A primer and its preparation method and application

Abstract

The present invention relates to the field of new material technology, and more particularly to a primer and a preparation method and application thereof. The primer includes 5-10wt% of polyester polyol; the primer also includes a composite resin; the mass ratio of the composite resin to the polyester polyol is (15-30): (5-10); the composite resin includes a polyurethane resin and an epoxy resin in a mass ratio of (10-20): (5-10). The present invention obtains a primer with excellent performance by optimizing the formula and the preparation process; the primer is used to form an adhesion layer on the surface of the substrate in advance, and then a conductive paste is used to form a conductive circuit on the surface of the adhesion layer, which can not only significantly improve the adhesion between the conductive circuit and the substrate, but also effectively prevent the problem of conductive paste overflow, thereby greatly reducing the printing line width.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a primer and a preparation method and application thereof. Background Art

[0002] In recent years, people in this field usually use conductive paste to form circuit patterns on a substrate to obtain conductive circuits; while flexible printed circuits (FPC) use flexible materials such as PI film (polyimide) and PET film (polyethylene terephthalate) as substrates, and use conductive paste to form circuit patterns on the above substrates. Flexible printed circuits have advantages that traditional rigid printed circuits do not have, and can be bent or extended within a certain range.

[0003] However, the flexible circuit boards in the prior art have poor adhesion between the conductive lines and the substrate, and the conductive lines are prone to falling off during actual applications. In addition, during the preparation of the flexible circuit boards, the conductive paste overflows significantly on the surface of the substrate, resulting in a larger printed line width.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a primer, which is used to form an adhesion layer on the surface of a substrate in advance, and then a conductive circuit is formed on the surface of the adhesion layer using a conductive paste. This can not only significantly improve the adhesion between the conductive circuit and the substrate, but also effectively prevent the problem of overflow of the conductive paste, thereby greatly reducing the printing line width; another object of the present invention is to provide a preparation method and application of the primer.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] The present invention provides a primer, which comprises 5-10wt% of polyester polyol;

[0008] The primer also includes a composite resin;

[0009] The mass ratio of the composite resin to the polyester polyol is (15-30):(5-10);

[0010] The composite resin comprises a polyurethane resin and an epoxy resin in a mass ratio of (10-20):(5-10).

[0011] The present invention aims to develop a primer for a printing substrate, and has tried a large number of binder monomers and binder compounding methods. During the research and development process, it was found that using polyester polyol as the main binder supplemented with a composite resin in a specific ratio has a better effect.

[0012] The mass ratio of the composite resin to the polyester polyol is further controlled to be between (15-30):(5-10), and the mass ratio of the polyurethane resin to the epoxy resin is (10-20):(5-10), and the primer effect obtained is more ideal.

[0013] Preferably, the molecular weight of the polyester polyol is 1500-2500; the polyester polyol with a molecular weight within the above range has better heat resistance and better overall effect after being compounded with the composite resin.

[0014] Preferably, the molecular weight of the polyurethane resin is 30,000-60,000.

[0015] Preferably, the epoxy resin is bisphenol F epoxy resin with a molecular weight between 1000-3000.

[0016] In the present invention, the polyurethane resin and the epoxy resin are selected and compounded, and the obtained composite resin can have both flexibility and water and alkali resistance.

[0017] Those skilled in the art can arrange other functional components in the formula according to common knowledge, and they can all obtain the effects equivalent to the above description of the present invention. However, there are also better technical solutions for other components, and for this reason, the present invention further explores and obtains the following preferred solutions.

[0018] Preferably, the primer further comprises 10-20wt% of a curing agent;

[0019] The curing agent is isocyanate.

[0020] In the present invention, a specific curing agent (especially isocyanate) is selected to synergize with the composite resin, thereby further accelerating the curing speed on the basis of increasing the bonding performance of the system.

[0021] Preferably, the primer further comprises 2-5wt% of a heat-resistant filler;

[0022] The heat-resistant filler is selected from one or more of calcium carbonate, talc, mica powder, silicon powder, barium sulfate, kaolin, wollastonite, silica, carbon black, and titanium dioxide.

[0023] Furthermore, the primer further comprises 10-20wt% of a coupling agent;

[0024] The coupling agent is selected from one or more of Dow Corning 6040, Dow Corning 6011, Dow Corning 6020, Dow Corning 6030, KH570, KH560, and KH550.

[0025] In the present invention, screening specific heat-resistant fillers can effectively improve the heat resistance of the system, but there is still some gap from the ideal state; the present invention also found that screening specific coupling agents, after compounding with the above-mentioned heat-resistant fillers, can further improve the heat resistance of the system, and the overall adhesion is also improved.

[0026] Preferably, the primer further comprises 20-70wt% of a solvent; the solvent is selected from one or more of DBE (dibasic acid ester), dimethyl adipate, diethyl adipate, dipropylene glycol methyl ether, propylene dimethyl ether acetate, benzyl alcohol, dipropylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether, and isophorone. The above solvents can improve the solubility of polyester polyols and accelerate the dissolution rate.

[0027] Preferably, the primer further comprises 0.5-1 wt % of a defoamer and 0.2-0.5 wt % of a leveling agent.

[0028] Furthermore, the defoaming agent is selected from one or more of GS-5333, GS-100, defom5400, defom6800k, defom5600, defom5300, and defom6600; the above defoaming agent can effectively eliminate bubbles in the system.

[0029] Furthermore, the leveling agent is selected from one or more of BYK3931, BYK354, BYK361, BYK3350, BYK3499, SY933, SY965, and SY935; the leveling agent can improve the fluidity and flatness of the system, and effectively prevent the occurrence of shrinkage holes in the adhesion layer formed by the primer.

[0030] Those skilled in the art can combine the above technical solutions according to common sense to obtain preferred embodiments of the primer of the present invention.

[0031] As a preferred embodiment of the present invention, the primer comprises the following components in parts by weight: 5-10 parts of polyester polyol, 10-20 parts of polyurethane resin, 5-10 parts of epoxy resin, 10-20 parts of curing agent, 2-5 parts of heat-resistant filler, 10-20 parts of coupling agent, 20-70 parts of solvent, 0.5-1 parts of defoaming agent and 0.2-0.5 parts of leveling agent.

[0032] As a preferred embodiment of the present invention, the primer comprises the following components in percentage by mass:

[0033] Polyester polyol 5-10wt%, polyurethane resin 10-20wt%, epoxy resin 5-10wt%, curing agent 10-20wt%, heat-resistant filler 2-5wt%, coupling agent 10-20wt%, solvent 20-70wt%, defoamer 0.5-1wt%, leveling agent 0.2-0.5wt%.

[0034] The present invention also provides a method for preparing the above-mentioned primer, comprising: uniformly mixing polyester polyol, polyurethane resin, epoxy resin, curing agent, heat-resistant filler, coupling agent, solvent, defoaming agent and leveling agent, and then grinding.

[0035] Preferably, the preparation method comprises the following steps:

[0036] (1) mixing a polyurethane resin and a solvent to obtain a first solution;

[0037] (2) mixing polyester polyol, curing agent and epoxy resin to obtain a second solution;

[0038] (3) mixing the first solution and the second solution to obtain a third solution;

[0039] (4) mixing a heat-resistant filler and a coupling agent to obtain a fourth solution;

[0040] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and then grind.

[0041] The present invention also finds that by mixing the components in the above manner, the uniformity of the product can be ensured while further ensuring that the product properties do not undergo differential changes.

[0042] Preferably, in step (1), the mixing is carried out at 70-90° C. for 3-5 hours.

[0043] Preferably, in step (2), the polyester polyol and the curing agent are first mixed at 20-30° C. for 20-40 min, and then the epoxy resin is added to the mixture of the polyester polyol and the curing agent and mixed evenly.

[0044] Preferably, in step (4), the mixing is carried out at 20-30° C. for 20-40 min. Mixing under the above conditions can promote the coupling agent to fully coat the heat-resistant filler, thereby increasing the compatibility of the coupling agent and the resin system, and avoiding the risk of precipitation of the heat-resistant filler after long-term storage.

[0045] As a preferred embodiment of the present invention, the preparation method comprises the following steps:

[0046] (1) mixing a polyurethane resin and a solvent at 70-90° C. for 3-5 hours to obtain a first solution;

[0047] (2) firstly mixing the polyester polyol and the curing agent at 20-30° C. for 20-40 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0048] (3) mixing the first solution and the second solution to obtain a third solution;

[0049] (4) mixing the heat-resistant filler and the coupling agent at 20-30° C. for 20-40 minutes to obtain a fourth solution;

[0050] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and then grind.

[0051] In a specific embodiment, grinding is performed using a triple roll mill.

[0052] The present invention also provides the use of the above-mentioned primer in a circuit board, preferably in a flexible circuit board.

[0053] The present invention also provides an electronic device, comprising a substrate, a conductive circuit and an adhesion layer located between the substrate and the conductive circuit, wherein the adhesion layer is formed by the primer described above.

[0054] Preferably, the conductive circuit is formed by printing a conductive paste and then heating and curing it; the curing temperature of the conductive paste is below 200°C.

[0055] Preferably, the substrate is made of elastic material.

[0056] Based on the above scheme, the beneficial effects of the present invention are as follows:

[0057] The present invention obtains a primer with excellent performance by optimizing the formula and preparation process; the primer is used to form an adhesion layer on the surface of the substrate in advance, and then a conductive circuit is formed on the surface of the adhesion layer using a conductive paste, which can not only significantly improve the adhesion between the conductive circuit and the substrate, but also effectively prevent the problem of conductive paste overflow, thereby greatly reducing the printing line width. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The flexible circuit board 1 in the test example 1;

[0059] Figure 2 This is the flexible circuit board II in Experimental Example 1. DETAILED DESCRIPTION

[0060] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0061] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0062] Example 1

[0063] This embodiment provides a primer, and its formula is as follows:

[0064] 6 parts by weight of polyester polyol, 10 parts by weight of polyurethane resin, 5 parts by weight of epoxy resin, 10 parts by weight of curing agent, 2 parts by weight of heat-resistant filler, 10 parts by weight of coupling agent, 56 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.5 parts by weight of leveling agent;

[0065] Among them, the molecular weight of the polyester polyol is 2000; the molecular weight of the polyurethane resin is 40000; the epoxy resin is bisphenol F epoxy resin with a molecular weight of 2000; the curing agent is isocyanate; the heat-resistant filler is gas silicone; the coupling agent is Dow Corning 6040; the solvent is DBE; the defoaming agent is defom5400; and the leveling agent is BYK3931.

[0066] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0067] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0068] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0069] (3) mixing the first solution and the second solution to obtain a third solution;

[0070] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0071] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0072] Example 2

[0073] This embodiment provides a primer, and its formula is as follows:

[0074] 10 parts by weight of polyester polyol, 10 parts by weight of polyurethane resin, 5 parts by weight of epoxy resin, 15 parts by weight of curing agent, 2 parts by weight of heat-resistant filler, 10 parts by weight of coupling agent, 47.3 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.2 parts by weight of leveling agent;

[0075] Among them, the molecular weight of the polyester polyol is 1500; the molecular weight of the polyurethane resin is 50000; the molecular weight of the epoxy resin is bisphenol F epoxy resin between 3000; the curing agent is isocyanate; the heat-resistant filler is talcum powder; the coupling agent is Dow Corning 6030; the solvent is dipropylene glycol methyl ether; the defoaming agent is defom6600; and the leveling agent is BYK354.

[0076] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0077] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0078] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0079] (3) mixing the first solution and the second solution to obtain a third solution;

[0080] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0081] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0082] Example 3

[0083] This embodiment provides a primer, and its formula is as follows:

[0084] 10 parts by weight of polyester polyol, 15 parts by weight of polyurethane resin, 5 parts by weight of epoxy resin, 10 parts by weight of curing agent, 2 parts by weight of heat-resistant filler, 10 parts by weight of coupling agent, 47.3 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.2 parts by weight of leveling agent;

[0085] Among them, the molecular weight of the polyester polyol is 2500; the molecular weight of the polyurethane resin is 60000; the epoxy resin is a bisphenol F epoxy resin with a molecular weight between 3000; the curing agent is isocyanate; the heat-resistant filler is mica powder; the coupling agent is KH550; the solvent is diethylene glycol butyl ether; the defoaming agent is defom5300; and the leveling agent is SY965.

[0086] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0087] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0088] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0089] (3) mixing the first solution and the second solution to obtain a third solution;

[0090] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0091] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0092] Example 4

[0093] This embodiment provides a primer, and its formula is as follows:

[0094] 5 parts by weight of polyester polyol, 15 parts by weight of polyurethane resin, 8 parts by weight of epoxy resin, 10 parts by weight of curing agent, 2 parts by weight of heat-resistant filler, 10 parts by weight of coupling agent, 49.3 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.2 parts by weight of leveling agent;

[0095] Among them, the molecular weight of the polyester polyol is 1800; the molecular weight of the polyurethane resin is 35000; the epoxy resin is a bisphenol F epoxy resin with a molecular weight between 1500; the curing agent is isocyanate; the heat-resistant filler is carbon black; the coupling agent is KH560; the solvent is DBE; the defoaming agent is defom5600; and the leveling agent is BYK3499.

[0096] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0097] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0098] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0099] (3) mixing the first solution and the second solution to obtain a third solution;

[0100] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0101] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0102] Example 5

[0103] This embodiment provides a primer, and its formula is as follows:

[0104] 5 parts by weight of polyester polyol, 14.3 parts by weight of polyurethane resin, 8 parts by weight of epoxy resin, 10 parts by weight of curing agent, 2 parts by weight of heat-resistant filler, 15 parts by weight of coupling agent, 45 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.2 parts by weight of leveling agent;

[0105] Among them, the molecular weight of the polyester polyol is 2200; the molecular weight of the polyurethane resin is 45000; the epoxy resin is a bisphenol F epoxy resin with a molecular weight between 2500; the curing agent is isocyanate; the heat-resistant filler is calcium carbonate; the coupling agent is KH570; the solvent is dimethyl adipate; the defoaming agent is defom5300; and the leveling agent is BYK354.

[0106] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0107] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0108] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0109] (3) mixing the first solution and the second solution to obtain a third solution;

[0110] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0111] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0112] Example 6

[0113] This embodiment provides a primer, and its formula is as follows:

[0114] 10 parts by weight of polyester polyol, 20 parts by weight of polyurethane resin, 8 parts by weight of epoxy resin, 10 parts by weight of curing agent, 4 parts by weight of heat-resistant filler, 15 parts by weight of coupling agent, 32.3 parts by weight of solvent, 0.5 parts by weight of defoaming agent, and 0.2 parts by weight of leveling agent;

[0115] Among them, the molecular weight of the polyester polyol is 2500; the molecular weight of the polyurethane resin is 60000; the epoxy resin is a bisphenol F epoxy resin with a molecular weight between 2800; the curing agent is isocyanate; the heat-resistant filler is mica powder; the coupling agent is Dow Corning 6020; the solvent is diethyl adipate; the defoaming agent is defom5600; and the leveling agent is SY935.

[0116] This embodiment further provides a method for preparing the above-mentioned primer, specifically:

[0117] (1) mixing a polyurethane resin and a solvent at 80° C. for 4 hours to obtain a first solution;

[0118] (2) firstly mixing the polyester polyol and the curing agent at 25° C. for 30 minutes, and then adding the epoxy resin to the mixture of the polyester polyol and the curing agent, and mixing them evenly to obtain a second solution;

[0119] (3) mixing the first solution and the second solution to obtain a third solution;

[0120] (4) mixing the heat-resistant filler and the coupling agent at 25° C. for 30 minutes to obtain a fourth solution;

[0121] (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and grind with a three-roll grinder.

[0122] Comparative Example 1

[0123] This comparative example provides a primer, which differs from Example 1 in that, in the formula, the amount of polyester polyol added is 13 parts, the amount of polyurethane resin added is 4 parts, and the amount of epoxy resin added is 4 parts.

[0124] Comparative Example 2

[0125] This comparative example provides a primer, which differs from Example 1 in that in the formula, the molecular weight of the polyester polyol is 3000.

[0126] Comparative Example 3

[0127] This comparative example provides a primer, which differs from Example 1 in that, in the formula, the molecular weight of the polyurethane resin is 20,000, and the epoxy resin is a bisphenol F epoxy resin with a molecular weight of 700.

[0128] Test Example 1

[0129] In this test example, the primer of Example 1 is used to form an adhesion layer on the surface of the PI film, and then a low-temperature conductive paste (i.e., a conductive paste with a curing temperature below 200°C) is used to print a circuit pattern on the surface of the adhesion layer, and a flexible circuit board I is obtained after heating and curing. In this test example, the above-mentioned circuit pattern is directly printed on the surface of the PI film using the above-mentioned low-temperature conductive paste, and a flexible circuit board II is obtained after heating and curing. The SEM picture of the flexible circuit board I is shown in FIG. Figure 1 , SEM picture of flexible circuit board II is shown in Figure 2 .Depend on Figure 1 and Figure 2 It can be seen that the conductive paste on the surface of flexible circuit board I does not overflow, and the printed line width can reach about 30 μm; while the conductive paste on the surface of flexible circuit board II overflows, and the printed line width is only about 70 μm. In addition, the primers of Examples 2-6 can also achieve the same effect as that of Example 1 above.

[0130] Test Example 2

[0131] In this test example, the primers of Examples 1-6 and Comparative Examples 1-3 were respectively applied to the surface of the PI film to form an adhesion layer, and then a low-temperature conductive paste (i.e., a conductive paste with a curing temperature below 200°C) was used to print a conductive circuit on the surface of the adhesion layer, and several flexible circuit boards (1 cm wide*10 cm long, 5 um thick) were obtained after heating and curing. The performance of each flexible circuit board was tested, as follows:

[0132] 1. Perform resistance tests on each flexible circuit board separately. The specific test method is: use a resistance tester to test each conductive circuit separately.

[0133] 2. Conduct adhesion tests on the conductive circuits on each flexible circuit board. The specific test method is: use 3M610 tape to adhere to the surface of the conductive circuit. After standing for 1 minute, use external force to quickly remove the 3M 610 tape and observe whether the conductive circuit has fallen off. If there is no falling off, the adhesion is good; if there is falling off (including partial falling off), the adhesion is poor.

[0134] 3. The test results are shown in Table 1.

[0135] Table 1 Resistance and adhesion test results of various flexible circuit boards

[0136]

[0137]

[0138] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A primer, characterized in that: The primer comprises the following components in parts by weight: 5-10 parts of polyester polyol, 10-20 parts of polyurethane resin, 5-10 parts of epoxy resin, 10-20 parts of curing agent, 2-5 parts of heat-resistant filler, 10-20 parts of coupling agent, 20-70 parts of solvent, 0.5-1 parts of defoaming agent, and 0.2-0.5 parts of leveling agent; in, The molecular weight of the polyester polyol is 1500-2500; The molecular weight of the polyurethane resin is 30000-60000; The epoxy resin is a bisphenol F epoxy resin with a molecular weight between 1000 and 3000; The curing agent is isocyanate; The heat-resistant filler is selected from one or more of calcium carbonate, talc, mica powder, silica powder, barium sulfate, kaolin, wollastonite, gas silica, carbon black, and titanium dioxide; The coupling agent is selected from one or more of Dow Corning 6040, Dow Corning 6011, Dow Corning 6020, Dow Corning 6030, KH570, KH560, and KH550; The solvent is selected from one or more of DBE, dimethyl adipate, diethyl adipate, dipropylene glycol methyl ether, propylene glycol dimethyl ether acetate, benzyl alcohol, dipropylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether, and isophorone; The defoaming agent is selected from one or more of GS-5333, GS-100, defom5400, defom6800k, defom5600, defom5300, and defom6600; The leveling agent is selected from one or more of BYK3931, BYK354, BYK361, BYK3350, BYK3499, SY933, SY965, and SY935; The primer forms an adhesion layer on the surface of the substrate in advance, and then a conductive paste is used to form a conductive circuit on the surface of the adhesion layer.

2. The method for preparing the primer according to claim 1, characterized in that: include: The polyester polyol, polyurethane resin, epoxy resin, curing agent, heat-resistant filler, coupling agent, solvent, defoaming agent and leveling agent are mixed uniformly and then ground.

3. The preparation method according to claim 2, characterized in that: The preparation method comprises the following steps: (1) mixing a polyurethane resin and a solvent to obtain a first solution; (2) mixing polyester polyol, curing agent and epoxy resin to obtain a second solution; (3) mixing the first solution and the second solution to obtain a third solution; (4) mixing a heat-resistant filler and a coupling agent to obtain a fourth solution; (5) Add the defoaming agent, the leveling agent and the fourth solution to the third solution in sequence, stir until uniform, and then grind.

4. The preparation method according to claim 3, characterized in that: In step (1), the mixing is carried out at 70-90° C. for 3-5 h; and / or, In step (2), the polyester polyol and the curing agent are first mixed at 20-30° C. for 20-40 min, and then the epoxy resin is added to the mixture of the polyester polyol and the curing agent and mixed evenly; and / or, In step (4), the mixing is performed at 20-30° C. for 20-40 min.

5. Use of the primer according to claim 1 in circuit boards.

6. Use of the primer according to claim 1 in a flexible circuit board.

7. An electronic device comprising a substrate, a conductive circuit and an adhesive layer between the substrate and the conductive circuit, characterized in that: The adhesive layer is formed from the primer according to claim 1 .

8. The electronic device according to claim 7, characterized in that: The conductive circuit is formed by printing conductive paste and heating and curing; the curing temperature of the conductive paste is below 200°C.

9. The electronic device according to claim 8, characterized in that: The material of the substrate is elastic material.

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