U.S. patent number RE30,009 [Application Number 05/872,297] was granted by the patent office on 1979-05-29 for vacuum skin package, and process and apparatus for making same.
This patent grant is currently assigned to W. R. Grace & Co.. Invention is credited to Le Roy F. Hoagland, Richard O. Kuehne, Richard R. Perdue.
United States Patent |
RE30,009 |
Perdue , et al. |
May 29, 1979 |
Vacuum skin package, and process and apparatus for making same
Abstract
In the prior art, vacuum skin packaging processes are performed
by placing the product to be packaged on an impervious backing
board; placing the product and board in a vacuum chamber;
positioning a sheet of thermoplastic film above the product and
backing board in the chamber; evacuating the chamber; then, either
pulling the film down over the product or pushing the product up
into the film; and, thereafter sealing the film to the board. In
the present invention, a portion of the film is drawn by
differential air pressure against the concave interior surface of
the upper portion of a vacuum chamber; the film is then heated by
surface contact; and then, after evacuation of the chamber, air
pressure is used to blow the film down over the product and against
the backing board. Thus, in the present invention, the film is
shaped in a concave fashion surrounding the upper portion of the
product and it is not necessary for the product to move. The height
of the chamber may be adjusted for different products so that
excess film is not used and wrinkling is prevented.
Inventors: |
Perdue; Richard R. (Greer,
SC), Hoagland; Le Roy F. (Greenville, SC), Kuehne;
Richard O. (Greenville, SC) |
Assignee: |
W. R. Grace & Co. (Duncan,
SC)
|
Family
ID: |
22178034 |
Appl.
No.: |
05/872,297 |
Filed: |
January 25, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
83398 |
Oct 23, 1970 |
03694991 |
Oct 3, 1972 |
|
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Current U.S.
Class: |
53/433 |
Current CPC
Class: |
B65B
11/52 (20130101); B65B 47/10 (20130101); B65B
31/02 (20130101) |
Current International
Class: |
B65B
11/52 (20060101); B65B 11/50 (20060101); B65B
47/10 (20060101); B65B 31/02 (20060101); B65B
47/00 (20060101); B65B 031/02 () |
Field of
Search: |
;53/22A,112A |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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3491504 |
January 1970 |
Young et al. |
3545163 |
December 1970 |
Mahaffy et al. |
|
Primary Examiner: McGehee; Travis S.
Attorney, Agent or Firm: Toney; John J. Lee, Jr.; William D.
Hardaway; John B.
Claims
Having thus described our invention, we claim:
1. A vacuum skin packaging process comprising:
a. placing the product to be packaged on a gas impervious
supporting member;
b. shaping a .Iadd.heat softenable, .Iaddend.flexible sheet member
into a concavity .Iadd.by differential air pressure; .Iaddend.
c. maintaining the concave shape of said sheet .Iadd.by said
differential air pressure while heating said sheet to its softening
and forming temperature; .Iaddend.
d. positioning said sheet over said product and supporting member
so that said sheet partially covers but does not contact either
said product or supporting member;
e. evacuating gases from the space between said sheet and said
supporting member, which contains said product .Iadd.while
maintaining said sheet in its concave shape at its softening and
forming temperature until it is released to move against the
product; .Iaddend.
f. moving said sheet from its concave shape and position so that it
closely contacts said product and supporting member; and,
g. sealing said sheet against said supporting member.
2. A process for vacuum skin packaging a product on an impervious
supporting member .Iadd.by forming a heat formable thermoplastic
member around said product .Iaddend.comprising the steps of:
a. drawing by differential air pressure .[.a.]. .Iadd.said
.Iaddend.formable plastic sheet member against a concave
surface;
b. heating said concave surface to at least the softening
temperature of said thermoplastic member;
c. maintaining said differential air pressure; while
d. positioning said sheet member over said product on said
supporting member;
e. evacuating the space between said supporting member and said
sheet member .Iadd.while retaining said sheet member against said
heated concave surface to maintain said sheet member at its
softening temperature until it is released to move against the
product; .Iaddend.
f. releasing the differential air pressure which maintained the
concave shape of said sheet member, thereby causing said sheet
member to collapse over and around said product and against said
supporting member; and,
g. sealing said thermoplastic sheet member to said supporting
member as it collapses thereagainst.
