CA2003582A1 - Thermal insulator made of phenolic triazine and related method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention is a thermal insulator and related method, made of phenolic traizine resin.

Description

zGo3saz THERMAL INSULATOR MADE OF
PHENOLIC TRIAZINE AND RELATED METHOD

~C~RQ~ OF THE INVENTION
The present invention i~ in the field of thermal insulators. More particularly, the present invention relates to a thermal insulator made of a phenolic triazine resins.
Cyanato group containing phenolic resins have been described in U.S. Patent Nos. 3,448,079 and 4,022,755 as well a~ in Delano, et al., Synthesis of Improved Phenolic Resins, Acures Corp/Aer¢therm, Acure~ Final Report 79-25/AS, September 4, 1979, prepared for NASA Lewis Research Center, Contract No. Nas3-21368, and iJ available through the United States Department of Commerce National ; Technical Information Service.
~ A recent reference, Heat Resistance Polymers by ;~ Critchley, et al., pp. 406-408 Plenum Press, New York, ~ 1986 has described phenolic triazine resins prepared from ~s 20 phenolic novolac or meta-cresol novolac which have ~ essentially the ~ame chemical structures as described in ;~ the above referonced patent~.
;~ The phenolic triazine~ which have been di~closed have .~; beon found to have high thermal stability. Copending U.S.
8er. No. 041,010 ~iled a~ PCT/V8 87/00123, and U.S. Ser.
No. 104,700 filed October 5, 1987, hereby incorporated by reference di~clo~e phenolic cyanate and phenolic triazine resins. The phenolic cyanate resins are disclosed to be ~table a~ me~Jured by gel time. The phenolic triazine resin~ are disclosed to be thermally stable as mea~ured by Thermal Gravimetric Analysis.
Novolac re~ins are highly flame resistant, but are ~ not high temperature resins. The temperature stability of "~ novolac resins is limited because of o~idative decompo~ition of methylene bridge leading to punking ~ (afterglow) upon e~positure to a flame.

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~(~03582 0~ o~ o~l ~ ~
~ C~,,~c~ C~

Decomposition of the pero~ide formed at the methylene linkage is an esothermic reaction and leading to significant loss of weight and strength as temperatures approach 200 C.
Many applications require the use of thermal insulation materials that can also withstand structural loads. Resin matris fiber reinforced composites are often used for this purpose. One E~ample where insulative/structural materials are required is in aircraft brake systems. These brakes are located within the main wheel cavities of the landing gear. For large commercial aircraft, the brake system in each wheel can generate up to 25,000 BTU's of heat for a normal stop, and up to 75,000 BTU's for a rejected take off (TRO). Most of this heat is absorbed by the friction material and other components of the wheel and brake.
Two areas that must be insulated from the thermal environment of the brake are the fluid in the brake hydraulic sy8tem and the main a~le.
The hydraulic fluid mu~t be protected by an insulator on the hot ~ide of the hydraulic piston. The a~le must be protected by an insulator between the a~le and the brake torque tube. Both of these applications involve sub8tantial structural loading of the insulator.
Conventional resin matri~ composite materials such as fiberglass reinforced epo~y, phenolic or silicone resin laminates offer sufficient strength and thermal insulative characteristics. However, these materials can not withstand temperatures above 45~ F without e~hibiting severe property degradation.
Fiberglass laminated composites prepared with thermosetting silicone resins e~hibit acceptable thermal stability, but mechanical properties are inadequate.

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Polyimides may provide acceptable properties as demonstrated on small experimental panels. However, processing of fiberglass reinforced components of the size and shape needed for these applications is beyond current 5 capability.
Pistons and insulator assemblies having structure as shown in Figure 1 are known e~cept for the makeup of insulator. The insulators are made of short asbestos fibers randomly reinforcing a phenolic resin. It is also known to use fiberglass layers reinforcing silicon resin.
Silicon resin has been found to deteriorate from e~posure to high temperatures.

SUMMA~Y_~F THE INVENTION
The present invention is an insulator comprising a reinforced phenolic triazine resin. The reinforcement is preferably a fibrous material. The reinforcement can be in the form of chopped fiber reinforcing filler or fibrous layers made from woven fabric layers of unidirectional fibers, or nonwoven fibrous mat.
In the preferred embodiment of the present invention, the insulator is made of a plurality of fibrouo layers.
Preferably, the fiber is a temperature resistant fiber guch as fibergla~, asbe~tos, carbon, graphite, boron, cellulose, titanate, metallic and mi~tures thereof. The fibrous layers are embedded in a phenolic triazine resin matri~. Preferably, there is from 50 to 80~ by volume of fiber and correspondingly, from 50 to 20~ of the phenolic triazine resin matri~.
A specific and preferred embodiment of the present invention is the use of the insulator in the shape of a cylinder preferably a hollow cylinder. In the preferred embodiment, the cylinder is reinforced with fibrous 3S materials. Preferably, the cylinder is made of a plurality of layers of the fibrous material made from the ; fibers recited above. The fibrous layers can be wrapped so that they form circumferential layers around the a~is .

