Ultralow-temperature curing latent epoxy composition as well as preparation method and application thereof

Abstract

The invention belongs to the field of adhesives, and particularly relates to an ultralow-temperature curing latent epoxy composition as well as a preparation method and application thereof. The ultralow-temperature curing latent epoxy composition provided by the invention contains epoxy resin, a curing agent, a catalyst and a stabilizer, the epoxy resin comprises bisphenol type epoxy resin and / or non-bisphenol type epoxy resin, and the non-bisphenol type epoxy resin does not contain alkaline organic elements; the curing agent is a compound with a structure as shown in a formula (1). The ultralow-temperature curing latent epoxy composition provided by the invention has low curing temperature and high storage stability, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of adhesives, and in particular relates to an ultra-low temperature curing latent epoxy composition, a preparation method and an application thereof. Background Art

[0002] Electronics assembly refers to the technical process of rationally laying out, reliably interconnecting, and installing electronic components according to electrical schematics or logic diagrams to ensure they are ready for use. Latent-curing adhesives are often used in electronic assembly for bonding, sealing, potting, and coating. Latent-curing adhesives are adhesives that exhibit a certain degree of storage stability at room temperature but rapidly cure under conditions such as heat, light, moisture, and pressure. Common latent-curing adhesives on the market are typically heat-curing, primarily at 80°C. In some applications, latent-curing adhesives that cure at 70°C or even 65°C are also available. However, high-temperature curing can damage heat-resistant electronic components and can also cause warping and other problems. For certain specific applications, such as camera assembly, lower curing temperatures, ideally below 50°C, are desirable. Therefore, ultra-low-temperature curing is of great significance for electronic assembly, saving energy and reducing damage to heat-sensitive electronic components. It can also significantly minimize warping and other problems caused by high temperatures.

[0003] Furthermore, a lower curing temperature means a lower temperature required to trigger the curing reaction, which places higher demands on storage stability. Latent-curing adhesives with good storage stability generally require high-temperature curing, and low-temperature curing generally struggles to achieve good storage stability. In other words, achieving low-temperature curing (curing temperatures below 50°C) and improving storage stability are inherently contradictory. How to achieve low-temperature curing while simultaneously improving storage stability is an urgent issue that needs to be addressed. Summary of the Invention

[0004] The first object of the present invention is to provide an ultra-low temperature curing latent epoxy composition having both low curing temperature and high storage stability.

[0005] Specifically, the ultra-low temperature curing latent epoxy composition provided by the present invention contains an epoxy resin, a curing agent, a catalyst and a stabilizer; the epoxy resin includes a bisphenol epoxy resin and / or a non-bisphenol epoxy resin, and the non-bisphenol epoxy resin does not contain a basic organic element; the curing agent is a compound having a structure represented by formula (1); the equivalent ratio of the thiol group in the curing agent to the epoxy group in the epoxy resin is (0.6-1.5):1;

[0006]

[0007] In formula (1), R1, R2, R3 and R4 are each independently a C1-C5 alkylene group.

[0008] The second object of the present invention is to provide a method for preparing the ultra-low temperature curing latent epoxy composition, which comprises uniformly mixing an epoxy resin, a curing agent, a catalyst and a stabilizer to obtain the ultra-low temperature curing latent epoxy composition.

[0009] The third object of the present invention is to provide the use of the ultra-low temperature curing latent epoxy composition as an ultra-low temperature curing adhesive.

[0010] A fourth object of the present invention is to provide an application of the ultra-low temperature curing latent epoxy composition in the assembly of electronic products.

[0011] The curing temperature of existing latent curing epoxy adhesives is generally higher than 60°C, and curing at temperatures below 50°C is usually not possible (i.e., ultra-low temperature curing is not possible). Furthermore, as mentioned above, achieving low-temperature curing and improving storage stability are inherently contradictory. Low-temperature curing means that the threshold for triggering curing is lowered, and curing reactions will occur in latent curing epoxy adhesives at lower temperatures, which usually makes room temperature storage difficult. Therefore, even if existing latent curing epoxy adhesives can achieve ultra-low temperature curing, they cannot meet the resulting poor room temperature storage stability problem. In addition, there are attempts in the prior art to adjust the equivalent ratio of thiol and epoxy groups to (0.1 to 0.5): 1, thereby adjusting the curing temperature and bonding strength of the thiol curing agent system, but such products still cannot reach a curing temperature of around 50°C, let alone the room temperature storage problems that may be caused by ultra-low temperature curing (curing temperatures above 65°C do not require excessive concerns about storage stability at room temperature).

[0012] After in-depth research, the inventors of the present invention unexpectedly discovered that the types of epoxy resin and curing agent have a significant impact on the curing temperature and storage stability. The introduction of alkaline organic elements into the epoxy resin can seriously affect the storage stability. The use of a bisphenol-type epoxy resin and / or a non-bisphenol-type epoxy resin without alkaline organic elements as the base resin can improve the storage stability. On this basis, this specific epoxy resin is cured with a trifunctional aliphatic curing agent with a specific structure and a mercapto group. At the same time, the equivalent ratio of the mercapto groups in the curing agent to the epoxy groups in the epoxy resin is controlled to (0.6-1.5):1. In addition, a stabilizer is added. Through the synergistic effect of the multiple components, the resulting epoxy resin system remains essentially unchanged at room temperature below 40°C and has high storage stability. Once the temperature rises to 45-50°C, the system's curing threshold is quickly reached, triggering the system to cure, thereby reducing the curing temperature from the current level above 65°C to 45-50°C. In other words, both the curing temperature and storage stability are simultaneously reduced.

[0013] In a preferred embodiment, when the epoxy resin is bisphenol A epoxy resin, combined with a specific curing agent structure, equivalent ratio and stabilizer, the room temperature stability and bonding strength can be more effectively improved without substantially affecting the degree of curing at 45-50°C.

[0014] In a preferred embodiment, the stabilizer is barbituric acid and / or triethyl borate, which is combined with a specific curing agent structure, epoxy resin, and equivalent ratio. This can more effectively improve storage stability without affecting the curing temperature. DETAILED DESCRIPTION

[0015] The ultra-low temperature curing latent epoxy composition provided by the present invention comprises an epoxy resin, a curing agent, a catalyst, and a stabilizer. The equivalent ratio of the thiol groups in the curing agent to the epoxy groups in the epoxy resin is (0.6-1.5):1, such as 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any value therebetween. More preferably, the equivalent ratio of the thiol groups in the curing agent to the epoxy groups in the epoxy resin is (0.9-1.1):1.

[0016] In the present invention, the epoxy resin must be a bisphenol-type epoxy resin and / or a non-bisphenol-type epoxy resin that does not contain alkaline organic elements, because the introduction of alkaline organic elements will seriously affect storage stability. The term "alkaline organic element" refers to an organic element that can provide lone pairs of electrons and combine with protons. The alkaline organic element is preferably N and / or P. The bisphenol-type epoxy resin can be selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol S epoxy resin, preferably bisphenol A epoxy resin and / or bisphenol F epoxy resin. The non-bisphenol-type epoxy resin that does not contain alkaline organic elements can specifically be selected from at least one of novolac epoxy resin, aliphatic glycidyl ether, and aromatic epoxy diluent. The epoxy resin is preferably a bisphenol-type epoxy resin, more preferably a bisphenol A epoxy resin and / or bisphenol F epoxy resin, and particularly preferably a bisphenol A epoxy resin. When the epoxy resin is a bisphenol-type epoxy resin, the system has advantages such as adjustable viscosity, moderate equivalent weight, and good bulk stability. When the epoxy resin is a bisphenol A epoxy resin, room temperature stability and bonding strength can be more effectively improved without substantially affecting the degree of curing at 45-50° C. The epoxy value of the bisphenol A epoxy resin is preferably 150-200 g / eq, such as 150, 160, 170, 180, 190, 200 g / eq, or any value therebetween.

[0017] In the present invention, the curing agent is a compound having a structure shown in formula (1);

[0018]

[0019] In formula (1), R1, R2, R3 and R4 are independently C1-C5 alkylene groups, preferably independently C1-C3 alkylene groups. The C1-C5 alkylene groups may be, for example, methylene, ethylene, n-propylene, isopropylene, n-butylene, sec-butylene, isobutylene, tert-butylene, n-pentylene, isopentylene, tert-pentylene or neopentylene.

