U.S. patent application number 16/378029 was filed with the patent office on 2019-08-01 for process for producing ultrasonic seal, and film structures and flexible containers with same.
The applicant listed for this patent is Dow Global Technologies LLC. Invention is credited to Selim Bensason, Gagan Saini, Jozef J. Van Dun.
Application Number | 20190232613 16/378029 |
Document ID | / |
Family ID | 50686221 |
Filed Date | 2019-08-01 |
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United States Patent
Application |
20190232613 |
Kind Code |
A1 |
Bensason; Selim ; et
al. |
August 1, 2019 |
Process for Producing Ultrasonic Seal, and Film Structures and
Flexible Containers with Same
Abstract
The present disclosure is directed to processes for producing
ultrasonic sealable film structures and flexible containers with
ultrasonic seals. The film structure includes a first multilayer
film and a second multilayer film. Each multilayer film includes a
backing layer and a seal layer. Each seal layer includes an
ultrasonic sealable olefin-based polymer (USOP) having the
following properties: (a) a heat of melting, .DELTA.Hm, less than
130 J/g, (b) a peak melting temperature, Tm, less than 125.degree.
C., (c) a storage modulus in shear (G') from 50 MPa to 500 MPa, and
(d) a loss modulus in shear (G'') greater than 10 MPa. The
multilayer films are arranged such that the seal layer of the first
multilayer film is in contact with the seal layer of the second
multilayer film. The seal layers form an ultrasonic seal having a
seal strength from 30 N/15 mm to 80 N/15 mm when ultrasonically
sealed at 4 N/mm seal force.
Inventors: |
Bensason; Selim;
(Rueschlikon, CH) ; Van Dun; Jozef J.; (Horgen,
CH) ; Saini; Gagan; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Global Technologies LLC |
Midland |
MI |
US |
|
|
Family ID: |
50686221 |
Appl. No.: |
16/378029 |
Filed: |
April 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14776862 |
Sep 15, 2015 |
10293575 |
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PCT/US2014/033427 |
Apr 9, 2014 |
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16378029 |
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61810123 |
Apr 9, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 66/71 20130101;
B29C 66/73115 20130101; B32B 27/08 20130101; B32B 27/36 20130101;
B32B 2307/31 20130101; B29C 66/71 20130101; B29C 65/8207 20130101;
B32B 15/08 20130101; B29C 66/73711 20130101; B29C 66/71 20130101;
B32B 27/34 20130101; B29C 66/73921 20130101; B29C 66/71 20130101;
B29C 66/71 20130101; B32B 27/32 20130101; B29C 66/71 20130101; B29C
66/9513 20130101; B29C 66/133 20130101; B29C 66/1122 20130101; B29C
66/431 20130101; B29C 66/71 20130101; B29C 66/9516 20130101; B29C
66/72321 20130101; B29C 66/9512 20130101; B29C 66/71 20130101; B29K
2023/38 20130101; B29K 2023/086 20130101; B29C 66/92431 20130101;
B29C 66/71 20130101; B29C 66/731 20130101; B32B 37/06 20130101;
B29C 66/71 20130101; B29K 2023/10 20130101; B29C 66/723 20130101;
B29C 66/71 20130101; B29C 66/71 20130101; B29C 66/112 20130101;
B29C 66/71 20130101; B29C 66/71 20130101; B29C 66/9292 20130101;
B32B 7/12 20130101; B29C 66/71 20130101; B29C 66/135 20130101; B29C
66/73713 20130101; B29C 65/08 20130101; B29C 66/7234 20130101; B29C
66/8322 20130101; B32B 2439/00 20130101; B29K 2077/00 20130101;
B29K 2023/065 20130101; B29K 2023/18 20130101; B29K 2067/003
20130101; B29K 2023/0625 20130101; B29K 2027/08 20130101; B29K
2023/12 20130101; B29K 2023/083 20130101; B29K 2023/0666 20130101;
B29K 2023/0633 20130101; B29K 2023/00 20130101 |
International
Class: |
B32B 7/12 20060101
B32B007/12; B32B 37/06 20060101 B32B037/06; B32B 27/34 20060101
B32B027/34; B29C 65/08 20060101 B29C065/08; B29C 65/82 20060101
B29C065/82; B29C 65/00 20060101 B29C065/00; B32B 15/08 20060101
B32B015/08; B32B 27/08 20060101 B32B027/08; B32B 27/32 20060101
B32B027/32; B32B 27/36 20060101 B32B027/36 |
Claims
1-15. (canceled)
16. A flexible container comprising: a multilayer film having a
backing layer and a seal layer, the multilayer film folded upon
itself to form a first film portion and a second film portion such
that opposing seal layers contact each other; each seal layer
comprising an ultrasonic sealable olefin-based polymer (USOP)
having the following properties: (a) a heat of melting, .DELTA.Hm,
less than 130 J/g, (b) a peak melting temperature, Tm, less than
125.degree. C., (c) a storage modulus in shear (G') from 50 MPa to
500 MPa, and (d) a loss modulus in shear (G'') greater than 10 MPa;
the multilayer films arranged such that the seal layer of the first
multilayer film is in contact with the seal layer of the second
multilayer film; and the seal layers form an ultrasonic seal having
a seal strength from 30 N/15 mm to 80 N/15 mm.
17. The flexible container of claim 16 wherein the second film
portion is superimposed on the first film portion to form a common
peripheral edge; a 2-fold zone and a 4-fold zone; and the 2-fold
zone and the 4-fold zone each forming an ultrasonic seal having a
seal strength from 30 N/15 mm to 80 N/15 mm.
18. The flexible container of claim 17 wherein the 2-fold zone
comprises at least a portion of the common peripheral edge.
19. The flexible container of claim 17 wherein the 4-fold zone
comprises at least a portion of a longitudinal seal.
20. The flexible container of claim 16 wherein the backing layer is
a material selected from the group consisting of PET, polyamide,
BOPP, and metal foil.
21. The flexible container of claim 16 wherein the USOP is a
material selected from the group consisting of PBPE, LLDPE, ULDPE,
POP, and combinations thereof.
22. The flexible container of claim 16 wherein the backing layer
comprises BOPP and the seal layer is a monolayer comprising a USOP
selected from the group consisting of a ULDPE, a POP and a PBPE and
the seal layers form an ultrasonic seal having a seal strength from
55 N/15 mm to 80 N/15 mm.
23. The flexible container of claim 16 wherein the backing layer is
PET and the seal layer is a monolayer comprising a USOP selected
from the group consisting of a ULDPE, a POP, and a PBPE and the
seal layers form an ultrasonic seal having a seal strength from 37
N/15 mm to 55 N/15 mm.
24. The flexible container of claim 16 wherein the seal layer is a
coextruded structure comprising a face layer, a core layer, and an
inner layer; the face layer comprises a USOP selected from the
group consisting of a ULDPE, a POP, and a PBPE; and the seal layers
form an ultrasonic seal having a seal strength from 35 N/15 mm to
55 N/15 mm.
25. The flexible container of claim 16 wherein the seal layer is a
coextruded structure comprising a face layer, a core layer, and an
inner layer; at least one of the core layer and the inner layer
comprises a USOP selected from the group consisting of a ULDPE, a
POP, and a PBPE; the face layer is void of a USOP; and the seal
layers form an ultrasonic seal having a seal strength from 35 N/15
mm to 50 N/15 mm.
Description
FIELD
[0001] The present disclosure is directed to processes for
producing ultrasonic sealable film structures and flexible
containers with ultrasonic seals.
