WO2022152514A1

WO2022152514A1 - Process for physical utilization of a polyurethane

Info

Publication number: WO2022152514A1
Application number: PCT/EP2021/086731
Authority: WO
Inventors: Delphine Delmas
Original assignee: Voith Patent Gmbh
Priority date: 2021-01-13
Filing date: 2021-12-20
Publication date: 2022-07-21
Also published as: CN116745085A; DE102021100483A1; EP4277774A1; JP2024504106A

Abstract

A process for physical utilization of a polyurethane from a press cover (6) or from a press roll or from a conveyor belt, especially for a machine for production or treatment of a fibrous material web, such as a paper, cardboard or tissue machine, wherein the press cover or press roll or conveyor belt comprises at least one layer (11) comprising a crosslinked polyurethane, wherein the polyurethane is heated to a temperature of greater than 100°C and hence melted, wherein the polyurethane comprises an aminic crosslinker. The invention further relates to a press cover (6) or a press roll or a conveyor belt, especially for a machine for production or treatment of a fibrous material web, such as a paper, cardboard or tissue machine, comprising at least one layer comprising a crosslinked polyurethane, wherein the polyurethane has been produced by the process.

Description

Process for the recycling of a polyurethane

The invention relates to a method for material utilization of a polyurethane from a press sleeve or from a press roller or from a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as a paper, cardboard or tissue machine, the press sleeve or the press roller or the conveyor belt comprises at least one layer comprising a crosslinked polyurethane, the polyurethane being heated to a temperature greater than 150° C. and thus being melted.

Press rolls are used in a large number of presses and, for example, in the form of shoe rolls in shoe presses, which in turn are used in particular for dewatering fibrous webs, such as paper webs. Such shoe presses are constructed from a shoe roll and a backing roll with a press nip formed between them. Shoe rolls consist of a stationary, ie non-rotating, pressing element, namely the shoe, and a flexible press jacket running around the shoe. Usually, the shoe is supported by a yoke that carries it and is pressed against the press jacket surrounding it by means of hydraulic pressing elements. An oil film is usually built up between the shoe and the press sleeve for lubrication. Due to the concave design of the shoe on its side opposite the backing roll, there is a comparatively long press nip, which is about 20 times longer than that of conventional presses consisting of two rotating rolls. During operation of the shoe press, a fibrous web is guided through the press nip together with one or two press felt(s) and/or another conveyor belt, with the liquid emerging from the fibrous web due to the pressure exerted on the fibrous web in the press nip, which, in addition to water, contains dissolved and undissolved compounds such as fibers, fiber fragments, fillers and/or additives, is temporarily taken up by the press felt and by depressions provided in the press sleeve surface. After leaving the press nip, the of liquid absorbed by the press jacket is thrown off the press jacket before the press jacket re-enters the press nip. In addition, the water absorbed by the press felt is removed with suction elements after leaving the press nip. Due to the relatively long press nip due to the concave design of the shoe, much better dewatering of the fibrous web is achieved with such a shoe press compared to a press consisting of two rotating rollers, so that the subsequent thermal drying can be correspondingly shorter. In this way, a particularly gentle and energy-efficient dewatering of the fibrous web is achieved.

Due to the high loads from water, fillers and/or additives as well as the mechanical stresses caused by the press impulse and the production speed, press sleeves and conveyor belts have a limited service life. After use, the worn press sleeves or conveyor belts are usually disposed of by either dumping them in a landfill or incinerating them, depending on the region.

A method for the utilization of polyurethane is known from publication EP3744812A1, which, however, involves pyrolysis and does not utilize the thermoplastic properties of a polyurethane.

The production of a thermoplastic rubber-polyurethane composite structure is known from publication EP3689935A1, which although it uses the thermoplastic properties of this polyurethane compound, is not suitable for use in press sleeves. This is because such a composite structure is not suitable for the high mechanical and chemical loads on the press sleeves and conveyor belts. In particular, the press sleeves in the shoe press are regularly treated with biocides and chemical cleaning agents, so a rubber content is not possible.

A method for recovering polyurethane is described in the publication EP0607735A1. This waste of thermoplastic polyurethane, the produced in a factory during the manufacture of shoe soles, are collected, cleaned and crushed in order to then be melted down again in a screw extruder at temperatures between 140°C and 160°C. There is no information in this publication about the chemical composition of the polyurethane used. However, it is not to be expected that such a polyurethane is a polyurethane which is suitable for use in a press jacket or a press roller or a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as paper, cardboard or tissue machine to be used.

