Patent Publication Number: US-2005133958-A1

Title: System and method for coloring a spray urethane skin for vehicle interior trim components and skins made thereby

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to spray formed polyurethane skins for vehicle interior trim components and method and systems for manufacturing such skins.  
      2. Background Art  
      Skins for interior trim components provide a durable plastic cover for interior trim component structures and their associated foam padding. Vinyl skins for interior trim components of a vehicle are made by rotocasting a liquid vinyl composition in a heated mold as it is rotated. It has been proposed and implemented in production processes to add liquid color concentrates into the liquid vinyl composition that is provided to rotational molds in rotational molding operations for armrests and small trim components. Vinyl rotocasting processes are labor intensive and are difficult to control and can result in parts having substantial variations in skin thickness. Vinyl skins are not readily recycled and tend to harden over time that may lead to splits in the skin surface over the life of the vehicle. Vinyl skins are also very sensitive to staining when in contact with polyurethanes and exposed to heat and ultraviolet light from the sun.  
      Recently, substantial efforts have been made to develop polyurethane skins for interior trim components. Polyurethane skins may be sprayed in a robotic spraying process that may be computer controlled to obtain uniform skin thickness. Aromatic polyurethane compositions are generally black or gray in color but may also be untinted resulting in an amber color. Aliphatic polyurethane compositions may be provided in many different colors. To assure precise color matching to a vehicle interior component, an in-mold coating is preferably applied to the polyurethane skin forming mold prior to spraying the polyurethane composition over the in-mold coating and onto the mold surface. Examples of interior components that may be made by the polyurethane spray forming operation include instrument panels, glove box doors, knee bolsters, door panels and other interior trim components.  
      Some vehicle interior components have complex shapes and may include difficult to access areas. For example, instrument panel brows may include a narrow section that cannot be easily and completely coated with an in-mold coating composition. Excessive in-mold coating material that may be applied to the surface of the material is wasted and may form runs or irregularities that can adversely effect part quality. In difficult to access areas, such as sharp radii and undercuts, gaps in the in-mold coating may be formed through which the polyurethane skin material may be visible. Moreover, with normal vehicle use and/or during the manufacturing process, scratching or marring in the in-mold coating may occur through which the polyurethane skin may be visible. If so, it may be necessary to paint the skins after forming in areas where there polyurethane skin is visible through the in-mold coating. Such post painting operations are labor intensive, may not produce the same color and gloss level, and require additional capital investment for post painting operation stations.  
      There is a need for a flexible and cost effective method of spray forming polyurethane parts with a continuous and complete color even where an in-mold coating is present having gaps or areas of inadequate coverage.  
      The above problems and needs are addressed by applicant&#39;s invention as summarized below.  
     SUMMARY OF THE INVENTION  
      According to at least one embodiment of the present invention, a method of making polyurethane skins for interior components is provided. The method comprises providing at least one liquid colorant source, providing a polyol source, providing an isocyanate source, providing a spraying device and providing a mixing chamber between the polyol source and the spraying device. The method further comprises introducing a stream of polyol from the polyol source and a stream of colorant from the colorant source into the mixing device to form a stream of colorant/polyol, introducing the stream of colorant/polyol and a stream of isocyanate from the isocyanate source into the spraying device to form a colored polyurethane composition, and spraying the colored polyurethane composition onto a mold to form a first colored polyurethane skin.  
      In a further embodiment of the method, a flush source is provided. The method further comprises providing a stream of flushant from the flush source to the spraying device to flush the spraying device, and, after flushing the spraying device, providing a second stream of colorant/polyol and a second stream of isocyanate to the spraying device to form a second colored polyurethane skin.  
      According to certain aspects of the present invention, the second colored polyurethane skin is a different color than the first colored polyurethane skin.  
      In certain other embodiments, the second colored polyurethane skin is the same color as the first colored polyurethane skin.  
      In at least one embodiment of the method, the at least one colorant source comprises a plurality of colorant sources.  
      According to another embodiment of the present invention, a system for manufacturing polyurethane skins for interior components is provided. The system comprises a source of at least one liquid colorant, a source of polyol, a source of isocyanate, a mixing chamber for mixing polyol with at least one colorant to form a colorant/polyol stream, a spraying device for spraying a mixture of isocyanate and colorant/polyol, and a mold having a mold surface toward which a mixture of isocyanate and colorant/polyol are sprayed by the spraying device onto the mold.  
      In a further embodiment of the system, the system further comprising providing a flush source for providing a stream of flushant to flush the spraying device.  
      In at least one embodiment, the mixing device includes a helical mixing element.  
      These and other aspects of the present invention will be readily understood by one of ordinary skill in the art in view of the attached drawings and following detailed description of the preferred embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic elevation view, partially in section, of one embodiment of a spray applicator assembly;  
       FIG. 2  is a cross-sectional view taken along the line  2 - 2  in  FIG. 1 ;  
       FIGS. 3 and 4  are cross-sectional views taken along the line  3 - 3  in  FIG. 1  showing the mix head with the metering rod in a recirculating and in a dispensing position, respectively;  
       FIG. 5  is a fragmentary perspective view of a polyurethane skin having a partial in-mold coating with a portion of the polyurethane skin visible through the in-mold coating.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that disclosed embodiments are merely exemplary of the invention that may be embodied in various alternative forms. The figures are not necessarily to scale, some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and/or a representative basis for teaching one skilled in the art to variously employ the present invention. Moreover, except where otherwise expressly indicated, all numerical quantities in this description and in the claims indicating amounts of materials or conditions of reactions and/or use are to be understood as modified by the word “about” in describing the broadest scope of this invention. Practice within the numeral limit stated is generally preferred. Also, unless expressly stated to the contrary, percent, “parts of”, and ratio values are by weight and the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more members of the group or class may be equally suitable or preferred.  
      Referring now to  FIG. 1 , a system  10  for spray forming polyurethane skins for vehicle interior trim components is schematically illustrated. A liquid isocyanate source  12  is provided. Any suitable liquid isocyanate, such as an aromatic isocyanate, can be used. Examples of suitable aromatic liquid isocyanates include, but are not necessarily limited to, MDI and TDI. Alternatively, liquid aliphatic isocyanate could also be used. The liquid isocyanate could have suitable additives, such as UV inhibitors/stabilizers. Suitable suppliers of suitable liquid isocyanates include Huntsman of Auburn Hills, Mich.; Bayer Polymers of Pittsburgh, Pa.; and Dow Chemical of Freeport, Tex.  
      A liquid polyol source  14  is provided. Any suitable liquid polyol can be used. In at least one embodiment, the polyol employed is a polyether polyol. Examples of suitable liquid polyols include, but are not necessarily limited to, graft polyols, PhD polyols, Polymer Polyols, and PIPA polyols. Suitable suppliers of suitable liquid polyols include Dow Chemical of Freeport, Tex.; BASF Corporation of Wyandotte, Mich.; and Bayer Polymer of Pittsburgh, Pa. The liquid polyol could have suitable additives, such as UV and antioxidant inhibitors/stabilizers, such as Irganox 1175, Tinuvin 765 and TIN B-75, from Ciba Specialty Chemicals of Terrytown, N.Y., and Cyasorb® Family UV stabilizers and antioxidants from Cytec Polymers of Stamford, Conn.  
      At least one liquid colorant source  16  is provided. As shown, the liquid colorant source  16  could include more than one individual sources  16   a - f  of color. In other words, a plurality of individual liquid colorant sources,  16   a - f,  each containing a different color, such as red, blue, black, etc, could be provided. Any suitable liquid colorant can be used. Examples of suitable liquid colorants include, but are not necessarily limited to, finely ground pigment dispersed in a liquid component useable in the formation of polyurethane, such as polyol and/or isocyanate. Other suitable colorants, such as liquid dyes, can also be used. Suppliers of suitable colorants include Rite Systems of West Chicago, Ill. and PolyOne of North Baltimore, Ohio. In certain embodiments, the liquid colorant includes a UV stabilizer, such as zinc, benzophones, benzotriazole, and benzoxazione to inhibit UV degradation should the resultant polyurethane skin be exposed to UV light. Other suitable additives could be included, such as, but not necessarily limited to, triazines and radical scavengers, as are available from Ciba Specialty Chemicals and Cytec Polymers.  
      A solvent flush source  18  is provided. Any suitable liquid solvent flush can be used. Suitable solvent flushes include solvents that do not react with the isocyanate and polyol. Examples of suitable liquid solvent flushes include, but are not necessarily limited to MEK (methyl ethyl ketone), DBE (dibasic ester), NMP (Naptha) and mineral spirts, as are available from Ashland Chemical of Dublin, Ohio and Shell Oil Solvents of Kent, Ohio.  
      A mixing device  22  is provided. The mixing device  22  receives a stream  24  of polyol and a stream  26  of colorant from the polyol source  14  and the colorant source  18 , respectively. In the mixing device  22 , the polyol and the colorant mix to form a colorant/polyol stream  32 . In a preferred embodiment, the mixing device includes a helical mixing element  34  that promotes mixing in the mixing device  22 .  
      A spraying device  40 , such as a conventional spray gun, is provided. The spraying device  40  receives the colorant/polyol stream  32  and an isocyanate stream  44  from the mixing device  22  and the isocyanate source  12 , respectively. The streams  32  and  44  mix in the mixing device  40  to form a liquid polyurethane composition which is sprayed from the spraying device  40  in the form of an aromatic polyurethane stream  50 . In at least one embodiment, the polyurethane composition is an aromatic composition. The polyurethane stream  50  is directed towards a spray mold  54  to form a colored polyurethane layer  60 , when dried. In at least one embodiment, the polyurethane layer  60  is aromatic.  
      In at least one embodiment, a second polyol stream (not shown) can be fed to the spray device  40  such that the polyurethane composition is formed by a mixture of the colorant/polyol stream  32 , the isocyanate stream  44  and the second polyol stream. In certain embodiments, the second polyol stream (not shown) can be mixed with a colorant in a similar manner as used to form the colorant/polyol stream  32 . In this embodiment, the colorant in the second polyol stream (not shown) can be the same or different than the colorant in the colorant/polyol stream  32 .  
      In at least one embodiment, the polyol, isocyanate and the colorants are maintained at elevated temperatures. In certain embodiments, the elevated temperatures are each independently 70-125° F., and in other embodiments 75-95° F. These elevated temperatures can be maintained withing the sources  12 ,  14  and  16 , the streams  24 ,  26  and  44 , the mixing device  22  and the spray device  40 . Each of the streams  32  and  44  may be provided at a pressure of between 600 psi and 2,000 psi to the spray device  40 .  
      In at least one embodiment, the colorant (i.e., dye or pigment) is provided in an amount of 1-20 wt. %, based on the total weight of the colorant/polyol stream  32 , and in other embodiments an amount of 3-10 wt. %, based on the total weight of the colorant/polyol stream  32 . In certain embodiments, the colorant is provided in an amount of 0.5-15 wt. %, based on the total weight of the polyurethane stream  50 , and in other embodiments an amount of 1-8 wt. %, based on the total weight of the polyurethane stream  50 .  
      In at least one embodiment of the present invention, the colored polyurethane layer  60  is made by first mixing a stream of polyol  24  with at least one stream of a colorant  26  in the mixing device  22  to form a stream of colorant/polyol  32 . In forming the stream of colorant/polyol  32 , the appropriate colorant  16   a - 16   f  is selected to mix with the stream of polyol  24 , depending upon the desired color of the colored polyurethane layer  60 . For instance, if the colored polyurethane layer  60  is desired to be blue, a stream of blue colorant ( 26 ) is sent to the mixing device  22  from the colorant source  16 . In at least one embodiment, a processor (CPU) can be provided to control the operation. The stream of colorant/polyol  32  is then mixed with the isocyanate stream  44  in the spray device  40  to form a colored polyurethane composition which is sprayed from the spraying device  40  in the form of a colored polyurethane stream  50  towards the spray mold  54  to form the colored polyurethane layer  60  of the desired color. In at least one embodiment, after each polyurethane layer  60  is formed, a solvent flush stream  84  is sent from the flush source  18 , through the mixing device  22 , and through the spray device  40  to clean the isocyanate, polyol and colorant from the mixing device  22  and the spray device  40  to prevent clogging of the equipment and/or undesired color mixing. In some embodiments, such as when consecutive runs of the same color polyurethane stream  50  is being used, a flush stream  88  is sent from the flush source  18  directly to the spray device  40 , primarily to prevent clogging. During the flushing step, the spray device  40  delivers a stream of flushant (not shown) into a waste receptacle (not shown) such as a waste bucket. After the spray device  40  has been flushed, the process can be repeated to form a colored polyurethane layer  60  of a desired color. This process allows the selective control of the colored polyurethane layer  60 . For instance, a different color could be selected for each successive colored polyurethane layer  60  that is being manufactured. Alternatively, the same color could be used for long production runs of the colored polyurethane layer  60 . In this case, flush stream  88  could be used. In certain embodiments, however, it may be desired to use both flush streams  84  and  88 .  
      In at least one embodiment, the spray device  40  could be such that the colorant/polyol stream  32  and the isocyanate stream  44  mix outside of the spray device  40  but before reaching the spray mold  54 . In this embodiment, three streams could be exiting the spray device  40  directed at each other to uniformly mix prior to contacting the spray mold  54 . The three streams would be the colorant/polyol stream  32 , the isocyanate stream  44 , and a second polyol stream (not shown) which could either be straight polyol or a mixture of colorant and polyol.  
      In at least one embodiment, the system and the method of the present invention is employed to form a polyurethane skin  70 . In certain embodiments, the polyurethane skin  70  comprises only the colored polyurethane layer  60 . In certain other embodiments, the polyurethane skin  70  comprises the colored polyurethane layer  60  and an in-mold coating (not shown) or paint layer (not shown) disposed over the polyurethane layer  60 . In at least one embodiment, when an in-mold coating (not shown) or paint layer (not shown) are provided, they are the same or similar color as the colored polyurethane layer  60 . In other embodiments, the polyurethane layer  60  is 80% to 95% color matched to the outer IMC or paint layer color with a ΔE of less than 3.0 and gloss level between 1.0 and 10.  
      The polyurethane skin  70  can form a portion of a trim product  80 , such as an instrument panel, glove box door, knee bolster, door panel and other interior trim component. In at least one embodiment, the trim panel  80  comprises the polyurethane skin  70  disposed over a foam layer  72  which is disposed over a substrate  74 , such an ABS substrate. In at least one embodiment, the colored polyurethane skin  70  is removed from the mold  54  and put in a forming tool (not shown) with, but spaced from, substrate  74  to allow foam layer  72  to form therebetween.  
      When the polyurethane skin  70  comprises an in-mold coating (not shown) or paint layer (not shown), the colored layer  60  and the trim panel  80  may have restricted access areas that correspond to areas of the mold  54  that are difficult to reach such as the brow portion of an instrument panel cover. In these instances, gaps in the in-mold coating may be found in restricted access areas and/or scratches may occur at some time during the use to form gaps. When gaps are formed, the colored polyurethane layer  60  may be visible in the gaps. In these instances, the colored polyurethane layer  60  reduces the visibility of any color differential between the colored polyurethane layer  60  and the in-mold coating (not shown) or paint layer (not shown). Also, the colored polyurethane layer  60  makes it possible to have an aesthetic outer appearance without the use of an in-mold coating (not shown) or paint layer (not shown).  
      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. Furthermore, the omission or schematic illustration of conventional equipment, such as pumps, valves, heaters, etc., should not be interpreted as certain convention equipment not being needed or present in the system or as limiting the invention in any manner. 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.