Liquid crystal / epoxy composite material as well as preparation method and application thereof

Abstract

The invention discloses a liquid crystal / epoxy composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: weighing and dissolving a photocuring monomer, a photosensitive diluent and an active diluent to prepare a resin matrix; adding 4-ethoxybenzylidene-4-butylaniline and 4-cyano-4-pentylbiphenyl into the resin matrix, stirring, cooling to room temperature, adding a photoinitiator into the mixed solution, and stirring to obtain a liquid crystal / epoxy mixed solution; the liquid crystal / epoxy mixed liquid is poured into a trough and stirred, so that the whole bottom of the trough is filled with the mixed liquid; printing and forming by using DLP (Digital Light Processing) to obtain a liquid crystal / epoxy composite material; the liquid crystal / epoxy composite material is oriented through a photocuring 3D printing technology, so that the material has anisotropy, and the thermal conductivity and mechanical toughness of the epoxy resin are also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical materials, and in particular relates to a liquid crystal / epoxy composite material and a preparation method and application thereof. Background Art

[0002] In recent years, the communication, automation, aerospace, biomedical, electrical and other industries have developed rapidly, which has put forward further requirements for related equipment and basic materials. Epoxy resin has the advantages of strong corrosion resistance and high electrical insulation performance, and is widely used in the fields of power equipment insulation and electronic packaging. However, due to the poor thermal conductivity and mechanical toughness of epoxy resin, the thermal conductivity of epoxy impregnated power equipment is poor and it is easy to crack under certain stress. This will undoubtedly become a huge safety hazard for epoxy impregnated power equipment, restricting the application of epoxy impregnated power equipment.

[0003] Liquid crystal has some properties of both liquid and crystal. Its molecules can move freely like liquid, and the time for liquid crystal molecules to move in a specific direction is longer than the time to move in other directions. Therefore, external environmental factors such as electric field, stress, and magnetic field can easily change the arrangement of liquid crystal molecules. Due to the unique properties of liquid crystal materials, they have great development prospects in solving the problems of epoxy power equipment. For example, the liquid crystal element contained in the liquid crystal epoxy resin monomer (LCE) can improve the thermal conductivity of the resin itself by regulating the orderliness of the cross-linked network structure. Intrinsically thermally conductive liquid crystal epoxy resin (LCER) is a composite liquid crystal material with high thermal conductivity obtained based on this method.

[0004] However, due to the weak performance of liquid crystal materials, and the high cost and complex process of its synthesis and processing, the application of liquid crystal materials is greatly restricted. The use of 3D printing to solidify and process composite liquid crystal materials will greatly simplify the processing difficulty of liquid crystal composite materials and reduce the application cost of liquid crystal composite materials. Therefore, the research on the relevant performance of 3D printed liquid crystal / epoxy composite materials is very promising and has a market. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a liquid crystal / epoxy composite material.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for preparing a liquid crystal / epoxy composite material, comprising:

[0009] Mixing and dissolving a photocurable monomer, a photosensitive diluent, and a reactive diluent to obtain a resin matrix;

[0010] 4-ethoxybenzylidene-4-butylaniline and 4-cyano-4-pentylbiphenyl are added to the resin matrix and stirred, and after cooling to room temperature, a photoinitiator is added to the mixture and stirred to obtain a liquid crystal / epoxy mixture;

[0011] Pour the liquid crystal / epoxy mixture into the tank and stir until the mixture fills the entire bottom of the tank;

[0012] After printing and molding, a liquid crystal / epoxy composite material is obtained;

[0013] The volume percentages of the photocurable monomer, the photosensitive diluent and the reactive diluent are 27-33%: 57-63%: 7-13%;

[0014] The photocurable monomer includes one or more of tripropylene glycol diacrylate, epoxy acrylate, and methacrylate; the photosensitive diluent includes one or more of glycidyl methacrylate and epoxy glycidyl ether;

[0015] The reactive diluent includes trimethylolpropane triacrylate;

[0016] The photoinitiator includes one or more of photoinitiator 819, TPO, and TPO-L.

[0017] As a preferred solution of the preparation method of the present invention, the volume percentage of the photoinitiator and the liquid crystal / epoxy mixed solution is 0.5-80%:100%.

