GB2167076A

GB2167076A - Method of producing polyurethane articles

Info

Publication number: GB2167076A
Application number: GB08524060A
Authority: GB
Inventors: Julius Peter; Fritz Koch; Klaus Witt
Original assignee: Continental Gummi Werke AG
Current assignee: Continental AG
Priority date: 1984-10-13
Filing date: 1985-09-30
Publication date: 1986-05-21
Also published as: DE3437643A1; IT8522218A0; IT1190390B; FR2571729A1; GB8524060D0

Abstract

A method of producing cross-linked polyurethane articles using a two-stage cross-linking process, whereby a mouldable polyurethane is produced on the basis of polyol, polyisocyanate in excess and diol having a molecular weight of up to 300. To improve the temperature stability of the polyurethane articles, peroxide is added as an additional cross-linking agent, the polyurethane article is then moulded in a manner known per se at temperatures below the decomposition temperature of the peroxide used and tempered, and finally the polyurethane article is heated to a temperature which lies above the decomposition temperature of the peroxide used.

Description

SPECIFICATION Method of producing polyurethane articles The present invention relates to a method of producing cross-linked polyurethane articles using a twostage cross-linking process, whereby a mouldable polyurethane is produced on the basis of polyol, polyisocyanate in excess and diol having a molecular weight of up to 300.

Methods of producing cross-linked polyurethane articles are known, whereby either isocyanates or peroxides are used as cross-linking agents. The articles produced according to these known methods, however, frequently only have a very low temperature stability.

In consequence, the invention seeks to provide a method which permits polyurethane articles which have been cross-linked from a mouldable polyurethane to be produced with a high temperature stability.

According to the invention, this object is achieved, in that peroxide is added as an additional crosslinking agent, the polyurethane article is then moulded in a manner knownper se at temperatures below the decomposition temperature of the peroxide used and tempered, and finally the polyurethane article is heated to a temperature which lies above the decomposition temperature of the peroxide used.

The invention can be used in a particular advantageous manner for driving and resilient suspension elements made of polyurethane. In consequence, rollers, solid tyres and drive belts which have been made in accordance with the invention not only exhibit an improved temperature stability, but they also exhibit an increased bearing strength. Favourable properties also result in respect of structural strength, wear-resistance and elasticity.

In order to produce polyurethane articles in accordance with the invention, a mouldable polyurethane is initially produced on the basis of polyester or polyether, diphenyl methane-4,4'-diisocyanate (MDI) and 1,4-butane diol in the prepolymer or one-shot method. A peroxide is additionally mixed therein. The urethane reaction is completed at approximately 120 C.

After removal from the mould, the polyurethane articles are tempered for twenty-four hours at approximately 100"C to achieve the optimum properties of a polyurethane. The moulded parts are subsequently vulcanised in a boiler for approximately 30 minutes at approximately 165"C under an air pressure of 2 to 10 bars. The peroxide thereby decomposes into radicals which produce cross-linkings between C atoms.

Cross-linking bridges are consequently produced with a thermal stability which is unusual for polyurethane.

Liquid or solid peroxides and soluble or dispersable peroxides may be used as the additional crosslinking agent. Finally, peroxide mixtures are also usable.

According to further embodiments of the invention, it is also possible to use the co-cross-linking agents, plasticizers, fillers and inflating agents generally used for elastomers; finally, mention should be made of the incorporation of unsaturated components, e.g. glycerin monoallyl ether. With regard to the use of MDI, it should be mentioned that MDI may also be used with a functionally 2.

The invention provides advantages, however, not only for the manufacture of solid tyres or rollers, but also for the production of polyurethane foam. In such case, the reaction may be effected with water and possibly in the presence of surface-active substances, e.g. Turkey-red oils, and conventional activators or retarders of the urethane reaction may be used.

Several examples are listed hereinafter. Example 1 in the list represents a reference mixture resulting from prior art, while, in Examples 2 to 6, mixtures are mentioned which are produced according to the method of the invention. In conclusion, the technological values for Examples 1 to 6 are compiled in a Table. The values were determined in accordance with DIN (German Industrial Standards) Specification Nos. 53505, 53479, 53504, 53512 and 53517, and the prescribed test plates were produced for this purpose.

Example 1 1,000 g of a polytetrahydrofuran having a molecular weight of 2,000 are drained of water under vacuum at 120"C for 30 minutes. 700 g of pure MDI are then added in powder form. After a reaction time of 15 minutes, 200 g of 1,4-butane diol are added and, after completion homogenisation, the starting solution is poured away. After 24-hour tempering at 110 C and subsequent press-heating for 20 minutes at 160"C, the production of the test plates is terminated.

Example 2 19 g of a 95% dicumyl peroxide (DCP) are added to the starting solution according to Example 1, and the test plates are produced as described above.

Example 3 38 g of a 95% DCP are added to the starting solution according to Example 1, and the test plates are produced as described above.

Example 4 38 g of DCP and 10 g of triallyl cyanurate (TAC) are admixed to the starting solution according to Example 1, and the test plates are produced as described above.

Example 5 38 g of DCP and 20 g of TAC are admixed to the starting solution according to Example 1, and the test plates are produced as described above.

Example 6 38 g of DCP and 40 g of TAC are admixed to the starting solution according to Example 1, and the test plates are produced as described above.

Technological values.

Example --1-- --2-- --3-- --4-- --5-- --6- Density gicm3 1.135 1.135 1.135 1.135 1.135 1.135 97/48 97/48 97:47 97!45 97145 97143 Strength N!mm2 44 38 31 21 26 26 Expansion % 520 430 350 260 250 230 DVR after 24 h at 70 C % 33 31 29 -- -- - 100 C % 41 40 35 31 32 32 130 C % -- -- -- 53 52 48 Impact elasticity % 50 47 47 54 53 52

Claims

1. A method of producing cross-linked polyurethane articles using a two-stage cross-linking process, whereby a mouldable polyurethane is produced on the basis of polyol, polyisocyanate in excess and diol having a molecular weight of up to 30û, in which peroxide is added as an additional cross-linking agent, the polyurethane article is then moulded in a manner known per se at temperatures below the decomposition temperature of the peroxide used and tempered, and finally the polyurethane article is heated to a temperature which lies above the decomposition temperature of the peroxide used.

2. A method as claimed in claim 1, in which a peroxide is used as an additional cross-linking agent and the decomposition temperature of the peroxide is above 100cm.

3. A method as claimed in claim 2, in which the decomposition temperature of the peroxide is approximately 150C.

4. A method as claimed in claim 1, in which a peroxide mixture is used as an additional cross-linking agent.

5. A method as claimed in any preceding claim, in which the polyisocyanate used is diphenyl methane-4,4'-diisocyanate (MDI)

6. A method as claimed in claim 5, in which the quantities of MDI and peroxide used are selected in such a manner that the molecular weight ratios of MDI : peroxide lie between 10 and 30.

7. A method as claimed in any preceding claim, in which a diol having unsaturated groups is used.

8. A method as claimed in any preceding claim, in which additional co-vulcanising agents are added.

9. A method as claimed in any preceding claim, in which water and conventional additives for polyurethane foams are used in the case of foam production to achieve a foam structure.

10. A method of producing constructed polyurethane articles as claimed in any preceding claim, substantially as hereinbefore described and exemplified in Examples 2 to 6.

11. Polyurethane articles having improved temperature stability, more especially solid tyres, rollers, drive belts or polyurethane elastomeric foams, whenever produced by a method as claimed in any one of claims 1 to 10.