Note: Descriptions are shown in the official language in which they were submitted.
377Z r
1--
BACK(;ROl]i!D 0~ T~IE l'.`~. E`;TIO.Y
The coating of metallic substrates with an un-
bonded plv of plastlcizecl thermoplastic resin has been
well established commerciallv heretofore. The incorpora-
tion in the resin coating compositions of various standardanti-o~idants, light stabilizers and other conventional
additives has resulted in coated metallic materials
manifesting a flexibility without cracking, an im~act
hardness and resistance to abrasion which makes them
particularly useful in a variety of applications includ-
ing chain-link fence.
The metallic substrate of these coated materials
is rendered vulnerable however, where a single-ply of un-
bonded plastic is present, because of the relative ease with
which the resin coatlng can be stripped from the substrate, a
particular concern, fo example, where the coated material
is chain-link fence and where this material is used in areas
subject to the activity of vandals, such as heavily industri-
alized locations, public playgrounds and the like.
The bonding of certain thermoplastic resin coatings
to a metallic substrate has been kno~n to reduce this ease
of removal. Bonding has been accomplished, illustratively,
by treating wire, for e~ample, with a primer heated to an
elevated temperature and the composite of wire and primer
passed through a fluidized bed of vinyl resin powder. The
wire substrate used com~ercially in the practice of this
latter process has been found to be ungalvanized steel.
Inherent in this process, additionally, has been the forma-
tion of a microporous coatlng of limited thickness, i.e.,
about 7-10 mils, and this vinyl coating has been found to
~;
~ ~1377z
-2--
evidence reduced resistance to ultra-violet radiation over
a sustained period. The relative thinness of the coating
which can be achieved by this method has been found to
permit corrosive atmospheres even in the absence of removal
of the coating. This w lnerability is, of course, of
particular significance where the substrate is, illustra-
tively, ungalvanized steel. The production of vinyl coated
metallic substrates employing plastisols or organosols of
vinyl chloride resins has also been projected, but the com-
bination of steps including particularly the removal of
diluents from the coating and the absorption of plasticizers
in the fusion phase tend to render the processes uneconomic,
both by reason of the reduced speeds at w'nich, for exanple,
wire must pass through the coating step, e.g., up to about
300 feet per minute, and the high temperature baking ovens
necessary for fusion, utilizing high levels of electric
energy.
Securing a plastic composition to a metal element
is disclosed specifically and by way of further illustra-
tion in U.S. patent 3,795,540. The bonding of an extruded
plastic cover of polyvinyl chloride, rubber, impregnated
paper or preferably polyethylene, for example, is suggested
by this reference using a copolymer of ethylene and an
ethylenically unsaturated carboxylic acid, particularly
ethylene-vinyl acetate copolymer. This reference is not
concerned with a product capable of being produced at high
speeds in a continuous process and incorporating a signifi-
cantly superior bond of coating to substrate. The formation
of an adhesive-coated substrate and a substrate to which the
polyethylene polymer is thereupon applied i.s undertaken
~9 ~7
--3~
under inherently slow moving conditions in which the adhesive
must be extruded into the substrate. Thus, the adhesive
employed provides a bond between a protective polymeric coat-
ing such as poly (vinyl chloride) and a metallic substrate
which is inadequate particularly for high-speed metal forming
operations; for example, the proudction of wire products such
as chain-link fence.
A further method suggested heretofore for pro-
ducing a metal component coated with a bonded plastic compo-
sition is that described in U.S. patent 2,531,169 wherein the
patentee describes the deposition upon wire of a phenol-
aldehyde modified polyvinyl enamel, a thermoset lacquer, as an
adhesive, with sequential baking~ and,in order to secure the
necessary thickness, passing the wire through the enamelling
bath and baking oven a number of times, after which the enamel-
led wire is transmitted through a vinyl dispersion or plastisol
with heating of the latter coating as well. This latter coating
step is also repeated several times. This method is obviously
cumbersome and uneconomic. This patent suggests that extrusion
techniques are unsuitable for deposition of thin plies of
plastic material because of the tendency to damage the under-
coat previously placed on the substrate and because of non-
uniformity in the resulting layer.
Certain of these disadvantages elucidated, illus-
tratively, in the disclosure of U.S. patent 2,531,169 are
apparent in U.S. patent 3,532,783 wherein a polyethylene coating
is attached by means of a hi~,density polyethylene modified
with maleic acid to a wire substrate. This latter patent sug-
- gests that polyvinyl chloride may be substituted for polyethy-
3~ lene if a suitable adhesive can be found. The adhesive
1~9~377Z
suggested is ~ICH, a vinyl chloride-vinyl acetate
copolymer that is deposited only from solution. Under
normal application this vinyl composition is air dried
or baked to eliminate residual solvents. However, even
if force dried, the desired state for application will
be effected only very slowly. Once deposited, in any
- event, on the metal substrate with a subsequent overcoat
layer of plasticized vinyl compound, the adhesive is
softened by the plasticizer of the vinyl chloride result-
ing in poor bond strength. The process described in this
patent proceeds inherently at a slow pace because of the
- necessity to heat the wire substrate that is to be coated
in order to effect a proper deposition of adhesive. The
solid flake adhesive employed, in addition, presents a
material problem in securing a uniform coat, enhancing
the dependency of the process on the preheating step.
~ 7 7Z
If, accordingly, a product could be devised
comprising a metallic substrate, and particularly wire,
and, as a second layer or ply, a hot melt polyamide
adhesive capable of bonding firmly the wire and a further
ply of extrudable thermoplastic resin and particularly
polyvinyl chloride or copolymers thereof having a uniform
thickness sufficient to provide effective and prolonged
protection to the wire substrate, a product of prolonged
life span would be obtainable, reducing, and indeed, sub-
stantially eliminating the replacement now periodically
required of materials which are increasingly expensive
or unavailable, and thus constitute a significant advance
in the state of the art. Similarly, if an economically
and technically feasible, continuous, high speed system of
providing a product such as the foregoing wherein the heat
absorbing qualities of the metallic substrate are used to
cool theadhesive could be devised, an advance of signifi-
cant merit would also be effected.
