Inkjet inks and their use

Abstract

The present application relates to a kind of jet printing inks, the jet printing ink includes the following weight parts of components: photosensitive prepolymer 100-150 parts;Active diluent 15-25 parts;Photoinitiator 5-10 parts.The present application also relates to the application of the jet printing ink in printed flexible circuit board.The present application also relates to a kind of flexible circuit board, the flexible circuit board is made by jet printing or printing the jet printing ink described on substrate.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, and in particular to a printing ink, the application of the printing ink in the printing of flexible circuit boards, and a flexible circuit board printed with the printing ink. Background Technology

[0002] This section provides background information relevant to this application, which does not necessarily constitute prior art.

[0003] Flexible printed circuits (FPCs), also known as flexible circuit boards or flexographic circuit boards, are highly reliable and extremely flexible printed circuits made with polyester film or polyimide as the substrate. Current FPC fabrication technologies involve electroplating a conductive network of pure copper onto a thin-film substrate (usually polyimide film), or laminating pre-formed thin copper foil to create a conductive circuit. This conductive circuit is attached to the substrate film, thus possessing a certain degree of flexibility and bending capability.

[0004] Existing processes for manufacturing flexible circuit boards (PCBs) belong to a long-process manufacturing system, requiring more than 10 major process stages to complete the product manufacturing. This process is cumbersome, and due to the numerous steps, the accumulated quality defects increase exponentially, making it difficult to improve the manufacturing yield of flexible PCBs. To improve the manufacturing yield of flexible PCBs, existing technical solutions employ a short-process manufacturing system. This involves using inkjet printing combined with etching technology to form conductive circuits on a flexible substrate. Specifically, inkjet printing technology coats the copper layer of the flexible circuit board with inkjet ink (ink that is sensitive to ultraviolet light and can be cured by ultraviolet light). The inkjet ink is cured by ultraviolet (UV) irradiation to form a cured layer. Then, etching technology is used to remove the portions of the copper layer not covered by the cured layer, and finally, the cured layer is removed to obtain the copper circuit (i.e., the conductive circuit).

[0005] The main resin of existing inkjet printing inks is polyurethane acrylate (PUA). Reactive diluents also need to be added to inkjet printing inks. Reactive diluents are usually functional acrylates with good flexibility.

[0006] Existing inkjet printing inks used in the fabrication of flexible circuit boards have the following technical problems:

[0007] 1. Existing inkjet inks have a high viscosity. If a large amount of reactive diluent is used to reduce their viscosity, it will result in a low solid content in the ink.

[0008] 2. Existing inkjet inks have poor compatibility and adhesion with polyimide flexible circuit boards. Summary of the Invention

[0009] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of the present invention is to provide a printing ink; another objective of the present invention is to provide a method for preparing the above-mentioned printing ink, the application of the printing ink on a printed flexible circuit board, and a flexible circuit board printed with the printing ink.

[0010] According to one aspect of the present invention, a printing ink is provided, the printing ink comprising the following components in parts by weight:

[0011] 100-150 parts of photosensitive prepolymer;

[0012] 15-25 parts of reactive diluent;

[0013] 5-10 parts of photoinitiator.

[0014] The reactive diluent is at least one of the following: hydroxyethyl methacrylate, hydroxyethyl acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate, isobornyl acrylate, isobornyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate, vinyl acetate, hydroxymethylpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate.

[0015] The photoinitiator is at least one of the following: diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (819), 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), 4-benzoyl-4'-methyl-diphenyl sulfide (BMS), 1-hydroxycyclohexylphenyl ketone (184), mixed triaryl sulfonium hexafluorophosphate (cationic GC-2291), diphenyl-(4-phenylthio)phenylsulfonium hexafluorophosphate (cationic GC-2391), triaryl hexafluoroantimonate (cationic GC-2671), bis(2,6-difluoro-3-pyrrolephenyldicyclopentadiene) (784), diphenyl ethyl ketone, α,α-diethoxyacetophenone, benzoin ether, benzoin butyl ether, and 1-chloro-4-propoxythioxanthrone.

