CN115403816B - A kind of preparation method of expandable thermoplastic foam microsphere - Google Patents

Abstract

The invention relates to a preparation method of expandable thermoplastic foaming microspheres, which comprises the following steps: providing a solid core material that generates a low boiling point gas by a chemical reaction; coating the solid core material with a water-soluble high molecular polymer and a crosslinking agent, and performing a crosslinking reaction to form the expandable thermoplastic foaming microsphere. The solid core material is at least one of sodium bicarbonate, azodicarbonamide or 4,4' -oxo-bis-benzenesulfonyl hydrazide. The invention has the following beneficial effects: 1. the molecular weight distribution of the microsphere foaming agent shell is narrower, and the particle size range of the prepared microsphere is narrower; 2. solves the problems of insufficient supporting force, larger retraction and the like of the microsphere foaming agent in the prior art, and expands the application field of the microsphere foaming agent; 3. solves the difficulty that the preparation process in the prior art needs too high pressure, enables large-scale industrial production to be possible, obviously shortens the time and greatly improves the production efficiency.

Description

A kind of preparation method of expandable thermoplastic foam microsphere

technical field

The invention relates to the technical field of foamed microspheres, in particular to a preparation method of expandable thermoplastic foamed microspheres.

technical background

The expandable microsphere foaming agent is a milky white tiny spherical plastic particle with a diameter of 10-45 microns. When heated to a certain temperature, the thermoplastic shell softens, the gas inside the shell expands, and the volume of the foaming agent can increase to dozens of times its own, while the core-shell structure is not destroyed, thereby achieving the effect of foaming.

This special blowing agent has a core-shell structure, the outer shell is thermoplastic acrylic polymer, and the inner core is spherical plastic particles composed of alkane gas. Its diameter is generally 10-30 microns, and the thickness of the polymer shell is 2-15 microns. The shell has good elasticity and can withstand high pressure. After heating and expanding, the foaming agent itself does not break and maintains itself. good performance.

Expansion principle of expandable microsphere blowing agent: After the expandable microsphere is heated, the polymer shell becomes soft, and the gas in the shell expands at the same time. The compound inside the shell expands to 20-50 times its original volume in a very short time. The microsphere shell after foaming will not break, and still maintain a complete sealed sphere. Microspheres have high resilience and are easy to compress. When the pressure is released, the microspheres will return to their original volume.

Existing expandable microspheres are mostly produced by coating low-boiling alkanes with polymeric materials. CN109414672 B, US2019233606A, WO2018011182A patent documents disclose thermally expandable thermoplastic microspheres and preparation methods thereof, but this type of method has the following disadvantages: the alkane used has a higher boiling point than normal temperature, such as pentane, hexane, etc., at normal temperature ( When it is lower than the boiling point of alkane), the alkane that becomes gaseous will become liquid again. For the microspheres, the expanded microspheres will retract a part, and for the foamed materials that have been made, it shows that the material has no The supporting force, and even the shaped foam material will shrink in volume to varying degrees after cooling. Ethane, methane or even nitrogen with a lower boiling point can be used as the core material of the microsphere blowing agent to solve the above disadvantages, but these core materials are extremely difficult to liquefy, and the synthesis reaction must be carried out under relatively high pressure, which is very easy to cause Synthesis failed.

Contents of the invention

The purpose of the present invention is to provide a preparation method of expandable thermoplastic foamed microspheres to solve the existing problems in the prior art.

In order to achieve the purpose of the above invention, the technical solution adopted in the present invention is: a preparation method of expandable thermoplastic foamed microspheres, comprising the following steps: providing a solid core material that generates a low-boiling point gas through a chemical reaction; using water-soluble The high molecular polymer and the cross-linking agent coat the solid core material, and undergo a cross-linking reaction to form expandable thermoplastic foamed microspheres.

The solid core material is at least one of sodium bicarbonate, azodicarbonamide or 4,4'-oxobisbenzenesulfonyl hydrazide.

The water-soluble polymer used is selected from at least one of polyvinyl alcohol, polyvinyl pyrrolidone, acrylonitrile, acrylic acid, and methyl methacrylate copolymer.

The crosslinking agent is a crosslinking agent containing two or three double bonds.

The crosslinking agent used is at least one of triallyl isocyanurate, trimethylolpropane triacrylate and trifunctional acrylate.

The preparation method also includes a pretreatment step of the solid core material, specifically: crushing the solid core material to 20-45 microns, and then performing surface hydrophobic modification with liquid paraffin to form a dense hydrophobic layer.

A method for preparing expandable thermoplastic foamed microspheres of the present invention, firstly pretreating the selected solid core material so that the particle diameter of the core material reaches 1-100 microns, and then performing surface modification with liquid paraffin to form a dense hydrophobic layer .

The preparation method that the present invention adopts does not directly adopt the alkane with lower boiling point as the core material, but adopts the material that is solid under normal temperature as the core material, and the coated core material undergoes a chemical reaction in a high-temperature preparation environment (150-200 degrees Celsius). The reaction will generate low boiling point gases such as nitrogen and carbon dioxide. The temperature generated by the gas is higher than the temperature required for the synthesis of the shell material. Even if the temperature drops after these gases are generated, the core material will not return to the solid or liquid state due to the reverse reaction. At the same time , these low-boiling-point gases can produce higher vapor pressure at the same temperature as the core material (isobutane, isopentane, etc.) described in the CN109414672B patent literature. The existence of the core material can react under relatively mild conditions, and does not require high pressure to maintain the liquid condition of the core material. Therefore, at room temperature (0-40 degrees Celsius), a higher supporting force can be improved, and stronger supporting force is the characteristic of the microsphere foaming agent. As a foaming material, this has the advantage of not only avoiding the synthesis difficulty caused by the low boiling point of the core material during the synthesis process, but also ensuring the supporting force of the expanded microspheres.

Existing microsphere blowing agents all use monomers such as acrylonitrile and methyl methacrylate for emulsion polymerization to form the shell of the microsphere blowing agent. The preparation requires at least 20 hours of reaction time , the composition of the reaction product is complex and difficult to control, and usually has a wide range of molecular weight distribution, which will greatly affect the performance of the microsphere blowing agent.

The present invention uses a mature polymerization process to make monomers into high-resolution polymers (polyvinyl alcohol, acrylonitrile and acrylate copolymers), and then adds crosslinking agents (triallyl isocyanurate, trimethylol Propane trimethacrylate), initiators (hydrogen peroxide, ammonium persulfate, one-tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, etc.), increase the molecular weight of the polymer through the polymer cross-linking reaction, and generate The molecular weight distribution of the outer shell is narrower, and the particle size range of the microspheres is narrower. During the above reaction process, the water-soluble polymer material is precipitated from water and deposited on the surface of the core material, and the shell formed by the precipitation deposition is more uniform. The reaction is relatively simple by this method, which reduces the difficulty of reflection and shortens the reaction time. Within 10 hours, the production efficiency is improved.

Of course, the above-mentioned solid core material must be pretreated by some methods before it can be used as the core material in the reaction. Firstly, the solid core material should be pulverized into a suitable particle size (20-45 microns) by a ball mill, and the particle size range can also be narrowed by sieving, and then these solid materials with a suitable particle size can be processed by spraying method or solvent method. Surface modification forms a dense hydrophobic layer on the surface, and these hydrophobic layers can make the solid core material stably dispersed in the aqueous phase system in the next reaction.

In the preparation method of the present invention, the solid core material accounts for 20-40% of the total weight, the polymer accounts for 60-80% of the total weight, the crosslinking agent accounts for 1.7-2.3% of the total weight, and deionized water accounts for 1.7-2.3% of the total weight. The initiator is 7-8 times of the total weight, and the initiator is 2-3% of the total weight, and the total weight refers to the total weight of the solid core material and the high molecular polymer.

Compared with the prior art, the present invention has the following beneficial effects: 1. The molecular weight distribution of the shell of the microsphere blowing agent formed by the polymer crosslinking reaction is narrower, and the range of the particle size of the microsphere is narrower; 2. The present invention is solved. There are problems such as insufficient supporting force and large retraction of the microsphere foaming agent in the prior art, which expands the application field of the microsphere foaming agent; 3. Solve the problem of excessive pressure required by the prior art preparation process, making large-scale industrial production possible , At the same time, the production time is also significantly shortened, which greatly improves the production efficiency.

Detailed ways

Weigh solid core materials of different weights, pulverize and sieve with an ultrafine pulverizer, spray-dry liquid paraffin for surface hydrophobic treatment, weigh high molecular polymers, cross-linking agents, add deionized water, and put them into a 250ml three-necked flask , 15000rpm homogenization under the homogenizer for 5 minutes, connected to the stirring and condensing reflux device, the temperature of the material water bath was raised to 60°C, and the initiator (1g diluted to 10g) was added dropwise, and the dropwise addition was completed within half an hour. After heat preservation at 65°C for 10 hours, filter, rinse the filter cake twice with n-heptane, then dry at 60°C until constant weight to obtain solid powder (particle size DN50 25 microns), and obtain microspheres after preparation. Among them, the solid core material accounts for 20-40% of the total weight, the polymer accounts for 60-80% of the total weight, the cross-linking agent accounts for 1.7-2.3% of the total weight, and the deionized water accounts for 7-8% of the total weight. times, the initiator is 2-3% of the total weight, and the total weight refers to the total weight of the solid core material and the high molecular polymer. The concrete numerical value of each embodiment is as follows:

The microsphere detection data that each embodiment obtains is as follows:

Example Bubble temperature Bubble break temperature Microsphere size Example 1 150°C 180°C DN50 25μm Example 2 150°C 180°C DN50 25μm Example 3 160°C 190°C DN50 20μm Example 4 160°C 180°C DN50 25μm

Detection of foaming temperature and foam breaking temperature: observe the microsphere foaming agent arranged in a single layer under a micro melting point apparatus, and set the heating rate of the micro melting point apparatus to 10 degrees Celsius/min at the same time. When the foaming phenomenon of the microsphere foaming agent in the lens is observed, record the current temperature value, which is the foaming temperature. Continue to observe the performance of the microsphere foaming agent at different temperatures. When the microsphere foaming agent under the lens is completely broken, record the temperature at this time, which is the foam breaking temperature.

In all the above examples, the microsphere foaming agent after foaming and cooling to room temperature has no concave phenomenon under microscope observation, and can still maintain a rounded spherical shape.

The examples of the present invention and the microspheres synthesized by the preparation method described in the CN109414672B patent document were used as comparative examples, and entered into the following comparison.

Comparative microspheres were prepared as follows: Colloidal silica (Bindzil 40 wt%, 130 m2/g, particle size 22 nm) (8 parts) and the polymerization catalyst bis(4-tert-butylcyclohexyl) peroxydicarbonate (0.5 parts) and maintained at a pH of about 4.5. The aqueous dispersion was mixed with monomer acrylonitrile (58 parts), methyl methacrylate (18 parts), vinylidene chloride (24 parts), blowing agent isopentane (16 parts) and crosslinking agent trihydroxy The oil phase of methylpropane trimethacrylate (0.35 parts) was mixed. The mixture was stirred and polymerized at 57°C for 20 hours in a sealed container.

1. Comparison of required vapor pressure and molecular weight distribution at the same temperature of 57°C

Vapor Pressure molecular weight Example 1 0.13MPa 40,000-50,000 Example 2 0.13MPa 50,000-60,000 Example 3 0.14MPa 50,000-60,000 Example 4 0.15MPa 60,000-70,000 comparative example 0.4MPa 50,000-80,000

It can be seen from the data in the table that the preparation method adopting the technical solution of the present invention has a vapor pressure at the same temperature that is far less than that required by the preparation method of the comparative example, and the molecular weight distribution of the formed microsphere blowing agent shell is narrower.

2. Comparison of microsphere supporting force test: First, the microspheres prepared in each embodiment of the present invention and the comparative example were measured with a 1ml graduated cylinder to accurately take 1ml of microspheres, and then poured into a 100ml graduated cylinder. Put the graduated cylinder into an oven with an appropriate temperature (the oven temperature is adjusted according to the foaming temperature of microsphere expansion), when the microsphere expands to the highest scale, read the value on the graduated cylinder as the expansion ratio N ml, according to the formula: N ml/1ml=N, that is, the foaming ratio is N times. For example, if the scale on the measuring cylinder is 100ml, the foaming ratio is 100 times. Then cool the measuring cylinder to 0 degrees Celsius and put a cardboard on the measuring cylinder, add different weights on the cardboard to get different data as follows:

In the above table, after the expansion magnification is after the addition code, and before the expansion magnification is before the addition code. The principle of the test is as follows: on the foamed microspheres that have been piled up into a cylinder, under the same conditions, a pressure of the same size (law code) is applied, and the foamed microspheres will shrink to varying degrees under the pressure. Reflected in the macroscopic view is the reduction of the expansion ratio. Through this test, it can be seen that under the same pressure, the foaming ratio decreases less and the supporting force is better.

3. Microspheres used in shoe material product expansion effect and support test comparison:

EVA is an ethylene-vinyl acetate copolymer foam material. It is made of EVA plastic particles heated and then foamed. The surface is rough. It is often used in jogging, jogging, casual shoes, and foot training shoes. After repeated stepping on a certain mileage, the air in the foam will be squeezed out, which will cause the EVA to fail to return to its original shape, and the cushioning performance will be significantly reduced. The intuitive feeling is that the foot feels hard. The present invention Microspheres are used in the preparation of sole materials, which can make the foam microspheres contained in the sole expand, and the volume of the elliptical microspheres containing micro air bubbles will increase dozens of times, making the sole elastic. Under the impact of external force (ground), the microspheres can be compressed to half their original size at most, which is very important for foot shock absorption. After the compression force disappears, the microsphere foam can quickly return to its original shape. The microspheres made of the present invention After repeated trampling, the sole can still maintain softness, cushioning performance and resilience for a long time, and has excellent fatigue resistance.

Each embodiment of the present invention and comparative example microspheres are used for the preparation of midsole material of shoes, and the foam product of making obtains comparison as follows through extrusion test (test with " HG/T4806-2015 rubber shoes, shoe sole test method compression deformation property "Testing Standard" is the testing method):

Deformation rate 500 times (%) Deformation rate 1000 times (%) Deformation rate 2000 times (%) Example 1 0.6 1.0 1.1 Example 2 0.7 1.2 1..3 Example 3 0.6 0.9 1 Example 4 0.5 0.8 1 comparative example 1 1.5 1.8

From the above test data, it can be seen that the supporting force of the microspheres prepared by the technical solution of the present invention is much higher than that of the comparative example, and the smaller the deformation rate, the stronger the supporting force.

The above examples are only some embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Various aspects and embodiments of the present invention as disclosed herein are only examples to illustrate specific ways of making and utilizing the present invention. The sequence of the embodiments and the specific operation do not impose any restrictions on the present invention, and within the technical scope disclosed by the present invention, the replacements and changes that can be easily conceived by any scientific researcher familiar with the technical field should be included in the protection scope of the present invention within.

Claims (4)

1. A preparation method for expandable thermoplastic foamed microspheres, characterized in that it may further comprise the steps: providing a solid core material that generates gas through a chemical reaction; Water-soluble polymer and cross-linking agent are used to coat the solid core material, and undergo cross-linking reaction to form expandable thermoplastic foamed microspheres; The water-soluble polymer is polyvinyl alcohol, polyvinylpyrrolidone and acrylonitrile, acrylic acid copolymer or the water-soluble polymer is polyvinyl alcohol, polyvinylpyrrolidone and acrylonitrile, acrylic acid, acrylate copolymer; The solid core material is crushed to 20-45 microns, and the surface is hydrophobically modified with liquid paraffin to form a dense hydrophobic layer. 2. The preparation method according to claim 1, wherein the solid core material is at least one of sodium bicarbonate, azodicarbonamide or 4,4'-oxobisbenzenesulfonylhydrazide. 3. The preparation method according to claim 1, characterized in that, the crosslinking agent is a crosslinking agent containing two or three double bonds. 4. preparation method according to claim 1, is characterized in that, the crosslinking agent that adopts is at least one in triallyl isocyanurate, trimethylolpropane triacrylate, trifunctional acrylate kind.