Various polyamide adhesives have been proposed
generally for use with polyvinyl chloride and with metals
but no mode of application, much less one that is economic-
ally efficacious, or capable of uniform and continuous per-
formance at high speeds; nor indeed any suggestion as to
specific adhesives appropriate for simultaneous application
to metals and polyvinyl chloride to secure a permanent
bond is apparent in these teachings.
SUMMARY OF THE INVE21TION
. . _ .
It is, therefore, a general object of this in-
vention to provide a laminate including a metallic substrate
S~7~2
and a protecti.ve thermoplastic resinous ply or coating
wherein the coating is bonded to the substrate in such a
manner as to preserve the composite assembly of coating
and substrate over an extended period of time and under
extremes of environmental attrition not attainable here-
tofore.
It is a further object of this invention to
provide means for producing, in a continuous process and
at speeds up to 2000 feet per minute, a wire to which has
been bonded an extrudable thermoplastic resin coating of
a thickness sufficient to assure protection against ex-
tremes of temperature and humidity, as well as against
abrasion and oxidizing agents such as mineral acids, sea
water and other dilute solutions of salt and alkali, while
conveying an esthetically pleasing effect.
A still further object of this invention is to
provide a coated wire such as provided hereinabove which
will have a flexibility sufficient so that it may be flexed
or bent to form chain-link fence fabric without cracking
and in which the thermoplastic resin employed is preferably,
and significantly so, polyvinyl chloride having improved
resistance to peeling and thus to deliberate human effort
to destroy it by cutting of the protective or insulated
coating.
Another and particular object of the invention
is to provide a method of bonding a vinyl chloride resin
composition to a galvanized steel wire suitable for use
in chain-link fabric in a high speed process wherein the
bonding component is a hot melt polyamide resin containing
composition.
-7~ ~ 77Z
- Accordingly, a novel metallic-based laminate of
unique durability, including significantly improved and
effective resistance to attrition by a vast variety of en-
vironmental agents and forces and comprising a metallic
substrate, a polyamide adhesive applied thereto and having
critical parameters of utility and a protective, extrudable
thermoplastic résin and particularly a plasticized vinyl
chloride resin outercoat permanently bonded by said adhesive
to said wire has now been devised. In addition, it has been
1~ discovered that the foregoing thermoplastic resin can be
bonded to its metallic substrate or core in a uniform thick-
ness at high speeds in a continuous manner by means of a
hot-melt polyamide resinous adhesive composition; the pro-
cess employing the heat absorbing qualities of the metallic
substrate to cool the hot-melt adhesives for effective bond-
ing at the linear speeds prescribed herein.
More particularly, the present invention provides a
protectively coated metallic substrate wherein the coating
comprises as a first ply a polyamide resin hot melt adhesive
coating bonded to said substrate, said polyamide hot melt
adhesive comprising the condensation product of alkylene
diamines of the formula:
H2 N(CH2~ x NH2
wherein x is an integer of from 2 to 20; and polymeric fat
acids having a dimeric fat acid content greater than about
90 percent by weight; the molar equivalent of amine employed
being about equal to the molar equivalent of carboxyl groups
present in said fat acid; and a second ply of an extrudable
thermoplastic resin adhering to said substrate by means of
said adhesive.
.,,~
9~ 72
-7a-
The present invention further provides a
process for applying and bonding a protective coating
to a metallic substrate that comprises applying to a
rapidly advancing length of said substrate a first ply
of a molten polyamide resin hot melt adhesive; said poly-
amide hot melt adhesive comprising the condensation pro-
duct of one or more alkylene diamines of the formula;
H2 N (CH2) x NH2
wherein x is an integer of from 2 to 20; and polymeric
fat acids having a dimeric fat acid content greater than
about 9O percent by weight; the molar equivalent of amine
employed being about equal to the molar equivalent of
~arboxyl groups present in said fat acids; cooling the
said adhesive composition to a flow resistant state; ex-
truding a molten extrudable thermoplastic resin compositionon to said adhesive composition whereby said adhesive com-
position is softened and cooling, whereby said thermoplastic
resin composition is bonded to said substrate by means of
said adhesive composition.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of the lami-
nated product prepared according to the present invention.
Figure 2 is a semi-diagrammatic illustrationlof
the method employed according to the invention in producing
the product of Figure 1.
Figure 3 is a perspective view of apparatus used
in the practice of the process according to the invention.
Figure 4 is a sectional view of an alternative
apparatus for use in the practice of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel product of the present invention com-
prises generally a protectively coated metallic substrate
F
-8- ~9~77Z
and an extrudable thermoplastic resin coating bonded
thereto by means of a hot melt resinous polyamide ad-
hesive composition.
The metallic substrate treated according to
the practice of this invention may vary substantially
as to conformation, flexibility and the metal employed.
Illustratively, the process herein described has appli-
cation to relatively smooth metallic surfaces such as
copper~ aluminum and aluminum-containing metals including
aluminum alloys, brass, magnesium, steel, whether gal-
vanized, ungalvanized, bethanized, aluminum coated or
high strength, 10~-7 alloy steels in which the alloy is,
for example, chromium, silicon, copper, nickel, phosphorus
alloy Csold by the U.$. Steel Corporation under the trade
ma~k CCR-TEN A steel~ or a manganese, chromium, vanadiu~
alloy ~sold by U,S~ Steel Corporation under the trademark
COR-TE~ B steeI~, or steel surface-treated with phosphoric
acid for example; and whether in the form of tubing, H-beams,
web constructions, flat plate, cable, filament or wire
.. . .
strands, and the like~ The invention herein described has
partiçul~r and unique a?plication, however, to wire having
most desirably a smooth, nodule-free surface as shown in
Figure 1, and that paid out at high speeds from a coil which,
after coating is completed, may be conveniently reformed
as a coil,
The preferred substrate is galvanized wire
suitable for use in the manufacture of chain-link fence
wherein the wire substrate is produced, according to
processes well-known to those skilled in the art, from
hot-rolled rods of controlled auality steel. The rods
-~ are cold drawn through dies to reduce the diameter of the rod
while increasing its length~ The cold drawing contributes
~i
g ~ 772
desirable properties of higher tensile strength and in-
creased stiffness. The resulting wire is then convention-
ally heat dip galvanized using slab zinc.
