System and method for producing chopped strands to make chopped strand mats

Abstract

The present invention relates to a system and a method for producing chopped strands (10) from discontinuous fibers to make chopped strand mats. The system comprises:-a first guiding device for the ribbon-shaped precursor; -a pair of opposing fibre distribution rollers (3, 4) with parallel horizontal axes, which rollers are arranged against each other in the tangential region therebetween and are rotatable in opposite directions along their axes. The first roller has a circumferentially slotted contoured surface consisting of alternating circumferential peaks (31) and valleys (32), and the second roller has a smooth surface (4 '). The space between the valley part and the smooth surface accommodates the part of the strip-shaped precursor; and the scraping plate (5) is positioned below the tangential area between the rollers, and a plurality of vertical tooth forks (51) are arranged at the top end of the scraping plate (5). Each fork is located near the bottom of the valley (32); a second guide means; and-a rotary cutter.

Description

Technical Field

[0001] This invention relates to the field of chopped strand mat technology, and more particularly to a system and method for producing chopped strands containing discontinuous fibers, the chopped strands being suitable for manufacturing chopped strand mat. Background Technology

[0002] As is well known, fiber-reinforced composites are the optimal choice for producing certain products requiring specific properties in specific areas. For example, for certain applications, such as the rear deck of a motor vehicle, a high flexural modulus and tensile modulus are desired in the final composite. The final composite should be as lightweight as possible, thus having a low density. Advantageously, the final composite should be as homogeneous as possible (symmetry of properties), which directly depends on the homogeneity of the initial fiber structure. The production of fiber-reinforced composites involves molding a fiber structure, such as felt, in a mold and then injecting a polymer-based resin to impregnate the structure. The resin is then cured by crosslinking or cooling, depending on whether it is thermosetting or thermoplastic. Therefore, the fiber structure must exhibit a range of properties. In particular, it must have good plasticity before impregnation, i.e., it must be easy to mold, thus easily deformed by hand without forming wrinkles. It is also desired that the structure has shape memory, i.e., retains the shape assigned to it, for example, by hand, and deforms as little as possible under its own weight. For a given unit area mass, the fiber structure must also be as permeable to the impregnating resin as possible and reinforce the final material as much as possible.

[0003] Chopped strand mat (CSM) is a fiber-reinforced composite material made from randomly laid-out chopped glass fiber filaments held together by adhesives or stitching, typically 2-5 cm in length. Compared to other composites, CSM offers advantages in its strength-to-weight ratio, specific stiffness, and uniform load distribution across its surface in all directions. CSM can be used between woven fabric layers to help rapidly increase thickness and facilitates good adhesion between all layers.

[0004] It is desirable to replace glass fiber with other fibers that have better mechanical properties, are more recyclable, are cheaper, or have lower carbon emissions in CSM.

[0005] Some of these new materials are discontinuous fibers, such as natural fibers. However, producing randomly distributed CSMs using discontinuous fibers presents several technical challenges.

[0006] One challenge is reducing the yarn weight of discontinuous fibers to 30-40 tex, a size that facilitates the production of uniform yet still permeable felt. Typically, discontinuous fibers, such as flax, cannot form stable yarns below 300 tex.

[0007] Patent document EP1478797 relates to a composite material comprising a fiber structure, the fiber structure comprising a felt. The felt comprises a homogeneous mixture of discontinuous glass fibers and discontinuous natural fibers, and a matrix comprising a thermosetting resin, the material being obtained after impregnating the fiber structure with the thermosetting resin. The disclosed invention also relates to a method of manufacturing the material, comprising molding the fiber structure in a mold and then impregnating the fiber structure with a thermosetting resin.

[0008] The composite material disclosed in EP1478797 is a felt comprising discontinuous natural fibers and discontinuous glass fibers, wherein the length of the natural fibers is less than 150 cm, while the length of the glass fibers is between 10 and 200 mm. The natural fibers are separated and combed, followed by needle punching; in other words, the resulting felt will have fibers arranged in the same direction. This is undesirable because the property of uniformly distributing loads in all directions is lost. Another technical challenge is to randomly distribute the chopped discontinuous fibers on a given surface, as discontinuous filaments tend to clump together.

[0009] Patent documents JP2022149483, EP3578711, ES2870850, JP6774651 and ES2884306 teach different methods and materials related to the production of randomly oriented chopped strand mats using discontinuous reinforcing fiber assemblies and matrix resins.

[0010] Patent documents EP3719078, EP2808433, EP2808432, EP2810979 and ES2539902 teach novel composite materials using randomly distributed carbon fiber bundles and methods for their manufacture.

[0011] The goal is to find new manufacturing methods that allow the use of new materials, particularly discontinuous fibers, to produce chopped strand mats. Summary of the Invention

[0012] In search of alternatives to known solutions, claim 1 discloses a system for producing chopped strands suitable for manufacturing chopped strand mats. The chopped strands to be produced can be made of discontinuous fibers (such as flax fibers) or continuous fibers (such as glass fibers and carbon fibers).

[0013] The system is characterized by including: - A first guiding device, configured to receive a strip of fiber and orient it in a vertical position; - A pair of opposing fiber distribution rollers having parallel horizontal axes, the rollers being arranged abutting each other in a tangential region between them and being rotatable in opposite directions along their axes, wherein the first roller of the fiber distribution roller is a slotted roller having a circumferentially slotted profile surface consisting of alternating circumferential peaks and valleys, the second roller of the fiber distribution roller having a smooth surface that contacts the peaks of the profile surface of the first roller in the tangential region, the space between the valleys and the smooth surface in the tangential region being configured to accommodate portions of a ribbon-like filament made of fibers, wherein a first guide device is positioned above the tangential region, and at least one of the fiber distribution rollers is connected to an electric motor; - A scraper is positioned at a certain distance below the tangential region between the fiber distribution rollers. The scraper has a plurality of vertical teeth at its top end, wherein each tooth is located in a corresponding valley of the grooved contour surface of the first roller of the fiber distribution roller, and the tooth is closer to the bottom of the valley than the peak. - A second guide device, arranged beside the scraper, forming a vertical channel below the top of the scraper; and - A rotary cutter is positioned at the lower end of the vertical channel of the second guide device.

