An adhesive for a flexible circuit board, a method for preparing the same, and an application thereof

Abstract

The application discloses an adhesive for a flexible circuit board and a preparation method and application thereof. The adhesive for the flexible circuit board comprises the following raw materials: an epoxy-modified acrylic resin, adipic acid dihydrazide, carboxyl nitrile rubber, a titanate coupling agent, silicon dioxide and a solvent. The adhesive prepared by the application has excellent adhesive property and high-temperature resistance. When the adhesive is applied to bonding of a metal reinforcing plate of a flexible printed circuit board, the adhesive can resist high-temperature soldering heat shock and has stable peeling strength in a high-temperature and high-humidity environment, and can be widely applied to bonding of composite materials.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to an adhesive for flexible circuit boards, its preparation method, and its application. Background Technology

[0002] Flexible printed circuit boards (FPCs), also known as flexible printed circuit boards or soft printed circuit boards, are products in which circuit patterns are designed and manufactured on a flexible substrate through printing. Among these are the gold fingers, which consist of numerous golden-yellow conductive contacts. They are called "gold fingers" because their surface is gold-plated and their arrangement resembles fingers.

[0003] In related technologies, the gold fingers of FPC are too soft, making insertion and removal difficult. To solve this problem, a common method is to bond polyimide reinforcing plates, stainless steel reinforcing plates, aluminum sheet reinforcing plates, and FR4 reinforcing plates to this location for reinforcement. However, the adhesives used require a dyne value greater than 40 on the bonded surface. But when silicone oil or release agent residue is present on the surface of the object being bonded, the dyne value is less than 40. After the adhesive is bonded to the stainless steel or aluminum sheet reinforcing plates, there are still problems such as low peel strength (less than 1.5 kgf / cm) and insufficient heat resistance.

[0004] Therefore, there is an urgent need to find an adhesive with high peel strength, good heat resistance, and suitable for flexible circuit boards. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes an adhesive for flexible circuit boards, its preparation method, and its application, which has excellent heat resistance and stable and high peel strength in high temperature and high humidity environments (temperature 85°C, humidity 85%RH).

[0006] The present invention also provides a method for preparing the above-mentioned adhesive for flexible circuit boards.

[0007] The present invention also provides the application of the above-mentioned adhesive for flexible circuit boards in the preparation of flexible circuit boards or printed circuit boards.

[0008] An adhesive for flexible circuit boards according to a first aspect embodiment of the present invention comprises the following raw materials:

[0009] Epoxy-modified acrylic resin, adipic dihydrazide, carboxylated nitrile rubber, titanate coupling agent, silica, and solvent.

[0010] The adhesive for flexible circuit boards according to embodiments of the present invention has at least the following beneficial effects:

[0011] This invention introduces a titanate coupling agent into an epoxy-modified acrylic copolymer to chelate with the metal surface, thereby improving the peel strength with the metal surface. Then, the crosslinking density of the adhesive composition is further improved by reacting the epoxy groups with adipate dihydrazide.

[0012] In this invention, adipic acid dihydrazide (ADH), a latent curing agent prepared by reacting organic acids with hydrazine, improves the adhesive properties of the adhesive by replacing ordinary phenolic and amino resin curing agents and synergistically working with other components in the adhesive. Furthermore, as a latent curing agent for epoxy resins, the addition of adipic acid dihydrazide to the adhesive system of this invention effectively improves the shelf life of the adhesive solution, resulting in a shelf life of up to one month for the adhesive film prepared at room temperature and a shelf life of more than six months for the adhesive solution.

[0013] The carboxylated nitrile rubber of the present invention can improve peel strength and reduce excess adhesive; the silica of the present invention is preferably hydrophobic silica obtained by treating dimethyldichlorosilane, hexamethyldisilazane, octylsilane, etc., and the addition of silica can effectively improve the heat resistance of solder.

