EP2118164A2

EP2118164A2 - Roller cover and method for the production thereof

Info

Publication number: EP2118164A2
Application number: EP07875254A
Authority: EP
Inventors: Michael Wokurek; Martin Breineder
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2006-12-18
Filing date: 2007-12-18
Publication date: 2009-11-18
Also published as: WO2009103301A2; WO2009103301A3

Abstract

The invention relates to a method for producing a sheath or cover (1) for a roller from an NDI-based polyurethane plastic. Moreover, in order to avoid tension cracks, the green strength weakness is to be overcome as quickly as possible by adding a hardener, which shortens the pot life to 5 to 60 seconds, to the polyurethane. The invention also relates to an NDI polyurethane for the production of a sheath or a cover (1) of a roller, formed by mixing an NDI prepolymer with a hardener, especially for carrying out the method. In this connection, it is essential that the hardener consists of 60 to 99% by weight of 1,4-dihydroxybutane, not more than 40% by weight of a diamine and not more than 1% by weight of a catalyst.

Description

Roll cover and method for its production

The invention relates to a method for producing a roll shell or roll cover of a roll made of an NDI-based polyurethane plastic.

The invention also relates to an NDI polyurethane for producing a roll shell or roll cover of a roll formed by mixing an NDI prepolymer with a curing agent.

Polyurethane elastomers which are formed by a one- or multistage reaction of NDI (naphthylene-1,5-diisocyanate) with mixtures of polyols, diols and diamines have been known for several decades.

NDI polyurethane elastomers are characterized by high tear and tear propagation resistance, high abrasion resistance, and high elasticity.

However, hardening causes excessive shrinkage and poor green strength.

The object of the invention is therefore to reduce the shrinkage and to improve the green strength, so as to expand the application possibilities of the plastic.

According to the invention, this object is achieved in that the curing agent added to the polyurethane prepolymer shortens the pot life to 5 to 60 s.

Due to the reduced pot life it comes to a rapid overcoming of green strength weakness, which significantly reduces the risk of stress cracks during curing of the plastic.

It is advantageous if the pot life is shortened to 8 to 20 s.

Due to the suitable choice of the hardener, the reaction rate and the increase in viscosity in the course of the crosslinking reaction between the NDI-based preparation and Polymer and the hardener are controlled so that the production of the roll mantle or the roll cover is possible by means of rotational molding.

This is further supported by the fact that the accelerated cross-linking reaction is a rapid passage through the period of pot-shaped material consistency in which the material is firm, but without significant mechanical strength and elasticity.

The plastic is applied to a cylindrical, rotatably mounted casting with a movable parallel to the axis of the casting pouring nozzle, wherein the temperature of the applied plastic should be between 90 and 150 ⁰ C.

To reduce the stress cracking tendency of the applied plastic during curing, it should contain a catalyst, which is preferably selected from the group of polyurethane polymerization catalysts. This group includes various organometallic compounds and salts of Zn, Co, Bi, Hg, Cd, K and the like. such as.:

Dibutyltin dilaurate, stannous octoate, dioctyltin diacetate, dibutyltin mercaptide, dibutyltin oxide, dimethyltin mercaptide, dioctyltin mercaptide, dimethyltin carboxylate, ... Further all tertiary amines such as:

Bis (2-dimethylaminoethyl) ether, alkylmorpholines, 1, 4-diazabicyclooctane, N ₁ N- Alkylbenzylamine, 1, 2-dimethylimidazole, N, N-dimethylcyclohexylamine, N, N, N ^', ^N' - tetramethylethylenediamine.

Especially when casting large hollow cylindrical components, such as press jackets or roll covers, it has proven to be advantageous if the peripheral speed of the casting is between 15 and 80 m / min and the casting nozzle is moved axially at a speed between 5 and 10 mm / revolution.