[0018] As a preferred embodiment of the preparation method of the present invention, the resin matrix is ​​prepared under light-proof conditions.

[0019] As a preferred embodiment of the preparation method of the present invention, in the liquid crystal / epoxy mixed solution, the mass percentages are: resin matrix: 4-ethoxybenzyl-4-butylaniline: 4-cyano-4-pentylbiphenyl = 93-100%: 0-7%: 7-0%.

[0020] As a preferred embodiment of the preparation method of the present invention, the 4-ethoxybenzylidene-4-butylaniline and 4-cyano-4-pentylbiphenyl are added to the resin matrix and stirred at 60-70° C. for 30-60 minutes.

[0021] As a preferred embodiment of the preparation method of the present invention, in the printing and forming process, the exposure time of the bottom layer for vertical printing is 14 to 20 s.

[0022] As a preferred embodiment of the preparation method of the present invention, in the printing and forming process, the exposure time of the bottom layer for parallel printing is 20 to 25 s.

[0023] As a preferred embodiment of the preparation method of the present invention, in the printing and forming process, the exposure time of the bottom layer for measuring the breakdown voltage is 60 to 80 s, and the exposure time of the bottom layer for measuring the dielectric constant is 35 to 40 s.

[0024] Another object of the present invention is to provide a liquid crystal / epoxy composite material.

[0025] Another object of the present invention is to provide the application of the liquid crystal / epoxy composite material as an electrical insulation material.

[0026] Advantages of the present invention:

[0027] (1) The present invention uses photocuring 3D printing to process composite liquid crystal materials, solving the problems of insufficient related properties of liquid crystal materials, cumbersome processing procedures, and high costs.

[0028] (2) The arrangement of liquid crystals changes under specific factors. The present invention orients the liquid crystal / epoxy composite material through photocuring 3D printing technology, making the material anisotropic.

[0029] (3) The present invention also improves the thermal conductivity and mechanical toughness of epoxy resin. Description of the drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0031] Figure 1 It is a physical diagram of the liquid crystal / epoxy mixture in Example 1 of the present invention.

[0032] Figure 2 It is a flowchart of the preparation by photocuring 3D printing in Example 1 of the present invention.

[0033] Figure 3 It is the thermal conductivity of samples with different EBBA contents (parallel printing) in each embodiment of the present invention.

[0034] Figure 4The thermal conductivity of samples with different EEBA contents in various embodiments of the present invention is compared with that of samples printed vertically and parallelly.

[0035] Figure 5 is the relative dielectric constant of samples with different EBBA contents in various embodiments of the present invention.

[0036] Figure 6 The mechanical properties of samples with different EBBA contents in various embodiments of the present invention are shown in FIG. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0040] Raw materials and reagents used in the present invention:

[0041]

[0042] Example 1 Preparation method of liquid crystal / epoxy composite material

[0043] 1. Weigh 8.37 g of photocurable monomer tripropylene glycol diacrylate TPGDA, 16.74 g of photosensitive diluent GMA, and 2.79 g of reactive diluent trimethylolpropane triacrylate TMPTA, and dissolve them to prepare a resin matrix;

[0044] 2. Add 1.5 g of 4-ethoxybenzylidene-4-butylaniline (5% by mass) and 0.6 g of 4-cyano-4-pentylbiphenyl (2% by mass) to 27.9 g of the resin matrix (93% by mass), and stir at 60° C. for 30 minutes using a magnetic stirrer (model JK-DMS-H);

[0045] 3. After cooling to room temperature, add 0.2g of photoinitiator 819 to the mixture and stir at room temperature for 20 minutes to obtain a liquid crystal / epoxy mixture. Figure 1 As shown;

[0046] 4. Perform light-curing 3D printing. The light-curing 3D printing preparation process is as follows: Figure 2 As shown, specifically:

[0047] The designed 3D model was exported in STL file format; the STL format of the designed 3D model was imported into CHITUBOX software, and the DLP printer parameters were set. The wavelength of the DLP printer was 405nm, the number of printing layers was set to 6, and the printing layer thickness was 15μm;

[0048] Then pour the prepared liquid crystal / epoxy mixed liquid into the clean 3D printing material tank, so that the mixed liquid fills the entire bottom of the tank, and wait for the material to level before starting the next step of light-curing 3D printing; during printing, the exposure time of the bottom layer of parallel printing is 20s, the exposure time of the bottom layer for measuring breakdown voltage is 60s, and the exposure time of the bottom layer for measuring dielectric constant is 35s;

[0049] 5. After printing, the printed model is thoroughly cleaned with alcohol, and after the surface is dried, it is post-cured to obtain a liquid crystal / epoxy composite material, and finally tested and characterized.

