Invisible magnetic stripe and preparation method and application thereof

Abstract

The invention relates to the technical field of magnetic stripes, and particularly discloses an invisible magnetic stripe and a preparation method and application thereof. The invisible magnetic stripe sequentially comprises a tape base, a release layer, a magnetic layer and an adhesive layer from bottom to top, and specifically limits resin used in the release layer and the magnetic layer and the dosage ratio of the resin. According to the method, specific resin is selected, the dosage proportional relation of the specific resin is determined, the arrangement structure of the invisible magnetic strip is limited, the phenomenon that the invisible magnetic strip is prone to curling due to uneven interlayer stress can be avoided, stress can be dispersed during embossed printing, coating cracking is prevented, and the prepared invisible magnetic strip is appropriate in release force, easy to strip and high in electromagnetic signal continuity.

Description

Technical Field

[0001] This invention relates to the field of magnetic strip technology, and in particular to an invisible magnetic strip, its preparation method, and its application. Background Technology

[0002] Currently, invisible magnetic stripe card technology is widely used. The preparation of invisible magnetic stripe cards involves laminating a magnetic stripe onto a PVC card base, then screen printing silver and white cover layers on the surface of the magnetic stripe, and finally printing the pattern designed for the magnetic card on the white cover layer, which increases the practicality and anti-counterfeiting features of the magnetic card.

[0003] Conventional invisible magnetic stripe card manufacturing processes typically require thick silver and white overlay layers to cover the color difference between the magnetic stripe and the card body's edge, which increases the interval loss of electromagnetic output signals to some extent. To eliminate this color difference, the magnetic stripe width needs to be increased to completely cover the card body. This manufacturing process eliminates the color difference between the magnetic stripe edge and the card body, effectively reducing the printing thickness of the silver and white overlay layers and further minimizing the interval loss of electromagnetic output signals. However, researchers have found that existing wide invisible magnetic stripes also have other problems, such as excessive curling of the stripe, which greatly reduces card manufacturing efficiency, and coating cracking at the embossed lettering locations during later printing. Therefore, providing an invisible magnetic stripe that effectively reduces the interval loss of electromagnetic output signals, solves the problem of easy curling of the magnetic stripe itself, and addresses the cracking problem of the embossed lettering coating is of great significance. Summary of the Invention

[0004] In view of this, the present invention provides an invisible magnetic strip, its preparation method and application.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: This invention provides an invisible magnetic strip, which, from bottom to top, comprises a base, a release layer, a magnetic layer, and an adhesive layer; The release layer comprises a first resin and a second resin in a mass ratio of (8~14):1; The magnetic layer comprises a third resin and a fourth resin in a mass ratio of (1~4):1; The first resin includes at least one of acrylic resin or vinyl chloride resin; The second resin includes at least one of fluorine-modified acrylic resin, silicone-modified acrylic resin, or polyester resin; The third resin includes at least one of polyester resin or polyurethane resin; The fourth resin includes at least one of aldehyde-ketone resin or chlorinated vinyl resin.

[0006] Compared to existing technologies, the invisible magnetic strip provided by this invention, by limiting the specific resins in the release layer and the proportions between the resins, can ensure appropriate release force between layers and improve interlayer flexibility through synergistic effects. This invention further limits the specific resins in the magnetic layer and the proportions between the resins. Through synergistic effects, the components can promote the uniform dispersion of magnetic particles to enhance the continuity of electromagnetic signals and reduce gap loss, and can also improve the bending resistance of the magnetic layer through the complementary toughness between the resins.

[0007] The invisible magnetic strip provided by this invention, by selecting specific resins and determining their proportions, as well as defining the arrangement structure of the release layer, magnetic layer and adhesive layer, can not only avoid the phenomenon of invisible magnetic strips easily curling due to uneven interlayer stress, but also disperse stress during embossed printing to prevent coating cracking. Furthermore, the resulting invisible magnetic strip has appropriate release force, is easy to peel off, and has strong electromagnetic signal continuity.

