A method for preparing a foamed hot melt powder

Abstract

This invention relates to the field of hot melt powder technology, and provides a foamed hot melt powder. The foamed hot melt powder is a creamy white powder with a particle size controlled at 80-250μm. It is prepared from the following raw materials and processes in parts by weight: using polyurethane hot melt adhesive particles with a particle size of 4-5mm as the base material, it is ground to a fine powder of 0-80μm by cryogenic grinding at -90℃. After being stored at room temperature, 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide are added sequentially. The mixture is stirred evenly by a disperser, then dissolved and dispersed a second time in a reactor at 130℃, and then melted, drawn into fibers, extruded and granulated by a granulator at 150℃, water-cooled, dehydrated and dried. By enabling gradient foaming to form rich three-dimensional textures, the powder's flowability and dispersibility are significantly improved. It is stable and does not agglomerate or clump during use. The adhesive powder foams evenly and fully without collapsing, adheres firmly to the substrate, and is resistant to water washing and friction. The overall process is simplified and efficient, and high-quality texture patterns can be formed in one step, making it suitable for industrial continuous production.

Description

Technical Field

[0001] This invention relates to the field of hot melt powder technology, specifically a method for preparing foamed hot melt powder. Background Technology

[0002] Hot melt adhesive powder, as a commonly used bonding material in heat transfer printing, garment printing, and other fields, has been widely used in various patterns for attachment and fixation. With the increasing demand for personalized decoration, printed products with three-dimensional texture effects are gradually gaining market favor. Ordinary hot melt adhesive powder can only achieve planar bonding and cannot create a textured feel and visual hierarchy with varying heights, making it difficult to meet the requirements of high-end processes such as texture painting and three-dimensional printing.

[0003] Existing foamed adhesives mostly employ a single foaming system, resulting in uniformly sized bubbles after heating. This leads to a stiff texture and insufficient layering. Furthermore, during grinding, storage, and powdering, problems such as agglomeration, clumping, and poor flowability easily occur, affecting the uniformity of the transferred pattern and the yield rate. Simultaneously, conventional foaming powders are prone to uneven foaming, collapse, and detachment during high-temperature pressing, exhibiting weak adhesion to fabric substrates. Long-term use or washing can easily lead to powdering and shedding, indicating that overall stability needs improvement.

[0004] To achieve the desired texture, some processes involve multiple powder application and repeated pressing to create three-dimensional layers. This is not only cumbersome and inefficient, but also prone to pattern deformation and blurred edges, increasing production costs and scrap rates. Therefore, developing a specialized foaming hot melt powder that can form gradient foaming upon heating, has uniform particle size, good flowability, excellent fastness, and is compatible with DTF heat transfer printing has become a pressing technical problem in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing foamed hot melt powder, solving problems such as the difficulty of existing hot melt adhesive powders in forming natural three-dimensional textures, the monotonous effect and poor layering of single foaming systems, the tendency of powders to agglomerate and clump, poor flowability, uneven foaming, collapse and detachment during high-temperature pressing, and insufficient bonding strength with the substrate. Furthermore, traditional processes require multiple steps, are cumbersome and inefficient, and cannot meet the requirements for efficient and stable production of DTF heat transfer textured paintings.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a foamed hot melt powder, wherein the foamed hot melt powder is a creamy white powder with a particle size controlled between 80-250 μm, and is prepared from the following raw materials and processes in parts by weight: Using polyurethane hot melt adhesive particles with a particle size of 4-5mm as the base material, the particles are ground to 0-80μm fine powder by freezing at -90℃. After being stored at room temperature, 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide are added in sequence. After being stirred evenly by a disperser, it is dissolved and dispersed a second time in a reactor at 130℃, and then melted, drawn into fibers, extruded and granulated in a granulator at 150℃, cooled with water, and dehydrated and dried. Add 3‰ silicon powder and mix evenly with a roller. Then, freeze and grind twice with liquid nitrogen at -100℃ and sieve to obtain a finished product of 80-250μm. The low, medium, and high foaming powders generate small, medium, and large amounts of gas respectively at 150°C, causing the adhesive powder to form a textured particle pattern with varying heights when heated.

[0007] Preferably, the low-foaming powder, medium-foaming powder, and high-foaming powder are thermally decomposable chemical foaming powders, which decompose and release gas at 150 degrees Celsius, with the bubble size increasing sequentially to form a gradient foaming effect.

[0008] Preferably, the nano zinc oxide particles have a particle size of no more than 100 nanometers and are used as a foaming regulator and dispersant to stabilize the foaming rate and improve the uniformity of powder dispersion.

[0009] Preferably, the silicon powder is a hydrophobic micro powder, and the addition amount is three parts per thousand, which is used to improve the flowability of the powder, prevent particle adhesion, and improve the uniformity of coating and powdering.

[0010] A method for preparing a foamed hot melt powder, used to prepare the foamed hot melt powder according to any one of claims 1-4, comprising the following steps: Step 1: Deep freeze the 4-5mm polyurethane hot melt adhesive particles at -90℃, grind them into 0-80μm fine powder using a low-temperature grinding mill, and store them at room temperature for one week to eliminate internal stress and stabilize the particle size. Step 2: Add 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide to the above fine powder in proportion, and put it into a high-speed disperser and stir until the powder is evenly dispersed and there are no agglomerates or lumps; Step 3: The uniformly mixed powder is fed into the reaction vessel, heated and melted at 130°C and then dispersed a second time to ensure that the components are fully miscible and the foaming system is uniform and stable. Step 4: The melted and dispersed material is fed into a granulator, where it is completely melted at a high temperature of 150°C, continuously drawn into fibers and extruded into granules. After granulation, it is quickly shaped by water cooling, and then dehydrated and dried. Step 5: Add 3‰ hydrophobic silica powder to the dried granules and mix thoroughly with a drum mixer to ensure that the silica powder evenly coats the surface of the granules, thereby improving flowability and anti-sticking properties. Step 6: Use liquid nitrogen to freeze the silicon powder coated particles to -100℃, perform secondary fine grinding, and then sieve through an 80-250μm grading sieve to remove coarse powder larger than 250μm and fine powder smaller than 80μm, to obtain a finished off-white foamed hot melt powder with a uniform particle size of 80-250μm.

[0011] Preferably, both steps one and six employ low-temperature cryogenic grinding, with the first grinding temperature at -90 degrees Celsius and the second grinding temperature at -100 degrees Celsius. The second grinding temperature is lower than the first grinding temperature, making the particles more brittle and the particle size more uniform.

[0012] Preferably, in step two, the stirring speed of the high-speed disperser is 800-1500 r / min, and the stirring time is 5-15 minutes.

[0013] Preferably, the dispersion temperature of the reactor in step three is 130 degrees Celsius, and the reactor is kept at this temperature and stirred for 10-30 minutes to ensure that the raw materials are fully melted and dispersed and that premature foaming does not occur.

[0014] Preferably, in step four, the melting temperature of the granulator is 150 degrees Celsius, and in step five, the stirring speed of the drum mixer is 30-80 r / min, and the stirring time is 10-20 minutes.

[0015] Preferably, step six employs a two-stage cascaded sieving process. First, an 80μm sieve is used to remove fine powder, and then a 250μm sieve is used to retain coarse powder, ultimately obtaining target powder with a concentrated particle size distribution of 80-250 micrometers, ensuring uniform mixing without dead corners.

[0016] This invention provides a method for preparing foamed hot melt powder. It has the following beneficial effects: 1. This invention utilizes a compound system of low, medium, and high foaming powders to effectively achieve gradient foaming under heat, resulting in a naturally textured granular surface after the powder solidifies. This significantly enhances the three-dimensional feel and visual depth of the pattern, meeting the professional effect requirements of texture painting printing.

[0017] 2. This invention significantly improves the uniformity and flowability of powder particles through a dual low-temperature freeze grinding and grading sieving process, avoiding problems such as agglomeration, wall adhesion, and uneven powder distribution during production and use, thereby improving the finished product qualification rate and transfer consistency.

[0018] 3. This invention employs specific melt dispersion, granulation and shaping, and surface anti-sticking treatment, which makes the adhesive powder foam stably under high temperature and heat treatment, without collapsing or dripping, and tightly bonded to the fabric substrate, significantly improving the adhesion, washability and abrasion resistance of the pattern, and extending the service life of the decorative pattern.

[0019] 4. The overall preparation process of this invention is simple and controllable, suitable for industrial continuous production, and can form a three-dimensional texture effect in one step without repeated processing. It simplifies the DTF heat transfer process, improves production efficiency, reduces production costs, and has good industrial application value. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Example: As one aspect of the present invention, the present invention provides a foaming hot melt powder, which is a creamy white powder with a particle size controlled at 80-250μm. It is based on polyurethane hot melt adhesive particles with a particle size of 4-5mm, which are cryogenically ground to a fine powder of 0-80μm at -90℃. After being stored at room temperature, 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide are added sequentially. The mixture is stirred evenly in a disperser, then dissolved and dispersed a second time in a reactor at 130℃. The mixture is then melt-drawn, extruded and granulated in a granulator at 150℃, water-cooled, dehydrated and dried. 3‰ silica powder is added and stirred evenly in a drum. The mixture is then cryogenically ground a second time at -100℃ with liquid nitrogen and sieved to obtain a finished product of 80-250μm. The low, medium and high foaming powders generate small, medium and large amounts of gas at 150℃, respectively, causing the adhesive powder to form a texture of staggered particles when heated.

[0022] Among them, the low-foaming powder, medium-foaming powder, and high-foaming powder are thermally decomposable chemical foaming powders, which decompose and release gas at 150°C, with the bubble size increasing sequentially; the nano zinc oxide particles have a diameter of no more than 100nm and serve as foaming regulators and dispersants; the silicon powder is a hydrophobic micro powder used to improve powder flowability, prevent sticking, and dispersibility.

[0023] In another aspect of the present invention, the preparation method of the above-mentioned foamed hot melt powder is as follows: Step 1: Freeze the 4-5mm polyurethane hot melt adhesive particles at -90℃, grind them into 0-80μm fine powder, and let them stand at room temperature for one week to eliminate internal stress in the powder. Step 2: Add 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide to the fine powder. Use a high-speed disperser to mix evenly at a speed of 800-1500 r / min for 5-15 minutes to ensure no agglomeration or stratification. Step 3: Feed the mixture into the reactor, heat and melt it at 130℃ and disperse it a second time. Keep it at the temperature and stir for 10-30 minutes to ensure that the components are fully miscible and prevent premature foaming. Step 4: The material enters the granulator, where it is completely melted at a high temperature of 150℃, continuously drawn into fibers and extruded into granules, rapidly shaped by water cooling, and then dehydrated and dried until the moisture content is below 0.5%. Step 5: Add 3‰ hydrophobic silica powder to the dried granules and mix them evenly with a drum mixer at a speed of 30-80 r / min for 10-20 minutes to ensure that the silica powder is evenly coated on the surface of the granules. Step 6: Freeze the material to -100℃ using liquid nitrogen, perform secondary fine grinding, and sieve it through a series of 80μm and 250μm screens to remove coarse powder larger than 250μm and fine powder smaller than 80μm, to obtain a finished off-white foamed hot melt powder with a uniform particle size of 80-250μm.

[0024] To better illustrate the formulation and process implementation of the foamed hot melt powder of the present invention, specific examples are given below: Example 1: A foaming hot melt powder, which is off-white powder with a finished particle size of 80-250μm, is prepared as follows: Step 1: Take 100 parts of polyurethane hot melt adhesive granules with a particle size of 4-5mm, freeze them in an environment of -90℃, grind them into fine powder of 0-80μm using a low temperature grinder, and let them stand at room temperature for 7 days to eliminate internal stress. Step 2: Add 5% low foaming powder, 5% medium foaming powder, 10% high foaming powder, and 0.1% nano zinc oxide to the above fine powder, put it into a high-speed disperser, and stir at 1000 r / min for 10 minutes to make the components evenly dispersed and free from agglomeration. Step 3: The uniformly mixed powder is fed into the reactor, heated and melted at 130°C and stirred for 20 minutes to perform a secondary dispersion, ensuring that the raw materials are fully miscible and the foaming system is stable. Step 4: The melted and dispersed material is fed into a granulator, where it is completely melted at a high temperature of 150°C, continuously drawn into fibers and extruded into granules. After granulation, it is quickly shaped by cooling water and then sent to a dehydration dryer to dry to a moisture content of 0.4%. Step 5: Add 0.3 parts of hydrophobic silica powder to the dried granules and stir with a drum mixer at 50 r / min for 15 minutes to make the silica powder evenly coat the surface of the granules. Step 6: Use liquid nitrogen to freeze the silicon powder coated particles to -100°C, perform secondary fine grinding, and then sieve them through a series of 80μm and 250μm sieves to remove coarse powder larger than 250μm and fine powder smaller than 80μm, to obtain a finished product of 80-250μm.

[0025] The resulting foamed hot melt powder exhibits excellent flowability and stable gradient foaming at 150℃, forming a medium-height three-dimensional texture, making it suitable for the production of conventional DTF heat transfer texture paintings.

[0026] Example 2: A foaming hot melt powder, which is off-white powder with a finished particle size of 80-250μm, is prepared as follows: Step 1: Take 100 parts of polyurethane hot melt adhesive granules with a particle size of 4-5mm, freeze them in an environment of -90℃, grind them into fine powder of 0-80μm using a low temperature grinder, and store them at room temperature for 7 days. Step 2: Add 8% low-foaming powder, 8% medium-foaming powder, 12% high-foaming powder, and 0.1% nano zinc oxide to the above fine powder, put it into a high-speed disperser, and stir at 1200 r / min for 8 minutes until it is evenly mixed. Step 3: Feed the mixture into the reactor, heat it to 130℃ to melt it, and keep it at that temperature while stirring for 15 minutes to complete the secondary dispersion; Step 4: The material is fed into a granulator, melted and extruded at 150℃, granulated, water-cooled and shaped, then dehydrated and dried to a moisture content of 0.3%. Step 5: Add 0.3 parts of hydrophobic silica powder to the particles and stir with a drum mixer at 60 r / min for 12 minutes to fully coat them; Step 6: Freeze the product in liquid nitrogen to -100℃ for secondary grinding, and then sieve it through 80μm and 250μm screens to obtain the 80-250μm finished product.

[0027] The resulting foaming hot melt powder has a high foaming ratio, strong three-dimensional texture, and obvious particle height difference, making it suitable for transferring thick, textured patterns.

[0028] Example 3: A foaming hot melt powder, which is off-white powder with a finished particle size of 80-250μm, is prepared as follows: Step 1: Take 100 parts of polyurethane hot melt adhesive granules with a particle size of 4-5mm, freeze them in an environment of -90℃, grind them at low temperature to 0-80μm fine powder, and store them at room temperature for 7 days. Step 2: Add 3% low-foaming powder, 3% medium-foaming powder, 8% high-foaming powder, and 0.1% nano zinc oxide to the fine powder. Stir with a high-speed disperser at 900 r / min for 12 minutes to disperse evenly. Step 3: The mixture is fed into the reactor, melted at 130℃ and stirred for 25 minutes to ensure that the components are fully miscible; Step 4: Feed the material into a granulator, melt it at 150℃, draw it into fibers, extrude it into granules, cool it with water, and then dehydrate and dry it to a moisture content of 0.5%. Step 5: Add 0.3 parts of hydrophobic silica powder and mix with a drum mixer at 40 rpm for 18 minutes to complete the anti-sticking treatment; Step 6: Secondary grinding under liquid nitrogen at -100℃, followed by sieving through 80μm and 250μm sieves to obtain 80-250μm finished product.

[0029] The resulting foaming hot melt powder produces a fine and soft foam with uniform particle distribution and no large lumps, making it suitable for transferring fine text, gradient patterns, and small-format textured paintings.

[0030] Experimental example: The foamed hot melt powder prepared in Examples 1-3 of this invention was selected and compared with commercially available ordinary hot melt powder as comparative examples. Performance comparison tests were conducted under the same DTF heat transfer process conditions. Test conditions: DTF printing, powdering, drying at 130℃, 150℃, 2kg, 8-second heat pressing, film peeling, 155℃ secondary baking for 10 seconds; Test indicators: Four indicators were tested: foaming height, texture uniformity, pattern peeling rate, and wash fastness grade. The results are shown in Table 1 below: The results show that the foaming hot melt powder prepared by the present invention has a higher foaming height, a more uniform and full texture, an extremely low pattern detachment rate, and a water wash fastness of level 5, which is far superior to ordinary hot melt powder and fully meets the requirements of DTF heat transfer texture painting for three-dimensional effect and firmness.

[0031] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A foamed hot melt powder, characterized in that, The foamed hot melt powder is a creamy white powder with a particle size controlled between 80-250 μm, and is prepared from the following raw materials and processes in parts by weight: Using polyurethane hot melt adhesive particles with a particle size of 4-5mm as the base material, the particles are ground to 0-80μm fine powder by freezing at -90℃. After being stored at room temperature, 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide are added in sequence. After being stirred evenly by a disperser, it is dissolved and dispersed a second time in a reactor at 130℃, and then melted, drawn into fibers, extruded and granulated in a granulator at 150℃, cooled with water, and dehydrated and dried. Add 3‰ silicon powder and mix evenly with a roller. Then, freeze and grind twice with liquid nitrogen at -100℃ and sieve to obtain a finished product of 80-250μm. The low, medium, and high foaming powders generate small, medium, and large amounts of gas respectively at 150°C, causing the adhesive powder to form a textured particle pattern with varying heights when heated.

2. The foamed hot melt powder according to claim 1, characterized in that, The low-foaming powder, medium-foaming powder, and high-foaming powder are thermally decomposable chemical foaming powders. They decompose and release gas at 150 degrees Celsius, with the bubble size increasing sequentially to create a gradient foaming effect.

3. The foamed hot melt powder according to claim 1, characterized in that, The nano zinc oxide particles have a diameter of no more than 100 nanometers and are used as foaming regulators and dispersants.

4. The foamed hot melt powder according to claim 1, characterized in that, The silicon powder is a hydrophobic micro powder, added at a rate of 0.3%, used to improve powder flowability, prevent sticking, and dispersibility.

5. A method for preparing a foamed hot melt powder, used to prepare the foamed hot melt powder according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Deep freeze the 4-5mm polyurethane hot melt adhesive particles at -90℃, grind them into 0-80μm fine powder using a low-temperature grinding mill, and store them at room temperature for one week to eliminate internal stress and stabilize the particle size. Step 2: Add 3%-10% low foaming powder, 3%-10% medium foaming powder, 5%-15% high foaming powder and 1‰ nano zinc oxide to the above fine powder in proportion, and put it into a high-speed disperser and stir until the powder is evenly dispersed and there are no agglomerates or lumps; Step 3: The uniformly mixed powder is fed into the reaction vessel, heated and melted at 130°C and then dispersed a second time to ensure that the components are fully miscible and the foaming system is uniform and stable. Step 4: The melted and dispersed material is fed into a granulator, where it is completely melted at a high temperature of 150°C, continuously drawn into fibers and extruded into granules. After granulation, it is quickly shaped by water cooling, and then dehydrated and dried. Step 5: Add 3‰ hydrophobic silica powder to the dried granules and mix thoroughly with a drum mixer to ensure that the silica powder evenly coats the surface of the granules. Step 6: Use liquid nitrogen to freeze the silicon powder coated particles to -100℃, perform secondary fine grinding, and then sieve through an 80-250μm grading sieve to remove coarse powder larger than 250μm and fine powder smaller than 80μm, to obtain a finished off-white foamed hot melt powder with a uniform particle size of 80-250μm.

6. The method for preparing a foamed hot melt powder according to claim 5, characterized in that, Both steps one and six employ cryogenic grinding, with the first grinding temperature at -90 degrees Celsius and the second grinding temperature at -100 degrees Celsius.

7. The method for preparing a foamed hot melt powder according to claim 5, characterized in that, The stirring speed of the high-speed disperser in step two is 800-1500 r / min, and the stirring time is 5-15 minutes.

8. The method for preparing a foamed hot melt powder according to claim 5, characterized in that, In step three, the dispersion temperature of the reactor is 130 degrees Celsius, and the mixture is kept at this temperature and stirred for 10-30 minutes to ensure that the raw materials are fully melted and dispersed without premature foaming.

9. The method for preparing a foamed hot melt powder according to claim 5, characterized in that, In step four, the granulator melt temperature is 150 degrees Celsius, and in step five, the drum mixer speed is 30-80 r / min, and the mixing time is 10-20 minutes.

10. The method for preparing a foamed hot melt powder according to claim 5, characterized in that, In step six, a two-stage cascade sieving process is used. First, an 80μm sieve is used to remove fine powder, and then a 250μm sieve is used to retain coarse powder, ultimately obtaining the target powder with a concentrated particle size distribution of 80-250 micrometers.

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