Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1983-12-12
1985-12-17
Dawson, Robert A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
53373, 156443, 156497, 156499, 493134, B32B 3112
Patent
active
045590923
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the sealing of lids to tray-like containers, such as are used for packaging of a variety of goods, principally foodstuffs. The containers have peripheral horizontal flanges to which separate flat lids are sealed, and are generally rectangular in plan.
Both the containers and the lids are usually formed of a cardboard material having their interior surfaces (i.e. their surfaces destined to form the interior surface of the finished pack) coated with a polyester film, such as polyethylene terephthalate, for heat resistance. The polyester may also serve as a heat-activatable adhesive for sealing the lid to the container. Hitherto such sealing has been effected by use of a heated platen which is brought down on to the positioned lid and held there until fusion of the coatings on the lid margin and the upper surface of the container flange has been effected. This process is slow, of the order of 2 to 3 seconds per container, because the heating of the coatings is indirect, i.e. through the thickness of the lid. In most cases, motion of the container has to be stopped while the platen is applied. Also, the apparatus is not readily adaptable to changes in container size. A further disadvantage of the use of heated platens is that in some applications the coatings on the container and lid are not heat-sealable together with the bond strength required for the finished pack.
An object of the present invention is to provide a method of sealing lids to such tray-like containers which will enable the rate of production to be increased, which may be more easily adaptable to containers of different sizes, and/or which may be used in applications where the interior surfaces of the container and lid are not compatible or otherwise are difficult to heat-seal together.
According to the invention, a method of sealing separate flat lids at margins thereof on to a series of generally rectangular tray-like containers having peripheral horizontal flanges, which comprises moving the containers continuously along a line while positioning a lid with its margin located above the peripheral flange of a respective container and sealing the margin of the lid to the peripheral flange of the respective container, is characterized by bending marginal side portions of the lid and/or side portions of the flange of the container so that, with the lid so positioned over the container, a V-section recess is formed between the side portions of the lid and flange along each of opposed sides of the container parallel to the line of movement; providing a heat-activatable adhesive in said recesses; directing hot gas into the receses to activate the adhesive within them and to heat the side portions of the lid and flange; pressing the side portions of the lid and flange into contact to seal them together; changing the movement of the containers so that what were previously marginal end portions of the lid and end portions of the flange are presented at each side of the line of movement; and sealing the said end portions of the lid and flange together.
The method of the invention is thus carried out while moving the containers continuously along the line and the adhesive within the recesses is heated directly by the hot gas, e.g. air, so that production rates can be much increased, typically from 15 containers per minute with the prior art to 120 containers per minute using the present invention.
The heat-activatable adhesive may be an overall heat-resistant polyester film coating as mentioned above applied to the sheet material of which the containers and lids are made, or it may be an additional coating of adhesive applied to the lid margins and/or the flanges of the containers either before or after the formation of the recesses. The adhesive may be a water-based adhesive which is sprayed into the recesses as a fine mist, and which thereafter is rendered tacky by the hot gas, as proposed in our co-pending U.K. Patent Application No. 8204889.
Preferably the bending of the side portions of the lid and/or of the container flan
REFERENCES:
patent: 3508376 (1970-04-01), Bemiss
patent: 3610114 (1971-10-01), Kaminsky
patent: 4249978 (1981-02-01), Baker
patent: 4282699 (1981-08-01), Embro
patent: 4384914 (1983-05-01), Mattiebe
patent: 4387551 (1983-06-01), Cowan
Dawson Robert A.
Metal Box Public Limited Company
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