Resin joint, connection structure, and connection method

Abstract

A resin joint according to the present invention is connected to a resin tube and comprises a connection end part to which the resin tube is connected. The connection end part has an inner tube part, and an outer tube part through which laser light passes, and which is positioned on the outer circumferential surface side of the inner tube part and forms, with the inner tube part, an annular recess that opens on the leading end side of the connection end part. The outer diameter of the inner tube part at the leading end is smaller than the outer diameter of the inner tube part in the recess. The inner tube part has an inner tube guide surface that guides the resin tube from the leading end to the recess. A connection structure according to the present invention comprises the resin joint, and the resin tube which is connected to the resin joint and through which laser light does not pass. The resin tube is welded to the outer tube part of the resin joint in a state of being inserted into the recess in the resin joint. In a connection method for connecting the resin tube to the connection end part of the resin joint, the connection end part is inserted into the resin tube while the resin tube is expanded by the connection end part.

Description

Resin Joint, Connection Structure, and Connection Method

[0001] One aspect of the present invention relates to a resin joint, a connection structure, and a connection method.

[0002] Conventionally, resin joints may be used to connect resin tubes to mating members such as pipes. In connecting a resin tube to a resin joint, it is necessary to maintain airtightness. As a method of airtightly connecting a resin tube and a resin joint, there are a method of mechanically sealing the resin tube and the joint using an O-ring or the like, and a method of welding the resin tube and the resin joint by melting at least one of the resin tube and the resin joint. As the latter welding method, a method using a laser beam as described in Patent Document 1 is known.

[0003] In the method described in Patent Document 1, a resin tube having a high absorption rate of laser light is inserted into a resin joint having a high transmittance of laser light. Then, by melting the resin tube by irradiation with laser light, the resin tube and the resin joint are welded together.

[0004] Japanese Patent Application Laid-Open No. 2022-155155

[0005] However, since the resin tube is not necessarily formed into a perfect circle, when the resin tube is inserted into the resin joint, a large gap may occur between the resin tube and the resin joint. In addition, since the outer diameter of the resin tube has variations, the outer diameter of the resin tube may be smaller than the inner diameter of the resin joint, or the outer diameter of the resin tube may be larger than the inner diameter of the resin joint. When the outer diameter of the resin tube is smaller than the inner diameter of the resin joint, a large gap may occur between the resin tube and the resin joint when the resin tube is inserted into the resin joint. When the outer diameter of the resin tube is larger than the inner diameter of the resin joint, when the resin tube is inserted into the resin joint, a part of the resin tube may be greatly compressed inward, and a large gap may occur between the resin tube and the resin joint. In such a case, even if the resin tube and the resin joint are welded by irradiation with laser light, there is a possibility that airtightness cannot be maintained, or that even if airtightness can be maintained, the bonding strength may be low.

[0006] One aspect of the present invention aims to provide a resin joint, a connection structure, and a connection method that can obtain high joint strength while maintaining airtightness when a resin tube and a resin joint are laser-welded together.

[0007] [1] A resin joint according to one aspect of the present invention is a resin joint connected to a resin tube, and comprises a connecting end to which the resin tube is connected, the connecting end comprising an inner cylinder portion and an outer cylinder portion located on the outer circumferential surface side of the inner cylinder portion, forming an annular recess between itself and the inner cylinder portion that opens toward the tip side of the connecting end, and having transparency to laser light, wherein the outer diameter of the inner cylinder portion at the tip is smaller than the outer diameter of the inner cylinder portion at the recess, and the inner cylinder portion has an inner cylinder guide surface that guides the resin tube from the tip to the recess.

