Envelopes – wrappers – and paperboard boxes – Paperboard box – With closure for an access opening
Patent
1989-09-06
1991-05-21
Elkins, Gary E.
Envelopes, wrappers, and paperboard boxes
Paperboard box
With closure for an access opening
118314, 118315, 156 78, 156578, 222485, 229136, 4272082, 427286, 493128, 493131, 493331, 493333, B65D 506
Patent
active
050168126
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a high-integrity closure carton, a method and an adhesive dispensing means and apparatus for producing same.
Hot melt thermoplastic adhesives are commonly used in packaging and cartoning applications, where the quick setting time of this type of adhesive is advantageous. At the operating speeds of commercial cartoning machines, the use of chemical or cold adhesives has decreased because of the relatively long setting time required for such adhesives. Hot melt adhesive applied to the flaps of a carton sets relatively quickly and substantially reduces the time in which compressive forces must be applied to the flaps while the adhesive bonds as compared to cold glue.
Despite the improvement over cold adhesives, thermoplastic adhesives also present problems in packaging and cartoning applications.
One of the most common problems with hot melt adhesives is that of compressing the adhesive after application so as to obtain sufficient surface contact between the adhesive and adhered substrate to achieve a good bond. The relatively high viscosity, high surface tension, and quick setting time of hot melt adhesives all combine to prevent the adhesive from spreading over a large surface area when the adhesive is applied as a liquid to the substrate. Instead of spreading, the liquid sets up as a thick bead on the structure. Even when quickly compressed between two flaps of a carton, the adhesive has been found difficult to spread. In most instances, when the two flaps which have been adhered together are pulled apart, the bond breaks the adhesive-to-substrate interface. This means that in order to increase the strength of the bond, the area of the interface or surface contact between the adhesive and the substrate must be increased.
As described in detail in U.S. Pat. No. 4,059,466, assigned to the assignee of this invention, it has been discovered that the adhesive strength of a bond achieved with a given quantity of hot melt adhesive may be appreciably improved if the adhesive is applied as a cellular foam rather than as a conventional non-foamed adhesive. A method of making and applying foamed hot melt adhesive is described in detail in said U.S. Pat. No. 4,059,466. The increased bonding strength of the foamed adhesive results at least in part from the fact that the foamed adhesive may be spread over at least twice the area compared with the same adhesive in the non-foamed state under the same compressive conditions. Since the strength of the bond is a function of the area wetted or covered by the adhesive, foaming of adhesive results in a bond approximately twice as strong as the same quantity of unfoamed adhesive. Expressed another way, the same bond strength may be achieved with approximately half the quantity of foamed adhesive compared with unfoamed adhesive, because of the much larger area wetted or covered by the foamed adhesive under the same compressive conditions.
So-called sift-proof cartons are high-integrity closure cartons usually fabricated by applying a block C- or block U-shaped pattern of adhesive to the end flap structure of a four-sided carton to form a continuous line or bead of adhesive along the carton edges to eliminate any minute channels or openings through which granular material in the carton could leak. In one type of four-sided carton, for example, the four flaps at each end of the carton include a pair of opposed minor flaps, and an inner major flap and outer major flap which are each formed with a width equal to the depth of the carton. In sealing the end flaps of such four-sided, sift-proof cartons, the opposed minor flaps are first folded inwardly toward the center of the carton. The two major flaps are placed in an open or spread position to receive hot melt adhesive. Usually, at least one strip or ribbon of hot melt adhesive is applied to each end of the inner major flap, transverse to its fold line. The outer major flap receives a block C-or a block U-shaped strip of hot melt adhesive including a strip at each end perpendicular to its fold line, and a t
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Elkins Gary E.
Nordson Corporation
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