In order to achieve a good mixing of the components, the mixture should be carried out with the hardener in a mixing chamber according to the rotor / stator principle. It is advantageous that rotor and stator are constructed so that the following conditions are met:

The gap width distribution between the rotor and the stator resulting from the structural design should be in the range of 1 to 5 mm and should be as narrow as possible in order to achieve as uniform as possible a shear stress on the reaction mixture and thereby prevent clogging of the mixing chamber in areas of low shear rate.

The dead volume of the mixing chamber should be as low as possible. Mixing chambers with a dead volume of 5 to 50 ml have proven particularly suitable for mixing a material volume flow of 0.5 to 10 l / min.

The resulting short residence times require very effective mixing which is achieved, on the one hand, by high rotor speeds in the range of 1000-5000 rpm and, on the other hand, by flow dividing elements on the rotor and stator which prevent a straight-line flow through the mixing chamber.

With regard to the NDI polyurethane, it is essential to the invention that the hardener consists of 60 to 99% by weight of 1, 4-butanediol, a maximum of 40% by weight of diamine and at most 1% by weight of a catalyst.

By means of such a hardener composition, the desired influence on the reaction rate and the increase in viscosity can be achieved particularly well in the course of the crosslinking reaction.

It is advantageous if the hardener contains at least 1% by weight of diamine and / or at least 0.01% by weight of a catalyst.

The diamine in the hardener mixture should advantageously be chosen from the following group: - A -

Diethyl toluene diamine, dimethylthiotoluene diamine, hexamethylene diamine, tetramethylene diamine, ethylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1, 4- diaminocyclohexane, 1, 2-diaminocyclohexane, 4,4 ^{'-Diaminodiphenylnnethan,} iso- phorondiamin, 4.4 ^* -Diaminodicyclohexylnnethan, 4.4 ^* -Methylene-bis- (3-chloro-aniline), 4.4 ^* -Methylene-bis- (3-chloro-2,6-diethylaniline), Trime thylenglycoldi-p-annino- benzoate, 1, 2-bis (2-aminophenylthio) ethane, 4,4 ^* diamino-3,3 ^* -dinnethyl-dicyclohexylmethane.

The NDI prepolymer is advantageously prepared immediately before the casting process by a chemical reaction of naphthylene-1, 5-diisocyanate with a polyol.

The procedure is that the polyol is placed in a reaction vessel and brought to a starting temperature of about 100-150 ⁰ C depending on the type.

Subsequently, the solid NDI is mixed quickly and with constant stirring.

During and after the decay of the incoming chemical reaction, the prepolymer is gradually degassed by applying a vacuum. The prepolymer thus prepared must be further processed within a period of 0.5-2 hours as described.

The polyol is advantageously chosen from the following group:

Polypropylene glycol, polytetramethylene glycol, polyester polyols, polycarbonate polyols, polybutadiene polyols, polycaprolactone polyols.

Preference is given to using linear diols having an average molecular weight in the range from 650 to 3000.

In some cases it is advantageous for the purpose of adjusting the viscosity to add a part of the polyol not in the course of the prepolymer preparation but in the course of the crosslinking reaction as admixture with the hardener component.

Alternatively, the recently available finished NDI prepolymers from BAYER, such as: Vulkollan 15 S37, can be used. The stoichiometry of the mixture, that is the molar ratio between the isocyanate content and the content of reactive hydrogen, should be between 0.80 and 1.20 in order to obtain an optimally balanced material property spectrum.

Such a produced roll shell or roll cover is very wear-resistant, heavy-duty and durable and is due to the high demands in particular for use in rolls in machines for producing and / or finishing a paper, cardboard, tissue or another fibrous web.

Preferably, the roll shell according to the invention is used in a soft roll of a calender.

The hardness of the NDI polyurethane in the roll cover is preferably between 80 Shore A and 75 Shore D.

Furthermore, the loss factor of the NDI polyurethane in the roll cover is preferably between 0.01 and 0.03. Due to the low damping, the roll cover is optimized in relation to the maximum possible load pairing pressure / load frequency.