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of the cylinder. Alernately, the fibrous layers can be lamianated in a direction perpendicular to the a~is. The cylinder can be solid. The cylinder can have an outside diameter of from 1 to 30 centimeters in length.
The insulator of the present invention, particularly where used in applications such as piston insulator, should have structural integrity. The insulator preferably has a compressive strength of greater than 50,000 psi and preferably greater than 60,000 psi as 10 measured according to ASTM D695.
The present invention also includes a method of insulating a heat source at a temperature up to 400 C.
The insulator is made of a composition comprising a phenolic triazine resin. 8Oth triazine as well as the 15 cyanate ester formation deactivate the benzene nucleus of the phenolic resin and thus inhibits pero~ide formation at the methylene linkage, through both steric and inductive effects. Thermal and o~idative stability is enhanced and the possibility of afterglow or punking is deminished. In 20 addition to thermal and o~idative stability, the mechanical properties of phenolic triazine resin are substantially improved through the contribution of the ether and triazine bridge.
The phenolic cyanate resin useful to make the 25 phenolic triazino of the present invention i3 derived from a cyanato group containing phenolic resin of Formula I:

FORMULA I
OZ
Z O ~ X ~ X ~ 02 (R~o ~ )r (R~)o (~)P
wherein:
n is a positive whole number greater than or equal to 1, preferably 4 to 20, and more preferably 4 to 10;
q and r are the same or different at each occurrence and are whole numbers from 0 to 3, with the proviso that X~)35~2 the sum of q and r at each occurrence is equal to 3, preferably of q is equal to 0 or r is equal to 3;
Z is -CN, or hydrogen and -CN;
o and p are the same or different at each occurrence 5 and are whole numbers from 0 to 4 with the proviso that the sum of o and p at each occurrence is equal to 4, preferably o is equal to 0 and p is equal to 4;
-X- is a divalent organic radical; and R3 is the same or different at each occurrence and 10 is a substituent other than hydrogen which is unreactive under conditions necessary to completely cure the copolymer.
There is from 5 to 100, preferably 10 to 100, more preferably 50 to 100, most preferably 70 to 100 and yet 15 more preferably 80 to 100 mole ~ -OCN groups based upon the sum of the moles of the -OCN and -OH groups.
X is preferably a radical selected from the group consisting of: -CH2-, -CO-, -SO2-, ~ CH2-, (S)y and -CH2 ~ CH2, with -CH2- preferred. y i8 a positive number greater or equal to 1 and preferably 1.
R is preferably Jelected from hydrogen and methyl groups.
- 25 ~ho cyanato group containing phenolic resin can be lncompletely ~partially) croJslinked or fully crosslinked to form the phenolic triazine resin of the present invent$on. The phenolic triazine can be formed by heating the cyanato group containing phenolic resin i8 stable and 30 has a long shelf life. This is indicated by the gel time of greater than 1 minute, preferably greater than 2 minutes, more preferably greater than 10 minutes at 155 C, and most preferably greater than 20 minutes at 155 C. The cyanato group containing phenolic resin cures to form a 35 phenolic triazine which can be characterized as having a thermal stability indicated by thermal decomposition temperature of at least 400 C and preferably of at least 450 C as measured by Thermal Gravimetric Analysis (TCA).

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This is important to enable articles made of compositions comprising phenolic triazine resin to provide insulation against heat sources up to 400 C.
The cyanato group containing phenolic resin useful to 5 make the phenolic triazine resin insulator of the present invention preferably has a number average molecular weight of from 300 to 2000, preferably 320 to about 1600, more preferably about 500 to 1500 and most preferably about 600 to 1500, and yet more preferably about 700 to 1300.
BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a piston and insulator assembly containing a piston insulator of the present invention.
Figure 2 is a schematic cross-sectional view of a piston and insulator as part of a brake assembly.
Figure 3 is a partial cross-section view of the piston insulator of the present invention in a disc brake environment.
Figure 4 is a partial cross-section view of the insulator of the present invention is a disc brake in an embodiment of an a~le insulator.
Figure 5 is partial isometric sectional view of the a~le in~ulator in a disc brake assembly.
D~ pTION OF THE PREFERRED EMBODIMENTS

The present invention i~ an article of manufacture comprising an insulator; and a method of insulating.
The insulator of the present invention comprises a reinforced phenolic triazine resin. The reinforcement can be a fibrous material. The fibrous material can be dispersed as a reinforcing filler throughout the resin or alternately be in a web-type construction. The web can be 35 woven, two or more of unidirectional fiber layers, or nonwoven.
In a preferred embodiment, the insulator is made of a plurality of fibrous layers. Useful fibers include but . . .

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are not limited to fibers that can be selected from the group consisting of fiberglass, asbestos, carbon, graphite, boron, cellulose, titanate, thermoplastic polymer, metallic fibers and mi~tures thereof.
Useful fibers can be selected from the group consisti~g of high~strength fibers such as polyaramides, boron, titanate and the like. The fibrous layers are embedded in a phenolic triazine resin matrix.
There is from 25 to 80, preferably from 50 to 80 and lO more preferably from 60 to 75% by volume of fiber.
A preferred insulator of the present invention is a cylindrical shaped insulator. In a specific embodiment, the cylindrical can be hollow. The cylinder can be used as a piston insulator or an a~le insulator in braking lS systems. Where the insulator is a cylinder, the cylinder can have an outside diameter of from 1 to 30, preferably from 2 to ~5 and more preferably from 3 to 17 centimeters. Typically, the cylinder is from 1 to 10, preferably from 2 to 8 and more preferably 3 to 8 20 centimeters high. In a preferred embodiment, the cylinder is hollow and has an outside diameter of from 15 to 18 centimeters, an inside diameter of from 13 to 16 centimeters and it is from 3 to 4 centimeters in eight.
The insulator of the present invention resists substantial - 25 1088 in mechanical propertie~ including strength and modulus when e~po~ed to temperatureJ of up to 400 C for 30 minute~.
The pre~ent invention includes a method of insulating a heat source which is at a temperature of up to 400 C;
30 can be as high as 450 C; and is typically in a range of from 159 C to 250 C, with an insulator comprising reinforced phenolic triazine resin as described above.
The insulator of the present invention has structurally satisfactory physical properties including a 35 compressive strength of at least 50,000 psi and preferably from 60,000 to 80,000 psi as measured according to ASTM
D695.

