Ethylene-propylene-diene monomer composition and preparation method and application of rubber compound of ethylene-propylene-diene monomer composition

Abstract

The invention belongs to the technical field of rubber gaskets, and particularly relates to an ethylene propylene diene monomer composition and a preparation method and application of a rubber compound of the ethylene propylene diene monomer composition. The ethylene propylene diene monomer composition provided by the invention comprises the following components in parts by weight: 100 parts of ethylene propylene diene monomer, 50-80 parts of reinforcing carbon black, 2-10 parts of a peroxide vulcanizing agent, 2-10 parts of a first assistant crosslinker, 1-5 parts of a second assistant crosslinker, 2-10 parts of zinc oxide, 1-4 parts of an anti-aging agent and 1-3 parts of a processing aid. The compression set performance of the EPDM rubber composition provided by the invention is remarkably improved, the defects of poor elasticity and poor pressure bearing are overcome, and when the EPDM rubber composition is used as an EPDM base material in an E + PTFE coated pad, the rebound resilience and the pressure bearing capacity of the E + PTFE coated pad are effectively improved, and the service life of the EPDM rubber composition is prolonged. Therefore, in the using process, the rebound speed of the E + PTFE coating pad can meet the requirements of pressure and temperature fluctuation impact, and leakage is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rubber gaskets, and particularly relates to a three-element ethylene propylene rubber composition and a preparation method and application of a rubber compound thereof. BACKGROUND

[0002] Plate heat exchanger is a kind of high-efficiency energy-saving heat exchange equipment, which is widely used in production and life. It is usually made of many thin plates punched with corrugations arranged at a certain interval, sealed by gaskets around, and overlapped and compressed by frames and compression screws. The four corner holes of the plate and the gasket can form fluid distribution pipes and collection pipes, and reasonably separate the cold and hot fluids, so that they flow in the flow channels on both sides of each plate respectively and exchange heat through the plate.

[0003] Plate heat exchanger is widely used due to its high heat exchange efficiency. However, the pressure-bearing capacity of plate heat exchanger is limited, and some chemical media have a large corrosion on rubber material sealing gaskets, which limits the use of plate heat exchanger. The gasket coated with polytetrafluoroethylene (PTFE) material on the outside of the EPDM base material (PTFE / EPDM composite gasket, E+PTFE coated gasket) can resist almost all media, but the elasticity of the EPDM base material is limited after being coated with PTFE material on the outside, resulting in low pressure-bearing capacity of the plate heat exchanger (generally can bear pressure to 1.3 MPa, and the highest does not exceed 1.6 MPa). Therefore, the EPDM base material of the E+PTFE coated gasket is limited by the current EPDM performance, and leakage occurs due to poor resilience during on-site pressure and temperature fluctuations or during start-up and shutdown. SUMMARY

[0004] The present application provides a kind of three-element ethylene propylene rubber composition and the preparation method and application of rubber compound thereof, and the method provided by the present application overcomes the defects of poor elasticity and poor pressure-bearing capacity of the EPDM base material of E+PTFE coated gasket, and the resilience speed of E+PTFE coated gasket during use can meet the requirements of pressure and temperature fluctuation impact, thereby avoiding leakage.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] The present application provides a kind of three-element ethylene propylene rubber composition, which comprises the following mass fractions of raw materials: 100 parts of three-element ethylene propylene rubber, 50-80 parts of reinforcing carbon black, 2-10 parts of peroxide vulcanizing agent, 2-10 parts of first crosslinking aid, 1-5 parts of second crosslinking aid, 2-10 parts of zinc oxide, 1-4 parts of antioxidant, and 1-3 parts of processing aid;The Mooney viscosity of the three-element ethylene propylene rubber is ≥80, the first crosslinking aid is an acrylic acid salt crosslinking aid, and the second crosslinking aid is a maleic anhydride liquid polybutadiene.

[0007] Preferably, the ethylene content of the EPDM rubber is 40-55%, the Mooney viscosity is 80-120, and the third monomer content is 1-10%.

[0008] Preferably, the reinforcing carbon black includes one or more of N550, N660, N990, and fumed carbon black.

[0009] Preferably, the peroxide curing agent 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).

[0010] Preferably, the acrylic salt crosslinking coagent includes zinc acrylate and / or magnesium methacrylate.

[0011] Preferably, the molecular weight of the maleated liquid polybutadiene is 2000-3000, and the maleated liquid polybutadiene has the following structural formula:

[0012]

[0013] Preferably, the antioxidant includes at least two of antioxidant 445, antioxidant 425, antioxidant MB, and antioxidant RD.

[0014] Preferably, the antioxidant includes a first antioxidant and a second antioxidant, the mass fraction of the first antioxidant is 0.5-2 parts, and the mass fraction of the second antioxidant is 0.5-2 parts.

[0015] The present application provides a method for preparing the rubber compound of the EPDM rubber composition, including the following steps:

[0016] The raw materials for preparing the EPDM rubber composition are sequentially mixed, deformed, thin-passed, and sheeted to obtain the rubber compound of the EPDM rubber composition.

[0017] The present application provides an application of the rubber compound of the EPDM rubber composition or the rubber compound prepared by the method to a sealing gasket.

[0018] The present application provides a kind of ethylene propylene terpolymer composition, including the following mass fraction of raw materials: ethylene propylene terpolymer 100 parts, reinforcing carbon black 50~80 parts, peroxide curing agent 2~10 parts, first auxiliary crosslinking agent 2~10 parts, second auxiliary crosslinking agent 1~5 parts, zinc oxide 2~10 parts, antioxidant 1~4 parts, processing aid 1~3 parts;The Mooney viscosity of the ethylene propylene terpolymer is ≥80, the first auxiliary crosslinking agent is acrylic acid salt crosslinking aid, and the second auxiliary crosslinking agent is maleic anhydride liquid polybutadiene. DETAILED DESCRIPTION

[0019] The present application provides a kind of ethylene propylene terpolymer composition, including the following mass fraction of raw materials: ethylene propylene terpolymer 100 parts, reinforcing carbon black 50~80 parts, peroxide curing agent 2~10 parts, first auxiliary crosslinking agent 2~10 parts, second auxiliary crosslinking agent 1~5 parts, zinc oxide 2~10 parts, antioxidant 1~4 parts, processing aid 1~3 parts;The Mooney viscosity of the ethylene propylene terpolymer is ≥80, the first auxiliary crosslinking agent is acrylic acid salt crosslinking aid, and the second auxiliary crosslinking agent is maleic anhydride liquid polybutadiene.

[0020] In the present application, all raw materials / components are commercially available products well known to those skilled in the art unless otherwise specified.

[0021] The raw material for preparing the EPDM composition provided by the present application comprises 100 parts of EPDM in terms of mass fraction. In the present application, the content of ethylene in the EPDM is preferably 40-55%, more preferably 45-50%. The Mooney viscosity (ML1+4, 125°C) of the EPDM is preferably 80-120, more preferably 90-110. The content of the third monomer in the EPDM is preferably 1-10%, more preferably 2-8%.

[0022] The raw material for preparing the EPDM composition provided by the present application comprises 50-80 parts of reinforcing carbon black in terms of mass fraction of the EPDM, which can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts or 80 parts in the examples. In the present application, the reinforcing carbon black preferably comprises one or more of N550, N660, N990 and spray carbon black. In the specific examples of the present application, the spray carbon black can be SP500 carbon black and / or SP700 carbon black produced by Jiangxi Heicat Carbon Black Co., Ltd.

[0023] The raw material for preparing the EPDM composition provided by the present application comprises 2-10 parts of peroxide vulcanizing agent in terms of mass fraction of the EPDM, which can be 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts in the examples. In the present application, the peroxide vulcanizing agent preferably comprises one or more of dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD) and 1,4-bis-tert-butylperoxyisopropylbenzene (BIPB).

