Patent Description:
An electrical wire sheath is used around a wire harness, which is routed in a vehicle or the like, to protect the wire harness from external forces. Such an electrical wire sheath is designed to cover the circumference of the electrical wire and thus to protect the electrical wire from external forces.

Examples of such an electrical wire sheath for protecting a wire harness include those disclosed in <CIT> and <CIT>, which include a thermoplastic resin foam sheet folded to form a tubular housing, which is to be provided around an electrical wire.

Specifically, the electrical wire sheath disclosed in <CIT> includes multiple walls that extend along the longitudinal direction of the electrical wire and form a housing for the electrical wire, in which the multiple walls include an outer sheath wall, an inner sheath wall overlapped and joined with the outer sheath wall, and side walls extending from both ends of the inner sheath wall to support the inner sheath wall.

The electrical wire sheath disclosed in <CIT> includes walls that form a housing and include a first wall having protrusions and a second wall having holes. The housing is formed by deforming at least the protrusions or the holes and inserting the protrusions into the holes to engage the first and second walls with each other.

<CIT> discloses a welding method in which a lid and a flange of a container are evenly welded.

<CIT> discloses a welding method in which a seat and a support body are welded by means of a horn equipped with a ring-shaped working surface.

<CIT> discloses a melt bonding method in which plastic plates made of foamed plastic are bonded by sandwiching heating wires with said plastic plates. The heating wires are wound with a covering material having a thermal contraction property.

The electrical wire sheaths disclosed in <CIT> and <CIT> each include a resin sheet, such as a thermoplastic resin foam sheet, which has surfaces overlapped and joined together to form a tubular housing or has protrusions and holes engaged together to form a tubular housing.

In this regard, it is desirable in terms of reducing material costs, if possible, to join parts of a resin sheet together without overlapping between its principal surfaces, because in such a case, the resin sheet necessary to form a joining structure, such as an electrical wire sheath, may have a reduced surface area. It is also desirable in terms of improving work efficiency, if possible, to join parts of a resin sheet together without formation of any protrusion or hole on or in the resin sheet, because in such a case, a joining structure, such as an electrical wire sheath, can be formed through a reduced number of working steps.

This applies not only to electrical wire sheaths but also to other joining structures, such as a joining structure including first and second resins joined together, in which the first resin includes a foamed resin, and the second resin includes a non-foamed or foamed resin.

It is an object of the present invention to provide a joining structure that can be formed by joining resin sheets with high work efficiency without using excessive portions of the resin sheets for the joint, to provide a method for producing such a joining structure, and to provide an electrical wire sheath including such a joining structure. Means for Solving the Problems.

The inventors have made a joining structure including: a first resin sheet including a first resin; a second resin sheet including a second resin; and a joint formed by mating and welding a principal surface portion of the first resin sheet and an end surface portion of the second resin sheet, in which the joint has a weld recess on a top surface of the first resin sheet and includes a weld overlay portion formed at the inside corner on a bottom surface of the first resin sheet by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify, and have completed the present invention based on findings that such a joining structure can be formed by joining the resin sheets with high work efficiency without overlapping between principal surfaces of the resin sheets.

<CIT> describes a joining structure according to the preamble of claim <NUM> and a method for producing a joining structure according to the preamble of claim <NUM> of the present invention. The subject-matter that primarily must be considered to be characteristic of the present invention is disclosed in the characterizing portion of claim <NUM> and the characterizing portion of claim <NUM>. Advantageous embodiments of the invention are claimed in the subclaims.

The present invention makes it possible to provide a joining structure that can be formed by joining resin sheets with high work efficiency without using excessive portions of the resin sheets for the joint, to provide a method for producing such a joining structure, and to provide an electrical wire sheath including such a joining structure.

Next, joining structures and electrical wire sheaths according to some embodiments of the present invention will be described below.

<FIG> are schematic views of the major portion (including a joint) of a joining structure, in which <FIG> is a plan view and <FIG> is an a-a sectional view (cross-sectional view) of <FIG>. <FIG> are schematic plan views of weld recesses in joints constituting joining structures according to different embodiments, in which <FIG> shows a case where the bottom of the weld recess has bumps and dents in a stripe pattern, <FIG> shows a case where the bottom of the weld recess has bumps and dents in an irregular pattern, and <FIG> shows a case where the bottom of the weld recess has a flat surface. <FIG> is a plan view of the geometry of a weld recess in the joint of a joining structure according to another embodiment. <FIG> are schematic views of the major portion (including a joint) of joining structures according to other embodiments, in which <FIG> shows a case where the weld overlay portion of the joint has a concave surface when the inside corner is viewed, and <FIG> shows a case where the weld overlay portion of the joint has a convex surface when the inside corner is viewed.

<FIG> shows a joining structure <NUM> including: a first resin sheet <NUM> including a first resin; a second resin sheet <NUM> including a second resin; and a joint <NUM> formed by mating and welding a principal surface portion <NUM> of the first resin sheet <NUM> and an end surface portion <NUM> of the second resin sheet <NUM>. In the joining structure <NUM>, the first resin is a foamed resin, and the second resin is a non-foamed resin (solid resin) or a foamed resin. The joint <NUM> has a weld recess <NUM> on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>. The joint <NUM> includes a weld overlay portion <NUM> formed at the inside corner 10a on the bottom surface 22b of the principal surface portion <NUM> by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify.

