E + PTFE coated pad as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sealing rings, and particularly relates to an E + PTFE coated pad and a preparation method and application thereof. According to the preparation method provided by the invention, the formula of a polytetrafluoroethylene resin material is improved, so that the produced E + PTFE coated pad is softer, the sealing property and the pressure-bearing capacity are improved, and the problems of high hardness and poor flexibility of a PTFE coated membrane are solved; and meanwhile, the polytetrafluoroethylene resin material provided by the invention is transparent in character, and even if bubbles are generated inside when the E + PTFE coating pad is prepared, the bubbles can be found and discharged in time, so that the product quality is ensured. And the formula of the adhesive used when the PTFE membrane and the EPDM base material are bonded is optimized, so that the cured structure of the E + PTFE coating pad is effectively prevented from being damaged when the E + PTFE coating pad is compressed and deformed. According to the preparation method provided by the invention, the obtained E + PTFE coated pad has no joint, and the loading capacity of the E + PTFE coated pad is improved, so that the application range of the plate heat exchanger can be expanded.

Description

Technical Field

[0001] This invention belongs to the field of sealing ring technology, specifically relating to an E+PTFE coated gasket, its preparation method, and its application. Background Technology

[0002] Semi-welded plate heat exchangers are highly efficient and energy-saving heat exchange equipment widely used in production and daily life. They are typically composed of many stamped corrugated thin plates spaced at regular intervals, sealed around the edges with sealing rings, and overlapped and pressed together by a frame and clamping screws. The four corner holes of the plates and gaskets form distribution and collection pipes for the fluid, while also effectively separating hot and cold fluids, allowing them to flow in the channels on both sides of each plate for heat exchange.

[0003] As a crucial component of plate heat exchangers, the sealing ring significantly impacts their service life. The sealing ring not only seals the medium to prevent leakage to the external environment but also prevents the mixing of heat exchange media. Problems with the sealing ring can lead to the malfunction of a semi-welded plate heat exchanger.

[0004] Currently, the sealing rings used in semi-welded plate heat exchangers are composite sealing rings made of polytetrafluoroethylene (PTFE) and ethylene propylene diene monomer (EPDM) rubber (i.e., E+PTFE coated gaskets). E+PTFE coated gaskets have excellent chemical resistance.

[0005] However, currently used E+PTFE coated gaskets suffer from problems such as low pressure resistance, numerous air bubbles between the EPDM substrate and PTFE, and weak adhesion between the EPDM substrate and PTFE. Summary of the Invention

[0006] The purpose of this invention is to provide an E+PTFE coated pad, its preparation method, and its application. The method for E+PTFE coated pads provided by this invention simultaneously solves the problems of low pressure bearing capacity of E+PTFE coated pads, excessive air bubbles between EPDM substrate and PTFE, and weak adhesion between EPDM substrate and PTFE.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing an E+PTFE coated pad, comprising the following steps:

[0009] The raw materials for preparing polytetrafluoroethylene (PTFE) resin are sequentially mixed, molded, and sintered to obtain a PTFE film. The PTFE film has a U-shaped groove structure, which is used to fill an EPDM rubber substrate. The PTFE resin material comprises the following raw materials in parts by weight: 90-100 parts PTFE, 1-10 parts organic additives, and 15-25 parts lubricant. The organic additives include perfluoroalkoxy resins and / or fluorinated ethylene propylene copolymers.

[0010] The inner surface of the U-shaped groove structure of the polytetrafluoroethylene membrane is sodium-treated to obtain a sodium-treated polytetrafluoroethylene membrane. The sodium treatment is carried out using a sodium naphthalene solution.

[0011] The inner surface of the U-shaped groove structure of the sodium-treated polytetrafluoroethylene (PTFE) membrane is coated with a resin adhesive, and then filled with an EPDM rubber substrate to obtain a PTFE membrane containing the substrate. The resin adhesive comprises a rubber component and a solvent component. The rubber component comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 20-60 parts carbon black, 0.5-3 parts antioxidant, 1.5-6 parts peroxide vulcanizing agent, and 2-10 parts co-crosslinking agent, wherein the co-crosslinking agent is maleic anhydride-modified liquid polybutadiene. The solvent component comprises at least two of cyclohexane, n-heptane, and ethyl acetate.

[0012] The polytetrafluoroethylene film containing the substrate is placed in a mold for compression molding and vulcanization to obtain the E+PTFE coated pad.

[0013] Preferably, the EPDM rubber substrate comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 50-80 parts reinforcing carbon black, 2-10 parts peroxide vulcanizing agent, 2-10 parts first co-crosslinking agent, 1-5 parts second co-crosslinking agent, 2-10 parts zinc oxide, 1-4 parts antioxidant, and 1-3 parts processing aid; the EPDM rubber has a Mooney viscosity ≥80, the first co-crosslinking agent is an acrylate crosslinking aid, and the second co-crosslinking agent is maleic anhydride-modified liquid polybutadiene.

[0014] Preferably, the raw materials for preparing the sodium naphthalene solution include naphthalene, tetrahydrofuran, and metallic sodium; the ratio of naphthalene, tetrahydrofuran, and metallic sodium is 5 kg: 10 L: 1 kg.

[0015] Preferably, the sodium treatment includes: coating and protecting the outer surface of the polytetrafluoroethylene film, and then immersing it in the sodium naphthalene solution for treatment, wherein the immersion temperature is room temperature and the time is 2 to 10 minutes.

[0016] Preferably, the compression molding vulcanization temperature is 170–190°C, the pressure is 8–15 MPa, and the time is 3–15 min.

[0017] Preferably, the perfluoroalkoxy resin is polymerized from tetrafluoroethylene and perfluoroalkoxy vinyl ether; the fluorinated ethylene propylene copolymer is copolymerized from tetrafluoroethylene and hexafluoropropylene; and the lubricant is petroleum ether.