[0014] In summary, the adhesive prepared using the raw materials of this invention has excellent adhesiveness and high temperature resistance. When applied to bonding flexible printed circuit board metal reinforcing plates, it can withstand the thermal shock of water and high-temperature soldering, and has stable peel strength in high temperature and high humidity environments (temperature 85°C, humidity 85%RH). The bonded reinforcing plates are not easy to fall off.

[0015] According to some embodiments of the present invention, the adhesive for flexible circuit boards comprises the following raw materials in parts by weight:

[0016] 20-30 parts of epoxy-modified acrylic resin;

[0017] 1-4 parts adipic acid dihydrazide;

[0018] 6-10 parts of carboxylated butadiene-acrylonitrile rubber;

[0019] Titanate coupling agent 0.05-0.2 parts;

[0020] 0.4-0.8 parts of silicon dioxide;

[0021] Solvent: 4-8 parts.

[0022] According to some embodiments of the present invention, the adhesive for flexible circuit boards comprises the following raw materials in parts by weight:

[0023] 24-26 parts of epoxy-modified acrylic resin;

[0024] 1-3 parts adipic acid dihydrazide;

[0025] 6-8 parts of carboxylated butadiene-acrylonitrile rubber;

[0026] Titanate coupling agent 0.05-0.1 parts;

[0027] 0.5-0.6 parts of silicon dioxide;

[0028] Solvent: 5-6 parts.

[0029] According to some embodiments of the present invention, the epoxy-modified acrylic resin comprises the following raw materials: acrylic acid, acrylonitrile, methyl acrylate, n-butyl acrylate, ethyl acrylate, and epoxy resin.

[0030] The epoxy-modified acrylic resin prepared by this invention has excellent chemical resistance and corrosion resistance, and also has excellent weather resistance and storage properties.

[0031] According to some embodiments of the present invention, the epoxy-modified acrylic resin comprises the following raw materials in parts by weight:

[0032] 12-18 parts acrylic acid;

[0033] 6-10 parts acrylonitrile;

[0034] 12-18 parts methyl acrylate;

[0035] 35-45 parts of n-butyl acrylate;

[0036] 85-96 parts of ethyl acetate;

[0037] 25-35 parts epoxy resin.

[0038] According to some embodiments of the present invention, the preparation method of the epoxy-modified acrylic resin includes the following steps: mixing the raw materials for preparing the epoxy-modified acrylic resin and reacting them at 90℃-110℃ for 6h-10h to obtain the resin.

[0039] According to some embodiments of the present invention, the temperature during the preparation process of the epoxy-modified acrylic resin is 100°C.

[0040] According to some embodiments of the present invention, the reaction time in the preparation process of the epoxy-modified acrylic resin is 8 hours.

[0041] According to some embodiments of the present invention, the adipic acid dihydrazide is adipic acid dihydrazide diluted to 50% with N,N-dimethylformamide.

[0042] In this invention, pre-diluting adipate dihydrazide with N,N-dimethylformamide effectively enhances surface wettability. Secondly, the fine particulate adipate dihydrazide helps to increase the surface roughness of the substrate, thereby improving the wettability of the adhesive and ensuring good adhesion to low-dyne substrates.

[0043] According to some embodiments of the present invention, the solvent is at least one selected from butanone, ethyl acetate, and butyl acetate.

[0044] According to some embodiments of the present invention, the particle size of the epoxy-modified acrylic resin, carboxylated nitrile rubber and silica is less than 10 μm.

[0045] A method for preparing an adhesive for flexible circuit boards according to a second aspect embodiment of the present invention includes the following preparation steps:

[0046] The adhesive is obtained by mixing and reacting the raw materials used in its preparation.

[0047] The method for preparing adhesives for flexible circuit boards according to embodiments of the present invention has at least the following advantages: the method for preparing adhesives for flexible circuit boards according to the present invention is simple and low in cost; the adhesive prepared by this method has good stability and high peel strength.

