GB2033916A

GB2033916A - Lubricants and release agents for rubber mouldings

Info

Publication number: GB2033916A
Application number: GB7935486A
Authority: GB
Original assignee: TH Goldschmidt AG
Current assignee: Evonik Operations GmbH
Priority date: 1978-10-16
Filing date: 1979-10-12
Publication date: 1980-05-29
Also published as: GB2033916B

Abstract

Compositions suitable for use both as lubricants and release agents for rubber mouldings comprise a curable silicone resin and an oil which does not dissolve or swell rubber, the components being present in a weight ratio of 5:1 to 1:20. These compositions enable the production of rubber mouldings, in particular seamless tubes or hoses, such that the moulded rubber is easily removed from the mould after vulcanisation.

Description

SPECIFICATION Lubricants and release agents for rubber mouldings The present invention relates to compositions suitable for use as lubricants and release agents for rubber mouldings.

Rubber mouldings are in general manufactured by pressing, casting, or extrusion of vulcanisable intermediate products. It must be possible to remove the mouldings easily from the mould after vulcanisation. For this purpose, silicone oils of medium viscosity or emulsions containing silicone oils of this type are frequently used.

If the rubber compositions which are to be vulcanised are extruded, as is customary, for example, in the manufacture of so-called long hoses or tubes which are extruded over mandrels, a release agent of this type must also have lubricating properties.

Thus, the rubber composition must neither stick to the mandrel nor should excessive friction occur when the composition slips over the mandrel.

Silicone oils or silicone oil emulsions are not capable of simultaneously having a release effect and improving the slip properties. Dispersions of polytetrafluoroethylene (Teflon) in solvents have proved suitable in practice. There are difficulties, however, in applying these dispersions uniformly and reproducibly to the surfaces of the shaping parts. Moreover, due to their high price, these dispersions can only be used to a limited extent.

It has therefore been desirable to find an agent which has both release and lubricating properties towards rubber compositions on moulding surfaces, and which can be applied in as thin a layer as possible to the surface of the mould which is to be shaped. The lubricating/release agents should: adhere well to the surface, be effective over as long a period as possible, not decompose under the process conditions, and not adversely affect the rubber orthe use properties of the rubber moulding obtained aftervulcanisation.

In accordance with the present invention there is provided a composition comprising a curable silicone resin and an oil which does not dissolve or swell rubber, in a weight ratio of 5:1 to 1; 20. The composition ofthe present invention can act both as a lubricant and as a release agent in the manufacture of rubber mouldings, and is of particular use in the manufacture of seamless tubes or hoses.

The present invention also provides a method of producing a rubber moulding which comprises moulding a vulcanisable rubber in contact with a surface which has been treated with a composition as defined above.

By curable silicone resins there are to be understood resins which contain silicon atoms and which can be fully cured on the shaping surface at a temperature from 120 to 1800C during a period of at most 10 to 30 minutes. Both pure silicone resins and silicone resins which have been modified with organic blocks can be used for this purpose.

Suitable pure silicone resins are especially methylsilicone resins and resins in which some of the methyl groups are replaced by phenyl groups.

Methylphenyl-silicone resins in which the ratio of methyl : phenyl groups is 1:1 are particularly suitable.

Suitable organically-modified silicone resins are in particular those which have been prepared by a reaction of reactive silicone resin precursors with polyester resins. Resins of this type are described, for example, in German Auslegeschrift 2,232,419.

According to the process described therein, alkyl- or aryl-substituted polyesters which carry SiO-alkyl groups are reacted with polyesters containing OH groups, block co-condensation products being formed. Organically-modified silicone resins which contain, as the organic members, compounds of the formula

wherein Rl and R2 denote alkylene radicals having 2 to 4 carbon atoms, can also be used.

The invention is not, however, restricted to the use of the abovementioned organically-modified silicone resins. In principle, all silicone resins which, in the indicated temperature range, fully cure to give a hard and smooth film, can be used.

Oils contained in the mixture, which have proved suitable, are silicone oils having a viscosity from 100 to 10,000 mPa . seconds. In general, the silicone oils contain the methyl radical as the substituent which is bonded organically to the silicon atom. It is, however, also possible to use different oils which are known to improve the slip properties by reducing friction. Neat's foot oil is an example of such an oil.

Further suitable oils are pentaerythritol tetrapelargonate, trimethylolpropane tripelargonate, soya oil and rapeseed oil.

