U.S. patent application number 10/465399 was filed with the patent office on 2004-02-12 for coated sheet materials and packages made therewith.
Invention is credited to Bletsos, Ioannis V., Mikhael, Michael G., Rodriguez-Parada, Jose M., Yializis, Angelo.
Application Number | 20040028931 10/465399 |
Document ID | / |
Family ID | 30003214 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040028931 |
Kind Code |
A1 |
Bletsos, Ioannis V. ; et
al. |
February 12, 2004 |
Coated sheet materials and packages made therewith
Abstract
A coated porous sheet material comprising a gas permeable sheet
material selected from the group consisting of flash spun
plexifilamentary nonwoven sheet, spunbonded-film-spunbonded
composite sheet, spun-laced polyester/wood pulp composite sheet and
paper and a polymeric coating on at least one side thereof, wherein
the permeability of the coated sheet material is substantially
equivalent to the permeability of an equivalent sheet material
without the coating. The coated porous sheet material is suitable
for use in heat sealable packages.
Inventors: |
Bletsos, Ioannis V.;
(Midlothian, VA) ; Mikhael, Michael G.; (Tucson,
AZ) ; Rodriguez-Parada, Jose M.; (Hockessin, DE)
; Yializis, Angelo; (Tucson, AZ) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
30003214 |
Appl. No.: |
10/465399 |
Filed: |
June 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60391864 |
Jun 26, 2002 |
|
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|
Current U.S.
Class: |
428/500 |
Current CPC
Class: |
B32B 2553/00 20130101;
B65D 75/30 20130101; B65D 65/42 20130101; D06N 3/042 20130101; B32B
5/022 20130101; Y10T 428/1362 20150115; B32B 2307/724 20130101;
Y10T 428/1334 20150115; Y10T 428/31855 20150401; Y10T 428/1352
20150115; B32B 27/06 20130101; B32B 2333/04 20130101 |
Class at
Publication: |
428/500 |
International
Class: |
B32B 027/00 |
Claims
What is claimed is:
1. A heat sealable package comprising: a first material which
comprises a fibrous sheet, said first material having a coating
covering at least one side, said coating comprising polyacrylate
having a thickness between about 0.05 and about 5 .mu.m; and a
second material; wherein portions of the coated side of the first
material can be heat-sealed to the second material such that the
first material and the second material cooperate to form a void
capable of containing an article.
2. The heat sealable package of claim 1, wherein the polyacrylate
of the coating is selected such that when the sealed package is
opened by separating the first material and the second material,
substantially no fiber tear results.
3. The heat sealable package of claim 1, wherein the coating
comprises a first layer of cross-linked polyacrylate and a second
layer comprising a compound selected from the group consisting of
hydrocarbon oligomers and mixtures of polyacrylates and hydrocarbon
oligomers.
4. The heat sealable package of claim 1, wherein the coating
comprises a first layer of cross-linked thermoset polymer and a
second layer of a heat sealable compound, and wherein when heat
sealed, the adhesion strength between the first layer and the first
material is greater than 350.3 N/m, the adhesion strength between
the first layer and the second layer is between 140.1 and 350.3 N/m
and the adhesion strength between the second layer and the second
material is between 175.1 and 350.3 N/m.
5. The heat sealable package of claim 1, wherein the second
material is a nonwoven fabric.
6. The heat sealable package of claim 1, wherein the second
material is a coated film.
7. The heat sealable package of claim 1, wherein the second
material is a thermoformable film.
8. The heat sealable package of claim 1, wherein the second
material is a rigid preformed tray.
9. The heat sealable package of claim 1, wherein the second
material is paper.
10. The heat sealable package of claim 1, wherein the coating
covers fibers of said fibrous sheet while leaving interstitial
spaces between said fibers substantially uncovered.
11. The heat sealable package of claim 1, wherein said fibrous
sheet is selected from the group consisting of flash spun
plexifilamentary nonwoven sheet, spunbonded-meltblown-spunbonded
composite sheet and fibrous paper.
12. A heat sealed package made from the heat sealable package of
any of claims 1-11.
13. The heat sealed package of claim 12, wherein the heat seal
between the first material and the second material has a seal
strength of 140.1 to 350.3 N/m.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to sheet materials such as
nonwovens and paper coated with thin uniform polymeric coatings
having porosity and permeability roughly equivalent to similar
sheet materials which are uncoated. The invention also relates to
heat sealed packages made from such coated sheets.
BACKGROUND OF THE INVENTION
[0002] Conventionally practiced means for coating substrates such
as fibrous nonwoven and paper sheet materials include knife
coating, hot melt coating, aqueous dispersion coating, gravure
coating, direct blade coating, roll coating, air doctor coating and
squeeze coating. There are a number of problems with these known
methods. Knife coating results in almost a complete surface
coverage of the substrate, thereby altering its porosity and
permeability properties. Only a small fraction of the permeability
of the substrate is maintained mainly through the cracks that
appear on the coating after drying. Hot melt coating, depending on
how it is applied, may result in three-dimensional dots or islands
of coating between the fibers of the substrates such that some of
the pores of the sheet material are covered completely while some
are partially covered.
[0003] The coating lines used in conventional methods are large and
costly in terms of investment. These methods are not flexible in
that a lot of coating material must be deposited, which is also
economically unattractive in situations when less material would be
sufficient for the end use application of the coated sheet.
Solution or dispersion coatings must be dried by evaporation of the
solvent or dispersion liquid in a way that the coating or the
substrate are not damaged, or their properties are not altered due
to exposure at high temperatures, which is a slow and costly step.
In addition, in solvent-based coatings, solvent recovery is
required which adds cost and complexity to the process. Coatings
applied as hot melts often alter the thermal characteristics of the
substrates resulting in a compromise of their original properties.
Another problem is that the air permeability and/or the porosity of
the uncoated substrate is almost always sacrificed once the coating
is applied. It would be desirable to enhance or impart certain
desired properties to a sheet material while leaving the air
permeability or porosity of the material unaffected.
[0004] U.S. Pat. No. 6,083,628 (Yializis) discloses a hybrid film
comprising a first polymer base film having at least one
plasma-treated surface and at least a second thin acrylate polymer
film disposed along the plasma-treated surface of the base film.
The acrylate film is formed by crosslinking a functionalized
acrylate monomer or oligomer. The hybrid film may additionally
comprise one or more metallic or ceramic coatings. The continuous
process for forming the hybrid film takes place within a vacuum
chamber and it consists of plasma treatment of the base film to
functionalize the film followed by vapor deposition of the acrylate
monomer onto the base film and then radiation polymerization to
crosslink the monomer. The hybrid film is useful in a number of
applications including food packaging to improve barrier
properties. In food packaging applications, the acrylate coating is
disclosed to be typically 0.5 to 2 .mu.m thick.
[0005] U.S. Pat. No. 4,842,893 (Yializis et al.) discloses a method
for coating a flexible substrate with a thin, "substantially
continuous" film by depositing a vapor of polyfunctional acrylate
monomer, under vacuum, on a movable substrate maintained at a
temperature such that the monomer condenses on the substrate. The
film is then exposed to radiation in order to polymerize the film.
The acrylate monomer coating may be formed having a thickness of
less than 4 .mu.m, preferably less than 2 .mu.m and possibly as
thin as 0.1 Mm. Such coatings are disclosed as useful in food
packaging and protective coatings for metal or other substrates
used in a variety of applications. U.S. Pat. No. 5,032,461 (Shaw et
al.) discloses a similar process in which the process of U.S. Pat.
No. 4,842,893 (Yializis et al.) is repeated many times to form a
multi-layered thin film structure having as many as 4,000 or more
layers.
[0006] WO 99/59185 and WO 99/58756 disclose a process for coating a
substrate in which the substrate is treated with a plasma and
coated with an acrylate monomer, and the monomer is subsequently
radiation polymerized. The plasma is generated using hollow
cathodes and focused at the surface of the substrate using an
electromagnetic or magnetic focusing means. According to WO
99/59185, the monomer coating may be applied using a capillary drip
system, by immersion in a solution bath or by vapor deposition.
According to WO 99/58756, the monomer is applied by vapor
deposition. WO 99/58756 also discloses apparatus for treating
industrial sized, continuous substrates, specifically such as
papermaking fabrics.
