Title of Invention	"A PROCESS FOR PREPARATION OF AN IMPROVED POLYMERIC COMPOSITE DIELECTRIC LAMINATE FOR MICROWAVE"
Abstract	According to this invention there is provided a process for preparation of an improved polymeric composite dielectric laminate for microwave comprising of following steps preparing polytetrafluoroethylene (PTFE) powder in a conventional manner in an amount of 74-95% by weight, blending of said poly tetrafluoroethylene powder in a clean mixture, mixing and blending of a glass powder in an amount of 5-25% by weight with the said blended poly tetrafluoroethylene powder, mixing and blending of molybdenum disulfide powder in an amount of 0.20 to 0.50% by weight with above mixture, compacting the said homogeneous blended powder to form composite laminate, treating the composite laminate in a sintering oven at 375°C for 2 to 4 hours and preparing composite laminate sheet through compaction at 300°C.

Title of Invention

"A PROCESS FOR PREPARATION OF AN IMPROVED POLYMERIC COMPOSITE DIELECTRIC LAMINATE FOR MICROWAVE"

Abstract

According to this invention there is provided a process for preparation of an improved polymeric composite dielectric laminate for microwave comprising of following steps preparing polytetrafluoroethylene (PTFE) powder in a conventional manner in an amount of 74-95% by weight, blending of said poly tetrafluoroethylene powder in a clean mixture, mixing and blending of a glass powder in an amount of 5-25% by weight with the said blended poly tetrafluoroethylene powder, mixing and blending of molybdenum disulfide powder in an amount of 0.20 to 0.50% by weight with above mixture, compacting the said homogeneous blended powder to form composite laminate, treating the composite laminate in a sintering oven at 375°C for 2 to 4 hours and preparing composite laminate sheet through compaction at 300°C.

