Melamine resin prepolymer modifier and preparation method of hot-pressed non-rebound low-formaldehyde melamine-based foam thereof

Abstract

The invention belongs to the technical field of melamine-based foam materials, and particularly discloses a melamine resin prepolymer modifier and a preparation method of hot-pressed non-rebound low-formaldehyde melamine-based foam. The preparation method comprises the following steps: firstly, carrying out polycondensation dehydration on a catalyst, diglycolamine and melamine to prepare a modifier; the preparation method comprises the following steps: controlling the feeding ratio of melamine to formaldehyde, adding sodium pyrosulfite, regulating and controlling the pH value of a reaction solution, preparing a resin prepolymer by adopting a constant-temperature reaction, adding a modifier before a reaction endpoint, continuing the reaction to the endpoint, and then adding a high-temperature formaldehyde catching agent; and then emulsifying with a functional auxiliary agent at a high speed, foaming by combining microwave gradient foaming and thermal radiation to obtain a primary foam product, and curing the foam by combining microwaves and wet and hot steam to obtain the product. The product has excellent flame retardance, weather resistance, sound absorption, mildew resistance, corrosion resistance, workability and the like, and can be applied to the fields of sound insulation, heat preservation, shock prevention, fire prevention, decoration filling, cleaning and the like.

Description

1. Technical field:

[0001] The invention belongs to the technical field of melamine-based foam materials, and particularly relates to a melamine resin prepolymer modifier and a method for preparing a hot-pressed non-rebound low-formaldehyde melamine-based foam. 2. Background technology:

[0002] Melamine foam is an intrinsic flame-retardant soft foam material based on melamine formaldehyde resin and prepared by microwave foaming process. The foam has excellent comprehensive properties such as sound absorption, heat insulation, moisture and heat resistance, physical cleanliness and good secondary processing properties. It has very important application value in aerospace, navigation, defense industry electromechanical, chemical equipment, construction venues, rail transit, electronic information, cleaning and other fields, especially in environments with high requirements for high and low temperature resistance, flame retardancy, sound absorption and lightweight.

[0003] However, the existing melamine foam products currently prepared also have some defects and deficiencies, such as: ① Under the condition of effective pressure of 300 kg, hot pressing temperature <230°C, hot pressing time <3 min, the thickness is difficult to be fixed, and the rebound ratio is >20%; under the condition of effective pressure of 300 kg, hot pressing temperature >230°C, hot pressing time >3 min, the surface turns yellow after hot pressing, and the mechanical properties deteriorate. ② Melamine foam also has a high free formaldehyde content.

[0004] In the resin structure, the distance between two rigid triazine rings connected by methylene or methylene ether bonds is the smallest. With the increase of the molar ratio of polyformaldehyde and melamine, one triazine ring can connect two or three triazine rings, making the foam rigid structure strong but with poor mechanical properties, and easy to rebound after hot pressing; in the resin prepolymer synthesis stage, the hydroxymethylation reaction of melamine and polyformaldehyde is a reversible reaction, and the conversion rate of formaldehyde cannot reach 100%. Therefore, there is a certain amount of free formaldehyde in the resin; at the same time, during the foaming and curing process, the unstable methylene ether and hydroxymethyl groups formed in the foam structure will further decompose and release formaldehyde in a warm and humid environment, making the foam have a high formaldehyde release. Therefore, improving the low-energy consumption, high-quality, hot-pressed and non-rebound performance of melamine foam and reducing the free formaldehyde content of foam formaldehyde can meet the needs of special requirements such as sound absorption and noise reduction in confined spaces, thermal insulation of chemical equipment pipelines, and cleaning of industrial equipment. 3. Summary of the invention:

[0005] The technical problem to be solved by the present invention is: based on the defects of existing melamine foam materials such as hot-pressing rebound and high free formaldehyde content, the present invention provides a melamine resin prepolymer modifier and a method for preparing a hot-pressing non-rebound low-formaldehyde melamine-based foam. The comprehensive melamine-based foam material prepared by the present invention, i.e., hot-pressing non-rebound low-formaldehyde melamine-based foam, has excellent flame retardancy, weather resistance, sound absorption, mildew resistance, corrosion resistance, easy processing and other properties, while improving the hot-pressing treatment stability, sanitation and environmental protection, mechanical properties and other indicators of the material, expanding the application of the material in the fields of sound insulation, heat preservation, shockproof, fireproof, decorative filling and cleaning.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for preparing a melamine resin prepolymer modifier, the preparation method comprising the following steps:

[0008] a. Melamine and diglycolamine are used as main raw materials, and phosphoric acid and hypophosphorous acid are used as catalysts;

[0009] b. Adding diglycolamine, melamine, phosphoric acid and hypophosphorous acid into a reactor in sequence, and then heating for reaction;

[0010] c. After the reaction is completed, the reaction liquid is cooled, and after cooling, the reaction liquid is vacuumed under nitrogen protection;

[0011] d. After evacuating in step c, slowly cool the reaction solution to ≤120°C, then (slowly) open the nitrogen valve and flush in nitrogen to eliminate the vacuum state and balance the system with the external air pressure;

[0012] e. Then, desalted water is added to the reaction solution to control the solid content of the reaction solution to 65-85%, and stirring is continued to make the reaction solution and the desalted water mix evenly, and then the pH is adjusted to 6-8 to obtain a brown-red viscous modifier, i.e., a melamine resin prepolymer modifier, which is sealed and stored for later use.

[0013] According to the preparation method of the melamine resin prepolymer modifier, expressed in parts by weight, the added amounts of the two main raw materials and the two catalysts in step a are 15 to 35 parts of melamine, 60 to 100 parts of diglycolamine, 0.5 to 1.0 parts of phosphoric acid and 0.1 to 0.6 parts of hypophosphorous acid, respectively.

[0014] According to the preparation method of the melamine resin prepolymer modifier, during the heating reaction in step b, the temperature of the reaction liquid is controlled to be 200-210° C., and the reaction material is kept warm for 15-20 hours after it becomes transparent.

[0015] According to the preparation method of the melamine resin prepolymer modifier, in step c, the reaction liquid is cooled to 150-210° C. and vacuumed until the liquid is in a sticky light yellow paste state and no liquid evaporates within 30 minutes.

[0016] According to the preparation method of the melamine resin prepolymer modifier, the stirring time in step e is controlled to be 1 to 5 minutes; and the pH value is adjusted to 6 to 8 using 20% ​​sodium hydroxide solution.

[0017] In addition, a method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam using the above-obtained modifier is provided, the method comprising the following steps:

[0018] 1) Preparation of high plasticity melamine-based resin prepolymer:

[0019] 1.1) Melamine, 96% paraformaldehyde solid, sodium pyrosulfite and deionized water are used as main raw materials; the addition amounts of the four main raw materials are 35-55 parts of melamine, 25-45 parts of 96% paraformaldehyde solid, 1-3 parts of sodium pyrosulfite and 20-40 parts of deionized water respectively by weight;

[0020] 1.2) According to the ratio of the four main raw materials in step 1.1), melamine, 96% paraformaldehyde solid, sodium metabisulfite and deionized water are weighed, and the four raw materials are added into a reactor, and then sodium hydroxide solution is added to adjust the pH value to 8-9; then steam is used for heating, and when the reaction temperature is heated to 80-100° C. (preferably 90-100° C.), a second batch of melamine raw materials is added and the reaction is carried out at a constant temperature for 1-3 hours;

[0021] 1.3) After the reaction, add 5 to 15 parts of the modifier prepared in claim 1 according to weight, continue stirring and reacting at 80 to 100° C. for 10 to 30 minutes (preferably 15 to 25 minutes), and determine the end point by turbidity method;

[0022] 1.4) cooling the reaction solution obtained in step 1.3) to 40-70° C., then adding an ethylene urea formaldehyde scavenger, stirring at a constant temperature for 0.5-2 hours, and then cooling to 20-40° C. (preferably 25-35° C.) to obtain a hot-pressing easy-setting melamine-based resin prepolymer, i.e., a high-plasticity melamine-based resin prepolymer;

[0023] 2) Preparation of functional foaming aid:

[0024] Add 25-35 parts of emulsifier, 30-40 parts of compound curing agent, 40-55 parts of compound foaming agent and 10-25 parts of fluoroether solvent into a 300Kg auxiliary agent reaction kettle in sequence, and then stir and mix evenly; after mixing various auxiliary agents, stir slowly to obtain a functional foaming auxiliary agent for standby use;

[0025] 3) Preparation of hot-pressed, easy-to-set low-formaldehyde melamine-based foam:

[0026] The heat-pressing and easy-setting melamine-based resin prepolymer prepared in step 1) is cooled to 0°C by a single screw, and then enters a twin-screw machine through a metering screw, and the metering screw flow rate is 1.5-2.5 Kg / min (accurate to g / min, preferably 2.0-2.5 Kg / min); the functional foaming aid obtained in step 2) is simultaneously entered into the twin-screw machine with the heat-pressing and easy-setting melamine-based resin prepolymer through a metering pump, and the metering pump flow rate is 400-450 g / min (accurate to mg / min, preferably 4 10-430g / min); the resin prepolymer and the auxiliary agent are mixed in a twin-screw machine for high-speed emulsification (the speed of the screw is 110 rpm), and the emulsified material (after being evenly distributed by a distribution trolley and then passed through a conveyor belt) is sent to a microwave foaming furnace for gradient foaming, the power of the microwave foaming furnace is 60-110KW (preferably 80-100KW), the foaming time is 15-50 minutes (preferably 30-40 minutes), and the hot air temperature is 40-80°C, and a melamine-based foam primary product is obtained after foaming;

[0027] 4) Optimization of hot-pressed, easy-to-shape, low-formaldehyde melamine-based foam:

[0028] The melamine-based foam primary product obtained in step 3) is subjected to secondary curing treatment by microwave and moist hot steam, wherein the microwave power is 120-220 KW (preferably 140-180 KW), the moist hot steam pressure is 0.1-0.3 MPa, the curing furnace temperature is 70-150° C. (preferably 100-150° C.), and the curing time is 40-120 minutes (preferably 80-100 minutes). After the curing treatment, a low-formaldehyde melamine-based foam with stable performance and easy to shape by hot pressing is obtained, i.e., a low-formaldehyde melamine-based foam that does not rebound by hot pressing is obtained.

[0029] According to the above method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam, the addition amounts of the four main raw materials in step 1.1) are 44-54 parts of melamine, 28-32 parts of 96% paraformaldehyde solids, 1.5-2.5 parts of sodium pyrosulfite, and 20-30 parts of deionized water;

[0030] In step 1.2), the amount of the second batch of melamine raw materials added accounts for 1 / 4 to 1 / 8 of the total amount of melamine added;

[0031] In step 1.3), the amount of ethylene urea formaldehyde scavenger added is 0.5-2% of the weight of the polyformaldehyde solid.

[0032] According to the above method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam, in step 2), the emulsifier is 28 to 32 parts, the compound curing agent is 31 to 36 parts, the compound foaming agent is 40 to 45 parts, and the fluoroether solvent is 15 to 20 parts;

[0033] When the stirring and mixing is uniform, the stirring speed is controlled to be 10 to 24 rpm and the stirring time is 20 to 40 min; when the slow stirring is performed, the stirring speed is controlled to be 5 to 10 rpm.

[0034] According to the above method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam, the emulsifier in step 2) is at least one of sodium dodecylbenzene sulfonate, sodium fatty alcohol sulfate, sodium alkylnaphthalene sulfonate, sodium secondary alkyl sulfonate, sodium α-olefin sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium lauryl polyoxyethylene ether sulfate, α-sulfo fatty acid methyl ester, sodium cocoyl isethionate and sodium dodecyl alcohol polyoxyethylene ether carboxylate;

[0035] The composite curing agent is prepared by mixing an organic protonic acid and an inorganic protonic acid; the organic protonic acid is at least one of formic acid, acetic acid, benzenesulfonic acid and p-toluenesulfonic acid, and the inorganic protonic acid is at least one of hydrochloric acid, sulfuric acid, boric acid and phosphoric acid;

[0036] The composite foaming agent is prepared by mixing n-pentane, isopentane and cyclopentane;

[0037] The fluoroether solvent is at least one of tetrafluoroethyl trifluoropropyl ether, perfluorobutyl methyl ether, tetrafluoroethyl methyl ether, hexafluoroisopropyl ether, and hexafluoroisopropyl ether.

[0038] During the secondary curing process of the melamine-based foam primary product of the present invention, the box of the curing furnace used is 20 meters long, and the first 1 / 3 of the length is distributed with a certain regular mesh plate, which can be passed through low-pressure steam (pressure is 0.1-1.0MPa), and the air outlet is installed below; the middle 1 / 3 is neatly distributed with 2450HZ microwave sources above and below, with a total power of 120 kilowatts; the top of the back 1 / 3 is the hot air inlet and outlet, and the bottom is the hot air outlet, with a temperature of 100-150°C. The advantages of this technical feature: the introduction of hot and humid steam in the first stage can effectively promote the breaking of unstable bonds in the foam, forming highly volatile small molecule formaldehyde; the second stage adopts a microwave drying process to volatilize small molecules such as water and formaldehyde in the foam from the inside to the outside, so that the entire foam is heated evenly, and the temperature of the entire box is controlled at 60-90°C, and the energy consumption is relatively low; the third stage adopts 100-150°C hot air for drying. The above process can greatly reduce the formaldehyde content of the foam on the one hand, and on the other hand, due to the short curing time and low aging temperature of this method, it is very easy to shape and stabilize it in the later hot pressing.

[0039] The technical scheme of the present invention comprises the following steps: under the action of a catalyst, a modifier is prepared by polycondensation and dehydration of diglycolamine and melamine; a resin prepolymer is prepared by a constant temperature reaction by controlling the feed ratio of melamine and formaldehyde, adding sodium pyrosulfite, and adjusting the pH value of the reaction liquid; the modifier prepared by the present invention is added before the reaction is about to reach an end point, the reaction is continued to the end point, a turbidity judgment method is adopted, the reaction temperature is cooled to 40-70 DEG C by using cold water, and a high-temperature formaldehyde scavenger is added; then, high-speed emulsification is performed with functional additives such as a curing agent, a foaming agent, and an emulsifier; after emulsification, a foaming process combining microwave gradient foaming and thermal radiation is performed to obtain a foam primary product; a process combining microwave and moist hot steam is adopted to cure the foam, which greatly reduces the formaldehyde content of the foam and improves the physical properties of the foam on the one hand, and reduces the curing temperature on the other hand, reduces the conversion between active functional groups between molecules, and improves the stability after hot pressing. The purpose of adding the modifier prepared by the present invention is to introduce a straight chain structure at the amino end of the rigid triazine ring, greatly reduce the distance between the triazine rings inside the molecule, increase the flexible molecular long chain, reduce the rigid structure between molecules, and improve the hot pressing setting property of the foam.

[0040] The positive beneficial effects of the present invention are:

[0041] 1. The technical solution of the present invention is to react two raw materials, melamine and diglycolamine, under the action of a catalyst, and increase the length of the melamine molecular chain through polycondensation and dehydration of the amino group of melamine and the hydroxyl group of diglycolamine, and prepare a modifier containing a flexible molecular chain, which is added to the melamine formaldehyde reaction liquid under certain conditions to enhance the distance between the high molecular triazine rings of the melamine formaldehyde prepolymer. The addition of the modified resin (modifier) ​​prepared by the present invention introduces a molecular flexible chain, greatly reduces the rigidity between macromolecules, and makes the later hot pressing easier to shape.

[0042] 2. The technical solution of the present invention is to add a high-temperature formaldehyde scavenger ethylene urea in the late stage of the synthesis of the resin prepolymer. The formaldehyde scavenger can well absorb the free formaldehyde remaining in the late stage of the high-temperature hot pressing process. The advantage of selecting the formaldehyde scavenger is that it avoids the deactivation of small molecule formaldehyde scavengers such as urea under high temperature conditions. At the same time, the addition of ethylene urea does not affect the mechanical properties of the foam.

[0043] 3. In the composite functional foaming aid adopted in the technical solution of the present invention, the emulsifier is an anionic surfactant, the curing agent is a compound of organic protonic acid and inorganic protonic acid, the foaming agent is a compound of isomers, and a hydrofluoroether compound is introduced, which greatly promotes the deep cross-linking of the hydroxymethyl in the molecule into methylene bonds, reduces the content of hydroxymethyl and methoxy groups that can release small molecules of free formaldehyde in the foam, and reduces the formaldehyde content in the product.

[0044] 4. The foaming process in the technical solution of the present invention adopts a process that combines microwave gradient foaming and thermal radiation to evenly match the foaming rate and the curing rate, ensuring that the product has a fine pore size and physical properties that are better than national enterprise standards.

[0045] 5. The secondary curing process in the technical solution of the present invention adopts a microwave and moist hot steam combined process to cure the foam. At present, melamine foam usually uses a hot air blower to deliver hot air above 200°C to the drying furnace, and dries for more than 2 hours to mature the foam to reduce the formaldehyde content of the foam. This method has the problems of high curing temperature, long curing time and high energy consumption, low temperature and high formaldehyde content in the core of the foam due to hot air from the outside to the inside, high curing time and temperature leading to difficulties in later hot pressing and increased material aging, shortening the service life. The present invention adopts microwave and moist hot steam combined heat from the inside to the outside to excite the heat, accelerate the escape speed of small molecular products such as free formaldehyde, water, alkane foaming agent, etc., the curing time is shortened by about half compared with the traditional process, the external hot air temperature is reduced from the traditional 200°C to 150°C, and the phenomenon of rapid aging of materials in a high temperature environment for a long time is also avoided.

[0046] 6. The performance comparison between the product prepared by the technical solution of the present invention and ordinary melamine foam is shown in Table 1.

[0047] Table 1 Comparison of relevant properties of the product of the present invention and ordinary melamine foam

[0048]

[0049] In summary, the technical scheme of the present invention uses melamine and diglycolamine as raw materials to prepare a modifier (thereby increasing the molecular chain length of the melamine formaldehyde resin and improving the foam's hot pressing and easy setting); then melamine and 96% of polyformaldehyde solid particles are added into a reactor in a certain proportion, and a self-made modifier, sodium pyrosulfite and a formaldehyde scavenger are added to synthesize a modified melamine formaldehyde resin prepolymer; then a composite functional auxiliary agent is added for microwave foaming, and the foam is cured and dried in a microwave and wet heat steam curing furnace to obtain a hot pressing non-rebound low-formaldehyde melamine-based foam. The material prepared by the present invention can meet the conditions of 1-2.5MPa setting pressure, 170-200℃ hot pressing temperature, and 30-90 seconds hot pressing time without rebound, and the free and hydrolyzed formaldehyde (water extraction method) standard test result according to "GB T2912.1-2009 Determination of Formaldehyde in Textiles" Part 1 is ≤16mg / kg (deemed as undetected). Therefore, the low-formaldehyde melamine-based foam without rebound after hot pressing prepared by the present invention improves the density of the melamine foam material through hot pressing shaping, and meets the limit requirements on the formaldehyde content of indoor decoration and materials directly contacted by infants and young children. The material of the present invention can be used as a material for sound insulation, heat preservation, shockproof, fireproof, decorative filling, cleaning, etc., thereby overcoming the defects of the current melamine foam, such as easy rebound after hot pressing, poor mechanical properties, high formaldehyde content, density less than 10kg / m3, complex hot pressing process and high energy consumption. 4. Description of the drawings:

[0050] Figure 1 The present invention is a schematic diagram of a curing oven that uses a combination of microwaves and moist heat steam to perform a curing process. V. Specific implementation methods:

[0051] The present invention is further described below in conjunction with embodiments, but the protection scope of the technical solution of the present invention is not limited thereto.

[0052] Embodiment 1:

[0053] The preparation method of the melamine resin prepolymer modifier of the present invention comprises the following detailed steps:

[0054] a. Melamine and diglycolamine are used as main raw materials, and phosphoric acid and hypophosphorous acid are used as catalysts; the addition amounts of the two main raw materials and the two catalysts are 20 parts of melamine, 65 parts of diglycolamine, 0.6 parts of phosphoric acid and 0.2 parts of hypophosphorous acid respectively;

[0055] b. Add diglycolamine, melamine, phosphoric acid and hypophosphorous acid into the reactor in order, and then heat the reaction; control the temperature of the reaction liquid to 205° C., and continue to keep the temperature for 16 hours when the reaction material becomes transparent;

[0056] c. After the reaction is completed, the reaction liquid is cooled to 180°C, and after cooling, the reaction liquid is vacuumed under nitrogen protection until the liquid becomes a sticky light yellow paste. When no liquid evaporates within 30 minutes, stop vacuuming;

[0057] d. After evacuating in step c, slowly cool the reaction solution to 100°C, then (slowly) open the nitrogen valve to flush in nitrogen to eliminate the vacuum state and balance the system with the external air pressure;

[0058] e. Then, desalted water was added to the reaction solution to control the solid content of the reaction solution to 75%, and stirring was continued for 3 min to uniformly mix the reaction solution and desalted water. A 20% sodium hydroxide solution was used to adjust the pH value to 6.5 to obtain a brown-red viscous modifier, i.e., a melamine resin prepolymer modifier, which was sealed and stored for later use.

[0059] Embodiment 2:

[0060] The preparation method of the melamine resin prepolymer modifier of the present invention comprises the following detailed steps:

[0061] a. Melamine and diglycolamine are used as main raw materials, and phosphoric acid and hypophosphorous acid are used as catalysts; the addition amounts of the two main raw materials and the two catalysts are 25 parts of melamine, 72 parts of diglycolamine, 0.8 parts of phosphoric acid and 0.3 parts of hypophosphorous acid respectively;

[0062] b. Add diglycolamine, melamine, phosphoric acid and hypophosphorous acid into the reactor in order, and then heat the reaction; control the temperature of the reaction liquid to 206° C., and continue to keep the temperature for 18 hours when the reaction material becomes transparent;

[0063] c. After the reaction is completed, the reaction liquid is cooled to 200°C, and after cooling, the reaction liquid is vacuumed under nitrogen protection until the liquid becomes a sticky light yellow paste. When no liquid evaporates within 30 minutes, stop vacuuming;

[0064] d. After evacuating in step c, slowly cool the reaction solution to 110°C, then (slowly) open the nitrogen valve and flush in nitrogen to eliminate the vacuum state and balance the system with the external air pressure;

[0065] e. Then, desalted water was added to the reaction solution to control the solid content of the reaction solution to 80%, and stirring was continued for 4 min to evenly mix the reaction solution and desalted water. A 20% sodium hydroxide solution was used to adjust the pH value to 7.5 to obtain a brown-red viscous modifier, i.e., a melamine resin prepolymer modifier, which was sealed and stored for later use.

[0066] Embodiment 3:

[0067] The preparation method of the melamine resin prepolymer modifier of the present invention comprises the following detailed steps:

[0068] a. Melamine and diglycolamine are used as main raw materials, and phosphoric acid and hypophosphorous acid are used as catalysts; the addition amounts of the two main raw materials and the two catalysts are 30 parts of melamine, 85 parts of diglycolamine, 0.9 parts of phosphoric acid and 0.5 parts of hypophosphorous acid respectively;

[0069] b. Add diglycolamine, melamine, phosphoric acid and hypophosphorous acid into the reactor in order, and then heat the reaction; control the temperature of the reaction liquid to 209° C., and continue to keep the temperature for 18 hours when the reaction material becomes transparent;

[0070] c. After the reaction is completed, the reaction liquid is cooled to 200°C, and after cooling, the reaction liquid is vacuumed under nitrogen protection until the liquid becomes a sticky light yellow paste. When no liquid evaporates within 30 minutes, stop vacuuming;

[0071] d. After evacuating in step c, slowly cool the reaction solution to 180°C, then (slowly) open the nitrogen valve and flush in nitrogen to eliminate the vacuum state and balance the system with the external air pressure;

[0072] e. Then, desalted water was added to the reaction solution to control the solid content of the reaction solution to 85%, and stirring was continued for 4.5 min to uniformly mix the reaction solution and desalted water. The pH value was adjusted to 7.7 with 20% sodium hydroxide solution to obtain a brown-red viscous modifier, i.e., a melamine resin prepolymer modifier, which was sealed and stored for later use.

[0073] Embodiment 4:

[0074] The present invention uses the modifier obtained in Example 1 to prepare a method for hot pressing non-rebound low-formaldehyde melamine-based foam, and the detailed steps are as follows:

[0075] 1) Preparation of high plasticity melamine-based resin prepolymer:

[0076] 1.1) Melamine, 96% paraformaldehyde solid, sodium pyrosulfite and deionized water are used as main raw materials; the addition amounts of the four main raw materials are 45 parts of melamine, 28 parts of 96% paraformaldehyde solid, 1.5 parts of sodium pyrosulfite and 25 parts of deionized water respectively in parts by weight;

[0077] 1.2) According to the ratio of the four main raw materials in step 1.1), melamine, 96% paraformaldehyde solid, sodium metabisulfite and deionized water are weighed, and the four raw materials are added into a reactor, and then sodium hydroxide solution is added to adjust the pH value to 8.0; then steam is used for heating, and when the reaction temperature is heated to 85° C., a second batch of melamine raw materials is added and the reaction is carried out at a constant temperature for 2 hours (the amount of the second batch of melamine raw materials added accounts for 1 / 5 of the total amount of melamine added);

[0078] 1.3) After the reaction, 10 parts of the modifier prepared in Example 1 were added according to weight, and the reaction was continued at 85° C. with stirring for 20 minutes. The end point was determined by turbidity method;

[0079] 1.4) cooling the reaction solution obtained in step 1.3) to 45° C., then adding 0.8% of the weight of the polyformaldehyde solid ethylene urea formaldehyde scavenger, stirring at a constant temperature for 1 hour, and then cooling to 25° C. to obtain a hot-pressing easy-setting melamine-based resin prepolymer, i.e., a high-plasticity melamine-based resin prepolymer;

[0080] 2) Preparation of functional foaming aid:

[0081] Into a 300Kg auxiliary agent reaction kettle, 30 parts of emulsifier sodium dodecylbenzene sulfonate, 32 parts of compound curing agent (including 15 parts of formic acid and 17 parts of phosphoric acid), 45 parts of compound foaming agent (30 parts of n-pentane and 15 parts of isopentane) and 16 parts of tetrafluoroethyl trifluoropropyl ether were added in sequence; then stirred and mixed (stirring speed was 15 rpm) for 30 minutes. After uniform mixing, the stirring speed was adjusted to 5 rpm for standby use;

[0082] 3) Preparation of hot-pressed, easy-to-set low-formaldehyde melamine-based foam:

[0083] The heat-pressing and easy-setting melamine-based resin prepolymer prepared in step 1) is cooled to 0°C by a single screw, and then enters a twin-screw machine through a metering screw, and the metering screw flow rate is 2.0 Kg / min; the functional foaming auxiliary agent obtained in step 2) enters the twin-screw machine simultaneously with the heat-pressing and easy-setting melamine-based resin prepolymer through a metering pump, and the metering pump flow rate is 420 g / min; the resin prepolymer and the auxiliary agent are mixed in the twin-screw machine for high-speed emulsification (the speed of the screw is 110 rpm), and the material obtained after emulsification is evenly distributed by a distribution trolley and then sent to a microwave foaming furnace through a conveyor belt for gradient foaming, the power of the microwave foaming furnace is 90 KW, the foaming time is 30 minutes, and the hot air temperature is 50°C, and the melamine-based foam primary product is obtained after foaming;

[0084] 4) Optimization of hot-pressed, easy-to-shape, low-formaldehyde melamine-based foam:

[0085] The melamine-based foam product obtained in step 3) is subjected to secondary curing treatment by microwave and moist hot steam, wherein the microwave power is 150KW, the moist hot steam pressure is 0.1-0.3MPa, the curing furnace temperature is 110°C, and the curing time is 82 minutes. After the curing treatment, a low-formaldehyde melamine-based foam with stable performance and easy to shape by hot pressing is obtained, that is, a low-formaldehyde melamine-based foam that does not rebound by hot pressing is obtained.

[0086] Embodiment 5:

[0087] The present invention uses the modifier obtained in Example 2 to prepare a method for hot pressing non-rebound low-formaldehyde melamine-based foam, and the detailed steps are as follows:

[0088] 1) Preparation of high plasticity melamine-based resin prepolymer:

[0089] 1.1) Melamine, 96% paraformaldehyde solid, sodium pyrosulfite and deionized water are used as main raw materials; the addition amounts of the four main raw materials are 48 parts of melamine, 30 parts of 96% paraformaldehyde solid, 1.8 parts of sodium pyrosulfite and 26 parts of deionized water respectively in parts by weight;

[0090] 1.2) According to the ratio of the four main raw materials in step 1.1), melamine, 96% paraformaldehyde solid, sodium metabisulfite and deionized water are weighed, and the four raw materials are added into a reactor, and then sodium hydroxide solution is added to adjust the pH value to 8.5; then steam is used for heating, and when the reaction temperature is heated to 90° C., a second batch of melamine raw materials is added and the reaction is carried out at a constant temperature for 2.5 hours (the amount of the second batch of melamine raw materials added accounts for 1 / 6 of the total amount of melamine added);

[0091] 1.3) After the reaction, 12 parts of the modifier prepared in Example 2 were added according to weight, and the reaction was continued at 90° C. with stirring for 25 minutes. The end point was determined by turbidity method;

[0092] 1.4) cooling the reaction solution obtained in step 1.3) to 45° C., then adding 1.0% of the weight of the polyformaldehyde solid ethylene urea formaldehyde scavenger, stirring at a constant temperature for 1.5 hours, and then cooling to 25° C. to obtain a hot-pressing easy-to-set melamine-based resin prepolymer, i.e., a high-plasticity melamine-based resin prepolymer;

[0093] 2) Preparation of functional foaming aid:

[0094] Into a 300Kg auxiliary agent reaction kettle, 31 parts of emulsifier fatty alcohol sodium sulfate, 32 parts of compound curing agent (12 parts of formic acid, 8 parts of acetic acid, 12 parts of hydrochloric acid), 42 parts of compound foaming agent (32 parts of n-pentane, 10 parts of cyclopentane) and 17 parts of perfluorobutyl methyl ether were added in sequence; then stirred and mixed (stirring speed was 16 rpm) for 25 min. After uniform mixing, the stirring speed was adjusted to 6 rpm for standby use;

[0095] 3) Preparation of hot-pressed, easy-to-set low-formaldehyde melamine-based foam:

[0096] The heat-pressing and easy-setting melamine-based resin prepolymer prepared in step 1) is cooled to 0°C by a single screw, and then enters a twin-screw machine through a metering screw, and the metering screw flow rate is 2.2 Kg / min; the functional foaming auxiliary agent obtained in step 2) enters the twin-screw machine simultaneously with the heat-pressing and easy-setting melamine-based resin prepolymer through a metering pump, and the metering pump flow rate is 423 g / min; the resin prepolymer and the auxiliary agent are mixed in the twin-screw machine for high-speed emulsification (the speed of the screw is 110 rpm), and the material obtained after emulsification is evenly distributed by a distribution trolley and then sent to a microwave foaming furnace through a conveyor belt for gradient foaming, the power of the microwave foaming furnace is 95 KW, the foaming time is 32 minutes, and the hot air temperature is 60°C, and the melamine-based foam primary product is obtained after foaming;

[0097] 4) Optimization of hot-pressed, easy-to-shape, low-formaldehyde melamine-based foam:

[0098] The melamine-based foam primary product obtained in step 3) is subjected to secondary curing treatment by microwave and moist hot steam, wherein the microwave power is 160KW, the moist hot steam pressure is 0.1-0.3MPa, the curing furnace temperature is 120°C, and the curing time is 85 minutes. After the curing treatment, a low-formaldehyde melamine-based foam with stable performance and easy to shape by hot pressing is obtained, i.e., a low-formaldehyde melamine-based foam that does not rebound by hot pressing is obtained.

[0099] Embodiment 6:

[0100] The present invention uses the modifier obtained in Example 3 to prepare a method for hot pressing non-rebound low-formaldehyde melamine-based foam, and the detailed steps are as follows:

[0101] 1) Preparation of high plasticity melamine-based resin prepolymer:

[0102] 1.1) Melamine, 96% paraformaldehyde solid, sodium pyrosulfite and deionized water are used as main raw materials; the addition amounts of the four main raw materials are 50 parts of melamine, 32 parts of 96% paraformaldehyde solid, 2 parts of sodium pyrosulfite and 28 parts of deionized water respectively in parts by weight;

[0103] 1.2) According to the ratio of the four main raw materials in step 1.1), melamine, 96% paraformaldehyde solid, sodium metabisulfite and deionized water are weighed, and the four raw materials are added into a reactor, and then sodium hydroxide solution is added to adjust the pH value to 8.8; then steam is used for heating, and when the reaction temperature is heated to 95° C., a second batch of melamine raw materials is added and the reaction is carried out at a constant temperature for 2.5 hours (the amount of the second batch of melamine raw materials added accounts for 1 / 7 of the total amount of melamine added);

[0104] 1.3) After the reaction, 14 parts of the modifier prepared in Example 3 were added according to weight, and the reaction was continued at 95° C. with stirring for 28 minutes. The end point was determined by turbidity method;

[0105] 1.4) cooling the reaction solution obtained in step 1.3) to 50° C., then adding 1.5% of the weight of the polyformaldehyde solid ethylene urea formaldehyde scavenger, stirring at a constant temperature for 1.8 hours, and then cooling to 25° C. to obtain a hot-pressing easy-setting melamine-based resin prepolymer, i.e., a high-plasticity melamine-based resin prepolymer;

[0106] 2) Preparation of functional foaming aid:

[0107] Into a 300Kg auxiliary agent reaction kettle, 32 parts of emulsifier sodium alkylnaphthalene sulfonate, 34 parts of compound curing agent (14 parts of formic acid, 5 parts of p-toluenesulfonic acid, 15 parts of hydrochloric acid), 44 parts of compound foaming agent (28 parts of n-pentane, 9 parts of isopentane, 7 parts of cyclopentane) and 20 parts of tetrafluoroethyl methyl ether were added in sequence; then stirred and mixed (stirring speed was 20 rev / sec) for 30 min. After uniform mixing, the stirring speed was adjusted to 6 rev / sec and the mixture was set aside.

[0108] 3) Preparation of hot-pressed, easy-to-set low-formaldehyde melamine-based foam:

[0109] The heat-pressing and easy-setting melamine-based resin prepolymer prepared in step 1) is cooled to 0°C by a single screw, and then enters a twin-screw machine through a metering screw, and the metering screw flow rate is 2.5Kg / min; the functional foaming auxiliary agent obtained in step 2) enters the twin-screw machine simultaneously with the heat-pressing and easy-setting melamine-based resin prepolymer through a metering pump, and the metering pump flow rate is 425g / min; the resin prepolymer and the auxiliary agent are mixed in the twin-screw machine for high-speed emulsification (the speed of the screw is 110 rpm), and the material obtained after emulsification is evenly distributed by a distribution trolley and then sent to a microwave foaming furnace through a conveyor belt for gradient foaming, the power of the microwave foaming furnace is 85KW, the foaming time is 30 minutes, and the hot air temperature is 70°C, and the melamine-based foam primary product is obtained after foaming;

[0110] 4) Optimization of hot-pressed, easy-to-shape, low-formaldehyde melamine-based foam:

[0111] The melamine-based foam product obtained in step 3) is subjected to secondary curing treatment by microwave and moist hot steam, wherein the microwave power is 170KW, the moist hot steam pressure is 0.1-0.3MPa, the curing furnace temperature is 140°C, and the curing time is 90 minutes. After the curing treatment, a low-formaldehyde melamine-based foam with stable performance and easy to shape by hot pressing is obtained, i.e., a low-formaldehyde melamine-based foam that does not rebound by hot pressing is obtained.

[0112] The relevant performance test data of the hot-pressed non-rebound low-formaldehyde melamine-based foam prepared in Examples 4-6 of the present invention are shown in Table 2.

[0113] Table 2 Relevant performance test data of the hot-pressed non-rebound low-formaldehyde melamine-based foam prepared in Examples 4-6 of the present invention

[0114]

Claims

1. A method for preparing a melamine resin prepolymer modifier, characterized in that: The preparation method comprises the following steps: a. Melamine and diglycolamine are used as main raw materials, and phosphoric acid and hypophosphorous acid are used as catalysts; b. Adding diglycolamine, melamine, phosphoric acid and hypophosphorous acid into a reactor in sequence, and then heating for reaction; c. After the reaction is completed, the reaction liquid is cooled, and after cooling, the reaction liquid is vacuumed under nitrogen protection; d. After evacuating in step c, slowly cool the reaction solution to ≤120°C, then open the nitrogen valve and flush in nitrogen to eliminate the vacuum state and balance the system pressure with the external air pressure; e. Then, desalted water is added to the reaction solution to control the solid content of the reaction solution to 65-85%, and stirring is continued to make the reaction solution and the desalted water mix evenly, and then the pH is adjusted to 6-8 to obtain a brown-red viscous modifier, i.e., a melamine resin prepolymer modifier, which is sealed and stored for later use.

2. The method for preparing the melamine resin prepolymer modifier according to claim 1, characterized in that: Expressed in parts by weight, the addition amounts of the two main raw materials and the two catalysts in step a are 15-35 parts of melamine, 60-100 parts of diglycolamine, 0.5-1.0 parts of phosphoric acid and 0.1-0.6 parts of hypophosphorous acid, respectively.

3. The method for preparing the melamine resin prepolymer modifier according to claim 1, characterized in that: During the heating reaction in step b, the temperature of the reaction solution is controlled to be 200-210° C., and the temperature is kept constant for 15-20 hours after the reaction material becomes transparent.

4. The method for preparing the melamine resin prepolymer modifier according to claim 1, characterized in that: In step c, the reaction liquid is cooled to 150-210° C. and vacuumed until the liquid becomes a sticky light yellow paste and no liquid evaporates within 30 minutes.

5. The method for preparing the melamine resin prepolymer modifier according to claim 1, characterized in that: In step e, the stirring time is controlled to be 1 to 5 minutes; and the pH value is adjusted to 6 to 8 using 20% ​​sodium hydroxide solution.

6. A method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam using the modifier obtained in claim 1, characterized in that: The method comprises the following steps: 1) Preparation of high plasticity melamine-based resin prepolymer: 1.1) Melamine, 96% paraformaldehyde solid, sodium pyrosulfite and deionized water are used as main raw materials; the addition amounts of the four main raw materials are 35-55 parts of melamine, 25-45 parts of 96% paraformaldehyde solid, 1-3 parts of sodium pyrosulfite and 20-40 parts of deionized water respectively by weight; 1.2) Weighing melamine, 96% paraformaldehyde solid, sodium metabisulfite and deionized water according to the ratio of the four main raw materials in step 1.1), adding the weighed four raw materials into a reactor, and then adding sodium hydroxide solution to adjust the pH value to 8-9; then heating with steam, when the reaction temperature is heated to 80-100° C., adding a second batch of melamine raw materials and reacting at a constant temperature for 1-3 hours; 1.3) After the reaction, add 5 to 15 parts of the modifier prepared according to claim 1 according to weight, continue stirring and reacting at 80 to 100° C. for 10 to 30 minutes, and determine the end point by turbidity method; 1.4) cooling the reaction solution obtained in step 1.3) to 40-70° C., then adding an ethylene urea formaldehyde scavenger, stirring at a constant temperature for 0.5-2 hours, and then cooling to 20-40° C. to obtain a hot-pressing easy-to-set melamine-based resin prepolymer, i.e., a high-plasticity melamine-based resin prepolymer; 2) Preparation of functional foaming aid: Add 25-35 parts of emulsifier, 30-40 parts of compound curing agent, 40-55 parts of compound foaming agent and 10-25 parts of fluoroether solvent into a 300Kg auxiliary agent reaction kettle in sequence, and then stir and mix evenly; after mixing various auxiliary agents, stir slowly to obtain a functional foaming auxiliary agent for standby use; 3) Preparation of hot-pressed, easy-to-set low-formaldehyde melamine-based foam: The heat-pressing and easy-setting melamine-based resin prepolymer prepared in step 1) is cooled to 0°C by a single screw, and then enters a twin-screw machine through a metering screw, and the metering screw flow rate is 1.5-2.5 Kg / min; the functional foaming auxiliary agent obtained in step 2) enters the twin-screw machine simultaneously with the heat-pressing and easy-setting melamine-based resin prepolymer through a metering pump, and the metering pump flow rate is 400-450 g / min; the resin prepolymer and the auxiliary agent are mixed in the twin-screw machine for high-speed emulsification, and the material obtained after emulsification is sent to a microwave foaming furnace for gradient foaming, the power of the microwave foaming furnace is 60-110 KW, the foaming time is 15-50 minutes, and the hot air temperature is 40-80°C, and the melamine-based foam primary product is obtained after foaming; 4) Optimization of hot-pressed, easy-to-shape, low-formaldehyde melamine-based foam: The melamine-based foam primary product obtained in step 3) is subjected to secondary curing treatment by microwave and moist hot steam, wherein the microwave power is 120-220 kW, the moist hot steam pressure is 0.1-0.3 MPa, the curing furnace temperature is 70-150° C., and the curing time is 40-120 minutes. After the curing treatment, a low-formaldehyde melamine-based foam with stable performance and easy to shape by hot pressing is obtained, i.e., a low-formaldehyde melamine-based foam that does not rebound by hot pressing is obtained.

7. The method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam according to claim 6, characterized in that: In step 1.1), the addition amounts of the four main raw materials are 44-54 parts of melamine, 28-32 parts of 96% paraformaldehyde solids, 1.5-2.5 parts of sodium pyrosulfite, and 20-30 parts of deionized water respectively; In step 1.2), the amount of the second batch of melamine raw materials added accounts for 1 / 4 to 1 / 8 of the total amount of melamine added; In step 1.3), the amount of ethylene urea formaldehyde scavenger added is 0.5-2% of the weight of the polyformaldehyde solid.

8. The method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam according to claim 6, characterized in that: In step 2), the emulsifier is 28-32 parts, the compound curing agent is 31-36 parts, the compound foaming agent is 40-45 parts, and the fluoroether solvent is 15-20 parts; When the stirring and mixing is uniform, the stirring speed is controlled to be 10 to 24 rpm and the stirring time is 20 to 40 min; when the slow stirring is performed, the stirring speed is controlled to be 5 to 10 rpm.

9. The method for preparing hot-pressed non-rebound low-formaldehyde melamine-based foam according to claim 6, characterized in that: Step 2) the emulsifier is at least one of sodium dodecylbenzene sulfonate, sodium fatty alcohol sulfate, sodium alkylnaphthalene sulfonate, sodium secondary alkyl sulfonate, sodium α-olefin sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium lauryl polyoxyethylene ether sulfate, α-sulfo fatty acid methyl ester, sodium cocoyl isethionate and sodium dodecyl alcohol polyoxyethylene ether carboxylate; The composite curing agent is prepared by mixing an organic protonic acid and an inorganic protonic acid; the organic protonic acid is at least one of formic acid, acetic acid, benzenesulfonic acid and p-toluenesulfonic acid, and the inorganic protonic acid is at least one of hydrochloric acid, sulfuric acid, boric acid and phosphoric acid; The composite foaming agent is prepared by mixing n-pentane, isopentane and cyclopentane; The fluoroether solvent is at least one of tetrafluoroethyl trifluoropropyl ether, perfluorobutyl methyl ether, tetrafluoroethyl methyl ether, hexafluoroisopropyl ether, and hexafluoroisopropyl ether.

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