Modified slush moldable TPU for instrument panels with seamless airbag deployment capability

Abstract
A vehicle instrument panel skin comprises residues of a thermoplastic urethane elastomer and a propylene-ethylene copolymer. The thermoplastic urethane elastomer includes a polyol, an organic diisocyanate, an optional chain extender, and an optional hindered amine light stabilizer and a benzotriazole ultraviolet stabilizing agent. A method for forming the instrument panel skin is also provided.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention


The present invention relates to resins that are useful for making instrument panel skins used in automobile interiors.


2. Background Art


Currently, three manufacturing processes dominate the vehicle instrument panel manufacturing arena. The dominant processes are slush molding, vacuum forming, and spray urethane. Although each process works reasonably well, there are associated issues.


Vacuum formed instrument panels have a hard “hand” and do not perform cleanly (no shredding or sharding) during −30° C. airbag deployment at −30° C. Moreover, long term weathering has shown that these products become brittle. Spray urethane (aliphatic with inherent light stability and aromatic where a coating is required for weatherability) have less desirable “hand.” Although the spray urethane exhibits property retention after aging and weathering, these materials also exhibit shredding and sharding during −30° seamless airbag deployment. Slush molding can utilize PVC and TPU elastomers. Although certain modified PVCs have acceptable unpainted “hand” for instrument panels, the same materials tend to exhibit the same shredding and sharding issues during −30° C. seamless airbag deployments.


Accordingly, there is a need for new material for forming vehicle instrument panels having acceptable aesthetic touch properties while exhibit proper function during low temperature airbag deployment.


SUMMARY OF THE INVENTION

The present invention solves one or more problems of the prior art by providing in at least one embodiment an instrument panel skin suitable for automobile interior applications. The instrument panel skin comprises residues of a thermoplastic urethane elastomer and a propylene-ethylene copolymer. Typically, the thermoplastic urethane elastomer includes a polyol, a chain extender, an organic diisocyanate, and a hindered amine light stabilizer and a benzotriazole ultraviolet stabilizing agent. Advantageously, the instrument panels of the present invention exhibit both improved touch characteristics while exhibiting acceptable low temperature airbag deployment characteristics.


In another embodiment, a method for forming the instrument panel skin set forth above is provided. The method of this embodiment includes a step of introducing a urethane-based resin composition and a propylene-ethylene copolymer into a mold tool. Typically, these compositions are in the form of a powder. The urethane based resin includes residues of a composition having polyol, a chain extender, an organic diisocyanate, and a hindered amine light stabilizer and a benzotriazole ultraviolet stabilizing agent. The urethane based resin composition is heated to a sufficient temperature to form a layer over at least a portion of the mold tool. Excess powder is poured from the mold tool and heating continued if necessary. The instrument panel skin is removed from the mold tool.





BRIEF DESCRIPTION OF THE DRAWINGS


FIGS. 1A and 1B area pictorial flowchart depicting an embodiment for forming an instrument panel skin; and



FIG. 2 is a pictorial flowchart depicting the application of a support structure to an instrument panel skin.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.


Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention.


It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.


It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.


Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.


With reference to FIGS. 1A and 1B, a pictorial flowchart depicting a slush molding method for forming an instrument panel skin is provided. The method of this embodiment comprises introducing urethane-based resin composition 10 into mold tool 12. At least a portion of mold tool 12 is made from a metal such as stainless steel or nickel. Urethane-based resin composition 10 comprises a thermoplastic urethane elastomer composition and a propylene-ethylene copolymer. Suitable compositions for the thermoplastic urethane elastomer composition are the light stable aliphatic thermoplastic urethane elastomers set forth in U.S. Pat. Nos. 5,824,738 and 6,187,859. The entire disclosures of these patents are incorporated by reference in their entirety.


In a variation of the present invention, the thermoplastic urethane elastomer includes residues of a composition having a polyol and an organic diisocyanate. In a refinement, the thermoplastic urethane elastomer includes a chain extender. In a further refinement, the urethane base resin further includes a hindered amine light stabilizer and/or a benzotriazole ultraviolet stabilizing agent.


In a subsequent step b), urethane based resin composition 10 is heated to a sufficient temperature to form layer 14 over at least a portion of mold tool 12. In one refinement, urethane based resin composition 10 is heated to a temperature between about 170° C. and 250° C. In step c), powder is poured out from mold tool 12. Mold is further heated if necessary so that all the powder melts. Finally, instrument panel skin 20 is removed from mold tool 12 is step e). Typically, instrument panel skin 20 has a thickness from about 0.5 mm to about 2 mm.


