U.S. patent application number 09/929929 was filed with the patent office on 2002-07-18 for method for protecting surfaces of packed articles.
Invention is credited to Jones, David C., Lim, Hyun Sung.
Application Number | 20020094742 09/929929 |
Document ID | / |
Family ID | 26923765 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094742 |
Kind Code |
A1 |
Jones, David C. ; et
al. |
July 18, 2002 |
Method for protecting surfaces of packed articles
Abstract
The present invention is directed to a method for packing an
article comprising providing a vapor permeable and substantially
water impermeable composite laminated sheet comprising a nonwoven
layer and a polymer film layer, said composite laminated sheet
having a trapezoidal tear strength of at least about 2 N in the
machine direction, and a smoothness measured on the polymer film
layer of less than 9 micrometers and placing the composite
laminated sheet on the surface of the article with the polymer film
layer contacting at least a portion of said surface.
Inventors: |
Jones, David C.;
(Midlothian, VA) ; Lim, Hyun Sung; (Midlothian,
VA) |
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: |
26923765 |
Appl. No.: |
09/929929 |
Filed: |
August 15, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60229946 |
Sep 1, 2000 |
|
|
|
Current U.S.
Class: |
442/394 ;
428/304.4; 442/327; 442/347; 442/370; 442/398 |
Current CPC
Class: |
Y10T 428/249953
20150401; Y10T 442/622 20150401; Y10T 442/678 20150401; D04H 1/60
20130101; B32B 27/12 20130101; Y10T 442/647 20150401; Y10T 442/674
20150401; Y10T 442/60 20150401 |
Class at
Publication: |
442/394 ;
442/327; 442/398; 428/304.4; 442/347; 442/370 |
International
Class: |
D04H 001/00; D04H
003/00; D04H 005/00; D04H 013/00 |
Claims
What is claimed is:
1. A method for packing an article comprising: providing a vapor
permeable and substantially water impermeable composite laminated
sheet comprising a nonwoven layer and a polymer film layer, said
composite laminated sheet having a trapezoidal tear strength of at
least about 2 N in the machine direction, and a smoothness measured
on the polymer film layer of less than 9 micrometers; and placing
the composite laminated sheet on the surface of the article with
the polymer film layer contacting at least a portion of said
surface.
2. The method according to claim 1, wherein said composite
laminated sheet has a trapezoidal tear strength of at least about
3.9 N.
3. The method according to claim 1, wherein said composite
laminated sheet has a slip angle of at least about 15 degrees,
measured on the polymer film layer.
4. The method according to claim 1, wherein said polymer film layer
comprises a vapor permeable polymer selected from the group
consisting of polyethylenes, polypropylene, polyesters,
polyurethanes, polyethers and polyvinyl alcohols and their
copolymers.
5. The method according to claim 4, wherein said polymer film layer
is an extruded monolithic film.
6. The method according to claim 4, wherein said polymer film layer
is a microporous film.
7. The method according to claim 1, wherein said nonwoven layer is
a powder-bonded nonwoven web.
8. The method according to claim 1, wherein said article has a
soft, high-gloss finished surface.
9. The method according to claim 8, wherein said article is a
painted automobile part.
10. The method according to claim 1, further comprising providing a
cushioning material for said article.
11. The method according to claim 11, wherein said cushioning
material is a nonwoven bulky composite laminated sheet.
12. The method according to claim 11, wherein said cushioning
material comprises an open-celled polymer foam layer incorporated
into said composite laminated sheet.
13. A protective cover for packing an article comprising a vapor
permeable and substantially water impermeable composite laminated
sheet comprising a nonwoven layer and a polymer film layer, said
composite laminated sheet having a trapezoidal tear strength of at
least about 2 N in the machine direction, and a smoothness measured
on the polymer film layer of less than 9 micrometers.
14. The protective cover according to claim 13, wherein said
composite laminated sheet has a trapezoidal tear strength of at
least about 3.9 N.
15. The protective cover according to claim 13, wherein said
composite laminated sheet has a slip angle of at least about 15
degrees, measured on the polymer film layer.
16. The protective cover according to claim 13, wherein said
polymer film layer comprises a vapor permeable polymer selected
from the group consisting of polyethylenes, polypropylene,
polyesters, polyurethanes, polyethers and polyvinyl alcohols and
their copolymers.
17. The protective cover according to claim 16, wherein said
polymer film layer is an extruded monolithic film.
18. The protective cover according to claim 16, wherein said
polymer film layer is a microporous film.
19. The protective cover according to claim 13, wherein said
nonwoven layer is a powder-bonded nonwoven web.
20. The protective cover according to claim 13, further comprising
a cushioning material for said article.
21. The protective cover according to claim 20, wherein said
cushioning material is an open-celled polymer foam layer
incorporated into said composite laminated sheet.
22. A vapor permeable, water impermeable composite laminated sheet
comprising a first layer of polymer film bonded to a second layer
of powder-bonded nonwoven web, wherein said polymer film is a
monolithic extrudate.
23. The vapor permeable, water impermeable composite laminated
sheet according to claim 22, wherein said composite laminated sheet
has a trapezoidal tear strength of at least about 2 N in the
machine direction, and a smoothness measured on the polymer film
layer of less than 9 micrometers.