[0020] In the present invention, specific examples of the catalyst include, but are not limited to, at least one of an imidazole compound, an amine compound, and a phosphorus compound, preferably an imidazole compound and / or an amine compound. Specific examples include: imidazole compounds and organic acid dihydrazides that are solid at room temperature; solid-dispersed amine adducts such as the reaction products of amine compounds and epoxy compounds (amine-epoxy adducts); and reaction products of amine compounds with isocyanate compounds or urea compounds. Furthermore, the catalyst content is preferably 0.5-10% of the total content of the epoxy resin and curing agent, such as 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, or any value therebetween.

[0021] In the present invention, the stabilizer can be any of the existing stabilizers based on epoxy resin and curing agent. From the perspective of improving storage stability, the stabilizer is preferably selected from at least one of liquid boric acid derivatives, aluminum chelates, and barbituric acid. Specific examples of the liquid borate ester compound include, but are not limited to, at least one of 2,2'-oxybis(5,5'-dimethyl-1,3,2-oxaborolane), trimethyl borate, triethyl borate, tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate, amyl borate, triallyl borate, trihexyl borate, tricyclohexyl borate, trioctyl borate, trinonyl borate, tridecyl borate, tridodecyl borate, trihexadecyl borate, trioctadecyl borate, triphenyl borate, tri-o-cresyl borate, tri-m-cresyl borate, and triethanolamine borate. The stabilizer is preferably barbituric acid and / or triethyl borate. After extensive research, the inventors of the present invention have discovered that when triethyl borate and / or barbituric acid are preferably used as the stabilizer, these stabilizers are particularly suitable for the epoxy system of the present invention, effectively improving storage stability without affecting the curing temperature. Furthermore, the stabilizer content is preferably 0.01% to 1% of the total content of the epoxy resin and curing agent, such as 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, or any value therebetween.

[0022] The preparation method of the ultralow temperature curing latent epoxy composition provided by the present invention comprises uniformly mixing an epoxy resin, a curing agent, a catalyst and a stabilizer to obtain an ultralow temperature curing latent epoxy composition. The present invention is not particularly limited to the manner in which the components are uniformly mixed, and the components can be added together in any order and then mixed. In addition, the type and amount of each component have been described above and are not repeated here.

[0023] The present invention will be described in detail below by way of examples. The examples of the examples are intended to explain the present invention and are not to be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the methods were performed according to the techniques or conditions described in the literature in the art or according to the product specifications. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be obtained commercially.

[0024] Example 1-2

[0025] Step 1: According to the ratio in Table 1, prepare epoxy resin (a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin, purchased from Nippon Steel, Japan, brand ZX1059), curing agent (having the structure shown in formula (1), R1 is ethylene, R2 is methylene, R3 is methylene, R4 is ethylene, purchased from Bofei Meike Reagent, brand DMPT), catalyst (imidazole compound, purchased from Ajinomoto, Japan, brand PN23), stabilizer (barbituric acid, purchased from Shijiazhuang Jack Chemical);

[0026] Step 2: The epoxy resin, curing agent, catalyst and stabilizer prepared in step 1 are stirred uniformly at a rotation speed of 2000 rpm to obtain an ultra-low temperature curing latent epoxy composition.

[0027] Example 3

[0028] Step 1: According to the ratio in Table 1, prepare epoxy resin (a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin, purchased from Nippon Steel, Japan, with the brand name ZX1059), curing agent (having the structure shown in formula (1), R1 is ethylene, R2 is methylene, R3 is methylene, R4 is ethylene, purchased from Bofei Meike Reagent, with the brand name DMPT), catalyst (imidazole compound, purchased from Ajinomoto, Japan, with the brand name PN23), and stabilizer (triethyl borate, purchased from Aladdin Reagent);

[0029] Step 2: The epoxy resin, curing agent, catalyst and stabilizer prepared in step 1 are stirred uniformly at a rotation speed of 2000 rpm to obtain an ultra-low temperature curing latent epoxy composition.

[0030] Example 4

[0031] Step 1: According to the ratio in Table 1, prepare epoxy resin (a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin, purchased from Nippon Steel, Japan, with the brand name ZX1059), curing agent (having the structure shown in formula (1), R1 is ethylene, R2 is methylene, R3 is methylene, R4 is ethylene, purchased from Bofei Meike Reagent, with the brand name DMPT), catalyst (imidazole compound, purchased from Ajinomoto, Japan, with the brand name PN23), and stabilizer (trimethyl borate, purchased from Aladdin Reagent);

[0032] Step 2: The epoxy resin, curing agent, catalyst and stabilizer prepared in step 1 are stirred uniformly at a rotation speed of 2000 rpm to obtain an ultra-low temperature curing latent epoxy composition.

[0033] Example 5

[0034] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the epoxy resin ZX1059 was replaced by the same weight of bisphenol A epoxy resin (purchased from DIC of Japan, brand 850CRP), and the amount of curing agent was adjusted so that the thiol and epoxy equivalent ratio in the system was the same as in Example 1. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0035] Example 6

[0036] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the epoxy resin ZX1059 was replaced with the same weight portion of bisphenol F epoxy resin (purchased from Nan Ya, brand NPEL170), and the amount of curing agent was adjusted so that the thiol and epoxy equivalent ratio in the system was the same as in Example 1. The remaining conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0037] Example 7

[0038] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the epoxy resin ZX1059 was replaced by an equal weight portion of a non-bisphenol epoxy resin (aliphatic glycidyl ether, purchased from Huntsman, brand Araldite DY026SP) that did not contain basic organic elements, and the amount of the curing agent was adjusted so that the thiol and epoxy equivalent ratio in the system was the same as that in Example 1. The remaining conditions were the same as those in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0039] Comparative Example 1

[0040] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the epoxy resin was replaced by an N-containing epoxy resin (aliphatic glycidyl ether, having a structure shown in formula (2)) in equal parts by weight, and the amount of the curing agent was adjusted so that the thiol and epoxy equivalent ratio in the system was the same as in Example 1. The remaining conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0041]

[0042] Comparative Example 2

[0043] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the curing agent was replaced by a curing agent having the structure shown in formula (3) with the same thiol equivalent. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0044]

[0045] Comparative Example 3

[0046] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the curing agent was replaced by a curing agent having the structure shown in formula (4) with the same thiol equivalent. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0047]

[0048] Comparative Example 4

[0049] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that no stabilizer was added. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0050] Comparative Example 5

[0051] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the amount of thiol was adjusted to 99.70 parts by weight so that the thiol and epoxy equivalent ratio in the system was controlled at 1.75:1. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0052] Comparative Example 6

[0053] An ultra-low temperature curing latent epoxy composition was prepared according to the method of Example 1, except that the amount of thiol was adjusted to 17.09 parts by weight so that the thiol and epoxy equivalent ratio in the system was controlled at 0.3:1. The other conditions were the same as in Example 1 to obtain an ultra-low temperature curing latent epoxy composition.

[0054] Test Case

[0055] (1) Degree of curing: The degree of curing of the sample is characterized by the DSC reaction heat. For uncured glue, use the DSC temperature program to scan from room temperature to 300°C at a heating rate of 10°C / min, and record the measured reaction heat H1. Scrape a 300μm thin film from the sample and cure it at 45°C for 1 hour. Run the DSC temperature program again under the same conditions as the uncured glue reaction heat measurement, and record the measured reaction heat H2. The degree of curing of the sample = (1-H2 / H1)*100%. It is generally considered that a degree of curing greater than 95% is considered to be completely cured.

[0056] (2) Storage stability: The viscosity of the ultra-low temperature curing latent epoxy composition obtained in each embodiment and comparative example was tested using a Mettler rheometer, and the viscosity was measured as V1. The sample was placed in a 25°C constant temperature box and allowed to stand for 24 hours. The viscosity was then taken out and re-measured, and the viscosity was measured as V2. The viscosity growth rate was calculated as (V2 / V1-1)*100%. It is generally believed that a viscosity growth rate below 25% is an excellent growth rate. A viscosity growth rate exceeding 25% without gelling will affect the stability of the glue to a certain extent, and gelling will greatly affect the stability of the glue.

[0057] (3) Bonding strength: The ultra-low temperature curing latent epoxy compositions obtained in each embodiment and comparative example were coated on stainless steel sheets, respectively, and pressed with stainless steel. The thickness of the adhesive layer was controlled with a 0.1 mm copper wire, and the adhesive layer area was 25.4 mm × 5 mm. The sample was heated to 45°C and cured for 60 min. After that, the two sheets were pulled apart in opposite directions using a universal testing machine. The measured force value was the bonding strength.

