Device and method for producing an extruded strand for a writing instrument with a helical casing layer

Abstract

A device for producing an extruded strand for a writing instrument comprises a first extrusion unit which is designed to form an extruded strand for the writing instrument, and a second extrusion unit which is connected downstream of the first extrusion unit and has an extrusion nozzle which is arranged so as to be rotatable about the extruded strand and which is designed to rotationally apply a helical casing layer to the extruded strand.

Description

[0001] Apparatus and method for producing an extrusion strand for a writing instrument with an egg-shaped coating layer

[0002] Technical field

[0003] The invention relates to a device and a method for producing an extrusion strand, in particular an extrusion strand for a writing instrument, with an egg-shaped coating layer by means of a rotating extrusion die.

[0004] background

[0005] The production of writing instruments, such as writing, drawing, erasing, and cosmetic pencils, using extrusion processes has established itself in recent years as a versatile and cost-effective alternative to traditional manufacturing methods. These extrusion processes typically utilize polymer-based plastics and / or wood-plastic composites (WPCs). Examples are described in German patent applications DE io 2008 034013 Ai and DE 10 2008 034015 Ai.

[0006] There is a need to further develop state-of-the-art processes in order to improve the shape and ergonomics of writing instruments manufactured using the extrusion process.

[0007] Summary

[0008] This problem is solved by a device for producing an extruded strand for a writing instrument according to independent claim 1 and by a method for producing an extruded strand for a writing instrument according to independent claim 10. The dependent claims relate to advantageous embodiments.

[0009] A device for producing an extruded strand for a writing instrument according to a first aspect of the invention comprises a first extrusion unit configured to form an extruded strand for the writing instrument; and a second extrusion unit downstream of the first extrusion unit, which has an extrusion die rotatably arranged around the extruded strand and configured to apply a spiral-shaped coating to the extruded strand in a rotating manner. The device according to the first aspect allows the production of writing instruments with a predetermined spiral-shaped profile, thereby improving the ergonomics and feel of the writing instrument.The manufacturing process can be carried out in two stages. First, the extrusion unit extrudes and shapes the extrusion strand for the writing instrument's barrel. Then, the second extrusion unit, located downstream of the first, applies the egg-shaped coating around the extrusion strand using a rotating extrusion die. This allows for the creation of an egg-shaped profile solely through extrusion, eliminating the need for subsequent material removal steps, such as machining the extrusion strand or the writing instrument's barrel. Because the extrusion die is rotatable, the extrusion strand itself does not need to rotate. This effectively prevents internal, torsion-induced stresses in the extrusion strand or the writing instrument's barrel, ensuring that the writing instrument's stability remains unaffected by its twisted geometry.

[0010] According to one embodiment, only the second extrusion unit comprises a rotatably arranged extrusion die, whereas the first extrusion unit can be designed without elements rotating around the extrusion strand.

[0011] For the purposes of the present invention, an extruded strand can be any extrudate which - possibly after further processing steps - is suitable as the shaft of a writing instrument.

[0012] For the purposes of the present invention, a writing instrument can be any pen-like device that has a shaft and is designed to create or remove a writing mark or material dispense from a medium. This includes, in particular, sharpenable pencils, sharpenable colored pencils, ballpoint pens, felt-tip pens, cosmetic pencils, or erasers.

[0013] The extruded strand or shaft of the writing instrument can have any shape. In particular, the extruded strand can be cylindrical, for example, circular cylindrical.

[0014] For the purposes of the invention, a (first or second) extrusion unit can be any device suitable for continuously dispensing a plastically or thermoplastically deformable mass under pressure from a shaping opening.

[0015] For the purposes of this invention, an extrusion die can be understood to be any device suitable as a shaping opening for an extrusion unit. It can also be referred to as a mouthpiece. Extrusion dies can have a variety of different geometries, and the geometry of an extrusion die can directly determine the geometry of the object extruded with it.

[0016] For the purposes of the invention, any layer which has a curved egg-shaped coating layer, at least partially, along a longitudinal direction of the extrusion strand can be described as a curved egg-shaped coating layer.

[0017] In some embodiments, the curved profile can extend along the entire longitudinal direction of the extruded strand. In other embodiments, the curved profile can be limited to sections of the extruded strand.

[0018] According to one embodiment, the direction or orientation of the turning profile can vary along the longitudinal direction of the extrusion strand.

[0019] Alternatively or additionally, the pitch and / or slope of the helix profile can also be varied along the longitudinal direction of the extrusion strand. Pitch can be understood as the distance along the longitudinal direction of the extrusion strand by which the helix shifts during one full rotation around the extrusion strand.

[0020] In some embodiments, the egg-shaped outer layer can have a polygonal cross-section, in particular a triangular or hexagonal cross-section. These profile shapes are ergonomically advantageous for some applications.

[0021] The solution according to the invention is not limited to writing instruments with a single flip-off profile. Rather, in some embodiments, the flip-off-shaped outer layer can have several flip-off profiles, optionally offset from one another along a longitudinal direction of the extrusion strand. The flip-off profiles can differ in their profile shape and / or pitch and / or slope. Alternatively or additionally, the flip-off profiles can differ in their material.

[0022] According to one embodiment, the device comprises a first cooling unit between the first extrusion unit and the second extrusion unit, wherein the first cooling unit is configured to cool the extrusion strand before the application of the coating layer, in particular by means of a cooling fluid.

[0023] The first cooling unit can improve or precisely adjust the dimensional stability of the extruded and formed extrusion strand. This simplifies the mechanical insertion of the extrusion strand into the second extrusion unit. Simultaneously, torsion of the extrusion strand during the application of the egg-shaped coating in the second extrusion unit, and thus internal stresses in the finished writing instrument, can be effectively reduced or avoided. The cooling fluid can consist of water and / or air.

[0024] According to one embodiment, the device comprises a transport unit which is configured to transport the extrusion strand along a longitudinal direction from the first extrusion unit to the second extrusion unit and to feed the extrusion strand to the second extrusion unit, in particular along the longitudinal direction.

[0025] In one embodiment, the transport unit can be an active transport unit.

[0026] In particular, the transport unit can include a peeling unit, which can be located downstream of the second extrusion unit, for example between the second extrusion unit and a singulation unit.

[0027] According to one embodiment, the transport unit can include transport rollers for the extrusion strand.

[0028] The transport rollers can be actively driven or passively driven.

[0029] By means of the transport unit or its pull-off unit and / or its transport rollers, the extruded and formed extrusion strand can be fed to the second extrusion unit and the downstream singulation unit with minimal stress and torsion.

[0030] In some embodiments, the system according to the invention may further comprise a second cooling unit, which is connected downstream of the second extrusion unit and is designed to cool the extrusion strand and its egg-shaped coating layer after extrusion by means of a second cooling fluid.

[0031] The second cooling unit can, for example, be arranged between the second extrusion unit and the peeling unit or the singulation unit.

[0032] The second cooling fluid can in turn consist of water and / or air.

[0033] According to one embodiment, the system comprises a control unit configured to set, vary, and / or regulate the linear speed of the extrusion strand's movement from the first extrusion unit and through the second extrusion unit, and / or to set, vary, and / or regulate the rotational speed and / or direction of rotation of the extrusion die. By setting, varying, and / or regulating the linear speed of the extrusion strand's movement and / or the rotational speed of the extrusion die, the pitch or slope of the reversible pen profile can be precisely adjusted or varied. Varying the rotational direction of the extrusion die also allows for adjusting the direction of rotation of the reversible pen profile. In this way, writing instruments with virtually any reversible pen profile or geometry can be manufactured.

[0034] The control unit can be communicatively connected to the first extrusion unit and / or the second extrusion unit and / or the transport unit.

[0035] In some embodiments, the control unit can include several control elements that are communicatively coupled.

[0036] In particular, a first control element can be communicatively coupled with the first extrusion unit and be configured to control the first extrusion unit and to set and / or vary and / or regulate the discharge speed of the extrusion strand.

[0037] The first control element can also be configured to adjust the ratio of extrusion components or the geometry of the extrusion strand in the case of multiple strand components.

[0038] A second control element can be communicatively coupled to the second extrusion unit and configured to control the second extrusion unit, in particular its rotatable extrusion die, specifically to set and / or vary and / or regulate a rotational speed and / or the rotational speed of the extrusion die and / or the discharge speed of a material for the coating layer. The second control element can also be configured to set the quantity ratio or the geometry of the coating layer in the case of multiple material components for the coating layer.

[0039] A third control element can be communicatively coupled to the transport unit and be configured to set and / or vary and / or regulate the transport speed of the extrusion strand.

[0040] For example, the third control element can be configured to match the pull-off speed of a pull-off unit to the discharge speed of the extruded strand. In some embodiments, the pull-off speed is selected to be a predetermined value or proportion higher than the discharge speed in order to keep the extruded strand under slight tension.

[0041] In other embodiments, the control unit can be designed as an integral control unit, which combines the functionalities of the first control element, the second control element and the third control element, and possibly further control functionalities.

[0042] The system according to the invention can further comprise a singulation unit which is downstream of the second extrusion unit and / or the second cooling unit and is configured to singulate the formed extrusion strand with egg-shaped coating into a plurality of extrusion strand elements.

[0043] Each of the extruded strand elements can subsequently be used as the barrel of a writing instrument or further processed into one. Additional processing steps may be desirable or necessary, such as the integration of ink reservoirs or refills, or the sharpening of the tip of the extruded strand element.

[0044] A particular advantage lies in the fact that a large number of different types of writing instruments can be manufactured using the extrusion process with the system according to the invention.

[0045] According to one embodiment, the extrusion strand comprises polypropylene and / or a wood-plastic composite material.

[0046] Such materials are useful, for example, for manufacturing hollow shafts into which ink reservoirs or writing refills can be fitted in a subsequent production step. If necessary, a polymer barrier layer surrounding the cavity can be provided inside the hollow shaft to counteract solvent migration.

[0047] A corresponding configuration with a migration barrier layer is described by way of example in the patent application DE 10 2013 001495 Ai.

[0048] In some embodiments, the polymer barrier layer can be co-extruded with the extrusion strand in the first extrusion unit.

[0049] According to one embodiment, the hollow extruded strand can also serve as the base for a cosmetic stick. For example, the hollow shaft can be filled with a cosmetic compound in a subsequent casting process. Foamed plastics can also be used as the extrudate for the cosmetic stick, either instead of or in addition to the materials listed above. An internal polymer barrier layer can, in turn, counteract solvent migration.

[0050] According to one embodiment, the extrusion strand is a hollow strand, in particular a hollow strand for receiving a color-emitting lead.

[0051] According to one embodiment, the extrusion strand can comprise a wood-plastic composite material and a polymeric binder.

[0052] Alternatively or additionally, the extrusion strand can also comprise a foamed polymer, in particular a polystyrene with a foaming additive.

[0053] Such material compositions are suitable, for example, for the production of a shaft that encloses a lead, such as for the production of sharpenable pencils or colored pencils.

[0054] The extrusion strand and the mine can, for example, be integrally connected.

[0055] In particular, the first extrusion unit can be set up to extrude the extrusion strand and the mine together (in a co-extrusion).

[0056] The mine may, in particular, comprise polystyrene or a styrene-acrylonitrile copolymer or SAN.

[0057] Furthermore, the mine may contain graphite and / or include a mineral filler and a pigment.

[0058] In one embodiment, the first extrusion unit is configured to extrude a mine as an extrusion strand, in particular to extrude only one mine.

[0059] The second extrusion unit can be set up to apply the lead to the egg-shaped sheath of a shaft in a rotating manner.

[0060] According to one embodiment, the first extrusion unit is configured to apply a layer of an adhesion promoter to a surface of the extrusion strand.

[0061] The adhesion promoter can support or simplify the subsequent application of the egg-shaped coating layer.

[0062] For example, the adhesion promoter may include a polymer-based adhesive, in particular an ethylene-vinyl acetate copolymer (EVA / EVAC).

[0063] The coating layer may comprise polyolefins, in particular polyethylene or polypropylene, and / or thermoplastic polymers, in particular thermoplastic polymers based on styrene block polymer, and / or a wood-plastic composite and / or an organic filler and / or an inorganic filler and / or color pigments.

[0064] According to a second aspect, the invention relates to a method for producing an extrusion strand for a writing instrument, comprising forming an extrusion strand in a first extrusion step; and applying an egg-shaped coating layer to the extrusion strand in a second extrusion step after the first extrusion step; wherein the coating layer is applied by means of an extrusion die rotating around the extrusion strand.

[0065] According to one embodiment, the method further comprises cooling the extruded and formed extrusion strand before and / or after the application of the egg-shaped coating layer, in particular by means of a cooling fluid.

[0066] The cooling fluid can consist of water and / or air.

[0067] According to one embodiment, the extrusion strand can be formed by means of a first extrusion unit, and the coating layer can be applied by means of a second extrusion unit downstream of the first extrusion unit. According to one embodiment, the method comprises transporting the formed extrusion strand from a first extrusion unit to a second extrusion unit, in particular along a longitudinal direction, and feeding the extrusion strand into the second extrusion unit, in particular along the longitudinal direction.

[0068] According to one embodiment, the transporting includes pulling off the extruded strand, in particular from the first extrusion unit and through the second extrusion unit.

[0069] According to one embodiment, the method includes adjusting and / or varying and / or controlling a linear speed of the extrusion strand.

[0070] Alternatively or additionally, the process may also include adjusting and / or varying and / or controlling a rotation speed and / or a rotation direction of the extrusion nozzle.

[0071] According to one embodiment, the process after the second extrusion step (and optionally after cooling with the cooling fluid described with reference to the preceding embodiment) comprises singulating the extruded strand, including the applied egg-shaped coating layer, into several extruded strand elements, wherein the singulating may in particular include cutting the extruded strand. According to one embodiment, the extruded strand is a hollow strand.

[0072] According to an alternative embodiment, the extruded extrusion strand encloses a mine.

[0073] According to one embodiment, the method comprises co-extruding a mine together with the extrusion strand, in particular prior to the application of the egg-shaped coating layer.

[0074] According to another embodiment, the extruded strand formed in the first extrusion step forms a refill of a writing instrument after singulation.

[0075] The egg-shaped coating layer applied in the second extrusion step can form the shaft of the writing instrument after singulation.

[0076] In one embodiment, the method comprises applying a layer of an adhesion promoter to the extrusion strand, in particular before applying the egg-shaped coating layer.

[0077] The adhesion promoter may in particular include a polymer-based adhesive, for example an ethylene-vinyl acetate copolymer (EVA / EVAC).

[0078] According to one embodiment, the writing instrument is a sharpenable pencil, a sharpenable colored pencil, a ballpoint pen, a felt-tip pen, a cosmetic pen or an eraser pen.

[0079] Character description

[0080] The properties and advantages of the solution according to the invention can best be understood from a description of exemplary embodiments with reference to the accompanying drawings, in which:

[0081] Fig. 1 schematically shows a device for producing an extrusion strand for the shaft of a writing instrument according to one embodiment;

[0082] Fig. 2 schematically and in further detail shows a device for producing an extrusion strand for the shaft of a writing instrument according to one embodiment;

[0083] Fig. 3a shows a writing instrument with co-extruded lead and triangular reversible profile in a perspective view;

[0084] Fig. 3b shows a writing instrument with a co-extruded lead and triangular reversible profile in a frontal view; Fig. 4a shows a writing instrument with a co-extruded lead and hexagonal reversible profile in a perspective view;

[0085] Fig. 4b shows a writing instrument with co-extruded lead and hexagonal reversible profile in a frontal view;

[0086] Fig. 5a shows a writing instrument with a hollow shaft and triangular reversible profile in a perspective view;

[0087] Fig. 5b shows a writing instrument with a hollow shaft and triangular reversible profile in a frontal view; and

[0088] Fig. 6 shows a flowchart of a process according to one embodiment.

[0089] Description of embodiments

[0090] Fig. 1 is a schematic representation of a device 10 for producing an extruded strand for the shaft of a writing instrument in a two-stage extrusion process according to one embodiment. The writing instrument can be, for example, a pencil that can be sharpened, a colored pencil that can be sharpened, a ballpoint pen, a felt-tip pen, a cosmetic pencil, or an eraser.

[0091] System 10 comprises a first extrusion unit 12, which is configured to extrude and form an extrusion strand. A second extrusion unit 14 is connected downstream of the first extrusion unit 12. This second extrusion unit has an extrusion die 16 that is rotatably arranged around the extrusion strand. The extrusion die is configured to apply an egg-shaped coating to the extrusion strand. The extrusion strand coated with this coating can be used as the barrel of a writing instrument or further processed into the barrel of a writing instrument.

[0092] The transport direction of the extrusion strand from the first extrusion unit 12 to the second extrusion unit 14 and through the second extrusion unit 14 is indicated by arrows in Figure 1.

[0093] Figure 2 schematically shows a device io' for producing an extruded strand for the barrel of a writing instrument according to one embodiment in additional details or with additional optional components. Elements corresponding to Fig. 1 are provided with the same reference numerals in Fig. 2.

[0094] The device io' is designed for the production of, for example, a sharpenable pencil or colored pencil using a co-extrusion process. The first extrusion unit 12 receives a base material for the lead of the writing instrument from a first reservoir 18, for example, a polystyrene with graphite or with a mineral filler and, if applicable, a pigment.

[0095] A base material for the barrel of the writing instrument is supplied to the first extrusion unit 12 from a second reservoir 20. This base material comprises, for example, a polymer-bonded wood substitute material comprising 50 to 80 wt.% of an organic filler, in particular wood flour or cellulose, and 15 to 30 wt.% of a polyolefin. The polymer-bonded wood substitute material may also comprise 1 to 30 wt.% of a wax, for example, an amide wax, and / or stearic acid. Further optional components in some embodiments include 0 to 20 wt.% of an inorganic filler, for example, a layered silicate, 0 to 10 wt.% of a color pigment, and / or 0 to 10 wt.% of an additive, for example, a lubricant, a plasticizer, a surfactant, and / or a thermal stabilizer.Such compositions are generally known in the prior art and are described, for example, in the patent applications DE 10 2008 034013 Ai and DE 10 2008 034015 Ai.

[0096] Alternatively, a foamed polymer, such as polystyrene with chemical foaming additives, can be supplied from the second reservoir 20. This reduces the density of the manufactured writing instrument and ensures good sharpenability.

[0097] A first adhesion promoter can optionally be added from a third reservoir 22, which improves the bonding of the polyolefin of the wood substitute material to the polystyrene of the mine. Suitable adhesion promoters can be formed from a styrene-butadiene copolymer and / or a styrene / ethenebutene / styrene block copolymer, as described in further detail in German patent application DE 10 2008 034015 Ai.

[0098] By means of co-extrusion through a stationary (non-rotating) extrusion die (not shown), the first extrusion unit 12 forms the circular cylindrical extrusion strand 24 from these raw materials. This strand is discharged as a continuous strand and moved by a transport unit 26 along its longitudinal direction towards and through the second extrusion unit 14. According to one embodiment, the transport unit 26 moves the extrusion strand 24 solely along its longitudinal direction. In particular, in this embodiment, the transport unit 26 does not rotate the extrusion strand 24 about its cylindrical axis. This reduces the risk of stresses, especially torsional stresses, forming in the extrusion strand 24 during cooling. In the embodiment shown in Fig.In the embodiment shown in Figure 2, the transport unit is designed as a pull-off unit 26, into which the extrusion strand 24 is threaded and which pulls the extrusion strand 24 under tension from the first extrusion unit 12 and through the second extrusion unit 14.

[0099] As further shown in Fig. 2, the transport unit 26 can additionally include a roller conveyor with several (driven or passive) transport rollers 28. Additional counter rollers may also be provided.

[0100] Alternatively or additionally, the transport unit 26 can also include other active or passive transport components, for example a conveyor belt or a sliding surface (not shown).

[0101] Optionally, the first extrusion unit 12 can add a second adhesion promoter from a fourth reservoir 30, which is applied to the outer surface of the extruded strand 24 and subsequently promotes bonding to the egg-shaped coating layer applied by the second extrusion unit 14. For example, a second polymer-based adhesion promoter, in particular a hot-melt adhesive such as ethylene vinyl acetate (EVA), can be used for this purpose.

[0102] The device io' optionally also includes a first cooling unit 32 along the transport path from the first extrusion unit 12 to the second extrusion unit 14. The transport unit 26 can, in particular, guide the extrusion strand 24 discharged from the first extrusion unit 12 through the cooling unit 32 before introducing the extrusion strand 24 into the second extrusion unit 14.

[0103] The first cooling unit 32 can actively cool the extrusion strand 24, for example, by means of air cooling. Alternatively or additionally, water cooling can also be used, whereby the cooling water can optionally be subsequently blown off the extrusion strand 24.

[0104] The first cooling unit 32 can support the formation of a dimensionally stable extrusion strand 24 and can thus, in particular, support the subsequent mechanical insertion of the extrusion strand 24 into the second extrusion unit 14. Cooling by means of the cooling unit 32 also prevents torsional stresses from forming in the extrusion strand 24 during the subsequent application of the egg-shaped coating layer by means of the second extrusion unit 14.

[0105] In one embodiment, the temperature of the extruded strand 24 from the first extrusion unit 12 is approximately 150 to 200 °C and can be selectively reduced to approximately 100 to 120 °C using the first cooling unit 32, for example, by active air cooling. Due to the cooling, the geometry of the extruded strand 24 is essentially frozen, so that the extruded strand 24 is sufficiently dimensionally stable to be subsequently mechanically inserted into the second extrusion unit 14. At the same time, the second adhesion promoter applied to the outside of the extruded strand 24, for example ethylene vinyl acetate (EVA), remains adhesively functional in the aforementioned temperature range of approximately 100 to 120 °C. Furthermore, sufficient residual heat remains in the extruded strand 24, which supports the subsequent bonding with the egg-shaped coating layer in the second extrusion unit 14.

[0106] As shown schematically in Fig. 2, after cooling, the extrusion strand 24 passes through the second extrusion unit 14 as a continuous strand. The second extrusion unit 14 receives a base material for the egg-shaped coating layer from at least one coating layer reservoir 34 and extrudes it by means of the extrusion die 16 rotatably arranged around the extrusion strand 24, so that an egg-shaped coating layer 46 is formed around the extrusion strand 24 and on the second adhesion promoter, which has an egg-shaped profile 36 in the form of a helix.

[0107] For example, a polyolefin, in particular polyethylene or polypropylene, alone or in mixture with a thermoplastic elastomer, for example on a styrene block polymer basis, can be used as the base material for the egg-shaped coating layer 46.

[0108] The encapsulation layer 46 can, for example, have the following composition:

[0109] 30-70% styrene-based thermoplastic elastomer;

[0110] 30-70% polyolefin, e.g., PE;

[0111] 0-10% color masterbatch based on polyol efin, e.g. PE.

[0112] Alternatively, the egg-shaped coating layer 46 can also be extruded from a polymer-bonded wood substitute material comprising 50-80 wt.% of an organic filler, in particular wood flour or cellulose, and 15-30 wt.% of a polyolefin.

[0113] If necessary, color pigments and / or other additives can be added to the egg-shaped coating layer 46 during extrusion, as previously described with reference to the formation of the extrusion strand 24 in the first extrusion unit 12.

[0114] According to one embodiment, the egg-shaped coating layer 46 is applied at a temperature of approximately 180–220 °C to the extrusion strand 24, which is still warm even after cooling in the first cooling unit 32 (“hot-on-hot”). This improves the bond between the extrusion strand 24 and the coating layer 46. In particular, the coating layer 46 shrinks onto the extrusion strand 24 during subsequent cooling.

[0115] The cooling of the coating layer 46 can optionally be supported in a second cooling unit 32' downstream of the second extrusion unit 14 by means of active fluid cooling, similar to that described above with reference to the first cooling unit 32.

[0116] The device io' shown schematically in Figure 2 further comprises a control unit 38, which is communicatively connected to the transport unit 26 and the first extrusion unit 12 and the second extrusion unit 14. The control unit 38 can be configured to set and / or vary and / or regulate the discharge speed of the extrusion strand 24 from the first extrusion unit 12 as well as the linear speed of the movement of the extrusion strand 24 from the first extrusion unit 12 through the first cooling unit 32 and the second extrusion unit 14. In addition, the control unit 38 can be configured to set and / or vary and / or regulate the rotational speed of the extrusion die 16.

[0117] By appropriately adjusting the linear speed of the extrusion strand 24 and the rotational speed of the extrusion die 16, a predetermined pitch or slope of the reversing profile 36 can be set. Furthermore, by varying the linear speed of the extrusion strand 24 and / or the rotational speed of the extrusion die 16, the pitch or slope of the reversing profile 36 along the extrusion strand 24 can be varied, allowing different sections of the extrusion strand 24 to be provided with a different reversing profile 36.

[0118] The control unit 38 can also be configured to vary the direction of rotation of the extrusion die 16, so that, for example, an extrusion die 16 that initially rotates clockwise subsequently rotates counterclockwise, or vice versa. In this way, the direction of rotation of the turning profile 36 along the extrusion strand 24 can be varied. This makes it easy to produce writing instruments with a variety of different external geometries using the io' system.

[0119] The transport unit 26 feeds the extrusion strand 24, provided with the egg-shaped coating layer and discharged from the second extrusion unit 14, after cooling in the second cooling unit 32', optionally to a singulation unit 40, which is located downstream of the second extrusion unit 14 and the second cooling unit 32' in the transport direction and which singulates the extrusion strand 24 into individual extrusion strand elements of predetermined length, for example by cutting them. The individual extrusion strand elements can subsequently be used as barrels of writing instruments 42 or further processed into barrels of writing instruments 42, for example by sharpening, printing on the coating layer 46 or similar downstream process steps, which are generally known from the prior art and are therefore not described here in further detail.

[0120] The shape of the reversible egg-shaped profile 36 of the reversible egg-shaped coating layer 46 is determined in particular by the geometry of the extrusion die 16. A threefold geometry, for example, leads to a triangular reversible egg-shaped profile 36, as shown schematically in Fig. 2.

[0121] Fig. 3a shows a writing instrument 42 with such a triangular reversible profile 36, as can be produced with the system 10 or io' in the two-stage extrusion process according to the invention, in a perspective view, Fig. 3b in an (enlarged) frontal view. In both figures, the writing instrument 42 can be seen from the inside out as consisting of the refill 44, the extrusion strand 24 co-extruded together with the refill, and the overlying sheath layer 46 with the triangular reversible profile 36, which together form the barrel of the writing instrument 42.

[0122] In contrast, a hexagonal geometry of the extrusion die 16 leads to a writing instrument 42' with a hexagonal reversible profile 48 of the writing instrument, as shown schematically in the perspective view of Fig. 4a and the (enlarged) frontal view of Fig. 4b.

[0123] In some embodiments, the extrusion die 16 can comprise several radially offset outlet openings for the extrudate. In this way, a spiral-shaped coating layer 46 can be applied to the extrusion strand 24 by means of the second extrusion unit 14. This coating layer has several spiral profiles that differ, for example, in their material and / or color.

[0124] With reference to Figures 2 to 4b, embodiments for forming a writing instrument 42, 42' with co-extruded lead, such as a pencil or colored pencil, have been described above.