Full Text	ABSTRACT OF THE INVENTION According to this invention there is provided a PTFE based polymeric composite dielectric laminate comprising HIFLON type PTFE, glass micro fiber and molybdenum disulfide and a process for preparation thereof. The proposed composite dielectric laminate surface has microwave applications and has low dielectric constant, low dissipation factor, high dielectric strength and high degree of isotropy. Further, the proposed dielectric laminate surface has good mechanical strength, better dimensional stability, low water absorption, higher surface resistivity and high resistance to thermal degradation. Moreover, it is non-toxic and non-flammable. The preparation of PTFE based polymeric composite dielectric laminate comprises of following steps: (i) preparation of HIFLON poly tetrafluoroethylene (PTFE) powder (ii) blending of poly tetrafluoroethylene (PTFE) powder in a clean mixture (iii) mixing and blending of glass powder with above poly tetrafluoroetylene powder (iv) mixing and blending of molybdenum disulfide powder with above mixture (v) compaction of homogenous composite laminate prepared in above manner (vi) treatment of above composite laminate in sintering oven (vii) preparation of composite laminate sheet. FIELD OF INVENTION This invention relates to an improved polymeric dielectric composite laminate for applications such as microwave and a process for preparation thereof. PRIOR ART A variety of polymeric composite materials are presently available for use as laminate for microwave electronic applications. Prevalent amongst these materials are composite systems based on fluoropolymers and specially polytclralluorocthylcne (PTFE). The microwave properties of PTFE are first realised in early 1950's. PTFE microwave laminates are made according to use/application. Addition of reinforcing materials into PTFE is intended to improve dimcnsonal stability, load-bearing capacity and to reduce the shrinkage, cold flow, wear properties etc. Glass and Ceramic reinforced PTFE laminates are most important for microwave applications. Laminates based on PTFE ceramic composite are designed for dimensional stability, low thermal expansion and low shrinkage. However, these PTFE ceramic composites, already known to the prior art, suffer from following disadvantages. Main disadvantage of such known PTFE ceramic composites is that these composites have high dielectric constant and as such they are suitable only for electronic and microwave circuit applications requiring high dielectric constant Another disadvantage of such known PTFE ceramic composites is that these composites have high dissipation factor. Another type of laminates Glass based microwave laminates are aimed for high reliability stripline and microstrip circuit applications. These glass based microwave laminates are again of basically three types. The first type of glass based composite laminate comprises of PTFE impregnated woven glass cloth. Such types of materials are known since early 1950's. Woven glass cloth reinforcement provides the dimensional stability of the laminate material. However, this also suffers from following disadvantages. Main disadvantage of such materials is that the dielectric constant of such materials varies according to thickness and PTFE constant. Another disadvantage of such materials is that these materials have poor flexibility and bending properties. Yet another disadvantage of such materials is that these materials have higher co¬efficient of thermal expansion in Z-axis as compared to the X-axis and Y-axis and as such these materials are unsuitable for many demanding microwave applications. The second type of glass based composite laminate comprises alternate layers of unreinforced PTFE and PTFE impregnated woven glass cot. This type of material offers low dielectric constant, low dissipation factor and better dimensional stability. However, because of presence of virgin PTFE layers, this laminate system suffers from poor foil adhesion and delimitation problems. The third type of composite laminate comprises homogeneous dielectric layer of random microfiber glass reinforced PTFE to make laminate with superior electrical performance. However, it also suffers from the disadvantage that it undergoes high dimensional change when subjected to processing. OBJECTS OF THE INVENTION Primary object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof for microwave applications. Another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which is poly tetrad uoroethylcnc (PTFE) based. Yet another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has low dielectric constant. Still another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has low dissipation factor. Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high dielectric strength. Yet further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high degree of isotropy. Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has good mechanical strength. Yet further object of the invention is to provide a polymeric composite dielectric laminate and a process for preparation thereof, which has good dimensional stability. Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for the preparation thereof, which has higher surface resistivity. Yet further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high volume resistivity. Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has low water absorption. Yet further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high resistance to thermal degradation. Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which is non- toxic and non-flammable. DESCRIPTION OF THE INVENTION According to the present invention there is provided a composite dielectric laminate substrate comprising: i) PTFE 74-95% by weight ii) Glass powder 5-25% by weight iii) Molybdenum disulfide .20-0.50% by weight PTFE used herein is generally Hiflon PTFE. Further, according to this invention there is provided a process for preparation of an improved polymeric composite dielectric laminate for microwave comprising of following steps: (i) preparing polytetrafluoroethylene (PTFE) powder, (ii) blending of polytetrafluoroethylene powder in a clean mixture,, mixing and blending of a glass powder with the said blended poly tetrafluoroethylene powder; (iii) mixing and blending of molybdenum disulfide powder with above mixture . (iv) compacting the said homogeneous blended powder to form composite laminate, (v) treating the composite laminate in a sintering oven and (vi) preparing of composite laminate sheet through compaction. PTFE powder The ultra fine while PTFE powder, 100% PTFE, is derived from grinding of HIFLON PTFE granular fibers. These granular libers lire made from suspension polymerisation of tclrnfluoroctliylcnc monomer. The specially-selected IIIFLON PTFE powder for this composite dielectric laminate substrate is 100% PTFE powder. IIIFLON PTFE powder has low dielectric constant, high breakdown voltage, high dielectric strength , high resistance to thermal degradation and wide working temperature from 200 °C to 260 °C. It is also non-toxic and non-llammablc. The characteristics of HIFLON PTFE powder is as below:- a) Particle Size b) Bulk Density c) Molding pressure d) Tensile strength e) Elongation at break f) Dielectric strength 20-100 micron 325 -525 gm/lit 250 kg/cm 2 350 kg/cm2 350% 88 kg/mm Glass powder The commercially available milled E-glass fiber (white powder) is used for the preparation of present dielectric laminate surface. Glass fibers are chemically inert and have little effect on electrical resistance of PTFE. a) Glass fiber length (Approx) : 1/32 inch b) Average fiber dia : 12-18 micron c) Bulk Density : 1100 ± 150 g/lit d) Density : 1.08g/cm3 Molybdenum disulfidc powder Molybdenum disulfide is a super fine dark gray powder having purity more than 98 %. Addition of small amount of molybdenum disulfide improves the hardness and stiffness of the laminate. It also reduces friction and imparts surface smoothness to the laminate substrate. a) Particle size : 0.65 - 0.75 um (Fisher) b) Bulk Density : 0.50 gm/cm3 According to present invention, preparation of HILFON PTFE based polymeric composite dielectric laminate substrate comprises of following steps. (i) Preparation of PTFE powder Ultra fine white PTFE is derived from grinding of 1III FLON PTFE granular fibers. These granular fibers are made from suspension polymerisation of tetrafluoroethylene monomer. (ii) Blending of PTFE powder Initially, HIFON PTFE powder is taken into a clean mixer and is blended at around 18 °C till all the lumps are broken. Blending is clone to avoid the lump formation in the powder. (Hi) Mixing of Glass Powder In the next step, glass powder is added into the blended H1FLON PTFE Powder. Blending and mixing are carried out at 18 °C till the colour of the mix becomes white and homogeneous. (iv) Mixing of Molybdenum disulfide powder Molybdenum disulfide (MoSi) powder is added into the glass PTFE mixture. Blending and mixing are carried out at around 18 °C till the resultant composite powder mixture is homogeneous and has gray colour. (v) Compaction of composite laminate Finally, the PTFE composite, prepared in above manner, is distributed evenly into a square shaped stainless steel mould and is compacted at a pressure about 8 Kg/cm under a hydraulic press to remove entrapped air inside the powder. Next, the pressure is raised to about 350 Kg/cm 2 (vi) Treatment of composite laminate substrate This compacted sheet is placed carefully into a programmable sintering oven. In the sintering oven, the temperature is raised up to 375 °C. Sintering is continued at this higher temperature (375 °C) for about 2 hours and is slowly cooled to room temperature. (vii) Preparation of composite laminate sheet The sintered sheet is again inserted in between two stainless steel (SS) plates of a hot hydraulic press and heated at temperature 300 °C. At this temperature, the composite sheet is compacted at a pressure 200 kg/cm2 and is decompressed slowly. The hot pressed sheet is cooled slowly to room temperature and taken out from the stainless steel plates. The edges of the laminate substrate sheet are trimmed by using a sharp knife. The process of the present invention will now be illustrated by specific working examples. It is to be understood that the working examples provided herein are by way of illustration and are not intended to be taken restrictively to imply any limitation on the scope of the invention. WORKING EXAMPLES EXAMPLE 1 About 74.73 gin of HIFLON PTFE powder is taken into a clean mixer and is blended at around 18°C. To this about 24.91 gm of glass powder is added and mixing is carried out at about l5 °C till the colour of the mixture becomes uniformly white. Next, about 0.36 m of molybdenum disulfide powder is added arid again blending is carried out at around 18 °C to produce a gray colour homogeneous mixture. The weight of the composite powder is 100 gm. The said composite mixture is distributed evenly into a square shaped stainless steel mould with a size of about 203 mm x 203 mm x 50 mm . The powder is compacted under hydraulic press at room temperature at a pressure of 8 kg/cm2 to remove the entrapped air and again at a final pressure of 300 kg/cm2 and is then decompressed. The compacted sheet is placed into a sintering oven. In the oven, the sheet is heated at around 375°C for about 2 hours and is slowly cooled to