Preparation method of ammonia-free phenolic curing agent

Abstract

The invention relates to the field of polymer chemistry, in particular to a preparation method of an ammonia-free phenolic curing agent, the ammonia-free phenolic curing agent is a powdery phenolic curing agent, and the preparation method of the ammonia-free phenolic curing agent comprises the following steps: firstly, synthesizing solvent type liquid phenolic resin; the preparation method comprises the following steps: mixing phenol and formaldehyde, adding organic amine as a catalyst, carrying out a constant-temperature reaction to an end point, dehydrating to a nearly anhydrous state, adding a solvent and the organic amine catalyst, and carrying out a reflux reaction until the polymerization speed reaches 30-40s. Secondly, the solvent type resin passes through a heatable rotary spray drying device, a solvent is completely removed and recycled, an obtained solid product can be filtered through a vibrating screen and directly packaged into a finished product, and therefore the powdery ammonia-free phenolic aldehyde curing agent with the melting point being 80-90 DEG C and the polymerization speed being 30-40 s is prepared. The product can be used for production and solidification of precoated sand, no ammonia gas is generated, the gas generation amount is small, the quality of the precoated sand is improved, the working conditions of workers are improved, and the environment is protected.

Description

Technical Field

[0001] The invention relates to the field of polymer chemistry, and in particular to a method for preparing a non-aminophenolic aldehyde curing agent. Background Art

[0002] The foundry industry is an important basic industry of the manufacturing industry. Its development is closely related to the development of the global economy. The quality of casting directly affects the quality of mechanical products. With the development of industry and the progress of society, the requirements for the quality of castings and the foundry industry are getting higher and higher. Coated sand is a modeling material for shell mold precision casting. It has the characteristics of good preservation, high dimensional accuracy and smooth surface of the produced castings. It can be used for the production of cast steel, cast iron, alloy castings and non-ferrous metal castings. Coated sand is usually made of quartz sand as the raw sand, supplemented by a binder and a curing agent.

[0003] The curing agent of the traditional coated sand binder is urotropine. Gas is generated during the curing process. In order to meet the strength requirements and longer heat resistance time, the amount of binder is usually increased, and the amount of urotropine added increases accordingly, resulting in an increase in the gas emission of the product, an increase in the porosity of the casting, and an impact on the quality of the casting. At the same time, the national environmental protection requirements are becoming increasingly stringent, and large amounts of gas emission pollute the atmosphere and endanger the health of workers. Patent Publication No. CN111299497 A curing agent for a coated sand binder and a preparation method thereof discloses a liquid curing agent for coated sand, which is prepared by direct reaction of phenol and formaldehyde; the curing agent prepared by this method is complex to use and has a slow curing speed, which greatly reduces the production efficiency of coated sand. Patent Authorization No. CN112743036 A curing agent for an inorganic coated sand and an inorganic coated sand core containing the same, which reacts with divalent metal oxides, disodium tetraacetate, and sodium dodecylsulfonate to form a stable multi-component complex. This product is an inorganic series, and has poor compatibility with organic phenolic resin, poor mixing effect, and poor uniformity of the performance of the finished coated sand. Therefore, it is of great significance to develop and prepare a curing agent that has excellent compatibility with phenolic resin, fast polymerization speed, environmental protection, and excellent comprehensive performance. Summary of the invention

[0004] The purpose of the present invention is to provide a coated sand curing agent that can replace urotropine. The curing agent is a powdered phenolic resin, which can solve the technical problem that when urotropine is used as a curing agent, gas is generated during the curing process, the amount of gas generated is large, the porosity of the casting is high, and the quality of the casting is affected. At the same time, a preparation method of the curing agent is provided.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: The ammonia-free phenolic resin curing agent of the present invention is a powdered phenolic resin, which is prepared by two steps of synthesis and spray molding.

[0006] Preferably, the solvent-based liquid phenolic curing agent is made of phenol, formaldehyde, a catalyst, a solvent, and a thermoplastic phenolic resin.

[0007] Preferably, the solvent-based liquid phenolic curing agent is made from the following raw materials in parts by weight: Phenol 100 parts Formaldehyde 80-140 parts 3-6 parts of organic amine catalyst 100 parts of solvent.

[0008] Preferably, the catalyst is triethylamine and / or triethanolamine.

[0009] Preferably, the solvent is methanol and / or ethanol.

[0010] The preparation method of the non-aminophenolic aldehyde curing agent of the present invention comprises the following steps: (a) mixing phenol and formaldehyde solution, adding an organic amine catalyst, heating for reaction, and vacuum dehydration to obtain product I; (b) adding a solvent and an organic amine to the product I, reflux reaction, taking a sample to measure the polymerization rate, and obtaining a solvent-based liquid resin. (c) The liquid resin is passed through a heated rotary spray drying device to evaporate and remove the solvent, and the solid powder is collected as the finished product.

[0011] The ammonia-free phenolic resin curing agent of the present invention is a special thermosetting phenolic resin with a weight average molecular weight greater than 1000, which is much higher than the general thermosetting phenolic resin. In the preparation method step a), due to the strong alkalinity of organic amines such as triethylamine, a large number of active hydroxymethyl groups are generated to ensure the reaction activity of the product prepared by the method of the present invention. After dehydration, a large amount of solvent is added, and methanol or ethanol solvent dissolves the phenolic resin inside, and at the same time plays a role in inhibiting polymerization. In step b), the material is kept at a pH of 7-8 to continue the reflux reaction, and a large number of macromolecular products containing a large number of methylene ether bonds are generated by the special catalytic mechanism of organic amines, which greatly improves the cross-linking strength after curing. The powdered phenolic resin curing agent prepared by the method of the present invention can replace urotropine. During the sand mixing process, it reacts with the casting binder thermoplastic phenolic resin, and a large number of hydroxymethyl groups react with the vacancies of the benzene ring of the thermoplastic phenolic resin, fully cross-linking, forming a body structure, and finally curing.

[0012] Compared with the prior art, the present invention has the following beneficial effects: (1) During the curing process, no ammonia is generated in the coated sand, and the amount of gas generated is small, which improves the quality of the coated sand, improves the working conditions of workers, and protects the environment.

[0013] (2) The curing strength of the product of the present invention and the coated sand is significantly improved. In the performance test, the tensile strength of the 8-shaped block after the product of the present invention and the coated sand is cured is 3.6-4.0 MPa, which is higher than the strength of the traditional curing process of 3.1-3.5 MPa. DETAILED DESCRIPTION

[0014] The present invention is described in detail below with reference to examples. It should be noted that unless otherwise specifically stated, the steps and values ​​described in these examples do not limit the scope of the present invention.

[0015] Example 1 (a) 100 g of phenol and 80 g of formaldehyde solution were mixed in a three-necked flask, 3 g of triethylamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 6 h until the solution was turbid and insoluble in water, and vacuum dehydration was performed until the solution was almost dry to obtain product I; (b) Add 100 g methanol and 3 g triethylamine to the product I, heat to reflux for 20 min, take a sample after 5 h to measure the curing time of 35 s, cool to 30° C., discharge, and obtain a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 80°C.

[0016] Example 2 (a) 100 g of phenol and 140 g of formaldehyde solution were mixed in a three-necked flask, 6 g of triethylamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 5 h until the solution was turbid and insoluble in water, and vacuum dehydration was started to obtain product I; (b) Add 100 g methanol and 6 g triethanolamine to the product I, heat to 72° C. for 20 min, reflux reaction, take a sample after 5 h to measure the curing time for 30 s, cool to 30° C., discharge, and obtain a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 86° C.

[0017] Example 3 (a) 100 g of phenol and 80 g of formaldehyde were mixed in a three-necked flask, 6 g of triethylamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 6 h until the solution was turbid and insoluble in water, and vacuum dehydration was started to obtain product I; (b) Add 100 g of ethanol and 5 g of ammonia water to the product I, heat to 74° C. for 20 min, reflux reaction, take a sample after 5 h to measure the curing time of 40 s, cool to 30° C., discharge, and obtain a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 80°C.

[0018] Example 4 (a) 100 g of phenol and 140 g of formaldehyde were mixed in a three-necked flask, 5 g of triethylamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 5 h until the solution became turbid and insoluble in water, and vacuum dehydration was started to obtain product I; (b) adding 100 g ethanol and 3 g triethylamine to the product I, heating to 72° C. for 20 min, reflux reaction, sampling after 5 h to measure the curing time of 35 s, cooling to 30° C., discharging, and obtaining a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 80°C.

[0019] Example 5 (a) 100 g of phenol and 140 g of formaldehyde were mixed in a three-necked flask, 3 g of triethanolamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 6 h until the solution was turbid and insoluble in water, and then dehydration was started to obtain product I; (b) Add 100 g methanol and 3 g triethylamine to the product I, heat to 72° C. for 20 min, reflux reaction, take a sample after 5 h to measure the curing time of 40 s, cool to 30° C., discharge, and obtain a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 90° C.

[0020] Example 6 (a) 100 g of phenol and 80 g of formaldehyde were mixed in a three-necked flask, 5 g of triethanolamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 8 h until the solution became turbid and insoluble in water, and vacuum dehydration was started to obtain product I; (b) adding 100 g methanol and 5 g triethylamine to the product I, heating the mixture to 75° C. for 20 min, and reflux reaction. After 5 h, sampling was performed to measure the curing time for 30 s, and the mixture was cooled to 30° C. and discharged to obtain a solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 84° C.

[0021] Example 7 (a) 100 g of phenol and 100 g of formaldehyde were mixed in a three-necked flask, 5 g of triethylamine was added, the temperature was raised to 75° C. within 20 min, and the temperature was kept for 8 h until the solution became turbid and insoluble in water, and vacuum dehydration was started to obtain product I; (b) Add 100g ethanol and 5g triethanolamine to the product I, heat to 75°C for 20min, reflux reaction, take a sample after 5h to measure the curing time of 30s, cool to 30°C, discharge, and obtain solvent-based liquid phenolic resin. (c) The solvent-based liquid phenolic resin is transported to a closed rotary spray dryer through a pipeline pump, and the solvent is evaporated and removed under high temperature conditions to obtain a uniform powdered resin as a finished product. The melting point of the sample is 87° C.

[0022] The above synthesized phenolic acid-free curing agent was used for the strength application test of coated sand. The results are shown in Table 1.

[0023] Comparative Example 1 is a conventional urotropine aqueous solution Application test of tensile strength of coated sand: heat the sand to 150°C, add the binder and the curing agent, stir for 150s, add calcium stearate and stir thoroughly for 80s, discharge through a 40-mesh test sieve, mold cure at 235°C for 150s, take out the sample, cool to room temperature, and measure the strength with a strength testing machine.

[0024] Gas emission measurement method: Weigh 1±0.001g of sand ground from the fracture of the strength sample and put it into a porcelain boat. Send the porcelain boat containing the coated sand sample into the red-hot part of the quartz tube of the gas emission meter, quickly seal the tube mouth with a stopper, and at the same time, the recording part of the gas emission meter starts working. After 3 minutes, the gas emission of the sample can be directly read from the recording paper.

[0025] Table 1 project Tensile strength (MPa) Gas generation (mL / g) Example 1 3.7 8 Example 2 3.8 9 Example 3 3.7 8 Example 4 3.9 10 Example 5 4.0 9 Example 6 3.6 12 Example 7 3.7 11 Comparative Example 1 3.2 16 The phenolic acid-free curing agent prepared by the method of the present invention has a polymerization speed of 30-40s and a melting point of 80-90°C, and can completely replace hexamethylenetetramine for use. The strength of the cured coated sand is also improved, and the gas emission is significantly reduced.

[0026] The curing strength of the product of the present invention and the coated sand is significantly improved. In the performance test, the tensile strength of the 8-shaped block after the product of the present invention and the coated sand is cured is 3.8-4.0 MPa, which is higher than the strength of the traditional curing process of 3.1-3.5 MPa.

Claims

1. A phenol-free curing agent, characterized in that: The curing agent is a powdered phenolic resin, and its preparation method comprises the following two steps: Step 1: Synthesis of solvent-based liquid phenolic resin by reacting phenol, formaldehyde and organic amine catalyst to dehydrate until it is basically free of water, then adding solvent and organic amine, continuing reflux reaction, and generating solvent-based liquid phenolic resin with certain polymerization rate index requirements; Step 2: Preparation of powdered curing agent as follows: Passing the above solvent-based liquid resin through a heatable rotary spray drying device to completely evaporate and remove the solvent for recovery, and then sieving and packaging the remaining solid powder to obtain the finished product.

2. The solvent-based liquid phenolic resin according to claim 1, characterized in that: Made from the following raw materials in parts by weight: Phenol 100 parts Formaldehyde 80-140 parts 3-6 parts of organic amine catalyst 100 parts of solvent.

3. The solvent-based liquid phenolic resin according to claim 2, characterized in that: The catalyst is triethylamine and / or triethanolamine.

4. The solvent-based liquid phenolic resin according to claim 3, characterized in that: The solvent is methanol and / or ethanol.

5. The method for preparing the non-aminophenolic aldehyde curing agent according to claim 4, wherein: The melting point of the finished product is 80-90℃ and the polymerization speed is 30-40s.