A conveying roller and a method for producing the same

Abstract: A conveying roller includes a shaft and a body member placed on a periphery of the shaft. The body member is provided with an inner layer placed on the periphery of the shaft and an outer layer placed on a periphery of the inner layer. The inner layer is made of a thermoplastic resin having a predetermined volume reduction rate. The outer layer is made of an elastomer. This conveying roller has an increased adhesion between the shaft and the body member.

Description: BACKGROUND OF THE INVENTION This invention relates to a conveying roller having an elastomer member disposed on the periphery of a shaft in a uniform thickness in the radial direction, and a method for producing the same. Hitherto has been known a conveying roller including an elastomer member placed on the periphery of a metal shaft in a uniform thickness in the radial direction. Such a conveying roller having a body member made of elastomer is advantageous in transferring paper in a copying machine, facsimile machine, printing machine, or the like because of flexibility of the elastomer member. Such conveying rollers have been generally produced by the so-called shaft press-in-fitting method where a shaft coated with an adhesive on the periphery is pressingly inserted in a center hole of a cylindrically formed elastomer body member, or the so-called elastomer winding method where an elastomer material is wound on a shaft coated with an adhesive on the periphery. The body member always comes into contact with paper or other object, and often comes into contact with chemical material such as developing solution. Accordingly, the body member requires material having high wear resistance and chemical resistance. In the shaft press-in-fitting method, a cylindrical body member is formed by extrusion molding. The cylindrical body member is formed with a center hole. A shaft is coated with an adhesive, and then pressingly inserted in the center hole of the body member. This method requires skillful and delicate operations. Accordingly, this method is low in the production efficiency while high in the production costs. The same problems have been found in the elastomer winding method. To solve these problems, the so-called injection molding method has been proposed. In the injection molding method, a conveying roller is produced by placing a shaft in a die, and injecting a molten elastomer into a mold space in the die. As mentioned above, the material for a body member of a conveying roller requires high wear and chemical resistances. However, elastomer having high wear resistance and chemical resistance has a low adhesion. Accordingly, there has been the problem that when a conveying roller produced in the injection molding method is placed in operation, the shaft and the elastomer body member slide over each other, impairing the integral rotation of the shaft and the body member. To increase the adhesion between the shaft and the body member in the injection molding method, there has been proposed addition of a step of applying an adhesive onto a periphery of a shaft placed in a molding die before a molten elastomer is injected into the die. However, this addition makes the production process complicated, and decreases the productivity of conveying roller. US-A-4 312 444 discloses a conveyor roller having a low noise level and a long life consisting of a steel shaft, an intermediate layer made of polymeric material bonded to the shaft, a helical steel spring wear element situated around the periphery of the intermediate layer, and an outer layer made of an abrasion-resistant polymeric material located at the outer periphery of the intermediate layer and between the turns of the wear element. SUMMARY OF THE INVENTION It is the object of the invention to provide a conveying roller and a method for producing a conveying roller having or enabling a simplified production process. This object is fulfilled by a conveying roller having the features disclosed in claim 1 and a method for producing a conveying roller having the features disclosed in claim 8. Preferred embodiments are defined in the dependent subclaims. According to an aspect of the present invention, a conveying roller comprises a shaft and a body member placed on a periphery of the shaft. The body member includes an inner layer placed on the periphery of the shaft and an outer layer placed on a periphery of the inner layer. The inner layer is made of a thermoplastic resin having a predetermined volume reduction rate. The outer layer is made of an elastomer. Furthermore, the inner layer has a melting temperature substantially identical to that of the outer layer such that the inner periphery surface of the outer layer is partially mixed with an outer periphery surface of the inner layer. According to another aspect of the present invention, a method for producing a conveying roller comprises the steps of placing a shaft in a first die having a first mold space, injecting a molten thermoplastic resin having a predetermined volume reduction rate into the first mold space to place the molten thermoplastic resin around a periphery of the shaft, cooling the first die to produce a preliminary mold product having an inner layer of thermoplastic resin on the periphery of the shaft, placing the preliminary mold product in a second die having a second mold space, injecting a molten elastomer having a melting temperature substantially identical to that of the inner layer into the second mold space to place the molten elastomer around a periphery of the inner layer of the preliminary mold product and to mix the outer periphery surface of the inner layer with the elastomer, and cooling the second die to produce a conveying roller having an outer layer of elastomer on the periphery of the inner layer. These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cut away perspective view showing a conveying roller embodying the invention; Fig. 2A is a sectional view taken along the line IIA-IIA in Fig. 1; Fig. 2B is a sectional view taken along the line IIB-IIB in Fig. 1; Fig. 3A is a perspective view showing a part of a first modified shaft; Fig. 3B is a perspective view showing a part of a second modified shaft; Fig. 3C is a perspective view showing a part of a third modified shaft; Fig. 3D is a perspective view showing a part of a fourth modified shaft; Fig. 3E is a perspective view showing a part of a fifth modified shaft; Fig. 3F is a perspective view showing a part of a sixth modified shaft; Figs. 4A and 4B are diagrams showing a first step of a producing method embodying the invention, Fig. 4A showing a state where a molten resin is injected into a first die mounted with a shaft, Fig. 4B showing a state where a preliminary molded product is taken out from the first die; and Figs. 5A and 5B are diagrams showing a second step of the producing method, Fig. 5A showing a state where a molten elastomer is injected into a second die mounted with the preliminary molded product, Fig. 5B showing a state where a molded conveying roller is taken out from the second die. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVNETION A conveying roller embodying the present invention will be described with reference to Figs. 1 to 2B. Indicated at 1 is a conveying roller which comprises a metal cylindrical shaft 2, and a body member 3 on the periphery of the shaft 2. The body member 3 includes an inner layer 4 placed on the periphery of the shaft 2, and an outer layer 5 placed on the periphery of the inner layer 4. Both ends of the inner layer 4 are covered with an end cover 41 formed on the outer layer 5. The ends of the inner layer 4 are not exposed to outside. The shaft 2 is made of a stainless steel, and in the form of a cylinder having no slit or groove in the surface. The inner layer 4 is made of a thermoplastic resin, such as polypropylene resin. The resin has a volume reduction rate from the molten state to the solid state, or shrinkage factor, in a range of 0.5% to 2.0%. In the case of using a thermoplastic resin having a volume reduction rate of 0.5% or more, as the molten resin covered on the periphery of the shaft 2 solidifies in a process of cooling, thus tightly adhering on the shaft 2. Accordingly, the shaft 2 is firmly prevented from shifting with respect to the body member. In the case of using a thermoplastic resin having a volume reduction rate of lower than 0.5%, the tightening effect on the shaft 2 is not sufficient. Accordingly, there is a likelihood that the shaft 2 slides out of the body member 3 when axial forces are oppositely applied to the shaft 2 and the body member 3. Also, there is a likelihood that the shaft 2 and the body member 3 slide over each other in circumferential directions when the weight or load of an article to be conveyed is great. On the other hand, in the case of using a thermoplastic resin having a volume reduction rate of larger than 2.0%, an excessive internal stress is liable to occur in the inner layer 4, resulting in a short life. The outer layer 5 is made of a thermoplastic elastomer having a melting temperature (molding temperature) nearly identical to that of the thermoplastic resin of the inner layer 4. The use of such elastomer has the following advantageous effect. In a process of molding, the molten elastomer can be placed on the periphery of the inner layer 4 whose surface portion is partially