BACKGROUND
[0002] Compared to conventional heat sealing, utilization of
ultrasonic sealing in flexible packaging, offers performance
advantages such as the ability: (i) to seal through contamination,
(ii) to form narrower seal zones, and (iii) to form seals at higher
line speeds and at lower temperature environment. Packaging systems
suitable for ultrasonic welding include vertical- or
horizontal-form-fill-sealing. Despite these benefits, ultrasonic
sealing has a significant drawback. Due to the contact geometry
between the horn and the anvil and oscillatory deformation,
ultrasonic sealing often leads to significant material outflow and
squeeze-out of polymer away from the seal area. This "squeeze-out"
phenomenon of ultrasonic sealing can cause damage, and eventual
destruction of the laminate structure in the formed ultrasonic
seal. Layer steps, i.e., step changes in the thickness of the
material between the horn and anvil (such as in gussets and folds,
and cross-section fin seals) are particularly susceptible to damage
when ultrasonically sealed. Faulty sealing in these areas reduces
seal strength (as measured by peeling tests), may destroy the
laminate in the seal zone, and create channel leakers resulting in
loss of barrier properties in packaging laminates with thin layers
of aluminum or barrier polymers, such as ethylene vinylalcohol
copolymers (EvOH).
[0003] Approaches proposed to mitigate the aforementioned problems
include (i) optimization of the contact geometry, especially the
energy director and (ii) control of horn displacement during
sealing both of which are subject to limitations
[0004] Careful selection of polymers and optimization of the
multilayer structures offers an alternate route to mitigate the
problems above. There is hence a need to identify polymers and
structures that can be sealed ultrasonically and offer a seal
strength comparable to that achievable by conventional heat
sealing. A need further exists for an ultrasonic sealing process
that increases ultrasonic seal strength. A need also exists for
strengthened ultrasonic seals that overcome the shortcomings of
contact geometry optimization or adjustment of seal force
displacement. A need further exists for improved ultrasonic
sealable films to meet the demand for more versatile uses of
flexible containers.
SUMMARY
[0005] The present disclosure is directed to a process for
producing ultrasonic seals, and film structures and flexible
containers containing the ultrasonic seals. The present process
includes a selection of polymers for ultrasonic sealing based on
four factors that influence material flow in the ultrasonic seal
area in addition to contact geometry optimization and seal force
adjustment. In addition, the process includes tailoring the film
composition and structure for further improvement of ultrasonic
seal strength.
[0006] The present disclosure provides a process for producing an
ultrasonic seal. The ultrasonic seal is formed between two
polymeric films. The process includes preparing a multilayer film
which has a backing layer and a seal layer. The seal layer includes
an ultrasonic sealable olefin-based polymer (USOP). The USOP is
selected based on the following properties: [0007] (a) a heat of
melting, .DELTA.Hm, less than 130 J/g, [0008] (b) a peak melting
temperature, Tm, less than 125.degree. C., [0009] (c) a storage
modulus in shear (G') from 50 MPa to 500 MPa, and [0010] (d) a loss
modulus in shear (G'') greater than 10 MPa.
[0011] The process includes contacting the seal layer of a first
multilayer film with the seal layer of a second multilayer film to
form a seal area. The process includes subjecting the seal area to
ultrasonic energy. The process includes forming an ultrasonic seal
between the two seal layers, the ultrasonic seal having a seal
strength from 30 N/mm to 80 N/mm.
[0012] The present disclosure provides a film structure. The film
structure includes a first multilayer film and a second multilayer
film. Each multilayer film includes a backing layer and a seal
layer. Each seal layer includes an ultrasonic sealable olefin-based
polymer (USOP) having the following properties: [0013] (a) a heat
of melting, .DELTA.Hm, less than 130 J/g, [0014] (b) a peak melting
temperature, Tm, less than 125.degree. C., [0015] (c) a storage
modulus in shear (G') from 50 MPa to 500 MPa, and [0016] (d) a loss
modulus in shear (G'') greater than 10 MPa.
[0017] The multilayer films are arranged such that the seal layer
of the first multilayer film is in contact with the seal layer of
the second multilayer film. The seal layers form an ultrasonic seal
having a seal strength from 30 N/15 mm to 80 N/15 mm when
ultrasonically sealed at 4 N/mm seal force.
[0018] The present disclosure provides a flexible container. The
flexible container includes a first multilayer film and a second
multilayer film. Each multilayer film includes a backing layer and
a seal layer. The seal layer includes an ultrasonic sealable
olefin-based polymer (USOP) having the following properties: [0019]
(a) a heat of melting, .DELTA.Hm, less than 130 J/g, [0020] (b) a
peak melting temperature, Tm, less than 125.degree. C., [0021] (c)
a storage modulus in shear (G') from 50 MPa to 500 MPa, and [0022]
(d) a loss modulus in shear (G'') greater than 10 MPa.
[0023] The multilayer films are arranged such that the seal layer
of each multilayer film is in contact with each other and the
second multilayer film is superimposed on the first multilayer film
to form a common peripheral edge. The flexible container includes a
2-fold zone and a 4-fold zone. The 2-fold zone and the 4-fold zone
each form an ultrasonic seal having a seal strength from 30 N/15 mm
to 80 N/15 mm when the zones are ultrasonically sealed at 4 N/mm
seal force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 a graph showing the plot of G' to G'' in accordance
with an embodiment of the present disclosure.
[0025] FIG. 2A is a schematic representation of a flexible
container with a flat ultrasonic seal geometry in accordance with
an embodiment of the present disclosure.
[0026] FIG. 2B is a schematic representation of ultrasonic sealing
with a flat sealing geometry in accordance with an embodiment of
the present disclosure.
[0027] FIG. 3A is a schematic representation of a flexible
container with a 2-fold zone and a 4-fold zone in accordance with
an embodiment of the present disclosure.
[0028] FIG. 3B is a schematic representation of ultrasonic sealing
of a 2-fold zone and a 4-fold zone with a 2-fold/4-fold sealing
geometry in accordance with an embodiment of the present
disclosure.
[0029] FIG. 4 shows graphs for ultrasonic seal strength vs. seal
force for ultrasonically sealed film structures in accordance with
embodiments of the present disclosure.
[0030] FIG. 5 shows graphs for ultrasonic seal strength vs. seal
force for ultrasonically sealed film structures in accordance with
embodiments of the present disclosure.
[0031] FIG. 6 shows graphs for ultrasonic seal strength vs. seal
force for ultrasonically sealed film structures in accordance with
embodiments of the present disclosure.
[0032] FIG. 7 shows graphs for ultrasonic seal strength vs. seal
force for ultrasonically sealed film structures in accordance with
embodiments of the present disclosure.
[0033] FIG. 8 shows graphs for ultrasonic seal strength vs. seal
force for ultrasonically sealed film structures in accordance with
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0034] The present disclosure provides a process for producing an
ultrasonic seal. The ultrasonic seal is formed between two
polymeric films. The process includes preparing a multilayer film
which has a backing layer and a seal layer. The seal layer includes
an ultrasonic sealable olefin-based polymer (USOP). The USOP is
selected based on the following properties: [0035] (a) a heat of
melting, .DELTA.Hm, less than 130 J/g, [0036] (b) a peak melting
temperature, Tm, less than 125.degree. C. [0037] (c) a storage
modulus in shear (G') from 50 MPa to 500 MPa, and [0038] (d) a loss
modulus in shear (G'') greater than 10 MPa.
[0039] The process includes contacting the seal layer of a first
multilayer film with the seal layer of a second multilayer film to
form a seal area. The process includes subjecting the seal area to
ultrasonic energy. The process includes forming an ultrasonic seal
between the two seal layers, the ultrasonic seal having a seal
strength from 30 N/mm to 80 N/mm.
[0040] The present process utilizes an ultrasonic sealing apparatus
to produce an ultrasonic seal between two polymeric films. An
ultrasonic sealing apparatus includes the following components.
[0041] (1) An anvil where films are placed to be contacted under
pressure. The anvil allows high frequency vibration to be directed
to the films in a seal area. The anvil includes an energy director
which contacts one of the films.
[0042] (2) An ultrasonic stack including (a) a converter (converts
electrical signal into a mechanical vibration), (b) a booster
(modifies the amplitude of the vibration) and (c) a horn (applies
the mechanical vibration to the parts to be welded or sealed). The
horn is also referred to as a sonotrode. All three elements of the
ultrasonic stack are tuned to resonate at the same ultrasonic
frequency (typically from 15 kHz, 20 kHz, 30 kHz, 35 kHz, to 40 kHz
or 70 kHz).
