Preparation method of bending-resistant and whitening-resistant TPU (thermoplastic polyurethane) heat transfer printing product

Abstract

The invention relates to the technical field of heat transfer printing materials, and discloses a preparation method of a bending-resistant and whitening-resistant TPU heat transfer printing product, which comprises the following steps: base material pretreatment, electrostatic spraying, curing treatment, hot melt adhesive film lamination and performance test treatment, and adopts a gradient coating structure of 50-80nm (SiO2 particle size is less than or equal to 50nm) of a bottom layer and 100-120nm (SiO2 particle size is more than or equal to 150nm) of a surface layer to prepare the bending-resistant and whitening-resistant TPU heat transfer printing product. Small-particle-size SiO2 at the bottom layer can be used for filling microdefects on the surface of the TPU base material and inhibiting crack initiation caused by stress concentration during bending; the large-particle-size SiO2 of the surface layer forms a rigid supporting network and hinders crack propagation, and actual tests show that after the garment trademark is bent by 180 degrees for 50,000 times, the whitening area is smaller than or equal to 2% and is far superior to that of a traditional TPU trademark, and the problem that the appearance of the garment trademark is degraded due to the fact that the garment trademark is bent and whitened in the long-term use process is thoroughly solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat transfer printing materials, in particular to a preparation method of a bending-resistant and whitening-resistant TPU heat transfer printing product. BACKGROUND

[0002] TPU (thermoplastic polyurethane) material is widely used in clothing trademarks, automotive interiors and other fields due to its excellent flexibility, wear resistance and environmental friendliness. However, after being bent multiple times, the surface of a black TPU heat transfer printing trademark is prone to whitening due to light scattering caused by microcracks, which seriously affects the appearance and service life of the product. In the prior art, solutions to the bending whitening of TPU mainly include: adding silicone additives to improve flexibility in the short term, but accelerating material aging (see "Polymer Materials Science and Engineering", No. 5, 2020); using a single hydrophobic coating, such as the technology disclosed in patent CN112795017A, which can only improve the surface hydrophobicity and cannot inhibit the initiation of microcracks; using bio-based TPU substrate: high cost, difficult to be applied on a large scale.

[0003] The above solutions do not simultaneously solve the synergistic problem of microcrack initiation and water molecule penetration, and have defects such as poor process compatibility and single function. In view of this, we propose a preparation method of a bending-resistant and whitening-resistant TPU heat transfer printing product. SUMMARY

[0004] The present application aims to provide a preparation method of a bending-resistant and whitening-resistant TPU heat transfer printing product to solve the problems raised in the background.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solution: a preparation method of a bending-resistant and whitening-resistant TPU heat transfer printing product, comprising the following steps:

[0006] Substrate pretreatment: the TPU substrate is sequentially subjected to alkaline degreasing, pickling and phosphating treatment, and then dried at 110°C to a water content of <0.5%;

[0007] Nano-SiO2 dispersion liquid preparation: SiO2 sol and deionized water are mixed at a mass ratio of 1:5, 0.5wt% KH-550 silane coupling agent is added, ultrasonic treatment is performed for 30min at 40kHz, the pH is adjusted to 8-9, and then stirring is performed at 300rpm and defoaming is performed for 2h after standing;

[0008] Electrostatic spraying: a high-voltage electrostatic spray gun is used to spray in a zigzag trajectory at a speed of 0.8m / s, a 50-80nm bottom layer is formed at a flow rate of 100g / min in the first stage, and a 100-120nm surface layer is formed at a flow rate of 200g / min in the second stage, and the total thickness is 150-200nm;

[0009] Curing treatment, immediately after spraying, curing at 180℃ for 30min, melting and cross-linking SiO2 particles;

[0010] Laminating hot melt adhesive film, laminating the cured TPU substrate with the hot melt adhesive film by a high-frequency heat sealer.

[0011] Optionally, in the base material pretreatment, the alkaline degreasing uses 5% NaOH solution, the treatment time is 5min, and the water temperature is controlled at 60℃; the pickling uses 10% H2SO4 solution, the treatment time is 3min; the phosphating treatment uses zinc-based phosphating solution, the treatment time is 2min, and the treatment temperature is room temperature.

[0012] Optionally, in the nano-SiO2 dispersion liquid, the particle size of the SiO2 sol is 20nm; the pH adjustment uses ammonia water, and the pH value change is monitored in real time during the adjustment process to ensure that the final pH is stable in the range of 8-9.

[0013] Optionally, the equipment parameters of the electrostatic spraying are: electrostatic voltage 70kV, vertical distance between the spray gun and the substrate 30cm, air compressor dew point <-40℃; the grounding resistance of the anti-static workbench in the auxiliary equipment is <1MΩ, the recovery device uses a combination of cyclone separation and filter core filtration, and the filter core filtration precision is 0.1μm.

