Siloxane modified novolaks, their production and their use for the production of friction linings

~ 1567~ The present invention relates to the use of siloxanemodified novolaks for the production of friction linings.

The use of novolaks for the production of friction linings is known (cf.

Gummi, Asbest, Kunststoffe 9, (1978), Vol. 31, pages 666 to 670).

Resins of this type are used for glueing numerous fillers and additives, and they enable the moulding compositions to be subsequently hardened by heating.

High-temperature-resistant mouldings, such as friction linings which are preferably used for the production of clutch and brake linings, are required to have a very high decomposition temperature and a low evaporation rate of thermal decomposition products.

In this context, high temperatures are generally understood to be temperatures in the range of from 250 to 800C.

The effectiveness of friction linings and their useful life is drastically reduced by the presence of a high proportion of volatile cracking products, such as mainly benzene, toluene, xylene, phenol and cresol, and by a lack of dimensional stability (breaking out of friction lining fragments) at high temperatures.

By the process described in German Offenlegungsschrift No. 2,306,463, in which phenol-formaldehyde resins and polysiloxanes are mixed in solution and the mouldings ,,~ ~ , 2 1 1~678~ are subsequently hardened subsequent to removal of the solvent, it is possible to obtain high-temperature--res~ istant mouldings from which friction linings can be produced.

l~owever, in comparison with friction linings produced on the basis of phenol novolaks, the friction linings obtained in this particular way show an increased breakout of fragments o~ the friction lining moulding at high temperatures. ~his would appear to be caused by an inadcquate bond between the low molecular weignt components of the novolak, and the silicone resin in the moulded friction lining.

The object of the present invention is to reduce distinctly this decom~osition of high--temperature-stressed phenol-formaldehyde and/or cresol-formaldehyde resins by suitable chemical modification thereof, and to increase their dimensional stability at high temperatures by improving their elasticity, tear propagation resistance and tensile strength.

It has now been found that phenol-formaldehyde and/or cresol-formaldehyde resins of the novolak type can be reacted with polysiloxanes containing terminal alkoxy, alkyl-aryloxy or aryloxy groups under acid-catalysed conditions with elimination of alcohol or phenol to form siloxane-modified novolaks which not only readily lend Le A 19 372 1 ~567~4 themselves to fabrication but also give high-temperature-resistant moulding compositions having improved elasticity, tear propagation resistance and tensile strength. The resins of the present invention may be processed into friction linings which, in addition to the akove mentioned properties, show considerably improved noise-damping properties and excellent dimensional stability at high temperatures.

Accordingly, the present invention provides a friction lining molded from a polysiloxane of the formula IR A _O - Si - - O-A wherein each A is a novolak residue, a Cl - C8 alkyl, a C6 - C12 aryl or a C7 - C12 alkaryl group; each R is a Cl - C8 alkyl, C - C cycloalkyl, C6 - C12 aryl or C7 C12 Y n is from 3 to 100 with the proviso that at least one A is a novolak residue, reacted with a formaldehyde donor and containing an organic or inorganic filler.

The novolak-containing polysiloxane used in the production of the friction linings of the present invention may be a process which is characterised in that a polysiloxane containing Cl - C8 alkyloxy, C6 - C12 aryloxy and/or C7 - C12 ~ ~56~ alkyl aryloxy groups is reacted with a phenol-formaldehyde and/or cresol-formaldehyde resin of the novolak type in the presence of an acid tranesterification catalyst at a temperature in the range of from 110 to 180C, the polysiloxane being used in quantities of from 20 to 120 parts by weight, based on 100 parts by weight of novolak, and the volatile fractions formed are distilled off.

In the above formula A and P represent a Cl - C8 alkyl radical, wuch as for example methyl, ethyl, propyl, _-, i_ or t-butyl, n- or i-pentyl, n- or i-hexyl, n- or i-heptyl and n or i_octyl; a C6 - C12 aryl radical such as, for example, phenyl or ~ -naphthyl, a C7 - C12 alkyl aryl radical such as, for example, tolyl, ~-tert.-butyl phenyl or n- or i-hexyl phenyl;

and/or novolak residue. In addition, R may represent a C6 - C18 cycloalkyl group.

