Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
13124~
-1- R. I. I-1979
BOR-86043AUS1-JR
TITLE OF THE INVENTION:
PROCESS FOR THE MANUFACTURE OF FRICTIONAL ELEMENTS
AND FP.ICTIONAL ELEMENTS PRODUCED THEREBY
BACKGROUND OF THE INVENTION
-
This in~rention relates to shaped frictional elements,
particularly brake linings, disc pads and clutch facings and to a
method of manufacturing the same which involves the use of liquid
phenolic resins and catalyst set at room temperature.
In the conventional process for the manufacture of shaped
frictional elements fillers such as asbestos fibres, barytes,
magnesia brass or zinc filings or turnings are mixed with a binder
comprising a powdered phenol formaldehyde novolak/hexamine blend
and hot pressed in a mould. The action of the hest from the
mould is first to fuse the binder and then to cure it.
It is, however, a disadvantage of thi~ process that noxious
gases and fumes of ammonia, formaldehyde and free phenol are
evolved during the curing process. The workers need to wear
gloves in order to handle the ejected cured moulding~ and
generally the conditions of work are very unpleasant.
2 0 It is a further disadvantage of the conventional process for
the production of shaped frictional products that the expenditure
of considerable energy is necessary to effect the fusion and
setting of the binder.
It is known to accelerate the cure of these materials by the
addition of acids or anhydrides. Many frictional materials, such as
asbestos, are, however, alkaline while many of the metals included
in frictional materials, while not alkallne, nevertheless react with
acids. In this way much, if not all, of the accelerating effect of
acids and anhydrides is vitiated when these materials are employed
in an attempt to accelertlte phenolic resins in bonding frictionnl
compositions. In addition, the presence of acids is undesirable for
a number of other reasons, such as their corrosive effect on
metals, both in manufacture and use, and the additional handling
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problems, environmental effects and health risks which their use
entails .
The present invention seeks to improve these aspects of
production by eliminating the heat curing steps during formation of
5 the shaped frictional materials. The reduction in energy brought
about by cold curing is a substantial economic advantsge of the
system but there is also a reduction in wear on the moulding tool
and the need for extensive ventilation is eliminated.
We have now found that shaped frictional articles can be
10 produced quickly and economicallv at room temperature, without
the hazards and inconveniences associated with heated moulds, by
a process in which a liquid highly alkaline phenol-formaldehyde
condensation product is employed as a binder, said binder is
intimately mixed with a cluantity of frictional filler and
15 subsequently with a second quantity of frictional filler which has
previously been mixed with a quantity of a liquid ester sufficient
to effect cure of the phenolic resin.
These compositions set at room temperature and therefore
demand less energy than the heat cured sy6tems previously used.
20 The low curing temperature results in the substantial elimination of
noxious fumes and the hazards associated with the handling of
heated moulds. Being free from acidic materials, corrosion
problems are greatly reduced or eliminated. In addition, because
they are catalyzed by alkalies, they set in the presence of alkaline
2 5 fillers such as asbestos .
SUMMARY OF THE INVENTION
Accordingly the present invention comprises a method for the
manufacture ~f shaped frictional elements which comprises mixing
frictional filler with from 5% to 30% of a liquid, alkaline,
3 o phenol-formaldehyde resin havin~ a formaldehyde to phenol
molecular ratio between 1:1 and 3 . 5 :1, a wei~ht average molecular
weight between 300 and 4000 and a pH greater than 10, mixing a
second portion of the same or a different frictional filler with a
,, li~uid ester curing agent for the phenol-formaldehyde resin,
. . .
~.3l2~a~
intimately mixing the two portions together and allowing the
resultant mixture to cure in a mould.
The invention also complqses a composition suitable for the
manufacture of brake linings, pads and clutch facings which
5 comprises a major proportion of frictional filler or a mixture of
frictional fillers, from 5% to 3096 of a liauid, alkaline,
phenol-formaldehyde resin with a formaldehyde to phenol molar
rat;o between 1:1 and 3 . 5 :1, 8 weight average molecular weight of
from 300 to 4000 and a pH value above 10 and from 10% to 110% on
10 the weight of the resin of an ester as catalyst therefor.
The invention further comprises a shaped frictional article
produced by the above process.
DETAILED DESCRIPTION OF THE INVENTION
Liquid alkaline phenol-formaldehyde resins suitable for use in
1 S the present invention are those in which the formaldehyde to
phenol ratio is within the range 1:1 to 3.5:1 and preferably within
the range 1. 5 :1 to 2 . 2 :1.
The alkali used may be sodium hydroxide or potassium
hydroxide or a mixture of these with alkaline earth oxides such as
2 0 calcium hydroxide, barium oxide, magnesium oxide, etc . We have
found that potassium hydroxide gives the best performance.
The proportion of alkali in the composition may vary with the
molar ratio of formaldehyde to phenol, the molecular weight of the
resin, the nature of the alkali and the nature of the frictional
25 material employed but must be sufficient in quantity and nature to
impart to the resin a pH value above 10. Preferably the resin will
have a pH value of 11 to 13. This can normally be achieved using
an alkali to phenol ratio within the range from 0.1:1 to 5 :1. It
will be obvious to those skilled in the art to adjust the quantity~ of
3 o alkali to obtain satisfactory results and this may be necessary to
compensate for the effects of the frictional components employed.
The weight average molecular weight (Mw) of the resin must
be high enough to allow gelation to occur, i.e., above 300. On
the other hand, both storage stability and final strengths will tend
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to fall with increase in molecular weight and products with
molecular weights in excess of 4000 (Mw) are generally unsuitable.
The preferred products are those with molecular weights within the
range 600 to 1700 (Mw3.
If desired, the solids content of the resin may be adjusted,
for example, by distillat;on, but this is not usually necessary and
the savings in time and energy thereby achieved constitute a
further advantage of the invention.
The frictional fillers employed in the present invention may be
any of the fillers normally employed in the brake lining industry
for the production of linings, pads, clutch facings, etc. Of
particular interest are the non-asbestos fillers: copper powder,
iron wool , iron powder , friction dust , graphite , barytes , etc .,
since they are becoming more widely used as the industry changes
away from asbestos for environmental pollution reasons. Another
suitable filler is Kevlar (trademark of DuPont) polyaramide fibers.
The alkaline phenolic resins do not react with fillers of this
nature .
- The curing catalyst used in the invention is an ester.
2 0 Suitable esters include low molecular weight lactones , e . g ., gamma
butyrolactone, propiolactone, valerolactone and caprolactone, and
esters of short and medium chain te. g., C1-(: 10~ fatty acids with
aliphatic mono- or polyhydroxy alcohols of chain lengths C1-Clû.
The amount of catalyst used can be as low as 10% and as high
as 110% of the liquid resin depending upon the molecular weight of
the ester and the degree of acceleration required. Preferably the
amount of ester is from 15% to 40% by weight of the weight of
liquid resin solution used.
A silane is preferably included in the phenolic resin to
3 o promote adhesion to the frictional fillers and thus increase the
strengths of the final cured frictional element. Amounts as low as
0. 05% by weight of the weight of liquid resin have some effect,
while little, if any, additional strength is gained from the addition
of amounts in excess of 5%. Consequently, we prefer to employ a
3 5 silane in an amount between 0 . 50% and 5% on the weight of the
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liquid resin and an amount between O . 2% and 1. 5~ is found to be
particularly effective.
Although gamma aminopropyl triethoxy silane is the preferred
material, other silanes may be substituted either wholly or in part.
The following examples illustrate the present invention.
Manufacture of phenol formaldehyde resin solution A
94 grams of 10096 phenol were dissolved in 67.3 grams of a 50%
aqueous solution of potassium hydroxide. The solution was heated
to reflux and 120 grams of 50% aqueous formaldehyde,
corresponding to a phenol: formaldehyde molar ratio of 1: 2, were
added 810wly, while maintaining reflux. The reaction mixture was
maintained under reflux until it attained a predetermined viscosity
corresponding to a weight average molecular weight of 1400. The
resin solution was cooled to 40C and 0.4% by weight on the weight
of the resin solution of gamma-aminopropyl triethoxysilane added.
Manufacture of phenol formaldehyde resin solution B
94 grams of 100% phenol were dissolved in 85.3 grams of a 50%
aqueous solution of potassium hydroxide. The solution was heated
to reflux and 96 grams of 50~6 aqueous formaldehyde,
corresponding to a phenol: formaldehyde mol~r ratio of 1:1. 6, were
added slowly, while maintaining reflux. The reaction mixture was
maintained under reflux until it attained a predetermined viscosity
corresponding to a weight average molecular weight of 1500. The
resin solution was cooled to 40C and 0. 4% by weight on the weight
of the resin solution of gamma-aminopropyl triethoxysilane added.
Testin~ of Resins
A) Viscosity - measured using an Oswald (U-tube)
viscometer at 25
3 o B ) Solids content - measured by heating a weighed sample
(200 1 0.1 g) in an air circulating oven for 3 hours at 100C.
1 3 ~
C) Molecular weight (Mw) - measured using gel permeation
chromatography. Samples were prepared by dissolving the resin
in tetrahydrofuran, neutralizing the resin solution by adding
sulphuric acid and separating the tetrahydrofuran solution used
for the determination.
Table 1 shows the parameters for two resins, hereinafter
referred to as Resin A and Resin B, prepared for evaluation:
Table 1
__________________________________________________________________
Alkaline phenolic resin composition
__________________________________________________________________
Solids
content Molecular
I)esignation P: F molar pH (3 h, Viscosity weight
of resin ratio value 100C) cSt at ~5C Mw
__________________________________________________________________
Resin A 1: 2 11. 8 63 150 1400
Resin B 1:1. 6 12 . 2 60 150 1500
______________________________________ ________~__________________
2 0 Example
(a) A filler blend was prepared of iron filings, iron wool and
barytes and 1275 g of this blended for 5 minutes with 152 g of the
resin Resin A. The resin was sprayed into the double Z mill from
a spray gun to avoid the formation of lumps.
(b) A second run of 1275 g of filler blend and 121 g of
butyrolactone was prepared in a similar manner. 100 g of (a) and
50 g (b) were placed into a 1 Ib lever lid tin and shaken
vigorously for 30 seconds and placed into a disc pad mould at room
temperature (20C) in a press. The metal backing plate had been
placed in the mould. The pressure was applied 50-55 seconds from
the time of initial blending.
Pressure was relaxed after 3 minutes. All mouldings were
sound on ejection and material had flowed sufficiently to fill the
holes in the backing plates perfectly.
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Shore R hardness varied with applied pressure
13 Qt 1 tonne per square inch pressure
21 at 2 tonnes per square inch pressure
Both measured immediately after stripping.
These pads were post cured for 16 hours at 200C and then
subjected to Girling type 16M brake rig tests. Results showed
great promise.
Example 2
Further pads were produced to the formulation of Example (1
with the following variations.
12/8955 7~ resin B (dry weight)
3: 1 resin B: butyrolactone
12/8956 7% resin B
4: 1 resin B: butyrolactone
12/8957 10% resin B
3: 1 resin B: butyrolactone
These pads were tested on Girling* type 16 M brake test rig
against a standard phenolic powdered resin/hexa system based on
the same fillers and resin loading (solid dry weight) and
20 equivalent frictional performance was obtained.
The results were sufficiently promising to instsll some of the
pads made with mix 12/8957 in a test car. Test track results were
reported as satisfactory in comparison with the performance
normally expected from heat-cured, novolak/hexa bonded pads.
2 5 While the invention has been disclosed in this patent
application by reference to the det~ils of preferred embodiments of
the invention, it is to be understood that this disclosure is
intended in an illustrative rather than in a limiting sense, as it is
contemplated that modifications will readily occur to those skilled in
3 o the art, within the spirit of the invention and the scope of the
appended claims.
*trade-mark
