WO2005021243A1 - Heat-sealing method - Google Patents

Heat-sealing method Download PDF

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Publication number
WO2005021243A1
WO2005021243A1 PCT/FI2004/000506 FI2004000506W WO2005021243A1 WO 2005021243 A1 WO2005021243 A1 WO 2005021243A1 FI 2004000506 W FI2004000506 W FI 2004000506W WO 2005021243 A1 WO2005021243 A1 WO 2005021243A1
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WO
WIPO (PCT)
Prior art keywords
sealing
air flow
air
polymer
heat
Prior art date
Application number
PCT/FI2004/000506
Other languages
French (fr)
Inventor
Risto Vesanto
Päivi MÄÄTTÄ
Original Assignee
Stora Enso Oyj
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 Stora Enso Oyj filed Critical Stora Enso Oyj
Publication of WO2005021243A1 publication Critical patent/WO2005021243A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B31—MAKING ARTICLES OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER; WORKING PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
    • B31B—MAKING CONTAINERS OF PAPER, CARDBOARD OR MATERIAL WORKED IN A MANNER ANALOGOUS TO PAPER
    • B31B50/00—Making rigid or semi-rigid containers, e.g. boxes or cartons
    • B31B50/60—Uniting opposed surfaces or edges; Taping
    • B31B50/64—Uniting opposed surfaces or edges; Taping by applying heat or pressure, e.g. by welding
    • 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
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
    • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
    • B29C66/9141—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the temperature
    • 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
    • B29C65/10—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using hot gases (e.g. combustion gases) or flames coming in contact with at least one of 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
    • B29C66/001—Joining in special atmospheres
    • B29C66/0012—Joining in special atmospheres characterised by the type of environment
    • B29C66/0014—Gaseous environments
    • B29C66/00143—Active gases
    • 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
    • B29C66/001—Joining in special atmospheres
    • B29C66/0012—Joining in special atmospheres characterised by the type of environment
    • B29C66/0016—Liquid environments, i.e. the parts to be joined being submerged in a liquid
    • 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
    • B29C66/72—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
    • B29C66/7232—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 comprising a non-plastics layer
    • B29C66/72327—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 comprising a non-plastics layer consisting of natural products or their composites, not provided for in B29C66/72321 - B29C66/72324
    • B29C66/72328—Paper
    • 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
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
    • B29C66/919—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges
    • 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
    • B29C66/71—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 composition of the plastics material of the parts to be joined
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • 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
    • B29K2711/00—Use of natural products or their composites, not provided for in groups B29K2601/00 - B29K2709/00, for preformed parts, e.g. for inserts
    • B29K2711/12—Paper, e.g. cardboard
    • B29K2711/123—Coated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2009/00—Layered products
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/712—Containers; Packaging elements or accessories, Packages

Definitions

  • This invention relates to a heat-sealing method, in which the polymer material forming the seal is melted or softened by blowing a hot air flow to the sealing point.
  • Heat sealing is a commonly used technique for bonding polymer films and polymer- coated papers and boards. During the bonding, the polymer is melted under heat and the surfaces to be bonded are placed face to face, the polymer being solidified while cooling, thus tightly bonding the surfaces to each other. Heat sealing is widely implemented in the packaging domain in the manufacture of bags, containers, casings and boxes and in the sealing of the products during packaging.
  • heat sealing comprises the use of hot air blowing towards the sealing point for melting or softening the polymer.
  • the heating of the air flow can be performed either by resistance heating or flame heating.
  • the present invention is based on the fresh observation that a flame-heated air flow may achieve a better sealing result than a resistance-heated air flow at the same heat-sealing temperature.
  • the polymer to be heat-sealed is polyester, such as e.g. polyethylene terephtalate (PET).
  • PET polyethylene terephtalate
  • the superiority of flame heating is evidently explained by the water vapour that is generated during the combustion reaction of hydrocarbon fuel and is entrained with the flue gases into the hot air flow directed to the sealing point. Water vapour increases the thermal capacity of the hot air flow and it may additionally have a chemical effect on the polymer that fosters heat sealing.
  • the invention derived from the findings mentioned above is characterised by introducing water into the air flow blown to the sealing point with a view to increased moisture content of the hot sealing air.
  • the air flow may be heated in a manner known er se, either by resistance heating, i.e. by electric current conducted through a resistor, or by flame heating by burning a liquid or gaseous fuel in the air flow directed to the sealing point.
  • resistance heating i.e. by electric current conducted through a resistor
  • flame heating by burning a liquid or gaseous fuel in the air flow directed to the sealing point.
  • the water addition of the invention allows the water vapour content of the sealing air to be increased to a considerably higher degree than does mere vapour addition generated by combustion.
  • Heat-sealing air is typically indoor air or similar air taken from the environment, which is heated and blown to the sealing point. Air at room temperature or outdoor air having possibly a lower temperature has very low water vapour content, regardless of the relative air humidity.
  • pure water is fed into the air flow directed to the sealing point, with the water evaporating during feeding, or then pure water vapour is supplied. Vapour can be added to the air flow at a stage preceding resistance or flame heating, however, water or vapour addition preferably takes place after the heating step, at a stage when the air flow has low relative humidity due to the heating.
  • Water or vapour is most advantageously added to the air flow at a rate such that after the addition, the moisture content of the air flow is at least approx. 30 g/m 3 , preferably in the range from approx. 50 to 250 g/m .
  • the amount of moisture to be added is accordingly slightly smaller than these moisture values, however, generally at least 10 g/m 3 calculated on the air flow directed to the sealing point.
  • Another manner of adding water to hot sealing air is using pure hydrogen as the fuel of flame heating, the combustion resulting in pure water vapour, which is mixed with the air flow.
  • the heat-sealing temperature depends on the varying softening or melting temperature of the polymer to be sealed in each case.
  • the temperature of the heat-sealing air is adjusted so as to be slightly higher than the melting temperature of the polymer.
  • the melting temperature of the most commonly used heat-sealing polymer low-density polyethylene (LDPE)
  • LDPE low-density polyethylene
  • the temperature of the sealing air is most advantageously above 120 °C.
  • polyesters such as polyethylene terephtalate melting at approx. 250 °C
  • the air temperature may be approx. 250 °C, even up to about 300 °C.
  • Preferred objects of application of the invention comprise bag, box, casing and container packages made of polymer-coated paper or board.
  • the package can be formed from a blank of polymer-coated paper or board by bending or folding the blank edges and subsequently sealing the joined edges. Similarly, folds produced during the folding of the blank can be bonded by means of coating polymer to the walls of the package.
  • the invention is particularly advantageous in the manufacture of frozen food board or oven tins made of PET coated packaging board for use as prepared food packages, these products being heatable at an oven temperature of 200-250 °C or in a microwave oven owing to their heat-resistant PET coating.
  • Figure 1 shows heat sealing of a polymer-coated packaging board in an embodiment of the invention, the air flow directed to the sealing point being heated by resistance heating,
  • Figure 2 shows the direction of the air flow to the sealing point in a section II-II of figure 1,
  • Figure 3 shows the opposite edges of the folded packaging board blank when joined and bonded to each other
  • Figure 4 corresponding to figure 1 shows a second embodiment of the invention, in which the air flow directed to the sealing point is heated by flame heating.
  • FIGS 1 and 2 are schematic views of air flow heating, humidification in accordance with the invention, and blowing the air flow to form heating air for heat sealing of a packaging board 2 equipped with a polymer coating, such as e.g. a polyester coating 1.
  • the air is indoor air taken from the environment of the heat sealer, having a temperature of e.g. approx 25 °C and relative humidity of e.g. approx. 50%.
  • the air is absorbed with a blower (not illustrated) into the air duct 3, where the air flow 4 hits the resistance heater 5, which heats the air flow with electric current to the heat-sealing temperature, which is e.g. 300 °C.
  • a device 6 has been provided in the air duct 3 for adding water 7 to the heated air flow passing in the duct 3.
  • the device 6 operates with a resistance heater 8, which boils the water to vapour 9, which is mixed with the heated dry air flow while humidifying the air flow to a moisture appropriate for heat sealing.
  • the amount of water to be added is at least 20 g, preferably approx. 40-200 g/m 3 of heated sealing air.
  • the air duct 3 terminates in the blowing nozzle 10, which, as shown in figures 1 and 2, spreads the heated and humidified air flow over an elongated sealing area 11, in which the hot air melts the polymer coating 1 on the board 2.
  • This counter surface may consist of a similar polymer-coated board 2', as in the case of figure 3 of the drawings, or of any surface to which the coating polymer 1 is capable of bonding in a molten state.
  • bonded boards 2, 2' may thus be formed with the opposite edges portions of one single packaging board blank, the edge portions having been brought opposite each other during the folding of the blank for subsequent bonding.
  • the coating polymer 1 of each edge 2, 2' of the blank can then be melted by the hot humidified air flow, as shown in figures 1 and 2, before being sealed as shown in figure 3.
  • the heat seal 11 forms when the polymer solidifies while cooling so that the polymer coatings of opposite surfaces are completely fused to each other along the sealing line 11.
  • the optional embodiment of the invention shown in figure 4 differs from the one above in that the heating of the air flow 4 is performed with a flame heater 12 mounted in the air duct 3, rather than with an electric heating resistor.
  • the heater 12 bums fuel oil or hydrogen-based fuel gas in the air flow generated by the blower so as to heat the air to the temperature required for heat sealing while the flue gases, which are mainly carbon oxides and water vapour, are mixed with the air flow.
  • the moisture content of the thus heated air flow is increased in accordance with the invention by feeding water vapour 9 into the air flow.
  • the amount of water to be added in this case may be at least 10 g, preferably approx. 30-200 g/m 3 of heated sealing air.
  • Figure 4 shows an optional embodiment of the water supply of figure 1, in which pressurised vapour is prepared outside the air duct 3 and is fed into the air flow from nozzles 13 provided in the duct.
  • pressurised vapour is prepared outside the air duct 3 and is fed into the air flow from nozzles 13 provided in the duct.
  • the aspects described above in conjunction with figures 1-3 apply to the embodiment of figure 4.
  • water can be added to the heated air flow by feeding vapour generated outside the heat-sealing plant into the air flow, or by supplying humid air, whose moisture content exceeds that of the heated air and thus increases the overall moisture content of the sealing air.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Composite Materials (AREA)
  • Package Closures (AREA)

Abstract

The invention relates to a heat-sealing method, in which a polymer material (1) forming the seal is melted or softened with an air flow (4) blown to the sealing point (11). In accordance with the invention, water (7, 9) is added to the air flow in order to increase the moisture content of the hot sealing air. The air is heated by resistance heating or flame heating and the water can be introduced in the hot air flow in the form of water, which subsequently evaporates, or in the form of water vapour. The method is suitable i.a. for producing packaging containers by sealing polymer­coated paper or board.

Description

Heat-sealing method
This invention relates to a heat-sealing method, in which the polymer material forming the seal is melted or softened by blowing a hot air flow to the sealing point.
Heat sealing is a commonly used technique for bonding polymer films and polymer- coated papers and boards. During the bonding, the polymer is melted under heat and the surfaces to be bonded are placed face to face, the polymer being solidified while cooling, thus tightly bonding the surfaces to each other. Heat sealing is widely implemented in the packaging domain in the manufacture of bags, containers, casings and boxes and in the sealing of the products during packaging.
Beside various heated sealing elements, heat sealing comprises the use of hot air blowing towards the sealing point for melting or softening the polymer. In this case, the heating of the air flow can be performed either by resistance heating or flame heating.
The present invention is based on the fresh observation that a flame-heated air flow may achieve a better sealing result than a resistance-heated air flow at the same heat-sealing temperature. This is particularly obviously the case when the polymer to be heat-sealed is polyester, such as e.g. polyethylene terephtalate (PET). According to the inventors, the superiority of flame heating is evidently explained by the water vapour that is generated during the combustion reaction of hydrocarbon fuel and is entrained with the flue gases into the hot air flow directed to the sealing point. Water vapour increases the thermal capacity of the hot air flow and it may additionally have a chemical effect on the polymer that fosters heat sealing.
The invention derived from the findings mentioned above is characterised by introducing water into the air flow blown to the sealing point with a view to increased moisture content of the hot sealing air.
In accordance with the invention, the air flow may be heated in a manner known er se, either by resistance heating, i.e. by electric current conducted through a resistor, or by flame heating by burning a liquid or gaseous fuel in the air flow directed to the sealing point. In the latter case, the water addition of the invention allows the water vapour content of the sealing air to be increased to a considerably higher degree than does mere vapour addition generated by combustion.
Heat-sealing air is typically indoor air or similar air taken from the environment, which is heated and blown to the sealing point. Air at room temperature or outdoor air having possibly a lower temperature has very low water vapour content, regardless of the relative air humidity. In accordance with the invention, pure water is fed into the air flow directed to the sealing point, with the water evaporating during feeding, or then pure water vapour is supplied. Vapour can be added to the air flow at a stage preceding resistance or flame heating, however, water or vapour addition preferably takes place after the heating step, at a stage when the air flow has low relative humidity due to the heating.
Water or vapour is most advantageously added to the air flow at a rate such that after the addition, the moisture content of the air flow is at least approx. 30 g/m3, preferably in the range from approx. 50 to 250 g/m . Considering the initial moisture contained in indoor air and the moisture generated from fossil or similar organic fuel during flame heating, the amount of moisture to be added is accordingly slightly smaller than these moisture values, however, generally at least 10 g/m3 calculated on the air flow directed to the sealing point.
Another manner of adding water to hot sealing air is using pure hydrogen as the fuel of flame heating, the combustion resulting in pure water vapour, which is mixed with the air flow.
The heat-sealing temperature depends on the varying softening or melting temperature of the polymer to be sealed in each case. In order to melt the polymer, the temperature of the heat-sealing air is adjusted so as to be slightly higher than the melting temperature of the polymer. The melting temperature of the most commonly used heat-sealing polymer, low-density polyethylene (LDPE), is in the range 100-120 °C depending on its quality, and then the temperature of the sealing air is most advantageously above 120 °C. When polyesters, such as polyethylene terephtalate melting at approx. 250 °C, are sealed, the air temperature may be approx. 250 °C, even up to about 300 °C.
