Zipper chain coater

Zipper chain is continuously electrostatically coated with powder to produce good coverage of the teeth, even upon its more obscured surfaces. The web is substantially uncoated, and is protected against deleterious heat effects.

BACKGROUND OF THE INVENTION 
In the course of manufacturing zippers, it is common practice to coat them 
with a variety of materials and for a number of reasons, such as to color 
or otherwise improve or modify their appearance, to afford protection 
against corrosion or the like, and to facilitate operation, e.g., by 
providing low-friction surfaces thereon. Conventionally, the coatings are 
produced by applying the material as a liquid; however, such an approach 
is often difficult, disadvantageous, or unfeasible. Thus, it is difficult 
to limit the coating to those areas on which it is desired (i.e., the 
teeth but not the fabric) while at the same time producing adequate 
coverage, especially on obscured surfaces lying between the teeth. In 
other cases, the coating material may not be suitable for application in 
liquid form, either because it does not readily dissolve or melt, or 
because the solvent or heat involved would have a deleterious effect upon 
the zipper. For example, when the fabric web is made from a heat-sensitive 
material, it may not be feasible to apply the coating as a melt, 
depending, of course, upon the temperatures involved. Similarly, a 
technique in which the deposited material requires post-heating may not be 
feasible when the web material is incapable of withstanding the elevated 
temperatures to which it would normally be subjected. 
Accordingly, it is a primary object of the present invention to provide a 
novel method and apparatus for continuously coating a zipper chain with a 
heat-fusible particulate coating material. 
It is also an object of the invention to provide such a method and 
apparatus whereby the coating may be produced on a zipper chain which 
includes a web made from a fabric that is adversely affected by exposure 
to elevated temperatures. 
Another object is to provide such a method and apparatus whereby the 
coating is produced uniformly upon substantially all exposed surfaces of 
the teeth of the zipper. 
Still another object of the invention is to provide such a method and 
apparatus which are adapted for the high speed production of coatings 
efficiently, conveniently, and relatively inexpensively. 
SUMMARY OF THE DISCLOSURE 
It has now been found that certain of the foregoing and related objects of 
the invention are readily attained in a method for continuously producing 
smooth, adherent coatings upon the teeth of a zipper chain, in which 
method a zipper chain, comprised of a fabric web having a multiplicity of 
metal teeth affixed thereto, is continuously moved along a travel path. 
Particles of a heat fusible powder are deposited upon the moving chain in 
areas substantially limited to the surfaces of the teeth, and the chain is 
heated only in such limited areas, to effect fusion and initial cohesion 
of the deposited particles. Thereafter, inadequately adhered particles are 
removed from the moving chain, and the "limited areas" thereof are heated 
to effect final cohesion of the particles and to produce, upon cooling of 
the chain, a smooth, adherent coating thereof on the teeth. 
Preferably, the particles of powder will be electrostatically charged, with 
the deposit being produced by electrostatic attraction of the particles to 
the teeth surfaces. Using such a technique, the particles are most 
desirably mechanically carried into close proximity to the teeth, with the 
conditions being such that the attractive force of the teeth upon the 
particles will be greater than that of the means carrying them, whereby 
transfer from the carrying means to the teeth is effected 
electrostatically. Ideally, the carrying means for the powder includes a 
member having a surface that is configured not only to maximize the 
quantity of powder presented to the teeth, but also to minimize the 
quantity thereof presented to the fabric web. 
In especially preferred embodiments of the method, heating of the chain 
will be produced by electromagnetic induction so as to substantially limit 
the heat generated to a surface effect. The electromagnetic flux pattern 
will, of course, desirably be configured to promote optimal heating of the 
teeth, and reheating will generally be produced in the same manner as the 
initial heating effect. The inadequately adhered particles can be removed 
effectively by brushing between the teeth of the zipper chain, in a 
direction generally parallel to the longitudinal axes thereof. 
Other objects of the invention are attained in apparatus comprising a base, 
means for continuously conveying a zipper chain along a travel path 
thereacross, and means for depositing particles of a heat fusible powder 
upon the zipper chain as it moves along the travel path, with the 
depositing means being effective to deposit powder in areas substantially 
limited to the surface of the teeth. Means is also included for heating 
the chain as it moves along the travel path to effect fusion and cohesion 
of the deposited particles, which heating means is effective to heat the 
chain substantially only in the "limited areas" coated with powder. 
Downstream of the initial heating means is means for removing inadequately 
adhered particles from the zipper chain, and means for reheating the 
"limited" areas of the zipper chain, as it moves further along the travel 
path, is provided to effect final cohesion of the particles and to 
produce, upon cooling of the chain, a smooth, adherent coating on the 
teeth. 
In preferred embodiments of the apparatus, the depositing means will effect 
electrostatic charging of the particles, so that the deposit will be 
produced by electrostatic attraction of the particles to the teeth 
surfaces. In such apparatus, the depositing means will most desirably 
include means for mechanically carrying the charged particles into close 
proximity to the teeth so that electrostatic transfer can be effected. 
Such carrying means beneficially comprises a pair of rotatable wheels, one 
of which is disposed on each side of the travel path to effectively 
present the powder to the chain, thereby permitting simultaneous coating 
of both sides. Ideally, such apparatus will additionally include 
electrostatic fluidized bed means, with the wheels being disposed to 
rotate therethrough, enabling deposits of the powder to be produced 
thereon. Since the zipper chain will generally move horizontally along the 
travel path, with a vertical orientation, such transfer wheels will 
normally be disposed at an angle of substantially 45.degree. with respect 
thereto, and will have an edge bevel of substantially 45.degree., thereby 
permitting close proximity to the surfaces of the zipper chain. For most 
effective coating, the wheel edges may be grooved to permit partial 
enclosure thereby of the teeth of the zipper chain. The circumferential 
edges of the wheels may be electrically insulated to reduce attraction of 
the charged particles, thereby ensuring effective transfer from the wheels 
to the chain. 
In the apparatus, the heating means is desirably an electromagnetic 
induction heater, which preferably will include elements dimensioned and 
configured to produce an electromagnetic flux pattern that is configured 
to promote optimal heating of the teeth. Specifically, such elements may 
comprise a pair of opposing, C-shaped heads within the coil of the heater, 
with the heads being dimensioned and configured to substantially surround 
the teeth as the chain passes therebetween. The apparatus may additionally 
include a second induction heater located downstream of the 
first-mentioned heater, for the purpose of reheating the chain, and the 
removing means may include a brush operative to brush between the teeth in 
a direction generally parallel to their longitudinal axes, with the brush 
being disposed between the first and second-mentioned heaters.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
The zipper chain for which the present invention is used is of conventional 
construction, and comprises parallel strips of a fabric web to the inside 
edges of which are affixed a multiplicity of metal teeth. FIGS. 4 and 5 of 
the appended drawings are illustrative, and will be discussed more fully 
hereinbelow. 
Turning now, however, to FIG. 1 of the drawings, therein illustrated is an 
electrostatic coating system embodying the present invention and 
specifically adapted for coating the zipper chains, generally designated 
by the numeral 16. The system consists of a base 10 having an upper 
surface or table 12, on which are mounted four zipper chain guides 14. 
Each of the guides 14 has an opening therethrough configured to support 
and properly orient the zipper chain 16, as it passes across the table 14 
and through the system. Mounted at one end of the table 12 is a roller 
guide 18, and a pair of drive wheels 22 are mounted thereon at its other 
end. As will be apparent, the wheels 22 are rotated countercurrently with 
the zipper chain 16 engaged therebetween, causing the chain to be pulled 
from its supply box 20, over and through the guides 18, 14, and past the 
several stations of the system. 
The first operation performed on the chain 16 occurs at the coating 
station, which is comprised of two electrostatic units, the details of 
which can be seen most readily in FIG. 2. Specifically, disposed to 
opposite sides of the travel path of the zipper chain 16 are two 
substantially identical, electrostatic coating chambers, generally 
designated by the numeral 24. The chambers are constructed in accord with 
the disclosure of Karr U.S. Pat. No. 4,030,446, and so need not be 
described in great detail. Nevertheless, it might be pointed out that each 
unit 24 includes a porous plate 26, upon which the coating powder is 
deposited and below which ionized gas is generated. Air enters the lower 
plenum 28 through the conduit 30, and flows upwardly therefrom through the 
electrically conductive metal plate 32 and into the upper plenum 34. The 
plate 32 has mounted thereon a multiplicity of brush-like electrodes 36, 
which are charged to a high electrical potential by connection through 
cable 37 to a high voltage D.C. source (not illustrated). The air flowing 
from the lower plenum 28 into the upper plenum 34 is directed to pass into 
contact with the ends of the bristles of the brush electrodes 36, and is 
thereby ionized. Upon passage thereafter through the porous plate 26 and 
into the fluidization chamber 27 thereabove, the air fluidizes and 
electrically charges the particles contained therein. 
Each of the electrostatic coating units is enclosed by a cover member 38, 
which is constructed with an elongated opening 39 and an adjacent bracket 
portion 40; the bracket portion 40 extends inwardly and upwardly at a 
45.degree. angle toward the travel path of the zipper chain, and it has a 
suitable bearing 41 secured within its outer end. The axels 42,44 are 
journalled between bearings 41 and bearing blocks 43; axel 42 has a pinion 
47 fixed to its inner end, and a bevel gear 48 spaced upwardly from it. 
The pinion 47 is in meshing engagement with a worm gear 50, and the latter 
is driven through belt 52 from drive means (not shown). A mating bevel 
gear 54 is mounted on the inner end of the axel 44, causing both of the 
axels to be rotated at precisely the same speed when the worm gear 50 is 
driven. Disposed between the wheels 46 and aligned beneath the travel path 
of the zipper chain 16 is a slotted conduit 56, which is incorporated into 
a typical vacuum recovery system (not shown); the conduit 56 serves to 
recover excess or loose powder. 
Mounted on the axels 42,44, and symmetrically positioned to either side of 
the travel path of the zipper chain 16, are transfer wheels 46, which 
serve to transfer the charged powder particles from the fluidized bed 
units to the zipper chain. Being electrically grounded, the wheels 46 
become coated with the powder as they are rotated through the fluidization 
chambers 27. Because they are dimensioned to intersect the travel path, 
the wheels 46 carry the powder, deposited upon their circumferential edges 
54, into close proximity to the zipper chain 16 as it passes therebetween, 
from which positions the powder transfers to the chain. It will be 
appreciated that the chain, like the transfer wheels, is grounded, and 
that the transfer of particles from the wheels is attributable to an 
electrical insulating effect. Thus, either because of inherent powder 
buildup on the wheels, or because they have intentionally been coated with 
an insulating material, the electrostatic attraction of the wheels to the 
charged particles is at a lower level than is that of the zipper chain; 
consequently, the particles jump when they are brought close enough to do 
so. It should also be appreciated that, although the edges 54 of the 
transfer wheels may be straight across, bevelled or otherwise configured, 
the grooved configuration illustrated is most advantageous. With such a 
profile, the powder will be presented to the top and bottom surfaces of 
the teeth of the zipper chain as well as to the sides thereof, thus 
promoting maximum coverage by the coating produced. 
At the next station of the system is provided an induction heating unit, 
generally designated by the numeral 58, and consisting of a set of 
C-shaped heads 60, supported by and mounted within a coil 62, which in 
turn is connected to a high frequency oscillator (not shown). The 
relationship and configuration of the heads 60, which are illustrated in 
FIG. 3, provide an optimum heating pattern for effecting the fusion of the 
powder, by most effectively concentrating the magnetic flux produced in 
the coil 62 for that purpose. 
After passing through the induction heating unit 58, the chain 16 is 
conveyed through an air-knife assembly, generally designated by the 
numeral 64; the assembly 64 consists of a pair of elongated nozzles 66, 
supported by brackets 68 above and to opposite sides of the travel path of 
the chain. A dust collector head 70, mounted below the travel path, has 
elongated slot-like openings 72, which are disposed to either side of the 
zipper chain and are aligned with it and with a corresponding one of the 
nozzles 66. As will be appreciated, air under pressure is introduced into 
the body of the nozzles 66 (by means and from a source not shown), to 
issue as a high velocity "sheet." Any inadequately fused particles of 
powder present on the zipper chain 16 will be dislodged thereby, and 
removed through the head 72 by an appropriate vacuum system. 
The thus precleaned chain then proceeds through the support 14 and into a 
brush cleaning station, generally designated by the numeral 74. This 
station consists of a symmetrical arrangement of two counter-rotating 
cylindrical brushes 76, which are mounted on opposite sides of the travel 
path, with their axes parallel thereto. Each brush 76 is journalled 
between a pair of brackets 78, which also mount a small electric motor 80 
to which the brush 76 is coupled by a drive belt 82. The two brushes 76 
operate simultaneously upon opposite sides of the zipper chain 16, with 
their bristles moving downwardly thereacross, thereby dislodging all but 
the most firmly adhered powder from the fabric web and from between the 
teeth of the chain. 
From the rotary brush station 74, the chain is conveyed through a second 
induction heating unit, generally designated by the numeral 84. Since it 
is substantially identical to heating unit 58, further description is 
unnecessary. Suffice to say that the function of the second induction 
heater 84 is to produce final fusion or curing of the deposited resin, as 
the case may be, to thereby develop the ultimate qualities of the coating. 
Before exiting from the system, the zipper chain 16 passes over a blower 
head 88, from which air (supplied by means not shown) is discharged into 
contact with its opposite faces. The purpose of the air is to cool and 
harden the heated resin, so as to ensure that the coating is not damaged 
in any way during movement through the drive assembly 22 or in the 
collection means (which is not shown, but which may simply be a box into 
which the chain is deposited). 
In FIGS. 4 and 5 the structure of a typical zipper chain 16 is depicted. Of 
particular note is FIG. 5, wherein the coating produced using the system 
of the invention is shown to be uniform and continuous on the surface of 
the teeth 86. Most notably, it can be seen that the coating 90 extends 
over substantially all surfaces of the teeth 86, including those which lie 
on the inner, normally obstructed portions thereof (i.e., between the 
teeth), and that the fabric web 92 is free of deposits. (It will be noted 
that, for numbering purposes, the presence of the coating is ignored in 
FIG. 4.) 
Although the drawings illustrate the preferred system, it will be 
appreciated that modifications can be made within the concepts of the 
invention. For example, other electrostatic coating means may be employed 
in which the powder is presented to the zipper chain in a less controlled 
manner, such as by simply conveying it through the cloud of charged 
particles generated over an electrostatic fluidized bed, or by using 
electrostatic powder spray guns. However, any such reduction in control of 
powder will tend to reduce commensurately the reliability of the system 
for the production of good quality coatings, and will increase the need 
for powder recovery capacity; it will also require more attention to 
removal of particles deposited upon the fabric of the chain. 
Moreover, airborne techniques will generally be less desirable because of 
the inherent propensity of the airstream to dislodge deposited particles. 
One of the most notable aspects of the invention relates, as has been 
indicated hereinbefore, to the high level of coating integrity that is 
obtained over all exposed surfaces of the teeth of the zipper, including 
those interior surfaces which lie between the teeth. This is believed to 
be due to the ability of the charged particles to search-out and deposit 
upon uncoated grounded surfaces, in preference to those surfaces which 
have already been covered. Again, the close proximity that is achieved 
using the preferred mechanical powder delivery apparatus is believed to 
enhance that effect. Because of the tendency for air channeling to occur 
between the teeth, the airborne techniques may cause some particle 
dislodgement and, to that extent, to be counterproductive, depending of 
course upon the force of the airstream. Presenting the particles to the 
chain as a relatively still air suspension (such as can be accomplished 
with a suitably hooded fluidized bed) will therefore usually be preferable 
to the use of air guns. In any event, it will be advantageous for the 
electrostatic coating means on the two sides of the travel path to be 
independently controllable, so as to permit dissimilar amounts of the 
powder to be provided; this may be desirable to compensate for the slight 
difference in the configuration of the teeth on the opposite sides of the 
chain. 
The powder used to produce the coating will normally be a synthetic resin, 
of either the thermoplastic or thermosetting type. The choice will depend 
upon the properties that are to be produced, and will be evident to those 
skilled in the art. For example, depending upon whether the deposit is to 
afford gloss, color change, protection against corrosion or deterioration 
(such as from washing solvents), dyeability, lubricity, or a combination 
of those or other qualities, the powder used may be a polyolefin, a 
halogenated polyolefin, a nylon, an epoxy or a polyester, etc. 
The results of heating will depend upon the powder employed, at least 
insofar as the mechanisms of cohesion and fusion are concerned. 
Specifically, when the powder is a thermoplastic resin the first heater 
will produce initial bonding and fusion, with the second producing 
reflowing of the resin for smoothness, gloss, and the like. In the case of 
thermosetting resins, on the other hand, while the ultimate effects will 
be the same, they will be produced through resin curing mechanisms, rather 
than by reflow. 
Use of induction heating is a significant feature of the invention, because 
it readily provides the necessary means by which heating in limited areas 
can be effected. Because an induction technique produces "skin" heating 
rather than a more pervasive effect, the main body of each tooth remains 
relatively cool and available as a heat sink. Consequently, after passing 
through the induction heater the zipper chain is "mass quenched" by its 
teeth, thereby further protecting the fabric web against the deleterious 
effects of heat. As a specific example, whereas it may be desirable to 
heat the deposited powder to a temperature of 450.degree. to 500.degree. 
Fahrenheit, the web may not be able to withstand temperatures in excess of 
about 350.degree. (such as when it is made of a polyester). By 
concentrating the effect in such a way as to avoid both direct heating of 
the fabric and also indirect heating by conduction from the teeth, the 
present invention accommodates chains having such a typical construction. 
Although not illustrated, it should be understood that the present system 
and method may be employed to coat the zipper chain in open (i.e., 
"unzipped") as well as closed position. Modifications will of course be 
made to the equipment for that purpose, such as to adapt the conveying, 
coating, heating and cleaning stations to accommodate the slight 
differences that would be involved. While still of outstanding benefit, 
the advantages of coating in the open condition are somewhat less 
pronounced, and the operations are somewhat less convenient; therefore, 
the illustrated technique is preferred. In any event, coating is carried 
out on a continuous basis, which affords a production capability not 
believed to be possible heretofore. Finally, although not illustrated, the 
coating wheels and the chain conveying wheels may be driven by the same, 
variable speed, motor, so as to facilitate modification of production 
rates without loss of necessary synchronization. 
Thus, it can be seen that the present invention provides a novel method and 
apparatus for continuously coating zipper chain with a heat-fusible 
particulate coating material. The coating may be produced on chain which 
includes a web made from a fabric that is deleteriously affected by 
exposure to elevated temperatures, and it uniformly covers substantially 
all exposed surfaces of the teeth of the zipper. The method and apparatus 
are adapted for high speed, efficient, convenient, and relatively 
inexpensive operation.