It is also possible to use addition products of ethylene oxide and propylene oxide or mixtures of the two with alcohols, in particularthose having 1 to 6 carbon atoms, or corresponding addition products with polyhydric alcohols, such as glycol, glycerol and TMP (trimethylolpropane). The extent of the addition of alkylene oxides is limited by the requirement that the products of the addition reaction must have an oily consistency. Such addition products generally have molecular weights from 1,000 to 10,000. As a rule, however, the suitability of oil-like substances which do not dissolve or swell rubber is yet further restricted by the fact that these oil-like substances must be resistant to water. This means that they must not be removable by water which is used for forcing the mandrels out.Oil-like substances which are water-soluble are thus unsuitable in these circumstances.

For application, the resin and the oil which are to be used according to the invention are advantageously dissolved in a common solvent. For this purpose, low-boiling chlorinated hydrocarbons, such as 1,1 ,1-trichloroethane, methylene chloride and trichloroethylene, are preferably chosen. Mixtures of solvents of this type can also be used. Advantageously, the solutions contain 3 to 10% by weight of active ingredients. The solution is sprayed onto the shap ing surfaces, for example the mandrel of an extrud ing machine, in the manufacture of hoses. After the solvent has evaporated, the resin is fully cured at elevated temperatures. In the course of cu ring, a certain segregation of the oil and the silicone resin occurs, so that a thin film of oil is formed on the surface.

The following Example illustrates typical formula tions for the compositions of the invention.

Example Slip/release agents are prepared by dissolving curable silicone resins and oils which do not dissolve or swell rubber, in a solvent mixture consisting of equal parts of 1,1,1-trichloroethane and methylene chloride. The following basic formulation was used: x /O by weight of the solution of a curable silicone resin y /O by weight of an oil which does not dissolve or swell rubber 100-x-y /O by weight of 1,1,1 -trichloroethane 2 100-x-y /O by weight of methylene chloride.

2 The curable silicone resins used were: a) a 60% strength solution of a silicone-modified polyester resin in xylene/cyclohexanone, which had been prepared by the method described in German Auslegeschrift 2,232,419, Example 19, b) a 50% strength solution of a methylsilicone resin in-toluene/butanol, having a viscosity of 60 mm2 s-1 at 293 K, a ratio of CH3 groups : silicon of 1.15 and a OH group content of 0.8% by weight, relative to solvent free silicone resin, or c) a 50% strength solution of a methylphenylsilicone resin in toluene/cyclohexanone, having a viscosity of 160 mm2 s~' at 293 K and a ratio of organic groups: silicon of 1.20, 20% of the organic groups being phenyl groups and 80% being methyl groups.Moreover, the resin contains 0.6% by weight of OH groups.

The oils used, which do not dissolve or swell rubber, are: a) dimethylpolysiloxanes which have viscosities of 1,000 mm2 s~' and 100 mm2 s' at 29 K and which are called silicone oils in the Table which follows b) a polyoxyethylene/polyoxypropylene monobutyl ether which has a molecular weight of 1,770 and a proportion of polyoxypropylene groups of 59.0 /O by weight and which is briefly called a polyether in the Table which follows, c) a commercially available rapeseed oil having the following characteristics: saponification number: 170 mg KOH/g iodine number: 98 d) a commercially available soya oil having the following characteristics: saponification number 193 mg KOH/g iodine number: 124 The mixing ratios between the curable silicone resins and the oils which do not dissolve or swell rubber, and the release forces obtained by the measurement method described in the following text are compiled in Table 1.

To measure the release forces, the mixtures, containing solvent, of curable silicone resin and oils which do not dissolve or swell rubber, are applied to a cylindrical stainless steel mandrel with a diameter of 30 mm and a length of 150 mm in such a way that about0.1g of the release agent combination is uniformly distributed over 100 cm2 of surface. The mandrel is then covered with a 10 cm wide, 6 mm thick strip which completely surrounds the periphery of the mandrel and consists of an unvulcanised rubber mixture. To ensure perfect moulding, two halfshells of stainless steel are now placed around the rubber strip and firmly joined to one another.The half-shells are formed in such a way that, during the subsequent vulcanisation and the expansion associated therewith, no rubber can- emerge from the sealing joints and mounting joints between the mould and the mandrel. The arrangement charged in this way is then transferred into a vulcanisation kettle and the rubber mixture is fully vulcanised at an appropriate temperature for an appropriate time.

In this Example, an acrylonitrile/butadiene rubber mixture, having a tensile strength (DIN 53,504) of 9.0 Nmm-2 and a Shore hardness (DIN 53,505) of 50 Shore A, was used. The vulcanisation time was 20 minutes at 423 K (150"C). After the end of vulcanisation, the arrangement was removed from the vulcanisation kettle and was cooled to 323 K (50"C). The Size of the force acting tangentially on the moulding which is necessary to displace the moulding relative to the mandrel was then measured. An initial force (static friction) is measured, which is necessary for initiating the displacement - designated release value in the Table - and a second force (sliding friction), is measured, which is necessary to continue the displacement- designated slip value in the Table. A good release agent should have a low release value and an even lowerslip value. In practice, particularly for the manufacture of so-called long hoses, it has proved possible to use those release agents which have a release value of < 10 and a slip value of < 3 without problems.

