# US 10,370,576 B2 · Polyester film with electrical insulation and heat conduction properties

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- Number: US 10,370,576 B2
- Document ID: US10370576B2
- Status: Granted
- Kind: B2
- Application number: 15/571,985
- Filed: 2016-04-27
- Published: 2018-05-17
- Granted: 2019-08-06
- Earliest claimed: 2015-05-07
- Assignees: DuPont Teijin Films U.S. Limited Partnership
- Applicants: Dupont Teijin Films U.S. Limited Partnership
- Inventors: Anna Ellett; Marianne Bausch-Koenig
- Web page: https://patentgrep.com/patent/US10370576B2

## CPC

- C09K 5/14: Solid materials, e.g. powdery or granular
- B29C 55/12: biaxial
- C08G 63/183: Terephthalic acids
- C08J 5/18: Manufacture of films or sheets
- C08K 3/38: Boron-containing compounds
- B29C 55/005: {characterised by the choice of materials}
- B29C 55/14: successively
- B29C 55/16: simultaneously
- B29C 71/02: Thermal after-treatment {(B29C71/0063 and B29C71/0072 take precedence)}
- B29C 2071/022: {Annealing}
- B29K 2067/003: {PET, i.e. poylethylene terephthalate}
- B29K 2509/00: Use of inorganic materials not provided for in groups {B29K2503/00 - B29K2507/00,} as filler
- C08J 2367/02: Polyesters derived from dicarboxylic acids and dihydroxy compounds; (C08J2367/06 takes precedence)
- C08K 2003/385: {Binary compounds of nitrogen with boron}
- C08K 2201/001: Conductive additives
- C09K: MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- B29K: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR {MOULDS, } REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS

## Abstract

A biaxially stretched thermally conductive and electrically insulating film comprising a polyester forming a matrix and a plurality of anisotropic thermally conductive particles dispersed within the matrix and A process for manufacturing said biaxially stretched polyester film in which the dimension of the anisotropic filler particles with the highest thermal conductivity is oriented out of the film plane, thus conferring on said film improved thermal conductivity properties in the direction perpendicular to the film plane.

## Claims

### Claim 1

A biaxially stretched electrically insulating monolayer film exhibiting both electrical insulation and heat conduction properties, said film comprising:
a polyester forming a matrix;
a plurality of anisotropic primary filler particles dispersed within the matrix, said particles being selected from the group consisting of boron nitride, aluminum nitride, silicon carbide, silicon nitride, aluminum oxide, gallium nitride, gallium arsenide, gallium phosphide, zinc oxide, indium phosphide, beryllium oxide, magnesium oxide, silicon, and mixtures thereof;
wherein the film is devoid of any carbon fibers;
wherein the particles are present in an amount ranging from 1.5 to 5 wt. % based on the total weight of the film, and
wherein the plane or the principal axis of at least 20% of the primary filler particles forms an angle of from 20° to 90° with respect to the film plane,
wherein the thermal conductivity of said film in the direction perpendicular to the film plane is at least 0.25 W/m·K.

### Claim 2 (depends on 1)

The biaxially stretched electrically insulating film of claim 1, in which a plurality of secondary filler particles are dispersed within the matrix, said particles being selected from the group consisting of silicon dioxide, magnesium silicon nitride, zinc sulfide, zirconium oxides, boron phosphide, titanium dioxide, calcium carbonate, barium sulfate, talcs, clays and mixtures thereof,
wherein the secondary filler particles are present in an amount ranging from 0.1 to 20 wt. % based on the total weight of the film.

### Claim 3 (depends on 1)

The biaxially stretched electrically insulating film according to claim 1, wherein the polyester is selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene isophthalate, polybutylene terephthalate (PBT), polybutylene isophthalate, polybutylene naphthalate, polytrimethylene terephthalate (PTT), polytrimethylene isophthalate, polytrimethylene naphthalate, poly(cyclohexylene-dimethanol-terephthalate (PCT), polymethylene 1,3-propylene terephthalate, polyhexamethylene terephthalate, polyisosorbide terephthalate (PEIT), polyhexamethylene naphthalate, polyarylates (Par) and copolymers thereof, preferably polyethylene terephthalate (PET) and copolymers thereof.

### Claim 4 (depends on 1)

The biaxially stretched electrically insulating film according to claim 1, wherein the polyester is a homopolymer or a copolymer of polyethylene terephthalate (PET) and the primary filler particles are boron nitride particles.

### Claim 5 (depends on 1)

An electric motor comprising the biaxially stretched electrically insulating film according to claim 1.

### Claim 6 (depends on 1)

The biaxially stretched electrically insulating film according to claim 1, which is devoid of any filler selected from the group consisting of graphite, graphene, diamond and carbon nanotubes.

### Claim 7 (depends on 1)

The biaxially stretched electrically insulating film according to claim 1, which is devoid of any filler made of carbon.

### Claim 8 (depends on 1)

A process for the preparation of the biaxially stretched electrically insulating monolayer film according to claim 1, said process comprising the steps of:
a) providing a mixture of a molten polyester and anisotropic primary filler particles selected from the group consisting of boron nitride, aluminum nitride, silicon carbide, silicon nitride, aluminum oxide, gallium nitride, gallium arsenide, gallium phosphide, zinc oxide, indium phosphide, beryllium oxide, magnesium oxide, magnesium silicon nitride, silicon and mixtures thereof;
wherein the particles are present in an amount ranging from 1.5 to 5 wt. % based on the total weight of the mixture;
b) feeding the mixture containing the polyester and the particles through a die to form a cast film;
c) heating the film at a temperature in the range of Tg+20° C. to Tg+80° C., where Tg is the glass transition temperature of the polyester measured through Differential Scanning Calorimetry at a scan rate of 20° C./min;
d) sequentially or simultaneously biaxially stretching the film in the MD direction and in the TD direction at a total stretching ratio of from 8 to less than 11 times.

### Claim 9 (depends on 8)

The process according to claim 8, comprising after step d), step e) of annealing the film at a temperature in the range of Tm−80° C. to Tm−10° C., where Tm is the melting temperature of the polyester measured through Differential Scanning Calorimetry at a scan rate of 20° C./min.

### Claim 10 (depends on 8)

The process according to claim 8, wherein the mixture of step a) comprises secondary filler particles selected from the group consisting of silicon dioxide, zinc sulfide, zirconium oxides, boron phosphide, titanium dioxide, calcium carbonate, barium sulfate, talcs, clays and mixtures thereof,
wherein the secondary filler particles are present in an amount ranging from 0.1 to 20 wt. % based on the total weight of the mixture.

### Claim 11 (depends on 8)

The process according to claim 8, wherein the molten polyester of step a) is obtained through a continuous polymerization process.

### Claim 12 (depends on 11)

The process according to claim 11, wherein the filler particles are first mixed with ethylene glycol thereby forming a dispersion, said dispersion being mixed with polyester monomers.

### Claim 13 (depends on 8)

The process according to claim 8, wherein step a) comprises the following substeps:
a-1) providing a polyester and anisotropic primary filler particles and optionally secondary filler particles;
a-2) mixing the polyester with the filler particles by applying heat and shear in an extruder.

### Claim 14 (depends on 8)

The process according to claim 8, wherein step a) comprises the following substeps:
a-1) providing a masterbatch in which the anisotropic primary filler particles and optionally the secondary filler particles are already incorporated and dispersed in the polyester;
a-2) mixing the masterbatch with a polyester by applying heat and shear in an extruder.