[0024] The raw material for preparing the EPDM composition provided by the present application comprises 2-10 parts of first crosslinking aid in terms of mass fraction of the EPDM, which can be 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts in the examples. In the present application, the first crosslinking aid is an acrylic acid salt crosslinking aid. The acrylic acid salt crosslinking aid preferably comprises zinc acrylate and / or magnesium methacrylate.

[0025] The raw material for preparing the EPDM composition provided by the present application comprises 1-5 parts of second crosslinking aid in terms of mass fraction of the EPDM, which can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts in the examples.

[0026] In the present application, the molecular weight (Mn) of the maleic anhydride liquid polybutadiene is preferably 2000-3000, and the structural formula of the maleic anhydride liquid polybutadiene is as follows:

[0027]

[0028] In the embodiment of the present application, the maleic anhydridized liquid polybutadiene is purchased from Shandong Bojin New Material Technology Co., Ltd., the product model is Perken-7017, the molecular weight (Mn) is 2800, the 1,2-vinyl content is 70%, the MAH grafting rate is 17%, the effective ingredient content is > 99.5%, and the appearance and shape are color-increasing viscous liquid.

[0029] In the embodiment of the present application, the mass fraction of the above-mentioned processing aid is preferably 1-3 parts, more preferably 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts.

[0030] In the embodiment of the present application, the mass fraction of the above-mentioned processing aid is preferably 1-3 parts, more preferably 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts.

[0031] In the embodiment of the present application, the mass fraction of the above-mentioned processing aid is preferably 1-3 parts, more preferably 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts.

[0032] The present application provides a mixing rubber preparation method of the above-mentioned ethylene-propylene-diene rubber composition, including the following steps:

[0033] The above-mentioned raw materials of the ethylene-propylene-diene rubber composition are sequentially mixed, discharged, thin-passed and sheeted to obtain the mixing rubber of the ethylene-propylene-diene rubber composition.

[0034] In the present application, the mixing preferably comprises the following steps: pre-thinning the EPDM rubber, the number of pre-thinning preferably being 3 times; then sequentially adding the first and second auxiliary cross-linking agents, the anti-aging agent, the zinc oxide and the processing aid to carry out the first stage mixing to obtain the first stage mixed rubber, the temperature of the first stage mixed rubber preferably being 105-110 ℃; adding the reinforcing carbon black to the first stage mixed rubber to carry out the second stage mixing to obtain the second stage mixed rubber, the time of the second stage mixing preferably being 4-5 min; adding the peroxide vulcanizing agent to the second stage mixed rubber to carry out the third stage mixing to obtain the third stage mixed rubber, the time of the third stage mixing preferably being 2-3 min, and the first, second and third stage mixing preferably being carried out in an internal mixer. The third stage mixed rubber is preferably discharged and then placed in an open mill to carry out thinning. The number of thinning preferably is 3 times.

[0035] The present application provides the application of the EPDM rubber composition or the mixed rubber prepared by the preparation method in a sealing gasket.

[0036] In the present application, the sealing gasket preferably is an E+PTFE coated gasket, and the E+PTFE coated gasket is preferably applied to a plate heat exchanger.

[0037] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0038] Example 1

[0039] The present application provides an EPDM rubber composition, specifically the following mass fractions of preparation raw materials: EPDM rubber 100 parts, reinforcing carbon black 75 parts, peroxide vulcanizing agent 3 parts, first auxiliary cross-linking agent 2 parts, second auxiliary cross-linking agent 2 parts, zinc oxide 5 parts, first anti-aging agent 1.2 parts, second anti-aging agent 1.2 parts, and processing aid 2 parts.

[0040] The preparation raw materials used in this example are as follows: the EPDM rubber has an ethylene content of 55%, a 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 auxiliary cross-linking agent is zinc acrylate, the second auxiliary cross-linking agent is Perken-7017, the first anti-aging agent is anti-aging agent 445, the second anti-aging agent is anti-aging agent RD, and the processing aid is release agent EXTON L-7.

[0041] The present application provides a preparation method of the mixed rubber of the EPDM rubber composition, comprising the following steps:

[0042] ① The ethylene-propylene-diene rubber was thin passed 3 times on an open mill, and weighed according to the mass fraction ratio.

[0043] ② The ethylene-propylene-diene rubber, the auxiliary crosslinking agent (the first auxiliary crosslinking agent and the second auxiliary crosslinking agent), the antioxidant (the first antioxidant and the second antioxidant), zinc oxide, and the processing aid were added into the internal mixer, and mixed until the temperature reached 100℃.

[0044] ③ The reinforcing carbon black was added, and mixed for 5 min.

[0045] ④ The peroxide vulcanizing agent was added, mixed for 2 min, and then the rubber was discharged.

[0046] ⑤ The above rubber was thin passed 3 times on an open mill.

[0047] ⑥ The roll gap was adjusted, and the mixed rubber was sheeted.

[0048] Test Example:

[0049] The mechanical properties of the ethylene-propylene-diene rubber composition provided by Example 1 and the ordinary ethylene-propylene rubber material were analyzed, and the results are shown in Tables 1 and 2. The compression permanent deformation performance (according to the high temperature A method and B method test in GB / T 7759.1-2015), hardness, tensile strength, elongation at break, tear strength, and 100% modulus were tested according to the following methods: a) Tensile strength and elongation at break according to GB / T 528; b) Tear strength according to GB / T 529; c) Hardness according to GB / T 531.1, GB / T 531.2, or IRHD measured according to GB / T 6031 method N; d) 100% modulus according to GB / T 528; and compression permanent deformation (the data corresponding to compression set-25% in Table 1) according to the high temperature A method and B method test in GB / T 7759.1-2015. The vulcanization conditions in Table 1 are as follows: vulcanization temperature: 175℃; pressure: 10 MPa; and vulcanization time: 5 min.

[0050] Table 1 Performance test results of the ethylene-propylene-diene rubber composition provided by Example 1

[0051]

[0052] The preparation method of the ordinary ethylene-propylene rubber material in Table 1 includes:

[0053] The ordinary ethylene-propylene rubber formula is as follows: ethylene-propylene-diene rubber Nordel IP 4570 100 parts by mass; carbon black N660 80 parts by mass; ZnO 5 parts by mass; dicumyl peroxide (DCP) 3 parts by mass; paraffin oil 3 parts by mass; processing aid WB422 parts by mass; crosslinking aid TAIC 2 parts by mass; PEG4000 2 parts by mass; antioxidant MB 2 parts by mass; and antioxidant RD 2 parts by mass.

[0054] (1) Equipment preparation: start the internal mixer and preheat to 50-60℃.

[0055] (2) Add raw rubber plasticizing: add Nordel IP 4570 (100 parts by mass). Plasticize for 30-60 seconds to cover the rotor with rubber.

[0056] (3) Add small materials: add ZnO, PEG4000, WB42, paraffin oil, anti-aging agents (anti-aging agent MB and anti-aging agent RD), and mix for 3 min.

[0057] (4) Add carbon black: add carbon black N660: when the temperature rises to 110-120℃; add sulfur: add vulcanizing agent DCP and co-crosslinking agent TAIC, mix for 1 min, then adjust the roll gap and cool the sheet after 3 times of thin pass on the mill.

[0058] As can be seen from Table 1, by optimizing the cooperation between the prepared materials in the formulation of the ethylene-propylene-diene rubber composition, mainly the interaction between the high Mooney viscosity ethylene-propylene rubber raw rubber, the reinforcing carbon black, the first co-crosslinking agent and the second co-crosslinking agent, and the peroxide vulcanizing agent, the ethylene-propylene-diene rubber composition obtained has excellent mechanical properties. According to the data in Table 1, the most significant improvement in the physical and mechanical properties of the ethylene-propylene-diene rubber composition provided by the present application is the compression set performance (tested according to the high temperature A method and B method in the national standard GB / T7759.1-2015). Therefore, the E+PTFE coated pad produced by using the ethylene-propylene-diene rubber composition provided by the present application has improved resilience and significantly improved pressure bearing capacity.

[0059] Example 2

[0060] The same as Example 1, except that the ethylene-propylene-diene rubber is 100 parts, the reinforcing carbon black is 50 parts, the peroxide vulcanizing agent is 2 parts, the first co-crosslinking agent is 2 parts, the second co-crosslinking agent is 1 part, the zinc oxide is 2 parts, the first anti-aging agent is 0.5 parts, the second anti-aging agent is 0.5 parts, and the processing aid is 1 part. The mechanical properties of the ethylene-propylene-diene rubber composition provided by the example are similar to those of Example 1.

[0061] Example 3

[0062] The same as Example 1, except that the ethylene-propylene-diene rubber is 100 parts, the reinforcing carbon black is 60 parts, the peroxide vulcanizing agent is 5 parts, the first co-crosslinking agent is 5 parts, the second co-crosslinking agent is 3 parts, the zinc oxide is 8 parts, the first anti-aging agent is 1 part, the second anti-aging agent is 1 part, and the processing aid is 2 parts. The mechanical properties of the ethylene-propylene-diene rubber composition provided by the example are similar to those of Example 1.

[0063] Example 4

[0064] An E+PTFE coated gasket was prepared by using the EPDM base material provided in Example 1 in the E+PTFE coated gasket. The specific preparation method included: ① The rubber compound obtained in Example 1 was extruded into a semi-finished rubber strip of the required size on an extruder. ② The semi-finished rubber strip was filled into a treated PTFE film (the treated PTFE film was a PTFE film coated with an adhesive and then dried, the adhesive was KEMLOK adhesive 205GB, and the PTFE film used in this example was DF-16A produced by Shandong Dongyue High Polymer Material Co., Ltd., which was obtained by pressing-sintering-turning-sodium treatment of PTFE 100 parts and 25 parts of petroleum ether). ③ The mold was heated on a flat vulcanizing machine to the vulcanization temperature (175°C). ④ The mold was vulcanized on a flat vulcanizing machine. (Vulcanization process: temperature, 175°C; time, 5 min; pressure, 10 MPa). ⑤ After removing the burrs, the required product was obtained.

[0065] An ordinary E+PTFE coated gasket was prepared by using the ordinary EPDM in Table 1 as the EPDM base material in the E+PTFE coated gasket.

[0066] The compression set performance of the E+PTFE coated gasket prepared in this example (according to the high temperature A method and B method test in the national standard GB / T7759.1-2015) was tested, and the test results are shown in Table 2.

[0067] Table 2 Test results of the compression set performance of the E+PTFE coated gasket prepared in Example 4

[0068]

[0069] As can be seen from Table 2, the most important performance of the E+PTFE coated gasket is the compression set, and the compression set of the E+PTFE coated gasket prepared by improving the base material is significantly improved compared with the ordinary EPDM produced by the E+PTFE coated gasket before the improvement.

[0070] Comparative Example 1

[0071] The same as Example 1, except that the "first auxiliary crosslinking agent 2 parts, second auxiliary crosslinking agent 2 parts" in Example 1 was replaced by "first auxiliary crosslinking agent 4 parts".

[0072] Comparative Example 2

[0073] The same as Example 1, except that the "first auxiliary crosslinking agent 2 parts, second auxiliary crosslinking agent 2 parts" in Example 1 was replaced by "second auxiliary crosslinking agent 4 parts".

[0074] 100 parts of EPDM rubber, 75 parts of reinforcing carbon black, 3 parts of peroxide vulcanizing agent, 2 parts of first crosslinking agent, 2 parts of second crosslinking agent, 5 parts of zinc oxide, 1.2 parts of first antioxidant, 1.2 parts of second antioxidant, and 2 parts of processing aid.

[0075] Comparative Example 3

[0076] It is basically the same as Example 1, except that the peroxide vulcanizing agent in Example 1 is adjusted from 3 parts to 1.5 parts.

[0077] Comparative Example 4

[0078] The process is basically the same as in Example 1, except that "2 parts of the first crosslinking agent and 2 parts of the second crosslinking agent" in Example 1 is replaced with "0 parts of the first crosslinking agent and 0 parts of the second crosslinking agent".

[0079] Table 3 shows the performance test results of the EPDM rubber sheet products prepared in the examples and comparative examples.

[0080]

[0081] As can be seen from the above embodiments, this invention optimizes the formulation method of EPDM rubber, including the types and mass ratios of raw materials. Furthermore, the first and second co-crosslinking agents in this invention have different roles in the formulation, each with its own focus: the maleic anhydride-modified liquid polybutadiene co-crosslinking agent can undergo esterification with the oxygen-containing polar groups on the surface of the PTFE membrane, and can also perform free radical crosslinking with EPDM rubber under the action of a peroxide vulcanizing agent, which helps the adhesion between the rubber substrate and the PTFE membrane. The double bonds in the zinc acrylate molecule can undergo free radical addition or crosslinking reactions with the EPDM rubber molecular chains, while simultaneously generating ionic crosslinking bonds within the vulcanized rubber, greatly improving the physical and mechanical properties of the rubber. The EPDM rubber composition obtained by this invention significantly improves the compression set performance, overcoming the defects of poor elasticity and poor pressure resistance. When used as the EPDM base material in E+PTFE-coated pads, the resilience and pressure resistance of the E+PTFE-coated pads are improved. Thus, the rebound speed of the E+PTFE-coated pads can meet the requirements of pressure and temperature fluctuation impacts during use, thereby avoiding leakage.

[0082] 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 intent, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A EPDM rubber composition, characterized in that, The preparation materials include the following parts by weight: 100 parts of EPDM rubber, 50-80 parts of reinforcing carbon black, 2-10 parts of peroxide vulcanizing agent, 2-10 parts of first co-crosslinking agent, 1-5 parts of second co-crosslinking agent, 2-10 parts of zinc oxide, 1-4 parts of antioxidant, and 1-3 parts of 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.

2. The EPDM rubber composition according to claim 1, 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%.

3. The EPDM rubber composition according to claim 1, characterized in that, The reinforcing carbon black includes one or more of N550, N660, N990, and spray-dried carbon black.

4. The EPDM rubber composition according to claim 1, characterized in that, 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.

5. The EPDM rubber composition according to claim 1, characterized in that, The acrylate crosslinking aids include zinc acrylate and / or magnesium methacrylate.

6. The EPDM rubber composition according to claim 1, characterized in that, The maleic anhydride-modified liquid polybutadiene has a molecular weight of 2000-3000, and its structural formula is as follows:

7. The EPDM rubber composition according to claim 1, characterized in that, The antioxidant includes at least two of antioxidant 445, antioxidant 425, antioxidant MB, and antioxidant RD.

8. The EPDM rubber composition according to claim 1 or 7, characterized in that, The antioxidant includes a first antioxidant and a second antioxidant, wherein the first antioxidant is present in a mass fraction of 0.5 to 2 parts and the second antioxidant is present in a mass fraction of 0.5 to 2 parts.

9. A method for preparing the compound of the EPDM rubber composition according to any one of claims 1 to 8, characterized in that, Includes the following steps: The raw materials for preparing the EPDM rubber composition are sequentially mixed, discharged, thin-passed, and sheeted to obtain the EPDM rubber compound.

10. The use of the EPDM rubber composition according to any one of claims 1 to 8 or the compound prepared by the preparation method according to claim 9 in sealing gaskets.

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