CA1139713A

CA1139713A - Plastic containers and lid therefor

Info

Publication number: CA1139713A
Application number: CA000315777A
Authority: CA
Inventors: Alex C. Chen
Original assignee: Consumers Glass Co Ltd
Current assignee: Consumers Glass Co Ltd
Priority date: 1978-11-03
Filing date: 1978-11-03
Publication date: 1983-01-18
Also published as: DE2944344A1

Abstract

A B S T R A C T

Reusable plastic container and plastic lid therefor, the lid being hermetically sealed to the container by a set adhesive. The set adhesive has a greater attraction for the lid plastic than for the container plastic. Such attraction is sufficient to ensure that, on removing the lid from the container, the adhesive is peeled from the container rim and removed with the reusable lid. This leaves the container rim essentially free of adhesive to reduce the likelihood of contaminating the contained product with adhesive chemicals. The lid or the container rim may be coated with the adhesive prior to heat-seal. In the instance where the container is coated with the adhesive, the rim ledge portion may be provided with at least one continuous circumferentially extending raised portion to facilitate coating of the container rim.
Processes for manufacturing the adhesive-coated container lid and forming the container rim portion and applying adhesive thereto are disclosed.

Description

~139`7~3 Field of the Invention This invention relates to reusable plastic containers and lids therefor and processes for making such containers and lids/ where the container is herme-tically sealed by a lid with a set adhesive.

Background of the Invention .

With the increasing demand of packaging perishable ~-goods for consumption, such as meat and dairy products, ~!~ medicinal and cosmetic products in reclosable containers, it is advantageous to devise a packaging which is sub-stantially less expensive than the standard glass jar with threaded cap and the like. Reusable plastic containers are suitable for this type of packaging because they are inexpensive to manufacture on a high speed basis, the plastic from the forming process is recyclable and the package, as waste, is recyclable. ;

, Available on the market are plastic containers ` ~ for perishable goods; however, the lids therefor which , provide the hermetic seal on the container to maintain ;~` 20 the freshness of the goods is usually not reusable. It is common, for example, to find a plastic container with .1 .
l an aluminum foil lid heat-sealed thereto to maintain the ; freshness of the product. Such foil is torn off the container leaving unsightly portions of foil on the container rim. An additional lid is usually provided .
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~3~ 3 with the container for reclosure of the container. Such a package is complex and results in wastage of the foil which is not reusable and adds costs to the package in terms of the required additional lid.

It is, therefore, desirable in packaging perishable goods to provide a container with a lid therefor which provides a hermetic seal and yet is reusable. The lid has a circumferential area which is heat-sealed to - the container rim and another portion remote therefrom, `~ lO which, in cooperating with a complementary portion on ` the container, provides for the reclosure of the container.
; In addition, the package, as heat-sealed, must be readily opened when it is desired to remove the heat-sealed lid from the container. Solven-t-based types of adhesives have been used in providing a seal between lid and container.
There are, however, several drawbacks in the use of solvent-` based adhesives, such as the extended drying ovens required to remove the solvent from the applied adhesive and the problem of solvent recovery to prevent air pollution.

Other existing processes for providing layers of adhesive on lids have other drawbacks due to their complexity in application of adhesives to the substrate and the extended processing times required in forming lids for containers. Formed lids may be subsequently coated with solvent-based adhesives; however, due to ~39~3 tha irregular shape of formed :Lids, there is usually an uneven layer oE adhesive applied to the lid.

The reusable plastic con-tainer and plastic lid thereEor and processes for making same of -this invention overcome the above-identified drawbacks. The :lids are readily manufactured on a high speed basis and are readily heat-sealed to containers. ~n reopening the heat-sealed container, the set adhesive is removed from the container rim. The process for coating the container rim with adhesive substantially reduces the amount of ` - adhesive used and, -therefore, cuts manufacturing costs.

