Bonded glass fabric edge

Feathered edges of fiberglass fabrics woven on a shuttleless or airjet loom are secured and prevented from ravelling by a glass yarn coated with a hot melt composition. The coated yarn is woven along the longitudinal edges of the fabric, typically in a leno weave, then heated to thermobond the adjacent glass fibers with the hot melt composition at their crossover points. A procedure for applying a hot melt to a yarn through a heated die is used.

This invention pertains to woven glass fiber fabrics and, in particular, to 
fiberglass cloths woven on a shuttleless loom having the edge yarns 
secured in place by a hot melt composition. Bonded glass fabric edges 
prevent the warp ends of the glass fabric from becoming unravelled. 
BACKGROUND OF THE INVENTION 
The shuttleless or airjet weaving process has been widely adopted for 
weaving glass fabrics of improved quality and edge to edge uniformity. 
However, the resulting product has a feathered edge that is apt to become 
unravelled during further processing and treatment of the woven glass 
cloth. The need to secure the feathered edges of glass fabrics woven on a 
shuttleless loom is apparent. Several procedures have been used in the 
past to stabilize yarns at their crossover points. This may take the form 
of stabilization throughout the full width of the fabric for specific 
applications, such as tire cords, as illustrated in U.S. Pat. No. 
3,695,326, or it may take the form of stabilizing only an edge of the 
fabric, as in U.S. Pat. No. 3,515,623. This latter patent describes 
securing the edge of a woven glass fiber fabric by weaving the fabric with 
a thermoplastic material such as nylon in strand form using the nylon yarn 
as selected warp ends. After weaving, the fabric is heated in the area of 
the woven nylon yarns. This heating locally melts the woven thermoplastic 
strand and serves to stabilize the fabric structure of the resulting 
product and to bond the warp and weft crossovers to provide security 
against ravelling. In the weave arrangement depicted in this patent, the 
thermoplastic strand material is woveninto the material in leno fashion. 
The use of a leno woven thermoplastic strand to locally stabilize a fabric 
structure has a number of disadvantages--significant temperatures are 
required to locally melt the thermoplastic strand material and to cause 
the overlapping glass fiber strands to bond. Typically, this heating 
required for thermobonding is in the range of 350.degree.-500.degree. F., 
however such high temperatures often cause brown discoloration at least at 
the edges of the glass fabric due to charring of the warp size and yarn 
binder, two processing adjuvants commonly used in the weaving of 
fiberglass cloth. Moreover, thermoplastic strand materials of this type 
tend to melt unevenly causing unacceptable lumps in the resulting glass 
fabric and thermoplastic build-up on the elements used to melt the 
thermoplastic yarn. Most annoying are the noxious fumes given off by 
certain of the thermoplastic yarns, particularly nylon and vinyl, during 
the heating or thermobonding operation. 
Other approaches to secure the edges of woven materials include the use of 
adhesive tapes attached to the ends of glass cloth, resin varnishes, or 
powdered hot melt resins as described in U.S. 4,428,995. 
None of these prior procedures is well suited to prevent edge ravelling of 
a glass fabric woven on a commercial scale on a shuttleless loom to 
produce a secured, feathered edge fiberglass fabric.

DETAILED DESCRIPTION OF THE INVENTION 
The outer edge warp yarns of a glass fabric produced by a shuttleless 
weaving process are secured and bonded together to prevent ravelling by 
the use of a pair of outside warp ends, typically woven as a leno weave, 
coated with a hot melt composition such that upon thermobonding the hot 
melt adhesive-coated yarns attach and bond to the adjacent glass fibers. 
More specifically, a glass fabric is prepared on a shuttleless or airjet 
loom that includes weaving two or more glass fiber yarns, one or more of 
which have hot melt adhesive coated, woven as a locking type leno weave 
adjacent the two longitudinal edges of the cloth. The leno yarns cross 
over each other and interlace one or more fill yarns. Once woven, the 
cloth is subjected to heat such as direct contact, hot air or radiant heat 
and the hot melt adhesive composition is thermobonded securing the fibers 
of the edge of the glass fabric and preventing edge ravelling. 
Also disclosed is an apparatus for coating a hot melt adhesive composition 
onto a yarn by passing the dipped yarn through a heated die. Although not 
limited to the type of yarn, glass fiber yarn, particularly for use in the 
present invention, is preferred. Thermoplastic coated fiberglass yarn is 
provided with a coating with variable coating content, depending upon the 
size of the orifice through which the yarn is pulled. As illustrated in 
FIG. 2 of the drawings, a yarn is removed from a package, dipped through a 
heated bath containing the hot melt adhesive in which the yarn is 
impregnated with the adhesive. Thereafter, the yarn is passed upwardly 
through a coating die which, when provided with the appropriately size 
orifice, squeezes the hot melt adhesive coating into the yarn bundle and 
removes or doctors off the excess coating. A molten hot melt is maintained 
by appropriate heating means (not shown) and the yarn to be impregnated 
passes through that hot melt. Using the appropriate hot melt adhesive, the 
coated yarn requires only a brief exposure to ambient temperatures in 
order to allow the coating to cool below the melt temperature, thus costly 
oven drying and/or curing procedures and arrangements are not required. In 
the apparatus depicted in FIG. 2, the yarn coated with the hot melt is 
rapidly cooled to below the melt temperature and the coated yarn is ready 
for use without further processing or drying steps. 
The disclosed hot melt, heated die method for coating yarn is not 
necessarily limited to glass fiber yarn so long as the yarn employed is 
stable and accommodates the temperature consistent with the hot melt 
temperature for the hot melt adhesive. Similarly, the hot melt adhesive is 
selected to form a melt at a temperature that does not degrade or 
substantially degrade the desirable characteristics of the yarn. A wide 
variety of hot melt materials suitable for application via a heated die 
are disclosed below. The amount of coating applied to the yarn or "add-on" 
is conveniently adjusted by choosing the appropriate die orifice in 
relation to the size of the yarn, thus operating with a fixed yarn size 
and orifice size, the amount of hot melt adhesive pick-up is not unduly 
affected by speed, temperature, or viscosity variations of the hot melt 
adhesive during operation. The procedure is simple, controllable, and 
eliminates the use of solvents, water, drying, curing or the application 
of heat to successfully coat yarns with hot melt adhesive compositions. 
Hot melt compositions, especially those based upon copolymers of ethylene 
with acrylic or methacrylic acid are described in U.S. Pat. No. 4,136,069 
and U.S. Pat. No. 4,401,782 and these disclosures are hereby incorporated 
by reference. Other hot melt adhesive compositions are referred to in U.S. 
Pat. No. 4,576,665 and this disclosure is incorporated by reference as 
well. These compositions are typically non-aqueous and are applied as a 
melt at elevated temperatures yet, when they cool under ambient 
conditions, they form a solid, non-tacky layer. The hot melt compositions 
used in the present invention constitute a major proportion of the total 
weight of the glass fibers used to bond the edge portions of the glass 
fabric. When calculated on the basis of coating content, a coating 
composition termed a "size" amounts to only about 3 to 4%, whereas the hot 
melt adhesive coated glass yarns of the present invention have a coating 
content of from about 40 to about 70%. These more significant quantities 
serve to secure adjacent glass fibers together rather than merely "size" 
individual glass fibers temporarily for further processing operations. 
Hot melt adhesives may be applied to the yarn in a number of different 
ways, however for purposes of the present invention, we prefer to apply 
the hot melt adhesive by passing the yarn through a die which provides the 
necessary thickness and wet pick-up to achieve the results desired. It is 
important that the hot melt adhesives used in the present invention 
exhibit a relatively low viscosity at application temperatures. Preferably 
less than 2,000 cps to reduce tension on the yarn during coating. Good 
performance is obtained with a hot melt adhesive having a viscosity of 
about 750 cps at 350.degree. F. This viscosity characteristic coupled with 
fast setting times, low remelt temperatures of about 220.degree. F., good 
pot life of up to 72 hours, and lock of toxicity, contribute to a useful 
hot melt adhesive. Indeed, many hot melt adhesives suitable for use are 
approved for food use whereas other thermoplastic materials, for instance 
nylon strands, smoke considerably and discolor under operational 
temperatures and are not fully acceptable for these reasons. 
Fiberglass fabrics prepared on a shuttleless or airjet loom have an edge or 
selvage different from a selvage prepared on a conventional loom which is 
woven with a continuous filling strand around the edge of the cloth. 
Feathered edged glass fabrics have filling tails extending beyond the 
cloth edge and these tails are held in place at the edge of the fabric by 
wrapper, usually leno, threads causing the tails to be feathered out. This 
results in a flat, uniform, and tight selvage along the edges of the 
fiberglass fabric, as well as other advantages inherent in glass fabrics 
having feathered edges. The body or woven portion of the fabric may be of 
any particular weave, and there are any number of weave patterns possible. 
Almost any weave construction can be woven from glass yarns that can be 
made from other types of yarn, natural or synthetic, however for 
industrial uses the weave pattern will be one of the following: plain 
weave, in which warp and filling threads cross alternately; twill weave, 
in which each end floats over at least two consecutive picks enabling a 
greater number of yarns per unit area than a plain weave; leno weave, 
having two or more warp threads cross over each other and interlace with 
one or more filling threads; a mock leno weave; a four harness satin, in 
which a filling thread floats over three warp threads then under one; and 
an eight harness satin, a 7 by 1 interlacing in which a filling thread 
floats over seven warp threads and then under one. In addition, the 
thickness of the glass fabric may vary widely as well as the weight 
(measured on the basis of square yards) which may range from less than one 
ounce to up to two pounds per square yard. The fabric construction, yarn 
size, twist and finish may also be varied in order to fit individual 
applications for the woven glass fiber product. 
Edge bonded glass fabrics produced by the procedure of the present 
invention exhibit excellent bonds along the fabric edge, the pair of leno 
coated glass yarns serving to secure the adjacent glass fill yarns without 
substantial wicking of the adhesive into the body of the fabric. Although 
leno weaves are preferred, the fabric edge shown in FIG. 1 does not 
highlight this fact. 
The invention will be further described with reference to the attached 
drawings and the following examples in which all parts and percentages are 
expressed by weight and all temperatures reported in .degree.F. 
EXAMPLE 
A fiberglass yarn, known in the industry as D 450's 1/0, was coated using 
the apparatus described in FIG. 2. A round tungsten carbide die, known 
generally as a wire die, available from Sancliff Company was used. The 
orifice in the die was a round hole 0.008" in diameter. The hot melt 
coating material was Eastabond A-620, hot melt adhesive made by Eastman 
Chemical Co. The hot melt bath and heated die were maintained at 
approximately 325.degree. F. Yarn was removed form the yarn supply package 
passed into the heated bath and drawn through the heated die at a speed of 
150 yards per minute. The hot melt coating solidified at ambient 
temperature in the span between the heated die and the turn around pulley 
about 9 feet. A smooth, uniformly coated yarn was obtained which had a 
coating pick-up of approximately 100% (50% coating content of coated 
yarn). 
This yarn was then used as the leno locking weave in a glass fabric woven 
on a shuttleless loom. Once woven into the glass fabric along its edges, 
the edge was bonded on the loom using a contact heating element maintained 
at about 300.degree. F. 
The resulting fabric exhibited a fused edge with an excellent bond and 
resisted ravelling upon further handling.