Abstract:
An improved, economical, high speed method for attaching a fibrous material to a plastic substrate involves positioning a fibrous material over a surface of a plastic substrate, directing a stream of heated air through the fibrous material and at the surface of the plastic substrate to melt the surface of the plastic substrate, compressing the fibrous material against the melted surface of the plastic substrate, and allowing the melted surface of the plastic substrate to cool and resolidify, whereby fibers of the fibrous material become embedded in the resolidified plastic.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a method for attaching a fibrous batt of material, such as sound absorbing material, to a heat fusible plastic substrate.  
         BACKGROUND OF THE INVENTION  
         [0002]    Sound absorbing fibrous materials or batts are commonly attached to the inner wall of plastic interior automotive panels to absorb sound and reduce noise in the passenger compartment of automobiles. The fibrous materials deaden noises generated by vibrating parts in the automobile and give the driver and passengers a feeling of riding in a more solid, well built vehicle. Among the most commonly employed sound absorbing materials used are shotties, which are fibrous sound insulating batts made by shredding and needling scrap and/or recycled materials, typically scrap and/or recycled plastics such as polypropylene, acrylonitrile-butadiene-styrene terpolymer (ABS), polyethylene terephthalate (PET), etc. Other examples of fibrous sound absorbing materials include glass fiber, synthetic fiber, natural fiber (such as wool, cotton, etc.), and combinations thereof.  
           [0003]    Sound absorbing fibrous materials are typically attached with adhesives to various plastic automotive interior panels, such as door panels, interior trim panels, pillar panels, headliners, dashes, lift-gate panels, visors, and the like. A disadvantage with the use of adhesives for attaching fibrous sound absorbing materials to plastic automotive interior panels is that a relatively high cycle time is required for each part, regardless of whether the adhesive is applied manually or with automated equipment. In either case, the equipment used to apply the adhesive is prone to require significant maintenance, especially on account of the tendency for plugging to occur at spray nozzles, metering orifices, and the like. Adhesives are also relatively expensive. A further disadvantage with adhesives is that there is inevitably a certain amount of adhesive material which will become air-borne during application and will pollute the immediate environment, presenting possible health concerns and requiring frequent cleaning of surfaces where air-borne adhesives accumulate.  
           [0004]    In an effort to eliminate the use of adhesives for attaching a fibrous sound absorbing material to plastic automotive interior panels, ultrasonic welding has been employed. Ultrasonic welding techniques involve the generation of high frequency vibrations which are directed toward a location on a plastic substrate, such as an automotive body panel. The vibrations cause polymer molecules at a selected location of the plastic substrate to vibrate and heat up to the melting point of the plastic. Thereafter, the fibrous material is pressed against the melted plastic and becomes physically bound to the plastic substrate as the melted plastic cools and resolidifies. Although the use of ultrasonic welding eliminates the need for adhesives, it is a relatively slow process, particularly for larger panels in which a plurality of welds are needed to securely attach the fibrous sound absorbing material to the plastic panel. Because of the high cost of ultrasonic welding equipment, a single ultrasonic welding device is used to sequentially create a plurality of welds for a single part. As a result, cycle times are relatively high, and ultrasonic welding does not, in practice, provide a substantial cost advantage over adhesives.  
           [0005]    Therefore, there remains a need for an economical method and apparatus for attaching a fibrous sound absorbing material to a plastic substrate without adhesives.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention provides an improved, economical, high speed method for attaching a fibrous material to a plastic substrate.  