Summary of the Invention .
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; To achieve -this removal of -the adhesive from the ` container rim when a heat-sealed container is opened, ; 15 it has been found tha-t an adhesive which has a greater - attraction or affinity for the lid plastic than for the container plastic results in peeling the adhesive from the container rim and removing it with -the reusable lid on opening a heat-sealed container. This aspect of the .
invention, therefore, provides a package for perishable goods which is a two-piece construction. The reusable lid provides a hermetic seal for the container, is removable from the container and upon such removal, peels the adhesive from the container rim to substantially reduce -; 2S any possibility of chemically contamina-ting the contained . , ' ' .

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~397~L3 products by adhesive falling thereinto.

A reusable plastic container may be provided with an adhesive about its rim. To facilitate the application of the adhesive to the rim, it has been found that the container rim may be modified wherein its ledge portion has at least one continuous circumferential raised portion of a height approximately less than twice the thickness of the ledge. Such raised portion allows the layer of adhesive applied to the container rim, by methods such as gravure application to flow to each side of the raised area. This prevents "tailing" or overflow of the adhesive to the outside of the rim or to the inner part of the container, thereby avoiding chemical contamination to goods to be placed in the container. The raised portion in the container rim may be formed during vacuum thermoforming, or injection molding of the container.

In instances, and according to an aspect of this invention, when it is desired to provide a hot-melt thermo- -plastic adhesive on the lid preparatory to heat-sealing the lid to the container, the inventive process comprises providing on a side of a sheet of thermoformable plastic lid substrate, an essentially uniform layer of such hot-melt thermoplastic adhesive. The applied layer of hot-melt adhesive is set by simply cooling without the need for extensive solvent recovery drying ovens. The coated sheet J79~

is heated to a thermoformable temperature of the plastic substrate and one or more lid shapes are vacuum formed in the sheet by the use of one or more male dies contacting the side of the sheet without the adhesive. This avoids contact with and disruption of the uniform adhesive layer.
The so formed lids are die-cut from the sheet and the resulting scrap removed and recycled. The selection of the adhesive is such that it has a greater attraction for the lid substrate material than for the material of the ' 10 container to ensure on opening of the heat-sealed containerthat the hot-melt adhesive is removed with the lid.

Description of the Drawings Preferred embodiments of the invention are shown in the drawings wherein:
~' Figure 1 is an isometric view of a container having a lid heat-sealed thereon, where a portion of the lid is removed to show details of the container lid reclosure, Figure 2 is a section along line 2-2 of Figure l;

Figure 3 is a section similar to Figure 2 showing an alternative embodiment for the container rim configuration, having a layer of adhesive applied thereto;

Figure 4 shows in section the container rim and lid portion being heat-sealed thereto;

Figure 5 is a section demonstrating the removal of lid from the heat-sealed container;

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~L3~3 Fiyure 6 is a side eleva-tion showiny a continued removal of the lid Erom the container as commenced in Figure 5;

Figure 7 shows in section another embodiment ; 5 respecting the ma-ting flt of lid to container rim and the desiyn of heat-seal plates which affect the hea-t-seal;

Figure 8 is a schematic of the appara-tus for making the lids from a con-tinuously formed sheet having :a layer of adhesive applied thereto;

~ ~ 10 Figure 9, located on the sheet o:E d:rawlngs Wi.t}l ; Figures 6 and 7, shows in section the confi.c3uration o:E
.~ the male die for vacuum khermoforminy -the lids in the sheets;

Fiyure lO is a schematlc of apparatus :Eor applying adhesive to the contalner rim of the type shown .
in Fiyure 3 and ,, , ~
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Figure 11 is a side elevation of the apparatus ~: schematically shown in E`iyure 10.

Detailed Descripti.on of the Preferred Embodiments of the-Invention . , .

.. . 20 ~ represen-tative circular plastic container lO.is shown in-Fiyure 1 of -the drawinys. The container has outwardly slopiny sidewall 12 merging in-to rim s-tacking shoulder 14, which continues upwardly in-to inwardly : sloping annular wall portion 16 which merge5 into rim ~ 25 . portion 18. The shape Qf rim stacking shoulder 14, , , ~ -6-~, ., . .
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~L3~t~3 ; annular wall portion 16 and the container rim 18 are shown in more detail in Figure 2.

; The complementary lid 20 for the container has an outwardly projecting lip portion 22, downwardly extending annular portion 2~ which has a lid stacking ,' indent 26. This in turn merges into the lid base 30 which includes strengthening annular raised portion 28~
The stacking indent portion 26, which extends circumfe-rentially of the lid, is shaped so as to allow stacking of . 10 an upper lid on a lower lid for purposes of storing and machine dispensing for application to the open top of a container 10. The annular indent portion 24 in the lid cooperates with the inwardly tapered portion 16 of the container to provide a snap fit of the lid and the container to permit reclosure of the container. This reclosure aspect of the container is most desirable in instances where not all of the contained goods are consumed. The lid when placed back :; on the container, provides a sufficiently air-tight seal . to lengthen the storage time of the goods under refrigeration such as yogurt, cottage cheese, pharmaceutical products, preserves, salads and the like.

After the container is filled wi-th the desired goods, the lid is hermetically sealed thereto by sealing the opposing lid and container portions; namely, the lip portion 22 o the lid to the container rim 18 around its .

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entire circumference. In this particular embodiment, ; the lid 20 may be proviaed, at least around its lip portion 22, with a hot-melt thermoplastic adhesive which melts upon application of heat to the lip 22 by a heat-sealing device.
On removal of the heat-sealing device, the hot~melt adhesive is allowed to set to provide a hermetic seal of lid to container to protect the contents~ In this particular embodiment, both the lip 22 and rim 18 are planar to provide a flush contact in heat-sealing th~ two together. This ` 10 relationship of the lid lip 22 and the rim 18 with the set adhesive 24 is shown in Figure 2.

The lid 20 may be vacuumed thermoformed from a sheet of plastic wherein the entire underside of the lid 32 is coated with the hot-melt adhesive. The technique for forming such a lid will be discussed with respect to the schematic representation of the apparatus as shown in Figure 8.

As an alternative to coating the entire underside of the lid 20 in providing a reusable lid which may be heat-sealed to a container, it has been found that the container rim may be coated, or have applied thereto, a layer of adhesive which subsequently serves for a hermetic heat-seal of lid to container. The preferred shape for the container rim in facilitating the adhesive application is shown in Figure 3. The container sidewall .'', ., -8- ~

~39~3 includes the stacking shoulder 1~, the inwardly sloping annular wall portion 16 and rim 18. The rim 18 includes an inner ledge portion 34 and an outer ledge portion 36 where intermediate of the ledge portions is a raised bead portion 38. In this instance, the bead is formed in the rim by displacing such portion of the rim. A preferred form of apparatus may be used to apply the layer of adhesive to the container rim, such as that schematIcally shown in Figure 10. A wheel coating device applies the layer of adhesive to the container rim to form a typical ; layer of adhesive 40 as shown in Figure 3. The layer 40 consists oE a central film or thin area of adhesive 41, to either or both sides o~ which may be larger bead portions 42 of adhesive. The adhesive remains with the container rim preparatory to having a lid hermetically sealed to the container. In so providing the bead 38 on the container rim, it has been found to avoid excess adhesive building on the rim. This prevents the adhesive from flowing over the outer ledge 36 and over the inner ledge 34 which could ~ 20 cause chemical contamination of the contained products ; during storage. It is appreciated, of course, that more than one circumferential head 38 bay be provided depending upon the width of the rim. Further the height of the bead 38, as shown here, is approximately equal to the thickness of the rim; however, it may in some instances be less or _g_ ' '.'~

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greater and it may be possible to use a bead height which is approximately equal to twice the thickness of rim 18.

Referring to Figure 4, a preferred arrangement for heat-sealing a lid 20 to the container 10 is shown.
In this instance, a hot-melt thermoplastic adhesive had been applied to the container rim, pressure in the direction of arrow 44 is applied to the planar rim 22 by flat annular heated die block 46. Support 48 is beneath the container rim portion 18. The hot-melt adhesive 40 is sandwiched . 10 between the raised portion 38 of the rim and the lip 22.
Heat is applied to hot-melt 40 as transferred throuc3h lid lip 22 by heated block 46. As will be understood by those skilled in the art, sufficient heat is transferred to the hot-melt 40 to melt same. Sufficient pressure is applied in this instance to very slightly deform ana flatten the the raised area 38 to the extent shown in Figure 4. This causes a secure bonding of the adhesive to the lid 22 and the rim 18 to provide a hermetic seal in closing the container to protect the contents. On removing the plates 46 and 48 of the heat-seal device, the hot-melt adhesive is allowed to set and provide the aforementioned bond.
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The container of Figure 1 with the lid sealed thereto provides a packaging system for perishable goods which are protected by the hermetic seal provided by the adhesive applied either to the lid or to the container rim . .

