Patent Publication Number: US-2022220278-A1

Title: Method of manufacturing rubber product

Description:
TECHNICAL FIELD 
     The present disclosure relates to a method of manufacturing a rubber product, and in particular to a method suitable for manufacturing rubber products that can flexibly respond to changes in the shape of the products. 
     The present application claims priority to Japanese Patent Application No. 2019-112262 filed on Jun. 17, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Known methods of manufacturing rubber products include a method of manufacturing a product by placing unvulcanized rubber in a mold that matches the shape of the product and vulcanizing the rubber by applying heat and pressure, as in Patent Literature (PTL) 1, and a method of placing unvulcanized rubber in a mold that is larger than the product, vulcanizing the rubber by applying heat and pressure, and then machining the rubber by cutting or the like to yield the shape of the product. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2004-107514 A 
     SUMMARY 
     Technical Problem 
     However, in the method of using a mold that matches the shape of the product, the mold needs to be modified or made anew when a change in the shape of the product occurs for a reason such as a change in product specifications. The production costs and the time and effort for processing have thus been problematic. Furthermore, in a method of using a mold larger than the product, there has been room for improvement in the manufacturing accuracy, such as dimensional accuracy during machining, depending on the physical properties of the rubber. 
     It is an aim of the present disclosure to provide a method of manufacturing a rubber product that can flexibly respond to changes in the shape of a product and can achieve high manufacturing accuracy. 
     Solution to Problem 
     We carefully studied how to solve the aforementioned problem and concluded that a desired product shape can be obtained without using a mold by repeating a formation process of supplying material and treating the material according to the properties of the material, and then stacking following the shape of the desired product. After further investigating the aforementioned additive manufacturing, we discovered that the additive manufacturing can be applied to rubber products by performing appropriate treatment on the powder of uncrosslinked rubber to be used as a material and further crosslinking the powder of the uncrosslinked rubber, thereby completing the present disclosure. 
     We provide the following. 
     A method of manufacturing a rubber product according to the present disclosure includes: 
     performing adhesion prevention treatment on uncrosslinked rubber powder, which is a material of the rubber product, to prevent mutual adhesion of the uncrosslinked rubber powder; and 
     sequentially and repeatedly forming by supplying raw rubber powder, on which the adhesion prevention treatment has been performed, and irradiating the supplied portion with an electron beam to crosslink the irradiated portion, so that the crosslinked portion is stacked following a shape of the rubber product. 
     “Supplying raw rubber powder, on which the adhesion prevention treatment has been performed, and irradiating the sprayed portion with an electron beam” preferably refers to the raw rubber powder being supplied and the electron beam being irradiated simultaneously, but the cases of the supply of raw rubber powder preceding the irradiation with the electron beam and the irradiation with the electron beam preceding the supply of raw rubber powder are also included. 
     Advantageous Effect 
     According to the present disclosure, a method of manufacturing a rubber product that, without use of a mold, can flexibly respond to changes in the shape of a product and can achieve high manufacturing accuracy can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a flowchart illustrating an outline of a method of manufacturing a rubber product according to an embodiment of the present disclosure; 
         FIG. 2  is a diagram illustrating an example of a rubber product manufactured by the method of manufacturing a rubber product according to an embodiment of the present disclosure; 
         FIG. 3  is a diagram illustrating thin pieces; 
         FIG. 4  is a perspective view schematically illustrating the configuration of an additive manufacturing apparatus; 
         FIG. 5A  is a perspective view schematically illustrating formation of a starting portion of raw rubber powder; 
         FIG. 5B  is a perspective view schematically illustrating a state in which a layer corresponding to a thin piece has been manufactured; 
         FIG. 5C  is a cross-sectional view schematically illustrating a state in which a layer corresponding to a thin piece has been manufactured; 
         FIG. 5D  is a cross-sectional view schematically illustrating treatment after the layer corresponding to a thin piece has been manufactured; 
         FIG. 5E  is a cross-sectional view schematically illustrating the manufacturing of the next layer corresponding to the next thin piece; 
         FIG. 5F  is a cross-sectional view schematically illustrating a state in which the formation has been repeated to stack the layers; 
         FIG. 6  is a perspective view transparently illustrating another example of a rubber product manufactured by the method of manufacturing a rubber product according to an embodiment of the present disclosure; and 
         FIG. 7  is a perspective view transparently illustrating yet another example of a rubber product manufactured by the method of manufacturing a rubber product according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Methods of manufacturing rubber products according to embodiments of the present disclosure are described below.  FIG. 1  is a flowchart illustrating an outline of a method of manufacturing a rubber product according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 1 , a method of manufacturing a rubber product according to an embodiment of the present disclosure includes performing adhesion prevention treatment on uncrosslinked rubber powder, which is a material of a rubber product, to prevent mutual adhesion of the uncrosslinked rubber powder (step S 1 ), acquiring data on a plurality of thin pieces of a rubber product (step S 2 ), and sequentially and repeatedly forming by supplying raw rubber powder, on which the adhesion prevention treatment has been performed, and irradiating the supplied portion with an electron beam to crosslink the irradiated portion, so that crosslinked portions are stacked following a shape of the rubber product (step S 3 ), thereby manufacturing a rubber product. 
       FIG. 2  illustrates a rubber product  10 , which is an example of a rubber product to be manufactured by the method of manufacturing a rubber product according to the present embodiment. As illustrated in  FIG. 2 , the rubber product  10  can, for example, have a cylindrical shape. 
     Here, thin pieces refer to layers that are divided by cutting at numerous planes orthogonal to the axis along the stacking direction of the rubber product to be manufactured. 
     In the example of the rubber product  10 , when the Z-axis direction is the stacking direction (height), a plurality of sliced layers are formed by cutting the cylindrical three-dimensional shape at numerous planes orthogonal to the Z-axis direction. Each layer in the plurality of sliced layers illustrated in  FIG. 3  is a thin piece of the rubber product  10 . The stacking direction in additive manufacturing of the rubber product  10  refers to the Z-axis direction in  FIGS. 2 and 3 , but a suitable direction can be used as the stacking direction according to the shape, size, and the like of the rubber product to be manufactured. 
     Although the thin pieces L 1  to L 3  from the first layer to the third layer in the Z-axis direction of the rubber product  10  are illustrated in  FIG. 3 , the rubber product  10  is actually converted into data on thin pieces L 1  to LN (N is a natural number) for the number of layers required to manufacture the rubber product  10 . 
     In this way, the shape of the rubber product  10  is converted into the data on a plurality of thin pieces, and the thin pieces are then stacked according to a manufacturing path based on this data to manufacture the rubber product  10 . 
     Each step is described in detail below. 
     [Adhesion Prevention Treatment] 
     In the adhesion prevention treatment step S 1 , uncrosslinked rubber powder, which is a material of the rubber product  10 , is treated to prevent mutual adhesion of the uncrosslinked rubber powder. 
     A material suitable for rubber products can be used as the material forming the uncrosslinked rubber powder in the present disclosure. Powders of polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile butadiene rubber (NBR), and other synthetic rubbers, in addition to natural rubber (NR), can be used as the rubber powder. Among these, powders of natural rubber (NR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR) are preferred. These rubber powders may be used alone, or a combination of two or more types thereof may be used. 
     The uncrosslinked rubber powder may also contain other materials other than natural rubber and synthetic rubber. As the other materials, fillers such as carbon black and silica, softeners, age resistors, zinc oxide, crosslinking accelerators, and the like may be selected as appropriate within a range not detrimental to the aim of the present disclosure. The other materials may be added not only by inclusion in the uncrosslinked rubber powder in advance but also after the treatment to prevent adhesion of the uncrosslinked rubber powder. 
     Furthermore, as an example of other materials, calcium oxide may be added. By the addition of calcium oxide into the uncrosslinked rubber powder, even when the rubber is heated to a temperature higher than the melting point during the crosslinking of the rubber, bubbles that might be generated in the rubber by heat can be suppressed, and cracks or tears can be prevented from occurring at the areas with bubbles. 
     The treatment on the uncrosslinked rubber powder to prevent mutual adhesion of the powder refers to the treatment for preventing the powder particles from adhering to each other and is suitably performed by coating the surface of the uncrosslinked rubber powder with an adhesion prevention agent. As the adhesion prevention agent, any of synthetic resin, talc, silica, calcium carbonate, calcium stearate, zinc stearate, carbon black, and the like, for example, or any combination thereof, can be used. 
     While the means for coating the surface of the uncrosslinked rubber powder with the adhesion prevention agent is not particularly limited, a powdered adhesion prevention agent having a diameter smaller than that of the uncrosslinked rubber powder can be stirred and mixed with the uncrosslinked rubber powder to coat the surface of the uncrosslinked rubber powder, for example. The surface of the uncrosslinked rubber powder may also be coated by applying a dissolved solution or an aqueous dispersion of the adhesion prevention agent to the surface of the uncrosslinked rubber powder. When a dissolved solution or aqueous dispersion of the adhesion prevention agent is used, a coating layer of uniform thickness can easily be formed on the surface of the uncrosslinked rubber powder, but a step of drying the uncrosslinked rubber powder is required after the application. A powdered adhesion prevention agent is preferably used to prevent an increase in the number of production steps. 
     The adhesion prevention treatment step may be a step included in the preparation of the uncrosslinked rubber powder that becomes the material of the rubber product  10  or may be a separate step performed after the preparation of the uncrosslinked rubber powder. 
     According to the adhesion prevention treatment step, mutual adhesion of the uncrosslinked rubber powder can be prevented. That is, lumps are not formed due to mutual adhesion of the uncrosslinked rubber powder. This facilitates handling of the uncrosslinked rubber powder. In particular, when the uncrosslinked rubber powder is stored or applied to the additive manufacturing apparatus  100  described below, the manufacturing accuracy of the rubber product can be improved, and the uncrosslinked rubber powder can be easily stored and supplied. 
     The average diameter of the uncrosslinked rubber powder (raw rubber powder) to which the adhesion prevention treatment is applied is preferably from 1 μm to 500 μm. By the average diameter being 1 μm or more, floating during storage and other times can be suppressed, and the mutual adhesion of the raw rubber powder can more effectively be suppressed. By the average diameter being 500 μm or less, the manufacturing accuracy of the rubber product can be further improved. 
     In the below steps from the thin piece data acquisition step onwards, the raw rubber powder is used to manufacture the rubber product  10 . The manufacturing apparatus is not particularly limited as long as the method of manufacturing a rubber product according to the present disclosure can be implemented, but an additive manufacturing apparatus  100  with the following form can, for example, be used. 
       FIG. 4  is a perspective view schematically illustrating the configuration of the additive manufacturing apparatus  100 . The stacking direction is hereinafter designated the Z-axis direction, and two orthogonal directions in any plane orthogonal to the Z-axis direction are designated the X-axis and the Y-axis. 
     As illustrated in  FIG. 4 , the additive manufacturing apparatus  100  includes a manufacturing table  110 , a powder supply nozzle  120 , and electron beam irradiation means  130 . 
     The manufacturing table  110  includes a manufacturing table body  111  for manufacturing a rubber product. A surface  111   a  is arranged on the top surface of the manufacturing table body  111 . The manufacturing table  110  has a rectangular plate-like shape in the illustrated example but may have a circular cylinder shape, polygonal cylinder shape, or the like. 
     The manufacturing table  110  may be supported by a support  112 . The support  112  can variably support the position. The support  112  can adjust the position of the manufacturing table  110  in some or all of the XYZ-axis directions. For example, a piston member using hydraulic or pneumatic pressure, or a ball screw, can be provided as means of adjusting the position of the manufacturing table  110  in the Z-axis direction. For example, a guide member that guides in the XY-axis direction or a rotating member that rotates the manufacturing table  110  about a point in plan view can be provided as means for adjusting the position of the manufacturing table  110  in the XY-axis direction. 
     The manufacturing table  110  can also be supported immovably. 
     In the additive manufacturing apparatus  100 , the powder supply nozzle  120  is arranged at a distance in the Z-axis direction with respect to the surface  111   a . Although any powder supply nozzle  120  can be used, the powder supply nozzle  120  in the illustrated example includes a powder housing  121  and a powder discharger  122 . 
     In the powder supply nozzle  120 , the powder housing  121  can house the raw rubber powder inside. In the illustrated example, the powder housing  121  is a space divided into a cylindrical shape, but the shape is not particularly limited. The powder housing  121  may be configured to allow direct filling of the raw rubber powder into the powder housing  121 , or to receive, via a tube or the like, raw rubber powder that was filled into another housing (not illustrated). 
     The powder discharger  122  includes a powder discharge passage  122   a  that is connected to the powder housing  121  and a powder discharge port  122   b  that opens to the outside from the powder discharge passage  122   a . The powder discharger  122  can supply the raw rubber powder in the powder housing  121  through the powder discharge passage  122   a  to the outside from the powder discharge port  122   b.    
     The powder supply nozzle  120  may be configured to supply the raw rubber powder to the outside by spraying. For example, inert gas ejection means can be provided at or around the powder discharge port  122   b , and an inert gas such as argon gas, nitrogen gas, or helium gas can be discharged from the powder discharge port  122   b  together with the raw rubber powder, so that the raw rubber powder is supplied by being sprayed onto the surface  111   a  of the manufacturing table  110 . 
     The powder supply nozzle  120  may include a support mechanism  123  (not illustrated). The support mechanism  123  supports the powder supply nozzle  120  and can adjust the position thereof in the XYZ-axis direction. 
     Furthermore, the powder supply nozzle  120  can adjust the supply amount, supply rate, supply diameter, and the like of the raw rubber powder. 
     Two powder supply nozzles  120  are depicted in  FIG. 4 , but one, or three or more, may be provided. 
     In the additive manufacturing apparatus  100 , the electron beam irradiation means  130  is arranged at a distance in the Z-axis direction with respect to the surface  111   a . Although any electron beam irradiation means  130  can be used, at least one electron beam source  131  and an electron beam adjusting means  132  are preferably used. 
     The electron beam source  131  can be a thermal electron emission type electron gun. More specifically, for example, thermal electrons are generated by heating a cathode formed by tungsten, LaB 6 , CeB 6 , or the like, and an electron beam is generated by accelerating the thermal electrons. 
     The electron beam adjusting means  132  can, for example, include a magnetic field generator  132   a  and a focus controller  132   b . Using the magnetic force of a permanent magnet, an electromagnet, or the like, the magnetic field generator  132   a  can adjust the convergence, deflection, and the like of the electron beam generated by the electron beam source  131 . The focus controller  132   b  can also adjust the focus of the electron beam at the irradiation target using an optical lens, an electromagnetic lens, or the like. Although one electron beam source  131  is depicted in the illustrated example, a plurality of electron beam sources  131  may be included, each of which may be controlled under different irradiation conditions. 
     The electron beam irradiation means  130  may include a support mechanism  133  (not illustrated). The support mechanism  133  may immovably support the electron beam irradiation means  130 , or may support the electron beam irradiation means  130  while being capable of adjusting the position of the powder supply nozzle  120  in the XYZ-axis directions. 
     By being housed in a chamber (not illustrated) or the like, the additive manufacturing apparatus  100  can be used in a near-vacuum environment during operation of the electron beam irradiation means  130 . 
     Furthermore, the additive manufacturing apparatus  100  can be connected over a network to a control device  200 . The control device  200  includes a hardware processor, such as a central processing unit, and includes a thin piece data acquisition interface  201  and a manufacturing controller  202 . 
     The thin piece data acquisition interface  201  can acquire the data on the thin pieces necessary for manufacturing the rubber product  10 . 
     The manufacturing controller  202  can control the additive manufacturing by providing instructions and information, via a network, to each component of the additive manufacturing apparatus  100  based on the data on the thin pieces. That is, the manufacturing controller  202  can control the operations of the manufacturing table  110 , the powder supply nozzle  120 , the electron beam irradiation means  130 , and the like, which configure the additive manufacturing apparatus  100 . 
     Each of the steps from the thin piece data acquisition process S 2  onwards in the method of manufacturing a rubber product according to the present embodiment will be described below in detail with an example using the additive manufacturing apparatus  100 . 
     [Thin Piece Data Acquisition] 
     In the thin piece data acquisition step S 2 , the thin piece data on the rubber product  10 , which is necessary for manufacturing the rubber product  10 , is acquired by the thin piece data acquisition interface  201  of the control device  200 . 
     The thin piece data can, for example, be acquired by converting three-dimensional manufacturing data on the rubber product  10 . More specifically, the thin piece data acquisition interface  201  acquires the three-dimensional manufacturing data from an apparatus such as another computer that is connected to the control device  200  or that can transmit information to the control device  200 . Here, the three-dimensional manufacturing data for manufacturing the rubber product  10  is, for example, three-dimensional manufacturing data designed by three-dimensional CAD, or three-dimensional manufacturing data captured by a three-dimensional scanner, digitizer, or the like. The three-dimensional manufacturing data may be converted into Standard Triangulated Language (STL) format, in which the surface of the three-dimensional rubber product  10  is represented as a collection of triangles. This three-dimensional manufacturing data on the rubber product  10  is acquired by the thin piece data acquisition interface  201  and converted into data on thin pieces L 1  to LN (N is a natural number). The thin piece data refers to the data on the thin pieces L 1  to LN and may include data on a manufacturing path based on the data on the thin pieces L 1  to LN. 