           [0007]    The method of attaching a fibrous material to a plastic substrate involves positioning the fibrous material over a surface of the plastic substrate, and directing a stream of heated air through the fibrous material and at the surface of the plastic substrate which is under the fibrous material. The quantity of air and the temperature of the heated air are sufficient to melt the surface of the plastic substrate which is under the fibrous material. After the surface of the plastic substrate has melted, the fibrous material is pressed against the melted surface of the plastic substrate to cause the fibers of the fibrous material to become immersed in the melted plastic at the surface of the plastic substrate. After the fibers are pressed against the melted plastic, the melted surface of the plastic substrate is allowed to cool and resolidify. The fibers which were immersed in the melted plastic become embedded in the resolidified plastic, thus providing a durable physical bond between certain individual fibers of the fibrous material and the surface of the plastic substrate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a side elevational view, partially in cross section, of an apparatus for attaching a fibrous material to a plastic substrate in accordance with the principles of this invention, with the tool positioned above the plastic substrate and fibrous material, before the fibrous material is attached to the plastic substrate;  
         [0009]    [0009]FIG. 2 is a side elevational view, partially in cross section, of the apparatus shown in FIG. 1, with the tool reciprocated downwardly into the fibrous material to achieve attachment of the fibrous material to the underlying plastic substrate;  
         [0010]    [0010]FIG. 3 is a side elevational view, partially in cross section, of the apparatus, fibrous material, and plastic substrate shown in FIGS. 1 and 2, after the tool has been reciprocated away from the fibrous material and plastic substrate, after the fibrous material has been attached to the plastic substrate;  
         [0011]    [0011]FIG. 4 is an enlarged side elevational view of the tool shown in FIGS.  1 - 3 ;  
         [0012]    [0012]FIG. 5 is a bottom view of the tool shown in FIG. 4;  
         [0013]    [0013]FIG. 6 is a top view of the tool shown in FIGS. 4 and 5;  
         [0014]    [0014]FIG. 7 is a fragmentary side view, partially in cross section, of a modified apparatus in accordance with the principles of the present invention; and  
         [0015]    [0015]FIG. 8 is a perspective of the adjustable support components of the apparatus of FIG. 7. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    An apparatus  10  for attaching a fibrous material  12  to a plastic substrate  14  is shown in FIGS.  1 - 3 . In the illustrated embodiment, apparatus  10  includes a fixture  16  for supporting plastic substrate  14  and fibrous material  12 , with fibrous material  12  generally positioned over plastic substrate  14 . Fixture  16  is mounted on a platform  18 . A support structure  19  is also mounted on platform  18 . Support structure  19  supports a workpiece-engaging tool  20 , and an actuator  22  for reciprocating workpiece-engaging tool  20  between a first position (as shown in FIGS. 1 and 3) in which workpiece-engaging tool  20  is spaced away from the surface of plastic substrate  14  and away from the overlying fibrous material  12 , and a second position (as shown in FIG. 2) in which workpiece-engaging tool  20  compresses fibrous material  12  against a surface of plastic substrate  14 . Illustrated actuator  22  is a pneumatic actuator comprising a cylinder  24  and a piston or rod  26  which reciprocates within cylinder  24 . Piston  26  is fixed, at its lower end, to support structure  19 . Attached to a lower end of cylinder  24  is a bracket  28  on which an air supply tube  30 , air heater  32 , and workpiece-engaging tool  20  are supported. Lower bracket  33  is fixed to air heater  32 , and includes a bearing that slidably engages the lower end  26 A of piston  26 . Air can be supplied to air tube  30  by a flexible air supply line  34 .  
         [0017]    Although illustrated actuator  22  is a pneumatic actuator, actuator  22  may, as an alternative, be a hydraulic actuator, a motor driven screw type linear actuator, or any other suitable mechanical actuator for reciprocating workpiece-engaging tool  20  toward and away from fixture  16 , plastic substrate  14 , and overlying fibrous material  12 .  
         [0018]    Although air heater  32  is preferably an electrical resistance heater, it is conceivable that other types of heating devices may be employed, such as a hot oil to air heat exchanger.  
         [0019]    As shown in FIGS.  4 - 5 , the illustrated workpiece-engaging tool  20  is a plug-like fitting, including a threaded upper portion  36  which can be screwed to a coupling  38  connected to the lower end of air supply tube  30 . The bottom of workpiece-engaging surface  40  conforms with the surface of plastic substrate  14  at which fibrous material  12  is attached to plastic substrate  14 . In most cases, it is desirable that workpiece-engaging surface  40  be substantially flat because in general, it will be desirable to attach the fibrous material  12  to a flat surface of plastic substrate  14 . However, the workpiece-engaging surface  40  of workpiece-engaging tool  20  can be curved, such as cylindrical or hemispherical, or comprised of two or more intersecting planar surfaces, to conform with more complicated surfaces of a plastic substrate if desired. In the illustrated embodiment, workpiece-engaging tool  20  includes five parallel bores or passageways  42  which extend longitudinally through the plug-like tool  20  from an upper surface  44  which is in fluid communication with air supply tube  30 , to the workpiece-engaging surface  40 , which is in contact with fibrous material  12  (as shown in FIG. 2) during the attachment operation. Also, the workpiece-engaging tool  20  includes two perpendicular grooves  47  formed on the flat end surface of the tool. The grooves  47  form a pair of crisscrossed raised ribs of fibrous material in the fibrous material  12  on the plastic substrate  14  that help stiffen and stabilize the fibrous material at the point of attachment, thus helping assure a good bond. The grooves  47  can also act as funnels for controlling air flow in a manner providing a more even distribution of heat. As illustrated, the bores  44  are positioned outside of the grooves  46 , but they may also be positioned in the bores  44  if desired.  