I~hile the dimensions of the substrate to be
coated are not narrowly critical, where wire is, for
example, being coated, preferred limits have been found
where, illustra,ively, the wire is to be used in making
chain-link fenee having a cross-seetional diameter within
the range of about .Q76 ineh ~o about 0.192 inch. Indeed,
the invention is espeeially praetieable for use with nor-
mally rigid wire of this diameter and having, in addition,
a tensile strength of 65,000 to 120,000 psi.
The vinyl resins forming the proteetive eoating
are eommercially available vinyl halide, and partieularly
vinyl chloride, homopolymers, as well as copolymers con-
taining at least 70 percent by weight of vinyl chloride and
up to about 30 percent by weight of one or more other poly-
merized comonomers, Illustrative of the vinyl comonomers
for use in the foregoing eopelymers are vinyl esters of
the following general formula: 0
CI2 CH2 = CH - 0 - C - R
wherein R is a lower alkyl moiety and one preferably of
from l to 4 carbon atoms~ Illustrative of the cemonomers
are vinyl acetate, vinyl butyrate and vinyl propionate.
The vinyl resin thus employèd in the practice
of this invention provide the most significantly effective
bond aecording to the practice, and under the conditions,
achieved hereunder in combination, by way of illustration,
with excellent protective properties including resistance to
B
-10- 1~ 3772
abrasion, weathering, oxidation and attack by a variety of
other chemicals while being relatively inexpensive and
easily handled.
Other significantly less preferred extrudable
thermoplastic resins which may also be used, however, in
the practice herein described include the polyolefins,
notably low density polyethylenes and most desirably those
having a low melt index of from about 0,2 to 0.4 as
measured by ASTM Procedure D-1238-65T; and polyamides, such
as nylon-6 and nylon-12, which are pigmented and stabilized
for long outdoor exposure.
The foregoing vinyl chloride homopolyers and
copolymers are combined with plasticizer and preferably
mixtures thereof, in an amount by weight of about 25 to
about 40, and preferably about 28 to 32, parts for every
100 parts of resin (phr). Included among these plasti--
cizers are liquid plasticizers among which are the alkyl
and alkoxy alkyl esters of dicarboxylic acids or the es-
ters of a polyhydric alcohol and a monobasic acid; and more
specifically, phthalate plasticizers, such as dioctyl
phthalate, butyl octyl phthalate, di-2-ethylhexyl phthalate,
di-isodecyl phthalate, N-octyl phthalate, dinonyl phthalate,
diisooctyl phthalate, butyl lauryl phthalate, butyl benzyl
phthalate, and ethyl phthalylethyl glycolate; dibasic acid
9~77Z
ester derivatives such as dioctyl adipate, dioctyl azelate,
dioctyl sebacate, dibutyl sebacate and glyceryl stearate.
Also contemplated as plasticizers are phosphates such as
trioctyl phosphate, triphenyl phosphate and tricresyl
phosphate; as well as chlorinated fatty acid esters, alkyl
epoxy stearates, epoxides of soya bean oil fatty acid,
and epoxy linseed oil.
A wide variety of plasticizers can be employed
in the vinyl polymer by virtue of the particular adhesives
employed herein which are substantially insoluble in the
commonly employed vinyl resin plasticizers.
Other conventional components include stabilizers
and pigments, normally from about 1 to 9 phr., and prefer-
ably about 3.5 to 5 phr. thereof. These components are
well known within the field and commercially available.
The stabilizers employed particularly are thermal and light
stabilizers, such as, illustratively, benzophenone and
benzotriazole derivatives usually in an amount by weight
of about 0.05 to 0.3 phr., and dibasic lead phosphite or
cadmium and zinc salts in an amount by weight of about
0.05 to 0.3 phr. Pigments, employed in amount of o.oo01
to 3.0 phr., are also well known and include, for example,
phthalocyanine green, phthalocyanine blue, carbon black
and titanium dioxide.
The resulting plasticized polyvinyl chloride
resin compositions contain most desirably, no fillers,
extenders or other extraneous matter. The colors or pig-
ments are stabilized with conventional stabilizers as
aforesaid, have a light fastness that shall withstand a
minimum Weather-O-Meter exposure of 4000 and up to 5000
-12 ~9~7~Z
hours without any deterioration (Test equipment operating
Light and Water Exposure Apparatus Carbon - Arc Type)
ASTM D 1499, E 42 Type and 649 as applied to wire and pipe
coating respectively. The extrusion grade semi-rigid vinyl
resin utilized will have most desirably a maximum specific
gravity of 1.30 to 1.32 (ASTM D 792); a hardness of about
Durometer A 75 to 95, Shore A durometer and preferably
about 90 to 95; a tensile strength of about 1500 to 3500
(pounds per square inch guage) psig and about 270 to 280
percent elongation (ASTM D 412). This protective vinyl
resin is characterized by high abrasion resistance, maximum
deformation of 15% at 120C. (Underwriter Laboratories
Test Procedure) under a 500 gram load and compression cut
through of 1500 psig to 1800 psig and preferably 1700 to
1800 psig (Bell Laboratory Test Procedure).
The vinyl chloride resin coating thus formu-
lated can be applied to the metallic core or wire under
the conditions recited herein including exceptionally high
speed with uniformity, from a conventional extruder in
effective thicknesses to achieve a protectively coated wire
having all of the desired properties necessary for impart-
ing an extended useful life to the product of the invention
under vigorous conditions to which, for example, chain-link
fence, as well as other products formed of the insulated
and protected metallic substrates produced according to the
invention, are subjected.
