A polyimide-modified epoxy resin, a preparation method and applications thereof

Abstract

The application provides a polyimide modified epoxy resin and a preparation method and application thereof, and the preparation method comprises the following steps: mixing an epoxy resin with a biphenyl or naphthyl group and an aromatic hot-melt polyimide without a phenolic hydroxyl group under a heating condition to form a homogeneous solution, adding a curing agent, performing step-by-step curing after the curing agent is completely dissolved in the homogeneous solution, and obtaining the polyimide modified epoxy resin after natural cooling. The polyimide modified epoxy resin has the advantages of good high-temperature resistance, high toughness, high mechanical strength, low linear expansion coefficient and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of epoxy resin, and particularly relates to a polyimide modified epoxy resin and a preparation method and application thereof. BACKGROUND

[0002] Epoxy resin is a compound containing not less than two epoxy groups in the molecular structure, and is the most important variety in the thermosetting polymer prepolymer. After the curing reaction of epoxy resin and curing agent (commonly used are amines and acid anhydes), a three-dimensional crosslinked network is formed, which exhibits excellent performance. Therefore, before curing, the epoxy resin has excellent processing performance; during the curing process, the volume shrinkage rate is low, and the curing temperature control range is wide; after curing, the three-dimensional crosslinked network has excellent comprehensive performance, including high mechanical strength, good chemical resistance, better heat resistance, and good bonding performance. Therefore, the epoxy resin is widely used in many fields such as aerospace, electronics and electrical, ship, automobile, and building as coating, adhesive, and composite material matrix resin, etc. However, the epoxy resin has the problems of high brittleness and low temperature resistance, which seriously restricts its application in aerospace, electronic packaging, etc. Under normal circumstances, although the general flexible structure toughening method can greatly improve the toughness, it inevitably causes a large decline in temperature resistance, strength and modulus.

[0003] Engineering plastic toughening epoxy resin as a typical toughening means is often used in the modification of epoxy resin, for example, polyether ether ketone, polyimide, polyphenylene sulfide, polysulfone has rigid unit, can absorb energy under stress, prevent micro crack propagation, has good effect on the toughness of epoxy resin, but according to the current literature report, due to the compatibility of engineering plastics and epoxy resin and other problems, few can make the glass transition temperature of epoxy resin increase to more than 240℃ while keeping the tensile strength to more than 70Mpa. Polyimide is usually obtained by condensation polymerization of dianhydride (acid) and diamine, and its high molecular main chain contains imide ring. Polyimide has many excellent properties, and is often used as high temperature structural adhesive and advanced composite matrix due to its excellent high temperature resistance. In the field of microelectronic information packaging and coating materials, polyimide also has excellent dimensional stability and good dielectric properties. Polyimide also has the characteristics of small thermal expansion coefficient, solvent resistance, etc., so it has the advantage of replacing metal, glass and other materials in the field of adhesive application. Invention patent CN113861421A discloses a kind of polyimide type epoxy resin toughening agent and its preparation method, the toughening agent is a kind of block type polyimide polymer, which is composed of structure segment containing phenolic hydroxyl group and structure segment not containing phenolic hydroxyl group. The structure segment containing phenolic hydroxyl group can participate in the curing reaction of epoxy resin, and the toughening agent is introduced into the crosslinked network of epoxy resin through chemical bond, which improves the compatibility and interface bonding force of the toughening agent and epoxy resin. On the other hand, the main chain contains rigid groups such as benzene ring and imide structure, which can maintain the good mechanical properties and heat resistance of epoxy resin. However, the epoxy resin modified by block type polyimide polymer is prone to incomplete curing due to the steric hindrance of curing agent, and the crosslinked network is loose, which has low glass transition temperature.

[0004] Therefore, it is a great challenge to increase the Tg of epoxy resin to more than 240℃, maintain high strength and modulus, and improve toughness at the same time.

[0005] At present, there are some related literatures on polyimide powder toughening epoxy resin, but there are generally the following problems:

[0006] (1) Most of the glass transition temperatures of cured epoxy resin are around 200℃, while the glass transition temperature of polyimide is above 300℃. During the curing process, phase separation will cause the glass transition temperature to increase slightly or even decrease.

[0007] (2) After mixing most of the epoxy resin with engineering plastic particles, the viscosity is too large and the processability is poor.

[0008] Therefore, how to prepare an epoxy resin with good compatibility, high heat resistance and good toughness is a research problem with important research significance and application prospect. SUMMARY

[0009] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide a polyimide modified epoxy resin and a preparation method thereof, which has the advantages of good high-temperature resistance, high toughness, high mechanical strength and low linear expansion coefficient. In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] In the first aspect, the present application provides a preparation method of a polyimide modified epoxy resin, comprising the following steps: mixing an epoxy resin with biphenyl or naphthyl and an aromatic hot-melt polyimide without phenolic hydroxyl under heating conditions to form a homogeneous solution, adding a curing agent, after the curing agent is completely dissolved in the homogeneous solution, step curing is carried out, and the polyimide modified epoxy resin is obtained after natural cooling.

[0011] Preferably, the mass ratio of the epoxy resin with biphenyl or naphthyl, the aromatic hot-melt polyimide without phenolic hydroxyl and the curing agent is 100:(1-4):(40-50).

[0012] Preferably, the epoxy resin with biphenyl or naphthyl is one or a combination of the epoxy resins with the following chemical structures

[0013]

[0014] Preferably, the epoxy resin with biphenyl or naphthyl is

[0015] Preferably, the epoxy resin with biphenyl or naphthyl is a combination of the epoxy resins with the following chemical structures, and the mass ratio of the two is (70-90):(30-10).

[0016] Preferably, the aromatic hot-melt polyimide without phenolic hydroxyl is in a powder state, and the chemical structure is

[0017]

[0018] wherein n=500-2000.

[0019] Preferably, the mixing temperature is 170-190℃.

[0020] Preferably, the chemical structure of the curing agent is

[0021]

[0022] Preferably, the dissolution temperature of the curing agent is 170-200℃, and the dissolution time is 10-20min.

[0023] Preferably, the step curing is in three stages, and the temperature and time of the three stages are 170-180℃ / 2h, 200-210℃ / 2h and 230-240℃ / 2h in turn.

[0024] In a second aspect, the present application provides a polyamide modified epoxy resin obtained by the above method.

[0025] In a third aspect, the present application provides an application of the above polyamide modified epoxy resin, which can be used in aerospace, electronic packaging, ship, automobile and building fields.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. The naphthyl or biphenyl type epoxy resin, especially the rigid planar conjugated structure of naphthalene ring, endows it with a series of excellent properties, such as low moisture absorption, high chemical stability, low CTE and excellent mechanical and thermal mechanical properties. However, the glass transition temperature of the bifunctional naphthyl epoxy resin after curing with most curing agents is about 200℃, which cannot meet the requirements of the aerospace and electronic packaging industries. By mixing the tetrafunctional epoxy resin into the bifunctional epoxy resin, the interaction force formed between the benzene rings can reduce the free volume of the epoxy resin, and under the premise of not changing the process performance of the resin, a small amount of tetrafunctional resin is added to increase the crosslinking density of the epoxy resin, reduce the linear expansion coefficient, and expand the application of the epoxy resin in the high temperature field.

[0028] 2. The present application preferably physically blends two epoxy resins with different functionality, and then adds a soluble polyimide at high temperature, and cures with a curing agent with high reactivity and rigid stereostructure. Compared with other epoxy resin systems, the high functionality of the epoxy resin and the curing agent can ensure that the resin system has a large crosslinking density and rigidity, and can significantly improve the glass transition temperature of the epoxy resin.

[0029] 3. The soluble polyimide powder used in the present application has good compatibility and operability with the epoxy resin at high temperature. In the case of adding a small amount of polyimide, the glass transition temperature is improved, and the strength and toughness of the epoxy resin are significantly improved. The glass transition temperature of the obtained epoxy resin is greater than 240℃, the tensile strength is greater than 80MPa, and the impact strength is greater than 20KJ / m 2 Therefore, the soluble polyimide powder provided by the present application can be directly melted with the epoxy resin at high temperature, and a small amount of powder can improve the performance of the resin, effectively avoiding the performance decline caused by incomplete curing or phase separation. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1DMA curve of the epoxy resin prepared for Example 1 of the present application;

[0031] Figure 2 Stress-strain curve of the epoxy resin prepared for Example 1 of the present application;

[0032] Figure 3 TGA curve of the epoxy resin prepared for Example 1 of the present application;

[0033] Figure 4 TMA curve of the epoxy resin prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0034] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other ways different from those described herein without departing from the scope of the present application, and those skilled in the art can make similar generalizations without departing from the scope of the present application, and therefore the present application is not limited to the specific embodiments disclosed below.

[0035] The present application provides a preparation method of a polyimide-modified epoxy resin, comprising the following steps: mixing an epoxy resin having a biphenyl or naphthyl group and an aromatic thermoplastic polyimide not containing a phenolic hydroxyl group under heating conditions at a temperature of 170-190°C to form a homogeneous solution, adding a curing agent at a temperature of 170-200°C, dissolving for 10-20 min, and then performing stepwise curing after the curing agent is completely dissolved in the homogeneous solution, and naturally cooling to obtain a polyimide-modified epoxy resin; the mass ratio of the epoxy resin having a biphenyl or naphthyl group, the aromatic thermoplastic polyimide not containing a phenolic hydroxyl group, and the curing agent is 100:(1-4):(40-50).

[0036] The epoxy resin having a biphenyl or naphthyl group is a combination of

[0037] with a mass ratio of (70-90):(30-10).

[0038] The aromatic thermoplastic polyimide is in a powder state and has a chemical structural formula of

[0039]

[0040] wherein n=500.

[0041] The curing agent has a chemical structural formula of

[0042]

[0043] The step-by-step curing is in three stages, and the temperature and time of the three stages are: 170-180°C / 2h, 200-210°C / 2h and 230-240°C / 2h.

[0044] The epoxy resin represented by the general formula (I) used in the above steps is a bifunctional naphthalene epoxy resin. Since it has good flowability and operability at high temperature, it is formed by mixing with different proportions of the tetrafunctional naphthalene epoxy resin represented by the general formula (II) at high temperature, thereby increasing the crosslinking density of the cured epoxy resin. The aromatic soluble phenol-hydroxyl-free polyimide powder represented by the general formula (III) is used in a small amount, and in the epoxy resin system, it can improve the heat resistance and toughness of the epoxy resin.

[0045] In another aspect according to the present application, a polyimide modified epoxy resin obtained by the above method is provided, and corresponding tests are performed to obtain its performance indicators.

[0046] The polyimide modified epoxy resin and the preparation method thereof of the present application are specifically described below by way of examples. The main raw materials and equipment used: in the absence of specific indications, the raw materials and equipment of each example and comparative example are the same; the materials without specific model or type are obtained from market purchase or common model available through common channels, and are not specifically limited.

[0047] Example 1

[0048] 9g of the epoxy resin represented by the general formula (I) biphenyl epoxy NC-3000H, 1g of the epoxy resin represented by the general formula (II) 4700, and 0.1g of the polyimide powder D7000 are mixed at 170°C to form a homogeneous solution, and then 2.27g of the curing agent 4,4'-diamino diphenyl sulfone (DDS) represented by the general formula (IV) is added. After the curing agent is completely dissolved at a high temperature of 190°C, the following temperature gradient is adopted for curing: 170-180°C / 2h, 200-210°C / 2h, 230-240°C / 2h, and the epoxy resin is obtained after natural cooling.

[0049] Example 2

[0050] After 8 g of epoxy resin biphenyl epoxy NC-3000H represented by general formula (I), 2 g of epoxy resin 4700 represented by general formula (II), and 0.1 g of polyimide powder D7000 are sufficiently mixed and homogenized at 170°C with constant stirring to form a homogeneous solution, 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) is added, and after the curing agent is completely dissolved at a high temperature of 190°C, curing is performed using the following temperature gradient: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h, and an epoxy resin is obtained after natural cooling.

[0051] Example 3

[0052] After 9 g of epoxy resin biphenyl epoxy NC-3000H represented by general formula (I), 1 g of epoxy resin 4700 represented by general formula (II), and 0.2 g of polyimide powder D7000 are sufficiently mixed and homogenized at 170°C with constant stirring to form a homogeneous solution, 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) is added, and after the curing agent is completely dissolved at a high temperature of 190°C, curing is performed using the following temperature gradient: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h, and an epoxy resin is obtained after natural cooling.

[0053] Example 4

[0054] After 8 g of epoxy resin biphenyl epoxy NC-3000H represented by general formula (I), 2 g of epoxy resin 4700 represented by general formula (II), and 0.2 g of polyimide powder D7000 are sufficiently mixed and homogenized at 170°C with constant stirring to form a homogeneous solution, 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) is added, and after the curing agent is completely dissolved at a high temperature of 190°C, curing is performed using the following temperature gradient: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h, and an epoxy resin is obtained after natural cooling.

[0055] Comparative Example 1

[0056] After 3.32 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) is added to 10 g of epoxy resin E-51, and completely dissolved at a high temperature of 190°C, curing is performed using the following temperature gradient: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h.

[0057] Comparative Example 2

[0058] After 10 g of epoxy resin E-51 and 0.1 g of polyimide powder D7000 were mixed well at 170°C under constant stirring to form a homogeneous solution, 3.32 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) was added and completely dissolved at 190°C. The following temperature gradient was used for curing: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h

[0059] Comparative Example 3

[0060] After 10 g of epoxy resin E-51 and 0.2 g of polyimide powder D7000 were mixed well at 170°C under constant stirring to form a homogeneous solution, 3.32 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) was added and completely dissolved at 190°C. The following temperature gradient was used for curing: 170°C-180°C / 2h, 200°C-210°C / 2h, 230°C-240°C / 2h

[0061] Performance test method

[0062] DMA: The test was performed using a TA Instruments Q800 DMA instrument in tensile mode at a frequency of 1 Hz and a heating rate of 5°C / min.

[0063] Tensile test: The tensile strength of the resin cured body was tested using a universal tensile testing machine. The test sample was a dumbbell-shaped sample with dimensions of 75 mm x 5 mm x 2 mm. The tensile testing machine had a tensile rate of 2 mm / min, and the sample gauge length was controlled at 30 mm. The stress-strain curve of the sample was obtained, and the elastic modulus data was automatically output by the tensile testing machine.

[0064] TGA: The test was performed using a TA Instruments Q500 TGA instrument with N2 as the protective gas at a heating rate of 10°C / min and a test range of 25°C-800°C.

[0065] TMA: The sample coefficient of thermal expansion (CTE) was measured using a TMA402 F1 / F3 Hyperion thermal mechanical analyzer in compression mode at a heating rate of 5°C / min.

[0066] The properties of the epoxy resins of the examples and comparative examples are shown in Table 1.

[0067] Table 1

[0068]

[0069] As can be seen from Table 1, compared with the E-51 epoxy resin used in Comparative Example 1, the use of biphenyl epoxy NC-3000H and 4700 epoxy resin can increase the glass transition temperature of the epoxy resin from the original 220.3°C to 248.2°C, increase the tensile strength to 80.2 MPa, increase the impact strength to 20.3 KJ*(m -2 ), and increase the initial decomposition temperature at 5% weight loss to 376.35. At the same time, as can be seen from Example 1 to Example 4, with the increase of the content of 4700 tetrafunctional epoxy resin and aromatic thermoplastic polyimide powder, the thermal stability and mechanical properties of the epoxy resin are improved to a certain extent.

[0070] Although some specific embodiments of the present application have been described in detail by way of example with reference to the drawings, it is to be understood that the examples are for illustrative purposes only and are not to be construed as limiting the scope of the present application. It is to be understood that modifications can be made to the above embodiments without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for preparing a polyimide-modified epoxy resin, characterized in that, The process includes the following steps: mixing an epoxy resin containing biphenyl or naphthyl groups and an aromatic, heat-melting polyimide without phenolic hydroxyl groups under heating conditions to form a homogeneous solution; adding a curing agent; and after the curing agent is completely dissolved in the homogeneous solution, performing stepwise curing; and obtaining a polyimide-modified epoxy resin after natural cooling; wherein the epoxy resin containing biphenyl or naphthyl groups is... The combination; The mass ratio of the epoxy resin with biphenyl or naphthyl groups, the aromatic hot-melt polyimide without phenolic hydroxyl groups, and the curing agent is 100:(1-4):(40-50). The The mass ratio is (70-90):(30-10); The aromatic, heat-melting polyimide without phenolic hydroxyl groups is in powder form, and its chemical structural formula is as follows: Where n = 500 to 2000.

2. The method according to claim 1, characterized in that, The chemical structural formula of the curing agent is:

3. The method according to claim 1, characterized in that, The mixing temperature is 170℃~190℃; the dissolution temperature of the curing agent is 170~200℃, and the dissolution time is 10~20min.

4. The method according to claim 1, characterized in that, The step-by-step curing process consists of three stages, with the temperature and time for each stage being: 170℃~180℃ / 2h, 200℃~210℃ / 2h, and 230℃~240℃ / 2h, respectively.

5. A polyamide-modified epoxy resin obtained by the method according to any one of claims 1-4.

6. An application of the polyamide-modified epoxy resin as described in claim 5, characterized in that, Used in aerospace, electronic packaging, marine, automotive or construction industries.

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