Urethane-based resin composition 10 optionally includes one or more pigments. In a refinement, the pigments are present in an amount from about 0.2 to about 10 weight percent of the total weight of the urethane-based resin composition.


In a variation of the present embodiment, mold tool 12 has a texture surface that contacts urethane-based composition 10 to impart a texture surface onto instrument panel skin 20.


With reference to FIG. 2, a flowchart showing the application of a backing to instrument panel skin 20 is provided. In step f), structural component 22 is applied to instrument panel skin 20. Such structural components are applied by any number of methods known to those skilled in the art. In one refinement, structural component 22 has a thickness from about 2 mm to about 20 mm. In some variations, foam resins such as Dow Specflex NM815 are utilized. In one variation, skin 22 may be placed in a mold that provides a predetermined shape and a urethane backing sprayed over the back of instrument panel skin 20. In another variation, structural component 22 can be molded onto instrument panel skin 20. In such circumstances thermoplastic resins may be used.


As set forth above, instrument panel skin 20 comprises the residues of urethane-based resin composition that includes thermoplastic urethane elastomer composition and a propylene-ethylene copolymer. The propylene-ethylene copolymer used in the present embodiment is characterized by a number of physical characteristics. In a refinement, the propylene-ethylene copolymer has a total crystallinity less than about 20%. In another refinement, the propylene-ethylene copolymer has a flexural modulus (1% secant) from about 1500 psi to about 2500 psi and a Shore A hardness from about 40 to about 80 (ISO 898 ASTM D2240). Examples of useful propylene-ethylene copolymers include, but are not limited to the Versify™ line or elastomers commercially available from The Dow Chemical Company. Versify™ 2400 is found to be particularly useful. Typically, the propylene-ethylene copolymer is present in an amount from about 1 to 25 weight percent of the urethane-based composition. In yet another refinement, the propylene-ethylene copolymer is present in an amount from about 5 to 20 weight percent of the urethane-based composition. In still another refinement, the propylene-ethylene copolymer is present in an amount of about 20% weight percent of the urethane-based composition.


The instrument panel skins of the present invention are found to have significant heat stability. In particular, the elongation properties are found to vary by less than 10% after 500 hours aging at 120° C. Moreover, the instrument panel skins maintain sufficient elongation to pass a −30° C. seamless airbag deployment test before and after heat aging 400 hours at 107° C. In a refinement, the instrument panel skins have a combination of low glass transition temperature and retained elongation greater than about 100% after aging for 500 hours at 120° C. Although the operation of the present invention is not limited to any particularly theory, it is believed that the use of the propylene-ethylene copolymer at least partially responsible for these properties.


As set forth above, the thermoplastic skin of the present invention includes the residues of a polyol. Suitable polyols are disclosed in U.S. Pat. Nos. 5,824,738 and 6,187,859. Specific examples, include, but are not limit to polyether polyols. In a variation, the polyol is formed in a process utilizing an organometallic catalyst that results in a polyol having a low level of terminal unsaturation. In one refinement, the polyol has a level of terminal unsaturation less than about 0.04 meq/g. In another refinement, the polyol has a level of terminal unsaturation less than about 0.02 meq/g. A representative example of such a polyol is Poly L 255-28 (sold by Olin corporation, Stamford, Conn.). Poly L 255-28 is a ethylene oxide capped poly (propylene oxide) polyol with an approximate molecular weight of 4000 and a hydroxyl number of 28. The polyol component can be present in amounts ranging from approximately 40% to 70% of the total weight of the thermoplastic urethane elastomer composition. in a refinement, the polyol is present in an amount between 40% and 60% of the total weight of the thermoplastic urethane elastomer composition. The amount of polyol is adjusted in this range to vary the hardness of the elastomer produced.


In a variation of the present embodiment, the thermoplastic urethane elastomer composition includes a chain extending agent. Suitable chain extending agents include aromatic secondary or aliphatic primary or secondary diamines, ethylene glycol, diethylene glycol, propylene glycol, pentane diol, 3-methylpentane-1,5-diol, hexane diol, HQEE [hydroquinone bis(2-hydroxyethyl) ether], CHDM (1,4-cyclohexanedimethanol), and HBPA (hydrogenated bisphenol A). A particularly useful chain extender is 1,4-butanediol. In a refinement, such chain extenders are present in concentrations varying from 6 weight % to 15 weight % of the total weight of the thermoplastic urethane elastomer composition. In another refinement, the chain extenders are present in an amount from 7% to 13% of the total weight of the thermoplastic urethane elastomer composition.


The thermoplastic urethane elastomer composition used in the present embodiment includes one or more isocyanates. Suitable isocyanates include aliphatic organic diisocyanates, or mixture of diisocyanates. Specific examples of organic isocyanates include, but are not limited to, (TMXDI) meta-tetramethylxylene diisocyanate and paratetramethylxylene diisocyanate, isophorone diisocyanate (IPDI), dibenzyl diisocyanate, xylene diisocyanate (XDI), 3,3′-bis toluene-4,4-diisocyanate, hexamethylene diisocyanate (HDI), hydrogenated MDI, hydrogenated XDI, cyclohexane diisocyanate, paraphenylene diisocyanate, mixtures and derivatives thereof and the like. In a refinement, the organic diisocyanates are present in an amount from 20 weight % to 50 weight % of the total weight of the thermoplastic urethane elastomer composition. In another refinement, the organic diisocyanates are present in an amount from 25 weight % to 40 weight % of the total weight of the thermoplastic urethane elastomer composition.


As set forth above, the thermoplastic urethane elastomer composition may include an ultraviolet stabilizing agent. Suitable ultraviolet stabilizing agents may include a combination of a hindered amine light stabilizers (HALS) and a benzotriazole. Examples of HALS include, but are not limited to, bis(1,2,2,6,6-pentamethyl-1-4-piperidinyl)sebacate (Chemical Abstract Number 41556-26-7, also known as Tinuvin 292 or 765 Ciba-Geigy Corp., Hawthorne, N.Y.). Examples of benxotriazoles include hydroxyphenyl benzotriazoles such as a benzotriazole mixture of poly(oxy-1,2-ethanediyl), alpha-[3-[3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropyl]-omega-hydroxy- and poly(oxy-1,2-ethanediyl), alpha-[3-[3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropyl)-omega-[3-[(2H-benzotriazol-2-yl)-5-(1,1,-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy)-, Chemical Abstract Number 104810-47-1 and polyethylene glycol with a molecular weight of 300 Chemical Abstract Number 25322-68-3 (also known as Tinuvin 1130 or 213 Ciba-Geigy Corp., Hawthorne, N.Y.) and any other suitable ultraviolet stabilizing agents. In a refinement, the combination of ultraviolet stabilizing agent are present in a ratio in a range of approximately 1:1 to 2:1 by weight. In another variation, the total concentration of ultraviolet stabilizing agents are present in an amount from about 0.5 to 2.0 weight %, of the total weight of the urethane elastomer composition.


In another variation of the present invention, the urethane elastomer composition includes an antioxidant. Virtually any suitable antioxidant, or mixture of antioxidants, may be used in the practice of the present invention. Representative examples include, but are not limited to, Irganox 1010 [tetrakis (methylene(3,5-di-tert-butyl-4-hydroxycinnamate)]methane from Ciba-Geigy; Irganox 1076 [Octodecyl 3,5 di-tert-butyl-4-hydroxyhydrocinnamate] from Ciba-Geigy; Irganox 245 [Ethylenebis(oxyethylene) bis-(3-tert-butyl-4-hydroxy-5-methylhydrocinnamate)] from Ciba-Geigy; and Vanox 830 (a proprietary blend of a phenolic compound, alkylated diphenylamines and trialkyl phosphite from R. T. Vanderbilt). The antioxidants may be present at a total concentration in a range of approximately 0.10 weight % to 1.0 weight % of the total weight of the urethane elastomer composition. In another refinement, the antioxidants may be present at a total concentration in a range of approximately 0.25 weight % to 0.75 weight % of the total weight of the urethane elastomer composition.


The following examples illustrate the various embodiments of the present invention. Those skilled in the art will recognize many variations that are within the spirit of the present invention and scope of the claims.


Table 1 provides the compositions of several test samples that were used to form skin layers via a slush molding process as set forth above. The components are blended together in a Leistritz twin screw extruder. The resulting pellets are cryogenically ground into a powder, dried, and molded into test panels using a Ford random square grain tool. Table 2 provides the properties of skins made from the test compositions. The aacct Elongation at break is after 500 hrs at 120° C.









TABLE 1







Sample compositions









Sample No.














1
2
3
4
5
6

















Bayer Texin
73.00
63.00
73.00
63.00
73.00
63.00


DP7-3042


3597478 lot


6236 (TPU


composition)


Dow Versify
20.00
30.00


2400


Dow Versify


20.00
30.00


3401


Dow Versify




20.00
30.00


4200


Clariant 3T4A
7.00
7.00
7.00
7.00
7.00
7.00


Medium Dark


Pebble


Concentrate


(pigment)



TOTAL
100.00
100.00
100.00
100.00
100.00
100.00
















TABLE 2





Physical properties.

















Sample No.
Method
Requirements





Skin Thickness
ISO 4593 AST, D374
0.5-2.0 mm or as specified on



Method C
engineering document


Hardness Shore “A”
ISO 898 ASTM D2240
80-90 or as specified on engineering


(ASTM D2240)
15 s dwell
document


Tear Strength
ISO 34 Method B Proc
40 kN/m


(ASTM D624) kN/M
ASTM D624, Die C, 50 m


Die C
mm/min


Tensile Strength at
ISO 527-2 50 mm/min
25 MPa


maximum load


(d3574


MPa


Elongation at break
ISO 527-2 50 mm/min
600%


Resistance to Heat
ISO 188 Method B ASTM
Rating 3 minimum No tackiness,


Aging Color
E145 Type IIA 500 hr
spewing, or staining. Hue change in


Stability(AATCC
120° C. ISO 105-A02
the positive delta b should be


color test)
AATCC Proc. 1
reported. Spotty or non-uniform




staining cause for rejection. Color




shift reversals after 16 hrs Xenon




acceptable. Topcoated & two-tone




tst per 3.8.2 after color & gloss


Cold Flexibility
180° at −20 C. with 19-20 mm
No cracks



mandrel 50 mm × 150 mm


Elongation at break
ISO 527-1 Type 2 ASTM
−5% change from original



D638 Mll 100 mm/min



remove foam



3.7.7 Fogging
SAE J1756 3 hr at 100° C.,
70 minimum N clear film droplest



21° C. cooling, post
or crystals



condition 1 & 16 hrs



Resistance to Fade,
Xenon Arc Weatherometer,
1504 kJ/m2 exposure, min Rating 3-4 min


SAE J1885
min (SAE J1885, ISO



105/A02/AATCC




Evaluation Procedure 1


Mandrel Bend after
19-20 mandrel, 180°,
No cracking, 180° m 19-20 mm


489 kJ
remove foam
mandrel


Resistance to Fade
Xenon Arc Weatherometer,
1504 kJ/m2 exposure, min Rating 3-4 min



min (SAE J1885, ISO



105/A02/AATCC



Evaluation Procedure 1


Mandrel Bend after
19-20 mandrel, 180°,
No cracking, 180° m 19-20 mm


1504 kJ
remove foam
mandrel


Cold Impact
FLTM BO 151-02, 35° C.,
Rating 0 max



90° pendulum angle


Resistance to
SAE J948 Taber, 250
Must be compatible with the


Abrasion
cycles, 500 gram weight,
unabraded adjacent area



CS10 wheels


Resistance to
SAE J365 250 cycles
No evidence of lifting, peeling or


Scuffing

excessive scuffing. Must be




compatible with adjacent unscuffed




area


Resistance to
SAE J365 10 cycles
No severe change in gloss, mar can


Marring

be removed with 4 rubs of the




thumb across mar


Resistance to
FLTM BN108-13
Rating 1 max at 2N with 1 mm


Scratching

Rating 1 max at 2N with 7 mm


Specific Gravity
ASTM D792















Sample No.
1
3
5







Skin Thickness
Thickness, mm:
Thickness, mm:
Thickness, mm: 1.08




1.00
1.02



Hardness Shore “A”
Mean: 70
Mean: 68
Mean: 79



(ASTM D2240)



Tear Strength
Mean: 31.4
Mean: 28
Mean: 29



(ASTM D624) kN/M



Die C



Tensile Strength at
Mean: 4.4
Mean: 4.6
Mean 4.4



maximum load



(d3574



MPa



Elongation at break
Mean: 200 σ 19
Mean: 230 σ 28
Mean: 206 σ 17



Resistance to Heat
Rating: 5
Rating: 5
Rating: 4-5



Aging Color
ΔE: 0.581
ΔE: 0.712
ΔE: 0.512



Stability(AATCC
Δb: 0.042
Δb: 0.710
Δb: 0.500



color test)



Cold Flexibility
No cracks
No cracks
No cracks



Elongation at break
(0%)
(−8.69%)
(−44%)




Mean: 200 σ 3.6
Mean: 210 σ 27
Mean: 115




Original: 200
Original: 230
Original: 206



3.7.7 Fogging
1 h 90(94, 95, 82)
1 h 94(96, 94, 93)
1 h 97(97, 98, 96)




Droplets
Droplets &
Slight fog 16 h




throughout 16 h
iridescence
98(98, 98, 97) Slight fog




99(99, 98, 98)
16 h 99(99, 98, 98)




Droplets around
Droplets




edges



Resistance to Fade,
489 kJ
489 kJ
489 kJ Rating: 4-5 489 kJ



SAE J1885
Sample 1 ΔE:
Sample 1 ΔE: 0.302
Rating: 4-5 489 kJ




0.855 Sample 2
Sample 2 ΔE: 0.234
ΔE: 0.141 489 kJ ΔE:




ΔE: 0.834

0.141 489 kJ Db:






−0.003 489 kJ Db:






−0.160



Mandrel Bend after
No cracks
No cracks
No cracks



489 kJ



Resistance to Fade
1504 kJ
1504 kJ
1504 kJ




Sample 1 ΔE:
Sample 1 ΔE: 0.401
Sample 1 ΔE: 0.245




0.589 Sample 2
Sample 2 ΔE: 0.417
Sample 2 ΔE: 0.264




ΔE: 0.682



Mandrel Bend after


No cracks



1504 kJ



Cold Impact
Rating: 0
Rating: 0
Rating: 0



Resistance to
Sample
Sample compatible
Sample compatible with the



Abrasion
compatible with
with the unabraded
unabraded adjacent area;




the unabraded
adjacent area
slight color transfer from




adjacent area

wheels; grain is intact



Resistance to
Evidence of
Sample is not
Sample is not compatible



Scuffing
excessive scuffing.
compatible with
with adjacent unscuffed




Sample is not
adjacent unscuffed
area; lifting and peeling




compatible with
area; scufffing is not




adjacent unscuffed
excessive




area.



Resistance to
No change in
No change in gloss;
No apparent change from



Marring
gloss, mar can be
mar can be removed
original state




removed with 4
with 4 rubs of the




rubs of the thumb
thumb across mar




across mar



Resistance to
2N Rating 1 mm:
2N Rating 1 mm: 1
2N Rating 1 mm: 1 2N



Scratching
1 2N Rating
2N Rating 7 mm: 1
Rating 7 mm: 1




7 mm: 1



Specific Gravity
1.06
1.05
1.042










While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims
  • 1. An instrument panel skin comprising: residues of a urethane-based resin composition consisting essentially of a urethane elastomer composition and a propylene-ethylene copolymer, the thermoplastic urethane elastomer composition having a polyether polyol, a chain extender, an organic diisocyanate, a hindered amine light stabilizer, a pigment, and a benzotriazole ultraviolet stabilizing agent, wherein the propylene-ethylene copolymer has a total crystallinity less than about 20% and the propylene-ethylene copolymer has a flexural modulus (1% secant) from about 1500 psi to about 2500 psi and wherein the propylene-ethylene copolymer is present in an amount from about 1 to 25 weight percent of the urethane-based resin composition.
  • 2. The instrument panel skin of claim 1 wherein the propylene-ethylene copolymer is present in an amount from about 5 to 20 weight percent of the urethane-based resin composition.
  • 3. The instrument panel skin of claim 1 wherein the propylene-ethylene copolymer is present in an amount from about 10 to 15 weight percent of the resin composition.
  • 4. The instrument panel skin of claim 1 wherein the propylene-ethylene copolymer has a Shore A hardness from about 40 to about 80.
  • 5. The instrument panel skin of claim 1 wherein the polyol has less than about 0.04 meq/g terminal unsaturation.
  • 6. The instrument panel skin of claim 1 wherein the polyol is present in an about of about 40 to 70 weight percent of the urethane elastomer composition.
  • 7. The instrument panel skin of claim 1 wherein the isocyanate is present in an about of about 20 to 50 weight percent of the urethane elastomer composition.
  • 8. The instrument panel skin of claim 1 wherein the urethane based resin composition further includes at least one antioxidant or a residue thereof.
  • 9. The instrument panel skin of claim 1 having at least one textured surface.
US Referenced Citations (7)
Number Name Date Kind
5824738 Humphrey et al. Oct 1998 A
6187859 Humphrey et al. Feb 2001 B1
6410638 Kaufhold et al. Jun 2002 B1
6896962 Valligny et al. May 2005 B1
7030189 Masubuchi Apr 2006 B2
20040092699 Ueno et al. May 2004 A1
20080233376 Weaver Sep 2008 A1
Foreign Referenced Citations (2)
Number Date Country
2001 207051 Jul 2001 JP
WO 2007033115 Mar 2007 WO
Related Publications (1)
Number Date Country
20090256276 A1 Oct 2009 US