     Three-dimensional manufacturing data may also be converted to thin piece data by an apparatus such as another computer that is connected to the control device  200  or is capable of transmitting information to the control device  200 , and the thin piece data may then be acquired by the thin piece data acquisition interface  201 . 
     [Raw Rubber Powder Supply and Electron Beam Irradiation] 
     Step S 3  and onwards, after the thin film data acquisition, will be described with reference to  FIGS. 5A to 5F . In  FIG. 5A  and subsequent figures, the control device  200  is omitted. 
     After the thin piece data acquisition, forming is carried out by supplying raw rubber powder, on which the adhesion prevention treatment has been performed, and irradiating the supplied portion with an electron beam to crosslink the irradiated portion, and the forming is sequentially repeated so that the crosslinked portions are stacked following the shape of the rubber product. 
       FIG. 5A  is a diagram illustrating the forming of the starting portion LM 1 , which is the first portion to be formed in the layer M 1  corresponding to the thin piece L 1 . The position of the starting portion LM 1  can be determined according to the manufacturing path based on the data on the thin piece L 1 . 
     As illustrated in  FIG. 5A , raw rubber powder, on which the adhesion prevention treatment has been performed, is supplied to the surface  111   a  of the manufacturing table  110 . The means for supplying the raw rubber powder on which the adhesion prevention treatment has been performed is not particularly limited. For example, the powder supply nozzle  120  can be used. The powder housing  121  is filled with the raw rubber powder, and the powder supply nozzle  120  can supply the raw rubber powder through the powder discharge passage  122   a  of the powder discharger  122  to the outside from the powder discharge port  122   b.    
     The powder supply nozzle  120  can also use an inert gas to adjust the supply rate and the like of the raw rubber powder from the powder discharge port  122   b . For example, an inert gas such as argon gas, nitrogen gas, or helium gas can be discharged from the powder discharge port  122   b  together with the raw rubber powder, so that the raw rubber powder is supplied by being sprayed onto the surface  111   a  of the manufacturing table  110 . 
     The position at which the raw rubber powder is supplied by the powder supply nozzle  120  is the position at which the starting portion LM 1  should be formed and can be adjusted by the support mechanism  123  of the powder supply nozzle  120 . 
     Furthermore, according to the shape and thickness of the starting portion LM 1 , the supply amount, supply rate, and supply diameter of the raw rubber powder can be adjusted by the powder supply nozzle  120 . 
     The thickness t 1  of the starting portion LM 1 , which is a thickness corresponding to the thin piece L 1 , can be adjusted according to the irradiation conditions of the electron beam described below, the average particle size of the raw rubber powder, and the like, but is preferably 500 μm or less for uniform crosslinking over the thickness direction. 
     In the illustrated example, two powder supply nozzles  120  are used to supply the raw rubber powder, but one, or three or more, powder supply nozzles  120  may be used. In the case in which a plurality of powder supply nozzles  120  is used, each powder supply nozzle  120  may be filled with a different type of raw rubber powder, and some of the powder supply nozzles  120  may be filled with a material other than raw rubber powder. If each powder supply nozzle  120  is filled with a different type of raw rubber powder, the type of the raw rubber powder can be changed during the manufacturing process according to the manufacturing conditions of the rubber product  10 , so that rubber products using a plurality of different raw rubber powders can easily be manufactured. Also, by simultaneously supplying a plurality of raw rubber powders or a raw rubber powder and other materials from a plurality of powder supply nozzles  120 , the materials can be mixed on the surface  111   a  of the manufacturing table  110  without needing to be mixed in the powder supply nozzles. 
     Formation is carried out by the above-described supply of the raw rubber powder, along with irradiation of the supplied portion of the raw rubber powder with an electron beam to crosslink the irradiated portion. The electron beam irradiation means is not particularly limited, but the electron beam irradiation means  130 , for example, can be used. The electron beam generated by the electron beam source  131  of the electron beam irradiation means  130  is converged and deflected by the magnetic field generator  132   a  to irradiate the position where the starting portion LM 1  is to be formed. The irradiation position of the electron beam may be adjusted by adjusting the position of the manufacturing table  110  with the support  112  so that the position where the starting portion LM 1  is to be formed is irradiated by the electron beam. Alternatively, the irradiation position may be adjusted by the magnetic field generator  132   a , or by adjusting the position of the electron beam irradiation means  130  with the support mechanism  133 . The focus controller  132   b  enables adjustment of the position where the electron beam achieves just focus, i.e., the focus. 
