Process for thermoforming

Abstract

The application pertains to a process for selectively forming a thermoplastic fibrous material. The process comprises the steps of providing a three-dimensional thermoplastic fibrous material, contacting the three-dimensional thermoplastic fibrous material with a male or female part of a mold from one side of the thermoplastic fibrous material, contacting the three-dimensional thermoplastic material with a counterpart of the mold from the opposite side, exerting pressure on the three-dimensional fibrous material by at least one part of the mold in such a way that the three-dimensional fibrous material is compressed and heating the fibrous material during pressing. The process is characterized in that one part of the mold is acoustically coupled to a source of ultrasound.

Description

[0001] CPD3296

[0002] Process for Thermoforming

[0003] Description:

[0004] The present application pertains to a seat cushion and a method to produce a seat cushion.

[0005] Seats are an indispensable feature of more or less any vehicle starting from the early new age’s stagecoach until modem trains, planes, cars and other vehicles. Even in vehicles which are mainly intended for the transport of goods and not of people, seats are at least necessary for the driver. Especially for longer travelling vehicles such as planes or long distance trains, seats - be it passenger seats or driver’s seats are required to provide cushion especially in the case of e.g. cars where the seat can only be left when also the vehicle is left.

[0006] With seats being indispensable also cushion is indispensable for all kinds of vehicles.

[0007] Especially if it comes to cushion from economically optimized mass production, the state of the art in this field are cushions which are made from polyurethane foam. Polyurethane foam is a well-established and cheap material which can be obtained by mixing one or more polyol components with one or more isocyanate component together with a blowing agent. The freshly made mixture is placed in a mold wherein it remains until the polycondensation reaction is complete. This is extremely important as the unreacted isocyanate component is typically very hazardous. For this reason, reaction times of up to 24 hours are necessary to produce a polyurethane cushion which requires large amounts of molds as the resting time of the mixture in the molds is extremely long.

[0008] Furthermore, as it is non-thermoplastic, polyurethane foam is very difficult to recycle and thus it is problematic from an environmental point of view. At the moment, the only possible ways of treating polyurethane waste are either deposition in landfills or incineration which are both non-sustainable and, especially in case of incineration, have a large CO2-footprint which is very undesired due to the problems resulting from global warming.

[0009] For this reason, alternative materials for seat cushions are considered intensively especially with the goal of providing seat cushions with better recyclability.

[0010] In this field, fibrous materials have been widely considered as alternatives to polyurethane foams, especially three-dimensional fibrous mats wherein filaments from thermoplastics or thermoplastic elastomers are intermingled and welded where they cross in such a manner that they from a self-supporting structure which provides the amount of resilience that is necessary for a seat cushion.

[0011] However, a modem vehicle seat is no longer merely a cushion with any kind of decorative or protective trim cover. A vehicle seat is a technical device which may comprise a lot of electronics such as sensors, heaters, ventilation, motors or even devices which have less to do with the primary function as a seat such as onboard entertainment systems. Along with the trim cover, a seat may thus comprise a lot of cables and devices which must be held in place and thus require fixation. However, a change of technology from polyurethane foam to fibrous material also is a challenge for the fixation of both the trim cover and all the other mentioned features to the cushion. In the case of polyurethan foam cushions, these problems had been frequently solved by metal wires which are embedded into the foam, however as the main goal of the fibrous cushions is a better recyclability, also the fixation of the additional cables and devices to the cushion should not hamper recyclability of the seat. Another obstacle for the recyclability of polyurethane foam seats is that these seats do not necessarily completely consist of polyurethane foam pads but also of other components such as support structures for the pads, fixation means for the trim and other devices which are comprised in the seat and make the seat a technical device. This complex structure of a seat is necessary as polyurethane foam pads are not able to both provide comfort and support for the body.

[0012] It is thus the object of the present application to provide a seat cushion which is easy to recycle and which, at the same time, offers fixation means for trim covers, cables and other devices which do not provide an obstacle to the recyclability of the seat.

