Rubber product and manufacturing method thereof

Abstract

The present invention provides a rubber product and a method for manufacturing the same, wherein the number of layers of reinforcing layers in a cylindrical portion is reduced while sufficient pressure resistance to internal pressure is ensured, thereby suppressing a decrease in productivity and moldability. A rubber product having a cylindrical section (3a) is manufactured by molding a cylindrical molded body (1A) in which a plurality of reinforcing layers (5) are coaxially laminated between an inner layer (4) and an outer layer (10), and vulcanizing the molded body (1A). Each of the reinforcing layers (5) is configured from a curtain fabric (6) in which a plurality of fiber cords (7) are aligned and subjected to a predetermined bonding treatment, and a coating rubber layer (9) that covers both surfaces of the curtain fabric (6), and is formed in a twill road structure in which the fiber cords (7) of the reinforcing layers (5) extend in a direction in which the fiber cords (7) intersect each other. A curtain fabric having a specification in which the tensile strength in the direction in which the fiber cords extend is 4320 N / cm or more and the weight is 950 g / m2 or less is used, the bending hardness after a predetermined bonding treatment is 30 g / cm or less, and the layer thickness of each of the coated rubber layers (9) is 0.2-1 mm (inclusive).

Description

Technical Field

[0001] The present invention relates to a rubber product and a method for manufacturing the same, and more particularly to a rubber product having a cylindrical portion in which a plurality of reinforcing layers are coaxially stacked and buried between an inner layer and an outer layer and a method for manufacturing the same. Background Art

[0002] In rubber products such as inflatable fenders or ship hoses, a reinforcement layer is buried in the cylindrical part. The reinforcement layer is buried to resist the internal pressure acting on the rubber product. For example, a reinforcement layer composed of a cord fabric having a plurality of aligned fiber cords and a coating rubber layer covering both surfaces thereof is used (see Patent Document 1). Generally speaking, a plurality of reinforcement layers are buried between the inner layer and the outer layer of the cylindrical part, and in adjacently stacked reinforcement layers, the fiber cords of both sides extend in a cross direction (forming a so-called diagonal grain structure). The coating rubber layer sandwiched between adjacently stacked cord fabrics is set to a corresponding layer thickness to ensure sufficient bonding strength.

[0003] If the number of layers of the reinforcing layer buried in the cylinder is increased in order to resist a greater internal pressure, the time required for the stacking operation of the reinforcing layer will be extended, which is not conducive to improving the productivity of the rubber product. If the number of layers of the reinforcing layer is increased, the weight will also increase, which will also lead to a decrease in the molding processability. In addition, if the thickness of the coating rubber layer is too large, the molding processability will be reduced. On the other hand, if the thickness of the coating rubber layer is too small, the bonding strength between the reinforcing layers or the bonding strength between the reinforcing layers and the adjacent components will be insufficient, which is not conducive to ensuring sufficient pressure resistance. Therefore, while ensuring sufficient pressure resistance for the internal pressure, the number of layers of the reinforcing layer buried in the cylinder is reduced to improve productivity, and there is room for improvement in suppressing the decrease in molding processability.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-157016 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The main object of the present invention is to provide a rubber product and a method for producing the rubber product which can reduce the number of stacked reinforcing layers buried in a cylindrical portion while ensuring sufficient pressure resistance to internal pressure, thereby improving productivity and suppressing a decrease in molding processability.

[0009] Technical means of solving problems

[0010] In order to achieve the above-mentioned object, the rubber product of the present invention is characterized in that it has a cylindrical portion in which a plurality of reinforcing layers are coaxially laminated and embedded between an inner layer and an outer layer, each of the reinforcing layers is composed of a cord fabric in which a plurality of fiber cords are aligned and subjected to a prescribed bonding treatment, and a coating rubber layer covering both surfaces of the cord fabric, and has a diagonal grain structure in which the fiber cords of the reinforcing layers extend in a direction intersecting each other, wherein as each of the cord fabrics, a rubber material having a tensile strength of 4320 N / cm or more in the extending direction of the fiber cords and a weight of 950 g / m 2 The curtain fabric has the following specifications, and the bending hardness of each of the curtain fabrics after the specified bonding treatment is 30 g / cm or less, and the thickness of each of the coating rubber layers is 0.2 mm or more and 1 mm or less in a neutral state where the cylindrical portion is not expanded.

[0011] The manufacturing method of the rubber product of the present invention is characterized in that a cylindrical molded body is formed in which a plurality of reinforcing layers are coaxially stacked between an inner layer and an outer layer, each of the reinforcing layers is composed of a cord fabric in which a plurality of fiber cords are aligned and subjected to a prescribed bonding treatment and a coating rubber layer covering both surfaces of the cord fabric, and a diagonal grain structure is formed in which the fiber cords of the reinforcing layers extend in intersecting directions, and the molded body is vulcanized, thereby manufacturing a rubber product having a cylindrical portion in which a plurality of reinforcing layers are coaxially stacked and buried between the inner layer and the outer layer, wherein as each of the cord fabrics, a rubber product having a tensile strength of 4320 N / cm or more in the extending direction of the fiber cords and a weight of 950 g / m 2 The invention provides curtain fabrics of the following specifications, wherein the bending hardness of each of the curtain fabrics after the predetermined bonding treatment is 30 g / cm or less, and the thickness of each of the coating rubber layers is 0.2 mm or more and 1 mm or less.

[0012] Effects of the Invention

[0013] According to the present invention, by using a cord fabric with a tensile strength of 4320 N / cm or more in the extending direction of the fiber cord as each of the cord fabrics, it is easy to ensure sufficient pressure resistance to the internal pressure acting on the rubber product even if the number of layers of the reinforcing layer buried in the cylindrical portion is reduced. This is conducive to improving the productivity of rubber products. In addition, by making the weight of each of the cord fabrics 950 g / m 2 Hereinafter, the bending hardness of each of the curtain fabrics after the predetermined bonding treatment is set to 30 g / cm or less, which is beneficial to suppressing the reduction of molding processability when manufacturing the rubber product. Furthermore, by setting the layer thickness of each of the coating rubber layers to be between 0.2 mm and 1 mm, it is easy to ensure sufficient bonding strength while suppressing the increase in weight, which is more beneficial to suppressing the reduction in molding processability while ensuring pressure resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an explanatory diagram showing an inflatable fender as an embodiment of a rubber product by partially cutting away a cylindrical portion in a neutral state where the cylindrical portion is not expanded, and viewed from a side.

[0015] Figure 2 This is an example from a frontal perspective. Figure 1 An explanatory diagram of the internal structure of the hemispherical portion.

[0016] Figure 3 Yes Figure 1 An explanatory diagram showing a partially enlarged view of the cylindrical portion of the embodiment of the present invention and illustrated from a cross-sectional perspective.

[0017] Figure 4 This is an explanatory diagram showing an example of a reinforcing layer from a cross-sectional perspective perpendicular to and crossing the fiber cords.

[0018] Figure 5 This is an explanatory diagram showing an example of a curtain fabric in a top view.

[0019] Figure 6 (A) shows an example of a manufacturing process of a fiber cord, Figure 6 (B) is an explanatory diagram schematically illustrating an example of a fiber cord in a cross-sectional view.

[0020] Figure 7 It is an explanatory diagram showing an example of the vulcanization process of a molded body.

[0021] Figure 8 The cylindrical part is partially cut and shown from a side view. Figure 1 An illustration of an inflatable fender in which the internal pressure of the main body is increased to a predetermined internal pressure and the fender is expanded into a predetermined shape.

[0022] Fig. 9 This is an explanatory diagram showing a partially enlarged example of an improved example of a cylindrical portion in a cross-sectional perspective.

[0023] Fig.10 This is an explanatory diagram showing a ship hose as an embodiment of a rubber product by partially cutting away a cylindrical portion and viewing it from a side.

[0024] Fig.11 This is shown as an example from a cross-sectional perspective. Fig.10 An illustration of a portion of the cylindrical portion. DETAILED DESCRIPTION

[0025] Hereinafter, taking a case where the rubber product is an inflatable fender as an example, the rubber product and the method for manufacturing the same according to the present invention will be described based on the embodiments shown in the drawings.

[0026] Figures 1 to 3 The inflatable fender 1 (hereinafter referred to as the fender 1) as an embodiment of a rubber product shown as an example in FIG. 1 includes: a main body 2 having hemispherical portions 3b connected to both ends of a cylindrical portion 3a; and a joint portion 11 provided on the main body 2. In this embodiment, the joint portion 11 is provided only on one hemispherical portion 3b, but it may be provided on the hemispherical portions 3b on both sides. The single-dot chain line CL in the figure indicates the cylinder axis of the cylindrical portion 3a, and the extension direction of the single-dot chain line CL is the cylinder axis direction.

[0027] In the cylindrical portion 3a, a plurality of cylindrical reinforcement layers 5 are coaxially stacked and buried between the cylindrical inner layer 4 and the cylindrical outer layer 10. In this embodiment, six layers of reinforcement layers 5 are stacked. That is, in the cylindrical portion 3a, the inner layer 4, the respective reinforcement layers 5, and the outer layer 10 are coaxially stacked. The number of stacked reinforcement layers 5 is determined by the pressure resistance required for the fender 1 to the internal pressure, and is, for example, about 4 or more and 12 or less.

[0028] like Figure 4 , Figure 5 As shown in the example, each reinforcement layer 5 is composed of a cord fabric 6 formed by aligning a plurality of fiber cords 7 and a coating rubber layer 9 covering both surfaces of the cord fabric 6. The fiber cords 7 are filled with rubber of the coating rubber layer 9. As described later, the extending directions of the fiber cords 7 of the cylindrical portion 3a and each hemispherical portion 3b are different, the cylindrical portion 3a has a diagonal structure, and each hemispherical portion 3b has a radial structure.

[0029] The curtain fabric 6 is bonded to the coating rubber layer 9 after a predetermined bonding treatment is performed. The predetermined bonding treatment is a well-known bonding treatment for improving the bonding property between the fiber cord 7 and the rubber. Specifically, after the fiber cord 7 is subjected to an epoxy treatment liquid and dried, a resorcinol-formaldehyde-latex (RFL) mixed liquid is applied and dried. The conditions of the bonding treatment (the amount of each liquid attached and the drying temperature, etc.) are set to an appropriate range, and the appropriate range is a range in which a target bonding force (a bonding force that does not cause problems in actual use) can be obtained by performing a prior test, etc.

[0030] like Figure 5 As shown in the example, in the curtain fabric 6, a plurality of fiber cords 7 extend in parallel, and cross cords 8 that cross these fiber cords 7 are arranged at intervals in the extending direction of the fiber cords 7. The density (embedding density) of the fiber cords 7 is, for example, about 30 cords / 5 cm or more and 70 cords / 5 cm or less.

[0031] Each transverse cord 8, for example, passes through the top and bottom of a plurality of fiber cords 7 and extends in a direction perpendicular to the extending direction of the fiber cords 7. The density (embedding density) of the adjacently arranged transverse cords 8 is very small compared to the density of the fiber cords 7, for example, about 2 cords / 5 cm or more and 8 cords / 5 cm or less.

[0032] As each curtain fabric 6, a curtain fabric having a tensile strength F of 4320 N / cm or more in the extending direction of the fiber cord 7 and a weight W of 950 g / m 2 The following specifications of the curtain fabric. The tensile strength F is measured based on the tensile strength test (A method) specified in JIS L1096, and is the value obtained by dividing the breaking load of the test piece (300 mm long and 50 mm wide) of the curtain fabric 6 by the width of the test piece. In this test, the tensile speed is 200 mm / min and the clamping interval is 200 mm. Since the tensile strength F of conventional curtain fabrics is less than 3000 N / cm, the tensile strength F is greatly improved in this embodiment. The upper limit of the tensile strength F of the curtain fabric 6 is, for example, 5500 N / cm, and the lower limit of the weight W is, for example, 700 g / m 2 .

[0033] In addition, the bending hardness H of each curtain fabric 6 after the above-mentioned prescribed bonding treatment is 30 g / cm or less, more preferably 25 g / cm or less, and further preferably 20 g / cm or less. The lower limit of the bending hardness H is, for example, 9 g / cm. In the present invention, the bending hardness H is the rigidity measured by the Gurley bending test method specified in JIS L1096. Specifically, the extending direction of the fiber cord 7 is used as the length direction, and the test piece obtained by cutting the curtain fabric 6 after the prescribed bonding treatment according to the prescribed width is measured, and the measured value X (mg / root) is multiplied by the embedding density of the fiber cord 7 (root / 5cm), and the unit is set to (g / cm), thereby calculating the bending hardness H. The calculation formula of the bending hardness H is as follows.

[0034] Bending hardness H (g / cm) = measured value X (mg / root) × embedding density (root / 5cm) / 5 / 1000 Figure 1As shown in the example, in the cylindrical portion 3a, the extending direction of each fiber cord 7 is inclined relative to the cylinder axis CL and is set to a predetermined cord angle A. Furthermore, the cylindrical portion 3a is formed into a diagonal grain structure in which the fiber cords 7 of the reinforcing layers 5 extend in intersecting directions. In this embodiment, the fiber cords 7 of the adjacently stacked reinforcing layers 5 extend in intersecting directions. Specifically, in the adjacent reinforcing layers 5, the cord angles A of the fiber cords 7 are substantially the same, and the inclination directions are set to opposite directions. Furthermore, in the stacked reinforcing layers 5, the angles A of the fiber cords 7 are substantially the same, and the inclination directions are also set to the same direction. Therefore, the inclination directions of the fiber cords 7 of the reinforcing layers 5 of the first, third, and fifth layers from the inner circumference are the same, and the inclination directions of the fiber cords 7 of the reinforcing layers 5 of the second, fourth, and sixth layers from the inner circumference are the same.

[0035] In the neutral state where the cylindrical portion 3a is not expanded, the cord angle A of the fiber cords 7 of each reinforcing layer 5 is set to be 25° or more and 45° or less. More preferably, the cord angle A is set to be 30° or more and 35° or less.

[0036] Each hemispherical portion 3b is formed into a radial structure in which a plurality of fiber cords 7 extend radially around the cylinder axis CL of the cylinder portion 3a and a plurality of fiber cords 7 extend concentrically around the cylinder axis CL of the cylinder portion 3a.

[0037] Known fiber cords such as polyester and nylon can be used as the fiber cord 7. In the neutral state where the cylindrical portion 3a is not expanded, the outer diameter of the fiber cord 7 (thickness h of the cord fabric 6) is, for example, about 1 mm to 1.5 mm.

[0038] The neutral state in which the cylindrical portion 3a is not expanded refers to a state in which the fiber cord 7 of the cylindrical portion 3a is substantially free of tension, and air is injected into the interior of the main body 2, and the internal pressure thereof is slightly higher than the atmospheric pressure (e.g., 10 kPa). In addition, the neutral state refers to a state in which the cylindrical portion 3a maintains a cylindrical shape and the hemispherical portion 3b maintains a hemispherical shape. The outer diameter of the cylindrical portion 3a in the neutral state is, for example, about 2 m or more and about 10 m or less.

[0039] like Figure 6As shown in the example, the fiber cord 7 is a twisted cord formed by twisting a plurality of strands 7a. In this embodiment, the fiber cord 7 is formed by twisting a plurality of strands 7a with a fineness of 1670 dtex. Two strands 7a are initially twisted in the same direction, and then three groups of these two strands 7a after initial twisting are combined and twisted in the opposite direction, thereby forming the fiber cord 7. That is, the fiber cord 7 has a 1670 / 2 / 3 structure, and the total fineness D is 10020 (=1670×6 strands) dtex. The fiber cord 7 is not limited to this structure, as long as the cord fabric 6 meets the above-mentioned specifications of weight W, tensile strength F, and bending stiffness H.

[0040] Since the fiber cord 7 has a multi-twist structure, it can obtain better fatigue resistance than a single-twist structure. The primary twist and the secondary twist may be different twists, but in order to obtain stability, it is preferably the same twist or substantially the same twist. Considering tensile strength, flexibility, etc., the total fineness D of the fiber cord 7 is about 10000 dtex or more and about 15000 dtex or less, and the number of strands 7a to be twisted is, for example, about 4 or more and about 8 or less.

[0041] The twist coefficient K defined by the following formula (1) is preferably a double twist degree T of about 1300 to about 2500. When the twist coefficient K is less than 1300, it is difficult to ensure sufficient durability, and when it exceeds 2500, it is difficult to ensure sufficient tensile strength. As a specific double twist degree T, for example, it is about 10 to about 20.

[0042] Twist coefficient K = T × D 1 / 2 · · · (1)

[0043] T: The twist of fiber cord 7 (twist / 10cm)

[0044] D: Total fineness of fiber cord 7 (dtex)

[0045] It should be noted that, in this embodiment, the specifications of the cross cords 8 are the same as those of the fiber cords 7, but they may be different in specifications.

[0046] The coating rubber layer 9 is formed of a known rubber, for example, natural rubber, butyl rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, or a rubber mixed with several of them. Adjacently stacked reinforcement layers 5 are bonded to each other via the opposing coating rubber layers 9. The innermost reinforcement layer 5 and the inner layer 4 are bonded via the coating rubber layer 9 of the reinforcement layer 5. The outermost reinforcement layer 5 and the outer layer 10 are bonded via the coating rubber layer 9 of the reinforcement layer 5.

[0047] The layer thickness t of each coating rubber layer 9 is 0.2 mm or more and 1 mm or less in the neutral state where the cylindrical portion 3a is not expanded. If the layer thickness t is less than 0.2 mm, it is difficult to ensure sufficient bonding strength. If the layer thickness t exceeds 1 mm, the weight becomes too large and the molding processability is reduced. The layer thickness t is more preferably 0.2 mm or more and 0.6 mm or less.

[0048] As the rubber forming the inner layer 4, for example, natural rubber, butyl rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, etc. can be used. As the rubber forming the outer layer 10, for example, natural rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, etc. can be used. In the neutral state where the cylindrical portion 3a is not expanded, the layer thickness of the inner layer 4 is, for example, about 2 mm or more and about 5 mm or less, and the layer thickness of the outer layer 10 is, for example, about 3 mm or more and about 12 mm or less.

[0049] Next, an example of a process for manufacturing the fender 1 will be described.

[0050] The structure and the inner layer 4 are formed by sequentially stacking the components as the outer layer 10, the reinforcing layer 5, and the inner layer 4 on the inner side of a known forming mold. Figures 1 to 3 The molded body 1A shown as an example is the same as the fender 1. That is, a cylindrical molded body 1A is molded in which a plurality of reinforcing layers 5 are coaxially stacked between an inner layer 4 and an outer layer 10. Unlike the fender 1, the molded body 1A contains unvulcanized rubber.

[0051] Then, if Figure 7 As shown in the example, the bag-shaped molded body 1 is placed inside a vulcanizing device 14 such as a known vulcanizing box. Then, the unvulcanized rubber constituting the molded body 1A is vulcanized through a vulcanizing process for a predetermined time in the vulcanizing device 14, and the components of the molded body 1A are firmly joined to form an integral body. As a result, a Figures 1 to 3 The fender 1 is shown as an example.

[0052] When the molded body 1A is formed, as described above, each curtain fabric 6 uses a fiber cord 7 having a tensile strength F of 4320 N / cm or more in the extending direction and a weight W of 950 g / m 2 The following specifications of the curtain fabric are provided. Furthermore, the bending hardness H of the curtain fabric 6 after the above-mentioned bonding treatment is set to 30 g / cm or less. The bending hardness H can be adjusted by, for example, changing the amount of RFL mixed liquid attached to the fiber cord 7. In addition, the layer thickness t of each coating rubber layer 9 is set to be greater than 0.2 mm and less than 1 mm. The layer thickness t hardly changes before and after the vulcanization process.

[0053] In the fender 1, since the curtain fabrics 6 are each made of a specification that the tensile strength F in the extending direction of the fiber cords 7 is 4320 N / cm or more, it is easy to ensure sufficient pressure resistance to the internal pressure acting on the fender 1 even if the number of layers of the reinforcing layer 5 buried in the cylindrical portion 3a is reduced. That is, in order to obtain the same pressure resistance, the number of layers of the reinforcing layer 5 can be reduced compared to conventional fenders. For example, in the past, when the curtain fabric 6 with a tensile strength F of 2500 N / cm was used, in order to obtain the same pressure resistance, if the curtain fabric 6 with a tensile strength F of 5000 N / cm was used, the number of layers of the reinforcing layer 5 may also need to be set to about half. In the molding process of the molded body 1A, the more the number of layers of the reinforcing layer 5 is stacked, the more working hours are required. Therefore, according to this embodiment, it is very advantageous to improve productivity while ensuring sufficient pressure resistance to the internal pressure of the fender 1.

[0054] In addition, by setting the weight W of each curtain fabric 6 to 950 g / m 2 The weight W and the bending hardness H after the predetermined bonding treatment are set to be 30 g / cm or less, and the burden of moving and deforming the reinforcing layer 5 is reduced in the molding process of the molded body 1A. Increasing the thickness h of the curtain fabric 6 (the thickness of the fiber cords 7) to ensure pressure resistance will lead to a decrease in molding processability, but by setting the weight W and the bending hardness H within the above range, it is easy to stack the reinforcing layer 5 at a predetermined position and form it into a cylindrical shape, so that the decrease in molding processability can be suppressed.

[0055] Furthermore, by setting the layer thickness t of each coating rubber layer 9 to be greater than or equal to 0.2 mm and less than or equal to 1 mm, it is easy to ensure sufficient bonding strength while suppressing weight increase. If the layer thickness t is increased, it is difficult to fully press-bond the reinforcing layers 5, the reinforcing layers 5 and the inner layer 4, and the reinforcing layers 5 and the outer layer 10 in the molding process of the molded body 1A, and the unvulcanized coating rubber layer 9 is easily deformed. As a result, the molding processability is reduced, but by setting the layer thickness t within the above range, it is more advantageous to ensure pressure resistance while suppressing the reduction of molding processability.

[0056] When the fender 1 is not in use during storage, transportation, installation, etc., the internal pressure is set to a low pressure of, for example, about 10 kPa, and Figure 1 As shown in the example, the cylindrical portion 3a is brought into a neutral state where it is not expanded. Furthermore, the air inside the main body 2 is exhausted to bring it into a folded state.

[0057] When the fender 1 is installed at the installation site, Figure 8Specifically, air is filled into the body 2 through a valve provided at the joint 11 to raise the pressure to a predetermined internal pressure P when the fender 1 is used. The predetermined internal pressure P is, for example, about 50 kPa or more and 100 kPa or less.

[0058] In the process of filling the interior of the main body 2 with air to reach a predetermined internal pressure P, in the cylindrical portion 3a, the cord angle A of each reinforcing layer 5 is increased to a stable static angle (54° to 55°). Here, shear force acts on the coating rubber layer 9 sandwiched between the reinforcing layers 5 (cord fabrics 6) extending in the direction in which the fiber cords 7 cross each other, causing shear deformation.

[0059] When the cord angle A is less than 25° in the neutral state of the cylindrical portion 3a, in order to increase the cord angle A to about the static angle, excessive shear stress will be generated in the coating rubber layer 9, which is not preferable, so the cord angle A is set to be greater than 25°, and more preferably greater than 30°. When the cord angle A is greater than 45°, when the cylindrical portion 3a is pressurized from the neutral state to the specified internal pressure P, the diameter expansion degree of the cylindrical portion 3a becomes small, so it is set to be less than 45°, and more preferably less than 35°.

[0060] When the pressure is increased to a predetermined internal pressure P, the outer diameter of the cylindrical portion 3a can be about 120% or more and 150% or less relative to the neutral state. In addition, when the pressure is increased to a predetermined internal pressure P, the axial length of the main body 2 (cylindrical portion 3a) is about 95% to 80% relative to the neutral state.

[0061] When the thickness t of the coating rubber layer 9 is less than 0.2 mm, the load on the coating rubber layer 9 due to the shear force when the cylindrical portion 3a expands becomes too large. In addition, when the thickness t of the coating rubber layer 9 is greater than 1 mm, the weight of the fender 1 becomes too large. Therefore, the thickness t of each coating rubber layer 9 is preferably set to be greater than 0.2 mm and less than 1 mm.

[0062] exist Fig. 9 In the fender 1 shown as an example, two layers of reinforcement layers 5 stacked and adjacent to each other constitute one group S (S1 to S4), and there are a plurality of groups S. In this embodiment, eight layers of reinforcement layers 5 are stacked on the cylindrical portion 3a, and there are four groups S. Each group S is composed of different reinforcement layers 5. The number of groups S is, for example, about 3 to 6, and preferably a plurality of groups.

[0063] In each group S of each reinforcement layer 5, the fiber cords 7 of each reinforcement layer 5 extend in the same direction at a prescribed cord angle A. In the stacked and adjacent groups S, the fiber cords 7 of the reinforcement layers 5 on both sides extend in the intersecting direction at a prescribed cord angle A. That is, in groups S1 and S2, the fiber cords 7 of the reinforcement layers 5 on both sides extend in the intersecting direction, in groups S2 and S3, the fiber cords 7 of the reinforcement layers 5 on both sides extend in the intersecting direction, and in groups S3 and S4, the fiber cords 7 of the reinforcement layers 5 on both sides extend in the intersecting direction. Therefore, in groups S1 and S3, the fiber cords 7 of the reinforcement layers 5 on both sides extend in parallel, and in groups S2 and S4, the fiber cords 7 of the reinforcement layers 5 on both sides extend in parallel. That is, taking the group S as a unit, the fiber cords 7 of the cylindrical portion 3a have a twill structure. When manufacturing the fender 1, a structure having the same twill structure as the fender 1 is formed. Fig. 9 The molded body 1A having the same structure as that shown as an example may be used.

[0064] In the fender 1, in the process of filling the inside of the main body 2 with air to reach a predetermined internal pressure P, the cord angle A of the fiber cords 7 of each reinforcing layer 5 is increased to a stable static angle (54° to 55°) in the cylindrical portion 3a. In each group S, the fiber cords 7 of each reinforcing layer 5 extend in the same direction at the predetermined cord angle A, so that shearing force does not substantially act on the coating rubber layer 9 sandwiched between these reinforcing layers 5 (cord fabrics 6).

[0065] On the other hand, since the fiber cords 7 of the reinforcement layers 5 of the stacked and adjacent groups S in the cylindrical portion 3a extend in the intersecting direction, shear force acts on the coating rubber layer 9 sandwiched between the groups S, causing shear deformation. In this way, when the cylindrical portion 3a is pressurized from the neutral state to the specified internal pressure P, the cord angle A of the fiber cords 7 of each reinforcement layer 5 in the cylindrical portion 3a increases to a stable static angle (54° to 55°), so that the cylindrical portion 3a expands and maintains a specified shape.

[0066] That is, when the cylindrical portion 3a expands, the shear force substantially acts only on the coating rubber layers 9 sandwiched between the stacked and adjacent groups S. Therefore, compared with the case where the shear force acts on all the coating rubber layers 9, the resistance when the cylindrical portion 3a expands is reduced, which is conducive to making the cylindrical portion 3a expand smoothly.

[0067] The embodiment of the rubber product is not limited to the fender 1. Fig.10 , Fig.11As shown in the example, there is also a case of a ship hose 12. The ship hose 12 has flanges 13 at both ends in the longitudinal direction, and the cylindrical portion 3a extends between the flanges 13. In the cylindrical portion 3a, a plurality of reinforcing layers 5 are coaxially stacked and buried between the inner layer 4 and the outer layer 10. The specifications of each reinforcing layer 5 are the same as those of the previous embodiment. In the ship hose 12, the inner peripheral area of ​​the inner layer 4 is a flow path 12a. In the floating ship hose 12, a buoyancy layer is provided between the outer layer 10 and the reinforcing layer 5.

[0068] The ship hose 12 can be manufactured by forming a cylindrical molded body using the above-mentioned member by a known method, and vulcanizing the molded body by a known method. In the ship hose 12, even if the number of stacked layers of the reinforcing layer 5 buried in the cylindrical portion 3a is reduced, it is easy to ensure sufficient pressure resistance to the internal pressure, which is advantageous for improving the productivity of the ship hose 12. In addition, it is advantageous for suppressing the reduction of molding processability when manufacturing the ship hose 12.

[0069] Example

[0070] As shown in Table 1, 8 types of curtain fabrics (conventional example, embodiments 1 to 5, comparative examples 1 to 3) with different specifications were prepared, and after the above-mentioned prescribed bonding treatment was implemented, the two surfaces of the curtain fabric were covered with a coating rubber layer to manufacture a reinforcing layer. In addition, each fiber cord 7 is a multi-twist structure with a primary twist having the same number of twists as the secondary twist T. The tensile strength F in the extending direction of the fiber cord 7 of each curtain fabric was measured, and the bending hardness H of each curtain fabric after the prescribed bonding treatment was measured. In addition, for each manufactured reinforcing layer, a test piece vulcanized under the same conditions was used to evaluate fatigue resistance as described below. The respective measurement results and evaluation results are shown in Table 1.

[0071] [Table 1]

[0072]

[0073]

[0074] [Fatigue resistance]

[0075] Evaluation was performed according to the disk fatigue strength (Goodrich method) specified in 2.2.2 of Annex 1 of JIS L1017 (2002). A fatigue test was performed using a test piece made of a vulcanized reinforcement layer, that is, the test piece was rotated at a strain of ±10% and a rotation speed of 2400 rpm for 24 hours at room temperature. After the fatigue test, the fiber cord was taken out from the test piece and the tensile strength was measured, and the retention rate relative to the tensile strength before the fatigue test was calculated. The higher the value of the retention rate, the better the fatigue resistance.

[0076] Regarding the pressure resistance in Table 1, when the tensile strength F is less than 4100 N / cm, it is evaluated that it is difficult to ensure sufficient pressure resistance for each reinforcing layer, which is indicated by ×, and when it is 4100 N / cm or more, it is evaluated that sufficient pressure resistance can be ensured for each reinforcing layer, which is indicated by 0. In addition, regarding the formability in Table 1, an operation of pasting an unvulcanized reinforcing layer of a specified width on a forming roller of a specified outer diameter is performed, and the ease of pasting and the deformation of the coating rubber layer after pasting are evaluated. The case where the pasting operation can be performed very smoothly and the deformation of the coating rubber layer is also small is evaluated as excellent formability, which is indicated by ◎. The case where the pasting operation can be performed without any problem and the deformation of the coating rubber layer is also at a level that is not problematic in practical use is evaluated as generally good formability, which is indicated by 0. The case where at least one of the pasting operation and the deformation of the coating rubber layer is at a level that is problematic in practical use is evaluated as poor formability, which is indicated by ×. That is, the order of excellent formability is ◎, 0, and ×.

[0077] From the results in Table 1, it can be seen that the reinforcing layers corresponding to Examples 1 to 5 have excellent pressure resistance and good formability. In addition, it can be seen that the reinforcing layers corresponding to Examples 1 to 5 have fatigue resistance that is equal to or better than that of the conventional example and have good fatigue resistance.

[0078] Description of Reference Numerals

[0079] 1: Inflatable fender

[0080] 1A: Molded body

[0081] 2: Main body

[0082] 3a: Cylinder

[0083] 3b: Hemispherical part

[0084] 4: Inner layer

[0085] 5: Enhancement layer

[0086] 6: Curtain fabric

[0087] 7: Fiber cord

[0088] 7a: Strands

[0089] 8: Crossing the cord

[0090] 9: Rubber coating

[0091] 10: Outer layer

[0092] 11: Joint

[0093] 12: Marine hose

[0094] 12a: Flow path

[0095] 13: Flange

[0096] 14: Vulcanization device

[0097] A: Cord Angle

[0098] S (S1, S2, S3, S4): Group of enhancement layers

Claims

1. A rubber product having a cylindrical portion in which a plurality of reinforcing layers are coaxially stacked and embedded between an inner layer and an outer layer, each of the reinforcing layers being composed of a cord fabric in which a plurality of fiber cords are aligned and subjected to a predetermined bonding treatment and a coating rubber layer covering both surfaces of the cord fabric, and having a diagonal grain structure in which the fiber cords of the reinforcing layers extend in directions intersecting each other, wherein As each of the cord fabrics, a cord fabric having a tensile strength of 4320 N / cm or more in the extending direction of the fiber cord and a weight of 950 g / m 2 The curtain fabric has the following specifications, and the bending hardness of each of the curtain fabrics after the specified bonding treatment is 30 g / cm or less, and the thickness of each of the coating rubber layers is 0.2 mm or more and 1 mm or less in a neutral state where the cylindrical portion is not expanded.

2. The rubber product according to claim 1, wherein: The rubber product is an inflatable fender or a hose for ships.

3. The rubber product according to claim 1, wherein: The rubber product is an inflatable fender. When the cylindrical portion is in a neutral state where the cylindrical portion is not inflated, the cord angle of each of the fiber cords relative to the cylinder axis direction of the cylindrical portion is set to be greater than 25° and less than 45°. When a specified internal pressure acts on the cylindrical portion when the rubber product is in use, the cord angle of each of the fiber cords is greater than 54° and less than 55°, so that the cylindrical portion is inflated and deformed.

4. A method for manufacturing a rubber product, wherein a cylindrical molded body is formed in which a plurality of reinforcing layers are coaxially stacked between an inner layer and an outer layer, each of the reinforcing layers is composed of a cord fabric in which a plurality of fiber cords are aligned and subjected to a predetermined bonding treatment, and a coating rubber layer covering both surfaces of the cord fabric, and the fiber cords of the reinforcing layers are formed into a diagonal grain structure extending in a direction intersecting each other, and the molded body is vulcanized, thereby manufacturing a rubber product having a cylindrical portion in which a plurality of reinforcing layers are coaxially stacked and buried between the inner layer and the outer layer, wherein As each of the cord fabrics, a cord fabric having a tensile strength of 4320 N / cm or more in the extending direction of the fiber cord and a weight of 950 g / m 2 The invention provides curtain fabrics of the following specifications, wherein the bending hardness of each of the curtain fabrics after the predetermined bonding treatment is 30 g / cm or less, and the thickness of each of the coating rubber layers is 0.2 mm or more and 1 mm or less.

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