Thermally expandable microspheres, process for their production and use thereof

Abstract

The application discloses thermally expandable microspheres, a preparation method and application thereof. The thermally expandable microspheres comprise, from inside to outside, a core, a transition layer and a functional layer. The core comprises isobutane and peroxide. The transition layer is a layer of acrylonitrile / glycidyl methacrylate copolymer. The functional layer comprises polydopamine and particles with antibacterial properties attached to the surface of the polydopamine. The thermally expandable microspheres have high thermal stability and can withstand 200 DEG C / 30 min heat pressing, and meanwhile have antibacterial properties. Further, the thermally expandable microspheres can further comprise a hydrophobic and / or flame-retardant layer. The thermally expandable microspheres have a wide range of applications and can meet different requirements.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and specifically relates to a thermally expandable microsphere, its preparation method, and its application. Background Technology

[0002] In the current papermaking industry, the addition of functional fillers is a key means to improve paper performance. Traditional expanded microspheres have the following technical defects: 1) Insufficient temperature resistance: The decomposition temperature of conventional microspheres is ≤180℃, which causes them to expand and rupture prematurely during paper hot pressing and drying (e.g., calender roll temperature ≥150℃), resulting in the collapse of the pore structure; 2) Single function: They only provide lightweighting and lack additional functions such as antibacterial, hydrophobic, and flame retardant properties; 3) Wide particle size distribution: Microspheres prepared by traditional emulsion polymerization have a D90 / D10 ratio >3.0, which leads to a decrease in paper uniformity. Summary of the Invention

[0003] To overcome the above-mentioned defects, the present invention provides a thermally expandable microsphere, its preparation method, and its application.

[0004] The first aspect of the present invention provides a thermally expandable microsphere comprising, from the inside out, a core, a transition layer and a functional layer; the core comprising isobutane and peroxide; the transition layer being an acrylonitrile / glycidyl methacrylate copolymer layer; and the functional layer comprising polydopamine and antibacterial particles attached to its surface.

[0005] According to one embodiment of the present invention, in the core, the mass ratio of isobutane to peroxide is 7-11:1; preferably, the peroxide is dicumyl peroxide or di-tert-butyl peroxide.

[0006] According to another embodiment of the present invention, the glass transition temperature of the transition layer is ≥85°C.

[0007] According to another embodiment of the present invention, a high-strength layer is further included between the transition layer and the functional layer, the high-strength layer being a polymethyl methacrylate layer and / or a polyallyl methacrylate layer, and the glass transition temperature of the high-strength layer being ≥105°C.

[0008] According to another embodiment of the present invention, the outer side of the functional layer further includes a perfluoroalkyl acrylate shell, wherein the contact angle of the perfluoroalkyl acrylate shell is ≥150°.

[0009] According to another embodiment of the present invention, the material of the perfluoroalkyl acrylate shell is one or more of perfluorooctyl ethyl acrylate, heptadecafluorodecyl acrylate, and tridecafluorooctyl acrylate.

[0010] According to another embodiment of the present invention, the outer side of the outer casing also includes a flame retardant.

[0011] According to another embodiment of the present invention, the weight ratio of the core, the transition layer, the functional layer and the outer shell is 45-55:80-100:10-15:7-10.

[0012] According to another embodiment of the present invention, the median particle size D50 of the thermally expandable microspheres is 13-17 μm, and the D90 / D10 ratio is ≤1.8.

[0013] According to another embodiment of the present invention, the antibacterial particles are selected from one or more of nano zinc oxide, nano copper oxide, and silver-loaded zeolite particles.

[0014] According to another embodiment of the present invention, the content of the antibacterial particles in the functional layer is 8-12%.

[0015] According to another embodiment of the present invention, the initial expansion temperature of the thermally expandable microspheres is greater than 190°C.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned thermally expandable microspheres, comprising: forming an oil phase with isobutane and peroxide; mixing the oil phase with water to form an O / W emulsion with a droplet diameter of 2-5 μm and D90 / D10 ≤ 1.8; forming a transition layer of acrylonitrile / glycidyl methacrylate copolymer; dispersing the microspheres in a Tris-HCl buffer solution of dopamine salt; introducing ozone to initiate oxidative polymerization to form polydopamine; and subsequently impregnating the microspheres in a dispersion containing antibacterial particles to form a functional layer.

[0017] According to one embodiment of the present invention, a high-strength layer is further formed between the formation of the transition layer and the functional layer; gradient temperature polymerization is used when forming the transition layer and the high-strength layer.

[0018] A third aspect of the present invention provides an application of the above-mentioned thermally expandable microspheres in a papermaking process.

[0019] According to one embodiment of the present invention, the amount of the thermally expandable microspheres added is 0.5-3 wt% of the oven-dry weight of the pulp, and the hot-pressing temperature is 190-210℃.

[0020] A fourth aspect of the present invention provides a paper comprising the above-described thermally expandable microspheres.

[0021] The thermally expandable microspheres of this invention exhibit high thermal stability, capable of withstanding hot pressing at 200°C for 30 minutes, and also possess antibacterial properties. Furthermore, the thermally expandable microspheres of this invention have a D90 / D10 ratio ≤ 1.8 and a narrow particle size distribution, which can improve the uniformity of paper. Even further, the thermally expandable microspheres of this invention may contain a hydrophobic and / or flame-retardant layer. The thermally expandable microspheres of this invention have a wide range of applications and can meet diverse needs. Detailed Implementation

[0022] To make the present invention clearer and easier to understand, the technical solution of the present invention will be further described below with reference to specific embodiments. The embodiments described below are only used to explain the present invention and are not intended to limit the present invention in any form or substance.

[0023] The thermally expandable microspheres of this invention comprise, from the inside out, a core, a transition layer, and a functional layer. The core comprises isobutane and peroxide. The transition layer is an acrylonitrile (AN) / glycidyl methacrylate (GMA) copolymer layer. The functional layer comprises polydopamine (PDA) and antibacterial particles attached to its surface.

[0024] In the core, the mass ratio of isobutane to peroxide is 7-11:1. The peroxide is dicumyl peroxide (DCP) or di-tert-butyl peroxide.

[0025] The glass transition temperature of the transition layer is ≥85℃. It is matched with a foaming agent with a high decomposition temperature (such as dicumyl peroxide, with a decomposition temperature of about 193℃), so that the outer shell of the microsphere hardens first and the inner core expands later when heated, thereby avoiding premature cracking.

[0026] A high-strength layer is also included between the transition layer and the functional layer. The high-strength layer is a polymethyl methacrylate (PMMA) layer and / or a polyallyl methacrylate (PALMA) layer. The glass transition temperature of the high-strength layer is ≥105℃. By incorporating the high-strength layer, mechanical strength can be improved, thus enhancing the mechanical strength of paper when applied to it, making it suitable for high-strength packaging paper.

[0027] The antibacterial particles in the functional layer can be selected from one or more of nano-zinc oxide (ZnO), nano-copper oxide, and silver-loaded zeolite particles. Preferably, the ZnO has a particle size of 20-30 nm and a specific surface area of ​​50 m² / g. The content of the antibacterial particles in the functional layer is 8-12%.

[0028] The functional layer also includes a perfluoroalkyl acrylate shell. The perfluoroalkyl acrylate shell has a contact angle ≥150°, imparting hydrophobicity to the thermally expandable microspheres, making it suitable for use in waterproof packaging paper. The perfluoroalkyl acrylate shell is made of one or more of perfluorooctyl ethyl acrylate (FOEA), heptadecafluorodecyl acrylate, and tridecafluorooctyl acrylate.

[0029] The weight ratio of the core, transition layer, functional layer and shell of the thermally expandable microsphere of the present invention is 45-55:80-100:10-15:7-10.

[0030] The outer shell also includes a flame retardant. SC-310 is preferred as the flame retardant. SC-310 has good thermal stability and good compatibility with other chemicals.

[0031] The median particle size D50 of the thermally expandable microspheres of the present invention is 13-17 μm, and the D90 / D10 ratio is ≤1.8.

[0032] The thermally expandable microspheres of this invention have an initial expansion temperature greater than 190°C. Therefore, when applied to paper, they do not expand and rupture prematurely during hot-pressing and drying, thus preventing the collapse of the pore structure and improving paper performance.

[0033] The preparation method of the above-mentioned thermally expandable microspheres includes: forming an oil phase with isobutane and peroxide; mixing the oil phase with water to form an O / W emulsion with a droplet diameter of 2-5 μm and D90 / D10 ≤ 1.8; forming a transition layer of acrylonitrile / glycidyl methacrylate copolymer; dispersing the microspheres in a Tris-HCl buffer solution of dopamine salt; introducing ozone to initiate oxidative polymerization to form polydopamine; and then impregnating the microspheres in a dispersion containing antibacterial particles to form a functional layer.

[0034] The process for forming an O / W emulsion can be any suitable process. For example, but not limited to, injecting the oil phase into the aqueous phase in a high-speed shear mill to form an O / W emulsion. The shear rate can be gradient-varying, for example, but not limited to, 12000 rpm (0-5 min) → 8000 rpm (5-15 min) → 5000 rpm (15-20 min) to control the droplet size distribution of the oil phase. The aqueous phase in the high-speed shear mill can be pre-dissolved with a surfactant to improve the dispersibility of the oil phase droplets. The surfactant can be sodium dodecyl sulfate (SDS), nonylphenol polyoxyethylene ether (OP-10, HLB=13.5), etc.

[0035] Subsequently, a transition layer forms on the surface of the oil droplets. This process is typically achieved through interfacial polymerization or emulsion polymerization. Specifically, polymeric monomers (acrylonitrile (AN) and glycidyl methacrylate (GMA)) are added to the aforementioned O / W emulsion system. Since the polymeric monomers have a certain distribution in the oil and aqueous phases, but lean more towards the oil phase, they diffuse into the oil droplets. Next, a water-soluble initiator (such as ammonium persulfate, APS) is added to initiate the polymerization reaction. The initiator decomposes in the aqueous phase to generate free radicals, which can diffuse to the surface of the oil droplets, thereby initiating the polymerization reaction on the oil droplet surface. As polymerization proceeds, the polymer chains gradually grow and deposit on the surface of the oil droplets, forming a transition layer composed of a random copolymer of AN and GMA.

[0036] When a high-strength layer is provided between the transition layer and the functional layer, the high-strength layer is formed after the transition layer. The polymerization temperature of the high-strength layer is higher than that of the transition layer. The high-strength layer can use a crosslinking agent, such as divinylbenzene (DVB), to improve its mechanical strength. Preferably, gradient temperature polymerization is used when forming the transition layer and the high-strength layer to obtain a gradient structure. That is, at a lower temperature (e.g., 60°C), the initiator, such as APS, decomposes slowly, and the polymerization reaction proceeds smoothly, forming the transition layer. Then, the temperature is increased (e.g., 75°C), and a crosslinking agent, such as DVB, is added to accelerate the polymerization reaction and form a crosslinked structure. Finally, monomers such as MMA and ALMA are added at an even higher temperature (e.g., 85°C) to further form the high-strength layer. Gradient temperature polymerization can form transition layers and high-strength layers with different Tg values, thereby further improving the thermal stability of the thermally expandable microspheres and avoiding cracking caused by sudden temperature changes.

[0037] Subsequently, a functional layer is formed. Microspheres are dispersed in a Tris-HCl buffer solution containing dopamine hydrochloride, and polymerization is initiated by ozone to form a polydopamine layer. The ozone concentration is 0.2-1.0 g / m³, and the reaction time is 20-40 min. This process can be sheared and emulsified using a microfluidic chip (200 μm channel width), controlling the flow rate to maintain a microsphere diameter D50 of 15 ± 2 μm. Coating the microsphere surface with a functional layer such as polydopamine (PDA) further enhances thermal stability due to PDA's excellent thermal stability and adhesion.

[0038] Subsequently, a perfluoroalkyl acrylate shell can be formed on the outside of the functional layer to increase the hydrophobicity of the microspheres. This also improves the thermal stability of the thermally expandable microspheres.

[0039] Finally, the outer shell can be coated with a flame retardant (e.g., SC-310, viscosity 60-100 mPa·s) to increase the flame retardant properties of the microspheres.

[0040] The thermally expandable microspheres of this invention are suitable for use in papermaking processes. The amount of thermally expandable microspheres added is 0.5-3 wt% of the oven-dry weight of the pulp, and the hot-pressing temperature is 190-210℃.

[0041] The present invention also provides a paper comprising the above-described thermally expandable microspheres.

[0042] The present invention is further described below through specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments and comparative examples are commercially available.

[0043] Example 1

[0044] The following steps were used to prepare thermally expandable microspheres.

[0045] Step 1: Core preparation (temperature controlled at 40±1℃)

[0046] Isobutane and DCP were mixed to form the oil phase; SDS and OP-10 were dissolved in deionized water (conductivity ≤ 5 μS / cm) to form the aqueous phase. The oil phase was injected into the aqueous phase at a rate of 0.5 mL / min into a high-speed shear press (12000 rpm) for 20 min to form an O / W emulsion.

[0047] Shear rate gradient: 12000rpm (0-5min) → 8000rpm (5-15min) → 5000rpm (15-20min), control D90 / D10≤1.3 (monitored by laser particle size analyzer).

[0048] Step 2: Forming a transition layer (first stage) and a high-strength layer (second stage)

[0049] Gradient temperature polymerization (N2 protection), reactor configuration: four-port glass reactor, anchor-type agitator (diameter-to-length ratio 0.9), reflux condenser + temperature programmable controller, parameters for each stage are shown in Table 1: Table 1

[0050] Step 3: Preparation of functional layer (PDA / ZnO functionalization, pH=8.5±0.2)

[0051] 1) In-situ oxidative polymerization: Microspheres were dispersed in Tris-HCl buffer (10mM), dopamine hydrochloride was added, and ozone (concentration 0.8g / m³, flow rate 0.6L / min) was introduced to initiate polymerization.

[0052] 2) Dynamic control: d[PDA] / dt=k[O3] 0.7 [Dopamine] was reacted for 30 min and then centrifuged to obtain PDA-coated microspheres (coating rate ≥95%, verified by XPS).

[0053] 3) ZnO loading: PDA microspheres were immersed in ZnO ethanol dispersion (ultrasonic power 300W, frequency 28kHz), and a vacuum of -0.08MPa was applied for 10min to embed ZnO into the PDA nanopores.

[0054] Load formula: m ZnO =0.18×SSA PDA ×t 0.5 (SSA = specific surface area, t = immersion time)

[0055] Step 4: Microfluidic particle size control (laminar flow mode):

[0056] 1) Chip parameters: Material: Quartz glass, Channel structure: Y-type manifold (main channel 200μm×100μm), Two-phase flow rate: Dispersed phase (microsphere emulsion): 0.05mL / min, Continuous phase (1wt% PVA aqueous solution): 0.15mL / min; 2) Particle size model: D=0.48Q d / Q c ×η c / ηd×(1+3.13Ca 0.5 (Q = flow rate, η = viscosity, Ca = capillary number) Step 5: Shell preparation (hydrophobic modification, solvothermal method) 1) Reaction system: microspheres:FOEA:ethanol = 1:0.1:20 (w / w / w), with 0.1wt% AIBN added.

[0057] 2) Process curve: 25℃→60℃ (heating rate 2℃ / min), hold at 60℃ for 1h (nitrogen bubbling to remove oxygen), cool to 30℃ and then centrifuge and wash.

[0058] Step 6: Coating with flame retardant

[0059] The microparticles were mixed with SC-310 and reacted at 60°C for 1 hour.

[0060] Step 7: Packaging Inspection

[0061] The raw materials and amounts used to prepare the thermally expandable microparticles in this embodiment are shown in Table 2.

[0062] Table 2: Example 1

[0063] The preparation processes of Examples 2-6 and Comparative Examples 1-2 are the same as those of Example 1. The specific raw materials and their amounts are shown in Tables 3-9.

[0064] Table 3: Example 2

[0065] Table 4: Example 3

[0066] Table 5: Example 4

[0067] Table 6: Example 5

[0068] Table 7: Example 6

[0069] Table 8: Comparative Example 1

[0070] Table 9: Comparative Example 2

[0071] The thermally expandable microspheres prepared in Examples 1-6 and Comparative Examples 1-2 were tested, and the testing process is as follows: Initial expansion temperature (°C) test: 1) Thermomechanical analysis (TMA) method is used, standard basis: ASTM E831-14, ISO11359-2. Test principle: microsphere heating → volume expansion → probe displacement → temperature-displacement curve → expansion start point, data can be generated; 2) Differential scanning calorimetry (DSC) is used for auxiliary confirmation, standard basis: ISO11357-3.

[0072] Antibacterial rate (%) test: 1) Quantitative suspension method (JISZ2801), standard basis: JISZ2801:2010, ISO22196; 2) Antibacterial ring method (qualitative), standard basis: AATCC147.

[0073] Contact angle (°) test: static drop contact angle measurement method, standard basis: ISO19403-2, ASTM D7334.

[0074] Tensile index increase (%) test: Paper physical property test, standard basis: ISO1924-2, TAPPIT494.

[0075] Retention rate (%) test: 1) Microsphere integrity test after hot pressing, standard basis: ISO5630-3 (thermal aging test); 2) Limiting oxygen index (LOI) test, standard basis: ISO4589-2, ASTM D2863.

[0076] Combustion rating test: Refer to building materials GB8624-97. Class A: Non-combustible materials (these materials hardly burn and have a high fire safety); Class B1: Flame-retardant materials (these materials are difficult to ignite, smolder, or carbonize when exposed to open flames or high temperatures in air, and combustion or smoldering stops immediately after the fire source is removed); Class B2: Combustible materials (these materials will ignite or smolder immediately when exposed to open flames or high temperatures in air, and can continue to burn or smolder after the fire source is removed); Class B3: Flammable materials (these materials are extremely easy to ignite, and the flame spreads rapidly, posing a great fire hazard).

[0077] The test results of the expandable microspheres in Examples 1-6 and Comparative Examples 1-2 are shown in Table 10.

[0078] Table 10

[0079] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A thermally expandable microsphere, characterized in that, From the inside out, it includes the kernel, the transition layer, and the functional layer; The core comprises isobutane and peroxide; The transition layer is an acrylonitrile / glycidyl methacrylate copolymer layer; and The functional layer includes polydopamine and antibacterial particles attached to its surface.

2. The thermally expandable microspheres according to claim 1, characterized in that, In the core, the mass ratio of isobutane to peroxide is 7-11:1; preferably, the peroxide is dicumyl peroxide or di-tert-butyl peroxide.

3. The thermally expandable microspheres according to claim 1, characterized in that, The glass transition temperature of the transition layer is ≥85℃.

4. The thermally expandable microspheres according to claim 1, characterized in that, A high-strength layer is further included between the transition layer and the functional layer. The high-strength layer is a polymethyl methacrylate layer and / or a polyallyl methacrylate layer, and the glass transition temperature of the high-strength layer is ≥105℃.

5. The thermally expandable microspheres according to claim 1, characterized in that, The functional layer also includes a perfluoroalkyl acrylate shell on its outer side, the perfluoroalkyl acrylate shell having a contact angle ≥150°; and / or The perfluoroalkyl acrylate shell is made of one or more of perfluorooctyl ethyl acrylate, heptadecafluorodecyl acrylate, and tridecafluorooctyl acrylate; and / or The outer shell also includes a flame retardant.

6. The thermally expandable microspheres according to claim 1, characterized in that, The weight ratio of the core, the transition layer, the functional layer, and the outer shell is 45-55:80-100:10-15:7-10; and / or The median particle size D50 of the thermally expandable microspheres is 13-17 μm, and the D90 / D10 ratio is ≤1.

8.

7. The thermally expandable microspheres according to claim 1, characterized in that, The antibacterial particles are selected from one or more of nano-zinc oxide, nano-copper oxide, and silver-loaded zeolite particles; and / or The content of the antibacterial particles in the functional layer is 8-12%.

8. The thermally expandable microspheres according to claim 1, characterized in that, The initial expansion temperature of the thermally expandable microspheres is greater than 190°C.

9. A method for preparing thermally expandable microspheres according to any one of claims 1-8, characterized in that, include: Isobutane and peroxide are used to form an oil phase, which is then mixed with water to form an O / W emulsion with droplet diameters of 2-5 μm and D90 / D10 ≤ 1.8; and A transition layer is formed in the acrylonitrile / glycidyl methacrylate copolymer; Microspheres were dispersed in a Tris-HCl buffer solution containing dopamine salt, and ozone was introduced to initiate oxidative polymerization to form polydopamine. Subsequently, the microspheres were impregnated in a dispersion containing antibacterial particles to form a functional layer.

10. The preparation method according to claim 9, characterized in that, The high-strength layer is further formed between the formation of the transition layer and the functional layer; gradient temperature polymerization is used when forming the transition layer and the high-strength layer.

11. The application of thermally expandable microspheres according to any one of claims 1-8 in a papermaking process, characterized in that, Preferably, the amount of the thermally expandable microspheres added is 0.5-3 wt% of the oven-dry weight of the pulp, and the hot-pressing temperature is 190-210℃.

12. A type of paper, characterized in that, Includes the thermally expandable microspheres according to any one of claims 1-8.

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