[0043] Subjecting the polymeric films to the ultrasonic energy
causes local melting of the plastic due to absorption of vibration
energy. The vibrations are introduced across the joint to be
welded.
[0044] Ultrasonic sealing is distinct from, and excludes heat
sealing. A heat sealing procedure includes hot metal sealing jaws
that are moved from an open position to a closed position. In the
closed position, the hot metal jaws come into direct contact with
the outermost layers of a film for a period of time (dwell time), a
predetermined sealing pressure, and a predetermined sealing
temperature. During the dwell time, heat is transferred through the
outermost layer of the film to melt and fuse opposing inner seal
layers to form a heat seal. Generally, the outermost layer has a
higher melting temperature than the seal layer. As such, while the
seal layer is melted to form a seal, the outermost layer of the
film does not melt and does not stick, or does not substantially
stick, to the sealing jaws. Surface treatments to the sealing jaw
bars may be applied to further reduce stickiness effects to the
films. After the sealing jaws reopen, the film is cooled to room
temperature.
[0045] In heat sealing, the opposing films are joined together via
material interdiffusion at the interface, facilitated by conductive
heat flow from the seal bars to the seal interface, whereby the
temperature of the heat seal bars and dwell time are the key
independent variables. In the case of semi-crystalline polymer
sealants like polyethylene for example, the heat seal bar
temperature needs be set to at least at the temperature
corresponding to the complete melting of the sealant, for the
formation of a strong seal.
[0046] Conversely, in ultrasonic sealing the seal bars (horn and
anvil pair) are typically at ambient temperature, and ultrasonic
generation and flow are dependent variables that are governed by
contact geometry, oscillation amplitude and frequency, static load
and material selection. The ultrasonic energy necessary to achieve
full melting at the interface is generated internally within the
polymer. For a given frequency and contact geometry, the process
variables influencing ultrasonic seal formation are the amplitude
of the oscillations and the superimposed seal force applied through
the horn. Elevated temperatures needed to facilitate ultrasonic
sealing are generated internally, by partial dissipation of
deformation energy into ultrasonic, as governed by viscoelastic
characteristics of the polymer. The dissipated energy gives rise to
an increase in temperature, the magnitude of which depends on the
ultrasonic capacity of the system.
[0047] In conventional ultrasonic weld systems, the seal force
translates the amplitude of the horn oscillations to oscillating
deformation within the material and inadvertently leads to the
gradual penetration of the anvil into the sealing zone. The
profiled and hemispherical shape of the energy director extending
into the seal area from the anvil further amplifies the stress
concentration in the seal area, further exacerbating the problem of
excessive material flow around the anvil.
[0048] For oscillatory deformation in the linear viscoelastic
regime, the rate of ultrasonic generation per unit volume (per
sinusoidal cycle of tensile deformation) is shown in Equation
(I):
{dot over (Q)}=.pi.f.epsilon..sup.2E'' (I)
[0049] where f is the frequency of oscillations,
[0050] .epsilon. is the deformation amplitude, and
[0051] E'' is the loss modulus.
[0052] Equation (I) shows that the rate of ultrasonic generation is
linearly proportional to loss modulus for a given amplitude and
frequency of deformation, whereas the dependence on oscillation
amplitude is to the second power. Direct application of Equation
(I) to ultrasonic sealing is problematic because (i) the
deformation is not homogenous, (ii) a substantial amount of the
material in the seal area is non-isothermal, and (iii) the
amplitude E in the above equation is not that of the horn, but that
of the deformation applied to the material, which depends on the
seal force which varies during the sealing cycle.
[0053] 1. Backing Layer and Seal Layer
[0054] The process includes preparing a multilayer film. The
multilayer film has a backing layer, a seal layer, and optional
adhesive layer(s). Nonlimiting examples of suitable material for
the backing layer include poly(ethylene terephthalate) (PET),
polyamide, propylene-based polymer (such as biaxially oriented
polypropylene or BOPP), and metal foil (such as aluminum foil).
[0055] The seal layer of the multilayer film includes an ultrasonic
sealable olefin-based polymer (USOP).
[0056] In view of Equation (I) above, Applicant has developed
parameters to determine whether a polymer is suited for ultrasonic
sealing. First, based on scaling between ultrasonic generation rate
and loss modulus, a polymer exhibiting a high loss modulus at the
onset of horn oscillations is desired for rapid ultrasonicing.
[0057] Second, the square dependence of rate of ultrasonic
generation on deformation amplitude suggests that polymers of lower
rigidity are desired as this will allow a larger deformation
amplitude to be realized in the polymer for a given seal force.
Even though increasing the seal force on the horn may enhance the
deformation amplitude in the polymer at the start of oscillations,
a minimal seal force to produce an ultrasonic seal is desired to
avoid squeezing of the polymer upon melting. Because the modulus of
a semi-crystalline polymer may drop more than two orders of
magnitude upon melting, using a large seal force will lead to
excessive squeezing of the melt from the seal zone. To ensure
maximum ultrasonic generation with a minimal seal force, it is
desired to select polymer with low modulus, so as to produce
maximal amplitude of oscillations early on in the sealing cycle.
Polymers with lower modulus at ambient conditions also have a
smaller difference between solid and melt-state modulus--an
additional factor that prevents excessive flow of material in the
melt. Based on foregoing, at the onset of deformation, polymers
featuring a high loss modulus combined with a low storage modulus
are desired.
[0058] Third, the ultrasonic generated due to viscoelastic
dissipation raises the temperature--thereby melting the
semi-crystalline at the interface, thereby allowing the formation
of a strong seal. Polymers with lower ultrasonic of melting
combined with a low temperature for complete melting are desired
for rapid ultrasonic sealing characteristics. For such polymers the
duration of oscillations necessary to transform the polymer into a
melt, can be significantly short, hence a shorter cycle time.
[0059] Fourth, a polymer having a rapid relaxation time is desired
to prevent solidification of a highly stressed melt which may be
pushed out of the seal area. A rapid relaxation time may be
obtained by one or more of the following factors, including a lower
molecular weight, a narrow molecular weight distribution, and
reduced or no long chain branching. The bead of squeezed-out
polymer material forms the region of initial stress in a peeling
geometry, therefore, strong adhesion of this bead to the
surrounding material as well as lack of large frozen-in stresses
are beneficial for high peel strength. Poor adhesion or regions
with frozen-in orientation may provide paths of lower resistance to
the initiation and propagation of a crack during a peel test.
[0060] Fifth, polyolefins with low molecular weight are desirable
for improved caulkability i.e., the ability of the sealant to flow
into gaps and around contaminants. Ultrasonic sealing is not
limited by hot tack strength (as is heat sealing) because
ultrasonic sealing utilizes cold sealing tools, which allow
efficient cooling of the seal while in contact with the tools. Such
cooling segment may be incorporated into the sealing cycle after
the cessation of oscillations--hence allowing rapid buildup of hot
tack strength and solidification of the polymer, much faster than
what is feasible in conventional ultrasonic sealing.
[0061] Hence compositions with a combination of caulkability and
packaging cycle time are enabled via the present ultrasonic sealing
process. All things being equal, lower molecular weight polyolefins
will perform better in ultrasonic sealing than high molecular
weight polyolefins.
[0062] In view of the foregoing principles, the present process
includes selecting an ultrasonic sealable olefin-based polymer for
seal layer. An "ultrasonic sealable olefin-based polymer," (or
USOP) as used herein, is an olefin-based polymer that forms a seal
when subjected to ultrasonic energy and has each of the following
properties:
[0063] (a) a heat of melting, .DELTA.Hm, less than 130 J/g and is
measured by differential scanning calorimetry (DSC) as described
herein;
[0064] (b) a peak melting temperature, Tm, less than 125.degree. C.
and is measured by the (DSC) method as described herein;
[0065] (c) a storage modulus in shear (G') at 10.degree. C. from 50
MPa to 500 MPa, where G' is the in-phase component of the modulus
measured by dynamic mechanical thermal analysis (DMTA) described
herein; and
[0066] (d) a loss modulus in shear (G'') at 10.degree. C. greater
than 10 MPa, where G'' is the out-of-phase component of the modulus
measured by dynamic mechanical thermal analysis (DMTA) described
herein.
