A release film for inkjet printing and an inkjet printing method

Abstract

The application discloses a release film for inkjet printing and an inkjet printing method, wherein the release film comprises a main resin, a crosslinking agent and a filler; the main resin comprises a thermosetting acrylic resin and a high-hydroxyl linear polyester resin, the crosslinking agent comprises a melamine formaldehyde resin; and the filler comprises silica powder, alumina powder, silicone oil and wax powder. The release film for inkjet printing can ensure that the release film and the substrate film have appropriate bonding force after hot stamping, and have uniform and consistent matte effects, so that the release film can realize any tearing, such as second tearing, hot tearing, warm tearing and cold tearing, after hot stamping, and the picture always maintains uniform and consistent matte effects after any tearing, thereby improving the inkjet printing efficiency and stability.

Description

Technical Field

[0001] This invention belongs to the field of inkjet printing film formulation design, specifically relating to a release film for inkjet printing and an inkjet printing method. Background Technology

[0002] In recent years, digital inkjet printing heat transfer film has gradually replaced traditional offset heat transfer and screen printing heat transfer. As the application of digital inkjet printing heat transfer film continues to expand, the industry is also putting forward higher requirements for this product. One of these requirements is to use automated equipment to improve production efficiency during the heat transfer process, so that the film can be torn off immediately after the heat transfer is completed, achieving "instant tearing" within 0-1 seconds, or tearing off the film according to the process of automated equipment. This requires that the tearing of the film is not constrained by the pause time after heat transfer, achieving "arbitrary tearing". Only in this way can the efficiency of inkjet printing heat transfer film be improved.

[0003] Based on the time required for cooling and peeling after hot stamping, the film is categorized into: instant peel, hot peel, warm peel, and cold peel. Hot peel refers to peeling the film after a 0-10 second cooling pause; warm peel refers to peeling the film after a 10-30 second cooling pause; cold peel refers to peeling the film after a 30-second cooling pause; and instant peel refers to peeling the film within a 0-1 second cooling pause.

[0004] However, products on the market exhibit varying degrees of matte finish after hot stamping due to different post-printing pause times. The matte finish and texture of the image vary depending on the pause time. Generally, hot-peeled surfaces maintain a more natural matte texture, while cold-peeled surfaces tend to appear glossier. This inconsistency in peeling pause times can lead to differences in appearance throughout a batch of products, resulting in variations in product quality. Furthermore, existing inkjet printing products suffer from a problem where the release film and substrate film adhere too tightly during peeling at certain times, causing fine lines and text to peel off. Summary of the Invention

[0005] One of the objectives of this invention is to provide a release film for inkjet printing that ensures appropriate adhesion between the release film and the substrate film after hot stamping, and has a uniform matte finish. This allows the release film to be torn in any way after hot stamping, including instant tearing, hot tearing, warm tearing, and cold tearing, and the image always maintains a uniform matte finish after any tear, thereby improving inkjet printing efficiency and stability.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] A release film for inkjet printing includes a main resin, a crosslinking agent, and fillers; the main resin includes thermosetting acrylic resin and high-hydroxyl linear polyester resin, the crosslinking agent includes melamine-formaldehyde resin, and the fillers include silica powder, alumina powder, silicone oil, and wax powder.

[0008] Further, it includes the following components in parts by weight: 40-50 parts of thermosetting acrylic resin, 10-15 parts of high hydroxyl linear polyester resin, 40-50 parts of melamine formaldehyde resin, and 10-15 parts of filler.

[0009] Furthermore, it includes the following components in parts by weight: 40-50 parts of thermosetting acrylic resin, 10-15 parts of high hydroxyl linear polyester resin, 40-50 parts of melamine formaldehyde resin, 0.5-0.8 parts of silica powder, 0.5-0.8 parts of alumina powder, 6-8 parts of silicone oil, and 6-8 parts of wax powder.

[0010] Furthermore, the silica powder is silica powder with a particle size of 3-4 micrometers.

