Method and device for producing recycled elastomer material to be crosslinked

Abstract

The invention relates to a method for producing rubber material to be crosslinked, the method comprising the continuous extrusion of crosslinked rubber as granules and / or chips, and comprising i) decrosslinking by mechanically shearing the granules and / or chips and increasing the temperature until a decrosslinked paste is formed; ii) cooling the decrosslinked paste by optionally adding at least one additive; and iii) mixing the cooling decrosslinked paste with at least one crosslinking agent and collecting, at the output of said continuous extrusion, a paste-like mixture forming the rubber material to be crosslinked.

Description

[0001] PROCESS AND DEVICE FOR PRODUCING RECYCLED ELASTOMER MATERIAL, READY FOR CROSSLINKING

[0002] The present invention relates to the field of recycling crosslinked elastomer waste and it relates in particular to a method and a device for producing, from this waste, a material ready for crosslinking, that is to say to be used directly for the production of new applications.

[0003] For environmental reasons, there has recently been a move to recycle crosslinked elastomer waste, such as vulcanized rubber. It is known to decrosslink or devulcanize this waste to form what is called a "regenerated" material.

[0004] DE10201 1 1 12081 relates to a discontinuous process for carrying out vulcanization of an elastomeric material or devulcanization. However, such a process is complex and expensive in that it requires several processing steps.

[0005] Crosslinking is understood according to the invention to mean crosslinking of elastomeric material with sulfur, which is more generally called vulcanization, or its crosslinking with other crosslinking agents such as peroxides. In the following, the terms crosslinking or decrosslinking will therefore include the terms vulcanization and devulcanization. Rubber or rubbery material are common terms for naming elastomers or elastomeric materials, which are more technical names, and these common terms will be used in the following, in this sense.

[0006] The aim of the present invention is to enable, from crosslinked waste, the production of rubber material ready for crosslinking which is efficient and which, in particular, is affordable. To solve this problem, the invention provides a method for producing rubber material ready for crosslinking, comprising: continuous extrusion of crosslinked rubber, in the form of grains and / or chips, comprising, preferably successively, the following steps:

[0007] - decrosslinking by mechanical shearing of said grains and / or chips of said crosslinked rubber and increasing the temperature until a decrosslinked paste is formed,

[0008] - cooling of the de-crosslinked paste, and

[0009] - mixing the cooled decrosslinked paste with at least one crosslinking agent, and collecting, at the outlet of this continuous extrusion, a pasty mixture forming said rubbery material ready for crosslinking, in particular during molding.

[0010] This method makes it possible to produce, in a continuous extrusion process, both the decrosslinking of the treated rubber granules or chips, the cooling of the resulting paste and the mixing of the compounded paste with at least one crosslinking agent, in particular accelerators and activators, which continuously gives a rubber material ready for crosslinking, which can immediately be transferred to molds or other shaping elements where crosslinking will take place.

[0011] This extrusion is advantageously carried out in an extruder, which ensures a continuous process.

[0012] It is possible to plan a succession of extruders while maintaining the continuous process.

[0013] The extruder may comprise at least one double screw, preferably co-rotating, which has a profile that can vary along its length depending on the action to be carried out (feeding, mixing, devulcanization). Advantageously, the decrosslinking step is carried out in a twin-screw type extruder (double screw), preferably co-rotating.

[0014] The cooling step is carried out in an extruder (twin-screw), preferably the one used to carry out the decrosslinking, preferably with a screw profile adapted to the use.

[0015] The mixing step is carried out in a twin-screw extruder, preferably the one used to carry out the decrosslinking, preferably with a screw profile adapted to the use.

[0016] According to the invention, it may be advantageous to carry out all the steps successively and continuously (deretlinking, cooling and mixing) in at least one extruder, or even a series of extruders while respecting the spirit of the invention.

[0017] The present invention makes it possible to provide a rubber material ready for crosslinking. This means that the continuous extrusion process allows devulcanization and preparation of a compounded rubber material. Thus, at the end of extrusion, the material is ready to be crosslinked.

