CN111098527A

CN111098527A - System for producing fully impregnated thermoplastic prepregs

Info

Publication number: CN111098527A
Application number: CN201811257152.4A
Authority: CN
Inventors: 张明福; 克里斯托弗·桑多瓦尔; 贾维德·阿斯拉尔
Original assignee: Johns Manville
Current assignee: Johns Manville
Priority date: 2018-10-26
Filing date: 2018-10-26
Publication date: 2020-05-05

Abstract

The present invention relates to a system for producing fully impregnated thermoplastic prepregs. In particular, the present invention relates to a thermoplastic prepreg comprising a web or web of fibres, wherein the web or web of fibres comprises chopped fibres. The thermoplastic prepreg further comprises a thermoplastic material that fully impregnates the web or mesh such that the thermoplastic prepreg has a void volume of less than 5%. The thermoplastic material is a polymer formed by in situ polymerization of a monomer or oligomer, wherein more than 90% of the monomer or oligomer reacts to form the thermoplastic material. The thermoplastic prepreg comprises between 5 and 95 wt% of the thermoplastic material and the chopped fibres forming the web or web are non-bonded.

Description

System for producing fully impregnated thermoplastic prepregs

Background

Fiber reinforced composites are increasingly being used in transportation, consumer products, wind energy and infrastructure. There are many reasons to choose composite materials rather than traditional materials such as metal, wood or unreinforced plastics, including light weight, corrosion resistance and increased mechanical strength. In the field of fiber reinforced polymeric composites, thermoplastic resins are increasingly being used as matrix resins instead of thermosetting resins due to better durability, recyclability, thermoformability, increased throughput, lower material costs and lower manufacturing costs.

Many continuous fiber reinforced thermoplastic composites are produced from impregnated tapes. These impregnated tapes may be unidirectional fibre tapes impregnated with a thermoplastic resin. They can be layered and thermoformed to produce a wide variety of different composite materials having the desired shape and strength. The production of impregnated tapes at low cost and high quality is accompanied by significant challenges. Traditionally, thermoplastic resins are melted and applied to the fibers, but the melted thermoplastic resin has a very high viscosity and, when combined with the high fiber content required, results in incomplete resin impregnation and/or low throughput. What is needed is a continuous manufacturing process with high throughput that produces fully impregnated thermoplastic prepregs without defects and good coupling between the fibers and the matrix resin. For conventional partially impregnated thermoplastic prepregs, high pressures are required in the consolidation step to promote additional impregnation, which introduces excessive resin matrix flow and causes undesirable changes in the fibre orientation in the final part. The fully impregnated thermoplastic prepreg of the present invention is advantageous in achieving the desired properties in the final composite part because no additional impregnation is required in the consolidation step.

Disclosure of Invention

Embodiments described herein provide fully impregnated thermoplastic prepreg products, particularly systems and methods for making them. According to one aspect, there is provided a system for manufacturing thermoplastic prepregs, the system comprising a double belt arrangement comprising an upper belt and a lower belt. The upper belt is placed on top of the lower belt to compress the web of fibers passing through the double belt arrangement. The lower belt has a longitudinal length substantially longer than the upper belt. The system also includes a drying device positioned atop the lower belt and configured to remove residual moisture from the web as the web moves through the drying device. The system also includes a resin application mold positioned atop the lower belt and configured to apply a monomer or oligomer to the fiber web as the fiber web moves through the resin application mold. The monomer or oligomer may be polymerized to form a thermoplastic polymer. The system additionally includes a curing oven configured to perform polymerization of the monomer or oligomer and thereby form the thermoplastic polymer as the fiber web moves through the curing oven. The fiber web includes chopped fibers and the double belt apparatus is configured to compress the fiber web and the applied monomer or oligomer as the fiber web passes through the curing oven such that the monomer or oligomer fully saturates the fiber web and the fiber web is fully impregnated with the thermoplastic polymer after polymerization of the monomer or oligomer.

According to another aspect, there is provided a method of forming a thermoplastic prepreg, the method comprising moving a fibrous web atop a lower belt of a double belt press device and drying the fibrous web via a drying device positioned atop the lower belt to remove residual moisture from the fibrous web. The method further includes applying a monomer or oligomer to the fiber web through a resin application die placed atop the lower belt and passing the fiber web and the applied monomer or oligomer between the lower belt and the upper belt of the dual belt press device to force the monomer or oligomer through the fiber web and thereby fully saturate the fiber web with the monomer or oligomer. The method also includes passing the fully saturated fiber web through a curing oven configured to polymerize the monomer or oligomer as the fiber web moves through the curing oven and thereby form the thermoplastic polymer. The fiber web comprises chopped fibers and, after polymerization of the monomer or oligomer, the fiber web is fully impregnated with the thermoplastic polymer.

According to yet another aspect, there is provided a thermoplastic prepreg comprising a fibrous web or web and a thermoplastic material fully impregnating the fibrous web or web. The fiber web or wire mesh comprises chopped fibers having a fiber length and a fiber diameter. The chopped fibers are non-bonded such that the web or mesh is not mechanically bonded and contains no binder other than the thermoplastic material that bonds the chopped fibers together. The thermoplastic prepreg has a void content (void content) of less than 5% and comprises between 5 and 95 wt% of the thermoplastic material. The thermoplastic material comprises or consists of a polymer formed by in situ polymerisation of a monomer or oligomer, wherein more than 90 wt% of the monomer or oligomer reacts to form the thermoplastic material.

Drawings

The techniques of the present invention are described in conjunction with the appended drawings, in which:

fig. 1A and 1B illustrate a system that can be used to produce prepregs that are fully impregnated with thermoplastic polymers.

Figure 2 illustrates a method of forming a fully impregnated thermoplastic prepreg product.

Figure 3 shows another method of forming a fully impregnated thermoplastic prepreg product.

Figure 4 shows an SEM micrograph of a cross section of a fully impregnated polyamide-6 prepreg.

Fig. 5-8 illustrate a system that can be used to produce prepregs that are fully impregnated with thermoplastic polymers.

Fig. 8A shows a system in which the fiber chopper is replaced with a fiber spreading device.

Fig. 8B illustrates a system including a winding device that winds fully cured chopped fiber thermoplastic prepreg into a rolled product.

Fig. 9-13 show an exemplary prepreg that is fully impregnated with a thermoplastic polymer.

Figure 14 shows another method of forming a fully impregnated thermoplastic prepreg product.

In the drawings, similar components and/or features may have the same numerical designation label. Moreover, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components and/or features. If only the first numerical designation label is used in this specification, the description applies to any of the similar components and/or features having that same first numerical designation label, regardless of the letter suffix.

Detailed Description

Embodiments described herein relate to fully impregnated thermoplastic prepreg products, and in particular systems and methods for making them. The prepreg product is fully impregnated with a thermoplastic material which allows the prepreg product to be reheated and moulded into a given shape. The prepreg products are manufactured using reactive resin materials, particularly monomers and oligomers. For example, in exemplary embodiments, the resin material is caprolactam which is extremely sensitive to moisture, wherein even small amounts of moisture can affect anionic polymerization of the caprolactam. Due to the high moisture sensitivity of these materials, it is very difficult to achieve high conversion of the reactive resin material to polymer.

In order to obtain a commercially viable prepreg product using monomeric or oligomeric materials (hereinafter resins, reactive resins or resinous materials), the conversion of the reactive resin to polymer needs to be higher than 90 wt%, more typically higher than 95 wt%. One skilled in the art will recognize that the conversion of the reactive resin to polymer can be readily determined. For example, the residual monomer or oligomer content in the prepreg can be measured by a solvent extraction method described below. In particular, when caprolactam is used as the reactive resin, the amount of residual caprolactam in the prepreg can be measured by extracting caprolactam from ground polyamide-6 (PA-6) prepreg powder using hot water. On the basis of the residual monomer or oligomer content, the conversion of the reactive resin can be deduced. High molecular weights of the thermoplastic polymers are also generally desirable. In a preferred embodiment, the resin material comprises caprolactam. The caprolactam-containing reactive resin material is extremely sensitive to moisture. The presence of moisture can stop or interfere with the anionic polymerization of caprolactam to polyamide-6 polymer. For example, moisture levels above 200ppm in the resin can significantly interfere with the polymerization process and reduce the conversion of the caprolactam material to below 90 wt.%. The terms "substantially moisture-free" or "substantially zero" when referring to humidity, should be recognized that a certain level or amount of humidity may be present in the air. However, as used herein, the term implies that any humidity present in the air is negligible, minimal, insignificant, or insignificant. For example, a "substantially moisture-free" environment may be created using a moisture removal device that may operate to maintain a relative humidity in the environment of less than 1% at a temperature range of 5-35 ℃.

The systems and methods described herein may be used to manufacture prepreg products using reactive resin materials. The resin conversion obtained by the systems and methods described herein is greater than 90 wt%, more typically greater than 95 wt%. In most embodiments, the resin has a conversion of greater than 98 wt% or even greater than 99 wt%. As described herein, the thermoplastic polymer in the prepreg product is formed by in situ polymerization, which is not a common technique in the manufacture of thermoplastic prepreg products. Moreover, the systems and methods described herein enable such high conversion rates to be achieved using a continuous process, wherein the fabric or felt material (woven or non-woven) is moved essentially constantly or continuously throughout the manufacturing process. The continuous process greatly increases the efficiency of the manufacturing process, which reduces the overall cost of the final prepreg product. For example, the manufacturing time between application of the reactive resin (e.g., caprolactam) and formation of a fully impregnated thermoplastic prepreg may be less than 20 minutes, typically less than 10 minutes. In many embodiments, the processing time may be less than 5 minutes.

The systems and methods described herein also enable sufficient and complete impregnation of the prepreg with the thermoplastic polymer. It should be appreciated that in the description and/or claims, the term "reactive resin" may be used instead of the term monomer and/or monomer or oligomer, if desired. The viscosity of the reactive resin when applied to the fabric or felt is less than 500mPa-s, typically less than 100mPa-s, more typically less than 10 mPa-s. The low viscosity of the reactive resin allows the resin to flow within the fabric or mat and fully saturate a single layer of the fabric or mat or multiple layers of these materials. Thus, the systems and methods described herein are capable of producing prepregs comprising a plurality of material layers, wherein each layer is fully saturated or impregnated with the thermoplastic polymer material. The final prepreg product can be made flexible with a high content of reinforcing fibres. Since the prepreg product is flexible, the prepreg can be wound into a roll product. In other embodiments, the prepregs may be cut into individual sheets of any desired length or width.

Embodiments described herein provide a method and apparatus that utilizes mixing of a reactive resin component that is then applied to a fabric or mat that may be formed from a variety of different fibrous materials described herein. The reactive resin component is then cured in an oven to form a fully impregnated prepreg with a thermoplastic polymer matrix. In a particular embodiment, caprolactam is polymerized to form polyamide-6 in the final prepreg. The system is designed to isolate the reactive resin component from atmospheric moisture in order to achieve high conversion from monomer to polymer. In particular, the system is designed to ensure a substantially moisture-free environment around the reactive resin-coated fabric or felt (woven or non-woven). The systems and methods described herein are designed to isolate the reactive component from atmospheric moisture in order to achieve high conversion from monomer to polymer. This is accomplished in part by controlling the environment surrounding the manufacturing process and/or by removing residual moisture from the fabric or mat (woven or non-woven) and/or any portion of the processing system.

As used herein, reactive resin means a resinous material comprising monomers or oligomers capable of polymerization to form a thermoplastic polymer. The reactive resin may include lactams such as caprolactam and laurolactam as well as lactones. In an exemplary embodiment, the reactive resin comprises caprolactam. In certain embodiments, mixtures of monomers and/or oligomers may be used. For example, a mixture of caprolactam and laurolactam may be used, which will be copolymerized in the curing oven to form a copolymer with tailored properties. As used herein, an activator can be any material that activates and accelerates the polymerization of a monomer or oligomer. Exemplary activators for anionic polymerization of caprolactam include blocked isocyanates and N-acyl caprolactams. As used herein, a catalyst may be any material that catalyzes the polymerization of a monomer or oligomer. Exemplary catalysts for anionic polymerization of caprolactam include alkali metal salts of caprolactam such as sodium caprolactam.

Various terms are used herein to describe fiber-based products. For example, the term "fabric" is used in this application to describe a fiber-based woven product. The present application includes the following terms to describe fiber-based nonwoven products: felts, nets, wire meshes, and the like. It should be understood that these terms are used interchangeably in the embodiments. Unless specifically stated, the present disclosure is not limited to any particular fiber-based product. Thus, it is contemplated that the terms may be substituted or altered in any of the described embodiments without departing from the intended scope of the description. Furthermore, the terms "fiber mat, web or fabric" or "fiber-based product" may be substituted in the description or claims and are intended to cover any and all fiber-based products or components described or contemplated herein.

