Note: Descriptions are shown in the official language in which they were submitted.
PERFO~ATED FILM WITH UNPERFORATED EDGE
FIELD OF TH~ INVENTION
The present invention relates to thermoplastic
film, and more particularly perforated film having an
unperforated edge suitable for use in applications such as
textile yarn dyeing.
BACKGROUND OF THE INVENTION
In the dyeing of textile yarns, such as cotton,
acrylic, wool and blends of various natural and synthetic
yarns, a slotted cylindrical plastic or stainless steel tube,
known as a dye tube, is typically used to hold a quantity of
yarn wound around the tube. This arrangement is known as a
yarn package or dye package. These yarn packages are pro-
cessed in a dyeing vat known as a dye kier. A dye of a suit-
ahle color typically heated up to about 150 ~C and at a pres-
sure of up to about 80 p.s.i., is forced through the yarn in
the dyeing process.
This process, because of the high temperature and
pressures involved, and the overall environment of the pro-
cess, can result in some damage to the yarn material, particu-
larly at the outer face of the yarn package.
An effective solution to this problem has been the
use of perforated films, of a type such as the PY film sold
by the Cryovac Division of W. R. Grace & Co.-Conn., to
overwrap the yarn package. If the film is also a shrink
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film, then a tight fitting but porous overwrap is provided
which helps to protect the yarn during the dyeing process,
while allowing the dye to flow through the yarn to the outer
circumference of the package, and vice versa.
One limitation of conventional perforated film is
that by nature of the perforation process, the edges of the
film tend to be jagged with truncated perforations. When
used in the yarn dyeing process just described, these jagged
edges can result in picking of the yarn when the edge of the
perforated film comes into contact with the yarn. Sometimes,
as the film shrinks around the yarn package, the edges of the
film will curl, which can accentuate the undesirable roughing
of the yarn during the yarn dyeing process.
The inventor has discovered that this problem can
be solved to a great extent by using a perforated film which
is perforated along the middle portion of the film, but
unperforated at one or both edges of the film. The jagged
edges just described for conventional perforated film are
largely or completely avoided and the roughness associated
with a shrunken film edge, and the interior surface of the
perforations at or near the edge of the film are also avoided
by means of the invention. This in turn results in reduced
picking or undesirable abuse of the yarn with economic bene-
fits. A yarn package that has a damaged surface may some-
times have to be rewound with the abused material discarded.
The invention helps to reduce the need for discarding or
rewinding dyed yarn material.
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It~is therefore an object of the invention to pro-
vide a film which allows for the substantial flow of a dye or
other liquid through the film, while reducing abuse created
`; by perforations at or near the edges of the film.
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SUMM~RY OF THE INVENTION
In one aspect, the present invention comprises a
film with a perforated middle portion, and an unperforated
edge portion.
In another aspect, the present invention is a pack-
age comprising a product, and a film wrapped around the prod-
uct, the film characterized by a perforated middle portion
and an unperforated edge portion.
DEFINITIONS
The term "perforation" means holes of various
shapes, density, size and distribution in a thermoplastic
film which can be introduced in the film during manufacture
of the film or subsequent to production of the film, by vari-
ous flame, needle, and other suitable processes.
The term "edge" is used herein in its conventional
sense to mean the edges of a roll stock film, and the margin-
al portions of a film i.e. its border or terminus as depicted
for e~ample in Figures 1 through 3 of the drawings. In the
case of a pouch or bag made from the inventive film, the
unperforated edge can include one or more of the longitudinal
or transverse edges of the final package, as long as some
benefit is obtained from the lack of perforation at or near
the appropriate edge of the packaging material.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, a prior art conventional
perforated film 10 shows a series of generally uniformly
distributed perforations 12 in a thermoplastic film. A commer-
cially available film is PY film sold by W. R. Grace &
Co.-Conn. through its Cryovac Division; other perforated
films are also available. The conventional film is character-
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ized by truncated perforations 14 occurring in either random
or controlled sequence along the edges 16 and 18 of the
film. These truncated perforations result in a jagged,
"sawtooth" edge. The film depicted in Figure 1 is a segment
of a film or a roll stock film of undefined beginning and end
point. In the preferred embodiment, roll stock film is cut
into a segment sufficiently long to wrap around a yarn pack-
age as depicted in Figure 3.
