Note: Descriptions are shown in the official language in which they were submitted.
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21757~DAD -1-
INJECTION MOLDING PROCESS FOR
PL~T~B~æ PLASTIC SUBSTR~TES
; This invention relates to the art of plating on
plastics and, mor~ particularly, to an injection molding
process for molding platable product substrates having
a skin layer of a first platable resin and an underlying
core o~ a second resin different from the first resin.
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In recent years, many plated products comprise a
molded plastic substrate which is first electrolessly
plated and then electrolytically pIated.
In conventional electroless plating processes, the
product substrat~ is first etched with a stro~g
oxidizing acid or base. The etched substrate is then
immersed in a solution containing a noble metal
catalyst, e.g., a tin-palladium catalyst. If required,
the subst:rate is then immersed in an activator solution,
e.g., e~osins the palladium of the tin-palladium
catalyst. F~n~lly, the activated substrate is immersed
in an autocatalytic electroless plating solution where
an initi~l coating of a conductive metal, such as copper
or nickel, is established on the substrate by chemical
deposition.
In a conventional electrolytic plating process, the
electrolessly plated plastic substrate is first immersed
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1 in cleaning solutions and 'then activated by immersion
in a dilute acid solution, e.g., a dilute sulfuric acid
solution. It is then immersed in one or more
electroplating baths wherein metal is deposited on the
sur~ace of the substrate electrolytically. In many
applications, for example, layers of copper, nickel, and
chromium are plated onto the substrate.
In the above electroless and electrolytic plating
processes, unplated product substrates are typically
mounted on plating racks. Conventional plating racks
comprise a metal framework having metal contacts for
holding the plastic substrates on the rack. ~ith
electrolytic plating racks, the contacts also provide
mPans for electrical communication between the racks and
the plastic substrates. The plastic substrates are
manually mounted on the contacts which hold the
substrates firmly so that they do not fall off the rac~s
in agitated plating solutions and, in the case of
electrolytic plating racks, to provide uninterr~pted
electrical contact with the substrates.
U.S. Patent NoO 4,714,535 assigned to Crown City
Plating Co. provides a product substrate assembly in
which product substrates are molded together with a
rack-engaging framework or xunner system. The molded
frameworX comprises supporting members to which product
substrates are attached and clips or other means for
releasably engaging the framework of a plating rack.
This obviates the need for individual rack contacts.
U.S. Patent No. 4,936,973 also assigned to Crown
City Plating Co. discloses ~ product substrate assembly
having an overflow assembly comprising support members
and clips or other means for releasably engaging the
framework of a plating rack.
The present invention provides a sec~enced
injection molding process particularly useful in the
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1 production of product subst:rate assemblies described in
the above-mentioned U.S. Patent Nos. 4,714,535 and
4,936,373.
Th~ injection molded process comprises first
injecting into a mold cavity for a product substrate a
first resin in an amount less than that requixed to fill
the entire mold cavity. The amount is sufficient to
cover at least a portion o~ the surface of the mold
cavity and preferably to cov~r the entire surface of the
mold cavity. A second resin different ~rom the first
resin is then injected into the mold cavity in an amount
which, in combination wlth the first resin is suff~cient
to Sill the cavity. The second resin is compatible,
i.e~, able to be molded with the first resin into an
integral product substrate.
In the process, the first resin flows into the mold
~- cavity and forms a skin layer over the surface of the
mold cavity. The second resin then flows into the mold
cavity filling the remainder of the cavity and forming
a second layer or core underlying the skin layer.
In a pref~rred embodiment of the invention, the
first resin is a platable resin. The second rPsin may
be platable, but need not be. The second resin may be
a low cost resin and/or a resin providing particular
physical properties, e.g. high strength, temperature
resistance, heavyweight, etc. as desired.
In a particularly preferred embodiment of the
invention there is provided a process ~or injection
molding a product substrate assembly having at least one
product substrate assembly attached to a runner system
or overflow assembly. In such a process, the mold
cavity c:omprises one or more product substrate cavities
connected to a runner system or overflow assembly
cavity. The process comprises injecting a first resin
into the mold cavity for the product substrate in an
amount sufficient to cover at least a portion and
.
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1 preferably all of the surfac:e of the product substrata
cavity, but less than that r.equired to fill the entire
product substrate cavity. A second resin, different
from the first resin is then injected into the product
substrate cavity in an amount, which in combination with
the first resin, is sufficient to fill the entire mold
cavity, including the product substrate cavity and
runner system or overflow assembly cavity.
; These and other faatures and advantages of the
present invention will be bel:ter understood by reference
to the following detailed cl~scriptio~ when considered
5in conjunction with the accompanying drawings wherein:
FIG. 1 is a side cross-sectional view of a product
substrate of the product substrate assembly of FIG. 2;
FIG. 2 is a top view of the product substrate
assembly;
10FIG. 3 is an end view of the product substrate
assembly of FIG. 2;
FIG. 4 is a cross-sectional schematic view showing
; a prefarrPd injection molding process according to the
present invention.
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The injection molding process of the present
invention is particularly applicable to the production
of a plastic product substrate assembly which can be
mounted on the framework of an electrolytic plating rack
and on the framework of an electroless plating rack.
FIGS. 1-3 show such a product substrate assembly.
The product substrate assembly 20 is a one-piece
injection molded unit and comprises a plurality of
; 10 product substrates 21 which, in the embodiment shown,
are automobile window regulator handles. The product
~ substrates 21 are attached to an overflow assembly or
; rack-engaging framework 22. In the embodiment shown,
the overflow assembly 22 comprises a pair of generally
horizontal primary supports 23 and a plurality of
secondary supports 24 which extend forwardly from the
primary support 23 to the product substrates 21 and are
attached to the back side of the product substrates 21
at gate 25. The overflow assembly 22 further comprises
a pair of end clips 26 for releasably attaching the
~ product substrate assembly 20 to the side rails of the
- framework of the electroplating rack.
In the embodiment shown, the overflow assembly 22
also comprises robbers 30 adjacent the product
substrates 21 to reduce the current density at high
current density locations, e.g., the sharp edges around
the rounded base of the window regulator handle. Rather
than, or in addition to robbers, the product substrate
assembly may comprise nonplatable shields to control the
current dlensity at different locations on the product
substrates.
The present invention provides a unique injection
molding process for preparing product substrate
assemhlies as described above. With reference to FIG.
4, there is shown schematically a particularly preferred
injection molding process. In this particular
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l embodiment, the process involves a two-shot molding
process with sequenced injec1:ion during the second shot.
In the first shot, a high strength insert 41 is
formed out of a suitable high strength resin which may
be a platable or nonplatable resin. The insert 4l is
the portion of the window regulator handle which engages
the rotatable shaft of the window regulator assembly of
an automobile. A presently preferred resin for forming
such an insert is polyetherimide. It is understood,
however, that any desired resin may be used. In fact,
rather than a two-shot molding process, a single shot
process may be used wherein a premolded insert is
positioned within the product substrate mold cavity.
In such a process, the premolded insert could be made
of any material including metal. It is also understood
that the presence of a high strength insert, while
desireable for this particular application, is not
required for the practice of the invention or even for
the manufacture of automobile window regulator handles.
In the two shot molding process, following the
first shot, the cavity for the remainder of the window
regulator handle and overflow assembly is moved into
place. A first platable resin 42 is introduced into the
product substrate cavity through runner 43 and gate 44.
The volume of the first platable resin 42 is controlled
and is less than that required to ~ill the entire
product substrate cavity of the mold. The first
plata~le resin 42 is followed by injection of a second
resin 45 in an amount which, combined with the first
resin, is sufficient to fill the entire mold cavity.
In the above process, the first platable resin 42
flows into the product substrate cavity and forms skin
layer 46. A portion of the first resin will also likely
flow into the mold cavities for the overflow assembly
48 and fo~m a skin layer over at least a portion of the
overflow runners. The second resin 45 flows into and
fills the remainder of the product substrate cavity
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1 forming an underlying layer 47 and also flows into and
fills the cavity for the overflow assembly 48.
In this arrangement, the product substrate will
have a skin layer of the first platable resin over its
surface. Underlying the skin layer in at least the
thicker sections of the product substrate will be the
second resin. ~oreover, the overflow assembly 48 well
may be formed primarily with the second resin.
The first resin is a thermoplastic resin which has
a viscosity that is variable with temperature. In the
practice of this process, the first resin is injected
into the mold cavity at a first temperature. Upon
contact with the surface of the mold cavity, the first
resin cools and the viscosity increases. This slows or
stops the flow of the resin contacting the mold surface.
The underlying resin, however, continues to flow until
it reaches other areas of the mold surface. Resins
; having a viscosity which is variable with shear velocity
may also be used for the first resin.
The amount of first resin used is sufficient to
form a sXin layer over at least the critical or Class
A surfaces of the product substrate, i.e~, those
surfaces which are clearly visible during use. For
window regulator handles as shown above, such critical
areas include the front surface of the handle which i5
visible during use. If the product substrate is to be
plated and if the second resin is a nonplatable resin,
the amount of first resin must be selected to assure the
formation of sufficient platable skin layer over non-
critical surfaces to assure electrical communication
between the electroplating rack and the critical areas
of the product substrate after electroless plating.
The second resin must be "compatiblel' with the
first resin. This means that the second resin must be
able to-combine with the first resin to form an integral
molded unit. To be compatible, second resins generally
exhibit a mold shrinkage comparable to or less than khat
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1 of the first resin. The second resin may be a
thermoplastic or thermosetting resin. Examples of
compatible first and second resins are platable grade
ABS as the first resin and non-platable grade ABS,
polypropylene or high impact styrene as the second
resin.
The second resin is selected depending on the goals
to be achieved. For example, if low cost is a goal, an
inexpensive resin may be used as the second resin.
; 10 Alternatively, the second resin may be selected to
control one or more physical properties such as
strength, weight, temperature resistance, impact
resistance, conductivity, permeability to gases,
moisture absorption and the like. The second resin may
contain fillers that the ~irst resin cannot due to the
detrimental effect of the fillers on the decorative
appearance of the first resin. 5uch fillers include
particles or fibers, for example, carbon, glass, metals
or minerals. Fillers, such as temperature-activated
blowing agent~ to provide weight reduction and to
control shrinkage of heavy section areas may be present
in the second resin. Other fillers and the physical
properties imparted by their presence are well known in
the art.
It is also understood, however, that the first
resin need not be platable. For example, the first
resin may be selected to provide a nonplated decorative
finish, if desired.
The present invention does not require the use of
double shot molding as described in the embodiment
above. However, such techniques may be used, not only
to provide inserts as described above, but may, for
example, be used to form the shields shown in FIG. 2
above out of a nonplatable plastic to obviate the need
for electrically isolating the shields after electroless
plating.
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1 The preceding descripti.on has been presented with
reference to the presently preferred embodiments of the
invention which are shown in the accompanying drawings.
Workers skilled in the art and technologv to which this
invention pertains will appreciate that other
alterations or changes in the described structures can
be practiced without meaningfully departing from the
principles, spirit and scope of this invention.
Accordingly, the foregoing description should not
be read as pertaining only to the precise structures
described, but rather should be read consistent with and
as support for the following claims which are to have
their fullest fair scope.
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