A common type of fiber used in the fabric or mat is glass fiber, although a variety of different other fibers may be used, such as carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers such as aramid fibers, and other inorganic fibers. As used herein, the term fabric or felt refers to a woven or non-woven material. The woven material is a material produced by weaving a plurality of roving bundles together. As used herein, the term roving refers to a bundle of fibers that are placed adjacent to one another to form a rope, string, or cord-like component. The roving bundles are typically woven such that a plurality of first fiber bundles extend in a first direction (e.g., the weft direction) and a plurality of second fiber bundles extend in a second direction (e.g., the warp direction) that is typically orthogonal to the first direction. The first plurality of fiber bundles are roughly parallel to each other, as are the second plurality of fiber bundles. The woven fabric or cloth may be unidirectional, in which all or most of the roving bundles run or extend in the same direction, or bidirectional, in which the roving bundles run in two generally orthogonal directions. Various different weaving methods may be used to form the fabrics or felts described herein, including: plain weave, twill weave, satin weave, multi-axial weave, or stitching. The woven cloth or fabric used may comprise any kind of woven fabric or multiaxial fibrous material. The fabric or mat may also contain chopped fibers in addition to or in place of continuous fibers. The fabric or felt may be a mixture of fibers from different types. For ease of describing the embodiments herein, embodiments generally refer to the use of glass fibers, although it should be recognized that various other fiber types may also be used.

As used herein, the term felt refers to a nonwoven material. As briefly described above, a non-woven fiber mat is used in addition to or in place of the woven reinforcing fabric. The nonwoven fiber mats are typically formed of fibers that are mechanically entangled, woven together, or chemically bonded, rather than woven in a uniform direction. The nonwoven fiber mats exhibit more uniform strength characteristics than the woven reinforcement fabric. In other words, the strength of the nonwoven fiber mat is generally less direction dependent. In contrast, the strength of the woven reinforcing fabric is direction dependent, whereby the fabric or cloth exhibits substantially higher strength in the direction aligned with the fibers and lower strength in the direction not aligned with the fibers. The reinforcing fabric or cloth is substantially stronger than the nonwoven mat when stretched in alignment with the fibers. For ease of describing the embodiments herein, the embodiments generally refer to fabrics or felts, which are intended to apply to both woven fabrics or cloths and non-woven fiber felts.

The fibers used in the fabric or felt may be treated with a sizing composition that includes a coupling agent that promotes adhesion between the reinforcing fibers and the polymeric resin. For example, the fibers may be sized with one or more coupling agents that covalently bond the thermoplastic resin to the fibers. Exemplary coupling agents may include coupling-activator compounds having a silicon-containing moiety and an activator moiety. Specific examples of coupling-activator compounds include 2-oxo-N- (3- (triethoxysilyl) propyl) azepane-1-carboxamide. Exemplary coupling agents may also include blocked isocyanate coupling compounds having a silicon-containing moiety and a blocked isocyanate moiety. Exemplary coupling agents may also include coupling compounds having functional groups that can react with the reactive resin to form covalent bonds. Specific examples of the coupling compound having a functional group include silane coupling agents having an amino, epoxy or ureido functional group.

The term thermoplastic polymer or material refers to a polymer that can be melted and molded or formed multiple times into a variety of different shapes. Thus, the fully impregnated thermoplastic prepreg may be placed in a mould and reshaped or remoulded into a variety of different desired shapes. Examples of polymeric materials or resins that may be used in embodiments herein include polyamides, and specifically include polyamide-6.

The description and/or claims herein may use relative terms in describing features or aspects of the embodiments. For example, the description and/or claims may use terms such as relative, about, substantially, between … …, about, and the like. These relative terms are intended to account for deviations that may occur in the practice and/or production of the embodiments described herein. For example, the specification describes the mixture from two holding tanks as being mixed into a "substantially homogeneous mixture". The present disclosure also describes purging the fabric or mat with a "substantially moisture-free gas" and "substantially constant movement" of the fabric or mat between a starting point and an ending point. The term "substantially" is used in these descriptions to describe small deviations or differences from a completely homogeneous mixture or a completely moisture-free gas or a completely constant movement. For example, one skilled in the art will recognize that the moisture-free gas may contain some negligible amount of moisture, and that there may be some negligible amount of non-uniformity within the homogeneous mixture. The skilled artisan will also recognize that some negligible stalling or movement of the fabric or mat may occur without departing from the spirit of the present disclosure. These deviations or differences may be as high as about 10%, but are typically less than 5% or even 1%. Similar rationale applies to any other relative term used herein.

In producing conventional thermoplastic prepregs, the process of fully impregnating or saturating the fabric or mat is rather expensive and/or difficult due to the high melt viscosity of the thermoplastic resin. In some cases, a solvent is added to the polymer resin/thermoplastic material to reduce the viscosity of the material. Although the reduced viscosity may assist in fully impregnating the reinforcement fabric, it is then necessary to remove the solvent from the fabric after the polymer resin/thermoplastic material is impregnated into the fabric. The removal of the solvent typically involves heating the fabric to evaporate the solvent, which adds cost and environmental concerns. In contrast to these systems, no solvent is used in the reactive resins described herein.

Other conventional techniques use pre-impregnated thermoplastic tapes of polymer resins and reinforcing fibers. These tapes are typically made as a single layer by applying a molten polymer resin on top of a flat roving. For example, glass rovings may be passed over a roller to flatten and stretch the fibers, which are then coated with a molten polymer resin. The tape is then cooled, causing the glass fibers to be encased within a hardened polymeric resin material. The tape can then be used for the production of other products, in particular by stacking and welding together several layers of tape. The process of stretching the fibers for resin impregnation is generally limited to rovings; because it is almost impossible to stretch the fibers in the fabric or felt. Furthermore, the stacked ribbons are typically rigid, which makes it difficult to mold complex shapes.

In contrast to conventional prepregs, the production of the thermoplastic prepregs described herein is fast and simple. For example, it is relatively easy to fully saturate the fabric or mat because the reactive resin material (e.g., caprolactam) has a low viscosity that is comparable to water. This low viscosity allows the resin material to flow easily within the fabric or mat and fully saturate the single or multiple layers of the fabric or mat. The capillary force of the rovings or fibers further helps to saturate the fabric or mat. The low viscosity of these materials also allows the materials to be applied to a constant or continuously moving sheet of material. The resin may then be converted to a thermoplastic polymer material such that the fabric or mat is fully impregnated by the thermoplastic material.

Although the embodiments described herein refer generally to the manufacture of polyamide-6 prepregs, other reactive resin systems may be readily adapted to work with the same or similar equipment to form thermoplastic prepregs comprising blends of thermoplastic polymers, such as blends of polyamides and polyesters, and other types of polyamides.

Having generally described several aspects of the embodiments, further aspects will become apparent by reference to the description of the several figures provided below.

System for controlling a power supply

Referring now to fig. 1A and 1B, a system that can be used to produce prepregs that are fully impregnated with thermoplastic polymers is shown. The system of fig. 1A and 1B is capable of producing the fully impregnated thermoplastic prepreg in a continuous process in which a fabric or mat 4 is continuously or constantly moved through the system. In other words, the term continuous process means that the process is not interrupted or paused in performing any of the process steps. Rather, each step in the process is performed continuously or constantly. For example, the fabric or mat is continuously moved from a roll stock, coated with a resin material, cured in an oven, and wound into a final product. In contrast, conventional systems are typically stopped or interrupted during one or more steps, such as during impregnation of the fibrous substrate with the high melt viscosity thermoplastic polymer resin.

In certain embodiments, the system comprises two vessels or silos (i.e., 1 and 2). The holding

tanks

1 and 2 may be heated and purged with nitrogen to ensure that any moisture that might otherwise reduce the reactivity of the raw materials and thus the conversion of the resin to polymer is removed. One of the holding tanks (e.g., holding tank 1) may contain a mixture of the resin and catalyst. In certain embodiments, the holding tank (e.g., tank 1) comprises caprolactam and a catalyst, such as sodium caprolactam or any other catalyst. Another holding tank (e.g., tank 2) may contain a mixture of the resin and activator. In a particular embodiment, the other holding tank (e.g., tank 2) comprises caprolactam and an activator such as N, N' -hexane-1, 6-diylbis (hexahydro-2-oxo-1H-azepin-1-carboxamide) or any other activator. The

sumps

1 and 2 are heated to a temperature that allows the reactants to melt. In certain embodiments, the temperature may be between about 70 and 120 ℃. The molten reactants (e.g., the resin and activator or catalyst) have a very low viscosity, e.g., less than 10 mPa-s.

The reactants from the two

storage tanks

1 and 2 are metered into a static mixer or mixing head 3, which ensures the correct ratio of resin, activator and catalyst. In one embodiment, the mixture from the two

storage tanks

1 and 2 can be provided to the static mixer at a ratio of 1/1. The mixtures from the two

storage tanks

1 and 2 are thoroughly mixed in a static mixer 3 to form a substantially homogeneous mixture.

In certain other embodiments, the system comprises a single or multiple containers or reservoirs. Each of the containers or reservoirs may contain a separate component or mixture of the reactive resin material. Each of the vessels or reservoirs is heated to a temperature that allows the reactants to melt.

A fabric or felt 4 is unrolled or otherwise provided to the system. The system may include a device that unrolls the fabric or mat and moves the fabric or mat through the system and along or around various different processes. In certain embodiments, the device may include a motorized drum or calender (calender) and/or a conveyor system that moves the fabric or mat through the system.

In certain embodiments, the activating agent is contained on the surface of the fiber. The fabric or mat may be comprised of glass fibers that have been pretreated with a sizing composition. For example, the sizing composition may include a coupling activator that covalently bonds a polymerization activator moiety to the glass fiber. In these cases, the adhesion between the thermoplastic polymer and the fibers may be significantly strengthened or enhanced. When the fabric or felt contains the activator, only a single holding tank (e.g., tank 1) containing the resin and catalyst may be used, or a reduced amount of the activator may be mixed with the resin in the second holding tank (e.g., tank 2). In certain embodiments, two

reservoirs

1 and 2 can be used, and each reservoir can contain a different resin material. For example, first holding tank 1 may contain caprolactam, while second holding tank 2 contains laurolactam. In these cases, a combination of two or more types of reactive monomers and/or oligomers may be applied to the fabric or mat.

In particular embodiments, the fiber sizing composition contains a mixture of silane coupling agents, polymeric film forming agents, and other additives designed to enhance the interfacial adhesion between the glass fibers and the polyamide-6 matrix. In particular, reactive silanes are used which allow some polymerization to start directly from the glass surface, thereby enhancing the coupling between the reinforcing fibers and the resin matrix to improve composite properties.

After or during the fabric or mat 4 is spread, the fabric or mat may be subjected to a drying device that removes residual moisture from one or more surfaces of the fabric or mat. For example, an infrared heater 5 may be used to raise the temperature of the fabric or mat and thereby remove any residual moisture. In certain embodiments, an infrared heater 5 may be placed on top of or over the fabric or felt 4 to remove residual moisture. In certain embodiments, a second heater may be placed on the opposite side (e.g., bottom side) of the fabric or felt 4 to further aid in the removal of residual moisture. In other embodiments, a pre-drying oven may be used instead of or in addition to the infrared heater 5. Preheating of the fabric or mat 4 and/or preheating of the resin may be used to prevent the monomer/oligomer from curing immediately upon contact with the fibers of the fabric or mat, which may ensure good wetting of the resin at higher line speeds.

The resin mixture is then applied to the fabric or felt 4 using a resin application die 6 or other resin application device. The resin application mold 6 may be a slit-type mold. The slot die 6 may be placed on top of or near one or more surfaces of the fabric or felt 4. The resin mixture is typically applied as close as possible to the entrance of the curing oven 8 in order to minimize exposure of the resin material to ambient air. To minimize exposure to ambient air, the slot die 6 may be placed directly near the entrance to the curing oven 8. In certain embodiments, the slots of the slot die 6 may have an opening of about 1.0mm or less, which enables the use of very thin dies. The thin mold allows the distal end of the mold to be placed substantially close to the curing oven 8 to minimize exposure of the resin mixture to the ambient environment. In certain embodiments, the distal end of the slot die 6 may be placed within 1.0 inch, preferably within 0.5 inch, of the entrance of the curing oven. The slit die 6 may be temperature-controlled within a temperature range higher than the melting point of the reactive resin. For a reactive resin comprising caprolactam, the temperature range may be between 70 ℃ and 120 ℃. The slot die 6 may contain thermocouples and heating cartridges or other heating means to ensure that the slot die 6 is maintained within the desired temperature range.