The publication DE102013200482A1 describes a method for processing fiber composite components. However, it is not primarily about reusing the matrix material, but about recovering high-quality reinforcing fibers in the matrix material, such as carbon fibers in components in the automotive industry. It is only mentioned that the aqueous phase, which contains the decomposition products of the plastic, can be processed into new chemical raw materials if necessary. Thus, the plastic matrix material, such as polyurethane, should first be broken down into its individual components.

The publication WO2016055414A1 describes a mat or a belt for use in track construction for rail vehicles, in road construction or as conveyor belts for the extraction of minerals in quarries, in gravel works or in mine construction. The mats or bands are produced in a scattering process without vulcanization and consist of at least two scattering layers of a thermoplastic elastomer compound in the form of a rubber powder-modified polymerization mixture of rubber powder and a main thermoplastic and at least one fabric layer.

A generic method described at the outset for recycling a polyurethane is described in patent application EP3808532A1, which was only published on April 21, 2021. Thermoplastic polyurethane, such as that used for toothed belts, is recycled by being remelted at temperatures between 50°C and 300°C. However, this teaches Publication that the crosslinker of the polyurethane to be recycled may only be formed from a polyol, such as a diol or triol, but not from amines.

In practice, press sleeves, in particular shoe press sleeves, are nowadays used in machines for producing or treating a fibrous web, such as a paper, cardboard or tissue machine, which comprise a polyurethane whose crosslinker consists partly of amines. With press jackets of this type, it was previously assumed that the amine-crosslinked polyurethane could not be melted down again because it did not have the necessary thermoplastic properties.

The object of the present invention is to improve the CC balance with regard to used press sleeves, in particular shoe press sleeves, press rolls, in particular their covers or conveyor belts in machines for the production or treatment of a fibrous web.

This object is achieved by a method and by a device according to the independent claims. The dependent claims relate to advantageous developments of the present invention.

Thus, according to a first aspect of the present invention, the object is achieved by a generic method as described at the outset, in which the polyurethane comprises an amine crosslinker.

It is to the credit of the inventor to have recognized that, contrary to a long-standing prejudice in the professional world, it is actually possible to produce polyurethane from a press jacket or from a press roller or from a conveyor belt which contains an amine in the crosslinker, such as a diamine , involves being melted down and thus relatively easily recycled. In view of the relatively short period of use, particularly in the case of shoe press belts, the combustion of large amounts of polyurethane can be avoided. This has a positive effect on the CC balance in the production of fibrous webs, such as paper webs, off. In fact, it was not foreseeable that the polyurethane, although it is provided with amines in the crosslinker, would have sufficient thermoplastic properties to be able to be reused in a sufficiently high quality manner, in particular to make a new press sleeve or a new press roller or press roller cover or to produce a new conveyor belt for a machine for the production or treatment of a fibrous web.

However, the amine component in the crosslinker of the polyurethane to be recycled should not be too large, so that the polyurethane does not lose its thermoplastic properties. The proportion of the amine crosslinking agent is preferably at least 2% by weight and/or at most 15% by weight, more preferably the proportion of the amine crosslinking agent is at least 3% by weight and/or at most 10% by weight and more more preferably, the proportion of the amine crosslinker is at least 4% by weight and/or at most 9% by weight. Such a proportion of amines has led to particularly good results in practice.

The percentage by weight is based on the total weight of the crosslinker. The crosslinker serves to crosslink polyols and isocyanates with one another. In the first production of such a press cover or a press roller or a press roller cover or a conveyor belt, the polyurethane is typically used as a so-called “cast polyurethane”. This means that the individual components of the polyurethane, such as polyols, isocyanates and crosslinkers, are only brought into contact with one another and only react with one another when the end product is manufactured. However, the same polyurethane can then be used as a so-called "mold polyurethane" during recycling. This means that it can be crushed and melted down again at the appropriate temperature. In doing so, it retains its physical properties to a sufficient extent to be able to be reused as a press cover, a press roll or press roll cover or a conveyor belt for a machine for the production of a fibrous web. If necessary, it can of course also be used for other products. In order to provide the thermoplastic properties of the polyurethane, at least part of the remaining crosslinker, preferably all of the remaining crosslinker, consists of the group of short-chain dialcohols, in particular 1,2-ethylene glycol and/or 1,4-butanediol and/or 1,6 -hexanediol.

Preferably the melting temperature of the polyurethane is between 150°C and 260°C. This can be achieved by a targeted mixture of the amines and short-chain dialcohols, in particular diols of the formula (I).

HO - (CH ₂ )X - OH (I), where in formula (I) x is an integer between 2 and 14, preferably between 2 and 6.