24. The vapor permeable, water impermeable composite laminated
sheet according to claim 22, further comprising a cushioning
layer.
25. The vapor permeable, water impermeable composite laminated
sheet according to claim 24, wherein said cushioning layer
comprises an open-cell polymer foam.
26. The vapor permeable, water impermeable composite laminated
sheet according to claim 22, in which at least 95 weight percent of
fibers in said nonwoven web are compatible with said polymer
film.
27. A vapor permeable, water impermeable composite laminated sheet
comprising a first layer of copolyether ester film and a second
layer of powder-bonded polyester nonwoven web.
28. A vapor permeable, water impermeable composite laminated sheet
consisting of a first layer of microporous polymer film bonded to a
second layer of powder-bonded nonwoven web and optionally a
cushioning layer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method for protecting packed
articles against surface damage, especially articles having painted
surfaces such as painted automobile components. More particularly,
the invention is directed to a method for protecting the surfaces
of packaged articles, which includes placing a vapor permeable and
substantially water impermeable composite laminated sheet on at
least a portion of the surface of the article. The composite
laminated sheet comprises a laminate of a vapor permeable,
substantially water impermeable film layer and a nonwoven
layer.
BACKGROUND OF THE INVENTION
[0002] Packaging materials to protect packed articles against
surface damage include plastic bubble wrap, paper, cardboard,
adhesive films, styrofoam, and sheeting material made of nylon,
polyester, and cotton.
[0003] When an article to be packed is made of or coated with a
synthetic material that releases low volatility solvents or other
gases, and which continues to release such low volatility solvents
or gases after packaging, it is important that the packaging
material not trap the released low volatility solvents or gases
between the packed article and packaging material. Such trapped
gases or side reactions between low volatility solvents and
moisture can generate undesirable discoloration or blemishes in the
finish on the packed article's surface. An example where this can
be a problem is in the packaging of automobile bumper fascia. Two
component paints that combine, for example, isocyanates with
hydroxyl functional material, react to create urethanes. These two
component systems are commonly referred to as "2K" and cure more
slowly than previously used one component "1K" paint systems. These
"2K" paints can continue to post cure for up to fourteen days after
exiting from the drying oven at the manufacturing facility. Because
there is often a shortage of storage space, the painted bumpers may
be shipped to the automobile assembly plants while they are still
post curing.
[0004] Published European Patent Application EP 959119 to Inoue et
al. discloses sheets for protecting the painted surfaces of
automobiles. The sheets comprise a nonwoven layer having a polymer
film laminated to at least one surface thereof and a
pressure-sensitive adhesive layer formed on the polymer film layer.
The sheets are adhered without wrinkling to the painted automobile
surfaces by the pressure-sensitive adhesive layer to prevent
permeation of rainwater, which can cause surface damage. The films
used in the laminates of Inoue et al. are not breathable and thus
do not allow for release of low volatility solvents or gases that
may be generated by off-gassing from the painted surfaces.
[0005] U.S. Pat. No. 5,763,336 to Jones et al. discloses a nonwoven
bulky composite sheet material suitable for use in protective
covers for articles such automobile bumpers. The composite sheet
comprises first and second layers of a water impermeable, water
vapor permeable synthetic sheet with a third layer of a bulky
flexible material bonded between the first and second layers, for
example by ultrasonic bonding. The first and second layers are
preferably fibrous bonded nonwoven sheets such as Tyvek.RTM.
flash-spun plexifilamentary polyethylene film-fibril sheet sold by
E.I. du Pont de Nemours and Company of Wilmington, Del. Tyvek.RTM.
flash-spun sheets are vapor permeable, are not abrasive, and are
inert to most painted surfaces. Other sheets which can be used as
the outer layers of the bulky composite include
spunbond/meltblown/meltblown/- spunbond ("SMMS") polypropylene
sheet material and microporous films such as Exxaire.TM. film sold
by Tredegar Company of Richmond, Va. Covers made from the bulky
laminates provide protection against surface damage, have good tear
resistance, are re-useable, and do not trap solvent gases which are
given off as a result of off-gassing from finishes such as curing
paint.
[0006] However, it has been found in some instances when the bulky
composites have been used in covers to protect freshly painted
automobile parts, that markings on the painted surface are formed
which correspond to the grid pattern created by the ultrasonic or
thermal bonding points in the bulky composite. This is possibly due
to different rates of diffusion of volatiles through the cover at
the bonded and unbonded portions of the bulky composite. In some
instances, an impression of the thermal point bond pattern on the
Tyvek.RTM. surface (rib or linen) has been left on the paint. In
addition, when dirt is trapped between the cover and the article
being protected, scratches can be formed on the surface of the
article by the dirt due to lateral movement of the protective cover
with respect to the surface of the article. This is especially a
problem when the article to be protected has a relatively soft
finish layer on the surface, such as painted automobile bumpers
where the paint has not cured completely prior to packaging. In
some cases, additional spot protection of automobile bumpers has
been used on the most commonly damaged areas of the bumper. For
example, Rapgard.RTM. tape (available from Kansai Company, Japan)
or Transeal.RTM. protective films have been used for spot
protection by applying the tape or film to selected sections of the
bumper prior to covering the bumper with a secondary protective
cover such as the bulky composite cover disclosed in U.S. Pat. No.
