Title of Invention

"A PROCESS FOR PREPARATION OF RUBBER BASED PASSIVE ACOUSTIC MATERIAL FOR CONSTRUCTION OF ACOUSTIC BAFFLES"

Abstract This invention relates to a process for preparation of a rubber based passive acoustic material. According to the process the fillers, carbon black and precipitated silica are subjected to the step of conditioning. The compounding materials are incorporated to styrene butadiene rubber through mill mixing procedure. Cooling said mixture and adding thereto acceelators followed addition of dibenzthiazyl disulphide and tetramethyl thiuram disulphide in the sequential order. And then mill rolling said mixture to obtain sheets and maturing it on flat bed.
Full Text This invention relates to a process for preparation of rubber based passive acoustic material for construction of acoustic baffles.
Acoustic baffles are used in large high performance sonar antenna (transducer arrays) for purposes of isolating ships noise as well as for improving directivity and sensitivity of the transducer elements. The buffles form a major passive element contributing to better performance of the system. The materials used for construction of baffles, are therefore required to possess specific acoustic and dynamic mechanical properties. As the application of baffles is in deep marine environment, the material used for the construction of baffles should also be compatible with the hostile marine conditions such as salinity, hydrostatic pressure, sub-ambient temperature, dynamic loading conditions, etc.
Rubbers show a unique combination of stiffness and energy absorption characteristics. The stiffness is expressed as dynamic modulus and energy absorption characteristics by mechanical damping factor. The rubber vulcanisates have a transition region where the modulii namely dynamic modulus-temperature and dynamic modulus frequency undergo rapid variations due to temperature/frequency changes.
In the rubbers used for underwater acoustic applications as that for acoustic baffles, the transition region in the mechanical properties is required to be far away from operational frequency/temperature range since the dynamic modulus of the material is related to acoustic velocity in the material and the acoustic velocity in the material undergoes drastic change in the transition region. It has been found that for a practical rubber vulcanisate,transition region is -70° to 0°C in temperature 103 to 108 Hz in the frequency range. Sonars generanlly over a wide frequency range starting for l KHz. to The rubbers used for acoustic baffle constriction should have a flat acoustic velocity i.e. the sound velocity should remain constant throughout the range of operating temeperature and frequency.
High performance acoustic baffles used in souar antennae are of sandwich construction wherein alternate leyers of compliant and rigid materials are used. The information on the process/material for this application is nOt cited in the literature The rubber based mnterial provided by the process of this invention serves as a high performance compliant. layer. it is a novel application Oriented material and hence comparison with the prior art is not feasible.
The primary object of the present invention is to propose a process for the preparation of a rubber based passive acoustic material for construction of acoustic baffles used in a large high performance sonar antenna.
Another object of the present invention is to propose a process for the preparation of rubber based passive acoustic material which has a flat acoustic velocity in the operational frequency of 1-10 KHz.
Still another object of the present invention is to propsoe e process for the preparation of rubber based passive acoustic material which has the mechanical properties for operation in deep sea conditions.
A further object of the present invention is to propose a process for the preparation of rubber based passive acoustic material which has the required sea-water resistance to withstand continuous deployment in undersea environment for a period not less than 5 years.These and other objects and advantages will be more clearly understood from the following detailed description, and specific example which are intended to be illustrative of the invention without limiting in anyway, on the scope of the invention.
According to the present there is provided a process for preparation of a rubber based passive acoustic material for the construction of baffles comprising the steps of :-
(i) conditioning as herein described the 10 part fillers, 70 parts carbon black and 20 parts precipitated silica, characterised in that is,
(ii) incorporating the compounding materials to 100 parts styrene butadiene rubber through mill mixing procedure,
(iii) cooling and adding accelators followed by addition of 1 part dibenzthiazyl disulphide and 1 part tetramethyl thiuram disulphide in the sequential order.
(iv) mill rolling to obtain sheets and maturing in on flat bed.
(v) The process for preparation of the
involves compounding into the base polymer, nstyrene. butadiene rubber with chemical agents for cross 1inking-sulphur, Zinc oxide and stearic acid, accelerators for eroailinking reaction Dibenzothiazyl disulphide, Tetramethyl thiuram disulphide(TMTD) , antidegradants-subatituted Trimethyl quinoline, P-Phenylene diamine, fillers- carbon black, precepitated silica and processing aid-napthenic oil.
A rubber for use on acoustic baffle compliant layer should optimally have a constant acoustic velocity. This in difficult to achieve with conventional compounding techniques as an increased filler loading causes an increase in Storage modulus. Whereas the compounding technique proposed in this invention involves the addition of. the Specific type of silica , which enables higher stiffness Without enhancing damping. The process has resulted in the shifting of transition frequency to the high frequency region and frequency dependence of dynamic mechanical properties is negligible in the operating frequency of 1 to 10 KHz.
The composition of the material obtained by the process expressed as quantity, parts by mass, are 100 parts rubber preferably SBR-1502, 1 part stearic acid, 5
parts zinc oxide, 2 parts 1,2 dihydro 2,2,4 trimethyl quinoline, 2 parts N-(1-3 dimethyl butyl) - N' Phenyl -P-henylene diamine, 70 parts GPF Carbon black, 20 parts preciptated silica , 10 parts napthenic oil, 1 part Tetra methyl thiuram disulphide, l part dibenzothiazyl disulphide and 0.75 sulphur.
