CA1289313C - Dielectric film of a copolymer of vinylidene fluoride and tetrafluoroethylene - Google Patents
Dielectric film of a copolymer of vinylidene fluoride and tetrafluoroethyleneInfo
- Publication number
- CA1289313C CA1289313C CA000539177A CA539177A CA1289313C CA 1289313 C CA1289313 C CA 1289313C CA 000539177 A CA000539177 A CA 000539177A CA 539177 A CA539177 A CA 539177A CA 1289313 C CA1289313 C CA 1289313C
- Authority
- CA
- Canada
- Prior art keywords
- film
- copolymer
- dielectric
- weight
- tetrafluoroethylene
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
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- Manufacture Of Macromolecular Shaped Articles (AREA)
- Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
Abstract
Abstract of the Disclosure A dielectric film of a molecularly oriented copolymer of vinylidene fluoride and tetrafluoroethylene, a process of preparing such film and a capacitor produced from such film are disclosed herein.
Description
~ 2~3~3~3 "A Dielectric Film of a Copolymer of Vinylidene Fluoride and Tetrafluoroethylene 5This invention relates to a film of a copolymer of vinyl-idene fluoride and tetrafluoroethylene which demonstrates a high dielectric constant and good dielectric strength. More particularly, it relates to a molecularly oriented film of a copolymer of at least about 85 weight % of vinylidene fluoride and at least about 3 weight % of tetrafluoroethylene. In addition, this invention relates to the process of preparing such dielectric and capacitors utilizing it.
i ~;~ t 39~ ~1. 3 STATEMENT OF THE INVENTION
This invention is a dielectric comprising a molecularly oriented film of a copolymer of at least about 85 weight %
of vinylidene fluoride and at least abou~ 3 weight % of tetra-fluoroethylene based on the weight of said copolymer, saidfilm having a dielectric constant at 100 Hz of at least 10 and a dielectric strength of at least about 400 volts per micron (~m) of film thickness.
The process for preparing the dielectric comprises forming a nonfibrous sheet of a copolymer of at least about 85 weight % of vinylidene fluoride and at least about 3 weight % of tetrafluoroethylene based on the weight of the copolymer, molecularly orienting said sheet by elongating it in at least one direction relative to a major dimension thereof to thereby produce a film having a thickness of no greater than about 75 microns and a dielectric constant at 100 Hz of at least 10.
Detailed Description of Invention The dielectric of this invention is a molecularly oriented copolymer film of vinylidene fluoride and tetra-fluoroethylene. The weight range of vinylidene fluoride in the copolymer is from about 85 to 97 % while the range of tetrafluoroethylene in the copolymer is from about 3 to 15%.
It is preferable, from the standpoint of improved dielectric properties that the vinylidene fluoride content of the copolymer be from abou~ 88 to 94 % while the tetrafluoro-`' .
^3 ethylene content should be about 12 to 6 %. While it ispreferred that the copolymer consist of only vinylidene fluoride and tetrafluoroethylene monomers, small proportions of other copolymerizable monomers, preferably fluorine-containing ethylenically unsaturated monomers, may beincluded.
The copolymers are formed by any convenient polymeriza-tion procedure including emulsion, suspension and solvent polymerization techniques. Emulsion and suspension poly-mersion procedures are preferred. The procedure detailedin U.S. Patent No. 4,360,652 is most preferred.
The copolymer film is prepared by first fabricating preformed sheets by solvent casting, melt extrusion, injection molding, pressing or calendaring. Such techniques are well known and need not be specifically described here.
The preformed sheets are of any thickness which will permit molecular orientation of the sheets by elongation in at least one major dimension into films of the desired thick-ness. Typically,the preform sheets have thicknesses ranging between about 45 and 200 microns.
In accordance with the process of this invention, the sheets are molecularly oriented, for example, by stretching, rolling or blowing, to provide film of improved dielectric properties. The techniques of molecular orientation of polymer film are well known and need not be specifically discussed here. An example of the stretch orientation of .
.3 .
polyvinylidene fluoride film may be found, for example, in U.S. Patent No. 3,197,538. The teaching of this patent may be extended to the copolymer films of this invention. The fabricated copolymer sheets are oriented uniaxially or biaxially to provide the desired improvement in dielectric properties. The orientation ratio will range from about 2:1 to about lO:l for both uniaxial orientation and biaxial orientation but the preferred orientation range is from about 4:1 to about 5:1 whether orientation is in one direc-tion or both. That i5, for example, if biaxial orientationis accomplished by stretching, the film is preferably stretched from 4 to 5 times in the machine direction and then from 4 to S times in the transverse direction.
After orientation, the film will have a thickness range extending up to about 75 microns but preferably no greater than about 13-15 microns.
.
E.YAMPLE
A copolymer resin for this invention is typically made as follows:
A horizontal stainless steel autoclave equipped with a stirrer is charged with water and the ammonium salt of a perfluorooctanoate as an emulsifier. Vinylidene fluoride monomer and tetrafluoroethylene monomer in the required molar proportions are added to the pressurized autoclave after purging with nitrogen. The reactor is Xeated to the "
:: ' , 1.3 reaction temperature and the reactants are agitated. A chain transfer agent may be added at any appropriate stage of the reaction. Monomers, in the required molar proportions are continuously fed into the reactor along with an initiator and chain transfer agent, if desired. Each monomer's pressure is maintained constant throughout the reaction. Upon completion of the reaction (effective initiator depletion), the reactor contents are cooled and the latex product drained from the reactor. The latex is concentrated and the copolymer resin recovered for use in the fabrication of a resinous sheet.
The resin is formed into a sheet by extrusion and the sheet subjected to molecular orientation by stretching to provide a continuous film of a thickness of about 12 microns.
One fabricated sheet of a copolymer of 90 weight % vinylidene fluoride and 10 weight % tetrafluoroethylene is unixally oriented at a ratio of about 3.8 to 1 to form the 12 micron thick film and another fabricated sheet of the same monomer content having a greater initial thickness is biaxially oriented at a machine direction stretch ratio of about 3.5 to 1 and then at a transverse stretch ratio of about 3.9 to 1 to also form a 12 micron thick film. The temperature at which the films were stretched was 100C for machine direc-tion stretch and 140C for transverse direction stretch.
The films were tested for dielectric properties and the results are reported in the following table.
.3 ,_ _ EE E
~~ ~L
.C ~ ~ --~ O~ o h N
g C
_~
_ _l ~ ~n O o o o o o r~
E-l ~ ~ O O O O O O ?-O E a~
1~ ~ _1 .
tJ 51 . 3 u ~ r~ ~ ~ ` ~ ~ u~ CJ~
~ _~ O O O O ~ ~ U
_1 ~ ~
u C E
~D O o o~ ~ o E c o U
C~
E u ~ ~ U r~
`~ X C C ~ X C ~ C _I
O ~ O rl rl 1~ ~rl CJ U~
C ~ Cl 5 ~ ~
:~ o ~ o 5 5 o ~ o ~ C E
rl O O
I ~ o ~ Ll ~ ~ ~ Gl E E ~ ~ ~ ~ C
~ ~ U
_I ~ E E E
~ o O :~ ~ P' O o o o o o O E E ~ Co4 Co4 ,1 :q ~
~ I ~C~ ~ ~ u'~ ~D
- .
' . .
.
The data of the above table show that the vinylidene fluoride-tetrafluoroethylene copolymer film of this invention is unexpectedly more amenable than the film of vinylidene fluoride homopolymer to the process conditions of molecular orientation whereby the dielectric constant is improved when the film is subjected to conditions developed in heat stretch orientation.
Further, the dielectric fllm of this invention when compared to the homopolymer fllm has less loss of dlelectric constant in thermocycling of the film as would ordlnarily occur when used in capacitor applicatlons.