[0067] In an embodiment, the USOP is an olefin-based polymer that
forms a seal when subjected to ultrasonic energy and has each of
the following properties:
[0068] (a) a heat of melting, .DELTA.Hm, from 50 J/g to less than
130 J/g;
[0069] (b) a peak melting temperature, Tm, greater than 90.degree.
C. to less than 125.degree. C.;
[0070] (c) a storage modulus in shear (G') at 10.degree. C. from 50
MPa to 350 MPa; and
[0071] (d) a loss modulus in shear (G'') from greater than 10 MPa
to 40 MPa.
[0072] In an embodiment, the ultrasonic sealable olefin-based
polymer is a propylene based plastomer or elastomer ("PBPE"). A
"propylene-based plastomer or elastomer" (or "PBPE") comprises at
least one copolymer with at least 50 weight percent of units
derived from propylene and at least about 5 weight percent of units
derived from a comonomer other than propylene. Such PBPE types of
polymers are further described in U.S. Pat. Nos. 6,960,635 and
6,525,157, incorporated herein by reference. Such PBPE is
commercially available from The Dow Chemical Company, under the
tradename VERSIFY, or from ExxonMobil Chemical Company, under the
tradename VISTAMAXX.
[0073] In an embodiment, the PBPE is further characterized as
comprising (A) between 60 and less than 100, between 80 and 99, or
between 85 and 99, wt % units derived from propylene, and (B)
between greater than zero and 40, or between 1 and 20, 4 and 16, or
between 4 and 15, wt % units derived from ethylene and optionally
one or more C.sub.4-10 .quadrature.-olefin; and containing an
average of at least 0.001, at least 0.005, or at least 0.01, long
chain branches/1000 total carbons, wherein the term long chain
branch refers to a chain length of at least one (1) carbon more
than a short chain branch, and wherein short chain branch refers to
a chain length of two (2) carbons less than the number of carbons
in the comonomer. For example, a propylene/1-octene interpolymer
has backbones with long chain branches of at least seven (7)
carbons in length, but these backbones also have short chain
branches of only six (6) carbons in length. The maximum number of
long chain branches in the propylene/ethylene copolymer
interpolymer does not exceed 3 long chain branches/1000 total
carbons.
[0074] In an embodiment, the PBPE copolymer has a melt temperature
(Tm) from 55.degree. C. to less than 125.degree. C.
[0075] A nonlimiting examples of suitable PBPE for the USOP include
VERSIFY 2000 and VERSIFY 2200, available from The Dow Chemical
Company.
[0076] In an embodiment, the ultrasonic sealable olefin-based
polymer is a linear low density polyethylene. Linear low density
polyethylene ("LLDPE") comprises, in polymerized form, a majority
weight percent of units derived from ethylene, based on the total
weight of the LLDPE. In an embodiment, the LLDPE is an interpolymer
of ethylene and at least one ethylenically unsaturated comonomer.
In one embodiment, the comonomer is a C.sub.3-C.sub.20
.alpha.-olefin. In another embodiment, the comonomer is a
C.sub.3-C.sub.8 .alpha.-olefin. In another embodiment, the
C.sub.3-C.sub.8 .alpha.-olefin is selected from propylene,
1-butene, 1-hexene, or 1-octene. In an embodiment, the LLDPE is
selected from the following copolymers: ethylene/propylene
copolymer, ethylene/butene copolymer, ethylene/hexene copolymer,
and ethylene/octene copolymer. In a further embodiment, the LLDPE
is an ethylene/octene copolymer.
[0077] In an embodiment, the LLDPE has a density in the range from
0.865 g/cc to 0.940 g/cc, or from 0.90 g/cc to 0.94 g/cc. The LLDPE
has a melt index (MI) from 0.1 g/10 min to 10 g/10 min, or 0.5 g/10
min to 5 g/10 min.
[0078] LLDPE can be produced with Ziegler-Natta catalysts, or
single-site catalysts, such as vanadium catalysts, constrained
geometry catalysts, and metallocene catalysts. In an embodiment,
the LLDPE is produced with a Ziegler-Natta type catalyst. LLDPE is
linear and does not contain long chain branching and is different
than low density polyethylene ("LDPE") which is branched or
heterogeneously branched polyethylene. LDPE has a relatively large
number of long chain branches extending from the main polymer
backbone. LDPE can be prepared at high pressure using free radical
initiators, and typically has a density from 0.915 g/cc to 0.940
g/cc.
[0079] In an embodiment, the LLDPE is a Ziegler-Natta catalyzed
ethylene and octene copolymer and has a density from 0.90 g/cc to
0.93 g/cc, or 0.92 g/cc. Nonlimiting examples of suitable
Ziegler-Natta catalyzed LLDPE are polymers sold under the tradename
DOWLEX, available from The Dow Chemical Company, Midland, Mich.
[0080] A nonlimiting example of suitable LLDPE for the USOP
includes DOWLEX 5056G available from The Dow Chemical Company.
[0081] In an embodiment, the ultrasonic sealable olefin-based
polymer is an ultra low density polyethylene. Ultra low density
polyethylene ("ULDPE") comprises, in polymerized form, a majority
weight percent of units derived from ethylene, based on the total
weight of the ULDPE. In an embodiment, the ULDPE is an interpolymer
of ethylene and at least one ethylenically unsaturated comonomer.
In one embodiment, the comonomer is a C.sub.3-C.sub.20
.alpha.-olefin. In another embodiment, the comonomer is a
C.sub.3-C.sub.8 .alpha.-olefin. In another embodiment, the
C.sub.3-C.sub.8 .alpha.-olefin is selected from propylene,
1-butene, 1-hexene, or 1-octene. In an embodiment, the ULDPE is
selected from the following copolymers: ethylene/propylene
copolymer, ethylene/butene copolymer, ethylene/hexene copolymer,
and ethylene/octene copolymer. In a further embodiment, the ULDPE
is an ethylene/octene copolymer.
[0082] In an embodiment, the ULDPE has a density in the range from
0.900 g/cc to 0.915 g/cc. The ULDPE has a melt index (MI) from 0.1
g/10 min to 10 g/10 min, or 0.5 g/10 min to 5 g/10 min
[0083] A nonlimiting example of suitable ULDPE for the USOP
includes ATTANE 4100 and ATTANE SL4102 available from The Dow
Chemical Company.
[0084] In an embodiment, ultrasonic sealable olefin-based polymer
is a polyolefin plastomer (or POP). A nonlimiting example of a
suitable POP includes ethylene/octene plastomer such as AFFINITY PL
1881G available from The Dow Chemical Company.
[0085] In an embodiment, the ultrasonic sealable olefin-based
polymer is an ethylene/acrylic acid copolymer (or EAA). A
nonlimiting example of a suitable ethylene/acrylic acid copolymer
is PRIMACOR 1410 available from The Dow Chemical Company.
[0086] In an embodiment, the USPO is a polybutene.
[0087] In an embodiment, the USOP is a propylene-based terpolymer,
such as propylene/butene/ethylene terpolymer.
[0088] The process includes contacting the seal layer of the first
multilayer film the seal layer of a second multilayer film to form
a seal area. The second multilayer film may be a component of a
multilayer film that is the same as or different than the first
multilayer film. The composition of the seal layer of the second
multilayer film may be the same or different than the composition
of the seal layer for the first multilayer film.
[0089] In an embodiment, the second multilayer film has the same
material composition and structure as the first multilayer
film.