Although the embodiments herein utilize a slot die 6 to apply the resin mixture to the fabric or mat 4, the low viscosity of these systems allows for a wide range of application techniques including, but not limited to, spray application, curtain coating, dip extrusion coating, kiss roll application, doctor blade application, or even powder coating of pre-ground solid resins, where the curing oven may also be used to melt the reactive components.

The liquid operating lines between the two

sumps

1 and 2 and the static mixer 3 and/or between the mixer 3 and the slot die 6 are typically insulated to minimize heat loss as the resin mixture flows through the operating lines. In certain embodiments, the liquid operating line is heated in addition to being insulated to ensure that the liquid materials (e.g., resin, catalyst, and activator) are maintained within a constant temperature range. Specifically, the liquid transport lines between the sumps 1 and 2 (or separate sumps) and the mixer 3 and/or between the mixer 3 and the slot die 6 are insulated and heated to maintain the liquid material within a temperature range above the melting point of the reactive resin. Controlling the temperature of the liquid material ensures that the resin does not cure and/or prematurely react within the operating line.

In the above process, the temperature of the resin is generally maintained within a temperature range above the melting point of the reactive resin in order to maintain the resin in a liquid or molten state while preventing premature polymerization of the resin before the material is cured in an oven. The resin component may need to be recycled, for example, between one or more of the holding

tanks

1 and 2 and the mixer 3. Ensuring that the resin is maintained within the desired temperature range is important to minimize or eliminate premature resin polymerization and/or material accumulation in the system and/or liquid handling lines.

It is also important to control the ambient environment around the coated fabric or mat 4 to ensure that the resin mixture is not exposed to ambient moisture. Exposure of the resin mixture to ambient moisture may reduce the conversion of the resin, which may result in a resin to polymer conversion of less than 90%. The system of fig. 1A and 1B is designed to isolate the resin mixture (i.e., the reactive components) from atmospheric moisture in order to obtain high conversion from monomer/oligomer to polymer. In certain embodiments, the entire system may be placed or enclosed in a room or area where the environment is controlled to maintain a substantially moisture-free environment. Various different dehumidification techniques may be used to remove moisture from the ambient air in a room or area. Exemplary dehumidification techniques include desiccant dehumidification, refrigeration dehumidification, and electrostatic dehumidification. In other embodiments, the system may use a moisture removal device operable to ensure that the humidity in the air surrounding the coated fabric or mat is substantially zero. In these embodiments, the moisture removal means need only be used around the slot die 6, as the fabric or felt 4 is free of the resin material before this point. The moisture removal device may be placed proximal to the slot die 6 or distal to the slot die 6 as desired. In either case, however, the moisture purging device should be placed relatively close to the slot die 6 to minimize exposure of the resin mixture to ambient air. For example, the system may be enclosed in an area that is purged with a substantially moisture-free gas.

In a particular embodiment, the moisture removal means comprises an air/gas header or pipe 7 of fig. 1A that blows a moisture free gas onto one or more surfaces of the coated fabric or mat 4. The air/gas headers or tubes 7 may be placed on top of the fabric or felt 4 or may be placed on the opposite side of the fabric or felt as desired. In particular embodiments, an air/gas header or tube 7 blows dry nitrogen gas over or on top of either or both the top or bottom surfaces of the fabric or mat 4. Air/gas headers or tubes 7 ensure that the area or perimeter around or near the coated fabric or mat 4 and/or near the entrance to the curing oven remains substantially free of moisture. Minimizing the exposure of the resin material to moisture is critical to ensure high conversion of the resin material. The use of drying means (e.g. infrared heaters 5) and/or moisture removal means (e.g. air/gas headers) is therefore important to ensure correct manufacture of the prepreg. In another particular embodiment, the resin application device and the coated fabric or mat may be enclosed in a tank 7 purged with substantially moisture-free gas as shown in fig. 1B.

After the fabric or mat 4 is coated and/or saturated with the resin and/or a sweep gas is applied to one or more surfaces of the coated fabric or mat 4, the resin impregnated fabric or mat 4 is then passed through a curing oven 8. The temperature of the curing oven 8 is maintained to ensure that the polymerization of the resin to the thermoplastic polymer is complete. In other words, the curing oven 8 is maintained at a polymerization temperature at which the monomers and/or oligomers begin to polymerize. For reactive resin compositions comprising caprolactam, the polymerization temperature may be about 120 ℃ or higher (e.g., about 120 ℃ to about 220 ℃). For a prepreg manufacturing process in which the polymerized resin matrix is not melted, the upper polymerization temperature limit of the monomer and/or oligomer may be the melting temperature of the polymer. For example, a reactive resin composition comprising caprolactam may have an upper polymerization temperature limit equal to the melting temperature of the PA-6 polymer (i.e., -220 ℃). The coated fabric or mat 4 may be exposed to a curing oven 8 for a time sufficient to ensure complete polymerization of the resin material. For example, for a reactive resin composition comprising caprolactam, the residence time of the coated fabric or mat in the curing oven may be about 3 minutes to ensure complete polymerization of the caprolactam.

As mentioned above, when the reactive resin composition is a combination of two or more types of reactive monomers and/or oligomers, the heating temperature of the resin-fiber mixture may be selected to be above the threshold polymerization temperature of one type of monomer/oligomer, but below the threshold polymerization temperature of another type of monomer/oligomer. For example, a reactive resin composition comprising both caprolactam and CBT may be heated to 120-170 ℃ which may polymerize the caprolactam to PA-6 without significantly polymerizing the CBT to polybutylene terephthalate (PBT). The resulting fiber-resin mixture combines a polymeric resin matrix comprising PA-6 with a polymerizable resin of CBT. The fiber-resin mixture can be processed into a reactive prepreg comprising a polymerized resin matrix of PA-6 and polymerizable CBT. The reactive prepreg may be incorporated into a fiber reinforced article, wherein processing conditions may include polymerizing the CBT into PBT. In other embodiments, mixtures of monomers and/or oligomers may be used. For example, a mixture of caprolactam and laurolactam may be used, which will be copolymerized in the curing oven to form a copolymer with tailored properties.

In certain embodiments, the coated fabric or mat 4 is subjected to a press arrangement that facilitates complete wetting of the reinforcing fibers by the resin. In one embodiment, the press device may include one or more calenders that press or squeeze the resin through the fabric or mat 4. In another embodiment, the curing oven 8 may be a dual belt compression oven, wherein the pressure on the belt is adjustable to promote complete wetting of the reinforcing fibers by the resin. Exposure of the coated fabric or mat to ambient moisture can be minimized by using an oil or electrically heated double belt press.

After leaving the curing oven 8, the fully cured prepreg 9 may be collected. In certain embodiments, the system comprises a winding device configured for winding the fully cured prepreg 9. In other embodiments, the fully cured prepreg may be cut into sheets that may be stacked on top of each other.

The system of fig. 1A and 1B is designed to enable the above process to be performed in 20 minutes or less, more typically 10 minutes or less. In certain embodiments, the process can be performed in 5 minutes or less. In particular, the length of time from when the fabric or mat 4 begins to unwind to when the prepreg exits the curing oven 8 may be 20 minutes or less, 10 minutes or less, or in some embodiments 5 minutes or less. Such speed and impregnation efficiency are not achievable by conventional systems using polymeric resin materials. Furthermore, when using a plurality of stacked layers of fabric or felt 4, the speed and efficiency are not severely affected. In contrast, the low viscosity resin mixture is able to readily penetrate and saturate the plurality of stacked layers of fabric or mat 4 such that the processing time of the stacked layers of fabric or mat is still short. Due to the low viscosity of the resin material, a complete impregnation of the layers of the stacked fabric or felt 4 may be achieved.

Thermoplastic prepregs, sometimes referred to as organic sheets, offer some superior properties compared to thermoset prepregs, such as impact resistance, thermoformability, and recyclability. However, conventional thermoplastic prepregs have anisotropic mechanical properties due to the orientation of the fibre orientation in the fabric, which presents significant challenges in designing composite parts to replace existing isotropic materials such as steel and aluminium. In addition, fabric-based thermoplastic prepregs may have limited conformability, which may increase the difficulty of forming composite parts with complex geometries.

As described herein, in certain embodiments, the thermoplastic prepregs may be formed from chopped strands or fibers (hereinafter referred to as chopped fibers). In particular, the fibrous material in the prepreg may comprise or consist of chopped fibres. The use of chopped fibers in thermoplastic prepregs may result in prepregs with more isotropic mechanical properties and improved conformability while maintaining high strength and impact resistance. These thermoplastic prepregs may be formed in a continuous manufacturing process which may include: (1) cutting the roving in-line into long fibers or bundles that are uniformly distributed on a moving belt to form a non-bonded chopped strand mat; (2) impregnating the chopped fibers or strand mat with a reactive resin such as molten caprolactam; (3) pressing the coated chopped fibers or strand mat to fully saturate the mat with the reactive resin (e.g., caprolactam); and (4) polymerizing the reactive resin in situ in an oven to form the chopped fiber or strand thermoplastic prepreg. In order to ensure complete polymerization of the reactive resin, in particular caprolactam, the fibers or rovings may be dried in-line prior to chopping and the chopped fibers or strand mat may be further dried prior to impregnation with the reactive resin (e.g. caprolactam). The system is also generally configured for maintaining a moisture free environment about the reactive resin coated chopped strand or strand mat prior to subjecting the reactive resin coated chopped strand or strand mat to the curing oven. Maintaining a moisture free environment substantially prevents exposure of the reactive resin, particularly caprolactam, to moisture.

The term chopped fibers refers to fibers cut from a continuous roving or tow. The chopped fibres may have a length of from 10mm to 100mm, preferably from 25mm to 50 mm. The fibers used herein may be selected from, but are not limited to, the following types of fibers: glass fibers, carbon fibers, basalt fibers, polymer fibers (including aramid fibers), natural fibers (including cellulose fibers), and other inorganic fibers. The fibers may be treated with a coupling agent that may improve the interfacial adhesion between the fibers and the thermoplastic resin matrix.

The chopped fibers are typically formed into a chopped fiber or strand mat that is a web or web of unbonded chopped fiber segments. The term non-bonded implies that the web or net of chopped fibers is not mechanically or chemically coupled or bonded together or coupled together by some other means. Nonwoven mats, on the other hand, typically comprise fibers randomly stacked on one another and bonded or coupled together using an applied binder or adhesive. In other embodiments, mechanical coupling may be used instead of chemical coupling. Mechanical coupling of the fibers may be achieved by mechanical needling, wherein needles or rods are inserted into the web to facilitate or perform entanglement of the fibers. In some cases, the nonwoven mat may include both chemical and mechanical coupling of the fibers. Woven fabrics are mechanically coupled together by weaving the fiber rovings or tows together.

In contrast to these conventional nonwoven mats, in the present application, the web or web of chopped fibers is non-bonded such that the individual chopped fibers are not chemically or mechanically bonded — i.e., no adhesive or glue is used, nor mechanical bonding techniques such as mechanical needling are used. Rather, the chopped fibers are merely stacked on top of each other with minimal physical engagement. The result is that the web or mesh of chopped fibers can be easily separated or pulled apart, such as by applying a gas over the web or mesh, prior to adding the reactive resin. It should be appreciated that a very low degree of physical entanglement or engagement may be encountered due to the random orientation of the chopped fibers in the web or screen, but typically the chopped fibers remain uncoupled or unbonded to one another such that the web or screen has very low structural integrity prior to application of the reactive resin and subsequent polymerization to form the thermoplastic polymer.

After the reactive resin is added to the chopped fiber web or mesh, the thermoplastic polymer resulting from the in situ polymerization of the reactive resin may serve to bind or adhere the chopped fibers together. Thus, the thermoplastic polymer acts as a tacky matrix that bonds or adheres the chopped fibers together. In certain embodiments, the chopped strand web or mesh may be used with a fabric or nonwoven mat such as those described herein. In these embodiments, the chopped strand web or mesh may be placed on one or both sides of the fabric or mat. Due to the very low viscosity of the reactive resins commonly used (e.g. caprolactam), a complete impregnation of the chopped fibre web or wire mesh is easily achieved in a short time, which ensures a high volume manufacturing process. Thus, the process described herein has significant advantages in both production efficiency and composite properties compared to conventional polymer melt impregnation processes that use high viscosity polymer resin melts to impregnate reinforcing fibers.

Although the description herein generally refers to the use of a non-bonded web or mesh of chopped fibers, it should be recognized that in some instances it may be desirable to couple the chopped fibers together by chemical means, mechanical means, or some other means. The reactive resin may then be added to the coupled or adhered chopped fiber web or mesh. To simplify the description of the various embodiments, the chopped strand web or mesh is commonly referred to as a chopped strand web or mesh or more simply as a fiber web or mesh. This general description of chopped strand webs or screens is meant to describe both unbonded or unbonded chopped strand webs or screens and bonded or bonded chopped strand webs or screens. The use of the term in the claims is also meant to cover both the non-bonded/non-adherent chopped strand web or screen and the bonded or adherent chopped strand web or screen, unless the claims specifically recite one of these webs or screens. Thus, if desired, the general description of chopped strand webs or meshes in the specification and/or claims may be replaced with more specific descriptions of non-bonded or non-bonded chopped strand webs or meshes or bonded chopped strand webs or meshes.

The resulting chopped strand thermoplastic prepreg contains randomly oriented chopped fibers and has primarily isotropic mechanical properties. Due to the excellent conformability of the chopped fibers, the chopped fiber thermoplastic prepregs described herein are capable of forming complex shaped composite parts with deep shrinkage cavities and large curvatures through high throughput processes such as compression molding. Other aspects and features of the chopped strand thermoplastic prepregs may be appreciated from the description of the various embodiments provided below.

Referring now to fig. 5, a system that may be used to produce thermoplastic prepregs comprising chopped fiber webs or webs is shown. As described herein, the resulting thermoplastic prepreg is fully impregnated with the thermoplastic polymer. The system of fig. 5 is capable of producing the fully impregnated thermoplastic prepreg in a continuous process in which the chopped fiber web or wire mesh is continuously or constantly moving through the system.

As shown in fig. 5, the system may include two vessels or reservoirs (i.e., 21 and 22). At least one of the holding tanks functions as a storage and delivery tank for the reactive resin, which is typically a monomer or oligomer that can be polymerized into a thermoplastic polymer. In certain embodiments, the monomer or oligomer may include or consist of a lactam, a lactone, Cyclic Butylene Terephthalate (CBT), methyl methacrylate, a precursor of a thermoplastic polyurethane, or a mixture thereof. The lactam may comprise or consist of caprolactam, laurolactam or mixtures thereof. The holding

tanks

21 and 22 may be heated and purged with nitrogen to ensure that any moisture that might otherwise reduce the reactivity of the raw materials and thus the conversion of the resin to polymer is removed. As previously described, one of the reservoirs (e.g., reservoir 21) may contain a mixture of resin and catalyst. In particular embodiments, the holding tank (e.g., tank 21) can contain caprolactam and a catalyst such as sodium caprolactam or any other catalyst. Another holding tank (e.g., tank 22) may contain a mixture of the resin and activator. In particular embodiments, the other holding tank (e.g., tank 22) comprises caprolactam and an activator such as N, N' -hexane-1, 6-diylbis (hexahydro-2-oxo-1H-azepin-1-carboxamide) or any other activator. The holding

tanks

21 and 22 may be heated to a temperature that allows the reactants to melt, for example between about 70 and 120 ℃ for a reactive resin comprising caprolactam. The molten reactants (e.g., the resin and activator or catalyst) have a very low viscosity, e.g., less than 10 mPa-s. The viscosity of the molten reactants can be measured according to test method ISO3104: 1999. As an example, molten caprolactam has a viscosity of 8.5mPa-s at a temperature of 80 ℃ when measured using ISO3104: 1999.

The reactants from the two holding

tanks

21 and 22 are typically metered into a static mixer or mixing head 25 which ensures that the correct ratio of the monomer and/or oligomer, activator and catalyst is delivered to the chopped fiber web or wire mesh. In one embodiment, the mixture from the two

hoppers

21 and 22 may be provided to the static mixer at a ratio of 1/1. The mixture from the two

storage tanks

21 and 22 is thoroughly mixed in a static mixer 25 to a substantially homogeneous mixture. The static mixer 25 may be heated to a temperature that allows the reactants to remain in a liquid non-polymerized state, for example a temperature between about 70 and 120 ℃ for a reactive resin comprising caprolactam.

The system also includes a double belt arrangement comprising an upper belt 32 and a lower belt 31. An upper belt 32 is placed on top of the lower belt 31 and the two belts are configured to press or squeeze the web of fibers through the double belt arrangement. At least a portion of the double belt assembly is placed within a curing oven 30. In certain embodiments, the upper belt 32 is completely enclosed within the curing oven 30. The lower belt 31 has a longitudinal length substantially longer than the upper belt 32 such that at least a portion of the lower belt 31 extends outwardly from the curing oven 30. As shown, the lower belt 31 may extend outwardly from the front edge of the curing oven 30 by an elongation L₁Said length L₁Typically between 2 and 15 feet, more typically between 3 and 10 feet. In a particular embodiment, the extension L of the lower belt 31₁Between 6 and 9 feet, and more specifically about 8 feet.

The lower belt 31 typically extends outwardly from the upper belt 32 and/or curing oven 30 so that one or more components of the system can be placed atop the lower belt 31. For example, the fiber chopper 27 is placed above the lower belt 31. The fiber chopper 27 is configured for cutting the fiber bundles or rovings 26 into chopped fiber bundles C, which form the chopped fiber web or wire mesh. The fiber chopper 27 is placed above the lower belt 31 so that when the fiber bundles or rovings 26 are cut into individual chopped fiber bundles C, the chopped fiber bundles C fall on top of the lower belt 31 and form the web or wire. The fiber bundles or rovings 26 may be provided by one or more spools 23a-c, which spools 23a-c may be placed on a creel (creel). The bundles or rovings provided by each bobbin 23a-c may be similar in fiber type or size, or may be different from the bundles or rovings provided by another bobbin. Thus, the chopped fiber web or mesh may be formed from the same type of fiber bundles or rovings 26, or may be formed from a variety of different fiber bundles or rovings. For example, the chopped fiber web or mesh may include a combination of different sized fibers and/or a combination of different types of fibers. In some cases, two or more different types of fiber bundles or rovings, including but not limited to glass, carbon, and aramid fibers, may be simultaneously cut by fiber chopper 27 to form a hybrid fiber web or mesh.

In certain embodiments, the fibers of the fiber bundles or rovings 26 may include a sizing composition having a coupling agent that promotes adhesion between the chopped fibers and the thermoplastic polymer. For example, the sizing composition may include a coupling activator that covalently bonds a polymerization activator moiety to the chopped fibers. In these cases, the bond between the thermoplastic polymer and the chopped fibers may be significantly strengthened or enhanced. In certain embodiments, the fiber sizing composition contains a mixture of silane coupling agents, polymeric film forming agents, and other additives designed to enhance interfacial adhesion between the chopped fibers and the polyamide-6 matrix. In particular, reactive silanes may be used which allow some polymerization to start directly from the chopped fiber surface, thereby enhancing the coupling between the reinforcing fibers and the resin matrix to improve composite properties.

In other cases, the activating agent may be included on the surface of the fibers of the fiber bundles or rovings 26 such that the chopped fiber web or screen includes the activating agent. In these cases, only a single holding tank (e.g., tank 21) containing the resin and catalyst may be used in the system, or a reduced amount of the activator may be mixed with the resin in a second holding tank (e.g., tank 22). In certain embodiments, the two

reservoirs

21 and 22 can each contain a different resin material. For example, first holding tank 21 may contain caprolactam, while second holding tank 22 contains laurolactam. In these cases, a combination of two or more types of reactive monomers and/or oligomers may be applied to the chopped fiber web or wire mesh.

The system may include a drying device 24 configured to dry the fiber tows or rovings 26 as the fiber tows or rovings 26 are unwound from the respective spools 23a-c and prior to cutting the fiber tows or rovings 26 by a fiber chopper 27. The drying device 24 may be a tubular heater through which the fiber bundles or rovings 26 are drawn. The system may include a single tube heater through which all of the fiber bundles or rovings 26 are drawn; or the system may include tube heaters through which each fiber strand or roving is independently drawn as it is unwound from the respective spool 23 a-c. The use of the drying device 24 reduces or eliminates residual moisture that may be present on the fiber bundles or rovings 26. The drying device 24 may have a drying temperature between 100 ℃ and 200 ℃, more typically between 100 ℃ and 150 ℃.

The fiber chopper 27 cuts the fiber bundles or rovings 26 into individual chopped fiber bundles C which fall on top of the underlying belt 31 and form the chopped fiber web or wire mesh. The individual chopped fiber bundles C are randomly oriented or aligned atop the lower belt 31 and form a web or web having a thickness and/or density that is dependent upon the speed of the lower belt 31, the chopping speed of the fiber chopper 27, the number and/or size of the fiber bundles or rovings 26, and the like. The chopped fiber web or mesh typically does not undergo chemical or mechanical bonding, and thus the chopped fiber web or mesh is typically non-bonded or non-adherent. In particular, prior to application of the reactive resin, the chopped fiber web or mesh generally does not contain a binder that binds or adheres the fiber mesh together, and the chopped fiber web or mesh generally does not undergo a mechanical entanglement process such as mechanical needling.

An underlying belt 31 carries or transports the chopped fiber web or wire mesh to other components of the system and/or to the entrance of a curing oven 30. The chopped fiber web or wire mesh may be subjected to a drying device 28, which removes residual moisture from the chopped fiber web or wire mesh. The drying device 28 may be placed on top of the lower belt 31 such that it is above the chopped fiber web or wire mesh. The drying device 28 dries the chopped fiber web or wire mesh as it moves under the drying device 28. The drying device 28 may be an infrared heater that raises the chopped fiber web or wire meshTemperature, thereby removing any residual extraneous moisture. Extension length L of lower belt 31₁One of the reasons for this is to ensure that the chopped fiber web or wire mesh can be sufficiently dried prior to application of the reactive resin and that the chopped fiber web or wire mesh can pass through each component of the system. The drying device 28 may remove traces of surface moisture from the chopped fiber web or wire mesh.

After the chopped fiber web or screen is dried by the drying device 28, the reactive resin is applied to the chopped fiber web or screen using a resin application device 33, the resin application device 33 being placed atop the underlying belt 31 and above or adjacent to the chopped fiber web or screen. The resin application device 33 applies a reactive resin R, typically a monomer and/or oligomer of a thermoplastic material, to the chopped strand web or screen as the chopped strand web or screen moves past and typically passes beneath the resin application device 33. In certain embodiments, the resin application device 33 is a slot die having a narrow opening, e.g., an opening of about 1.0mm or less, through which the reactive resin R flows. The reactive resin R is delivered from the static mixer 25 to the resin application device 33 via line 29, which line 29 may be heated to maintain the temperature of the reactive resin.

The reactive resin R may be applied to the chopped fiber web or wire mesh in the vicinity of the curing oven 30 in order to minimize exposure of the reactive resin to ambient air and the environment. In certain embodiments, the resin application device 33 may be placed within 10 inches of the curing oven inlet, more typically within 5.0 inches or even 1.0 inches of the curing oven inlet. In other embodiments, the distal or delivery end of the resin application device 33 may be placed within the hood or cover of the curing oven 30, as shown in FIG. 5. The resin application means 33 may be temperature controlled within a desired temperature range, for example a temperature between 70 ℃ and 120 ℃ for a reactive resin comprising caprolactam. The resin applicator 33 may include a thermocouple and a heating cartridge or other heating means to ensure that the resin applicator 33 remains within a desired temperature range.

As an alternative to the slot die, the resin application device 33 may also comprise spray application, curtain coating, dip and squeeze coating, wet roll application, blade application or even powder coating of a solid resin that has been previously ground, wherein the curing oven melts the reactive component.

As previously described, the liquid handling line 29 between the accumulator, static mixer and resin application die is typically insulated and/or heated to minimize heat loss as the resin mixture flows through the handling line. Controlling the temperature of the liquid material ensures that the resin R does not cure and/or prematurely react within the process line. The temperature of the reactive resin is also typically maintained within a desired temperature range in order to maintain the reactive resin in a liquid or molten state while preventing premature polymerization of the resin before the material is cured in an oven. Likewise, after the chopped fiber web or wire mesh is coated with the reactive resin R, the ambient environment surrounding the coated chopped fiber web or wire mesh is typically controlled to ensure that the reactive resin is not exposed to the ambient moisture in the environment. Exposure of the reactive resin R to ambient moisture may reduce the conversion of the reactive resin, which may result in a degree of polymerization of less than 90%.

As previously described, the ambient environment may be controlled by placing or enclosing the system in a room or area in which the environment is maintained substantially free of moisture. Various dehumidification techniques may also be used to remove moisture from the ambient air in the room or area. Exemplary dehumidification techniques include desiccant dehumidification, refrigeration dehumidification, and electrostatic dehumidification. More typically, the system utilizes a moisture removal device operable to ensure that the humidity in the air surrounding the coated chopped strand web or wire mesh is substantially zero. For example, the system may utilize a moisture removal device operable to maintain a relative humidity in the air surrounding the coated chopped strand web or wire mesh of less than 1%. Typically, the moisture scavenging device need only be used around the periphery of the resin application device 33, as the chopped fiber web or wire mesh is free of reactive resin R prior to the resin application device 33. The moisture removal device may be positioned proximal to the resin application device 33 or distal to the resin application device 33 as desired. In either case, however, the moisture removal device should be placed relatively close to the resin application device 33 to minimize exposure of the reactive resin to ambient air.

