FR2703699A1 - Process for the production of a fibre lap pre-impregnated with a thermal setting resin and fibre lap thus obtained - Google Patents

Abstract

This process for the production of a fibre lap (1) pre-impregnated with a resin without solvent, in which at least one of its faces is coated with the said resin, involves, after the coating of the fibre lap (1) by the resin, subjecting the assembly thus obtained concomitantly to a temperature rise in combination with the application of a pressure to the said coated fibre lap, followed by a cooling phase, with the coated fibre lap being maintained under pressure. It also involves coating and maturing the fibre lap (1) in the conventional way and then maintaining the latter under pressure during the cooling stage.

Description

PROCESS FOR THE PRODUCTION OF A PRE FIBROUS TABLECLOTH
IMPREGNATED WITH A THERMOSETTING RESIN AND TABLECLOTH
FIBROUSER THUS OBTAINED
The invention relates to a new process intended to allow the production, in particular continuously, of textile fibrous webs, prepreg of a thermosetting resin, and in particular of epoxy resin. It also relates to the prepreg fibrous webs obtained by this process.

 Many industries are increasingly resorting to the use of laminates, the role of which, when integrated into a defined structure, is either to impart mechanical reinforcing properties (sliding sports), or to impart a shape particular (automotive industry), or even, to ensure these two functions simultaneously. Indeed, by their lightness on the one hand, and their mechanical resistance on the other hand, they make it possible both to lighten the total mass of the structure to be produced, and to confer on it interesting mechanical properties, while being able to give it a particular shape.

 These laminates can be obtained in various ways, among which, the so-called "wet" process, dirty, long to implement, and above all difficult to automate, and the so-called "prepreg" process. This latter technique, which is now well known, makes it possible to handle a laminate in a non-tacky state, which facilitates the automation of the manufacturing processes. However, the production of such prepregs requires rigorous implementation.

 This technique of pre-impregnating a fibrous material, based on glass fibers, carbon, or aramid fibers (KEVLAR - registered trademark) with a resin, in particular an epoxy resin, consists in first of all mixing resin-hardener, added with a solvent of the methyl ethyl ketone type, in order to make said resin-hardener mixture more fluid, and therefore to facilitate the impregnation of the fibers of the material. The prepreg is then in a stage called A, in which the hardening resin mixture is in the tacky state.

 This resin-hardener mixture impregnated in said fibrous material is then made to mature, in order to make it pass to the so-called B stage, or pregel stage, in which the resin-hardener mixture is in a tacky, non-dirtying state. This ripening step is generally carried out by a controlled temperature rise, which induces both the evaporation of the solvents initially incorporated in the resin-hardener mixture, and in addition the controlled initiation of the pre-curing of the resin under l action of the hardener. To date, this ripening is carried out without concomitant application of pressure on the fibrous web, by means of specially adapted installations, very bulky and very expensive.

 Following this ripening step, the prepreg thus obtained is rolled up with a polyethylene interlayer film, then stored cold, typically at -18 ° C., before being used for the production of laminate pieces according to its use. final.

In addition to the fact that the production of such prepregs presupposes installations as already said to be expensive and bulky, this technique also has the following drawbacks
- First of all, the prepreg obtained can only be cured at fairly high temperatures, at least 120 C, preferably 140 to 150 OC for a relatively long period, and at least half an hour. This ripening step leads, as already said, to the evaporation of the solvent in the ambient medium, generating in addition to pollution which is increasingly sought to be overcome, an additional cost in terms of the cost price of these prepregs;
- the production of these prepregs continuously requires rigorous control of the settings of the ripening installation;
- finally, the control of the ripening state of the prepregs must be very strict, always according to its final use.

 The object of the invention is to propose a new process for producing, in particular continuously, prepregs, using an impregnating resin without solvent.

 This process for producing a fibrous web pre-impregnated with a solvent-free resin in which at least one of its faces is coated with said resin, is characterized in that, after coating of the fibrous web with the resin , the assembly thus obtained is subjected concomitantly to a rise in temperature combined with the application of pressure on said coated fibrous web, then to a cooling step while maintaining the coated fibrous web under pressure.

 In other words, the invention consists in coating a textile sheet with a solvent-free resin, then in impregnating it to the core by in particular the application of pressure, then in obtaining the curing of said resin by temperature rise, thereby enabling the viscous nature of the resin to be overcome, the cooling step stopping the evolution of the resin in a maturing state, therefore of non-dirtying tackiness desired.