Thus, when the weld recess <NUM> is formed on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, the first resin is pushed in the depth direction of the weld recess <NUM>, allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM>, and welded to the end surface portion <NUM> of the second resin sheet <NUM>. As a result, the end surface portion <NUM> of the second resin sheet <NUM> is joined to the principal surface portion <NUM> of the first resin sheet <NUM> with a relatively large joint area provided between them. In particular, not only the first resin, which forms the principal surface portion <NUM> of the first resin sheet <NUM>, but also the second resin, which forms the end surface portion <NUM> of the second resin sheet <NUM>, can be melted to form a layer of a mixture of the first and second resins at the boundary between the first and second resin sheets <NUM> and <NUM>. In this way, the first and second resin sheets <NUM> and <NUM> can be joined together by welding. Thus, the first and second resin sheets <NUM> and <NUM> can be joined together by welding without joining principal surfaces of the first and second resin sheets <NUM> and <NUM>, which means that the first and second resin sheets <NUM> and <NUM> can be joined together without using excessive portions of the resin sheets and that the resin sheets can be joined with high work efficiency when the joining structure <NUM> is produced.

As used herein, the term "welding" refers to plastic welding. In an embodiment of the present invention, the plastic welding is preferably ultrasonic plastic welding. The term "plastic welding" refers to a technique that includes heating multiple resin sheets including thermoplastic resin to above their melting point to bond them together or heating multiple portions of a single resin sheet to above the melting point to bond them together. The term "ultrasonic welding" refers to a technique that includes melting multiple resin sheets using ultrasonic vibrations and pressure to bond them together or melting multiple portions of a single resin sheet using ultrasonic vibrations and pressure to bond them together.

The first resin sheet <NUM> includes the first resin, and the second resin sheet <NUM> includes the second resin.

In this regard, parts of a single resin sheet may be used as the first and second resin sheets <NUM> and <NUM>, or different resin sheets may be used as the first and second resin sheets <NUM> and <NUM>. In a case where parts of a single resin sheet are used as the first and second resin sheets <NUM> and <NUM>, the single resin sheet may be folded to form the first and second resin sheets <NUM> and <NUM>. In this case, a middle portion of the single resin sheet may form the first resin sheet <NUM>, and an end portion of the single resin sheet may form the second resin sheet <NUM>. In this case, the joining structure <NUM> can be formed using a smaller number of components and thus can be formed with higher work efficiency.

Out of the first and second resins of the first and second resin sheets <NUM> and <NUM>, at least the first resin is preferably a thermoplastic resin type, such as polyethylene resin, polypropylene resin, polycarbonate resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyamide resin, polyphenylene sulfide resin, polystyrene resin, polyvinyl chloride resin, polyvinyl acetate resin, polytetrafluoroethylene resin, or acrylic resin. Preferably, one or both of the first and second resins include polypropylene resin.

The first and second resins may include the same resin type or different resin types. Particularly in a case where the first and second resins include the same resin type, the first and second resin sheets <NUM> and <NUM> can be joined with higher strength.

Depending on the application, the first and second resins may contain any additive that is used for common resins. Examples of such an additive that may be used include, but are not limited to, one or more selected from the group consisting of a filler, an antioxidant, a stabilizer, a flame retardant, a metal deactivator, a UV absorber, a light stabilizer, a plasticizer, a nucleating agent, a compatibilizing agent, a clarifying agent, an antistatic agent, and a lubricant.

Out of the first and second resins, at least the first resin includes a foamed resin. When melted, such a foamed resin will release air bubbles and shrink, so that the melted resin area will be less likely to expand in the principal surface direction of the first or second resin sheet <NUM> or <NUM>. In this case, the first resin of the first resin sheet <NUM> is particularly easy to push in the depth direction of the weld recess <NUM> being formed in the first resin sheet <NUM>. Thus, this will facilitate the solidification of the welded resin and prevent the resin from melting and flowing more than necessary, so that the resin will be less likely to flow out of the joint <NUM>.

As a non-limiting example, the foamed resin may have a density in the range of <NUM>/m<NUM> or more and <NUM>,<NUM>/m<NUM> or less. In particular, the density of the foamed resin is preferably <NUM>,<NUM>/m<NUM> or less, more preferably <NUM>/m<NUM> or less, even more preferably <NUM>/m<NUM> or less for the purpose of providing light weight and high mechanical impact-absorbing ability to application products using the joining structure <NUM>, such as electrical wire sheaths and sheathed wire harnesses. On the other hand, the density of the foamed resin is preferably <NUM>/m<NUM> or more for the purpose of ensuring the mechanical strength of the foamed resin and facilitating the melting and flowing of the foamed resin during the formation of the weld recess <NUM>.