The hot melt polyamide adhesive compositions
employed in the practice herein described are high molec-
ular weight polymeric polyamide compositions thermally
stable as melts in the Brookfield melt viscosity ranges re-
cited hereinbelow and produced preferably and substantiallyfrom polymeric fatty acids and one or more and preferably a
mixture of non-aromatic diamines, and at least in excess of
. . ,
' -13- ~9 ~7 ~
fifty percent by weight of the total amine employed of
alkylene diamines having from about 2 to 20, or more de-
sirably 18, carbon atoms and preferably 2 to 6 carbor.
atoms. Illustrative non-aromatic diamines employed, in
admixture with the major Portion of alkylene diamines re-
cited are 1,4 -diaminocyclohexane, ethylene-1,2-bis (4-
piperidine) and piperazine. The oregoing polyamides can
include desirably, and in addition an aliphatic or cyclo-
aliphatic saturated or unsaturated dicarboxylic acid or
mixtures thereof containing from about 6 to 36-carbon atoms;
illustratively sebacic acid, adipic acid and 1, 10 - decane-
dioic acid, and the isomers of 1, 4 - cyclohexanedicarboylic
acid. The proportion of these dicarboxylic acids incorporat-
ed in the polyamides of the instant invention are not permit-
ted normally to exceed 30 weight percent of the total acidcontent incorpora~ed in the polyamide adhesives utilized
herein.
The significantly preferred polymeric fatty
acids employed in this invention are fractionated poly-
meric fatty acids having in excess of about 90 percent byweight of the total fat acid present incorporated in the
form of the dimer acid. The remaining 10 weight percent
is composed substantially of monomeric acid and some higher
polymeric forms. Significantly preferred fatty or fat
acids for use in the practice herein defined are ethyl-
enically unsaturated monobasic aliphatic acids, contain-
ing from preferably about 10 to 24 carbon atoms, and most
desirably 16 to 20 carbon atoms. Of these the most pre-
ferred is linoleic acid and oleic acid. Mixtures of these
acids are found in tall oil fatty acids, mixtures which
provide a convenient source for preparation of the poly-
meric fatty acids employed herein.
~(~9~772
_1~
Illustrative compositions (on a weight percent
basis) of co~nercially available polymeric fatty acids,
based on unsaturated C18 tall oil fatty acids that are
subject to fractionation before use in forming the poly-
amide employed in the practice of the invention are:
C18 monobasic acids("monomer") 5-15%
C36 dibasic acids ("dimer") 60-80%
Cs4 (and higher) ("trimer") 10-35%
These acids are reacted, in the formation of
the polyamides employed herein, either as the acid
se or as an equivalent derivative capable of forming
amides in a reaction with a diamine, such as the lower
alkyl alcohol esters, wherein the alkyl moiety contains
from about 1 to 8 carbon atoms, of polymeric fatty acids.
The fatty acid or derivative is fractionated
by, for example, conventional distillation or solvent ex-
traction methods. They may optionally be partially hydro-
genated to reduce unsaturation using hydrogen pressure in
the presence of a hydrogenation catalyst in accordance
with methods well known to those skilled in the art to
which this invention pertains.
The term "fatty acid" or t'fat acid" is intended
to encompass monobasic aliphatic acids. The terms "monomer"
or "monomeric fatty acid," "dimer" or "dimeric fatty acid,"
and "trimer" or "trimeric fatty acid" or equivalent terms,
are intended to describe the unpolymerized monomeric fatty
acids or derivatives present in the polymeric fatty acids;
the dimeric fatty acids or derivatives (formed by the
dimerization of two fatty acid molecules); and the residual
higher polymeric forms composed primarily of trimeric acids
or derivatives, but containing usually some higher poly-
meric forms, respectively.
~9~77Z
-15-
; For the purposes of this invention, monomeric,
dimeric and trimeric fat acid contents are defined fur-
'~ ther by a micromolecular distillatlon analytical method.
The method is that of Paschke, R.E., et al., J. Am. Oil
Chem. Soc. XXXl (No. 1) 5, (1954), wherein the distilla-
i, tion is carried out under high vacuum (below 5 microns~ and
~, the monomeric fraction is calculated from the weight of
product distilling a~ 155C., the dimeric fraction is
calculated from that distilling between 155C. and 250C.,
and the trimeric (or higher) fraction is based on the
residue.
The alkylene diamines employed herein in com-
bination with the foregoing fatty acids are preferably
alkylene diamines having from 2 to 16 carbon atoms. These
diamines are further defined by the formula:
H2 N (CH2) x NX2
wherein x is an integer of from 2 to 20, and preferably 2
to 6 carbon atoms. Illustrative and preferred of these
diamines is ethylene diamine and 1, 6 - diaminohexane.
Further illustrative of these diamines are 1~3-diaminb
butane, 1,4-diamino butane, and, although less preferred,
1,8-diaminooctane, l,10-diaminodecane, l,9-diaminononane,
1,12-diaminodGdecane and 1,18-di-aminooctadecane.
The polyamide compositions employed in the
practice of the invention are prepared by reaction of one
molar equivalent of amine with one molar equivalent of
carboxyl group present. The time and temperature of the
reaction of diamine and fractionated fatty acid,other acid or
acid derivative are not narrowly critical but are normally
within the range of from 150 Centigrate (C.) to 300C.
,, .
F
j
-16-
~9~772
for a period of from one-half hour to 8 hours; the
longer period being employed at the lower temperatures.
The polyamide resins for use herein are those
effecting a superior bond with the metallic substrate
and thermoplastic resinous coating at the temperatures
and within the other operating parameters described
hereinbelow.
Thus, in order that the resins be readily
applied preferably as a liquid and in a thickness neces-
sary for effective bonding of the resin coat and metallic
substrate thereby at the high rates of speed defined
herein, it is significantly preferred that they manifest
a softening point of from about 112Centigrade (C.) to
138C. (233 Fahrenheit (F.~ to 280F.), and preferably
135C. to 138C; a Brookfield melt viscosity of 10 to 100
poises, and preferably 40 to 60 poises, at 210C.; a tensile
strength of from about 400 pounds per square inch (psi~ to
500 psi and preferably about 450 psi and a percentage (lo)
elongation of from 400 to 600, and preferably about 550.
The softening point referred to hereinabove is
the ball and ring softening point as measured by ASTM E28-
59T.
The tensile strength and elongation are measured
on an Instron Tensile Tester Model TTC using ASTM 1708-59T.
