Note: Descriptions are shown in the official language in which they were submitted.
This invention relates generally to composite
tubing and more particularly to a hose fox transmitting
fluids under pressure in a spraying apparatus such as a
paint spray.
Apparatus ~or spraying liquids such as paint is
provided with a pump and hose assembly for transmitting
liquid under pressure from a supply tank to a spray gun
nozzle. An electrically conductive ground wire is usually -
included throughout the length of the hose to drain off
any static electricity developed at the spray nozzle of
the hose to prevent sparking when it approaches a conductor ~
such as a steel beam or the like. A hose having a flexible j~ `
polymeric core tube, fibrous reinforcing material wound
about the core tube and a protective sheath is used to ~;~
convey the li~uid at a pressure which is sufficiently high
to produce a spray. The hose must be capable of expanding -~
radially under the pulsation of the pump in order to act as
an accumulator which attentuates the pulses so as to minimize
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pulsating at the nozzle and thereby produce a relatively smooth ~ `
and uniform spray of li~uid. On electric motor operated paint :
spray systems, the accumulator action also retards the rate
of pressure change affecting the motor controlling pressure
switch, thereby reducing the number of stops and starts of
the motor controlling the fluid pump.
It has been proposed heretofore to wind a ground
wire about the core tube as one of the braids of the
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reinforcing layer. However, the wire fre~uently broke
under pressure and the abrasion of the braid by the
wire sometimes resulted in bursting of the hose.
It is proposed in U.S. Patents 3,~45,583,
3,~43,803 and 3,780,208 to provide hoses for transmitting
liquids from a pulsating source with a grounding wire
helically wound about the core tube and enclosed within
a rupture resistant sleeve. ~ :
While the disclosed hoses have been found to
be adapted for successfully transmitting paints under
most conditions, the inclusion of a grounding wire
enclosed in a plastic sleeve introduces additional steps
in the manufacture of the hose and it has been found in
practice that the ground wire sometimes ruptures and the
fragments are not confined sufficiently to maintain
continuity of the static discharge system. Also, the
fragments may penetrate the core or sheath causing a
:' premature failure of the hose.
It is therefore an object of this invention to
provide an improved composite hose having a means for
static discharge. Another object of the invention is
to provide a composite hose for use with a paint spray-
ing apparatus or the like which is adapted for transmission
. of pulsating fluids and has a static discharge means which
is conveniently incorporated in the hose and effectively
discharges static electricity throughout the life of the
hose. A further object of the invention is to provide a
`' composite hose with a grounding means coextensive with
the length of the hose which is not ruptured or otherwise
broken by the pulsating action of the hose.
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Other objects will become apparent from
the following description with reference to the accom-
panying drawing wherein
Figure 1 is a cut-away side elevation, partially
in section, of one embodiment of the invention; and
Figure 2 is a cross-section ta]~en along the
line 2-2 of Figure 1.
The foregoing objects and others are accom- ;
plished in accordance with this invention, generally
speaking, by providing a composite reinforced paint hose
having a core tube shaped from two layers of synthetic
thermoplastic resin which are in intimate contact with
each other with the outer layer of the tube wall being
a semi-conductive material, one or more layers of a
fibrous reinforcing material disposed about the core tube -
and a protective synthetic resinous sheath disposed about
the fibrous reinforcing material. The composite core tube
has an inner wall adapted to resist chemical attack by
the fluid conveyed by the hose while the coextensive
outer layer o~ the core tube serves as a means for
conducting any static electricity along the length of
the hose to a suitable ground wire. The invention thus
provides a flexible paint hose having a synthetic resinous
core tube, a fibrous reinforcing layer about the core tube,
a protective sheath about the fibrous layer and a grounding
means forming an integral part of the wall of the core tube.
Although the laminated core tube may be formed by spraying
the inner layer with a conductive coating or by dipping
the inner layer in a conductive resin, the core tube is
preferably formed by coaxially extruding--t~70 di~ferent
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extrudable synthetic polymers to provide a flexible tube
having a wall of two synthetic resinous layers. The two
layers may be extruded in two separate extrusion steps
or they may be simultaneously coextruded so that the
layers are melt fused together. The conductive layer
extends throughout the entire length of the hose and is
in electrical contact with a grounded hose fittinq. The
grounding layer is a synthetic polymer which is semi-con-
ductive, i.e., i-t exhibits a volume resistivity of 10
ohm-cm or less.