The novolak residue and the novolak resin used in the production process may be formed from phenol-formaldehyde and/or cresol-formaldehyde resins obtained in known manner by reacting phenols and/or cresols with, for example, aqueous formaldehyde solutions in a molar ratio -5 1 ~5~7~ of from 1:1.05 to 1:1.4 in the presence of an acid catalyst (cf.

Ullmanns Encyclopadie der techn.

Chemie, Vol.

13, page 459, Publishers: Urban & Schwarzenberg, Munich Berlin, 1962).

The resin is preferably bound to the polysiloxane through a hydroxy methylene group from which a hydroqen atom is eliminated during the reaction.

The phenol groups present in the resin are slow in reaction and, for this reason, only react towards the end of the reaction, if at all.

The polysiloxane used for the production of the polysiloxanes of the present invention correspond to the following formula:

R B - - 0-Si -0-B R n wherein each B is a Cl-C8 alkyl, C6-C12 aryl or C7-C12 alkyl aryl 20radical, each R represents a Cl-C8 alkyl, C6-C18 cycloalkyl, C6-C12 aryl, or C7-C12 alkyl aryl radical, and n represents numbers of from 3 to 100.

hese polysiloxane resins may be dissolved in a solvent, such as benzene, toluene or xylene, although they are Le A 19 372 1 ~67~ preferably used in solvent~free form. The solvent--free polysiloxanes are liquids and generally have a viscosity of from 40 to 20,000 c/Stokes (measured at 20C).

Polysiloxane resins such as these may be produced by processes known from the literature, for example by the controlled hydrolysis of silanes corresponding to the general formula (R2) Si(X)2, where R as hereinbefore defined and each X is for example, a chlorine atom or an O-alkyl group containing from 1 to 8 carbon atoms, optionally in the presence of organic solvents, such as toluene or xylene, and optionally in thc presence of an alkali or an acid and a suitable quantity of chain-terminating Cl-C8 hydroxy alkyls, C6-C12 hydroxy aryls or C7-C12 hydroxy alkyl aryls (cf. for example W.

Noll, 'Chemie und Technologie der Silicone", Verlag Chemie GmbH, 1~einheim/Bergstra3e 1968, pages 162 - 171).

So far as the novolaks used are concerned, reference is made to the comments hereinabove.

The quantity in which the polysiloxane is used for the reaction preferably amounts to between 30 and 80 parts by weight, based on lOO parts by weight of the novolak.

The reaction is preferably carried out in the presence of fromO.OOOlto 0.05% by weight of an acid transesterification catalyst (based on the total weight of the reaction mixture), such as for exam~le an organic or inorganic acid, such as oxalic acid, formic acid, acetic acid, trichloro- Le A 19 372 ~ J ~ 15~7~4 --8~ acetic or trifluoroacetic acid, benzene sulphonic acid, ~toluene sulphonic acid, hydrochloric acid, sulphuric acid, phosphoric acid or a Lewis acid, such as aluminium chloride, iron (III) chloride, zinc chloride, antimony(III) chloride, 5 germanium dioxide or zinc oxide.

.he reaction temperature is preferably in the range of f~om 130 to 170C. The "B-radical" eliminated during the reaction may be distilled off under normal pressure, but is preferably distilled off under a vacuum of from 1 to 10 500 mbars.

me liquid viscous resin of the present invention is drained off from the reaction vessel and worked up, advantageously on a ~elletising belt or a cooling roller. It may then be ground.

me resins of the present invention thus obtained generally have a softening point of from 60 to 110C preferably of from 70 to 100C (as nieasured in accordance with DIN 53 180). They have a higher average molecular weight (as measured ~y osmometryi than the components used for the 20 reaction. For example, the reaction of a novolak having a molecular weight MoS of 530 with a polysiloxane containing terminal methoxy groups and having a molecular weight Mos of 510 gives an end product having a molecular weight MoS of 760. The chemical reaction of the novolak with the 25 polysiloxane may readily be monitored and established through Le A 19 372 1 ~ 5 G 7~ --9.

this molecular weight analysis.

To obtain friction linings, the resins of the present invention are thoroughly ~ ed with inorganic and/or organic fillers, such as metals and/or metal oxides, fluorspar, asbestos, silica or butyl, nitrile and/or chloroprene rubber, in the presence of formaldehyde donors, such as hexamethylene tetramine or trioxy or tetraoxy methylene in standard mixing units, such as kneaders or internal mixers, at temperatures preferably in the range of from 60 to 150C. me form aldehyde donors are added in quantities of from 4 to 16% by weight and preferably in quantities of from 7 to 14% by weight, based on 100 parts by weight of the resin of the present invention.

me muxtures thus obtained are generally moulded at 140 to 15 180C and more particularly at 140 to 160C, optionally under a pressure of from 150 to 250 bars, to form friction linings (cf.

Vieweg/Becker "Kunststoffhandbuch", Vol.

10, Duroplaste, pages 93 to 95, Carl Hanser Verlag, Munich, 1968).

The thermal properties of the mouldings obtained are shown in Table 1 below which contains data on the weight loss of 2 resin samples as determined by thermogravimetry under nitrogen ~heating rate: 20C per minute).

Le A 19 372 l 15~7~4 --10-Table 1: Thermogravimetric analysis ~1eight losses in % by weight Temp (C) Resin 1 (x) Resin 2 (xx) 100 4.0 0 5 150 4.5 0.7 200 5.0 1.1 250 5.5 1.3 300 6.0 1.7 350 6.6 2.0 400 7.5 2.4 450 11.0 2.8 500 15.5 3.5 550 22.4 6.0 600 28.o 8.5 650 33.2 12.6 700 37.0 14.0 750 40.1 16.1 800 42.4 17.2 x) Resin 1: phenol-formaldehyde resin (MoS = 530) mixed with 12~ by weight of hexamethylene te~ramine xx) Resin 2: siloxane-modified novolak prepared according to the procedures of Example 1 described hereinafter mixed with 12Po by weight Gf hex amethylene tetramine.

The present invention is further illustrated by the following examples.

Le A 19 372 1 ~ 5~7g~ Example 1 A novolak produced in known manner from phenol andformaldehyde in a molar ratio of ~`1.08 in the presence of an acid catalyst, such as oxalic acid, an~ having a molecular weight Mos f 530 and an Ol~ number of 535 (cf.

Ullmanns Encyclopadie der technischen Chemie, Vol. 13, page 459, Publishers Urban Schwarzenberg, Munich-~erlin, 1962) is used in a quantity of 660 g.

This novolak is reacted with 330 g of a diphenyl-polysiloxane containing terminal methoxy groups and having the following characteristic data:

M = 510 os viscosity (DIN 53 015): llO c/Stokes ~ by weight of methoxy groups 14 to 16 The reaction is carried out at 160C in the presence of 0.002 % by weight p-toluene sulphonic acid (based on the total weight of the reaction mixture).

After reaction under a nitrogen atmosphere for 1 hour with intensive stirring at 160C, 36.5 g of methanol is distilled off under a pressure 20 of 350 to lO mbars.

At the same time, 3.0 g of phenol and water are removed by distillation.

me liquid viscous resin obtained is subsequently removed from the reaction vessel and ground after cooling.

The product has the following characteristic data:

softening point (according to DI~ 54 180): 8gC Le A 19 372 1 ~567~ -12 os OH-number = 330 silicon content: 6.2% The resin produced in accordance with the procedure of Example 1 was ground, mixed with 12~ by weight of hexamethylene tetramine and analysed by thermogravimetry (cf. resin 2 of Table 1).

At temperatures above 300~C, the friction linings produced from the resin of Example 1 are characterised not only by the considerably lower evaporation rate of low molecular weight compounds indicated by way of example in Table 1, but are also characterized by increased elasticity, tear propagation resistance and tensile strength and greater hardness than friction linings produced from a phenol formaldehyde resin or from a mixture of polysiloxaneand phenolic resin (cf.

Table 2).

Table 2 compares th~ properties of friction lining mixtures produced A) from a mixture of acrylonitrile/butadiene copclymer and a phenol-formaldehyde novolak having an average molecular weight Mos of 530 and an OH number of 535, B) from a mixture of acrylonitrile/butadiene copolymer and a siloxane-modified novolak of the present invention corresponding to the resin produced in Example 1, and C) from a mixture of an acrylonitrile/butadiene copolymer Le A 19 372 I ~$~7~ -13 and a phenol novolak/silicone resin mixture corresponding to resins4 of German Offenlegungsschrift No. 2,306,463.