Figure 2 illustrates schematically the film 20 of
the present invention. This fi~m is distinguished from the
prior art film of Figure 1 in two ways. First, the jagged
"sawtooth" edges resulting from truncated perforations 14 in
Figure 1 are largely or completely absent from the inventive
film of Figure 2. Instead, a substantially smooth edge 24a
and/or 24b are provided. The second distinction from the
prior art film is that an unperforated area 22a and/or 22b is
provided in the inventive film. When being used in a yarn
dyeing application, this film therefore provides an
unperforated portion for the top and/or bottom of the yarn
package. If the film is a shrinkable film, some wrinkling of
the film will occur especially at the edges 24a and 24b.
However, because of the lack of any significant perforation
of the film 20 in the areas of 22a and 22b of the inventive
film, and because of the lack of jagged truncated perfora-
tions 14, the inventive film is more compatible with, and
less abusive to the yarn of the yarn package, especially
during the physical stresses associated with the yarn dyeing
process.
Although the invention preferably involves an
unperforated portion at both longitudinal edges of the film,
some benefit is still obtained by having a perforated film
with an unperforated portion at or near one of the edges of
the film. This alternative embodiment is also within the
scope of the invention.
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In addition, the width of the unperforated portions
22a and/or 22b can vary from each other, and can vary in
width depending on the desired end use of the film, economic
and manufacturing considerations, and the like. The pre-
ferred width of the unperforated portions 22a and 22b is the
width of the film necessary to prevent substantial picking or
abuse of the underlying yarn material. One type of yarn
material may be more susceptible to abuse from perforated
film than another type of yarn. For example, cotton may
react differently from polyester or other materials.
As a generality, a preferred width for each of the
unperforated portions 22a or 22b is 1% to 30%, more prefera-
ble 5% to 25%, even more preferable 10% to 20%, and most
preferable about 15% of the total width of film 20. The
width of unperforated portions 22a and 22b can be the same or
can differ, depending for example on the geometry of the yarn
package.
To the extent that the unperforated portions 22a
and/or 22b comprise a significant portion of the width of
film 20, the total perforated area of the film and the abili-
ty of the film to transmit heated dye or other liquids will
be reduced. To the degree that unperforated portions 22a
and/or 22b are of lesser width with respect to the total
width of film 20, with the same given density and size of
perforations, the film will have a greater perforated area
for transmission of heated dye or other liquids but also have
a greater number or area of perforations which can adversely
affect the yarn material. One skilled in the art will readi-
ly ascertain the optimal density, distribution, shape and
size of perforations, and especiall~ the appropriate widths
of unperforated portions 22a and/or 22b for the particular
end use for the inventive film.
The film 20 of the present invention can be made by
conventional processes well known in the art, including
extrusion and coextrusion, and extrusion coating and conven-
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tional lamination processes for producing monolayer or
multilayer films. In the case of monolayer and multilayer
films, various thermoplastic polymers and copolymers can be
used, especially materials such as polypropylene or propylene
ethylene copolymer, and olefinic polymers and copolymers.
The introduction of perforations in the material
can be done in many conventional ways, including flame, nee-
dle, and heating/vacuum/blowing operations as long as perfora-
tions of suitable density, size, shape and distribution can
be imparted to the film.
Perforated films according to the present invention
can also be monoaxially or biaxially oriented, by blown bub-
ble process or tenter frame process well known in the art.
Referring to Figure 3, an especially suitable end
use for the film of the present invention is in wrapping a
yarn package for dyeing yarn by processes well known in the
art. Yarn package 30 includes inventive film 20 overwrapped
about yarn 34 in turn wrapped about a central slotted tube 32
of cylindrical cross section. The film may be a shrinkable
film which forms a tight overwrap about the yarn 34. A heat
seal, for example a trim seal 36 may be used to attach a
segment of film 20 around yarn 34. Sometimes a second heat
seal (not shown) like the seal 36 will be located about half-
way around the yarn package from the first heat seal. As can
be seen in Figure 3, perforations 12 occux along the middle
portion of the film, but do not occur in unperforated por-
tions 22a, or 22b (not shown). The upper edge 24a of the
film is substantially or totally free of any jagged edges
caused by truncated perforations. By conventional processes
not shown, a heated dye is forced under pressure through the
cylindrical core 3~ and out through the yarn and the perfora-
tions 12 of film 20. The process is typically then reversed,
resulting in a dyed yaxn enclosed within the overwrap created
by sealed and preferably shrunken film 20.
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The invention has been described by reference to
preferred embodiments of the invention, but modifications to
the invention will readily occur to those skilled in the art
after a review of the specification. For example, the inven-
tive film with perforated middle portion and at least on~
unperforated edge portion can be used to overwrap a variety
of products, not necessarily cylindrical in shape, as long as
benefits are obtained by the substantial absence of jagged
edges and/or perforations from at least one edge portion of
the film.
The scope of the invention is therefore limited
only by the claims which follow.
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