Method and apparatus for manufacturing paint rollers

A method of manufacturing paint rollers includes the steps of extruding a cylindrical plastic core through a rotating extruder head, and securing an absorbent sheet material onto an outer surface of the core in a continuous process.

FIELD OF THE INVENTION 
The invention relates to a continuous process for fabricating a paint 
roller having an extruded plastic core and a hellically-wound absorbent 
fabric bound to the exterior surface of the core. 
BACKGROUND OF THE INVENTION 
Paint rollers are and have been commonly used to apply paints and other 
coating materials to surfaces for many years. Paint rollers have a unique 
set of required specifications due to the physical nature of the 
application process and due to the wide range of paints and other coating 
materials that the roller may be exposed to in routine use. Paint rollers 
must have a rigid inner core that is manufactured in a cylindrical shape 
with a high level of precision so that when the paint roller rotates 
relative to the surface to be painted, it coats evenly. The cylindrical 
shape of the roller should not yield, bend or deform under significant 
stress even when the outer fabric has absorbed paint over an extended 
period. Even slight deformation of the roller shape may cause uneven paint 
application. 
A manufacturer of paint rollers must assume that the roller could be 
exposed to any of a wide range of fluid compositions. Some paints are 
water-based and others are oil or solvent-based. Many different pigments, 
solubilizing agents, surfactants, viscosifiers, emulsifiers, etc., are 
used in paints, stains and other surface coating compositions. Ideally, 
the roller core should be inert or at least resistant to all such 
ingredients so that its rigid cylindrical shape is maintained even after 
long periods of use, washing and reuse. A sturdy solvent-resistant core 
yields a longer effective life-time for the roller which is an important 
objective for those who buy and use paint rollers. 
Paint rollers typically have an absorbent fabric material fixed to the 
external surface of the core. The fabric should be uniformly absorbent and 
bonded to the core in a manner which remains in tact when the roller is 
exposed to paint. The fabric must also be applied and bonded to the core 
in a precise and continuous configuration so that there is no overlap or 
gaps in the fabric which could result in a non-uniform paint application 
pattern. 
Various procedures have been used by others to produce paint rollers that 
satisfy to some extent the specifications discussed above. However, a 
significant disadvantage with prior manufacturing processes is that they 
require multiple on and off-line procedures. For example, a desirable core 
material due to its water and solvent resistivity is extruded plastic such 
as polyethylene or polypropylene. Typically the core material is extruded, 
formed and cooled in one process, then put through at least a second 
process where the core is wrapped with fabric. Multiple on and off-line 
processing sequences add to manufacturing costs and manual work 
requirements. Thus, there is a need for a paint roller manufacturing 
method in which a high quality, solvent-resistant paint roller can be 
fabricated in a single continuous on-line process. 
SUMMARY OF THE INVENTION 
The invention provides a method, system and apparatus for manufacturing 
paint rollers through the use of an extruder employing a rotating head so 
that a plastic core can be extruded and rotated simultaneously while other 
process steps including application of an outer absorbent material are 
performed downstream in a single continuous process. The result is a 
reduction in manufacturing cost compared to prior methods, and a high 
quality paint roller product, in particular, a solid rigid core that is 
highly durable and resistant to water and solvents. 
In a preferred embodiment of the invention, a cylindrical polypropylene 
core is extruded. The rotating core then translates through a vacuum 
sizing and cooling chamber. Next, the core passes through a winding and 
pulling station which is coordinated with the drive unit of the extruder. 
The core is subsequently plasma-treated prior to extruding an epoxy 
adhesive layer on the external surface of the core. Finally, the core is 
heated, wrapped with fabric and cut into discrete paint rollers. All of 
the steps are performed in a continuous time- and location-coordinated 
procedure with minimal if any manual involvement.

DETAILED DESCRIPTION OF THE INVENTION 
The invention provides a system and process for producing paint rollers in 
a continuous process including extrusion of a highly solvent resistant 
core and bonding of an absorbent fabric material downstream. The 
continuous processing feature of the invention allows significant 
reduction in manufacturing costs and improvement in overall efficiency and 
product quality compared to prior processes. 
FIG. 1 is a schematic diagram illustrating process steps in a preferred 
embodiment of the invention. The first step 20 involves extrusion of a 
plastic cylindrical pipe or core 21. Extruder 22 receives plastic resin, 
preferably polypropylene, through hopper 24. The plastic resin melts and 
is extruded through rotating head 26 into a hollow cylindrical form, core 
21, that rotates around axis 28, while translating forward at a constant 
velocity, under control of drive unit 29. The size of extruder 22 is based 
on the plastic resin used and the desired output in pounds per hour of 
plastic core 21. In a preferred embodiment of the invention, a 31/2 inch 
24:1 L/D air-cooled Meritt Extruder from Meritt Davis Corporation, as 
shown in FIG. 2, is used along with a rotating extruder head, as shown in 
FIG. 3, from Guill Tool & Engineering Company of Rhode Island. 
Further details of extruder 22 and head 26 are illustrated in FIGS. 2 and 
3. FIG. 2 shows extruder 22 including hopper 24 at one end for receiving 
raw materials such as polypropylene pellets or particles for subsequent 
melting and extrusion through rotating head 26, as shown in FIG. 3, which 
is attached to output end 30 of extruder 22. FIG. 3 is a drawing of 
rotating head assembly 26 including die 31 that defines the outer diameter 
of extruded core 21, and tip 32 that defines the inner diameter of 
extruded core 21. The gap between die 31 and tip 32 defines the thickness 
of core 21. Sprocket or gear 33 facilitates rotation of die 31 and tip 32 
around rotational axis 28. Seals 34 prevent melted material from reaching 
bearings 35 that are used to permit smooth rotational movement of die 31 
and tip 32 relative to the outer housing. In the present invention, die 31 
and tip 32 rotate at approximately between 100-140 rpms. 
Rotating head 26 is powered by SCR drive motors in drive unit 29 to drive 
both die 31 and tip 32 of head 26 to allow for the extrusion to be rotated 
in an exact relationship to the forward movement of the extruding core. 
Controls are used to maintain a plus/minus ratio of 0.01-percent between 
extruder 22 and head 26. This allows for maximum control of the helical 
angle at which the core rotates in relation to the forward motion of the 
core to assure a uniform seam at the fabric application station 
downstream. Preferably, core 21 moves 3.375 inches of lineal forward 
movement per 360 degrees of rotation of the core. This is required to 
accommodate the 2.875 inch slit width fabric used to cover the core 
downstream. The motors that control the rotation of head 26 are adjustable 
for fine tuning to assure proper butting of the seam in the fabric 
application step of the process. 
In the second step 37 of the process shown in FIG. 1, plastic core 21 
enters a vacuum sizing and cooling tank 38 where a vacuum is applied to 
the exterior of core 21 along with chilled water spray that cools core 21 
down to a "Freeze Point" of about 225.degree. F. This is the point at 
which full stability is achieved in the plastic. The dimensions are set 
with a tolerance of +/-0.005 inch to the outside and inside diameters. 
Typically the inside diameter of the paint roller is 1.485 inches. The 
wall thickness is 0.045 inch with larger walls as required by the 
professional market. 
FIG. 4 shows a perspective view of vacuum sizing and cooling tank 38. 
Vacuum sizing and cooling tank 38 can be procured from Extrusion Services, 
Inc. of Akron, Ohio. Tank 38 employs a stainless steel tunnel or chamber 
39 through which the core translates after extrusion. Polypropylene core 
21 is approximately 500.degree. F. when it exits head 26 of extruder 22. 
By the time the core reaches entry end 39a of chamber 39, core 21 has 
cooled to approximately 400-450.degree. F. Water jets or spray inside 
chamber 39 continue to cool core 21 so that by the time it exits output 
end 39b of chamber 39, core 21 is approximately 200-225.degree. F. 
In the third step 40, as illustrated in FIG. 1, core 21, after traveling 
approximately 2-3 feet from output end 39b of chamber 39, enters guide 42 
made of a hollow steel mandrel that has an inside diameter of 0.010 inches 
larger than the outside diameter of plastic core 21. The length of guide 
42 is about 30 inches. The end of guide 42 is located within approximately 
2 inches from the leading edge of winding belt 44. Belt 44 is configured 
to pull and continue rotation of plastic core 21. Winding belt 44 is 
controlled by drive unit 29 of extruder 22 so that winding belt 44 
precisely maintains the rotation rate and translational velocity of core 
21 to match the rate at which core 21 is exiting and rotating from 
extruder 22. After core 21 exits winding belt 44, it enters a second 
hollow steel guide 46 of the same diameters as first guide 42. This allows 
core 21 to be properly aligned and positioned for the next step. 
Coordination of the rotational drive functions of extruder head 26 and 
winding belt 44 on opposite sides of cooling chamber 38 is an important 
feature of the invention because it allows core 21 to be rotated, in sync 
with fabric wrapping downstream, without deformation of the core's 
cylindrical shape even when core 21 is somewhat fluid as it exits extruder 
22. 
In the fourth step 50 of the process illustrated in FIG. 1, the external 
surface of core 21 is treated with high voltage electrical plasma in order 
to attract and accommodate adhesive applied in the next step of the 
process. In a preferred embodiment a surface treater obtained from 
Intercon Industries Corporation of Wisconsin is used. The surface treater 
employs a corona discharge head including two electrodes that generate an 
air blown electrical arc to form a treatment plasma. The corona discharge 
electrodes are positioned approximately 1/4 inch away from the external 
surface of rotating core 21. The plasma treatment increases the surface 
energy and tension on the outer surface of plastic core 21 which allows 
easier application and improved adhesion of epoxy in the next step. As 
shown in FIG. 5, surface treater 52 employs corona discharge head 53 which 
includes electrodes 54 and 56. Electrode 54 generates a plasma treatment 
area 57 that is elliptical in shape on the external surface of core 21 as 
it rotates and translates past surface treater 52. Similarly, electrode 56 
generates a plasma treatment pattern 58 on the external surface of core 21 
adjacent plasma treatment pattern 57. Other numbers of heads, electrodes 
and combinations of treatment patterns can be used. The important thing is 
that, given the rates of forward movement and rotation of core 21, the 
overall treatment should totally cover the external surface of core 21. 
Between plasma treatment step 50 and the next step 60, as shown in FIG. 1, 
core 21 should have at least about 3-4 seconds to react before application 
of epoxy in step 60. A thin layer of epoxy is applied to the surface in 
step 60. This is accomplished by use of gear pumps for both the "a" and 
"b" resins, driven by an SCR-type motor which extrudes a thin film of 
epoxy onto the surface of plastic core 21. Adhesive resins which work well 
for this application are sold under the trademarks MASTER 5200A and 5200B, 
and MASTER GRIP 5200A and 5300B, which are available from Fielco 
Industries of Huntingdon Valley, Pa. 
FIG. 6 illustrates an epoxy extrusion unit for dispensing a thin layer of 
epoxy resin, parts A and B, on the external surface of core 21. A 
cross-section of core 21 is seen in FIG. 6 with its axis of rotation 
perpendicular to the page. Core 21 is held against V-block 22, in part, by 
the fabric wrapping unit downstream. A doctor blade or knife bar 23 is 
positioned near the external surface of core 21 for the purpose of 
metering the thickness of the adhesive layer being applied to core 21. The 
thickness of the extruder adhesive layer is preferably approximately 3-5 
thousandths of an inch. Subparts of the adhesive are combined and mixed in 
dispenser 24 prior to dispensing the adhesive through tip 25 near the edge 
of doctor blade 23. 
Once the film is applied, it is heated to 300.degree. F. by use of a 
parabolic infrared heater in step 70. This allows the epoxy film to 
rapidly set so the continuous core can be cut in a short amount of time. 
Fabric is introduced in step 80 at the proper helical angle to match the 
angle of core rotation originally established by extruder 22 and rotating 
head 26 at the beginning of the process, and as perpetuated by winding 
belt 44 in the third step 40 of the process. The fabric is guided onto the 
core by use of a fabric stand and tensioning device. The tension on the 
fabric is preferably about 5-7 pounds to assure that the fabric is 
embedded into the epoxy film. Core 21 travels approximately 30 feet after 
fabric winding step 80 to accommodate completion of epoxy curing. 
Finally, in step 90 fabric-covered core 21 enters traveling cut-off saw 92 
which is programmed to cut the core into pre-selected lengths. The cut 
cores are discharged onto an accumulation table. The core lengths are then 
ready to be processed into finished lengths and packaged.