A high shelf-life anisotropic conductive film and its preparation method

Abstract

The application belongs to the technical field of anisotropic conductive adhesive film, and relates to a high-quality-period anisotropic conductive adhesive film and a preparation method thereof. The application discloses a high-quality-period anisotropic conductive adhesive film. Raw materials of the high-quality-period anisotropic conductive adhesive film include a first solution, a second solution and an initiator in a mass ratio of (12-20):(20-26):1. The first solution includes an adhesive, a curing agent and a free radical polymerization inhibitor, and the content of the free radical polymerization inhibitor in the first solution is 0.1-0.5%. The second solution includes a resin base material, conductive particles and carboxyl-modified graphene, and the content of the carboxyl-modified graphene in the second solution is 2.1-4.5%. The application further discloses a preparation method of the high-quality-period anisotropic conductive adhesive film. The application achieves the effects of solving the side effect of low curing modulus caused by excessive low-temperature initiator and prolonging the shelf life of the anisotropic conductive adhesive film.

Description

Technical Field

[0001] This invention belongs to the field of anisotropic conductive film technology, and relates to an anisotropic conductive film with a long shelf life and its preparation method. Background Technology

[0002] Anisotropic conductive adhesives need to cure in 5 to 10 seconds at 140 to 200°C. Therefore, an excessive amount of low-temperature initiator is added to the raw material formulation system, and it needs to be stored at -10°C. However, the addition of excessive low-temperature initiator still causes the anisotropic conductive adhesive film to slowly react and deteriorate at room temperature to -18°C. Therefore, the shelf life of the anisotropic conductive adhesive film at -10°C is only 6 months, and the shelf life at room temperature is one week.

[0003] Therefore, it is necessary to seek new formulation systems that, while ensuring the application of anisotropic conductive adhesives, also ensure the stability of the system and prevent curing reactions during storage, while suppressing problems such as incomplete curing, low curing modulus, decreased bonding strength, and poor conductivity after reliability testing caused by excessive low-temperature initiators, and ensuring a long shelf life. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in the prior art by proposing an anisotropic conductive film that guarantees high curing effect and long shelf life, as well as its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A high-shelf-life anisotropic conductive adhesive film, wherein the raw materials of the high-shelf-life anisotropic conductive adhesive film include a first solution, a second solution, and an initiator in a mass ratio of (12-20):(20-26):1;

[0007] The first solution includes an adhesive, a curing agent, and a free radical polymerization inhibitor, wherein the content of the free radical polymerization inhibitor in the first solution is 0.1% to 0.5%.

[0008] The second solution includes a resin substrate, conductive particles, and carboxyl-modified graphene, with the content of carboxyl-modified graphene in the second solution being 2.1% to 4.5%.

[0009] In the formulation system of this invention, a free radical polymerization inhibitor is added to the first solution and fixed on the carboxyl-modified graphene in the second solution, so that the polymerization inhibitor is evenly dispersed; and the polymerization inhibitor reacts chemically with the carboxyl-modified graphene to be loaded on the surface of the carboxyl-modified graphene. The supported polymerization inhibitor will be slowly released. When free radicals appear in the system, the polymerization inhibitor will react to form free radicals, resulting in a better effect.

[0010] Preferably, the free radical polymerization inhibitor accounts for 0.08 to 0.2% of the total raw material mass; and the carboxyl-modified graphene accounts for 1.2 to 2.5% of the total raw material mass.

[0011] Preferably, the free radical polymerization inhibitor is a combination of phenols and quinones, or a combination of phenols.

[0012] More preferably, the free radical polymerization inhibitor includes two or more of hydroquinone, tert-butylcatechol, p-benzoquinone, p-hydroxyanisole (4-methoxyphenol), 2-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, tetrachlorobenzoquinone, and 1,4-naphthoquinone.

[0013] Preferably, the adhesive in the first solution includes one or more of rosin, thermoplastic acrylate, and cyanoacrylate.

[0014] Preferably, the curing agent in the first solution is one or more of oligomeric polyols, polyisocyanates, fatty amines, and acid anhydrides.

