阅读说明：本技术 一种高温热膨胀微胶囊及其制备方法和应用 (High-temperature thermal expansion microcapsule and preparation method and application thereof ) 是由 贾伟艺 刘莉莉 李洪娟 孙可凡 王亚涛 李建华 于 2021-01-25 设计创作，主要内容包括：本发明涉及热膨胀微胶囊技术领域,具体公开一种高温热膨胀微胶囊及其制备方法和应用。所述高温热膨胀微胶囊,包括囊芯和囊壁,所述囊芯为固体碳酰胺微粒,所述囊壁为双重交联的苯乙烯-丙烯腈-丙烯酸酯共聚物。所述热膨胀微胶囊的制备方法为：采用双分子层乳液模板技术并通过原位聚合法,实现苯乙烯–丙烯腈–丙烯酸酯共聚物对固体碳酰胺微粒的包覆。本发明的热膨胀微胶囊在应用于高温油墨印刷品时,不仅具有在高温条件下热膨胀的功能,而且在气化过程中,不产生有机挥发物,是一种绿色环保型的热膨胀微胶囊,具备良好的经济效益和发展前景。(The invention relates to the technical field of thermal expansion microcapsules, and particularly discloses a high-temperature thermal expansion microcapsule and a preparation method and application thereof. The high-temperature thermal expansion microcapsule comprises a capsule core and a capsule wall, wherein the capsule core is solid carbamide particles, and the capsule wall is a double-crosslinked styrene-acrylonitrile-acrylate copolymer. The preparation method of the thermal expansion microcapsule comprises the following steps: the coating of the styrene-acrylonitrile-acrylate copolymer on the solid carbamide particles is realized by adopting a bilayer emulsion template technology and an in-situ polymerization method. When the thermal expansion microcapsule is applied to high-temperature printing ink printed matters, the thermal expansion microcapsule not only has the function of thermal expansion under the high-temperature condition, but also does not generate organic volatile matters in the gasification process, is an environment-friendly thermal expansion microcapsule, and has good economic benefit and development prospect.)

1. A high-temperature thermal expansion microcapsule comprises a capsule core and a capsule wall, wherein the capsule core is solid carbamide particles, and the capsule wall is a double-crosslinked styrene-acrylonitrile-acrylate copolymer.

2. The high-temperature thermal expansion microcapsule according to claim 1, wherein the double-crosslinked styrene-acrylonitrile-acrylate copolymer is prepared by radical polymerization using styrene, acrylonitrile and acrylate monomers as raw materials and divinylbenzene and ethylene glycol dimethacrylate as crosslinking agents.

3. The high-temperature thermal expansion microcapsule according to claim 2, wherein the acrylic monomers are butyl acrylate, bisphenol a epoxy diacrylate and methyl methacrylate; and/or

The average particle diameter of the solid carbamide particles is 5-60 mu m.

4. The method for preparing high-temperature thermal expansion microcapsules according to any one of claims 1 to 3, comprising the steps of:

step one, adding solid carbamide particles into an insoluble dispersion solvent under inert atmosphere, uniformly mixing, adding a macromolecular surfactant, uniformly stirring and mixing, then adding a nonionic surfactant, uniformly stirring and mixing, then adding an anionic surfactant, and continuously stirring and uniformly mixing to obtain a core material emulsion;

step two, uniformly mixing the acrylate monomer, the styrene and the acrylonitrile, adding the divinyl benzene and the ethylene glycol dimethacrylate cross-linking agent and the initiator, and uniformly mixing to obtain a wall material emulsion;

and step three, heating the core material emulsion to 64.5-65.5 ℃ under the inert atmosphere and stirring condition, then adding the wall material emulsion, carrying out heat preservation reaction for 5-6h, then aging for 12-24h at the same temperature, filtering, washing and drying to obtain the high-temperature thermal expansion microcapsule.

