Stable-release residue-free DTF transfer film and preparation method thereof

Abstract

The invention provides a stable-release residue-free DTF transfer film and a preparation method thereof, and belongs to the technical field of polymer film materials. In the DTF thermal transfer pressing and stripping process, the thermal expansion deformation and elastic recovery effects of the double-shell thermal expansion microspheres are utilized, and the synergistic effect of the self-cleaning function is combined, so that the force needed by stripping is remarkably reduced, it is ensured that no colloid is left on the surface of a transfer pattern after stripping, and the stripping quality is improved. The surface of the intelligent release film is coated with a single-layer composite release coating containing a special structure functional unit, the stripping behavior and the self-cleaning function of the intelligent release film are automatically triggered by process heat, external intervention is not needed, and the intelligent release film has autonomous sensing and response capabilities. The problems that an existing DTF transfer printing film is large in stripping force, microscopic residues exist, response is not synchronous during multifunctional design, and collaboration is poor are solved. The DTF transfer printing film has the advantages of being stable in structure, good in durability and clear and clean in transfer printing pattern, and is suitable for the DTF digital printing and transfer printing fields of crystal marks, embroidery-imitating printing films and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane technology, specifically to a release-stable, residue-free DTF transfer film and its preparation method. Background Technology

[0002] Direct-to-Film (DTF) digital transfer technology is widely used in textiles, signage, and decorative materials due to its excellent ability to reproduce complex patterns. In this process, the pattern is first printed onto a release film using a digital printer. Then, hot melt adhesive powder is applied and heated to adhere to the pattern. Finally, this film is pressed onto a substrate and then peeled off, transferring the pattern to the substrate surface. Therefore, the release film is a crucial part of the DTF process. An ideal release film needs to peel smoothly from the cured adhesive layer after printing and powder application, without any residue affecting the adhesion strength and appearance of the subsequent heat transfer. However, existing DTF release films still have some problems in practical use.

[0003] To achieve sufficiently low release force, traditional release films mostly use low surface energy release agents such as silicone and fluorine. Under DTF heat transfer conditions, the strong adhesion between the hot melt adhesive and the release layer leads to excessive initial adhesion force during peeling. Operators need to apply high force to tear off the film, increasing the difficulty of the process. When the transfer area is large or the pattern is complex, this high peel force is more likely to cause defects such as tearing of the pattern edge or misalignment. CN120287741A discloses a heat transfer film that can be peeled off efficiently and its preparation process. First, a release layer with a nanoporous structure is constructed on the substrate. When heated, this structure can effectively weaken the bonding force between the release layer and the pattern layer above, forming a preset easy-peel interface. A rigid dielectric reinforcement layer is set below the pattern layer to ensure that the pattern layer can be pulled up as a whole during peeling, avoiding cracking due to local stress concentration. Furthermore, the bottom ternary blend hot melt adhesive layer can also form a strong bond with the substrate after hot pressing. However, this method of suppressing ink diffusion and assisting in peeling by physically binding ignores the thermal motion of polymer chains and the melting and wetting mechanisms during the heat transfer process. These mechanisms are dominant in the heat transfer process, and therefore, under long-term or complex stress, the material is prone to new interfaces or brittle fracture risks.

[0004] Another approach involves coating the release film with a release agent to reduce its release force, thus making it easier to peel off. CN118406354B discloses an easy-to-peel PET release film and its preparation process. It utilizes glycidyl methacrylate to prepare vinyl-rich modified graphene, which is then reacted with hydrogen-containing silicone oil and dodecafluoroheptyl methacrylate to synthesize modified silicone oil. The addition of modified silicone oil and modified glycidyl methacrylate gives the release film a lighter and more stable release force, thus achieving easy peeling. Simultaneously, graphene oxide can be used to improve the material's conductivity, antistatic properties, and wear resistance. The introduction of fluoroalkyl long chains also gives the release film a superhydrophobic surface, thus providing it with anti-fouling and self-cleaning effects. However, for release layers, the long-term stability of release force depends on the extreme uniformity and controllability of the chemical properties of the release layer surface. Therefore, this method of forcibly combining various monomers with silicone resin will cause uneven micro-regions or phase separation to form on the surface of the material during curing or long-term use. Furthermore, the risk of micro-cracks in coatings containing nanosheet fillers is greatly increased when subjected to bending stress from repeated peeling of tape, which in turn affects the requirements for smooth peeling and no residue.