~035~32 The phenolic cyanate resin useful to make the ~henolic triazine resin useful in the present invention has Formula I where X is preferably a radical selected from the group consisting of: -CH2-, -CO-, -SO2-, ~ - CH2-, (S)Y and -CH2 ~ CH2-, with -CH2- preferred. R is preferably selected from hydrogen and methyl groups.
The phenolic cyanate resin has improved gel time and long shelf life. The gel time as measured by the Hot Plate Stroke Cure Method of greater than 1 minute, preferably 2 minutes, more preferably greater than 10 minutes, and most preferably greater than 20 minutes at 15 155 C. The phenolic triazine resin has low volatiles, and escellent char yield and thermal properties. Useful resin having these properties is described in U.s. Serial No.
104,700 filed October 5, 1987 and hereby incorporated by reference. This reference sets forth the Plate Stroke 20 Case Method.
The thermal stability of the phenolic triazine resin useful in the present invention is indicated by whether the reins is capable of forming a phenolic triazine resin having the thermal decomposition temperature of at least 25 400 C and preferably of at least 450 C as measured by Thermal Gravimetric Analysis (TG~). The thermal docomposition temperature is when the sample begins to have a measured weight loss. The phenolic triazine resin of the present invention has a char value (weight loss) at 30 800 C of at least 50% by weight, preferably from 50 to 70%
by weight, and more preferably 60 to 70% by weight.
It is believed that the improved properties of the resin of the phenolic cyanate resin used in the present invention are attributed to the purity of the resin, 35 preferably the resin has a residual amount of a dialkyl cyanamide, typically diethyl cyanamide of less than 2~ by weight, preferably less than 1% by weight and most ` ``~PW . n~, XO~)3~R~

preferably substantially none. The diethyl cyanamide is undesirable because it generates smoke upon curing.
Preferably, the cyanato group containing phenolic re~in has a residual amount of phenyl cyanate of less than 5 2~ by weight and preferably less than 1~ by weight and most preferably less than 0.5% by weight. This is desirable since it has been found that the phenyl cyanate is a volatile material that contributes to thermal instability and the formation of smoke during curing of 10 the resin. In addition, phenyl cyanate acts as a chain inhibitor for cyclotrimerization reaction.
The phenolic cyanate resin useful in the present invention is satisfactory and results in satisfactory cured triazine materials regardless of molecular weight.
15 The preferred molecular weight range of the phenolic cyanate resin is a number average molecular weight of 300 to 2000, preferably 320 to about 1600, more preferably about 500 to 1500 and most preferably from about 600 to 1500 and yet more preferably 750 to 1300. The molecular 20 weight distribution and number average molecular weight of the cyanato group containing phenolic resin can be determined by gel permeation chromatography(GPC) using tetrahydrofuran a~ a solvent.
The phenolic cyanate resin forms a phenolic triazine 2S network upon heating and/or in the presence of a curing agent. Typical curing conditions are from 150 to 250 C at 100 to 500 p8i pressure for .1 to 1 hour depending on sample size, or by autoclave at low pressures including pres~ures below 100 psi. The high density of cross 30 linkage of the cured products results in escellent characteristics including thermal properties and a glass transition temperature of 300 C or higher.
Thla phenolic triazine resin useful in the insulator of the present in~ention is formed by the curing of the 35 cyanato group containing phenolic resin. The curing reaction is known as "cyclotrimerizationn. As used herein, "completely cured" phenolic triazine resin includes those in which the glass transition temperature ~0358X

~o--of the cured resin is greater than 300C, measured by DMA, dynamic mechanical analysis.
A preferred phenolic triazine resin begins with a phenolic novolac backbone. This is reacted with cyanogen 5 halide such as cyanogen bromide (CNBr) is presence of an organic base, such as triethylamine (Et3N) in a solvent such as tetrahydrofuran (THF) to form phenolic cyanate ~ o~
~ C~ ~ C~ t-~)C~
oc-J oC~ o~l o~

~ C~, ~ C~L~ C~
m and n are integers, typically there are 80 to 100 percent of n units and 20 to 0 percent m units. Vnder the influence of heat and/or a suitable catalyst phenolic-cyanate forms phenolic cyanate-phenolic triazine 20 precursor.
~ CH~ ~CI~L ~ C~l,~

25 ,,,C~I~C'`o~ ~ 3' o' ~ o~
The phenolic cyanate-phenolic triazine precursor resin can be used to form phenolic-triazine resin.

- C~ ~ C~ ~

~C~

The phenolic cyanate resin of the present invention can be derived from a phenolic novolac. Useful phenolic ~00;~8~

novolac resins are known in the art. A typical and useful one is disclosed in U.S. Patent No. 4,022,755 at column 2 beginning at line 27. Particularly useful phenols include phenol, cresol and ~ylenol.
A preferred method of making the phenolic triazine useful in the insulator of the present invention is to make the cyanato group containing phenolic resin recited above. This comprises the steps of reacting novolac resin and a trialkyl amine in ~ suitable organic solvent, 10 preferably a cylic ether solvent to form the trialkylammonium salt, followed by reacting this trialkylammonium salt with cyanogen halide in the cyclic ether to form the cyanato group containing phenolic resin. The method is conducted at a temperature range of 15 below -%C, preferably from -5 C to -65 C, more preferably from -30 C to -65 C and most preferably from -g5 C to -60 C.
The reaction product is in solution in the cyclic ether. This reaction product is a cyanato group 20 containing phenolic resin. In is separated from the solution by a suitable separation technique. The preferred technique is precipitation into a non~olvent - vehicle. Useful nonsolvents ae alcohols with isopropanol beinq preferred. The separation is preferably conducted 25 at atmospherlc pressure. While it can be conducted at room temperature, the temperature is typically from -0 C
to -45 C, preferably -5 C to -25 C. Precipitation is preferably conducted with agitation.
The improved properties of the resin used in the 30 pregent invention are due to reacting the phenolic cyanate resin and a triakyl amine in a cyclic ether solvent to form the trialkylammonium salt of novolac resin this is followed by reacting the trialkylammonium ~alt with a cyanogen halide in the cyclic ether to form the phenolic 35 cyanate resin. The reaction is conducted at below about -5 C, preferably to -5 C to -65 C, more preferably from -30 C to -65 C and most preferably from -4S C to -60 C.

.

'~003~2 The cyclic ether solvent has been found to be an important reaction medium to form the phenolic cyanate resin of the present invention. The cyclic ether solvent is preferably selected from the group consisting of:
5 tetrahydrofuran; 1,4 diosan; and furan. The trialkyl amine can be selected from triethyl amine, tripropylamine and triethylcyclohesyl amine. Additionally, the raction medium can contain other bases to control the pH to help control the rate of the reaction.
The relative amount of solvent i.e. tetrahydrofuran, trialkylamine, and phenolic resin used should be controlled to control gel time of the cyanato group containing phenolic resin. Concentrations can be measured as a function of the weight percent of the trialkyammonium 15 salt which could theoretically be calculated based,on the weight of the trialkylamine, phenolic resin and solvent.
Preferably, the amount of trialkylammonium salt is from 5 to 35, more preferably 10 to 25, and most preferably from 10 to 20 percent by weight. The preferred concentration 20 can vary depending on the specific solvents and reactants used.
The formation of the phenolic cyanate resin used to make the insulator of the present invention is followed by reinforcing this resin. The reinforcing fiber can be ~S mi~ed into the phenolic cyanate resins by methods known to mi~ ~uch fiber~ into phenolic re~in. Fibros webs can be coated with phenolic cyanate resins by methods known to coat fibrous with phenolic resin.
The reinforced resin can be cured by the application 30 of heat or by the use of a suitable catalyst or a combination of both. Ths phenolic cyanate resin can be cured into a phenolic triazine resin in a suitable form and the cured structure shaped by appropriate means such as cutting into the suitable configuration for an 35 article. Alternatively, the resin can be incompletely cured followed by forming into an insulator. The article formed of the incompletely cured resin can be used as a blank.

;~0035~2 The blank can be further formed and then cured to form the phenolic triazine insulator.
Preferred insulators of the present invention comprise the resin of the present invention and 5 reinforcement, preferably a reinforcing fiber. The insulator can be made of compositions comprising short fiber up to l/2 inch long and preferably from l/16 to l/4 of an inch long, and/or long fibers greater than l/2 inch long. More preferred ar insulators made using long or lO continuous fibers, coated with resin in impregnated into resin layers.
When short fibers are used, the composition comprises from 5 to 150 and preferably 25 to 75 weight percent of the short fibers. When long fibers or continuous fibers 15 are used, the composition comprises from 5 to 150 and preferably 25 to 75 percent by weight of the long fibers.
The fiber to resin volume ratio depends on the application to be used. Properties to be considered - include impact resistance, heat resistant, wear 20 resistance, flamability resistance. Preferably, the resin impregnated articles of the present invention contain coated fibers having 25 to 80, preferably 50 to 80, and more preferably 60 to 75 volume percent fiber.
; The fibers may be pre-coated with the phenolic cyante 25 resin or partially cured phenoliccyanate resin of the presont invention. The coated fiber~ can be pultruded, filament wound, or formed into layers.
Tho coating may be applied to the fiber in a variety of way~. One method is to apply the resin of the coating 30 material to the fibers either as a liquid, a sticky solid or particles in suspension, or in a fluidized bed.
Alernately, the coating may be applied as a solution in a suitable solvent which doe~ not adversely affect the properties of the fiber at the temperature of the 35 application. While any liquid capable of dissolving or dispersing the resin of the present invention can be used, preferred groups of solvents include acetone, methyl ethyl ketone, methylene chloride and methyl isobutyl ketone ~MI~R). The techniques used to dissolve or disperse the ;~0(~35~

coating resin in solvents will be those conventionally used for coating of similar resin materials on a variety of substrates.
The fibrous web can be coated or embedded in phenolic 5 cyanate resin to form single layers which are called prepreg layers. The prepreg layers can be made of the fiber impregnated or coated with phenolic cynate resin.
The prepreg layers can be cured to make a phenolic triazine resin composite insulator.
The fiber used in the prepreg layer can be any fibrous network woven or non-woven. Useful fibers include fiberglass, asbestos, carbon, graphite, boron, cellulose, titanates, polymers such as polyesters, polyamides, polyaramides, polyacrylics, ultra high molecular weight 15 polyolefins including polyethylene and polyvinyl alcohol, metallics, amorphous metals such as those sold under the tradename Metglas by Allied-Signal, Inc. and mistures thereof.
The composite articles of the present invention can 20 be made of fibers arranged in networks having various configurations. A plurality of fibers can be grouped together to form a twisted or untwisted yarn. The fibers or yarn can be formed into felt, knitted or woven (plain, basket, satin and crow feet weaves, etc.) into a network 25 fabr~cated into non-woven fabric articles in parallel arr~y, layered or formed into a fabric by any of a variety of convention~l techniques.
A u~eful technique for preparing preferred prepregs of the pre8ent invention comprised of substantially 30 parallel, unidirectionally aligned fiber-~ includes the steps of pulling fiber through a bath containing a solution of the resin, and helically winding the fiber into a single sheet-like layer around and along the length of a suitable form, such as a cylinder. The solvent is 35 then evaporated leaving a prepreg sheet of fiber embedded ln a phenolic cyanate matri~ that can be removed from the cylinder after proper curing. Alternately, a plurality of fibers can be simultaneously pulled through the bath of ~0035F~

the resin solution and laid down in closely positioned, in substantially parallel relation to one another on a suitable surface. Evaporation of the solvent leaves a prepreg sheet comprised of the resin coated fibers which S are substantially parallel and sligned along a common iber direction. The sheet is ~ubsequently processed such as by laminating one sheet to another.
Yarn useful in composites can be produced by pulling a group of filaments through the solution of the phenolic 10 cyanate resin to substantially coat each of the individual filaments, and then evaporating the solvent to form coated yarn. The yarn can then for e~ample be employed to form fabrics, which in turn can be used to form composite structurers. The yarn can also be processed into lS compositeg by employing conventional filament winding techniques. For e~ample the composite can have coated yarn formed wound into overlapping f iber layers. Fabrics can also be coated with the phenolic cyanate resin of the present invention. Such fabrics can include woven fabrics 20 as described above as well as non-woven mats.
The insulator of the present invention can be laminated with a polymeric and/or metal films adjacent to the outer surfaces of the phenolic cyanate resin prepreg or phenolic triazine layer.
Figure 1 illustrates a piJton and insulator a~sembly 10 which haJ tho in~ulator of the present invention. The insulator comprise~ a reinforced phenolic tirazine resin.
The assembly comprises a piston 14 and the piston insulator 18. The outside diameter of the piston and 30 piston insulator are preferably equal. Thr piston insulator 18 is cylindrical in shape having an insulator piston end 20 and an insulator front end 22. Planes through the insulator piston end 20 and insulator from end 22 are preferably perpendicular to the a~is 21 of the 35 cylindrical insulator 18. The insulator 18 can be connected to the piston 14. The insulator and piston are a~ially connected by suitable connecting means. A
preferred connecting means illustrated in Figure 1 is to .

~00~58~

have a tubular clip 24 connected into an a~ial opening in the top surface 16 or the piston. The insulator is connected to the piston by an insulator hold down pin 26 which passes through an insulator pin shaft in 28. The 5 shaft 28 passes from insulator front end through the insulator to the insulator piston end and is connected to the tubular clip. Preferably, the shaft 28 is a~ial and shaped into a form similar t the outer diameter of the insulator hold-down pin. The insulator 18 to the top 16 10 of piston 14. In Figure 1 this means is a flared end 30 which presses against front end 22 of the insulator 18.
The insulator hold-down pin 26 has a connecting end 32 which fits into tubular clip 24 to maintain piston insulator lB in place.
The piston insulator illustrated in Figure l is about 2.54 cm long, 3.175 cm out~ide diameter and 1.5 cm inside diameter. It is made of layers of fiberglass impregnated with resin. The layers are perpendicular to the a~is of the piston insulator cylinder.
Pistons and insulator assemblies having the structure as shown in Figure 1 are known e~cept for the makeup of insulator. The insulators are made of short asbestos fibers randomly reinforcing a phenolic resin. It is also known to use fiberglas~ layers reinforcing silicone 25 re~in. Silicone re~in ha~ been found to deteriorate from e~pooure to high temperature~. The phenolic triazine resin of the present invention has been found to have improved thermal and physical properties compared to silicone resin.
Preferably there can be an insulator protector plate 34 on the insulator front end. The insulator protector plate 34 can be connected to the front end 22 of the insulator 18 by hold-down pin 26. The insulator protector is preferably made of a hard metal composition which would 35 protect the front end 22 of the insulator 18 as it pushes against corresponding elements in the brake or other in which the piston with the piston insulator is located.

~0~35~

The piston insulator thermally insulatest he piston from a heat source which may directly or indirectly come into contact with the front end 22 of the insulator 18.
Were the insulator not there, the heat source would then 5 come directly in contact with metallic elements of the piston. Materials used to make pistons such as steel and steel alloy rapidly transfer heat and as such the whole piston assembly would heat up. This would help to transfer heat throughout the brake assembly including the 10 transfer of heat to hydraulic lines. The heat would cause vaporization of hydraulic fluid when brake temperatures increased sufficiently. The insulator must have sufficient structural strength to withstand repeated compression cycle~ at high temperatures and stresses.
Figure 2 illustrates the piston assembly 10 in a piston housing where the piston and insulator assembly is shown in its environment.
The piston 14 is set in a piston housing 38. The piston housing has a piston housing boar 40 which the 20 piston is located. The piston base 42 is in contact with hydraulic fluid passages 44 through which fluid can assert pressure on the piston base 42 forcing it in the direction of the front end 22 of the insulator. The in~ulator is Jhown with a in~ulator protection plate 34. The insulator 25 protection plate i~ forcod against a pressure plate 46.
The pre~ure plate activate~ the brake mechanism. This is accompliJhed by cau~ing rotor disc~ to contact stator disc~. The thermal energy generated by the friction between the rotating and ~tationary discs causes them to 30 heat to temperature~ as high as 1500 C with surface temperatures reaching up to 3000 C in aircraft brakes.
The insulator resists the heat flow from the hot brakes to t the hydraulic fluid.
Figure 3 further shows the illustration of the piston 35 assembly shown in Figure 2 in the environment of a braking mechanism. The as~embly is generally shown in a sectional view of a disc brake. The piston and insulator X0035~;~

assembly 10 ~orces the rotar 48 and stator 50 elements of the disc brake together causing the brake to engage.
The insulator of the present invention can be molded into a hollow cylindrical shape to make an a~le insulator 5 also used as part of disc brake assemblies. One such axle insulator in a disc brake is shown as reference character 52 in Figure 4. The a~le insulator insulates a~le 54 from the heat generating braking environment of the rotor and stator elements which cause housing 56 to heat up. The 10 a~ial insulator 52 is loca~ed between torque tube 56 and a~le support 58. In this way the a~ial is separated from the heat source which in this case is the friction elements.
Figure 5 illustrates a brake assembly showing the l5 a~le insulator in position.
The present invention includes a new use of a known material. The known material is the phenolic tirazine resin. Phenolic triazine resin reinforced with fiberglass are known from companion patent application Serial No.
20 232,407 filed August 15, 1988. There is no disclosure or suggestion that a reinforced phenolic triazine resin could be used as a thermal insulator particularly when it is reinforced. As indicated above the present invention has found such a use in an aircraft brake system as insulators 25 for the pigton and for the a~le. This in~ulator of the pre~ent invention has low thermal conductivity ~appro~imately 1 .8TU per foot hour degree F) and good mechanical properties. The compressive strength is preferably at least 50,000 psi when measured in accordance 30 with ASTM D695, and the interlaminar shear strength is preferably greater than 5,000 psi when measured according to ASTM D2344. The mechanical properties must be retained over a temperature range of from -65 to 750 F. The insulator of the present invention considering both fabric 35 and phenolic triazine resin must be resistant to fluids commonly encountered in their environments including lubricants, hydraulic fluids and solvents.

XG035~Z

The phenolic triazine resin of the present invention can be made by methods such as disclosed in our co-pending applications. PCT US~8/00119 and U.S. Serial No. 104,700, both hereby incorporated by reference.
Several e~amples are set forth below to illustrate the nature of the invention and method of carrying it out. However, the invention and method of carrying it out. However, the invention should not be considered as being limited to the details thereof. All parts are by 10 weight unless otherwise indicated.

This e~ample illustrates the preparation of an 15 insulator of the present invention.

a. Phenolic cyanate resin was synthesized from phenolic novolac resin. The phenolic novolac resin had a number average molecular weight of about 620 as measured 20 according to vapor phase osmometry. 1378 grams was dried in a vacuum oven at 40~C for 48 hours. This was added to a 12 liter 3 neck round bottom flask which was equipped with an air driven stirrer. There was a nitrogen inlet and an addition funnel. Seven liter~ of tetrahydrofuran 25 wa~ charged to the fla~k under nitroqen. The dried novolac re~in wa~ di~olved in the tetrahydrofuran at room temperature under tho nitrogen. 1433 grams of triethylamine (TEA), which h~d been stored over a molecular siev (4A) overnight, was placed in the addition 30 funnel and slowly added to the novolac solution over a period of 90 minute~ under nitrogen atmosphere at room temperature. The resulting solution was slightly hazy and pink.
Cyanogen bromide (CN8r) ~olution was prepreg. A 22 35 liter 4 neck round bottom blask was charged with 7 liters of tetrahydrofuran (THF) and fitted with a nitrogen inlet. A thermometer, an addition funnel and an air ~0035~Z

driven stirrer were also fitted to the flask. Th~ whole step-up was placed in a dry-ice/acetone cooling bath which was at a te~perature of -65 C. 1623 grams of cyanogen bromide was dissolved in the tetrahydorfuran at room 5 temperature and nitrogen purge was begun.
The te~perature of the cyanogen bromide solution was brought to -60 C. The novolac triethylamine salt solution prepared was placed in the addition funnel and slowly added to the cyano~en bromide solution. The addition time 10 was 3 hours. The reaction temperature was maintained at appro~imately -40 C. As the reaction proceeded, the by-product triethylammonium bromide salt was seen as a white solid. The reaction product formed was the cyanated phenolic novolac resin.
After the cyanation reaction, the reaction mi~ture was filtered through a cour~e fritted glass funnel coated with about 1/8 inch of silica gel produced by Merck, Grade 60, 60 angstroms. The filtrate was a clear yellow solution and stored in a refrigerator. The 20 triethylammonium bromide salt was discarded.
The reaction product (novolac cyanate re~in) was precipitated in a 15 gallon bucket. 2B liters of isopropanol (IPA) was charged to the bucket and coled to -20 C on a dry ice/acetone cooling bath. The filtrate was 25 placed in an addition funnel and added to the isopropanol over a period of 2 hours under vigorous stirring. After preclpitation, the product misture was filtered through a 60 micron filter cloth made of nylon and transferred to a 5 gallon bucket. Two gallons of isopropanol was added to 30 the white product and this misture was stirred for one half hour at room temperature and the product was filtered again. The isopropanol washing was repeated twice. The product was filtered and dried on a Buchnel funnel overnight and then transferred to a room temperature 35 vacuum open todry until the solid content reached greater than 98~ by weight. This material was then the phenolic cyanate resin.

, ~C~0;;~5F32 The phenolic cyanate resin was impregnated onto a 7781 E fiberglass cloth finished with UM 619 Volan finish, an adhesive sizing product of Uniglass Industries, New York. This is compatible with eposy and phenolics. The 5 ~iberglass was coated using 250 ml of a 50 weight percent solution of the phenolic cyanate resin in methyl ethyl ketone ~MEK). This solution was poured into a throgh. A
piece of 7 inch by 7 inch by 0.029 inch fib0rglass fabric was pulled through the resin solution through two rolls.
10 The clearance between the two rolls was set to 0.356 mm.
The fabric was pulled through the rolls after a 3 minute immersion in the phenolic triazine resin solution. This impregnated fiber was considered to be a prepreg. The prepreg was then placed on a pi~ce of Teflon sheet under 15 a hood in order to evaporate the MEK solvent. After 4a hours under the hood, the resin content of the prepreg was determined to be 35 to 40 weight percent.
The fiberglass impregnated with phenolic cyanate resin was compression molded to form laminat~s. 29 plies 20 of 6 inch by 6 inch prepregs were loaded into a mold. A
ply is one prepreg layer. The mold was put into a platen press where the platens were preheated to 115 C. The mold was compresJed under contact pressure and held or 20 minutes after the temperature of the mold reached 115 C.
25 The mol~ was pressurizod to 1000 psi and heated to 200 C
and held for on- hour. The mold wa~ cool~d to room temporature at a pressure of 1000 psi. The resin content of the laminate was determined to be about 30 to 35% by weight. The laminate was 0.25 inches thick.
A second laminate was made using 57 piles of circular prepreg sheet~ having a diameter of 2.a75 inches. The laminate was made as described above with the pressure at 1000 psi and heated to 200 C where it was held for one hour. The mold was cooled to room temperature at a 35 pressure 1000 p9i pressure. The resin content of the laminate was determined to be 35 to 48 percent by weight.
The laminate was 0.5 inches thick.

~03~

The tow laminates prepared above was subjected to the following post cure cycle in an oven in air at ambient pressure.

S TAB~ 1 C hr.

0 - 150 1~2 The laminates were machined into test specimens for mechanical property testing.
For comparative purposes laminates available by Synthan-Taylor as GSC laminates NEMA (National Electrical 20 Manufacturer's Association) Grade G-7 were used. This laminate is fiberglass reinforced with a thermosetting silicone resin matri~. Test specimens in Tables 2 and 3 of equal size were made. changes in properties with temperature increa~o has been compared.
Fle~ural te~t~ wore performed with accordance with A8TM D790. Sp-cimen~ were 6 inche~ long and 0.5 inche~
wide by 0.25 inch-~ thick. 3 point loading with a 4.2 inch ~pace wa~ u~ed.
Compre~ion teJt~ were performed in accordance with 30 ASTM D695. Specimens were 1/2 inch cubes.
Test results are summarized in Table 2 for composite laminates made using 29 plie~ as recited above. Test results are summarized in Table 3 for composite laminate made using 57 plies as recited above. In Table 3, results 35 are shown for two separate laminated panels made using 57 plies. ~A and B) In the Table PT represents phenolic triazine resin/fiberglass laminates and silicone represents silicone resin/fiberglass laminates.

~03~j~X

T~E 2 Fle~r~ Ptc~ a~ PT~Fl~ Q~th L~ (29 ~11~) RT ~0F 650F 750F
Fl~ral S~th, (103 ~d) S11 im~ 17.0 7.8 - -PT 46.8 36.9 35.5 26.2 S1lim~ 3.3 2.1 PT 3.9 3.4 3-3 3.1 1111~E 3 ~1~ P~ ~ PI~J Cld;h 1~ (57 RES) Rl 50F 650F 750F
20 ~oS~, (1~3pl) Slliax~ 48.4 37.2 39.6 4~.1 A 95.0 73.7 59.4 62.3 3 88.8 - - 74.2 T~t t~, (106 ~1) Slllm~ o.a~ o.~o 0.56 0.57 PT
A 1.16 1 03 1 99 ,

Claims (25)

1. An insulator comprising a reinforced phenolic triazine resin.

2. The insulator of the claim 1 wherein the phenolic triazine resin derived from a cyanato group containing phenolic resin of the formula wherein:
n is a positive whole number greater than or equal to 1;
q and r are the same or different at each occurrence and are whole numbers from 0 to 3, with the proviso that the sum of q and r at each occurrence is equal to 3;
Z is -CN, or hydrogen and -CN;
o and p are the same or different at each occurrence and are whole numbers from 0 to 4 with the proviso that the sum of o and p at each occurrence is equal to 4;
-X- is a divalent organic radical; and R3 is the same or different at each occurrence and is a substituent other than hydrogen which is unreactive under conditions necessary to completely cure the copolymer.