[0016] The method for synthesizing the photosensitive prepolymer includes the following steps:

[0017] Step 1: Mix bisphenol A type epoxy resin and organic solvent evenly to obtain the first mixture;

[0018] Step 2: Add the polymerization inhibitor and p-toluenesulfonic acid to the first mixture and mix them evenly to obtain the second mixture;

[0019] Step 3: Heat the second mixture to 75-80℃ and then slowly add pentenoic acid to obtain the third mixture;

[0020] Step four: Heat the third mixture to 90-95℃ and maintain the reaction at this temperature until the difference between the measured acid value and the initial acid value is <5mg(KOH) / g, to obtain the fourth mixture;

[0021] Step 5: Add cis-3,4-dihydroxyfuran to the fourth mixture, then heat to 100-110℃ and maintain the reaction until the amount of water separated is the theoretically calculated value, to obtain the fifth mixture;

[0022] Step six: Distill the fifth mixture under reduced pressure to remove the organic solvent and obtain the photosensitive prepolymer.

[0023] In step three, the addition of pentenoic acid should be completed within 2 hours.

[0024] In step one, the mass of the organic solvent is 65%-75% of the mass of the bisphenol A epoxy resin. Preferably, the organic solvent is a hydrocarbon compound, including aliphatic hydrocarbons such as n-hexane, octane, and n-decane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and cumene; and hydrocarbon solvents such as mineral oil, naphtha, kerosene, and petroleum ether.

[0025] The polymerization inhibitor is at least one of p-hydroxyanisole and hydroquinone. Preferably, the amount of polymerization inhibitor added is 100-200 ppm based on the total mass of the organic solvent and bisphenol A epoxy resin, and the polymerization inhibitor is removed during vacuum distillation.

[0026] While the conversion rate of the synthesized photosensitive prepolymer increases with increasing p-toluenesulfonic acid content, it is difficult to separate out during subsequent purification processes. Residual p-toluenesulfonic acid in the product may affect the final performance of the inkjet printing ink, especially its electrical properties. Preferably, the amount of p-toluenesulfonic acid added is 50-80 ppm, based on the total mass of the organic solvent and bisphenol A epoxy resin.

[0027] According to another aspect of the present invention, a method for preparing the above-mentioned inkjet printing ink is also provided, comprising the following steps: mixing the above-prepared photosensitive prepolymer, reactive diluent and photoinitiator in proportion to obtain inkjet printing ink.

[0028] According to another aspect of the invention, the application of the inkjet ink in the printing of flexible circuit boards is also provided.

[0029] According to another aspect of the present invention, a flexible circuit board is also provided, which is manufactured by inkjet spraying or printing the aforementioned inkjet ink onto a substrate.

[0030] Compared with existing inkjet printing ink synthesis technologies, the present invention has the following advantages and beneficial effects:

[0031] 1. The substrate of flexible circuit boards is mostly polyimide. The inkjet ink prepared by this invention can be applied to flexible circuit boards and has excellent compatibility and adhesion with flexible circuit boards.

[0032] 2. The inkjet printing ink provided by this invention has excellent performance in terms of flexibility, flexural strength, printability, drying speed, water resistance, and color vibrancy;

[0033] 3. The ink provided by this invention has the advantages of moderate viscosity, good insulation and protection effect, and fast curing rate. This ink facilitates the printing of flexible circuit boards by inkjet printing, simplifies the ink printing steps, and the printed circuit board can be quickly cured by UV exposure, which is convenient for production. Areas that do not need to be cured can also be cleaned by organic solvents.

[0034] 4. The inkjet printing ink prepared by this invention has moderate viscosity, low content of reactive diluent, and correspondingly high content of photosensitive prepolymer. After the ink film is formed, it has high crosslinking degree and good overall performance.

[0035] The following description uses a specific embodiment as an example. Detailed Implementation

[0036] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0037] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0038] It should be noted that the acid value determination described in this invention specifically includes the following steps: accurately weigh 1g of sample (accurate to 0.001g) into a 250mL conical flask, add an equal volume of benzene-ethanol mixed solution, and dissolve. Add 3 drops of phenolphthalein indicator, and titrate with potassium hydroxide-ethanol standard solution until a pink endpoint is reached, while simultaneously performing a blank experiment.

[0039] Acid value (a) is calculated using the following formula:

[0040] a = c × V × 56.1 / m

[0041] In the formula:

[0042] 'a' represents the acid value, mg(KOH) / g;

[0043] c is the concentration of the KOH-ethanol solution, in mol / L;

[0044] V represents the volume of potassium hydroxide-ethanol solution consumed, in mL;

[0045] 56.1 is the molar mass, in g / mol;

[0046] m is the sample mass, in grams.

[0047] It should be noted that, depending on actual needs, commonly used additives such as anti-skinning agents (hydroquinone, methyl ethyl ketone oxime, etc.), dispersants (anionic dispersants, nonionic dispersants, etc.), wetting agents (ethoxylated nonionic surfactants, ethylene glycol, etc.), and stabilizers (pH stabilizers) can also be added to the ink provided by this invention.