On the other hand, the second resin of the second resin sheet <NUM> may include a non-foamed resin or may include a foamed resin as described above. Particularly in a case where the second resin includes a non-foamed resin, the first and second resin sheets <NUM> and <NUM> can be joined with higher strength.

The thickness t<NUM> of the first resin sheet <NUM> and the thickness t<NUM> of the second resin sheet <NUM> are each preferably, but not limited to, <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, for example, for the purpose of improving the balance between mechanical strength and ease of welding through the formation of the weld recess <NUM>.

The joining structure <NUM> includes the first resin sheet <NUM> including the first resin; the second resin sheet <NUM> including the second resin; and the joint <NUM> formed by mating and welding the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>. In this structure, as shown in <FIG>, the joint <NUM> is a portion formed by mating and welding the bottom surface (lower side surface in <FIG>) of the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>.

The joint <NUM> has a weld recess <NUM>, which is located on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>. In this structure, the top surface 22a of the principal surface portion <NUM> is on the side opposite to the side where the end surface portion <NUM> of the second resin sheet <NUM> abuts the first resin sheet <NUM>. At the weld recess <NUM> in the joint <NUM>, at least the first resin of the first resin sheet <NUM> has been pushed in the depth direction of the weld recess <NUM> and allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM> so that the flowing resin melt has been fused to the end surface portion <NUM> of the second resin sheet <NUM> to form a weld overlay portion <NUM>, which will be described later. The resin that is allowed to melt and flow during the formation of the weld recess <NUM> may include the second resin in addition to the first resin.

The bottom <NUM> of the weld recess <NUM> may include a non-foamed resin. Specifically, the first resin often melts at the bottom <NUM> of the weld recess <NUM> when the first resin is pushed in the depth direction of the weld recess <NUM> and allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM>. This often results in the formation of a non-foamed resin at the bottom <NUM> of the weld recess <NUM>.

In the structure, the width w of the bottom <NUM> of the weld recess <NUM> in the thickness direction of the second resin sheet <NUM> (the X1 direction in <FIG>) is preferably equal to or greater than the thickness t<NUM> of the second resin sheet <NUM>. In this case, the bottom <NUM> of the weld recess <NUM> is preferably formed to cover the positions of both principal surfaces of the second resin sheet <NUM> as viewed in the thickness direction (X1 direction) of the second resin sheet <NUM>. The width w of the bottom <NUM> of the weld recess <NUM> is also preferably greater than the thickness t<NUM> of the second resin sheet <NUM> by more than <NUM> to <NUM>. When the weld recess <NUM> is formed in such a manner, the resin pushed in the depth direction of the weld recess <NUM> will be easily allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM>. Alternatively, the width w of the bottom <NUM> of the weld recess <NUM> may be smaller than the thickness t<NUM> of the second resin sheet <NUM>.

The surface of the bottom <NUM> of the weld recess <NUM> may be shaped to have bumps and dents in a grid pattern, for example, as shown in <FIG>. Such bumps and dents in a grid pattern may be formed by pressing a diamond-knurled, leading end of a welding horn against the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM> as described later. This allows the resin to be easily pushed in the depth direction of the weld recess <NUM>.

The surface geometry of the bottom <NUM> of the weld recess <NUM> should not be limited to the grid pattern of bumps and dents shown in <FIG>. For example, as shown in <FIG>, the bottom <NUM> of the weld recess <NUM> may be shaped to have bumps and dents in a stripe pattern using a spline-knurled, leading end of a welding horn. Alternatively, as shown in <FIG>, the bottom <NUM> of the weld recess <NUM> may be shaped to have bumps and dents in an irregular pattern using a blasted leading end of a welding horn. Alternatively, as shown in <FIG>, the bottom <NUM> of the weld recess <NUM> may be shaped to have a flat surface.

The shape of the weld recess <NUM> may be not only rectangular as shown in <FIG> but also, for example, circular as shown in <FIG>.

As shown in <FIG>, the joint <NUM> includes a weld overlay portion <NUM>, which is formed at the inside corner 10a on the bottom surface 22b by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify. The inside corner 10a is formed by the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>. This increases the joint area between the end surface portion <NUM> of the second resin sheet <NUM> and the principal surface portion <NUM> of the first resin sheet <NUM> and enables successful welding of the first and second resin sheets <NUM> and <NUM>.

The weld overlay portion <NUM> may have any shape. For example, as shown in <FIG>, a joint 10E may be formed including a weld overlay portion 27E that has a concave surface when the inside corner 10a is viewed, or as shown in <FIG>, a joint 10F may be formed including a weld overlay portion 27F that has a convex surface when the inside corner 10a is viewed.