[0015] Preferably, the carboxyl content in the carboxyl-modified graphene in the second solution is 3–7 wt.%.

[0016] Preferably, the resin substrate in the second solution is a mixture of supporting resin and curing resin in a mass ratio of (0.9 to 1.7):1.

[0017] More preferably, the resin substrate in the second solution includes two or more of nitrile rubber, chloroprene rubber, epoxy resin, and polyurethane resin.

[0018] Preferably, the conductive particles in the second solution are one or more of the following: metallic nickel spheres, gold spheres, nickel / gold spheres, nickel spheres with plastic cores, and gold spheres with plastic cores.

[0019] Preferably, the initiator is at least two of the following: organic peroxides and azo compounds.

[0020] Preferably, the raw materials for the high-shelf-life anisotropic conductive film, by weight, include: 35-80 parts of resin substrate, 10-30 parts of curing agent, 5-30 parts of adhesive, 1-10 parts of initiator, 1-10 parts of conductive particles, 0.01-0.5 parts of free radical polymerization inhibitor, and 0.01-5 parts of carboxyl-modified graphene.

[0021] This invention also discloses a method for preparing a high-shelf-life anisotropic conductive film. The preparation method includes: weighing raw materials, mixing an adhesive, a curing agent, and a free radical polymerization inhibitor with a first solvent to prepare a first solution, mixing a resin substrate, conductive particles, and carboxyl-modified graphene with a second solvent to prepare a second solution, then mixing the first solution and the second solution, and simultaneously adding an initiator; after mixing evenly, coating to obtain a high-shelf-life anisotropic conductive film.

[0022] Preferably, the first solvent and the second solvent are the same or different; specifically, they are one or more of butyl acetate, ethyl acetate, toluene, methyl ethyl ketone, and methyl isobutyl ketone.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The anisotropic conductive film with a long shelf life of the present invention adds a free radical polymerization inhibitor to the formulation system, which solves the side effect of low curing modulus caused by excessive low temperature initiator and extends the shelf life of the anisotropic conductive film.

[0025] 2. In this invention, a first solution containing a free radical polymerization inhibitor is mixed with a second solution containing carboxyl-modified graphene, so that the free radical polymerization inhibitor is fixed on the carboxyl-modified graphene, which promotes uniform dispersion of the polymerization inhibitor and improves its effect.

[0026] 3. In this invention, a free radical polymerization inhibitor is added to the formulation system to replace an excessive amount of low-temperature initiator. The free radical polymerization inhibitor can capture free radicals at room temperature to prevent resin polymerization. Furthermore, when heated, the free radical initiator releases a large number of free radicals, which consume the polymerization inhibitor and allow the polymerization reaction to proceed normally.

[0027] 4. The preparation method of the present invention is simple, controllable, and efficient.

[0028] 5. By adjusting the formulation system and preparation method, the present invention enables the anisotropic conductive film with a long shelf life to be stored at room temperature for 1 month and at -10℃ for 3 years, and the bonding curing rate can still reach 88%. Detailed Implementation

[0029] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0030] Example 1

[0031] Weigh the raw materials according to the following parts by weight: 60 parts of resin base material (35 parts of nitrile rubber, 25 parts of polyurethane resin), 20 parts of curing agent (polyisocyanate), 25 parts of adhesive (hydrogenated rosin ester), 3 parts of initiator (1 part of azobisisobutyronitrile, 2 parts of diacyl peroxide), 6 parts of conductive particles (plastic core coated nickel ball), 0.2 parts of free radical polymerization inhibitor (0.1 parts of hydroquinone, 0.1 parts of p-benzoquinone), and 2 parts of carboxyl-modified graphene (carboxyl content of 5 wt.%).

[0032] The adhesive, curing agent, and free radical polymerization inhibitor are mixed and then added to a first solvent (ethyl acetate) to prepare a first solution. The resin substrate, conductive particles, and carboxyl-modified graphene are mixed and then added to a second solvent (methyl isobutyl ketone) to prepare a second solution. The first solution and the second solution are then mixed, and an initiator is added at the same time. After being mixed evenly, the mixture is coated to obtain an anisotropic conductive film with a long shelf life.

