U.S. patent application number 10/445979 was filed with the patent office on 2003-11-06 for gas-assisted two-shot injection molding process.
This patent application is currently assigned to Cascade Engineering, Inc.. Invention is credited to Bull, Kevin Allen, Gedritis, David Anthony.
Application Number | 20030206985 10/445979 |
Document ID | / |
Family ID | 25403493 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030206985 |
Kind Code |
A1 |
Gedritis, David Anthony ; et
al. |
November 6, 2003 |
Gas-assisted two-shot injection molding process
Abstract
A process for injection molding a composite of rigid
thermoplastic and soft thermoplastic, the soft thermoplastic
including a cavity established with pressurized assist gas or an
assist liquid. The process includes the steps of: injecting a hard
molten thermoplastic into a first mold chamber; injecting a soft
molten thermoplastic into a second mold chamber; establishing
communication between the first chamber and the second chamber so
that the rigid thermoplastic and soft thermoplastic integrally
bond; and injecting an assist fluid into the soft thermoplastic to
form a cavity. In a preferred embodiment, the formed composite is
an automotive cowl where the rigid thermoplastic forms the rigid
body portion of the cowl and the integrally bonded soft
thermoplastic forms a compressible bulb seal.
Inventors: |
Gedritis, David Anthony;
(Grand Rapids, MI) ; Bull, Kevin Allen; (Cedar
Springs, MI) |
Correspondence
Address: |
Warner, Norcross & Judd LLP
Intellectual Property Practice Group
900 Fifth Third Center
111 Lyon Street, N.W.
Grand Rapids
MI
49503
US
|
Assignee: |
Cascade Engineering, Inc.
Grand Rapids
MI
|
Family ID: |
25403493 |
Appl. No.: |
10/445979 |
Filed: |
May 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10445979 |
May 27, 2003 |
|
|
|
09894761 |
Jun 28, 2001 |
|
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Current U.S.
Class: |
425/130 |
Current CPC
Class: |
B29C 45/1639 20130101;
B29C 45/1676 20130101; B29C 45/1704 20130101 |
Class at
Publication: |
425/130 |
International
Class: |
B29C 045/16 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A process for fluid-assist injection molding and composite
article comprising the steps of: providing a mold; injecting a shot
of hard thermoplastic resin in molten form into the mold; injecting
a shot of soft thermoplastic resin in molten form into the mold, a
first portion of the soft thermoplastic resin bonding to the hard
thermoplastic resin, a second portion of the soft thermoplastic
resin having a viscous interior; and injecting assist fluid into
the heated viscous interior to establish a cavity in the second
portion of the soft thermoplastic resin.
2. The process of claim 1 comprising the step of allowing the hard
thermoplastic and soft thermoplastic to cool and solidify.
3. The process of claim 2 wherein the hard thermoplastic is
polypropylene and the soft thermoplastic is a thermoplastic
elastomer.
4. The process of claim 1 wherein the mold defines a first chamber
and a second chamber selectively separated by a core slide.
5. The process of claim 4 wherein the core slide is moveable
between a protracted position and retracted position.
6. The process of claim 5 wherein the soft thermoplastic is
prevented from bonding to the hard thermoplastic when the core
slide is in a protracted position and wherein the soft
thermoplastic and hard thermoplastic bond to one another when the
core slide is in a retracted position.
7. A process for injection molding a composite article comprising
the steps of: injecting a hard thermoplastic into a first mold
chamber; injecting a soft thermoplastic into a second mold chamber;
establishing communication between said first mold chamber and the
second mold chamber so that the hard thermoplastic and soft
thermoplastic bond to one another; and introducing a pressurized
gas into said soft thermoplastic whereby a cavity is formed in the
soft thermoplastic.
8. The process of claim 7 wherein the soft thermoplastic with the
cavity therein forms a bulb seal.
9. The process of claim 7 wherein the first and second mold
chambers are selectively separated by a retractable mold
insert.
10. The process of claim 9 wherein said establishing step includes
retracting the mold insert.
11. The process of claim 7 wherein the soft thermoplastic is chosen
from the group consisting of thermoplastic elastomer, thermoplastic
polyurethane, polyvinyl chloride, thermoplastic olefin and
ionomers.
12. The process of claim 8 wherein the hard thermoplastic is chosen
from the group consisting of: polypropylene, polyethylene,
acrylonitrile-butadiene-styrene, polystyrene, polycarbonate,
thermoplastic olefin, nylon, polyacetal, polyethylene
terephthalate, polybutylene terephthalate, acrylonitrile styrene
acrylate, polybutylene terephalate and polyester.
13. A automotive cowl formed by the process of claim 7.
14. A cowl for use in a vehicle between a windshield and a hood of
the vehicle, the cowl comprising: a rigid thermoplastic body
including a top surface, a bottom surface, an elongated front edge,
an elongated back edge, sides extending from said back edge to said
front edge; a compressible bulb seal integrally molded to said
rigid thermoplastic body along said front edge, said seal formed
from a material that is soft relative to said rigid thermoplastic
body and adapted to provide an interface between the cowl and the
vehicle hood.
15. The cowl according to claim 14 wherein said rigid thermoplastic
body is constructed of materials chosen from : polypropylene,
polyethylene, acrylonitrile-butadiene-styrene, polystyrene,
polycarbonate, thermoplastic olefin, nylon, polyacetal,
polyethylene terephthalate, polybutylene terephthalate,
acrylonitrile styrene acrylate, polybutylene terephalate and
polyester.
16. A cowl according to claim 15 wherein the bulb seal is
constructed from materials chosen from thermoplastic elastomer,
thermoplastic polyurethane, polyvinyl chloride, thermoplastic
olefin and ionomers.
17. An apparatus for injection molding composite articles
comprising: a mold including a first chamber and a second chamber;
a retractable insert capable of selectively separating said first
chamber from said second chamber; means for injecting a hard
thermoplastic shot into said first chamber; means for injecting a
soft thermoplastic shot into said second chamber; means for
retracting said insert so that the hard thermoplastic and soft
thermoplastic communicate with and bond to one another; means for
injecting an assist fluid into the soft thermoplastic in the second
chamber to form a cavity in the soft thermoplastic.
18. The apparatus of claim 17 wherein the first mold chamber is in
of a shape corresponding to an automotive cowl body.
19. The apparatus of claim 18 wherein the second mold chamber is of
a shape corresponding to an exterior of a bulb seal.
Description
BACKGROUND
[0001] The present invention relates to injection molding a
composite article including a rigid thermoplastic and a soft
thermoplastic.
[0002] In many industries, it is desirable to combine the
structural characteristics of a rigid thermoplastic with the
sealing abilities of a soft and flexible thermoplastic. For
example, in the automotive industry, a cowl--the transition trim
part between the hood and windshield--typically includes a rigid
piece of plastic and a soft, blade-like seal bonded to an edge of
the rigid piece. The rigid piece forms the body of the cowl and is
secured to a body panel of the automobile. The blade seal engages
the hood, providing an interface between the cowl and the hood to
prevent water from leaking into the engine compartment and to
suppress engine noise.
[0003] Conventional rigid/soft thermoplastic composites such as
cowls are made with a "two-shot" injection molding process. This
process uses a mold that is initially separated by a retractable
mold insert into two chambers--a body chamber corresponding to the
body of the cowl, and a seal chamber corresponding to the blade
seal. In the process, molten structural or "hard" thermoplastic is
injected into and fills the body chamber. Next, the mold insert is
retracted to expose an edge of the structural thermoplastic to the
seal chamber. Then, a molten soft thermoplastic is injected into
and fills the seal chamber, and simultaneously bonds to the exposed
edge to form a rigid/soft thermoplastic composite cowl.
[0004] Although the resultant rigid/soft composite cowl includes
the desired structural rigidity and sealing capability, it suffers
a significant shortcoming. Due to repeated contact with the hood
and exposure to excessive heat from the engine, the blade seal
deforms from its original shape, and becomes incapable of
satisfactorily engaging the hood to provide the required seal. This
loss of sealing ability of the blade seal is common in many other
rigid/soft thermoplastic composite applications as well.
[0005] In an unrelated field, pressurized gas conventionally is
used to add rigidity to hard thermoplastic bodies. In one
application, pressurized gas is injected into molten hard
thermoplastic resin as the resin is injected into a mold. The gas
pushes resin out of its way to form cavities within the hard resin.
When the hard resin cools, the completed hard plastic body includes
cavities that enhance the rigidity and structural strength of the
body. This use of pressurized gas provides a way to increase
rigidity of hard plastic bodies; however, many opportunities exist
to use pressurized gas in novel applications.
SUMMARY OF THE INVENTION
[0006] The aforementioned problems are overcome in the present
invention that provides a single mold injection process in which a
rigid thermoplastic is bonded to a soft thermoplastic and
pressurized assist gas is injected into the soft thermoplastic to
establish a cavity and thereby form a compressible bulb seal.
[0007] In a preferred embodiment, the present invention generally
includes the steps of: injecting a molten rigid thermoplastic into
a first mold chamber; injecting a molten soft thermoplastic into a
second mold chamber; establishing fluid communication between the
first and second mold chambers so that the rigid and soft
thermoplastics bond to one another along an edge; and injecting
pressurized assist gas or liquid into the soft thermoplastic to
establish a cavity in the soft thermoplastic. Preferably, the
pressurized gas pushes molten soft plastic out of the gases' way
and the space occupied by the gas forms the tube-like cavity
through the soft plastic. After the thermoplastics cool, the
resultant composite is removed from the mold. With the cavity
formed in the soft thermoplastic, the soft thermoplastic portion of
the composite forms a compressible and resilient seal with a cross
section resembling a light bulb--hence the name "bulb seal."
[0008] The present inventive process provides an efficient and
economical way to integrally bond a rigid thermoplastic to a soft
thermoplastic that includes a bulb seal in a single mold process.
With the process, resilient bulb seals may now be integrated into a
variety rigid/soft thermoplastic composite articles including
automotive trim pieces, such as cowls, doors and door jambs;
household appliance trim; construction materials, such as doorways
and windows; and the like. Accordingly, these composite articles
offer improved sealing capabilities because the integral bulb seal
is less prone to deformation over time due to repeated contact with
an item against which it interfaces.
[0009] Additionally, the present invention provides a novel use of
assist gas. Rather than use assist gas to make hard thermoplastic
parts more rigid and strong, the present invention uses assist gas
to make soft plastic bodies more supple and resilient.
[0010] These and other objects, advantages and features of the
invention will be more readily understood and appreciated by
reference to the detailed description of the preferred embodiments
and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a sectional view of an automotive cowl composite
formed according to a process of the present invention;
[0012] FIG. 2 is a sectional view of a mold used in the process of
the present invention as hard thermoplastic is injected into the
mold;
[0013] FIG. 3 is a sectional view of the mold when the hard
thermoplastic has been injected into the mold;
[0014] FIG. 4 is a sectional view of the mold as a core is
retracted and soft thermoplastic is injected into the mold;
[0015] FIG. 5 is a sectional view of the mold as pressurized assist
fluid is injected into the soft thermoplastic; and
[0016] FIG. 6 is a sectional view of a completed composite cowl
within the mold.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] In the preferred embodiment, the present invention is
described in connection with the manufacture of injection molded
thermoplastic automotive trim cowls. With reference to FIG. 1, cowl
10, formed according to the process of the present invention,
includes body 20 and bulb seal 30. Body 20 is constructed of a
rigid or hard thermoplastic or resin and bulb seal 30 is
constructed of a supple or soft thermoplastic or resin. The rigid
thermoplastic 21 of the body 20 is integrally bonded to the soft
thermoplastic 31 of the bulb seal 30 at interface 25. In a
preferred embodiment, the hard thermoplastic or resin is
polypropylene (PP) and the soft resin a thermoplastic elastomer
(TPE).
[0018] Optionally, the hard thermoplastic may be any commercially
available hard or rigid thermoplastic including but not limited to
the following: polyethylene (PE), acrylonitrile-butadiene-styrene
(ABS), polystyrene (PS), polycarbonate (PC), thermoplastic olefin
(TPO), nylon (PA), polyacetal (PMMA), polyethylene terephthalate
(PET), polybutylene terephthalate (PBT), acrylonitrile styrene
acrylate (ASA), polybutylene terephalate (PBT) and polyester.
Optionally, mineral, glass fiber or synthetic fiber-filled versions
of rigid thermoplastic, including those above, may be used.
Further, commercially available blends of rigid thermoplastic may
be used, such as ABS-ASA, ABS-PA, ABS-PBT, and the like. The soft
thermoplastic may be any commercially available soft or supple
thermoplastic including but not limited to the following:
[0019] thermoplastic polyurethane (TPU), polyvinyl chloride (PVC),
thermoplastic olefin (TPO) and ionomers.
[0020] The cowl body 20 includes top surface 22, bottom surface 23,
side edge 26 (opposite side edge 26 not shown), an elongated back
edge 24 and an elongated front edge--not visible as it is
coincident with the interface 25 of the rigid thermoplastic 21 and
the soft thermoplastic 31. The elongated back edge 24 abuts the
windshield 110 of the automobile.
[0021] With further reference to FIG. 1, the bulb seal 30 includes
cavity or void 32 extending therethrough. As used herein, "bulb
seal" refers to an article constructed of soft thermoplastic
including an internal cavity of any size, shape or dimension formed
using a gas or liquid assist process. The bulb seal 30 engages the
hood 120 to form a seal when the hood 120 is in a closed position
as depicted. Because bulb seal 30 is constructed of soft
thermoplastic 31 and includes cavity 32 therein, it is compressible
and resilient, and thereby capable of enduring repeated and
continuous sealing engagement with the hood over the useful life of
the vehicle without deforming.
[0022] With reference to FIG. 2, the injection molding equipment 50
of the preferred embodiment will now be described. The injection
molding equipment 50 generally includes upper 52 and lower 54 mold
halves operatively movable between open (not shown) and closed
positions with commercially available hydraulic, pneumatic, or
electric systems. In the closed position, the upper 52 and lower 54
mold halves meet together along mold interface 53. The mold halves
52, 54 define first mold cavity 56 and second mold cavity 58.
[0023] A mold insert or slide core 62 is adapted to slide in
channel 51, which is defined by the upper mold 52. Slide core 62
includes a block, plate or member which prevents materials in the
first mold cavity 56 from communicating with materials in the
second mold cavity 58 when it is in its extended or protracted
position as depicted in FIG. 2. Optionally, the slide core is of
any size, shape or dimension. The slide core 62 is movable from the
protracted position shown in FIG. 2 to a retracted position shown
in FIG. 4, preferably by a hydraulic cylinder 64. Hydraulic
cylinder.64 is in fluid communication with a control pump (not
shown) via hydraulic supply line 66. The hydraulic cylinder 64 is
optionally controlled by a microprocessor (not shown) to move the
slide core 62 as desired. Optionally, the slide core is moveable by
any commercially available actuating mechanism, for example, an
electric servo motor, pneumatic drive, gear drive, rack and pinion
drive, or the like.
[0024] With further reference to FIG. 2, the upper mold 52 further
includes rigid resin injection barrel 72, which is in fluid
communication with a rigid resin supply (not shown) via supply line
74. The hard resin injection barrel is preferably located in the
first mold chamber to deliver a shot or predetermined quantity of
rigid or hard thermoplastic resin--in molten or liquid form--into
the first mold chamber 56.
[0025] The upper mold 52 also includes a soft resin injection
barrel 76, which is in fluid communication with a soft resin supply
(not shown) via supply line 78. The soft resin injection barrel 76
is preferably located in the second mold chamber to deliver a shot
of soft thermoplastic resin--in molten or liquid form--into the
second mold chamber 58.
[0026] Additionally, a gas injection port 80 is disposed in the
upper mold, in communication with second mold chamber 58 and
further in communication with a gas supply (not shown) via gas
supply line 82. The gas injection port is capable of injecting
pressurized gas into the soft thermoplastic resin as that resin is
injected from soft resin injection barrel 76 into the second mold
chamber 58. Optionally, the gas injection port may be disposed in
the lower mold. As will be appreciated by those skilled in the art,
other gas injection systems may be substituted for the injection
ports to inject gas into the mold. For example, the gas may be
injected directly into a resin feed machine (not shown) used to
deliver resin to the mold. Optionally, in cases where resin is
injected through a runner system (not shown) into the mold, the gas
may be injected directly into the runner system.
[0027] Preferably, the pressurized inert gas is nitrogen, however
any commercially available assist gas may be used. Optionally, any
commercially available assist liquid, for example water, may be
used as well. In such an option, the assist liquid would be
injected through the port 80 into the soft thermoplastic resin 31
and operate under principles similar to that of an assist gas. As
used herein, assist fluid refers to any commercially available
assist gas or assist liquid.
[0028] Additionally, temperature and pressure sensors (not shown)
may be distributed throughout the upper and lower 52, 54 mold
halves to monitor temperature and pressure within the chambers 56,
58 at preselected locations. These sensors can be employed with
supply sensors (not shown) monitoring the amount of materials
injected through the hard resin injection barrel 72, the soft resin
injection barrel 76 and the gas injection port 80, to input
information to a microprocessor (not shown) which consequently
controls the injection molding process.
[0029] As will be appreciated, the hard resin injection barrel,
soft resin injection barrel, gas assist injection port 80, slide
core 62 and hydraulic cylinder 64 may be disposed in any
combination in either the upper 52 or lower mold 54. Optionally,
additional molds and slide cores may be combined with the upper 52
and lower 54 molds to create the desired configuration of the hard
resin/soft resin composite. Further, a commercially available
cooling system may be integrated into the upper 52 and lower 54
molds to facilitate cooling of injected resins.
[0030] Method of Manufacture
[0031] Referring now to FIGS. 2-6, the preferred process of the
invention will now be described in connection with the manufacture
of injection molded thermoplastic automotive trim cowls. When the
slide core 62 is moved to its protracted position as depicted in
FIG. 2, the mold halves 52, 54 are clamped together with suitable
clamping pressure to define first mold chamber 56 and second mold
chamber 58. The first mold chamber 56 corresponds to the rigid body
of the cowl and the second mold chamber corresponds to the bulb
seal of the cowl. At this time, a first molten thermoplastic resin,
preferably a rigid thermoplastic 21 is injected into the first mold
chamber through to hard resin injection barrel 72 until the first
mold chamber 56 is satisfactorily filled as depicted in FIG. 3.
[0032] With reference to FIG. 4, the clamping pressure between the
upper 52 and lower mold halves 54 may then be relieved. The slide
core 62 is then retracted in the direction as indicated by the
arrow by hydraulic cylinder 64 into the channel 51 to expose the
rigid thermoplastic body 20, which still may be partially molten,
to the second mold chamber 58.
[0033] With further reference to FIG. 4, after the slide core 62 is
retracted, the upper and lower molds 52, 54 are again clamped
together with pressure. As will be appreciated, this may not be
necessary if pressure between upper and lower mold halves is not
relieved. A soft thermoplastic resin shot is injected through soft
thermoplastic resident barrel 76 into the second chamber 58. Almost
simultaneously, pressurized assist gas from a gas supply (not
shown) is pumped through line 82 and into the second mold cavity 58
via gas injection port 80.
[0034] With reference to FIG. 5, the soft resin shot 31 continues
to pump into the second mold chamber 58 through soft resin
injection barrel 76. As the soft resin fills the second mold
chamber 58, the innermost portion of the soft resin 31 remains
heated and viscous. Accordingly, when pressurized assist gas is
injected into the second mold chamber 58 via gas injection port 80,
the gas pushes the soft thermoplastic resin 31 outwards (as
depicted by the arrows) to form an expanding cavity 32.
[0035] As further depicted in FIG. 5, the soft thermoplastic resin
31 begins to fuse and integrally bond to the rigid thermoplastic 20
at interface 25. Injection of the soft thermoplastic 31 and
pressurized assist gas into second mold cavity 58 continues at a
rate and for a duration of time experimentally determined until the
cavity 32 is expanded to desired dimensions and the soft
thermoplastic resin 31 bonds to rigid thermoplastic 20 along
interface 25. Optionally, assist liquid, rather than assist gas,
may be injected into the soft thermoplastic 31 to form the cavity
32. In another step, the soft thermoplastic is allowed to cool.
[0036] Upon cooling, the soft thermoplastic resin 31 is fully
bonded with interface 25 to the rigid thermoplastic 20 as depicted
in FIG. 6. Cavity 32 is formed so that the soft thermoplastic 31
defines a bulb seal 30. At this point, any excess pressure within
the cavity 32 caused by the pressurized assist gas or assist liquid
therein may be relieved through an exhaust port (not shown) or back
through assist gas injection port 80. After cooling and release of
pressure from the cavity 32, the clamping pressure is relieved, and
the mold halves 52, 54 are separated. The completed cowl is removed
from the mold halves 52, 54.
[0037] The completed cowl is composite in nature, including rigid
thermoplastic body 20 and soft thermoplastic bulb seal 30, which is
bonded at interface 25 to the rigid thermoplastic body 20. The
completed cowl preferably has an appearance of cowl 10 as depicted
in FIG. 1
[0038] The above descriptions are those of the preferred
embodiments of the invention. Various alterations and changes can
be made without departing from the spirit and broader aspects of
the invention as defined in the appended claims, which are to be
interpreted in accordance with the principles of patent law
including the doctrine of equivalents. Any references to claim
elements in the singular, for example, using the articles "a,"
"an," "the," or "said," is not to be construed as limiting the
element to the singular.
* * * * *