[0005] In summary, existing technologies for improving the removal difficulties and residue issues of DTF transfer films each have limitations. Simply piecing together multiple technologies often results in asynchronous functional responses and mutual interference between components. Furthermore, if the functional components lack an overall design and are merely superimposed, the effect is often only a limited accumulation of individual functions, failing to fundamentally solve the problem. Therefore, a systematic and innovative solution is urgently needed to achieve smooth, residue-free, and stable release at key points in the DTF release film removal process. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a release-stable, residue-free DTF transfer film and its preparation method. This invention utilizes the thermal expansion deformation and elastic recovery of double-shell thermally expandable microspheres during the DTF thermal transfer pressing and peeling process to form micro-island anti-adhesion structures at the interface and induce separation. Simultaneously, combined with the self-cleaning function of a catalyst, this significantly reduces the peeling force required and ensures no adhesive residue remains on the surface of the transferred pattern after peeling. This results in a single-layer composite release coating with specially structured functional units. Its peeling behavior and self-cleaning function are automatically triggered by process heat, requiring no external intervention. This intelligent release film possesses autonomous sensing and response capabilities. It solves the technical problems in existing DTF transfer processes, such as excessive peeling force leading to operational difficulties, microscopic residues affecting transfer adhesion and appearance after peeling, asynchronous functional responses, component interference, and limited or unreliable effects due to a lack of synergistic effects when simply combining multiple technologies.

[0007] This invention discloses a release-stable and residue-free DTF transfer film, comprising a substrate film and a single-layer composite release functional layer. The release layer uses carboxyl-modified saturated polyester resin as the continuous phase matrix resin and uniformly disperses two types of functional particles forming functional micro-units. The two types of functional particles include double-shell thermally expandable microspheres and core-shell structure mesoporous silica carrier microparticles. The silica carrier microparticles are loaded with an organotin / titanium ester composite catalyst and encapsulated with a double layer of organic wax.

[0008] This invention also discloses a method for preparing a release-stable, residue-free DTF transfer film, such as... Figure 1 As shown, the specific technical solution is as follows: Step 1: The copolymer is used as the shell material of the microspheres, and low-boiling-point liquid alkane is used as the foaming agent to act as the core of the microspheres. The organic phase and aqueous phase are prepared in the reactor and formed into suspension droplets under high-speed stirring. Then, the mixture is polymerized at high temperature. After cooling, washing and drying of the product, double-shell thermally expanded microspheres are obtained.

[0009] Step 2: Using mesoporous silica powder as a carrier, it is impregnated in an ethanol solution of organotin / titanium ester composite catalyst to allow the catalyst to fully enter the silica pores. The silica powder loaded with catalyst is then dried under reduced pressure. Subsequently, the powder is encapsulated in two layers with two kinds of organic wax to obtain core-shell structured mesoporous silica catalyst microcapsules.

[0010] Step 3: Prepare the release layer matrix resin into a resin solution, add crosslinking agent and stir evenly, then add thermal expansion microspheres and catalyst microcapsules to the resin solution, and then stir at high speed until a uniform and fine milky white coating liquid is formed. Let it stand, vacuum degas, filter to remove coarse impurities, and obtain the release coating coating.

[0011] Step 4: Apply the release coating material evenly to the PET base film using a coating machine, and then immediately heat and cure it in sections in an oven. After cooling, a stable and residue-free DTF transfer film is obtained.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By designing a double-shell microsphere structure with specific thermomechanical properties, it can precisely realize the functions of thermal expansion deformation and elastic recovery. That is, under the high temperature of transfer printing, it expands in situ to form a micro-island structure, which significantly reduces the actual contact area between the adhesive layer and the film surface (similar to the lotus leaf effect), weakening the adhesion force from the root. During cooling and peeling, the difference in thermal shrinkage rate between the microsphere and the adhesive layer and the elastic recovery force of the microsphere itself are used to generate directional microscopic shear stress at the interface, actively inducing interface separation. This avoids the pattern damage caused by the external force tearing of traditional release films, while ensuring a smooth and stable peeling process without local stress concentration problems.

[0013] 2. A composite structure of core-shell support and double-layer wax seal is used to load and encapsulate the catalyst. By designing a gradient of the melting points of the inner and outer wax materials, the catalyst release process is precisely matched with the process temperature curve. The outer wax melts at a lower preheating stage to facilitate dispersion, while the inner wax melts and releases the active catalyst at the core high temperature stage when the adhesive layer is cured. This timing control ensures that the catalyst is released and reaches the action site only when the new interface is formed, achieving on-demand supply and greatly improving the utilization efficiency and cleaning specificity of the catalyst.

[0014] 3. By tightly mixing the above microspheres with the catalyst support at the microscale, countless tiny functional response units are constructed within the monolayer film. When the microspheres induce interfacial separation through thermal expansion deformation and elastic recovery, the resulting local micro-region mechanical stress and interfacial renewal will create channels for the diffusion and penetration of the adjacent catalyst and expand the reaction contact area. The immediate action of the catalyst can further weaken the cohesive strength of the residue, making it easier to be removed by physical action.

[0015] 4. Through careful design and screening of the catalyst molecular structure, its catalytic degradation activity on specific chemical bonds in the transfer adhesive layer is much higher than its activity on the main resin of the release layer. This high selectivity ensures that the cleaning process can efficiently and specifically target and remove residual adhesive substances, while having little impact on the structure of the release layer itself. Thus, while achieving excellent cleaning effect, it maintains the mechanical integrity, thermal stability and long-term durability of the release layer itself, resolving the contradiction between cleaning and self-damage. Attached Figure Description

[0016] Appendix Figure 1 This is a flowchart illustrating the preparation process of the DTF transfer film of the present invention. Appendix Figure 2 This is a schematic diagram illustrating the peel strength of the DTF transfer film in the examples and comparative examples. Appendix Figure 3 This is a schematic diagram illustrating the change in peel force required for the DTF transfer film in the 100mm peeling process of the examples and comparative examples. Appendix Figure 4 The diagram shows the peel strength of the DTF transfer films in the examples and comparative examples after undergoing high-temperature aging and high-humidity aging, respectively. Detailed Implementation

[0017] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0018] This invention proposes a release-stable, residue-free DTF transfer film and its preparation method, such as... Figure 1 As shown, the specific technical solution is as follows: 1. Preparation of double-shell thermally expandable microspheres By using suspension polymerization, thermally expandable microspheres with a double-shell structure are formed and polymerized in a reaction system using specific copolymer monomers as the outer shell material and low-boiling-point liquid alkanes as the core blowing agent. A specific ratio of copolymer monomers is chosen as the outer shell material because the polymer segments formed after polymerization provide specific glass transition temperatures and mechanical properties. During polymerization, the low-boiling-point liquid alkanes are encapsulated within monomer droplets, becoming the blowing agent that subsequently vaporizes upon heating. In the suspension polymerization synthesis of microspheres, the aqueous phase acts as the continuous phase, dispersing and stabilizing the oil phase droplets. Heating initiates the polymerization reaction, causing the monomers to crosslink and solidify at the droplet interface and within, thus forming microspheres with the blowing agent as the core and the polymer as the shell. These double-shell microspheres expand in situ at high transfer temperatures, forming raised micro-island structures on the microscopic surface, significantly reducing the actual contact area between the adhesive layer and the film surface (similar to the lotus leaf effect). During the cooling and peeling stage, the difference in thermal shrinkage rates between the microsphere shell and the adhesive layer, as well as the elastic recovery force of the microspheres, generates microscopic shear stress at the interface, inducing interfacial separation.

[0019] 2. Preparation of catalyst support microcapsules A composite catalyst was loaded into the pores of mesoporous silica using an impregnation-adsorption method. A double-layer encapsulation technique with two organic waxes of different melting points was then employed to obtain core-shell catalyst microcapsules exhibiting temperature gradient-responsive release characteristics. Mesoporous silica possesses a high specific surface area and well-defined nanoscale pores. Its abundant silanol groups can efficiently load composite catalyst molecules such as organotin / titanium esters through physical adsorption or weak chemical interaction. After impregnation, the solvent was removed through a vacuum drying process, allowing the catalyst to remain stably within the pores. The subsequent double-layer wax encapsulation structure acts like two locks with different melting points for the catalyst. During the pre-curing stage after coating, only the outer low-melting-point wax melts, which helps optimize particle flow and distribution within the coating. However, the catalyst remains securely protected by the inner high-melting-point wax. Only when the film undergoes the high temperature of DTF curing does the inner wax melt, releasing the catalyst and dispersing it within the release layer matrix. This two-step unlocking mechanism perfectly matches the temperature history of the process, ensuring that the catalyst is not prematurely released and deactivated or interferes with coating formation. Instead, it is precisely delivered to the action area only when its cleaning function is most needed. Although the organotin / titanium ester composite catalyst has a certain catalytic effect on polyester, the catalyst's movement is restricted in the resin due to the cross-linking and curing between the polyester resin and the PET base film. This prevents it from penetrating deeply to hydrolyze the firmly cross-linked polyester network. As the thermally expanded microspheres generate a heat island structure between the release layer and the adhesive layer, the catalyst is also squeezed towards the release layer-hot melt adhesive interface, thus accumulating on the surface. When subsequent peeling begins, the cooling and contraction of the thermally expanded microspheres will generate microcracks at the interface between the release layer and the hot melt adhesive. At this time, the catalyst can quickly act on the highly active sites exposed in the microcrack network, selectively catalytically cleaving the ester bonds or urethane bonds in the hot melt adhesive layer that are in a stress-activated state. This drastically reduces the cohesive strength of the molecular chain, causing the residual adhesive to undergo low cohesive destruction under microscopic shearing, ultimately achieving interface cleaning and residue-free removal.

[0020] 3. Preparation of release coating paint After dissolving the release layer matrix resin and adding a crosslinking agent, the previously prepared thermally expanded microspheres and catalyst microcapsules were sequentially incorporated. Through efficient mechanical stirring and subsequent processing, a uniformly dispersed and stable composite release coating was prepared. The film-forming polymer was dissolved in a suitable solvent to form a homogeneous solution as the continuous matrix of the coating. A crosslinking agent was added to prepare for the formation of a three-dimensional network structure during subsequent thermal curing. Subsequently, two functional solid particles were added to the resin solution. The strong shear force generated by high-speed stirring was used to break up any possible soft agglomerates and uniformly disperse them in the viscous resin liquid phase. Air bubbles entrained during stirring were removed by allowing the mixture to stand and then vacuuming to prevent defects during coating. The optimized dispersion process achieved highly uniform and stable dispersion of various heterogeneous functional particles in the resin matrix, while maintaining the structural integrity of each functional particle to the greatest extent. Uniform dispersion is a prerequisite for ensuring the consistent performance of the final release film. Any agglomeration will lead to local over- or under-functionality. Furthermore, the optimized high-speed stirring process conditions can ensure sufficient dispersion while avoiding damage to the shell of the thermally expanded microspheres or the wax-sealing structure of the catalyst microcapsules due to excessive shear force.

[0021] 4. Coating and curing to form a film The coating solution is applied to a PET base film and then cured by stepwise heating to form a film with built-in functional micro-unit structures. Using a coating machine, the coating is uniformly applied to a clean PET base film at a set wet film thickness. Immediately following, a stepwise heating and curing process is performed. The first stage of curing typically uses a relatively mild temperature, slightly higher than the melting point of the outer wax layer but significantly lower than the melting point of the inner wax layer and the microsphere expansion initiation temperature. The purpose is to allow the solvent to evaporate rapidly, the resin to initially crosslink, the coating to set and fix the position of each functional particle, and to melt the outer wax layer of the catalyst microcapsules to optimize their distribution. The second stage of curing rapidly heats up to the core high-temperature zone of the DTF process. In this stage, the resin is fully crosslinked and cured to achieve final mechanical strength. The inner wax layer of the catalyst microcapsules melts and releases the catalyst into the matrix. The foaming agent inside the thermally expanding microspheres vaporizes, driving the microspheres to expand in situ and form micro-island structures. The outer shell strength adapts to the expansion requirements, preventing excessive deformation or breakage. By matching the precisely calibrated curing temperature program with the thermal response characteristics of each functional component, the release layer is successfully cured and stabilized in a fully functional preset response state. In the initial stage of segmented curing, the resin matrix is ​​initially cross-linked and shaped at a lower temperature, thereby constructing a stable coating skeleton and effectively suppressing the migration and uneven distribution of functional particles that may occur due to thermal convection in the subsequent high-temperature stage. In the subsequent high-temperature curing stage, the complete cross-linking of the matrix resin, the controlled release of the catalyst, and the thermal expansion of the microspheres are synergistically achieved, so that the interior of the final release layer is in a state where the catalyst is uniformly dispersed in the matrix and is in an active and ready state, while the microspheres remain in a critical mechanically stable state after thermal expansion. This state has high thermodynamic stability, and its preset response behavior is only triggered when subjected to specific external mechanical shear stimuli, ensuring the reliability and high consistency of the intelligent response behavior of the final product.

[0022] The following are some specific embodiments of the present invention, and Table 1 shows the raw material information used in the embodiments.

[0023] Table 1 Raw Material Information Table

[0024] Example 1 S1: Add 800g of deionized water and 4.0g of hydroxypropyl methylcellulose to a reactor, heat to 40℃ and stir until completely dissolved to form the aqueous phase. Separately weigh 60g of acrylonitrile, 36g of vinyl acetate, and 24g of methyl methacrylate and mix them evenly to form the organic phase. Then add 1.2g of azobisisobutyronitrile and 24g of isopentane. Under continuous nitrogen protection and vigorous stirring at 1200rpm, slowly add the organic phase to the aqueous phase and emulsify for 30min. Then raise the system temperature to 75℃ and keep the system at a constant temperature for 2h for polymerization. Then raise the system temperature to 90℃ and continue the reaction for 1h. After the reaction is completed, cool and filter the product, wash it three times with deionized water, and finally dry it in a vacuum drying oven at 50℃ for 12h to obtain white double-shell thermally expanded microspheres.

[0025] S2: Dissolve 4.0g of stannous octoate and 3.3g of tetraisopropyl titanate in 200mL of anhydrous ethanol and stir until homogeneous to form a composite catalyst solution. Impregnate 74.7g of fumed SiO2 powder in the composite catalyst solution and sonicate for 1h. Remove the solvent by rotary evaporation under reduced pressure at 60℃ to obtain a catalyst-loaded carrier powder. Then, put the powder into a fluidized bed and spray molten polyethylene wax at 110℃ (8% of the powder mass) at an inlet air temperature of 105℃. After cooling and solidification, an inner layer encapsulation is formed. Raise the inlet air temperature to 70℃ and spray molten Fischer-Tropsch wax at 80℃ (5% of the powder mass) to form an outer layer encapsulation. After cooling, discharge the material to obtain a double-layer wax-encapsulated catalyst microcapsule.

[0026] S3: Weigh 100g of carboxyl-modified saturated polyester resin and dissolve it in 100g of ethyl acetate / methyl ethyl ketone (MEK) 1:1 mixed solution. Then weigh 16g of poly(melamine-CO-formaldehyde) methanol and dissolve it in 4g of ethyl acetate / MEK 1:1 mixed solution. Add the two mixed solutions and 150g of ethyl acetate / MEK 1:1 mixed solution sequentially to the hopper of a planetary centrifugal mixer and stir at 500rpm for 10min to form a homogeneous resin base liquid. Weigh 30g of the double-shell thermally expanded microspheres prepared in S1 and the double-layer wax-encapsulated microspheres prepared in S2. 15g of catalyst microcapsules were added to another container and physically premixed by stirring with a glass rod. The premixed powder was then mixed with 20g of resin base liquid and ground evenly with a grinder. The evenly ground slurry was slowly added to the remaining resin base liquid while stirring slowly. After the addition was complete, the stirring speed was increased to 2000rpm and a vacuum was drawn to -0.08MPa to remove air bubbles. This process was continued for 60min to form a uniform and fine milky white slurry. The slurry was then filtered through a 100-mesh stainless steel filter screen, and the filtrate was collected to obtain the release coating liquid.

[0027] S4: Using a precision slot coater, the coating obtained in S3 is uniformly coated to a thickness of 15μm onto the surface of a 50μm corona-treated PET base film. The coated film is then baked at 110℃ for 1 minute, and then baked at 130℃ for 2 minutes. Finally, the baked coated film is removed and allowed to cool naturally to room temperature to obtain a DTF transfer film with stable release and no residue.

[0028] Example 2 The preparation method according to Example 1 differs in that: S1: Weigh 54g acrylonitrile, 30g vinyl acetate, 21.6g methyl methacrylate, 1.2g azobisisobutyronitrile and 15.84g isopentane into the organic phase. The isothermal polymerization temperature is 70℃ and the reaction time is 1.5h. Then the temperature is increased to 85℃ and the reaction time is 0.75h. S2: The amount of fumed SiO2 powder is 95.45g, the amount of Fischer-Tropsch wax is 3% of the powder mass, the spraying temperature is 75℃, the amount of polyethylene wax is 6% of the powder mass, and the spraying temperature is 105℃. S3: The amount of thermally expanded microspheres added is 25g, the amount of catalyst microcapsules is 15g, and the vacuum stirring time is 45min; S4: The coating thickness is set to 12μm. The first stage curing temperature is 105℃ and the time is 45s. The second stage curing temperature is 125℃ and the time is 1.5min. All other steps are the same.

[0029] Example 3 The preparation method according to Example 1 differs in that: S1: 66g acrylonitrile, 42g vinyl acetate, 26.4g methyl methacrylate, 1.2g azobisisobutyronitrile and 33.6g isopentane were weighed into the organic phase. The isothermal polymerization temperature was 85℃ and the reaction time was 2.5h. Then the temperature was increased to 95℃ and the reaction time was 1.5h. S2: The amount of fumed SiO2 powder is 60.87g, the amount of Fischer-Tropsch wax is 7% of the powder mass, the spraying temperature is 85℃, the amount of polyethylene wax is 10% of the powder mass, and the spraying temperature is 115℃. S3: The amount of thermally expanded microspheres added is 40g, the amount of catalyst microcapsules is 15g, and the vacuum stirring time is 75min; S4: The coating thickness is set to 18μm, the first stage curing temperature is 115℃ and the time is 90s, the second stage curing temperature is 135℃ and the time is 2.5min, and the remaining steps are the same.

[0030] Example 4 The preparation method according to Example 1 differs in that: S1: 62g acrylonitrile, 32g vinyl acetate, 25g methyl methacrylate, 1.2g azobisisobutyronitrile and 28g isopentane were weighed into the organic phase. The isothermal polymerization temperature was 80℃ and the reaction time was 1.75h. Then the temperature was increased to 93℃ and the reaction time was 1.25h. S2: The amount of fumed SiO2 powder is 83.9g, the amount of Fischer-Tropsch wax is 4.5% of the powder mass, the spraying temperature is 77℃, the amount of polyethylene wax is 7.5% of the powder mass, and the spraying temperature is 108℃. S3: The amount of thermally expanded microspheres added is 35g, the amount of catalyst microcapsules is 15g, and the vacuum stirring time is 50min; S4: The coating thickness is set to 16μm, the first stage curing temperature is 112℃ and the time is 75s, the second stage curing temperature is 128℃ and the time is 2.25min, and the remaining steps are the same.

[0031] Comparative Example 1 The preparation method according to Example 1 differs in that: S2: Remove the consumer wax encapsulation layer and encapsulate the catalyst with only polyethylene wax. The remaining steps are the same.

[0032] This comparative example shows the preparation of a DTF transfer film obtained by simplifying the encapsulation process using a single layer of organic wax.

[0033] Comparative Example 2 The preparation method according to Example 1 differs in that: S1: Weigh 75g of methyl methacrylate, 15g of acrylonitrile, 1.2g of azobisisobutyronitrile, and 30g of liquid isobutane as the organic phase. After emulsifying the organic phase in the aqueous phase, raise the system temperature to 65℃ and perform a constant-temperature polymerization reaction for 4h to obtain acrylonitrile monolayer shell thermal expansion microspheres. The remaining steps are the same.

[0034] This comparative study prepared a DTF transfer film using monolayer acrylonitrile thermal expansion microspheres, which resulted in thermal expansion deformation and loss of elastic recovery function.

[0035] Comparative Example 3 The preparation method according to Example 1 differs in that: S2: Replace the stannous octoate / tetraisopropyl titanate composite catalyst with 4.0g of p-toluenesulfonic acid, and the remaining steps are the same.

[0036] This comparative preparation uses a powerful, non-selective catalyst that strongly protonates and hydrolyzes the ester bonds of both polyester and polyurethane to obtain a DTF transfer film.

[0037] Experimental Example 1 The DTF transfer film samples prepared in Examples 1-4 and Comparative Examples 1-3 were placed in an environment of 25°C and 55% relative humidity and left to stand for 24 hours. Then, white ink was printed on the release layer surface of the samples according to the standard DTF process, and polyurethane hot melt adhesive powder was sprinkled on top. The samples were then placed in a 150°C oven for 120 seconds to cure the adhesive powder, forming a composite structure of PET base film-release layer-hot melt adhesive layer. The composite sample was cut into strips with a width of 25 mm and a length of 300 mm, with the hot melt adhesive layer facing down against a clean and dry substrate. Align the 304 stainless steel test plates, cover the back of the PET base film with a flat polyester film release sheet, and then place the entire stack in a hot press preheated to 160℃. Press it for 10 seconds under a pressure of 0.4MPa to firmly bond the adhesive layer to the steel plate. After pressing, remove the polyester release film, and immediately roll it three times unidirectionally on the sample with a 2kg, 100mm long metal roller at a speed of 10mm / s. Then place the sample in an environment of 25℃ and 55% relative humidity for 20 minutes. Afterward, remove the sample, clamp the steel plate vertically on the fixture of the testing machine, and wrap the free end of the PET base film of the transfer film around a 20mm diameter guide roller and clamp it in the lower fixture to form a 180° peel angle. The testing machine pulls the lower clamp downwards at a constant speed of 300 mm / min, peeling the PET base film along with the release film from the adhesive layer on the steel plate. The peeling stroke is 150 mm. Discarding the data from the first and last 25 mm, the average force value within the middle 100 mm of the stable peeling stroke is calculated. This average value represents the force required to peel the release layer from the cured adhesive layer, i.e., the peel performance of the release layer. The test results are shown in Table 2 and... Figure 2 , Figure 3 As shown.

[0038] Table 2. Peel performance of release layers in the examples and comparative samples

[0039] From Table 2 and Figure 2 , Figure 3As can be seen, the DTF transfer films prepared in the examples all have low peel strength, and the peel force required within a 100mm peel stroke shows a very stable trend with almost no fluctuation. This indicates that the samples in the examples, through the synergistic effect of thermal expansion deformation, elastic recovery function, and cleaning effect, can provide ultra-low and stable peel force throughout the peeling process, achieving smooth peeling. In contrast, the DTF film prepared using a single-layer wax seal in Comparative Example 1 suffers from a mismatch between the melting point of the single-layer polyethylene wax and the coating curing temperature, leading to uncontrolled catalyst release and an inability to form an effective catalytic concentration at the peeling interface, thus losing its immediate chemical cleaning effect. Meanwhile, the uneven distribution of catalyst microcapsules in the coating prevents them from effectively synergizing with the stress field generated by the thermally expanded microspheres. As a result, the peeling process lacks sufficient cushioning and chemical weakening, requiring the overcoming of large and unstable adhesive forces to achieve separation. Consequently, the average peel strength increases, and the force required during peeling fluctuates significantly. Comparative Example 2 shows a DTF film prepared using monolayer shell expanded microspheres. Due to the singular thermomechanical properties of polypropylene monolayer shell expanded microspheres, their expansion and rupture occur almost simultaneously. During the 130℃ hot-pressing curing stage, a large number of microspheres reach their rupture threshold and release gas prematurely. Therefore, when actually peeling is performed, there is almost no cushioning effect at the interface, which cannot effectively reduce the adhesive force in the initial stage of peeling. The peeling process mainly relies on overcoming the adhesion between the adhesive layer and the detachment layer. The intermolecular forces between the release layers significantly increase the peel force. Uneven gas release before release also causes large fluctuations in the peel force curve. Comparative Example 3 uses a potent non-selective catalyst to prepare the DTF film. Replacing the highly selective organotin / titanium ester composite catalyst in the examples with a protic acid catalyst causes the ester bonds in the polyester resin backbone of the release layer to undergo violent hydrolysis during baking, curing, and subsequent hot pressing. This disrupts the polymer crosslinking network, leading to numerous structural fractures within the release layer. Consequently, a high peel force is required to tear the release layer material itself during peeling. Furthermore, complex chemical bonds are formed at the release layer-adhesive layer interface, resulting in extremely unstable peel force during peeling.

[0040] Experiment Example 2 The DTF transfer film samples prepared in Examples 1-4 and Comparative Examples 1-3 were cut into two sets of strips, each 25 mm wide and 200 mm long. One set of strips was aged in a 70°C circulating air drying oven for 168 h, while the other set was aged in a constant temperature and humidity chamber at 40°C and 95% relative humidity for 96 h. After the aging process, their peel strength was tested according to the method in Experimental Example 1, and the attenuation rate was calculated by comparing it with the unaged sample in Experimental Example 1. The results are shown in Table 3 and... Figure 4 As shown.

[0041] Table 3. Comparison of the stability of the release layer of the examples and comparative samples.

[0042] From Table 3 and Figure 4 As can be seen, the sample in the examples retained relatively low peel strength after both high-temperature aging and low-temperature high-humidity aging, and the difference between the two aging methods had little effect on the peel strength of the sample in the examples. This indicates that the double-shell microsphere and double-wax-sealed structure of the sample in the examples significantly helps to maintain the stability of thermal expansion deformation and elastic recovery function and resist environmental stress. The selective catalyst can also prevent the material from self-degrading, thus achieving a long service life. In contrast, the single-wax-sealed structure of the sample in Comparative Example 1 is prone to premature cracking of the single-wax seal during high-temperature aging, causing premature catalyst deactivation. High-humidity aging allows water molecules to penetrate the wax seal defects and interlayer interfaces, leading to accelerated hydrolysis and failure of the catalyst, resulting in increased peel strength with large fluctuations. The single-shell microsphere structure of the sample in Comparative Example 2 cannot meet the on-demand triggering of the air cushion effect. High-temperature aging causes thermal relaxation and softening, and partial loss of isopentane as a foaming agent, resulting in a severe decline in the air cushion function. During high-humidity aging, the humid and hot environment further plasticizes the polymer of the microsphere shell, significantly reducing its glass transition temperature and mechanical strength. Moisture may also penetrate into the microsphere shell, accelerating the permeation and loss of the foaming agent isopentane, causing the microsphere to almost fail as a physical triggering unit, resulting in a significant increase in peel strength, and the peeling process may be accompanied by irregular breakage; the sample in Comparative Example 3 contains a strong non-selective catalyst, which can significantly accelerate the catalytic hydrolysis of the polyester release layer by strong acid during high-temperature aging, leading to matrix embrittlement. High-humidity aging provides an ideal environment for acid-catalyzed hydrolysis reaction, resulting in deep and extensive hydrolysis and chain breakage of the release layer, a sharp decline in mechanical properties, severe powdering of the sample surface, and further increase in peel strength after aging.

Claims

1. A release-stable, residue-free DTF transfer film, comprising a PET base film and a release coating formed thereon, characterized in that: The release coating is a single-layer composite release layer, comprising a resin matrix and functional micro-units dispersed therein; the resin matrix is ​​a carboxyl-modified saturated polyester resin, and the functional micro-units are composed of double-shell thermally expandable microspheres and core-shell structured mesoporous silica carrier microcapsules; the double-shell thermally expandable microspheres contain isopentane as a volatile foaming agent, the silica carrier is loaded with a selective catalyst, and is encapsulated with a double-layer organic wax; the selective catalyst is a stannous octoate / tetraisopropyl titanate composite catalyst, and the double-layer organic wax is an inner Fischer-Tropsch wax and an outer polyethylene wax.

2. The release-stable, residue-free DTF transfer film according to claim 1, characterized in that: The shell of the double-shell expandable microsphere is polymerized from copolymer monomers; the copolymer monomers include acrylonitrile, vinyl acetate, and methyl methacrylate in a molar ratio of (4.5~5.5):(2.5~3.5):(1.8~2.2); the loading of silica on the catalyst is 8~12wt%; the encapsulation amount of Fischer-Tropsch wax is 3%~7% of the carrier mass, and the encapsulation amount of polyethylene wax is 6%~10% of the carrier mass; the mass ratio of the thermally expandable microspheres to the microcapsules is (5:3)~(8:3).

3. The release-stable, residue-free DTF transfer film according to claim 1, characterized in that: The average peel strength at room temperature is <1.5N / 25mm, and the average peel strength after high temperature aging and high humidity aging is <2.0N / 25mm.

4. A method for preparing a release-stable, residue-free DTF transfer film according to any one of claims 1 to 3, characterized in that, It is prepared by the following method: S1: The copolymer is used as the outer shell material of the microspheres, and isopentane is used as the foaming agent to act as the core of the microspheres. The organic phase and the aqueous phase are prepared in the reactor. After the organic phase is added to the aqueous phase, it is stirred at high speed to form a suspension droplet. Then, the inner shell polymerization and outer shell polymerization are carried out at high temperature. After cooling, washing and drying of the product, double-shell thermally expanded microspheres are obtained. S2: Mesoporous silica powder was used as a carrier and impregnated in an ethanol solution of organotin / titanium ester composite catalyst to allow the catalyst to fully enter the silica channels. The silica powder loaded with the catalyst was obtained by vacuum drying. Subsequently, the powder was encapsulated in two layers using an outer layer of Fischer-Tropsch wax and an inner layer of polyethylene wax to obtain core-shell structured mesoporous silica catalyst microcapsules. S3: Prepare the release layer matrix resin into a resin solution, add crosslinking agent and stir evenly, add thermal expansion microspheres and catalyst microcapsules to the resin solution, and then stir at high speed until a uniform and fine milky white coating liquid is formed. Vacuum degassing and filtration are used to remove coarse impurities to obtain the release coating coating. S4: Apply the release coating material evenly to the PET base film using a coating machine, and then immediately heat and cure it in sections in an oven. After cooling, a stable release DTF transfer film without residue is obtained.

5. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The organic phase in S1 is a mixed solution of copolymer monomers and isopentane, and the aqueous phase is an aqueous solution of hydroxypropyl methylcellulose.

6. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The amount of foaming agent added in S1 is 15%~25% of the copolymer monomer mass. The polymerization temperature of the inner shell is 70~85℃ and the polymerization time is 1.5~2.5h. The polymerization temperature of the outer shell is 85~95℃ and the polymerization time is 0.75~1.5h.

7. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The encapsulation temperature of the Fischer-Tropsch wax described in S2 is 75~85℃, and the encapsulation temperature of the polyethylene wax is 105~115℃.

8. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The solvent of the resin solution in S3 is a mixed solvent of ethyl acetate and methyl ethyl ketone in a ratio of 1:1, and the crosslinking agent is poly(melamine-CO-formaldehyde)methanol.

9. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The vacuum degassing time described in S3 is 45~75 minutes.

10. The method for preparing a release-stable, residue-free DTF transfer film according to claim 4, characterized in that: The coating described in S4 is applied to the base film with a thickness of 12~18μm. In the segmented heating and curing process, the curing temperature of the first stage is 105~115℃ and the curing time is 45~90s. The curing temperature of the second stage is 125~135℃ and the curing time is 1.5~2.5min.

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