3. A vacuum skin packaging process comprising:
a. providing a supporting platform within the lower portion of a
vacuum chamber;
placing a product on an impervious backing member on said
supporting platform;
c. shaping a heat softenable thermoplastic film in the cavity of
the upper portion of said vacuum chamber;
d. retaining said thermoplastic film in said shape while
e. heating said film to its softening and forming temperature;
f. positioning said upper portion of said chamber over said product
and closing said chamber, said thermoplastic film being clamped
between the upper and lower portions of said chamber;
g. evacuating said chamber .Iadd.while maintaining said film at its
softening and forming temperature until it is released to move
against the product; .Iaddend.and,
h. releasing said thermoplastic film from its retained position
whereby it collapses around said product and is driven against said
supporting member.
4. The process of claim 3 including the step of adjusting the
height of the upper portion of said chamber in accordance with the
height of the product to be packaged by adding a shim member to the
lower periphery of said chamber.
5. The process of claim 3 wherein the thermoplastic material is
polyethylene.
6. The process of claim 3 wherein the polyethylene is coated with a
polymer of ethylene vinyl acetate.
7. The process of claim 3 wherein the impervious supporting member
is made from thermoplastic foam.
8. The process of claim 7 wherein the thermoplastic foam is
polystyrene foam and the heat softenable material is polyethylene
coated with a polymer of ethylene vinyl acetate. .Iadd. 9. A
process for vacuum skin packaging a product positioned between two
impervious sheet members one of which supports the product
comprising the steps of:
a. drawing by differential air pressure one of said impervious
sheet members which is a heat-softenable, formable plastic material
against a concave surface which is shaped to partially enclose the
product to be packaged;
b. maintaining said differential air pressure while;
c. heating said concave surface to at least the forming and
softening temperature of said heat softenable and formable plastic
sheet member;
d. positioning one sheet member over said product on said
supporting member with the product therebetween and said formable
sheet member on said concave surface partially enclosing said
product; and
e. evacuating the space between said supporting member and said
sheet member while retaining by said differential air pressure the
formable sheet member in contact with said heated concave surface
to maintain said formable sheet member at its forming and softening
temperature;
f. then increasing the air pressure on the exterior of the formable
sheet member to cause it to be released from contact with the
concave surface thereby causing the formable sheet member to
collapse around and into conforming contact with the product and
against said other sheet member; and
g. sealing the heat formable and softenable sheet member to the
other sheet member as the heat formable and softenable sheet member
collapses thereagainst..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates generally to skin packaging and specifically
to vacuum skin packaging of both food and non-food items.
The term "vacuum" as used herein means a differential fluid
pressure where the fluid can be either a gas or a liquid.
BACKGROUND OF THE INVENTION
Skin packaging is essentially a vacuum forming process. In a
typical process, a sheet of thermoplastic film is placed in a
frame, and below the frame is a vacuum plate upon which a piece of
backing board is placed. The product to be skin packaged is
positioned on top of the backing board and heat is applied to the
thermoplastic film in the frame. When the film has been heated to
become sufficiently soft, the frame is lowered and the plastic
sheet drapes itself over the product. As this happens, a partial
vacuum is created through the vacuum plate and the air underneath
the plastic film is withdrawn through the backing board. The air
pressure differential between the top and the bottom of the plastic
sheet causes the sheet to be tightly pressed around the product.
The film may be coated with an adhesive or the backing board may be
so coated. Where the two contact each other, a strong bond is
formed resulting in a package in which the product is tightly held
to the backing board for safe shipping and for subsequent rack
display in retail stores.
Vacuum skin packaging differs from the above described skin
packaging process in that both the thermoplastic film and the
backing board are impervious to gases and the resulting package can
be evacuated and hermetically sealed, if desired. The same end
result is sought, i.e. the product is to be tightly held by the
transparent film to the backing board. The conventional method
employs a backing board which is porous or which is perforated so
that the vacuum may be drawn directly through the backing board.
The vacuum skin packaging processes generally employs a vacuum
chamber with an open top. The product on an impervious backing
board is placed on a platform within the vacuum chamber. The top of
the chamber is then covered by a sheet of film which is clamped
tightly against the chamber to form a vacuum type closure. The
chamber is evacuated while the film is heated to forming and
softening temperatures. The platform can then be raised to drive
the product into the softened film and air pressure can be used
above the film to force it tightly around the product. This type of
process is disclosed in French Pat. No. 1,258,357 issued to Alain
G. Bresson on Mar. 6, 1961.
A refinement to the process described in the Bresson French Pat. is
disclosed in French Pat. No. 1,286,018 issued on Jan. 22, 1962 to
Laroch Freres, Limited. In the Laroch Freres process, after the
chamber has been evacuated and the product driven into the heat
softened film, the vacuum is released and ambient air is permitted
to enter the chamber so that the thermoplastic film molds more or
less on the product since there is a vacuum on the product side of
the film and ambient air pressure on the other side of the
film.
