Heat sealable shrink laminate

A heat sealable laminate having high unidirectional shrinkage and the ability to produce an effective seal when exposed to an elevated temperature. The heat sealable laminates of the present invention are used to label containers without application of an additional adhesive.

FIELD OF THE INVENTION 
The present invention is directed to polymeric shrink films and processes 
for producing polymeric shrink films. More particularly, the present 
invention is directed to polymeric shrink films using oriented polymeric 
films and laminates which are particularly advantageous in labeling 
articles, such as beverage containers, having irregular shapes. 
BACKGROUND OF THE INVENTION 
A distinguishing characteristic of shrink film is its capacity, upon 
exposure to some level of heat, to shrink or, if restrained, to create 
shrink tension within the film. When such a shrink film is used in a 
process to label or wrap a container, and then is subjected to certain 
temperature, this process causes the film to shrink around the product 
producing a tight, transparent or opaque, wrapping that conforms to the 
contour of the article and provides useful functions required of label or 
packaging materials. 
The ability of a film to shrink upon exposure to some level of heat arises 
from the orientation of the film during manufacture. During film 
manufacture, the films are usually heated to their orientation temperature 
range, which varies with the different polymers used for the films, but is 
usually above room temperature and below the melting temperature of the 
polymer. The film is then stretched, either sequentially or 
simultaneously, in the longitudinal or machine direction (MD) and in the 
cross or transverse direction (TD) to orient it. After being stretched, 
the film is rapidly cooled, thus freezing the film in its biaxially 
oriented state. Upon heating, the orientation stresses are relaxed and the 
film will begin to shrink back to its original, unoriented dimension. 
The polyvinyl chloride (PVC), polystyrene, polyester, and polyolefin 
families of shrink films provide a wide range of physical and performance 
film characteristics. Film characteristics play an important role in the 
selection of a particular film and may differ for each type of packaging 
or labeling application. 
Polyolefins have been most successful with applications where moderate to 
high shrink forces are preferred. Polyolefin films are also used on 
automatic, high speed shrink wrapping equipment where shrink and sealing 
temperature ranges are more clearly controlled. Polyolefin films are 
particularly suitable for this application because polyolefin films tend 
to be cleaner, leaving fewer deposits and less residue, which extend the 
life of the equipment as well as reducing equipment maintenance. 
The shrink films have been subjected to subsequent processing steps such as 
printing, metallizing, or laminating in order to fashion labels for use on 
containers. Typically, the shrink film is applied to the container to be 
labeled, and an amount of an adhesive is applied to the shrink film in 
order to produce tight smooth continuous seams. The application of 
adhesive to the shrink film is done after fabrication of the shrink film. 
Application of the adhesive must be accomplished with great care in order 
to preserve the aesthetics of the label produced from the shrink film. The 
application of the adhesive layer also is an additional step which may 
require an amount of time to develop green strength of the adhesive at the 
seam prior to subsequent processing of labels which high speed labeling 
and packaging operations may not be able to tolerate. 
SUMMARY OF THE INVENTION 
The instant invention is directed to a heat sealable shrink laminate 
comprising biaxially oriented polymer film having an imbalance of 
shrinkage consisting essentially of a machine direction (MD) shrinkage 
greater than a transverse direction (TD) shrinkage in a MD/TD ratio of at 
least 2:1 and a heat seal layer applied to a surface of the biaxially 
oriented film. The heat seal layer is capable of forming an effective seal 
at a sealing temperature less than or equal to a shrinking temperature 
which produces a MD shrinkage of 10% or less.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is directed to a heat sealable shrink laminate 
comprising a biaxially oriented polymer shrink film on which is applied a 
heat seal layer, the process of making the heat sealable shrink laminate 
and articles such as cans bottles and the like, labeled or covered with 
the heat sealable shrink laminate. 
Production of the biaxially oriented polymer shrink film having utility in 
the present invention is based on the control of temperature, machine draw 
parameters and film parameters that allow for regulation of resultant 
shrinkage of a biaxially oriented polymeric film. More particularly, by 
achieving a balance of temperature, draw ratio, line speed, and oriented 
polymer film properties, biaxially oriented polymeric films of utility in 
the present invention are able to produce enhanced machine direction (MD) 
shrinkage with a very low degree of transverse direction (TD) shrinkage. 
This balancing of MD and TD shrinkage, particularly in oriented 
polypropylene (OPP) films, imparts the unique shrink label and packaging 
characteristics to the present invention. 
The MD re-orientation involves placing a conventional OPP film on a series 
of heated rolls or in an oven and, by raising the temperature of the 
heated rolls or oven to a temperature below the melting temperature of the 
film, the stress necessary to orient the film is reduced. For example, 
polypropylene begins to shrink near 100.degree. C. and shrinkage continues 
to increase until melting at greater than about 160.degree. C. The MD 
re-orientation can take place after the OPP film is produced or, in some 
cases, the re-orientation can take place in line while the OPP film is 
being produced. Most polymer products respond to this orientation with an 
enhanced high temperature shrinkage. The majority of the products' 
response is in the direction of the imposed strain. 