5,763,336. However these methods also have some drawbacks. For
example, Rapgard.RTM. tape is not breathable and therefore does not
allow off-gassing of volatiles on the areas where it is applied.
Although the Transeal.RTM. film is breathable, it requires
pre-heating using expensive equipment in order to apply the film to
the bumpers. Microporous films such as Aptra.RTM. film, available
from Amoco, have been used as slip sheets under the bulky composite
covers to eliminate the need for spot protection. However,
microporous films are generally difficult to handle and easily
torn, resulting in higher than desired yield losses and increased
cost.
[0007] There is a need for a simplified, cost-effective method for
protecting articles from surface damage caused by impact with other
articles or by dirt which may find its way between protective
covers and the article, as well as damage which can be caused by
trapped volatile materials that are created during off-gassing of
finished articles.
SUMMARY OF THE INVENTION
[0008] A first embodiment of the present invention is directed to a
method for packing an article comprising providing a vapor
permeable and substantially water impermeable composite laminated
sheet comprising a nonwoven layer and a polymer film layer, said
composite laminated sheet having a trapezoidal tear strength of at
least about 2 N in the machine direction, and a smoothness measured
on the polymer film layer of less than 9 micrometers and placing
the composite laminated sheet on the surface of the article with
the polymer film layer contacting at least a portion of said
surface.
[0009] A second embodiment of the present invention is a protective
cover for packing an article comprising a vapor permeable and
substantially water impermeable composite laminated sheet
comprising a nonwoven layer and a polymer film layer, said
composite laminated sheet having a trapezoidal tear strength of at
least about 2 N in the machine direction, and a smoothness measured
on the polymer film layer of less than 9 micrometers.
[0010] Another embodiment of the present invention is a vapor
permeable, water impermeable composite laminated sheet comprising a
first layer of polymer film bonded to a second layer of
powder-bonded nonwoven web, wherein said polymer film is a
monolithic extrudate.
[0011] Another embodiment of the present invention is a vapor
permeable, water impermeable composite laminated sheet consisting
of a first layer of microporous polymer film bonded to a second
layer of powder-bonded nonwoven web and optionally a cushioning
layer.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 is a schematic representation of a process by which
the composite laminated sheet structure of the invention can be
made.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The current invention provides a method for protecting
packed articles against surface damage which includes the step of
placing a vapor permeable and substantially water impermeable
composite laminated sheet on at least a portion of the surface of
the part. The composite laminated sheet comprises a polymeric film
layer and a nonwoven layer. The composite laminated sheet is placed
on the surface of the article to be packed such that the film side
of the composite laminated sheet contacts at least a portion of the
surface of the article. Preferably, the composite laminated sheet
is sufficiently strong and durable to be re-used several times.
[0014] The term "vapor permeable" as used herein is intended to
encompass permeation of both water vapor, solvent vapors and other
such gases.
[0015] The term "nonwoven fabric, sheet, or web" as used herein
means a structure of individual fibers or filaments that are
positioned in a random manner to form a planar material without an
identifiable pattern by means other than knitting or weaving. As
used herein, the term "fiber" means an elongated strand of defined
length, such as staple fibers formed by cutting a continuous strand
into lengths and the term "filament" means a generally continuous
strand that has a very large ratio of length to diameter.
[0016] As used herein, the "machine direction" is the long
direction within the plane of a sheet, i.e., the direction in which
the sheet is produced. The "cross direction" is the direction
within the plane of the sheet that is perpendicular to the machine
direction.
[0017] The term "powder-bonded nonwoven" as used herein refers to a
bonded nonwoven fabric formed by depositing a powder adhesive,
which melts at a temperature below the melting point of the fibers
of the carded web, onto an unbonded carded fibrous web so that the
powder adhesive is distributed throughout the thickness of the
carded web. Thereafter, the powder-containing web is heated to melt
the powder adhesive without melting the fibers of the carded web to
form a powder-bonded nonwoven. Powder-bonded nonwovens are
distinguished from sheets made using powder lamination methods such
as that described in Shehata U.S. Pat. No. 5,445,874 where an
activated web consisting of an adhesive material is formed from an
adhesive powder. In powder lamination, the powder adhesive bonds
two substrates together, such as a woven or nonwoven substrate with
a film layer and the adhesive powder is concentrated primarily at
the interface between the two substrates. In powder lamination, the
powder adhesive does not contribute to any significant degree to
the bonding within the nonwoven substrate.
[0018] The term "spunbond" as used herein means a nonwoven formed
by melt extrusion of a polymer into strands that are quenched and
drawn, usually by high velocity air, to strengthen the filaments.
The filaments are collected on a forming surface and bonded, often
by application of heat and pressure using a patterned bonding
roll.
