Intermediate materials and methods of making such materials

Abstract

An intermediate material (132) for producing a composite component is disclosed, comprising a prepreg layer (116) and an interleaf (120), the interleaf consisting of at least two thermally bonded thermoplastic interleaf material sections (120a, 120b). The invention relates to a method for producing such an intermediate material.

Description

[0001] The present invention relates to an intermediate material for composite fabrication comprising prepreg layers and cross-plies intended to prevent self-sticking of the prepreg layers, in particular relatively long and narrow strips of such intermediate material. The invention also relates to a method of manufacturing the intermediate material.

[0002] Composite materials are well known and are often used to prepare strong and lightweight parts. In one manufacturing technique, fiber components (e.g., carbon fibers or glass fibers) are pre-impregnated with a matrix material (usually a polymer, such as a thermoplastic polymer). The matrix material is not cured when used for impregnation, thereby maintaining a certain degree of flexibility. The "prepreg" material can be processed or stored before cutting and shaping, and even before curing to form the final (hardened) product. Prepreg materials are usually in the form of rolls, so as to be easy to store and transport.

[0003] An increasingly popular manufacturing technique utilizes automated fiber placement (AFP) equipment to deposit prepreg onto a surface (e.g., a three-dimensional mold). Using AFP avoids the waste associated with cutting preforms from large sheets. AFP typically involves depositing prepreg tapes via a movable automated head.

[0004] Narrow strips or tapes of prepreg (typically 3 to 50 mm wide) are fed to the AFP head for deposition. These tapes may be derived from large wide (typically in the order of meters, e.g. 2 meters) sheets of the main prepreg. In such a case, the main prepreg sheets may be cut into tapes using a cutting machine configured to make multiple cuts simultaneously (e.g. 49 cuts for a 2 m wide main sheet, producing 50 40 mm strips). Each tape may then be wound, e.g. on a spool, for transport to the AFP machine.

[0005] The primary prepreg to be cut into narrow strips may be provided as a pre-manufactured sheet, typically in the form of a roll, in which case it may include one or more backing layers or interleaving layers which may be removed prior to cutting the sheet into narrow strips. Alternatively, cutting of the primary prepreg may be carried out as it is formed, i.e. without intervening winding and storage, so that production of the primary prepreg and its cutting may be part of a single continuous process.

[0006] Prepregs typically have at least a certain degree of surface stickiness, so in order to prevent the prepreg from adhering to itself when the cut strips of the prepreg are wound up, the strips can be provided with a backing sheet, also referred to as an interleaving material. The backing sheet can be formed from a polymer material or a blend thereof (e.g., a polyolefin, more particularly polyethylene, such as LDPE or HDPE), and can be a single or multilayer polymer sheet. Typically, the interleaving material is 30 to 70 microns thick. The interleaving material is typically provided in the form of a reel or spool, and its width is often 3 to 12 mm wider than the prepreg strip. The interleaving material is wound on a spool with the prepreg strip. The combination of the resulting layered prepreg and the interleaving material represents an intermediate step in the manufacturing method, and is therefore referred to as an "intermediate material" in this application.

[0007] There is an increasing demand for relatively long lengths of prepreg strips, in particular for use in the AFP process to reduce the need to stop applying material to replace exhausted prepreg rolls with fresh rolls. In particular, the length of narrow / cut prepreg required is at least 3000m, and often much longer than this. Prepreg strips of such length can be prepared directly, for example by cutting a continuous formed sheet of prepreg as a step in an integrated manufacturing process, or by cutting a long length of preformed prepreg stored as rolls. However, in the latter case, the rolls will be very large and heavy and therefore difficult to prepare, transport and handle. Alternatively, long strips of narrow prepreg can be formed by cutting a relatively large number of rolls of wide preformed prepreg of short lengths and joining the strips formed from the various rolls together. Devices for joining lengths of narrow strips of prepreg are known.