[0013] The object is surprisingly solved by a process for selectively forming a thermoplastic fibrous material comprising the steps of, providing a three- dimensional thermoplastic fibrous material, contacting the three-dimensional thermoplastic fibrous material with a male or female part of a mold from one side of the thermoplastic fibrous material, contacting the three-dimensional thermoplastic material with a counterpart of the mold from the opposite side, exerting pressure on the three-dimensional fibrous material by at least one part of the mold in such a way that the three-dimensional fibrous material is compressed, heating the fibrous material during pressing, characterized in that one part of the mold is acoustically coupled to a source of ultrasound.

[0014] It has been found that a cushion which is formed according to the process according to the present application is able to provide comfort and support for the human body and, at the same time, allows for fixation of other devices on a structure which is made from one single material and thus much better to recycle than the cushions of the prior art.

[0015] It is understood that the person skilled in the art knows that all embodiments presented in the present application can be combined with each other.

[0016] According to the present application “forming” means that a polymeric material is deformed plastically, i.e. that a force is applied to the polymeric material and deforms said material and that the form the polymeric material had during application of the force is, at least in part, retained also after the force has been released. Thus, unless otherwise stated, the term “forming” according to the present application is a synonym for plastic deformation. The opposite effect where a polymer returns to its form prior to deformation after release of the deformation force is called “elastic deformation”.

[0017] Typically, plastic deformation requires at least a certain amount of force and / or heating of the polymer.

[0018] Throughout this application, the term “thermoplastic” means any polymeric material that softens and melts upon heating. What is explicitly not covered by the term “thermoplastic” are inorganic materials which may melt at temperatures of more than 700°C such as glass. Thus, the term “thermoplastic” according to the present application is limited to organic macromolecular materials.

[0019] A fibrous material according to the present application is any material that comprises fibers by at least 50% by weight. A fiber according to the present application is any member that has a length which is at least hundred times as large as the next largest dimension perpendicular to the length. However, a fiber can have a length that is a thousand, several thousand or even several million times as large as the largest dimension perpendicular to the length. In general, compared to the length, the thickness of fibers is negligible. The length of a fiber according to the present application may vary between several centimeters and several kilometers. With this definition, it is possible that the whole content of a yam bobbin consists of one single fiber. Fibers which are longer than half a meter are also known under the term “filaments”. Filaments are typically produced in an extrusion process where a liquid such as a molten or dissolved polymer is extruded through one or more orifices and then consolidated by solidification or precipitation. Extrusion processes allow for the production of fibers or filaments of more or less infinite length.

[0020] The fibrous material may comprise any kind of fibers known to the person skilled in the art such as natural fibers originating from plants or animals such as cotton, flax, hemp, ramie, jute, abaca, bagasse, nettle, silk or any kind of wool such as wool from rabbits, sheep, goats, or camels of both the genus Lama or Camelus. The fibrous material according to the present application comprises at least 20 % by weight of man-made fibers from thermoplastic polymers. In an embodiment, the fibrous material consist of man-made fibers from thermoplastic polymers. In an embodiment, the fibrous material comprises 99% or 95% of man-made fibers from thermoplastic polymers which thermoplastic polymer may be polyethylene terephthalate (PET). In an embodiment, the fibrous material comprises at least 1 wt.-% or 2 wt.-% and at most 5 wt.-% or 4-wt.% polytrimethylene terephthalate (PTT) and / or polybutylene terephthalate (PBT). In an embodiment, the fibrous material comprises only two polymer components such as PET and PTT or PET and PBT. Possible thermoplastic polymers are polyolefins like polyethylene or polypropylene, polyamides such as polyam ide-6, polyam ide-6,6, polyam ide-4, 10, polyam ide-10 or polyam ide-11 , polyesters such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polycaprolactone, polylactide or polybutylene succinate. The thermoplastic polymer according to the present application may also be a thermoplastic elastomer. Thermoplastic elastomers are copolymers, thus polymers which comprise at least two, in most cases at least three different monomers wherein the polymeric chains have domains which show strong intermolecular interactions which intermolecular interactions lead to both flexibility and dimensional stability but which can be loosened at elevated temperatures such that the thermoplastic elastomer loses its dimensional stability and can be plastically deformed. Typical thermoplastic elastomers are e.g. co-polyesters which comprise one diacid component and two or more polyol components or two diacid components and one polyol component. The fibrous material according to the present application is three-dimensional which means that it has a thickness which is non-negligible compared to its further dimensions. A typical three-dimensional item has three dimensions out of which the largest is called “length” and the second largest perpendicular to the length is called “width”. The third largest dimension which is perpendicular to both the length and the width is called “thickness”. In many known fibrous materials known to the person skilled in the art, the thickness is negligible compared to the width and the thickness if it is e.g. one or two millimeters for a fibrous material that length and / or a width in the range of a meter or more. This is e.g. the case for many woven, knitted or nonwoven fabrics used e.g. in the textile industry. However, there are also fibrous materials which have non-negligible thicknesses even compared to lengths and / or widths that are in the range of a meter or even tens of meters or more. A non-negligible thickness according to the present application is a thickness of at least five millimeters. In an embodiment, the thickness is at least 10 millimeters, 15 millimeters, 20 millimeters or 25 millimeters. In an embodiment, the thickness of the fibrous material is at most 500 millimeters, at most 250 millimeters, at most 100 millimeters, at most 50 millimeters or at most 30 millimeters. The three-dimensional fibrous material may be any three- dimensional fibrous material known to the person skilled in the art such as a three- dimensional or multi-layered woven fabric, a three-dimensional knitted fabric or a three-dimensional non-woven fabric.

[0021] A three-dimensional nonwoven fabric may have different shapes or constructions. In an embodiment, a three-dimensional nonwoven fabric is a three-dimensional fibrous mat of thermoplastic filaments which filaments are entangled and welded where they cross.

[0022] A possible production technique for such three-dimensional mats is extrusion of a molten polymer such as a thermoplastic elastomer through an array of orifices into a cooling bath such as a water tank wherein the molten filaments are cooled down. During the consolidation process the filaments may be formed by e.g. rotating belts which support the process of intermingling. In addition, during intermingling the at least partially molten material gets welded at points where the filaments get in contact with each other.

[0023] Using such a process or any other processes known to the person skilled in the art, three-dimensional mats may be formed which are self-carrying voluminous structures wherein the fibers form kind of a framework around a large amount of empty space, gas or air. Especially if the fibers are of a thermoplastic elastomeric material, the three-dimensional mat provides a resilience which is strong enough to serve as a long-lived cushion e.g. in a vehicle seat or also in furniture such as sofas or matrasses.

[0024] A mold according to the present application is any kind of member which can be used to provide a material with a certain form. In general, a mold can even be a tool such as a seal or a stamp. However, a mold according to the present application is always a two-part device. One part of the mold may be considered to be a forming device while the other part may be considered a counter pressure element. However, it is also possible that both parts of the mold comprise a certain kind of form. In an embodiment, the forms of the two molds may be complementary to each other like the die and the counter-die of an embossing seal. The form of the mold which is connected to the sonotrode is also known as “A face” to the person skilled in the art or it is also called “sonotrode” by itself. A part which is not connected to a sonotrode is also called “B face” or “anvil”.

[0025] The forms provided by the mold are not particularly limited and may be hooks, clamps, bolts or any other fixation means.

[0026] In an embodiment, at least one of the parts of the mold has a three-dimensional structure and not only a planar surface. A three-dimensional structure can be any kind of texture that is e.g. encarved into a planar surface or to which a surface is formed. In an embodiment, the three-dimensional structure of at least one part of the mold could be the form of a hook, a clamp or a loop or of a part thereof.