The polymer is compression molded as a 6" x 6"
sheet of approximately 0,04 inches thickness, at a tem-
~D
~ 9~7~Z
perature near its melting point (usually a few degrees
lower than the melting point) and at 40,000 lbs. load or
higher using cellophane* as the parting agent in the mold.
From this sheet, test specimens are die-cut to conform to
ASTM 1708-59T.
Test specimen is clamped in the jaws of the
Instron. Crosshead speed is usually 0.5 inchtminute at
100 lbs. full scale load. Chart speed is 0.5 inch/minute.
Tensile strength (reference: ASTM D-638-52T) is calculated
as:
Tensile strength = maximum load in pounds
cross sectional area (sq.inc.)
Percent elongation is calculated as:
gage length at break minus
% Elongation = gage length at O load X 10
gage length at O load
The polyamides employed herein may be, and are
preferably, used as such, or may have incorporated there-
with cvnventional additives well known to those skilled in
the art, notably inert inorganic fillers such as calcium
carbonate, in amounts, for example, up to 40 percent by
weigh* of the adhesive composition, and standard plastici-
zers such as ortho and para toluene ethyl sulfonamide.
These plasici~ers are employed, illustratively, in amounts
of up to 5, and preferably up to 3, percent by weight of
the total adhesive compositions. The incorporation of
fillers and plastici~ers, although economically effica-
cious, tends to lead to a less effective bond.
Other polyamides, including copolyamides suitable
for use in the practice of the invention are disclosed
in United States patents 3,454,412; 3,398,164; 3,377,303;
*trademark
~17-
!D
-18~ 877Z
and 3,449,273 together with the additives recited there-
in and provided, with respect to the significantly pre-
ferred polyamides coming within the disclosure of these
patents, that they manifest softening points, melt
viscosities, tensile strengths, and percentages of elonga-
tion, coming within the ranges recited hereinabove. In
addition, those polyamides containing substantial amounts
of tertiary amine moieties or other base-forming groups
tend to be significantly less preferred in the practice
herein described since they are prone, when heated, to cause
decomposition of contiguously disposed resin.
The products of the invention and the process
by which they are prepared are further illustrated by
detailed reference to the accompanying drawing wherein
the preferred embodiment of the invention is manifested.
Thus, there is shown in Figure 1 the coated and bonded
wire 10 incorporating the metallic substrate 12 prefer-
ably formed of galvanized steel, and surrounding this
substratej a continuous ply of hot melt polyamide
adhesive 14 as characterized hereinabove and to which
is bonded in turn as the exterior ply, a coating, most
desirably, of a vinyl halide resin composition 16.
The composite wire product 10 of Figure 1 is
- prepared in accordance with a preferred embodiment of the
invention as shown in Figure 2 wherein standard equipment
well known to those skilled in the art is employed,except
where otherwise expressly indicated. Thus, a continuous
metallic wire core 12 is drawn at speeds of up to about
2000 feet per minute through a plurality of treatment
--19- ~9~3772
zones in which it receives successive resinous plies
(designated by the numerals 14 and 16 in Figure 1) and
is subjected to several significant variations in
temperature.
More particularly, according to this process
a coil of untreated wire 12 is uncoiled from a supply
stand or pay-off frame 20 which may be of standard design
and drawn through successive treatment æones at a line
rate of speed of between about 200 to approximately 2000
feet per minute and preferably within the range of about
800 to about 1500 feet per minute.
Indeed, in a preferred embodiment, the bond
between the galvanized steel wi.re 12 and the extruded
vinyl coating 16 provided by the hot melt adhesive 14 is
improved with increased line speed as is the esthetic
appeal of the coated product as reflected in the high
surface gloss achieved at these increased rates of speed,
thus enhancing the useful life and desirable appearance
of the product while decreasing its cost of manufacture.
While not intended to be limited to any particular theory
of operation, it is believed that this phenomenon is
attained by virtue of the increased activation afforded
the adhesive when it comes into contact with the extruded
vinyl resin which at the higher rates of line transmission
will be extruded onto the wire more rapidly and at higher
temperatures within the ranges recited in accordance with
the invention.
The initially uncoiled wire is, in any event,
first cleaned by standard physical means such as brushes
or cloth 17, or alternatively by conventional chemical
~9877Z
-20-
reagents to remove dust, oil or other foreign substances
from the substrate or core 12. In a preferred embodiment
of this invention a lightly oxidized layer of zinc and, most
desirably, a substantially mono~,olecular layer thereof, is present
on the wire surface after cleaning is complete. This
oxidized surface includes normally oxides as well as
hydroxides, of zinc which adhere to the wire surface
assiduously through the cleaning operation and result in
enhanced adhesion of the polyamide resin adhesive composi-
tion thereto. The surface of the wire may, optionally,
be roughened by mechanical means to enhance, perhaps,
adhesion of the polyamide, but it is neither essential
nor, indeed, particularly desirable to do so. After the
cleaning step is completed the wire is transmitted through
a first treatment zone 24 comprising, in a preferred em-
bodiment, the device of ~igure 3, an insulated heated
dippi.ng tank 27 preferably of rigid double wall construc-
tion, containing an entry orifice 28 with a suitable entry
die (not shown) through which the wire 12 is advanced into
the tanl 27 thus preventing leakage of adhesive present
in the molten state within the tank 27 from about the
advancing wire 12. Heating elements (not shown) are dis-
posed within or about the walls of the tank in standard manner
to secure the elevated temperatures required to melt the
normally solid adhesive and achieve the temperature neces-
sary to effective coating of the wire 12. Positioned at
the level of the entry orifice 28, but in the wall opposite
that 29 in which the entry orifice 28 is defined, is an
exit orifice 31 comprising a sizing die of the requisite
diameter to provide the desired thickness of adhesive
-21- ~9~77z
coating 14 on the wire core 12 leaving the first treatment
zone~ The dipping tank 27 is preferred particularly
because the viscosity of the adhesive may vary within
a broader range than where other applicator means are used.
