U.S. patent number 3,906,071 [Application Number 05/355,900] was granted by the patent office on 1975-09-16 for dip molding process.
This patent grant is currently assigned to Leon Chemical & Plastics Div. of U.S. Industries Inc.. Invention is credited to William J. Cook, Gordon A. Ellens.
United States Patent |
3,906,071 |
Cook , et al. |
September 16, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Dip molding process
Abstract
A dip molding process for producing seat belt housings or the
like in which a portion of a heated mold or die is dipped
relatively quickly into a plastisol having a first durometer rating
and is then, after a delay to allow the first coat to gel and cool
somewhat, subsequently dipped into a second plastisol having a
different durometer rating. In the first dip, only a portion of the
mold is dipped. In the second dip, the mold is dipped to a depth
and for a time sufficient that the rest of the effective mold
surface is coated to a desired thickness. The two plastisols are
arranged in adjacent tanks and sets of molds are conveyed from a
preheating oven to the plastisol tanks and then to subsequent
conventional operations. The molds are heated in the preheating
oven to a temperature higher than the temperature normally used to
dip mold into the second plastisol and to a temperature which is
sufficiently high to allow for the heat loss which will be
experienced from the time the mold is first dipped into the first
plastisol until the time it is first dipped into the second
plastisol. The dip tanks can be raised and lowered at different
rates to provide a means for adjusting the length of the dip cycle.
The dip cycle time for the second plastisol is set to give the
desired thickness and to avoid drips, running and air bubbles. The
dip cycle time for the first plastisol is set for a relatively
quick run to create a delay from the end of the first dip until the
initiation of the second dip and to compensate for the higher
temperature of the molds and to thereby prevent excessive plastisol
buildup on the mold. The resultant seat belt housing has one
portion, either the base or the snout, which is more flexible than
the other so that the snout will flex more readily with respect to
the other.
Inventors: |
Cook; William J. (Rockford,
MI), Ellens; Gordon A. (Grand Rapids, MI) |
Assignee: |
Leon Chemical & Plastics Div.
of U.S. Industries Inc. (Grand Rapids, MI)
|
Family
ID: |
23399266 |
Appl.
No.: |
05/355,900 |
Filed: |
April 30, 1973 |
Current U.S.
Class: |
264/255;
264/297.8; 264/306; 264/305; 425/93; 264/303 |
Current CPC
Class: |
B29C
41/14 (20130101) |
Current International
Class: |
B29C
41/14 (20060101); B29D 009/00 () |
Field of
Search: |
;117/5.1,72,94,47H,DIG.6,26,5.3 ;264/255,306,305,303,297
;425/93,269,270 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Konopacki; Dennis C.
Attorney, Agent or Firm: Price, Heneveld, Huizenga &
Cooper
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A dip molding process comprising: providing a first source of a
first dip molding plastisol having a first durometer rating and a
second source of a second dip molding plastisol having a second
durometer rating; heating a dip molding mold to a temperature
higher than the temperature normally required to dip mold in the
second plastisol; dipping said mold into said first plastisol a
distance sufficient to coat only a portion of the mold surface and
for a time sufficient to coat said portion to the desired
thickness; subsequently dipping the partially coated mold into the
second plastisol a distance greater than said portion and for a
time sufficient to coat the first coated portion and the portions
of said mold not already coated to a desired thickness; delaying
the initiation of said subsequent dip into said second plastisol
for a period of time of approximately 30 to 90 seconds after said
mold leaves said first plastisol and maintaining said mold in an
atmosphere cooler than the temperature of said mold during said
delaying step to allow the first coating of plastisol on said mold
to gel somewhat and allowing the surface of said coating to cool
somewhat prior to initiation of said subsequent dip; and
subsequently removing the resulting molded article from said
mold.
2. The dip molding process of claim 1 comprising: heating said mold
to a temperature approximately 15.degree. to 45.degree. F. higher
than the temperature normally required to dip into
3. The dip molding process of claim 3 comprising: dipping said mold
into said second plastisol in approximately 1 minute of the time
said mold leaves said first plastisol.