[0050] Example 2 Preparation method of liquid crystal / epoxy composite material

[0051] The difference from Example 1 is that 1.5 g of 5% by mass 4-ethoxybenzyl-4-butylaniline and 0.6 g of 2% by mass 4-cyano-4-pentylbiphenyl in step 2 are replaced by 2.1 g of 7% by mass 4-ethoxybenzyl-4-butylaniline.

[0052] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0053] Example 3 Preparation method of liquid crystal / epoxy composite material

[0054] The difference from Example 1 is that 1.5 g of 5% by mass of 4-ethoxybenzylidene-4-butylaniline and 0.6 g of 2% by mass of 4-cyano-4-pentylbiphenyl in step 2 are replaced by 2.1 g of 7% by mass of 4-cyano-4-pentylbiphenyl.

[0055] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0056] Example 4 Preparation method of liquid crystal / epoxy composite material

[0057] The difference from Example 1 is that: 1.5 g of 5% by mass of 4-ethoxybenzyl-4-butylaniline and 2% of 0.6 g of 4-cyano-4-pentylbiphenyl in step 2 are replaced by 3% by mass of 0.9 g of 4-ethoxybenzyl-4-butylaniline and 4% of 0.12 g of 4-cyano-4-pentylbiphenyl.

[0058] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0059] Example 5 Performance Test of Liquid Crystal / Epoxy Composite Material

[0060] 1. Thermal conductivity test:

[0061] The sample was polished into a square piece with a side length of 10 mm and a thickness of 1 mm. The thermal diffusivity (α) of the sample along the thickness direction was tested using an LFA467 laser thermal conductivity instrument. A layer of black graphite oil was sprayed on the surface of the sample so that it could absorb most of the laser pulse energy. The thermal conductivity of the material can be calculated by measuring the energy added to the hot plate, the temperature gradient, and the thickness of the two samples. The constant pressure specific heat capacity of the sample was measured by comparing it with the reference sample, and the density of the sample was measured by measuring the actual volume and weight of the sample. Then, the formula λ = α / (ρ×C p ) Calculate the thermal conductivity of the sample; In this experiment, a laser voltage of 250V with a pulse width of 0.60ms was selected to carry out the test at room temperature (20 degrees Celsius).

[0062] like Figure 3 As shown in the figure, when 4-ethoxybenzyl-4-butylaniline (EBBA) and 4-cyano-4-pentylbiphenyl (5CB) are blended, the thermal conductivity is higher than when they are used alone. For example, when the content of 4-ethoxybenzyl-4-butylaniline (EBBA) is 5wt% and the content of 5CB is 2wt%, the thermal conductivity is the highest, which is 0.245.

[0063] like Figure 4 As shown in the figure, when EEBA and 5CB are not added, the thermal conductivity of the pure resin does not change much within the error range whether it is printed vertically or parallel, indicating that the polymer is not anisotropic; when EBBA and 5CB are added, the thermal conductivity of the sample printed in parallel is always greater than the thermal conductivity of the sample printed vertically. Therefore, the liquid crystal composite material has a certain anisotropy after photocuring 3D printing, and the EBBA content is preferably 5wt% and the 5CB content is preferably 2wt%.

[0064] 2. Dielectric performance test:

[0065] When measuring dielectric properties, the sample length and width need to be 10 to 20 mm and the thickness 0.5 to 1.5 mm.

[0066] The main steps to measure the relative dielectric constant are: first, when the space between the two plates is filled with air, measure the capacitance of the capacitor, which is C 0 ; Then use the same capacitor plates, and the distance between the two plates remains unchanged, add the dielectric material to be tested between the plates and measure the capacitance using the same method, which is calculated as Cx; Finally, E r =Cx / C 0 Calculate the value of the relative dielectric constant.