[0014] Optionally, in the nano-SiO2 gradient spraying, the SiO2 particle size in the bottom layer formed by the first stage spraying is ≤50nm, and the SiO2 particle size in the surface layer formed by the second stage spraying is ≥150nm; during the spraying process, the adjacent path distance of the "zigzag" trajectory of the spray gun is 5cm.

[0015] Optionally, the curing treatment is carried out in a curing furnace, the heating rate is 5℃ / min, the temperature is raised from room temperature to 180℃ and then maintained for 30min, and then naturally cooled to room temperature; when laminating the hot melt adhesive film, the temperature of the high-frequency heat sealer is controlled at 120-150℃, the pressure is 0.3MPa, and the heat sealing time is 10s.

[0016] Optionally, the performance test process includes:

[0017] Hydrophobicity test, using a contact angle measuring instrument, taking the average value of the contact angles of 3 different test points in an environment of 25℃ and 50% relative humidity, and the contact angle ≥115° is qualified;

[0018] Abrasion resistance test, using a Taber abrasion tester, using CS-10 wheels, loading 1kg load, rotating 1000 turns, measuring the abrasion rate, and the abrasion rate ≤0.12mg / 1000 turns is qualified;

[0019] The anti-bending test is carried out by using a bending tester, and the sample is bent 50000 times at 25 DEG C, the bending angle is 180 DEG, and the bending speed is 30 times / min, and the sample is qualified if the whitening area is less than or equal to 2% after the test.

[0020] The application also provides a preparation method of the anti-bending and anti-whitening TPU heat transfer product based on the nano-SiO2 gradient spraying, and the anti-bending and anti-whitening TPU heat transfer trademark prepared by the method comprises a TPU base layer, a nano-SiO2 gradient coating layer and a hot melt adhesive film layer, the thickness of the bottom layer of the nano-SiO2 gradient coating layer is 50-80 nm, the thickness of the surface layer is 100-120 nm, and the total thickness is 150-200 nm, the thickness of the TPU base layer is 0.3 mm, and the thickness of the hot melt adhesive film layer is 0.05-0.1 mm; the trademark has a whitening area of less than or equal to 2% after 50000 times of bending, a contact angle of greater than or equal to 115 DEG, an abrasion rate of less than or equal to 0.12 mg / 1000 turns, and a peeling area of the coating layer and the TPU base layer of less than 3%.

[0021] Compared with the prior art, the application provides a preparation method of the anti-bending and anti-whitening TPU heat transfer product, which has the following beneficial effects:

[0022] 1. The preparation method of the anti-bending and anti-whitening TPU heat transfer product adopts a gradient coating structure of a bottom layer of 50-80 nm (SiO2 particle size is less than or equal to 50 nm) and a surface layer of 100-120 nm (SiO2 particle size is greater than or equal to 150 nm), the small-particle-size SiO2 in the bottom layer can fill the micro-defects on the surface of the TPU base layer and inhibit the crack initiation caused by stress concentration during bending, and the large-particle-size SiO2 in the surface layer forms a rigid support network to hinder crack propagation; actual tests show that the whitening area is less than or equal to 2% after 50000 times of 180 DEG bending, which is much better than the traditional TPU trademark, and the appearance degradation problem of the garment trademark caused by whitening due to bending during long-term use is completely solved.

[0023] 2. The preparation method of the anti-bending and anti-whitening TPU heat transfer product precisely matches the particle size and thickness of the gradient coating layer, which not only retains the flexibility of the TPU base layer itself, but also improves the surface hardness through the melting and cross-linking of the SiO2 particles, so that the Shore hardness is improved from 85A to 92A, the defects of single coating being too rigid and brittle or too soft and easy to crack are avoided, and the use requirements of the trademark in complex deformation scenarios are met; after the nano-SiO2 coating layer is modified by a KH-550 silane coupling agent, a hydrophobic group (-Si-O-) is formed on the surface, the contact angle is greater than or equal to 115 DEG, and the nano-SiO2 coating layer can effectively repel liquid stains such as water and oil stains. Experimental data show that the rolling speed of water droplets on the surface of the coating layer is increased by 3 times, and the amount of stain adhesion is reduced by 70%, which significantly reduces the cleaning and maintenance cost of the trademark. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0025] The present application provides a technical solution: a preparation method of a bending-resistant and whitening-resistant TPU heat transfer product, comprising the following steps:

[0026] S1, substrate pretreatment, the TPU substrate is sequentially subjected to alkaline degreasing, pickling and phosphating treatment, and then dried at 110 DEG C to a water content of <0.5%; the alkaline degreasing in the substrate pretreatment uses a 5% NaOH solution, the treatment time is 5 min, and the water temperature is controlled at 60 DEG C; the pickling uses a 10% H2SO4 solution, the treatment time is 3 min; the phosphating treatment uses a zinc-based phosphating solution, the treatment time is 2 min, and the treatment temperature is room temperature; a nano-SiO2 dispersion liquid is prepared, mixed according to a mass ratio of SiO2 sol to deionized water 1:5, 0.5wt% KH-550 silane coupling agent is added, ultrasonic treatment is performed for 30 min at 40 kHz, the pH is adjusted to 8-9, and after stirring at 300 rpm, defoaming is performed for 2 h; in the nano-SiO2 dispersion liquid, the particle size of the SiO2 sol is 20 nm; ammonia is used for pH adjustment, the pH value change is monitored in real time during the adjustment process, and the final pH is ensured to be stable within the range of 8-9.

[0027] S2, electrostatic spraying, using a high-voltage electrostatic spray gun, spraying at a speed of 0.8 m / s in a zigzag trajectory, forming a 50-80 nm bottom layer at a flow rate of 100 g / min in the first stage, and forming a 100-120 nm surface layer at a flow rate of 200 g / min in the second stage, the total thickness being 150-200 nm; the equipment parameters for electrostatic spraying are: electrostatic voltage 70 kV, vertical distance between the spray gun and the substrate 30 cm, air compressor dew point < -40 DEG C;

[0028] Among them, the grounding resistance of the anti-static workbench in the auxiliary equipment is <1 MΩ, the recovery device adopts a combination of cyclone separation and filter core filtration, and the filter core filtration precision is 0.1 μm; the SiO2 particle size in the bottom layer formed in the first stage is ≤50 nm, and the SiO2 particle size in the surface layer formed in the second stage is ≥150 nm; in the spraying process, the adjacent path distance of the zigzag trajectory of the spray gun is 5 cm, ensuring uniform and complete coating coverage.

[0029] S3, curing treatment, immediately after spraying, curing at 180℃ for 30min, so that the SiO2 particles are fused and crosslinked; the curing treatment is carried out in a curing oven, the heating rate is 5℃ / min, from room temperature to 180℃, and then kept for 30min, and then naturally cooled to room temperature; when the hot melt adhesive film is attached, the temperature of the high-frequency heat sealing machine is controlled at 120-150℃, the pressure is 0.3MPa, and the heat sealing time is 10s.

[0030] S4, attaching the hot melt adhesive film, the cured TPU substrate is attached to the hot melt adhesive film by a high-frequency heat sealing machine.

[0031] S5, performance test treatment, including hydrophobicity test, wear resistance test and bending resistance test;

[0032] The hydrophobicity test uses a contact angle measuring instrument, the average value of the contact angles of three different test points is taken under the condition of 25℃ and 50% relative humidity, and the contact angle ≥115° is qualified;

[0033] The wear resistance test uses a Taber abrasion tester, uses CS-10 wheels, loads 1kg load, rotates 1000 turns, measures the wear rate, and the wear rate ≤0.12mg / 1000 turns is qualified;

[0034] The bending resistance test uses a bending tester, the sample is bent 50000 times at 25℃, the bending angle is 180°, the bending speed is 30 times / min, and the whitening area after test ≤2% is qualified.

[0035] The embodiment also provides a preparation method of a bending-resistant and whitening-resistant TPU heat transfer product, and a bending-resistant and whitening-resistant TPU heat transfer trademark prepared by the method is prepared based on nano-SiO2 gradient spraying, and includes a TPU substrate layer, a nano-SiO2 gradient coating layer and a hot melt adhesive film layer; the nano-SiO2 gradient coating layer has a bottom layer thickness of 50-80nm, a surface layer thickness of 100-120nm and a total thickness of 150-200nm; the TPU substrate layer has a thickness of 0.3mm, and the hot melt adhesive film layer has a thickness of 0.05-0.1mm; the trademark has a whitening area ≤2% after 50000 times of bending, a contact angle ≥115°, a wear rate ≤0.12mg / 1000 turns and an adhesive force falling area of the coating layer and the TPU substrate layer <3%.

[0036] As an application of the embodiment: by using the gradient coating structure of 50-80nm (SiO2 particle size ≤50nm) of the bottom layer and 100-120nm (SiO2 particle size ≥150nm) of the surface layer, the small particle size SiO2 of the bottom layer can fill the micro-defects on the surface of the TPU substrate, and inhibit the crack initiation caused by stress concentration when bending; the large particle size SiO2 of the surface layer forms a rigid support network to hinder crack propagation; actual test shows that after 50000 times of 180° bending, the whitening area is ≤2%, which is much better than the traditional TPU brand, and the appearance deterioration problem caused by whitening due to bending in long-term use of the clothing brand is completely solved.

[0037] The above has made a detailed description of the application in general, but some modifications or improvements can be made on the basis of the application, which is obvious to those skilled in the art. Therefore, the modifications or improvements without departing from the spirit of the application are within the protection scope of the application.

Claims

1. A method for preparing a bend-resistant, whitening-resistant TPU heat transfer product, characterized in that, The method comprises the following steps: The substrate pretreatment, the TPU substrate is sequentially subjected to alkaline degreasing, pickling and phosphating treatment, and then dried at 110℃ until the water content is less than 0.5%; The nano-SiO2 dispersion liquid is prepared by mixing SiO2 sol and deionized water at a mass ratio of 1:5, adding 0.5wt% KH-550 silane coupling agent, ultrasonic treatment for 30min at 40kHz, adjusting the pH to 8-9, and stirring at 300rpm and then standing for 2h for defoaming; The electrostatic spraying is performed by using a high-voltage electrostatic spray gun to spray in a zigzag trajectory at a speed of 0.8m / s, the first stage is to form a 50-80nm bottom layer at a flow rate of 100g / min, and the second stage is to form a 100-120nm surface layer at a flow rate of 200g / min, and the total thickness is 150-200nm; The curing treatment is performed immediately after spraying at 180℃ for 30min to make the SiO2 particles melt and crosslink; The cured TPU substrate is bonded with the hot melt adhesive film by using a high-frequency heat sealing machine.

2. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, The alkaline degreasing in the substrate pretreatment uses 5% NaOH solution, and the treatment time is 5min, and the water temperature is controlled at 60℃; The pickling uses 10% H2SO4 solution, and the treatment time is 3min; the phosphating treatment uses zinc-based phosphating solution, and the treatment time is 2min at room temperature.

3. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, In the nano-SiO2 dispersion liquid, the particle size of SiO2 sol is 20nm; the pH adjustment is performed by using ammonia, and the pH value change is monitored in real time during the adjustment process to ensure that the final pH is stable in the range of 8-9.

4. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, The equipment parameters of the electrostatic spraying are as follows: electrostatic voltage 70kV, vertical distance between spray gun and substrate 30cm, and air compressor dew point <-40℃; The grounding resistance of the anti-static workbench in the auxiliary equipment is less than 1MΩ, and the recovery device adopts a combination of cyclone separation and filter core filtration, and the filter core filtration precision is 0.1μm.

5. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, In the nano-SiO2 gradient spraying, the SiO2 particle size in the bottom layer formed in the first stage is ≤50nm, and the SiO2 particle size in the surface layer formed in the second stage is ≥150nm; during the spraying process, the distance between adjacent paths of the zigzag trajectory of the spray gun is 5cm.

6. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, The curing treatment is performed in a curing furnace at a heating rate of 5℃ / min, and after being raised from room temperature to 180℃, it is kept for 30min, and then naturally cooled to room temperature; when bonding the hot melt adhesive film, the temperature of the high-frequency heat sealing machine is controlled at 120-150℃, the pressure is 0.3MPa, and the heat sealing time is 10s.

7. The preparation method of the anti-whitening TPU heat transfer product with bending resistance according to claim 1, characterized in that, The performance test process comprises hydrophobicity test, wear resistance test and bending resistance test; The hydrophobicity test uses a contact angle measuring instrument, and the average value of the contact angles of three different test points is taken under the condition of 25℃ and 50% relative humidity, and the contact angle ≥115° is qualified; The wear resistance test uses a Taber abrasion tester, uses CS-10 wheels, loads 1kg, rotates 1000 times, measures the wear rate, and the wear rate ≤0.12mg / 1000 turns is qualified; The bending resistance test adopts a bending tester, and the sample is bent 50000 times at 25 DEG C, the bending angle is 180 DEG, the bending speed is 30 times / min, and the whitening area after the test is ≤2% for being qualified.

8. A bending-resistant whitening-preventing TPU heat transfer label based on nano-SiO2 gradient spraying, which is prepared by the method for preparing the bending-resistant whitening-preventing TPU heat transfer label according to any one of claims 1-7, characterized in that, The trademark includes a TPU substrate layer, a nano-SiO2 gradient coating and a hot melt adhesive film layer; the nano-SiO2 gradient coating has a bottom layer thickness of 50-80 nm, a surface layer thickness of 100-120 nm and a total thickness of 150-200 nm; the TPU substrate layer has a thickness of 0.3 mm, and the hot melt adhesive film layer has a thickness of 0.05-0.1 mm; the trademark has a whitening area of ≤2% after 50000 times of bending, a contact angle of ≥115 DEG, an abrasion rate of ≤0.12 mg / 1000 turns and a coating adhesion falling area of <3% with the TPU substrate layer.