[0018] The mixing is carried out under stirring, with the stirring speed being 15-30 r / min and the time being 10-20 min;

[0019] The molding process includes sequentially performing a first molding, a second molding, and a third molding. The pressure of the first molding is 10–20 MPa. After the first molding is degassed, the second molding is performed. The pressure of the second molding is 25–35 MPa. The pressure of the third molding is 30–40 MPa, and the holding time is 5–10 minutes.

[0020] The sintering process includes: heating from room temperature to a first temperature at a first heating rate and holding for a first time; then heating from the first temperature to a second temperature at a second heating rate and holding for a second time; and then cooling from the second temperature to room temperature; wherein the first heating rate is 10–20°C / h, the first temperature is 200–250°C, the first holding time is 1–2h, the second heating rate is 10–15°C / h, the second temperature is 350–380°C, the second holding time is 30–240min, and the cooling rate is 10–30°C / h.

[0021] Preferably, the antioxidant includes one or more of antioxidant BBM, antioxidant 445, antioxidant MB, and antioxidant RD; the peroxide curing agent includes one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,4-di-tert-butylperoxyisopropylbenzene; the maleic anhydride-modified liquid polybutadiene has a molecular weight of 2000-3000, and the structural formula of the maleic anhydride-modified liquid polybutadiene is as follows:

[0022]

[0023] The solvent component contains ethyl acetate, and the volume fraction of ethyl acetate in the solvent component is 10-15%.

[0024] The mass ratio of the rubber component to the volume ratio of the solvent component is (1-4) g: 5 mL.

[0025] Preferably, the ethylene propylene diene monomer (EPDM) rubber contains 40-55% ethylene, has a Mooney viscosity of 80-120, and a third monomer content of 1-10%; the reinforcing carbon black includes one or more of N550, N660, N990, and spray-dried carbon black; the peroxide vulcanizing agent includes one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,4-di-tert-butylperoxyisopropylbenzene; the acrylate crosslinking aid includes zinc acrylate and / or magnesium methacrylate; the maleic anhydride-modified liquid polybutadiene has a molecular weight of 2000-3000, and the structural formula of the maleic anhydride-modified liquid polybutadiene is as follows:

[0026]

[0027] The antioxidant includes at least two of antioxidant 445, antioxidant 425, antioxidant MB, and antioxidant RD.

[0028] The present invention provides an E+PTFE coated pad prepared by the preparation method described in the above technical solution.

[0029] This invention provides the application of the E+PTFE coated gasket described above as a sealing ring in a plate heat exchanger.

[0030] This invention provides a method for preparing an E+PTFE coated gasket. The invention improves the formulation of the polytetrafluoroethylene (PTFE) resin material. By adding organic additives and optimizing the mass ratio of each raw material in the PTFE resin material, the resulting PTFE resin material exhibits better flexibility, leading to a softer E+PTFE coated gasket with improved sealing and pressure resistance. This solves the problem of high hardness and poor flexibility in PTFE coated films. Furthermore, the transparent nature of the PTFE resin material allows for timely detection and removal of air bubbles during E+PTFE coated gasket preparation, ensuring product quality. The invention also produces a PTFE film through mixing, molding, and sintering, resulting in a one-piece molded PTFE film without joints. This avoids the problem of weak joints cracking under high pressure or when equipment plates shift, preventing the EPDM substrate from contacting the medium, causing substrate swelling, corrosion, and seal failure, ultimately leading to heat exchanger leaks. Furthermore, this invention optimizes the formulation of the adhesive used for bonding PTFE membranes and EPDM substrates. The resin adhesive provided by this invention uses EPDM rubber as the main raw material in the rubber component, and simultaneously combines maleic anhydride-modified liquid polybutadiene as a co-crosslinking agent. Combined with the remaining raw materials of the rubber component and solvent components, under suitable raw material ratios, the adhesive provided by this invention can completely fuse and react with the EPDM rubber substrate during high-temperature vulcanization. Under the synergistic effect of the co-crosslinking agent, it crosslinks with the EPDM rubber substrate to form a network structure. Simultaneously, the resin adhesive provided by this invention can react with the surface of the PTFE membrane (the rubber component in the resin adhesive contains a co-crosslinking agent; maleic anhydride-modified liquid polybutadiene can undergo esterification with the oxygen-containing polar groups on the surface of the PTFE membrane; and maleic anhydride-modified liquid polybutadiene can also undergo free radical crosslinking with EPDM rubber under the action of a peroxide vulcanizing agent), thereby forming not only a physical bond between the PTFE membrane and the EPDM rubber substrate, but also a chemical bond. Furthermore, the resin adhesive provided by this invention contains EPDM rubber and maleic anhydride-modified liquid polybutadiene as a crosslinking agent, which enables it to form a flexible adhesive structure after curing, effectively preventing the cured structure from being destroyed when the E+PTFE-coated pad is compressed and deformed. In summary, the adhesive provided by this invention can completely fuse with the EPDM rubber base pad, forming a unified structure through vulcanization. Moreover, it stretches and compresses with the deformation of the E+PTFE-coated pad, resulting in excellent adhesion between the PTFE film and the rubber substrate, and significantly improved peel strength.

[0031] In summary, the preparation method provided by this invention results in a seamless E+PTFE coated pad, which improves its pressure-bearing capacity and expands the application range of plate heat exchangers.

[0032] Furthermore, this invention improves the formulation of the EPDM rubber substrate. In this invention, the EPDM rubber substrate comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 50-80 parts reinforcing carbon black, 2-10 parts peroxide vulcanizing agent, 2-10 parts first co-crosslinking agent, 1-5 parts second co-crosslinking agent, 2-10 parts zinc oxide, 1-4 parts antioxidant, and 1-3 parts processing aid; the EPDM rubber has a Mooney viscosity ≥80, the first co-crosslinking agent is an acrylate crosslinking aid, and the second co-crosslinking agent is maleic anhydride-modified liquid polybutadiene. This includes the types and mass ratios of the raw materials. The second co-crosslinking agent, maleic anhydride-modified liquid polybutadiene, can undergo esterification with the oxygen-containing polar groups on the surface of the PTFE membrane. Simultaneously, the maleic anhydride-modified liquid polybutadiene can also undergo free radical crosslinking with the EPDM rubber under the action of the peroxide vulcanizing agent, which facilitates the adhesion between the rubber substrate and the PTFE membrane. The double bonds in acrylate crosslinking aids can undergo free radical addition or crosslinking reactions with ethylene propylene rubber molecular chains, simultaneously generating ionic crosslinking bonds within the vulcanized ethylene propylene diene monomer (EPDM) rubber composition, significantly improving the physical and mechanical properties of the rubber substrate. Consequently, the compression set of the EPDM rubber composition obtained by this invention is significantly improved, overcoming the defects of poor elasticity and poor pressure resistance. When used as the EPDM substrate in E+PTFE-coated gaskets, the resilience and pressure resistance of the E+PTFE-coated gaskets are enhanced, ensuring that the rebound speed of the E+PTFE-coated gaskets meets the requirements of pressure and temperature fluctuations during use, thus preventing leakage. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall structure and cross-section of the E+PTFE coated pad provided by the present invention;

[0034] Figure 2 Comparison images of actual E+PTFE coated pads provided by this invention;

[0035] Figure 3 This is the intermediate product taken out of the mold after molding in the manufacturing of the polytetrafluoroethylene film in Comparative Example 1 of this invention. Detailed Implementation

[0036] This invention provides a method for preparing an E+PTFE coated pad, comprising the following steps:

[0037] The raw materials for preparing polytetrafluoroethylene (PTFE) resin are sequentially mixed, molded, and sintered to obtain a PTFE film. The PTFE film has a U-shaped groove structure, which is used to fill an EPDM rubber substrate. The PTFE resin material comprises the following raw materials in parts by weight: 90-100 parts PTFE, 1-10 parts organic additives, and 15-25 parts lubricant. The organic additives include perfluoroalkoxy resins and / or fluorinated ethylene propylene copolymers.

[0038] The inner surface of the U-shaped groove structure of the polytetrafluoroethylene membrane is sodium-treated to obtain a sodium-treated polytetrafluoroethylene membrane. The sodium treatment is carried out using a sodium naphthalene solution.

[0039] The inner surface of the U-shaped groove structure of the sodium-treated polytetrafluoroethylene (PTFE) membrane is coated with a resin adhesive, and then filled with an EPDM rubber substrate to obtain a PTFE membrane containing the substrate. The resin adhesive comprises a rubber component and a solvent component. The rubber component comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 20-60 parts carbon black, 0.5-3 parts antioxidant, 1.5-6 parts peroxide vulcanizing agent, and 2-10 parts co-crosslinking agent, wherein the co-crosslinking agent is maleic anhydride-modified liquid polybutadiene. The solvent component comprises at least two of cyclohexane, n-heptane, and ethyl acetate.

[0040] The polytetrafluoroethylene film containing the substrate is placed in a mold for compression molding and vulcanization to obtain the E+PTFE coated pad.

[0041] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0042] This invention involves sequentially mixing, molding, and sintering the raw materials for preparing polytetrafluoroethylene (PTFE) resin to obtain a PTFE membrane. The PTFE membrane has a U-shaped groove structure, which is used to fill an EPDM rubber substrate. The PTFE resin includes the following raw materials in parts by weight: 90-100 parts PTFE, 1-10 parts organic additives, and 15-25 parts lubricant. The organic additives include perfluoroalkoxy resin (PFA) and / or fluorinated ethylene propylene copolymer (FEP).

[0043] The polytetrafluoroethylene membrane prepared by this invention is a U-shaped polytetrafluoroethylene membrane.

[0044] Based on mass parts, the raw materials for preparing the polytetrafluoroethylene resin material provided by the present invention include 90 to 100 parts of polytetrafluoroethylene, preferably 95 to 100 parts, and in the examples, 95 parts, 96 parts, 97 parts, 98 parts, 99 parts, or 100 parts.

[0045] Based on the mass fraction of the polytetrafluoroethylene (PTFE), the raw materials for preparing the PTFE resin material provided by this invention include 1 to 10 parts of organic additives, which in the examples can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. In this invention, the perfluoroalkoxy resin is preferably polymerized from tetrafluoroethylene and perfluoroalkoxy vinyl ether. The fluorinated ethylene propylene copolymer is preferably copolymerized from tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). In a specific embodiment of this invention, the perfluoroalkoxy resin is preferably a Shandong Dongyue DF-16 series fluororesin. The fluorinated ethylene propylene copolymer is preferably a Shandong Dongyue DF-10 series fluororesin and / or a Shandong Dongyue DF-20 series fluororesin.

[0046] In this invention, when the additive includes a perfluoroalkoxy resin and a fluorinated ethylene propylene copolymer, the perfluoroalkoxy resin is preferably in the amount of 0.5 to 3 parts by mass, and in the examples it can be 0.5, 1, 2 or 3 parts; the fluorinated ethylene propylene copolymer is preferably in the amount of 0.5 to 9 parts, and in the examples it can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8 or 9 parts.

[0047] Based on the mass fraction of the polytetrafluoroethylene (PTFE), the raw materials for preparing the PTFE resin material provided by this invention include 15 to 25 parts of lubricant, which in the examples can be 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 parts. In this invention, the lubricant is preferably petroleum ether.

[0048] This invention involves mixing the raw materials for preparing the polytetrafluoroethylene resin material to obtain a mixture. In this invention, the mixing is preferably carried out in a container mixer. The mixing is preferably carried out under stirring. The stirring speed is preferably 15–30 r / min, and the stirring time is preferably 10–20 min.

[0049] After obtaining the mixture, the present invention places the mixture in a mold for molding to obtain a blank. In the present invention, the molding preferably includes a first molding, a second molding, and a third molding in sequence. The pressure of the first molding is preferably 10-20 MPa. The present invention preferably performs the second molding after venting in the first molding, and the pressure of the second molding is preferably 25-35 MPa. The pressure of the third molding is preferably 30-40 MPa, and the holding time of the third molding is preferably 5-10 minutes.

[0050] After obtaining the raw material, the present invention sintersulates the raw material to obtain the polytetrafluoroethylene resin film. In the present invention, the sintering is preferably carried out in an oven. The sintering preferably includes: heating from room temperature to a first temperature at a first heating rate and holding for a first time; then heating from the first temperature to a second temperature at a second heating rate and holding for a second time; and then cooling from the second temperature to room temperature. The first heating rate is preferably 10–20°C / h, the first temperature is preferably 200–250°C, the first holding time is preferably 1–2 h, the second heating rate is preferably 10–15°C / h, the second temperature is preferably 350–380°C, the second holding time is preferably 30–240 min, and the cooling rate is preferably 10–30°C / h. In the present invention, after the sintering is completed, the sintered product is preferably cut and machined sequentially to obtain the polytetrafluoroethylene film. The present invention does not have special requirements for the specific implementation of the cutting and machining.

[0051] After obtaining the polytetrafluoroethylene (PTFE) membrane, the inner surface of the U-shaped groove structure of the PTFE membrane is sodium-treated to obtain a sodium-treated PTFE membrane. The sodium treatment is performed using a sodium naphthalene solution. In this invention, the raw materials for preparing the sodium naphthalene solution preferably include naphthalene, tetrahydrofuran, and metallic sodium. The preferred ratio of naphthalene, tetrahydrofuran, and metallic sodium is 5 kg: 10 L: 1 kg. The preferred method for preparing the sodium naphthalene solution includes: adding naphthalene to the tetrahydrofuran under stirring; obtaining a mixed solution; adding metallic sodium to the mixed solution to react and obtain the sodium naphthalene solution. During the reaction, the reaction solution is stirred every 1-2 hours, and the preferred reaction time is 10-15 hours.

[0052] In this invention, the sodium treatment preferably includes: coating and protecting the outer surface of the polytetrafluoroethylene (PTFE) membrane, and then immersing it in the sodium naphthalene solution for treatment. The coating and protection are preferably achieved using adhesive tape. The immersion temperature is room temperature, and the time is 2–10 minutes. After the immersion, the PTFE membrane is preferably cleaned after removing the coating and protection, preferably using alcohol as the cleaning agent, and finally dried to obtain the sodium-treated PTFE membrane.

[0053] After sodium-treated polytetrafluoroethylene (PTFE) membranes, the present invention coats the inner surface of the U-shaped groove structure of the sodium-treated PTFE membranes with a resin adhesive, and then fills it with an EPDM rubber substrate to obtain a PTFE membrane containing the substrate. In the present invention, the resin adhesive comprises a rubber component and a solvent component; the rubber component comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 20-60 parts carbon black, 0.5-3 parts antioxidant, 1.5-6 parts peroxide vulcanizing agent, and 2-10 parts co-crosslinking agent, wherein the co-crosslinking agent is maleic anhydride-modified liquid polybutadiene; the solvent component comprises at least two of cyclohexane, n-heptane, and ethyl acetate.

[0054] The resin adhesive provided by this invention includes a rubber component. The rubber component comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 20-60 parts carbon black, 0.5-3 parts antioxidant, 1.5-6 parts peroxide vulcanizing agent, and 2-10 parts co-crosslinking agent, wherein the co-crosslinking agent is maleic anhydride-modified liquid polybutadiene.

[0055] The raw materials for preparing the rubber component include 100 parts of EPDM rubber by weight. The EPDM rubber is the main raw material for the rubber component, enabling the resin adhesive provided by this invention to form an integral structure with the EPDM rubber substrate after molding and vulcanization, and also increasing the elasticity of the cured resin adhesive.

[0056] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the rubber component include 20-60 parts of carbon black, preferably 25-55 parts, and in the examples, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, or 60 parts. In this invention, the carbon black is preferably one or more of N990 carbon black, N550 carbon black, spray-dried carbon black, and O-carbon. In the examples, N990 carbon black is Kencabor N990, and N550 carbon black is Cabot N550. In a specific embodiment of this invention, the spray-dried carbon black can be SP500 carbon black and / or SP700 carbon black produced by Jiangxi Black Cat Carbon Black Co., Ltd.

[0057] In the examples, carbon O can be

[0058] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the rubber component include 0.5 to 3 parts of antioxidant, which in the examples can be 0.5, 1, 1.5, 2, 2.5, or 3 parts. In this invention, the antioxidant preferably includes one or more of antioxidant BBM, antioxidant 445, antioxidant MB, and antioxidant RD. The antioxidant BBM (4,4'-butylenebis(6-tert-butyl-m-cresol)) is preferably purchased from Kawaguchi, Japan, under the brand name ANTAGE.

[0059] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the rubber component include 1.5 to 6 parts of peroxide vulcanizing agent, which in the examples can be 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, or 6 parts. The peroxide vulcanizing agent preferably includes one or more of dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD), and 1,4-bis-tert-butylperoxyisopropylbenzene (BIPB).

[0060] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the rubber component include 2 to 10 parts of a crosslinking agent, wherein the crosslinking agent is maleic anhydride-modified liquid polybutadiene.

[0061] In this invention, the molecular weight (Mn) of the maleic anhydride-modified liquid polybutadiene is preferably 2000-3000, and the structural formula of the maleic anhydride-modified liquid polybutadiene is as follows:

[0062]

[0063] In an embodiment of the present invention, the maleic anhydride-modified liquid polybutadiene was purchased from Shandong Bojin New Material Technology Co., Ltd., with the product brand name Perken-7017, a molecular weight (Mn) of 2800, and a 1,2-vinyl content of 70%. The MAH grafting rate was 17%, the effective ingredient content was >99.5%, and the appearance and shape were a color-enhanced viscous liquid.

[0064] In this invention, the method for preparing the rubber component preferably includes the following steps:

[0065] The rubber component comprises the following raw materials in parts by weight, which are sequentially subjected to intensive mixing and thin-pass milling to obtain the rubber component. The intensive mixing is preferably carried out in an internal mixing process. The thin-pass milling is preferably carried out in an open mill. Preferably, the rubber component obtained after thin-pass milling is sheared to obtain small pieces of the rubber component for easy storage.

[0066] The resin adhesive provided by this invention includes a solvent component. The solvent component includes at least two of cyclohexane, n-heptane, and ethyl acetate.

[0067] In this invention, the solvent component preferably contains ethyl acetate. The volume fraction of ethyl acetate in the solvent component is preferably 10-15%.

[0068] In this invention, the solvent component is preferably a mixture of cyclohexane and ethyl acetate, or preferably a mixture of n-heptane and ethyl acetate, or preferably a mixture of cyclohexane, n-heptane and ethyl acetate.

[0069] The preferred volume ratio of cyclohexane to ethyl acetate in the cyclohexane and ethyl acetate mixture is 9:1. The preferred volume ratio of n-heptane to ethyl acetate in the n-heptane and ethyl acetate mixture is 9:1. The preferred volume ratio of the total volume of cyclohexane and n-heptane to the volume of ethyl acetate in the cyclohexane, n-heptane, and ethyl acetate mixture is 9:1. There are no special requirements regarding the volume ratio of cyclohexane to n-heptane in the cyclohexane, n-heptane, and ethyl acetate mixture.

[0070] In this invention, the mass ratio of the rubber component to the volume ratio of the solvent component is (1-4) g: 5 mL.

[0071] The resin adhesive provided by this invention can be in a two-component form or a solution form. When the resin adhesive provided by this invention is in a two-component form, the rubber component and the solvent component are packaged separately. When the resin adhesive provided by this invention is in a solution form, the rubber component and the solvent component are mixed to form a solution product.

[0072] In this invention, the method for preparing the resin adhesive preferably includes the following steps:

[0073] The rubber component is dissolved in the solvent component, and the resulting adhesive solution is the resin adhesive. This invention does not have specific requirements for the method of dissolution; stirring at room temperature is sufficient.

[0074] In this invention, the coating is preferably applied twice, and the coating amount for each application is preferably 100-200 g / cm³. 2 .

[0075] In this invention, the EPDM rubber substrate preferably comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 50-80 parts reinforcing carbon black, 2-10 parts peroxide vulcanizing agent, 2-10 parts first co-crosslinking agent, 1-5 parts second co-crosslinking agent, 2-10 parts zinc oxide, 1-4 parts antioxidant, and 1-3 parts processing aid; the EPDM rubber has a Mooney viscosity ≥80, the first co-crosslinking agent is an acrylate crosslinking aid, and the second co-crosslinking agent is maleic anhydride-modified liquid polybutadiene.

[0076] The raw materials for preparing the EPDM rubber substrate provided by this invention, by weight, comprise 100 parts of EPDM rubber. In this invention, the ethylene content in the EPDM rubber is preferably 40-55%, more preferably 45-50%. The Mooney viscosity (ML1+4, 125°C) of the EPDM rubber is preferably 80-120, more preferably 90-110. The content of the third monomer in the EPDM rubber is preferably 1-10%, more preferably 2-8%.

[0077] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by this invention include 50-80 parts of reinforcing carbon black, which in the embodiments can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, or 80 parts. In this invention, the reinforcing carbon black preferably includes one or more of N550, N660, N990, and spray-dried carbon black. In a specific embodiment of this invention, the spray-dried carbon black can be SP500 carbon black and / or SP700 carbon black produced by Jiangxi Black Cat Carbon Black Co., Ltd.

[0078] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by this invention include 2 to 10 parts of a peroxide vulcanizing agent, which in the examples can be 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. In this invention, the peroxide vulcanizing agent preferably includes one or more of dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD), and 1,4-di-tert-butylperoxyisopropylbenzene (BIPB).

[0079] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by this invention include 2 to 10 parts of a first co-crosslinking agent, which in the examples can be 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. In this invention, the first co-crosslinking agent is an acrylate crosslinking aid. The acrylate crosslinking aid preferably includes zinc acrylate and / or magnesium methacrylate.

[0080] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by the present invention include 1 to 5 parts of a second crosslinking agent, which can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts in the examples.

[0081] In this invention, the molecular weight (Mn) of the maleic anhydride-modified liquid polybutadiene is preferably 2000-3000, and the structural formula of the maleic anhydride-modified liquid polybutadiene is as follows:

[0082]

[0083] In an embodiment of the present invention, the maleic anhydride-modified liquid polybutadiene was purchased from Shandong Bojin New Material Technology Co., Ltd., with the product brand name Perken-7017, a molecular weight (Mn) of 2800, and a 1,2-vinyl content of 70%. The MAH grafting rate was 17%, the effective ingredient content was >99.5%, and the appearance and shape were a color-enhanced viscous liquid.

[0084] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by the present invention include 2 to 10 parts of zinc oxide, which can be 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts in the examples.

[0085] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by this invention include 1 to 4 parts of antioxidant, which in the embodiments can be 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, or 4 parts. In this invention, the antioxidant preferably includes at least two of antioxidants 445, 425, MB, and RD. In this invention, the antioxidant includes a first antioxidant and a second antioxidant. The mass fraction of the first antioxidant is preferably 0.5 to 2 parts, more preferably 0.5 parts, 1 part, 1.5 parts, or 2 parts; the mass fraction of the second antioxidant is preferably 0.5 to 2 parts, more preferably 0.5 parts, 1 part, 1.5 parts, or 2 parts. The first antioxidant preferably includes antioxidants 445, 425, MB, or RD. The second antioxidant preferably includes antioxidants 445, 425, MB, or RD. The first antioxidant and the second antioxidant are of different types.

[0086] Based on the mass fraction of the EPDM rubber, the raw materials for preparing the EPDM rubber substrate provided by this invention include 1 to 3 parts of processing aids, which in the examples can be 1 part, 1.5 parts, 2 parts, 2.5 parts, or 3 parts. In this invention, the processing aids preferably include one or more of PEG4000, release agent EXTON L-7, Aflux16, and WB16. When the processing aids are two or more of the above substances, this invention does not have special requirements on the amount of the above substances used.

[0087] In this invention, the method for preparing the EPDM rubber substrate preferably includes the following steps:

[0088] The raw materials for preparing the EPDM rubber substrate are sequentially mixed, discharged, thinned, and sheeted to obtain the EPDM rubber substrate.

[0089] In this invention, the mixing process preferably includes the following steps: pre-passing the EPDM rubber through a thin pass, preferably three times; then sequentially adding a first crosslinking agent, a second crosslinking agent, an antioxidant, zinc oxide, and a processing aid for a first-stage mixing process to obtain a first-stage compound, wherein the temperature of the first-stage compound is preferably 105–110°C; adding reinforcing carbon black to the first-stage compound for a second-stage mixing process to obtain a second-stage compound, wherein the mixing time of the second-stage compound is preferably 4–5 minutes; adding the peroxide vulcanizing agent to the second pinch-up compound for a third-stage mixing process to obtain a third-stage compound, wherein the mixing time of the third-stage compound is preferably 2–3 minutes. The first, second, and third-stage mixing processes are preferably carried out in an internal mixer. Preferably, after discharge, the third-stage compound is placed in an open mill for thin-passing. The number of thin-passing processes is preferably three.

[0090] In this invention, the filling is preferably achieved by pressing the EPDM rubber substrate into the U-shaped groove structure of the sodium-treated polytetrafluoroethylene membrane.

[0091] After obtaining the polytetrafluoroethylene film containing the substrate, the present invention places the polytetrafluoroethylene film containing the substrate in a mold for compression molding and vulcanization to obtain the E+PTFE coated pad.

[0092] In this invention, the molding is preferably performed on a flat vulcanizing machine. The molding vulcanization temperature is preferably 170–190°C, the pressure is preferably 8–15 MPa, and the time is preferably 3–15 min. After the molding vulcanization is completed, excess EPDM rubber burrs are removed from the obtained product to obtain the E+PTFE coated gasket.

[0093] The present invention provides an E+PTFE coated pad prepared by the preparation method described in the above technical solution.

[0094] This invention provides the application of the E+PTFE coated gasket described above as a sealing ring in a plate heat exchanger.

[0095] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0096] Example 1

[0097] This embodiment provides a method for preparing an E+PTFE coated pad, including the following steps:

[0098] (1) Preparation of U-shaped polytetrafluoroethylene film:

[0099] The raw materials for preparing the U-shaped polytetrafluoroethylene (PTFE) membrane are: 100 parts by weight of PTFE, 2 parts by weight of PFA, 8 parts by weight of FEP, and 25 parts by weight of petroleum ether. The PFA is Shandong Dongyue DF-16 series fluororesin, and the FEP is Shandong Dongyue DF-10 series fluororesin.

[0100] The method for preparing a U-shaped polytetrafluoroethylene film includes the following steps;

[0101] 1. Mixing: Mix 100 parts by weight of polytetrafluoroethylene, 2 parts by weight of PFA, 8 parts by weight of FEP, and 25 parts by weight of petroleum ether. Weigh the above raw materials according to the ratio and add them into a container mixer. Stir and mix for 20 minutes at a speed of 30 r / min.

[0102] 2. Molding: The uniformly mixed raw materials are loaded into the corresponding mold for molding. The initial molding pressure is 20 MPa, followed by one venting. Then, the pressure is increased to 35 MPa for molding again. Finally, the pressure is increased to 40 MPa and maintained at this pressure for 10 minutes.

[0103] 3. Sintering: Place the molded blanks into an oven. Slowly increase the oven temperature from room temperature to 250℃ at a rate of 20℃ / h. Hold at this temperature for 2 hours to allow all small molecules to volatilize. Then increase the temperature to 380℃ at a rate of 15℃ / h. Hold at this temperature for 240 minutes, depending on the wall thickness. Finally, slowly decrease the temperature to room temperature at a rate of 30℃ / h.

[0104] 4. Cut the blank into the required size.

[0105] 5. Turn it into a U-shaped diaphragm.

[0106] (2) Sodium treatment is performed on the inside of the U-shaped polytetrafluoroethylene membrane.

[0107] Preparation of sodium naphthalene solution:

[0108] ①Naphthalene kg:Tetrahydrofuran L:Sodium metal kg=5:10:1;

[0109] ② Add tetrahydrofuran to the reactor.

[0110] ③ Slowly add naphthalene while stirring continuously until all the added naphthalene dissolves in the tetrahydrofuran solution.

[0111] ④ Chop the sodium metal into small pieces before adding it to the reactor.

[0112] ⑤ Stir the reactor every 1 to 2 hours, and the reaction time is 10 to 15 hours to obtain sodium naphthalene solution.

[0113] Protect the machined U-shaped PTFE membrane with adhesive tape, then soak it in a prepared sodium naphthalene solution for 10 minutes. Remove the treated PTFE membrane, remove the adhesive tape, and clean it with alcohol. After cleaning, allow the PTFE membrane to air dry before proceeding to the next step.

[0114] (3) Preparation of a polytetrafluoroethylene membrane containing a substrate:

[0115] The inner surface of the U-shaped groove structure of the sodium-treated polytetrafluoroethylene membrane is coated with a resin adhesive. The resin adhesive used in this embodiment includes a rubber component and a solvent component.

[0116] The rubber component comprises the following components in parts by weight: 100 parts by weight of EPDM rubber, 20 parts by weight of carbon black (N990 carbon black), 0.5 parts by weight of antioxidant (BBM), 1.5 parts by weight of peroxide vulcanizing agent (DCP), and 2 parts by weight of crosslinking agent (maleic anhydride liquid polybutadiene, Perken-7017).

[0117] The preparation method of the rubber component includes: mixing the above-mentioned components in the above-mentioned mass parts and then mixing them in an internal mixer; the resulting compound is then passed through a two-roll mill; the resulting rubber compound is cut into small pieces to obtain the rubber component.

[0118] The solvent components are cyclohexane and ethyl acetate, with a volume ratio of 9:1.

[0119] In this embodiment, the mass ratio of the rubber component to the volume ratio of the solvent component in the resin adhesive is 4g:5mL.

[0120] In this embodiment, the rubber component is soaked in the solvent component. After the rubber compound is basically dissolved, it is stirred and homogenized to obtain a resin adhesive (adhesive solution).

[0121] Apply the resin adhesive twice to the U-shaped groove structure side of the sodium-treated polytetrafluoroethylene film to ensure that every part of the U-shaped groove structure is coated with resin adhesive.

[0122] The EPDM rubber substrate used in this invention is specifically composed of the following raw materials in parts by weight: 100 parts EPDM rubber, 75 parts reinforcing carbon black, 3 parts peroxide vulcanizing agent, 2 parts first crosslinking agent, 2 parts second crosslinking agent, 5 parts zinc oxide, 1.2 parts first antioxidant, 1.2 parts second antioxidant, and 2 parts processing aid.

[0123] The raw materials used in this embodiment are: ethylene propylene diene monomer (EPDM) rubber with an ethylene content of 55%, Mooney viscosity (ML1+4, 125℃) of 120, and a third monomer content of 1%. The reinforcing carbon black is N550, the peroxide vulcanizing agent is DCP, the first co-crosslinking agent is zinc acrylate, the second co-crosslinking agent is Perken-7017, the first antioxidant is antioxidant 445, the second antioxidant is antioxidant RD, and the processing aid is mold release agent EXTON L-7.

[0124] The method for preparing the EPDM rubber substrate used in this invention includes the following steps:

[0125] ① Pass the EPDM rubber through a two-roll mill three times and weigh it according to the mass fraction ratio.

[0126] ② Add EPDM rubber, crosslinking agents (first and second crosslinking agents), antioxidants (first and second antioxidants), zinc oxide, and processing aids into a mixer and mix until the temperature reaches 100℃.

[0127] ③ Add reinforcing carbon black and mix for 5 minutes.

[0128] ④ After adding the peroxide vulcanizing agent and mixing for 2 minutes, discharge the glue.

[0129] ⑤ Pass the above rubber compound through a two-roll mill three times.

[0130] ⑥ Adjust the roller gap and sheet the mixed rubber.

[0131] An EPDM rubber substrate is pressed into the U-shaped groove structure of a polytetrafluoroethylene (PTFE) membrane coated with resin adhesive to obtain a PTFE membrane containing the substrate.

[0132] (4) Compression vulcanization

[0133] A polytetrafluoroethylene (PTFE) film containing the substrate is placed into a molding die and subjected to compression molding on a flat vulcanizing machine. Molding temperature: 175℃; Molding pressure: 10MPa (flat vulcanizing machine); Vulcanization time: 5min. Excess EPDM rubber burrs are removed to obtain the E+PTFE coated gasket product.

[0134] A physical image of the E+PTFE-coated pad prepared in this embodiment is shown below. Figure 2 The gray products shown in the exhibition Figure 2 The white product in the example is an E+PTFE coated pad produced from the PTFE membrane in Comparative Example 1.

[0135] Comparative Example 1

[0136] The preparation method is basically the same as that in Example 1, except that:

[0137] The PTFE membrane used in this comparative example is DF-16A, a product of Shandong Dongyue Polymer Materials Co., Ltd., which is obtained by pressing, sintering, turning, and sodium treatment of 100 parts PTFE and 25 parts petroleum ether.

[0138] The adhesive used in this comparative example is Chemlock (205GB);

[0139] The rubber substrate used in this comparative example is ordinary EPDM rubber. The preparation method of ordinary EPDM rubber substrate includes:

[0140] Common EPDM rubber formulation: EPDM Nordel IP 4570 100 parts by weight; Carbon black N660 80 parts by weight; ZnO 5 parts by weight; DCP 3 parts by weight; Paraffin oil 3 parts by weight; Processing aid WB422 parts by weight; Crosslinking aid TAIC 2 parts by weight; PEG4000 2 parts by weight; Antioxidant MB 2 parts by weight; Antioxidant RD 2 parts by weight;

[0141] (1) Equipment preparation: Start the internal mixer and preheat it to 50-60℃.

[0142] (2) Add raw rubber and masticate: Add Nordel IP 4570 (100 parts by weight). Masticate for 30-60 seconds to coat the rotor with rubber.

[0143] (3) Add ingredients: Add ZnO, PEG4000, WB42, paraffin oil, and antioxidants (antioxidant MB and antioxidant RD), and mix for 3 minutes.

[0144] (4) Add carbon black: Add carbon black N660: When the temperature rises to 110-120℃; Add sulfur: Add vulcanizing agent DCP and crosslinking agent TAIC, mix for 1 minute, then discharge the glue and pass through the open mill 3 times, then adjust the roller gap and cool the sheet.

[0145] The specific preparation process of the E+PTFE coated pad in this comparative example is basically the same as that in Example 1 except for the preparation method of the raw materials.

[0146] The compression set properties of the E+PTFE coated pads prepared in Example 1 and the comparative example (tested according to the high temperature A and B methods in national standard GB / T7759.1-2015) are shown in Table 1.

[0147] Table 1. Compression set test results of the E+PTFE coated pads prepared in Example 1 and Comparative Example 1.

[0148]

[0149] As can be seen from the above embodiments, the present invention provides a method for preparing a high-pressure E+PTFE coated gasket for a semi-welded heat exchanger. The E+PTFE coated gasket prepared by the present invention is jointless and solves the problems of low pressure bearing capacity of E+PTFE coated gasket, excessive air trapped between EPDM substrate and PTFE, and weak adhesion between EPDM substrate and PTFE.

[0150] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an E+PTFE coated pad, characterized in that, Includes the following steps: The raw materials for preparing polytetrafluoroethylene (PTFE) resin are sequentially mixed, molded, and sintered to obtain a PTFE film. The PTFE film has a U-shaped groove structure, which is used to fill an EPDM rubber substrate. The PTFE resin material comprises the following raw materials in parts by weight: 90-100 parts PTFE, 1-10 parts organic additives, and 15-25 parts lubricant. The organic additives include perfluoroalkoxy resins and / or fluorinated ethylene propylene copolymers. The inner surface of the U-shaped groove structure of the polytetrafluoroethylene membrane is sodium-treated to obtain a sodium-treated polytetrafluoroethylene membrane. The sodium treatment is carried out using a sodium naphthalene solution. The inner surface of the U-shaped groove structure of the sodium-treated polytetrafluoroethylene (PTFE) membrane is coated with a resin adhesive, and then filled with an EPDM rubber substrate to obtain a PTFE membrane containing the substrate. The resin adhesive comprises a rubber component and a solvent component. The rubber component comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 20-60 parts carbon black, 0.5-3 parts antioxidant, 1.5-6 parts peroxide vulcanizing agent, and 2-10 parts co-crosslinking agent, wherein the co-crosslinking agent is maleic anhydride-modified liquid polybutadiene. The solvent component comprises at least two of cyclohexane, n-heptane, and ethyl acetate. The polytetrafluoroethylene film containing the substrate is placed in a mold for compression molding and vulcanization to obtain the E+PTFE coated pad.

2. The preparation method according to claim 1, characterized in that, The EPDM rubber substrate comprises the following raw materials in parts by weight: 100 parts EPDM rubber, 50-80 parts reinforcing carbon black, 2-10 parts peroxide vulcanizing agent, 2-10 parts first co-crosslinking agent, 1-5 parts second co-crosslinking agent, 2-10 parts zinc oxide, 1-4 parts antioxidant, and 1-3 parts processing aid; the EPDM rubber has a Mooney viscosity ≥80, the first co-crosslinking agent is an acrylate crosslinking aid, and the second co-crosslinking agent is maleic anhydride-modified liquid polybutadiene.

3. The preparation method according to claim 1, characterized in that, The raw materials for preparing the sodium naphthalene solution include naphthalene, tetrahydrofuran, and metallic sodium; the ratio of naphthalene, tetrahydrofuran, and metallic sodium is 4-5 kg: 10-12 L: 1-1.5 kg.

4. The preparation method according to claim 1 or 3, characterized in that, The sodium treatment includes: coating and protecting the outer surface of the polytetrafluoroethylene film, and then immersing it in the sodium naphthalene solution for treatment. The immersion temperature is room temperature and the time is 2 to 10 minutes.

5. The preparation method according to claim 1, characterized in that, The compression molding vulcanization temperature is 170–190℃, the pressure is 8–15 MPa, and the time is 3–15 min.

6. The preparation method according to claim 1, characterized in that, The perfluoroalkoxy resin is polymerized from tetrafluoroethylene and perfluoroalkoxy vinyl ether; the fluorinated ethylene propylene copolymer is copolymerized from tetrafluoroethylene and hexafluoropropylene; the lubricant is petroleum ether; The mixing is carried out under stirring, with the stirring speed being 15-30 r / min and the time being 10-20 min; The molding process includes sequentially performing a first molding, a second molding, and a third molding. The pressure of the first molding is 10–20 MPa. After the first molding is degassed, the second molding is performed. The pressure of the second molding is 25–35 MPa. The pressure of the third molding is 30–40 MPa, and the holding time is 5–10 minutes. The sintering process includes: heating from room temperature to a first temperature at a first heating rate and holding for a first time; then heating from the first temperature to a second temperature at a second heating rate and holding for a second time; and then cooling from the second temperature to room temperature; wherein the first heating rate is 10–20°C / h, the first temperature is 200–250°C, the first holding time is 1–2h, the second heating rate is 10–15°C / h, the second temperature is 350–380°C, the second holding time is 30–240min, and the cooling rate is 10–30°C / h.

7. The preparation method according to claim 1, characterized in that, The antioxidant includes one or more of antioxidant BBM, antioxidant 445, antioxidant MB, and antioxidant RD; the peroxide curing agent includes one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,4-di-tert-butylperoxyisopropylbenzene; the maleic anhydride-modified liquid polybutadiene has a molecular weight of 2000-3000, and the structural formula of the maleic anhydride-modified liquid polybutadiene is as follows: The solvent component contains ethyl acetate, and the volume fraction of ethyl acetate in the solvent component is 10-15%. The mass ratio of the rubber component to the volume ratio of the solvent component is (1-4) g: 5 mL.

8. The preparation method according to claim 2, characterized in that, The ethylene propylene diene monomer (EPDM) rubber contains 40-55% ethylene, has a Mooney viscosity of 80-120, and a third monomer content of 1-10%. The reinforcing carbon black includes one or more of N550, N660, N990, and spray-dried carbon black. The peroxide vulcanizing agent includes one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,4-di-tert-butylperoxyisopropylbenzene. The acrylate crosslinking aid includes zinc acrylate and / or magnesium methacrylate. The maleic anhydride-modified liquid polybutadiene has a molecular weight of 2000-3000, and its structural formula is as follows: The antioxidant includes at least two of antioxidant 445, antioxidant 425, antioxidant MB, and antioxidant RD.

9. The E+PTFE coated pad prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the E+PTFE coated gasket of claim 9 as a sealing ring in a plate heat exchanger.

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