[0048] According to some embodiments of the present invention, the reaction temperature is 120°C-180°C.

[0049] According to some embodiments of the present invention, the reaction time is 1h-2h.

[0050] The application of an adhesive for flexible circuit boards according to a third aspect of the present invention in the preparation of flexible circuit boards or printed circuit boards.

[0051] According to the application of the embodiments of the present invention, at least the following beneficial effects are achieved: the composite material formed by the adhesive has high peel strength and excellent heat resistance.

[0052] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0053] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0054] In the description of this invention, the terms "one embodiment," "some embodiments," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0055] In an embodiment of the present invention, adipic acid dihydrazide was purchased from Mitsui Chemicals, and it was necessary to add DMF solvent to dilute the adipic acid dihydrazide solvent to 50% before use.

[0056] Carboxylated nitrile rubber was purchased from Kaiyin Chemical.

[0057] The titanate coupling agent was purchased from Wuhan Lanabai Pharmaceutical Co., Ltd., model (item number) 201 or 401;

[0058] The CAS number for silica is 14808-60-7; the CAS number for methyl ethyl ketone (MEK) is 78-93-3; the CAS number for acrylic acid is 79-10-7; the CAS number for acrylonitrile is 107-13-1; the CAS number for methyl acrylate is 96-33-3; the CAS number for n-butyl acrylate is 141-32-2; the CAS number for ethyl acrylate is 13532-94-0; and the CAS number for epoxy resin is 61788-97-4.

[0059] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0060] Example 1

[0061] This embodiment provides an adhesive for flexible circuit boards, which is prepared from the following raw materials in parts by weight:

[0062] 25 parts of epoxy-modified acrylic resin;

[0063] 1 part adipicohydrazide;

[0064] 8 parts of carboxylated butadiene-acrylonitrile rubber;

[0065] 0.1 parts of titanate coupling agent;

[0066] 0.6 parts silicon dioxide;

[0067] 5 parts of methyl ethyl ketone (MEK).

[0068] The epoxy-modified acrylic resin is prepared from the following raw materials. The specific steps are as follows: weigh 15 parts of acrylic acid, 8 parts of acrylonitrile, 15 parts of methyl acrylate, 40 parts of n-butyl acrylate, 92 parts of ethyl acrylate and 30 parts of epoxy resin, mix them evenly, pour them into a reaction vessel, and react at 100°C for 8 hours to obtain the final product.

[0069] Example 2

[0070] This embodiment provides an adhesive for flexible circuit boards, which is prepared from the following raw materials in parts by weight:

[0071] 25 parts of epoxy-modified acrylic resin;

[0072] 2 parts of adipic acid dihydrazide;

[0073] 8 parts of carboxylated butadiene-acrylonitrile rubber;

[0074] 0.1 parts of titanate coupling agent;

[0075] 0.6 parts silicon dioxide;

[0076] 5 parts of methyl ethyl ketone (MEK).

[0077] The epoxy-modified acrylic resin is prepared from the following raw materials. The specific steps are as follows: weigh 15 parts of acrylic acid, 8 parts of acrylonitrile, 15 parts of methyl acrylate, 40 parts of n-butyl acrylate, 92 parts of ethyl acrylate and 30 parts of epoxy resin, mix them evenly, pour them into a reaction vessel, and react at 100°C for 8 hours to obtain the final product.

[0078] Example 3

[0079] This embodiment provides an adhesive for flexible circuit boards, which is prepared from the following raw materials in parts by weight:

[0080] 25 parts of epoxy-modified acrylic resin;

[0081] 3 parts adipic acid dihydrazide;

[0082] 8 parts of carboxylated butadiene-acrylonitrile rubber;

[0083] 0.1 parts of titanate coupling agent;

[0084] 0.6 parts silicon dioxide;

[0085] 5 parts of methyl ethyl ketone (MEK).