[0090] The process further includes subjecting the seal area to (i)
ultrasonic energy and (ii) a seal force from 2 N/mm, or 3 N/mm, or
4 N/mm to 5 N/mm, or 6 N/mm and forming an ultrasonic seal between
the seal layers having a seal strength from 30 N/15 mm, or 31 N/15
mm, or 32 N/15 mm, or 33 N/15 mm, or 34 N/15 mm, or 35 N/15 mm, or
36 N/15 mm, or 37 N/15 mm, or 38 N/15 mm, or 39 N/15 mm, or 40 N/15
mm, or 45 N/15 mm, or 50 N/15 mm, or 55 N/15 mm, or 60 N/15 mm, or
65 N/15 mm, to 70 N/15 mm, or 75 N/15 mm, or 80 N/15 mm.
[0091] Nonlimiting examples of ultrasonic energy and seal force
parameters are provided in Table A below. The subjecting step may
include any combination of the parameters shown in Table A
below.
TABLE-US-00001 TABLE A Ultrasonic energy Seal force 20, 30, 35, 40,
or 70 kHz 1-12 N/mm Anvil: 2.5 millimeter (mm) radius 2-6 N/mm Horn
width: 220 mm 2-5 N/mm Cycle: 200 millisecond (ms) sealing, 3-5
N/mm 300 ms rest Amplitude 10-50 microns Sample width: 100 mm
[0092] Applicant discovered polymeric materials fulfilling the
requirements for a USOP (properties (a)-(d)) unexpectedly enable
strong ultrasonic seal formation (30-80 N/mm) using minimal seal
force (2-6 N/mm). Bounded by no particular theory, it is believed
selection of USOPs with the aforementioned properties (a)-(d)
synergistically minimizes the seal force required to produce
suitable ultrasonic seals. Minimal seal force (2-6 N/mm)
advantageously (i) reduces stress on the film polymers, (ii)
reduces or eliminates damage to other film layers (such as barrier
layers, for example), (iii) reduces or eliminates "squeeze out" of
polymer from the seal area, and (iv) enables seal formation when
contaminants are present in the seal area. Tailoring properties
(a)-(d) to match a specific ultrasonic seal application, the
present process advantageously increases production efficiencies by
using less energy (minimizing load strength) and minimizing seal
defects--each of which is advantageous during commercial-scale
production of flexible pouches, as in FFS production, for
example.
[0093] In an embodiment, the seal layer of the first multilayer
film and the seal layer of the second multilayer film are the same
material.
[0094] In an embodiment, the multilayer film is folded upon itself
such that opposing seal layers face each other and form the seal
area. In this embodiment, the first multilayer film is the first
portion of the folded film and the second multilayer film is a
second portion of the folded film that is folded upon itself. In
other words, the second multilayer film is a portion of the
multilayer film that is folded over and placed in opposing relation
to the seal layer. The manipulation a single multilayer film to
place portions of the same seal layer in opposing relation to each
other in order to form a seal occurs in a form, fill, and seal
packaging systems, for example.
[0095] In an embodiment, the film portions in the seal area are in
contact with a horn and an anvil of an ultrasonic seal apparatus.
The process includes moving the horn a distance from 0 microns, or
greater than 0 microns, or 2 microns, or 5 microns to 10 microns,
or 15 microns, or 20 microns during the forming step. Horn
displacement during the sealing process can be measured with a
laser sensor, for example. In this way, the present process
advantageously reduces, or eliminates, horn displacement into the
seal area during the ultrasonic sealing process.
[0096] In an embodiment, the backing layer is poly(ethylene
terephthalate) (or PET) and the seal layer is a monolayer and
includes a USOP. The USOP present in the seal layer is selected
from a ULDPE and a POP. The process includes subjecting the seal
area to ultrasonic energy and a seal force from 4 N/mm to 6 N/mm,
or 4 N/mm, and forming an ultrasonic seal having a seal strength
from 37 N/mm to 55 N/mm.
[0097] In an embodiment, the backing layer is BOPP and the seal
layer is a monolayer and includes a USOP selected from a ULDPE, a
PBPE, and a POP. The process includes subjecting the seal area to
ultrasonic energy and a seal force from 3 N/mm to 6 N/mm or 4 N/mm;
and forming an ultrasonic seal having a seal strength from 55 N/15
mm to 80 N/15 mm.
[0098] In an embodiment, the seal layer includes a coextruded
structure. The coextruded structure includes a face layer, a core
layer, and an inner layer. The backing layer is laminated to the
coextruded structure. This forms a multilayer film with the
following layer structure: backing/adhesive/inner/core/face. The
face layer is the contact layer. The inner layer is located between
the backing layer and the core layer. The core layer includes a
USOP selected from a ULDPE, a PBPE and a POP. The process includes
subjecting the seal area to ultrasonic energy and 4 N/mm seal force
and forming an ultrasonic seal having a seal strength from 35 N/mm
to 55 N/mm.
[0099] In an embodiment, the seal includes the coextruded
structure. The coextruded structure includes the face layer, the
core layer, and the inner layer. The core layer and optionally the
inner layer include a USOP. The face layer is void of USOP. The
process includes forming an ultrasonic seal having a seal strength
from 35 N/mm to 50 N/mm. With proper selection of the USOP, the
present process advantageously enables placement of the USOP in one
of the coextruded layers that is not the face layer. Applicant
unexpectedly discovered selection of a USOP with properties (a)-(d)
does not require the USOP to be present in the face layer to
produce strong ultrasonic seals (30-80 N/mm).
[0100] 2. Blends
[0101] Any layer in the first multilayer film and the second
multilayer film may be a blend of two or more components.
[0102] In an embodiment, the multilayer film includes the
coextruded structure that is the seal layer. The core layer and
optionally the inner layer includes a blend of low density
polyethylene and USOP. The face layer is void of LDPE. The term
"low density polyethylene or "LDPE" is a polyethylene made in an
autoclave or in a high pressure polymerization process, such as a
tubular high pressure polymerization process. In a further
embodiment, the LDPE excludes linear low density polyethylene and
high density polyethylene. The LDPE has a melt index (MI) from 0.2
g/10 min, or 0.5 g/10 min to 10 g/10 min, or 20 g/10 min, or 50
g/10 min.
[0103] The LDPE has a density from 0.915 g/cc, to 0.925 g/cc, or
0.930 g/cc, 0.935 g/cc, or 0.940 g/cc.
[0104] In an embodiment, the multilayer film includes a barrier
layer. The barrier layer is an inner layer located between the
backing layer and the seal layer. Suitable polymers for barrier
layer include HDPE, LLDPE, LDPE, ethylene vinyl alcohol copolymer
(EVOH), maleic anhydride-modified polyethylene, polyamide (PA),
cyclic olefin copolymer (COC), ethylene vinyl acetate (EVA),
propylene homopolymer (PP), and vinylidene chloride polymer, and
combinations thereof.
[0105] In many commercial applications two ultrasonic sealable
flexible films are used together such that the second multilayer
film is superimposed on the first multilayer film so that the seal
layer of the first multilayer film is in contact with the seal
layer of the second multilayer film. In other applications a single
multilayer film or a single sheet may be folded such that two
surfaces of the same seal layer are in contact with each other.
[0106] The present process may comprise two or more embodiments
disclosed herein.
[0107] 3. Film Structure
[0108] The present process produces sealed film structures. In an
embodiment, the process produces a film structure. The film
structure includes a first multilayer film and a second multilayer
film. Each multilayer film includes a backing layer and a seal
layer. Each seal layer includes an ultrasonic sealable olefin-based
polymer (USOP) having the following properties: [0109] (a) a heat
of melting, .DELTA.Hm, less than 130 J/g, [0110] (b) a peak melting
temperature, Tm, less than 125.degree. C., [0111] (c) a storage
modulus in shear (G') from 50 MPa to 500 MPa, and [0112] (d) a loss
modulus in shear (G'') greater than 10 MPa.
[0113] The multilayer films arranged such that the seal layer of
the first multilayer film is in contact with the seal layer of the
second multilayer film. The seal layers form an ultrasonic seal
having a seal strength from 30 N/15 mm to 80 N/15 mm when
ultrasonically sealed at 4 N/mm seal force.
[0114] In an embodiment, when ultrasonically sealed at 4 N/mm, the
seal layers form an ultrasonic seal having a seal strength from 30
N/15 mm, or 31 N/15 mm, or 32 N/15 mm, or 33 N/15 mm, or 34 N/15
mm, or 35 N/15 mm, or 36 N/15 mm, or 37 N/15 mm, or 38 N/15 mm, or
39 N/15 mm, or 40 N/15 mm, or 45 N/15 mm, or 50 N/15 mm, or 55 N/15
mm, or 60 N/15 mm, or 65 N/15 mm, to 70 N/15 mm, or 75 N/15 mm, or
80 N/15 mm.
[0115] In an embodiment, the backing layer of the film structure is
a material selected from PET, polyamide, BOPP, metal foil, and
combinations thereof.
[0116] In an embodiment, the USOP of the film structure is a
material selected from PBPE, LLDPE, ULDPE, POP, and combinations
thereof.
[0117] In an embodiment, the multilayer film includes a barrier
layer.
[0118] In an embodiment, the first multilayer film and the second
multilayer film are components of a single flexible sheet. The
single flexible sheet is folded to superimpose the second
multilayer film on the first multilayer film.
[0119] In an embodiment, film structure includes a multilayer film
wherein the backing layer includes BOPP and the seal layer is a
monolayer comprising a USOP selected from ULDPE, a POP and a PBPE.
The seal layers form an ultrasonic seal having a seal strength from
55 N/15 mm to 80 N/15 mm when ultrasonically sealed at 4 N/mm seal
force.
[0120] In an embodiment, the film structure includes a multilayer
film wherein the backing layer is PET and the seal layer is a
monolayer comprising a USOP selected from a ULDPE, a POP, and a
PBPE. The seal layers form an ultrasonic seal having a seal
strength from 37 N/15 mm to 55 N/15 mm when ultrasonically sealed
at 4 N/mm seal force
[0121] In an embodiment, the film structure includes a multilayer
film wherein the seal layer is a coextruded structure including a
face layer, a core layer, and an inner layer. The face layer
includes a USOP selected from a ULDPE, a POP, and a PBPE. The seal
layers form an ultrasonic seal having a seal strength from 35 N/15
mm to 55 N/15 mm when ultrasonically sealed at 4 N/mm seal
force.
[0122] In an embodiment, the film structure includes a multilayer
film wherein the seal layer is a coextruded structure including a
face layer, a core layer, and an inner layer. At least one of the
core layer and the inner layer includes a USOP selected from a
ULDPE, a POP, and a PBPE. The face layer is void of a USOP. The
seal layers form an ultrasonic seal having a seal strength from 35
N/15 mm to 50 N/15 mm when ultrasonically sealed at 4 N/mm seal
force.
[0123] In an embodiment, the film structure includes a multilayer
film wherein the second multilayer film is superimposed on the
first multilayer film to form a common peripheral edge. The
ultrasonic seal is located along the common peripheral edge.
[0124] In an embodiment, the ultrasonic seal is a hard seal.
[0125] In an embodiment, the ultrasonic seal is a frangible
seal.
[0126] In an embodiment, the present disclosure includes a flexible
container including the present film structure. Nonlimiting
examples of suitable flexible containers include a pouch, a sachet,
a stand-up pouch, and a form-fill-and seal pouch.
[0127] The present film structure may comprise two or more
embodiments disclosed herein.
[0128] 4. Flexible Container
[0129] The present process produces flexible containers. In an
embodiment, the flexible container includes a first multilayer film
and a second multilayer film. Each multilayer film includes a
backing layer and a seal layer. The seal layer includes an
ultrasonic sealable olefin-based polymer (USOP) having the
following properties: [0130] (a) a heat of melting, .DELTA.Hm, less
than 130 J/g, [0131] (b) a peak melting temperature, Tm, less than
125.degree. C., [0132] (c) a storage modulus in shear (G') from 50
MPa to 500 MPa, and [0133] (d) a loss modulus in shear (G'')
greater than 10 MPa.
[0134] The multilayer films are arranged such that the seal layer
of each multilayer film is in contact with each other and the
second multilayer film is superimposed on the first multilayer film
to form a common peripheral edge. The flexible container includes a
2-fold zone and a 4-fold zone. The 2-fold zone and the 4-fold zone
each form an ultrasonic seal having a seal strength from 30 N/15 mm
to 80 N/15 mm when the zones are ultrasonically sealed at 4 N/mm
seal force.
[0135] In an embodiment, the 2-fold zone and the 4-fold zone are
ultrasonically sealed at 4 N/mm and form an ultrasonic seal having
a seal strength from 30 N/15 mm, or 31 N/15 mm, or 32 N/15 mm, or
33 N/15 mm, or 34 N/15 mm, or 35 N/15 mm, or 36 N/15 mm, or 37 N/15
mm, or 38 N/15 mm, or 39 N/15 mm, or 40 N/15 mm, or 45 N/15 mm, or
50 N/15 mm, or 55 N/15 mm, or 60 N/15 mm, or 65 N/15 mm, to 70 N/15
mm, or 75 N/15 mm, or 80 N/15 mm.
[0136] In an embodiment, the 2-fold zone includes at least a
portion of the common peripheral edge.
[0137] In an embodiment, the 4-fold zone includes at least a
portion of a longitudinal seal.
[0138] In an embodiment, the multilayer film of the flexible
container includes a backing layer that is selected from PET and
BOPP.
[0139] In an embodiment, the flexible container includes a
multilayer film wherein the seal layer is a monolayer and includes
a USOP selected from the group consisting of ULDPE, POP, PBPE, and
combinations thereof.
[0140] In an embodiment, the 2-fold zone is a gusset seal.
[0141] In an embodiment, the 4-fold zone is a cross-section fin
seal.
[0142] Nonlimiting examples of suitable flexible containers include
a pouch, a sachet, a stand-up pouch, and a form-fill-and seal
pouch.
[0143] Nonlimiting examples of contents suitable for containment by
the flexible container include comestibles (beverages, soups,
cheeses, cereals, snacks, crackers, potato chips), liquids,
shampoos, oils, waxes, emollients, lotions, moisturizers,
medicaments, pastes, surfactants, gels, adhesives, suspensions,
solutions, enzymes, soaps, cosmetics, liniments, flowable
particulates, and combinations thereof.
[0144] The present flexible container may comprise two or more
embodiments disclosed herein.
Definitions
[0145] Unless stated to the contrary, implicit from the context, or
customary in the art, all parts and percents are based on weight,
and all test methods are current as of the filing date of this
disclosure.
[0146] The term "composition," as used herein, includes a mixture
of materials which comprise the composition, as well as reaction
products and decomposition products formed from the materials of
the composition.
[0147] The term "comprising," and derivatives thereof, is not
intended to exclude the presence of any additional component, step
or procedure, whether or not the same is disclosed herein. In order
to avoid any doubt, all compositions claimed herein through use of
the term "comprising" may include any additional additive,
adjuvant, or compound whether polymeric or otherwise, unless stated
to the contrary. In contrast, the term, "consisting essentially of"
excludes from the scope of any succeeding recitation any other
component, step or procedure, excepting those that are not
essential to operability. The term "consisting of" excludes any
component, step or procedure not specifically delineated or listed.
The term "or", unless stated otherwise, refers to the listed
members individually as well as in any combination.
[0148] The term, "ethylene-based polymer," as used herein, refers
to a polymer that comprises, in polymerized form, a majority amount
of ethylene monomer (based on the weight of the polymer), and
optionally may comprise one or more comonomers.
[0149] The term, olefin-based polymer", as used herein, refers to a
polymer that comprises, in polymerized form, a majority amount of
olefin monomer, for example ethylene or propylene, (based on the
weight of the polymer).
[0150] The term "propylene-based polymer," as used herein refers to
a polymer that comprises, in polymerized form, a majority amount of
propylene monomer (based on weight of the polymer), and optionally
may comprise one or more comonomers.
[0151] The term "propylene/ethylene copolymer," as used herein,
refers to a polymer that comprises, in polymerized form, a majority
amount of propylene monomer (based on the weight of the polymer),
and a minority amount of ethylene comonomer and optionally may
comprise one or more additional comonomers.
Test Methods
[0152] Density is measured in accordance with ASTM D792.
[0153] DMTA (dynamic mechanical thermal analysis)
[0154] Samples are compression molded from granules at 185.degree.
C., and solidified at an average cooling rate of 10.+-.5.degree.
C./min. Rectangular samples are cut out from molded sheets for
measurements. Dynamic mechanical measurements in torsion are
performed in a rotational rheometer ARES by TA Instruments in a
range of temperatures from -100.degree. C. to near the complete
melting temperature of the sample. The temperature is raised in
steps of 5.degree. C. with a soak time per step of 120 seconds.
Dynamic oscillatory deformation of 0.1% at a frequency of 10 rad/s
is applied to a rectangular sample of 30 mm length, 12.7 mm width
and 2.8 mm thickness. The measured torque is used to calculate the
storage and loss shear modulus, G' and G'', as a function of
temperature.
[0155] Differential Scanning calorimetry (DSC)
[0156] Differential Scanning calorimetry (DSC) is used to measure
melting and crystallization behavior of polymers (e.g.,
ethylene-based (PE) polymers). The sample is first melt pressed
into a thin film at ca 175.degree. C. and then cooled to room
temperature. About 5 to 8 mg of polymer film sample is cut with a
die punch and is weighed and placed into a DSC pan. The lid is
crimped on the pan to ensure a closed atmosphere. The sample pan is
placed into a calibrated DSC cell purged with nitrogen gas, and
then heated at a rate of approximately 10.degree. C./min, to a
temperature of 180.degree. C. for PE. The sample is kept at this
temperature for three minutes. Then the sample is cooled at a rate
of 10.degree. C./min to -40.degree. C. to record the
crystallization trace, and kept isothermally at that temperature
for three minutes. The sample is next reheated at a rate of
10.degree. C./min, until complete melting and the resultant second
melting trace is used to calculated heat of melting and melting
temperature. The percent crystallinity is calculated by dividing
the heat of melting (H.sub.m), determined from the second heating
curve, by a theoretical heat of fusion of 292 J/g for PE (165 J/g,
for PP), and multiplying this quantity by 100 (for example, %
cryst.=(H.sub.m/292 J/g).times.100 (for PE)).
[0157] Unless otherwise stated, peak melting point (T.sub.m) is
determined from the second heating curve and corresponds to the
temperature of the highest peak in the endotherm. The
crystallization temperature (T.sub.c) is determined from the
cooling curve (peak Tc).
[0158] Melt flow rate, or MFR is measured in accordance with ASTM D
1238, Condition 230.degree. C./2.16 kg.
[0159] Melt index, or MI, is measured in accordance with ASTM D
1238, Condition 190.degree. C./2.16 kg.
[0160] Seal Strength
[0161] Sealing is performed with 100 mm wide samples by aligning
the seal bar in the cross-direction of the constituent blown films.
Three samples of 15 mm width are cut for measurement of seal
strength. The procedure is repeated three times to get a total of
nine specimens for seal strength testing. The seal strength is
measured in accordance with DIN 55529. The rate of pull is 100
mm/minute for 50 mm long arms loaded in T-peel geometry Seal
strength is determined from the maximum of the force elongation
curve. The values reported are mean and standard deviation of seal
strength for nine specimens.
[0162] Some embodiments of the present disclosure will now be
described in detail in the following Examples.
EXAMPLES
[0163] 1. Materials
[0164] Materials for inventive examples and comparative samples are
provided in Table 1 below.
TABLE-US-00002 TABLE 1 Storage Loss Modulus Modulus in in Shear
Shear G'' at I2 Density G' at 10.degree. C. 10.degree. C. .DELTA.Hm
Tm Commercial Name Type (g/10 min) (g/cm.sup.3) (MPa) (MPa) (J/g)
(.degree. C.) DOWLEX LLDPE 1.0 0.919 242.3 19.7 143.5 119.6 5056G
DOWLEX LLDPE 1.0 0.930 399.9 27.4 167.8 123.8 2042G DOWLEX 2740G
LLDPE 1.0 0.940 593.5 31.9 178.1 127.8 ATTANE LLDPE 1.0 0.905 104.4
11.5 111.7 122.1 SL4102G ATTANE LLDPE 1.0 0.912 144.7 14.2 127.2
116.6 SL4100G VERSIFY 2000 Propylene 2.0 297.3 33.9 63 108.7
copolymer 5% E AFFINITY Ethylene/octene 0.903 82.0 11.6 104.4 99.7
PL1881G POP PRIMACOR EAA copolymer 1.5 N/A 263.8 38.2 107.8 98.8
1410 (9.7 wt % 10% AA) Surlyn 1601 Sodium ionomer 1.3 0.94 153.1
11.8 73.2 96.1 PB 0300M Polybutene 4.0 0.915 157.5 27.7 42.4 115.6
Greenflex FD20 EVA copolymer 0.5 0.924 145.7 18.1 128.1 102.7 with
5 wt % VA Terpolymer Propylene/butane/ 7 (MFR) 0.90 465.7 41.4 85.8
128.9 ethylene terpolymer Dow LDPE 310E LDPE 0.75 0.923 (tubular)
TNS20 BOPP Hostaphan RN PET Dowlex, Attane, Affinity, Primacor,
Versify are commercial product families made by The Dow Chemical
Company. Surlyn 1601 is a sodium ionomer supplied by DuPont.
PB0300M is a polybutene-1 resin from LyondellBasell Polymers.
Cosmoplene FL7641L is a polypropylene terpolymer from Polyolefin
Company (Singapore) Pte Ltd. Greenflex FD20 is an ethylene vinyl
acetate copolymer (EVA) from Polimeri Europe of 5% VA content TNS20
is BOPP from Taghleef Industries S.p.A., Italy Hostaphon RN is PET
from Puetz GmbH + Co Folien KG Germany
[0165] FIG. 1 shows a plot of G' vs G'' for several USOPs including
the USOPs of Table 1.
Example 1
[0166] The seal layer may be a monolayer structure or a coextruded
structure formed by blown film extrusion. [0167] 1. Monolayer blown
films are prepared on a Covex blown film line with a 45 mm (28 L/D)
extruder and a 150 mm diameter die. The die gap is 1.5 mm for LLDPE
and ethylene copolymers, 1.0 mm for LDPE, and 2.0 mm for propylene
copolymers. Films of 50 micron gauge are produced at 22.5 kg/h
using a blow-up ratio of 2.5. The melt temperature is 220.degree.
C. The films are corona treated for 44 dynes surface tension.
[0168] 2. Coextruded multilayer blown films are prepared on an
Alpine line featuring two 50 mm skin extruders (30 L/D) and a 65 mm
core layer extruder (30 L/D) and 200 mm diameter die equipped with
internal bubble cooling. The die gap is 2.5 mm. Films of 50 micron
gauge are produced at a total output rate of 115 kg/h, using a
nominal thickness ratio of 1:3:1 for the three-layer structure. The
blow-up ratio is 2.5 and the melt temperature is ca 230.degree. C.
The films are corona treated on the side of sealant for 44 dynes
surface tension.
[0169] Multilayer films are produced by laminating a backing layer
(12 micron PET layer or 20 micron BOPP layer) onto a 50 micron seal
layer (either monolayer structure or coextruded structure). The
backing layer is laminated to the seal layer using an adhesive
layer. The lamination is oven-cured to completely cure the adhesive
and form the ultrasonic sealable flexible film structures. When the
seal layer is the coextruded structure, the multilayer film has the
following layer configuration: Backing (12 or 20)/adhesive/inner
(10)/core (30)/face (10), with thickness, microns, in
parentheses).
[0170] Multilayer films are ultrasonically sealed under the
conditions provided in Table 2 below.
[0171] Table 2 provides the ultrasonic seal conditions used to
evaluate the multilayer films.
TABLE-US-00003 TABLE 2 Ultrasonic Seal Conditions Ultrasonic Seal
Conditions Equipment Dialog Touch - Hermann Ultraschalltechnik GmbH
Conditions 20 KHz, 220 mm horn width Anvil: 2.5 mm radius,
stainless steel (also used for ultrasonic sealing curves) Cycle:
200 ms sealing - 300 ms rest Oscillation: amplitude: 25 microns
Sample width: 100 mm, sealed parallel to CD, 15 mm width samples
cut Sealing force: 1 N/mm to 6 N/mm, 4 N/mm Multilayer films: 50
micron blown films (monolayer or coextruded), laminated to 12
micron PET or 20 micron BOPP Seal strength testing (DIN 55529) -
rate of pull: 100 mm/min for 50 mm arms
[0172] The seal layers of opposing multilayer films are placed into
contact with each other and subjected to the ultrasonic seal
conditions in Table 2 above.
[0173] FIG. 2A is a schematic representation of an ultrasonic seal
produced with flat sealing geometry as schematically represented in
FIG. 2B.
[0174] FIG. 3A is a schematic representation of ultrasonic seals
for 2-fold zones and 4-fold zones produced with 2-fold/4-fold
sealing geometry as schematically represented in FIG. 3B.
[0175] Table 3 below provides properties for inventive ultrasonic
heat seals and comparative samples.
TABLE-US-00004 TABLE 3 USS AT Ratio USS Seal 4 N/mm Ratio USSpeak/
USS Seal Force Seal Example Backing Film Geometry Resin PHSS Seal
Force USS/PHSS USS PEAK PHSS at Peak N/mm Force.sup.& 1 PET
mono flat dowlex2740 52 1.1** 0.02 22.7 0.44 6 6 2 PET mono flat
dowlex2042 50 4.4** 0.09 26.6 0.53 6 5 3 PET mono flat dowlex5056
43 30.4 0.70 35.3 0.82 6 4 4 PET mono flat attane 4100 46 39.0 0.85
41.8 0.91 5 3 5 PET mono flat attane 4102 49 38.7 0.79 46 0.94 5 3
6 PET mono flat affinity 1881G 40 43.1 1.06 43.1 1.06 4 2 7 PET
mono flat versify2000 48 51.5 1.08 50.8 1.07 3 2 8 PET mono flat
versify2200 40 49.7 1.25 49.7 1.25 4 2 9 PET mono flat surlyn1601
26 3.7** 0.15 29.5 1.15 7 5 10 PET mono flat primacor1410 43 31.4
0.73 49.2 1.14 5 2 11 PET mono flat amplify io 36 9.5** 0.26 37.5
1.04 6 5 12 PET mono flat ldpe320 43 20.2** 0.47 29.2 0.68 6 4 13
BOPP mono flat affinity 1881G 82 70.7 0.86 70.7 0.86 4 3 14 BOPP
mono flat attane 4102 77 75.4 0.98 75.4 0.98 4 2 15 BOPP mono flat
versify2200 67 59.1 0.88 58.7 0.88 2 1 16 PET coex 1:3:1* flat
affinity 1881G 51 50.7 1.00 50.7 1.00 4 3 17 PET coex 1:3:1* flat
attane 4102 46 45.7 1.00 45.7 1.00 4 3 18 PET coex 1:3:1* flat
versify2200 50 19.6** 0.39 38.9 0.78 6 4 19a PET mono bag 2fold
dowlex5056 45 24.8** 0.55 42.4 0.94 5 4 19b bag 4fold 44 21.5**
0.49 27.7 0.63 5 4 20a PET mono bag 2fold attane 4100 41 36.8 0.90
45.4 1.10 6 3 20b bag 4fold 44 22.1** 0.50 39.8 0.90 1 1 21a PET
mono bag 2fold attane 4102 47 40.3 0.86 47.3 1.01 6 3 21b bag 4fold
38 38.1 1.00 41.3 1.08 1 1 22a PET mono bag 2fold affinity 1881G 40
43.9 1.11 43.9 1.11 4 3 22b bag 4fold 35 36.4 1.04 39.2 1.12 3 3
23a PET mono bag 2fold versify2000 49 50.1 1.02 49.6 1.01 3 3 23b
bag 4fold 44 39.7 0.91 39.7 0.91 3 1 24a PET mono bag 2fold
versify2200 30 39.9 1.32 39.9 1.32 4 3 24b bag 4fold 35 47.2 1.36
47.2 1.36 4 1 25a PET Mono bag 2fold Primacor1410 45 28.9** 0.64
41.4 0.92 6 3 25b bag 4fold 49 24.7** 0.51 34.3 0.70 2 1 26a BOPP
mono bag 2fold affinity 1881G 66 64.1 0.97 64.1 0.97 4 3 26b bag
4fold 55 47.1 0.86 35.1 0.64 1 1 27a BOPP mono bag 2fold attane
4102 78 68.3 0.87 68.3 0.87 4 2 27b bag 4fold 68 44.2 0.65 54.8
0.81 2 1 28a BOPP mono bag 2fold versify2200 74 78.9 1.06 79.6 1.07
3 2 28b bag 4fold 75 52.1 0.69 69.7 0.93 1 1 29 PET coex
1:1:1.sup.+ flat Dowlex 5056 53.2 28.8** 0.54 42.1 0.79 5 4 30 PET
coex 1:1:1.sup.# flat see footnotes 52.2 42.5 0.81 49.4 0.95 5 3 31
PET coex 1:1:1.sup.$ flat see footnotes 53.8 38.8 0.72 38.8 0.72 4
3 EXPLANATIONS FOR COEX STRUCTURES: *for examples 16, 17, 18: The
face layer is shown in resin column F, the core layer and inner
layer is: Dowlex 5056G + 20% LDPE 310E .sup.+example 29: all layers
are Dowlex 5056G .sup.#example 30: face layer is Versify 2000 - the
core layer and other skin layer are Dowlex 5056G .sup.$example 31:
face layer and inner layer are Dowlex 5056G, the core layer is
Versify 2000 .sup.&USS seal force needed to obtain seal
strength of 15 N/15 mm **Comparative sample PHSS--plateau heat seal
strength determined in accordance with DIN 55529 (N/15 mm)
USS--Ultrasonic seal strength determined in accordance with DIN
55529 (N/15 mm)
Discussion
[0176] FIGS. 4-6 show ultrasonic seal strength (US S) v. seal force
curves for multilayer films with monolayer seal layer and PET
backing layer or BOPP backing layer.
[0177] FIG. 7 shows USS v. seal force for monolayer seal layers and
coextruded seal layers. The monolayer seal in Example 6 is the same
as face layer in Example 16 (AFFINITY 1881G). The monolayer seal in
Example 5 is the same as the face layer in Example 17 (ATTANE
4102). The monolayer in Example 8 is the same as the face layer in
Example 18 (VERSIFY 2200).
[0178] FIG. 8 shows USS v. seal force curves for ultrasonic seals
made with 2-fold/4-fold sealing geometry.
[0179] A. Applicant discovered that the presence of a USOP in: (i)
monolayer seal layer, (ii) face layer of coextruded seal layer, or
(iii) core and/or inner layer of coextruded seal layer and void
from face layer and a seal force produces an ultrasonic seal with a
seal strength from 35-55 N/mm. In other words, the USOP does not
need to be in the face layer to contribute to the production of
strong ultrasonic seal.
[0180] B. Applicant discovered that when the USOP in the seal layer
is tailored to the backing layer, the backing layer synergistically
contributes to strengthened USS. When backing layer is BOPP, a seal
force of 4-6 N/mm, or 4 N/mm produces an ultrasonic seal with a
seal strength from 55 N/mm to 80 N/mm. With proper selection of the
backing layer and the USOP, the layer contributes to the
improvement in seal strength.
[0181] C. Applicant discovered that use of USOP in flexible film
container with 2-fold zone and 4-fold zone and ultrasonically
sealed with 4 N/mm seal force has a USS greater than 0.8 of the
same 2-fold/4-fold seal that has been heat sealed (USS:PHSS ratio
greater than 0.8).
[0182] It is specifically intended that the present disclosure not
be limited to the embodiments and illustrations contained herein,
but include modified forms of those embodiments including portions
of the embodiments and combinations of elements of different
embodiments as come within the scope of the following claims.
* * * * *