[0014] It should be noted that the ribbon-like filaments made of fibers are formed by flattening and spreading the fibers to create a ribbon-like structure, which has a cross-section that is wider than its thickness.

[0015] The fiber distribution roller distributes and divides the fiber material by compacting the fibrous material of the ribbon filament into the valley of the first roller, producing a corresponding set of ribbon filament portions. Since these portions tend to remain embedded in the valley due to the nature of the fibers, a scraper separates the portions, resulting in a set of filaments. The lower ends of these filaments are then driven and / or pulled to a rotary cutter to cut each filament into shorter filaments, referred to as chopped filaments.

[0016] According to another feature of the system of the invention, the vertical distance between the tangential region (or the closest point between the fiber distribution rollers) between the top of the scraper and the fiber distribution roller is between 2 mm and 10 mm. Preferably, the vertical distance is about 8 mm.

[0017] According to a particular embodiment of the system, the vertical distance between the tangential region (the closest point between the rollers) between the top of the scraper and the fiber distribution roller is between 2 and 6 times the thickness of the chopped filament to be produced by the system.

[0018] According to a preferred embodiment, the distance between the edge of the peak and the bottom of the valley of the grooved contour surface is between 0.8 and 2.0 times the distance between two consecutive peaks, preferably 1.0 times.

[0019] Preferably, the first and second rollers of the fiber distribution rollers have equal diameters. The rollers are arranged to abut against each other with contact pressure in the tangential region. The first roller is connected to a motor, and the second roller rotates due to contact with the rotating first roller.

[0020] The grooved contour surface of the first roller of the fiber distribution roller is preferably made of a hardened metal material, while the smooth surface is made of a hardened metal material, rubber, or plastic material. When processing flax fibers, the smooth surface is made of a hardened metal material; when processing carbon fibers, the smooth surface is made of rubber with a hardness of 80-100 Shore A; when processing recycled glass fibers, the smooth surface is made of rubber with a hardness of 75-80 Shore A. The scraper is preferably made of iron or steel.

[0021] According to another preferred embodiment, the first roller of the fiber distribution roller is provided with an air circulation device and / or an air cooling device.

[0022] The rotary cutter of the preferred embodiment of the system includes two cutting surfaces, wherein the first cutting surface is a holding surface and the second cutting surface is a cutting blade arranged in a plane perpendicular to the tangential region between the rollers. Thus, the cutting blade cuts, according to the horizontal cutting plane, the filament removed by a scraper from the valley of the grooved contour surface of the first roller of the fiber distribution roller, the filament being made from a portion of a strip-shaped filament placed within the valley and subjected to pressure.

[0023] Preferably, the first cutting surface is a fixed serrated or slotted surface, and the cutting blade of the second cutting surface is capable of rotating around a cutter rotation axis that is parallel to the tangential region between the fiber distribution rollers and perpendicular to the roller rotation axis.

[0024] More preferably, the first cutting surface is configured as a vertical channel with a through-hole having a transverse cross-section of an elliptical arc or a bean shape, the wall of the through-hole having a retaining device to retain one or more portions of a ribbon-like filament made of fiber. The retaining device provided on the wall of the through-hole is a slotted surface with teeth provided along the inner circumference of the through-hole.

[0025] Furthermore, in a preferred embodiment of the system, the rotary cutter has a plurality of second cutting surfaces arranged radially relative to the cutter's rotation axis.

[0026] According to a preferred embodiment of the system, it further includes a traction device below the rotary cutter, which is in the form of two opposing traction rollers with their axes parallel to the axis of the fiber distribution roller. The traction rollers are arranged abutting against each other and are rotatable in opposite directions along their axes. The traction device pulls the filament before it is cut by the rotary cutter, and once cut into chopped filaments, it throws the chopped filaments out in a uniform manner, so that they are correctly and randomly distributed on the surface to produce chopped filament mat.

[0027] Each of the two traction rollers has a slotted profile surface. The slotted profile surface is configured with grooves forming finger threads or round threads. In this way, the filaments generated by the distribution of the ribbon filaments in the fiber distribution roller remain separated and do not re-merge as they would in the ribbon filaments.

[0028] A preferred embodiment of the system takes into account that the surface roughness of the drawing roller is very low, i.e., its Ra is approximately between 0.2 and 0.3. This avoids the raw yarn getting embedded in the drawing roller, thus eliminating the need for a scraper.

[0029] The pressure between the traction rollers is very low because it is undesirable for the fibers to be compacted. The preferred distance between the surfaces of the traction rollers is between 0.05 and 0.1 mm.

[0030] Regarding a second aspect of the invention, a method for producing chopped strands suitable for manufacturing chopped strand mats from fibers is disclosed. The method of the invention is characterized by comprising the following steps: a) Provide ribbon-like precursor fibers made of discontinuous fibers; b) Orient the ribbon-shaped precursor fiber in a vertical position; c) The oriented ribbon filament is introduced between a pair of opposing fiber distribution rollers having parallel horizontal axes, the width of the ribbon filament extending along the axial direction of the fiber distribution rollers, the rollers being arranged abutting each other in a tangential region between them and being rotatable in opposite directions along their axes, wherein the first roller of the fiber distribution roller is a slotted roller having a circumferentially slotted profile surface composed of alternating circumferential peaks and valleys, and the second roller of the fiber distribution roller has a smooth surface that contacts the peaks of the profile surface of the first roller along the tangential region, wherein when the ribbon filament is driven downward through the space between the fiber distribution rollers, the space between the valleys and the smooth surface in the tangential region is configured to accommodate a portion of the ribbon filament, wherein at least one roller is connected to a motor; d) Remove a portion of the ribbon-like filament contained at the bottom of the valley as the roller rotates using a scraper, separating it from the first roller; the removed portion constitutes the filament. e) Guiding the precursor fiber through a vertical channel below the top of the scraper; and f) Cut the raw filament with a rotary cutter located at the lower end of the vertical channel to obtain chopped raw filament.

[0031] According to a preferred variant of the method, before the filament is cut, the lower part of the filament passes through a rotary cutter and is pulled downward by a pulling device, which takes the form of two opposing pulling rollers with their axes parallel to the axis of the fiber distribution roller. The pulling rollers are arranged abutting each other and are rotatable in opposite directions along their axes, wherein each of the two pulling rollers has a slotted profiled surface. The pulling rollers are those disclosed above with respect to the system for the purposes of this invention.

[0032] Preferably, the width of the ribbon filament is between 0.5 cm and 8.0 cm, and the thickness is between 0.12 mm and 2.0 mm. The ribbon filament can be made of natural discontinuous or continuous fibers. For example, the method of the present invention has been implemented starting with a flax fiber ribbon filament with a width of 2.5 cm and a thickness of 0.3 mm, and also with a carbon fiber ribbon filament with a width of 1.0 cm and a thickness of 0.15 mm.

[0033] The method of the present invention is implemented by a system previously disclosed according to the first aspect of the present invention.

[0034] Regarding a third aspect of the invention, a chopped filament made of fiber is disclosed, characterized in that it can be obtained by the method according to a second aspect of the invention.

[0035] The resulting chopped filament fibers are 30 to 40 tex, flat, without twist or crimp, and preferably about 50 mm in length.

[0036] The fourth aspect of the invention relates to a chopped strand mat made of fibers, characterized in that it comprises chopped strands obtained by the method according to the second aspect of the invention, or the chopped strands can be obtained by the method according to the second aspect of the invention.

[0037] A preferred chopped strand mat made of fibers according to a fourth aspect of the invention comprises chopped strands made of flax fibers, chopped strands made of carbon fibers, and chopped strands made of glass fibers.

[0038] Brief description of the attached figures In the accompanying drawings, preferred embodiments of the system, method, and chopped strand mat to which the invention is subject are illustrated by way of non-limiting example. In the drawings: Figure 1 This is a schematic diagram showing a strip of raw filament made of discontinuous fibers being introduced between a first slotted roller and a second smooth roller of a fiber distribution roller; Figure 2 This is a schematic diagram showing how a scraper removes a portion of the strip-shaped filament contained in the valley of the first grooved roller of the fiber distribution roller to form a filament; Figure 3This is a schematic diagram showing how the fiber filaments are pulled by the traction rollers and then cut into short filaments by the rotary cutter; Figure 4 This is a perspective view showing a preferred embodiment of the system according to the invention (but the traction roller is not shown). Figure 5 yes Figure 4 A sectional view of the system along the vertical direction; Figure 6 This is a side view showing a preferred embodiment of the first roller of the fiber distribution roller, the scraper, and the second guide device; Figure 7 This is a schematic diagram showing details of the tangential region between the peaks and valleys of the slotted surface of the first fiber distribution roller and the smooth surface of the second fiber distribution roller. Figure 8 It is a perspective view showing details of the peaks and valleys of the grooving roller and the scraper tooth fork; Figure 9 This is a partial bottom view, showing... Figure 4 A preferred embodiment of the rotary cutter of the system; Figure 10 A photograph shows a strip of flax fiber wound on a bobbin; Figure 11 A photograph is shown of a chopped flax fiber mat made from chopped flax fibers produced according to the present invention; Figure 12 A photograph is shown of a chopped strand mat made of flax fibers and glass fibers according to the present invention; Figure 13 Photographs of chopped flax fibers, chopped carbon fibers, and chopped glass fibers produced according to the present invention are shown; and Figure 14 This is a stress-strain curve of a chopped flax fiber felt sample. Detailed Implementation

[0039] Figure 4 and Figure 5 A system 100 for producing chopped strands 10 is described, for example, producing chopped strands suitable for manufacturing chopped strand mats from discontinuous fibers. Although the following description refers to chopped strands 10 made of discontinuous fibers, the system 100 is also capable of producing chopped strands 10 from continuous fibers such as glass fibers and carbon fibers.

[0040] System 100 includes: - First guiding device 2, configured to receive a strip of raw filament 11 made of discontinuous fibers and orient it in a vertical position; - A pair of opposing fiber distribution rollers 3,4 with parallel horizontal axes, arranged abutting each other and rotatable in opposite directions along their axes; - The scraper 5 is positioned at a certain distance below the nearest point between the fiber distribution rollers 3 and 4, that is, below the tangential area between the rollers 3 and 4 but closer to the first roller 3; - A second guide device 6 is arranged beside the scraper 5, forming a vertical channel 61 below the top of the scraper 5; and - The rotary cutter 7 is arranged at the lower end of the vertical channel 61 of the second guide device 6.

[0041] Regarding the fiber distribution rollers 3 and 4, they are arranged abutting each other in the tangential region between them and are rotatable in opposite directions along their axes as previously described. Figure 6 As shown, the first roller 3 is a slotted roller, having a circumferentially slotted profile surface 3' composed of alternating circumferential peaks 31 and valleys 32 (see Figure 3). Figure 7 The second roller 4 has a smooth surface 4' opposite the peak 31 of the profile surface of the first roller 3. The space between the valley 32 and the smooth surface 4' in the tangential region between the fiber distribution rollers 3 and 4 is configured to accommodate a portion of a ribbon filament 11 made of, for example, discontinuous fibers (see...). Figure 10 The first roller 3 is connected to a motor, and the second roller 4 rotates by contacting the first roller 3 in the tangential region. The fiber distribution rollers 3 and 4 rotate at the same speed.

[0042] The area and size of the peaks 31 and valleys 32 of the first roller 3 are suitable for dividing the ribbon filament 11 into portions 11' and accommodating them within the space formed between the valleys 32 and the smooth surface 4'. In other words, the ribbon filament 11 is divided and distributed into portions 11' by the peaks 31 and the smooth surface 4', and the fibrous material of each portion is accumulated and compacted by the smooth surface within the valleys 32. The number, area, shape, and depth of the valleys 32 will depend on the material, thickness, and fiber density of the initial ribbon filament 11 used. The ribbon filament may not be used from the beginning, but it should undergo a widening process. Suitably, the ribbon filament 11 should not be wider than the grooved profile surface 3' of the first roller 3.

[0043] Figure 7 An example of the grooved profile surface 3' of the first roller 3 is shown, specifically for processing flax fiber ribbon filaments 11. The distance between two consecutive peaks 33 is approximately 0.8 mm, and the peaks 33 have a generally triangular shape with a top plane between 0.1 and 0.2 mm. The bottom of the valley 32 preferably has a radius of 0.3 mm and a side angle of approximately 60°.

[0044] For the manufacture of the first and second rolls 3,4, the starting point is a heat-treated steel cylinder with a hardness of 65 HrC. The cylinder of the first roll 3 is then machined to create valleys 32 and peaks 33. In addition, a series of holes are drilled from front to back to allow coolant to circulate through the interior of the first roll 3.

[0045] The first guide device 2 is positioned above the tangential region between rollers 3 and 4. Figure 4 and Figure 5 In the middle, the first guide device 2 is made of two flat rectangular plates arranged in a V shape, with its lower end bent to form a vertical channel.

[0046] Regarding scraper 5 Figure 8 The top of the roller 3 is shown to have a plurality of vertical toothed forks 51. Each toothed fork 51 is located in a corresponding valley 32 of the grooved contour surface of the first roller 3, and the toothed fork 51 is closer to the bottom of the valley 32 than the peak 31.

[0047] The vertical distance between the top of the scraper 5 and the tangential region between the rollers 3 and 4 is between 2 and 10 mm. This vertical distance depends on various factors, such as the nature of the discontinuous fiber, its "adhesion" to the valley 32, the fiber density of the ribbon filament 11, or its bending resistance. For example, when producing chopped strands 10 from flax fibers, the vertical distance is preferably about 8 mm.

[0048] On the other hand, the vertical distance between the top of the scraper 5 and the tangential area between the fiber distribution rollers 3 and 4 (i.e. the closest point between the rollers 3 and 4) can also be selected as 2 to 6 times the thickness of the chopped filaments to be produced by the system 100.

[0049] Regarding the rotary cutter 7, Figure 9 The image is described in detail, including a first cutting surface 71 and a plurality of second cutting surfaces 72. In this example, there are five second cutting surfaces 72, which are cutting blades arranged in a plane perpendicular to the tangential region between rollers 3 and 4. The blades of the second cutting surfaces 72 are arranged radially relative to the cutter rotation axis 7' and rotate about this axis.

[0050] The first cutting surface 71 is a serrated or slotted vertical surface fixed to the frame of the system 100. In practice, the first cutting surface 71 is configured as a vertical channel for a through-hole, which is opened in a plate below the vertical channel 61 of the second guide device 6 of the system 100. The transverse cross-section of the through-hole has an elliptical arc or bean shape. The through-hole wall has retaining devices for retaining one or more portions of the strip-shaped filament 11 made of fibers removed by the scraper 5 from the valley 32 of the first roller 3. The retaining devices are teeth or grooves forming the serrated or slotted surface arranged along the inner circumference of the through-hole.

[0051] exist Figure 3As can be seen, below the rotary cutter 7 is a traction device, which takes the form of two opposing traction rollers 9, whose axes are parallel to the axes of the fiber distribution rollers 3 and 4. The traction rollers 9 are arranged abutting against each other and are rotatable in opposite directions along their axes. Each of the two traction rollers 9 has a grooved profile surface configured with grooves forming finger threads or round threads. The surfaces of the traction rollers 9 have a very low surface roughness, i.e., their Ra is approximately between 0.2 and 0.3. The pressure between the traction rollers 9 is very low because it is undesirable for the fibers to be compacted. The preferred distance between the surfaces of the traction rollers is between 0.05 and 0.1 mm.

[0052] Before being cut by the rotary cutter 7, the lower part of the filament 12 passes through the first cutting surface 71 and is pulled downwards by two opposing traction rollers 9. Then, while being pulled downwards, the filament 12 is cut into chopped filaments 10 by the second cutting surface 72. The circular threads on the surface of the traction rollers 9 prevent the filaments 12, which have become separated after passing through the fiber distribution rollers 3, 4 and the scraper 5, from re-merging or joining, which would otherwise affect the distribution of the chopped filaments 10 in the felt. The low surface roughness of the traction rollers 9 prevents the filaments 10 from embedding into the traction rollers 9, thus eliminating the need for an additional scraper.

[0053] When the raw filaments 12 pass through the vertical channel 61 of the second guide device 6, they reach the through-hole of the first cutting surface 71, which has a bean-shaped or elliptical arc shape. The through-hole has vertical walls with a serrated or slotted surface. Figure 9 As shown, the groove extends vertically, but the wall may have another holding device. When the lower end of the filament 12 passes through the through hole and is pulled by the traction roller 9, one of the cutting blades of the rotating second cutting surface 72 will cut the filament 12. The cutting will be performed cleanly because the filament 12 will not slip or tend to slip due to the movement of the cutting surface 72, because the slotted surface of the through hole wall of the first cutting surface 71 holds the filament 12 in one position until they encounter the cutting blade, and because the lower end of the filament 12 is pulled by the traction roller 9.

[0054] A second cutting surface 72 can be added to the body of the rotary cutter 7. The arc length of the circular trajectory between two consecutive second cutting surfaces 72 and the rotational speed of the rotary cutter 7 determine the length of the chopped filament 11. Different lengths of chopped filament 11 can even be obtained using the same rotary cutter 7 by separating two consecutive second cutting surfaces 72 with a shorter distance and separating another two consecutive second cutting surfaces 72 with a longer distance.

[0055] Once the filament 12 is cut, the traction roller 9 projects the chopped filament 10 out in a random direction to form a projection cone, depositing the chopped filament 10 in a region in a Gaussian manner.

[0056] In one particular embodiment, the length of the chopped filament 10, i.e. the distance at which the filament 12 is cut, is similar to the length of the discontinuous fibers constituting the filament 12.

[0057] The disclosed system 100 is one of the methods for implementing a method for producing chopped strands 10 suitable for manufacturing chopped strand mats from discontinuous fibers. This method also allows for obtaining chopped strands 10 of continuous fibers. The method includes the following steps.

[0058] Step a) involves providing a ribbon-like filament 11 made of discontinuous fibers. When using conventional filaments, a broadening preparation step can be performed. The thickness of the ribbon-like filament 11 depends on the available free area between the peaks 31 and valleys 32 of the grooved profile of the first roller 3 and the smooth surface 4' of the second roller 4, so that it can be completely separated and contained. Specifically, the following ribbon-like filaments 11 having the characteristics shown in Table 1 have been tested: Table 1 At the end of the method, the length of the chopped raw fibers 10 obtained from these ribbon-like raw fibers was approximately 50 mm (e.g., Figure 13 (As shown).

[0059] In step b), the strip material stored in spool form is unwound and conveyed to the first guide device 2, which orients the strip filament 11 toward the tangential region formed between the slotted profile surface 3' of the first roller 3 and the smooth surface 4' of the second roller 4. The width of the strip filament 11 must be in the axial direction of the rollers 3 and 4.

[0060] Then, in step c), the ribbon material filament 11 is introduced between a pair of opposing fiber distribution rollers 3, 4. Driven by the opposite rotation of the rollers 3, 4, the ribbon filament 11 moves downward, passing between the peak 31 and valley 32 of the grooved profile surface 3' of the first roller 3 and the smooth surface 4' of the second roller 4, and is divided and accommodated in the valley 32 of the grooved profile of the first roller 3 to form a portion 11' of the ribbon filament 11.

[0061] In step d), a portion 11' of the strip filament 11 is removed from the valley 32 of the first roller 3 using a scraper 5. The removed portion 11' will be referred to as filament 12 (see...). Figure 2 ).

[0062] Next, in step e), the raw filament 12 is conveyed by the second guide device 6, which forms a vertical channel 61 to prevent the raw filament 12 from tangling and guide it to the cutting device.

[0063] Then, in step f), the raw filament 12 pulled downward by the traction roller 9 is cut according to a cutting plane perpendicular to the length of the raw filament 12, and the resulting chopped raw filament 10 comes out of the traction roller 9 (see...). Figure 3 The filaments are dispersed in random directions without crossing, forming a projection cone, and short chopped protofilaments are deposited in a Gaussian manner.

[0064] As the chopped filaments 10 are cut from their respective filaments 12 by the rotary cutter 7 and pulled by the traction roller 9, they are ejected in random directions. Due to gravity, the chopped filaments 10 fall and are evenly distributed on a suitable support layer, such as a acrylic layer or a textile layer, for the production of... Figure 11 The chopped filament felt shown.

[0065] The reason for including the traction roller 9 is that the chopped filament 10 lacks weight after the filament 12 is cut. Because the fiber material is so light, the filament 12 may get stuck anywhere in the system 100 once it has been cut and processed, as the sum of gravity and mass makes them too light to fall with sufficient stability and may not be able to overcome any small blockages caused by a single fiber.

[0066] Therefore, a pull roller 9 is provided to help discharge the chopped filament 10. Thus, the pull roller 9 has two functions: to help the filament 12 achieve a better cutting effect and to conveniently eject the chopped filament 10.

[0067] Typically, the support layer advances on a conveyor or any other transport device located below the rotary cutter 7, and the chopped filaments 10 are uniformly deposited on the support layer. Alternatively, the chopped filaments 10 are uniformly deposited on the substrate, but oriented in multiple different directions simply to allow them to deposit on the support. In a subsequent stage, at the end of the conveyor, the chopped filaments 10 are stitched together several times to maintain their distribution and are then impregnated with resin. The stitches 90 pass through the thickness of the deposited chopped filaments 10. Figure 11 and Figure 12 The zigzag stitches 90 can be seen, securing flax chopped strands 10a and glass fiber chopped strands 10b together, or securing flax chopped strands 10a together without glass fiber chopped strands 10b. Other strands, such as carbon fiber chopped strands 10c (see...), are also present. Figure 13 They can also be combined. Stitching is a known procedure in the production of chopped fiber mat. It is very convenient that, by performing the procedure disclosed in the above-described reference system 100, chopped fibers 10 produced from discontinuous fibers or other types of fibers can be processed like other chopped fibers to produce chopped fiber mat.

[0068] Controlling the distance (height) between the rotary cutter 7 and the upper layer or support of the conveyor via a control device is convenient because if the fibers are heavy, such as carbon fiber, a greater distance must be allowed to allow the fibers to further open the Gaussian bell curve. In the case of flax fibers, due to their lightness, a smaller distance (height) is required because beyond a certain distance, they no longer exhibit controllable behavior; their low weight causes them to slow down during descent, and they may fall like feathers rather than with the inertia transmitted when the rotary cutter 7 cuts the filament 12.

[0069] Example 1: Manufacturing of chopped flax fibers The following describes a specific embodiment particularly suitable for manufacturing chopped filaments 10 made from flax fibers.

[0070] As the source material, flax fiber ribbon filaments 11 from GOTAX were used. The flax fiber ribbon filaments 11 listed in Table 1 are used in the aforementioned system 100. See also... Figure 10 The ribbon-like protofilament 11 in the middle.

[0071] Flax fiber ribbon filament 11 is unwound in the form of a spool and fed into a first guide device 2, which guides the ribbon filament 11 to a pair of opposing fiber distribution rollers 3, 4.

[0072] When the flax fiber ribbon 11 is inserted between the two fiber distribution rollers 3 and 4, it is segmented by occupying the space between the valley 32 of the first roller 3 and the smooth surface 4' at the height of the tangential region. The fiber density, thickness, and dimensions of the flax fiber ribbon 11 used are proven suitable for being segmented and contained by the rollers 3 and 4, avoiding clogging and overheating. On the other hand, the area and dimensions of the valley 32 of the first roller 3 are proven suitable for containing a portion of the flax fiber ribbon 11, which is then compacted to form a portion 11' of the ribbon 11, transforming it into a flax fiber filament 12 of approximately 30-40 tex.

[0073] Once portions 11' of the flax fiber filaments pass through the tangential region of the fiber distribution rollers 3,4, they tend to detach from the first roller 3 and leave the valley 32 due to their resistance to the bending force exerted by the rotation of the first roller 3. This detachment is facilitated by a scraper 5 with a toothed fork 51, which removes any remaining portions 11' of the flax fiber filaments from the valley 32. The distance between the scraper toothed fork 51 and the tangential region of the fiber distribution rollers 3,4 is approximately 8 mm. This distance is calculated taking into account the maximum bending resistance point of the flax fiber portions 11' to achieve detachment in the gentlest possible manner.

[0074] Once portions 11' of the flax fiber filaments leave the fiber distribution rollers 3,4, they are conveyed by the second guide device 6, which forms a vertical channel 61 to prevent the flax fiber filaments 12 from rewinding. Figure 9 The cutting device is of the form of a rotary cutter 7, as described above.

[0075] Before cutting, a portion of the flax fiber filament extends 50 mm from the cut point, and after passing through the traction roller 9, it forms a short flax fiber filament 10 with a length of about 50 mm and a linear density of 93 g / km.

[0076] The specific configuration of the drawing roller 9 allows the chopped flax fiber filaments 10 to be projected in random directions without crossing, forming a projection cone that deposits the chopped flax fiber filaments 10a in a Gaussian manner at 195 g / m². 2 On acrylic textiles, as described below.

[0077] Example 2: Manufacturing of chopped carbon fiber precursors Similar to Example 1, starting from the carbon fiber ribbon precursor 11 in Table 1, using the same system 100 and performing the same steps as described in Example 1, carbon fiber chopped precursor 10c was manufactured (see Example 1). Figure 13 ).

[0078] The obtained carbon fiber chopped precursor fiber 10c has a length of approximately 50 mm and a linear density of 135 g / km.

[0079] Example 3: Manufacturing of chopped strand mat Multiple chopped filament mats were manufactured using flax chopped filament 10a obtained in Example 1 and carbon fiber chopped filament 10c obtained in Example 2. The flax chopped filament 10a and carbon fiber chopped filament 10c were drawn by a traction roller 9 and deposited in a Gaussian manner onto a support layer of acrylic textile.

[0080] Some chopped strand mats also contain glass fiber chopped strands 10b with a linear density of 40 g / km, but in this case, the glass fiber chopped strands 10b are not produced from ribbon strands 11, nor are they cut and dispersed using components of system 100, because glass fibers do not have the same problems as discontinuous fibers, and they can be produced by known methods and systems belonging to the prior art.

[0081] Regardless of the material, once the chopped strands 10a, 10b, and 10c are randomly and uniformly deposited onto the acrylic textile, they are impregnated with resin. Specifically, the resin used is commercially available under the trade name DISTRITON® 429 v1,2 from Polynt Composites. This resin is an unsaturated polyester resin in styrene, belonging to the phthalic acid type. The properties of the liquid resin and the properties of the unreinforced resin after curing are shown in Tables 2 and 3 below, respectively.

[0082] Table 2 Table 3 Table 4 below describes the density and composition of seven different types of chopped strand mats, which constitute the types of subsequent test samples.

[0083] Table 4 Twenty-one days after resin impregnation, the chopped flax mat was tested. Examples of chopped flax mats made from chopped flax fibers, based on FLL reference in Table 4, are shown below. Figure 11 As shown.

[0084] Tensile test The purpose of these tests is to determine the stress-strain curves of material samples in order to compare their structural responses under pure tensile testing.

[0085] Thirty-five specimens (flat rectangular specimens) were tested, with five different specimens of each type tested according to Table 4. The nominal width of the specimens was 20 mm. The thickness of the specimens varied.

[0086] The following tests were conducted in July 2023 by a laboratory called LERMA (Laboratory of Elasticity and Material Strength), which was founded in 1970 by the Department of Elasticity and Material Strength of ETSEIB (Industrial Engineering Institute of Barcelona) affiliated with UPC (Polytechnic University of Catalonia).

[0087] The main characteristics of these tests are as follows: • Test speed: 5 mm / min.

[0088] • All tensile tests were performed using the Instron 3366 (universal testing machine).

[0089] • Fixture spacing: 60 mm.

[0090] • Strain is measured using an extensometer.

[0091] The operation method is as follows: • Measure all relevant dimensions for each specimen.

[0092] • Zero the sensor before each test.

[0093] • A gradual displacement is applied during the test. The force is measured using a 10kN force sensor. The displacement is measured using an extensometer located at the specimen.

[0094] • Record the stress-strain curve until the initial crack appears. However, the test continues (without using the strain values ​​measured by the extensometer) until the maximum axial load is reached.

[0095] • Some recommendations defined in ASTM D634-14 were used for experimental testing and material parameter calculations. However, these experimental tests did not meet all the requirements of ASTM D634-14, such as the shape of the tensile specimen.

[0096] The tensile strength has been calculated using Formula 1.

[0097] (Formula 1) σ max = F max / A 0 F max Maximum axial load.

[0098] A 0: Original cross-sectional area.

[0099] The elastic modulus (E) is calculated as the slope of the initial linear portion of the stress-strain curve for each sample.

[0100] Tensile testing of FLL samples Table 5 provides the width and thickness of the five tested FLL (chopped flax fiber mat) samples, as well as their tensile strength and modulus of elasticity.

[0101] Table 5 Figure 14 The stress-strain curves for each FLL sample up to the first crack initiation are shown. The values ​​for tensile strength and elastic modulus can be found in Table 6. Tensile strength can be obtained after the initial crack initiation (when extensometer measurements are invalid due to the cracking process); therefore, the tensile strength may be higher than [previous values]. Figure 14 The maximum stress in.

[0102] Tensile test of FC sample Table 6 provides the width and thickness of the five tested FC samples (carbon fiber chopped strand mat samples), along with their tensile strength and modulus of elasticity. Tensile strength was obtained after the initial crack appeared (when extensometer measurements were invalid due to the cracking process).

[0103] Table 6 Tensile testing of FV samples Table 7 provides the width and thickness of the five tested FV samples (glass fiber chopped strand mat samples), along with their tensile strength and modulus of elasticity. Tensile strength was obtained after the initial cracking (when extensometer measurements are invalid due to the cracking process).

[0104] Table 7 Tensile testing of chopped strand mat samples made from a combination of glass fiber, carbon fiber, and / or flax fiber Table 8 provides the width and thickness of five tested FLL+FV samples (chopped strand mat samples of flax fiber (50% by weight) + glass fiber (50% by weight)).

[0105] Table 8 Table 9 provides the width and thickness of five tested FLL+FC samples (flax fiber (83% by weight) + carbon fiber (17% by weight) chopped strand mat samples).

[0106] Table 9 Table 10 provides the width and thickness of five tested FV+FC samples (chopped strand mat samples of glass fiber (83% by weight) + carbon fiber (17% by weight)). The HT2 values ​​of the samples were highly outlier and were therefore ignored when calculating the mean and standard deviation.

[0107] Table 10 Table 11 provides the width and thickness of five tested FLL+FV+FC samples (chopped strand mat samples of flax fiber (41% by weight) + glass fiber (41% by weight) + carbon fiber (18% by weight)).

[0108] Table 11 Any combination containing flax appears to outperform any combination using mineral fibers alone. The combination of natural and mineral fibers results in superior performance compared to the lower performance of single-type samples; the blend creates a multiplier effect. Although the material cost may be higher when using flax fibers, the superior performance makes for a better price-to-mechanical-performance ratio. Furthermore, the combination of glass fiber and flax fibers means lower emissions during transport and use, as well as a lower carbon footprint, making this an attractive option not only for the environment but also for cost.

Claims

1. A system (100) for producing chopped filaments (10) suitable for manufacturing chopped filament mats, characterized in that... include: - A first guiding device (2) is configured to receive a strip of fiber filament (11) and orient it in a vertical position; - A pair of opposing fiber distribution rollers (3,4) with parallel horizontal axes, the fiber distribution rollers are arranged abutting each other in a tangential region between them and are rotatable in opposite directions along their axes, wherein the first roller (3) of the fiber distribution roller is a slotted roller with a circumferentially slotted profile surface (3') consisting of alternating circumferential peaks (31) and valleys (32), the second roller (4) of the fiber distribution roller has a smooth surface (4') that contacts the peaks (31) of the slotted profile surface (3') of the first roller (3) in the tangential region, the space between the valleys (32) and the smooth surface (4') in the tangential region is configured to accommodate portions (11') of a ribbon filament (11) made of fiber, wherein a first guide device (2) is positioned above the tangential region, and at least one of the fiber distribution rollers (3,4) is connected to an electric motor; - A scraper (5) is placed at a certain distance below the tangential region between the fiber distribution rollers (3,4). The scraper (5) has a plurality of vertical toothed forks (51) at its top end, wherein each toothed fork (51) is located in the corresponding valley (32) of the grooved contour surface (3') of the first roller (3). The toothed fork (51) is closer to the bottom of the valley than the peak (31). - A second guide device (6) is arranged beside the scraper (5), forming a vertical channel (61) below the top of the scraper (5); and - A rotary cutter (7) is arranged at the lower end of the vertical channel (61) of the second guide device (6).

2. The system (100) according to claim 1, characterized in that, The vertical distance between the top of the scraper (5) and the tangential region between the fiber distribution rollers (3,4) is between 2 and 10 mm.

3. The system (100) according to claim 1, characterized in that, The vertical distance between the top of the scraper (5) and the tangential region between the fiber distribution rollers (3,4) is between 2 and 6 times the thickness of the chopped filaments (10) to be produced by the system (100).

4. The system (100) according to any of the preceding claims, characterized in that, The first roller (3) and the second roller (4) of the fiber distribution roller have the same diameter.

5. The system (100) according to any of the preceding claims, characterized in that, The rotary cutter (7) includes two cutting surfaces (71, 72), wherein the first cutting surface (71) is a holding surface and the second cutting surface (72) is a cutting blade arranged in a plane perpendicular to the tangential region between the fiber distribution rollers (3, 4).

6. The system (100) according to claim 5, characterized in that, The first cutting surface (71) is a fixed surface, and the cutting blade of the second cutting surface (72) can rotate around the cutter rotation axis (7') which is parallel to the tangential region between the fiber distribution rollers (3,4) and perpendicular to the rotation axis of the rollers (3,4).

7. The system (100) according to claim 6, characterized in that, The first cutting surface (71) is configured as a vertical channel with a through hole having a transverse cross section of elliptical arc or bean shape, the wall of the through hole having a retaining device to retain one or more portions of a strip filament (11) made of fiber.

8. The system (100) according to claim 7, characterized in that, The retaining device provided on the wall of the through hole is a slotted surface with grooves or teeth along the inner circumference of the through hole.

9. The system (100) according to any one of claims 5 to 8, characterized in that, The rotary cutter (7) has a plurality of second cutting surfaces (72) arranged radially relative to the cutter rotation axis (7').

10. The system (100) according to any of the preceding claims, characterized in that, The fiber distribution rollers (3,4) are arranged to abut against each other with contact pressure in the tangential region.

11. The system (100) according to any of the preceding claims, characterized in that, The distance between the edge of the peak (31) and the bottom of the valley (32) of the grooved contour surface (3') is between 0.8 and 2.0 times the distance between two consecutive peaks (31), preferably 1.0 times.

12. The system (100) according to any of the preceding claims, characterized in that, The grooved contour surface (3') of the first roller (3) of the fiber distribution roller (3,4) is made of metal, and the smooth surface (4') of the second roller (4) of the fiber distribution roller (3,4) is made of metal, rubber or plastic.

13. The system (100) according to any of the preceding claims, characterized in that, The scraper (5) is made of iron or steel.

14. The system (100) according to any of the preceding claims, characterized in that, The first roller (3) of the fiber distribution rollers (3,4) is equipped with an air circulation device and / or an air cooling device.

15. The system (100) according to any of the preceding claims, characterized in that, It also includes a traction device below the rotary cutter (7), which is in the form of two opposing traction rollers (9) with their axes parallel to the axes of the fiber distribution rollers (3,4), the traction rollers (9) being arranged abutting each other and rotatable in opposite directions along their axes, wherein each of the two traction rollers (9) has a slotted profile surface.

16. The system (100) according to claim 15, characterized in that, The grooved profile surface of each of the two pull rollers (9) is configured with grooves that form finger threads or round threads.

17. A method for producing chopped filaments (10) suitable for manufacturing chopped filament mats from fibers, characterized in that... Includes the following steps: a) Provide ribbon-like filaments made of discontinuous fibers (11); b) Orient the strip-shaped precursor fiber (11) in a vertical position; c) The oriented ribbon filament (11) is introduced between a pair of opposing fiber distribution rollers (3,4) having parallel horizontal axes. The width of the ribbon filament (11) extends along the axial direction of the fiber distribution rollers (3,4). The rollers (3,4) are arranged abutting each other in the tangential region between them and are rotatable in opposite directions along their axes. The first roller (3) of the fiber distribution rollers is a slotted roller with a circumferentially slotted profile surface (3') consisting of alternating circumferential peaks (31) and valleys. The component (32) is configured such that the second roller (4) of the fiber distribution roller (3,4) has a smooth surface (4') that contacts the peak (31) of the contour surface (3') of the first roller (3) in the tangential region. When the ribbon filament (11) is driven downward between the fiber distribution rollers (3,4), the space between the valley (32) and the smooth surface (4') in the tangential region is configured to accommodate the portion (11') of the ribbon filament (11), wherein at least one roller (3,4) is connected to a motor. d) Remove a portion (11') of the strip filament (11) contained at the bottom of the valley (32) as the rollers (3,4) rotate using a scraper (5), and separate it from the first roller (3), the removed portion constituting the filament (12). e) Guide the precursor fiber (12) through the vertical channel (61) below the top of the scraper (5); and f) Cut the raw filament (12) with a rotary cutter (7) arranged at the lower end of the vertical channel (61) to obtain chopped raw filament (10).

18. The method according to claim 17, characterized in that, Before the raw filament (12) is cut, the lower part of the raw filament (12) passes through the rotary cutter (7) and is pulled downward by a pulling device in the form of two opposing pulling rollers (9) whose axes are parallel to the axis of the fiber distribution rollers (3,4). The pulling rollers (9) are arranged abutting each other and are rotatable in opposite directions along their axes, wherein each of the two pulling rollers (9) has a grooved profile surface.

19. The method according to claim 18, characterized in that, The grooved profile surface of each of the two pull rollers (9) is configured with grooves that form finger threads or round threads.

20. The method according to any one of claims 17 to 19, characterized in that, The width of the strip-shaped precursor fiber (11) is between 0.5 and 8.0 cm, and the thickness is between 0.12 and 2.0 mm.

21. The method according to any one of claims 17 to 20, characterized in that, The ribbon-like filament (11) is made of natural discontinuous fibers.

22. The method according to any one of claims 17 to 21, characterized in that, It is implemented by the system (100) according to any one of claims 1 to 16.

23. A chopped filament (13) made of fiber, characterized in that, It can be obtained by the method according to any one of claims 17 to 22.

24. A chopped strand mat made of fibers, characterized in that, It comprises chopped raw fibers (10) obtained by the method according to any one of claims 17 to 22 or chopped raw fibers (10) as described in claim 23.

25. The chopped strand mat made of fiber according to claim 24, characterized in that, It comprises chopped filaments (10) made of flax fibers, chopped filaments (10) made of carbon fibers, and chopped filaments (10) made of glass fibers.

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