A photopolymerizable catalytic printing ink for preparing flexible circuits

Abstract

The present invention discloses a photopolymerization catalytic printing ink for preparing a metal layer of a flexible circuit, wherein a photoreaction accelerator in the form of a eutectic liquid is added to the ink, and the ink belongs to the field of flexible electronics, and relates to the preparation of a metal layer of a flexible circuit. Adding a small amount of photoreaction accelerator to the ink can increase the curing rate of the ink, reduce the amount of the corresponding photoinitiator, and the amount of metal catalytic active substances in the ink is relatively small, which can effectively reduce the preparation cost of the ink. The ink printed on the surface of a flexible substrate can form an active bridging layer on the surface of the flexible substrate after ultraviolet curing, and then the preparation of the metal layer of the flexible circuit is achieved through subsequent chemical deposition, and the surface of the printed substrate does not need to be pre-treated physically or chemically to obtain a metal layer with good adhesion and conductivity. The process of the present invention has the advantages of simple operation process, green and pollution-free, low cost, high production efficiency and wide application range.

Description

Technical Field

[0001] The invention relates to the field of flexible electronics, and in particular to a method for preparing a photopolymerizable catalytic printing ink for preparing a flexible circuit. Background Art

[0002] 1. With the continuous development of Internet technology and the improvement of the intelligence level of electronic products, the demand for the electronics market continues to grow rapidly, and people's functional requirements for electronic products have begun to diversify, especially portable and wearable flexible electronics. In addition, the design difficulties and manufacturing costs of flexible electronic products are more concentrated in the metallization of electronic circuit graphics, which puts forward new requirements for electronic manufacturing technology, makes it face many challenges, and requires continuous technological innovation.

[0003] 2. At present, the preparation of the metal layer of the flexible circuit is mostly achieved by printing metal conductive ink on the flexible substrate using printing technology and subsequent high-temperature sintering. Although this preparation method can successfully prepare the corresponding flexible circuit, most of them require high-temperature sintering, which will cause a series of irreversible effects on the substrate such as softening and deformation. Even if the sintering temperature of the optimized metal conductive ink is reduced, there are still problems such as complex preparation process and expensive metal materials. The method of using printing technology to print the photopolymerization catalytic printing ink on the surface of the flexible substrate to form a flexible circuit graphic active ink layer and then combining it with chemical deposition to prepare the metal layer has many advantages: the photopolymerization catalytic printing ink does not contain organic solvents, and no volatile organic substances harmful to the environment are generated during the production and preparation process. There is no harmful gas emission. It is an environmentally friendly ink that can be quickly cured at room temperature, and the printed product production speed is fast, and there is no need to wait for drying time; the use of chemical deposition technology to prepare the circuit metal layer has the advantages of simple process, no need for power supply, wide application range, low cost, low investment, and the chemical plating solution can be recycled, no toxic substances, and environmentally friendly.

[0004] 3. Currently, most flexible substrates are made of polymer materials, which have low surface energy, small roughness, are difficult to metallize, and have poor adhesion between the metal layer and the substrate, making it difficult to provide good metal adhesion. Therefore, before preparing the metal layer of the flexible circuit, the substrate needs to be pretreated on the surface, such as polishing, corona, chemical modification, etc., to enhance the adhesion between the substrate surface and the metal coating. This will make the flexible circuit preparation process more complicated, the production cost higher, and the production efficiency lower. The present invention uses a preparation scheme of preparing a bridging layer on the surface of the substrate by photopolymerization catalytic printing ink and then preparing the flexible circuit metal layer by subsequent chemical deposition. A metal copper layer with high adhesion can be obtained without pretreating the substrate surface.

[0005] 4. The photoinitiator in the photopolymerization catalytic printing ink is a key component involved in the photocuring reaction. If the content of photoinitiator in the photopolymerization catalytic printing ink is high, it will accelerate the photooxidation reaction, making the ink prone to aging and yellowing, affecting the storage time and life. In addition, too high a photoinitiator content is not conducive to reducing the preparation cost of the ink. If the amount of photoinitiator added is insufficient, it will reduce the absorption of ultraviolet light and reduce the photocuring effect, resulting in a slower curing speed of the ink.

[0006] Based on the above problems, the present invention has developed a photopolymerization catalytic printing ink containing a photoinitiator accelerator in the form of a eutectic liquid, which can be used to prepare a metal layer of a flexible circuit. Summary of the invention

[0007] The present invention provides a photopolymerization catalytic printing ink for preparing a metal layer of a flexible circuit. The amount of metal catalytic active substances in the ink is relatively small, which can effectively reduce the preparation cost of the ink. A photoreaction accelerator in the form of a eutectic liquid is added to the ink, which can reduce the amount of photoinitiator, thereby reducing the cost of the ink formulation while ensuring that the ink has a good curing effect and curing speed. The ink printed on the surface of a flexible substrate can form an active bridging layer on the surface of the flexible substrate after ultraviolet curing, and then the preparation of the metal layer of the flexible circuit is achieved through subsequent chemical deposition. The surface of the printing substrate does not need to be pre-treated physically or chemically to obtain a metal layer with good adhesion and conductivity.

[0008] The technical solution of the present invention is achieved in this way:

[0009] 1. The present invention prepares a photopolymerization catalytic printing ink for preparing a flexible circuit, characterized in that a photoreaction accelerator in the form of a eutectic liquid is added to the printing ink, wherein the photoreaction accelerator in the form of a eutectic liquid is prepared from a mixture of the following compounds S1 and S2:

[0010] S1, at least one selected from benzaldehyde, phenol formaldehyde, propylene benzoate.

[0011] S2, at least one selected from alanine, dimethylformamide, and allylamine;

[0012] 2. The photoreaction accelerator is a mixture of one or more compounds of S1 and S2, wherein the mass ratio of S1 to S2 in the mixture is between 0.25 and 0.75, and the mixture is heated at a temperature higher than the melting point of the mixture to form a photoreaction accelerator in the form of a eutectic liquid;

[0013] 3. A photopolymerizable catalytic printing ink for preparing a flexible circuit, characterized in that it comprises 1-4% by weight of a photoreaction accelerator, 1-6% by weight of a photoinitiator, 30-50% by weight of polyurethane diacrylate, 5-9% by weight of a catalytically active substance complex, and 30-55% by weight of a diluent monomer;

[0014] At least one of the photoinitiators is selected from 1-hydroxycyclohexyl phenyl ketone, benzophenone, 4-benzoylbenzamide, 2-(dimethylamino)phenyl ketone, and benzoylbenzene; the catalytically active substance complex is a stable complex formed by dissolving one or more of platinum salt, palladium salt and silver salt in sec-butylamine, isopropanolamine or ethylenediamine; the diluent monomer is one or more of N-methylacrylamide, trimethylolpropane triacrylate, and 2-hydroxyethyl butyl acrylate;

[0015] 4. The polyurethane diacrylate is dissolved in the diluted monomer, and after preliminary stirring and dispersion, the catalytic active substance complex is added, and then the photoinitiator and the photoreaction accelerator are added. The mixed material is stirred for 100 to 180 minutes at a stirring speed of 200 to 500 r / min. After sufficient stirring and mixing, a photopolymerization catalytic printing ink for preparing a metal layer of a flexible circuit is obtained.

[0016] 5. The present invention also provides a method for preparing a metal layer of a flexible circuit using the photopolymerizable catalytic printing ink, which is characterized by comprising the following steps:

[0017] Step 1: Using the prepared photopolymerizable catalytic printing ink to form a specific flexible circuit pattern liquid ink layer on the surface of the flexible substrate by using printing technology;

[0018] Step 2: Curing the flexible circuit pattern liquid ink layer printed in step 1 in a UV box for 1 to 200 seconds to form a highly adherent flexible circuit pattern solid ink layer with the flexible substrate;

[0019] Step 3: Place the solid ink layer of the flexible circuit pattern obtained in step 2 in a chemical plating solution at a temperature of 38-50° C., deposit for 20-30 minutes, then take it out and rinse it with deionized water, and finally dry it at 50° C. for 5 minutes to obtain the flexible circuit metal layer.

[0020] 6. Furthermore, the printing technology in step 1 includes inkjet printing, screen printing, flexographic printing, and gravure printing; the flexible substrate includes paper, fabric, polyethylene terephthalate, polyimide, and epoxy resin;

[0021] 7. The photopolymerizable catalytic printing ink prepared by the present invention for preparing flexible circuits creatively utilizes several compounds in claim 1 to prepare a photoreaction accelerator in the form of a eutectic liquid, and the eutectic liquid simultaneously has structures such as an aromatic ring, an aldehyde group, and an amino group. When the photoinitiator generates free radicals under ultraviolet irradiation, the aromatic aldehyde structure in the eutectic liquid can capture the excited free radicals and convert them into stable intermediates. The amino group can also react with the free radical intermediates in a targeted manner, providing a reaction center for hydrogen atoms or electrons, and helping the free radicals to react stably and quickly. The photopolymerizable catalytic printing ink is printed on the surface of a flexible substrate. After ultraviolet irradiation, the ink layer on the surface of the substrate can change from liquid to solid, forming a strong adhesion with the substrate, and the catalytically active substances are evenly distributed in the ink layer, providing active sites for subsequent chemical deposition.

[0022] 8. Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The present invention adds a photoreaction accelerator to the catalytic printing ink, and only 1-6% of the photoinitiator is required to ensure that the ink has a good curing effect, which effectively reduces the amount of photoinitiator used and the residual photoinitiator after the photoreaction, reduces the side reactions of the photoreaction, reduces the preparation cost of the ink, and can ensure that the ink undergoes a stable and rapid polymerization reaction, and the preparation form is novel;

[0024] (2) The photopolymerization catalytic printing ink prepared by the present invention does not contain organic solvents, and does not produce volatile organic substances harmful to the environment during the production and preparation process. There is no harmful gas emission, and it is an environmentally friendly ink. The use of ultraviolet curing technology can make the ink form a firm adhesion on the surface of the substrate, and can be quickly cured at room temperature without causing a series of irreversible effects on the substrate such as softening and deformation. The product production speed is fast and there is no need to wait for drying time. In addition, the printing substrate does not need to be physically and chemically pretreated, which greatly simplifies the preparation process of the flexible circuit and reduces production costs;

[0025] (3) The metal layer of the flexible circuit is prepared by chemical deposition process. The preparation process is simple, no electricity is required, and the application range is wide. The cost is low, the investment is small, and the chemical plating solution can be recycled. It does not contain toxic substances and is environmentally friendly.

[0026] (4) The photopolymerizable catalytic printing ink has good printability and adjustable performance parameters. It can be used to prepare flexible circuits on the surfaces of various flexible substrates using different printing technologies. It has the prospect of industrial production and lays the foundation for the manufacture of ultra-low-cost flexible-based circuit systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0028] Figure 1The optical photographs of the flexible circuit metal layer obtained in Example 1 and the comparative example are compared, wherein (a) is the flexible circuit metal layer obtained in Example 1, and (b) is the flexible circuit metal layer obtained in the comparative example. DETAILED DESCRIPTION Example

[0029] Step 1: Dissolve 45.5g of polyurethane diacrylate in 42g of diluted monomer, add 9g of catalytic active substance complex after initial stirring and dispersion, then add 2g of photoinitiator, and finally add 1.5g of photoreaction accelerator, stir and mix thoroughly to obtain photopolymerization catalytic printing ink.

[0030] Step 2: Printing the photopolymerizable catalytic printing ink prepared in step 1 on the surface of a flexible substrate by printing technology to form a flexible circuit pattern liquid ink layer, and then placing the flexible circuit pattern liquid ink layer in a UV box for curing for 6 seconds to form a highly adherent flexible circuit pattern solid ink layer with the flexible substrate;

[0031] Step 3: Place the solid ink layer of the flexible circuit pattern obtained in step 2 in a chemical plating solution, chemically deposit it at 45°C for 30 minutes, then take out the obtained flexible circuit, rinse it with deionized water, and finally dry it at 50°C for 5 minutes to obtain a flexible circuit metal layer on the surface of the flexible substrate.

[0032] The specific steps of Examples 2-6 are the same as those of Example 1. The specific formula and UV curing time are shown in Table 1:

[0033] Table 1 Example scheme

[0034] Polyurethane diacrylate (g) Diluted monomer (g) Catalytically active substance complex (g) Photoinitiator (g) Photoinitiator accelerator (g) UV curing time (s) Example 2 35 48 9 6 2 21 Example 3 48 43 5 3 1 15 Example 4 36 50 8 4 2 19 Example 5 41 42 7 6 4 17 Example 6 40 49 6 3 2 11

[0035] Comparative Example:

[0036] Step 1: Dissolve 45.5 g of polyurethane diacrylate in 42 g of diluent monomer, add 9 g of catalytic active substance complex after initial stirring and dispersion, and finally add 2 g of photoinitiator, stir and mix thoroughly to obtain photopolymerization catalytic printing ink.

[0037] Step 2: Printing the photopolymerizable catalytic printing ink prepared in step 1 on the surface of a flexible substrate to form a flexible circuit pattern liquid ink layer, and then placing the flexible circuit pattern liquid ink layer in a UV box for curing for 6 seconds to form a highly adherent flexible circuit pattern solid ink layer with the flexible substrate;

[0038] Step 3: Place the solid ink layer of the flexible circuit pattern obtained in step 2 in a chemical plating solution, chemically deposit it at 45°C for 30 minutes, then take out the obtained flexible circuit, rinse it with deionized water, and finally dry it at 50°C for 5 minutes to obtain a flexible circuit metal layer on the surface of the flexible substrate.

[0039] Table 2 shows the curing time of the photopolymerizable catalytic printing ink, the conductivity of the metal layer of the flexible circuit, and the adhesion between the metal layer and the flexible substrate.

[0040] Table 2 Performance test of photopolymerization catalytic printing ink

[0041] Curing time (s) Metal layer resistivity (μΩ·cm) Metal layer adhesion grade Example 1 6 2.98 5B Example 2 21 4.56 2B Example 3 15 3.58 4B Example 4 19 3.97 3B Example 5 17 3.72 4B Example 6 11 3.32 5B

[0042] Figure 1 The optical photographs of the flexible circuit metal layer obtained in Example 1 and the comparative example are compared, wherein (a) is the flexible circuit metal layer obtained in Example 1, and (b) is the flexible circuit metal layer obtained in the comparative example. Figure 1 It can be seen that the metal layer pattern prepared after adding the photoreaction accelerator is clear and has a metallic luster, while the metal layer pattern prepared without adding the photoreaction accelerator is fuzzy, the metal layer is discontinuous and dense, and the quality of the metal layer is poor. The reason is that the photopolymerization catalytic printing ink prepared by the present invention adds a photoreaction accelerator, which can effectively improve the curing effect of the photocuring reaction and ensure that the photocuring reaction is carried out efficiently and stably, thereby obtaining a flexible circuit metal layer with excellent performance.

[0043] In all the above examples except the comparative example, the photoreaction accelerator is not limited to a certain substance. As long as the description of the photoreaction accelerator in the content of the invention is followed, any photoreaction accelerator in the form of a eutectic liquid formed by a combination can solve the technical problem of the present invention and achieve the technical effect of the present invention.

Claims

1. A photopolymerizable catalytic printing ink for preparing a flexible circuit, characterized in that A photoreaction accelerator in the form of a eutectic liquid is added to the printing ink containing the catalytically active substance complex, wherein the photoreaction accelerator in the form of a eutectic liquid is a mixture of the following compounds S1 and S2: S1, at least one selected from benzaldehyde, phenol formaldehyde, propylene benzoate; S2, at least one selected from alanine, dimethylformamide, and allylamine.

2. A photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 1, characterized in that One or more compounds in S1 and S2 are mixed, the mass ratio of S1 to S2 in the mixture is between 0.25 and 0.75, and finally the mixture is heated at a temperature higher than the melting point of the mixture to form a photoreaction accelerator in the form of a eutectic liquid.

3. The photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 2, characterized in that: The invention comprises 1-4% by weight of a photoreaction accelerator, 1-6% by weight of a photoinitiator, 30-50% by weight of polyurethane diacrylate, 5-9% by weight of a catalytically active substance complex, and 30-55% by weight of a diluent monomer.

4. The photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 3, characterized in that: At least one of the photoinitiators is selected from 1-hydroxycyclohexyl phenyl ketone, benzophenone, 4-benzoylbenzimide, 2-(dimethylamino)phenyl ketone, and benzoylbenzene.

5. A photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 4, characterized in that The catalytic active substance complex is a stable complex formed by dissolving one or more of platinum salt, palladium salt and silver salt in sec-butylamine, isopropanolamine or ethylenediamine.

6. The photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 5, characterized in that: The diluting monomer is one or more of N-methyl acrylamide, trimethylolpropane triacrylate, and 2-hydroxyethyl butyl acrylate.

7. A photopolymerizable catalytic printing ink for preparing a flexible circuit according to claim 6, characterized in that 30-50% of polyurethane diacrylate is dissolved in 30-55% of diluent monomer, and after preliminary stirring and dispersion, 5%-9% of the catalytic active substance complex is added, followed by 1-6% of a photoinitiator and 1-4% of a photoreaction accelerator. The mixed material is stirred for 100-180 minutes at a stirring speed of 200-500 r / min, and after sufficient stirring and mixing, a photopolymerization catalytic printing ink for preparing a flexible circuit is obtained.

8. A method for preparing a metal layer of a flexible circuit using the photopolymerizable catalytic printing ink according to any one of claims 1 to 7, characterized in that The following steps are involved: Step 1: Using the prepared photopolymerizable catalytic printing ink to form a specific flexible circuit pattern liquid ink layer on the surface of the flexible substrate by using printing technology; Step 2: Curing the flexible circuit pattern liquid ink layer printed in step 1 in a UV box for 1 to 200 seconds to form a highly adherent flexible circuit pattern solid ink layer with the flexible substrate; Step 3: Place the solid ink layer of the flexible circuit pattern obtained in step 2 in a chemical plating solution at a temperature of 38-50° C., deposit for 20-30 minutes, then take it out and rinse it with deionized water, and finally dry it at 50° C. for 5 minutes to obtain the flexible circuit metal layer.

9. The method for preparing a metal layer of a flexible circuit according to claim 8, characterized in that A flexible circuit graphic liquid ink layer is formed on the surface of paper, fabric, polyethylene terephthalate, polyimide, and epoxy resin substrates through screen printing, inkjet printing, flexographic printing, and gravure printing technology.

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