[0067] like Figure 5 As shown, the relative dielectric constant first increases and then decreases with the increase of EBBA content in the sample. When the EBBA content is 5wt% and the 5CB content is preferably 2wt%, the dielectric properties are better. The relative dielectric constant increases from 5.3F / m at 0wt% EBBA content to 7.2F / m at 5wt% EBBA content.

[0068] 3. Mechanical properties test

[0069] Mechanical property tests mainly include tensile and bending properties.

[0070] Before measuring the tensile properties, you need to measure the standard length and cross-sectional area of ​​the sample. When fixing the sample, try to clamp both ends of the sample tightly and firmly to reduce errors and sample slippage caused by inaccurate standard length. Pay attention to the change of tension during measurement. When the tension changes suddenly, that is, when the sample breaks, stop the experiment and save the data.

[0071] When measuring bending properties, the area of ​​the fracture surface should be measured after the sample breaks. This experiment uses the mechanical properties tester of WanCe Group for testing. After the test results come out, draw the stress-strain curve, and finally find the highest point of the curve. The stress at this point is the tensile strength. Fit the middle section of the curve with a straight line to get the slope value of the fitted straight line. Shift this straight line until it passes through the point (0.2, 0). The ordinate of the intersection of the straight line and the original curve is the yield strength. The abscissa when the curve changes suddenly is the elongation at break.

[0072] like Figure 6As shown in the figure, both tensile strength and yield strength decrease with the increase of EBBA content in the sample, the tensile strength decreases from 30.002MPa at 0wt% EBBA to 21.274MPa at 7wt% EBBA; the yield strength decreases from 26.074MPa at 0wt% EBBA to 17.813MPa at 7wt% EBBA. The elongation at break increases with the increase of EBBA content in the sample, from 7.1% at 0wt% EBBA to 15.2% at 7wt% EBBA. When EEBA is blended with 5CB, the data of tensile strength, yield strength and elongation at break are relatively concentrated. When considering the balance of elongation at break, tensile strength and yield strength, the material blended with EEBA and 5CB is preferred. Therefore, the EBBA content is preferably 3%.

[0073] Since liquid crystal materials have the properties related to liquid crystals, according to the definition of liquid crystals, liquid crystals have both the anisotropy of crystals and the fluidity of liquids. Different printing directions result in different arrangement effects, thus affecting the thermal conductivity of liquid crystal composite materials. Taking the tensile test as an example, when the printing direction is parallel to the tensile test direction, it is vertical printing, and when the printing direction is perpendicular to the tensile test direction, it is parallel printing. Regardless of whether the EBBA content in the liquid crystal composite material is 0%, 3%, 5%, or 7%, the thermal conductivity of samples with the same EBBA content when printed in parallel is greater than the thermal conductivity when printed vertically.

[0074] The performance tests of the liquid crystal / epoxy composite materials of Examples 1 to 4 are shown in Table 1.

[0075] Table 1

[0076]

[0077] In summary, after the liquid crystal / epoxy composite material is subjected to photocuring 3D printing, the mechanical, dielectric and thermal conductivity of the material have changed to a certain extent compared with the products printed by pure 5CB liquid crystal or pure EBBA liquid crystal. In insulating electrical equipment, when the sample needs to have a higher thermal conductivity and relative dielectric constant, the liquid crystal product blended with EEBA and 5CB is preferred; in mechanical equipment, when the material needs to have a strong tensile strength, the EBBA content is preferably between 2wt% and 3wt%, but if a balance between strength and ductility is required, the EBBA content needs to be selected between 2% and 5%.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that the photoinitiator is replaced by TPO.

[0080] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0081] The results show that TPO has a slightly lower initiation efficiency than 819, a slightly lower curing speed than 819, and slightly lower mechanical properties of the cured resin than 819, making it a more suitable material to replace photoinitiator 819.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is that the photoinitiator is replaced by TPO-L.

[0084] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0085] The results show that TPO-L has a similar structure to TPO, but the initiation efficiency of TPO-L is much lower than that of TPO. TPO-L is suitable for two-photon polymerization and high-precision 3D printing. Under the same conditions, it requires longer exposure time and higher light intensity to achieve the same curing effect as 819, and its curing speed is moderate (slower than photoinitiator 819).

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that the photoinitiator is replaced by ITX.

[0088] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0089] The results showed that it cannot be quickly photocured; its curing speed is low, which can easily lead to incomplete curing and affect the mechanical strength of the final material; the printing accuracy is reduced; and its compatibility with DLP is low.

[0090] Comparative Example 4

[0091] The difference between this comparative example and Example 1 is that the photocurable monomer is replaced by epoxy acrylate.

[0092] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0093] The results showed that when the formula ratio remained unchanged, after replacing TPGDA with epoxy acrylate, the viscosity of the overall printing material became higher, making it difficult to adapt to the process requirements of DLP printing, increasing the difficulty of printing.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that the photocurable monomer is replaced by methacrylate.

[0096] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0097] The results showed that when the formula ratio remained unchanged, after replacing TPGDA with methacrylate, the volume shrinkage of the overall printing material increased and the 3D printing accuracy decreased.

[0098] Comparative Example 6

[0099] The difference between this comparative example and Example 1 is that the photosensitive diluent is replaced by epoxy glycidyl ether.

[0100] The remaining steps and processes are all referred to Example 1 to obtain the liquid crystal / epoxy composite material of this example.

[0101] The results showed that when the formula ratio remained unchanged, after replacing glycidyl methacrylate (GMA) with epoxy glycidyl ether, the curing speed of the material was reduced, and it was difficult to have the high cross-linking density after curing of glycidyl methacrylate, and its mechanical strength was reduced.

[0102] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a liquid crystal / epoxy composite material, characterized in that: include, Mixing and dissolving a photocurable monomer, a photosensitive diluent, and a reactive diluent to obtain a resin matrix; 4-ethoxybenzylidene-4-butylaniline and 4-cyano-4-pentylbiphenyl are added to the resin matrix and stirred, and after cooling to room temperature, a photoinitiator is added to the mixture and stirred to obtain a liquid crystal / epoxy mixture; Pour the liquid crystal / epoxy mixture into the tank and stir until the mixture fills the entire bottom of the tank; After printing and molding, a liquid crystal / epoxy composite material is obtained; The mass percentages of the photocurable monomer, the photosensitive diluent and the reactive diluent are 27-33%: 57-63%: 7-13%; The photocurable monomer includes one or more of tripropylene glycol diacrylate, epoxy acrylate, and methacrylate; the photosensitive diluent includes one or more of glycidyl methacrylate and epoxy glycidyl ether; The reactive diluent includes trimethylolpropane triacrylate; The photoinitiator includes one or more of photoinitiator 819, TPO, and TPO-L.

2. The method for preparing the liquid crystal / epoxy composite material according to claim 1, characterized in that: The volume percentage of the photoinitiator and the liquid crystal / epoxy mixed liquid is 0.5-80%:100%.

3. The method for preparing the liquid crystal / epoxy composite material according to claim 2, characterized in that: The resin matrix is ​​prepared under light-proof conditions.

4. The method for preparing the liquid crystal / epoxy composite material according to any one of claims 1 to 3, characterized in that: In the liquid crystal / epoxy mixed solution, according to the mass percentage of the mixed solution, the resin matrix: 4-ethoxybenzylidene-4-butylaniline: 4-cyano-4-pentylbiphenyl = 93-100%: 0-7%: 7-0%.

5. The method for preparing the liquid crystal / epoxy composite material according to claim 4, characterized in that: The 4-ethoxybenzylidene-4-butylaniline and 4-cyano-4-pentylbiphenyl are added to the resin matrix and stirred at 60-70° C. for 30-60 minutes.

6. The method for preparing the liquid crystal / epoxy composite material according to claim 5, characterized in that: In the printing process, the exposure time of the bottom layer of vertical printing is 14 to 20 seconds.

7. The method for preparing the liquid crystal / epoxy composite material according to any one of claims 1 to 3, 5 or 6, characterized in that: In the printing process, the exposure time of the bottom layer of parallel printing is 20 to 25 seconds.

8. The method for preparing the liquid crystal / epoxy composite material according to claim 7, characterized in that: In the printing process, the exposure time of the bottom layer for measuring the breakdown voltage is 60 to 80 seconds, and the exposure time of the bottom layer for measuring the dielectric constant is 35 to 40 seconds.

9. The liquid crystal / epoxy composite material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the liquid crystal / epoxy composite material according to claim 9 as an electrical insulating material.

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