[0086] The epoxy-modified acrylic resin is prepared from the following raw materials. The specific steps are as follows: weigh 15 parts of acrylic acid, 8 parts of acrylonitrile, 15 parts of methyl acrylate, 40 parts of n-butyl acrylate, 92 parts of ethyl acrylate and 30 parts of epoxy resin, mix them evenly, pour them into a reaction vessel, and react at 100°C for 8 hours to obtain the final product.

[0087] Comparative Example 1

[0088] This comparative example provides an adhesive for flexible circuit boards, prepared from the following raw materials in parts by weight:

[0089] 25 parts of epoxy-modified acrylic resin;

[0090] 1 part phenolic resin;

[0091] 0.1 parts of titanate coupling agent;

[0092] 0.6 parts silicon dioxide;

[0093] 5 parts of methyl ethyl ketone (MEK).

[0094] The epoxy-modified acrylic resin is prepared from the following raw materials. The specific steps are as follows: weigh 15 parts of acrylic acid, 8 parts of acrylonitrile, 15 parts of methyl acrylate, 40 parts of n-butyl acrylate, 92 parts of ethyl acrylate and 30 parts of epoxy resin, mix them evenly, pour them into a reaction vessel, and react at 100°C for 8 hours to obtain the final product.

[0095] Comparative Example 2

[0096] This comparative example provides an adhesive for flexible circuit boards, prepared from the following raw materials in parts by weight:

[0097] 25 parts of epoxy-modified acrylic resin;

[0098] 1 part phenolic epoxy resin;

[0099] 0.1 parts of titanate coupling agent;

[0100] 0.6 parts silicon dioxide;

[0101] 5 parts of methyl ethyl ketone (MEK).

[0102] The epoxy-modified acrylic resin is prepared from the following raw materials. The specific steps are as follows: weigh 15 parts of acrylic acid, 8 parts of acrylonitrile, 15 parts of methyl acrylate, 40 parts of n-butyl acrylate, 92 parts of ethyl acrylate and 30 parts of epoxy resin, mix them evenly, pour them into a reaction vessel, and react at 100°C for 8 hours to obtain the final product.

[0103] Application examples

[0104] 1. Test materials

[0105] (1) The adhesives prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. In order to facilitate understanding of the present invention, the component ratios of the adhesives prepared in Examples 1-3 and Comparative Examples 1-2 were statistically analyzed, as shown in Table 1.

[0106] Table 1. Raw material ratios for adhesive preparation (by weight percentage)

[0107] Components Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Epoxy modified acrylic resin 25 25 25 25 25 Adipic acid dihydrazide 1 2 3 - - Phenolic resin - - - 1 - Phenolic epoxy - - - - 1 Carboxylated nitrile rubber 8 8 8 - - titanate coupling agent 0.1 0.1 0.1 0.1 0.1 silicon dioxide 0.6 0.6 0.6 0.6 0.6 Butanone 5 5 5 5 5

[0108] In this application example, the epoxy-modified acrylic resin comprises the following raw materials by weight:

[0109] 15 parts acrylic acid, 8 parts acrylonitrile, 15 parts methyl acrylate, 40 parts n-butyl acrylate, 92 parts ethyl acrylate, and 30 parts epoxy resin.

[0110] The preparation method of epoxy-modified acrylic resin is as follows: Mix the above-mentioned raw materials for preparing epoxy-modified acrylic resin evenly, add them to a reaction vessel, and react at 100°C for 8 hours to obtain the resin.

[0111] (2) Other materials: 304 stainless steel substrate, FR-4 substrate and polyimide (PI) substrate.

[0112] 2. Test methods

[0113] (1) Adhesive preparation

[0114] According to the formulation in Table 1, epoxy-modified acrylic resin, adipic acid dihydrazide, carboxylated nitrile rubber, titanate coupling agent, silica, and methyl ethyl ketone were mixed and reacted at 150°C for 1.5 h to obtain the adhesive. The epoxy-modified acrylic resin, carboxylated nitrile rubber, and silica were ground to a fineness of less than 10 μm before use.

[0115] (2) Performance Testing

[0116] Peel strength test: The adhesive is applied to the release film and pre-dried to obtain an adhesive layer. The pre-drying temperature is 120-180℃ and the time is 100-300s. After the adhesive layer cools to 50-100℃, it is pressed with the release paper for testing.

[0117] Solder heat resistance test: Refer to standard IPC-TM-650-2.3.13;

[0118] Surface tension test: Refer to national standard GB-T 22237-2008;

[0119] Peel strength test under high temperature and high humidity: The peel strength was tested after 4 days of treatment at 85℃ and 85% (RH) according to the method of standard IPC-TM-650-2.4.9.

[0120] 3. Test Results

[0121] The properties of the adhesives prepared in Examples 1-3 and Comparative Examples 1-2 of the present invention were tested, and the test results are shown in Table 2.

[0122] Table 2 Performance Test Results

[0123]

[0124] Note: "OK" in the table means that the heat resistance is qualified and there is no blistering or delamination.

[0125] As can be seen from Tables 1 and 2, compared with Example 1, Comparative Examples 1 and 2 did not add adipic dihydrazide and carboxylated nitrile rubber, but instead used conventional phenolic resin or phenolic epoxy resin. The test results show that the adhesive with both adipic dihydrazide and carboxylated nitrile rubber added has better adhesion and higher peel strength than the adhesive with phenolic resin or phenolic epoxy resin added.

[0126] Secondly, as can be seen from Examples 1 to 3, the peel strength of the adhesive prepared by the present invention increases with the increase of the content of adipic acid dihydrazide. This is mainly because the adipic acid dihydrazide curing system can effectively improve the crosslinking density, so that it still has good peel strength on low dyne surfaces. In addition, the adhesive of the present invention has a wide range of applications and has excellent adhesion and weather resistance on 304 stainless steel substrates, FR4 substrates and PI substrates.

[0127] In summary, the adhesive prepared using the raw materials of this invention has excellent adhesiveness and high temperature resistance. When applied to bonding flexible printed circuit board metal reinforcing plates, it can withstand the thermal shock of water and high-temperature soldering, and has stable peel strength in high temperature and high humidity environments (temperature 85°C, humidity 85%RH). The bonded reinforcing plates are not easy to fall off.

[0128] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An adhesive for a flexible wiring board, characterized by, According to the weight parts, the preparation raw materials include the following: Epoxy modified acrylic resin 20-30 parts, adipic acid dihydrazide 1-4 parts, carboxyl nitrile rubber 6-10 parts, titanate coupling agent 0.05-0.1 parts, silicon dioxide 0.4-0.8 parts and solvent 4-8 parts; The preparation raw materials of the epoxy modified acrylic resin include the following components according to the weight parts: Acrylic acid 12-18 parts, acrylonitrile 6-10 parts, methyl acrylate 12-18 parts, n-butyl acrylate 35-45 parts, ethyl ester 85-96 parts, epoxy resin 25-35 parts.

2. The adhesive according to claim 1, wherein The preparation method of the epoxy modified acrylic resin includes the following steps: Mix the preparation raw materials of the epoxy modified acrylic resin, and obtain at 90-110℃ for 6-10h.

3. The adhesive according to claim 1 or 2, characterized in that, The solvent is at least one of butanone, ethyl ester and butyl ester.

4. A method for producing the adhesive for a flexible wiring board according to any one of claims 1 to 3, characterized by, The preparation method includes the following preparation steps: Mix the preparation raw materials of the adhesive, and obtain after reaction.

5. The production method according to claim 4, characterized by, The temperature of the reaction is 120-180℃.

6. The preparation method according to claim 4, characterized in that, The time of the reaction is 1-2h.

7. Use of the adhesive for flexible circuit board according to any one of claims 1-3 in the preparation of flexible circuit board or printed circuit board.

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