The biaxially oriented polymer shrink film used in the instant invention is 
disclosed in U.S. patent application Ser. No. 07/651,966, incorporated 
herein by reference. The process for producing the biaxially oriented 
polymer shrink film involves subjecting a biaxially oriented polymer film 
to processing conditions and temperature effective to produce biaxially 
oriented polymer shrink films having thermal shrink properties including 
shrinkage in the machine direction of the film and transverse direction of 
the film as a function of the MD reorientation mechanical MD/TD draw 
ratio. The conditions include an MD reorientation mechanical MD/TD draw 
ratio between about 1.01 and about 7.5, preferably 1.01 to 1.5, more 
preferably 1.10 to 1.40. The MD reorientation mechanical draw ratio is 
defined herein as the ratio of the maximum to minimum roll speed of a 
machine performing the MD reorientation of the biaxially oriented polymer 
film in the formation of the biaxially oriented polymer shrink film. 
Preferably, the biaxially oriented polymer shrink film of the present 
invention has a film reorientation MD/TD mechanical draw ratio within the 
range of about 1.01 to about 1.5. Preferably the reorientation MD/TD 
mechanical draw ratio is within the range of about 1.1 to about 1.37; more 
preferably, the reorientation MD/TD mechanical draw ratio is within the 
range of about 1.12 to about 1.35. 
The conditions also include a corresponding line speed comprising an input 
roll speed within the range of about 200 ft/min to about 1,500 ft/min and 
an output roll speed within the range of about 201 ft/min to about 1,501 
ft/min. More preferably, the MD reorientation mechanical MD/TD draw ratio 
is between about 1.10 and 2.00 and the corresponding input roll speed is 
within the range of about 750 ft/min to about 850 ft/min. The output roll 
speed is within the range of about 935 ft/min to about 1500 ft/min, and 
most preferably wherein the input roll speed is about 800 ft/min and the 
output roll speed is within the range of about 1100 ft/min to about 1300 
ft/min. 
The basic processes for producing biaxially oriented polymer shrink films 
for use in accordance with the present invention may be selected from the 
group of conventional processes for producing biaxially oriented 
polypropylene (BOPP) films, such as the tubular and tenter techniques. 
In general, in the tubular or bubble process, molten polymer is extruded 
from an annular die and then quenched to form a tube. The wall thickness 
of the tube is controlled partly by the annular die gap and partly by the 
relative speeds of extrusion and haul-off. The tube passes through slow 
running nip rolls and is then re-heated to a uniform temperature. 
Transverse drawing is achieved by increasing the air pressure in the tube, 
the draw ratio, and/or by adjustments to the volume of entrapped air. The 
air is trapped by pinch rolls at the end of the bubble remote from the 
extruder and these are generally run at a faster speed than the first 
pair, thus causing drawing of the film in the machine direction. The 
tubular process thus obtains simultaneous transverse and forward 
orientation. 
In the second of the previously mentioned processes, i.e., the tenter 
process, the polymer is extruded through a slot die and quenched. The 
extruded sheet is normally oriented in two sequential steps. The first 
step is usually longitudinal orientation between rolls running at 
different speeds. In the second stage, the film enters a tenter frame, 
where it is stretched laterally by means of diverging chains of clips. 
Whereas the bubble process operates at constant pressure, the tenter frame 
process operates at a constant rate of elongation. Somewhat higher 
stretching forces are required in the second stage which may be carried 
out at slightly higher temperatures. This is mainly due to crystallization 
of the film during the first stretching operation. The tenter frame 
process can also be carried out as a simultaneous operation in which an 
extruded sheet with beaded edges is biaxially oriented in a tenter frame 
equipped with diverging roller grips for holding and stretching the film. 
The tenter or tenter frame operation has the advantage of considerable 
versatility, producing films with a wide range of shrink properties. 
After stretching, polymer orientation is locked into the oriented film by 
cooling. When the oriented film is subsequently heated up to temperatures 
in the vicinity of the stretching temperature, the frozen-in stresses 
become effective and the film shrinks. Strains and stresses which are 
related to the degree of orientation and the forces which are applied 
during stretching are thereby recovered. 
The biaxially oriented polymer shrink film is produced by subjecting a 
biaxially oriented polymer film to processing conditions and temperatures 
effective to produce biaxially oriented polymer shrink films having 
thermal shrink properties including shrinkage in the machine direction of 
the film and transverse direction of the film as a function of 
temperature, wherein the processing temperature is within the range of 
about 70.degree. C. to about 160.degree. C., preferably within a range of 
about 90.degree. C. to about 130.degree. C., and more preferably within 
the range of about 100.degree. C. to about 120.degree. C. 
Preferably, the heated biaxially oriented film is drawn under conditions 
effective to extend the heated biaxially oriented film at least 1.10 times 
its original length in the machine direction; and cooling the drawn film 
while the film is still under tension, whereby a biaxially oriented 
polymeric shrink film is produced with thermal shrinkage properties being 
a function of temperature. 