Table 1 shows that the comparison formulations 1 to 8 which are not in accordance with the invention do not give adequate release/slip values. Although the pure methyl-silicone resin and also the pure silicone oils give good release values, the lubricating effect, expressed by the slip value, is insufficient, whereas the mixtures according to the invention (formulations 9 to 18) give both good release values and good slip values.

TABLE 1

Slip/release Curable silicone resin Oil component Release Agent No. forces Parts Type of silicone Parts Type of oil Release slip by resin by value value weight weight 1 8.0 Silicone polyester 11.0 7.4 60g strength 2 0.0 Methylsilicone 8.5 6.3 resin 50% strength 3 0.0 Methylphenyl- 14.2 7.0 silicone resin 50% strength 4 5.0 Silicone oil 7.8 5.5 1,000 mms- 5 5.0 Silicone oil oo mm2S-1 8.9 4.8 6 5.0 olyether 18.0 6.3 TABLE 1 CONT'D

Slip/release Curable silicone resin Oil component Release Agent No. forces Parts Type of silicone Parts Type of oil Release slip by resin by value value weight weight 7 5.0 Rapeseed oil 14.1 5.8 8 5.0 Soya oil 11.6 6.2 9 8.0 Silicone polyester 5.0 Silicone oil 8.5 2.5 60% strength 1.000 mms- 10 8.0 Silicone polyester 1.0 Silicone oil 8.8 2.8 2 -l 60% strength l,ooo mm s 11 4.0 Silicone polyester 5.0 Silicone oil 6.3 1.8 2 -1 60X strength 1,000 mm s 12 8.0 Silicone polyester 1.0 Rapeseed oil 8.4 2.4 60% strength TABLE 1 CONT'D

SlipZrelease Curable silicone resin oil Component Release Agent No. forces Parts Type of silicone Parts Type of oil Release slip by resin by j value value weight weight 13 10.0 Netbylsilicone 2.5 Silicone oil 6.0 2.1 resin 100 mm2s- 50% strength 14 10.0 Methylsilicone 2.5 Polyether 8.0 1.5 resin 50X strength 15 lo.o Methylphenyl- 5.0 Silicone oil 6.5 2.5 silicone resin 1,000 mm2s 50% strength 16 2.0 Nethylphenyl- 5.0 Silicone oil 5.0 1.0 silicone resin 1,000 nrm2sl 50% strength TABLE 1 CONT'D

Slip/release Curable silicone resin Oil Component Release Agent No. (pe forces Parts Type of silicone Parts Type of oil Release slip by resin by value value weight weight 17 10.0 Methylphenyl- 2.0 Soya oil 7.9 2.3 silicone resin 50% strength 18 5.0 Methylphenyl-. 5.0 Soya oil 8.1 2.8 silicone resin 50X strength Nos. 1 to 8 not according to the invention Nos. 9 to 18 according to the invention

Claims

1. A composition comprising a curable silicone resin and an oil which does not dissolve or swell rubber, in a weight ratio of 5:1 to 1:20.

2. A composition according to claim 1 wherein the silicone resin is a methyl-silicone resin, a methyl-phenyl silicone resin or an organically modified silicone resin.

3. A composition according to claim 2 wherein the silicone resin is a methyl-phenyl silicone resin in which the ratio of methyl:phenyl groups is about 1:1.

4. A composition according to claim 2 wherein the silicone resin is organically modified by reaction with a polyester resin.

5. A composition according to any one of the preceding claims, wherein the oil is a silicone @@@@hav- ing a viscosity of 100 to 10,000 mPa, seconds.

6. A composition according to any one of claims 1 to 4, wherein the oil is rapeseed oil, soya oil or an addition product of ethylene oxide and/or propylene oxide with a monohydric or polyhydric alcohol.

7. A composition according to any one of the preceding claims, wherein the silicone resin and oil are dissolved in an organic solvent.

8. A composition according to claim 7 wherein the solvent is a chlorinated hydrocarbon.

9. A composition according to claim 7 or 8 which contains 3 to 10% by weight of the silicone resin and oil constituents.

10. A composition according to claim 1 substantially as hereinbefore described with reference to the Example.

11. A method of producing a rubber moulding which comprises moulding a vulcanisable rubber in contact with a surface which has been treated with, as lubricatinglrelease agent, a composition as claimed in any of the preceding claims.

12. A method according to claim 11 wherein the rubber moulding is a seamless tube or hose.