room temperature. Next, the sintered PTFE composite sheet is inserted in between two stainless steel plates of a hot hydraulic press each having the size of about 203 mm x 203 mm x 20 mm, and temperature is raised up to 300 °C. At 300 °C the composite substrate sheet is compressed at a pressure of 200 kg/cm2 and then the pressure is released. The compacted sheet is allowed to cool slowly to room temperature. After cooling, the sheet is removed from the SS plate and all the edges of laminate substrate sheet are trimmed by using a sharp knife to desired dimension (200 mm x 200 mm x 0.8 mm). The composite dielectric laminate substrate sheet is gray colour with smooth surface finish. Final weight of the sheet is 70 gm. EXAMPLE 2: 5231.10 gm (74.73% by wt) of HIFLON PTFF powder is taken into a clean mixture and is blended at 18 C. To this 1743.7 gm (24.91 % by wt) of glass powder is added and mixing is carried out at 18 °C till the colour of the mixture becomes uniformly white. To this mix, 25.20 gm (0.36% by wt) of molybdenum disulfide powder is added and again mixing is carried out at the same temperature (18 °C) to produce a gray colour homogeneous mixture. The weight of the composite powder is 7000 gm. PTFE composite mix is distributed evenly into a cylindrical mould (inner dia 150 mm) assembled with a central mandrel (dia 50 mm). The powder is compacted under hydraulic press at room temperature at a pressure of 8 kg/cm to remove the entrapped air and again at a final pressure of 350 kg/cm2. Next, it is decompressed slowly. The compacted PTFE bush is taken out from the mould carefully. The compacted PTFE bush is placed into a sintering oven and heated at a temperature is 375 °C for 4 hours and then it is cooled to room temperature and is taken out from the oven. The sintered PTFE based composite bush of size 147.5 mm (outer dia) x 49.2 mm (inner dia) x 206 mm (height) is skived in the form of continuous sheet of thickness 1.2 mm and width 206 mm using a special type of skiving lathe machine. Above skived sheet is cut into pieces of length 206 mm and width 206 mm and sintered once again at 375 °C for one hour and cooled to room temperature. Next, the re-sintered PTFE composite sheet piece is inserted in between two SS plates (each 203 mm length x 203 mm width x 20 mm height) of hot hydraulic press and temperature is raised to 300 °C. At 300 C the composite substrate sheet is compressed at a pressure of 200 kg/cm2 and then the pressure is released. The compacted sheet is then allowed to cool slowly to room temperature. After cooling, the sheet is removed from the SS plate and then all the edges of laminate substrate sheet are trimmed by using a sharp knife to desired dimensions (Length 200 mm x width 200 mm w x thickness 0.8 mm). The finally prepared composite dielectric laminate substrate sheet is of gray colour having smooth surface finish. The properties of the composite dielectric laminate sheet, prepared in the above manner, have been given below. S. No. Property Value 1. Dielectric constant 2.2-2.4 at 9.1 GHz 2. Surface resistivity > 5.0 x 10 n ohm 3. Volume resistivity 2.2 x 10 l2 ohm 4. Dielectric Strength 5. Melting Point 6. Thermal conductivity (Approx) 7. Coefficient of thermal expansion 8. Tensile Strength (Approx) 9. Elongation of break 10 I lardness 11 Specific gravity 12. Water absorption 445 kv/mm 327 °C 0.27 W/(mk) 146 ppm/k 200-240 Kg/cm 140-200% 63-65 Shore-D 2.2 0.02 % It is to be understood that the process of present invention is susceptible to adaptations, changes, modifications by those skilled in the art. Such adaptations, changes, modifications are intended to be within the scope of the present invention which is further set forth by the following claims: I CLAIM; 1. A process for preparation of an improved polymeric composite dielectric laminate for microwave comprising of following steps: (vii) preparing polytetrafluoroethylene (PTFE) powder in a conventional manner in an amount of 74-95% by weight, (viii) blending of said poly tetrafluoroethylene powder in a clean mixture, mixing and blending of a glass powder in an amount of 5-25% by weight with the said blended poly tetrafluoroethylene powder, (ix) mixing and blending of molybdenum disulfide powder in an amount of 0.20 to 0.50% by weight with above mixture, (x) compacting the said homogeneous blended powder to form composite laminate, (xi) treating the composite laminate in a sintering oven at 375°C for 2 to 4 hours and (xii) preparing composite laminate sheet through compaction at 300°C. 2. A process for preparation of dielectric laminate as claimed in claim 1 wherein the said mixing and blending of PTFE powder is carried out at 18°C. 3. A process as claimed in claim 1 wherein the said mixing and blending of glass powder in step (ii) is carried out at 18°C, 4. A process as claimed in claim 1 wherein said mixing and blending of molybdenum disulpide with mixture in step (ii) is carried out at 18°C. 5. A process as claimed in claim 1 wherein said compaction of homogeneous composite laminate is carried out at a pressure 350 Kg/cm2. 6. A process as claimed in claim 1 wherein the said treatment of composite laminate comprises sintering of compacted sheet at around 375°C in a sintering oven for about 2 hours and then cooling it to room temperature. 7. A process as claimed in claim 1 wherein the said preparation of laminate substrate sheet through compaction comprises heating of said treated sheet between steel plates of hydraulic press up to about 300°C, then compacting it at pressure around 200 Kg/cm2. 8. A process for the preparation of an improved polymeric composite dielectric laminate for microwave substantially as herein described and illustrated by examples herein.

