Method for preparing high-strength tpu melt-blown nonwoven fabric by reaction and product thereof

Abstract

This invention discloses a method for preparing high-strength TPU meltblown nonwoven fabric and its product via a reaction process. The method involves using isocyanate, polyol, chain extender, and optionally added catalyst required for TPU synthesis to obtain a TPU melt with a molecular weight below 100,000 g / mol through a twin-screw extrusion reaction. This melt is then directly pumped into a meltblown die via a melt metering pump. Under the stretching effect of hot air, fibers are formed, laid into a web, and cured to obtain a high-strength TPU meltblown nonwoven fabric with a molecular weight above 130,000 g / mol. The twin-screw extrusion reaction temperature is 150-220℃; the meltblown die temperature is 210-270℃; the hot air temperature is 210-270℃, and the air pressure is 0.1-0.5 MPa; the curing temperature is 35-45℃. This invention solves the problem of the inability to simultaneously achieve the processability and strength of TPU meltblown fibers. The one-step production method eliminates the TPU granulation and granule drying processes, simplifying the production process and reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of thermoplastic polyurethane elastomer (TPU) technology, specifically to a method for preparing high-strength TPU meltblown nonwoven fabric by reaction and the product thereof. Background Technology

[0002] As a forming process for hot-melt nonwoven fabric, the strength of meltblown nonwoven fabric mainly depends on the strength of the monofilament and the effective bonding points between fibers. The strength of the monofilament is mainly determined by the molecular structure and molecular weight, while the effective bonding points between fibers are mainly determined by the meltblowing process.

[0003] Meltblown nonwoven fabric is produced by heating and melting raw materials in a screw extruder, then stretching them through a die under high-temperature, high-speed air jets to form ultrafine fibers. The meltblown nonwoven fabric process requires high flowability of the raw materials; common PP raw materials require a flowability of 1500g / 10min. This is because the die openings in meltblown fabric are typically 0.1-0.4mm fine. Insufficient flowability can cause excessive pressure on the die, potentially damaging it and affecting the hot air stretching of the fibers.

[0004] TPU, as a thermoplastic elastomer, can also be processed using meltblown technology. For example, patent specification CN1445390A discloses a method for manufacturing polyurethane elastic nonwoven fabric by meltblown web formation. Polyurethane particles with an average molecular weight of 50,000–750,000 are fed into a screw extruder, heated and melted at 180–260°C, and then extruded from the spinneret. The melt is stretched into ultrafine fibers by hot airflow at a velocity of 50–300 m / sec and a temperature of 280–500°C from both sides of the spinneret, forming a self-adhesive polyurethane elastic nonwoven fabric. As another example, patent specification CN115387023A discloses a method for preparing TPU / PLA meltblown composite nonwoven fabric, using polyurethane elastomer with a melting point of 210–220°C as an auxiliary raw material for PLA.

[0005] The search revealed that existing technologies basically use TPU particles that have been almost completely reacted as raw materials for screw extrusion and meltblowing.

[0006] The low strength of TPU nonwoven fabrics has been a persistent problem. Maintaining high flowability requires a low molecular weight for TPU, resulting in low strength in the monofilaments and consequently, low strength in the nonwoven fabric. Conversely, maintaining a high molecular weight necessitates high-temperature processing to ensure flowability, but TPU degrades rapidly at high temperatures, causing a sharp drop in molecular weight and again resulting in low monofilament strength. Furthermore, due to the unique synthesis process of TPU, controlling excessively high molecular weights increases production difficulty. Currently, high molecular weight TPU is generally between 200,000 and 300,000 g / mol; exceeding this range becomes significantly more challenging to control. Summary of the Invention