Indeed, the use of the dipping tank is essential to attain
rates of speed and uninterrupted operatlon within the pre-
ferred limits recited hereinabove. Illustrative alterna-
tives are however available for use at significantly re-
duced speeds as, for example, that shown in Figure 4, where-
in the wire core 12 may be transmitted through a cross-
head applicator 32 that constitutes the first treatment
zone 24. The fluid adhesive, normally solid at ambient
or room temperatures, is pumped into the applicator at
an elevated temperature sufficient to render it a molten
plastic or through the feed screw of a conventional extruder
apparatus into the foregoing cross-head applicator or die
32. The adhesive is heated in part by the frictional or
shearing forces exerted by kneading of the resinous adhesive
in the barrel of a conventional extruder and more particularly
by heating means disposed in conventional manner in a jacket
mounted about the feed screw barrel or other passage or
mixing chamber through which the adhesive is conveyed to
the applicator head. A commercially available hot melt
applicator is that designated by the trade name Spraymation
and particularly thatbearing the grade designation 84300
manufactured by Spraymation, Inc., Little Falls, New Jersey
used to supply adhesive to a cross-head applicator or die
32. The applicator 32 comprises a die body 33, having an
annular passage 34 flared at its opposite ends 35 and 36
and adapted to receive in threaded engagement therewith
-22 ~98~Z
threaded dies 37 and 38 having axially dis osed orifices,
the entry orifice 39 and the exit orifice 40 respectively,
of uniform cross-sectional diameter. The first of these
orifices 39 defines the point of entry of the wire 12
into the first treatment zone formed by the annular
passage or reservoir 34 and has a larger cross-sectional
diameter than the exit orifice 40 which forms a sizing
die controlling the thickness of the adhesive coating
applied to the wire 12 in the initial trëatment zone.
Intermediate the opposite ends 35 and 36 of the passage
34 there is disposed an entry port 41 through which the
adhesive however fed thereto is transmitted into the
passage which thus serves as a reservoir in which the
molten adhesive is applied to the advancing wire.
Whichever of the foregoing means of application
is used, however, the temperature to which the normally
solid adhesive is elevated to induce the necessary vis-
cosity and resulting adhesion to the metal substrate is
23-
~9~77Z
normally from about 300F. to about 450F. and preferably
about 350~F. to about 450F., the temperatures varying
with the particular composition of the adhesive formula-
tion, and the thickness of the adhesive coating 14 to be
formed. The preferred range is employed particularly
where the limitations on viscosity of the adhesive are
more severe, that is, for example, where the cross-head
applicator of Figure 4 is utilized. Within the preferred
parameters for practice of the present invention as
defined herein, the temperature of the adhesive composi-
tion when applied in the first treatment zone is about
350F. to about 450F. to effect the continuous uniform
coating required. The thickness of the coating is nor-
mally within the range of about 0.25 mils (.00025 inch)
to about 5 mils (.005 inch) and preferably about 2 mils
(.002 inch).
Upon leaving the first treatment zone 24 the
adhesive coated wire passes in a substantially linear
manner through the ambient atmosphere, which is maintained
- 20 normally at approximately 65F. to 78F., and constitutes
a second treatment zone 42, in which the adhesive is
- returned to its substantially solid state. This zone has
a length normally of about 2 to 20 feet for a residence
time of about 0.06 second to 6 sec. and preferably about
4 feet to about 8 feet a residence time of about .16 to
.6 sec. The most desirable cooling to enable the adhesive
to assume the flexible, soft but solid and resistant to
flow properties best adapted for effective entry into and
activation of the adhesive 14 deposited about the wire 12
in the third treatment zone is generally about 6 feet or
_24
~9~772
a residence time of about .24 to .45 sec. The ambient
air provides the cooling medium of the second treatment
zone, together~ significantly it has been found
with the matallic core 12 which functions as
a heat sink for the elevated temperatures imparted to
the adhesive in the first treatment zone
The second treatment zone or cooling span 42
terminates in the third or vinyl resin deposition zone
43. This zone is composed of the annular passage defined
by a cross-head die, also designated in this embodiment
by the numeral 43. The passage through which the wire
is transmitted in this zone may, illustratively, be smooth
bore of uniform diameter or tapered to a relatively
constricted diameter intermediate the opposite ends of
the passage. The method involved is well known to those
skilled in the art. The extrusion process involves, by
way of illustration, blending vinyl halide resin in the
form of a fine powder with plasticizer and other additives
to form pellets, usually. This thermoplastic resin com-
position is then fed through a hopper (not shown) into one
end of a conventional plastic extruder from which the
plastic is then fed onto a standard screw 45 mounted in
the circular passage or barrel 47 with a close clearance
between barrel and screw surface of, for example, 0.001
inch per inch of screw diameter. The screw 45 is drawn
by a variable speed motor (not shown) which is cap~ble
normally of inducing a screw speed of 30 to 100 revolutions
per minute (rpm). The barrel 47 is usually heated elec-
trically and together with the heat resulting from the
shearing of the pelletized vinyl resin composition advanced
9~37~
through the barrel 47 from the hopper by the screw 45
attains a molten state as it approaches the extruder head
composed of the constricted passage of the adaptor 48
and cross-head die 43. The faster the line speed of the
wire to be coated, the faster the speed of screw rotation
and the higher the shearing temperature effected within
the barrel 47. Consequently, the higher the temperature
of the resin composition as it enters the cross-head die
43 and the more effective the bond achieved between the
adhesive and vinyl coating. The temperature induced in
the barrel 47 of the screw feed is sufficient to activate
the hot melt adhesive advancing into the cross-head die
from the second treatment zone, where the adhesive has
been cooled and rendered sufficiently solid to pass unim-
peded into the cross-head die without clogging of the
latter at and about the point of entry of the adheive-
coated wire into the die.
The temperature attained in the extruder head
or die of the third treatment zone is from about 300F.
to about 425~F. and preferably about 350F. to about 400F.;
temperatures sufficient tosecure an effective bond between
the vinyl coating and the wire 12 without degradation of
the adhesive or vinyl resin composition.
The coating applied in the cross-head die of
the extruder is most desirably about O.OlS inch to about
0.025 inch in thickness where the product wire is to be
woven into chain-link fence fabric.