The elastic modulus of the NDI polyurethane in the roll cover is preferably between 100 and 3000 N / mm ² .

The invention will be explained in more detail with reference to an exemplary embodiment. In the accompanying drawing, the figure shows a schematic cross section through a casting apparatus.

In this case, a plastics material for forming a roll cover 1 is applied to a rotatably mounted casting body 2 in the form of a cylindrical roll base body by rotational molding. This is done via a suitably formed pouring nozzle 3, which receives the liquid plastic with a temperature between 130 and 140 ⁰ C from a mixing chamber 4.

The dynamic mixing chamber 4 operates on the rotor / stator principle.

During application, the casting body 2 rotates at a preferably constant peripheral speed, which lies between 15 and 80 m / min. The parallel to the axis of rotation 5 of the casting 2 movable casting nozzle 3 is moved at a speed between 2 and 15, usually between 5 and 10 mm / revolution, so that a uniformly strong relation to the casting 2 is applied.

The output of the pouring nozzle 3 is between 500 and 10,000 g / min.

To produce a roll cover 1 which is as resistant as possible, the plastic is formed by NDI polyurethane, which is produced by mixing an NDI prepolymer with a hardener in the mixing chamber 4.

The hardener should shorten the pot life to values between 8 and 12 s. This accelerated crosslinking allows the application of the rotational casting process.

This is achieved here by a hardener consisting of 96% by weight of 1, 4-butanediol, 4.95% by weight of p-phenylenediamine and 0.05% by weight of dioctyltin mercaptide.

The proportion of diamine determined by its extremely fast reaction rate, the flow behavior of the plastic mixture at the time of exit from the casting nozzle 3 and in the first 2-5 seconds after. This flow behavior is crucial for successful process control. Too low a viscosity, depending on the speed and diameter of the rotating casting body 2, results in rapid draining or spilling off of the used-up material and thus limits the achievable layer thickness. Too high viscosity prevents uniform flow of the plastic, resulting in an undesirable coarse surface texture (ribs) and air pockets.

The catalyst subsequently causes a rapid re-drawing of the butanediol isocyanate crosslinking reaction. He is thus responsible for a very rapid passage through the period of the potting material consistency (cheesy state) during which the workpiece is extremely susceptible to the occurrence of fatal stress cracks.

The combined use of both hardener components allows both to set the required for the Rotationsgußsprozess flow behavior of the plastic mixture, as well as to ensure a stress-crack-free end product.

The Stöchiomiethe of the mixture is 85% (isocyanate excess).

This is particularly advantageous in the production of rolls for use in machines for producing and / or finishing a paper, board, tissue or another fibrous web. Such rolls are subjected to a very high load and have lengths of up to 10 m and a diameter of up to 2 m.

The process as well as the plastic are also suitable for the production of flexible roll shells. These are usually reinforced by fibers embedded in the plastic, threads or the like and are mainly used in the dewatering or smoothing of the fibrous web.

The roll shells are made in an analogous manner by applying the plastic to a cylindrical casting 2, wherein the finished roll shell, however, withdrawn from the casting 2 or the casting 2 is removed from the cast roll shell. Roll covers 1 or roll shells produced in this manner are distinguished by an increase in the permanent load capacity with regard to line load and machine speed and the extension of possible grinding intervals for machining the jacket surface.

Claims

claims

1. A method for producing a roll shell or roll cover (1) of a roll of an NDI-based polyurethane plastic, characterized in that the polyurethane prepolymer added hardener shortens the pot life to 5 to 60 s.

2. The method according to claim 1, characterized in that the pot life is shortened to 8 to 12 s.

3. The method according to claim 1 or 2, characterized in that the

Production by means of rotational molding takes place.

4. The method according to claim 3, characterized in that the plastic on a cylindrical, rotatably mounted casting body (2) with a parallel to the axis (5) of the casting body (2) movable pouring nozzle (3) is applied.