In order to support the recycling process, it is advantageous if the polyurethane is melted at a pressure greater than or equal to 10 barA. The unit "barA" stands for "bar absolute", i.e. without taking the ambient air pressure into account.

In order to give the product the necessary stability, it is advantageous if the press cover or the press roller or the conveyor belt also includes a reinforcement structure, such as a supporting fabric, which is preferably completely surrounded by polyurethane. Thread scrims or knitted fabrics, for example, can also be used as suitable reinforcement structures.

One embodiment of the method according to the invention provides that the polyurethane layer, the polyurethane of which is melted down, is free of the reinforcement structure. In other words, only polyurethane in which no reinforcement structure is embedded is recycled. If, for example, the reinforcement structure is only provided in a middle layer of a shoe press jacket, only the polyurethane of the radially inner and/or the radially outer layer can be separated and melted down again. This saves the effort of separating the non-fusible reinforcement structure from the polyurethane immediately surrounding it.

However, provision can be made for non-meltable fractions, in particular dirt or parts of a reinforcement structure, such as a supporting fabric, to be removed from the molten polyurethane, in particular by sieving, raking, decanting or skimming.

It is irrelevant whether the process for material recycling of the polyurethane is carried out continuously or in closed process steps, the so-called batch process. If the process is continuous, it can also be advantageous to continuously remove the non-meltable fractions and thus divide the molten polyurethane into different grades.

As an alternative or in addition, non-meltable parts, in particular dirt or parts of a reinforcement structure, such as a supporting fabric, can also be mechanically separated from the polyurethane layer before the melting process, in particular by machining.

The polyurethane can be recycled particularly well if the polyurethane is melted in a closed conveying device, in particular in a screw extruder, preferably with the exclusion of oxygen. The conveying device can include a conveying area, a compression area, an area for homogenization, a heating area and/or one or more devices for degassing.

The conveying device can be selected in such a way that the working pressure of more than 10 barA and the melting temperature of the thermoplastic polyurethane of more than 150° C. can be achieved. A device for degassing can ensure that oxygen can be removed, in particular by means of a connected vacuum. In addition, water vapor from a Moisture content of the comminuted polyurethane or hygroscopically bound water arises, are removed by the device for degassing.

After the polyurethane to be recycled has been melted again, a bead-like granulate can be created from the molten polyurethane, suitable for use in further process steps, such as in an injection molding and/or extrusion process, for the production of new products, in particular for the production of a press sleeve or a Press roller or a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as a paper, cardboard or tissue machine.

Another aspect of the present invention relates to a press cover or a press roll or a press roll cover or a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as a paper, cardboard or tissue machine, comprising at least one layer comprising a crosslinked polyurethane, wherein the Polyurethane is prepared according to the inventive method for recycling of a polyurethane described above.

The invention is explained below with reference to figures. The figures show in detail:

Figure 1: a schematic view of a shoe press with a press jacket according to an embodiment of the present invention and

FIG. 2: a schematic view of a method for recycling a press cover according to an exemplary embodiment of the present invention.

FIG. 1 shows a schematic cross section of a shoe press 1 which includes a shoe roll 2 and a counter roll 3 . While the counter-roller 3 consists of a rotating cylindrically configured roller, the Shoe roller 2 composed of a shoe 4, a standing yoke 5 supporting this and a press cover 6. The shoe 4 is supported by the yoke 5 and is pressed against the press jacket 6 running around it via hydraulic press elements (not shown). Due to the concave design of the shoe 4 on its side opposite the counter-roller 3, there is a comparatively long press gap 7.

The shoe press 1 is particularly suitable for dewatering fibrous webs 8, such as paper webs. During operation of the shoe press 1, a fibrous web 8 is guided through the press nip 7 with one or two press felts 9, with the liquid emerging from the fibrous web 8 due to the pressure exerted on the fibrous web 8 in the press nip 7, which, in addition to water, contains dissolved and undissolved compounds , such as fibers, fiber fragments, fillers and/or additives, is temporarily received by the press felt(s) 9 and by depressions provided in the press jacket surface, such as grooves or blind bores (not shown). After leaving the press gap 7, the liquid taken up by the press jacket 6 is thrown off the press jacket 6 before the press jacket 6 enters the press gap 7 again. In addition, the water taken up by the press felt 9 is removed with suction elements after leaving the press nip 7 .

Due to the relatively long press nip 7 due to the concave design of the shoe 4 on the side opposite the counter-roller 3, such a shoe press 1 achieves considerably better dewatering of the fibrous web 8 compared to a press consisting of two rotating rollers, so that the subsequent thermal Drying can be correspondingly shorter. In this way, a particularly gentle dewatering of the fibrous web 8 is achieved.