Advantageously, the coating temperature of the resin is between 30 and 50 ° C. and that of the curing at around 120 "C. The pressure exerted during the curing is between 1 and 1.5. 105
Pascals, the duration of the heating to obtain the curing of the resin is between 1 min 30 s and 2 min.

 This relatively high temperature has the effect of rapidly fluidizing the epoxy resin-hardener mixture, facilitating its penetration within the fibrous network, and therefore its rapid ripening at this level.

 The low pressure applied facilitates, as already said, the wetting at the heart of the fibrous network, without however generating excessive creep of the epoxy resin / hardener assembly.

 According to an advantageous characteristic of the invention, this impregnation process is carried out continuously; the fibrous web is stored in the form of a coil, and the resin-hardener assembly is in the form of a film deposited on a sheet of silicone paper, the whole being wound up to form a second coil, and the coating of resin on the fibrous web being obtained by applying the resin film under pressure thereon by simultaneously unwinding the two coils.

 The invention also relates to a method for producing a fibrous web pre-impregnated with a solvent-free resin, in which at least one of its faces is coated with said resin, and then only after coating of the fibrous sheet by the resin, the assembly thus obtained is subjected to a rise in temperature in order to ripen the resin, followed by a cooling phase to block the development of the ripening.

 This process is characterized in that the cooling phase is carried out while maintaining the coated fibrous web under pressure.

 In other words, the invention also relates to a process for producing a fibrous web conventionally coated with a resin without solvent, but in which the cooling phase, intended, in known manner, to freeze the ripening of the resin, is carried out under pressure. This leads to the production of prepregs calibrated in thickness, which we could not do in a simple and reproducible way to date.

 According to another advantageous characteristic of the invention, a second resin film is applied under pressure to the fibrous web already impregnated with resin rendered non-tacky following the ripening operation.

 According to another characteristic of the invention, the temperature variations and the application of pressure are carried out by means of pressure rollers whose temperature is regulated by a fluid at the required temperature.

 In a variant of the invention, the silicone paper is replaced with a waterproof plastic hot-melt or thermosetting adhesive film, which is introduced onto the complex consisting of the textile web and the resin film before the impregnation / curing step. , or after it.

 In another variant of the invention, the plastic film of thermosetting adhesive consists of an epoxy resin film occurring in stage B of pre-gelling or completely cured.

 The invention also relates to fibrous webs pre-impregnated with solvent-free resin. These plies comprise at least on one of their faces a sealed plastic film of hot-melt or thermosetting adhesive.

 The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the example of embodiment which follows, given by way of indication and without limitation in support of the appended figures.

 Figure I is a schematic representation of the device for implementing the method according to the invention.

 Figures 2 to 5 schematically represent variants of the methods of the invention.

 In a first embodiment of the invention, the implementation device of which is shown schematically in FIG. 1, a fibrous textile web (1) is continuously coated, typically constituted by a uni-, bi- or multidirectional reinforced with glass fibers, carbon fibers or aramid fibers (KEVLAR - registered trademark), an epoxy resin and its hardener, all without solvent, by passage through a bath (2) of the mixture thus defined. In known manner, the mixture is distributed uniformly on the two faces of the fibrous web (1), by means of distributing rollers (3) positioned at the outlet of the fibrous web (1) out of the bath (2 ).

 The fibrous web (I) thus coated is then subjected, continuously, on the one hand to a rise in temperature and on the other hand and simultaneously to the application of pressure, this treatment being advantageously carried out by means of a sets of heating cylinders (5), heated in known manner for example by hot water or steam or any other heat transfer fluid. These cylinders thus make it possible to raise the temperature of the resin to approximately 120 ° C. for approximately two minutes, so that the resin / hardener mixture becomes fluid, and penetrates the interior of the textile web. Furthermore, this increase in temperature induces the start of the firing of said resin, generated by the activation of the hardener by the heat then produced.

Said cylinders concomitantly ensure the application of a pressure, typically between I and 1.5. 105 Pascals, which is relatively weak, capable of favoring the impregnation of the fibrous sheet (1) without exaggerating the creep of the resin.