In airless paint spraying processes, it is un-
desirable to accumulate more than 1400 static volts at the
spray gun of the spraying apparatus because of the danger
of igniting the air-solvent mixture about the spray gun.
Preferably, a safety factor of ~:1 should be maintained
which means that the static voltage on the spray end of
the hose should not exceed 350 volts. The hose provided
by this invention has a ground which is a semi-conductive
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layer of polymer which will drain off the static potential
so a frightening or dangerous electrical-arc between the
spray gun and ground is avoided.
Any suitable conductive synthetic polymer may
be used. Preferably/ the conductive synthetic polymer
is one which will melt fuse to the polymer of the first
layer when the two polymers are coa~ially extruded. The
conductive polymer must have the required electrical
properties. While a semi-conductive polymer having a
volume resistivity after application and other processing
of as high as 100,000 ohm-cm at ambient temperature may
be used, usually the volume resistivity will no-t be more
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than about 2000 ohm-cm. It is preferred to use one ~
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having a calculated volume resistivity of not more
than about 500 ohm-cm. In fact, best results have
been obtained so far with a polymer having a volume
resistivity of 40 or less ohm-cm. The volume resis-
tivity may be calculated by the method described in
"NFPA Journal No. 77, Static Electricity, 1972."
Examples of suitable polymers are ethylene-ethyl
acrylate, ethylene-vinyl acrylate and thermoplastic
rubber having the desired volume resistivity but it is
preferred to use a polyurethane of the desired volume
resistivity in hoses having a nylon inner layer where
kink resistance is desirable because the polyurethane
bonds well to the nylon and can be bonded to the
reinforcing material.
The semi-conductive polymer may have carbon
particles including graphite particles, silver particles,
copper particles or other suitable electrically conductive
particles dispersed substantially uniformly therein to
provide the polymer with a volume resistivity within
the requirements of the hose.
The invention permits the manufacture of a com-
posite reinforced semi-conductive paint hose having some
particularly desirable physical property without substantial
compromise of other desirable properties combined with
~ a means for effectively draining static electricity
; from the hose. For example, a substantially chemically
resistant polymer such as nylon may be chosen for the
, inside layer of the core tube wall and a layer of a more
- flexible polymer such as an elastomeric polyurethane
having electrically conductive particles dispersed therein
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may be fused thereto as the outer surface to provide
improved flexibility, kink resistance and means for
preventing sparking of static electricity at the
nozzle of the hose. The outer layer containing
electrically conductive particles may be shaped from
a resin such as a polyurethane which can be solvated
with a polar solvent to adhesively bond the core tube
to the adjacent layer of reinforcing material and to
improve the strength of the hose. In such a hose, the
; 10 relative thickness of the nylon and conductive polyure-
thane layers may be varied to further modify the
properties of the hose.
The core tube may be fabricated by any suitable
simultaneous coaxial extrusion procesæ which will produce
melt fusion of two different layers of synthetic thermo-
plastic resins together to the extent that the two
layers will not separate at the interface under elonga-
tion and other conditions to which the hose will be
exposed. The most practical method of making the core
-tube is to supply two different synthetic thermoplastic
resins or two different types of the same thermo~plastic
resin to a single extrusion head from different extruders
operating under conditions whereby the resin which will
be the inner portion of the core tube is still molten
when the molten resin for the other portion of the core
tube wall is applied thereover and the two molten synthetic
resins are extruded through the same extrusion die.
i It has been found that two layers of selected
thermoplastic synthetic resin with one being electrically
conductive will melt fuse together along the interface
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99~2 L~
and become so firmly bonded together that the core
tube will not delaminate in a hose used to convey
fluids under high pressure even if the physical prop-
erties of the two layers are significantly different.
For example, nylon and a semi-conductive thermoplastic
polyurethane having particles of carbon black uniformly
dispersed therein will melt fuse together in accordance
with the process of the invention. Hence, the invention
contemplates a semi-conductive paint hose having a core
]0 tube with a layer of nylon melt fused to a layer of
thermoplastic substantially non-porous polyurethane.
Usually, the nylon layer will be the innermost layer
because of its chemical resistance. The semi-conductive
polyurethane layer imparts flexibility to the hose and
may also be used ~or making an adhesive to bond the
core tube to the fibrous reinforcing layer so it is
usually disposed on the outside of the core tube.
The invention also provides composite reinforced
; hoses having a core tube of two or more layers of synthetic
resin of the same general chemical composition but
modified to provide different physical properties. For
example, a relatively hard thermoplastic polyurethane
having a hardness of Shore D 50 to 60 and a relatively
soft thermoplastic polyurethane having a hardness of
Shore A 80 to 95 may be coextruded to form a core tube.