[0008] In this resin joint, the connecting end has an inner cylinder portion and an outer cylinder portion located on the outer circumferential surface side of the inner cylinder portion, forming an annular recess between the inner cylinder portion and the connecting end portion, opening towards the tip of the connecting end portion, and having transparency to laser light. Therefore, when a resin tube is inserted into the recess and laser light is shone on the connecting end portion from the surroundings, the laser light passes through the outer cylinder portion and irradiates the resin tube. As a result, the resin tube is heated and melted, and further, heat is conducted from the resin tube to the outer cylinder portion, causing the outer cylinder portion to also be heated and melted, thereby welding the resin tube and the outer cylinder portion together. Moreover, in this resin joint, the outer diameter of the inner cylinder portion at the tip of the connecting end portion is smaller than the outer diameter of the inner cylinder portion at the recess portion, and the inner cylinder portion has an inner cylinder guide surface that guides the resin tube from the tip of the connecting end portion into the recess portion. Therefore, the resin tube is inserted into the recess portion while being expanded by the inner cylinder guide surface. Therefore, the resin tube can be brought into close contact with the inner surface of the outer cylinder, and by irradiating the connection end with laser light from the surroundings in this state and welding the resin tube and the outer cylinder, high joint strength can be obtained while maintaining airtightness.

[0009] [2] In the resin joint described in [1], the inner cylinder portion may extend further toward the tip than the outer cylinder portion. In this resin joint, since the inner cylinder portion extends further toward the tip of the connecting end than the outer cylinder portion, the resin tube can be easily inserted into the recess.

[0010] [3] In the resin joint described in [1] or [2], the inner cylinder guide surface may be a tapered surface that expands in diameter from the tip side toward the recess side. In this resin joint, since the inner cylinder guide surface is a tapered surface that expands in diameter from the tip side toward the recess side of the connecting end, the resin tube can be inserted into the recess while gradually expanding. This makes it possible to suppress the rapid deformation of the resin tube when inserting it into the recess. This makes it possible to suppress, for example, the breakage of the resin tube.

[0011] [4] In the resin joint described in any of [1] to [3], the inner cylinder guide surface may be a curved surface that expands in diameter from the tip side towards the recess side and curves convexly from the tip side towards the recess side. In this resin joint, since the inner cylinder guide surface is a curved surface that expands in diameter from the tip side towards the recess side and curves convexly from the tip side towards the recess side, the contact area between the resin tube and the inner cylinder guide surface when inserting the inner cylinder into the resin tube can be reduced. Therefore, the insertion force of the inner cylinder into the resin tube can be reduced.

[0012] [5] In the resin joint described in any of [1] to [4], the outer cylinder portion may have an outer cylinder guide surface that guides the resin tube into the recess. In this resin joint, since the outer cylinder portion has an outer cylinder guide surface that guides the resin tube into the recess, the resin tube can be inserted into the recess even more easily.

[0013] [6] In the resin joint described in [5], the outer cylinder guide surface may be formed in a shape in which the end of the outer cylinder portion on the inner cylinder portion side and the tip end is chamfered. In this resin joint, since the outer cylinder guide surface is formed in a shape in which the end of the outer cylinder portion on the inner cylinder portion side and the tip end of the connecting end is chamfered, the resin tube that is in contact with the outer cylinder guide surface can be directed toward the back of the recess.

[0014] [7] A connection structure according to one aspect of the present invention comprises a resin joint described in any of [1] to [6] and a resin tube connected to the resin joint that is impermeable to laser light, wherein the resin tube is welded to the outer cylindrical portion of the resin joint while inserted into a recess of the resin joint.

[0015] In this connection structure, a resin tube that is impermeable to laser light is inserted into the recess of the resin joint described above and welded to the outer cylinder portion of the resin joint. Therefore, when laser light is irradiated onto the connection end from the surroundings while the resin tube is in close contact with the inner circumferential surface of the outer cylinder portion, the resin tube and the outer cylinder portion can be welded together. As a result, high joint strength can be obtained while maintaining airtightness.

[0016] [8] A connection method according to one aspect of the present invention is a connection method for connecting a resin tube to the connection end of a resin joint, wherein the connection end is inserted into the resin tube while expanding the resin tube with the connection end.

[0017] In this connection method, the connection end is inserted into the resin tube while expanding it with the connection end, allowing the resin tube to be brought into close contact with the inner surface of the outer cylinder. Therefore, by irradiating the connection end with laser light from the surroundings in this state and welding the resin tube and the outer cylinder, a high joint strength can be obtained while maintaining airtightness.

[0018] According to one aspect of the present invention, when a resin tube and a resin joint are laser-welded together, high joint strength can be obtained while maintaining airtightness.

