Plastic clip bonding method and plastic clip

Abstract: To provide a method for bonding a plastic clip onto a natural fiber based porous member and a plastic clip for use in the bonding method that the clip can be bonded with a low energy without any of heat affection and any dent on a rear side of the clip, and the excessive molten portions will be handled well. A plastic clip 1 comprises a base 5 having a bonding side including a welding region 6 and a non-welding region 7. The welding region 6 includes a plurality of fusible projections 9 extending to the natural fiber based porous member and a plurality of recesses 10 adjacent the projections for receiving the excessive molten portions of the projections. The non-welding region 7 is formed with a reference level portion 11 to set the welding height of the plastic clip.

Description: The present invention relates to a method of bonding a plastic clip such as a retainer onto a natural fiber based porous member such as an automobile door trim by welding, and a plastic clip for use in the bonding method. As a door trim or the like of an automobile, for weight reduction and cost saving, natural fiber based porous members including epoxy plastic as a binder are often utilized. Since the door trim or the like contains as much as 70% in weight of natural fiber, stamping is used for its forming. Therefore, the plastic clip such as the retainer for attaching the door trim to the automobile body is formed separately from the door trim which is made of the natural fiber based porous member. Therefore, the plastic clip such as the retainer is required to be integrally connected with the natural fiber based porous member of the door trim. To this end, ultrasonic welding or the like has been used. For example, Japanese Patent Laid-open No. 04-208656 discloses a method of attaching a fastener of a plastic clip to a roof lining having a glass fiber substrate by ultrasonic welding. It is described that, in accordance with that attaching method, a portion of the attaching side of the plastic clip is melted into the glass fiber portions and voids thereof, so that a tangled bond of plastic and the glass fibers can be obtained. To apply it to a case where the plastic clip is bonded onto the natural fiber based porous member by welding, this attaching method must be somewhat improved As described above, in the automobile door trim, the natural fiber based porous member including epoxy plastic as a binder is often used. When the epoxy plastic clip is ultrasonic-welded onto the natural fiber based porous member including epoxy plastic as a binder, its bond strength often is not stabilized. Therefore, in order to obtain higher bond strength than a certain level, very high ultrasonic energy and very large pressure force are required for welding. As a result, the deformations due to heat affections and the pressed dents of the ultrasonic welding tip may appear on the bonding side and the rear side of the clip. Thus, it is desired to provide a method that can bond the clip with low energy, without any heat affections and any dents to the rear side of the clip when the plastic clip is bonded onto the natural fiber based porous member. Japanese Patent Laid-Open No. 03-67722 discloses a method of ultrasonic-welding a plastic retainer clip onto a door trim. In this patent, the problems of the heat affection and dent are pointed out, and a proposal is made to eliminate the boundary gap between the door trim and the retainer bracket. In particular, a projected ridge is formed on the attaching side of the retainer bracket, the projected ridge is positioned in recess of the attaching side of the door trim and then melted for bonding by ultrasonic-welding to fill a gap between the recess on the attaching side of the door trim and the outer side of the retainer bracket. In this method, there is a restriction in molding of the door trim because a recess for receiving the retainer bracket is necessary on the attaching side of the door trim. Therefore, it is desired to bond the plastic clip onto the natural fiber based member, without such restriction, any heat affections and any dents to the rear side, and also with lower energy. Other technologies for welding another plastic part onto a plastic member are described in Japanese Patent Laid-Open No. 63-212532, Japanese Patent Laid-Open No. 63-278821, and Japanese U. M. Laid-Open No. 02-124131. In Japanese Patent Laid-Open No. 63-212532, the projected leg is formed on the attaching side of the plastic bracket and is ultrasonic-welded so that the plastic brackets are bonded onto the plastic roof lining of the automobile. However, this welding method must be improved because there is no consideration for the excessive molten portions of the legs. Also, in Japanese Patent Laid-Open No. 63-278821, a plastic retainer for holding a small accessory is welded onto a plastic product so as to attach the small accessory on the plastic product. For the purpose of welding the retainer, there is provided projection having sharp tip end on the bonding side of the retainer. This projection is then melted to bond the retainer onto the plastic product. This welding method must also be improved because there is no consideration for the excessive molten portions of the projections. In Japanese U. M. Laid-Open No. 02-124131, a projected portion is formed as a welding site in a core material portion of the wooden fiber based mat so as to ultrasonic-weld the plastic part onto the wooden fiber based mat. A welding portion of the plastic part is positioned on the projected portion for ultrasonic-welding. The melted welding portion of the plastic part preferably tends to be penetrated into the core material of the wooden fiber based mat, however, it is troublesome to form the projected portion as the site for welding in the core portion of the wooden fiber based mat. Japanese Patent Laid-Open 63-176134 discloses a method in accordance with the preamble of claim 1 for ultrasonic-welding fitting parts to a ligneous board, wherein the fitting parts are mounted on a holding jig with protrusions turning upward and then the ligneous board is mounted on each of the fitting parts. An ultrasonic vibration is given to ligneous board from the opposite side by an ultrasonic horn descending onto the ligneous board and causes the protrusions to turn fittable into the ligneous board thereby welding the fitting parts to the ligneous board. Japanese Patent Laid-Open 63-176134 further discloses a plastic clip in accordance with the preamble of claim 2. Therefore, an object of the present invention is to provide a method of bonding a plastic clip and a plastic clip for use in the bonding method, wherein when the plastic clip is bonded onto the porous member, there is no restriction on the shape of the natural fiber based porous member, wherein the clip can be bonded with low energy, without any heat affections and any dents on rear side of the clip, and wherein the excessive molten portions will be handled well. To accomplish such object, according to the present invention, there is provided a method of bonding a plastic clip onto a natural fiber based porous member by welding in accordance with independent claim 1. The method comprises steps of; forming a plurality of projections in a welding region of the bonding side of a base of the plastic clip to extend to the natural fiber based porous member and a plurality of recesses adjacent the projections in the welding region for receiving the excessive molten portions of the melted projections; positioning the bonding side of the plastic clip at a predetermined position of the natural fiber based porous member; and fusing the bonding side to weld and bond the plastic clip onto the porous member, wherein fusing energy is transferred to the clip by a flat shaped tip of an ultrasonic horn contacting a flat side of the base of the clip, and the welding height of the projections and the depth of the recesses refer to a common reference plane defined by a reference level portion which is provided in a region other than the welding region at the bonding side of the plastic clip. According to the present invention, there is also provided a plastic clip in accordance with independent claim 2 for use in the above plastic clip bonding method. The base of the plastic clip comprises a welding region and a non-welding region, the welding region is formed with a plurality of fusible projections extending to the natural fiber based porous member and a plurality of recesses adjacent the projections for receiving the excessive molten portions of the projections, and the welding height of the projections and the depth of the recesses refer to a common reference plane defined by a reference level portion of a non-welding portion of the plastic clip, and that opposite the bonding side .the base is provided with a flat side adapted to receive the flat tip of an ultrasonic horn. In the plastic clip, the projections and recesses may be alternately formed with each of the projections and recesses being aligned in a line. The clip may also be made of material having a high grade of melt flow index (M.F.I.). This insures that the molten plastic material can easily impregnate into voids of the natural fibers, thus high energy is unnecessary, and both the bonding strength and the peeling resistance are increased. A plastic clip bonding according to the present invention will now be described with reference to the drawings. Fig. 1 shows a plastic clip 1 according to one embodiment of the present invention. The plastic clip 1 is bonded onto a natural fiber based porous member of the door trim or the like of an automobile, and is used as a retainer for attaching it to a panel of the mobile body. Examples of the natural fibers suited for use include kenaf, hemp, sisal, flax, bagasse (sugarcane), palm, and the like. Fig. 1(A) is a top view of the clip 1, and Fig. 1(B) is a partial cross sectional view showing a right half cross sectioned portion of the clip 1. On the upper side of the clip 1, a hook 2 is formed for attaching the porous member of door trim to the panel, and the lower portion thereof is formed as a conical trapezoid-like support portion 3. A bottom portion of the clip 1 is a base 5 to be bonded onto the natural fiber based porous member, and in that embodiment of the clip 1, as shown in Fig. 1(A), is formed in a ring shape. The clip 1 shown is only an example. The plastic clip according to the present invention may be of any other shape, and it may be any clip that provides connection with other members, not being limited to the retainer. The plastic clip 1 is molded with any plastic material having a property that is flowable when melted. The desirable material has a high grade of melt flow index (M.F.I.). This insures that the molten plastic material can easily be impregnated into voids of the natural fibers so that without need of high energy, the bonding strength and the peeling resistance are increased. For example, in the door trim or the like, polypropylene (PP) is used as a binder for the natural fibers, therefore, the same polypropylene (PP) is preferable when it is used as a retainer for the door trim of the automobile. This enables to increase the welding strength after melted. In this case, other plastic materials may be used, for example, materials having high melt flow index and high viscosity after melted, such as ABS (acrylonitrile-butadiene-styrene) resin or AAS (acrylonitrile-rubber-styrene) resin may be used. In any case, plastic materials which have the property of both high melt flow index and high viscosity when melted, which tend to impregnate easily into the voids of the natural fibers when melted, and which are stiff to provide high bonding strength are preferable. The features of the plastic clip 1 according to the present invention resides in a bottom side of the base 5, that is, a bonding side to be bonded to the natural fiber based porous member. This bonding side will now be described with reference to Fig. 2. Fig. 2 is a sectional view of a portion surrounded by a circle II of Fig. 1 (B). The bonding side of the base 5 of the plastic clip 1 includes a welding region 6 at the center of the ring-like base and a non-welding region 7 except this welding region 6. Furthermore, the non-welding region 7 is a portion not to be welded, typically, positioned outside of the welding region 6. The non-welding region 7 may also be inside of the welding region 6 or other places. For purpose of description, the non-welding region 7 is assumed to be outside of the welding region 6. The welding region is formed with a plurality of fusible (or melt-able) projections 9 extending to the natural fiber based porous member which is the member to be bonded. In addition, a plurality of recesses 10 for receiving the excessive molten portions of the projections 9 are formed adjacent the projections 9. As shown in Fig. 2, the projections 9 and the recesses 10 are alternately formed and each of them is aligned in a line. In this embodiment, as shown by broken lines of Fig. 1 (A), a plurality of the projections 9 and a plurality of the recesses 10 are alternately formed with each of them being in a line extending radially. Such lines are formed at equal distances circumferentially. Furthermore, it is preferable that the projections 9 and the recesses 10 are alternately positioned with the line shape, however, they may not necessarily be alternately positioned in a line. The recesses 10 may arbitrarily be positioned adjacent the projection 9 as possible as they can receive the excessive molten portion of the projection 9. In the present invention, the non-welding portion 7 is also formed with a reference level portion 11 for defining or setting the welding height of the plastic clip 1. Since the reference height portion 11 is formed in the non-welding portion 7, it is not melted during the welding operation, resulting in maintaining the welding height of the clip 1 constant. If there is no reference level portion 11, then the height of the base 5 might be changed in accordance with the degree of melting of the projection 9. As a result, the depth of the adjacent recess 10 might be changed. If the base 5 is forced against the bonding side of the member or workpiece under the condition that the projections 9 is in the molten state, the depth of the recesses 10 might become shallow, and thus, the excessive molten portion of the projection 9 might become increased. Accordingly, the recesses 10 could not adequately receive the excessive molten portion of the projection 9, thus the excessive molten portion might be pushed out of the bonding side. However, in the present invention, with the provision of the reference level portion 11, the depth of the recesses 10 is maintained constant and the excessive molten portions of the projections 9 are adequately received without being pushed out of the bonding side. The shape of the recesses 10 may be formed in a half sphere (as shown in Fig. 2), but they may have other any shapes. Figs. 3 (A), and 3 (B) show other various recess shapes. In Fig. 3(A), the recesses 13 are formed as round holes extending through the base 5. In Fig. 3 (B), the recesses 14 are formed as elongated holes extending through the base 5. Similarly, the shape of the projections 9 may be also formed in a half sphere (Fig. 2), but they may have other any shapes. Figs. 4 (A) - (C) show other various projection shapes. In Fig. 4 (A), the projections 15 are formed in a quadrangular shape, and the recesses 17 can be also formed in a quadrangular shape. In Fig. 4 (B), the projections 18 are also formed in a triangular shape, and the recesses 19 are formed as a triangular shape. In Fig. 4 (C), the projections 21 are as a triangle rib shape, and the recesses 22 are formed in a triangular valley. In this way, the projections and the recesses may be formed in any shape. Fig. 5 shows a welding condition of a plastic clip 25 to a natural fiber based porous member 26 by ultrasonic-welding wherein the clip 25 is slightly modified in shape from the plastic clip 1 for the purpose of the illustration, and the clip 25 is bonded onto the member 26 by the ultrasonic welding. For example, the natural fiber based porous member 26 is an automobile door trim made of material comprising natural fibers connected to each other by using PP (polypropylene) as a binder. The ultrasonic horn 29 of the ultrasonic welding apparatus is positioned on a base 27 of the clip 25 which is located at the predetermined position on the porous member 26, so that a tip of the ultrasonic horn 29 is in contact with the base 27. Under this condition, ultrasonic energy is radiated from the horn 29, and then, the projections 30 on the bonding side of the base 27 of the clip 25 begin to melt from the portions which are in contact with the porous member 26. Before its melting begins, the clip 25 vibrates by vibration due to radiation of ultrasonic energy from the horn 29, but the clip 25 is prevented from shifting from the predetermined position because the projections 30 are engaged with the porous member 26. Furthermore, since the projections 30 and the recesses 31are alternately positioned with each being in a line, the melted region of the projections 30 tend to impregnate into the voids between the fibers of the porous member 26, thus a high anchor effect is obtained after welding. Also, since the excessive molten portions of the projections 30 are received in the recesses 31, they will never be pushed out. This welding process continues until the reference level portion 33 firmly comes into contact with the porous member 26. After contacted, the operation comes to its end. Fig. 6 shows a condition after the clip 25 has been welded onto the porous member 26. In Fig. 5, the tip of the ultrasonic horn 29 is shaped flat so that the ultrasonic energy is efficiently transferred to the clip 25. This is because both the projections 30 and the recesses 31 do not exist on a side of the base 27 to which the ultrasonic horn 29 contacts. Thus, the side of base 27 can be flat. This improves the efficiency of ultrasonic energy transferred from the ultrasonic horn 29 to the clip 25. Accordingly, the welding process can be accomplished with low energy, so as to reduce any heat affections and the force required to press the clip 25, resulting in eliminating any dent. In addition, by providing the reference level portion 33, the depth of the recesses 31 is held constant, thus the excessive molten portions of the projections 30 are adequately received, and will never be pushed out from the bonding surface of the clip 25. In the meantime, the above embodiment utilizes the ultrasonic welding for bonding, however, any other welding may be used. For example, vibration welding may be used. According to the present invention, the projections on the bonding side of the plastic clip prevent the clip from shifting relative to the natural fiber based porous member during ultrasonic welding. A portion of the projections is melted (or fused) and impregnated into the natural fiber based porous member to attribute its bonding. This melting of the projections can be accomplished with low energy, therefore any heat affections and any dents on the rear side can be prevented. The recesses formed adjacent the projections facilitate impregnation of molten portion into the voids between fibers of the porous member, resulting in a high bonding effect. Also, since the excessive molten portions of the projections are received in the adjacent recesses, it will never be pushed out. Furthermore, since the reference level portion is provided in the region except the welding region, not only the welding height is stably defined (or set) at constant level, but also the depth of the recesses is held constant for receiving the excessive molten portions of the projections adequately. Accordingly, the resulted bonding has high bonding strength at the bonding site without any pushing-out of the excessive molten portion. Fig. 1 shows a plastic clip according to the present invention, in which (A) is a plan view, and (B) is a half sectional view of the clip. Fig. 2 is a sectional view of a clip portion of the circle II of Fig. 1 (B). Figs. 3 (A), (B) show various shapes of variations of the recesses, in which (A) is a view showing a shape of the through holes, and (B) is a view showing another recesses having elongated through holes. Figs. 4 (A) - (C) show various shapes of variations of the projections, in which (A) is a view showing the projections having quadrangular shape, (B) is a view showing other projections having triangular shape, and (C) is a view showing still other projections having a triangle rib shape. Fig. 5 is a view showing a condition wherein the ultrasonic horn of an ultrasonic welding apparatus is positioned on the clip as located at the predetermined position of the porous member in order to weld the plastic clip onto the natural fiber based porous member. Fig. 6 is a view showing a condition after the plastic clip has been welded onto the natural fiber based porous member.

Claims: A method of bonding a plastic clip (1) onto a natural fiber based porous member (26) by welding, comprising steps of; forming a plurality of projections (9) in a welding region (6) of the bonding side of a base (5) of the plastic clip (1) to extend to the natural fiber based porous member (26) and a plurality of recesses (10) adjacent the projections (9) in the welding region (6); positioning the bonding side of the plastic clip (1) at a predetermined position of the natural fiber based porous member (26); and fusing the bonding side to weld and bond the plastic clip (1) onto the porous member (26), whereby the melted region of the projections tend to impregnate into the voids between the fibers of the porous member, characterised in that fusing energy is transferred to the clip (1) by a flat shaped tip of an ultrasonic horn contacting a flat side opposite the bonding side of the base of the clip (1), and the welding height of the projections (9) and the depth of the recesses (10) refer to a common reference plane defined by a reference level portion (11) which is provided in a region other than the welding region (6) at the bonding side of the plastic clip (1) and which is arranged in such a manner that the recesses receive the excessive molten portions of the melted projections (9). A plastic clip for use in the method of claim 1, wherein the bonding side of the base (5) of the plastic clip (1) includes a welding region (6) and a non-welding region (7), the welding region (6) is formed with a plurality of fusible projections (9) for extending to the natural fiber based porous member (26) and a plurality of recesses (10) adjacent the projections (9), so that the melted region of the projections can impregnate into the voids between the fibers of the porous member, characterised in that the welding height of the projections (9) and the depth of the recesses (10) refer to a common reference plane defined by a reference level portion (11) which is provided in a region other than the welding region (6) of the bonding side of the plastic clip (1) and which is arranged in such a manner, that the recesses can receive the excessive molten portions of the melted projections (9), and that opposite the bonding side the base (5) is provided with a flat side adapted to receive the flat tip of an ultrasonic horn. A plastic clip as claimed in claim 2, characterised in that the projections (9) and the recesses (10) are alternately formed with each of the projections (9) and recesses (10) being aligned in a line. A plastic clip as claimed in claim 2, characterised in that the clip is made of ABS (acrylonitrile-butadiene-styrene) resin or AAS (acrylonitrile-rubber-styrene) resin.

Inventors: INOUE T, KAKEHI T, INOUE, T., KAKEHI, T.
Applicants: NEWFREY LLC
Application year: 2000
Main classification: B29C65
IPC codes: B60R13, F16B5, B29C65, B60J5, F16B11