[0008] The problem with forming rolls from such long, narrow prepreg strips is the difference between the length of the prepreg strip and the length provided for the interlaced lining, which is usually much shorter. In particular, rolls of interlaced material are usually no longer than 2,500 m, while prepreg strips can be at least 3,000 m long, and often much longer than this. This means that multiple lengths of interlaced material must be joined together to cover the entire length of the prepreg tape. The method currently used to join two or more lengths of interlaced material is to use adhesive tape to join the lengths at their ends. These "splices" can be produced by butt joints or overlapping (lap) joints.

[0009] The same technique can also be used in the unlikely event that the interlaced material breaks.

[0010] One problem with this technique is that the tape tends to pick up foreign matter - known as foreign object debris (FOD). In addition, misplaced or loose pieces of tape can also become FOD. This FOD can be transferred to the prepreg tape (which is itself tacky), which is a significant problem as it may interfere with the winding of the tape and / or its subsequent use. In particular, FOD may interfere with the operation of the AFP head and may furthermore adversely affect the mechanical properties of the final composite.

[0011] The present invention aims to generally obviate or at least alleviate the above-mentioned problems and / or to provide improvements.

[0012] According to the present invention, there are provided intermediate materials and methods as described herein and / or defined in any one of the appended claims.

[0013] The present invention provides an intermediate material for manufacturing a composite component, the intermediate material comprising:

[0014] Flat and elongated prepreg layers; and

[0015] an interleaving layer in contact with at least one side of the prepreg layer, the interleaving layer comprising at least two sections of thermoplastic interleaving material, each of the sections of thermoplastic interleaving material being joined by heat to at least one other section of thermoplastic material to form a continuous length of interleaving material;

[0016] The intermediate material is wound so that the staggered layers reduce or eliminate self-contact of the prepreg layers.

[0017] The present invention further provides a method for producing an intermediate material, comprising the steps of:

[0018] a) providing a length of a main prepreg having a first width;

[0019] b) cutting the main prepreg into a plurality of longitudinal prepreg strips, each of said strips having a width smaller than the width of the main prepreg;

[0020] c) providing a first section of thermoplastic interlaced material having a length less than a length of each of the prepreg strips;

[0021] d) placing a first end of a first thermoplastic interleaving material section in contact with a first end of one of the prepreg strips, the first thermoplastic interleaving material section having a width equal to or greater than a width of the prepreg strip;

[0022] e) gradually bringing the length of the first thermoplastic interlacing material section into contact with the length of the prepreg strip;

[0023] f) providing a second section of thermoplastic interlaced material having a width equal to or greater than the width of the prepreg strip before the second end of the first section of thermoplastic interlaced material contacts the prepreg strip, and joining the second end of the first section of thermoplastic interlaced material to the first end of the second section of thermoplastic interlaced material by applying heat to form a continuous length of thermoplastic interlaced material;

[0024] g) once the second end of the first thermoplastic interlacing material section contacts the prepreg strip, gradually contacting the length of the second thermoplastic interlacing material section with the length of the prepreg strip;

[0025] h) repeating steps f) and g) if necessary until the entire length of the prepreg strip is in contact with the continuous length of thermoplastic interlacing material; and

[0026] i) winding a strip of said prepreg material in contact with a continuous layer of thermoplastic interleaving material such that the interleaving material reduces or eliminates self-contact of the prepreg layers.

[0027] Advantageously, the thermoplastic backing / interlacing material bond is melted with heat, and preferably also pressure. When the melted section cools, there is no residual stickiness (unlike a tape bond), whereby the risk of picking up FOD is significantly reduced.

[0028] Preferably, the joint between the two interlaced material sections is configured to withstand a tensile force in the machine direction of at least 500 psi, measured without separation according to ISO 527-3. The preferred range of tensile strength is 500 to 40,000 psi.

[0029] Preferably, the interlaced material joints should be strong enough to survive subsequent processing and remain intact:

[0030] Co-winding with prepreg materials;

[0031] ·Tension to the AFP head through the feeding system;

[0032] Feed through the AFP head;

[0033] Separated from the prepreg material at the AFP head.

[0034] In the intermediate material of the present invention, the interleaved layer includes at least two segments of thermoplastic interleaved material, each segment of thermoplastic interleaved material is thermally bonded to at least one other segment of thermoplastic interleaved material to form a continuous length of interleaved material. Thus, it should be understood that when the interleaved layer includes only two segments of thermoplastic interleaved material, these segments are bonded together by a single bond zone. Alternatively, when the interleaved layer includes more than two segments of thermoplastic interleaved material, the two end segments are each bonded to another segment, and each center (non-end) segment is bonded to two other segments (via a joint at each end).

[0035] When the intermediate material of the present invention comprises more than two segments of thermoplastic interlaced material joined together to form a continuous length of interlaced material, different forms of joining zones and / or methods of joining may be used, but preferably each joining zone is formed by heating, and most preferably each joining zone is formed in substantially the same manner.

[0036] In the method of the present invention, by bringing the length of the thermoplastic interlaced material segment into contact with the length of the prepreg tape "gradually", this means that once the first end of the thermoplastic interlaced material segment has been brought into contact with the prepreg tape, for example at the first end of the prepreg tape, then the area of ​​the thermoplastic interlaced material segment proximate the first end is brought into contact with the area of ​​the prepreg tape proximate the first contact point, and the method continues along the length of the thermoplastic interlaced material segment until the second end of the length of the thermoplastic interlaced material is reached, at which point the prepreg tape is connected to the second thermoplastic interlaced material segment, and the method continues from this point. The segment of thermoplastic interlaced material and the prepreg tape may be brought into contact in this manner, for example, by passing the two materials through a nip, for example between two rollers that apply pressure to join the two materials.

[0037] In the method of the present invention, each of the sections of thermoplastic interleaving material has a width that is the same as or greater than the width of the prepreg tape, and preferably each of the sections of thermoplastic interleaving layers has the same width.

[0038] In one embodiment of the present invention, applying heat to form a joining zone between the thermoplastic interlaced material segments causes partial melting of at least one, and preferably both, of the joined ends of the two thermoplastic interlaced material segments. In particular, it is preferred that the heating does not cause complete melting of either end of the thermoplastic interlaced material, as this would reduce the strength of the joining zone or even make it impossible to form the joining zone.

[0039] In one embodiment of the invention, the step of applying heat to form the joint between the segments of thermoplastic interlaced material also includes applying pressure. In this embodiment, the pressure is preferably released in a manner such that the integrity of the joint is not significantly reduced. This can be achieved by allowing the joint to cool sufficiently to form, for example by stopping heating while pressure is still applied, or by slowly releasing the pressure so that the joint cools before completely removing the pressure applying means. The release rate depends on many factors, but the time and rate of releasing the pressure is determined by when the joint is stable.

[0040] In one embodiment of the present invention, the step of joining two segments of thermoplastic interlaced material comprises the following steps: overlapping the ends of the two segments so that they are joined by a lap joint, preferably wherein the length of the overlapping portion is 5 mm to 100 mm, more preferably 10 mm to 80 mm, and most preferably 20 mm to 50 mm.

[0041] In one embodiment of the invention, the ends of two thermoplastic interlacing material sections are joined at a continuous joining region spanning the width of the two thermoplastic interlacing material sections, and preferably the interlacing layers have a longitudinal axis, wherein the joining region extends parallel to a transverse axis perpendicular to the longitudinal axis.

[0042] In one embodiment of the invention, the ends of the two thermoplastic interlaced material sections are joined at a plurality of discrete joining areas across the width of the two thermoplastic interlaced material sections, and preferably each of the plurality of joining areas is elongated and parallel to the longitudinal direction of the thermoplastic interlaced material.

[0043] In one embodiment of the invention, the joining region is formed by contact with a heating wire.

[0044] In one embodiment of the invention, the thermoplastic interleaf layer formed by joining sections of thermoplastic interleaf material is wider than the prepreg strip so that it overhangs the prepreg strip at one or both ends.

[0045] In one embodiment of the present invention, the length of the prepreg strip, and therefore also the length of the intermediate material of the present invention, is at least 3,000 m, preferably 3,000 m to 25,000 m, more preferably 5,000 m to 15,000 m.

[0046] In one embodiment of the present invention, the width of the main prepreg before cutting is at least 0.075 m, preferably 0.075 m to 3 m, more preferably 0.5 to 1.5 m.

[0047] In one embodiment of the present invention, each of the plurality of longitudinal prepreg strips cut from the main prepreg in step b) has a width of 2 mm to 100 mm, preferably 3 mm to 55 mm.

[0048] In one embodiment of the invention, in step b), the main prepreg is cut into at least 2 longitudinal prepreg strips, preferably at least 5 strips, more preferably 5 to 100 strips, most preferably 25 to 50 strips.

[0049] In one embodiment of the method of the invention, the length of each prepreg strip is greater than the length of the main prepreg, and the method comprises the further steps of cutting at least one further length of the main prepreg into a further plurality of longitudinal prepreg strips, and joining each of the further plurality of longitudinal prepreg strips to the first plurality of longitudinal prepreg strips. In this embodiment, each length of the main prepreg is 50m to 2,000m long, preferably 700m to 1500m long, before joining.

[0050] In one embodiment of the method of the present invention, the length of each thermoplastic interlaced material segment is preferably from 100 m to 4,000 m, more preferably from 500 m to 3,000 m.

[0051] In one embodiment of the invention, steps c) to i) are performed on at least two of the plurality of longitudinal prepreg strips, preferably on all of the plurality of prepreg strips. In this embodiment, preferably, each of the prepreg strips on which steps c) to i) are to be performed is processed substantially at the same time.

[0052] In one embodiment of the invention, the step of applying heat in step f) comprises applying heat using a hand-held heating device, preferably wherein the hand-held heating device is a battery powered device.

[0053] A "handheld" device of the present application means a device that is generally portable and can be easily carried in one hand (and therefore has a mass greater than 2 kg). The device may be battery operated for easy portability. Preferably, the device has a pair of jaws (e.g., a press anvil arrangement) that are resiliently biased to an open position. The gripping force from the user's hand can be used to bring the jaws together to clamp and seal the interlaced material.

[0054] In one embodiment, both sides of the apparatus (the press and anvil mentioned above) may include heating elements, thereby heating both sides of the interlaced material.

[0055] The heating device may comprise one or more heating wires or may have a heating "head" having a different shape or configuration, such as hatching / cross hatching / a matrix of multiple "dots", etc.

[0056] The use of a hand-held heating device is particularly suitable for use in the method of the present invention, especially in embodiments in which multiple prepreg cut strips are processed by applying staggered layers simultaneously, because such a device can be used with existing equipment, i.e., no fixed sealing unit needs to be added. Likewise, the area in which the joining of the staggered material sections needs to occur is strictly limited, and in particular when many prepreg strips are processed in parallel, the hand-held devices can be moved relatively quickly and easily to wherever they are needed. In addition, when heat is applied, only a small amount of force is required to join the sections (less than the human grip force of about 500N for an adult). Still further, because it may be necessary to stop the equipment completely when joining the staggered material sections, the use of a hand-held device is advantageous because it can be quickly maneuvered into place, which limits the "down time" when stopping the equipment.

[0057] Examples of intermediate materials, interleaved layers, and manufacturing methods are described below with reference to the accompanying drawings, in which:

[0058] Figure 1A is a schematic side view of an apparatus and method for producing an intermediate material according to the invention in a first operating stage;

[0059] Figure 1B yes Figure 1A A schematic plan view of an apparatus and method;

[0060] Figure 1C yes Figure 1A A schematic side view of the apparatus and method in a second stage of operation;

[0061] Figure 2A is a plan view of a first stage in a second method of manufacturing a staggered layer;

[0062] Figure 2B yes Figure 2A A plan view of the second stage in the method for manufacturing the staggered layers;

[0063] Figure 3 yes Figure 2A A plan view of the third stage in the method for manufacturing the staggered layers;

[0064] Figure 4 yes Figure 2A A plan view of an alternative third stage in the method of manufacturing the staggered layers; and

[0065] Figure 5 It is used to implement Figure 4 Side view of the device in stages.

[0066] Reference Figure 1A and Figure 1B, shows an apparatus 100 for performing the manufacturing method according to the present invention. The apparatus 100 comprises a main reel 102, a cutting assembly 104, a tensioning assembly 106, an interlaced material reel 108 and a spool winder 110.

[0067] The main reel 102 has an uncured (or partially cured) main pre-impregnated ("prepreg") material 112 wound thereon. The main prepreg material 112 has a width W in the transverse direction T (perpendicular to the longitudinal direction L). In this embodiment, the width is 1 m, but those skilled in the art will appreciate that other widths are possible. The length Lp of the main prepreg material 112 stored on the main reel is 1000 m in this embodiment, but is typically 700 to 1,500 meters. During the process, the prepreg material moves in the longitudinal direction L.

[0068] The cutting assembly 104 includes a plurality of sets of N cutting blades 114 spaced apart in the transverse direction T. Each cutting blade is configured to cut through the thickness of the prepreg material as the prepreg material moves in the longitudinal direction. The cutting blades 114 are equally spaced apart so that N+1 strips or tapes 116 of prepreg material having a width w are produced, where w=W / (N+1).

[0069] Although not shown in FIG. 1 for simplicity, once all of the material 112 on the master roll 102 has been cut, a new master roll substantially identical to the first master roll 102 is arranged for cutting using the cutting assembly 104 to produce a further plurality of tapes substantially identical to the first plurality of tapes 116, each of which is joined to one of the first plurality of tapes 116 such that the length of each of the individual tapes 116 is greater than the length of the prepreg 112 on the master roll 102. The cut tapes may be joined in any convenient manner, and the process is preferably continuous such that as soon as a new cut tape is formed (i.e., before the remainder of the further tape is formed by cutting from the master tape), the first end of the new cut tape is joined to the second end of the original cut tape 116. If desired, a number of master rolls 102 of prepreg material may be joined in this manner to produce a desired length of wound intermediate material 132. For example, nine master rolls 102 each 1,000 m long may be joined to produce approximately 9,000 m of intermediate material 132 .

[0070] Figure 1B and Figure 1C The process is shown occurring on one of the N+1 strips 116, but it will be appreciated that in a typical process, all N+1 strips are processed simultaneously in this manner.

[0071] The strip 116 passes through a tensioning assembly 106 , which includes a series of rollers 118 .

[0072] A first length of interleaving material 120a is provided, wound on a first interleaving material roll 108a. The interleaving material is typically 3 to 12 mm wider than the prepreg tape 116, but critically is typically provided in a length that is shorter than the desired length of the intermediate material 132.

[0073] The interleaving material 120a is unwound from the roll 108a and passed over the roller 122 to the assembly roller 124. At this point, the first end of the interleaving material 120a begins to contact the prepreg tape 116, and as the prepreg tape 116 and the first interleaving material section 120a pass over the assembly roller 124, they gradually form a planar contact starting from the first end of the first interleaving material section 120a.

[0074] The interlaced material 120 is typically a thermoplastic polymer material, in this case LDPE (low density polyethylene). Such material is typically provided in the order of hundreds of meters and up to about 2,500 m. Typically, the available length Li of the interlaced material will therefore be less than the total length Lp of the prepreg strip material used for the process, i.e., the length of the prepreg strip made by joining lengths of prepreg cut from multiple master rolls or by cutting a master prepreg having an extremely long length. More typically, Li<2xLp. It is not uncommon for Li to be an order of magnitude smaller than Lp, for example Li can be of the order of hundreds of meters and up to about 2,500 m, where Lp is of the order of several thousand meters, for example 9,000 m or more.

[0075] In order to provide a length of interleaved material 120 suitable for plying a significant length, if not the entire length, of a length of prepreg tape 116 according to the present invention, multiple lengths of interleaved material 120a, 120b, etc. are joined as part of a process as described below.

[0076] Before roll 108a is exhausted (i.e., interlaced material 120a has been used up), a second roll 108b of interlaced material 120b is provided. The second length of interlaced material 120b is joined to the first length 120a at a joining region 126. A typical joining region 126 is shown in FIG. Figure 1C In an embodiment of the present application, the apparatus 100 is stopped to facilitate the joining. Further details of how the first length of interlaced material 120a is joined to the second length of interlaced material 120b are given below.

[0077] The wider interleaving material 120 overhangs the prepreg tape 116 on both sides. Because the prepreg is tacky, the assembled prepreg tape 116 and interleaving material 120 form an intermediate material 132. The intermediate material 132 is wound on the spool winder 110 so that the interleaving material 120 is radially inside the prepreg tape 116 when it is wound. This prevents the tacky prepreg from sticking to itself.

[0078] The resulting roll 110 of intermediate material 132 comprising the interleaved material of the stack and the prepreg can then be passed to automated fiber placement equipment for deposition. It will be appreciated that after unwinding, the AFP equipment will separate the interleaved material prior to depositing the prepreg.

[0079] Figure 2A and Figure 2B A first manner in which the bond zone 126 can be formed is shown. The two segments 120a, 120b are overlapped to form an overlap 128, and heat and pressure are applied to form the bond zone 126 ( Figure 2B ) as a lap joint. The overlap is usually 20 mm to 50 mm in the longitudinal direction.

[0080] Figure 3 A first manner in which heat and pressure may be applied to the overlapped portion 128 is shown. In this example, equal heat and pressure are applied across the overlapped portion 128 to melt the segments 120a, 120b. The heat and pressure may be applied by a handheld device, preferably a battery powered handheld device, having a heating head having a width equal to the width of the joining region 128 in the longitudinal direction and a length equal to the width of the two interlaced material segments 120a, 120b.

[0081] Figure 4 A second manner in which heat and pressure may be applied to the overlap portion 128 is shown. In this example, equal heat and pressure are applied to three separate longitudinally extending regions 130a, 130b, 130c of the overlap portion 128 to melt the segments 120a, 120b. In this embodiment, the heat and pressure may be applied by a small heating element, such as a heating wire, extending in the longitudinal direction, as discussed below.

[0082] exist Figure 3 and Figure 4 In each of the embodiments, it should be noted that the lateral edges of the overlapping portion 128 (and therefore the sections 120a, 120b) are sealed. This is advantageous because it ensures that there is less likelihood of snagging and other such problems that may be caused by loose ends / edges.

[0083] exist Figure 1A , Figure 1B , Figure 1C , Figure 2A , Figure 2B , Figure 3 and Figure 4 In the embodiment shown in , the heating to form the junction is preferably performed using a handheld device, most preferably a battery powered handheld device.

[0084] Reference Figure 5, showing a device 200 for joining two sections 120a, 120b. The device includes an anvil 202 and a press 204. The press includes a single heating wire 206. The press 204 can move toward the anvil 202 to apply heat and pressure from the heating wire 206 to the overlapping portion 128 at the same time. This produces a first joining area 130a. The device 200 then moves in a lateral direction to form a second joining area 130b, and then moves again to form a third joining area 130c (but it should be understood that the three joining areas can be formed in any order, or more joining areas can be formed if necessary). In one embodiment, both sides of the device 200 (press 204 and anvil 202) can include heating elements, thereby heating both sides of the interlaced material. When the heating wire is not used, the joining device 200 can be equipped with a heating "head" with different shapes and configurations, such as hatching, cross hatching, or a plurality of "dot" matrices, etc. The device is preferably a handheld device, and most preferably a battery-powered handheld device.

[0085] Application of heat to the thermoplastic interwoven material may partially melt and tackify the material, thereby bonding the material to the opposing sections.

[0086] When using the apparatus 200 in the method of the present invention, it is preferred to release the pressure slowly after sealing (in these embodiments it takes about 2 seconds). The release rate depends on many factors, but the time and rate of releasing the pressure is determined by when the joint is stable. This can be achieved by allowing the joint to cool sufficiently to form, or by stopping heating while the press is still closed, or by slowly releasing the press so that the joint cools before the press and the anvil are completely separated.

[0087] Once cooled, the interlaced material will not exhibit additional tack.

[0088] In one example of joining lengths of interlaced material according to the invention, the respective ends of two 9 mm wide and 50 μm thick LDPE strips (PE Hoods Blue, available from Plasthill BV) were overlapped to give an overlap of 25 mm and joined together by applying heat and pressure using a battery powered handheld device (Bheema Mini Portable Handy Plastic Bag Sealer Sealing Machine, available from Amazon, UK). The device is small (approximately 110 mm x 45 mm x 25 mm) and lightweight (approximately 58 g) and does not require connection to a separate power source, so it can be used particularly conveniently in the confined space available on a production line for making narrow prepreg strips with interlaced material layers. The full melting point of LDPE is about 124°C, but it softens and becomes pliable when heated to 40°C to 110°C. Therefore, although the optimal temperature for forming a joint between strips of LDPE is 70°C to 110°C, pressure must also be applied in order to fully form the joint. Using pressures within a range that can be conveniently achieved with a manual squeezing device (ie, 30 N to 400 N), a joint can be formed in 2 seconds (using temperatures near the upper end of the range) to 8 seconds (using temperatures near the lower end of the range).

[0089] When the sealer device is used, the act of releasing the pressure breaks the circuit, whereby the resistive heating of the wires in the device ceases, causing their temperature to drop, allowing relatively rapid cooling of the LDPE polymer sheet, consolidating the joint and making the material easier to handle. The resulting joint area has a tensile strength within the range reported by the supplier for non-joined LDPE, in this case greater than 21 MPa in the machine direction.

[0090] Variations are within the scope of the invention.

Claims

1. A method for producing an intermediate material, comprising the following steps: a) providing a length of a main prepreg having a first width; b) cutting the main prepreg into a plurality of longitudinal prepreg strips, each of the strips having a width less than the width of the main prepreg, each of the strips having a certain length; c) providing a first section of thermoplastic interlaced material having a length less than the length of each of the prepreg strips, the first section of thermoplastic interlaced material having a first end and a second end; d) placing a first end of the first thermoplastic interleaving material section in contact with a first end of one of the prepreg strips, the first thermoplastic interleaving material section having a width equal to or greater than a width of the prepreg strip; e) gradually bringing the length of the first thermoplastic interlacing material section into contact with the length of the prepreg strip; f) providing a second section of thermoplastic interlaced material having a length and having a width equal to or greater than the width of the prepreg strip before the second end of the first section of thermoplastic interlaced material contacts the prepreg strip, and joining the second end of the first section of thermoplastic interlaced material to the first end of the second section of thermoplastic interlaced material by applying heat to form a continuous length of thermoplastic interlaced material; g) once the second end of the first thermoplastic interlacing material section contacts the prepreg strip, thereafter gradually contacting the second thermoplastic interlacing material section along the length of the prepreg strip; h) repeating steps f) and g) if necessary until the entire length of the prepreg strip is in contact with the continuous length of thermoplastic interlacing material; and i) winding the prepreg strip in contact with a continuous length of thermoplastic interleaving material such that the interleaving material reduces or eliminates self-contact of the prepreg strip, wherein the continuous length of the thermoplastic interlaced material is wider than the strip of prepreg; wherein the step of applying heat in step f) also includes applying pressure; Wherein the step of joining the two thermoplastic interlaced material sections in step f) further comprises overlapping the ends of the two sections such that they are joined by a lap joint, the lap joint also comprising lateral edges; and wherein the length of the lap joint is 20 mm to 50 mm.

2. The method of claim 1, wherein the lap joint is formed by contact with a heated wire.

3. The method of claim 1, wherein the step of applying heat in step f) comprises applying heat using a hand-held heating device.

4. The method of claim 3, wherein the handheld heating device is a battery powered device.

5. The method of claim 2, wherein the lateral edges of the lap joint are sealed.

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