FIG. 2 shows a device 10 for a method for the recycling of press sleeves 6 . A part of a polyurethane layer 11 is first removed mechanically from the press cover 6, which is then fed into a conveyor device 12. melted and processed into granules. In the exemplary representation, the conveyor device 12 is designed as a screw press 13 . The conveying device 12 has one or more degassing devices 14 , a conveying area 15 , a compression area 16 , a homogenization area 17 , and one or more heating elements 18 which melt part of the polyurethane layer 11 in a heating area 19 . After an optional cleaning to remove residues 21 that cannot be melted, a polyurethane granulate 20 that can be used for recycling 10 can then be produced by cooling and decompression.

In general, it should also be noted that when an “amine” crosslinker or an “amine” component is mentioned in this application, this is to be understood synonymously with “aminic” crosslinker or “aminic” component. In the professional world, both terms, "am in" and "aminic" are known.

Reference List

1 shoe press

2 shoe press roller

3 counter roll

4 shoe

5 standing yoke

6 press jacket

7 press nip

8 fibrous web

9 press felt

10 device for the recycling of a polyurethane

11 polyurethane layer

12 conveyor

13 screw press

14 Device for degassing

15 funding area

16 compression area

17 Homogenization area

18 heating element

19 heating area

20 polyurethane granulate

21 non-fusible residues

Claims

patent claims

1 . Process for material utilization of a polyurethane from a press cover (6) or from a press roll or from a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as a paper, cardboard or tissue machine, the press cover or the press roll or the conveyor belt comprises at least one layer (11) comprising a crosslinked polyurethane, the polyurethane being heated to a temperature greater than 150°C and thus being melted, characterized in that the polyurethane comprises an amine crosslinker.

2. The method according to claim 1, characterized in that the proportion of the amine crosslinking agent at least

2% by weight and/or at most 15% by weight.

3. The method according to claim 1 or 2, characterized in that the proportion of the amine crosslinking agent at least

3% by weight and/or at most 10% by weight.

4. The method according to any one of the preceding claims, characterized in that the proportion of the amine crosslinking agent at least

4% by weight and/or at most 9% by weight.

5. The method according to any one of the preceding claims, characterized in that at least part of the remaining crosslinker, preferably all of the remaining crosslinker, consists of the group of short-chain dialcohols, in particular 1,2-ethylene glycol and/or 1,4- butanediol and/or 1,6-hexanediol.

6. The method according to any one of the preceding claims, characterized in that the melting temperature of the polyurethane is between 150 °C and 260 °C.

7. The method according to any one of the preceding claims, characterized in that the melting of the polyurethane takes place at a pressure greater than or equal to 10 barA.

8. The method according to any one of the preceding claims, characterized in that the press cover or the press roller or the conveyor belt also comprises a reinforcing structure, such as a supporting fabric, which is preferably completely surrounded by polyurethane.

9. The method according to claim 8, characterized in that the polyurethane layer, the polyurethane of which is melted down, is free of the reinforcing structure.

10. The method according to any one of the preceding claims, characterized in that non-meltable portions, in particular dirt or parts of a or the reinforcement structure, such as a supporting fabric, are removed from the molten polyurethane, in particular by sieving, raking, decanting or skimming.

11 . Method according to one of the preceding claims, characterized in that non-meltable parts, in particular dirt or parts of a or the reinforcement structure, such as a supporting fabric, are mechanically separated from the polyurethane layer (11) before the melting process, in particular by machining removal. - 14 - Method according to one of the preceding claims, characterized in that the melting of the polyurethane takes place in a closed conveyor (12), in particular in a screw press (13), preferably with the exclusion of oxygen. The method of claim 12, characterized in that the conveying device (12) has a conveying area (15), a compression area (16), an area for homogenization (17), a heating area (19) and/or one or more devices for degassing (14) includes. Method according to one of the preceding claims, characterized in that a bead-like granulate (20) is created from the molten polyurethane, suitable for use in further process steps, such as in an injection molding and / or extrusion process, for the production of new products, in particular for Manufacture of a press cover (6) or a press roller or a conveyor belt, in particular for a machine for the manufacture or treatment of a fibrous web, such as a paper, cardboard or tissue machine. Press jacket (6) or press roller or conveyor belt, in particular for a machine for the production or treatment of a fibrous web, such as a paper, cardboard or tissue machine, comprising at least one layer comprising a crosslinked polyurethane, the polyurethane according to the material utilization process being derived from a polyurethane is made according to any one of the preceding claims.