In Australian Pat. No. 245,774 issued to Colbro Proprietary Limited
and Cole and Son Proprietary Limited on July 16, 1963, a vacuum
skin packaging process is described in which an article to be
packaged is inserted within the lower half of a vacuum chamber on a
backing board, a thermoplastic film is placed over the open face of
the lower half of the chamber, the chamber is closed and both
halves are brought to essentially the same state of vacuum, the
film heated and softened, and then atmospheric air is introduced
into the upper half of the chamber so that it alone forces the
thermoplastic film 6 down around the product and against the
backing board.
Still another variation which can be found in the prior art, is
that disclosed in U.S. Pat. No. 3,491,504 issued to W. E. Young et
al. on Jan. 27, 1970. The Young patent discloses a process in which
the softened film can be physically moved down over a stationary
product and, in combination with air pressure, the softened
thermoplastic film will be molded onto the product.
In all of the above described prior art processes, the
thermoplastic film is stretched across the open face of a vacuum
chamber. The product is then either driven up into the film, the
film pulled down over the product, or air pressure is used to move
the film. Having to physically move the film or the product slows
down the packaging process and, in addition, requires that the
product be strong enough to withstand the force of contacting the
film. Furthermore, when the film is stretched flat and straight
across the vacuum chamber, excess film is required and wrinkling of
the film may occur due to unnecessary movement of the film. These
disadvantages are overcome and many advantages are provided by the
invention described hereinbelow.
SUMMARY OF THE INVENTION
In its broadest aspect the present invention is a vacuum skin
packaging process comprising the steps of: shaping a cavity in a
sheet of flexible packaging material, said cavity at least
partially enclosing a product on an impervious backing board;
generating a pressure differential across said sheet; and, moving
said sheet against the product and into sealing engagement with the
backing board by means of said pressure differential. The cavity
which partially encloses the product allows a minimum of sheet
packaging material to be used and at the same time provides a
minimal distance for the film or sheet to be moved before
contacting the product thus giving little opportunity for wrinkling
of the sheet.
In a narrower aspect, the process of the present invention
comprises placing the product to be packaged on a gas impervious
supporting member; shaping a flexible sheet member into a
concavity; maintaining the concave shape of the sheet; positioning
said sheet over said product and supporting member so that said
sheet partially coves but does not contact either the sheet or
supporting member; evacuating the space between said sheet and said
supporting member; moving said sheet from its concave shape and
position so that it closely contacts said product and supporting
member; and sealing the supporting member to the sheet member. In
even more limited aspects, the present process includes the use of
a flexible sheet member which is made from a formable thermoplastic
film and includes heating the thermoplastic film to its forming
temperature when it is in the concave shape. The film, of course
could be preheated to its forming temperature before being shaped
into a cavity and this requires that the film be maintained at its
forming temperature until it is moved against the product and
supporting member. A preferred method of shaping and moving the
thermoplastic film is to use differential air pressure.
The apparatus which constitutes a part of the present invention
will perform the above-described process. In particular, the
apparatus comprises a vacuum chamber having an open top; means for
supporting objects to be packaged within said chamber; means for
evacuating the chamber; and closure means for the chamber which
comprises a concave inner surface, a means for creating
differential air pressure on the concave surface and means for
heating the surface. A means for adjusting the height of the
chamber for differing product heights is also included.
The process and apparatus of the present invention may be better
understood by reference to the following detailed description and
drawings.
DESCRIPTION OF THE DRAWINGS
In the drawings which form a part of this specification:
FIG. 1 is a schematic representation of a section through the
closure means for the vacuum chamber of the subject invention
showing a flexible packaging sheet member across the opening of the
cavity in said closure means;
FIG. 1A is a sectional view of the closure means of FIG. 1 showing
the arrangement of the heating elements, vacuum ports, and height
adjusting means for the closure means;
FIG. 2 is a schematic representation of the vacuum chamber and
closure means with the sheet member formed into a concave shape and
the product and supporting member in place within the chamber;
FIG. 3 is a schematic representation of the evacuation of the space
between the sheet member and the supporting member;
FIG. 4 is a schematic representation of the packaging sheet member
after it has been moved against the product and into sealing
engagement with the supporting member; and,
FIG. 5 is a schematic representation of a vacuum skin package.
