Coating for glass-based fingerprint sensor, preparation method and fingerprint sensor

Abstract

The invention discloses a coating for a glass-based fingerprint sensor, a preparation method of the coating and the fingerprint sensor, the coating comprises a primer layer and a finish paint layer, the finish paint layer is prepared from the following raw materials in parts by mass: 100 parts of polyurethane acrylate coating and 0.01-2 parts of conductive material, the polyurethane acrylate coating comprises 70 to 90 parts of polyurethane acrylate, 0.1 to 5 parts of siloxane, 2 to 8 parts of an initiator, 10 to 15 parts of a first curing agent and 80 to 105 parts of an auxiliary agent. The coating provided by the invention has antistatic performance, so that the surface of the glass-based fingerprint sensor is in an insulated state, the material surface after electrostatic discharge does not generate breakdown traces, the fingerprint acquisition process of the glass-based fingerprint sensor is not influenced, and the fingerprint unlocking rate is high.

Description

Technical Field

[0001] The present invention relates to the technical field of functional coatings, and in particular to a coating for a glass-based fingerprint sensor, a preparation method thereof, and a fingerprint sensor. Background Art

[0002] Electrostatic discharge (ESD) is increasingly causing interference in circuits, and damaging components, circuits, and interface circuits. Mobile phones are becoming increasingly powerful, while circuit boards are becoming smaller and more integrated. This makes them more sensitive to ESD and more susceptible to damage from static electricity. Furthermore, the dry weather in northern China can easily cause static electricity to breakdown in mobile phone circuits, leading to sudden damage to poorly designed phones. During mobile phone development, ESD-induced failures are common, such as silent speakers, blank or black LCD screens, screen flickering, and system freezes and restarts. ESD poses a serious threat to electronic devices. The main damage mechanisms include two: thermal failure caused by heat generated by the ESD current, and insulation breakdown caused by excessive voltage induced by ESD. Both types of damage can occur simultaneously within a single device. For example, insulation breakdown can induce high currents, further leading to thermal failure. Furthermore, the human body is prone to carrying some electrical charge. When a charged human body comes into contact with electronic components, electrostatic discharge (ESD) can easily occur. The voltage of this transient discharge can reach thousands or even tens of thousands of volts. As a device that often comes into contact with human hands, fingerprint sensors are easily harmed by ESD, especially glass-based fingerprint sensors. Their special structure determines that inductive coupling is very likely to occur above their driver integrated circuit (IC), resulting in large currents in the IC, further causing heat and ultimately damaging the IC.

[0003] For situations like fingerprint sensors, which come into contact with the human body and generate ESD, leading to device failure, one approach is to "block" the enclosure. This involves increasing the thickness of the enclosure, specifically the distance between the enclosure and the circuit board, or by using equivalent methods to increase the air gap within the enclosure. This can prevent or significantly reduce the intensity of ESD energy. Structural improvements can increase the air gap between the enclosure and the internal circuitry, significantly attenuating the ESD energy. Experience shows that an 8kV ESD energy typically decays to zero after a distance of 4mm. A second approach is to "drain" the enclosure by spraying conductive paint on the inside. This acts as a metal shield, directing static electricity to the enclosure. Connecting the enclosure to the ground of the printed circuit board (PCB) diverts the static electricity away from the ground. This approach not only prevents static electricity but also effectively suppresses interference from the conductive ink. If sufficient space is available, a metal shield can be used to protect the circuitry within, connected to the PCB ground point. In short, ESD enclosure design requires careful consideration, minimizing ESD entry and minimizing the energy that does enter.

[0004] Due to the special device structure of the mutual capacitance glass-based fingerprint sensor, when identifying the fingerprint, the IC and the finger surface are separated by only an insulating layer of 100μm, and this distance cannot be further increased. This means that the traditional anti-ESD method that relies on increasing the thickness of the insulating layer cannot be used in principle. On the other hand, "conductivity" or "dissipation" is a relatively feasible method for mutual capacitance glass-based fingerprint sensors. For example, a layer of conductive material is added to the insulating layer above the IC. The conductive material can be ITO, silver paste, copper foil and other conductive materials. However, in mutual capacitance glass-based fingerprint sensors, this simple method of using conductive materials will still generate large currents at the IC position due to inductive coupling and charging, causing abnormal operation of the IC, and such materials will seriously affect the appearance of the coating. The method of "dissipating" electrostatic discharge by adding conductive phases to resin materials, such as silver nanowires, carbon nanotubes, graphene, etc., is also widely used. However, the antistatic coatings prepared by this method often have general insulation properties, with a surface resistivity of 10× 6 -10× 10 This is sufficient for common anti-static scenarios, but in mutual capacitive glass-based fingerprint sensors, the resistivity is less than 10× 11 Ω·m cannot successfully capture fingerprint images. Furthermore, most polymer materials exhibit surface breakdown and scratching after electrostatic discharge. Specifically, after 15 cycles of 15kV air discharge testing, electric shock marks appear on the coating surface. Therefore, they are not suitable for mutual capacitive glass-based fingerprint sensors. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a coating and a preparation method for a glass-based fingerprint sensor, and a fingerprint sensor, wherein the coating has excellent antistatic properties and can realize the smooth collection of fingerprint images, and at the same time, there is no breakdown or scratching on the surface of the material after electrostatic discharge.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a coating for a glass-based fingerprint sensor, the coating comprising a primer layer and a topcoat layer;

[0007] The raw materials for preparing the coating of the topcoat layer include, by mass, 100 parts of polyurethane acrylate coating and 0.01-2 parts of conductive material, wherein the polyurethane acrylate coating includes 70-90 parts of polyurethane acrylate, 0.1-5 parts of siloxane, 2-8 parts of initiator, 10-15 parts of first curing agent, and 80-105 parts of auxiliary agent.

