Abstract:
The present invention is a hollow article with an integral impact absorbing rib and the method of manufacturing the same. The apparatus is a hollow article made of thermoplastic resin and integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing. There is an integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib between the walls and one or more hollow ribs adjacent to each of two side ends of the flat rib. The impact absorbing rib is disposed at intervals and in an impact action direction. The rib is uniform in shape, dimensions and wall width, and free from reduction of wall width of the inner rib, yet possessing proper structural support and mechanical strength, and excellent in impact absorbing performance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority under 35 U.S.C. Section 119 from a Japanese Patent Application No. 2000-54898 filed on Feb. 29, 2000, and a Japanese Patent Application No. 2000-394056 filed on Dec. 26, 2000, which is incorporated herein by reference for all purpose.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field of the Invention  
           [0003]    The present invention relates to thermoplastic hollow articles that are excellent in rigidity and impact absorption qualities, as well as to the manufacturing process for producing the hollow articles.  
           [0004]    2. Background Art  
           [0005]    Hollow articles are well known in the art and used in a variety of industries and applications. These plastic hollow articles are lightweight, strong, and relatively inexpensive to manufacture using injection or blow molding techniques.  
           [0006]    There are numerous examples of products that employ hollow articles, such as ducts, panels, or housings for electronics, appliances, automobiles, and house wares. In many homes these hollow articles are found in walls, partitions, and panels, such as entrance doors, and indoor air conditioning ducts. Furniture is also manufactured with hollow structures, and includes top plates of desk, partition panels, and bookshelf panels.  
           [0007]    In the appliance sector, housings of some of the components are hollow such as used for refrigerators and televisions. The hollow articles are also used in office equipment, such as the housings of copy machines, facsimile machines and computer peripherals.  
           [0008]    Panels and ducts of dwelling facilities, furniture panel, housing of electric household appliances, housing of office equipment and automotive parts are often required to have a high rigidity. Hollow articles used in such applications are manufactured in integral structures combining a first wall and a second wall by means of a rib linking them mutually within a hollow space. In cases where the appearance is important on both face and back surfaces, a structure termed an “inner rib” is employed. Thus, the first wall and the second wall are projected, in blow molding, until a part of the second wall contacts with a wall to be linked integrally within the hollow space there between.  
           [0009]    The automobile industry uses hollow articles because of the mechanical properties and weight characteristics. Automotive parts include console box lid, hood, door panel, and air conditioning duct. For example, in order to assure the rigidity as a product or to protect the crew from impact of collision, an automotive roof side duct is disposed near both sides of ceiling as explained below (Japanese Patent Application Laid-Open No. 2000-43541).  
           [0010]    The automobile industry is particularly interested in increasing the safety of the vehicles, and at a minimum, complying with the certain safety guidelines. According to the Federal Motor Vehicle Safety Standards (FMVSS), the hollow articles must have a minimum level of impact absorption. The guidelines are established under the Department of Transportation by the National Highway Traffic Safety Administration. There are a number of guidelines and requirements, including FMVSS 201 that addresses occupant protection in interior impact. There are other guidelines that describe related topics such as resistance to roof crushing. Head injuries are calculated according to a ‘heading injury criteria’ (HIC) that is obtained from the deceleration of the head during the duration of the impact. These federal standards must be satisfied in order for vehicle to enter the U.S. market. And, these regulations are continuously being updated as new innovations and features result in improved safety characteristics.  
           [0011]    There are many studies that demonstrate that significant head injuries and trauma occur when the driver or passengers head strikes the interior roof and side panels. A rigid interior wall offers little impact absorbing qualities when struck by a human head. There are a number of techniques used to impart some shock absorbing qualities into the roof and interior panels, but the strict government standards continue to increase and demand greater safety thresholds. The use of ceiling air bags and structural modifications to the support elements are designed to address the impact absorbing qualities however there are issues such as cost and manufacturability that limit the wide-spread use of such features.  
           [0012]    As shown in prior art FIG. 11, the inner rib of a roof side duct is integrally formed by blow molding, wherein an inside wall  101  facing a ceiling interior member  107  and an outside wall  102  facing an inner panel  106  of car body confront each other. A flat impact absorbing rib  103  is disposed along the longitudinal direction in a space  110  between the inside wall  101  and outside wall  102 . A general manufacturing method of this roof side duct is explained by referring to FIG. 12 and FIG. 13.  
