Aramid composite paper and preparation method and application thereof

Abstract

The application discloses aramid composite paper and a preparation method and application thereof, and relates to the technical field of aramid paper. The application provides aramid composite paper, which comprises three layers of fiber structure layers which are sequentially stacked, the first layer of fiber structure layer comprises aramid short-cut fibers and polyphenylene sulfide pulp, the second layer of fiber structure layer comprises plant fibers, and the third layer of fiber structure layer comprises aramid fibrids and polyimide fibers. The three-layer structure of the aramid composite paper of the application strengthens the compactness and uniformity of the insulating paper from two aspects of macro and micro, thereby enhancing the mechanical and electrical strength. Meanwhile, the specific selection of the specific first layer and third layer can better cooperate with the second layer of fiber structure layer, strengthen the local overheating identification function of the aramid composite paper, and solve the problems of the non-ideal uniformity of the existing aramid composite paper and the incapability of identifying local overheating on the basis of maintaining the excellent electrical insulation and heat resistance of the original aramid paper.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aramid paper, and particularly relates to an aramid composite paper and a preparation method and application thereof. BACKGROUND

[0002] The aramid paper is prepared from aramid short fibers and aramid fibrids as raw materials, and is obtained by forming, pressing, drying and hot pressing. The aramid paper produced by wet papermaking has excellent mechanical properties, insulation properties, flame retardancy, radiation resistance and the like, and has become a new type of material urgently needed to be developed in the fields of aerospace, ship, rail transportation, electrical insulation, military and the like.

[0003] On the one hand, in the preparation process of the aramid paper, the aramid short fibers are too long, and flocculation easily occurs in the forming process of the paper machine, so that the uniformity of the produced paper is not ideal, and the mechanical and electrical properties are affected. On the other hand, the aramid paper is wrapped on the transformer winding as an insulating material and is applied in the field of transformers. Since the running environment of the aramid paper is a sealed environment wrapped by insulating oil, when the transformer winding fails and local overheating occurs, the insulation properties of the aramid paper are damaged, and the aramid paper cannot be opened and monitored in time, which may cause greater accidents.

[0004] Therefore, the aramid paper capable of identifying local overheating problems and monitoring local overheating conditions of the transformer in time has important significance. SUMMARY

[0005] Based on this, the present application aims to overcome the shortcomings of the prior art and provide an aramid composite paper and a preparation method and application thereof.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: an aramid composite paper, which comprises three layers of fiber structure layers stacked in sequence, a first layer of fiber structure layer comprising aramid short fibers and polyphenylene sulfide pulp, a second layer of fiber structure layer comprising plant fibers, and a third layer of fiber structure layer comprising aramid fibrids and polyimide fibers.

[0007] Preferably, the absolute dry mass ratio of the first layer of fiber structure layer, the second layer of fiber structure layer and the third layer of fiber structure layer is first layer of fiber structure layer: second layer of fiber structure layer: third layer of fiber structure layer = (30-35):(30-40):(30-35).

[0008] Preferably, the absolute dry mass ratio of the aramid short fibers and the polyphenylene sulfide pulp in the first layer of fiber structure layer is 1:(1-3); the beating degree of the aramid short fiber pulp is 40-60°SR, the average length of the aramid short fibers before beating is 5-7mm, the beating degree of the polyphenylene sulfide pulp is 40-60°SR, and the average diameter of the polyphenylene sulfide pulp before beating is 4-10μm.

[0009] Preferably, the plant fiber in the second fiber structure layer is at least one of coniferous wood fiber, broadleaf wood fiber, hemp fiber, bamboo fiber, and grass fiber; preferably, the beating degree of the pulp in the second fiber structure layer is 20-30°SR, and the average length of the plant fiber before beating is 0.7-1.5mm.

[0010] Preferably, the hemp fiber includes at least one of Manila hemp, ramie, hemp, jute, and sisal.