[0048] Examples 1-6 of the present invention provide a printing ink, and the specific composition is shown in Table 1, wherein the same photosensitive prepolymer is used in Examples 4-6.

[0049] When preparing the ink, weigh each component according to the ingredients and corresponding weight parts listed in Table 1, and mix them evenly to obtain the inkjet printing ink. When using this inkjet printing ink, fill the inkjet printing device with the inkjet ink and print the polyimide flexible circuit board. After the polyimide flexible circuit board is inkjet printed, it is UV cured by multiple 30W ultraviolet lamps to complete the printing work.

[0050] Table 1

[0051]

[0052] The synthesis methods of the photosensitive prepolymers used in the embodiments of the present invention all include the following steps:

[0053] Step 1: Mix bisphenol A type epoxy resin and organic solvent evenly to obtain the first mixture;

[0054] Step 2: Add the polymerization inhibitor and p-toluenesulfonic acid to the first mixture and mix them evenly to obtain the second mixture;

[0055] Step 3: After heating the second mixture to the first reaction temperature, slowly add pentene diic acid to obtain the third mixture. The addition of pentene diic acid should be completed within 2 hours.

[0056] Step four: Heat the third mixture to the second reaction temperature and maintain the reaction at this temperature until the difference between the measured acid value and the initial acid value is <5 mg (KOH) / g, to obtain the fourth mixture;

[0057] Step 5: Add cis-3,4-dihydroxyfuran to the fourth mixture, then heat to the third reaction temperature and maintain the reaction until the amount of water separated is the theoretically calculated value, to obtain the fifth mixture;

[0058] Step six: Distill the fifth mixture under reduced pressure to remove the organic solvent and obtain the photosensitive prepolymer.

[0059] Table 2 shows the specific raw materials and conditions for preparing the photosensitive prepolymers in Examples 1-4 of this invention.

[0060] Table 2

[0061]

[0062] The specific process for using the inkjet printing ink provided in the embodiments of the present invention to prepare FPC includes:

[0063] Step 1: Perform substrate pretreatment, including cleaning the substrate surface, removing oil and dirt, and drying.

[0064] Step 2: Fill the inkjet printing device with inkjet printing ink and print the polyimide flexible substrate by inkjet printing.

[0065] Step 3: After the polyimide flexible circuit board is inkjet printed, it is UV cured for 5 minutes by multiple 30W ultraviolet lamps. The inkjet ink undergoes a cross-linking reaction and hardens under ultraviolet light catalysis, thus completing the UV curing.

[0066] Step 4, developing: Rinse the cured substrate with developer for 2 minutes. The ink that has undergone cross-linking reaction cannot be washed away, while the ink that has not received UV catalysis has not undergone cross-linking reaction. Therefore, this part of the ink is washed away by developer.

[0067] Step 5, perform etching: clean the substrate surface, then dry it, and immerse the dried substrate in the etching solution for 15-30 minutes;

[0068] Step 6, perform stripping: Prepare a stripping solution and immerse the etched substrate in the stripping solution for 5 minutes. At this time, the cured ink on the wires is removed, and the printed flexible polyimide circuit board is obtained.

[0069] The performance of the inkjet printing inks provided in Examples 1-6 was tested, specifically in a laboratory environment (working temperature approximately 25°C, relative humidity 60% RH) as follows:

[0070] Surface drying time test: The inkjet printing ink is evenly applied to the surface of a polytetrafluoroethylene (PTFE) plate and cured under UV light at a set light source and exposure time. According to GB1728-79, a filter paper is pressed onto the cured film with a 200g drying weight. After a certain time, the weight is removed, and the cured film is turned over. If the filter paper can fall off freely, it is considered to be surface dry. The surface drying time of the ink is then measured.

[0071] Viscosity analysis and characterization: Tested using a rotational viscometer.

[0072] Stability testing: Thermal stability and mechanical stability analysis were used to characterize the ink. For thermal stability analysis, the ink was placed in a 50℃ constant temperature oven and its appearance was observed to change over time. The time required for stratification was recorded. For mechanical stability analysis, the ink was placed in a centrifuge tube and centrifuged at 8000 r / min for 20 min. Whether stratification occurred was observed.

[0073] Ink leveling test: The ability of a wet film to flow and eliminate paint marks after ink application. In this embodiment, the leveling test method is expressed as the time required for the coating film to recover or achieve a uniform and smooth surface. A coating film that levels within 5 minutes is considered to have excellent leveling properties, and a coating film that levels within 10 minutes is considered to have good leveling properties.

[0074] Determination of mechanical properties of ink-cured films: The mechanical properties of photocured films were determined in accordance with GB13022–91.

[0075] Water resistance is characterized by water absorption rate, tested according to the method of GB / T1733–93.

[0076] The adhesion was determined according to the method of GB / T9286–1998.

[0077] The test results are shown in Table 3.

[0078] Table 3

[0079] Surface stem(s) 14 16 16 15 15 14 Viscosity (Pa·s) 1377 1448 1302 1122 1158 1141 stability No layering No layering No layering No layering No layering No layering Leveling excellent excellent excellent excellent excellent excellent Elongation at break (%) 9.7 9.8 9.8 9.9 9.9 9.9 Water absorption rate (%) 1.06 1.01 1.02 0.95 0.99 0.98 Adhesion Level 0 Level 0 Level 0 Level 0 Level 0 Level 0

[0080] For inkjet printing inks, the shorter the surface drying time, the greater the tensile strength and flexibility (i.e., the greater the elongation at break), the better the overall performance of the inkjet printing ink. The inkjet printing inks prepared in this invention have surface drying times of less than 17 seconds, viscosity concentrated between 1100-1500 Pa·s, no stratification in thermal and mechanical stability analyses, excellent leveling properties, elongation at break greater than 9.7%, low water absorption, and good adhesion of inkjet printing ink to the cut edges. Therefore, the comprehensive performance of the inkjet printing inks prepared in this invention, such as curing rate and film mechanical properties, fully meets the requirements for FPC preparation.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A printing ink, characterized in that, The inkjet printing ink comprises the following components in parts by weight: 100-150 parts of photosensitive prepolymer; 15-25 parts of reactive diluent; 5-10 parts of photoinitiator; The method for synthesizing the photosensitive prepolymer includes the following steps: Step 1: Mix bisphenol A type epoxy resin and organic solvent evenly to obtain the first mixture; Step 2: Add the polymerization inhibitor and p-toluenesulfonic acid to the first mixture and mix them evenly to obtain the second mixture; Step 3: Heat the second mixture to 75-80℃ and then slowly add pentenoic acid to obtain the third mixture; Step four: Heat the third mixture to 90-95℃ and maintain the reaction at this temperature until the difference between the measured acid value and the initial acid value is <5mg(KOH) / g, to obtain the fourth mixture; Step 5: Add cis-3,4-dihydroxyfuran to the fourth mixture, then heat to 100-110℃ and maintain the reaction until the amount of water separated is the theoretically calculated value, to obtain the fifth mixture; Step six: The fifth mixture is distilled under reduced pressure to remove the organic solvent to obtain the photosensitive prepolymer; The organic solvent is 65%-75% of the mass of the bisphenol A epoxy resin, and the organic solvent is a hydrocarbon compound. The polymerization inhibitor is at least one of p-hydroxyanisole and hydroquinone, and the amount of the polymerization inhibitor added is 100-200 ppm based on the total mass of the organic solvent and the bisphenol A type epoxy resin. Based on the total mass of the organic solvent and the bisphenol A type epoxy resin, the amount of p-toluenesulfonic acid added is 50-80 ppm.

2. The inkjet printing ink according to claim 1, characterized in that, The reactive diluent is at least one selected from hydroxyethyl methacrylate, hydroxyethyl acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate, isobornyl acrylate, isobornyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate, vinyl acetate, methylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate.

3. The inkjet printing ink according to claim 1, characterized in that, The photoinitiator is at least one selected from diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 4-benzoyl-4'-methyl-diphenyl sulfide, 1-hydroxycyclohexylphenyl ketone, mixed triaryl sulfonium hexafluorophosphate, diphenyl-(4-phenylthio)phenylsulfonium hexafluorophosphate, triaryl hexafluoroantimonate, bis(2,6-difluoro-3-pyrrolephenyldicyclopentadiene), diphenyl ethyl ketone, α,α-diethoxyacetophenone, benzoin ether, benzoin butyl ether, and 1-chloro-4-propoxythioxanthrone.

4. The application of the inkjet printing ink according to claim 1 in the printing of flexible circuit boards.

5. A flexible circuit board, characterized in that, The flexible circuit board is manufactured by inkjet printing or printing the inkjet ink of claim 1 onto a substrate.

Images