The coated wire product 10 is then advanced into
the final treatment zone 49 prior to being rewound on the
take-up reel 22 driven by conventional electric motor or
other drive means (not shown).
- 26-
~9~772
The final treatment zone comprises an inter-
mediate air space or heat transfer zone 50 of about 2 to
20 feet or more in length and preferably about 5 to 15
feet, and a cooling bath or trough 52 through which cold
- water is circulated. TLIe further removed from the cross-
head die 43, the water-containing cooling bath 52 is
positioned within the recited parameters,the better the
bonding of the vinyl resin coating 16 secured to the
metallic substrate or core 12, since greater opportunity
is given for activation of the adhesive 14 and a conse-
quently improved bond. The residence time in the heat
transfer zone 50 will vary within the range of from about
0.08 second (sec.) to 6 sec. with a preferred range of
about 0.2 sec. to 1.2 sec.
The cooling bath 52, containing desirably a cir-
culating stream of water operating at a temperature within
the range most desirably of 50F. to 70F., serves to
assure solidification of the adhesive and vinyl resin plies
14 and 16 respectively, so that the product 10 can be re-
coiled or otherwise stored or used after leaving the bath
52. The residence time within the bath is not narrowly
critical. A minimum period of time is normally about 0.05
minute.
The resinous adhesives thus evolved are charac-
terized by excellent adhesion to the vinyl resins and
metallic substrates at the temperatures and within the
other parameters set forth herein.
The coated wire combines, as will be evident
from the accompanying description, means for producing a
product of unusually desirable characteristics in a sig-
nificantly efficient and inexpensive manner.
-27- ~9~772
The following examples are further illus-
trative of the invention. In the examples all parts
and percentages are by weight unless otherwise expres-
sly indicated.
Example 1
This example illustrates the production of
wire having a protective coating bonded thereto in
accordance with the invention.
A continuous substrate of galvanized steel
wire 12 having a cross-sectional diameter of 0.106 inch
and a tensile strength of 100,000 psig is advanced at a
rate of 250 feet per minute through mechanical cleaning
means 17 and thence through the cross-head die of a dip
tank hot melt resin applicator such as described herein-
above and illustrated in Figure 3 wherein the sizing die
through which the adhesive coated wire is advanced into
the second treatment zone has a dimension identical to
that of the exit orifice therein and in which a temper-
ature of 390F. is maintained and wherein a polyamide hot
melt adhesive composition in the molten state and having
a temperature of 390~F. is applied to the wire or filament
12 in a thickness of about 0.002 inch.
The normally solid hot melt adhesive is a
thermoplastic polyamide resin prepared by charging fraction-
ated polymerized tall oil fatty acids manifesting the fol-
lowing properties upon analysis:
Saponification Equivalent: 285
Neutralization Equivalent: 290
Monomer 1.1
Dimer 98.2
Trimer (and higher ~olv-
basic acid residue) 0.7
-28- ~D9~772
together with a mixture of diamines including ethyl-
ene diamine and hexamathylene diamine into a reactor
equipped with a stirrer, thermocouple and distillation
head. One molar equivalent of amine is charged to the
reactor for each mole of carboxyl there introduced.
The reaction mixture is stirred successively for 1.25
hours at 36C. (96.8F.) to 160C. (320F.~; 0.75
hour at 160C. (320F); 0.5 hour at 160C. (320F.)
to 250C. (482F.); 0.5 hour at 250C; and then under
vacuum for 2.25 hours at 250C. The adhesive is char-
acterized by a ball and ring softening point of 138C.;
a tensile strength of 450 psi and a percent elongation
of 550.
From the exit orifice die of the dip tank (27
of Figure 3) termed the first treatment zone, the
wire is advanced in a substantially linear manner
through the ambient atmosphere constituting the
second treatment zone 40 having a length of about 40
feet, in which the adhesive coated wire is permitted
to cool and solidify. The coated wire is then de-
livered to the third treatment zone 42 formed by the
smooth annular bore of a cross-head die into which
molten vinyl chloride resin composition Colorite 9813
Black, a plasticized poly (vinyl chloride) containing
low temperature (-20C.) plasticizer, a mixture of thermal
and ultra-violet stabilizers and pigment with no other fillers,
~9~377Z
- extenders or other extraneous matter present ! iS fed
from a conventional screw feed extruder 43~
The vinyl chloride resin composition feed has
a light fastness sufficient to withstand (1) a minimum
Weather~O-Meter exposure of 4000 hours without deteriora-
tion (Test Equipment Operating l,ight and Water Exposure
Apparatus Carbon - Arc Type) ASTM D 1499, E 42 Type E,
and (2) an accelerated aging test of 2000 hours at 145F.
without cracking or peeling. The resin has, in addition,
a tensile strength of 2700 psi, ultimate elongation of
275%; a specific gravity of 1.30 maximum, a hardness not
less than Durometer A 90 + 5: maximum deformation of 15%
at 120C. under a 500 gram load and a compression cut
through of 1500 psi; when measured by the appropriate
test procedures recited in the description appearing here-
inabove. The screw is rotated in the heated extruder
barrel at a rate sufficient to knead the foregoing resin
and exert a shearing force adequate, in turn, to induce a
temperature in the plasticized resin being advanced in the
barrel 45 and the extruder head or die 42 to about 350F.
The cross-sectional diameter of the die is
sufficient to provide a resin coating of .020 inch and
define an outside diameter of about 0.146 inch to the
product wire 10 when the coating operation is complete.
The wire is next passed into the final treat-
ment zone 49 including a cooling trough 52 in which water
is circulated. This trough is removed from the die 43
by about fifteen feet in which span the coated wire
travels in a linear path through a room temperature
atmosphere. In this span the vinyl resin coating and hot
- 3n ~9~2
melt adhesive perfect the bond initiated in the vinyl
extruder's cross-head die and is cooled sufficiently to
avoid accumulation of coating resin on the guide rolls
of the trough. The coated wire is then advanced through
the trough or dam 52 which is maintained at about 69F.
to 75F. and the finished product recovered therefrom
after a residence time of about 2.5 seconds. This product
evidences good adhesion five minutes after its recovery
from the final treatment zone and may be stripped from
the wire substrate only with difficulty.
Example 2
This example illustrates the use of an increased
line speed in the practice of the invention.
The procedure of Example 1 is repeated using
a line rate of speed in the various treatment zones of
600 feet per minute. The plasticized vinyl resin at the
point of application in the cross-head die achieves a
temperature of about 390F. The surface finish is found
improved to a glossy condition over that of Example 1.
Adhesion of the vinyl coating is found improved over that
secured in the product of Example 1.
Example 3
This example illustrates the use of a line rate
of speed significantly faster than that of Examples 1 and
2.
The procedure of Example 1 is repeated using
a line rate of speed in the several treatment zones of
about 900 feet ~er minute. The vinyl resin has a tempera-
ture of about 370F. in the cross-head die. The surface
gloss and adhesion were substantially improved over those
-31- ~9~77Z
-secured at the lower rates of speed of Examples 1 and 2.
The degree of surface gloss secured is significant in
that the vinyl resin coating effected is important not
only for its protective character but for its esthetic
appeal as well, particularly where it is to be employed
in the manufacture of chain-link fence.
Example 4
This example illustrates the use of a line speed
significantly faster than that of the prior examples.
The procedure of Example 1 is repeated using
a line rate of speed in the several treatment zones of
about 1000 feet per minute. The surface gloss is excel-
lent, and the adhesion to the wire substrate of the vinyl
resin coating as good as that secured in Example 3. The
outside diameter of the product wire secu~ed under condi-
tions otherwise identical to those recited in Examples
1 to 4 was 0.148 inch, with a vinyl coat of .022 inch
thickness. The speed of the coating operation is limited
by the take-up capability of the apparatus used; not by
the effectiveness or speed of application.
Example 5
This example illustrates the use of a cross-
head die of different construction for application to the
wire substrate of the hot melt adhesive.
The procedure of Example 1 is repeated using
a line rate of speed of about 500 feet per minute and
employing a Spraymation applicator 84300 described here-
inabove with the cross-head applicator of Figure 4 affixed
to the outlet end thereof and the entry orifice 39 of the
cross-head applicator has a uniform cross-sectional diameter
of 0.110 inch to provide a uniform coating of hot melt
-32- ~cæ987 ~ Z
adhesive of 0.002 inch in the bare wire having a diameter
of 0.106 inch.
Example 6
.
This example illustrates the practice of the
invention as described in Example l employing variable
conditions coming there within.
The procedure of Example 1 was employed using
a line rate of speed of about 975 feet per minute; The
cross-sectional diameter of the wire, the slab zinc sur-
face of which is lightly oxidized and other~ise brush
cleaned, is 0.106 inch. The temperature of the dip tank
along the path of adhesive application was 400F, The
adhesive was a polyamide of the type, and the preparation
of which is, described in Example l; characterized by a
15 - ball and ring softening point of about 138C.; a ~rook-
field melt viscocity at 2'0C of about 45 poises; a
polymer tensile strength of'about 450 psi; and a percent
elongation of about 550. The adhesive is deposited on
the wire'substratè in a thickness of 2 mils, The vinyl
20 ' resin, identical to that of Example 1 is deposited in the
manner therein described, in a thickness of about 20 mils
to provide a coated product wire with an outside diameter
of about 0.105 inch, The adhesive and vinyl resin coat-
... .
ings deposited are substantially uniform in thickness,
The product wire manifested a peel strength of about 65
pounds (to strip).
Example 7
.
This example illustrates the pracLice of the
, invention as applied to different metallic wire substrate
than that employed in the prior examples.
33 1~9~377Z
The procedure of Example 6 was repeated
substituting an aluminum alloy wire substrate having
a cross-sectional diameter of 0.120 inch chemically
cleaned to remove oil and other foreign substances
from its surface. The adhesive was applied at a tem~
perature of 400F. in a thickness of about 2 mils to
the wire which advanced through the various treatment
zones at a rate of 400 feet per minute. The identical
plasticized vinyl chloride resin composition of Example
6 was extruded into the resulting adhesive coat in the
manner of Example 6 in a thickness of 13 to 14 mils to
provide a finished coated wire having an outside or
cross-sectional diameter of 0.150 inch. The peel strength
of this product was found to be excellent.
The determination of the extent of bonding of
vinyl resin coating to the metal substrate described as
peel strength where referred to in the foregoing examples
is made uslng a six inch length of specimen wire which is
suspended vertically from the grips of a tensile tester,
The upper five inches of this wire sample are stripped
of thermoplastic resin coating. The other extremity of
the wire that is stripped is positioned within the annular
orifice or band of adjustable diameter of a steel stripping
fixture adapted to receive the wire. The stripping fix-
ture is, itself, mounted in the lower grips of the fore-
going tensile tester. The diameter of the orifice is
adapted to receive the stripped wire but not the coated
portion of the wire which is one inch in length and abuts
the lower end of the stripping fixture. The stripping
fixture or device is, in performance of the test, lowered
under pressure to effect peeling of the bonded resinous
~9 ~7
-34-
coating from the wire substrate. The maximum tensile
load or weight necessary to strip the wire, characterized
as break-down force, is recorded on a load cell of the
tensile tester.
Various epoxy and acrylic adhesives and zinc
chromate primers employed under conditions similar to
those recited above evidence normally either slight or
no adhesion. Where any adhesion is secured the bond is
brittle. Other acrylic resin adhesives such as that sold
ky Hughson Chemical Comp~ny in a two component system under
the trade mark designation HUGHSON 521 accelerator ~3
(lacquer) modified acrylic adhesive system, exhibited
good adhesion but required that the system be run at a
very reduced line rate of speed.
It w;ll be evident that the terms and expres-
sions which have been employed are used as terms of
description and not of limitation. There is no intention
in the use of such terms and expressions of excluding
equivalents of the feat~res shown and described or por-
tions thereof and it is recognized that various modifi-
cations are possible within the scope of the invention
claimed~
B