[0011] Preferably, the oven-dry mass ratio of polyimide fiber and aramid precipitated fiber in the third fiber structure layer is 1:(1-3); the freeness of the aramid precipitated fiber slurry is 60-80°SR, and the average length of the aramid precipitated fiber before freeing is 0.5-1.1 mm; the freeness of the polyimide fiber slurry is 40-60°SR, and the average length of the polyimide fiber before freeing is 2-6 mm.

[0012] The first fiber structure layer of this invention comprises aramid chopped fibers and polyphenylene sulfide pulp. The chopped fibers have a rigid cylindrical shape with uniform thickness at both ends, a smooth surface, and a very small amount of adhesive material on the surface. They are obtained through dry and wet spinning. The polyphenylene sulfide pulp can be obtained by pulping polyphenylene sulfide microfiber nonwoven fabric. The third fiber structure layer comprises aramid precipitated fibers and polyimide fibers. The aramid precipitated fibers have a thin film-like wrinkled structure.

[0013] The three-layer structure of the aramid composite paper of this invention enhances the density and uniformity of the aramid composite paper from both macroscopic and microscopic perspectives, thereby improving its mechanical and electrical strength. This is mainly manifested in the following ways: In the third layer, polyimide fibers containing amide structures and aramid precipitated fibers form an ordered hydrogen bond network, enhancing intermolecular bonding forces from a microscopic perspective and improving the mechanical strength of the aramid paper. In the first layer, polyphenylene sulfide exhibits good adhesion after hot pressing, spreading across the surface and pores of the plant fibers in the second layer after hot pressing, improving paper uniformity and reducing porosity, thus improving the mechanical and electrical strength of the aramid paper from a macroscopic perspective. When subjected to localized overheating, the plant fibers in the second layer degrade into small molecules such as furfural and methanol, which dissolve in the insulating oil. The presence of overheating can be determined by detecting the insulating oil. The invention features a specific three-layer fiber structure that works in combination. The first fiber structure layer, which contains aramid chopped fibers and polyphenylene sulfide pulp, and the third fiber structure layer, which contains aramid precipitated fibers and polyimide fibers, improve the mechanical and electrical strength of aramid paper from both macroscopic and microscopic perspectives. At the same time, the specific selection of the first and third layers allows for better synergy with the second fiber structure layer, enhancing the local overheat detection function of the aramid composite paper. While maintaining the excellent electrical insulation and heat resistance of the original aramid paper, this invention solves the problems of unsatisfactory uniformity and inability to detect local overheating in existing aramid composite papers.

[0014] Preferably, the slurry preparation method corresponding to the three fiber structure layers is as follows:

[0015] S1. The aramid chopped fiber pulping treatment: The aramid chopped fibers are pulped and fully dispersed in a pulping machine, wherein the pulping speed is 3000-5500 rpm, the pulping concentration is 3.0-5.0%, and the pulping degree is 30-60°SR, to obtain an aramid chopped fiber suspension.

[0016] S2. The polyphenylene sulfide pulp beating treatment: after cutting the polyphenylene sulfide microfiber nonwoven fabric into pieces, the pulping treatment is carried out for 30-60 minutes, the pulping speed is 3000-5500 rpm, the pulping concentration is 2.0-5.0%, and the freeness is 30-60°SR, to obtain wet pulp, which is then vacuum dried to obtain polyphenylene sulfide microfiber pulp.

[0017] S3. The plant fiber pulping treatment: The plant fiber is pulped, and its beating degree and fiber length are controlled to obtain plant fiber pulp b; wherein, the average length of the plant fiber before pulping is 0.7-1.5mm, and the beating degree is 20-80°SR.

[0018] S4. The aramid precipitated fiber pulping treatment: the pulping speed of the aramid precipitated fiber is 5000-7500 rpm, the pulping concentration is 2.0-5.0%, and the pulping degree is 40-70°SR, to obtain an aramid chromatography fiber suspension.

[0019] S5. Polyimide fiber treatment: The polyimide fiber is pulped for 30-60 minutes, at a pulping speed of 3000-5500 rpm, with a pulping concentration of 2.0-5.0% and a freeness of 30-60°SR, to obtain a polyimide fiber suspension.

[0020] Furthermore, the present invention provides a method for preparing the aforementioned aramid composite paper, the method being as follows:

[0021] (1) After mixing the slurries obtained in S1 and S2, add defoamer and dispersant to obtain slurry a; after mixing the slurries obtained in S4 and S5, add defoamer and dispersant to obtain slurry c;

[0022] (2) The pulp a, pulp b and pulp c corresponding to the three fiber structure layers are respectively fed to the wire mesh for forming and drying to obtain the initial paper sample a, initial paper sample b and initial paper sample c. Then, the initial paper sample a, initial paper sample b and initial paper sample c are stacked together in sequence and then subjected to hot pressing to obtain the aramid composite paper.

[0023] Preferably, the defoamer is a polyether ester defoamer, which has good stability, high temperature resistance, and low surface tension, making it easy to disperse and emulsify, thus achieving a defoaming effect during paper forming. The dispersant includes at least one of polyethylene oxide, anionic polyacrylamide, and hydroxymethyl cellulose. The dispersant can increase fiber dispersibility, improve the uniformity of aramid paper, and enhance the performance of aramid paper.

[0024] Preferably, the defoamer has a mass percentage content of 0.01%-0.06% in slurry a, a mass percentage content of 0.01%-0.06% in slurry c, a mass percentage content of 0.2%-0.5% in slurry a, and a mass percentage content of 0.2%-0.5% in slurry c.

[0025] Preferably, the hot pressing conditions are: hot pressing temperature of 250-270℃, hot pressing pressure of 6.0-10.0MPa, and hot pressing time of 0.5-1.0h.

[0026] Furthermore, the present invention provides the application of the aramid composite paper in the field of transformers.

[0027] Compared to existing technologies, the beneficial effects of this invention are as follows: The three-layer structure of the aramid composite paper of this invention enhances the density and uniformity of the insulating paper from both macroscopic and microscopic perspectives, thereby improving its mechanical and electrical strength. This is mainly manifested in the following ways: In the third layer, polyimide fibers containing amide structures and aramid precipitated fibers form an ordered hydrogen bond network, enhancing the intermolecular bonding force from a microscopic perspective and improving the mechanical strength of the aramid paper from a microscopic perspective; the polyphenylene sulfide in the first layer exhibits good adhesion after hot pressing, spreading on the surface and within the pores of the plant fibers in the second layer after hot pressing, improving paper uniformity and reducing paper porosity, thus improving the mechanical and electrical strength of the aramid paper from a macroscopic perspective. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0029] Defoamer: Polyether ester defoamer, commercially available.

[0030] Dispersant: Polyethylene oxide, commercially available.

[0031] Examples 1-10 and Comparative Examples 1-6

[0032] Example 1

[0033] A method for preparing aramid composite paper includes the following steps:

[0034] The preparation method of the slurry corresponding to the three fiber structure layers is as follows:

[0035] S1. The aramid chopped fiber pulping treatment: The aramid chopped fibers are pulped and fully dispersed in a pulping machine, wherein the pulping speed is 5000 rpm, the pulping concentration is 3.0%, and the pulping degree is 50°SR, to obtain an aramid chopped fiber suspension, wherein the average length of the chopped fibers before pulping is 5 mm.

[0036] S2. The polyphenylene sulfide pulp beating treatment: after cutting the polyphenylene sulfide microfiber nonwoven fabric into pieces, the beating time is 60 min, the beating speed is 5000 rpm, the beating concentration is 3.0%, and the beating degree is 50°SR, to obtain wet pulp, which is then vacuum dried to obtain polyphenylene sulfide microfiber pulp. The average diameter of the polyphenylene sulfide pulp before beating is 4 μm.

[0037] S3. Plant fiber pulping treatment: The plant fiber is pulped, and its beating degree and fiber length are controlled to obtain plant fiber pulp b; wherein, the average length of the plant fiber before pulping is 1mm and the beating degree is 20°SR.

[0038] S4. The aramid precipitated fiber pulping treatment: the aramid precipitated fiber pulping speed is 5000 rpm, the pulping concentration is 2.0%, and the pulping degree is 70°SR, to obtain an aramid chromatography fiber suspension; wherein, the average length of the aramid precipitated fiber before pulping is 0.5 mm.

[0039] S5. Polyimide fiber treatment: The polyimide fiber is pulped for 60 minutes, at a pulping speed of 5000 rpm, with a pulping concentration of 3.0% and a pulping degree of 50°SR, to obtain a polyimide fiber suspension.

[0040] The preparation method of the aramid composite paper is as follows:

[0041] (1) After mixing the slurries obtained in S1 and S2, add defoamer and dispersant to obtain slurry a; after mixing the slurries obtained in S4 and S5, add defoamer and dispersant to obtain slurry c; the mass percentage of defoamer in slurry a is 0.01%, the mass percentage of defoamer in slurry c is 0.01%, the mass percentage of dispersant in slurry a is 0.2%, and the mass percentage of dispersant in slurry c is 0.2%.

[0042] (2) The pulp a, pulp b and pulp c corresponding to the three fiber structure layers are respectively fed to the wire mesh for forming and drying to obtain the initial paper sample a, initial paper sample b and initial paper sample c. Then, the initial paper sample a, initial paper sample b and initial paper sample c are stacked together in sequence and then subjected to hot pressing to obtain the aramid composite paper.

[0043] The oven-dry mass ratio of the first, second, and third fiber structural layers is 30:40:30; the oven-dry mass ratio of aramid chopped fibers to polyphenylene sulfide pulp in the first fiber structural layer is 1:3, and the oven-dry mass ratio of polyimide fibers to aramid precipitated fibers in the third fiber structural layer is 1:3; the hot-pressing conditions are: hot-pressing temperature of 250℃, hot-pressing pressure of 10.0MPa, and hot-pressing time of 1.0h.

[0044] Example 2

[0045] Compared with Example 1, only the pulping process of S2 polyphenylene sulfide pulp is different, with a freeness of 60°SR. The preparation methods of the rest of S2 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as those in Example 1.

[0046] Example 3

[0047] Compared with Example 1, only the pulping process of S2 polyphenylene sulfide pulp is different, with a freeness of 20°SR. The preparation methods of the rest of S2 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as those in Example 1.

[0048] Example 4

[0049] Compared with Example 1, only the pulping process of S2 polyphenylene sulfide pulp is different, with a freeness of 80°SR. The preparation methods of the rest of S2 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as those in Example 1.

[0050] Example 5

[0051] Compared with Example 1, only the pulping process of the plant fiber described in S3 is different, with a pulping degree of 30°SR. The preparation methods in S3 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as in Example 1.

[0052] Example 6

[0053] Compared with Example 1, only the pulping process of the plant fiber described in S3 is different, with a pulping degree of 10°SR. The preparation methods in the rest of S3 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as in Example 1.

[0054] Example 7

[0055] Compared with Example 1, only the pulping process of the plant fiber described in S3 is different, with a pulping degree of 50°SR. The preparation methods in S3 are exactly the same, and the remaining components, weight parts and preparation methods are exactly the same as in Example 1.

[0056] Example 8

[0057] Compared with Example 1, the only difference is the oven-dry mass ratio of the first, second, and third fiber structure layers in the aramid composite paper, which is 35:30:35.

[0058] Example 9

[0059] Compared with Example 1, the only difference is the oven-dry mass ratio of the first, second, and third fiber structure layers in the aramid composite paper, which is 40:25:35.

[0060] Example 10

[0061] Compared with Example 1, the only difference is the oven-dry mass ratio of the first, second, and third fiber structure layers in the aramid composite paper, which is 25:45:30.