[0007] A system and apparatus useful for vacuum deposition polymer
coating in which a web surface is coated with inorganic and organic
compositions is described in R. E. Ellwanger, M. G. Mikhael, A.
Yializis and A. Boufelfel, "Vacuum Functionalization of Web
Surfaces via Plasma Treatment and Polymer Coating," Vacuum
Technology & Coating (February 2001). The system includes
treating the surface with plasma to remove low molecular weight
material and to functionalize the surface with polar groups,
depositing materials such as radiation curable acrylates onto the
surface by vacuum evaporation coating and polymerization of
acrylates with either an electron beam or an ultraviolet lamp.
Among the applications of the coated substrates disclosed are high
barrier films, printable films and nonwoven fabrics.
[0008] U.S. Pat. Nos. 5,260,095, 5,547,508 and 5,395,644 (Affinito)
disclose a process and apparatus for forming solid polymer layers
under vacuum, including the step of degassing the monomer material
prior to injection into the vacuum. The advantages of forming
polymer layers in a vacuum are said to be that photoinitiator is
not needed for polymerization, polymerization is faster, there are
fewer impurities in the polymer, and the polymer has a greater
density and a smoother finished surface.
[0009] WO 98/18852 discloses a process for coating substrates such
as polypropylene, polyester or nylon sheet materials with
crosslinked acrylate and a layer of metal. Acrylate monomer is
evaporated using flash evaporators and condensing the acrylate onto
the sheet as a monomer film, and subsequently polymerizing the film
by irradiation by electron beam or ultraviolet light. The adhesion
of the acrylate on the sheet material is enhanced by plasma
treatment immediately before coating. Both the plasma treatment and
the coating are conducted under vacuum. The resulting coated sheet
is has low oxygen permeability and is especially useful for food
packaging.
[0010] U.S. Pat. Nos. 5,811,183 and 5,945,174 (Shaw et al.)
disclose sheet materials including paper and film coated with
acrylate polymer release coatings made by a process in which
silicon-containing and fluorine-containing acrylate prepolymer
having a molecular weight between 200 and 3000 is vapor deposited
on the sheet material and radiation polymerized. Coating layers of
between 0.5 and 1 .mu.m thick are disclosed.
[0011] Fiber tear is an important problem with current medical
packaging in which at least one fibrous sheet, such as a nonwoven
or paper, and a second sheet have been heat sealed together to form
a pocket capable of containing an article such as a sterile medical
device. Fiber tear occurs during the opening of a package (i.e.,
upon peeling the two heat sealed sheets away from each other), and
begins by separating a fiber or a bundle of fibers from the surface
of the fibrous sheet. Fiber tear is unacceptable in the case of
medical packaging because foreign particles are thereby introduced
into the sterile field of the operating room. It would be desirable
to eliminate the incidence of fiber tear from heat sealed packages
which include at least one fibrous sheet, without greatly affecting
the permeability of the fibrous sealing sheet.
[0012] Additionally, it is often necessary to provide printed
information on the surface of heat sealed sheets, especially on
medical packaging. However, depending upon the nature of the
substrate used as the heat sealed sheet, such printing can be
rubbed off of the surface rather easily. It would be desirable to
provide a coating on such substrates which would enhance ink
adhesion to the heat sealed sheet/package.
[0013] Additionally, many sheet materials which are used in
protective environments, such as in the medical field for use in
making gowns, masks, drapes, boots, etc., are subject to contact
with fluids which may present either chemical or biological
hazards. Accordingly, such materials are typically rated as to
their resistance to fluid strike-through, particularly blood
strike-through in the medical field. It would be desirable to
provide coatings for such sheet materials which would enhance fluid
strike-through resistance without significantly affecting the air
permeability of the sheet, such that the wearer will enjoy
increased protection from fluid strikethrough while still being
comfortable when wearing such garments.
SUMMARY OF THE INVENTION
[0014] In one embodiment, the present invention relates to a coated
porous sheet material comprising a gas permeable sheet material
selected from the group consisting of flash spun plexifilamentary
nonwoven sheet, spunbonded-film-spunbonded composite sheet,
spunbonded-meltblown-spunbond- ed composite sheet, spun-laced
polyester/wood pulp composite sheet and paper and a polymeric
coating covering at least one side thereof, wherein the
permeability of the coated sheet material is substantially
equivalent to the permeability of an equivalent sheet material
without the coating.
[0015] In another embodiment, the present invention is directed to
a coated fibrous sheet comprising a sheet selected from the group
consisting of flash spun plexifilamentary nonwoven sheet,
spunbonded-film-spunbonded composite sheet,
spunbonded-meltblown-spunbond- ed composite sheet, spun-laced
polyester/wood pulp composite sheet and paper, comprising fibers
and interstitial spaces between the fibers, and a coating on at
least one side of the sheet comprising a compound selected from the
group consisting of oligomers, polyacrylates, low molecular weight
(MW) polymers and mixtures thereof, and wherein the coating covers
the fibers while leaving the interstitial spaces substantially
uncovered.
[0016] A heat sealable package comprising a first material which
comprises a fibrous sheet, said first material having a coating
covering at least one side, said coating comprising polyacrylate
having a thickness between about 0.05 and about 5 .mu.m; and a
second material; wherein portions of the coated side of the first
material can be heat-sealed to the second material such that the
first material and the second material cooperate to form a void
capable of containing an article. The first material is preferably
selected from the group consisting of flash spun plexifilamentary
nonwoven sheet, spunbonded-meltblown-spunbonded composite sheet,
and fibrous paper.
[0017] A coated fibrous sheet made by the process comprising (a)
selecting a fibrous substrate selected from the group consisting of
flash spun plexifilamentary nonwoven sheet,
spunbonded-film-spunbonded composite sheet,
spunbonded-meltblown-spunbonded composite sheet, spun-laced
polyester/wood pulp composite sheet and paper, comprising fibers
and interstitial spaces between the fibers; (b) atomizing monomers,
oligomers or low MW polymers or solutions or slurries thereof; (c)
vaporizing the monomers, oligomers or low MW polymers in a flash
evaporator; (d) condensing the vapor substantially only on the
surface of the fibers of the substrate; and (e) solidifying the
condensate to form a coating; wherein the steps (c) through (e) are
carried out in an environment of a vacuum on the order of between
1.33.times.10.sup.-3 and 1.33.times.10.sup.-7 kPa; and wherein the
coating covers the fibers of the substrate while leaving the
interstitial spaces between said fibers substantially
uncovered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more thorough explanation of the invention will be
provided in the detailed description of the preferred embodiments
of the invention in which reference will be made to the following
drawings.
[0019] FIG. 1 is a schematic view of an apparatus for making the
product of the invention.
[0020] FIG. 2 is a cross-sectional view of a coated substrate in
accordance with one embodiment of the present invention.
[0021] FIG. 3 is a cross-sectional view of a heat sealed
package.
[0022] FIG. 4 is a scanning electron microscopy micrograph of a
prior art uncoated control sample.
[0023] FIG. 5 is a scanning electron microscopy micrograph of a
vapor deposition coated sample having a single coating layer
according to the present invention.
[0024] FIG. 6 is an atomic force microscopy micrograph of a vapor
deposition coated sample having a single coating layer according to
the present invention.
[0025] FIG. 7 is a scanning electron microscopy micrograph of a
two-layer vapor deposition coated sample according to the present
invention.
[0026] FIG. 8 is a scanning electron microscopy micrograph of a
prior art conventionally coated sample.
[0027] FIG. 9 is a bar graph comparing the percent good seals in
heat sealed packages using coated sheet according to the invention
compared with a control uncoated sheet at various heat seal
temperatures.
[0028] FIGS. 10-12 are bar graphs comparing the percent good seals
in heat sealed packages using coated sheets according to the
invention with control uncoated sheets at various heat seal
temperatures.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present inventors have discovered that the desired
effects listed above can be obtained by vapor deposition of
various, extremely thin polymeric coatings onto various substrates.
The thickness of the vapor deposition coatings depends on the
intended application. For example, for applications in which water,
alcohol or oil repellency is important, the thickness could be a
few tens of nanometers. For applications in which the substrate
will be heat sealed to form a package, the coating may be thicker,
for example between 0.05 and 5 .mu.m. In any case, the thickness of
the vapor deposition coatings is preferably on the order of the
diameter of the fibers on the surface of the fibrous substrate.
