Polyimide modified epoxy resin as well as preparation method and application thereof

Abstract

The invention provides polyimide modified epoxy resin as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing epoxy resin with biphenyl or naphthyl and aromatic hot-melt polyimide without phenolic hydroxyl group under a heating condition to form a homogeneous solution, adding a curing agent, and stirring to obtain a curing solution; and after the curing agent is completely dissolved in the homogeneous solution, carrying out step-by-step curing, and naturally cooling to obtain the polyimide modified epoxy resin. 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 invention belongs to the field of epoxy resins, and in particular relates to a polyimide-modified epoxy resin and a preparation method and application thereof. Background Art

[0002] Epoxy resin is a compound containing no less than two epoxy groups in its molecular structure and is the most important variety of thermosetting polymer prepolymers. After the epoxy resin and curing agent (commonly used are amines and anhydrides) are cured, a three-dimensional cross-linked network is formed, showing excellent performance. Therefore, before curing, epoxy resin has excellent processing properties; during the curing process, the volume shrinkage is low and the curing temperature control range is wide; after curing, the three-dimensional cross-linked network has excellent comprehensive properties, including high mechanical strength, good chemical resistance, good heat resistance, and good bonding performance. Therefore, epoxy resin is widely used in aerospace, electronics, ships, automobiles, construction and other fields as coatings, adhesives and composite matrix resins. However, epoxy resin has the problems of high brittleness and low temperature resistance, which seriously restricts its application in aerospace, electronic packaging and other fields. Under normal circumstances, the use of general flexible structure toughening methods can greatly improve its toughness, but it will inevitably cause a significant decrease in temperature resistance, strength and modulus.

[0003] Engineering plastic toughened epoxy resin is a typical toughening method and is often used in the modification of epoxy resin. For example, polyetheretherketone, polyimide, polyphenylene sulfide, and polysulfone have rigid elements, which can absorb energy under stress and prevent the spread of microcracks, and have a good effect on improving the toughness of epoxy resin. However, according to current literature reports, due to problems such as the compatibility of engineering plastics with epoxy resin, there are few methods that can increase the glass transition temperature of epoxy resin to above 240°C while maintaining the tensile strength to above 70Mpa. Polyimide is usually a polymer obtained by condensation polymerization of dianhydride (acid) and diamine, and its polymer main chain contains imide rings. Polyimide has many excellent properties. With its excellent high temperature resistance, it is often used as a high temperature structural adhesive and advanced composite material matrix. 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 and solvent resistance, which makes it have the advantage of replacing metal, glass and other materials in the field of adhesive applications. Invention patent CN113861421A discloses a polyimide-type epoxy resin toughening agent and a preparation method thereof. The toughening agent is a block polyimide polymer, which is composed of a structural segment containing phenolic hydroxyl groups and a structural segment without phenolic hydroxyl groups. The structural segment containing phenolic hydroxyl groups can participate in the curing reaction of the epoxy resin, and the toughening agent is introduced into the epoxy resin cross-linking network through chemical bonds to improve the compatibility and interfacial bonding between the toughening agent and the epoxy resin; on the other hand, its main chain contains rigid groups such as benzene rings and imide structures, which can maintain the good mechanical properties and heat resistance of the epoxy resin. However, the epoxy resin modified by the block polyimide polymer is prone to incomplete curing due to the steric hindrance of the curing agent, and the cross-linking network is loose and the glass transition temperature is low.

[0004] Therefore, the Tg of epoxy resin is higher than 240°C, and it is a huge challenge to maintain high strength and modulus while improving toughness.

[0005] At present, there are some reports on the use of polyimide powder to toughen epoxy resin, but the following problems are common:

[0006] (1) The glass transition temperature of most epoxy resins after curing is around 200°C, while the glass transition temperature of polyimide is above 300°C. During the curing process, phase separation will cause the glass transition temperature to increase slightly or even decrease.

[0007] (2) After mixing most epoxy resins with engineering plastic particles, problems such as excessive viscosity and poor processability will occur.

[0008] Therefore, how to prepare epoxy resin with good compatibility, high heat resistance and good toughness is a research issue with important research significance and application prospects. Summary of the invention

[0009] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a polyimide-modified epoxy resin and a preparation method thereof, wherein the polyimide-modified epoxy resin 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 invention adopts the following technical scheme to achieve it:

[0010] In a first aspect, the present invention provides a method for preparing a polyimide-modified epoxy resin, comprising the following steps: mixing an epoxy resin having a biphenyl or naphthyl group and an aromatic hot-melt polyimide not containing a phenolic hydroxyl group 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 step-by-step curing, and obtaining a polyimide-modified epoxy resin after natural cooling.

[0011] Preferably, the mass ratio of the epoxy resin having biphenyl or naphthyl groups, the aromatic hot-melt polyimide not containing phenolic hydroxyl groups, and the curing agent is 100:(1-4):(40-50).

[0012] Preferably, the epoxy resin having biphenyl or naphthyl groups is one or a combination of epoxy resins having the following chemical formulas:

[0013]

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

[0015] The combination of the two has a mass ratio of (70-90):(30-10).

[0016] Preferably, the aromatic hot-melt polyimide containing no phenolic hydroxyl group is in powder form, and has a chemical structural formula of

[0017]

[0018] Where n=500~2000.

[0019] Preferably, the mixing temperature is 170°C to 190°C.

[0020] Preferably, the chemical structural formula of the curing agent is

[0021]

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

[0023] Preferably, the step-by-step curing is divided into three stages, and the temperature and time of the three stages are: 170°C to 180°C / 2h, 200°C to 210°C / 2h and 230°C to 240°C / 2h.

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

[0025] In a third aspect, the present invention provides an application of the polyamide-modified epoxy resin, which can be used in the fields of aerospace, electronic packaging, shipbuilding, automobiles and construction.

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

[0027] 1. Naphthyl or biphenyl epoxy resins, especially the rigid planar conjugated structure of naphthalene rings, give them a series of excellent properties, such as low moisture absorption, high chemical resistance, low CTE and excellent mechanical and thermomechanical properties. However, since the glass transition temperature of difunctional naphthyl epoxy resins is around 200°C after curing with most curing agents, it cannot meet the requirements of the aerospace and electronic packaging industries. When tetrafunctional epoxy resins are mixed into difunctional epoxy resins, the interaction forces formed between benzene rings can reduce the free volume of epoxy resins, and a small amount of tetrafunctional resins can be added without changing the process properties of the resins, thereby increasing the crosslinking density of epoxy resins, reducing the linear expansion coefficient, and expanding the application of epoxy resins in the field of high temperature resistance.

[0028] 2. The present invention preferably physically blends two epoxy resins with different functionalities, then adds a fusible polyimide at high temperature, and solidifies with a curing agent with high reactivity and rigid three-dimensional structure. Compared with epoxy resins of other systems, high-functionality epoxy resins and curing agents can ensure that the resin system has a larger crosslinking density and rigidity, and can significantly increase the glass transition temperature of the epoxy resin.

[0029] 3. The fusible polyimide powder used in the present invention has good compatibility and operability with epoxy resin at high temperature. When a small amount of polyimide is added, the strength and toughness of the epoxy resin are significantly improved while the glass transition temperature is increased. The glass transition temperature of the obtained epoxy resin is greater than 240°C, the tensile strength is greater than 80MPa, and the impact strength is greater than 20KJ / m 2 Therefore, the fusible polyimide powder provided by the present invention can be directly melted with epoxy resin at high temperature, and the addition of a small amount of powder can improve the performance of the resin, effectively avoiding the performance degradation caused by incomplete curing or phase separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1DMA curve of the epoxy resin prepared in Example 1 of the present invention;

[0031] Figure 2 The stress-strain curve of the epoxy resin prepared in Example 1 of the present invention;

[0032] Figure 3 is the TGA curve of the epoxy resin prepared in Example 1 of the present invention;

[0033] Figure 4 This is the TMA curve of the epoxy resin prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited by the specific implementation methods disclosed below.

[0035] The invention provides a method for preparing a polyimide-modified epoxy resin. The method comprises the following steps: mixing an epoxy resin having biphenyl or naphthyl groups and an aromatic hot-melt polyimide not containing phenolic hydroxyl groups under heating conditions at a temperature of 170°C to 190°C to form a homogeneous solution, adding a curing agent at a temperature of 170°C to 200°C for a dissolution time of 10 to 20 minutes, curing in steps 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 biphenyl or naphthyl groups, the aromatic hot-melt polyimide not containing phenolic hydroxyl groups, and the curing agent is 100:(1-4):(40-50).

[0036] The epoxy resin having biphenyl or naphthyl groups is

[0037] The combination of the two has a mass ratio of (70-90):(30-10).

[0038] The aromatic hot-melt polyimide is in powder form and has a chemical structural formula of

[0039]

[0040] Where n=500.

[0041] The chemical structural formula of the curing agent is

[0042]

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

[0044] The epoxy resin represented by the general formula (I) used in the above steps is a difunctional naphthyl epoxy resin. Since it has good fluidity and operability at high temperature, it is formed by mixing with different proportions of the tetrafunctional naphthyl epoxy resin represented by the general formula (II) at high temperature, thereby increasing the crosslinking density of the epoxy resin after curing. The aromatic fusible polyimide powder without phenolic hydroxyl group 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] According to another aspect of the present invention, 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 invention are specifically described below by way of examples. Main raw materials and equipment used: Unless otherwise specified, the raw materials and equipment of each embodiment and comparative example are the same; materials without specifying the specific model or type are from the common same model purchased from the market or available through common channels, and are not specifically limited.

[0047] Example 1

[0048] 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 0.1 g of polyimide powder D7000 were fully mixed and stirred at 170°C to form a homogeneous solution, and then 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) was added. After the curing agent was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C~180°C / 2h, 200°C~210°C / 2h, 230°C~240°C / 2h, and the epoxy resin was obtained after natural cooling.

[0049] Example 2

[0050] 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 were fully mixed and stirred at 170°C to form a homogeneous solution, and then 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) was added. After the curing agent was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C~180°C / 2h, 200°C~210°C / 2h, 230°C~240°C / 2h, and the epoxy resin was obtained after natural cooling.

[0051] Example 3

[0052] 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 were fully mixed and stirred at 170°C to form a homogeneous solution, and then 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) was added. After the curing agent was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C~180°C / 2h, 200°C~210°C / 2h, 230°C~240°C / 2h, and the epoxy resin was obtained after natural cooling.

[0053] Example 4

[0054] 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 were fully mixed and stirred at 170°C to form a homogeneous solution, and then 2.27 g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) represented by general formula (IV) was added. After the curing agent was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C~180°C / 2h, 200°C~210°C / 2h, 230°C~240°C / 2h, and the epoxy resin was obtained after natural cooling.

[0055] Comparative Example 1

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

[0057] Comparative Example 2

[0058] 10g of epoxy resin E-51 and 0.1g of polyimide powder D7000 were fully mixed at 170°C and stirred continuously to form a homogeneous solution, and then 3.32g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) was added. After it was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C ~ 180°C / 2h, 200°C ~ 210°C / 2h, 230°C ~ 240°C / 2h

[0059] Comparative Example 3

[0060] 10g of epoxy resin E-51 and 0.2g of polyimide powder D7000 were fully mixed at 170°C and stirred continuously to form a homogeneous solution, and then 3.32g of curing agent 4,4'-diaminodiphenyl sulfone (DDS) was added. After it was completely dissolved at a high temperature of 190°C, the following temperature gradient was adopted for curing: 170°C ~ 180°C / 2h, 200°C ~ 210°C / 2h, 230°C ~ 240°C / 2h

[0061] Performance Testing Methods

[0062] DMA: In the tensile mode, the test was carried out using a TA Instruments Q800 DMA instrument with a frequency of 1 Hz and a heating rate of 5 °C / min.

[0063] Tensile test: A universal tensile testing machine is used to test the tensile strength of the resin cured product. The test specimen uses a dumbbell-shaped specimen with a size of 75mm×5mm×2mm. The tensile rate of the tensile machine is 2mm / min, and the specimen gauge length is controlled at 30mm. The stress-strain curve of the specimen is obtained, and the elastic modulus data is automatically output by the tensile machine.

[0064] TGA: Select N 2 As the protective gas, the heating rate is 10℃ / min, the test range is 25℃~800℃, and the test is carried out using TA Instruments Q500 TGA instrument.

[0065] TMA: The coefficient of linear expansion (CTE) of the samples was measured using a TMA402F1 / F3 Hyperion thermomechanical analyzer in compression mode with a heating rate of 5°C / min.

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

[0067] Table 1

[0068]

[0069] It can be seen from Table 1 that compared with the E-51 epoxy resin used in Comparative Example 1, the use of biphenyl epoxy NC-3000H and 4700 epoxy resins 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 80.2MPa, and increase the impact strength to 20.3KJ*(m -2 ), the initial decomposition temperature of 5% weight loss is increased to 376.35. At the same time, it can be seen from Examples 1 to 4 that with the increase of the content of 4700 tetrafunctional epoxy resin and aromatic hot-melt 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 invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for preparing a polyimide-modified epoxy resin, characterized in that: The method comprises the following steps: mixing an epoxy resin having biphenyl or naphthyl groups and an aromatic hot-melt 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 step-by-step curing, and obtaining a polyimide-modified epoxy resin after natural cooling.

2. The method according to claim 1, characterized in that The mass ratio of the epoxy resin having biphenyl or naphthyl groups, the aromatic hot-melt polyimide not containing phenolic hydroxyl groups, and the curing agent is 100:(1-4):(40-50).

3. The method according to claim 1, characterized in that The epoxy resin having biphenyl or naphthyl groups is one or a combination of the following epoxy resins of chemical formula:

4. The method according to claim 1, characterized in that: The epoxy resin having biphenyl or naphthyl groups is The combination of the two has a mass ratio of (70-90):(30-10).

5. The method according to claim 1, characterized in that The aromatic hot-melt polyimide containing no phenolic hydroxyl group is in powder form and has a chemical structural formula of Where n=500~2000.

6. The method according to claim 1, characterized in that The chemical structural formula of the curing agent is 7. The method according to claim 1, characterized in that The mixing temperature is 170° C. to 190° C.; the dissolving temperature of the curing agent is 170° C. to 200° C., and the dissolving time is 10 to 20 minutes.

8. The method according to claim 1, characterized in that The step-by-step curing is divided into three stages, and the temperature and time of the three stages are: 170°C-180°C / 2h, 200°C-210°C / 2h and 230°C-240°C / 2h.

9. A polyamide-modified epoxy resin obtained according to the method according to any one of claims 1 to 8.

10. A use of the polyamide modified epoxy resin as claimed in claim 9, characterized in that: It can be used in aerospace, electronic packaging, marine, automotive and construction fields.

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