When measured from the weld recess <NUM> and determined regardless of the direction of measurement, the minimum thickness t<NUM> of the joint <NUM> is preferably <NUM> or more, more preferably <NUM> or more. In this regard, the preferred lower limit of the minimum thickness t<NUM> of the joint <NUM> may be <NUM> or <NUM>. The minimum thickness t<NUM> of the joint <NUM> measured from the weld recess <NUM> may be smaller than <NUM>. However, when the minimum thickness t<NUM> of the joint <NUM> is <NUM> or more, the joint <NUM> can have a sufficient thickness (sufficient total thickness of the first and second resin sheets <NUM> and <NUM>) even at and near the weld recess <NUM> so that the first resin will be less likely to break at the joint <NUM>. On the other hand, when measured from the weld recess <NUM>, the minimum thickness t<NUM> of the joint <NUM> preferably has an upper limit of <NUM>, more preferably an upper limit about <NUM> smaller than the thickness of the sheet (the thickness of the first resin sheet <NUM>). For example, in a case where the first resin sheet <NUM> has a thickness of <NUM>, the upper limit of the minimum thickness t<NUM> of the joint <NUM> may be <NUM> when set approximately <NUM> smaller than the thickness of the sheet. For example, in a case where the first resin sheet <NUM> has a thickness of <NUM>, the upper limit of the minimum thickness t<NUM> of the joint <NUM> may be <NUM>. When the upper limit of the minimum thickness t<NUM> of the joint <NUM> measured from the weld recess <NUM> is <NUM> or approximately <NUM> smaller than the thickness of the sheet, the first and second resin sheets <NUM> and <NUM> will be joined with high strength because of ease of pushing the resin during the formation of the weld recess <NUM>.

When measured at the bottom of the weld recess <NUM> of the joint <NUM>, the minimum thickness t<NUM> of the first resin in the thickness direction of the first resin sheet <NUM> is preferably <NUM> or more, more preferably <NUM> or more. In this regard, the preferred lower limit of the minimum thickness t<NUM> of the first resin may be <NUM> or <NUM>. The minimum thickness t<NUM> of the first resin at the bottom of the weld recess <NUM> may be smaller than <NUM>. However, when the minimum thickness t<NUM> of the first resin is <NUM> or more, the first resin will be less likely to break at the joint <NUM>. On the other hand, when the minimum thickness t<NUM> of the first resin at the bottom of the weld recess <NUM> is set to <NUM> or less, more preferably <NUM> or less, the first and second resin sheets <NUM> and <NUM> can be joined with higher work efficiency because of ease of pushing the resin during the formation of the weld recess <NUM>. In such a case, the end surface portion <NUM> of the second resin sheet <NUM> can also be easily melted by ultrasound U vibrations when the joining structure <NUM> is formed using ultrasonic welding described later. The minimum thickness t<NUM> of the first resin in the thickness direction of the first resin sheet <NUM> is often the thickness of the first resin sheet <NUM> measured at the deepest part of the bottom <NUM> of the weld recess <NUM>. Alternatively, the minimum thickness t<NUM> of the first resin may be the thickness of the first resin sheet <NUM> measured at any other position.

In the joint <NUM>, the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM> are preferably mated together at an angle in the range of <NUM>° or more and <NUM>° or less, more preferably in the range of <NUM>° or more and <NUM>° or less as measured on the acute angle side. When the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM> are mated together at an angle in such a range, the resin being pushed in the depth direction of the weld recess <NUM> will be easily allowed to melt and flow toward both sides of the end surface portion <NUM> of the second resin sheet <NUM>.

An electrical wire sheath <NUM> including the joining structure <NUM> is provided, which is to be provided around an electrical wire <NUM>.

Hereinafter, the electrical wire sheath <NUM> will be specifically described with reference to the drawings. <FIG> is a schematic perspective view of the structure of the electrical wire sheath <NUM>. The electrical wire sheath <NUM> includes a wall <NUM> extending along the longitudinal direction X2 of the electrical wire <NUM> and has a housing <NUM> that is formed by the wall <NUM> surrounding the space to accommodate the electrical wire <NUM>. The electrical wire sheath <NUM> including the joining structure <NUM> can be formed by joining the resin sheets with high work efficiency without using excessive portions of the resin sheets for the joint. Thus, the resulting electrical wire sheath <NUM> is light-weight and suitable for protecting the electrical wire <NUM>. The electrical wire <NUM> shown in <FIG> is in the form of a single cylinder. Alternatively, the electrical wire <NUM> may be replaced by a bundle of two or more electrical wires, such as a wire harness, or a branched wire if necessary.

The electrical wire sheath <NUM> may have any shape. For example, as shown in <FIG>, the wall <NUM> of the electrical wire sheath <NUM> may include a single resin sheet folded to form multiple corners 30a, 30b, and 30c. In this case, the wall <NUM> of the electrical wire sheath <NUM> is preferably shaped to surround the entire circumference of the electrical wire <NUM>. The electrical wire sheath <NUM> including a single resin sheet as shown above can be formed more efficiently by joining a smaller number of portions of the resin sheet.

The present invention provides a sheathed wire harness <NUM> including: a wire harness <NUM> including an electrical wire <NUM>; and the electrical wire sheath <NUM> described above, in which the electrical wire sheath <NUM> is provided around the wire harness <NUM>. In this structure, the electrical wire sheath <NUM> protects at least part of a bundle of electrical wires in the wire harness <NUM> or at least part of a group of electrical wires including multiple separate bundles of electrical wires branched and extending from a bundle of electrical wires.

Next, a method for producing the joining structure <NUM> will be described. <FIG> is a flowchart of a method for producing the joining structure <NUM>. The production method includes: a positioning step ST1 including mating and positioning a bottom surface 22b of a principal surface portion <NUM> of a first resin sheet <NUM> including a first resin and an end surface portion <NUM> of a second resin sheet <NUM> including a second resin; a welding horn pressing step ST2 including pressing a leading end <NUM> of a welding horn <NUM> against a top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM> while the principal surface portion <NUM> of the first resin sheet <NUM> is mated with the end surface portion <NUM> of the second resin sheet <NUM>; and a joint forming step ST3 including welding the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>, which are mated together, to form a joint <NUM> using ultrasound U emitted from the welding horn <NUM>.

First, provided are a first resin sheet <NUM> including a first resin and a second resin sheet <NUM> including a second resin. The first resin of the first resin sheet <NUM> is preferably a foamed resin. When the first resin sheet <NUM> includes a foamed resin, the first resin will be easy to push in the depth direction of the weld recess <NUM> and will shrink while releasing air bubbles during the joint forming step ST3, which includes melting the first resin using ultrasound U and follows the welding horn pressing step ST2 described below including pressing the leading end <NUM> of the welding horn <NUM> against the first resin sheet <NUM>. This will facilitate the solidification of the welded resin and prevent the first resin from melting and flowing more than necessary, so that the first resin will be less likely to flow out of the joint <NUM>. On the other hand, the second resin of the second resin sheet <NUM> may be any of a non-foamed resin and a foamed resin.

The first and second resin sheets <NUM> and <NUM> are subjected to the positioning step ST1. The positioning step ST1 includes mating and positioning the bottom surface 22b of the principal surface portion <NUM> of the first resin sheet <NUM> including the first resin and the end surface portion <NUM> of the second resin sheet <NUM> including the second resin. For example, in the production of the electrical wire sheath <NUM> including the joining structure <NUM>, the positioning step ST1 may include positioning the first and second resin sheets <NUM> and <NUM> such that a housing <NUM> of a desired size will be formed in a desired position for accommodating an electrical wire <NUM>.

In the positioning step ST1, the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM> may be positioned using a means for holding them in a predetermined position, such as a dedicated positioning jig formed to conform to the shape and dimensions of the resin sheets, in such a way that while the principal surface portion <NUM> of the first resin sheet <NUM> is brought into contact with the end surface portion <NUM> of the second resin sheet <NUM>, the positional relationship between them is fixed.

<FIG> are schematic diagrams for illustrating a method for producing the joining structure and for illustrating an example of the welding horn pressing step and an example of the joint forming step. The positioning step ST1 is followed by the welding horn pressing step ST2, which includes, as shown in <FIG>, pressing a leading end <NUM> of a welding horn <NUM> against the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM> while the principal surface portion <NUM> of the first resin sheet <NUM> is mated with the end surface portion <NUM> of the second resin sheet <NUM>. Thus, the leading end <NUM> of the welding horn <NUM> is positioned relative to the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>.

The leading end <NUM> of the welding horn <NUM> preferably has a convex protrusion shape. This feature makes the welding horn <NUM> less likely to deform at its base and allows a large force per unit area to act on the principal surface portion <NUM> of the first resin sheet <NUM> during the welding horn pressing step ST2, which includes pressing the leading end <NUM> of the welding horn <NUM> against the principal surface portion <NUM> of the first resin sheet <NUM>, so that the first resin will be easily pushed in the depth direction of the weld recess <NUM> during the joint forming step ST3 described later, which includes forming the weld recess <NUM>.

<FIG> are schematic diagrams each showing an example of the geometry of the leading end of a welding horn for use in the method for producing a joining structure according to another embodiment. <FIG> shows the structure of a welding horn having a leading end surface with bumps and dents formed by knurling. <FIG> shows the structure of a welding horn, of which the leading end has a convex protrusion with top surface irregularities formed by blasting. <FIG> shows the structure of a welding horn, of which the leading end has a convex protrusion with a convex top surface formed by filleting.

As shown in <FIG>, the leading end <NUM> of the welding horn <NUM> may have multiple bumps and dents formed on at least part of its surface by spline or diamond knurling. Alternatively, as shown in <FIG>, the leading end <NUM> of the welding horn <NUM> may have a convex protrusion, and at least part of the surface of the leading end <NUM> may have irregularities formed by blasting. Thanks to the bumps and dents or irregularities on the surface of the leading end <NUM> or <NUM> of the welding horn <NUM> or <NUM>, the leading end <NUM> or <NUM> can come into contact with the first resin sheet <NUM> in a small area so that the contact pressure on the first resin sheet <NUM> can concentrate on the dent portions and that ultrasound U vibrations can also concentrate on the dent portions during the joint forming step ST3 described later. As a result, at least the first resin can be easily pushed in the depth direction of the weld recess <NUM>.