For purposes of the present invention, and particularly for shrink films 
and laminates thereof used to label articles in accordance with the 
present invention, MD shrinkage is greater than about 10%, preferably 
greater than about 15%, more preferably greater than about 20% at 
140.degree. C. 
For purposes of the present invention, the biaxially oriented polymer 
shrink film may be selected from the group consisting of clear films and 
opaque films; the biaxially oriented polymer shrink film may also be 
selected from the group consisting of monolayer films, multilayer films, 
coextruded films, extrusion coated films and coated films. Biaxially 
oriented polymer shrink films of utility in the present invention are 
composed of polyolefins, such as polypropylene. Preferably, the biaxially 
oriented polymer shrink film has a thickness within the range of about 50 
to about 200 gauge, and more preferably within the range of about 70 to 
about 140 gauge. 
The thermal shrink properties of the biaxially oriented polymer shrink 
films and laminates of utility in the present invention differ from 
conventional oriented polymer films while still maintaining the useful 
characteristics of oriented polymer film. Thermal shrink properties of the 
biaxially oriented polymer films of utility in the present invention are 
characterized by shrinkage in the machine direction (MD) and transverse 
direction (TD) as a function of temperature. 
It is critical that the biaxially oriented polymer shrink film manifest a 
resistance to MD alteration in dimension during typical label preparation 
and application to maintain uniform repeat length and registration as 
imparted by applied heat/or tension history. The biaxially oriented 
polymer shrink film also must be resistent to MD and/or TD lamination curl 
to maintain uniform lamination flatness. The biaxially oriented polymer 
shrink film should maintain overall web flatness, as exhibited by typical 
oriented polyolefin films, as well as single web or lamination stiffness 
as required for conventional printing, laminating, and label-to-container 
feeding operation. 
The MD re-orientation of BOPP film is more complex than for conventional 
films due at least in part to initial residual stresses placed on the 
film. For example, in accordance with the present invention, it has been 
discovered that at a 140.degree. C. shrink temperature, BOPP films may 
shrink 15% in the machine direction (MD) or transverse direction (TD). 
After this same film is subjected to a film reorientation MD/TD mechanical 
draw ratio, a 5-30% transverse direction reduction in film width results 
and 140.degree. C. film shrinkage is biased in the MD direction, i.e. 
140.degree. C. MD shrinkage equals 25% and 140.degree. C. TD shrinkage 
equals 5%. 
For purposes of the present invention, the following procedure, derived 
from ASTM method D2732-83, which is designed to measure unrestrained 
linear shrinkage in both the machine and transverse directions, was used 
for measuring unrestrained linear thermal film shrinkage in a single 
direction at a time. 
A polydimethylsiloxane fluid bath, having a viscosity of 0.5 centistokes 
(cs), is preheated to desired temperatures within the range of about 
100.degree. C. to 140.degree. C. 
Film samples are precut to 0.5".times.22 cm and a 20 cm span is marked in 
the sample center. Ends are left on a film sample so the film sample can 
be anchored for immersion. One end of each film sample is placed in an 
immersion rack. A 1.2 g metal alligator clip is attached to a free long 
end of each film sample to keep the film sample from floating in the bath. 
The machine direction and the transverse direction are tested for each 
film sample. The heater/stirrer is then turned off and the film samples on 
the rack are immersed into the proper temperature bath for a count of five 
seconds prior to being removed from the liquid. The film samples are 
immediately measured and their % shrinkage calculated. For example, with a 
film sample having a 20 cm span, a shrinkage of 1 mm equals 0.5% 
shrinkage. The average % shrinkage of all the film samples run in one 
direction (MD or TD) is then recorded for a particular film sample. If 
there is an elongation rather than a shrinkage, a negative value is 
reported. 
Thermal shrink properties of the biaxially oriented polymer shrink films of 
utility in the present invention are characterized by shrinkage in the 
machine direction (MD) and transverse direction (TD) as a function of 
temperature. These shrink characteristics are outlined as follows: 
______________________________________ 
Temperature .degree.C. 
Shrinkage MD (%) 
Shrinkage TD (%) 
______________________________________ 
100 4 to 15 -8 to 5 
110 6 to 25 -8 to 7 
120 7 to 30 -20 to 10 
130 10 to 40 -20 to 15 
140 11 to 40 -20 to 15 
150 15 to 40 -20 to 15. 
______________________________________ 
The thermal shrink properties, combined with the tensile properties of the 
biaxially oriented polymer shrink films of utility in the present 
invention allow for the useful practice of using conventional labeling 
equipment. 
The tensile properties of the biaxially oriented polymer shrink film are 
characterized as follows: 
______________________________________ 
Tensile Properties 
______________________________________ 
Modulus (psi) 
MD 350,000 to 850,000 
TD 100,000 to 500,000 
Tensile Strength (psi) 
MD 10,000 to 50,000 
TD 10,000 to 40,000 
Ultimate Elongation (%) 
MD 20 to 175 
TD 50 to 250 
______________________________________ 
The tensile strength, elongation and modulus were measured using the ASTM 
D882 test procedure. 
The processes of the present invention, as described with respect to herein 
for producing heat sealable shrink laminate and resultant shrink film 
layers and laminates are polyolefin films such as polypropylene. In this 
regard, the polypropylene character of the film is preferably a 
homopolymer, although copolymers of propylene with minor amounts of 
ethylene or an alpha-olefin and the respective blends can also be used. 
Typical commercially available film-forming propylene homopolymers are 
crystalline or isotactic in their molecular structure and normally have a 
melt flow rate of about 2 to 10 dg/min. Conventionally, the polypropylene 
is compounded with conventional additives such as anti-oxidants, light 
stabilizers, inorganic antacids, such as calcium oxide or magnesium 
aluminum hydroxide carbonate hydrate in addition to fatty acid amide slip 
agents. 
In accordance with the present invention, biaxially oriented polymer shrink 
films can be a single web or formed into a laminate, with use as a 
laminate being particularly beneficial. 
For purposes of the present invention, any conventional lamination process 
may be used inasmuch as the biaxially oriented polymer shrink films have 
been observed to be capable of being suitably laminated using known 
technology, e.g., selected from the group consisting of wet bonding, dry 
bonding, hot melt or wax laminating, extrusion lamination, and thermal or 
heat laminating; however, dry bonding and thermal or heat laminating are 
preferred. 
Dry bonding involves applying adhesive to one of the films or webs. The 
solvent is evaporated from the adhesive and the adhesive-coated web is 
combined with the other web material by heat and pressure or by pressure 
only. 
Thermal laminating brings together coated substrates under heat and 
pressure. Typically, the webs are heated to the softening point of the 
coating; however, improved results, e.g. in clarity, are obtained when 
using preheat rolls and a steam box. 
Related to this, labels are normally printed and the printing is expected 
to be permanent. If the exposed printed surface is abraded, then the 
printing can be removed or scuffed. If, however, the printing is on the 
inside surface of a clear film and this clear film is laminated to another 
film, the printing is protected by the clear film. Alternatively, the 
printing can be on the inside surface of the clear or opaque web laminated 
to the clear protective overweb. In addition, the outermost surface of the 
laminate can be made matte, glossy, of low coefficient of friction, 
different in surface tension or composition, independent from the nature 
of the surface required to accept inks. Also, the adhesion of the printed 
film to a container can be influenced by the presence of ink. For example, 
a typical failure of a film-to-container bond will occur by separation at 
the weakest point or at the ink from the film, with no failure of the 
adhesive. By placing the ink between the layers of a laminated film this 
weak point is removed, allowing for the adhesive to bond directly from 
laminate surface to the container. Printing can also be applied to a clear 
film layer and either a clear or opaque film, or a metallized version of 
either type of film, can be laminated to the printed web. For purposes of 
the present invention, biaxially oriented polymer shrink films may be 
printed using conventional printing techniques including flexographic 
printing and rotogravure printing. 
Flexographic printing procedures typically employ presses selected from the 
group consisting of stack, central-impression, and in-line presses; 
flexographic printing which employs a central impression or common 
impression plate is preferred. 
Plate preparation for flexography involves taking the art work through 
standard engraving procedures to form a zinc plate. At this point, a 
phenolic resin negative of the zinc plate is made from which the rubber 
positive of the zinc plate can be formed by standard molding methods using 
0.0125-inch-thick rubber sheeting formulated for platemaking. Alternately, 
photosensitive glass and plastics, may be used instead of the zinc plates. 
A typical method of mounting the plate employs a pressure sensitive 
material to adhere the rubber plate to the plate cylinder; vulcanizing the 
rubber plate to a metal brace that can be clamped around the plate 
cylinder may also be used for this purpose. 
A conventional flexographic press consists of four sections: An unwind 
station for the web to be printed, a printing section, a drying oven, and 
a windup for the finished printed web. 
The unwind section provides for the mounting of two additional rolls and a 
flying splice mechanism that allows for automatic splicing of the new roll 
to the expiring roll going through the press. Similarly, the windup 
section is provided with multiple windup spindles, usually two, and a 
mechanism for cutting the web when the roll on one spindle has reached a 
desired size and for attaching the free end to a core mounted on the 
second spindle for continuous output. 
Web tension has a definite effect on print register and on slit roll 
quality, and particularly on central-impression flexographic presses, the 
web should be pulled tight around the central drum to eliminate wrinkles 
or flatness deficiencies. 
Drying is performed with high-velocity hot air generated by gas burners, 
distribution ducts, and between-color dryers. The latter are a major aid 
in trapping the ink laid down in one color station before the next color 
is printed. This prevents the new color from causing the previous color to 
smear. 
Drying temperature should be as high as possible to ensure best solvent 
removal; however, drying temperature should not be high as to cause film 
shrinkage. A suitable manner for determining proper temperature is to 
increase heat until film shrink begins, i.e., 2 to 5%, and then back off 
5.degree. F. For purposes of the present invention, web temperature is 
preferably approximately 170.degree. F.; although the printing process may 
run at a slightly higher drying temperature. 
The rotogravure process uses a metal cylinder printing member into which 
the design to be printed has been etched. Rotogravure equipment resembles 
an in-line flexographic press in that it, too, requires an unwind, a 
printing section, a dryer, and a rewind. However, each color station has a 
dryer designed to dry one color completely. 
