A flame retardant, low VOC polyurethane adhesive and its preparation method and application

Abstract

The present invention provides a flame retardant, low VOC polyurethane adhesive and a preparation method and application thereof, wherein the flame retardant, low VOC polyurethane adhesive comprises: 50-70 parts of modified polyurethane prepolymer, 2-5 parts of chain extender, 1-3 parts of plasticizer, 1-5 parts of nano material, 1-5 parts of auxiliary agent, 0.01-0.1 parts of catalyst, and 20-40 parts of solvent; wherein the modified polyurethane prepolymer is a polyurethane prepolymer grafted and modified by a reactive flame retardant, and the reactive flame retardant is a phosphorus-containing organic silane. On the one hand, the present invention forms a stable flame retardant network by grafting phosphorus-containing organic silane on the polyurethane prepolymer, significantly improves the flame retardant properties of the polyurethane prepolymer, and prevents the migration and volatilization of the flame retardant component, thereby ensuring a continuous and stable flame retardant property; on the other hand, nano materials are introduced to further improve the flame retardant properties of the adhesive, and maintain excellent bonding properties and durability; at the same time, a low VOC or VOC-free solvent is selected to increase the solid content of the adhesive and reduce VOC emissions.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a flame retardant, low-VOC polyurethane adhesive and a preparation method and application thereof. Background Art

[0002] Polyurethane (PU) adhesive refers to adhesives containing carbamate groups (-NHCOO-) or isocyanate groups (-NCO) in the molecular chain, which can be divided into two categories: polyisocyanates and polyurethanes. Since polyurethane adhesives contain these two groups and show high activity and polarity, they are used in many kinds of substrates, such as porous materials such as foam, plastic, wood, leather, fabric, paper, ceramics, and materials with smooth surfaces such as metal, glass, rubber, and plastics, and have excellent adhesion to them. It is precisely because of the excellent bonding performance of polyurethane adhesives and their adaptability to bonding a variety of substrates that their application areas are constantly expanding, making them the fastest-growing adhesive at home and abroad.

[0003] However, most polyurethane adhesives are flammable and produce smoke and toxic gases when burned, which limits their application in special fields that require flame retardancy, such as aerospace, electronic product potting and bonding. At the same time, most polyurethane adhesives also have the defects of low solid content, high VOC content and poor bonding performance, which need to be further improved.

[0004] The flame retardant polyurethane adhesive in the prior art, such as CN107513317A, adds a large amount of nitrogen-phosphorus flame retardant and bromine flame retardant to the components of polyurethane, and the amount of flame retardant is greater than 20%. When burning, a large amount of toxic and harmful gases are released; and the flame retardant components will volatilize during storage, reducing the flame retardant effect of the adhesive and polluting the environment. Therefore, it is urgent to develop a highly efficient flame retardant and environmentally friendly polyurethane adhesive. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a flame retardant, low-VOC polyurethane adhesive to solve the problem of poor flame retardant effect of polyurethane adhesives in the prior art. At the same time, the present invention will also provide a method for preparing the flame retardant, low-VOC polyurethane adhesive; in addition, the present invention will also provide applications of the flame retardant, low-VOC polyurethane adhesive.

[0006] In order to achieve the above-mentioned object and other related objects, the present invention provides the following technical solutions:

[0007] The first aspect of the present invention provides a flame retardant, low VOC polyurethane adhesive, comprising the following raw materials in parts by weight: 50-70 parts of modified polyurethane prepolymer, 2-5 parts of chain extender, 1-3 parts of plasticizer, 1-5 parts of nanomaterial, 1-5 parts of auxiliary agent, 0.01-0.1 parts of catalyst, and 20-40 parts of solvent.

[0008] Wherein, the modified polyurethane prepolymer is a polyurethane prepolymer graft-modified by a reactive flame retardant; and the reactive flame retardant is a phosphorus-containing organic silane.

[0009] During the synthesis process of polyurethane, reactive flame retardants can undergo a bonding reaction with polyols or isocyanates, thereby being grafted onto polyurethane prepolymers to form a stable flame retardant network, which can not only significantly improve the flame retardant properties of polyurethane prepolymers, but also prevent the migration and volatilization of flame retardant components, thereby ensuring sustained and stable flame retardant properties, while also maintaining the mechanical properties and environmental characteristics of polyurethane prepolymers.

[0010] Furthermore, the modified polyurethane prepolymer is obtained by the following preparation method:

[0011] (1) Add the degassed polyol into the reactor and continuously introduce an inert atmosphere for protection;

[0012] (2) Add the reactive flame retardant while stirring to fully mix it with the polyol;

[0013] (3) slowly adding isocyanate, controlling the reaction temperature between 50-90° C., then adding a catalyst, continuing the reaction for 2-4 hours, and degassing after the reaction to obtain the modified polyurethane prepolymer.

[0014] Preferably, the reactive flame retardant is selected from (3-phosphoethyl)aminopropyltrimethoxysilane.

[0015] Preferably, the polyol is selected from polyether polyol, polyester polyol, castor oil or polybutadiene polyol.

[0016] Preferably, the isocyanate is selected from 4,4'-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI) or 4,4'-dicyclohexylmethane diisocyanate (HMDI).

[0017] Preferably, the catalyst includes at least one of an organic tin catalyst, an organic bismuth catalyst, and a tertiary amine catalyst;

[0018] More preferably, the catalyst is selected from dibutyltin dilaurate (DBTDL), dioctyltin dilaurate, bismuth tricarboxylate or N,N-dimethylcyclohexylamine.

[0019] Preferably, the mass ratio of the polyol, the isocyanate, the reactive flame retardant and the catalyst is (40-60): (30-50): (3-10): (0.02-0.1).

[0020] Preferably, a certain amount of non-polar solvent can be added into the reaction kettle to help reduce the reaction viscosity and control the reaction rate; the non-polar solvent includes xylene or toluene.

[0021] Preferably, the reaction time is determined by titrating the NCO content in the reaction mixture. When the NCO content reaches a predetermined target value, heating and stirring are stopped, and the reactor is cooled to room temperature.

[0022] Furthermore, the chain extender is selected from 1,4-butanediol or ethylenediamine (EDA), which is used to adjust the molecular weight and hardness of the polyurethane.

[0023] Furthermore, the plasticizer is selected from dioctyl phthalate (DOP).

[0024] Furthermore, the nanomaterial includes at least one of nano silicon dioxide, nano clay, nano graphene oxide, and layered double hydroxide (LDH). The nanomaterial can improve the flame retardant properties of the material by forming a dense carbon layer and improving the thermal barrier property, and the nanomaterial can form a uniform dispersion state in the polyurethane, improve the tear resistance of the adhesive and increase the tensile strength of the adhesive. In addition, the nanomaterial can also increase the contact area and friction between the polyurethane adhesive and the bonding surface, thereby improving its bonding performance.

[0025] Furthermore, the auxiliary agent includes at least one of a defoamer, a thickener, a wetting agent, and a dispersant;

[0026] Specifically, the defoamer is selected from BYK-028 or BYK-141; the thickener is selected from carboxymethyl cellulose and hydroxyethyl cellulose; the dispersant is selected from BYK-163; and the wetting agent is selected from polyether siloxane or BYK-306.

[0027] Furthermore, the catalyst includes at least one of an organic tin catalyst, an organic bismuth catalyst, and a tertiary amine catalyst. The catalyst preferably uses bismuth tricarboxylate to replace the traditional organic tin catalyst to reduce environmental and health risks.

[0028] Furthermore, the solvent includes at least one of water, ethyl acetate, lactate, ethanol, and methyl propylene glycol. The present invention selects low-VOC or no-VOC solvents, which generally have lower vapor pressure and volatilization rate, thereby reducing pollution to the environment during use.

[0029] The present invention can significantly improve the flame retardant safety of polyurethane adhesive by selecting polyurethane prepolymer modified by reactive flame retardant and introducing nanomaterials. The used components are green and environmentally friendly and have little impact on the environment. The raw material composition and proportion of the adhesive are adjusted to increase the solid content and reduce VOC emissions while maintaining excellent bonding performance and durability.

[0030] A second aspect of the present invention provides a method for preparing a flame retardant, low VOC polyurethane adhesive, comprising the following steps:

[0031] S1. Weigh each raw material in proportion and set aside;

[0032] S2. First add the solvent into the reaction kettle, slowly add the plasticizer while stirring, and stir thoroughly until it is evenly dispersed;

[0033] S3. Under stirring, slowly add the modified polyurethane prepolymer to the mixed solution, then add the nanomaterial and stir evenly, and heat the reactor to the reaction temperature;

[0034] S4, adding a chain extender, stirring and reacting at the reaction temperature for a period of time;

[0035] S5. Adding additives and catalysts in sequence, continuing stirring for a period of time, and then filtering and degassing to obtain the flame-retardant, low-VOC polyurethane adhesive.

[0036] Furthermore, the reaction temperature is between 40-60°C.

[0037] Furthermore, in step S4, the reaction time is 1-2 hours.

[0038] Furthermore, in step S5, the reaction time is 0.5-1 h.

[0039] Furthermore, in step S5, the mesh size of the sieve used for filtration is between 80 and 120 meshes.

[0040] The third aspect of the present invention provides an application of a flame retardant, low VOC polyurethane adhesive, wherein the flame retardant, low VOC polyurethane adhesive is used to prepare adhesive tape.

[0041] As described above, the flame retardant, low VOC polyurethane adhesive of the present invention and its preparation method and application have the following beneficial effects:

[0042] 1. The present invention forms a stable flame retardant network by grafting phosphorus-containing organosilane on the polyurethane prepolymer, which can not only significantly improve the flame retardant properties of the polyurethane prepolymer, but also prevent the migration and volatilization of the flame retardant components, thereby ensuring continuous and stable flame retardant properties; and a certain proportion of phosphorus-containing organosilane grafting can improve the wettability of the polyurethane prepolymer and improve its compatibility with other components, thereby enhancing the bonding ability of the polyurethane adhesive.

[0043] 2. The present invention introduces nanomaterials into polyurethane adhesives. Nanomaterials can not only significantly improve the flame retardant properties of the materials, but also form a uniform dispersion state in the polyurethane, improve the tear resistance of the adhesive and increase the tensile strength of the adhesive. In addition, nanomaterials can also increase the contact area and friction between the polyurethane adhesive and the bonding surface, thereby improving its bonding performance.

[0044] 3. The preparation method of the present invention is simple to operate and the conditions are easy to control. Low-VOC or VOC-free solvents are selected in the preparation process of the polyurethane adhesive, and degassing treatment is used at the end of the preparation process, which can reduce the VOC content in the adhesive to the greatest extent. The prepared product has suitable viscosity, ultra-low VOC content, low odor, and is safe and environmentally friendly. DETAILED DESCRIPTION

[0045] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0046] Example 1

[0047] A modified polyurethane prepolymer is obtained by the following preparation method:

[0048] (1) Degas 400 g of polyether polyol (molecular weight 2000-2200) at 80 °C, then add it into the reactor and continuously introduce nitrogen atmosphere for protection;

[0049] (2) While stirring, add 50 g of (3-ethylphosphophosphate)aminopropyltrimethoxysilane and mix it thoroughly with the polyol;

[0050] (3) Slowly add 300 g of 4,4'-diphenylmethane diisocyanate, control the reaction temperature at 80°C, then add 0.5 g of dibutyltin dilaurate, continue the reaction for 3 h, cool to room temperature, and degas to obtain a modified polyurethane prepolymer.

[0051] Example 2

[0052] A modified polyurethane prepolymer is obtained by the following preparation method:

[0053] (1) Degas 450 g of polyethylene adipate diol (molecular weight 2800-3000) at 80°C, then add it into the reactor and continue to introduce nitrogen atmosphere for protection;

[0054] (2) While stirring, add 50 g of (3-ethylphosphophosphate)aminopropyltrimethoxysilane and mix it thoroughly with the polyol;

[0055] (3) Slowly add 300 g of toluene diisocyanate, control the reaction temperature at 70°C, then add 0.5 g of bismuth tricarboxylate, continue the reaction for 3 h, cool to room temperature, and degas to obtain a modified polyurethane prepolymer.

[0056] Example 3

[0057] A flame retardant, low VOC polyurethane adhesive, comprising the following raw materials in parts by weight: 60 parts of the modified polyurethane prepolymer of Example 1, 3 parts of ethylenediamine, 2 parts of dioctyl phthalate, 2 parts of layered double hydroxide, 0.5 parts of a defoamer, 0.5 parts of a thickener, 0.3 parts of a wetting agent, 0.3 parts of a dispersant, 0.05 parts of dibutyltin dilaurate, and 25 parts of ethyl acetate;

[0058] The preparation method of the flame retardant, low VOC polyurethane adhesive is:

[0059] S1. Weigh each raw material according to the above ratio and set aside;

[0060] S2, first add ethyl acetate into the reaction kettle, slowly add dioctyl phthalate under stirring, and stir thoroughly until evenly dispersed;

[0061] S3. While stirring, slowly add the modified polyurethane prepolymer of Example 1 to the mixed solution, then add the layered double hydroxide and stir evenly, and heat the reactor to 50° C.;

[0062] S4, adding ethylenediamine as a chain extender, stirring the reaction at the reaction temperature for 1 hour;

[0063] S5. Add defoamer, thickener, wetting agent, dispersant and dibutyltin dilaurate in sequence, continue stirring for 30 minutes, and then obtain the flame-retardant, low-VOC polyurethane adhesive after filtering and degassing.

[0064] Example 4

[0065] Compared with Example 3, the only difference is that the nano material in the raw material is nano silicon dioxide.

[0066] Example 5

[0067] A flame retardant, low VOC polyurethane adhesive comprises the following raw materials in parts by weight: 60 parts of the modified polyurethane prepolymer of Example 2, 3 parts of ethylenediamine, 2 parts of dioctyl phthalate, 2 parts of layered double hydroxide, 0.5 parts of a defoamer, 0.5 parts of a thickener, 0.3 parts of a wetting agent, 0.3 parts of a dispersant, 0.05 parts of bismuth tricarboxylate, and 25 parts of ethyl acetate.

[0068] Example 6

[0069] A flame retardant, low VOC polyurethane adhesive comprises the following raw materials in parts by weight: 70 parts of the modified polyurethane prepolymer of Example 2, 5 parts of ethylenediamine, 2 parts of dioctyl phthalate, 3 parts of layered double hydroxide, 0.5 parts of defoamer, 0.5 parts of dispersant, 0.05 parts of bismuth tricarboxylate, and 40 parts of water.

[0070] Comparative Example 1

[0071] A polyurethane adhesive comprises the following raw materials in parts by weight: 60 parts of polyurethane prepolymer not modified by a reactive flame retardant, 3 parts of ethylenediamine, 2 parts of dioctyl phthalate, 2 parts of layered double hydroxide, 0.5 parts of a defoamer, 0.5 parts of a thickener, 0.3 parts of a wetting agent, 0.3 parts of a dispersant, 0.05 parts of dibutyltin dilaurate, and 25 parts of ethyl acetate.

[0072] Comparative Example 2

[0073] A polyurethane adhesive comprises the following raw materials in parts by weight: 60 parts of polyurethane prepolymer not modified by a reactive flame retardant, 3 parts of ethylenediamine, 2 parts of dioctyl phthalate, 0.5 parts of a defoamer, 0.5 parts of a thickener, 0.3 parts of a wetting agent, 0.3 parts of a dispersant, 0.05 parts of dibutyltin dilaurate, and 25 parts of ethyl acetate.

[0074] The performance of the polyurethane adhesives of Examples 3-6 and Comparative Examples 1-2 was tested after curing for 168 hours at 25°C and 50% RH. The specific method is as follows:

[0075] Tensile strength: GB / T2568 method;

[0076] Elongation at break: GB / T1040.2-2006 tensile properties of plastics;

[0077] Peel strength: GB / T2792-2014 Test method for peel strength of adhesive tape;

[0078] Oxygen index: GB / T2406-93 method.

[0079] The test results are shown in Table 1:

[0080] Table 1. Performance test results

[0081]

[0082] With reference to Comparative Examples 1 and 2, it can be seen that by introducing nanomaterials into polyurethane, the nanomaterials can not only significantly improve the flame retardant properties of the material, but also can improve the tensile strength of the polyurethane adhesive as a reinforcing phase, and the nanomaterials form a uniform dispersion state in the polyurethane, improving the tear resistance of the adhesive. In addition, the nanomaterials can also increase the contact area and friction between the polyurethane adhesive and the bonding surface, thereby improving its bonding performance. With reference to Examples 3 and 4, it can be seen that the reinforcing effect of layered double hydroxide is better than that of nano-silicon dioxide, and it can be used as the first choice for adding nanomaterials.

[0083] Referring to Example 3 and Comparative Example 1, it can be seen that by grafting phosphorus-containing organosilane on the polyurethane prepolymer, a flame retardant network can be formed, which significantly improves the flame retardant properties of the material; and a certain proportion of phosphorus-containing organosilane can improve the wettability of the polyurethane prepolymer and improve its compatibility with other components, thereby enhancing the bonding ability of the polyurethane adhesive.

[0084] With reference to Examples 3 and 5, it can be seen that bismuth tricarboxylates have a better catalytic effect than organic tin catalysts, and can increase the degree of cross-linking of micro-network molecules, thereby improving the strength and bonding ability of polyurethane adhesives.

[0085] In summary, on the one hand, the present invention forms a stable flame retardant network by grafting phosphorus-containing organosilane on the polyurethane prepolymer, significantly improves the flame retardant properties of the polyurethane prepolymer, and prevents the migration and volatilization of the flame retardant components, thereby ensuring continuous and stable flame retardant properties; on the other hand, nanomaterials are introduced to further improve the flame retardant properties of the adhesive, and maintain excellent bonding properties and durability; at the same time, low-VOC or VOC-free solvents are selected to increase the solid content of the adhesive and reduce VOC emissions. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0086] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A flame retardant, low VOC polyurethane adhesive, characterized in that: The invention comprises the following raw materials in parts by weight: 50-70 parts of modified polyurethane prepolymer, 2-5 parts of chain extender, 1-3 parts of plasticizer, 1-5 parts of nano material, 1-5 parts of auxiliary agent, 0.01-0.1 parts of catalyst and 20-40 parts of solvent; the nano material is selected from nano graphene oxide or layered double hydroxide; The modified polyurethane prepolymer is a polyurethane prepolymer grafted with a reactive flame retardant, the reactive flame retardant is selected from (3-phosphoethyl)aminopropyltrimethoxysilane, and the modified polyurethane prepolymer is obtained by the following preparation method: (1) adding the degassed polyol into a reaction kettle, into which a non-polar solvent is also added, wherein the non-polar solvent includes xylene or toluene, and an inert atmosphere is continuously introduced for protection; (2) Add the reactive flame retardant while stirring to fully mix it with the polyol; (3) slowly adding isocyanate, controlling the reaction temperature between 50-90° C., then adding a catalyst, continuing the reaction for 2-4 hours, and degassing after the reaction to obtain the modified polyurethane prepolymer; The mass ratio of the polyol, isocyanate, reactive flame retardant and catalyst is (40-60): (30-50): (3-10): (0.02-0.1); the catalyst is selected from dibutyltin dilaurate, dioctyltin dilaurate, bismuth tricarboxylate or N,N-dimethylcyclohexylamine.

2. The flame retardant, low VOC polyurethane adhesive according to claim 1, characterized in that: The chain extender is selected from 1,4-butanediol or ethylenediamine.

3. The flame retardant, low VOC polyurethane adhesive according to claim 1, characterized in that: The auxiliary agent includes at least one of a defoamer, a thickener, a wetting agent and a dispersant.

4. The flame retardant, low VOC polyurethane adhesive according to claim 1, characterized in that: The solvent includes at least one of water, ethyl acetate, lactate, ethanol and methyl propylene glycol.

5. A method for preparing the flame retardant, low VOC polyurethane adhesive according to any one of claims 1 to 4, characterized in that: The steps include: S1. Weigh each raw material in proportion and set aside; S2. First add the solvent into the reaction kettle, slowly add the plasticizer while stirring, and stir thoroughly until it is evenly dispersed; S3. Under stirring, slowly add the modified polyurethane prepolymer to the mixed solution, then add the nanomaterial and stir evenly, and heat the reactor to the reaction temperature; S4, adding a chain extender, stirring and reacting at the reaction temperature for a period of time; S5. Adding additives and catalysts in sequence, continuing stirring for a period of time, and then filtering and degassing to obtain the flame-retardant, low-VOC polyurethane adhesive.

6. Use of the flame retardant, low VOC polyurethane adhesive according to any one of claims 1 to 4, characterized in that: The flame retardant, low VOC polyurethane adhesive is used to prepare adhesive tape.

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