Processing method of MDI fine screen

Abstract

The invention relates to a processing method of an MDI fine screen, which belongs to the technical field of polyurethane screen plates, and comprises the following steps: a conventional pouring step: sealing by 4, 4 '-diaminodiphenylmethane MDA, dispersing in liquid hydroxyl-terminated nitrile rubber, and at room temperature, enabling the liquid to be almost inactive, not to generate gel when being mixed with a prepolymer without heating, and obtaining a liquid with proper viscosity; the closed 4, 4 '-diaminodiphenylmethane MDA can be mixed with the prepolymer at normal temperature without melting, but when the closed 4, 4'-diaminodiphenylmethane MDA is heated to 120 DEG C and uniformly mixed with the NCO-terminated prepolymer, the closed 4, 4 '-diaminodiphenylmethane MDA begins to dissociate, and the dissociated diamine rapidly reacts with the prepolymer to form a tough polyurethane elastomer. And the device is particularly suitable for fine screening products with complex shapes or large areas, low in cost and easy and convenient to operate. The obtained MDI type polyurethane fine screen has the performance similar to that of an MOCA vulcanized elastomer, can be manually operated, and can also be automatically poured by a pouring machine.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane sieve plates, and in particular to a processing method of an MDI fine sieve. Background Art

[0002] Nowadays, polyurethane sieve plates have been widely used in screening operations in many industries such as mining, metallurgy, power plants, and construction. Most of the commonly used polyurethane sieve plates are made of two components such as MDI prepolymer and BDO. When BDO is cured, the system viscosity is high, the demoulding time of the sieve plate is long, the production efficiency is low, and it is inconvenient to use. The room temperature casting elastomer process includes steps such as mixing, pouring, and vacuum degassing, which requires a certain time difference. Due to the high activity of MDA, rapid reaction, and extremely short gel time, the mixing effect of MDA and PU prepolymer is poor. 4,4'-Diaminodiphenylmethane MDA is an aromatic diamine with no steric hindrance of amino groups. It is very active, has poor mixing effect with PU prepolymer, and has an extremely short gel time, and it is impossible to prepare an ideal cast polyurethane elastomer. CN202211003105.3 A method for preparing an MDI wear-resistant sieve plate uses non-ionic polyacrylamide to coat MDA for stabilization and reduce activity. However, it is not applicable to production in large and complex fine screens. The process of fine screen processing is difficult to control, and the cost of polyacrylamide coating is high. In summary, it is necessary to develop a processing method for MDI fine screen. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention aims to provide a method for processing an MDI fine screen.

[0004] A processing method for MDI fine screen comprises conventional pouring steps, namely, preheating the mold to 85-90°C, starting the motor of the mixing head of a RIM machine, pouring into the mold preheated to 115-120°C, heating to 120-130°C for aging for 10-15min, demoulding, and continuing to age at 85-90°C for 12h, and also comprising the following steps: the first step, vacuum dehydration treatment at 120°C for 3-4h in polyether polyol; the second step, taking a mixture of polyether polyol with a molar ratio of -NCO to -OH of 1:2-2.1 and liquefied MDI, adding it into a reaction kettle equipped with a stirring paddle and a thermometer, adding 0.05wt% of the above mixture as a catalyst dibutyltin dilaurate, stirring the prepolymerization reaction at 60°C for 4h, controlling the -N CO% is 3.5% to 3.58%, and it is sealed for standby use; the third step, MDA sealing: by weight fraction, 100 parts of 4,4'-diaminodiphenylmethane are dissolved in 300 to 400 parts of industrial ethanol, heated to 60°C, 100 parts of bromide salt are added to the solution while stirring, and then placed at 60°C for 30 minutes and then cooled to room temperature, filtered, dried at 40°C to constant weight, and then dispersed into liquid terminal hydroxy-nitrile rubber to obtain the sealed MDA; the fourth step, the prepared prepolymer is added to the A component storage tank of the three-component RIM machine, the catalyst is added to the B component tank of the RIM machine, and the sealed MDA is added to the C component tank, and the material temperature is controlled to 30°C to 45°C, wherein the amount of the sealed MDA accounts for 3.4% to 3.5% of the total weight of the system.

[0005] Furthermore, the first step polyether polyol is polytetramethylene ether glycol with a molecular weight of 1950-2050.