[0019] Figure 1 is a cross-sectional view of a connection structure according to an embodiment. Figure 2 is an enlarged cross-sectional view of a part of an example of a resin tube. Figure 3 is a cross-sectional view of a resin joint according to an embodiment. Figure 4 is a side view of the resin joint shown in Figure 3. Figure 5 is an enlarged cross-sectional view of a part of Figure 3. Figure 6 is a cross-sectional view illustrating a method of connecting a resin tube and a resin joint. Figure 7 is a cross-sectional view illustrating a method of connecting a resin tube and a resin joint. Figure 8 is a cross-sectional view illustrating a method of connecting a resin tube and a resin joint. Figure 9 is a cross-sectional view of a modified resin joint. Figure 10 is a cross-sectional view illustrating a method of connecting a resin tube and the resin joint shown in Figure 9. Figure 11 is a cross-sectional view of a modified resin joint. Figures 12(a), 12(b), and 12(c) are cross-sectional views illustrating a method of connecting a resin tube and the resin joint shown in Figure 11. Figure 13 is a cross-sectional view of a modified resin joint. Figure 14 is a cross-sectional view of a modified resin joint. Figure 15 is a cross-sectional view of a modified resin joint. Figure 16 is a side view of the resin joint shown in Figure 15.

[0020] The resin joint, connection structure, and connection method according to the embodiment will be described below with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numeral, and redundant explanations are omitted.

[0021] Figure 1 is a cross-sectional view of the connection structure 1 according to this embodiment. As shown in Figure 1, the connection structure 1 according to this embodiment is a structure in which a resin tube 2 and a resin joint 3 are connected.

[0022] The resin tube 2 is a resin tube used for the passage of fluids such as liquids and gases. The resin tube 2 is used, for example, as piping in the cooling system and fuel system of an automobile. Examples of resin tubes 2 include corrugated tubes and smooth tubes.

[0023] The resin tube 2 is opaque to laser light. Opaque to laser light means that when irradiated with laser light, it absorbs at least a portion of the laser light and melts due to heat generation. The opacity to laser light may apply to the entire resin tube 2, or to only a part of it.

[0024] Figure 2 is an enlarged cross-sectional view of a part of an example of a resin tube 2. The resin tube 2 shown in Figure 2 has a two-layer structure in which an outer layer 21 and an inner layer 22 located on the inner circumference side of the outer layer 21 are laminated. Note that the resin tube 2 does not have to be a two-layer structure. For example, the resin tube 2 may be a single-layer structure or a three-layer or more-layer structure. The outer layer 21 is made of a polyamide resin such as PA12 (polyamide 12 resin). The inner layer 22 is made of PP (polypropylene resin) such as PP. The outer layer 21 contains a black material such as carbon black to provide opacity to laser light. Note that the outer layer 21 may be made opacity to laser light by means other than containing a black material. Also, if the inner layer 22 is to be made opacity to laser light, the inner layer 22 may also contain a black material such as carbon black.

[0025] As shown in Figure 1, the resin joint 3 according to this embodiment is a component that is connected to the resin tube 2 and also to a mating member (not shown), such as a pipe, in order to connect the resin tube 2 to the mating member. The resin joint 3 is connected to the resin tube 2 by welding.

[0026] Figure 3 is a cross-sectional view of the resin joint 3 according to the embodiment. Figure 4 is a side view of the resin joint 3 shown in Figure 3. Figure 5 is an enlarged cross-sectional view of a part of Figure 3. As shown in Figures 3 to 5, the resin joint 3 comprises a flow path 31, a first connecting end 32, and a second connecting end 33.

[0027] The flow path 31 is a through-hole that penetrates the resin joint 3 from the first connecting end 32 to the second connecting end 33. The first connecting end 32 is located at one end of the flow path 31, and the second connecting end 33 is located at the other end of the flow path 31. The tip of the first connecting end 32 is called the tip 34. The tip 34 is the tip of the flow path 31 on the side of the first connecting end 32, and is also the tip of the flow path 31 opposite to the second connecting end 33. The flow path 31 is open at the tip 34.

[0028] The flow path 31 may or may not extend in a straight line. For example, if the resin joint 3 extends in a straight line, the flow path 31 may extend in a straight line. On the other hand, if the resin joint 3 is bent in an L-shape, the flow path 31 may extend in an L-shape or curved.