[0008] As an improvement of the above solution, the raw materials for preparing the coating of the primer layer include, by mass: 35-50 parts of acrylic polyol, 3-9 parts of hydroxyl-containing polyester, 15-23 parts of a second curing agent, 15-25 parts of an organic solvent and 0.05-0.5 parts of a first leveling agent.

[0009] As an improvement of the above solution, the conductive material is selected from one or more of carbon nanotubes, carbon fibers, graphene, graphite powder, silver nanowires, and gold nanowires;

[0010] The conductive material has a diameter of 5-200 nm and a length of 0.5-150 μm.

[0011] As an improvement of the above solution, the mass ratio of the conductive material to the polyurethane acrylate coating is (0.5-2):100.

[0012] As an improvement of the above solution, the siloxane is a siloxane containing a vinyl group.

[0013] As an improvement of the above solution, the vinyl-containing silicone includes one or more of double-end vinyl-terminated methyl silicone oil, double-end hydroxypropyl silicone oil, hydroxyl-terminated methyl vinyl silicone oil, and methyl vinyl silicone oil.

[0014] As an improvement to the above solution, the first curing agent is diisocyanate;

[0015] The auxiliary agent includes 80-100 parts of a diluent, 0.5-3 parts of a second leveling agent and 0.1-1 parts of a wetting agent, wherein the diluent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, cyclohexanone, butyl acetate and styrene, and the second leveling agent includes silicone.

[0016] As an improvement to the above solution, the second curing agent is a trimer isocyanate;

[0017] The organic solvent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone;

[0018] The first leveling agent includes fluorine-modified polyacrylate;

[0019] The hydroxyl-containing polyester is a hydroxyl-containing hyperbranched polyester;

[0020] The primer layer also includes 5-10 parts of dye, which includes, by weight, 100 parts of organic solvent, 5-15 parts of carbon black, 5-10 parts of dispersant and 0.05-2 parts of defoaming agent.

[0021] A second aspect of the present invention further provides a method for preparing the coating for a glass-based fingerprint sensor, comprising:

[0022] (1) Applying the primer layer to the surface of the mutual capacitance glass-based fingerprint sensor, drying it at 70-90° C. after the surface is dry;

[0023] (2) Continue to apply the coating of the topcoat layer, irradiate with ultraviolet light after the surface is dried, and finally bake at 110-130° C. to obtain a coating.

[0024] A third aspect of the present invention further provides a fingerprint sensor, which is a mutual capacitance glass-based fingerprint sensor. The fingerprint sensor includes a glass substrate for collecting fingerprints, and the coating, which is coated on the glass substrate.

[0025] The implementation of the present invention has the following beneficial effects:

[0026] The coating of the present invention comprises a primer layer and a topcoat layer. The topcoat layer is formed by curing a polyurethane acrylate coating, a conductive material, silicone, and an additive. The primer layer exhibits excellent adhesion to the glass substrate. Applying this coating to the surface of a glass-based fingerprint sensor improves the sensor's antistatic properties without affecting its image acquisition process. Furthermore, the coating prevents the sensor from experiencing breakdown and scarring during electrostatic discharge testing. Furthermore, the coating maintains an insulating state after curing. The coating exhibits excellent adhesion to the glass substrate, resists flaking, exhibits no discoloration, and exhibits a favorable appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : A schematic structural diagram of a mutual capacitive glass-based fingerprint sensor coated with a coating in the present invention;

[0028] Figure 2 : Fingerprint recognition image of the mutual capacitance glass-based fingerprint sensor obtained in Example 3 of the present invention;

[0029] Figure 3 : Fingerprint recognition image of the mutual capacitance glass-based fingerprint sensor obtained in Example 6 of the present invention;

[0030] Figure 4 : Fingerprint recognition image of the mutual capacitance glass-based fingerprint sensor obtained in Comparative Example 4 of the present invention;

[0031] Figure 5 : Surface appearance of the mutual capacitive glass-based fingerprint sensor obtained in Example 3 of the present invention after ESD testing;

[0032] Figure 6 : Surface appearance of the mutual capacitive glass-based fingerprint sensor obtained in Comparative Example 14 of the present invention after ESD testing.

[0033] Reference numerals: 1 - driver IC; 2 - glass substrate; 3 - primer layer; 4 - topcoat layer. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail with reference to specific embodiments below.

[0035] In the existing technology, in order to avoid IC failure caused by inductive coupling and charging during ESD testing, the distance between the IC and the finger contact surface can be increased to 4mm by increasing the thickness of the insulation layer. However, at this thickness, the glass-based fingerprint sensor can no longer recognize fingerprints normally. Moreover, the insulation layer is a conductive material surface covering the upper part of the IC, which can easily cause the coating to collapse and fall off during the ESD test.

[0036] To solve the above problems, the present invention provides a coating for a glass-based fingerprint sensor in a first aspect, the coating comprising a primer layer and a topcoat layer;

[0037] The raw materials for preparing the coating of the topcoat layer include, by mass, 100 parts of polyurethane acrylate coating and 0.01-2 parts of conductive material, wherein the polyurethane acrylate coating includes 70-90 parts of polyurethane acrylate, 0.1-5 parts of siloxane, 2-8 parts of initiator, 10-15 parts of first curing agent, and 80-105 parts of auxiliary agent.

[0038] The primer layer has good adhesion to the glass base surface.

[0039] In the present invention, the glass-based fingerprint sensor is a mutual capacitance glass-based fingerprint sensor. Through the synergistic effect of the primer layer and the topcoat layer, the coating formed has good antistatic properties, hardness and wear resistance. Moreover, the coating will not change in color after ESD testing, and has strong adhesion to the glass base surface, and the coating is not easy to fall off.

[0040] Specifically, the synergistic effect of a polyurethane acrylate coating and a conductive material as a topcoat layer can improve the antistatic properties of the coating without affecting fingerprint image recognition. A very small amount of conductive material is added and evenly coated on the surface of a mutual capacitance glass-based fingerprint sensor. Charge is "dissipated" by the tiny conductive phase in the primer layer, allowing ESD to pass through the device, thereby improving the antistatic properties of the mutual capacitance glass-based fingerprint sensor. Furthermore, due to the extremely small amount of conductive phase added, the primer layer can be insulated after curing. Neither the intermediate layer nor the topcoat layer contains conductive material, resulting in an overall insulating coating. This eliminates the need to increase the thickness of the insulating layer, reducing the impact of the insulating layer's thickness on fingerprint recognition and preventing discoloration of the coating. Furthermore, the coating exhibits wear resistance and a certain degree of hardness, meeting the hardness and wear resistance requirements of mutual capacitance glass-based fingerprint sensors. However, the coating exhibits poor adhesion to the glass substrate. Therefore, a primer layer is provided between the topcoat layer and the glass substrate to improve the adhesion of the topcoat layer to the glass substrate and reduce the risk of coating detachment.

[0041] In addition, polyurethane acrylic resin coating and conductive material are compounded to make the resistivity of mutual capacitive glass-based fingerprint sensor not less than 10× 11 Ω·m, while protecting the IC from electrostatic discharge damage, it does not affect the device's fingerprint image recognition and unlocking rate. This solves the problem that has been reported that carbon nanotube antistatic coatings used in mutual capacitance glass-based fingerprint sensors cannot distinguish the fingerprint texture when recognizing fingerprint patterns, resulting in a gray recognition result.

[0042] Preferably, the conductive material is selected from one or more of carbon nanotubes, carbon fibers, graphene, graphite powder, silver nanowires, and gold nanowires; the conductive material has a diameter of 5-200 nm and a length of 0.5-150 μm, can be uniformly dispersed and stably present in the system, and can form a conductive network to improve the antistatic properties of the coating; further preferably, the conductive material has a diameter of 7-100 nm and a length of 0.5-100 μm; even more preferably, the conductive material has a diameter of 7-80 nm and a length of 0.5-20 μm.

[0043] Furthermore, in the prior art, the entire surface of the ITO material is sputtered on the device surface, which may cause the fingerprint image to be unable to be collected. The mass ratio of the conductive material to the polyurethane acrylate coating is controlled to be (0.5-2):100, and exemplary mass ratios are 0.5:100, 0.75:100, 1:100, 1.25:100, 1.5:100, and 2:100, but not limited thereto. Since the amount of conductive phase added is extremely small, the coating as a whole is insulated, which can ensure that ESD passes without affecting fingerprint image recognition, and can enable the mutual capacitance glass-based fingerprint sensor to pass the air discharge 15kV test 15 times. If the amount of conductive material added is too much, the fingerprint unlocking rate will be reduced or even unrecognizable, and the adhesion and wear resistance of the coating will be significantly reduced.

[0044] Preferably, the addition of the siloxane reacts with the conductive material, grafting long alkyl chains containing epoxy groups onto the surface of the conductive material. This improves the high-temperature stability of the coating, ensuring strong adhesion to the primer layer even after high-temperature treatment, and preventing discoloration and detachment. Electric shock tracking on the coating surface is caused by the formation of microscopic pathways on the coating surface, which generate localized currents and, in turn, high temperatures, ultimately leading to radial discoloration of the coating surface. The siloxane is a vinyl-containing siloxane. During the reaction between the diisocyanate and the polyurethane acrylate, the vinyl groups in the siloxane are opened by the photoinitiator and participate in the reaction between the diisocyanate and the polyurethane acrylate. As a result, after photocuring, the long siloxane chains are embedded in the three-dimensional network formed by the acrylic resin as long blocks. Since the pyrolysis temperature of the siloxane segments is much higher than that of the carbon chains, introducing the siloxane segments into the three-dimensional network of the carbon-based polyurethane resin can improve the coating's resistance to electric shock tracking and prevent discoloration after ESD testing.

[0045] Furthermore, the vinyl-containing silicone includes one or more of double-end vinyl-terminated methyl silicone oil, double-end hydroxypropyl silicone oil, hydroxyl-terminated methylvinyl silicone oil, and methylvinyl silicone oil.

[0046] In some preferred embodiments, the structural formula of the double-end vinyl-terminated methyl silicone oil is as shown in Formula 1;

[0047]

[0048] The structural formula of the double-terminated hydroxypropyl silicone oil is shown in Formula 2. Examples include Huangshan Qiangli Chemical Co., Ltd.: QL-2311VDV100, QL-2311VDV230, QL-2311VDV350, QL-2311VDV500, QL-2311VDV1000, QL-2311VDV2000, QL-2311VDV3500, QL-2311VDV5000, and QL-2311VDV10000;

[0049]

[0050] The structural formula of the hydroxyl-terminated methyl vinyl silicone oil is shown in Formula 3;

[0051]

[0052] The structural formula of the methyl vinyl silicone oil is shown in Formula 4.

[0053]

[0054] The siloxane in the present invention may also be other long siloxane chains having two or more vinyl or acrylic groups.

[0055] Preferably, the initiator is a photoinitiator, including but not limited to 1-hydroxycyclohexyl phenyl ketone.

[0056] Preferably, the first curing agent is a diisocyanate, including but not limited to isophorone diisocyanate.

[0057] Preferably, the auxiliary agent includes 80-100 parts of diluent, 0.5-3 parts of second leveling agent and 0.1-1 part of wetting agent.

[0058] Furthermore, the diluent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, cyclohexanone, butyl acetate, and styrene.

[0059] Furthermore, the second leveling agent includes silicone, and at the same time, by reducing the surface tension of the topcoat layer to enhance the spread of the coating of the topcoat layer, thereby improving its adhesion to the surface of the primer layer, and at the same time, by reducing the surface tension, improving its surface state and eliminating surface defects. Examples include BYK-3450, BYK370, TEGO 2100, etc.

[0060] Furthermore, the wetting agent may be a conventional wetting agent in the art, and examples thereof include TEGO wet270, Clariant Emulsogen LCN 70, and the like.

[0061] In some preferred embodiments, the coating of the topcoat layer is prepared by:

[0062] S1. Preparation of polyurethane acrylate coating: The polyurethane acrylate is mixed with the additive, stirred at 1800-2300r / min for 20-40min, followed by addition of siloxane, initiator, and finally the first curing agent to obtain;

[0063] S2. Take the polyurethane acrylate coating prepared in S1 and mix it with the conductive material, stir it at 1800-2300 r / min for 20-40 min, and obtain the coating of the topcoat layer.

[0064] Furthermore, the conductive material is formed into a dispersion and then mixed, wherein the solvent of the dispersion includes but is not limited to ethylene glycol methyl ether. By adding the conductive material in the form of a dispersion, the conductive material is evenly dispersed in the coating, so that the electrostatic charge in the IC is evenly "dissipated", achieving a better antistatic effect.

[0065] Preferably, the topcoat layer further comprises 3-8 parts of matte powder, which can be added during the preparation of the polyurethane acrylate coating, specifically before adding the siloxane.

[0066] Preferably, the raw materials for preparing the coating of the primer layer include, by mass, 35-50 parts of acrylic polyol, 3-9 parts of hydroxyl-containing polyester, 15-23 parts of a second curing agent, 15-25 parts of an organic solvent and 0.05-0.5 parts of a first leveling agent. In the primer layer, the acrylic polyol and the hydroxyl-containing polyester are cured under the action of the curing agent to obtain a polyester-modified polyurethane acrylate coating as the primer layer, which not only has strong adhesion to the glass base surface, but also has good compatibility with the topcoat layer. The topcoat layer has strong adhesion on the primer layer.

[0067] Furthermore, the primer layer has good adhesion to the glass substrate, and the viscosity of the acrylic polyol at 25°C is 5000-7000 cps, which can be exemplified by RPD 980-B, etc.; the hydroxyl-containing polyester is a hydroxyl-containing hyperbranched polyester, and the viscosity of the hydroxyl-containing polyester at 23°C is 2-10 Pa·s. Examples of brands include BASF HPE 1170B, etc.

[0068] Furthermore, the second curing agent is a trimer isocyanate, including but not limited to HDI (hexamethylene diisocyanate) trimer, TDI (toluene diisocyanate) trimer, etc.

[0069] Furthermore, the organic solvent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone.

[0070] Furthermore, the first leveling agent includes fluorine-modified polyacrylate, which is used to improve the uniformity and fluidity of the coating in the primer layer, improve the adhesion of the primer layer coating to the glass base surface, and improve the adhesion with the topcoat layer coating. Examples include LD-91084, LD-91085, Deqian 839, EFKA-3777, Walker VOK-5103, Walker VOK-5105, etc.

[0071] Furthermore, the organic solvent is selected from one or more of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone; more preferably, isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone.

[0072] Preferably, the preparation method of the coating of the primer layer is: after mixing the acrylic polyol and the organic solvent, adding the hydroxyl-containing polyester, stirring at 300-600 r / min for 5-20 min, then adding the first leveling agent and the second curing agent, stirring at 300-600 r / min for 5-20 min, to obtain the coating.

[0073] Furthermore, the primer layer also includes 5-10 parts of dye, which, by weight, includes: 100 parts of organic solvent, 5-15 parts of carbon black, 5-10 parts of dispersant and 0.05-2 parts of defoaming agent. It is finally added to the coating of the primer layer or the coating of the intermediate layer and stirred evenly at a speed of 300-500r / min.

[0074] Preferably, the dispersant is a conventional dispersant in the art, and examples thereof include BYK dispersant, sodium lauryl sulfate, polyvinyl pyrrolidone, octylphenol polyoxyethylene ether, etc. The BYK dispersant includes but is not limited to BYK-9076.

[0075] Preferably, the defoaming agent is a conventional defoaming agent in the art, including but not limited to silicone, polyether, polyether-modified silicone, and mineral oil.

[0076] Accordingly, the present invention also provides a method for preparing the coating for a glass-based fingerprint sensor, comprising:

[0077] (1) Applying the primer layer to the surface of the mutual capacitance glass-based fingerprint sensor, drying it at 70-90° C. after the surface is dry;

[0078] (2) Continue to apply the coating of the topcoat layer, irradiate with ultraviolet light after the surface is dried, and finally bake at 110-130° C. to obtain a coating.

[0079] Preferably, the surface drying time in step (1) and step (2) is 3-7 minutes.

[0080] Preferably, the baking time in step (1) is 20-40 minutes.

[0081] Preferably, the ultraviolet irradiation time in step (2) is 2-5 minutes, and the baking time is 20-40 minutes.

[0082] Preferably, the coating method includes but is not limited to spraying, roller coating, and brushing; more preferably, spraying.

[0083] Accordingly, the present invention also provides a fingerprint sensor, which is a mutual capacitance glass-based fingerprint sensor. The fingerprint sensor includes a glass substrate 2 for collecting fingerprints, and the coating, which is coated on the glass substrate 2. The specific structure is as follows: Figure 1 A driver IC 1 is provided at one end of the glass substrate 2 , and the coating comprises a primer layer 3 and a topcoat layer 4 . The primer layer 3 is coated on the glass substrate 2 , and the topcoat layer 4 is coated on the primer layer 3 .

[0084] It should be noted that the parts in the Examples and Comparative Examples are all parts by mass.

[0085] The present invention will be further described below with specific embodiments:

[0086] Example 1

[0087] This embodiment provides a coating for a glass-based fingerprint sensor, comprising a primer layer and a topcoat layer;

[0088] The raw materials for preparing the coating of the primer layer are: 42 parts of acrylic polyol ( RPD 980-B), 6 parts of hydroxyl-containing hyperbranched polyester ( HPE 1170B), 20 parts of organic solvent (5 parts of isopropyl alcohol, 5 parts of n-butanol, 5 parts of ethylene glycol monobutyl ether and 5 parts of cyclohexanone), 0.3 parts of fluorine-modified polyacrylate leveling agent, 18 parts of trimer polyisocyanate (TDI trimer) and 8 parts of black dye, wherein the black dye is a mixture of 25 parts of isopropyl alcohol, 25 parts of n-butanol, 25 parts of ethylene glycol monobutyl ether, 25 parts of cyclohexanone, 0.1 parts of silicone defoamer, 7.5 parts of BYK-9076 and 10 parts of carbon black.

[0089] Prepare the primer coating by the following method:

[0090] Take acrylic polyol, isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, cyclohexanone, and hydroxyl-containing hyperbranched polyester and mix them in a container, and stir them at 500 r / min for 10 minutes; then add fluorine-modified polyacrylate leveling agent and trimer polyisocyanate curing agent, and stir them at 500 r / min for 10 minutes; finally, add the prepared black dye, stir at 500 r / min for 10 minutes and mix them evenly.

[0091] The raw materials for preparing the coating of the topcoat layer include: 100 parts of polyurethane acrylate coating and 0.01 parts of carbon nanotubes, wherein the polyurethane acrylate coating includes 80 parts of polyurethane acrylate (polydipentaerythritol hexaacrylate, CAS number: 29570-58-9), diluent (specifically 5 parts of isopropyl alcohol, 10 parts of n-butanol, 10 parts of ethylene glycol monobutyl ether, 10 parts of cyclohexanone, 30 parts of butyl acetate and 25 parts of styrene), 0.6 parts of wetting agent, 2 parts of silicone leveling agent, 2 parts of double-end vinyl-terminated methyl silicone oil (Huangshan Qiangli Chemical Co., Ltd.: QL-2311VDV100), 6 parts of 1-hydroxycyclohexyl phenyl ketone, 12 parts of isophorone diisocyanate and 6 parts of matte powder.

[0092] Prepare the topcoat coating by the following method:

[0093] S1. Take polyurethane acrylate and isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone in a container, add butyl acetate, styrene, a wetting agent, a silicone leveling agent, and a matte powder in sequence, and stir at 2000 rpm for 30 minutes to mix; then add vinyl-terminated siloxane and continue to add 1-hydroxycyclohexyl phenyl ketone; then add isophorone diisocyanate and stir at 500 rpm for 10 minutes to mix evenly to obtain a polyurethane acrylate coating;

[0094] S2. Take 100 parts of the prepared polyurethane acrylate coating, add 0.01 parts of carbon nanotubes (length 5-15 μm, diameter 20-70 nm), and stir at 2000 r / min for 30 minutes to obtain a topcoat coating, wherein the carbon nanotubes are added in the form of a dispersion, and the solvent in the carbon nanotube dispersion is ethylene glycol methyl ether.

[0095] This embodiment also provides a method for preparing a coating for a glass-based fingerprint sensor:

[0096] (1) Spray the primer layer onto the surface of the mutual capacitance glass-based fingerprint sensor, allow it to dry in air for 5 minutes, and then bake it in a forced air oven at 80°C for 30 minutes;

[0097] (2) Spray the topcoat coating onto the surface of the mutual capacitance glass-based fingerprint sensor obtained in (1), dry the surface for 5 minutes, irradiate with 365nm ultraviolet light for 3 minutes, and bake at 120°C for 30 minutes after the irradiation to obtain a coating.

[0098] The coatings for the topcoat layers of Examples 2-6 and Comparative Examples 1-5 were formulated according to Table 1 below, and the ratios of the primer layer and the polyurethane acrylate coating were the same as in Example 1.

[0099] Table 1 Coating ratios of the topcoat layers of Examples 1-6 and Comparative Examples 1-5

[0100] Polyurethane acrylate coating / part Carbon nanotubes / unit Example 1 100 0.01 Example 2 100 0.1 Example 3 100 0.5 Example 4 100 1.0 Example 5 100 1.5 Example 6 100 2.0 Comparative Example 1 100 0 Comparative Example 2 100 0.001 Comparative Example 3 100 2.5 Comparative Example 4 100 20 Comparative Example 5 100 30

[0101] 1. The mutual capacitance glass-based fingerprint sensor structures obtained in Examples 1-4 and Comparative Examples 1-2 and 4-5 were subjected to performance tests on surface resistivity, fingerprint unlocking rate, and ESD. The test results are shown in Table 2 below.

[0102] (1) Surface resistivity: Surface resistivity is measured according to the national standard GB / T 1410-2006;

[0103] (2) Fingerprint unlocking rate: The module needs to be installed on the door handle tool and the fingerprint verification is performed as usual. Then select test personnel (no less than 5 people), each of whom records 10 fingerprints, and each finger is unlocked and verified 10 times. The number of successful and failed verifications for each person is recorded. After the test is completed, the rejection rate is calculated. Rejection rate = (total number of failures / total number of valid verifications), fingerprint unlocking rate = 1-rejection rate.

[0104] (3) ESD: It should comply with the requirements of severe level 4 specified in GB / T 17626.2-2006 (contact discharge: 8kV, air discharge: 15kV).

[0105] Judgment criteria: Mutual capacitive glass-based fingerprint sensors that experience temporary failure (failure duration greater than 3 seconds), permanent failure (failure that does not recover), or peeling or color change are considered unqualified (NG). Those that experience screen flickering or self-recovery within 3 seconds are considered qualified (PASS).

[0106] Table 2 Test results of Examples 1-4 and Comparative Examples 1-2, 4-5

[0107] Resistivity / Ω·m Fingerprint unlocking rate / % ESD Example 1 Insulator 99.9 PASS Example 2 Insulator 99.1 PASS Example 3 Insulator 95 PASS Example 4 Insulator 80 PASS Comparative Example 1 Insulator 99.9 NG Comparative Example 2 Insulator 99.9 NG Comparative Example 4 <![CDATA[4.2×10 10 ]]> Unrecognizable PASS Comparative Example 5 <![CDATA[7.3×10 7 ]]> Unrecognizable PASS

[0108] Insulator: Insulator (surface resistivity > 10× 11 Ω·m).

[0109] From the above results, it can be seen that adding carbon nanotube conductive material to the polyurethane acrylate coating in the topcoat layer can increase the resistivity of the mutual capacitance glass-based fingerprint sensor, protect the IC from electrostatic discharge damage, and do not affect the device's fingerprint image recognition and fingerprint unlocking rate. However, if the amount of conductive material added is too little, the mutual capacitance glass-based fingerprint sensor will not be able to pass the ESD test. If the amount of conductive material added is too much, the resistivity of the mutual capacitance glass-based fingerprint sensor will be reduced and the fingerprint cannot be recognized. However, if the amount added is too little, it will not pass the ESD test.

[0110] 2. The topcoat layers obtained in Examples 3-6 and Comparative Examples 1 and 3 were tested for adhesion and abrasion resistance. The test results are shown in Table 3 below.

[0111] (4) 100-grid adhesion: The adhesion strength was measured according to the ASTM D3359 standard, and then the obtained mutual capacitance glass-based fingerprint sensor structure was boiled in water at 80°C for 30 minutes and then its 100-grid adhesion was measured;

[0112] (5) Abrasion resistance: tested according to ASTM F2357, rubbing RCA paper tape 200 times. The definition is PASS if no bottom exposure occurs after rubbing RCA paper tape 200 times, and NG if bottom exposure occurs.

[0113] (6) Pencil hardness: Tested in accordance with standard GB / T 9286-2021.

[0114] Table 3 Test results of Examples 3-6 and Comparative Examples 1 and 3

[0115]

[0116] The above results show that the amount of carbon nanotubes added to the topcoat layer has a certain impact on the wear resistance of the coating. If the carbon nanotube content is too high, the wear resistance of the coating will be reduced. It can also be explained that the topcoat layer has high hardness but poor adhesion to the glass substrate, while the adhesion to the primer layer is very good.

[0117] 3. The mutual capacitance glass-based fingerprint sensor structures obtained in Example 3, Example 6, and Comparative Example 4 were used for fingerprint recognition and the fingerprint recognition images were recorded. The results are shown in the attached Figure 2-4 .

[0118] Figure 2 is the fingerprint recognition image of Example 3, Figure 3 is the fingerprint recognition image of Example 6, Figure 4 This is the fingerprint recognition image of Comparative Example 4. Figure 2 and Figure 3 The lines of the fingerprint are clearly visible. Figure 4 The fingerprint pattern cannot be distinguished. Figure 2-4It can be seen that the amount of carbon nanotubes added in the topcoat layer can affect the fingerprint recognition effect of the mutual capacitance glass-based fingerprint sensor. If the amount of carbon nanotubes added is too much, the mutual capacitance glass-based fingerprint sensor will not be able to distinguish the texture of the fingerprint when recognizing the fingerprint pattern, resulting in the final recognition result being gray.

[0119] Comparative Example 6

[0120] This comparative example provides a coating for a glass-based fingerprint sensor, comprising a primer layer and a topcoat layer;

[0121] The raw materials for preparing the coating of the primer layer include: 42 parts of acrylic polyol (Joncryl RPD 950-B), 6 parts of hydroxyl-containing hyperbranched polyester ( HPE 1170B), 20 parts of organic solvent (5 parts of isopropyl alcohol, 5 parts of n-butanol, 5 parts of ethylene glycol monobutyl ether and 5 parts of cyclohexanone), 0.3 parts of fluorine-modified polyacrylate leveling agent, 18 parts of trimer polyisocyanate (TDI trimer), 0.05 parts of carbon nanotubes and 8 parts of black dye, wherein the black dye is a mixture of 25 parts of isopropyl alcohol, 25 parts of n-butanol, 25 parts of ethylene glycol monobutyl ether, 25 parts of cyclohexanone, 0.1 parts of silicone defoamer, 7.5 parts of BYK-9076 and 10 parts of carbon black.

[0122] Prepare the primer coating by the following method:

[0123] S1. Take acrylic polyol, isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, cyclohexanone, hydroxyl-containing hyperbranched polyester mixed in a container and stirred at 500r / min for 10 minutes; then add fluorine-modified polyacrylate leveling agent, trimer polyisocyanate curing agent, stirred at 500r / min for 10 minutes; finally add the black dye configuration, stir at 500r / min for 10 minutes to mix evenly to obtain a base coating of the primer layer;

[0124] S2. Take 100 parts of the prepared base coating of the primer layer, and add 0.05 parts of carbon nanotubes, and stir at 2000r / min for 30min to obtain, wherein the carbon nanotubes are added in the form of a dispersion, and the solvent in the carbon nanotube dispersion is ethylene glycol methyl ether.

[0125] The topcoat layer was prepared from 100 parts of polyurethane acrylate coating, the components of which were the same as those in Example 1. The primer layers obtained in Example 1 and Comparative Examples 6-10 were subjected to ESD testing, adhesion testing on a glass substrate, and pencil hardness testing. The test results are shown in Table 4 below.

[0126] Table 4 Coating ratios and test results of the primer layer of Comparative Examples 6-10

[0127]

[0128] The above data demonstrates that while incorporating a conductive material into the primer layer improves the coating's antistatic properties, it significantly reduces its adhesion after heat treatment at 80°C, increasing the risk of coating peeling. This also demonstrates that the primer layer, despite its low hardness, exhibits excellent adhesion to the glass substrate.

[0129] The coatings for the topcoat layers of Examples 7-12 were formulated according to Table 5 below. The ratios of the primer layer and the polyurethane acrylate coating were the same as in Example 1. The fingerprint unlocking rate and ESD tests of the obtained mutual capacitive fingerprint sensors were performed. The test results are shown in Table 5.

[0130] Table 5 Coating ratios and test results of the topcoat layers of Examples 1, 7-12

[0131]

[0132]

[0133] From the above results, it can be seen that when the added amount of carbon nanotubes is certain, the topcoat made of carbon nanotubes with a length of 0.5-100μm can play an anti-static role, but when its length exceeds 20μm, it will affect the unlocking rate of the fingerprint sensor, and the longer the carbon nanotubes, the more obvious the impact on the fingerprint sensor. The diameter of the carbon nanotubes in the range of 7-80nm has no obvious effect on the anti-static effect of the coating and the fingerprint unlocking rate.

[0134] The coatings for the topcoat layer of Example 13 and Comparative Examples 11-13 were formulated according to Table 6 below, and the ratio of the primer layer and the polyurethane acrylate coating was the same as that of Example 1, wherein the length of the carbon fiber was 7-15 μm and the diameter was 1 μm.

[0135] The fingerprint unlocking rate, ESD test, wear resistance, and 100-grid adhesion tests were conducted. The test results are shown in Table 6.

[0136] Table 6 Coating ratios and test results of the topcoat layers of Examples 1, 13, and Comparative Examples 1, 11-13

[0137]

[0138] The above results indicate that adding conductive filler to the topcoat requires a ratio of polyurethane acrylate to carbon fiber of 100:9 to achieve good antistatic properties, protecting the IC from 15kV ESD damage. However, at this point, the coating's adhesion has already significantly decreased. Therefore, for general conductive materials, a large amount of filler is required to achieve antistatic properties, but large additions often degrade the coating's mechanical properties.

[0139] Comparative Example 14

[0140] This comparative example provides a coating for a glass-based fingerprint sensor, which differs from Example 3 in that:

[0141] Urethane acrylate coatings do not include vinyl terminated siloxanes.

[0142] Take photos to record the surface appearance of Example 3 and Comparative Example 14 after ESD testing. The results are shown in the attached figure. Figure 5-6 shown.

[0143] Figure 5 In the embodiment, the coating obtained in Example 3 was applied on the glass surface of the mutual capacitance glass-based fingerprint sensor. After the ESD test, the coating did not fall off or change color. Figure 6 When the coating obtained in Comparative Example 14 was applied, the surface of the coating changed color after the ESD test. This shows that only the polyurethane acrylate coating structure described in this application can ensure that the coating does not change color or fall off after the ESD test, achieving the same coating stability as that achieved with an amorphous fluororesin layer.

[0144] Comparative Example 15

[0145] This comparative example provides a coating for a glass-based fingerprint sensor, specifically a copper foil layer.

[0146] Comparative Example 16

[0147] This comparative example provides an antistatic coating for a glass-based fingerprint sensor, specifically a silver paste layer.

[0148] Comparative Example 17

[0149] This comparative example provides an antistatic coating for a glass-based fingerprint sensor, specifically an indium tin oxide layer.

[0150] Comparative Example 18

[0151] This comparative example provides an antistatic coating for a glass-based fingerprint sensor, specifically a polyethylenedioxythiophene layer.

[0152] The working conditions (current, temperature) of the surface IC of the mutual capacitance glass-based fingerprint sensor structures obtained in Example 3 and Comparative Examples 15-18 were tested after ESD testing. The results are shown in Table 7 below.

[0153] Table 7 Surface IC working condition test results after ESD test for Example 3 and Comparative Examples 15-18

[0154]

[0155] From the above results, it can be seen that the use of the coating in this application can prevent ESD from causing the mutual capacitance glass-based fingerprint sensor to generate large current in the IC, thereby avoiding the generation of large amounts of heat, protecting the normal operation of the IC, and reducing the probability of IC damage.

[0156] The above disclosure is only a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A coating for a glass-based fingerprint sensor, characterized in that: The coating layer includes a primer layer and a topcoat layer; The raw materials for preparing the coating of the topcoat layer include, by mass, 100 parts of polyurethane acrylate coating and 0.01-2 parts of conductive material, wherein the polyurethane acrylate coating includes 70-90 parts of polyurethane acrylate, 0.1-5 parts of siloxane, 2-8 parts of initiator, 10-15 parts of first curing agent, and 80-105 parts of auxiliary agent.

2. The coating for a glass-based fingerprint sensor according to claim 1, wherein: The raw materials for preparing the coating of the primer layer include, by mass, 35-50 parts of acrylic polyol, 3-9 parts of hydroxyl-containing polyester, 15-23 parts of a second curing agent, 15-25 parts of an organic solvent and 0.05-0.5 parts of a first leveling agent.

3. The coating for a glass-based fingerprint sensor according to claim 1, wherein The conductive material is selected from one or more of carbon nanotubes, carbon fibers, graphene, graphite powder, silver nanowires, and gold nanowires; The conductive material has a diameter of 5-200 nm and a length of 0.5-150 μm.

4. The coating for a glass-based fingerprint sensor according to claim 1, wherein: The mass ratio of the conductive material to the polyurethane acrylate coating is (0.5-2):

100.

5. The coating for a glass-based fingerprint sensor according to claim 1, wherein: The siloxane is a siloxane containing a vinyl group.

6. The coating for a glass-based fingerprint sensor according to claim 1, wherein: The vinyl-containing silicone includes one or more of double-end vinyl-terminated methyl silicone oil, double-end hydroxypropyl silicone oil, hydroxyl-terminated methylvinyl silicone oil, and methylvinyl silicone oil.

7. The coating for a glass-based fingerprint sensor according to claim 1, wherein: The first curing agent is diisocyanate; The auxiliary agent includes 80-100 parts of a diluent, 0.5-3 parts of a second leveling agent and 0.1-1 parts of a wetting agent, wherein the diluent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, cyclohexanone, butyl acetate and styrene, and the second leveling agent includes silicone.

8. The coating for a glass-based fingerprint sensor according to claim 2, wherein: The second curing agent is a trimer isocyanate; The organic solvent is selected from at least one of isopropyl alcohol, n-butanol, ethylene glycol monobutyl ether, and cyclohexanone; The first leveling agent includes fluorine-modified polyacrylate; The hydroxyl-containing polyester is a hydroxyl-containing hyperbranched polyester; The primer layer also includes 5-10 parts of dye, which includes, by weight, 100 parts of organic solvent, 5-15 parts of carbon black, 5-10 parts of dispersant and 0.05-2 parts of defoaming agent.

9. The method for preparing a coating for a glass-based fingerprint sensor according to any one of claims 1 to 8, wherein: include: (1) Applying the primer layer to the surface of the mutual capacitance glass-based fingerprint sensor, drying it at 70-90° C. after the surface is dry; (2) Continue to apply the coating of the topcoat layer, irradiate with ultraviolet light after the surface is dried, and finally bake at 110-130° C. to obtain a coating.

10. A fingerprint sensor, characterized in that: The fingerprint sensor is a mutual capacitance glass-based fingerprint sensor, comprising a glass substrate for collecting fingerprints, and the coating according to any one of claims 1 to 8, wherein the coating is coated on the glass substrate.

Images