 One thus obtains an impregnation of the resin-hardener assembly at the heart of the ply (1), and as a corollary, the resin matures by activating the action of the hardener, generated by the elevation of temperature. In fact, a non-tacky coated sheet is obtained, the ripening of the resin of which is stopped by cooling, also carried out under pressure. This cooling step is also advantageously carried out by means of cooling cylinders (6), in which a cold fluid circulates. In fact, the shorter the time separating the cooling from the heating and pressurizing step, the better the ripening of the prepreg obtained is reproducible.

 We then obtain a dry prepreg, which can be handled, and which presents itself in a non-fouling state of tack, which can be used immediately or stored in a cold room for several days. The actual stratification of the fibrous network can then be obtained by the traditional route under the combined action of heating, at a minimum temperature of 120 ° C., and the application of a pressure, typically between 5 and 10. 105 Pascals for an average duration varying from 10 to 20 minutes, inducing the total hardening of the epoxy resin.

 The different parameters involved in this process, and in particular in this ripening phase, namely, the durations of each of the phases, respectively of heating and cooling, the temperature and the pressure are correlated with each other.

 It is therefore conceivable that by this continuous process, simple and quick to implement, not inducing the use of bulky and expensive installations, it is possible to achieve the preparation of prepregs in a simple manner, without common measure. with the prepreg processes implemented to date. In addition, just-in-time production then becomes possible, which, combined with the production of a non-dirty prepreg, makes it possible to implement own molding techniques in the various manufacturing structures, and therefore automatable.

 In a variant of the invention shown in FIG. 2, a strip of silicone paper (4) is continuously unrolled from a reel (7), strip on which a layer of a previously produced mixture of resin is deposited. epoxy and hardener (2), all without solvent. A first complex (8) is therefore obtained, consisting firstly of the strip of silicone paper (4) and secondly of the coating layer of said assembly.

 This resin / hardener assembly is in the viscous state, and is distributed uniformly over the entire width of the strip by means of a doctor blade (not shown), and in a known manner.

 After this coating, a textile sheet (1) of the type described above is deposited on this complex (8), coming from a supply reel (9). A fibrous network (10) is thus obtained, comprising on one of its faces the resin / hardener assembly.

 After this operation, a second silicone paper can also be placed on the opposite face of said fibrous network (10), also unwound from a reel. These two silicone papers therefore enclose the fibrous network (10) which is then desired on the one hand, to impregnate at heart with the epoxy resin of the mixture (2) in contact with one of its faces, and on the other hand , ripen after impregnation. These two silicone papers are only intended to allow the automatic handling of said complex during its formation at the level of the various rollers and cylinders of return or progression. They are then removed from the complex obtained when the latter is used.

 The complex thus obtained undergoes the same steps as those described above, namely a first impregnation and curing step, carried out by means of heating rollers (5) exerting a defined pressure at the level of said complex, then a cooling step, intended to stop the advancement of ripening at a determined stage, suitable for making the prepreg non-tacky, and therefore easily handled.

 In a variant of the invention, a post-coating of the resin-hardener mixture is positioned on the fibrous web (I), a hot-melt or thermosetting adhesive film (11) on said fibrous network (10). The positioning of this film (11) can be carried out either before (shown in solid lines) at the impregnation / ripening stage, or afterwards (shown in dashed lines) thereto, but before cooling step, so as to benefit from the pressurization by the cylinders, either heating (5) or cooling (6), in order to ensure the cohesion of the complex thus obtained. it is nevertheless understood that said heating (5) and cooling (6) cylinders can respectively ensure only the heating and cooling of the impregnation resin of the web (1), and that in this case, the pressure is exerted by a train of so-called pressure rollers (5,6) shown in FIG. 3.

 The trains of pressure rollers (5,6) can be replaced by presses mounted for example on rollers, operating in step by step mode, and subjected for example to an alternating movement of closing then opening. When the presses are closed, they travel at the running speed of the textile web. When they are open, they quickly go back, then close again on said textile sheet, and the process is thus repeated.

 Advantageously, the plastic film (11) is waterproof, so that for certain applications, it can fulfill the role of barrier between reagents capable of exhibiting chemical incompatibility or, on the contrary, too great an affinity. In addition, it can advantageously serve as a bonding intermediate, in particular in the context of the production of complex molded structures, and in particular the manufacture of skis. It is made of a material such as polyamides, polyesters, polyether block amides (PEBAX), or thermoplastic polyurethanes.