[0029] The first connecting end 32 is the part to which the resin tube 2 is connected. The second connecting end 33 is the part to which the mating member is connected. The second connecting end 33 has a bulge (a protruding portion extending in the circumferential direction of the second connecting end 33) formed on it, for example, to prevent the mating member connected to the second connecting end 33 from easily coming off the second connecting end 33.

[0030] The first connecting end 32 has an inner cylindrical portion 35 and an outer cylindrical portion 36.

[0031] The inner cylinder portion 35 is formed in a cylindrical shape. The inner circumferential surface of the inner cylinder portion 35 forms the flow path 31 at the first connecting end 32. The inner cylinder portion 35 extends to the tip 34. In other words, the inner cylinder portion 35 forms the tip 34.

[0032] The outer cylinder portion 36 is located on the outer circumferential surface side of the inner cylinder portion 35 and forms an annular recess 37 between itself and the inner cylinder portion 35 that opens toward the tip 34. The outer cylinder portion 36 has a cylindrical portion 36a formed in a cylindrical shape and a bottom portion 36b that extends from the end of the cylindrical portion 36a opposite to the tip 34 to the inner cylinder portion 35. The cylindrical portion 36a is formed, for example, in a cylindrical shape concentric with the inner cylinder portion 35. The cylindrical portion 36a, together with the inner cylinder portion 35, constitutes a double tube. The bottom portion 36b extends from the end of the cylindrical portion 36a opposite to the tip 34 to the inner cylinder portion 35, thereby closing the recess 37 from the side opposite to the tip 34.

[0033] The outer cylinder portion 36 does not extend to the tip 34. In other words, the inner cylinder portion 35 extends further toward the tip 34 than the outer cylinder portion 36. Also, the inner cylinder portion 35 protrudes from the outer cylinder portion 36 toward the tip 34.

[0034] The recess 37 is located between the inner cylinder portion 35 and the outer cylinder portion 36, and is the region into which the resin tube 2 is inserted. The recess 37 is formed in an annular shape that extends over the entire circumferential area of ​​the inner cylinder portion 35 and the outer cylinder portion 36. The recess 37 also opens towards the tip 34.

[0035] The outer diameter D1 of the inner cylinder portion 35 at the tip 34 is smaller than the outer diameter D2 of the inner cylinder portion at the recess 37. The outer diameter D2 is the maximum outer diameter of the inner cylinder portion 35 at the recess 37. The outer diameter D1 is less than or equal to the inner diameter D3 of the resin tube 2. The outer diameter D2 is larger than the inner diameter D3 of the resin tube 2.

[0036] The inner cylinder portion 35 has an inner cylinder guide surface 38 that guides the resin tube 2 from the tip 34 to the recess 37. The resin tube 2 is inserted into the recess 37 while being expanded by the guidance of the inner cylinder guide surface 38. Here, the wall thickness of the resin tube 2 is defined as wall thickness T (see Figure 1), and the wall thickness of the resin tube 2 after being expanded by the guidance of the inner cylinder guide surface 38 and inserted into the recess 37 is defined as wall thickness T' (see Figure 1). The width W of the recess 37 may be, for example, smaller than wall thickness T and smaller than wall thickness T'. Note that the resin tube 2 becomes thinner (stretched) when expanded, so the wall thickness T' is smaller than the wall thickness T (T' < T).

[0037] The inner cylinder guide surface 38 can have any shape as long as it can guide the resin tube 2 from the tip 34 to the recess 37 when inserting the resin tube 2 into the recess 37. In this embodiment, as an example, the inner cylinder guide surface 38 is a tapered surface that widens in diameter from the tip 34 side to the recess 37 side. The inner cylinder guide surface 38 is formed such that, for example, a virtual surface V offset by the wall thickness T of the resin tube 2 from the inner cylinder guide surface 38 intersects the inner circumferential surface of the outer cylinder portion 36 on the inner cylinder portion 35 side.

[0038] The tip of the inner cylinder guide surface 38 on the side facing the tip 34 is located closer to the tip 34 than the recess 37. The tip of the inner cylinder guide surface 38 on the side facing the tip 34 may be located at the tip 34, or it may be located at a position spaced away from the tip 34. In this embodiment, as an example, the tip of the inner cylinder guide surface 38 on the side facing the tip 34 is located at the tip 34. The tip of the inner cylinder guide surface 38 opposite to the tip 34 may be located closer to the tip 34 than the recess 37, may be located inside the recess 37, or may be located at the opening end of the recess 37. When the tip of the inner cylinder guide surface 38 opposite to the tip 34 is located inside the recess 37, when inserting the resin tube 2 into the recess 37, the tip of the resin tube 2 is more likely to come into contact with the inner circumferential surface of the outer cylinder portion 36 on the inner cylinder portion 35 side, making it easier to guide the resin tube 2 into the recess 37.

[0039] The resin joint 3 is transparent to laser light. Being transparent to laser light means that when irradiated with laser light, it has the property of transmitting at least a portion of the laser light. The transparency to laser light may be the entire resin joint 3 or only a part of it. If the transparency to laser light is only a part of the resin joint 3, then at least the outer cylindrical portion 36 of the first connecting end 32 is transparent to laser light.

[0040] The resin joint 3 can be made of the same material as the resin tube 2, taking into consideration compatibility when welding it to the resin tube 2. If the resin tube 2 has a multilayer structure, the resin joint 3 can be made of the same material as the outer layer of the resin tube 2. For example, as shown in Figure 2, if the resin tube 2 has a two-layer structure of an outer layer 21 and an inner layer 22, and the outer layer 21 is made of a polyamide resin such as PA12 (polyamide 12 resin), then the resin joint 3 can be made of a polyamide resin such as PA12 (polyamide 12 resin), similar to the outer layer 21. Furthermore, the resin joint 3 may be made of an uncolored natural material to provide transparency to laser light. Transparency to laser light may be provided to the resin joint 3 by means other than being made of an uncolored natural material. In addition, to provide high rigidity to the resin joint 3, the resin joint 3 may contain fillers such as glass fiber reinforcement. Such a resin joint 3 can be manufactured, for example, by injection molding.

[0041] Next, we will explain how to connect the resin tube 2 and the resin fitting 3.

[0042] Figures 6 to 8 are cross-sectional views illustrating the method of connecting the resin tube 2 and the resin fitting. When connecting the resin tube 2 and the resin fitting 3, the inner cylinder portion 35 is inserted into the resin tube 2, as shown in Figures 6 and 7. Then, as shown in Figures 7 and 8, the inner cylinder portion 35 is pressed into the resin tube 2 while expanding it with the inner cylinder guide surface 38. In other words, as the inner cylinder portion 35 is inserted, the resin tube 2 is expanded by the inner cylinder guide surface 38 and moves towards the recess 37. The resin tube 2 is then inserted into the recess 37 in close contact with the inner circumferential surface of the outer cylinder portion 36.

[0043] Next, as shown in FIG. 8, the first connection end portion 32 is irradiated with laser light from the surroundings. The irradiation of the laser light is performed, for example, from a direction orthogonal to the central axis of the first connection end portion 32 toward the first connection end portion 32 over the entire circumference of the first connection end portion 32. Then, the laser light passes through the outer cylinder portion 36 and is irradiated onto the resin tube 2. As a result, the resin tube 2 is heated and melted, and further, by heat conduction from the resin tube 2 to the outer cylinder portion 36, the outer cylinder portion 36 is also heated and melted, so that the resin tube 2 and the outer cylinder portion 36 are welded together. Thereby, the resin tube 2 is welded to the outer cylinder portion 36 of the resin joint 3 in a state where it is inserted into the recess 37 of the resin joint 3.

[0044] As described above, in the resin joint 3 according to the present embodiment, the first connection end portion 32 includes an inner cylinder portion 35 and an outer cylinder portion 36 that is located on the outer peripheral surface side of the inner cylinder portion 35 and forms an annular recess 37 that opens toward the tip 34 side between the inner cylinder portion 35 and the outer cylinder portion 具有, and the outer cylinder portion 36 has transparency to laser light. Therefore, when the resin tube 2 is inserted into the recess 37 and the first connection end portion 32 is irradiated with laser light from the surroundings, the laser light passes through the outer cylinder portion 36 and is irradiated onto the resin tube 2. As a result, the resin tube 被加热熔化, and further, by heat conduction from the resin tube 2 to the outer cylinder portion 36, the outer cylinder portion 36 is also heated and melted, so that the resin tube and the outer cylinder portion 36 are welded together. Moreover, in this resin joint

[0045] Further, in this resin joint 3, since the inner cylinder portion 35 extends to the tip 34 side beyond the outer cylinder portion 36, the resin tube 2 can be easily inserted into the recess 37.

[0046] Further, in this resin joint 3, since the inner cylinder guide surface 38 is a tapered surface that expands in diameter from the tip 34 side toward the recess 37 side, the resin tube 2 can be inserted into the recess 37 while gradually expanding the resin tube 2. Therefore, when the resin tube 2 is inserted into the recess 37, it is possible to suppress the resin tube 2 from being rapidly deformed. Thereby, for example, breakage of the resin tube 2 can be suppressed.

[0047] In the connection structure 1 according to the present embodiment, since the resin tube 2 having non-transparency to laser light is welded to the outer cylinder portion 36 of the resin joint 3 in a state of being inserted into the recess 37 of the resin joint 3, the resin tube 2 is in a state of being closely attached to the inner peripheral surface of the outer cylinder portion 36, and laser light is irradiated from the surroundings to the first connection end portion 32, so that the resin tube 2 and the outer cylinder portion 36 can be welded together. Therefore, it is possible to obtain high joint strength while maintaining airtightness.

[0048] In the connection method according to the present embodiment, since the first connection end portion 32 is inserted into the resin tube 2 while expanding the resin tube 2 by the first connection end portion 32, the resin tube 2 can be deformed into a shape along the first connection end portion 32. Therefore, the resin tube 2 can be closely attached to the inner peripheral surface of the outer cylinder portion 36, and in this state, by irradiating laser light from the surroundings to the first connection end portion 32 to weld the resin tube 2 and the outer cylinder portion 36, it is possible to obtain high joint strength while maintaining airtightness.

[0049] As described above, the embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

[0050] For example, as shown in FIG. 9, the outer cylinder portion may have an outer cylinder guide surface for guiding the resin tube 2 into the recess. FIG. 9 is a cross-sectional view of a resin joint 3A according to a modified example. The first connection end portion 32A of the resin joint 3A shown in FIG. 9 has an outer cylinder portion 36A corresponding to the outer cylinder portion 36 according to the above embodiment, and the outer cylinder portion 36A has an outer cylinder guide surface 39 for guiding the resin tube 2 into the recess 37.

[0051] The outer cylinder guide surface 39 is a surface that guides the resin tube 2 into the recess 37 when the resin tube 2 is inserted into the recess 37. The outer cylinder guide surface 39 is formed with a chamfered shape at the end of the outer cylinder portion 36A that is on the inner cylinder portion 35 side and the tip 34 side. The outer cylinder guide surface 39 may be a flat surface or a curved surface.

[0052] The outer cylinder guide surface 39 is formed such that the tip of the resin tube 2 contacts it when the resin tube 2 is inserted into the recess 37, for example, guided by the inner cylinder guide surface 38. The outer cylinder guide surface 39 is also formed at a position where a virtual surface V, offset by the wall thickness T of the resin tube 2, intersects the inner cylinder guide surface 38. In this case, the outer cylinder guide surface 39 may be inclined toward the inner cylinder portion 35 with respect to the direction perpendicular to the virtual surface V.

[0053] Figure 10 is a cross-sectional view illustrating the method of connecting the resin tube 2 to the resin joint 3A shown in Figure 9. As shown in Figure 10, when the inner cylinder portion 35 is inserted into the resin tube 2 while expanding the resin tube 2, the tip of the resin tube 2 comes into contact with the outer cylinder guide surface 39. Then, the tip of the resin tube 2 is directed towards the back of the recess 37, and the resin tube 2 is inserted into the recess 37.

[0054] Thus, since the outer cylinder portion 36A has an outer cylinder guide surface 39 that guides the resin tube 2 into the recess 37, the resin tube 2 can be inserted into the recess even more easily.

[0055] Furthermore, since the outer cylinder guide surface 39 is formed with a chamfered shape at the end of the outer cylinder portion 36A on the inner cylinder portion 35 side and the tip 34 side, the resin tube 2 that is in contact with the outer cylinder guide surface 39 can be directed toward the back of the recess 37.

[0056] Furthermore, as shown in Figures 11 to 14, the inner cylinder guide surface may have various shapes.

[0057] Figure 11 is a cross-sectional view of a modified resin joint 3B. The first connecting end 32B of the resin joint 3B shown in Figure 11 has an inner cylinder portion 35B corresponding to the inner cylinder portion 35 in the above embodiment, and the inner cylinder portion 35B has an inner cylinder guide surface 38B that guides the resin tube 2 from the tip 34 to the recess 37.

[0058] The inner cylinder guide surface 38B is a curved surface that widens in diameter from the tip 34 side towards the recess 37 side, and also curves convexly from the tip 34 side towards the recess 37 side.

[0059] Figures 12(a), 12(b), and 12(c) are cross-sectional views illustrating the method of connecting the resin tube 2 to the resin joint 3B shown in Figure 11. As shown in Figures 12(a) and 12(b), when the inner cylinder portion 35B is inserted into the resin tube 2, the inner cylinder portion 35B is pressed into the resin tube 2 while expanding the resin tube 2 with the inner cylinder guide surface 38B. At this time, since the inner cylinder guide surface 38B is a curved surface that curves convexly from the tip 34 side to the recess 37 side, it contacts the resin tube 2 with a small contact area such as line contact, and pushes the resin tube 2 open. Then, the inner cylinder portion 35B is inserted into the resin tube 2 while changing the contact position between the resin tube 2 and the inner cylinder guide surface 38B.

[0060] As described above, the inner cylinder guide surface 38B widens in diameter from the tip 34 side towards the recess 37 side and is a curved surface that curves convexly from the tip 34 side towards the recess 37 side, thereby reducing the contact area with the resin tube 2. Therefore, the insertion force of the inner cylinder portion 35B into the resin tube 2 can be reduced, and buckling of the resin tube 2 when inserting the inner cylinder portion 35B into the resin tube 2 can be suppressed.

[0061] Figure 13 is a cross-sectional view of a modified resin joint 3C. The first connecting end 32C of the resin joint 3C shown in Figure 13 has an inner cylinder portion 35C corresponding to the inner cylinder portion 35 in the above embodiment, and the inner cylinder portion 35C has an inner cylinder guide surface 38C that guides the resin tube 2 from the tip 34 to the recess 37.

[0062] The inner cylinder guide surface 38C has a first inner cylinder guide surface 38Ca located on the tip side 34 and a second inner cylinder guide surface 38Cb located on the opposite side from the tip side 34. Both the first inner cylinder guide surface 38Ca and the second inner cylinder guide surface 38Cb are tapered surfaces that widen in diameter from the tip side 34 towards the recess side 37. The second inner cylinder guide surface 38Cb is a tapered surface with a larger taper angle than the first inner cylinder guide surface 38Ca.

[0063] In this way, by making the taper angle of the first inner cylinder guide surface 38Ca, located on the tip side 34, smaller than the taper angle of the second inner cylinder guide surface 38Cb, located on the opposite side from the tip 34, the resin tube 2 becomes easier to expand.

[0064] Figure 14 is a cross-sectional view of a modified resin joint 3D. The first connecting end 32D of the resin joint 3D shown in Figure 14 has an inner cylinder portion 35D corresponding to the inner cylinder portion 35 in the above embodiment, and the inner cylinder portion 35D has an inner cylinder guide surface 38D that guides the resin tube 2 from the tip 34 to the recess 37.

[0065] The inner cylinder guide surface 38D has a first inner cylinder guide surface 38Da located on the tip side 34 and a second inner cylinder guide surface 38Db located on the opposite side from the tip side 34. The second inner cylinder guide surface 38Db is a tapered surface that widens in diameter from the tip side 34 towards the recess side 37. The first inner cylinder guide surface 38Da is located between the tip side 34 and the second inner cylinder guide surface 38Db and is formed as a circumferential surface with no change in outer diameter. In other words, the tapered surface of the inner cylinder guide surface 38D is formed at a position spaced apart from the tip side 34.

[0066] In this way, even if the tapered surface of the inner cylinder guide surface 38D is spaced apart from the tip 34, the resin tube 2 can be inserted into the recess 37 while expanding.