     When the position on the surface  111   a  of the manufacturing table  110  where the raw rubber powder is supplied, which is also position where the starting portion LM 1  is to be formed, is irradiated with the electron beam, the rubber molecules of the raw rubber powder are provided with energy by high-speed electrons. The high-speed electrons cleave the molecular bonds, which generates radicals, and the radicals react between molecular chains to form a three-dimensional structure, yielding a crosslinking reaction. 
     According to the electron beam crosslinking means, the location to be crosslinked can be changed by controlling the position where the electron beam is irradiated, thus eliminating the need to prepare a mold and other such hassle, and enabling a flexible response to changes in product shape. Furthermore, a high manufacturing accuracy can be achieved. Rubber products with complex shapes that are difficult to remove from a mold, or that cannot be manufactured with a mold, can also be manufactured. 
     The irradiation conditions of the electron beam can be controlled by the control device  200  based on the thin piece data on the rubber product  10  that is to be manufactured. The specific irradiation conditions of the electron beam can be adjusted appropriately according to factors such as the shape and thickness of the starting portion LM 1  and the average diameter of the raw rubber powder. For example, the following irradiation conditions can be used. 
     For example, the focusing of the electron beam is preferably set to achieve just focus on the surface of the supplied portion (the surface of the starting portion LM 1 ) to generate a sufficient crosslinking reaction in the rubber. 
     Although the temperature at the time of electron beam irradiation is not particularly limited, the supply of the raw rubber powder and the irradiation with the electron beam are preferably performed in a temperature environment lower than the melting point of the rubber. According to the above configuration, the crosslinking reaction can be produced at a lower temperature than with means for vulcanizing rubber by heating. Bubbles that might be generated in the rubber by heating can therefore be suppressed, and cracks or tears can be prevented from occurring at the areas with bubbles. 
     Furthermore, the electron beam irradiation is preferably performed in a high vacuum environment to prevent deactivation of the radicals by oxygen. For example, when the additive manufacturing apparatus  100  is housed in a chamber or the like, a high vacuum is created in the chamber. 
     As described above, the crosslinked portion can be formed as the starting portion LM 1  by supplying the raw rubber powder and irradiating the supplied portion with an electron beam. 
       FIG. 5B  is a perspective view schematically illustrating a state in which the layer M 1  corresponding to the thin piece L 1  has been manufactured.  FIG. 5C  is a cross-sectional view schematically illustrating a state in which the layer M 1  corresponding to the thin piece L 1  has been manufactured and schematically illustrates a cross-section along line II-II of  FIG. 5B . By sequentially repeating the supply of the raw rubber powder and the irradiation of the supplied portion with the electron beam while adjusting the supply position of the raw rubber powder and the irradiation position of the electron beam according to the data on the manufacturing path based on the thin piece data, a ring-shaped layer M 1  corresponding to the thin piece L 1  can be manufactured as in the illustrated example. 
       FIG. 5D  is a diagram illustrating the treatment after the layer M 1  corresponding to the thin piece L 1  has been manufactured. After the layer M 1  is manufactured, the supply position of the raw rubber powder and the irradiation position of the electron beam in the Z-axis direction are adjusted to manufacture the layer M 2  corresponding to the next thin piece L 2  to be stacked on the thin piece L 1 . In the illustrated example, the supply position of the raw rubber powder and the irradiation position of the electron beam are adjusted by lowering the manufacturing table  110  by the thickness of the layer M 1 . Adjustment is not limited to the adjusting means in the illustrated example, and the supply position of the raw rubber powder and the irradiation position of the electron beam may be adjusted by raising the positions of the powder supply nozzle  120  and the electron beam irradiation means  130  in the Z-axis direction by the thickness of the layer M 1 . 
       FIG. 5E  is a diagram illustrating the manufacturing of the next layer M 2  corresponding to the next thin piece L 2 . As illustrated in  FIG. 5E , raw rubber powder is supplied by the powder supply nozzle  120  onto the surface of the layer M 1 . 
     The supply position, supply amount, supply rate, and supply diameter of the raw rubber powder by the powder supply nozzle  120  can be adjusted appropriately in the same manner as the formation of the starting portion LM 1  in the layer M 1 . 