According to the proposed process, the process for preparation of rubber based passive acoustic material comprises of incorporating of compounding materials on a mixing mill having rolls between 150 and 155mm in diameter. The mill is equipped with retaining guides with a distance between the guides at the nip of 250 to 280mm. The speed of the slow roll is 24 ±0.05 rpm and the ratio between slow and fast roll is 1:(1.4). The clearance between the rolls is adjustable from 0.2 to 8mm.
The process of incorporating, i.e. capturing and dispersion of compounding materials to the mix to ensure uniformity of composition, comprises of the following steps:-
(a) conditioning the fillers, carbon black arid
commercial rubber grade silica, before weighing, by
for example heating at/about 125 degree celsius for about l to 2
hours in a dehumidifier assisted tray drier. This is followed by cooling and weighing.
(b) masticating raw styrene butadiene rubber for 5
minutes on a standard two roll mill.
(c) adding sulphur slowly and evenly across the mill
at a uniform rate.
(d) addiing stearic acid evenly and making one 3/4 cut
from each end of the mill roll after the stearic acid
has been incorporated.
(e) adding anti - degradents 1,2 dihydro 2,2,4
trimethyl quinoline and N-(l-3 dimethyl butyl) - 'N'
Phenyl-P- Phenylene diamine and mixing well
(f) adding carbon black obtained from step (a)
evenly across the mill at a uniform rate and
incorporating completely.
(g) after complete incorporation of carbon black,
adding conditioned and cooled silica (obtained by stzep
(a)) and naphthenic oil. When all the added compounding
materials are incorporated, opening mill to l.4mm and
giving one 3/4 cut from each side.
(h) adding zinc oxide uniformly and evenly at 1.4mm setting and making three 3/4 cutting out from each side and cutting out the batch from the mill.
(i) setting the rolls at 0.8mm and passing the rolled batch endwise through the mill six times.
(j) opening the mill to give a sheet thickness of 4nun and taking out the batch from the mill as 4mm thick sheet and cooling the sheet to room temperature.
(k) banding the batch again on the rolls at a setting of 1.4mm and adding accelerators dibenzothiazyl disulphide and tetra methyl thiuran disulphide (TMTD)
(Vulcacit thiurum) evenly across the mill, at a uniform rate.
(1) opening the mill to a minimum batch thickness of 4mm and passing the stock through the mill 3-4 times folding it back on itself each time and taking out the material as 4mm thickness sheet and keeping it flat bed for masturing. The mill roll temperature is maintained within 40 to 60 degree Celsius preferably within the range of 45 to 50 degree Celsius throughout.
(m) checking the batch mass and discarding it, if it differs from the theoretical value by more than 0.5%.
It is to be clearly understood that the process is not an admixture of compounding materials. The starting raw rubber styrene butadiene is an amorphous co-polymer of styrene and butadiene having a random molecular arrangement. It is a high molecular weight liquid of low strength susceptible to viscous flow. When compound is heated with sulphur, the molecules are tied together by sulphur to form sulphur bonds leading to a three dimensional network structure. The compounding materials like sulphur, accelerators and zinc oxide lead to chemical changes namely cross-linking of molecules. Some of the compounding materials bring about physical changes like re¬inforcement by addition of carbon black, plasticisation by addition of organic esters. The final vulcanisate has a unique and specific combination of properties which is distinctively different from the individual properties of compounding materials. Before cross linking, rubber is physically less elastic and more viscous solid whereas after cross linking, it becomes a soft, more elastic and less viscous solid. Raw rubbers are completely soluble in certain liquids but cross-linked rubber are virtually insoluble.
The invention will now be illustrated by the following example, which is intended to be a typical of rather than in any way limiting on the scope of the present invention.
EXAMPLE
About lOOOg of GPF Carbon black (N660) and 250g of precipitated silica (superfine, mesh 400) are conditioned at about 125 degree Celsius in a dehumidifier assisted tray drier in separate trays for about l hour. The depth of the material is not kept more than 5mm. After conditioning, the materials are stored in moisture proof container. The ingradients are added and mixed in a 10kg capacity mill in the order that follows. 1kg of styrene butadiene rubber (SBR 1502) is masticated for 5 minutes. 7.5g of sulphur is
added slowly and evenly across the mill at a uniform rate. About lOg of stearic acid is added evenly and mixed. 20g of qenoline and 20g of diamine are added and mixed well. This is followed by addition of carbon black already conditioned seperately and mixed well. 50g of zinc oxide is added uniformly and mixed. Thereafter precipitated silica already dried, and lOg napthenic oil are added in succession. The sheet is mill rolled at temperature of 50 degree Celsius and 4mm thick sheet obtained is cooled to room temperaturee. Thereafter accelerators lOg of tetra methyl thiuram disulphide(TMTD) and lOg fo dibenzothiazyl disulphide are incorporated. The 4mm thick sheet obtained is matured on a flat bed.
When the product obtained by the above process is compression moulded at temperature of 150 degree Celsius and pressure of 75 kg /cm2 for 12 minutes, the product exhibits the following physical and mechanical properties.
1. Physical and mechanical properties
(a) Hardness - Shore A (ASTM-2240) = 75+/- 5%
(b) Specific gravity - (Wallace =1.25 +/- 0.05
specific gravity balance
method Cat. ref. X.13)
(c) Modulus at 200% Elong. = 8.65+7- 0.5 MPa
(ASTM-D 412)
(d) Tensile Strength (ASTM-D 412) = 10.80 +/- 0.5 MPa
(e) Elongation at break = 240 +/- 8%
(ASTM-D 412)
(f) Tear Strength (ASTM D-624, = 433 +/-10 N CM-I
Die 'C')
(g) Compression Seet (%) @ 70 =10.0 + /- 1.00%
degreee Celsius 22 hrs
(ASTM D-395 'B') (h) Water absorption (ASTMD-471) = 0.70%
24 hrs ion distilled water at
30+/- 30 deegree Celsius)
The dynamic mechanical properties of the material obtaineed by the process of the proposed invention are an under:-
Dynamic Mechanical Properties
(a) Using Dupont DMA 983 & DMA Time-temperature software version 4.0, the product obtained exhibits the following dynamic mechanical properties:-