5. The method according to any one of the preceding claims, characterized in that the temperature of the applied plastic is between 90 and 150 ⁰ C.

6. The method according to any one of the preceding claims, characterized in that the curing agent contains a catalyst which preferably originates from the group of PU Polymeriastionskatalystoren and in particular is formed by organometallic compounds, salts or tertiary amines.

7. The method according to any one of claims 4 to 6, characterized in that the peripheral speed of the casting body (2) is between 15 and 80 m / min.

8. The method according to any one of claims 4 to 7, characterized in that the casting nozzle (3) is moved axially at a speed between 2 and 15, in particular between 5 and 10, mm / revolution.

9. The method according to any one of the preceding claims, characterized in that the mixture is carried out with the hardener in a mixing chamber (4) according to the rotor / stator principle.

10. NDI polyurethane for producing a roll shell or roll cover (1) of a roll formed by mixing an NDI prepolymer with a curing agent, in particular for carrying out the process according to any one of the preceding claims, characterized in that the hardener from 60 to 99 weight % 1, 4-butanediol, at most 40% by weight of diamine and at most 1% by weight of a catalyst.

1 1. NDI polyurethane according to claim 10, characterized in that the NDI prepolymer is prepared from at least one polyol from the following group:

Polypropylene glycol, polytetramethylene glycol, polyester polyols, polycarbonate polyols, polybutadiene polyols, polycaprolactone polyols, polyester diols, polycaprolactone diols, polycarbonate diols.

12. NDI polyurethane according to claim 10, characterized in that the hardener contains at least 1% by weight of diamine.

13. NDI Polyurehtan according to claim 10 or 1 1, characterized in that the curing agent contains at least 0.01% by weight of a catalyst.

14. NDI polyurethane according to any one of claims 10 to 12, characterized in that the diamine is selected from the following group: diethyltoluenediamine, dimethylthiotoluene diamine, hexamethylenediamine, tetramethylenediamine, ethylenediamine, o-phenylenediamine, m-phenylenediamine, p- Phe- nylendiamin, 1, 4-diaminocyclohexane, 1, 2-diaminocyclohexane, 4,4 ^'-Diamin- odiphenylmethan, isophoronediamine, ^{4,4'-diaminodicyclohexylmethane,} 4,4 ^{^} -Methy- lene-bis (3-chloro- aniline), 4.4 ^* -Methylene-bis- (3-chloro-2,6-diethyl-aniline), trimethyl-p-aminobenzoate thylenglycoldi, 1, 2-bis (2-aminophenylthio) ethane, 4,4 ^{^} -Diamino-3,3 ^{^} -dimethyl-dicyclohexylmethane.

15. NDI polyurethane according to any one of claims 10 to 13, characterized in that the catalyst is selected from the group of PU Polymeriastionskatalystoren and is preferably formed by organometallic compounds, salts or tertiary amines.

16. NDI polyurethane according to one of claims 10 to 14, characterized in that the mixing ratio between the prepolymer and the curing agent corresponds to 80 to 120% stoichiometry.

17. NDI polyurethane according to one of claims 10 to 15, characterized in that the hardness is between 80 Shore A and 75 Shore D.

18. Roller having a roll core and a peripheral surface of the roll core at least partially surrounding roll cover, wherein the roll cover comprises a NDI polyurethane according to one of the preceding claims.

19. Roller according to claim 18, characterized in that the hardness of the NDI polyurethane in the roll cover between 80 Shore A and 75 Shore D.

20. Roller according to claim 18 or 19, characterized in that the

Loss factor of the NDI polyurethane in the roll cover is between 0.01 and 0.03.

21. Roller according to one of claims 18 to 20, characterized in that the

Elastic modulus of the NDI polyurethane in the roll cover between 100 and 3000 N / mm ² .

22. Application of the roller according to one of the preceding claims in a machine for producing and / or finishing a paper, cardboard, tissue or another fibrous web.

23. Application of the roller according to one of the preceding claims as a soft roller in a calender.