EP1456005A1

EP1456005A1 - Method for producing composite materials using a thermoplastic matrix

Info

Publication number: EP1456005A1
Application number: EP02782614A
Authority: EP
Inventors: Peter Maskus; Christian Kruse; Eduard Schmid; Anreas Mettier; Jonny Lohmiller
Original assignee: EMS Chemie AG
Current assignee: EMS Chemie AG
Priority date: 2001-12-20
Filing date: 2002-12-17
Publication date: 2004-09-15
Also published as: WO2003053661A1; AU2002347115A1; KR20040071235A; CN1615215A; JP2005513206A; US20050214465A1

Abstract

The invention relates to a method for producing a composite material (33) consisting of reinforcing elements (29) and a thermoplastic polyamide, said method permitting high-speed production with continuous process control, using simple equipment. The method is characterised by the following steps: the supplied reinforcing elements (29) are impregnated with a lactam melt (11) that is activated for anionic polymerisation, at a temperature, at which the activated lactam melt (11) does not polymerise; the impregnated reinforcing element (30) is heated and polymerised in a heating unit (17) without passing through a heated die and in an essentially contactless manner; the resultant hot polymerised composite material (31) is cooled in a cooling unit (18). The lactam melt (11) that is activated for anionic polymerisation is produced by first melting the lactam or more precisely the mixture of lactams to obtain a monomer melt (3) and a liquid initiator (6) is added to the monomer melt (3) immediately prior to the impregnation process of the reinforcing element (29), said liquid initiator (6) containing simultaneously the activator and the catalyst function in solute form.

Description

DESCRIPTION

TITLE

Process for the production of composite materials with thermoplastic matrix

TECHNICAL AREA

The present invention relates to a method for producing a composite material from reinforcing agents and a thermoplastic polyamide as a matrix.

STATE OF THE ART

For the production of composite materials from reinforcing agents and a thermoplastic polyamide as a matrix, methods are used on the one hand in which the monomer is polycondensed and on the other hand the anionic polymerization, which takes place in the absence of water. The anionic polymerization of lactams is catalyzed by lactamate, and can additionally by using so-called activators, for. B. in the form of acyl lactams or isocyanates (activated anionic polymerization, see, for example, Plastics Manual Volume 3/4 Technical Thermoplastic Polyamides, published by Ludwig Bottenbruch and Rudolf Binsack, Carl Hanser Verlag, Munich Vienna, 1998, especially pages 48ff). The activated anionic polymerization of lactams has a connection hydrolytic polymerization has the advantage of a higher reaction rate, and therefore basically offers the possibility of higher production speeds.

The production of semi-finished products, hollow bodies, organic sheets, profiles etc. with fiber-reinforced braids, scrims, fiber or filament fabrics or rovings and a thermoplastic matrix using polyamide usually takes place in a so-called pultrusion process, in which the with monomer or pre -Polymer impregnated or impregnated reinforcing agents for the polymerization immediately after the impregnation are brought into a mold or drawn through a mold which is kept at a temperature at which the polymerization takes place completely and in which the final shape of the body to be produced is produced under pressure (See, for example, "Introduction to the Technology of Fiber Composite Materials", published by W. Michaeli et al., Carl Hanser Verlag, 1989). In connection with the pultrusion of reinforced thermoplastic parts, which, among other things, in contrast to thermoset parts, have the advantage of being thermoplastic, the problem basically arises that polymer melts of thermoplastic materials usually have a low fluidity at melting temperature (high viscosity ), and the matrix is in the solid state at room temperature. In order to still be able to work with a pultrusion process using thermoplastic materials, higher temperatures are usually required for the impregnation / impregnation of the fibers used for the reinforcement or the like (although the temperature is of course limited by the temperature at which the polymer decomposes ), but even then, due to the high viscosity, there is still the problem that when the impregnated reinforcing agent is introduced into the pultrusion mold, there is considerable backflow and backflow of the melt at the entrance to the mold (so-called "bird's nest", cf. B. "Kunststoffe", 88 (1998) 5, page 485ff, Carl Hanser Verlag, Munich), in which even fibers of the reinforcing agent can be entrained, and in the worst case can even be blocked by cooling the melt at the entrance. The melt reflux and the high viscosity of the melt (in addition there are high shear forces on the mold) generally limit the speed of the production process, since this has to be adapted to the possible tensile force at the end of the production process, which is essentially determined by the tensile stability of the reinforcing agent (see. eg to. B. "Processing of continuous fiber reinforced thermoplastic plastics" by Prof. AG. Gibson, paper presented at the "7 ^lh Lausanne polymer meeting, Processing and Properties of thermoplastic matrix Composites, Lausanne, July 21-22, 1992, organized by the Ecole Polytechnique Federale de Lausanne (EPFL) "). While in pultrusion of thermosets, tensile speeds of up to 3 m / min are possible (see, for example, "Introduction to the Technology of Fiber Composites", published by W. Michaeli et al., Carl Hanser Verlag, 1989), only significantly lower train speeds are possible when using thermoplastics such as polyamide as a matrix. Higher train speeds are only possible with processes in which the reinforcement yarn is already premixed with polymer fibers (e.g. hybrid yarn).