A typical rotogravure color unit includes an impression roll, a printing 
(engraved) cylinder or roll, an ink supply, e.g. an ink pen or fountain, 
and a doctor blade. The printing cylinder rotates in the ink fountain, 
picking up excess ink. The doctor blade, which oscillates parallel to the 
axis of the printing cylinder to prevent accumulation of dirt behind the 
blade that can cause streaks, removes the excess, permitting ink to remain 
only in the cells of the engraved part of the roll, since the bottom of 
the cells are below the surface of the cylinder. The impression cylinder, 
which is rubber covered, squeezes the web to be printed against the 
engraved roll, causing the web to remove ink from the engraving as it 
leaves the nip, thus accomplishing transfer of ink from the printing 
cylinder to the moving web. In flexography, the printing is done by a 
molded rubber plate using a metal impression roll. In rotogravure, the 
printing plate is an engraved metal roll and the impression roll is rubber 
covered. 
A typical rotogravure press arrangement also includes two color stations, 
although eight color presses that can print several-tone cylinders and 
line cylinders, e.g., for type and can apply an overall high-gloss lacquer 
in-line are also typical. Rotogravure presses may also having flying 
splice unwinds with precise tension controls. 
The process of using the biaxially oriented polymer shrink films to produce 
laminates which are applied to an article in accordance with the present 
invention has been discovered to overcome the previously mentioned 
disadvantages. In this regard, the present invention allows for a single 
printing operation to produce as many as four laminate variations. Also, 
shrinkable webs with different shrinkage properties can be laminated to a 
common printed shrinkable web to give laminates with different shrinkage 
properties tailored to the particular container or the requirements of the 
application. In addition, shrinkable webs of different shrinkage 
properties can also be laminated together to give a laminate whose 
shrinkage properties might be difficult to achieve using only a single 
film. 
The character of a polymer surface can be changed in several ways. One 
method is to expose the surface to an energy source, such as a corona 
discharge, plasma, or an x-ray or electron bombardment. This can be done 
over a broad temperature range in an inert atmosphere or reactive 
atmosphere. Depending on the temperature, intensity, rate of application, 
and frequency of the energy and the nature and concentration of the 
chemical medium in contact with the surface before, during, and/or after 
energy application, a wide range of physical and/or chemical modifications 
of the film surface can be effected. 
A second way to change a polymer surface is to cause an internal chemical 
additive to bloom to the surface by the application or removal of heat 
from the film. Alternatively, a substance on the surface of the film can 
be made to migrate inside of the film and away from the surface by the 
application or removal of heat from the film. The chemical nature of the 
substance or additive and the time/temperature history to which it is 
exposed can lead to a wide range of possible surface modifications. 
A third way to change a polymer surface is to cause a change in surface 
morphology by the application of heat and/or pressure to the film. The 
physical and topological nature of the surface can be altered, for 
example, by annealing a film and changing the crystalline structure 
present on the film surface. 
The biaxially oriented polymer shrink film may be composed of two or more 
polymer shrink films. Each polymer shrink film may function on its own as 
a heat shrinkable label or each polymer shrink film may be clear or 
opaque, metallized or non metallized, have similar or dissimilar surface 
character and shrinkage properties. In these embodiments, each polymer 
shrink film is preferably composed of polypropylene, a copolymer of 
polypropylene or a blend of polypropylene and a copolymer of 
polypropylene. Each polymer shrink film is preferably biaxially oriented, 
providing high strength in all directions of the film plane, unlike 
uniaxially oriented films which are strong in the orientation direction 
but weak in the perpendicular direction. 
On a surface of the biaxially oriented polymer shrink film is a heat seal 
layer. Heal seal layers of utility in the present invention are capable of 
forming a effective seal at a sealing temperature less than or equal to a 
shrinking temperature which produces a MD shrinkage of 10% or less in the 
biaxially oriented shrink film. Heat seal layers of utility in the present 
invention have thicknesses from 1 to 20 gauge, preferably from 2 to 10 
gauge. 
In order to determine if a seal is "effective", the following procedure is 
performed. A pair of laminates having surfaces to be sealed are 
superimposed on one another so that the heat seal layers to be sealed are 
in contact with one another and placed in a sealing device. The sealing 
device has an upper heated metal jaw which is capable of pressing against 
a resilient anvil. The resilient anvil is not heated. Both the upper metal 
jaw and the resilient anvil are covered with non-stick surface, such as a 
polytetrafluoroethylene covered glass tape, in order to prevent sticking 
of either the upper heated metal jaw or the resilient anvil surfaces to 
the laminate after the seal has been formed. The sealing device is capable 
of producing a seal one inch in width. A Fin seal or a Lap seal may be 
produced using the above-described sealing device. Laminates are subjected 
to a temperature and 20 psi of applied pressure within a 0.5 second time 
period to fuse the laminates together thereby producing a seal. 
The previously produced seal is subsequently tested using ASTM standard 
test method F 88-85, "Standard Test Method for Seal Strength of Flexible 
Barrier Materials". Seals which are 50 g/in or more on a Fin Seal and 100 
g/in or more on a Lap Seal are considered "effective". The temperature of 
the pair heated metal platens at which an "effective" seal is produced for 
a particular laminate is defined herein as the "sealing temperature" of 
that laminate. 
The heat seal layer may be applied to the biaxially oriented polymer shrink 
film through coating techniques, laminating techniques or through 
coextrusion techniques. Also, the heat seal layer may be applied after the 
formation of the biaxially oriented polymer shrink film or prior to its 
formation by applying the heat seal layer to the biaxially oriented 
polymer film. 
The heat seal layer may be of any polymer composition known to those of 
ordinary skill in the art for sealing films. Preferably, the heat seal 
layer is composed of alpha-olefins, more preferably composed of copolymers 
of propylene and ethylene, still more preferably composed of terpolymers 
of propylene, butene and ethylene. 
The heat seal layer may be either clear or opaque. The heat seal layer may 
contain additives commonly known in the art, including but not limited to, 
stabilizers, antioxidants, coefficient of friction modifiers, and fillers. 
Referring now to FIG. 1, an embodiment of the heat sealable shrink laminate 
of the instant invention 10 is depicted in cross-section. The biaxially 
oriented polymer shrink film 11 is depicted with the heat seal layer 12 
applied to one of its surfaces. This embodiment is of a two-layer 
laminate. 
Referring now to FIG. 2, another embodiment of the heat sealable shrink 
laminate of the instant invention is depicted in cross-section. This 
embodiment is of a four-layer laminate 20 where two biaxially oriented 
polymer shrink film are attached to one another at one surface 21 while 
two heat seal layers are arranged on a second surface 22. 
Referring now to FIG. 3, another embodiment of the heat sealable shrink 
laminate of the instant invention is depicted in cross-section. This 
embodiment is of a three-layer laminate 30 where one biaxially oriented 
polymer shrink film 11 has a heat seal layer 12 attached to each of its 
surfaces. 
The process according to the present invention may be further appreciated 
by reference to the following examples which are only representative of 
the present invention and in no way are meant to limit the present 
invention in any way to the particulars which are disclosed. Thus, the 
following are given merely as non-limiting examples to further explain the 
present invention. 
EXAMPLES 
Example 1 
(Two-Layer Laminates) 
Using the method described in U.S. patent application Ser. No. 07/651,966 
incorporated herein by reference, films composed of polyolefins in both 
clear and opaque formulations were produced. The above films had 
coextruded heat seal layers. Formulations of the various heat seal layers 
are as follows: Formulation A is a copolymer of propylene and ethylene, 
(Z9470HB available from Fina Chemical Company); Formulation B is a 
copolymer of propylene and ethylene, (8573 or 8573HB available from Fina 
Chemical Company); and Formulation C is a terpolymer of propylene, butene 
and ethylene, (W.S.709-S4 available from Sumitomo Chemical Company). 
Each of the films were biaxially oriented using conventional techniques. 
The films were subjected to a secondary orientation in the MD according to 
the teachings of U.S. patent application Ser. No. 07/651,966. 
The resulting products were two-layer embodiments of the instant invention. 
These laminates are listed in Table 1. The shrinkage properties of the 
above-identified laminates are found in Table 2. 
TABLE 1 
______________________________________ 
TWO-LAYER LAMINATE 
Secondary 
Orientation 
Film Nominal MD Mechanical 
Sealant 
Type ID Gauge Draw Type 
______________________________________ 
Clear 1001-150-7 
80 1.20 A 
Clear 1001-150-8 
80 1.31 A 
Clear 1001-159-12 
70 1.14 C 
Clear 1001-159-13 
70 1.19 C 
Clear 1001-159-14 
70 1.24 C 
Clear 1001-177-3 
70 1.15 C 
Clear 1001-177-4 
70 1.10 C 
Clear 1001-180-2 
70 1.10 C 
Clear 1001-180-3 
70 1.16 C 
Clear 1001-180-4 
70 1.20 C 
Opaque 1001-150-4 
135 1.38 B 
Opaque 1001-150-5 
135 1.38 B 
Opaque 1001-150-6 
135 1.38 B 
Opaque 1001-177-1 
135 1.20 B 
Opaque 1001-177-2 
135 1.30 B 
Opaque 1001-180-5 
135 1.20 C 
Opaque 1001-180-6 
135 1.30 C 
Opaque 1001-180-7 
13 1.20 C 
Opaque 1001-180-9 
135 1.30 C 
______________________________________ 
TABLE 2 
______________________________________ 
TWO-LAYER LAMINATE 
Film Shrinkage, MD/TD, % 
Type ID 100.degree. C. 
120.degree. C. 
140.degree. C. 