Thus, enough coating material is provided for the intended
application and the vapor deposition coatings conform to the
surface morphology of fibers without covering the interstitial
spaces between fibers. The maximum coating thickness allowable
before the permeability of the substrate is affected depends on the
porosity of the substrate, that is, the void space that can be
filled by the coating, and on the porosity of the coating.
[0030] The process used in making the coated substrate of the
invention is illustrated by the schematic shown in FIG. 1. The
process includes the optional initial step of plasma treating the
substrate and the steps of vapor deposition coating the substrate
and optional polymerization of the coating. The process is
conducted in a vacuum chamber 8 maintained at an atmosphere of
between 1.33.times.10.sup.-3 and 1.33.times.10.sup.-7 kPa. The
substrate 16 to be coated is fed from feed roll 12.
[0031] The surface of the substrate 16 is first optionally exposed
to plasma in order to remove loosely held low molecular weight
compounds and functionalize its surface. Consequently, the surface
energy of the substrate is modified to improve its wetting by the
condensing vapor. The plasma treatment may be carried out by an
apparatus 14 such as that disclosed in U.S. Pat. No. 6,066,826, WO
99/58757 and WO 99/59185.
[0032] The substrate is then coated with a radiation polymerizable
monomer, an oligomer or a low MW polymer by a flash evaporation
deposition process using a flash evaporation apparatus 18, the
process and apparatus being described in U.S. Pat. Nos. 4,722,515,
4,696,719, 4,842,893, 4,954,371, 5,032,461 and 5,097,800, all of
which are incorporated herein by reference. The radiation
polymerizable monomer, oligomer or low MW polymer, in the form of a
liquid or a slurry, should be provided in a continuous flow through
inlet tubing 19 in order to create a uniform coating. The radiation
polymerizable monomer, oligomer or low MW polymer liquid or slurry
is preferably degassed prior to injecting it as a vapor into the
vacuum chamber, as described in U.S. Pat. No. 5,547,508. In the
event more than one coating is desired, multiple flash evaporation
apparatuses 18 and 19 can be used in series, or if the additional
coatings are desired on the opposite surface of substrate 16,
additional flash evaporation apparatuses, 20 and 21 can be provided
as shown in FIG. 1.
[0033] Cooling the substrate to be coated during vapor deposition
enhances the efficiency of the monomer/oligomer condensation, as
described in U.S. Pat. No. 4,842,893 and WO 98/18852. This may be
accomplished by passing the substrate over a cooled drum as in U.S.
Pat. No. 4,842,893 during vapor deposition. Cryoplates (not shown)
may also be employed for this purpose, located such that they cool
the substrate prior to vapor deposition.
[0034] The condensed coating is solidified within a matter of
milliseconds after condensation onto the surface of the substrate,
such as by using a radiation source 22 such as an electron beam or
ultraviolet source to polymerize the monomer, and/or by natural
solidification upon cooling of an oligomer or low MW polymer. In
some cases, the oligomers can be further polymerized or crosslinked
by the radiation source. In the case that an electron beam gun is
chosen, the energy of the electrons should be sufficient to
polymerize the coating in its entire thickness as described in U.S.
Pat. No. 6,083,628, incorporated herein by reference. The
polymerization of the monomer/oligomer coating is also described in
U.S. Pat. Nos. 4,842,893, 4,954,371 and 5,032,461. For oligomers or
low MW polymers that are solid at room temperature polymerization
may not be required as described in U.S. Pat. No. 6,270,841. The
coated substrate is finally wound up on a take-up roll 24.
[0035] The thickness of the coating is controlled by the line speed
and vapor flux of the flash evaporator used in the vapor deposition
process. As the coating thickness increases, the energy of the
electron beam must be adjusted in order for the electrons to
penetrate through the coating and achieve effective polymerization.
For example, an electron beam at 10 kV and 120 mA can effectively
polymerize acrylate coatings up to 2 .mu.m thick.
[0036] It has been found that the above process may be applied to a
fibrous substrate 16 such as a nonwoven sheet or paper to form a
coated fibrous sheet. Suitable nonwoven sheets for use in the
invention include flash spun plexifilamentary nonwoven sheets,
spunbonded meltspun webs and composite sheets,
spunbonded-meltblown-spunbonded composite sheets,
spunbonded-film-spunbonded composite sheets, spun-laced
polyester/wood pulp composite sheets and others.
[0037] The process described above has been employed to generate a
number of new products, which are embodiments of the present
invention.
[0038] In one embodiment of the invention, a porous sheet material
is coated so as to cover at least one side with a polymeric
material such that the permeability of the coated sheet material is
substantially equivalent to the permeability of an equivalent sheet
material without the coating; that is, the coating apparently has
substantially no effect on the permeability of the material. By
`substantially equivalent permeability` is meant that the
permeability of the coated sheet material is within 64% of the
permeability of the uncoated sheet material, which is a normal
variation of air permeability in uncoated Tyvek.RTM. flash spun
plexifilamentary polyethylene sheet. The term "an equivalent sheet
material" refers to the same sheet material as used in the coated
sheet material prior to being coated. The term "permeability" is
herein defined to mean the gas permeability, especially air
permeability, as measured by the most appropriate test for the
particular sheet material. For instance, for some materials, this
would be Gurley Hill Porosity and for other materials, it would be
Frazier Permeability. By "cover" or "covering" we mean that the
entire fiber surface of the sheet material is coated with the
coating material, unlike fabrics which are coated with a series of
discrete patches of a coating material, leaving substantial
portions of the fiber surface uncoated.
[0039] Porous sheet materials for use in this embodiment of the
invention include nonwoven sheet and paper which are permeable to
gases and/or liquids. A preferred example of a nonwoven sheet
material suitable for use in the invention is flash spun
plexifilamentary film-fibril material such as Tyvek.RTM., made from
high density polyethylene, available from E. I. du Pont de Nemours
and Company, Inc. Suitable flash spun plexifilamentary film-fibril
materials may also be made from polypropylene. Other examples of
nonwoven sheets useful in this embodiment of the present invention
include spunbonded meltspun webs and composite sheets,
spunbonded-meltblown-spunbonded composite sheets (SMS),
spunbonded-film-spunbonded composite sheets (SFS) and spun-laced
polyester/wood pulp composite sheets such as Sontara.RTM. and paper
made from a fibrous material such as wood pulp or recycled paper.
These different sheet materials are useful in different
applications. For instance, according to the present invention,
coated Tyvek.RTM. and coated paper are especially suited for use in
heat sealed packaging (e.g., medical packaging) in which they
reduce the incidence of fiber tear. Coated SMS, coated SFS and
coated Sontara.RTM. are useful in applications where repellency of
liquids is important, such as medical gowns, surgical drapes,
etc.
[0040] The hydrostatic head of coated Tyvek.RTM. sheet with a
coating thickness of up to approximately 0.5 .mu.m in accordance
with this embodiment of the invention has also surprisingly been
found to be substantially equivalent to that of uncoated Tyvek.RTM.
sheet. This has been especially unexpected in the case of
hydrophilic coatings, which allow water to wet and spread onto the
surface of Tyvek.RTM., which is inherently hydrophobic. By
`substantially equivalent hydrostatic head` is meant that the
hydrostatic head of the coated Tyvek.RTM. sheet is within 34% of
the hydrostatic head of the uncoated Tyvek.RTM. sheet, which is
within the normal variation of hydrostatic head in Tyvek.RTM.. For
coating thickness greater than 0.5 .mu.m we have observed the
variation in the hydrostatic head of vapor deposition coated
Tyvek.RTM. to be within 75% of the hydrostatic head of uncoated
Tyvek.RTM..
[0041] According to another embodiment of the invention, a fibrous
porous sheet material is coated in such a way that the fibers of
the sheet material are coated individually while leaving the
interstitial spaces between the fibers substantially uncovered by
the coating material. By "substantially uncovered" is meant that at
least 35% of the interstitial spaces between the fibers are free of
coating.