EP 0544049 A1 describes a pultrusion process in the so-called 2-pot process, in which anionically activated lactam melt is used to impregnate the fibers, and the temperature in the tool, i. H. is raised in the mold at least in the melting range of the polyamide (polyamide 6). This is said to lead to improved properties and an improved surface of the pultrusion profile. The lactam melt is provided in such a way that a first part of the lactam melt is mixed with catalyst and in another container the second part of the lactam melt with activator. The two melts are brought together and mixed immediately before the impregnation process. The form for pultrusion used in this document is described in US 4,635,432 and is a tubular body, the inner diameter of which corresponds to the desired outer diameter of the pultrudate. Particularly with regard to short forms, this document refers to the problem of melt dripping, and it is proposed to make the form at least 15 to 30 times as long as the diameter of the pultrudate.

No. 5,424,388 also describes the pultrusion of molded parts using activated anionic lactam melt in a two-pot process, in which the reinforcing material supplied is impregnated with the melt and is then immediately drawn into a hot mold in which the matrix polymerizes. Attention is drawn to a maximum possible train speed of less than 0.5 m / min.

In addition to the two-pot process, as described in EP 0544049 A1 and in US Pat. No. 5,424,388, there is also the possibility of working with liquid initiators which contain liquid catalyst and activator (so-called one-pot process). EP 0791618 A1 describes e.g. B. a process for the production of thermally deformable composites with a lactam matrix using activated anionic polymerization, in which the lactam melt is admixed with a liquid initiator immediately before the impregnation of a reinforcing agent, and is mixed to the activated anionic lactam melt, the liquid initiator being mixed with both Contains catalyst as well as the activator in dissolved form. In this context, EP 0872508 A1 describes in particular such liquid initiators which are stable in storage at room temperature and are suitable for anionic lactam polymerization. Other possible systems of liquid initiators are described in the two documents by the applicant DE 19961818 A1 and DE 19961819 A1, in which the catalyst and activator are not present separately in the liquid system, but to a certain extent one unit can take over or inherently have both functions, and both when mixed with lactam Functions are made available. In this context, mention should also be made of DE 19527154 C2, which proposes methods for producing thermoplastically deformable composite materials, using anionically activated lactam polymerisation. The 2-pot process or a powder mixing process is used in turn, and the fibers are impregnated at a temperature at which a so-called pre-polymer stage occurs, that is to say work is carried out in a temperature range in which the liquid lactam melt passes directly into the liquid polymer melt during impregnation.

PRESENTATION OF THE INVENTION

The invention is therefore based on the object of providing a method for producing a composite material from reinforcing agents and a thermoplastic polyamide, which is simple, i. H. can be realized with a simple device, and which allows high process speeds in the continuous production process, in particular in the case of raw, that is to say non-pre-impregnated, reinforcing agents. This is done using the activated anionic lactam polymerisation. The generic term “polyamide” is understood to mean homopolyamides, copolyamides and mixtures thereof.

The solution to this problem is achieved by using the following process steps:

the supplied reinforcing agents are impregnated with a lactam melt activated for anionic polymerization, at a temperature at which the activated lactam melt does not yet substantially polymerize,

the impregnated reinforcing agent is subsequently heated and polymerized in a heating unit without passing through a heated or unheated mold, the impregnated reinforcing agent being guided in the heating unit essentially without contact,

- The resulting hot polymerized composite material is then cooled in a cooling unit, the lactam melt activated for the anionic polymerization being produced by first melting the lactam or the mixture of lactams into a monomer melt, and essentially a liquid initiator immediately before the impregnation process of the reinforcing agent is mixed into the monomer melt, which liquid initiator simultaneously contains the activator and catalyst functions in solution.

The essence of the invention thus consists on the one hand in completely dispensing with the use of an actual pultrusion mold, ie an actual molding tool. As mentioned above, the use of a pultrusion mold leads to a strong limitation of the possible train speeds. Surprisingly, it has now been shown that a pultrusion mold can be completely dispensed with, that is to say it is possible for the impregnated reinforcing agent to run essentially directly into a heating unit in which the matrix polymerizes at the appropriate temperature. Any necessary profiling of the strand can optionally be carried out after the polymerization by means of thermoplastic deformation (e.g. roll forming). The high tensile forces or friction or braking forces that occur when using a pultrusion form can thus be completely avoided, which enables much higher production speeds.

The activated lactam melt is usually produced according to the prior art in the so-called 2-pot process, i. H. that the lactam melt activated for the anionic polymerization is produced using two separate lactam melts, one of which contains the catalyst and the other the activator, and which are brought together and mixed intensively essentially immediately before the impregnation process of the reinforcing agent. A problem with such a process is the fact that the two pots of lactam melts which are necessarily kept at the melting temperature of the monomer tend to polymerize or otherwise react as a result of the presence of activator or catalyst. This makes the 2-pot process unsuitable for continuous processes, since the pots must be kept ready all the time. According to the present invention, however, the lactam melt activated for the anionic polymerization is prepared by first melting the lactam or the mixture of lactams, optionally with the addition of fillers or other additives (for example heat and UV stabilizers or dyes), to form a monomer melt is, and essentially only immediately before the impregnation process of the reinforcing agent, a liquid initiator is added to the monomer melt, which liquid initiator contains both activator and catalyst function in solution, and which liquid initiator is particularly, but not necessarily, stable in storage and liquid at room temperature. It is only this surprisingly simple possible control of the process with the separate provision of storage-stable monomer melt and liquid initiator, which takes on both the catalyst and the activator function, wherein the monomer melt and liquid initiator are only mixed immediately before the impregnation, permits a continuous, economical process in which the abovementioned Problems can be avoided since the monomer melt, which is kept at the melting temperature and possibly under inert gas (for example dry nitrogen), is stable in storage without the addition of a catalyst or activator.