[0027] In an embodiment, the parts of the mold are made of metal such as steel, copper, titanium, brass or bronze. The mold may furthermore comprise a coating that avoids sticking of molten or softened material to the mold such as a coating of silicone or polytetrafluoroethylene or any other anti-stick-material known to the person skilled in the art.

[0028] The parts of the mold are called male or female depending on whether the mold has protruding or encarved features. Typically, the male and the female part of the mold are put together during the forming process with the material to be formed in between. The material in between would be the fibrous material according to the present application.

[0029] In an embodiment, the parts of the mold are small compared to the three- dimensional fibrous material they should act on. Small in this sense means that the surface area of one part of the mold is covering is at most 5% of the surface area of the three-dimensional fibrous material to be formed whereby the surface area if the three-dimensional fibrous material is understood as the envelope of the three-dimensional fibrous material, not as the total surface area of the fibers.

[0030] In an embodiment, the method according to the present application is intended to form only a part of the three-dimensional fibrous structure.

[0031] It is important to notice that in the process according to the present application, it is not necessary that any part of the two parts of the mold touch each other when carrying out the process according to the present application. In an embodiment, the two parts of the mold are separated by the fibrous material or the formed fibrous material during the whole forming process. The formed fibrous material according to the present application means the fibrous material after the forming process which does not necessarily still have its fibrous entity. It is thus possible that during the forming process, the fibrous material is compacted in a manner that several fibers are united in a similar manner a several spaghetti which are sticked to each other on a part of the their length or they may even be melt-fused in such a manner that the fibrous character has completely been lost and that the polymer forming the fibers is formed to a compact form such as the form of a hook. In an embodiment, the structure resulting from the forming process is connected to a part of the fibrous material that has not been affected by the forming process and has thus retained its fibrous character. In this way, the process according to the present application allows for the formation of e.g. connection means which are connected to the three-dimensional fibrous material and which, at the same time, consist of the same material as the three-dimensional fibrous material. This way, e.g. a seat cushion can be produced which comprises fixation means for a trim cover, for cables, for pneumatic hoses, ventilators or any other devices and which connection means are of the same material as the cushion which simplifies recycling of the cushion reasonably.

[0032] More in general, using the method presented herein, three-dimensional structures such as fixation means can be formed from the three-dimensional fibrous material which have a detailed structure and are not mere densifications of the three- dimensional fibrous material. Thus, the process according to the present application allows for the formation of e.g. loops, hooks and / or clamps could be formed. Thus, such parts would no longer have to be produced separately and be embedded into the material but can be from the three-dimensional material.

[0033] Furthermore, this allows for fixation of e.g. a trim or any other means or devices on the three-dimensional fibrous material in a reversible manner as distinct fixation means can be formed and not only densifications in which external fixation means can only be fixed by partial destruction of the densification e.g. by drilling holes. Reversible fixation in the sense of the present application means that a fixation can be loosened without any changes to the fixation means such that the fixation can also be re-installed after loosening.

[0034] In an embodiment, the fixation means formed by the method disclosed herein allow for fixation of any externa device or structure to the three-dimensional fibrous material without providing any damage to the three-dimensional fibrous material after the fixation means have been formed. Thus, drilling or cutting of holes into the three-dimensional fibrous material to fix any external structure therein would not be necessary.

[0035] The two parts of the mold contact the three-dimensional fibrous material from two different sides. This does not mean that the three-dimensional fibrous material has to have different or opposite surfaces to be suitable for a process according to the present application. It only means that the two parts of the mold move towards each other and the e.g. also a spherical fibrous material could be approached by the two parts of the mold which may form either the whole fibrous material or a part of it.

[0036] During the forming process, pressure is exerted to the fibrous material in between the two parts of the mold. Pressure is exerted by moving the parts of the mold towards each other. By the pressure, the fibrous material may be plastically or elastically deformed, depending on the amount of pressure that is exerted and also depending on the material characteristics of the fibrous material. In any case, the pressure that is exerted must be sufficient to compress the fibrous material. Furthermore, during or after compression of the fibrous material, the fibrous material is also heated by the mold. Heating may lower the force that is necessary to deform the fibrous material and especially the limit to plastically deform the fibrous material.

[0037] In an embodiment, heating is over the melting temperature of the fibrous material leading to melting or at least partial melting of the fibrous material. The melting of the fibrous material may lead to a collapse of a part of the fibrous material, e.g. of the part of the fibrous material which is compressed between the parts of the mold. Said collapsed material may be compacted and / or melt-fused to a different form which does no longer have a fibrous character but which still may be connected to the rest of the three-dimensional fibrous material.

[0038] Heating of the fibrous material is carried out by ultrasound which means that at least one part of the mold is put under high-frequency vibration.

[0039] Ultrasonic vibration according to the present application is a vibration which is higher than the upper limit frequencies which can be head by the human ear. Normally, a frequency higher than 20 kHz will be considered to be ultrasound while the upper limit of ultrasonic vibration is 1 GHz. In an embodiment, the process will be carried out at 20 kHz, 30 kHz or 40 kHz.

[0040] The friction between the vibrating part of the mold and the fibrous material leads to a local heating of the fibrous material. Heating by ultrasound has the advantage that it can be carried out extremely locally and without devices such as the mold being heated. This allows for heating an extremely limited area of the fibrous material. Thus also softening and melting can be induced only in a very limited area which allows for a very precise forming process which does not affect the adjacent parts of the fibrous material.

[0041] In an embodiment, the source of ultrasound is a sonotrode. A sonotrode is a tool which connects a ultrasound source such as a piezoelectric speaker or a magnetostrictive source to the mold which is acoustically coupled to the sonotrode. In an embodiment, the sonotrode may comprise the ultrasound source. Acoustic coupling means that the mold is connected to the sonotrode - or any other source of ultrasonic vibration - in such a manner that the vibration is transferred from the source into the mold. This requires a connection with a strong mechanical contact and may necessitate that gaps between elements such as the mold and the sonotrode may be filled with e.g. polymeric materials, gels or any other substance, no matter how narrow they may be.

[0042] In an embodiment, only one part of the mold is coupled to a source of ultrasonic vibration while the other one serves as counter pressure element. This may allow for an even more local and more limited heating as there is only one small source of heating in the whole system. The function of the part of the mold that is not coupled to a source of ultrasonic vibration may be similar to the function of an anvil. In another embodiment, the part of the mold which is not coupled to a source of ultrasonic vibration may be movable and be moved towards the part of the mold which is connected to a source of ultrasonic vibration.

[0043] A big advantage of ultrasonic heating is that heating can be carried out very locally and that the polymer of the three-dimensional fibrous material is not confronted with heated molds or tools which can heat parts of the material which should not be heated. Thus, ultrasonic heating prevents the polymer of the three-dimensional from thermal degradation. Furthermore, as the heating is very local and the amount of heat which is transferred into the three-dimensional material thus very limited, colling of the molded parts is very fast.

[0044] A requirement for the use of ultrasound is that the structures which are formed from the three-dimensional fibrous material are small compared to the fibrous material. Small in this sense means that one formed structure does not comprise more than 2 wt.-% of the material of the entire three-dimensional fibrous material.

[0045] In an embodiment, ultrasound is provided to at least one part of the mold while the fibrous material is compressed between the two parts of the mold. Provision of ultrasound to the mold leads to local heating of the fibrous material by friction between the part of the mold and the fibrous material and may thus induce local softening or melting of the fibrous material. In such a manner, the part of the mold which coupled to a source of ultrasonic vibration may kind of collect material while passing through the fibrous material. Thus, the material of molten fibers may be compacted to a desired structure while the part of the mold passes through the fibrous material.

[0046] The present application further pertains to a vehicle seat cushion which comprises parts that have been formed by a process according to the present application.