[0019] The term "plexifilamentary" as used herein, means a
three-dimensional integral network of a multitude of thin,
ribbon-like film-fibril elements of random length and with a mean
film thickness of less than about 4 microns and a median fibril
width of less than about 25 microns. In plexifilamentary
structures, the film-fibril elements are generally co-extensively
aligned with the longitudinal axis of the structure and they
intermittently unite and separate at irregular intervals in various
places throughout the length, width, and thickness of the structure
to form a three-dimensional network. Plexifilamentary film-fibril
fibers are obtained by a flash-spinning process. In the process for
making flash-spun fibers, as disclosed in U.S. Pat. No. 3,081,519
to Blades et al. (assigned to DuPont), a solution of fiber-forming
polymer in a liquid spin agent that is not a solvent for the
polymer below the liquid's normal boiling point, is maintained at a
temperature above the normal boiling point of the liquid and at
autogenous pressure or greater, and is then spun into a zone of
lower temperature and substantially lower pressure to generate
plexifilamentary film-fibril strands.
[0020] The polymeric film and nonwoven layers of the composite
laminated sheet are selected and combined in such a way to form a
composite laminated sheet that is both vapor permeable and
substantially water impermeable. The composite laminated sheet
preferably has a hydrostatic head of at least 100 cm, preferably
greater than 400 cm and a moisture vapor transmission rate of at
least 100 g/m.sup.2/24 hr, preferably at least 800 g/m.sup.2/24 hr
and a trapezoidal tear strength of at least about 2 N in the
machine direction. The composite laminated sheet should be flexible
and drapeable so that it conforms to the surface of the article to
be protected during packaging. The film layer and nonwoven layer
are combined to form the composite laminated sheet in such a way
that the outer surface of the film layer is substantially smooth
and does not leave a visible imprint on or other markings on the
surface of the article to be protected. This is especially
important where the article to be packaged has a soft, high-gloss
finished surface such as freshly painted surface that may not have
fully hardened or cured prior to packaging. The film layer of the
composite laminated sheet also preferably has a smoothness of less
than about 9 micrometers, preferably less than 7 micrometers when
measured using a Parker Print Surf Test.
[0021] It is also important that once the composite laminated sheet
has been contacted with the article during packaging that the
composite laminated sheet does not move laterally or shift its
position relative to the surface of the article to be packaged.
Therefore, in addition to being smooth, a film layer is chosen that
is somewhat tacky, i.e. which has good anti-slip properties. This
further prevents surface damage of the article being packaged,
especially when dirt inadvertently becomes trapped between the film
layer of the composite laminated sheet and the surface of the
article that is packaged. The trapped dirt could cause scratching
of the article's surface finish if the composite laminated sheet
shifts laterally relative to the finished surface. Using a film
layer with an anti-slip surface also avoids the need for use of an
adhesive layer on the polymeric film which would, in addition to
increasing the cost of the composite laminated sheet, cause
potential problems with adhesive residue being left on the article
to be packaged after removal of the composite laminated sheet.
Point-bonded flash-spun Tyvek.RTM. sheets used in protective covers
described in Jones et al. U.S. Pat. No. 5,763,336 have a slip angle
of 3.9 to 15.1 degrees when measured according to TAPPI Method
T-503. The composite laminated sheet used in the method of the
current invention preferably has a slip angle of at least about 15
degrees, and more preferably at least about 31 degrees when
measured on the polymer film side. The higher the slip angle, the
greater the anti-slip properties of the sheet. The bond strength
between the polymer film and nonwoven layer of the composite
laminated sheet is preferably at least 0.1 lb/in (0.18 N/cm), and
more preferably greater than about 0.15 lb/in (0.26 N/cm).
[0022] Suitable nonwoven layers include powder-bonded,
saturation-bonded, needlepunched, spunbond, and flash-spun nonwoven
fabrics. The surface of a nonwoven layer that is adjacent the
polymer film layer should be relatively smooth so as to avoid
transfer of any pattern caused by the surface topography of the
nonwoven layer through the film layer and onto the surface of the
packaged article. The nonwoven layer preferably has a basis weight
in the range of 0.4 oz/yd.sup.2 to 2 oz/yd.sup.2 (13.6 g/m.sup.2 to
68 g/m.sup.2), more preferably in the range of 0.5 oz/yd.sup.2 to
1.0 oz/yd.sup.2 (17 g/m.sup.2 to 34 g/m.sup.2). If the basis weight
of the nonwoven layer is too low, it will not impart sufficient
strength to the composite laminate which may cause the composite
laminate to tear during handling. The composite laminated sheet
preferably has a tensile strength of at least 3.3 N/cm and a
trapezoidal tear strength of at least about 2 N in the machine
direction, and more preferably at least about 3.9 N in either or
both of the machine and cross directions. If the basis weight of
the nonwoven layer is too high, the composite laminated sheet will
not be sufficiently flexible or drapeable to conform to the surface
of the article to be protected during packaging.
[0023] In a preferred embodiment, the nonwoven layer is a
powder-bonded nonwoven web. Powder-bonded nonwoven webs useful in
the current invention are prepared using methods known in the art,
such as the process described in Zimmerman et al. U.S. Pat. No.