Preferred objects of application of the invention comprise bag, box, casing and container packages made of polymer-coated paper or board. The package can be formed from a blank of polymer-coated paper or board by bending or folding the blank edges and subsequently sealing the joined edges. Similarly, folds produced during the folding of the blank can be bonded by means of coating polymer to the walls of the package. The invention is particularly advantageous in the manufacture of frozen food board or oven tins made of PET coated packaging board for use as prepared food packages, these products being heatable at an oven temperature of 200-250 °C or in a microwave oven owing to their heat-resistant PET coating.
The invention is explained in greater detail below by means of examples and with reference to the accompanying drawings, in which
Figure 1 shows heat sealing of a polymer-coated packaging board in an embodiment of the invention, the air flow directed to the sealing point being heated by resistance heating,
Figure 2 shows the direction of the air flow to the sealing point in a section II-II of figure 1,
Figure 3 shows the opposite edges of the folded packaging board blank when joined and bonded to each other, and
Figure 4 corresponding to figure 1 shows a second embodiment of the invention, in which the air flow directed to the sealing point is heated by flame heating.
Figures 1 and 2 are schematic views of air flow heating, humidification in accordance with the invention, and blowing the air flow to form heating air for heat sealing of a packaging board 2 equipped with a polymer coating, such as e.g. a polyester coating 1. The air is indoor air taken from the environment of the heat sealer, having a temperature of e.g. approx 25 °C and relative humidity of e.g. approx. 50%. The air is absorbed with a blower (not illustrated) into the air duct 3, where the air flow 4 hits the resistance heater 5, which heats the air flow with electric current to the heat-sealing temperature, which is e.g. 300 °C. After the heater 5, a device 6 has been provided in the air duct 3 for adding water 7 to the heated air flow passing in the duct 3. In figure 1, the device 6 operates with a resistance heater 8, which boils the water to vapour 9, which is mixed with the heated dry air flow while humidifying the air flow to a moisture appropriate for heat sealing. In this exemplifying case, the amount of water to be added is at least 20 g, preferably approx. 40-200 g/m3 of heated sealing air. The air duct 3 terminates in the blowing nozzle 10, which, as shown in figures 1 and 2, spreads the heated and humidified air flow over an elongated sealing area 11, in which the hot air melts the polymer coating 1 on the board 2. Immediately after this, while the polymer is still in a molten state, the board is joined to the surface to which it will adhere by sealing. This counter surface may consist of a similar polymer-coated board 2', as in the case of figure 3 of the drawings, or of any surface to which the coating polymer 1 is capable of bonding in a molten state. As shown in figure 3, bonded boards 2, 2' may thus be formed with the opposite edges portions of one single packaging board blank, the edge portions having been brought opposite each other during the folding of the blank for subsequent bonding. The coating polymer 1 of each edge 2, 2' of the blank can then be melted by the hot humidified air flow, as shown in figures 1 and 2, before being sealed as shown in figure 3. The heat seal 11 forms when the polymer solidifies while cooling so that the polymer coatings of opposite surfaces are completely fused to each other along the sealing line 11.
The optional embodiment of the invention shown in figure 4 differs from the one above in that the heating of the air flow 4 is performed with a flame heater 12 mounted in the air duct 3, rather than with an electric heating resistor. The heater 12 bums fuel oil or hydrogen-based fuel gas in the air flow generated by the blower so as to heat the air to the temperature required for heat sealing while the flue gases, which are mainly carbon oxides and water vapour, are mixed with the air flow. The moisture content of the thus heated air flow is increased in accordance with the invention by feeding water vapour 9 into the air flow. The amount of water to be added in this case may be at least 10 g, preferably approx. 30-200 g/m3 of heated sealing air. Figure 4 shows an optional embodiment of the water supply of figure 1, in which pressurised vapour is prepared outside the air duct 3 and is fed into the air flow from nozzles 13 provided in the duct. In other respects, the aspects described above in conjunction with figures 1-3 apply to the embodiment of figure 4.
It is obvious to those skilled in the art that the embodiments of the invention are not restricted to the examples above, but may vary within the scope of the accompanying claims. Thus, for instance, water can be added to the heated air flow by feeding vapour generated outside the heat-sealing plant into the air flow, or by supplying humid air, whose moisture content exceeds that of the heated air and thus increases the overall moisture content of the sealing air.