[0018] This provides significant advantages in the rubber industry and the recovery sectors associated with rubber waste. Thus, the user benefits from a ready-to-use product at a competitive cost with an efficient and competitive process.

[0019] It is also possible to store the paste obtained at the end of extrusion. Its transport and delivery can be ensured while maintaining the initial quality level.

[0020] The compounded material or compounded paste preferably includes the crosslinking agent which comprises a vulcanizing agent, an accelerator and an activating agent.

[0021] According to one embodiment of the invention, said increase in temperature is generated by an input of external thermal energy, by self-heating of said grains and / or chips during mechanical shearing, or by both phenomena at the same time.

[0022] The mechanical shearing of the material, produced during the beginning of the extrusion, generates an increase in the temperature of the sheared rubber. The mechanical shearing and possibly the temperature communicated by heating, for example from the first barrel elements of the extrusion apparatus, cause the crosslinking bonds of the crosslinked rubber to break. The material, introduced in the form of granules or chips of crosslinked rubber, leaves the decrosslinking stage in the form of deformable and malleable paste, also called regenerated material.

[0023] Mechanical shear is preferably applied by means of an extruder which may be equipped with a twin-screw (co-rotating).

[0024] It should be noted that each rubber has its own preferred decrosslinking temperature, depending on its nature and its constituents, and that the temperature increase caused and / or communicated during shearing must exceed this decrosslinking temperature. Generally this temperature is higher than 80°C, particularly higher than 100°C.

[0025] Advantageously, the decrosslinking step is carried out at a temperature below 350°C, preferably above 80°C and below 350°C.

[0026] According to a particular embodiment of the invention, said material ready for crosslinking has a crosslinking temperature and the mixing of the cooled decrosslinked paste with said at least one crosslinking agent takes place at a temperature lower than this crosslinking temperature. It is desirable in fact that the aforementioned mixing step takes place sufficiently far from the decrosslinking step so that the decrosslinked paste can be cooled before the introduction of said at least one crosslinking agent, and this to avoid any premature reaction of the latter with the paste. Preferably, the introduction of said at least one crosslinking agent takes place at a location where the temperature of the decrosslinked paste is lower than 120°C, preferably lower than 80°C and in particular lower than 60°C.

[0027] Advantageously, additional cooling of said rubbery material ready for crosslinking takes place, during harvesting, by forced convection to stop any possible premature reaction between the crosslinking agents and the decrosslinked material paste.

[0028] Preferably, this cooling takes place outside the extruder.

[0029] According to a preferred embodiment of the invention, said continuous extrusion further comprises compounding of the decrosslinked material with at least one additive, during or after its cooling.

[0030] As additives to be compounded with the decrosslinked paste, powdery, granular, liquid or pasty materials can be considered, and in particular reinforcing fillers, such as carbon black, diluting fillers, such as clays, plasticizers, oils, antioxidants, metal oxides, anti-ozone protectors and their mixtures.

[0031] As crosslinking agent, sulfur is provided as vulcanizing agent, CBS (N-cyclohexyl-2-benzothiazolesulfenamide) as accelerator and zinc oxide as activator. There are obviously other types of accelerators (MBTS, TMTD, among others) and activators and the choice of one or the other is guided by the rheological and mechanical characteristics of the products that one wishes to manufacture with the compounded material. As stated above, there are other types of crosslinking where, for example, the crosslinking agents are peroxides, metal oxides, phenolic resins, for example. Other features of the process according to the invention are indicated in the claims.

[0032] There is also provided, according to the invention, a device for producing rubber material ready for crosslinking, comprising a continuous extrusion apparatus having an upstream inlet end provided with a system for supplying crosslinked rubber, in grains and / or chips, and a downstream end for collecting said rubber material ready for crosslinking, and, between these ends, successively a sector for decrosslinking said grains and / or chips coming from the supply system, where said crosslinked rubber is transformed into a decrosslinked paste, a cooling sector, where the decrosslinked paste is cooled and a mixing sector provided with said downstream end, in which at least one metering device is provided for introducing into the cooled decrosslinked paste at least one crosslinking agent.

[0033] Advantageously, the continuous extrusion apparatus consists of an extruder comprising the aforementioned decrosslinking, cooling and mixing sectors in linear succession between said upstream inlet end and said downstream harvesting end.

[0034] The continuous extrusion apparatus may also comprise several extruders in succession. For example, the continuous extrusion apparatus may comprise a first extruder, which comprises said upstream inlet end, said decrosslinking and cooling sectors in linear succession and an outlet for said cooled decrosslinked paste, and a second extruder, which comprises an inlet, into which said cooled decrosslinked paste is directly fed from the outlet of the first extruder, said mixing sector and said downstream harvesting end.

[0035] According to a particular embodiment of the invention, each of said sectors comprises a static sheath consisting of at least one sheath element and in each sheath element at least one screw driven in rotation by a motor. Depending on the sectors, the extrusion apparatus will comprise one or more screws, which, depending on the case, will be used for shearing the material, for its mastication, for its conveyance from upstream to downstream, for a mixture of the material with other constituents.

[0036] Advantageously, in the cooling sector, at least one supply device is provided for introducing at least one additive into the decrosslinked paste.

[0037] The characteristics mentioned for the device can also be applied to the method according to the invention and vice versa.

[0038] Other embodiments of the device according to the invention are indicated in the claims.

[0039] Other details and particularities of the invention will emerge from the description, given below without limitation and with reference to the appended drawings, of two exemplary embodiments according to the invention.

[0040] Figures 1 and 2 schematically represent two embodiments of a production device according to the invention.

[0041] In the various figures, identical or similar elements are indicated by the same references.

[0042] Advantageously, the decrosslinked paste, obtained after the decrosslinking step, comprises a soluble fraction in an amount of between 1-40% by weight, preferably between 10-35% by weight, more preferably between 20-35% by weight, even more preferably between 3-15% by weight, relative to the total weight of the decrosslinked paste.

[0043] According to an advantageous embodiment, the soluble fraction comprises low molecular weight molecules and macromolecules. These macromolecules are present when decrosslinking allows a part of the skeleton of the decrosslinked material to be broken (dercrosslinked paste). The soluble fraction makes it possible to characterize the decrosslinking step. Preferably, the paste ready for crosslinking has a Mooney viscosity of between 10-120, preferably between 10-80, determined according to the ISO-289 standard.

[0044] According to a preferred embodiment, the decrosslinking step is carried out at a temperature below 350°C, preferably above 80°C and below 350°C.

[0045] Particularly advantageously, the successive stages of decrosslinking, cooling and mixing take place in a twin-screw extruder, preferably co-rotating.

[0046] The device illustrated in Figure 1 comprises an extrusion apparatus 1 which is formed of a single extruder 2. This comprises a barrel, made up of several barrel elements 3, in which one or more screws are rotated by a rotary motor 4. The extruder 2 is divided into three successive sectors, a decrosslinking sector A, a cooling sector B and a mixing sector C, which each comprise several barrel elements.

[0047] In the decrosslinking sector A of the illustrated device, a system for feeding the extruder with granules or chips of crosslinked rubber is provided in the form of a gravimetric doser 5 and a pipe 6, arranged between the gravimetric doser 5 and the extruder 2, guides the granules or chips into the extruder, via an open barrel element intended to receive the rubber granules or chips. In the barrel elements of the decrosslinking sector A, the screws have different roles, depending on the case, the transfer of the granules which enter the extruder to the downstream of the extruder and / or a shearing of the granules or chips and / or a mastication of the conveyed rubber material for example. The screws are therefore formed from an assembly of several screw elements depending on the role they have to play. There are conveying elements, masticating elements, shearing elements, etc.The screw profile can therefore have different shapes, these shapes being imposed by the sequence of these different screw elements. In the de-crosslinking sector A, we can notably use, for example, a double screw.

[0048] To allow for possible heating, the sheath elements of the de-crosslinking sector A are advantageously provided, for example, with built-in electrical resistance means.

[0049] In cooling sector B, the decrosslinking paste cools during its travel or is cooled by heat exchange. In this sector, the decrosslinked material can be compounded with various additives which can then be introduced into the extruder using conventional feed devices, only one of which, which has been given the reference 7, is shown. Depending on the additive, which can be powdery, granular, pasty or liquid, use will be made, for example, of gravimetric dosers, syringe pumps, forced-feeding elements, known per se.

[0050] In mixing sector C, chemical additives are introduced into the extruder, as crosslinking agents, via at least one conventional dosing device, only one of which is shown and has been given the reference 8.

[0051] At the outlet of the mixing sector, the extruder 2 is equipped with a collection nozzle 9 through which a rubbery material ready for crosslinking emerges.

[0052] The extrusion apparatus 10, as shown in Figure 2, comprises two extruders in succession 11 and 12, each of which comprises a barrel, formed of several barrel elements 13 and respectively 14. The screw or screws of each of these extruders are driven by a separate motor 15 and respectively 16.

[0053] The first extruder 11 is arranged upstream and covers, in the example illustrated, the decrosslinking sectors A and cooling B in linear succession. The second extruder is arranged downstream and covers the mixing sector C. It could be provided that each of the extruders covers another succession of sectors, and that for example the second extruder covers all or part of the cooling sector. It could also be envisaged a larger number of successive extruders, mutually connected so as to allow continuous extrusion.

[0054] The second extruder 12 has an inlet, into which the decrosslinked, cooled and compounded paste is fed directly from the outlet of the first extruder 11.

[0055] The start of the process implemented in the extrusion devices illustrated consists of setting in motion the screw of the extruder located in sector A. Advantageously this screw is a double screw. Below the feed channel 6 coming from the gravimetric metering device 5, the screw elements are conveyors whose role is to transfer forward the granules which enter the extruder. These granules are first transported to the center of the extruder, then sheared and masticated as they pass through the corresponding barrel and screw elements. There, the movement of the screw elements generates a mechanical shearing and masticating stress on the rubber granules. Once the extruder has stabilized, it is desirable to increase the granule flow rate while increasing the mechanical shear speed (speed of the two screws for example).Mechanical shearing of the material causes an increase in the temperature of the sheared rubber and the temperature generated, and / or communicated by the heating of barrel elements, causes the rubber crosslinking bonds to break, resulting in the formation of a high temperature decrosslinked paste.

[0056] In the same extruder or in a second or more continuously connected extruders, the decrosslinked paste is then cooled and, in the examples illustrated, directly mixed with various additives. In sector B of the extrusion apparatus, the paste comprising decrosslinked rubber is thus continuously compounded with other components, such as reinforcing fillers, plasticizers, oils, and other common additives for rubbers. These additives are introduced using standard equipment, depending on their nature.

[0057] The advantageously compounded paste passing through sector B of the extrusion apparatus cools gradually. It is desirable that upon entering sector C for mixing with crosslinking agents, such as crosslinking accelerators or activators, the paste has a sufficiently low temperature to avoid a premature crosslinking reaction thereof. Advantageously, this temperature is less than 140°C, preferably 80°C and ideally 60°C. Preferably, fillers, oils and plasticizers are therefore introduced first, if necessary, and only then the accelerators / activators which are required for crosslinking to take place. The crosslinking agents are advantageously introduced as far as possible from the sector where the paste which has just been decrosslinked is at high temperature. It is possible to cool certain barrel elements of the compounding sector B.The distance between the dosers that supply crosslinking agents and the downstream end of the extrusion apparatus (which is the outlet nozzle 9 for the decrosslinked, activated material, ready for example to be molded) must be sufficient to properly mix the crosslinking agents and the decrosslinked material. However, it must not be too long to avoid, as previously stated, a premature crosslinking reaction.

[0058] The rubbery material collected from the extrusion machine is a mixture that contains all the elements necessary for crosslinking. It is ready to be crosslinked again, for example in molds or other shaping devices. Only a temperature increase to the crosslinking temperature is still necessary.

[0059] It may be advantageous to further cool the rubbery material collected at the outlet of the extrusion device by forced convection.

[0060] The soluble fraction can be determined by the following method:

[0061] 1. Sample preparation:

[0062] Weigh 10 to + / - 0.5 g of devulcanized rubber / compounds. Extract for 16 hours in an extraction apparatus (Test Methods D297) to remove all acetone-soluble matter. Remove the sample from the apparatus and allow it to dry for 16 hours in a ventilated oven at 70°C + / -2. Cool the sample to 25°C.

[0063] 2. Determination of the soluble fraction:

[0064] Weigh the previously prepared sample (MO). Immerse the sample in 200 + / - 10 cm 3 solvent (toluene for example).

[0065] Other solvents can also be used (list in Appendix XI - standard ASTM-6814-12).

[0066] Allow the sample to swell at room temperature for 72 hours, without mixing. Carefully replace the solvent every 24 hours. After 72 hours, remove the sample from the solvent and gently remove the excess solvent using absorbent paper. Weigh the sample (Ml) on a precision balance, dry the sample in a ventilated oven at 70°C + / -2 (24 to 72 hours depending on the nature of the rubber). Remove the sample from the oven and bring it back to room temperature (23°C = / - 2). Weigh the sample (M2).

[0067] The soluble fraction is calculated as follows:

[0068] %FS = (M0-M2)*100 / M0

[0069] Preferably, the soluble fraction as defined in the invention of the devulcanized (compounded) material is between 1 and 40%, preferably between 3 and 15% by weight, relative to the total weight of the decrosslinked paste. In the context of the present invention, the decrosslinking step makes it possible to break CS or SS bonds of the material to be decrosslinked. Advantageously, this decrosslinking extends to the skeleton of the material to be decrosslinked, which makes it possible to break CC bonds.

[0070] Thus, when the soluble fraction is obtained, it contains macromolecules and molecules of low molecular weight, which characterizes decrosslinking.

[0071] Particularly advantageously, the paste according to the invention (dereticularized and / or compounded) has a devulcanization rate of between 50 and 98%, preferably between 70 and 95%, more preferably between 80 and 90%, measured according to ASTM-D6814-12.

[0072] Example 1 - sole under sleeper

[0073] The process according to the invention makes it possible to provide final products that can be used in different sectors. This example 1 concerns a sole under a sleeper.

[0074] Thus, aircraft tires are provided which are pre-treated to provide chips, which constitute the material of interest. These chips are introduced into a co-rotating twin-screw extruder as described in the present invention.

[0075] The first step is to devulcanize the chips by applying mechanical shear using the twin-screw extruder. This causes self-heating, which contributes to the breaking of the CS and SS bonds of the elastomer. Part of the elastomer skeleton also breaks. Next, the resulting decured paste is cooled and then mixed with a vulcanizing agent (sulfur), an activating agent (ZnO), and at least one accelerator (CBC). This provides a compounded paste ready for crosslinking. This process is carried out continuously. The compounded paste has the following characteristics:

[0076] - Soluble fraction of 7% relative to the total weight of the decrosslinked paste;

[0077] - Devulcanization rate of 85%.

[0078] With the resulting paste, it is possible to make a sole under the sleeper.

[0079] It should be understood that the invention is in no way limited to the exemplary embodiments described above and that many modifications may be made thereto without departing from the scope of the claims.

Claims

DEMANDS 1. A process for producing ready-to-crosslink rubber material, comprising a continuous extrusion of crosslinked rubber, in granules and / or chips, including: - a decrosslinking by mechanical shearing of said grains and / or chips of said crosslinked rubber and an increase in temperature until the formation of a decrosslinked paste, -cooling of the decrosslinked paste, and -a mixture of the cooled decrosslinked paste with at least one crosslinking agent, and a collection, at the outlet of this continuous extrusion, of a pasty mixture forming said rubbery material ready for crosslinking.

2. A method according to claim 1, characterized in that said temperature increase is generated by an input of external thermal energy and / or by the self-heating of said grains and / or chips during said shearing.

3. A process according to any one of claims 1 and 2, characterized in that said material ready for crosslinking has a crosslinking temperature and in that said mixing of the cooled decrosslinked paste takes place at a temperature lower than this crosslinking temperature.

4. A method according to any one of claims 1 to 3, characterized in that it comprises additional cooling by forced convection of said rubbery material during harvesting.

5. A method according to any one of claims 1 to 4, characterized in that said continuous extrusion further comprises a compounding of the decrosslinked material with at least one additive, during or after its cooling.

6. A process according to claim 5, characterized in that said at least one additive to be added during compounding is selected from reinforcing fillers, diluting fillers, plasticizers, oils, antioxidants, ozone protectors and mixtures thereof.

7. A method according to any one of claims 1 to 6, characterized in that said at least one crosslinking agent is selected from crosslinking agents of elastomers, sulfur, peroxides, metal oxides, phenolic resins and mixtures thereof.

8. A process according to any one of the preceding claims, characterized in that said decrosslinked paste, obtained after the decrosslinking step, comprises a soluble fraction in an amount of between 1-40% by weight, preferably between 10-35% by weight, more preferably between 20-35% by weight, more preferably still between 3-15% by weight, relative to the total weight of the decrosslinked paste.

9. A process according to any one of the preceding claims, characterized in that the ready-to-crosslink paste has a Mooney viscosity of between 10-120, preferably between 10-80, determined according to ISO-289.

10. A process according to any one of the preceding claims, characterized in that the decrosslinking step is carried out at a temperature below 350 °C, preferably above 80 °C and below 350 °C. 1 1. A process according to any one of the preceding claims, characterized in that the successive steps of decrosslinking, cooling and mixing take place in a twin-screw type extruder.

12. Device for producing ready-to-crosslink rubber material, comprising a continuous extrusion apparatus (1, 10) having an upstream inlet end equipped with a feeding system (5) in crosslinked rubber, in granules and / or chips, and a downstream end for collecting said rubbery material ready for crosslinking, and, between these ends, successively a decrosslinking sector (A) of the crosslinked rubber in granules and / or chips from the feeding system (5) where said crosslinked rubber is transformed into a decrosslinked paste, a cooling sector (B) where the decrosslinked paste is cooled, and a mixing sector (C) provided with said downstream end, in which at least one metering device (8) is provided for introducing into the cooled decrosslinked paste at least one crosslinking agent.

13. Device according to claim 12, characterized in that the continuous extrusion apparatus (1) is an extruder (2) comprising the aforementioned decrosslinking (A), cooling (B) and mixing (C) sectors in linear succession between said upstream inlet end and said downstream harvesting end.

14. Device according to claim 12, characterized in that the continuous extrusion apparatus (10) comprises several extruders (11, 12) in succession.

15. Device according to claim 14, characterized in that the continuous extrusion apparatus (10) comprises a first extruder (11), which includes said upstream inlet end, the aforementioned decrosslinking (A) and cooling (B) sectors in linear succession and an outlet for said cooled decrosslinked paste, and a second extruder (12), which includes an inlet, into which said cooled decrosslinked paste is directly brought from the outlet of the first extruder, said mixing sector (C) and said downstream harvesting end.

16. Device according to any one of claims 12 to 15, characterized in that, in the cooling sector (B), at least one supply device (7) is provided to introduce, into the decrosslinked paste, at least one additive.

17. Device according to any one of claims 12 to 16, characterized in that each of said sectors comprises a sheath static consisting of at least one sleeve element (3, 13, 14) and in each sleeve element at least one screw driven in rotation by motor (4, 15).

18. Device according to any one of claims 12 to 17, characterized in that said reticulated rubber feeding system (5), in grains and / or chips, is a gravimetric doser connected by a pipe (6) to the upstream inlet end of the continuous extrusion apparatus.

19. Device according to any one of claims 12 and 18, characterized in that at least one sheath element of the decrosslinking sector (A) is heated.

20. Device according to any one of claims 12 to 19, further comprising, at said downstream harvesting end of said rubbery material ready for crosslinking, a forced convection cooling system for this material.

Images