4. The dip molding process of claim 2 which comprises: dipping said
mold into said first plastisol approximately 10 to 30 seconds less
than one would normally dip into said first plastisol.
5. The dip molding process of claim 2 comprising: dipping said mold
into said second plastisol sufficiently soon after it leaves said
first plastisol that the temperature of said mold drops only
approximately 30.degree. F. from the time at which it is first
dipped into said first plastisol and the time that it is first
dipped into said second plastisol.
6. The dip molding process of claim 5 in which said first plastisol
has a durometer rating of no greater than approximately 95 on the
Shore A scale and said second plastisol has a different durometer
rating of no less than approximately 70 on the Shore A scale.
7. The dip molding process of claim 5 in which said first plastisol
has a durometer rating of no less then approximately 70 on the
Shore A scale and said second plastisol has a different durometer
rating of no greater than approximately 95 on the Shore A
scale.
8. The dip molding process of claim 1 in which said mold is heated
to a temperature sufficiently high to allow for the heat loss which
will be experienced from the time said mold is first dipped into
said first plastisol until the time said mold is first dipped into
said second plastisol.
9. The process of claim 1 comprising: providing at least said first
plastisol of a composition which gels to a roughened surface
shortly after dipping is completed.
10. The process of claim 1 comprising: providing said first
plastisol of a mixture of first resin particles having an average
particle size of less than 500 microns, a similar resin having
particles whose size with relationship to said first resin
particles is in the range of approximately 6.5 to 1 to 200 to 1,
and a suitable plasticizer.
11. The process of claim 1 comprising: providing first and second
plastisols of a mixture of first resin particles having an average
particle size of less than 500 microns, a similar resin having
particles whose size with relationship to said first resin
particles is in the range of approximately 6.5 to 1 to 200 to 1,
and a suitable plasticizer.
12. A dip molding process comprising: providing a first source of a
first dip molding plastisol having a first durometer rating and a
second source of a second dip molding plastisol having a second
durometer rating; positioning said first and second sources
adjacent one another; providing conveying means for conveying molds
to and from said first and second sources; positioning a plurality
of sets of molds, each set having at least one mold therein, on
said conveying means at spaced intervals, each interval from center
to center being approximately the same as the spacing between the
centers of said frst and second sources; providing means for
differentially varying the dip times for said first and second
sources; setting the dip time for said second source for a length
of time sufficient to coat a mold to the desired thickness without
any undersirable dripping, running, or bubbling; setting the dip
time of said first source for a shorter length of time then the dip
time of said second source, sufficient only to coat a portion of
the mold to a desired thickness and sufficiently short to create a
delay from the time a set of molds leaves said first source until
it enters said second source; conveying said sets of molds through
an oven at a temperature and for a time sufficient to preheat said
molds to a temperature higher than the temperature normally
required to dip mold in said second plastisol and sufficiently high
to allow for the heat loss which will be experienced from the time
a mold is first dipped into said first source until it is first
dipped into said second source whereby when a mold is finally
dipped into said second source, it will have sufficient heat to
acquire an adequate plastic coating; conveying said sets of molds
to said first and second sources; generally simultaneously
initiating the dipping of adjacent sets of molds in said first and
second sources and sequentially dipping each set of molds first
into said first source and then into said second source whereby a
portion of each mold will be first coated with said first plastisol
in said first source while the coated portion and uncoated portion
of said mold will be coated in said second source; and subsequently
removing the resulting molded article from said mold.
13. The process of claim 12 in which said mold is maintained in an
atmosphere cooler than the temperature of said mold during the
delay between the end of the dip into the first plastisol until the
initiation of the dip into the second plastisol, whereby the
surface of the first coating of plastisol on said mold has an
opportunity to cool somewhat prior to initiation of said subsequent
dip.
14. The dip molding process of claim 12 comprising: heating said
mold to a temperature approximately 15.degree. to 45.degree. F.
higher than the temperature normally required to dip into the
second plastisol.
15. The dip molding process of claim 14 comprising dipping said
mold into said second plastisol approximately 30 to 90 seconds
after said mold leaves said first plastisol.