4,845,583. A carded web is prepared from staple fibers, the fibers
preferably having a length between 1 and 2 inches (2.54 to 5.08 cm)
and denier between 1 denier per filament (1.1 dtex) and 2 denier
per filament (2.2 dtex). The carded web is optionally passed
through a web spreading section prior to applying a powdered
adhesive material. The adhesive powder is applied to the carded web
using a powder-depositing device. The powder drops onto the web and
is distributed through the web by gravity. Excess powder falls
through the web and is collected for recycling. The weight of
powder deposited in the web is preferably between about 8 to about
30 weight percent, more preferably between about 10 to about 20
weight percent based on the total weight of the carded web and
powder adhesive. The bonding powder should have a lower melting
point than the fibers in the carded web. In general, the bonding
powder will be a thermoplastic material that is compatible with the
fibers of the carded web so as to form a good adhesive bond with
the fibers of the carded web. When polyester fibers are used to
form the nonwoven layer, it is particularly preferred to use a
polyester or copolyester bonding powder such as those available
from EMS-American Grilon, Inc. Typical copolyester powder adhesives
have melting points of from 100 to 130.degree. C. and are available
as coarse powders (200-420 microns or 70-40 U.S. standard mesh),
medium powders (80-200 microns or 200-70 U.S. standard mesh) and
fine powders (80 microns or less, or finer than 200 U.S. standard
mesh), the medium powders being preferred when mechanical
applicators are used to apply the adhesive powder to the web.
Bonding of the powder-containing web can be achieved by passing the
powder-containing web through an oven, such as an infrared oven
causing the adhesive powder to fuse and bond the fibers of the web
at fiber crossover points where the fibers and the adhesive come
into contact. Upon leaving the oven, the web is generally subjected
to light pressure by means of a nip roll. Preferably the nip roll
has a smooth surface, resulting in a powder-bonded nonwoven fabric
having a smooth surface for bonding to the film layer in the
composite laminate.
[0024] The polymer film layer of the composite laminated sheet is
vapor permeable and substantially liquid (especially water)
impermeable and is selected from materials that are inert to the
painted or otherwise finished surfaces of packaged article.
Polyethylene, polypropylene, polyesters, and polyurethanes have all
been found to be compatible with current automotive paint systems.
A pre-formed film can be laminated to the nonwoven layer using
thermal and adhesive laminating methods known in the art; or the
polymer film layer can be a monolithic film or a microporous film
precursor, extruded directly onto one of the surfaces of the
nonwoven layer and adhered thereto without the application of an
adhesive. This avoids problems associated with handling of thin
films. Preferably, the film layer is less than 25 microns thick,
more preferably less than 15 microns thick, and most preferably
less than 12 microns thick and is essentially free of pinholes. The
film layer is preferably comprised of a block polyether copolymer
such as a block polyether ester copolymer, a poly(etheramide)
copolymer, a polyurethane copolymer, and a poly(etherimide) ester
copolymer, polyvinyl alcohols, or a combination thereof. Preferred
copolyether ester block copolymers are segmented elastomers having
soft polyether segments and hard polyester segments, such as those
disclosed in Hagman, U.S. Pat. No. 4,739,012. Suitable copolyether
ester block copolymers are sold by DuPont under the name of
Hytrel.RTM.. Hytrel.RTM. is a registered trademark of DuPont.
Suitable copolyether amide polymers are copolyamides available
under the name Pebax.RTM. from Atochem Inc. of Glen Rock, N.J.,
USA. Pebaxe is a registered trademark of Elf Atochem, S.A. of
Paris, France. Suitable polyurethanes are thermoplastic urethanes
available under the name Estane.RTM. from The B.F. Goodrich Company
of Cleveland, Ohio, USA. Suitable copoly(etherimide) esters are
described in Hoeschele et al., U.S. Pat. No. 4,868,062. Films of
the above polymers are non-porous and are impermeable to water but
permeable to vapors. For example, vapors are absorbed by and
transported through the polymeric film layer from the side having
higher vapor pressure, diffusing it across membrane to the side
having the lower vapor pressure, where they are eliminated. In a
preferred embodiment, the composite laminated sheet comprises a
powder-bonded polyester nonwoven layer and a copolyether ester or
polyurethane film layer. Alternately, a laminate of a powder-bonded
polyamide nonwoven and a poly(etheramide) film can be used.
[0025] A composite laminated sheet with excellent tensile and peel
strength, that does not emit loose fibers, can be produced using a
carded web of staple fiber that is powder-bonded with an adhesive
that is compatible with the fibers of the web. The composite
laminated sheet is produced by extrusion coating the powder-bonded
web with a molten thin film that is also compatible with the fibers
of the web and the powder adhesive. "Compatibility" of
thermoplastic materials is an art-recognized term that refers,
generally, to the degree to which the thermoplastic materials are
miscible with each other and/or interact with each other.
"Incompatible" materials, as used herein, means materials that are
substantially immiscible with each other or do not interact with
each other. Incompatible materials do not wet or adhere well to
each other, even when heated. As used herein, "compatible"
materials are materials that are not "incompatible" with each
other, as defined above. For purposes of this application, a fiber
is deemed to be compatible with a synthetic adhesive or with
another polymer if the adhesive or other polymer is miscible with
material that comprises the majority of the fiber and if the
adhesive or other polymer readily wets the fiber or if the adhesive
or polymer can adhere well to the fiber. In a preferred embodiment,
the composite laminated sheet of the present invention is composed
of powder-bonded nonwoven web materials in which at least 95 weight
percent of fibers in said nonwoven web are compatible with said
polymer film.
[0026] When the polymer of the film layer is incompatible with the
polymer of the nonwoven layer, the adhesion between the layers can
be improved by addition of a compatibilizer to the film layer or by
use of an adhesive layer or a co-extruded tie layer between the
film layer and the nonwoven layer. Suitable compatibilizers are
described in Carroll et al. published PCT Application WO 97/45259.
For example, the polyether-based block copolymer films described
above are not chemically compatible with nonwoven polyolefin webs.
When the nonwoven layer comprises a polyolefin such as
polypropylene or polyethylene, the film layer can comprise at least
about 50 percent by weight of a Fraction A consisting essentially
of a polymer from the group of block copolyether esters, block
copolyether amides, polyurethanes, and combinations thereof, at
least 5 weight percent of a Fraction B consisting essentially of a
polymer from the group of homopolymers of an alpha-olefin,
copolymers or terpolymers containing an alpha-olefin and one or
more other monomers, and a block copolymer of a vinylarene and a
conjugated diene, and at least 0.1 weight percent of a Fraction C
consisting essentially of a compatibilizer for Fractions A and B.
Examples of compounds suitable as Fraction B include copolymers of
ethylene and propylene, ethylene vinyl acetate copolymers,
copolymers of ethylene and acrylic derivatives (e.g. copolymers of
ethylene, carbon monoxide and n-butyl acrylate), copolymers of
ethylenically unsaturated carboxylic acid monomers (e.g. acrylic
acid, methacrylic acid, crotonic acid, etc.) or the neutralized
metallic salts thereof. The film Fraction C preferably consists
essentially of homopolymers, copolymers and terpolymers with
backbones that are compatible with Fraction B, the backbones being
grafted with a monomer having a functional group that is compatible
with Fraction A. Film Fraction C is preferably a polymer with a
backbone identical to Fraction B, which backbone is grafted with
monomer selected from the group of alpha- and beta-ethylenically
unsaturated carbonic acids and anhydrides, and derivatives thereof.
Preferred backbones for Fraction C include low density
polyethylene, linear low density polyethylene, high density
polyethylene, very low density polyethylene and polypropylene. The
reactive group of Fraction C may be a grafting monomer that is
grafted to this backbone and is or contains at least one alpha- or
beta-ethylenically unsaturated carbonic acid or anhydride, or a
derivative thereof. Examples of such carboxylic acids and
anhydrides, which may be mono-, di-, or polycarboxylic acids, are
acrylic acids, methacrylic acid, maleic acid, fumaric acid,
itaconic hydride, maleic anhydride, and substituted maleic
anhydride (e.g. dimethyl maleic anhydride). Examples of derivatives
of the unsaturated acids are salts, amides, imides and esters (e.g.
mono- and disodium maleate, acrylamide, maleimide and diethyl
fumarate). Maleic anhydride is a preferred grafting monomer for the
reactive group of Fraction C.
[0027] Other polymer film layers which are useful in preparing the
composite laminated sheet for use in the current invention include
polyethylene or polypropylene microporous films such as Exxaire.TM.
microporous film available from Tredegar and Aptra.RTM. microporous
film available from Amoco. Microporous films can be formed by
mixing a matrix polymer with a substantial quantity of an organic
or inorganic particulate filler and extruding a film from the
blend. The film is heated and stretched which causes voids to form
in the area surrounding the filler particles.
[0028] The microporous films can be combined with nonwoven layers
in the manner disclosed in U.S. Pat. No. 5,865,926, to provide a
composite laminated sheet for use in the current invention. A
microporous film/spunbond composite laminated sheet called
Vaporweb.TM., which is made by a one-step process which involves
production of a spunbonded web, extrusion/lamination of
CaCO.sub.3-filled polymer film onto the spunbonded web and biaxial
stretching of the film/spunbond composite, can be used for the
current invention. A detailed description of the Vaporweb.TM. is
published by Reifenhauser GmbH &Co, Germany at 9.sup.th Annual
Nonwovens TANDEC conference held Nov. 10-12, 1999.
[0029] One preferred means for applying the film layer to the
nonwoven layer is the extrusion process illustrated in FIG. 1. Melt
processable polymer is fed in pellet form, along with any
additives, into an inlet 26 of an extruder hopper 24, preferably
under a nitrogen purge. The polymer is melted and mixed in a screw
extruder 20 at a screw speed in the range of 100 to 200 rpm,
depending on the dimensions of the extruder and the properties of
the polymer. The melted mixture is discharged from the extruder
under pressure through a heated line 28 to a flat film die 38. The
30 polymer is discharged from the flat film die 38 at a temperature
above the melting temperature of the polymer, and preferably at a
temperature in the range of 180.degree. C. to 240.degree. C. The
polymer melt 40 discharging from the flat film die 38 coats the
fibrous nonwoven web 22 provided from supply roll 30.
