WO2015097097A1

WO2015097097A1 - Prepregs having prolonged stability, process for production thereof and uses of the prepregs

Info

Publication number: WO2015097097A1
Application number: PCT/EP2014/078833
Authority: WO
Inventors: Andreas Niepel; Andreas Hartwig; Manfred Peschka; Andreas Lühning; Thomas Kowalik
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2013-12-23
Filing date: 2014-12-19
Publication date: 2015-07-02
Also published as: DE102013227142A1; DE102013227142B4; DE102013227142A8

Abstract

The invention relates to the impregnation or textile fibers (for example in the form of mats, fibers, yarns, wovens, nonwovens) with an aqueous formulation comprising a dispersion of at least one reactive resin and at least one crosslinking agent. The formulation is especially free of volatile organic solvents. After the impregnated textile has been dried, the result is an uncrosslinked, efficiently meterable, contamination-free, further-processible, fiber-reinforced textile semifinished product (prepreg). The latter is storage-stable, non-tacky and flexible at room temperature, and hence can be rolled up without separation film. The prepreg can rapidly be crosslinked permanently in a further step by means of the action of heat, and optionally with the assistance of pressure and/or radiation (e.g. UV light), to give a fiber-reinforced plastic having high strength and good chemical resistance, and is suitable inter alia for the production of structural components in motor vehicle construction.

Description

Long-term stable prepregs, processes for their preparation and uses of the prepregs

The invention relates to the impregnation of textile fibers (for example in the form of mats, fibers, yarns, fabrics, nonwovens) with an aqueous preparation comprising a dispersion of at least one reactive resin and at least one crosslinking agent. The preparation is especially free from volatile organic solvents. After drying of the impregnated textile results in a non-crosslinked, well-dosed, contamination-free,

further processable, fiber-reinforced semi-finished textile product (prepreg). This is storage stable at room temperature, not sticky, flexible and thus rollable without release film. In a further step, the prepreg can be permanently crosslinked by the action of heat and, if necessary, by pressure and / or irradiation (eg UV light), rapidly to a fiber-reinforced plastic with high strength and good resistance to chemicals, and is used, inter alia, for the production of Structural components suitable in vehicle construction. Fiber-reinforced plastics are increasingly being used for structural components in industrial and leisure applications. The technology is currently used primarily in motorsport, aerospace and rail vehicle and aircraft applications. Even slight differences in weight lead to savings in energy and fuel consumption. Long distances in connection with long product life cycles lead to a decisive competitive advantage over conventional materials such as steel, aluminum or wood, despite the cost intensity (caused by storage conditions, environmental protection, occupational safety, low degree of automation and long processing times, for example).

Fiber plastic matrix compositions are generally referred to as "fiber composite plastics" or simply "composite plastics". A variety of different combinations is already described in the literature and is in use. The fiber can be a natural or synthetic fiber, your orientation is largely responsible for the mechanical properties of the final product.

The plastic matrix in which the fibers are embedded may be a thermoplastic or thermosetting plastic. This fixes the fiber against slipping and protects it from environmental influences (for example chemicals, water, solvents, acids and alkalis). The structural components are dominated by thermosetting resin systems. Often, the fibers and reactive resin composition are combined and cured immediately thereafter to form the final fiber reinforced plastic.

Alternatively, the fibers and resin may be combined with suitable hardeners and stored in an uncured state. The crosslinking to the fiber-reinforced plastic typically takes place at a later time. This method preimpregnated to produce uncured, textile semi-finished products is generally referred to as "prepreg process".

A prepreg typically comprises a textile reinforcement embedded in an uncured reactive resin matrix. The thermosetting crosslinkable matrix resin composition typically consists of one or more liquid (viscous) di- or polyfunctional epoxy resins and one or more acidic or aminic hardeners. The uncured resin matrix may also contain additives such as accelerators, impact modifiers, flame retardants, fillers, and the like. In general, epoxy prepregs are cured at temperatures in the range of 50 ° C to 200 ° C to fiber composite plastic.

Epoxy prepregs are shelf stable only for a limited time due to the presence of hardeners and accelerators in the resin matrix. For example, a prepreg employing 1-methylimidazole as a crosslinking agent in the epoxy matrix and which can be crosslinked at a temperature of 60 ° C has a storage stability at room temperature of less than 2 days and thereafter is a semi-finished storage product for producing a fiber-reinforced one Plastic unusable.

To slow down the premature crosslinking of such reactive systems, these prepreg types must be stored at low temperatures (about -20 ° C) and thawed prior to further processing in forming tools. The necessary increase in temperature has a detrimental effect on the pot life within which a high quality end product can be made.

In addition, it is important that the matrix resin does not flow out of the fiber reinforcement of the prepreg during storage or processing or that the matrix resin does not detach from the fiber. This can be achieved by the formulation of partially solid or high viscosity resins (high molecular weight resins) (see US 6,787,237 B2).

It is often desirable for at least one side of the prepreg to have some contact tack. This is achieved in US 6,787,237 B2 by adding low molecular weight substances. The contact tack usually facilitates the processing of several layers of prepregs in forming tools (eg alignment of fibers). The disadvantage is the use of release films, which should prevent during storage a Aneinanderkleben multiple prepreg layers. Another disadvantage is the heavy contamination of equipment.

Prepregs are usually tacky at room temperature, which is why processing with simple textile technology methods is not possible. Therefore, prior art prepregs are well suited for manufacturing processes, but not for the automated production of high volume products.

Furthermore, it is desirable for the prepreg to have a certain flexibility so that it can be rolled up in a space-saving manner after the impregnation in a continuous process, unrolled again at a later time shortly before processing, and fed to shaping tools. The flexibility is usually by viscous resins or in the case of solid resins by mixing low molecular weight substances i. Plasticizers (see, e.g., U.S. Patent 6,787,237 B2).

Based on this, it was the object of the present invention to provide a textile reactive-hardenable semifinished product with tack-free, i. non-sticky room temperature, improved storage stability, flexibility and handling, and a method of making the same. Furthermore, it was an object to point out possible uses of the textile semifinished product and to provide a fiber composite material that can be produced from the textile semifinished product.

This object is achieved in terms of a prepreg with the features of claim 1, with respect to a method for producing the prepreg according to the invention with the features of claim 12, with respect to a fiber composite material, prepared from the prepreg according to the invention with the features of claim 17 and with respect to uses of the prepreg with the Characteristics of claim 18 solved. The respective dependent claims represent advantageous developments.

According to the invention, a prepreg is provided which

a) at least one semifinished textile product which contains or consists of at least one fiber selected from the group consisting of carbon fibers, glass fibers and natural fibers; b) at least one at least partially uncured reactive resin composition containing at least one solid at 25 ° C reactive resin and at least one water-stable crosslinking agent, wherein the resin composition wets the fiber at least partially,

contains or consists of, characterized in that the prepreg is prepared by at least partially wetting the textile semifinished product with an aqueous preparation of the reactive resin composition containing a dispersion of at least one solid at 25 ° C reactive resin and at least one water-stable crosslinking agent and then at least partial drying of the textile semifinished product.

The prepreg according to the invention is characterized in particular in that it has a non-adhesive surface at 25 ° C. This may be accomplished by having the uncured reactive resin composition have a glass transition temperature of> 25 ° C.

The surface of the fibers of the semi-finished textile product in the prepreg according to the invention is at least partially coated or embedded in a reactive resin composition. In the resin composition, the reactive resins are particularly preferably in solid form, the crosslinking agents may be present as a mixture with the reactive resin, but also in a separate form next to it. Surprisingly, it has been found that by wetting or impregnating the fibers of the semifinished textile product with an aqueous preparation containing the reactive resin and a crosslinking agent, it is possible to produce a prepreg which has a tack-free surface and moreover has a long shelf life.

According to the invention, the reactive resin composition is thus in the form of an aqueous preparation or is prepared to such. Subsequently, the semi-finished textile product is impregnated with this preparation at least partially and then dried. The term "prepreg" thus means according to the invention an uncrosslinked textile semifinished product which is impregnated at least in regions with an uncrosslinked polymer The prepreg can be cured to a duromer in a later process. In a preferred embodiment of the manufacturing process, the aqueous preparation of the reactive resin composition contains at least one aqueous dispersion of the 25 ° C. solid reactive resin and the water-stable crosslinking agent. In addition, the at least partially wetting of the semi-finished textile product in the production process may comprise or consist of applying the reactive resin composition in the form of an aqueous preparation to the at least one textile semi-finished product at least in regions, in particular to the entire surface of the at least one a textile semifinished product. Furthermore, the at least partial drying may comprise or consist of (preferably complete) evaporation of water, the prepreg having a surface which is tack-free at 25 ° C., in particular after evaporation of the water. The particles of the reactive resin dispersion preferably have an average

Diameter of <10 μιη, preferably <1 μιη, more preferably <0.5 μιη, determined with dynamic light scattering on. The crosslinking agent can be dissolved in the aqueous phase of the dispersion, in the form of crystallites or in encapsulated form. In the event that the crosslinking agent is not dissolved in the aqueous phase of the dispersion, it preferably has an average diameter of <10 μιη, preferably <1 μιη, more preferably <0.5 μιη, determined with dynamic light scattering on.

According to the invention, a surface is tack-free if it has no tack in the rolling ball test according to ASTM 3121, i. the ball does not stop within the test length of 20 cm. Alternatively, it is also possible to test with the loop tack test according to AFERA 4015. A surface is considered to be tack-free if a test value of 0 results. The surface of the uncured prepreg is at room temperature

(20 ° C to 25 ° C) no contact stickiness. The uncured prepreg has sufficient flexibility for textile processing. Moreover, when the prepreg is deformed (rolled) in a molding process, there is no peeling phenomenon of the mixture containing reactive resin and crosslinking agent from the fiber. Other components may be included in the resin composition (eg, surfactants, nucleating agents, fillers, flexibilizers, and other additives commonly used in polymers of the prior art). The other components are preferably dispersed in water or are dispersed in water. The other components are therefore preferably present as a finely divided solid in the water. It is also possible that some of the components are completely or partially soluble in the water. It is important that the components do not decompose or otherwise change in the presence of water. In a preferred embodiment, the prepreg has a share

Resin composition of 10-90 wt .-%, preferably 30-70 wt .-%, based on the total mass of the prepreg, on.

The water content of the reactive resin composition before the coating of the at least one fiber of the textile semifinished product is preferably 30-90% by weight, particularly preferably 40-60% by weight.

In particular, the composition has a viscosity suitable for the impregnation of the semi-finished textile product.

The prepreg is characterized in that the textile semifinished product is impregnated at least in regions with the reactive resin composition. The textile semifinished product or the fiber or a plurality of fibers may be impregnated only partially or completely with the reactive resin composition.

The prepreg according to the invention thus has the advantage that it is storage stable at room temperature, not sticky, flexible and easy to handle. Several prepregs can thus be rolled up without a separating film between the prepregs without sticking to one another. The resin composition of the prepreg is stable in storage at 20 ° C. for at least 3 months (reduction of the reaction enthalpy measured with DSC less than 20%, preferably less than 10%) and remains storable even with a moderate increase in temperature. The prepregs can be processed like thermoplastic semi-finished products, but after curing a thermosetting, fiber-reinforced material is produced. The crosslinking agent is preferably embedded in a solid matrix (dried reactive resin and / or at least one of the further components), optionally encased therein at least in regions, and forms a, preferably microscopic, separate phase.

Preferably, the at least one (dispersed at 25 ° C in water) reactive resin selected from the group consisting of epoxy resins, preferably di- or polyfunctional epoxy compounds, in particular oligomeric diglycidyl ethers, polyglycidyl ethers, epoxy compounds of bisphenol-A, bisphenol-B, bisphenol-F , Novolaks and resoles; benzoxazines; urethanes; Phenolic resins and mixtures and combinations thereof.

The reactive resins according to the invention carry reactive groups which are suitable for crosslinking chemically covalently with a crosslinking agent to form a thermoset.

Particularly preferred reactive resins are epoxy resins, in particular oligomeric diglycidyl ethers and polyglycidyl ethers of bisphenol A, bisphenol B, and bisphenol F, as well as novolak and resole.

The epoxy resins are preferably characterized by 200 to 4000 g / mol, preferably 300 to 2000 g / mol, particularly preferably 350 to 1000 g / mol of epoxide equivalents, determined according to DIN 16945 or ASTM D-1652.

The prepreg may be characterized in that the at least one reactive resin has a melting point of more than 25 ° C or more than 35 ° C, preferably more than 25 ° C to 100 ° C, in particular more than 35 ° C to 60 ° C. ,

The crosslinking agent contained in the reactive resin composition may be contained therein in solid, crystalline or liquid form. It is also possible to encapsulate the crosslinking agent and add it according to the reactive resin composition. Here, the crosslinking agent in the reactive resin composition is in a phase other than the reactive resin. With regard to the morphology after drying of the formulation on the textile semifinished product, there are several possibilities how the crosslinking agent can be present in the reactive resin composition. The crosslinking agent is preferably present as a solid solution in the solid, in particular particulate reactive resin. Likewise, there is the possibility that the surface of the reactive resin particles is at least partially wetted with the crosslinking agent or the crosslinking agent is also present in particulate form adjacent to the reactive resin particles and / or embedded in the reactive resin particles, and / or encapsulated, the capsules in addition to the reactive resin particles and / or may be embedded in the reactive resin particles.

In order to ensure a spatial separation of reactive resin and crosslinking agent after drying, which then leads to a particularly high storage stability of the prepreg, the drying process is conducted so that reactive resin and crosslinking agent do not form a homogeneous film, but the layer is still heterogeneous. Often this is recognized by a haze of the film which becomes clear as soon as it has been heated beyond the film-forming temperature.

With regard to morphology, the following possibilities in particular come into question:

1. The crosslinking agent is dissolved in the aqueous phase of the preparation and, after drying, forms again a solid which is present next to the resin domains,

2. The crosslinking agent is dispersed as a solid and is present as particles in addition to the particles of the resin dispersion

3. The cross-linking agent is encapsulated, this is done in each case in a separate step. As a special case, encapsulation in the particles of a dispersion (e.g., the flexibilizer or any non-crosslinking polymer reacting polymer) is also possible.

In particular, it is preferred if the crosslinking agent is included in the particles of a polymer dispersion, wherein the polymer forming the dispersion is not reactive with the crosslinking agent at 20 ° C. and the dispersion sion particles have a mean diameter of less than 5 μm, preferably less than 2 μm, and particularly preferably less than 500 nm determined by means of dynamic light scattering. According to a particularly preferred embodiment, they are located in front of the

Hardening of the prepreg, the crosslinking agent and the reactive resin in separate phases. As a result, the reactive dry prepreg has a high storage stability under ambient conditions. This leaves sufficient time for the processing of the prepreg until, in a further step, the cross-linking of the prepreg to the thermosetting fiber composite material takes place. Fast cure can be achieved e.g. by increasing the temperature of the prepreg.

Crosslinking agents used as preferred crosslinking agents are those which react with the reactive resin by polyaddition.

The at least one crosslinking agent may be stoichiometric with respect to the reactive resin or contained in an amount of ± 20 mol% relative to the amount of the reactive resin and may be selected from the group consisting of organic aliphatic or organic aromatic amines.

Carboxylic acids, phenols, dicyanamide, cyanamide and mixtures or combinations thereof.

Likewise, catalytically active crosslinking agents can be used. Consequently, the crosslinking agent may be present in catalytic amounts with respect to the reactive resin and be selected from the group consisting of imidazoles, uroks, photochemically or thermally activatable crosslinking agents, preferably, latent superacids and latent superbases, in particular organic sulfonium, iodonium and ammonium salts Hexafluoroantimonate or hexafluorophosphonium as counterions, or combinations thereof.

When the crosslinking agents cure the resins by a polyaddition reaction (eg, dicyanamide, cyanamide, amines, carboxylic acids, phenols), they are preferably added in an equimolar amount. Deviations thereof are in a conventional manner by application tests in the Determined for optimal curing. If the crosslinking agent acts catalytically, ie in particular imidazoles, latent superacids or latent superbases, the at least one crosslinking agent in the resin composition may contain from 0.1 to 5% by weight, preferably from 0.5 to 2% by weight, based on the total amount of the resin composition. Curing agents can also be combined, for example an approximately equimolar amount of dicyanamide based on the epoxide groups combined with a catalytically active amount of an imidazole, for example 1-methylimidazole.

A particularly high latency with high reactivity after activation is achieved by crosslinking agents which form a separate phase or are in a separate phase from the phase of the reactive resin. These include e.g. Dicyanamide and cyanamide, which are soluble in water and crystallize during drying of the aqueous reactive resin composition applied to the semi-finished textile product and thus do not mix with the reactive phase forming a separate phase.

The mixing of the components can then be carried out by increasing the temperature, preferably to a temperature at which all components are melted. When drying the impregnated prepreg is therefore to be noted that the drying temperature is chosen so low that the reactive resin composition is not filmed, but still has separate phases.

In a further preferred embodiment, the crosslinking agent is present in encapsulated form, preferably at least partially encapsulated in a polymer and / or a flexibilizer (for example a plastic polymer). Here, for example, a microencapsulation or Nanoverkapse- ment into consideration (ie capsules with a mean diameter in the range of <10 μιη, preferably <1 μιη). Due to this small dimensioning, a rapid mixing of the crosslinking agent from the nanocapsules with the reactive resin can take place during the thermal activation, which is associated with the possibility of an immediate reaction. Such nanoencapsulation can be achieved, for example, by dispersing the crosslinking agent and a polymer which does not react with the crosslinking agent in water, it being possible to add a surfactant as a dispersant. The polymer may, for example, be a polyurethane which may have a flexibilizing effect. Thus, the polymer used for the nanoencapsulation of the curing agent can act as a flexibilizer for the resin composition.

In the polymer (e.g., polyurethane), preferably before the preparation of the aqueous preparation, the crosslinking agent (e.g., imidazole, latent super acid, or latent superbase) may be dissolved or dispersed. The polymer dispersion thus prepared in water can then be mixed with the dispersion of a solid epoxy resin and other formulation ingredients. The incorporation of the crosslinking agent in the unreacted polymer-in-water dispersion is possible during or after the polymer is dispersed in water. However, subsequent incorporation requires that the crosslinking agent be soluble in the polymer, therefore mixing these components prior to dispersing the polymer in water is preferred. The result is in each case an aqueous dispersion comprising reactive resin and a crosslinking agent encapsulated in polymer and / or flexibilizer. A particularly preferred embodiment of this principle has already been described above or in claim 7. All conceivable crosslinking agents for the particular reactive resin used are suitable for the encapsulation, as long as they have a sufficiently low solubility in water. Accordingly, low molecular weight aliphatic amines are not suitable, but very well aromatic amines. The crosslinking agents latent superacids and superbases also have the

Advantage that they release the required for chemical curing species only by a thermal or photochemical activation, whereby a particularly high latency of the chemical curing and thus storage stability of the prepreg is achieved. In this case, the latency is thus not only by the physical distance (separate phases) or physical barrier (encapsulation), but also by the requirement of a chemical Activation extended without significantly reducing the reactivity during curing. In the event that latent superacids or superbases are used as the crosslinking agent, it is also not necessary for them to be in a separate phase in the dispersion or after drying on the prepreg, even for even higher latency even for this

Case is preferred.

The use of photoactivatable superacids as hardeners is a particularly preferred embodiment of the invention, since at room temperature (20 ° C to 25 ° C) very long stable semi-finished products can be prepared. These can then be irradiated shortly before processing to trigger chemical crosslinking. The crosslinking is then completed thermally during or after the molding of the prepreg into a component. The reactive aqueous resin composition necessary for providing the prepregs according to the invention and consequently also the prepreg produced therewith can have at least one surfactant which is preferably selected from the group consisting of alkanesulfonates, alkylbenzenesulfonates, fatty alcohol sulfonates, fatty alcohol polyglycol ethers, fatty alcohol ether sulfonates, fatty acid methyl ester sulfonates and quaternary Ammonium and phosphonium compounds.

The content of the surfactant in the preparation containing the reactive aqueous resin composition is preferably 0.05 to 10% by weight, more preferably 0.1 to 3% by weight, based on the total mass of the aqueous preparation.

The surfactant is advantageous because it improves the preparation of the aqueous preparation containing reactive resin and crosslinking agent and in particular ensures that a stable dispersion is formed in water. A stable dispersion is characterized in that water and dispersed portions between dispersion preparation and preparation of the prepregs do not separate macroscopically from each other. Normally neither the particle size nor the creaming or sedimentation of the dispersion constituents change over a period of at least 2 days. The typical dispersions can be processed without alteration for several weeks. The reactive resin composition may contain at least one flexibilizer, which is preferred

a) is selected from the group consisting of plastic polymers, preferably elastomers and thermoplastics, particularly preferably reactive and non-reactive rubbers, especially carboxy-terminated

Butadiene nitrile rubbers (CTBN), silicones, fluoroelastomers, polyurethanes optionally hydroxy-terminated, polyesters, polyethers, polyamides, polyolefins, hydroxy-terminated polyurethanes, polysulfones, polyoxymethylene and polyvinyl butyrals;

b) in particulate form, preferably in capsule form, is present;

c) has a number average molecular weight M _n of> 500 g / mol, preferably> 2000 g / mol;

d) does not chemically react with the reactive resin at a temperature of 20 ° C to 25 ° C;

e) is dispersible in water; and or

f) is contained in the resin composition to 0.1 to 40 wt .-%, preferably 5 to 20 wt .-%, based on the total amount of the reactive resin.

It is known that uncured reactive resins (e.g., epoxy resins) of high molecular mass are brittle at room temperature and peel off upon deformation. This is often perceived as detrimental and even annoying, since thus dosing errors can occur. A flexibilizer in reactive resin composition or in the prepreg enables continuous production and easy processing of the prepreg. By adding the flexibilizer, a deformation of the prepreg is possible without the brittle reactive resin flaking off the fiber.

The flexibilizer should be capable of forming a stable hybrid dispersion with the reactive resin and the crosslinking agent. After drying, no contact stickiness should result. In addition, the flexibilizer serves to reduce the brittleness of the finished cured dumbered polymer and thus results in higher strength and elasticity, which often referred to as Zähelastifizierung and is characterized by an increase in fracture energy.

When the flexibilizer is a crystallizable polymer, it is advantageous to use it in combination with the prior art

Technique for the respective polymer suitable nucleating agents. These prevent the formation of large crystallites and thus ensure a finely crystalline morphology. Thus, the crystallites are so small that the polymer can be dispersed in the water without sedimentation of the dispersion. In addition, it is known in the prior art that particularly high strength and elongation at break of the cured duromer result when the thermoplastic crystallizable flexibilizers are used in combination with nucleating agents (see DE 10 2012 221 677). Further, the prepreg may commonly contain fillers or additives known in the polymer art, such as carbon black, silica, alumina, aluminum powder, titanium dioxide, aluminum hydroxide, talc, accelerators, thermoplastics, core-shell rubbers, flame retardants, wetting agents, pigments, UV absorbers , Viscosity modifiers and / or antioxidants.

The prepreg may be characterized in that the textile semifinished product a) contains or consists of a mat, a woven fabric, a plurality of fibers, a yarn or a fleece;

b) at least one fiber selected from the group consisting of carbon fibers, glass fibers and natural fibers, and in particular cellulose fibers, hemp fibers, wood wool fibers, sisal fibers, jute fibers, coconut fibers, ramie fibers, bamboo fibers, bast fibers, cotton, wool, animal hair and fibers based on contains or consists of chitin, chitosan or their combination; and or

c) in the prepreg to 10 to 70 wt .-%, preferably 30 to 60 wt .-%, particularly preferably 35 to 55 wt .-%, based on the total weight of the prepreg is included. It is further preferred that the prepreg and / or the reactive resin composition is free of property-enhancing substances to increase the tackiness of the surface, as required by US Pat. No. 6,787,237. Furthermore, a method for producing the prepreg according to the invention is provided, comprising the following steps:

a) providing an aqueous preparation of a reactive resin composition, wherein the preparation contains a dispersion of at least one at 25 ° C solid reactive resin and at least one water-stable crosslinking agent (providing or preparation of this aqueous preparation can by dispersing at least one at 25 ° C solid Reactive resin in water and adding at least one water-stable crosslinking agent carried out);

b) at least partially wetting of at least part of the fibers of the semi-finished textile product with the aqueous preparation, and

c) drying of the textile semifinished product.

Water stability is understood to mean that the crosslinking agent does not react with water. Preferably, heating is carried out until the reactive resin melts to produce the aqueous preparation. To prepare the dispersion, it is preferred to stir vigorously and optionally to add a surfactant. The mixture is then cooled, resulting in an aqueous preparation containing in particular solid particles of the reactive resin.

If the melting point of the reactive resin is above the boiling point of water, the preparation can be prepared under pressure or the acetone method known in the art can be used by temporarily lowering the melting temperature of the resin by adding a suitable solvent.

The crosslinking agent can be present in physically blocked form (eg in the form of crystallites and / or in encapsulated form) and / or in chemically activatable form (eg photoactivatable form). Preferably, the crosslinking encapsulated in at least one flexibilizer and / or polymer.

In a preferred embodiment, the crosslinking agent is encapsulated before step a) or added in step a) an encapsulated crosslinking agent, preferably in a mean capsule diameter in the range <10 μιη, preferably <1 μιη.

In the process according to the invention, in step a) 1 to 80% by weight, preferably 2 to 70% by weight, particularly preferably 5 to 60% by weight, of reactive resin in water, based on the total amount of water, can be dispersed.

The steps a) to c) can be carried out continuously, it is preferred in step b)

a) the textile semi-finished continuously unwound from a roll;

b) the textile semi-finished product at least partially immersed in the preparation, optionally excess preparation removed via pulleys; and or

c) the preparation at least partially sprayed onto the semi-finished textile, transferred with rollers, geräkelt or applied with other known in the art application method on the textile semifinished product.

The aqueous preparation can be applied once or several times (for example by dipping, knife coating, roller transfer or spraying) onto the semifinished textile product in order to achieve higher polymer contents.

It is important that the proportion of the reactive resin formulation on the semi-finished textile product is so high that the component produced therefrom does not necessarily have pores, which is due to a too small proportion of the reactive resin formulation. In principle, one could work with a minimum proportion of reactive resin preparation and create preformed porous components with such semi-finished textile products, in which the pores are subsequently filled with a liquid reactive resin known in the art. Due to the further manufacturing step, this procedure would be disadvantageous. In a preferred embodiment, the drying in step c) is carried out with dry air, preferably with flowing dry air with overpressure or underpressure. In particular, the drying can be carried out to a residual moisture content of the textile mat of <2%. A strong drying is advantageous because larger amounts of water can adversely affect the quality of the fiber composite plastic, in particular can lead to bubbles in the thermal curing.

In a preferred embodiment, the drying in step c) does not cause the polymer dispersion to be filmed, so that in the dried layer the particles from the preparation did not run into each other, i. are arranged as separate domains on the textile semifinished product. In this way, reactive resin and crosslinking agent are further kept separate from each other. This leads to a long shelf life and because it is very small domains for rapid mixing after the prepreg is heated during subsequent curing to a temperature above the glass transition temperature or melting temperature of all components. This rapid mixing is in turn a prerequisite for rapid curing. The filming can be avoided by keeping the temperature during drying below the film-forming temperature, which is specific for the particular reactive resin composition.

Preferably, in step b), the application of the uncured resin composition in the form of the aqueous preparation on the textile semifinished product at a temperature <60 ° C, preferably room temperature (T = 20 ° C to 25 ° C) performed. If too high a temperature is used, the uncured resin composition may prematurely mix and thereby prematurely crosslink, which has a negative effect on storage stability.

The prepregs can be rolled up after step c) (the drying) without additional use of release liners, stored at room temperature, unrolled if necessary at a later date without prior thawing and / or cut to the desired geometry. The draping of individual mats of the prepreg or the construction of an impregnated yarn can be carried out by techniques known per se. In a preferred embodiment, the individual layers of the prepreg according to the invention are not sticky and can slip against each other. If this is unfavorable for the specific component, it can be locally heated (eg with hot air) in order to achieve a bonding of the now melted materials at this point. In this way, dimensionally stable fabrics are obtained which are fed to the subsequent shaping and hardening processes.

One or more layers of prepreg can be added to the fiber-reinforced plastic in a hot press or in an autoclave. For this purpose, the prepregs may be placed in a mold or formed into an already three-dimensional component. Especially in heating presses can be produced by deep drawing or pressing into a shape three-dimensional parts. This is from deep drawing of

Sheet metal known, but also of fiber composites with thermoplastic polymers.

By means of the formulations and processes according to the invention it is now also possible to use these processes for the production of thermosetting fiber composites. Processing is the same as for thermoplastics, however, resulting in components that include a thermoset resin as a matrix resin. The dry prepregs according to the invention now permit the production of duromer fiber composite materials with high-volume processes.

The molds are usually equipped with mold release agents according to the prior art. This is time consuming and leads to contamination, which must be removed for subsequent processes again. The components are therefore particularly preferably produced with polymeric release films according to the prior art. These are known as FlexPlas films and described in DE 10 2012 207 149 AI and WO 2013/160437 AI. This further simplifies a large-scale production, since the handling of liquid release agents and a cleaning of the components omitted. At the same time, the release film forms a contamination protection and needs to be removed shortly before further processing. The invention further provides a fiber composite material which can be produced by treating at least one prepreg according to the invention with heat, preferably at temperatures of 60 ° C. to 200 ° C., preferably 90 ° C. to 200 ° C., particularly preferably 100 ° C. to 150 ° C. , and optionally additionally pressure and / or irradiation, preferably with UV radiation.

Thus, according to the invention is also a process for the preparation of the fiber composite material described above, in which the aforementioned procedure is carried out.

In the process of making the fiber composite, it is indispensable to treat the prepreg with heat, i. elevated temperatures of at least 60 ° C. Optionally, a pressurization can take place, in particular in order to press the prepreg into the desired shape of the fiber composite material. The curing of the reactive resin composition can optionally be accelerated by irradiation before or during the shaping and curing process, in particular with UV light.

By carrying out this process, it is ensured that the reactive resin composition melts, and the reactive resin and the crosslinker contained therein are intimately mixed and reacted. The reactive resin and the crosslinking agent thus crosslink to form a thermoset or thermosets. The fibers of the fiber composite material are embedded in these thermosets.

The curing time used may be less than 5 hours, preferably less than 2 hours, and more preferably less than 1 hour. Here, the curing of the reactive resin composition, which is located on the textile semi-finished, to a dumber polymer. According to the invention, a prepreg is thus provided whose polymer matrix has the properties of a typical thermoplastic, wherein the thermoplastic can subsequently harden to a duromer in or after a shaping process.

After crosslinking of the prepreg to the fiber composite material, the resulting thermoset is, if at least one flexibilizer as further grain component was added, tough and has a sufficiently high strength for the application. This can be adjusted in addition to the type and amount of fibers by the choice of the reactive resin, crosslinking agent and the curing conditions. Typical tensile strengths of the fiber-reinforced plastics produced with the inventive prepregs are more than 20 MPa.

In addition, the use of the prepreg according to the invention for the production of components for vehicle construction, aircraft, the construction industry, the window industry, the furniture industry, the electrical industry, sports equipment, toys, mechanical and apparatus engineering, the packaging industry, agriculture or the safety technology proposed.

Reference to the following example, the subject invention is to be explained in more detail, without wishing to limit this to the specific embodiments shown here.

Example 1. Preparation of a hybrid dispersion according to the invention

To 100 parts of epoxy resin dispersion (EPI-REZ Resin 3522, Momentive, solids content 60%, particle size 1.1-3.4 μιη, data sheet information) were depending on the recipe structure varying proportions of the polyurethane dispersion (Dispercoll U42, Bayer, solids content 50%, particle size 300 nm , Data sheet data) / polyvinyl butyraldispersion (butvar) were added and mixed for 5 minutes at room temperature in a planetary mixer at a constant speed of 3200 rpm.

Dicyandiamide (Alzchem) was dissolved in 20 parts of distilled water at about 60 ° C within 5 min also at a speed of 3200 U / min in the planetary mixer.

The additionally used curing accelerator (2-MAOK-PW, Shikoku) was subsequently stirred into the warm dicyandiamide solution. The final mixing of the individual components was carried out by mixing the epoxy resin-polyurethane (polyvinyl butyral) mixture and crosslinker / accelerator mixture also in the planetary mixer for five minutes.

Table 1

2. Preparation of prepregs according to the invention

From the dispersions mentioned above, prepregs can be prepared using the carbon fiber fabric Hexforce G0926D in 50 cm x 50 cm

150 cm is cut. After cutting, check the correct geometry of the fabric with an angle of 90 ° and correct if necessary. Subsequently, the cut edges of the fabric are fixed with adhesive tape against the slipping of the fibers. The carbon fiber fabric was placed on Teflon release film and then each a dispersion of point 1 with a hand roller or a wooden spatula evenly apply without exerting pressure on the fiber applied.

After 60 minutes of drying at room temperature (25 ° C), the fabric was turned over and the process repeated to achieve complete wetting (impregnation). From the prepregs were 10 cm x 10 cm rectangles with 0 ° / 90 ° and

+ 45% 45 ° orientation cut out. Thereafter, with the prepregs, an anisotropic, 8-ply laminate with orientations 0 ° / 90 °, ± 45 °, 0 ° / 90 °, ± 45 °, ± 45 °, 0 ° / 90 °, ± 45 °, 0 ° / 90 ° and provided with Flexplas separating film at the top and bottom. The laminate can then be fully cured by means of a hot press for 10 minutes at 150 ° C and a force of 30 kN.

3. Properties of the prepregs

The prepregs were then stored for two days at room temperature. The DSC thermogram shows the glass transition temperatures of Epirez 3522, Dispercoll U42 and the melting temperature of dicyandiamide.

Even after three months of storage at room temperature, there is no change in the glass transition temperatures and reaction enthalpies of the starting materials in the uncured mixture (i.e., in the prepreg). Even after three months of storage at room temperature after curing, no significant changes in the properties of the duromer are observed.

The addition of the flexibilizer, the Dispercoll U42 polyurethane dispersion, lowers the glass transition temperature Tg of the carbon fiber fabric coating, while increasing the flexibility of the prepreg (Table 2). The glass transition temperature is well above 25 ° C for all three dried dispersions, which provides a good prerequisite for a tack-free surface.

-: low, +: high; ++: very high

Claims

claims

Prepreg, that

a) at least one semifinished textile product which contains or consists of at least one fiber selected from the group consisting of carbon fibers, glass fibers and natural fibers;

b) at least one at least partially uncured reactive resin composition comprising at least one solid at 25 ° C reactive resin and at least one water-stable crosslinking agent, wherein the resin composition wets the fiber at least partially

Prepreg according to claim 1, characterized in that

i) the aqueous preparation of the reactive resin composition contains at least one aqueous dispersion of the 25 ° C solid reactive resin and the water-stable crosslinking agent;

and or

ii) the at least partially wetting comprises or consists of the step of applying the reactive resin composition in the form of an aqueous preparation at least partially to the at least one semi-finished textile product, in particular to the entire surface of the at least one semi-finished textile product; and or iii) the at least partial drying comprises or consists of, preferably complete, evaporation of water, the prepreg having a non-tacky surface at 25 ° C. and / or the glass transition temperature of the uncured reactive resin composition is> 25 ° C., especially after evaporation of the water.

3. Prepreg according to one of claims 1 or 2, characterized in that the at least one at 25 ° C solid dispersed in water reactive resin is selected from the group consisting of epoxy resins, preferably di- or polyfunctional epoxy compounds, in particular oligomeric diglycidyl ethers, polyglycidyl ethers, epoxy compounds bisphenol A, bisphenol B, bisphenol F, novolacs and resoles; benzoxazines; urethanes; Phenolic resins and mixtures and combinations thereof.

