Note: Descriptions are shown in the official language in which they were submitted.
~ .....
Attorney Docket No.: NEW-408-CIP-3
METHOD AND APPARATUS FOR MANUFACTURING PAINT ROLLER
AND PRODUCT PRODUCED THEREBY
FIELD OF THE INVENTION
The present invention relates generally to the manufacture of composite
thermoplastic products
and more specifically to an improved method of manufacturing paint rollers and
the product
produced thereby. More particularly, the present invention relates to methods
far conditioning the
surface of a thermoplastic tube to receive a variety of adhesives, which
includes thermoplastic and
thermosetting adhesives, suitable for adhering a thermoplastic compatible
fabric strip to the
thermoplastic tube which, for purposes of illustration, will be a
thermoplastic paint roller core such
as, for example, polypropylene which is the current material of choice in the
paint roller industry.
BACKGROUND OF THE INVENTION
Currently in the manufacture of paint rollers, strips of pile fabric are used
which are wound
around a plastic or cardboard tube or core. More specifically, among the
devices currently employef
is a type of machine illustrated in Spanish Utility Model No. 293,980, filed
on May 6, 1986, and
2p granted on September 1, 1986, which includes a rotating cylinder over which
the cardboard or plastic
tube is mounted, and onto which a strip of pile fabric is applied through a
guide oriented obliquely and
situated on and carried by a carriage
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which is mounted in fixed fashion over a sliding apparatus. The bonding of the
tube and strip of
pile fabric is accomplished either by the application of adhesive material in
the case of a cardboard
tube or, in the case of a plastic tube, gas flame heating by which gas burners
heat the tube to bond
it to the strip of pile fabric, thereby forming a single body.
In the first case, i.e., where conventional adhesive is used as the means of
bonding between
the cardboard tube and strip of pile fabric, the manufacture of paint rollers
presents significayt
problems, all resulting from the difficulty of applying the adhesive
uniformly, plus the fact tha
very specific adhesives must be used to produce the bond between the cardboard
tube and the strip
of pile fabric so that, when the rollers are used, these adhesives do not
separate due to the solvents
contained in the paint and in the fluids used to clean the roller.
These problems considerably increase the cost of manufacturing paint rollers
because of the
cost of the adhesives and the time needed for the adhesives to harden.
The second system mentioned above, though a significant advance in the art
over what had
been earlier used, does present certain problems, all resulting from the
increased safety cost;
required by installations that use gas as a fuel source for the gas flame
heating. Further, thf;
heating of the plastic tube can produce undesirable products of combustion and
high noise, both
effects being potentially harmful for the operators and expensive to
eliminate; all of this thereforf;
has the result of raising the cost of the final product.
SUMMARY OF THE INVENTION
The object of the present invention is a procedure for manufacturing paint
rollers and the;
product produced thereby, of the type in which a strip of pile fabric is wound
helically over a
plastic base structure, such as a tube or core, preferably formed from a
thermoplastic material sucy
. ~
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as polypropylene, with an adhesive substance interposed there-between, with
the result that the sitrip
of pile fabric and the plastic base structure form a single, integral
composite end product.
Specifically, an intermediate thermoplastic adhesive substance is applied onto
a plastic tube
in the area adjacent to the area of the winding of a fabric strip on the tube,
the adhesive substance
being heated. If the adhesive substance is molten it may be applied through a
nozzle connected
to a reservoir where the thermoplastic adhesive is heated, which nozzle is
mounted on a carri,~ge
on which the pile fabric strip applicator is also located. Suitable adhesives
include polypropylene,
polyethylene, a mixture of polypropylene and polyethylene, any of a variety of
polyamieles,
polyolefin based compounds, polyester based compounds, polyurethane based
compounds,
polyamide "hot melt" adhesives sold under the designations HB FULLER HOT
MELT(TM) 6542-PE;L
and HL2021, HOT MELT(TM) 2167PL, epoxies, urethanes and other suitable
adhesives compatible
with a thermoplastic tube, such as a polypropylene tube, a polyethylene tube,
a nylon tube, or a
combination of polypropylene and polyethylene, and resistant to the
anticipated solvents found in the
paint, stain, shellac or varnish and the solvents used to clean the roller.
The anticipated solvents
include turpentine, mineral spirits, aliphatic compounds, ketones or aromatics
in petroleum based
solvents including naphtha, chlorinated hydrocarbons, alcohol based solvents,
acetone, toluene arid
water including soapy water and ammoniated water.
Chemically, polypropylene (PP) is very inert and very difficult to bond,
because the structure
is all C-H bonds. There are no adhesives available that can chemically break
the very strong C-H
bonds, and there are no other bonding sites available on PP. This lack of
bonding sites and 'the
geometry of the chains, which makes the PP so unbondable, is reflected in the
physical
measurements of contact angle 87° and surface energy 29 dynes/cm. These
are similar to the
contact angles and surface energies of fluorocarbons, like Teflon, which.range
from 79-96° contact
angle and 22-37 dynes/cm surface, energy, which means PP is like fluorocarbons
in being virtually
unbondable.
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In general, the lower the contact angle, the more wettable the surface. Some
surfaces are so
wettable that a contact angle can not even be measured. The reverse is true
for surface energy --
the higher the value, the more wettable or bondable the surface is. The
surface energy can be lab
tested using a series of test solutions. For a surface, typically, to be
considered bondable, the
contact angle needs to be <40 ° and the surface energy needs to be >70
dynes/cm. This is a general
rule for clean surfaces, but is not absolute. This is not always true because
the surface layer of
the material is not always well bonded to the substrate. Two examples are rust
on iron and an oily
layer on a metal; the contact angle could be unmeasurable, but a strong,
permanent bond will not
be made. This is because the rust and the oil are not strongly bonded to the
base material,
resulting in a very weak boundary layer. But it is true to state that unless a
material's contact
angle and surface energy are in the bondable range, an adhesive will not work.
To achieve a
strong bond with a material not in range, the surface of that material must be
modified to lower
the contact angle and increase the surface energy.
Therefore to bond to polypropylene, the PP must be changed to make it more
bondable. The
key is to change the surface to make it more wettable/bondable (lowering the
contact
angle/increasing the surface energy), while retaining a strong boundary layer.
Then once the
surface is modif ed, almost any adhesive can be used -- the final bond
strength will be determined
by the effectiveness of the surface modification method and adhesives.
For adhesion, modification of the surface characteristics can be achieved by
either (or both)
mechanical and chemical methods. Mechanically, the surface can be roughened
(to add more
surface area, thereby reducing contact angle). There are a variety of chemical
methods: 1)
chemical etching (a very traditional method, such as an acid etch); 2) priming
(where the primer
is more aggressive than the adhesive -- basically, another form of etching);
3) flame treating
(where the surface is lightly burned so there are now functional sites
available -- too much burning
could cause a charred layer which may be a weak boundary layer); 4)
electrically treating (using
high voltage energy -- plasma or corona -- or high intensity light energy ~ -
~V -- to break the
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strong bonds, allowing these sites to react with an adhesive, the local
oxygen, or other gases in the
immediate area); 5) ozone treating (where the highly reactive ozone can attack
the surface breaking
bonds and allowing the oxygen in the ozone to bond) -- this method can be
enhanced if used with
UV light (note this is easy as UV damps in air will produce ozone gas); or G)
chemical grafting
either using plasma or a chemical reactive (adding a layer of another chemical
having a more
optimal functional group for the bonding application). The effectiveness of
the methods differ
depending on the material being treated, the processing time, and the
treatment.
Mechanical roughening is not a viable option for PP,.because the surface
energy is so very low
even with the resulting increased surface area. Neither is flame treatment
effective, because PP
melts at such a low temperature. There are primers available, but they are not
as effective as other
methods, because to be effective they must be very aggressive to break the C-H
bonds. Chemical
primers generally are just not aggressive enough for PP, a chemical etch is
better. Chemical (arid)
etching and grafting, and electrical and UV/ozone treatments are the most
effective to varying
degrees depending on the process and the required results. Corona only reduces
the angle to ~?~5°.
An ozone/LTV treatment will reduce it to near 30°. Plasma, plasma
grafting, and chemical grafting
are the best methods; some processes reducing the contact angle to
approximately 20°.