[0042] Suitable materials for use in the coating layers of the
coated substrates include vacuum compatible monomers, oligomers or
low MW polymers and mixtures thereof. Vacuum compatible monomers,
oligomers or low MW polymers should have high enough vapor pressure
to evaporate rapidly in the evaporator without undergoing thermal
degradation or polymerization, and at the same time should not have
vapor pressure so high as to overwhelm the vacuum system. The ease
of evaporation depends on the molecular weight and the
intermolecular forces within the monomers, oligomers or polymers.
Typically, vacuum compatible monomers, oligomers and low MW
polymers useful in this invention can have weight average molecular
weights up to approximately 1200. Vacuum compatible monomers used
in this invention should be radiation polymerizable, either alone
or with the aid of a photoinitiator, and include acrylate monomers
functionalized with hydroxyl, ether, carboxylic, sulfonic acid and
other functionalities. Vacuum compatible oligomers or low molecular
weight polymers include diacrylates, triacrylates and higher
molecular weight acrylates functionalized as described above,
aliphatic, alicyclic or aromatic oligomers or polymers and
fluorinated acrylate oligomers or polymers. Fluorinated acrylates,
which exhibit very low intermolecular interactions, useful in this
invention can have weight average molecular weights up to
approximately 6000. Preferred acrylates have at least one double
bond, and preferably at least two double bonds within the molecule,
to provide high speed polymerization. Examples of acrylates that
are useful in the coating of the present invention and average
molecular weights of the acrylates are described in U.S. Pat. No.
6,083,628 and WO 98/18852.
[0043] The coating material may be a crosslinked hydrophilic
compound or composition. Examples of such compounds are mono-, di-
and triacrylates functionalized with groups such as hydroxyl,
ether, carboxylic acid, sulfonic and amine groups. Such materials
are particularly suitable as coatings for nonwoven and paper sheets
to be used as printing substrates. The ink adhesion of sheet
materials coated with crosslinked hydrophilic compounds is
improved. Ink pick-off from flexographic printing on Tyvek.RTM.
coated according to this invention is virtually non-existent
compared with similar printing on uncoated Tyvek.RTM.. Also, the
ink rub-off resistance when rubbing with gasoline from flexographic
printing on Tyvek.RTM. coated according to this invention is
virtually eliminated compared with uncoated Tyvek.RTM.. Such
materials are also suitable as coatings for sheets to be used in
heat sealing applications.
[0044] Alternatively, the coating material may be a hydrophobic
compound or composition. The coating material may be a
crosslinkable, hydrophobic and oleophobic fluorinated acrylate,
according to one preferred embodiment of the invention. Such a
coating is generally useful in applications in which alcohol, water
and/or oil repellency is desired. When a crosslinkable hydrophobic
and oleophobic fluorinated acrylate is used as the coating
material, it has been found that the coated nonwoven sheet of the
present invention can have an alcohol/water repellency rating
between 6 and 10. A rating of 10 means that a drop of neat
isopropanol does not penetrate the sheet, but rather remains on the
surface. The coated sheet can also have an oil repellency rating
between 3 and 6. Such coated nonwoven sheet materials are
especially useful in medical garment applications in which blood or
fluid strike-through is sought to be avoided. Typical sheet
materials used in medical garments (e.g., gowns, masks, boots,
etc.) which are useful in this application are flash spun
plexifilamentary film-fibril structures such as Tyvek.RTM.,
spunbonded meltspun webs and composite sheets,
spunbonded-meltblown-spunbonded composite sheets (SMS),
spunbonded-film-spunbonded composite sheets (SFS), spun-laced
polyester/wood pulp composite sheets such as Sontara.RTM., and
others. The exact level of repellency depends on the nature of the
coating material and the amount of coating present on the nonwoven
sheet which, in turn, depends on the speed of the coating line, the
flux of vapor condensing onto the substrate and the polymerization
efficiency of the electron beam or the UV radiation. The level of
repellency also depends on the material that the nonwoven sheet is
made of, the structure of the nonwoven sheet and its porosity and
pore size distribution. For example, SMS structures are typically
more porous so that imparting repellency to them is more
challenging than to Tyvek.RTM. structures used in medical
packaging. According to one embodiment of the invention, a fibrous
sheet material coated with a hydrophobic fluorinated acrylate may
be further coated with an absorbent hydrophilic coating.
[0045] When a crosslinkable hydrophobic and oleophobic fluorinated
acrylate is used as the coating material on paper, it has been
found that the paper, which prior to coating has no alcohol/water
or oil repellency, shows alcohol/water and oil repellency
comparable to similarly coated nonwovens. Such coated paper is
especially useful in medical applications.
[0046] It has been found that the coated sheet material of the
invention is well suited for use in packaging wherein the coated
surface of the coated sheet material is heat sealed to a second
material to form a pocket capable of containing an article. Such
packaging is commonly used to package medical devices such as
surgical instruments, which are sterilized in the package and are
required to remain sterile as they are removed from the package to
be used. A cross-sectional view of a heat sealed package according
to the present invention is shown in FIG. 3. The package 40
comprises a first sheet material 32 having a coating 33 thereon
which is heat sealed to a second material 34, the coated sheet and
the second material cooperating to form a void capable of
containing an article 35. In order to be useful in medical
packaging, the sheet material must be porous to sterilizing gases.
The second material may comprise a nonwoven sheet such as, but not
limited to, a spunbonded plexifilamentary nonwoven sheet; it may
also comprise a coated polymeric film such as poly(ethylene
terephthalate) (PET), a thermoformable film such as Surlyne
coextruded with poly(ethylene-co-vinyl acetate) (i.e.,
EVA/Surlyn.RTM./EVA), nylon, a preformed tray or paper. Preferably
in heat sealed packaging applications, the coating on the sheet
material comprises two layers, as shown in FIG. 2. The first layer
28 adjacent the sheet material 26 being a polyacrylate, and the
second layer 29 adjacent the first layer being a mixture of
hydrocarbon oligomers and/or poly(acrylate) oligomers.
[0047] Both sides of the first sheet material may be coated, for
instance when one side is to be heat sealed to a second material to
form a package and the other side is to be printed. Referring again
to FIG. 2, sheet 30 for use in heat sealed packaging may also
comprise coating 31 on the surface opposite the first layer 28 to
enhance printability.
[0048] A benefit of the present invention is that the incidence of
fiber tear upon the opening of a heat sealed package made from a
coated fibrous sheet material of the invention, i.e., when the
heat-sealed sheets are separated from each other, is virtually
eliminated. It is believed that this is because the peeling does
not occur directly on the surface of the fibrous sheet. In the case
of a single layer coating, peeling occurs between the single layer
coating and the second material. This is also achieved by coating
the fibrous sheet with two coating layers and by choosing the
adhesion and heat-seal strengths of the coating layers
appropriately. The first coating layer 28 can be a protective layer
of a thermoset crosslinked polyacrylate having an adhesion to the
substrate greater than the adhesion between the first and the
second coating and between the second coating and the second
material. The second coating layer 29, applied directly to the
first coating layer, comprises hydrocarbon oligomers or a blend of
hydrocarbon oligomers with functionalized acrylate oligomers
heat-sealable to the second sheet material which cooperates with
the coated sheet to form the package, typically a thermoformable
film. The second coating layer must adhere to the first coating
layer, and must adhere to the second material with a heat seal
strength that is less than the adhesion of the first coating layer
to the first sheet.
[0049] The total thickness of the coating can be from about 0.05 to
5 micrometers, preferably between about 0.2 to 3 micrometers, more
preferably between about 0.2 to 2 micrometers. In a particularly
preferable embodiment, the protective polyacrylate layer is about 1
micrometer thick and the heat-sealable layer comprising hydrocarbon
oligomers is about 1 micrometer thick.
[0050] For certain medical packaging wherein the first sheet is a
fibrous sheet material and the second material is a film, it is
typical for the adhesion strength between the first and second
coating layers to be about 175 to about 350 N/m, which should also
be the level of seal strength between the second layer and the
film. When these conditions are fulfilled, peeling occurs away from
the surface of the fibrous sheet material, either between the two
coating layers, or between the second coating layer and the film.
The peeling will then occur in one of two ways. Either the first
coating layer remains on the fibrous sheet material and the second
coating layer peels away from the first coating layer, or both
coating layers remain on the fibrous sheet material and the film
peels away from the second coating layer. In either case, the
peeling does not occur directly on the exposed fibrous sheet
material surface and therefore substantially no fiber tear results
when the package is opened. By "substantially no fiber tear" is
meant that no fiber tear occurs in the nonwoven sheet in at least
90% of the packages that are opened, as exemplified below.