[0067] Furthermore, as shown in Figures 15 and 16, irregularities may be formed on the outer circumferential surface of the inner cylinder portion.

[0068] Figure 15 is a cross-sectional view of a modified resin joint 3E. Figure 16 is a side view of the resin joint 3E shown in Figure 15. The resin joint 3E shown in Figures 15 and 16 has an inner cylinder portion 35E corresponding to the inner cylinder portion 35 in the above embodiment, and irregularities 35Ea are formed on the outer circumferential surface of the inner cylinder portion 35E.

[0069] The irregularities 35Ea are formed, for example, by at least one groove formed on the outer circumferential surface of the inner cylindrical portion 35E. This at least one groove may extend, for example, in a direction along the central axis of the first connecting end portion 32.

[0070] As described above, the uneven surface 35Ea formed on the outer circumferential surface of the inner cylinder portion 35E reduces the contact area between the resin tube 2 and the inner cylinder portion 35E when the resin tube 2 is inserted into the recess 37. Therefore, the insertion force of the inner cylinder portion 35E into the resin tube 2 can be reduced, and buckling of the resin tube 2 when the inner cylinder portion 35E is inserted into the resin tube 2 can be suppressed.

[0071] 1...Connection structure, 2...Resin tube, 3...Resin fitting, 3A...Resin fitting, 3B...Resin fitting, 3C...Resin fitting, 3D...Resin fitting, 3E...Resin fitting, 21...Outer layer, 22...Inner layer, 31...Flow path, 32...First connection end, 32A...First connection end, 32B...First connection end, 32C...First connection end, 32D...First connection end, 33...Second connection end, 34...Tip, 35...Inner cylinder section, 35B...Inner cylinder section, 35C...Inner cylinder section, 35D...Inner cylinder section, 35E...Inner cylinder section, 3 5Ea...concave and concave, 36...outer cylinder part, 36a...cylindrical part, 36b...bottom part, 36A...outer cylinder part, 37...concave, 38...inner cylinder guide surface, 38B...inner cylinder guide surface, 38C...inner cylinder guide surface, 38Ca...first inner cylinder guide surface, 38Cb...second inner cylinder guide surface, 38D...inner cylinder guide surface, 38Da...first inner cylinder guide surface, 38Db...second inner cylinder guide surface, 39...outer cylinder guide surface, D1...outer diameter, D2...outer diameter, D3...inner diameter, T...wall thickness, T'...wall thickness, V...virtual surface, W...width.

Claims

1. A resin joint connected to a resin tube, comprising a connecting end to which the resin tube is connected, wherein the connecting end comprises an inner cylinder portion and an outer cylinder portion located on the outer circumferential surface side of the inner cylinder portion, forming an annular recess between itself and the inner cylinder portion that opens toward the tip side of the connecting end, and having transparency to laser light, wherein the outer diameter of the inner cylinder portion at the tip is smaller than the outer diameter of the inner cylinder portion at the recess, and the inner cylinder portion has an inner cylinder guide surface that guides the resin tube from the tip to the recess.

2. The resin joint according to claim 1, wherein the inner cylinder portion extends further toward the tip than the outer cylinder portion.

3. The resin joint according to claim 1 or 2, wherein the inner cylinder guide surface is a tapered surface that widens in diameter from the tip side toward the recess side.

4. The resin joint according to any one of claims 1 to 3, wherein the inner cylinder guide surface is a curved surface that expands in diameter from the tip side toward the recess side and curves convexly toward the recess side toward the tip side.

5. The resin joint according to any one of claims 1 to 4, wherein the outer cylinder portion has an outer cylinder guide surface for guiding the resin tube into the recess.

6. The resin joint according to claim 5, wherein the outer cylinder guide surface is formed in a shape in which the end of the outer cylinder portion on the inner cylinder portion side and the tip end side is chamfered.

7. A connection structure comprising: a resin joint according to any one of claims 1 to 6; and a resin tube connected to the resin joint, which is impermeable to laser light, wherein the resin tube is welded to the outer cylindrical portion of the resin joint while inserted into the recess of the resin joint.

8. A connection method for connecting a resin tube to the connecting end of a resin fitting, wherein the connecting end is inserted into the resin tube while expanding the resin tube with the connecting end.

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