Alternatively, as shown in <FIG>, at least part of the surface of the leading end <NUM> of the welding horn <NUM> may be a curved surface, and more specifically, the leading end <NUM> may have a convex protrusion with a convex chamfered top surface formed by filleting. Such a curved surface of the leading end <NUM> of the welding horn <NUM> can come into contact with the first resin sheet <NUM> in a small area so that the contact pressure on the first resin sheet <NUM> can concentrate on the top and that ultrasound U vibrations can also concentrate on the top during the joint forming step ST3 described later. As a result, at least the first resin can be easily pushed in the depth direction of the weld recess <NUM>. Moreover, thanks to the curved surface of the leading end <NUM>, the top of the leading end <NUM> can be pushed shallowly into the first resin sheet <NUM> when the top of the curved surface of the leading end <NUM> is pressed against the overlap between the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>. As a result, the thickness of the first resin sheet <NUM> at the formed weld recess <NUM> (specifically, the minimum thickness t<NUM> of the first resin sheet <NUM> measured from the weld recess <NUM>) can be easily set as desired.

Next, as shown in <FIG>, the joint forming step ST3 is performed, which includes welding the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>, which are mated together, to form a joint <NUM> using ultrasound U emitted from the welding horn <NUM>. Vibrations caused by the ultrasound U emitted from the welding horn <NUM> allow, out of the first and second resins, at least the first resin to heat and melt, and the melted resin is pushed by the welding horn <NUM>. In this step, part of the end surface portion <NUM> of the second resin sheet <NUM> may be allowed to melt together with the first resin so that a mixture of the second resin and the first resin being pushed may be formed. The resin being pushed is allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM> and to form a weld at the inside corner 10a between the bottom surface 22b of the principal surface portion <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>, which results in the formation of the joint <NUM>. In this step, the welding horn <NUM> is pressed against a portion of the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the weld recess <NUM> is formed at that portion. Together with the weld recess <NUM>, the weld overlay portion <NUM> is formed at the inside corner 10a, which is formed between the bottom surface 22b of the principal surface portion <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>.

In this way, the joining structure <NUM> is obtained in which the joint <NUM> has the weld recess <NUM>, which is formed on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the weld overlay portion <NUM>, which is formed at the inside corner 10a of the joint <NUM> on the bottom surface 22b of the principal surface portion <NUM> by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify.

While some embodiments of the present invention have been described above, it will be understood that the embodiments are not intended to limit the present invention and may be altered or modified in various ways within the scope of claims.

Next, inventive examples (examples according to the present invention) and comparative examples will be described to further clarify the advantageous effects of the present invention. It should be noted that the inventive examples are not intended to limit the present invention.

A foamed resin sheet made of a foamed polypropylene resin with a density of <NUM>/m<NUM> was used for both the first and second resin sheets <NUM> and <NUM>. The thickness t<NUM> of the first resin sheet <NUM> and the thickness t<NUM> of the second resin sheet <NUM> were both <NUM>. The first and second resin sheets <NUM> and <NUM> were colored differently so that it could be easily checked how they were welded together.

The positioning step ST1 was performed on the first and second resin sheets <NUM> and <NUM>, in which the bottom surface 22b of the principal surface portion <NUM> of the first resin sheet <NUM> made of the first resin was mated at a right angle with the end surface portion <NUM> of the second resin sheet <NUM> made of the second resin, they were positioned using a positioning jig while they were in contact with each other, and the positional relationship between them was maintained. In other words, the mating angle between the principal surface portion <NUM> of the first resin sheet <NUM> and the end surface portion <NUM> of the second resin sheet <NUM> was <NUM>°.

The welding horn pressing step ST2 was then performed, in which while the principal surface portion <NUM> of the first resin sheet <NUM> was mated with the end surface portion <NUM> of the second resin sheet <NUM>, the leading end <NUM> of the welding horn <NUM> was pressed against the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>. As shown in <FIG>, the leading end <NUM> of the welding horn <NUM> used had a convex protrusion with a <NUM> wide, <NUM> long top surface having bumps and dents formed by diamond knurling with a module (m) of <NUM> according to JIS B <NUM>. The leading end <NUM> of the welding horn <NUM> was pressed against the first resin sheet <NUM> and the second resin sheet <NUM> such that the width (transverse) direction of the leading end <NUM> matched the thickness direction of the second resin sheet <NUM>. During the pressing, equal portions of the leading end <NUM> of the welding horn <NUM> were allowed to protrude from the second resin sheet <NUM> in its thickness direction.

While the leading end <NUM> of the welding horn <NUM> was pressed against the first resin sheet <NUM> and the second resin sheet <NUM>, the joint forming step ST3 was performed using ultrasound U emitted from the welding horn <NUM>. A small welder (P128 (model number) manufactured by Ultrasonic Engineering Co. ) was used for the emission of ultrasound U from the welding horn <NUM>. The ultrasound U was emitted at a power of <NUM> W and a frequency of <NUM> for <NUM> seconds. The welding horn <NUM> was thrust to a depth of <NUM> to weld the first and second resin sheets <NUM> and <NUM> so that the joint <NUM> was formed to produce the joining structure <NUM>.