Another object of the present invention is the provision of a paint roller
which is structurylly
integral as a result of the bonding of the adhesive with the strip of the pile
fabric and the plastic
tube.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated more or less diagrammatically in the accompanying
drawing
wherein:
Figure 1 is a side view, partially in section and with standard components
indicated
diagrammatically, of a method of producing a plastic paint roller;
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Figure 2 is a side view, partly in section. of an alternative method of
producing a paint roller;
Figure 3 is a side view of a plasma jet discharge head usable in the
embodiment of Figure 1;
Figure 4 is a right end view of Figure 3;
Figure 5 is a top view of the current input box for the discharge head which
connects khe
discharge head to the power unit;
Figure 6 is a plan view of an alternative embodiment in which a plastic tube
is mounted over
a rotating roller and the strip of pile fabric is wound helically and further
including a movable
carriage on which are situated the applicator of the pile fabric strip and the
nozzle for applyiing
thermoplastic adhesive in a molten state;
Figure 7 is a plan view of an alternative embodiment in which a plastic tube
is mounted on
a rotating roller which is moved longitudinally by means of a drive unit, the
strip of helica.lly
wound pile fabric and the applicator of the thermoplastic adhesive in a molten
state being locaked
on a fixed carriage;
Figure 8 is a section view of either of Figures 6 or 7 showing a section of
the roller already
constructed, wherein the strip of pile fabric, the thermoplastic adhesive and
the plastic tube form
a single body; and
Figure 9 is a side view, partly in section, of a further embodiment of the
invention in which,
if desired, a supporting mandrel may be dispensed with.
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DETAILED DESCRIPTION OF THE INVENTION
Referring first to the embodiment of Figure 1 a supporting mandrel is
indicated at 10, thc:
mandrel being supported in suitable bearings, not shown. A plastic tube, which
forms thf°
structural core of the final product, here a paint roller, is indicated at 11,
the core being driven irr
the direction of arrow 12 by any suitable means, such as a conventional Ford
drive, indicated
diagrammatically at 19, located near the left end of the processing sequence
shown in Figure 1.
The tube may be composed of any suitable thermoplastic material such as
polypropylene,
polyethylene, polyamides, polyolefms or mixtures thereof. For paint rollers
polypropylene is the,
industry's material of choice. The core may be either cold or heated as it
enters the processing
steps to be subsequently described hereafter. If heated to the point where
cooling to root'
temperature will cause an internal dimensional contraction, the mandrel 10 may
be slightly tapered
in a leftward direction to accommodate the shrinkage. If possible the core
should be heated so a5
to decrease the additional heat energy which must be supplied to complete the
processing.
An adhesive substance, here a thermoplastic material in strip form which is
compatible in <~
bond and strength sense with the core and fabric which will later be added, is
indicated at 15. The,
adhesive substance, which may for example be polypropylene or any one of the
other substance;
above mentioned in conjunction with the core, or slight modification thereof,
is fed from a suitablf;
source of supply and is wrapped around the core in such fashion that the laps
butt snugly against
one another.
Preferably, though not essentially, the adhesive substance is at an elevated
temperature to
facilitate bonding to core 11. In this instance a process is illustrated in
which supplemental hea
energy is added to the core to ensure good bonding between the core and the
adhesive substance.
The supplemental heat energy may be supplied by any suitable means such as
flame burners;
electrical resistance heating, radio frequency, infra red, quartz, induction,
ultrasonic or plasma jest
electrical discharge means. Mere the latter has been illustrated, said plasma
jet system consisting
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_g_
of a power unit, indicated generally at 16, and a discharge head, indicated
generally at 17, thfa
discharge head being connected to the power unit by leads 18. It should be
understood that thE;
ultimate objective of insuring a good bond between the adhesive substance and
the core is a matteir
of proper selection of the above described heating forms. Thus, if the core 11
has a high hear
content, as it would if it were freshly extruded at a location just to the
right of the right end of
Figure l, and the adhesive substance 15 was also either freshly extruded, or
freshly heated, the jek
plasma or alternate heating system may be omitted. If on the other hand the
core 11 is cold, that
is, at room temperature at the start of the process, then the use of the
plasma jet or alternatf;
heating system will probably be essential. It may be most convenient to use
the adhesive substance
in coil form at room temperature. In this event the adhesive substance 15 may
have its outeir
surface, that is, the surface which will subsequently come in contact with the
pile fabric, heated,
or, if desired, just the inner surface, or both, heated. Any one of the
foregoing heating system:
may be used, the selection of which one dependent on operating parameters
pertaining to eac~i
installation, including cost. In essence, the heating sources used and the
extent to which they arE;
15 used, can be tailored to the conditions which are present in each factory,
and those basic operating
conditions - space, power availability, economies of production inherent in a
given location, etc.
- will vary from factory to factory.
A pile fabric in strip form is indicated at 20, the fabric being wrapped about
the core-adhesive
substance structure, indicated generally at 21, in such fashion that the
individual wraps butt tightl~~
against one another.
Again, the primary objective is to form a tight bond between the back side of
the fabric and
the structure 21. Although heating the back side of the fabric 20 may be
feasible in some cases9
this is not usually preferred due to possible over heating and consequent
degradation of the fabric;
pile. If the surface temperature of structure 21 is hot enough and,
preferably, the surface of thE,
wrapped adhesive soft enough to be flowable into the interstices on the back
side of the fabric, nc>
additional heat may be required and a good bond formed merely by the pressure
contact between
CA 02178360 2002-03-28
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the fabric and structure 21. If the surface temperature of structure 21 is not
hot enough, heat from
a supplemental heat source, which may be any one of the above described means,
i.e., flame
burners, electrical resistance heating, radio frequency, infra red, quartz,
ultrasonic, or plasma jet
electrical discharge, may be added to the surface of structure, 21 prior to
application of fabric 20.
A press shoe or press roller may be used, if required, to ensure good pressure
contact between the
fabric and structure 21.
If core 11 is part of a continuous process, as it would be if the core is
extruded upstream from
the processing steps illustrated in Figure 1, a conventional traveling cut-off
mechanism may be
used to separate the continuous formed structure 22 into discrete roller
lengths suitable, if need be,
for further processing such as edge trimming; see Figure 7. It should also be
noted that if mandrel
10 is stationary and core 11 is to be rotated, it may be more convenient to
use a drive system, such
as Ford drive 19, in contact with the core 11 at a location just to the right,
i.e., upstream, of the
discharge head 17. In this arrangement, any possible stretching of the core or
other components which
might occur from the illustrated placement of Ford drive 19 would be
eliminated.
I S If, on the other hand core 11 is a discrete length as it would be if pre-
made and stored until
wrapping is required, a cutting mechanism can be omitted or performed
sequentially, but
separately, from the illustrated forming process.
An alternative form of the invention is illustrated in Figure 2 in which the
adhesive substance
is formed as a separate envelope, such as by extrusion about the core.
A mandrel is illustrated at 10 and a core at 11. The mandrel may rotate,
carrying the core 11 with
it in the direction of the arrow 32. Alternatively, the mandrel may be
stationary and the core, in
effect, pulled in the direction of arrow 32 by a drive mechanism, such as a
conventional Ford drive
system indicated generally at 19 and located near the end ofthe processing
sequence and after fabric
has been applied.
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An adhesive substance, in this instance an envelope which has, preferably,
though not
necessarily, been extruded at the right end of the processing sequence, is
indicated at 34. The
displacement of the adhesive substance envelope 31 away from the core 11 has
been somewhat
exaggerated to indicate the recent formation thereof and its capacity for
shrinkage about the core
31 to form a good bond with the core. It should be understood that the
envelope 34 may be quite
structurally sound with only its interior surface, at least, heated, or it may
be in a mushy or barely
self supporting state depending on its heat content. Preferably the surface of
core 11 is heated, as
it would be for example if it was freshly extruded, or heat may be applied to
a room temperature
or insufficiently hot surface by flame burners, electrical resistance heating,
radio frequency, infra
red, quartz, induction, ultrasonic, the plasma jet system of Figure 1, or any
other suitable form of
heating or surface preparation including chemical priming of the type
disclosed in the "Chemical Priming
for Extrusion Coating" by Roger Isbister on page 101-104 of the May, 1988
issue of the TAPPI
Journal.
After adhesion of the envelope 34, whether in structurally solid and strong or
in near molten
condition, to core 11; a base structure 36 is formed. Immediately after
formation of base structure
36, fabric 20 in strip form is wrapped therearound in such fashion that the
edges of adjacent wraps
abut against one another to form a peripherally continuous fabric surface.
Again a press roller or
press shoe may be employed to apply pressure to the fabric-base structure
junction. As mentioned
above, the fabric backing may be heated, though this may not be expedient in
all environments.
Again, no supplementary heat may be needed to ensure a good bond between base
structure 36 and
fabric 35 but it will usually be advantageous to apply supplemental heat to
the exterior of base
structure 36 just upstream of the junction of fabric 20 with the base
structure to ensure a good
bond. If envelope 34 was near molten or very hot and tacky when it came in
contact with core
11 , only a modest amount of supplemental heat may be needed to ensure a good
bond. Again, the
operating parameters will vary from installation to installation and the
processing sequence
disclosed herein will have to be adjusted accordingly. If supplemental heat is
required, flame
burners, electrical resistance heating, radio frequency, infra red, quartz,
induction, ultrasonic or jet
CA 02178360 2002-03-28
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plasma heating -may be employed, with or without chemical priming, to ensure
the primary
objective of a good bond.
The plasma jet heating system illustrated diagrammatically in Figure 1 is
illustrated in greater
detail in Figures 3-S. The discharge head 17 includes a head 40 having a
discharge end
41. A mounting plate is indicated .at 42, tl~e mounting plate having a
connector 43 which receives
the lead 18 which extends from the power unit 16. A junction box is indicated
at 44, said junction
box being secured to mounting plate 42 by bolts 45, and it has two pairs of
sockets 46, 47 for
auxiliary uses. A blower is indicated at 48. It will be understood that said
plasma jet system may
be of conventional construction such as those available from Corotec
Corporation, Collinsville, CT
as model nos. PJ-11, -12, -21, -22, all 120V and 2, 4 or 8 amps at 60Hz. PJ-11
has an
output/discharge of, for example, lOKV, 25mA, and 60Hz. The power unit
converts incoming
single phase 120 volt power to the high voltage necessary for plasma
discharge. The discharge
head utilizes a high performance brushless DC blower which moves air across
the electrodes at a
rate which is controlled and monitored by the power unit.
ror bonding polypropylene, in a roller cover application, using traditional
thermoset adhesives
such as epoxies and urethanes, the PP must be surface modified as mentioned
earlier. rrom a
manufacturing standpoint, in-line corona or UV/ozone treaters are available.
The more effective
plasma treatments and plasma grafting are usually done in a vacuum, so large
cores should be done
in batch processing units, then bonded with an adhesive to the fabric in a
separate step. Chemical
grafting would also probably be a batch process.
Figure 6 illustrates a system having a rotating mandrel 50 on which the
plastic tube 11 is
mounted. A carriage is indicated at 52 which, in rigure 6, is movable parallel
to the longitudinal
axis of the rotating mandrel. The carriage 52 includes a feed mechanism not
shown, for pile fabric
strip 20 which is helically wound around the plastic tube 11.
CA 02178360 2002-03-28
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Initially a pre-formed plastic tube 11 is mounted over the rotating mandrel 50
and thereafter
the strip of pile fabric20 is wound helically over the plastic tube 11 through
the applicator located
on the movable carriage 52.
The fundamental feature of the procedure illustrated in Figures 6-8 for the
manufacture of
S paint rollers consists of applying a thermoplastic adhesive in a molten
state onto the area of the
plastic tube 11 where the strip 20 will be closely wound. It will be
understood that the specific
thermoplastic adhesive material applied to the junction region between the
tube and fabric is not
critical to the invention. However, it must be compatible with the plastic
tube selected, the pile
fabric and the solvents contained in the paint, stain, varnish or shellac as
well as the solvents used
to clean the roller if the roller is the reusable type. The thermoplastic
adhesive is applied by the
outlet mouth of a nozzle 54 mounted over the movable carriage 52, which nozzle
54 is connected
to a reservoir where the thermoplastic adhesive is heated.
In the embodiment of Figure 7, the plastic tube 11 is mounted over a rotating
roller 55. The
plastic tube may be moved longitudinally by a drive unit 56, while the
carriage 52 and the rotating
roller SS remain axially fixed.
The systems of Figures 6 and 7 each include a cutter 57 which produces the
roller units in a
condition ready for the subsequent assembly of the handle, axis and cap. In
the embodiment of
Figure 6, the cutter 57 does not move horizontally when cutting. In the
embodiment of Figure 7
it will be understood that the cutter 57 will be arranged to move in
synchronism with the horizontal
movement of the tube 11 when cutting.
The embodiment of Figure 9 illustrates a system in which a mandrel is not an
essential
component, though it may be used as a precautionary measure. A plurality of
pre-made cores are
indicated at 60 and are fed to the system by a suitable race and delivery
system, not shown. A
support for the continuous core forming station is indicated generally at 61,
the support including
CA 02178360 2002-03-28
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a trough member 62 with which each core 60 makes initial contact. A welder is
indicated at 63
which functions to join adjacent cold tubes 60a and 60b together by a butt
weld at joint 64. The
welder may be a sonic welder, a flame melt welder, or any other type capable
of forming a solid
junction. The welder is moved to the right during the welding process since
the core and its
subsequent accretions move continually to the right as indicated by arrow 65.
A drive system, here a conventional Ford drive, is indicated generally at 19.
Since the cores 60 will either be cold, i.e., at room temperature, or only at
a slightly elevated
temperature, a preheater or surface treater may be required. Here such a
preheater or surface
treater is indicated at 67. It may be any of the above described types since
its purpose is to
condition the surface of the now unitary core 68 to bond tightly to an
adhesive substance. A
corona discharge or plasma jet system may be especially efficient.
An adhesive substance dispenser is indicated generally at 69. The dispenser
dispenses a
suitable adhesive substance, such as liquified polypropylene, polyethylene or
other bond forming
substances compatible with the unitary core 68 and the later applied pile
fabric. In this instance
the adhesive substance is dispensed through a ring type of extruder, indicated
at 70, which forms
a layer of the adhesive substance, indicated at 71, on the unitary core 68.
A strip of pile fabric is indicated at 20, the fabric being joined to the
coated core while the
layer 72 of the adhesive substance is still hot and tacky enough to form a
tight bond with the
backing of the fabric. It will be understood that supplemental heat may be
applied downstream
from the extruder 70 and upstream from the core-fabric junction if, without
it, the outer surface
of the layer 71 has cooled too low to form a good bond.
Another support is indicated generally at 73, this support including a trough
74 which is
slightly larger than trough 62 since trough 78 must accommodate the larger
diameter composite
CA 02178360 2002-03-28
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product 75 which inchtdes the layer of adhesive substance 20 and pile fabric
72. A traveling cut-
off is indicated at 74.
All of the above described systems produce a composite paint roller due to the
bonding
produced between the plastic tube and the strip of pile fabric, together with
the interposition of a
compatible adhesive substance which is capable of forming a strong bond. The
exact temperatures
used in the processes will of course vary slightly from material to material
and other factors unique
to a specific operation as will be readily apparent to one skilled in the art.
The preferred adhesive substances include polypropylene, polyethylene, a
mixture of
polypropylene and polyethylene, one preferred mixture having a
polypropylene:polyethylene ratio
of about 80:20, polyamide or a mixture of polyamides, polyolefin based
compounds, polyester
based compounds, polyurethane based compounds, polyamide "hot melt" adhesives
sold under the
designations HB FULLER HOT MELT(TM) 6542-PEL and HL2021 and HOT MELT(TM)
2167PL as
well as other suitable adhesives compatible with a plastic tube which may be
fabricated from
polypropylene. Alternative materials for fabricating the core include other
polymeric materials including
polyethylene, a mixture of polyethylene and polypropylene, polyethylene with
added talc, polyester and
other plastics. The adhesive substance must also be compatible with the
plastic tube and pile fabric, and
be resistant to the anticipated solvents used in connection with painting.
These solvents include water,
water with ammonia, soapy water, mineral spirits, turpentine, aromatic
compounds, aliphatic
compounds, alcohols, ketones, acetone, toluene, chlorinated hydrocarbons and
other solvents
foreseeabiy used with paint, including both water and oil based paints,
shellac and varnish.
Although several embodiments of the invention have been illustrated and
described, it will at
once be apparent to those skilled in the art that modifications and
improvements may be made
within the scope of the invention. Accordingly it is intended that the scope
of the invention not
be limited by the foregoing exemplary description, but only by the hereafter
appended claims.