~, The harder thermoplastic polyurethane has better chemical
, resistance than the softer one so the harder one is
usually the inner layer of the core tube while the softer
one contains particles of an electrical conductor and
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is the outer layer. The presence of the layer of softer
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polyurethane improves the flexibility of the hose as
well as providing a semi-conductor for static electricity.
Other combinations of synthe-tic resins whic~
may be co-axially extruded simultaneously or in tandem -to
form a core tube having two or more layers are those dis-
closed in our Canadian Pat. Appl. No. 248,9~0~ filed M~rch 29/76. For example,segmented co-polyesters such as "Hytrel" as one layer and
a polyvinyl chloride compound for the conductive layer.
A segmented co-polyester may be used for one layer and a
conductive substantially non-porous thermoplastic poly-
urethane as the other layer. A mechanical mixture of an
aromatic polyester such as poly(tetramethylene terephthalate)
and a segmented co-polyester may be used as one layer and
a conductive polyvinyl chloride polymer as the outer layer.
The laminated core tubes combining a layer of "~ytrel" or
a mixture of a segmented co-polyester and an aromatic
polyester and a layer of polyvinyl chloride compound or
polyurethane will usually have the layer containing the
segmented co-polyester on the inside as the non-conductive
layer. A mechanical mixture of segmented co-polyester and
polyurethane may also be used for one of the layers, usually
the outer layer~ The inner layer of tlle core tube may be
a mixture containing from about 5 to about 95% by weight
polyurethane and 95 to S% by weight aromatic polyester in
; combination with any of the outer layers disclosed herein.
The inner layer may also be a mixture of polyacetal and
polyurethane in combination with any of the outer layers.
In these embodiments, the outer layer contains particles
which are electrically conductive.
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Examples of suitable thermoplastic aromatic
polyesters are "Valox", aromatic polyester sold bv the
General Electric Co., "Tenite", aromatic polyester sold
by Eastman Kodak Co. and "Celanex", aromatic polyester
sold by Celenese Plastics Co.
Any suitable relative proportions of aromatic
polyester such as "Valox" and seomented co-polyester such
as "Hytrel" may be used in the mixtures thereof extruded
to form a layer of the core tube. For example, from
about 5~ to about 60% by weight aromatic polyester such
as "Valox" and 95~ to about 40~ by weight segmented co-
polyester such as "Hytrel" may be used. Any suitable mix-
ture of polyurethane and co-segmented polyester may be used,
but it is preferred to use from abou~ 99~ to about 50% thermo-
plastic polyurethane and 1% to about 50% by weight co-seg-
mented polyester.
Best results have been obtained so far with a
hose having a core tube with an inner nylon surface and
a semi-conductive polyurethane surface so such a core
tube is preferred. However, other polymers which are
resistant to chemical action by the paint may be used for
the inner layer such as a segmented co-polyester such as
"Hytrel" sold by E.I. duPont de Nemours of Wilmington,
Delaware.
The core tube may be adhesively honded to the
surface of the reinforcing material by the application of
an adhesive material or by activating the surface of -the
~ core tube wi-th a solvating or softening agent to form an
- adhesive in situ from the resin on the other surface of
the core tube. For example, a polyurethane surface of
a core tube may be activated by wetting it with a suitable
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polar solvent such as, for example, N-methyl pyrrolidone
or the like. However, it is preferred to apply an
adhesive material such as a solution of polyurethane
between the surface of the core tube and aLdjacent layer
of fibrous reinforcing material because the use of a
solvating agent to solvate the surface disturbs the
uniformity of the distribution of electrically conductive
particles and affects the electrical conductivity of the
semi-conductive polymer layer. The reinforcin~ fibrous
material is then applied under tension about the adhesively
wet core tube whereby the strands of reinforcing material
become embedded and partially encapsulated by the adhesive.
In this way, the fibrous reinforcing layer becomes bonded -
to the core tube and the strength of the hose is improved.
It has been found that simultaneously coextruded
properly selected synthetic thermoplastic polymers will
become bonded together by melt fusion even though one of
the polymers contains particles of electrically conductive
material and that an intermediate adhesive is not necessary.
For example, nylon will fuse to a thermoplastic elastomeric
polyurethane containing carbon black particles if the two
molten synthetic polymers are fed separately to an extrusion
head and coextruded one over the other while still molten.