PREFERRED EMBODIMENTS
Referring first to FIG. 1, a schematic sectional view of upper
vacuum head 3 is shown. Vacuum head 3 serves as the closure means
for the vacuum chamber described hereinbelow. The detail of the
vacuum head 3 can best be appreciated by viewing both FIGS. 1 and
1A. In these figures it can be seen that inwardly sloping wall 15
and the horizontal wall portion containing ports 14 define a
concave space or cavity within the vacuum head 3. Above the ports
14 is manifold space 4 having an exterior port 6. Heating elements
5 are placed within the manifold area for heating the wall
containing the ports 14. These heating elements may either be steam
lines with inlet 12 and outlet 13 feeding steam to elements 5; or,
the elements may be electrically operated radiant heaters or
resistance type heaters.
Vacuum head 3 has a vertical peripheral wall or leg 16 to which can
be added a shim member 17 to extend or shorten the height of wall
16. The shim 17 conforms to the shape of the opening of the cavity
in the vacuum head 3 and makes it possible to adjust the height of
the head for different product sizes.
Turning now to FIG. 2, vacuum chamber 9 can be seen having platform
8 placed therein which is carried by platform supports 10. In
position on the platform 8 is backing board or package supporting
member 7 upon which has been placed the product 2 which is to be
packaged. Flexible packaging film 1 is shown lining the cavity of
the closure means 3. Chamber 9 has a manifold or cavity region 18
which has an exterior port 11 and which has a passageway to the
head cavity which is defined by the space between chamber 9 and
platform 8.
Returning now to FIG. 1 to describe the method of the present
invention, a sheet of flexible packaging material 1 is shown
stretched across the opening to the cavity in head 3. In most
packaging applications, it is preferred that the sheet material 1
be transparent. Particularly suitable packaging materials are the
thermoplastics such as polyethylene, cross-linked polyethylene,
polypropylene, saran, nylon, polyvinylchloride, or the like and
laminates of any of these materials. When thermoplastic materials
are used, they will be relatively stiff or semi-rigid before being
heated to a softened and formable stage. The present invention
contemplates the use of such heat softenable thermoplastic
materials and when such materials are placed across the opening to
the cavity of head 3 as shown in FIG. 1, they may be either
preheated to partially soften them, or they may be heated to
softening temperatures by the radiant, conductive, and convective
action of heaters 5.
After positioning the packaging material or film 1 as shown in FIG.
2, a pressure differential or vacuum is applied as shown in FIG. 2
by the arrow and the abbreviation "vac." This pressure
differential, or vacuum, acts through ports 14, through manifold
region 4, and through the exhaust ports 6. Any conventional vacuum
pump can be used to apply this pressure differential. Upon the
application of the pressure differential, the film 1 will assume
the shape shown in FIG. 2. In this shape, the film 1 lines the
cavity of the head 3 and is formed in the same concave shape as the
cavity in the head. That is, a cavity is formed in the film 1 at
this point.
Still referring to FIG. 2, it can be seen that product 2 has
already been placed upon supporting member 7 which, in turn, has
been placed upon platform 8. The supporting member 7 is preferably
a gas impervious material and may be a metal such as aluminum sheet
or foil; a plastic material such as polystyrene foam; a laminate of
paper board with a gas impervious plastic coating; or, in general,
any sheet-like clear or opaque material.
As shown in FIG. 2, the film 1 shaped into a concave form or cavity
has been positioned over the product 2 and supporting member 7. At
this point the vacuum head 3 has not been closed upon the chamber
9. The closing of the chamber is accomplished as shown in FIG. 3.
During this whole sequence of operation as shown in FIGS. 2 and 3,
vacuum is constantly applied through ports 14, manifold 4, and port
6 to retain the concave shape of the film 1. In FIG. 3, with the
chamber closed by closure member or head 3, vacuum or pressure
differential is applied through port 11 and the application of this
vacuum is illustrated by the downwardly pointing arrow and the
abbreviation "vac. Arrows on either side of platform 8 are used to
demonstrate the evacuation of the air and gas from the region or
space between supporting member 7 and film 1. The path of the
evacuated gases or air is from the vicinity or product 2, around
the peripheral space between chamber 9 and platform 8 into the
chamber cavity or manifold 18, and out through port 11. As stated
before, during the evacuation of the chamber, the concave shape of
the film 1 is retained preferably by application of vacuum through
ports 14 and manifold 4. During this process further heating can be
supplied to soften the film 1 when it is a thermoplastic
material.