<FIG> shows the result of observing a cross-section of the resulting joining structure <NUM>, which is perpendicular to the first and second resin sheets. The result of the observation shown in <FIG> indicates that in the joint forming step ST3, the first resin of the first resin sheet <NUM> and the second resin of the second resin sheet <NUM> were locally melted by heating caused by ultrasound U emission and that the melted first resin with reduced air voids was pushed by the welding horn <NUM>. It was also found that while forming a mixture with the melted second resin, the first resin being pushed was allowed to melt and flow in the vicinity of the end surface portion <NUM> of the second resin sheet <NUM> and fused to form a weld overlay portion <NUM> at the inside corner 10a between the bottom surface 22b of the principal surface portion <NUM> and the end surface portion <NUM> of the second resin sheet <NUM>.

The joint <NUM> of the resulting joining structure <NUM> had a weld recess <NUM> on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the bottom <NUM> of the weld recess <NUM> had bumps and dents in a grid pattern. The width and length of the bottom <NUM> of the weld recess <NUM> were approximately the same as those of the leading end <NUM> of the welding horn <NUM>. Specifically, the width w of the bottom <NUM> of the weld recess <NUM> was around <NUM> in the thickness direction of the second resin sheet <NUM>.

In the resulting joining structure <NUM>, the minimum thickness t<NUM> of the joint <NUM> measured from the weld recess <NUM> was <NUM> regardless of the direction of measurement. The position of the top of the end surface portion <NUM> of the second resin remained substantially the same as the original position of the principal surface portion <NUM> of the first resin sheet <NUM> before the formation of the joint <NUM>, and the minimum thickness t<NUM> of the first resin measured at the deepest part of the bottom <NUM> of the weld recess <NUM> was <NUM> in the thickness direction of the first resin sheet <NUM>.

The joint strength of the resulting joining structure <NUM> was measured by pulling apart the joint <NUM> in the depth direction of the weld recess <NUM> using an Autograph tensile tester manufactured by Shimadzu Corporation (model number: AGS-X, <NUM> N to <NUM> kN). The measured joint strength was <NUM> N.

A joining structure <NUM> was produced as in Inventive Example <NUM> except that the leading end <NUM> of the welding horn <NUM> used had a convex protrusion with a <NUM> wide, <NUM> long top surface having bumps and dents formed by diamond knurling with a module (m) of <NUM> according to JIS B <NUM>.

As in Inventive Example <NUM>, the joint <NUM> of the resulting joining structure <NUM> had a weld recess <NUM> on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the bottom <NUM> of the weld recess <NUM> had bumps and dents in a grid pattern. The width and length of the bottom <NUM> of the weld recess <NUM> were approximately the same as those of the leading end <NUM> of the welding horn <NUM>. Specifically, the width w of the bottom <NUM> of the weld recess <NUM> was around <NUM> in the thickness direction of the second resin sheet <NUM>.

In the resulting joining structure <NUM>, the minimum thickness t<NUM> of the joint <NUM> measured from the weld recess <NUM> was <NUM> regardless of the direction of measurement. The minimum thickness t<NUM> of the first resin measured at the deepest part of the bottom <NUM> of the weld recess <NUM> was <NUM> in the thickness direction of the first resin sheet <NUM>.

The joint strength of the resulting joining structure <NUM> was <NUM> N as measured in the same way as in Inventive Example <NUM>.

A joining structure <NUM> was produced as in Inventive Example <NUM> except that as shown in <FIG>, the leading end <NUM> of the welding horn <NUM> used had a <NUM> long, angle protrusion whose cross-section was <NUM> wide and <NUM> long and whose top surface had irregularities formed by blasting.

As in Inventive Example <NUM>, the joint <NUM> of the resulting joining structure <NUM> had a weld recess <NUM> on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the bottom <NUM> of the weld recess <NUM> had geometries directly transferred from the angle protrusion of the welding horn <NUM>. The dimensions and shape of the bottom <NUM> of the weld recess <NUM> were approximately the same as those of the leading end <NUM> of the welding horn <NUM>. Specifically, the width w of the bottom <NUM> of the weld recess <NUM> was around <NUM> in the thickness direction of the second resin sheet <NUM>.

A joining structure <NUM> was produced as in Inventive Example <NUM> except that as shown in <FIG>, the leading end <NUM> of the welding horn <NUM> used had a convex protrusion whose cross-section was <NUM> wide and <NUM> long and which had a convex top surface with a height of <NUM> formed by <NUM> radius filleting.

As in Inventive Example <NUM>, the joint <NUM> of the resulting joining structure <NUM> had a weld recess <NUM> on the top surface 22a of the principal surface portion <NUM> of the first resin sheet <NUM>, and the bottom <NUM> of the weld recess <NUM> had geometries directly transferred from the convex protrusion of the welding horn <NUM>. The dimensions and shape of the bottom <NUM> of the weld recess <NUM> were approximately the same as those of the leading end <NUM> of the welding horn <NUM>. Specifically, the width w of the bottom <NUM> of the weld recess <NUM> was around <NUM> in the thickness direction of the second resin sheet <NUM>.

A joining structure <NUM> was produced as in Inventive Example <NUM> except that the welding horn <NUM> was thrust to a depth of <NUM> when the joint <NUM> was formed.

A joining structure <NUM> was produced as in Inventive Example <NUM> except that the thickness t<NUM> of the first resin sheet <NUM> was <NUM>, the thickness t<NUM> of the second resin sheet <NUM> was <NUM>, and the welding horn <NUM> was thrust to a depth of <NUM> when the joint <NUM> was formed.

In Comparative Example <NUM>, the joining structure shown in FIG. <NUM> of <CIT> was formed. Through holes were formed in the first resin sheet <NUM>, and protrusions were formed on the top of the end surface portion <NUM> of the second resin sheet <NUM>. Each of the protrusions had a wide head and a narrow neck. The wide head formed the top of the protrusion, and the narrow neck connected the head to the surface of the first resin sheet <NUM> to be mated. Next, the head and then neck of each protrusion were inserted through each through hole of the principal surface portion <NUM> of the first resin sheet <NUM> from the bottom surface side while both ends of the wide head of the protrusion were folded, so that the end surface portion <NUM> of the second resin sheet <NUM> was mated at a right angle with the first resin sheet <NUM>. Both ends of the head were then unfolded to the original state, so that a joining structure was formed, in which the necks of the protrusions passed through the through holes.

In Comparative Example <NUM>, the formation of the protrusions on the top of the end surface portion <NUM> of the second resin sheet <NUM> required a larger resin sheet than in Inventive Examples. The joint strength of the resulting joining structure was up to <NUM> N as measured in the same way as in Inventive Example <NUM>.

In Comparative Example <NUM>, holes were formed in the first resin sheet <NUM>, and protrusions were formed on the top of the end surface portion <NUM> of the second resin sheet <NUM>. Next, the protrusions on the end surface portion <NUM> of the second resin sheet <NUM> were inserted through the holes of the principal surface portion <NUM> of the first resin sheet <NUM> from the bottom surface side, so that the end surface portion <NUM> of the second resin sheet <NUM> was mated at a right angle with the first resin sheet <NUM>. Portions of the protrusions on the end surface portion <NUM> of the second resin sheet <NUM>, which protruded from the holes of the principal surface portion <NUM> of the first resin sheet <NUM>, were melted by heating so that caulking was performed to fix the end surface portion <NUM> of the second resin sheet <NUM> to the principal surface portion <NUM> of the first resin sheet <NUM>.

In Comparative Example <NUM>, the formation of the protrusions on the top of the end surface portion <NUM> of the second resin sheet <NUM> also required a larger resin sheet than in Inventive Examples. The joint strength of the resulting joining structure was up to <NUM> N as measured in the same way as in Inventive Example <NUM>.

As shown above, the joining structures <NUM> of Inventive Examples <NUM> to <NUM> all had a joint strength of more than <NUM> N and were successfully formed by joining the first and second resin sheets <NUM> and <NUM> with no need to use excessive portions of the resin sheets for the joint, such as portions for forming the protrusions on the top of the end surface portion <NUM> of the second resin sheet <NUM>. Moreover, when the joining structures of Inventive Examples <NUM> to <NUM> were produced, the first and second resin sheets <NUM> and <NUM> were joined with high work efficiency by welding using ultrasound U emitted from the welding horn <NUM>.

Thus, the joining structures <NUM> of Inventive Examples <NUM> to <NUM> were produced by joining the resin sheets with high work efficiency without using excessive portions of the resin sheets for the joint.

In particular, the joining structures <NUM> of Inventive Examples <NUM> to <NUM>, in which the minimum thickness t<NUM> of the first resin in the thickness direction of the first resin sheet <NUM> was in the range of <NUM> or more and <NUM> or less as measured at the bottom of the weld recess <NUM>, had a high joint strength over <NUM> N, which indicated that the resin sheets were strongly joined together. This suggests that the minimum thickness t<NUM> of the first resin in the thickness direction of the first resin sheet <NUM> should preferably be in the range of <NUM> or more and <NUM> or less as measured at the bottom of the weld recess <NUM> particularly in order to make it possible to increase the joint strength and to strongly join the resin sheets without using excessive portions of the resin sheets for the joint.

Claim 1:
A joining structure (<NUM>, 1A - 1F) comprising: a first resin sheet (<NUM>, 21A - 21D) comprising a first resin; a second resin sheet (<NUM>) comprising a second resin; and a joint (<NUM>, 10A - 10F) formed by mating and welding a principal surface portion (<NUM>) of the first resin sheet (<NUM>, 21A - 21D) and an end surface portion (<NUM>) of the second resin sheet (<NUM>),
the first resin being a foamed resin,
the second resin being a non-foamed or foamed resin,
the joint (<NUM>, 10A - 10F) having a weld recess (<NUM>, 25A - 25F) on a top surface (22a) ,
characterized in that
the joint (<NUM>, 10A - 10F) comprises a weld overlay portion (<NUM>, 27E, 27F) formed at an inside corner on a bottom surface (22b) by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify.