A valve sealing rubber certified by NSF and its preparation process

Abstract

This invention discloses an NSF-certified valve sealing rubber and its preparation process, belonging to the field of valve sealing material technology. The key technical point is an NSF-certified valve sealing rubber comprising the following raw materials in parts by weight: 85-120 parts of nitrile rubber 350L, 4-7 parts of zinc oxide, 1-3 parts of stearic acid, 0.2-2 parts of sulfur, 2-5 parts of antioxidant, 60-110 parts of carbon black, 10-20 parts of processing oil TP-90B, 10-20 parts of processing oil TP-95, 4-15 parts of crosslinking agent TB-7, and 1-5 parts of accelerator. The antioxidant is a mixture of ketone amine compounds and benzimidazole zinc compounds; the accelerator is a mixture of thiuram and sulfenamide compounds. Through optimized selection of each raw material type, a non-toxic valve sealing rubber capable of NSF61 certification is obtained.

Description

Technical Field

[0001] This invention relates to the field of valve sealing materials technology, and in particular to a valve sealing rubber certified by NSF and its preparation process. Background Technology

[0002] NSF61 certification is crucial in the field of food contact materials and products. As public awareness of food safety continues to rise, safety requirements for all materials and products that may come into contact with food are becoming increasingly stringent. NSF61 certification aims to ensure that food contact materials and products will not pose a hazard to food during use, encompassing numerous aspects such as food processing equipment, drinking water treatment systems, and products for children. This certification plays a key role in protecting public health and food safety, driving the entire food contact materials industry towards greater safety and reliability. Simultaneously, it prompts relevant companies to continuously improve and innovate their production technologies to meet increasingly stringent certification standards.

[0003] To achieve the sealing function of valves, existing technologies typically employ a method of covering the inner cavity of the valve body with a rubber layer and equipping it with a metal valve plate. During valve operation, the rotation and opening of the valve plate causes the rubber layer to be compressed and deformed through continuous rotation, thus achieving a sealing effect. For the rubber sealing strips of valves, not only must their static tensile strength, elongation at break, hardness, and elasticity meet the sealing requirements, but they also need to possess abrasion and tear resistance under dynamic, frequent opening and closing conditions. In practice, companies will adjust the formulation and processing of rubber materials according to different usage scenarios and requirements to meet these performance requirements as much as possible.

[0004] However, existing technologies have significant shortcomings. In terms of toxicology, current valve sealing rubbers are insufficient to meet relevant requirements, which is a major challenge currently facing research efforts. Furthermore, the lack of effective testing methods for trace element toxicology in China further increases the difficulty of manufacturing non-toxic valves, making existing valve sealing rubbers unable to adequately meet the NSF61 certification requirements for food contact safety. Summary of the Invention

[0005] To meet customers' requirements for non-toxic rubber, this invention provides a valve sealing rubber certified by NSF and its preparation process. By optimizing the selection of various raw material types, a non-toxic valve sealing rubber that can pass NSF61 certification is obtained.

[0006] The first aspect of this invention is to provide a valve sealing rubber that has passed NSF certification, employing the following technical solution: A valve sealing rubber certified by NSF, the sealing rubber comprising the following raw materials in parts by weight: 85-120 parts of nitrile rubber 350L, 4-7 parts of zinc oxide, 1-3 parts of stearic acid, 0.2-2 parts of sulfur, 2-5 parts of antioxidant, 60-110 parts of carbon black, 10-20 parts of processing oil TP-90B, 10-20 parts of processing oil TP-95, 4-15 parts of crosslinking agent TB-7, and 1-5 parts of accelerator; The antioxidant is a mixture of ketamine compounds and benzimidazole zinc compounds; The accelerator is a mixture of thiuram and sulfenamide.

[0007] By adopting the above technical solution, adding zinc oxide and stearic acid to nitrile rubber has an activating effect on nitrile rubber, which can accelerate the formation of a cross-linked three-dimensional network structure from the linear structure of nitrile rubber. Through the synergistic effect between zinc oxide and stearic acid, the tensile strength, elasticity and hardness of nitrile rubber material are enhanced. In addition, the addition of carbon black to nitrile rubber has more pores, and nitrile rubber and carbon black can easily form carbon black gel through adsorption or inclusion, which effectively increases the wear resistance and tear resistance of nitrile rubber material and improves the service life of nitrile rubber.

[0008] The antioxidants of this invention are selected from ketone amine compounds and benzimidazole zinc compounds, the accelerators are selected from thiuram compounds and sulfenamide compounds, and the types of processing oil and nitrile rubber are selected. The selection of raw material types avoids the introduction of toxic groups. Secondly, when the crosslinking agent TB-7 is used instead of the crosslinking agent DTDM, the precipitation of the toxic group N-nitrosomorpholine is avoided.

[0009] In summary, the nitrile rubber material obtained by this invention not only has high tensile properties, tensile strength, tear strength and good hardness, but also passes NSF61 certification and has a non-toxic effect.

[0010] Preferably, the carbon black comprises carbon black N550 and carbon black N326 in a weight ratio of 3:1.

[0011] By adopting the above technical solution, valve sealing rubber is prepared using carbon black N550 and carbon black N326 in a weight ratio of 3:1. Carbon black N550 has good processing and reinforcing properties, enabling the rubber to have good physical and dynamic properties. Carbon black N326 can enhance the rubber's wear resistance and tear resistance. The combination of the two can ensure that the rubber meets the physical property requirements of valve sealing, such as tensile strength, elongation at break, hardness, elasticity, abrasion resistance, and tear resistance. At the same time, the synergistic effect of the two carbon blacks can limit the excessive use of one material and prevent the release of some groups during vulcanization, which helps to reduce the content of harmful components in the rubber. This allows the valve sealing rubber to meet NSF certification requirements, obtain non-toxic nitrile rubber material, and ensure that the valve sealing rubber will not cause harm to food when in contact with food.

[0012] Preferably, the antioxidant comprises antioxidant ZMTI and antioxidant BLE in a weight ratio of 1:1.

[0013] Preferably, the accelerator comprises accelerator TMTD and accelerator CBS in a weight ratio of 4:1.

[0014] Preferably, the rubber content of the sealing rubber is 50-60 wt%.

[0015] A second aspect of the present invention is to provide a manufacturing process for NSF-certified valve sealing rubber as described above, comprising the following steps: S1. Plasticize 350L of nitrile rubber; S2. Add the antioxidant to step S1 and mix well; S3. Add zinc oxide to step S2 and pound until homogeneous; S4. Add stearic acid and one-third carbon black to step S3 and mix well. S5. Add the processing oil and the remaining carbon black from step S4, pound them evenly, and then cut them into sheets and cool them. S6. After the film obtained in step S5 has cooled to room temperature, roll the film, add crosslinking agent, accelerator and sulfur, mix evenly and then sheet and cool to obtain compound rubber. S7. The compound rubber is vulcanized to obtain sealing rubber.

[0016] Different mixing sequences not only affect the degree of dispersion of raw materials but may also cause agglomeration of the compounded rubber in different parts, reducing the physical properties of nitrile rubber materials and leading to the precipitation of toxic groups due to uneven dispersion. In this application, by adopting the above-mentioned technical solution, the antioxidant is added in advance, which can improve the effective mixing of nitrile rubber and antioxidant. Moreover, the carbon black is added in stages, which enhances the reinforcing effect of carbon black on nitrile rubber materials and improves the tensile strength, hardness, and other performance properties of nitrile rubber materials.

[0017] Therefore, the preparation method of this application enhances the uniformity of mixing by adding each raw material to the nitrile rubber in steps, while avoiding the precipitation of toxic groups.

[0018] Preferably, the compound obtained in step S6 is placed at 23±2℃ for 8-72 hours before vulcanization.

[0019] Preferably, the vulcanization conditions in step S7 are: vulcanization pressure of 5-8 MPa, vulcanization temperature of 150-170℃, and vulcanization time of 30-50 min.