[0062] Comparative Example 1

[0063] Compared with Example 1, Comparative Example 1 does not contain the first fiber structure layer, but the second and third fiber structure layers are exactly the same as those in Example 1, and the preparation methods are exactly the same. The oven-dry mass ratio of the second and third fiber structure layers is 55:45.

[0064] Comparative Example 2

[0065] Compared with Example 1, Comparative Example 2 does not contain the second fiber structure layer. The first and third fiber structure layers are exactly the same as those in Example 1, and the preparation methods are exactly the same. The oven-dry mass ratio of the first and third fiber structure layers is 50:50.

[0066] Comparative Example 3

[0067] Compared with Example 1, Comparative Example 3 does not contain the third fiber structure layer. The first and second fiber structure layers are exactly the same as those in Example 1, and the preparation methods are exactly the same. The oven-dry mass ratio of the first and second fiber structure layers is 45:55.

[0068] Comparative Example 4

[0069] Compared with Example 1, Comparative Example 4 differs only in the first fiber structure layer, which is composed of aramid chopped fibers and does not contain polyphenylene sulfide pulp. The second and third fiber structure layers are identical to those in Example 1, and the preparation methods are exactly the same.

[0070] Comparative Example 5

[0071] Compared with Example 1, Comparative Example 5 differs only in the third fiber structure layer, which is an aramid precipitated fiber and does not contain polyimide fiber. The first and second fiber structure layers are exactly the same as those in Example 1, and the preparation methods are exactly the same.

[0072] Comparative Example 6

[0073] Compared with Example 1, Comparative Example 6 differs in the first and third fiber structure layers. The first fiber structure layer contains aramid precipitated fibers and polyphenylene sulfide pulp, while the third fiber structure layer contains aramid chopped fibers and polyimide fibers. The rest is exactly the same as in Example 1.

[0074] Performance test 1: Furfural content determination.

[0075] Testing standards and procedures: The furfural content in transformer insulating oil samples was determined according to the method in NB / SH / T 0812-2010 "Determination of 2-furfural and related components in mineral insulating oil".

[0076] The aramid composite paper prepared in the examples and comparative examples was placed in 500 mL of insulating oil and subjected to simulated aging at 150 °C for 96 h and at 60 °C for 96 h, respectively. Transformer insulating oil samples were collected and the furfural content in the insulating oil samples was tested.

[0077] Test results are shown in Table 1.

[0078] Performance test 2: Performance test of aramid composite paper.

[0079] Test standards and procedures: Breakdown voltage is tested according to GB / T20628.2-2006; uniformity index is tested according to GB / T1041-2007; tensile strength is tested according to GB / T 12914-2018; thickness is tested according to GB / T20628.2-2006.

[0080] Test results are shown in Table 2.

[0081] Table 1

[0082]

[0083]

[0084] Table 2

[0085]

[0086]

[0087] As can be seen from the comparison of Examples 1-7, the beating degree of the pulp affects the mechanical and electrical strength of the prepared aramid composite paper. The beating degree affects parameters such as the shape and length of the polyphenylene sulfide pulp. When the beating degree is appropriate, the pulp spreads more evenly on the surface and in the pores of the second layer of plant fibers during hot pressing, reducing paper porosity and improving paper uniformity, thereby improving the mechanical and electrical strength of the aramid paper. For plant fibers, in addition to serving as a source of degradation into furfural under overheated conditions, they also act as a "scaffold" or "skeleton" in the composite paper as an intermediate layer. Too high a beating degree will make the plant fibers smaller, affecting their "scaffold" or "skeleton" function.

[0088] A comparison of Examples 1-4 shows that when the freeness of polyphenylene sulfide pulp is 50-60°SR, the furfural content is higher, and the tensile strength, breakdown voltage, and uniformity index are also higher. A comparison of Examples 1 and Examples 5-7 shows that when the freeness of plant fiber is 20-30°SR, the furfural content is higher, and the tensile strength, breakdown voltage, and uniformity index are also higher.

