A solvent-free heat-resistant flame-retardant polyurethane adhesive and a preparation method thereof

Abstract

The application discloses a kind of solventless heat-resistant flame-retardant polyurethane adhesive and preparation method thereof, belong to polyurethane adhesive technical field.Pre-polymer is prepared by IPDI and phthalic anhydride diethylene glycol reaction, dihydroxy alkylate hypophosphorous acid (DAHA) ammonium salt is obtained by the reaction of hypophosphorous acid, paraformaldehyde and ammonia water, DAHA ammonium salt, 1,4-butanediol and terephthalic acid are mixed to prepare flame-retardant polyester polyol by intermittent process method, pre-polymer is mixed uniformly with flame-retardant polyester polyol to prepare solventless heat-resistant flame-retardant polyurethane adhesive.The solventless heat-resistant flame-retardant polyurethane adhesive prepared by the application has low viscosity, excellent flame-retardant heat-resistant performance, T type peel strength at room temperature is 5.4N / mm, T type peel strength at 80 DEG C can reach 3.1N / mm, flame-retardant effect reaches UL-94V-0 level, solve the shortcomings that polyurethane adhesive heat resistance and flame-retardant performance are poor, have significant economic benefit and social benefit.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane adhesive technology, specifically relating to a solvent-free, heat-resistant, and flame-retardant polyurethane adhesive and its preparation method. Background Technology

[0002] Thermoplastic polyurethane adhesives possess excellent low-temperature resistance, as well as good flexibility, toughness, and wettability on various substrates. A significant advantage of these materials is their ability to be customized to meet the diverse requirements of different industrial applications. However, as the operating temperature of the material increases, the inherently poor heat resistance of thermoplastic polyurethane leads to a sharp decline in the peel strength of polyurethane adhesives. Furthermore, polyurethane generally has a LOI value below 21%, classifying it as a flammable material. When burned, it releases large amounts of toxic gases and fumes such as HCN, HNCO, CO, NO, and NO2, posing a significant threat to human life and property. Therefore, improving the flame retardancy of polyurethane materials is of great importance. Currently, flame retardants in polyurethane are mainly additive flame retardants and reactive flame retardants. Additive flame retardants have low compatibility with the substrate, and their use often leads to a decrease in the mechanical and adhesive properties of the product. In contrast, reactive flame retardants can overcome these shortcomings and impart durable flame retardancy to the adhesive. Summary of the Invention

[0003] The purpose of this invention is to develop a solvent-free heat-resistant and flame-retardant polyurethane adhesive that is both heat-resistant and has excellent flame-retardant properties, in order to solve the problem of poor heat resistance and flame-retardant properties of current polyurethane adhesives, thereby broadening the application fields of polyurethane adhesives.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A solvent-free, heat-resistant, and flame-retardant polyurethane adhesive is a thermoplastic and two-component type. Component A is a prepolymer prepared by reacting IPDI with phthalic anhydride and diethylene glycol; component B is a flame-retardant polyester polyol, mainly containing nitrogen and phosphorus flame-retardant elements, with a benzene ring structure in its molecular structure and a functionality of 2. The preparation method is as follows:

[0006] (1) The preparation steps of the prepolymer are as follows: add measured amounts of IPDI and diethylene glycol phthalic anhydride to the reactor, heat to 80°C under nitrogen atmosphere and stir for 3 hours to obtain polyurethane adhesive prepolymer.

[0007] (2) The preparation steps of flame-retardant polyester polyol are as follows: Deionized water is added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixed solution is then heated to 80°C while stirring, and paraformaldehyde is slowly added dropwise to the solution using a reflux device. The reaction is kept at a high temperature for 8 hours under a nitrogen atmosphere. After the reaction is completed, the reaction solution is cooled to room temperature, and ammonia is added dropwise to the reaction solution while stirring. When the pH of the reaction solution is greater than or equal to 7, the dropwise addition is stopped. Then, excess water in the reaction solution is removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkyl hypophosphite (DAHA) ammonium salt. DAHA ammonium salt is added to the reaction vessel, along with a measured amount of terephthalic acid, 1,4-butanediol, and 60 ppm of tetrabutyl titanate catalyst. Flame-retardant polyurethane polyol is prepared by batch synthesis under a nitrogen atmosphere. The first stage involves rapid heating and dehydration; the second stage involves further heating to carry out a polycondensation reaction to remove excess alcohol and water.

[0008] (3) The preparation steps of solvent-free heat-resistant and flame-retardant polyurethane adhesive are as follows: the prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C, coated onto the surface of the bonding substrate, and then cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0009] Furthermore, in step (1), the molar ratio of IPDI to diethylene glycol phthalic anhydride is 2.1 to 2.8. Preferably, the molar ratio is 2.4.

[0010] Furthermore, in step (2), the molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite is 2.1 to 2.5, preferably 2.3.

[0011] Furthermore, in step (2), the alcohol-acid ratio of terephthalic acid to DAHA ammonium salt and 1,4-butanediol is 1.05 to 1.4, preferably 1.2.

[0012] Furthermore, in step (2), the molar ratio of DAHA ammonium salt to 1,4-butanediol is 0.4 to 0.6, preferably 0.5.

[0013] Furthermore, the synthesis process of the flame-retardant polyester polyol in step (2) adopts a batch method. The reaction temperature of the first stage is 130~160℃ and the reaction time is 2.0~3.5 hours; the reaction temperature of the second stage is 200~230℃ and the reaction time is 3.0~5.5 hours. The preferred reaction temperature of the first stage is 150℃ and the reaction time is 2.5 hours, and the preferred reaction temperature of the second stage is 220℃ and the reaction time is 4.0 hours.

[0014] Furthermore, in step (3), the R-value ratio of the prepolymer to the flame-retardant polyester polyol (-NCO / -OH) is 1.2 to 1.8. Preferably, the R-value ratio is 1.4.

[0015] As a preferred technical solution:

[0016] In the above step (1) scheme, in addition to using IPDI as isocyanate, MDI, HDI, TDI and HMDI can also be used as isocyanates. In this invention, IPDI is preferred.

[0017] In step (2) above, hypophosphite can be replaced with monohydrate and sodium hypophosphite, paraformaldehyde can be replaced with formaldehyde solution, tetrabutyl titanate catalyst can be replaced with one or more of p-toluenesulfonic acid and methanesulfonic acid, 1,4-butanediol can be replaced with one or more of 1,6-hexanediol, diethylene glycol, ethylene glycol, and 1,3-propanediol, and terephthalic acid can be replaced with one or more of isophthalic acid, phthalic anhydride, and adipic acid. The present invention preferably uses hypophosphite, paraformaldehyde, 1,4-butanediol, terephthalic acid, and tetrabutyl titanate as raw materials for the preparation of flame-retardant polyester polyols.

[0018] In this invention, the isocyanate value of the prepolymer prepared from IPDI and diethylene glycol is 8.2-8.7%, the acid value of the prepared flame-retardant polyester polyol is 0.5-3.0 mgKOH / g, the hydroxyl value is 50-100 mgKOH / g, the viscosity of the prepolymer and the flame-retardant polyester polyol when mixed at 80℃ is 2500-3700 mPa·s, the T-peel strength at room temperature after complete curing reaches 5.4 N / mm, the peel strength at 80℃ is 3.1 N / mm, and the flame retardant effect reaches UL-94V-0 level. The solvent-free flame-retardant heat-resistant polyurethane adhesive obtained by this invention is green, environmentally friendly, and pollution-free, with low viscosity, high peel strength, and excellent heat resistance and flame retardant properties.

[0019] The principle of this invention is as follows:

[0020] The hypophosphite in this invention has strong reducing properties, while the aldehyde group has oxidizing properties. Paraformaldehyde decomposes into formaldehyde under the catalysis of hydrochloric acid to form a formaldehyde solution. Hypophosphite reacts with formaldehyde in a redox reaction to generate dihydroxyalkyl hypophosphite (DAHA). Then, ammonia water is used to neutralize the acid radical ions in DAHA to form DAHA ammonium salt. Subsequently, the hydroxyl groups of DAHA ammonium salt and 1,4-butanediol undergo a polycondensation reaction with the carboxyl groups of terephthalic acid to form a flame-retardant polyester polyol with hydroxyl-terminated chains. Since this flame-retardant polyester polyol contains a large amount of nitrogen and phosphorus flame-retardant elements, the polyurethane adhesive prepared with it has a good flame-retardant effect. Furthermore, this flame-retardant polyester polyol also contains a large number of benzene ring structures with good heat resistance, so the polyurethane adhesive prepared with it also has a good heat resistance effect.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) The heat-resistant and flame-retardant polyurethane adhesive of the present invention is solvent-free. The mixed viscosity of the adhesive at 80°C is 2500~3700mPa·s, and the T-type peel strength after complete curing is 5.4N / mm. It has the advantages of low coating viscosity, high peel strength, and being green, environmentally friendly and pollution-free.

[0023] (2) The heat-resistant and flame-retardant polyurethane adhesive of the present invention has excellent heat resistance due to the introduction of a large number of benzene ring structures with excellent heat resistance. The T-peel strength at an operating temperature of 80°C is 3.1 N / mm, which has excellent heat resistance.

[0024] (3) The heat-resistant and flame-retardant polyurethane adhesive of the present invention is a reactive flame retardant polyester polyol containing a large amount of nitrogen and phosphorus flame retardant elements. This avoids the disadvantage of adding additive flame retardants to the matrix and causing deterioration of other mechanical properties of the material. The flame retardant effect can reach UL-94V-0 level without affecting the mechanical properties of the material, and has excellent flame retardant performance. Attached Figure Description

[0025] Figure 1 The image shows the FTIR spectrum of the flame-retardant polyester polyol in Example 1.

[0026] Figure 2 The image shows the XPS spectrum of the flame-retardant polyester polyol in Example 1. Detailed Implementation

[0027] To better describe the solvent-free, heat-resistant, and flame-retardant polyurethane adhesive and its preparation method according to the present invention, the following will be further illustrated with some specific embodiments. It is worth noting that the following content is only an explanation of the performance of the present invention, and any improvements and adjustments made based on the present invention should be considered within the scope of protection of the present invention.

[0028] Example 1 (alcohol-acid ratio 1.2, DAHA ammonium salt to BDO molar ratio 0.5)

[0029] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0030] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 0.5, followed by terephthalic acid at an alcohol-acid ratio of 1.2 and 60 ppm tetrabutyl titanate catalyst. The mixture was thoroughly mixed, and flame-retardant polyurethane polyols were prepared by batch synthesis under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0031] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0032] Example 2 (alcohol-acid ratio 1.3, DAHA ammonium salt to BDO molar ratio 0.5)

[0033] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0034] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 0.5, followed by terephthalic acid at an alcohol-acid ratio of 1.3 and 60 ppm tetrabutyl titanate catalyst. After thorough mixing, flame-retardant polyurethane polyols were prepared using a batch synthesis process under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0035] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0036] Comparative Example 1 (alcohol-to-acid ratio 1.5, DAHA ammonium salt to BDO molar ratio 0.5)

[0037] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0038] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 0.5, followed by terephthalic acid at an alcohol-acid ratio of 1.5 and 60 ppm tetrabutyl titanate catalyst. After thorough mixing, flame-retardant polyurethane polyols were prepared using a batch synthesis process under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0039] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0040] Comparative Example 2 (alcohol-to-acid ratio 1.2, DAHA ammonium salt to BDO molar ratio 1.0)

[0041] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0042] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 1.0, followed by terephthalic acid at an alcohol-acid ratio of 1.2 and 60 ppm tetrabutyl titanate catalyst. The mixture was thoroughly mixed, and flame-retardant polyurethane polyols were prepared by batch synthesis under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0043] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0044] Comparative Example 3 (alkyd ratio 1.2, DAHA ammonium salt to BDO molar ratio 0.3)

[0045] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0046] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 0.3, followed by terephthalic acid at an alcohol-acid ratio of 1.2 and 60 ppm tetrabutyl titanate catalyst. The mixture was thoroughly mixed, and flame-retardant polyurethane polyols were prepared by batch synthesis under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0047] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0048] Comparative Example 4 (alkyd ratio 1.2, DAHA ammonium salt to BDO molar ratio 0.1)

[0049] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0050] (2) Preparation of flame-retardant polyester polyol: Deionized water was added to the reaction vessel, followed by hypophosphite and a few drops of concentrated hydrochloric acid. The mixture was then heated to 80°C while stirring, and paraformaldehyde was slowly added dropwise to the solution using a reflux device. The reaction was maintained at this temperature for 8 hours under a nitrogen atmosphere, with a molar ratio of paraformaldehyde (converted to formaldehyde) to hypophosphite of 2.3. After the reaction was completed, the reaction solution was cooled to room temperature, and ammonia was added dropwise to the reaction solution while stirring. The addition was stopped when the pH of the reaction solution was greater than or equal to 7. The excess water in the reaction solution was then removed by rotary evaporation to obtain ammonia-neutralized dihydroxyalkylated hypophosphite (DAHA) ammonium salt. DAHA ammonium salt and 1,4-butanediol were added to a reactor at a molar ratio of 0.1, followed by terephthalic acid at an alcohol-acid ratio of 1.2 and 60 ppm tetrabutyl titanate catalyst. The mixture was thoroughly mixed, and flame-retardant polyurethane polyols were prepared by batch synthesis under a nitrogen atmosphere. The first stage reaction temperature was 150℃ and the reaction time was 2.5 hours; the second stage reaction temperature was 220℃ and the reaction time was 4.0 hours.

[0051] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0052] Comparative Example 5 (alkyd ratio 1.2, without DAHA ammonium salt)

[0053] (1) Preparation of prepolymer: IPDI and diethylene glycol phthalic anhydride were added to the reactor with an isocyanate value (R) of 2.4. The mixture was heated to 80°C and stirred for 3 hours under a nitrogen atmosphere to obtain polyurethane adhesive prepolymer.

[0054] (2) Preparation of polyester polyol: 1,4-Butanediol and terephthalic acid were added to the reactor at an alcohol-acid ratio of 1.2, and then 60 ppm of tetrabutyl titanate catalyst was added. The mixture was mixed evenly and flame-retardant polyurethane polyol was prepared by batch synthesis under nitrogen atmosphere. The reaction temperature of the first stage was 150℃ and the reaction time was 2.5 hours; the reaction temperature of the second stage was 220℃ and the reaction time was 4.0 hours.

[0055] (3) Preparation of solvent-free heat-resistant and flame-retardant polyurethane adhesive: The prepolymer prepared in step (1) and the flame-retardant polyester polyol prepared in step (2) are mixed evenly at 80°C with an R value ratio of 1.4. The mixture is then coated onto the surface of the bonding substrate and cured completely at 80°C. The bonding substrate is a TPU / PBT fiber layer.

[0056] Performance testing

[0057] Test method:

[0058] (1) T-peel strength test: The T-peel strength test was carried out at room temperature in accordance with GB / T2791-1995 "Test method for T-peel strength of adhesives and flexible materials to flexible materials";

[0059] (2) Heat resistance test: Place the bonded TPU / PBT strip in a constant temperature oven at 80°C for 2 hours, and then quickly perform a T-peel strength test. The test standard is GB / T2791-1995 "Test method for T-peel strength of adhesives, flexible materials to flexible materials".

[0060] (3) Vertical burning test: Cut the cured polyurethane adhesive into test strips with a specification of 125mm×10mm×4mm. The UL-94 level test standard shall be in accordance with GB / T 2408-2008.

[0061] (3) Limiting Oxygen Index (LOI): The cured polyurethane adhesive is cut into test strips of 140mm×6mm×3mm and flame retardancy is tested according to ASTM D2863-2000 standard.

[0062] The flame-retardant polyester polyol and solvent-free heat-resistant flame-retardant polyurethane adhesives prepared in the examples and comparative examples were subjected to performance tests, and the results are shown in Tables 1 and 2 (the methods for determining the technical indicators of the present invention are all standard methods used in the art).

[0063]

[0064]

[0065] As can be seen from Examples 1, 2 and Comparative Example 1 in Table 1, a higher alkyd-acid ratio leads to a significant increase in the hydroxyl value of the prepared flame-retardant polyester polyol. This indicates that the relative molecular mass of the prepared flame-retardant polyester polyol decreases as the alkyd-acid ratio increases.

[0066] Table 2 shows that the viscosity of the polyurethane adhesives in all examples and comparative examples did not change significantly. However, data from Examples 1, 2, and 1 (Comparative Example 1) revealed that when the molar ratio of DAHA ammonium salt to 1,4-butanediol was the same, a higher alkyd ratio led to a decrease in the peel strength and heat resistance of the adhesive. This is because a higher alkyd ratio reduces the relative molecular mass of the flame-retardant polyester polyol, thus lowering the cohesive energy of the prepared polyurethane adhesive, resulting in decreased peel strength and heat resistance. Furthermore, data from Examples 1, 2, 3, 4, and 5 (Comparative Example 5) showed that when the alkyd ratio was the same, a decrease in the molar ratio of DAHA ammonium salt to 1,4-butanediol slightly increased the peel strength and heat resistance of the polyurethane adhesive, but resulted in poor flame retardancy, failing to meet the UL-94V-0 rating. This is because the addition of DAHA ammonium salt slightly reduces the cohesive energy of polyurethane adhesives, resulting in a slight decrease in peel strength and heat resistance; however, when the amount of DAHA added is reduced, the content of flame-retardant elements nitrogen and phosphorus in the prepared flame-retardant polyester polyol is also reduced, resulting in a significant decrease in the flame-retardant properties of polyurethane adhesives.

[0067] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A process for the preparation of a solvent free heat resistant flame retardant polyurethane adhesive characterized by: The adhesive is thermoplastic and two-component type, wherein component A is a prepolymer prepared by reacting isocyanate with phthalic anhydride diethylene glycol; component B is a flame-retardant polyester polyol, the flame-retardant elements are nitrogen and phosphorus, the molecular structure contains benzene ring structure, and the functionality is 2; the preparation method comprises the following steps: (1) preparation of the prepolymer: isocyanate and phthalic anhydride diethylene glycol are stirred and reacted at 80 DEG C for 3 hours under nitrogen atmosphere to obtain the prepolymer; (2) preparation of the flame-retardant polyester polyol: hypophosphorous acid and concentrated hydrochloric acid are added in deionized water, and the mixture is heated to 80 DEG C while stirring, and then polyformaldehyde is slowly added dropwise, and the mixture is kept at temperature for 8 hours under nitrogen atmosphere, and then cooled to room temperature, and ammonia water is added dropwise while stirring until the pH of the reaction solution is greater than or equal to 7, and then rotary evaporation is performed to obtain DAHA ammonium salt, and then acid, alcohol and catalyst are added, and the flame-retardant polyester polyol is prepared by using intermittent synthesis process under nitrogen atmosphere; (3) preparation of the adhesive: the prepolymer and the flame-retardant polyester polyol are mixed uniformly at 80 DEG C, and then coated on a TPU / PBT fiber layer, and then cured completely at 80 DEG C; In step (2), the alcohol acid ratio is 1.05-1.4, and the molar ratio of DAHA ammonium salt to alcohol is 0.4-0.

6.

2. The method of claim 1, wherein: In step (1), the molar ratio of isocyanate to phthalic anhydride diethylene glycol is 2.1-2.8, and the isocyanate value of the prepared prepolymer is 8.2-8.7%.

3. The method of claim 1, wherein: In step (1), the isocyanate is at least one of IPDI, MDI, HDI, TDI and HMDI.

4. The method of claim 1, wherein: In step (2), the molar ratio of polyformaldehyde (converted into formaldehyde) to hypophosphorous acid is 2.1-2.5, and the acid value of the prepared flame-retardant polyester polyol is 0.5-3.0 mgKOH / g, and the hydroxyl value is 50-100 mgKOH / g.

5. The method of claim 1, wherein: In step (2), the acid is one or more of terephthalic acid, isophthalic acid and phthalic anhydride; the alcohol is one or more of 1,4-butanediol, 1,6-hexanediol, diethylene glycol and ethylene glycol; and the catalyst is one or more of tetrabutyl titanate, p-toluenesulfonic acid and methane sulfonic acid.

6. The method of claim 1, wherein: In step (2), the intermittent synthesis process parameters are as follows: the reaction temperature of the first stage is 130-160 DEG C, and the reaction time is 2.0-3.5 hours; the reaction temperature of the second stage is 200-230 DEG C, and the reaction time is 3.0-5.5 hours.

7. The method of claim 1, wherein: In step (3), the R value of the polyurethane is 1.2-1.8.

Images