Claims

Claims
1. A heat-sealing method, in which the polymer material (1) forming the seal is melted or softened by means of a hot air flow (4) blown to the sealing point (11), characterised in that water (7, 9) is added to the air flow (4) for increased moisture content of the hot sealing air.
2. A method as defined in claim 1, characterised in that the air flow (4) is heated by resistance heating (5).
3. A method as defined in claim 1, characterised in that the air flow (4) is heated by flame heating (12).
4. A method as defined in any of the preceding claims, characterised in that the air is indoor air or any similar air taken from the environment, which is heated and blown to the sealing point (11).
5. A method as defined in any of the preceding claims, characterised in that water (7) is fed into the heated air flow (4) and vaporised, or water vapour (9) is fed into the heated air flow (4).
6. A method as defined in any of the preceding claims, characterised in that the hot sealing air (4) has a temperature of at least 100 °C and a moisture content of at least 9 1
30 g/m , preferably at least 50 g/m , after water addition.
7. A method as defined in any of the preceding claims, characterised in that the sealing polymer is polyester, such as polyethylene terephtalate (PET).
8. A method as defined in claim 7, characterised in that the temperature of the hot sealing air (4) is at least approx. 250 °C, preferably approx. 300 °C.
9. A method as defined in any of the preceding claims, characterised in that the method is used in the heat-sealing of polymer-coated paper or board (2).
10. A method as defined in claim 9, characterised in that the method is used for heat-sealing a blank which is made of polymer-coated board (2) and folded or bent in the shape of a container, and whose edges (2, 2') have been placed opposite each other in order to be bonded.
PCT/FI2004/000506 2003-09-03 2004-09-01 Heat-sealing method WO2005021243A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20031247 2003-09-03
FI20031247A FI119018B (en) 2003-09-03 2003-09-03 Heat Sealing Method

Publications (1)

Publication Number Publication Date
WO2005021243A1 true WO2005021243A1 (en) 2005-03-10

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ID=27838920

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Application Number Title Priority Date Filing Date
PCT/FI2004/000506 WO2005021243A1 (en) 2003-09-03 2004-09-01 Heat-sealing method

Country Status (2)

Country Link
FI (1) FI119018B (en)
WO (1) WO2005021243A1 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783062A (en) * 1972-01-27 1974-01-01 Cons Bathurst Ltd Method for flame bonding by use of high velocity,high temperature direct flame
EP0529336A1 (en) * 1991-08-01 1993-03-03 Toppan Printing Co., Ltd. Method of thermal fusion

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783062A (en) * 1972-01-27 1974-01-01 Cons Bathurst Ltd Method for flame bonding by use of high velocity,high temperature direct flame
EP0529336A1 (en) * 1991-08-01 1993-03-03 Toppan Printing Co., Ltd. Method of thermal fusion

Also Published As

Publication number Publication date
FI119018B (en) 2008-06-30
FI20031247A (en) 2005-03-04
FI20031247A0 (en) 2003-09-03

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