 In a variant of the invention, more specifically shown in FIG. 3, the sets of cylinders, respectively heating (5) and cooling (6) can be replaced by trains of rollers of smaller diameter, while ensuring the same function .

 In a variant of the invention, more particularly shown in FIG. 4, the coating of the resin-hardener mixture (2) is replaced by a film (12) of said mixture, stored in the form of a reel (13), put in place on the silicone paper (4), or even directly on the textile tablecloth.

The resin is then at the level of this film at stage B, that is to say non-tacky. The impregnation of the resin at the heart of the fibrous sheet (1) takes place during the rise in temperature, inducing a fluidization of said resin, and therefore, under the action of the concomitant pressure exerted, its migration within of the tablecloth. This embodiment has the advantage of a simplification of the installation, and also of a more uniform distribution of said mixture over the entire width of the textile web.

 According to a last embodiment of the invention schematically represented in FIG. 5, on the fibrous web (1) already impregnated with resin according to one of the preceding variants, resin which may be present in stage B of pregelling, it is applied under pressure a second resin film (14), also in stage B, previously stored in the form of a reel (16), said resin resting on a film of silicone paper (15). In the embodiment shown in FIG. 5, the application of the second resin film (14) is carried out prior to the step of impregnating / curing the first resin.

 This second resin film (14) therefore constitutes a waterproof and thermosetting film, capable of giving the fibrous web thus impregnated and coated with particular applications, as soon as products are used, and in particular other resins with antagonistic behavior. or rhédibitoire with the impregnation resin.

 The method of the invention therefore makes it possible to considerably simplify the production of prepregs, since it can be carried out continuously. Consequently, it makes it possible to obtain laminates quickly and easily, which can also be calibrated in thickness, while increasing their production rate, and this, taking into account the curing process used.

Claims (9)

 1 / Method for producing a fibrous sheet (1) pre-impregnated with a solvent-free resin in which at least one of its faces is coated with said resin characterized in that after coating the fibrous sheet (1) with the resin, the assembly thus obtained is subjected concomitantly to a rise in temperature combined with the application of pressure on said coated fibrous web, followed by a cooling phase while maintaining the coated fibrous web under pressure.  2 / A method according to claim 1, characterized in that the temperature of the fibrous web during the impregnation and curing step is located around 120 OC, and in that the pressure exerted at said web is between 1 and 1.5. 105 Pascals, the heating time being between 1 min 30 s and 2 min.  3 / Method according to one of claims 1 and 2, characterized in that it is carried out continuously, the fibrous web (1) being stored in the form of a coil, and the resin-hardener mixture (2) is in the form of a film deposited on a sheet of silicone paper (4), the whole being wound up to form a second coil, the coating of resin on the fibrous web (1) being obtained by the application under pressure of resin film on it by simultaneously unwinding the two coils.  4 / Method for producing a fibrous sheet (1) pre-impregnated with a solvent-free resin in which at least one of its faces is coated with said resin, then in that after the coating of the fibrous sheet by the resin, the assembly thus obtained is subjected to a rise in temperature in order to ripen the resin, followed by a cooling phase to block the development of the ripening, characterized in that the cooling phase is carried out while maintaining the pressure coated fibrous web.  5 / Method according to one of claims 1 to 4, characterized in that the temperature variations and the application of pressure are carried out by means of rollers, pressing cylinders, or presses operating in step by step mode, of which the temperature is regulated by a fluid brought to the required temperature.  6 / Method according to one of claims 3 and 5, characterized in that the silicone paper (4) is replaced by a waterproof plastic film of hot melt or thermosetting adhesive, positioned on the fibrous complex formed by the textile web and the film of resin, and this prior to the impregnation / curing step, or after it but before the pressure cooling step.  7 / A method according to claim 6, characterized in that the waterproof plastic film of hot-melt adhesive is chosen from the group consisting of polyamides, polyesters, block amide polyethers, and thermoplastic polyurethanes.  8 / A method according to claim 6, characterized in that the plastic film of thermosetting adhesive consists of an epoxy resin film occurring in stage B of pre-gelling or fully cured.  9 / fibrous web (1) pre-impregnated with a solvent-free resin according to the method of claims 1 to 8, characterized in that it comprises on at least one of its faces a waterproof plastic film of adhesive  thermofusible (11) or thermosetting (14).