Insulated Plastic Container

Abstract

A double walled container wherein at least one of the enclosed sides of the opposing walls has a portion of its surface provided with a foam covering associated with said wall.

Description

The present invention relates to a double walled container and more specifically to a double walled container having a foam surface on at least one of the inner opposing walls.

Thin wall plastic disposable containers have been used for some time to hold hot and cold liquids. It is well-known, however, that when such containers are used to hold hot liquids, they cannot be held without some discomfort due to the heat transfer through the container sidewalls.

More recently, thin wall containers have been developed which have at least partially resolved the heat transfer problem. Unfortunately, however, these solutions have not been sufficient in terms of either reduction of heat transfer and/or the cost of producing such containers to warrant commercial acceptance over the noninsulated thin wall plastic containers now generally in use.

Some of the solutions to this problem have involved thickened foam container walls, plastic containers having variously shaped gripping fins around thin outer walls, solid plastic containers which either have a foam outer strip or have been partially foamed and double thin walled plastic containers which have been somewhat intricately designed to maintain an air space between the walls. The present invention is an improvement in insulating containers obtained by an unusual and unique combination of insulating factors resulting in a highly insulated thin walled container which is both simple and economical to produce.

The primary object of the present invention is to provide a plastic container which may be held by a user without discomfort when filled with hot liquid.

Another object of the present invention is to provide a strong but lightweight container which will not substantially deflect in a user's hand.

A further object of the present invention is to provide a highly heat insulated container which can be easily and economically constructed.

These and other objects are accomplished by a container of double thin wall construction wherein a portion of one of the inner opposing walls is provided with a foam surface.

Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a partial, sectional side view of a container constructed in accordance with the principles of the present invention.

FIG. 2 is a partial, sectional side view of an alternated container constructed in accordance with the principles of the present invention wherein the bottom of the container is also provided with a foam interlayer.

FIG. 3 illustrates a stepwise process by which the container of FIG. 2 may be made.

Referring to the drawings and more specifically FIG. 1, there is shown a sectional side view of a container 10 which comprise two interfitting or telescopically associated thin wall plastic receptacles 12 and 14 having a foam portion 16 provided on the outer side 18 of the sidewall 20 of the receptacle 14. The receptacles 12 and 14 are held in place by the double curl 22 at the mutual top of both receptacles. In this embodiment the foam portion 16 may be attached or provided on either the outer side 18 of the sidewall 20 or the inner side of the sidewall 24 by any suitable means, i.e., adhesives, etc., or is preferably an integral part of one of the receptacle sidewalls.

In FIG. 2, there is shown a container 22 comprising interfitting or telescopically associated receptacles 26 and 28. In this embodiment the foam portion 30 extends around and down covering the bottom side 32 of the inner receptacle 28. Although the foam portion 30 may be bonded as a separate piece to one of the receptacle sidewalls, it is preferably provided by a rather unique technique which is referred to herein as the "partial foaming process" which is described more in detail in U.S. Pat. No. 3,262,625. More specifically, a thin wall receptacle 40 shown in step a FIG. 3 is partially immersed in a solvent 42 contained in a tank 44 as shown in step b of FIG. 3 and held for a sufficient period of time to permit solvent to be absorbed to a predetermined depth within the wall of the receptacle 40 from its immersed outer surface 46. The receptacle 40 is then removed from the solvent 42 and heated by any means, i.e., lamps 48 shown in step c of FIG. 3 resulting in the formation of a foamed outer covering on the outer surface 46 of the receptacle 40 extending partially within the wall of the original receptacle. The partially foamed receptacle 40 from step c is then fitted into a second but unfoamed receptacle similar to that shown in step a resulting in a double wall internally insulated container such as shown in step d of FIG. 3 producing a relatively thin double wall container which is extremely strong and of a highly heat insulating character. The word "similar" as used herein means that the two receptacles are shaped such that both receptacles can be fitted together without substantial difficulty and yet not be overly loose. Consequently, it is obvious that one receptacle could be configured somewhat differently to include for example, a container gripping section, stacking means and the like which might not be included in the other receptacle.