As shown in fig. 5, the moisture removal device includes an air/gas header or tube 34 that blows a moisture free gas G onto the chopped fiber web or wire mesh. An air/gas header or tube 34 is placed atop the lower belt 31 and atop the chopped fiber web or wire mesh. The air/gas header or tube 34 may be placed directly adjacent to the resin application device 33 as shown in fig. 5 so that the moisture-free gas G is blown directly onto the chopped fiber web or screen as the chopped fiber web or screen is coated with the reactive resin R from the resin application device 33. In certain embodiments, an air/gas header or tube 34 blows dry nitrogen gas onto the chopped fiber web or wire mesh. An air/gas header or tube 34 ensures that the area or perimeter around or near the coated chopped fiber web or screen and/or near the entrance to the curing oven remains substantially free of moisture.

After coating the chopped fiber web or screen with a reactive resin R and/or applying the purge gas G to the coated chopped fiber web or screen, the coated chopped fiber web or screen is then subjected to a press arrangement that promotes complete wetting of the chopped fibers by the reactive resin. The function of the press is normally performed by an upper belt 32 and a lower belt 31, which form a double belt compression device. As shown in FIG. 5, the distal end of the upper belt 32 may be positioned L from the proximal end of the curing oven entrance₂At a distance that ensures sufficient space for the distal end of the resin application device 33 and the air/gas header or tube 34 to be placed within the curing oven 30 between the upper belt 32 and the curing oven entrance. Distance L₂And may be between 0.2 and 2.0 feet, and more typically between 0.5 and 1.0 feet. When the fibre or silk net is throughWhile passing through the curing oven 30, the coated chopped fiber web or mesh is compacted by an upper belt 32 and a lower belt 31. The compaction of the coated chopped fiber web or mesh facilitates the reactive resin (e.g., monomer and/or oligomer) to fully saturate the chopped fiber web or mesh. Fully saturating the chopped fiber web or wire mesh means that the reactive resin fully impregnates each chopped fiber bundle of the mesh or wire mesh. The compression of the coated chopped strand web or screen between the upper belt 32 and the lower belt 31 also minimizes exposure of the coated chopped strand web or screen to ambient moisture in the surrounding environment. In certain embodiments, the pressing function may be accomplished by one or more calenders or rolls that press or squeeze the reactive resin through the chopped fiber web or wire mesh.

Lower and

upper belts

31 and 32 pass the coated chopped fiber web or screen through a curing oven 30. The temperature of the curing oven 30 is maintained at a temperature that ensures complete polymerization of the reactive resin. In other words, the curing oven 30 is maintained at a polymerization temperature at which the monomers and/or oligomers begin to polymerize, typically about 100 ℃ or greater. For reactive resin compositions comprising caprolactam, the polymerization temperature may be about 120 ℃ or higher (e.g., about 120 ℃ to about 220 ℃). For a prepreg manufacturing process in which the polymerised resin matrix is not melted, the upper polymerisation temperature limit of the monomer and/or oligomer may be the melting temperature of the polymer. For example, a reactive resin composition comprising caprolactam may have an upper polymerization temperature limit equal to the melting temperature of the polyamide-6 (i.e., -220 ℃). The coated chopped fiber web or screen may be exposed to a curing oven 30 for a time sufficient to ensure complete polymerization of the reactive resin material. For example, for a reactive resin composition comprising caprolactam, the residence time of the coated web or screen in the curing oven may be about 3 minutes to ensure complete polymerization of the caprolactam. After polymerization of the reactive resin, the chopped fiber web or wire mesh is fully impregnated with the thermoplastic polymer. As used herein, the description that the chopped fiber web or wire mesh is fully impregnated with a thermoplastic polymer means that the thermoplastic polymer impregnates the chopped fiber web or wire mesh to an extent such that the chopped fiber web or wire mesh has a composite void volume of less than 5 volume percent based on the total volume of the thermoplastic prepreg, more typically less than 3 volume percent based on the total volume of the thermoplastic prepreg. In certain embodiments, the chopped fiber web or wire mesh may have a composite void volume of less than 1 volume percent based on the total volume of the thermoplastic prepreg. The void content of the resulting prepreg can be measured according to test method ASTM D2734-16.

In certain instances, the system may be configured to ensure that the viscosity of the reactive resin remains low before the chopped fiber web or wire mesh is fully impregnated with the reactive resin R. In particular, the polymerization of the reactive resin R may be controlled to ensure that the chopped fiber web or wire mesh is fully saturated with the resin prior to polymerization of the resin.

In certain embodiments, the distal end of the oven or housing 30 contains a cooling device 35, the cooling device 35 configured to cool the fully solidified chopped fiber thermoplastic prepregs 36. The cooling device 35 may cool the chopped strand thermoplastic prepregs 36 to allow the chopped strand thermoplastic prepregs 36 to be cut into shape, to be handled individually, to reduce or prevent warping of the chopped strand thermoplastic prepregs 36, or for any other reason. The cooling device 35 typically cools the chopped strand thermoplastic prepregs 36 to less than 50 ℃, more typically to at or near ambient temperature, which allows the chopped strand thermoplastic prepregs 36 to be handled by an individual without burning or damaging the individual. The cooling means 35 may comprise cold water cooling. After exiting the curing oven 30, a fully cured chopped fiber thermoplastic prepreg 36 is formed or produced. The system may include a cutting device 38, the cutting device 38 configured to cut the fully cured chopped fiber thermoplastic prepregs 36 into sheets that may be stacked on top of one another. In other embodiments, the system may include a winding device configured to wind the fully cured chopped fiber thermoplastic prepreg into a rolled product.

The system of fig. 5 is designed such that the process is performed in 20 minutes or less, more typically 10 minutes or less. In certain embodiments, the process can be performed in 5 minutes or less. When multiple layers of fibrous material are used, such as in the systems of fig. 6-8, the speed and efficiency of the system is not severely affected. In contrast, the low viscosity reactive resin is able to readily penetrate and saturate the plurality of layers of fibrous material such that the overall processing time remains short and relatively unaffected. Due to the low viscosity of the resin material, a complete impregnation of the stacked layers may also be achieved.

Although the lower belt 31 is shown as extending from the entrance of the curing oven 30, in certain embodiments the lower belt 31 may be completely enclosed within the curing oven 30 or within a hood or cover of the curing oven. In these embodiments, the lower belt 31 extends beyond the distal or leading edge of the upper belt 32 so that other components of the system (i.e., the fiber chopper 27, drying device 28, resin application device 33, etc.) can remain placed over the lower belt 31. In such embodiments, the other components of the system are typically enclosed within the curing oven 30 or within a hood or lid of the curing oven 30.

Fig. 6 shows a similar system, except that the system contains multiple fiber shredders. Specifically, the system includes a first fiber chopper 27a and a second fiber chopper 27b, each of which is positioned atop a lower belt 31 and configured to cut fiber bundles or rovings. A first fiber chopper 27a cuts a first fiber strand or roving 26a unwound from a respective spool 23 a-c. The first chopped fiber bundles or rovings 26a fall on top of the underlying belt 31 and form a first layer of chopped fiber web or mesh. The first bundle or roving 26a may pass through a first roving heater 24a that dries the first bundle or roving 26 a. The thickness and/or density of the first layer is controlled by the speed of the first fiber chopper 27a, the number and size of the individual rovings in 26a, and the speed of the underlying belt 31. A second fiber chopper 27b cuts a second fiber strand or roving 26b unwound from the respective spool 23 d-e. The second chopped fiber bundles or rovings 26b fall on top of the underlying belt 31 and/or the first layer and form a second layer of chopped fiber web or mesh. The second bundle or roving 26b may pass through a second roving heater 24b that dries the second bundle or roving 26 b. The thickness and/or density of the second layer is controlled by the speed of the second fiber chopper 27b, the number and size of the individual rovings in 26b, and the speed of the underlying belt 31.

The resulting chopped fiber web or wire mesh may have a layered construction, wherein at least one property of the first layer is different from a property of the second layer. The difference in properties may be in fiber type, fiber length, fiber diameter, fiber or layer density, layer thickness, etc. In certain embodiments, the first and second bundles or

rovings

26a and 26b may be of different fiber types, different fiber sizes, and/or have different fiber characteristics. In other embodiments, the chopped fibers produced by the first and

second fiber choppers

27a, 27b may fall on top of the underlying belt 31 to form a hybrid layer from the chopped fibers. The hybrid layer may comprise a mixture of chopped fibers from the first and

second fiber choppers

27a and 27 b. The plurality of fiber choppers may be simply used to cut bundles or rovings having different properties. The layered or commingled chopped fiber web or wire mesh may then be subjected to other processes of the system, such as a drying device 28, a resin application device 33, a gas purging device 34, a dual belt compression device, a curing oven 30, and the like. In certain embodiments, the first and second

roving heaters

24a and 24b may be the same heater. If desired, the system may also include additional fiber choppers (not shown) that cut additional fiber bundles or rovings to form additional layers of the chopped fiber web or mesh.

In certain embodiments, the fiber chopper 27 of fig. 5 may be replaced with a fiber scattering device (see fiber scattering device 37 of fig. 8A). In these embodiments, the system appears essentially similar to the system of fig. 8A, except that the system will not include a cylinder 41 around which the fabric or felt 40 is placed. In these embodiments, the fiber scattering device 37 scatters or disperses the pre-cut chopped fiber segments C atop the underlying belt 31. The pre-cut chopped fiber segments C are typically loaded or placed in a hopper and may be accessed by a fiber distribution device 37. The chopped fiber segments C may be uniformly sprinkled on top of the underlying belt 31 to form a chopped fiber web or wire mesh. In other embodiments, the first fiber chopper 27a and/or the second fiber chopper 27b of fig. 6 may be replaced with a fiber spreading device 37 to form multiple webs or layers of mesh and/or to disperse different fiber sizes or types within the webs or layers of mesh. The chopped fiber segments C may be completely dried before being scattered or dispersed atop the underlying belt 31. The system may include various other components described herein, or may exclude one or more of the described components, as desired.

Fig. 7 illustrates a hybrid system in which the thermoplastic prepreg is formed from both the chopped fiber web or mesh and a woven/non-woven fabric or mat. The system comprises a drum 41 around which a fabric or felt 40 is placed. The system is configured to unwind the fabric or felt 40 from the drum and move the fabric or felt 40 atop the underlying belt 31. The fiber chopper 27 is positioned above the lower belt 31 and the fabric or mat 40 such that the chopped fibers C fall on top of the fabric or mat 40 and generally form a chopped fiber web or mesh layer atop the fabric or mat 40. The thickness of the chopped fiber web or wire mesh may be controlled by controlling the speed of the fiber chopper 27 and/or the speed of the underlying belt 31. In certain embodiments, the fiber chopper 27 may be replaced with a fiber scattering device.

In certain embodiments, the chopped fibers C may fall within the fabric or mat 40 to form a hybrid layer of fabric or mat 40 and the chopped fiber web or mesh. In these embodiments, the fabric or mat 40 must be sufficiently porous to allow the chopped fibers C to fall into the fabric or mat 40 and pass through the fabric or mat 40. The fibers or bundles 26 may be cut into pieces small enough to facilitate dispersion of the chopped fibers C within the fabric or mat 40.

The resulting layered or hybrid mat is then moved through a drying device 28 and residual moisture is removed from the layered or hybrid mat. The layered or hybrid mat is then moved through a resin application device 33 such that the reactive resin is applied to the mat, and through a gas purge device 34 such that moisture free gas G is applied to the layered or hybrid mat. The layered or hybrid mat is then moved through the double belt apparatus to fully saturate the layered or hybrid mat and through a curing oven 30 to polymerize the reactive resin. After polymerization of the reactive resin, the thermoplastic polymer fully impregnates the layered or hybrid mat.

The layered or hybrid mat may provide several advantages over thermoplastic prepregs using only woven/non-woven fabrics or mats. In particular, the layered or hybrid mat may have improved conformability. The improved conformability of the thermoplastic prepreg allows the prepreg to more easily conform to molds having complex shapes. Therefore, the prepreg is more easily molded into a complicated shape. The use of the fabric or mat generally provides improved strength compared to prepregs using only chopped fibre webs or screens.