Still further, the fllm-of thls lnvention has less elevatlon in dielectrlc loss with increase in temperature than the homopolymer film.
Whlle both the homopolymer and the copolymer film both retain physical stability when heat annealed, the copolymer has better dielectrlc constant stabllity.
The copolymer film of this invention may be heat annealed to provlde dlmenslonal stability at elevated tem-peratures. For example, the fllm may be annealed by holdlngit under tenslon on all sldes whlle subjecting it to a temperature of from about 120 to 175C and then allowlng the fllm to cool whlle malntaining it under tenslon.
For use in a capacitor, the film is typically coated, for example by vapor deposltlon, wlth an electroconductive coating, for example, silver, copper, aluminum, chromium, zinc, tin, nickel or other conductive material. Other methods of applying the coating are, for example, electro-plating, spray painting, sputtering, laminating and the like.
Electrode foils and dielectric film may also be wound to S form the capacitor. Method and materials for the manufactu,re of capacitors are well known and can be used with the film of this invention without specific instructions to those skilled in this art. The coated film, having conductive leads extending from the electroconductive coating or layer m~y be rolled into a capacitor.
i ~;~ t 39~ ~1. 3 STATEMENT OF THE INVENTION
This invention is a dielectric comprising a molecularly oriented film of a copolymer of at least about 85 weight %
of vinylidene fluoride and at least abou~ 3 weight % of tetra-fluoroethylene based on the weight of said copolymer, saidfilm having a dielectric constant at 100 Hz of at least 10 and a dielectric strength of at least about 400 volts per micron (~m) of film thickness.
The process for preparing the dielectric comprises forming a nonfibrous sheet of a copolymer of at least about 85 weight % of vinylidene fluoride and at least about 3 weight % of tetrafluoroethylene based on the weight of the copolymer, molecularly orienting said sheet by elongating it in at least one direction relative to a major dimension thereof to thereby produce a film having a thickness of no greater than about 75 microns and a dielectric constant at 100 Hz of at least 10.
Detailed Description of Invention The dielectric of this invention is a molecularly oriented copolymer film of vinylidene fluoride and tetra-fluoroethylene. The weight range of vinylidene fluoride in the copolymer is from about 85 to 97 % while the range of tetrafluoroethylene in the copolymer is from about 3 to 15%.
It is preferable, from the standpoint of improved dielectric properties that the vinylidene fluoride content of the copolymer be from abou~ 88 to 94 % while the tetrafluoro-`' .
^3 ethylene content should be about 12 to 6 %. While it ispreferred that the copolymer consist of only vinylidene fluoride and tetrafluoroethylene monomers, small proportions of other copolymerizable monomers, preferably fluorine-containing ethylenically unsaturated monomers, may beincluded.
The copolymers are formed by any convenient polymeriza-tion procedure including emulsion, suspension and solvent polymerization techniques. Emulsion and suspension poly-mersion procedures are preferred. The procedure detailedin U.S. Patent No. 4,360,652 is most preferred.
The copolymer film is prepared by first fabricating preformed sheets by solvent casting, melt extrusion, injection molding, pressing or calendaring. Such techniques are well known and need not be specifically described here.
The preformed sheets are of any thickness which will permit molecular orientation of the sheets by elongation in at least one major dimension into films of the desired thick-ness. Typically,the preform sheets have thicknesses ranging between about 45 and 200 microns.
In accordance with the process of this invention, the sheets are molecularly oriented, for example, by stretching, rolling or blowing, to provide film of improved dielectric properties. The techniques of molecular orientation of polymer film are well known and need not be specifically discussed here. An example of the stretch orientation of .
.3 .
polyvinylidene fluoride film may be found, for example, in U.S. Patent No. 3,197,538. The teaching of this patent may be extended to the copolymer films of this invention. The fabricated copolymer sheets are oriented uniaxially or biaxially to provide the desired improvement in dielectric properties. The orientation ratio will range from about 2:1 to about lO:l for both uniaxial orientation and biaxial orientation but the preferred orientation range is from about 4:1 to about 5:1 whether orientation is in one direc-tion or both. That i5, for example, if biaxial orientationis accomplished by stretching, the film is preferably stretched from 4 to 5 times in the machine direction and then from 4 to S times in the transverse direction.
After orientation, the film will have a thickness range extending up to about 75 microns but preferably no greater than about 13-15 microns.
.
E.YAMPLE
A copolymer resin for this invention is typically made as follows:
A horizontal stainless steel autoclave equipped with a stirrer is charged with water and the ammonium salt of a perfluorooctanoate as an emulsifier. Vinylidene fluoride monomer and tetrafluoroethylene monomer in the required molar proportions are added to the pressurized autoclave after purging with nitrogen. The reactor is Xeated to the "
:: ' , 1.3 reaction temperature and the reactants are agitated. A chain transfer agent may be added at any appropriate stage of the reaction. Monomers, in the required molar proportions are continuously fed into the reactor along with an initiator and chain transfer agent, if desired. Each monomer's pressure is maintained constant throughout the reaction. Upon completion of the reaction (effective initiator depletion), the reactor contents are cooled and the latex product drained from the reactor. The latex is concentrated and the copolymer resin recovered for use in the fabrication of a resinous sheet.
The resin is formed into a sheet by extrusion and the sheet subjected to molecular orientation by stretching to provide a continuous film of a thickness of about 12 microns.
One fabricated sheet of a copolymer of 90 weight % vinylidene fluoride and 10 weight % tetrafluoroethylene is unixally oriented at a ratio of about 3.8 to 1 to form the 12 micron thick film and another fabricated sheet of the same monomer content having a greater initial thickness is biaxially oriented at a machine direction stretch ratio of about 3.5 to 1 and then at a transverse stretch ratio of about 3.9 to 1 to also form a 12 micron thick film. The temperature at which the films were stretched was 100C for machine direc-tion stretch and 140C for transverse direction stretch.
The films were tested for dielectric properties and the results are reported in the following table.
.3 ,_ _ EE E
~~ ~L
.C ~ ~ --~ O~ o h N
g C
_~
_ _l ~ ~n O o o o o o r~
E-l ~ ~ O O O O O O ?-O E a~
1~ ~ _1 .
tJ 51 . 3 u ~ r~ ~ ~ ` ~ ~ u~ CJ~
~ _~ O O O O ~ ~ U
_1 ~ ~
u C E
~D O o o~ ~ o E c o U
C~
E u ~ ~ U r~
`~ X C C ~ X C ~ C _I
O ~ O rl rl 1~ ~rl CJ U~
C ~ Cl 5 ~ ~
:~ o ~ o 5 5 o ~ o ~ C E
rl O O
I ~ o ~ Ll ~ ~ ~ Gl E E ~ ~ ~ ~ C
~ ~ U
_I ~ E E E
~ o O :~ ~ P' O o o o o o O E E ~ Co4 Co4 ,1 :q ~
~ I ~C~ ~ ~ u'~ ~D
- .
' . .
.
The data of the above table show that the vinylidene fluoride-tetrafluoroethylene copolymer film of this invention is unexpectedly more amenable than the film of vinylidene fluoride homopolymer to the process conditions of molecular orientation whereby the dielectric constant is improved when the film is subjected to conditions developed in heat stretch orientation.
Further, the dielectric fllm of this invention when compared to the homopolymer fllm has less loss of dlelectric constant in thermocycling of the film as would ordlnarily occur when used in capacitor applicatlons.
Still further, the fllm-of thls lnvention has less elevatlon in dielectrlc loss with increase in temperature than the homopolymer film.
Whlle both the homopolymer and the copolymer film both retain physical stability when heat annealed, the copolymer has better dielectrlc constant stabllity.