Full Text

ABSTRACT OF THE INVENTION
According to this invention there is provided a PTFE based polymeric composite dielectric laminate comprising HIFLON type PTFE, glass micro fiber and molybdenum disulfide and a process for preparation thereof. The proposed composite dielectric laminate surface has microwave applications and has low dielectric constant, low dissipation factor, high dielectric strength and high degree of isotropy. Further, the proposed dielectric laminate surface has good mechanical strength, better dimensional stability, low water absorption, higher surface resistivity and high resistance to thermal degradation. Moreover, it is non-toxic and non-flammable. The preparation of PTFE based polymeric composite dielectric laminate comprises of following steps:
(i) preparation of HIFLON poly tetrafluoroethylene (PTFE) powder (ii) blending of poly tetrafluoroethylene (PTFE) powder in a clean mixture (iii) mixing and blending of glass powder with above poly tetrafluoroetylene
powder
(iv) mixing and blending of molybdenum disulfide powder with above mixture (v) compaction of homogenous composite laminate prepared in above manner (vi) treatment of above composite laminate in sintering oven (vii) preparation of composite laminate sheet.

FIELD OF INVENTION
This invention relates to an improved polymeric dielectric composite laminate for applications such as microwave and a process for preparation thereof.
PRIOR ART
A variety of polymeric composite materials are presently available for use as laminate for microwave electronic applications. Prevalent amongst these materials are composite systems based on fluoropolymers and specially polytclralluorocthylcne (PTFE). The microwave properties of PTFE are first realised in early 1950's. PTFE microwave laminates are made according to use/application. Addition of reinforcing materials into PTFE is intended to improve dimcnsonal stability, load-bearing capacity and to reduce the shrinkage, cold flow, wear properties etc. Glass and Ceramic reinforced PTFE laminates are most important for microwave applications.
Laminates based on PTFE ceramic composite are designed for dimensional stability, low thermal expansion and low shrinkage. However, these PTFE ceramic composites, already known to the prior art, suffer from following disadvantages.
Main disadvantage of such known PTFE ceramic composites is that these composites have high dielectric constant and as such they are suitable only for electronic and microwave circuit applications requiring high dielectric constant
Another disadvantage of such known PTFE ceramic composites is that these composites have high dissipation factor.
Another type of laminates Glass based microwave laminates are aimed for high reliability stripline and microstrip circuit applications. These glass based microwave laminates are again of basically three types.
The first type of glass based composite laminate comprises of PTFE impregnated woven glass cloth. Such types of materials are known since early 1950's. Woven glass cloth reinforcement provides the dimensional stability of the laminate material. However, this also suffers from following disadvantages.
Main disadvantage of such materials is that the dielectric constant of such materials varies according to thickness and PTFE constant.
Another disadvantage of such materials is that these materials have poor flexibility and bending properties.
Yet another disadvantage of such materials is that these materials have higher co¬efficient of thermal expansion in Z-axis as compared to the X-axis and Y-axis and as such these materials are unsuitable for many demanding microwave applications.

The second type of glass based composite laminate comprises alternate layers of unreinforced PTFE and PTFE impregnated woven glass cot. This type of material offers low dielectric constant, low dissipation factor and better dimensional stability. However, because of presence of virgin PTFE layers, this laminate system suffers from poor foil adhesion and delimitation problems.
The third type of composite laminate comprises homogeneous dielectric layer of random microfiber glass reinforced PTFE to make laminate with superior electrical performance. However, it also suffers from the disadvantage that it undergoes high dimensional change when subjected to processing.
OBJECTS OF THE INVENTION
Primary object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof for microwave applications.
Another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which is poly tetrad uoroethylcnc (PTFE) based.
Yet another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has low dielectric constant.
Still another object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has low dissipation factor.
Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high dielectric strength.
Yet further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has high degree of isotropy.
Still further object of the invention is to provide an improved polymeric composite dielectric laminate and a process for preparation thereof, which has good mechanical strength.
Yet further object of the invention is to provide a polymeric composite dielectric laminate and a process for preparation thereof, which has good dimensional stability.

Still further object of the invention is to provide an improved polymeric
composite dielectric laminate and a process for the preparation thereof, which has
higher surface resistivity.
Yet further object of the invention is to provide an improved polymeric
composite dielectric laminate and a process for preparation thereof, which has high
volume resistivity.
Still further object of the invention is to provide an improved polymeric
composite dielectric laminate and a process for preparation thereof, which has
low water absorption.
Yet further object of the invention is to provide an improved polymeric
composite dielectric laminate and a process for preparation thereof, which has
high resistance to thermal degradation.
Still further object of the invention is to provide an improved polymeric
composite dielectric laminate and a process for preparation thereof, which is non-
toxic and non-flammable.
DESCRIPTION OF THE INVENTION
According to the present invention there is provided a composite dielectric laminate substrate comprising:

i) PTFE 74-95% by weight
ii) Glass powder 5-25% by weight
iii) Molybdenum disulfide .20-0.50% by weight
PTFE used herein is generally Hiflon PTFE.
Further, according to this invention there is provided a process for preparation of an improved polymeric composite dielectric laminate for microwave comprising of following steps:
(i) preparing polytetrafluoroethylene (PTFE) powder,
(ii) blending of polytetrafluoroethylene powder in a clean mixture,, mixing and blending of a glass powder with the said blended poly tetrafluoroethylene powder;
(iii) mixing and blending of molybdenum disulfide powder with above mixture .
(iv) compacting the said homogeneous blended powder to form composite laminate,
(v) treating the composite laminate in a sintering oven and
(vi) preparing of composite laminate sheet through compaction.

PTFE powder
The ultra fine while PTFE powder, 100% PTFE, is derived from grinding of HIFLON PTFE granular fibers. These granular libers lire made from suspension polymerisation of tclrnfluoroctliylcnc monomer. The specially-selected IIIFLON PTFE powder for this composite dielectric laminate substrate is 100% PTFE powder. IIIFLON PTFE powder has low dielectric constant, high breakdown voltage, high dielectric strength , high resistance to thermal degradation and wide working temperature from 200 °C to 260 °C. It is also non-toxic and non-llammablc. The characteristics of HIFLON PTFE powder is as below:-

a) Particle Size
b) Bulk Density
c) Molding pressure
d) Tensile strength
e) Elongation at break
f) Dielectric strength

20-100 micron 325 -525 gm/lit 250 kg/cm 2 350 kg/cm2 350% 88 kg/mm

Glass powder
The commercially available milled E-glass fiber (white powder) is used for the
preparation of present dielectric laminate surface. Glass fibers are chemically inert and
have little effect on electrical resistance of PTFE.
a) Glass fiber length (Approx) : 1/32 inch
b) Average fiber dia : 12-18 micron
c) Bulk Density : 1100 ± 150 g/lit
d) Density : 1.08g/cm3

Molybdenum disulfidc powder
Molybdenum disulfide is a super fine dark gray powder having purity more than 98 %. Addition of small amount of molybdenum disulfide improves the hardness and stiffness of the laminate. It also reduces friction and imparts surface smoothness to the laminate substrate.
a) Particle size : 0.65 - 0.75 um (Fisher)
b) Bulk Density : 0.50 gm/cm3
According to present invention, preparation of HILFON PTFE based polymeric composite dielectric laminate substrate comprises of following steps.
(i) Preparation of PTFE powder
Ultra fine white PTFE is derived from grinding of 1III FLON PTFE granular fibers. These granular fibers are made from suspension polymerisation of tetrafluoroethylene monomer.
(ii) Blending of PTFE powder
Initially, HIFON PTFE powder is taken into a clean mixer and is blended at around 18 °C till all the lumps are broken. Blending is clone to avoid the lump formation in the powder.
(Hi) Mixing of Glass Powder
In the next step, glass powder is added into the blended H1FLON PTFE Powder. Blending and mixing are carried out at 18 °C till the colour of the mix becomes white and homogeneous.
(iv) Mixing of Molybdenum disulfide powder
Molybdenum disulfide (MoSi) powder is added into the glass PTFE mixture. Blending and mixing are carried out at around 18 °C till the resultant composite powder mixture is homogeneous and has gray colour.
(v) Compaction of composite laminate
Finally, the PTFE composite, prepared in above manner, is distributed evenly into a square shaped stainless steel mould and is compacted at a pressure about 8 Kg/cm