FIG. 8 illustrates another hybrid system in which multiple fiber choppers and a single fabric or felt are used. It should be appreciated that the configuration of the system of FIG. 8 may be reversed so that multiple fabrics or felts and a single fiber chopper are used. Alternatively, if desired, the system of fig. 8 may use both multiple fabrics or mats and multiple fiber choppers to form thermoplastic prepregs having the desired chopped fiber web or mesh and fabric or mat construction.

In FIG. 8, a first fiber chopper 27a is positioned atop the distal end of the lower belt 31. A first fiber chopper 27a cuts a first fiber strand or roving 26a that is unwound from about a respective spool 23 a-c. The first chopped fiber bundles or rovings 26a fall on top of the underlying belt 31 and form a first layer of chopped fiber web or mesh. The first bundle or roving 26a may pass through a first roving heater 24a that dries the first bundle or roving 26 a. The thickness and/or density of the first layer is controlled by the speed of the first fiber chopper 27a, the number and size of the individual rovings in 26a, and the speed of the underlying belt 31. The system also includes a drum 41 around which the fabric or felt 40 is placed. The fabric or mat 40 is unwound from a roll 41 and moved atop a chopped fiber web or web formed from the first chopped fiber bundles or rovings 26 a. A roller 42 may be placed above the lower belt 31 to properly direct the fabric or mat 40 onto and atop the chopped fiber web or mesh. A second fiber chopper 27b is positioned adjacent to fabric or felt drum 41 and is configured to cut a second fiber tow or roving 26b unwound from about a corresponding spool 23 d-f. The second chopped fiber bundles or rovings 26b fall atop the fabric or mat 40 and form a second layer of chopped fiber web or mesh atop the fabric or mat 40. The second bundle or roving 26b may pass through a second roving heater 24b that dries the second bundle or roving 26 b. The thickness and/or density of the second layer is controlled by the speed of the second fiber chopper 27b, the number and size of the individual rovings in 26b, and the speed of the underlying belt 31. Thus, the fabric or mat 40 is sandwiched between two layers of chopped fiber web or mesh. The fabric or mat and chopped fiber web or mesh are then moved through the system to remove residual moisture, apply the reactive resin, and polymerize the reactive resin. The resulting hybrid thermoplastic prepreg 36 may then be cut into sheets by a cutting device 38 as described herein.

Fig. 8A shows a hybrid system in which the fiber chopper is replaced by a fiber seeding device 37. The fiber spreading device 37 is configured for spreading or dispersing the pre-cut chopped fiber segments C that are loaded or placed in the hopper. In certain embodiments, the chopped fiber segments C are uniformly scattered atop the underlying belt 31 to form a chopped fiber web or wire mesh. In these embodiments, the system of fig. 8A does not include a drum 41 and a fabric or felt 40. In other embodiments, the chopped fiber segments C are uniformly sprinkled on top of the fabric or mat 40 to form a layer of the chopped fiber web or mesh on top of the fabric or mat 40. The system of fig. 8A may include additional fiber spreading devices 37 and/or fiber choppers to form additional webs or layers of mesh and/or to disperse different fiber sizes or types within the web or mesh. The chopped fibers C may be completely dried before being spread or dispersed on the top of the underlying belt 31 or fabric or mat 40. The system may include various other components described herein, or may exclude one or more of those components, if desired.

Fig. 8B illustrates a hybrid system in which the fully cured chopped fiber thermoplastic prepreg 36 is wound into a roll product by a winding device 39. The thermoplastic prepreg may be formed from only a chopped fiber web or mesh, or may be formed from both the chopped fiber web or mesh and a woven/non-woven fabric or mat. When the thermoplastic prepreg is formed from the chopped fibre web or mesh and woven/non-woven fabric or mat, the system comprises a drum 41 around which a fabric or mat 40 is placed as previously described. The system of fig. 8B may include one or more fiber choppers and/or drums 41 to form any type of layered prepreg desired.

Exemplary prepreg

The system described above can be used to manufacture fully impregnated thermoplastic prepregs. The thermoplastic prepreg may comprise a fabric or felt, a chopped strand web or mesh, or a hybrid web or felt. In one embodiment, the fabric or felt may comprise a plurality of rovings woven together. Each roving may contain a bundle of continuous glass fibers or any other fibers. In another embodiment, the fabric or felt may comprise a plurality of randomly oriented entangled and intermeshed fibers. In another embodiment, a non-bonded web or mesh of chopped fibers may be used. The prepreg further comprises a thermoplastic polymer fully impregnated within the fabric or mat, chopped strand web or screen, or hybrid web or mat. The thermoplastic polymer is formed by polymerizing a reactive resin (e.g., caprolactam, CBT, etc.) to form the thermoplastic polymer (e.g., polyamide-6, PBT, etc.). As described herein, more than 90, 95, 98, or even 99 weight percent of the resin reacts to form the thermoplastic polymer. When the fully impregnated thermoplastic prepreg is subjected to a subsequent heating and/or pressure process, the thermoplastic polymer melts or softens to allow the thermoplastic prepreg to be molded or formed into a composite part.

In certain embodiments, the fully impregnated thermoplastic prepreg is a roll product. In certain other embodiments, the fully impregnated thermoplastic prepreg may be cut into sheets. The thermoplastic prepreg may then be formed into a composite part. For example, one or more layers of the thermoplastic prepreg may be compression molded into a desired composite part. Exemplary techniques for forming the prepreg into a fiber-reinforced composite article may include compression molding a single layer of prepreg, multiple layers of prepreg, and/or prepreg pellets into a fiber-reinforced article. When the prepreg comprises a partially polymerized resin, the compression moulding process may include a heating step (e.g. hot pressing) to fully polymerize the resin. Heat may also be used in compression molding of fully polymerized prepregs to melt the prepreg and mold it into the shape of the final article.

The prepregs may also be used in combination with other fibre and resin materials to produce the final composite article. For example, the prepreg may be placed in selected sections of a tool or mold to reinforce the article and/or provide material where it is difficult to reach for thermosetting and/or thermoplastic resins. For example, the prepreg may be applied to acute angles and other highly structured areas of a mold or nip plate used in a reactive injection molding process (RIM), a structural reactive injection molding process (SRIM), a resin transfer molding process (RTM), a vacuum assisted resin transfer molding process (VARTM), a spray-on process, a filament winding process, a filament injection molding process, and the like. The prepregs may also be used as local reinforcement during injection and compression moulding processes including LFT (long fiber thermoplastic) and D-LFT (oriented long fiber thermoplastic) or for insert moulding (overmolding).

Exemplary composite products that can be formed from the prepreg include: automotive components, wind turbine blade components, building components, electrical components, sports and leisure components and/or other components. Exemplary automotive components include: a cockpit, a seat, an instrument panel, a side sill, a floor side sill, a door trim, an exterior panel, an opening, a underbody, a front/rear module, an engine compartment, an engine hood, a battery mount, an oil pan, a valve cover/hood, a baffle, a tail fin, and the like.

An exemplary wind turbine blade component includes: spar caps, shells, root inserts, and the like. An exemplary building element includes: a column, a triangular eaves, a dome, an inner wall plate, a window profile, a ladder bar and the like. Exemplary electrical components include: lamp pole, circuit board, terminal box etc. Exemplary sports and leisure members include: golf club shafts, golf carts, and the like. Other components that may be molded from the prepreg include: components for mass transit transportation, agricultural equipment, and trailers/RVs include passenger seats, standing backs (standbacks), wall covering panels, floors, large panels for trailer walls, truck and tractor cabs, bus body shells, cargo containers, and the like.

In certain embodiments, a battery tray or case for an electric car or vehicle may be molded using the fully impregnated thermoplastic prepregs described herein. The battery case may be molded from a single piece of prepreg material, eliminating the need to reinforce these areas of the battery case with unidirectional tape at the corners or edges as is done in conventional processes.

Referring to fig. 9, a thermoplastic prepreg that may be formed by one of the systems and/or methods described herein is illustrated. The thermoplastic prepreg comprises a web or screen 50 comprising a plurality of chopped fibres 51 having a fibre length and a fibre diameter. The fiber length is typically between 10 and 100mm, more typically between 25 and 50 mm. The fiber diameter is typically between 1 and 30 μm, more typically between 5 and 20 μm. As described herein, the web or screen 50 is generally non-bonded prior to application of the reactive resin, and thus, the web or screen 50 is generally not mechanically bonded and contains no binder other than the thermoplastic material that binds the chopped fibers together. The webs or gauzes 50 are also typically not coupled together by some means other than the thermoplastic material. The web or screen 50 can comprise a variety of fiber types and/or fiber sizes described herein that are uniformly or homogeneously dispersed within the web or screen 50 and form a hybrid fiber screen. The chopped fibers 51 may include a sizing composition having a coupling agent that promotes adhesion between the chopped fibers 51 and the thermoplastic polymer. The chopped fibers may comprise or consist of glass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers, inorganic fibers, or combinations thereof. In some instances, it may be beneficial to use a chemically or mechanically coupled web or screen 50, and thus, unless specifically recited in the claims, the web or screen 50 is not limited to a particular configuration (i.e., bonded or unbonded).

The thermoplastic material fully impregnates the web or mesh 50 such that the thermoplastic prepreg has a void volume of less than 5%, more typically less than 3%. In most embodiments, the thermoplastic prepreg has a void fraction of less than 3%, and sometimes less than 1%. As described herein, the thermoplastic material comprises or consists of a polymer formed by in situ polymerization of a monomer or oligomer, wherein more than 90, 95, 98 or even 99 weight percent of the monomer or oligomer reacts to form the thermoplastic material. The thermoplastic prepreg comprises 5 to 95 weight percent of the thermoplastic material. The thermoplastic material may comprise or consist of nylon, PMMA, PBT, Thermoplastic Polyurethane (TPU) or mixtures thereof.

Fig. 10 shows another thermoplastic prepreg, wherein the web or web comprises a first layer of fibres 50a formed from first chopped fibres 51a and a second layer of fibres 50b formed from second chopped fibres 51 b. The first and second chopped

fibers

51a and 51b generally have different fiber types and/or fiber sizes. The composition of each fibrous layer, the density of each fibrous layer, and/or the thickness of each fibrous layer may be selected on the basis of a given application of the thermoplastic prepreg and/or on the basis of desired prepreg properties. The first and second chopped

fibers

51a, 51b are generally not entangled or intermingled with each other except at the interface between the first and

second layers

50a, 50 b. The thermoplastic material completely impregnates the web or mesh. The thermoplastic prepregs may have a void fraction and a percent polymerization as described herein. The thermoplastic prepreg of fig. 10 may be formed by the system shown in fig. 6.

Fig. 11 shows a thermoplastic prepreg having a layered construction in which each layer contains a different fibre-reinforcement material. Specifically, the first layer of thermoplastic prepreg comprises a web or screen 50 of chopped fibers and the second layer of thermoplastic prepreg comprises a woven fabric or non-woven mat 52. As described herein, the woven fabric or nonwoven mat 52 is typically formed from a continuous bundle of fibers or a plurality of entangled or bonded fiber segments. The composition of each layer, the density of each layer, and/or the thickness of each layer may be selected on the basis of a given application of the thermoplastic prepreg and/or on the basis of desired prepreg properties. The thermoplastic material completely impregnates the fiber reinforcement material. The thermoplastic prepregs may have a void fraction and a percent polymerization as described herein. The thermoplastic prepreg of fig. 11 may be formed by the system shown in fig. 7.

Fig. 12 shows a thermoplastic prepreg having a layered construction in which a woven fabric or nonwoven mat 52 is sandwiched between an upper 50 and a lower 53 chopped fiber web or screen. The composition of each layer, the density of each layer, and/or the thickness of each layer may be selected on the basis of a given application of the thermoplastic prepreg and/or on the basis of desired prepreg properties. The thermoplastic material completely impregnates the fiber reinforcement material. The thermoplastic prepregs may have a void fraction and a percent polymerization as described herein. The thermoplastic prepreg of fig. 12 may be formed by the system shown in fig. 8.

Fig. 13 shows a thermoplastic prepreg that also has a layered construction, but that is the reverse of the construction of fig. 12 in that a chopped fiber web or mesh 50 is sandwiched between an upper woven fabric or nonwoven mat 52 and a lower woven fabric or nonwoven mat 54. The composition of each layer, the density of each layer, and/or the thickness of each layer may be selected on the basis of a given application of the thermoplastic prepreg and/or on the basis of desired prepreg properties. The thermoplastic material completely impregnates the fiber reinforcement material. The thermoplastic prepregs may have a void fraction and a percent polymerization as described herein. The thermoplastic prepreg of fig. 14 may be formed by a system similar to that shown in fig. 8, using a single fiber chopper and using two fabrics or felts. Alternatively, a thermoplastic prepreg formed by the system of fig. 1A or 1B may be thermoplastically bonded to a thermoplastic prepreg formed by any of the systems of fig. 5-7.