The copolymer film of this invention may be heat annealed to provlde dlmenslonal stability at elevated tem-peratures. For example, the fllm may be annealed by holdlngit under tenslon on all sldes whlle subjecting it to a temperature of from about 120 to 175C and then allowlng the fllm to cool whlle malntaining it under tenslon.
For use in a capacitor, the film is typically coated, for example by vapor deposltlon, wlth an electroconductive coating, for example, silver, copper, aluminum, chromium, zinc, tin, nickel or other conductive material. Other methods of applying the coating are, for example, electro-plating, spray painting, sputtering, laminating and the like.
Electrode foils and dielectric film may also be wound to S form the capacitor. Method and materials for the manufactu,re of capacitors are well known and can be used with the film of this invention without specific instructions to those skilled in this art. The coated film, having conductive leads extending from the electroconductive coating or layer m~y be rolled into a capacitor.
Claims (11)
1. A dielectric comprising a molecularly oriented film of a copolymer comprising at least about 85% by weight of vinylidene fluoride and at least about 3% by weight of tetrafluoroethylene, said film having a dielectric constant of at least 10 at 100 Hz and at room temperature and a dielectric strength of at least about 400 volts per micron of film thickness.
2. The dielectric of Claim 1 wherein the copolymer is from about 88 to 94 weight % of vinylidene fluoride and from about 6 to 12 weight % of tetrafluoroethylene.
3. The dielectric of Claim 1 wherein the film has a thickness of no greater than about 15 microns.
4. A process for preparing a dielectric which comprises forming a nonfibrous sheet of a copolymer comprising at least about 85% by weight of vinylidene fluoride and at least about 3 % by weight of tetrafluoroethylene, molecularly orienting said sheet by elongating it in at least one direction relative to a major dimension thereof to thereby produce a film having a thickness of no greater than about 75 microns, a dielectric constant of at least 10 at 100 Hz and at room temperature and a dielectric strength of at least 400 volts per micron of film thickness.
5. The process of Claim 4 wherein the copolymer is from about 88 to 94 % by weight of vinylidene fluoride and about
6 to 12 % by weight of tetrafluoroethylene.
6. The process of Claim 4 wherein the molecular orientation of the film in at least one direction is at an elongation ratio ranging from about 4 to about 5.
6. The process of Claim 4 wherein the molecular orientation of the film in at least one direction is at an elongation ratio ranging from about 4 to about 5.
7. The process of Claim 6 wherein the molecular orientation is uniaxial orientation by heat stretching.
8. The process of Claim 6 wherein the molecular orientation is biaxial orientation by heat stretching.
9. The process of Claim 4 wherein the film is heat annealed after orientation.
10. A capacitor comprising the dielectric of Claim 1.
11. The capacitor of Claim 10 and an electroconductive coating or foil.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87393686A | 1986-06-13 | 1986-06-13 | |
| US873,936 | 1986-06-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1289313C true CA1289313C (en) | 1991-09-24 |
Family
ID=25362640
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000539177A Expired - Lifetime CA1289313C (en) | 1986-06-13 | 1987-06-09 | Dielectric film of a copolymer of vinylidene fluoride and tetrafluoroethylene |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS6366234A (en) |
| CA (1) | CA1289313C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11479647B2 (en) * | 2016-09-28 | 2022-10-25 | Daikin Industries. Ltd. | Film including a fluoropolymer |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1282540C (en) * | 2002-05-27 | 2006-11-01 | 株式会社德山 | Process for producing photochromic layered product |
-
1987
- 1987-06-09 CA CA000539177A patent/CA1289313C/en not_active Expired - Lifetime
- 1987-06-12 JP JP14544487A patent/JPS6366234A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11479647B2 (en) * | 2016-09-28 | 2022-10-25 | Daikin Industries. Ltd. | Film including a fluoropolymer |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6366234A (en) | 1988-03-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |