A protocatechuic acid modified epoxy resin and its preparation method and application

Abstract

The present invention relates to the field of adhesive materials, and in particular to a protocatechuic acid-modified epoxy resin, and its preparation method and application. The preparation method of the modified epoxy resin comprises: using protocatechuic acid and epoxy resin I as raw materials to carry out a chain extension reaction; wherein the epoxy resin I is one or a combination of several of bisphenol A epoxy resin, bisphenol F epoxy resin, ethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether. The adhesive made from the modified epoxy resin has good room temperature bonding strength and high temperature bonding strength; specifically, the shear strength of the adhesive at room temperature reaches more than 20MPa, the shear strength at 150°C reaches more than 10MPa, the peel strength at room temperature reaches 3KN / m, and the aging performance at 250°C is also significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of adhesive materials, and in particular to a protocatechuic acid modified epoxy resin and a preparation method and application thereof. Background Art

[0002] Bisphenol A epoxy resin is widely used in adhesives, achieving high bond strength in room-temperature adhesive systems. However, unmodified epoxy resins still suffer from two issues: 1) high brittleness, resulting in low lap shear and peel strengths; and 2) poor heat resistance, with conventional epoxy adhesives exhibiting virtually no bonding performance above 150°C. To address the first issue, commonly used methods include adding liquid rubber, core-shell acrylic copolymers, and polyurethane to adhesives. These methods aim to improve toughness by introducing flexible segments, forming a two-phase structure, and modifying the crosslinked network structure, but these methods are less effective in maintaining material modulus and heat resistance. To address the second issue, trifunctional and tetrafunctional epoxy resins such as AG-80 and AFG-90 are commonly used to increase crosslink density and enhance heat resistance. However, these commercially available trifunctional and tetrafunctional epoxy resins have lower molecular weights, are more brittle than bisphenol A epoxies, and are expensive, making their application uneconomical.

[0003] Protocatechuic acid, also known as 3,4-dihydroxybenzoic acid, has three active groups. This bio-based phenolic acid has great potential for application in epoxy resins. For example, CN111040131A discloses a trifunctional epoxy resin obtained by reacting protocatechuic acid with epichlorohydrin. The cured product has a glass transition temperature of 210°C. However, the synthesis process disclosed in the aforementioned patent document produces a large amount of by-product salts, which require column chromatography to remove, making it difficult to achieve industrial success.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a modified epoxy resin, wherein the epoxy resin is modified by using protocatechuic acid. The obtained modified epoxy resin is a multifunctional epoxy resin, and the preparation process is simple without generating wastewater or waste salt. Another object of the present invention is to provide the modified epoxy resin prepared by the method and its application.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a modified epoxy resin, comprising: using protocatechuic acid and epoxy resin I as raw materials to carry out a chain extension reaction;

[0008] Wherein, the epoxy resin I is one or a combination of bisphenol A epoxy resin, bisphenol F epoxy resin, ethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

[0009] The present invention finds that the chain extension reaction of protocatechuic acid and a specific epoxy resin is carried out, the preparation process is simple, no wastewater or waste salt is generated, and the obtained modified epoxy resin is a multifunctional epoxy resin; the adhesive made from the modified epoxy resin has excellent high-temperature bonding performance.

[0010] Those skilled in the art can set the parameters in the process according to common knowledge, which can all achieve the same effects as described above. However, there are also more optimal technical solutions for other parameters. To this end, the present invention has further explored and obtained the following preferred solutions.

[0011] Preferably, the chain extension reaction is carried out under the action of a catalyst; the catalyst is one or a combination of tetramethylammonium bromide, benzyltriethylammonium chloride, benzyltriethylammonium bromide, benzyltrimethylammonium chloride, and benzyltrimethylammonium bromide. Using the above compounds as catalysts can increase the efficiency of the chain extension reaction.

[0012] Preferably, the mass ratio of protocatechuic acid:epoxy resin I:catalyst is (10-50):100:0.1.

[0013] According to the reaction system of the present invention, the mass ratio of protocatechuic acid, epoxy resin I and catalyst is controlled to be between (10-50):100:0.1, so that the efficiency of the chain extension reaction is the highest.

[0014] Preferably, the chain extension reaction is carried out at 80-130°C.

[0015] Furthermore, the preparation method is specifically as follows: after mixing protocatechuic acid and epoxy resin I, heating to 80-130°C, distilling at normal pressure for 30-60 minutes and then distilling at reduced pressure for 15-30 minutes, then adding a catalyst and keeping the mixture at 80-130°C for 1-2 hours; the modified epoxy resin prepared by the above method has the best quality.

[0016] The present invention also provides a modified epoxy resin, which is prepared by the above method.

[0017] The present invention also provides application of the modified epoxy resin in adhesives.

[0018] The adhesive comprising the modified epoxy resin provided by the present invention is particularly suitable for steel-steel surface bonding; specifically, the protocatechuic acid in the modified epoxy resin can undergo a chelating reaction at the adhesive-steel interface, thereby effectively increasing the bonding strength and aging resistance.

[0019] The present invention also provides an adhesive comprising: the modified epoxy resin and a dicyandiamide curing agent;

[0020] Preferably, the mass ratio of the modified epoxy resin to the dicyandiamide curing agent is (15-50):(3-6).

[0021] The present invention also finds that the modified epoxy resin is a multifunctional epoxy resin, which increases the cross-linking density of the reaction system during the curing process, so that the resulting adhesive has better room temperature bonding strength and high temperature bonding strength.

[0022] The mass ratio of the modified epoxy resin to the dicyandiamide curing agent is further controlled within the range of (15-50):(3-6), and the room temperature bonding strength and high temperature bonding strength of the obtained adhesive are better.

[0023] Preferably, the adhesive further comprises: epoxy resin II and inorganic filler;

[0024] The epoxy resin II is one or a combination of bisphenol A epoxy resin, bisphenol F epoxy resin, phenol novolac epoxy resin, and hydantoin epoxy resin;

[0025] The inorganic filler is one or a combination of glass fiber, silicon dioxide, titanium dioxide, aluminum oxide, calcium carbonate, and silicon micropowder.

[0026] Furthermore, the adhesive comprises the following components in parts by weight: 30-70 parts of the modified epoxy resin described above, 30-50 parts of epoxy resin II, 6-9 parts of dicyandiamide curing agent, and 5-10 parts of inorganic filler; the adhesive prepared according to the above formula has the best performance.

[0027] As one of the better technical solutions, the adhesive comprises the following components in parts by weight: 50 parts of the modified epoxy resin according to claim 6, 50 parts of bisphenol A epoxy resin, 7 parts of dicyandiamide curing agent, and 10 parts of silicon powder.

[0028] As a second preferred technical solution, the adhesive comprises the following components in parts by weight: 30 parts of the modified epoxy resin described in claim 6, 30 parts of bisphenol A epoxy resin, 20 parts of novolac epoxy resin, 6 parts of dicyandiamide curing agent, and 5 parts of aluminum oxide.

[0029] As a third preferred technical solution, the adhesive comprises the following components in parts by weight: 70 parts of the modified epoxy resin described in claim 6, 10 parts of phenolic epoxy resin, 20 parts of hydantoin epoxy resin, 9 parts of dicyandiamide curing agent, and 9 parts of silicon dioxide.

[0030] The present invention also provides a method for preparing the adhesive described above, which comprises: mixing the components according to a matching ratio.

[0031] The adhesive provided by the present invention has good room temperature bonding strength and high temperature bonding strength; specifically, the shear strength of the adhesive at room temperature reaches above 20 MPa, the shear strength at 150°C reaches above 10 MPa, the room temperature peel strength reaches 3 kN / m, and the aging performance at 250°C is also significantly improved. DETAILED DESCRIPTION

[0032] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0033] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0034] Example 1

[0035] This embodiment provides a modified epoxy resin, the preparation method of which includes the following steps:

[0036] First, add 100g of bisphenol A epoxy resin E-51 and 20g of protocatechuic acid into the reactor, heat to 110℃, distill at normal pressure for 30min and then distill at reduced pressure for 20min, then add 0.1g of tetramethylammonium bromide and keep warm at 110℃ for 2h to obtain a light brown modified epoxy resin.

[0037] Example 2

[0038] This embodiment provides a modified epoxy resin, the preparation method of which includes the following steps:

[0039] First, add 100g of ethylene glycol diglycidyl ether and 30g of protocatechuic acid into the reactor, heat to 120℃, distill at normal pressure for 30min and then distill at reduced pressure for 15min, then add 0.1g of benzyltriethylammonium bromide and keep warm at 130℃ for 2h to obtain a light brown modified epoxy resin.

[0040] Example 3

[0041] This embodiment provides a modified epoxy resin, the preparation method of which includes the following steps:

[0042] First, 100g of bisphenol A epoxy resin and 30g of protocatechuic acid were added to the reactor, heated to 110°C, distilled at normal pressure for 45min and then distilled at reduced pressure for 20min, and then 0.1g of benzyltrimethylammonium bromide was added and kept at 110°C for 2h to obtain a light brown modified epoxy resin.

[0043] Example 4

[0044] This embodiment provides an adhesive, which is mixed by the following components in parts by weight: 50 parts of the modified epoxy resin of Example 1, 50 parts of bisphenol A epoxy resin E-51, 7 parts of dicyandiamide curing agent, and 10 parts of silica powder.

[0045] Example 5

[0046] This embodiment provides an adhesive, which is mixed by the following components in parts by weight: 30 parts of the modified epoxy resin of Example 2, 30 parts of bisphenol A epoxy resin E-51, 20 parts of novolac epoxy resin F-51, 6 parts of dicyandiamide curing agent, and 5 parts of aluminum oxide.

[0047] Example 6

[0048] This embodiment provides an adhesive, which is mixed by the following components in parts by weight: 70 parts of the modified epoxy resin of Example 3, 10 parts of novolac epoxy resin F-51, 20 parts of hydantoin epoxy resin, 9 parts of dicyandiamide curing agent, and 9 parts of silicon dioxide.

[0049] Comparative Example 1

[0050] This comparative example provides an adhesive, which is prepared by mixing the following components in parts by weight: 100 parts of bisphenol A epoxy resin E-51 and 6 parts of dicyandiamide curing agent.

[0051] Test Example 1

[0052] This test example is based on the adhesives of Examples 4 to 6 and Comparative Example 1, and the details are as follows:

[0053] A steel test piece was used as the bonding test piece, with a curing pressure of 0.03-0.1 MPa, a curing temperature of 150°C, and a curing time of 2 h.

[0054] Adhesive performance test method is as follows:

[0055] Determination of tensile shear strength: Test according to GB / T 7124-2008 tensile shear strength test method;

[0056] Determination of heat aging resistance: The cured specimens were placed in an oven at 250°C for 48 hours, cooled to room temperature, and then tested for tensile shear strength according to GB / T7124-2008.

[0057] 90° peel strength: tested according to GJB446-1988 peel strength test method.

[0058] The test results are shown in Table 1;

[0059] Table 1

[0060]

[0061] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An adhesive, characterized in that: include: Modified epoxy resin, dicyandiamide curing agent, epoxy resin II and inorganic filler; The preparation method of the modified epoxy resin comprises: using protocatechuic acid and epoxy resin I as raw materials to carry out a chain extension reaction; the chain extension reaction is carried out at 80-130° C.; Wherein, the epoxy resin I is one or a combination of bisphenol A epoxy resin, bisphenol F epoxy resin, ethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether; The chain extension reaction is carried out under the action of a catalyst; the catalyst is one or a combination of tetramethylammonium bromide, benzyltriethylammonium chloride, benzyltriethylammonium bromide, benzyltrimethylammonium chloride, and benzyltrimethylammonium bromide; By mass ratio, protocatechuic acid: epoxy resin I: catalyst = (10-50): 100: 0.1; The preparation method is specifically as follows: after mixing protocatechuic acid and epoxy resin I, heating to 80-130° C., distilling at normal pressure for 30-60 minutes, then distilling at reduced pressure for 15-30 minutes, then adding a catalyst, and keeping the temperature at 80-130° C. for 1-2 hours; The mass ratio of the modified epoxy resin to the dicyandiamide curing agent is (15-50): (3-6); The epoxy resin II is one or a combination of bisphenol A epoxy resin, bisphenol F epoxy resin, phenol novolac epoxy resin, and hydantoin epoxy resin; The inorganic filler is one or a combination of glass fiber, silicon dioxide, titanium dioxide, aluminum oxide, calcium carbonate, and silicon micropowder.

2. The adhesive according to claim 1, characterized in that The invention comprises the following components in parts by weight: 30-70 parts of modified epoxy resin, 30-50 parts of epoxy resin II, 6-9 parts of dicyandiamide curing agent and 5-10 parts of inorganic filler.

Images