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~3~7~3 preparatory to the heat-sealing step. The lid is provided with a reclosure means which in this embodiment is the annular portion 24 cooperating with the inwardly sloped portion 16 of the container. The reclosure means is remote from the area which is sealed to the container. On removal of the lid which has been sealed to the container, the reclosure portion remains unspoiled and has no adhesive applied thereto so that the container may be reclosed for ~ refrigeration. This is particularly desirable for bulk ; 10 packaging where considerably more than a single serving is -~ placed in the container.
., In making the lid of the package from a material different from that used in making the container,~by proper selection of an adhesive and package materials, it ; 15 has been found that a selected adhesive can have a greater affinity for the lid plastic than for the container plastic.
This, of course, has no effect on the security of the seal while unbroken; however, lt provides the following distinct advantage. On commencing the opening of a sealed container by gripping the lid tab portion 21, due to the adhesive's differential in affinity for the lid, the layer of adhesive is peeled from the container rim 18 and removed with the lid.

; Referring to Figure 5, a hot-melt thermoplastic adhesive had been applied to the container rim. On lifting ''~

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~13~3 the tab 21 in the direction of arrow 50, the set adhesive, in having a greater affinity for the lid 22 r begins to peel from the rim 18 and upon continued removal of the lid results in substantially complete transfer to the lid. This unexpected advantage from the selection oE adhesives, where the adhesive has been applied to the container rim and unexpectedly peels therefrom on opening the containerr results in a package system where the adhesive is removed from the container so that the goods are not chemically contaminated by pieces of adhesive remaining on the container rim. The adhesive r in being removed with the lid, does not affect the reclosure aspect. Further the reclosure means provides r in its resistance to opening of the containerr a slow gradual removal of the lid from the ~; 15 container to ensure a smooth peeling of the adhesive 40 from the container rim in its transfer to the lid. As shown in Figure 6 r this is demonstrated wherein the heat-sealed lid is partially opened in the direction of arrow 50.
The remainder of the lid 20a remains in contact with the container rim 18a due to the ~ombined effect of the set adhesive and the gripping of the closure system between lid and container. It is appreciated that in some instances not all of the adhesive would be removed from the container ` rim due to uncontrollable imperfections in the sealing process r contamination of the adhesive or foreign substances on the ; .
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~3g~3 inner surfaces oE the lid lip which prevent~s good bonding of the adhesive to the lid.

The presence of the raised portion 38 011 the con-tainer rim also assists in the transfer oE the adhesive 40 -to the lid during opening of a sealed con-tainer. This is due -to the resultant spacing between the lip 22 of -the lid and the container rim 18 whi.cll provides an undercut area ~0 in the adhesive bond -to loca-te the action of initiatiny the peeling of the adhesive from the container rim.

: 10 The aforementioned grea-ter a-fLi.nity of -the adhesive to the lid i.s thought to be due to ph~sical alld/ol.
electrical a-ttrac-tions between the mo:Lecules o:E -the adhesive and ~id material. To attain a di.:E:Eerential in this af.Eini-ty, the van der Waal forces, hydrogen bonding or other attractions between molecules of the aclhesive and the lid must be greater than be-tween the molecules of the adhesive and the container. For example, in using an ethylene-vinylacetate hot-melt thermoplastic adhesive w~th an acrylic multipolymer lid, the acetate molecules of 2p the adhesive have a greater affinity :Eor the molecules of the acrylic multipolymer than for the molecules of the high impact polys-tyrene container. This difference in afEinity is sufficien-t to ensure a greater bonding of the adhesive to -the lid than to the container,.yet maintain the :., . 25 desired hermetic seal on the container after heat-sealing .~ ~ .

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However, in removing the lid from the heat-sealed container, as previously explained, this differential in affinity results in the transfer of the adhesive from the container rim to the lid.

` As an alternative to the hot-melt adhesive applied to the container rim, a layer -of pressure-sensitive adhesive may be applied. Such pressure-sensitive adhesive may be in the form of a wa-ter-based emulsion prior to its applica-tion. With proper selection of the pressure-sensitive adhesive, the above-discussed greater aEfinity for the lid may be realized to achieve the desired transfer of adhesive from container rim to lid on removing lid from the container.
With this type of adhesive, it is necessary to apply pressure to opposing portions of lid and container rim to effect the desired hermetic bonding of lid to container.

- 15 Turning to Figure 7, an alternative arrangement for a container lid 52 as it cooperates with container 54 which in this embodiment is heat-sealed thereto. The lip portion 56 includes a recess 58, which makes with the shape of the raised portion 60 on the container rim 62. Sana-wiched between the lid and container is a layer of adhesive 64 which had been previously applied to the container rim ; in a manner such as that to be discussed with respect to ; Figure 10. The heat-sealing plates 66 and 68 of the heat-sealing device are correspondingly shaped where die 66, which is heated and pressed downwardly in the direction of arrow ~.39~

68, includes a recessed portion 70 to receive the raised area on the upper edge of the lip 56. The support portion 6~ includes an annular ridge portion 72 which projects into the resulting recess on the underside of container rim 62. Such an arrangement provides more uniorm contact of the adhesive between container lid and rim. In some instances this results in a better seal by providing a more uniform heating of the hot-melt adhesive. This can also enhance the affinity of the set adhesive for the lid to ensure a peeling of the adhesive from the container rim on opening the heat-sealed container.

It is common to provide reclosable lids for containers by vacuum forming them from a sheet of thermo-formable plastic. In the past it has been the practice to coat the lid with an adhesive substance after it has been vacuumed formed to provide for subsequent heat-sealing of lid to container. This usually results in an uneven distribution of adhesive on the lid due to the irregularities of the lid.

~` 20 Turning to Figure 8, schematically is shown an apparatus in which a process is carried out for forming '~!
, a lid from a sheet of plastic which already has applied thereto a layer of hot-melt adhesive. The sheet of plastic, from which the lids are to be formed, is with-drawn from an extruder head 74 which extrudes a relatively `~`

~L3~7~3 thin sheet of plastic material 76 onto chill rollers generally designated 78. The now cooled sheet of material is fed through roller system 80 into compartment 82 which houses a hot-melt adhesive applicator 84. The applicator has a wheel 86 which applies to the underside of sheet 76 a layer of hot-melt 88 from the hot-melt reservoir 90. The now coated sheet is passed over chill ; rollers 92 and 94 to lower the -temperature of the hot-melt to the point where it is no longer tacky. The sheet is then passed over further tensioning rollers and delivery rollers 96 to position the sheets for travel through an oven 98 which heats the sheet via, in this instance, infrared lamps 100 fed by power conductor 102 to a tempera-ture such that it may be readily thermoformed. It has been founa in using hot melts having relatively high viscosities up to approximately 5,000 cps at 300F and as low as 600 cps at 300F, that the hot-melt remains on the sheet during this heating step in preparation for the thermoforming of the lids from the sheet.

The sheet exits from the oven 98 and passes to ~; the thermoforming station 104. ~ male die 106 contacts the upper uncoated side of the sheet 76 to vacuum form therein the lid shape. The sheet is then advanced to the next station where the formed lid 108 is die-cut from ~, 25 the sheet. The scrap resulting from the die-cut operation . -:

~3~7~3 is continuously removed from the system to provide a continuous expeditious process for manufacturing lids on a high production basis.

Referring to Figure 9, the shape and function of the male die 106 is shown in more detail. The male die is provided with vacuum ports 110 to which vacuum is applied as the male die is pushed against and into the sheet 76.
On the underside of the die 106, is an open recessed area defined by the boundary 112 of mandril 114. The vacuum causes the heated sheet of material to take on the shape of the external surfaces of the male die 106 to give the desired lid shape. ~he male die is then extracted from the formed lid. An important aspec~ of this arrangement is in the provision of a die which does not contact the side of the sheet which carries the adhesive. It has been found that the underside of the sheet may be coated with a hot-melt adhesive by a simple economical wheel applicator and that such sheet may be passed directly , through the heating oven 98 to bring the sheet to the desired temperature without loss of adhesive from the under-side of the sheets. It has also been found that such `` hot-melt adhesive does not leave the underside of the lid during the vacuum forming operation. As a result, a lid is produced which has on the underside thereof and in particular the lip portion 22, a uniform coating of hot-, ~' ., ~, .`'~ - .

~13~ 3 melt adhesive to facilitate subsequent heat-sealing of ;~ the lid to complementary container.

It is understood, of course, that co-extrusions ; may be provided from various types of plastic to form a sheet 76 having several layers~ On the upper side may be a tough oxygen impervious layer with intermediate layer of scrap material and a bottom layer of material for which the adhesive has a greater affinity than for the container plastic.

It is understood that other methods of applying or providing a layer of hot-melt adhesive on the sheet from . ~
which lids are formed may be employed. Examples of other methods for making the lid involve co-extruding a layer of the selected hot-melt adhesive together with the layers for the lid substrate. In co-extruding the sheet, care must , be taken not to disrupt the uniformity of the sheet in applying sufficient cooling -to protect the adhesive and not to attain temperatures which degrade the characteristics of the adhesive. Other techniques involve the use of gravure, extrusion or curtain coating of the sheet with .~, ~ . .
the hot-melt, or in some instances, the hot-melt may be ~; sprayed onto the substrate.

;!;' Figures 10 and 11 schematically illustrate apparatus in which a process may be carried out for coating the rims of the containers. A supply of containers 116 are ~:

1~39~L3 individually dropped onto conveyor 118. The con-tainers 120 are transferred -to a reciprocating plunger device 122 which is timed to push the containers individually upwardly in the direction of 124 to be received by the rotating carousel 126. The carousel p:Late 126 includes apertures 128 which are of a size to permit the plate to snugly receive the containers about the base of rim stacking shoulder 18. The carousel rotates in the direction of arrow 130 to pass each container rim above a wheel applicator 132 which applies to the surface oF the container rim a layer of adhesive from the hot-melt adhesive reservoir 134.

The position of the carousel 126 is such to ensure that the wheel 132 is slightly spaced apart from the raised ` bead portion on the container. The spacing between the '~ 15 wheel and the raised bead portion determines the thickness of the layer of adhesive applied to the container rim.
Whe.re the wheel applicator 132 rotates in the same direction .~ and at the same speed as the movement of the container 120 .~ determined by carousel 126, usually a layer of adhesive is applied to the raised bead portion of a thickness approxi-mately 75% of the thickness of the adhesive carried by the :` wheel. For example, should it be desired to apply approxi-mately a 3 mil thickness of adhesive to the bead, where the wheel carries approximately a 4 mil thickness of adhesive, it has been found that, in spacing the bead 3 mil from the `:

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11397~3 wheel, the desired thickness of adhesive is applied to the rim. Due to imperfections in the rim height around the container, the raised portion allows adhesive to flow ; down either side or both sides of the bead to take up and thereby prevent excess adhesive being pushed to the outside of the rim or to the inside of the container. This, as mentioned, avoids chemical contamination of the products to be stored in the container and results in a fairly - uniform layer of adhesive being applied to the rim portion.
Continued rotation of the carousel 126 passes the containers, as coated, to reciprocal ram 136 which forces the containers downwardly and outwardly away from the carousel onto conveyor ` system 138.

The type of heat-seal device, as shown in the drawings, is a thermoconduction type device which applies heat to the area which is to be heat-sealed. It is, of - course, understood that other types of heat-sealing devices may be used, such as high frequency heat-sealing !~ .
devices which may be used with substrates containing polar ; 20 molecules such as polyvinyl chloride. Another example of a heat-seal device, which may be employed, is a magnetic heat-sealing unit which requires incorporating into the layer of adhesive finely divided iron particles which, when exposed to a high strength magnetic field, heats the layer of adhesive to achieve the desired bonding.

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~.1397:13 Various lid and conta.iner substrates may be used, : such as those alréady discussed, and among others include:
: Substrate Supplier High impact polystyrene Dow Chemical - 5 (HIPS) (Styron 456*) Polyurethane: Texan* 480A Bayer Texan* 985A
.~ (used as heat resistan~ coati.ng ' for HIPS in co-extrusion)-. 10 Polyvinylchloride (PVC) Hoechst Acrylic (Cyrolite* G-20) Cy/Ro Industries i~ , - . Polypropylene (PP) Shell Chemical Styrene - Maleic Anhydride Arco Polymer . . .
Copolymer (Dylark* 240) * (trademark`) : Various types of adhesives may be used in the hot-melt.category such as ethylene-vinylace-ta-te co-polymer (EVA), èthylene-ethy1acryl~te copolym~r (~,EA~, ; ethylenemethylacrylate copolymer (EMA), low density polyethylene (PE), polyvinylacetate (PVA), polyamide (PA). Such examplary adhesives may be obtained from the following suppliers:
~ Adhesives : Suppllers .:~ EVA (5.5% VA) ' Exxon Chemical : 25 EVA (10-18% VA) Dupont .~i . ,~

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~L39~7~L3 Adhesives Suppllers EVA ~Iot Melt H009 Industrial ~dhes:Lves EVA Ho-t Melt (Evacote* 7611) In-ternational Waxes EEA Union Carbide EMA ~ Gulf oil Chemical PVA (NA3944) Parrie ~dhesives Ltd.
* ~trademark~

In view of the government regulations in some countries respecting the amount of chemical components which May come into con-~act wlth consumable goods, -the most acceptable container composition is high impact polystyrene and -the mos-t acceptable lid composition is acrylic multipolymer. It has been found -tha-t, to give an excellent seal which is peelable, for the combination of acrylic lid and high impact polys-tyrene container, in using heat conduction-type heat-sealing device, the temperature of the plates was approximately 300 to 360F
If teflon coating is used on the plates, a higher plate temperature lS reguired. Such high temperatures may be in the range of 400F to 460F. The plas-tics were held under pressure for approximately 1 to 2 seconds. This pressure was in the range of 20 to 45 psi. The selected adhesive was an EVA, such as "Evacote" (trademark) supplied by International Waxes. Such adhesive has a greater afEinity for the lid substrate than for the container substrate, so - , ; ~.

' 11397~3 -that on opening the heat-sealed container, the adhesive was transferred from the container rim to the lid on lid removal.

As mentioned, pressure-sensitive adhesivesmay be " 5~ ' used as applied to con-tainer rim or lid. The'water-based ~, `~ ~ emulsion is par-ticularly~suitable for application to the container rlm and may be applied using the whee~appllcator of the type descrlbed~ln~Figure 10. The selection of the ;
pressure-sensitive adheslve may be such to provlde the desired gre~a-ter afflnity for the lid composition than for the container composition. ~n example oE ~uch comhination would be for a high impact polystyrene container, acryllc 'lid and an acrylic copolymer pressure-se~nsitive adhes~ive,~
such as that~prcvided~by the Grace ChemiCal Limited and~
sold under the trademark "Daratak 74L". The emulsion,~as applied to the container~rim, is allowed to dry by evapo~
ration of the~ water whère there is no need for solvent~
recovery and no hazard~in~the wor]clng erlvironment. To effect the~seal cf the~lid to the~con-tainer, pressure~ls~
; 20 applied to the cpposing surfaces of lid and contalner rim~ , to effect the desired herme-tic seal. Due to the acrylate based adhesive;havin~ a greater affinity for lts like~
! ~ : famlly oE pclymers in the acrylic lid, on opening the sealed container, essentlally all cf the thin layer cf adheslve~is peeled from the container~rim~and removed with the lid.
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- It is appreciated that, in using various types of ` hot-melt adhesives with the lids and containers, variations in the heat-seal temperatures and pressure dwell time will be necessary. It should also be noted that terpene-phenolic resins may be incorporated in the ethylene-vinylacetate copolymer hot-melt to improve its hot tack and grease resistance during the heat-seal and setting of the adhesive.

The package system of this invention provldes a container which may be reclosed. It includes a hermetic seal of lid to container where opening oE such heat-seal container does not disturb the reclosure aspects thereof.
The significant advantage of using an adhesive with differing lid and container substrates where the adhesive has greater affinity for lid than container to provide transfer of adhesive from container rim to lid on opening of the heat-seal container,avoids chemical contamination of the contained products.

The advantages of the process in providing raised areas on the container rim portion to ensure uniform distri-bution of a layer of hot-melt adhesive around the container rim substantially reduces the quantity of adhesive used.
The provision of the raised area on the rim has the additional advantage of preventing "tailing" or displacing the layer of hot-melt adhesive to the inside of the container lip, thereby avoiding chemical contamination of products "

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which are to be placed into the con-tainer prior to the heat-sealing operation.

The process for making the lids, when it is desired to coat lids with an adhesive, provides a compact economical approach to forming lids. A simple layering of adhesives on the underside of the sheet with a wheel coating device may be used. Subsequent thermoforming of the lid does not detract from the quality of the adhesive coating.

Although various preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto ~ithout departing from the spirit of the invention or the scope of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Reusable plastic container and plastic lid therefor, the plastic of said container being different from the plastic of said lid, said lid being hermetically sealed to said container by a set hot-melt thermoplastic adhesive between opposing surfaces of cooperating lid and container rim, said thermoplastic adhesive being applied to said container rim prior to said lid being heat sealed thereto, said thermoplastic adhesive when set having a greater affinity for the lid plastic material than for the container plastic material, such affinity being sufficient to ensure that on removing said lid from said container, such thermoplastic adhesive is peeled from the container rim and thereby removed with the reusable lid.

2. A reusable plastic container of claim 1, wherein said lid and container are provided with releasable cooperating closure means to permit reclosure of the opened heat-sealed container and lid, said closure means being remote from said opposing surfaces which were heat sealed together by the set adhesive.

3. A reusable plastic container of claim 1, wherein said container plastic is of high-impact polystyrene, said lid plastic is an acrylic multipolymer and said hot-melt adhesive is ethylene-vinylacetate copolymer composition.

4. A reusable plastic container of claim 1, said container rim having a ledge portion with at least one continuous circumferentially extending raised portion of a height less than twice the thickness of said ledge, said container having said adhesive about its ledge portion.

5. A reusable container of claim 4, wherein each raised portion is a bead extending around said rim.

6. A reusable container of claim 5, wherein a ledge portion extends around the outer periphery of an outermost bead and another ledge portion around the inner periphery of the same bead or innermost bead.

7. A reusable container of claim 4, wherein the lid therefor has a continuous circumferentially extending recess portion adapted to mate with said raised portion on the container rim.

8. A reusable container of claim 4, wherein said container has releasable closure means beneath its rim which cooperates with a lid to provide reclosure of an opened heat-sealed container.

9. A reusable container of claim 4, wherein the outermost reaised portion assists in commencing such peeling of said set adhesive from the rim of a heat-sealed container by virtue of said raised portion providing an area of separation between lid and container rim.

10. A process for sealing a container with a lid comprising forming in said container rim at least one continuous circumferential raised portion of a height less than twice the thickness of said rim, applying to said rim a layer of adhesive which has a greater attraction for the plastic of a lid than for the plastic of the container, heat sealing a complementary lid to said container, sufficient pressure and heat being applied to opposing portions of lid and container rim to melt such adhesive on said container rim and bond it to said lid, said attraction of adhesive to lid being sufficient to ensure that on opening a heat-sealed container, such adhesive is peeled from the container rim and removed with the lid.

11. A process of claim 10, wherein a hot-melt thermoplastic adhesive is applied to said rim.

12. A process of claim 10, wherein a pressure-sensitive thermoplastic adhesive is applied to said rim.