[0011] Furthermore, the alumina powder is alumina powder with a particle size of 50-100 nanometers.

[0012] Furthermore, the silicone oil is an amino-modified silicone oil.

[0013] Furthermore, the wax powder comprises paraffin wax and modified low-melting-point PE wax, wherein the weight ratio of paraffin wax to modified low-melting-point PE wax is 1:1.

[0014] This application also provides an inkjet printing method, including:

[0015] The main resin and crosslinking agent are stirred and mixed, and filler is added during the stirring and mixing process to prepare the release film according to any one of claims 1-7;

[0016] The release film is coated onto the substrate film using an anilox roller.

[0017] The ink-absorbing layer is applied onto the release film using a micro-grooved roller.

[0018] An inkjet-printed pattern is formed on the ink-absorbing layer;

[0019] The release film, ink-absorbing layer, and inkjet printed pattern are transferred to the substrate.

[0020] Furthermore, the release film and the substrate film are separated within 0-30 seconds, allowing the release film, ink-absorbing layer, and inkjet printed pattern to be transferred to the substrate.

[0021] Furthermore, the ink-absorbing layer includes an ink-absorbing resin, which includes water-based acrylic and water-based polyurethane.

[0022] The beneficial effects of this invention are:

[0023] The main resins in this application include thermosetting acrylic resin and high-hydroxyl linear polyester resin, and the crosslinking agent includes melamine-formaldehyde resin, which is methyl etherified high-imino melamine diluted with isopropanol. Melamine-formaldehyde resin has a low bridging temperature of 90-170℃, a high acid value of 60-80mgKOH / g, and relatively high reactivity and crosslinking density. The modified polyester resin can capture effective reactive groups, so that the active groups of the entire system are basically completely reacted, and the surface tension of the release film is reduced to less than 36 dynes before the addition of silicone oil and wax. At the same time, the modified polyester resin has very low adhesion to the ink-absorbing layer resin, such as thermoplastic acrylic or polyurethane, producing only temporary low adhesion. In addition, the modified polyester resin has very low peel strength in the tape adhesion and pull test, usually less than 500g / 3CM. Therefore, the main resin provided in this application has very high reactivity and very high crosslinking density, resulting in excellent adhesion to the substrate film. At the same time, it has a dense surface and low surface polarity, which reduces its adhesion to ink-absorbing layer resins, such as waterborne acrylic resin and waterborne polyurethane resin, making it easier to peel off the ink-absorbing layer resin applied later.

[0024] The fillers in this application include silica powder and alumina powder. The combination of the two can create a suitable matte appearance and texture. The coarser powder has a higher matting efficiency and can achieve a certain degree of matteness with a smaller amount. The fine powder has a good sense of delicacy and filling capacity, making the entire matte surface delicate, skin-like and dense.

[0025] The fillers in this application also include silicone oil and wax powder. Silicone oil can reduce the surface polarity of the release film and has a relatively small release force, which can effectively improve the release effect and make the subsequent ink absorption layer easier to peel off. The wax powder melts at high temperature during hot stamping. The melted wax powder gives the release film good release force and ensures smooth peeling over a long period of time, which helps to achieve arbitrary tearing of the release film. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to specific examples:

[0027] Based on the time required for cooling and peeling after hot stamping, the film is categorized into: instant peel, hot peel, warm peel, and cold peel. Hot peel refers to peeling the film after a 0-10 second cooling pause; warm peel refers to peeling the film after a 10-30 second cooling pause; cold peel refers to peeling the film after a 30-second cooling pause; and instant peel refers to peeling the film within a 0-1 second cooling pause.

[0028] To achieve "anytime tear," the release film must be loose at any time after hot stamping. This requires coating the substrate film with a release layer that exhibits low release force across a temperature range of room temperature to 150°C. "Anytime tear" means that the film can be peeled off at any time after hot stamping.

[0029] While achieving arbitrary tearing, it is also necessary to ensure image clarity and preferably maintain a matte finish. Therefore, the release film must be made matte, and the uniformity of matte light absorption must be ensured when tearing the film at different temperatures.

[0030] This application provides a release film for inkjet printing, which achieves consistent release force under different temperature conditions and defines corresponding testing indicators. Specifically, it includes a main resin, a crosslinking agent, and fillers; the main resin includes thermosetting acrylic resin and high-hydroxyl linear polyester resin; the crosslinking agent includes melamine-formaldehyde resin; and the fillers include silica powder, alumina powder, silicone oil, and wax powder.

[0031] In this application, the main function of the main resin is to adhere to the PET substrate film and to serve as the matrix for carrying various functional components. Therefore, the main resin should be selected to have good adhesion to the PET film, be easily miscible with the various functional materials, and not interfere with the performance of the functional materials.

[0032] The main resin can be selected using the following approach:

[0033] ① Select the thermosetting type resin according to the conditions of the coating production equipment, and the thermosetting conditions should meet 90-170℃.

[0034] ② Select resins with strong reactivity and high cross-linking density based on their adhesion to PET films.

[0035] ③ Select a resin with low adhesion to general water-based acrylic resin and water-based polyurethane resin according to the subsequent process of coating the ink-absorbing layer.

[0036] ④ Select the optimal mixing ratio based on the different types and proportions of curing agents.

[0037] Therefore, the main resin range includes: modified polyester resin; melamine-formaldehyde resin; acrylic resin; isocyanate resin; special polyurethane resin; isocyanate resin; epoxy resin; amino resin, etc. Experiments have shown that thermosetting acrylic resin combined with melamine-formaldehyde resin exhibits the best performance and release effect. Therefore, the main resins in this application include thermosetting acrylic resin and high-hydroxyl linear polyester resin, wherein the thermosetting acrylic resin is the main component of the main resin, the high-hydroxyl linear polyester resin is the auxiliary component of the main resin, and the melamine-formaldehyde resin is the crosslinking agent.

[0038] The solid content of the main resin in the total formulation was reduced from 90% to 10%, and a test was conducted for every 5% decrease. A total of 17 sets of data were collected. The experiment showed that the effect was best when the weight of the main resin in the release film was 50-65 parts.

[0039] In this application, the high-hydroxyl polyester resin can capture effective reactive groups, ensuring that the active groups in the entire system react completely. This results in a coating surface tension reduction to less than 36 dynes (before the addition of silicone oil and wax). Consequently, it exhibits very low adhesion to subsequent thermoplastic acrylic or polyurethane coatings, producing only temporary low adhesion. The high-hydroxyl linear polyester resin also exhibits very low peel strength in tape adhesion tests, typically below 500 g / 3 cm. Specifically, the high-hydroxyl linear polyester resin can be selected from TM6080 elastic polyester resin from Tensei Corporation of Japan, with an OH value of 58, a solid content of 82%, and an acid value (relative to solids) ≤2.

[0040] The melamine-formaldehyde resin in this application has a low bridging temperature, specifically 90-170℃, and a high acid value, specifically 60-80 mgKOH / g. Therefore, the melamine-formaldehyde resin has relatively high reactivity and crosslinking density, exhibiting high reactivity and a high tendency for self-condensation.

[0041] In this application, the thermosetting acrylic resin is added in a ratio of 40-50 parts, the high-hydroxyl linear polyester resin in a ratio of 10-15 parts, and the melamine-formaldehyde resin in a ratio of 40-45 parts. This formulation exhibits very high reactivity and very high crosslinking density, resulting in excellent adhesion to the PET substrate film. Simultaneously, it produces a dense surface with low surface polarity, exhibiting low adhesion to general water-based acrylic resins and water-based polyurethane resins. Therefore, it facilitates easy peeling of the subsequent water-based acrylic and water-based polyurethane ink-absorbing layer resins. To achieve these curing conditions and effects, the baking temperature of the release film needs to be increased to 180-190℃, the baking time approximately 20 seconds, and after coating and drying, it should be cured in a 50℃ curing chamber for 48 hours.

[0042] Based on the market demand for a matte finish in traditional offset heat transfer printing, digital inkjet heat transfer films also opt for a matte finish. Therefore, the release layer is designed with a matte surface to replicate the matte effect onto the heat transfer surface. The formation of the matte surface requires filling the release film formula with fillers of different particle sizes, resulting in varying degrees of matteness after drying. In this application, the filler addition ratio is 7-8.6 parts.

[0043] This application employed various fine-particle materials, including organobentonite, diatomaceous earth, talc, kaolin, quartz powder, and alumina powder, in multiple experiments ranging from 0.5µm to 10µm. Ultimately, silica powder with a particle size of 3-4 micrometers was selected, with an addition ratio of 0.5-0.8 parts; and alumina powder with a particle size of 50-100 nanometers was selected, also with an addition ratio of 0.5-0.8 parts. Their function is to create a suitable matte finish. Coarser particles have higher matting efficiency, achieving a certain level of matteness with a smaller amount, while finer particles provide excellent smoothness and filling power, resulting in a delicate, skin-like, and dense matte surface. Finally, silica and alumina powders were optimally combined with existing suitable fineness and proportions to achieve a uniform and consistent matte effect.

[0044] Digital inkjet heat transfer film is ultimately used to transfer images onto clothing or fabric. Therefore, the printed image must be peelable from the PET substrate film, and the peeling force must be very low to ensure that fine lines and small fonts can be completely detached from the transfer. Achieving a "tear-on-demand" effect means that the release liner must be loose at any time after heat transfer. This requires coating the PET film with a peelable release layer that exhibits low release force within a temperature range of 150℃ to room temperature.

[0045] Generally, two materials are easily separated due to two main reasons: low surface polarity and low cohesiveness, leading to easy breakage. Low surface polarity alone makes subsequent coating processes difficult; conversely, easily breakable surfaces make it difficult to ensure consistent separation force under different temperature conditions. Therefore, this application combines reducing material surface polarity and reducing material cohesiveness, utilizing their synergistic effect to reduce the release force of the release film.

[0046] Specifically, this application selects silicone oil as a material to reduce surface polarity. After testing different types of silicone oils, such as methyl silicone oil, ethyl silicone oil, methyl hydroxy silicone oil, epoxy modified silicone oil, and amino modified silicone oil, and comparing the proportion of silicone oil in the total content from 5%, 10%, 15%, 20%, 25%, and 30%, amino modified silicone oil was finally selected as the preferred material. Silicone oil can effectively improve the release effect, making the subsequent ink absorption layer easy to peel off. After adding silicone oil, the release force of the release film is very small. However, if the amount of silicone oil added is too high, the surface polarity of the release film will be too low, which will cause pinholes in the subsequent ink absorption layer coating process. Therefore, this application limits the addition ratio of amino modified silicone oil to 6-8 parts.

[0047] This application selects wax powder as the easily breakable material. During hot stamping, the high temperature melts the wax, creating a very light release force, ensuring smooth peeling over a long period. Various waxes were tested, including PE wax, polyamide wax, Mondan wax, PP wax, and carnauba wax. Ultimately, paraffin wax and a special modified low-melting-point PE wax were selected as the optimal choices. The paraffin wax and modified low-melting-point PE wax were added at a ratio of 3-4 parts each. The presence of these wax powders makes easy peeling a reality. The modified low-melting-point PE wax refers to PE wax produced by wax powder manufacturers through melting, refining, and grinding various types of wax into refined wax powder, maintaining its melting point at 80-90℃.

[0048] Therefore, this application provides a release film for inkjet printing, comprising the following components in parts by weight: 40-50 parts of thermosetting acrylic resin, 10-15 parts of high-hydroxyl linear polyester resin, 40-50 parts of melamine-formaldehyde resin, 0.5-0.8 parts of silica powder with a particle size of 3-4 micrometers, 0.5-0.8 parts of alumina powder with a particle size of 50-100 nanometers, 6-8 parts of amino-modified silicone oil, 3-4 parts of paraffin wax, and 3-4 parts of modified low-melting-point PE wax.

[0049] This application also provides an inkjet printing method, including:

[0050] S1: Stir and mix the main resin and crosslinking agent, and add filler during the stirring and mixing process to prepare a release film as described above;

[0051] Specifically, the main resin and crosslinking agent are first mixed at high speed for 15 minutes. Then, fillers such as silica powder, alumina powder, silicone oil and wax powder are slowly added while stirring. Finally, the mixture is stirred at high speed for 30 minutes until homogeneous. After filtration through a 200-mesh filter, it is ready for use.

[0052] S2: The release film is coated onto the substrate film using an anilox roller.

[0053] Specifically, the release material is coated using an 180-mesh anilox roller, and the drying section temperature is set as follows: 80℃, 120℃, 150℃, 190℃, 190℃, 180℃, 150℃, 120℃, with a baking time of approximately 30 seconds; 75μm x 1220mm PET is used as the substrate for the process.

[0054] Apply the prepared coating to the machine using a 180-mesh anilox roller to coat the release film, with a coating amount of 1-1.5 grams per square meter.

[0055] S3: Apply the ink-absorbing layer onto the release film using a micro-grooved roller. Specifically, after applying the release film, apply the water-based acrylic resin and water-based polyurethane resin ink-absorbing layer using a micro-grooved roller. The coating should have a uniform and delicate appearance, free from defects such as mesh spots, pinholes, runs, and transverse zebra stripes. The dry coating amount is 2-3 grams per square meter.

[0056] S4: Form an inkjet printed pattern on the ink-absorbing layer;

[0057] S5: Transfer the release film, ink-absorbing layer, and inkjet printed pattern to the substrate.

[0058] During the transfer process, this application can achieve any tearing effect, such as instant tearing, hot tearing, warm tearing, and cold tearing. The hot stamping peeling effect meets the smoothness requirements of a series of peeling methods, such as instant tearing, hot tearing, warm tearing, and cold tearing. After peeling, the surface gloss test meets the range of 2-8 degrees of matte finish.

[0059] Example 1

[0060] This application provides a release film for inkjet printing, specifically comprising a main resin, a crosslinking agent, and fillers; specifically comprising the following components in parts by weight: 40-50 parts of thermosetting acrylic resin, 10-15 parts of high-hydroxyl linear polyester resin, 40-50 parts of melamine-formaldehyde resin, 0.5-0.8 parts of silica powder with a particle size of 3-4 micrometers, 0.5-0.8 parts of alumina powder with a particle size of 50-100 nanometers, 6-8 parts of amino-modified silicone oil, 3-4 parts of paraffin wax, and 3-4 parts of modified low-melting-point PE wax.

[0061] This embodiment also provides an inkjet printing method, including:

[0062] S1: Mix the main resin and crosslinking agent at high speed for 15 minutes. Then, slowly add fillers such as silica powder, alumina powder, silicone oil and wax powder while stirring. Finally, stir at high speed for 30 minutes until the mixture is homogeneous. Filter the mixture through a 200-mesh screen and set aside for later use.

[0063] S2: Apply release material using an 180-mesh anilox roller. Drying section temperature settings: 80℃, 120℃, 150℃, 190℃, 190℃, 180℃, 150℃, 120℃. Baking time is approximately 30 seconds. Use 75μm x 1220mm PET as the substrate.

[0064] Using the prepared coating material, apply the release film to the PET substrate film using a 180-mesh anilox roller, with a coating amount of 1-1.5 grams per square meter.

[0065] S3: After applying the release film, use a micro-grooved roller to apply the water-based acrylic resin and water-based polyurethane resin ink-absorbing layer. The coating should be uniform and delicate, without defects such as mesh points, pinholes, runs, or transverse zebra stripes. The dry coating amount is 2-3 grams per square meter.

[0066] S4: Form an inkjet printed pattern on the ink-absorbing layer;

[0067] S5: Transfer the release film, ink-absorbing layer, and inkjet printed pattern to the substrate.

[0068] The test sample used a full-page solid print pattern with hot melt adhesive powder of 100-250μm particle size. After melting at 130℃, the adhesive-coated transfer film was heat-pressed onto pure cotton fabric at 150℃ for 10 seconds, and then a peel tensile test was performed. After the heat-pressed transfer film was peeled off, the surface gloss of the black and white blocks was tested with a gloss meter (60° angle). The test results are shown in Table 1.

[0069] Table 1. Test data of release film after arbitrary tearing in Example 1.

[0070]

[0071] Conclusions: 1. At any time interval after hot stamping, the release force is <20 g / 3 cm; 2. The surface gloss after peeling is within the range of 2-8. This indicates that the transfer process of this application can achieve any peeling effect, including instant peeling, hot peeling, warm peeling, and cold peeling, and the hot stamping peeling effect meets the smoothness requirements of the series of peeling methods such as instant peeling, hot peeling, warm peeling, and cold peeling. The surface gloss test after peeling is within the range of 2-8 degrees of matte finish.

[0072] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A release film for inkjet printing, characterized by, The product comprises a main resin, a crosslinking agent, and fillers. The main resin includes thermosetting acrylic resin and high-hydroxyl linear polyester resin; the crosslinking agent includes melamine-formaldehyde resin; the fillers include silica powder, alumina powder, silicone oil, and wax powder. Specifically, it comprises the following components in parts by weight: 40-50 parts thermosetting acrylic resin, 10-15 parts high-hydroxyl linear polyester resin; 40-50 parts melamine-formaldehyde resin, 0.5-0.8 parts silica powder, 0.5-0.8 parts alumina powder, 6-8 parts silicone oil, and 6-8 parts wax powder. The silica powder is silica powder with a particle size of 3-4 micrometers; the alumina powder is alumina powder with a particle size of 50-100 nanometers; the silicone oil is amino-modified silicone oil; the wax powder comprises paraffin wax and modified low-melting-point PE wax, with a weight ratio of paraffin wax to modified low-melting-point PE wax of 1:

1. The high-hydroxyl linear polyester resin has a peel strength of less than 500 g / 3 cm in the tape adhesion and pull test; the high-hydroxyl linear polyester resin has an OH value of 58, a solid content of 82%, and an acid value of ≤2; the bridging temperature of the melamine-formaldehyde resin is 90-170℃, and the acid value of the melamine-formaldehyde resin is 60-80 mgKOH / g. During the formation of the release film, the baking temperature of the release film needs to be increased to 180-190℃, the baking time is 20 seconds, and after coating and drying, it is placed in a 50℃ curing chamber for 48 hours to mature.

2. An inkjet printing method, characterized by, include: The main resin and crosslinking agent are stirred and mixed, and filler is added during the stirring and mixing process to prepare the release film as described in claim 1; The release film is coated onto the substrate film using an anilox roller. The ink-absorbing layer is applied onto the release film using a micro-grooved roller. An inkjet-printed pattern is formed on the ink-absorbing layer; The release film, ink-absorbing layer, and inkjet printed pattern are transferred to the substrate.

3. The inkjet printing method according to claim 2, characterized by, The release film and the substrate film separate within 0-30 seconds, allowing the release film, ink-absorbing layer, and inkjet printed pattern to be transferred to the substrate.

4. The inkjet printing method according to claim 2, wherein The ink-absorbing layer includes an ink-absorbing resin, which includes water-based acrylic resin and water-based polyurethane resin.

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