FIELD OF INVENTION
The invention relates to friction materials having benzoxazine resins incorporated therein and to a process for producing the same. The friction materials are used in many applications such as brake pads, brake linings, brake blocks, clutch facings.
PRIOR ART
Friction materials are broadly classified into four classes viz. ceramic, sintered metallic, organic based and carbon-carbon composites. Organic based can be further subdivided into Non asbestos organic (NAO) based and asbestos based organic. Since asbestos was found to be carcinogenic, it is being shelved progressively in the friction materials.
Organic based friction materials are multi criteria optimized multi ingredient systems, typically containing 10-15 ingredients. The number of raw materials used so far has exceeded thousand. For the convenience sake, these though are generally multifunctional, are classified as binders, reinforcements, friction modifiers and fillers based on the major role they perform. Binder provides the mechanical integrity to the composite while reinforcements in the form of fibers (organic and inorganic) provide strength and desired tribo-properties. Friction modifiers are to tailor the friction level and fillers are primarily to reduce the cost without any adverse effect on other performance properties of the composites. Since asbestos, a thermally resistant mineral fiber was a wonderful material which used to contribute for excellent friction level, resistance to fade and wear along with a low cost. However, it proved to be a health hazard. It was extremely difficult to find a single substitute for it. It was successfully replaced by the group of fibers.
A lot of ingredients from three categories viz. reinforcement, friction modifiers and fillers are reportedly used to make NAO materials. However, not adequate efforts are focused to replace the binder by suitable resins. In friction Industry, Phenolics or its modified versions are invariably used for Organic based (both asbestos 85 non-asbestos) friction materials due to its combination of very good thermal, mechanical and tribological properties along low costs. The powdery mixture of oligomers of resol or novolacks along with a curing agent (Hexamine « 10% etc) is supplied by the resin manufacturers. It is then moulded by the user at site. However phenolics have serious short comings such as:
• Poor shelf life. (It gets partially cured during storage or transportation even at ambient conditions and is no more free flowing powder and has to be discarded).
• Since polymerization/curing of a supplied mixture is based on condensation reaction with lot of noxious volatiles such as NH3, HCHO etc., it is a threat to the environment and workers along with serious flaws such as cracks, voids and shrinkage in the final product.
There have been efforts to replace phenolics which till date could not be successful in industries due to either high cost of suggested resins or inefficiency in meeting all the expected performance properties. Further, in the known art brake pads are molded by applying pressure of 5-9 MPa for 7 minute at 150°C followed by four-hour post curing at 150°C without pressure.
The resin capable of replacing phenolics in these aspects should have better performance properties also. Moreover it should have very good compatibility with heterogeneous ingredients in the friction composites.
If the processing of these composites can be done on the existing infrastructure in the industries with available know-how and under similar operating conditions, it will prove as a great advantage.
The friction composites based on such alternate resins are expected to be free from all problems associated with phenolics.
OBJECT OF THE INVENTION
An object of this invention is to propose friction composites using resins capable of replacing/substituting phenols.
Another object of this invention is to propose a process for producing friction composites using benzoxazine resins capable of substituting phenols.
Still another object of this invention is to propose friction composites using resins capable of substituting phenols which has a higher performance µ in comparison to phenols.
Yet another object of this invention is to propose friction composites using resins capable of substituting phenols which exhibit less amount of fade.
A further object of this invention is to propose friction composites using benzoxazine resins capable of substituting phenols, which exhibit lower fade in friction level and higher recovery in friction level.
A still further object of this invention is to propose friction composites using benzoxazine resins capable of substituting phenols which do not have any problems associated with conventional resins such as possibility of cracks, voids etc since the condensation products are not at all generated as in case of pheonolics.
Yet a further object of this invention is to propose friction composites using benzoxazine resins capable of substituting phenols which can be stored or transported without any possibility of degradation since the resins used have infinite shelf life (unless heated to curing temperature of 180°c).
Still another object of this invention is to propose a friction composite using benzoxazine resin capable of more uniform distribution than phenolics. This is because Benzoxazine transforms from monomelic stage to polymeric stage during molding where as phenolics transcends , from oligomeric to polymeric stage.
Yet another object of this invention is to propose a process of fabricating/molding friction composite using benzoxazines resins wherein the post-curing or stoving is optional unlike the prior art.
Yet another object of this invention is to propose a process of fabricating/molding friction composite using benzoxazine resins with less and intermittent pressure compared to the prior art requiring continuous pressure.
Further objects and advantages of this invention will be more apparent from the ensuing description.
STATEMENT OF INVENTION
According to this invention there is provided a friction material having benzoxazine resin comprising of 8-30% by wt. of a resin, 25-45% by wt. of fibers, 8-20% by wt. of friction modifiers and 26-48% by wt. of space fillers.
Further, according to this invention there is provided a process for preparation of a friction material having resin comprising step of :
mixing of a resin, fibers, friction modifiers and space filler followed by molding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig. 1 shows: Generic structure for benzoxazines resins.
Fig. 2 shows: Structure of mono functional benzoxazines.
Fig. 3 shows: Fade and Recovery trace from kruass test machine of the
composite based on resin polybenzoxazine-A.
Fig. 4 shows: Fade and Recovery trace from kruass test machine of the
composite based on resin polybenzoxazine-mt.
Fig. 5 shows: Fade and Recovery trace from kruass test machine of the composite based on resin polybenzoxazine-ot.
Fig. 6 shows: Fade and Recovery trace from kruass test machine of the composite based on resin polybenzoxazine-pt.
Fig.7 shows: the variation of coefficient of friction and also temperature rise in the disc of a phenolic pad.
Fig. 8 shows: the variation of coefficient of friction and also temperature rise in disc of a commercial pad.
Fig. 9 shows: chemical structure of polybenzoxazine-A Fig. 10 shows: chemical structure of polybenzoxazine-mt Fig. 11 shows: chemical structure of polybenzoxazine-ot Fig. 12 shows: chemical structure of polybenzoxazine-pt
DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO
THE ACCOMPANYING DRAWINGS
Resins were used in the amount of 8 to 30% and those resins were employed capable of substituting pheolics. The other ingredients are; fibers (Aramid, PAN, Lapinus Rb 220, glass, steel, ceramic and brass- 25-45 wt.%), friction modifiers (alumina, graphite, cashew dust, 8-20%) and space fillers- 26-48 wt. %). The ingredients are mixed in a plough type mixer. The addition of ingredients during mixing is in a sequence to ensure uniform mixing. The mixing schedule is of ten to twenty minutes duration. Brake-pads of four alternate resins composites are molded as per conditions indicated in the examples.
Resins
The benzoxazines resins used has the following generic structure.
(Figure Removed)
where R is H3C-C-CH3 and Rl, R2 are methyl substituted phenyl. The position of substitution is ortho, meta and para. The resins can be used in combination with one another apart from other mono functional benzoxazines shown in Figure 2.
(Figure Removed)
The ratio of mixture of different benzoxazines varies from 1:99 to 99:1. The other possible structures for R can be C=0, CH2, 0=S=0, S, 2e_, siloxane unit, cyclo alkyl etc.,
The other possible structures for Rl, R2, R3 can be alkyl having C1 to C6, mono or di-alkyl substituted phenyl, mono or di-halo substituted phenyl, cyclo alkyl, etc.,
Fibers
The fibers that can be used are the combination of the following: aramid (para and meta), glass, polyacrylonitrile (PAN), steel wool, brass scrap, ceramic. The combinations of the fibers can be from among these optionally leaving out one or some of those also.
Friction Modifiers
The friction modifiers that can be used are the combination of graphite, silica, alumina, molybdenum sulphide, cashew dust optionally leaving out one or few of those mentioned.Fillers
The fillers that can be used are the combination of barite, calcium
carbonate, vermiculite, talc and clay opting out one or few of those
mentioned.
The brake pads were tested to Krauss machine as per ECR-90 schedule
against pearlitic and grey cast iron rotor disc of passenger car. The
resultant graphs are shown in Fig. 3 to Fig. 8.
Table 1: Test Results of Brake pads as per ECR-90 Schedule.
These composites have shown higher performance \i than the Ph which is a desirable property. This was in the order: P (0.443) Fig. 6 > O (0.43) Fig. 5 > M (0.398) Fig.4 > A (0.389) Fig.3 >_Ph (0.386) Fig.7
As compared to Ph all showed less amount of fade. Composites A was most fade resistant (8%) Fig.3 followed by O (10%) Fig.5 and M (11%) Fig. 4. Composite P (14%) Fig. 6 was almost similar to Ph (15%) Fig.7-Fade resistance is one of the most important performance property of friction material which decides the utility of material under sever operating conditions.
The plots based on 70 brakings of 7 cycles (1-cold, 5-fade, 1-recovery) Fig.3-Fig.8 confirmed that the µ of new resins based composites was associated with significantly less fluctuations as compared to composite Ph. Thus new composites rendered higher & more stable µ under severe operating conditions of fade 85 recovery tests than that of commercial resin based (Ph). This is very important selection criteria for friction materials.
Example 1
A friction composite containing 12 ingredients was fabricated by utilizing resin polybenzoxazine-A (8 to 30%) wherein resin polybenzoxazine-A is as shown in the fig. 9. The other ingredients were; fibers (25-45%) (Aramid, PAN, Lapinus Rb 220, glass, steel and brass), friction modifiers (alumina, graphite, cashew dust) (8-20%) and space filler (26-48%). The ingredients were mixed in a plough type shear mixer. The addition of ingredients during mixing was in a particular sequence. Aramid and glass fibers were added initially followed by other pulpy materials and finally by powdery materials. The mixing schedule was of ten to twenty minute duration. Brake pads were molded by applying pressure of 5-8 MPa for a minute at 160°C-190°C followed by twenty to twenty five minutes holding in the mold finally for two to five minutes a pressure of 5-9 MPa was applied.
Example 2
A friction composite containing 12 ingredients was fabricated by utilizing resin polybenzoxazine-mt (8 to 30%) wherein polybenzoxazine-mt is as shown in the fig. 10. The other ingredients were; fibers (25-45%) (Aramid, PAN, Lapinus Rb 220, glass, steel and brass), friction modifiers (alumina, graphite, cashew dust) (8-20%) and space filler (26-48%). The ingredients were mixed in a plough type shear mixer. The addition of ingredients during mixing was in a particular sequence. Aramid and glass fibers were added initially followed by other pulpy materials duration. Brake pads were molded by applying pressure of 5-8 MPa for a minute at 160°C -190°C followed by twenty to twenty five minutes holding in the mold finally for two to five minutes a pressure of 5-9 MPa was applied.
Example 3
A friction composite containing 12 ingredients was fabricated by utilizing resin polybenzoxazine-pt (8 to 30%) wherein resin polybenzoxazine-pt is shown in the fig. 12. The other ingredients were; fibers (25-45%) (Aramid, PAN, Lapinus Rb 220, glass, steel and brass), friction modifiers (alumina, graphite, cashew dust) (8-20%) and space filler (26-48%). The ingredients were mixed in a plough type shear mixer. The addition of ingredients during mixing was in a particular sequence. Aramid and glass fibers were added initially followed by other pulpy materials and finally by powdery materials. The mixing schedule was of ten to twenty minutes duration. Brake pads were molded by applying pressure of 5-8 MPa for a minute at 160°C -190°C followed by twenty to twenty five minutes holding in the mold and finally for two to five minutes a pressure of 5-9 MPa was applied.
Example 4
A friction composite containing 12 ingredients was fabricated by utilizing resin polybenzoxazine-ot (8 to 30%) wherein resin polybenzoxazine-ot is as shown in the fig. 11. The other ingredients were; fibers (25-45%) (Aramid, PAN, Lapinus Rb 220, glass, steel and brass), friction modifiers (alumina, graphite, cashew dust) (8-20 %) and space filler (26-48%). The ingredients were mixed in a plough type shear mixer. The addition of ingredients during mixing was in a particular sequence. Aramid and glass fibers were added initially followed by other pulpy materials and finally by powdery materials. The mixing schedule was of ten to twenty minutes duration. Brake pads were molded by applying pressure of 5-8 MPa for a minute at 160°C -190°C followed by twenty to twenty five minutes holding in the mold finally for two to five minutes a pressure of 5-9 MPa was applied.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-

WE CLAIM
1. Friction material having benzoxazine resins comprising of 8 to 30 % by wt. of a resin, 25-45 % by wt. of fibers, 8-20 % by wt. of friction modifiers and 26-48% by wt. of space fillers.
2. A process for preparation of a friction material having resin comprising step of:
- mixing of a resin, fibers, friction modifiers and space filler followed by molding.
3. The friction material and a process for preparation thereof as
claimed in claim 1 or 2, wherein the resin is selected from the
family of benzoxazine as shown in the following structure where
R is H3G-C-CH3 and Rl, R2 are methyl substituted phenyl and
the position of substitution is ortho, meta and para.
(Figure Removed)
4. The friction material and a process for preparation thereof as claimed in claim 3 wherein the resins can be provided in combination with one another apart from other mono functional benzoxazine s shown in Figure 2. wherein

(Figure Removed)
the ratio of mixture of different benzoxazines varies from 1:99 to 99:1 and the other structures for R can be C=O, CH2, 0=S=O, S, 2e, siloxane unit, cyclo alkyl etc., and the other structures for Rl, R2, R3 can be alkyl having C1 to C6, mono or di-alkyl substituted phenyl, mono or di-halo substituted phenyl, cyclo alkyl, etc.,
The friction material and a process for preparation thereof as claimed in any of the preceding claims, wherein the fibers is any one selected from Aramid, PAN, Lapinus, glass, steel, _ceramic and brass or any combination thereof.
The friction material and a process for preparation thereof as claimed in any of the preceding claims, wherein said friction modifiers is any one selected from Alumina, graphite and cashew dust or any combination thereof, and the fillers is any one selected from barite, calcium, carbonate, vermiculite, talc and clay or any combination thereof.
The friction material and a process for preparation thereof as claimed in claim 2 wherein the resin is 8-30% by wt, fibers is 25-45 % by wt. friction modifiers is 8-20% by wt. and space filler is 26-48% by wt.
8. A process for preparation of a friction material having resin as claimed in claim 2 wherein the mixing is carried out for 10-20 minutes for uniform mixing to obtain brake pad pre-mix.
9. A process for preparation of a friction material having resin as
claimed in claim 8 wherein the brake pad is molded from the pre-
mix by applying pressure of 5-8 Mpa for a minute at 160-190°C
followed by holding the brake pad in the mold for 20-25 minutes
and applying a pressure of 5-9 Mpa for 2-5 minutes.
10. The friction material as claimed in any of the preceding
claims can be a brake pad, brake linings, brake block or clutch
facing.