           [0013]    Prior art FIG. 12 a  shows a molten parison  300  being poured into opened split molds  201 ,  202 , and then the molds are closed. Next, a rib forming plate  203  is projected toward the second mold  202 , and a neck  303  is formed in the area of first wall  301  of the parison, and its leading end is pressed tightly to the area of second wall  302 . Then, as shown in FIG. 12 a , the rib forming plate  203  is pulled in, the pressurized air is introduced into the parison  300 , and is inflated into a shape along the cavity by the internal pressure of the pressurized air, and the neck  303  is pressed and deformed in the direction of the arrows, while confronting walls are fused integrally, so that an impact absorbing rib  304  is formed.  
           [0014]    According to the prior art, as shown in FIG. 13, when pulling in the rib forming plate  203 , after projecting the rib forming plate and forming a neck at first wall side of the parison, the neck is dragged in the backward direction of the rib forming plate  203 , or is elongated by the blow pressure in the blow process, and the wall thickness and width of the flat rib formed as the confronting walls of the neck are compressed from both sides by internal pressure of the pressurized air are decreased. Thus, at portion  305  the inner rib is reduced in wall width and the shape, and the dimensions and wall thickness of the flat rib are not uniform on the whole. As a result, the rigidity and other mechanical strength of the impact absorbing rib  304  are lowered, and the duct having sufficient impact absorbing performance is not produced. Furthermore, the varying thickness of the inner rib results in inconsistent products with differing impact absorbing qualities. In the described application, such a product may result in inadequate protection in the event of a collision. Other applications may result in improper rigidity and strength and at the very least, inconsistency in the produced hollow article.  
           [0015]    What is needed is a hollow article with a rib of uniform shape, dimensions and wall width. The rib should have excellent mechanical strength and properties. In one embodiment, such as automotive, the hollow article with the rib should have impact absorbing qualities to protect the driver and passengers. The manufacturing method for such an improved hollow article should be cost-effective and have a low defect rate.  
         SUMMARY OF THE INVENTION  
         [0016]    The invention is devised in the light of the problems of the prior art described herein. The present invention is a hollow article having an impact absorbing rib uniform in shape, dimensions and wall width on the whole, especially free from reduction of wall width of the inner rib, yet possessing proper rigidity and mechanical strength, and excellent impact absorbing performance.  
           [0017]    Another aspect of the invention is to ensure compliance with the FMVSS 201 regulations addressing interior head injury criteria. According to FMVSS 201, the interior of the vehicle in the U.S. marketplace must have a head injury criteria (HIC) of less than 1000. The value is determined by striking a dummy head of a certain mass into the regions of the vehicle interior at a certain speed and measuring the shock value. The present invention results in an article that is well within the federal guidelines. In addition, present invention has a greater consistency and repeatability as compared to prior art products that have a higher rate of failure of compliance. The prior art components are generally unable to satisfy the HIC standards, and therefore cannot pass the FMVSS 201 specifications. For example, the roof side ducts of the prior art were tested and the HIC was found to be approximately 1500, which is above the 1000 HIC threshold.  
           [0018]    One object of the invention is a hollow article made of a thermoplastic resin and integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing, an integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib projecting from the second wall to the first wall, and a hollow rib adjacent to each of two side ends of the flat rib, wherein the flat rib and the hollow rib are fused to an inner side of the first wall.  
           [0019]    A further object is the hollow article, wherein the hollow rib is tapered with a more narrow portion at the first wall. Additionally, wherein the integral rib is disposed along a longitudinal direction of the hollow article. And, wherein a plurality of the integral ribs are disposed at a mutual spacing.  
           [0020]    An additional object is the hollow article, wherein the integral rib is disposed in an impact action direction. Also, wherein the hollow article is an automobile component  
           [0021]    An object of the invention is a hollow article made of thermoplastic resin, integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing, an integral rib disposed between the first wall and the second wall, wherein the integral rib comprises a first flat rib projecting from the first wall to a fusion portion, a first hollow rib adjacent to each of two side ends of the first flat rib, a second flat rib projecting from the second wall to the fusion portion, a second hollow rib adjacent to each of two side ends of the second flat rib, wherein the first flat rib and the second flat rib are fused to each other at the fusion portion, and wherein the first hollow rib and the second hollow rib are fused to each other at the fusion portion.  
           [0022]    Another object is the hollow article, wherein the first hollow rib and the second hollow rib form a combined concave hollow rib. Also, the hollow article, wherein the integral rib is disposed along a longitudinal direction of the hollow article. Additional objects of the invention include the hollow article, wherein a plurality of the integral ribs are disposed at a mutual spacing, and also wherein the integral rib is disposed in an impact action direction.  
           [0023]    An object of the invention is a method of blow molding a hollow article having a first wall and a second wall confronting across a spacing, with an integral rib disposed between the first wall and the second wall, comprising the steps of opening a split mold, wherein the split mold has a first mold half with a cavity, a slide core and a pair of support cores on either side of the slide core, and a second mold half with a cavity, a slide core and a pair of support cores on either side of the slide core. Extruding a parison of molten thermoplastic resin between the split mold and closing the split mold, thereby deforming the parison with each sliding core and each of the pair of support cores and forming a first recess and a second recess, wherein a leading end of the first recess and a leading end of the second recess are fused. Next, retracting each of the slide cores and introducing a pressure substance into the parison and inflating the parison along a cavity surface of the split molds and the support cores and forming the integral rib between the first wall and the second wall, wherein the integral rib comprises a pair of flat ribs and a pair of hollow ribs, and cooling the split mold, opening the split mold and removing the hollow article.  
           [0024]    And additional object is the method of blow molding, wherein the step of retracting the slide cores is simultaneous with the step of introducing the pressure substance. Also, wherein the pressurized substance is a gas.  
           [0025]    An object of the invention is a method of blow molding a hollow article having a first wall and a second wall confronting across a spacing, with an integral rib disposed between the first wall and the second wall, comprising the steps of opening a split mold, wherein the split mold has a first mold half with a cavity, and a second mold half with a cavity, a slide core and a pair of support cores on either side of the slide core, extruding a parison of molten thermoplastic resin between the split mold, closing the split mold, deforming the parison with the sliding core and the pair of support cores and forming a recess, wherein a leading end of the recess is fused to an inner surface of an opposing wall side. Finally, retracting the slide core, introducing a pressure substance into the parison, inflating the parison along a cavity surface of the split molds and the support cores and forming the integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib and a pair of hollow ribs, cooling the split mold, opening the split mold and removing the hollow article.  
           [0026]    A further object is the blow melding method, wherein the step of retracting the slide cores is simultaneous with the step of introducing the pressure substance. Furthermore, wherein the pressurized substance is a gas.  
           [0027]    An object of the invention is an apparatus for blow molding a hollow article from a thermoplastic resin, having a first wall and a second wall confronting across a hollow space, and an integral rib disposed for providing structural support and absorbing impact between the first wall and the second wall, comprising a split mold with a first mold half and a second mold half, a slidably engageable slide core for forming a flat rib disposed in at least one of the mold halves, a pair of support cores disposed on at least one of the mold halves for forming a hollow rib and adjacent to each of two side ends of the slide core, and a means of retracting the sliding core.  
           [0028]    Additionally, the apparatus for blow molding, wherein the pair of support cores is integrally disposed in the mold halves. And, wherein the pair of support cores is retractable from within the mold halves. Finally, the apparatus for blow molding wherein a surface of the slide core is treated with fluorine film coating so as to slide smoothly with the parison.  
           [0029]    Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:  
         [0031]    [0031]FIG. 1 a  shows a hollow article for automobile according to a first embodiment of the invention, in which A is a schematic partial perspective view broken in the portion of impact absorbing rib  
         [0032]    [0032]FIG. 1 b  shows a hollow article for automobile according to a first embodiment of the invention showing a schematic partial sectional view along line A-A in FIG. 1 a    
         [0033]    [0033]FIG. 2 a  shows a hollow article for automobile according to a second embodiment of the invention, showing a schematic partial perspective view broken in the portion of impact absorbing rib  
         [0034]    [0034]FIG. 2 b  shows a hollow article for automobile according to a second embodiment of the invention, showing a schematic partial sectional view along line A-A in FIG. 2 a    
         [0035]    [0035]FIG. 3 is an explanatory diagram showing an example of use of the hollow article for an automobile  
         [0036]    [0036]FIG. 4 a  is an example of a manufacturing method of the hollow article for an automobile, with an explanatory diagram showing a state of disposing a parison between opened molds  
         [0037]    [0037]FIG. 4 b  is an example of a manufacturing method for the hollow article for an automobile, showing a schematic sectional view along line A-A in FIG. 4 a.    
         [0038]    [0038]FIG. 5 a  shows a completely closed state of the molds after the process shown in FIG. 4 a , illustrating a schematic partial sectional view along the axial direction of parison  
         [0039]    [0039]FIG. 5 b  shows a completely closed state of the molds after the process shown in FIG. 4 a , illustrating a schematic sectional view along line A-A in FIG. 5 a    
         [0040]    [0040]FIG. 6 a  shows a completely withdrawn state of the slide core after the process shown in FIG. 5 a , depicting a schematic partial sectional view along the axial direction of parison  
         [0041]    [0041]FIG. 6 b  shows a completely withdrawn state of the slide core after the process shown in FIG. 5 a , depicting a schematic sectional view along line A-A in FIG. 6 a    
         [0042]    [0042]FIG. 7 a  shows a completely introduced state of the pressurized air after the process shown in FIG. 6 a , showing a schematic partial sectional view along the axial direction of parison  
         [0043]    [0043]FIG. 7 b  shows a completely introduced state of the pressurized air after the process shown in FIG. 6 a , showing a schematic sectional view along line A-A in FIG. 7 a    
         [0044]    [0044]FIG. 8 a  is another example of a manufacturing method of a hollow article for the automobile, depicting an explanatory diagram showing a state of disposing a parison between opened molds  
         [0045]    [0045]FIG. 8 b  is another example of a manufacturing method of a hollow article for the automobile, depicting a schematic sectional view along line A-A in FIG. 8 a.    
         [0046]    [0046]FIG. 9 a  shows a completely closed state of the molds after the process shown in FIG. 8 a , illustrating a schematic partial sectional view along the axial direction of parison  
         [0047]    [0047]FIG. 9 b  shows a completely closed state of the molds after the process shown in FIG. 8 a , illustrating a schematic sectional view along line A-A in FIG. 9 a    
         [0048]    [0048]FIG. 10 a  shows a completely introduced state of the pressurized air after the process shown in FIG. 9 a , showing a schematic partial sectional view along the axial direction of parison  
         [0049]    [0049]FIG. 10 b  shows a completely introduced state of the pressurized air after the process shown in FIG. 9 a , showing a schematic sectional view along line A-A  
         [0050]    [0050]FIG. 11 is a prior art schematic sectional view after installation of an inner panel, showing a conventional roof side duct.  
         [0051]    [0051]FIG. 12 a  is a prior art process for manufacturing the roof side duct shown in FIG. 11, depicting a schematic sectional view showing a forming state with the narrow neck in the parison by the rib forming plate  
         [0052]    [0052]FIG. 12 b  is a prior art process for manufacturing the roof side duct shown in FIG. 11 a , depicting a schematic sectional view showing a state upon completion of the introduction of pressurized air  
         [0053]    [0053]FIG. 13 is a prior art schematic sectional view along line X-X in FIG. 12 b    
         [0054]    [0054]FIG. 14 is a sectional view side view showing shape of the hollow rib for the embodiment using two sliding cores, wherein the combined hollow ribs are concave in appearance  
         [0055]    [0055]FIG. 15 is a sectional view side view shape of the hollow rib for the embodiment using one sliding core, wherein the hollow rib is tapered in appearance  
         [0056]    Reference Numerals  
         [0057]    [0057]FIGS. 1 a ,  1   b ,  14   
         [0058]    [0058] 1  Hollow matter for automobile  
         [0059]    [0059] 2  First wall  
         [0060]    [0060] 3  Second wall  
         [0061]    [0061] 4  First side wall  
         [0062]    [0062] 5  Second side wall  
         [0063]    [0063] 6  First flat rib  
         [0064]    [0064] 7  Second flat rib  
         [0065]    [0065] 8  First hollow rib  
         [0066]    [0066] 9  Second hollow rib  
         [0067]    [0067] 10  Impact absorbing rib  
         [0068]    [0068] 11  Fusion portion  
         [0069]    [0069]FIGS. 2 a ,  2   b ,  15   
         [0070]    [0070] 21  Hollow matter for automobile  
         [0071]    [0071] 22  First wall  
         [0072]    [0072] 23  Second wall  
         [0073]    [0073] 26  Flat rib  
         [0074]    [0074] 27  Hollow rib  
         [0075]    [0075] 30  Impact absorbing rib  
         [0076]    [0076] 31  Fusion portion  
         [0077]    [0077]FIG. 3 
         [0078]    [0078] 2  First wall  
         [0079]    [0079] 3  Second wall  
         [0080]    [0080] 4  First side wall  
         [0081]    [0081] 5  Second side wall  
         [0082]    [0082] 35  Connection duct  
         [0083]    [0083] 35   a ,  35   b  Junction  
         [0084]    [0084] 36  Discharge port  
         [0085]    [0085]FIGS. 4 a ,  4   b    
         [0086]    [0086] 41  First mold  
         [0087]    [0087] 41   a ,  42   b  Cavity  
         [0088]    [0088] 42  Second mold  
         [0089]    [0089] 43  Extrusion head  
         [0090]    [0090] 44  Parison  
         [0091]    [0091] 45 ,  47  Slide core  
         [0092]    [0092] 46 ,  48  Support core  
         [0093]    [0093]FIGS. 5 a ,  5   b    
         [0094]    [0094] 44   a  First recess  
         [0095]    [0095] 44   b  Second recess  
         [0096]    [0096] 51  Fusion portion  
         [0097]    [0097]FIG. 6 
         [0098]    [0098] 44  Parison  
         [0099]    [0099]FIGS. 7 a ,  7   b    
         [0100]    [0100] 1  Hollow matter for automobile  
         [0101]    [0101] 2  First wall  
         [0102]    [0102] 3  Second wall  
         [0103]    [0103] 6  First flat rib  
         [0104]    [0104] 7  Second flat rib  
         [0105]    [0105] 8  First hollow rib  
         [0106]    [0106] 9  Second hollow rib  
         [0107]    [0107] 51  Fusion portion  
         [0108]    [0108]FIGS. 8 a ,  8   b    
         [0109]    [0109] 61  First mold  
         [0110]    [0110] 62  Second mold  
         [0111]    [0111] 63  Extrusion head  
         [0112]    [0112] 64  Parison  
         [0113]    [0113] 65  Slide core  
         [0114]    [0114]FIGS. 9 a ,  9   b    
         [0115]    [0115] 64  Parison  
         [0116]    [0116] 64   a  Recess  
         [0117]    [0117] 65  Slide core  
         [0118]    [0118] 66  Support core  
         [0119]    [0119] 71  Fusion portion  
         [0120]    [0120]FIGS. 10 a ,  10   b    
         [0121]    [0121] 22  First wall  
         [0122]    [0122] 23  Second wall  
         [0123]    [0123] 24  First side wall  
         [0124]    [0124] 25  Second side wall  
         [0125]    [0125] 26  Flat rib  
         [0126]    [0126] 31  Fusion portion  
         [0127]    [0127] 61  First mold  
         [0128]    [0128] 61   a  Cavity  
         [0129]    [0129] 62  Second mold  
         [0130]    [0130] 65  Slide core  
         [0131]    [0131] 66  Support core  
         [0132]    [0132]FIG. 11 
         [0133]    [0133] 101  Inside wall  
         [0134]    [0134] 102  Outside wall  
         [0135]    [0135] 103  Impact absorbing rib  
         [0136]    [0136] 106  Inner panel  
         [0137]    [0137] 107  Ceiling interior member  
         [0138]    [0138] 110  Space  
         [0139]    [0139]FIGS. 12 a ,  12   b    
         [0140]    [0140] 201  Split mold  
         [0141]    [0141] 202  Split mold  
         [0142]    [0142] 203  Rib forming plate  
         [0143]    [0143] 300  Parison  
         [0144]    [0144] 301  Support core  
         [0145]    [0145] 302  Second wall  
         [0146]    [0146] 303  Neck  
         [0147]    [0147] 304  Impact absorbing rib  
         [0148]    [0148]FIG. 13 
         [0149]    [0149] 304  Impact absorbing rib  
         [0150]    [0150] 305  Reduced portion  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0151]    A first embodiment of the hollow article of the present invention, typically used in the automobile industry, is described in detail herein. FIG. 1 a  shows the hollow article as a partial perspective view broken in the portion of impact absorbing rib. FIG. 1 b  is a partial sectional view along line A-A in FIG. 1 a.    
         [0152]    The hollow article  1  of FIG. 1 a  is made of thermoplastic resin that is integrally formed by blow molding. It includes a first wall  2  and a second wall  3  mutually confronting across a space in an impact acting direction. The impact absorbing direction refers to the orientation of the hollow article in the desired application. For example, if the hollow article  1  were deployed in a roof of an automobile, either the first or second wall  2 ,  3  would be facing the interior of the vehicle and subject to being struck by the head of driver and/or passengers.  
         [0153]    In this particular described embodiment the first wall  2  and second wall  3  are inclined with respect to each other. There is a first side wall  4  and a second side wall  5  formed consecutively to both side ends of the first wall  2  and second wall  3  confronting nearly parallel to each other.  
         [0154]    The sectional shape of the hollow article  1  is not limited to the trapezoidal shape as shown in the embodiment of FIG. 1 a  with respect to the mutually confronting first wall  2  and second wall  3  being inclined. The article  1  may be formed as a square, rectangle, parallelogram or other arbitrary shape depending on the application and still be within the scope of the present invention.  
         [0155]    Between the first wall  2  and second wall  3 , there is an impact absorbing rib  10  formed integrally by blow molding. This impact absorbing rib  10  includes a first flat rib  6  projecting from the first wall  2  with a first hollow rib  8  adjacent to both side ends of the first flat rib  6 . A second flat rib  7  projects from the second wall  3  with a second hollow rib  9  adjacent to both side ends of the second flat rib  7 . The first and second flat rib  6 ,  7  meet at the fusion portion  11  as do the first and second hollow rib  8 ,  9 . In a preferred embodiment the flat rib  6 ,  7  is generally rectangular with side ends connected to the hollow ribs  8 ,  9 .  
         [0156]    In the embodiment shown in FIG. 14, the shape of the interconnected first and second hollow ribs  8 ,  9  is concave. The concave appearance is a result of the mating of the first hollow rib  8  and the second hollow rib  9  at the fusion portion  11 . The first hollow rib  8  and second hollow rib  9  are both tapered such that they are more narrow at the fusion portion  11 , resulting in a concave structure in one embodiment of the invention. The tapered appearance of the first and second hollow rib  8 ,  9  is affected by the shape of the support core to some extent. Thus, in one of the embodiment, a tapered support core with a narrow portion extending to the fusion portion affects the shape of the hollow rib. However, the present invention is not limited to a concave shape for the hollow rib  8 ,  9 .  
         [0157]    A second embodiment of a hollow article  21 , also useful in the automobile industry is described and depicted in FIGS. 2 a  and  2   b . FIG. 2 a  shows a hollow article  21  according to the second embodiment, a schematic partial perspective view broken in the portion of impact absorbing rib. FIG. 2 b  is a schematic partial sectional view along line A-A in FIG. 2 a.    
         [0158]    A hollow article  21  is made of thermoplastic resin formed integrally by blow molding, and includes first wall  22  and second wall  23  mutually confronting across a space in an impact acting direction. The second wall  23  is inclined to the first wall  22  in this embodiment. A first sidewall  24  and second sidewall  25  are formed consecutively to both side ends of the first wall  22  and second wall  23  respectively and confront nearly parallel to each other.  
         [0159]    Between the first wall  22  and second wall  23 , there is an impact absorbing rib  30  formed integrally by blow molding. This impact absorbing rib  30  includes a flat rib  26  projecting from second wall  23  to first wall  22  and a hollow rib  27  adjacent to both side ends of the flat rib  26  which are integrated through a fusion portion  31 .  
         [0160]    As shown in FIG. 15, the shape of the impact absorbing rib  30  is tapered. The tapered appearance is a result of the mating of the hollow rib  27  to the fusion portion  31 . The hollow rib  27  is both tapered such that it is more narrow at the fusion portion  31 . However, the present invention is not limited to a tapered shape for the impact absorbing rib  30 .  
         [0161]    The thermoplastic resin used for blow molding the hollow article is not particularly limited, and any of the thermoplastic grade materials are acceptable. Various compounds may be used for the present invention, and preferred examples include high density polyethylene, medium density polyethylene, polypropylene, denatured polyphenylene oxide, polycarbonate, polyamide, and ABS resin.  
         [0162]    The hollow article of the present invention may be used in automobile applications, such as for automobile damper, hood, door, console box lid, air conditioning duct, and other interior and exterior parts. The implementation of the present invention in the automotive industry can enhance the safety of the vehicle and provide better protection for the driver and passengers.  
         [0163]    The head injury criteria obtained by the present invention was approximately 800, which is within the guidelines established by FMVSS 201. Prior art hollow articles tested had a head injury criteria that was above the limit set by FMVSS 201. In addition, one of the advantages of the present invention is the repeatability, reliability and consistency of the hollow articles. Prior art articles tend to have a much greater variability in the thickness and dimensions of the impact absorbing rib and effecting the head injury criteria.  
         [0164]    [0164]FIG. 3 illustrates an example of the hollow article shown in FIG. 1 a  in the air conditioning duct for an automobile, disposed at both sides of the car compartment ceiling. As shown in FIG. 3, the hollow article  1  is disposed at both sides of the car compartment ceiling and shows two impact absorbing ribs  10  disposed at an interval along the longitudinal direction of the compartment ceiling ducts. One end of the ducts interconnect with junctions  35   a ,  35   b  which are disposed at both sides of a connection duct  35  and the second end side of the duct is closed. First wall  2  and second side wall  5  face the inside of the compartment, and second wall  3  and first side wall  4  face the car body side, and a discharge port  36  is provided at a position not forming the impact absorbing rib  10  of first wall  2 .  
         [0165]    The air conditioning air supplied from the air conditioner (not shown) through the connection duct  35  is discharged toward the passengers and driver through a passage of the hollow article  1  formed at both sides of the impact absorbing rib  10 , from the discharge port  36 , so that the compartment can be air conditioned uniformly.  
         [0166]    In the event of a car crash, if the head of a driver or passenger collides against the first wall  2 , this impact is absorbed by the impact absorbing rib  10  lessening the effects or damages from the impact.  
         [0167]    The impact absorbing rib  10  as described herein is not limited to a single rib per article. As shown in FIG. 3, two or more impact absorbing ribs  10  may be disposed as required at a mutual spacing. The determination of the mutual spacing depends upon many factors including the required structural support, length of the article, dimension of the article, compounds used to manufacture the article, as well the intended impact absorbing qualities desired.  
         [0168]    An example of a manufacturing system of the hollow article is explained in detail in FIGS. 4 a  and  4   b . This particular embodiment utilizes two sliding cores  45 ,  47 . A first mold  41  and second mold  42  are opened. In one embodiment the support cores  46 ,  48  and slide cores  45 ,  47  are projecting to a position where the leading ends  45   a ,  47   a  of the sliding cores are nearly flush with leading ends  46   a ,  48   a  of the support cores  46 ,  48 , and wherein the sliding core is a generally rectangular flat plate disposed between the support cores.  
         [0169]    The first mold  41  includes a cavity  41   a  for defining the outer surface of nearly half of the first wall  2  side of the hollow article, the slide core  45  for forming first flat rib  6 , and a pair of support cores  46  for forming first hollow rib  8  disposed adjacently to both side ends of first flat rib  6 . By contrast, the second mold  42  includes a cavity  42   a  for defining the outer surface of the remaining portion of the second wall  3  side of the hollow article, the slide core  47  for forming second flat rib  7 , and a pair of support cores  48  for forming second hollow rib  9  disposed adjacently to both side ends of second flat rib  7 .  
         [0170]    The support cores  46 ,  48  are not limited to the illustrated example. Retractable support cores  66  like those shown in FIG. 8 may be also used in the present invention.  
         [0171]    Next, a parison  44  made of molten thermoplastic resin is extruded from an extrusion head  43  of an extruder (not shown) and is poured into the opened molds  41 ,  42 , and then the molds  41 ,  42  are gradually closed.  
         [0172]    As the molds  41 ,  42  are being closed, with or without a time delay, the slide core  45  and support cores  46  of the first mold project towards the slide core  47  and support cores  48  of the second mold  42 . As the molds are being closed, as shown in FIGS. 5 a  and  5   b , the first wall side of the parison  44  is pushed and deformed by the slide core  45  and support cores  46  of the first mold  41  and one recess  44   a  is formed, while the second wall side of the parison  44  is pushed and deformed by the slide core  47  and support cores  48  of the second mold  42  and second recess  44   b  is formed. When the molds  41 ,  42  are completely closed, the leading end of first recess  44   a  and leading end of second recess  44   b  are fused, and a fusion portion  51  is formed.  
         [0173]    Then the slide cores  45 ,  47  are retracted as shown in FIGS. 6 a  and  6   b . In this case, both sides of first recess  44   a  and second recess  44   b  are fixed at their positions by the support cores  46 ,  48 . Only slide cores  45 ,  47  are drawn back, and therefore as the slide cores  45 ,  47  are retracted, the recesses  44   a ,  44   b  formed in the parison  44  are not dragged. The combination of the elements contribute to the hollow rib being formed about the support cores with uniform and consistent structural dimensions. Contributing to the production is the surface tension of the thermoplastic material at the fusion portion to maintain the shape within the molds  41 ,  42  while the sliding cores  45 ,  47  are retracted.  
         [0174]    An inflation or blow means such as a blow needle (not shown) is poked into the parison  44 , and pressurized air is introduced to inflate the parison  44  into a shape along the outer surface of the cavities  41   a ,  42   a  and support cores  46 ,  48 , and the wall surfaces facing the recesses  44   a ,  44   b  are pressed and deformed by internal pressure of the pressurized air, as shown in FIGS. 7 a  and  7   b . Although pressurized air is used in this embodiment, it is also within the scope of the invention to utilize pressurized gases to inflate the parison  44 .  
         [0175]    As a result of the pressurized air, the first wall  2  and second wall  3  are disposed in a confronting orientation. Between the first wall  2  and second wall  3 , the leading ends of the first flat rib  6  project from the first wall  2 . The first hollow rib  8 , adjacent to both side ends of first flat rib  6 , projects from the first wall  2 . The leading ends of the second flat rib  7  project from second wall  3 . The second hollow rib  9 , adjacent to both side ends of second flat rib  7 , projects from the second wall  3 . The first flat rib  6  and second flat rib  7  are integrated through the fusion portion  11 , thereby completing impact absorbing rib  10 .  
         [0176]    After cooling in the molds  41 ,  42 , and opening the molds, the hollow article  1  is removed and deflashed.  
         [0177]    Another example of a manufacturing method of the hollow article of the present invention is explained herein. As shown in FIGS. 8 a ,  8   b , first mold  61  and second mold  62  are opened with the slide core  65  and support core  66  of the first mold  61  and second mold  62  retracted as shown.  
         [0178]    Herein, the first mold  61  includes a cavity  61   a  for defining the outer surface of nearly half of the first wall  22  side of the hollow article  21 . By contrast, the second mold  62  includes a cavity  62   a  for defining the outer surface of the remaining portion of the second wall  23  side of the hollow article  21 , the slide core  65  for forming a flat rib  26 , and a pair of support cores  46  for forming a pair of hollow ribs  27  disposed adjacently to both side ends of the flat rib  26 . In this particular embodiment the pair of support cores  46  are retractable. The support cores not limited to the illustrated retractable example, but may be disposed integrally in the second mold  62 .  
         [0179]    A parison  64  made of molten thermoplastic resin is extruded from an extrusion head  63  of an extruder not shown in the diagram, and is poured into the opened molds  61 ,  62 , and the molds are closed.  
         [0180]    As the molds  61 ,  62  are being closed, with or without a time delay, the slide core  65  and support core  66  project toward the second mold  66 , as shown in FIG. 9 a  and  9   b . The first wall side of the parison  64  is pushed and deformed and a recess  64   a  is formed, then the leading end of the recess  64   a  is fused to the inner surface of the second wall side of the parison, and a fusion portion  71  is formed.  
         [0181]    After closing the molds  61 ,  62 , while the support core  66  is projecting, the slide core  65  is retracted. As the slide core  65  is retracted, the recess  64   a  formed in the parison  64  is not dragged or otherwise deformed.  
         [0182]    Next, blow means, such as a blow needle (not shown), is poked into the parison  64 , and pressurized air is introduced to inflate the parison  64 , as shown in FIGS. 10 a  and  10   b  into a shape along the outer surface of the cavities  61   a ,  62   a  and support core  66 . The wall surface facing the recess  64   a  is pressed and deformed by internal pressure of the pressurized air. Other means of introducing pressurization are well known in the art and are within the scope of the present invention.  
         [0183]    As defined herein, the term gas includes air, other gases, and any combination of gases and air. The use of such gases for pressurization is known in the art, the present invention is not limited to air. Other gases are well within the scope of the invention such as nitrogen gas.  
         [0184]    As a result, the confronting first wall  62  and second wall  63  are disposed at an interval to provide proper rigidity and impact absorbing qualities. The ribs are orientated in the impact action direction between the first wall  62  and second wall  63 . The leading ends of the flat rib  26  projecting from first wall  62  to second wall  63  and the hollow rib  27  adjacent to both side ends of the flat rib  26  are integrated through the fusion portion  71  on the inner surface from second wall  63 , thereby completing the impact absorbing rib  30 .  
         [0185]    The final step involves cooling in the molds, opening the molds  61 ,  62 , removing the hollow article  21 , and deflashing. The support cores, if retractable, can be retracted once the hollow ribs are formed.  
         [0186]    In the manufacturing method of the hollow article according to the invention, the surface of the slide core retractably disposed in the mold may be covered with a coating layer made of fluoroplastic resin which makes it easier to slide. The application of the coating layer of fluoroplastic resin is improved by roughening the surface of the slide core and then applying a coating layer of fluoroplastic resin on the rough surface.  
         [0187]    The coating layer is not limited to a thin layer of fluoroplastic resin, but can also be formed by co-deposition of fluoroplastic resin and plating solution such as electroless nickel in a treating solution, and applying and baking the treating solution on the surface of the slide core. Alternatively, the coating layer can also be prepared by forming an electroless nickel coating on the surface of the slide core, and impregnating fluoroplastic resin in this electroless nickel coating.  
         [0188]    The hollow article of the present invention, used for example in the automotive industry, encompasses an impact absorbing rib made of flat rib and hollow rib disposed adjacently to both side ends of the flat rib and is integrally formed between the confronting first wall and second wall disposed at an interval in impact action direction. There is an impact absorbing rib uniform in shape, dimensions and wall thickness on the whole and is integrally formed by blow molding. As a result, a hollow article useful with an excellent impact absorbing performance is obtained.  
         [0189]    The objects and advantages of the invention may be further realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.