[0020] By adopting the above technical solution, as the vulcanization time increases, the degree of vulcanization of the compound increases rapidly at first and then slows down. This is mainly because excessive vulcanization time will result in over-vulcanization, which has little effect on the performance of nitrile rubber materials and instead wastes process time and costs. Therefore, when the vulcanization time is 30-50 minutes, nitrile rubber has better comprehensive performance and lower process costs.

[0021] In summary, the present invention has the following beneficial effects: by selecting and adding each raw material in stages, this application effectively avoids the formation of toxic groups during the mixing process of nitrile rubber, while also ensuring the various physical properties of the nitrile rubber material. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments. All reagents, unless otherwise specified, are commercially available conventional reagent products.

[0023] Example 1

[0024] An NSF-certified valve sealing rubber comprising the following raw materials: Acrylic rubber 350L 8.5kg, zinc oxide 0.4kg, stearic acid 0.1kg, sulfur 0.02kg, antioxidant 0.2kg, carbon black 6kg, processing oil TP-90B 1kg, processing oil TP-95 1kg, crosslinking agent TB-7 0.4kg, accelerator 0.1kg; Among them, the antioxidants include antioxidant ZMTI and antioxidant BLE in a weight ratio of 1:1; Carbon black includes carbon black N550 and carbon black N326 in a weight ratio of 3:1; The accelerators include accelerator TMTD and accelerator CBS in a weight ratio of 4:1; Its preparation process includes the following steps: S1. Put 350L of nitrile rubber into the roller and plasticize until the nitrile rubber completely covers the roller without any cracks or openings. S2. Slowly add antioxidant to step S1, and mix thoroughly until the color of the rubber compound is uniform after cutting. S3. Add zinc oxide to step S2 and pound until homogeneous; S4. Add stearic acid and carbon black to step S3 and mix well. S5. Add processing oil TP-90B, processing oil TP-95 and remaining carbon black (added in two batches) to step S4. After pounding for 20 minutes to ensure uniform distribution of raw materials, the rubber compound is sheeted and cooled. The roller gap is 3mm during pounding. S6. After the film obtained in step S5 has been left to stand for more than 4 hours and cooled to room temperature, the film is rolled on a machine, crosslinking agent TB-7, accelerator and sulfur are added and mixed evenly, then the film is cooled to obtain a compound. The compound is placed at 23±2℃ for 8 hours. S7. The compound rubber is vulcanized to obtain sealing rubber. The vulcanization conditions are: vulcanization pressure 5MPa, vulcanization temperature 150℃, and vulcanization time 30min.

[0025] Example 2

[0026] An NSF-certified valve sealing rubber comprising the following raw materials: Acrylic rubber 350L 10kg, zinc oxide 0.5kg, stearic acid 0.2kg, sulfur 0.1kg, antioxidant 0.4kg, carbon black 8kg, processing oil TP-90B 1.5kg, processing oil TP-95 1.5kg, crosslinking agent TB-7 1.0kg, accelerator 0.3kg; Among them, the antioxidants include antioxidant ZMTI and antioxidant BLE in a weight ratio of 1:1; Carbon black includes carbon black N550 and carbon black N326 in a weight ratio of 3:1; The accelerators include accelerator TMTD and accelerator CBS in a weight ratio of 4:1; Its preparation process includes the following steps: S1. Put 350L of nitrile rubber into the roller and plasticize until the nitrile rubber completely covers the roller without any cracks or openings. S2. Slowly add antioxidant to step S1, and mix thoroughly until the color of the rubber compound is uniform after cutting. S3. Add zinc oxide to step S2 and pound until homogeneous; S4. Add stearic acid and carbon black to step S3 and mix well. S5. Add processing oil TP-90B, processing oil TP-95 and remaining carbon black (added in two batches) to step S4. After pounding for 25 minutes to ensure uniform distribution of raw materials, the rubber compound is sheeted and cooled. The roller gap is 3mm during pounding. S6. After the film obtained in step S5 has been left to stand for more than 4 hours and cooled to room temperature, the film is rolled on a machine, crosslinking agent TB-7, accelerator and sulfur are added and mixed evenly, then the film is cooled to obtain a compound. The compound is placed at 23±2℃ for 48 hours. S7. The compound rubber is vulcanized to obtain sealing rubber. The vulcanization conditions are: vulcanization pressure 6MPa, vulcanization temperature 160℃, and vulcanization time 40min.

[0027] Example 3

[0028] An NSF-certified valve sealing rubber comprising the following raw materials: Acrylic rubber 350L 12kg, zinc oxide 0.7kg, stearic acid 0.3kg, sulfur 0.2kg, antioxidant 0.5kg, carbon black 11kg, processing oil TP-90B 2kg, processing oil TP-95 2kg, crosslinking agent TB-7 1.5kg, accelerator 0.5kg; Among them, the antioxidants include antioxidant ZMTI and antioxidant BLE in a weight ratio of 1:1; Carbon black includes carbon black N550 and carbon black N326 in a weight ratio of 3:1; The accelerators include accelerator TMTD and accelerator CBS in a weight ratio of 4:1; Its preparation process includes the following steps: S1. Put 350L of nitrile rubber into the roller and plasticize until the nitrile rubber completely covers the roller without any cracks or openings. S2. Slowly add antioxidant to step S1, and mix thoroughly until the color of the rubber compound is uniform after cutting. S3. Add zinc oxide to step S2 and pound until homogeneous; S4. Add stearic acid and carbon black to step S3 and mix well. S5. Add processing oil TP-90B, processing oil TP-95 and remaining carbon black (added in two batches) to step S4. After pounding for 25 minutes to ensure uniform distribution of raw materials, the rubber compound is sheeted and cooled. The roller gap is 3mm during pounding. S6. After the film obtained in step S5 has been left to stand for more than 4 hours and cooled to room temperature, the film is rolled on a machine, crosslinking agent TB-7, accelerator and sulfur are added and mixed evenly, then the film is cooled to obtain a compound. The compound is placed at 23±2℃ for 72 hours. S7. The compound rubber is vulcanized to obtain sealing rubber. The vulcanization conditions are: vulcanization pressure 8MPa, vulcanization temperature 170℃, and vulcanization time 50min.

[0029] Comparative Example 1

[0030] A valve sealing rubber differs from Example 1 in that an equal amount of nitrile rubber NBR 2845 is used instead of nitrile rubber 350L, an equal amount of antioxidant BLE is used instead of antioxidant DNP, and an equal amount of crosslinking agent DTDM is used instead of TB-7. The types and amounts of other components are the same as in Example 1.

[0031] Performance testing

[0032] The tensile properties, hardness, tear strength, compression set and abrasion of the sealing rubber obtained in the above embodiments were further tested, and the test results are shown in Table 1.

[0033] Tensile strength testing shall be conducted in accordance with the relevant provisions of ASTM D412-2006; Hardness testing was conducted in accordance with the relevant provisions of ASTM D2240-2005. The 100% elongation test is conducted in accordance with the relevant provisions of ASTM D412-2006; Tear strength testing was conducted in accordance with the relevant provisions of ASTM D624-2007; The compression set (100℃*70h*25%) was tested according to the relevant provisions in ASTM 395B-2003; Wear was tested in accordance with the relevant provisions of GB / T1689-1998.

[0034] Table 1. Results of performance tests on sealing rubber Tensile strength / MPa 15.2 15.3 15.3 14.5 Elongation at break / % 328 333 330 314 Hardness / Shore A 72 72 72 72 100% elongation / MPa 3.73 3.81 3.79 3.55 Tear strength (KN / m) 45.23 46.54 45.89 43.82 Compression permanent deformation / % 10.89 10.92 10.93 11.72 <![CDATA[Abrasion loss cm 3 / 1.61km]]> 0.263 0.262 0.262 0.279 As can be seen from Table 1, the sealing rubbers obtained in Examples 1-3 of this application have good tensile strength, elongation at break, hardness, 100% elongation, tear strength, compression set and certain wear resistance. It can be seen that the synergistic cooperation among the above components of this application effectively ensures the physical properties of the sealing rubber.

[0035] Compared with Example 1, Comparative Example 1 replaced Nitrile Rubber 350L with an equal amount of Nitrile Rubber NBR 2845, replaced Antioxidant DNP with an equal amount of Antioxidant BLE, and replaced TB-7 with an equal amount of Crosslinking Agent DTDM. As a result, the properties of the sealing rubber obtained in Comparative Example 1 were all reduced compared with those in Example 1. This shows that the synergistic effect between the components of this application also improves the various properties of the valve sealing rubber.

[0036] The sealing rubber obtained in Example 2 was subjected to NSF certification testing. 151 toxic substances were tested, and the results for all 151 toxic substances were below the standard detection limits and normalized limits in the NSF certification standard, indicating that the sealing rubber obtained in this application is non-toxic and can be used in materials that come into contact with food. However, the solution in Comparative Example 1 failed the NSF test. The substances that failed the test are listed below. The final test results were obtained after normalization according to the standard requirements, and the specific results are as follows: Table 2. List of substances in rubber that failed NSF certification tests as obtained in Comparative Example 2.

[0037] In the technical solution of Comparative Example 2, the contents of benzene, toluene, xylene, o-xylene, nitrosodiphenylamine, nitrosodiethylamine, dimethylnitrosamine, and nitrosomorpholine were all higher than the detection limits in the standard. This further illustrates that by adjusting the selection of component types, not only can non-toxic sealing rubber be obtained, but also the various physical properties of the sealing rubber can be relatively improved.

[0038] The physical properties of the sealing rubbers obtained in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0039] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A valve sealing rubber certified by NSF, characterized in that: The sealing rubber comprises the following raw materials in parts by weight: 85-120 parts of nitrile rubber 350L, 4-7 parts of zinc oxide, 1-3 parts of stearic acid, 0.2-2 parts of sulfur, 2-5 parts of antioxidant, 60-110 parts of carbon black, 10-20 parts of processing oil TP-90B, 10-20 parts of processing oil TP-95, 4-15 parts of crosslinking agent TB-7, and 1-5 parts of accelerator; The antioxidant is a mixture of ketamine compounds and benzimidazole zinc compounds; The accelerator is a mixture of thiuram and sulfenamide.

2. The valve sealing rubber certified by NSF according to claim 1, characterized in that: The carbon black comprises carbon black N550 and carbon black N326 in a weight ratio of 3:

1.

3. The valve sealing rubber certified by NSF according to claim 1, characterized in that: The antioxidants include antioxidant ZMTI and antioxidant BLE in a weight ratio of 1:

1.

4. The valve sealing rubber certified by NSF according to claim 1, characterized in that: The accelerators include accelerator TMTD and accelerator CBS in a weight ratio of 4:

1.

5. The valve sealing rubber certified by NSF according to claim 1, characterized in that: The rubber content of the sealing rubber is 50-60 wt%.

6. A manufacturing process for NSF-certified valve sealing rubber as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Plasticize 350L of nitrile rubber; S2. Add the antioxidant to step S1 and mix well; S3. Add zinc oxide to step S2 and pound until homogeneous; S4. Add stearic acid and one-third carbon black to step S3 and mix well. S5. Add the processing oil and the remaining carbon black from step S4, pound them evenly, and then cut them into sheets and cool them. S6. After the film obtained in step S5 has cooled to room temperature, roll the film, add crosslinking agent, accelerator and sulfur, mix evenly and then sheet and cool to obtain compound rubber. S7. The compound rubber is vulcanized to obtain sealing rubber.

7. The manufacturing process of NSF-certified valve sealing rubber according to claim 6, characterized in that: The compound obtained in step S6 is placed at 23±2℃ for 8-72 hours and then subjected to vulcanization.

8. The manufacturing process of NSF-certified valve sealing rubber according to claim 6, characterized in that: The vulcanization conditions for step S7 are: vulcanization pressure 5-8 MPa, vulcanization temperature 150-170℃, and vulcanization time 30-50 min.

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