In FIG. 4, the film 1 is shown collapsed around and formed on
product 2 and in contact with supporting member 7. The vacuum or
pressure differential has been maintained through port 11 and the
vacuum through port 6 has been released and atmospheric pressure
has been admitted as shown by the downwardly pointing arrow from
the word "atmosphere." Super-atmospheric pressure can be applied
through port 6 to move the film more rapidly and securely against
product 2; or sub-atmospheric pressure could be applied to slow
down the movement and stretching rate of the film. To move the film
1 against the product 2 and supporting member 7, it is only
necessary that the pressure on the lower side of the film be less
than the pressure on the upper side. For instance, in the step
illustrated in FIG. 3, the vacuum applied on the upper side of film
1 through ports 14 must necessarily be equal to or greater than the
vacuum applied below the film through port 11 in order to retain
the concave shape of the film; but, when the film 1 is moved
against the product 2 as shown in FIG. 4, the action of the vacuum
acting through port 11 serves to pull the film against the product
2. Or, viewed in another manner, the action of the atmosphere
pushes the film 1 down on the product 2.
To hold and retain the cavity or concave shape of the film 1 as
shown in the steps illustrated in FIGS. 2 and 3, it is usually
necessary to draw a vacuum in excess of 20 inches of mercury
through ports 14; and, to ensure complete package evacuation, a
vacuum in excess of 20 inches of mercury is usually applied through
vacuum port 11. For best results, a vacuum of about 29 inches of
mercury through both ports is preferred. As long as the vacuum
applied above the film is greater than, or no less than, the vacuum
applied below the film, the film will remain in place. However,
when the vacuum is released above the film, it will move downward.
When the film moves downwardly, it has to move only through a short
distance before it contacts the top of the product 2. This short
distance is occasioned by the concave shape of the film and gives
the film little opportunity to wrinkle before contacting the
product 2 and forming on it.
A further advantage of shaping the film 1 into a cavity prior to
forming it around the product is that the film 1 can be clamped at
approximately the same level as the supporting member 7. (See FIG.
3) When the product 2 and supporting member 7 are located well
below the opening to the vacuum chamber 9, the edges of the film 1
will be stretched disproportionately and will not adhere to the
edges of the supporting member 1 without difficulty and excess,
unusable film around the periphery of the supporting membr 7 will
result. Furthermore, in the present process, after being placed in
the vacuum chamber the product and backing board remain stationary
and do not have to be moved. This means that there is less
likelihood of the product moving out of its position on the backing
board 7 and less likelihood of the product 2 being distorted or
even crushed by the physical movement of the product into the film.
FIG. 5 shows a finished package made according to the present
invention. Product 2, rectangular in shape, is covered by film 1
which closely conforms to the shape of the product. In other words,
product 2 has served as the forming or die member for the film 1.
The film 1 is sealed against the supporting member 7 which carries
product 2. Preferably, the packaging film 1 will be of an
impervious material, that is, one having relatively low air or
oxygen transmission and the same will be true for the supporting
member 7. The sealing between film 1 and supporting member 7 can be
accomplished in several different manners. For example, the film 1
can be coated with an adhesive which can be heat activatable. Thus,
when the film is heated by contact with the wall 15 of the cavity
of head 3 under the influence of heaters 5 (see FIG. 2), the
adhesive will be activated and subsequently, when the film is moved
against the backing board 7 as shown in FIG. 4, the adhesive will
seal to supporting member 7. When polyethylene is used as the film
1, a coating of ethylene vinyl acetate makes a very satisfactory
heat activatable adhesive. Another means of sealing is to coat the
supporting member 7 with a material such as polyethylene which will
be the same material used in the film 1. Thus, when sufficiently
heated, the like materials will bond or seal one to the other.
Still another method of sealing is to put a pressure sensitive
adhesive or heat activatable adhesive on the backing board and rely
upon heat within the chamber to activate the adhesive.
The present invention is particularly suitable in packaging food
products where an evacuated package is necessary to extend the
shelf lifetime of the product. Various food items require packaging
materials having differing moisture vapor transmission rates and
oxygen permeability rates. Within the scope of this invention,
packaging materials can be selected and used with properties that
match the requirements for the packaged food item. Also, various
atmospheres can be used for the product. For instance, the space
containing the product can be flushed with an inert gas such as
nitrogen and then a pressure differential applied to the film 1
through ports 14 to push it against the product 2 and backing
member 7. Once sealed, a hermetically closed package is thus
made.
* * * * *