GB2154504A - Improvements in or relating to the formation of seams - Google Patents

Improvements in or relating to the formation of seams Download PDF

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Publication number
GB2154504A
GB2154504A GB08504574A GB8504574A GB2154504A GB 2154504 A GB2154504 A GB 2154504A GB 08504574 A GB08504574 A GB 08504574A GB 8504574 A GB8504574 A GB 8504574A GB 2154504 A GB2154504 A GB 2154504A
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GB
United Kingdom
Prior art keywords
layers
sheet
seal
slot
jets
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.)
Withdrawn
Application number
GB08504574A
Other versions
GB8504574D0 (en
Inventor
Roger John Meredith
William Henry Johnston
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MAGNETRONICS Ltd
Gallaher Ltd
Original Assignee
MAGNETRONICS Ltd
Gallaher Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by MAGNETRONICS Ltd, Gallaher Ltd filed Critical MAGNETRONICS Ltd
Publication of GB8504574D0 publication Critical patent/GB8504574D0/en
Publication of GB2154504A publication Critical patent/GB2154504A/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
    • B29C65/14—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using wave energy, i.e. electromagnetic radiation, or particle radiation
    • B29C65/1403—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using wave energy, i.e. electromagnetic radiation, or particle radiation characterised by the type of electromagnetic or particle radiation
    • B29C65/1425—Microwave radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
    • B29C65/14—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using wave energy, i.e. electromagnetic radiation, or particle radiation
    • B29C65/1487—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using wave energy, i.e. electromagnetic radiation, or particle radiation making use of light guides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/76—Making non-permanent or releasable joints
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/003—Protecting areas of the parts to be joined from overheating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/01—General aspects dealing with the joint area or with the area to be joined
    • B29C66/05—Particular design of joint configurations
    • B29C66/10—Particular design of joint configurations particular design of the joint cross-sections
    • B29C66/11—Joint cross-sections comprising a single joint-segment, i.e. one of the parts to be joined comprising a single joint-segment in the joint cross-section
    • B29C66/112—Single lapped joints
    • B29C66/1122—Single lap to lap joints, i.e. overlap joints
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/40—General aspects of joining substantially flat articles, e.g. plates, sheets or web-like materials; Making flat seams in tubular or hollow articles; Joining single elements to substantially flat surfaces
    • B29C66/41—Joining substantially flat articles ; Making flat seams in tubular or hollow articles
    • B29C66/43—Joining a relatively small portion of the surface of said articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/70—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material
    • B29C66/73—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset
    • B29C66/739—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the material of the parts to be joined being a thermoplastic or a thermoset
    • B29C66/7392—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the material of at least one of the parts being a thermoplastic
    • B29C66/73921—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the intensive physical properties of the material of the parts to be joined, by the optical properties of the material of the parts to be joined, by the extensive physical properties of the parts to be joined, by the state of the material of the parts to be joined or by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the material of the parts to be joined being a thermoplastic or a thermoset characterised by the material of at least one of the parts being a thermoplastic characterised by the materials of both parts being thermoplastics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/80—General aspects of machine operations or constructions and parts thereof
    • B29C66/82—Pressure application arrangements, e.g. transmission or actuating mechanisms for joining tools or clamps
    • B29C66/826—Pressure application arrangements, e.g. transmission or actuating mechanisms for joining tools or clamps without using a separate pressure application tool, e.g. the own weight of the parts to be joined
    • B29C66/8266—Pressure application arrangements, e.g. transmission or actuating mechanisms for joining tools or clamps without using a separate pressure application tool, e.g. the own weight of the parts to be joined using fluid pressure directly acting on the parts to be joined
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/80—General aspects of machine operations or constructions and parts thereof
    • B29C66/83—General aspects of machine operations or constructions and parts thereof characterised by the movement of the joining or pressing tools
    • B29C66/836—Moving relative to and tangentially to the parts to be joined, e.g. transversely to the displacement of the parts to be joined, e.g. using a X-Y table
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/78—Arrangements for continuous movement of material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
    • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
    • B29C2035/0855—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using microwave
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/16—Cooling
    • B29C2035/1658—Cooling using gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/70—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material
    • B29C66/72—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the structure of the material of the parts to be joined
    • B29C66/723—General aspects of processes or apparatus for joining preformed parts characterised by the composition, physical properties or the structure of the material of the parts to be joined; Joining with non-plastics material characterised by the structure of the material of the parts to be joined being multi-layered
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/80—General aspects of machine operations or constructions and parts thereof
    • B29C66/81—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps
    • B29C66/812—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps characterised by the composition, by the structure, by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps
    • B29C66/8126—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps characterised by the composition, by the structure, by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps characterised by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps
    • B29C66/81262—Electrical and dielectric properties, e.g. electrical conductivity
    • B29C66/81263—Dielectric properties

