Low-shrinkage polyurethane pouring sealant and preparation method thereof

Abstract

The application relates to a low-shrinkage polyurethane pouring sealant and a preparation method thereof, and belongs to the technical field of pouring sealants. The preparation method of the low-shrinkage polyurethane pouring sealant comprises the following steps: adding polyhydric alcohol, reinforcing filler, coupling agent and plasticizer into a reactor, adding a defoaming agent to obtain an A component; mixing isocyanate, epoxy resin and a diluent at room temperature to obtain a B component; mixing the A component and the B component and adding into a reaction kettle, adding a flame-retardant reinforcing agent, uniformly stirring and mixing, reducing the temperature to 80 DEG C, adding a curing agent, then, degassing in a vacuum oven at 60 DEG C, discharging, storing to obtain a two-component polyurethane pouring sealant. In the technical scheme, the epoxy resin enhances the flame-retardant performance, and the polyurethane has excellent comprehensive performance, including reducing the curing shrinkage of the polyurethane, improving the mechanical and thermal performance of the polyurethane and the like. The shrinkage of the polyurethane pouring sealant prepared by the application is as low as 1.2%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pouring sealant, and particularly relates to a low-shrinkage polyurethane pouring sealant and a preparation method thereof. BACKGROUND

[0002] The polyurethane material gradually becomes the mainstream material for electronic device pouring because of excellent water resistance, oil resistance, shock absorption, electrical insulation, low-temperature resistance and wide adjustable range of mechanical properties, and can be used in a wide temperature range and can be adjusted to achieve the purpose of adjusting the curing speed and mechanical properties in different environments.

[0003] In the resin polymerization reaction, the volume shrinkage and shrinkage stress generated by the resin are inevitable. Before the polymerization reaction occurs, the force between monomers is van der Waals force, and after the polymerization reaction occurs, the force between monomers becomes covalent bond force. The covalent bond force is obviously stronger than the van der Waals force, and the intermolecular distance is reduced, which is manifested in macroscopic as volume reduction, resulting in volume shrinkage. Before the gel point of the polymerization reaction, the monomers can reduce the volume shrinkage by flowing by themselves, and at this time, no shrinkage stress is generated. After the gel point is generated, the monomers cannot flow due to solidification and cannot compensate the volume shrinkage, resulting in shrinkage stress. The volume shrinkage generated by the resin makes it difficult to control the size of the material, which easily leads to deformation, fracture and adhesion reduction of the material, and restricts its application in a wider field. Therefore, it is necessary to produce a low-shrinkage and heat-resistant polyurethane pouring sealant. SUMMARY

[0004] The purpose of the application is to provide a low-shrinkage polyurethane pouring sealant and a preparation method thereof. By forming an interpenetrating polymer network system between the polyurethane and the epoxy resin, the curing shrinkage performance of the polyurethane is reduced. By adding a double-bond-containing flame-retardant reinforcing agent, an interpenetrating network structure can be formed between the epoxy resin, and the flame-retardant performance of the epoxy resin is improved. In the synthesis process of the polyurethane, nano calcium oxide is added to adsorb CO2 gas in the reaction process, which prevents the foaming of the polyurethane. In addition, the nano calcium oxide adsorbing CO2 gas can be linked with the flame-retardant reinforcing agent to achieve better flame retardation.

[0005] The technical problem to be solved by the application is that in the resin polymerization reaction, the volume shrinkage and shrinkage stress generated by the resin are inevitable. The volume shrinkage generated by the resin makes it difficult to control the size of the material, which easily leads to deformation, fracture and adhesion reduction of the material, and restricts its application in a wider field. Therefore, it is necessary to produce a low-shrinkage and heat-resistant polyurethane pouring sealant.

[0006] The purpose of the application can be achieved by the following technical scheme:

[0007] A preparation method of a low-shrinkage polyurethane pouring sealant, comprising the following steps:

[0008] S1, polyol 50-100 parts, reinforcing filler 20-30 parts, coupling agent 1-2 parts and plasticizer 10-20 parts are added into the reactor, keeping the vacuum degree (-0.08) - (-0.09) MPa stirring 1.5 h, adding defoaming agent 0.05-0.1 parts, to get A component;

[0009] S2, isocyanate 40-90 parts, epoxy resin 10-20 parts and diluent 30-40 parts are mixed at room temperature, to get B component;

[0010] S3, A component and B component are mixed and added to the reaction kettle, dehydrated at 120-130℃, vacuum degree (-0.09) - (-0.1) MPa for 10 min, adding flame retardant reinforcing agent 5-10 parts, stirring and mixing uniformly, then the temperature is reduced to 80℃, adding curing agent 0.1-0.2 parts, then the mixture is degassed in vacuum oven at 60℃ for 10 min, discharging, storage, to get two-component polyurethane pouring sealant.