[0089] As can be seen from the comparison of Examples 1 and Examples 8-10, when the oven-dry mass ratio of the first fiber structure layer, the second fiber structure layer, and the third fiber structure layer is 30:40:30, the furfural content is higher, and the tensile strength, breakdown voltage, and uniformity index are also higher.

[0090] As can be seen from Examples 1 and Comparative Examples 1-3, Comparative Example 1 does not contain the first fiber structure layer, and Comparative Example 3 does not contain the third fiber structure layer, resulting in an increased proportion of the second fiber structure layer. Therefore, the furfural content in the oil of Comparative Examples 1 and 3 is slightly higher than that of Example 1. However, because Comparative Examples 1 and 3 only have a plant layer and another polymer layer, their tensile strength, breakdown voltage, and uniformity index are much worse than those of Example 1, failing to meet the requirements for the use of aramid composite paper. Comparative Example 2 does not contain the second fiber structure layer, so its tensile strength, breakdown voltage, and uniformity index are slightly better than those of Example 1. However, because it does not contain the second fiber structure layer, its furfural content is 0, making it impossible to identify local overheating problems and monitor the local overheating of the transformer in a timely manner.

[0091] As can be seen from Example 1 and Comparative Examples 4-6, Comparative Examples 4-6 do not contain some fiber pulp or the pulp used is not within the scope of the present invention. As can be seen from Table 1-2, the mechanical and electrical strength is significantly worse. Furthermore, due to the change in the fiber structure of the first and third layers in Comparative Examples 4-6, the identification of local overheating problems by the aramid composite paper is indirectly affected, and the local overheating of the transformer cannot be monitored in a timely manner.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An aramid composite paper, characterized in that, The aramid composite paper comprises three fiber structure layers stacked sequentially. The first fiber structure layer contains aramid chopped fibers and polyphenylene sulfide pulp, the second fiber structure layer contains plant fibers, and the third fiber structure layer contains aramid precipitated fibers and polyimide fibers. The chopped fibers have a rigid cylindrical microstructure, and the aramid precipitated fibers have a thin film-like wrinkled structure. The oven-dry mass ratio of the first fiber structure layer, the second fiber structure layer, and the third fiber structure layer is (30-35):(30-40):(30-35). The oven-dry mass ratio of aramid chopped fibers and polyphenylene sulfide pulp in the first fiber structure layer is 1:(1-3); the freeness of the aramid chopped fiber pulp is 40-60°SR, and the freeness of the polyphenylene sulfide pulp is 40-60°SR. The beating degree of plant fiber pulp is 20-30°SR; The oven-dry mass ratio of polyimide fiber and aramid precipitated fiber in the third fiber structure layer is 1:(1-3); the freeness of the aramid precipitated fiber slurry is 60-80°SR, and the freeness of the polyimide fiber slurry is 40-60°SR.

2. The aramid composite paper as described in claim 1, characterized in that, The plant fiber in the second fiber structure layer is at least one of coniferous wood fiber, broadleaf wood fiber, hemp fiber, bamboo fiber, and grass fiber.

3. The method for preparing aramid composite paper according to any one of claims 1-2, characterized in that, The preparation method is as follows: the pulp corresponding to the three fiber structure layers is fed to the wire mesh for forming and drying to obtain initial paper sample a, initial paper sample b and initial paper sample c. Then, the initial paper sample a, initial paper sample b and initial paper sample c are stacked together in sequence and subjected to hot pressing to obtain the aramid composite paper.

4. The method for preparing aramid composite paper as described in claim 3, characterized in that, The hot pressing conditions are as follows: hot pressing temperature is 250-270℃, hot pressing pressure is 6.0-10.0MPa, and hot pressing time is 0.5-1.0h.

5. The application of the aramid composite paper as described in any one of claims 1-2 in the field of transformers.

Images