3. The insulator of claim 1 wherein the phenolic triazine resin has a thermal stability of at least 400°C
as measured by thermal gravimetric analysis.

4. The method as recited in claim 1 wherein the phenolic triazine resin has a char yield of at least 50%
by weight at 800°C.

5. The method as recited in claim 1 wherein n is from 4 to 20.

6. The insulator of claim 1 reinforced with a fibrous material.

7. The insulator of claim 6 wherein the insulator is made of a plurality of layers of fiber selected from the group consisting of fiberglass asbestos, carbon, graphite, boron, cellulose, titanate, thermoplastic polymers, metallic and mixtures thereof, wherein the fiber is in a phenolic triazine resin matrix.

8. The insulator of claim 6 wherein there is from 25 to 80 percent by volume of fiber.

9. The insulator of claim 1 wherein the insulator has a comprisive strength of 50,000 to 100,000 psi as measured according to ASTM D695.

10. A cylinder comprising a reinforced phenolic triazine resin.

11. The cylinder of claim 10 reinforced with a fibrous material.

12. The cylinder as recited in claim 11 wherein the cylinder is made of a plurality of layers of fiber selected from the group consisting of fiberglass asbestos, carbon, graphite, boron, cellulose, titanate, thermoplastic polymers, metallic and mixtures thereof, wherein the fiber is in a phenolic triazine resin matrix.

13. The cylinder as recited in claim 11 wherein there is from 25 to 80 percent by volume of fiber.

14. The cylinder of claim 10 wherein the cylinder is hollow and has an outside diameter of from 1 to 30 centimeters, an inside diameter of from 0.5 to 28 centimeters and is from 1.5 to 8 centimeters in length.

15. The cylinder of claim 10 wherein the phenolic triazine resin derived from a cyanato group containing phenolic resin of the formula:

wherein:
n is a positive whole number greater than or equal to 1;
q and r are the same or different at each occurrence and are whole numbers from 0 to 3, with the proviso that the sum of q and r at each occurrence is equal to 3;

Z is -CN, or hydrogen and -CN;
o and p are the same or different at each occurrence and are whole numbers from 0 to 4 with the proviso that the sum of o and p at each occurrence is equal to 4;
-X- is a divalent organic radical; and R3 is the same or different at each occurrence and is a substituent other than hydrogen which is unreactive under conditions necessary to completely cure the copolymer.

16. The cylinder of claim 10 having a compression strength of at least 50,000 psi as measured according to ASTM D695.

17. A piston insulator comprising a cylinder comprising a reinforced phenolic triazine resin.

18. The piston insulator as recited in claim 17 reinforced with a fibrous material.

19. The piston insulator as recited in claim 18 wherein the cylinder is made of a plurality of layers of fiber selected from the group consisting of fiberglass asbestos, carbon, graphite, boron, cellulose, titanate, thermoplastic polymers, metallic and mixtures thereof, wherein the fiber is in a phenolic triazine resin matrix.

20. The piston insulator as recited in claim 17 wherein there is from 25 to 80 percent by volume of fiber.

21. The piston insulator as recited in claim wherein the piston insulator has an outside diameter of from 1 to 6 centimeters, an inside diameter of from 0.5 to 2 centimeters and is from 3 to 10 centimeters in length.

22. The piston insulator of claim 21 wherein the phenolic triazine resin derived from a cyanato group containing phenolic resin of the formula wherein:
n is a positive whole number greater than or equal to 1;

q and r are the same or different at each occurrence and are whole numbers from o to 3, with the proviso that the sum of q and r at each occurrence is equal to 3;
Z is -CN, or hydrogen and -CN;
o and p are the same or different at each occurrence and are whole numbers from 0 to 4 with the proviso that the sum of o and p at each occurrence is equal to 4;
-X- is a divalent organic radical; and R3 is the same or different at each occurrence and is a substituent other than hydrogen which is unreactive under conditions necessary to completely cure the copolymer.

23. A method comprising the step of insulating a heat source at a temperature of up to 400 C with an insulator comprising a reinforced phenolic triazine resin.

24. The method of claim 23 wherein the heat source is from -65°F to 750°F.

25. The method of claim 23 wherein the phenolic triazine resin is derived from a cyanato group containing phenolic resin of the formula:

wherein:
n is a positive whole number greater than or equal to 1;
q and r are the same or different at each occurrence and are whole numbers from 0 to 3, with the proviso that the sum of q and r at each occurrence is equal to 3;
Z is -CN, or hydrogen and -CN;
o and p are the same or different at each occurrence and are whole numbers from 0 to 4 with the proviso that the sum of o and p at each occurrence is equal to 4;
-X- is a divalent organic radical; and R3 is the same or different at each occurrence and is a substituent other than hydrogen which is unreactive under conditions necessary to completely cure the copolymer.