5. The method for preparing a high-temperature thermal expansion microcapsule according to claim 4, wherein in the first step, the dispersion solvent is a mixture of acetonitrile and formamide with a mass ratio of 4-10:1, and the mass percentage of the dispersion solvent in the core material emulsion is 50.0-55.0%; and/or

In the first step, the macromolecular surfactant is polymethyl pyrrolidone, the nonionic surfactant is tween 20, and the anionic surfactant is sodium dodecyl benzene sulfonate.

6. The method for preparing a high-temperature thermal expansion microcapsule according to claim 4 or 5, wherein in the first step, the mass ratio of the macromolecular surfactant, the nonionic surfactant and the anionic surfactant is 1:0.8-1.2: 0.8-1.2; and/or

In the first step, the mass percentage of the total amount of the macromolecular surfactant, the nonionic surfactant and the anionic surfactant in the core material emulsion is 3.0-5.0%.

7. The method for preparing high-temperature thermal expansion microcapsules according to claim 4, wherein in the second step, the acrylate monomers are butyl acrylate, bisphenol A epoxy diacrylate and methyl methacrylate; and/or

In the third step, the wall material emulsion is added into the core material emulsion in a dropwise manner, wherein the dropwise addition time is 1-1.5 h.

8. The method for preparing high-temperature thermal expansion microcapsules according to claim 7, wherein in the second step, the mass percent of each reactant is as follows: 15.0-20.0% of styrene, 10.0-15.0% of acrylonitrile, 15.0-20.0% of butyl acrylate, 15.0-20.0% of bisphenol A epoxy diacrylate, 10.0-15.0% of methyl methacrylate, 7.0-10.0% of divinylbenzene, 5.0-10.0% of ethylene glycol dimethacrylate and 0.2-0.3% of initiator.

9. The method for producing high-temperature thermal expansion microcapsules according to claim 4 or 7, wherein the mass ratio of the solid carbamide particles to the total amount of styrene, acrylonitrile and acrylate monomers is 1: 1.5-2.0.

10. Use of the high temperature thermal expansion microcapsules according to any one of claims 1 to 3 in the field of high temperature printing inks.

Technical Field

The invention relates to the technical field of thermal expansion microcapsules, in particular to a high-temperature thermal expansion microcapsule and a preparation method and application thereof.

Background

The traditional thermal expansion microcapsule for printing is generally formed by wrapping a low-boiling-point organic solvent serving as a foaming agent in a thermoplastic polymer shell by using a microcapsule technology to form spherical particles with the particle size of 5-100 mu m and a core-shell structure. The ink containing the heat expansion microcapsules is printed on a bearing object such as paper, fabric or a hard plane through screen printing and is solidified, an organic solvent at the core part of the heat expansion microcapsules in the ink is heated and volatilized through a local heating mode, and the microcapsules are expanded and enlarged through internal vapor pressure generated by gasification, so that printed patterns or characters show a remarkable stereoscopic vision effect. The development of the thermal expansion microcapsule synthesis technology is of great help to the improvement of the application technology level of the related ink, the aesthetic feeling of the printed matter can be increased, the quality of the printed matter is obviously improved, and the method is beneficial to obtaining greater social and economic benefits, so that the technical development of the thermal expansion microcapsule synthesis technology is paid extensive attention in recent years.

In recent years, with the expansion of the application field of printing ink, the printing ink has been gradually developed from the middle and low temperature field which is currently used more to the high temperature application field, and therefore, it is required that the thermal expansion processing temperature of the thermal expansion microcapsules in the applied printing ink is matched with the thermal expansion processing temperature. However, the conventional organic alkane foaming agent is rapidly volatilized at a high foaming temperature, so that microcapsules are easily broken, the effect of generating the 3D concave-convex effect cannot be effectively exerted, and the organic alkane volatilized by the broken microcapsules can pollute the environment. Therefore, the development of the environment-friendly high-temperature thermal expansion microcapsule has very important significance for expanding the application field of printing ink.

Disclosure of Invention

The invention provides a high-temperature thermal expansion microcapsule, a preparation method and application thereof, aiming at the problems that in the prior art, a thermal expansion microcapsule is mainly foamed at a medium-low temperature, is difficult to apply to the field of high-temperature printing ink and is easy to cause environmental pollution after foaming.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a high-temperature thermal expansion microcapsule comprises a capsule core and a capsule wall, wherein the capsule core is solid carbamide particles, and the capsule wall is a double-crosslinked styrene-acrylonitrile-acrylate copolymer.

Compared with the prior art, the microcapsule provided by the invention takes the solid carbamide particle foaming agent as the core, and adopts the double-crosslinked styrene-acrylonitrile-acrylate copolymer as the shell material, so that the microcapsule with a core-shell structure and solid-phase thermal expansion at high temperature is formed; wherein, after being coated by the polymer as a solid foaming agent, the carbamide particles can be completely decomposed into ammonia gas and carbon dioxide within the range of 160-180 ℃, generate larger internal air pressure to expand the microcapsule, obviously improve the foaming multiplying power of the microcapsule and have no residue; the selected double-crosslinked styrene-acrylonitrile-acrylate copolymer has higher glass transition temperature, improves the high temperature resistance of the microcapsule, meets the requirement that the capsule wall cannot be decomposed and damaged at the temperature of 160-210 ℃, also considers the high elasticity of the shell layer, can expand along with the increase of gas pressure, provides sufficient strength, toughness, resilience and high temperature resistance for the shell layer of the microcapsule, and can still keep the integrity and the elasticity of the capsule body under the impact action of larger internal pressure generated by the decomposition of the carbamide in the core part. The combination of the core material and the wall material not only ensures that the prepared thermal expansion microcapsule is suitable for higher thermal expansion processing temperature, but also avoids the pollution of organic volatile compounds (VOC) generated by the foaming of the traditional organic hydrocarbon foaming agent under the high-temperature processing condition to the environment, thereby being the green and environment-friendly high-temperature thermal expansion microcapsule for printing ink.

The foaming temperature of the high-temperature thermal expansion microcapsule prepared by the invention is 160-210 ℃, the foaming multiplying power can reach more than 7 times, and the high-temperature foaming microcapsule can maintain good form stability and structural integrity, has good foaming performance, overcomes the defect that the existing thermal expansion microcapsule is only suitable for medium-low temperature thermal expansion processing at present, and the carbamide in the core part of the microcapsule is completely decomposed into ammonia gas and carbon dioxide after foaming, avoids the pollution of organic volatile compounds (VOC) generated by the high-temperature processing foaming of the traditional organic alkane foaming agent to the environment, and has good economic benefit and development prospect.

Preferably, the average particle diameter of the solid carbamide particles is 5-60 μm.

Preferably, the average particle size of the high-temperature thermal expansion microcapsules is 50 to 70 μm.

According to the invention, the solid carbamide particles are selected as the core material, the particle size of the thermal expansion microcapsule can be simply and effectively controlled by controlling the particle size of the solid carbamide particles according to the requirement on the expansion height of characters and patterns in the printing and processing application of the ink, the problem that the particle size is difficult to control in the process of preparing the thermal expansion microcapsule by coating the liquid organic hydrocarbon foaming agent in the prior art is solved, the controllability of the preparation process is stronger, and the expanded production is more facilitated.

Preferably, the double-crosslinked styrene-acrylonitrile-acrylate copolymer is prepared by taking styrene, acrylonitrile and acrylate monomers as raw materials and taking divinylbenzene and ethylene glycol dimethacrylate as crosslinking agents through free radical polymerization.

Further preferably, the acrylate monomers are butyl acrylate, bisphenol a epoxy diacrylate and methyl methacrylate.

The optimized wall material adopts soft-hard segment chain interaction, introduces bisphenol A epoxy diacrylate to obviously improve the glass transition temperature of the shell material, adopts divinyl benzene and ethylene glycol dimethacrylate as a cross-linking agent to carry out double cross-linking, improves the cross-linking density, provides sufficient strength, toughness, resilience force and high heat resistance for the shell layer of the thermal expansion microcapsule, not only improves a larger expansion space for a foaming agent and is beneficial to improving the foaming multiplying power, but also can ensure that the shell layer has better compactness and integrity under the processing condition of high-temperature thermal expansion, better protects the core material and ensures that the thermal expansion microcapsule is suitable for higher processing temperature.

The invention also provides a preparation method of the high-temperature thermal expansion microcapsule, which at least comprises the following steps:

step one, adding solid carbamide particles into an insoluble dispersion solvent under inert atmosphere, uniformly mixing, adding a macromolecular surfactant, uniformly stirring and mixing, then adding a nonionic surfactant, uniformly stirring and mixing, then adding an anionic surfactant, and continuously stirring and uniformly mixing to obtain a core material emulsion;

step two, uniformly mixing the acrylate monomer, the styrene and the acrylonitrile, adding the divinyl benzene and the ethylene glycol dimethacrylate cross-linking agent and the initiator, and uniformly mixing to obtain a wall material emulsion;

and step three, heating the core material emulsion to 64.5-65.5 ℃ under the inert atmosphere and stirring condition, then adding the wall material emulsion, carrying out heat preservation reaction for 5-6h, then aging for 12-24h at the same temperature, filtering, washing and drying to obtain the high-temperature thermal expansion microcapsule.

The preparation method comprises the steps of firstly, dispersing formamide by using a carbonyl amide insoluble dispersion solvent by using a bilayer emulsion template technology, then assembling styrene, acrylonitrile and acrylate monomers, and a divinyl benzene and polyethylene glycol dimethacrylate cross-linking agent to the surface of solid carbonyl amide particles by adopting a mode of mixing and emulsifying a macromolecular surfactant, a nonionic surfactant and an anionic surfactant, and then coating a carbonyl amide solid-phase foaming agent by using a double-cross-linked styrene-acrylonitrile-acrylate copolymer by using an in-situ free radical polymerization method, thereby forming the thermal expansion microcapsule with a typical core-shell structure.

Preferably, in the first step, the dispersion solvent is a mixture of acetonitrile and formamide with a mass ratio of 4-10:1, and the mass percentage of the dispersion solvent in the core material emulsion is 50.0-55.0%.

The preferred dispersing solvent allows the formation of a uniform suspension of the carbamide, does not affect the performance of the carbamide, and facilitates the sufficient emulsification of the subsequent carbamide.

Preferably, in the first step, the macromolecular surfactant is polymethyl pyrrolidone, the nonionic surfactant is tween 20, and the anionic surfactant is sodium dodecyl benzene sulfonate.

Preferably, in the first step, the mass ratio of the macromolecular surfactant to the nonionic surfactant to the anionic surfactant is 1:0.8-1.2: 0.8-1.2.

Preferably, in the first step, the total amount of the macromolecular surfactant, the nonionic surfactant and the anionic surfactant accounts for 3.0-5.0% by mass of the core material emulsion.

The preferable surfactant and the dosage are favorable for fully emulsifying the carbamide to obtain a bilayer stable solid carbamide particle emulsion template system, and further favorable for assembling the divinylbenzene and the polyethylene glycol dimethacrylate cross-linking agent on the surface of the solid carbamide particle in the follow-up process, thereby realizing the coating of the double cross-linked styrene-acrylonitrile-acrylate copolymer on the carbamide solid-phase foaming agent.

Preferably, in the second step, the acrylate monomers are butyl acrylate, bisphenol a epoxy diacrylate and methyl methacrylate.

Preferably, in the third step, the wall material emulsion is added into the core material emulsion in a dropwise manner, wherein the dropwise addition time is 1-1.5 h.

Preferably, in the second step, the mass percentages of the reactants are as follows: 15.0-20.0% of styrene, 10.0-15.0% of acrylonitrile, 15.0-20.0% of butyl acrylate, 15.0-20.0% of bisphenol A epoxy diacrylate, 10.0-15.0% of methyl methacrylate, 7.0-10.0% of divinylbenzene, 5.0-10.0% of ethylene glycol methyl diacrylate and 0.2-0.3% of initiator.

The shell material has balanced proportion of soft and hard sections, and the double cross-linking agent is introduced, so that the cross-linking density is improved, the coating rate and the heat resistance of the microcapsule are improved, a reliable expansion space is provided for the foaming agent, and the foaming agent is suitable for higher expansion processing temperature.

Preferably, the initiator is azobisisobutyronitrile.

Preferably, the mass ratio of the solid carbamide particles to the total amount of the styrene, the acrylonitrile and the acrylate monomers is 1: 1.5-2.0.

The preferable mass ratio of the core material to the wall material is beneficial to better coating the core material and improving the coating rate of the microcapsule.

The inert atmosphere in the invention is provided by inert gas, and the inert gas can be nitrogen, argon and the like.

The invention also provides application of the high-temperature thermal expansion microcapsule in the field of high-temperature foaming ink.

The thermal expansion microcapsule prepared by the invention has higher foaming ratio, the foaming temperature is 160-210 ℃, the thermal expansion microcapsule is suitable for foaming ink for high-temperature thermal expansion processing, not only can provide visual and tactile 3D concave-convex three-dimensional effect, but also can not generate organic volatile compounds (VOC) after foaming, can not cause pollution to the environment, is an environment-friendly high-temperature thermal expansion microcapsule, greatly widens the application range of the thermal expansion microcapsule, and has wide application prospect.

Drawings

FIG. 1 is an electron scanning electron microscope image of the high temperature thermal expansion microcapsules prepared in example 5 of the present invention before expansion.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

The embodiment of the invention provides a high-temperature thermal expansion microcapsule, and the preparation method comprises the following steps:

step one, grinding large-particle solid carbamide to particles with the average particle size of 50-60 mu m by using a ball mill to obtain solid carbamide particles;

step two, under the protection of nitrogen, adding 46.0g of solid carbamide particles, 46.0g of acetonitrile and 5.0g of formamide into a three-opening reaction bottle, uniformly dispersing, then adding 1.0g of polymethyl pyrrolidone, continuously stirring at 400rpm for 30min at room temperature, then adding 0.8g of tween 20, continuously stirring for 40min, adding 1.2g of sodium dodecyl benzene sulfonate, and continuously stirring for 1h to obtain a core material emulsion;

step three, adding 20.0g of styrene, 10.0g of acrylonitrile, 15.0g of butyl acrylate, 19.7g of bisphenol A epoxy diacrylate, 15.0g of methyl methacrylate, 10.0g of divinylbenzene, 10.0g of ethylene glycol methyl diacrylate and 0.3g of azobisisobutyronitrile into a single-mouth bottle, and stirring and mixing uniformly to obtain a wall material emulsion;

and step four, heating the core material emulsion to 65 ℃ under the condition of continuous stirring, then dropwise adding the wall material emulsion into the core material emulsion for 1.2h, keeping the same temperature for aging for 12 h after dropwise adding is completed, then filtering the reaction mixture, washing for 3 times by deionized water and alcohol respectively, and drying at room temperature until the washing solvent is completely volatilized to obtain the high-temperature thermal expansion microcapsule.

Example 2

The embodiment of the invention provides a high-temperature thermal expansion microcapsule, and the preparation method comprises the following steps:

step one, grinding large-particle solid carbamide to particles with the average particle size of 15-20 mu m by using a ball mill to obtain solid carbamide particles;

step two, under the protection of nitrogen, adding 46.0g of solid carbamide particles, 40.8g of acetonitrile and 10.2g of formamide into a three-opening reaction bottle, uniformly dispersing, then adding 1.0g of polymethyl pyrrolidone, continuously stirring at 500rpm for 30min at room temperature, then adding 1.2g of tween 20, continuously stirring for 40min, adding 0.8g of sodium dodecyl benzene sulfonate, and continuously stirring for 1h to obtain a core material emulsion;

step three, adding 15.0g of styrene, 15.0g of acrylonitrile, 18.0g of butyl acrylate, 20.0g of bisphenol A epoxy diacrylate, 14.7g of methyl methacrylate, 7.0g of divinylbenzene, 10.0g of ethylene glycol methyl diacrylate and 0.3g of azobisisobutyronitrile into a single-mouth bottle, and stirring and mixing uniformly to obtain a wall material emulsion;

and step four, heating the core material emulsion to 65 ℃ under the condition of continuous stirring, then dropwise adding the wall material emulsion into the core material emulsion for 1.5h, keeping the same temperature for aging for 15 h after dropwise adding is completed, then filtering the reaction mixture, washing for 3 times by using deionized water and alcohol respectively, and drying at room temperature until the washing solvent is completely volatilized to obtain the high-temperature thermal expansion microcapsule.

Example 3

The embodiment of the invention provides a high-temperature thermal expansion microcapsule, and the preparation method comprises the following steps:

step one, grinding large-particle solid carbamide to particles with the average particle size of 15-20 mu m by using a ball mill to obtain solid carbamide particles;

step two, under the protection of nitrogen, adding 42.0g of solid carbamide particles, 50.0g of acetonitrile and 5.0g of formamide into a three-opening reaction bottle, uniformly dispersing, then adding 1.0g of polymethyl pyrrolidone, continuously stirring at 400rpm for 40min at room temperature, then adding 1.0g of tween 20, continuously stirring for 40min, adding 1.0g of sodium dodecyl benzene sulfonate, and continuously stirring for 1h to obtain a core material emulsion;

step three, adding 18.0g of styrene, 15.0g of acrylonitrile, 19.0g of butyl acrylate, 15.0g of bisphenol A epoxy diacrylate, 13.0g of methyl methacrylate, 10.0g of divinylbenzene, 9.8g of ethylene glycol methyl diacrylate and 0.2g of azobisisobutyronitrile into a single-mouth bottle, and stirring and mixing uniformly to obtain a wall material emulsion;

and step four, heating the core material emulsion to 65 ℃ under the condition of continuous stirring, then dropwise adding the wall material emulsion into the core material emulsion for 1.0h, keeping the same temperature for aging for 18 hours after dropwise adding is completed, then filtering the reaction mixture, washing for 3 times by using deionized water and alcohol respectively, and drying at room temperature until the washing solvent is completely volatilized to obtain the high-temperature thermal expansion microcapsule.

Example 4

The embodiment of the invention provides a high-temperature thermal expansion microcapsule, and the preparation method comprises the following steps:

step one, grinding large-particle solid carbamide to particles with the average particle size of 30-40 mu m by using a ball mill to obtain solid carbamide particles;

step two, under the protection of nitrogen, adding 44.5g of solid carbamide particles, 42.5g of acetonitrile and 8.5g of formamide into a three-opening reaction bottle, uniformly dispersing, then adding 1.5g of polymethyl pyrrolidone, continuously stirring at 400rpm for 30min at room temperature, then adding 1.5g of tween 20, continuously stirring for 40min, adding 1.5g of sodium dodecyl benzene sulfonate, and continuously stirring for 1h to obtain a core material emulsion;

step three, adding 20.0g of styrene, 15.0g of acrylonitrile, 20.0g of butyl acrylate, 20.0g of bisphenol A epoxy diacrylate, 10.0g of methyl methacrylate, 9.7g of divinylbenzene, 5.0g of ethylene glycol methyl diacrylate and 0.3g of azobisisobutyronitrile into a single-mouth bottle, and stirring and mixing uniformly to obtain a wall material emulsion;

and step four, heating the core material emulsion to 65 ℃ under the condition of continuous stirring, then dropwise adding the wall material emulsion into the core material emulsion for 1.2h, keeping the same temperature for aging for 24h after dropwise adding is completed, then filtering the reaction mixture, washing for 3 times by using deionized water and alcohol respectively, and drying at room temperature until the washing solvent is completely volatilized to obtain the high-temperature thermal expansion microcapsule.

Example 5

The embodiment of the invention provides a high-temperature thermal expansion microcapsule, and the preparation method comprises the following steps:

step one, grinding large-particle solid carbamide to particles with the average particle size of 5-10 mu m by using a ball mill to obtain solid carbamide particles;

step two, under the protection of nitrogen, adding 46.0g of solid carbamide particles, 44.6g of acetonitrile and 6.4g of formamide into a three-opening reaction bottle, uniformly dispersing, then adding 1.0g of polymethyl pyrrolidone, continuously stirring at 400rpm for 30min at room temperature, then adding 1.0g of tween 20, continuously stirring for 40min, adding 1.0g of sodium dodecyl benzene sulfonate, and continuously stirring for 1h to obtain a core material emulsion;

step three, adding 17.0g of styrene, 14.0g of acrylonitrile, 19.0g of butyl acrylate, 18.7g of bisphenol A epoxy diacrylate, 14.0g of methyl methacrylate, 9.0g of divinylbenzene, 8.0g of ethylene glycol methyl diacrylate and 0.3g of azobisisobutyronitrile into a single-mouth bottle, and stirring and mixing uniformly to obtain a wall material emulsion;

and step four, heating the core material emulsion to 65 ℃ under the condition of continuous stirring, then dropwise adding the wall material emulsion into the core material emulsion for 1.3h, keeping the same temperature for aging for 12 h after dropwise adding is completed, then filtering the reaction mixture, washing for 3 times by deionized water and alcohol respectively, and drying at room temperature until the washing solvent is completely volatilized to obtain the high-temperature thermal expansion microcapsule.

An electron scanning microscope picture of the high-temperature expansion microcapsule prepared in the embodiment before foaming and expansion is shown in fig. 1, and it can be seen from the picture that the average particle size of the microcapsule is 50-70 μm, the size is uniform, and the microcapsule before foaming and expansion has a regular spherical shape.

Testing the foaming performance of the heat-expandable microcapsule: measured by a thermo-mechanical analyzer TMA Q-400 manufactured by TA Instrument Co. The specific operation is as follows: the TMA test site was placed in a quartz crucible having an inner diameter of 3.4mm and a depth of 14.2mm, a zero position was set, 1.0mg of the thermal expansion microcapsule prepared in example 5 was placed in the crucible, the initial height of the probe was read, the temperature of the sample was raised from ambient temperature to 230 ℃ at a temperature-raising rate of 20 ℃/min, and a force of 0.06N was applied from the probe, and the analysis was carried out by measuringMeasuring the vertical displacement of the probe to obtain the initial foaming temperature T_s(temperature at which probe displacement starts to increase), maximum foaming temperature T_m(temperature at which probe displacement reaches maximum), the minimum bubble density ρ was calculated by testing_minAnd initial density of microspheres ρ₀The expansion ratio of the microspheres is calculated as rho₀/ρ_min。

The test results show that the microcapsules prepared in this example have an initial foaming temperature of 170 ℃, a temperature at which the maximum expansion is reached of 210 ℃ and an expansion ratio of 7.3 times.

The above examples 1 to 4 all achieved substantially equivalent foaming properties to example 5.

If the foaming height of the ink is too high, it shows poor adhesion of the microcapsules to the ink, and thus, the adhesion of the thermally-expansible microcapsules prepared in the examples of the present invention to the ink was tested as follows. The formula of the ink is as follows:

printing virgin pulp (50 wt%), water-based acrylic resin (25 wt%), water (5 wt%), color paste (9 wt%), thermal expansion microcapsules (10 wt%), defoaming agent (0.2 wt%) and flatting agent (0.8 wt%). The raw materials are prepared into the ink according to the conventional ink preparation method.

The adhesion was rated according to ISO 12944 international standards (level 0 indicating a completely smooth cut edge with no one off, level 1 indicating a little coating off at the intersection and no significant more than 5% affected area, level 2 indicating a coating off at or along the cut edge and 5-15% affected area) using a cross-hatch spacing of 2 mm.

Test results show that the adhesive force between the thermal expansion microcapsules prepared in the embodiments 1 to 5 of the invention and the ink can reach 0 to 1 grade.

In the above test, the additives in the ink, such as the defoaming agent and the leveling agent, can be conventional substances in the field of ink, and the difference in the types of the substances does not have obvious influence on the adhesion test result.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.