Method for painting window lineal members

A method for painting a plastic lineal member comprises heating the surface of the lineal member to a temperature greater than about 130.degree. F., coating the lineal member with an aqueous solution, drying the lineal member, painting the lineal member, and curing the paint on the lineal member.

TECHNICAL FIELD 
This invention relates to painting elongated or lineal members, 
particularly such lineals members as are useful for making window sashes 
and window frames. In one its more specific aspects, this invention 
relates to the preparation of the surface of plastic lineal members in 
order to be in the best possible condition for receiving a coat of paint. 
BACKGROUND ART 
In the manufacture of lineal members, it is well known to use an 
electrostatic spray painting process to paint the members. The lineal 
members can be pultruded members or other types of elongated work pieces. 
For example, the lineal members could be wood molding strips which are 
sprayed with a varnish solution in a continuous process. Other lineal 
members have a plastic surface. Examples of these are pultruded members, 
extruded members, and other inline molded lineal members. An example of 
these is a lineal used in a fiberglass window frame, i.e., a lineal 
comprised of a glass wool core and a hard resinous outer coat. 
Electrostatically painting these inherently nonconductive surfaces creates 
some problems. One of the solutions to enable an electrostatic painting 
process to be successful on a non-conductive product is to bury a 
conductive wire or web beneath the surface of the lineal member. The 
conductive material could then be grounded to provide an electrically 
attractive force for the charged paint particles in an electrostatic 
painting process. Another solution to the problem is to coat the lineal 
with a conductive solution, particularly a salt solution, which, when 
evaporated, will leave salt ions on the surface of the lineal. The salt 
ions remaining on the surface provide a sufficient conductive layer in 
order to act as a ground, thereby attracting the charged spray painted 
particles. 
It has been found that when a plastic surface is to be spray painted, the 
use of a solvent as the carrier for the salts to be applied to the surface 
is very advantageous. The solvent evaporates quickly, and enables the 
conductive solution to disperse and spread uniformly on the surface of the 
lineal, thereby evenly distributing the salt ions on the lineal surface. 
Unfortunately, the use of a solvent based conductive solution in 
preparation for an electrostatic painting process has some drawbacks. The 
solvents are potentially hazardous materials, and their use results in 
health and safety issues, and hazardous waste disposal penalties. Attempts 
to replace the solvent based conductive solutions with aqueous conductive 
solutions have not been successful. Aqueous solutions do not disperse as 
uniformly as solvent based solutions on the surface of plastic lineals. 
Also aqueous systems do not dry as readily as the solvent based conductive 
solutions. 
It would be useful to have a non solvent-based carrier for the conductive 
solution, while still maintaining the solvent advantages of dispersibility 
on the lineal surface and quick evaporation of the carrier medium. 
DISCLOSURE OF THE INVENTION 
The present invention is directed to a method for applying an aqueous 
conductive solution which avoids the problem of the systems heretofore 
known for applying a conductive solution to a plastic lineal member. The 
method comprises heating the lineal member to a temperature of at least 
130.degree. F. prior to the application of the conductive solution. It has 
been found that when the lineal member is heated, preferably to at least 
140.degree. F., the aqueous solution readily disperses uniformly, and the 
heat of the lineal member causes the aqueous medium to evaporate from the 
surface rather quickly. 
According to this invention, there is provided a method for painting a 
plastic lineal member comprising heating the surface of the lineal member 
to a temperature greater than about 130.degree. F., coating the lineal 
member with an aqueous conductive solution, drying the lineal member, 
painting the lineal member, and curing the paint on the lineal member. 
In a particular embodiment of the invention, the surface of the lineal 
member is heated to a temperature within the range of from about 
135.degree. F. to about 190.degree. F. In a preferred embodiment of the 
invention, the surface of the lineal member is heated a temperature within 
the range of from about 140.degree. F. to about 160.degree. F. 
In yet another embodiment of the invention, the surface of the lineal 
member is abraded prior to the coating step. The abrading step can be 
carried out by washing the surface of the lineal with water and aluminum 
oxide particles. Most preferably, the surface is washed with a mixture of 
water, aluminum oxide and glass beads. 
The aqueous conductive solution is preferably a saline solution, and in a 
specific embodiment of the invention, the solution comprises calcium 
chloride, lithium chloride, and ethoxylated nonyl phenol. 
In an alternate embodiment of the invention, the aqueous conductive 
solution itself can be heated, rather than having the lineal heated, in 
order to provide the beneficial effect of uniform dispersement of the 
conductive solution and rapid evaporation of the aqueous medium. 
Preferably, the conductive solution is heated to a temperature greater 
than about 140.degree. F. It is believed that the heating of the lineal 
member, or the alternatively, the heating of the conductive solution 
itself, causes a change in the surface tension of the solution and makes 
it wet the surface more uniformly. 
In a specific embodiment of the invention, the conductive solution is 
heated to a temperature within the range of from about 150.degree. F. to 
about 200.degree. F. In a preferred embodiment of the invention, the 
conductive solution is heated to a temperature within the range of from 
about 160.degree. F. to about 190.degree. F.

BEST MODE OF CARRYING OUT THE INVENTION 
As shown in FIG. 1 the lineal members 10 are carried through the various 
process stations by conveyor 12. The conveyor can be any suitable means 
for conveying the lineal members through the process steps. For purposes 
of explaining the method of the invention, a process for painting a lineal 
comprised of a glass wool core and a hard resin outer coat of thermoset 
polyester will be described. It is to be understood that other lineal 
members having plastic outer surfaces can be painted according to the 
method of this invention. 
One of the first process steps that the lineal is subjected to is the step 
of abrading the surface of the lineal. The lineal passes through washing 
booth 14 where an abrasive material is applied to the surface of the 
lineal member. The primary reason for this is to remove excessive styrene 
from the polyester resin surface coating of the lineal. Preferably, the 
abrasion step is accomplished by washing the surface of the lineal with 
water and aluminum oxide, such as 54-80 grit aluminum oxide from 
Exolon-ESK Co., Tonawanda, N.Y. Glass beads, such as size B glass beads 
from Potters Industries can be added to the water and aluminum oxide to 
limit the abrasive effects of the aluminum oxide (95% glass beads to 5% 
aluminum oxide by weight). The abrasive mixture can be approximately 2 
lbs. of aluminum oxide per gallon of water, and the washing process can be 
operated at approximately 18 psi at speeds varying from 3 to 20 feet per 
minute to remove surface contaminants and slightly abrade the surface of 
the lineal to enhance the wettablity of the surface. A washing booth 
suitable for use with the invention is a model No. 035 by Kleiber and 
Schulz, Melville, N.Y. 
It is believed that the abrasion process, which may be necessary to remove 
styrene and other impurities from the surface of the lineal member, opens 
up the surface portion of the lineal member, thereby enabling the lineal 
member to become somewhat penetrated by the aqueous conductive solution. 
Excessive absorption can result in trapped moisture beneath the paint of 
the finished lineal, thereby producing paint blisters, or other visual 
defects. The use of the preheating step prior to the application of the 
conductive solution minimizes the amount of penetration of the conductive 
solution into the surface of the lineal member. 
In the next process step the lineal passes through a lineal heating 
station, such as prep oven 16. In the prep oven, the surface of the lineal 
member is heated to a temperature greater than about 130.degree. F. This 
can be accomplished by any suitable means, such as by the circulation of 
hot air. Preferably, the temperature of the surface of the lineal member 
is raised to a temperature within the range from about 135.degree. F. to 
about 190.degree. F. Most preferably, the temperature is raised to within 
the range of from about 140.degree. F. to about 160.degree. F. Subsequent 
to the heating of the lineal, the conductive solution is sprayed from prep 
spray nozzles 18 onto the lineal. The nozzles can be any suitable nozzles 
for spraying an aqueous solution onto a lineal member. Preferably, the 
nozzles for the conductive solution are air atomized nozzles operating at 
10 lbs. air pressure, although any suitable nozzles can be employed. 
The conductive solution preferably is a saline solution. It has been found 
that a conductive solution comprising calcium chloride, lithium chloride 
and an ethoxylated nonyl phenol can be effective when used with the 
invention. A suitable conductive solution of this type is available as 
solution ECC519 from HSC Corporation, Detroit, Mich. Such a solution 
contains roughly 99% deionized water, and 1% of the ECC 519. 
The fact that the lineal has been preheated to a temperature of at least 
130.degree. F. means that the aqueous solution will readily disperse on 
the surface of the lineal, and the aqueous medium will readily evaporate 
prior to the painting process. 
After the conductive solution is applied, the lineals pass a drying station 
in which a heat lamp or convection hot air dryer, such as dryer 20, can be 
used to complete the drying before the painting process. Under certain 
conditions, the drying could be accomplished by contact with ambient air, 
either static or with forced convection. 
The drying process has as its goal drying the product to a nearly 
completely dry condition prior to the painting. Once the lineal is 
completely dry, the salt ions will attract water from the air as long as 
there is sufficient relative humidity (at least 5%) in the air, thereby 
creating the necessary conductive ionized coating on the surface of the 
lineal. 
The next step is application of paint, by any suitable means, such as paint 
nozzles 22, which are well known in the prior art. The paint can be any 
suitable paint for use on painting plastic lineal members in an 
electrostatic manner. Such paints are available from various 
manufacturers, such as from Sherman Williams, as will be well known to 
those skilled in the art. The paint is applied in an electrostatic paint 
process with electrically charged paint nozzles, and a grounded lineal. 
The residue from the conductive solution on the lineals ensures a widely 
dispersed electrically conductive surface for adequate grounding of the 
surface of the lineal, and the attraction of the paint particles to all 
areas of the lineal. 
Subsequent to the painting process, the lineal is transported into the 
paint curing area, such as paint oven 24 where the paint is cured. 
As shown in FIG. 2, the conveyor can be adapted with frame members, such as 
frames 26 which depend from the conveyor. The frames can be adapted with 
holding members, such as holding pins 28, for attaching to the lineal and 
supporting the lineal as it travels through the various stations of the 
process. The frame can also be adapted with a grounding member, such as 
grounding pins 30 for contact with the surface of the lineal member. In 
operation, the conveyor itself is grounded, and the ground travels through 
the frame and the grounding pin to the surface of the lineal. The charged 
paint particles are attracted to the ground on the surface of the lineal 
member. It is to be understood that multiple lineals can be mounted from 
each set of frames. 
As shown in FIG. 3, the lineal can be comprised of a glass wool core 32 and 
hard resin outer coat 34. As shown, the holding pin can be positioned 
offset from the center of gravity of the lineal member, thereby biasing 
the lineal member into contact with the grounding member. The lineal 
member rotates as shown by the arrow, and is biased at an angle alpha 
toward the grounding pin to ensure good electrical contact between the 
grounding pin and the surface of the lineal. 
As shown in FIGS. 2 and 3, the surface of the lineal is necessarily 
maintained in contact with the grounding pin during the painting process. 
This will create a small unpainted area on the lineal member. Preferably, 
this area is positioned on a non exposed or non critical surface, such as 
glazing surface 36, which is normally covered up by the glazing material 
when the lineal is used to manufacture a window sash, for example. 
In an alternate embodiment of the invention, the aqueous solution itself is 
heated to a temperature greater than about 140.degree. F. prior to the 
coating of the lineal member with the conductive solution. More 
preferably, the conductive solution is heated to a temperature within the 
range of from about 150.degree. F. to about 200.degree. F. Most 
preferably, the conductive solution is heated to a temperature of from 
about 160.degree. F. to about 190.degree. F. In this way, the lineal need 
not be heated, and yet the advantages of dispersibility and rapid 
evaporation of the aqueous medium can still be realized. 
It will be evident from the foregoing that various modifications can be 
made to this invention. Such, however, are considered as being within the 
scope of the invention. 
INDUSTRIAL APPLICABILITY 
This invention will be found to be useful in the preparation and painting 
of lineals employed as window sash and frame members for windows.