[0033] After being stored at room temperature for one month, the bonding curing rate of the prepared anisotropic conductive film was 88.2%. After being stored at -10℃ for three years, the bonding curing rate was 91.8%; the 90° peel strength was 793 N / m, and the conductivity was 0.12 Ω. (The performance is similar to that of anisotropic conductive film prepared by coating with an anisotropic conductive film coating solution after storage for the same period of time under the same conditions.)

[0034] See Table 1 for specific performance details.

[0035] Example 2

[0036] Compared with Example 1, the difference lies in the following raw materials weighed in the following parts by weight: 60 parts of resin substrate (35 parts of nitrile rubber, 35 parts of polyurethane resin), 20 parts of curing agent (fatty amine), 30 parts of adhesive (hydrogenated pine), 3 parts of initiator (1 part of azobisisobutyronitrile, 2 parts of diacyl peroxide), 6 parts of conductive particles (nickel / gold spheres), 0.2 parts of free radical polymerization inhibitor (0.1 parts of hydroquinone, 0.1 parts of 1,4-naphthoquinone), and 2 parts of carboxyl-modified graphene (carboxyl content of 5 wt.%).

[0037] The specific properties of the high-shelf-life anisotropic conductive film are shown in Table 1.

[0038] Example 3

[0039] Compared with Example 1, the difference is that the free radical polymerization inhibitor is 0.1 parts hydroquinone and 0.1 parts 2-tert-butylhydroquinone.

[0040] The specific properties of the high-shelf-life anisotropic conductive film are shown in Table 1.

[0041] Example 4

[0042] Compared with Example 1, the difference is that the free radical polymerization inhibitor is 0.1 parts of p-benzoquinone and 0.1 parts of tetrachlorobenzoquinone.

[0043] The specific properties of the high-shelf-life anisotropic conductive film are shown in Table 1.

[0044] Comparative Example 1

[0045] Compared to Example 1, the difference is that no free radical polymerization inhibitor and carboxyl-modified graphene are added.

[0046] The specific properties of the prepared anisotropic conductive film are shown in Table 1.

[0047] Comparative Example 2

[0048] The difference from Example 1 is that carboxyl-modified graphene is not added.

[0049] The specific properties of the prepared anisotropic conductive film are shown in Table 1.

[0050] Comparative Example 3

[0051] Compared with Example 1, the difference is that the amount of free radical polymerization inhibitor added is 0.5 parts; that is, the content of free radical polymerization inhibitor in the first solution is 1.1%, and the free radical polymerization inhibitor accounts for 0.43% of the total raw material mass.

[0052] The specific properties of the prepared anisotropic conductive film are shown in Table 1.

[0053] Comparative Example 4

[0054] Compared with Example 1, the difference lies in the addition amount of free radical polymerization inhibitor being 0.4 parts and the addition amount of carboxyl-modified graphene being 1 part; that is, the content of free radical polymerization inhibitor in the first solution is 0.88%, and the free radical polymerization inhibitor accounts for 0.35% of the total raw material mass, while the content of carboxyl-modified graphene in the second solution is 1.49%, and the carboxyl-modified graphene accounts for 0.87% of the total raw material mass.

[0055] The specific properties of the prepared anisotropic conductive film are shown in Table 1.

[0056] Table 1. Performance data of anisotropic conductive films

[0057]

[0058]

[0059] As shown in Table 1, the anisotropic conductive film prepared in this application has a long shelf life. After being stored at room temperature for one month or at -10°C for three years, the bonding curing rate, 90° peel interface adhesion, and conductivity are all good. In Examples 1 and 2, the free radical polymerization inhibitors used were a blend of phenols and quinones; in Example 3, the free radical polymerization inhibitor was a blend of phenols; and in Example 4, the free radical polymerization inhibitor was a blend of quinones. In Examples 1 and 2, the phenol-quinone blended polymerization inhibitors showed higher efficiency during the polymerization inhibition process. This is because although phenolic polymerization inhibitors themselves have good effects, they are difficult to function effectively without oxygen. Quinone polymerization inhibitors also have good polymerization inhibition effects, but their inhibitory effect on monomers is selective. Furthermore, if a single polymerization inhibitor is desired to achieve the desired effect, there is a problem of overuse, which affects the subsequent curing reaction. While the combination of two phenols in Example 3 was more effective than that of a single phenol, the inhibitory effect of phenols requires the presence of oxygen in the system. Anisotropic conductive films have a low probability of contact with oxygen, which could affect the effectiveness of the phenolic inhibitors. In Example 4, a combination of two quinones was used. However, since quinone inhibitors are selective for monomers, the presence of two quinone inhibitors cannot compensate for this disadvantage, and slow curing reactions may still occur during storage.

[0060] In Comparative Example 1, the absence of free radical polymerization inhibitors and carboxyl-modified graphene led to the initiator's slow decomposition at low temperatures, triggering free radical polymerization. This resulted in ineffective curing of the anisotropic conductive film before use, reducing monomer content and viscosity. Consequently, poor bonding occurred during pre-bonding, ultimately leading to a significant decrease in adhesive strength and failure. This resulted in anisotropic conductive films that could only be stored at low temperatures and had a short shelf life. In Comparative Example 2, the absence of carboxyl-modified graphene resulted in uneven dispersion of the polymerization inhibitor, leading to an unsatisfactory polymerization inhibition effect and a short shelf life. The overall performance was poor. In Comparative Example 3, the amount of free radical inhibitor added was too large, which caused the initiator to decompose and be quickly terminated by the inhibitor. The amount of initiator in the system was too small, the curing reaction was incomplete, the curing rate was low, and the bonding strength was further reduced, resulting in poor overall performance. In Comparative Example 4, the amount of free radical inhibitor added was too large, and the amount of carboxyl-modified graphene added was too small, which resulted in uneven dispersion at the beginning, affecting the inhibition effect. A small part of it reacted, resulting in poor bonding. The excessive amount of inhibitor during bonding also led to a low curing rate, which reduced the bonding strength and resulted in poor overall performance.

[0061] In summary, this invention adds a free radical polymerization inhibitor to the formulation system, which extends the shelf life of the anisotropic conductive film while ensuring the curing effect; and adds carboxyl-modified graphene, which fixes the free radical polymerization inhibitor on the carboxyl-modified graphene, promoting uniform dispersion of the polymerization inhibitor and better effect; thus, the anisotropic conductive film can be stored at room temperature for 1 month and at -10℃ for 3 years, and the curing rate of the obtained anisotropic conductive film can still reach 88%.

[0062] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a high shelf-life anisotropic conductive adhesive film, characterized by, The application relates to a high-quality-period anisotropic conductive adhesive film. The raw materials are weighed according to the following weight parts: 35 parts of resin base material nitrile rubber, 25 parts of resin base material polyurethane resin, 20 parts of curing agent polyisocyanate, 25 parts of adhesive hydrogenated rosin ester, 1 part of initiator azobisisobutylene, 2 parts of initiator diacyl peroxide, 6 parts of conductive particle plastic core coated nickel ball, 0.1 part of free radical polymerization inhibitor hydroquinone, 0.1 part of free radical polymerization inhibitor p-benzoquinone and 2 parts of carboxyl-modified graphene, wherein the carboxyl content of the carboxyl-modified graphene is 5 wt.%. The adhesive, the curing agent and the free radical polymerization inhibitor are mixed to prepare a first solution by adding a first solvent ethyl acetate, the resin base material, the conductive particle and the carboxyl-modified graphene are mixed to prepare a second solution by adding a second solvent methyl isobutyl ketone, then the first solution and the second solution are mixed, and the initiator is added; after uniform mixing, the high-quality-period anisotropic conductive adhesive film is coated.

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