[0125] The techniques according to the invention are also suitable for producing a writing instrument 42" with a hollow shaft, i.e., with an extruded strand 24' which has an internal cavity 50 into which, for example, a refill or an ink reservoir can be inserted in a production step following the two-stage extrusion and singulation. Such a writing instrument 42" with a hollow shaft 24' and a triangular helical profile is shown by way of example in Figures 5a and 5b, wherein Figure 5a – similar to Figure 3a – shows a schematic perspective view and Figure 5b – similar to Figure 3b – shows an (enlarged) frontal view.

[0126] The method and apparatus for forming the writing instrument 42" with a hollow extruded strand 24' are, in some embodiments, largely similar to the embodiments described above with reference to Figures 2 to 4b. However, in this case, the first extrusion unit 12 does not perform a co-extrusion of an extruded strand 24 and a lead 44. Instead, the first extrusion unit 12 extrudes a hollow, for example, hollow cylindrical extruded strand 24' with the inner cavity 50. The extrusion die of the first extrusion unit 12 can, for example, be designed as an annular die.

[0127] Optionally, the inner wall of the cavity 50 can be formed by a polymeric barrier layer (not shown in Figures 5a and 5b), which protects the writing instrument against solvent migration from a subsequently inserted ink reservoir. This polymeric barrier layer can, for example, be formed in co-extrusion in the first extrusion unit 12 together with the extrusion strand 24'.

[0128] The subsequent process steps of transporting the hollow extrusion strand 24' to the second extrusion unit 14, possibly after applying an adhesion promoter such as EVA and / or with intermediate cooling by means of the first cooling unit 32, and of applying the coating layer 46 with the helical profile 36 can be completely identical to those of the embodiment described above with reference to the extrusion strand 24.

[0129] After singulation in the singulation unit 40, a writing instrument 42" can be produced from the hollow extrusion strand 24', which can be used, for example, as a felt-tip pen or ballpoint pen. An ink reservoir or ballpoint pen refill is inserted into the cavity 50. For this application, the hollow extrusion strand 24' can be made of polypropylene or a wood-plastic composite, as described above with reference to the sharpenable pencils. The coating layer 46 applied by the second extrusion unit 14 can be made of the same material, but to improve the feel, it can also be mixed with thermoplastic elastomers, for example, based on styrene block polymers. For example, in one embodiment, the coating layer 46 can consist of 49% by weight of polyethylene, 49% by weight of a styrene block polymer, and 2% by weight of a colorant.

[0130] The 42" writing instrument with a 24" hollow shaft can alternatively be used as an eraser pen. In such applications, a refill made of an eraser material, for example based on a thermoplastic elastomer, is used instead of an ink reservoir or a ballpoint pen refill.

[0131] The writing instrument 42" with hollow shaft 24' can alternatively also be used as a cosmetic pen, whereby the material used for the extrusion of the extrusion strand 24' in the first extrusion unit 12 can also be in a foamed state.

[0132] A 24' hollow shaft, for example, can have the following composition:

[0133] 50 - 100% polymer, e.g. polystyrene, and / or copolymers of polystyrene;

[0134] 0-25% plasticizers e.g. ATBC (acetyltributyl citrate) and / or ESBO (epoxidized soybean oil);

[0135] 0-25% filler, e.g. chalk, kaolin, etc.;

[0136] 0-10% colorants, e.g. pigments;

[0137] 0-5% chemical foaming additive, e.g. citric acid and / or a carbonate with a suitable decomposition temperature.

[0138] In such applications, the cavity 50 is filled with a cosmetic mass instead of an ink reservoir or a ballpoint pen refill after the application of the coating layer 46 and, if necessary, singulation in the singulation unit 40, for example using casting processes.

[0139] Fig. 6 shows a flow diagram of a method for producing an extrusion strand for a writing instrument, for example one of the writing instruments 42, 42“, 42“, described above with reference to Figures 3a to 5b, according to one embodiment.

[0140] In a first extrusion step S10, an extrusion strand is formed. In a subsequent second extrusion step S12, an egg-shaped coating layer is applied to the extrusion strand, whereby the coating layer is applied by means of an extrusion die rotating around the extrusion strand.

[0141] Using the described method, a writing instrument with a longitudinally twisted geometry can be produced stress-free or with minimal stress by extrusion, without the need for subsequent machining. The method according to the invention allows the production of writing instruments in a wide variety of geometries and materials.

[0142] The exemplary embodiments presented above with reference to the figures serve solely to illustrate the teaching of the invention and are not intended to limit it. The scope of protection is instead defined by the following claims.

[0143] Reference symbol io, io ' Device for producing an extruded strand

[0144] 12 first extrusion unit

[0145] 14 second extrusion unit

[0146] 16 Extrusion die

[0147] 18 first reservoir of the first extrusion unit 12

[0148] 20 second reservoir of the first extrusion unit 12

[0149] 22 third reservoir of the first extrusion unit i2

[0150] 24 extrusion strand

[0151] 24' Hollow strand

[0152] 26 Transport unit / Pull-off unit

[0153] 28 transport rollers

[0154] 30 fourth reservoir of the first extrusion unit 12

[0155] 32 first cooling unit

[0156] 32' second cooling unit

[0157] 34 Envelope reservoir

[0158] 36 triangular helical profile

[0159] 38 Control unit

[0160] 40 singulation units

[0161] 42, 42", 42" writing instrument

[0162] 44 Mine

[0163] 46 Envelope layer

[0164] 48 hexagonal helical profile

[0165] 50 Cavity of the hollow strand 24'

Claims

Claims 1. Device (10, 10') for producing an extrusion strand (24, 24') for a writing instrument (42, 42", 42"), wherein the device (10, 10') comprises: a first extrusion unit (12) configured to form an extrusion strand (24, 24") for the writing instrument (42, 42", 42"); and a second extrusion unit (14) downstream of the first extrusion unit (12) and comprising an extrusion die (16) rotatably arranged about the extrusion strand (24, 24"), which is configured to apply a spiral-shaped coating layer (46) to the extrusion strand (24, 24") in a rotating manner.

2. Device (10, io') according to claim 1, further comprising: a first cooling unit (32) between the first extrusion unit (12) and the second extrusion unit (14), wherein the first cooling unit (32) is configured to cool the extrusion strand (24, 24') before the application of the coating layer (46), in particular by means of a cooling fluid.

3. Device (10, 10') according to claim 1 or 2, further comprising: a transport unit (26) which is configured to transport the extrusion strand (24, 24') along a longitudinal direction from the first extrusion unit (12) to the second extrusion unit (14) and to supply the extrusion strand (24, 24') to the second extrusion unit (14), in particular along the longitudinal direction.

4. Device (10, io') according to one of the preceding claims, further comprising: a control unit (38) which is configured to set and / or vary and / or control a linear speed of a movement of the extrusion strand (24, 24') from the first extrusion unit (12) and through the second extrusion unit (14) and / or which is configured to set and / or vary and / or control a rotation speed and / or a rotation direction of the extrusion die (16). 5- Device (10, io') according to one of the preceding claims, wherein the extrusion strand is a hollow strand (24'), in particular a hollow strand (24') for receiving a color-releasing lead.

6. Device (10, io') according to one of claims 1 to 4, wherein the extrusion strand (24) comprises a mine (44), wherein in particular the extrusion strand (24) and the mine (44) are co-extruded.

7. Device (10, io') according to claim 6, wherein the first extrusion unit (12) is configured to extrude the extrusion strand (24) and the mine (44) together.

8. Device (10, 10') according to one of the preceding claims, wherein the first extrusion unit (12) is configured to apply a layer of an adhesion promoter to a surface of the extrusion strand (24, 24').

9. Device (10, io') according to one of the preceding claims, wherein the covering layer (46) comprises polyolefins, in particular polyethylene or polypropylene, and / or thermoplastic elastomers, in particular thermoplastic elastomers based on styrene block polymer, and / or a wood-plastic composite material and / or an organic filler and / or an inorganic filler and / or color pigments.

10. Method for producing an extruded strand (24, 24') for a writing instrument (42, 42", 42"), the method comprising: Forming an extruded strand (24, 24') in a first extrusion step (S10); and Applying an egg-shaped coating layer (46) to the extrusion strand (24, 24') in a second extrusion step (S12) after the first extrusion step (S10); wherein the coating layer (46) is applied by means of an extrusion die (16) rotating around the extrusion strand (24, 24').

11. The method of claim 10, further comprising: Cooling the extrusion strand (24, 24') before and / or after the application of the coating layer (46), in particular by means of a cooling fluid.

12. A method according to one of claims 10 or 11, further comprising: Setting and / or varying and / or controlling a linear speed of the extrusion strand (24, 24'); and / or Adjusting and / or varying and / or controlling a rotation speed and / or a rotation direction of the extrusion nozzle (16).

13. Method according to any one of claims 10 to 12, further comprising: Co-extruding a mine (44) together with the extrusion strand (24, 24'), especially before applying the coating layer (46).

14. Method according to any one of claims 10 to 13, further comprising: Applying a layer of adhesion promoter to the extrusion strand (24, 24'), especially prior to applying the coating layer (46).

15. Method according to any one of claims 10 to 14, wherein the writing instrument (42, 42', 42") is a sharpenable pencil, a sharpenable colored pencil, a ballpoint pen, a felt-tip pen, an eraser pen or a cosmetic pen.

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