of heated pinch rollers, as shown in Figure 7 · The grooves in the lower roller and the projections in the upper roller are each 2.54 cm wide. The rollers are brought into contact using adjustable springs.

Four of the seven ribbons taken alternately pass from the roller at the base of the tower into the grooves of the upper roller while the three intermediate ribbons pass through the grooves of the lower roller. In this way, the seven ribbons are brought into contact side by side to form a band with a width of 2.54 cm which passes almost immediately into the throat of the%

heated pinch roller. At the same time as the strip passes between the rollers, it is brought into contact on the upper surface as well as on the lower surface with a continuous film of resin deposited on a detachable support paper with a width of 2.54 cm.

The pinch rollers are heated to 70 ° C and the springs are adjusted so that the thickness of the strip is

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I w— from 3> 56 x 10 “² cm '

The strips are wound on a spool driven so that the cables pass through the device at the speed of 0.6 meters per minute, without removing the backing paper from the two resin films so that the support remains in place as a layer detachable intermediate.

The laminates prepared by superimposing the strips can be consolidated by heating for 1 hour at 70 ° G under a pressure of 7 kg / cm.

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