under a hydraulic press to remove entrapped air inside the powder. Next, the pressure is raised to about 350 Kg/cm 2
(vi) Treatment of composite laminate substrate
This compacted sheet is placed carefully into a programmable sintering oven. In the sintering oven, the temperature is raised up to 375 °C. Sintering is continued at this higher temperature (375 °C) for about 2 hours and is slowly cooled to room temperature.
(vii) Preparation of composite laminate sheet
The sintered sheet is again inserted in between two stainless steel (SS) plates of a hot hydraulic press and heated at temperature 300 °C. At this temperature, the composite sheet is compacted at a pressure 200 kg/cm2 and is decompressed slowly. The hot pressed sheet is cooled slowly to room temperature and taken out from the stainless steel plates. The edges of the laminate substrate sheet are trimmed by using a sharp knife.
The process of the present invention will now be illustrated by specific working examples. It is to be understood that the working examples provided herein are by way of illustration and are not intended to be taken restrictively to imply any limitation on the scope of the invention.
WORKING EXAMPLES
EXAMPLE 1
About 74.73 gin of HIFLON PTFE powder is taken into a clean mixer and is blended at around 18°C. To this about 24.91 gm of glass powder is added and mixing is carried out at about l5 °C till the colour of the mixture becomes uniformly white. Next, about 0.36 m of molybdenum disulfide powder is added arid again blending is carried out at around 18 °C to produce a gray colour homogeneous mixture. The weight of the composite powder is 100 gm. The said composite mixture is distributed evenly into a square shaped stainless steel mould with a size of about 203 mm x 203 mm x 50 mm . The powder is compacted under hydraulic press at room temperature at a pressure of 8 kg/cm2 to remove the entrapped air and again at a final pressure of 300 kg/cm2 and is then decompressed. The compacted sheet is placed into a sintering oven. In the oven, the sheet is heated at around 375°C for about 2 hours and is slowly cooled to room temperature.
Next, the sintered PTFE composite sheet is inserted in between two stainless steel plates of a hot hydraulic press each having the size of about 203 mm x 203 mm x 20 mm, and temperature is raised up to 300 °C. At 300 °C the composite substrate sheet is compressed at a pressure of 200 kg/cm2 and then the pressure is released. The compacted sheet is allowed to cool slowly to room temperature. After cooling, the sheet is removed
from the SS plate and all the edges of laminate substrate sheet are trimmed by using a sharp knife to desired dimension (200 mm x 200 mm x 0.8 mm). The composite dielectric laminate substrate sheet is gray colour with smooth surface finish. Final weight of the sheet is 70 gm.
EXAMPLE 2:
5231.10 gm (74.73% by wt) of HIFLON PTFF powder is taken into a clean mixture and is blended at 18 C. To this 1743.7 gm (24.91 % by wt) of glass powder is added and mixing is carried out at 18 °C till the colour of the mixture becomes uniformly white. To this mix, 25.20 gm (0.36% by wt) of molybdenum disulfide powder is added and again mixing is carried out at the same temperature (18 °C) to produce a gray colour homogeneous mixture. The weight of the composite powder is 7000 gm.
PTFE composite mix is distributed evenly into a cylindrical mould (inner dia 150 mm) assembled with a central mandrel (dia 50 mm). The powder is compacted under hydraulic press at room temperature at a pressure of 8 kg/cm to remove the entrapped air and again at a final pressure of 350 kg/cm2. Next, it is decompressed slowly. The compacted PTFE bush is taken out from the mould carefully.
The compacted PTFE bush is placed into a sintering oven and heated at a temperature is 375 °C for 4 hours and then it is cooled to room temperature and is taken out from the oven. The sintered PTFE based composite bush of size 147.5 mm (outer dia) x 49.2 mm (inner dia) x 206 mm (height) is skived in the form of continuous sheet of thickness 1.2 mm and width 206 mm using a special type of skiving lathe machine. Above skived sheet is cut into pieces of length 206 mm and width 206 mm and sintered once again at 375 °C for one hour and cooled to room temperature.
Next, the re-sintered PTFE composite sheet piece is inserted in between two SS plates (each 203 mm length x 203 mm width x 20 mm height) of hot hydraulic press and temperature is raised to 300 °C. At 300 C the composite substrate sheet is compressed at a pressure of 200 kg/cm2 and then the pressure is released. The compacted sheet is then allowed to cool slowly to room temperature. After cooling, the sheet is removed from the SS plate and then all the edges of laminate substrate sheet are trimmed by using a sharp knife to desired dimensions (Length 200 mm x width 200 mm w x thickness 0.8 mm). The finally prepared composite dielectric laminate substrate sheet is of gray colour having smooth surface finish.
The properties of the composite dielectric laminate sheet, prepared in the above manner, have been given below.
S. No. Property Value
1. Dielectric constant 2.2-2.4 at 9.1 GHz
2. Surface resistivity > 5.0 x 10 n ohm
3. Volume resistivity 2.2 x 10 l2 ohm

4. Dielectric Strength
5. Melting Point
6. Thermal conductivity (Approx)
7. Coefficient of thermal expansion
8. Tensile Strength (Approx)
9. Elongation of break
10 I lardness
11 Specific gravity
12. Water absorption

445 kv/mm 327 °C 0.27 W/(mk) 146 ppm/k 200-240 Kg/cm 140-200% 63-65 Shore-D 2.2 0.02 %

It is to be understood that the process of present invention is susceptible to adaptations, changes, modifications by those skilled in the art. Such adaptations, changes, modifications are intended to be within the scope of the present invention which is further set forth by the following claims:

I CLAIM;
1. A process for preparation of an improved polymeric composite
dielectric laminate for microwave comprising of following steps:
(vii) preparing polytetrafluoroethylene (PTFE) powder in a
conventional manner in an amount of 74-95% by weight, (viii) blending of said poly tetrafluoroethylene powder in a clean
mixture, mixing and blending of a glass powder in an
amount of 5-25% by weight with the said blended poly
tetrafluoroethylene powder, (ix) mixing and blending of molybdenum disulfide powder in an
amount of 0.20 to 0.50% by weight with above mixture, (x) compacting the said homogeneous blended powder to form
composite laminate, (xi) treating the composite laminate in a sintering oven at 375°C
for 2 to 4 hours and (xii) preparing composite laminate sheet through compaction at
300°C.
2. A process for preparation of dielectric laminate as claimed in claim
1 wherein the said mixing and blending of PTFE powder is carried
out at 18°C.
3. A process as claimed in claim 1 wherein the said mixing and
blending of glass powder in step (ii) is carried out at 18°C,

4. A process as claimed in claim 1 wherein said mixing and blending
of molybdenum disulpide with mixture in step (ii) is carried out at
18°C.
5. A process as claimed in claim 1 wherein said compaction of
homogeneous composite laminate is carried out at a pressure 350
Kg/cm2.
6. A process as claimed in claim 1 wherein the said treatment of
composite laminate comprises sintering of compacted sheet at
around 375°C in a sintering oven for about 2 hours and then
cooling it to room temperature.
7. A process as claimed in claim 1 wherein the said preparation of
laminate substrate sheet through compaction comprises heating of
said treated sheet between steel plates of hydraulic press up to
about 300°C, then compacting it at pressure around 200 Kg/cm2.
8. A process for the preparation of an improved polymeric composite
dielectric laminate for microwave substantially as herein described
and illustrated by examples herein.

Documents:

894-del-2000-abstract.pdf

894-del-2000-claims.pdf

894-del-2000-correspondence-others.pdf

894-del-2000-correspondence-po.pdf

894-del-2000-description (complete).pdf

894-del-2000-form-1.pdf

894-del-2000-form-19.pdf

894-del-2000-form-2.pdf

894-del-2000-form-3.pdf

894-del-2000-gpa.pdf

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Patent Number

217900

Indian Patent Application Number

894/DEL/2000

PG Journal Number

17/2008

Publication Date

25-Apr-2008

Grant Date

29-Mar-2008

Date of Filing

06-Oct-2000

Name of Patentee

THE ADDITIONAL DIRECTOR (IPR)

Applicant Address

DEFENCE RESEARCH & DEVELOPMENT ORGANISATION MINISTRY OF DEFENCE, GOVERNMENT OF INDIA,B-341 SENA BHAWAN,DHQ P.O NEW DELHI -110011

Inventors:

#	Inventor's Name	Inventor's Address
1	BHARGAVA CHAITANYA MEHTA	HINUSTAN FLUOROCARBONS LTD 1402,BABUKHAN ESTATE, BASHEERBAGH HAYDERABAD-500 001 INDIA
2	PARTHA SARATHI DAS	HINUSTAN FLUOROCARBONS LTD 1402,BABUKHAN ESTATE, BASHEERBAGH HAYDERABAD-500 001 INDIA

PCT International Classification Number

B32B 27/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA