Abstract:
A method attaches a liquid-repellent filter to an air vent of a resin molded article accommodating a component/electronic part. A thermal processing tip and a thermally welding tip and a molded article are provided. The thermal processing tip ( 22 ) forms a filter attachment surface ( 14 ) at the inlet or outlet of an air vent ( 16 ) in a thermoplastic resin molded article ( 13 ). A filter fixing rib ( 15 ) is formed around the attachment surface. The porous filter ( 18 ) is dropped onto the filter attachment surface, and a thermal welding tip ( 2 ) is used to melt the filter fixing rib such that the melted resin flows onto and covers a circumferential edge portion of the filter, penetrating the body of the filter. The melted resin penetrating the filter  18  and covering the circumferential edge portion of the filter are cooled to solid, whereby the filter is fixed to the filter attachment surface.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method for attaching a filter having water repellency with ensured air ventilation to an inlet or an outlet of an air vent formed in a thermoplastic resin molded article, a thermally processing tip and a thermally welding tip used in the attaching method, and a molded article. 
       BACKGROUND ART 
       [0002]    In recent years, as the functionality of a mobile phone and an electronic part for an automobile advances, these parts are accommodated in thermoplastic resin cases. 
         [0003]    The case is provided with an air vent that allows communication between the interior of the case and the outside air so that the electronic part is not adversely affected by a change in temperature and a change in atmospheric pressure. 
         [0004]    However, the air vent with no protection may allow rain water to enter the case through the air vent, resulting in a problem in some cases. To avoid the problem, a filter that ensures air ventilation but prevents entry of rain water is attached to the air vent. 
         [0005]    Further, since the case is strongly required to be compact and lightweight, the filter to be used is increasingly made thinner year by year. 
         [0006]    From the viewpoints described above, as a method for attaching a filter to an air vent provided in a case, Patent Literature 1 discloses a thermally welding method including forming a recess in a thermoplastic resin molded article by using a heated plate, bringing a filter into the recess, and fixing the filter. 
         [0007]    Further, as a method for welding a filter for filtering ink to a thermoplastic resin molded article, Patent Literature 2 discloses a method including providing a filter fixing portion with a plurality of fixing ribs, fixing an outer circumferential portion of the filter to the filter fixing portion, and further swaging the welding ribs to surround and fix the outer circumference of the filter. 
         [0008]    Further, as a method for welding and fixing a water-repellent filter to a waterproofing resin product, Patent Literature 3 discloses a thermally caulking method including providing the circumference of the water-repellent filter with a thermally caulking rib, thermally deforming the rib in such a way that the rib is rounded inward and stacked on a circumferential edge portion of the water-repellent filter, and simultaneously using a welding hone to weld and fix the circumferential edge portion of the water-repellent filter to a water-repellent filter attachment portion. 
       CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open No. 2006-231139 
     Patent Literature 2: Japanese Patent Laid-Open No. 08-118672 
     Patent Literature 3: Japanese Patent Laid-Open No. 11-111381 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    In the method disclosed in Patent Literature 1 described above, however, the filter is fixed to the recess formed by a heated plate, but an outer circumferential portion of the filter remains unfixed. Therefore, when the filter is used, the unfixed outer edge portion is lifted up and broken or peeled off in some cases. Caution is therefore undesirably required in work using the filter. 
         [0010]    In the method disclosed in Patent Literature 2 described above, a welding head is used to fix the filter with the double convex welding ribs and the filter outer circumference is fixed by swaging (turning down) the outer circumferential rib. In this case, however, the height of the filter changes as the front ends of the convex welding ribs are thermally deformed, resulting in wrinkles produced over the surface of the filter and along the outer circumference of the filter. Further, three welding apparatus, a welding apparatus, a swaging apparatus, and a rib-crashing, flat-finishing apparatus, are required, undesirably causing an increase in the number of steps and positional shift at the time of transition from each of the steps to another. 
         [0011]    In the method disclosed in Patent Literature 3 described above, since the outer circumferential rib is deformed and covers the outer circumferential edge of the filter, there is no concern about the peeling off or separation of an outer edge portion, unlike in the Patent Literature 1. However, since the method includes thermally deforming the outer circumferential rib in such a way that the rib is rounded inward and stacked on the circumferential edge portion of the water-repellent filter and simultaneously using a welding hone to weld the circumferential edge portion of the water-repellent filter to the water-repellent filter attachment portion, the filter needs to have rigidity (thickness) to some extent. Therefore, in a case where the filter is made of a soft material or has a small film thickness (fluorine-based porous membrane having thickness of 0.3 mm or smaller, in particular, 0.1 mm or smaller), positional shift and wrinkles easily occur, resulting in insufficient water tightness in some cases. 
         [0012]    Further, in this case, since it is assumed that the filter itself has meltability in the first place, the method cannot be applied to a filter made of a material having no meltability or a filter having a melting point higher than that of a molded article to which the filter is attached. 
         [0013]    The present invention relates to a filter that is attached to an air vent in a thermoplastic resin molded article and particularly has a film thickness of 0.3 mm or smaller and is hence soft, for example, a filter that has no firm body and is hence flimsy, a filter that is prone to adhering to almost everything due to static electricity, or filters having any other undesirable physical properties, and an object of the present invention is to provide a filter attaching method that allows a filter to be precisely fixed to a filter attachment portion with no positional shift or wrinkle and prevents the filter from peeling off over time, a thermally processing tip for forming a filter attachment portion and a thermally welding tip for attaching a filter that allow efficient filter attachment, and a molded article with a filter attached to an inlet or an outlet of an air vent. 
       Solution to Problem 
       [0014]    To achieve the object described above, the invention described in claim  1  relates to a method for attaching a filter to an air vent, characterized in that the method includes: a. forming a filter fixing rib around an inlet or an outlet of an air vent formed in a thermoplastic resin molded article; b. then dropping a filer inside the filter fixing rib; c. then heating and melting the filter fixing rib to cause the melted resin to flow onto a circumferential edge of the filter and cover the circumferential edge of the filter and to penetrate the filter body at the same time; and d. then cooling the resin covering the circumferential edge of the filter and penetrating the filter body to allow the resin to solidify so that the filter is fixed to an inlet or outlet portion of the air vent. 
         [0015]    The invention described in claim  2  is characterized in that in the filter attaching method described in claim  1 , the air vent includes a sound hole 
         [0016]    The invention described in claim  3  is characterized in that in the filter attaching method described in claim  1  or  2 , the filter has a ventilation property and a liquid-repellency property. 
         [0017]    The invention described in claim  4  is characterized in that in the filter attaching method described in any one of claims  1  to  3 , the filter has a gap or a minute hole through which the melted resin penetrates the filter. 
         [0018]    The invention described in claim  5  is characterized in that in the filter attaching method described in any one of claims  1  to  4 , the filter has a thickness ranging from 30 to 300 μm. 
         [0019]    The invention described in claim  6  is characterized in that in the filter attaching method described in any one of claims  1  to  5 , the filter is made of a fluorine-based porous resin. 
         [0020]    The invention described in claim  7  is characterized in that in the filter attaching method described in any one of claims  1  to  6 , the filter has a melting point higher than a melting point of a molded article to which the filter is attached. 
         [0021]    The invention described in claim  8  is characterized in that in the filter attaching method described in any one of claims  1  to  7 , a surface of a filter drop portion surrounded by the fixing rib is lower than, flush with, or higher than a surface of the molded article. 
         [0022]    The invention described in claim  9  is characterized in that in the filter attaching method described in any one of claims  1  to  8 , the filter fixing rib formed in the molded article is molded integrally with the molded article when the molded article is molded. 
         [0023]    The invention described in claim  10  is characterized in that in the filter attaching method described in any one of claims  1  to  9 , the filter has a circular or polygonal contour. 
         [0024]    The invention described in claim  11  relates to a filter attachment portion forming method including heating and melting a front end of a thermally processing tip while causing the front end to sink into a circumferential edge portion of an inlet or an outlet of an air vent formed in a thermoplastic resin molded article to form a filter attachment surface at an inlet or outlet portion of the air vent in such a way that the filter attachment surface is lower than the inlet or outlet portion and raise the melted resin around the inlet or outlet portion by the sinking so as to form a filter attachment portion in the inlet or outlet portion of the air vent of the molded article, a filter fixing rib being formed in the inlet or outlet portion. 
         [0025]    The invention described in claim  12  relates to a thermally processing tip for forming a filter attachment portion, characterized in that the thermally processing tip is formed by forming a center rib to be inserted into an inlet or an outlet of an air vent formed in a thermoplastic resin molded article, the center rib formed at a center of a front end surface of a tip main body, forming a heat generating surface around a base of the center rib, further forming a vertical wall surface in a vertical direction from a periphery of the heat generating surface, and further forming a positioning flange in a position recessed from the vertical wall surface. 
         [0026]    The invention described in claim  13  relates to a thermally welding tip for attaching a filter, characterized in that the thermally welding tip is formed by forming a thermally processing rib on a front end surface of a tip main body, forming a gate rib in a periphery of the front end surface with an amount of protrusion of the gate rib smaller than an amount of protrusion of the thermally processing rib, and forming a heat generating press surface between the gate rib and the thermally processing rib. 
         [0027]    The invention described in claim  14  is characterized in that the thermally processing tip described in claim  12  or the thermally welding tip described in claim  13  is based on an impulse heating method. 
         [0028]    The invention described in claim  15  relates to a thermoplastic resin molded article characterized in that a filter having a water-repellency property and a ventilation property is attached to an inlet or an outlet of an air vent of the thermoplastic resin molded article based on a melted resin penetration effect. 
       Advantageous Effects of Invention 
       [0029]    According to the invention described in claim  1 , a filter is dropped into a stepped portion formed at an inlet or an outlet of an air vent, a filter fixing rib is melted, the melted resin is caused to flow onto and cover a circumferential edge portion of the filter in the stepped portion and penetrate a body of the filter at the same time, and then the melted resin is so cooled as to solidify to fix the filter in the stepped portion. 
         [0030]    As a result, no wrinkle or gap is produced when the filter is attached because no particular load is applied to the filter, whereby the filter is securely fixed with no concern about entry of rain water via the circumference edge portion of the filter. 
         [0031]    Further, the invention described in claim  1 , in which the filter is attached to the filter attachment portion formed with the thermally processing tip described in claim  12  by using the thermally welding tip described in claim  13 , allows formation of the filter attachment portion at the inlet or the outlet of the air vent of the thermoplastic resin molded article and an increase in efficiency in the work of attaching the filter to the attachment portion. 
         [0032]    Further, according to the invention described in claim  1 , since the attached filter does not protrude into the space around the inlet or the outlet of the air vent, there is no concern about breakage of the filter due to contact with a hand or another part. 
         [0033]    Further, according to the invention described in claim  1 , since the melted resin covers the circumferential edge portion of the filter, the circumferential edge of the filter is fixed throughout the entire circumference. As a result, a situation in which separation occurs at the circumferential edge of the filter can be avoided. 
         [0034]    Next, according to the invention described in claim  2 , the present invention is also directed to a sound hole formed in a thermoplastic resin molded article. 
         [0035]    Next, according to the invention described in claim  3 , the present invention is directed to a filter having a ventilation property and a liquid-repellency property. 
         [0036]    Next, according to the invention described in claim  4 , the filter is fixed with further increased strength resulting from solidification of the penetrated resin. 
         [0037]    Next, according to the invention described in claim  5 , the present invention is also directed to a very thin filter. 
         [0038]    Next, according to the invention described in claim  6 , a filter having a ventilation property and a liquid-repellency property and readily allowing penetration of melted resin can be formed. 
         [0039]    Next, according to the invention described in claim  7 , the filter can be attached to the air vent of the resin molded article in a single step. 
         [0040]    Next, according to the invention described in claim  8 , the filter can be set in a correct position. 
         [0041]    Next, according to the invention described in claim  9 , formation of the filter fixing rib in a molded article requires no specific step, whereby the productivity is improved and the cost can be reduced. 
         [0042]    Next, according to the invention described in claim  10 , the filter can be selected and used in accordance with the shape of the air vent. 
         [0043]    Next, according to the invention described in claim  11 , the filter attachment portion can be processed in a production site in accordance with the size of the filter. 
         [0044]    Next, according to the invention described in claim  12 , the filter attachment portion can be readily formed in one-touch operation. 
         [0045]    Next, according to the invention described in claim  13 , since the filter can be readily attached, and the gate rib formed around the heat generating press surface comes into contact with the thermoplastic resin molded article as the thermally processing tip descends, a situation in which the melted resin extends off toward the outer circumference of the resin article is avoided, and the outer edge portion of the filter can be reliably fixed. 
         [0046]    Next, according to the invention described in claim  14 , the tip can be efficiently heated and readily controlled. 
         [0047]    Next, according to the invention described in claim  15 , since the filter is reliably attached to the air vent, a reliably molded article can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0048]      FIG. 1  shows a thermoplastic resin molded article having an air vent to which a filter is attached. 
           [0049]      FIG. 2  is an enlarged view of a filter attachment portion. 
           [0050]      FIG. 3  is an exterior view of a thermally processing tip for attaching the filter to the air vent. 
           [0051]      FIG. 4  is a cross-sectional view of the thermally processing tip for attaching the filter to the air vent according to a first embodiment, the filter, and the air vent of the resin molded article. 
           [0052]      FIG. 5( a )  is a cross-sectional view in a case where a filter attachment surface is flush with a surface of the thermoplastic resin molded article, and  FIG. 5( b )  is a cross-sectional view in a case where the filter attachment surface is higher than the surface of the thermoplastic resin molded article. 
           [0053]      FIGS. 6( a ) to 6( f )  describe filter attaching steps described in claim  1 . 
           [0054]      FIG. 7  is an exterior view of a thermally processing tip for forming a filter attachment portion. 
           [0055]      FIG. 8  is a cross-sectional view of the thermally processing tip for forming a filter attachment portion and an air vent of a resin molded article. 
           [0056]      FIGS. 9( a ) to 9( e )  describe a method for forming the filter attachment portion described in claim  2 . 
           [0057]      FIGS. 10( a ) and 10( b )  describe concepts if attachment of a filter to a plurality of air vents. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0058]    In the present invention, two types of a thermally welding tip will be described: One is a thermally welding tip used to form a filter attachment portion that allows a filter to be attached to an inlet or an outlet of an air vent provided in a thermoplastic resin molded article; and the other is a thermally welding tip used to attach a filter to the formed attachment portion. 
       Embodiments 
       [0059]    A first embodiment of the present invention relates to a filter attaching method described in claim  1 , a thermally processing tip and a thermally welding tip used to carry out the method and described in claims  12  and  13 , respectively. 
         [0060]    A thermally welding tip for filter attachment will first be described with reference to  FIGS. 3 and 4 . A thermally processing tip  2  of a thermally welding apparatus  1  has a heat generating press surface  6  so formed at a front end  3  of the tip  2  as to surround a clearance hole  4 . A ring-shaped thermally processing rib  5  is so provided as to protrude from the inner side of the heat generating press surface  6 , and a gate rib  7  is so provided as to protrude from the outer circumferential edge of the heat generating press surface  6 . 
         [0061]    The thermally processing rib  5  is higher than the gate rib  7  by 0.5 mm (or an arbitrary dimension according to the shape of the thermally processing rib in a case where the height difference is greater than or equal to 0.1 mm). 
         [0062]    Reference characters  8  and  8   a  denote cooling air flow-out windows formed on the side having the rear of the heat generating press surface  6  and in symmetric positions. Reference characters  9  and  9   a  denote slits  15  formed on opposite side surfaces of the thermally processing tip  2  and in symmetric positions. Reference character  10  denotes a cooling air pipe. Reference characters  11  and  11   a  denote lead wires for voltage application. Reference character  12  denotes an insulator. Reference character  13  denotes a thermoplastic resin molded article. Reference character  14  denotes a filter attachment surface. Reference character  15  denotes a filter fixing rib. Reference character  16  denotes an air vent formed in the thermoplastic resin molded article  13 . Reference character  17  denotes cooling air blown through the cooling air pipe  10 . Reference character  18  denotes a water-repellent filter to be attached. 
         [0063]    Providing the clearance hole  4  at the center of the front end of the thermally processing tip  2  prevents heat produced by the heat generating press surface  6  from affecting the filter  18 . 
         [0064]    In  FIG. 4 , in which the filter attachment surface  14  is formed at the inlet or the outlet of the air vent  16  of the thermoplastic resin molded article  13 , and the filter fixing rib  15  is formed around the filter attachment surface  14 , the filter  18  is dropped to and set at the filter attachment surface  14  manually or by using an automatic loader, as shown in  FIG. 6   a.    
         [0065]    The filter  18  in the present first embodiment is a porous membrane made of a fluorine resin (PTFE) with t=0.1 mm and φ=11.0 mm. 
         [0066]    The thermally processing rib  5  of the thermally processing tip  2  has an outer diameter φ of 10.0 mm and an inner diameter φ of 9.0 mm. The gate rib  7  of the thermally processing tip  2  has an outer diameter φ of 17.0 mm. The step between the front end of the thermally processing rib  5  and the heat generating press surface  6  has a dimension of 0.8 mm. The step between the front end of the thermally processing rib  5  and the front end of the gate rib  7  has a dimension of 0.5 mm. 
         [0067]    The thermoplastic resin molded article  13 , to which the filter  18  is welded, is made of an ABS resin and provided with the air vent  16  having a diameter φ of 4.0 mm. 
         [0068]    A method for attaching the filter  18  will next be described with reference to  FIGS. 6 a    to  6   f.    
         [0069]      FIG. 6 a    shows a state in which the filter  18  is dropped on the filter attachment surface  14 , which is formed at the inlet of the air vent  16  of the thermoplastic resin molded article  13 , and the thermally processing tip  2  of the thermally processing apparatus  1  is moved to a position above the filter  18  and is ready for processing. 
         [0070]      FIG. 6 b    shows a state in which the thermally processing tip  2  descends to a point where the heat generating press surface  6  of the thermally processing tip  2  comes into contact with the filter fixing rib  15  and a front end portion of the thermally processing rib  5  comes into contact with the filter  18  at the same time. At this point, when a power supply (not shown) applies voltage to the lead wires  11  and  11   a,  the heat generating press surface  6 , which is formed at the front end of the thermally welding tip  2 , generates heat due to the electric resistance of the heat generating press surface  6 . 
         [0071]    The temperature to which the thermally welding tip  2  is heated is controlled by the power supply, and it is further effective to perform feedback control using a thermocouple (not shown) attached to the front end of the thermally welding tip  2 . 
         [0072]    The temperature to which the thermally welding tip  2  is heated can be set as appropriate by selection of the materials of the filter  18  and the thermoplastic resin molded article  13 , but the temperature to which the thermally welding tip  2  is heated needs to be higher than the melting point of the thermoplastic resin molded article  13  by at least 50° C. but lower than the melting point of the filter  18 . 
         [0073]    In the first embodiment, the material of the thermoplastic resin molded article  13  is an ABS resin having a melting point of 110° C. The filter  18  is made of a porous polytetrafluoroethylene having a melting point of 327° C. The temperature to which the thermally welding tip  2  is heated is 260° C. 
         [0074]    At the same time, the thermally welding tip  2  is pressed at an appropriate pressure by a drive apparatus that is not shown against the molded article  13 . 
         [0075]    The filter fixing rib  15  heated by and pressed against the heat generating press surface  6  of the thermally welding tip  2  starts melting from above and spreads rightward and leftward along the heat generating press surface  6 , and the thermally welding tip  2  further descends accordingly, as shown in  FIG. 6   c.    
         [0076]    The thermally processing rib  5  of the thermally welding tip  2  having descended then comes into contact with the filter  18 , as shown in  FIG. 6 d   . The thermally processing rib  5  heats the periphery of the filter  18  while pressing the filter  18 . 
         [0077]    In this process, when the thermally processing rib  5  descends (lowers), the thermally processing rib  5  gives the filter  18  force that widens the filter  18  from the center thereof toward the outer circumference thereof, whereby the filter  18  does not wrinkle. 
         [0078]    The thermally processing rib  5  causes the filter  18  to lower onto the filter attachment surface  14  of the thermoplastic resin molded article  13  while deforming the filter  18  in a concave shape, and the melted resin of the thermally processing rib  5  penetrates the body of the filter  18  at the same time. 
         [0079]    At this point, the filter fixing rib  15  having been heated and having therefore melted spreads rightward and leftward along the heat generating press surface  6  but does not reach the circumferential edge of the filter  18 . 
         [0080]    When the thermally welding tip  2  further descends, the melted resin reaches from an outer portion  15   a  of the filter fixing rib  15  to the gate rib  7  but is blocked by the gate rib  7  because the front end of the gate rib  7  is in contact with the thermoplastic resin molded article  13 , as shown in  FIG. 6 e   . The melted resin thus does not flow out of the gate rib  7 . 
         [0081]    An inner portion  15   b  of the melted filter fixing rib  15  therefore flows downward along the thermally processing rib  5  and eventually covers a circumferential edge portion of the filter  18 . 
         [0082]    The position to which the thermally welding tip  2  descends is set in advance. In the present first embodiment, the descent position is set at a position where the thermally processing rib  5  comes into contact with the top of the filter  18  having a certain thickness (0.1 mm) and the thickness is reduced by one-half (0.05 mm). 
         [0083]    Further, in the descent position, a state in which the gate rib  7  intrudes into the thermoplastic resin molded article  13  by 0.3 mm is achieved. As a result, a situation in which the outer portion  15   a  of the melted filter fixing rib  15  extends off is avoided, and a front end  20  of the gate rib  7  forms a parting groove  7   a  having a depth of 0.3 mm around the filter attachment surface  14  at the same time, whereby post-process exterior appearance is improved (see  FIGS. 6 e  and 6 f   ). 
         [0084]    Setting the volume (cross-sectional area) of the filter fixing rib  15  in such a way that the post-process volume is smaller than the pre-process volume allows the filter fixing rib  15  melted in the position to which the thermally welding tip  2  descends to be pressurized between the thermally processing rib  5  and the gate rib  7 , whereby the melted resin penetrates the filter  18 . The ratio of the post-process volume of the filter fixing rib  15  to the pre-process volume thereof is selected as appropriate and ranges from 90 to 99%. The ratio is set at 95% in the present first embodiment. 
         [0085]      FIG. 2  shows a state in which the melted resin penetrates the filter  18  and covers the circumferential edge of the filter  18 . 
         [0086]    After a preset heating period elapses with the thermally welding tip  2  in the set descent position, the voltage application is terminated, and cooling air  17  is supplied through the cooling air pipe  10  provided as part of the thermally welding tip  2  at the same time, as shown in  FIG. 6 e   . Therefore, the cooling air  17  is blown to the rear side of the heat generating press surface  6 , and the pressure of the blown air internally cools the front end  3  of the thermally welding tip  2  including the heat generating press surface  6  of the thermally processing tip  2 . 
         [0087]    The cooling air  17  is then discharged out of the thermally welding tip  2  through the flow-out windows  8  and  8   a  and the slits  9  and  9   a.    
         [0088]    As described above, cooling the front end  3  of the thermally welding tip  2  for a period set in advance allows the thermally processing rib  5 , the heat generating press surface  6 , and the gate rib  7  to be cooled, and the outer portion  15   a  and the inner portion  15   b  of the melted filter fixing rib  15  solidify. Further, resin  18   a  penetrating the filter  18  is cooled and solidifies, and the solidification of the penetrated resin more securely fixes the filter  18  to the thermoplastic resin molded article  13 . 
         [0089]    Thereafter, the supply of the cooling air  17  is terminated, and the thermally welding tip  2  is so lifted as to be separate above from the filter  18 . 
         [0090]    As a result, the filter  18  is fixed to the inlet of the air vent  16  of the thermoplastic resin molded article  13 , as shown in  FIG. 6   f.    
         [0091]      FIG. 1  is a cross-sectional view after the filter is attached. 
         [0092]    In the present embodiment, the filter attachment surface  14  is lower than a surface of the thermoplastic resin molded article  13 , as shown in  FIG. 5 a   . The filter can be attached in the same manner also in a case where the filter attachment surface  14  is flush with the surface of the thermoplastic resin molded article  13 , as shown in  FIG. 5 a   , or a case where the filter attachment surface  14  is higher than the surface of the thermoplastic resin molded article  13 , as shown in  FIG. 5   b.    
         [0093]    Further, each of the shape of the filter  18  and the shape of the air vent  16  of the filter attachment portion is not limited to a circular shape, and the present invention can be implemented in a case where each of the shapes is a polygonal shape. The invention can still further be implemented in a case where a plurality of air vents  16  are present, as shown in  FIG. 10 a   , and in a case where each air vent  16  has a roughly rectangular shape and a cross-shaped beam is present, as shown in  FIG. 10 b   . As clearly seen in the examples described above, the present invention can be applied to air vents  16  and filters  18  having a variety of shapes. 
         [0094]    A second embodiment of the present invention relates to a thermally processing tip for forming a filter attachment portion described in claim  12  and a method for forming the filter attachment portion by using the tip. 
         [0095]      FIGS. 7 and 8  show the structure of the thermally processing tip, and  FIGS. 9 a  to 9 e    show the method for forming the filter attachment portion described in claim  2 . 
         [0096]    A thermally processing tip  22  is used to form the filter attachment portion  14  and the filter fixing rib  15 . 
         [0097]      FIG. 7  is a perspective view of a thermally processing apparatus for forming the filter attachment portion.  FIG. 8  is a longitudinal cross-sectional view of a central portion of the thermally processing apparatus.  FIGS. 9 a  to 9 e    describe the formation method. Reference character  21  denotes the overall thermally processing apparatus, and reference character  22  denotes the thermally processing tip. 
         [0098]    In the thermally processing tip  22 , a cylindrical, centrally hollow guide portion  24  is so provided as to protrude from a heat generating surface  23  at the front end of the thermally processing tip  22 , a chamfered portion  25   a  is formed around a potion recessed from the front end of the guide portion  24  and a filter attachment surface formation portion  25   b  is so formed as to follow the chamfered portion  25   a,  and a flange  27  is formed around the outer circumference  26  of the heat generating surface  23  and in a position recessed from the filter attachment surface formation portion  25   b.    
         [0099]    The front end of the guide portion  24  has a rounded portion having a radius of 0.3, and the outer circumference of the guide portion  24  has a 2°-tapered portion. The rounded portion and the tapered portion allow the thermally processing tip  22  to be smoothly inserted into the air vent  16  of the thermoplastic resin molded article  13  and the thermally processing tip  22  to be readily positioned. 
         [0100]    Reference characters  8  and  8   a  denote cooling air flow-out windows formed in the side surface of the thermally processing tip  22  and in symmetric positions on the side facing the rear of the heat generating surface  23 . Reference characters  9  and  9   a  denote vertically cut slits formed in the side surface of the thermally processing tip  22  and in symmetric positions. Reference character  10  denotes a cooling air pipe. Reference characters  11  and  11   a  denote lead wires for voltage application. Reference character  12  denotes an insulator. Reference character  13  denotes a thermoplastic resin molded article. Reference character  16  denotes an air vent formed in the thermoplastic resin molded article  13 . Reference character  17  denotes cooling air blown through the cooling air pipe  10  after the thermally processing tip  22  melts and forms the filter attachment portion in  FIG. 9 d    described above to cool the melted portion with blown cooling wind and cause the melted portion to solidify. 
         [0101]    A method for processing the filter attachment portion will next be described with reference to  FIGS. 9 a    to  9   e.    
         [0102]      FIG. 9 a    shows a state in which the guide portion  24  of the thermally processing tip  22  is inserted into the air vent  16  of the thermoplastic resin molded article  13 . At this point, when a power supply (not shown) applies voltage to the lead wires  11  and  11   a,  the heat generating surface  23 , which is formed at the front end of the thermally processing tip  22 , generates heat due to the electric resistance of the heat generating surface  23 . 
         [0103]    At the same time, the thermally processing tip  22  is pressed at an appropriate pressure by a drive apparatus that is not shown against the molded product  13 . 
         [0104]    The diameter of the guide portion  24  at the base of the tapered portion thereof and at the boundary between the base and the chamfered portion  25   a  is equal to the diameter of the air vent  16 . Further, since the guide portion  24  separates away from the heat generating surface  23  with distance toward the front end of the guide portion  24 , the temperature in the guide portion  24  does not increase toward the front end thereof. 
         [0105]    Therefore, when the melting starts, a circumferential edge portion of a rib around the air vent  16  that is in contact with the chamfered portion  25   a  is caused to flow toward the filter attachment surface formation portion  25   b  along the slope of the chamfered portion  25   a.  When the heating further advances, the portion in contact with the filter attachment surface formation portion  25   b  melts, but no resin flows toward the front end of the guide portion  24  but is caused to flow out of the filter attachment surface formation portion  25   b,  as shown in  FIG. 9   b.    
         [0106]    No burr is therefore formed in the air vent  16 , and entry of foreign matter resulting from any burr into the air vent  16  can be avoided. 
         [0107]    When the thermally processing tip  22  further descends, the filter attachment surface formation portion  25   b  of the thermally processing tip  22  sinks into the surface of the molded article  13  in a portion around the inlet of the air vent  16 , and the heated, melted resin is pushed out toward the outer circumference  26  and raised there, as shown in  FIG. 9 c   . Eventually, the front end of the raised resin reaches the flange  27 , as shown in  FIG. 9   d.    
         [0108]    As described above, the thermally processing tip  22  having sunk into the portion around the air vent  16  melts and pushes the resin corresponding to the amount of sink outward to form the filter attachment surface formation portion  25   b,  and the outer circumference  26  and the flange  27  form the filter attachment portion (stepped portion to which filter is dropped)  14  and the filter fixing rib  15  at the inlet of the air vent  16 . 
         [0109]    The position to which the thermally processing tip  22  descends is set in advance. In the present second embodiment, the descent position is set at a position where the filter attachment surface formation portion  25   b  and the filter fixing rib  15  are formed as intended in terms of dimension. 
         [0110]    After a heating period elapses with the thermally processing tip  22  located in the set descent position, the voltage application is terminated, and cooling air  17  is supplied through the cooling air pipe  10  provided in the thermally processing tip  22  at the same time, as shown in  FIG. 9 d   . Therefore, the cooling air  17  is blown to the rear side of the heat generating surface  23 , and the pressure of the blown air internally cools the front end of the thermally processing tip  22  including the rear side of the heat generating surface  23  of the thermally processing tip  22 . 
         [0111]    The cooling air  17  is then discharged out of the thermally processing tip  22  through the flow-out windows  8  and  8   a,  the slits  9  and  9   a,  and the hole of the guide  24 . 
         [0112]    As described above, cooling the heat generating surface  23  of the thermally processing tip  22  for a period set in advance allows the guide  24 , the chamfered portion  25   a,  the filter attachment surface formation portion  25   b,  the outer circumference  26 , and the flange  27  to be cooled, and the melted, raised resin solidifies into the filter fixing rib  15  having an annular shape in a plan view. Thereafter, the supply of the cooling air  17  is terminated, and the thermally processing tip  22  is lifted so that the thermally processing tip  22  is separated from the thermoplastic resin molded article  13 . 
         [0113]    As a result, the filter attachment surface  14  and the filter fixing rib  15  are formed around the inlet of the air vent  16  of the thermoplastic resin molded article  13 , as shown in  FIG. 9   e.    
         [0114]    The configuration of the thermally processing tip  22 , which forms the filter attachment portion and the method for forming the filter attachment portion have been described. 
         [0115]    The filter  18  is attached to the thus formed filter attachment portion by using the thermally welding tip  2  described in the first embodiment. 
         [0116]    In the present second embodiment, the material of the thermoplastic resin molded article  13  is an ABS resin, and the temperature of the thermally processing tip  22  is set at 260° C. 
         [0117]      FIG. 10 a    is a conceptual view of an example in which in a case where the molded article  13  is provided with a plurality of air vents  16 , the single filter  18  covers the plurality of air vents  16  together, and the filter fixing rib  15  fixes the filter  18 , and  FIG. 10 b    is a conceptual view of an example in which air vents  16  are formed in the form of a lattice in the molded article  13 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Thermally processing apparatus 
           2  Thermally welding tip 
           3  Front end 
           4  Clearance hole 
           5  Thermally processing rib 
           6  Heat generating press surface 
           7  Gate rib 
           8  Cooling air flow-out window 
           9  Slit 
           10  Cooling pipe 
           11 ,  11   a  Lead wires 
           12  Insulator 
           13  Thermoplastic resin molded article 
           14  Filter attachment surface 
           15  Filter fixing rib 
           16  Air vent 
           17  Cooling air 
           18  Filter 
           18   a  Resin penetrating filter 
           21  Thermally processing apparatus 
           22  Thermally processing tip 
           23  Heat generating surface 
           24  Guide portion 
           25   a  Chamfered portion 
           25   b  Filter attachment surface formation portion 
           26  Outer circumference 
           27  Flange