[0011] Preferably, the reinforcing filler is selected from nano calcium oxide, particle size is 10-30 nm.

[0012] Preferably, the coupling agent is selected from one of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane, γ-aminopropyl triethoxysilane, 3-(2,3-epoxypropoxy) propyl trimethoxysilane.

[0013] Preferably, the plasticizer is selected from one or more of dioctyl phthalate, polyol ester, citric acid ester.

[0014] Preferably, the defoaming agent is selected from BYK1794 or polymer type defoaming agent BYK1790.

[0015] Preferably, the diluent is selected from one or several of butanone, ethyl silicate, 1.4-butylene glycol ester, 1.6-hexanediol ester and low hydroxyl value acrylic resin in any ratio.

[0016] The present application considers that the epoxy resin has the advantages of high modulus, high adhesion, low shrinkage, good corrosion resistance, etc., but has the disadvantage of poor flame retardant performance, so a specific flame-retardant reinforcing agent is selected. In the condensed phase, the phosphorus-containing flame retardant releases phosphoric acid such as metaphosphoric acid and other strong acids through thermal decomposition, promoting dehydration of the matrix to form carbon. At the same time, the double bonds in the flame retardant internally crosslink with the epoxy resin to form an interpenetrating network structure, improving the stability and density of the carbon layer and preventing heat release and smoke leakage. In the gas phase, the phosphorus in the flame retardant quenches active groups such as ·H and ·HO in the combustion chain reaction and other free radicals by releasing ·PO and ·PO2, thereby terminating the chain reaction. In addition, nitrogen-containing radicals produce non-combustible gases, reducing the oxygen content. In summary, the interpenetrating network structure produced by the double bond crosslinking reaction and the synergistic effect of phosphorus and nitrogen enables the epoxy resin to have excellent flame retardant performance.

[0017] The enhancement of the flame retardant performance of the epoxy resin enables the epoxy resin to form an interpenetrating network structure with the polyurethane, thereby imparting excellent comprehensive performance to the polyurethane, including reducing the curing shrinkage of the polyurethane and improving the mechanical and thermal performance of the polyurethane.

[0018] It should be noted that considering that CO2 is inevitably generated during the synthesis of the polyurethane, the present application introduces calcium oxide as the reinforcing filler component during the synthesis of the polyurethane. Calcium oxide acts as a CO2 adsorption material and a reinforcing material during the synthesis of the polyurethane. The calcium oxide adsorbed with CO2 can play a synergistic role with the flame-retardant reinforcing agent in the later flame-retardant effect. The principle is that high temperature promotes the release of CO2 in calcium oxide, thereby reducing the oxygen concentration around the flame and achieving the flame-retardant effect.

[0019] Preferably, the polyol is selected from a polyether polyol or a polyester polyol.

[0020] Preferably, the isocyanate is selected from an aromatic polyisocyanate, and the aromatic polyisocyanate is selected from one of a polyphenyl polymethylene polyisocyanate, a diphenylmethane diisocyanate, and a toluene diisocyanate.

[0021] It should be noted that the present application considers the stabilizing effect of the flame-retardant reinforcing agent in the polyurethane system, and selects an aromatic polyisocyanate. Through π-π conjugation between benzene rings, the flame-retardant reinforcing agent is stably present in the polyurethane system, achieving better flame-retardant effect.

[0022] Synthesis of the flame-retardant reinforcing agent:

[0023] Cinnamaldehyde (13.216 g, 0.1 mol), 4,4'-diaminodiphenyl methane (9.92 g, 0.05 mol), flame retardant intermediate DOPO (21.6 g, 0.1 mol) and 250 mL of ethanol were mixed in a three-necked flask, the reaction temperature was raised to 80°C and stirred at this temperature for 0.5 h, when the solid was completely dissolved, 10 mL of formic acid was added to the reaction system, and the reaction was kept at constant temperature for 4 h. Then, the solution was filtered to obtain a yellow precipitate, which was then washed with distilled water several times. Finally, it was dried in an oven at 80°C for 24 h to remove the moisture, to obtain a flame retardant enhancer, the structural formula of which is as follows:

[0024]

[0025] It should be noted that the flame retardant enhancer in the present application contains -NH, which can react with the epoxy group during the curing process of the epoxy resin, thereby promoting the curing of the epoxy resin.

[0026] The beneficial effects of the present application are:

[0027] (1) In the technical scheme of the present application, a specific flame retardant enhancer is selected, which contains a phosphorus-containing flame retardant that releases phosphoric acid, such as metaphosphoric acid, a strong acid, to promote dehydration and carbonization of the matrix in the condensed phase. At the same time, the double bonds in the flame retardant are internally crosslinked with the epoxy resin to form an interpenetrating network structure, which improves the stability and density of the carbon layer and prevents heat release and smoke leakage. In the gas phase, the phosphorus in the flame retardant quenches active groups such as ·H, ·HO and other free radicals in the combustion chain reaction by releasing ·PO, ·PO2, thereby terminating the chain reaction. In addition, nitrogen-containing free radicals produce non-combustible gases, reducing the oxygen content. In addition, the interpenetrating network structure produced by the double bond crosslinking reaction and the synergistic effect of phosphorus and nitrogen enables the epoxy resin to have excellent flame retardant properties.

[0028] (2) In the technical scheme of the present application, the enhancement of the flame retardant properties of the epoxy resin enables the epoxy resin to impart excellent comprehensive properties to the polyurethane after forming an interpenetrating network structure with the polyurethane, including reducing the curing shrinkage of the polyurethane, improving the mechanical and thermal properties of the polyurethane, etc. The shrinkage of the polyurethane potting adhesive prepared by the present application is as low as 1.2%.

[0029] (3) In the technical scheme of the present application, considering that CO2 is inevitably generated during the synthesis of polyurethane, the component of the reinforcing filler introduced in the synthesis of polyurethane in the present application is calcium oxide, which acts as a CO2 adsorption material and a reinforcing material during the synthesis of polyurethane. The calcium oxide adsorbed with CO2 can play a synergistic role with the flame retardant enhancer in the later flame retardant effect, the principle of which is: high temperature promotes the release of CO2 in calcium oxide, reduces the concentration of oxygen around the flame, and plays a flame-retardant role.

[0030] (4) In the technical scheme of the present application, the flame-retardant reinforcing agent contains -NH, which can react with the epoxy group during the curing process of the epoxy resin, thereby promoting the curing of the epoxy resin. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0032] In the present application, the main raw materials used are as follows:

[0033] Polyether polyol NJ-305, Jurong Ningwu New Material Co., Ltd.;

[0034] Polyester polyol PDP-70, Nanjing Jinling Stepan Chemical Co., Ltd.;

[0035] Epoxy resin E-51, Condis Chemical Industry (Hubei) Co., Ltd.

[0036] Synthesis of flame-retardant reinforcing agent:

[0037] Cinnamyl aldehyde (13.216 g, 0.1 mol), 4,4'-diaminodiphenyl methane (9.92 g, 0.05 mol), flame retardant intermediate DOPO (21.6 g, 0.1 mol) and 250 mL of ethanol were mixed in a three-necked flask, the reaction temperature was raised to 80℃ and stirred at this temperature for 0.5 h, when the solid was completely dissolved, 10 mL of formic acid was added to the reaction system, and the reaction was carried out at constant temperature for 4 h. Then, the solution was filtered to obtain a yellow precipitate, which was then washed with distilled water several times. Finally, it was dried in an oven at 80℃ for 24 h to remove the water, and the flame-retardant reinforcing agent was obtained.

[0038] Example 1

[0039] A preparation method of a low-shrinkage polyurethane pouring sealant, comprising the following steps:

[0040] S1, polyether polyol NJ-305 50 g, reinforcing filler (nano calcium oxide) 20 g, coupling agent (N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane) 1 g and plasticizer (dioctyl phthalate) 10 g were added into a reactor, the vacuum degree was kept at (-0.08)-(-0.09) MPa, and stirring was carried out for 1.5 h, defoaming agent (BYK1794) 0.05 g was added, and component A was obtained;

[0041] S2, isocyanate (diphenyl methane diisocyanate) 40g, epoxy resin (E-51) 10g and diluent (butanone, ethyl silicate) 30g are mixed at room temperature under stirring to obtain component B;

[0042] S3, component A and component B are mixed and added into a reaction kettle, dehydrated at 120℃ under vacuum degree (-0.09)-(-0.1) MPa for 10 min, then flame-retardant reinforcing agent 5g is added, after uniform stirring, the temperature is reduced to 80℃, then curing agent (4,4'-diamino diphenyl methane) 0.1g is added, then the mixture is degassed in a vacuum oven at 60℃ for 10 min, discharged, stored, to obtain two-component polyurethane pouring sealant.

[0043] Example 2

[0044] A method for preparing a low-shrinkage polyurethane pouring sealant, comprising the following steps:

[0045] S1, polyester polyol PDP-70 80g, reinforcing filler (nano calcium oxide) 25g, coupling agent (γ-aminopropyl triethoxysilane) 1.5g and plasticizer (polyol ester) 15g are added into a reactor, vacuum degree is kept at (-0.08)-(-0.09) MPa, stirred for 1.5h, defoaming agent (polymer defoaming agent BYK1790) 0.08g is added to obtain component A;

[0046] S2, isocyanate (polyphenyl poly-methylene polyisocyanate) 70g, epoxy resin (E-51) 15g and diluent (butanone, ethyl silicate and 1.4-butylene glycol ester) 35g are mixed at room temperature under stirring to obtain component B;

[0047] S3, component A and component B are mixed and added into a reaction kettle, dehydrated at 120℃ under vacuum degree (-0.09)-(-0.1) MPa for 10 min, then flame-retardant reinforcing agent 8g is added, after uniform stirring, the temperature is reduced to 80℃, then curing agent (4,4'-diamino diphenyl methane) 0.15g is added, then the mixture is degassed in a vacuum oven at 60℃ for 10 min, discharged, stored, to obtain two-component polyurethane pouring sealant.

[0048] Example 3

[0049] A method for preparing a low-shrinkage polyurethane pouring sealant, comprising the following steps:

[0050] S1, polyether polyol NJ-305 100 g, reinforcing filler (nano calcium oxide) 30 g, coupling agent (3-(2, 3-epoxy propoxy) propyl trimethoxysilane) 2 g and plasticizer (citrate) 20 g were added into the reactor, vacuum degree was kept at (-0.08) - (-0.09) MPa, stirring for 1.5 h, defoaming agent (BYK1794) 0.1 g was added, to obtain component A;

[0051] S2, isocyanate (toluene diisocyanate) 90 g, epoxy resin (E-51) 20 g and diluent (butanone) 40 g were mixed at room temperature, to obtain component B;

[0052] S3, component A and component B were mixed and added into the reaction kettle, dehydrated at 120℃, vacuum degree (-0.09) - (-0.1) MPa for 10 min, flame-retardant reinforcing agent 10 g was added, stirring and mixing uniformly, then the temperature was reduced to 80℃, curing agent (4, 4'-diamino diphenyl methane) 0.2 g was added, then the mixture was degassed in a vacuum oven at 60℃ for 10 min, discharged, stored, to obtain two-component polyurethane pouring sealant.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 2 is that no reinforcing filler is added in component A, and the rest of the steps and raw materials are implemented synchronously with Example 2.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 2 is that no epoxy resin is added in component B, and the rest of the steps and raw materials are implemented synchronously with Example 2.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 2 is that no flame-retardant reinforcing agent is added in step S3, and the rest of the steps and raw materials are implemented synchronously with Example 2.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 2 is that the polyphenyl polymethylene polyisocyanate is replaced by aliphatic isocyanate AD I, and the rest of the steps and raw materials are implemented synchronously with Example 2.

[0061] The polyurethane pouring sealant prepared in Examples 1-3 and Comparative Examples 1-4 was tested for performance, and the pouring sealant prepared in Examples 1-3 and Comparative Examples 1-4 was placed at room temperature for 7 days, then tested according to ASTM D412 "Tensile Testing Methods for Vulcanized Rubber and Thermoplastic Elastomers", ASTM E1545 "Standard Test Method for Glass Transition Temperature Using Thermal Mechanical Analysis", and flame retardant grade according to UL-94 standard;

[0062] Thermal conductivity is tested according to GB / T3139-2005 standard, and shrinkage is tested: the shrinkage of the sample after complete curing is tested, and the test results are shown in Table 1 below.

[0063] Table 1

[0064]

[0065] As can be seen from Example 2 and Comparative Example 1, in the embodiment of the present application, the addition of the reinforcing filler (nano calcium oxide) can improve the thermal conductivity of the material, and in addition, the flame retardant efficiency and elongation of the material are increased, and the shrinkage is reduced. The reduction of the shrinkage is considered to be due to the filling of nano calcium oxide and the interpenetration of the epoxy resin, achieving better effect of reducing the shrinkage.

[0066] As can be seen from Example 2 and Comparative Example 2, the addition of the epoxy resin has a great influence on the shrinkage of the polyurethane pouring sealant. It is considered that the increase of the shrinkage is due to the loss of the interpenetration of the polyurethane and the epoxy resin, and the thermal conductivity is also affected.

[0067] As can be seen from Example 2 and Comparative Example 3, the increase of the flame retardant synergist can well play the effect of flame retardation. As can be seen from Comparative Example 1, the flame retardant synergist plays a major role in flame retardation.

[0068] As can be seen from Example 2 and Comparative Example 4, the polyurethane synthesized by using aliphatic isocyanate AD I has a lower flame retardant grade. It is considered that the aliphatic does not have a benzene ring group, and the interaction between the flame retardant synergist is weak, resulting in deviation of the flame retardant performance of the system.

[0069] As can be seen from the above, the pouring sealant prepared in Examples 1-3 has better tensile strength and elongation, and also has lower shrinkage and better thermal conductivity, and the flame retardant grade is V0 grade, which can be better used in the pouring sealant of the electrical appliance.

[0070] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace, as long as the modifications or supplements do not deviate from the invention or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

Claims

1. A method for preparing a low shrinkage polyurethane pour-in-place gasketing compound, characterized by, The method comprises the following steps: S1, adding 50-100 parts of polyol, 20-30 parts of reinforcing filler, 1-2 parts of coupling agent and 10-20 parts of plasticizer into a reactor, keeping the vacuum degree at (-0.08)-(-0.09) MPa, stirring for 1.5 h, adding 0.05-0.1 parts of defoaming agent to obtain component A; S2, mixing isocyanate 40-90 parts, epoxy resin 10-20 parts and diluent 30-40 parts at room temperature to obtain component B; S3, mixing component A and component B into a reaction kettle, dehydrating at 120-130℃ under vacuum degree (-0.09)-(-0.1) MPa for 10 min, adding 5-10 parts of flame-retardant reinforcing agent, stirring uniformly, then reducing the temperature to 80℃, adding 0.1-0.2 parts of curing agent, then degassing the mixture in a vacuum oven at 60℃ for 10 min, discharging, storing to obtain two-component polyurethane pouring sealant; The reinforcing filler is selected from nano calcium oxide with particle size of 10-30 nm; The epoxy resin is E-51 epoxy resin; The isocyanate is selected from aromatic polyisocyanate, and the aromatic polyisocyanate is selected from one of polyphenyl polymethylene polyisocyanate, diphenyl methane diisocyanate and toluene diisocyanate; Synthesis of the flame-retardant reinforcing agent: Mixing cinnamyl aldehyde, 4,4'-diamino diphenyl methane, flame-retardant intermediate DOPO and ethanol at room temperature, increasing the reaction temperature to 80℃ and stirring at the temperature for 0.5 h, when the solid is completely dissolved, adding formic acid into the reaction system, constant temperature reaction for 4 h, then filtering the solution to obtain the precipitate, then washing with distilled water for several times, finally drying in an oven at 80℃ for 24 h to remove the moisture to obtain the flame-retardant reinforcing agent.

2. The method for preparing the low-shrinkage polyurethane potting compound according to claim 1, characterized in that, The coupling agent is selected from one of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane, γ-aminopropyl triethoxysilane and 3-(2,3-epoxypropoxy) propyl trimethoxysilane.

3. The method for preparing the low-shrinkage polyurethane potting compound according to claim 1, characterized in that, The plasticizer is selected from one or more of dioctyl phthalate, polyol ester and citric acid ester.

4. The method for preparing the low-shrinkage polyurethane potting compound according to claim 1, characterized in that, The defoaming agent is selected from BYK1794 or polymer type defoaming agent BYK1790.

5. The method for preparing the low-shrinkage polyurethane potting compound according to claim 1, characterized in that, The diluent is selected from one or several of butanone, ethyl silicate, 1.4-butylene glycol ester, 1.6-hexanediol ester and low hydroxyl value acrylic resin in any ratio.

6. The method for preparing the low-shrinkage polyurethane potting compound according to claim 1, characterized in that, The polyol is selected from polyether polyol or polyester polyol.

7. A low shrinkage polyurethane pouring sealant prepared by the method of any one of claims 1-6.

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