[0047] The present application further pertains to a cushion comprising a fibrous material, the fibrous material comprising a thermoplastic polymeric material and a compact polymer structures of the same thermoplastic polymeric material as the fibrous material which are fixedly connected to the cushion and which have been formed from the fibrous material of the cushion in a process according to the present application. In an embodiment, the cushion may be a cushion for a vehicle seat such as a seat for a car, a bus, a truck, or a train. In an embodiment, the cushion is a cushion for a seat of an airplane.

[0048] In an embodiment, the fibrous material of the cushion comprises a thermoplastic elastomer.

[0049] In an embodiment, the compact polymer structure in the cushion is a fixation means.

[0050] Figure description

[0051] Fig. 1 shows an embodiment of the process according to the present application. It is noted that this picture is just an example and should not restrict the disclosure of this application in any sense.

[0052] Fig. 1 a) shows a thermoplastic fibrous material 1 prior to the forming process according to the present application. Over the fibrous material 1 , a female part of a mold A is placed while underneath the fibrous material 1 the male part of the mold B is placed. The female part of the mold A is connected to a sound of ultrasound which may be a sonotrode (not shown).

[0053] In Fig. 1 b) the female part of the mold A and the male part of the mold B are approached to each other in such a manner that they exert pressure to the fibrous material. 1 . Under the effect of both pressure and heat resulted from the ultrasound effect on the female part of the mold A, the fibrous material 1 melts and results in molten fibrous material 2 in between the two parts of the sonotrode.

[0054] Fig. 1c) shows the fibrous material 1 with a molded part 3 that is connected to the fibrous material 1 after the two parts of the mold A and B have been released.

Claims

Process for ThermoformingClaims:

1. Process for selectively forming a fixation means from a part of a thermoplastic fibrous material comprising the steps of• Providing a three-dimensional thermoplastic fibrous material,• Contacting the three-dimensional thermoplastic fibrous material with a male or female part of a mold from one side of the thermoplastic fibrous material,• Contacting the three-dimensional thermoplastic material with a counterpart of the mold from the opposite side,• Exerting pressure on the three-dimensional fibrous material by at least one part of the mold in such a way that the three-dimensional fibrous material is compressed,• Heating the fibrous material during pressing, characterized in that one part of the mold is acoustically coupled to a source of ultrasound and that the parts of the mold are small compared to the thermoplastic fibrous material.

2. The process of claim 1 wherein the source of ultrasound is a sonotrode.

3. The process of claim 1 or 2 wherein one part of the mold is not coupled to a source of ultrasound and serves as counter pressure element.

4. The process of any one or more of the previous claims wherein compression of the material is carried out while ultrasound is provided to the mold.

5. The process of any one or more of the previous claims wherein heating is carried out over the melting point of the thermoplastic fibrous material.

6. The process of claim 6 wherein the thermoplastic fibrous material is entirely molten in between the two parts of the mold.

7. The process of claim 7 wherein the material in between the two parts of the mold completely loses its fibrous shape.

8. The process of anyone or more of the previous claims wherein the thermoplastic fibrous material comprises a thermoplastic elastomer.

9. The process of any one or more of the previous claims wherein only a part of the fibrous material is compressed between parts of the mold.

10. The process of claim 9 wherein the part that is compressed between parts of the mold is formed to a compact polymer structure that is fixedly connected to the remaining part of the fibrous material.11 . The process of claim 10 wherein the compact polymer structure is a fixation means.

12. A cushion, preferably a vehicle seat cushion, which is formed according to the process according to anyone or more of claims 1 to 11 .

13. A cushion, preferably a vehicle seat cushion comprising a fibrous material, the fibrous material comprising a thermoplastic polymeric material and compact polymer structures of the same thermoplastic polymeric material as the fibrous material which have been formed from the fibrous material according to a process of anyone or more of claims 1 to 11 .

14. The cushion of claim 13 wherein the thermoplastic polymeric material is a thermoplastic elastomer.

15. The cushion of claim 13 or 14 wherein the compact polymer structure is a fixation means.

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