As previously indicated, the structure of the container which has been described provides unusual heat insulating characteristics due to the combined effect of the double wall and inner foam. In addition, the inner foam portion serves to maintain a distance between the opposing walls which is important for high heat insulating characteristics while at the same time providing an improved structural stability with a minimum of material usage. In the case of lightweight disposable cups, particularly of the vending variety, the combination of thin wall, lightweight construction with high heat insulating character is especially of importance for containing hot liquids such as coffee. Also, due to its composite structure the container may be easily structured to incorporate such additional effects as finger grips, stacking rings and the like. In general, any substantially thermoplastic resin material capable of being shaped in the form of a thin wall receptacle may be utilized to produce a double walled container having an internal foam section associated with at least one of the walls of the container. If the partial forming process is used to produce the foam the plastic of the receptacle which is treated has to be capable of absorbing or being admixed with an expanding agent.

In general, the present invention is concerned with thin wall containers which might be used in vending machines or as over-the-counter disposable cups particularly for hot coffee, chocolate or other heated beverages. For these purposes the wall of each of the two telescopically associated receptacles will generally be in the order of 3 to 20 mils preferably 5 to 15 mils while the foam thickness between the wall would generally be in the order of 3 to 30 mils preferably 3 to 20 mils. In addition, it is apparent the wall thickness of one receptacle might be different from its associated receptacle. In any event, the composite nature of the walls wherein the foam is associated with at least one wall of the container imparts unusual strength to the overall structure.

In its broadest sense the containers of the present invention can be manufactured by various means. For example, the receptacles may be formed by any of the known plastic systems, i.e., thermoforming using a plug assist, vacuum forming and the like. The foaming is generally applied or produced on the plastic after the plastic shaping step although it is possible to do it prior to the shaping step by molding the foam and solid plastic together. The foam portion may be applied to the wall of the receptacle by any means such as adhering a foam strip to the wall of the container, coating the wall with a foamable coating which is subsequently foamed or by preferably utilizing what is referred to as the "partial foaming process."

As indicated above, the preferred technique for providing a foam covering on the wall of the receptacle is by the partial foaming technique which in its broad sense involves the expansion of an expanding agent within the wall of at least one of the receptacles used to form the the container. The expanding agent may be incorporated into the receptacle wall either before the formation of the receptacle, i.e; during the extrusion process or preferably after the formation of the receptacle such as described in U.S. Pat. No. 3,262,626. More specifically, the expanding agent is incorporated into the wall of at least one of the receptacles by exposing the wall surface of the receptacle to a medium absorbable by the plastic of the receptacle or a volatile solvent by immersion, brush, spray or the like for a predetermined length of time to permit the medium or solvent to be absorbed partially into the receptacle wall and subsequently heating the receptacle to produce a foam covering on that portion of wall which was exposed and heated. The thickness of the foam will generally depend on the length of time the plastic is exposed to the solvent. The heating step necessary to produce the foam covering may be carried out prior to interfitting the receptacles to form the double wall container or even after the receptacles are interfitted. The latter procedure might be advantageous if subsequent heat operations are employed, for example, to form a rim or other operation which might be used to mate the upper portion of both receptacles. It is, of course, apparent that both receptacles may be solvent treated to produce a double foaming effect, if desired. Although a rim is generally formed on the container which helps to secure both receptacles together, the frictional effect of the foam between the walls of the container is such that it may be possible to eliminate a separate receptacle mating operation, i.e., heat seal, particularly if the fit is tight.

While the preferred embodiments of the invention have been shown and described herein, it is obvious that many structural details may be changed without departing from the spirit and scope of the appended claims .

Claims

I claim:

1. A container having an improved combination of insulating and structural characteristics comprising two substantially similarly shaped thin walled thermoplastic receptacles, each having a bottom wall and a sidewall extending generally upwardly from the margin of said bottom wall, said receptacles being telescopically associated such that the inner surface of the sidewall of the outer receptacle opposes the outer surface of the sidewall of the inner receptacle and wherein at least a portion of one of said opposing surfaces is provided with a foamed layer, such layer having been formed from the plastic material of the sidewall upon which the said one opposing surface is disposed, the face of said foamed layer which is remote from said one opposing surface being heat sealed to the other of said opposing surfaces.