Method and apparatus for RF sealing of thermoplastic layers

Claim 3

The method according to claim 1 wherein said step of pressing is accomplished by applying a pressure die of the same configuration as said electrode die and in substantial registration therewith against the surface of said thermoplastic material remote from said electrode die.

Claim 4

The method according to claim 2, including the step of applying more pressure at the outer edges of said pressure die so that said thermoplastic layers are cut through at portions thereof corresponding to said outer edges, but are sealed at the portions corresponding to the remainder of the configuration of the dies.

Claim 5

The method according to claim 3 wherein said step of applying more pressure includes forming a parting line for promoting the removal of excess material from the periphery of the seal.

Claim 6

The method according to claim 1, wherein said RF current has a frequency of at least 10 Megahertz.

Claim 7

The method according to claim 4, wherein said RF current has a frequency of 15-30 Megahertz.

Claim 8

The method according to claim 1, further comprising, after removing said RF current, the step of circulating liquid to said electrode die to carry away heat generated by said RF current.

Claim 9

Apparatus for bonding two or more layers of thermoplastic material to one another to form a seal therebetween comprising, at least one conductive electrode die having a configuration in plan to define the shape of the seal to be formed between said layers of thermoplastic material a sheet of dielectric material disposed on said electrode die; an electrode plate on said sheet of dielectric material and separated thereby from said electrode die to support the layers of thermoplastic material; means for pressing said layers of thermoplastic material against said electrode plate; and means for applying an RF current to a circuit formed by said electrode die and said electrode plate so that sufficient localized heat is formed in the portions of said dielectric material overlying said electrode die to cause said thermoplastic material to soften sufficiently to form the seal.

Claim 10

Apparatus for bonding two or more layers of thermoplastic material to one another to form a seal therebetween comprising, at least one conductive electrode die having a configuration in plan to define the shape of the seal to be formed between said layers of thermoplastic material a sheet of dielectric material disposed on said electrode die; an electrode plate on said sheet of dielectric material and separated thereby from said electrode die to support the layers of thermoplastic material; means for pressing said layers of thermoplastic material against said electrode plate; and means for applying an RF current to a circuit formed by said electrode die and said electrode plate so that sufficient localized heat is formed in the portions of said dielectric material overlying said electrode die to cause said thermoplastic material to soften sufficiently to form the seal.

Claim 11

Apparatus according to claim 8, wherein said pressing means includes a pressure die having the same configuration as said electrode die.

Claim 12

Apparatus according to claim 9, wherein said dies have outer and inner edges, and said pressure die is arranged to apply more pressure at the outer edge than at the inner edge so that said thermoplastic layers are cut through at the portions thereof corresponding to said outer edges, but are sealed together at the portions corresponding to the remainder of the configuration of the die betwen said outer and inner edges.

Claim 13

Apparatus according to claim 9, wherein said pressure die is formed of a nonconductive material.

Claim 14

Apparatus according to claim 11, wherein said non-conductive material is acetal.

Claim 15

Apparatus according to claim 11, wherein said non-conductive material is polytetrafluoroethylene.

Claim 16

Apparatus according to claim 8, wherein said electrode plate comprises a nickel-chromium alloy.

Claim 17

Apparatus according to claim 14, wherein said electrode plate is nichrome sheet steel less than about 0.01 in thickness.

Claim 18

Apparatus according to claim 8, wherein said sheet of dielectric material is less than about 0.015 inches thick.

Claim 19

Apparatus according to claim 8, wherein said dielectric material is phenolic-impregnated paper.

Claim 20

Apparatus according to claim 8, wherein said dielectric material is fish paper.

Claim 21

Apparatus according to claim 8 further comprising releasing means on the surface of said electrode plate remote from said electrode die for preventing said layers from sticking to said plate.

Claim 22

Apparatus according to claim 19, wherein said releasing means includes a sheet of polytetrafluoroethylene.

Claim 23

Apparatus according to claim 8 wherein said RF current has a frequency of at least 10 Megahertz.

Claim 24

Apparatus according to claim 8 further comprising liquid cooling means for removing heat from said electrode die by means of a flowing liquid.

Claim 25

Apparatus for bonding two or more layers of thermoplastic material to one another to form a seal therebetween comprising, upper and lower superposed conductive electrode dies having generally complementary configuration in plan to define the shape of the seal formed between said layers of thermoplastic material; upper and lower sheets of dielectric material each supported on a respective one of said conductive dies; upper and lower electrode plates each disposed on a respective one of said dielectric sheets; means for moving at least one of said upper and lower dies, together with its respective dielectric sheet and electrode plate toward and away from the other for selectively pressing the sheets against said layers of thermoplastic material; and means for applying an RF current to a circuit formed by said upper electrode die and electrode plate and to a circuit formed by said lower electrode die and electrode plate, so that sufficient localized heat is formed in the portions of said dielectric sheets overlying the respective dies to cause said thermoplastic material to soften sufficiently to form a seal.

Claim 26

Apparatus for bonding two or more layers of thermoplastic material to one another to form a seal therebetween comprising, upper and lower superposed conductive electrode dies having generally complementary configuration in plan to define the shape of the seal formed between said layers of thermoplastic material; upper and lower sheets of dielectric material each supported on a respective one of said conductive dies; upper and lower electrode plates each disposed on a respective one of said dielectric sheets; means for moving at least one of said upper and lower dies, together with its respective dielectric sheet and electrode plate toward and away from the other for selectively pressing the sheets against said layers of thermoplastic material; and means for applying an RF current to a circuit formed by said upper electrode die and electrode plate and to a circuit formed by said lower electrode die and electrode plate, so that sufficient localized heat is formed in the portions of said dielectric sheets overlying the respective dies to cause said thermoplastic material to soften sufficiently to form a seal.

Claim 27

Apparatus according to claim 23, further comprising releasing means disposed on the side of each said sheet remote from the respective die for preventing said layers of thermoplastic material from sticking to said sheets.