Frequency Flexural Storage Modulus E' (Pa)Flexural loss Modulus E" (Pa)Tan

(Table Removed)
(b) Glass Transition' Temperature (Reference tan delta peak at l Hz) = -30°+_2° c
The cure characteristics of the product are observed as under:-
Cure Characteristics
(Monsanto Rheometer - R100 - ®3°C are 150°C)
scorch time 3.50 +/- 0.25 min
Scorch time ts23.5 +/- 0.25minMaximum torque (MH)85 +/- 5 Ib.in
Minimum torque (ML) 17 +/- 2 Ib.in
Cure time (tc2 90) 11.5 min
It is to be understood that the above description of the present invention is susceptible to considerable modifications, changes and adaptation by those skilled in the art. Such modifications are intended to be considered to be within the scope of the present invention which is set forth by the following claims:




WE CLAIM:
1. A process for preparation of a rubber based passive acoustic material
for the construction of baffles comprising the steps of :-
(i) conditioning as herein described the 10 part fillers, 70 parts
carbon black and 20 parts precipitated silica, characterised in that
is, (ii) incorporating the compounding materials to 100 parts styrene
butadiene rubber through mill mixing procedure, (iii) cooling and adding accelators followed by addition of 1 part
dibenzthiazyl disulphide and 1 part tetramethyl thiuram
disulphide in the sequential order. (iv) mill rolling to obtain sheets and maturing in on flat bed.
2. A process as claimed in claim 1 wherein the said anti-degradents
preferably used are 1,2 dihydro 2,2,4 trimethyl quinoline and N-(l-3
dimethyl butyl)-N' phenyl-p-phenylene diamine.
3. A process as claimed in claims 1 and 3 wherein said accelerators
preferably used are dibenzothiazyl disulphide and teteramethyl
thiuram disulphide.
4. A process as claimed in claims 1 and 3 wherein the said mill-rolling is
carried at 40 to 60°C.
5. A process as claimed in claim 4 wherein said milling rolling is carried
out preferably in the temperature range of 45 to 50°C.
6. A process as claimed in claim 1 wherein said precipitated silica filler is
rubber grade silica.
6. A process as claimed in claim 1 wherein said fillers, carbon black and
precipitated silica are conditioned separately by heating at a
temperature of 100-125°C for a period of 1 to 2 hours.
7. A process for the preparation of a rubber based acoustic material
substantially as herein described.

Documents:

56-del-1997-abstract.pdf

56-del-1997-claims.pdf

56-del-1997-correspondence-others.pdf

56-del-1997-correspondence-po.pdf

56-del-1997-description (complete).pdf

56-del-1997-form-1.pdf

56-del-1997-form-19.pdf

56-del-1997-form-2.pdf

56-del-1997-form-3.pdf

56-del-1997-gpa.pdf


Patent Number 230757
Indian Patent Application Number 56/DEL/1997
PG Journal Number 11/2009
Publication Date 13-Mar-2009
Grant Date 27-Feb-2009
Date of Filing 08-Jan-1997
Name of Patentee THE CHIEF CONTORLLER, RESEARCH AND DEVELOPMENT ORGANISATION
Applicant Address **TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN, DHQ P.O., NEW DELHI-110 011, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 VELAYUDHAN PILLAI BALAKRISHNA PILLAI **TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011.
2 JANARDHANAN PILLAI NARAYANA DAS **TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011.
PCT International Classification Number E04B 1/82
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA