U.S. patent application number 13/641056 was filed with the patent office on 2014-02-27 for multilayer thermoformable materials and sanitary food containers made therefrom.
This patent application is currently assigned to Converter Manufacturing, Inc.. The applicant listed for this patent is Millard F. Wallce. Invention is credited to Millard F. Wallce.
Application Number | 20140054292 13/641056 |
Document ID | / |
Family ID | 50147086 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140054292 |
Kind Code |
A1 |
Wallce; Millard F. |
February 27, 2014 |
Multilayer Thermoformable Materials and Sanitary Food Containers
Made Therefrom
Abstract
A multilayer stack of polymeric sheets can be used in
thermoforming processes to make objects wherein each sheet has
substantially the same shape. The stack includes at least one sheet
of a thermoformable polymer, and can include many such sheets. A
barrier layer is interposed between at least an overlapping portion
at least two of the polymeric sheets in order to prevent fusion of
the sheets in the overlapping portion during the thermoforming
process. The barrier layer can include an adhesive that adheres the
sheets in the overlapping portion. In formed articles including
such an adhesive, the sheets can be manually peeled from one
another if a suitable adhesive is selected. The stack (and object
formed using the stack) can include polymeric sheets that are not
thermoformable, but are adhered to the surface of a thermoformable
sheet. The sheets and objects can include multiple separable and/or
peelable sheets. The stack can be used, for example, to make
peelable, re-usable food service trays. In such trays, a rigid base
has multiple peelable sheets adhered to at least one surface
thereof, the sheets being peelable from the surface to reveal a
sanitary surface amenable to food contact.
Inventors: |
Wallce; Millard F.;
(Orwigsburg, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wallce; Millard F. |
Orwigsburg |
PA |
US |
|
|
Assignee: |
Converter Manufacturing,
Inc.
Orwigsburg
PA
|
Family ID: |
50147086 |
Appl. No.: |
13/641056 |
Filed: |
April 12, 2011 |
PCT Filed: |
April 12, 2011 |
PCT NO: |
PCT/US11/32111 |
371 Date: |
July 25, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12762887 |
Apr 19, 2010 |
|
|
|
13641056 |
|
|
|
|
11734285 |
Apr 12, 2007 |
7721910 |
|
|
12762887 |
|
|
|
|
12620460 |
Nov 17, 2009 |
|
|
|
11734285 |
|
|
|
|
61323239 |
Apr 12, 2010 |
|
|
|
60855597 |
Oct 31, 2006 |
|
|
|
60794409 |
Apr 24, 2006 |
|
|
|
Current U.S.
Class: |
220/495.03 ;
220/574.3 |
Current CPC
Class: |
B32B 7/12 20130101; B65D
25/16 20130101; B29K 2067/00 20130101; B32B 15/08 20130101; B65D
1/34 20130101; B29K 2023/12 20130101; B29K 2027/06 20130101; B32B
37/12 20130101; Y02W 30/807 20150501; B29K 2023/06 20130101; Y02W
30/80 20150501; B29C 51/10 20130101; B29C 51/14 20130101; B32B 7/06
20130101; A47G 23/06 20130101; B29L 2009/001 20130101; B32B 38/1866
20130101; A47G 19/022 20130101; B32B 38/0012 20130101; B32B 27/08
20130101; B32B 2309/105 20130101; B29L 2009/003 20130101; B44D
3/126 20130101; B29K 2077/00 20130101; B32B 2307/718 20130101; B29C
51/425 20130101; B32B 38/145 20130101; B29C 2791/006 20130101; B29K
2025/00 20130101; B32B 2439/70 20130101 |
Class at
Publication: |
220/495.03 ;
220/574.3 |
International
Class: |
A47G 19/02 20060101
A47G019/02; B65D 25/16 20060101 B65D025/16; A47G 23/06 20060101
A47G023/06 |
Claims
1. A peelable, multi-use food service container comprising a
relatively rigid sheet of a thermoformable polymer, wherein a first
surface of the rigid sheet has a conformation adapted for holding a
food service item; at least one second sheet of a polymer, each of
which overlaps the rigid sheet at the first surface and conforms to
the shape of the first surface, each second having a sanitary face
and an adhesion face; a first barrier composition interposed
between and adhering the rigid sheet and the adhesion face of the
second sheet adjacent the rigid sheet; and, if the container
comprises more than one second sheet, a second barrier composition
interposed between and peelably adhering the adhesion and sanitary
faces of adjacent second sheets, whereby each of the second sheets
is peelably removable from the container.
2. The container of claim 1, comprising a plurality of the second
sheets.
3-7. (canceled)
8. The container of claim 1, wherein the first barrier composition
peelably adheres the rigid sheet and the adhesion face of the
second sheet adjacent the rigid sheet.
9. The container of claim 1, wherein the first surface is
sanitary.
10. The container of claim 1, comprising at least three second
sheets.
11. The container of claim 1, comprising at least six second
sheets.
12. The container of claim 1, comprising at least ten second
sheets.
13-16. (canceled)
17. The container of claim 1, further comprising a protective coat
that removably overlaps the second sheet most distal from rigid
sheet at over the entire first surface.
18. (canceled)
19. The container of claim 1, having a conformation adapted to fit
within an orifice defined by a rack.
20. The container of claim 19, having a conformation wherein a
cavity defined by the first surface extends into the orifice and a
flange surrounding the cavity engages the rack.
21-25. (canceled)
26. The container of claim 1, having the conformation of a
generally rectangular pan.
27. The container of claim 1, having the conformation of a
generally circular pan.
28. The container of claim 1, wherein the adhesion face of the
second sheets, the sanitary face of the second sheets, and the
second barrier composition are selected such that the second
barrier composition adheres selectively to the adhesion face,
relative to the sanitary face, of adjacent second sheets.
29-35. (canceled)
36. The container of claim 1, wherein the rigid sheet is made of a
material selected from the group consisting of polyethylene
terephthalates, high density polyethylenes, high molecular weight
polyethylenes, polypropylenes, polystyrenes, polyvinyl chlorides,
copolymers of these, and combinations of these.
37. The container of claim 1, wherein each second sheet is made
from a material independently selected from the group consisting of
polyethylenes, polypropylenes, polyethylene terephthalates, nylons,
polyvinyl chlorides, copolymers of these, and combinations of
these.
38-42. (canceled)
43. The container of claim 1, further comprising a movable lid
adapted to cover a recess of the container that abuts the first
surface.
44. (canceled)
45. A food service station comprising a rack having a conformation
adapted to hold the container of claim 1.
46. The station of claim 45, wherein the rack has a conformation
adapted to hold a plurality of containers of claim 1,
47. (canceled)
48. A method of operating a food station, the method comprising
assembling a first food product from components stored in the
multiple food containers, including at least a selected component
stored in the peelable food container of claim 1, peeling a second
sheet from the peelable food container, adding more of the selected
component to the peelable food container, and assembling a second
food product from components stored in the multiple food
containers, including at least the selected component.
49-51. (canceled)
52. A method of maintaining sanitation of a food station, the
method comprising storing multiple food service items in the food
station, wherein a plurality of first food service items are stored
in the peelable container of claim 1, dispensing at least one of
the first food service items from the food station, removing any
remaining first food service items from the peelable container,
peeling a second sheet from the peelable container, and thereafter
storing additional first food service items in the peelable
container.
53-88. (canceled)
Description
BACKGROUND OF THE DISCLOSURE
[0001] This disclosure relates generally to
multiple-polymeric-layer thermoformable materials and articles
formed from such materials. In one aspect, the present disclosure
relates generally to containers for hygienically containing food,
including containers having multiple peelable layers on a surface
which contacts the food, such that the same container can be used
multiple times to hygienically contain food without the need to
sanitize the food-contacting surface between uses.
[0002] The disclosure also relates to other containers having
peelable surface layers, such as paint trays.
[0003] Paint Trays
[0004] Paint is commonly applied to walls and other surfaces with a
paint roller comprised of a roll of napped textile material or
other paint absorbent substrate carried on a handle, and a metal or
plastic paint-holding tray into which the roller is placed to load
the roll with paint. While useful in quickly applying a uniform
paint coating to large surfaces, a major disadvantage of the use of
this system is the required messy and time consuming chore of
cleaning the roller and tray after use. The present application
relates to an improved tray that enables the user to avoid tray
cleaning, and to a tray with two wells divided by a flat section
designed specifically to properly distribute paint on the roller
nap. The tray configuration is also designed to lend itself to
thermoforming.
[0005] In an attempt to minimize cleaning, the prior art describes
a preformed paint tray liner that is placed into the interior of a
paint tray. Generally, these liners are thermoformed from a plastic
sheet having a thickness of from about 0.008 to about 0.03 inches.
The paint is poured into this liner, which is removed and discarded
along with any adhered paint after the paint job is completed.
While effective in eliminating the need to clean the paint tray,
these preformed liners are sufficiently expensive that many users
attempt to clean and reuse the liners. Their thickness adds
significantly to environmental waste upon disposal and require
significant amounts of energy to produce. The preformed tray liners
also require separate additional storage prior to use.
[0006] Other prior art as exemplified by U.S. published patent
application no. 2004/0112902 to Campbell and U.S. published patent
application no. 2006/0037960 to Rosa manually presses an impervious
plastic sheet having a thickness of from about 0.5 to about 5 mils
and an adhesive backing into a previously formed paint tray so that
the sheet approximately conforms to the tray. The sheet is peeled
away and discarded after use. While using less material than
preformed tray liners, these sheets are awkward and time consuming
to individually hand press into place and do not provide a
functional liner that exactly conforms to the tray interior,
especially in the corners of the tray.
[0007] Food Service Containers
[0008] Food is commonly held in bins, trays, pans, and other
containers during its preparation, presentation, and serving. In
order to minimize transmission of food-borne illnesses and to
comply with applicable regulations regarding food sanitation, food
and food-implement containers must be frequently sanitized. This is
particularly true in situations in which food containers are used
over long periods, refilled, or accessed frequently by individuals
removing items therefrom. Examples of containers of these types
include pans used in buffet or steam tables, bins recessed in a
food preparation surface, salad bar pans, bulk condiment
containers, cutlery bins, hot and cold soup kettles, and chafing
dish inserts. In food service settings, it is desirable to maintain
hygienic conditions even for containers that do not hold food or
implements intended for human consumption (e.g., bins used for
busing tables and other utility bins).
[0009] Some food service situations require use of many food
storage containers to separately contain different food items.
Examples of such situations include salad and buffet displays at
restaurants, cafeterias, and groceries at which customers select
food desired for purchase from the containers. Other examples
include food preparation stations (e.g., food preparation tables
such as those shown in U.S. Pat. No. 6,385,990) located in
restaurant, cafeteria, or grocery settings, at which an employee of
the establishment selects food (e.g., sandwich components and
condiments) from a variety of trays accessible to the employee in
response to requests from a customer. In these settings, containers
having standardized sizes are frequently used to facilitate
replacement of a used container with a fresh one. Retailer food
service practices or government regulations often specify how
frequently used containers must be sanitized or replaced, rather
than simply refilled with new food items or implements. Frequently,
the containers are not refilled, and are instead removed and
sanitized prior to being refilled with food and reused, or are
simply discarded.
[0010] Food storage containers are used to hold foods that must be
maintained at cool temperatures (e.g., perishable products such as
meats, cheeses, lettuce, tomatoes, and yogurts), foods that are
maintained at warm or hot temperatures (e.g., soups or cooked
entrees), and food service items that are maintained at ambient
temperatures (e.g., breads and crackers, eating utensils, and foods
intended for near-immediate consumption). For food storage
containers in which heat transfer (either into or from the food
contained therein) is desired, it is known to make the containers
from materials that exhibit thermal conductivity and heat capacity
characteristics suited to the desired use of the container.
[0011] Conventional food service containers have a variety of
shapes, such as rectangular and circular pans having an open top. A
flange or rim typically extends around the perimeter of the open
pan top to hold the container in a fitting, such as a frame or
rack. When used in a heated or chilled table setting, the flange
can also provide a seal around the perimeter of the container,
improving energy efficiency (i.e., by preventing loss of heating or
cooling medium) and appearance. The flange can also act as a
convenient surface for lifting, supporting, and carrying the
container. When used in a steam table, buffet table, salad bar, or
the like, the body (e.g., the portion containing the food) and
flange of a container are typically dimensioned so that the body of
the container is received into an opening in the table or bar and
is supported by its flange resting upon the edges of the table or
bar opening or upon a frame or rack fitted to the bar or table.
[0012] Food storage containers sometimes have corresponding lids
that are adapted to fit an orifice of the container (e.g., a soup
tureen having a fitted lid, optionally with a recessed section to
accommodate the handle of a ladle when the tureen and lid are
assembled). The lid can serve to exclude contaminants, to prevent
gain or loss of heat, or some combination of these functions.
[0013] Reusable food service containers of these types are made
from a variety of materials, and are frequently made from either
metals (e.g., stainless steel) or relatively durable plastics
(e.g., polycarbonates). However, disposable food containers made
from lower-cost plastics (e.g., various polyethylenes, polyesters,
and polypropylenes) are also used.
[0014] Regardless of whether reusable or disposable food storage
containers are employed, use of the containers typically involves
generation of significant quantities of waste. Disposable
containers both preclude cost savings that are realized with
re-usable containers (since a new container must be used each time)
and generate solid waste which must be disposed of properly.
Although reusable containers avoid the economic waste of single use
containers, they require sanitation procedures that are costly,
time consuming, and generate significant quantities of (usually
liquid) waste materials. Furthermore, sanitation of reusable food
containers tends to generate solid and liquid wastes (e.g., food
particles, fats, and greases) that are not soluble in water and for
which disposal in wastewater systems tends to be regulated. Thus,
commercial scale sanitation of reusable food containers often
requires investment in equipment that isolates such wastes (e.g.,
grease traps), inspections to monitor compliance with applicable
regulations, or both. In general, disposal of solid wastes (which
are generally removed by truck, rather than by cloggable pipes and
sewers) is less regulated and more flexible than disposal of liquid
wastes containing non-water-soluble components, in addition to
conserving water used for washing.
[0015] Others have proposed fitting disposable liners to food
service containers in order to alleviate the waste and
inconvenience associated with cleaning reusable food service
containers. Such liners can be difficult to install and to remove
in a sanitary fashion. Also, they are susceptible to bypass if food
products from the interior of the liner are spilled or migrate
beneath the liner. When such liners are not adapted specifically to
the food service container, problems of fitting and use arise from
the unmatched dimensions of the liners and containers. For example,
non-fitted liners can fold or crease to create pockets in which
food products can accumulate or be hidden, leading to spoilage or
bacterial growth that can contaminate food products in the
remainder of the container. Fitted liners have the drawback that
they fit only a specific container, but not others. Inserted liners
also have the drawback that they tend to move or slide around in
the food service container when foodstuffs are manipulated therein.
Furthermore, known liners also have disadvantages stemming from the
fact that they are formed (like plastic bags) by welding, adhering,
or otherwise sealing plastic sheets along a seam. The seams can
often leak or tear, defeating the purpose of the liner. Insertable
liners also tend to be relatively unsightly and expensive.
[0016] There is a continuing need for a food container that can
hygienically contain food and food service items and that can be
rapidly and conveniently recycled for multiple uses, preferably
without generation of excessive waste materials and while
presenting a favorable appearance. The subject matter of the
present disclosure addresses this need.
BRIEF SUMMARY OF THE DISCLOSURE
[0017] Various types of subject matter are described in this
disclosure.
[0018] In prior related applications (U.S. patent applications No.
12/620,460, filed 17 Nov. 2009 and Ser. No. 11/734,285, filed 12
Apr. 2007, and U.S. provisional patent applications 60/794,409,
filed 24 Apr. 2006 and 60/855,597, filed 31 Oct. 2006), use of
technology similar to that described herein was described in the
context of making articles such as paint trays for use in applying
paint to a surface with a paint roller, and in particular to a
paint tray having a one or more layers of a peelable surface film,
whereby the paint tray can be cleaned after use by peeling away the
upper film surface. Those applications also related to methods for
converting multiple layers of material into a stack or roll and
forming the paint tray or other container with adhered layers. It
was recognized that those methods could lend themselves to a number
of markets other than paint trays, i.e., trash cans, buckets, metal
paint trays, cat litter containers, camping plates, medical trays,
etc.
[0019] In one aspect, the subject matter described herein relates
to a peelable, multi-use food service container. The container
includes a relatively rigid sheet of a thermoformable polymer and
at least one, and preferably a plurality of, second sheets of a
polymer, each second sheet having a sanitary face and an adhesion
face. A first surface of the rigid sheet has a conformation adapted
for holding, supporting, or containing a food service item. Each of
the second sheets overlaps the rigid sheet at the first surface and
conforms to the shape of the first surface. Interposed between the
rigid sheet and the adjacent second sheet is a first barrier
composition that adheres (e.g., peelably) the rigid sheet and the
adhesion face of the adjacent second sheet. A second barrier
composition (identical to or different from the first) is
interposed between the adhesion and sanitary faces of adjacent
second sheets. The second barrier composition peelably adheres the
second sheets to one another. The container thus has one or a
plurality of hygienic second sheets peelably adhered to a surface
adapted for holding, supporting, or containing a food service item.
In one embodiment, the second barrier composition is identical
between all second sheets. In another embodiment, a second sheet
more distal from the rigid sheet is more easily peeled from the
second sheet underlying it than is a second sheet more proximal to
the rigid sheet. The container can have a protective coat layer
applied atop the uppermost second sheet to prevent contamination of
and physical damage to the second sheet(s), such as might occur
during manufacture, storage, shipping, or installation of the
container.
[0020] In another aspect, the disclosure relates to method of
operating a food station. The method involves assembling one or
more first food products (e.g., a sandwich or salad) from
components stored in multiple food containers, including at least
one selected component that is held in a peelable food container
described herein. After assembling first food product(s) (for
example, when the ingredients in the container are depleted, at the
end of a business day or shift, or after a pre-selected period of
time), a second sheet is peeled from the peelable food container
(revealing a sanitary surface that can be contacted with fresh food
components), and more of the selected component is added to the
peelable food container. One or more second food products
(identical to or different from the first food products) are then
assembled from components stored in the food containers, including
at least the selected component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view of a roll of stacked liner
sheets and a substrate sheet (master PAD roll) ready for
thermoforming.
[0022] FIG. 2 is a sectional side view of a tray sheet section
positioned between heaters prior to thermoforming.
[0023] FIG. 3 is a sectional side view of a heated tray sheet
section positioned in a thermoforming apparatus prior to
thermoforming.
[0024] FIG. 4 is a sectional end view of a thermoformed tray system
prior to ejection from the thermoforming apparatus.
[0025] FIG. 5 is a detailed sectional side view of a segment of a
stack of liner sheets and a substrate sheet.
[0026] FIG. 6 is a top view of a preferred tray system.
[0027] FIG. 7 is a top view of an alternative preferred tray
system.
[0028] FIG. 8 is a side view of an alternative tear tab
assembly.
[0029] FIG. 9 is a side view of another alternative tear tab
assembly.
[0030] FIG. 10 is a side view of yet another alternative tear tab
assembly.
[0031] FIG. 11 is a side view of yet another tear tab assembly.
[0032] FIG. 12 is a side view of a pad of liner sheets.
[0033] FIG. 13 is a sectional side view of a stamping apparatus and
a pad of liner sheets.
[0034] FIG. 14 is a side view of a stack of substrate and
sheets.
[0035] FIG. 15 is a sectional side view of a stack of substrate and
sheets in preparation for molding into a female cavity mold.
[0036] FIG. 16 is a sectional side view of a stack of substrate and
sheets molded into a female cavity mold.
DETAILED DESCRIPTION
[0037] In this disclosure, terms such as horizontal, upright,
vertical, above, below, beneath, and the like, are used solely for
the purpose of clarity in illustrating the subject matter disclosed
herein, and should not be taken as words of limitation. The
drawings are for the purpose of illustrating the subject matter
disclosed herein and are not intended to be to scale.
[0038] The subject matter of this disclosure relates to various
embodiments.
[0039] Thermoformable Stack
[0040] In one embodiment, the subject matter of this disclosure
relates to a thermoformable stack. The stack includes a first sheet
of a thermoformable polymer and at least a second polymeric sheet
(sometimes referred to herein as a "liner" sheet) that overlaps the
first sheet at an overlapping region. The first and second sheets
can have the same composition and thickness, or these
characteristics can be different. The stack can include multiple
second polymeric sheets (made of the same or different polymers and
having the same or different thicknesses). The stack can also
include sheets of other materials, such as metal sheets. A layer of
a first barrier composition is interposed between faces of the
first and second sheets in at least a portion of the overlapping
region, preferably including substantially all of the first
surface. The first barrier composition prevents fusion of the
surfaces of the first and second sheets at the thermoforming
condition. When the stack is subjected to the thermoforming
condition, the first sheet assumes a thermoformed shape, the shape
of the second sheet conforms to the shape of the first sheet, and
the first and second sheets do not fuse in the portion of the
overlapping region.
[0041] When the stack includes at least one pressure-deformable
sheet, such as a metal sheet, as a first and/or second sheet, the
stack can be shaped using ordinary bending, stamping, and other
pressure-based shaping methods. Such stacks preferably include
first and second sheets that can withstand pressure, shear,
deformation, and stretching forces inherent in pressure-based
shaping methods without tearing or becoming punctured. By way of
example, thin, stretchable nylon sheets can be adhered to an
aluminum sheet, with a first barrier composition interposed between
the aluminum sheet and the adjacent nylon sheet and a second
barrier composition interposed between adjacent nylon sheets. Such
an aluminum/nylon stack can be subjected to a press that deforms
the aluminum sheet into a desired shape, with the nylon sheets
stretching to match the shape without becoming substantially
de-adhered from the surface of the aluminum sheet or from one
another. In this manner, shaped metal objects having peelable
polymeric layers can be made, as can articles made from other
pressure-deformable materials (e.g., uncured ceramic pastes).
[0042] The second sheet is made of a material that is selected such
that it is capable of maintaining its structural integrity at a
thermoforming condition at which the first sheet can be
thermoformed. The second sheet is capable of conforming to the
shape of the first sheet as the first sheet is thermoformed at the
thermoforming condition. If desired, the second sheet can be a
material that is also thermoformable at the thermoforming
condition, but this is not a requirement. However, if a
non-thermoformable second sheet is used, the second sheet may
detach, deform, or pull away from the first sheet following
thermoforming. Even if the second sheet is thermoformable, these
behaviors can nonetheless manifest themselves if the first and
second sheets are made of different materials (owing, for example,
to different coefficients of thermal expansion). When the second
sheet is a non-thermoformable material, the characteristics of the
second sheet and any adhesive in the adjacent barrier compositions
should be selected to retain the desired configuration of first and
second sheets in the finished article. By way of example, if one or
more of the second sheets is an elastic material, then the elastic
material should be selected such that it can temporarily deformed
at the thermoforming conditions, the adhesive(s) should be selected
such that they will adherently oppose the tendency of the elastic
material to resume its original shape after thermoforming, or some
combination of these. An adhesive in the interposed barrier
composition can thereby cause a second sheet to remain conformed to
the shape of the underlying thermoformed surface, even if the
second sheet itself is not thermoset at the thermoforming
temperature.
[0043] One or more tabs can be interposed between the first sheet
and second sheets. If a tab extends beyond an edge of either sheet,
the tab can be used to facilitate separation of the first and
second sheets after thermoforming. The tab can be adhered to either
sheet or to neither.
[0044] In one embodiment, the tab is relatively fixedly adhered to
the second sheet and either peelably adhered to or not adhered to
the first sheet, such that the second sheet can be peeled from the
first by grasping the tab and pulling the second sheet away from
the first by way thereof.
[0045] In a second embodiment, the tab is relatively fixedly
adhered to the first sheet and either peelably adhered to or not
adhered to the second sheet, such that the second sheet can be
peeled from the first by scratching (e.g., with a fingernail or an
edged instrument, such as the tine of a fork) the edge of the
second sheet that overlies the tab to begin partial peeling of the
second sheet at the location of the tab, and then grasping the
partially peeled portion of the second sheet and manually peeling
the remainder of the second sheet away from the first by pulling on
the partially peeled portion. In this second embodiment, if the
second sheet is peelably adhered to the tab (i.e., rather than not
adhered at all to the tab), then adhesion of the second sheet to
the tab can exclude materials (e.g., dust, liquids, or food
particles) from the space between the tab and second sheet,
rendering the tab surface clean upon peeling the second sheet
therefrom. This can be of particular significance in applications
(e.g., in food service containers) in which preservation of a
sanitary surface upon peeling is desired.
[0046] Although a loose stack of polymeric sheets can be
thermoformed using the materials and methods described herein, it
can be convenient to bind the first and second sheets to one
another (and to bind multiple second sheets together, where
multiple second sheets are present) prior to thermoforming (e.g.,
to facilitate combination, storage, shipping, handling,
manufacture, and alignment of the sheets). The means used to bind
the sheets to one another is not critical, but preferably does not
affect the properties of the sheets in the region(s) of the sheets
that are to be thermoformed. By way of example, the sheets can be
bound together using a glue applied to a common edge of the first
and second sheets, by fusion of a common edge of the first and
second sheets, by stapling the first and second sheets together, by
adhering the sheets together using an adhesive applied between the
sheets at an inter-sheet area distinct from the shaped section of
the sheets, or by other means.
[0047] In order to prevent detachment or deformation of the second
sheet away from the first sheet after thermoforming, the first
barrier composition can include an adhesive that peelably adheres
the first and second sheets. By incorporating such an adhesive into
the first barrier composition, thermoformed articles can be made in
which the second sheet can be peeled away from the first sheet,
preferably (i.e., by judicious selection of an adhesive) without
tearing either of the first and second sheets. All, or only a
portion, of the overlapping region can be coated with the
adhesive-containing first barrier composition. When a tab is
interposed between polymer sheets, the tab can be adhered to the
adhesive and used to pull the edge of the sheet to which the tab is
adhered away from the adjacent sheet to which the tab is not
adhered. In alternative configurations, the adhesive can be
incorporated into the barrier composition or the adhesive can be a
composition discrete from the barrier compositions. By way of
example, a barrier composition having perforations or holes
therethrough can be interposed between sheets and a separate
adhesive interposed between the sheets on one side of the barrier
composition (i.e., the adhesive contacting both sheets through the
holes or perforations), with the adhesive preventing fusion of the
sheets, but adhering them where it is present and the barrier
composition preventing fusion of the sheets where the adhesive is
not present.
[0048] An important embodiment of the subject matter disclosed
herein is a stack (sometimes referred to herein as a "master pad
roll" when provided in the form of a rolled stack) of overlapping
polymeric sheets. This stack includes the first sheet, which is a
thermoformable polymer, and at least one, and preferably a
plurality (e.g., 2, 3, 6, 10, or 20), of second polymeric sheets.
Each second sheet overlaps the first sheet at the overlapping
region, is capable of maintaining its structural properties (i.e.,
each sheet maintains its integrity and, preferably, its pliability
and approximate thickness) at the thermoforming condition, is
capable of conforming to the shape of the first sheet as the first
sheet is thermoformed at the thermoforming condition, and has a
layer of a second barrier composition interposed between it and
each adjacent second sheet in a portion of the overlapping region.
The first barrier composition prevents fusion of the surfaces of
the first sheet and the adjacent second sheet at the thermoforming
condition. The second barrier composition (which may be identical
to the first) prevents fusion of the surfaces of adjacent second
sheets at the thermoforming condition. When the stack is subjected
to the thermoforming condition, the first sheet assumes a
thermoformed shape, the shape of each of the second sheets conforms
to the shape of the first sheet, and the sheets do not fuse in the
portion of the overlapping region. In this embodiment, each of the
second sheets can have different, identical, or substantially the
same composition. Likewise, the compositions of the first sheet and
any or all of the second sheets can be different, identical, or
substantially the same.
[0049] As with the first barrier composition, the second barrier
composition can include an adhesive (i.e., the same adhesive as the
first or a different adhesive). Such a second barrier composition
peelably adheres adjacent second sheets. An article made by
thermoforming a stack of this sort will have multiple peelable
layers. Such articles are desirable when, for example, a renewably
clean and/or sanitary surface is required of an article, and
particularly in situations in which cleaning of the surface is
difficult, time-consuming, distasteful, or hazardous. In one
embodiment, an article having a relatively thick (e.g., 10 to 40
mils) base (substrate) layer made from a thermoformed polymer can
have multiple thin (e.g., 1 to 7 mils) peelable layers that are
separately peelably adhered to the base in a stacked configuration.
The base can provide shape and rigidity to the article (e.g., a
paint tray, a toilet seat, or a food service container), and the
peelable layers can provide a renewably clean surface upon peeling
of individual layers.
[0050] The stack described herein has at least one second sheet on
at least one face of the first sheet, as described above. Multiple
second sheets can be arranged on the first sheet, adjacent one
another, at a distance from one another, overlapping one another,
or any combination of these. The second sheets can be stacked atop
one another, with the edges of the stacked second sheets coinciding
perfectly or nearly perfectly with one another, with the edges of
each stacked second sheet completely covering one or more edges of
the sheet over which it is stacked, with the edges of each stacked
sheet receded away from one or more edges of the sheet over which
it is stacked, or any combination of these. Furthermore, second
sheets can be arranged on one or both faces of the first sheet. On
each face of the first sheet, there can be a single second sheet,
multiple non-overlapping second sheets, multiple
partially-overlapping second sheets, or multiple stacked second
sheets.
[0051] When tabs are interposed between adjacent sheets, at least a
portion of the tab should extend beyond an edge of one of the
adjacent sheets, to facilitate grasping of the tab, the edge of the
sheet, or both. If an adhesive is interposed between the adjacent
sheets, the tab can facilitate peeling of the adjacent sheets,
particularly if the adhesive completely fills the gap (i.e., all
the way to the edges of the sheets) between the adjacent sheets. If
no adhesive is interposed between the adjacent sheets, the tab can
nonetheless facilitate separation of the adjacent sheets by
relieving any pressure or electrostatic attraction in the
inter-sheet gap, by providing a region in which electrostatic
forces between the sheet surfaces are disrupted, or simply by
providing a mechanical lever by which expansion of the inter-sheet
gap can be initiated.
[0052] In an advantageous embodiment, tabs are interposed between
sheets in such a manner that the tabs between sheets alternate
between one side of the shaped article (or stack) and the other
side, for example so that peeling a sheet using a tab interposed
between the top sheet and the next (i.e., underlying) sheet on the
right side of the shaped article exposes a tab interposed between
the next sheet and the third sheet on the left side of the shaped
article. (See, e.g., FIG. 11.) Particularly when stack materials
are provided in rolled form, it can be advantageous to have the
tabs arranged symmetrically along the sides of the rolls, so that
the rolled stack material has approximately the same size at both
ends of the roll.
[0053] In one embodiment, tabs extend beyond the edges of both
adjacent sheets between which the tab is interposed. In this
embodiment, the tab can be grasped independently of the sheets and
used to initiate peeling. While this embodiment has the advantages
of ease of use and visibility, it has the disadvantages that the
tabs can be unsightly and compromise sanitation (e.g., by providing
a spot at which sheets can be inadvertently peeled and an
otherwise-sanitary surface between the peeled sheets can be exposed
to environmental contaminants).
[0054] In another embodiment, the tab is fixedly adhered to one of
two adjacent sheets and peelably adhered to the other sheet, which
does not completely cover the tab. In this embodiment, the tab is
not used as a handle or grasping point for peeling either sheet to
which it is attached. Instead, the tab provides a surface (e.g., a
scratch-resistant surface) from which a portion of the sheet that
is peelably adhered thereto can be peeled by scratching, abrading,
or picking the edge of that sheet at the tab surface. When a
plurality of such tabs are used in a stack of sheets, the tabs can,
for example, be arranged such that the tab for facilitating peeling
of the uppermost (relative to the first sheet) second sheet runs
down the right of the stack, with the uppermost second sheet
completely obscuring the tab for facilitating peeling of the
underlying second sheet, which runs down the left of the stack.
Upon peeling of the uppermost sheet, the tab for facilitating
peeling of the uppermost sheet will be completely exposed (i.e.,
because the portion of that tab that was partially obscured by the
uppermost sheet prior to peeling will now be exposed), and the tab
for facilitating peeling of the underlying second sheet will be
partly exposed (part of that tab being obscured by that underlying
second sheet, which can be peeled therefrom in like manner as for
the uppermost sheet). A similar side-to-side alternating
arrangement can be used for multiple second sheets, with the width
of the sheets increasing with proximity to the first sheet (i.e.,
such that each second sheet completely obscures all but one of the
tabs underlying it and partially obscures that remaining tab (at
which peeling of the sheet can be initiated).
[0055] In embodiments in which a tab is peelably adhered to and
partially covered by an upper second sheet and relatively fixedly
adhered to an underlying (relative to the first sheet) second
sheet, it can be convenient to include on the tab indicia for
indicating the operability of the tab. For instance, because the
tab is partially covered by the upper sheet, the non-covered
portion of the tab can be imprinted with the first designation "
PEELHERE ", with the upper portion of the letters adjacent the
overlying edge of the upper sheet, to indicate the edge of the
upper sheet which should be peeled from the tab. The obscured
portion of the tab can be imprinted with the second designation
"vvvv DO NOT vvvv" immediately above the first, so that when the
upper sheet has been peeled from the tab (i.e., when the tab is no
longer useful), the full indicium [0056] "DO NOT [0057] XXXX XXXX
[0058] PEEL HERE"
[0059] (i.e., a combination of the first and second designations)
is visible. Other suitable indicia can be used.
[0060] The stack described herein can be prepared and provided in
the form of multi-sheet leaves, folded bundles, or rolls, for
example. In many polymer-processing operations, rolls of polymeric
materials are preferred for ease of handling. Rolls of the stack
described herein can be prepared simply by winding the stack about
itself, or about a core such as a paper or wooden tube or cylinder,
in a rotary fashion. In order to minimize unintended interactions
between the bottom of the stack in one layer of the roll and the
top of the stack in an adjacent layer of the roll, a release agent
can be interposed between layers of stack as it is rolled. In one
embodiment, the release agent is a sheet of a material such as
paper or waxed paper. In another embodiment, the release agent is
an oil or other liquid agent which inhibits or prevents
irreversible interaction of stack layers. By way of example, a thin
film of a silicone-based compound (e.g., a liquid
polysiloxane-containing composition, such as a silicone oil) can be
applied to the top, bottom, or both top and bottom of the stack as
it is rolled. The release agent should either be an agent which
does not affect thermoforming operations on the stack or an agent
which can be separated from the stack prior to thermoforming
operations.
[0061] Images, text, designs, or other printed matter can be
included on one or more of the sheets of the stack and articles
made by thermoforming the stack. By way of example, label text and
graphics can be printed on the outermost second sheet (i.e., the
second sheet on the "top" of the stack, having no other second
sheets atop it). Such label information can be printed on the
exterior of the sheet (i.e., on the surface of the product) or, if
the outermost second sheet is not opaque, the information can be
printed on the inner surface (i.e., first-sheet-side) of that
sheet. Such printed matter should encapsulated between the sheet
and the barrier composition that is interposed between the
outermost sheet and the adjacent sheet. Encapsulation of the
printed matter can ensure that the printed matter is peeled off
with the outermost sheet (i.e., does not adhere to the adjacent
sheet) when the outermost sheet is peeled away from the adjacent
sheet. Printed matter can be applied to the inner and/or outer
faces of any of the sheets described herein in the same manner.
Judicious selection of surface treatments (e.g., Corona treatment)
and adjacent adhesives can ensure that the printed matter remains
bound to a desired surface when the adjacent adhesive (and any
polymeric or other sheet adhered to the desired surface by the
adhesive) is peeled away.
[0062] When printed matter is included on a surface of the shaped
articles described herein, the precise materials and methods used
to print the matter on the surface are not critical, other than
that they should be selected such that the printed matter will
remain attached to the surface to which it is applied during normal
use of the shaped article (unless detachment of the printed matter
is considered acceptable). By way of example, in one embodiment of
the thermoformed, multiple-peelable-layer paint tray disclosed
herein, the outermost peelable layer is transparent and the printed
matter is applied to the underside of that layer (i.e., the face of
the layer that is adhered to the underlying surface) such that an
adhesive in the barrier composition between that layer and the
underlying surface adheres to the printed matter (and thence to the
outermost layer) when the outermost layer is peeled away from the
underlying surface. In another embodiment, the penultimate peelable
layer (i.e., the second sheet adjacent the first sheet) is
transparent and the printed matter (e.g., text reading, "This is
the final peelable layer!") is applied to the underside of that
layer (i.e., the face of the layer that is adhered to the surface
of the first sheet) such that the printed matter is removed,
together with any adhesive present in the first barrier
composition, when the penultimate peelable layer is peeled away
from the first sheet.
[0063] Included in embodiments of this disclosure are shaped
articles that include multiple, substantially identically-shaped
sheets of thermoformable polymers that overlap at an overlapping
region. Interposed between each pair of sheets, in at least a
portion of the overlapping region, is a layer of a barrier
composition. Because the barrier composition prevents the sheets
from fusing across their entire faces (i.e., the sheets do not fuse
at the portions of the overlapping region at which the barrier
composition is present when the sheets are thermoformed) the
article is separable into multiple, substantially
identically-shaped subarticles upon separation of the sheets. The
barrier composition can be omitted from at least a portion of the
gap at the overlapping portion of the sheets in order to form an
article in which the substantially identically-shaped subarticles
remain bound together at the overlapping portion that lacked the
barrier composition during thermoforming. Alternatively, that
portion of the gap can be filled with an adhesive to (reversibly or
irreversibly) bind the overlapping portions corresponding to the
sub-articles. Such bundles of subarticles can often be stored,
shipped, handled, manufactured, and used more conveniently and more
energy-efficiently than an equivalent number of separate
subarticles, and the subarticles can be separated from one another
at a convenient time and place simply by breaking, cutting, or
otherwise separating individual articles from the bound overlapping
portion. Such an article can include multiple (e.g., 2, 6, 10, or
20) discrete egg cartons, cookie trays, cups, blister packs,
computer keyboard covers, food containers, or paint tray liners
that can be separated from one another as desired. The multiple
items can have substantially the same thickness, different
thicknesses, or a combination thereof.
[0064] The subject matter described in this disclosure includes a
shaped article that includes a shaped thermoformable polymer sheet,
a plurality of second polymer sheets, and first and second barrier
compositions. The second sheets overlap the thermoformable sheet at
an overlapping region and conform to the shape of the
thermoformable sheet at substantially the entire overlapping
region. The first barrier composition is interposed between and
peelably adheres the thermoformable sheet and the adjacent second
sheet. The second barrier composition is interposed between and
peelably adheres adjacent second sheets. In an article of this
type, the second sheets are peelably removable from the article.
The article can include tabs interposed between adjacent second
sheets and a tab between the thermoformable sheet and the adjacent
second sheet. By way of example, the shaped article can be a paint
tray having peelable liner layers, as described herein. Further by
way of example, the shaped article can be a food service container,
as described herein.
[0065] Further details of the materials and methods suitable for
use in the articles, methods, and compositions described herein are
provided in the ensuing sections of this disclosure.
[0066] Thermoformable Polymer Sheets
[0067] The identity and composition of thermoformable polymer
sheets used in the articles and methods described herein are not
critical. A skilled artisan will recognize that substantially any
thermoformable polymeric material can be used. Examples of suitable
thermoformable polymeric materials include polyethylene
terephthalates, polyesters, polyethylenes (including high density
polyethylenes and high molecular weight polyethylenes),
polypropylenes, polyvinylchlorides, polystyrenes, nylons,
copolymers of these, and combinations of these.
[0068] A skilled artisan can select a thermoformable polymeric
material, or combinations of such materials, suitable for use in
substantially any application by considering such properties as the
shrink rate, crystallinity, heat deflection temperature, tear
strength, draw ratio, thickness, rigidity, melt temperature,
thermal conductivity, heat capacity, and polymer backbone
orientation of the material(s). Selection of materials can also be
guided by properties that do not necessarily directly impact the
thermformability of the materials, such as cost, color, opacity,
recycled material content, environmental impact, surface energy,
chemical resistance, and surface sheen of the materials.
[0069] In selecting appropriate materials, an artisan should
consider at least two sets of conditions: the environmental
conditions to which the finished, shaped article will be subjected
(e.g., during transportation, storage, and use) and the conditions
that the materials will experience during the thermoforming
process. Materials should be selected so as to exhibit the desired
color, shape, strength, rigidity, and peelability, for example,
once the materials have been shaped in the thermoforming process
into their final, desired form. The materials should also be
selected, together with the thermoforming conditions, so as to
allow assembly and shaping of the materials into their final,
desired form using thermoforming conditions available to the
artisan.
[0070] Peelable Polymer Sheets
[0071] The identity and composition of peelable polymer sheets used
in the articles and methods described herein are not critical. A
skilled artisan will recognize that substantially any peelable
polymeric material can be used.
[0072] In some embodiments, peelable sheets preferably have
sufficient structural integrity that they do not tear or
significantly stretch when subjected to forces necessary to peel
them from surfaces to which they are adhered with a peelable
adhesive. For example, when a paint tray having peelable surface
layers is made as described herein, each of the peelable surface
layers can preferably be peeled from the underlying surface as a
single, integral sheet (i.e., no holes or tears) while containing
paint coating its non-adhered surface. Peelable sheets that tear,
stretch, or puncture are acceptable in embodiments in which
containment of liquid within the peelable sheet is not required.
For food service containers, as described herein, the maker should
consider the characteristics of the peelable sheets at the
temperature at which the sheets are likely to be peeled (e.g.,
either room temperature or a higher or lower temperature used,
respectively, for storing heated or cooled foods).
[0073] The peelable sheets are preferably thin (e.g., 1 to 4 mils,
preferably 1-2 mils thick) and highly flexible. Sheets having a
thickness in excess of 8 mils can be difficult to peel, and so
sheets thicker than 8 mils are not preferred. The peelable sheets
can be made from substantially any polymeric material(s) and by
substantially any sheet-forming process. By way of example,
suitable polymer sheets can be made by blowing, molding, casting,
or extruding suitable polymer materials, or by some combination of
these processes. When made of thermoformable materials, the
peelable sheets are preferably thermoformed simultaneously with the
substrate sheet of thermoformable material to which they are
adhered. When made of non-thermoformable materials, the peelable
sheets should be capable of maintaining their structural integrity
at a thermoforming conditions at which the substrate sheet to which
they are adhered is thermoformable. Examples of suitable polymers
for peelable sheets include polyethylenes, polypropylenes,
polyethylene terephthalates, nylons, polyvinyl chlorides,
copolymers of these, and combinations of these.
[0074] Peelable sheets can be selected to be rigid (i.e., retain
their shape after peeling, e.g., akin to prior art molded paint
tray liners that can be lifted out of a paint tray and retain their
shape when subjected to small forces) or substantially non-rigid
(e.g., blown polymeric sheets such as the material used in trash
can liners and trash bags).
[0075] The peelable nature of an individual peelable sheet can
derive from surface attraction between the peelable sheet and the
surface underlying it. Preferably, however, an adhesive is
interposed between the sheet and the surface (e.g., in the barrier
composition) and the peelable nature of the sheet derives primarily
from the adhesive forces exerted by the adhesive upon the sheet and
the surface. An adhesive can be selected (e.g., based on the
chemical identity or the surface treatment of the peelable sheet or
the surface to which it is adhered) so that, upon peeling of the
peelable sheet, the adhesive preferentially remains adhered to the
peelable sheet, or to the surface. For instance, when the function
of the peelable sheet is to expose the surface free of adhesive and
other contaminants, the adhesive can be selected so that it both
adheres the peelable sheet and the surface and adheres more
strongly (i.e., more tenaciously) to the peelable sheet so that,
upon peeling, the adhesive is removed from the surface along with
the peelable sheet.
[0076] Differences in the tenacity with which an adhesive binds the
opposed surfaces of two polymer sheets can be controlled in a
number of ways, including by coating one or more portions of one
surface with a composition that inhibits binding of the adhesive to
the surface. Preferably, however, differences in the tenacity of
adhesive-binding are controlled by selecting or treating the
polymer sheets such that their opposed surfaces exhibit a
difference in surface energies. If the difference between the
surface energies of the two surfaces is relatively large--at least
5 Dynes--then the adhesive will bind significantly more tenaciously
to one surface than the other. As the difference in surface
energies of the two surfaces increases beyond 5 Dynes, the
likelihood that all of the adhesive will remain with one sheet when
the two sheets are separated increases. A difference of 5 to 14
Dynes between the adhered surfaces of the two sheets is considered
appropriate.
[0077] It may be possible to separate two surfaces having an
adhesive interposed between them, even if the surface energies of
the surfaces differ by less than 5 Dynes. In this situation, the
adhesive may adhere to each of the two surfaces with roughly equal
tenacity, meaning that the adhesive may adhere to both surfaces (at
various portions) after the two surfaces are separated from one
another. In many applications, it is desirable to have most or all
of the adhesive to adhere to the surface of only a single one of
the polymer sheets (usually the one being peeled away from the
remaining sheets or substrate). For such applications, the two
surfaces contacted by the adhesive should preferably have surface
energies that differ by at least about 5 Dynes.
[0078] The amount of force needed to separate peelable sheets from
their underlying surface is not critical, but is preferably
sufficiently small to prevent tearing and substantial stretching of
the peelable sheet upon manual peeling of the sheet from the
surface. The amount of separation force needed is a function of the
materials selected for the peelable sheets, the underlying surface,
and any barrier composition or adhesive interposed between them.
Practically speaking, the tenacity of adhesion between a peelable
sheet and the underlying surface should be selected so that the
sheet can be peeled away from the surface using normal human
strength, but not so tenacious that the sheet must be torn or
punctured by a person peeling the sheet from the surface. A skilled
artisan recognizes that the numerous variables (e.g., the angle at
which the sheet is pulled from the surface, whether fingernails are
applied to the sheet surface, the speed with which the sheet is
peeled, the temperature of the shaped article at the time of
peeling) can affect the peeling characteristics of the sheet, and
the materials described herein include all materials that are
operable under the ambient conditions corresponding to anticipated
uses of the materials and shaped articles.
[0079] To the extent that an objective measure of the force needed
to peel a sheet from an underlying substrate surface is desired, a
standardized test of peel strength can be used. An example of a
suitable test is ASTM D3330/D3330M, which is a standardized test
for peel adhesion of pressure-sensitive tape. A modification of
this procedure (e.g., substituting a sheet of the substrate
material in place of the standard steel sheet in ASTM D3330/D3330M
and selecting a peel angle appropriate for the intended use of the
shaped article being tested) can also be used. In each case, the
characteristics of the shaped article or stack should be selected
such that the peel strength of the finished article is within the
limits of human strength.
[0080] Various surface treatments and polymer sheet ingredients can
be used to affect the surface energy
[0081] In one embodiment of the stack and shaped articles described
herein, multiple adjacent polymer sheets are made of the same
material. Unless treated non-identically, the two faces of a
polymer sheet will normally have the same surface energy.
Therefore, in stacks and articles which include multiple identical
polymer sheets, it is important that the two faces of the identical
polymer sheets (e.g., the adhesion and sanitary faces of second
sheets of food service containers described herein) be treated
differently, so as to yield a polymer sheet having different
surface energy values for each of its two faces. Such sheets are
preferably treated such that the surface energies of their faces
differ by 5 Dynes or more. Many compositions and methods for
affecting the surface energy of polymer sheets are known to skilled
artisans in this field, and substantially any of those methods may
be employed. Such methods include conventional surface finishing
techniques such as grinding and polishing, annealing processes,
Corona treatment, and plasma contact techniques such as
atmospheric, chemical, and flame plasma techniques. Compositions
for affecting the surface energy of a surface of a polymer sheet
are also well known, and include compounds that can be contacted or
reacted with the surface to modify its chemical or physical
properties (affecting its surface energy).
[0082] An example of a suitable surface treatment is the process
known as Corona treatment or Corona discharge treatment, which
involves application to a surface of a high-frequency, high voltage
electrical discharge. Corona treatment raises the surface energy of
a polymeric surface. Applied to one face of a polymer sheet having
two otherwise identical faces, Corona treatment will raise the
surface energy of the face, relative to the opposite face of the
sheet. The power applied in a Corona treatment can be controlled to
limit the treatment substantially to one side of a sheet. At very
high power, the treatment can raise the surface energy of both
faces of the same sheet which, in the absence of other surface
treatments, will not yield a polymer sheet having different surface
energies on its two faces. If a polymer sheet is Corona treated at
or near the time it is formed, the surface energy-raising effects
of the treatment can endure for weeks, months, or years. If the
sheet is Corona treated days, weeks, or later after the sheet is
made, the surface energy-raising effects of the treatment can be
more transitory (e.g., enduring only for days or weeks). Polymer
sheets that are Corona treated at or very near the time they are
formed can be used in the stacks and articles described herein.
Polymer sheets can also be "bump-treated" (i.e., be Corona treated
regardless of how long it has been since the sheet was formed)
shortly before making the stacks and articles described herein.
[0083] Peelable sheets can be made from clear, translucent, or
colored materials, ingredients and method for imparting each of
these characteristics being known in the art. Colorants and opacity
agents should be selected in view of the intended use of the
container. By way of example, non-toxic, and preferably
substantially non-leaching, agents should be used in food service
containers as described herein. Where a shaped article is desired
to have a selected color, that can be achieved by making the
peelable sheets that color, or by making the rigid sheets that
color and the peelable sheets clear or substantially
transparent.
[0084] Barrier Compositions
[0085] The identity and composition of barrier compositions
interposed between polymer sheets used in the articles and methods
described herein are not critical. A skilled artisan will recognize
that substantially any material can be used as a barrier
composition between two polymers, so long as it substantially
prevents fusion of two polymers under conditions at which at least
one of the polymers can be thermoformed. A wide variety of such
compositions are known for this purpose.
[0086] Examples of suitable barrier compositions include adhesives
(e.g., peelable adhesives such as pressure-sensitive adhesives),
known polymer release agents, a polymeric or paper film interposed
between polymer layers, and various liquids, including
low-viscosity silicone oils.
[0087] A composition interposed between two surfaces (e.g., between
the first and second polymer sheets, or between two second polymer
sheets, as described herein) can act as a barrier composition
between the two surfaces if the composition coats at least one of
the two surfaces at a thermoforming condition, thereby preventing
surface-to-surface contact and fusion of the two surfaces at the
thermoforming condition.
[0088] A barrier composition prevents fusion of opposed polymeric
surfaces only when it is interposed between the surfaces at the
thermoforming condition. For that reason, the barrier composition
must be interposed between the surfaces over the entire area for
which fusion between the surfaces is not desired. This can be
achieved in various ways, including use of liquid and solid barrier
compositions. When a stack is to be thermoformed to make a
plurality of shaped objects that are not fused over some portions,
but fused at at least one portion (e.g., a stack of cookie trays
fused only at a single, frangible extension of the trays at one
corner), the barrier composition is interposed among the polymer
sheets in the non-fused areas, but is not interposed between the
polymer sheets in the area in which fusion is desired. Multiple
barrier compositions can be interposed between different portions
of a pair of sheet such that, together, the barrier compositions
cover at least one surface of the two sheets at every overlapping
portion and prevent fusion between the two sheets. If desired,
certain portions can be left uncovered by barrier compositions,
such that those portions fuse or adhere to one another upon
thermoforming (e.g., if peeled sheets are to remain attached to the
surface from which they are peeled).
[0089] Liquid barrier compositions should be selected such that
they completely coat (i.e., wet) at least one of the surfaces over
the entire area for which fusion is not desired. This can be
achieved by selecting a liquid barrier composition (i.e., a
composition that is a liquid at at least the thermoforming
condition, regardless of whether it is a liquid at which it is
contacted with the surface) that has a surface tension
significantly greater (i.e., at least 2 Dynes, and preferably at
least 10 Dynes greater) than the surface energy of the surface with
which it is contacted. This surface energy difference should ensure
that the liquid barrier composition completely wets (i.e., coats)
the area of the surface for which fusion is not desired.
Preferably, the liquid barrier composition has a surface tension
significantly greater than the surface energy of both surfaces, so
that the liquid is not displaced from between the surfaces at
points at which the two surfaces are urged tightly against one
another.
[0090] Solid barrier compositions (e.g., polymer sheets) should be
selected so that the solid covers the entire area for which fusion
is not desired. The identity of the solid is not critical, so long
as it does not prevent the portions of a polymer sheet that are to
be thermoformed from reaching the thermoforming condition. Solid
barrier compositions can prevent fusion of the surfaces (and/or)
fail to fuse to one or both surfaces for a variety of reasons, any
of which are sufficient to render a material suitable as a solid
barrier composition. Some solids can be predicted to act as
suitable barrier compositions, while other may require empirical
testing (e.g., thermoforming two sheets of the polymer with the
solid interposed between them) in order to determine their
suitability. Either way, selection of an appropriate solid barrier
composition is within the ken of a skilled artisan in this
field.
[0091] Another type of barrier composition that can be used is a
composition incorporated as an additive into one or both of the
polymer sheets. These compositions melt and "bloom" to the surface
of a polymer when heated, pressed, stretched, or otherwise
manipulated. If such a composition is included in one or both of
the polymer sheets such that the composition blooms at the surface
of at least one sheet at the thermoforming condition and prevents
contact between the polymer sheets themselves, then the composition
can be used as a barrier composition in the articles and methods
described herein. A wide variety of compositions that exhibit such
blooming behavior are known in the art.
[0092] Adhesives
[0093] The identity and composition of adhesive interposed between
polymer sheets used in the articles and methods described herein
are not critical. A skilled artisan will recognize that
substantially any material can be used as an adhesive between two
polymers, so long as it reversibly binds the two polymer layers (at
least when peelability of the two sheets is desired) and requires
no more force to separate the polymer layers than can be
practically applied to the polymer layers by a person of ordinary
strength. A wide variety of such compositions are known for this
purpose.
[0094] The adhesives used between a peelable polymer sheet and an
underlying surface are preferably peelable, meaning that the
polymer sheet can be peeled from the surface by a person of
ordinary strength, preferably without tearing or substantially
stretching the sheet. Preferably, an adhesive having a coat weight
of roughly 0.6 to 15 ounces per inch is used to adhere a peelable
sheet to an underlying surface. A skilled artisan in this field is
able to select a standard coat weight for a given adhesive,
empirically determine an appropriate coat weight, or both. Thus,
selection of an appropriate amount of adhesive is well within the
ken of an ordinarily-skilled artisan in this field.
[0095] A wide variety of suitable adhesives are known in the art
and can be used as described herein. Pressure-sensitive adhesives
are among the suitable adhesives that can be used. Likewise,
adhesives that adhere preferentially to one of two adhered
surfaces, upon peeling of one of the surfaces away from the other)
are suitable and are preferred in certain embodiments. By way of
example, if an adhesive adheres more strongly to a peelable polymer
sheet than to a surface to which the sheet is adhered by the
adhesive, the adhesive will tend to remain with the sheet when it
is peeled from the surface.
[0096] Various compounds and surface treatments can be used to
reduce the force needed to pull an adhesive from a surface, and
such compounds and treatments can be used to modulate adhesion of
an adhesive to a surface described herein.
[0097] Specific examples of adhesives that can be used in the
articles described herein include polysiloxane-based adhesives,
rubber cement, and acrylic adhesives (e.g., waterborne
pressure-sensitive, acrylic adhesives of the MULTI-LOK.TM. brand
family of acrylic adhesives manufactured by National Adhesives of
Bridgewater, N.J.).
[0098] Printing
[0099] Text, images, or other graphical material can be printed
onto one or more faces of one or more of the polymer sheets
described herein. A wide variety of materials and methods can be
used to print such material onto the surface of a polymer sheet. A
difficulty inherent in printing on polymer materials is that the
printed matter can often easily be displaced from the polymer
surface by heat, light, or mechanical abrasion, leading to reduced
print quality. Furthermore, it can be undesirable for the materials
used for printing to contact materials that will be in contact with
the polymer. For example, it can be undesirable to have printing
inks contact paint on the interior surface of a paint tray or food
on the interior surface of a food service container. These effects
can be avoided by applying a clear polymer sheet or layer over top
of the printed matter, thereby securing it in place and preventing
its displacement. However, the clear layer often cannot be peeled
off without severely damaging the printed matter and/or leaving
portions of the printed matter on the peeled sheet and the
underlying surface.
[0100] In one embodiment of the stacks and shaped articles
described herein, printed matter is incorporated between polymer
sheets and is peelable coherently with one sheet. In this
embodiment, the printed matter is printed (preferably "reverse"
printed, in that the printed matter is intended to be viewed
through the sheet, rather than by viewing the printed surface of
the sheet) onto the face of a clear (or at least translucent or
not-completely-opaque) polymer sheet, and that face of the clear
sheet is adhered to an underlying sheet. The tenacity with which
the printed matter clings to the clear sheet and the tenacity to
which adhesive overlying the printed matter clings to the printed
matter (and thence to the clear sheet) is greater than the tenacity
with which the adhesive overlying the printed matter adheres to the
underlying sheet. Thus, when the clear sheet is peeled away from
the underlying sheet, the printed matter (and the adhesive
overlying it) come away with the clear sheet, leaving the
underlying surface free of adhesive and/or printed matter.
[0101] The tenacity of binding of printed matter to a polymer sheet
can, as described herein for adhesives, be affected by surface
treatment of the polymer sheet prior to printing upon it. Corona
treatment and plasma discharge techniques, for example, can raise
the surface energy of a polymer surface, rendering it susceptible
to more tenacious binding by the printed matter. Likewise, surface
treatment (e.g., Corona treatment) of a polymer surface having
printed matter thereon can raise the surface energy of the surface
(including the portion on which the printed matter appears). By
applying to the printed portion of the surface an adhesive that
adheres more tenaciously to the printed portion than to the opposed
underlying surface, adhesion of the adhesive with the printed
matter can be maintained upon peeling of the sheet carrying the
printed matter from the underlying surface.
[0102] In another embodiment, a release agent can be interposed
between adhesive contacting a sheet having printed matter carried
thereon and an opposed surface. The release agent overlies the
printed matter and prevents (or weakens) binding between the
adhesive that contacts that printed matter and the portion of the
opposed surface that is adjacent the printed matter on the sheet.
When the sheet is peeled from the surface, the poor (or lack of)
adhesion between the sheet and the surface in the region where the
printed matter occurs prevents damage to the printed matter, which
is peeled off with the sheet.
[0103] Thermoforming Apparatus and Conditions
[0104] The articles described herein can be made using known
thermoforming apparatus and conditions. Of course, the apparatus
and conditions should be selected based on the identity and the
characteristics of the materials to be processed. Selection of
appropriate thermoforming conditions, based on the identity(ies) of
the materials to be processed is within the ken of a skilled
artisan in this field.
[0105] Paint Trays and Other Thermoformed Articles
[0106] In one embodiment, the subject matter disclosed herein
includes a paint tray with a plurality of peelable liners that are
simultaneously thermoformed with the tray, with the liners being
thermoformed to the shape of the tray interior surface at the same
time the tray is formed. As used herein, the term "thermoformed" is
intended to encompass various methods of shaping a thermoplastic
sheet or stacked sheets by heating the sheet and applying a
pressure differential to the opposed side of the sheet to conform
the sheet to the shape of a mold surface.
[0107] While the subject matter of this disclosure is occasionally
described in terms of the preferred embodiment of simultaneously
thermoforming a substrate and a plurality of liner sheets or
simultaneously thermoforming a plurality of similar thin wall
substrates with a release agent/barrier on the inner or bottom
surface, it will be understood after reading the disclosure that
the subject matter also includes simultaneously forming a substrate
and a single liner sheet, and shaping the liner sheets and
substrate by other means, e.g., by stamping, injection molding or
blow molding. The substrate, while preferably a thermoformable
plastic, may also be of other materials, e.g., metals.
[0108] In one example of thermoforming known as vacuum molding, a
sheet is positioned adjacent a female (or male) mold section and a
vacuum is applied to draw the sheet against the mold surface. A
male mold section may be pressed against the sheet on the opposite
side of the sheet from the female mold section to assist in
conforming the sheet to the shape of the female mold section. In
other processes, such as pressure forming, the heated sheet is
pressed against a male mold section (or, more frequently, into a
female mold section), usually with the assistance of a vacuum to
conform the sheet to the mold shape.
[0109] In a preferred embodiment of the subject matter disclosed
herein, at least one, and preferably a plurality of stacked planar
sheets of thin plastic serving as disposable liners ("liner
sheets") are positioned on a surface of a planar substrate sheet of
a greater thickness to be formed into a paint tray or other shaped
article (e.g., a food service container). The combination of liner
sheets and a single substrate makes a "stack" (as disclosed
elsewhere herein) or "tray sheet" when the stack is used for making
trays. The liner sheets will preferably be significantly thinner
than the substrate sheet, e.g., the liner sheets may be from about
1 mil to about 6 mils thick, while the substrate sheet may be from
about 10 mils to about 40 mils thick.
[0110] Each liner sheet has an adhesive on its inner or bottom
surface to secure the liner sheets to the immediately adjacent
sheet, with the innermost or bottom liner sheet being adhered to
the top surface of the substrate sheet. Preferably, the adhesive
backing is a uniform coating of adhesive over the entire inner
surface of the sheets except where tear tabs are located. While
applying the adhesive in making the liner sheets, the tabs can be
added in line, anywhere in part or whole around the perimeter of
where the tray will be formed. This can be done by deadening the
adhesive. Tabs are applied to each liner sheet to facilitate
separation of the sheets. Suitable adhesives will be apparent to
one skilled in the art, the requirement being that the adhesive is
a peelable adhesive, i.e., an adhesive that will permit separation
of one liner sheet from another liner sheet or the substrate
without tearing the liner sheet.
[0111] The tray sheets can be shipped in either sheet form or roll
form. For convenience in shipping, storage, and thermoforming, the
tray sheet may be provided to the thermoformer in a continuous roll
form ("master pad roll"). The roll can be continuously fed through
the thermoformer, with each length of tray sheet being indexed,
then thermoformed into a shape, i.e., paint tray. The roll length
and width can be as desired. For example, the master pad roll can
be 5'' to 48'' in width. As another example, the master pad roll
can be 60'' in width.
[0112] The combined stack of sheets (i.e., stack or tray sheets),
is thermoformed as a unit into the shape of the desired product,
e.g., a paint tray with the liner sheets being on the interior of
the paint tray. Upon cooling, the tray sheet maintains its
thermoformed configuration due to the thickness of the substrate
sheet, while the configuration of the liner sheets is assisted by
the presence of the adhesive backing.
[0113] The paint tray is used like one would use an ordinary paint
tray that does not have a liner. However, unlike the prior art
trays described above, there is no need to place a preformed liner
into the tray or attempt to hand shape a sheet of thin plastic to
conform to the tray interior. After use, the upper liner sheet can
be simply peeled away along with the paint residue, exposing the
next liner sheet as a clean paint tray ready for use.
[0114] The mold, and thereby the thermoformed tray system, can be
of various shapes. Generally, the resultant tray will have an
open-top interior cavity with a floor and continuous side walls.
The paint tray may include at least one paint well and a flat
section, normally ridged, for removal of excess paint from a roller
dipped into paint within the paint well. In a preferred embodiment,
the improved tray may be comprised of two paint wells divided by a
horizontal, flat central section so that paint can be placed in
both wells. The flat section is connected to opposed ramps tapering
upwardly from the paint wells.
[0115] In another embodiment of the subject matter disclosed
herein, multiple containers such as plastic egg cartons, cookie
trays, dessert gelatin containers, blister packs, rigid paint tray
liners etc., are produced by simultaneously thermoforming multiple
layers of plastic sheets having the same thickness. Sheets used in
this application are generally from about 0.006'' to about 0.025''
thick. Preferably, a stack of sheets, e.g., from 4 to 6 sheets, are
provided to the thermoformer in roll form. A release agent, e.g., a
coating, adhesive barrier or release film is applied between the
sheets to prevent the sheets from melting/bonding together during
the thermoforming process, and to allow the finished containers to
be separated easily (e.g., a form of silicone may be introduced
between the layers of sheets. A zone coat of adhesive (e.g., 1 inch
wide) may be applied along the edge of the substrate to allow for
easier transport of the rolls of substrates and sheets by keeping
the material together in roll form more effectively. Stacks of
sheets are thermoformed by being drawn or pressed into a mold
having the desired cavity shape.
Descriptions of Embodiments Illustrated in the Drawings
[0116] As illustrated in FIGS. 1 and 5, tray sheet 10, comprised of
a plurality of liner sheets 12 and a bottom substrate sheet 14, is
shipped to the thermoformer as a roll 16.
[0117] As illustrated in FIG. 2, tray sheet 10 is pulled via the
thermoforming machine from roll 16 and positioned within a
thermoforming apparatus comprised of upper and lower heaters 22 and
23 to heat the sheet to a moldable state. While both ovens can be
heated simultaneously, they also may need to be adjusted
independently of one another. The heated sheet is then pulled
further to a position over a vacuum source 24 as illustrated in
FIG. 3. A female mold 26 conforming to the desired shape of the
tray system is positioned in communication with vacuum source 24.
Heated sheet segment 10 is lowered onto mold 26 and a vacuum is
drawn on mold 26 with vacuum source 24, shaping sheet segment 10 to
the interior contours of mold 26 as shown in FIG. 4. The molded
tray system is then cooled and ejected from mold 26, and edge
trimmed if desired.
[0118] The resultant product is a thermoformed tray system
comprised of a substrate sheet in the shape of the desired tray,
with a plurality of liner sheets stacked thereon and held in place
by adhesive layers, both natural or man made, between the liner
sheets and the lowermost liner sheet and the upper surface of the
substrate sheet. All sheets are molded into the shape of the
desired tray.
[0119] A preferred paint tray 30 is illustrated in FIG. 6. Tray 30
is comprised preferably of a horizontal, flat central shelf 32 with
ridges 34 to remove excess paint from a paint roller rolled across
shelf 32, down ramps 40 and paint wells 36 and 38 on opposite sides
of ramps 40. Tear tab 42 can be located anywhere on the perimeter
of all liner sheets, or all or part of the entire perimeter of the
liner sheet can form a tab 43 for use in separating the liners. An
alternative tray configuration is illustrated in FIG. 7, showing
the addition of feet 44 for added stability.
[0120] Various other means may be used to include tabs to
facilitate separation of the tapes. For example, as shown in FIG.
8, the layers of liner sheets 50 may be stepped during the
converting process where the substrate 52 and liner sheets 50 are
formed into a roll. The resulting look will be like steps 54 on the
edges, allowing the consumer to see the edges of all the
layers.
[0121] In another alternative shown in FIG. 9, the liner sheets 60
may be "strip coated" before it is made into the roll form. That
is, adhesive is applied to the body of the liner sheets 60, except
for the area of the tabs 62. Thus, the liner sheets 60 have
adhesive except for the edges (e.g., 1/2''), either on one side or
both sides of the liner sheets. The end result is the edges of the
paint tray will have no adhesive on the "tabs" 62, allowing the
consumer to identify and begin peeling the layers.
[0122] Yet another alternative as shown in FIG. 10, is to use
actual separate tabs 70 on the edges of the liner sheets 72 to
distinguish between layers. The separate tabs 70 could be tape/film
of plastic or paper (e.g. 3/4'' wide, with or without adhesive) to
be applied on the ends of the protective tape on either the top or
bottom preferably the bottom (this side of the protective tape has
the adhesive). This tape/film could be of various colors and
designs and will serve as an aid for the consumer to pull apart the
layers of liner sheets 72.
[0123] Yet another alternative is shown in FIG. 11, using actual
separate tabs 56 on the edges of the liner sheets 66 to distinguish
between layers, however tabs 56 are applied on opposing edges of
sequencing liner sheets 66, while liner sheets 66 are shifted,
creating a pitter patter effect with tabs 56 hidden underneath top
liner sheets 66 until top layer is removed. The separate tabs 56
could be tape/film of plastic or paper (e.g. 3/4'' wide, with or
without adhesive) to be applied on the ends of the protective tape
on either the top or bottom, preferably the bottom (this side of
the protective tape has the adhesive). This tape/film could be of
various colors and designs and will serve as an aid for the
consumer to pull apart the layers of liner sheets 66.
[0124] While the subject matter disclosed in this section is
described primarily in terms of the manufacture of a paint tray
with a stack of thermoformed sheet liners conforming to the
interior dimensions of the paint tray, it will be apparent that the
broad concept of the subject matter disclosed herein can be
modified for other applications. For example, as illustrated in
FIGS. 12 and 13, instead of simultaneously shaping the substrate
that forms the tray or other product and the liner sheets, the
substrate can be initially formed into the tray, or the tray can be
otherwise manufactured. A pad of liner sheets 80 can then be formed
within the tray. That is, a mold of the image of the product, e.g.,
paint tray 82, is suspended above the product (e.g., paint tray in
plastic or metal) and sandwiched in between is a continuous roll of
liner sheets 80. The paint tray will be moving along a conveyor 84
and when the paint tray is nested opposing the mold image of the
product 86, the two parts are "stamped" together, thus creating the
finished product with the pads of liner sheets.
[0125] In another alternative illustrated in FIGS. 14-16, multiple
layers of plastic sheets 90 having the same thickness, instead of
liner sheets, can be thermoformed simultaneously, in order to make
multiple products. Applications for this would include various
containers such as plastic egg cartons, cookie trays, dessert
gelatin containers, computer keyboard covers, blister packs,
(non-peelable) food service containers, rigid paint tray liners
etc. The multiple plastic sheets that can be used are analogous to
the substrate (i.e., relatively rigid) material used in the
peelable articles described herein, rather than the liner sheets
which are more stretchable and pliable (i.e., like a garbage bag)
but generally unable to retain their shape under the influence of
gravity unless adhered to a more rigid body such as the substrate.
That is, the plastic sheets 90 that can be used in this process can
be of a lesser thickness than the paint tray (i.e., they can be
less than 30 mils thick), but they are generally not as thin as the
liners (i.e., they are thicker than 1-2 mils).
[0126] By way of example, this simultaneous multi-article
thermoforming process can thermoform a stack that is 3 to 6 layers
thick (i.e., 3-6 thermoformable plastic layers having appropriate
barrier compositions therebetween) and delivered in roll form. A
greater number of thermoformable sheets (e.g., 10) can also be
simultaneously formed and thereafter separated. However, the
process can be limited by the thickness of the stack, whereby a
stack that cannot practically be heated to a thermoformable
temperature within a commercially reasonable time, without melting
exterior layers, or that is too thick to be thermoformed may be
impractical. The upper limit on the thickness and number of sheets
in the stack depends on the materials used in the stack layers and
can both be understood by a skilled artisan in this field and
empirically determined through ordinary trial and error procedures.
For instance, the maximum practical thickness of a stack of
materials that exhibits a relatively low thermal conductivity may
be about 50 mils, while the maximum practical thickness of a stack
of materials that exhibits a greater thermal conductivity may be
about 70-80 mils. A coating, adhesive barrier, release agent, or
film can be applied to or placed in between the sheets where needed
and in any combination to prevent the sheets from melting/bonding
together in the thermoforming process, and for allowing the
finished products to be separated easily (e.g., a form of silicone
may be introduced between the layers of sheets while a zone coat of
adhesive (e.g., 1 inch wide) may be applied along the edge of the
substrate). This adhesion allows for easier transport of the roll
of sheets by keeping the material together in roll form more
effectively. Multiple sheets of approximate thickness 0.010'' each
are stacked together with a barrier/adhesion between each layer.
The multi-sheet layers are rolled together and then sold to various
thermoforming companies. Ultimately time and money are saved by the
thermoformers, allowing them to be more efficient. Sheets 90 are
thermoformed by being drawn or pressed into a mold 92 having the
desired cavity shape.
[0127] Food Service Containers
[0128] An important embodiment of the subject matter disclosed
herein relates to peelable food service containers that are made
using the thermoformable stack described herein.
[0129] For practical uses, food service containers must have
sufficient rigidity to contain their intended contents under their
intended conditions of use. For example, cutlery bins can be free
standing (i.e., having the capacity to contain cutlery without
breaking or substantially sagging without the assistance or support
of a rack or other frame or container) or held within a rack (in
which case, the support provided by the rack can render the
rigidity of the bin relatively unimportant, so long as the bin is
sufficiently rigid to contain cutlery without its sides collapsing
within the rack and preventing access to its contents). Further by
way of example, pans configured to be suspended within a rack
(e.g., a wire or shaped metal frame, a countertop, or table top) of
a buffet table, sandwich assembly station, or steam table need to
be sufficiently rigid that they the can support foods that are
placed within them when installed on the rack without collapsing or
falling through the rack. Such suspended food containers typically
have a flange or rim that surrounds one or more cavities defined by
the peelable surface of the container, such that some or all of the
weight of the container and its contents is borne by the rack when
the container is installed therein. Food service containers must
therefore be relatively rigid, the rigidity required being a
function of the intended uses of the containers and readily
understood by skilled artisans in this field.
[0130] Food service containers are sometimes used in situations in
which heat transfer into of from the food service items therein is
desired. The food service containers described herein can be used
in such situations, with the materials used and number of peelable
layers being selected to facilitate desired or required heat
transfer characteristics (e.g., thermal conductivity and heat
capacity of the materials) for the container. Such selection and
construction is within the ordinary level of skill in this field,
in view of the disclosure made herein.
[0131] Food service containers must also present a sanitary surface
for contacting food service items such as foods, components of
foods, and utensils used for preparing or consuming food. Such
surfaces must be hygienic such that they are free of filth and
pathogens which could present health hazards upon contact with food
service items. These health hazards can be physical,
microbiological, biological, or chemical agents of disease. A
thorough review of food sanitation is beyond the scope of this
disclosure. However, it is recognized that surfaces that contact
food and other food service items during processing, preparation,
storage, serving, and consumption of foods should be free from
pathogens and potentially pathogenic wastes. Relevant wastes that
should be excluded include human and animal feces, residues of food
that previously contacted the surface, residues of washing and
sanitizing reagents, residues from industrial processes for making
the container, airborne dirt and grime, mold, mildew, microbial
growth (including both microbes themselves and materials on or in
which microbes can survive and reproduce), and contaminants that
may contact the surface during manufacturing, shipping, handling,
and installation of the container.
[0132] It is well known to make reusable food service containers
from materials (e.g., stainless steel, porcelain, glass, and
plastics) that exhibit formability, durability, and resistance to
cleaning- and sanitizing-agents. Such containers can be used
multiple times and sanitized between uses to maintain the sanitary
state of the surface that contacts the food or other food service
item. By way of example, baking pans and salad bar component trays
are often made of metal and their food-contacting surface is washed
and sanitized between individual uses. It is also well known to
make single-use containers having a sanitary food-contacting
surface, where the container is used only a single time and
discarded. Hybrid products are known, such as baking trays having
disposable inserts (e.g., paper cups inserted into depressions in
muffin baking trays). Use of disposable liners for food service
containers not expressly made to receive them is also known, such
as when baking dishes are lined with aluminum foil, temperature
resistant plastic sheets, or paper liners.
[0133] Reusable food containers have the disadvantage that they
must be cleaned and sanitized. Disposable single-use food
containers lack that shortcoming, but can be uneconomical and
generate significant amounts of waste, since the entire container
is discarded following each use. Use of disposable liners in a
reusable base mitigates the shortcomings of both types of
containers, but presents the difficulty of matching or shaping
liners to fit the re-usable base. Disposable liners also have the
shortcoming that they must be constructed of relatively thick
materials in order to facilitate handling and installation.
Relative to the peelable layers of food service containers
described herein, such liners require substantially more polymeric
material and energy to fabricate, leading to significantly greater
costs. Disposable liners are typically made by joining one or more
sheets of plastic material into a bag-like structure, and they
include seams that can puncture, tear, of fail to join.
Furthermore, disposable liners do not adhere to the food service
container across substantially the entire food-contacting surface
of the container, meaning that tilting or inversion of the
container can displace the liner from the container, limiting or
eliminating its usefulness.
[0134] Disclosed herein are food service containers that have
peelable, disposable liners "built in" to a reusable base. Such
containers do not require matching or fitting of liners and permit
multiple uses of the same base. Furthermore, after the supply of
liners is exhausted, the base can be either reused (i.e., like an
ordinary reusable container) or recycled to make a new container
having disposable liners assembled therewith. Such a peelable,
multi-use food service container is believed to represent a
substantial advance over existing reusable and disposable food
service containers and liners.
[0135] The peelable, multi-use food service container disclosed
herein is formed from a relatively rigid sheet of a thermoformable
polymer and has at least one, and preferably a plurality (e.g., 2,
5, 10, or 20) of thin second sheets of a polymer peelably attached
thereto. Each of the second sheets can be individually peeled from
the container, yielding a sanitary surface upon each peeling. The
container can thus be reused relatively rapidly, since a soiled
surface can be sanitized simply by peeling a second sheet from the
surface to expose a fresh, sanitary surface ready for reuse.
[0136] Describing the thermoformable polymer sheet as "relatively
rigid" means that the container formed from the sheet exhibits
sufficient rigidity and integrity to contain food service items
without rupturing or spilling its contents under its intended
conditions of use. This sheet is referred to herein as the "rigid"
sheet to differentiate it from the peelable "second" sheets, which
need not exhibit any significant rigidity.
[0137] By way of example, a tray holding sliced meats or cheese
during assembly of sandwiches ordinarily becomes soiled upon
contact with the meats or cheese. Prior to reusing the tray,
sanitary practice requires cleaning and sanitation of the tray.
Where this is achieved by washing, the delay in reusing the tray is
typically caused by removing the tray to the site of washing, by
rinsing, washing, rinsing again, sanitizing, and drying the tray,
returning the tray to the site of use, and refilling. This process
also generates considerable liquid wastes which must be disposed of
in a sewer, septic, or other system. If a peelable, multi-use tray
as described herein is used in its place, sanitation of the tray
can be achieved simply by peeling a second sheet from the tray
(optionally without even removing the tray from its place at the
sandwich-assembly station or any remaining food or residue from the
tray), and the tray can be immediately refilled. The soiled second
sheet can be disposed of with other solid wastes (e.g., in a
wastebasket), and the entire operation can be performed without the
sandwich assembler leaving his station.
[0138] Thus, in one aspect, the subject matter described herein
relates to a peelable, multi-use food service container. The
container includes a substantially rigid sheet of a thermoformable
polymer and one or a plurality of second sheets of a polymer, each
second sheet having a sanitary face and an adhesion face. A first
surface of the rigid sheet has a conformation adapted for holding a
food service item. Each of the second sheets overlaps the rigid
sheet at the first surface and conforms to the shape of the first
surface. Interposed between the rigid sheet and the adjacent second
sheet is a first barrier composition that adheres (e.g., peelably
or permanently) the rigid sheet and the adhesion face of the
adjacent second sheet. A second barrier composition (identical to
or different from the first) is interposed between the adhesion and
sanitary faces of adjacent second sheets. The second barrier
composition peelably adheres the second sheets to one another. The
container thus has a plurality of hygienic second sheets peelably
adhered to a surface adapted for holding a food service item.
[0139] In one embodiment, the second barrier composition is
identical between all second sheets. In another embodiment, a
second sheet more distal from the rigid sheet is more easily peeled
from the second sheet underlying it (i.e., by using a less
tenacious adhesive, or a lower concentration of the same adhesive,
between the sheets) than is a second sheet more proximal to the
rigid sheet. Alternatively, portions of the adhesive in barrier
compositions between more distal second sheets can be deadened or
omitted by applying a non-adhesive barrier composition at those
portions, resulting in a lower force necessary to separate the two
adjacent second sheets.
[0140] As with other containers described in this disclosure, the
first and second barrier compositions can be applied to a single
portion of the rigid and second sheets or as a grid or pattern of
dots (or other shapes and conformations). In an important
embodiment, the first barrier composition is interposed between the
rigid sheet and the adjacent second sheet over substantially the
entire surface of the second sheet. In another important
embodiment, the second barrier composition is interposed between
adjacent second sheets over at least substantially the entire
portion of the first surface. The remainder of the second sheets in
this important embodiment can be free (i.e., grippable), or they
can be adhered to the underlying sheet, especially about their
perimeter, optionally with a tab interposed between the second
sheet and the underlying surface at one or more portions along the
perimeter.
[0141] The food service containers described herein can have
movable or removable lids that cover an orifice of the container.
The lid can be simply a unitary piece of material (e.g., the same
material as the rigid sheet) or, alternatively, it can have
peelable second sheets adhered thereto in at least the portion of
the lid that covers the orifice.
[0142] In one embodiment of the food service container, the first
surface of the rigid sheet is sanitary and the adjacent second
sheet is peelably adhered to the sanitary first face of the rigid
sheet. In this embodiment, the rigid sheet can be permitted to
contact the food service item (i.e., because the first surface is
sanitary) prior to recycling, discarding, or cleaning and
sanitizing the rigid sheet.
[0143] In another embodiment, the first surface is not necessarily
a sanitary surface, but the first barrier composition is selected
such that the second sheet adjacent the rigid sheet cannot be (or
cannot conveniently be) peeled from the rigid sheet under the
normal operating conditions (e.g., room temperature) of the
container. In this embodiment, the rigid sheet is not intended to
be contacted with the food service item during normal use, it being
shielded therefrom by the adjacent second sheet, which has a
sanitary face. Preferably, the first barrier composition is
selected such that the adjacent second sheet can be easily removed
(e.g., peeled) from the rigid sheet under selected (e.g.,
relatively high temperature) conditions, such as conditions that
would be encountered during recycling of the materials used to make
the rigid sheet. In this way, the adjacent second sheet can be
segregated from the rigid sheet materials and the two materials
handled separately. If the first barrier composition remains
associated with the second sheet, this also improves the relative
purity of the material used to make the rigid sheet during
recycling of that rigid sheet.
[0144] The container includes at least one, and preferably two or
more, second sheets. When multiple second sheets are present, the
second sheets have interposed between them a second barrier
composition that peelably adheres adjacent second sheets to one
another. Each second sheet has a sanitary face and an adhesive
face. When assembled, the adhesive face of each second sheet is
nearer (more proximal to) the rigid sheet than is the sanitary
face. Thus, for adjacent second sheets, the sanitary face of the
more proximal second sheet is nearer the rigid sheet than is the
interposed second barrier composition, which itself is nearer the
rigid sheet than is the adhesive face of the more distal second
sheet. The characteristics of each of the sanitary face of the more
proximal sheet, the interposed second barrier composition, and the
adhesive face of the more distal sheet is selected so that when the
more distal sheet is peeled away from the more proximal sheet, the
second barrier composition remains substantially (preferably
virtually exclusively) with the adhesive face of the more distal
sheet. This leaves a sanitary face that is substantially free of
the second barrier composition. Because the sanitary face is
substantially free of the second barrier composition, potential
interactions between that second barrier composition and any food
service items placed in the container are minimized. This can be
achieved, for example, by controlling the surface energies (e.g.,
by selecting materials in multi-layer composite second sheets or by
corona treatment or other surface treatments of the second sheets)
of the sanitary and adhesive faces of second sheets such that the
difference in surface energy between the two faces is at least
about 5 Dynes.
[0145] The container can have one or more tabs associated with the
second sheets. The tabs can, for example, be interposed between
adjacent second sheets for facilitating separation of the adjacent
second sheets. In one embodiment, the tab is interposed between
adjacent second sheets and simply prevents the two second sheets
from tightly adhering to one another (i.e., regardless of whether
one or both second sheets adhere to the tab). The tab creates a
region at which the adjacent second sheets can be manually
separated from one another. In one embodiment, the tab adheres to
the adhesion face of one of a pair of adjacent second sheets, but
does not adhere to the sanitary face of the other adjacent second
sheet. If the second sheets are cut across the area including the
tab, a user can pull the two second sheets apart by grasping the
tab and the second sheet to which it adheres and pulling these away
from the other second sheet (to which the tab does not adhere). If
desired, the user can insert an object (e.g., the tip of a
fingernail or a knife) between the tab and the non-adhered second
sheet to facilitate the separation.
[0146] The tab can also extend beyond the edges of one or both
second sheets, which provides a convenient surface for grasping and
pulling by a user. In a food service environment, however, tabs
that extend beyond the sanitary surfaces of second sheets can
provide opportunities for soiling and cross-contamination between
layers of second sheets, and it is recognized that tabs that are
not obscured by an over-lying second sheet are not appropriate for
all food service uses. In such situations, tabs are preferably
completely overlaid by a second sheet or, at least, do not extend
beyond the edge of an over-lying second sheet.
[0147] For food service containers, it is desirable to maintain a
clean and sanitary face on an underlying surface prior to when an
overlying second sheet is peeled therefrom. Separation or peeling
of an overlying second sheet during manufacture, shipping, or
storage offers an opportunity for environmental contaminants to
contact the underlying surface. Tabs that are not adhered to both
an overlying second sheet and the underlying surface present an
opportunity for such separation or peeling to occur. In order to
prevent this, tabs are preferably adhered to both overlying second
sheet(s) and the underlying surface in the food service containers
described herein. Tabs should be peelably adhered to at least one
of the adjacent surfaces, to facilitate peeling of second sheets
(and, optionally, the tabs).
[0148] In one embodiment, a container having multiple second sheets
has tabs interposed between those second sheets to facilitate their
peeling from the container. Each tab is peelably adhered to one of
the adjacent second sheets, preferably at least along substantially
the entire portion of the tab that is overlapped by that second
sheet. The tab is also adhered (either peelably or relatively
fixedly, such as by fusion or tenacious adhesion) to the other
adjacent second sheet, again preferably along substantially the
entire portion of the tab that overlaps that other second sheet.
Such an arrangement facilitates peeling of a second sheet from the
container, either by peeling a second sheet from the tab and thence
from the container or by peeling the tab attached to an overlying
second sheet away from an underlying second sheet and using the
partially peeled tab as a handle to peel the overlying sheet from
the underlying sheet. If the tab is peelably attached to both
adjacent second sheets (either with equal or unequal tenacity),
then one second sheet can be peeled from the other by aid of the
tab, and the tab can thereafter be peeled from the second sheet to
which it remains attached.
[0149] By way of example, a tab can be peelably adhered across its
entire surface to a portion of a proximal (relative to the first
sheet) second sheet near one edge of the container and peelably
adhered across only the overlapping portion of a distal second
sheet that overlaps the tab at one edge of the distal second sheet.
In this conformation, the gap between the proximal and distal
second sheets contains the tab at the edge of the distal second
sheet and is sealed both above and below the tab by the peelable
adhesive (the second barrier composition). Thus, the gap resists
introduction of contaminants between the proximal and distal second
sheets prior to peeling of the distal second sheet. The distal
second sheet can be peeled from the proximal sheet by drawing an
instrument (e.g., a fingernail or the edge of a spatula) across the
edge of the distal sheet where it overlaps the tab, thereby
initiating peeling of the distal sheet from the tab. By pulling on
the distal sheet using the thus-displaced edge thereof, the distal
sheet can be peeled from the container, leaving the proximal sheet
attached thereto, with the tab remaining attached to the proximal
sheet. If desired, the tab can be peeled from the proximal
sheet.
[0150] When tabs are included in a container as described herein,
the tabs can be aligned with one another, such that peeling of one
second sheet and its associated tab reveals another tab located at
the same location on the container (albeit one second sheet-layer
closer to the rigid sheet). However, this aligned arrangement of
tabs can cause difficulty, in that a user desiring to peel only the
upper-most second sheet (i.e., the one most distal from the rigid
sheet) may inadvertently disturb multiple sheets while attempting
to manipulate only the tab associated with the upper-most sheet.
This difficulty can be avoided if the tabs corresponding to
different second sheets are placed at different locations along (or
near) the perimeter of the container. If these tabs are physically
separated from one another (e.g., tabs separated left-to-right,
when viewing the container from the distal surface), a user may be
able to more easily manipulate only the tab corresponding to the
upper-most second sheet without disturbing the tabs (and the
sanitary surface) corresponding to other second sheets.
[0151] The tabs can be the same color and composition as a second
sheet and can, in fact, be simply an extension of one of the second
sheets (i.e., the second sheet that is peeled when the tab is
pulled). However, tabs are preferably made a different color and
from a different material, so that they can be more easily
identified and manipulated by a user. In one embodiment, each tab
is made from a material that is different in color from and
attached to the adhesion face of the second sheet that is peeled
upon pulling the tab. One or more of the tabs can also include an
indicium of the number of second sheets that remain attached to the
container. By way of example, each second sheet can have a tab
attached to the adhesion face thereof, with the tab bearing a
numeral equal to the number of second sheets that remain adhered to
the rigid sheet upon peeling the sheet to which the tab is
attached. By way of an alternative example, all tabs can be white,
with the tab associated with the second sheet that is adjacent the
first sheet being red or bearing a star, the text "Last Use," or
the like.
[0152] As with the tabs, the colors of the rigid and second sheets
are immaterial, yet selectable. In instances in which either the
rigid sheet or the second sheets will be viewed by customers (e.g.,
at a sandwich assembly station at a restaurant in which customers
stand within view of the station), it may be desirable to select
sheets having particular colors (e.g., matching the decor of the
restaurant) or appearances. In one embodiment, the rigid sheet has
a color selected for a particular purpose (e.g., consistency with
the color scheme of a food service station such as a buffet table),
and the second sheets adhered thereto are substantially clear, so
that the container has substantially the appearance of the rigid
sheet, regardless of how many second sheets remain adhered thereto.
For functional reasons (e.g., keeping track of how many peelable
layers remain), it can also be desirable to impart a color or
appearance to different layers of the container. By way of example,
if it is desired that the rigid layer not be used to contact food
service items, then the rigid layer can be made from materials
having one color (e.g., black), while the second sheets that are
peelably adhered to the rigid sheet are made from materials having
a different color (e.g., white). Thus, in this example, if a white
surface is revealed upon peeling a second sheet, the user knows
that the revealed surface is that of a desirable second sheet,
while the user knows that if the revealed surface is black, then
the revealed surface is the non-desired rigid sheet. Although
printing is generally not used on surfaces used for food contact,
the printing methods described herein can nonetheless be used to
print images, text, or other indicia on the second sheets of the
container described herein.
[0153] Food service containers are sometimes intended to facilitate
heat transfer either into or away from food service items held in
the container. By way of example, forks held in a compartment at a
salad bar are often chilled, as are lettuce, dressings, and other
salad components. Soups, cooked entrees intended for consumption
while warm, and steam tray contents are often heated. Other
components (e.g., crackers and breads) may be neither heated nor
cooled. Such heating and cooling is typically effected by
contacting a fluid (e.g., air, steam, or water) against the surface
of the container on the face opposite the face that contacts the
food service item contained therein.
[0154] Where heating or cooling of container contents is desired,
the materials used to make the food service container should be
selected to facilitate the anticipated operating conditions and the
desired heat flux characteristics. Thus, in situations in which
relatively high heat flux is desired, materials which have
relatively high thermal conductivity should be used and the number
of second sheet layers should be controlled. Selection of
appropriate materials is both within the ken of the ordinary
designer and determinable through routine empirical
observation.
[0155] A wide variety of polymer materials may be used to form the
rigid and second sheets for food service containers as described
herein. Selection of appropriate materials is within the level of
skill of an ordinary artisan in the field of thermoforming. An
important consideration when selecting materials for use in food
service containers is statutes, regulations, and other requirements
that are relevant to materials used in contact with food in the
locale in which the container is to be used. By way of example, in
the United States, materials used to contact food during
manufacture, shipping, storage, and preparation are regulated by
the Food and Drug Administration's Center for Food Safety and
Applied Nutrition. In addition to processes for applying for
approval for contacting food service items with various materials,
most relevant regulatory agencies maintain lists of materials that
are generally approved for use in contacting foods. In the U.S.,
such materials are referred to as "Generally Regarded as Safe"
(GRAS), and lists of GRAS materials for food contact substances are
maintained by the U.S. Food and Drug Administration. Many of these
materials can be used to make the rigid and second sheets and
barrier compositions described herein.
[0156] Materials useful for making the containers described herein
can also be selected from materials identified and/or described by
private or non-profit standard-setting organizations (e.g., NSF
International of Ann Arbor, Mich.), that report or recommend
materials safe for contact with food and food-preparation
surfaces.
[0157] Likewise, a wide variety of barrier compositions can be used
in the food service containers described herein. The barrier
compositions should provide sufficient adhesion between the second
sheet and the underlying sheet that the second sheet is not
disturbed or peeled by normal air currents and handling operations.
It is sufficient, for example, if the barrier composition provides
only sufficient adhesive strength to keep a substantially rigid
peelable sheet from falling out of the container when the container
is inverted. At the same time, the adhesion provided by the barrier
compositions must not be so great that the second sheet cannot be
peeled from the underlying surface without damaging the second
sheet or the underlying surface. The barrier compositions should
also be selected for chemical and physical compatibility with the
food service items and environmental conditions that the containers
are likely to encounter. By way of example, barrier compositions
intended for use in food service containers for holding hot soup
should maintain their adhesive properties at anticipated soup
temperatures, should not substantially dissolve in aqueous fluids
(i.e., in the event the soup contacts the barrier composition near
an edge of or through a breach through a second sheet), and should
preferably be peelable both at anticipated soup temperatures and at
20 degrees Celsius. A variety of GRAS barrier compositions are
available and, provided they conform with the other characteristics
described herein, suitable for use in the containers.
[0158] For containers intended for use in contact with consumable
food items, good manufacturing processes, consistent with practices
common in the food industry for maintaining sanitation, should be
used to make, package, ship, store, and use the food service
containers described herein.
[0159] In an important embodiment, the food service container has a
standardized shape and conformation. Standardized containers are
used in a wide variety of settings in the food and restaurant
industries. Examples include salad bars, sandwich assembly
stations, steam tables, chafing dishes, cafeteria serving counters,
cafeteria utensil stands, and buffet tables. The sizes and
conformations of food service containers used in such settings are
widely known and often vary by manufacturer of the setting
furniture. An advantage of the food service containers described
herein is that they can be manufactured to fit substantially any
known standardized racks or furniture. They can also be used to
form free-standing containers, such as baking pans, serving trays,
and cookie sheets.
[0160] The food service containers described in this section are
made in substantially the same ways as other containers described
in this application (except that more sanitary manufacturing
requirements may be necessary than are used, for example, for
making paint trays). For relatively shallow containers (e.g., those
in which the most-displaced portions of the thermoformed stack are
displaced only 1-2 inches from the pre-thermoforming position of
the stack), standard thermoforming apparatus and procedures are
appropriate. For deeper containers (e.g., those in which one or
more portions of the thermoformed stack are displaced >6 inches
from the pre-thermoforming position of the stack or in which
relatively steep sides are formed), standard thermoforming methods
can lead to creasing, overlapping, excessive thinning, puncture, or
some combination of these, of one or more sheets in the stack,
including the relatively thinner second sheets. To avoid this, it
is desirable to control the conformation of the stack during the
forming operation, so that when the stack is engaged by the
thermoforming mold, it is not creased, folded, excessively thinned,
or punctured.
[0161] In one method of controlling the conformation during
forming, a stack including the rigid sheet and multiple second
sheets is assembled and heated to about a temperature appropriate
for thermoforming. Prior to engaging the heated stack with the
thermoforming mold, pressure (negative or positive) is applied to
one face of the stack, so that the stack is deflected by
atmospheric pressure into a shape that roughly approximates the
shape of the thermoforming mold while maintaining the stack in a
smooth conformation. The pressure is preferably applied by
adjusting the atmospheric or the gas pressure at the stack face,
for example by applying a vacuum. Apparatus for applying such
pressure are well known and include, for example, devices commonly
referred to as "vacuum boxes" and "pressure boxes." Any apparatus
used to apply such pressure preferably does not physically contact
any portion of the stack that is to be thermoformed (to avoid heat
transfer that would affect the thermoformability of the contacted
portion). After the stack has been pressure-deformed, the stack is
contacted with one or more thermoforming molds, per normal
thermoforming procedures. As in standard thermoforming procedures,
the stack can be drawn against a mold by application of negative
pressure on the face of the stack that contacts the mold, forced
against a mold by application of positive pressure on the face
opposite that which contacts the mold, or both.
[0162] In one embodiment of the food service containers described
herein, the rigid sheet is made from a recyclable polymeric
material, while the second sheets are made from thin, disposable
polymer that preferably degrades relatively quickly in landfill
conditions. This embodiment relates to a container that
significantly reduces waste generation corresponding to use of food
service containers. Each second sheet can be simply discarded with
solid wastes (i.e., garbage) after use. The rigid sheet that
supports the second sheets can be recycled, either through a
municipal recycling service provider or by returning it to the
manufacturer to be re-melted and again formed into rigid plastic
sheeting (or other materials for which recycled food containers may
be more appropriate). In one version of this embodiment, the first
barrier composition is selected such that it relatively tightly
adheres the adjacent second sheet to the rigid sheet, so that that
adjacent second sheet cannot be easily removed from the rigid sheet
during normal use. When returned to a recycler, the adjacent second
sheet (which may be soiled from use) can either be recycled
together with the rigid sheet (especially if it is made of the same
polymer as the rigid sheet) or it can be removed by subjecting the
container to a condition (e.g., high temperature) at which the
first barrier composition adheres the adjacent second sheet less
tenaciously to the rigid sheet, permitting removal of the second
sheet prior to recycling of the rigid sheet. In this embodiment,
the level of impurities in the recycled rigid sheet materials can
be significantly improved by removing the potentially soiled second
sheets therefrom.
[0163] The peelable, multi-use food service container described
herein can be used as a component of a food service station, such
as a salad bar or a sandwich assembly station. In such a station, a
rack, countertop, or other apparatus has a conformation adapted to
hold at least one peelable container. The station can, of course,
hold multiple peelable containers of the same or different sizes
and shapes. In normal food storage and dispensing operations, such
a station is essentially indistinguishable from stations having
non-peelable containers. However, when cleaning or sanitation of
one of the containers is desired, a difference becomes apparent.
Rather than removing a container and either replacing it with
another container or washing and replacing the same container, as
in a traditional station, a peelable container can be cleaned and
sanitized simply by peeling a second sheet from the first surface
thereof. The peeled container can thereafter be refilled and
immediately re-used, with the peeled sheet discarded. The cleaning
and sanitation achieved by peeling both improves the rapidity with
which the station can be maintained and reduces the waste
associated with maintaining it.
[0164] In some instances, containers at food service stations are
refilled in a kitchen or other food preparation area prior to being
brought to the station to replace soiled containers. In such
instances, the peelable containers described herein can nonetheless
be advantageous, in that they reduce the time and waste associated
with cleaning soiled containers, whether that cleaning is performed
at the station itself or in a kitchen or other preparatory
area.
[0165] In another aspect, the disclosure relates to method of
operating a food station. The method involves assembling one or
more first food products from components stored in multiple food
containers, including at least one selected component that is held
in a peelable food container described herein. After assembling
first food product(s), a second sheet is peeled from the peelable
food container (revealing a sanitary surface that can be contacted
with fresh food components), and more of the selected component is
added to the peelable food container. One or more second food
products (identical to or different from the first food products)
are then assembled from components stored in the food containers,
including at least the selected component.
[0166] The peelable food service containers described herein will
typically be manufactured at a site distant from the location at
which they will be used, transported between the manufacture and
use locations, and stored at one or more intermediate locations. At
each of these steps, the containers can be exposed to environmental
contaminants (e.g., dirt, dust, rodents, liquids) that are not
compatible with maintenance of sanitary surfaces. When a peelable
food service container as described herein is contacted with such
contaminants, the outermost second sheet (i.e., the one which will
have contacted the contaminant) can simply be peeled off to remove
the contamination and reveal a fresh, sanitary face useful for food
service. However, it is preferable to avoid manufacturing,
storage-, and transportation-contamination in the first place.
[0167] In order to prevent contamination of the sanitary face of
the outermost second sheet, the containers can be packaged in a
wrapper, box, or the like. Alternatively, a protective coat layer
can be included as the uppermost (i.e., most distal from the rigid
sheet) layer in the stack. The protective coat should overlap the
uppermost second sheet, at least over the first surface (i.e., the
portion of the uppermost second sheet that will contact food
service items), and should be relatively easily removable
therefrom, for example by peeling or rinsing with water. Because
the purpose of the protective coat is simply to prevent contact
between environmental contaminants and the uppermost second sheet,
the composition, color, and thickness of the protective coat are
not critical, and any relatively inexpensive material can be used.
The protective coat contacts the uppermost second sheet over
substantially the entire sanitary face of that second sheet. The
protective coat can be held in place simply by electrostatic
attraction, and is preferably peelably adhered to the second sheet.
The protective coat can also be made from a material that resists
scratching, whereby the protective coat can protect the container
from both contamination and physical damage. The protective coat
material can be selected such that it can be printed upon or
accepts adhesive labels, so that the protective coat can provide
both shielding and marketing or labeling functions. The protective
coat can be peeled from the container and discarded (or recycled)
by the user prior to filling the container with a food service item
for the first time.
Example
[0168] A food service container designed to be inserted into a rack
for holding multiple food service containers as a part of a
sandwich assembly station was fabricated. The concave interior
portion of the container had the approximate conformation of a
tapered rectangular cuboid having rounded edges and dimensions of
about 101/2 inch length (tapering to about 113/4 inch at the
opening).times.about 43/4 inch width (tapering to about 53/4 inch
at the opening).times.51/2 inch depth. The corners of the interior
cuboid had radii of about 7/8 inch. A flange extended about the
opening, having a length of about 123/4 inches and a width of about
67/8 inches, with rounded corners (about 3/4 inch radius).
[0169] In this embodiment, the rigid sheet was composed of PET
(polyethylene terephthalate), black in color, approximately 30 mils
(i.e., ca. 0.03 inch) in thickness. The container included ten
second sheets peelably adhered to the rigid sheet. Each of the
second sheets was composed of polyethylene, was white in color, and
approximately 2 mils in thickness. Interposed between each of the
second sheets was a second barrier composition that was composed of
a water-based acrylic pressure sensitive adhesive, which was flood
coated on the adhesive face of each second sheet. A first barrier
composition identical in composition to the second was interposed
between the rigid sheet and the adjacent second sheet, and was
present by virtue of the adhesive face of the adjacent second sheet
having been flood coated therewith.
[0170] Tabs were interposed between at least several pairs of
adjacent second sheets at one of the corners of the flange. The
tabs extended diagonally across the corner of the flange and were
trimmed flush with the edges of the second sheets between which
they were interposed. Each tab was peelably adhered to the second
sheet that overlaid the tab and was not adhered to the second sheet
beneath (i.e., more proximal to the rigid sheet) the tab. Second
sheets could be peeled from the container by scratching or picking
at the tab beneath the uppermost second sheet to begin peeling the
tab and uppermost second sheet from the second sheet underlying
them. By pulling the sheet and tab approximately across the cavity
in the container (i.e., generally tangentially across the top of
the container), the uppermost second sheet could be peeled
therefrom without substantially disturbing any of the other second
sheets of the container. This could be done multiple times, once
for each of the second sheets of the container. The lowermost
second sheet could similarly be peeled from the rigid sheet.
[0171] The appropriateness of the container for holding and storing
food service products was tested by pouring food products with
easily detected residues (i.e., pickles with brine, oils, etc.)
into the cavity of the container, permitting them to remain there
for about one day, and then removing the food products. Upon
peeling the second sheet that contacted the food products, no
residue could be detected by its characteristic scent or by wiping
the interior of the cavity after peeling the top sheet. This
confirmed that the containers so tested contained the food products
without permitting them to leak after about 24 hours--a longer
period than the normal period of storage for food service
containers of this type in, for example, a buffet or steam
table.
[0172] Certain modifications and improvements will occur to those
skilled in the art upon a reading of the foregoing description. It
should be understood that all such modifications and improvements
have been deleted herein for the sake of conciseness and
readability but are properly within the scope of the following
claims.
* * * * *