16. The dip molding process of claim 14 comprising: dipping said
mold into said second plastisol in approximately one minute of the
time said mold leaves said first plastisol.
17. The dip molding process of claim 14 which comprises: dipping
said mold into said first plastisol approximately 10 to 30 seconds
less than one would normally dip into said first plastisol.
18. The dip molding process of claim 14 comprising: dipping said
mold into said second plastisol sufficiently soon after it leaves
said first plastisol that the temperature of said mold drops only
approximately 30.degree. F. from the time at which it is first
dipped into said first plastisol and the time that it is first
dipped into said second plastisol.
19. The dip molding process of claim 18 in which said first
plastisol has a different durometer rating of no greater the
approximately 95 on the Shore A scale and said second plastisol has
a durometer rating of no less than approximately 70 on the Shore A
scale.
20. The dip molding process of claim 18 in which said first
plastisol has a durometer rating of no less than approximately 70
on the Shore A scale and said second plastisol has a different
rating of no greater than approximately 95 on the Shore A
scale.
21. The process of claim 12 comprising: providing at least said
first plastisol of a composition which gels to a roughened surface
shortly after dipping is completed.
22. The process of claim 12 comprising: providing said first
plastisol of a mixture of first resin particles having an average
particle size of less than 500 microns, a similar resin having
particles whose size with relationship to said first resin
particles is in the range of approximately 6.5 to 1 to 200 to 1,
and a suitable plasticizer.
23. The process of claim 22 in which said second plastisol is the
same as said first plastisol.
24. A dip molding process comprising: providing a first source of a
first dip molding plastisol having a durometer rating of no less
than approximately 70 on the Shore A scale; providing a second
source of a second dip molding plastisol having a different
durometer rating of no greater than approximately 95 on the Shore A
scale; preheating a dip molding to a temperature higher than the
temperature normally required to dip mold in the second plastisol
and sufficiently high to allow for the heat loss which will be
experienced from the time a mold is first dipped into said first
source until the time at which it is subsequently dipped into said
second source whereby when a mold is finally dipped into said
second source, it will have sufficient heat to acquire a
satisfactory plastic coating; dipping a portion of said mold into
said first plastisol at a dip rate substantially faster than one
would normally dip into said first plastisol; subsequently dipping
said mold into the second plastisol a distance greater then said
portion for a time sufficient to coat the coated portion and
noncoated portions of said mold to a desired thickness; delaying
the initiation of said subsequent dip into said second plastisol
for a period of time following said first dip into said first
plastisol sufficient to allow the first coating of plastisol on
said mold to gel somewhat and allowing the surface of said first
coating to cool somewhat prior to initiation of said subsequent
dip; and subsequently removing the resulting molded article from
said mold.
25. The dip molding process of claim 24 comprising: heating said
mold to a temperature approximately 15.degree. to 45.degree. F.
higher than the temperature normally required to dip into the
second plastisol.
26. The dip molding process of claim 25 comprising dipping said
mold into said second plastisol approximately 30 to 90 seconds
after said mold leaves said first plastisol.
27. The dip molding process of claim 25 comprising: dipping said
mold into said second plastisol in approximately one minute of the
time said mold leaves said first plastisol.
28. The process of claim 27 in which said mold is maintained in an
atmosphere cooler than the temperature of said mold during said
delaying step whereby the surface of the first coating of plastisol
on said mold has an opportunity to cool somewhat prior to
initiation of said subsequent dip.
29. The dip molding process of claim 28 comprising: dipping said
mold onto said second plastisol sufficiently soon after it leaves
said first plastisol that the temperature of said mold drops only
approximately 30.degree. F. from the time at which it is first
dipped into said first plastisol and the time that it is first
dipped into said second plastisol.
30. The process of claim 24 comprising maintaining said mold in an
atmosphere cooler than the temperature of said mold following
completion of the first dip into said first plastisol during said
delaying step.
31. The process of claim 24 comprising: providing at least said
first plastisol of a composition which gels to a roughened surface
shortly after dipping is completed.
32. The process of claim 24 comprising: providing at least said
first plastisol of a mixture of first resin particles having an
average particle size of less than 500 microns, a similar resin
having particles whose size with relationship to said first resin
particles is in the range of approximately 6.5 to 1 to 200 to 1,
and a suitable plasticizer.
33. The process of claim 32 in which said second plastisol is the
same as said first plastisol.
Description
BACKGROUND OF THE INVENTION
This invention relates to dip molding, and particularly to vinyl
dip molding. In dip molding, a mold having a desired configuration
is heated and then dipped into a dip molding plastisol, typically a
vinyl plastisol. The basic dip molding process is well-known to
those skilled in the dip molding art.
For some purposes, it is desirable to reinforce a dip-molded
article. In a seat belt retractor housing, for example, it is in
some applications desirable to provide a rigid base for covering
the retractor and a softer, flexible snout for housing the belt
portion. Contrawise, it might be desirable to provide a more
flexible base to facilitate mounting of the housing and yet have a
more rigid snout in order to keep the end of the seat belt located
in a generally constant position in the car.
One can obtain the desired flexibility for the flexible portion of
the article by using a vinyl plastisol having a lower durometer
rating. The more rigid portion of the article can be formed by
using a reinforcing insert. Such inserts are inserted into the
housing just after it is dip molded. While it might at first blush
seem more economical to mold around an insert, one problem
encountered in such situations is that it is difficult to
interconnect the reinforcing insert to the dip molding mold.
Further, the presence of such an insert causes running and dripping
since it provides another surface which complicates the flow
pattern of the plastisol around the dip-molding mold. Accordingly,
the inserts are laboriously inserted into the hot molding just
after it is stripped off the mold.
Another type of housing has heretofore been made by dipping a mold
first partially into one plastisol of one durometer rating and then
immediately, within 5 or 10 seconds, into a second plastisol of a
second durometer rating in an attempt to crease a housing having
one portion more flexible with respect to the other. The second dip
was performed immediately after the first in order to make sure the
mold was still hot enough when dipped into the second plastisol to
coat. If the mold cools too much, it will not coat.
One problem with the housing made by this method is that the second
plastisol coats too heavily over the first plastisol coating,
thereby wasting plastisol. Further, where the second plastisol is
of a higher durometer rating (yielding a more rigid plastic), the
effect of the lower durometer plastic is minimized and the housing
does not have the desired degree of flexibility of one portion with
respect to the other. Another problem is that the process does not
lend itself readily to commercialization. If the length of time of
the first dip is set the same as the time for the second dip, the
first coating will be unnecessarily thick since the mold is only
partially dipped. Yet, if the first dip time is made shorter than
the second, one of the dip tanks must be idle while the other is
being used. This is so the mold can be kept in the preheating over
until just prior to the first dip and then dipped from the first
dip to the second without delay. Thus, the problem of making a dip
molded article with one portion more flexible than the other has
heretofore not been satisfactorily solved.
SUMMARY OF THE INVENTION
The present invention comprises a dip molding process in which a
preheated dip molding mold is dipped first into a first source of
plastisol having a first durometer rating and is delayed in the
atmosphere for a time sufficient to allow the first coating to gel
and cool somewhat before the mold is dipped into a second source of
plastisol having a second durometer rating. A product is produced
having one portion which is relatively flexible and another portion
which is relatively rigid. In spite of the delay, the two portions
are integrally adhered to one another to form a single integral
part. First and second sources of plastisol are maintained at a
temperature suitable for dip molding. A dip molding mold is heated
to a temperature higher than the temperature normally required to
dip mold into the second plastisol. The heated mold is dipped into
the first plastisol a distance sufficient to coat only a portion of
the mold and for a time sufficient to coat the portion to a desired
thickness. Following the aforesaid delay, the mold is dipped into
the second plastisol a greater distance for a time sufficient to
coat the portion of the mold not already coated to a desired
thickness. Subsequently, conventional dip molding operations are
performed.
Preferably, molds are mounted in sets on a conveying means. The
sets are spaced at center-to-center intervals corresponding to the
space between the centers of the adjacent plastisol dip tanks.
Means are provided for differentially varying the dip times for the
first and second dip tanks so that the first dip is faster than the
second. The dip cycle time for the second plastisol is set
sufficiently long to facilitate coating of the mold to a desired
thickness without any undesirable dripping, running, or bubbling.
The dip time for the first plastisol is set for a shorter length of
time sufficient only to coat a portion of the mold to a desired
thickness. Not only does this provide a time delay following the
first dip during which the mold is exposed to the surrounding
atmosphere, but also this compensates for the fact that the mold is
probably slightly higher in temperature than it normally would be
when it is dipped into the first tank. The delay gives the first
plastisol coating on the mold on a chance to gel and allows the
surface of the first coating to cool before it is dipped into the
second tank. Apparently because the plastic is an insulating
material, the heat of the mold will not tend to flow to the outer
surface of the first plastisol coating. Thus, when the mold is
subsequently dipped into the second plastisol, there will be less
tendency for the second plastisol to coat over the first plastisol
coating. Further, because the first plastisol coating has had a
chance to gel somewhat before it has been dipped, it will not tend
to simply "mix" with the second plastisol material as it coats onto
the mold.
One product which can be manufactured using this process is a seat
belt housing of the type shown in either FIG. 3 or FIG. 4. Both
housings are integrally formed of plastic but include a relatively
rigid portion and a relatively flexible portion. This makes the
snout flex or deflect aside more readily with respect to the base.
When a person bumps against the snout, the snout tends to deflect
more readily thereby decreasing the chance of scraping or bruising
a person. Yet, no reinforcements are required to achieve this
result.
These and other objects, aspects, and features of the present
invention will be more fully understood and appreciated by
reference to the written specification and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a seat belt housing made in
accordance with the present invention;
FIG. 2 is a perspective view of a dip molding mold used to produce
the housing of FIG. 1;
FIG. 3 is a cross-sectional view taken along plane III--III of FIG.
1 with a portion (encircled) of the bottom of the housing exploded
away and enlarged;
FIG. 4 is a perspective and cross-sectional view of an alternative
embodiment housing made in accordance with the present
invention;
FIG. 5 is a plan, schematic view of the apparatus employed in the
dip molding process of the present invention; and
FIG. 6 is a front elevational schematic view of the apparatus
employed in the dip molding process of the present invention.
PREFERRED EMBODIMENT
In the preferred embodiment, sets of dip molding molds, such as
mold 10 (FIG. 2), are carried by a conveyor 20 (FIGS. 5 and 6)
through a preheating over 30 to a first dip tank 40, a second dip
tank 50, and to other stations where conventional dip molding
process steps are performed (FIGS. 5 and 6). Dip tank 40 contains
vinyl plastisol of a durometer rating of approximately 70 on the
Shore A scale and dip tank 50 contains a similar vinyl plastisol of
a durometer rating of approximately 95 on the Shore A scale. The
molds 10 are heated in oven 30 to a temperature higher than that
normally required to dip into the plastisol in the second dip tank
50 and to a temperature which is sufficiently high to compensate
for the heat loss which will be experienced from the time the molds
are first dipped into dip tank 40 until the time they are first
dipped into dip tank 50. The heated molds are dipped a portion of
the way into the first tank and then, after a delay which allows
the first plastisol to gel and to cool somewhat, are dipped
generally all of the way into the second dip tank 50. They are then
conveyed to other conventional dip molding work stations and the
finished housings (FIGS. 1 and 3) are stripped off of the molds at
a suitable work station located along the length of conveyor 20.
The housing 80 has a lower portion or base 81 formed primarily of a
layer of vinyl plastic 90 having a durometer rating of
approximately 70 on the Shore A scale (FIG. 3). The upper portion
or snout 82 of housing 80 is formed of a vinyl 100 having a
hardness of approximately 95 on the Shore A scale. Only a slight
thickness of the higher durometer plastic 100 forms over the lower
durometer plastic 90 at the lower portion 81 of housing 80.
As a result, the housing 80 is more flexible at its lower portion
81 than would be the case if the entire housing were made only out
of the higher durometer plastic 100. Accordingly, the housing 80 is
easier to work with during installation. It is easier to spread the
flaps at the lower portion 81 apart to fit them over the seat belt
mounting hardware. Similarly, the flexibility in the lower portion
81 makes it possible to more easily deflect the upper portion or
snout 82 to the left or to the right than would be the case if the
entire housing 80 were made out of the higher durometer plastic
100. Yet, the snout 82 is more rigid than the lower portion 81
thereby more positively locating the end of the seat belt with
respect to the user. The more rigid 95-durometer vinyl 100 provides
this desired rigidity without the need for any reinforcing
inserts.
In order to attain this product, a plurality of molds 10 are
mounted to spaced racks 21 which are carried on conveyor 20 (FIG.
6). Each mold 10 includes a mounting portion or mounting flange 11
which is not intended to to coated. Rather, mounting flange 11 is
provided solely to facilitate mounting to a carriage 21. Bolt holes
12 are provided through flange 11 to facilitate the bolting of mold
10 to carriage 21.
The carriages 21 are mounted on conveyor 20 at spaced intervals
such that the distance between the centers of the carriage 21
corresponds to the distance between the centers of the adjacent dip
molding tanks 40 and 50. This arrangement makes it possible to be
dipping different sets of molds 10 into the different dip tanks 40
and 50 simultaneously.
The molds 10 mounted on carriages 21 are conveyed through a
preheating over 30. Such ovens are well-known in the art. The dip
molding molds must be preheated before the vinyl plastisol will
coat on them. As is well-known in the art, many factors are
considered before selecting a specific mold temperature for a
particular plastisol.
In the present invention, the molds 10 are heated to a temperature
which is higher than the temperature normally required for dipping
in the plastisol which is in the second dip tank 50. Further, the
molds 10 are heated to a temperature which is sufficiently high to
compensate for the heat which will inevitably be lost from the time
the molds are first dipped into the first dip tank 40 until the
time they are dipped into the second dip tank 50. There is
approximately a 30.degree. drop in temperature from the time mold
10 is first dipped into dip tank 40 until it is dipped into dip
tank 50. This may vary from 15.degree. to 45.degree. F. under
different circumstances. Because of the 30.degree. heat loss, the
molds 10 are preferably heated to a temperature ranging to as high
as 15.degree. to 45.degree. F. higher than one would normally heat
the mold for dipping into dip tank 50. Typically, it will be about
30.degree. F. higher. By the time they reach dip tank 50, they
still have sufficient heat to effect suitable coating with the 95
durometer plastisol that is in dip tank 50.
On the other hand, as will be appreciated by those skilled in the
art, the molds 10 will be at an abnormally high temperature for
dipping into the 70 durometer plastisol composition which is in dip
tank 40. As a result, the dip cycle used for dipping the molds 10
into dip tank 40 is relatively shorter than it would normally be. A
rapid dip cycle makes up for the fact that the molds are carrying
excess heat at this point. While one would normally dip more slowly
in order to avoid running, this is not as great a problem on the
first dip into dip tank 40 since minor imperfections created in the
first dip will pretty generally be covered during the more
deliberate second dip into dip tank 50.
The dip tanks 40 and 50 are mounted on elevators 41 and 51
respectively (FIGS. 5 and 6). Each of the elevators includes
supports 42 and 52 respectively, extending laterally therefrom for
supporting dip tank 40 or dip tank 50 respectively. The elevators
41 and 51 are provided with conventional controls for controlling
the dip cycle. The cycle 10 are dipped by actually raising the dip
tank 40 or 50 until the molds 10 are positioned within the
plastisol. Conventional means are provided for raising and lowering
the different tanks at different rates. This makes it possible to
use a rapid dip cycle for tank 40 and a more deliberate dip time
for tank 50.
When the molds 10 are dipped into dip tank 40, they are dipped only
so that the lower portion thereof is covered by the lower durometer
plastisol which is located in dip tank 40. As a result, only the
lower portion 81 of seat belt housing 80 is made of the more
flexible 70-durometer vinyl plastic 90 (FIG. 3). As noted above,
the dip cycle time for the molds 10 into dip tank 40 is fairly
rapid in order to make up for the fact that the mold temperature is
abnormally high for dipping into the 70-durometer plastisol. If one
proceeded too slowly, one would get an excessive buildup of the
70-durometer plastisol on the lower portion of mold 10. The exact
time for this first dip cycle will vary depending on conventional
considerations. Once the conventional time is determined, however,
the actual time used in this case should be shortened by about 10
to 30 seconds.
Further, the dip cycle time for the first dip in the dip tank 40 is
shorter than the cycle time for the dip in the dip tank 50 is
intended to create a delay which gives the first plastisol and
opportunity to gel on the surface of mold 10. As a result, the
first coating has integrity and continuity when it is dipped into
the second plastisol in dip tank 50. If the mold is dipped quickly
into the second dip tank 50, the first coating would be too fluid
at the time of the second dip into dip tank 50 and there would be
more of a tendency for the first plastisol to intermix with the
second plastisol thereby defeating the purpose of the first dip.
Secondly, the delay which exists from the time the molds 10 leave
the first dip tank 40 until they enter the second dip tank 50
enables the surface of the first plastisol coating to cool off
somewhat. Because the first plastisol coating is an insulator, the
heat of the mold tends to be held in by the first partial coating,
and it is also prevented from being conducted to the outer surface
of the plastisol coating as a result of the insulating effect.
Accordingly, this cooler surface of the first coating tends to pick
up less of a coating of the second plastisol in the second dip tank
50. Thus, it is preferable that there in fact be a delay between
the time the molds 10 leave dip tank 40 until they enter dip tank
50, thereby exposing them to the cooler atmosphere surrounding the
work area. The initiation of the dipping of adjacent sets of molds
into the adjacent tanks 40 and 50 is done generally simultaneously.
But the dip cycle time for the first tank 40 is shorter, thereby
yielding the aforesaid desired delay.
The dip into the 95-durometer plastisol in dip tank 50 is more
deliberate, and is governed by conventional considerations
well-known to those skilled in the dip molding art. The relative
time for the first and second dips should be optimumly adjusted so
that there is approximately about a 30 to 90 second delay,
preferably about a 1-minute delay from the time the molds 10 leave
the plastisol in dip tank 40 until they are actually dipped into
the plastisol in dip tank 50. The 1-minute delay is sufficient to
allow the first plastisol coating to gel somewhat and to allow the
surface of the first coating to cool somewhat prior to the dip into
dip tank 50. Further, the heat loss experienced in mold 10 during
this 1-minute interval is only approximately 30.degree. F. The
partial covering of the mold 10 with the first plastisol coating
tends to insulate mold 10 and minimize the heat loss from the mold
which is experienced. The range of time for effecting a delay
sufficient to allow gelling and cooling, yet short enough to keep
the heat loss from mold 10 within desirable limits is from about 30
seconds to about 90 seconds.
After the molds 10 have been dipped into the first dip tank 40 and
been delayed slightly in the atmosphere, they are ready for dipping
into dip tank 50. Conveyor 20 moves them into position over dip
tank 50, and elevator 51 elevates dip tank 50 so the plastisol
flows around the partially coated molds 10. The second plastisol
only coats the first plastisol to a slight degree as is indicated
by the cross-sectional view, FIG. 3. That portion of vinyl 100
which covers vinyl 90 is relatively thin compared to the overall
thickness of vinyl 100 in the upper or snout portion 82 of housing
80. The reason for this only slight coating is that the first
coating 90 has been allowed to cool and first coating 90 tends to
insulate and prevent the heat of the mold from migrating to the
surface of the coating, thereby minimizing plastisol pickup. In the
case of housing 80, this slight coating of higher durometer
plastisol 100 does tend to make the bottom portion 81 more rigid
than would be the case if only 70-durometer plastisol 90 were
located at the base portion 81. And, it does create a harder outer
surface than would otherwise be the case. However, the bottom
portion 81 is still more flexible than would be the case if the
95-durometer plastic 100 were the only coating at the bottom
81.
After the second dip, the molds 10 are conveyed through subsequent
conventional dip molding steps until the finished housings are
finally stripped off of mold 10.
Dip molding compositions are well-known in the art. Typically,
polyvinyl chloride resins are compounded with various plasticizers
to create a desired plastisol. The pthalate plasticizers are one
example of plasticizers which can be used. These and other vinyl
resins and plasticizers for dip molding are readily available from
any of a number of producers and suppliers.
While it is not absolutely necessary to use one specific type of
vinyl plastisol, it is believed that superior results are achieved
in the present method by using plastisols of the type described and
claimed in U.S. Pat. No. 3,584,096, issuing on June 8, 1971, to
Sarkis M. Kassouni and Arthur S. Nicholas and assigned to Vinyl
Industrial Products, Inc., the disclosure of which is specifically
incorporated herein by reference. Such plastisols fuse to form a
suede-like finish. They are formulated by mixing a resin having an
average particle size of less than 500 microns with the same or a
similar resin having larger particle sizes. The relationship of the
smaller particle sizes to the larger particle sizes is in the range
of from about 1 to 6.5 to 1 to 200. A suitable plasticizer is then
added to form the plastisol. Such plastisols have a suede-like,
nonreflective finish as they gel up on the heated mold. Even before
being passed through the fusing oven, these plastisols coat to a
roughened surface finish. It is believed that the roughened surface
of the initial coating helps to yield a better adhesion between the
second plastisol layer and the first plastisol layer thereby
minimizing any tendency of the second layer to peel away from the
first layer after final curing and fusing A vinyl plastisol having
a 95-durometer rating on the Shore A scale can be obtained from
Vinyl Industrial Products under the basic code designation of
"95DLD 10-101A." A vinyl plastisol having a 70-durometer rating on
the Shore A scale can be obtained from Vinyl Industrial Products
under the basic code designation of "70DLR 10-097B." These
plastisols are available in various colors. References to the
durometer ratings for plastisols or for the fused plastic will be
understood throughout, including in the claims, to refer to the
durometer reading which the fused plastic has on the Shore A
scale.
The housing 80 discussed above is manufactured in accordance with
this process by placing a lower durometer rating vinyl plastisol in
dip tank 40 and a higher durometer rating plastisol in dip tank 50.
In this way, housing 80 is produced with a more flexible base
portion 81 and a more rigid snout 82. However, the process can be
used in reverse, i.e., with a higher durometer rating plastisol in
dip tank 40 and a lower durometer rating plastisol in dip tank 50.
Housing 110 of FIG. 4 is made in this way. As a result, housing 110
has a very rigid lower portion 111 and a more flexible upper snout
112. This can be seen by reference to the cross-sectional portion
of FIG. 4. The lower portion 111 of the housing consists primarily
of a 95-durometer vinyl plastic 100. Snout 112 is made of a more
flexible 70-durometer vinyl plastic 90, with some of the more
flexible vinyl 90 forming a thin coating over vinyl 100 in the base
area 111. As a result, one has a housing 110 formed integrally in
one piece of plastic which has a rigid base portion 111 for
providing a rigid cover over a seat belt retractor and a flexible
snout portion 112 to serve as a guide and carrier for the seat
belt. Snout 112 should be made of a material sufficiently rigid
that it acts to locate the end of the seat belt generally adjacent
the user. Yet, snout 112 is sufficiently flexible that if one
accidentally bumps against it with their leg, for example, it
merely deflects aside without injuring the person.
As a result of the precess of this invention, a product can be
made, as for example the seat belt housings 80 and 110, which has a
more rigid portion and a more flexible portion. Yet, the product
can be made integrally in one piece of plastic. The need for
separate reinforcing members is eliminated. One can diminish the
possibility of scarring or bruising a person by utilizing either
housing 80 or 110. In the case of housing 80, the base is slightly
more flexible so that if one brushes against the snout 82, it bends
at base 81 more readily. In the case of housing 110, the base 111
is more rigid, but the snout 112 is sufficiently flexible that if
one brushes against it, it tends to bend aside, rather than
injure.
Of course, it will be understood that the above is merely a
preferred embodiment of the invention and that other dip molded
products can be made by the invention and that various changes and
alterations can be made without departing from the spirit and
broader aspects of the invention.
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