JP2007296712A - Manufacturing method for rubber product for water service - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a rubber product for the water service which can reduce the amount of an organic carbon (total organic carbon) which exudes into the water service water. <P>SOLUTION: On the surface of a valve body 12 for a water service gate valve, a rubber coating layer 22 consisting of a rubber composition of which the major component is an EPDM polymer is formed. The rubber composition is obtained in such a manner that a mixture comprising an organic peroxide added as a crosslinking agent to the EPDM polymer is formed into a sheet form. The rubber coating layer 22 is formed in such a manner that the sheet-form rubber composition is compression-molded on the surface of the valve body 12, and at the same time, is primarily crosslinked, and then, is secondarily crosslinked at a preset temperature for a specified period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing rubber products for water supply such as seals and packings used for pipe joints and valves for water supply.

Conventionally, what was described, for example in patent document 1 is proposed as a rubber composition used for the rubber product for waterworks. In this rubber composition, an additive such as a crosslinking agent or a reinforcing agent is added to an ethylene-propylene-diene terpolymer (hereinafter referred to as EPDM polymer) obtained by copolymerizing ethylene and propylene with a diene monomer. It is a rubber composition obtained by crosslinking by mixing the mixed mixture. In this rubber composition, the content of the diene monomer in the EPDM polymer is set in the range of 5 to 13% by weight, and the methylene group which is a diene component side chain in the rubber composition is increased more than usual. As a result, attack of chlorine in tap water can be concentrated on the methylene group of the side chain, and the main chain is prevented from being broken to improve the chlorine water resistance.
Japanese Patent Laid-Open No. 2004-210821

  By the way, the evaluation item of the quality of tap water is related to the amount of organic carbon (total organic carbon) leached from tap rubber products into tap water. This is to evaluate the amount of free carbon present in rubber products and organic substances such as plasticizers that are dissolved in tap water. However, the rubber composition of Patent Document 1 only improves the chlorine water resistance, and does not have an effect of reducing organic substances that dissolve into tap water.

  The objective of this invention is providing the manufacturing method of the rubber product for waterworks which can reduce the quantity of the organic carbon (total organic machine carbon) leached in tap water.

  In order to achieve the above object, the invention described in claim 1 is characterized in that a cross-linking agent is mixed into an ethylene-propylene-diene terpolymer produced by copolymerizing ethylene and propylene and a diene monomer. A method for producing a rubber product for water supply by heat-molding a mixture, characterized in that after molding, secondary crosslinking is performed under preset conditions.

The invention described in claim 2 is characterized in that, in the invention described in claim 1, an organic peroxide is used as the crosslinking agent.
(Function)
In the first and second aspects of the invention, secondary crosslinking is performed on the heat-molded rubber product under preset conditions. For this reason, free carbon remaining in the rubber composition after molding in the primary crosslinking performed under conditions such as temperature and time set for thermoforming the mixture mainly composed of EPDM polymer is the rubber composition. Captured inside. Further, the low molecular weight component of the carbon compound such as a plasticizer is dissipated from the rubber composition. Accordingly, the amount of organic carbon (total organic carbon) leached from the rubber product into the tap water is reduced.

  According to the invention described in claim 2, the heat resistance of the rubber product is improved. Moreover, the unreacted part of the organic peroxide used as the crosslinking agent is dissipated from the rubber composition by secondary crosslinking with respect to the rubber composition after molding.

  According to this invention, the manufacturing method of the rubber product for waterworks which can reduce the quantity of the organic carbon (total organic carbon) leached in tap water can be provided.

Next, an embodiment in which the present invention is applied to a water gate valve will be described with reference to FIGS.
A water gate valve 10 shown in FIG. 1 is interposed in the middle of a water pipe embedded in a road or the like, and is integrally formed of cast iron. The water gate valve 10 includes a valve box 11 having a pair of flanges 11a connected to a water pipe. The valve box 11 can be displaced in the vertical direction by a valve body operating mechanism (not shown). A supported valve body 12 is arranged.

  As shown in FIGS. 2 and 4, the valve box 11 is formed with a water channel 14 that communicates with the water pipe, and a valve body housing portion that opens upward at the center in the extending direction of the water channel 14. 15 is formed. In the valve body accommodating portion 15, valve body guide protrusions 16 extending in the vertical direction are formed on both walls in the width direction of the water channel 14. A first valve seat 17 having a taper shape is formed in the valve body accommodating portion 15 at a position corresponding to the upper portion of the water channel 14, and the inner peripheral surface of the lower portion of the water channel 14 is formed on the first valve seat 17. The second valve seat 18 is connected.

  As shown in FIGS. 3 and 5A, 5B, the valve body 12 is formed by covering the entire surface of a core body 12a made of cast iron with a rubber coating layer 22 made of synthetic rubber. This synthetic rubber is a rubber composition mainly composed of an ethylene-propylene-diene terpolymer (hereinafter referred to as EPDM polymer) obtained by copolymerizing ethylene and propylene and a diene monomer.

  The valve body 12 has a shape in front view corresponding to the cross-sectional shape of the water channel 14, and the support portions 19 formed on both sides thereof have grooves 19 a into which the valve body guide protrusions 16 are fitted. Is formed. A first seal portion 20 that can be in close contact with the first valve seat 17 of the valve box 11 is formed on the upper outer peripheral edge of both side surfaces of the valve body 12 facing the direction of extension of the water channel 14. A second seal portion 21 that can be in close contact with the second valve seat 18 is formed on the lower outer peripheral surface of the valve body 12 corresponding to the lower inner peripheral surface of the water channel 14.

  The valve element 12 is guided to be displaceable in the vertical direction in the valve element accommodating portion 15 by fitting the valve element guide protrusions 16 in both grooves 19a, and the valve element operating mechanism causes the valve element 12 to move in the vertical direction. Is supported at an arbitrary displacement position. The valve body 12 closes the water passage 14 at a valve closed position where the first seal portion 20 is in close contact with the first valve seat 17 and the second seal portion 21 is in close contact with the second valve seat 18. On the other hand, the valve body 12 opens the water channel 14 at a valve open position where the first seal portion 20 is separated from the first valve seat 17 and the second seal portion 21 is separated from the second valve seat 18.

Next, the rubber composition for forming the rubber coating layer 22 will be described in detail.
This rubber composition is obtained by appropriately adding a reinforcing agent, a softening agent, a crosslinking agent, an anti-aging agent, a filler, an adhesion-imparting agent, a coloring agent, a lubricant, a release agent, etc., to the EPDM polymer as a main component. is there.

  In the EPDM polymer, the content of the diene monomer that determines the number of double bonds, that is, the number of diene component chains, that causes deterioration due to chlorine water in tap water is larger than the content of the diene monomer in a general EPDM polymer. A large range of 5 to 13% by weight is set. Further, the ethylene content which forms a main chain in the structure of the EPDM polymer and greatly affects the mechanical strength of the rubber composition is set in a range of 60 to 80% by weight. The EPDM polymer is a mixture of two or more types of EPDM polymers having different diene monomers and ethylene contents. By adjusting the mixing ratio of the plurality of types of EPDM polymers, the final of the diene monomers and ethylene can be obtained. Content is adjusted.

  The content of the diene monomer greatly affects the durability of the rubber composition against chlorine water. In this embodiment, the structure of the diene component chain, which originally deteriorates the chlorine water resistance, is intentionally created and the molecular resistance of the main chain is actively prevented to prevent the rubber composition from having a resistance to resistance. Chlorine water is improved.

As the reinforcing agent, in addition to white carbon (silica) and calcined clay, which have a low chlorine adsorption capacity, that is, a low water-absorbing substance, carbon having a CTAB (Cetyl Tri-methyl Ammonium Bromide) adsorption specific surface area is common. FT (Fine Thermal Black) type or MT (Medium Thermal Black) type carbon black which is 20 m ² / g or less smaller than black is used. The amount of white carbon mixed with the EPDM polymer is in the range of 5 to 100 parts by weight with respect to 100 parts by weight of the EPDM polymer. Further, the mixing amount of the calcined clay with respect to the EPDM polymer is 95 parts by weight or less with respect to 100 parts by weight of the EPDM polymer. Further, the mixing amount of white carbon and calcined clay with respect to the EPDM polymer is 100 parts by weight or less in total with respect to 100 parts by weight of the EPDM polymer. The amount of carbon black mixed with the EPDM polymer is 50 parts by weight or less with respect to 100 parts by weight of the EPDM polymer.

  Carbon black usually used as a reinforcing agent has the property of adsorbing chlorine in tap water due to its water absorption, and exhibits the effect of promoting the deterioration of EPDM polymer by chlorine due to this adsorption of chlorine. In this embodiment, deterioration of the rubber composition made of chlorine-resistant water due to the water absorption of the reinforcing agent is suppressed by using a reinforcing agent that has lower water absorption than general carbon black.

  As the crosslinking agent, an organic peroxide (peroxide) capable of improving the heat resistance of the rubber composition as compared with sulfur crosslinking, for example, dicumyl peroxide having a decomposition temperature of 145 ° C. is used.

Next, the manufacturing method of the rubber coating layer 22 in the valve body 12 will be described.
First, two or more types of EPDM polymers having different contents of diene monomer and ethylene are mixed, and EPDM polymers having final contents of diene monomer and ethylene of 5 to 13% by weight and 60 to 80% by weight, respectively. obtain.

Next, a reinforcing agent is added to the EPDM polymer and mixed to obtain a primary mixture.
Next, additives such as a crosslinking agent, a softening agent, an anti-aging agent, and a filler are added to the primary mixture and mixed to obtain a secondary mixture.

Next, the secondary mixture is formed into a sheet shape to obtain a sheet-like uncrosslinked rubber composition.
Next, the core body 12a and the sheet-like rubber composition are set inside a compression mold (not shown) having a cavity corresponding to the surface shape of the core body 12a of the valve body 12.

  Next, the sheet-shaped rubber composition is pressed against the surface of the core body 12a for about 20 minutes while heating the compression mold in the range of 160 to 165 ° C. By this step, the sheet-like rubber composition is melted and coated on the entire surface of the core body 12a and is primarily crosslinked.

The rubber coating layer 22 that covers the surface of the core body 12a is formed by the above steps.
Finally, the valve body 12 on which the rubber coating layer 22 is formed is put into an oven (not shown) and secondarily crosslinked. In this secondary crosslinking, a temperature of about 150 ° C. is applied to the rubber coating layer 22 formed on the surface of the core body 12a for about 6 hours. By this secondary crosslinking, the organic carbon in the free state existing in the rubber coating layer 22 after the primary crosslinking reacts with the crosslinking agent and is taken into the rubber coating layer 22. Further, due to the secondary crosslinking, a low molecular weight component of a carbon compound such as a plasticizer present in the rubber coating layer 22 is dissipated from the rubber coating layer 22. Further, the unreacted portion of the organic peroxide used as the crosslinking agent is dissipated from the rubber coating layer 22 by the secondary crosslinking. As a result, in the rubber coating layer 22, a certain amount of organic carbon that may leach into tap water is removed from the rubber coating layer 22. In addition, although the said manufacturing method demonstrated the case where the rubber coating layer 22 was formed by compression molding, it can also be formed by injection molding.

  Now, in the valve closed state or valve open state of the water gate valve 10, both side surfaces of the valve body 12 facing the extension direction of the water channel 14 are exposed to tap water in the water channel 14. In contrast, in the rubber coating layer 22 that covers the surface of the valve body 12, the amount of organic carbon that may leach into tap water is reduced by secondary crosslinking. For this reason, the amount of organic carbon leached from the rubber coating layer 22 into the tap water is reduced.

  Next, an example of the rubber coating layer 22 used in the water gate valve 10 configured as described above will be described together with a comparative example.

  As the rubber coating layer 22, an EPDM polymer using sulfur as a cross-linking agent and a peroxide using “organic carbon (total organic carbon (TOC))” (mg) specified by JWA K156 by the Japan Water Works Association / L) "is measured. Furthermore, about the thing using a peroxide, the value of TOC is measured about what does not perform secondary bridge | crosslinking, and what performed secondary bridge | crosslinking on several conditions, respectively. Note that JWWA Z108 is applied as a test method.

表１に示すように、二次架橋を行わない比較例１，２において、架橋剤として硫黄を用いた比較例１は、ＴＯＣの値が１．７ｍｇ／Ｌとなった。また、架橋剤としてパーオキサイドを用いた比較例２は、ＴＯＣの値が１７．４ｍｇ／Ｌとなった。従って、架橋剤としてパーオキサイドを用いたものは、硫黄を用いたものよりもＴＯＣの値が悪化する。

As shown in Table 1, in Comparative Examples 1 and 2 in which secondary crosslinking was not performed, Comparative Example 1 using sulfur as a crosslinking agent had a TOC value of 1.7 mg / L. Moreover, the value of TOC of the comparative example 2 which used the peroxide as a crosslinking agent became 17.4 mg / L. Therefore, those using peroxide as a crosslinking agent have a worse TOC value than those using sulfur.

  On the other hand, in Examples 1 to 6 in which secondary crosslinking was performed for those using peroxide as a crosslinking agent, the value of TOC was improved as compared with Comparative Example 2. Further, as is apparent from the results of Examples 1 to 6 performed by changing the secondary crosslinking temperature and the secondary crosslinking time, the secondary crosslinking temperature was set to 150 ° C. and the secondary crosslinking time was set to 6 hours. 6 achieved 0.5 mg / L or less, which is the TOC quality rule stipulated by the Japan Water Works Association. Therefore, the value of TOC can be improved by secondary-crosslinking the rubber product that has been heat-molded and primary-crosslinked under preset conditions.

The embodiment described above in detail has the following effects.
(1) A rubber coating layer 22 is formed on the surface of the valve body 12 by mixing a crosslinking agent with an EPDM polymer obtained by copolymerizing ethylene and propylene and a diene monomer, and heat-molding the rubber composition. After that, the valve body 12 was subjected to secondary crosslinking for a predetermined time in a predetermined temperature atmosphere. For this reason, in the primary crosslinking performed under the conditions of the temperature and time set for heat-molding the rubber composition, free organic carbon remaining in the rubber composition after molding, plasticizer, etc. The molecular weight and the unreacted content of the organic peroxide used as the crosslinking agent are reduced in the rubber coating layer 22 after the secondary crosslinking. Therefore, the amount of organic carbon (total organic carbon) leached into tap water can be reduced.

  (2) Physical property values such as hardness and tensile strength of the rubber coating layer 22 are stabilized by secondary crosslinking, and variations between products with respect to design values are reduced. For this reason, in the valve closed state, the closeness of the first seal portion 20 and the second seal portion 21 with respect to the first valve seat 17 and the second valve seat 18 of the valve box 11 is stabilized between products. Therefore, the water stoppage of the water gate valve 10 is stabilized between products, and the occurrence of defects is suppressed.

It should be noted that the present invention can be modified and embodied as follows.
In the rubber composition for forming the rubber coating layer 22, the content of the diene monomer with respect to the EPDM polymer is less than 5% by weight as in the case of a general EPDM polymer. Also in this case, the amount of organic carbon (total organic carbon) leached from the rubber coating layer 22 into the tap water is reduced.

  The present invention is embodied in water pipe fittings, rubber seals for various valves, rubber packings, and rubber diaphragms.

The disassembled perspective view which shows the gate valve for water supply of one Embodiment. The longitudinal cross-sectional view which shows the gate valve for water supplies. The cross-sectional view which shows a valve body. The longitudinal cross-sectional view which shows the gate valve for water supplies. (A) is a front view which shows a valve body, (b) is a side view similarly.

Explanation of symbols

  22 ... Rubber coating layer as a rubber product for waterworks.

Claims (2)

A method for producing a rubber product for waterworks in which a crosslinking agent is mixed with an ethylene-propylene-diene terpolymer produced by copolymerizing ethylene and propylene and a diene monomer, and the mixture is thermoformed.
A method for producing a rubber product for water supply, characterized in that after the molding, secondary crosslinking is performed under preset conditions.   The method for producing a rubber product for water supply according to claim 1, wherein an organic peroxide is used as the crosslinking agent.

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