Preparation method of adhesive A

Abstract

The invention discloses a preparation method of an adhesive A. The preparation method comprises the following steps: step 1, mixing a centrifugal mother solution, a formaldehyde solution, methanol and melamine, adding liquid caustic soda to adjust and maintain the pH value to be 8-9, and heating and preserving heat while stirring; 2, after heat preservation is finished, quantitatively feeding materials at the bottom of the reaction kettle into a centrifugal machine, filtering out a large amount of mother liquor, and preserving heat of the mother liquor for later use; putting the solid intermediate wet material into a reaction kettle; 3, methanol is added for an etherification reaction; 4, after the etherification reaction is finished, adding alkali liquor to adjust the pH value to be greater than or equal to 9; and distilling and filtering to obtain a product. In the hydroxylation process, methanol is used for replacing part of a reaction solvent to reduce the water content of a centrifugal material, and a corresponding amount of methanol is used for etherification reaction according to the water content in the material and heating decrement, so that the drying process of an intermediate HMM in a two-step process is reduced, the synthesis process period is shortened, and the production cost is reduced. The environmental pollution caused by HMM drying is avoided; and meanwhile, the potential safety hazard risk of the process is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemicals, and in particular relates to a method for preparing an adhesive A. Background Art

[0002] The information disclosed in this background technology section is only intended to increase some understanding of the overall background of the invention, and should not be necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in this field.

[0003] Adhesive A is a methanol-etherified melamine formaldehyde resin. This product is a mixture of monomers, dimers, trimers and polymers. The monomer molecule is 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine. The molecular weight of the polymer will increase with the degree of polymerization. It is commonly called amino resin in the industry. It is a very important type of methanol-etherified melamine formaldehyde resin among amino resins. This resin developed rapidly abroad in the 1960s and has accounted for a large proportion of melamine resins in the United States. For example, in 1985, the consumption of melamine resins for coatings in the United States was 38,000 tons, of which methanol-etherified resins accounted for 70%. Since the mid-1980s, melamine resins in my country have entered a stage of sustained and comprehensive development, especially since Sichuan Chemical General Plant introduced melamine production equipment from the Netherlands, the production of melamine has increased rapidly. However, except for the butanol etherified melamine formaldehyde resin, which has been mature for a long time, the high etherification degree methanol etherified melamine formaldehyde resin (referred to as adhesive A) is still in the research stage. With the development of my country's coil steel industry and car industry and the increasing attention to environmental protection, the development and research of high etherification degree methanol etherified melamine formaldehyde resin has become an important topic in the field of coating research.

[0004] At present, most of the preparation methods of adhesive A use formaldehyde and melamine to react to generate an intermediate HMM, then filter and dry the intermediate, and then etherify the treated HMM with methanol to obtain adhesive A. Because the reaction system contains a large amount of water, the degree of etherification will be reduced, resulting in unqualified products. Therefore, a simple process, a green and environmentally friendly process, and a high-yield preparation method for highly methylated melamine formaldehyde resin are still important research directions for those skilled in the art. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for preparing an adhesive A, so as to achieve the purpose of simple production process, easy operation, energy saving, green environmental protection, and reduction of three waste emissions.

[0006] The technical solution adopted by the present invention is as follows: The present invention provides a method for preparing an adhesive A, comprising the following steps: Step 1: Mix the centrifuged mother liquor, formaldehyde solution, methanol and melamine, control the temperature to 80-90°C, add liquid alkali to control the pH to 7-8, keep the temperature for reaction, and then start cooling, control the temperature to 15°C-20°C per hour, stop cooling after cooling to 35°C, and the reaction is completed; the molar ratio of formaldehyde to melamine in the reaction material is 7.3-7.5:1, and the molar ratio of water to methanol in the reaction material is 5.2-5.4:1; Step 2: After the reaction is completed, the materials at the bottom of the reactor are quantitatively fed into the centrifuge to filter out the mother liquor, and the mother liquor is centrifuged and temperature controlled at 70-90°C for standby use; the solid material after centrifugation is sent for inspection, and the weight of the solid material is determined as M1, and the water content V1 (w / w), methanol content V2 (w / w) and heating loss V3 (w / w) in the solid material are determined; Step 3: Add the solid material and methanol after centrifugation into the etherification reaction vessel. The amount of solid material M1 and the amount of methanol M2 after centrifugation are calculated according to the following formula: M2=(1-V3)×M1×32.04×20÷306.43+M1×(4V1-V2); Step 4: After the feeding is completed, the temperature in the etherification reaction system is controlled to 50-55° C., and hydrochloric acid is added to the reaction system to adjust and maintain the pH value at 3-4 to carry out the etherification reaction; Step 5: After the etherification reaction is completed, add alkali solution to adjust the pH to ≥ 8; obtain the product adhesive A through distillation and filtration.

[0007] In the present invention, in the step 1, the centrifugal mother liquor is the centrifugal mother liquor obtained in step 2, and the centrifugal mother liquor obtained in step 2 can enter the next step 1 for preparing adhesive A.

[0008] In the present invention, in step 1, the reaction material refers to a mixture of centrifuged mother liquor, formaldehyde solution, methanol and melamine.

[0009] Preferably, in step 1, the hydroxylation reaction temperature is 85° C.; the molar ratio of formaldehyde to melamine in the reaction material is 7.4:1, and the molar ratio of water to methanol in the reaction material is 5.3:1; and the amount of centrifuged mother liquor is 3.0-3.2 times the mass of melamine.

[0010] Preferably, in step 1, the mass fraction of the formaldehyde solution is 55%.

[0011] Preferably, in step 1, the insulation reaction time is 0.5 hours.

[0012] Preferably, in step 1, during the cooling process, the reaction system is cooled using a circulating water cooling system.

[0013] Preferably, in step 2, the temperature of the centrifuged mother liquor is controlled at 80° C. by steam condensation water.

[0014] Preferably, in step 4, the etherification reaction temperature is controlled at 53°C.

[0015] Preferably, in step 4, the etherification reaction time is 1 hour.

[0016] Preferably, in step 5, the vacuum degree of the distillation process is controlled to be above -0.096, and the distillation temperature is controlled to be 115°C-125°C.

[0017] The initial reaction of the present invention: a method for preparing an adhesive A, the steps are as follows: Step 1: add melamine, formaldehyde solution and methanol to a hydroxylation reaction container, start stirring and heating, adjust the pH to 8-9 with liquid alkali when the temperature rises to 80-90°C, start cooling the materials in the hydroxylation reaction container with circulating water after the reaction is kept warm, control the temperature drop within 15-20°C per hour, stop cooling after the temperature drops to 35°C, and the hydroxylation reaction is completed in 2.9 hours; the weight ratio of the melamine, formaldehyde solution and methanol is: 1: (5-5.5): (0.7-0.8); the mass fraction of the formaldehyde solution is 55%; Step 2: After the reaction is completed, centrifugal filtration is performed to obtain the initial centrifugal mother liquor and solid material (filter cake). The centrifugal mother liquor is kept at 70-90°C for standby use. The filter cake is sent for inspection and weighed as M1. The water content V1, methanol content V2 and heating loss V3 in the filter cake are measured and transferred to the etherification reaction vessel; Step 3: Add the solid material and methanol after centrifugation into the etherification reaction vessel. The amount of solid material M1 and the amount of methanol M2 after centrifugation are calculated according to the following formula: M2=(1-V3)×M1×32.04×20÷306.43+M1×(4V1-V2); Step 4: After the feeding is completed, the temperature in the etherification reaction system is controlled to 50-55° C., and hydrochloric acid is added to the reaction system to adjust and maintain the pH value at 3-4 to carry out the etherification reaction; Step 5: After the etherification reaction is completed, add alkali solution to adjust the pH to ≥ 8; obtain the product adhesive A through distillation and filtration.

[0018] In the present invention, heating loss refers to the mass lost by a material during the heating process, which is usually caused by the evaporation or decomposition of water, volatile components, etc. in the material at high temperature.

[0019] Reaction mechanism and beneficial effects of the present invention: In step 1, the centrifugal mother liquor used is the centrifugal mother liquor after the temperature is controlled at 70-90°C by steam condensation water (90°C-100°C) in step 2, which can greatly reduce the amount of steam used for material insulation reaction, greatly shorten the time used for material heating, and is conducive to temperature control, effectively avoiding excessive heating causing violent product reaction, thereby increasing by-products; during the hydroxylation reaction, the reaction material is cooled by circulating water, and the effect of intermediate precipitation, crystallization and granulation is achieved by slowly controlling the cooling rate of the reaction material; during the hydroxylation reaction, methanol is added to replace part of water as the reaction solvent to reduce the water content of the wet material after centrifugation, effectively reduce the amount of methanol input in the etherification reaction process, and improve the unit yield; in step 2, the mother liquor filtered in the centrifuge can be used in the next preparation of adhesive A, that is, as a solvent for the hydroxylation reaction, and also provides formaldehyde raw material, reducing the input of raw material formaldehyde; by calculating the moisture content and methanol content in the intermediate wet material during the centrifugation process, the optimal range of methanol dosage is determined to reduce excessive use of raw material methanol; Calculate the dosage ratio of 55% formaldehyde and methanol required for the complete recycling of the mother liquor, so as to achieve the reuse of excess formaldehyde in the mother liquor and the complete recycling of wastewater, effectively reducing the excessive consumption of raw materials and the generation of three wastes; in step 3, after determining the feed amount of centrifugal wet material, the feed amount of methanol can be determined according to the formula M2=(1-V3)×M1×32.04×20÷306.43+M1×(4V1-V2), so as to avoid the methanol feed ratio caused by fluctuations in the moisture and methanol content of each batch of wet material after centrifugation. The error is eliminated, and the difference between product batches is effectively controlled. In step 5, the water content of the distilled mother liquor is detected online during the negative pressure distillation process. The distilled liquid with a water content of <2% in the early stage can be used as the etherification raw material for the next batch, and the distilled liquid with a water content of ≥2% is rectified to purify the distilled liquid with methanol for reuse, thereby greatly reducing the amount of mother liquor distillation, thereby reducing steam consumption. After the distillation is completed, the filtered liquid is the product adhesive A, and the filter cake is sodium chloride waste salt, which is sent to the solid waste treatment workshop for treatment.

[0020] The present invention uses part of methanol to replace water as the solvent for the hydroxylation reaction, thereby reducing the water content in the centrifugal wet material, canceling the drying process of the centrifugal wet material, shortening the method of continuously centrifuging the intermediate into the etherification kettle instead of filtering and drying the intermediate and then etherifying, reducing the drying process of the intermediate HMM (hexahydroxymethyl melamine) in the two-step process, shortening the synthesis process cycle, avoiding environmental pollution caused by HMM drying, and reducing the risk of process safety hazards; the methylated melamine formaldehyde resin obtained by the present invention has a controllable degree of etherification, a colorless, clear and transparent appearance, a low free formaldehyde content, and a low batch quality difference. It is used in combination with a methylene acceptor to bond rubber to skeleton materials such as steel wire. The method of the present invention overcomes the cumbersome process of synthesizing adhesive A in the two-step process, and provides a new method for the research and development of the preparation process of adhesive A. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0023] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0024] In the following examples, melamine, methanol, 55% formaldehyde, liquid alkali and hydrochloric acid used are all commercially available products; the yield is calculated as follows: mass of product obtained / theoretical mass of product.

[0025] The formaldehyde content in the circulating mother liquor is detected by titration.

[0026] Initial reaction example A method for preparing adhesive A, comprising the following steps: Step 1: Add 1kg melamine, 5.20kg 55% formaldehyde and 0.78kg methanol to a 10L reaction vessel, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction vessel, controlling the temperature drop within 15-20°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 2.9h.

[0027] Step 2: After the reaction is completed, centrifugal filtration is performed; 3.095 kg of the filtrate (centrifugal mother liquor) is kept warm at 75°C for later use, and the filter cake is sent for inspection, weighed to be 3.896 kg (M1) and transferred to a 15L reaction container; the filter cake test results: V1 = 20.7%, V2 = 6.9%, V3 = 40.2%, and the formula M2 = (1-V3) × M1 × 32.04 × 20 ÷ 306.43 + M1 × (4V1-V2) is used to calculate the amount of methanol M2 added to the reaction container, 7.829 kg, and stirred to increase the temperature; Step 3: Raise the temperature of the reaction system to 52°C, adjust the pH of the reaction system to 3-4 with hydrochloric acid (37w / w%), and continue the reaction at this temperature for 1 hour; Step 4: After the heat preservation reaction is completed, the pH of the reaction system is adjusted to 9 with liquid alkali, and the reaction is completed. The material is transferred to a distillation flask for negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 41.3% and the free formaldehyde content is 0.2% detected by titration. The heating loss is 0.6%, the viscosity at 25°C is 3650mpa·s, and the yield is 88.2%.

[0028] Product index requirements: Appearance: colorless and transparent liquid, combined formaldehyde content ≥40.0%, free formaldehyde content ≤0.5%, heating loss ≤2.0%.

[0029] Example 1 A method for preparing adhesive A, comprising the following steps: Step 1: Add 1kg melamine, 2.51kg 55% formaldehyde, 0.38kg methanol and 3.09kg centrifuged mother liquor in the initial reaction case to a 10L reaction vessel, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction vessel, controlling the temperature drop within 15-20°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 3.0h.

[0030] Step 2: After the reaction is completed, centrifugal filtration is performed; 4.35 kg of the filtrate is kept at 75°C for later use, the filter cake is sent for inspection, weighed to be 4.03 kg (M1) and transferred to a 15L reaction container; the filter cake test results: V1 = 21.1%, V2 = 6.8%, V3 = 39.6%, calculated by the formula M2 = (1-V3) × M1 × 32.04 × 20 ÷ 306.43 + M1 × (4V1-V2), add 8.218 kg of methanol M2 to the 15L reaction container, stir and heat; Step 3: Raise the temperature of the reaction system to 52°C, adjust the pH of the reaction system to 3-4 with hydrochloric acid (37w / w%), and continue the reaction at this temperature for 1 hour; Step 4: After the heat preservation reaction is completed, the pH of the reaction system is adjusted to 9 with liquid alkali, and the reaction is completed. The material is transferred to a distillation flask for negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 41.1% and the free formaldehyde content is 0.2% detected by titration. The heating loss is 0.7%, the viscosity at 25°C is 3850mpa·s, and the yield is 93.2%.

[0031] Example 2 A method for preparing a methylated melamine formaldehyde resin, comprising the following steps: Step 1: Add 1kg melamine, 2.51kg 55% formaldehyde, 0.38kg methanol and 3.09kg centrifugal mother liquor in the initial reaction case to a 10L reaction vessel, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction vessel, controlling the temperature drop within 15-20°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 3.2h.

[0032] Step 2: After the reaction is completed, centrifugal filtration is performed; 4.30 kg of the filtrate is kept at 75°C for later use, the filter cake is sent for inspection, weighed to be 4.02 kg (M1) and transferred to a 15L reaction container; the filter cake test results: V1 = 20.5%, V2 = 6.9%, V3 = 39.8%, calculated by the formula M2 = (1-V3) × M1 × 32.04 × 20 ÷ 306.43 + M1 × (4V1-V2), add 8.080 kg of methanol M2 to the 15L reaction container, stir and heat; Step 3: Raise the temperature of the reaction system to 52°C, adjust the pH of the reaction system to 3-4 with hydrochloric acid (37w / w%), and continue the reaction at this temperature for 1 hour; Step 4: After the heat preservation reaction is completed, the pH of the reaction system is adjusted to 9 with liquid alkali, and the reaction is completed. The material is transferred to a distillation flask for negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 41.2% and the free formaldehyde content is 0.3% detected by titration. The heating loss is 0.8%, the viscosity at 25°C is 3770mpa·s, and the yield is 93.3%.

[0033] Example 3 A method for preparing a methylated melamine formaldehyde resin, comprising the following steps: Step 1: Add 1kg melamine, 2.51kg 55% formaldehyde, 0.38kg methanol and 3.09kg centrifugal mother liquor in the initial reaction case to a 10L reaction vessel, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction vessel, controlling the temperature drop within 15-20°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 3.2h.

[0034] Step 2: After the reaction is completed, centrifugal filtration is performed; 4.30 kg of the filtrate is kept at 75°C for later use, and the filter cake is sent for inspection, weighed to be 4.01 kg (M1) and transferred to a 15L reaction container; the filter cake test results: V1 = 20.7%, V2 = 6.9%, V3 = 40.1%, and the formula M2 = (1-V3) × M1 × 32.04 × 20 ÷ 306.43 + M1 × (4V1-V2) is used to calculate that 8.067 kg of methanol M2 is added to the 15L reaction container, and the mixture is stirred and heated; Step 3: Raise the temperature of the reaction system to 52°C, adjust the pH of the reaction system to 3-4 with hydrochloric acid (37w / w%), and continue the reaction at this temperature for 1 hour; Step 4: After the heat preservation reaction is completed, the pH of the reaction system is adjusted to 9 with liquid alkali, and the reaction is completed. The material is transferred to a distillation flask for negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 41.5% and the free formaldehyde content is 0.2% detected by titration. The heating loss is 0.6%, the viscosity at 25°C is 3380mpa·s, and the yield is 93.1%.

[0035] The degree of etherification refers to the combination ratio of methanol and hexamethylol melamine. For example, the degree of hexamethylol melamine is 6 methanols combined with one hexamethylol melamine, corresponding to a combined formaldehyde content of 48%; the degree of etherification of the adhesive A in this embodiment is ≥5 methylol melamine, corresponding to a combined formaldehyde content of ≥40%).

[0036] Comparative Example 1 A method for preparing a methylated melamine formaldehyde resin, comprising the following steps: Step 1: Add 1kg melamine, 2.51kg 55% formaldehyde, 0.38kg methanol and 4.09kg centrifuged mother liquor to a 10L reaction container, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction container, controlling the temperature drop within 25-30°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 1.9h.

[0037] Step 2: After the reaction is completed, centrifugal filtration is performed. However, centrifugation is difficult and the experiment fails.

[0038] Reason for failure: The temperature dropped too fast during the hydroxylation reaction, and the intermediate HMM precipitated too quickly, resulting in a too small particle size. The effect of forming microbeads during the crystallization precipitation process was not achieved, which was not conducive to centrifugal filtration and resulted in poor centrifugal effect. The experiment failed.

[0039] Comparative Example 2 A method for preparing a methylated melamine formaldehyde resin, comprising the following steps: Step 1: Add 1kg melamine, 2.51kg 55% formaldehyde, 0.38kg methanol and 2.09kg centrifuged mother liquor to a 10L reaction container, start stirring and heating, adjust pH to 8-9 with liquid alkali when the temperature rises to 85°C, keep the reaction for 0.5h, adjust the stirring speed from 50Hz to 10Hz, and start using circulating water to cool the materials in the reaction container, controlling the temperature drop within 15-20°C per hour. Stop cooling after cooling to 35°C, and the hydroxylation reaction is completed after 3.2h.

[0040] Step 2: After the reaction is completed, centrifugal filtration is performed. Due to the reduction in the amount of centrifugal mother liquor, the consistency of the material increases after the reaction is completed, and the centrifugal filtration fails.

[0041] Comparative Example 3 A method for preparing adhesive A, comprising the following steps: Step 1: Add 1 kg HMM to 1.9 kg methanol, heat to 50 °C, adjust the pH of the reaction system to 3-4 with hydrochloric acid (37%), continue to keep warm for 1 hour, then adjust the pH of the reaction system to 9 with liquid alkali, and the reaction is complete; Step 2: The material is subjected to negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 41.5% and the free formaldehyde content is 0.20% as detected by titration. The heating loss is 0.8%, the viscosity at 25°C is 3350mpa·s, and the yield is 92.8%.

[0042] This method uses the intermediate HMM to directly synthesize adhesive A, and the product quality is excellent. However, drying HMM requires additional process steps, and the formaldehyde emitted during the drying process is difficult to handle, resulting in the production cost of dried HMM being much higher than that of using wet HMM, and the environmental pollution problem caused is also difficult to solve.

[0043] Comparative Example 4 A method for preparing adhesive A, comprising the following steps: Step 1: Add 1 kg of melamine to 4.5 kg of formaldehyde, adjust the pH to 8-9 with liquid alkali, start stirring and heating; when the temperature rises to 80°C, continue to keep the temperature for 2 hours, during which time liquid alkali is used to control the pH of the reaction system to 8-9.

[0044] Step 2: Keep the temperature for 2 hours; start cooling down the reaction system to 70°C, add 5kg of methanol to the reaction vessel, control the temperature to 50°C, adjust the pH of the reaction system to 3-4 with 31% hydrochloric acid, continue keeping the temperature for 1 hour, then adjust the pH of the reaction system to 8-9 with liquid alkali, and the reaction is complete; Step 3: Transfer the material to the distillation equipment for negative pressure distillation. After the distillation is completed, cool the temperature to 70°C, add 4kg of methanol to the reaction container, control the temperature to 50°C, adjust the pH of the reaction system to 3-4 with 31% hydrochloric acid, continue to keep warm for 10 minutes, then adjust the pH of the reaction system to 8-9 with liquid alkali, and the reaction is completed.

[0045] Step 4: The material is transferred to a distillation flask for negative pressure distillation. After the distillation is completed, the material in the distillation flask is filtered to obtain the product adhesive A. The appearance of the obtained product is a colorless transparent liquid. The bound formaldehyde content is 40.8% and the free formaldehyde content is 0.21% detected by titration. The heating loss is 0.8%, the viscosity at 25°C is 4050mpa·s, and the yield is 90.1%.

[0046] This method is to directly carry out the next etherification reaction process after synthesizing the intermediate. The product quality of this method is qualified, but it is impossible to recycle the centrifugal mother liquor during the strengthening process, resulting in a large amount of formaldehyde raw material waste. In addition, the process is complicated, the equipment consumption is large, the single batch production cycle is long, the unit yield is low, and the production cost is high.

[0047] In summary, the preparation method of adhesive A provided by the present invention has simple process operation, short cycle, environmental protection, safety, low cost, high product quality and yield, and meets the requirements of green product production.

[0048] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing an adhesive A, characterized in that: The steps include: Step 1: Mix the centrifuged mother liquor, formaldehyde solution, methanol and melamine, control the temperature to 80-90°C, add liquid alkali to control the pH to 7-8, keep the temperature for reaction, start cooling, control the cooling temperature to 15°C-20°C per hour, stop cooling after cooling to 35°C, and the reaction is completed; the molar ratio of formaldehyde to melamine in the reaction material is 7.3-7.5:1, and the molar ratio of water to methanol in the reaction material is 5.2-5.4:1; Step 2: After the reaction is completed, the material at the bottom of the reactor enters the centrifuge quantitatively to filter out the mother liquor, and the centrifuged mother liquor is temperature-controlled at 70-90°C for standby use; the solid material after centrifugation is sent for inspection, and the weight of the solid material is measured as M1, the water content V1, the methanol content V2 and the heating loss V3 in the solid material are measured; Step 3: Add the solid material and methanol after centrifugation into the etherification reaction vessel. The amount of solid material M1 and the amount of methanol M2 after centrifugation are calculated according to the following formula: M2=(1-V3)×M1×32.04×20÷306.43+M1×(4V1-V2); Step 4: After the feeding is completed, the temperature in the etherification reaction system is controlled to 50-55° C., and hydrochloric acid is added to the reaction system to adjust and maintain the pH value at 3-4 to carry out the etherification reaction; Step 5: After the etherification reaction is completed, add alkali solution to adjust the pH to ≥ 8; obtain the product adhesive A through distillation and filtration.

2. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 1, the centrifugal mother liquor is the centrifugal mother liquor obtained in step 2, and the centrifugal mother liquor obtained in step 2 can enter the next step 1 of preparing adhesive A.

3. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 1, the mass fraction of the formaldehyde solution is 55%.

4. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 1, the heat preservation reaction time is 0.5 hours.

5. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 1, the hydroxylation reaction temperature is 85°C; the molar ratio of formaldehyde to melamine in the reaction material is 7.4:1, and the molar ratio of water to methanol in the reaction material is 5.3:

1.

6. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 2, the temperature of the centrifuged mother liquor is controlled at 80° C. by steam condensation water.

7. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 4, the etherification reaction temperature is controlled at 53°C.

8. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 4, the etherification reaction time is 1 hour.

9. The method for preparing the adhesive A according to claim 1, characterized in that: In the step 5, the vacuum degree of the distillation process is controlled to be above -0.096, and the distillation temperature is controlled to be 115°C-125°C.

10. The method for preparing the adhesive A according to claim 1, characterized in that: The initial steps are as follows: Step 1: add melamine, formaldehyde solution and methanol to a hydroxylation reaction container, start stirring and heating, adjust the pH to 8-9 with liquid alkali when the temperature rises to 80-90°C, start cooling the materials in the hydroxylation reaction container with circulating water after the reaction is kept warm, control the temperature drop within 15-20°C per hour, stop cooling after the temperature drops to 35°C, and the hydroxylation reaction is completed in 2.9 hours; the weight ratio of the melamine, formaldehyde solution and methanol is: 1: (5-5.5): (0.7-0.8); the mass fraction of the formaldehyde solution is 55%; Step 2: After the reaction is completed, centrifugal filtration is performed to obtain the initial centrifugal mother liquor and solid material (filter cake). The centrifugal mother liquor is kept at 70-90°C for standby use. The filter cake is sent for inspection and weighed as M1. The water content V1, methanol content V2 and heating loss V3 in the filter cake are measured and transferred to the etherification reaction vessel; Step 3: Add the solid material and methanol after centrifugation into the etherification reaction vessel. The amount of solid material M1 and the amount of methanol M2 after centrifugation are calculated according to the following formula: M2=(1-V3)×M1×32.04×20÷306.43+M1×(4V1-V2); Step 4: After the feeding is completed, the temperature in the etherification reaction system is controlled to 50-55° C., and hydrochloric acid is added to the reaction system to adjust and maintain the pH value at 3-4 to carry out the etherification reaction; Step 5: After the etherification reaction is completed, add alkali solution to adjust the pH to ≥ 8; obtain the product adhesive A through distillation and filtration.