[0007] To address the aforementioned technical problems and shortcomings in this field, this invention provides a method for preparing high-strength TPU meltblown nonwoven fabric using a reaction method. The method employs a reaction-based meltblown TPU process, where raw materials for TPU synthesis (including isocyanate, polyol, chain extender, etc.) and a catalyst are directly reacted in a twin-screw extruder, and then the TPU nonwoven fabric is produced by directly connecting the melt metering pump to the meltblown die. When TPU is produced using a twin-screw reaction method, it does not directly synthesize a product with the desired molecular weight. The degree of reaction in the twin-screw extruder generally cannot directly reach the desired molecular weight, requiring a subsequent curing process to achieve further molecular weight growth and reach the desired molecular weight. The main advantage of this invention is that it utilizes the characteristics of the twin-screw TPU reaction. By controlling the reaction temperature and catalyst, the degree of TPU reaction can be controlled, ensuring that the TPU is in a low molecular weight state when passing through the meltblown die, thus achieving high flowability. The low molecular weight TPU melt is then directly transported to the meltblown die by a metering pump for meltblowing into fabric. The resulting TPU nonwoven fabric can be further cured through subsequent heat treatment, further increasing the molecular weight to the designed molecular weight, thereby ensuring the strength of the monofilaments. The method of this invention perfectly solves the problem that the processability of TPU and the strength of TPU meltblown fibers cannot be achieved simultaneously. Moreover, the one-step production method eliminates the TPU granulation and granule drying processes, which greatly simplifies the production process and reduces production costs.

[0008] The specific technical solution is as follows:

[0009] A method for preparing high-strength TPU meltblown nonwoven fabric by reaction includes: reacting isocyanate, polyol, chain extender and selectively added catalyst required for TPU synthesis with twin-screw extrusion to obtain TPU melt with a molecular weight of less than 100,000 g / mol (preferably 50,000 to 100,000 g / mol), then directly conveying it to the meltblown die by melt metering pump, forming fibers and laying web under the stretching action of hot air and curing to obtain high-strength TPU meltblown nonwoven fabric with a molecular weight of more than 130,000 g / mol;

[0010] The temperature of the twin-screw extrusion reaction is 150-220℃;

[0011] The temperature of the meltblown die head is 210-270℃;

[0012] The temperature of the hot air is 210-270℃, and the air pressure is 0.1-0.5MPa;

[0013] The ripening temperature is 35-45℃, and the time can be determined as needed, for example, it can be 1 week.

[0014] The method for preparing high-strength TPU meltblown nonwoven fabric by the reaction method described above, wherein the isocyanate can be an aromatic diisocyanate and / or an aliphatic diisocyanate.

[0015] In the method for preparing high-strength TPU meltblown nonwoven fabric by the reaction method, the polyol can be a polyester polyol and / or a polyether polyol.

[0016] The method for preparing high-strength TPU meltblown nonwoven fabric by the reaction method described above, wherein the chain extender can be at least one of ethylene glycol, butanediol, hexanediol, 2,2-dimethyl-1,3-propanediol, diethylene glycol, 1,4-cyclohexanediol, neopentyl glycol, and hydroquinone dihydroxyethyl ether (HQEE).

[0017] The method for preparing high-strength TPU meltblown nonwoven fabric by the aforementioned reaction method may use a tertiary amine catalyst or an organometallic compound as the catalyst.

[0018] In a preferred embodiment, the method for preparing high-strength TPU meltblown nonwoven fabric by reaction includes an organometallic compound comprising at least one of titanate and compounds of iron, tin, zirconium, and bismuth.

[0019] In a preferred embodiment, the method for preparing high-strength TPU meltblown nonwoven fabric by reaction is wherein the temperature of the twin-screw extrusion reaction is 200-220°C.

[0020] In a preferred embodiment, the method for preparing high-strength TPU meltblown nonwoven fabric by reaction is based on the mass of the polyol, and the amount of catalyst added is 0-200 ppm.

[0021] As a general inventive concept, the present invention also provides a high-strength TPU meltblown nonwoven fabric prepared by the method.

[0022] Compared with the prior art, the beneficial effects of this invention are as follows:

[0023] The method of this invention uses a reaction-based meltblown TPU process. The raw materials for synthesizing TPU (including isocyanate, polyol, chain extender, etc.) and catalyst are directly reacted through a twin-screw extruder and then directly connected to a meltblown die via a melt metering pump to produce TPU nonwoven fabric.

[0024] The main advantage of the method of the present invention is that by controlling the reaction temperature and catalyst, the degree of reaction of TPU can be controlled so that TPU is in a low molecular weight state when it passes through the meltblown die, thereby obtaining high fluidity and being more conducive to meltblown processing.

[0025] The TPU nonwoven fabric produced by this invention can be further cured through subsequent heat treatment, and the molecular weight can be further increased to the designed molecular weight, thereby ensuring the strength of the monofilaments. The molecular weight of the meltblown fabric is the designed molecular weight or slightly lower, and there is no situation where the molecular weight decreases significantly, resulting in insufficient strength of the meltblown fabric. In contrast, when conventional TPU particles are used for meltblowing, the molecular weight of the meltblown fabric is much lower than the molecular weight of the added TPU particles due to the screw shearing and thermal degradation.

[0026] The method of this invention perfectly solves the problem that the processability of TPU and the strength of TPU meltblown fibers cannot be achieved simultaneously. It enables the production of high molecular weight meltblown fabric products while ensuring meltblown processability, thereby significantly improving the strength of meltblown fabric. Moreover, the one-step production method eliminates the TPU granulation and granule drying process, greatly simplifying the production process and reducing production costs. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer.

[0029] The following embodiments are carried out using the following methods:

[0030] The raw materials and catalyst for synthesizing thermoplastic polyurethane elastomers are fed into a twin-screw extruder for reaction. The catalyst is pre-added to the polyol raw material, and different reaction degrees can be achieved by adjusting the amount of catalyst added. Then, the product is directly delivered to the meltblown die via a melt metering pump, where it is stretched and cured by hot air to form meltblown nonwoven fabric. The screw reaction zone temperature of the twin-screw extruder is set at 200-220℃, the meltblown die temperature is set at 250℃, the hot air temperature is 250℃, and the air pressure is 0.2MPa.

[0031] The molecular weights measured in each embodiment are data molecular weights, obtained by GPC.

[0032] Example 1

[0033] MDI (4,4'-diphenylmethane diisocyanate) 5.27 g / s, polybutylene adipate 10.08 g / s, BDO (1,4-butanediol) 1.45 g / s, and dibutyltin dilaurate catalyst 50 ppm (based on the mass of polybutylene adipate) were pre-added to polybutylene adipate and mixed evenly. The mixture was added to a twin-screw extruder at the above flow rate and reacted. The mixture was then pumped to a meltblown die for meltblown fabric preparation. The meltblown fabric was then placed in a greenhouse at 35-45°C for one week for curing before being removed.

[0034] The molecular weight of the filament produced by the meltblown die is 53,000 g / mol, and the molecular weight after curing is 141,000 g / mol.

[0035] Example 2

[0036] MDI (4,4'-diphenylmethane diisocyanate) 5.27 g / s, polybutylene adipate 10.08 g / s, BDO (1,4-butanediol) 1.45 g / s, and dibutyltin dilaurate catalyst 100 ppm (based on the mass of polybutylene adipate) were pre-added to polybutylene adipate and mixed evenly. The mixture was added to a twin-screw extruder at the above flow rate and reacted. The mixture was then pumped to a meltblown die for meltblown fabric preparation. The meltblown fabric was then placed in a greenhouse at 35-45°C for one week for curing before being removed.

[0037] The molecular weight of the filament produced by the meltblown die is 68,000 g / mol, and the molecular weight after curing is 144,000 g / mol.

[0038] Example 3

[0039] MDI (4,4'-diphenylmethane diisocyanate) 5.27 g / s, polybutylene adipate 10.08 g / s, BDO (1,4-butanediol) 1.45 g / s, and dibutyltin dilaurate catalyst 200 ppm (based on the mass of polybutylene adipate) were pre-added to polybutylene adipate and mixed evenly. The mixture was added to a twin-screw extruder at the above flow rate and reacted. The mixture was then pumped to a meltblown die for meltblown fabric preparation. The meltblown fabric was then placed in a greenhouse at 35-45°C for one week for curing before being removed.

[0040] The molecular weight of the filament produced by the meltblown die is 83,000 g / mol, and the molecular weight after curing is 152,000 g / mol.

[0041] Example 4

[0042] MDI (4,4'-diphenylmethane diisocyanate) 5.6 g / s, PTMEG (polytetrahydrofuran) with a molecular weight of 1000 g / mol 10.08 g / s, BDO (1,4-butanediol) 1.12 g / s, and dibutyltin dilaurate catalyst 100 ppm (based on the mass of PTMEG) were pre-added to PTMEG and mixed evenly. The mixture was added to a twin-screw extruder at the above flow rate and reacted. The mixture was then pumped to a meltblown die for meltblown fabric to obtain meltblown fabric. The meltblown fabric was placed in a greenhouse at 35-45℃ for 1 week for curing before being taken out.

[0043] The molecular weight of the filament produced by the meltblown die is 54,000 g / mol, and the molecular weight after curing is 138,000 g / mol.

[0044] Example 5

[0045] MDI (4,4'-diphenylmethane diisocyanate) 5.61 g / s, PTMEG (1000 g / mol) 10.08 g / s, BDO (1,4-butanediol) 1.11 g / s, and dibutyltin dilaurate catalyst 100 ppm (based on the mass of PTMEG) were pre-added to PTMEG and mixed evenly. The mixture was then fed into a twin-screw extruder at the above flow rates and transported to a meltblown die by a melt pump to obtain meltblown fabric. The meltblown fabric was then placed in a greenhouse at 35-45°C for one week to mature before being removed.

[0046] The molecular weight of the filament produced by the meltblown die is 57,000 g / mol, and the molecular weight after curing is 164,000 g / mol.

[0047] Comparative Example 1

[0048] MDI (4,4'-diphenylmethane diisocyanate) 5.27 g / s, polybutylene adipate 10.08 g / s, BDO (1,4-butanediol) 1.45 g / s, and dibutyltin dilaurate catalyst 100 ppm (based on the mass of polybutylene adipate) were pre-added to polybutylene adipate and mixed evenly. The mixture was added to a twin-screw extruder at the above flow rate and reacted at 200-220℃. The mixture was then extruded and granulated to produce TPU granules. After the granules were placed in a greenhouse at 35-45℃ for 1 week of curing, the molecular weight was measured to be 152,000 g / mol.

[0049] Then, TPU particles with a molecular weight of 152,000 g / mol after curing are added to an extruder and melted according to an existing process similar to CN1445390A. The extrusion is then performed through the spinneret of the die head and stretched by hot air to form meltblown nonwoven fabric. The screw temperature is 200-220℃, the die head temperature is 250℃, the hot air temperature is 250℃, and the air pressure is 0.2MPa.

[0050] The molecular weight of the TPU filament exiting the meltblown die is 77,000 g / mol, and the molecular weight after curing is 96,000 g / mol. High molecular weight TPU particles are decomposed during the high-temperature shearing and meltblowing process of the screw, and even with re-curing, it is difficult to obtain high molecular weight, high-strength TPU meltblown nonwoven fabric.

[0051] As can be seen from the above embodiments and comparative examples, the melt of the outlet die head produced by the reaction method of the present invention has a low molecular weight (below 100,000 g / mol), which is suitable for meltblown processing. Moreover, the molecular weight can be adjusted by adding a catalyst, and after aging, a higher molecular weight (above 130,000 g / mol) can be obtained, achieving a significant increase in molecular weight and higher strength of the monofilament.

[0052] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing high-strength TPU meltblown nonwoven fabric by reaction, characterized in that, include: The isocyanate, polyol, chain extender and catalyst required for TPU synthesis are obtained by twin-screw extrusion reaction to obtain TPU melt with a molecular weight of less than 100,000 g / mol. Then, it is directly transported to the meltblown die by melt metering pump. Under the stretching action of hot air, it is formed into fibers, laid into web and cured to obtain high-strength TPU meltblown nonwoven fabric with a molecular weight of more than 130,000 g / mol. The temperature of the twin-screw extrusion reaction is 150-220℃; The temperature of the meltblown die head is 210-270℃; The temperature of the hot air is 210-270℃, and the air pressure is 0.1-0.5 MPa; The ripening temperature is 35-45℃.

2. The method according to claim 1, characterized in that, The molecular weight of TPU melt is 50,000 to 100,000 g / mol.

3. The method according to claim 1, characterized in that, The isocyanate is an aromatic diisocyanate and / or an aliphatic diisocyanate.

4. The method according to claim 1, characterized in that, The polyol is a polyester-type polyol and / or a polyether-type polyol.

5. The method according to claim 1, characterized in that, The chain extender is at least one of ethylene glycol, butanediol, hexanediol, 2,2-dimethyl-1,3-propanediol, diethylene glycol, 1,4-cyclohexanediol, neopentyl glycol, and hydroquinone dihydroxyethyl ether.

6. The method according to claim 1, characterized in that, The catalyst is a tertiary amine catalyst or an organometallic compound.

7. The method according to claim 6, characterized in that, The organometallic compounds include titanates and at least one of compounds of iron, tin, zirconium, and bismuth.

8. The method according to claim 1, characterized in that, The temperature of the twin-screw extrusion reaction is 200-220℃.