WO1997016294A1

WO1997016294A1 - Method of manufacturing a painted vehicle part

Info

Publication number: WO1997016294A1
Application number: PCT/US1996/017313
Authority: WO
Inventors: Larry J. Winget; David J. Davis
Original assignee: Winget Larry J
Priority date: 1995-11-01
Filing date: 1996-10-30
Publication date: 1997-05-09
Also published as: AU7481596A

Abstract

A method is provided for manufacturing a painted plastic part such as a painted air bag cover (10) including a one-piece thermoplastic elastomeric body (16) or structural substrate and a painted one-piece film carrier (30) of a thermoplastic material compatible with the thermoplastic elastomer of the body (16). A bottom contact surface (32) of the film carrier (30) bonds with a front contact surface (22) of a front panel (20) of the body (16) by diffusion between the contact surfaces thereof. The resulting air bag cover (10) is cooled beneath the softening point of both plastics so that a molecular concentration gradient is formed at an interface between the first and second plastics by diffusion within a mold cavity (262) of an injection mold (210) separate from the mold cavity of a vacuum mold (310) which is utilized to vacuum-mold the film carrier (30) after the film carrier (30) is painted.

Description

METHOD OF MANUFACTURING A PAINTED VEHICLE PART

Technical Field

This invention relates to methods of manufac- turing painted parts, and in particular to methods of manufacturing painted plastic parts adapted for use on motor vehicles such as air bag covers and doors.

Background Art

Typically, plastic automotive parts are painted after they are molded. Sometimes such plastic parts are composite plastic parts wherein an outer layer of the part is in-molded with a structural substrate of the part.

Supplemental occupant restraint systems for motor vehicles (i.e., air bags) typically require plastic covers which allow an air bag to exit the air bag cover when deployed. One type of air bag cover includes a front panel which has a predetermined tear seam design formed therein to allow the air bag to exit the air bag cover when deployed. Another type of air bag cover (i.e., on the passenger side) has a predeter¬ mined tear seam design formed in one of its side panels to also allow the air bag to exit the air bag cover when deployed.

Not only must the air bag cover perform the utilitarian function of breaking apart along its prede¬ termined tear seam design, but it should also match the vehicle interior decor and trim materials such as the instrument panel, seats, door panels, steering wheel and posts .

Also, not only must the air bag cover allow the air bag to exit the air bag cover when deployed, but also the air bag cover must stay together to the extent that it does not break apart so as to present projec¬ tile (s) which may injure an occupant of the motor vehi¬ cle.

Also, while it is desirable that the air bag cover be relatively stiff so as to be properly secured to the rest of the air bag system and also possibly during horn actuation, it is also desirable that the surface of the air bag which faces the occupants of a vehicle be soft and smooth to the touch.

Finally, most air bag covers must be painted after molding in order to match or conform the air bag cover to the styling and aesthetic requirements of the associated interior trim products. However, painting such air bag covers may have its own pitfalls, especial- ly where the paint used may have difficulty adhering to the plastic used in the air bag cover. Also, such painting requires a manufacturing step with all the attendant costs and timing problems associated there¬ with. Finally, if too much paint is used, deployment of the air bag may be effected.

U.S. Patent No. 5,354,397 discloses a molding product, such as an interior automotive product, which is covered with a "soft touch feeling" sheet and is produced by placing the sheet in a mold and covering the sheet with a resin. U.S. Patent No. 5,178,708 discloses a multi¬ layer molded article, such as an automotive part, including a fiber-reinforced resin sheet in a vertical press and which has a "soft feeling".

U.S. Patent No. 5,401,449 discloses an automo¬ tive door panel having a "soft luxurious feel" made by laying a facing layer of soft trim on a mold, placing a reinforced fiber mat, a foam layer, and an adhesive layer over the facing layer and injecting plastic into the mold.

U.S. Patent No. 5,362,342 discloses a method of producing a molded panel for a vehicle using a low pressure stream of two-component foamable liquid.

U.S. Patent Nos. 5,304,273 and 5,106,679 disclose molded panels for vehicles having laminated fibrous layers.

U.S. Patent No. 5,261,984 discloses a stamp press for printing decorative textures in thermoplastic composites.

Summary OfThe Invention

An object of the present invention is to provide a method for manufacturing a painted vehicle part while addressing paint quality issues such as: drips, runs, spits, dry spray, light coverage, gloss, color match, contamination and paint adhesion.

Another object of the present invention is to provide a method for manufacturing a painted vehicle part and reducing molding scrap due to splay, flow marks and minor surface imperfections which can be completely covered.

Yet still another object of the present invention is to provide a method for manufacturing a painted vehicle part, such as a composite air bag cover, wherein the air bag cover has increased durability.

In carrying out the above objects and other objects of the present invention a method is provided for manufacturing a painted plastic part adapted for use on a motor vehicle. The method includes the steps of providing a bondable film carrier having top and bottom surfaces, coating the top surface of the film carrier with a layer of paint to obtain a painted film carrier and placing the painted film carrier in a mold cavity of an injection mold having a shape defining the plastic part. The method further includes the step of injecting a thermoplastic elastomer into the mold cavity of the injection mold to generate a structural substrate for the plastic part. The generation of the structural substrate creates sufficient pressure and heat to bond the structural substrate to the bottom surface of the film carrier to form the painted plastic part.

Further in carrying out the above objects and other objects of the present invention, a method is provided for manufacturing a painted air bag cover for an inflatable air bag system. The method includes the steps of providing a bondable film carrier having top and bottom surfaces, coating the top surface of the film carrier with a layer of paint to obtain a painted film carrier and placing the painted film carrier in a mold cavity of an injection mold having a shape defining the air bag cover. The method also includes the step of injecting a thermoplastic elastomer into the mold cavity of the injection mold to generate a structural substrate for the air bag cover. The generation of the structural substrate creates sufficient pressure and heat to bond the structural substrate to the bottom surface of the film carrier to form the air bag cover.

The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.

Brief Description Of The Drawings

FIGURE 1 is an environmental view showing two types of air bag covers constructed in accordance with the method of the present invention;

FIGURE 2 is a front elevational view of one type of air bag cover adapted to be mounted at an end of a steering wheel post;

FIGURE 3 is a sectional view of the air bag cover of Figure 2 taken along lines 3-3 in Figure 2;

FIGURE 4 is a sectional view of the air bag cover of Figure 2 taken along lines 4-4 in Figure 2;

FIGURE 5 is a front elevational view of the second type of air bag cover adapted to be secured within an opening formed in a dashboard or instrument panel on the passenger side; FIGURE 6 is a sectional view of the air bag cover of Figure 5 taken along lines 6-6 of Figure 5;

FIGURE 7 is a sectional view of the air bag cover of Figure 5 taken along lines 7-7 of Figure 5;

FIGURE 8 is a schematic view of a conventional injection molding system and a conventional vacuum molding system which may be utilized to make the air bag covers of the present invention; and

FIGURE 9 is a block diagram flow chart illus- trating the various method steps taken to practice the method of the present invention in order to make the air bag covers.

Best Mode For Carrying Out The Invention

Referring now to the drawing figures, there is illustrated in Figure 1 an environmental view showing first and second embodiments of an air bag cover, generally indicated at 10 and 110, respectively, con¬ structed in accordance with the method of the present invention. The air bag cover 10 preferably is installed over an inflatable air bag system, a portion of which is shown at 12 in Figure 4, mounted at the end of a steer¬ ing wheel post (not shown) having a steering wheel 14. The occupant restraint air bag system is typically mounted at the interior end of the steering wheel post within the steering wheel 14 so that the air bag may deploy between the vehicle driver and the steering wheel post to prevent injury during an accident or other period of sudden deceleration. The air bag cover 110 is typically mounted in a surface 112 of a dashboard or instrument panel, generally indicated at 114, located in underlying rela¬ tionship to a sloped front windshield 116.

Referring now to Figures 2-4, there is illus¬ trated in detail the first embodiment of the air bag cover 10 constructed in accordance with the present invention. The air bag cover 10 includes a one-piece thermoplastic elastomeric body, generally indicated at 16, which is preferably injection molded in an injection mold (Figure 8) and has a predetermined tear seam design as indicated at 18. The thermoplastic elastomeric body 16 includes a front panel 20 having front contact and back surfaces 22 and 24, respectively, and side panels 26 and 28 which extend from the back surface 24 of the front panel 20 and which are adapted to secure the air bag cover 10 over an inflatable air bag system by incorporating holes therein to enable fastening members such as screws to secure the air bag cover 10 to a canister or mounting plate 12 of the air bag system.

The air bag cover 10 also includes a painted one-piece outer layer, generally indicated at 30, vacuum molded in a vacuum mold (Figure 8) from a thermoplastic material compatible with the thermoplastic elastomer of the body 20 so that a bottom contact surface 32 of the film carrier 30 bonds with the front contact surface 22 of the front panel 20 by diffusion between the surfaces 22 and 32 thereof in the injection mold to prevent the body 20 from separating from the film carrier 30 during use of the air bag cover 10.

The plastic material of the film carrier 30 is painted or covered by wiping with a "soft touch" flexi- ble paint which gives the perception of a soft feel to the outer surface of the cover or door. Alternatively, the soft feel may be achieved by wiping a clear, low- gloss coating 33 over a layer of two component paint 31. Preferably, the film carrier can be PVC, urethane or other similar bondable film such as is currently avail¬ able from Kay Automotive Graphics located in Auburn Hills, Michigan. Also, preferably, the thermoplastic elastomer of the body 16 is TPO, polyester or similar thermoplastic. The durometer and elastic or flex modulus of the materials can vary depending on the desired stiffness of the cover. Typically, the duro¬ meter of the body 20 will be in the range of about 37 Shore D to 52 Shore D, while the flexural modulus will be in the range of about 30,000 to 70,000 psi. Also, typically, the durometer of the film carrier 30 will be in the range of about 85 Shore A to 90 Shore A if urethane and 30 Shore D to 40 Shore D if PVC.

As illustrated in Figure 4, the film carrier 30 does not have a predetermined tear seam design formed therein coincident with the predetermined tear seam designed 18 formed in the front panel 20. Rather, the thickness of the film carrier 30 is so small (i.e., typically 6.5 to 9.5 mm with paint if urethane and 5 to 8 mm with paint if PVC) that the film carrier 30 tears to allow the air bag to exit the air bag cover 10 when deployed.

As illustrated in Figures 3 and 4, the front panel 20 has curved side contact surfaces 36 and 38 extending from the front surface 22 and wherein the contact surface 32 of the film carrier 30 is bonded with the contact surfaces 36 and 38 of the front panel 20 by diffusion between the surfaces. Referring now to Figures 5-7, there is illus¬ trated a second embodiment of the air bag cover 110 constructed in accordance with the present invention. The unitary composite air bag cover 110 also includes a one-piece thermoplastic elastomeric body, generally indicated at 118, which is injection molded in an injection mold (Figure 8) with a predetermined tear seam design 120 formed therein, as illustrated in Figure 7. The body 118 also includes a panel 122 having front contact and back surfaces 124 and 126, respectively. The body 118 also includes side panels 128 which extend from the back surface 126 of the panel 122 and which are adapted to secure the air bag cover 110 over an inflat¬ able air bag system (not shown) by being apertured at holes 130. The holes 130 are adapted to receive screws or other fasteners to secure the air bag cover 110 to a canister or mounting plate of its covered air bag system.

The air bag cover 110 also includes a painted one-piece film carrier, generally indicated at 132, which is vacuum molded in a vacuum mold (Figure 8) from a thermoplastic material compatible with the thermoplas¬ tic elastomer of the body 118 so that a bottom contact surface 134 of the film carrier 132 bonds with the contact surface 124 of the front panel 122 by diffusion between the contact surfaces 124 and 134 thereof in the injection mold (Figure 8) to prevent the body 118 from separating from the outer layer 132 during use of the air bag cover 110.

The film carrier 132 is painted in the same fashion as the film carrier 30 so that the painted film carrier 132 has a "soft touch" . Preferably, the thermoplastic elastomer of the body 118 is TPO, polyester or similar thermoplastic and the corresponding thermoplastic material of the film carrier 132 is PVC, urethane, or similar thermoplastic, as in the case of the air bag cover 10.

As shown in Figure 7, one of the side panels 128 of the body 118 has the predetermined tear seam 120 formed therein to allow the air bag to exit the air bag cover 110 when deployed.

As illustrated in Figures 6 and 7, the panel

122 has curved side contact surface 136 extending from the front contact surface 124 and the contact surface 134 of the film carrier 132 is bonded with the contact surfaces 136 of the front panel 122 by diffusion between the contact surfaces 136 and 134 by the temperature and pressure within the mold cavity of the injection mold.

Referring now to Figure 8, there is illustrat¬ ed a conventional injection molding system, generally indicated at 210, and a conventional vacuum molding system, generally indicated at 310, for collectively making a unitary composite air bag cover (either 10 or 110) of the present invention.

Briefly, the injection molding system 210 includes an injection molding machine, generally indi- cated at 212, having a nozzle, generally indicated at 214, for injecting predetermined amounts or shots of molten resin. The injection molding machine 212 in¬ cludes a hydraulic screw ram 216 which is disposed in a bore 218 formed in a barrel 220 of the injection molding machine 212. The ram 216 plasticizes and advances resin towards the nozzle 214. Upon complete plasticization of -li¬ the resin, the screw ram 216 is hydraulically advanced towards threaded portions 222 of the barrel 220 to inject molten plastic through the nozzle 214, as is well known in the art.

The system 210 also includes a mold or mold body generally indicated at 228. As illustrated in Figure 8, the mold 220 comprises a two-plate mold body. One of the plates includes a locating ring 230 for locating the injection end of the nozzle 214. The locating ring 230 is mounted on a clamp plate 232 which, in turn, is fixably connected to a cavity retainer plate or cavity plate 234. A sprue bushing 236 is disposed within the locating ring 230 and is supported by the clamp plate 232. Leader pins 238 on the cavity plate 234 provide the male half of the male-female connection of the first plate with the second plate of the two- plate mold 228. In particular, the second plate in¬ cludes leader pin bushings (not shown) which slidably receive and retain the leader pins therein in the closed position of the mold 228. The leader pin bushings are retained within a core retainer plate 242. The core retainer plate 242 is fixably connected to a support plate 244 which in turn is connected to an injector retainer plate 246. The injector retainer plate 246 is connected to an injector plate 248 which, in turn, is supported by support pillars 250. Support plate 244 is also fixably connected to the ends of a U-shaped ejector housing 252 to which the support pillars 250 are also connected. The plate 246 supports a plurality of return pins 254 and ejector pins 256 which extend toward the plate 234 and through the plates 242 and 244. The ejector pins 256 are provided for ejecting particular injection molded part(s) from the mold 228. Opposing surfaces of male and female mold parts 258 and 260 respectively define a mold cavity 262.

The mold part 258 is supported on the plate 242 and the mold part 260 is supported on the cavity retainer plate 234.

As illustrated in Figure 8, there is illus¬ trated how a one-piece thermoplastic film carrier 300 is first vacuum molded in the vacuum molding system 310 and then placed in the mold cavity 262. Thereafter, the body or structural substrate is molded in the plastic injection molding system 210 to form a completed unitary composite air bag cover wherein the one-piece painted film carrier 302 is bonded to the body.

Referring now to Figure 9, there is illustrat- ed the various process steps of the method of the present invention.

At block 400, coat the top surface of the bondable film carrier such as by wiping with a layer of two-component paint.

At block 402, coat the layer of paint with a clear, low-gloss, "soft-feel" coating, if necessary.

At block 404, place the painted film carrier into a vacuum mold and operate the mold to form a pre¬ form.

At block 405, open the vacuum mold, remove the preform from the vacuum mold and cut edge portions of the preform if necessary. Then, insert the preform into the injection mold. At block 406, insert a molten resin into a mold cavity of the injection mold through its injection aperture at a temperature and pressure sufficient to melt a bottom surface layer of the preform.

At block 408, cool the resulting air bag cover to a temperature beneath the softening point of both resins.

Finally, at block 410, the injection mold is open and the completed air bag cover is removed.

In this way, a one-piece TPO polyester-type plastic or similar thermoplastic substrate, which includes a predetermined tear seam design to allow the air bag to exit the cover when deployed is molded with a painted preform formed in a vacuum molding system. After this procedure, the substrate and the painted film carrier are bonded through the thermoplastic injection process to produce an air bag cover.

The body 16 or 18 of the air bag cover 10 or 110, respectively, may also be formed from polypropyl- ene, TPO (thermoplastic olefin) , TPU (thermoplastic ure¬ thane) or other similar thermoplastic. The correspond¬ ing film carrier 30 or 132 must be compatible with the plastic of the body 16 or 118 so that diffusion (i.e., bonding) between contact surfaces occurs.

The unique features of the driver's side air bag and the passenger's side air bag cover are: i) a soft outer shell or layer to increase customer's satisfaction; ii) a stiff inner material to support the air bag cover during deployment (and during horn actuation with respect to the driver's side air bag cover) ; iii) reduction and/or elimination of paint problems such as drips, runs, spits, dry spray, light coverage and gloss and improved color match and paint adhesion; iv) reduced molding scrap due to splay, flow marks and minor surface imperfections, which can be completely covered; and v) increased durability of the air bag cover.

It should be understood that the film carrier can be positioned in the injection mold either by way of preform, as described above, or by way of a film roll supply. In this way, one can mold in the color at the press or mold thereby avoiding a secondary painting operation.

While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.

Claims

What Is Claimed Is:

1. A method of manufacturing a painted plastic part adapted for use on a motor vehicle, the method comprising the steps of : providing a bondable film carrier having top and bottom surfaces; coating the top surface of the film carrier with a layer of paint to obtain a painted film carrier; placing the painted film carrier in a mold cavity of an injection mold having a shape defining the plastic part; and injecting a thermoplastic elastomer into the mold cavity of the injection mold to generate a struc¬ tural substrate for the plastic part, the generation of the structural substrate creating sufficient pressure and heat to bond the structural substrate to the bottom surface of the film carrier to form the painted plastic part .

2. The method as claimed in claim 1 wherein the step of coating includes the step of wiping the paint on the top surface of the film carrier.

3. The method as claimed in claim 1 wherein the paint is a soft touch, flexible paint.

4. The method as claimed in claim 1 wherein the method further comprises the step of coating the layer of paint with a clear, low-gloss, soft-feel coating.

5. The method as claimed in claim 1 further comprising the step of forming the film carrier to a predetermined shape prior to the step of placing to obtain a preform, and wherein the step of placing includes the step of laying the preform on a support surface of the mold at a predetermined orientation.

6. The method as claimed in claim 1 wherein the bondable film carrier is a thermoplastic carrier.

7. The method as claimed in claim 6 wherein the thermoplastic carrier is a PVC-based film carrier.

8. The method as claimed in claim 6 wherein the thermoplastic carrier is a urethane-based film carrier.

9. The method as claimed in claim 1 wherein the painted film carrier is cut from a roll of painted film and further comprising the steps of unrolling the roll of painted film and cutting the film carrier from the roll prior to the step of placing.

10. The method as claimed in claim 1 wherein the paint is a two component paint .

11. The method as claimed in claim 5 wherein the step of forming includes the steps of placing the painted film carrier in a mold cavity of a vacuum mold having a shape defining the preform.

12. The method as claimed in claim 11 wherein the step of forming further includes the step of cutting a peripheral edge portion of the vacuum molded preform.

13. A method of manufacturing a painted air bag cover for an inflatable air bag system, the method comprising the steps of : providing a bondable film carrier having top and bottom surfaces; coating the top surface of the film carrier with a layer of paint to obtain a painted film carrier; placing the painted film carrier in a mold cavity of an injection mold having a shape defining the air bag cover; and injecting a thermoplastic elastomer into the mold cavity of the injection mold to generate a struc- tural substrate for the air bag cover, the generation of the structural substrate creating sufficient pressure and heat to bond the structural substrate to the bottom surface of the film carrier to form the painted air bag cover.

14. The method as claimed in claim 13 wherein the step of coating includes the step of wiping the paint on the top surface of the film carrier.

15. The method as claimed in claim 13 wherein the paint is a soft touch, flexible paint.

16. The method as claimed in claim 13 wherein the method further comprises the step of coating the layer of paint with a clear, low-gloss, soft-feel coating.

17. The method as claimed in claim 13 wherein the structural substrate has a predetermined tear seam design formed therein in the injection mold and the film carrier is a thermoplastic which forms a one-piece outer layer.

18. The method of claim 17 wherein the structural substrate includes a front panel having the predetermined tear seam design formed therein to allow an air bag to exit the air bag cover when deployed.

19. The method of claim 17 wherein the structural substrate includes side panels adapted to secure the air bag cover over the inflatable air bag system and wherein one of the side panels has the predetermined tear seam design formed therein to allow the air bag to exit the air bag cover when deployed.

20. A method of manufacturing a painted air bag cover for an inflatable air bag system, the method comprising the steps of: providing a bondable film carrier having top and bottom surfaces; coating the top surface of the film carrier with a layer of paint to obtain a painted film carrier; placing the painted film carrier in a mold cavity of a vacuum mold having a shape defining a preform; vacuum molding the painted film carrier in the mold cavity to obtain the preform; placing the preform in a mold cavity of an injection mold having a shape defining the air bag cover; and injecting a thermoplastic elastomer into the mold cavity of the injection mold to generate a struc¬ tural substrate for the air bag cover, the generation of the structural substrate creating sufficient pressure and heat to bond the structural substrate to the bottom surface of the film carrier to form the painted air bag cover.

21. The method as claimed in claim 20 wherein the step of coating includes the step of wiping the paint on the top surface of the film carrier.