In certain embodiments, the thermoplastic prepregs described herein may not be fully polymerized. Thus, the thermoplastic prepreg may comprise residual resin content, for example residual monomer or oligomer content. The residual resin content is constituted by monomers or oligomers which have not been polymerized into the thermoplastic material. For example, the thermoplastic material of the thermoplastic prepreg may comprise between 0.5 and 5% of said residual monomer or oligomer, more typically between 1 and 3% or between 1 and 2% of said residual monomer or oligomer. The percentage of residual monomers or oligomers present in the thermoplastic material is determined with respect to the amount of resin initially added to the fiber-reinforced material. For example, a residual monomer or oligomer content of between 0.5 and 5% means that 0.5-5% of the resin added to the fiber reinforcement material remains in the unpolymerized state. The content of residual monomers or oligomers in the prepreg can be measured by a solvent extraction method described below. For example, the amount of residual caprolactam in polyamide-6 prepreg can be measured by extracting ground prepreg powder with hot water. The thermoplastic material of the thermoplastic prepreg may have a higher molecular weight than conventional thermoplastic prepregs. For example, the thermoplastic prepreg may comprise a higher molecular weight polyamide-6 material. In these embodiments, the higher molecular weight thermoplastic material may be evidenced by insolubility of the polyamide-6 material in a solvent in which conventional hydrolysis polymerized polyamide-6 resins are typically soluble. For example, polyamide-6 resins formed by in situ anionic polymerization of caprolactam may be insoluble in solvents such as Hexafluoroisopropanol (HFIP), whereas conventional hydrolyzed polymerized polyamide-6 is soluble in HFIP.

The thermoplastic prepregs of fig. 9-13 may be roll-formed products or may be cut into individual sections as desired. In one embodiment, the thermoplastic prepreg may comprise 30 to 80 wt% of fibrous material and 20 to 70 wt% of thermoplastic polymer. In another embodiment, the thermoplastic prepreg may comprise 50 to 70 weight percent fibrous material and 30 to 50 weight percent thermoplastic polymer.

Method of producing a composite material

Fig. 2 illustrates a method 200 of forming a fully impregnated thermoplastic prepreg product. At block 210, the fabric or mat is moved from a starting point to an ending point. The fabric or mat undergoes a plurality of processes between the starting and ending points and moves substantially constantly between the starting and ending points. At block 220, the fabric or mat is dried to remove residual moisture from one or more surfaces of the fabric or mat. At block 230, the monomer or oligomer is mixed with a catalyst and an activator to form a reactive resin mixture. The catalyst and activator facilitate polymerization of the monomer or oligomer to form a thermoplastic polymer. In certain embodiments, a portion of the monomer or oligomer may be mixed with the catalyst in a first tank, and a portion of the monomer or oligomer may be mixed with the activator in a second tank separate from the first tank. In these embodiments, mixing the monomer or oligomer with the catalyst and activator comprises mixing the materials from the first and second tanks in a static mixer.

At block 240, the reactive resin mixture is applied to the fabric or felt. The reactive resin mixture may have a viscosity of less than 10 mPa-s. At block 250, the reactive resin mixture coated fabric or mat is passed through a calender or press that presses the reactive resin mixture through the fabric or mat such that the reactive resin mixture fully saturates the fabric or mat. At block 260, the reactive resin mixture coated fabric or mat is passed or moved through a curing oven to polymerize the reactive resin mixture and thereby form the thermoplastic polymer. The environment surrounding the coated fabric or mat is controlled to maintain the humidity in the air at substantially zero during at least a portion of the above process. More than 90, 95, 98 or even 99 weight percent of the reactive resin mixture may react to form the thermoplastic polymer.

In certain embodiments, the method may further comprise applying a moisture free gas to one or more surfaces of the reactive resin mixture coated fabric or felt to control the environment surrounding the fabric or felt. In particular embodiments, nitrogen may be applied to one or more surfaces of the reactive resin mixture coated fabric or felt. In certain embodiments, the method may further comprise winding the cured thermoplastic prepreg into a roll product. In certain embodiments, the curing oven may be a double belt compression oven. In these embodiments, blocks 250 and 260 may be performed simultaneously.

Fig. 3 illustrates another method 300 of forming a fully impregnated thermoplastic prepreg product. At block 310, a reactive resin is applied to the fabric or mat, the resin incorporating a catalyst and an activator that facilitates polymerization of the resin to form a thermoplastic polymer. The catalyst and activator may be placed in separate holding tanks with or without the resin, and may be mixed with the resin prior to applying the resin to the fabric or mat. Alternatively, the catalyst or activator may be pre-applied to the fibers of the fabric or felt, and other materials may be applied to the fabric or felt along with the resin. At block 320, the resin coated fabric or mat is passed or moved through a calender or press to fully saturate the fabric or mat with the resin. At block 330, the resin coated fabric or mat is passed or moved through a curing oven to polymerize the resin and thereby form the thermoplastic polymer. In other words, the resin coated fabric or mat is passed or moved through the oven to polymerize the resin and thereby form the polymer. Maintaining the moisture at the periphery of the coated fabric or mat at substantially zero during at least a portion of the above process. Further, the above process occurs in 20 minutes or less, 10 minutes or less, or 5 minutes or less.

In certain embodiments, the method further comprises drying the fabric or mat prior to applying the resin to remove residual moisture from one or more surfaces of the fabric or mat. In these embodiments, an infrared heater, pre-dryer, or other drying device may be used to remove residual moisture from the fabric or mat.

In certain embodiments, the method further comprises applying a moisture free gas to one or more surfaces of the fabric or mat to maintain the moisture at substantially zero at the perimeter of the fabric or mat. In these embodiments, nitrogen gas may be blown over or onto one or more surfaces of the coated fabric or mat. In certain embodiments, the method further comprises winding the fully impregnated thermoplastic prepreg into a roll product. In certain other embodiments, the method further comprises cutting the fully impregnated thermoplastic prepreg into sheets.

Fig. 14 illustrates a method 400 of forming a thermoplastic prepreg product. At block 410, the fiber web is moved on top of the lower belt of the dual belt press device. The fiber web includes chopped fibers. At block 420, the fiber web is dried by a drying device placed atop the lower belt and configured to remove residual moisture from the fiber web. At block 430, a monomer or oligomer is applied to the fiber web through a resin application mold placed atop the lower belt. At block 440, the fiber web and the applied monomer or oligomer are passed between a lower belt and an upper belt of the dual belt press device to force the monomer or oligomer through the fiber web and thereby fully saturate the fiber web with the monomer or oligomer. At block 450, the fully saturated fiber web is passed through a curing oven configured to polymerize the monomer or oligomer and thereby form the thermoplastic polymer as the fiber web moves through the curing oven. After polymerization of the monomer or oligomer, the fiber web is fully impregnated with the thermoplastic polymer. The method may further comprise winding the thermoplastic prepreg into a roll product or cutting the thermoplastic prepreg into sheets.

In certain embodiments, the method may further comprise mixing the monomer or oligomer with a catalyst and an activator to form a reactive resin mixture. The catalyst and activator may facilitate polymerization of the monomer or oligomer to form the thermoplastic polymer. The method may further comprise applying a moisture free gas to the fibrous web after applying the monomer or oligomer to substantially prevent exposure of the monomer or oligomer to ambient moisture in the surrounding environment. The upper belt of the double belt assembly may be completely enclosed within the curing oven.

In certain embodiments, the method may further comprise cutting fiber bundles or rovings by a fiber chopper positioned above the lower belt to form the chopped fibers. The fiber chopper may be positioned such that when the fiber bundles or rovings are cut, the chopped fibers fall on top of the underlying belt and form the fiber web. In these embodiments, the method may further include drying the fiber bundles or rovings by a second drying device while unwinding the fiber bundles or rovings from one or more spools and before the fiber bundles or rovings are cut to form the chopped fibers.

The fiber chopper may be a first fiber chopper and the chopped fibers may be first chopped fibers. In these embodiments, the method may also include cutting a second fiber strand or roving through a second fiber chopper positioned above the lower belt to form a second chopped fiber. The second fiber chopper may be positioned such that when the second fiber bundles or rovings are cut, the second chopped fibers fall on top of the first chopped fibers and form a layered or intermingled fiber web.

The method may additionally include unwinding a fabric or nonwoven mat from a roll and moving the fabric or nonwoven mat atop the underlying belt such that the chopped fibers are disposed above or below the fabric or nonwoven mat and forming a layered or hybrid fiber web containing or consisting of the chopped fibers and the fabric or nonwoven mat. The layered or hybrid fiber web may be subjected to the drying means, resin application mold, double belt means and curing oven such that the monomer or oligomer fully saturates the layered or hybrid fiber web and the thermoplastic polymer fully impregnates the layered or hybrid fiber web after polymerization of the monomer or oligomer.

In certain embodiments, the method may further comprise applying a sizing composition to the fibers of the fiber web. The sizing composition may have a coupling agent that promotes adhesion between the fibers and the thermoplastic polymer. The fiber mesh may comprise glass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers, inorganic fibers, or combinations thereof. The monomer or oligomer may comprise or consist of a lactam, a lactone, Cyclic Butylene Terephthalate (CBT), methyl methacrylate, a precursor of a thermoplastic polyurethane, or a mixture thereof. The lactam may comprise or consist of caprolactam, laurolactam or mixtures thereof.

Exemplary materials and systems

Using the system shown in FIG. 1A, a weight per unit area of 670g/m would be made up of 1200tex glass fiber roving²Using two heated tanks to separately melt caprolactam-catalyst and caprolactam-activator.1,000 grams of caprolactam (Br ü ggemann, AP nylon grade) and 74.0 grams of caprolactam are added to the first tank

C10 catalyst (containing sodium caprolactam.) A mixture of caprolactam and C10 was melted at 100 ℃ separately, 1,000 g caprolactam (Br ü ggemann, AP nylon grade) and 27.0 g caprolactam were added to the second tank

C20 activator (containing N, N' -hexane-1, 6-diyl bis (hexahydro-2-oxo-1H-azepin-1-carboxamide)). The mixture of caprolactam and C20 was melted at 100 ℃. The melts from the two tanks were then mixed in a 1:1 ratio in a static mixer and the reactive resin mixture was then applied to the fabric through a slot die with a 0.33mm opening.

In the experiment, a double belt press oven with two teflon coated belts was used to compress and cure the reactive resin mixture. The dual belt press was electrically heated and the oven temperature was set at 390 ° f. The line speed was set such that the residence time of the coated fabric in the oven was about 3.5 minutes. The resin application rate was adjusted to achieve a target resin content of 30% in the prepreg.

Example 1

The experiment was performed without using Infrared (IR) heating as shown in fig. 1A. Residual moisture on the fabric negatively affects anionic polymerization of caprolactam. A significant amount of caprolactam fumes was observed at the exit of the double belt press oven and the coated fabric was observed to adhere to the belt. Caprolactam fume at the furnace outlet indicates incomplete polymerization of caprolactam.

Example 2

The experiment was performed using IR heating, and the fabric was heated to a temperature of 330 ° f prior to applying the reactive resin mixture. The slot die was placed approximately 10 inches from the entrance of the furnace. No nitrogen purge or cabinet was used to protect the coated fabric from exposure to ambient moisture. A significant amount of caprolactam fumes was observed at the exit of the double belt press oven and the coated fabric was observed to adhere to the belt. Caprolactam fume at the furnace outlet indicates incomplete polymerization of caprolactam.

Example 3

The experiment was performed using IR heating, and the fabric was heated to a temperature of 330 ° f prior to applying the reactive resin mixture. The slot die was placed about 1.0 inch from the entrance of the furnace. Nitrogen was blown through the perforations in the stainless steel tube onto the coated fabric to prevent exposure of the coated fabric to ambient moisture. Complete polymerization was achieved and very little caprolactam fume was observed at the exit of the double belt press furnace. No adhesion of the coated fabric to the belt was observed. The resulting prepreg was subjected to Scanning Electron Microscopy (SEM) analysis to check impregnation. Fig. 4 is a typical SEM micrograph of a cross section of the prepreg showing that the fabric is fully impregnated with thermoplastic polyamide-6 resin.

As will be readily understood by those skilled in the art, the residual monomer or oligomer content in the prepreg can be measured by solvent extraction. For example, to measure the amount of residual monomer in a polyamide-6 prepreg, a powder sample can be prepared by cryogenically grinding small pieces of the prepreg in a grinder in the presence of liquid nitrogen. The powder samples can then be extracted with water at 150 ℃ using an Accelerated Solvent Extractor (ASE). The water in the extraction flask was then evaporated in a turbo-evaporator at 65 ℃ under a stream of nitrogen. The residue may be dried in a vacuum oven at 55 ℃ and then weighed to determine the amount of monomer extracted. The conversion can be calculated on the basis of the amount of residual monomer extracted and the starting amount of monomer used for impregnation.

