Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With waveguide or long line
Patent
1994-06-13
1995-07-11
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With waveguide or long line
324202, 73 52, 73 493, G01R 3328
Patent
active
054324378
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a high frequency magnetic field exposure meter for use in an induction heat sealing process for heat sealing the metal foil wad elements in a closure to a container to be closed by said closure, during which operation each closure passes beneath an induction coil of an induction heat sealing apparatus.
Heat sealing processes of the above indicated type are well-known in the industry and are used to tightly close containers of different type, for instance in the food processing industry, in the pharmaceutical industry, etc.
Before describing the invention in detail, it is first necessary to understand the induction heat sealing process as used for sealing foil membranes across the openings of non-metallic bottles, jars and containers.
Induction heat sealing is a long established technique well known to those in the field of packaging. The system is explained by reference to FIGS. 1, 2 and 3 which show closures and FIGS. 4 and 5 showing the induction sealing operation.
FIG. 1 shows a section through a plastic closure (1) which comprises a body (2), which is screw-on (as shown) or snap-on, and an internal wad (3), which, on a conventional closure, forms the sealing surface with the neck of the container (4).
FIG. 2 shows cross-sections through different wads, comparing the constructions used in conventional (no induction heat-seal) wads in FIG. 2(a) with that of induction heat-sealable wads in FIG. 2(b). In FIG. 2, (5) represents the main component of the wad, a paper, paperboard, or sometimes plastic or foamed plastic disc. For wet products, the paper-based wads are bonded by an adhesive layer (6) to a water-(or product-) resistant plastic film (7).
For induction heat sealable wads, shown in FIG. 2(b), this conventional structure is bonded by a wax layer (8), which may be continuous, in a grid pattern or in a dot pattern, to a second structure comprising the laminate (9), (10), (11). Layer (9) is a paper layer designed to be able to absorb the wax layer when it is melted during induction heat sealing. Layer (10) is an aluminum foil in which electrical currents are induced during the induction heat sealing process, and which forms the eventual foil membrane across the neck of the bottle, and layer (11) is a heat sealable plastic layer or adhesive layer selected for compatibility with the material of the (non-metallic) bottleneck (4).
After the correct exposure under an induction coil, the heat generated by the currents induced in the foil (10) melt and bond the plastic layer (11) to the rim of the bottle (4), and melt the wax layer (8) allowing it to be absorbed into the paper layer (9) so that the wax no longer bonds the upper part of the wad (5, 6, 7) to the lower foil membrane part of the wad (9, 10, 11),
FIG. 3 illustrates the situation after successful induction heat sealing when the closure (1) is removed from the container (4). The conventional wad.(3) comprising layers (5),(6),(7) remains still attached to the closure body (2), leaving the foil (10) (still sandwiched between layers (9) and (11)) bonded as a seal across the neck of the container (4). The foil seal provides a second and high integrity closing system for the bottle, and provides tamper evidence required by many products.
Examples of the use of this type of induction heat sealing are to be found in pharmaceuticals, oil products, chemicals, and milk and fruit juice containers.
The induction sealing equipment is illustrated schematically in FIG. 4. Typically it comprises a mains voltage driven power supply (12) which generates high frequency currents which are fed to the induction coil (13), which is mounted over a conveyor (14) which transports the filled containers (15), with the pre-applied induction heat seal closures (1) beneath the coil (13). The power supply has a power controller shown by (16) and an output power indicator shown by (17). Basically the power supply unit generates a resonant high frequency, high current between an internal capacitor, shown as (18), and the inductance of the induction coil (13)
REFERENCES:
patent: 3604882 (1971-09-01), Seyfried
patent: 3914689 (1975-10-01), Wright
patent: 4634969 (1987-01-01), Edlin et al.
patent: 4659984 (1987-04-01), Doss
patent: 4684554 (1987-08-01), Ou-Yang
By V. Sudnik et al., "Butt Pressure Welding Machine", Soviet Inventions Illustrated, Jun. 1970, SU 396,220, vol. V, No. 23.
Koninklijke Emballage Industrie Van Leer B.V.
Wardas Mark A.
Wieder Kenneth A.
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