         [0020]    The invention has been illustrated with respect to a fibrous material  12  attached to plastic substrate  14  with an apparatus comprising a single tool for bonding the fibrous material  12  to plastic substrate  14 . However, in most cases a plurality of tools would be used simultaneously for fusing fibrous material  12  to plastic substrate  14  at a plurality of different locations. For example, in the case of a relatively large plastic substrate  14 , such as a door panel, it may be desirable to utilize twelve apparatuses  10  simultaneously to bond fibrous material  12  to a door panel at, for example, five to twenty distinct areas.  
         [0021]    Fibrous material  12  is attached to plastic substrate  14  by first positioning plastic substrate  14  in registry with fixture  16 , and thereafter positioning fibrous material  12  over plastic substrate  14 , as shown in FIG. 1. Thereafter, actuator  22  is activated causing workpiece-engaging tool  20  to be displaced toward plastic substrate  14 , compressing fibrous material  12  between plastic substrate  14  and workpiece-engaging surface  40  of tool  20 . Hot air is blown through passageways  42  of tool  20 , through fibrous material  12 , and impinges upon a surface of plastic substrate  14 , causing a surface portion  46  of plastic substrate  14  to melt. The pressure imposed upon fibrous material  12  by workpiece-engaging tool  20  causes fibers of fibrous material  12  to become immersed in melted plastic  46 . Thereafter, tool  20  is reciprocated away from fibrous material  12 , as shown in FIG. 3, and melted plastic portion  46  cools and resolidifies causing fibers of fibrous material  12  to become embedded within plastic substrate  14 , thereby forming a strong physical bond between fibrous material  12  and plastic substrate  14 . At the point of attachment, the fibrous material  12  forms a depression  46 A having a pair of raised ribs of fibrous material in the shape of the grooves  47  that criss-cross the depression  46 A in a manner adding strength to the fibrous material at the attachment.  
         [0022]    Suitable plastic substrates generally include any of the thermoplastic materials typically employed in automotive interior panels, such as polypropylene, ABS, PET, etc. The fibrous material  12  is generally any fibrous material commonly employed in the automotive industry for sound absorption. Suitable sound absorbing fibrous materials include non-woven batts comprised of glass fibers, synthetic fibers, including shredded thermoplastic and/or thermoset resins, natural fibers, and combinations thereof.  
         [0023]    The flow rate of hot air emerging from tool  20 , penetrating fibrous material  12 , and impinging upon plastic substrate  14 , to melt a portion of plastic substrate  14 , depends upon a variety of factors, including the thickness, composition and density of fibrous material  12 , the melting point temperature of plastic substrate  14 , and the desired area of the bond between fibrous material  12  and plastic substrate  14 . Other factors which may be considered include the contact time between tool  20  and fibrous material  12 , and the number, size and hole pattern for passageways  42 . In the illustrated embodiment, workpiece-engaging surface  40  is approximately square, with dimensions of ⅜ inches by ⅜ inches. It has been found that for the illustrated tool, a hot air flow rate of about 80 standard and cubic feet per minute (SCFM), heated with a 400-watt heater, can be used to bond a quarter inch thick shotty to polypropylene in about 6 seconds. A suitable diameter for each of the five passageways  42  is about 0.063 inches. Smaller or larger passageways  42  may be used if desired. However, it is desirable that the cumulative cross-sectional area of all of the passageways  42  should be about equivalent to the cross-sectional area of a single one-quarter inch diameter passageway when a flow rate of 80 SCFM is used with a 400-watt heater. A plurality of passageways  42 , such as five, is preferred as compared to a single passageway having an equivalent cross-sectional area. This is because a single one-quarter inch passageway tends to concentrate too much heat into too small of an area, causing certain fibrous materials, such as typical shotties to burn or otherwise deteriorate. A suitable pressure of tool  20  on fibrous material  12  is about 80 psi, although this can be varied as desired depending upon the fibrous material employed. Tool  20  can be made from generally any machinable material, with brass currently being a preferred material. However, it is believed that a ceramic tool may have advantages, because it will remain cooler, whereby more heat will be directed toward plastic substrate  14 , where it is most desired, not at fibrous material  12 .  
         [0024]    A four passageway  42  pattern as shown in FIGS. 5 and 6 is most preferred, as it provides uniform heating and results in an excellent bond between a typical substrate (e.g., polypropylene) and typical shotty batts. Preferably a plurality of edge passageways engaging surface  40  are preferred, with the edge passageways preferably being about {fraction (1/16)} inch or less from the edge of workpiece-engaging surface  40 . The edge passageways are preferably uniformly angularly spaced apart around the center of workpiece-engaging surface  40 , irrespective of whether there is a cooler passageway.  
         [0025]    A modified apparatus  10 A (FIGS.  7 - 8 ) includes features and components that are similar to and/or that are identical to the apparatus  10 . In modified apparatus  10 A, these similar and identical features and components are identified by using identical numbers along with a letter “A”. This is done to reduce redundant discussion, and not for another reason.  
         [0026]    The support structure  19 A includes a plate  50 A (FIG. 8) having an opening  51 A. An L bracket  52 A includes a first leg  53 A attached by two bolts  54 A and  55 A that extend through a hole  56 A and a slot  57 A into threaded holes in the plate  50 A. The slot  57 A extends arcuately around the hole  56 A, such that the L bracket  52 A can be rotated even with the bolts  54 A and  55 A in place. Specifically, by loosening the bolts  54 A and  55 A, the bracket  52 A can be angularly adjusted by rotation about hole  56 A to a desired position. Thereafter, the bolts  54 A and  55 A are re-tightened to hold the selected position. The bracket  52 A includes a second leg  60 A that extends downwardly. A C-shaped bracket  61 A includes a vertical leg  62 A and top and bottom horizontal legs  63 A and  64 A. The vertical leg  62 A abuts the second leg  60 A, and is secured to the second leg  60 A by bolts  65 A and  66 A that extend through a hole  67 A and slot  68 A into threaded holes in the vertical leg  62 A. By loosening the bolts  65 A and  66 A, the bracket  61 A can be anularly adjusted by rotation about hole  67 A to a desired position. Thereafter, the bolts  65 A and  66 A are re-tightened to hold the selected position. This “two angle” adjustment is important because it allows an operator to setup the apparatus  10 A so that the tool  20 A extends perpendicularly into engagement with the fibrous material  12 A and substrate  14 A, despite angled surfaces  13 A that occur in the substrate  14 A.  
         [0027]    Cylinder  24 A of actuator  22 A is attached to the top leg  63 A, and the extendable rod  26 A (the lower end of which is hex shaped in cross section to resist rotation) extends through the top leg  63 A and through the bottom leg  64 A, slidably engaging the bottom leg  64 A. The actuator  22 A is connected to a fluid source as previously described in regard to apparatus  10 . A bracket  33 A is attached to the lower end of the rod  26 A, and includes a first bracket plate  70 A attached directly to the rod  26 A and a second bracket plate  72 A. A threaded stop rod  74 A is threaded into the first bracket plate  70 A, and is adjusted to a position where the stop rod  74 A will engage a stop on the tool  16 A to prevent damage to the apparatus  10 A. The second bracket plate  72 A is bolted to the first bracket plate  70 A by bolts  76 A and  78 A, with the bolt  76 A extending through a hole and the bolt  78 A extending through a slot in the second plate  72 A. Thus, the second bracket plate  72 A is angularly adjustable in a fashion similar to the earlier described arrangements for pairs of bolts  54 A and  55 A, and also bolts  65 A and  66 A. This allows for quick and easy adjustment at the point of use of apparatus  10 A, even when the equipment is hot.  
         [0028]    An elongated batt-holder device  80 A (FIG. 7) includes a bracket plate  82 A attached to the plate  50 A (either to its top surface or its bottom surface) by bolts  84 A and  86 A. Where desired, the bolts  84 A and  86 A can extend through a hole and slot as previously described in regard to bolts  65 A and  66 A, thus allowing adjustability of the bracket plate  82 A. A rigid rod  88 A extends downwardly from the bracket plate  82 A. A pressure foot  89 A includes a threaded rod  90 A that threadingly engages a threaded hole in the end of the rigid rod  88 A, and further includes a rubber foot  92 A. By adjusting the threaded rod  90 A and locking it in an adjusted position by the lock nut  94 A, the foot  92 A can be adjusted so that it contacts the fibrous material  12 A and substrate  14 A to hold them in position while the apparatus  10 A works.  
         [0029]    During operation of apparatus  10 A, the fixture  16 A is initially raised, such that the fibrous material  12 A and substrate  14 A come into contact with the foot  92 A. The actuator  22 A extends piston  26 A, causing the assembly of the bracket plate  70 A and  72 A and air supply heater  30 A to extend and heat the selected location, which results in the melted plastic  46 A. The actuator  22 A extends about {fraction (1/16)} inch to ¼ inch when it is extended, causing the tool  20 A to press the fibrous material  12 A against the substrate  14 A. After a surface of the substrate is melted, the pressure is held for a short time, which results in the depression  46 A (FIG. 1).  
         [0030]    Although the invention has been described with respect to attachment of fibrous material to automotive interior panels, such as door panels, interior trim panels, pillar panels, headliners, dashes, lift-gate panels, and visors, the apparatus and methods of the invention can be employed for attaching any of a variety of fibrous materials, especially non-woven fibrous batts, to any of a variety of thermoplastic substrates, for generally any application.  
         [0031]    It will become apparent to those skilled in the art that various modifications to the preferred embodiments of the invention can be made without departing from the spirit or scope of the invention as defined by the appended claims.