"ASTM" refers to the American Society for Testing and materials, and is used to identify test methods by number. The year of the test method is identified by the suffix following the test number or the latest test method before the priority date of this document. For any other test methods or measurement standards defined or described herein, the relevant test method or measurement standard is the most recent test method or measurement standard before the priority date of this document. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, 0, or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, no specific numerical designation includes plural designations unless the context clearly dictates otherwise. Thus, for example, reference to "a method" includes a plurality of such methods, and reference to "the glass fiber" includes reference to one or more glass fibers and equivalents thereof known to those skilled in the art, and so forth. The invention has now been described in detail for purposes of clarity and understanding. It should be recognized, however, that certain changes and modifications may be practiced within the scope of the appended claims.

Furthermore, the terms "comprises" and "comprising," when used in this specification and the following claims, are intended to specify the presence of stated features, integers, components or steps, but do not preclude the presence or addition of one or more other features, integers, components, steps, acts or groups thereof.

Claims

1. A system for manufacturing a thermoplastic prepreg, the system comprising:

a double belt arrangement comprising an upper belt and a lower belt, the upper belt being placed atop the lower belt so as to compress a web of fibers passing through the double belt arrangement, and the lower belt having a longitudinal length substantially longer than the upper belt;

a drying device positioned atop the lower belt and configured to remove residual moisture from the web as the web moves through the drying device;

a resin application mold positioned atop the lower belt and configured for applying a monomer or oligomer to the fiber web as the fiber web moves through the resin application mold, wherein the monomer or oligomer is polymerizable to form a thermoplastic polymer; and

a curing oven configured to perform polymerization of the monomer or oligomer as the coated fibrous web moves through the curing oven and thereby form the thermoplastic polymer; wherein

The fiber web comprises chopped fibers; and is

The double belt means compresses the web and the applied monomer or oligomer as the web passes through the curing oven so that the monomer or oligomer fully saturates the web and the web is fully impregnated with the thermoplastic polymer after polymerization of the monomer or oligomer.

2. The system of claim 1, further comprising a gas application device positioned to blow a moisture free gas onto the coated fiber web so as to substantially prevent exposure of the monomer or oligomer to ambient moisture in the surrounding environment.

3. The system of claim 1, wherein the upper belt of said double belt assembly is completely enclosed within said curing oven.

4. The system of claim 1, further comprising a cooling device configured to cool the thermoplastic prepreg after polymerization of the monomer or oligomer.

5. The system of claim 1, further comprising a fiber chopper positioned above the lower belt, the fiber chopper configured to cut fiber bundles or rovings to form the chopped fibers, the fiber chopper positioned such that when the fiber bundles or rovings are cut, the chopped fibers fall atop the lower belt and form the fiber web.

6. The system of claim 5, wherein the fiber bundles or rovings comprise a plurality of fiber types or fiber sizes, and wherein the fiber bundles or rovings fall atop the underlying belt such that the plurality of fiber types or fiber sizes are uniformly mixed to form a hybrid fiber web.

7. The system of claim 5, wherein the fiber web does not contain a binder that binds or adheres the chopped fibers in the fiber web together prior to applying the monomer or oligomer.

8. The system of claim 5, wherein the fiber chopper is a first fiber chopper and the chopped fibers are first chopped fibers, and wherein the system further comprises a second fiber chopper positioned above the underlying belt, the second fiber chopper configured for cutting a second fiber bundle or roving to form second chopped fibers, the second fiber chopper positioned such that when the second fiber bundle or roving is cut, the second chopped fibers fall above the first chopped fibers and form a layered or hybrid fiber web.

9. The system of claim 5, further comprising a second drying device configured to dry the fiber bundles or rovings as they are unwound from one or more spools and before they are cut to form the chopped fibers.

10. The system of claim 5, further comprising a drum around which a roll of woven or nonwoven mat is placed, wherein the system is configured for unwinding the woven or nonwoven mat from the drum and moving the woven or nonwoven mat atop the underlying belt such that the chopped fibers are placed above or below the woven or nonwoven mat and form a layered or hybrid fiber web comprising the chopped fibers and the woven or nonwoven mat, wherein the layered or hybrid fiber web is subjected to the drying apparatus, resin application mold, dual belt apparatus, and curing oven such that the monomer or oligomer fully saturates the layered or hybrid fiber web and the thermoplastic polymer fully impregnates the layered or hybrid fiber web after polymerization of the monomer or oligomer.

11. The system of claim 1, further comprising a fiber spreading device positioned above the lower belt, the fiber spreading device configured to spread pre-cut chopped fibers atop the lower belt and form the web of fibers.

12. The system of claim 1, further comprising a mixing means that mixes the monomer or oligomer with at least one of a catalyst and an activator, wherein the catalyst and activator facilitate polymerization of the monomer or oligomer to form the thermoplastic polymer.

13. The system of claim 12, wherein prior to applying the monomer or oligomer to the fiber web, the mixing member and resin application mold are heated to maintain the temperature of the monomer or oligomer above the melting point of the monomer or oligomer.

14. The system of claim 1, wherein the fiber web comprises fibers treated with a sizing composition having a coupling agent that promotes adhesion between the fibers and the thermoplastic polymer.

15. The system of claim 1, wherein the fiber web comprises glass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers, inorganic fibers, or combinations thereof.

16. The system of claim 1, further comprising a winding device that winds the thermoplastic prepreg into a roll product, the winding device being positioned after the curing oven.

17. The system of claim 1, further comprising a cutting device that cuts the thermoplastic prepreg into sheets, the cutting device being positioned after the curing oven.

18. The system of claim 1, wherein the monomer or oligomer comprises a lactam, a lactone, Cyclic Butylene Terephthalate (CBT), methyl methacrylate, a precursor to a thermoplastic polyurethane, or a mixture thereof.

19. The system of claim 18, wherein the lactam comprises caprolactam, laurolactam, or a mixture thereof.

20. The system of claim 1, further comprising a single storage tank comprising the monomer or oligomer or a mixture of the monomer or oligomer and either the catalyst or activator, wherein activator or catalyst not contained within the single storage tank is pre-applied to fibers of the fibrous web.

21. The system of claim 20, wherein the single storage tank comprises a mixture of the monomer or oligomer and the catalyst, and wherein the activator is pre-applied to the fibers of the fiber web.

22. The system of claim 20, wherein the single storage tank comprises the monomer or oligomer, and wherein the catalyst is pre-applied to the fibers of the fiber web.

23. A method of forming a thermoplastic prepreg, the method comprising:

moving the fiber screen on the belt top below the double-belt press device;

drying the fiber web by a drying device placed atop the lower belt to remove residual moisture from the fiber web;

applying a monomer or oligomer to the fiber web through a resin application mold placed atop the underlying belt;

passing the web of fibers and the applied monomer or oligomer between a lower belt and an upper belt of the double belt press device to force the monomer or oligomer through the web of fibers and thereby fully saturate the web of fibers with the monomer or oligomer; and

passing the fully saturated fibrous web through a curing oven configured to polymerize the monomer or oligomer and thereby form the thermoplastic polymer as the coated fibrous web moves through the curing oven; wherein:

the fiber web comprises chopped fibers; and is

After polymerization of the monomer or oligomer, the fiber web is fully impregnated with the thermoplastic polymer.

24. The method of claim 23, further comprising mixing the monomer or oligomer with at least one of a catalyst or an activator to form a reactive resin mixture, the catalyst and activator promoting polymerization of the monomer or oligomer to form the thermoplastic polymer.

25. The method of claim 23, further comprising applying a moisture free gas to the fiber web after applying the monomer or oligomer to substantially prevent exposure of the monomer or oligomer to ambient moisture in the surrounding environment.

26. The method of claim 23, wherein the upper belt of said double belt assembly is completely enclosed within said curing oven.

27. The method of claim 23, further comprising cutting fiber bundles or rovings by a fiber chopper positioned above the lower belt to form the chopped fibers, the fiber chopper positioned such that when the fiber bundles or rovings are cut, the chopped fibers fall atop the lower belt and form the fiber web.

28. The method of claim 23, further comprising passing the thermoplastic prepreg through a cooling device after polymerization of the monomer or oligomer.

29. The method of claim 27, wherein said fiber chopper is a first fiber chopper and said chopped fibers are first chopped fibers, and wherein said method further comprises cutting second fiber bundles or rovings with a second fiber chopper positioned above said underlying belt to form second chopped fibers, said second fiber chopper positioned such that when said second fiber bundles or rovings are cut, said second chopped fibers fall atop said first chopped fibers and form a layered or hybrid fiber web.

30. The method of claim 27, further comprising drying the fiber bundles or rovings by a second drying device as the fiber bundles or rovings are unwound from one or more spools and before the fiber bundles or rovings are cut to form the chopped fibers.

31. The method of claim 27, further comprising unwinding a fabric or nonwoven mat from a roll and moving said fabric or nonwoven mat atop said underlying belt such that said chopped fibers are disposed above or below said fabric or nonwoven mat and form a layered or hybrid fiber web comprising said chopped fibers and said fabric or nonwoven mat, wherein said layered or hybrid fiber web is subjected to said drying apparatus, resin application mold, double belt apparatus and curing oven such that said monomer or oligomer fully saturates said layered or hybrid fiber web and said thermoplastic polymer fully impregnates said layered or hybrid fiber web after polymerization of said monomer or oligomer.

32. The method of claim 23, further comprising applying a sizing composition to the fibers of the fiber web, the sizing composition having a coupling agent that promotes adhesion between the fibers and the thermoplastic polymer.

33. The method of claim 23, wherein the fiber web comprises glass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers, inorganic fibers, or combinations thereof.

34. The method of claim 23, further comprising winding the thermoplastic prepreg into a roll product.

35. The method of claim 23, further comprising cutting the thermoplastic prepreg into sheets.

36. The method of claim 23, wherein the monomer or oligomer comprises a lactam, a lactone, Cyclic Butylene Terephthalate (CBT), methyl methacrylate, a precursor to a thermoplastic polyurethane, or a mixture thereof.

37. The process of claim 36 wherein the lactam comprises caprolactam, laurolactam, or a mixture thereof.

38. A thermoplastic prepreg, comprising:

a fiber web or screen comprising chopped fibers having a fiber length and a fiber diameter; and

a thermoplastic material fully impregnating the web or screen such that the thermoplastic prepreg has a void volume of less than 5%, the thermoplastic material being a polymer formed from polymerisation of a monomer or oligomer, wherein more than 90% of the monomer or oligomer polymerises to form the thermoplastic material; wherein:

the thermoplastic prepreg comprises 5 to 95 weight percent of the thermoplastic material; and is

The web or mesh is not mechanically bonded and contains no binder other than the thermoplastic material binding the chopped fibers together.

39. The thermoplastic prepreg of claim 38 wherein the chopped fibers comprise fibers having a fiber length between 10mm and 100 mm.

40. The thermoplastic prepreg of claim 39 wherein the chopped fibers comprise fibers having a fiber length between 25mm and 50 mm.

41. The thermoplastic prepreg of claim 38 wherein the web or web comprises a first layer of fibers formed from first chopped fibers and a second layer of fibers formed from second chopped fibers wherein the first and second chopped fibers are not entangled or intermingled except at the interface between the first and second layers of fibers.

42. The thermoplastic prepreg of claim 38 wherein said web or web comprises a plurality of fiber types or fiber sizes uniformly or homogeneously dispersed within said web or web and forming a hybrid fiber web.

43. The thermoplastic prepreg of claim 38 wherein the web or web comprises a fabric or nonwoven mat formed of continuous fiber bundles or a plurality of entangled or bonded fibers.

44. The thermoplastic prepreg of claim 43 wherein the web or mesh has a layered construction wherein the chopped fibers are placed on one or both sides of the fabric or nonwoven mat.

45. The thermoplastic prepreg of claim 43 wherein said web or mesh has a uniform configuration wherein said chopped fibers are uniformly dispersed on one or both sides of said fabric or nonwoven mat.

46. The thermoplastic prepreg of claim 38 wherein the fibers of the fiber web or wire mesh comprise a sizing composition having a coupling agent that promotes adhesion between the fibers and the thermoplastic polymer.

47. The thermoplastic prepreg of claim 38 wherein the chopped fibers comprise glass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers, inorganic fibers, or combinations thereof.

48. The thermoplastic prepreg of claim 38 wherein the thermoplastic prepreg is a roll product.

49. The thermoplastic prepreg of claim 38 wherein the thermoplastic prepreg is a sheet product.

50. The thermoplastic prepreg of claim 38 wherein the thermoplastic material comprises nylon, PMMA, PBT, TPU or mixtures thereof.