Flame-retardant thermally expandable microsphere and method for preparing the same

Abstract

The application relates to the field of flame-retardant technology, and particularly discloses a flame-retardant thermal expansion type foaming microsphere and a preparation method thereof. The thermal expansion type foaming microsphere has a core-shell structure and sequentially comprises a capsule core, an inner layer capsule wall and an outer layer flame-retardant capsule wall from inside to outside. Raw materials of the outer layer flame-retardant capsule wall include a phosphazene flame retardant, cobalt naphthenate and cyclohexanone peroxide. The flame-retardant thermal expansion type foaming microsphere provided by the application is coated with the phosphazene flame retardant which does not contain halogen, and the combination and coating rate of the phosphazene flame retardant and the foaming microsphere are improved through the cobalt naphthenate and the cyclohexanone peroxide, so that the flame-retardant efficiency and the flame-retardant stability of the foaming microsphere are significantly improved. In addition, the cobalt naphthenate and the cyclohexanone peroxide can promote the phosphazene flame retardant to degrade rapidly when a fire occurs, so that a dense carbon layer is rapidly formed on the surface of the foaming microsphere, and good flame-retardant and ablation-resistant effects are achieved. Therefore, the foaming microsphere has good foaming performance and flame-retardant performance, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flame-retardant technology, and in particular to a flame-retardant thermal expansion type foaming microsphere and a preparation method thereof. BACKGROUND

[0002] Thermal expansion microspheres are microspheres composed of a thermoplastic polymer shell and a foaming agent core. When the microspheres are heated to the softening point of the polymer, the vapor pressure generated by the internal foaming agent causes the microspheres to expand. After cooling, the microspheres remain in the foamed state. The expanded microspheres have good low-temperature expandability and large expansion capacity, and are widely used in sound absorption, heat insulation, thermal insulation, lightweight, and other fields. In recent years, with the development of various fields, higher requirements for the high performance and integration of expanded microspheres have been put forward.

[0003] In the prior art, thermoplastic materials are generally used as the shell of thermal expansion microspheres. Thermoplastic materials generally do not have flame-retardant properties, and are prone to melt and decompose to produce flammable gases under high temperature conditions, which is low in safety and greatly limits their application and development. Therefore, it is of great significance to improve the thermal stability and flame retardancy of thermal expansion microspheres.

[0004] In recent years, the flame-retardant modification of thermal expansion microspheres has mainly been achieved by adding appropriate flame-retardant chemicals to change their combustion characteristics. Powder-type flame retardants are difficult to effectively adhere to the surface of thermal expansion microspheres, and have poor flame-retardant effect. Halogen-based flame retardants have good flame-retardant effect, but produce toxic gases during combustion or degradation, which is harmful to human health and the environment. Therefore, it is necessary to develop a new type of environmentally friendly flame-retardant thermal expansion microsphere to expand its application field. SUMMARY

[0005] In view of the low flame-retardant efficiency and poor environmental friendliness of thermal expansion microspheres in the prior art, the present application provides a flame-retardant thermal expansion type foaming microsphere and a preparation method thereof.

[0006] To solve the above technical problems, the technical solution provided by the present application is as follows:

[0007] A flame-retardant thermal expansion type foaming microsphere has a core-shell structure and includes, from inside to outside, a capsule core, an inner layer capsule wall, and an outer layer flame-retardant capsule wall.

[0008] The raw material of the outer layer flame-retardant capsule wall includes a phosphazene flame retardant, cobalt naphthenate, and cyclohexanone peroxide.

[0009] Compared with the prior art, the flame-retardant thermal expansion type foaming microsphere provided by the present application is coated with a halogen-free phosphazene flame retardant, and the combination and coating rate of the phosphazene flame retardant and the foaming microsphere are improved by using naphthenic acid cobalt and cyclohexanone peroxide, so that the flame-retardant efficiency and stability of the foaming microsphere are significantly improved. In addition, the naphthenic acid cobalt and cyclohexanone peroxide can promote the rapid degradation of the phosphazene flame retardant when a fire occurs, so that a dense carbon layer is quickly formed on the surface of the foaming microsphere, and good flame-retardant and ablation-resistant effects are achieved. The naphthenic acid cobalt and cyclohexanone peroxide can also improve the strength of the shell layer and the structural stability of the microcapsule after expansion, so that the foaming microsphere has good foaming and flame-retardant properties, which is beneficial to expanding the application field of the foaming microsphere and has a wide application prospect.

[0010] Preferably, the polymer monomers of the inner layer capsule wall include the following components in mass percentage: 70-76% of methyl methacrylate, 15-24% of N,N-dimethyl acrylamide, 1-5% of isobornyl methacrylate, 1-6% of poly(ethylene glycol) methacrylate, and 1-3% of hexafluorobutyl methacrylate.

[0011] The polymer formed by the above monomers can be used as the main wall material to form a capsule wall with high polymerization degree and good stability, so that the capsule wall has better tightness and integrity, and provides more foaming space for the foaming agent, thereby being beneficial to significantly improving the expansion rate of the foaming microsphere. In addition, the preferred wall material has better compatibility with the phosphazene flame retardant, which is beneficial to improving the coating rate of the phosphazene flame retardant on the foaming microsphere, thereby being beneficial to improving the flame-retardant efficiency and stability.

[0012] The present application also provides a preparation method of the above flame-retardant thermal expansion type foaming microsphere, which comprises the following steps:

[0013] S1, uniformly mixing thermal expansion type foaming microspheres, phosphazene flame retardant, naphthenic acid cobalt and cyclohexanone peroxide to obtain a mixture;

[0014] S2, adding a diluent to the mixture and uniformly mixing to obtain a mixed slurry;

[0015] S3, heating the mixed slurry to be solvent-free and drying to obtain the flame-retardant thermal expansion type foaming microsphere.

[0016] The present application uses liquid heating conditions and adds naphthenic acid cobalt and cyclohexanone peroxide to promote the combination of the phosphazene flame retardant and the foaming microsphere, which effectively improves the coating rate of the phosphazene flame retardant on the foaming microsphere, thereby being beneficial to significantly improving the flame-retardant property of the foaming microsphere, and the preparation method is simple and convenient for industrialized production and application.

[0017] Preferably, the mass ratio of the thermally expandable microsphere to the phosphazene flame retardant is 4-9:1.

[0018] Preferably, the cobalt naphthenate is added in an amount of 0.3%-0.4% of the mass of the thermally expandable microsphere.

[0019] Preferably, the cyclohexanone peroxide is added in an amount of 3%-4% of the mass of the thermally expandable microsphere.

[0020] Preferably, the amounts of the phosphazene flame retardant, the cobalt naphthenate and the cyclohexanone peroxide are effective in improving the flame retardant property of the microsphere.

[0021] Preferably, the diluent is added in an amount of 50%-150% of the mass of the mixture.

[0022] Preferably, the diluent is at least one of isopropyl alcohol, methanol or anhydrous ethanol.

[0023] The amount of the diluent is added to ensure that the raw materials are sufficiently dispersed, and the diluent has high volatility and does not remain in the product, so as not to affect the foaming property and the flame retardant property of the microsphere. The temperature and time of heating are such that the diluent in the mixed slurry is completely volatilized within 20-60 minutes.

[0024] Preferably, the phosphazene flame retardant is hexakis(4-hydroxymethylphenoxy)cyclotriphosphazene.

[0025] Preferably, the phosphazene flame retardant has excellent flame retardant property and good compatibility with the inner capsule wall of the microsphere, can effectively coat the microsphere, improve the flame retardant property of the microsphere, and can also ensure that the elasticity and toughness of the inner capsule wall are not affected, and the coating has as little adverse effect on the foaming property as possible.

[0026] Preferably, the method for preparing the thermally expandable microsphere comprises the following steps:

[0027] The polymer monomer and the inert alkane are added to the polyvinylpyrrolidone solution, mixed uniformly, and then an initiator is added under an inert atmosphere, and reacted at 80-120°C for 3-7 hours, cooled, washed, and dried to obtain the thermally expandable microsphere.

[0028] Preferably, the polymer monomer comprises the following components in the following mass percentages: methyl methacrylate 70%-76%, N,N-dimethylacrylamide 15%-24%, isobornyl methacrylate 1%-5%, poly(ethylene glycol) methacrylate 1%-6%, and hexafluorobutyl methacrylate 1%-3%.

[0029] Preferably, the mass ratio of the polymer monomer, inert alkane, initiator and polyvinyl pyrrolidone solution is 100:50-70:1-10:750-900; wherein the concentration of the polyvinyl pyrrolidone solution is 15-25 g / L.

[0030] Preferably, the inert alkane is at least one of n-hexane, isooctane, isopentane, neopentane or n-heptane.

[0031] Preferably, the initiator is 2,2'-azobisdimethylvaleronitrile.

[0032] The inert atmosphere in the present application is provided by an inert gas, which can be nitrogen, argon or the like, preferably nitrogen.

[0033] The thermal expansion type foaming microsphere provided by the present application has an expansion rate of 440% or more, an average particle size of 20-50 μm, a relatively concentrated particle size distribution, an ultimate oxygen index of 27% or more and a carbon residue rate of 21% or more, has a simple preparation method, meets the production and use requirements, does not contain halogen in the foaming microsphere system, does not pollute and damage the environment, and has good economic benefits and development prospects. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application.

[0035] Example 1

[0036] The present application provides a preparation method of flame-retardant thermal expansion type foaming microsphere, which comprises the following steps:

[0037] S1, preparing thermal expansion type foaming microsphere:

[0038] The polymer monomer, isopentane, polyvinyl pyrrolidone solution with a concentration of 20 g / L and 2,2'-azobisdimethylvaleronitrile are weighed according to the mass ratio of 100:60:850:5, the polymer monomer and isopentane are added into the polyvinyl pyrrolidone solution and mixed uniformly, then 2,2'-azobisdimethylvaleronitrile is added under an inert atmosphere, and the mixture is reacted at 100°C for 5 h, cooled, washed, placed, filtered, dried, crushed to obtain thermal expansion type foaming microsphere;

[0039] The polymer monomer comprises the following components with the following mass percentage: methyl methacrylate 72%, N,N-dimethyl acrylamide 17%, isobornyl methacrylate 5%, poly(ethylene glycol) methacrylate 3% and hexafluorobutyl methacrylate 3%;

[0040] S2, preparing flame-retardant thermally expandable microspheres:

[0041] According to the mass ratio of 15:85, mix hexakis(4-hydroxymethylphenoxy)cyclotriphosphazene and the above prepared thermally expandable microspheres uniformly, add 0.35% of cobalt naphthenate by mass of the thermally expandable microspheres and 3.5% of cyclohexanone peroxide by mass of the thermally expandable microspheres, stir and mix uniformly, and obtain a mixture;

[0042] Add 1 times of anhydrous ethanol by mass of the mixture to the mixture, and disperse uniformly to obtain a mixed slurry;

[0043] Heat the mixed slurry to 75°C, heat for 40 min, make the mixed slurry into a loose block, dry, and grind to obtain flame-retardant thermally expandable microspheres.

[0044] Example 2

[0045] S1, preparing thermally expandable microspheres:

[0046] According to the mass ratio of 100:50:750:1, weigh the polymer monomer, n-hexane, polyvinylpyrrolidone solution with a concentration of 15 g / L, and 2,2'-azobis (isobutylamidine) dihydrochloride, mix the polymer monomer and n-hexane into the polyvinylpyrrolidone solution, mix uniformly, then add 2,2'-azobis (isobutylamidine) dihydrochloride under inert atmosphere, react at 120°C for 3 h, cool, wash, stand, filter, dry, and crush to obtain thermally expandable microspheres;

[0047] The polymer monomer includes the following components with mass percentage: methyl methacrylate 76%, N,N-dimethyl acrylamide 15%, isobornyl methacrylate 1%, poly(ethylene glycol) methacrylate 6%, and hexafluorobutyl methacrylate 2%;

[0048] S2, preparing flame-retardant thermally expandable microspheres:

[0049] According to the mass ratio of 10:90, mix hexakis(4-hydroxymethylphenoxy)cyclotriphosphazene and the above prepared thermally expandable microspheres uniformly, add 0.3% of cobalt naphthenate by mass of the thermally expandable microspheres and 4% of cyclohexanone peroxide by mass of the thermally expandable microspheres, stir and mix uniformly, and obtain a mixture;

[0050] Add 50% of methanol by mass of the mixture to the mixture, and disperse uniformly to obtain a mixed slurry;

[0051] Heat the mixed slurry to 60°C, heat for 20 min, make the mixed slurry into a loose block, dry, and grind to obtain flame-retardant thermally expandable microspheres.

[0052] Example 3

[0053] S1, preparing thermally expandable foaming microspheres:

[0054] According to the mass ratio of 100:70:900:10, the polymer monomer, isooctane, polyvinylpyrrolidone solution with a concentration of 25 g / L and 2,2'-azobis (isobutylamidine) dihydrochloride are weighed, the polymer monomer and isooctane are added to the polyvinylpyrrolidone solution, mixed uniformly, then 2,2'-azobis (isobutylamidine) dihydrochloride is added under inert atmosphere, and the mixture is reacted at 80°C for 7h, cooled, washed, settled, filtered, dried, crushed, and thermally expandable foaming microspheres are obtained;

[0055] The polymer monomer includes the following components with the mass percentage: methyl methacrylate 70%, N,N-dimethyl acrylamide 24%, isobornyl methacrylate 4%, poly(ethylene glycol) methacrylate 1%, and hexafluorobutyl methacrylate 1%;

[0056] S2, preparing flame-retardant thermally expandable foaming microspheres:

[0057] According to the mass ratio of 18:82, hexakis (4-hydroxymethylphenoxy) cyclotriphosphazene and the thermally expandable foaming microspheres prepared above are mixed uniformly, and 0.4% of cobalt naphthenate and 3% of cyclohexanone peroxide by mass of the thermally expandable foaming microspheres are added, and the mixture is stirred and mixed uniformly to obtain a mixture material;

[0058] Isopropyl alcohol with 150% of the mass of the mixture material is added and dispersed uniformly to obtain a mixed slurry;

[0059] The mixed slurry is heated to 70°C and heated for 60 min to make the mixed slurry into a loose block object, dried, ground, and flame-retardant thermally expandable foaming microspheres are obtained.

[0060] Comparative Example 1

[0061] This comparative example provides a thermally expandable foaming microsphere, the raw material composition and the preparation method of which are the same as those of Example 1, and the only difference is that no cobalt naphthenate and cyclohexanone peroxide are added.

[0062] Comparative Example 2

[0063] This comparative example provides a thermally expandable foaming microsphere, the raw material composition and the preparation method of which are the same as those of Example 1, and the only difference is that hexafluorobutyl methacrylate is replaced by an equal amount of methyl methacrylate, and cobalt naphthenate is replaced by an equal amount of cyclohexanone peroxide.

[0064] Foaming performance test:

[0065] Take the thermal expansion microspheres prepared in Example 1, randomly sample 5, on the glass slide, on the thermal stage of the constant temperature controller, heat, then adjust the microscope objective to observe the foaming process of the thermal expansion microspheres on the glass slide, record the initial foaming temperature, the highest foaming temperature, and the diameter of the initial microspheres and the diameter of the expanded microspheres after foaming, and the results are shown in Table 1.

[0066] Wherein, the formula of the microsphere diameter expansion rate is: diameter expansion rate % = (expanded diameter - unexpanded diameter) / unexpanded diameter * 100%.

[0067] Table 1 Foaming performance test results of Example 1

[0068] Group 1 2 3 4 5 Before expansion diameter (μm) 36 31 28 34 30 After expansion diameter (μm) 195 172 161 196 169 Diameter expansion rate (%) 441 454 475 476 463

[0069] Flame retardant performance test:

[0070] The thermal expansion microcapsules prepared in Examples 1-3 and Comparative Examples 1-2 are tested for flame retardant performance according to GB / T23864 standard, and the results are shown in Table 2.

[0071] Table 2 Performance comparison

[0072]

[0073]

[0074] The flame retardant microcapsules prepared in Examples 1-3 are tested for char yield, and the char yield test method is: the char yield at 480℃ is obtained from the thermal gravimetric (TG) test data, and the test is performed using a differential scanning calorimeter, under N2 atmosphere, with a temperature rise rate of 10℃ / min, and a temperature range of 30-600℃. The specific test results are shown in Table 3.

[0075] Table 3

[0076] Sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Char yield 22.5％ 21.6％ 21.9％ 17.3％ 19.4％

[0077] The products of the above examples are used in the coating of fabrics to make textiles, and the afterflame time and afterglow time are tested using GB / T5455-1997 "Textile Burning Performance Test Vertical Method". The prepared textiles are placed in a specified combustion test box and ignited with a specified fire source for 12s, and the afterflame time and afterglow time of the sample are measured after removing the fire source, and the results are shown in Table 4.

[0078] Table 4

[0079] After flame time (s) After glow time (s) Example 1 2 2 Example 2 3 3 Example 3 4 3 Comparative Example 1 15 12 Comparative Example 2 7 6

[0080] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement or improvement made in the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A flame-retardant thermally expandable microsphere, characterized by, The microsphere has a core-shell structure, and comprises, from inside to outside, a thermal expansion type foaming microsphere and an outer layer of flame-retardant capsule wall; the thermal expansion type foaming microsphere comprises a capsule core and an inner layer of capsule wall; The raw material of the outer layer of flame-retardant capsule wall is composed of phosphazene flame retardant, cobalt naphthenate and cyclohexanone peroxide; the mass ratio of the thermal expansion type foaming microsphere to the phosphazene flame retardant is 4-9:1; the addition amount of the cobalt naphthenate is 0.3%-0.4% of the mass of the thermal expansion type foaming microsphere; and the addition amount of the cyclohexanone peroxide is 3%-4% of the mass of the thermal expansion type foaming microsphere. The polymer monomer of the inner layer of capsule wall comprises the following components in the following mass percentages: methyl methacrylate 70%-76%, N,N-dimethyl acrylamide 15%-24%, isobornyl methacrylate 1%-5%, poly(ethylene glycol) methacrylate 1%-6% and hexafluorobutyl methacrylate 1%-3%.

2. A process for the production of the flame-retardant thermally expandable microspheres according to claim 1, characterized in that The method comprises the following steps: S1, uniformly mixing the thermal expansion type foaming microsphere, the phosphazene flame retardant, the cobalt naphthenate and the cyclohexanone peroxide to obtain a mixture; S2, adding a diluent to the mixture and uniformly mixing to obtain a mixed slurry; S3, heating the mixed slurry to be solvent-free, drying to obtain the flame-retardant thermal expansion type foaming microsphere.

3. The method of producing flame-retardant thermally expandable microspheres according to claim 2, wherein The addition amount of the diluent is 50%-150% of the mass of the mixture.

4. The method of producing flame-retardant thermally expandable microspheres according to claim 2, wherein The phosphazene flame retardant is hexakis(4-hydroxymethylphenoxy)cyclotriphosphazene; and / or The diluent is at least one of isopropyl alcohol, methanol or anhydrous ethanol.

5. The method for preparing flame-retardant thermally expanding foamed microspheres as described in claim 2, characterized in that, The preparation method of the thermal expansion type foaming microsphere comprises the following steps: adding the polymer monomer and the inert alkane to the polyvinylpyrrolidone solution, uniformly mixing, then adding an initiator under an inert atmosphere, reacting at 80-120°C for 3-7h, cooling, washing, drying to obtain the thermal expansion type foaming microsphere.

6. The method of producing flame-retardant thermally expandable microspheres according to claim 5, wherein The mass ratio of the polymer monomer, the inert alkane, the initiator and the polyvinylpyrrolidone solution is 100:50-70:1-10:750-900; wherein the concentration of the polyvinylpyrrolidone solution is 15-25g / L.

7. The method for preparing flame-retardant thermally expanding foamed microspheres as described in claim 5, characterized in that, The inert alkane is at least one of n-hexane, isooctane, isopentane, neopentane or n-heptane; and / or The initiator is 2,2'-azobisdimethylamidinum dihydrochloride.

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