Strand packages

A package having a stretch membrane convolutely position about an unwindable wound body of strand where a tacky surface of the membrane contacts the outer layer of strands. The tacky surface also interlocks multiple layers of the membrane together.

TECHNICAL FIELD 
This invention relates to a package of unwindable strands. 
BACKGROUND ART 
Packages for filaments, strands, or rovings of continuous glass fibers are 
numerous. The packages facilitate unwinding of the strand from the package 
and minimize related processing problems. The packages typically are a 
membrane surrounding wound strands. One package incorporates an adhesive 
between the membrane and outer layer of strand to retain the strand 
against the inner wall of the membrane. Often, however, the adhesive peels 
off the film. The adhesive then contaminates the strand rendering it 
useless for reinforcing plastics. Other packages used shrink film as the 
membrane. Heat shrinkable film allows the membrane to adhere to the outer 
periphery of the package to an extent sufficient to retain the strand in 
contact with the membrane until the strand is substantially completely 
withdrawn from the package. 
All of these packages found wide acceptance in industry. However, at 
temperatures above 90.degree. F. the exterior membrane in which the 
package is wrapped tends to relax with the result that the strand being 
withdrawn tends to birdnest and become entangled in a guide eye. 
DISCLOSURE OF THE INVENTION 
I have improved the film package concept even further by employing a 
stretch film which is tacky on the outside. By reverse winding the 
package, the tacky side holds the outside layer of strands. By using 2 or 
more layers of film, the tacky side also holds the package together to 
give the necessary support for complete unwinding of the strands. This 
differential cling eliminates the need to heat the stretch film. My 
packaging is a stretch film and it does not shrink. 
The tacky side of the film holds the roving for 100% runout and holds the 
strand and for excellent package to package transfer. An overwrap machine 
applies three to five wraps of one sided tacky stretch film to each 
package. The tacky side of the film directly contacts the strands. 
Preferably, the stretch film is a linear low density polyethylene with a 
true one sided (outside) differential cling. The tack in my film is a part 
of the film and does not peel off as an adhesive would.

DETAILED DESCRIPTION OF THE INVENTION 
While the preferred embodiment of this invention pertains to continuous 
glass fiber rovings, this invention pertains to any wound body of strand 
from which the strand is withdrawn from the interior of the body. Such 
bodies can comprise natural or synthetic fibers, organic fibers or mineral 
fibers of any length, diameter or quality. Such packages are generally 
formed by winding a continuous strand on a rotatable collet to form a 
hollow core package from which the strand is pulled out through the 
opening formed by the position occupied by the rotating collet. 
The package can be of any size and shape. Because such packages wound on a 
collet, they will generally be cylindrical in shape. The outer periphery 
of the wound body usually develops a plurality of undulations, or ridges, 
of irregular height which act to adhere to the outer wrap and, hence, to 
preserve the cylindrical shape of the package as it is being unwound. 
The use of a stretch film herein is in contrast to the frequent use of 
shrink films to wrap food-stuffs. Shrink film packaging involves the use 
of thermoplastic films that have been stretched or oriented during 
manufacturing and have the property of shrinking during the application of 
heat. Shrink film is normally applied loosely because it does not stretch 
well at room temperatures. 
Stretch film involves the use of thermoplastic film that has been specially 
formulated to easily stretch at room temperatures. Stretch film is 
normally produced in thickness ranging from 0.7 mils to 1.5 mils. 
The membrane can be wrapped around the package in any number of 
convolutions, or portion thereof, and can be of any suitable thickness, 
for example, within from about 0.7 mil to about 1.35 mil, preferably from 
about 0.8 to about 1 mil. Applying the film under tension holds the film 
in position during formation of the package. 
The wound body of strand can be encased fully or partially within the 
membrane. Preferably, the membrane will be positioned in contact with the 
entire longitudinal surface of the package although the membrane can 
extend over any portions of the ends of the package. The membrane can be 
wound on the package of strand by any suitable means and at any time after 
the formation of the package. 
The one sided tacky film may be blown or cast, with blown film being 
preferred. 
Both blown and cast film processes melt resin pellets (extrude) through 
basically the same method. They use a screw which conveys, compresses and 
pumps the resin through the extruder chamber to the die opening. Each 
process uses a different shaped die. The cast uses a flat or slot shaped 
die which forms a single flat sheet of film. The blown uses a circular die 
which forms a tube of film. These differences in die geometry are due to 
the process itself and they affect the films orientation. In the blown 
process film is oriented in an upward direction (machine) and an outward 
direction (cross/transverse). Whereas cast film is only oriented in the 
machine direction. 
The next major process difference is the way in which the blown molten 
polymer (plastic) is cooled. Blown film is cooled by an air ring which 
surrounds a tube with cooler air. Whereas the cast film is cooled by 
chilled rolls--temperature is controlled internally with chilled water. 
Another processing differences is the temperature the molten polymer is 
at--cast 450.degree.-600.degree. F. vs. blown 350.degree.-45.degree. F. 
This is due to the different resin types used in each process. 
The resins used in blown film have a higher molecular weight (the size of 
the molecule in relation to process. The lower the molecular weight the 
higher the melt index. (the flow characteristics of polymer at a certain 
temperature and pressure) therefore, the blown film resins have a lower 
melt index which allows it to stretch in both directions with greater 
strength than cast. These things combine to allow blown film to achieve 
greater levels of load retention and overall strength at higher levels of 
stretch than cast film. The blown film process uses a resin with a higher 
viscosity (lower melt index) than the cast film process. 
The film has the ability to adhere to itself. This is necessary to 
interlock layers of film to one another and to secure the film to the 
package. The film has one-sided cling--only one side of the film contains 
a tackifier. 
INDUSTRIAL APPLICABILITY 
Preferably, the stretch film is a linear low density polyethylene blend 
with a true one sided (outside) differential cling. This thermoplastic is 
an extra strong, blown film. It has outstanding coil-cling properties that 
allow packaging at temperatures down to 0.degree. F. Differential cling 
means the film has high cling on one side and virtually no cling on the 
other. 
An overwrap machine applies three to five layers of film to each package. 
Because of the type of stretch film I use, no heating is necessary to 
shrink the package. 
The wrapping operation runs at room temperature down to 0.degree. F. The 
resulting package provides 100% runout and holds the strand for excellent 
package to package transfer. 
The preferred film comes in rolls of standard lengths and widths (typically 
6000 feet by 20 feet) and has the following properties: 
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gauge (mils) 0.8 
manufacturing process blown 
tensile strength (p.s.i.) 
6800 
cling (lbs./in.) 2.5 
use temperature range (.degree.F.) 
0-120 
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