I In those instances where one layer of the core tube is
difficult to melt fuse to another layer, an intermediate
layer of a third synthetic resin which will melt fuse to
both layers may be interposed therebetween but it is
preferred to melt fuse the semi-conductive layer directly
i
to the inner layer of the core tube.
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Referring now to the drawing, a semi-conductive
~ paint hose 10 having a core tube I.D. of 0.25 inch is
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illustrated in Figures 1 and 2. Composite hose 10 has
a core tube 17 formed by the simultaneous coaxial
extrusion of a layer of nylon 11 about 0.025 inch
thick and a semi-conductive thermoplastic elastomeric
polyurethane outer layer 12 about 0.015 inch thick
and containing carbon particles and having a volume
resistivity at room temperature (about 20C.~ of about
100 ohm-cm. The two synthetic resins become fused
together at the interface to form a core tube 17 which
will not delaminate when the hose 10 is used for conveying
a paint under pulsating pressure. The outer surface of
polyurethane of core tube 17 is wet with an adhesive
solution 13 of a polyurethane in N-methyl pyrrolidone.
A reinorcing layer 14 of nylon filaments is braided
under tension around the core tube while the adhesive `
on the surface of core tube 17 is wet. The filaments
become bonded to the surface of the core tube 17 forming
an elastomeric bond of the fibrous reinforcing material
with the core tube. A second reinforcing layer 15 of
poly(ethylene -terephthalate)ester is braided over layer
1~. A protective p~lyurethane sheath 16 about 0.025
inch thick is e~truded over fibrous reinforcing layer 15
by extrusion of a thermoplastic elastomeric polyurethane
thereover. Sheath 16 may be adhesively bonded to the
surface of layer 15.
Any other core tube similar to those disclosed
as suitable herein may be substituted in the foregoing
embodiment of the invention for core tube 17 and the core
tube I7 may or may not be bonded to the reinorcing layer
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l 30 depending upon the particular requirements of the hose.
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The polyurethane layer 12 of core tube 17 may
be extruded from any suitable thermoplastic polyurethane
such as the one sold under the trademark "Pellethane"
by the Upjohn Company. The polyurethane disclosed in
U.S. Patents 3,116,760 and 3,722,550 and disclosed in the
book by Saunders and Frisch, entitled "Polyurethanes:
Chemistry and Technology", published by Interscience
Publishers, copyright 1964 may also be used. Reaction
products of poly(tetramethylene ether)glycol, suitable
chain extender such as 1,4 butane diol, and 4,4'-diphe--
nylmethane diisocyanate and polyurethanes prepared by
reacting an inner ester such as poly~e-caprolactone~ester
; and a suitable chain extender such as 1,4 butane diol
with an aromatic diisocyanate such as 4,4'-diphenylmethane
diisocyanate are preferred. The sheath 16 may also be
extruded from any other suitable synthetic resin such
as, for example, nylon in some embodiments of the invention.
The fibrous reinforcing material may be formed
by braiding filaments or by helically winding strands
of filaments of any sultable synthetic resinous material,
such as, for example, a poly(alkylene terephthalate)ester,
nylon, aromatic polyamide or the like or combinations
thereof. Suitable nylon fibrous reinforcing material is
disclosed in U.S. Patent 3,334,164 while suitable poly-
(alkylene terephthalate)ester fibrous reinforcing material
is disclosed in U.S. Patent 3,062,241. Such fibers
h~ve a tenacity of about 7 to about 11 grams per
denier and an elongation at break of about 9% to
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about 17%. In one embodiment of the invention, the
hose may be provided with a relnforcing layer of braided
or helically wound filaments having a tenacity of at
least 13 grams per denier and up to about 25 grams per
denier and an elongation at break of ~rom about 2% to
about 7% such as the aromatic polyamide fiber marketed
by E.I. duPont de Nemours & Co. under the trademark
"Kevlar". Suitable reinforcing material containing
synthetic aromatic polyamide filaments is disclosed in
U.S. Patent No. 3,905,398 issued September 16, 1975. A
fibrous reinforcing material of aromatic polyamide fibers
may be used to advantage in composite hoses having a high
burst strength.
The core tube can be shaped by extrusion with
any suitable extrusion apparatus having a separate
extruder for feeding each synthetic thermoplastic resin
to a single extrusion head.
Although the invention has been described in
detail for the purpose of illustration, it is to be
understood that such detail is solely for that purpose
and that variations can be made therein by those skilled
in the art without departing from the spirit and scope
I of the invention except as it may be limited by the claims.
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