______________________________________ 
Clear 1001-150-7 
-- 14.6/-7.3 
20.6/-5.0 
Clear 1001-150-8 
-- 19.0/-15.4 
24.9/-12.0 
Clear 1001-159-12 
4.4/-2.3 7.9/-2.5 
12.1/1.8 
Clear 1001-159-13 
6.5/-3.7 10.7/-4.3 
15.1/-0.1 
Clear 1001-159-14 
8.3/-5.0 13.0/-6.5 
17.7/-2.8 
Clear 1001-177-3 
-- 9.3/-4.3 
14.2/0.6 
Clear 1001-177-4 
-- 7.0/-2.3 
11.4/3.6 
Clear 1001-180-2 
4.1/-1.8 6.9/-1.8 
10.9/2.7 
Clear 1001-180-3 
5.9/-2.9 9.2/-3.6 
13.2/1.4 
Clear 1001-180-4 
7.8/-4.3 11.9/-5.4 
16.0/-1.9 
Opaque 1001-150-4 
-- 21.9/-15.5 
29.5/-13.4 
Opaque 1001-150-5 
-- 22.3/-16.3 
28.7/-13.7 
Opaque 1001-150-6 
-- 21.2/-15.5 
28.3/-10.9 
Opaque 1001-177-1 
-- 11.7/-5.6 
17.9/0.4 
Opaque 1001-177-2 
-- 16.8/-10.2 
23.1/-5.2 
Opaque 1001-180-5 
6.3/-4.4 9.5/-6.2 
12.1/-5.3 
Opaque 1001-180-6 
9.8/-6.4 14.6/-9.6 
18.5/-6.9 
Opaque 1001-180-7 
6.1/-4.1 10.1/-5.6 
12.0/-4.5 
Opaque 1001-180-9 
7.9/-6.5 13.0/-10.4 
16.3/-10.6 
______________________________________ 
Example 2 
(Four-Layer Laminates) 
Two-layer laminates of example 1 were subsequently laminated to one another 
with the heat seal layers arranged on the outside surface of the resultant 
laminates, and the biaxially oriented polymer shrink films positioned in a 
superimposed arrangement with each other. The two laminates were adhered 
to one another using a dry bond lamination technique. 
Shrinkage properties of the above-identified four-layer laminates are found 
in Tables 3A and 3B. Strength of seals produced from the above-identified 
four-layer laminates are found in Table 4 and 5. 
TABLE 3A 
______________________________________ 
FOUR-LAYER LAMINATE 
Shrinkage, % 
100.degree. C. 
120.degree. C. 
140.degree. C. 
Type ID MD/TD MD/TD MD/TD 
______________________________________ 
C/C Laminate 
1022-7-1 3.0/-1.0 5.7/-1.0 
10.0/2.0 
Clear (C) 1001-180-2 
C/W Laminate 
1022-7-5 4.0/-1.0 9.0/-1.3 
13.0/1.0 
Clear (C) 1001-180-2 
Opaque (W) 
1001-180-6 
C/W Laminate 
1022-7-8 5.0/-2.3 10.0/-4.0 
14.0/-2.0 
Clear (C) 1001-180-4 
Opaque (W) 
1001-180-9 
______________________________________ 
TABLE 3B 
__________________________________________________________________________ 
FOUR-LAYER LAMINATE 
Shrinkage, %* 
90.degree. C. 
110.degree. C. 
130.degree. C. 
140.degree. C. 
Type ID MD TD 
MD TD 
MD TD MD TD 
__________________________________________________________________________ 
C/W Laminate 
29222-95-1 
3.0/-2.0 
6.0/-2.0 
10.0/-1.0 
18.0/-0.7 
Clear (C) 
1001-177-4 
Opaque (W) 
1001-177-1 
C/W Laminate 
29222-95-6 
4.0/-2.0 
7.0/-3.0 
12.7-4.0 
16.0/-2.0 
Clear (C) 
1001-159-14 
Opaque (W) 
1001-177-1 
__________________________________________________________________________ 
*Oil bath shrink test 
TABLE 4 
__________________________________________________________________________ 
FOUR-LAYER LAMINATE 
Seal Strength v. Temperature 
__________________________________________________________________________ 
Heat Seal 
Seal Strength (lb/in.)* 
ID Temp, .degree.F. 
190 200 
210 220 
230 240 
250 
__________________________________________________________________________ 
29222-95-1 2.2 3.5 
6.5 7.5 
8.4 8.6 
10.6 
29222-95-6 1.9 4.1 
5.3 7.2 
8.7 10.5 
11.9 
__________________________________________________________________________ 
Heat Seal 
Temp, .degree.F. 
150 160 
170 180 
190 
__________________________________________________________________________ 
1022-7-1 1.8 5.6 
9.0 15.5 
15.3 
-- -- 
1022-7-5 2.2 6.3 
10.1 
12.7 
14.0 
-- -- 
1022-7-8 -- 2.6 
6.0 11.0 
12.9 
-- -- 
__________________________________________________________________________ 
*Lap seals, 20 psi, 0.5 sec 
TABLE 5 
__________________________________________________________________________ 
FOUR-LAYER LAMINATE 
Seal Strength v. Temperature 
Heat Seal 
Seal Strength (g/in.)* 
ID Temp, .degree.F. 
200 
210 220 230 240 
250 
260 
270 
280 
__________________________________________________________________________ 
29222-95-1 -- -- -- 9.3 13.9 
20.4 
26.7 
235 
235 
29222-95-6 -- -- -- 16.5 
21.6 
44.1 
61.7 
218 
228 
1022-7-1 25.5 
209 303 326 -- -- -- -- -- 
1022-7-5 57.3 
183 253 316 -- -- -- -- -- 
1022-7-8 35.6 
173 336 420 -- -- -- -- -- 
__________________________________________________________________________ 
*fin-seal g/in, 20 psi, 0.5 sec 
Novel heat sealable shrink laminates in accordance with the present 
invention have been discovered to be particularly advantageous in labeling 
articles having irregular shapes. For purposes of the present invention, 
the article may be a straight-walled or contoured aluminum, steel, metal, 
plastic, glass, composite, or tubular or spiral wound cardboard container 
(especially a can or tin) for beverages (especially soda and beer), foods, 
or aerosols. 
In this regard, either a single laminate or multiple laminate layers of 
novel heat sealable shrink laminates in accordance with the present 
invention is capable of being heat shrunk onto an article, such as a 
beverage can, the upper and bottom parts of which are tapered inwardly. 
The novel heat sealable shrink laminates and laminates of novel heat 
sealable shrink laminates in accordance with the present invention are 
particularly advantageous in labeling more modern beverage cans which 
taper inwardly at the upper and lower extremities so that a label must 
either avoid extending to these extremities or must conform closely to the 
shapes thereof: for example, in accordance with the procedures disclosed 
in U.S. Pat. No. 4,844,957, the disclosure of which is hereby incorporated 
herein in its entirety by reference thereto. 
To prepare the embodiment of the present invention, incoming packages are 
spaced by an infeed worm and transferred, via the infeed star, to a 
central rotary carousel. Here, firmly located between a base platform and 
overhead centering bell, they are caused to rotate about their own axes. 
As a label is withdrawn laterally from a magazine, it is wrapped around 
the circumference of the article and cut to a desired length. A means for 
sealing the heat sealable shrink laminate, such as a heater bar, applies 
sufficient heat and pressure to fuse the heat seal layer thereby producing 
a seal, usually in the form of an overlap bond. The seal is formed at or 
above the "sealing temperature" but below a "shrinking temperature" which 
is defined as the temperature required to conform or shrink the heat 
sealable shrink laminate to the profile of the article being labeled. The 
article is subsequently exposed to a temperature at or above the 
"shrinking temperature" causing the heat sealable shrink laminate to 
conform to the profile of the article and thereby producing fully labeled 
article. 
The fully labelled articles are then transferred, via the discharge 
star-wheel, to the down-stream conveyor. The size of the label is such 
that it extends (top and bottom) beyond the cylindrical portion of the 
bottle or can. After labelling, bottles or cans are passed through a 
heating sector to ensure the upper and lower label areas shrink tightly 
and uniformly to the bottle contours. For purposes of the present 
invention, it has been discovered that hot air preferably should be 
directed towards the top and bottom of the label or other specific area of 
the labelled container where a non-uniform contour is located to allow 
preferential shrinkage of the heat shrink label in these areas. 
In contrast to the present invention, none of the conventional labels or 
other known labels have been observed to be as suitable for labeling of 
irregularly shaped beverage containers, and other irregularly shaped 
articles, as contemplated in accordance with the present invention. For 
example, conventional labels have been observed to distort during the 
process of applying the same to irregular shaped articles, for example by 
heat shrinking. More importantly, however, such conventional labels, and 
particularly laminated labels, do not readily conform to the irregular 
shape of the article, for example, especially at the tapered extremes of 
beverage containers, such as cans. 
Referring now to FIG. 4, a labeled article of the instant invention 40 is 
depicted in cross-section. The heat sealable shrink laminate 10 is 
depicted as conforming to the profile of the labeled article, in this case 
a beverage can 41. A seam 42 can be seen also conforming to the profile of 
the labeled article. The position of the heat shrink laminate in an 
non-shrunken state 43 prior to exposure to shrinking temperature is 
depicted in phantom. 
Thus, in accordance with the present invention, an irregular shape article, 
such as a beverage container, which includes a cylindrical wall of metal, 
glass, or plastic and a top and a bottom on the wall, wherein the wall 
tapers inwardly adjacent to the top/bottom to form top and bottom tapered 
portion is provided with a heat shrinkable layer, or laminated layers of 
novel heat sealable shrink laminate produced in accordance with the 
present invention, to encircle the wall and conform to the tapered 
portions, for example, as disclosed in U.S. Pat. Nos. 4,704,173 and 
4,844,957 which teach apparatus and methods for applying heat seal labels 
to articles, the disclosures of which are hereby incorporated in their 
entireties by reference thereto herein. Preferably, the label comprises 
first and second layers in laminated relationship. 
Although the invention has been described with reference to particular 
means, materials and embodiments, from the foregoing, one skilled in the 
art can easily ascertain the essential characteristics of the present 
invention; and various changes and modifications may be made to various 
usages and conditions without departing from the spirit and scope of the 
invention as described in the claims that follow.