melted by the heat of the molten elastomer. Accordingly, the resin of the inner layer 4 and the elastomer are partially mixed, and the inner layer 4 and outer layer 5 are securely integrated in the boundary zone. In this embodiment, more specifically, the outer layer 5 is made of olefin elastomer having a melting temperature identical to the melting point (165°C) of the polypropylene resin of the inner layer 4. With the construction of the conveying roller 1, the inner layer 4 is tightly adhered on the periphery of the shaft 2 because of the shrinkage of the thermoplastic resin, and the outer layer 5 is integrated with the inner layer 4. Accordingly, the body member 3 including the inner and outer layers 4 and 5 is firmly bonded on the shaft 2, thus securely preventing the shaft 2 from shifting in the body member 3. An article to be conveyed, such as print paper, can be flexibly and securely conveyed by the outer layer made of elastomer. The inner layer 4 is pressingly adhered onto the periphery of the shaft 2 because of the shrinkage, resulting in no clearance between the shaft 2 and the inner layer 4. Also, the polypropylene, which the inner layer 4 is made of, is resistant to chemicals. Accordingly, even in the case where the conveying roller 1 is immersed in a chemical solution such as developing solution, the chemical solution will not enter and stay between the periphery of the shaft 2 and the inner surface of the inner layer 4. Corrosion of the conveying roller 1 due to chemical solution can be suppressed securely. Figs. 3A to 3F respectively show first to sixth shaft modifications of the inventive conveying roller. A shaft 2a in the first modification shown in Fig. 3A has a plurality of ridges 21a extending in an axial direction in a periphery thereof. The plurality of ridges 21a are spaced in a circumferential direction at an equal interval. The adhesion of an inner layer 4 onto the periphery of the shaft 2a is enhanced because the inner layer 4 comes into spaces between the ridges 21a. This renders the body member 3 rotate securely together with the shaft 2a. A shaft 2b in the second modification shown in Fig. 3B has a plurality of intersecting grooves 21b in a periphery thereof. The adhesion of an inner layer 4 onto the periphery of the shaft 2b is enhanced because the inner layer 4 comes into the intersecting grooves 21b. This renders the body member 3 rotate securely together with the shaft 2b. A shaft 2c in the third modification shown in Fig. 3C has a plurality of annular grooves 21c in a periphery thereof. The plurality of annular grooves 21c are arranged in an axial direction of the shaft 2c at specified intervals. The adhesion of an inner layer 4 onto the periphery of the shaft 2c is enhanced because the inner layer 4 comes into the annular grooves 21c. This renders the body member 3 rotate securely together with the shaft 2c. A shaft 2d in the fourth modification shown in Fig. 3D has a plurality of rectangular holes 21d in a periphery thereof. The plurality of rectangular holes 21d are arranged in the periphery at specified intervals in axial and circumferential directions. The adhesion of an inner layer 4 onto the periphery of the shaft 2d is enhanced because the inner layer 4 comes into the rectangular holes 21d. This renders the body member 3 rotate securely together with the shaft 2d. A shaft 2e in the fifth modification shown in Fig. 3E has a plurality of through holes 21e extending in radial directions. The plurality of through holes 21e are arranged at specified intervals in an axial direction. The adhesion of an inner layer 4 onto the periphery of the shaft 2e is enhanced because the inner layer 4 comes into the through holes 21e. This renders the body member 3 rotate securely together with the shaft 2e. A shaft 2f in the sixth modification shown in Fig. 3F has an intermediate portion whose cross section is square. An inner surface of an inner layer 4 is made to contact with the intermediate portion having the square cross section. Accordingly, the adhesion of the inner layer 4 onto the periphery of the shaft 2f increases, thus rendering the body member 3 rotate securely together with the shaft 2f. Figs. 4A to 5B are diagrams explaining a production of a conveying roller of the invention. Fig. 4A shows a state where a molten resin P is injected into a first die 6 mounted with a shaft 2. Fig. 4B shows a state where a preliminary molded product is taken out from the first die 6. Fig. 5A shows a state where a molten elastomer E is injected into a second die 7 mounted with the preliminary molded product 10. Fig. 5B shows a state where a molded conveying roller 1 is taken out from the second die 7. The first die 6 includes an upper mold member 61 and a lower mold member 62 as shown in Fig. 4A. A mold space 63 is formed by coupling the upper mold member 61 and the lower mold member 62 while a shaft 2 is held between them. The mold space 63 corresponds to a molded shape of an inner layer 4. An injection hole 64 is formed in an end wall of the lower mold member 62. The injection hole 64 extends in an axial direction of the shaft 2 to be placed in the mold space 63. Molten polypropylene P is supplied into the mold space 63 from an injecting machine 65 through the injection hole 64. In this embodiment, the polypropylene P is heated to 180 to 200°C in the injecting machine 65. The second die 7 includes an upper mold member 71 and a lower mold member 72 as shown in Fig. 5. A mold space 73 is formed by coupling the upper mold member 71 and the lower mold member 72 while the preliminary molded product 10 is held between them. The mold space 73 corresponds to a molded shape of the outer layer 5. An injection hole 74 is formed in an end wall of the lower mold member 72. The injection hole 74 extends in an axial direction of the shaft 2 to be placed in the mold space 73. Molten olefin elastomer E is supplied into the mold space 73 from an injecting machine 75 through the injection hole 74. In this embodiment, the olefin elastomer E is heated to 190 to 200°C in the injecting machine 75. The dies 6 and 7 each are provided with a cooler for cooling the upper mold and lower mold members. The dies 6 and 7 are cooled to 20 to 30°C by the cooler. An inventive conveying roller 1 is produced as follows. First, as shown in Fig. 4A, a shaft 2 is held between the upper mold member 61 and lower mold member 62. Thereafter, a specified amount of molten polypropylene P is injected into the mold space 63 through the injection hole 64 from the injecting machine 65. Consequently, the mold space 73 is filled with molten polypropylene P, and the shaft 2 is covered with molten polypropylene P. In this state, the polypropylene P is cooled to 20 to 30°C by the cooler to produce a preliminary molded product 10 in which the shaft 2 is adhered with an inner layer 4. This preliminary molded product 10 is taken out from the mold space 63 by opening the upper mold member 61 as shown in Fig. 4B, and is transferred to a second step. In the second step, as shown in Fig. 5A, the preliminary molded product 10 is held between the upper mold member 71 and the lower mold member 72. In this state, both end of the shaft 2 project out from the second die 7. A specified amount of molten olefin elastomer E is supplied into the mold space 73 from the injecting machine 75 through the injection hole 74. The preliminary molded product 10 in the mold space 73 is covered with the molten olefin elastomer E. In this state, the second die 7 is cooled to 20 to 30°C by the cooler. Thereafter, a conveying roller 1 covered with the elastomer outer layer 4 is take out by opening the upper die 71, as shown in Fig. 5B. The present invention is not limited to the foregoing embodiment. However, the following may be appreciated. (1) In the foregoing embodiment, the inner layer 4 is formed into a cylindrical shape. However, the inner layer 4 may be formed into a shape having a triangular cross section, polygonal cross section, stellate cross section, etc. (2) In the foregoing embodiment, polypropylene is used as material for the inner layer 4. However, it may be appreciated to use polystyrene, polyethylene, or the like in place of polypropylene. In the foregoing embodiment, as material for the outer layer 5, olefin elastomer is used. However, it may be appreciated to use styrene thermoplastic elastomer, polyamide elastomer, or the like in place of olefin elastomer. (3) Alternatively, according to the present invention, it may be possible to use thermosetting elastomer, such as polyester elastomer, polyurethane elastomer, as material for the outer layer 5. In this case of using thermosetting elastomer, after injecting thermosetting elastomer into the second die 7 at a room temperature, the die 7 is heated to melt a surface portion of the inner layer 4 of thermoplastic resin and solidify the thermosetting elastomer. (4) In the sixth modification, the shaft 2f has the intermediate portion having a square cross section. Further, it may be appreciated to use a shaft having an intermediate portion having a triangular cross section , a polygonal cross section, a stellate cross section, or the like. (5) In the foregoing embodiment, the shaft 2 is made of metal. However, instead of metal, the shaft 2 may be made of resin or ceramics. (6) In the foregoing embodiment, the molding material is supplied into the mold space 63 or 73 through the injection holes 64 or 74 in the axial direction to render the molecular orientation of the resin of the inner layer 3 or the elastomer of the outer layer 4 parallel to the shaft 2. This axial parallel orientation reduces the bending stress of the shaft. In the case of the length of shaft being as short as 300 mm or less, however, it may be appreciated to form an injection hole in a radial direction of the shaft 2. As described above, an inventive conveying roller is provided with a shaft and a body member placed on a periphery of the shaft. The body member includes an inner layer placed on the periphery of the shaft and an outer layer placed on a periphery of the inner layer. The inner layer is made of a thermoplastic resin having a predetermined volume reduction rate. The outer layer is made of an elastomer. In the inventive conveying roller, the body member is constructed by the inner layer and the outer layer. The inner layer, which is in direct contact with the shaft, is made of thermoplastic resin having a predetermined volume reduction rate. Accordingly, the inner layer tightly grips the shaft, thus assuredly preventing the shaft from sliding with respect to the body member. The body member and the shaft can be integrated securely. The conveying efficiency will be remarkably improved as compared with the conventional conveying rollers. An inventive conveying roller is produced by the novel method of injecting a molten thermoplastic resin having a predetermined volume reduction rate into a first mold space formed in a first die to place the molten thermoplastic resin around a periphery of a shaft held in the first die, cooling the first die to produce a preliminary mold product having an inner layer of thermoplastic resin on the periphery of the shaft, thereafter placing the preliminary mold product in a second die having a second mold space, and injecting a molten elastomer into the second mold space to place the molten elastomer around a periphery of the inner layer of the preliminary mold product, and cooling the second die to produce a conveying roller having an outer layer of elastomer on the periphery of the inner layer. This inventive method eliminates the application of adhesive on the periphery of a shaft, and also eliminates the insertion of a shaft in a body member, thus simplifying the production process. This makes it possible to greatly reduce the production costs. As material which comes into direct contact with a shaft, thermoplastic resin having a predetermined volume reduction rate is used. The thermoplastic resin noticeably shrinks in the course of solidification, strongly gripping the shaft. Accordingly, this method can produce a conveying roller having a great adhesion between the shaft and the body member. The shaft is formed with recesses, grooves, holes, or other irregularity in the periphery of the shaft. The thermoplastic resin of the inner layer comes into the irregular gaps, consequently increasing the adhesion between the shaft and the inner layer. Displacement of shift between the shaft and the body member can be reliably prevented. The both ends of the inner layer are covered with the outer layer of elastomer. The boundary between the inner layer and the outer layer is not exposed. This will assure an increased life duration and an improved appearance for the conveying roller. The outer layer is made of elastomer having a melting temperature substantially identical to that of the thermoplastic resin of the inner layer. Specifically, in the production process, a periphery surface of the inner layer of thermoplastic resin is heated and partially melted by the molten thermoplastic elastomer. Consequently, the thermoplastic resin of the inner layer and the elastomer of the outer layer mix with each other in a boundary between them. Accordingly, the adhesion between the inner layer and the outer layer will be enhanced. As the thermoplastic resin for the inner layer, polypropylene, polystyrene, or polyethylene is used. These thermoplastic resins have so large a volume reduction rate as 0.5% to 2.0%. Accordingly, these thermoplastic resins are preferable for the inner layer. As the elastomer for the outer layer is used thermoplastic elastomer such as olefin elastomer, styrene elastomer, or polyamide elastomer, or thermosetting elastomer such as polyester elastomer or polyurethane elastomer. These elastomers have a melting temperature substantially identical to that of polypropylene, polystyrene, or polyethylene for the inner layer, thereby ensuring an increased mixing with the thermoplastic resin of the inner layer. Thus, the adhesion between the inner layer and the outer layer will be increased. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.

Claims: A conveying roller (1) comprising: a shaft (2); and a body member ( 3 ) placed on a periphery of the shaft, the body member ( 3 ) including: an inner layer (4) molded on the periphery of the shaft (2), the inner layer (4) being made of a thermoplastic resin having a predetermined volume reduction rate; and an outer layer (5) molded on a periphery of the inner layer (4), the outer layer (5) being made of an elastomer, wherein the inner layer (4) has a melting temperature substantially identical to that of the outer layer (5) such that the inner periphery surface of the outer layer (5) is partially mixed with an outer periphery surface of the inner layer (4). A conveying roller (1) according to claim 1, wherein both ends of the inner layer (4) are covered by the outer layer (5). A conveying roller (1) according to claim 1 or 2, wherein the shaft (2) is formed with a recess, groove (21a; 21b; 21c) or hole (21d; 21e) in the periphery thereof. A conveying roller (1) according to one or more of claims 1 to 3, wherein the thermoplastic resin is a resin selected from the group consisting of polypropylene, polystyrene, and polyethylene. A conveying roller (1) according to one or more of claims 1 to 4, wherein the outer layer (5) is made of a thermoplastic elastomer. A conveying roller (1) according to claim 5, wherein the thermoplastic elastomer is an elastomer selected from the group consisting of olefin elastomer, styrene elastomer, and polyamide elastomer. A conveying roller according to one or more of claims 1 to 6, wherein the thermoplastic resin has a volume reduction rate of 0.5 to 2.0 percent. A method for producing a conveying roller (1) comprising the steps of: placing a shaft (2) in a first die (6) having a first mold space (63); injecting a molten thermoplastic resin having a predetermined volume reduction rate into the first mold space (63) to place the molten thermoplastic resin around a periphery of the shaft (2) ; cooling the first die (6) to produce a preliminary mold product having an inner layer (4) of thermoplastic resin on the periphery of the shaft (2) ; placing the preliminary mold product in a second die (7) having a second mold space (73) ; injecting a molten elastomer having a melting temperature substantially identical to that of the inner layer (4) into the second mold space (73) to place the molten elastomer around a periphery of the inner layer (4) of the preliminary mold product and to mix the outer periphery surface of the inner layer (4) with the elastomer; and cooling the second die (7) to produce a conveying roller (1) having an outer layer (5) of elastomer on the periphery of the inner layer (4). A method according to claim 8, wherein in the step of injecting a molten elastomer, the molten elastomer is placed on both ends of the inner layer (4) in addition to the placement of the molten elastomer around a periphery of the inner layer (4) . A method according to claim 8 or 9, wherein the thermoplastic resin is a resin selected from the group consisting of polypropylene, polystyrene, and polyethylene. A method according to one or more of claims 8 to 10, wherein the elastomer is a thermoplastic or thermosetting elastomer. A method according to claim 11, wherein the thermoplastic elastomer is an elastomer selected from the group consisting of olefin elastomer, styrene elastomer, and polyamide elastomer. A method according to claim 11, wherein the thermosetting elastomer is an elastomer selected from the group consisting of polyester elastomer and polyurethane elastomer. A method according to one or more of claims 8 to 13, wherein the thermoplastic resin has a volume reduction rate of 0.5 to 2.0 percent.

Inventors: TSUJI HIDEKI, TSUJI, HIDEKI
Applicants: NORITSU KOKI CO LTD, NORITSU KOKI CO., LTD.
Application year: 1998
Main classification: B65G39
IPC codes: F16C13, B65H5, B65G39, B32B1