[0030] Preferably, the fibrous web 22 passes under the die at a
speed that is coordinated with the speed of the extruder so as to
obtain a very thin film that preferably has a thickness of less
than 25 microns. The coated web enters a nip formed between nip
roll 35 and roll 36, which rolls are maintained at a temperature
selected to obtain a composite laminated sheet with a desired bond
strength and moisture vapor permeability. The temperature of rolls
35 and 36 is preferably within the range of 10.degree. C. to
120.degree. C. Higher roll temperatures yield a composite laminated
sheet having a higher bond strength, while lower roll temperatures
yield composite laminated sheets with a higher moisture vapor
permeability. Preferably, nip roll 35 is a smooth rubber roll with
a low-stick surface coating while roll 36 is a metal roll. Nip roll
35 can also have a matte or finely textured finish to prevent
sticking of the film layer. Passing the coated web through the nip
formed between cooled rolls 35 and 36 quenches the polymer melt
while at the same time pressing the polymer melt 40 into contact
with the fibers and adhesive of the fibrous web 22. The nip
pressure applied should be sufficient to get the desired bonding
between the film and the nonwoven but not so great as to create
pinholes in the film layer. A water dip pan 46 with associated roll
48 can be used to increase the quench rate and to prevent sticking.
The coated composite 10 is transferred from the roll 36 to another
smaller roll 39 before being wound up on a collection roll 44.
[0031] The protective composite laminated sheets according to the
present invention can further comprise additional layers laminated
or bonded therein. For example, a layer of vapor permeable,
open-celled polymer foam, such as polyurethane foam, can be flame
laminated to the nonwoven layer surface of the composite laminated
sheet described above to provide cushioning protection against
mechanical damage to the underlying packed articles. Additionally,
the outer surface of the open-celled polymer foam can be flame
laminated to another nonwoven layer, such as a nonwoven web, to
form a polymer film/nonwoven web composite laminated to a polymer
foam/nonwoven web cushioning layer, without significant diminution
of the vapor permeability of the composite laminated sheet.
Alternatively, the open-celled polymer foam can be interposed
between the polymer film layer and the nonwoven layer of the
composite laminate.
[0032] In another embodiment, a microporous film is bonded to one
side of a nonwoven web and the other side of said nonwoven web has
an open-celled polymer foam, such as polyurethane foam, flame
laminated thereto. Likewise, another layer of a nonwoven web can be
flame laminated to the opposite side of the polymer foam to form a
microporous film/nonwoven web composite laminated to a polymer
foam/nonwoven web cushioning layer, according to the present
invention. When the composite of the current invention has
incorporated therein a cushioning layer as disclosed above, it is
unnecessary to provide additional cushioning protection for the
articles to be packaged.
[0033] In the method of the current invention, the composite
laminated sheet is cut to the desired size and draped over the
surface of the article to be packaged. When additional protection
from impact with other articles is needed, a secondary protective
cover can be applied around the article that has been draped with
or otherwise covered by the composite laminated sheet. Preferably,
the secondary cover is made of a cushioning material. In the case
of painted automobile bumpers, a section of composite laminated
sheet of the present invention is first draped over the bumper,
then a padded protective cover can be placed around the covered
bumper. For example, a secondary protective cover can be fabricated
from a bulky composite sheet as described in Jones et al. U.S. Pat.
No. 5,763,336. Protective covers for automobile bumpers can be
fabricated from the bulky composite sheet by cutting an elongated
oval section of the bulky sheet and stitching around its perimeter
with an elastic band to form a cover resembling a shower cap. The
elastic band holds the cover in place on the bumper.
EXAMPLES
[0034] In the description above and 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 for Testing and Materials, TAPPI refers to the
Technical Association of Pulp and Paper Industry, and ISO refers to
the International Organization for Standardization.
[0035] Basis weight was determined by ASTM D-3776 and is reported
in g/m.sup.2.
[0036] Tensile strength and Work to Break were determined by ASTM
D-5035-95, with the following modifications. In the test a 2.54 cm
by 20.32 cm (1 inch by 8 inch) sample was clamped at opposite ends
of the sample. The clamps were attached 12.7 cm (5 in) from each
other on the sample. The sample was pulled steadily at a speed of
5.08 cm/min (2 in/min) until the sample broke. The force at break
was recorded in pounds/inch and converted to Newtons/cm as the
breaking Tensile Strength. The Work to Break is a function of
breaking tensile strength and elasticity and was recorded in Newton
meters (Nm).
[0037] Puncture Resistance was determined by ASTM D-3420 and is
reported in Newtons (N).
[0038] Trapezoidal Tear Strength was determined by ASTM D-5733 and
is reported in Newtons (N).
[0039] Film thickness and composite thickness was determined by
ASTM Method D1777-64 and is reported in micrometers.
[0040] Elongation to Break of a sheet is a measure of the amount a
sheet stretches prior to failure (breaking)in a strip tensile test.
A 1.0 inch (2.54 cm) wide sample is mounted in the clamps, set 5.0
inches (12.7 cm) apart, of a constant rate of extension tensile
testing machine such as an Instron table model tester. A
continuously increasing load is applied to the sample at a
crosshead speed of 2.0 in/min (5.08 cm/min) until failure. The
measurement is given in percentage of stretch prior to failure. The
test generally follows ASTM D 5035-95.
[0041] Hydrostatic head was measured according to ISO 811, which
measures the resistance to water penetration on a 7 in.times.7 in
(18 cm.times.18 cm ) test sample. Water pressure is applied at a
rate of 60 cm/min to the film side of the test specimen until the
sample is penetrated by water at three places. The hydrostatic
pressure is measured in inches and converted to SI units and is
reported in cm of water. The equipment used to measure hydrostatic
head is made by Aspull Engineering Ltd, England.
[0042] Moisture Vapor Transmission Rate (MVTR) is reported in
g/m.sup.2/24 hrs and was measured with a Lyssy Instrument using
test method TAPPI T-523.
[0043] Slip angle is measured according to TAPPI Method T-503 and
is reported in degrees. The higher the slip angle, the greater the
resistance of the film to lateral sliding on a steel surface.
[0044] Smoothness of a film surface was measured to TAPPI Method
T-555 in micrometers using a Parker Print Surf (PPS) test.
Example 1
[0045] The powder-bonded nonwoven used in this example was a 100%
polyester powder-bonded nonwoven having a basis weight of 0.5
oz/yd.sup.2 (17 g/m.sup.2) (obtained from HDK Company, Greenville,
S.C.). The powder-bonded nonwoven layer was formed from DuPont
Dacron.RTM. Type 54W polyester staple fibers 1.5 inches (3.81 cm)
in length and having a denier per filament of 1.5. A copolyester
powder adhesive is used at a loading of 18 percent by weight based
on the total weight of the powder adhesive and staple fibers in the
nonwoven web.
[0046] The powder-bonded composite nonwoven layer was extrusion
coated with a polymer film layer of Hytrel.RTM. G4778 copolyether
ester (melting point 208.degree. C., vicat softening temperature of
175.degree. C., a shore hardness of 47 D, and a water absorption of
2.3%, sold by DuPont) using the process shown in FIG. 1. The
Hytrel.RTM. polymer was fed in pellet form into a 3 inch (7.6 cm)
diameter screw extruder and melted at a temperature of between
430.degree. F. and 440.degree. F. (221.degree. C.-227.degree. C.)
and fed to a 30 mil (762.mu.) by 102 cm die opening in a heated die
block maintained at 232.degree. C. The powder-bonded nonwoven
substrate was spaced about 12 inches (30.5 cm) below the opening of
the die. The film thickness of 0.55 mil (14 microns) was laminated
at 116 ft/min (35.4 m/min). The film was joined to the fibrous
powder-bonded nonwoven substrate by passing the coated web through
a pair of nip rolls with a nip roll pressure of 100 psi. The nip
roll that faced the polymer melt was a silicone rubber roll having
a matte finish. The quench bath temperature was maintained at
80.degree. F. (27.degree. C.).
[0047] The composite laminated sheet had the physical properties
given in Table 1.
[0048] Comparative Example 1 is a single layer of Aptra.RTM.
microporous film (available from Amoco) and Comparative Example 2
is a single layer of Tyvek.RTM. 1461 point bonded (linen.times.rib)
flash-spun polyethylene sheet (available from DuPont). As can be
seen from the data in Table 1, the Aptra.RTM. microporous film has
very low tear strength which makes it very difficult to handle but
it has very good slip resistance and smoothness. The Tyvek.RTM.
1461 flash-spun sheet has acceptable smoothness but does not have
good slip resistance. The composite laminated sheet of Example 1
has a good combination of tear resistance, surface smoothness, and
anti-slip properties.
1 TABLE 1 Example 1 Comp. Ex. 1 Comp. Ex. 2 Basis Weight
(g/m.sup.2) 32.3 25.4 59.9 Thickness (micrometers) 57.2 29.9 185.6
MVTR (g/m.sup.2/24 hrs) 1136 1244 844 Hydrostatic head (cm) >400
>90* >90 Tensile Strength (N/cm) MD.sup.1 10.4 5.5 23.5
CD.sup.2 3.3 4.4 30.2 Elongation (%) MD 25.1 98.4 11.6 CD 68.3 44.1
17.2 Work to Break (Nm) MD 0.7 1.3 0.6 CD 0.4 0.5 1.1 Puncture
Resistance (N) 32.2 24.5 177.5 Trapezoidal Tear (N) MD 3.9 0.5 59.3
CD 15.9 3.7 31.7 Slip Angle (degrees) 25.8-31.8 17.2-23.4 3.9-15.1
(linen side) Smoothness (micrometers) 5.0-6.7 0.9-1.0 4.0-5.8
(linen side) .sup.1Machine Direction .sup.2Cross Direction *The
microporous film of Comparative Example 1 physically burst during
the test.
[0049] The composite laminated sheet of Example 1 was used as the
primary material to contact the painted surface of automobile
bumpers that had been painted with a "2K" paint system in
preparation for shipping. A piece of the composite laminated sheet
measuring approximately 132 inches long by 31 inches (335.2 cm by
78.7 cm) was draped over each bumper with the Hytrel.RTM. film
layer facing the painted surface of the bumper fascia.
[0050] A bulky protective cover was made according to Example 4 in
Jones et al. U.S. Pat. No. 5,763,336 and placed over the composite
laminated sheet around each automobile bumper and the bumper was
nested and stacked with other similarly covered bumpers and shipped
from an equipment parts manufacturer to a vehicle manufacturing
plant. Upon inspection of the bumpers after being transported,
there was no evidence of damage or marking of the painted surfaces
that is sometimes found when the bulky protective cover is used
alone.
* * * * *