[0008] During the experiment, the inventors discovered that when the ratio of the first resin to the second resin is too small, the release force of the release layer and the magnetic layer is too small, which will cause the magnetic layer and the release layer to peel off; when the ratio of the first resin to the second resin is too large, the release force of the release layer and the magnetic layer is too large, which will lead to the problem that the base layer and the release layer are not easy to peel off from the magnetic layer or the base layer is broken off.

[0009] When the ratio of the third and fourth resins is too small, the invisible magnetic strip will curl up, have poor flatness, and the embossed characters will easily crack. When the ratio of the third and fourth resins is too large, the slurry will not disperse well, resulting in the magnetic and electromagnetic output characteristics of the invisible magnetic strip being unqualified.

[0010] Preferably, the release layer comprises the following raw material components in parts by weight: 120-145 parts of first resin, 10-20 parts of second resin, 45-60 parts of filler, 5-10 parts of first curing agent, and 300-500 parts of first solvent.

[0011] Preferably, the magnetic layer comprises the following raw material components in parts by weight: 8-16 parts of third resin, 4-8 parts of fourth resin, 160-180 parts of magnetic powder, 1-2 parts of additives, 1-2 parts of second curing agent, and 150-200 parts of second solvent.

[0012] This invention further defines the specific composition of the release layer and the magnetic layer, which is beneficial to further improving the performance of the invisible magnetic strip.

[0013] More preferably, the mass ratio of the first resin to the second resin is (10~12):1.

[0014] More preferably, the mass ratio of the third resin to the fourth resin is (2~3):1.

[0015] The present invention further limits the ratio of the first resin and the second resin, as well as the ratio of the third resin and the fourth resin, so that the resulting invisible magnetic strip has appropriate release force, good edge adhesion, excellent electromagnetic output characteristics and printing characteristics, and the raised characters are not easy to crack.

[0016] More preferably, the first resin includes at least one of the following: DS-2050 solvent-based hydroxyl polyol acrylic resin from Smaio Chemical Technology (Nantong) Co., Ltd., ACR6580 acrylic resin from Guangdong Dieson Tongde Resin Co., Ltd., or TP-500A ternary chloroacetic acid resin from Hanwha Chemical (Ningbo) Co., Ltd.

[0017] More preferably, the second resin includes at least one of the following: LRF6758 fluorine-modified polyester acrylic polyol resin from Xiamen Aikema Chemical Co., Ltd., 024 organosilicon-modified acrylic resin from Shenzhen Jipeng Silicon Fluorine Materials Co., Ltd., or SM1046 organosilicon-modified polyester resin from Sanmu Group.

[0018] Preferably, the filler comprises at least one of fumed silica or titanium dioxide.

[0019] Specifically, the particle size of the fumed silica is 25 μm, and the particle size of the titanium dioxide is 35 μm.

[0020] The selected filler can improve the slipperiness and separation effect between layers, while enhancing the structural stability of the release layer.

[0021] Preferably, the first curing agent includes at least one of solvent-based isocyanate curing agents or amine curing agents.

[0022] By further defining the specific composition of the first curing agent, it is beneficial to improve the adhesion of the release layer to the substrate.

[0023] More preferably, the first curing agent includes at least one of triethanolamine or IPDI curing agent.

[0024] Preferably, the first solvent includes at least one of toluene or butanone.

[0025] More preferably, the mass ratio of toluene to butanone is 2:3.

[0026] Preferably, the thickness of the release layer is 1~4µm.

[0027] This invention limits the thickness of the release layer. When the thickness is too large, it will cause material waste; when the thickness is too small, it will result in poor release effect.

[0028] More preferably, the thickness of the release layer is 2~3µm.

[0029] Preferably, the third resin includes at least one of Hongda Polyurethane HD-325TB or Hanhai Polyester AL098M.

[0030] Preferably, the fourth resin includes at least one of TP-500A ternary chloroacetic acid resin from Hanwha Chemical (Ningbo) Co., Ltd. or aldehyde-ketone resin A81 from Greenlink (Jining) Chemical Technology Co., Ltd.

[0031] Preferably, the magnetic powder includes at least one of the following: magnetic powder 2750H from Tangyin Zhongke or magnetic powder RY-620B from Anhui Jiulian.

[0032] Preferably, the additive includes at least one of carbon black, phosphate ester or organosilicon leveling agent.

[0033] Preferably, the second curing agent includes at least one of solvent-based isocyanate curing agents or amine curing agents.

[0034] More preferably, the second curing agent includes at least one of triethanolamine or IPDI curing agent.

[0035] Preferably, the second solvent includes at least one of toluene or butanone.

[0036] More preferably, the mass ratio of toluene to butanone is 2:3.

[0037] Preferably, the thickness of the magnetic layer is 13~20µm.

[0038] More preferably, the thickness of the magnetic layer is 15~18µm.

[0039] Preferably, the substrate includes any one of PVC, PC or PET.

[0040] More preferably, the substrate is PET.

[0041] For example, the adhesive layer provided by the present invention comprises the following raw material components in parts by weight: 45 parts of chloroacetic acid resin, 60 parts of polyester resin, 15 parts of silica, 5 parts of silane coupling agent and 400 parts of solvent.

[0042] This invention provides a method for preparing the above-mentioned invisible magnetic strip, comprising the following steps: S1. Disperse the first resin, the second resin, the filler and the first solvent evenly, and then add the first curing agent to obtain the release layer slurry; S2. Mix the third resin, fourth resin, magnetic powder, additives and second solvent evenly, and then add the second curing agent to obtain magnetic layer slurry; S3. Sequentially apply the release layer paste, magnetic layer paste, and adhesive layer paste to the substrate, and dry to obtain an invisible magnetic strip.

[0043] The method for preparing invisible magnetic strips provided by this invention is simple in steps, convenient in operation, and suitable for large-scale production. Furthermore, the separate preparation of each layer of slurry ensures that the raw material components are fully and evenly dispersed, guaranteeing the performance stability of the release layer and magnetic layer. The sequential coating in layers allows for precise control of the thickness and adhesion effect of each layer. Through synergistic effects, the layers further consolidate the advantages of invisible magnetic strips in resisting curling, preventing cracking of the embossed printing coating, and reducing electromagnetic signal interval loss.

[0044] It should be further noted that in S1 and S2, before adding the first curing agent and the second curing agent respectively, the uniformly mixed materials need to be dispersed by sand milling using a basket mill or a horizontal mill. The conditions for sand milling and dispersion are no longer further limited, and can be operated according to the conventional technical means mastered by those skilled in the art.

[0045] Preferably, in S3, the coating can be bar coating, gravure coating, extrusion coating, or reverse roller coating.

[0046] This invention provides the application of the above-mentioned invisible magnetic stripe in the preparation of invisible magnetic cards.

[0047] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention further reduces the interval loss of electromagnetic output signals by reducing the printing thickness of the masking layer; (2) The invisible magnetic strip provided by the present invention is flat and flexible. After being made into an invisible magnetic card, the embossed printing does not crack due to the coating. (3) The invisible magnetic strip provided by the present invention has excellent electromagnetic output characteristics. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the invisible magnetic strip provided in Example 1; 1 is the base layer, 2 is the release layer, 3 is the magnetic layer, and 4 is the adhesive layer. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0050] Unless otherwise specified, the raw materials and reagents used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0051] The adhesive layer provided in the embodiments and comparative examples of the present invention comprises the following raw material components in parts by weight: 45 parts of chloroacetic acid resin LVC-450 from Tianjin Bohong Resin Technology Co., Ltd., 60 parts of polyester resin PA-198 from Suzhou Jianxing Chemical Technology Co., Ltd., 15 parts of silica, 5 parts of silane coupling agent GX-D300 from Anhui Sibao Organosilicon New Materials Co., Ltd., and 400 parts of solvent; the solvent comprises a mixture of toluene and methyl ethyl ketone in a mass ratio of 2:3. The preparation method of the adhesive layer slurry includes the following steps: The weighed components are added to the high-speed dispersion tank in sequence and mixed evenly. The mixed slurry is then dispersed by a 15L horizontal sand mill for later use.

[0052] Example 1 This embodiment provides an invisible magnetic strip, which includes, in sequence, a base, a release layer, a magnetic layer, and an adhesive layer; The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 120 parts of solvent-based hydroxyl polyol acrylic resin DS-2050, 15 parts of fluorine-modified polyester acrylic polyol resin LRF6758, 45 parts of fumed silica, 5 parts of triethanolamine, and 300 parts of the first solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the first solvent is 2:3. The magnetic layer comprises the following raw material components in parts by weight: 8 parts of Hongda Polyurethane HD-325TB, 5 parts of TP-500A ternary chloroform resin, 180 parts of magnetic powder 2750H from Tangyin Zhongke, 1 part of carbon black, 1 part of phosphate ester, 1 part of triethanolamine, and 200 parts of a second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This embodiment provides a method for preparing the above-mentioned invisible magnetic strip, including the following steps: S1. Mix the other raw material components in the release layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the release layer slurry; S2. Mix the other raw material components in the magnetic layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 1µm, the thickness of the magnetic layer is 16µm, and the thickness of the adhesive layer is 3.5µm.

[0053] Example 2 This embodiment provides an invisible magnetic strip, which includes, in sequence, a base, a release layer, a magnetic layer, and an adhesive layer; The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 145 parts of acrylic resin ACR6580, 12 parts of silicone-modified acrylic resin 024, 60 parts of fumed silica, 10 parts of IPDI curing agent, and 500 parts of the first solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the first solvent is 2:3. The magnetic layer comprises the following raw material components in parts by weight: 16 parts of Hongda Polyurethane HD-325TB, 8 parts of TP-500A ternary vinyl chloride resin, 160 parts of Anhui Jiulian magnetic powder RY-620B, 0.5 parts of BYK 306 leveling agent, 0.5 parts of phosphate ester, 2 parts of IPDI curing agent, and 150 parts of a second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This embodiment provides a method for preparing the above-mentioned invisible magnetic strip, including the following steps: S1. Mix the other raw material components in the release layer except for the IPDI curing agent, disperse them evenly using a horizontal sand mill, and then add the IPDI curing agent to obtain the release layer slurry; S2. Mix the other raw material components in the magnetic layer except for the IPDI curing agent, disperse them evenly using a horizontal sand mill, and then add the IPDI curing agent to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 2.5µm, the thickness of the magnetic layer is 18µm, and the thickness of the adhesive layer is 3µm.

[0054] Example 3 This embodiment provides an invisible magnetic strip, which includes, in sequence, a base, a release layer, a magnetic layer, and an adhesive layer; The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 140 parts of TP-500A ternary chloroacetic acid resin, 10 parts of silicone-modified polyester resin SM1046, 50 parts of fumed silica, 8 parts of IPDI curing agent, and 400 parts of the first solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the first solvent is 2:3. The magnetic layer comprises the following raw material components in parts by weight: 14 parts of Hanhai polyester AL098M, 4 parts of TP-500A ternary vinyl chloride resin, 170 parts of Anhui Jiulian magnetic powder RY-620B, 1.5 parts of phosphate ester, 2 parts of IPDI curing agent, and 170 parts of the second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This embodiment provides a method for preparing the above-mentioned invisible magnetic strip, including the following steps: S1. Mix the other raw material components in the release layer except for the IPDI curing agent, disperse them evenly using a horizontal sand mill, and then add the IPDI curing agent to obtain the release layer slurry; S2. Mix the other raw material components in the magnetic layer except for the IPDI curing agent, disperse them evenly using a horizontal sand mill, and then add the IPDI curing agent to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 3.5µm, the thickness of the magnetic layer is 20µm, and the thickness of the adhesive layer is 3.5µm.

[0055] Comparative Example 1 This comparative example provides an invisible magnetic strip, which differs from Example 1 in that the ratio of the first resin to the second resin is 7:1, and the ratio of the third resin to the fourth resin is 0.8:1, as detailed below: The invisible magnetic strip consists of a base, a release layer, a magnetic layer, and an adhesive layer. The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 105 parts of solvent-based hydroxyl polyol acrylic resin DS-2050, 15 parts of fluorine-modified polyester acrylic polyol resin LRF6758, 45 parts of fumed silica, 5 parts of triethanolamine, and 300 parts of the first solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the first solvent is 2:3. The magnetic layer comprises the following raw material components in parts by weight: 4 parts of Hongda Polyurethane HD-325TB, 5 parts of TP-500A ternary chloroform resin, 180 parts of magnetic powder 2750H from Tangyin Zhongke, 1 part of carbon black, 1 part of phosphate ester, 1 part of triethanolamine, and 200 parts of a second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This comparative example provides a method for preparing the aforementioned invisible magnetic strip, comprising the following steps: S1. Mix the other raw material components in the release layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the release layer slurry; S2. Mix the other raw material components in the magnetic layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 1µm, the thickness of the magnetic layer is 16µm, and the thickness of the adhesive layer is 3.5µm.

[0056] Comparative Example 2 This comparative example provides an invisible magnetic strip, which differs from Example 1 in that the ratio of the first resin to the second resin is 15:1, and the ratio of the third resin to the fourth resin is 5:1, as detailed below: The invisible magnetic strip consists of a base, a release layer, a magnetic layer, and an adhesive layer. The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 120 parts of solvent-based hydroxyl polyol acrylic resin DS-2050, 8 parts of fluorine-modified polyester acrylic polyol resin LRF6758, 45 parts of fumed silica, 5 parts of triethanolamine, and 300 parts of the first solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the first solvent is 2:3. The magnetic layer comprises the following raw material components in parts by weight: 8 parts of Hongda Polyurethane HD-325TB, 1.6 parts of TP-500A ternary vinyl chloride resin, 180 parts of magnetic powder 2750H from Tangyin Zhongke, 1 part of carbon black, 1 part of phosphate ester, 1 part of triethanolamine, and 200 parts of a second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This comparative example provides a method for preparing the aforementioned invisible magnetic strip, comprising the following steps: S1. Mix the other raw material components in the release layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the release layer slurry; S2. Mix the other raw material components in the magnetic layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 1µm, the thickness of the magnetic layer is 16µm, and the thickness of the adhesive layer is 3.5µm.

[0057] Comparative Example 3 This comparative example provides a magnetic strip, which sequentially includes a base, a release layer, a UV layer, a magnetic layer, and an adhesive layer; The components with the same base are the same as in Example 1; The release layer comprises the following raw material components in parts by weight: 50 parts of Evonik SILIKOFTAL silicone polyester resin HTFMPA / MBA, 5 parts of polyester resin L411, 3 parts of dibutyltin dilaurate, 5 parts of HDI curing agent, 2 parts of BYK-310 leveling agent, and 20 parts of methyl ethyl ketone (MEK). The UV layer comprises the following raw material components in parts by weight: 30 parts of aliphatic polyurethane methacrylate GENOMER 420, 25 parts of CR93856 hexafunctional polyurethane acrylate resin, 5 parts of XMT-3124 waterborne polyurethane resin, 20 parts of Changxing pentaerythritol triacrylate EM235, 8 parts of initiator 184, 6 parts of PTFE wear-resistant filler from Nanjing Tianshi New Material Technology Co., Ltd., 2 parts of BYK-310 leveling agent, and 40 parts of methyl ethyl ketone (MEK). The composition of the magnetic layer is the same as in Example 1; This comparative example provides a method for preparing the aforementioned invisible magnetic strip, comprising the following steps: S1. Mix the other raw material components in the release layer except for the HDI curing agent, test its solid content to be in the range of 15%~20%, then add the HDI curing agent and stir evenly to obtain the release layer slurry. S2. Mix the other raw material components in the UV layer except for PTFE wear-resistant filler and initiator 184, then add PTFE wear-resistant filler and disperse at high speed for 30 minutes. After sand milling 3 times, the solid content is in the range of 15%~20%. After passing the test, add initiator 184 and stir for 15 minutes to obtain magnetic layer slurry. S3. The preparation method of the magnetic layer slurry is the same as in Example 1; The other raw material components in the magnetic layer, except for triethanolamine, are mixed and dispersed evenly using a horizontal sand mill. Then, triethanolamine is added to obtain the magnetic layer slurry. S3. Apply release layer slurry to the substrate in sequence using a rod coating method. After drying and curing, apply UV layer slurry using an anilox roller coating method. After drying and curing, apply magnetic layer and adhesive layer using a reverse roller coating method to obtain invisible magnetic strip. The thickness of the substrate is 20µm, the thickness of the release layer is 0.8µm, the thickness of the UV layer is 2µm, the thickness of the magnetic layer is 16µm, and the thickness of the adhesive layer is 3.5µm.

[0058] Comparative Example 4 This comparative example provides an invisible magnetic strip, which differs from Example 1 in that the release layer of Example 1 is replaced with the release layer of Comparative Example 3, as detailed below: The tape base is PET tape base; The release layer comprises the following raw material components in parts by weight: 50 parts of Evonik SILIKOFTAL silicone polyester resin HTFMPA / MBA, 5 parts of polyester resin L411, 3 parts of dibutyltin dilaurate, 5 parts of HDI curing agent, 2 parts of BYK-310 leveling agent, and 20 parts of methyl ethyl ketone (MEK). The magnetic layer comprises the following raw material components in parts by weight: 8 parts of Hongda Polyurethane HD-325TB, 5 parts of TP-500A ternary chloroform resin, 180 parts of magnetic powder 2750H from Tangyin Zhongke, 1 part of carbon black, 1 part of phosphate ester, 1 part of triethanolamine, and 200 parts of a second solvent; wherein the mass ratio of toluene to methyl ethyl ketone in the second solvent is 2:3. This comparative example provides a method for preparing the aforementioned invisible magnetic strip, comprising the following steps: S1. Mix the other raw material components in the release layer except for the HDI curing agent, test its solid content to be 15%~20%, then add the HDI curing agent and stir evenly to obtain the release layer slurry. S2. Mix the other raw material components in the magnetic layer except for triethanolamine, disperse them evenly using a horizontal sand mill, and then add triethanolamine to obtain the magnetic layer slurry; S3. Apply release layer paste, magnetic layer paste and adhesive layer paste to the substrate in sequence by rod coating, and dry to obtain invisible magnetic strip; The thickness of the substrate is 20µm, the thickness of the release layer is 1µm, the thickness of the magnetic layer is 16µm, and the thickness of the adhesive layer is 3.5µm.

[0059] Application examples The performance of the magnetic strips obtained in Examples 1-3 and Comparative Examples 1-4 of this invention was tested, and the specific testing standards are as follows: 1. Rectangularity (magnetic properties) test method: The ratio of the residual magnetization to the saturation magnetization of a magnetic stripe was measured using a ferromagnetic instrument.

[0060] 2. Edge warping (curling) test method: Cut the magnetic strip into 40cm*40cm sheets, lay them flat on the table, and use a steel ruler to test the maximum warping of the edge of the strip.

[0061] 3. Release force test method: The magnetic stripe was hot-pressed onto the PVC card base using a magnetic card laminator (temperature 130℃, pressure 2.5MPa, the same below), then cut into 12.7mm wide strips. A self-made release force tester was used to test the force at which the PET stripe peeled off from the PVC card body.

[0062] 4. Printing characteristic test methods: The magnetic stripe is hot-pressed onto the PVC card base. After peeling off the PET tape base, silver ink, white ink, and pattern printing are applied to the surface of the magnetic stripe. The pattern is uniform, has good coverage, and excellent adhesion to be considered qualified.

[0063] 5. Electromagnetic output characteristic test method: Tested using a Qcard magnetic stripe analyzer according to ISO 7811-6 standard.

[0064] 6. Embossed lettering printing test method: Press the magnetic stripe onto the PVC card base with heat. After peeling off the PET strip, print the numbers 1 to 9 from the back of the PVC card using an embossing printer. Then, observe the embossed areas for any cracks in the coating.

[0065] The test results are shown in Table 1: Table 1

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An invisible magnetic strip, characterized in that, From bottom to top, it includes a base layer, a release layer, a magnetic layer, and an adhesive layer; The release layer comprises a first resin and a second resin in a mass ratio of (8~14):1; The magnetic layer comprises a third resin and a fourth resin in a mass ratio of (1~4):1; The first resin includes at least one of acrylic resin or vinyl chloride resin; The second resin includes at least one of fluorine-modified acrylic resin, silicone-modified acrylic resin, or polyester resin; The third resin includes at least one of polyester resin or polyurethane resin; The fourth resin includes at least one of aldehyde-ketone resin or chlorinated vinyl resin.

2. The invisible magnetic strip as described in claim 1, characterized in that, The release layer comprises the following raw material components in parts by weight: 120-145 parts of first resin, 10-20 parts of second resin, 45-60 parts of filler, 5-10 parts of first curing agent, and 300-500 parts of first solvent. The magnetic layer comprises the following raw material components in parts by weight: 8-16 parts of third resin, 4-8 parts of fourth resin, 160-180 parts of magnetic powder, 1-2 parts of additives, 1-2 parts of second curing agent, and 150-200 parts of second solvent.

3. The invisible magnetic strip as described in claim 1 or 2, characterized in that, The filler includes at least one of fumed silica or titanium dioxide; The first curing agent includes at least one of solvent-based isocyanate curing agents or amine curing agents; The first solvent includes at least one of toluene or butanone.

4. The invisible magnetic strip as described in claim 2, characterized in that, The additives include at least one of carbon black, phosphate ester or organosilicon leveling agent; The second curing agent includes at least one of solvent-based isocyanate curing agents or amine curing agents; The second solvent includes at least one of toluene or butanone.

5. The invisible magnetic strip as described in claim 2, characterized in that, The thickness of the release layer is 1~4µm.

6. The invisible magnetic strip as described in claim 5, characterized in that, The thickness of the release layer is 2~3µm.

7. The invisible magnetic strip as described in claim 2, characterized in that, The thickness of the magnetic layer is 13~20µm.

8. The invisible magnetic strip as described in claim 7, characterized in that, The thickness of the magnetic layer is 15~18µm.

9. A method for preparing an invisible magnetic strip according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Disperse the first resin, the second resin, the filler and the first solvent evenly, and then add the first curing agent to obtain the release layer slurry; S2. Mix the third resin, fourth resin, magnetic powder, additives and second solvent evenly, and then add the second curing agent to obtain magnetic layer slurry; S3. Sequentially apply the release layer paste, magnetic layer paste, and adhesive layer paste to the substrate, and dry to obtain an invisible magnetic strip.

10. The use of the invisible magnetic stripe according to any one of claims 1 to 8 in the preparation of invisible magnetic cards.

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