The mixture of phenol novolak and silicone resin corresponding to resins4 of German Offenlegungsschrift No. 2,306,463 is produced as follows:

33% by weight (based on solids content) of a methyl silicone resin containing 3 mole percent of phenyl siloxane, in the form of a 51% solution in xylene which has a viscosity of from 40 to 60 cSt tas measured at 20CC) is mixed with 60% by weight of a phenol novolak having a molecular weight MoS of 530 and an OH number of 535.

This mixture is thoroughly mixed with the abovementioned-acrylonitr.ile/butadiene copolymer and with the other components of the friction lining mixture, _he xylene being removed at 80C and 100 mbars pressure.

The friction lining mixtures (A), (B) and (C) are hardened by moulding for 30 minutes at 150C under a pressure of 200 kp/cm2. 4 mm thick plates ~ere produced and made up into standard test bars.

Table 2 (I) Production of the friction lining mixtures:

(A) (B) (C~ Perbunan N 3307 NS 59.1 59.1 59.1 Phenol-formaldehyde resin (=resin 1 of Table 1) 50.0 ~ Le A 19 372 ~ f~-~De ,~ 1 1567~ -14 Table 2 Contd:

(A) (B) (C) Siloxane-modified novclak according to ~xample 1 (= resin 2 of Table 1) - 50.0 Resin 4 according to German Offenlegungsschrift No. 2306463 page 5 - - 50.0 Stearic acid 2.43 2.43 2.43 Styrene/butadiene resin containing 60% by weight of styrene 27.3 27.3 27.3 Colophony 10.9 10.9 10.9 Kaolin 118.0 118.0 118.0 Calcium silicate 18.2 18.2 18.2 Active zinc oxide 9.1 9.1 9.1 Iron oxide pigment 9.1 9.1 9.1 Sulphur 3.64 3.64 3.64 Cyclohexyl benzthiazole sulphenamide 1.69 1.69 1.69 Hexamethylene tetramine granulate - 4.0 4.0 Mooney viscosity (ML -4 at 76 53 51 100 C) .

(II) Mechanical values, as measured on standard test bars after vulcanisation for 30 minutes at 150C Mixtures (A) F ¦ D HD¦ E WRF 14.3 40 67 1 22 49.1 , HL 120C/ 1 day: 18.0 27 74 1 25 29;2 Le A 19 372 1 ~5~7~ -15 Mixtures (A) F D ¦ HD E WRF I HL 120C/ 3 days: l9.I 20 ¦ 7S 25 28.4 ¦ HL 12_C/ 5_da~s._ _ _ 19.8 20 l 75 _25 _ 22 . 9 !

(B) F D HDE WRF 15.9 20 70 _ 28 52.6 HL 120C/ 1 day: 20.7 10 78 30 31.6 HL 120CC/ 3 days: 21.710 78 31 31.1 HL 120C/ 5 days: 20.6 10 79 _ 31 29.1 (C) F D HD E WRF 12.6 57 6422 45.6 HL 120C/ 1 day: 16.4 30 70 24 31.9 I~L 120C/ 3 days: ~ 18.8 20 74 26 28.6 HL 120C/ 5 days: 20.2 17 74 26 23.8 ~:

F = tensile strength (MPa) D = elongation at break (~) HD = hardness (~hore D) E = shock elasticity (~) WRF = tear propagation resistance (N/mm) HL-120C = hot-air ageing at 120C Le A 19 372 ~5~J8~ Friction linings produced from the siloxane-modified novolaks of the present invention are distinguished by lower mixing viscosities and hence by more favourable prGcessing behaviour in comparison with friction linings 5 containing phenol novalaks (cf. the ~ooney viscosity values in Table 2). In addition, tensile strength (F), elasticity (E) and tear propagation resistance (WRF), which are measures of the dimensional stability of the ~riction lining, are distinctly improved in comparison 10 with a friction lining based on a phenol novolak/silicone r~sin mixture (cf. mixtures (B) and (C) in Table 2, II).

The hardening effect of the resins of the present invention in friction lining mixtures is also greater than that of a pure phenol novolak/silicone resin mixture (cf. HD 15 values in Table 2, II for mixtures (A), (B) and (C)).

Le A 19 372