     Formation is carried out by the above-described supply of the raw rubber powder, along with irradiation of the supplied portion of the raw rubber powder with an electron beam on the surface of the layer M 1  to crosslink the irradiated portion. 
     The irradiation conditions of the electron beam may be the same as the irradiation conditions at the time of formation of the starting portion LM 1  in the layer M 1 , or may be different. 
     For example, in the first layer M 1 , the focusing of the electron beam may be controlled so that the electron beam achieves just focus on the surface of the supplied portion, and in the second layer M 2 , a plurality of electron beam supply sources may be used and the electron beams controlled to achieve just focus on the surface of the supplied portion and on the boundary with the adjacent layer M 1  immediately below the layer M 2 . According to the above configuration, the supplied portion in the layer M 2  can be sufficiently crosslinked, and the crosslinked portions of the adjacent layers M 1  and M 2  can be bonded together. 
     The focusing of the electron beam can be controlled so that the focusing is always the same, or the focusing can be changed. 
     Although the temperature at the time of electron beam irradiation is not particularly limited during manufacturing of the layer M 2  either, the crosslinking is preferably performed in a temperature environment lower than the melting point of the rubber, as during the manufacturing of the layer M 1 . According to the above configuration, the manufacturing accuracy can be further enhanced, and deterioration of the rubber product due to heating can be prevented. 
     In  FIG. 5F , the formatting of the crosslinked portion is repeated, and the layers M 1  to M 8  are stacked. After manufacturing of the layer M 2  as described above, in order to manufacture the layer M 3  corresponding to the next thin piece L 3  to be stacked on the thin piece L 2 , formation is repeated by adjusting the supply position of the raw rubber powder and the irradiation position of the electron beam in the Z-axis direction, supplying the raw rubber powder onto the surface of the layer manufactured immediately before, and irradiating the supplied portion with the electron beam to crosslink the irradiated portion, so that the crosslinked portions are stacked following the shape of the rubber product  10  to manufacture the rubber product  10 . 
     The method of manufacturing a rubber product including each of the above steps can flexibly respond to changes in the shape of the product and achieve high manufacturing accuracy. Furthermore, since the raw material rubber powder is supplied following the shape of the rubber product  10 , there is no need to process the uncrosslinked raw material rubber powder, and even if uncrosslinked raw material rubber powder remains, only a small amount remains. The work time can thus be shortened. 
     Another example of the rubber product is a rubber product  11  having a shape such that a cylindrical hollow  11   a  is formed inside a cylinder, as illustrated in  FIG. 6 . According to the method for manufacturing a rubber product including the above steps S 1  to S 3 , the rubber product  11  having a hollow  11   a  can be manufactured. Furthermore, according to the above method of manufacturing, since the raw rubber powder is supplied following the shape of the rubber product  11 , nearly no uncrosslinked raw rubber powder remains in the hollow  11   a . A hollow rubber product can therefore easily be manufactured without processing uncrosslinked raw rubber powder. 
     Another example of the rubber product is a rubber product  12  having a shape such that the entire outer circumference is curved, and a hollow is formed inside, as illustrated in  FIG. 7 . According to the method for manufacturing a rubber product including the above steps S 1  to S 3 , the rubber product  12  having a hollow can be manufactured. Furthermore, according to the above method of manufacturing, since the raw rubber powder is supplied following the shape of the rubber product  12 , nearly no uncrosslinked raw rubber powder remains in the hollow. A hollow rubber product can therefore easily be manufactured. 
     INDUSTRIAL APPLICABILITY 
     The method of manufacturing a rubber product of the present disclosure can be suitably applied to the manufacturing of rubber products such as anti-vibration rubber, seismic isolation rubber, tires, and tire treads. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 ,  11 ,  12  Rubber product 
               100  Additive manufacturing apparatus 
               110  Manufacturing table 
               111  Manufacturing table body 
               111   a  Surface 
               112  Support 
               120  Powder supply nozzle 
               121  Powder housing 
               122  Powder discharger 
               122   a  Powder discharge passage 
               122   b  Powder discharge port 
               130  Electron beam irradiation means 
               131  Electron beam source 
               132   a  Magnetic field generator 
               132   b  Focus controller 
               200  Control device 
               201  Thin piece data acquisition interface 
               202  Manufacturing controller 
             L 1 , L 2 , L 3  Thin piece 
             LM 1  Starting portion 
             M 1  to M 8  Layer