[0051] Reducing fiber tear is especially challenging in the case of
fibrous paper, which inherently is less resistant to puncture, tear
propagation and fiber tear. Applying one or two coating layers to
the surface of a fibrous paper according to the present invention
ensures that peeling does not occur directly on the surface and
significantly improves the performance with respect to fiber
tear.
[0052] According to one embodiment for heat sealing applications,
the first coating layer comprises a crosslinked polyacrylate-based
formulation to prevent fiber tear, and the second coating layer
comprises thermoplastic oligomers/polymers, or a mixture of
oligomers, or a mixture of oligomers and polyacrylates for heat
sealing. The hydrophobic hydrocarbon oligomers may be aliphatic,
alicyclic or aromatic. In the case of coatings of hydrocarbon
oligomers, no polymerization step is necessary as hydrocarbon
oligomers solidify readily upon condensation and cooling. Materials
useful for heat sealing applications must soften or melt at
temperatures, dwell times and pressures that can produce robust
seals without damaging or altering the properties of the substrate
or the second material. Aliphatic, alicyclic and aromatic
hydrocarbon oligomers and their blends with functionalized acrylate
monomers are useful starting materials to meet these
requirements.
[0053] Hydrocarbon oligomers are hydrophobic, but not oil or
alcohol repellent, therefore they are not useful as the outer
coating layer in embodiments of the invention to be used in
applications where repellency of alcohol and oil is required.
[0054] Additional coating layers may be deposited on the first
coating layer. Too thick a coating may result in a reduction of the
air permeability of the sheet material; however, according to this
embodiment of the invention, the interstitial spaces between the
fibers remain substantially uncovered by the coating material.
[0055] The nonwoven or paper sheet, coated on one surface with a
hydrophobic hydrocarbon oligomer compound for use in heat sealing
applications according to the present invention, may also be coated
with a cross-linkable hydrophilic coating on the opposite surface
to provide good ink adhesion for printing of package design, etc.,
without compromising the hydrostatic head properties of the
substrate.
[0056] In any of the above embodiments, the coating material may
include pigments or dyes to impart color to the surface of the
coated sheet material. In the case that both sides of the sheet are
coated with different coating materials, the resulting sheet may
have a different color on each side. During the vapor deposition
process, masks can be placed between the slit that the vapor exits
the evaporator and the sheet to be coated in order to impart a
desired design to the coated sheet.
[0057] In any of the above embodiments, the coating material may
include other known additives, including additives to impart
antistatic and antimicrobial functionality.
[0058] According to yet another embodiment of the present
invention, a heat sealed package is provided as described above
with the exception that the coated sheet is a polymeric film rather
than a nonwoven sheet or paper. Preferably, the film is coated with
formulations as described herein of a polyacrylate, then a
hydrophobic composition containing a polyacrylate on the side that
is heat sealed. The opposite side of the film may also be coated
with a hydrophilic compound or composition to promote good ink
adhesion in the case that the film is to be printed. The thickness
of the coating is 0.05-2 .mu.m.
[0059] The improved properties that are realized with the present
invention are made more apparent by the following non-limiting
examples.
EXAMPLES
[0060] In the non-limiting examples that follow, the following test
methods were employed to determine various reported characteristics
and properties. ASTM refers to the American Society of Testing
Materials. ISO refers to the International Standards Organization.
TAPPI refers to Technical Association of Pulp and Paper
Industry.
[0061] Basis weight was determined by ASTM D-3776, which is hereby
incorporated by reference and reported in g/m.sup.2.
[0062] Seal Strength of heat seals was measured according to ASTM
F8800. The load cell was set at 2.248 lbs. (10 Newtons).
[0063] Seal integrity of heat seals was tested according to ASTM
F192998.
[0064] Hydrostatic head was measured using ISO 811, which is hereby
incorporated by reference and is reported in cm of water. This test
measures the resistance of a sheet to the penetration of liquid
water under a static load. A 100 cm.sup.2 sample is mounted in a
Shirley Hydrostatic Head Tester (manufactured by Shirley
Developments Limited, Stockport, England). Water is pumped against
one side of the sample until three points of leakage appear on the
surface.
[0065] Oil repellency was measured as follows. A drop of each of
the solutions in Table 1 was deposited on the surface of the sheet
to be measured. If the liquid drop of a particular solution (1-6)
does not wet the surface within 5 minutes, then the surface is
considered phobic for that liquid.
1TABLE 1 Oil Repellency Rating Composition 1 Kaydol (mineral oil) 2
65/35 Kaydol/n-hexadecane 3 n-hexadecane 4 n-tetradecane 5
n-dodecane 6 n-decane
[0066] Alcohol/water repellency was measured as follows. Fifteen
droplets from each of 10 different solutions of alcohol in water,
numbered from 1 to 10 according to % isopropanol (wherein the
number represents the % isopropanol divided by 10), are placed 2.54
cm apart along the width of the sheet to be measured. The width of
the sheet that is tested corresponds to the width of the roll
sample that was vapor deposition coated. After 5 minutes, each
droplet is examined for signs of wetting and penetration to the
other side of the sheet. The alcohol/water repellency of the sheet
is calculated as the number of the alcohol/water solution which
caused the sheet to show signs of wetting minus one, which is also
the highest number of solution at which there were no signs of
wetting and penetration to the other side of the sheet.
[0067] Gurley Hill Porosity is a measure of the barrier of the
sheet material for gases. In particular, it is a measure of how
long it takes for a volume of gas to pass through an area of
material wherein a certain pressure gradient exists. Gurley-Hill
porosity is measured in accordance with TAPPI T-460 om-88 using a
Lorentzen & Wettre Model 121D Densometer. This test measures
the time of which 100 cubic centimeters of air is pushed through a
2.54 cm diameter sample under a pressure of approximately 12.45 cm
of water. The result is expressed in seconds and is usually
referred to as Gurley Seconds.
[0068] Frazier Permeability is a measure of air permeability of
porous materials and is reported in units of m.sup.3/m.sup.2/min.
It measures the volume of air flow through a material at a
differential pressure of 1.27 cm water. An orifice is mounted in a
vacuum system to restrict flow of air through sample to a
measurable amount. The size of the orifice depends on the porosity
of the material. Frazier permeability is measured in units of
ft.sup.3/ft.sup.2/min using a Sherman W. Frazier Co. dual manometer
with calibrated orifice and the measurements were converted to
m.sup.3/m.sup.2/min by multiplying by a conversion factor of
0.3048.
[0069] Electron Spectroscopy for Chemical Analysis (ESCA) (also
known as XPS or X-Ray Photoelectron Spectroscopy) is used to
identify surface functional groups (e.g., C--C bonding as in
polyethylene or hydrocarbon oligomers, --C(.dbd.O)O as in
acrylates, etc.) and to provide semiquantitative surface elemental
composition (i.e., atom %, that is the % of the atoms on the
surface, i.e., carbon, oxygen, fluorine, etc., excluding hydrogen).
The sampling depth of ESCA as used here is approximately 10 nm;
consequently, the information that it provides is characteristic of
the surface top chemistry. The ESCA spectra of the peeled surfaces
of the fibrous substrate side were compared to those of the film
side and to those of their respective control surfaces (i.e., the
uncoated fibrous substrate, the coated fibrous substrate and the
film). By matching the chemistry of the peeled surfaces, the
location of the peeling was determined. In a single layer coating,
peeling may occur either adhesively or cohesively. In adhesive
peeling, the peeling occurs between the single layer coating and
the fibrous substrate or between the single layer coating and the
second material. In cohesive peeling, the peeling occurs within the
single layer coating or within the fibrous substrate (i.e., fiber
tear, determined also by visual inspection), or within the second
material (i.e., film tear determined also by visual inspection). In
two layer coatings, the peeling may occur adhesively between the
coating layers or between a coating layer and the fibrous material
or between a coating layer and the second material, or cohesively
within any of the layers, or within the fibrous substrate or within
the second material.
[0070] Ink Adhesion was measured by adhering a pressure sensitive
adhesive tape to printed areas of printed substrates and then
peeling it off. The ink transfer onto tape, also known as "ink
pick-off," and the condition of the print after the peel were
evaluated.
[0071] Ink Adhesion with gasoline rubbing was measured by dipping a
cotton swab in gasoline and rubbing the cotton swab onto the print
on a printed substrate. The level of print transferred onto the
cotton swab and the smear of the print due to rubbing are
evaluated. Since the test is subjective, the results are useful
only when comparing results measured by the same operator.
[0072] Receding and advancing water contact angles were measured
using a Rame-Hart: NRL C.A. Goniometer model 100-00-115. A syringe
with the test fluid is lowered to the appropriate height above the
surface of the test sample and a drop is dispensed that contacts
the surface. The field of view is adjusted to be able to read the
correct advancing and receding angles. The drop is then slowly
expanded while the protractor is simultaneously adjusted. As the
drop develops a constant shape as it is slowly moving, the
advancing contact angle is read with the protractor as the tangent
of the surface of the sample and the drop. For the receding angle,
the test liquid is slowly withdrawn, collapsing the drop and
causing it to retract. As the shape becomes constant and the
protractor is simultaneously adjusted, the receding angle is read
with the protractor as the tangent of the surface of the sample and
the drop.
[0073] In the following examples, the benefits of the coatings of
the present invention were investigated on two different Tyvek.RTM.
flash spun plexifilamentary sheet materials, a first sheet material
having a basis weight of about 74.6 g/m.sup.2, hereinafter "Sheet
A", and a second sheet material having a basis weight of about 55.9
g/m.sup.2, hereinafter "Sheet B". Sheet A has found use in heat
sealed medical packaging and in general performs very well. However
in a typical heat sealing packaging line it is difficult to control
the heat sealing temperatures in a narrow temperature window with
temperatures creeping upward. Packages sealed at these higher
temperatures tend to exhibit fiber tear when opened.
[0074] These problems are exacerbated when attempting to use Sheet
B, having the lower basis weight, as the sealing material. For
example, the lower basis weight material of Sheet B is much more
susceptible to fiber tear upon opening of the package than the
higher basis weight Sheet A material. Furthermore, when Sheet A or
B are coated via conventional means they lose part of their gas
permeability, which makes gas sterilization procedures, for example
sterilization with ethylene oxide or steam, more inefficient, due
to slower infusion of the sterilizing gas into the package and
slower complete removal of the gas after sterilization.
[0075] The following examples demonstrate that coatings according
to the present invention act to greatly reduce or even eliminate
fiber tear, even in use of the lower basis weight material of Sheet
B, and extend the useful heat sealing temperature range.
Examples 1-3
Surface Morphology of Vapor Deposition Coated Fibrous
Substrates
[0076] The chemistry of the vapor deposition coatings of the
present invention and their physical structure (i.e., thickness,
continuity, coverage and conformation with the surface of the
substrate) determine the product functionalities that impart the
improved properties of the present invention. FIG. 4 shows a
Scanning Electron Microscopy (SEM) micrograph of a control sample
of uncoated Sheet B ("Sheet B Control") at 3,000.times.
magnification. The micrograph shows individual fibers and bundles
of fibers that range in thickness from less than 1 .mu.m for
individual fibers to more than 10 .mu.m for small bundles. Their
interstitial spaces show layers of fibers and, although open, they
support a certain height of liquid water (hydrostatic head) and
allow gases to flow through while preventing particles and
microbial spores from penetrating to the other side. The fibers on
the surface may be connected at their intersections and appear
flattened due to the bonding process that consolidates them into a
strong structure.
[0077] A 457.2 meter sample roll of Sheet B having a basis weight
of 55.9 g/m.sup.2 was treated with Ar/O.sub.2 plasma at 200 W. The
sample was then coated with an acrylate-based formulation
functionalized with carboxylic and sulfonic acid groups, and
hydroxyl and ether groups. The coating was then polymerized using
an electron beam at 10 kV and 120 mA (Example 1). FIG. 5 is an SEM
micrograph of Example 1 taken at the same magnification as the
Sheet B Control. There is no significant visual difference between
Example 1 and control, except that the coated fibers appear to be
smoother than in the control sample. The coating conforms to the
morphology of the fibers without filling the interstitial spaces,
which still remain open. Example 2 was produced exactly as Example
1, except that the coating onto Sheet B consisted of a mixture of
monoacrylate and hydrocarbon oligomers. FIG. 6 shows an Atomic
Force Microscopy (AFM) micrograph of a 3 .mu.m.times.3 .mu.m area
on the top side of a single fiber of Example 2. The smooth area in
the figure shows the surface of the fiber that is covered by the
coating. The rough area shows an uncoated part of the surface of
the fiber. The roughness is due to the crystalline and amorphous
domains of high density polyethylene on the surface of the fiber.
The height difference between the coated and uncoated areas, which
is equivalent to the height of the single coating layer, is
approximately 45 nm. FIG. 7 is an SEM micrograph of a thicker
two-layer vapor deposition coating onto Sheet B (Example 3).
Example 3 was taken from a 457.2 meter sample roll of Sheet B which
was treated with Ar/O.sub.2 plasma at 200 W and subsequently coated
with an monomeric acrylate-based formulation functionalized with
carboxylic and sulfonic acid groups, and with hydroxyl and ether
groups. The coating was then polymerized using an electron beam at
10 kV and 120 mA. Then onto the first coating a second coating of a
mixture of monomeric acrylate and hydrocarbon oligomers was vapor
deposited and polymerized under the same conditions as the first
coating. There was no plasma treatment between the first and second
coating. The coating of Example 3 shown in FIG. 7 appears to have
covered some of the interstitial spaces, but still its thickness is
much less than the thickness of the smallest fibers, since they are
still visible and the coating conforms well with the surface of
Tyvek.RTM. and the overall surface morphology of the fibers.
[0078] FIG. 8 shows a conventional coating of Sheet B at
1,000.times. magnification. The coating completely covers the
fibers; in fact, there is no evidence of the Tyvek.RTM. beneath it.
Typical thickness of conventional coatings may range in the tens of
.mu.m. Gases still penetrate through these thick coatings but the
breathability of Tyvek.RTM. is considerably reduced.
Examples 1 and 4
Contact Angle
[0079] The receding and advancing water contact angles were
measured for the coated and uncoated sides of Example 1 as well as
for both sides of an uncoated sample of Sheet B Control (Comparison
1). The advancing and receding contact angles were measured with
water droplets using a drop-on-plate goniometer. The results are
given in Table 2.
[0080] A sample of Sheet A having a basis weight of 74.6 g/m.sup.2
was treated with plasma and coated in exactly the same manner as
the Sheet B sample of Example 1.
[0081] The receding and advancing water contact angles were
measured for the coated and uncoated sides of Sheet A (Example 4),
as well as for both sides of an uncoated sample of Sheet A Control
(Comparison 2). The results are given in Table 2.
2 TABLE 2 Water Contact Angle (degrees) Advancing Receding Example
1 Coated side 0 0 Uncoated side 124 74 Comparison 1 Uncoated side 1
132 64 Uncoated side 2 133 72 Example 4 Coated side 0 0 Uncoated
side 124 73 Comparison 2 Uncoated side 1 124 66 Uncoated side 2 131
68
[0082] Contact angles of zero indicate that water spreads and wets
the surface of the sample upon contact, while contact angles
greater than 100 degrees indicate that the water does not wet the
surface at all.
[0083] As can be seen from the results in Table 2, the coated sides
of Examples 1 and 4 of the present invention are hydrophilic such
that water spreads and wets them immediately upon contact. This is
contrasted with the uncoated sides of Examples 1 and 4, which
remain hydrophobic, such that water droplets do not spread but
remain as droplets on their surface. The uncoated sides of Examples
1 and 4 remain hydrophobic like the uncoated Tyvek.RTM. of
Comparison 1 and 2. These coatings provide significant
hydrophilicity to Tyvek.RTM., which is specific to the surface of
the side the coatings are applied to, leaving the other side
unaffected.
Examples 5 and 6
Heat Sealability of Crosslinked Acrylates to LDPE/Mylar.RTM. and to
Thermoformable Film
[0084] A 457.2 meter sample of Sheet B was treated with Ar/O.sub.2
plasma at 100 W. The sample was then coated with a monomeric
acrylate-based formulation functionalized with carboxylic and
sulfonic acid groups, and hydroxyls and ether groups. The coating
was polymerized with an electron beam at 10 kV and 100 mA. Coated
sides of Sheet B sheets were then heat sealed to low density
polyethylene (LDPE) coated Mylar.RTM. polyester film
(LDPE/Mylar.RTM.) to form at least thirty heat seals in the form of
strips at each heat sealing temperature ("Example 5 seals").
Various heat sealing temperatures were used to form the heat sealed
strips from 116.degree. C. to 143.degree. C. For comparison, the
same number of uncoated Sheet B Control sheets were also heat
sealed to LDPE/Mylar.RTM. at the same heat sealing temperatures,
dwell time and pressure ("control seals").
[0085] All of the seals, the Example 5 seals and the controls, were
then peeled and each seal was judged to be "good" or not, based on
whether or not there was any fiber tear on the Tyvek.RTM.) sheet or
film tear on the LDPE/Mylar.RTM. film. In good seals, the
Tyvek.RTM. and film peeled away from each other cleanly with no
fiber or film tear.
[0086] FIG. 9 is a bar graph showing the percentage of good seals
of the Example 5 and control seals. All of the seals that had been
heat sealed at temperatures of 116.degree. C. and 121.degree. C.
were good seals, but at heat sealing temperatures of 127.degree. C.
to 143.degree. C., only the example seals are free of fiber tear.
Even at the heat sealing temperature of 143.degree. C., the example
seals peeled without any fiber tear, although there was some film
tear of the LDPE/Mylar.RTM..
[0087] A 457.2 meter sample of Sheet A was coated using the process
described herein under the same conditions and coating formulation
as in Example 5. The coated surfaces of Sheet A sheets were then
heat sealed to LDPE/Mylar.RTM. to form at least thirty heat seals
in the form of strips for each heat sealing temperature ("Example 6
seals"). Various heat sealing temperatures were used to form the
heat sealed strips from 116.degree. C. to 149.degree. C. For
comparison, the same number of uncoated Sheet A Control sheets were
also heat sealed to LDPE/Mylar.RTM. at the same heat sealing
temperatures dwell time and pressures ("control seals").
[0088] FIG. 10 is a bar graph showing the percentage of good seals
of the Example 6 and the control seals. All of the seals that had
been heat sealed at 116.degree. C. were good seals, but at heat
sealing temperatures of 121.degree. C. to 132.degree. C., only the
Example 6 seals are free of fiber tear. At heat sealing
temperatures above 138.degree. C., the example seals peeled with
film tear of the LDPE/Mylar.RTM., and no fiber tear, but the
control seals exhibited both fiber and film tear.
[0089] The coated surfaces of Examples 5 and 6 were heat sealed at
132.degree. C. to LDPE/Mylar.RTM. to form at least thirty seals
("Sheet B example seals" and "Sheet A example seals"). For
comparison, the uncoated surfaces of Examples 5 and 6 were also
heat sealed to LDPE/Mylar.RTM. at the same heat sealing
temperature, dwell time and pressure ("control seals").
[0090] All of the seals, the examples and the controls, were then
peeled and each seal was judged to be "good" or not based on
whether or not there was any fiber tear on the Tyvek.RTM. sheet or
film tear on the LDPE/Mylar.RTM. film.
[0091] FIG. 11 is a bar graph showing the percent of the Sheet B
example seals, the Sheet A example seals, the Sheet B Control seals
and the Sheet A control seals, which were deemed to be "good"
seals, the percent which exhibited fiber tear and the percent which
exhibited film tear. All Sheet B example seals, i.e., those made
with the coated side of Sheet B, were good and had no fiber tear,
while all Sheet B control seals, i.e., those made with the uncoated
side of the same sheet exhibited fiber tear. Similarly, most of the
Sheet A example seals were good seals, free of fiber tear, although
some of them exhibited film tear of the LDPE/Mylar.RTM.. All of the
Sheet A control seals, however, exhibited fiber and film tear.
These coatings impart to Tyvek.RTM. significant improvements in
heat sealability, which are specific to the surface of the side the
coatings are applied to, leaving the other side unaffected.
[0092] Five hundred pouches were made by heat sealing Example 5 to
LDPE/Mylar.RTM.. The heat sealing conditions are summarized in
Table 3. Two hundred and fifty of the packages were peeled open and
no fiber tear was observed. The seal strength was also measured for
each heat sealing condition (according to ASTM F88-00) and the
results are included in Table 3. Four heat sealing samples were cut
from the same location around the sealed area and tested from each
of four pouches per heat sealing setting. The pouches that were
measured were produced at the same time side-by-side along the
width of the roll. The seal strength is the average of 16
measurements per heat sealing condition. Pouches made under the
heat sealing conditions of Table 3 were tested (according to ASTM
F1929-98) and no leaks were detected.
3 TABLE 3 Seal Strength Seal T Dwell time Pressure Unsupported
Supported 180.degree. C. (.degree. C.) (s) (kPa) (N/m) (N/m) 129
0.9 414 122.6 350.3 129 1.1 414 131.3 420.3 132 0.9 414 148.9 437.8
132 1.1 414 157.6 437.8
[0093] The coated Sheet B of Example 5 was also heat sealed to a
thermoformable film consisting of a layer of Surlyn.RTM. ionomer
resin between two layers of ethylene vinyl acetate
(EVA/Surlyn.RTM./EVA) (available from DuPont) to form at least 30
seals ("Example 5a seals"). Various heat sealing temperatures were
used to form the seals from 121.degree. C. to 154.degree. C. For
comparison, the same number of uncoated Sheet B Control sheets were
also heat sealed to the EVA/Surlyn.RTM./EVA film at the same heat
sealing conditions ("control seals").
[0094] All of the packages, the Example 5a seals and the controls,
were then peeled and each seal was judged to be "good" or not based
on whether or not there was any fiber tear on the Tyvek.RTM. sheet
or film tear on the film.
[0095] FIG. 12 is a bar graph showing the percentage of good seals
of the Example 5a packages and the control packages. The use of the
EVA/Surlyn.RTM./EVA film resulted in no incidence of film tear, so
that the heat seals were considered unacceptable only because of
fiber tear of Sheet B. It is clear that the Sheet B Controls
exhibited significant fiber tear when heat sealed at temperatures
greater than 121.degree. C., while the coated Sheet B of Example 5a
produced good seals when heat sealed in the range of 127.degree. C.
to 154.degree. C., although it became partially transparent at
temperatures greater than 138.degree. C.
Example 5
Adhesive Peeling Between Vapor Deposition Coating and
LDPE/Mylar
[0096] Matched areas of peeled surfaces of the vapor deposition
coated Sheet B and the LDPE/Mylar.RTM. sides of Example 5 seals
were analyzed by ESCA. The ESCA spectrum of the peeled surface on
the Tyvek.RTM. side is characteristic of carbon atoms bonded to
other carbon atoms by single bonds and to oxygen atoms by single
and double bonds, which is consistent with the acrylate coating and
is the same as the spectrum of the vapor deposition coated Sheet B
before heat sealing. The ESCA spectrum of the peeled surface on the
LDPE/Mylar.RTM. side is characteristic of carbon atoms bonded to
other carbon atoms by single bonds, which is indicative of the LDPE
of the LDPE/Mylar.RTM. and it is the same as the spectrum of the
LDPE/Mylar.RTM. before heat sealing. The ESCA spectra show that the
peeling of heat seals of Example 5 occurs adhesively between the
crosslinked acrylic coating on the surface of Sheet B and the LDPE
of the Mylar.RTM. film. The presence of the crosslinked acrylic
coating on the surface of the Tyvek.RTM. after peeling means two
things. First, the crosslinked acrylic coating is more strongly
adhered to the surface of the Tyvek.RTM. than to the
LDPE/Mylar.RTM. and second the peeling did not occur directly on
the surface of the Tyvek.RTM., but rather between the crosslinked
acrylic coating and the LDPE of LDPE/Mylar.RTM.. The heat seals of
Example 5 showed no fiber tear unlike the control seals, which
exhibited considerable fiber tear above 127.degree. C.
Examples 7-9
Heat Sealability of Crosslinked Acrylates and Their Mixtures with
Hydrocarbon Oligomers to LDPE/Mylar.RTM. and Thermoformable
Films
[0097] Example 7 is a 457.2 meter sample of Sheet B that was coated
using the same process conditions as Example 5 with a mixture of
monoacrylate/diacrylate functionalized with carboxylic and sulfonic
acid groups and hydrocarbon oligomers. Example 8 is a 457.2 meter
sample of Sheet A that was coated exactly as Example 7 except that
it had a different diacrylate. Example 9 is a 457.2 meter sample of
Sheet B that was produced using the same formulation and conditions
as Example 6. Examples 7, 8 and 9 were then heat sealed to
LDPE/Mylar.RTM. and to EVA/Surlyn.RTM./EVA thermoformable film to
form at least 200 packages for each heat sealing temperature. The
heat sealing conditions and seal strength (unsupported) are
presented in Table 4 below. Heat seals of Table 4 were tested
(according to ASTM F1929-98) and no leaks were detected.
4 TABLE 4 Seal T Dwell time Pressure Seal Strength Sample (.degree.
C.) (sec) (kPa) (N/m) Examples 7 and 8 heat sealed to LDPE/Mylar
.RTM. Example 7 126 0.6 275.8 245.2 127 0.8 137.9 227.7 Example 8
127 0.6 275.8 227.7 127 0.8 275.8 315.2 132 1 275.8 332.7 Examples
7 and 9 heat sealed to thermoformable EVA/Surlyn .RTM./EVA Example
7 132 1.2 345 157.6 134 1.2 345 175.1 Example 9 132 1.2 345 140.1
135 1.2 345 157.6 135 1.5 345 175.1
Examples 8 and 10
Peeling Under High Adhesive Loads
[0098] To further test the robustness of the coatings on the
surface of Tyvek.RTM., the following test was performed. The side
to be tested of each of five 5.08 cm.times.10.16 cm samples was
adhered to the top surface of a double-sided tape, selected to have
slightly higher adhesion than a typical medical package, the other
side of which was adhered to a rigid aluminum plate. To ensure good
and reproducible adhesion of the samples to the double-sided tape,
a 16.3 kg steel disk was rolled over the top of silicone rubber
placed over the samples. A 2.54 cm tag end of the sample not
adhered to the double-sided tape was attached to a high speed
Instron tensile tester. A second 1.27 cm tag end at the other end
of the sample was not allowed to be adhered to the tape. The
Instron peeled the Tyvek.RTM. sample at an angle of nearly
180.degree. and a peeling rate of 70 in/sec, a typical rate at
which some medical packages are peeled open by a nurse in use. The
force required to peel the 2 in wide sample from the double-sided
tape was recorded. Then the Tyvek.RTM. sample was inspected for
fiber tear as well as the tape for residues of the coatings and a
determination was made whether there was a clean peel or fiber
tear. Matched areas of the Tyvek.RTM. peeled side and the tape were
also analyzed by ESCA to determine whether the peeling occurred
between the Tyvek.RTM. and the first layer of coating, within the
coating layer or between the coating layer and the tape. The test
was performed for uncoated Sheet B Control, Example 8, Sheet B
vapor deposition coated as in Example 7 with a mixture of
diacrylate, monoacrylate and hydrocarbon oligomers (Example 10) and
Sheet B coated with a thick conventional coating. The results are
shown in Table 5.
5TABLE 5 Peel Fiber Sample Force (N/m) Tear (%) Peeling Sheet B
(control) 525.4 80 Cohesive failure in Tyvek .RTM. Example 8 437.8
0 Adhesive between coating and tape Example 10 525.4 0 Adhesive
between coating and tape Sheet B coated with 175.1 0 Cohesive in
coating conventional air knife coating
[0099] The results in Table 5 show that even at seal strengths as
high as 437.8-525.4 N/m and fast peel rates, the vapor deposition
coatings peel adhesively from the surface of the tape and remain
intact on the surface of Tyvek.RTM. with no evidence of fiber tear.
These results indicate that if the vapor deposition coated samples
were heat sealed to a film with heat seal strengths as high as
525.4 N/m, then peeling would occur on the surface of the vapor
deposited coatings with no fiber tear. Thick conventional coatings
peel cohesively leaving residues on both the Tyvek.RTM. and film
side at lower seal strength. Sheet B Control fails cohesively
producing fiber tear in 80% of the samples tested under the
conditions of the test.
Examples 3, 5, 6 and 11-18
Basis Weight, Gurley Hill Porosity and Hydrostatic Head
[0100] Table 6 compares the average values of basis weight (BW),
Gurley Hill porosity (GH) and hydrostatic head (HH) of Examples 3,
5, 6, and 11-18 with the corresponding properties of Sheet B and
Sheet A Controls. Examples 11-18 were prepared under the same
process conditions as Example 6. Examples 11-13 were prepared by
coating Sheet B and Examples 14-18 were prepared by coating Sheet
A.
[0101] The aim and range for each of these properties for Sheet A
and Sheet B are also listed in Table 6. The BW and GH of the vapor
deposition coated samples are within the commercial Tyvek.RTM.
product specifications. In fact, the commercial products cannot be
distinguished from the vapor deposition coated samples with regard
to BW or GH. Apparently, any modification that the vapor deposition
coatings may have introduced to the samples is too small to
influence these properties. The vapor deposition coatings, although
they are so thin and light so as not to affect the GH and BW, do
influence the HH of Sheet B and to a smaller extent that of Sheet
A. The hydrostatic head of Example 3 was measured to be lower than
the specifications for Sheet B Control. Also, in one Sheet A sample
that was coated with two coatings, we measured the hydrostatic head
of the coated side to be lower than the specification of the
uncoated product.
6 TABLE 6 BW GH HH (cm H.sub.2O) (g/m.sup.2) (s) Coated Uncoated
Example 5 56.3 18 137 152 Example 11 55.3 17 104 127 Example 12
55.6 26 127 124 Example 13 55.3 18 142 127 Example 3 56.3 21 99 137
Sheet B product specifications: Aim 55.9 18 145 Low 52.9 8 124 High
60.0 28 165 Example 6 78.6 22 165 -- Example 14 75.6 19 140 140
Example 15 74.9 22 107 107 Example 16 75.9 18 152 150 Example 17
76.3 24 107 150 Example 18 75.9 19 41 122 Sheet A product
specifications: Aim 74.6 22 157 Low 71.2 8 104 High 78.0 36 211
Examples 19-21
[0102] A 457.2 meter sample roll of Sontara.RTM. 8830 was vapor
deposition coated with a fluoroacrylate formulation based on
Zonyl.RTM., including a photoinitiator, on both the poly(ethylene
terephthalate) (PET) and the wood pulp sides (Example 19). The
coating process and the polymerization of the coating were carried
out in a vacuum atmosphere of 1.33.times.10.sup.4 kPa. The surfaces
of the Sontara.RTM. were not plasma treated before coating since
the formulation readily wets Sontara.RTM..
[0103] Another sample of Sontara.RTM. 8830 was vapor deposition
coated with the same formulation on both the PET and the wood pulp
side under higher vacuum (1.33.times.10.sup.-5 kPa), higher vapor
flux and faster polymerization (Example 20).
[0104] Another sample of Sontara.RTM. 8830 was vapor deposition
coated with the same formulation on both the PET and the wood pulp
side under similar conditions as Example 20 (Example 21). The
polymerization of the coating was effected by an electron beam at
10 kV and 120 mA in Examples 19-21.
[0105] The oil and alcohol/water repellency were measured for each
side of each sample. As a comparison, a sample of uncoated
Sontara.RTM. 8830 (Control) was also tested. The data is given in
Table 7.
7 TABLE 7 Oil Repellency Alcohol/Water Repellency Example 19 PET
side 5 3 Wood pulp side 6 5 Example 20 PET side 4 8 Wood pulp side
5 7 Example 21 PET side 6 10 Wood pulp side 6 10 Control PET side 0
0 Wood pulp side 0 0
[0106] As can be seen from the results, the coating imparts
significant alcohol/water and oil repellency on either side of both
samples as compared with uncoated Sontara.RTM. 8830, which has no
alcohol/water or oil repellency. The level of repellency can be
adjusted by appropriately tuning process parameters. The coatings
in both examples did not affect the physical properties of
Sontara.RTM. 8830.
* * * * *