Abstract

The invention relates to a method of producing a releasable, peelable seal between two layers of thermoplastic sheet material such as for example comprising a pouch for containing products having a volatile constituent. The seal is made by passing the plastics layers through a welding region of a microwave heating device having two portions (2,4) forming a waveguide (8) with a slot (6) therebetween to receive the material in a continuous manner. Cooling air jets (12) are directed towards the external surfaces of the material to be joined to minimise distortion. The layers are subjected to microwave energy in the frequency range 800-12000 MHz, preferably 2450 MHz, which is polarized in the plane of the material to be sealed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the formation of seams The invention is concerned with improvements in or relating to the formation of seams in plastics sheet materials, particularly seams which are readily releasable by peeling said material apart.
The facility for the release of welded seams is particularly useful for example in the manufacture of containers, such as bags, sachets or pouches, suitable to protect products which have a volatile constituent from deterioration during storage or transit before use. For example an aromatised product such as tobacco may be maintained therein in a clean sweet condition, and prevented from drying out before use.
A technique for the production of releasably welded seams for containers of this type has been described in European Patent Application serial No. 0024596 in which electrical energy of the order of 27MHz may be used to weld plastics sheet materials releasably together while the sheet materials are lightly pressed together between welding jaws.
It is an object of the present invention to provide a high quality releasable seal between plastics sheet materials which seal preferably does not require the use of machine jaw parts in contact with the materials to be sealed.
The invention provides a method of producing a releasably welded seal betwen at least two layers of thermoplastic sheet material, comprising subjecting the material layers to microwave energy in the region of the desired seal substantially in the frequency range of 800-1 2000MHz, the resultant welded seal being capable of parting by a peeling action.
Advantageously the layers of material to be sealed are superimposed and arranged to travel along a pathway through a welding region of a suitable apparatus. Preferably the layers are kept in contact one with another by means of air-jets which impinge on the outer surface of the outermost layer at regions covering and flanking the desired area to be sealed. It wil be appreciated that the air-jets act as cooling means for the outer surface, thus providing a temperature gradient increasing towards the confronting faces of the layers to be welded to one another. The result of this is that any tendency towards heat distortion is kept to a minimum, since the temperature is relatively low at the outer surface.Advantageously the air-jets also act as a clamping force to clamp the confronting surfaces together during heating and for a short distance subsequently, to maintain the clamping and cooling effect until the materials have cooled and the seal is complete.
Conveniently, the plastics sheet materials to be welded may be laminated layers, the surfaces to be joined comprising a relatively thin layer of low melting point plastics material secured upon a thicker substrate of material having a higher melting (softening) point and a high microwave power loss factor. Thus the substrate may be heated by microwave energy causing conventional heat flow to conduct heat to the lower melting point surface layer.
Alternatively the plastics sheet material may consist of an assembly of separate sheets of material seamed together at spaced line contacts, for example at margins thereof, by a conventional welding step. If desired, an intermediate sheet may be interposed between the plastics sheets and trapped in place within the welded margins. This intermediate sheet, which may be paper, having an electrical property e tan 8 suitable for heating by microwave energy, will thus heat a first plastics sheet of the layer assembly so as to form a releasable weld with the confronting first plastics sheet of another assembly or another remote region of the same assembly. This first plastics sheet will have a low softening temperature and the second, outer, sheet will be cooled by the cooling means.
The invention further provides apparatus for use in the method of the invention comprising a microwave heating device including two body portions forming a wave-guide, a slot-like passageway between said portions to receive layers of materials in a continuous manner therethrough, and a source of microwave energy to supply a high value electric field within the slot-like passageway.
There will now be described three examples of apparatus suitable for carrying out the method according to the invention. It will be understood that the description, which is to be read with reference to the drawings, is given by way of example only and not by way of limitation.
In the drawings: Figure 1 is a schematic perspective view of a first example of heat sealing apparatus; Figures 2 and 3 are transverse and longitudinal sectional views respectively through a second example of heat sealing apparatus; and Figures 3 and 4 are similar views through a third example of heat sealing apparatus.
The apparatus shown in Figure 1 is a microwave heating device comprising an upper portion 2 and a lower portion 4 having a narrow space or slot 6 through which superimposed thermoplastic sheets (not shown) are passed in the direction of the arrow A. The distance between the portions 2 and 4 is shown exaggerated for clarity. The two portions form a waveguide 8 terminated in a short circuit at 10, the mirowave input being in the direction of arrow B so that a high value electric field at 2450MHz is polarised in the plane of the film to be sealed. A narrow path (x) is provided for the sealing of the two layers of material, controlled by the transverse dimension of the guide 8. Cold compressed air is directed through inlets 12 so as to impinge as jets on the material as it passes through the slot 6.These air jets create a mechanical force on the materials to hold them in contact so that the confronting surface thereof are welded together in the required manner, without physical clamping contact being made. The jets also act to cool the outer surfaces of the plastics materials.
In Figure 2, an apparatus is shown which is formed in two portions 14, 16 in a manner similar to that of the apparatus of Figure 1. slot 18 is formed between the two portions 14,16 and the two superimposed sheets of thermoplastics material 20 travel through the slot in the direction of the arrow C. Compressed air is provided at 22 to form cooling jets and to impinge on the material 20. In the present example partitioning walls 30 may be provided which form air chambers within the wave guide 26.
The microwave input is at 24 and a waveguide 26 terminates in a short circuit at 28. The depth of the slot 28 is selected to be substantially one quarter waveguide wavelength. The wave impedance at the mouth of the slot is therefore high providing a high value for the electric field (desirable for efficient heating) and a low value for transverse magnetic field (desirable for low level of microwave leakage outwards from the slot).
Although in the present example the waveguides operate in the Hol mode and are oriented so that the E field vector is at right angles to the direction of travel of the film, it will be evident that the other modes could also be used.
The waveguides may be plain air filled as in the first example described above, or may have a wall arrangement 30 of dielectric material shaped to form a chamber with an open nozzle to control the flow pattern of the air. Alternatively the waveguides may be dielectric-filled, for example with alumina. In this case the size of the waveguide is reduced by , 1(for alumina ,1 = 9, e1 being the dielectric constant) giving a useful reduction in size. The alumina may have hollow air passages formed therein to provide the jets of air.
As described, the efficiency of the system, defined as microwave power generated power dissipated in the material 20 is low. It may be raised by using resonance to increase the value of the electric field stress (E) in the interaction zone with the film. This can be achieved by means of an iris plate assembly (as shown at 32 in Figures 2 and 3), matching stub, or double stub tuner as examples of methods well-known to those skilled in the microwave art. Afurther intensification of E can be achieved by operating the waveguide close to cut-off for the H01 mode, in which the broad dimension of the rectangular waveguide is chosen to be only slightly greater (e.g. 1-10%) than a half-wavelength.
In experiments a pair of laminated plastics sheets 20 were fused together at a rate of 1.83mlminute using a non-resonant microwave system at 2450MHz with a power of 400 watts, with an air flow of 0.17 cu.m. per min. total through nozzles measuring 2mm by 30mm. The joint was well sealed and it was possible to peel the weld apart without tearing the surface of either sheet.
In Figures 4 and 5 is shown a modified apparatus comprising the upper and lower waveguides 34 and 36, which have at their junction with a heating gap 38, a series of air-jet apertures 40 each connected to a manifold 42. These apertures are suitably spaced to form jets to cool the workpiece as it passes through the gap 38 in the direction of arrow D and apply mechanical pressure whilst the materials are in a heated condition until they are cooled to a temperature at which the seal is complete. The apertures 40 therefore extend beyond the heating zone in the direction of travel of the workpiece. It will be noted that the apertures 40 are not required along the whole width of the waveguide 34 and 36, only at that portion where the plastics material is in a softened condition.
In other experiments, releasable (peelable) seals were formed at rate of 10-20 metres/min. between composite assemblies of plastics sheet material each comprising a first, thermosplastics sheet at the seal face and a second, outer, sheet of polyethylene. These are welded permanently together at the margins only and an intermediate sheet comprising paper, for example printed with advertising or explanatory material is captive within the sealed zone between the two plastics sheets. Good peelable seals were achieved between confronting thermoplastic sheets of each layer assembly and as the outer polyethylene sheets were air cooled there was no significant visible marking on the outer surfaces of the combined layers.
Various modifications may be made within the scope of the invention as defined in the following claims.

Claims (16)

1. A method of producing a releasably welded seal between at least two layers of thermoplastic sheet material, comprising subjecting the material layers to microwave energy in the region of the desired seal substantially in the frequency range of 800-12000MHz, the resultant welded seal being capable of parting by a peeling action.
2. A method as claimed in claim 1 wherein each layer comprises a laminated assembly of plastics material in which the thermoplastics material is secured to a substrate of a second material having a higher softening temperature.
3. A method as claimed in claim 1 wherein each layer comprises an assembly of a first sheet of thermoplastics material and a second sheet of a second plastics material having a higher softening temperature, sheets being secured together only in spaced apart line contacts.
4. A method as claimed in claim 3, wherein an intermediate sheet is interposed between said first and second sheets, said intermediate layer being capable of transferring to the first layer by conduction heat produced by the action of the microwave energy.
5. A method as claimed in any one of the preceding claims in which a flow of cooling gas is directed towards exterior surfaces of the layers during the formation of the releasable seal.
6. Apparatus for use in the method according to claim 1, comprising a microwave heating device including two body portions forming a waveguide, a slot-like passageway between said portions to receive layers of materials in a continuous manner therethrough, and a source of microwave energy to supply a high value electric field within the slot-like pasageway.
7. Apparatus as claimed in claim 6, wherein the value of the electric field is substantially 2450MHz and is polarised in the plane of the material to be sealed.
8. Apparatus as claimed in claim 6, wherein jets for cooling gas are provided which are directed into the slot-like passageway.
9. Apparatus as claimed in claim 8, wherein the jets provide cold compressed air.
10. Apparatus as claimed in any one of claims 6 to 9, wherein partitioning walls are provide within the waveguide.
11. Apparatus as claimed in claim 10, wherein the walls are of dielectric material.
12. Apparatus as claimed in any one of claims 6 to 9, wherein the waveguides are at least partially filled with dielectric material.
13. Apparatus as claimed in claim 12, wherein the dielectric material is alumina.
14. Apparatus as claimed in either one of claims 12 and 13 wherein bores formed in the dielectric material form the jets of cooling gas.
15. A method of producing a releasably welded seal between at least two layers of thermoplastic material, substantially as hereinbefore described with reference to the examples.
16. Apparatus for carrying out the method of claim 15 constructed and arranged substantially as hereinbefore described with reference to a) Figure 1 b) Figures 2 and 3 c) Figures 4 and 5 of the drawings.
GB08504574A 1984-02-23 1985-02-22 Improvements in or relating to the formation of seams Withdrawn GB2154504A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB848404804A GB8404804D0 (en) 1984-02-23 1984-02-23 Formation of seams

Publications (2)

Publication Number Publication Date
GB8504574D0 GB8504574D0 (en) 1985-03-27
GB2154504A true GB2154504A (en) 1985-09-11

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GB08504574A Withdrawn GB2154504A (en) 1984-02-23 1985-02-22 Improvements in or relating to the formation of seams

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GB848404804A Pending GB8404804D0 (en) 1984-02-23 1984-02-23 Formation of seams

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2262258A (en) * 1991-12-04 1993-06-16 Cookson Group Plc Joining polymer-containing materials
US11745438B2 (en) 2018-02-28 2023-09-05 Branson Ultraschall Niederlassung Der Emerson Technologies Gmbh & Co. Ohg Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1403326A (en) * 1972-05-30 1975-08-28 Arco Polymers Inc Method for bonding expanded polymeric parts
GB1432603A (en) * 1972-05-23 1976-04-22 Tetra Pak Int Devices for heat-sealing plastics or plastic-coated material

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1432603A (en) * 1972-05-23 1976-04-22 Tetra Pak Int Devices for heat-sealing plastics or plastic-coated material
GB1403326A (en) * 1972-05-30 1975-08-28 Arco Polymers Inc Method for bonding expanded polymeric parts

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2262258A (en) * 1991-12-04 1993-06-16 Cookson Group Plc Joining polymer-containing materials
US11745438B2 (en) 2018-02-28 2023-09-05 Branson Ultraschall Niederlassung Der Emerson Technologies Gmbh & Co. Ohg Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide
US11820083B2 (en) 2018-02-28 2023-11-21 Branson Ultraschall Niederlassung Der Emerson Technologies Gmbh & Co. Ohg Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide

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GB8504574D0 (en) 1985-03-27

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