[0058] The results are shown in Table 1.

[0059]

[0060] The results in Table 1 show that the ultra-low temperature curing latent epoxy compositions of Examples 1-3 can achieve a degree of cure of over 95% at 45°C, indicating sufficient cure. Furthermore, the viscosity growth rate after 24 hours of constant temperature storage at 25°C can be controlled to within 25%, demonstrating good storage stability. This means that the compositions exhibit both low curing temperatures and high storage stability. A comparison of Examples 1-3 with Example 4 shows that when the non-preferred stabilizer, trimethyl borate, is used, the degree of cure at 45°C is high, but the viscosity growth rate after 24 hours of constant temperature storage at 25°C is higher. In contrast, when barbituric acid and / or triethyl borate are used as stabilizers in Examples 1-3, storage stability is more effectively improved without substantially affecting the degree of cure. A comparison of Examples 1 with Examples 5-7 shows that when the epoxy resin is bisphenol A epoxy resin, room temperature stability and bonding strength are more effectively improved without substantially affecting the degree of cure. From the comparison between Example 1 and Comparative Example 1, it can be seen that when an epoxy resin containing an alkaline organic element is selected, the system will gel after being placed at room temperature for 24 hours and cannot be used. From the comparison between Example 1 and Comparative Examples 2-3, it can be seen that when the curing agent does not have the structure shown in formula (1), the corresponding latent epoxy composition has a curing degree of less than 85% at 45°C, which cannot meet the use requirements. From the comparison between Example 1 and Comparative Example 4, it can be seen that when no stabilizer is added to the system, the corresponding latent epoxy composition completes gel curing in about 2 minutes, and the operating time is too short to meet the use requirements. From the comparison between Example 1 and Comparative Examples 5-6, it can be seen that when the equivalent ratio of mercapto groups to epoxy groups in the system exceeds 1.5, the viscosity growth rate after being placed at a constant temperature for 24 hours at 25°C far exceeds 25%, and the storage stability is poor. When the equivalent ratio of mercapto groups to epoxy groups in the system is less than 0.6, the curing degree at 45°C is less than 85%, which cannot meet the use requirements.

[0061] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A latent epoxy composition curable at ultra-low temperature, characterized in that: The ultra-low temperature curing latent epoxy composition comprises an epoxy resin, a curing agent, a catalyst and a stabilizer; the epoxy resin comprises a bisphenol epoxy resin and / or a non-bisphenol epoxy resin, and the non-bisphenol epoxy resin does not contain an alkaline organic element; the curing agent is a compound having a structure represented by formula (1); the equivalent ratio of the thiol group in the curing agent to the epoxy group in the epoxy resin is (0.6-1.5):1; In formula (1), R1, R2, R3 and R4 are independently C1-C5 alkylene groups.

2. The ultra-low temperature curing latent epoxy composition according to claim 1, characterized in that The equivalent ratio of the mercapto group in the curing agent to the epoxy group in the epoxy resin is (0.9-1.1):

1.

3. The ultra-low temperature curing latent epoxy composition according to claim 1, characterized in that The bisphenol epoxy resin is bisphenol A epoxy resin and / or bisphenol F epoxy resin.

4. The ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 3, characterized in that: The basic organic element is N and / or P.

5. The ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 3, characterized in that: In formula (1), R1, R2, R3 and R4 are each independently a C1-C3 alkylene group.

6. The ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 3, characterized in that: The catalyst is an imidazole compound and / or an amine compound; preferably, the content of the catalyst is 0.5-10% of the total content of the epoxy resin and the curing agent.

7. The ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 3, characterized in that: The stabilizer is selected from at least one of boric acid derivatives, aluminum chelating agents and barbituric acid, preferably triethyl borate and / or barbituric acid; preferably, the content of the stabilizer is 0.01-1% of the total content of the epoxy resin and the curing agent.

8. The method for preparing the ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 7, characterized in that: The method comprises the steps of uniformly mixing an epoxy resin, a curing agent, a catalyst and a stabilizer to obtain an ultra-low temperature curing latent epoxy composition.

9. Use of the ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 7 as an ultra-low temperature curing adhesive.

10. Use of the ultra-low temperature curing latent epoxy composition according to any one of claims 1 to 7 in the assembly of electronic products.

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