In order to achieve a high production speed, highly reactive initiators or activators must be used which, for the reasons mentioned above, are kept separate from the lactam melt and only immediately before use with the Lactam melt should be brought into contact, which in practice can only be achieved economically and technically with the 1-pot process.

The lactam melt activated for the anionic polymerization used in the present invention is essentially a melt of aliphatic lactam, particularly preferably of butyrolactam, valerolactam, caprolactam, enantholactam or of laurolactam or from a mixture of the lactams mentioned, the lactam melt being a liquid initiator with catalyst - contains and activated activator function. In the case of the mixtures, that of caprolactam and laurolactam from which copolyamide 6/12 is formed by polymerization is preferred.

Liquid systems such as those described in EP 0791618 A1 or EP 0872508 A1 can be used as liquid initiators. With regard to the liquid initiator, the disclosure content of these two documents is explicitly included in the disclosure content of this document.

According to a further preferred embodiment, the liquid initiator contains a catalyst in the form of an alkali metal, a tetraalkylammonium or alkaline earth metal lactamate, in particular a sodium or potassium lactamate, lactamates with 5 to 13 ring members, preferably lactamates with 5 to 7 ring members, and particularly preferably caprolactamate.

According to another preferred embodiment, the liquid initiator contains an activator which activates the anionic polymerization in the form of an acyl lactam, a carbodiimide, a polycarbodiimide, a monoisocyanate, and / or a diisocyanate, and / or in the form of a mixture of these activators, the activators also preferably being included Lactam or hydroxy-fatty alkyloxazolines are blocked.

Another preferred embodiment is characterized in that in the liquid initiator ^' the catalyst and activator function is taken over by at least one initiator component in dissolved form, which initiator component has the necessary structural elements in a free or partially to completely inherent manner in order to achieve both the contact with lactam To form catalyst as well as the activator. In particular, such a structure can be provided in that the initiator component is a reaction product of isocyanate and / or carbodiimide with a protic compound and a base in an aprotic solvation agent. In other words, the liquid initiator may e.g. B. is a system as described in the documents DE 19961818 A1 and DE 19961819 A1 of the applicant. With regard to the liquid initiator, the disclosure content of these two documents is explicitly included in the disclosure content of the present application.

The division of the content of liquid initiator in the lactam melt activated for the anionic polymerization, as used for impregnation, becomes as follows carried out that the polymerization in the heating unit runs essentially completely, ie at the temperature prevailing there within the lead time through the heating unit. For this purpose, the liquid initiator is usually mixed into the monomer melt in an amount of 1 to 10% by weight, in particular 2 to 4% by weight, based on 100% activated anionic lactam melt. The dosage also depends on the reactivity of the activator.

Another preferred embodiment is that the lactam melt activated for the anionic polymerization additionally contains fillers or other additives, e.g. Heat and UV stabilizers or dyes. Heat stabilizers are also called antioxidants.

The reinforcement means can be a wide variety of structures such. B. to glass fibers, carbon fibers, aramid fibers, high-temperature polyamide fibers, metal fibers or combinations of the fibers mentioned (z. B. in the form of wound continuous filaments, yarns, staple fiber yarns, strands such as rovings, etc.), and / or textile structures the fibers mentioned (e.g. fleece web, needle felt, etc. or woven textiles such as knitted fabrics, woven fabrics, braids, knits, embroidery, laid fabrics, etc.) or combinations of the fibers mentioned and / or the textile structures mentioned. The method according to the invention has proven to be very particularly suitable for fibers, or generally reinforcing agents, which are brittle, brittle, and / or have high moduli (such as carbon fibers) and corresponding textile structures in which pressure is applied during impregnation and / or shear in highly viscous melts (in a pultrusion form) leads to considerable fiber damage (fiber breaks). Thanks to the rapid and pressure-free coating with a monomer melt and the free polymerization without the use of force, undamaged composite materials of high quality are obtained.

The reinforcing agent is furthermore preferred, e.g. dried and / or preheated in a preheating unit, the latter in particular to a temperature which is above the melting temperature of the for. the anionic polymerization of activated lactam melt lies. The preheated reinforcement material can be impregnated or soaked particularly well with melt, for. B. in an immersion bath, optionally using several squeeze / immersion cycles, or in a hollow profile with a stripping point.

According to a further preferred embodiment of the method according to the invention, the reinforcing agent is continuously passed through the preheating unit in the form of one or more webs or threads, if necessary conveyed with tension-controlled feed rollers, impregnated with the lactam melt activated for anionic polymerization, passed through the heating unit and the cooling unit , and withdrawn behind the cooling unit by extraction devices. The take-off devices can be rollers, caterpillars, pulling devices with clamps or winders. The composite can are preferably conveyed through the process at a speed of at least 1 m / min, in particular of at least 5 m / min. Speeds of more than 10 m / min are particularly preferred and economically very advantageous.