4. Prepreg according to the preceding claim, characterized in that the epoxy resin 200 to 4000 g / mol, preferably 300 to 2000 g / mol, more preferably 350 to 1000 g / mol epoxide equivalents, determined according to DIN 16945 or ASTM D-1652.

5. Prepreg according to one of the preceding claims, characterized in that the at least one reactive resin has a melting point of more than 25 ° C or more than 35 ° C, preferably more than 25 ° C to 100 ° C, in particular 35 ° C to 60 ° C, has.

6. Prepreg according to one of the preceding claims, characterized in that the water-stable crosslinking agent is present in solid, crystalline or liquid form and / or encapsulated.

7. Prepreg according to one of the preceding claims, characterized in that the reactive resin is particulate and the crosslinking agent

is contained as a solid solution in the particulate reactive resin,

at least partially wetting the surface of the reactive resin particles, present in particulate form next to the reactive resin particles and / or embedded in the reactive resin particles, and / or

is encapsulated, the capsules being present next to the reactive resin particles and / or embedded in the reactive resin particles.

8. Prepreg according to one of the preceding claims, characterized in that the crosslinking agent in the particles of a

Polymer dispersion is included, characterized in that the dispersion-forming polymer at 20 ° C is not reactive with the crosslinking agent and the dispersion particles have a determined by dynamic light scattering average diameter of less than 5 μιη, preferably less than 2 μιη and more preferably less than 500 nm.

9. Prepreg according to one of the preceding claims, characterized in that the at least one crosslinking agent a) is stoichiometric with respect to the reactive resin or in an amount of ± 20 mol .-% relative to the amount of reactive resin and is selected from the group consisting of organic aliphatic or organic aromatic amines, carboxylic acids, phenols, dicyanamide, cyanamide and mixtures or combinations thereof and / or;

b) is contained in catalytic amounts with respect to the reactive resin and is selected from the group consisting of imidazoles, uroks, photochemically or thermally activatable crosslinking agents, preferably, latent superacids and latent suberbases, in particular organic sulfonium, iodonium and ammonium salts with hexafluoroantimonate or Hexafluorophosphonium as counterions, or combinations thereof.

10. Prepreg according to the preceding claim, characterized in that the crosslinking agent is contained in catalytic amount with respect to the reactive resin and a weight proportion of 0.1 to 5 wt .-%, preferably 0.5 to 2 wt .-%, in particular about 1 wt%, based on the total amount of the resin composition. A prepreg according to any one of the preceding claims, characterized in that at least one flexibilizer is included in the resin composition, with the flexibilizer being preferred

a) is selected from the group consisting of plastic polymers, preferably elastomers and thermoplastics, especially before given to reactive and non-reactive rubbers, especially carboxy-terminated butadiene nitrile rubbers (CTBN), silicones, Flu orelastomere, polyurethanes, which are optionally hydroxy-terminated, polyesters, polyethers, polyamides, Polyolefins, hydroxy-terminated polyurethanes, polysulfones, polyoxymethylene and

polyvinylbutyrals;

b) in particulate form, preferably in capsule form, is present;

e) is dispersible in water; and or

Prepreg according to one of the preceding claims, characterized in that the semi-finished textile product

a) contains or consists of a mat, a woven fabric, a plurality of fibers, a yarn or a fleece; and or

b) in the prepreg to 10 to 70 wt .-%, preferably 30 to 60 wt .-%, particularly preferably 35 to 55 wt .-%, based on the Gesamtmas se of the prepreg, is included.

13. A method for producing the prepreg according to one of the preceding claims, comprising the steps a) providing an aqueous preparation of a reactive resin composition, wherein the preparation contains a dispersion of at least one at 25 ° C solid reactive resin and at least one water-stable crosslinking agent;

b) wetting at least some of the fibers of the semi-finished textile product with the aqueous preparation, and c) drying the textile semifinished product.

A method according to the preceding claim, characterized in that in step a) at least one surfactant, at least one water-dispersible flexibilizer, at least one nucleating agent and / or at least one water-soluble or

dispersible additive is added or is already contained in the aqueous preparation.

Method according to one of the two preceding claims, characterized in that in step a) 1 to 80 wt .-%, preferably 2 to 70 wt .-%, particularly preferably 5 to 60 wt .-%, of reactive resin in water, based on the Total amount of water is dispersed.

Method according to one of claims 13 to 15, characterized in that the steps a) to c) are carried out continuously, and in particular in step b)

the textile semi-finished product is unwound continuously from a roll; the textile semifinished product is at least partially immersed in the aqueous preparation, optionally excess preparation is removed via deflection rollers; and or

the preparation is at least partially sprayed onto the textile semifinished product or applied by means of roller or doctor blade application.

A method according to any one of claims 13 to 16, characterized in that the drying in step c) is carried out according to claim 13 with dry air, preferably with flowing dry air with over or under pressure, in particular the drying up to a Nem residual moisture content of the textile mat of <2% is performed.

18. fiber composite material, producible by treatment of a prepreg according to one of claims 1 to 12 with heat. 19. Use of the prepreg according to one of claims 1 to 12 for the production of components for vehicle construction, aircraft construction, construction industry, window construction, furniture industry, sports equipment, toys, mechanical and apparatus engineering, packaging industry, agriculture or the safety technology.