[0006] Furthermore, the liquefied MDI is carbodiimide-modified MDI diphenylmethane diisocyanate, and the NCO content of the liquefied MDI is 25-28%.

[0007] Furthermore, the bromide salt in the third step is cadmium bromide or zinc bromide.

[0008] Furthermore, the liquid hydroxy-terminated nitrile rubber in the third step is HTBN-A or HTBN-B.

[0009] RIM is the abbreviation of Reaction Injection Molding, also known as reaction injection molding. RIM machine refers to a molding machine that measures two or more components separately with high-pressure metering devices, enters a mixing head, mixes with high-pressure impact, and then injects them into a mold.

[0010] Beneficial effects of the present invention: The invention discloses a processing method of MDI fine screen, which comprises conventional pouring steps, and is sealed by 4,4'-diaminodiphenylmethane MDA and dispersed in liquid terminal hydroxyl nitrile rubber. At room temperature, it is almost inactive, and no gel will appear when mixed with prepolymer without heating. The liquid with suitable viscosity can be mixed with prepolymer at room temperature without melting. However, when heated to 120°C, it is evenly mixed with terminal NCO group prepolymer, and the sealed 4,4'-diaminodiphenylmethane MDA begins to dissociate, and the free diamine reacts quickly with the prepolymer to form a strong and tough polyurethane elastomer. It is particularly suitable for fine screen products with complex shapes or large areas, with low cost and simple operation. The obtained MDI type polyurethane fine screen has similar performance to MOCA vulcanized elastomer, and can be manually operated or automatically poured by a pouring machine. DETAILED DESCRIPTION

[0011] The present invention is described below with specific examples, but is not intended to be limiting of the present invention. Example 1

[0012] Raw materials: 4,4'-diaminodiphenylmethane solvent from Hehai Chemical in Yancheng; zinc bromide from Tianfu Chemical in Weifang; liquid hydroxy-terminated nitrile rubber HTBN-B from Tianyuan; tetramethylene ether glycol from Mitsubishi PTMG2000; MM103C liquefied MDI carbodiimide-modified MDI diphenylmethane diisocyanate, the NCO content of liquefied MDI is 28%.

[0013] A processing method for MDI fine screen includes conventional pouring steps, namely, preheating the mold to 90°C, starting the motor of the RIM machine mixing head, pouring into the mold preheated to 120°C, heating to 130°C, aging for 15 minutes, demoulding, and continuing to mature at 90°C for 12 hours, and also including the following steps: the first step, vacuum dehydration treatment at 120°C for 4 hours in polyether polyol to dehydrate to a water content of less than 0.04wt%; the second step, taking -NCO and - A mixture of polyether polyol and liquefied MDI with an OH molar ratio of 1:2.1 is added to a reactor equipped with a stirring blade and a thermometer, and 0.05wt% of the catalyst dibutyltin dilaurate is added to the above mixture. The prepolymerization reaction is stirred at 60°C for 4h, and the -NCO% is controlled to be 3.5%, and the mixture is sealed for standby use; Step 3, MDA sealing: Dissolve 100 parts of 4,4′-diaminodiphenylmethane in 400 parts of industrial ethanol by weight and heat to 60°C. Add 100 parts of zinc bromide to the solution under stirring, place it at 60°C for 30 minutes, cool it to room temperature, filter it, dry it at 40°C to constant weight, and disperse it in liquid terminal hydroxy-nitrile rubber to obtain a closed MDA liquid with a solid content of 45%; Step 4, add the prepared prepolymer to the component A storage tank of the three-component RIM machine, add the catalyst to the component B tank of the RIM machine, add the closed MDA to the component C tank, and control the material temperature to 45°C, wherein the amount of closed MDA accounts for 3.5% of the total weight of the system. Example 2

[0014] Yancheng Hehai Chemical Solvent MDA4,4'-diaminodiphenylmethane; Jiaxing Sicheng Chemical Cadmium Bromide; Tianyuan Liquid Hydroxyl-Terminated Nitrile Rubber HTBN-B. Tetramethylene Ether Glycol Mitsubishi PTMG2000. MDI-100LL liquefied MDI is MDI diphenylmethane diisocyanate modified by carbodiimide, and the NCO content of liquefied MDI is 25%.

[0015] A processing method for MDI fine screen comprises conventional pouring steps, namely, preheating the mold to 85°C, starting the motor of the mixing head of a RIM machine, pouring into the mold preheated to 115°C, heating to 120°C, aging for 10 minutes, demoulding, and aging at 85°C for 12 hours, and also comprising the following steps: the first step, vacuum dehydration treatment at 120°C for 3 hours in polyether polyol to dehydrate to a water content of less than 0.04wt%; the second step, taking a mixture of polyether polyol with a molar ratio of -NCO to -OH of 1:2 and liquefied MDI, adding it into a reaction kettle equipped with a stirring paddle and a thermometer, adding 0.05wt% of the above mixture as a catalyst dibutyltin dilaurate, stirring the prepolymerization reaction at 60°C for 4 hours, controlling -N CO% is 3.5%, and it is sealed for use; the third step, MDA sealing: by weight, 100 parts of 4,4′-diaminodiphenylmethane are dissolved in 300 parts of industrial ethanol, heated to 60°C, 100 parts of cadmium bromide are added to the solution under stirring, and then placed at 60°C for 30 minutes and then cooled to room temperature, the product is filtered, dried to constant weight at 40°C, and dispersed in liquid terminal hydroxy-nitrile rubber with a solid content of 45% to obtain the sealed MDA; the fourth step, the prepared prepolymer is added to the A component storage tank of the three-component RIM machine, the catalyst is added to the B component tank of the RIM machine, the sealed MDA is added to the C component tank, and the material temperature is controlled to 30°C, wherein the amount of the sealed MDA accounts for 3.4% of the total weight of the system.

[0016] The MDA wear-resistant polyurethane sieve plates of Examples 1 to 2 were subjected to performance tests. The performance test results are shown in Table 1. Table 1 Performance test results of MDA wear-resistant polyurethane sieve plates of Example 1 and Example 2

[0017] Note: Refer to GB / T33091-2016 polyurethane sieve plate.

Claims

1. A method for processing an MDI fine screen, characterized in that: The method comprises conventional pouring steps, namely, preheating the mold to 85-90°C, starting the motor of the RIM machine mixing head, pouring into the mold preheated to 115-120°C, heating to 120-130°C for aging for 10-15min, demoulding, and continuing to age at 85-90°C for 12h. The method also comprises the following steps: the first step, vacuum dehydration treatment at 120°C for 3-4h in the polyether polyol; the second step, taking a mixture of polyether polyol and liquefied MDI with a molar ratio of -NCO to -OH of 1:2-2.1, adding it to a reaction kettle equipped with a stirring paddle and a thermometer, and adding 0.05wt% of the catalyst dibutyltin dilaurate of the above mixture, stirring the prepolymerization reaction at 60°C for 4h, and controlling the -NCO% to be 3.5 %~3.58%, seal for standby use; Step 3, MDA sealing: by weight fraction, dissolve 100 parts of 4,4'-diaminodiphenylmethane in 300~400 parts of industrial ethanol, heat to 60℃, add 100 parts of bromide salt to the solution while stirring, place it at 60℃ for 30min, cool to room temperature, filter, dry to constant weight at 40℃, and then disperse it in liquid terminal hydroxy-butadiene nitrile rubber to obtain the sealed MDA; Step 4, add the prepared prepolymer to the A component storage tank of the three-component RIM machine, add the catalyst to the B component tank of the RIM machine, add the sealed MDA to the C component tank, control the material temperature to 30℃~45℃, wherein the amount of the sealed MDA accounts for 3.4%~3.5% of the total weight of the system.

2. The method for preparing the MDA wear-resistant screen plate according to claim 1, characterized in that: The first step polyether polyol is polytetramethylene ether glycol with a molecular weight of 1950-2050.

3. The method for preparing the MDA wear-resistant screen plate according to claim 1, characterized in that: The liquefied MDI is carbodiimide-modified MDI diphenylmethane diisocyanate, and the NCO content of the liquefied MDI is 25-28%.

4. The method for preparing the MDA wear-resistant screen plate according to claim 1, characterized in that: The third-step bromide salt is cadmium bromide or zinc bromide.

5. The method for preparing the MDA wear-resistant screen plate according to claim 1, characterized in that: The liquid hydroxy-terminated nitrile rubber in the third step is liquid hydroxy-terminated nitrile rubber HTBN-A or liquid hydroxy-terminated nitrile rubber HTBN-B.

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