According to another preferred embodiment, essential process steps take place under a protective gas atmosphere (in an inert gas atmosphere) in order to largely prevent the oxidation of the lactam melt. This means that the impregnated reinforcing agent is conducted at least in the heating unit under a protective gas atmosphere, in particular under a (dry) nitrogen atmosphere, and that, particularly preferably, the area in which the reinforcing agent is heated or dried, the area in which the impregnation takes place, and the containers in which lactam melt and possibly even that of the liquid initiator and the cooling unit are kept under a protective gas atmosphere. In particular in the heating unit and in the cooling unit, a counterflow through the protective gas used proves to be advantageous, i. H. that the protective gas in the area of the heating of the reinforcing agent, in the area of the impregnation, and in particular in the area of the heating and cooling unit, is guided in counterflow against the direction of flow. The countercurrent of the protective gas in combination with the slightly increased pressure on the transported material on the one hand leads to problems of sublimation (sublimation of lactams and corresponding undesired removal of monomer from the impregnated reinforcing agent as well as deposition of desublimated lactams on the walls delimiting the process, e.g. the channel in the form of a hollow profile) can be greatly reduced. Apparently, the overflow of the impregnated reinforcing agent leads to a reduced sublimation and / or to a better removal of sublimate from the guide system. In particular, if the protective gas is applied to a certain extent from behind, first through the cooling unit, then through the heating unit, and up to at least the area immediately behind the impregnation, this control can also be used to achieve a homogeneous, steady (ie balanced, not abrupt) temperature control ( Warming up or cooling down) are ensured, which on the one hand is energetically advantageous and on the other hand also reduces sublimate deposits. This procedure is particularly advantageous when using caprolactam, which tends to sublimate much more strongly than laurolactam.

In particular, in order to prevent the volume charged with protective gas from becoming too large, the entire process section (preheating unit, impregnation, heating and cooling unit) is advantageously designed in the form of a channel. The cross-section of this channel is adapted to the cross-section of the impregnated reinforcing agent in such a way that there is sufficient space all around between the impregnated reinforcing agent and the channel walls, both for the (dry) nitrogen flowing through and for guiding the impregnated reinforcing agent through the channel essentially without contact , The channel or the wall of the passage area is preferably made of Teflon. In order to avoid entraining too much lactam melt, the impregnated reinforcing agent can pass a stripping point in the running direction essentially immediately after the impregnation and essentially before entering the heating unit, at which excess lactam is stripped off. Alternatively, the lactam melt required can also be supplied by means of a metering or regulating device (for example a pump).

According to a particularly preferred embodiment, laurin lactam is used as the lactam, which is melted, i.e. heated above the melting point of 151 degrees Celsius (usually to about 170 degrees Celsius) and mixed with a liquid initiator kept at room temperature and mixed to form the lactam melt activated for the anionic polymerization. The continuously supplied reinforcing agent, preheated in the range of 170 degrees Celsius, is impregnated at a temperature of in the range of 170 degrees Celsius, in the heating unit at a temperature in the range of 200 to 250 degrees Celsius for a period of 30 seconds to 5 minutes, polymerized in particular for a period of 1 to 3 minutes free and essentially contactless, under guidance in a channel and under a protective gas atmosphere, and then cooled to a temperature of less than 150 degrees Celsius in the cooling unit.

According to another particularly preferred embodiment, the lactam used is caprolactam, which is melted, i.e. heated above the melting point of 69 degrees Celsius (usually to about 170 degrees Celsius) and mixed with a liquid initiator kept at room temperature and mixed to form the lactam melt activated for the anionic polymerization. The continuously supplied reinforcing agent, preheated in the range of 170 degrees Celsius, is impregnated at a temperature of in the range of 170 degrees Celsius, in the heating unit at a temperature in the range of 230 to 240 degrees Celsius for a period of 30 seconds to 5 minutes, polymerized in particular for a period of 1 to 3 minutes free and essentially contactless, under guidance in a channel and under a protective gas atmosphere, and then cooled to a temperature of less than 200 degrees Celsius in the cooling unit. It is also possible to operate the heating unit at a temperature below the melting point of polycaprolactam, i.e. H. to lead below 222 degrees Celsius and allow the polymerization to proceed at this lower temperature. The process then runs correspondingly slower and requires longer guidance through the heating unit, or the reaction must be accelerated by increasing the addition of liquid initiator.

When manufacturing very wide-area structures, it can be advantageous to support the textile structure to be impregnated by means of a moving conveyor belt and thus to guide it through the entire process section.

Another embodiment is characterized in that the polymerized composite material is either in line, for example using processes such as roll forming or Interval hot presses are processed into profiles, or later subjected to a thermoplastic aftertreatment. In addition, the polymerized composite material can be assembled into completely impregnated semi-finished fiber composite plastics (eg organic sheets), which can then be pressed into three-dimensional molded parts. The complete fiber impregnation carried out according to the invention enables very short molding times and thus high economy. The production of long fiber reinforced granules is also possible in this way, ie by cutting the polymerized composite strand with the cutting wheel of a granulator. Such granules can e.g. B. in the injection molding or extrusion process, which results in moldings with excellent mechanical properties. But also used composite materials can be crushed later, optionally with additives and z. B. be fed by injection molding or pressing material recycling.

Further preferred embodiments of the method are described in the dependent claims. The finished semifinished product can be processed further by thermoplastic aftertreatment, preferably selected from the group consisting of thermoforming, extrusion, deep drawing, pressing, connecting with thermoplastics (of the same or a different type). The connection with thermoplastics is preferably done by injection molding, pressing or welding processes, with the injection molding process also special processes such. B. overmolding, spraying, extrusion coating and injection are counted.

In addition, the present invention relates to an apparatus for carrying out a method as described above.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawings. Show it:

Figure 1 is a schematic representation of an apparatus for performing a method for producing a composite material from reinforcing agents and a thermoplastic polyamide matrix using an anionically activated lactam polymerisation. and

Fig. 2 shows an embodiment of an arrangement for impregnation and introduction into the heating unit.

WAYS OF CARRYING OUT THE INVENTION

The present method is to be illustrated with the aid of FIG. 1, which represents a device for carrying out the method in a schematic representation. It is a 1-pot process, that is, a process in which the Anionically activated lactam melt is produced by adding a liquid initiator to the lactam melt shortly before the impregnation.

The reinforcing means 29 is first supplied from the left. In the case shown here, six webs of fiber rolls 13 are fed and brought into a suitable relative position by a pair of guide rolls 14. However, the reinforcing means 29 can equally be a plurality of threads, rovings, etc., each of which is fed from bobbins and introduced into the process in the desired arrangement. It is also possible, for. B. in the case of a woven or non-woven textile reinforcement, this only from a roll 13. As already mentioned at the beginning, the reinforcement means 29 can have a wide variety of structures and. Materials such as B. glass fibers, carbon fibers, aramid fibers, high-temperature polyamide fibers, metal fibers or combinations of the fibers mentioned. This z. B. in the form of spooled continuous filaments, yarns, staple fiber yarns, strands such as rovings etc., which are then introduced into the process in a suitable arrangement via a large number of bobbins 13 and guide rollers 14. Alternatively or additionally (combination of fibers and textiles), however, it can also be textile structures made from the fibers mentioned or from combinations of the fibers mentioned. This z. B. in the form of nonwoven webs, needle felts, etc., or of woven textiles. The method according to the invention has proven to be very particularly suitable for fibers, or generally reinforcing agents, which are brittle, brittle, and / or have high moduli (such as carbon fibers) and corresponding textile structures, in which pressure is applied during impregnation and / or shear in highly viscous melts (in a pultrusion form) leads to considerable fiber damage (fiber breaks). If such brittle fibers are impregnated with a thermoplastic matrix in a pultrusion process, the high tensile forces due to the high viscosity of the melt lead to fiber breaks and thus to a pronounced formation of the bird's nests mentioned at the beginning with fibers at the entrance to the pultrusion mold. In addition, the fiber breaks lead to a reduction in the quality of the finished composite materials. The fast and pressure-free impregnation with a monomer melt and the free polymerization without the use of force result in undamaged composite materials with intact fibers.

The supplied reinforcing agent 29 is continuously introduced and processed in a first step a. The web or the strand is guided through a preheating unit 15, in which the reinforcing means 29 is both dried and preheated to the necessary temperature. It is heated to a temperature which is slightly above the temperature at which the activated lactam supplied as a melt does not solidify. The temperature of the reinforcing agent at the moment of impregnation should not, however, already be so high that the lactam melt undergoes substantial polymerization before it enters the heating unit. Usually, it proves sufficient to set a temperature in the preheating unit 15 which is in the range from 5 to 30 degrees Celsius above that The melting temperature of the lactam is preferably a temperature which is in the range from 10 to 20 degrees above this melting temperature. The heated and dried reinforcing agent 29 is then, if necessary, guided into the region 16 of the impregnation with the aid of tension-controlled feed rollers 35. The feed rollers have the function of leading particularly sensitive textiles into the impregnation zone without tension and distortion and guaranteeing impeccable impregnation. In this context, tension-controlled means that the drive of the feed rollers is controlled in such a way that the tension in the textile web (or strand) at the point of impregnation is low.

In addition, a lactam melt 3 is prepared in a lactam container 1. It is heated above its melting point, so that a low-viscosity melt is present. The lactam melt 3 may contain other conventional additives, such as. B. plasticizers, stabilizers etc. and fillers. In addition, in a liquid initiator container 4, a liquid initiator is usually kept at room temperature, which contains both the catalyst and the activator functions in dissolved form. Liquid initiators such as are described in EP 0791618 A1 and in EP 0872508 A1 are particularly suitable. Liquid initiators as described in the applicant's published documents, DE 19961818 A1 and DE 19961819 A1 are also possible.

The monomer melt 3 is fed via a heated monomer line 7 and the liquid initiator via a feed 9 for the liquid initiator to a mixer 10, where the two components are mixed intensively with one another. The polymerization is controlled by the type of liquid initiator, the ratio of liquid initiator to lactam melt 3, and the reaction temperature. Static mixing elements are particularly suitable as mixers 10, for example those from Sulzer, Winterthur (CH).

The activated anionic lactam melt 11 resulting behind the mixer 10 is now passed directly into the area 16 of the impregnation and passed onto the dried and preheated reinforcing agent supplied. In the region 16 there is advantageously a temperature above the melting temperature of the activated anionic lactam melt 11, in particular a temperature which corresponds to the temperature of the preheated reinforcing agent 29, ie, for example 10 to 20 degrees Celsius above the melting point of the lactam melt. The low-viscosity melt impregnates and penetrates essentially completely through the continuously supplied reinforcing agent 29. In the case of a web-shaped textile reinforcing agent, it may be sufficient to simply let the lactam melt drip onto the web, but normally the reinforcing agent 29 must be passed through an immersion bath, a channel or through a veil of lactam melt. The impregnated reinforcing agent 30 is then optionally passed through a stripping unit 23, so that excess matrix material 24 is stripped off before the polymerization of the matrix has used significantly and thus the viscosity is too high for stripping at a fast production speed.

Subsequently, the impregnated reinforcing agent 30, which is advantageously guided in a channel at the latest, which touches the impregnated reinforcing agent 30 as little as possible (the channel (inner) wall is made of Teflon, for example), is led into a heating unit 17, at which there is a temperature at which the activated anionic lactam polymerization takes place practically completely within the time in which the impregnated reinforcing agent 30 is located in the heating unit 17. Typically, the polymerization takes about one to two minutes for its practically complete completion, the necessary length of the heating unit 17 being calculated from the desired production speed and the time set for the polymerization via the type and amount of initiator or activator added. In order not to have to make the heating unit exceptionally long (e.g. 40 meters). it is possible to redirect the impregnated reinforcing agent in the heating unit several times with the aid of rollers (the rollers are advantageously made of Teflon), in which case the heating unit is more in the form of a chamber than a channel. In principle, however, the impregnated reinforcing agent is largely largely contactless, especially in the initial area of the polymerization, so that the highest possible production speed is possible. As an alternative to the free guidance of the endless textile structure, it is also possible, in the case of nonwoven webs that would tear under their own weight after the impregnation, on a base, e.g. B. a conveyor belt made of steel or Teflon, through the heating unit.

Behind the heating unit, the now polymerized composite material 31 is led into a cooling unit 18, in which the composite material is cooled at least to a temperature which is below the solidification temperature of the polyamide. Behind the cooling unit 18, the polymerized composite material 32 is conveyed by pulling rollers 27 or caterpillars and pulled through the process. The polymerized composite material 32 can then be subjected to a finishing 26.

Since lactam and polyamide melts are fundamentally sensitive to oxidation, those areas of the process in which the lactam or polyamide are in molten form are kept under an inert gas atmosphere 25 (eg nitrogen). Oxidation should be prevented in particular in the heating unit 17. In addition, the inert gas (eg N ₂ ) should be dry so that the initiator is not partially consumed by water. For this purpose, the process line can be supplied with dry nitrogen via a supply 19 of nitrogen. In order to be able to take advantage of the cooling effect of the nitrogen used, the nitrogen can already be guided into the channel somewhat behind the heating unit 17 in the cooling unit 18, so that countercurrent cooling in the area of the cooling unit or countercurrent in the heating unit occurs. The nitrogen atmosphere can essentially only be maintained in the area of the heating unit 17 and the cooling unit 18, ie up to the limit 22, but it is also possible to do so Area 16 of the impregnation and area 15 of the preheating unit for the reinforcing fibers are to be charged with nitrogen and the nitrogen is only discharged behind the preheating unit 15 via a line 20. An inert gas atmosphere 2 should also be maintained above the lactam melt 3, just as a corresponding inert gas atmosphere 5 may be advantageous above the liquid initiator 6.

The finished composite can then either be used directly without additional post-treatment, or it can be cut (assembled) or wound on a roll, and since it is a thermoplastic composite, it can also be used in a thermal molding process in line or in a separate one Post-process to final form. Typical composite materials contain 30 to 75% by weight of fiber material. For the composite materials that can be used directly without additional post-treatment, e.g. (airtight) coated fabrics as well as rods or bars.

The procedure is to be carried out in more detail using the following examples:

example 1

In container 1, laurolactam pills are melted under a nitrogen atmosphere at a temperature of 170 degrees Celsius. In the container 4, a liquid initiator, as described in experiment 7 of DE 19961818 A1, is kept at room temperature. According to Table 1 a) of DE 19961818 A1, the liquid initiator of Experiment No. 7 is a reaction product of dicyclohexylcarbodiimide (DCC) with the protic compound Nylostab S-EED (Ny) and the base sodium methylate in the aprotic solvating agent N-octylpyrrolidone (NOP ). Liquid initiator 6 and lactam 12 melt are used in a ratio of 3.5: 96.5% by weight. Liquid initiator 6 and lactam 12 melt are mixed intensively in mixer 10 and passed in a low-viscosity state (such as water) to a preheated and dried reinforcing agent.

The reinforcing agent, a 12K (120,000 filament) roving made of carbon fibers of the type 5N21 from Tenax Fibers, Wuppertal (DE), is fed from optionally several coils, and preheated and dried in a preheating unit 15 at a temperature of 170 degrees Celsius. The fiber strand 29 is inserted behind the preheating unit 15 into a Teflon channel 34, into which the line 11 opens after about 15 to 25 cm, through which the activated anionic lactam is supplied in a low-viscosity form for impregnation (cf. FIG. 2). Immediately in the running direction 28 behind the introduction of the activated anionic lactam, the channel 34 has a constriction or stripping point 23, so that, to a certain extent, an immersion bath is formed in the channel section in front of the constriction, the excess 24 of activated anionic Lactam melt is discharged at the entrance of channel 34. However, the supply of lactam melt can also be adjusted or throttled in such a way that no excess is removed at all. Behind the stripping point 23, the impregnated reinforcing means 30 is guided into the heating unit 17 essentially hanging freely, ie touching the channel as little as possible. Before being introduced into the heating unit 17, the discharge 21 branches off from the channel, which at this point can be made either of glass or of Teflon. Since the constriction 23, which is essentially completely flooded with lactam melt, is located upstream of this discharge 21, essentially no nitrogen escapes uncontrollably through this constriction through the opening of the channel into which the reinforcing agent is introduced. In addition, the nitrogen already passed through the heating unit 17 leads to a homogeneous and constant warming or to an increase in the temperature to the reaction temperature of the impregnated reinforcing agent between the entry into the heating unit and the discharge 21 of the nitrogen; accordingly, it is advantageous to bring the discharge 21 as close as possible to the Stripping point 23 to be arranged. This specific supply of the lactam melt via a channel or a hollow profile with a stripping point acc. Figure 2 proves to be advantageous in general, and not only in connection with this particular embodiment.

Another possibility of impregnating the reinforcing agent is to guide the reinforcing agent 29 into an immersion bath 11 via rollers.

The process of impregnation in area 16 is kept at 170 degrees Celsius. In the heating unit through which the impregnated reinforcing agent is passed, there is a temperature in the range of 250 degrees Celsius, the heating unit 17 has a length that results in a dwell time in the heating unit of in the range of 2 min at the specified running speed, which with the initiator type used for the complete polymerization of the matrix to polyamide 12 is sufficient. The strand 30 is guided in a furnace-shaped heating unit 17 of the test arrangement in a Teflon channel, and only the interior of this channel is pressurized with nitrogen. The channel protrudes about 50 cm behind the heating unit 17 and is charged with cold nitrogen in the opposite direction to the running direction 28 via a T-piece. Behind it is a take-off device in the form of two rollers 27 which pull the finished composite material 33 at the desired speed.

The finished composite material 33 usually does not yet have an exact cross-sectional shape and in many cases does not yet represent the end product. Thanks to the thermoplastic matrix, however, it can be thermoformed directly in line or later to the final cross-section. Example 2

Caprolactam pills are melted in container 1 under a nitrogen atmosphere 2 at a temperature above 80 degrees Celsius. The same liquid initiator as in Example 1 is kept in the container 4 at room temperature. Liquid initiator 6 and lactam 6 melt are used in a ratio of 3.5: 96.5% by weight. Liquid initiator 6 and lactam 6 melt are mixed intensively in the mixer 10 and passed in a low-viscosity state (such as water) to a preheated and dried reinforcing agent.

The reinforcing agent, the same as in Example 1, is supplied from several coils, and preheated and dried in a preheating unit 15 at a temperature of 170 degrees Celsius. The process is then carried out analogously to Example 1, but in the heating unit through which the impregnated reinforcing agent is passed, the temperature is 230 degrees Celsius, i.e. somewhat lower than in Example 1 in order to keep the sublimation of caprolactam as low as possible.

In principle, it is also possible to further reduce sublimation, especially with caprolactam, in the heating unit even below the melting point of the resulting polyamide 6, because the polymerization rate is sufficient for many cases even at 200 degrees Celsius.

LIST OF REFERENCE NUMBERS

1 lactam container

2 nitrogen atmosphere over lactam

3 lactam, monomer melt

4 liquid initiator tanks

5 nitrogen atmosphere via liquid initiator

6 liquid initiator

7 monomer feed (heated)

9 Feed for liquid initiator

10 mixers

11 Feeding of the activated monomer mixture, lactam melt activated for the anionic polymerization

12 Feeding the reinforcing fibers

13 fiber roll (spool) with semi-finished reinforcement

14 pair of guide rollers

15 Preheating unit for the reinforcing fibers

16 impregnation unit

17 heating unit

18 cooling unit

19 Supply of nitrogen

20 Removal of nitrogen

21 alternative nitrogen discharge

22 alternative limitation of the nitrogen range

23 stripping unit

24 Removal of excess matrix material

25 nitrogen atmosphere

26 assembly unit

27 take-off device (pull rollers)

28 Running direction

29 reinforcing fibers 30 impregnated reinforcing fibers

31 polymerized composite (hot)

32 polymerized composite (cold)

33 composite material

34 channel

35 feed rollers

a Preparation of matrix and fibers b Impregnation and polymerisation c Cooling and finishing

Claims

A method for producing a composite material (33) from reinforcing agents (29) and a thermoplastic polyamide, characterized in that

the impregnating agents (29) supplied are impregnated with a lactam melt (11) activated for the anionic polymerization at a temperature at which the activated lactam melt (11) essentially does not yet polymerize,

the impregnated reinforcing agent (30) is heated and polymerized in a heating unit (17) without passing through a heated mold, the impregnated reinforcing agent (30) being guided in the heating unit (17) essentially without contact,

- The resulting hot polymerized composite material (31) is cooled in a cooling unit (18), the lactam melt (11) activated for the anionic polymerization being produced by first melting the lactam or the mixture of lactams into a monomer melt (3), and essentially immediately before the impregnation process of the reinforcing agent (29), a liquid initiator (6) of the monomer melt (3) is admixed, which liquid initiator (6) simultaneously contains the activator and catalyst functions in solution.

A method according to claim 1, characterized in that the monomer melt (3) activated for the anionic polymerization is essentially a melt of aliphatic lactam, particularly preferably of butyrolactam, valerolactam, caprolactam, enantholactam or laurin lactam or a mixture of the above Lactame acts.

Method according to one of the preceding claims, characterized in that the liquid initiator (6) is stable in storage and liquid at room temperature.

Method according to one of the preceding claims, characterized in that the catalyst function of the liquid initiator (6) is taken over in dissolved form by a catalyst in the form of an alkali metal, tetraalkylammonium or alkaline earth metal lactamate, in particular a sodium or potassium lactamate, wherein Lactamates with 5 to 13 ring members, preferably lactamates with 5 to 7 ring members, and particularly preferably caprolactamate, are used.

Method according to one of the preceding claims, characterized in that the activator function of the liquid initiator (6) by an activator which activates the anionic polymerization in the form of an acyl lactam, a carbodiimide, a polycarbodiimide, a monoisocyanate, and / or a diisocyanate, and / or a mixture these activators, preferably capped with lactam or hydroxy-fatty alkyloxazolines, are taken over in dissolved form.

Method according to one of the preceding claims, characterized in that the catalyst and activator function of the liquid initiator (6) is taken over by at least one initiator component in dissolved form, which initiator component has the necessary structural elements in a free or partially to completely inherent manner to be in contact with Lactam to form both the catalyst and the activator.

7. The method according to claim 6, characterized in that the initiator component is a reaction product of isocyanate and / or of carbodiimide with a protic compound and a base in an aprotic solvation agent.

Method according to one of the preceding claims, characterized in that the liquid initiator (6) of the monomer melt (3) in an amount of 1 to 10% by weight, in particular 2 to 4% by weight, based on 100% activated anionic lactam melt (11 ), is added.

Method according to one of the preceding claims, characterized in that the lactam melt (11) activated for the anionic polymerization additionally contains fillers or further additives.

10. The method according to any one of the preceding claims, characterized in that the reinforcing means (29) are glass fibers, carbon fibers, aramid fibers, high-temperature polyamide fibers, metal fibers or combinations of the fibers mentioned, in particular in the form of continuous threads, yarns, staple fiber yarns , Strands, rovings, and / or around textile Formed from the fibers mentioned or from combinations of the fibers mentioned, such as knitted fabrics, woven fabrics, braids, knitted fabrics, embroideries, scrims, nonwovens.

11. The method according to any one of the preceding claims, characterized in that the reinforcing agent (29) is dried and / or preheated before impregnation, the latter in particular to a temperature which is above the melting temperature of the lactam melt (11) activated for anionic polymerization.

12. The method according to any one of the preceding claims, characterized in that the reinforcing agent (29) in the form of one or more webs or threads continuously fed, impregnated with the lactam melt (11) activated for the anionic polymerization, by the heating unit (17) and the cooling unit (18) is guided, and is withdrawn behind the cooling unit (18) by extraction devices (27).

13. The method according to claim 12, characterized in that the composite material (33) is conveyed through the process at a speed of at least 1 m / min, in particular of at least 5 m / min, particularly preferably at over 10 m / min.

14. The method according to any one of the preceding claims, characterized in that the impregnated reinforcing agent (30) is performed at least in the heating unit (17) under a protective gas atmosphere, in particular under a dry nitrogen atmosphere, and that in particular preferably also the area (15) in which the Reinforcing agent (29) is heated or dried, the area (16) in which the impregnation takes place, and the containers (1, 4) in which lactam melt (s) and optionally also liquid initiator (6) and the cooling unit (18) be kept under a protective gas atmosphere.

15. The method according to claim 14, characterized in that the protective gas in the area (15) of the heating of the reinforcing agent (29), in the area (16) of the impregnation, and in particular in the area (17) of the heating unit and in the area of the cooling unit (18th ) in particular in a coherent manner between the areas (15-18) in countercurrent against the running direction (28).

6. The method according to any one of the preceding claims, characterized in that the heating unit (17) and / or the cooling unit (18) has the shape of a channel, which channel is adapted to the cross section of the impregnated reinforcing agent (30) so that between the impregnated Reinforcing means (30) and the walls of the channel have sufficient free space on all sides to guide the impregnated reinforcing means (30) through the channel essentially without contact, the channel according to. one of claims 14 or 15 is supplied with protective gas.

17. The method according to any one of the preceding claims, characterized in that the impregnated reinforcing means (30) in the running direction (28) after the impregnation and essentially before entering the heating unit (17) passes a stripping point (23) at which excess lactam is stripped becomes.

18. The method according to any one of the preceding claims, characterized in that laurin lactam is used as the lactam, this is melted at a temperature of over 151 degrees Celsius and mixed with a liquid initiator (6) kept at room temperature and to the lactam melt activated for the anionic polymerization (11 ) is mixed that continuously supplied reinforcing agent (29) preheated in the range of 170 degrees Celsius is impregnated in the heating unit (17) at a temperature in the range of 200 to 250 degrees Celsius in the range of 170 degrees Celsius is polymerized free and without contact for a period of 30 seconds to five minutes, in particular for a period of 1 to 3 minutes, and then cooled in the cooling unit (18) to a temperature of less than 150 degrees Celsius.

19. The method according to any one of claims 1 to 18, characterized in that the lactam used is caprolactam, this is melted at a temperature of over 69 degrees Celsius and mixed with a liquid initiator (6) kept at room temperature and to the lactam melt activated for anionic polymerization (11) is mixed so that continuously supplied reinforcing agent (29) preheated in the range of 170 degrees Celsius is impregnated in the heating unit (17) at a temperature in the range of 230 to 240 at a temperature of in the range of 170 degrees Celsius Degrees Celsius, or also below the melting point of polycaprolactam, is polymerized free and without contact for a period of 30 seconds to five minutes, in particular for a period of 1 to 3 minutes, and then in the cooling unit (18) to a temperature of less than 200 Degrees Celsius is cooled.

20. The method according to any one of the preceding claims, characterized in that the polymerized composite material is used directly without additional aftertreatment.

21. The method according to any one of claims 1 to 19, characterized in that the polymerized composite material is subjected to a thermoplastic aftertreatment either in line or later.

22. The method according to any one of claims 1 to 19, characterized in that the polymerized composite material is assembled into semi-finished products.

23. The method according to claim 21, characterized in that the aftertreatment comprises in line roll molds and interval hot presses.

24. The method according to claim 22, characterized in that the finished semi-finished product is further processed by thermoplastic post-treatment selected from the group thermoforming, extrusion, deep drawing, pressing, connecting with thermoplastics.

25. The method according to claim 24, characterized in that the connection with thermoplastics is done by injection molding, pressing or welding processes.

26. The method according to claim 22, characterized in that the manufacturing comprises the production of long fiber reinforced granules.

27. The method according to any one of the preceding claims, characterized in that used composite materials are later comminuted, optionally provided with additives and are fed to material recycling by injection molding or pressing.

28. Device for carrying out a method according to one of claims 1 to 27.